Concerning the mechanism of pexelizumab's benefit in acute myocardial infarction

The heart-bone connection: relationships between myocardial infarction and osteoporotic fracture

Myocardial infarction (MI) and osteoporotic fracture (Fx) are two of the leading causes of mortality and morbidity worldwide. Although these traumatic injuries are treated as if they are independent, there is epidemiological evidence linking the incidence of Fx and MI, thus raising the question of whether each of these events can actively influence the risk of the other. Atherosclerotic cardiovascular disease and osteoporosis, the chronic conditions leading to MI and Fx, are known to have shared pathoetiology. Furthermore, sustained systemic inflammation after traumas such as MI and Fx has been shown to exacerbate both underlying chronic conditions. However, the effects of MI and Fx outside their own system have not been well studied. The sympathetic nervous system (SNS) and the complement system initiate a systemic response after MI that could lead to subsequent changes in bone remodeling through osteoclasts. Similarly, SNS and complement system activation following fracture could lead to heart tissue damage and exacerbate atherosclerosis. To determine whether damaging bone-heart cross talk may be important comorbidity following Fx or MI, this review details the current understanding of bone loss after MI, cardiovascular damage after Fx, and possible shared underlying mechanisms of these processes.

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.

The Role of Complement in Myocardial Infarction Reperfusion Injury: An Underappreciated Therapeutic Target

This article reviews the pathogenetic role of the complement system in myocardial infarction reperfusion injury. The complement activation pathways involved in myocardial tissue injury are identified, as are the complement-derived effector molecules. The results of past anti-complement therapies are reviewed; as the more recent therapeutic concept of complement depletion with humanized CVF described.

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.

The complement system in ischemia-reperfusion injuries

Tissue injury and inflammation following ischemia and reperfusion of various organs have been recognized for many years. Many reviews have been written over the last several decades outlining the role of complement in ischemia/reperfusion injury. This short review provides a current state of the art knowledge on the complement pathways activated, complement components involved and a review of the clinical biologics/inhibitors used in the clinical setting of ischemia/reperfusion. This is not a complete review of the complement system in ischemia and reperfusion injury but will give the reader an updated view point of the field, potential clinical use of complement inhibitors, and the future studies needed to advance the field.

Is it time to translate ischemic preconditioning's mechanism of cardioprotection into clinical practice?

After three decades of intense research on cardioprotection, we still do not have an approved intervention for limiting infarct size in the patient with acute myocardial infarction (AMI) aside from reperfusion therapy. Yet approximately 25% of patients with AMI that are reperfused are still at risk for heart failure because of excessive muscle necrosis. This article will try to make the case that ischemic preconditioning (IPC), still the most potent anti-infarct intervention ever described, is ready for serious clinical testing now. Over the past 25 years, IPC's mechanism has been largely elucidated and targets a reperfusion injury. Ischemic preconditioning was never considered an intervention for AMI because of its need for pretreatment. However, knowledge of IPC's mechanism has revealed a large number of drugs and interventions that will activate IPC's signaling pathway at the time of reperfusion. Several small clinical trials suggest that they can be quite effective, but so far industry seems to have little interest in developing them. So, while basic scientists are in a continuous cycle of discovery and publication for new and novel cardioprotectants, there has been little effort devoted to translating these interventions into clinical practice. We believe that there are suitable IPC-based interventions that are ready for clinical testing today and the time has come for large-scale clinical trials.

Anticomplement therapy

The complement system is an important part of innate immunity; however, as with other parts of the immune system, the complement system can become pathologically activated and create or worsen disease. Anticomplement reagents have been studied for several years, but only recently have they emerged as a viable therapeutic tool. Here, we describe the role of the complement system in a wide array of diseases, as well as the use of anticomplement therapy as treatment for these diseases in animal models and in human clinical trials. Specifically, we will discuss the role of anticomplement therapy in paroxysmal nocturnal hemoglobinuria, glomerulonephritis, and heart disease, including coronary artery disease, myocardial infarction, and coronary revascularization procedures such as percutaneous coronary angioplasty and coronary artery bypass graft surgery.

