The Role of Iron and Erythropoietin in the Association of Fibroblast Growth Factor 23 with Anemia in Chronic Kidney Disease in Humans.

Anemia in chronic kidney disease (CKD) is an almost universal complication of this condition. Fibroblast growth factor 23 (FGF23), a key-player in mineral metabolism, is reportedly associated with anemia and hemoglobin levels in non-dialysis CKD patients. Here, we sought to further characterize this association while taking into account the biologically active, intact fraction of FGF23, iron metabolism, and erythropoietin (EPO). Hemoglobin, EPO, iron, and mineral metabolism parameters, including both intact and c-terminal-FGF23 (iFGF23 and cFGF23, respectively) were measured cross-sectionally in 225 non-dialysis CKD patients (stage 1-5, median eGFR: 30 mL/min./1.73m2) not on erythropoiesis stimulating agents or intravenous iron therapy. Statistical analysis was performed by multiple linear regression. After adjustment for eGFR and other important confounders, only cFGF23 but not iFGF23 was significantly associated with hemoglobin levels and this association was largely accounted for by iron metabolism parameters. cFGF23 but not iFGF23 was also associated with mean corpuscular hemoglobin (MCH) and mean corpuscular volume (MCV), again in dependence on iron metabolism parameters. Similarly, EPO concentrations were associated with cFGF23 but not iFGF23, but their contribution to the association of cFGF23 with hemoglobin levels was marginal. In pre-dialysis CKD patients, the observed association of FGF23 with hemoglobin seems to be restricted to cFGF23 and largely explained by the iron status.

Calcification Propensity of Serum is Independent of Excretory Renal Function.

Vascular calcification is a component of cardiovascular disease, which is leading cause of death in patients with chronic kidney disease (CKD). A functional assay (T50-test) measuring the propensity of human serum to calcify associates with mortality and cardiovascular events in CKD patients. Calcification propensity is known to increase with CKD stage. We investigated whether the T50 readout is directly dependent on excretory kidney function (eGFR) or rather explained by deranged parameters of bone and mineral metabolism in the course of CKD. T50, along with markers implicated in calcification and mineral metabolism, were measured in a cross-sectional cohort of 118 patients with CKD stage 1-5. Associations of T50 with measured parameters were analysed and partial correlations performed to test to which extent the association of T50 with eGFR can be attributed to variation of these parameters. T50 correlates with eGFR, but serum levels of phosphate and calcium largely explain this association. Phosphate, magnesium, fetuin A, albumin, bicarbonate, and serum cross-laps but not Parathyroid Hormone or Fibroblast Growth Factor 23 are associated with T50 in multivariate adjusted models. These findings indicate that T50 values depend mainly on the concentration of promoters and inhibitors of calcification in serum, but not excretory kidney function.

Sclerostin declines during hemodialysis and appears in Dialysate.

BACKGROUND/AIMS: Sclerostin, a soluble inhibitor of Wnt-signaling, inhibits bone formation. We assessed the impact of dialysis on serum sclerostin and whether sclerostin is detectable in effluent dialysates. METHODS: In a prospective study of 54 prevalent hemodialysis patients, parameters of bone and mineral metabolism were assessed at the beginning and at the end of dialysis. In a subset of patients (n = 19) sclerostin was measured in serum at start, 1, 2, and 3 h of dialysis and in the effluent dialysate at several points in time. RESULTS: Sclerostin serum levels decreased from median 71.4 pmol/l to 43.5 pmol/l during dialysis (p < 0.0001). In patients with high pre-dialysis sclerostin serum levels, sclerostin was detected in the dialysate. Higher Kt/V correlated with greater relative decrease of sclerostin (r = 0.467; p = 0.001). CONCLUSION: Sclerostin is dialysable. Furthermore, sclerostin serum levels decrease during dialysis. Whether targeting lower sclerostin levels by means of improved dialysis adequacy has direct relevance to bone disease remains to be shown.

Correlations and time course of FGF23 and markers of bone metabolism in maintenance hemodialysis patients.

OBJECTIVE: Parathyroid hormone (iPTH) and fibroblast growth factor 23 (FGF23) are elevated in secondary hyperparathyroidism. In hemodialysis, higher dialysate calcium (1.5 mmol/L) induces intradialytic suppression of iPTH, whereas its impact on FGF23 and markers of bone metabolism is unknown. We assessed the time course of FGF23 and markers of bone metabolism in relationship to dialysate calcium. DESIGN AND METHODS: In this prospective cohort study of 19 patients on maintenance hemodialysis, we measured serum calcium (sCa), inorganic phosphate (iP), blood urea nitrogen (BUN), ß2-microglobulin (ßMG), iPTH, FGF23, aminoterminal propeptide type 1 procollagen (P1NP), C-telopeptide of type I collagen for bone degradation (CTX-I), osteocalcin (OC), bone specific alkaline phosphatase (BALP), and tartrate-resistant acid phosphatase (TRAP5b) during a single hemodialysis session at baseline, 1, 2, and 3h of dialysis. The time course of measured parameters was compared according to groups of prescribed dialysate calcium of 1.25 mmol/L and 1.5 mmol/L. RESULTS: iPTH declined in the 1.5 mmol/L dialysis group as serum calcium increased whereas it tended to increase in the 1.25 mmol/L group without significant changes in serum calcium. Patients on long-term dialysate calcium of 1.5 mmol/L had significantly lower CTX-I levels and tended to lower levels of iPTH, FGF23, OC, P1NP and TRAP5b at the start of dialysis compared to those on 1.25 mmol/L. CTX-I, FGF23 and OC but not BALP, P1NP and TRAP5b decreased during dialysis independent of dialysate calcium. CONCLUSIONS: In spite of immediate effects on iPTH, dialysate calcium does not acutely affect other parameters of bone and mineral metabolism. SHORT SUMMARY: Dialysate calcium concentration is known to have both immediate and longer-term impact on parathyroid hormone levels in hemodialysis patients. Little is known about the acute impact of dialysate calcium on bone metabolism. In this cross-sectional study of prevalent hemodialysis patients, we found no evidence of immediate short-term dialysate calcium-induced changes of fibroblast growth factor 23 or anabolic and catabolic markers of bone turnover during hemodialysis. However, differences in CTX-I and to a lesser extent other parameters between groups of higher and lower dialysate calcium suggest a longer-term effect that remains to be validated.

