Efeito anti-osteoporótico do extrato de Ginkgo biloba em ratas Wistar com osteoporose induzida por glicocorticoides

Abstract

Introduction: Among the major mechanisms that lead to osteoporosis is the use of glucocorticoids. Glucocorticoids induce apoptosis in osteoblasts and reduce the total bone volume. Several products are used in the treatment of osteoporosis and among them, some natural products such as phytoestrogens. Studies with Ginkgo biloba extract (EGb) showed promising effects in the treatment of osteoporosis. This study aims to evaluate the effects of EGb on the apoptosis of osteoblasts, bone mineral density and bone structure of Wistar rats with glucocorticoid-induced osteoporosis. Methods: 60 rats were divided into 5 groups: control, osteoporosis, alendronate (alendronate sodium - 0.2 mg/kg/day), EGb1 (EGb 28mg/kg/day) and EGb2 (EGb 56mg/kg/day). Osteoporosis was induced by injections of dexamethasone. The bone alkaline phosphatase was measured in serum and immunohistochemical analysis of the proteins Bcl-2 and Bax were evaluated in histological sections of the mandible and femur. In the tibia were evaluated the bone mineral density (BMD), the radiographic density, the cortical mineral density and the biomechanical parameters. The control group was compared to the osteoporosis group ("t" test/ Mann Whitney). The other groups, except the controls, were analyzed by ANOVA followed by Tukey or Dunnett's T3 post hoc test (p <0.05). Results: In the osteoporosis group the levels of bone alkaline phosphatase and the anti-apoptotic protein Bcl-2 expression were significantly reduced. The BMD, cortical mineral density of the distal diaphysis, stiffness, resilience and load of the tibia reduced (p<0.05). The radiographic density of the distal tibial epiphysis and the expression of the pro-apoptic protein Bax increased (p<0.05). Alendronate group decreased the expression of Bax (20 days), and increased the expression of the Bcl-2 (30 days) and the BMD of the tibia (20 and 30 days) (p<0.05). EGb1 and EGb2 (30 days) increased the levels of bone alkaline phosphatase (p<0.05). EGb2 increased BMD (20 and 30 days) (p<0.05). EGb1 and EGb2 increased the expression of Bcl-2 (20 and 30 days) (p<0.05). EGb2 (20 days), EGb1 and EGb2 (30 days) reduced the expression of Bax (p<0.05). EGb1 and EGb2 (20 and 30 days) reduced radiographic density (p<0.05). However treatment with alendronate sodium and EGb did not increase significantly the biomechanical parameters. Conclusion: EGb increased BMD, the expression of anti-apoptotic proteins and bone alkaline phosphatase. The EGb reduced the radiographic density and the expression of pro-apoptotic proteins. This study suggests that EGb reduces apoptosis of osteoblastic cells and increases the formation of bone tissue. It suggests that the EGb may be effective in the treatment of osteoporosis