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Saito T, Ichimura Y, Oda M, Saitoh H. Preferential meropenem absorption activated by 1α,25-dihydroxyvitamin D 3 and shared with foscarnet, a phosphate transporter substrate, in the rat ileum. Drug Metab Pharmacokinet 2024; 55:100997. [PMID: 38367298 DOI: 10.1016/j.dmpk.2024.100997] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/03/2023] [Revised: 12/24/2023] [Accepted: 01/09/2024] [Indexed: 02/19/2024]
Abstract
Meropenem (MEPM) is used for the treatment of serious infectious diseases solely as. INJECTABLE: Therefore, the development of an oral formulation would expand its clinical utility. To this end, an exact understanding of the absorption characteristics of MEPM is essential. In this study, MEPM absorption in the rat small intestine was investigated using an in situ loop technique and an in vitro diffusion chamber method. The disappearance ratios of MEPM (0.1 mM) were in the order of ileum > duodenum > jejunum. The extensive MEPM disappearance in the ileum was significantly reduced in the presence of foscarnet, a Na+-dependent phosphate transporter (NaPi-T) substrate, whereas glycylsarcosine, thiamine, taurocholic acid, and biapenem had no effects. The mucosal-to-serosal (M-to-S) permeation of MEPM across the rat ileal segments was very small under normal experimental conditions. However, on addition of 1α,25-dihydroxyvitamin D3 (1,25(OH)2D3) to the experimental medium, the M-to-S permeation of MEPM markedly increased, showing a more than 7-fold greater apparent permeation coefficient. The present results suggest that MEPM is preferentially absorbed in the rat ileum, sharing with foscarnet, and that 1,25(OH)2D3 potentially activates the absorption of MEPM there. A likely candidate for involvement in MEPM absorption was NaPi-T or a related transporter.
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Affiliation(s)
- Toshihide Saito
- Department of Pharmaceutics, School of Pharmaceutical Sciences, Health Sciences University of Hokkaido, Ishikari, Tobetsu, Hokkaido, 061-0293, Japan
| | - Yuichi Ichimura
- Department of Pharmaceutics, School of Pharmaceutical Sciences, Health Sciences University of Hokkaido, Ishikari, Tobetsu, Hokkaido, 061-0293, Japan
| | - Masako Oda
- Department of Pharmaceutics, School of Pharmaceutical Sciences, Health Sciences University of Hokkaido, Ishikari, Tobetsu, Hokkaido, 061-0293, Japan
| | - Hiroshi Saitoh
- Department of Pharmaceutics, School of Pharmaceutical Sciences, Health Sciences University of Hokkaido, Ishikari, Tobetsu, Hokkaido, 061-0293, Japan.
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2
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Turner ME, Beck L, Hill Gallant KM, Chen Y, Moe OW, Kuro-o M, Moe S, Aikawa E. Phosphate in Cardiovascular Disease: From New Insights Into Molecular Mechanisms to Clinical Implications. Arterioscler Thromb Vasc Biol 2024; 44:584-602. [PMID: 38205639 PMCID: PMC10922848 DOI: 10.1161/atvbaha.123.319198] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/12/2024]
Abstract
Hyperphosphatemia is a common feature in patients with impaired kidney function and is associated with increased risk of cardiovascular disease. This phenomenon extends to the general population, whereby elevations of serum phosphate within the normal range increase risk; however, the mechanism by which this occurs is multifaceted, and many aspects are poorly understood. Less than 1% of total body phosphate is found in the circulation and extracellular space, and its regulation involves multiple organ cross talk and hormones to coordinate absorption from the small intestine and excretion by the kidneys. For phosphate to be regulated, it must be sensed. While mostly enigmatic, various phosphate sensors have been elucidated in recent years. Phosphate in the circulation can be buffered, either through regulated exchange between extracellular and cellular spaces or through chelation by circulating proteins (ie, fetuin-A) to form calciprotein particles, which in themselves serve a function for bulk mineral transport and signaling. Either through direct signaling or through mediators like hormones, calciprotein particles, or calcifying extracellular vesicles, phosphate can induce various cardiovascular disease pathologies: most notably, ectopic cardiovascular calcification but also left ventricular hypertrophy, as well as bone and kidney diseases, which then propagate phosphate dysregulation further. Therapies targeting phosphate have mostly focused on intestinal binding, of which appreciation and understanding of paracellular transport has greatly advanced the field. However, pharmacotherapies that target cardiovascular consequences of phosphate directly, such as vascular calcification, are still an area of great unmet medical need.
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Affiliation(s)
- Mandy E. Turner
- Division of Cardiovascular Medicine, Department of Medicine, Center for Interdisciplinary Cardiovascular Sciences, Brigham and Women’s Hospital, Harvard Medical School, Boston, MA, USA
| | - Laurent Beck
- Nantes Université, CNRS, Inserm, l’institut du thorax, F-44000 Nantes, France
| | - Kathleen M Hill Gallant
- Department of Food Science and Nutrition, University of Minnesota, St. Paul, Minnesota, USA
- Division of Nephrology, Department of Medicine, Indiana University School of Medicine, Indianapolis, IN, USA
| | - Yabing Chen
- Department of Pathology, University of Alabama at Birmingham
- Research Department, Veterans Affairs Birmingham Medical Center, Birmingham, AL, USA
| | - Orson W Moe
- Charles and Jane Pak Center for Mineral Metabolism and Clinical Research, University of Texas Southwestern Medical Center, Dallas, TX, USA
- Department of Internal Medicine, University of Texas Southwestern Medical Center, Dallas, TX, USA
- Department of Physiology, University of Texas Southwestern Medical Center, Dallas, TX, USA
| | - Makoto Kuro-o
- Division of Anti-aging Medicine, Center for Molecular Medicine, Jichi Medical University 3311-1 Yakushiji, Shimotsuke, Tochigi 329-0498, Japan
| | - Sharon Moe
- Division of Nephrology, Department of Medicine, Indiana University School of Medicine, Indianapolis, IN, USA
| | - Elena Aikawa
- Division of Cardiovascular Medicine, Department of Medicine, Center for Interdisciplinary Cardiovascular Sciences, Brigham and Women’s Hospital, Harvard Medical School, Boston, MA, USA
- Division of Cardiovascular Medicine, Department of Medicine, Center for Excellence in Vascular Biology, Brigham and Women’s Hospital, Harvard Medical School, Boston, MA, USA
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3
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Lucea S, Chopo-Escuin G, Guillén N, Sosa C, Sorribas V. Intestinal and Renal Adaptations to Changes of Dietary Phosphate Concentrations in Rat. FUNCTION 2023; 5:zqad063. [PMID: 38033458 PMCID: PMC10686248 DOI: 10.1093/function/zqad063] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/09/2023] [Revised: 11/05/2023] [Accepted: 11/07/2023] [Indexed: 12/02/2023] Open
Abstract
We have studied the role of the intestine, kidney, and several hormones when adapting to changes in dietary P concentration. Normal and parathyroidectomized (PTX) rats were fed pH-matched diets containing 0.1%, 0.6%, and 1.2% P concentrations. 32Pi uptake was determined in the jejunum and kidney cortex brush border membrane vesicles. Several hormone and ion concentrations were determined in the blood and urine of rats. Both jejunum and kidney cortex Pi transport was regulated with 5 d of chronic feeding of P diets in normal rats. Acute adaptation was determined by switching foods on day 6, which was only clearly observed in the kidney cortex of normal rats, with more statistical variability in the jejunum. However, no paradoxical increase of Pi uptake in the jejunum was reproduced after the acute switch to the 1.2% P diet. Pi uptake in the jejunum was parathyroid hormone (PTH)-independent, but in the kidney, the chronic adaptation was reduced, and no acute dietary adaptations were observed. The NaPi2a protein was more abundant in the PTX than the sham kidneys, but contrary to the modest or absent changes in Pi uptake adaptation, the transporter was similarly regulated by dietary P, as in the sham rats. PTH and fibroblast growth factor 23 (FGF23) were the only hormones regulated by all diet changes, even in fasting animals, which exhibited regulated Pi transport despite similar phosphatemia. Evidence of Pi appetite effects was also observed. In brief, our results show new characteristics of Pi adaptations, including a lack of correlation between Pi transport, NaPi2a expression, and PTH/FGF23 concentrations.
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Affiliation(s)
- Susana Lucea
- Laboratory of Molecular Toxicology, Department of Biochemistry and Cell and Molecular Biology, University of Zaragoza, E50013 Zaragoza, Spain
| | - Gema Chopo-Escuin
- Laboratory of Molecular Toxicology, Department of Biochemistry and Cell and Molecular Biology, University of Zaragoza, E50013 Zaragoza, Spain
| | - Natalia Guillén
- Laboratory of Molecular Toxicology, Department of Biochemistry and Cell and Molecular Biology, University of Zaragoza, E50013 Zaragoza, Spain
| | - Cecilia Sosa
- Laboratory of Molecular Toxicology, Department of Biochemistry and Cell and Molecular Biology, University of Zaragoza, E50013 Zaragoza, Spain
| | - Víctor Sorribas
- Laboratory of Molecular Toxicology, Department of Biochemistry and Cell and Molecular Biology, University of Zaragoza, E50013 Zaragoza, Spain
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Oda N, Sugihara K, Uebanso T, Ohminami H, Ohnishi K, Masuda M, Yamanaka-Okumura H, Taketani Y. Dietary phosphate disturbs of gut microbiome in mice. J Clin Biochem Nutr 2023; 73:221-227. [PMID: 37970557 PMCID: PMC10636580 DOI: 10.3164/jcbn.23-9] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/12/2023] [Accepted: 02/25/2023] [Indexed: 11/17/2023] Open
Abstract
Disorder of phosphate metabolism is a common pathological condition in chronic kidney disease patients. Excessive intake of dietary phosphate deteriorates chronic kidney disease and various complications including cardiovascular and infectious diseases. Recent reports have demonstrated that gut microbiome disturbance is associated with both the etiology and progression of chronic kidney disease. However, the relationship between dietary phosphate and gut microbiome remains unknown. Here, we examined the effects of excessive intake of phosphate on gut microbiome. Five-week-old male C57BL/6J mice were fed either control diet or high phosphate diet for eight weeks. Analysis of the gut microbiota was carried out using MiSeq next generation sequencer, and short-chain fatty acids were determined with GC-MS. In analysis of gut microbiota, significantly increased in Erysipelotrichaceae and decreased in Ruminococcaceae were observed in high phosphate diet group. Furthermore, high phosphate diet induced reduction of microbial diversity and decreased mRNA levels of colonic tight junction markers. These results suggest that the excessive intake of dietary phosphate disturbs gut microbiota and affects intestinal barrier function.
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Affiliation(s)
- Naoko Oda
- Department of Clinical Nutrition and Food Management, Institute of Biochemical Sciences, Tokushima University Graduate School, 3-18-15 Kuramoto-cho, Tokushima 770-8503, Japan
| | - Kohei Sugihara
- Department of Clinical Nutrition and Food Management, Institute of Biochemical Sciences, Tokushima University Graduate School, 3-18-15 Kuramoto-cho, Tokushima 770-8503, Japan
| | - Takashi Uebanso
- Department of Preventive Environment and Nutrition, Institute of Biochemical Sciences, Tokushima University Graduate School, 3-18-15 Kuramoto-cho, Tokushima 770-8503, Japan
| | - Hirokazu Ohminami
- Department of Clinical Nutrition and Food Management, Institute of Biochemical Sciences, Tokushima University Graduate School, 3-18-15 Kuramoto-cho, Tokushima 770-8503, Japan
| | - Kohta Ohnishi
- Department of Clinical Nutrition and Food Management, Institute of Biochemical Sciences, Tokushima University Graduate School, 3-18-15 Kuramoto-cho, Tokushima 770-8503, Japan
| | - Masashi Masuda
- Department of Clinical Nutrition and Food Management, Institute of Biochemical Sciences, Tokushima University Graduate School, 3-18-15 Kuramoto-cho, Tokushima 770-8503, Japan
| | - Hisami Yamanaka-Okumura
- Department of Clinical Nutrition and Food Management, Institute of Biochemical Sciences, Tokushima University Graduate School, 3-18-15 Kuramoto-cho, Tokushima 770-8503, Japan
| | - Yutaka Taketani
- Department of Clinical Nutrition and Food Management, Institute of Biochemical Sciences, Tokushima University Graduate School, 3-18-15 Kuramoto-cho, Tokushima 770-8503, Japan
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5
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Kalantar-Zadeh K, Forfang D, Bakris G, Martin KJ, Moe SM, Sprague SM. Managing Phosphate Burden in Patients Receiving Dialysis: Beyond Phosphate Binders and Diet. KIDNEY360 2023; 4:1650-1656. [PMID: 37870525 PMCID: PMC10695651 DOI: 10.34067/kid.0000000000000262] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 05/15/2023] [Accepted: 09/07/2023] [Indexed: 10/24/2023]
Abstract
Most patients receiving dialysis rely on dietary restriction and phosphate binders to minimize the risk of hyperphosphatemia, which is associated with increased mortality. However, dietary restriction is difficult because of hidden phosphate additives in processed foods and medications. Restriction of dietary phosphate sources such as protein may increase the risk of malnutrition. Phosphate binders, the only pharmacologic option for phosphate management since aluminum salts were introduced several decades ago, are often insufficient for binding the 1400-2500 mg of phosphate potentially consumed daily. Over the last decade, serum phosphate levels in the United States have risen, and >69% of patients receiving dialysis exhibited a most recent phosphate level >4.5 mg/dl (above the normal range), indicating an urgent need for new, more effective therapies to manage phosphate burden. Novel, nonbinder therapies such as transcellular and paracellular phosphate absorption inhibitors may be used for phosphate management, and future studies should examine whether they allow fewer dietary restrictions for patients receiving dialysis, potentially improving patient quality of life and nutritional status. It is imperative that we collaborate to move beyond the restrictive approaches available today and provide patients and clinicians with an array of strategies so that they may choose the most appropriate patient-centered therapy.
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Affiliation(s)
- Kamyar Kalantar-Zadeh
- Division of Nephrology, Hypertension and Kidney Transplantation, University of California Irvine, Irvine, California
| | - Derek Forfang
- The Co-Chair of the National Forum of ESRD Network's Kidney Patient Advisory Council (KPAC), Henrico, Virginia
- National Kidney Foundation, Public Policy Committee, New York, New York
| | - George Bakris
- Section of Endocrinology, Diabetes and Metabolism, Department of Medicine, University of Chicago, Chicago, Illinois
| | - Kevin J. Martin
- Department of Internal Medicine, Division of Nephrology, Saint Louis University School of Medicine, St. Louis, Missouri
| | - Sharon M. Moe
- Division of Nephrology and Hypertension, Indiana University School of Medicine, Indianapolis, Indiana
| | - Stuart M. Sprague
- Division of Nephrology and Hypertension, NorthShore University Health System-University of Chicago Pritzker School of Medicine, Evanston, Illinois
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6
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Expression of phosphate and calcium transporters and their regulators in parotid glands of mice. Pflugers Arch 2023; 475:203-216. [PMID: 36274099 PMCID: PMC9849193 DOI: 10.1007/s00424-022-02764-x] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/01/2022] [Revised: 10/07/2022] [Accepted: 10/13/2022] [Indexed: 02/01/2023]
Abstract
The concentration of inorganic phosphate (Pi) in plasma is under hormonal control, with deviations from normal values promptly corrected to avoid hyper- or hypophosphatemia. Major regulators include parathyroid hormone (PTH), fibroblast growth factor 23 (FGF-23), and active vitamin D3 (calcitriol). This control is achieved by mechanisms largely dependent on regulating intestinal absorption and renal excretion, whose combined actions stabilise plasma Pi levels at around 1-2 mM. Instead, Pi concentrations up to 13 and 40 mM have been measured in saliva from humans and ruminants, respectively, suggesting that salivary glands have the capacity to concentrate Pi. Here we analysed the transcriptome of parotid glands, ileum, and kidneys of mice, to investigate their potential differences regarding the expression of genes responsible for epithelial transport of Pi as well as their known regulators. Given that Pi and Ca2+ homeostasis are tightly connected, the expression of genes involved in Ca2+ homeostasis was also included. In addition, we studied the effect of vitamin D3 treatment on the expression of Pi and Ca2+ regulating genes in the three major salivary glands. We found that parotid glands are equipped preferentially with Slc20 rather than with Slc34 Na+/Pi cotransporters, are suited to transport Ca2+ through the transcellular and paracellular route and are potential targets for PTH and vitamin D3 regulation.
