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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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Fibroblast growth factor 23 (FGF23) level is associated with ultrafiltration rate in patients on hemodialysis. Heart Vessels 2020; 36:414-423. [PMID: 33000285 PMCID: PMC7872991 DOI: 10.1007/s00380-020-01704-y] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 05/11/2020] [Accepted: 09/18/2020] [Indexed: 11/18/2022]
Abstract
Fibroblast growth factor 23 (FGF23) is a bone-derived hormone that regulates renal phosphate reabsorption and vitamin D synthesis in renal proximal tubules. High circulating FGF23 levels are associated with increased mortality in patients with chronic kidney disease and those on dialysis. Current data also suggest higher circulating levels of FGF23 are associated with cardiovascular mortality, vascular calcification, and left ventricular hypertrophy; however, evidence on the role of FGF23 in patients on dialysis is incomplete, and some of the data, especially those on cardiovascular disease (CVD), are controversial. This study aimed to evaluate factors associated with FGF23 in hemodialysis patients with or without CVD. Randomly selected 76 patients on maintenance hemodialysis at a single hemodialysis center were enrolled. After the exclusion of eight patients with extremely outlying FGF23 levels, 68 patients, including 48 males and 46 patients with a CVD history, were included in the study. The mean age was 64.4 ± 12.1 years, and the mean dialysis duration was 12.7 ± 7.1 years. Dialysis duration, time-averaged concentration of urea (TAC-urea), ultrafiltration rate (UFR), blood pressure during hemodialysis session, laboratory data, and echocardiographic parameters including interventricular septum thickness (IVST), left ventricular mass indices (LVMI), and ejection fraction were included in univariate and multivariate analyses. The median lgFGF23 levels in the overall cohort and in those with and without CVD were 2.14 (interquartile range, IQR − 0.43 to − 4.23), 2.01 (− 0.52 to 4.12), and 2.59 (0.07 to 4.32), respectively, and there was no difference between the patients with and without CVD (p = 0.14). The univariate analysis revealed that FGF23 was significantly associated with age (r = − 0.12, p < 0.01), duration of hemodialysis (r = − 0.11, p < 0.01), TAC-urea (r = 0.29, p = 0.01), UFR (r = 0.26, p = 0.04), alkaline phosphatase (ALP; r = − 0.27, p = 0.03), corrected serum calcium (cCa; r = 0.32, p < 0.01), serum phosphate (iP, r = 0.57, p < 0.01), intact parathyroid hormone (iPTH; r = 0.38, p < 0.01), IVST (r = 0.30, p = 0.01), and LVMI (r = 0.26, p = 0.04). In multivariate regression analysis, FGF23 was significantly associated with cCa (F = 25.6, p < 0.01), iP (F = 22.5, p < 0.01), iPTH (F = 19.2, p < 0.01), ALP (F = 5.34, p = 0.03), and UFR (F = 3.94, p = 0.05). In addition, the univariate analysis after the categorization of patients according to CVD indicated that FGF23 was significantly associated with cCa (r = 0.34, p = 0.02), iP (r = 0.41, p < 0.01), iPTH (r = 0.39, p = 0.01), and TAC-urea (r = 0.45, p < 0.01) in patients with CVD, whereas only IVST (r = 0.53, p = 0.04) was associated with FGF23 in those without CVD. FGF23 levels in hemodialysis patients were extremely high and associated not only with mineral bone disease-related factors but also with UFR. Additionally, dialysis efficacy might be associated with lower FGF23 levels in patients with CVD.
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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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Büyükkaragöz B, Bakkaloglu SA, Kandur Y, Isiyel E, Akcaboy M, Buyan N, Hasanoglu E. The evaluation of bone metabolism in children with renal transplantation. Pediatr Transplant 2015; 19:351-7. [PMID: 25819470 DOI: 10.1111/petr.12469] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Accepted: 03/11/2015] [Indexed: 01/16/2023]
Abstract
This study aims to evaluate BMD and bone biomarkers and to investigate the effects of immunosuppressives on bone disease after RTx. Thirty-three RTR aged 16.7 ± 3.7 yr and healthy controls (n = 32) were enrolled. There was no difference between pre-RTx BMD and BMD at the time of study (45.9 ± 30.9 months after RTx), while both values were lower than controls (p < 0.01 and p < 0.05, respectively). Worst BMD scores were obtained at sixth month after RTx (-0.2 ± 0.9) and best at fourth year (1.4 ± 1.3). 25-hydroxy-(OH) vitamin D and OPG were higher in RTR (p < 0.001). BMD z scores negatively correlated with OPG and cumulative CS doses at the time of study (r = -0.344, p < 0.05 and r = -0.371, p < 0.05, respectively). Regression analysis revealed OPG as the only predictor of BMD (β -0.78, 95% CI -0.004 to -0.013, p < 0.001). The increase in OPG, a significant predictor of BMD, could either be secondary to graft dysfunction or for protection against bone loss. CS doses should be minimized to avoid their untoward effects on bone metabolism.
