Onion (Allium cepa L.) flavonoids extract ameliorates osteoporosis facilitating osteoblast proliferation and differentiation, and inhibiting RANKL-induced osteoclastogenesis

Abstract Osteoporosis, a bone metabolic disease, is a global chronic health problem. Flavonoids, a group of natural active compounds widely existing in vegetables, fruits, beans and cereals, were reported to be anti-osteoporosis. Onion is a common vegetable rich in flavonoids. In this study, bone mineral density (BMD) was increased significantly after taking onion flavonoids extract (OFE) orally in an ovariectomized (OVX)-induced rat model, the trabecular structure and serum biomarkers were both improved, with effects similar to estradiol. Compared with the OVX rats, the contents of E2, calcium and phosphorus in the serum of rats were enhanced, but ALP and Trap levels in serum were decreased. In addition, the activity of on bone health was assessed by human osteoblast-like cells MG-63 and osteoclast precursor Raw 264.7 cells in vitro as well. After treated with OFE, MG-63 cells proliferation and mineralization were promoted, and alkaline phosphatase (ALP) activity and mRNA expression of OPG/RANKL were increased significantly. Moreover, RANKL-induced osteoclastogenesis of Raw 264.7 cells and osteoclast activity were inhibited with decrease of tartrate-resistant acid phosphatase (TRAP) activity, and mRNA expression of remarkable enzymes was down-regulated in cells. Furthermore, it was demonstrated that OFE regulated activity of osteoblast mainly via the OPG/RANKL signaling pathway and osteoclastogenesis. The results provided evidence a new model of dietary supplements for preventing osteoporosis.