Pexelizumab in ischemic heart disease: A systematic review and meta-analysis on 15,196 patients

Immunomodulation and immunopharmacology in heart failure

The immune system is intimately involved in the pathophysiology of heart failure. However, it is currently underused as a therapeutic target in the clinical setting. Moreover, the development of novel immunomodulatory therapies and their investigation for the treatment of patients with heart failure are hampered by the fact that currently used, evidence-based treatments for heart failure exert multiple immunomodulatory effects. In this Review, we discuss current knowledge on how evidence-based treatments for heart failure affect the immune system in addition to their primary mechanism of action, both to inform practising physicians about these pleiotropic actions and to create a framework for the development and application of future immunomodulatory therapies. We also delineate which subpopulations of patients with heart failure might benefit from immunomodulatory treatments. Furthermore, we summarize completed and ongoing clinical trials that assess immunomodulatory treatments in heart failure and present several therapeutic targets that could be investigated in the future. Lastly, we provide future directions to leverage the immunomodulatory potential of existing treatments and to foster the investigation of novel immunomodulatory therapeutics.

Potential role for pentoxifylline as an anti‑inflammatory drug for patients with acute coronary syndrome

The link between inflammation and acute coronary syndrome (ACS) remains to be sufficiently elucidated. It has been previously suggested that there is an inflammatory process associated with ACS. Pentoxifylline, a methylxanthine derivate, is known to delay the progression of atherosclerosis and reduce the risk of vascular events, especially by modulating the systemic inflammatory response. The present study is a single-blind, randomized, prospective study of pentoxifylline 400 mg three times a day (TID) added to standard therapy vs. standard therapy plus placebo in ACS patients with non-ST elevation myocardial infarction (NSTEMI). Patients with ACS were randomized to receive standard therapy plus placebo in one arm (group A; aspirin, clopidogrel or ticagrelor, statin) and in the other arm (group B) pentoxifylline 400 mg TID was added to standard therapy. The primary outcome was the rate of major adverse cardiovascular events (MACEs) at 1 year. A total of 500 patients underwent randomization (with 250 assigned to group A and 250 to group B) and were followed-up for a median of 20 months. The mean age of the patients was 62.3±10.3 years, 80.4% were male, 20.8% had diabetes, 49.4% had hypertension, and 42% were currently smoking. The statistical analysis was performed for 209 patients in group A and 210 patients in group B (after dropouts due to study drug discontinuation). A primary endpoint occurred in 12.38% (n=26) of patients in group B, as compared with 15.78% (n=33) of those in group A [relative risk (RR), 0.78; 95% confidence interval (CI), 0.486-0.1.263; P=0.40], including cardiovascular death (RR, 0.93; 95% CI, 0.48-1.80, P=0.84), non-fatal myocardial infarction (RR, 1.1; 95% CI, 0.39-3.39, P=0.78), stroke (RR, 0.99; 95% CI, 0.14-6.99, P=0.99) and coronary revascularization (RR, 0.12; 95% CI, 0.015-0.985, P=0.048). Thus, adding pentoxifylline to standard treatment in patients with ACS did not improve MACE at 1 year but had some benefit on the need for coronary revascularization.

Acute Coronary Syndromes (ACS)-Unravelling Biology to Identify New Therapies-The Microcirculation as a Frontier for New Therapies in ACS

In acute coronary syndrome (ACS) patients, restoring epicardial culprit vessel patency and flow with percutaneous coronary intervention or coronary artery bypass grafting has been the mainstay of treatment for decades. However, there is an emerging understanding of the crucial role of coronary microcirculation in predicting infarct burden and subsequent left ventricular remodelling, and the prognostic significance of coronary microvascular obstruction (MVO) in mortality and morbidity. This review will elucidate the multifaceted and interconnected pathophysiological processes which underpin MVO in ACS, and the various diagnostic modalities as well as challenges, with a particular focus on the invasive but specific and reproducible index of microcirculatory resistance (IMR). Unfortunately, a multitude of purported therapeutic strategies to address this unmet need in cardiovascular care, outlined in this review, have so far been disappointing with conflicting results and a lack of hard clinical end-point benefit. There are however a number of exciting and novel future prospects in this field that will be evaluated over the coming years in large adequately powered clinical trials, and this review will briefly appraise these.

Expression of antibody fragments in Saccharomyces cerevisiae strains evolved for enhanced protein secretion

Monoclonal antibodies, antibody fragments and fusion proteins derived thereof have revolutionized the practice of medicine. Major challenges faced by the biopharmaceutical industry are however high production costs, long processing times and low productivities associated with their production in mammalian cell lines. The yeast Saccharomyces cerevisiae, a well-characterized eukaryotic cell factory possessing the capacity of post-translational modifications, has been industrially exploited as a secretion host for production of a range of products, including pharmaceuticals. However, due to the incompatible surface glycosylation, few antibody molecules have been functionally expressed in S. cerevisiae. Here, three non-glycosylated antibody fragments from human and the Camelidae family were chosen for expression in a S. cerevisiae strain (HA) previously evolved for high α-amylase secretion. These included the Fab fragment Ranibizumab (Ran), the scFv peptide Pexelizumab (Pex), and a nanobody consisting of a single V-type domain (Nan). Both secretion and biological activities of the antibody fragments were confirmed. In addition, the secretion level of each protein was compared in the wild type (LA) and two evolved strains (HA and MA) with different secretory capacities. We found that the secretion of Ran and Nan was positively correlated with the strains' secretory capacity, while Pex was most efficiently secreted in the parental strain. To investigate the mechanisms for different secretion abilities in these selected yeast strains for the different antibody fragments, RNA-seq analysis was performed. The results showed that several bioprocesses were significantly enriched for differentially expressed genes when comparing the enriched terms between HA.Nan vs. LA.Nan and HA.Pex vs. LA.Pex, including amino acid metabolism, protein synthesis, cell cycle and others, which indicates that there are unique physiological needs for each antibody fragment secretion.

