| 1. |
- Krajisnik, Tijana, 1981-
(författare)
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Fibroblast growth factor-23 and Klotho in bone/mineral and parathyroid disorders
- 2009
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Fibroblast growth factor-23 (FGF23) is a novel, bone-produced hormone that regulates renal phosphate (Pi) reabsorption and calcitriol metabolism. Disorders of mineral and bone metabolism, such as autosomal dominant hypophosphatemic rickets (ADHR) and hyperostosis-hyperphosphatemia syndrome (HHS), witness the importance of well-balanced serum levels of FGF23. Patients with chronic kidney disease (CKD) are highly morbid due to Pi retention/hyperphosphatemia and calcitriol deficiency, which lead to elevated serum levels of parathyroid hormone (PTH) and secondary hyperparathyroidism (sHPT). As a response to hyperphosphatemia, CKD patients have also remarkably high serum FGF23 levels, which are associated with cardiovascular risk factors and increased mortality in CKD. The overall aim of this dissertation was to discern a possible role of FGF23 in parathyroid biology. Our in vitro experiments on isolated bovine parathyroid cells demonstrate that FGF23 directly and dose-dependently suppresses the PTH production and secretion, while increasing the expression of the 25-hydroxyvitamin D3-activating enzyme 1α-hydroxylase. We investigated possible expressional changes in the FGF23 receptor co-factor Klotho in hyperparathyroid disorders and found that Klotho expression is decreased or absent and inversely correlated to serum calcium (Ca) in adenomas of primary HPT (pHPT). In the hyperplastic parathyroid glands of sHPT, Klotho expression declines in parallel with the kidney function and correlates with the glomerular filtration rate. Moreover, Klotho expression is suppressed by Ca and FGF23, increased by calcitriol, but unaffected by Pi and PTH in vitro. Finally, we identified a novel missense mutation in the gene encoding GALNT3, which is normally involved in the post-translational glycosylation of FGF23, as the cause of aberrant FGF23 processing in a patient with HHS. In summary, we provide evidence for a novel bone/parathyroid axis in which FGF23 functions as a direct, negative regulator of the PTH production. High extracellular Ca is a major determinant of the Klotho expression in pHPT, whereas the Klotho levels in sHPT may be attributed to a combination of the high FGF23 and Ca, and low calcitriol levels associated with CKD. Hence, the decreased Klotho expression in sHPT could explain the concomitantly high FGF23 and PTH levels, as well as the failure of FGF23 to prevent or mitigate the development of sHPT in CKD.
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| 2. |
- Krajisnik, Tijana, et al.
(författare)
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Fibroblast growth factor-23 regulates parathyroid hormone and 1alpha-hydroxylase expression in cultured bovine parathyroid cells
- 2007
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Ingår i: Journal of Endocrinology. - 0022-0795 .- 1479-6805. ; 195:1, s. 125-131
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Tidskriftsartikel (refereegranskat)abstract
- Fibroblast growth factor-23 (FGF23) is a circulating factor that decreases serum levels of inorganic phosphate (Pi) as well as 1,25-dihydroxyvitamin D(3). Recent studies also suggest a correlation between serum levels of FGF23 and parathyroid hormone (PTH) in patients with chronic kidney disease. It is, however, unknown whether FGF23 directly modulates PTH expression, or whether the correlation is secondary to abnormalities in Pi and vitamin D metabolism. The objective of the current study was therefore to elucidate possible direct effects of FGF23 on bovine parathyroid cells in vitro. Treatment of parathyroid cells with a stabilized form of recombinant FGF23 (FGF23(R176Q)) induced a rise in early response gene-1 mRNA transcripts, a marker of FGF23 signaling. FGF23(R176Q) potently and dose-dependently decreased the PTH mRNA level within 12 h. In agreement, FGF23(R176Q) also decreased PTH secretion into conditioned media. In contrast, FGF23(R176Q) dose-dependently increased 1alpha-hydroxylase expression within 3 h. FGF23 (R176Q) did not affect cell viability nor induce apoptosis, whereas a small but significant increase in cell proliferation was found. We conclude that FGF23 is a negative regulator of PTH mRNA expression and secretion in vitro. Our data suggest that FGF23 may be a physiologically relevant regulator of PTH. This defines a novel function of FGF23 in addition to the previously established roles in controlling vitamin D and Pi metabolism.
