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Mouse Models of Mineral Bone Disorders Associated with Chronic Kidney Disease. Int J Mol Sci 2023; 24:ijms24065325. [PMID: 36982400 PMCID: PMC10048881 DOI: 10.3390/ijms24065325] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/08/2023] [Revised: 02/27/2023] [Accepted: 03/03/2023] [Indexed: 03/14/2023] Open
Abstract
Patients with chronic kidney disease (CKD) inevitably develop mineral and bone disorders (CKD–MBD), which negatively impact their survival and quality of life. For a better understanding of underlying pathophysiology and identification of novel therapeutic approaches, mouse models are essential. CKD can be induced by surgical reduction of a functional kidney mass, by nephrotoxic compounds and by genetic engineering specifically interfering with kidney development. These models develop a large range of bone diseases, recapitulating different types of human CKD–MBD and associated sequelae, including vascular calcifications. Bones are usually studied by quantitative histomorphometry, immunohistochemistry and micro-CT, but alternative strategies have emerged, such as longitudinal in vivo osteoblast activity quantification by tracer scintigraphy. The results gained from the CKD–MBD mouse models are consistent with clinical observations and have provided significant knowledge on specific pathomechanisms, bone properties and potential novel therapeutic strategies. This review discusses available mouse models to study bone disease in CKD.
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Abstract
PURPOSE OF REVIEW Progressive forms of chronic kidney disease (CKD) exhibit kidney inflammation and fibrosis that drive continued nephron loss; however, factors responsible for the development of these common pathologic features remain poorly defined. Recent investigations suggest pathways involved in maintaining urinary phosphate excretion in CKD may be contributing to kidney function decline. This review provides an update on recent evidence linking altered phosphate homeostasis to CKD progression. RECENT FINDINGS High dietary phosphate intake and increased serum concentrations of fibroblast growth factor 23 (FGF23) both increase urinary phosphate excretion and are associated with increased risk of kidney function decline. Recent investigations have discovered high concentrations of tubular phosphate promote phosphate-based nanocrystal formation that drives tubular injury, cyst formation, and fibrosis. SUMMARY Studies presented in this review highlight important scientific discoveries that have molded our current understanding of the contribution of altered phosphate homeostasis to CKD progression. The collective observations from these investigations implicate phosphaturia, and the resulting formation of phosphate-based crystals in tubular fluid, as unique risk factors for kidney function decline. Developing a better understanding of the relationship between tubular phosphate handling and kidney pathology could result in innovative strategies for improving kidney outcomes in patients with CKD.
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Affiliation(s)
- Kyle P Jansson
- The Jared Grantham Kidney Institute
- Department of Internal Medicine, Division of Nephrology & Hypertension, University of Kansas Medical Center, Kansas City, Kansas 66160, USA
| | - Alan S L Yu
- The Jared Grantham Kidney Institute
- Department of Internal Medicine, Division of Nephrology & Hypertension, University of Kansas Medical Center, Kansas City, Kansas 66160, USA
| | - Jason R Stubbs
- The Jared Grantham Kidney Institute
- Department of Internal Medicine, Division of Nephrology & Hypertension, University of Kansas Medical Center, Kansas City, Kansas 66160, USA
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3
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Hanudel MR, Czaya B, Wong S, Jung G, Chua K, Qiao B, Gabayan V, Ganz T. Renoprotective effects of ferric citrate in a mouse model of chronic kidney disease. Sci Rep 2022; 12:6695. [PMID: 35461329 PMCID: PMC9035171 DOI: 10.1038/s41598-022-10842-4] [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: 01/21/2022] [Accepted: 04/06/2022] [Indexed: 11/09/2022] Open
Abstract
AbstractIn chronic kidney disease, ferric citrate has been shown to be an effective phosphate binder and source of enteral iron; however, the effects of ferric citrate on the kidney have been less well-studied. Here, in Col4α3 knockout mice—a murine model of progressive chronic kidney disease, we evaluated the effects of five weeks of 1% ferric citrate dietary supplementation. As expected, ferric citrate lowered serum phosphate concentrations and increased serum iron levels in the Col4α3 knockout mice. Consistent with decreased enteral phosphate absorption and possibly improved iron status, ferric citrate greatly reduced circulating fibroblast growth factor 23 levels. Interestingly, ferric citrate also lessened systemic inflammation, improved kidney function, reduced albuminuria, and decreased kidney inflammation and fibrosis, suggesting renoprotective effects of ferric citrate in the setting of chronic kidney disease. The factors mediating possible ferric citrate renoprotection, the mechanisms by which they may act, and whether ferric citrate affects chronic kidney disease progression in humans deserves further study.
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Gerber C, Wang X, David V, Quaggin SE, Isakova T, Martin A. Long-Term Effects of Sglt2 Deletion on Bone and Mineral Metabolism in Mice. JBMR Plus 2021; 5:e10526. [PMID: 34368611 PMCID: PMC8328801 DOI: 10.1002/jbm4.10526] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 12/14/2020] [Revised: 05/20/2021] [Accepted: 06/16/2021] [Indexed: 12/30/2022] Open
Abstract
Sodium‐glucose cotransporter 2 (SGLT2) inhibitors improve kidney and cardiovascular outcomes in patients with type 2 diabetes mellitus (T2DM). However, bone fragility has emerged as a side effect in some but not in all human studies. Because use of SGLT2 inhibitors in humans affects mineral metabolism, we investigated the long‐term effects of genetic loss of Sglt2 function on bone and mineral metabolism in mice. Slc5a2 nonsense mutation in Sweet Pee (SP) mice results in total loss of Sglt2 function. We collected urine, serum, and bone samples from 15‐week‐old and 25‐week‐old wild‐type (WT) and SP mice fasted from food overnight. We measured parameters of renal function and mineral metabolism and we assessed bone growth, microarchitecture, and mineralization. As expected, 15‐week‐old and 25‐week‐old SP mice showed increased glucosuria, and normal kidney function compared to age‐matched WT mice. At 15 weeks, SP mice did not show alterations in mineral metabolism parameters. At 25 weeks, SP mice showed reduced fasting 24‐hour urinary calcium excretion and increased fractional excretion of phosphate, but normal serum calcium and phosphate, parathyroid hormone (PTH), vitamin D (1,25(OH)2D), and fibroblast growth factor (FGF23) levels. At 25 weeks, but not at 15 weeks, SP mice showed reduced body weight compared to WT. This was associated with reduced femur length at 25 weeks, suggesting impaired skeletal growth. SP mice did not show trabecular or cortical bone microarchitectural modifications but showed reduced cortical bone mineral density compared to WT mice at 25 weeks. These results suggest that loss of Sglt2 function in mice in the absence of T2DM does not alter regulatory hormones FGF23, PTH, and 1,25(OH)2D, but may contribute to bone fragility over the long term. Future studies are required to determine how loss of Sglt2 function impacts bone fragility in T2DM. © 2021 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)
