The Molecular Biology and Pathophysiology of Vascular Calcification

Abstract

Vascular calcification (VC), commonly encountered in renal failure, diabetes, and aging, is associated with a large increase in the risk for cardiovascular events and mortality. Calcification of the arterial media and of heart valves clearly plays a mediating role in this regard, whereas it is less clear how calcification of plaque influences atherogenesis and risk for plaque rupture. Vascular calcification is an active process in which vascular smooth muscle cells (VSMCs) adopt an osteoblastic phenotype and deposit hydroxyapatite crystals; apoptosis of VSMCs also promotes this deposition. Drivers of this phenotypic transition, which include elevated serum phosphate, advanced glycation end–products, bone morphogenetic proteins, inflammatory cytokines, and leptin, invariably induce oxidative stress in VSMCs, which appears to be a necessary and sufficient condition for induction of the runt–related transcription factor 2 gene (RUNX2) and the shift to osteoblastic behavior. Magnesium antagonizes the impact of phosphate on VSMC osteoblastic transition, both by a direct effect within VSMCs and by suppressing absorption of dietary phosphate. Antioxidants that suppress reduced nicotinamide adenine dinucleotide phosphate oxidase activity may have the potential to block the osteoblastic transition of VSMCs. Minimizing the absorption of dietary phosphate may also be helpful in this regard, particularly in renal failure, and it can be achieved with plant–based dietary choices, avoidance of phosphate additives, and administration of pharmaceutical phosphate binders, supplemental magnesium, and niacin. Good vitamin K status opposes VC by optimizing the γ–carboxylation of matrix Gla protein, a physiological antagonist of VC. Adequate but not excessive vitamin D status also appears to discourage VC. Etidronate, a structural analogue of pyrophosphate, has shown potential for blocking VC.