Effects of Egb 761 on bone mineral density, bone microstructure, and osteoblast function: Possible roles of quercetin and kaempferol

The effects of standardized and concentrated extract of Ginkgo biloba, Egb 761, were studied on estrogen deficiency-induced bone loss in ovariectomized (OVx) rats rendered osteopenic. Upon osteopenia development, Egb 761 was administered at a dose of 100 mg kg−1 day−1 by oral gavage to OVx rats whereas control group received vehicle. Following 5 weeks of treatment, the OVx + Egb 761 group (n = 12) of rats exhibited significantly higher whole body BMD and lower bone turnover markers (serum alkaline phosphatase and osteocalcin) than OVx rats that were given vehicle (n = 12). BMD levels in excised bones were also found to be higher in both trabecular (most robustly in lumbar vertebrae) and cortical bones of OVx + Egb 761 compared with OVx + vehicle group. Egb 761 did not exhibit estrogen agonistic activity at the uterine level. Microcomputed tomography demonstrated that OVx + Egb 761 group had better bone microarchitectural parameters compared with OVx + vehicle group. Moreover, OVx + Egb 761 group had higher femoral mRNA levels of osterix, type I collagen and osteocalcin compared with OVx + vehicle group. Determination of levels of three flavonoids of Egb 761, that are known to have bone conserving property, in serum and bone marrow suggests that kaempferol and quercetin, and not rutin, likely mediate the beneficial actions observed with Egb 761 treatment. These results show for the first time that oral administration of Egb 761 restores bone mass in aged OVx rats.