- Claire Gerber
- Division of Nephrology and Hypertension, Feinberg School of Medicine Northwestern University Chicago IL USA.,Center for Translational Metabolism and Health, Institute for Public Health and Medicine Northwestern University Chicago IL USA
| | - Xueyan Wang
- Division of Nephrology and Hypertension, Feinberg School of Medicine Northwestern University Chicago IL USA.,Center for Translational Metabolism and Health, Institute for Public Health and Medicine Northwestern University Chicago IL USA.,Feinberg Cardiovascular and Renal Research Institute Northwestern University Chicago IL USA
| | - Valentin David
- Division of Nephrology and Hypertension, Feinberg School of Medicine Northwestern University Chicago IL USA.,Center for Translational Metabolism and Health, Institute for Public Health and Medicine Northwestern University Chicago IL USA.,Feinberg Cardiovascular and Renal Research Institute Northwestern University Chicago IL USA
| | - Susan E Quaggin
- Division of Nephrology and Hypertension, Feinberg School of Medicine Northwestern University Chicago IL USA.,Feinberg Cardiovascular and Renal Research Institute Northwestern University Chicago IL USA
| | - Tamara Isakova
- Division of Nephrology and Hypertension, Feinberg School of Medicine Northwestern University Chicago IL USA.,Center for Translational Metabolism and Health, Institute for Public Health and Medicine Northwestern University Chicago IL USA
| | - Aline Martin
- Division of Nephrology and Hypertension, Feinberg School of Medicine Northwestern University Chicago IL USA.,Center for Translational Metabolism and Health, Institute for Public Health and Medicine Northwestern University Chicago IL USA.,Feinberg Cardiovascular and Renal Research Institute Northwestern University Chicago IL USA
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Abstract
Phosphorus plays a vital role in diverse biological processes including intracellular signaling, membrane integrity, and skeletal biomineralization; therefore, the regulation of phosphorus homeostasis is essential to the well-being of the organism. Cells and whole organisms respond to changes in inorganic phosphorus (Pi) concentrations in their environment by adjusting Pi uptake and altering biochemical processes in cells (local effects) and distant organs (endocrine effects). Unicellular organisms, such as bacteria and yeast, express specific Pi-binding proteins on the plasma membrane that respond to changes in ambient Pi availability and transduce intracellular signals that regulate the expression of genes involved in cellular Pi uptake. Multicellular organisms, including humans, respond at a cellular level to adapt to changes in extracellular Pi concentrations and also have endocrine pathways which integrate signals from various organs (e.g., intestine, kidneys, parathyroid glands, bone) to regulate serum Pi concentrations and whole-body phosphorus balance. In mammals, alterations in the concentrations of extracellular Pi modulate type III sodium-phosphate cotransporter activity on the plasma membrane, and trigger changes in cellular function. In addition, elevated extracellular Pi induces activation of fibroblast growth factor receptor, Raf/mitogen-activated protein kinase/ERK kinase (MEK)/extracellular signal-regulated kinase (ERK) and Akt pathways, which modulate gene expression in various mammalian cell types. Excessive Pi exposure, especially in patients with chronic kidney disease, leads to endothelial dysfunction, accelerated vascular calcification, and impaired insulin secretion.
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Affiliation(s)
- Kittrawee Kritmetapak
- Division of Nephrology, Department of Medicine, Faculty of Medicine, Khon Kaen University, Khon Kaen, 40002, Thailand
- Division of Nephrology and Hypertension, Departments of Medicine, Biochemistry and Molecular Biology, Mayo Clinic, 200 First Street Southwest, Rochester, MN, 55902, USA
| | - Rajiv Kumar
- Division of Nephrology and Hypertension, Departments of Medicine, Biochemistry and Molecular Biology, Mayo Clinic, 200 First Street Southwest, Rochester, MN, 55902, USA.
- Nephrology Research, Medical Sciences 1-120, 200 First Street Southwest, Rochester, MN, 55902, USA.
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6
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Inflammation both increases and causes resistance to FGF23 in normal and uremic rats. Clin Sci (Lond) 2020; 134:15-32. [PMID: 31860056 DOI: 10.1042/cs20190779] [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: 08/05/2019] [Revised: 12/03/2019] [Accepted: 12/20/2019] [Indexed: 12/19/2022]
Abstract
Fibroblast growth factor 23 (FGF23) increases phosphorus excretion and decreases calcitriol (1,25(OH)2D) levels. FGF23 increases from early stages of renal failure. We evaluated whether strict control of phosphorus intake in renal failure prevents the increase in FGF23 and to what extent inflammation impairs regulation of FGF23. The study was performed in 5/6 nephrectomized (Nx) Wistar rats fed diets containing 0.2-1.2% phosphorus for 3 or 15 days. FGF23 levels significantly increased in all Nx groups in the short-term (3-day) experiment. However, at 15 days, FGF23 increased in all Nx rats except in those fed 0.2% phosphorus. In a second experiment, Nx rats fed low phosphorus diets (0.2 and 0.4%) for 15 days received daily intraperitoneal lipopolysaccharide (LPS) injections to induce inflammation. In these rats, FGF23 increased despite the low phosphorus diets. Thus, higher FGF23 levels were needed to maintain phosphaturia and normal serum phosphorus values. Renal Klotho expression was preserved in Nx rats on a 0.2% phosphorus diet, reduced on a 0.4% phosphorus diet, and markedly reduced in Nx rats receiving LPS. In ex vivo experiments, high phosphorus and LPS increased nuclear β-catenin and p65-NFκB and decreased Klotho. Inhibition of inflammation and Wnt signaling activation resulted in decreased FGF23 levels and increased renal Klotho. In conclusion, strict control of phosphorus intake prevented the increase in FGF23 in renal failure, whereas inflammation independently increased FGF23 values. Decreased Klotho may explain the renal resistance to FGF23 in inflammation. These effects are likely mediated by the activation of NFkB and Wnt/β-catenin signaling.
