A rapid and transient ROS generation by cadmium triggers apoptosis via caspase-dependent pathway in HepG2 cells and this is inhibited through N-acetylcysteine-mediated catalase upregulation.
Although reactive oxygen species (ROS) have been implicated in cadmium (Cd)-induced hepatotoxicity, the role of ROS in this pathway remains unclear. Therefore, we attempted to determine the molecular mechanisms relevant to Cd-induced cell death in HepG2 cells. Cd was found to induce apoptosis in the HepG2 cells in a time- and dose-dependent fashion, as confirmed by DNA fragmentation analysis and TUNEL staining. In the early stages, both rapid and transient ROS generation triggered apoptosis via Fas activation and subsequent caspase-8-dependent Bid cleavage, as well as by calpain-mediated mitochondrial Bax cleavage. The timing of Bid activation was coincided with the timing at which the mitochondrial transmembrane potential (MMP) collapsed as well as the cytochrome c (Cyt c) released into the cytosol. Furthermore, mitochondrial permeability transition (MPT) pore inhibitors, such as cyclosporin A (CsA) and bongkrekic acid (BA), did not block Cd-induced ROS generation, MMP collapse and Cyt c release. N-acetylcysteine (NAC) pretreatment resulted in the complete inhibition of the Cd-induced apoptosis via catalase upregulation and subsequent Fas downregulation. NAC treatment also completely blocked the Cd-induced intracellular ROS generation, MMP collapse and Cyt c release, indicating that Cd-induced mitochondrial dysfunction may be regulated indirectly by ROS-mediated signaling pathway. Taken together, a rapid and transient ROS generation by Cd triggers apoptosis via caspase-dependent pathway and subsequent mitochondrial pathway. NAC inhibits Cd-induced apoptosis through the blocking of ROS generation as well as the catalase upregulation.
Oh
Seon-Hee
SH
Research Center for Resistant Cells, College of Medicine, Chosun University, Seosuk-dong, Dong-gu, Gwangju 501-759, South Korea.
Lim
Sung-Chul
SC
D000111:Acetylcysteine / Q000494:pharmacology*; D017209:Apoptosis / Q000187:drug effects*; D002104:Cadmium / Q000633:toxicity*; D006528:Carcinoma, Hepatocellular / Q000188:drug therapy / Q000201:enzymology* / Q000473:pathology; D020169:Caspases / Q000378:metabolism*; D002374:Catalase / Q000096:biosynthesis; D002460:Cell Line; D002470:Cell Survival / Q000187:drug effects; D053938:DNA Fragmentation; D004305:Dose-Response Relationship, Drug; D004338:Drug Combinations; D004785:Environmental Pollutants / Q000633:toxicity*; D006801:Humans; D020287:In Situ Nick-End Labeling; D008564:Membrane Potentials / Q000187:drug effects; D008930:Mitochondria, Liver / Q000187:drug effects / Q000378:metabolism; D017382:Reactive Oxygen Species / Q000378:metabolism*; D015398:Signal Transduction / Q000187:drug effects; D015854:Up-Regulation / Q000187:drug effects; D019014:fas Receptor / Q000378:metabolism
D004338:Drug Combinations; D004785:Environmental Pollutants; D017382:Reactive Oxygen Species; D019014:fas Receptor; D002104:Cadmium; D002374:Catalase; D020169:Caspases; D000111:Acetylcysteine