18F-FDG PET imaging-monitored anti-inflammatory therapy for acute myocardial infarction: Exploring the role of MCC950 in murine model

Synthesis and Evaluation of [11C]MCC950 for Imaging NLRP3-Mediated Inflammation in Atherosclerosis

Overexpression of the NLRP3 inflammasome has been attributed to the progressive worsening of a multitude of cardiovascular inflammatory diseases such as myocardial infarction, pulmonary arterial hypertension, and atherosclerosis. The recently discovered potent and selective NLRP3 inhibitor MCC950 has shown promise in hindering disease progression, but NLRP3-selective cardiovascular positron emission tomography (PET) imaging has not yet been demonstrated. We synthesized [¹¹C]MCC950 with no-carrier-added [¹¹C]CO₂ fixation chemistry using an iminophosphorane precursor (RCY 45 ± 4%, >99% RCP, 27 ± 2 GBq/μmol, 23 ± 3 min, n = 6) and determined its distribution both in vivo and ex vivo in C57BL/6 and atherogenic ApoE^-/- mice. Small animal PET imaging was performed in both strains following intravenous administration via the lateral tail vein and revealed considerable uptake in the liver that stabilized by 20 min (7-8.5 SUV), coincident with secondary renal excretion. Plasma metabolite analysis uncovered excellent in vivo stability of [¹¹C]MCC950 (94% intact). Ex vivo autoradiography performed on excised aortas revealed heterogeneous uptake in atherosclerotic plaques of ApoE^-/- mice in comparison to C57BL/6 controls (48 ± 17 %ID/m² vs 18 ± 8 %ID/m², p = 0.002, n = 4-5). Treatment of ApoE^-/- mice with nonradioactive MCC950 (5 mg/kg, iv) 10 min prior to radiotracer administration increased uptake in the intestine (5.3 ± 1.8 %ID/g vs 11.0 ± 3.7 %ID/g, p = 0.04, n = 4-6) and in aortic lesions (48 ± 17 %ID/m² vs 104 ± 15 %ID/m², p = 0.0002, n = 5) by 108% and 117%, respectively, without significantly increasing plasma free fraction (f_p, 1.3 ± 0.4% vs 1.7 ± 0.8%, n = 2). These results suggest that [¹¹C]MCC950 uptake demonstrates specific binding and may prove useful for in vivo NLRP3 imaging in atherosclerosis.

Exosomes and Exosomal Cargos: A Promising World for Ventricular Remodeling Following Myocardial Infarction

Exosomes are a pluripotent group of extracellular nanovesicles secreted by all cells that mediate intercellular communications. The effective information within exosomes is primarily reflected in exosomal cargos, including proteins, lipids, DNAs, and non-coding RNAs (ncRNAs), the most intensively studied molecules. Cardiac resident cells (cardiomyocytes, fibroblasts, and endothelial cells) and foreign cells (infiltrated immune cells, cardiac progenitor cells, cardiosphere-derived cells, and mesenchymal stem cells) are involved in the progress of ventricular remodeling (VR) following myocardial infarction (MI) via transferring exosomes into target cells. Here, we summarize the pathological mechanisms of VR following MI, including cardiac myocyte hypertrophy, cardiac fibrosis, inflammation, pyroptosis, apoptosis, autophagy, angiogenesis, and metabolic disorders, and the roles of exosomal cargos in these processes, with a focus on proteins and ncRNAs. Continued research in this field reveals a novel diagnostic and therapeutic strategy for VR.

