Benjamin W. Van Tassell

The inflammasome promotes adverse cardiac remodeling following acute myocardial infarction in the mouse

Acute myocardial infarction (AMI) initiates an intense inflammatory response that promotes cardiac dysfunction, cell death, and ventricular remodeling. The molecular events underlying this inflammatory response, however, are incompletely understood. In experimental models of sterile inflammation, ATP released from dying cells triggers, through activation of the purinergic P2X7 receptor, the formation of the inflammasome, a multiprotein complex necessary for caspase-1 activation and amplification of the inflammatory response. Here we describe the presence of the inflammasome in the heart in an experimental mouse model of AMI as evidenced by increased caspase-1 activity and cytoplasmic aggregates of the three components of the inflammasome—apoptosis speck-like protein containing a caspase-recruitment domain (ASC), cryopyrin, and caspase-1, localized to the granulation tissue and cardiomyocytes bordering the infarct. Cultured adult murine cardiomyocytes also showed the inducible formation of the inflammasome associated with increased cell death. P2X7 and cryopyrin inhibition (using silencing RNA or a pharmacologic inhibitor) prevented the formation of the inflammasome and limited infarct size and cardiac enlargement after AMI. The formation of the inflammasome in the mouse heart during AMI causes additional loss of functional myocardium, leading to heart failure. Modulation of the inflammasome may therefore represent a unique therapeutic strategy to limit cell death and prevent heart failure after AMI.

Interleukin-1 Blockade With Anakinra to Prevent Adverse Cardiac Remodeling After Acute Myocardial Infarction (Virginia Commonwealth University Anakinra Remodeling Trial [VCU-ART] Pilot Study)

Acute myocardial infarction (AMI) initiates an intense inflammatory response in which interleukin-1 (IL-1) plays a central role. The IL-1 receptor antagonist is a naturally occurring antagonist, and anakinra is the recombinant form used to treat inflammatory diseases. The aim of the present pilot study was to test the safety and effects of IL-1 blockade with anakinra on left ventricular (LV) remodeling after AMI. Ten patients with ST-segment elevation AMI were randomized to either anakinra 100 mg/day subcutaneously for 14 days or placebo in a double-blind fashion. Two cardiac magnetic resonance (CMR) imaging and echocardiographic studies were performed during a 10- to 14-week period. The primary end point was the difference in the interval change in the LV end-systolic volume index (LVESVi) between the 2 groups on CMR imaging. The secondary end points included differences in the interval changes in the LV end-diastolic volume index, and C-reactive protein levels. A +2.0 ml/m(2) median increase (interquartile range +1.0, +11.5) in the LVESVi on CMR imaging was seen in the placebo group and a -3.2 ml/m(2) median decrease (interquartile range -4.5, -1.6) was seen in the anakinra group (p = 0.033). The median difference was 5.2 ml/m(2). On echocardiography, the median difference in the LVESVi change was 13.4 ml/m(2) (p = 0.006). Similar differences were observed in the LV end-diastolic volume index on CMR imaging (7.6 ml/m(2), p = 0.033) and echocardiography (9.4 ml/m(2), p = 0.008). The change in C-reactive protein levels between admission and 72 hours after admission correlated with the change in the LVESVi (R = +0.71, p = 0.022). In conclusion, in the present pilot study of patients with ST-segment elevation AMI, IL-1 blockade with anakinra was safe and favorably affected by LV remodeling. If confirmed in larger trials, IL-1 blockade might represent a novel therapeutic strategy to prevent heart failure after AMI.

Targeting interleukin-1 in heart disease.