Comparative Effectiveness of Anti-Inflammatory Drug Treatments in Coronary Heart Disease Patients: A Systematic Review and Network Meta-Analysis

Methods

We conducted a network meta-analysis of randomized controlled trials that studied the effects of anti-inflammatory medications on cardiovascular outcomes of coronary artery disease patients. We searched the electronic database until March 2020 for relevant studies.

Results

Nineteen trials examining the efficacy of eight anti-inflammatory medications (pexelizumab, anakinra, colchicine, darapladib, varespladib, canakinumab, inclacumab, and losmapimod) were selected for analysis. Overall, there is no statistically significant difference in all-cause mortality, cardiovascular mortality, revascularization, and major cardio and cerebrovascular events (MACCE) with the use of anti-inflammatory drugs. However, we found the use of colchicine significantly reduces the odds of developing stroke by approximately 75% (OR 0.26, CI 0.10-0.63). Colchicine use was also associated with a lower risk of revascularization and MACCE compared to the other agents. Our subgroup analyses comparing the timing of medication initiation (within 7 days vs. >7 days) and clinical presentation (ACS vs. non-ACS) revealed a significant reduction in the risk of recurrent MI in the group that received medication after seven days (OR 0.92, CI 0.86-0.99) and the non-ACS group (OR 0.88, CI 0.80-0.98).

Conclusion

Although many anti-inflammatory medications have failed to reduce adverse cardiovascular outcomes in the CAD population, selected medications show promise among subgroups of patients without ACS or after the first week following an acute ischemic event. Future studies examining the proper timing and targetable anti-inflammatory pathways are warranted.

[Monoclonal antibodies in cardiovascular diseases and metabolic disorders today]

The use of monoclonal antibodies in cardiovascular diseases and metabolic disorders is still in its infancy. Recent development of anti-PCSK9 monoclonal antibodies for the treatment of dyslipidemia and of patients in secondary prevention is a breakthrough in the field. Anti- PCSK9 antibodies significantly improved LDL cholesterol reduction in patients with familial hypercholesterolemia. These antibodies have also demonstrated a significant reduction of clinical events in patients with previously established atherosclerotic disease such as myocardial infarction, ischemia stroke or peripheral artery disease. Other targets are under investigation such as inflammatory cells and cytokines to reduce atherosclerosis or myocardial lesions following myocardial infarction.

Inflammatory and Molecular Pathways in Heart Failure-Ischemia, HFpEF and Transthyretin Cardiac Amyloidosis

Elevated pro-inflammatory biomarkers and cytokines are associated with morbidity and mortality in heart failure (HF). Preclinical and clinical studies have shown multiple inflammatory mechanisms causing cardiac remodeling, dysfunction and chronic failure. Therapeutics in trials targeting the immune response in heart failure and its effects did not result in evident benefits regarding clinical endpoints and mortality. This review elaborates pathways of immune cytokines in pathogenesis and worsening of heart failure in clinical and cellular settings. Besides the well-known mechanisms of immune activation and inflammation in atherosclerosis causing ischemic cardiomyopathy or myocarditis, attention is focused on other mechanisms leading to heart failure such as transthyretin (TTR) amyloidosis or heart failure with preserved ejection fraction. The knowledge of the pathogenesis in heart failure and amyloidosis on a molecular and cellular level might help to highlight new disease defining biomarkers and to lead the way to new therapeutic targets.

Immunomodulatory interventions in myocardial infarction and heart failure: a systematic review of clinical trials and meta-analysis of IL-1 inhibition

Following a myocardial infarction (MI), the immune system helps to repair ischaemic damage and restore tissue integrity, but excessive inflammation has been implicated in adverse cardiac remodelling and development towards heart failure (HF). Pre-clinical studies suggest that timely resolution of inflammation may help prevent HF development and progression. Therapeutic attempts to prevent excessive post-MI inflammation in patients have included pharmacological interventions ranging from broad immunosuppression to immunomodulatory approaches targeting specific cell types or factors with the aim to maintain beneficial aspects of the early post-MI immune response. These include the blockade of early initiators of inflammation including reactive oxygen species and complement, inhibition of mast cell degranulation and leucocyte infiltration, blockade of inflammatory cytokines, and inhibition of adaptive B and T-lymphocytes. Herein, we provide a systematic review on post-MI immunomodulation trials and a meta-analysis of studies targeting the inflammatory cytokine Interleukin-1. Despite an enormous effort into a significant number of clinical trials on a variety of targets, a striking heterogeneity in study population, timing and type of treatment, and highly variable endpoints limits the possibility for meaningful meta-analyses. To conclude, we highlight critical considerations for future studies including (i) the therapeutic window of opportunity, (ii) immunological effects of routine post-MI medication, (iii) stratification of the highly diverse post-MI patient population, (iv) the potential benefits of combining immunomodulatory with regenerative therapies, and at last (v) the potential side effects of immunotherapies.