Myocardial ischemia and reperfusion injury is dependent on both IgM and mannose-binding lectin

Complement activation has been shown to play an important role in the inflammation and tissue injury following myocardial ischemia and reperfusion (MI/R). Several recent studies from our laboratory demonstrated the importance of mannose-binding lectin (MBL) as the initiation pathway for complement activation and the resulting pathological effects following MI/R. However, other studies from the past suggest an important role of the classical pathway and perhaps natural antibodies. In the present study, we used newly generated genetically modified mice that lack secreted IgM (sIgM), MBL-A, and MBL-C (sIgM/MBL null) in a plasma reconstitution mouse model of MI/R. Following 30 min of ischemia and 4 h of reperfusion, left ventricular ejection fractions were significantly higher in sIgM/MBL null mice reconstituted with MBL null or sIgM/MBL null plasma compared with reconstitution with wild-type (WT) plasma or WT mice reconstituted with WT plasma following MI/R. Serum troponin I concentration, myocardial polymorphonuclear leukocyte infiltration, and C3 deposition were dependent on the combined presence of sIgM and MBL. These results demonstrate that MI/R-induced complement activation, inflammation, and subsequent tissue injury require both IgM and MBL. Thus MBL-dependent activation of the lectin pathway may not be completely antibody independent in I/R models.

Humanized cobra venom factor decreases myocardial ischemia-reperfusion injury

Cobra venom factor (CVF) is a complement activating protein in cobra venom, which functionally resembles C3b, and has been used for decades for decomplementation of serum to investigate the role of complement in many model systems of disease. The use of CVF for clinical practice is considered impractical because of immunogenicity issues. Humanization of CVF was recently demonstrated to yield a potent CVF-like molecule. In the present study, we demonstrate that mice treated with recombinant humanized CVF (HC3-1496) are protected from myocardial ischemia-reperfusion (MI/R) injuries with resultant preservation of cardiac function. Also, C3 deposition in the myocardium following MI/R was not observed following treatment with HC3-1496. HC3-1496 led to complement activation and depletion of C3, but preserved C5 titers. These data suggest, unlike CVF, HC3-1496 does not form a C5 convertase in the mouse, similar to recent studies in human sera/plasma. These results suggest that humanized CVF (HC3-1496) protects the ischemic myocardium from reperfusion injuries induced by complement activation and represents a novel anti-complement therapy for potential clinical use.

Novel complement inhibitor limits severity of experimentally myasthenia gravis

OBJECTIVE

Complement mediated injury of the neuromuscular junction is considered a primary disease mechanism in human myasthenia gravis and animal models of experimentally acquired myasthenia gravis (EAMG). We utilized active and passive models of EAMG to investigate the efficacy of a novel C5 complement inhibitor rEV576, recombinantly produced protein derived from tick saliva, in moderating disease severity.

METHODS

Standardized disease severity assessment, serum complement hemolytic activity, serum cytotoxicity, acetylcholine receptor (AChR) antibody concentration, IgG subclassification, and C9 deposition at the neuromuscular junction were used to assess the effect of complement inhibition on EAMG induced by administration of AChR antibody or immunization with purified AChR.

RESULTS

Administration of rEV576 in passive transfer EAMG limited disease severity as evidenced by 100% survival rate and a low disease severity score. In active EAMG, rats with severe and mild EAMG were protected from worsening of disease and had limited weight loss. Serum complement activity (CH(50)) in severe and mild EAMG was reduced to undetectable levels during treatment, and C9 deposition at the neuromuscular junction was reduced. Treatment with rEV576 resulted in reduction of toxicity of serum from severe and mild EAMG rats. Levels of total AChR IgG, and IgG(2a) antibodies were similar, but unexpectedly, the concentration of complement fixing IgG(1) antibodies was lower in a group of rEV576-treated animals, suggesting an effect of rEV576 on cellular immunity.

INTERPRETATION

Inhibition of complement significantly reduced weakness in two models of EAMG. C5 inhibition could prove to be of significant therapeutic value in human myasthenia gravis.

