Herb medicines against osteoporosis: Active compounds & relevant biological mechanisms.

Osteoporosis is one of common bone disorders, affecting millions of people worldwide. Treatments of osteoporosis consist of pharmacotherapy and non-pharmacological interventions, such as mineral supplementation, lifestyle changes, and exercise programs. Due to the minimum side effects and favorable cost-effective therapeutic effects, herbal medicine has been widely applied in clinical practices for more than 2,000 years in China. Of the many traditional formulas reported for treating bone diseases, 4 single herbs namely (1) Herba Epimedii, (2) Rhizoma Drynariae, (3) Fructus Psoraleae, and (4) Cortex Eucommiae, are considered as the featured "Kidney-Yang" tonics, and frequently and effectively applied for preventing and treating osteoporosis. With the accruing development of modern chemistry, hundreds of active compounds have been identified and isolated for their anti-osteoporotic effects. This review would first sketch the phytochemistry of these featured "Kidney -Yang" tonics and present the pharmacological characteristics of the most abundant and bioactive compounds derived from the herb Herba Epimedii and Rhizoma Drynariae, including icariin and naringin. Then, the cellular and molecular underpinnings under anti-osteoporotic effects of icariin and naringin are discussed. The concerned structure-function relationships of the featured active herbal compounds would also be reviewed so as to pave the way for future drug design in treating osteoporosis.