Abstract 296: B7-33, a Functionally Selective Relaxin Receptor 1 Agonist, Exerts Protective Effects Against Myocardial ischemia-Reperfusion Injury in Mice

Abstract

Background: B7-33 is a peptide derived from the B-chain of human relaxin, and is shown to elicit biased signaling at relaxin receptor 1 (RXFP1) in human cell lines. The influence of B7-33 on myocardial ischemia-reperfusion (IR) injury and associated cardiac adverse remodeling is unknown. Methods and Results: Primary cardiomyocytes and cardiac fibroblasts were isolated from adult CD1 mice and subjected to simulated ischemia-reoxygenation (SIRO). Myocytes were placed in 1% O 2 chamber for 40 min, followed by 1 h of reoxygenation with control (myocyte media) or B7-33 (10, 50 or 100 nM)-infused media. Trypan blue staining showed a significant decrease in cell death with B7-33 concentrations of 50 nM and 100 nM ( Fig. A ).Treating myocytes with B7-33 for 15 min exhibited a dose-dependent increase in Erk1/2 phosphorylation, which reached statistical significance at 100 nM ( Fig. B ). Fibroblasts subjected to 4 h of hypoxia and 15 h of reoxygenation had increased viability (MTT assay) with B7-33 at all concentrations ( Fig. C ). In vivo , CD1 mice were subjected to IR injury via coronary artery ligation for 30 min, followed by 24 h of reperfusion. Vehicle (saline) or B7-33 (10 μg/kg) was injected i.p. at the onset of reperfusion. After 24 h, B7-33-treated mice demonstrated decreased infarct size (TTC stain) ( Fig. D ) and preserved fractional shortening (M-mode echo, Fig. E ) compared to vehicle-treated mice. Conclusion: Reperfusion therapy with B7-33 reduces infarct size post-MI, preserves cardiac function and protects cardiomyocytes and fibroblasts against SIRO. We propose that B7-33 might be effective against acute MI and a possible alternative to recombinant relaxin for clinical utility.