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| 3. |
- Marsell, Richard, et al.
(författare)
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Fibroblast growth factor-23 is associated with parathyroid hormone and renal function in a population-based cohort of elderly men.
- 2008
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Ingår i: European journal of endocrinology / European Federation of Endocrine Societies. - 1479-683X .- 0804-4643. ; 158:1, s. 125-9
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Tidskriftsartikel (refereegranskat)abstract
- OBJECTIVE: Fibroblast growth factor-23 (FGF23) is a circulating factor involved in phosphate (Pi) and vitamin D metabolism. Serum FGF23 is increased at later stages of chronic kidney disease due to chronic hyperphosphatemia and decreased renal clearance. Recent studies also indicate that FGF23 may directly regulate the expression of parathyroid hormone (PTH) in vitro. Therefore, the objective of the current study was to determine the relationship between FGF23, PTH, and other biochemistries in vivo in subjects with no history of renal disease. DESIGN: Serum biochemistries were measured in a subsample of the population-based Swedish part of the MrOS study. In total, 1000 Caucasian men aged 70-80 years were randomly selected from the population. METHODS: Intact FGF23, Pi, calcium, albumin, estimated glomerular filtration rate (eGFR, calculated from cystatin C), PTH, and 25(OH)D3 were measured. Association studies were performed using linear univariate and multivariate regression analyses. RESULTS: The median FGF23 level was 36.6 pg/ml, ranging from 0.63 to 957 pg/ml. There was a significant correlation between log FGF23 and eGFR (r=-0.21; P<0.00001) and log PTH (r=0.13; P<0.001). These variables remained as independent predictors of FGF23 in multivariate analysis. In addition, log PTH (beta=0.082; P<0.05) and eGFR (beta=-0.090; P<0.05) were associated with log FGF23 in subjects with eGFR>60 ml/min. Only eGFR (beta=-0.35; P<0.0001) remained as a predictor of log FGF23 in subjects with eGFR<60 ml/min. CONCLUSIONS: Serum FGF23 and PTH are associated in vivo, supporting recent findings that FGF23 directly regulates PTH expression in vitro. Additionally, eGFR is associated with FGF23 in subjects with normal or mildly impaired renal function, indicating that GFR may modulate FGF23 levels independent of serum Pi.
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| 4. |
- Mirza, Majd, 1982-, et al.
(författare)
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Serum Fibroblast Growth Factor-23 (FGF-23) and Fracture Risk in Elderly Men
- 2011
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Ingår i: Journal of Bone and Mineral Research. - : Wiley. - 1523-4681 .- 0884-0431. ; 26:4, s. 857-864
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Tidskriftsartikel (refereegranskat)abstract
- A normal mineral metabolism is integral for skeletal development and preservation of bone integrity. Fibroblast growth factor 23 (FGF-23) is a bone-derived circulating factor that decreases serum concentrations of inorganic phosphorous (P-i) and 1,25-dihydroxyvitamin D-3 [1,25(OH)(2)D-3]. Increased FGF-23 expression is a direct or indirect culprit in several skeletal disorders; however, the relation between FGF-23 and fracture risk remains undetermined. We evaluated the prospective relation between serum intact FGF-23 (measured by a two-site monoclonal antibody ELISA) and fracture risk employing the Swedish part of the population-based Osteoporotic Fractures in Men Study (MrOS; n = 2868; mean age 75.4 +/- 3.2 years; median follow-up period 3.35 years). The incidence of at least one validated fracture after baseline was 20.4 per 1000 person-years. FGF-23 was directly related to the overall fracture risk [age-adjusted hazard ratio (HR) per SD increase = 1.20, 95% confidence interval (CI) 1.03-1.40] and vertebral fracture risk (HR = 1.33, 95% CI 1.02-1.75). Spline models revealed a nonlinear relation between FGF-23 and fracture risk, with the strongest relation at FGF-23 levels above 55.7 pg/mL. FGF-23 levels above 55.7 pg/mL also were associated with an increased risk for hip and nonvertebral fractures (HR = 2.30, 95% CI 1.16-4.58, and HR = 1.63, 95% CI 1.01-2.63, respectively). These relations remained essentially unaltered after adjustment for bodymass index (BMI), bone mineral density (BMD), glomerular filtration rate, 25(OH)(2)D-3, parathyroid hormone (PTH), and other fracture risk factors. In conclusion, FGF-23 is a novel predictor of fracture risk in elderly men. (C) 2011 American Society for Bone and Mineral Research.
