Increased cardiac IL-18 mRNA, pro-IL-18 and plasma IL-18 after myocardial infarction in the mouse; a potential role in cardiac dysfunction.

OBJECTIVE: Interleukin (IL)-18 has been reported to be an important predictor for mortality in ischemic heart disease. IL-18 has proinflammatory properties, induces cell death and stimulates nitric oxide production. We hypothesized that following myocardial infarction (MI) an increased myocardial IL-18 production occurs, which may be involved in the pathogenesis of post-ischemic heart failure. METHODS AND
RESULTS: Seven days after induction of MI in the mouse, myocardial hypertrophy and pulmonary edema were observed. RNase protection assay of tissue from the non-infarcted left ventricular myocardium revealed an increase in IL-18 (2.0-fold; P<0.001) and IL-1 beta (1.6-fold; P<0.001) mRNA after MI. Enhanced abundance of pro-IL-18 (1.4-fold; P<0.05), IL-18 receptor (3.5-fold; P<0.05) and IL-18 binding proteins (1.6-fold; P<0.05) was also demonstrated, whereas cardiac IL-18 protein decreased by 25% (P<0.05) following MI. However, the concentration of circulating IL-18 was significantly elevated (MI; 90.4+/-11.7 pg/ml, sham; 47.2+/-4.2 pg/ml; P<0.001). After MI, enhanced cardiac activity of the pro-IL-18 processing enzyme, caspase-1, was measured. Additionally, a 3.4-fold increase (P<0.001) in the activity of the IL-18 degrading enzyme, caspase-3, was found in cardiac tissue, which may explain the observed reduction of cardiac IL-18 protein abundance. Finally, IL-18 reduced shortening of electrically stimulated adult cardiomyocytes and left ventricular contractility in vivo.
CONCLUSIONS: After MI in the mouse, increased production of cardiac IL-18 mRNA and pro-IL-18, as well as circulating IL-18 occurs. Since IL-18 also reduced myocardial contractility, we suggest that IL-18 may be involved in the pathogenesis of contractile dysfunction following MI.