Heme oxygenase-1 protects human hepatocytes in vitro against warm and cold hypoxia

Background/Aims: Hepatic injury induced by ischemia/reperfusion following surgery, transplantation, or circulatory shock combined with resuscitation is a major clinical problem. Methods: In this study, hypoxic and inflammatory conditions were mimicked by exposing human hepatocytes to N-2 (at 4 and 37degreesC or to cytokines/endotoxin to investigate the potential protective effects of heme oxygenase-1 (HO-1). Incubation of human hepatocytes with single cytokines (IFN-gamma, IL-1beta, TNF-alpha) or LPS, as well as a combination of all four stimuli (CM, cytomix) caused a time-dependent HO-1 mRNA expression over 12 h and a decline by 24 h. In parallel, we observed a time-dependent membrane leakage for LDH and AST and a maximum HO-1 protein expression between 3-24 h. Results: Warm and cold hypoxia showed similar results in HO-1 mRNA and protein expression and the release of LDH and AST. CoPP, a potent HO-1 inducer, and bilirubin, a co-product of the HO-pathway, protected human hepatocytes from warm and cold hypoxia. HO-1 enzyme activity was highest during warm hypoxia, followed by cold hypoxia and CM which was confirmed by intracellular Fe2+ formation. Conclusions: Taken together, we demonstrated, that HO-I induction protected human hepatocytes against warm and cold hypoxia. Our results also suggest that HO-1 induction may have therapeutic potential against inflammatory insults. (C) 2004 European Association for the Study of the Liver. Published by Elsevier B.V. All rights reserved.