Current status of inflammasome blockers as anti-inflammatory drugs

Toward targeted treatments for silicosis

PURPOSE OF REVIEW

There has been a rapid increase in silicosis cases, particularly related to artificial stone. The key to management is avoidance of silica exposure. Despite this, many develop progressive disease and there are no routinely recommended treatments. This review provides a summary of the literature pertaining to pharmacological therapies for silicosis and examines the plausibility of success of such treatments given the disease pathogenesis.

RECENT FINDINGS

In-vitro and in-vivo models demonstrate potential efficacy for drugs, which target inflammasomes, cytokines, effector cells, fibrosis, autophagy, and oxidation.

SUMMARY

There is some evidence for potential therapeutic targets in silicosis but limited translation into human studies. Treatment of silicosis likely requires a multimodal approach, and there is considerable cross-talk between pathways; agents that modulate both inflammation, fibrosis, autophagy, and ROS production are likely to be most efficacious.

Exploring the role of the inflammasomes on prostate cancer: Interplay with obesity

Obesity is a weight-related disorder characterized by excessive adipose tissue growth and dysfunction which leads to the onset of a systemic chronic low-grade inflammatory state. Likewise, inflammation is considered a classic cancer hallmark affecting several steps of carcinogenesis and tumor progression. In this regard, novel molecular complexes termed inflammasomes have been identified which are able to react to a wide spectrum of insults, impacting several metabolic-related disorders, but their contribution to cancer biology remains unclear. In this context, prostate cancer (PCa) has a markedly inflammatory component, and patients frequently are elderly individuals who exhibit weight-related disorders, being obesity the most prevalent condition. Therefore, inflammation, and specifically, inflammasome complexes, could be crucial players in the interplay between PCa and metabolic disorders. In this review, we will: 1) discuss the potential role of each inflammasome component (sensor, molecular adaptor, and targets) in PCa pathophysiology, placing special emphasis on IL-1β/NF-kB pathway and ROS and hypoxia influence; 2) explore the association between inflammasomes and obesity, and how these molecular complexes could act as the cornerstone between the obesity and PCa; and, 3) compile current clinical trials regarding inflammasome targeting, providing some insights about their potential use in the clinical practice.

NLRP3 inflammasome in hepatic diseases: A pharmacological target

The NOD-like receptor family pyrin domain containing 3 (NLRP3) inflammasome pathway is mainly responsible for the activation and release of a cascade of proinflammatory mediators that contribute to the development of hepatic diseases. During alcoholic liver disease development, the NLRP3 inflammasome pathway contributes to the maturation of caspase-1, interleukin (IL)-1β, and IL-18, which induce a robust inflammatory response, leading to fibrosis by inducing profibrogenic hepatic stellate cell (HSC) activation. Substantial evidence demonstrates that nonalcoholic fatty liver disease (NAFLD) progresses to nonalcoholic steatohepatitis (NASH) via NLRP3 inflammasome activation, ultimately leading to fibrosis and hepatocellular carcinoma (HCC). Activation of the NLRP3 inflammasome in NASH can be attributed to several factors, such as reactive oxygen species (ROS), gut dysbiosis, leaky gut, which allow triggers such as cardiolipin, cholesterol crystals, endoplasmic reticulum stress, and uric acid to reach the liver. Because inflammation triggers HSC activation, the NLRP3 inflammasome pathway performs a central function in fibrogenesis regardless of the etiology. Chronic hepatic activation of the NLRP3 inflammasome can ultimately lead to HCC; however, inflammation also plays a role in decreasing tumor growth. Some data indicate that NLRP3 inflammasome activation plays an important role in autoimmune hepatitis, but the evidence is scarce. Most researchers have reported that NLRP3 inflammasome activation is essential in liver injury induced by a variety of drugs and hepatotropic virus infection; however, few reports indicate that this pathway can play a beneficial role by inducing liver regeneration. Modulation of the NLRP3 inflammasome appears to be a suitable strategy to treat liver diseases.

A novel dual NLRP1 and NLRP3 inflammasome inhibitor for the treatment of inflammatory diseases

Objectives

Inflammasomes induce maturation of the inflammatory cytokines IL-1β and IL-18, whose activity is associated with the pathophysiology of a wide range of infectious and inflammatory diseases. As validated therapeutic targets for the treatment of acute and chronic inflammatory diseases, there has been intense interest in developing small-molecule inhibitors to target inflammasome activity and reduce disease-associated inflammatory burden.

Methods

We examined the therapeutic potential of a novel small-molecule inhibitor, and associated derivatives, termed ADS032 to target and reduce inflammasome-mediated inflammation in vivo. In vitro, we characterised ADS032 function, target engagement and specificity.

Results

We describe ADS032 as the first dual NLRP1 and NLRP3 inhibitor. ADS032 is a rapid, reversible and stable inflammasome inhibitor that directly binds both NLRP1 and NLRP3, reducing secretion and maturation of IL-1β in human-derived macrophages and bronchial epithelial cells in response to the activation of NLPR1 and NLRP3. ADS032 also reduced NLRP3-induced ASC speck formation, indicative of targeting inflammasome formation. In vivo, ADS032 reduced IL-1β and TNF-α levels in the serum of mice challenged i.p. with LPS and reduced pulmonary inflammation in an acute model of lung silicosis. Critically, ADS032 protected mice from lethal influenza A virus challenge, displayed increased survival and reduced pulmonary inflammation.