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7
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Burstad KM, Cladis DP, Vorland CJ, Wastney ME, Biruete A, Dominguez JM, O'Neill KD, Chen NX, Moe SM, Hill Gallant KM. Acute High Dietary Phosphorus Following Low-Phosphorus Diet Acclimation Does Not Enhance Intestinal Fractional Phosphorus Absorption in Nephrectomized Male Rats. JBMR Plus 2022; 6:e10698. [PMID: 36530183 PMCID: PMC9751657 DOI: 10.1002/jbm4.10698] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Figures] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 07/15/2022] [Revised: 10/05/2022] [Accepted: 10/27/2022] [Indexed: 05/21/2024] Open
Abstract
Dietary phosphorus restriction and phosphorus binders are commonly prescribed for patients with chronic kidney disease (CKD). However, occurrences of non-adherence to these interventions are common. As low-phosphorus (LP) diets have been consistently experimentally shown in vitro to increase intestinal phosphorus absorption efficiency, a bout of non-adherence to diet or binders may cause an unintended consequence of enhanced intestinal phosphorus absorption. Thus, we aimed to determine the effect of a single bout of high-phosphorus (HP) intake after acclimation to a LP diet. Male Sprague Dawley rats with 5/6 nephrectomy (n = 36) or sham operation (n = 36) were block-randomized to 1 of 3 diets: LP (0.1% P w/w), HP (1.2%), or LP followed by acute HP (LPHP 0.1% then 1.2%). Phosphorus absorption tests were conducted using 33P radioisotope administrated by oral gavage or intravenously (iv). Although the overall two-way ANCOVA model for intestinal fractional phosphorus absorption was non-significant, exploratory comparisons showed intestinal fractional phosphorus absorption efficiency tended to be higher in rats in the LP compared with HP or LPHP groups. Rats in the HP or LPHP groups had higher plasma phosphorus compared with rats in the LP group, but the LPHP group was not different from the HP group. Gene expression of the major intestinal phosphate transporter, NaPi-2b, was lower in the jejunum of rats in the LPHP group compared with rats in the HP group but not different in the duodenum. These results demonstrate that an acute HP load after acclimation to a LP diet does not lead to enhanced intestinal fractional phosphorus absorption efficiency in 5/6 nephrectomized male rats. These data provide evidence against the notion that dietary phosphorus restriction or binder use adversely increases absorption efficiency after a single instance of dietary or binder non-adherence. However, other adverse consequences of fluctuating dietary phosphorus intake cannot be ruled out. © 2022 The Authors. JBMR Plus published by Wiley Periodicals LLC on behalf of American Society for Bone and Mineral Research.
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Affiliation(s)
- Kendal M Burstad
- Department of Food Science and NutritionUniversity of MinnesotaSaint PaulMNUSA
- Department of Nutrition SciencePurdue UniversityWest LafayetteINUSA
| | - Dennis P Cladis
- Department of Food Science and NutritionUniversity of MinnesotaSaint PaulMNUSA
- Department of Nutrition SciencePurdue UniversityWest LafayetteINUSA
| | - Colby J Vorland
- Department of Nutrition SciencePurdue UniversityWest LafayetteINUSA
- Department of Applied Health ScienceIndiana University School of Public Health‐BloomingtonBloomingtonINUSA
| | - Meryl E Wastney
- Department of Nutrition SciencePurdue UniversityWest LafayetteINUSA
| | - Annabel Biruete
- Department of Nutrition SciencePurdue UniversityWest LafayetteINUSA
- Department of Medicine‐Division of NephrologyIndiana University School of MedicineIndianapolisINUSA
- Department of Nutrition and DieteticsIndiana University‐Purdue University IndianapolisIndianapolisINUSA
| | - James M Dominguez
- Department of Medicine‐Division of NephrologyIndiana University School of MedicineIndianapolisINUSA
| | - Kalisha D O'Neill
- Department of Medicine‐Division of NephrologyIndiana University School of MedicineIndianapolisINUSA
| | - Neal X Chen
- Department of Medicine‐Division of NephrologyIndiana University School of MedicineIndianapolisINUSA
| | - Sharon M Moe
- Department of Medicine‐Division of NephrologyIndiana University School of MedicineIndianapolisINUSA
- Department of Anatomy and Cell BiologyIndiana University School of MedicineIndianapolisINUSA
- Department of MedicineRoudebush Veterans Affairs Medicine CenterIndianapolisINUSA
| | - Kathleen M Hill Gallant
- Department of Food Science and NutritionUniversity of MinnesotaSaint PaulMNUSA
- Department of Nutrition SciencePurdue UniversityWest LafayetteINUSA
- Department of Medicine‐Division of NephrologyIndiana University School of MedicineIndianapolisINUSA
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Maemoto M, Hirata Y, Hosoe S, Ouchi J, Uchii M, Takada H, Akizawa E, Yanagisawa A, Shuto S. Development of potent non-acylhydrazone inhibitors of intestinal sodium-dependent phosphate transport protein 2b (NaPi2b). Bioorg Med Chem 2022; 71:116944. [DOI: 10.1016/j.bmc.2022.116944] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/13/2022] [Revised: 07/16/2022] [Accepted: 07/19/2022] [Indexed: 11/02/2022]
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9
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Phosphate Frustration: Treatment Options to Complement Current Therapies. Int J Nephrol 2022; 2022:9457440. [PMID: 36045900 PMCID: PMC9424003 DOI: 10.1155/2022/9457440] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/26/2022] [Accepted: 07/16/2022] [Indexed: 11/18/2022] Open
Abstract
Hyperphosphatemia eventually develops in almost all patients with advanced chronic kidney disease and is associated with negative clinical outcomes. Thus, guidelines recommend targeting treatment to normal phosphate levels in patients with chronic kidney disease. Despite low phosphorus diets, clearance by dialysis, and phosphate binder use, many patients with chronic kidney disease on dialysis are unable to consistently achieve and maintain serum phosphate concentrations <5.5 mg/dL. A chart audit of patients on dialysis receiving phosphate binders showed that 74 to 86% were unable to consistently achieve serum phosphate ≤5.5 mg/dL over 6 months. Furthermore, although there is evidence that serum phosphate concentrations <4.5 mg/dL are associated with improved survival and cardiovascular outcomes, real-world phosphate control data suggest achieving and maintaining this goal for most patients would be extremely challenging, if not near impossible, using current therapies. As phosphate binders can only remove approximately 300 mg of the 2,500 mg or more daily dietary phosphate intake, therapeutic innovations are necessary to improve phosphate management. We present treatment options to complement current therapies including tenapanor, a novel sodium/hydrogen exchanger isoform 3 inhibitor that blocks the dominant paracellular phosphate absorption pathway and has been shown to reduce phosphate levels in several clinical trials.
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Rubio-Aliaga I, Krapf R. Phosphate intake, hyperphosphatemia, and kidney function. Pflugers Arch 2022; 474:935-947. [PMID: 35511366 PMCID: PMC9338892 DOI: 10.1007/s00424-022-02691-x] [Citation(s) in RCA: 9] [Impact Index Per Article: 4.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/02/2022] [Revised: 04/11/2022] [Accepted: 04/12/2022] [Indexed: 12/25/2022]
Abstract
Phosphate is essential in living organisms and its blood levels are regulated by a complex network involving the kidneys, intestine, parathyroid glands, and the skeleton. The crosstalk between these organs is executed primarily by three hormones, calcitriol, parathyroid hormone, and fibroblast growth factor 23. Largely due to a higher intake of ultraprocessed foods, dietary phosphate intake has increased in the last decades. The average intake is now about twice the recommended dietary allowance. Studies investigating the side effect of chronic high dietary phosphate intake suffer from incomplete dietary phosphate assessment and, therefore, often make data interpretation difficult. Renal excretion is quickly adapted to acute and chronic phosphate intake. However, at the high ends of dietary intake, renal adaptation, even in pre-existing normal kidney function, apparently is not perfect. Experimental intervention studies suggest that chronic excess of dietary phosphate can result in sustained higher blood phosphate leading to hyperphosphatemia. Evidence exists that the price of the homeostatic response (phosphaturia in response to phosphate loading/hyperphosphatemia) is an increased risk for declining kidney function, partly due by intraluminal/tubular calcium phosphate particles that provoke renal inflammation. High dietary phosphate intake and hyperphosphatemia are progression factors for declining kidney function and are associated with higher cardiovascular disease and mortality risk. This is best established for pre-existing chronic kidney disease, but epidemiological and experimental data strongly suggest that this holds true for subjects with normal renal function as well. Here, we review the latest advances in phosphate intake and kidney function decline.
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Affiliation(s)
- Isabel Rubio-Aliaga
- Institute of Physiology, National Center of Competence in Research NCCR Kidney.CH, University of Zurich, Winterthurerstrasse 190, 8057, Zurich, Switzerland.
| | - Reto Krapf
- Synlab Suisse, 6002, Lucerne, Switzerland
- Department of Medicine, University of Basel, 4056, Basel, Switzerland
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11
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Hu Y, van Baal J, Hendriks WH, Resink JW, Liesegang A, van Krimpen MM, Bikker P. High dietary Ca and microbial phytase reduce expression of Ca transporters while enhancing claudins involved in paracellular Ca absorption in the porcine jejunum and colon. Br J Nutr 2022; 129:1-23. [PMID: 35912696 PMCID: PMC10011584 DOI: 10.1017/s0007114522002239] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/20/2022] [Revised: 06/28/2022] [Accepted: 07/07/2022] [Indexed: 11/06/2022]
Abstract
Expression levels of genes (RT-qPCR) related to Ca and P homeostasis (transporters and claudins (CLDN)) were determined in porcine jejunal and colonic mucosa. Forty growing pigs (BW 30.4±1.3 kg) received a low and high Ca content (2.0 and 9.6 g/kg, respectively) diet with or without microbial phytase (500 FTU/kg) for 21 days. Dietary Ca intake enhanced serum Ca and alkaline phosphatase concentration and reduced P, 1,25(OH)2D3, and parathyroid hormone concentration. Jejunal TRPV5 mRNA expression was decreased (32%) with phytase inclusion only, while colonic transient receptor potential vanilloid 5 (TRPV5) mRNA was reduced by dietary Ca (34%) and phytase (44%). Both jejunal and colonic TRPV6 mRNA expression was reduced (30%) with microbial phytase. Calbindin-D9k mRNA expression was lower in colonic but not jejunal mucosa with high dietary Ca (59%) and microbial phytase (37%). None of the mRNAs encoding the Na-P cotransporters (NaPi-IIc, PiT-1, PiT-2) were affected. Jejunal, but not colonic expression of the phosphate transporter XPR1, was slightly downregulated with dietary Ca. Dietary Ca downregulated colonic CLDN-4 (20%) and -10 (40%) expression while CLDN-7 was reduced by phytase inclusion in pigs fed low dietary Ca. Expression of colonic CLDN-12 tended to be increased by phytase. In jejunal mucosa, dietary Ca increased CLDN-2 expression (48%) and decreased CLDN-10 (49%) expression, while phytase slightly upregulated CLDN-12 expression. In conclusion, compared to a Ca deficient phytase-free diet, high dietary Ca and phytase intake in pigs downregulate jejunal and colonic genes related to transcellular Ca absorption and upregulate Ca pore-forming claudins.
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Affiliation(s)
- Yixin Hu
- Wageningen University and Research, Wageningen Livestock Research, Wageningen, 6700, the Netherlands
- Wageningen University and Research, Animal Nutrition Group, Wageningen, the Netherlands
| | - Jurgen van Baal
- Wageningen University and Research, Animal Nutrition Group, Wageningen, the Netherlands
| | - Wouter H. Hendriks
- Wageningen University and Research, Animal Nutrition Group, Wageningen, the Netherlands
| | | | - Annette Liesegang
- University of Zurich, Institute of Animal Nutrition, Vetsuisse Faculty, Zürich, Switzerland
| | - Marinus M. van Krimpen
- Wageningen University and Research, Wageningen Livestock Research, Wageningen, 6700, the Netherlands
| | - Paul Bikker
- Wageningen University and Research, Wageningen Livestock Research, Wageningen, 6700, the Netherlands
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12
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Abstract
Phosphate homeostasis is dependent on the interaction and coordination of four main organ systems: thyroid/parathyroids, gastrointestinal tract, bone and kidneys, and three key hormonal regulators, 1,25-hydroxyvitamin D3, parathyroid hormone and FGF23 with its co- factor klotho. Phosphorus is a critical nutritional element for normal cellular function, but in excess can be toxic to tissues, particularly the vasculature. As phosphate, it also has an important interaction and inter-dependence with calcium and calcium homeostasis sharing some of the same controlling hormones, although this is not covered in our article. We have chosen to provide a current overview of phosphate homeostasis only, focusing on the role of two major organ systems, the gastrointestinal tract and kidneys, and their contribution to the control of phosphate balance. We describe in some detail the mechanisms of intestinal and renal phosphate transport, and compare and contrast their regulation. We also consider a significant example of phosphate imbalance, with phosphate retention, which is chronic kidney disease; why consequent hyperphosphatemia is important, and some of the newer means of managing it.
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Affiliation(s)
- Joanne Marks
- Department of Neuroscience, Physiology & Pharmacology, University College London, London, United Kingdom
| | - Robert J Unwin
- Department of Neuroscience, Physiology & Pharmacology, University College London, London, United Kingdom; Department of Renal Medicine, University College London, London, United Kingdom.
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13
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Chaouche AA, Houot L, Duché D, Iobbi-Nivol C, Giudici-Orticoni MT, Fons M, Méjean V. The Tol-Pal system of Escherichia coli plays an unexpected role in the import of the oxyanions chromate and phosphate. Res Microbiol 2022; 173:103967. [PMID: 35660524 DOI: 10.1016/j.resmic.2022.103967] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/25/2022] [Revised: 05/23/2022] [Accepted: 05/24/2022] [Indexed: 10/18/2022]
Abstract
Chromate is a toxic metal that enters bacteria by using oxyanion importers. Here, we show that each mutant of the Tol-Pal system of Escherichia coli exhibited increased chromate resistance. This system, which spans the cell envelope, plays a major role in envelope integrity and septation. The ΔtolQR mutant accumulated three-fold less chromate than the wild-type. Addition of phosphate but not sulfate to rich medium drastically reduced chromate toxicity and import in the wild-type strain. Furthermore, the intracellular concentration of free inorganic phosphate was significantly reduced for the ΔtolR mutant in comparison to the wild-type strain. Moreover, extracellular labelled phosphate was significantly less incorporated into the ΔtolR mutant. Finally, two distinct TolQR mutant complexes, specifically affected in Tol-Pal energization without affecting the TolQRA complex structure, did not complement the ΔtolQR mutant for inorganic phosphate accumulation. We thus propose that, while the Pst system is well known to import inorganic phosphate, the Tol-Pal system participates to phosphate uptake in particular at medium to high extracellular phosphate concentrations. Since mutations disabling the Tol-Pal system lead to pleiotropic effects, chromate resistance and reduced inorganic phosphate import could occur from an indirect effect of mutations in components of the Tol-Pal system.
