17β-estradiol attenuates homocysteine-induced oxidative stress and inflammatory response as well as MAPKs cascade via activating PI3-K/Akt signal transduction pathway in Raw 264.7 cells

Oxidative stress, inflammatory response, and mitogen-activated protein kinases (MAPKs) cascade are significant pathogenic factors of osteoporosis. It has been reported that elevated homocysteine (Hcy) may activate oxidative stress and reduce bone mineral density in post-menopausal osteoporosis. Moreover, hormone replacement therapy has been widely used in clinic to prevent and treat post-menopausal women with osteoporosis and osteoporotic fracture, but the molecular mechanisms and relevant signal transduction pathways underlying the action of Hcy remain unclear. In this study, we investigated the effects of 17 beta-estradiol (17 beta-E-2) on the Hcy-induced oxidative stress, inflammatory response and MAPKs cascade, as well as the underlying signal transduction pathway in murine Raw 264.7 cells. The reactive oxygen species (ROS) was assessed by fluorospectrophotometry. The proinflammatory cytokines tumor necrosis factor-alpha (TNF-alpha) and interleukin (IL)-1 beta were analyzed by double-immunofluorescence labeling and reverse transcriptase polymerase chain reaction assay, respectively. Furthermore, phosphorylation levels of MAPKs cascade were measured by western blot analysis. A specific phosphatidylinositol 3-kinase (PI3-K) inhibitor, Wortmannin (1 mu M) was employed to determine whether PI3-K/Akt signaling pathway mediated the 17 beta-E-2's effect on Raw 264.7 cells. 17 beta-E-2 markedly decreased the ROS production induced by Hcy, the expression of TNF-alpha and IL-1 beta at protein and mRNA levels, and down-regulated the phosphorylation of MAPKs (ERK1/2, JNK and p38). These suppressing effects of 17 beta-E-2 on Hcy-induced changes were reversed by pretreatment with PI3-K inhibitor Wortmannin. The results indicate that 17 beta-estradiol may attenuate Hcy-induced oxidative stress, inflammatory response and up-regulation of MAPKs in Raw 264.7 cells via PI3-K/Akt signal transduction pathway.