Vitamin D receptor activators inhibit vascular smooth muscle cell mineralization induced by phosphate and TNF-α

Background. Vascular calcification is a highly regulated process. Tumor necrosis factor-alpha (TNF-alpha) has been shown to accelerate the highly regulated osteogenic process in vascular smooth muscle cells (VSMCs). Vitamin D receptor activators (VDRAs) have been associated with beneficial cardiovascular outcomes in patients with chronic kidney disease. We examined whether maxacalcitol, a vitamin D3 analog, exhibits a suppressive effect on VSMC mineralization induced by phosphate and TNF-alpha. Methods. Human VSMCs were treated with either vehicle, maxacalcitol (10(-9) to 10(-7) M), or calcitriol (10(-9) to 10(-7) M) in 2.5 mM of phosphate media with TNF-alpha (1 ng/mL) for 9 days. VSMC mineralization was determined and expression of genes associated with the osteogenic process was examined by real-time reverse transcription-polymerase chain reaction. Expression of matrix metalloproteinase-2 (MMP-2) messenger RNA (mRNA) in VSMCs and MMP-2 protein in media was also analyzed. Results. Vehicle-treated VSMCs exhibited massive mineralization, which was inhibited by maxacalcitol in a concentration-dependent manner. Calcitriol also inhibited the mineralization. While vehicle-treated VSMCs exhibited increased mRNA expression of genes associated with the osteogenic process (Cbfa1/Runx2 and osteocalcin) compared with VSMCs grown in normal media without TNF-alpha (control), maxacalcitol and calcitriol suppressed the increase in mRNA species. Furthermore, vehicle-treated VSMCs exhibited increased MMP-2 mRNA and protein in the media that were suppressed notably by maxacalcitol. Conclusions. Both the VDRAs abrogated the acceleration of the osteogenic process induced by phosphate and TNF-alpha in VSMCs, which was linked to inhibition of mineralization in VSMCs. MMP-2 blockade by VDRAs may contribute to an inhibitory effect on vascular calcification.