The structure of OMCI, a novel lipocalin inhibitor of the complement system

The complement (C) system is a potent innate immune defence system against parasites. We have recently characterised and expressed OmCI, a 16 kDa protein derived from the soft tick Ornithodoros moubata that specifically binds C5, thereby preventing C activation. The structure of recombinant OmCI determined at 1.9 A resolution confirms a lipocalin fold and reveals that the protein binds a fatty acid derivative that we have identified by mass spectrometry as ricinoleic acid. We propose that OmCI could sequester one of the fatty acid-derived inflammatory modulators from the host plasma, thereby interfering with the host inflammatory response to the tick bite. Mapping of sequence differences between OmCI and other tick lipocalins with different functions, combined with biochemical investigations of OmCI activity, supports the hypothesis that OmCI acts by preventing interaction with the C5 convertase, rather than by blocking the C5a cleavage site.

Update on the management of cardiogenic shock

PURPOSE OF REVIEW

Cardiogenic shock is a life-threatening emergency that occurs frequently with acute coronary syndromes. If rapid myocardial reperfusion following acute myocardial infarction is not obtained, either with thrombolytics or by revascularization, cardiogenic shock frequently develops and the mortality rate is high. This review summarizes recent advances in the pathophysiology, incidence and treatment of cardiogenic shock. Particular attention is given to pharmacologic advances.

RECENT FINDINGS

Cardiogenic shock continues to occur in 5-10% of patients who suffer a myocardial infarction and the mortality remains over 50% in most studies. Treatment preference is referral to a cardiac center capable of reperfusion using multiple therapies. While no delay in reperfusion is acceptable, emphasis on implementing supportive treatment such as vasopressors, inotropes, and fluids remains critical. There is a wide variance in treatment standards despite established guidelines. Overall mortality from cardiogenic shock has decreased but the incidence remains unchanged.

SUMMARY

Emerging pharmacological interventions designed to counteract the underlying proinflammatory pathophysiologic mechanisms may, in combination with early revascularization, result in improved patient outcomes, but there is no magic bullet on the horizon. Attention to the timeliness of transport and treatment of patients with a focus on revascularization is required for cardiogenic shock patients.

A novel interpretation of immune redundancy and duality in reperfusion injury with important implications for intervention in ischaemic disease

The majority of ischaemia related injury occurs upon tissue reperfusion. Knock-out mouse models have recently shed light on the underlying molecular mechanisms, and suggest that this may be the result of an innate autoimmune response. Based on these new findings we present a novel model of immune redundancy and duality in reperfusion injury. Natural antibody, mannan-binding lectin and toll-like receptor 4 are three pre-formed innate immune receptors that recognise pathogenic molecular patterns. Removing either significantly ameliorates reperfusion injury. We propose that these three receptors serve as key parallel recognition elements that respond to the same or similar ischaemic neo-antigens, of which at least one may have a lipopolysaccharide-like motif. This would fit both with the ligand preference of the three receptors, and the observation that giving monoclonal antibody to lipopolysaccharide reduces reperfusion injury. The consequent injury caused by receptor activation appears to be mainly related to the complement anaphylatoxins, and less to phagocytes, oxidative radicals, and the membrane attack complex. C5a levels in particular are predictive of overall injury, and we suggest this anaphylatoxin causes most of reperfusion injury via both direct toxic effects and a generalised immune activation. The former is illustrated by the recent observation that excess C5a alone can cause cardiac dysfunction. As for the latter, there is evidence that adaptive immunity (especially CD4+ cells) and other serum cascades (coagulation and kallikrein) are involved, and may have been recruited by complement. Furthermore, excess C5a can cause innate immune overactivation that paralyses neutrophils, reduces complement lytic function, and leads to systemic inflammation. This is analogous to what happens in sepsis, and would explain the passive role in IRI of normal immune effectors. Finally, there is a duality complement's function in reperfusion, as some elements are conductive of damage, whilst others may help inflammatory resolution. Most important among the latter are the opsonins, like C3b and apparently C1q, which help macrophages clear apoptosing cells before they undergo secondary necrosis. This model has important implications for clinical interventions. Firstly, redundancy means that inhibiting multiple receptors may achieve a larger mortality reduction than the small and inconsistent one seen in the published monotherapy trials. Secondly, duality means that a non-specific inhibition of complement would reduce both injury and resolution. Therefore, a specific inhibition of the lectin pathway and/or an inhibition of the downstream effectors upon which the receptors converge (e.g. C5a) seem to be a better interceptive strategy.