NLRP3 Inflammasome/Pyroptosis: A Key Driving Force in Diabetic Cardiomyopathy

Diabetic cardiomyopathy (DCM), a serious diabetic complication, is a kind of low-grade inflammatory cardiovascular disorder. Due to the high risk of morbidity and mortality, DCM has demanded the attention of medical researchers worldwide. The pathophysiological nature of DCM is intricate, and the genesis and development of which are a consequence of the coaction of many factors. However, the exact pathogenesis mechanism of DCM remains unclear. Pyroptosis is a newly identified programmed cell death (PCD) that is directly related to gasdermin D(GSDMD). It is characterized by pore formation on the cell plasma membrane, the release of inflammatory mediators, and cell lysis. The initiation of pyroptosis is closely correlated with NOD-like receptor 3 (NLRP3) activation, which activates caspase-1 and promotes the cleaving of GSDMD. In addition to adjusting the host’s immune defense, NLRP3 inflammasome/pyroptosis plays a critical role in controlling the systemic inflammatory response. Recent evidence has indicated that NLRP3 inflammasome/pyroptosis has a strong link with DCM. Targeting the activation of NLRP3 inflammasome or pyroptosis may be a hopeful therapeutic strategy for DCM. The focus of this review is to summarize the relevant mechanisms of pyroptosis and the relative contributions in DCM, highlighting the potential therapeutic targets in this field.

MCC950, a Selective NLRP3 Inhibitor, Attenuates Adverse Cardiac Remodeling Following Heart Failure Through Improving the Cardiometabolic Dysfunction in Obese Mice

Obesity is often accompanied by hypertension. Although a large number of studies have confirmed that NLRP3 inhibitors can improve cardiac remodeling in mice with a normal diet, it is still unclear whether NLRP3 inhibitors can improve heart failure (HF) induced by pressure overload in obese mice. The purpose of this study was to explore the role of MCC950, a selective NLRP3 inhibitor, on HF in obese mice and its metabolic mechanism. Obese mice induced with a 10-week high-fat diet (HFD) were used in this study. After 4 weeks of HFD, transverse aortic constriction (TAC) surgery was performed to induce a HF model. MCC950 (10 mg/kg, once/day) was injected intraperitoneally from 2 weeks after TAC and continued for 4 weeks. After echocardiography examination, we harvested left ventricle tissues and performed molecular experiments. The results suggest that in obese mice, MCC950 can significantly improve cardiac hypertrophy and fibrosis caused by pressure overload. MCC950 ameliorated cardiac inflammation after TAC surgery and promoted M2 macrophage infiltration in the cardiac tissue. MCC950 not only restored fatty acid uptake and utilization by regulating the expression of CD36 and CPT1β but also reduced glucose uptake and oxidation via regulating the expression of GLUT4 and p-PDH. In addition, MCC950 affected the phosphorylation of AKT and AMPK in obese mice with HF. In summary, MCC950 can alleviate HF induced by pressure overload in obese mice via improving cardiac metabolism, providing a basis for the clinical application of NLRP3 inhibitors in obese patients with HF.

Signaling pathways and targeted therapy for myocardial infarction

Although the treatment of myocardial infarction (MI) has improved considerably, it is still a worldwide disease with high morbidity and high mortality. Whilst there is still a long way to go for discovering ideal treatments, therapeutic strategies committed to cardioprotection and cardiac repair following cardiac ischemia are emerging. Evidence of pathological characteristics in MI illustrates cell signaling pathways that participate in the survival, proliferation, apoptosis, autophagy of cardiomyocytes, endothelial cells, fibroblasts, monocytes, and stem cells. These signaling pathways include the key players in inflammation response, e.g., NLRP3/caspase-1 and TLR4/MyD88/NF-κB; the crucial mediators in oxidative stress and apoptosis, for instance, Notch, Hippo/YAP, RhoA/ROCK, Nrf2/HO-1, and Sonic hedgehog; the controller of myocardial fibrosis such as TGF-β/SMADs and Wnt/β-catenin; and the main regulator of angiogenesis, PI3K/Akt, MAPK, JAK/STAT, Sonic hedgehog, etc. Since signaling pathways play an important role in administering the process of MI, aiming at targeting these aberrant signaling pathways and improving the pathological manifestations in MI is indispensable and promising. Hence, drug therapy, gene therapy, protein therapy, cell therapy, and exosome therapy have been emerging and are known as novel therapies. In this review, we summarize the therapeutic strategies for MI by regulating these associated pathways, which contribute to inhibiting cardiomyocytes death, attenuating inflammation, enhancing angiogenesis, etc. so as to repair and re-functionalize damaged hearts.

