Aspirin and the Nonsteroidal Anti-inflammatory Drugs

The interaction between platelets and the inflammatory system are numerous. It is therefore no surprise that interventions aimed at inhibiting platelet function may exert, in parallel, significant anti-inflammatory effects. Aspirin has a compelling mortality benefit during AMI. In addition to its antiplatelet properties, aspirin exerts some anti-inflammatory effects that may contribute to some of the mortality benefit observed after myocardial infarction. ^, In animal models, aspirin triggers the synthesis of lipoxins (known as the aspirin-triggered LXA4) that vigorously inhibits leukocyte chemotaxis during ischemia and reperfusion injury. Nonsteroidal anti-inflammatory drugs (NSAIDs), on the other hand, have been extensively studied because of their possible deleterious effect on the endothelium and on atherosclerotic plaques. In dogs, ibuprofen has been shown to reduce both the infarct size and leukocyte accumulation inside the infarcted tissue. This is in the context, however, of the well-established effect of indomethacin on impairing infarct healing and leading to aneurysm formation.

In a retrospective study meant to assess the effect of NSAIDs in the pre-aspirin era, Sajadieh and colleagues looked at the pre-randomization use of NSAIDs among the Danish Verapamil Infarction Trial (DAVIT) II trial. The authors hypothesized that NSAIDs other than aspirin may also improve the prognosis after AMI. After correction for age, sex and hypertension, the use of NSAIDs before myocardial infarction was associated with a non-significant reduction in mortality (hazard ratio [HR], 0.59; 95% confidence interval [CI], 0.28 to 1.25; P = .17), and major cardiac events (HR, 0.67; 95% CI, 0.37 to 1.19; P = .17). While this is useful for hypothesis generation, the association may well be due to confounding.

Prostacyclin (PGI ₂ ) is a member of the eicosanoid family that naturally prevents the formation of clot by inhibiting platelet activity and by causing arterial vasodilatation. In experimental settings, prostacyclin was shown to facilitate fibrinolysis and reduce myocardial stunning following infarction. These early experiments served as the bases for the Thrombolysis and Angioplasty in Myocardial Infarction (TAMI)-4 trial which tested iloprost, a synthetic analogue of prostacyclin, in combination to rt-PA in 50 patients with evolving ST-segment elevation myocardial infarction (STEMI). Compared with rt-PA alone, the combination of intravenous iloprost (2 ng/kg/min for 48 hr) and rt-PA neither affected the rates of infarct-related vessel patency at 90 minutes (44% vs. 66% respectively, P = .26) nor improved the ejection fraction recovery at 7 days (+2.9% vs. −2.3% respectively, P = .05).

The inhibitors of cyclooxygenase-2 (COX-2) have been linked to increased cardiovascular risk when administered for chronic conditions. Paradoxically, a selective COX-2 inhibition has been shown to reduce the macrophage infiltration and to preserve the ventricular function after myocardial infarction in rodents. At least one trial has suggested a protective effect of short-term administration of COX-2 inhibitor to patients with acute coronary syndrome. In the Nonsteroidal Anti-Inflammatory Drugs in Unstable Angina Treatment-2 (NUT-2) pilot study, patients with non–ST-segment elevation myocardial infarction (NSTEMI) randomized to 30 days of meloxicam (a selective COX-2 inhibitor) experienced less recurrent angina, myocardial infarction, or death than the patients randomized to placebo (21.7% vs. 48.3% respectively, P = .004, n = 120) at 90 days after initial hospitalization. In this small study, the benefits were mainly driven by the high rates of recurrent angina in the placebo-treated patients. Neither the investigators nor the patients were blinded to the treatment assignment. These findings await validation in a large double-blind trial.

Corticosteroids

Corticosteroids have a pleiotropic effect on the immune system. They were among the first immunomodulators studied in AMI. Corticosteroids exert adverse effects on the cardiovascular system, such as dyslipidemia and hypertension. Since the 1970s, several case series have linked the use of corticosteroids with left ventricular free wall rupture in the days following AMI. The mechanism by which corticosteroids prevent healing of myocardial infarction is not entirely known; it may relate to impaired scar formation of the degenerative process responsible for the peripheral myopathy seen in patients treated with chronic corticosteroids. The steroid-dependent attenuation of the sympathetic innervations of the infarct region could also contribute to impaired healing. On the other hand, the powerful immunosuppressive effect of corticosteroids may modulate the inflammatory response that could have beneficial effects in the short term.

