Abstract
Vitamin K is a cofactor for γ-glutamyl carboxylase (GGCX), which is an essential enzyme for the γ-carboxylation of vitamin K-dependent proteins such as osteocalcin (OC). Associations among dietary vitamin K intake, vitamin K status, and bone metabolism have not been thoroughly investigated. Recently, it has been reported that single nucleotide polymorphisms of GGCX (R325Q, 974G>A) were associated with age-related bone loss and the kinetic affinity for the substrate. In the present study, we investigated the associations among dietary vitamin K intake, the level of serum vitamin K, and the ratio of undercarboxylated OC (ucOC) to intact OC. The subjects were 60 healthy young male volunteers (mean age, 22.6 y; standard deviation, 1.6). Dietary nutrient intake was assessed by consecutive individual 3-d food records taken before the day of blood examinations. Serum concentrations of vitamin K (phylloquinone: PK, menaquinone 4: MK-4, and menaquinone 7: MK-7), ucOC, and intact OC were measured. All subjects were genotyped for polymorphism (R325Q) presence. Dietary vitamin K intake from vegetables was significantly correlated with the level of serum PK, and vitamin K intake from fermented beans, natto, was also significantly correlated with the level of serum MK-7. The ratio of ucOC to intact OC showed a negative association with the total vitamin K intake (r=−0.331, p=0.010) and serum MK-7 (r=−0.394, p=0.002). Interestingly, grouped by the GGCX genotype, a significant interaction between the ratio of ucOC to intact OC with serum MK-7 was observed in 325R homozygotes (r=−0.572, p=0.003), but not in heterozygotes, nor in 325Q homozygotes. This is the first report to suggest the effects of the single nucleotide polymorphism R325Q in the GGCX gene on the correlation between the level of serum MK-7 and γ-carboxylation of serum OC.
