Abstract
Background: Proinflammatory cytokines such as tumor necrosis factor α (TNF-α), interleukin (IL)-6, and IL-8 have been implicated in myocardial injury following cardiopulmonary bypass (CPB). However, little evidence is currently available to directly confirm such a relationship. We have previously documented that a newly discovered ‘four and a half LIM-only protein 2’ (FHL2) is exclusively expressed in myofibres. We hypothesized that the upregulation of FHL2 is proportional to the degree of myocardial injury and investigated the myocardial expression of FHL2 together with these cytokine messenger RNAs (mRNAs) during clinical CPB.
Methods: Intermittent hypothermic blood cardioplegia was used in all patients. Atrial myocardial biopsies were obtained immediately at the onset and at the end of CPB in 33 consecutive patients undergoing valvular or coronary artery surgery. TNF-α, IL-6, and IL-8 mRNA expressions in these myocardial samples were determined by semi-quantitative reverse transcription-polymerase chain reaction. Myocardial FHL2 expression was determined by Western blot analysis. Serum levels of the MB isoenzyme of creatine kinase (CK-MB) and cardiac troponin-I (cTnI) before surgery and 24 h after the end of CPB were also measured.
Results: The duration of aortic crossclamping and CPB was 70±33 and 99±37 min, respectively. No elevated myocardial TNF-α mRNA expression was found after CPB. IL-6 mRNA expressions were detected in 14 pairs of the myocardial biopsies and were elevated in 11 (33%) post-CPB biopsies. Similarly, IL-8 mRNA expressions were detected in 19 pairs of samples and were elevated in 14 (42%) post-CPB biopsies. Among the 17 pairs of biopsies with positive FHL2 expression, FHL2 levels were increased in 11 (33%) post-CPB samples. Moreover, the elevated FHL2 expression was associated with an increase in IL-6 (
P=0.018) and IL-8 (
P=0.024) mRNA expression after CPB. Postoperative CK-MB and cTnI levels were significantly higher in patients with myocardial FHL2 expressions than those without (CK-MB, 13.5±2.3 vs. 6.5±0.8 ng/ml,
P=0.022; cTnI, 10.7±2.0 vs. 3.5±0.6 ng/ml,
P=0.0013).
Conclusions: Our findings demonstrate for the first time that both IL-6 and IL-8 mRNAs are upregulated in human cardiac myocytes following CPB and these cytokines may be involved in myocardial ischemia-reperfusion injury, as reflected by their association with an increased expression of FHL2.