Itaconate confers tolerance to late NLRP3 inflammasome activation

Itaconate is a unique regulatory metabolite that is induced upon Toll-like receptor (TLR) stimulation in myeloid cells. Here, we demonstrate major inflammatory tolerance and cell death phenotypes associated with itaconate production in activated macrophages. We show that endogenous itaconate is a key regulator of the signal 2 of NLR family pyrin domain containing 3 (NLRP3) inflammasome activation after long lipopolysaccharide (LPS) priming, which establishes tolerance to late NLRP3 inflammasome activation. We show that itaconate acts synergistically with inducible nitric oxide synthase (iNOS) and that the ability of various TLR ligands to establish NLRP3 inflammasome tolerance depends on the pattern of co-expression of IRG1 and iNOS. Mechanistically, itaconate accumulation upon prolonged inflammatory stimulation prevents full caspase-1 activation and processing of gasdermin D, which we demonstrate to be post-translationally modified by endogenous itaconate. Altogether, our data demonstrate that metabolic rewiring in inflammatory macrophages establishes tolerance to NLRP3 inflammasome activation that, if uncontrolled, can result in pyroptotic cell death and tissue damage

Perioperative platelet and monocyte activation in patients with critical limb ischemia

BackgroundPatients with critical limb ischemia (CLI) have a high rate of adverse cardiovascular events, particularly when undergoing surgery. We sought to determine the effect of surgery and vascular disease on platelet and monocyte activation in vivo in patients with CLI.MethodsAn observational, cross-sectional study was performed at a tertiary referral hospital in the southeast of Scotland. Platelet and monocyte activation were measured in whole blood in patients with CLI scheduled for infrainguinal bypass and compared with matched healthy controls, patients with chronic intermittent claudication, patients with acute myocardial infarction, and those undergoing arthroplasty (n = 30 per group). Platelet and monocyte activation were quantified using flow cytometric assessment of platelet-monocyte aggregation, platelet P-selectin expression, platelet-derived microparticles, and monocyte CD40 and CD11b expression.ResultsCompared with those with intermittent claudication, subjects with CLI had increased platelet-monocyte aggregates (41.7% ± 12.2% vs 32.6% ± 8.5%, respectively), platelet microparticles (178.7 ± 106.9 vs 116.9 ± 53.4), and monocyte CD40 expression (70.0% ± 12.2% vs 52.4% ± 15.2%; P < .001 for all). Indeed, these levels were equivalent (P-selectin, 4.4% ± 2.0% vs 4.9% ± 2.2%; P > .05) or higher (platelet-monocyte aggregation, 41.7% ± 12.2% vs 33.6% ± 7.0%; P < .05; platelet microparticles, 178.7 ± 106.9 vs 114.4 ± 55.0/μL; P < .05) than in patients with acute myocardial infarction. All platelet and monocyte activation markers remained elevated throughout the perioperative period in patients with CLI (P < .01) but not those undergoing arthroplasty.ConclusionsPatients undergoing surgery for CLI have the highest level of in vivo platelet and monocyte activation, and these persist throughout the perioperative period. Additional antiplatelet therapy may be of benefit in protecting vascular patients with more severe disease during this period of increased risk.Clinical RelevancePeripheral arterial disease is increasingly common and is associated with a significant risk of cardiovascular complications, especially at the time of surgery. Despite this, patients are poorly provided with evidence-based therapies such as antiplatelet and lipid-lowering medications. Platelets play a key role in the pathogenesis of atherothrombosis, with elevated levels of in vivo platelet activation prognostic of adverse clinical events. This study demonstrates, for the first time to our knowledge, significantly greater levels of platelet activation in patients with severe peripheral arterial disease compared with patients with acute myocardial infarction or patients undergoing other moderate- to high-risk surgical procedures. This further emphasizes the need for improved risk stratification and cardioprotection of this vulnerable group