Increased oxidative stress in cirrhotic rat livers: A potential mechanism contributing to reduced nitric oxide bioavailability.
In cirrhotic livers, decreased nitric oxide (NO) bioavailability is a major factor increasing intrahepatic vascular tone. In several vascular disorders, an increase in superoxide (O(2) (-)) has been shown to contribute to reduced NO bioavailability through its reaction with NO to form peroxynitrite. This study was aimed to test the hypothesis that, in cirrhotic livers, increased O(2) (-), by reacting with NO, reduces NO bioavailability. In control and cirrhotic rat livers, NO bioavailability was evaluated by the measurement of cyclic guanosine monophosphate in liver tissue and by 4-amino-5-methylamino-2',7'-difluorofluorescein diacetate (DAF-FM-DA) fluorescence in isolated sinusoidal endothelial cells (SEC); the O(2) (-) content was determined by dihydroethidium staining in fresh liver sections. In addition, the role of endothelial nitric oxide synthase (eNOS), xanthine oxidase (XO), and cyclooxygenase (COX) as possible sources of O(2) (-) and the role of superoxide dismutase (SOD) enzymatic activity as an O(2) (-) scavenger were determined in liver homogenates. Protein-nitrotyrosination, a marker of the NO-O(2) (-) reaction, was evaluated in liver homogenates. Furthermore, in control SEC and bovine aortic endothelial cells, NO modulation by O(2) (-) was evaluated. Cirrhotic livers exhibited increased O(2) (-) levels. This was due, at least in part, to increased production by COX and XO but not eNOS and to reduced scavenging by SOD. Increased O(2) (-) was associated with a significant reduction in NO bioavailability and increased nitrotyrosinated proteins. In endothelial cells, an inverse relationship between O(2) (-) levels and NO bioavailability was observed.


CONCLUSIONS
Our data show that oxidative stress may contribute to reduced NO bioavailability in cirrhotic livers, supporting the evaluation of O(2) (-) reduction as a potential mechanism to restore NO content.
Gracia-Sancho
Jorge
J
Hepatic Hemodynamic Laboratory, Liver Unit, Institut de Malalties Digestives i Metabòliques (IMDiM), Hospital Clínic, Centro de Investigación Biomédica en Red de Enfermedades Hepáticas y Digestivas, University of Barcelona, Spain.
Laviña
Bàrbara
B
Rodríguez-Vilarrupla
Aina
A
García-Calderó
Héctor
H
Fernández
Mercedes
M
Bosch
Jaume
J
García-Pagán
Joan-Carles
JC
D000818:Animals; D042783:Endothelial Cells / Q000378:metabolism; D008103:Liver Cirrhosis / Q000378:metabolism*; D008297:Male; D009569:Nitric Oxide / Q000378:metabolism*; D018384:Oxidative Stress / Q000502:physiology*; D011451:Prostaglandin-Endoperoxide Synthases / Q000378:metabolism; D051381:Rats; D017208:Rats, Wistar; D013482:Superoxide Dismutase / Q000378:metabolism; D013481:Superoxides / Q000378:metabolism*; D014969:Xanthine Oxidase / Q000378:metabolism
D013481:Superoxides; D009569:Nitric Oxide; D011451:Prostaglandin-Endoperoxide Synthases; D013482:Superoxide Dismutase; D014969:Xanthine Oxidase