Studies On The Inhibitory Mechanisms Of (+)-Catechin In Cell Apoptosis And Oxidative Stress

The dissertation studied the mechanism of the inhibitory effects of (+)-catechin on oxidative stress and inflammation in vitro. The signaling transduction pathways of (+)-catechin pharmacological functions, including DNA protective effect, apoptotic inhibitory impact, and mitochondrial regulatory function, were demonstrated in the study. In addition, the inhibitory mechanism of (+)-catechin on excessive activation of murine microglia cells (N9) was investigated in this study.As the results show, after exposure to the oxidative agent tert-butylhydroproxide (tBHP), DNA single strand were broken, subsequently cell cycle phase was arrested. These changes caused cell death eventually. (+)-Catechin inhibited the oxidative stress through scavenging of reactive oxygen spieces (ROS) and increasing the activation of antioxidative enzymes catalase (CAT) and superoxida superoxide dismutase (SOD), and the damaged DNA was repaired by the augmented expression of PARP (poly-(ADP-ribose) polymerase). Importantly, the results indicated that (+)-catechin inhibited the phosphorylation of I-κB, the inhibitory factor of nuclear factor kappa B (NF-κB), subsequently blocked the activation of NF-κB. Those effects reversed N9 cell cycle arrest. Moreover the change of NF-κB activation increased the phosphorylation of extracellular signal-regulated protein kinase (ERK), which acts on cell survival.Cell death was induced by discontinuous exposure to sublethal doses of tBHP for several times. Cells appeared to have the apoptotic characteristic by Hoechst 33258 staining and DNA agarose gel electrophoresis analysis, respectively. However, N9 cell apoptosis was blocked by (+)-catechin treatment at the early stage, and these were detected by flow cytometry using Annxin V-PI staining. All the results indicated that the inhibitory effect of (+)-catechin on tBHP-induced cell apoptosis was related to its protective function upon mitochondria. (+)-Catechin improved and partially renewed the mitochondrial membrane potential (Δψ), those subsequently increased mitochondrial redox and ATP synthesis. Furthermore, the release of pro-apoptosis factor cytochrome c from mitochondria was blocked by (+)-catechin treatment. The results also showed that (+)-catechin up-regulated...