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Affiliation(s)
- Amine Ali Chaouche
- Aix Marseille Univ, CNRS, BIP UMR 7281, IMM, IM2B, 31 Chemin Joseph Aiguier, CS70071, 13402, Marseille Cedex 09, France.
| | - Laetitia Houot
- Aix Marseille Univ, CNRS, LISM UMR 7255, IMM, IM2B, 31 Chemin Joseph Aiguier, CS70071, 13402, Marseille Cedex 09, France.
| | - Denis Duché
- Aix Marseille Univ, CNRS, LISM UMR 7255, IMM, IM2B, 31 Chemin Joseph Aiguier, CS70071, 13402, Marseille Cedex 09, France.
| | - Chantal Iobbi-Nivol
- Aix Marseille Univ, CNRS, BIP UMR 7281, IMM, IM2B, 31 Chemin Joseph Aiguier, CS70071, 13402, Marseille Cedex 09, France.
| | - Marie-Thérèse Giudici-Orticoni
- Aix Marseille Univ, CNRS, BIP UMR 7281, IMM, IM2B, 31 Chemin Joseph Aiguier, CS70071, 13402, Marseille Cedex 09, France.
| | - Michel Fons
- Aix Marseille Univ, CNRS, BIP UMR 7281, IMM, IM2B, 31 Chemin Joseph Aiguier, CS70071, 13402, Marseille Cedex 09, France.
| | - Vincent Méjean
- Aix Marseille Univ, CNRS, BIP UMR 7281, IMM, IM2B, 31 Chemin Joseph Aiguier, CS70071, 13402, Marseille Cedex 09, France
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14
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Elliott J, Geddes RF. New concepts in phosphorus homeostasis and its impact on renal health with particular reference to the cat. Vet J 2022; 283-284:105842. [PMID: 35577278 DOI: 10.1016/j.tvjl.2022.105842] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/12/2021] [Revised: 05/08/2022] [Accepted: 05/10/2022] [Indexed: 11/17/2022]
Abstract
New discoveries relating to phosphorus homeostasis include the hormones fibroblast growth factor-23 and klotho produced by bone and kidney. These hormones, together with novel understanding of how calcium and phosphate ions are carried in colloidal form as calciprotein particles, have changed our view of how phosphorus is regulated. Recognition that high dietary intake of inorganic forms of phosphorus in humans is a risk factor for both cardiovascular and renal diseases have led to re-examination of the impact of inorganic sources of phosphorus in prepared cat foods on renal health. Data suggest that when homeostatic mechanisms lead to proximal tubular (S3 segment) phosphate concentrations exceeding 3.25mmol/L for a significant part of the day, tubular stress and structural kidney damage ensues. Recent experimental rodent studies support the concept that calciprotein particles form in the proximal tubule at these prevailing phosphate concentrations and trigger proximal tubular damage. Long-term feeding studies in cats suggest that carefully formulated prepared diets containing 1g/Mcal of inorganic phosphorus (in the form of sodium tripolyphosphate or potassium monophosphate and pyrophosphate), resulting in estimated tubular phosphate concentrations <2.5mmol/L can be fed to healthy adult cats without detectable adverse effects on renal health.
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Affiliation(s)
- Jonathan Elliott
- Department of Comparative Biomedical Sciences, Royal Veterinary College, Royal College Street, London NW1 0TU, UK.
| | - Rebecca F Geddes
- Department of Clinical Science and Services, Royal Veterinary College, Hawkshead Lane, Hatfield, Hertfordshire AL9 7TA, UK
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15
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Wang X, Xu Y, Yu X, Dey A, Zhang HY, Zink CM, Wodka D, Porter G, Matter WF, Porras L, Reidy CA, Peterson JA, Mattioni BE, Haas JV, Kowala MC, Wetterau JR. Effects of pharmacological inhibition of the sodium-dependent phosphate cotransporter 2b (NPT2b) on intestinal phosphate absorption in mouse and rat models. Pharmacol Res Perspect 2022; 10:e00938. [PMID: 35194979 PMCID: PMC8863579 DOI: 10.1002/prp2.938] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/06/2021] [Revised: 01/25/2022] [Accepted: 01/27/2022] [Indexed: 11/08/2022] Open
Abstract
An excess phosphate burden in renal disease has pathological consequences for bone, kidney, and heart. Therapies to decrease intestinal phosphate absorption have been used to address the problem, but with limited success. Here, we describe the in vivo effects of a novel potent inhibitor of the intestinal sodium-dependent phosphate cotransporter NPT2b, LY3358966. Following treatment with LY3358966, phosphate uptake into plasma 15 min following an oral dose of radiolabeled phosphate was decreased 74% and 22% in mice and rats, respectively, indicating NPT2b plays a much more dominant role in mice than rats. Following the treatment with LY3358966 and radiolabeled phosphate, mouse feces were collected for 48 h to determine the ability of LY3358966 to inhibit phosphate absorption. Compared to vehicle-treated animals, there was a significant increase in radiolabeled phosphate recovered in feces (8.6% of the dose, p < .0001). Similar studies performed in rats also increased phosphate recovered in feces (5.3% of the dose, p < .05). When used in combination with the phosphate binder sevelamer in rats, there was a further small, but not significant, increase in fecal phosphate. In conclusion, LY3358966 revealed a more prominent role for NPT2b on acute intestinal phosphate uptake into plasma in mice than rats. However, the modest effects on total intestinal phosphate absorption observed in mice and rats with LY3359866 when used alone or in combination with sevelamer highlights the challenge to identify new more effective therapeutic targets and/or drug combinations to treat the phosphate burden in patients with renal disease.
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Affiliation(s)
- Xiaojun Wang
- Lilly Research Laboratories, Eli Lilly and Company, Indianapolis, Indiana, USA
| | - Yanping Xu
- Lilly Research Laboratories, Eli Lilly and Company, Indianapolis, Indiana, USA
| | - Xiaohong Yu
- Lilly Research Laboratories, Eli Lilly and Company, Indianapolis, Indiana, USA
| | - Asim Dey
- Lilly Research Laboratories, Eli Lilly and Company, Indianapolis, Indiana, USA
| | - Hong Y Zhang
- Lilly Research Laboratories, Eli Lilly and Company, Indianapolis, Indiana, USA
| | - Charity M Zink
- Lilly Research Laboratories, Eli Lilly and Company, Indianapolis, Indiana, USA
| | - Derek Wodka
- Lilly Research Laboratories, Eli Lilly and Company, Indianapolis, Indiana, USA
| | - Gina Porter
- Lilly Research Laboratories, Eli Lilly and Company, Indianapolis, Indiana, USA
| | - William F Matter
- Lilly Research Laboratories, Eli Lilly and Company, Indianapolis, Indiana, USA
| | - Leah Porras
- Lilly Research Laboratories, Eli Lilly and Company, Indianapolis, Indiana, USA
| | - Charles A Reidy
- Lilly Research Laboratories, Eli Lilly and Company, Indianapolis, Indiana, USA
| | - Jeffrey A Peterson
- Lilly Research Laboratories, Eli Lilly and Company, Indianapolis, Indiana, USA
| | - Brian E Mattioni
- Lilly Research Laboratories, Eli Lilly and Company, Indianapolis, Indiana, USA
| | - Joseph V Haas
- Lilly Research Laboratories, Eli Lilly and Company, Indianapolis, Indiana, USA
| | - Mark C Kowala
- Lilly Research Laboratories, Eli Lilly and Company, Indianapolis, Indiana, USA
| | - John R Wetterau
- Lilly Research Laboratories, Eli Lilly and Company, Indianapolis, Indiana, USA
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16
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Xue J, Thomas L, Murali SK, Levi M, Fenton RA, Dominguez Rieg JA, Rieg T. Enhanced phosphate absorption in intestinal epithelial cell-specific NHE3 knockout mice. Acta Physiol (Oxf) 2022; 234:e13756. [PMID: 34978760 PMCID: PMC9286053 DOI: 10.1111/apha.13756] [Citation(s) in RCA: 10] [Impact Index Per Article: 5.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/22/2021] [Revised: 11/16/2021] [Accepted: 01/01/2022] [Indexed: 12/11/2022]
Abstract
Aims The kidneys play a major role in maintaining Pi homeostasis. Patients in later stages of CKD develop hyperphosphatemia. One novel treatment option is tenapanor, an intestinal‐specific NHE3 inhibitor. To gain mechanistic insight into the role of intestinal NHE3 in Pi homeostasis, we studied tamoxifen‐inducible intestinal epithelial cell‐specific NHE3 knockout (NHE3IEC‐KO) mice. Methods Mice underwent dietary Pi challenges, and hormones as well as urinary/plasma Pi were determined. Intestinal 33P uptake studies were conducted in vivo to compare the effects of tenapanor and NHE3IEC‐KO. Ex vivo Pi transport was measured in everted gut sacs and brush border membrane vesicles. Intestinal and renal protein expression of Pi transporters were determined. Results On the control diet, NHE3IEC‐KO mice had similar Pi homeostasis, but a ~25% reduction in FGF23 compared with control mice. Everted gut sacs and brush border membrane vesicles showed enhanced Pi uptake associated with increased Npt2b expression in NHE3IEC‐KO mice. Acute oral Pi loading resulted in higher plasma Pi in NHE3IEC‐KO mice. Tenapanor inhibited intestinal 33P uptake acutely but then led to hyper‐absorption at later time points compared to vehicle. In response to high dietary Pi, plasma Pi and FGF23 increased to higher levels in NHE3IEC‐KO mice which was associated with greater Npt2b expression. Reduced renal Npt2c and a trend for reduced Npt2a expression were unable to correct for higher plasma Pi. Conclusion Intestinal NHE3 has a significant contribution to Pi homeostasis. In contrast to effects described for tenapanor on Pi homeostasis, NHE3IEC‐KO mice show enhanced, rather than reduced, intestinal Pi uptake.
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Affiliation(s)
- Jianxiang Xue
- Department of Molecular Pharmacology and Physiology Morsani College of Medicine University of South Florida Tampa Florida USA
| | - Linto Thomas
- Department of Molecular Pharmacology and Physiology Morsani College of Medicine University of South Florida Tampa Florida USA
| | | | - Moshe Levi
- Department of Biochemistry and Molecular & Cellular Biology Georgetown University Washington District of Columbia USA
| | | | - Jessica A. Dominguez Rieg
- Department of Molecular Pharmacology and Physiology Morsani College of Medicine University of South Florida Tampa Florida USA
- James A. Haley Veterans' Hospital Tampa Florida USA
| | - Timo Rieg
- Department of Molecular Pharmacology and Physiology Morsani College of Medicine University of South Florida Tampa Florida USA
- James A. Haley Veterans' Hospital Tampa Florida USA
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17
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Doshi SM, Wish JB. Past, Present, and Future of Phosphate Management. Kidney Int Rep 2022; 7:688-698. [PMID: 35497793 PMCID: PMC9039476 DOI: 10.1016/j.ekir.2022.01.1055] [Citation(s) in RCA: 15] [Impact Index Per Article: 7.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/15/2021] [Revised: 01/12/2022] [Accepted: 01/17/2022] [Indexed: 11/20/2022] Open
Abstract
Cardiovascular (CV) disease (CVD) accounts for >50% of deaths with known causes in patients on dialysis. Elevated serum phosphorus levels are an important nontraditional risk factor for bone mineral disease and CVD in patients with chronic kidney disease (CKD). Given that phosphorus concentrations drive other disorders associated with increased CV risk (e.g., endothelial dysfunction, vascular calcification, fibroblast growth factor-23, parathyroid hormone), phosphate is a logical target to improve CV health. Phosphate binders are the only pharmacologic treatment approved for hyperphosphatemia. Although their safety has improved since inception, the mechanism of action leads to characteristics that make ingestion difficult and unpleasant; large pill size, objectionable taste, and multiple pills required for each meal and snack make phosphate binders a burden. Side effects, especially those affecting the gastrointestinal (GI) system, are common with binders, often leading to treatment discontinuation. The presence of “hidden” phosphates in processed foods and certain medications makes phosphate management even more challenging. Owing to these significant issues, most patients on dialysis are not consistently achieving and maintaining target phosphorus concentrations of <5.5 mg/dl, let alone more normal levels of <4.5 mg/dl, indicating novel approaches to improve phosphate management and CV health are needed. Several new nonbinder therapies that target intestinal phosphate absorption pathways have been developed. These include EOS789, which acts on the transcellular pathway, and tenapanor, which targets the dominant paracellular pathway. As observational evidence has established a strong association between phosphorus concentration and clinical outcomes, such as mortality, phosphate is an important target for improving the health of patients with CKD and end-stage kidney disease (ESKD).
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18
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Novel intestinal dialysis interventions and microbiome modulation to control uremia. Curr Opin Nephrol Hypertens 2022; 31:82-91. [PMID: 34846313 DOI: 10.1097/mnh.0000000000000753] [Citation(s) in RCA: 7] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/22/2022]
Abstract
PURPOSE OF REVIEW In patients with chronic kidney disease (CKD), the gut plays a key role in the homeostasis of fluid and electrolyte balance and the production and disposal of uremic toxins. This review summarizes the current evidence on the gut-targeted interventions to control uremia, fluid overload, hyperkalemia and hyperphosphatemia in CKD. RECENT FINDINGS Studies have emerged that support the concept of intestinal dialysis, such as colonic perfusion with a Malone antegrade continence enema stoma or colonic irrigation with a rectal catheter, as a promising adjuvant approach to control uremia in CKD, although most findings are preliminary. The use of AST-120, an oral adsorbent, has been shown to reduce circulating levels of indoxyl sulfate and p-cresol sulfate and have potential renoprotective benefits in patients with advanced CKD. Diarrhea or inducing watery stools may modulate fluid retention and potassium and phosphorus load. Accumulating evidence indicates that plant-based diets, low-protein diets, and pre-, pro-, and synbiotic supplementation may lead to favorable alterations of the gut microbiota, contributing to reduce uremic toxin generation. The effects of these gut-targeted interventions on kidney and cardiovascular outcomes are still limited and need to be tested in future studies including clinical trials. SUMMARY Interventions aimed at enhancing bowel elimination of uremic toxins, fluid and electrolytes and at modulating gut microbiota may represent novel therapeutic strategies for the management of uremia in patients with CKD.
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19
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Fishbane SN, Nigwekar S. Phosphate Absorption and Hyperphosphatemia Management in Kidney Disease: A Physiology-Based Review. Kidney Med 2021; 3:1057-1064. [PMID: 34939015 PMCID: PMC8664730 DOI: 10.1016/j.xkme.2021.07.003] [Citation(s) in RCA: 6] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022] Open
Abstract
Phosphate absorption occurs in the gastrointestinal tract through paracellular absorption and transcellular transport. The paracellular pathway does not saturate and has a significantly higher absorption capacity than does the transcellular pathway. Evidence indicates that this pathway is the primary mechanism of intestinal phosphate absorption, particularly with Western diets containing high amounts of phosphorus. Elevated serum phosphorus concentrations are associated with cardiovascular morbidity and mortality but serum phosphorus concentrations > 5.5 mg/dL are highly prevalent despite best efforts with dietary phosphate restriction, dialysis, and the use of phosphate binders. The efficacy of phosphate binders may be inherently limited because the mechanism of action does not target any phosphate absorption pathway. Thus, therapeutic innovations are needed to address the limitations of phosphate binders. Novel therapies leveraging new mechanistic understandings of phosphate absorption and the primacy of the paracellular pathway may improve phosphate control. Phosphate absorption inhibitors that target the pathway are a novel therapeutic class. Tenapanor is an investigational first-in-class nonbinder phosphate absorption inhibitor that inhibits the sodium-hydrogen exchanger isoform 3 to reduce paracellular permeability specific to phosphate. Phosphate absorption inhibitors may represent a new mechanistic approach to phosphate management with the potential to improve clinical outcomes.