Exacerbated post-infarct pathological myocardial remodelling in diabetes is associated with impaired autophagy and aggravated NLRP3 inflammasome activation

Background

Diabetes mellitus (DM) patients surviving myocardial infarction (MI) have substantially higher mortality due to the more frequent development of subsequent pathological myocardial remodelling and concomitant functional deterioration. This study investigates the molecular pathways underlying accelerated cardiac remodelling in a well‐established mouse model of diabetes exposed to MI.

Methods and results

Myocardial infarction in DM mice was established by ligating the left anterior descending coronary artery. Cardiac function was assessed by echocardiography. Myocardial hypertrophy and cardiac fibrosis were determined histologically 6 weeks post‐MI or sham operation. Autophagy, the NLRP3 inflammasome, and caspase‐1 were evaluated by western blotting or immunofluorescence. Echocardiographic imaging revealed significantly increased left ventricular dilation in parallel with increased mortality after MI in DM mice (53.33%) compared with control mice (26.67%, P < 0.05). Immunoblotting, electron microscopy, and immunofluorescence staining for LC3 and p62 indicated impaired autophagy in DM + MI mice compared with control mice (P < 0.05). Furthermore, defective autophagy was associated with increased NLRP3 inflammasome and caspase‐1 hyperactivation in DM + MI mouse cardiomyocytes (P < 0.05). Consistent with NLRP3 inflammasome and caspase‐I hyperactivation, cardiomyocyte death and IL‐1β and IL‐18 secretion were increased in DM + MI mice (P < 0.05). Importantly, the autophagy inducer and the NLRP3 inhibitor attenuated the cardiac remodelling of DM mice after MI.

Conclusion

In summary, our results indicate that DM aggravates cardiac remodelling after MI through defective autophagy and associated exaggerated NLRP3 inflammasome activation, proinflammatory cytokine secretion, suggesting that restoring autophagy and inhibiting NLRP3 inflammasome activation may serve as novel targets for the prevention and treatment of post‐infarct remodelling in DM.

Selective Inhibition of NLRP3 Inflammasome Reverses Pressure Overload-Induced Pathological Cardiac Remodeling by Attenuating Hypertrophy, Fibrosis, and Inflammation

Activation of the NLRP3 inflammasome promotes pathological cardiac remodeling induced by pressure overload. However, the therapeutic effects of NLRP3 inhibition after cardiac remodeling remain unknown. The present study aimed to investigate whether the selective NLRP3 inhibitor, MCC950, could reverse transverse aortic constriction (TAC)-induced cardiac remodeling. Mice were divided into four groups based on the treatment given: sham, sham + MCC950, TAC, and TAC + MCC950. MCC950 (10 mg/kg, intraperitoneal injection, once per day) was administered from two weeks after TAC or sham surgery for four weeks. Echocardiography, histological analysis, RT-PCR, and Western blotting were performed to explore the function of MCC950 after TAC. We found that MCC950 reversed cardiac dysfunction after TAC. MCC950 attenuated cardiac hypertrophy by down-regulating calcineurin expression and inhibiting MAPK activation. Further, it also alleviated cardiac fibrosis post-TAC by inhibiting the TGF-β/Smad4 pathway, and reduced cardiac inflammation and macrophage infiltration post-TAC, including both M1 and M2 macrophages. Taken together, MCC950 can attenuate cardiac remodeling due to pressure overload by inhibiting hypertrophy, fibrosis, and inflammation. Our study provides a basis for the clinical application of NLRP3 inhibitors in the treatment of non-ischemic heart failure.

