Update on fibroblast growth factor 23 in chronic kidney disease

Chronic kidney disease (CKD) is a public health epidemic that affects millions of people worldwide. Presence of CKD predisposes individuals to high risks of end-stage renal disease (ESRD), cardiovascular disease, and premature death. Disordered phosphate homeostasis with elevated circulating levels of fibroblast growth factor 23 (FGF23) is an early and pervasive complication of CKD. CKD is likely the most common cause of chronically elevated FGF23 levels, and the clinical condition in which levels are most markedly elevated. Although increases in FGF23 levels help maintain serum phosphate in the normal range in CKD, prospective studies in populations of pre-dialysis CKD, incident and prevalent ESRD, and kidney transplant recipients demonstrate that elevated FGF23 levels are independently associated with progression of CKD and development of cardiovascular events and mortality. It was originally thought that these observations were driven by elevated FGF23 levels acting as a highly sensitive biomarker of toxicity due to phosphate. However, FGF23 itself has now been shown to mediate ‘off-target,’ direct, end-organ toxicity in the heart, which suggests that elevated FGF23 levels may be a novel mechanism of adverse outcomes in CKD. This report reviews recent advances in FGF23 biology relevant to CKD, the classical effects of FGF23 on mineral homeostasis, and the studies that established FGF23 excess as a biomarker and novel mechanism of cardiovascular disease. The report concludes with a critical review of the effects of different therapeutic strategies targeting FGF23 reduction and how these might be leveraged in a future randomized trial aimed at improving outcomes in CKD

OR13-3 Effects of Iron Isomaltoside versus Ferric Carboxymaltose on Hormonal Control of Phosphate Homeostasis: The PHOSPHARE-IDA04/05 Randomized Controlled Trials

Iron isomaltoside (IIM) and ferric carboxymaltose (FCM) are newer intravenous iron preparations that can be administered in high-doses to rapidly correct iron deficiency anemia (IDA). FCM can cause hypophosphatemia due to fibroblast growth factor 23 (FGF23) mediated renal phosphate wasting, which has been associated with osteomalacia, but the comparative effects of IIM are unknown. In two separate, identically designed, open label randomized controlled trials, we 1:1 randomized 245 adults with IDA to receive IIM (single infusion of 1000 mg) or FCM (FDA-approved dosing schedule: 2 infusions of 750 mg administered 1 week apart). We compared the incidence, severity and duration of hypophosphatemia, and effects on renal phosphate excretion, FGF23, PTH, vitamin D, and biomarkers of bone turnover measured in blood and urine samples collected at study visits at baseline (day 0) and on days 1, 7, 8, 14, 21, and 35. In pooled analyses of both trials, the incidence of hypophosphatemia 35 days. FCM but not IIM also induced changes in vitamin D and calcium homeostasis that triggered secondary hyperparathyroidism, which likely contributed to persistence of hypophosphatemia. Consistent with case reports of pathological fractures following FCM use, FCM also induced significant elevations of biomarkers of bone turnover that are associated with osteomalacia

Effects of etelcalcetide on fibroblast growth factor 23 in patients with secondary hyperparathyroidism receiving hemodialysis

Background: Etelcalcetide is an intravenous calcimimetic approved for treatment of secondary hyperparathyroidism (sHPT) in patients receiving hemodialysis. Besides lowering parathyroid hormone (PTH), etelcalcetide also significantly reduces fibroblast growth factor 23 (FGF23), but the mechanisms are unknown. Methods: To investigate potential mediators of etelcalcetide-induced FGF23 reduction, we performed secondary analyses of the 26-week randomized trials that compared the effects on PTH of etelcalcetide (n = 509) versus placebo (n = 514) and etelcalcetide (n = 340) versus cinacalcet (n = 343) in adults with sHPT receiving hemodialysis. We analyzed changes in FGF23 in relation to changes in PTH, calcium, phosphate and bone turnover markers. We also investigated how concomitant treatments aimed at mitigating hypocalcemia altered the FGF23-lowering effects of etelcalcetide. Results: Etelcalcetide reduced FGF23 [median % change (quartile 1-quartile 3)] from baseline to the end of the trial significantly more than placebo [-56% (-85 to -7) versus +2% (-40 to +65); P < 0.001] and cinacalcet [-68% (-87 to -26) versus -41% (-76 to +25); P < 0.001]. Reductions in FGF23 correlated strongly with reductions in calcium and phosphate, but not with PTH; correlations with bone turnover markers were inconsistent and of borderline significance. Increases in concomitant vitamin D administration partially attenuated the FGF23-lowering effect of etelcalcetide, but increased dialysate calcium concentration versus no increase and increased dose of calcium supplementation versus no increase did not attenuate the FGF23-lowering effects of etelcalcetide. Conclusion: These data suggest that etelcalcetide potently lowers FGF23 in patients with sHPT receiving hemodialysis and that the effect remains detectable among patients who receive concomitant treatments aimed at mitigating treatment-associated decreases in serum calcium