Corticosteroids have been tested in patients with acute coronary syndrome. In the Muna randomized trial, methylprednisone was compared with placebo in patients with recent-onset unstable angina. While 48 hours of methylprednisone decreased C-reactive protein levels compared with placebo, it had no apparent effect on subsequent coronary events. In fact, a trend toward a better event-free survival was seen in the placebo-control group. The trial was underpowered to address the effect of steroids on clinical events. In 1986, the Solu-Medrol Sterile Powder AMI Studies Group reported the results of a double-blind, placebo controlled trial that tested whether a single dose of methylprednisolone (30 mg/kg IV) reduced 28-day mortality in 1118 patients with recent myocardial infarction complicated by cardiac failure. Per design, the trial hypothesized that an effect of methylprednisolone could depend on time since symptom onset. When administered within 6 hours of symptoms onset, methylprednisolone did not seem to affect mortality compared with placebo (11.7% vs. 9.9%, P = NS). However, when started more than 6 hours after the onset of symptoms, Solu-Medrol significantly reduced mortality at 48 hours (10.4% vs. 14.7%, P = .04) and at 6 months ( P = .03). Interestingly, similar rates of cardiac aneurysms (1.2% vs. 0.5%, P = .45), and cardiac ruptures (1.7% vs. 2.5%, P = .47) were observed between methylprednisolone and placebo-treated patients.

In a recent meta-analysis of 11 controlled trials including 2646 patients, a 26% relative mortality reduction was observed with the use of corticosteroids within the first few hours following AMI (odds ratio [OR], 0.74; 95% CI, 0.59 to 0.94; P = .02). In a sensitivity analysis which excluded the non-randomized study, the previously observed mortality benefit with steroids was no longer present (OR, 0.95; 95% CI, 0.72 to 1.26). Importantly, no clear association was observed between myocardial rupture and corticosteroids, calling into question the conventional wisdom that steroids impair infarct healing. While none of the trials was performed in the modern era of thrombolytics and aggressive percutaneous revascularization, the available evidence suggests no evidence of either substantial benefit or harm from corticosteroids in AMI.

Statins

Just like aspirin, long-term statin administration improves the prognosis of patients across the entire spectrum of acute coronary syndromes (ACS). However, the short-term benefits of statin therapy early after ACS are equivocal. In a recent meta-analysis, the initiation of a statin within 14 days following the onset of an acute coronary event did not reduce death, myocardial infarction (MI), or stroke at 4 months. Fewer studies have assessed the protective role of statins when present before the occurrence of an ACS. In this regard, the Atorvastatin for Reduction of Myocardial Damages during Angioplasty (ARMYDA)-trial has provided interesting insights on the mechanism of action of statins. In ARMYDA, a pretreatment with 80 mg of atorvastatin at least 12 hours before the percutaneous coronary intervention (PCI) resulted in a significant reduction of the composite incidence of death, myocardial infarction, and unplanned revascularization at 30 days (5% vs. 17% for placebo, P = .01), mainly through a reduction in peri-procedural infarctions. Atorvastatin resulted in a lower average percent increase of C-reactive protein level after the PCI (63% ± 114% vs. 147% ± 274% for placebo). After adjusting for key clinical predictors (NSTEMI, left ventricular ejection fraction [LVEF] below 40%, the use of glycoprotein IIb/IIIa inhibitors and beta blockers), atorvastatin remained a significant predictor of favorable clinical outcome. In a substudy of ARMYDA, the levels of soluble intercellular cell adhesion molecule-1 (ICAM-1) and E-selectin were significantly less increased at 24 hours following the PCI in patients treated with atorvastatin, suggesting a modulatory effect of statin on leukocytes and endothelial cell interactions.

The acute benefit seen with statins in ACS patients cannot be solely explained by the cholesterol-lowering effect, which requires a longer duration of treatment. This so-called pleiotropic effect of statins could be in part due to a favorable modulation of the inflammatory system. ^, Animal experiments have suggested that statins can reduce the infarct size, related to a decrease in endothelial expression of P-selectin on endothelial cells and CD18 on leukocytes, leading to a reduced neutrophil extravasation into the reperfused myocardium. ^, Together with the stabilization of the endothelial function and the microcirculatory vasodilatation, the immunomodulatory effects of statins appear to favor survival of cardiomyocytes following ischemia/reperfusion.

