Stefano Toldo

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.

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 …

Suppression of histone deacetylases worsens right ventricular dysfunction after pulmonary artery banding in rats.

RATIONALE Inhibitors of histone deacetylases (HDACs) reduce pressure-overload-induced left ventricular hypertrophy and dysfunction, but their effects on right ventricular (RV) adaptation to pressure overload are unknown. OBJECTIVES Determine the effect of the broad-spectrum HDAC inhibitors trichostatin A (TSA) and valproic acid (VPA) on RV function and remodeling after pulmonary artery banding (PAB) in rats. METHODS Chronic progressive RV pressure-overload was induced in rats by PAB. After establishment of adaptive RV hypertrophy 4 weeks after surgery, rats were treated for 2 weeks with vehicle, TSA, or VPA. RV function and remodeling were determined using echocardiography, invasive hemodynamic measurements, immunohistochemistry, and molecular analyses after 2 weeks of HDAC inhibition. The effects of TSA were determined on the expression of proangiogenic and prohypertrophic genes in human myocardial fibroblasts and microvascular endothelial cells. MEASUREMENTS AND MAIN RESULTS TSA treatment did not prevent the development of RV hypertrophy and was associated with RV dysfunction, capillary rarefaction, fibrosis, and increased rates of myocardial cell death. Similar results were obtained with the structurally unrelated HDAC inhibitor VPA. With TSA treatment, a reduction was found in expression of vascular endothelial growth factor and angiopoietin-1, which proteins are involved in vascular adaptation to pressure-overload. TSA dose-dependently suppressed vascular endothelial growth factor, endothelial nitric oxide synthase, and angiopoietin-1 expression in cultured myocardial endothelial cells, which effects were mimicked by selective gene silencing of several class I and II HDACs. CONCLUSIONS HDAC inhibition is associated with dysfunction and worsened remodeling of the pressure-overloaded RV. The detrimental effects of HDAC inhibition on the pressure-overloaded RV may come about via antiangiogenic or proapoptotic effects.

Phosphodiesterase-5 Inhibitor, Tadalafil, Protects Against Myocardial Ischemia/Reperfusion Through Protein-Kinase G–Dependent Generation of Hydrogen Sulfide

Background— Tadalafil is a novel long-acting inhibitor of phosphodiesterase-5. Because cGMP-dependent protein kinase (PKG) signaling plays a key role in cardioprotection, we hypothesized that PKG activation with tadalafil would limit myocardial ischemia/reperfusion (I/R) injury and dysfunction. Additionally, we contemplated that cardioprotection with tadalafil is mediated by hydrogen sulfide (H2S) signaling in a PKG-dependent fashion. Methods and Results— After baseline transthoracic echocardiography (TTE), adult ICR mice were injected i.p. with vehicle (10% DMSO) or tadalafil (1 mg/kg) with or without KT5823 (KT, PKG blocker, 1 mg/kg) or dl-propargylglycine (PAG, Cystathionine-γ-lyase [CSE, H2S-producing enzyme] blocker; 50 mg/kg) 1 hour before coronary artery ligation for 30 minutes and reperfusion for 24 hours, whereas C57BL wild-type and CSE-knockout mice were treated with either vehicle or tadalafil. After reperfusion, TTE was performed and hearts were collected for infarct size (IS) measurement using TTC staining. Survival was increased with tadalafil (95%) compared with control (65%, P<0.05). Infarct size was reduced with tadalafil (13.2±1.7%) compared to vehicle (40.6±2.5%; P<0.05). KT and PAG abolished tadalafil-induced protection (IS: 39.2±1% and 51.2±2.4%, respectively) similar to genetic deletion of CSE (47.2±5.1%). Moreover, tadalafil preserved fractional shortening (FS: 31±1.5%) compared to control (FS: 22±4.8%, P<0.05). Baseline FS was 44±1.7%. KT and PAG abrogated the preservation of LV function with tadalafil by decline in FS to 17±1% and 23±3%, respectively. Compared to vehicle, myocardial H2S production was significantly increased with tadalafil and was abolished with KT. Conclusion— PKG activation with tadalafil limits myocardial infarction and preserves LV function through H2S signaling.

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.

Interleukin-18 mediates interleukin-1-induced cardiac dysfunction

Patients with heart failure (HF) have enhanced systemic IL-1 activity, and, in the experimental mouse model, IL-1 induces left ventricular (LV) systolic dysfunction. Whether the effects of IL-1 are direct or mediated by an inducible cytokine, such as IL-18, is unknown. Recombinant human IL-18-binding protein (IL-18BP) or an IL-18-blocking antibody (IL-18AB) was used to neutralize endogenous IL-18 after challenge with the plasma of patients with HF or with recombinant murine IL-1β in adult male mice. Plasma levels of IL-18 and IL-6 (a key mediator of IL-1-induced systemic effects) and LV fractional shortening were measured in mice sedated with pentobarbital sodium (30-50 mg/kg). Mice with genetic deletion of IL-18 or IL-18 receptors were compared with matching wild-type mice. A group of mice received murine IL-18 to evaluate the effects on LV fractional shortening. Plasma from HF patients and IL-1β induced LV systolic dysfunction that was prevented by pretreatment with IL-18AB or IL-18BP. IL-1β failed to induce LV systolic dysfunction in mice with genetic deletion of IL-18 signaling. IL-1β induced a significant increase in plasma IL-18 and IL-6 levels. Genetic or pharmacological inhibition of IL-18 signaling failed to block the induction of IL-6 by IL-1β. In conclusion, IL-1 induces a release of active IL-18 in the mouse that mediates the LV systolic dysfunction but not the induction of IL-6. IL-18 blockade may therefore represent a novel and more targeted therapeutic approach to treat HF.