Suppressive effects of Anoectochilus formosanus extract on osteoclast formation in vitro and bone resorption in vivo

Anoectochilus formosanus, a plant native to Taiwan, is used as a folk medicine. It was found that oral administration of A. formosanus extract (AFE) (500 mg/kg) for 4 weeks suppressed bone weight loss and trabecular bone loss in ovariectomized mice, an experimental model of osteoporosis. Although AFE at 12.5 and 25 μg/ml inhibited osteoclast formation in co-culture of osteoblasts and bone marrow cells, AFE did not inhibit the formation of osteoclast progenitor cells and preosteoclast cells in bone marrow cells and RAW264 cells. However, AFE (at 12.5 and 25 μg/ml) decreased RANKL expression. These results suggested that AFE might suppress the bone loss caused by estrogen deficiency through suppression of RANKL expression required for osteoclast formation.