We have previously reported that N-ethylmaleimide induces apoptosis through 
activation of K(+), Cl(-)-cotransport in HepG2 human hepatoblastoma cells. In 
this study, we investigated the role for reactive oxygen species as a mediator 
of the apoptosis induced by N-ethylmaleimide. N-ethylmaleimide induced a 
significant elevation of intracellular level of reactive oxygen species. 
Treatment with antioxidants (N-acetyl cysteine, 
N,N'-diphenyl-p-phenylenediamine) which markedly suppressed generation of 
reactive oxygen species, significantly inhibited the N-ethylmaleimide-induced 
activation of K(+), Cl(-)-cotransport and apoptosis. Inhibitors of NADPH oxidase 
(diphenylene iodonium, apocynin, D-(+)-neopterine) also significantly blunted 
the generation of reactive oxygen species, activation of K(+), Cl(-)-cotransport 
and apoptosis induced by N-ethylmaleimide. These results suggest that reactive 
oxygen species generated through activation of NADPH oxidase may play a role in 
the N-ethylmaleimide-induced stimulation of K(+), Cl(-)-cotransport and 
apoptosis in HepG2 cells.