Abstract Body (Do not enter title and authors here): Background: Myocardial ischemia-reperfusion (IR) injury exacerbates cardiomyocyte death following acute myocardial infarction. Macrophage migration inhibitory factor (MIF) is a redox-sensitive cytokine and atypical chemokine known to exert context-dependent cardioprotective effects. The mechanisms are incompletely understood. We hypothesized that recombinant MIF (moMIF), when administered at reperfusion, may mitigate myocardial injury by scavenging neutrophil-derived reactive oxygen species (ROS) / hypochlorous acid (HOCl), a major oxidative effector of reperfusion injury, despite MIF’s effect on neutrophil attraction and its promoting effect on neutrophil priming.
Methods: Human neutrophil chemotaxis was quantified using a 3D μ-Slide chamber following stimulation with MIF (40 nM), oxidized MIF (noxMIF, 40 nM) or HOCl (100 nM). Migration was quantified by forward migration index (FMI). In parallel, male C57BL/6N mice (n=18) underwent 60 min left anterior descending (LAD) coronary occlusion followed by 48 h of reperfusion. Mice received intravenous phosphate buffer (control), mouse MIF (moMIF), or noxMIF (10 μg) 5 min before reperfusion. Myocardial infarct size (IS) and area at risk (AAR) were determined by Evans blue/TTC staining. Data were analyzed by one-way ANOVA with Bonferroni post-hoc correction.
Results: MIF significantly enhanced neutrophil migration (FMI 0.16±0.05 vs. control 0.02±0.02, P=0.0257), while, similar to HOCl control, noxMIF lacked chemotactic activity (FMI 0.03±0.05, P>0.9999; FMI -0.06±0.09, P=0.2090). In vivo, moMIF markedly reduced IS/AAR (39.23% ± 9.5%) compared to control (65.44% ± 14.03%, P=0.041). noxMIF did not confer protection (55.48% ± 7.6%, P=0.620 vs. control; P=0.056 vs. moMIF).
Conclusions: These findings identify moMIF as a dual-function cardioprotective agent when administered at reperfusion: it protects cardiomyocytes from IR damage, but also recruits neutrophils and enhances their HOCl production capacity. Our current data comparing the capacities of MIF vs noxMIF on neutrophil migration and cardiac IR damage in vivo, collectively identify noxMIF formation as a ROS/HOCl scavenging mechanism that also serves to limit the inflammatory recruitment response. Targeting MIF-ROS/HOCl interactions may represent a novel translational strategy to attenuate myocardial reperfusion injury.