镉对背角无齿蚌主要组织谷胱甘肽含量和相关酶活性的影响

为了进一步探明谷胱甘肽系统对镉引起的氧化损伤的防御作用,根据背角无齿蚌(Anodonta woodiana woodiana)96 h镉的半致死浓度,设置5个染毒组(4.22、8.43、16.86、33.72、67.45 mg·L-1)和1个对照组,处理24、48、72、96 h分别测定鳃与肝脏中还原型谷胱甘肽(GSH)、氧化型谷胱甘肽(GSSG)含量和谷胱甘肽硫转移酶(GST)、谷胱甘肽还原酶(GR)的活性。实验结果显示,与对照组相比,除48 h、4.22 mg·L-1处理组鳃中GSSG含量出现显著性升高(P0.05)外,GSH和GSSG含量均表现为显著或极显著性降低(P0.05,P0.01);随着时间的延长,GSH/GSSG比值在低浓度(4.22、8.43 mg·L-1)处理组先降后升,在高浓度(33.72、67.45 mg·L-1)处理组则逐渐下降,且与对照组相比差异显著(P0.05)。与对照组相比,在24 h鳃中GST活性呈梯度型降低(P0.01);在48、72、96 h GST活性整体呈升高趋势,且在低浓度组升高、高浓度组降低,呈现显著性或极显著性差异(P0.05,P0.01)。鳃中GR活性在48 h、8.43 mg·L-1,72 h、67.45 mg·L-1和96 h、4.22 mg·L-1处理组出现显著性升高。随着浓度的升高和时间的延长,肝脏中GSH含量和GSH/GSSG比值呈显著或极显著性降低(P0.05,P0.01)。肝脏中GST活性整体呈升高趋势且有极显著性差异(P0.01);在24 h、4.22 mg·L-1处理组GST活性达到最高。同一时间,随着镉浓度的升高,肝脏中GST活性逐渐降低。肝脏中GR活性整体呈升高趋势且有显著性或极显著性差异(P0.05,P0.01),在72 h、4.22 mg·L-1处理组浓度达到最高。研究表明,肝脏中GSH含量的变化对镉引起的损伤反应灵敏且发挥了重要作用,GST解毒酶对镉的毒性反应灵敏,且肝脏较鳃的反应迅速。GSH含量、GST活性和肝脏分别可以作为环境监测的生化指标和靶器官。

Effects of Cadmium on Glutathione Contents and Activities of Glutathione Related Enzymes in Gill and Hepatopancreas of Anodonta woodiana woodiana

Glutathione system is an important defense system against oxidative damages. In this study, an experiment was designed to examine the dynamics of glutathione contents and activities of glutathione related enzymes in Anodonta woodiana woodiana under six Cd treatments(0, 4.22, 8.43, 16.86, 33.72 mg·L^-1 and 67.45 mg·L^-1 of Cd) for 24 h, 48 h, 72 h and 96 h, according to 134.9 mg·L^-1 of LC50 for Cd within 96 h. The reduced glutathione(GSH) and oxidized glutathione(GSSG) concentrations as well as glutathione transferase(GST) and glutathione reductase(GR) activities were measured in the gill and hepatopancreas tissues. Compared with the control, Cd treatments significantly decreased both GSH and GSSG concentrations in the gills, with exception of one treatment group(4.22 mg·L^-1, 48 h). The ratio of GSH/GSSG was decreased in two treatment groups(4.22 mg·L^-1 and 8.43 mg·L^-1, 48 h). However, this ratio was increased in some other groups(67.45 mg·L^-1 in 24 h, 48 h and 96 h, 4.22 mg·L^-1 in 72 h and 8.43 mg·L^-1 in 96 h). The GST activity in the gills rose by Cd treatments, except the groups treated for 24 h, in which GST showed a gradient decrease. The GR activity increased in three groups(8.43 mg·L^-1 in 48 h, 67.45 mg·L^-1 in 72 h and 4.22 mg·L^-1 in 96 h) in the gills. In the hepatopancreas, GSH content and GSH/GSSG ratio significantly reduced as the Cd concentration and exposure time increased. The activity of GST in the hepatopancreas was dependent on Cd concentrations and treatment time, with the greatest activity observed in 4.21 mg·L^-1 in 24 h. It decreased at higher Cd concentrations and extended time. In the hepatopancreas, the GR activity was increased in the following treatment groups(4.22 and 8.43 mg·L^-1 in 24 h, 4.22 mg·L^-1, 16.86 mg·L^-1 and 67.45 mg·L^-1 in 72 h and all concentrations in 96 h except for 67.45 mg·L^-1). In conclusion, our results show that Cd exposure can decrease the concentrations of GSH and GSSG but increase the levels of GST and GR in the gill and hepatopancreas, indicating that the antioxidant defense system is activated in response to Cd-induced oxidative damages in Anodonta woodiana woodiana. The GSH in hepatopancreas showed a consistent decrease in response to Cd toxicity regardless of concentrations and time of Cd exposure, and GST activity was also sensitive to Cd toxicity. Hepatopancreas had a faster response than gills did. Therefore, the GSH level and GST activity in hepatopancreas can be used as biological indicators for monitoring contamination by metals such as Cd.