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Omede F, Zhang S, Johnson C, Daniel E, Zhang Y, Fields TA, Boulanger J, Liu S, Ahmed I, Umar S, Wallace DP, Stubbs JR. Dietary phosphate restriction attenuates polycystic kidney disease in mice. Am J Physiol Renal Physiol 2020; 318:F35-F42. [DOI: 10.1152/ajprenal.00282.2019] [Citation(s) in RCA: 8] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/29/2022] Open
Abstract
Studies in rodents with reduced nephron mass have suggested a strong positive correlation between dietary phosphate consumption and CKD progression. Prior work by our group demonstrated that dietary phosphate restriction can prevent tubular injury and microcyst formation in rodents with glomerulonephritis. Tubular injury and cystic dilation of tubules are key contributors to kidney function decline in polycystic kidney disease (PKD). Here, we determined whether dietary phosphate restriction slows renal cyst growth and fibrosis in a mouse model of PKD. Pcy/pcy mice received a normal phosphate (0.54%) or a phosphate-restricted (0.02%) diet ( n = 10/group) from 7 to 20 wk of age. All of the other major dietary constituents, including protein source and content, were comparable between the two diets. At 20 wk, body weight, kidney weight-to-body weight ratio (KW/BW), cystic area, cyst number, and kidney fibrosis were quantified. Pcy/pcy mice fed a phosphate-restricted diet had lower serum phosphate, fibroblast growth factor 23, and parathyroid hormone levels, along with elevated serum calcium levels and increased kidney Klotho gene expression compared with mice that consumed the control diet. Dietary phosphate restriction resulted in a 25% lower KW/BW ratio and reduced the cyst number, cystic index, and gene expression for the tubular injury markers neutrophil gelatinase-associated lipocalin and interleukin-18. Mice fed the phosphate-restricted diet exhibited lower kidney expression for pathways involved in collagen deposition and myofibroblast activation (collagen type I-α1, phosphorylated SMAD3, and α-smooth muscle actin); however, histological differences in kidney fibrosis were not appreciated. Dietary phosphate restriction slows cystogenesis and inhibits the activation of key pathways in the generation of kidney fibrosis in PKD mice.
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Affiliation(s)
- Faith Omede
- The Jared Grantham Kidney Institute, University of Kansas Medical Center, Kansas City, Kansas
| | - Shiqin Zhang
- The Jared Grantham Kidney Institute, University of Kansas Medical Center, Kansas City, Kansas
| | - Cassandra Johnson
- The Jared Grantham Kidney Institute, University of Kansas Medical Center, Kansas City, Kansas
| | - Emily Daniel
- The Jared Grantham Kidney Institute, University of Kansas Medical Center, Kansas City, Kansas
| | - Yan Zhang
- The Jared Grantham Kidney Institute, University of Kansas Medical Center, Kansas City, Kansas
| | - Timothy A. Fields
- The Jared Grantham Kidney Institute, University of Kansas Medical Center, Kansas City, Kansas
- Pathology and Laboratory Medicine, University of Kansas Medical Center, Kansas City, Kansas
| | | | | | - Ishfaq Ahmed
- Department of Surgery, University of Kansas Medical Center, Kansas City, Kansas
| | - Shahid Umar
- Department of Surgery, University of Kansas Medical Center, Kansas City, Kansas
| | - Darren Paul Wallace
- The Jared Grantham Kidney Institute, University of Kansas Medical Center, Kansas City, Kansas
- Department of Internal Medicine, Division of Nephrology and Hypertension, University of Kansas Medical Center, Kansas City, Kansas
| | - Jason R. Stubbs
- The Jared Grantham Kidney Institute, University of Kansas Medical Center, Kansas City, Kansas
- Department of Internal Medicine, Division of Nephrology and Hypertension, University of Kansas Medical Center, Kansas City, Kansas
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Delitsikou V, Jarad G, Rajaram RD, Ino F, Rutkowski JM, Chen CD, Santos CXC, Scherer PE, Abraham CR, Shah AM, Feraille E, Miner JH, de Seigneux S. Klotho regulation by albuminuria is dependent on ATF3 and endoplasmic reticulum stress. FASEB J 2019; 34:2087-2104. [PMID: 31907991 DOI: 10.1096/fj.201900893r] [Citation(s) in RCA: 15] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/16/2019] [Revised: 10/31/2019] [Accepted: 11/13/2019] [Indexed: 12/11/2022]
Abstract
Proteinuria is associated with renal function decline and cardiovascular mortality. This association may be attributed in part to alterations of Klotho expression induced by albuminuria, yet the underlying mechanisms are unclear. The presence of albumin decreased Klotho expression in the POD-ATTAC mouse model of proteinuric kidney disease as well as in kidney epithelial cell lines. This downregulation was related to both decreased Klotho transcription and diminished protein half-life, whereas cleavage by ADAM proteases was not modified. The regulation was albumin specific since it was neither observed in the analbuminemic Col4α3-/- Alport mice nor induced by exposure of kidney epithelial cells to purified immunoglobulins. Albumin induced features of ER stress in renal tubular cells with ATF3/ATF4 activation. ATF3 and ATF4 induction downregulated Klotho through altered transcription mediated by their binding on the Klotho promoter. Inhibiting ER stress with 4-PBA decreased the effect of albumin on Klotho protein levels without altering mRNA levels, thus mainly abrogating the increased protein degradation. Taken together, albuminuria decreases Klotho expression through increased protein degradation and decreased transcription mediated by ER stress induction. This implies that modulating ER stress may improve proteinuria-induced alterations of Klotho expression, and hence renal and extrarenal complications associated with Klotho loss.
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Affiliation(s)
- Vasiliki Delitsikou
- Department of Cell Physiology and Metabolism, Faculty of Medicine, CMU, University of Geneva, Geneva, Switzerland.,Laboratory of Nephrology, Department of Internal Medicine Specialties, HUG, Geneva, Switzerland
| | - George Jarad
- Division of Nephrology, Department of Medicine, Washington University School of Medicine, St. Louis, Missouri
| | - Renuga Devi Rajaram
- Department of Cell Physiology and Metabolism, Faculty of Medicine, CMU, University of Geneva, Geneva, Switzerland.,Laboratory of Nephrology, Department of Internal Medicine Specialties, HUG, Geneva, Switzerland
| | - Frédérique Ino
- Department of Cell Physiology and Metabolism, Faculty of Medicine, CMU, University of Geneva, Geneva, Switzerland.,Laboratory of Nephrology, Department of Internal Medicine Specialties, HUG, Geneva, Switzerland
| | - Joseph M Rutkowski
- Touchstone Diabetes Centre, Department of Internal Medicine, The University of Texas Southwestern Medical Center, Dallas, Texas.,Department of Medical Physiology, Texas A&M College of Medicine, College Station, Texas
| | - Ci-Di Chen
- Department of Biochemistry, Boston University School of Medicine, Boston, Massachusetts
| | - Celio X C Santos
- King's College London British Heart Foundation Centre of Excellence, School of Cardiovascular Medicine & Sciences, London, UK
| | - Philipp E Scherer
- Touchstone Diabetes Centre, Department of Internal Medicine, The University of Texas Southwestern Medical Center, Dallas, Texas
| | - Carmela R Abraham
- Department of Biochemistry, Boston University School of Medicine, Boston, Massachusetts
