Calciprotein particle inhibition explains magnesium-mediated protection against vascular calcification

Background. Phosphate (Pi) toxicity is a strong determinant of vascular calcification development in chronic kidney disease (CKD). Magnesium me+) may improve cardiovascular risk via vascular calcification. The mechanism by which Mg2+ counteracts vascular calcification remains incompletely described. Here we investigated the effects of mg(2+) on Pi and secondary crystalline calciprotein particles (CPP2)-induced calcification and crystal maturation. Methods. Vascular smooth muscle cells (VSMCs) were treated with high Pi or CPP2 and supplemented with Mg2+ to study cellular calcification. The effect of Mg(2+ )on CPP maturation, morphology and composition was studied by medium absorbance, electron microscopy and energy dispersive spectroscopy. To translate our findings to CKD patients, the effects of M2+ on calcification propensity (T-50) were measured in sera from CKD patients and healthy controls. Results. Mg2+ supplementation prevented Pi-induced calcification in VSMCs. Mg2+ dose-dependently delayed the maturation of primary CPP1 to CPP2 in vitro. Mg2+ did not prevent calcification and associated gene and protein expression when added to already formed CPP2. Confirmatory experiments in human serum demonstrated that the addition of 0.2 mmol/L Mg2+ increased T-50 from healthy controls by 51 +/- 15 min (P < 0.05) and CKD patients by 44 +/- 13 min (P < 0.05). Each further 0.2 mmol/L addition of Mg2+ led to further increases in both groups. Conclusions. Our results demonstrate that crystalline CPP2 mediates Pi-induced calcification in VSMCs. In vitro, Mg2+ delays crystalline CPP2 formation and thereby prevents Pi-induced calcification.