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Moe OW. Familial tumoral calcinosis: a valuable vehicle for discovery. Nephrol Dial Transplant 2014; 29:2155-7. [PMID: 25147226 DOI: 10.1093/ndt/gfu270] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/14/2023] Open
Affiliation(s)
- Orson W Moe
- Departments of Internal Medicine and Physiology, and Charles and Jane Pak Center for Mineral Metabolism and Clinical Research, University of Texas Southwestern Medical Center, Dallas, TX, USA
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Calcium regulation and bone mineral metabolism in elderly patients with chronic kidney disease. Nutrients 2013; 5:1913-36. [PMID: 23760058 PMCID: PMC3725483 DOI: 10.3390/nu5061913] [Citation(s) in RCA: 22] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/18/2013] [Revised: 04/25/2013] [Accepted: 05/08/2013] [Indexed: 12/20/2022] Open
Abstract
The elderly chronic kidney disease (CKD) population is growing. Both aging and CKD can disrupt calcium (Ca2+) homeostasis and cause alterations of multiple Ca2+-regulatory mechanisms, including parathyroid hormone, vitamin D, fibroblast growth factor-23/Klotho, calcium-sensing receptor and Ca2+-phosphate product. These alterations can be deleterious to bone mineral metabolism and soft tissue health, leading to metabolic bone disease and vascular calcification and aging, termed CKD-mineral and bone disorder (MBD). CKD-MBD is associated with morbid clinical outcomes, including fracture, cardiovascular events and all-cause mortality. In this paper, we comprehensively review Ca2+ regulation and bone mineral metabolism, with a special emphasis on elderly CKD patients. We also present the current treatment-guidelines and management options for CKD-MBD.
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Dietary phosphate restriction suppresses phosphaturia but does not prevent FGF23 elevation in a mouse model of chronic kidney disease. Kidney Int 2013; 84:713-21. [PMID: 23698235 PMCID: PMC3758787 DOI: 10.1038/ki.2013.194] [Citation(s) in RCA: 27] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/01/2012] [Revised: 02/25/2013] [Accepted: 03/07/2013] [Indexed: 01/09/2023]
Abstract
Fibroblast growth factor 23 (FGF23) is a phosphaturic hormone that in end-stage renal disease is markedly increased in serum; however, the mechanisms responsible for this increase are unclear. Here, we tested whether phosphate retention in chronic kidney disease (CKD) is responsible for the elevation of FGF23 in serum using Col4α3 knockout mice, a murine model of Alport disease exhibiting CKD. We found a significant elevation in serum FGF23 in progressively azotemic 8 and 12 week-old CKD mice along with an increased fractional excretion of phosphorus. Both moderate and severe phosphate restriction reduced fractional excretion of phosphorus by 8 weeks, yet serum FGF23 levels remained strikingly elevated. By 12 weeks, FGF23 levels were further increased with moderate phosphate restriction, while severe phosphate restriction led to severe bone mineralization defects and decreased FGF23 production in bone. CKD mice on a control diet had low serum 1,25(OH)2D levels and 3-fold higher renal Cyp24α1 gene expression compared to wild-type mice. Severe phosphate restriction increased 1,25(OH)2D levels in CKD mice by 8 weeks and lowered renal Cyp24α1 gene expression despite persistently elevated serum FGF23. Renal klotho gene expression declined in CKD mice on a control diet, but improved with severe phosphate restriction. Thus, dietary phosphate restriction reduces the fractional excretion of phosphorus independent of serum FGF23 levels in mice with CKD.
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Bonewald LF, Wacker MJ. FGF23 production by osteocytes. Pediatr Nephrol 2013; 28:563-8. [PMID: 22983423 PMCID: PMC3582753 DOI: 10.1007/s00467-012-2309-3] [Citation(s) in RCA: 78] [Impact Index Per Article: 7.1] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 05/18/2012] [Revised: 08/27/2012] [Accepted: 08/28/2012] [Indexed: 12/20/2022]
Abstract
Fibroblast growth factor 23 (FGF23), a known regulator of phosphate homeostasis, is produced by cells residing in bone, namely, osteocytes, to target a distant organ, the kidney. Elevated FGF23 levels have recently been found systemically and in osteocytes in patients and animal models of chronic kidney disease. Associations between serum FGF23 level and vascular dysfunction, vascular calcification, and increased risk of cardiovascular disease have also been observed. In this review we discuss FGF23 expression in osteocytes and the potential means to regulate expression and function of this protein at the osteocyte level.
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Affiliation(s)
- Lynda F Bonewald
- School of Dentistry, University of Missouri, 650 East 25th Street, Kansas City, MO, 64108-2784, USA.