| | - Ajay M Shah
- King's College London British Heart Foundation Centre of Excellence, School of Cardiovascular Medicine & Sciences, London, UK
| | - Eric Feraille
- Department of Cell Physiology and Metabolism, Faculty of Medicine, CMU, University of Geneva, Geneva, Switzerland
| | - Jeffrey H Miner
- Division of Nephrology, Department of Medicine, Washington University School of Medicine, St. Louis, Missouri
| | - Sophie de Seigneux
- Department of Cell Physiology and Metabolism, Faculty of Medicine, CMU, University of Geneva, Geneva, Switzerland.,Laboratory of Nephrology, Department of Internal Medicine Specialties, HUG, Geneva, Switzerland
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Fibroblast growth factor 23 and α-Klotho co-dependent and independent functions. Curr Opin Nephrol Hypertens 2019; 28:16-25. [PMID: 30451736 DOI: 10.1097/mnh.0000000000000467] [Citation(s) in RCA: 27] [Impact Index Per Article: 5.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/01/2023]
Abstract
PURPOSE OF REVIEW The current review examines what is known about the FGF-23/α-Klotho co-dependent and independent pathophysiological effects, and whether FGF-23 and/or α-Klotho are potential therapeutic targets. RECENT FINDINGS FGF-23 is a hormone derived mainly from bone, and α-Klotho is a transmembrane protein. Together they form a trimeric signaling complex with FGFRs in target tissues to mediate the physiological functions of FGF-23. Local and systemic factors control FGF-23 release from osteoblast/osteocytes in bone, and circulating FGF-23 activates FGFR/α-Klotho complexes in kidney proximal and distal renal tubules to regulate renal phosphate excretion, 1,25 (OH)2D metabolism, sodium and calcium reabsorption, and ACE2 and α-Klotho expression. The resulting bone-renal-cardiac-immune networks provide a new understanding of bone and mineral homeostasis, as well as identify other biological effects FGF-23. Direct FGF-23 activation of FGFRs in the absence of α-Klotho is proposed to mediate cardiotoxic and adverse innate immune effects of excess FGF-23, particularly in chronic kidney disease, but this FGF-23, α-Klotho-independent signaling is controversial. In addition, circulating soluble Klotho (sKl) released from the distal tubule by ectodomain shedding is proposed to have beneficial health effects independent of FGF-23. SUMMARY Separation of FGF-23 and α-Klotho independent functions has been difficult in mammalian systems and understanding FGF-23/α-Klotho co-dependent and independent effects are incomplete. Antagonism of FGF-23 is important in treatment of hypophosphatemic disorders caused by excess FGF-23, but its role in chronic kidney disease is uncertain. Administration of recombinant sKl is an unproven therapeutic strategy that theoretically could improve the healt span and lifespan of patients with α-Klotho deficiency.
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Koppe L, Fouque D. The Role for Protein Restriction in Addition to Renin-Angiotensin-Aldosterone System Inhibitors in the Management of CKD. Am J Kidney Dis 2018; 73:248-257. [PMID: 30149957 DOI: 10.1053/j.ajkd.2018.06.016] [Citation(s) in RCA: 64] [Impact Index Per Article: 10.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/03/2017] [Accepted: 06/18/2018] [Indexed: 01/13/2023]
Abstract
In experimental studies a low-protein diet (LPD) and renin-angiotensin-aldosterone system (RAAS) inhibitors are both reported to slow the progression of chronic kidney disease (CKD) and reduce proteinuria. RAAS activity contributes to increased blood pressure, fluid retention, and positive sodium balance, but also to kidney damage by enhancing glomerular capillary filtration pressure and synthesis of profibrotic molecules such as transforming growth factor β. It has been well established that an LPD decreases glomerular hyperfiltration and the generation of uremic toxins, as well as the burden of acid load, phosphorus, and sodium. In different animal CKD models, a significant reduction in proteinuria and glomerulosclerosis has been achieved when an RAAS inhibitor and LPD were combined. To date, high-quality intervention trials investigating this combined strategy are lacking. We summarize the experimental and clinical studies that have examined a potential additive action of these therapies on CKD progression. We outline potential mechanisms of action and additive efficacy of an LPD and RAAS inhibitors in CKD, with a particular emphasis on phosphate levels, uremic toxin production, acid load, and salt intake. Finally, although the evidence is inadequate to recommend combining RAAS inhibitors and an LPD to slow the progression of CKD, we provide a perspective to support a large-scale randomized clinical trial to study this combination.
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Affiliation(s)
- Laetitia Koppe
- University Lyon, CARMEN, Department of Nephrology, Centre Hospitalier Lyon Sud, Pierre-Benite, France
| | - Denis Fouque
- University Lyon, CARMEN, Department of Nephrology, Centre Hospitalier Lyon Sud, Pierre-Benite, France.
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Pawlak D, Znorko B, Kalaska B, Domaniewski T, Zawadzki R, Lipowicz P, Doroszko M, Łebkowska U, Grabowski P, Pawlak K. LP533401 restores bone health in 5/6 nephrectomized rats by a decrease of gut-derived serotonin and regulation of serum phosphate through the inhibition of phosphate co-transporters expression in the kidneys. Bone 2018; 113:124-136. [PMID: 29792935 DOI: 10.1016/j.bone.2018.05.022] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 03/03/2018] [Revised: 04/28/2018] [Accepted: 05/20/2018] [Indexed: 11/17/2022]
Abstract
LP533401 is an orally bioavailable small molecule that inhibits tryptophan hydroxylase-1, an enzyme responsible for the synthesis of gut-derived serotonin (GDS). Recently, we showed that increased GDS in rats with chronic kidney disease (CKD) affected bone strength and metabolism. We tested the hypothesis that treatment with LP533401 could reverse CKD-induced bone loss in uremia. Sixteen weeks after 5/6 nephrectomy, rats were randomized into untreated (CKD), treated with vehicle (VEH) and LP533401 at a dose of 30 or 100 mg/kg daily for 8 weeks. Treatment with LP533401 decreased serotonin turnover and restored bone mineral status, microarchitecture, and strength in CKD rats to the values observed in the controls. In parallel with the reduction of serotonin, serum phosphate levels also decreased, particularly in the LP533401, 100 mg/kg group. The mechanism underlying this phenomenon resulted from decreased expression of the renal VDR/FGF1R/Klotho/Npt2a/Npt2c axis, leading to elevated phosphate excretion in the kidneys. The elevated urinary phosphate excretion resulted in improved bone mineral status and strength in LP533401-treated rats. Unexpectedly, the standard VEH used in this model was able to reduce renal VDR/FGF1R/Klotho/Npt2a expression, leading to a compensatory increase in Npt2c mRNA levels, secondary disturbances in phosphate-regulated hormones and partial improvement in the mineral status of the trabecular bone. The decrease of serotonin synthesis together with the simultaneous reduction of renal Npt2a and Npt2c expression in rats treated with LP533401, 100 mg/kg led to an increase in 1,25(OH)2D3 levels; this mechanism seems to be particularly beneficial in relation to the mineral status of cortical bone.
