Isoflavone and bone metabolism: Its cellular mechanism and preventive role in bone loss

Bone loss with increasing age induces osteoporosis. This loss may be due to increased bone resorption and decreased bone formation. Osteoporosis with a decrease in bone mass is widely recognized as a major public health problem. Pharmacological and nutritional factors may prevent bone loss with increasing age. The chemical compounds in food that act on bone metabolism, however, are poorly understood. Genistein is a natural isoflavonoid phytoestrogen found in Leguminosae and has been demonstrated to have an anabolic effect on bone metabolism, suggesting its role in the prevention of osteoporosis. Genistein has a stimulatory effect on bone formation and mineralization in the tissue culture system in vitro, and it can stimulate protein synthesis in osteoblastic cells. Moreover, genistein has been shown to inhibit osteoblastic bone resorption by preventing the formation and differentiation of osteoclast-like cells from bone marrow cells, and the apoptosis of mature osteoclasts is induced by genistein through the Ca2+ signaling mechanism. Also, the suppressive effect of genistein on rat bone osteoclasts is partly involved in the inhibition of protein kinase and the activation of protein tyrosine phosphatase in osteoclasts. Daidzein, an isoflavone, did not have a greater effect than genistein. Various polyphenols [glycitein, resveratol, quercetin, catechin, and (-)-epicgallocatechin gallate] found in food and plants did not have an anabolic effect on bone calcification in tissue culture in vitro. Genistein may be of significance in the prevention of bone loss with increasing age. The dietary intake of isoflavone (genistein and daidzein) could prevent bone loss in ovariectomized rats which are model animals of osteoporosis. In addition, the preventive effect of genistein on bone loss with aging is enhanced by the combination of zinc or casein phosphopeptides as food factors. Genistein is a useful biofactor in the prevention of osteoporosis.