Adenosine and its Agonists

Adenosine is an endogenous purine nucleoside that antagonizes several of the metabolic, biochemical and inflammatory pathways that may be involved in reperfusion injury ( Fig. 25-3 ). Adenosine and its receptor appear to be important elements of the intrinsic protective mechanism of the myocardium against ischemic insult. When subjected to hypoxia, myocardial and endothelial cells naturally release adenosine which, in turn, brings myocardial cells into a phenotype of sustained tolerance against ischemia. This phenomenon, called preconditioning, is incompletely understood but involves the inhibition of oxygen free radical formation, the repletion of cardiomyocytes and endothelial cells with high-phosphate stores, and the increase in nitric oxide bioavailability. Equally important is the cardioprotective effect of adenosine through the modulation of inflammation. Adenosine has a marked inhibitory effect on neutrophils by limiting their reactive oxygen species generation and their adherence to endothelial cells, possibly via a down-modulation of CD11/CD18 expression. In addition to its antineutrophil effects, adenosine may also serve as a metabolic switch that senses tissue injury and acts to reduce the production of inflammatory cytokines, such as tumor necrosis factor-α, interleukin-12, or macrophage inflammatory protein (MIP)-1a. In animal models of reperfusion injury, adenosine has consistently improved coronary blood flow, reduced infarct size, and improved left ventricular functional recovery.

Anti-inflammatory pathways impacted by adenosine. A summary of pathways of adenosine formation and catabolism in the heart and their potential modulation during ischemia-reperfusion. Broken arrows reflect regulatory processes, with plus ( + ) and minus ( − ) symbols denoting activation or inhibition of pathways during de-energization/ischemia, respectively. Whereas catabolism of adenosine to inosine, hypoxanthine, xanthine, and uric acid is shown within the myocytes, deamination also occurs extracellularly, and these reactions occur with high activity in vascular cells. AK, adenosine kinase; AMP-DA, AMP deaminase; Cr, creatine; ECTO-5′-NUC, ecto-5′-nucleotidase; HPRT, hypoxanthine phosphoribosyl transferase; 5′-NUC, 5′-nucleotidase; PCr, phosphocreatine; P _i , inorganic phosphate; PKC, protein kinase C; PLC, phospholipase C; PLD, phospholipase D; PNP, purine nucleoside phosphorylase; TNF-α, tumor necrosis factor-α; XDH/XO, xanthine dehydrogenase/xanthine oxidase.

(Reproduced with permission from Headrick JP, Hack B, Ashton KJ: Acute adenosinergic cardioprotection in ischemic-reperfused hearts. Am J Physiol Heart Circ Physiol 2003;285:H1797-H1818.)

The cardioprotective effect of adenosine and its agonists has been assessed in distinct clinical scenarios, including acute coronary syndromes, high-risk PCI, and coronary artery bypass graft (CABG) surgery. The Acute Myocardial Infarction Study of ADenosine (AMISTAD)-I and AMISTAD-I trials assessed the role of adenosine in myocardial infarction. The 236-patient AMISTAD-I trial showed a 33% reduction ( P = .03) in infarct size measured by single-photon-emission computed tomography (SPECT) ^99m Tc sestamibi with adenosine compared with placebo. In the subgroup of patients with anterior wall infarction, the difference was even more important, with a 67% relative reduction in final infarct size (15% vs. 45.5% of left ventricle respectively, P = .01). While the number of adverse clinical events was low, there was a numerical excess of death (10 vs. 6) and congestive heart failure (13 vs. 8) among patients treated with adenosine. These findings prompted the AMISTAD-II trial, a phase III randomized, double-blind trial designed to compare progressive doses of adenosine to placebo in 2118 patients with anterior STEMI. In this setting, adjunctive adenosine was no better than placebo at prolonging event-free survival (death, in-hospital congestive heart failure [CHF] and rehospitalization for CHF) at 6 months (84% vs. 82%, P = .43). Interestingly, in a substudy, patients treated with adenosine tended to have smaller median infarct size compared with patients treated with placebo (17% vs. 27% of the left ventricle, P = .07). Moreover, patients treated with the highest dose of adenosine (70 µg/kg/min) had the smallest infarct size, suggesting a dose-response relationship (11% of the left ventricle, P = .02 vs. placebo). As noted by the investigators, there was a significant association between the infarct size and the occurrence of CHF or death. The discrepancy between the actual effect of adenosine on infarct size and the clinical outcomes remains unexplained, but may relate to the relatively low power of this moderately sized trial. It also, however, calls into question the validity of surrogate outcomes—such as infarct size—to assess the clinical effects of investigational new drugs.

