Active vitamin D treatment in CKD patients raises serum sclerostin and this effect is modified by circulating pentosidine levels.

BACKGROUND AND AIMS: 1,25(OH)2Vitamin D increases the expression of the sclerostin gene. Whether vitamin D receptor activation (VDRA) influences serum sclerostin in CKD and whether compounds interfering with VDRA like Advanced Glycosylation End Products (AGEs) may alter the sclerostin response to VDRA is unknown. METHODS AND RESULTS: Eighty-eight stage G3-4 CKD patients randomly received 2 µg paricalcitol (PCT)/day (n = 44) or placebo (n = 44) for 12 weeks. Sclerostin, a major AGE compound like pentosidine, and bone mineral disorder biomarkers were measured at baseline, at 12 weeks and 2 weeks after stopping the treatments. At baseline, in the whole study population sclerostin correlated with male gender (P = 0.002), BMI (P < 0.001), waist circumference (P < 0.001), serum pentosidine (P = 0.002) and to a weaker extent, with diabetes (P = 0.04), 1,25(OH)2Vitamin D (r = 0.22, P = 0.04) and serum phosphate (r = -0.26, P = 0.01). Sclerostin increased during PCT treatment (average + 15.7 pg/ml, 95% CI: -3.0 to +34.3) but not during placebo (P = 0.03) and the PCT effect was abolished 2 weeks after stopping this drug. The increase in sclerostin levels induced by PCT was modified by prevailing pentosidine levels (P = 0.01) and was abolished by statistical adjustment for simultaneous changes in PTH but not by FGF23 changes. CONCLUSIONS: VDRA by paricalcitol causes a moderate increase in serum sclerostin in CKD patients. Such an effect is abolished by adjustment for PTH, suggesting that it may serve to counter PTH suppression. The sclerostin rise by PCT is attenuated by pentosidine, an observation in keeping with in vitro studies showing that AGEs alter the functioning of the VDRA.

Serum phosphate modifies the vascular response to vitamin D receptor activation in chronic kidney disease (CKD) patients.

BACKGROUND AND AIMS: Vitamin D receptor activation (VDRA) ameliorates endothelial dysfunction in CKD patients but also increases phosphate and FGF-23, which may attenuate the beneficial effect of VDRA on endothelial function. METHODS AND RESULTS: This is a pre-specified secondary analysis of the PENNY trial (NCT01680198) testing the effect of phosphate and FGF-23 on the flow mediated vasodilatory (FMD) response to paricalcitol (PCT, 2 µg/day) and placebo over a 12-weeks treatment period. Eighty-eight stage G3-4 CKD patients were randomized to PCT (n = 44) and Placebo (n = 44). Endothelial function was assessed by measuring endothelium dependent forearm blood flow (FBF) response to ischemia. The FMD response was by the 61% higher in PCT treated patients than in those on placebo (P = 0.01). Phosphate (+11%, P = 0.039), calcium (+3%, P = 0.01) and, particularly so, FGF23 (+164%, P < 0.001) increased in PCT treated patients. Changes in FMD by PCT associated inversely with phosphate (r = -0.37, P = 0.01) but were independent of FGF-23, calcium and PTH changes. The response to PCT was maximal in patients with no changes in phosphate (1st tertile), attenuated in those with mild-to-moderate rise in phosphate (2nd tertile) and abolished in those with the most pronounced phosphate increase (3rd tertile) (effect modification P = 0.009). No effect modification by FGF-23 and other variables was observed. CONCLUSIONS: The beneficial effect of PCT on endothelial function in CKD is maximal in patients with no or minimal changes in phosphate and it is abolished in patients with a pronounced phosphate rise. These findings generate the hypothesis that the endothelium protective effect by VDRA may be potentiated by phosphate lowering interventions.