Preventive effects of genistein on the alterations of bone vascularization and bone remodeling in ovariecotomized rats

Abstract

The objective of this study was to examine the roles of genistein in ovariectomized induced-bone microvascular dysfunction and bone loss. Female Wistar rats (116 rats) were divided into 4 groups : sham[subscriptveh] (daily treated with vehicle; DMSO, sc; 100 ul/day), ovariectomized rat treated with vehicle (OVX[subscript veh]), 17B-estradiol treated-ovariectomized rat (OVX[subscript E2] , 5 ug/kgBW/day, sc) and genistein treated-ovariectomized rat (0.25 mg/kgBW/day, sc; OVX[subscript gen]). The study effect of genistein on bone mineral contents at 3-wk and 6-wk after ovariectomy involve 3 groups; Sham[subscript veh], OVX[subscript gen]. The other studies at 1 and 3 weeks after the ovariectomy were consisted of 4 groups, bone mineral content and bone biochemical markers were determined and represented by percentage of ash/dry matter, osteocalcin and alkaline phosphatase activity (using chemiluminescense immunoassay (CLIT), serum VEGF, serum TNF-a and IL-6 were determined by using ELISA kits. The bone microvasculature was observed under Cofocal laser microscope (EZ-C1, Nikon, Japan). An objective lens of 10x was used. 50 ul of 0.5% Fluoresein isothiocyanate-dextran (FITC-dextran) MW 250,000 (Sigma Chemical, USA) was injected intravenously to visualize the intralumen of microvessels. Bone capillary density was measuremented by using a digital image processing software, Image Pro (Plus Software Media Cybernatics, Inc, USA). The results showed that at 6-wk of after ovariectomy (OVX[subscript veh]), bone mineral content of tibial bone significantly decrease compared to sham[subscript veh]. At 1-wk, increase in TNF-a was occurred, bone capillary density significantly decreased in OVX[subscript veh]. At 3-wk after ovariectomy. Increases in TNF-a, osteocalcin, and alkaline phosphatase activity, concomitant with decreases of VEGF and bone capillary density were found in OVX[subscript veh] siginifcantly. However, the level of IL-6 did not change after ovariectomy. These abnormalities after ovariectomy could be decreased by administration of genistein. In addition, the results of our relationship analyses demonstrated that there is a significant close link between OVX-induced microvascular dysfunction and bone remodeling abnormality. In conclusion, our results indicated that bone microvascular abnormality was occurred prior the decrease in bone loss. Genistein supplementation could inhibit bone microvascular dysfunction and bone loss mediated in part through: prevent reduction of VEGF maintain capillary density, prevent induction of TNF-a, prevent endothelial dysfunction, and prevent bone resorption. Therefore, our findings suggested that genistein supplementation at early phase of estrogen depletion should be used for prevention postmenopausal induced osteoporosis.