Adiposity, Cardiometabolic Risk, and Vitamin D Status: The Framingham Heart Study

OBJECTIVE: Because vitamin D deficiency is associated with a variety of chronic diseases, understanding the characteristics that promote vitamin D deficiency in otherwise healthy adults could have important clinical implications. Few studies relating vitamin D deficiency to obesity have included direct measures of adiposity. Furthermore, the degree to which vitamin D is associated with metabolic traits after adjusting for adiposity measures is unclear. RESEARCH DESIGN AND METHODS: We investigated the relations of serum 25-hydroxyvitamin D (25[OH]D) concentrations with indexes of cardiometabolic risk in 3,890 nondiabetic individuals; 1,882 had subcutaneous adipose tissue (SAT) and visceral adipose tissue (VAT) volumes measured by multidetector computed tomography (CT). RESULTS: In multivariable-adjusted regression models, 25(OH)D was inversely associated with winter season, waist circumference, and serum insulin (P < 0.005 for all). In models further adjusted for CT measures, 25(OH)D was inversely related to SAT (−1.1 ng/ml per SD increment in SAT, P = 0.016) and VAT (−2.3 ng/ml per SD, P < 0.0001). The association of 25(OH)D with insulin resistance measures became nonsignificant after adjustment for VAT. Higher adiposity volumes were correlated with lower 25(OH)D across different categories of BMI, including in lean individuals (BMI <25 kg/m2). The prevalence of vitamin D deficiency (25[OH]D <20 ng/ml) was threefold higher in those with high SAT and high VAT than in those with low SAT and low VAT (P < 0.0001). CONCLUSIONS: Vitamin D status is strongly associated with variation in subcutaneous and especially visceral adiposity. The mechanisms by which adiposity promotes vitamin D deficiency warrant further study.National Institutes of Health's National Heart, Lung, and Blood Institute (N01-HC-25195, R01-DK-80739): American Heart Associatio

A Prospective Cohort Study of Mineral Metabolism After Kidney Transplantation.

BACKGROUND: Kidney transplantation corrects or improves many complications of chronic kidney disease, but its impact on disordered mineral metabolism is incompletely understood. METHODS: We performed a multicenter, prospective, observational cohort study of 246 kidney transplant recipients in the United States to investigate the evolution of mineral metabolism from pretransplant through the first year after transplantation. Participants were enrolled into 2 strata defined by their pretransplant levels of parathyroid hormone (PTH), low PTH (\u3e65 to ≤300 pg/mL; n = 112), and high PTH (\u3e300 pg/mL; n = 134) and underwent repeated, longitudinal testing for mineral metabolites. RESULTS: The prevalence of posttransplant, persistent hyperparathyroidism (PTH \u3e65 pg/mL) was 89.5%, 86.8%, 83.1%, and 86.2%, at months 3, 6, 9, and 12, respectively, among participants who remained untreated with cinacalcet, vitamin D sterols, or parathyroidectomy. The results did not differ across the low and high PTH strata, and rates of persistent hyperparathyroidism remained higher than 40% when defined using a higher PTH threshold greater than 130 pg/mL. Rates of hypercalcemia peaked at 48% at week 8 in the high PTH stratum and then steadily decreased through month 12. Rates of hypophosphatemia ( CONCLUSIONS: Persistent hyperparathyroidism is common after kidney transplantation. Further studies should determine if persistent hyperparathyroidism or its treatment influences long-term posttransplantation clinical outcomes.This is an open-access article distributed under the terms of the Creative Commons Attribution-NonCommercial-NoDerivatives 3.0 License, where it is permissible to download and share the work provided it is properly cited. The work cannot be changed in any way or used commercially. http://creativecommons.org/licenses/by-nc-nd/3.0

Creatinine- versus cystatin C-based renal function assessment in the Northern Manhattan Study