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Affiliation(s)
- Dariusz Pawlak
- Department of Pharmacodynamics, Medical University of Bialystok, Bialystok, Poland
| | - Beata Znorko
- Department of Monitored Pharmacotherapy, Medical University of Bialystok, Bialystok, Poland
| | - Bartlomiej Kalaska
- Department of Pharmacodynamics, Medical University of Bialystok, Bialystok, Poland
| | - Tomasz Domaniewski
- Department of Monitored Pharmacotherapy, Medical University of Bialystok, Bialystok, Poland
| | - Radosław Zawadzki
- Department of Radiology, Medical University of Bialystok, Bialystok, Poland
| | - Paweł Lipowicz
- Institute of Biocybernetics and Biomedical Engineering, Faculty of Mechanical Engineering, Bialystok University of Technology, Bialystok, Poland
| | - Michał Doroszko
- Department of Mechanics and Applied Computer Science, Faculty of Mechanical Engineering, Bialystok University of Technology, Bialystok, Poland
| | - Urszula Łebkowska
- Department of Radiology, Medical University of Bialystok, Bialystok, Poland
| | - Piotr Grabowski
- Department of Monitored Pharmacotherapy, Medical University of Bialystok, Bialystok, Poland
| | - Krystyna Pawlak
- Department of Monitored Pharmacotherapy, Medical University of Bialystok, Bialystok, Poland.
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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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Abstract
PURPOSE OF REVIEW This review examines the role of fibroblast growth factor-23 (FGF-23) in mineral metabolism, innate immunity and adverse cardiovascular outcomes. RECENT FINDINGS FGF-23, produced by osteocytes in bone, activates FGFR/α-Klotho (α-Kl) complexes in the kidney. The resulting bone-kidney axis coordinates renal phosphate reabsorption with bone mineralization, and creates a counter-regulatory feedback loop to prevent vitamin D toxicity. FGF-23 acts to counter-regulate the effects of vitamin D on innate immunity and cardiovascular responses. FGF-23 is ectopically expressed along with α-Kl in activated macrophages, creating a proinflammatory paracrine signaling pathway that counters the antiinflammatory actions of vitamin D. FGF-23 also inhibits angiotensin-converting enzyme 2 expression and increases sodium reabsorption in the kidney, leading to hypertension and left ventricular hypertrophy. Finally, FGF-23 is purported to cause adverse cardiac and impair neutrophil responses through activation of FGFRs in the absence of α-Kl. Although secreted forms of α-Kl have FGF-23 independent effects, the possibility of α-Kl independent effects of FGF-23 is controversial and requires additional experimental validation. SUMMARY FGF-23 participates in a bone-kidney axis regulating mineral homeostasis, proinflammatory paracrine macrophage signaling pathways, and in a bone-cardio-renal axis regulating hemodynamics that counteract the effects of vitamin D.
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Bansal S, Friedrichs WE, Velagapudi C, Feliers D, Khazim K, Horn D, Cornell JE, Werner SL, Fanti P. Spleen contributes significantly to increased circulating levels of fibroblast growth factor 23 in response to lipopolysaccharide-induced inflammation. Nephrol Dial Transplant 2018; 32:960-968. [PMID: 27836924 DOI: 10.1093/ndt/gfw376] [Citation(s) in RCA: 20] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/20/2016] [Accepted: 09/20/2016] [Indexed: 12/19/2022] Open
Abstract
Background Circulating levels of fibroblast growth factor 23 (FGF23) increase progressively and correlate with systemic inflammation in chronic kidney disease (CKD). The aim of this study was to identify and characterize the causal relationship between FGF23 and inflammation in CKD. Methods Circulating FGF23 and inflammatory cytokines were correlated in healthy subjects and patients with varying levels of CKD. In addition, FGF23 expression in blood and solid organs was measured in normal mice that were exposed acutely (one time) or chronically (2-week) to low-dose lipopolysaccharide (LPS); chronic exposure being either sustained (subcutaneous pellets), intermittent (daily injections) or combined sustained plus acute (subcutaneous pellets plus acute injection on the day of sacrifice). Blood was analyzed for both terminal (cFGF23) and intact (iFGF23) FGF23 levels. Solid tissues were investigated with immunohistochemistry, enzyme-linked immunosorbent assay and reverse transcription polymerase chain reaction. Results FGF23 levels correlated significantly with neutrophil gelatinase-associated lipocalin ( r = 0.72, P < 0.001), C-reactive protein ( r = 0.38, P < 0.001), tumor necrosis factor-α ( r = 0.32, P = 0.001) and interleukin-6 ( r = 0.48, P < 0.001). Acute LPS administration increased tissue FGF23 mRNA and plasma levels of cFGF23 but not iFGF23. Neither chronic sustained nor chronic pulsatile LPS increased the tissue or circulating levels of FGF23. However, acute on chronic LPS raised tissue FGF23 mRNA and both circulating cFG23 and iFGF23. Interestingly, the spleen was the major source of FGF23. Conclusion Acute on chronic exposure to LPS stimulates FGF23 production in a normal mouse model of inflammation. We provide the first evidence that the spleen, under these conditions, contributes substantially to elevated circulating FGF23 levels.
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Affiliation(s)
- Shweta Bansal
- Division of Nephrology, Department of Medicine, University of Texas Health Sciences Center at San Antonio, San Antonio, TX 78229, USA.,Renal Section, South Texas Veterans Healthcare System, San Antonio, TX, USA
| | - William E Friedrichs
- Division of Nephrology, Department of Medicine, University of Texas Health Sciences Center at San Antonio, San Antonio, TX 78229, USA
| | - Chakradhar Velagapudi
- Division of Nephrology, Department of Medicine, University of Texas Health Sciences Center at San Antonio, San Antonio, TX 78229, USA.,Renal Section, South Texas Veterans Healthcare System, San Antonio, TX, USA
| | - Denis Feliers
- Division of Nephrology, Department of Medicine, University of Texas Health Sciences Center at San Antonio, San Antonio, TX 78229, USA
| | - Khaled Khazim
- Faculty of Medicine, Galilee Medical Center, Bar-Ilan University, Safed, Israel
| | - Diane Horn
- Department of Pathology, University of Texas Health Sciences Center at San Antonio and South Texas Veterans Healthcare System, San Antonio, TX, USA
| | - John E Cornell
- Department of Epidemiology & Biostatistics, University of Texas Health Sciences Center at San Antonio, San Antonio, TX, USA
| | - Sherry L Werner
- Department of Pathology, University of Texas Health Sciences Center at San Antonio and South Texas Veterans Healthcare System, San Antonio, TX, USA
| | - Paolo Fanti
- Division of Nephrology, Department of Medicine, University of Texas Health Sciences Center at San Antonio, San Antonio, TX 78229, USA
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15
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Stöhr R, Schuh A, Heine GH, Brandenburg V. FGF23 in Cardiovascular Disease: Innocent Bystander or Active Mediator? Front Endocrinol (Lausanne) 2018; 9:351. [PMID: 30013515 PMCID: PMC6036253 DOI: 10.3389/fendo.2018.00351] [Citation(s) in RCA: 40] [Impact Index Per Article: 6.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 02/26/2018] [Accepted: 06/11/2018] [Indexed: 11/13/2022] Open
Abstract
Fibroblast growth factor-23 (FGF23) is a mainly osteocytic hormone which increases renal phosphate excretion and reduces calcitriol synthesis. These renal actions are mediated via alpha-klotho as the obligate co-receptor. Beyond these canonical "mineral metabolism" actions, FGF23 has been identified as an independent marker for cardiovascular risk in various patient populations. Previous research has linked elevated FGF23 predominantly to left-ventricular dysfunction and consecutive morbidity and mortality. Moreover, some experimental data suggest FGF23 as a direct and causal stimulator for cardiac hypertrophy via specific myocardial FGF23-receptor activation, independent from alpha-klotho. This hypothesis offers fascinating prospects in terms of therapeutic interventions, specifically in patients with chronic kidney disease (CKD) in whom the FGF23 system is strongly stimulated and in whom left-ventricular dysfunction is a major disease burden. However, novel data challenges the previous stand-alone hypothesis about a one-way road which guides unidirectionally skeletal FGF23 toward cardiotoxic effects. In fact, recent data point toward local myocardial production and release of FGF23 in cases where (acute) myocardial damage occurs. The effects of this local production and the physiological meaning are under current examination. Moreover, epidemiologic studies suggest that high FGF-23 may follow, rather than induce, myocardial disease in certain conditions. In summary, while FGF23 is an interesting link between mineral metabolism and cardiac function underlining the meaning of the bone-heart axis, more research is needed before therapeutic interventions may be considered.