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| 5. |
- Westerberg, Per-Anton, et al.
(författare)
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Fibroblast growth factor-23 and mineral metabolism after unilateral nephrectomy
- 2010
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Ingår i: Nephrology, Dialysis and Transplantation. - : Oxford University Press (OUP). - 0931-0509 .- 1460-2385. ; 25:12, s. 4068-4071
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Tidskriftsartikel (refereegranskat)abstract
- Background. Fibroblast growth factor -23 (FGF-23) is a key regulator of mineral metabolism. It regulates renal phosphate (Pi) reabsorption and calcitriol synthesis, and has an inhibitory effect on parathyroid hormone (PTH) secretion. FGF-23 increases early in chronic kidney disease (CKD), but the regulation of FGF-23 in mild -to -moderate renal dysfunction is not fully understood. Methods. Nine healthy kidney donors underwent unilateral nephrectomy. Estimated glomerular filtration rate (eGFR) calculated from cystatin C and parameters of mineral metabolism: (Pi, ionized calcium, biointact PTH, intact FGF-23, calcitriol, and urinary excretion of calcium and Pi) were analysed before surgery, and one day, one week and three to six months after surgery. Results. On the first post-operative day, PTH increased due to a decrease in the calcium level. One week after nephrectomy, the FGF-23 level increased from 31.8 +/- 12.3 pg/mL to 55.8 +/- 15.1 pg/mL, while PTH, Pi and calcium levels were unchanged compared towith baseline. On follow-up, eGFR improved compared with its one-week value, and PTH and FGF-23 were unchanged compared towith baseline. The calcitriol level decreased but was in the normal range at all points in time. The total amount of Pi in urine did not change, while the calcium excretion decreased significantly. Conclusions. Pi homeostasis after nephrectomy is maintained by PTH on the first day. When serum calcium is stabilized and food intake resumed, FGF-23 rises, possibly in response to the Pi- load in relation to GFR.
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| 6. |
- Westerberg, Per-Anton, et al.
(författare)
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Fibroblast growth factor 23, mineral metabolism and mortality among elderly men (Swedish MrOs).
- 2013
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Ingår i: BMC nephrology. - : Springer Science and Business Media LLC. - 1471-2369. ; 14:1
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Tidskriftsartikel (refereegranskat)abstract
- BACKGROUND: Fibroblast growth factor 23 (FGF23) is the earliest marker of disturbed mineral metabolism as renal function decreases. Its serum levels are associated with mortality in dialysis patients, persons with chronic kidney disease (CKD) and prevalent cardiovascular disease (CVD), and it is associated with atherosclerosis, endothelial dysfunction and left ventricular hypertrophy in the general population. The primary aim of this study is to examine the association between FGF23 and mortality, in relation to renal function in the community. A secondary aim is to examine the association between FGF23 and CVD related death. METHODS: The population-based cohort of MrOS Sweden included 3014 men (age 69--81 years). At inclusion intact FGF23, intact parathyroid hormone (PTH), 25 hydroxyl vitamin D (25D), calcium and phosphate were measured. Mortality data were collected after an average of 4.5 years follow-up. 352 deaths occurred, 132 of CVD. Association between FGF23 and mortality was analyzed in quartiles of FGF23. Kaplan-Meier curves and Log-rank test were used to examine time to events. Cox proportional hazards regression was used to examine the association between FGF23, in quartiles and as a continuous variable, with mortality. The associations were also analyzed in the sub-cohort with estimated glomerular filtration rate (eGFR) above 60 ml/min/1.73 m2. RESULTS: There was no association between FGF23 and all-cause mortality, Hazard ratio (HR) 95% confidence interval (CI): 1.02 (0.89-1.17). For CVD death the HR (95% CI) was 1.26 (0.99 - 1.59)/(1-SD) increase in log(10)FGF23 after adjustment for eGFR, and other confounders. In the sub-cohort with eGFR > 60 ml/min/1.73 m2 the HR (95% CI) for CVD death was 55% (13--111)/(1-SD) increase in log(10)FGF23 CONCLUSIONS: FGF23 is not associated with mortality of all-cause in elderly community living men, but there is a weak association with CVD death, even after adjustment for eGFR and the other confounders. The association with CVD death is noticeable only in the sub-cohort with preserved renal function.
