Protective effects of anti-neutrophil antibody against myocardial ischemia/reperfusion injury in rats

Immune cells as targets for cardioprotection: new players and novel therapeutic opportunities

New therapies are required to reduce myocardial infarct (MI) size and prevent the onset of heart failure in patients presenting with acute myocardial infarction (AMI), one of the leading causes of death and disability globally. In this regard, the immune cell response to AMI, which comprises an initial pro-inflammatory reaction followed by an anti-inflammatory phase, contributes to final MI size and post-AMI remodelling [changes in left ventricular (LV) size and function]. The transition between these two phases is critical in this regard, with a persistent and severe pro-inflammatory reaction leading to adverse LV remodelling and increased propensity for developing heart failure. In this review article, we provide an overview of the immune cells involved in orchestrating the complex and dynamic inflammatory response to AMI-these include neutrophils, monocytes/macrophages, and emerging players such as dendritic cells, lymphocytes, pericardial lymphoid cells, endothelial cells, and cardiac fibroblasts. We discuss potential reasons for past failures of anti-inflammatory cardioprotective therapies, and highlight new treatment targets for modulating the immune cell response to AMI, as a potential therapeutic strategy to improve clinical outcomes in AMI patients. This article is part of a Cardiovascular Research Spotlight Issue entitled 'Cardioprotection Beyond the Cardiomyocyte', and emerged as part of the discussions of the European Union (EU)-CARDIOPROTECTION Cooperation in Science and Technology (COST) Action, CA16225.

Ticagrelor attenuates myocardial ischaemia-reperfusion injury possibly through downregulating galectin-3 expression in the infarct area of rats

AIMS

The full benefits of myocardial revascularization strategies applied to acute myocardial infarction patients might be reduced by myocardial ischaemia and reperfusion (I/R) injury. It is known that inflammation plays an important role in the pathogenesis of I/R injury and galectin-3, a known inflammatory factor, is actively involved in ischaemia-induced inflammation and fibrosis of various organs. Previous studies demonstrated that anti-platelets therapy with ticagrelor, a new P2Y12 receptor antagonist, could effectively attenuate myocardial I/R injury and I/R injury-related inflammatory responses. It remains unknown whether the cardioprotective effects of ticagrelor are also mediated by modulating myocardial galectin-3 expression.

METHODS

We determined the ratio of infarct area (IA)/area at risk (AAR), expression of galectin-3, TNF-α and IL-6 in infarct area of rats treated with placebo (equal volume saline per gastric gavage immediately after LAD ligation, then once daily till study end) or ticagrelor (150 mg kg^-1 dissolved in saline per gastric gavage immediately after LAD ligation, then once daily till study end) at 24 h, 3 and 7 days post I (45 min)/R injury. Sham-operated rats served as control.

RESULTS

Our results showed that ticagrelor treatment significantly reduced IA/AAR ratio at 3 and 7 days post I/R, downregulated mRNA and protein expression of galectin-3, as well as mRNA expression of TNF-α and IL-6 in infarct area at 24 h, 3 and 7 days post I/R.

CONCLUSIONS

Our results suggest that the cardioprotective effects of ticagrelor might partly be mediated by downregulating galectin-3 expression in infarct area in this rat model of myocardial I/R injury.

Efferocytosis and Outside-In Signaling by Cardiac Phagocytes. Links to Repair, Cellular Programming, and Intercellular Crosstalk in Heart

Phagocytic sensing and engulfment of dying cells and extracellular bodies initiate an intracellular signaling cascade within the phagocyte that can polarize cellular function and promote communication with neighboring non-phagocytes. Accumulating evidence links phagocytic signaling in the heart to cardiac development, adult myocardial homeostasis, and the resolution of cardiac inflammation of infectious, ischemic, and aging-associated etiology. Phagocytic clearance in the heart may be carried out by professional phagocytes, such as macrophages, and non-professional cells, including myofibrolasts and potentially epithelial cells. During cardiac development, phagocytosis initiates growth cues for early cardiac morphogenesis. In diseases of aging, including myocardial infarction, heightened levels of cell death require efficient phagocytic debridement to salvage further loss of terminally differentiated adult cardiomyocytes. Additional risk factors, including insulin resistance and other systemic risk factors, contribute to inefficient phagocytosis, altered phagocytic signaling, and delayed cardiac inflammation resolution. Under such conditions, inflammatory presentation of myocardial antigen may lead to autoimmunity and even possible rejection of transplanted heart allografts. Increased understanding of these basic mechanisms offers therapeutic opportunities.