Failure to Launch: Targeting Inflammation in Acute Coronary Syndromes

The importance of inflammation and inflammatory pathways in atherosclerotic disease and acute coronary syndromes (ACS) is well established. The success of statin therapy rests not only on potently reducing levels of low-density lipoprotein cholesterol, but also on the many beneficial, pleiotropic effects statin therapy has on various inflammatory mechanisms in atherosclerotic disease, from reducing endothelial dysfunction to attenuating levels of serum C-reactive protein. Due to the growing awareness of the importance of inflammation in ACS, investigators have attempted to develop novel therapies against known markers of inflammation for several decades. Targeted pathways have ranged from inhibiting C5 cleavage with a high-affinity monoclonal antibody against C5 to inhibiting the activation of the p38 mitogen-activated protein kinase signaling cascades. In each of these instances, despite promising early preclinical and mechanistic studies and phase 2 trials suggesting a potential benefit in reducing post-MI complications or restenosis, these novel therapies have failed to show benefits during large, phase 3 clinical outcomes trials. This review discusses several examples of novel anti-inflammatory therapies that failed to show significant improvement on clinical outcomes when tested in large, randomized trials and highlights potential explanations for why targeted therapies against known markers of inflammation in ACS have failed to launch.

MethotrexaTE THerapy in ST-Segment Elevation MYocardial InfarctionS

Purpose:

Methotrexate is an anti-inflammatory drug that has been shown to have anti-ischemic effects. Our aim was to evaluate if methotrexate could reduce infarct size in patients with ST-segment elevation myocardial infarction (STEMI).

Methods:

We randomly assigned patients with STEMI to receive either methotrexate or placebo. Primary outcome was infarct size determined by calculating the area under the curve (AUC) for creatine kinase (CK) release. Secondary outcomes were AUC of CK MB (CK-MB) and AUC of troponin I; peak CK, peak CK-MB, and troponin I; B-type natriuretic peptide (BNP) level, high-sensitivity C-reactive protein (hsCRP) result, and erythrocyte sedimentation rate (ESR); left ventricular ejection fraction (LVEF); thrombolysis in myocardial infarction (TIMI) frame count; Killip score; mortality and reinfarction incidence; and incidence of adverse reactions.

Results:

We included 84 patients. Median AUC of CK was 78 861.0 in the methotrexate group and 68 088.0 in the placebo group ( P = .10). Patients given methotrexate and placebo exhibited, respectively, median AUC for CK-MB of 9803.4 and 8037.0 ( P = .42); median AUC for troponin of 3691.1 and 2132.6 ( P = .09); peak CK of 2806.0 and 2147.0 ( P = .05); peak CK-MB of 516.0 and 462.3 ( P = .25); and peak troponin of 121.0 and 85.1 ( P = .06). At 3 months, LVEF was lower in patients who received methotrexate (49.0% ± 14.1%) than in patients given placebo (56.4% ± 10.0%; P = .01). There were no differences in hsCRP, ESR, BNP, Killip scores, TIMI frame count, reinfarction, and mortality rates. There was a higher median serum glutamic–pyruvic transaminase levels in the methotrexate group.

Conclusion:

Methotrexate did not reduce infarction size and worsened LVEF at 3 months ( Clinicaltrials.gov identifier NCT01741558).

Correlation between leukocyte count and infarct size in ST segment elevation myocardial infarction

INTRODUCTION

Regarding the inflammatory mechanisms involved in ischemic heart disease, currently the leukocyte count is the subject of studies related to its association with the prognosis and mortality of ST segment elevation myocardial infarction (STEMI). Our aim is correlate the leukocyte count rise with the size of STEMI, evaluated with the area under the curve (AUC) and the peak of necrosis markers release.

MATERIAL AND METHODS

This study is a sub-analysis of the TETHYS trial, a clinical trial that evaluated the effects of methotrexate in STEMI. We evaluated the correlation between quantitative variables with Pearson's correlation, and the variables that did not follow a normal distribution were subjected to logarithmic transformation to base 10. The value of p < 0.05 indicated statistical significance.

RESULTS

Males accounted for 73% of the participants, who had an average age of 59 years. A total of 58% were hypertensive and 53% smokers. The leukocyte count at hospital admission was significantly correlated with the AUC creatine kinase (CK) (r = 0.256, p = 0.021), troponin AUC (r = 0.247, p = 0.026), peak CK (r = 0.270, p = 0.015) and troponin peak (r = 0.233, p = 0.037). The leukocyte count at 72 h was significantly correlated with CK AUC (r = 0.238, p = 0.032), AUC of MB portion of CK (r = 0.240, p = 0.031) and peak CK (r = 0.224, p = 0.045).

CONCLUSIONS

White blood cell count correlates with STEMI size assessed by serial cardiac biomarker levels.

The complement system and toll-like receptors as integrated players in the pathophysiology of atherosclerosis

Despite recent medical advances, atherosclerosis is a global burden accounting for numerous deaths and hospital admissions. Immune-mediated inflammation is a major component of the atherosclerotic process, but earlier research focus on adaptive immunity has gradually switched towards the role of innate immunity. The complement system and toll-like receptors (TLRs), and the crosstalk between them, may be of particular interest both with respect to pathogenesis and as therapeutic targets in atherosclerosis. Animal studies indicate that inhibition of C3a and C5a reduces atherosclerosis. In humans modified LDL-cholesterol activate complement and TLRs leading to downstream inflammation, and histopathological studies indicate that the innate immune system is present in atherosclerotic lesions. Moreover, clinical studies have demonstrated that both complement and TLRs are upregulated in atherosclerotic diseases, although interventional trials have this far been disappointing. However, based on recent research showing an intimate interplay between complement and TLRs we propose a model in which combined inhibition of both complement and TLRs may represent a potent anti-inflammatory therapeutic approach to reduce atherosclerosis.

Targeting pathogenic postischemic self-recognition by natural IgM to protect against posttransplantation cardiac reperfusion injury

BACKGROUND

Natural IgM antibodies represent a class of innate pattern recognition receptors that recognize danger-associated molecular patterns expressed on stressed or dying cells. They play important roles in tissue homeostasis by disposing of prenecrotic cells and suppressing inflammation. However, ischemic insult leads to a pathogenic level of IgM binding and complement activation, resulting in inflammation and injury. We investigate the role of self-reactive IgM in the unique setting of transplantation where the donor organ undergoes both cold and warm ischemia and global ischemic insult.