The benefits suggested by the AMISTAD trials were not confirmed by the ATTenuation by Adenosine of Cardiac Complications (ATTACC) trial. In ATTACC, 608 patients with STEMI were randomized to either adjunctive low-dose adenosine (10 µg/kg/min) or placebo, administered with fibrinolysis. The relatively small dose of adenosine was chosen after concerning rates of adverse events were observed with higher doses (40 µg/kg/min). In this context, the LVEF was similar between the adenosine and the placebo-treated patients (44% vs. 45% respectively, P = NS), along with the wall motion score index (1.53 vs. 1.50, respectively, P = NS). Based on this apparent lack of benefit, recruitment in the trial was stopped after less than two thirds of the patients originally planned had been enrolled. At 12 months, the cardiovascular mortality was 8.9% with adenosine and 12.1% with placebo (OR, 0.71; 95% CI, 0.4 to 1.2; P = .2). As was the case with AMISTAD-I, the effect size appeared to be more impressive in the subgroup of patients with anterior STEMI (OR, 0.53; 95% CI; 0.23 to 1.24; P = .09). Because of the early termination of recruitment, the results should be interpreted with caution.

In parallel to the AMISTAD and ATTACC trials, a series of trials have assessed the use of adjunctive adenosine agonist during AMI. The adenosine agonist AMP579 has mixed affinities for the adenosine A1 and A2 receptors. The A1 receptor is of major importance in mediating the anti-ischemic action of adenosine. The A2 receptor, on the other hand, has a more controversial contribution but appears to reduce the neutrophil adherence and the subsequent damages during reperfusion injury. In animal models of myocardial reperfusion injury, AMP579 has demonstrated superior cardioprotective effects compared with adenosine, possibly due to a superior inhibition of the vascular and myocardial tissue injury induced by neutrophils. The AmP579 Delivery for Myocardial Infarction REduction (ADMIRE) trial was designed to find the most efficient dose of AmP579 in patients with STEMI treated with primary PCI. To this end, 311 patients were randomized to either three different doses of AmP579 or placebo intravenously over 6 hours. No differences were seen in the final infarct size or the myocardial salvage index after adjustment for infarct-related artery, the time to reperfusion, and the initial TIMI flow. Likewise, the rates of adverse events were similar between the groups at 4 weeks and 6 months. ADMIRE did not demonstrate a benefit of AmP579 on infarct size or clinical outcomes.

Taken together, the trials presented in this section fail to show a clear clinical benefit of adjunctive adenosine with a timely reperfusion therapy. Additional studies are required, however, to fully explore the consequence of the beneficial effect of adenosine on infarct size and microvascular function.

Anti-Leukocyte Therapies

The endothelium serves as a natural barrier that protects the organ tissue from certain elements circulating in the blood. The endothelium is normally responsible to orchestrate the trafficking of leukocytes into the myocardium (see Fig. 25-3 ). In response to hypoxia, the endothelium undergoes a series of transcriptional and non-transcriptional changes similar to those seen during acute inflammation. PMNs normally migrate into the ischemic tissue. Once in place, PMNs are thought to cause direct tissue damage and to amplify the inflammatory response during the reperfusion. During an AMI, the microvascular damage and disruption of the endothelium barrier allow a massive influx of PMNs into the necrotic core and the surrounding viable myocardium. Likewise, PMNs secrete factors that disrupt the endothelial barrier and favor the formation of tissue edema.

Leukocytes transmigrate tissue through a series of complex steps that involve anchoring molecules expressed by the endothelium. Circulating neutrophils expressing P-selectin glycoprotein ligand 1 (PSGL-1) are initially caught by the endothelial receptor P-selectin (CD62P). This low-affinity interaction allows the neutrophils to slow their course and roll on the endothelium until they adhere more firmly. This process is mediated by the ligation of the leukocyte β2 integrins CD11a/CD18 and the endothelial ICAM-1. Once tightly bound to the endothelium, the leukocytes can transmigrate into the ischemic tissue, where they release toxic reactive oxygen species and other proinflammatory substances.

After a myocardial infarction, the pharmacologic interventions targeting the leukocytes can be regrouped in three distinct targets: the inhibition of leukocyte adhesion molecule synthesis (such as CD11a/CD18), the inhibition of receptor engagement and endothelial cell adhesion (such as P-selectin), and the inhibition of inflammatory mediator release, such as platelet activation factor (PAF), and leukotriene B ₄ (LTB ₄ ). Both P-selectin and CD11a/CD18 have recently been tested in patients with STEMI.