Background Accurate glomerular filtration rate estimation informs drug dosing and risk stratification. Body composition heterogeneity influences creatinine production and the precision of creatinine-based estimated glomerular filtration rate (eGFRcr) in the elderly. We compared chronic kidney disease (CKD) categorization using eGFRcr and cystatin C-based estimated GFR (eGFRcys) in an elderly, racially/ethnically diverse cohort to determine their concordance. Methods The Northern Manhattan Study (NOMAS) is a predominantly elderly, multi-ethnic cohort with a primary aim to study cardiovascular disease epidemiology. We included participants with concurrently measured creatinine and cystatin C. eGFRcr was calculated using the CKD-EPI 2009 equation. eGFRcys was calculated using the CKD-EPI 2012 equation. Logistic regression was used to estimate odds ratios and 95% confidence intervals of factors associated with reclassification from eGFRcr≥60ml/min/1.73m2 to eGFRcys<60ml/min/1.73m2. Results Participants (n = 2988, mean age 69±10yrs) were predominantly Hispanic, female, and overweight/obese. eGFRcys was lower than eGFRcr by mean 23mL/min/1.73m2. 51% of participants’ CKD status was discordant, and only 28% maintained the same CKD stage by both measures. Most participants (78%) had eGFRcr≥60mL/min/1.73m2; among these, 64% had eGFRcys65 years, obesity, current smoking, white race, and female sex. Conclusions In a large, multiethnic, elderly cohort, we found a highly discrepant prevalence of CKD with eGFRcys versus eGFRcr. Determining the optimal method to estimate GFR in elderly populations needs urgent further study to improve risk stratification and drug dosing

Cardiac Biomarkers and Risk of Atrial Fibrillation in Chronic Kidney Disease: The CRIC Study.

Background We tested associations of cardiac biomarkers of myocardial stretch, injury, inflammation, and fibrosis with the risk of incident atrial fibrillation (AF) in a prospective study of chronic kidney disease patients. Methods and Results The study sample was 3053 participants with chronic kidney disease in the multicenter CRIC (Chronic Renal Insufficiency Cohort) study who were not identified as having AF at baseline. Cardiac biomarkers, measured at baseline, were NT-proBNP (N-terminal pro-B-type natriuretic peptide), high-sensitivity troponin T, galectin-3, growth differentiation factor-15, and soluble ST-2. Incident AF ("AF event") was defined as a hospitalization for AF. During a median follow-up of 8 years, 279 (9%) participants developed a new AF event. In adjusted models, higher baseline log-transformed NT-proBNP (N-terminal pro-B-type natriuretic peptide) was associated with incident AF (adjusted hazard ratio [HR] per SD higher concentration: 2.11; 95% CI, 1.75, 2.55), as was log-high-sensitivity troponin T (HR 1.42; 95% CI, 1.20, 1.68). These associations showed a dose-response relationship in categorical analyses. Although log-soluble ST-2 was associated with AF risk in continuous models (HR per SD higher concentration 1.35; 95% CI, 1.16, 1.58), this association was not consistent in categorical analyses. Log-galectin-3 (HR 1.05; 95% CI, 0.91, 1.22) and log-growth differentiation factor-15 (HR 1.16; 95% CI, 0.96, 1.40) were not significantly associated with incident AF. Conclusions We found strong associations between higher NT-proBNP (N-terminal pro-B-type natriuretic peptide) and high-sensitivity troponin T concentrations, and the risk of incident AF in a large cohort of participants with chronic kidney disease. Increased atrial myocardial stretch and myocardial cell injury may be implicated in the high burden of AF in patients with chronic kidney disease

Inflammation and glucose intolerance. A prospective study of gestational diabetes mellitus

