The role of estrogens and estrogen-like molecules in regu-

lating bone cell activities is central to understanding the etiology and treatment of postmenopausal osteoporosis. In the past few years, natural estrogen-like molecules, the phytoestrogens, have attracted attention for their potential roles in osteoporosis prevention and treatment. In contrast to the isoflavone-type phytoestrogens such as genistein, lignan-type phytoestrogens have rarely been studied, although they are widely distributed in the plant kingdom. Cereals, grains, berries, and garlic are good dietary sources of lignans. Recently, lignans have received considerable attention for their potential role in the prevention of osteoporosis. Lignans are metabolized into the more biologically active mammalian lignans enterodiol and enterolactone by microbiota in the colon. Osteoblasts play a crucial role in bone formation through proliferation and differentiation. Osteoblast differentiation, an important process for its function, confers marked rigidity and strength on bone while still maintaining some degree of elasticity. Thus stimulation of osteoblast differentiation has been suggested to be an important therapeutic approach for the prevention and treatment of bone disease such as osteoporosis. While the isoflavone genistein and arylnaphthalene-type lignans have been shown to increase the differentiation of osteoblast-like cells, the effect of enterolignans, enterodiol and enterolactone, are unknown. Therefore we carried out the present research to determine whether enterodiol and enterolactone (Fig. 1) have stimulatory effects on osteoblast differentiation. MATERIALS AND METHODS