Mechanism of salutary effects of melatonin-mediated liver protection after trauma-hemorrhage: p38 MAPK-dependent iNOS/HIF-1α pathway.

Hsu JT, Le PH, Lin CJ et al.

Chang Gung Memorial Hospital at Linkou

American journal of physiology. Gastrointestinal and liver physiology. Mar 2017.

Although melatonin attenuates the increases in inflammatory mediators and reduces organ injury during trauma-hemorrhage, the mechanisms remain unclear. This study explored whether melatonin prevents liver injury after trauma-hemorrhage through the p38 mitogen-activated protein kinase (MAPK)-dependent, inducible nitrite oxide (iNOS)/hypoxia-inducible factor (HIF)-1α pathway. After a 5-cm midline laparotomy, male rats underwent hemorrhagic shock (mean blood pressure approximately 40 mmHg for 90 min) followed by fluid resuscitation. At the onset of resuscitation, rats were treated with vehicle, melatonin (2 mg/kg), melatonin plus p38 MAPK inhibitor SB203580 (2 mg/kg), or melatonin plus melatonin receptor antagonist luzindole (2.5 mg/kg). At 2 hours after trauma-hemorrhage, the liver tissue myeloperoxidase activity, malondialdehyde, adenosine triphosphate, serum alanine aminotransferase and asparate aminotransferase levels were significantly increased compared with sham-operated control. Trauma-hemorrhage resulted in a significant decrease in the p38 MAPK activation compared with that in the sham-treated animals. Administration of melatonin after trauma-hemorrhage normalized liver p38 MAPK phosphorylation, iNOS and HIF-1α expression, and attenuated cleaved caspase 3 and receptor interacting protein kinase-1 levels. Co-administration of SB203580 or luzindole abolished the melatonin-mediated attenuation of the trauma-hemorrhage-induced increase of iNOS/HIF-1α protein expression and liver injury markers. Taken together, our results suggest that melatonin prevents trauma-hemorrhage-induced liver injury in rats, at least in part, through melatonin receptor-related, p38 MAPK-dependent iNOS/HIF-1α pathway.