Pexelizumab reduces death and myocardial infarction in higher risk cardiac surgical patients

Complement activation during cardiopulmonary bypass and association with clinical outcomes

In this prospective, single-centre observational study of 30 patients undergoing cardiopulmonary bypass (CPB), the effect of unfractionated heparin (UFH), CPB surgery and protamine sulphate on complement and on post-operative blood loss were assessed. Although C3 and C4 levels decreased significantly immediately following the administration of UFH, C3a, C5a, Bb fragment and SC5b-9 remained unchanged. During CPB, C3 and C4 continued to fall whilst both alternative and classical pathways activation markers, Bb, C3a, C5a and SC5b-9 increased significantly. Protamine sulphate had no effect on classical pathway components or activation markers but decreased alternative pathway activation marker Bb. Over the 12-24 h post-surgery, both classical and alternative pathway activation markers returned to baseline, whilst C3 and C4 levels increased significantly but not to baseline values. Total drain volume 24 h after the surgery showed a moderate inverse correlation with post-protamine C3 (r = -0.46, p = 0.01) and C4 (r = -0.57, p = 0.0009) levels, whilst a moderate positive correlation was observed with post-protamine C3a (r = 0.46, p = 0.009), C5a (r = 0.37, p = 0.04) and SC5b-9 (r = 0.56, p = 0.001) levels but not with Bb fragment (r = 0.25, p = 0.17). Thus, inhibition of complement activation may be a therapeutic intervention to reduce post-operative blood in patients undergoing CPB.

Role of complement in diabetes

Accumulating evidence suggests a role for the complement system in the pathogenesis of diabetes and the vascular complications that characterise this condition. Complement proteins contribute to the development of type 1 diabetes (T1D) by enhancing the underlying organ-specific autoimmune processes. Complement upregulation and activation is also an important feature of insulin resistance and the development of type 2 diabetes (T2D). Moreover, animal and human studies indicate that complement proteins are involved in the pathogenic mechanisms leading to diabetic microvascular and macrovascular complications. The adverse vascular effects of complement appear to be related to enhancement of the inflammatory process and the predisposition to a thrombotic environment, eventually leading to vascular occlusion. Complement proteins have been considered as therapeutic targets to prevent or treat vascular disease but studies have been mainly conducted in animal models, while human work has been both limited and inconclusive so far. Further studies are needed to understand the potential role of complement proteins as therapeutic targets for reversal of the pathological processes leading to T1D and T2D and for the prevention/treatment of diabetic vascular complications.

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.

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.

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.

Structural and mechanistic insight into how antibodies inhibit serine proteases

Antibodies display great versatility in protein interactions and have become important therapeutic agents for a variety of human diseases. Their ability to discriminate between highly conserved sequences could be of great use for therapeutic approaches that target proteases, for which structural features are conserved among family members. Recent crystal structures of antibody-protease complexes provide exciting insight into the variety of ways antibodies can interfere with the catalytic machinery of serine proteases. The studies revealed the molecular details of two fundamental mechanisms by which antibodies inhibit catalysis of trypsin-like serine proteases, exemplified by hepatocyte growth factor activator and MT-SP1 (matriptase). Enzyme kinetics defines both mechanisms as competitive inhibition systems, yet, on the molecular level, they involve distinct structural elements of the active-site region. In the steric hindrance mechanism, the antibody binds to protruding surface loops and inserts one or two CDR (complementarity-determining region) loops into the enzyme's substrate-binding cleft, which results in obstruction of substrate access. In the allosteric inhibition mechanism the antibody binds outside the active site at the periphery of the substrate-binding cleft and, mediated through a conformational change of a surface loop, imposes structural changes at important substrate interaction sites resulting in impaired catalysis. At the centre of this allosteric mechanism is the 99-loop, which is sandwiched between the substrate and the antibody-binding sites and serves as a mobile conduit between these sites. These findings provide comprehensive structural and functional insight into the molecular versatility of antibodies for interfering with the catalytic machinery of proteases.

Redefining the Systemic Inflammatory Response

From the first description of the “systemic inflammatory response” in the early 1990s, it has been recognized that this is a multifaceted response of the body to the combined insult of cardiothoracic surgery with bypass, involving causation by “activation of complement, coagulation, fibrinolytic, and kallikrein cascades, activation of neutrophils with degranulation and protease enzyme release, oxygen radical production, and the synthesis of various cytokines from mononuclear cells.” Yet the intervening 15 years have seen a narrowing of research into individual systems and interventions naively targeted at single pathways without achieving clinically meaningful benefits. The time has come to redefine the systemic inflammatory response so that research can be more productively focused on objectively measuring and interdicting this multisystem disorder. A key concept of this new understanding is that translation into a hard adverse event occurs when the systemic imbalance is combined with a localized trigger. Triggers might be inadvertently provided by transient episodes of ischemia/malperfusion to vulnerable organs or handling trauma to major vessels. Future research should be directed at suppressing systemic activation with combinations of drugs and improved circuit coating, whereas changes in clinical practice and continuous monitoring of perfusion parameters can help eliminate localized triggering events.

Genomics: risk and outcomes in cardiac surgery

Coronary artery bypass graft surgery is associated with several frequent postoperative adverse events. Outcome prediction is valued by patients and practitioners, because it provides some measure of balancing risks and benefits and provides expensive or higher-risk therapies to individuals at highest risk. Surgeons and anesthesiologists traditionally have relied on demographic, preoperative, and intraoperative risk factors to predict outcomes after cardiac surgery. Yet, such predictions often have poor positive and negative predictive value for the individual patient. Perioperative genetics attempts to determine the impact of an individual's genetic variation on the risk of developing adverse postoperative outcomes. In this article, the authors discuss emerging evidence that a patient's genetic makeup predisposes him or her to adverse outcomes following cardiac surgery and provide examples from perioperative bleeding, myocardial injury/infarction, and atrial fibrillation.