P-Selectin Inhibitors

P-selectin (CD62P) is an adhesion molecule that plays a critical role in the migration of leukocytes through the vascular walls. The ligand of P-selectin, PSGL-1, is constitutively expressed by leukocytes. P-selectin is involved in the adhesion of platelets to the endothelium and has been shown to play an important role in the process of atherogenesis. Convincing studies have shown that animals lacking P-selectin have a decreased tendency to develop atherosclerotic plaques. After promising animal experiments, the interference between P-selectin and PSGL-1 by the way of a monoclonal antibody was expected to facilitate the fibrinolysis and to decrease the infarct size by controlling the migration of leukocytes into the necrotic areas. Because of its anti-thrombotic and anti-inflammatory effects, P-selectin inhibition appeared to be a promising target during acute MI.

The P-selectin Antagonist Limiting Myonecrosis (PSALM) trial tested a recombinant P-selectin glycoprotein ligand-immunoglobulin (rPSGL-Ig) in patients with STEMI presenting within 6 hours of symptom onset and treated with alteplase. The engineered P-selectin antagonist combined the high-affinity ligand of the amino-terminal portion of PSGL-1 with an Fc (fragment crystallizable) region of the human IgG1. Patients were randomly assigned to a single intravenous bolus of either 75 mg of rPSGL-Ig, 150 mg of rPSGL-Ig, or placebo. The study tested the potential benefit of rPSGL-Ig on infarct size reduction using positron emission tomography to quantify the myocardial blood flow in the infarct territory, normalized for the systemic equilibrated blood pool. A total of 88 patients were enrolled before the trial was prematurely stopped by the sponsor. At 5 days, the normalized infarct size was not statistically different between the patients treated with placebo and the patients treated with either the low or the high doses of rPSGL-Ig (9.1% vs. 3.8% vs. 4.3%). The PSALM trial was stopped after a larger trial (RHAPSODY) failed to show any benefit of adjunctive rPSGL-Ig on the speed of ST-segment resolution and the reduction of infarct size in nearly 600 STEMI patients treated with fibrinolysis. ^, The RHAPSODY trial failed to show any significant effect of rPSGL-Ig on improvement of the LVEF, and the occurrence of death, stroke, and MI at 30 or 180 days. Unlike what was expected based on the animal data, there was a significant delay in myocardial reperfusion seen in patients treated with rPSGL-Ig, as shown by a significant prolongation of time to ST-segment resolution ( P = .008). The redundancy of the inflammatory pathways in mammals may account for the lack of efficacy of a selective inhibition of P-selectin.

CD11/CD18 Integrin Receptor Blockade

Neutrophils start to accumulate at the periphery of the necrotic myocardium as early as 8 hours after the start of the infarction. Leukocytes transmigrate after they ligate their β ₂ integrins CD11a/CD18 to ICAM-1. Using a rationale similar to with the P-selectin inhibitors, the blockade CD11/CD18 integrin receptor has been tested in two independent randomized controlled trials. The LIMIT-AMI trial was designed to define the safety and the efficacy of a rhuMAb CD18, a recombinant humanized monoclonal antibody against the CD18 subunit of the β ₂ integrin adhesion receptors in 394 patients with AMI. This randomized, double-blind trial compared two intravenous doses of the study drug (0.5 mg/kg vs. 2.0 mg/kg) to placebo, administered concomitantly with thrombolytic therapy. At 90 minutes after the start of fibrinolysis, the corrected TIMI frame count (primary end point) was similar between the groups, as was the percent of patients with a resolution of their ST-segment elevation resolution at 3 hours. The myocardial infarct size (assessed by ^99m Tc-sestamibi SPECT) was also similar, as were the rates of adverse clinical events. Compared to placebo, the systemic administration of the study drug resulted in a peak of circulating white blood cells at 24 hours, which rapidly resolved by 72 hours, with no apparent effect on other blood compartments.

The HALT-MI trial tested whether Hu23F2G, a humanized antibody directed against all the isoforms of the CD11/CD18 integrin receptors, would reduce the infarct size in patients with AMI treated with primary PCI. The HALT-MI randomized 420 patients either to Hu23F2G (0.3 mg/kg or 1.0 mg/kg) or placebo given prior to primary PCI. The left ventricle infarct size measured by SPECT was used as the primary study end point. The study drug was administered as a single intravenous bolus over 1 to 2 minutes. The doses of Hu23F2G used in the trial were shown to saturate up to 80% of the CD11/CD18 integrin receptors for 12 to 24 hours in healthy volunteers. The final infarct size for the intention-to-treat population was similar in the 0.3 mg/kg, 1.0 mg/kg, and the placebo groups (16% vs. 17.2% vs. 16.4%, respectively; P = .80). Infarct sizes measured at baseline with the creatine kinase MB (CK-MB) area under the curve (AUC) for 24 hours were also similar. No difference in the rate of adverse clinical events at 30 days was detected. As was the case for the LIMIT-AMI trial, minor infections (mainly urinary tract infection) were more common in the active treatment groups. Together, the LIMIT-AMI and the HALT-MI trial show lack of beneficial cardiac effects of CD18 blockade in patients with AMI.

