Anti-inflammatory therapies in myocardial infarction: failures, hopes and challenges

Abstract

In the infarcted heart, the damage-associated molecular pattern proteins released by necrotic cells trigger both myocardial and systemic inflammatory responses. Induction of chemokines and cytokines and up-regulation of endothelial adhesion molecules mediate leukocyte recruitment in the infarcted myocardium. Inflammatory cells clear the infarct of dead cells and matrix debris and activate repair by myofibroblasts and vascular cells, but may also contribute to adverse fibrotic remodelling of viable segments, accentuate cardiomyocyte apoptosis and exert arrhythmogenic actions. Excessive, prolonged and dysregulated inflammation has been implicated in the pathogenesis of complications and may be involved in the development of heart failure following infarction. Studies in animal models of myocardial infarction (MI) have suggested the effectiveness of pharmacological interventions targeting the inflammatory response. This article provides a brief overview of the cell biology of the post-infarction inflammatory response and discusses the use of pharmacological interventions targeting inflammation following infarction. Therapy with broad anti-inflammatory and immunomodulatory agents may also inhibit important repair pathways, thus exerting detrimental actions in patients with MI. Extensive experimental evidence suggests that targeting specific inflammatory signals, such as the complement cascade, chemokines, cytokines, proteases, selectins and leukocyte integrins, may hold promise. However, clinical translation has proved challenging. Targeting IL-1 may benefit patients with exaggerated post-MI inflammatory responses following infarction, not only by attenuating adverse remodelling but also by stabilizing the atherosclerotic plaque and by inhibiting arrhythmia generation. Identification of the therapeutic window for specific interventions and pathophysiological stratification of MI patients using inflammatory biomarkers and imaging strategies are critical for optimal therapeutic design.

Figure 1

The inflammatory response following MI can be divided into three phases: the alarm phase, the leukocyte mobilization phase and the resolution phase. Necrotic cardiomyocytes (CM) release alarmins (heat shock proteins [HSP], high mobility group box 1 [HMGB1], extracellular RNA/eRNA, IL‐1α and other danger signals) that activate innate immune signalling pathways. ECM fragments also trigger inflammatory signalling. Induction of pro‐inflammatory cytokines, such as IL‐1, and chemokines mediates recruitment of neutrophils (N) and pro‐inflammatory monocytes (Mo) through interactions with endothelial cells (EC) that involve selectins and integrins. Clearance of dead cells and matrix debris from the infarct triggers transition to the resolution phase. Anti‐inflammatory lymphocyte (L) and macrophage (Ma) subsets release mediators that suppress pro‐inflammatory signalling, such as IL‐10, TGF‐β and pro‐resolving lipid mediators. Experimental studies suggest that inhibition of the complement cascade, IL‐1β antagonism, CCL2 inhibition, selectin and leukocyte integrin neutralization may be promising therapeutic strategies for patients with MI. F, fibroblast.