Effects of paricalcitol on biomarkers of inflammation and fibrosis in kidney transplant recipients: results of a randomized controlled trial

Aims: Paricalcitol, a selective vitamin D activator, decreases proteinuria and may reduce graft failure risk in kidney transplant recipients. In this study, we evaluated the effect of paricalcitol on renin-angiotensin system (RAS) activity as well as interleukin (IL)-6 and transforming growth factor (TGF)-beta plasma concentrations as biomarkers of inflammation and fibrosis. Methods: This placebo-controlled, double-blind trial enrolled a national cohort of kidney transplant recipients with urinary protein-to-creatinine ratio (UPCR) = 20 mg/mmol despite optimization of the RAS blockade. Patients were randomly assigned to receive 24 weeks of treatment with 2 mu g/day paricalcitol or placebo. The primary endpoint was the percent change in geometric mean UPCR. In this secondary analysis, we examined the effect of paricalcitol on plasma renin activity (PRA) and aldosterone levels as well as IL-6 and TGF-beta plasma concentrations from baseline to last measurement during treatment. Results: Of the 168 patients with UPCR = 20 mg/mmol who consented to undergoing randomization, 83 were allocated to paricalcitol and 85 to placebo. Baseline patient demographics, clinical characteristics, PRA, and aldosterone levels were similar between groups. Mean change in IL-6 was-29% (from 2.53 to 2.02 pg/mL) in the paricalcitol group and 23% (from 2.07 to 2.54 pg/mL) in the placebo group (p < 0.001). Mean change in TGF-beta was-12% (from 8,011 to 6,935 pg/mL) in the paricalcitol group and 21% (from 7,418 to 8,992 pg/mL) in the placebo group (p < 0.001). Conclusion: In kidney transplant recipients, the addition of 2 mu g/day paricalcitol to RAS inhibition lowers IL-6 and TGF-beta concentrations, which may be beneficial for reducing graft inflammation and fibrosis.