Vitamin D and methylarginines in chronic kidney disease (CKD).

BACKGROUND

Vitamin D associates with the plasma concentration of the endogenous inhibitor of the nitric oxide system asymmetric dimethyl arginine (ADMA) and cross-sectional studies in CKD patients treated with the vitamin D receptor activator paricalcitol show that plasma ADMA is substantially less than in those not receiving this drug.

METHODS

In the frame of a randomized, double-blind, placebo controlled trial, the Paracalcitol and ENdothelial fuNction in chronic kidneY disease (PENNY), we investigated whether vitamin D receptor activation by paricalcitol (2 μg/day x 12 weeks) affects the plasma concentration of ADMA and symmetric dimethyl arginine (SDMA) in 88 patients with stage 3 to 4 CKD.

RESULTS

Paricalcitol produced the expected small rise in serum calcium and phosphate and a marked PTH suppression. However, ADMA [Paricalcitol: baseline 0.75 μMol/L (95%CI: 0.70-0.81), 12 week 0.72 μMol/L (95%CI: 0.66-0.78); Placebo: baseline 0.75 μMol/L (95%CI: 0.70-0.90) 12 weeks 0.70 μMol/L (95%CI: 0.66-0.74)] and SDMA [Paricalcitol: baseline 0.91 μMol/L (95%CI: 0.82-1.00), 12 week 0.94 μMol/L (95%CI: 0.82-0.1.06); Placebo: baseline 0.91 μMol/L (95%CI: 0.82-1.06) 12 weeks 0.99 μMol/L (95%CI: 0.88-1.10)] remained unchanged during the trial and 2 weeks after stopping these treatments.

CONCLUSIONS

Paricalcitol does not modify plasma ADMA and SDMA in patients with stage 3-4 CKD. The apparent beneficial effects of paricalcitol on ADMA registered in cross-sectional studies is likely attributable to confounding by indication rather than to a true effect of this drug on ADMA metabolism.