Conclusion

ADS032 is the first described dual inflammasome inhibitor and a potential therapeutic to treat both NLRP1- and NLRP3-associated inflammatory diseases and also constitutes a novel tool that allows examination of the role of NLRP1 in human disease.

In Silico Structural and Functional Analyses of NLRP3 Inflammasomes to Provide Insights for Treating Neurodegenerative Diseases

Inflammasomes are cytoplasmic intracellular multiprotein complexes that control the innate immune system's activation of inflammation in response to derived chemicals. Recent advancements increased our molecular knowledge of activation of NLRP3 inflammasomes. Although several studies have been done to investigate the role of inflammasomes in innate immunity and other diseases, structural, functional, and evolutionary investigations are needed to further understand the clinical consequences of NLRP3 gene. The purpose of this study is to investigate the structural and functional impact of the NLRP3 protein by using a computational analysis to uncover putative protein sites involved in the stabilization of the protein-ligand complexes with inhibitors. This will allow for a deeper understanding of the molecular mechanism underlying these interactions. It was found that human NLRP3 gene coexpresses with PYCARD, NLRC4, CASP1, MAVS, and CTSB based on observed coexpression of homologs in other species. The NACHT, LRR, and PYD domain-containing protein 3 is a key player in innate immunity and inflammation as the sensor subunit of the NLRP3 inflammasome. The inflammasome polymeric complex, consisting of NLRP3, PYCARD, and CASP1, is formed in response to pathogens and other damage-associated signals (and possibly CASP4 and CASP5). Comprehensive structural and functional analyses of NLRP3 inflammasome components offer a fresh approach to the development of new treatments for a wide variety of human disorders.

MCC950 attenuates inflammation-mediated damage in canines with Staphylococcus pseudintermedius keratitis by inhibiting the NLRP3 inflammasome

BACKGROUND

Bacterial keratitis is a common eye disease in dogs and can seriously affect vision. This study investigated the anti-inflammatory effect of MCC950 in the cornea of canines infected with Staphylococcus pseudintermedius (S. pseudintermedius).

METHODS

In vitro, canine cornea epithelial cells were pretreated with MCC950 and PDTC and then infected with S. pseudintermedius. The key proteins of the NF-κB pathway and NLRP3 inflammasome were detected by Western blotting, the levels of inflammatory factors were detected by qPCR, and the levels of MDA and LDH were detected by assay kit. In vivo, the canine keratitis model was established by injecting S. pseudintermedius into the corneal stroma layer. After treatment with MCC950, slit-lamp examinations were performed. Cornea tissue protein and RNA were extracted, and Western blotting was used to detect key proteins of the NF-κB pathway and NLRP3 inflammasome. qPCR was used to detect the inflammatory factors. Paraffin sections of corneal tissue were prepared for HE staining and immunohistochemical staining.

RESULTS

After MCC950 treatment, the expression levels of key proteins in the NF-κB pathway and NLRP3 inflammasome in canine cornea epithelial cells and corneal tissues were decreased, and the expression levels of IL-1β, IL-6, IL-8, IL-18 and TNF-α were reduced. Cellular MDA and LDH levels were decreased. In vivo, the degree of corneal opacity, edema, neovascularization and corneal injury area decreased after MCC950 treatment. Canine corneal sections showed that MCC950 attenuated neutrophil infiltration.

CONCLUSION

MCC950 alleviates the inflammatory response to canine keratitis caused by S. pseudintermedius by inhibiting the activation of the NLRP3 inflammasome.

Indomethacin attenuates neuroinflammation and memory impairment in an STZ-induced model of Alzheimer's like disease

Objective: Non-steroidal anti-inflammatory drugs (NSAIDs) exposure might be considerably associated with a decreased risk of Alzheimer's disease (AD). Therefore, we conducted an experiment to investigate the impact of indomethacin (IND) on inflammasome as a key player of neuroinflammation.Methods: The Alzheimer's-like condition was induced by streptozotocin (STZ) in rats. IND was injected intraperitoneally 1 d prior to STZ administration and resumed with 2 d interval up to 60 d. Morris water maze (MWM) was utilized to assess learning and memory. The expression level of genes that contribute to the inflammasome pathway was measured using real-time polymerase chain reaction (PCR). To authenticate the obtained outcomes, immunostaining for caspase-1, interleukin-1β (IL-1β), and phosphorylated tau (p-Tau) protein was conducted.Results: Behavioral experiments indicated that IND treatment was able to improve learning and memory performance (p<.05). A significant decrease in C-terminal caspase recruitment domain [CARD] domain-containing protein 4 (NLRC4), nucleotide-binding oligomerization domain [NOD]-like receptor protein 3 (NLRP3), IL-1β, and apoptosis-associated speck-like protein containing CARD (ASC) mRNA expression was recorded in IND administered group compared with the STZ group (p<.05). Furthermore, expression levels of IL-18 and caspase-1 in the hippocampus of IND-treated group tended to decrease. Immunostaining evaluations showed that few positive cells for caspase-1, IL-1β, and p-Tau protein in IND treated animals, whereas the number of positive cells was considerably increased in STZ treated animals (p<.05).Conclusion: It could be deduced that IND improves neuroinflammation and memory impairment in AD through decreasing IL-1β and caspase-1 that are associated with suppression of NLRC4 and NLRP3 inflammasome genes. This holds the potential to introduce valuable targets in the field for successful combat against AD.