METHODS AND RESULTS

By transplanting hearts from wild-type donor mice into antibody-deficient mice reconstituted with specific self-reactive IgM monoclonal antibodies, we identified neoepitopes expressed after transplantation and demonstrated a key role for IgM recognition of these epitopes in graft injury. With this information, we developed and characterized a therapeutic strategy that exploited the postischemia recognition system of natural antibodies. On the basis of neoepitope identification, we constructed an anti-annexin IV single-chain antibody (scFv) and an scFv linked to Crry, an inhibitor of C3 activation (scFv-Crry). In an allograft transplantation model in which recipients contain a full natural antibody repertoire, both constructs blocked graft IgM binding and complement activation and significantly reduced graft inflammation and injury. Furthermore, scFv-Crry specifically targeted to the transplanted heart and, unlike complement deficiency, did not affect immunity to infection, an important consideration for immunosuppressed transplant recipients.

CONCLUSIONS

We identified pathophysiologically important epitopes expressed within the heart after transplantation and described a novel translatable strategy for targeted complement inhibition that has several advantages over currently available approaches.

Role of vascular inflammation in coronary artery disease: potential of anti-inflammatory drugs in the prevention of atherothrombosis. Inflammation and anti-inflammatory drugs in coronary artery disease

Coronary artery disease (CAD) and acute myocardial infarction (AMI) are inflammatory pathologies, involving interleukins (ILs), such as IL-1β, IL-6 and tumor necrosis factor (TNF)-α, and acute phase proteins production, such as for C reactive protein (CRP). The process begins with retention of low-density lipoprotein (LDL) and its oxidation inside the intima, with the formation of the "foam cells." Toll-like receptors and inflamassomes participate in atherosclerosis formation, as well as in the activation of the complement system. In addition to innate immunity, adaptive immunity is also associated with atherosclerosis through antigen-presenting cells, T and B lymphocytes. AMI also increases the expression of some ILs and promotes macrophage and lymphocyte accumulation. Reperfusion increases the expression of anti-inflammatory ILs (such as IL-10) and generates oxygen free radicals. Although CAD and AMI are inflammatory disorders, the only drugs with anti-inflammatory effect so far widely used in ischemic heart disease are aspirin and statins. Some immunomodulatory or immunosuppressive promising therapies, such as cyclosporine and colchicine, may have benefits in CAD. Methotrexate also has potential cardioprotective anti-inflammatory effects, through increased adenosine levels. The TETHYS trial (The Effects of mETHotrexate Therapy on ST Segment Elevation MYocardial InfarctionS trial) will evaluate low-dose methotrexate in ST elevation AMI. The CIRT (Cardiovascular Inflammation Reduction Trial), in turn, will evaluate low-dose methotrexate in patients with a high prevalence of subclinical vascular inflammation. The CANTOS (The Canakinumab Antiinflammatory Thrombosis Outcomes Study) will evaluate canakinumab in patients with CAD and persistently elevated CRP. The blockage of other potential targets, such as the IL-6 receptor, CC2 chemokine receptor and CD20, could bring benefits in CAD.

Complement factor B activation in patients with preeclampsia

Preeclampsia is a leading cause of maternal and fetal morbidity and mortality. Bb, the active fragment of complement factor B (fB), has been reported to be a predictor of preeclampsia. However, conflicting results have been found by some investigators. We hypothesized that the disagreement in findings may be due to the racial/ethnic differences among various study groups, and that fB activation is significant in women of an ethnic minority with preeclampsia. We investigated the maternal and fetal levels of Bb (the activated fB fragment) in pregnant women of an ethnic minority with or without preeclampsia. We enrolled 291 pregnant women (96% of an ethnic minority, including 78% African-American). Thirteen percent of these were diagnosed with preeclampsia. Maternal venous blood was collected from all participants together with fetal umbilical cord blood samples from 154 deliveries in the 291 women. The results were analyzed using the Mann-Whitney U test and multivariate analyses. Maternal Bb levels were significantly higher in the preeclamptic group than in the nonpreeclamptic group. Levels of Bb in fetal cord blood were similar in both groups. Subgroup analyses of African-American patients' results confirmed the study hypothesis that there would be a significant increase in Bb in the maternal blood of the preeclamptic group and no increase in Bb in the fetal cord blood of this group. These results suggest that a maternal immune response through complement fB might play a role in the development of preeclampsia, particularly in African-American patients.

A vital role for complement in heart disease

Heart diseases are common and significant contributors to worldwide mortality and morbidity. During recent years complement mediated inflammation has been shown to be an important player in a variety of heart diseases. Despite some negative results from clinical trials using complement inhibitors, emerging evidence points to an association between the complement system and heart diseases. Thus, complement seems to be important in coronary heart disease as well as in heart failure, where several studies underscore the prognostic importance of complement activation. Furthermore, patients with atrial fibrillation often share risk factors both with coronary heart disease and heart failure, and there is some evidence implicating complement activation in atrial fibrillation. Moreover, Chagas heart disease, a protozoal infection, is an important cause of heart failure in Latin America, and the complement system is crucial for the protozoa-host interaction. Thus, complement activation appears to be involved in the pathophysiology of a diverse range of cardiac conditions. Determination of the exact role of complement in the various heart diseases will hopefully help to identify patients that might benefit from therapeutic complement intervention.

Leucocyte expression of complement C5a receptors exacerbates infarct size after myocardial reperfusion injury

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.

