Superoxide-induced changes in endothelin (ET) receptors in hepatic stellate cells.
OBJECTIVE
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.
Gabriel
A
A
Thomas E. Starzl Transplantation Institute, University of Pittsburgh, PA 15213, USA.
Kuddus
R H
RH
Rao
A S
AS
Watkins
W D
WD
Gandhi
C R
CR
D017667:Adipocytes / Q000378:metabolism*; D000818:Animals; D016718:Arachidonic Acid / Q000378:metabolism; D002478:Cells, Cultured; D003513:Cycloheximide / Q000494:pharmacology; D003609:Dactinomycin / Q000494:pharmacology; D019332:Endothelin-1 / Q000096:biosynthesis; D008099:Liver / Q000166:cytology / Q000378:metabolism*; D008297:Male; D051381:Rats; D017207:Rats, Sprague-Dawley; D017382:Reactive Oxygen Species; D044022:Receptor, Endothelin A; D044023:Receptor, Endothelin B; D017466:Receptors, Endothelin / Q000096:biosynthesis* / Q000235:genetics; D013481:Superoxides / Q000494:pharmacology*; D014969:Xanthine Oxidase / Q000494:pharmacology
D019332:Endothelin-1; D017382:Reactive Oxygen Species; D044022:Receptor, Endothelin A; D044023:Receptor, Endothelin B; D017466:Receptors, Endothelin; D013481:Superoxides; D003609:Dactinomycin; D016718:Arachidonic Acid; D003513:Cycloheximide; D014969:Xanthine Oxidase