The Supportive Role of NSC328382, a P2X7R Antagonist, in Enhancing the Inhibitory Effect of CRID3 on NLRP3 Inflammasome Activation in Rats with Dextran Sodium Sulfate-Induced Colitis

Purpose

The NLRP3 inflammasome is a substantial component of the inflammation process. The complex pathogenesis of and the implication of a vast number of components in the inflammasome-activation pathway prompted us to search for compounds that have a wide therapeutic index and act at the level of multiple cellular targets. Although CRID3 blocks NLRP3 with high specificity in the laboratory, clinical trials of the compound reported weaker potency.

Methods

We used NSC328382, a P2X7R antagonist, as an adjunctive therapy and generated a strategy to potentiate the effects of CRID3 in rats with DSS-induced colitis.

Results

NSC328382/CRID3 combined therapy exhibited a significantly increased efficacy compared with either of the monotherapies. NSC328382/CRID3 was more efficient in 1) attenuating colon shortening and disease activity; 2) improving goblet cell density and both the macroscopic and microscopic scenario of the injured colon; 3) improving the antioxidant defense mechanisms of the inflamed colon against oxidative stress; and 4) mitigating the inflammation state by downregulating the proinflammatory cytokines. Pyroptotic cell death was also conspicuously restrained. Additionally, NSC328382 interrupted the MyD88/NF-κB axis. Moreover, NSC328382/CRID3 exhibited the ability to alter Th1/Th2 dominance.

Conclusion

The clinical application of NSC328382/CRID3 may result in the generation of a novel approach for the treatment of IBDs.

Blocking the inflammasome: A novel approach to treat uveitis

Uveitis is a complex ocular inflammatory disease often accompanied by bacterial or viral infections (infectious uveitis) or underlying autoimmune diseases (non-infectious uveitis). Treatment of the underlying infection along with corticosteroid-mediated suppression of acute inflammation usually resolves infectious uveitis. However, to develop more effective therapies for non-infectious uveitis and to better address acute inflammation in infectious disease, an improved understanding of the underlying inflammatory pathways is needed. In this review, we discuss the disease aetiology, preclinical in vitro and in vivo uveitis models, the role of inflammatory pathways, as well as current and future therapies. In particular, we highlight the involvement of the inflammasome in the development of non-infectious uveitis and how it could be a future target for effective treatment of the disease.

Association of P2X7 receptor genetic polymorphisms and expression with rheumatoid arthritis susceptibility in a sample of the Iranian population: a case-control study

OBJECTIVE

Rheumatoid arthritis (RA) is a complex inflammatory autoimmune disease with joint eruption, systemic manifestation, and numerous predisposing genetic factors. The P2X7 receptor is an essential ligand-gated channel that contributes to many physiological processes, especially inflammation. However, genetic variations can alter the P2X7 receptor function. Therefore, the present study aimed to explore the impact of P2X7 genetic polymorphisms and expression on susceptibility to RA in a sample of the Iranian population.

METHODS

We enrolled 160 (145 female, 15 male) RA patients and 160 (142 female, 18 male) healthy individuals in this study. Genotyping was performed using tetra amplification refractory mutation system-polymerase chain reaction (TARMS-PCR) for rs1718119, rs2230912, rs2393799, rs28360457, rs35933842, and allele-specific PCR for rs1653624 and rs3751143. Furthermore, 44 new cases of RA and 48 healthy controls were recruited to investigate whether P2X7 mRNA expression is associated with RA susceptibility.

RESULTS

The results revealed that the rs2393799 significantly increased the risk of RA in all genetic models (p<0.05), while rs3751143 in codominant (CC vs. AA, OR=0.49, 95% CI=0.26-0.92), dominant (AC+CC, OR=0.59, 95% CI=0.37-0.94), C allele (OR=0.63, 95% CI=0.46-0.88), and rs2230912 in codominant (AG vs. AA, OR=0.56, 95% CI=0.34-0.94), dominant (AG+GG vs. AA, OR=0.59, 95% CI=0.35-0.99), and overdominant (AG vs. AA+GG, OR=0.57, 95% CI=0.33-0.98) significantly decreased the RA risk (p<0.05). Furthermore, the rs1718119 and rs1653624 were not associated with susceptibility of RA (p>0.05), and rs28360457 and rs35933842 were not polymorphic in our study. The mRNA expression level of P2X7 in both groups revealed that the P2X7 gene was significantly upregulated in RA (3.18±0.43) compared to healthy subjects (1.47±0.15, p<0.001).

CONCLUSION

Our results suggest that rs2393799, rs3751143, and rs2230912 variants of the P2X7 gene are associated with RA's susceptibility in a sample of the Iranian population. Also, P2X7 mRNA expression was higher in our new RA patients. The P2X7 receptor has been considered as a potential pharmacologic target in RA. Key Points • P2X7 variants (rs2393799, rs2230912, rs3751143) were associated with RA susceptibility in a sample of the Iranian population. • rs2393799 increases the risk of RA, while rs2230912 and rs3751143 decrease the risk of RA. • P2X7 expression was significantly upregulated in new RA patients compared to controls.

miRNAs as attractive diagnostic and therapeutic targets for Familial Mediterranean Fever

Familial Mediterranean Fever (FMF) is a hereditary early-onset disease that causes periodical fever attack, excessive release of IL-1β, serositis, arthritis and peritonitis. Genetic analyses conducted on FMF patients (mutated and non-mutated) have highlighted that additional contributing factors such as epigenetics and environment play a role in clinical manifestations of FMF. Recently researchers report that microRNAs (miRNAs), implicated in epigenetic mechanisms, may contribute to the pathogenesis of FMF. miRNAs, a member of the captivating noncoding RNA family, are the single-strand transcripts that work in physiological and pathophysiological processes by regulating target gene expression. Recent studies have shown that miRNAs are associated with various mechanisms involved in the pathogenesis of FMF, such as apoptosis, inflammation and autophagy. Moreover, these miRNAs molecules might have potential use in treatment, therapeutic response monitoring and the diagnosis of subtypes of the disease in the future. Motivated by these potential benefits (diagnostic and therapeutic) of miRNAs, we focus on recent advances of clinical significances and potential action mechanisms of miRNAs in FMF pathogenesis and discuss their potential use for FMF.