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Affiliation(s)
- Robert Stöhr
- Department of Cardiology, University Hospital of the RWTH Aachen, Aachen, Germany
- *Correspondence: Robert Stöhr
| | - Alexander Schuh
- Department of Cardiology, University Hospital of the RWTH Aachen, Aachen, Germany
| | - Gunnar H. Heine
- Department of Nephrology, University Hospital Homburg-Saar, Homburg, Germany
| | - Vincent Brandenburg
- Department of Cardiology, University Hospital of the RWTH Aachen, Aachen, Germany
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16
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Zhou S, Glowacki J. Chronic kidney disease and vitamin D metabolism in human bone marrow-derived MSCs. Ann N Y Acad Sci 2017; 1402:43-55. [PMID: 28926112 PMCID: PMC5659722 DOI: 10.1111/nyas.13464] [Citation(s) in RCA: 16] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/23/2017] [Revised: 08/09/2017] [Accepted: 08/09/2017] [Indexed: 12/18/2022]
Abstract
Vitamin D that is synthesized in the skin or is ingested undergoes sequential steps of metabolic activation via a cascade of cytochrome P450 enzymatic hydroxylations in the liver and kidney to produce 1α,25-dihydroxyvitamin D (1α,25(OH)2 D). There are many tissues that are able to synthesize 1α,25(OH)2 D, but the biological significance of extrarenal hydroxylases is unresolved. Human marrow-derived mesenchymal stem cells (marrow stromal cells, hMSCs) give rise to osteoblasts, and their differentiation is stimulated by 1α,25(OH)2 D. In addition to being targets of 1α,25(OH)2 D, hMSCs can synthesize it; on the basis of those observations, we further examined the local autocrine/paracrine role of vitamin D metabolism in osteoblast differentiation. Research with hMSCs from well-characterized subjects provides an innovative opportunity to evaluate the effects of clinical attributes on the regulation of hMSCs. Like the renal 1α-hydroxylase, the enzyme in hMSCs is constitutively decreased with age and chronic kidney disease (CKD); both are regulated by PTH1-34, insulin-like growth factor 1, calcium, 1α,25(OH)2 D, 25(OH)D, and fibroblast growth factor 23. CKD is associated with impaired renal biosynthesis of 1α,25(OH)2 D, low bone mass, and increased fracture risk. Studies with hMSCs from CKD patients or aged subjects indicate that circulating 25(OH)D may have an important role in osteoblast differentiation on vitamin D metabolism and action in hMSCs.
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Affiliation(s)
- Shuanhu Zhou
- Department of Orthopedic Surgery, Brigham and Women's Hospital and Harvard Medical School, Boston, Massachusetts
| | - Julie Glowacki
- Department of Orthopedic Surgery, Brigham and Women's Hospital and Harvard Medical School, Boston, Massachusetts
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17
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Geddes RF, Biourge V, Chang Y, Syme HM, Elliott J. The Effect of Moderate Dietary Protein and Phosphate Restriction on Calcium-Phosphate Homeostasis in Healthy Older Cats. J Vet Intern Med 2016; 30:1690-1702. [PMID: 27527663 PMCID: PMC5032885 DOI: 10.1111/jvim.14563] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/11/2015] [Revised: 06/25/2016] [Accepted: 07/18/2016] [Indexed: 12/12/2022] Open
Abstract
Background Dietary phosphate and protein restriction decreases plasma PTH and FGF‐23 concentrations and improves survival time in azotemic cats, but has not been examined in cats that are not azotemic. Hypothesis Feeding a moderately protein‐ and phosphate‐restricted diet decreases PTH and FGF‐23 in healthy older cats and thereby slows progression to azotemic CKD. Animals A total of 54 healthy, client‐owned cats (≥ 9 years). Methods Prospective double‐blinded randomized placebo‐controlled trial. Cats were assigned to test diet (protein 76 g/Mcal and phosphate 1.6 g/Mcal) or control diet (protein 86 g/Mcal and phosphate 2.6 g/Mcal) and monitored for 18 months. Changes in variables over time and effect of diet were assessed by linear mixed models. Results A total of 26 cats ate test diet and 28 cats ate control diet. There was a significant effect of diet on urinary fractional excretion of phosphate (P = 0.045), plasma PTH (P = 0.005), and ionized calcium concentrations (P = 0.018), but not plasma phosphate, FGF‐23, or creatinine concentrations. Plasma PTH concentrations did not significantly change in cats fed the test diet (P = 0.62) but increased over time in cats fed the control diet (P = 0.001). There was no significant treatment effect of the test diet on development of azotemic CKD (3 of 26 (12%) test versus 3 of 28 (11%) control, odds ratio 1.09 (95% CI 0.13–8.94), P = 0.92). Conclusions and Clinical Importance Feeding a moderately protein‐ and phosphate‐restricted diet has effects on calcium‐phosphate homeostasis in healthy older cats and is well tolerated. This might have an impact on renal function and could be useful in early chronic kidney disease.
