NLRP3 inflammasome activation during myocardial ischemia reperfusion is cardioprotective.

BACKGROUND: The innate immune receptor NLRP3 recognizes tissue damage and initiates inflammatory processes through formation multiprotein complexes with the adaptor protein ASC and caspase-1, i.e. NLRP3 inflammasomes, which through cleavage of pro-IL-1ß mediates release of bioactive IL-1ß. We hypothesized that NLRP3 mediates tissue damage during acute myocardial infarction (MI) and sought to investigate the mechanisms herein in an experimental MI model in mice. METHODS AND RESULTS: The left coronary artery (LCA) of WT, NLRP3(-/-) and ASC(-/-) mice of both genders was ligated for 30 min followed by 3 or 24 h reperfusion. For pre-conditioning studies, the TLR2 agonist Pam3CSK4 or PBS was injected intraperitoneally 60 min prior to LCA ligation. For mechanistic investigations, blood plasmas and left ventricle tissues were collected, and a hypothesis-driven selection of protein or mRNA targets was investigated. Surprisingly, hearts from NLRP3-deficient mice featured larger infarct size than WT mice (p = 0.0048). In general, there were only modest changes with no significant pattern in myocardial infiltration of neutrophils and macrophages and systemic and myocardial cytokine expression between the three genotypes. Preconditioning with the TLR2 agonist Pam3CSK4 induced Akt phosphorylation and reduced infarct size in WT but not NLRP3 -or ASC -deficient hearts. CONCLUSION: Absence of NLRP3 results in increased myocardial infarct size after in vivo ischemia reperfusion, seemingly due to dysfunction of the cardioprotective RISK pathway. Our data imply that NLRP3 contributes to cardio-protection during I/R and do not support a role for NLRP3 or ASC inhibition in the management of acute MI including revascularization therapy.

Increased interleukin-1ß levels are associated with left ventricular hypertrophy and remodelling following acute ST segment elevation myocardial infarction treated by primary percutaneous coronary intervention.

OBJECTIVES: To assess the relationship between interleukin (IL)-1-related molecules, infarct size and left ventricular (LV) remodelling following acute myocardial infarction (MI). METHODS: Forty-two patients with first-time diagnosis of ST segment elevation MI (STEMI), with a single occluded vessel successfully revascularized by primary percutaneous coronary intervention (PCI), were recruited to this observational study conducted at a university teaching hospital and followed for 1 year. MAIN OUTCOME MEASURES: Plasma levels of IL-1ß, IL-1 receptor antagonist (IL-1Ra), IL-18 and caspase-1 were analysed before and 2 days, 1 week and 2 months after PCI. Serial cardiac magnetic resonance imaging (CMR) was used for the assessment of infarct size and LV remodelling. CMR findings at 1 year was the primary outcome variable. RESULTS: Univariate analysis showed that IL-1-related mediators were strongly (IL-1 ß), moderately (caspase-1) and weakly (IL-1Ra) associated with impaired myocardial function and noninfarct mass, but not infarct size, 1 year after reperfused STEMI. In multivariate analyses, troponin T predicted LV ejection fraction (LVEF), infarct size and LV end-diastolic (LVEDVi) and end-systolic volume index (LVESVi). However, significant additional variance was explained by IL-1ß, IL-18 and caspase-1. IL-1ß levels at 2 months, IL-18 at 2 days and pre-PCI caspase-1 were predictors of LVEF. Caspase-1 and in particular IL-1ß at 2 days were the only predictors of noninfarct mass. IL-1ß and IL-18 at 2 days were predictors of LVEDVi, whilst pre-PCI levels of IL-1ß contributed to prediction of LVESVi. By contrast, pro-B-type natriuretic peptide, C-reactive protein, IL-6 and transforming growth factor-ß1 (TGF-ß1) had no or only a weak (TGF-ß1) association with these CMR parameters in multivariate analyses. CONCLUSIONS: IL-1ß levels after STEMI were strongly associated with impaired myocardial function and noninfarct LV mass after 1 year, suggesting a potential role for IL-1ß as a predictor of maladaptive myocardial remodelling following reperfused MI.