P2X7 receptor and the NLRP3 inflammasome: Partners in crime

Adenosine triphosphate (ATP) is a molecule that on one hand plays a central role in cellular energetics and which on the other is a ubiquitous signaling molecule when released into the extracellular media. Extracellular ATP accumulates in inflammatory environments where it acts as a damage-associated molecular pattern and activates the purinergic P2X receptor 7 (P2X7) in immune cells. P2X7 receptor activation induces the formation of the nucleotide-binding domain, leucine-rich-containing family, pyrin domain-containing 3 (NLRP3) inflammasome and the activation of the inflammatory caspase-1. Caspase-1 causes an inflammatory type of cell death called pyroptosis through the release of pro-inflammatory cytokines and intracellular content. Consequently, intense research efforts have been devoted to the design of novel anti-inflammatory therapies, focusing in particular on the P2X7 receptor and the NLRP3 pathway and the introduction of new blocking molecules in early phase clinical trials.

Contribution of inflammasome complex in inflammatory-related eye disorders and its implications for anti-inflammasome therapy

Inflammasome complex is regarded as a major molecular regulator that exerts a significant function in caspase-1 activation and consequently, the development of cytokines like interleukin-1β (IL-1β) and interleukin-18 (IL-18). The secretion of these cytokines may induce inflammation. The role of inflammasomes in the pathologic process of eye-related illnesses like glaucoma, age-related macular degeneration (AMD), and diabetic retinopathy has been well studied over the past decade. However, the detailed pathogenic mechanism of inflammasomes in these retinal diseases is still unknown. Therefore, further investigation and understanding various aspects of inflammasome complexes as well as their pivotal roles in the immunopathology of human ocular illnesses are essential. The present review aims to describe the significant involvement of inflammasomes in the immunopathology of important inflammatory retinal illnesses, including glaucoma, age-related macular degeneration (AMD), and diabetic retinopathy focusing on anti-inflammasome therapy as a promising approach in the treatment of inflammation-related eye diseases.

P2X7 receptor mediates NLRP3 inflammasome activation in depression and diabetes

The increasing prevalence of depression and diabetes mellitus has become a major public health problem worldwide. Studies have shown that people with diabetes are at a high risk of being diagnosed with depression, and diabetes complicates depression treatment by promoting the deterioration of glycemic control, reducing self-care ability and quality of life, and causing severe functional disability and early mortality. Moreover, health deterioration dramatically increases the financial cost of social and health care system. Thus, how to treat depression, diabetes, and diabetes complicated by depression has become one of the world’s urgent concerns. The activation of nod-like receptor family pyrin domain containing 3 (NLRP3) is closely related to mental illness. This finding provides a new perspective for studying depression. NLRP3 plays an important role in the development of diabetes. In this review, we elaborate the definition and epidemiology of depression, diabetes, and diabetic depression and introduce the functional characteristics of an NLRP3 inflammasome and upstream P2X7 receptor. Moreover, related research on NLRP3 inflammasomes and P2X7 receptors is summarized and used as a reference for confirming that the excessive activation of P2X7- NLRP3 leads to the increased release of inflammatory cytokines, such as IL-1β, in depression and diabetes. We provide insights into the P2X7–NLRP3–IL-1β pathway as an important pathological mechanism and novel therapeutic target in diabetes and depression. Given that the P2X7–NLRP3–IL-1β pathway may play an important role in diabetes confounded by comorbid depression, the possibility of intervention with baicalin is proposed.

The NLRP3 inflammasome: a therapeutic target for inflammation-associated cancers

Introduction: Inflammasomes are large multimeric intracellular complexes that are capable of maturation and secretion of pro-inflammatory cytokines, IL-1β and IL-18, in response to danger signal molecules. As a member of the inflammasome family, the NLRP3 inflammasome has recently been under intense investigation revealing its possible role in several human diseases especially cancers.Areas covered: In this review, we will discuss the biology and mechanism of NLRP3 inflammasome activation, its role in specific types of tumors and the novel therapeutic modalities targeting this complex.Expert opinion: The NLRP3 inflammasome and its components including the adapter apoptosis-associated speck-like (ASC) protein and caspase-1 impose different and sometimes contrasting effects in tumorigenesis depending on various contexts. Considering the novel role of this complex in the initiation and progression of neoplasia, the NLRP3 inflammasome and its pathways provide desirable therapeutic targets for prevention, treatment, and prognosis of certain types of cancer. To date, several agents have been introduced for this purpose, some of which have shown promising results in the clinic.

