Role of Phytochemicals in the Prevention of Menopausal Bone Loss: Evidence from In Vitro and In Vivo, Human Interventional and Pharmacokinetic Studies

Substantial body of data generated from cultured bone cells and rat models of osteoporosis supports a significant bone-conserving effect of phytochemicals. Flavonoids including isoflavones, stilbenes and lignans with variable efficacy have shown promising therapeutic application in osteoporosis. Majority of the phytochemicals assessed for their effects on bone cells revealed multiple beneficial actions such as promoting osteoblast functions, and inhibiting osteoclast and adipocyte functions. A variety of molecular targets mediate multiple effects of phytochemicals in bone cells. In vivo, quite a few phytochemicals have been found to afford bone-sparing effect and in some cases even bone restoring effect. However, important pharmacokinetic and bioavailaibility studies associated with these phytochemicals are mostly lacking. As a result, translating these findings to the clinic has been challenging, and so far only a few clinical studies have attempted to evaluate the effect of phytochemicals in menopausal osteoporosis. Clinical studies so far performed are with dietary supplements rather than pure phytochemicals. Clinical trials with pure molecules necessitate preclinical regulatory and safety studies that are not available with the phytochemicals except ipriflavone with bone-conserving properties. Ipriflavone is the only marketed anti-osteoporosis agent that was obtained following a lead from natural substance. As phytochemicals have multiple beneficial influences on bone cells, making analogues of the most potent molecule for developing synthetic series with rational drug design approach could pay rich dividends in menopausal osteoporosis therapy.