Inflammation is a coordinated cellular-humoral response to injury. A close interaction between resident cells (ie, endothelial cells, fibroblasts, and dendritic cells) and leukocytes regulates the initiation and resolution of the acute inflammatory response. Constitutive membrane and cytoplasmic receptors function as guardians that “signal the alarm” when activated by products of cell destruction or microbial invasion. This first-line innate immune response initiates a process of leukocyte mobilization from the bone marrow, recruitment to the “activated” endothelium, and migration to the site of tissue injury to prevent infection and to facilitate tissue repair. Although critical for many forms of repair, the inflammatory response may also become a mechanism for progressive injury, impaired healing, and disease. Interleukin-1 (IL-1) is an apical proinflammatory mediator in acute and chronic inflammation and a powerful inducer of the innate immune response.1,2 The production and activity of IL-1 are finely regulated at multiple levels, and very small concentrations of exogenous IL-1 can induce a sepsis-like syndrome and shock.1,2 IL-1 induces the synthesis and expression of several hundreds of secondary inflammatory mediators.1,2 IL-1 also induces its own production and processing, and this step is key in the pathogenesis of many autoinflammatory diseases.1,3 Two related genes code for 2 different proteins (IL-1α and IL-1β) that bind the same receptor (type I). IL-1α is synthesized as a fully active peptide that remains membrane bound or may be released from the cytoplasm during cell death. IL-1α thereby participates more prominently in local response to injury and less in the systemic inflammatory response.1,2 IL-1β, the main form of circulating IL-1, is initially synthesized as a precursor (proIL-1β) that becomes activated by caspase-1 cleavage in the setting of a macromolecular structure known as the inflammasome.1,4 Caspase-1 …

Benefits of β blockers in patients with heart failure and reduced ejection fraction: network meta-analysis

Objective To clarify whether any particular β blocker is superior in patients with heart failure and reduced ejection fraction or whether the benefits of these agents are mainly due to a class effect. Design Systematic review and network meta-analysis of efficacy of different β blockers in heart failure. Data sources CINAHL(1982-2011), Cochrane Collaboration Central Register of Controlled Trials (-2011), Embase (1980-2011), Medline/PubMed (1966-2011), and Web of Science (1965-2011). Study selection Randomized trials comparing β blockers with other β blockers or other treatments. Data extraction The primary endpoint was all cause death at the longest available follow-up, assessed with odds ratios and Bayesian random effect 95% credible intervals, with independent extraction by observers. Results 21 trials were included, focusing on atenolol, bisoprolol, bucindolol, carvedilol, metoprolol, and nebivolol. As expected, in the overall analysis, β blockers provided credible mortality benefits in comparison with placebo or standard treatment after a median of 12 months (odds ratio 0.69, 0.56 to 0.80). However, no obvious differences were found when comparing the different β blockers head to head for the risk of death, sudden cardiac death, death due to pump failure, or drug discontinuation. Accordingly, improvements in left ventricular ejection fraction were also similar irrespective of the individual study drug. Conclusion The benefits of β blockers in patients with heart failure with reduced ejection fraction seem to be mainly due to a class effect, as no statistical evidence from current trials supports the superiority of any single agent over the others.

Enhanced Interleukin-1 Activity Contributes to Exercise Intolerance in Patients with Systolic Heart Failure

Background Heart failure (HF) is a complex clinical syndrome characterized by impaired cardiac function and poor exercise tolerance. Enhanced inflammation is associated with worsening outcomes in HF patients and may play a direct role in disease progression. Interleukin-1β (IL-1β) is a pro-inflammatory cytokine that becomes chronically elevated in HF and exerts putative negative inotropic effects. Methods and Results We developed a model of IL-1β-induced left ventricular (LV) dysfunction in healthy mice that exhibited a 32% reduction in LV fractional shortening (P<0.001) and a 76% reduction in isoproterenol response (P<0.01) at 4 hours following a single dose of IL-1β 3 mcg/kg. This phenotype was reproducible in mice injected with plasma from HF patients and fully preventable by pretreatment with IL-1 receptor antagonist (anakinra). This led to the design and conduct of a pilot clinical to test the effect of anakinra on cardiopulmonary exercise performance in patients with HF and evidence of elevated inflammatory signaling (n = 7). The median peak oxygen consumption (VO2) improved from 12.3 [10.0, 15.2] to 15.1 [13.7, 19.3] mL·kg–1·min–1 (P = 0.016 vs. baseline) and median ventilator efficiency (VE/VCO2 slope) improved from 28.1 [22.8, 31.7] to 24.9 [22.9, 28.3] (P = 0.031 vs. baseline). Conclusions These findings suggest that IL-1β activity contributes to poor exercise tolerance in patients with systolic HF and identifies IL-1β blockade as a novel strategy for pharmacologic intervention. Trial Registration ClinicalTrials.gov NCT01300650

