Pham T N D, Marion M, Denizeau F, Jumarie C
Département de Chimie, Centre TOXEN, Université du Québec à Montréal, C.P. 8888, Succ. Centre-Ville, Montréal, Québec, Canada H3C 3P8.
Toxicol In Vitro. 2006 Dec;20(8):1331-42. doi: 10.1016/j.tiv.2006.05.005. Epub 2006 May 23.
Cadmium (Cd) is a well-known hepatotoxic environmental pollutant. Depending on the exposure conditions, Cd may cause necrosis or apoptosis. Oxidative stress is believed to participate in Cd toxicity but the molecular signaling responsible for Cd-induced apoptosis in non-malignant liver cells still needs to be clarified. Therefore we have studied apoptosis in primary cultures of rat hepatocytes incubated with low levels of Cd for short exposure times. Studies of nuclear morphology, chromatin condensation, and oligonucleosomal DNA fragmentation demonstrate that 1-5 microM Cd induces apoptosis as early as 6-12 h with minor effects on MTT activity. A concomitant time- and concentration-dependent increase in caspase-9 and -3 activities was observed, whereas Cd did not affect caspase-8 activity as much, suggesting a minor role of the death-receptor pathway. Significant release of cytochrome c into the cytosol demonstrated the involvement of a mitochondrial-dependent apoptotic pathway. However, cell pre-treatment with caspase inhibitors (Z-VAD-fmk or Ac-DEVD-CHO) did not prevent apoptosis. Increases in the cytosolic levels of the mitochondrial apoptosis-inducing factor (AIF) were also observed: kinetics of cytochrome c and AIF release were similar. These results show that Cd-induced apoptosis in rat hepatocytes is time- and concentration-dependent. The early apoptotic events involved mitochondrial-dependent pathways but not necessarily caspase-dependent signaling.
镉（Cd）是一种广为人知的具有肝毒性的环境污染物。根据暴露条件的不同，镉可能会导致坏死或凋亡。氧化应激被认为参与了镉的毒性作用，但非恶性肝细胞中镉诱导凋亡的分子信号仍有待阐明。因此，我们研究了原代培养的大鼠肝细胞在短时间内暴露于低水平镉后的凋亡情况。对细胞核形态、染色质凝聚和寡核苷酸DNA片段化的研究表明，1 - 5 microM的镉早在6 - 12小时就可诱导凋亡，对MTT活性的影响较小。同时观察到caspase - 9和 - 3活性随时间和浓度的依赖性增加，而镉对caspase - 8活性的影响不大，这表明死亡受体途径的作用较小。细胞色素c大量释放到细胞质中表明存在线粒体依赖性凋亡途径。然而，用caspase抑制剂（Z - VAD - fmk或Ac - DEVD - CHO）对细胞进行预处理并不能阻止凋亡。还观察到线粒体凋亡诱导因子（AIF）的细胞质水平升高：细胞色素c和AIF释放的动力学相似。这些结果表明，镉诱导大鼠肝细胞凋亡具有时间和浓度依赖性。早期凋亡事件涉及线粒体依赖性途径，但不一定涉及caspase依赖性信号传导。
