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Aims: Restoration of coronary blood flow is crucial in the treatment of acute myocardial infarction. Reperfusion, however, induces ischaemia-reperfusion (IR) injury, which further deteriorates myocardial function. The innate immune system plays an important role in this process, mediating rapid influx of immune cells into the reperfused myocardium. Leukotriene B4 is an important leucocyte chemoattractant, performing its actions through binding to its specific receptor BLT1. We hypothesized that treatment with LSN2792613, a selective BLT1 antagonist, reduces infarct size (IS) in a mouse model of myocardial IR injury., Methods and Results: Male C57Bl/6J mice were subjected to myocardial ischaemia for 30 min by surgical coronary artery ligation, followed by reperfusion. Mice received either LSN2792613 or vehicle, three times daily (orally) for up to 72 h after reperfusion. BLT1 inhibition with LSN2792613 reduced IS compared with vehicle treatment (26.9 ± 2.7 vs. 34.9 ± 2.2%, P = 0.030) at 24 h after reperfusion. The levels of IL-6 and keratinocyte chemoattractant were reduced in the infarcted tissue of LSN2792613-treated mice. Reduced apoptosis in LSN2792613-treated mice was suggested by increased levels of phosphorylated JNK and GSK3α/β, and confirmed by flow cytometric analysis showing less apoptotic and necrotic cardiomyocytes in the infarcted myocardium. Echocardiography at 4 weeks after myocardial IR showed a slightly higher ejection fraction and stroke volume in mice treated with LSN2792613 compared with vehicle-treated mice, whereas left ventricular volumes were comparable., Conclusion: Selective BLT1 inhibition with LSN2792613 reduces inflammation and apoptosis following IR, resulting in reduced IS, and therefore might be a promising strategy to prevent myocardial IR injury., (Published on behalf of the European Society of Cardiology. All rights reserved. © The Author 2015. For permissions please email: journals.permissions@oup.com.)

Aims: Early reperfusion is mandatory for the treatment of acute myocardial infarction. This process, however, also induces additional loss of viable myocardium, called ischaemia-reperfusion (IR) injury. Complement activation plays an important role in IR injury, partly through binding of C5a to its major receptor (C5aR). We investigated the role of C5aR on infarct size and cardiac function in a model for myocardial IR injury., Methods and Results: BALB/c (WT) mice and C5aR(-/-) mice underwent coronary occlusion for 30 min, followed by reperfusion. Infarct size, determined 24 h after IR, was reduced in C5aR(-/-) mice compared with WT mice (28.5 ± 2.1 vs. 35.7 ± 2.5%, P = 0.017). Bone marrow (BM) chimaera experiments showed that this effect was due to the absence of C5aR on circulating leucocytes, since a similar reduction in infarct size was observed in WT mice with C5aR-deficient BM cells (25.3 ± 2.2 vs. 34.6 ± 2.8%, P < 0.05), but not in C5aR(-/-) mice with WT BM cells. Reduced infarct size was associated with fewer neutrophils, T cells, and macrophages in the infarcted area 24 h after IR in C5aR(-/-) mice, and also with lower levels of Caspase-3/7 indicating less inflammation and apoptosis. Echocardiography 4 weeks after IR showed an improved ejection fraction in C5aR(-/-) mice (25.8 ± 5.5 vs. 19.2 ± 5.4%, P < 0.001)., Conclusion: The absence of C5aR on circulating leucocytes reduces infarct size, is associated with reduced leucocyte infiltration and with less apoptosis in the infarcted myocardium, and improves cardiac function in a mouse model of myocardial IR injury. Selective blocking of C5aR might be a promising strategy to prevent myocardial IR injury., (Published on behalf of the European Society of Cardiology. All rights reserved. © The Author 2014. For permissions please email: journals.permissions@oup.com.)

