Vitamin K1 to Slow Progression of Vascular Calcification in Hemodialysis Patients

Patients on hemodialysis (HD) exhibit an immensely increased cardiovascular mortality associated with extensive vascular calcification (VC). This forms - at least partially - the reason for the excessively increased cardiovascular mortality in this population.

In the past years the development of VC was discovered to be actively regulated and as being influenced by inhibitors of calcification (e.g. matrix-Gla-protein, fetuin-A). Matrix Gla protein (MGP) is a powerful vascular wall-based inhibitor of VC. MGP is produced by vascular smooth muscle cells and needs post-translational modification by vitamin K dependent gamma-carboxylation to be fully active. The role of MGP was discovered in knock-out mice, which died from rupture of a massively calcified aorta. Functional vitamin K deficiency induced by administration of warfarin leads to the development of VC, which in turn can be inhibited by subsequent administration of vitamin K1. Warfarin inhibits the vitamin K mediated gamma-carboxylation, which leads to the production of noncarboxylated and inactive MGP (ucMGP).

Warfarin is widely used due to its inhibitory capacity on the activation of coagulation factors. Now it has been discovered that the use of vitamin K inhibitors influences vascular health: long-term use of warfarin is associated with an increased prevalence and extent of VC in the normal population and HD patients. Warfarin is also a crucial risk factor for the development of calciphylaxis, a life-threatening complication in HD patients characterised by calcified cutaneous vessels. In turn, administration of vitamin K1 was accompanied by reduced intima-media-thickness (IMT) and increased elasticity of vessels in postmenopausal women.

Based on the demonstration of increased PIVKA-II levels, about 97% of all HD patients exhibit insufficient carboxylation activity. Together with the increased VC they represent an ideal population for interventional trials in the vitamin K system. Recently we were able to demonstrate that supplementation of vitamin K1 in such patients is well tolerated, shows only very few side effects and induces a dose dependent decrease of the inactive form Dephosphorylated noncarboxylated matrix Gla protein (dpucMGP) in serum over a six weeks period. In this trial we also observed that all dialysis patients included had insufficient vitamin K serum levels, indicating no substantial influence of food intake on vitamin K deficiency. In addition, this demonstrates that all patients have insufficient vitamin K levels to facilitate adequate MGP carboxylation.