Cardioprotective effects of a novel calpain inhibitor SNJ-1945 for reperfusion injury after cardioplegic cardiac arrest

Abstract

We have previously indicated that calpain inhibitor-1 prevents the heart from ischemia- reperfusion injury associated with the impairment of total Ca2+ handling by inhibiting the proteolysis of α-fodrin. However, this inhibitor is insoluble with water and inappropriate for clinical application. The aim of the present study was to investigate the protective effect of a newly developed calpain inhibitor, SNJ-1945 (SNJ), with good aqueous solubility on left ventricular (LV) mechanical work and energetics in the cross-circulated rat hearts. SNJ (150 μM) was added to KCl (30 meq) cardioplegia (CP). Mean end-systolic pressure at midrange LV volume (ESPmLVV) and systolic pressure-volume area (PVA) at mLVV (PVAmLVV; a total mechanical energy per beat) were hardly changed after CP plus SNJ arrest-reperfusion (post-CP + SNJ), whereas ESPmLVV and PVAmLVV in post-CP group were significantly ( P < 0.01) decreased. Mean myocardial oxygen consumption for the total Ca2+ handling in excitation-contraction coupling did not significantly decrease in post-CP + SNJ group, whereas it was significantly ( P < 0.01) decreased in post-CP group. The mean amounts of 145- and 150-kDa fragments of α-fodrin in the post-CP group were significantly larger than those in normal and post-CP + SNJ groups. In contrast, the mean amounts of L-type Ca2+ channel and sarcoplasmic reticulum Ca2+-ATPase were not significantly different among normal, post-CP, and post-CP + SNJ groups. Our results indicate that soluble SNJ attenuates cardiac dysfunction due to CP arrest-reperfusion injury associated with the impairment of the total Ca2+ handling in excitation-contraction coupling by inhibiting the proteolysis of α-fodrin.