Cyclic nucleotides, gut physiology and inflammation

Misregulation of gut function and homeostasis impinges on the overall well-being of the entire organism. Diarrheal disease is the second leading cause of death in children under 5 years of age, and globally, 1.7 billion cases of childhood diarrhea are reported every year. Accompanying diarrheal episodes are a number of secondary effects in gut physiology and structure, such as erosion of the mucosal barrier that lines the gut, facilitating further inflammation of the gut in response to the normal microbiome. Here, we focus on pathogenic bacteria-mediated diarrhea, emphasizing the role of cyclic adenosine 3',5'-monophosphate and cyclic guanosine 3',5'-monophosphate in driving signaling outputs that result in the secretion of water and ions from the epithelial cells of the gut. We also speculate on how this aberrant efflux and influx of ions could modulate inflammasome signaling, and therefore cell survival and maintenance of gut architecture and function.

Inflammasomes: An Emerging Mechanism Translating Environmental Toxicant Exposure Into Neuroinflammation in Parkinson's Disease

Evidence indicates that complex gene-environment interactions underlie the incidence and progression of Parkinson's disease (PD). Neuroinflammation is a well-characterized feature of PD widely believed to exacerbate the neurodegenerative process. Environmental toxicants associated with PD, such as pesticides and heavy metals, can cause cellular damage and stress potentially triggering an inflammatory response. Toxicant exposure can cause stress and damage to cells by impairing mitochondrial function, deregulating lysosomal function, and enhancing the spread of misfolded proteins. These stress-associated mechanisms produce sterile triggers such as reactive oxygen species (ROS) along with a variety of proteinaceous insults that are well documented in PD. These associations provide a compelling rationale for analysis of sterile inflammatory mechanisms that may link environmental exposure to neuroinflammation and PD progression. Intracellular inflammasomes are cytosolic assemblies of proteins that contain pattern recognition receptors, and a growing body of evidence implicates the association between inflammasome activation and neurodegenerative disease. Characterization of how inflammasomes may function in PD is a high priority because the majority of PD cases are sporadic, supporting the widely held belief that environmental exposure is a major factor in disease initiation and progression. Inflammasomes may represent a common mechanism that helps to explain the strong association between exposure and PD by mechanistically linking environmental toxicant-driven cellular stress with neuroinflammation and ultimately cell death.

Pattern Recognition Receptor-Mediated Chronic Inflammation in the Development and Progression of Obesity-Related Metabolic Diseases

Obesity-induced chronic inflammation is known to promote the development of many metabolic diseases, especially insulin resistance, type 2 diabetes mellitus, nonalcoholic fatty liver disease, and atherosclerosis. Pattern recognition receptor-mediated inflammation is an important determinant for the initiation and progression of these metabolic diseases. Here, we review the major features of the current understanding with respect to obesity-related chronic inflammation in metabolic tissues, focus on Toll-like receptors and nucleotide-binding oligomerization domain-like receptors with an emphasis on how these receptors determine metabolic disease progression, and provide a summary on the development and progress of PRR antagonists for therapeutic intervention.

The reduction of XIAP is associated with inflammasome activation in RPE: implications for AMD pathogenesis

Background

Age-related macular degeneration (AMD) is a multifactorial chronic disease of the eye. Several candidate pathways have been hypothesized to play a role in AMD pathogenesis. Our work and those of others suggests inflammasome activity as a mechanism associated with retinal pigment epithelial (RPE) cell demise. X-linked inhibitor of apoptosis protein (XIAP), an anti-apoptosis factor, has recently been shown to regulate inflammasome activity in non-ocular cells. The purpose of this study is to characterize XIAP’s regulatory role in RPE.

Methods

Protein lysates of eye tissues from rats (vinpocetine- or aurin tricarboxylic acid complex-treated, ATAC, vs naïve) and mice (wild type vs Caspase-4^−/−) were utilized to analyze XIAP protein levels. Immunohistochemistry was used to detect NLRP3 levels in the RPE layer. In vitro inflammasome activation on RPE cells was achieved with L-leucyl-L-leucine methyl ester (Leu-Leu-OMe) stimulation. Levels of XIAP mRNA and 18S RNA were quantified by RT-PCR. Cell culture supernatants were tested directly for secreted IL-1β by ELISA or concentrated for the detection of secreted IL-18 by western blot. Protein lysates from RPE in cell culture were collected for the measurement of cleaved caspase-1 p20, XIAP, and GAPDH. Data are presented as Mean ± SD. p < 0.05 is considered statistically significant.

Results

The XIAP protein level was significantly increased when the inflammasome was inhibited at the “activation” step by ATAC, but not the “priming” step, in vivo. Concomitantly, NLRP3 immunoreactivity was lower in the RPE layer of animals fed with ATAC. In mice where caspase-1 cleavage was impaired by the genetic deficiency in caspase-4, the XIAP protein level increased in eye tissues. In RPE cell culture, Leu-Leu-OMe stimulation led to caspase-1 cleavage, cytokine secretion, and XIAP reduction, which can be abolished by Z-YVAD-FMK. When XIAP siRNA was given as a pre-treatment to RPE in vitro, Leu-Leu-OMe induced IL-1β/IL-18 secretion was enhanced, whereas overexpressing XIAP reduced IL-1β secretion under inflammasome activation, both compared to controls cells.

Conclusions

Together, these data suggest XIAP-mediated inhibition of inflammasome activity in RPE may provide insights into the biological consequences of inflammasome activation in RPE and reveals the caspase-1/XIAP/IL-1β/IL-18 axis as a target for broader applications in AMD biology and treatment design.

Electronic supplementary material

The online version of this article (10.1186/s12974-019-1558-5) contains supplementary material, which is available to authorized users.