Treatment with anti-RANKL antibody reduces infarct size and attenuates dysfunction impacting on neutrophil-mediated injury

Selective pharmacological treatments targeting reperfusion injury produced modest protective effects and might be associated with immunosuppression. In order to identify novel and better-tolerated approaches, we focused on the neutralization of receptor activator of nuclear factor kappa-B ligand [RANKL], a cytokine recently shown to activate inflammatory cells (i.e. neutrophils) orchestrating post-infarction injury and repair. Myocardial ischemia (60min) and reperfusion injury was surgically induced in C57Bl/6 mice. In hearts and serum, RANKL was early upregulated during reperfusion. A "one-shot" injection with neutralizing anti-RANKL IgG during ischemia ameliorated myocardial infarct size and function, but not adverse remodeling (determined by Magnetic Resonance Imaging [MRI]) as compared to Vehicle or control IgG. These beneficial effects were accompanied in vivo by reduction in cardiac neutrophil infiltration, reactive oxygen species (ROS) and MMP-9 release. Anti-RANKL IgG treatment suppressed sudden peak of neutrophil granule products in mouse serum early after reperfusion onset. In vitro, RANK mRNA expression was detected in isolated mouse neutrophils. Co-incubation with neutralizing anti-RANKL IgG abrogated RANKL-induced mouse neutrophil degranulation and migration, suggesting a critical role of RANKL in neutrophil-mediated injury. Conversely, anti-RANKL IgG did not affect salvage pathways in cardiac cells (i.e. ERK p42/p44, Akt and STAT-3) or macrophage cardiac infiltration. Finally, treatment with anti-RANKL IgG showed no effect on B and T lymphocyte polarization (in serum, spleen and infarcted myocardium) and circulating chemokines as compared with Vehicle or control IgG. In conclusion, acute treatment with anti-RANKL IgG improved cardiac infarct size and function by potentially impacting on neutrophil-mediated injury and repair.

Volatile anaesthetics reduce neutrophil inflammatory response by interfering with CXC receptor-2 signalling

BACKGROUND

Growing evidence suggests a protective effect of volatile anaesthetics in ischaemia-reperfusion (I/R)-injury, and the accumulation of neutrophils is a crucial event. Pro-inflammatory cytokines carrying the C-X-C-motif including interleukin-8 (IL-8) and CXC-ligand 1 (CXCL1) activate CXC receptor-1 (CXCR1; stimulated by IL-8), CXC receptor-2 (CXCR2; stimulated by IL-8 and CXCL1), or both to induce CD11b-dependent neutrophil transmigration. Inhibition of CXCR1, CXCR2, or both reduces I/R-injury by preventing neutrophil accumulation. We hypothesized that interference with CXCR1/CXCR2 signalling contributes to the well-established beneficial effect of volatile anaesthetics in I/R-injury.

METHODS

Isolated human neutrophils were stimulated with IL-8 or CXCL1 and exposed to volatile anaesthetics (sevoflurane/desflurane). Neutrophil migration was assessed using an adapted Boyden chamber. Expression of CD11b, CXCR1, and CXCR2 was measured by flow cytometry. Blocking antibodies against CXCR1/CXCR2/CD11b and phorbol myristate acetate were used to investigate specific pathways.

RESULTS

Volatile anaesthetics reduced CD11b-dependent neutrophil transmigration induced by IL-8 by >30% and CD11b expression by 18 and 27% with sevoflurane/desflurane, respectively. This effect was independent of CXCR1/CXCR2 expression and CXCR1/CXCR2 endocytosis. Inhibition of CXCR1 signalling did not affect downregulation of CD11b with volatile anaesthetics. Blocking of CXCR2-signalling neutralized effects by volatile anaesthetics on CD11b expression. Specific stimulation of CXCR2 with CXCL1 was sufficient to induce upregulation of CD11b, which was impaired with volatile anaesthetics. No effect of volatile anaesthetics was observed with direct stimulation of protein kinase C located downstream of CXCR1/CXCR2.

