In this study, we evaluated the synergistic effects of genistein and zinc on bone metabolism, bone mineral density, and the femoral metaphyseal histomorphology in the ovariectomized rats. Sixty female Sprague-Dawley rats, aged 13 weeks, were divided into sham-operated group (SHAM), ovariectomized group (OVX), genistein-treated group (OVX-Gen), zinc-treated group (OVX-Zn), genistein combined zinc-treated group (OVX-Gen-Zn), and 17β-estradiol-treated group (OVX-E) (n = 10). Genistein, zinc, and 17β-estradiol injections were started immediately after OVX and continued for 10 weeks. The OVX-Gen group was subcutaneous injections of genistein (5 mg/kg once every day). The OVX-Zn group was given intragastric ZnSO4 (0.25 mg/kg once every day) after bilateral ovariectomy. The OVX-Gen-Zn group was subcutaneous injections of genistein (5 mg/kg), at the same time intragastric ZnSO4 (0.25 mg/kg once every day). OVX-E group were intraperitoneally injected with 17β-estradiol (10 μg/kg) once every other day. The results showed that genistein and zinc did not alter body weight in OVX rats. The soluble ZnSO4 had no effect to uterus weight loss. Genistein and zinc supplementation significantly increased the BMD of the femur and lumbar spine in OVX rats (P < 0.05, vs. OVX control group). The BMD of the lumbar spine and femur in the OVX-Gen-Zn group is higher than that in the OVX-Gen and OVX-Zn groups (P < 0.05), and there were no differences of BMD among the OVX-Gen-Zn, OVX-E, and SHAM groups (P > 0.05). The femoral metaphyseal morphology and bone histomorphometric parameters revealed that the trabecular volume and thickness in the OVX-Gen-Zn and OVX-E groups were similar to that of SHAM group, and the OVX-Gen-Zn group had more trabecular volume than the OVX-Gen and OVX-Zn groups. Serum zinc was found to be significantly reduced in the OVX group when compared with SHAM. Serum zinc levels were enhanced in the OVX-Zn, OVX-Gen-Zn, and OVX-E groups and restored to normal levels. Serum calcium and serum phosphorus in the OVX-Gen-Zn group was greater than that in the OVX-Gen and OVX-Zn groups (P < 0.05); the serum calcium, phosphorus, and ALP in the OVX-Gen-Zn group were similar to that of SHAM and OVX-E groups (P > 0.05). The OVX group had higher osteocalcin, CTX, and RANKL than the SHAM group (P < 0.01). They were lower in the OVX-Gen and OVX-Zn groups (P < 0.05), and they were significantly lower in the OVX-Gen-Zn and OVX-E groups, than in the OVX group. There were no significant differences of osteocalcin, CTX, and RANKL among the OVX-Gen-Zn, OVX-E, and SHAM groups (P > 0.05). OPG and OPG/RANKL ratios were significantly higher in the OVX-Gen and OVX-Zn groups than that in the OVX group (P < 0.05). The OPG and OPG/RANKL ratio in the OVX-Gen-Zn group is higher than that in the OVX-Gen and OVX-Zn groups (P < 0.05, vs. OVX-Gen group; P < 0.01, vs. OVX-Zn group). The differences of the OPG and OPG/RANKL ratios between the OVX-Gen-Zn, OVX-E, and the SHAM groups were not significant (P > 0.05). The results above indicate that the genistein and zinc have synergistic effects on both stimulation of bone formation and suppression of bone resorption in ovariectomized rats, thereby increasing bone mass.