One of the major therapeutic challenges in the arena of interventional cardiology is to design strategies aimed at reducing myocardial tissue damage after myocardial infarction. In response to tissue injury, an innate immune response is initiated that orchestrates homeostatic responses and is a prerequisite for subsequent wound healing. An exaggerated inflammatory reaction, however, countervenes these beneficial effects and contributes to maladaptive tissue damage. Herein, we discuss the pathways involving the innate immune system that have been investigated in the setting of myocardial ischaemia and reperfusion injury. Endogenous 'danger' signals [danger-associated molecular patterns (DAMPs)] are expressed following tissue injury and alert the innate immune system. Toll-like receptors and the complement system are activated, resulting in an inflammatory reaction involving inflammatory cell influx and the production and release of inflammatory cytokines. A potential involvement of cell-derived microparticles in the modulation of the innate immune response following myocardial injury will also be discussed. Our future challenge lies within the counteraction of maladaptive inflammatory cascades, without interfering in the benign wound healing response, and in translating these anti-inflammatory strategies into clinical practice.

Aims: Neutrophil gelatinase-associated lipocalin (NGAL) is an effector molecule of the innate immune system. One of its actions is the prolongation of matrix metalloproteinase-9 (MMP-9) activity by the formation of a degradation-resistant NGAL/MMP-9 complex. We studied NGAL in human atherosclerotic lesions and we examined whether NGAL could act as a target for molecular imaging of atherosclerotic plaques., Methods and Results: Increased levels of NGAL and the NGAL/MMP-9 complex were associated with high lipid content, high number of macrophages, high interleukin-6 (IL-6) and IL-8 levels, and low smooth muscle cell content in human atherosclerotic lesions obtained during carotid endarterectomy (n= 122). Moreover, plaque levels of NGAL tended to be higher when intra-plaque haemorrhage (IPH) or luminal thrombus was present (n= 77) than without the presence of IPH or thrombus (n= 30). MMP-9 and -8 activities were strongly related to NGAL levels. The enhancement on magnetic resonance (MR) images of the abdominal aorta of ApoE(-/-)/eNOS(-/-) mice was observed at 72 h after injection of NGAL/24p3-targeted micelles. The specificity of these results was validated by histology, and co-localization of micelles, macrophages, and NGAL/24p3 was observed., Conclusion: NGAL is highly expressed in atheromatous human plaques and associated with increased MMP-9 activity. NGAL can be detected in murine atherosclerotic arteries using targeted high-resolution MR imaging. Therefore, we conclude that NGAL might serve as a novel imaging target for the detection of high-risk plaques.

Aims: Adaptive collateral artery growth (arteriogenesis) is an important mechanism to maintain tissue perfusion upon arterial obstruction. Leucocytes and inflammatory mediators play a crucial role in this process. Depletion of the nuclear factor kappa B (NF-κB) p50 subunit modulates inflammatory processes in cardiovascular disease. We hypothesized that NF-κB p50 is a regulator of the inflammatory response after arterial occlusion and subsequent collateral perfusion., Methods and Results: Unilateral femoral artery ligation was performed in NF-κB p50-/- and wild-type (Wt, B6/129PF2) mice. Seven days after arterial occlusion, tissue perfusion restoration was significantly enhanced in NF-κB p50-/- mice compared with Wt mice (42.9 ± 3.9 vs. 32.0 ± 2.6% perfusion recovery, P = 0.04). Transplantation of NF-κB p50-/- bone marrow (bm) into Wt mice and vice versa showed that the effect of p50 subunit depletion can be predominantly attributed to the bone marrow-derived circulating cells (NF-κB p50-/- bm in Wt mice 42.1 ± 1.5%, Wt bm in NF-κB p50-/- mice 35.4±1.5% perfusion recovery). Histological analyses revealed a more elaborate extravasation of monocytes in hindlimb tissue of NF-κB p50-/- mice. Chemotaxis assays confirmed the increased migration ability of NF-κB p50-/- monocytes, which may be due to an observed increased integrin expression. Upon stimulation of blood from NF-κB p50-/- and Wt mice more interleukin-6 was produced, confirming the pro-inflammatory phenotype in absence of the p50 subunit., Conclusion: Depletion of the NF-κB p50 subunit enhances collateral artery growth. Its absence in circulating cells improves tissue perfusion restoration after femoral artery ligation by increasing macrophage influx into the growing collateral vessels.

