Hepatic ischemia/reperfusion upregulates the susceptibility of hepatocytes to confer the induction of inducible nitric oxide synthase gene expression

During hepatic ischemia/reperfusion (I/R), proinflammatory cytokines such as tumor necrosis factor alpha and interleukin (IL) 1 beta stimulate the induction of inducible nitric oxide synthase (iNOS) in hepatocytes, followed by massive production of nitric oxide. We hypothesized that I/R upregulated the susceptibility of hepatocytes to confer the induction of iNOS gene expression. This study was designed to investigate whether cell susceptibility occurs in response to I/R and to delineate the mechanisms underlying the susceptibility. Hepatocytes were isolated from rats with hepatic I/R or sham, cultured, and treated with IL-1 beta. The iNOS induction and its signal including inhibitor kappa B (I kappa B) kinase/nuclear factor kappa B (NF-kappa B) and Akt/type 1 interleukin 1 receptor (IL-1R1) were analyzed. Hepatocytes isolated from rats with I/R markedly increased the production of nitric oxide when stimulated by IL-1 beta as compared with sham control. Ischemia/R also increased the levels of iNOS protein and its messenger RNA. Furthermore, I/R enhanced the activation of transcription factor NF-kappa B and the transactivation of iNOS promoter. However, I/R had no effects on the degradation Of I kappa B and the nuclear translocation of p65 subunit of NF-kappa B. In contrast, I/R increased the phosphorylation of Akt and the upregulation of IL-1R1 induction, which is essential signal for the transcriptional activation of iNOS in addition to I kappa B kinase/NF-kappa B. These results demonstrate that I/R may augment hepatocyte susceptibility for the induction of iNOS gene expression through the enhancement of IL-1R1.