Huiliang Xie

Fibroblast growth factor 23 is elevated before parathyroid hormone and phosphate in chronic kidney disease

Fibroblast growth factor 23 (FGF23) regulates phosphorus metabolism and is a strong predictor of mortality in dialysis patients. FGF23 is thought to be an early biomarker of disordered phosphorus metabolism in the initial stages of chronic kidney disease (CKD). We measured FGF23 in baseline samples from 3879 patients in the Chronic Renal Insufficiency Cohort study, which is a diverse cohort of patients with CKD stage 2-4. Mean serum phosphate and median parathyroid hormone (PTH) levels were in the normal range, but median FGF23 was markedly greater than in healthy populations, and increased significantly with decreasing estimated glomerular filtration rate (eGFR). High levels of FGF23, defined as being above 100 RU/ml, were more common than secondary hyperparathyroidism and hyperphosphatemia in all strata of eGFR. The threshold of eGFR at which the slope of FGF23 increased was significantly higher than the corresponding threshold for PTH based on non-overlapping 95% confidence intervals. Thus, increased FGF23 is a common manifestation of CKD that develops earlier than increased phosphate or PTH. Hence, FGF23 measurements may be a sensitive early biomarker of disordered phosphorus metabolism in patients with CKD and normal serum phosphate levels.

Fibroblast growth factor 23 and risks of mortality and end-stage renal disease in patients with chronic kidney disease.

CONTEXT A high level of the phosphate-regulating hormone fibroblast growth factor 23 (FGF-23) is associated with mortality in patients with end-stage renal disease, but little is known about its relationship with adverse outcomes in the much larger population of patients with earlier stages of chronic kidney disease. OBJECTIVE To evaluate FGF-23 as a risk factor for adverse outcomes in patients with chronic kidney disease. DESIGN, SETTING, AND PARTICIPANTS A prospective study of 3879 participants with chronic kidney disease stages 2 through 4 who enrolled in the Chronic Renal Insufficiency Cohort between June 2003 and September 2008. MAIN OUTCOME MEASURES All-cause mortality and end-stage renal disease. RESULTS At study enrollment, the mean (SD) estimated glomerular filtration rate (GFR) was 42.8 (13.5) mL/min/1.73 m(2), and the median FGF-23 level was 145.5 RU/mL (interquartile range [IQR], 96-239 reference unit [RU]/mL). During a median follow-up of 3.5 years (IQR, 2.5-4.4 years), 266 participants died (20.3/1000 person-years) and 410 reached end-stage renal disease (33.0/1000 person-years). In adjusted analyses, higher levels of FGF-23 were independently associated with a greater risk of death (hazard ratio [HR], per SD of natural log-transformed FGF-23, 1.5; 95% confidence interval [CI], 1.3-1.7). Mortality risk increased by quartile of FGF-23: the HR was 1.3 (95% CI, 0.8-2.2) for the second quartile, 2.0 (95% CI, 1.2-3.3) for the third quartile, and 3.0 (95% CI, 1.8-5.1) for the fourth quartile. Elevated fibroblast growth factor 23 was independently associated with significantly higher risk of end-stage renal disease among participants with an estimated GFR between 30 and 44 mL/min/1.73 m(2) (HR, 1.3 per SD of FGF-23 natural log-transformed FGF-23; 95% CI, 1.04-1.6) and 45 mL/min/1.73 m(2) or higher (HR, 1.7; 95% CI, 1.1-2.4), but not less than 30 mL/min/1.73 m(2). CONCLUSION Elevated FGF-23 is an independent risk factor for end-stage renal disease in patients with relatively preserved kidney function and for mortality across the spectrum of chronic kidney disease.

