Degradation of myocardial structural proteins in myocardial infarcted dogs is reduced by Ep459, a cysteine proteinase inhibitor.

The purpose of this study is to clarify whether cysteine proteinases play an important role in the degradation of myocardial proteins in the infarcted tissue. We studied the effects of a cysteine proteinase inhibitor, Ep459, on degradation of cardiac structural proteins caused by ischemia due to coronary artery ligation for 24 h. Proteolytic effects of purified cysteine proteinases on isolated cardiac tissue were also examined. Using sodium dodecyl sulfate-polyacrylamide gel electrophoresis, degradation of cardiac structural proteins, particularly of myosin heavy chain, alpha-actinin and troponin-I was observed in the infarcted tissue. Treatment with Ep459 significantly reduced protein degradation and total activity of cathepsins B and L in the infarcted tissue, compared with the findings in the untreated group. The electrophoretic pattern of the infarcted myocardium was similar to that of myofibrillar proteins degraded by cathepsins B and L. These results suggest that cysteine proteinases, particularly cathepsins B and L, are involved in degradation of myofibrillar proteins in myocardial infarction.