Inhibitory effect of vitamin K-2 (menatetrenone) on bone resorption in ovariectomized rats: A histomorphometric and dual energy X-ray absorptiometricstudy

To clarify how vitaming K-2 prevents bone loss in vivo, it was given to ova riectomized 20-week-old rats for 2 weeks. Bone mineral density (BMD) in the whole femur and in 7 specific portions (FI to F7 from the proximal to the distal end) was determined by dual-energy X-ray absorptiometry, and histomo rphometry was also performed in proximal tibial metaphysis. Ovariectomy (OV X) resulted in significant decreases in the BMD in the whole femur and the F1, F2, F6 and F7 portions. Histomorphometrical analysis of the tibia showe d that the bone volume / tissue volume (BV/TV), trabecular thickness (Tb.Th ) and trabecular number (Tb.N) were decreased, while trabecular separation (Tb.Sp) and osteoclast number / bone surface (Oc.N/BS) were increased by OV X. The parameters for bone formation were not changed by OVX. These data in dicate that the bone loss within 2 weeks is due to the enhancement of bone resorption. Vitamin K-2 at 50 mg/kg inhibited the decrease in the BMD of th e whole femur together with the F6 and F7 portions. Vitamin K-2 also inhibi ted the decrease in Tb.N and the increases in Tb.Sp, Oc.N/BS and osteoclast surface / bone surface (Oc.S/BS) caused by OVX. These results suggest that vitamin K-2 prevents bone loss through the inhibition of bone resorption a nd osteoclast formation in vivo.