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Affiliation(s)
- Steven N. Fishbane
- Department of Medicine, Zucker School of Medicine at Hofstra, Hempstead, Great Neck, NY
- Northwell, Great Neck, NY
| | - Sagar Nigwekar
- Department of Medicine, Harvard Medical School, Boston, MA
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20
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Yee J, Rosenbaum D, Jacobs JW, Sprague SM. Small Intestinal Phosphate Absorption: Novel Therapeutic Implications. Am J Nephrol 2021; 52:522-530. [PMID: 34515051 DOI: 10.1159/000518110] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/18/2021] [Accepted: 06/24/2021] [Indexed: 01/19/2023]
Abstract
BACKGROUND Chronic kidney disease (CKD) affects approximately 15% of adults in the USA. As CKD progresses, urinary phosphate excretion decreases and results in phosphate retention and, eventually, hyperphosphatemia. As hyperphosphatemia is associated with numerous adverse outcomes, including increased cardiovascular mortality, reduction in phosphorus concentrations is a guideline-recommended, established clinical practice. Dietary phosphate restriction, dialysis, and phosphate binders are currently the only options for phosphate management. However, many patients with hyperphosphatemia have phosphorus concentrations >5.5 mg/dL, despite treatment. SUMMARY This review pre-sents recent advances in the understanding of intestinal phosphate absorption and therapeutic implications. Dietary phosphate is absorbed in the intestine through two distinct pathways, paracellular absorption and transcellular transport. Recent evidence indicates that the paracellular route accounts for 65-80% of total phosphate absorbed. Thus, the paracellular pathway is the dominant mechanism of phosphate absorption. Tenapanor is a first-in-class, non-phosphate binder that inhibits the sodium-hydrogen exchanger 3 or solute carrier family 9 member 3 (SLC9A3) encoded by the SLC9A3 gene, and blocks paracellular phosphate absorption. Key Messages: Targeted inhibition of sodium-hydrogen exchanger 3 effectively reduces paracellular permeability of phosphate. Novel therapies that target the paracellular pathway may improve phosphate control in chronic kidney disease.
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Affiliation(s)
- Jerry Yee
- Nephrology and Hypertension, Henry Ford Hospital, Detroit, Michigan, USA
| | | | | | - Stuart M Sprague
- Division of Nephrology and Hypertension, NorthShore University Health System, Evanston, Illinois, USA
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21
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Stremke ER, Wiese GN, Moe SM, Wastney ME, Moorthi RN, Hill Gallant KM. Intestinal Phosphorus Absorption in Moderate CKD and Healthy Adults Determined Using a Radioisotopic Tracer. J Am Soc Nephrol 2021; 32:2057-2069. [PMID: 34244325 PMCID: PMC8455256 DOI: 10.1681/asn.2020091340] [Citation(s) in RCA: 16] [Impact Index Per Article: 5.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/18/2020] [Accepted: 03/15/2021] [Indexed: 02/04/2023] Open
Abstract
BACKGROUND Reducing intestinal phosphorus absorption is a cornerstone in CKD-MBD management. Yet, knowledge gaps include how CKD pathophysiology affects intestinal phosphorus absorption. In vivo rodent studies suggest that intestinal phosphorus absorption remains inappropriately normal in early-moderate CKD, despite declining 1,25-dihydroxyvitamin D (1,25D). We measured intestinal phosphorus absorption in patients with moderate CKD versus healthy adults using a direct radiotracer method. METHODS Patients with CKD and healthy adults matched for age, sex, and race were enrolled in this 8-day controlled diet study: the first 6 days outpatient and the final 2 days inpatient. Oral and intravenous doses of 33P and serial blood and urine sampling determined intestinal phosphorus absorption during the final 2 days. Secondary outcomes included fasting biochemistries and 24-hour urine phosphorus (uP). RESULTS In total, n=8 patients with CKD (eGFR=29-55 ml/min per 1.73 m2) and n=8 matched healthy controls completed the study. On a controlled diet, no difference in fractional intestinal phosphorus absorption was detected between patients with CKD and healthy adults (0.69 versus 0.62, respectively; P=0.52), and this was similar for 24-hour uP (884 versus 935 mg/d, respectively; P=0.70). Fractional intestinal phosphorus absorption was not significantly related to 24-hour uP. Patients with CKD had higher serum intact PTH and intact FGF23 and lower 1,25D. The relationship between 1,25D and fractional intestinal phosphorus absorption was not statistically significant. CONCLUSIONS Intestinal phosphorus absorption with typical dietary intake did not differ in patients with moderate CKD compared with controls, despite lower serum 1,25D levels. In this setting, a relationship between 24-hour uP and fractional or absolute intestinal absorption was not evident. Further investigation is needed to determine what factors influence intestinal phosphorus absorption in CKD and the apparent lack of compensation by the intestine to limit phosphorus absorption in the face of declining kidney function and reduced 1,25D. Whether this is evident across a range of dietary phosphorus intakes, as well as CKD severity, also needs to be determined. CLINICAL TRIAL REGISTRY NAME AND REGISTRATION NUMBER Phosphorus Absorption in Healthy Adults and in Patients with Moderate Chronic Kidney Disease, NCT03108222.
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Affiliation(s)
- Elizabeth R. Stremke
- Department of Nutrition Science, Purdue University, West Lafayette, Indiana
- Division of Epidemiology and Community Health, University of Minnesota, Minneapolis, Minnesota
| | - Gretchen N. Wiese
- Department of Nutrition Science, Purdue University, West Lafayette, Indiana
| | - Sharon M. Moe
- Division of Nephrology, Department of Medicine, Indiana University School of Medicine, Indianapolis, Indiana
- Department of Medicine, Roudebush Veterans Administration Medical Center, Indianapolis, Indiana
| | - Meryl E. Wastney
- Department of Nutrition Science, Purdue University, West Lafayette, Indiana
- Metabolic Modeling Services, West Lafayette, Indiana
| | - Ranjani N. Moorthi
- Division of Nephrology, Department of Medicine, Indiana University School of Medicine, Indianapolis, Indiana
| | - Kathleen M. Hill Gallant
- Department of Nutrition Science, Purdue University, West Lafayette, Indiana
- Division of Nephrology, Department of Medicine, Indiana University School of Medicine, Indianapolis, Indiana
- Department of Food Science and Nutrition, University of Minnesota, St. Paul, Minnesota
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22
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Kritmetapak K, Kumar R. Novel Insights into Mechanisms of Intestinal Phosphate Absorption in Patients with Chronic Kidney Disease. J Am Soc Nephrol 2021; 32:1830-1832. [PMID: 34330767 PMCID: PMC8455260 DOI: 10.1681/asn.2021050610] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/06/2021] [Accepted: 05/07/2021] [Indexed: 02/04/2023] Open
Affiliation(s)
- Kittrawee Kritmetapak
- Division of Nephrology and Hypertension, Department of Medicine, Mayo Clinic, Rochester, Minnesota,Division of Nephrology, Department of Medicine, Khon Kaen University, Khon Kaen, Thailand
| | - Rajiv Kumar
- Division of Nephrology and Hypertension, Department of Medicine, Mayo Clinic, Rochester, Minnesota
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23
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Gallant KMH, Vorland CJ. Intestinal phosphorus absorption: recent findings in translational and clinical research. Curr Opin Nephrol Hypertens 2021; 30:404-410. [PMID: 34027902 PMCID: PMC8153371 DOI: 10.1097/mnh.0000000000000719] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/13/2022]
Abstract
PURPOSE OF REVIEW The purpose of this review is to discuss recent findings in intestinal phosphorus absorption pathways, particularly the contributions of paracellular versus transcellular absorption, and the differential findings from studies using in vitro versus in vivo techniques of assessing phosphorus absorption in experimental animal studies. RECENT FINDINGS Experimental animal studies show that in vivo effects of low phosphorus diets, 1,25D, and chronic kidney disease on intestinal phosphorus absorption efficiency contradict effects previously established ex vivo/in vitro. Recent in vivo studies also suggest that the paracellular pathway accounts for the majority of phosphorus absorption in animals across very low to high luminal phosphate concentrations. The data from experimental animal studies correspond to recent human studies showing the effectiveness of targeted inhibition of paracellular phosphate absorption. Additionally, recent human studies have demonstrated that NaPi-2b inhibition alone does not appear to be effective in lowering serum phosphate levels in patients with chronic kidney disease. Pursuit of other transcellular phosphate transporter inhibitors may still hold promise. SUMMARY In vivo animal and human studies have added to our understanding of intestinal phosphorus absorption pathways, regulation, and mechanisms. This is beneficial for developing effective new strategies for phosphate management in patients with chronic kidney disease.
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Affiliation(s)
- Kathleen M. Hill Gallant
- Department of Food Science and Nutrition, University of Minnesota, Minneapolis-St. Paul, MN
- Department of Medicine/Division of Nephrology, Indiana University School of Medicine, Indianapolis, IN
| | - Colby J. Vorland
- Department of Applied Health Science, Indiana University School of Public Health-Bloomington, Bloomington, IN
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24
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Tang X, Liu X, Liu H. Mechanisms of Epidermal Growth Factor Effect on Animal Intestinal Phosphate Absorption: A Review. Front Vet Sci 2021; 8:670140. [PMID: 34195248 PMCID: PMC8236626 DOI: 10.3389/fvets.2021.670140] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/20/2021] [Accepted: 05/03/2021] [Indexed: 01/15/2023] Open
Abstract
Phosphorus is one of the essential mineral elements of animals that plays an important role in animal growth and development, bone formation, energy metabolism, nucleic acid synthesis, cell signal transduction, and blood acid–base balance. It has been established that the Type IIb sodium-dependent phosphate cotransporters (NaPi-IIb) protein is the major sodium-dependent phosphate (Pi) transporter, which plays an important role in Pi uptake across the apical membrane of epithelial cells in the small intestine. Previous studies have demonstrated that epidermal growth factor (EGF) is involved in regulating intestinal Pi absorption. Here we summarize the effects of EGF on active Pi transport of NaPi-IIb under different conditions. Under normal conditions, EGF inhibits the active transport of Pi by inhibiting the expression of NaPi-IIb, while, under intestinal injury condition, EGF promotes the active absorption of Pi through upregulating the expression of NaPi-IIb. This review provides a reference for information about EGF-regulatory functions in Pi absorption in the animal intestine.
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Affiliation(s)
- Xiaopeng Tang
- State Engineering Technology Institute for Karst Desertfication Control, School of Karst Science, Guizhou Normal University, Guiyang, China
| | - Xuguang Liu
- State Engineering Technology Institute for Karst Desertfication Control, School of Karst Science, Guizhou Normal University, Guiyang, China
| | - Hu Liu
- State Key Laboratory of Grassland Agro-Ecosystems, International Centre for Tibetan Plateau Ecosystem Management, Engineering Research Center of Arid Agriculture and Ecological Remediation of Ministry of Education, School of Life Sciences, Lanzhou University, Lanzhou, China
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25
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Asowata EO, Olusanya O, Abaakil K, Chichger H, Srai SKS, Unwin RJ, Marks J. Diet-induced iron deficiency in rats impacts small intestinal calcium and phosphate absorption. Acta Physiol (Oxf) 2021; 232:e13650. [PMID: 33749990 DOI: 10.1111/apha.13650] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/10/2020] [Revised: 02/26/2021] [Accepted: 03/17/2021] [Indexed: 12/31/2022]
Abstract
AIMS Recent reports suggest that iron deficiency impacts both intestinal calcium and phosphate absorption, although the exact transport pathways and intestinal segment responsible have not been determined. Therefore, we aimed to systematically investigate the impact of iron deficiency on the cellular mechanisms of transcellular and paracellular calcium and phosphate transport in different regions of the rat small intestine. METHODS Adult, male Sprague-Dawley rats were maintained on a control or iron-deficient diet for 2 weeks and changes in intestinal calcium and phosphate uptake were determined using the in situ intestinal loop technique. The circulating levels of the hormonal regulators of calcium and phosphate were determined by ELISA, while the expression of transcellular calcium and phosphate transporters, and intestinal claudins were determined using qPCR and western blotting. RESULTS Diet-induced iron deficiency significantly increased calcium absorption in the duodenum but had no impact in the jejunum and ileum. In contrast, phosphate absorption was significantly inhibited in the duodenum and to a lesser extent the jejunum, but remained unchanged in the ileum. The changes in duodenal calcium and phosphate absorption in the iron-deficient animals were associated with increased claudin 2 and 3 mRNA and protein levels, while levels of parathyroid hormone, fibroblast growth factor-23 and 1,25-dihydroxy vitamin D3 were unchanged. CONCLUSION We propose that iron deficiency alters calcium and phosphate transport in the duodenum. This occurs via changes to the paracellular pathway, whereby upregulation of claudin 2 increases calcium absorption and upregulation of claudin 3 inhibits phosphate absorption.
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Affiliation(s)
- Evans O. Asowata
- Department of Neuroscience, Physiology & Pharmacology University College London London UK
| | - Oluwatobi Olusanya
- Department of Neuroscience, Physiology & Pharmacology University College London London UK
| | - Kaoutar Abaakil
- Department of Neuroscience, Physiology & Pharmacology University College London London UK
| | - Havovi Chichger
- Biomedical Research Group School of Life Sciences Anglia Ruskin University Cambridge UK
| | - Surjit K. S. Srai
- Institute of Structural and Molecular Biology University College London London UK
| | - Robert J. Unwin
- Department of Renal Medicine University College London London UK
| | - Joanne Marks
- Department of Neuroscience, Physiology & Pharmacology University College London London UK
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Sprague SM, Martin KJ, Coyne DW. Phosphate Balance and CKD-Mineral Bone Disease. Kidney Int Rep 2021; 6:2049-2058. [PMID: 34386654 PMCID: PMC8343779 DOI: 10.1016/j.ekir.2021.05.012] [Citation(s) in RCA: 18] [Impact Index Per Article: 6.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/21/2021] [Accepted: 05/10/2021] [Indexed: 12/29/2022] Open
Abstract
Chronic kidney disease–mineral bone disorder (CKD-MBD) is a common comorbidity in patients with CKD. Characterized by laboratory abnormalities, bone abnormality, and vascular calcification, CKD-MBD encompasses a group of mineral and hormone disturbances that are strongly associated with increased cardiovascular (CV) morbidity and mortality. Abnormal serum phosphate concentrations are an independent risk factor for CV morbidity and mortality, and overall mortality. Phosphate retention plays a central role in initiating and driving many other disturbances in CKD-MBD (e.g., increased parathyroid hormone and fibroblast growth factor 23 concentrations, hypocalcemia, low vitamin D) that are also linked to increased CV risk. Thus, effective phosphate control is a logical therapeutic target for CKD-MBD treatment. Current phosphate management strategies (dietary restrictions, dialysis, phosphate binders) are insufficient to consistently achieve and maintain target phosphate concentrations in patients on dialysis. Phosphate binders reduce available phosphate for intestinal absorption but do not impair the dominant phosphate absorption pathway. Novel therapies that consider new mechanistic understandings of intestinal phosphate absorption are needed. One such therapy is tenapanor, a targeted sodium-hydrogen exchanger isoform 3 inhibitor that has been shown to reduce serum phosphate concentrations in multiple clinical trials. Tenapanor has a novel mechanism of action that reduces intestinal phosphate absorption in the primary paracellular phosphate absorption pathway.
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Affiliation(s)
- Stuart M Sprague
- Division of Nephrology and Hypertension, NorthShore University Health System, Evanston, IL, USA
| | | | - Daniel W Coyne
- Department of Medicine, Washington University School of Medicine, St. Louis, MO, USA
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Pastor-Arroyo EM, Rodriguez JMM, Pellegrini G, Bettoni C, Levi M, Hernando N, Wagner CA. Constitutive depletion of Slc34a2/NaPi-IIb in rats causes perinatal mortality. Sci Rep 2021; 11:7943. [PMID: 33846411 PMCID: PMC8042035 DOI: 10.1038/s41598-021-86874-z] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/10/2020] [Accepted: 03/15/2021] [Indexed: 11/23/2022] Open
Abstract
Absorption of dietary phosphate (Pi) across intestinal epithelia is a regulated process mediated by transcellular and paracellular pathways. Although hyperphosphatemia is a risk factor for the development of cardiovascular disease, the amount of ingested Pi in a typical Western diet is above physiological needs. While blocking intestinal absorption has been suggested as a therapeutic approach to prevent hyperphosphatemia, a complete picture regarding the identity and regulation of the mechanism(s) responsible for intestinal absorption of Pi is missing. The Na+/Pi cotransporter NaPi-IIb is a secondary active transporter encoded by the Slc34a2 gene. This transporter has a wide tissue distribution and within the intestinal tract is located at the apical membrane of epithelial cells. Based on mouse models deficient in NaPi-IIb, this cotransporter is assumed to mediate the bulk of active intestinal absorption of Pi. However, whether or not this is also applicable to humans is unknown, since human patients with inactivating mutations in SLC34A2 have not been reported to suffer from Pi depletion. Thus, mice may not be the most appropriate experimental model for the translation of intestinal Pi handling to humans. Here, we describe the generation of a rat model with Crispr/Cas-driven constitutive depletion of Slc34a2. Slc34a2 heterozygous rats were indistinguishable from wild type animals under standard dietary conditions as well as upon 3 days feeding on low Pi. However, unlike in humans, homozygosity resulted in perinatal lethality.
