Effects of preconditioning on ischemia/reperfusion injury of hepatocytes determined by immediate early gene transcription

Abstract.

Ischemia reperfusion (I-R) of the liver induces various events leading to cell death (apoptosis) and subsequent cells proliferation. Recent experimental studies have described the protective effect of ischemic preconditioning (IPC) on I-R injury of the liver. However, the mechanisms involved in this protection remain unknown. The protein products of immediate early genes (IEGs) behave as crucial transcriptional regulators not only in apoptosis but also in cell proliferation. Here, we evaluated the effects of IPC on IEG transcription after I-R injury, using a rat liver I-R injury model. Injury to hepatocytes was evaluated by measuring serum levels of aspartate transaminase (AST), alanine transaminase (ALT), and lactate dehydrogenase (LDH) and that to endothelial cells by plasma concentration of hyaluronic acid (HA). The extent of necrosis was evaluated by H&E staining, while cell proliferation and apoptosis were evaluated by proliferating cell nuclear antigen (PCNA) and terminal deoxy(d)-UTP nick end labelling (TUNEL) staining, respectively. Alterations in the transcription of IEGs (c-fos and c-jun) were examined by Northern blotting. Rats subjected to 40-min liver ischemia, preceded by 10-min preconditioning, showed significantly lower AST, ALT, LDH, and HA levels at 6 h after I-R than untreated animals (P < 0.05; n at least 5 rats per group). The percentage of necrotic areas at 24 h after I-R was significantly lower in IPC-treated animals than in the controls. The numbers of apoptotic cells at 24 h after I-R and the numbers of PCNA-positive cells at 24 and 48 h after I-R were significantly lower in IPC-treated rats than in controls. Transcription levels of IEGs were low in IPC-treated rats, particularly c-jun at 1 and 1.5 h after I-R (P < 0.05). Our results indicate that IPC provides a significant protective effect on for liver cells against I-R injury and that its effect is evidenced by a significant decrease in the transcription levels of IEGs following the insult.