Molecular mechanisms of methylmercury-induced cell death in human HepG2 cells.
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.
Cuello
Susana
S
Departamento de Química Analítica, Facultad de Químicas, Universidad Complutense, Madrid, Spain.
Goya
Luis
L
Madrid
Yolanda
Y
Campuzano
Susana
S
Pedrero
Maria
M
Bravo
Laura
L
Cámara
Carmen
C
Ramos
Sonia
S
D000975:Antioxidants / Q000494:pharmacology; D017209:Apoptosis / Q000187:drug effects; D053148:Caspase 3 / Q000096:biosynthesis; D002470:Cell Survival / Q000187:drug effects; D004785:Environmental Pollutants / Q000633:toxicity*; D004789:Enzyme Activation / Q000187:drug effects; D005978:Glutathione / Q000378:metabolism; D056945:Hep G2 Cells; D022781:Hepatocytes / Q000187:drug effects* / Q000378:metabolism / Q000473:pathology; D006801:Humans; D008767:Methylmercury Compounds / Q000633:toxicity*; D009336:Necrosis / Q000139:chemically induced; D018384:Oxidative Stress / Q000187:drug effects; D010088:Oxidoreductases / Q000378:metabolism; D012402:Rotenone / Q000494:pharmacology; D013997:Time Factors; D014475:Uncoupling Agents / Q000494:pharmacology
D000975:Antioxidants; D004785:Environmental Pollutants; D008767:Methylmercury Compounds; D014475:Uncoupling Agents; D012402:Rotenone; D010088:Oxidoreductases; D053148:Caspase 3; D005978:Glutathione