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Affiliation(s)
- Eva Maria Pastor-Arroyo
- Institute of Physiology, University of Zürich, Winterthurerstrasse 190, 8057, Zurich, Switzerland
| | - Josep M Monné Rodriguez
- Laboratory for Animal Model Pathology (LAMP), Institute of Veterinary Pathology, Vetsuisse Faculty, University of Zurich, Winterthurerstrasse 268, 8057, Zurich, Switzerland
| | - Giovanni Pellegrini
- Laboratory for Animal Model Pathology (LAMP), Institute of Veterinary Pathology, Vetsuisse Faculty, University of Zurich, Winterthurerstrasse 268, 8057, Zurich, Switzerland
| | - Carla Bettoni
- Institute of Physiology, University of Zürich, Winterthurerstrasse 190, 8057, Zurich, Switzerland
| | - Moshe Levi
- Department of Biochemistry and Molecular and Cellular Biology, Georgetown University, Washington, DC, USA
| | - Nati Hernando
- Institute of Physiology, University of Zürich, Winterthurerstrasse 190, 8057, Zurich, Switzerland.
| | - Carsten A Wagner
- Institute of Physiology, University of Zürich, Winterthurerstrasse 190, 8057, Zurich, Switzerland.
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The Roles of Sodium-Independent Inorganic Phosphate Transporters in Inorganic Phosphate Homeostasis and in Cancer and Other Diseases. Int J Mol Sci 2020; 21:ijms21239298. [PMID: 33291240 PMCID: PMC7729900 DOI: 10.3390/ijms21239298] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/12/2020] [Revised: 11/29/2020] [Accepted: 12/02/2020] [Indexed: 12/13/2022] Open
Abstract
Inorganic phosphate (Pi) is an essential nutrient for the maintenance of cells. In healthy mammals, extracellular Pi is maintained within a narrow concentration range of 0.70 to 1.55 mM. Mammalian cells depend on Na+/Pi cotransporters for Pi absorption, which have been well studied. However, a new type of sodium-independent Pi transporter has been identified. This transporter assists in the absorption of Pi by intestinal cells and renal proximal tubule cells and in the reabsorption of Pi by osteoclasts and capillaries of the blood–brain barrier (BBB). Hyperphosphatemia is a risk factor for mineral deposition, the development of diseases such as osteoarthritis, and vascular calcifications (VCs). Na+-independent Pi transporters have been identified and biochemically characterized in vascular smooth muscle cells (VSMCs), chondrocytes, and matrix vesicles, and their involvement in mineral deposition in the extracellular microenvironment has been suggested. According to the growth rate hypothesis, cancer cells require more phosphate than healthy cells due to their rapid growth rates. Recently, it was demonstrated that breast cancer cells (MDA-MB-231) respond to high Pi concentration (2 mM) by decreasing Na+-dependent Pi transport activity concomitant with an increase in Na+-independent (H+-dependent) Pi transport. This Pi H+-dependent transport has a fundamental role in the proliferation and migratory capacity of MDA-MB-231 cells. The purpose of this review is to discuss experimental findings regarding Na+-independent inorganic phosphate transporters and summarize their roles in Pi homeostasis, cancers and other diseases, such as osteoarthritis, and in processes such as VC.
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Laflamme D, Backus R, Brown S, Butterwick R, Czarnecki-Maulden G, Elliott J, Fascetti A, Polzin D. A review of phosphorus homeostasis and the impact of different types and amounts of dietary phosphate on metabolism and renal health in cats. J Vet Intern Med 2020; 34:2187-2196. [PMID: 33159358 PMCID: PMC7694857 DOI: 10.1111/jvim.15961] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/27/2020] [Revised: 10/11/2020] [Accepted: 10/27/2020] [Indexed: 12/14/2022] Open
Abstract
Elevated concentrations of serum phosphate are linked with progression and increased case fatality rate in animals and humans with chronic kidney disease. Elevated concentrations of serum phosphate can be a risk factor for development of renal and cardiovascular diseases or osteoporosis in previously healthy people. In rodents, an excess intake of dietary phosphorus combined with an inverse dietary calcium : phosphorus ratio (<1 : 1) contributes to renal calcification. Renal injury also has occured in cats fed experimental diets supplemented with highly soluble phosphate salts, especially in diets with inverse calcium : phosphorus ratios. However, not all phosphorus sources contribute similarly to this effect. This review, which focuses on cats, summarizes the published evidence regarding phosphorus metabolism and homeostasis, including the relative impact of different dietary phosphorus sources, and their impact on the kidneys. No data currently shows that commercial cat foods induce renal injury. However, some diets contain high amounts of phosphorus relative to recommendations and some have inverse Ca : P ratios and so could increase the risk for development of kidney disease. While limiting the use of highly soluble phosphates appears to be important, there are insufficient data to support a specific upper limit for phosphate intake. This review also proposes areas where additional research is needed in order to strengthen conclusions and recommendations regarding dietary phosphorus for cats.
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Affiliation(s)
| | - Robert Backus
- Department of Veterinary Medicine and Surgery, College of Veterinary Medicine, University of Missouri, Columbia, Missouri, USA
| | - Scott Brown
- College of Veterinary Medicine, University of Georgia, Athens, Georgia, USA
| | | | | | - Jonathan Elliott
- Royal Veterinary College, University of London, London, United Kingdom
| | - Andrea Fascetti
- Department of Molecular Biosciences, University of California, Davis, California, USA
| | - David Polzin
- Veterinary Clinical Sciences Department, College of Veterinary Medicine, University of Minnesota, St Paul, Minnesota, USA
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Pastor‐Arroyo EM, Knöpfel T, Imenez Silva PH, Schnitzbauer U, Poncet N, Biber J, Wagner CA, Hernando N. Intestinal epithelial ablation of Pit-2/Slc20a2 in mice leads to sustained elevation of vitamin D 3 upon dietary restriction of phosphate. Acta Physiol (Oxf) 2020; 230:e13526. [PMID: 32564464 DOI: 10.1111/apha.13526] [Citation(s) in RCA: 16] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/06/2020] [Revised: 05/27/2020] [Accepted: 06/15/2020] [Indexed: 12/31/2022]
Abstract
AIM Several Na+ -dependent phosphate cotransporters, namely NaPi-IIb/SLC34A2, Pit-1/SLC20A1 and Pit-2/SLC20A2, are expressed at the apical membrane of enterocytes but their contribution to active absorption of phosphate is unclear. The aim of this study was to compare their pattern of mRNA expression along the small and large intestine and to analyse the effect of intestinal depletion of Pit-2 on phosphate homeostasis. METHODS Intestinal epithelial Pit-2-deficient mice were generated by crossing floxed Pit-2 with villin-Cre mice. Mice were fed 2 weeks standard or low phosphate diets. Stool, urine, plasma and intestinal and renal tissue were collected. Concentration of electrolytes and hormones, expression of mRNAs and proteins and intestinal transport of tracers were analysed. RESULTS Intestinal mRNA expression of NaPi-IIb and Pit-1 is segment-specific, whereas the abundance of Pit-2 mRNA is more homogeneous. In ileum, NaPi-IIb mRNA expression is restricted to enterocytes, whereas Pit-2 mRNA is found in epithelial and non-epithelial cells. Overall, their mRNA expression is not regulated by dietary phosphate. The absence of Pit-2 from intestinal epithelial cells does not affect systemic phosphate homeostasis under normal dietary conditions. However, in response to dietary phosphate restriction, Pit-2-deficient mice showed exacerbated hypercalciuria and sustained elevation of 1,25(OH)2 vitamin D3 . CONCLUSIONS In mice, the intestinal Na+ /phosphate cotransporters are not coexpressed in all segments. NaPi-IIb but not Pit-2 mRNA is restricted to epithelial cells. Intestinal epithelial Pit-2 does not contribute significantly to absorption of phosphate under normal dietary conditions. However, it may play a more significant role upon dietary phosphate restriction.
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Affiliation(s)
| | - Thomas Knöpfel
- Institute of Physiology University of Zürich Zürich Switzerland
| | | | | | - Nadège Poncet
- Institute of Physiology University of Zürich Zürich Switzerland
| | - Jürg Biber
- Institute of Physiology University of Zürich Zürich Switzerland
| | | | - Nati Hernando
- Institute of Physiology University of Zürich Zürich Switzerland
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31
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Serna J, Bergwitz C. Importance of Dietary Phosphorus for Bone Metabolism and Healthy Aging. Nutrients 2020; 12:E3001. [PMID: 33007883 PMCID: PMC7599912 DOI: 10.3390/nu12103001] [Citation(s) in RCA: 43] [Impact Index Per Article: 10.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/20/2020] [Revised: 09/25/2020] [Accepted: 09/26/2020] [Indexed: 12/13/2022] Open
Abstract
Inorganic phosphate (Pi) plays a critical function in many tissues of the body: for example, as part of the hydroxyapatite in the skeleton and as a substrate for ATP synthesis. Pi is the main source of dietary phosphorus. Reduced bioavailability of Pi or excessive losses in the urine causes rickets and osteomalacia. While critical for health in normal amounts, dietary phosphorus is plentiful in the Western diet and is often added to foods as a preservative. This abundance of phosphorus may reduce longevity due to metabolic changes and tissue calcifications. In this review, we examine how dietary phosphorus is absorbed in the gut, current knowledge about Pi sensing, and endocrine regulation of Pi levels. Moreover, we also examine the roles of Pi in different tissues, the consequences of low and high dietary phosphorus in these tissues, and the implications for healthy aging.
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Affiliation(s)
- Juan Serna
- Yale College, Yale University, New Haven, CT 06511, USA;
| | - Clemens Bergwitz
- Section of Endocrinology and Metabolism, Department of Internal Medicine, Yale School of Medicine, New Haven, CT 06519, USA
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Abstract
Phosphate is an essential nutrient for life and is a critical component of bone formation, a major signaling molecule, and structural component of cell walls. Phosphate is also a component of high-energy compounds (i.e., AMP, ADP, and ATP) and essential for nucleic acid helical structure (i.e., RNA and DNA). Phosphate plays a central role in the process of mineralization, normal serum levels being associated with appropriate bone mineralization, while high and low serum levels are associated with soft tissue calcification. The serum concentration of phosphate and the total body content of phosphate are highly regulated, a process that is accomplished by the coordinated effort of two families of sodium-dependent transporter proteins. The three isoforms of the SLC34 family (SLC34A1-A3) show very restricted tissue expression and regulate intestinal absorption and renal excretion of phosphate. SLC34A2 also regulates the phosphate concentration in multiple lumen fluids including milk, saliva, pancreatic fluid, and surfactant. Both isoforms of the SLC20 family exhibit ubiquitous expression (with some variation as to which one or both are expressed), are regulated by ambient phosphate, and likely serve the phosphate needs of the individual cell. These proteins exhibit similarities to phosphate transporters in nonmammalian organisms. The proteins are nonredundant as mutations in each yield unique clinical presentations. Further research is essential to understand the function, regulation, and coordination of the various phosphate transporters, both the ones described in this review and the phosphate transporters involved in intracellular transport.
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Affiliation(s)
- Nati Hernando
- University of Zurich-Irchel, Institute of Physiology, Zurich, Switzerland; Department of Medicine, University of Louisville School of Medicine, Louisville, Kentucky; and Robley Rex VA Medical Center, Louisville, Kentucky
| | - Kenneth Gagnon
- University of Zurich-Irchel, Institute of Physiology, Zurich, Switzerland; Department of Medicine, University of Louisville School of Medicine, Louisville, Kentucky; and Robley Rex VA Medical Center, Louisville, Kentucky
| | - Eleanor Lederer
- University of Zurich-Irchel, Institute of Physiology, Zurich, Switzerland; Department of Medicine, University of Louisville School of Medicine, Louisville, Kentucky; and Robley Rex VA Medical Center, Louisville, Kentucky
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Motta SE, Imenez Silva PH, Daryadel A, Haykir B, Pastor-Arroyo EM, Bettoni C, Hernando N, Wagner CA. Expression of NaPi-IIb in rodent and human kidney and upregulation in a model of chronic kidney disease. Pflugers Arch 2020; 472:449-460. [PMID: 32219532 DOI: 10.1007/s00424-020-02370-9] [Citation(s) in RCA: 15] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/06/2020] [Revised: 02/29/2020] [Accepted: 03/20/2020] [Indexed: 01/07/2023]
Abstract
Na+-coupled phosphate cotransporters from the SLC34 and SLC20 families of solute carriers mediate transepithelial transport of inorganic phosphate (Pi). NaPi-IIa/Slc34a1, NaPi-IIc/Slc34a3, and Pit-2/Slc20a2 are all expressed at the apical membrane of renal proximal tubules and therefore contribute to renal Pi reabsorption. Unlike NaPi-IIa and NaPi-IIc, which are rather kidney-specific, NaPi-IIb/Slc34a2 is expressed in several epithelial tissues, including the intestine, lung, testis, and mammary glands. Recently, the expression of NaPi-IIb was also reported in kidneys from rats fed on high Pi. Here, we systematically quantified the mRNA expression of SLC34 and SLC20 cotransporters in kidneys from mice, rats, and humans. In all three species, NaPi-IIa mRNA was by far the most abundant renal transcript. Low and comparable mRNA levels of the other four transporters, including NaPi-IIb, were detected in kidneys from rodents and humans. In mice, the renal expression of NaPi-IIa transcripts was restricted to the cortex, whereas NaPi-IIb mRNA was observed in medullary segments. Consistently, NaPi-IIb protein colocalized with uromodulin at the luminal membrane of thick ascending limbs of the loop of Henle segments. The abundance of NaPi-IIb transcripts in kidneys from mice was neither affected by dietary Pi, the absence of renal NaPi-IIc, nor the depletion of intestinal NaPi-IIb. In contrast, it was highly upregulated in a model of oxalate-induced kidney disease where all other SLC34 phosphate transporters were downregulated. Thus, NaPi-IIb may contribute to renal phosphate reabsorption, and its upregulation in kidney disease might promote hyperphosphatemia.
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Affiliation(s)
- Sarah E Motta
- Institute of Physiology, Switzerland and National Center of Competence in Research NCCR Kidney, University of Zurich, Winterthurerstrasse 190, CH-8057, Zurich, Switzerland
| | - Pedro Henrique Imenez Silva
- Institute of Physiology, Switzerland and National Center of Competence in Research NCCR Kidney, University of Zurich, Winterthurerstrasse 190, CH-8057, Zurich, Switzerland
| | - Arezoo Daryadel
- Institute of Physiology, Switzerland and National Center of Competence in Research NCCR Kidney, University of Zurich, Winterthurerstrasse 190, CH-8057, Zurich, Switzerland
| | - Betül Haykir
- Institute of Physiology, Switzerland and National Center of Competence in Research NCCR Kidney, University of Zurich, Winterthurerstrasse 190, CH-8057, Zurich, Switzerland
| | - Eva Maria Pastor-Arroyo
- Institute of Physiology, Switzerland and National Center of Competence in Research NCCR Kidney, University of Zurich, Winterthurerstrasse 190, CH-8057, Zurich, Switzerland
| | - Carla Bettoni
- Institute of Physiology, Switzerland and National Center of Competence in Research NCCR Kidney, University of Zurich, Winterthurerstrasse 190, CH-8057, Zurich, Switzerland
| | - Nati Hernando
- Institute of Physiology, Switzerland and National Center of Competence in Research NCCR Kidney, University of Zurich, Winterthurerstrasse 190, CH-8057, Zurich, Switzerland
| | - Carsten A Wagner
- Institute of Physiology, Switzerland and National Center of Competence in Research NCCR Kidney, University of Zurich, Winterthurerstrasse 190, CH-8057, Zurich, Switzerland.
