Moderate hypothermia during cardiopulmonary bypass reduces intramyocardial expression of tumor necrosis factor alpha via inhibition of AP-1

Background and aim

Moderate hypothermia during CPB inhibits intramyocardial tumor necrosis factor alpha (TNF-α) synthesis. Since the expression of TNF-α and other inflammatory mediators such as cyclooxygenase-2 (COX-2) and inducible nitric oxide synthase (iNOS) is regulated by the NF-κB and activator protein (AP)-1 pathways, this study was intended to analyze the effect of moderate hypothermia during CPB on these signaling pathways in the myocardium.

Methods

Twelve young pigs were randomly mounted on standardized CPB in moderate hypothermia or normothermia (temperature 28°C or 37°C, respectively, n = 6 each group). Myocardial probes were sampled from the right ventricle before, during and 6 hours after CPB. Messenger RNA encoding for TNF-α was assessed by competitive RT-PCR. Protein levels of TNF-α, iNOS, and COX-2 were assessed by western blot. Activation of NF-κB and phosphorylation of its inhibitory protein IkBa, activation of AP-1 and phosphorylation of its complex c-Jun as well as of mitogen-activated protein kinase (MAPK) p38 were assessed by electrophoretic mobility shift assay with supershift and/or western blot, respectively.

Results

Both TNF-α mRNA and TNF-α protein were detected as soon as 30 min after initiation of bypass in both groups. At that time, expression of TNF-α mRNA and protein levels tended to be lower in pigs operated on under moderate hypothermia than those operated on under normothermia (P < 0.1, respectively). Moreover, pigs operated on under moderate hypothermia showed lower expression of TNF-α mRNA and protein levels that the others 6 hours after CPB (P < 0.05, respectively). The course of the expression of COX-2 but not that of iNOS during and after CPB paralleled that of TNF-α. The activation of p38 MAPK and of its downstream effector AP-1 was lower in animals operated on in hypothermia than in the others (P < 0.05, respectively). In contrast, phosphorylation of IkB and NF-κB activity were similar in both groups.

Conclusion

This study shows that the inhibition of the intramyocardial expression of TNF-α and of its secondary mediator COX-2 related to moderate hypothermia during CPB is associated with the inhibition of p38 MAPK–AP-1, but not of the NF-κB pathway.