PET Imaging of Post-infarct Myocardial Inflammation

PURPOSE OF REVIEW

To examine the use of positron emission tomography (PET) for imaging post-infarct myocardial inflammation and repair.

RECENT FINDINGS

Dysregulated immune responses after myocardial infarction are associated with adverse cardiac remodelling and an increased likelihood of ischaemic heart failure. PET imaging utilising novel tracers can be applied to visualise different components of the post-infarction inflammatory and repair processes. This approach could offer unique pathophysiological insights that could prove useful for the identification and risk-stratification of individuals who would ultimately benefit most from emerging immune-modulating therapies. PET imaging could also bridge the clinical translational gap as a surrogate measure of drug efficacy in early-stage clinical trials in patients with myocardial infarction. The use of hybrid PET/MR imaging, in particular, offers the additional advantage of simultaneous in vivo molecular imaging and detailed assessment of myocardial function, viability and tissue characterisation. Further research is needed to realise the true clinical translational value of PET imaging after myocardial infarction.

Pharmacological Inhibition of the Nod-Like Receptor Family Pyrin Domain Containing 3 Inflammasome with MCC950

Activation of the Nod-like receptor family pyrin domain containing 3 (NLRP3) inflammasome drives release of the proinflammatory cytokines interleukin (IL)-1β and IL-18 and induces pyroptosis (lytic cell death). These events drive chronic inflammation, and as such, NLRP3 has been implicated in a large number of human diseases. These range from autoimmune conditions, the simplest of which is NLRP3 gain-of-function mutations leading to an orphan disease, cryopyrin-associated period syndrome, to large disease burden indications, such as atherosclerosis, heart failure, stroke, neurodegeneration, asthma, ulcerative colitis, and arthritis. The potential clinical utility of NLRP3 inhibitors is substantiated by an expanding list of indications in which NLRP3 activation has been shown to play a detrimental role. Studies of pharmacological inhibition of NLRP3 in nonclinical models of disease using MCC950 in combination with human genetics, epigenetics, and analyses of the efficacy of biologic inhibitors of IL-1β, such as anakinra and canakinumab, can help to prioritize clinical trials of NLRP3-directed therapeutics. Although MCC950 shows excellent (nanomolar) potency and high target selectivity, its pharmacokinetic and toxicokinetic properties limited its therapeutic development in the clinic. Several improved, next-generation inhibitors are now in clinical trials. Hence the body of research in a plethora of conditions reviewed herein may inform analysis of the potential translational value of NLRP3 inhibition in diseases with significant unmet medical need. SIGNIFICANCE STATEMENT: The nod-like receptor family pyrin domain containing 3 (NLRP3) inflammasome is one of the most widely studied and best validated biological targets in innate immunity. Activation of NLRP3 can be inhibited with MCC950, resulting in efficacy in more than 100 nonclinical models of inflammatory diseases. As several next-generation NLRP3 inhibitors are entering proof-of-concept clinical trials in 2020, a review of the pharmacology of MCC950 is timely and significant.

Hyperpolarized 13 C magnetic resonance imaging for noninvasive assessment of tissue inflammation

Inflammation is a central mechanism underlying numerous diseases and incorporates multiple known and potential future therapeutic targets. However, progress in developing novel immunomodulatory therapies has been slowed by a need for improvement in noninvasive biomarkers to accurately monitor the initiation, development and resolution of immune responses as well as their response to therapies. Hyperpolarized magnetic resonance imaging (MRI) is an emerging molecular imaging technique with the potential to assess immune cell responses by exploiting characteristic metabolic reprogramming in activated immune cells to support their function. Using specific metabolic tracers, hyperpolarized MRI can be used to produce detailed images of tissues producing lactate, a key metabolic signature in activated immune cells. This method has the potential to further our understanding of inflammatory processes across different diseases in human subjects as well as in preclinical models. This review discusses the application of hyperpolarized MRI to the imaging of inflammation, as well as the progress made towards the clinical translation of this emerging technique.