Biol. Pharm. Bull. 30(4) 814—817 (2007)

which results in increased bone fragility and fracture risk. Estrogen deficiency which occurs at menopause plays a major role in the development of osteoporosis in elderly women. Therefore, estrogen replacement therapy (ERT) has been widely used for prevention of postmenopausal osteoporosis. However, ERT also shows other undesirable side effects including increased incidence of breast cancer and heart disease. Recently, there is a growing interest in searching for alternatives from dietary natural plant products. Phytoestrogens are naturally occurring polyphenolic plant-derived compounds of nonsteroidal structure that are similar to the mammalian estrogen, such as estradiol. They can bind to estrogen receptor (ER), thus exerting estrogenic activity. Many investigators have reported that phytoestrogens are effective in preventing bone loss in an ovariectomized rats and postmenopausal women. Phytoestrogen includes various families of compounds such as isoflavonoids, flavonoids, lignans and stilbenes. Isoflavonoids, such as daidzein and genistein, which are abundant in soybean, have extensively investigated and have been demonstrated to have beneficial effects against bone loss in a clinical study and various experimental models. Lignans, another group of phytoestrogens, are widely distributed throughout plants. Especially, cereals, grains, berries and garlic are good dietary sources of lignans. Recently, lignans have received considerable attention for their potential role in prevention of osteoporosis. Secoisolariciresinol diglycoside from flaxseed showed anti-osteoporotic activity in postmenopausal women. Isotaxiresinol from Taxux yunnanensis prevented bone loss in ovariectomized model. We previously isolated lignans from the barks of Machilus thunbergii SIEB. et ZUCC (Lauraceae) and evaluated their neuroprotective activity. In the present study, we further tried to evaluate anti-osteoporotic potentials of these lignans (Fig. 1). We employed primary cultures of mouse osteoblasts as an in vitro assay system and evaluated effect of lignans on osteoblast differentiation by measuring several osteoblast differentiation makers such as alkaline phosphatase (ALP), collagen content and calcium deposition. We further attempted to elucidate their mechanism using ER antagonist, tamoxifen. 814 Vol. 30, No. 4 Notes