Fibroblast Growth Factor-23 and Cardiovascular Events in CKD

An elevated level of fibroblast growth factor-23 (FGF-23) is the earliest abnormality of mineral metabolism in CKD. High FGF-23 levels promote left ventricular hypertrophy but not coronary artery calcification. We used survival analysis to determine whether elevated FGF-23 is associated with greater risk of adjudicated congestive heart failure (CHF) and atherosclerotic events (myocardial infarction, stroke, and peripheral vascular disease) in a prospective cohort of 3860 participants with CKD stages 2-4 (baseline estimated GFR [eGFR], 44±15 ml/min per 1.73 m(2)). During a median follow-up of 3.7 years, 360 participants were hospitalized for CHF (27 events/1000 person-years) and 287 had an atherosclerotic event (22 events/1000 person-years). After adjustment for demographic characteristics, kidney function, traditional cardiovascular risk factors, and medications, higher FGF-23 was independently associated with graded risk of CHF (hazard ratio [HR], 1.45 per doubling [95% confidence interval (CI), 1.28 to 1.65]; HR for highest versus lowest quartile, 2.98 [95% CI, 1.97 to 4.52]) and atherosclerotic events (HR per doubling, 1.24 [95% CI, 1.09 to 1.40]; HR for highest versus lowest quartile, 1.76 [95% CI, 1.20 to 2.59]). Elevated FGF-23 was associated more strongly with CHF than with atherosclerotic events (P=0.02), and uniformly was associated with greater risk of CHF events across subgroups stratified by eGFR, proteinuria, prior heart disease, diabetes, BP control, anemia, sodium intake, income, fat-free mass, left ventricular mass index, and ejection fraction. Thus, higher FGF-23 is independently associated with greater risk of cardiovascular events, particularly CHF, in patients with CKD stages 2-4.

Fibroblast Growth Factor 23 and Inflammation in CKD

BACKGROUND AND OBJECTIVES Levels of fibroblast growth factor 23 (FGF23) and inflammatory markers are commonly elevated in CKD, and each is associated with adverse clinical outcomes. This study tested the hypothesis that FGF23 is independently associated with inflammation in CKD. DESIGN, SETTING, PARTICIPANTS, & MEASUREMENTS The association between levels of FGF23 and the inflammatory markers IL-6, C-reactive protein (CRP), TNF-α, and fibrinogen was assessed in a cross-sectional analysis of 3879 participants enrolled in the Chronic Renal Insufficiency Cohort (CRIC) study between June 2003 and September 2008. RESULTS FGF23 correlated directly with IL-6 (r=0.4), CRP (r=0.2), TNF-α (r=0.4), and fibrinogen (r=0.3; P<0.001 for each). In univariate and multivariable-adjusted linear regression analyses, natural log (ln) transformed FGF23 was significantly associated with lnIL-6, lnCRP, lnTNF-α, and fibrinogen (P<0.001 for each). Each unit higher lnFGF23 was associated with severe inflammation, defined as levels of all inflammatory markers in the highest 25th percentile, in univariate (odds ratio [OR], 2.4 [95% confidence interval (CI), 2.0-2.9]) and multivariable-adjusted (OR, 2.0 [95% CI, 1.6-2.5]) logistic regression analyses. Ascending FGF23 quartiles were independently associated with severe inflammation (OR, 5.6 for the highest versus lowest FGF23 quartile [95% CI, 2.3-13.9]; P for trend < 0.001). CONCLUSIONS Higher FGF23 levels are independently associated with higher levels of inflammatory markers in patients with CKD and with significantly greater odds of severe inflammation. Future studies should evaluate whether inflammation modifies the association between FGF23 and adverse outcomes in CKD.

Effects of Dietary Phosphate Restriction and Phosphate Binders on FGF23 Levels in CKD

BACKGROUND Elevated levels of fibroblast growth factor 23 (FGF23) are associated with increased risk of adverse outcomes in patients with CKD. Reducing dietary phosphate intake or absorption may decrease FGF23 levels, but data on the combined effects of dietary phosphate restriction and phosphate binders in CKD are limited. DESIGN, SETTING, PARTICIPANTS, & MEASUREMENTS In this 2×2 factorial, single-blinded, placebo-controlled, 3-month study, conducted between July 2009 and March 2012, 39 patients with CKD stages 3 or 4 and normal serum phosphate levels were randomly assigned to one of four groups: ad libitum diet plus lanthanum carbonate (LC) placebo (n=10), 900-mg phosphate diet plus LC placebo (n=10), ad libitum diet plus LC (n=11), or 900-mg phosphate diet plus LC (n=8). The dose of LC was 1000 mg three times daily with meals. Dietary restriction was accomplished with outpatient counseling. The primary end point was change in FGF23 levels from baseline. RESULTS Compared with ad libitum diet, the 900-mg phosphate diet did not significantly reduce FGF23 levels (diet × time interaction, P=0.05). Compared with placebo, LC alone also did not significantly reduce FGF23 levels (LC × time interaction, P=0.21). However, the dual intervention significantly decreased FGF23 levels throughout the study period (diet × LC × time interaction, P=0.02), resulting in a 35% (95% confidence interval, 8%-62%) reduction by study end. CONCLUSION The combination of LC plus counseling for a phosphate-restricted diet decreased FGF23 levels in patients with CKD stages 3-4 and normal serum phosphate levels.