Mannan-binding lectin in cardiovascular disease

Cardiovascular disease remains the leading cause of mortality and morbidity worldwide so research continues into underlying mechanisms. Since innate immunity and its potent component mannan-binding lectin have been proven to play an important role in the inflammatory response during infection and ischaemia-reperfusion injury, attention has been paid to its role in the development of cardiovascular complications as well. This review provides a general outline of the structure and genetic polymorphism of MBL and its role in inflammation/tissue injury with emphasis on associations with cardiovascular disease. MBL appears to be involved in the pathogenesis of atherosclerosis and, in consequence, coronary artery disease and also inflammation and tissue injury after myocardial infarction and heart transplantation. The relationship between MBL and disease is rather complex and depends on different genetic and environmental factors. That could be why the data obtained from animal and clinical studies are sometimes contradictory proving not for the first time that innate immunity is a "double-edge sword," sometimes beneficial and, at other times disastrous for the host.

Delineating the relationships among the formation of reactive oxygen species, cell membrane instability and innate autoimmunity in intestinal reperfusion injury

Acute intestinal ischemia is a medical emergency with a high mortality rate, attesting to the need for a better understanding of its pathogenesis and the development of effective therapies. The goal of this study was to delineate the relationships among intracellular and extracellular events in intestinal ischemia/reperfusion (I/R) injury, particularly the formation of reactive oxygen species (ROS), cell membrane instability associated with lipid peroxidation and the innate autoimmune response mediated by natural IgM and complement. A murine model of natural IgM-mediated intestinal I/R was used. Mice overexpressing anti-oxidant enzyme SOD1 were found to have significantly reduced intestinal tissue damage and complete blockage of IgM-mediated complement activation compared with WT controls. To determine if cell membrane instability was an event intermediate between ROS formation and natural IgM-mediated innate autoimmune response, the cell membrane stabilizer (trehalose) was administered to WT mice prior to the induction of intestinal ischemia. Treatment with trehalose significantly protected animals from I/R injury and inhibited IgM-mediated complement activation although it did not prevent membrane lipid peroxidation. These data indicate that in normal mice subjected to I/R injury, intracellular ROS formation is an event upstream of the lipid peroxidation which results in cell membrane instability. The membrane instability leads to an innate autoimmune response by natural IgM and complement. Trehalose, a nontoxic disaccharide tolerated well by animals and humans, has promise as a protective agent for patients with medical conditions related to acute intestinal ischemia.

Myocardial protection in cardiac surgery: a historical review from the beginning to the current topics

Myocardial protection has become an essential adjunctive measure in cardiac surgery for a couple of decades, because since the 1950s, the methods of cardioprotection (cardioplegic solutions and related procedures) have been improved by the mechanism of myocardial ischemia/reperfusion-induced damage being unveiled through the untiring efforts of researchers and clinicians. The concept of myocardial protection in cardiac surgery was proposed along with introduction of hypothermic crystalloid potassium cardioplegia in the beginning and has been diversified by pharmacological additives, blood cardioplegia, temperature modulation (warm; tepid), retrograde cardioplegia, controlled reperfusion, integrated cardioplegia, and pre-and postconditioning. This historical review summarized experimental and clinical studies dealing with the methods and results of myocardial protection in cardiac surgery, introducing the newly developed concepts for the last decade and the current topics.

Acute but transient release of terminal complement complex after reperfusion in clinical kidney transplantation

BACKGROUND

Ischemia/reperfusion (I/R) injury has a major impact on kidney graft function and survival. Animal studies have suggested a role for complement activation in mediating I/R injury; however, results are not unambiguous. Whether complement activation is involved in clinical I/R injury in humans is still unclear.

METHODS

In the present study, we assessed the formation and release of C5b-9 during early reperfusion in clinical kidney transplantation in living donor, brain-dead donor, and cardiac dead donor kidney transplantation. By arteriovenous measurements and histologic studies, local terminal complement activation in the reperfused kidney was assessed.

RESULTS

There was no release of soluble C5b-9 (sC5b-9) from living donor kidneys, nor was there a release of C5a. In contrast, instantly after reperfusion, there was a significant but transient venous release of sC5b-9 from the reperfused kidney graft in brain-dead donor and cardiac dead donor kidney transplantation. This short-term activation of the terminal complement cascade in deceased-donor kidney transplantation was not reflected by renal tissue deposition of C5b-9 in biopsies taken 45 min after reperfusion.

CONCLUSIONS

This systematic study in human kidney transplantation shows an acute but nonsustained sC5b-9 release on reperfusion in deceased-donor kidney transplantation. This instantaneous, intravascular terminal complement activation may be induced by intravascular cellular debris and hypoxic or injured endothelium.

Complement in immune and inflammatory disorders: therapeutic interventions

With the awareness that immune-inflammatory cross-talk is at the heart of many disorders, the desire for novel immunomodulatory strategies in the therapy of such diseases has grown dramatically. As a prime initiator and important modulator of immunological and inflammatory processes, the complement system has emerged as an attractive target for early and upstream intervention in inflammatory diseases and has moved into the spotlight of drug discovery. Although prevalent conditions such as age-related macular degeneration have attracted the most attention, the diverse array of complement-mediated pathologies, with distinct underlying mechanisms, demands a multifaceted arsenal of therapeutic strategies. Fortunately, efforts in recent years have not only introduced the first complement inhibitors to the clinic but also filled the pipelines with promising candidates. With a focus on immunomodulatory strategies, in this review we discuss complement-directed therapeutic concepts and highlight promising candidate molecules.

