Calcification Inhibitors and Wnt Signaling Proteins Are Implicated in Bovine Artery Smooth Muscle Cell Calcification in the Presence of Phosphate and Vitamin D Sterols

Abstract

Administration of active vitamin D sterols to treat secondary hyperparathyroidism in patients with chronic kidney disease receiving dialysis has been associated with elevated serum calcium and phosphorus levels, which may lead to increased risk of vascular calcification. However, calcimimetics, by binding to the parathyroid gland calcium-sensing receptors, reduce serum parathyroid hormone, calcium, phosphorus, and the calcium-phosphorus product. Using cultured bovine aorta vascular smooth muscle cells (BASMCs), an in vitro model of vascular calcification, we compared calcification levels and gene expression profiles after exposure to the phosphate source ss-glycerolphosphate (BGP), the active vitamin D sterols calcitriol and paricalcitol, the calcimimetic R-568, or BGP with the active vitamin D sterols or R-568. Cells exposed to BGP (10 mM) alone or with calcitriol or paricalcitol showed dose-dependent BASMC calcification. No change in calcification was observed in cultures exposed to BGP with R-568, consistent with the observed lack of calcium-sensing receptor expression. Microarray analysis using total cellular RNA from cultures exposed to vehicle or BGP in the absence and presence of 10(-8) M calcitriol or paricalcitol for 7 days showed that cells exposed to BGP with calcitriol or BGP with paricalcitol had virtually identical gene expression profiles, which differed from those of cells treated with BGP or vehicle alone. Several osteoblast- and chondrocyte-associated genes were modulated by BGP and vitamin D exposure. In this study, exposure of BASMCs to phosphate and active vitamin D sterols induced calcification and changes in expression of genes associated with mineralized tissue.

A Randomized, Double-Blind, Placebo-Controlled Trial of Niacinamide for Reduction of Phosphorus in Hemodialysis Patients

“…Hyperphosphatemia is linked to cardiovascular risk as well as bone disease (19,20), and the hyperphosphatemic milieu may promote vascular calcification through cellular changes in vascular smooth muscle cells (21). Previous open-label studies by Takahashi et al (10) and Sampathkumar et al (22) demonstrated that niacinamide lowers serum phosphorus levels in maintenance hemodialysis patients when traditional binding agents are withheld.…”

Vitamin D and Cardiovascular Disease

“…42 In the VDR −/− and Low-Density Lipoprotein receptor −/− mouse model, a low vitamin D diet increased aortic calcification via a mechanism involving upregulation of osteoblast transcription factors. 44 These differences in the influence of 1,25(OH) 2 D or its analogs on both calcification and the gene expression of calcification factors may be pharmacological rather than physiological. Because vitamin D is activated to 1,25(OH) 2 D in the kidney, uremia changes homeostatic mechanisms, where vitamin D signaling plays a critical role, with vitamin D agonists offering therapeutic benefits.…”

Mechanistic Insights into Vascular Calcification in CKD

“…VSMCs express the vitamin D receptor and have functional 1-a hydroxylase and 25-hydroxylase enzyme systems so that all vitamin D metabolites can be utilized by them in an autocrine/paracrine fashion. 71 VDRAs promote calcification by upregulating Runx2, osterix, and osteocalcin 72,73 and also increasing calcium transport into the VSMCs. 74 However, other studies show that vitamin D has protective effects by increasing calcification inhibitory proteins such as MGP and osteopontin, 75 reducing proinflammatory cytokines, such as IL-6, IL-1b, and TGF-b.…”