Naringin Improves Osteoblast Mineralization and Bone Healing and Strength through Regulating Estrogen Receptor Alpha-Dependent Alkaline Phosphatase Gene Expression

Phytoestrogens are strongly recommended for treating osteoporosis. Our previous study showed that naringin, a citrus flavonoid, can enhance the bone mass in ovariectomized rats. In this study, we further elucidated the mechanisms of naringininduced osteoblast maturation and bone healing. Treatment of human osteoblasts with naringin increased cell viability and proliferation. In parallel, exposure to naringin enhanced translocation of estrogen receptor alpha (ER alpha) to nuclei and its transactivation activity. Sequentially, naringin induced alkaline phosphatase (ALP) mRNA and protein expression and its enzyme activity. Pretreatment with methylpiperidinopyrazole (MPP), a specific inhibitor of ER alpha, attenuated naringin-induced augmentations in ER alpha transactivation activity, ALP gene expression, and cell mineralization. The beneficial effects of naringin were also confirmed in mouse MC3T3-E1 cells. Moreover, administration of mice with a bone defect with naringin increased levels of ER alpha and ALP in damaged sites and simultaneously enhanced the healing rate and bone strength. Nevertheless, treatment with MPP weakened naringin-triggered expression of ER alpha and ALP and improved bone healing and mass. Therefore, naringin could improve osteoblast mineralization and bone healing via regulating ER alpha-dependent ALP gene expression. Naringin can be clinically applied for treatment of osteoporosis-related bone diseases.