Anti-Inflammatory Strategies for Ventricular Remodeling Following ST-Segment Elevation Acute Myocardial Infarction

Acute myocardial infarction (AMI) leads to molecular, structural, geometric, and functional changes in the heart in a process known as ventricular remodeling. An intense organized inflammatory response is triggered after myocardial ischemia and necrosis and involves all components of the innate immunity, affecting both cardiomyocytes and noncardiomyocyte cells. Inflammation is triggered by tissue injury; it mediates wound healing and scar formation and affects ventricular remodeling. Many therapeutic attempts aimed at reducing inflammation in AMI during the past 3 decades presented issues of impaired healing or increased risk of cardiac rupture or failed to show any additional benefit in addition to standard therapies. More recent strategies aimed at selectively blocking one of the key factors upstream rather than globally suppressing the response downstream have shown some promising results in pilot trials. We herein review the pathophysiological mechanisms of inflammation and ventricular remodeling after AMI and the results of clinical trials with anti-inflammatory strategies.

A novel pharmacologic inhibitor of the NLRP3 inflammasome limits myocardial injury after ischemia-reperfusion in the mouse.

Background: The formation of the NLRP3 inflammasome in the heart during acute myocardial infarction amplifies the inflammatory response and mediates further damage. Glyburide has NLRP3 inhibitory activity in vitro but requires very high doses in vivo, associated with hypoglycemia. The aim of this study was to measure the effects on the NLRP3 inflammasome of 16673-34-0, an intermediate substrate free of the cyclohexylurea moiety, involved in insulin release. Methods and Results: We synthesized 16673-34-0 (5-chloro-2-methoxy-N-[2-(4-sulfamoylphenyl)ethyl]benzamide) that displayed no effect on glucose metabolism. HL-1 cardiomyocytes were treated with lipopolysaccharide and ATP to induce the formation of the NLRP3 inflammasome, measured as increased caspase-1 activity and cell death, and 16673-34-0 prevented such effects. 16673-34-0 was well tolerated with no effects on the glucose levels in vivo. Treatment with 16673-34-0 in a model of acute myocardial infarction because of ischemia and reperfusion significantly inhibited the activity of inflammasome (caspase-1) in the heart by 90% (P < 0.01) and reduced infarct size, measured at pathology (by >40%, P < 0.01) and with troponin I levels (by >70%, P < 0.01). Conclusions: The small molecule 16673-34-0, an intermediate substrate in the glyburide synthesis free of the cyclohexylurea moiety, inhibits the formation of the NLRP3 inflammasome in cardiomyocytes and limits the infarct size after myocardial ischemia–reperfusion in the mouse, without affecting glucose metabolism.

Interleukin-1β modulation using a genetically engineered antibody prevents adverse cardiac remodelling following acute myocardial infarction in the mouse

Division of Cardiology/VCU Pauley Heart Center, Virginia Commonwealth University, 1200 East Broad Street West Hospital, 10th Floor, East Wing, Room 1041, PO Box 980281, Richmond, VA 23298-0281, USA; Victoria Johnson Center, Virginia Commonwealth University, Richmond, VA, USA; School of Pharmacy, Virginia Commonwealth University, Richmond, VA, USA; and School of Medicine, University of Colorado, Aurora, CO, USA

Alpha-1 antitrypsin inhibits caspase-1 and protects from acute myocardial ischemia–reperfusion injury

