Background and purpose: Naringin, a flavanone glycoside in citrus fruits, has been recently reported to stimulate bone formation in vitro and in vivo. The present study was designed to determine if naringin could exert oestrogen-like protective actions in bone.
Experimental approach: Young C57/BL6J mice were ovariectomized (OVX) and treated orally with naringin (0.2 or 0.4 mg*g(-1)*day(-1)), 17beta-oestradiol (2 microg*g(-1)*day(-1)) or its vehicle for 6 weeks. Bone mineral densities (BMD) and polar stresss-train index (SSI) were measured by peripheral quantitative computed tomography. Rat osteoblast-like UMR-106 cells were co-incubated with the oestrogen receptor (ER) antagonist ICI 182780 to determine if the effects of naringin on osteoblastic functions were ER dependent. Functional transactivation of ERalpha and ERbeta as well as ERalpha phosphorylation by naringin were also studied.
Key results: Naringin at 0.4 mg*g(-1)*day(-1) increased BMD at trabecular-rich bone in OVX mice. Naringin (at both doses) significantly increased SSI at distal femur and lumbar spine and increased biomechanical strength (ultimate load and energy for breaking) at tibia diaphysis in OVX mice. The stimulatory effects of naringin on osteoblastic functions could be abolished by co-incubation with ICI 182780 in UMR-106 cells. Naringin failed to stimulate ERalpha- or ERbeta-mediated oestrogen response element-dependent luciferase activity but could significantly induce ERalpha phosphorylation at serine 118, in UMR-106 cells.
Conclusions and implications: Naringin was effective in protecting against OVX-induced bone loss in mice and its actions might be mediated through ligand-independent activation of ER in osteoblastic cells.