Late Versus Early Myocardial Remodeling After Acute Myocardial Infarction: A Comparative Review on Mechanistic Insights and Clinical Implications

In the setting of acute myocardial infarction (AMI), adverse myocardial remodeling (AMR) has been universally regarded as an early-onset phenomenon generally arising within the first few weeks (usually within days in the infarct zone) following myocardial injury. On the other hand, onset of cardiac morphological changes in this setting may potentially extend far beyond this time frame (usually beyond several months after the index AMI), suggesting a prolonged latent period in certain cases. In clinical practice, this delayed form of post-AMI remodeling, namely late AMR, has emerged as an interesting and underrecognized phenomenon with poorly understood mechanisms. Notably, systemic inflammation and associated growth factors seem to play a pivotal role in this setting. Accordingly, the present article primarily aims to discuss potential mechanisms and clinical implications of late AMR (in a comparative manner with its classical early counterpart) among AMI survivors along with a particular emphasis on potential benefits of certain anti-inflammatory strategies in this setting.

Pigment Nephropathy: Novel Insights into Inflammasome-Mediated Pathogenesis

Pigment nephropathy is an acute decline in renal function following the deposition of endogenous haem-containing proteins in the kidneys. Haem pigments such as myoglobin and haemoglobin are filtered by glomeruli and absorbed by the proximal tubules. They cause renal vasoconstriction, tubular obstruction, increased oxidative stress and inflammation. Haem is associated with inflammation in sterile and infectious conditions, contributing to the pathogenesis of many disorders such as rhabdomyolysis and haemolytic diseases. In fact, haem appears to be a signalling molecule that is able to activate the inflammasome pathway. Recent studies highlight a pathogenic function for haem in triggering inflammatory responses through the activation of the nucleotide-binding domain-like receptor protein 3 (NLRP3) inflammasome. Among the inflammasome multiprotein complexes, the NLRP3 inflammasome has been the most widely characterized as a trigger of inflammatory caspases and the maturation of interleukin-18 and -1β. In the present review, we discuss the latest evidence on the importance of inflammasome-mediated inflammation in pigment nephropathy. Finally, we highlight the potential role of inflammasome inhibitors in the prophylaxis and treatment of pigment nephropathy.

Purinergic receptors and the inflammatory response mediated by lipids

The inflammatory response is regulated by the production of different extracellular mediators, including lipids and extracellular nucleotides. In the extracellular environment, intermediate lipids activate specific G-protein-coupled receptors (GPCRs) in target cells and promote cell recruitment and activation. Extracellular nucleotides activate two types of receptors, the ionotropic purinergic P2X and the metabotropic purinergic P2Y receptors, inducing the release of cytokines and promoting cell recruitment. Several P2X receptors are associated with an increase in the production of immunoactive lipids mediators, which in turn are able to interfere with the activation of different P2Y receptors, establishing a tight signalling link between purinergic receptors and lipid mediators. In this review, we summarise recent studies indicating signalling crosstalk between purinergic P2X and P2Y receptor activation and lipid mediators with a focus on inflammatory diseases. Novel concepts arising from this crosstalk would result in the development of combinatorial therapies targeting lipid synthesis together with individual P2 receptors for the management of inflammatory diseases.

The Potential Role of the NLRP3 Inflammasome Activation as a Link Between Mitochondria ROS Generation and Neuroinflammation in Postoperative Cognitive Dysfunction

Postoperative cognitive dysfunction (POCD) is commonly observed in perioperative care following major surgery and general anesthesia in elderly individuals. No preventive or interventional agents have been established so far. Although the role of interleukin-1β (IL-1β)-mediated neuroinflammation following surgery and anesthesia is strongly implicated in POCD, the exact mechanism of action remains to be explored. Growing evidence has shown that mitochondria-derived reactive oxygen species (mtROS) are closely linked to IL-1β expression through a redox sensor known as the nod-like receptor pyrin domain-containing 3 (NLRP3) inflammasome. Therefore, we hypothesize that the mechanisms underlying POCD involve the mtROS/NLRP3 inflammasome/IL-1β signaling pathway. Furthermore, we speculate that cholinergic anti-inflammatory pathway induced by α7 nicotinic acetylcholine receptor (a7nAChR) may be the potential upstream of mtROS/NLRP3 inflammasome/IL-1β signaling pathway in POCD. For validating the hypotheses, we provide experimental plan involving different paradigms namely; microglial cells and behavioral studies. The link between mtROS, the NLRP3 inflammasome, and IL-1β within and between these different stages in combination with mtROS and NLRP3 inflammasome agonists and inhibitors could be explored using techniques, such as knockout mice, small interference ribonucleic acid, flow cytometry, co-immunoprecipitation, and the Morris Water Maze test. We conclude that the NLRP3 inflammasome is a new preventive and therapeutic target for POCD.

Nucleotides regulate the common molecular mechanisms that underlie neurodegenerative diseases; Therapeutic implications

Neurodegenerative diseases (ND) are a heterogeneous group of neurological disorders characterized by a progressive loss of neuronal function which results in neuronal death. Although a specific toxic factor has been identified for each ND, all of them share common pathological molecular mechanisms favouring the disease development. In the final stages of ND, patients become unable to take care of themselves and decline to a total functional incapacitation that leads to their death. Some of the main factors which contribute to the disease progression include proteasomal dysfunction, neuroinflammation, synaptic alterations, protein aggregation, and oxidative stress. Over recent years, evidence has been accumulated to suggest that purinergic signaling plays a key role in the aforementioned molecular pathways. In this review, we revise the implications of the purinergic signaling in the common molecular mechanism underlying the ND. In particular, we focus on the role of the purinergic receptors P2X7, P2Y₂ and the ectoenzyme tissue-nonspecific alkaline phosphatase (TNAP).