Complement anaphylatoxins C3a and C5a induce a failing regenerative program in cardiac resident cells. Evidence of a role for cardiac resident stem cells other than cardiomyocyte renewal

Cardiac healing, which follows myocardial infarction, is a complex process guided by intricate interactions among different components. Some resident cell populations with a potential role in cardiac healing have already been described in cardiac tissues. These non-cardiomyocyte cell subsets, globally described as cardiac pluripotent/progenitor cells (CPCs), are able to differentiate into all three major cardiac cell lineages (endothelial, smooth muscle and cardiomyocyte cells) in experimental settings. Nevertheless, physiological cardiac healing results in a fibrous scar, which remains to be fully modelled experimentally. Since a role for complement anaphylatoxins (C3a and C5a) has been described in several regeneration/repair processes, we examined the effects that C3a and C5a exert on a defined population of CPCs. We found that C3a and C5a are able to enhance CPC migration and proliferation. In vitro studies showed that this effect is linked to activation of telomerase mRNA and partial preservation of telomere length, in an NFκB-dependent manner. In addition, anaphylatoxin signalling modulates the CPC phenotype, increasing myofibroblast differentiation and reducing endothelial and cardiac gene expression. These findings may denote that C3a and C5a are able to maintain/increase the cardiac stem cell pool within the heart, whilst simultaneously facilitating and modulating resident cell differentiation. We found that this modulation was directed towards scar forming cells, which increased fibroblast/myofibroblast generation and suggests that both these anaphylatoxins could play a relevant role in the damage-coupled activation of resident cells, and regulation of the cardiac healing process after injury.

Preservation of myocardium during coronary artery bypass surgery

Myocardial protection aims to prevent reversible post-ischemic cardiac dysfunction (myocardial stunning) and irreversible myocardial cell death (myocardial infarction) that occur as a consequence of myocardial ischemia and/or ischemic-reperfusion injury. Although the mortality rate for isolated coronary artery bypass grafting has been markedly reduced during the past decade, myocardial death, as evidenced by elevation in creatine kinase-myocardial band and/or cardiac troponin, is common. This is ascribed to suboptimal myocardial protection during cardiopulmonary bypass or with off-pump technique, early graft failure, distal embolization, and regional or global myocardial ischemia during surgery. An unmet need in contemporary coronary bypass surgery is to find more effective cardioprotective strategies that have the potential for decreasing the morbidity and mortality associated with suboptimal cardioprotection. In the present review article on myocardial protection in contemporary coronary artery bypass surgery, we attempt to elucidate the clinical problems, summarize the outcomes of selected phase III trials, and introduce new perspectives.

STEC-HUS, atypical HUS and TTP are all diseases of complement activation

Haemolytic uraemic syndrome (HUS) and thrombotic thrombocytopaenic purpura (TTP) are diseases characterized by microvascular thrombosis, with consequent thrombocytopaenia, haemolytic anaemia and dysfunction of affected organs. Advances in our understanding of the molecular pathology led to the recognition of three different diseases: typical HUS caused by Shiga toxin-producing Escherichia coli (STEC-HUS); atypical HUS (aHUS), associated with genetic or acquired disorders of regulatory components of the complement system; and TTP that results from a deficiency of ADAMTS13, a plasma metalloprotease that cleaves von Willebrand factor. In this Review, we discuss data indicating that complement hyperactivation is a common pathogenetic effector that leads to endothelial damage and microvascular thrombosis in all three diseases. In STEC-HUS, the toxin triggers endothelial complement deposition through the upregulation of P-selectin and possibly interferes with the activity of complement regulatory molecules. In aHUS, mutations in the genes coding for complement components predispose to hyperactivation of the alternative pathway of complement. In TTP, severe ADAMTS13 deficiency leads to generation of massive platelet thrombi, which might contribute to complement activation. More importantly, evidence is emerging that pharmacological targeting of complement with the anti-C5 monoclonal antibody eculizumab can effectively treat not only aHUS for which it is indicated, but also STEC-HUS and TTP in some circumstances.

Mesenchymal stromal cells in renal ischemia/reperfusion injury

Ischemia/reperfusion (I/R) injury is an inevitable consequence of organ transplantation and a major determinant of patient and graft survival in kidney transplantation. Renal I/R injury can lead to fibrosis and graft failure. Although the exact sequence of events in the pathophysiology of I/R injury remains unknown, the role of inflammation has become increasingly clear. In this perspective, mesenchymal stromal cells (MSCs) are under extensive investigation as potential therapy for I/R injury, since MSCs are able to exert immune regulatory and reparative effects. Various preclinical studies indicate the beneficial effects of MSCs in ameliorating renal injury and accelerating tissue repair. These versatile cells have been shown to migrate to sites of injury and to enhance repair by paracrine mechanisms instead of by differentiating and replacing the injured cells. The first phase I studies of MSCs in human renal I/R injury and kidney transplantation have been started, and results are awaited soon. In this review, preliminary results and opportunities of MSCs in human renal I/R injury are summarized. We might be heading towards a cell-based paradigm shift in the treatment of renal I/R injury.

Pexelizumab fails to inhibit assembly of the terminal complement complex in patients with ST-elevation myocardial infarction undergoing primary percutaneous coronary intervention. Insight from a substudy of the Assessment of Pexelizumab in Acute Myocardial Infarction (APEX-AMI) trial

BACKGROUND

Reasons for pexelizumab lack of benefit in ST-elevation myocardial infarction patients undergoing primary percutaneous coronary intervention remain unclear. In a substudy of the APEX-AMI trial, we explored the hypothesis that early complement activation preceding drug administration explained the failure.

METHODS

A panel of terminal complement complex proteins and fragments and biomarkers of inflammation, apoptosis, and high-risk features were assessed in serum obtained before and 24 hours after administration of placebo or pexelizumab and primary percutaneous coronary intervention (n = 356) and in human umbilical vein endothelial cell cultures coincubated with serum (n = 45).

