Intermittent ischemia reduces warm hypoxia-reoxygenation-induced JNK(1)/SAPK(1) activation and apoptosis in rat hepatocytes

Prolonged liver ischemia followed by reperfusion (I/R) causes functional an d structural damage to liver cells, resulting in necrosis and apoptosis. c- jun N-terminal kinase 1/stress-activated protein kinase 1 (JNK(1)/SAPK(1)) is activated during UR and participates in the onset of the apoptosis progr am. Excessive blood loss during surgery can hinder postoperative recovery. Intermittent portal triad clamping (PTC) is better tolerated than prolonged continuous ischemia. This study was designed to demonstrate that intermitt ent ischemia could improve postischemic survival rates by a decrease of JNK 1/SAPK1 and caspase 3 activation, which were involved in the apoptosis proc ess. Rats were subjected to intermittent 1-hour ischemia (15-minute ischemi a/5-minute reperfusion, 4 times), followed by 220-minute reperfusion, or to continuous ischemia (I hour), followed by 240-minute reperfusion. Mortalit y rates were assessed on day 7. Serum aspartate transaminase (AST), alanine transaminase (ALT), and lactate deshydrogenase levels (LDH) were measured 6 hours after ischemia. This study was completed in primary cultured isolat ed rat hepatocytes, subjected to the same continuous or intermittent hypoxi c conditions. The activation status of JNK(1)/SAPK(1) was evaluated by immu noprecipitation or Western blotting experiments. Apoptosis was assessed by measuring caspase activation and by terminal deoxynucleotidyl transferase-m ediated dUTP biotin nick end labeling (TUNEL) reaction. Eighty percent of t he intermittent-ischemia group was alive 7 days after surgery and serum enz yme levels were significantly decreased. Intermittent hypoxia or ischemia d id not lead to JNK1/SAPK1 activation, but at least 3 hypoxia-reoxygenation (H/R) sets were necessary to inhibit kinase activation. Consequently, caspa se 3 activation and apoptosis were dramatically reduced. Intermittent ische mia is a powerful, protective way to reduce UR damage of the liver, by redu ction of JNK(1)/ SAPK(1) activation associated with a down-regulation of ca spase 3 activity, which leads to inhibition of hepatocyte apoptosis.