The time elapsed between the start of the myocardial infarction and the administration of the blockers of the CD11/CD18 integrin receptor varied significantly between animals and humans. This difference has been suggested as part of the explanation for the discrepant findings seen between the animal experiments and this (and other) clinical trials. In most animal experiments, the study drug was administered within 45 to 60 minutes after the ligation of the coronary artery. In the LIMIT-AMI study, the median time to symptom onset was 2.7 hours, for instance. The delays seen in humans may have resulted in a greater burden on endothelial cell barrier rupture. Assuming this were true, the greater endothelial permeability may in return have allowed a free circulation of neutrophils into the injured myocardium therefore bypassing the usual Mac-1 intercellular adhesion mechanism. Interestingly, no favorable effects were seen with the late administration of the CD11/CD18 integrin receptor blocker in experimental myocardial infarction.

ITF-1697

ITF-1697 is a chemically modified LyS-Pro tetrapeptide (Gly-(Et)Lys-Pro-Arg) that corresponds to the sequence 113 to 116 of C-reactive protein. ITF-1697 exerts an antianaphylactic activity and has been tested in at least two distinct clinical trials on patients with MI. ^, While virtually no preclinical information has been formally published, before the trials came out in 2004, ITF-1697 was said to reduce reperfusion injury by preventing PMN adhesion and extravasation and by limiting the increase in vascular permeability and microcapillary plugging seen during no reflow. In the Protect Against Reperfusion Injury in acute Myocardial Infarction (PARI-MI), four dose regimens of adjunctive ITF-1697 were compared with placebo in patients with AMI who were eligible for PCI. In PARI-AMI, neither a dose-relation nor a benefit could be seen in terms of infarction size, post-procedural coronary blood flow, or clinical outcome.

Erythropoietin

In the past decade, our understanding of the role played by erythropoietin (EPO) has gradually shifted from a concept of strictly hematopoiesis to a broader role including anti-hypoxia. Erythropoietin appears to play an important role in the development of the heart, and its defense against injury. During embryogenesis, the inactivation of the erythropoietin receptors leads to defects in cardiac morphogenesis. The discovery that the cardiomyocytes express the receptor for erythropoietin has opened the way to a series of investigations to test for a protective role during ischemic stress. Treatment with human recombinant erythropoietin in animal models of ischemia-reperfusion has been associated with reduced myocardial infarct size and improved left ventricular functional recovery. ^, Erythropoietin stimulates postnatal neovascularization by enhancing endothelial precursor cell mobilization from the bone marrow. Likewise, erythropoietin inhibits cardiac myocyte hypoxia-induced apoptosis through PI3K-Akt-dependent pathways, ^, which could favor myocardial healing. Erythropoietin also exerts a potent anti-inflammatory effect in the myocardium, where it has been shown to directly inhibit IL-6, tumor necrosis factor-α (TNF-α), and monocyte chemoattractant protein ^, and to block the acute inflammatory component of reperfusion injury by inducting AP-1. Erythropoietin significantly reduces inflammatory cell infiltration and fibrosis in animal models of myocardial infarction ^, and chronic congestive heart failure.

It is not known whether erythropoietin has a protective effect against ischemia-reperfusion injury in humans. Recently, high endogenous erythropoietin levels were associated with a smaller infarct size in patients treated with primary percutaneous coronary intervention. The efficacy of recombinant erythropoietin is currently being tested in several small trials of patients with ACS. In a pilot study testing a single dose of epoitin-α on patients with non–ST-segment elevation ACS, no significant reduction in myocardial damage was found when compared with placebo. Instead, an increase in systolic blood pressure was observed in the hours following erythropoietin (+10 mm Hg ± 16 mm Hg for epoitin vs. −6 mm Hg ± 16 mm Hg for placebo, P = .007), which is a surprising finding for a short-term therapy. In patients with STEMI treated with primary PCI, a single intravenous high dose of darbepoetin alfa or erythropoietin was safe and well tolerated. In 2009, Binbrek and colleagues. reported on the effect of β-EPO (single 30,000 IU IV bolus before tenecteplase) compared with standard care in 236 patients admitted with STEMI within less than 6 hours of onset of symptoms. Despite EPO, the infarct size index was virtually identical in the EPO and control groups (12.4 ± 0.9 vs. 13.2 ± 0.1 creatine kinase-MB gram equivalents, respectively, data presented as mean ± SE, P = NS). At discharge, the LVEF was similar in both groups. The results of this trial prompted larger confirmatory trials that are currently underway to test the effect of EPO in patients with STEMI.