RESULTS

In the placebo group, C5a and sC5b-9 levels increased by 37% (7.9-14.2 ηg/mL, P = .007) and 96% (442-845 ηg/mL, P < .0001), respectively, during the first 24 hours. Pexelizumab prevented the increase in C5a (P = .01 vs placebo), but not that of sC5b-9 (502-1,157 ηg/mL, not significant vs placebo). Levels of C-reactive protein, interleukin (IL) 6, IL-1ß, Regulated on Activation, Normal T Cell Expressed and Secreted (RANTES) or Chemokine C-C motif ligand 5 (CCL5), and N-terminal probrain natriuretic peptide increased significantly in both groups; those of IL-10, IL-12, IL-1ra, and Interferon gamma-induced protein 10 (IP-10) or C-X-C motif chemokine 10 (CXCL10) decreased. Pexelizumab halved the increase in IL-6 (+92% vs 156%, P = .01) without effects on other markers, including C-reactive protein and N-terminal probrain natriuretic peptide. In cell culture, pexelizumab inhibited C5a, sC5b-9, and membrane-bound C5b-9 by 92%, 75%, and 78%, respectively (all P < .0001), without influencing cytokine levels and cell apoptosis.

CONCLUSIONS

The blockage of both C5a and terminal complement in cell culture, but of C5a only in vivo with minimal effects on inflammation and risk biomarkers, supports the hypothesis that late administration of pexelizumab after the ischemia/reperfusion insult precluded adequate myocardial protection, resulting in a negative trial.

Role of complement and perspectives for intervention in ischemia-reperfusion damage

Reperfusion of an organ following prolonged ischemia instigates the pro-inflammatory and pro-coagulant response of ischemia / reperfusion (IR) injury. IR injury is a wide-spread pathology, observed in many clinically relevant situations, including myocardial infarction, stroke, organ transplantation, sepsis and shock, and cardiovascular surgery on cardiopulmonary bypass. Activation of the classical, alternative, and lectin complement pathways and the generation of the anaphylatoxins C3a and C5a lead to recruitment of polymorphonuclear leukocytes, generation of radical oxygen species, up-regulation of adhesion molecules on the endothelium and platelets, and induction of cytokine release. Generalized or pathway-specific complement inhibition using protein-based drugs or low-molecular-weight inhibitors has been shown to significantly reduce tissue injury and improve outcome in numerous in-vitro, ex-vivo, and in-vivo models. Despite the obvious benefits in experimental research, only few complement inhibitors, including C1-esterase inhibitor, anti-C5 antibody, and soluble complement receptor 1, have made it into clinical trials of IR injury. The results are mixed, and the next objectives should be to combine knowledge and experience obtained in the past from animal models and channel future work to translate this into clinical trials in surgical and interventional reperfusion therapy as well as organ transplantation.

Interactions between coagulation and complement--their role in inflammation

The parallel expression of activation products of the coagulation, fibrinolysis, and complement systems has long been observed in both clinical and experimental settings. Several interconnections between the individual components of these cascades have also been described, and the list of shared regulators is expanding. The co-existence and interplay of hemostatic and inflammatory mediators in the same microenvironment typically ensures a successful host immune defense in compromised barrier settings. However, dysregulation of the cascade activities or functions of inhibitors in one or both systems can result in clinical manifestations of disease, such as sepsis, systemic lupus erythematosus, or ischemia-reperfusion injury, with critical thrombotic and/or inflammatory complications. An appreciation of the precise relationship between complement activation and thrombosis may facilitate the development of novel therapeutics, as well as improve the clinical management of patients with thrombotic conditions that are characterized by complement-associated inflammatory responses.

Inhibiting the C5-C5a receptor axis

Activation of the complement system is a major pathogenic event that drives various inflammatory responses in numerous diseases. All pathways of complement activation lead to cleavage of the C5 molecule generating the anaphylatoxin C5a and, C5b that subsequently forms the terminal complement complex (C5b-9). C5a exerts a predominant pro-inflammatory activity through interactions with the classical G-protein coupled receptor C5aR (CD88) as well as with the non-G protein coupled receptor C5L2 (GPR77), expressed on various immune and non-immune cells. C5b-9 causes cytolysis through the formation of the membrane attack complex (MAC), and sub-lytic MAC and soluble C5b-9 also possess a multitude of non-cytolytic immune functions. These two complement effectors, C5a and C5b-9, generated from C5 cleavage, are key components of the complement system responsible for propagating and/or initiating pathology in different diseases, including paroxysmal nocturnal hemoglobinuria, rheumatoid arthritis, ischemia-reperfusion injuries and neurodegenerative diseases. Thus, the C5-C5a receptor axis represents an attractive target for drug development. This review provides a comprehensive analysis of different methods of inhibiting the generation of C5a and C5b-9 as well as the signalling cascade of C5a via its receptors. These include the inhibition of C5 cleavage through targeting of C5 convertases or via the C5 molecule itself, as well as blocking the activity of C5a by neutralizing antibodies and pharmacological inhibitors, or by targeting C5a receptors per se. Examples of drugs and naturally occurring compounds used are discussed in relation to disease models and clinical trials. To date, only one such compound has thus far made it to clinical medicine: the anti-C5 antibody eculizumab, for treating paroxysmal nocturnal hemoglobinuria. However, a number of drug candidates are rapidly emerging that are currently in early-phase clinical trials. The C5-C5a axis as a target for drug development is highly promising for the treatment of currently intractable major human diseases.