CONCLUSION

Volatile anaesthetics attenuate neutrophil inflammatory responses elicited by CXC cytokines through interference with CXCR2 signalling. This might contribute to the beneficial effect of volatile anaesthetics in I/R-injury.

Activation of hypoxia-inducible factor-1 via prolyl-4 hydoxylase-2 gene silencing attenuates acute inflammatory responses in postischemic myocardium

Emerging research suggests that oxidant-driven transcription of key cytokine/chemokine networks within the myocardium plays a crucial role in producing ischemia-reperfusion (I/R) injury. We recently showed that activation of hypoxia-inducible factor-1 (HIF-1) attenuated cardiac I/R injury. Diminished injury in these prior studies was associated with significant reductions in circulating interleukin-8 levels, suggesting that HIF-1 may play an important role in modulating postischemic cardiac inflammation. In the current study, we examined the role of HIF-1 activation in modulating proinflammatory chemokine [macrophage inflammatory protein (MIP)-2, cytokine-induced neutrophil chemoattractant factor (KC), and lipopolysaccharide-induced CXC chemokine (LIX)] and adhesion molecule [intercellular adhesion molecule (ICAM)-1] expression in murine cardiomyocytes in vitro (HL-1 cell line) and in intact murine hearts following in vivo I/R injury. Our results show that HIF-1 activation induced both pharmacologically by the prolyl hydroxylase inhibitor dimethyloxallyl glycine and via small-interfering RNA (siRNA)-mediated prolyl-4 hydroxylase-2 (P4HA2) gene silencing significantly attenuated tumor necrosis factor-α-induced chemokine (KC and LIX) and ICAM-1 expression in cardiomyocytes. In vivo, postischemic hearts obtained from animals receiving the P4HA2 siRNA (HIF-1 activation) exhibited significantly reduced CXC chemokine (MIP-2, KC, and LIX), CC chemokine (monocyte chemoattractant protein-1), and ICAM-1 expression when compared with postischemic hearts from either saline I/R controls or postischemic hearts from animals receiving a nontargeting control siRNA (no HIF-1 activation). Diminished chemokine and adhesion molecule expression in HIF-1-activated postischemic hearts was associated with significantly reduced polymorphonuclear leukocyte infiltration and myocardial infarct size (>60% reduction P4HA2 siRNA I/R vs. saline I/R, P < 0.001, n = 6). In conclusion, these results demonstrate for the first time that HIF-1 activation following infusion of siRNA to P4HA2 plays a key role in modulating I/R-associated cardiac inflammatory responses.

ELR+ CXC chemokines and their receptors (CXC chemokine receptor 1 and CXC chemokine receptor 2) as new therapeutic targets

ELR+ CXC chemokines, by direct interaction with their cell surface receptors CXC chemokine receptor 1 (CXCR1) and CXC chemokine receptor 2 (CXCR2), are believed to be crucially involved in the direct migration and activation of leukocytes. ELR+ CXC chemokines are supposed to play a key role in several inflammatory diseases and this makes ELR+ CXC chemokines and their receptors attractive therapeutic targets. The first aim of this review is to discuss the potential pathological role of ELR+ CXC chemokines in different pathologies, including ulcerative colitis (UC), ischaemia/reperfusion injury (RI), bronchiolitis obliterans syndrome (BOS) and tumor progression. Moreover, the most recently described inhibitors of ELR+ CXC chemokines and their therapeutic indications will be reviewed. Finally, the mode of action and the potential therapeutical use of reparixin, a new potent and selective inhibitor of CXCR1/2 activity, and its chemical derivatives are also discussed.