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Affiliation(s)
- R F Geddes
- Department of Clinical Science and Services, Royal Veterinary College, North Mymms, Hatfield, UK.
| | | | - Y Chang
- Department of Comparative Biological Sciences, Royal Veterinary College, Camden, London, UK
| | - H M Syme
- Department of Clinical Science and Services, Royal Veterinary College, North Mymms, Hatfield, UK
| | - J Elliott
- Department of Comparative Biological Sciences, Royal Veterinary College, Camden, London, UK
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18
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Pei L, Solis G, Nguyen MTX, Kamat N, Magenheimer L, Zhuo M, Li J, Curry J, McDonough AA, Fields TA, Welch WJ, Yu ASL. Paracellular epithelial sodium transport maximizes energy efficiency in the kidney. J Clin Invest 2016; 126:2509-18. [PMID: 27214555 DOI: 10.1172/jci83942] [Citation(s) in RCA: 70] [Impact Index Per Article: 8.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/27/2015] [Accepted: 04/05/2016] [Indexed: 12/12/2022] Open
Abstract
Efficient oxygen utilization in the kidney may be supported by paracellular epithelial transport, a form of passive diffusion that is driven by preexisting transepithelial electrochemical gradients. Claudins are tight-junction transmembrane proteins that act as paracellular ion channels in epithelial cells. In the proximal tubule (PT) of the kidney, claudin-2 mediates paracellular sodium reabsorption. Here, we used murine models to investigate the role of claudin-2 in maintaining energy efficiency in the kidney. We found that claudin-2-null mice conserve sodium to the same extent as WT mice, even during profound dietary sodium depletion, as a result of the upregulation of transcellular Na-K-2Cl transport activity in the thick ascending limb of Henle. We hypothesized that shifting sodium transport to transcellular pathways would lead to increased whole-kidney oxygen consumption. Indeed, compared with control animals, oxygen consumption in the kidneys of claudin-2-null mice was markedly increased, resulting in medullary hypoxia. Furthermore, tubular injury in kidneys subjected to bilateral renal ischemia-reperfusion injury was more severe in the absence of claudin-2. Our results indicate that paracellular transport in the PT is required for efficient utilization of oxygen in the service of sodium transport. We speculate that paracellular permeability may have evolved as a general strategy in epithelial tissues to maximize energy efficiency.
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19
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Bover J, Ureña-Torres P, Lloret MJ, Ruiz-García C, DaSilva I, Diaz-Encarnacion MM, Mercado C, Mateu S, Fernández E, Ballarin J. Integral pharmacological management of bone mineral disorders in chronic kidney disease (part I): from treatment of phosphate imbalance to control of PTH and prevention of progression of cardiovascular calcification. Expert Opin Pharmacother 2016; 17:1247-58. [DOI: 10.1080/14656566.2016.1182155] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/09/2023]
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20
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Nagamani S, Muthusamy K, Marshal JJ. E-pharmacophore filtering and molecular dynamics simulation studies in the discovery of potent drug-like molecules for chronic kidney disease. J Biomol Struct Dyn 2016; 34:2233-2250. [PMID: 26513595 DOI: 10.1080/07391102.2015.1111168] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/18/2022]
Abstract
Chronic kidney disease (CKD) is a prominent health issue reported globally. The level of the vitamin D receptor (VDR) and cytochrome P450 enzyme 24-hydroxylase (CYP24A1) are crucial in the pathogenesis of secondary hyperparathyroidism (sHPT) in CKD. An elevated expression of the CYP24A1 leads to the deficiency of vitamin D and resistance to vitamin D therapy. Hence, VDR agonists and CYP24A1 antagonists are suggested to CKD patients for the management of biochemical complications. CTA-018 is a recently reported analog and acts as a potent CYP24A1 inhibitor. It inhibits CYP24A1 with an IC50 27 ± 6 nM, about 10 times more potentially than the non-selective inhibitor ketoconazole (253 ± 20 nM), and it is also been reported to induce the VDR expression. Thus, CTA-018 is under clinical trial among CKD patients. In this study, combined molecular docking and pharmacophore filtering were employed to identify compounds better than CTA-018. A huge set of 9127 compounds from Sweet Lead database were docked into the active site of VDR using Glide XP program. E-pharmacophore was developed from both the targets along with CTA-018. The compounds retrieved from the two different pharmacophore-based screening were re-docked into the active site of CYP24A1. The hits that bind well at both the active sites and matched with the pharmacophore models were considered as possible dual functional molecules against VDR and CYP24A1. Further, molecular dynamics simulation and subsequent energy decomposition analyses were also performed to study the role of specific amino acids in the active site of both VDR and CYP24A1.
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Affiliation(s)
- Selvaraman Nagamani
- a Department of Bioinformatics , Alagappa University , Karaikudi 630 004 , India
| | | | - J John Marshal
- a Department of Bioinformatics , Alagappa University , Karaikudi 630 004 , India
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21
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Abstract
High circulating levels of fibroblast growth factor 23 (FGF23) have been demonstrated in kidney failure, but mechanisms of this are not well understood. Here we examined the impact of the kidney on the early regulation of intact FGF23 in acute uremia as induced by bilateral or unilateral nephrectomy (BNX and UNX, respectively) in the rat. BNX induced a significant increase in plasma intact FGF23 levels from 112 to 267 pg/ml within 15 min, which remained stable thereafter. UNX generated intact FGF23 levels between that seen in BNX and sham-operated rats. The intact to C-terminal FGF23 ratio was significantly increased in BNX rats. The rapid rise in FGF23 after BNX was independent of parathyroid hormone or FGF receptor signaling. No evidence of early stimulation of FGF23 gene expression in the bone was found. Furthermore, acute severe hyperphosphatemia or hypercalcemia had no impact on intact FGF23 levels in normal and BNX rats. The half-life of exogenous recombinant human FGF23 was significantly prolonged from 4.4 to 11.8 min in BNX rats. Measurements of plasma FGF23 in the renal artery and renal vein demonstrated a significant renal extraction. Thus the kidney is important in FGF23 homeostasis by regulation of its plasma level and metabolism.
