Forensic significance of CaMKIIδ/RyR2/calpain-1 axis as a diagnostic biomarker of clinical and postmortem sudden cardiac death triggered by acute myocardial infarction

Abstract Background Acute myocardial infarction (AMI) is a complex, life-threatening, and challenging issue in clinical and forensic settings. Thus, emerging novel biomarkers could provide promising insights into the pathophysiology of AMI for precise diagnostic and therapeutic strategies. Hence, we designed AMI rat models at different time points in order to elucidate the role of various specific biomarkers in the pathogenesis of AMI, along with investigating the postmortem stability of such markers. Rats were subjected to permanent left anterior descending artery (LAD) ligation, then allocated into four different groups based on the ligation time (30, 60, 90, and 120 min; n = 6/time point). Results Our findings revealed significant elevation of myocardial injury biomarkers including myocardial function enzymes, proinflammatory cytokines such as interleukin-6 (IL-6), tumor necrosis factor-alpha (TNF-α), and interleukin-1 beta (IL-1β), as well as cardiac troponin I (cTnI) levels in prolonged ischemic AMI model rats (> 60 min) when compared to sham and short ischemia time (< 60 min) groups. Moreover, the cardiac tissue of AMI model groups revealed a substantial rise of Ca+2 level and mRNA expression of Ca+2/calmodulin-dependent protein kinase II delta (CaMKIIδ), ryanodine receptor 2 (RyR2), calpain-1, and caspase-3 alongside a marked decline of the antioxidant capacity, particularly in prolonged ischemic groups (> 60 min), when compared to the sham group. Histopathological and immunohistochemical analysis revealed progressive myocardial damage characterized by increasing severity of interstitial edema, inflammatory cell infiltration, and cardiac muscle necrosis, with marked tissue deterioration in prolonged ischemic groups (> 60 min). Immunohistochemical examination showed significant upregulation of caldesmon and inducible nitric oxide synthase (iNOS) expression in the cardiac tissue of AMI groups, with maximum expression observed in prolonged ischemic groups (> 60 min) compared to the sham group. Conclusion Our study unveiled the temporal dynamics of such biomarkers as a complementary tool in determining the duration and severity of AMI, since prolonged ischemia could trigger the transition from reversible to irreversible myocardial damage. Furthermore, clarifying the crucial role of CaMKIIδ/RyR2/calpain-1 cascade as a potential specific biomarker of cardiac Ca+2 overload and AMI. Such a cascade offered good postmortem stability and could provide promising insights as a valuable forensic tool in estimating the postmortem interval (PMI) and postmortem diagnosis of AMI.