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| 7. |
- Westerberg, Per-Anton, et al.
(författare)
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Preoperative tumor localization by means of venous sampling for fibroblast growth factor-23 in a patient with tumor-induced osteomalacia
- 2008
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Ingår i: Endocrine Practice. - 1530-891X .- 1934-2403. ; 14:3, s. 362-7
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Tidskriftsartikel (refereegranskat)abstract
- OBJECTIVE: To report on a novel strategy for tumor localization in a 62-year-old man with hypophosphatemic tumor-induced osteomalacia (TIO). METHODS: Repeated computed tomographic and magnetic resonance imaging scans failed to localize any tumor in a patient with adult-onset hypophosphatemic osteomalacia. Therefore, venous sampling for fibroblast growth factor-23 (FGF23)--a circulating hormone that has been identified as a causative factor for TIO--in major veins was conducted. Serum FGF23 was measured from collected samples by an intact FGF23 enzyme-linked immunosorbent assay. RESULTS: Venous sampling suggested a local increase in serum FGF23 in the left femoral vein; this finding prompted performance of octreotide scintigraphy restricted to the left leg. A tumor was located at the lateral condyle of the left femur, which was also confirmed by magnetic resonance imaging. Surgical resection of the tumor normalized the serum phosphorus and 1,25-dihydroxyvitamin D3 levels within 5 to 10 days, and FGF23 declined to normal levels within 24 hours. Histologic analysis supported the diagnosis of a soft-tissue giant cell tumor. CONCLUSION: Our study case demonstrates the diagnostic complexity and difficulties in localizing a small tumor in a patient with TIO. Venous sampling for FGF23 may be helpful in tumor localization in sporadic cases of hypophosphatemic osteomalacia, especially when noninvasive diagnostic techniques prove insufficient.
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| 8. |
- Westerberg, Per-Anton, et al.
(författare)
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Regulation of fibroblast growth factor-23 in chronic kidney disease
- 2007
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Ingår i: Nephrology, Dialysis and Transplantation. - : Oxford University Press (OUP). - 0931-0509 .- 1460-2385. ; 22:11, s. 3202-3207
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Tidskriftsartikel (refereegranskat)abstract
- BackgroundFibroblast growth factor-23 (FGF23) is a circulatingfactor that regulates the renal reabsorption of inorganic phosphate(Pi) and is increased in chronic kidney disease (CKD). The aimof the current investigation was to study the regulation ofFGF23 in CKD subjects with various degree of renal function.As such, we analysed the relationship between FGF23, Pi, calcium,parathyriod hormone (PTH), 25(OH) vitamin D3(25(OH)D3), 1,25(OH)2vitamin D3(1,25(OH)2D3) and estimated glomerular filtrationrate (eGFR).MethodsIntact FGF23 and other biochemical variables were analysedin 72 consecutive adult out-patients with various stages ofCKD (eGFR ranging from 4–96 ml/min.) Association studieswere performed using linear univariate and multivariate analysis.ResultsFGF23 was significantly elevated at CKD stage 4 (266± 315 pg/ml, P < 0.001) and 5 (702 ± 489 pg/ml,P < 0.001) compared with CKD 1–2 (46 ± 43 pg/ml).In CKD 4–5 an independent association between log FGF23and Pi (P < 0.001), 25(OH)D3 (P < 0.05) as well as eGFR(P < 0.01) was observed. In contrast, in CKD 1–3 logPTH (P < 0.05) was the only independent predictor of logFGF23 in multivariate analysis. In CKD 1–5, Pi (P <0.00001) and log PTH (P < 0.01) were explanatory variablesfor log FGF23 in multivariate analysis.ConclusionsWe conclude that serum FGF23 increases in CKD 4–5,in parallel with the emerging hyperphosphataemia. Serum Pi isthe most important predictor of FGF23 when GFR is less than30 ml/min. In contrast, our data suggest that Pi may not bean important determinant of FGF23 in normophosphataemic CKDsubjects. Finally, the association between FGF23 and PTH inCKD may suggest a co-regulation that remains to be further elucidated.
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