It has been recently reported that vitamin K
2 (menaquinone-4: menatetrenone, VK
2) has an anti-atherogenic effect as well as the ability to produce clotting factors and improve osteoporosis. However, the mechanism by which VK
2 acts on atherosclerosis is still unclear. In this paper, we investigated the effects of vitamin K and its side chain on NO production as an anti-atherogenic substance in a cultured vascular system. Treatment of bovine vascular smooth muscle cells (SMC) with VK
2 (30μM) caused a time-dependent (24-72h) increase in the nitrite (NO
-2) level in the conditioned medium, but not in bovine vascular endothelial cells. Classical NOS inhibitor (L-nitro arginine) and iNOS-specific inhibitors completely blocked the increased nitrite level induced by VK
2 treatment, but D-nitro arginine could not it. Immunostaining and western blotting analysis showed that VK
2 induced iNOS protein in the SMC. VK
2 has a naphtoquinone nucleus, which is identical in menadione (VK
3), and an unsaturated side chain, which is called geranylgeraniol (GGO). To determine whether the structure of VK
2 was related to an increasing nitrite level, we investigated the nitrite level in conditioned medium treated with VK
3 or GGO. Neither VK
3 nor GGO treatment of SMC increased the nitrite level. In addition, warfarin, an inhibitor of VK
2-dependent y-carboxylation, did not affect the increased nitrite level induced by VK
2 in SMC. In conclusion, VK
2 caused NO production through iNOS induction in bovine SMC, that was not related to the structure of VK
2, naphtoquinone nucleus or its side chain, independently of γ-carboxylation.
View full abstract