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Stein DR, Feldman HA, Gordon CM. Vitamin D status in children with chronic kidney disease. Pediatr Nephrol 2012; 27:1341-50. [PMID: 22453735 PMCID: PMC3749087 DOI: 10.1007/s00467-012-2143-7] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 09/23/2011] [Revised: 02/09/2012] [Accepted: 02/14/2012] [Indexed: 10/28/2022]
Abstract
BACKGROUND The role of vitamin D status in patients with renal insufficiency and its relation to dietary intake and parathyroid hormone (PTH) secretion is of utmost interest given the morbidity and mortality associated with the disordered mineral metabolism seen in chronic kidney disease (CKD). METHODS We conducted a cross-sectional study of 100 pediatric patients with a diagnosis of CKD stage 1-5 at Children's Hospital Boston, measuring blood levels of 25-hydroxyvitamin D [25(OH)D], 1,25-dihydroxyvitamin D [1,25(OH)(2)D], and parathyroid hormone and obtaining data on nutrient intake and other variables related to vitamin D status. RESULTS Subjects ranged in age from 6 months to 18 years, and 60 were male, 40 female. Of the 100 patients, 16 % were deficient in 25(OH)D (≤ 20 ng/mL) and another 24 % were insufficient (≤ 30 ng/mL), with 40 % in the suboptimal range. Serum 25(OH)D and dietary vitamin D intake were not correlated. CONCLUSIONS We found a high prevalence of hyperparathyroidism in early-stage CKD and a significant relationship between 25(OH)D and PTH regardless of calcitriol level. Our study results support the suggestion that optimization of vitamin D levels may provide additional benefit in preventing or improving hyperparathyroidism in patients with early CKD and likely remains important as an adjunctive therapy in children with advanced CKD.
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Affiliation(s)
- Deborah R. Stein
- Corresponding Author: Deborah R. Stein MD, Children’s Hospital Boston Division of Nephrology, 300 Longwood Avenue, Hunnewell 319, Boston, MA 02115, Ph: 617.355.6129, Fax: 617.730.0569,
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Hu P, Xuan Q, Hu B, Lu L, Wang J, Qin YH. Fibroblast growth factor-23 helps explain the biphasic cardiovascular effects of vitamin D in chronic kidney disease. Int J Biol Sci 2012; 8:663-71. [PMID: 22606047 PMCID: PMC3354624 DOI: 10.7150/ijbs.3886] [Citation(s) in RCA: 18] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/30/2011] [Accepted: 02/23/2012] [Indexed: 12/16/2022] Open
Abstract
Hypovitaminosis D is highly prevalent in chronic kidney disease (CKD). Recently, vitamin D has sparked widespread interest because of its potential favorable benefits on cardiovascular disease (CVD). Evidence from clinical studies and animal models supports the existence of biphasic cardiovascular effects of vitamin D, in which lower doses suppress CVD and higher doses stimulate CVD. However, the mechanism for the different effects remains unclear. Fibroblast growth factor-23 (FGF-23) is a recently identified member of the FGF family, and thought to be actively involved in renal phosphate and vitamin D homeostasis. More specifically, Vitamin D stimulates FGF-23 secretion and is inhibited by increased FGF-23. Given this background, we hypothesize that FGF-23 may provide a unique tool to explain the biphasic cardiovascular effects of vitamin D in CKD. The data presented in this review support the hypothesis that FGF-23 may be linked with the high cardiovascular risk in CKD through accelerating the onset of vascular calcification, secondary hyperparathyroidism, left ventricular hypertrophy and endothelial dysfunction. Therefore, modulation of FGF-23 may become a potential therapeutic target to lowing cardiovascular risk in CKD. Several clinical interventions, including decreased phosphate intake, phosphate binders, cinacalcet plus concurrent low-dose vitamin D, C-terminal tail of FGF-23 and renal transplantation, have been employed to manipulate FGF-23.
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Affiliation(s)
- Peng Hu
- Department of Pediatrics, the First Affiliated Hospital of Anhui Medical University, No. 218 Ji-Xi Road, Hefei 230022, PR China.
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Abstract
Vertebrates evolved elaborating a structure made up of more than 200 bones and cartilages articulated with one another to form the skeleton, through which locomotion, organ protection, lodging of hematopoiesis, and mineral homeostasis are allowed. Skeletogenesis starts at the fetal stage, along with marrow hematopoiesis, and evolves postnatally through modeling and remodeling processes that permit skeletal mass buildup. Preservation of skeletal mass is then implemented by balanced remodeling, which ensures continuous renovation of the tissue to allow its mechanical, structural, and metabolic properties to remain unaltered until ageing or diseases disrupt this equilibrium. Skeletal homeostasis is fulfilled by specialized bone cells in association with systemic and local regulators. Herein I review landmark discoveries that shed light on the intricate mesh connecting bone cells among themselves and with other systems, thus representing the cellular basis of normal and abnormal bone development and homeostasis.
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Affiliation(s)
- Anna Teti
- Department of Experimental Medicine, University of L'Aquila, Via Vetoio-Coppito 2, 67100, L'Aquila, Italy.
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