13-methylpalmatine alleviates myocardial ischemia/reperfusion injury by potentially targeting the C5a-C5aR1 axis to inhibit neutrophil extracellular trap formation.

The complement system activation-induced inflammation is a critical contributor to myocardial ischemia/reperfusion (I/R) injury. However, effective therapeutic targets and pharmacological interventions remain limited. In this study, we identified 13-methylpalmatine (13-Me-PLT), a natural isoquinoline alkaloid isolated from Coptidis chinensis, as a cardio-protective agent that improved cardiac function and reduced inflammation in a rat model of myocardial I/R injury. RNA sequencing (RNA-seq) analysis revealed significant up-regulation of neutrophil extracellular trap (NET) formation-related signaling pathway and C5ar1 gene in myocardial I/R, both of which were reversed by 13-Me-PLT treatment. Bioinformatics analysis, biophysical assays, and flow cytometry confirmed that 13-Me-PLT effectively inhibited C5a receptor 1 (C5aR1) on neutrophils. However, the role of the C5a-C5aR1 axis in NET formation during myocardial I/R injury has remained unclear. In this study, using a pharmacological inhibitor of C5aR1, we demonstrated that activation of the C5a-C5aR1 axis promoted myocardial I/R injury by inducing NET formation, and that 13-Me-PLT effectively inhibited both processes in a BM213 (C5aR1 agonist)-treated rat model. In vitro, 13-Me-PLT suppressed the expression of NET-associated proteins and alleviated fibrous NET structures in neutrophils, further supporting its cardio-protective effects. In conclusion, our findings revealed that C5a-C5aR1 axis activation exacerbated myocardial I/R injury in a NET-dependent manner. 13-Me-PLT exerted cardio-protective effects by potentially inhibiting C5a-C5aR1 axis-mediated NET formation, highlighting its potential as a therapeutic candidate for myocardial I/R injury.