Physiological and pathological tissue remodeling needs an orderly degradation of the extracellular matrix. Matrix metalloproteinases (MMPs) are proteases capable of degrading different extracellular matrix components, including collagen and elastin. MMP expression is strongly enhanced in vascular pathologies such as stenosis following balloon dilation, in-stent restenosis, sustained flow changes, aneurysm formation, and atherosclerosis. Experimental studies have revealed that some biological actions of MMPs aggravate a pathological condition, whereas others may be beneficial for the patient suffering from atherosclerotic disease. Therefore, a better understanding of the biological consequence and regulation of MMP activity is critical for the design and potential application of specific MMP inhibitors in vascular disease. In this review, we will give an overview of preclinical experimental studies using MMP inhibitors with the objective to influence vascular occlusive diseases, and we will also highlight new targets that influence MMP expression and activity and that possess potential for therapeutic interventions.

Background: Furin-like proprotein convertases (PCs) are proteolytic activators of proproteins, like membrane type 1-matrix metalloproteinase (MT1-MMP) and transforming growth factor beta (TGF-beta), that are described in the arterial response to injury. However, the involvement of furin-like PCs in the arterial response to injury has not been studied yet. We studied furin, MT1-MMP, MMP levels and TGF-beta signaling after arterial injury. We also investigated the effect of an inhibitor of furin-like PCs, alpha1-antitrypsin Portland (alpha1-PDX), on arterial injury following balloon dilation., Methods and Results: NZW rabbit femoral and iliac arteries (N=42) were balloon dilated unilaterally and harvested after 2, 7, 14, 28 or 42 days. Furin mRNA levels were increased after 2 and 7 days. MMP-2 and MT1-MMP levels were increased after day 7 and TGF-beta signaling, by phosphorylating Smad 1/5 and 2/3, was increased at all time points. Inhibition of furin-like PCs, by adenoviral over-expression of alpha1-PDX, blocked proTGF-beta activation and Smad phosphorylation, and reduced MT1-MMP and MMP-2 activation (N=5). In vivo adventitial inhibition of furin-like PCs (N=9) resulted in a reduction of 13.1+/-5.2% in advential and 23.6+/-7.9% in intimal areas (P<0.05), but had no effect on lumen size due to decreased vessel areas., Conclusions: This study demonstrates that furin-like PCs are involved in the arterial response to injury possibly through activation of the TGF-beta-Smad signaling pathway and identifies furin-like PCs as a possible target to inhibit intimal hyperplasia.

Background: Toll like receptors (Tlr) are essential in activation of the innate immune system. We recently described that peptidoglycan, an exogenous Tlr2 specific ligand, is present in human atherosclerotic plaques and associated with histological markers for plaque vulnerability. Also, endogenous Tlr2 ligands can be expressed in atherosclerotic tissues. Here, we determined whether Tlr2 stimulation promotes pro-inflammatory cytokine/chemokine production in vitro and augments neointima formation and development of atherosclerotic plaques in vivo., Methods and Results: We detected Tlr2 using Western blot and RT-PCR in human coronary arteries and primary adventitial fibroblasts. RNAse protection assay demonstrated significant induction of IL-1, IL-6, IL-8 and MCP-1 mRNA after Tlr2 stimulation in human adventitial fibroblasts in vitro. ELISA demonstrated induction of IL-6, IL-8 and MCP-1. In vivo application of Pam(3)Cys-SK(4), a synthetic Tlr2 ligand, on femoral arteries of C57BL/6 wild type (WT) mice using a peri-adventitial cuff, significantly enhanced neointima formation compared to control arteries. This increased inflammatory response was not observed in Tlr2 knockout (Tlr2-/-) mice. In ApoE knockout mice (ApoE-/-), application of the same Tlr2 ligand led to a significant increase in atherosclerotic plaque development., Conclusion: Local arterial Tlr2 stimulation induced neointima and atherosclerotic plaque formation in mouse femoral arteries. Tlr2 stimulation may be an important mediator in arterial occlusive disease.