Inflammasomes: Pandora's box for sepsis

Sepsis was known to ancient Greeks since the time of great physician Hippocrates (460-377 BC) without exact information regarding its pathogenesis. With time and medical advances, it is now considered as a condition associated with organ dysfunction occurring in the presence of systemic infection as a result of dysregulation of the immune response. Still with this advancement, we are struggling for the development of target-based therapeutic approach for the management of sepsis. The advancement in understanding the immune system and its working has led to novel discoveries in the last 50 years, including different pattern recognition receptors. Inflammasomes are also part of these novel discoveries in the field of immunology which are <20 years old in terms of their first identification. They serve as important cytosolic pattern recognition receptors required for recognizing cytosolic pathogens, and their pathogen-associated molecular patterns play an important role in the pathogenesis of sepsis. The activation of both canonical and non-canonical inflammasome signaling pathways is involved in mounting a proinflammatory immune response via regulating the generation of IL-1β, IL-18, IL-33 cytokines and pyroptosis. In addition to pathogens and their pathogen-associated molecular patterns, death/damage-associated molecular patterns and other proinflammatory molecules involved in the pathogenesis of sepsis affect inflammasomes and vice versa. Thus, the present review is mainly focused on the inflammasomes, their role in the regulation of immune response associated with sepsis, and their targeting as a novel therapeutic approach.

Inflammasomes in Tissue Damages and Immune Disorders After Trauma

Trauma remains a leading cause of death worldwide. Hemorrhagic shock and direct injury to vital organs are responsible for early mortality whereas most delayed deaths are secondary to complex pathophysiological processes. These processes result from imbalanced systemic reactions to the multiple aggressions associated with trauma. Trauma results in the uncontrolled local and systemic release of endogenous mediators acting as danger signals [damage-associated molecular patterns (DAMPs)]. Their recognition by the innate immune system triggers a pro-inflammatory immune response paradoxically associated with concomitant immunosuppression. These responses, ranging in intensity from inappropriate to overwhelming, promote the propagation of injuries to remote organs, leading to multiple organ failure and death. Some of the numerous DAMPs released after trauma trigger the assembly of intracellular multiprotein complexes named inflammasomes. Once activated by a ligand, inflammasomes lead to the activation of a caspase. Activated caspases allow the release of mature forms of interleukin-1β and interleukin-18 and trigger a specific pro-inflammatory cell death termed pyroptosis. Accumulating data suggest that inflammasomes, mainly NLRP3, NLRP1, and AIM2, are involved in the generation of tissue damage and immune dysfunction after trauma. Following trauma-induced DAMP(s) recognition, inflammasomes participate in multiple ways in the development of exaggerated systemic and organ-specific inflammatory response, contributing to organ damage. Inflammasomes are involved in the innate responses to traumatic brain injury and contribute to the development of acute respiratory distress syndrome. Inflammasomes may also play a role in post-trauma immunosuppression mediated by dysregulated monocyte functions. Characterizing the involvement of inflammasomes in the pathogenesis of post-trauma syndrome is a key issue as they may be potential therapeutic targets. This review summarizes the current knowledge on the roles of inflammasomes in trauma.

Selective NLRP3 (Pyrin Domain-Containing Protein 3) Inflammasome Inhibitor Reduces Brain Injury After Intracerebral Hemorrhage

BACKGROUND AND PURPOSE

Intracerebral hemorrhage (ICH) is a devastating disease without effective treatment. As a key component of the innate immune system, the NOD-like receptor (NLR) family, NLRP3 (pyrin domain-containing protein 3) inflammasome, when activated after ICH, promotes neuroinflammation and brain edema. MCC950 is a potent, selective, small-molecule NLRP3 inhibitor that blocks NLRP3 activation at nanomolar concentrations. Here, we examined the effect of MCC950 on brain injury and inflammation in 2 models of ICH in mice.

METHODS

In mice with ICH induced by injection of autologous blood or bacterial collagenase, we determined the therapeutic potential of MCC950 and its mechanisms of neuroprotection.

RESULTS

MCC950 reduced IL-1β (interleukin-1β) production and attenuated neurodeficits and perihematomal brain edema after ICH induction by injection of either autologous blood or collagenase. In mice with autologous blood-induced ICH, the protection of MCC950 was associated with reduced leukocyte infiltration into the brain and microglial production of IL-6. MCC950 improved blood-brain barrier integrity and diminished cell death. Notably, the protective effect of MCC950 was abolished in mice depleted of either microglia or Gr-1⁺ myeloid cells.

CONCLUSIONS

These results indicate that the NLRP3 inflammasome inhibitor, MCC950, attenuates brain injury and inflammation after ICH. Hence, NLRP3 inflammasome inhibition is a potential therapy for ICH that warrants further investigation.

Antidiabetic drug glyburide modulates depressive-like behavior comorbid with insulin resistance

Background

Abundant reports indicated that depression was often comorbid with type 2 diabetes and even metabolic syndrome. Considering they might share common biological origins, it was tentatively attributed to the chronic cytokine-mediated inflammatory response which was induced by dysregulation of HPA axis and overactivation of innate immunity. However, the exact mechanisms remain obscure. Herein, we mainly focused on the function of the NLRP3 inflammasome to investigate this issue.