APT070 (Mirococept), a membrane-localised complement inhibitor, inhibits inflammatory responses that follow intestinal ischaemia and reperfusion injury

Activation of the complement system has been shown to play a major role in the mediation of reperfusion injury. Here, we assessed the effects of APT070 (Mirococept), a novel membrane-localised complement inhibitor based on a recombinant fragment of soluble CR1, on the local, remote and systemic injuries following intestinal ischaemia and reperfusion (I/R) in the rat. In a model of mild I/R injury (30 min of ischaemia and 30 min of reperfusion), APT070 dose-dependently (1-10 mg kg(-1)) inhibited the increase in vascular permeability of and neutrophil influx into intestine and lungs. Maximal inhibition occurred at 10 mg kg(-1). Following severe I/R injury (120 min of ischaemia and 120 min of reperfusion), APT070 (10 mg kg(-1)) markedly prevented neutrophil influx and the increase in vascular permeability both in the intestine and the lungs.APT070 also effectively suppressed the increase of tissue (intestine and lungs) and serum concentrations of TNF-alpha and IL-6, but not those of IL-1beta or IL-10. There was no significant reduction of mortality in the APT070 group. In conclusion, treatment with the membrane-targeted complement inhibitor APT070 significantly reduced the hyperinflammatory response after mild and severe ischaemia and reperfusion injury (I/RI) in rats. APT070 may be effective in therapeutic indications involving gut I/RI.

The balance between the production of tumor necrosis factor-alpha and interleukin-10 determines tissue injury and lethality during intestinal ischemia and reperfusion

A major goal in the treatment of acute ischemia of a vascular territory is to restore blood flow to normal values, i.e. to "reperfuse" the ischemic vascular bed. However, reperfusion of ischemic tissues is associated with local and systemic leukocyte activation and trafficking, endothelial barrier dysfunction in postcapillary venules, enhanced production of inflammatory mediators and great lethality. This phenomenon has been referred to as "reperfusion injury" and several studies demonstrated that injury is dependent on neutrophil recruitment. Furthermore, ischemia and reperfusion injury is associated with the coordinated activation of a series of cytokines and adhesion molecules. Among the mediators of the inflammatory cascade released, TNF-alpha appears to play an essential role for the reperfusion-associated injury. On the other hand, the release of IL-10 modulates pro-inflammatory cytokine production and reperfusion-associated tissue injury. IL-1beta, PAF and bradykinin are mediators involved in ischemia and reperfusion injury by regulating the balance between TNF-alpha and IL-10 production. Strategies that enhance IL-10 and/or prevent TNF-alpha concentration may be useful as therapeutic adjuvants in the treatment of the tissue injury that follows ischemia and reperfusion.

Cryptococcal capsular glucuronoxylomannan reduces ischaemia-related neutrophil influx

BACKGROUND

The capsular polysaccharide glucuronoxylomannan (GXM) of Cryptococcus neoformans interferes with the chemotaxis and transendothelial migration of neutrophils. Intravenous administration of purified GXM has been shown to reduce the influx of inflammatory cells in an animal model of bacterial infection. Here we show that isolated GXM can also interfere with neutrophil migration in a model of inflammation not related to infection. We assessed the effects of intravenous GXM on neutrophil infiltration in a rat model of myocardial ischaemia, where neutrophil infiltration has been shown to contribute to postischaemic reperfusion injury.

MATERIALS AND METHODS

Rats were subjected to coronary artery ligation followed by a 3-h reperfusion period. Myeloperoxidase-activity was measured in the ischaemic tissues as a marker of neutrophil infiltration.

RESULTS

Intravenous administration of GXM markedly reduced the influx of neutrophils in the ischaemic myocardium as measured by a 65% reduction of tissue MPO activity. This reduction of MPO activity was clearly correlated to the serum concentration of GXM. As complement activation by GXM was minimal at the doses applied in vivo, it is unlikely that generation of chemotactic C5a in the circulation by GXM caused the observed reduction in leucocyte migration.

CONCLUSION

Purified cryptococcal GXM has the ability to reduce neutrophil influx even outside the scope of infection.

