On Northern blot analysis, osteocalcin mRNA expression on 1,25(OH) 2D 3-treated cells was enhanced by vitamin K 2 treatment, but vitamin K 2 alone did not induce osteocalcin mRNA expression. However, vitamin K 2 alone did not induce osteocalcin production in the human osteoblasts. Moreover, vitamin K 2 enhanced the 1,25(OH) 2D 3-induced osteocalcin accumulation in the cells and the extracellular matrix (cell layer), but inhibited the osteocalcin content in the medium produced by the 1,25(OH) 2D 3 treatment.

Vitamin K 2 promoted the 1,25(OH) 2D 3-induced mineralization, but slightly inhibited the 1,25(OH) 2D 3-induced ALP activity. Human osteoblasts were mineralized and showed the enhanced ALP activity on treatment with 10 -9 M of 1,25(OH) 2D 3 for 20 or 25 days after confluence. Vitamin K 2 (2-methyl-3-all-trans-tetraphenyl-1,4-naphthoquinone: menatetrenone) was the most potent of these vitamin K analogs it slightly inhibited alkaline phosphatase (ALP) activity. Vitamin K 1 and K 2, but not vitamin K 3, at 2.5 μM enhanced in vitro mineralization when cells were cultured with vitamin K for 20 days after reaching confluence in vitro. The effect of vitamin K on mineralization by human periosteal osteoblasts was investigated in the absence and presence of 1α,25 dihydroxyvitamin D 3 (1,25(OH) 2D 3).

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