Alpha-1-antitrypsin (AAT) possesses anti-inflammatory and tissue-protective properties. Here, we studied the effects of exogenously administered AAT on caspase-1 activity and on the outcome of ischemia-reperfusion injury (I/R) in a mouse model of acute myocardial infarction (AMI). Adult male mice underwent 30 min of coronary artery ligation followed by reperfusion and were randomly assigned to receive clinical-grade AAT or albumin at reperfusion. Infarct size was evaluated after 1 and 7 days. Caspase-1 activity was measured in homogenates of heart tissue. Left ventricular (LV) end-diastolic diameter (EDD) and end-systolic diameter (ESD) were measured and LV fractional shortening (FS) and ejection fraction (EF) were calculated using transthoracic echocardiography. The effect of AAT on caspase-1 activity was determined in cultures of mouse HL-1 cardiomyocytes stimulated with LPS and triggered with nigericin or when HL-1 cells were exposed to simulated ischemia. AAT-treated mice had significantly smaller infarct sizes (-30% day 1 and -55% day 7) compared with mice treated with albumin. AAT treatment resulted in >90% reduction in caspase-1 activity in homogenates of hearts 24h after I/R. Seven days after AMI, AAT-treated mice exhibited a >90% smaller increase in LVEDD and LVESD and smaller reduction in LVEF. The increase in caspase-1 activity in HL-1 cells induced by LPS and nigericin or following exposure to simulated ischemia was reduced by >80% and AAT similarly reduced cell death by >50%. In conclusion, exogenous administration of clinical grade AAT reduces caspase-1 activity in the ischemic myocardium leading to preservation of viable myocardium and prevention of adverse cardiac remodeling.

Metabolic Gene Remodeling and Mitochondrial Dysfunction in Failing Right Ventricular Hypertrophy Secondary to Pulmonary Arterial Hypertension

Background— Right ventricular (RV) dysfunction (RVD) is the most frequent cause of death in patients with pulmonary arterial hypertension. Although abnormal energy substrate use has been implicated in the development of chronic left heart failure, data describing such metabolic remodeling in RVD remain incomplete. Thus, we sought to characterize metabolic gene expression changes and mitochondrial dysfunction in functional and dysfunctional RV hypertrophy. Methods and Results— Two different rat models of RV hypertrophy were studied. The model of RVD (SU5416/hypoxia) exhibited a significantly decreased gene expression of peroxisome proliferator-activated receptor-&ggr; coactivator-1&agr;, peroxisome proliferator-activated receptor-&agr; and estrogen-related receptor-&agr;. The expression of multiple peroxisome proliferator-activated receptor-&ggr; coactivator-1&agr; target genes required for fatty acid oxidation was similarly decreased. Decreased peroxisome proliferator-activated receptor-&ggr; coactivator-1&agr; expression was also associated with a net loss of mitochondrial protein and oxidative capacity. Reduced mitochondrial number was associated with a downregulation of transcription factor A, mitochondrial, and other genes required for mitochondrial biogenesis. Electron microscopy demonstrated that, in RVD tissue, mitochondria had abnormal shape and size. Lastly, respirometric analysis demonstrated that mitochondria isolated from RVD tissue had a significantly reduced ADP-stimulated (state 3) rate for complex I. Conversely, functional RV hypertrophy in the pulmonary artery banding model showed normal expression of peroxisome proliferator-activated receptor-&ggr; coactivator-1&agr;, whereas the expression of fatty acid oxidation genes was either preserved or unregulated. Moreover, pulmonary artery banding-RV tissue exhibited preserved transcription factor A mitochondrial expression and mitochondrial respiration despite elevated RV pressure-overload. Conclusions— Right ventricular dysfunction, but not functional RV hypertrophy in rats, demonstrates a gene expression profile compatible with a multilevel impairment of fatty acid metabolism and significant mitochondrial dysfunction, partially independent of chronic pressure-overload.