Synergistic toxicity induced by prolonged glutathione depletion and inhibition of nuclear factor-kappaB signaling in liver cells

Abstract

TNF-α, GSH depletion and CYP2E1 are factors that play an important role in alcoholic liver disease. Activation of NF-κB prevents hepatocyte damage caused by TNF-α. This work describes the effect of NF-κB inhibition on toxicities caused by GSH depletion or arachidonic acid (AA) treatment in liver cells, and evaluates the possible influence of CYP2E1 overexpression. Cells were exposed to the NF-κB inhibitor BAY11-7082, in the absence or presence of l-buthionine sulfoximine (BSO) to block GSH synthesis. BSO toxicity was higher in CYP2E1-expressing E47 HepG2 cells compared to control cells; the incubation with BAY11-7082 potentiated BSO toxicity in both cell lines comparably. Several other agents which suppress activation of NF-κB increased BSO toxicity in E47 cells. NF-κB inhibition, however, did not sensitize E47 cells to AA toxicity. Suppressing activity of NF-κB also potentiated BSO, but not AA toxicity, in isolated rat hepatocytes. BAY11-7082 plus BSO induced a greater p38 MAPK activation as compared to BAY11-7082 or BSO alone, and a p38 MAPK inhibitor protected against the synergistic toxicity. In summary, inhibition of NF-κB sensitizes liver cells to toxicity linked to GSH depletion, probably accelerating the processes of thiol homeostasis deregulation and induction of apoptosis through a mechanism mediated by p38 MAPK.