OpiCa1 Modulates Cardiomyocyte Viability Through PI3K/Akt Inhibition with Minimal Systemic Impact Beyond RyR Targeting

Calcins represent a class of novel peptide ligands for ryanodine receptors (RyRs), demonstrating therapeutic potential against Ca²⁺ dysregulation-related cardiac diseases. Nevertheless, their biological effects beyond RyR modulation and underlying mechanisms remain unexplored. This study employed Opicalcin1 (OpiCa1), the most bioactive calcin member, revealing that while it reduced cytosolic Ca²⁺ in H9c2 cardiomyocytes, it concurrently diminished cell viability and promoted apoptosis. Transcriptomics and Western blot analyses identified suppression of the negatively regulatory PI3K/Akt pathway as the mechanistic basis. In acute/chronic in vivo studies, high-dose OpiCa1 (≥50 mg/kg i.v.) exhibited minimal impact on body weight, histopathology, and organ indices, while accompanied with subtle alterations in serum indicators, including slight elevations in AST, ALT, and LDH, alongside mild reductions in CK-MB and TBIL-Z. These findings unveil OpiCa1's modulation on cardiomyocyte viability through PI3K/Akt inhibition with minimal systemic impact, providing new insights into non-RyR-mediated actions of calcins and critical toxicological support for developing calcin-based therapies targeting Ca²⁺-dysregulated cardiac pathologies.