Vitamin K2
All About Vitamin K2
Vitamin K2 is a newly discovered essential vitamin that is building a significant body of clinical evidence demonstrating its crucial significance in the fight against the most common and devastating diseases of our time: osteoporosis and cardiovascular disease. These conditions contribute to difficulties in the functioning of society and are the most common cause of death worldwide, and both can be linked to a deficiency in vitamin K2.
The Vitamin K family consists of a group of fat-soluble vitamins that are divided into vitamin K1 – one molecule (phylloquinone) – and vitamin K2 – a group of molecules (menaquinones). Menaquinones is the group name for a family of related compounds, generally subdivided into short-chain menaquinones (with MK-4 as the most nutritionally important) and the long-chain menquinones, of which MK-7, MK-8, and MK-9 are the most nutritionally recognized.
Vitamins K1 and K2 are similar in structure: they share a “quinone” ring, but differ in the length and degree of saturation of the carbon tail and the number of side chains.1 The number of side chains (isoprene units) is indicated in the name of the particular menaquinone. For example, MK-7 denotes 7 isoprene units attached to the carbon tail; and this influences the transport to different target tissues.
The mechanism of action of vitamin K2 is similar to vitamin K1. K vitamins play an essential role as cofactor for the enzyme γ-glutamyl carboxylase, which is involved in carboxylation of the vitamin K-dependent proteins – specifically, the conversion of peptide-bound glutamic acid (Glu) to γ-carboxy glutamic acid (Gla).
Carboxylation of vitamin K-dependent proteins (called Gla-proteins) serves as a recycling pathway to recover vitamin K from its epoxide metabolite (KO) for reuse in carboxylation. Several human Gla-containing proteins synthesized in several different types of tissues have been discovered.
Vitamin K2’s isoprenoid units (ex. MK-7) are geranylgeranyl derivatives that influence bone function via another mechanism than as a cofactor for enzymatic carboxylation. The mechanism for the anti-osteoclastogenic properties of vitamin K been suggested that the geranylgeranyl-like side chain on vitamin K2 may induce apoptosis of osteoclasts in vitro or may act by down-regulating protein kinase C.
MK-7 affects the function of the osteoblasts by inducing the expression of osteoblast-specific genes [ex: osteocalcin, osteoprotegerin, receptor activator of NF-kB (RANK) and RANK ligand (RANKL)]. Interestingly, in contrast to what was observed for vitamin K2, the scientists failed to identify any anti-NF-κB activity associated with vitamin K1.