Sclerostin serum levels correlate positively with bone mineral density and microarchitecture in haemodialysis patients.

BACKGROUND: Sclerostin is a soluble inhibitor of osteoblast function. Sclerostin is downregulated by the parathyroid hormone (PTH). Here, it was investigated whether sclerostin levels are influenced by intact (i) PTH and whether sclerostin is associated with bone turnover, microarchitecture and mass in dialysis patients. METHODS: Seventy-six haemodialysis patients and 45 healthy controls were included in this cross-sectional study. Sclerostin, Dickkopf-1 (DKK-1), intact parathyroid hormone (iPTH), vitamin D and markers of bone turnover were analysed. A subset of 37 dialysis patients had measurements of bone mineral density (BMD) using dual-energy X-ray absorptiometry and bone microarchitecture using high-resolution peripheral quantitative computed tomography. RESULTS: Dialysis patients had significantly higher sclerostin levels than controls (1257 pg/mL versus 415 pg/mL, P < 0.001). Significant correlations were found between sclerostin and gender (R = 0.41), iPTH (R = -0.28), 25-hydroxy-cholecalciferol (R = 0.27) and calcium (R = 0.25). Gender and iPTH remained significantly associated with sclerostin in a multivariate analysis. Sclerostin serum levels were positively associated with BMD at the lumbar spine (R = 0.46), femoral neck (R = 0.36) and distal radius (R = 0.42) and correlated positively mainly with trabecular structures such as trabecular density and number at the radius and tibia in dialysis patients. DKK-1 was related neither to bone measures nor to serologic parameters. CONCLUSIONS: Considering that sclerostin is an inhibitor of bone formation, the observed positive correlations of serum sclerostin with BMD and bone volume were unexpected. Whether its increase in dialysis patients has direct pathogenetic relevance or is only a secondary phenomenon remains to be seen.

A simple micro-photometric method for urinary iodine determination.

BACKGROUND: Urinary iodide concentration (UIC) is useful to evaluate nutritional iodine status. In clinical settings UIC helps to exclude blocking of the thyroid gland by excessive endogenous iodine, if diagnostic or therapeutic administration of radio-iodine is indicated. Therefore, this study established a simple test for the measurement of UIC. METHODS: UIC was analyzed in urine samples of 200 patients. Samples were pre-treated at 95°C for 45 min with ammonium persulfate in a thermal cycler, followed by a photometric Sandell-Kolthoff reaction (SK) carried out in microtiter plates. For method comparison, UIC was analyzed in 30 samples by inductivity coupled plasma mass spectro-metry (ICP-MS) as a reference method. RESULTS: Incubation conditions were optimized concerning recovery. The photometric test correlated well to the reference method (SK=0.91*ICP-MS+1, r=0.962) and presented with a functional sensitivity of 20 µg/L. UIC of patient samples ranged from <20 to 750 µg/L (median 110 µg/L); 90% of the urine samples had iodide concentrations below 210 µg/L. CONCLUSION: The modified SK-test takes approximately 90 min for analyses of 20 urine samples compared with 27 h for ICP-MS. The photometric test provides satisfactory results and can be performed with the basic equipment of a clinical laboratory.

Myeloperoxidase predicts progression of carotid stenosis in states of low high-density lipoprotein cholesterol.

OBJECTIVES: We investigated the effect of myeloperoxidase (MPO) on progression of carotid stenosis in states of high and low high-density lipoprotein-cholesterol (HDL-C) and low-density lipoprotein-cholesterol (LDL-C) levels. BACKGROUND: Myeloperoxidase is pivotally involved in the pathogenesis of atherosclerosis. In vitro data suggest that MPO exerts deleterious effects via oxidative modulation of lipoproteins. METHODS: We prospectively studied 1,019 of 1,268 consecutive patients who were asymptomatic with respect to carotid artery disease. Patients underwent serial carotid ultrasound investigations at baseline and after a follow-up interval of median 7.5 months (range 6 to 9 months), categorizing carotid arteries as 0% to 29%, 30% to 49%, 50% to 69%, 70% to 89%, or 90% to 99% stenosed or occluded. The MPO, HDL-C, and LDL-C levels were measured at baseline, grouped by medians, and correlated with progression of carotid atherosclerosis. RESULTS: Progression of carotid atherosclerosis was found in 100 of 1,019 patients (9.8%). Myeloperoxidase (p = 0.014) but not HDL-C (p = 0.95) or LDL-C (p = 0.30) were associated with progressive disease. However, MPO > or =310 ng/ml was significantly associated with progressive disease (adjusted odds ratio [OR] 2.57, 95% confidence interval [CI] 1.39 to 4.75) only in patients with HDL-C levels <49 mg/dl. Otherwise, in patients with higher HDL-C levels (> or =49 mg/dl), MPO > or =310 ng/ml did not predict disease progression (adjusted OR 1.42, 95% CI 0.72 to 2.78). No interaction of MPO with LDL-C was observed. CONCLUSIONS: Myeloperoxidase was associated with progression of carotid atherosclerosis in patients with HDL cholesterol levels below 49 mg/dl.