A randomized, double-blind, placebo-controlled, multicenter study to evaluate the cardioprotective effects of MC-1 in patients undergoing high-risk coronary artery bypass graft surgery: MC-1 to Eliminate Necrosis and Damage in Coronary Artery Bypass Graft Surgery Trial (MEND-CABG) II--study design and rationale

BACKGROUND

Coronary artery bypass graft (CABG) surgery is effective in relieving angina and improving survival and quality of life in patients with obstructive coronary artery disease; however, recurrent angina, myocardial infarction, neurological injury, and death can occur in the perioperative and postoperative period. MC-1 (pyridoxal 5'-phosphate) is a novel agent that has shown promise in reducing myocardial necrosis by reducing cellular calcium overload after percutaneous coronary intervention and CABG surgery in high-risk patients undergoing these procedures.

METHODS

MEND-CABG II is a phase III study evaluating the efficacy and safety of MC-1 in reducing cardiovascular morbidity and mortality after CABG. High-risk patients undergoing CABG surgery will be randomly assigned to receive either MC-1 (250 mg/d) or matching placebo immediately before and continuing for 30 days after the procedure. The primary end point is the occurrence of cardiovascular death or nonfatal myocardial infarction through postoperative day 30. A total of 3023 patients were enrolled at 130 sites in Canada, the United States, and Germany between October 2006 and September 2007, with results anticipated shortly after completion of 90-day follow-up in March 2008.

CONCLUSIONS

The data from the MEND-CABG II trial will establish whether peri- and postoperative treatment with MC-1 can decrease the short- and intermediate-term morbidity and mortality of high-risk patients undergoing CABG surgery.

Beneficial effects of complement inhibition with soluble complement receptor 1 (TP10) during cardiac surgery: is there a gender difference?

BACKGROUND

TP10, a potent inhibitor of complement activation during cardiopulmonary bypass (CPB) has been shown to significantly reduce the incidence of death and myocardial infarction (MI) in high-risk male patients undergoing cardiac surgery. However, the effect of TP10 in females was undefined because of the limited number of females studied. To examine the possibility of a gender effect, this phase 2 multi-center trial was undertaken to determine whether TP10 would also limit ischemic damage in a larger sample size of high-risk females undergoing cardiac surgery on cardiopulmonary bypass (CPB).

METHODS AND RESULTS

This prospective, double-blind, placebo-controlled, multi-center trial involved 297 high-risk (urgent surgery, CABG + Valve, reoperations, ejection fraction <30%) female patients randomized to receive a 5 mg/kg dose of TP10 (n=150) or placebo (n=147) as a 30-minute intravenous infusion before surgery. The primary end point was the incidence of death or MI at 28 days after surgery. Complement activation was assessed by levels of CH50 and SC5b-9 during and after CPB. TP10 was well tolerated and there were no differences in the safety profiles of the 2 groups. Although TP10 effectively suppressed complement activation (at 2 hours after CPB CH50 (mean+SD % change from baseline) 50+/-17% placebo versus 4+/-14% TP10; P=0.0001; SC5b-9 (ng/mL) 917+/-1067 placebo versus 204+/-79 TP10; P=0.0001), there was no difference in the primary end point between the groups (17% placebo versus 21% TP10; P=0.2550).

CONCLUSIONS

The benefits of TP10 appear to be gender-related. and mechanisms other than complement activation may be responsible for myocardial injury in high-risk female patients during cardiac surgery on CPB.

Myocardial infarction following coronary artery bypass graft surgery increases healthcare resource utilization

OBJECTIVE

To assess the health economic impact of perioperative myocardial infarction in a cohort of patients undergoing coronary artery bypass graft surgery.

DESIGN

Retrospective cohort analysis using data from hospital bills and uniform billing forms.

SETTING

A total of 147 geographically diverse hospitals in the United States.

PATIENTS

The study population consisted of 2,102 coronary artery bypass graft surgery patients enrolled in the PRIMO-CABG trial at U.S. sites between January 2002 and February 2003.

INTERVENTIONS

None.

MEASUREMENTS AND MAIN RESULTS

Resource utilization and costs during the index hospitalization and during a 6-month follow-up period were compared between patients who had a myocardial infarction by postoperative day 4 and those who did not. Linear regression was used to examine whether myocardial infarction by day 4 was associated with index hospitalization costs, after adjusting for baseline characteristics. Myocardial infarction occurred in 191 (9.1%) patients undergoing coronary artery bypass graft surgery. Myocardial infarction was associated with a doubling of intensive care unit time (3.5 days among patients with no myocardial infarction and 7.1 days among patients with myocardial infarction, p < .01) and a 48% increase in hospital length of stay. Myocardial infarction by day 4 was associated with a 43% increase in hospital costs, a 29% increase in physician service costs, a 41% increase in total costs during the index hospitalization, and a 38% increase in cumulative 6-month costs. After baseline adjustment, myocardial infarction continued to be associated with higher index hospitalization costs.

CONCLUSIONS

Myocardial infarction following coronary artery bypass graft surgery was associated with a significant increase in intensive care unit time, hospital length of stay, and overall costs, which contributed to greater hospital and physician service costs. Healthcare resource utilization is increased in patients sustaining a myocardial infarction following coronary artery bypass graft surgery.