WSTĘP. Podwyższony poziom leukocytów w surowicy krwi jest wskaźnikiem procesu zapalenia, który, jak wykazują badania prospektywne, wiąże się z rozwojem cukrzycy typu 2. Chociaż cukrzyca ciążowa oraz cukrzyca typu 2 mają dużo wspólnych mechanizmów patofizjologicznych, w niewielu pracach badano związek zapalenia z rozwojem cukrzycy ciążowej. MATERIAŁ I METODY. W badaniu oceniano w sposób prospektywny liczbę leukocytów w próbkach krwi pobranych podczas pierwszej rutynowej wizyty kontrolnej w grupie 2753 kobiet w ciąży &#8212; wieloródek z prawidłową wartością glikemii. U 98 (3,6%) z nich wystąpiła później cukrzyca ciążowa. Pacjentki podzielono na podgrupy w zależności od kwartyla liczby leukocytów i porównano wyniki przeprowadzanego w trzecim trymestrze przesiewowego testu tolerancji glukozy oraz częstość cukrzycy ciążowej wśród kobiet należących do poszczególnych kwartyli. Zastosowano test regresji logistycznej, aby obliczyć skorygowane względem jednego i wielu czynników względne ryzyko wystąpienia cukrzycy ciążowej w zależności od kwartyla leukocytozy. WYNIKI. U kobiet, u których doszło do rozwoju cukrzycy ciążowej, stężenie leukocytów w surowicy krwi było wyższe (10,5 &plusmn; 2,2 vs. 9,2 &plusmn; 2,2 × 103 komórek/ml; p < 0,01) niż u pacjentek, u których metabolizm węglowodanów pozostał prawidłowy. Wraz ze wzrostem kwartyla leukocytozy obserwowano liniowy wzrost glikemii po obciążeniu glukozą (p < 0,01), pola pod krzywą testu tolerancji glukozy (p < 0,01) oraz częstości cukrzycy ciążowej (kwartyl 1. &#8212; 1,1%; kwartyl 2. &#8212; 2,5%; kwartyl 3. &#8212; 4,2% i kwartyl 4. &#8212; 6,4%; p < 0,01). W analizie wieloczynnikowej, wraz ze wzrostem kwartyla leukocytozy, liniowy trend względnego ryzyka (RR, relative risk) rozwoju cukrzycy ciążowej pozostał statystycznie istotny [kwartyl 1. &#8212; referencyjny, kwartyl 2. &#8212; RR 2,3 (95% CI 0,9-5,7), kwartyl 3. &#8212; RR 3,3 (1,4&#8211;7,8), kwartyl 4. &#8212; RR 4,9 (2,1&#8211;11,2); p < 0,01]. WNIOSKI. Podwyższony poziom leukocytów we wczesnym okresie ciąży jest w sposób niezależny, liniowy związany z wynikami testów przesiewowych w kierunku cukrzycy ciążowej oraz ryzykiem wystąpienia tej choroby. Brak wyraźnej granicy w rozkładzie liczby leukocytów sprawia, że wskaźnik ten nie może mieć zastosowania klinicznego, chociaż dane sugerują, że proces zapalenia wiąże się z rozwojem cukrzycy ciążowej. Może to być kolejny mechanizm patofizjologiczny, łączący występowanie cukrzycy ciążowej z rozwojem w przyszłości cukrzycy typu 2.INTRODUCTION. Increased leukocyte count is a marker of inflammation that has been associated with the development of type 2 diabetes in prospective studies. Although gestational diabetes mellitus (GDM) and type 2 diabetes share certain pathophysiological mechanisms, few studies have examined inflammation and risk of GDM. MATERIAL AND METHODS. We prospectively examined routine leukocyte counts collected at the first prenatal visit in a cohort of 2,753 nulliparous euglycemic women, 98 (3.6%) of whom were later diagnosed with GDM. Subjects were divided into quartiles of leukocyte count, and the results of third-trimester glucose screening tests and the incidence of GDM among these quartiles were compared. Logistic regression was used to calculate univariate and multivariable-adjusted relative risks (RRs) of GDM according to leukocyte quartiles. RESULTS. Leukocyte counts were increased among women who subsequently developed GDM compared with those who remained free of GDM (10.5 &#177; &#177; 2.2 vs. 9.2 &#177; 2.2 × 103 cells/ml; P < 0.01). There was a linear increase in postloading mean glucose levels (P for trend < 0.01), the area under the glucose tolerance test curves (P for trend < 0.01), and the incidence of GDM (quartile 1, 1.1; quartile 2, 2.5; quartile 3, 4.2; and quartile 4, 6.4%; P for trend < 0.01) with increasing leukocyte quartiles. In the multivariable-adjusted analysis, the linear trend in the RR of GDM with increasing leukocyte quartiles remained statistically significant (quartile 1, reference; quartile 2, RR 2.3 [95% CI 0.9&#8211;5.7]; quartile 3, 3.3 [1.4&#8211;7.8]; quartile 4, 4.9 [2.1&#8211;11.2]; P for trend < 0.01). CONCLUSIONS. Increased leukocyte count early in pregnancy is independently and linearly associated with the results of GDM screening tests and the risk of GDM. Although overlap in the leukocyte count distributions precludes it from being a clinically useful biomarker, these data suggest that inflammation is associated with the development of GDM and may be another pathophysiological link between GDM and future type 2 diabetes