The Protective Effect Of Vitamin E On Pancreatic Beta Cells Damaged By Streptozotocin And Its Relevant Mechanism

Objective: To investigate the protective effect of vitamin E on streptozotocin (STZ) -induced pancreatic beta cells impairment and relevant mechanism.Methods: 1.Groups: Isolated and cultured beta cells from pancreas of newborn Wistar rats were divided into four groups:①normal control group;②vitamin E group: only vitamin E was added to the culture medium at the concentration of 0.1mM for 60 minutes;③STZ group: only STZ was added to the culture medium at the concentration of 2.2mM for 30 minutes;④vitamin E protective group: I-IV protective group. Islet cells were treated for 60 minutes with 0.0125mM,0.025mM,0.05mM and 0.1mM vitamin E respectively,then 2.2mM STZ was added for 30 minutes . Culture medium was removed at specific time and the cells were resuspended with normal culture medium, then the following procedures were undertaken after 18 hours of recovery period. 2. Measurements: Insulin contents of cell superna- tant were examined by radioimmunoassay; the SOD activity and the MDA levels were evaluated by spectrometer respectively; the apoptotic cells were identified by transmission electron microscope and Hoechest33258 fluoresc- ence staining under fluorescent microscope as well as quantified by flow cytometry; the activity of caspase-3 was also measured by spectrometer.Results: The insulin contents, the activity of SOD, the MDA levels,the apoptosis rate and the activity of caspase-3 in vitamin E group showed no significant differences from normal control group(p﹥0.05). In STZ group, the insulin contents and the activity of SOD were lower, but the MDA levels,the apoptosis rate and the activity of caspase-3 were higher than those in normal control group(p﹤0.05).The apoptotic beta cells were identified by transmission electron microscope and Hoechest33258 fluorescence staining under fluorescent microscope. In the four protective groups, the insulin contents, the activity of SOD and the MDA levels did not return to the normal levels, but they were inhibited significantly by vitamin E (compared with STZ group, p﹤0.05),and the inhibited effects of vitamin E were shown in a concentration-dependent trend manner(p﹤0.05 compared among the four protective groups),with the strongest protective effect in 0.1mM vitamin E protective group. The apoptosis rate and the activity of caspase-3 were 7.84±1.75% and 0.153±0.034 in 0.1mM protective group respectively, there were significant differences between the ZTZ group and the 0.1mM protective group. (p﹤0.05).Conclusion: Vitamin E can protect panctratic beta cells from STZ damage in a concentration-dependent trend manner, its mechanism is probably correlated with its capability of increasing the SOD activity, scavenging ROS and decreasing the activity of caspase-3.Antioxidation may be one of its different pathways in the protection of the pancreatic beta cells.