Cardiovascular disease in chronic kidney failure: the role of VDR activators

Vitamin D3 is modified by vitamin D3 25-hydroxylase in the liver, and by 25-hydroxyvitamin D3 1alpha-hydroxylase (CYP27B1) in the kidney, to form the active metabolite 1alpha,25-dihydroxyvitamin D3. Several vitamin D receptor (VDR) activators, including paricalcitol and calcitriol, are currently available for the treatment of hyperparathyroidism secondary to chronic kidney disease (CKD). CKD patients encounter a much higher risk of cardiovascular disease than do members of the general public, and recent clinical observations have shown that VDR activator therapy provides survival benefit for CKD patients in the rank order of paricalcitol > calcitriol > no VDR activator therapy, independent of parathyroid hormone, phosphorus and calcium. One possible explanation for this observation is that VDR activators exert a positive impact on cardiovascular functions. Studies in animals with disrupted genes involved in the vitamin D signaling pathway have provided some interesting data. For example, in mice lacking VDR or CYP27B1, it was found that in addition to the expected phenotype (hypocalcemia, secondary hyperparathyroidism and osteomalacia), expression of renin or atrial natriuretic peptide was elevated. The mice also developed hypertension and cardiac hypertrophy. Gene expression profiling studies have revealed that VDR may play a role in regulating smooth-muscle-cell (SMC) proliferation, thrombosis, fibrinolysis and vessel relaxation. Paricalcitol and calcitriol are equally potent at suppressing plasminogen activator inhibitor-1 synthesis and inhibiting cellular proliferation in human coronary artery SMCs. The effect of VDR activators on the modulation of renin expression and vascular functions may be factors that contribute to reduced mortality and morbidity risk in VDR-activator-treated CKD patients. In this review, we discuss recent preclinical and clinical data regarding the role of VDR and its ligands in the cardiovascular system.