Objective: In the arterial response to injury, collagen breakdown has been studied extensively, but little is known on collagen synthesis and fiber formation. Here, we studied in vivo collagen synthesis and collagen fiber content in relation to collagen breakdown following arterial balloon injury., Methods and Results: Twenty-five New Zealand White rabbits were balloon dilated in femoral and iliac arteries and terminated at 2, 7, 14 and 28 days. From day 7, both constrictive arterial remodeling and intimal hyperplasia were observed. Collagen degradation, synthesis and fiber content were studied using zymography, quantitative Polymerase Chain Reaction, Western blotting and picrosirius red staining. Collagen synthesis, reflected by procollagen I and heat shock protein 47 (Hsp47) expression, increased at day 2 with a maximum at day 14 and was accompanied by increased collagen breakdown as reflected by matrix metalloproteinase-1 and -2 levels. Collagen content in media and adventitia only increased between days 2 and 7 after balloon injury., Conclusions: In the first week after arterial injury, increased collagen content is associated with increased collagen synthesis and degradation. However, after 1 week, collagen turnover remains high in contrast to increased collagen fiber content. This suggests that after 1 week, collagen turnover is used for other processes like cell migration and arterial remodeling.

Objective: Haptoglobin is a novel cell migration factor that is expressed in arteries after sustained flow changes and involved in arterial restructuring. Arterial restructuring is the major determinant of arterial shrinkage after balloon dilation. Although the function of extrahepatic haptoglobin expression is not yet understood, local haptoglobin expression may provide the tissue with functionally different haptoglobin due to post-translational modifications. We hypothesized that haptoglobin expression is increased during arterial restructuring after balloon dilation and compared glycosylation patterns between arterial and liver haptoglobin., Methods: Arterial haptoglobin expression was studied in rabbits at 0, 2, 7, 14 and 28 days after balloon dilation (n=36) using real-time polymerase chain reaction, Western blotting and in situ hybridization. Two-dimensional gel electrophoresis and lectin affinity blotting were used to identify liver and arterial haptoglobin glycoforms., Results: Arterial haptoglobin mRNA (5.7-fold, P=0.01) and protein levels (1.4-fold, P=0.01) were increased after balloon dilation whereas liver haptoglobin expression remained constant. Haptoglobin was expressed in the adventitia of balloon dilated rabbit arteries, which was confirmed in human atherosclerotic arteries. Comparison between liver and arterial haptoglobin demonstrated the expression of artery-specific haptoglobin glycoforms., Conclusions: This study demonstrates that arterial haptoglobin expression is increased early after balloon dilation whereas liver haptoglobin expression does not change. Furthermore, arterial haptoglobin consists of an unique set of glycoforms compared to haptoglobin produced in the liver.

Objective: Constrictive arterial remodeling following balloon angioplasty has been related to adventitial collagen accumulation and subsequent thickening and can be prevented by matrix metalloproteinase (MMP) inhibition. Following balloon dilation, we examined the effect of MMP inhibition on collagen turnover and the relationship between adventitial area and degree of constrictive remodeling., Methods: In 12 non-atherosclerotic landrace pigs, balloon dilation was performed in 39 peripheral arteries with and without MMP inhibition. Follow up with intravascular ultrasound was performed at 42 days. Collagen content was quantified using polarized light and digital image microscopy. Procollagen expression was determined using immunochemistry and Western blotting., Results: In the MMP inhibitor group, constrictive remodeling was inhibited at 42 days follow up. In control and MMP inhibitor groups, a positive relation was observed between adventitial thickness and degree of constrictive remodeling (P<0.001). Adventitial thickening and adventitial collagen content were reduced in the MMP inhibitor group (P=0.002 and P=0.001, respectively). Procollagen immunostaining, but not protein analysis on Western blotting, was decreased in the MMP inhibitor group., Conclusion: MMP inhibition impaired adventitial thickening by reduction of collagen content 42 days after balloon dilation. This might explain its inhibitory effect on constrictive remodeling.

Arterial remodeling is currently being recognized as an important determinant in vascular pathology in which narrowing of the lumen is the predominant feature. Not only expansive remodeling (enlargement), but also constrictive remodeling (shrinkage) is observed in de novo atherosclerosis, in restenosis and in transplant vasculopathy. Expansive remodeling prevents and constrictive remodeling enhances luminal narrowing by plaque formation or intimal hyperplasia. The mechanisms of the opposite remodeling modes is unknown. Insight into the processes that determine the direction of local arterial remodeling may help to develop new strategies to prevent arterial occlusive disease. In the present paper the current status of research in the field of arterial remodeling in cardiovascular disease is reviewed. Mechanisms of arterial remodeling, potential interventions to influence the mode of remodeling as well as the methodological limitations of remodeling studies are discussed.