Cell Therapy

Inflammation is a putative target of cell therapy in the diseased heart. Certain cell populations may be naturally predisposed to inhibit inflammation. For instance, the mesenchymal stem cells (MSCs) have been used with apparent success in advanced inflammatory conditions, such as refractory Crohn disease or steroid-resistant graft-versus-host disease. ^, Mesenchymal stem cells or marrow stromal cells are a rare population in the bone marrow that forms the supportive niche required by the hematopoietic tissue to maintain their function. Transplanted MSCs have been shown to down-modulate the inflammatory response in multiple experimental models, including after AMI. MSCs secrete a vast array of pro-angiogenic cytokines and growth factors. ^, During in vivo experiments, MSCs transplanted into ischemic milieu deliver cytokines into the surrounding tissues, which is thought to favor vasculogenesis and reduce apoptosis. In addition to a possible regenerative effect, the paracrine secretion of cytokines and growth factors has been proposed as one of the mechanisms for the cardioprotective effects of MSCs during ischemic injury. ^, MSCs do not express major histocompatibility complex class II and co-stimulatory molecules. For this reason, MSCs can directly interact with cells of the immune system to modulate the anti-inflammatory environment that can promote healing and survival of damaged cells. Whether MSCs can truly escape reaction by the immune system is controversial. The clinical experience with MSCs on cardiac patients is limited, however. Compared to placebo, the intravenous administration of heterologous MSCs (Provacel) has been associates with an encouraging protective signal in patients with recent STEMI. Interestingly, a significant improvement in the forced expiratory volume in 1 second (FEV ₁ ) was observed in all patients treated with cells, suggesting a possible anti-inflammatory lung effect. A larger trial use is currently underway to assess the efficacy of MSCs in patients with STEMI.

Not every cell population seems to have beneficial anti-inflammatory effect. In the ASTAMI trial, bone marrow mononuclear cells (BMMNCs) were not superior to placebo at improving the left ventricular function following a STEMI. In the study, the intracoronary injection of autologous BMMNCs resulted in a transient, yet pronounced augmentation of both the circulating IL-6 and the expression of TNF-α mRNA, along with a lesser decrease in C-reactive protein in the days following the AMI. Interestingly, investigators have suggested that the improvement in cardiac function after BMMNC therapy was associated with a transient increase in myocardial infarction. A better understanding of the role played by the immune system in cardiac repair following a myocardial infarction will open the way to better cell-based regenerative strategies.

FX06

FX06 is a naturally occurring fibrinogen product that was initially developed as a laboratory test to monitor thrombogenesis in acute coronary syndrome. FX06 is a 28-amino-acid peptide derived from the peptide sequence Bβ15-42 of human E1 fibrin fragment. ^, It is released by plasmin during fibrinolysis and binds to vascular endothelial (VE)-cadherin to interfere with the diapedesis of leukocytes across the endothelium. The receptor for FX06 has not been identified, but the receptor CD11c expressed by neutrophils and monocytes has been proposed. In animal models of ischemia-reperfusion, FX06 has been shown to substantially reduce the circulating levels of IL-6. Likewise, it decreased the infiltration of leukocytes into the injured myocardium, therefore reducing the infarct size and subsequent scar formation. ^, FX06 has a plasma half-life ranging from 11 to 17 minutes (in healthy volunteers).

In the FX06 in the Prevention of Myocardial Reperfusion Injury (F.I.R.E) trial, the interplay of fibrin fragments, leukocytes and VE-cadherin was assessed in 234 patients presenting with STEMI undergoing primary PCI within 6 hours of onset of symptoms. Patients were randomly assigned to either the study drug (two IV boluses; 200 mg before coronary guidewire crossed the lesion and 200 mg 10 minutes later) or their matching placebo. F.I.R.E used the infarct size at 5 days as a primary end point, measured by late gadolinium enhancement (LGE) on cardiac magnetic resonance (CMR), with adjustment for the rates of TIMI 0/1 flow, and the presence of collaterals before the primary PCI. Of note, the infarct size at baseline was not assessed. At 5 days, the adjusted infarct size was not different between groups (19.7% for FX06 vs. 19.8% for placebo, P = .48). Interestingly, a significant difference was seen in the size of the necrotic core zone (1.8 g vs. 4.2 g; P <.025, favoring FX06). Likewise, FX06 resulted in numerically lower rates of microvascular obstruction (27.6% vs. 37.5%, P = .09) measured by CMR. At 4 months, no significant differences in total LGE improvement could be seen by CMR. Overall, there were no differences across the groups in rates of treatment-related adverse events.