Repertaxin, a novel inhibitor of rat CXCR2 function, inhibits inflammatory responses that follow intestinal ischaemia and reperfusion injury

1. Neutrophils are thought to play a major role in the mediation of reperfusion injury. CXC chemokines are known inducers of neutrophil recruitment. Here, we assessed the effects of Repertaxin, a novel low molecular weight inhibitor of human CXCL8 receptor activation, on the local, remote and systemic injuries following intestinal ischaemia and reperfusion (I/R) in the rat. 2. Pre-incubation of rat neutrophils with Repertaxin (10(-11)-10(-6) m) inhibited the chemotaxis of neutrophils induced by human CXCL8 or rat CINC-1, but not that induced by fMLP, PAF or LTB(4), in a concentration-dependent manner. Repertaxin also prevented CXCL8-induced calcium influx but not CXCL8 binding to purified rat neutrophils. 2. In a model of mild I/R injury (30 min of ischaemia and 30 min of reperfusion), Repertaxin dose-dependently (3-30 mg kg(-1)) inhibited the increase in vascular permeability and neutrophil influx. Maximal inhibition occurred at 30 mg kg(-1). 4. Following severe I/R injury (120 min of ischaemia and 120 min of reperfusion), Repertaxin (30 mg kg(-1)) markedly prevented neutrophil influx, the increase in vascular permeability both in the intestine and the lungs. Moreover, there was prevention of haemorrhage in the intestine of reperfused animals. 5. Repertaxin effectively suppressed the increase in tissue (intestine and lungs) and serum concentrations of TNF-alpha and the reperfusion-associated lethality. 6. For comparison, we also evaluated the effects of an anti-CINC-1 antibody in the model of severe I/R injury. Overall, the antibody effectively prevented tissue injury, systemic inflammation and lethality. However, the effects of the antibody were in general of lower magnitude than those of Repertaxin. 7. In conclusion, CINC-1 and possibly other CXC chemokines, acting on CXCR2, have an important role during I/R injury. Thus, drugs, such as Repertaxin, developed to block the function of the CXCR2 receptor may be effective at preventing reperfusion injury in relevant clinical situations.

Association of peripheral neutrophilia with adverse angiographic outcomes in ST-elevation myocardial infarction

We hypothesized that absolute and relative neutrophilia would be associated with adverse angiographic outcomes in the 394 patient Limitation of Myocardial Infarction Following Thrombolysis in Acute Myocardial Infarction (LIMIT) Acute Myocardial Infarction (AMI) trial of fibrinolysis in ST-elevation myocardial infarction. The mean neutrophil count was 7.9 x 10(9)/L, with a mean neutrophil percentage of 72%. Patients with time from symptom onset to fibrinolytic treatment more than the median (2.7 hours) had a higher neutrophil count and percentage of neutrophils than patients with shorter time to treatment. Patients with a closed infarct-related artery at 90 minutes (Thrombolysis In Myocardial Infarction [TIMI] grade 0/1 flow) had higher neutrophil counts (8.8 +/- 3.8 vs 7.6 +/- 3.0, p = 0.02) but no difference in the percentage of neutrophils than patients with an open artery. Higher neutrophil counts were also mildly correlated with longer corrected TIMI frame counts (CTFC) in the infarct-related artery (r = 0.14, p = 0.02). Patients with impaired myocardial perfusion by TIMI myocardial perfusion grade (TMPG) had a greater percentage of neutrophils (73.2 +/- 10.7% for TMPG 0/1 vs 69.9 +/- 12.6% for TMPG 2/3, p = 0.047) but no detectable difference in neutrophil counts (8.2 +/- 3.3 vs 7.7 +/- 2.9, p = 0.24). There were no significant associations between other indexes in the cell differential and angiographic or clinical outcomes. Higher neutrophil counts remained independently associated with both closed arteries and CTFC in multivariable models controlling for age, left anterior descending artery infarct location, time to treatment, and pulse and blood pressure on admission. A greater percentage of neutrophils remained independently associated with impaired microvascular perfusion in a similar multivariable model. In patients with ST-elevation myocardial infarction, absolute and relative neutrophilia were associated with impaired epicardial and microvascular perfusion.