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Cozzolino M, Ketteler M, Wagner CA. An expert update on novel therapeutic targets for hyperphosphatemia in chronic kidney disease: preclinical and clinical innovations. Expert Opin Ther Targets 2020; 24:477-488. [PMID: 32191548 DOI: 10.1080/14728222.2020.1743680] [Citation(s) in RCA: 11] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/06/2023]
Abstract
Introduction: The management of hyperphosphatemia in patients with chronic kidney disease (CKD) is complicated, requiring a multidisciplinary approach that includes dietary phosphate restriction, dialysis, and phosphate binders.Areas covered: We describe key players involved in regulating inorganic phosphate homeostasis and their differential role in healthy people and different stages of CKD. The contribution of paracellular and transcellular intestinal absorptive mechanisms are also examined. Finally, we illuminate recent therapeutic approaches for hyperphosphatemia in CKD. We searched PubMed/Medline (up to November 2019) using the following terms: chronic kidney disease, dialysis, diet, hyperphosphatemia, NaPi2b, nicotinamide, phosphate binder, secondary hyperparathyroidism, tenapanor and vascular calcification.Expert opinion: The precise mechanisms regulating intestinal phosphate absorption in humans is not completely understood. However, it is now established that this process involves two independent pathways: a) active transport (i.e. transcellular route, via specific ion transporters) and inactive transport (i.e. paracellular route across tight junctions). Dietary phosphate restriction and phosphate-binder use can lead to an undesirable maladaptive increase in phosphate uptake and promote active phosphate transport by increased expression of the gastrointestinal sodium-dependent phosphate transporter, NaPi2b. Nicotinamide may overcome these limitations through the inhibition of NaPi2b, by improved efficacy and reduced phosphate binder use and better compliance.
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Affiliation(s)
- Mario Cozzolino
- Renal Division, ASST Santi Paolo E Carlo, Department of Health Sciences, University of Milan, Milan, Italy
| | - Markus Ketteler
- Department of General Internal Medicine and Nephrology, Robert-Bosch-Krankenhaus, Stuttgart, Germany
| | - Carsten Alexander Wagner
- Institute of Physiology, University of Zurich, Zurich, Switzerland.,National Center of Competence in Research, NCCR Kidney. CH, Zurich, Switzerland
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Vorland CJ, Biruete A, Lachcik PJ, Srinivasan S, Chen NX, Moe SM, Hill Gallant KM. Kidney Disease Progression Does Not Decrease Intestinal Phosphorus Absorption in a Rat Model of Chronic Kidney Disease-Mineral Bone Disorder. J Bone Miner Res 2020; 35:333-342. [PMID: 31618470 PMCID: PMC7012714 DOI: 10.1002/jbmr.3894] [Citation(s) in RCA: 12] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 05/29/2019] [Revised: 09/29/2019] [Accepted: 10/13/2019] [Indexed: 11/05/2022]
Abstract
The Cy/+ rat has been characterized as a progressive model of chronic kidney disease-mineral bone disorder (CKD-MBD). We aimed to determine the effect of kidney disease progression on intestinal phosphorus absorption and whole-body phosphorus balance in this model. A total of 48 Cy/+ (CKD) and 48 normal littermates (NL) rats were studied at two ages: 20 weeks and 30 weeks, to model progressive kidney function decline at approximately 50% and 20% of normal kidney function. Sodium-dependent and sodium-independent intestinal phosphorus absorption efficiency were measured by the in situ jejunal ligated loop method using 33 P radioisotope. Our results show that CKD rats had slightly higher sodium-dependent phosphorus absorption compared to NL rats, and absorption decreased from 20 to 30 weeks. These results are in contrast to plasma 1,25OH2 D, which was lower in CKD rats. Gene expression of the major intestinal phosphorus transporter, NaPi-2b, was not different between CKD and NL rats in the jejunum but was lower in CKD rats versus NL rats in the duodenum. Jejunal ligated loop phosphorus absorption results are consistent with percent net phosphorus absorption results obtained from metabolic balance: higher net percent phosphorus absorption values in CKD rats compared with NL, and lower values in 30-week-olds compared with 20-week-olds. Phosphorus balance was negative (below zero) in CKD rats, significantly lower in 30-week-old rats compared with 20-week-old rats, and lower in CKD rats compared with NL rats at both ages. These results demonstrate no reduction in intestinal phosphorus absorption with progression of CKD despite lower 1,25OH2 D status when assessed by an in situ ligated loop test, which is in contrast to the majority of in vitro studies, and if confirmed in further studies, could challenge the physiological relevance of in vitro findings. © 2019 American Society for Bone and Mineral Research.
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Affiliation(s)
- Colby J Vorland
- Department of Nutrition Science, Purdue University, West Lafayette, IN, USA
| | - Annabel Biruete
- Division of Nephrology, Department of Medicine, Indiana University School of Medicine, Indianapolis, IN, USA
| | - Pamela J Lachcik
- Department of Nutrition Science, Purdue University, West Lafayette, IN, USA
| | - Shruthi Srinivasan
- Division of Nephrology, Department of Medicine, Indiana University School of Medicine, Indianapolis, IN, USA
| | - Neal X Chen
- Division of Nephrology, Department of Medicine, Indiana University School of Medicine, Indianapolis, IN, USA
| | - Sharon M Moe
- Division of Nephrology, Department of Medicine, Indiana University School of Medicine, Indianapolis, IN, USA
- Department of Anatomy and Cell Biology, Indiana University School of Medicine, Indianapolis, IN, USA
- Department of Medicine, Roudebush Veterans Affairs Medical Center, Indianapolis, IN, USA
| | - Kathleen M Hill Gallant
- Department of Nutrition Science, Purdue University, West Lafayette, IN, USA
- Division of Nephrology, Department of Medicine, Indiana University School of Medicine, Indianapolis, IN, USA
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36
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Developmental Changes in Phosphate Homeostasis. Rev Physiol Biochem Pharmacol 2020; 179:117-138. [PMID: 33398502 DOI: 10.1007/112_2020_52] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/14/2022]
Abstract
Phosphate is a multivalent ion critical for a variety of physiological functions including bone formation, which occurs rapidly in the developing infant. In order to ensure maximal bone mineralization, young animals must maintain a positive phosphate balance. To accomplish this, intestinal absorption and renal phosphate reabsorption are greater in suckling and young animals relative to adults. This review discusses the known intestinal and renal adaptations that occur in young animals in order to achieve a positive phosphate balance. Additionally, we discuss the ontogenic changes in phosphotropic endocrine signalling as it pertains to intestinal and renal phosphate handling, including several endocrine factors not always considered in the traditional dogma of phosphotropic endocrine signalling, such as growth hormone, triiodothyronine, and glucocorticoids. Finally, a proposed model of how these factors may contribute to achieving a positive phosphate balance during development is proposed.
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Yaguchi A, Akahane K, Tsuchioka K, Yonekubo S, Yamamoto S, Tamai Y, Tatemichi S, Takeda H. A comparison between the combined effect of calcium carbonate with sucroferric oxyhydroxide and other phosphate binders: an in vitro and in vivo experimental study. BMC Nephrol 2019; 20:465. [PMID: 31830936 PMCID: PMC6909506 DOI: 10.1186/s12882-019-1655-9] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/13/2019] [Accepted: 12/03/2019] [Indexed: 02/06/2023] Open
Abstract
Background Approximately 30% of patients on dialysis received combination therapy for their phosphate binder prescription; however, few studies for combined effects of phosphate binders are reported. For the purpose of evaluating the efficacy of combination therapy, we compared the efficacy of sucroferric oxyhydroxide (PA21) combined with calcium carbonate with that of lanthanum carbonate hydrate, sevelamer hydrochloride, and ferric citrate hydrate combined with calcium carbonate. Methods For in vitro studies, calcium carbonate and the other phosphate binders alone or in combination were stirred in phosphate solution at pH 2–8 for 2 h. After centrifuging the suspension, the phosphorus level in the supernatant was determined. For in vivo studies, rats were orally administered calcium carbonate and the other phosphate binders (except for sevelamer hydrochloride) alone or in combination, followed by oral administration of phosphate solution adjusted to pH 2 or 7. Serum samples were collected from the rats at predetermined timepoints and the serum phosphorus levels were determined and analyzed using a two-way analysis of variance. Results In the in vitro study, the measured phosphate-binding capacity of combining sevelamer hydrochloride, PA21, and lanthanum carbonate hydrate with calcium carbonate was approximately equal to or greater than the theoretical values under most conditions. Furthermore, these combined effects were insensitive to pH in that order. The measured phosphate-binding capacity of ferric citrate hydrate combined with calcium carbonate was smaller than the theoretical values, and the combination did not exhibit efficacy under any of the tested conditions. In the in vivo study, the combined effect of PA21 and calcium carbonate at both pH values and that of lanthanum carbonate hydrate and calcium carbonate at pH 2 were additive. In contrast, the combined effect of lanthanum carbonate hydrate and calcium carbonate at pH 7 and that of ferric citrate hydrate and calcium carbonate at pH 2 were antagonistic. Conclusions These results suggest that coadministration of PA21 and calcium carbonate showed good and relatively stable efficacy throughout the range of the gastrointestinal pH and that combining lanthanum carbonate hydrate and ferric citrate hydrate with calcium carbonate may not produce the expected efficacy under certain conditions.
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Affiliation(s)
- Atsushi Yaguchi
- Pharmacology Research Group, Pharmacology and Pharmacokinetics Research Laboratory, R&D, Kissei Pharmaceutical Co., Ltd., 4365-1 Kashiwabara, Hotaka, Azumino, Nagano, 399-8304, Japan.
| | - Kenji Akahane
- Pharmacology Research Group, Pharmacology and Pharmacokinetics Research Laboratory, R&D, Kissei Pharmaceutical Co., Ltd., 4365-1 Kashiwabara, Hotaka, Azumino, Nagano, 399-8304, Japan
| | - Kumi Tsuchioka
- Pharmacology Research Group, Pharmacology and Pharmacokinetics Research Laboratory, R&D, Kissei Pharmaceutical Co., Ltd., 4365-1 Kashiwabara, Hotaka, Azumino, Nagano, 399-8304, Japan
| | - Saori Yonekubo
- Pharmacology Research Group, Pharmacology and Pharmacokinetics Research Laboratory, R&D, Kissei Pharmaceutical Co., Ltd., 4365-1 Kashiwabara, Hotaka, Azumino, Nagano, 399-8304, Japan
| | - Shota Yamamoto
- Pharmacology Research Group, Pharmacology and Pharmacokinetics Research Laboratory, R&D, Kissei Pharmaceutical Co., Ltd., 4365-1 Kashiwabara, Hotaka, Azumino, Nagano, 399-8304, Japan
| | - Yasuaki Tamai
- Pharmacology Research Group, Pharmacology and Pharmacokinetics Research Laboratory, R&D, Kissei Pharmaceutical Co., Ltd., 4365-1 Kashiwabara, Hotaka, Azumino, Nagano, 399-8304, Japan
| | - Satoshi Tatemichi
- Pharmacology Research Group, Pharmacology and Pharmacokinetics Research Laboratory, R&D, Kissei Pharmaceutical Co., Ltd., 4365-1 Kashiwabara, Hotaka, Azumino, Nagano, 399-8304, Japan
| | - Hiroo Takeda
- Pharmacology Research Group, Pharmacology and Pharmacokinetics Research Laboratory, R&D, Kissei Pharmaceutical Co., Ltd., 4365-1 Kashiwabara, Hotaka, Azumino, Nagano, 399-8304, Japan
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Knöpfel T, Himmerkus N, Günzel D, Bleich M, Hernando N, Wagner CA. Paracellular transport of phosphate along the intestine. Am J Physiol Gastrointest Liver Physiol 2019; 317:G233-G241. [PMID: 31169994 DOI: 10.1152/ajpgi.00032.2019] [Citation(s) in RCA: 46] [Impact Index Per Article: 9.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 01/31/2023]
Abstract
Inorganic phosphate (Pi) is crucial for many biological functions, such as energy metabolism, signal transduction, and pH buffering. Efficient systems must exist to ensure sufficient supply for the body of Pi from diet. Previous experiments in humans and rodents suggest that two pathways for the absorption of Pi exist, an active transcellular Pi transport and a second paracellular pathway. Whereas the identity, role, and regulation of active Pi transport have been extensively studied, much less is known about the properties of the paracellular pathway. In Ussing chamber experiments, we characterized paracellular intestinal Pi permeabilities and fluxes. Dilution potential measurements in intestinal cell culture models demonstrated that the tight junction is permeable to Pi, with monovalent Pi having a higher permeability than divalent Pi. These findings were confirmed in rat and mouse intestinal segments by use of Ussing chambers and a combination of dilution potential measurements and fluxes of radiolabeled 32Pi. Both techniques yielded very similar results, showing that paracellular Pi fluxes were bidirectional and that Pi permeability was ~50% of the permeability for Na+ or Cl-. Pi fluxes were a function of the concentration gradient and Pi species (mono- vs. divalent Pi). In mice lacking the active transcellular Pi transport component sodium-dependent Pi transporter NaPi-IIb, the paracellular pathway was not upregulated. In summary, the small and large intestines have a very high paracellular Pi permeability, which may favor monovalent Pi fluxes and allow efficient uptake of Pi even in the absence of active transcellular Pi uptake.NEW & NOTEWORTHY The paracellular permeability for phosphate is high along the entire axis of the small and large intestine. There is a slight preference for monovalent phosphate. Paracellular phosphate fluxes do not increase when transcellular phosphate transport is genetically abolished. Paracellular phosphate transport may be an important target for therapies aiming to reduce intestinal phosphate absorption.
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Affiliation(s)
- Thomas Knöpfel
- University of Zürich, Institute of Physiology, Zürich, Switzerland
| | - Nina Himmerkus
- Christian-Albrechts-Universität zu Kiel, Physiologisches Institut, Kiel, Germany
| | - Dorothee Günzel
- Charité - Universitätsmedizin Berlin, Campus Benjamin Franklin, Institut für Klinische Physiologie, Berlin, Germany
| | - Markus Bleich
- Christian-Albrechts-Universität zu Kiel, Physiologisches Institut, Kiel, Germany
| | - Nati Hernando
- University of Zürich, Institute of Physiology, Zürich, Switzerland
| | - Carsten A Wagner
- University of Zürich, Institute of Physiology, Zürich, Switzerland
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Lacerda-Abreu MA, Russo-Abrahão T, Cosentino-Gomes D, Nascimento MTC, Carvalho-Kelly LF, Gomes T, Rodrigues MF, König S, Rumjanek FD, Monteiro RQ, Meyer-Fernandes JR. H +-dependent inorganic phosphate transporter in breast cancer cells: Possible functions in the tumor microenvironment. Biochim Biophys Acta Mol Basis Dis 2019; 1865:2180-2188. [PMID: 31034992 DOI: 10.1016/j.bbadis.2019.04.015] [Citation(s) in RCA: 11] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/23/2018] [Revised: 12/20/2018] [Accepted: 01/06/2019] [Indexed: 12/18/2022]
Abstract
Tumor microenvironment has a high concentration of inorganic phosphate (Pi), which is actually a marker for tumor progression. Regarding Pi another class of transporter has been recently studied, an H+-dependent Pi transporter, that is stimulated at acidic pH in Caco2BBE human intestinal cells. In this study, we characterized the H+-dependent Pi transport in breast cancer cell (MDA-MB-231) and around the cancer tissue. MDA-MB-231 cell line presented higher levels of H+-dependent Pi transport as compared to other breast cell lines, such as MCF-10A, MCF-7 and T47-D. The Pi transport was linear as a function of time and exhibited a Michaelis-Menten kinetic of Km = 1.387 ± 0.1674 mM Pi and Vmax = 198.6 ± 10.23 Pi × h-1 × mg protein-1 hence reflecting a low affinity Pi transport. H+-dependent Pi uptake was higher at acidic pH. FCCP, Bafilomycin A1 and SCH28080, which deregulate the intracellular levels of protons, inhibited the H+-dependent Pi transport. No effect on pHi was observed in the absence of inorganic phosphate. PAA, an H+-dependent Pi transport inhibitor, reduced the Pi transport activity, cell proliferation, adhesion, and migration. Arsenate, a structural analog of Pi, inhibited the Pi transport. At high Pi conditions, the H+-dependent Pi transport was five-fold higher than the Na+-dependent Pi transport, thus reflecting a low affinity Pi transport. The occurrence of an H+-dependent Pi transporter in tumor cells may endow them with an alternative path for Pi uptake in situations in which Na+-dependent Pi transport is saturated within the tumor microenvironment, thus regulating the energetically expensive tumor processes.
