Superoxide-induced changes in endothelin (ET) receptors in hepatic stellate cells.

BACKGROUND/AIMS: Reactive oxygen species are mediators of various pathophysiologic events, including postischemic reperfusion injury and inflammation. Generation of reactive oxygen species and consequent organ injury are associated with increased levels of a powerful vasoconstrictor peptide endothelin-1. Current evidence suggests that actions of endothelin-1 on the contractile and fibrogenic transdifferentiated stellate cells may play a critical role in hepatic pathophysiology. The aim of this investigation was to determine whether reactive oxygen species modulate the synthesis of endothelin-1 and its receptors in stellate cells.

METHODS

Primary cultures of transdifferentiated stellate cells were exposed to reactive oxygen species-generating system, hypoxanthine/xanthine oxidase, before determination of endothelin-1 and its receptors.

RESULTS

The treatment caused an initial decrease in ET-1 receptor density (about 30% at 30 min), followed by a significant increase over the basal level at 6 h. The increase in the receptors, which occurred specifically in the ET(B) subtype, progressed thereafter up to 24 h and was accompanied by an augmented functional response, as indicated by an enhanced endothelin-1-induced release of [3H]arachidonic acid from the prelabeled cells. Furthermore, treatment of cells for 24 h but not 30 min caused increased expression of ET(B) mRNA as determined by semi-quantitative polymerase chain reaction. The release of endothelin-1 in the culture medium was also enhanced by hypoxanthine/xanthine oxidase treatment. These effects of hypoxanthine/xanthine oxidase were inhibited by superoxide dismutase and dimethyl sulfoxide. ET-1-induced [3H]arachidonic acid release was also inhibited by the ET(B) receptor antagonist BQ788, but not by the ET(A) receptor antagonist BQ123.

CONCLUSIONS

These findings indicate that interactions between ET-1 and stellate cells during episodes of the generation of reactive oxygen species can be an important mechanism in the pathophysiology of hepatic disorders.