Mineral Metabolites and CKD Progression in African Americans

CKD progresses more rapidly to ESRD among African Americans compared with Caucasians. Disordered mineral metabolism is more severe among African Americans with CKD, which might partially explain the accelerated progression of their kidney disease. Here, using data from the African American Study of Kidney Disease and Hypertension, we evaluated longitudinal changes in serum levels of fibroblast growth factor-23 (FGF23), parathyroid hormone (PTH), phosphate, and 25-hydroxyvitamin D in a subset of 420 participants followed for a median of 4 years. We also examined the association of baseline levels of mineral metabolites with risk for ESRD or death in 809 participants. FGF23, PTH, and phosphate levels rose over time; participants with faster rates of decline in measured GFR had the greatest increases in these parameters (P<0.01 for each). Higher baseline levels of FGF23, PTH, and phosphate each associated with increased risk for ESRD or death independent of GFR. FGF23 exhibited a dose-response relationship with outcomes (HR=1.30 per doubling, 95% CI=1.15-1.47; HR=2.24 for highest compared with lowest quartile, 95% CI=1.39-3.60), whereas PTH and phosphate showed nonlinear relationships. Vitamin D insufficiency (<30 ng/ml) was present in 95% of participants, but lower levels did not independently associate with outcomes. Using death-censored ESRD as the outcome produced qualitatively similar results. In conclusion, abnormalities of mineral metabolism worsen with progressive CKD and associate with higher risk for ESRD among African Americans with hypertensive nephrosclerosis.

Fibroblast Growth Factor 23 in Patients Undergoing Peritoneal Dialysis

BACKGROUND AND OBJECTIVES Fibroblast growth factor 23 (FGF23) is an independent risk factor for mortality in patients with ESRD. Before FGF23 testing can be integrated into clinical practice of ESRD, further understanding of its determinants is needed. DESIGN, SETTING, PARTICIPANTS, & MEASUREMENTS In a study of 67 adults undergoing peritoneal dialysis, we tested the hypothesis that longer dialysis vintage and lower residual renal function and renal phosphate clearance are associated with higher FGF23. We also compared the monthly variability of FGF23 versus parathyroid hormone (PTH) and serum phosphate. RESULTS In unadjusted analyses, FGF23 correlated with serum phosphate (r = 0.66, P < 0.001), residual renal function (r = -0.37, P = 0.002), dialysis vintage (r = 0.31, P = 0.01), and renal phosphate clearance (r = -0.38, P = 0.008). In adjusted analyses, absence of residual renal function and greater dialysis vintage associated with higher FGF23, independent of demographics, laboratory values, peritoneal dialysis modality and adequacy, and treatment with vitamin D analogs and phosphate binders. Urinary and dialysate FGF23 clearances were minimal. In three serial monthly measurements, within-subject variability accounted for only 10% of total FGF23 variability compared with 50% for PTH and 60% for serum phosphate. CONCLUSIONS Increased serum phosphate, loss of residual renal function, longer dialysis vintage, and lower renal phosphate clearance are associated with elevated FGF23 levels in ESRD patients undergoing peritoneal dialysis. FGF23 may be a more stable marker of phosphate metabolism in ESRD than PTH or serum phosphate.

Inhibitors of mTOR and risks of allograft failure and mortality in kidney transplantation

