Effects of menatetrenone on prednisolone-induced bone loss in rats.

This study was carried out to evaluate the effect of menatetrenone, a vitamin K2 with 4 isoprene units, on prednisolone-induced bone loss. Three experiments were performed in rats which received menatetrenone as a dietary supplement. In experiment 1, a soluble form of prednisolone, dissolved in drinking water, was administered to rats at 7 mg/kg/day for 9 weeks. The length, dry weight, and bone density of femurs and tibiae, as well as urinary gamma-carboxyglutamic acid (Gla) content, were significantly lower in the prednisolone-control group than in the intact group. Menatetrenone (17 mg/kg/day) significantly inhibited the decrease in these bone parameters, especially in tibiae, and completely inhibited the decrease in urinary Gla content. In experiments 2 and 3, prednisolone (10 mg/kg), dissolved in cottonseed oil, was given to rats intramuscularly three times a week for 4 and 10 weeks, respectively. In experiment 2, bone length, bone strength and calcium content in the femur were reduced by 4-week prednisolone treatment. These reductions were significantly improved by menatetrenone (21 mg/kg/day). In experiment 3, 10-week prednisolone treatment reduced bone length and the calcium and hydroxyproline content of the femur. Menatetrenone (0.4, 10, and 50 mg/kg/day) significantly inhibited the reduction of calcium content in the femur. These results suggest that menatetrenone may inhibit the bone loss induced by corticosteroid treatment.