Departamento de Química Analítica, Facultad de Químicas, Universidad Complutense, Madrid, Spain.
Food Chem Toxicol. 2010 May;48(5):1405-11. doi: 10.1016/j.fct.2010.03.009. Epub 2010 Mar 10.
Methylmercury (MeHg) has been suggested to exert cytotoxicity through multiple mechanisms, but the precise biochemical machinery has not been fully defined. This study was aimed at investigating the time-course (0-24h) effect of 2mg/L MeHg on cell death in human HepG2 cells. MeHg decreased cell viability in a time-dependent manner, which was concomitant with increased LDH leakage, reduced GSH levels, CAT activity and altered activity of the antioxidant enzymes GPx and GR at the longest times of incubation (16 and 24h). Activity of the detoxifying enzyme GST was also early enhanced (2h). Caspase-3 activity reached a maximum value at 8h and continued increased up to 24h. This feature was preceded by an enhancement in the caspase-9 activity (2h), whereas caspase-8 activity remained unchanged. MeHg early diminished Bcl-x(L)/Bcl-x(S) ratio and increased levels of the pro-apoptotic Bax and Bad. Moreover, MeHg-induced cytotoxicity was completely inhibited by the antioxidants (GSH and NAC) and notably by the mitochondrial complex I inhibitor rotenone, but not by the NADH oxidase inhibitor DPI. In summary, MeHg induced an oxidative stress responsible for apoptosis in HepG2 cells through direct activation of the caspase cascade and altered the cellular antioxidant and detoxificant enzymatic system to later provoke necrosis at later stages.
甲基汞（MeHg）被认为通过多种机制发挥细胞毒性作用，但确切的生化机制尚未完全定义。本研究旨在研究 2mg/L MeHg 对人 HepG2 细胞细胞死亡的时间进程（0-24 小时）影响。MeHg 呈时间依赖性降低细胞活力，同时伴随着 LDH 漏出增加、GSH 水平降低、CAT 活性降低以及抗氧化酶 GPx 和 GR 的活性改变（孵育时间最长为 16 和 24 小时）。解毒酶 GST 的活性也较早增强（2 小时）。Caspase-3 活性在 8 小时达到最大值，并持续增加至 24 小时。这一特征之前是 caspase-9 活性的增强（2 小时），而 caspase-8 活性保持不变。MeHg 早期降低了 Bcl-x(L)/Bcl-x(S) 比值，并增加了促凋亡 Bax 和 Bad 的水平。此外，抗氧化剂（GSH 和 NAC），特别是线粒体复合物 I 抑制剂鱼藤酮，完全抑制了 MeHg 诱导的细胞毒性，但 NADH 氧化酶抑制剂 DPI 则没有。总之，MeHg 通过直接激活半胱氨酸蛋白酶级联反应诱导 HepG2 细胞发生氧化应激诱导细胞凋亡，并改变细胞抗氧化和解毒酶系统，随后在后期引发坏死。
