镉暴露对黑斑蛙精巢ROS的诱导及其蛋白质氧化损伤作用机理

Toxicity mechanism of Cadmium-induced reactive oxygen species and protein oxidation in testes of the frog Rana nigromaculata

重金属镉对精巢发育、呼吸及神经系统信号转导等途径均有不良影响,被认为是造成两栖动物种群数量急剧下降的重要原因之一。然而,有关镉对精巢损伤的分子机理还不清楚。通过对镉暴露后的黑斑蛙精巢活性氧自由基(ROS)、蛋白质羰基(PCO)以及DNA蛋白质交联(DPC)等指标的系统分析,探讨了镉对精巢毒害的分子作用机理。随镉浓度的增加,黑斑蛙精巢细胞线粒体ROS随镉暴露浓度的增加而升高,0.5、1.0 mg/L镉染毒组与对照组比较有显著性差异(P<0.05);精巢组织PCO和DPC也随镉暴露浓度的增加而逐渐上升,且均呈明显的浓度-效应关系。结果表明:镉诱导机体产生ROS,进而导致蛋白质氧化损伤以及DNA损伤,说明精巢组织ROS的产生是镉致雄性生殖毒效应机制的重要因素之一。

Abstract： Exorbitant heavy metal embodies certain underlying toxic effects that have been regarded as one of the culprits rendering amphibian populations decline and extinct at a fast clip in recent decades. Cadmium （Cd） is a ubiquitous environmental pollutant that has been concerned as globe issue. The previous study has fotLnd that Cd could induce testicular damage, respiratory and nervous system disorders. However, the toxicity mechanism of Cd has not been addressed. Here, we explored the toxicity mechanism study of Cd by investigating the effect of chronic exposure to CdC12 on the reproductive system and examine the toxicity mechanism of Cd2~ in male Rana nigromaculata. Based on the levels of the Integrated Wastewater Discharge Standard （GB3838--1988） of China and 96h acute toxicity te,~t, six test concentrations, i.e. 0. 005, 0.01, 0.05, 0.1, 0.5, 1.0 mg/L, were adopted for the chronic toxicity test by epidermal uptake of CdC1z solution. 140 adult male frogs were randomly divided into seven groups, each group embraced twenty. The group treated only with distilled water was set aside as control. All frogs were sacrificed and the testis tissues were collected in the wake of 30 days treatment for the measurement of reactive oxygen species （ROS） , protein carbonylation （PCO） and DNA-protein crosslinks （DPCs） levels. The results showed that with the increasing of CdC12 concentrations, ROS of test groups became higher than that of control group. In 0.5 mg/L or 1.0 mg/L CdC12 groups, ROS increased significantly in comparison with contrnl irrtqlln （ P 〈 0.05） The content of PCO increased notablv alone with the increasing of Cd2＋ . taken on strong,dose-dependent relationship （Rz = 0. 9603, P〈0.05 ）. In the presence of 0.5mg/L or 1.0mg/L of Cd2~, PCO content was significantly higher than that of control group （P〈0.05）. Cd2＋ also induced DPCs levels increasing, which showed obvious dose-dependent relationship （ R2 = 0. 909, P〈0.05 ）. Compared with control group, we observed significantly difference when the groups treated with 0.5mg/L and 1.0mg/L Cdz~. Regression analysis showed that quadratic curve regression were found between PCO content and ROS levels （R2 = 0. 5547 ） , while linear regression occurred between DPCs levels and PCO content （R2 = 0. 8394）. Above results indicated that ROS accumulation could induce the PCO content increasing and the PCO might be the upstream signal for Cd-induced DNA damage in the testes of R. nigromaculata. Finally, we proposed that ROS introduced by cadmium played a central role in male reproductive toxicity and ROS may induce the cascade reaction of protein oxidation damage and DNA impairment.