Data on long‐term outcomes of users of inhibitors of the mammalian target of rapamycin (mTORI) are lacking in kidney transplantation. In an analysis of 139 370 US kidney transplant recipients between 1999 through 2010, we compared clinical outcomes among users of mTORIs versus calcineurin inhibitors (CNI) in their primary immunosuppresive regimen. During the first 2 years posttransplantation, primary use of mTORIs without CNIs (N = 3237) was associated with greater risks of allograft failure and death compared with a CNI‐based regimen (N = 125 623); the hazard ratio (HR) of the composite outcome ranged from 3.67 (95% confidence interval [CI], 3.12–4.32) after discharge to 1.40 (95% CI 1.26–1.57) by year 2. During years 2–8, primary use of mTORIs without CNIs was independently associated with greater risks of death (HR 1.25; 95% CI, 1.11–1.41) and the composite (HR 1.17; 95%CI, 1.08–1.27) in fully adjusted analyses. The results were qualitatively unchanged in subgroups defined by medical history, immunological risk and clinical course during the index transplant hospitalization. In a propensity‐score matched cohort, use of mTORIs was associated with significantly worse outcomes during the first 2 years and greater risks of death (HR 1.21; 95% CI, 1.05–1.39) and the composite (HR 1.18; 95% CI, 1.08–1.30) in years 2–8. Compared with CNI‐based regimens, use of an mTORI‐based regimen for primary immunosuppression in kidney transplantation was associated with inferior recipient survival.

Earlier Onset and Greater Severity of Disordered Mineral Metabolism in Diabetic Patients With Chronic Kidney Disease

OBJECTIVE Disordered mineral metabolism is a common complication of chronic kidney disease (CKD) and a novel risk factor for CKD progression, cardiovascular disease, and mortality. Although diabetes is the leading cause of CKD and is associated with worse clinical outcomes than other etiologies, few studies have evaluated mineral metabolism in CKD according to diabetes status. RESEARCH DESIGN AND METHODS Using the Chronic Renal Insufficiency Cohort Study, we tested the hypothesis that diabetes is independently associated with lower serum calcium and higher serum phosphate, parathyroid hormone (PTH), and fibroblast growth factor 23 (FGF23). RESULTS Compared with participants without diabetes (n = 1,936), those with diabetes (n = 1,820) were more likely to have lower estimated glomerular filtration rate (eGFR), lower serum albumin, and higher urinary protein excretion (all P < 0.001). Unadjusted serum phosphate, PTH, and FGF23 levels were higher and calcium was lower among those with compared with those without diabetes (all P < 0.001). After multivariate adjustment, diabetes remained a significant predictor of serum phosphate, PTH, and FGF23 but not calcium. The eGFR cut point at which 50% of participants met criteria for secondary hyperparathyroidism or elevated FGF23 was higher in participants with diabetes compared with those without (PTH: eGFR 30–39 vs. 20–29, P < 0.001; FGF23: eGFR 50–59 vs. 40–49, P < 0.001). CONCLUSIONS Disordered mineral metabolism begins earlier in the course of CKD and is more severe among CKD patients with compared with those without diabetes. Future studies should explore mechanisms for these differences and whether they contribute to excess risks of adverse clinical outcomes among diabetic patients with CKD.

Daily Variability in Mineral Metabolites in CKD and Effects of Dietary Calcium and Calcitriol

BACKGROUND AND OBJECTIVES Primary prevention of disordered mineral metabolism in CKD necessitates knowledge of its early pathophysiology. This study evaluated daily fluctuations in mineral metabolites in patients with CKD stages 3 and 4 before and after short-term calcitriol treatment and tested the effects of dietary calcium and calcitriol supplementation on these parameters in the dynamic postprandial setting. DESIGN, SETTING, PARTICIPANTS, & MEASUREMENTS Twelve CKD patients received calcitriol (0.25 μg daily for 1 week) with hourly assessments of mineral metabolites made throughout the day and in the context of standardized meals before and after treatment. Calcium content (250 versus 500 mg) in the breakfasts constituted the dietary calcium intervention. Twelve healthy volunteers were used as controls. RESULTS At baseline, compared with controls, fasting CKD subjects had higher parathyroid hormone and fibroblast growth factor 23 levels and greater fractional excretion of phosphate. After breakfast, urinary calcium excretion increased and parathyroid hormone levels dipped transiently in both groups, but they rose soon thereafter, reaching higher peaks in CKD. Calcitriol decreased fasting parathyroid hormone levels, and when combined with dietary calcium load, it normalized the postprandial parathyroid and calcemic responses. Daily variability in mineral metabolites was preserved in CKD before and after calcitriol. Fibroblast growth factor 23 levels increased after calcitriol, although the response was heterogeneous. CONCLUSIONS Short-term treatment with calcitriol and dietary calcium supplementation normalizes the parathyroid and calcemic postprandial responses in patients with CKD, in whom the diurnal rhythms of mineral metabolites are preserved. Future studies should investigate the variable fibroblast growth factor 23 response to calcitriol in CKD.