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22
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Stubbs JR, Zhang S, Friedman PA, Nolin TD. Decreased conversion of 25-hydroxyvitamin D3 to 24,25-dihydroxyvitamin D3 following cholecalciferol therapy in patients with CKD. Clin J Am Soc Nephrol 2014; 9:1965-73. [PMID: 25183657 DOI: 10.2215/cjn.03130314] [Citation(s) in RCA: 36] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/23/2022]
Abstract
BACKGROUND AND OBJECTIVES Elevated concentrations of fibroblast growth factor 23 (FGF23) are postulated to promote 25-hydroxyvitamin D (25[OH]D) insufficiency in CKD by stimulating 24-hydroxylation of this metabolite, leading to its subsequent degradation; however, prospective human studies testing this relationship are lacking. DESIGN, SETTING, PARTICIPANTS, & MEASUREMENTS An open-label prospective study was conducted from October 2010 through July 2012 to compare the effect of 8 weeks of oral cholecalciferol therapy (50,000 IU twice weekly) on the production of 24,25(OH)2D3 in vitamin D-insufficient patients with CKD (n=15) and controls with normal kidney function (n=15). Vitamin D metabolites were comprehensively profiled at baseline and after treatment, along with FGF23 and other mineral metabolism parameters. RESULTS Vitamin D3 and 25(OH)D3 concentrations increased equivalently in the CKD and control groups following cholecalciferol treatment (median D3 change, 8.6 ng/ml [interquartile range, 3.9-25.6 ng/ml] for controls versus 12.6 ng/ml [6.9-41.2 ng/ml] for CKD [P=0.15]; 25(OH)D3 change, 39.2 ng/ml [30.9-47.2 ng/ml] for controls versus 39.9 ng/ml [31.5-44.1 ng/ml] for CKD [P=0.58]). Likewise, the absolute increase in 1α,25(OH)2D3 was similar between CKD participants and controls (change, 111.2 pg/ml [64.3-141.6 pg/ml] for controls versus 101.1 pg/ml [74.2-123.1 pg/ml] for CKD; P=0.38). Baseline and post-treatment 24,25(OH)2D3 concentrations were lower in the CKD group; moreover, the absolute increase in 24,25(OH)2D3 after therapy was markedly smaller in patients with CKD (change, 2.8 ng/ml [2.3-3.5 ng/ml] for controls versus 1.2 ng/ml [0.6-1.9 ng/ml] for patients with CKD; P<0.001). Furthermore, higher baseline FGF23 concentrations were associated with smaller increments in 24,25(OH)2D3 for individuals with CKD; this association was negated after adjustment for eGFR by multivariate analysis. CONCLUSIONS Patients with CKD exhibit an altered ability to increase serum 24,25(OH)2D3 after cholecalciferol therapy, suggesting decreased 24-hydroxylase activity in CKD. The observed relationship between baseline FGF23 and increments in 24,25(OH)2D3 further refutes the idea that FGF23 directly contributes to 25(OH)D insufficiency in CKD through stimulation of 24-hydroxylase activity.
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Affiliation(s)
- Jason R Stubbs
- The Kidney Institute, University of Kansas Medical Center, Kansas City, Kansas;
| | - Shiqin Zhang
- The Kidney Institute, University of Kansas Medical Center, Kansas City, Kansas
| | - Peter A Friedman
- Department of Pharmacology & Chemical Biology, University of Pittsburgh School of Medicine, Pittsburgh, Pennsylvania; and
| | - Thomas D Nolin
- Department of Pharmacy and Therapeutics, Center for Clinical Pharmaceutical Sciences, and Department of Medicine, Renal-Electrolyte Division, University of Pittsburgh Schools of Pharmacy and Medicine, Pittsburgh, Pennsylvania
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23
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Abstract
The emergence of fibroblast growth factor 23 as a potentially modifiable risk factor in CKD has led to growing interest in its measurement as a tool to assess patient risk and target therapy. This review discusses the analytical and clinical challenges faced in translating fibroblast growth factor 23 testing into routine practice. As for other bone mineral markers, agreement between commercial fibroblast growth factor 23 assays is poor, mainly because of differences in calibration, but also, these differences reflect the variable detection of hormone fragments. Direct comparison of readout from different assays is consequently limited and likely hampers setting uniform fibroblast growth factor 23-directed targets. Efforts are needed to standardize assay output to enhance clinical use. Fibroblast growth factor 23 is robustly associated with cardiovascular and renal outcomes in patients with CKD and adds value to risk assessments based on conventional risk factors. Compared with most other mineral markers, fibroblast growth factor 23 shows better intraindividual temporal stability, with minimal diurnal and week-to-week variability, but substantial interindividual variation, maximizing discriminative power for risk stratification. Conventional therapeutic interventions for the CKD-mineral bone disorder, such as dietary phosphate restriction and use of oral phosphate binders or calcimimetics, are associated with variable efficacy at modulating circulating fibroblast growth factor 23 concentrations, like they are for other mineral metabolites. Dual therapy with dietary phosphate restriction and noncalcium-based binder use achieves the most consistent fibroblast growth factor 23-lowering effect and seems best monitored using an intact assay. Additional studies are needed to evaluate whether strategies aimed at reducing levels or antagonizing its action have beneficial effects on clinical outcomes in CKD patients. Moreover, a better understanding of the mechanisms driving fibroblast growth factor 23 elevations in CKD is needed to inform the use of therapeutic interventions targeting fibroblast growth factor 23 excess. This evidence must be forthcoming to support the use of fibroblast growth factor 23 measurement and fibroblast growth factor 23-directed therapy in the clinic.
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Affiliation(s)
- Edward R Smith
- Department of Nephrology, The Royal Melbourne Hospital, Melbourne, Victoria, Australia
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24
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Christov M, Jüppner H. Dietary phosphate: the challenges of exploring its role in FGF23 regulation. Kidney Int 2014; 84:639-41. [PMID: 24080872 DOI: 10.1038/ki.2013.198] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/15/2023]
Abstract
Fibroblast growth factor 23 (FGF23) is an important regulator of phosphate homeostasis, yet efforts to control its circulating levels by manipulating dietary phosphate intake in humans and animals with normal or impaired kidney function have yielded conflicting results. In the study by Zhang et al., severe phosphate restriction in a genetic mouse model of progressive kidney dysfunction failed to cause a uniform FGF23 reduction, again highlighting the complexity of FGF23 regulation.
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Affiliation(s)
- Marta Christov
- 1] Endocrine Unit, Massachusetts General Hospital and Harvard Medical School, Boston, Massachusetts, USA [2] Division of Nephrology, Beth Israel Deaconess Medical Center, Boston, Massachusetts, USA
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25
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Gutiérrez OM. The connection between dietary phosphorus, cardiovascular disease, and mortality: where we stand and what we need to know. Adv Nutr 2013; 4:723-9. [PMID: 24228204 PMCID: PMC3823521 DOI: 10.3945/an.113.004812] [Citation(s) in RCA: 29] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/16/2022] Open
Abstract
Disorders of phosphorus metabolism are independent risk factors for cardiovascular disease. Because excess dietary phosphorus intake is common in the general population and plays a central role in disturbances in phosphorus homeostasis, these findings have fueled interest in restricting phosphorus intake as a potential therapy for improving cardiovascular outcomes. Although experimental and observational data support this possibility, current limitations in the assessment of dietary phosphorus consumption in free-living populations and the lack of reliable biomarkers of the effects of dietary phosphorus on cardiovascular health pose major barriers to the design and conduct of trials assessing the efficacy of phosphorus restriction in improving cardiovascular health. Fibroblast growth factor 23 and Klotho are novel mediators of phosphorus metabolism that are tightly linked to dietary phosphorus intake and show promise as integrated biomarkers of phosphorus excess and its long-term health consequences. Advances in the understanding of how these hormones are associated with diet and phosphorus metabolism will likely bolster future efforts to assess the true health consequences of excess phosphorus intake and whether restricting phosphorus intake has salutary effects on cardiovascular health.
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