SUPEROXIDE-INDUCED CHANGES IN ENDOTHELIN (ET) RECEPTORS IN HEPATIC STELLATE CELLS

Background/Aims: Reactive oxygen species are mediators of various path ophysiologic events, including postischemic reperfusion injury and inf lammation. Generation of reactive oxygen species and consequent organ injury are associated with increased levels of a powerful vasoconstric tor peptide endothelin-1. Current evidence suggests that actions of en dothelin-1 on the contractile and fibrogenic transdifferentiated stell ate cells may play a critical role in hepatic pathophysiology. The aim of this investigation was to determine whether reactive oxygen specie s modulate the synthesis of endothelin-1 and its receptors in stellate cells. Methods: Primary cultures of transdifferentiated stellate cell s were exposed to reactive oxygen species-generating system, hypoxanth ine/xanthine oxidase, before determination of endothelin-1 and its rec eptors. Results: The treatment caused an initial decrease in ET-1 rece ptor density (about 30% at 30 min), followed by a significant increase over the basal level at 6 h, The increase in the receptors, which occ urred specifically in the ETB subtype, progressed thereafter up to 24 h and was accompanied by an augmented functional response, as indicate d by an enhanced endothelin-1-induced release of [H-3]arachidonic acid from the prelabeled cells. Furthermore, treatment of cells for 24 h b ut not 30 min caused increased expression of ETB mRNA as determined by semi-quantitative polymerase chain reaction. The release of endotheli n-1 in the culture medium was also enhanced by hypoxanthine/xanthine o xidase treatment. These effects of hyposanthine/xanthine oxidase were inhibited by superoxide dismutase and dimethyl sulfoxide, ET-1-induced [H-3]arachidonic acid release was also inhibited by the ETB receptor antagonist BQ788, but not by the ETA receptor antagonist BQ123, Conclu sions: These findings indicate that interactions between ET-1 and stel late cells during episodes of the generation of reactive oxygen specie s can be an important mechanism in the pathophysiology of hepatic diso rders.