Moderate hypothermia during cardiopulmonary bypass (CPB) inhibits the intramyocardial synthesis of TNF-α: a role of p38 MAP kinase

Background and aim

Moderate hypothermia during CPB inhibits intramyocardial 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 MAP kinases (p38 and ERK1/2 MAPK), and by the NF-κB pathway, 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 assigned to a temperature (T°) regimen during standarized CPB: normothermia (T° = 37°C; n = 6) or moderate hypothermia (T° = 28°C; n = 6). Myocardial probes were sequentially sampled from the right ventricle before, during and 6 hours after CPB. Myocardial expression of TNF-α, COX-2, and iNOS were detected and quantified by competitive RT-PCR and/or western blot. Phosphorylation of p38 MAP and ERK1/2 MAP kinases, and of IκB was detected by western blot. Intracellular localisation of TNF-α, COX-2, iNOS, and NF-κB p65 and p50 were ensured by immunohistochemical staining.

Results

Both TNF-α mRNA and protein levels were detected as soon as 30 min after initiation of CPB and before aortic clamping in both groups, but were lower in pigs that were on hypothermia than in the others (P < 0.05, respectively). This difference persisted during and after CPB. The levels of iNOS and COX-2 were detected during and after CPB but without any difference between groups. Phosphorylation of p38 MAP and ERK1/2 MAP kinases and of IκB was detected before, during and after CPB. Levels of phospho-p38 MAP kinase but not of ERK1/2 MAP kinase and IκB tended to be lower in animals on hypothermia than in the others (P < 0.1).

Conclusion

This study shows for the first time that cardiac surgery induces the expression of TNF-α in the myocardium as soon as 30 min after institution of CPB, before aortic clamping. This is associated with the activation of p38 MAP and ERK1/2 MAP kinases and NF-κB pathway. The inhibition of TNF-α expression by hypothermia is related to the inhibition of p38 MAP kinase.