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Affiliation(s)
- Marco Antonio Lacerda-Abreu
- Instituto de Bioquímica Médica Leopoldo de Meis, Universidade Federal do Rio de Janeiro, RJ, Brazil; Instituto Nacional de Ciência e Tecnologia em Biologia Estrutural e Bioimagem, Rio de Janeiro, RJ, Brazil
| | - Thais Russo-Abrahão
- Instituto de Bioquímica Médica Leopoldo de Meis, Universidade Federal do Rio de Janeiro, RJ, Brazil; Instituto Nacional de Ciência e Tecnologia em Biologia Estrutural e Bioimagem, Rio de Janeiro, RJ, Brazil
| | - Daniela Cosentino-Gomes
- Instituto de Bioquímica Médica Leopoldo de Meis, Universidade Federal do Rio de Janeiro, RJ, Brazil; Instituto Nacional de Ciência e Tecnologia em Biologia Estrutural e Bioimagem, Rio de Janeiro, RJ, Brazil
| | - Michelle Tanny Cunha Nascimento
- Instituto de Bioquímica Médica Leopoldo de Meis, Universidade Federal do Rio de Janeiro, RJ, Brazil; Instituto Nacional de Ciência e Tecnologia em Biologia Estrutural e Bioimagem, Rio de Janeiro, RJ, Brazil
| | - Luiz Fernando Carvalho-Kelly
- Instituto de Bioquímica Médica Leopoldo de Meis, Universidade Federal do Rio de Janeiro, RJ, Brazil; Instituto Nacional de Ciência e Tecnologia em Biologia Estrutural e Bioimagem, Rio de Janeiro, RJ, Brazil
| | - Tainá Gomes
- Instituto de Bioquímica Médica Leopoldo de Meis, Universidade Federal do Rio de Janeiro, RJ, Brazil
| | | | - Sandra König
- Instituto de Ciência Biomédicas, Universidade Federal do Rio de Janeiro, RJ, Brazil
| | - Franklin David Rumjanek
- Instituto de Bioquímica Médica Leopoldo de Meis, Universidade Federal do Rio de Janeiro, RJ, Brazil
| | - Robson Q Monteiro
- Instituto de Bioquímica Médica Leopoldo de Meis, Universidade Federal do Rio de Janeiro, RJ, Brazil
| | - José Roberto Meyer-Fernandes
- Instituto de Bioquímica Médica Leopoldo de Meis, Universidade Federal do Rio de Janeiro, RJ, Brazil; Instituto Nacional de Ciência e Tecnologia em Biologia Estrutural e Bioimagem, Rio de Janeiro, RJ, Brazil.
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Saurette M, Alexander RT. Intestinal phosphate absorption: The paracellular pathway predominates? Exp Biol Med (Maywood) 2019; 244:646-654. [PMID: 30764666 DOI: 10.1177/1535370219831220] [Citation(s) in RCA: 16] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/28/2023] Open
Abstract
IMPACT STATEMENT This review summarizes the work on transcellular intestinal phosphate absorption, arguing why this pathway is not the predominant pathway in humans consuming a "Western" diet. We then highlight the recent evidence which is strongly consistent with paracellular intestinal phosphate absorption mediating the bulk of intestinal phosphate absorption in humans.
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Affiliation(s)
- Matthew Saurette
- 1 Department of Physiology, University of Alberta, Edmonton, Alberta T6G 2R7, Canada.,2 The Women's & Children's Health Research Institute, Edmonton, Alberta T6G 1C9, Canada
| | - R Todd Alexander
- 1 Department of Physiology, University of Alberta, Edmonton, Alberta T6G 2R7, Canada.,2 The Women's & Children's Health Research Institute, Edmonton, Alberta T6G 1C9, Canada.,3 Department of Pediatrics, University of Alberta, Edmonton, Alberta T6G 2R7, Canada
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Coltherd JC, Staunton R, Colyer A, Thomas G, Gilham M, Logan DW, Butterwick R, Watson P. Not all forms of dietary phosphorus are equal: an evaluation of postprandial phosphorus concentrations in the plasma of the cat. Br J Nutr 2019; 121:270-284. [PMID: 30420000 PMCID: PMC6390407 DOI: 10.1017/s0007114518003379] [Citation(s) in RCA: 20] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/01/2018] [Revised: 10/04/2018] [Accepted: 10/22/2018] [Indexed: 11/08/2022]
Abstract
Phosphorus is present in diets as naturally occurring P from raw materials or added as an inorganic salt. However, little is known about postprandial kinetics of P absorption in cats. Here, we describe several studies quantifying postprandial kinetics following the ingestion of diets of varying composition. Briefly, cats were fed a meal consisting of 50 % of their metabolic energy requirement in a randomised crossover design. A pre-meal baseline blood sample was taken via cephalic catheter and repeated measurements taken regularly up to 6 h post-meal to assess the whole blood ionised Ca, plasma P and parathyroid hormone concentrations. A diet containing 4·8 g total P/4184 kJ (1000 kcal), 3·5 g P from sodium dihydrogen phosphate (NaH2PO4)/4184 kJ (1000 kcal) and Ca:P 0·6 caused a marked increase in plasma P from baseline to a peak of 1·976 (95% CI 1·724, 2·266) mmol/l (P <0·001), whereas a diet containing 3·38 g total P/4184 kJ (1000 kcal), no added inorganic P and Ca:P 1·55 resulted in a postprandial decrease in plasma P (P = 0·008). Subsequent data indicate that added inorganic P salts in the diet above 0·5 g P/4184 kJ (1000 kcal) cause an increase in plasma P in cats, while diets below this do not. The data presented here demonstrate that sources of added inorganic P salts cause a temporary postprandial increase in plasma P in a dose-dependent manner, prolonged in diets with Ca:P <1·0. Dietary P derived from natural food ingredients (e.g. meat or vegetable matter) does not appear to have any effect on postprandial plasma P.
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Affiliation(s)
| | - Ruth Staunton
- WALTHAM Centre for Pet Nutrition, Melton Mowbray, Leicestershire LE14 4RT, UK
| | - Alison Colyer
- WALTHAM Centre for Pet Nutrition, Melton Mowbray, Leicestershire LE14 4RT, UK
| | - Gäelle Thomas
- WALTHAM Centre for Pet Nutrition, Melton Mowbray, Leicestershire LE14 4RT, UK
| | - Matthew Gilham
- WALTHAM Centre for Pet Nutrition, Melton Mowbray, Leicestershire LE14 4RT, UK
| | - Darren W. Logan
- WALTHAM Centre for Pet Nutrition, Melton Mowbray, Leicestershire LE14 4RT, UK
| | - Richard Butterwick
- WALTHAM Centre for Pet Nutrition, Melton Mowbray, Leicestershire LE14 4RT, UK
| | - Phillip Watson
- WALTHAM Centre for Pet Nutrition, Melton Mowbray, Leicestershire LE14 4RT, UK
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Effects of the long-term feeding of diets enriched with inorganic phosphorus on the adult feline kidney and phosphorus metabolism. Br J Nutr 2018; 121:249-269. [PMID: 30572965 PMCID: PMC6390406 DOI: 10.1017/s0007114518002751] [Citation(s) in RCA: 21] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/28/2022]
Abstract
Renal disease has a high incidence in cats, and some evidence implicates dietary P as well. To investigate this further, two studies in healthy adult cats were conducted. Study 1 (36 weeks) included forty-eight cats, stratified to control or test diets providing 1·2 or 4·8 g/1000 kcal (4184 kJ) P (0 or approximately 3·6 g/1000 kcal (4184 kJ) inorganic P, Ca:P 1·2, 0·6). Study 2 (29 weeks) included fifty cats, stratified to control or test diets, providing 1·3 or 3·6 g/1000 kcal (4184 kJ) P (0 or approximately 1·5 g/1000 kcal (4184 kJ) inorganic P, Ca:P 1·2, 0·9). Health markers, glomerular filtration rate (GFR) and mineral balance were measured regularly, with abdominal ultrasound. Study 1 was halted after 4 weeks as the test group GFR reduced by 0·4 (95 % CI 0·3, 0·5) ml/min per kg, and ultrasound revealed changes in renal echogenicity. In study 2, at week 28, no change in mean GFR was observed (P >0·05); however, altered renal echogenicity was detected in 36 % of test cats. In agreement with previous studies, feeding a diet with Ca:P <1·0, a high total and inorganic P inclusion resulted in loss of renal function and changes in echogenicity suggestive of renal pathology. Feeding a diet containing lower total and inorganic P with Ca:P close to 1·0 led to more subtle structural changes in a third of test cats; however, nephrolithiasis occurred in both diet groups, complicating data interpretation. We conclude that the no observed adverse effects level for total dietary P in adult cats is lower than 3·6 g/1000 kcal (4184 kJ), however the effect of inorganic P sources and Ca:P require further investigation.
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Sorribas V, Guillén N, Sosa C. Substrates and inhibitors of phosphate transporters: from experimental tools to pathophysiological relevance. Pflugers Arch 2018; 471:53-65. [DOI: 10.1007/s00424-018-2241-x] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/26/2018] [Revised: 11/21/2018] [Accepted: 11/25/2018] [Indexed: 12/26/2022]
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44
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Systemic network for dietary inorganic phosphate adaptation among three organs. Pflugers Arch 2018; 471:123-136. [DOI: 10.1007/s00424-018-2242-9] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/05/2018] [Revised: 11/26/2018] [Accepted: 11/27/2018] [Indexed: 12/22/2022]
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Vorland CJ, Lachcik PJ, Aromeh LO, Moe SM, Chen NX, Hill Gallant KM. Effect of dietary phosphorus intake and age on intestinal phosphorus absorption efficiency and phosphorus balance in male rats. PLoS One 2018; 13:e0207601. [PMID: 30452474 PMCID: PMC6242370 DOI: 10.1371/journal.pone.0207601] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/19/2018] [Accepted: 10/26/2018] [Indexed: 12/31/2022] Open
Abstract
Intestinal phosphorus absorption is an important component of whole-body phosphorus metabolism, and limiting dietary phosphorus absorption is particularly of interest as a therapeutic target in patients with chronic kidney disease to manage mineral bone disorders. Yet, mechanisms and regulation of intestinal phosphorus absorption have not been adequately studied and discrepancies in findings exist based on the absorption assessment technique used. In vitro techniques show rather consistent effects of dietary phosphorus intake level and age on intestinal sodium-dependent phosphate transport. But, the few studies that have used in vivo techniques conflict with these in vitro studies. Therefore, we aimed to investigate the effects of dietary phosphorus intake level on phosphorus absorption using the in situ ligated loop technique in three different aged rats. Male Sprague-Dawley rats (n = 72), were studied at 10-, 20-, and 30-weeks-of-age on a low (0.1%), normal (0.6%), or high (1.2%) phosphorus diet in a 3x3 factorial design (n = 8/group). Rats were fed their assigned diet for 2-weeks prior to absorption testing by jejunal ligated loop as a non-survival procedure, utilizing 33P radioisotope. Metabolic cages were used for determination of calcium and phosphorus balance over the final four days prior to sacrifice, and blood was collected at the time of sacrifice for biochemistries. Our results show that phosphorus absorption was higher in 10-week-old rats compared with 20- and 30-week-olds and this corresponded to higher gene expression of the major phosphate transporter, NaPi-2b, as well as higher whole-body phosphorus balance and net phosphorus absorption. Dietary phosphorus intake level did not affect jejunal phosphorus absorption or NaPi-2b gene expression. Our results contrast with studies utilizing in vitro techniques, but corroborate results of other rodent studies utilizing in situ or in vivo methods. Thus, there is need for additional studies that employ more physiological methods of phosphorus absorption assessment.
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Affiliation(s)
- Colby J. Vorland
- Department of Nutrition Science, Purdue University, West Lafayette, IN, United States of America
| | - Pamela J. Lachcik
- Department of Nutrition Science, Purdue University, West Lafayette, IN, United States of America
| | - Loretta O. Aromeh
- Division of Nephrology, Department of Medicine, Indiana University School of Medicine, Indianapolis, IN, United States of America
| | - Sharon M. Moe
- Division of Nephrology, Department of Medicine, Indiana University School of Medicine, Indianapolis, IN, United States of America
- Department of Anatomy and Cell Biology, Indiana University School of Medicine, Indianapolis, IN, United States of America
- Department of Medicine, Roudebush Veterans Affairs Medicine Center, Indianapolis, IN, United States of America
| | - Neal X. Chen
- Division of Nephrology, Department of Medicine, Indiana University School of Medicine, Indianapolis, IN, United States of America
| | - Kathleen M. Hill Gallant
- Department of Nutrition Science, Purdue University, West Lafayette, IN, United States of America
- * E-mail:
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46
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Marks J. The role of SLC34A2 in intestinal phosphate absorption and phosphate homeostasis. Pflugers Arch 2018; 471:165-173. [PMID: 30343332 PMCID: PMC6325986 DOI: 10.1007/s00424-018-2221-1] [Citation(s) in RCA: 25] [Impact Index Per Article: 4.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/27/2018] [Revised: 10/08/2018] [Accepted: 10/10/2018] [Indexed: 12/13/2022]
Abstract
There has recently been significant interest in the concept of directly targeting intestinal phosphate transport to control hyperphosphatemia in patients with chronic kidney disease. However, we do not have a complete understanding of the cellular mechanisms that govern dietary phosphate absorption. Studies in the 1970s documented both active and passive pathways for intestinal phosphate absorption. However, following the cloning of the intestinal SLC34 cotransporter, NaPi-IIb, much of the research focused on the role of this protein in active transcellular phosphate absorption and the factors involved in its regulation. Generation of a conditional NaPi-IIb knockout mouse has demonstrated that this protein is critical for the maintenance of skeletal integrity during periods of phosphate restriction and that under normal physiological conditions, the passive sodium-independent pathway is likely be the more dominant pathway for intestinal phosphate absorption. The review aims to summarise the most recent developments in our understanding of the role of the intestine in phosphate homeostasis, including the acute and chronic renal adaptations that occur in response to dietary phosphate intake. Evidence regarding the overall contribution of the transcellular and paracellular pathways for phosphate absorption will be discussed, together with the clinical benefit of inhibiting these pathways for the treatment of hyperphosphatemia in chronic kidney disease.
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Affiliation(s)
- Joanne Marks
- Department of Neuroscience, Physiology and Pharmacology, Royal Free Campus, University College London, Rowland Hill Street, London, NW3 2PF, UK.
