抄録
Vitamin K (VK) is a fat-soluble vitamin, and an essential factor for blood coagulation and bone structure formation. All VK analogues have an activity as a cofactor for post-translational formation of Gla-proteins (ex., clotting factors, osteocalcin (bone Gla-protein), matrix Gla-protein (MGP), and so on). Recent studies revealed that menaquinone-4 (MK-4=VK2), out of VK analogues, has specific activities for various important physiological functions. Most of the menaquinone analogues (MK-n) are synthesized by microorganisms including intestinal microbiota, but many researchers have reported that MK-4 is unique in being synthesized by the conversion of orally ingested phylloquinone (VK1) or MK-n (VK2) by endogenous enzyme action in the major tissues of higher animals. Actually, MK-4 has specific activities as follows; 1) bone resorption decreasing activity by inducing apoptosis of osteoclast cells through the suppression of RANKL, 2) apoptosis inducing activity in cultured leukemia cells (= anti-cancer activity), 3) anti-atherosclerotic activity, 4) binding activity to nuclear steroid X receptor (SXR or PXR), 5) anti-diabetic activity, 6) anti-inflammatory effect through down regulation of IL-6 expression, and 7) direct effect on inducing steroid hormone (testosterone) biosynthesis in testis, though VK1 or MK-n could be also effective when applied in vivo because ingested VK1 or MK-n can be converted into MK-4 in various tissues.
