Ipriflavone inhibits murine osteoclast formation in vitro.

Ipriflavone, one of the isoflavone derivatives, is a therapeutic drug for osteoporosis. The mechanism is thought to be the inhibition of bone resorption. In the present paper, we report that ipriflavone inhibited formation of osteoclasts from murine spleen cells co-cultured with stromal cells cloned from murine bone marrow. In this system, ipriflavone inhibited osteoclast generation in a dose-dependent manner (10(-7)-10(-5) M). Ipriflavone also inhibited prostaglandin E2 production in MC3T3-E1 cells, which are widely employed as osteoblasts. Moreover, ipriflavone inhibited the proliferation of stromal cells (10(-6)-10(-5) M), but not osteoblastic cells. These results suggest that one mechanism for the inhibitory effects of ipriflavone on bone resorption is the inhibition of osteoclast formation through inhibiting prostaglandin E2 production in osteoblasts and thereby suppressing proliferation of stromal cells.