In the event of a myocardial infarction, current interventions aim to reopen the occluded vessel to reduce myocardial damage and injury. Although reperfusion is essential for tissue salvage, it can cause further damage and the onset of inflammation. We show a novel anti-inflammatory effect of a fibrin-derived peptide, Bbeta15-42. This peptide competes with the fibrin fragment N-terminal disulfide knot-II (an analog of the fibrin E1 fragment) for binding to vascular endothelial (VE)-cadherin, thereby preventing transmigration of leukocytes across endothelial cell monolayers. In acute or chronic rat models of myocardial ischemia-reperfusion injury, Bbeta15-42 substantially reduces leukocyte infiltration, infarct size and subsequent scar formation. The pathogenic role of fibrinogen products is further confirmed in fibrinogen knockout mice, in which infarct size was substantially smaller than in wild-type animals. Our findings conclude that the interplay of fibrin fragments, leukocytes and VE-cadherin contribute to the pathogenesis of myocardial damage and reperfusion injury. The naturally occurring peptide Bbeta15-42 represents a potential candidate for reperfusion therapy in humans.

Objective-Interleukin (IL)-33 is the most recently described member of the IL-1 family of cytokines and it is a ligand of the ST2 receptor. While the effects of IL-33 on the immune system have been extensively studied, the properties of this cytokine in the cardiovascular system are much less investigated.

Interleukin-33 (IL-33) is a recently described member of the IL-1 family of cytokines, which was identified as a ligand for the ST2 receptor. Components of the IL-33/ST2 system were shown to be expressed in normal and pressure overloaded human myocardium, and soluble ST2 (sST2) has emerged as a prognostic biomarker in myocardial infarction and heart failure. However, expression and regulation of IL-33 in human adult cardiac myocytes and fibroblasts was not tested before. In this study we found that primary human adult cardiac fibroblasts (HACF) and human adult cardiac myocytes (HACM) constitutively express nuclear IL-33 that is released during cell necrosis. Tumor necrosis factor (TNF)-α, interferon (IFN)-γ and IL-1β significantly increased both IL-33 protein and IL-33 mRNA expression in HACF and HACM as well as in human coronary artery smooth muscle cells (HCASMC). The nuclear factor-κB (NF-κB) inhibitor dimethylfumarate inhibited TNF-α- and IL-1β-induced IL-33 production as well as nuclear translocation of p50 and p65 NF-κB subunits in these cells. Mitogen-activated protein/extracellular signal-regulated kinase inhibitor U0126 abrogated TNF-α-, IFN-γ-, and IL-1β-induced and Janus-activated kinase inhibitor I reduced IFN-γ-induced IL-33 production. We detected IL-33 mRNA in human myocardial tissue from patients undergoing heart transplantation (n = 27) where IL-33 mRNA levels statistically significant correlated with IFN-γ (r = 0.591, p = 0.001) and TNF-α (r = 0.408, p = 0.035) mRNA expression. Endothelial cells in human heart expressed IL-33 as well as ST2 protein. We also reveal that human cardiac and vascular cells have different distribution patterns of ST2 isoforms (sST2 and transmembrane ST2L) mRNA expression and produce different amounts of sST2 protein. Both human macrovascular (aortic and coronary artery) and heart microvascular endothelial cells express specific mRNA for both ST2 isoforms (ST2L and sST2) and are a source for sST2 protein, whereas cardiac myocytes, cardiac fibroblasts and vascular SMC express only minor amounts of ST2 mRNA and do not secrete detectable amounts of sST2 antigen. In accordance with the cellular distribution of ST2 receptor, human cardiac fibroblasts and myocytes as well as HCASMC did not respond to treatment with IL-33, as recombinant human IL-33 did not induce NF-κB p50 and p65 subunits nuclear translocation or increase IL-6, IL-8, and monocyte chemoattractant protein (MCP-1) level in HACF, HACM and HCASMC. In summary, we found that endothelial cells seem to be the source of sST2 and the target for IL-33 in the cardiovascular system. IL-33 is expressed in the nucleus of human adult cardiac fibroblasts and myocytes and released during necrosis. Proinflammatory cytokines TNF-α, IFN-γ and IL-1β increase IL-33 in these cells in vitro, and IL-33 mRNA levels correlated with TNF-α and IFN-γ mRNA expression in human myocardial tissue.