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Sasaki S, Segawa H, Hanazaki A, Kirino R, Fujii T, Ikuta K, Noguchi M, Sasaki S, Koike M, Tanifuji K, Shiozaki Y, Kaneko I, Tatsumi S, Shimohata T, Kawai Y, Narisawa S, Millán JL, Miyamoto KI. A Role of Intestinal Alkaline Phosphatase 3 (Akp3) in Inorganic Phosphate Homeostasis. Kidney Blood Press Res 2018; 43:1409-1424. [PMID: 30212831 DOI: 10.1159/000493379] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/02/2018] [Accepted: 08/31/2018] [Indexed: 12/19/2022] Open
Abstract
BACKGROUND/AIMS Hyperphosphatemia is a serious complication of late-stage chronic kidney disease (CKD). Intestinal inorganic phosphate (Pi) handling plays an important role in Pi homeostasis in CKD. We investigated whether intestinal alkaline phosphatase 3 (Akp3), the enzyme that hydrolyzes dietary Pi compounds, is a target for the treatment of hyperphosphatemia in CKD. METHODS We investigated Pi homeostasis in Akp3 knockout mice (Akp3-/-). We also studied the progression of renal failure in an Akp3-/- mouse adenine treated renal failure model. Plasma, fecal, and urinary Pi and Ca concentration were measured with commercially available kit, and plasma fibroblast growth factor 23, parathyroid hormone, and 1,25(OH)2D3 concentration were measured with ELISA. Brush border membrane vesicles were prepared from mouse intestine using the Ca2+ precipitation method and used for Pi transport activity and alkaline phosphatase activity. In vivo intestinal Pi absorption was measured with oral 32P administration. RESULTS Akp3-/- mice exhibited reduced intestinal type II sodium-dependent Pi transporter (Npt2b) protein levels and Na-dependent Pi co-transport activity. In addition, plasma active vitamin D levels were significantly increased in Akp3-/- mice compared with wild-type animals. In the adenine-induced renal failure model, Akp3 gene deletion suppressed hyperphosphatemia. CONCLUSION The present findings indicate that intestinal Akp3 deletion affects Na+-dependent Pi transport in the small intestine. In the adenine-induced renal failure model, Akp3 is predicted to be a factor contributing to suppression of the plasma Pi concentration.
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Affiliation(s)
- Shohei Sasaki
- Department of Molecular Nutrition, Institute of Biomedical Sciences, University of Tokushima Graduate School, Tokushima, Japan
| | - Hiroko Segawa
- Department of Molecular Nutrition, Institute of Biomedical Sciences, University of Tokushima Graduate School, Tokushima,
| | - Ai Hanazaki
- Department of Molecular Nutrition, Institute of Biomedical Sciences, University of Tokushima Graduate School, Tokushima, Japan
| | - Ruri Kirino
- Department of Molecular Nutrition, Institute of Biomedical Sciences, University of Tokushima Graduate School, Tokushima, Japan
| | - Toru Fujii
- Department of Molecular Nutrition, Institute of Biomedical Sciences, University of Tokushima Graduate School, Tokushima, Japan
| | - Kayo Ikuta
- Department of Molecular Nutrition, Institute of Biomedical Sciences, University of Tokushima Graduate School, Tokushima, Japan
| | - Miwa Noguchi
- Department of Molecular Nutrition, Institute of Biomedical Sciences, University of Tokushima Graduate School, Tokushima, Japan
| | - Sumire Sasaki
- Department of Molecular Nutrition, Institute of Biomedical Sciences, University of Tokushima Graduate School, Tokushima, Japan
| | - Megumi Koike
- Department of Molecular Nutrition, Institute of Biomedical Sciences, University of Tokushima Graduate School, Tokushima, Japan
| | - Kazuya Tanifuji
- Department of Molecular Nutrition, Institute of Biomedical Sciences, University of Tokushima Graduate School, Tokushima, Japan
| | - Yuji Shiozaki
- Department of Molecular Nutrition, Institute of Biomedical Sciences, University of Tokushima Graduate School, Tokushima, Japan
| | - Ichiro Kaneko
- Department of Molecular Nutrition, Institute of Biomedical Sciences, University of Tokushima Graduate School, Tokushima, Japan
| | - Sawako Tatsumi
- Department of Molecular Nutrition, Institute of Biomedical Sciences, University of Tokushima Graduate School, Tokushima, Japan
| | - Takaaki Shimohata
- Department of Preventive Environment and Nutrition, Institute of Biomedical Sciences, University of Tokushima Graduate School, Tokushima, Japan
| | - Yoshichika Kawai
- Department of Food Science, Institute of Biomedical Sciences, University of Tokushima Graduate School, Tokushima, Japan
| | - Sonoko Narisawa
- Sanford Children's Health Research Center, Sanford Burnham Prebys Medical Discovery Institute, La Jolla, California, USA
| | - José Luis Millán
- Sanford Children's Health Research Center, Sanford Burnham Prebys Medical Discovery Institute, La Jolla, California, USA
| | - Ken-Ichi Miyamoto
- Department of Molecular Nutrition, Institute of Biomedical Sciences, University of Tokushima Graduate School, Tokushima, Japan
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48
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Hernando N, Wagner CA. Mechanisms and Regulation of Intestinal Phosphate Absorption. Compr Physiol 2018; 8:1065-1090. [PMID: 29978897 DOI: 10.1002/cphy.c170024] [Citation(s) in RCA: 41] [Impact Index Per Article: 6.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/26/2022]
Abstract
States of hypo- and hyperphosphatemia have deleterious consequences including rickets/osteomalacia and renal/cardiovascular disease, respectively. Therefore, the maintenance of appropriate plasma levels of phosphate is an essential requirement for health. This control is executed by the collaborative action of intestine and kidney whose capacities to (re)absorb phosphate are regulated by a number of hormonal and metabolic factors, among them parathyroid hormone, fibroblast growth factor 23, 1,25(OH)2 vitamin D3 , and dietary phosphate. The molecular mechanisms responsible for the transepithelial transport of phosphate across enterocytes are only partially understood. Indeed, whereas renal reabsorption entirely relies on well-characterized active transport mechanisms of phosphate across the renal proximal epithelia, intestinal absorption proceeds via active and passive mechanisms, with the molecular identity of the passive component still unknown. The active absorption of phosphate depends mostly on the activity and expression of the sodium-dependent phosphate cotransporter NaPi-IIb (SLC34A2), which is highly regulated by many of the factors, mentioned earlier. Physiologically, the contribution of NaPi-IIb to the maintenance of phosphate balance appears to be mostly relevant during periods of low phosphate availability. Therefore, its role in individuals living in industrialized societies with high phosphate intake is probably less relevant. Importantly, small increases in plasma phosphate, even within normal range, associate with higher risk of cardiovascular disease. Therefore, therapeutic approaches to treat hyperphosphatemia, including dietary phosphate restriction and phosphate binders, aim at reducing intestinal absorption. Here we review the current state of research in the field. © 2017 American Physiological Society. Compr Physiol 8:1065-1090, 2018.
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Affiliation(s)
- Nati Hernando
- National Center for Competence in Research NCCR Kidney.CH, Institute of Physiology, University Zurich-Irchel, Zurich, Switzerland
| | - Carsten A Wagner
- National Center for Competence in Research NCCR Kidney.CH, Institute of Physiology, University Zurich-Irchel, Zurich, Switzerland
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Aniteli TM, de Siqueira FR, Dos Reis LM, Dominguez WV, de Oliveira EMC, Castelucci P, Moysés RMA, Jorgetti V. Effect of variations in dietary Pi intake on intestinal Pi transporters (NaPi-IIb, PiT-1, and PiT-2) and phosphate-regulating factors (PTH, FGF-23, and MEPE). Pflugers Arch 2018; 470:623-632. [PMID: 29372301 DOI: 10.1007/s00424-018-2111-6] [Citation(s) in RCA: 15] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/19/2017] [Revised: 01/10/2018] [Accepted: 01/11/2018] [Indexed: 11/29/2022]
Abstract
Hyperphosphatemia is a common condition in patients with chronic kidney disease (CKD) and can lead to bone disease, vascular calcification, and increased risks of cardiovascular disease and mortality. Inorganic phosphate (Pi) is absorbed in the intestine, an important step in the maintenance of homeostasis. In CKD, it is not clear to what extent Pi absorption is modulated by dietary Pi. Thus, we investigated 5/6 nephrectomized (Nx) Wistar rats to test whether acute variations in dietary Pi concentration over 2 days would alter hormones involved in Pi metabolism, expression of sodium-phosphate cotransporters, apoptosis, and the expression of matrix extracellular phosphoglycoprotein (MEPE) in different segments of the small intestine. The animals were divided into groups receiving different levels of dietary phosphate: low (Nx/LPi), normal (Nx/NPi), and high (Nx/HPi). Serum phosphate, fractional excretion of phosphate, intact serum fibroblast growth factor 23 (FGF-23), and parathyroid hormone (PTH) were significantly higher and ionized calcium was significantly lower in the Nx/HPi group than in the Nx/LPi group. The expression levels of NaPi-IIb and PiT-1/2 were increased in the total jejunum mucosa of the Nx/LPi group compared with the Nx/HPi group. Modification of Pi concentration in the diet affected the apoptosis of enterocytes, particularly with Pi overload. MEPE expression was higher in the Nx/HPi group than in the Nx/NPi. These data reveal the importance of early control of Pi in uremia to prevent an increase in serum PTH and FGF-23. Uremia may be a determining factor that explains the expressional modulation of the cotransporters in the small intestine segments.
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Affiliation(s)
| | | | | | | | | | - Patrícia Castelucci
- Department of Anatomy, Institute of Biomedical Sciences, Universidade de São Paulo, São Paulo, Brazil
| | - Rosa Maria Affonso Moysés
- Medical School, Division of Nephrology, Universidade de São Paulo, São Paulo, Brazil.,Universidade Nove de Julho - UNINOVE, São Paulo, Brazil
| | - Vanda Jorgetti
- Medical School, Division of Nephrology, Universidade de São Paulo, São Paulo, Brazil. .,Faculdade de Medicina, Serviço de Nefrologia, Universidade de São Paulo, Av. Dr. Arnaldo, 455, 3° andar, sala 3342, São Paulo, SP, 01246-903, Brazil.
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Ikuta K, Segawa H, Sasaki S, Hanazaki A, Fujii T, Kushi A, Kawabata Y, Kirino R, Sasaki S, Noguchi M, Kaneko I, Tatsumi S, Ueda O, Wada NA, Tateishi H, Kakefuda M, Kawase Y, Ohtomo S, Ichida Y, Maeda A, Jishage KI, Horiba N, Miyamoto KI. Effect of Npt2b deletion on intestinal and renal inorganic phosphate (Pi) handling. Clin Exp Nephrol 2017; 22:517-528. [PMID: 29128884 DOI: 10.1007/s10157-017-1497-3] [Citation(s) in RCA: 28] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/02/2017] [Accepted: 10/13/2017] [Indexed: 12/16/2022]
Abstract
BACKGROUND Hyperphosphatemia is common in chronic kidney disease and is associated with morbidity and mortality. The intestinal Na+-dependent phosphate transporter Npt2b is thought to be an important molecular target for the prevention of hyperphosphatemia. The role of Npt2b in the net absorption of inorganic phosphate (Pi), however, is controversial. METHODS In the present study, we made tamoxifen-inducible Npt2b conditional knockout (CKO) mice to analyze systemic Pi metabolism, including intestinal Pi absorption. RESULTS Although the Na+-dependent Pi transport in brush-border membrane vesicle uptake levels was significantly decreased in the distal intestine of Npt2b CKO mice compared with control mice, plasma Pi and fecal Pi excretion levels were not significantly different. Data obtained using the intestinal loop technique showed that Pi uptake in Npt2b CKO mice was not affected at a Pi concentration of 4 mM, which is considered the typical luminal Pi concentration after meals in mice. Claudin, which may be involved in paracellular pathways, as well as claudin-2, 12, and 15 protein levels were significantly decreased in the Npt2b CKO mice. Thus, Npt2b deficiency did not affect Pi absorption within the range of Pi concentrations that normally occurs after meals. CONCLUSION These findings indicate that abnormal Pi metabolism may also be involved in tight junction molecules such as Cldns that are affected by Npt2b deficiency.
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Affiliation(s)
- Kayo Ikuta
- Department of Molecular Nutrition, Institute of Biomedical Sciences, Tokushima University Graduate School, 3-18-15 Kuramoto-Cho, Tokushima, Tokushima, 770-8503, Japan
| | - Hiroko Segawa
- Department of Molecular Nutrition, Institute of Biomedical Sciences, Tokushima University Graduate School, 3-18-15 Kuramoto-Cho, Tokushima, Tokushima, 770-8503, Japan.
| | - Shohei Sasaki
- Department of Molecular Nutrition, Institute of Biomedical Sciences, Tokushima University Graduate School, 3-18-15 Kuramoto-Cho, Tokushima, Tokushima, 770-8503, Japan
| | - Ai Hanazaki
- Department of Molecular Nutrition, Institute of Biomedical Sciences, Tokushima University Graduate School, 3-18-15 Kuramoto-Cho, Tokushima, Tokushima, 770-8503, Japan
| | - Toru Fujii
- Department of Molecular Nutrition, Institute of Biomedical Sciences, Tokushima University Graduate School, 3-18-15 Kuramoto-Cho, Tokushima, Tokushima, 770-8503, Japan
| | - Aoi Kushi
- Department of Molecular Nutrition, Institute of Biomedical Sciences, Tokushima University Graduate School, 3-18-15 Kuramoto-Cho, Tokushima, Tokushima, 770-8503, Japan
| | - Yuka Kawabata
- Department of Molecular Nutrition, Institute of Biomedical Sciences, Tokushima University Graduate School, 3-18-15 Kuramoto-Cho, Tokushima, Tokushima, 770-8503, Japan
| | - Ruri Kirino
- Department of Molecular Nutrition, Institute of Biomedical Sciences, Tokushima University Graduate School, 3-18-15 Kuramoto-Cho, Tokushima, Tokushima, 770-8503, Japan
| | - Sumire Sasaki
- Department of Molecular Nutrition, Institute of Biomedical Sciences, Tokushima University Graduate School, 3-18-15 Kuramoto-Cho, Tokushima, Tokushima, 770-8503, Japan
| | - Miwa Noguchi
- Department of Molecular Nutrition, Institute of Biomedical Sciences, Tokushima University Graduate School, 3-18-15 Kuramoto-Cho, Tokushima, Tokushima, 770-8503, Japan
| | - Ichiro Kaneko
- Department of Molecular Nutrition, Institute of Biomedical Sciences, Tokushima University Graduate School, 3-18-15 Kuramoto-Cho, Tokushima, Tokushima, 770-8503, Japan
| | - Sawako Tatsumi
- Department of Molecular Nutrition, Institute of Biomedical Sciences, Tokushima University Graduate School, 3-18-15 Kuramoto-Cho, Tokushima, Tokushima, 770-8503, Japan
| | - Otoya Ueda
- Fuji Gotemba Research Labs., Research Division, Chugai Pharmaceutical Co., Ltd., 1-135, Komakado, Gotemba, Shizuoka, Japan
| | - Naoko A Wada
- Fuji Gotemba Research Labs., Research Division, Chugai Pharmaceutical Co., Ltd., 1-135, Komakado, Gotemba, Shizuoka, Japan
| | - Hiromi Tateishi
- Chugai Research Institute for Medical Science, Inc., 1-135, Komakado, Gotemba, Shizuoka, Japan
| | - Mami Kakefuda
- Chugai Research Institute for Medical Science, Inc., 1-135, Komakado, Gotemba, Shizuoka, Japan
| | - Yosuke Kawase
- Chugai Research Institute for Medical Science, Inc., 1-135, Komakado, Gotemba, Shizuoka, Japan
| | - Shuichi Ohtomo
- Fuji Gotemba Research Labs., Research Division, Chugai Pharmaceutical Co., Ltd., 1-135, Komakado, Gotemba, Shizuoka, Japan
| | - Yasuhiro Ichida
- Fuji Gotemba Research Labs., Research Division, Chugai Pharmaceutical Co., Ltd., 1-135, Komakado, Gotemba, Shizuoka, Japan
| | - Akira Maeda
- Fuji Gotemba Research Labs., Research Division, Chugai Pharmaceutical Co., Ltd., 1-135, Komakado, Gotemba, Shizuoka, Japan
| | - Kou-Ichi Jishage
- Fuji Gotemba Research Labs., Research Division, Chugai Pharmaceutical Co., Ltd., 1-135, Komakado, Gotemba, Shizuoka, Japan
- Chugai Research Institute for Medical Science, Inc., 1-135, Komakado, Gotemba, Shizuoka, Japan
| | - Naoshi Horiba
- Fuji Gotemba Research Labs., Research Division, Chugai Pharmaceutical Co., Ltd., 1-135, Komakado, Gotemba, Shizuoka, Japan
| | - Ken-Ichi Miyamoto
- Department of Molecular Nutrition, Institute of Biomedical Sciences, Tokushima University Graduate School, 3-18-15 Kuramoto-Cho, Tokushima, Tokushima, 770-8503, Japan
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