New insights of an old defense system: structure, function, and clinical relevance of the complement system

The complement system was discovered a century ago as a potent defense cascade of innate immunity. After its first description, continuous experimental and clinical research was performed, and three canonical pathways of activation were established. Upon activation by traumatic or surgical tissue damage, complement reveals beneficial functions of pathogen and danger defense by sensing and clearing injured cells. However, the latest research efforts have provided a more distinct insight into the complement system and its clinical subsequences. Complement has been shown to play a significant role in the pathogenesis of various inflammatory processes such as sepsis, multiorgan dysfunction, ischemia/reperfusion, cardiovascular diseases and many others. The three well-known activation pathways of the complement system have been challenged by newer findings that demonstrate direct production of central complement effectors (for example, C5a) by serine proteases of the coagulation cascade. In particular, thrombin is capable of producing C5a, which not only plays a decisive role on pathogens and infected/damaged tissues, but also acts systemically. In the case of uncontrolled complement activation, “friendly fire” is generated, resulting in the destruction of healthy host tissue. Therefore, the traditional research that focuses on a mainly positive-acting cascade has now shifted to the negative effects and how tissue damage originated by the activation of the complement can be contained. In a translational approach including structure-function relations of this ancient defense system, this review provides new insights of complement-mediated clinical relevant diseases and the development of complement modulation strategies and current research aspects.

Ischemia/reperfusion injury: The role of immune cells

Ischemia/reperfusion (I/R) injury is an inflammatory condition that is characterized by innate immunity and an adaptive immune response. This review is focused on the acute inflammatory response in I/R injury, and also the adaptive immunological mechanisms in chronic ischemic disease that lead to increased vulnerability during acute events, in relation to the cell types that have been shown to mediate innate immunity to an adaptive immune response in I/R, specifically myocardial infarction. Novel aspects are also highlighted in respect to the mechanisms within the cardiovascular system and cardiovascular risk factors that may be involved in the inflammatory response accompanying myocardial infarction. Experimental myocardial I/R has suggested that immune cells may mediate reperfusion injury. Specifically, monocytes, macrophages, T-cells, mast cells, platelets and endothelial cells are discussed with reference to the complement cascade, toll-like receptors, cytokines, oxidative stress, renin-angiotensin system, and in reference to the microvascular system in the signaling mechanisms of I/R. Finally, the findings of the data summarized in this review are most important for possible translation into clinical cardiology practice and possible avenues for drug development.

CMR for characterization of the myocardium in acute coronary syndromes

The utility of cardiac magnetic resonance imaging (CMR) as a diagnostic technique is well established. CMR enables tissue characterization, distinction between myocardial scar tissue and viable tissue, and evaluation of myocardial perfusion and contractile function. To date, CMR has been mostly applied in the assessment of stable disease; however, a role for CMR in the acute setting is also emerging. An accurate appraisal of the myocardium with CMR in the first hours after the onset of chest pain could provide supporting information to standard diagnostic tools, such as electrocardiography and measurement of blood biomarkers, which could help guide the selection of appropriate treatment. The aims of this integrated approach include positive identification of an ischemic syndrome, estimation of downstream areas at risk of damage, evaluation of epicardial artery patency and small vessel integrity, quantification of infarct size, and determination of myocardial function. This Review critically evaluates both established and emerging CMR techniques, and relates the imaging findings to the underlying pathophysiological processes in acute coronary syndromes. A more thorough understanding of CMR techniques will clarify their potential clinical applications and limitations, and assess the practicality of CMR in the setting of acute coronary syndromes, where early intervention is crucial to save myocardium at risk of irreversible injury.

Blockade of self-reactive IgM significantly reduces injury in a murine model of acute myocardial infarction

AIMS

Coronary artery occlusion resulting in ischaemia/reperfusion (I/R) injury is a major cause of mortality in the western world. Circulating natural IgM has been shown to play a significant role in reperfusion injury, leading to the notion of a pathogenic response against self by the innate immune system. A specific self-antigen (non-muscle myosin heavy chain II) was recently identified as the major target of pathogenic natural IgM. Therefore, we hypothesized that a synthetic peptide mimetope (N2) or monoclonal antibodies directed against the self-antigen would prevent specific IgM binding to the self-antigen and reduce reperfusion injury in the heart.

METHODS AND RESULTS

We find that treatment with N2 peptide reduces infarct size by 47% and serum cardiac troponin-I levels by 69% following 1 h ischaemia and 24 h reperfusion. N2 peptide or an anti-N2 F(ab')(2) (21G6) is also effective at preventing IgM and complement deposition. Additionally, N2 peptide treatment significantly reduces monocyte and neutrophil infiltration at 24 h and collagen deposition at 5 days. Finally, we show that human IgM (hIgM) also includes specificity for the highly conserved self-antigen and that myocardial injury in antibody-deficient mice reconstituted with hIgM is blocked by treatment with N2 peptide or 21G6 F(ab')(2).

CONCLUSION

The findings in this study identify potential therapeutics [i.e. N2 peptide or 21G6 F(ab')(2)] that prevent specific IgM binding to ischaemic antigens in the heart, resulting in a significant reduction in cardiac I/R injury.

Pathogenesis of myocardial ischemia-reperfusion injury and rationale for therapy

Since the initial description of the phenomenon by Jennings et al 50 years ago, our understanding of the underlying mechanisms of reperfusion injury has grown significantly. Its pathogenesis reflects the confluence of multiple pathways, including ion channels, reactive oxygen species, inflammation, and endothelial dysfunction. The purposes of this review are to examine the current state of understanding of ischemia-reperfusion injury, as well as to highlight recent interventions aimed at this heretofore elusive target. In conclusion, despite its complexity our ongoing efforts to mitigate this form of injury should not be deterred, because nearly 2 million patients annually undergo either spontaneous (in the form of acute myocardial infarction) or iatrogenic (in the context of cardioplegic arrest) ischemia-reperfusion.