[Vitamin K, bone metabolism and vascular calcification in chronic kidney disease]

Atherosclerosis is the main cause of morbidity and mortality in the general population, and premature death in patients with chronic kidney disease (CKD) especially dialysis ones. Besides the typical cardiovascular risk factors there is a considerable vascular calcification of intima media in these patients. Vitamin K - dependent proteins play an essential role in the pathogenesis of mineral and bone disorders related to CKD, including vascular calcification. Vitamin K is a family of vitamins, varying in the number of isoprenoid groups (saturated or unsaturated) connected into 2-methyl-1,4-naphthoquinone ring in C3 position. Vitamin K-dependent proteins require carboxylation (VKDPs) for biological activation. The coagulant factors are the most well-known VKDPs, but the role of the other proteins, like Matrix Gla Protein (MGP), Growth Arrest Specific Gene 6 (Gas-6) and osteocalcin has been recently discovered. MGP prevents vascular calcification and Gas-6 affects vascular smooth muscle cell apoptosis and movement. Carboxylation of osteocalcin promotes bone formation. Additionally vitamin K increases proliferation of osteoblasts and apoptosis of osteoclasts, influencing on bone remodeling. There is few studies indicating for decreased consumption of vitamin K in the general population. The restrictive diet recommended for dialysis patients additionally diminishes its daily supply, increasing the chance for vitamin K deficiency in this population. Clinical consequences of inhibition of epoxide reductase by generally used anticoagulants, that inhibiting vitamin K cycle and preventing gamma-carboxylation of Gla proteins, in the peripheral tissue is hardly known. This paper summaries the state of the art knowledge focused on the role of vitamin K in mineral and bone metabolism disorders in CKD patients.