Cyclosporine and Analogues

Cyclosporine A has been used for decades as an immunosuppressive drug to prevent rejection after the transplantation of solid organs. Cyclosporine forms with cyclophilin D a complex that inhibits calcineurin, a potent transcription inducer of IL-2 and other lymphokines. More recently, cyclosporine and its analogues have been shown to inhibit the opening of mitochondrial permeability transition pores. The defective mitochondria are thought to play a major adverse role during reperfusion injury seen with organ transplantation. ^, The mitochondrial permeability transition pores are found in the inner membrane of the mitochondria. In normal conditions, these pores nonspecifically conduct low-molecular-weight solutes. During ischemia and reperfusion, the calcium and reactive oxygen species cause the pores to reopen, ^, resulting in mitochondrial depolarization with uncoupling of oxidative phosphorylation. The uncoupling of the respiratory chain causes the cells to become deplete in adenosine triphosphate (ATP), which leads to cell death. The accompanying release of pro-apoptotic cytochrome C by the mitochondria may further result in cardiomyocyte death.

The pharmacologic suppression of mitochondrial permeability transition pore during ischemia and reperfusion has recently been tested in a pilot study. Piot and colleagues tested the efficacy and safety of a single cyclosporine bolus given at the time of reperfusion in patients with STEMI treated with primary PCI. The size of the myocardial infarction as measured by the 72-hour CK AUC was significantly reduced in patients treated with cyclosporine, compared with placebo (relative infarct size reduction, 40%; P = .04). Smaller infarct sizes were also measured among cyclosporine-treated patients enrolled in the cardiac magnetic resonance sub-study (relative infarct size reduction, 27%; P = .04). The rates of adverse clinical events were similar between the groups. At 3 months, the mean left ventricular ejection fraction as measured by echocardiography were similar in both groups (cyclosporine, 50% ± 2% vs. placebo, 47% ± 3%; P = .32). In the study, the blood concentration of cyclosporine was nearly undetectable in a majority of patients 12 hours after the administration of the drug.

In addition to its effect on the mitochondrial permeability transition pores, cyclosporine has additional effects that could contribute to myocardial protection during ischemia/reperfusion. In vitro, cyclosporine A appears to be effective at lowering the neutrophil chemotaxis, as well as release of toxic lysozyme and superoxide anion in response to stimulation. Likewise, cyclosporine regulates the expression of inducible nitric oxide synthase (iNOS), which has been shown to protect the myocardium in ischemic conditions. Proof-of-concept clinical trials with N -methyl-4-isoleucine cyclosporin (N1M811C), a cyclosporine analogue with no known immunosuppressive effect, will help to clarify the role played by the mitochondrial permeability transition pore during the reperfusion injury.

p38 Mitogen-Activated Protein Kinase Inhibitor

The p38 mitogen-activated protein kinase (MAPK) plays a key role in the initiation and the amplification of inflammatory processes. P38 MAPK activity increases early after myocardial infarction and appears to stay activated for several weeks thereafter. In vitro, p38 MAPK has been involved in the regulation of myocyte hypertrophy and apoptosis. In experimental settings, p38 MAPK inhibition has resulted in infarct size reduction in the acute phase. Likewise, it has been shown to favorably remodel the left ventricle in the chronic phase following an acute infarction. Importantly, p38 MAPK inhibition has modified the atherogenic process in animal models of chronic coronary artery disease. Because of its simultaneous action on the coagulation system and the inflammatory system, p38 MAPK is an appealing target for the treatment of acute coronary syndromes.

In humans, p38 MAPK has been shown to upregulate coagulation processes by increasing the expression of tissue factor on the endothelial cells and the monocytes. ^, In a phase I trial, oral inhibitors of the p38 MAPK attenuated the surge of circulating proinflammatory cytokines TNF-α, IL-6, and IL-8 in response to endotoxin stimulation. ^, Oral p38 MAPK inhibitors have been tested with limited success in chronic inflammatory conditions, such as rheumatoid arthritis and Crohn disease. ^, Clinical trials are under way to investigate p38 MAPK as a target for cardiovascular protection in patients with ACS.