Methods

Male C57BL/6 mice were subjected to 12 weeks of chronic unpredictable mild stress (CUMS), some of which were injected with glyburide or fluoxetine. After CUMS procedure, behavioral and metabolic tests were carried out. In order to evaluate the systemic inflammation associated with inflammasome activation, IL-1β and inflammasome components in hippocampi and pancreases, as well as corticosterone and IL-1β in serum were detected separately. Moreover, immunostaining was performed to assess morphologic characteristics of pancreases.

Results

In the present study, we found that 12 weeks’ chronic stress resulted in depressive-like behavior comorbid with insulin resistance. Furthermore, antidiabetic drug glyburide, an inhibitor of the NLRP3 inflammasome, was discovered to be effective in preventing the experimental comorbidity. In brief, it improved behavioral performance, ameliorated insulin intolerance as well as insulin signaling in the hippocampus possibly through inhibiting NLRP3 inflammasome activation by suppressing the expression of TXNIP.

Conclusions

All these evidence supported our hypothesis that chronic stress led to comorbidity of depressive-like behavior and insulin resistance via long-term mild inflammation. More importantly, based on the beneficial effects of blocking the activation of the NLRP3 inflammasome, we provided a potential therapeutic target for clinical comorbidity and a new strategy for management of both diabetes and depression.

P2X7 Receptor Induces Tumor Necrosis Factor-α Converting Enzyme Activation and Release to Boost TNF-α Production

Tumor necrosis factor (TNF)-α is a major pro-inflammatory cytokine produced in response to toll-like receptor stimulation. TNF-α release is controlled by the activity of TNF-α converting enzyme (TACE) that cut membrane-bound TNF-α to shed its ectodomain as a soluble cytokine. The purinergic receptor P2X ligand-gated ion channel 7 (P2X7) is activated in response to elevated concentrations of extracellular ATP and induces different pro-inflammatory pathways in macrophages to establish an inflammatory response. P2X7 receptor promotes the activation of the inflammasome and the release of interleukin-1β, the production of inflammatory lipids, and the generation of reactive oxygen species. In this study, we analyzed the mechanism of P2X7 receptor responsible of TNF-α release after priming macrophages with LPS doses ≤100 ng/ml. We found that P2X7 receptor increases the extracellular activity of TACE through the release of the mature form of TACE in exosomes. This effect was blocked using P2X7 receptor inhibitors or in macrophages obtained from P2X7 receptor-deficient mice. Elevation of intracellular Ca²⁺ and p38 mitogen-activated protein kinase after P2X7 receptor activation were involved in the release of TACE, which was able to process TNF-α on nearby expressing cells. Finally, we observed an increase of TNF-α in the peritoneal lavage of mice treated with LPS and ATP. In conclusion, P2X7 receptor induces the release of TACE in exosomes to the extracellular compartment that could amplify the pro-inflammatory signal associated to this receptor. These results are important for the development of therapeutics targeting P2X7 receptor.

Inflammasome as a Therapeutic Target for Cancer Prevention and Treatment

Chronic inflammation is a critical modulator of carcinogenesis through secretion of inflammatory cytokines, which leads to the formation of an inflammatory microenvironment. In this process, the inflammasome plays an important role in the expression and activation of interleukin (IL)-1β and IL-18 to promote cancer development. The inflammasome is a multiprotein complex consisting of several nucleotide-binding domain and leucine-rich repeat containing receptor, adaptor proteins, and caspase 1 (CASP1). It senses the various intracellular (damage-associated molecular patterns) and extracellular (pathogen-associated molecular patterns) stimuli. A primed inflammasome recruits adaptor proteins, activates CASP1 to enhance the proteolytic cleavage of pro-IL-1β and IL-18, and sends the signal to respond to each insult. Depending on stimuli and cell contexts, several inflammasomes are closely associated with the initiation and promotion of carcinogenesis. In contrast, inflammasomes also show an ambivalent effect on carcinogenesis by enhancing inflammatory cell death (pyroptosis) and repairing damaged tissues. Although the inflammasome plays a controversial role in carcinogenesis, it may be a promising target for human cancer prevention and treatment. A more in-depth study on the role of the inflammasome in carcinogenesis, based on stimuli, cell contexts, and cancer stages, can lead to the development of novel therapeutic strategies against malignant human cancers.

Off-Target Anti-Inflammatory Activity of the P2X7 Receptor Antagonist AZ11645373

We have found that a well-characterized P2X7 receptor antagonist AZ11645373 blocked production of pro-inflammatory chemokine IL-8 in endothelial cells treated with OxPAPC. The effect was not due to toxicity of AZ11645373 as documented by cellular metabolic activity assay. The mechanism of inhibition by AZ11645373 was apparently independent of the P2X7 receptor because this receptor was not involved in induction of IL-8 under our experimental conditions. In support of this notion, two P2X7 agonists ATP and BzATP did not upregulate IL-8. On the other hand, a chemically different P2X7 receptor antagonist A740003 did not inhibit OxPAPC-induced production of IL-8. The inhibitory action of AZ11645373 was observed at the level of IL-8 protein and messenger RNA (mRNA) induction. Furthermore, AZ11645373 inhibited induction of mRNA encoding for COX-2 (PTGS2) suggesting that its anti-inflammatory potential is not limited to suppression of IL-8 production. In addition to inhibiting stimulation by OxPAPC, AZ11645373 suppressed induction of IL-8 by TNFα and LPS. To summarize, AZ11645373 inhibits in a P2X7-independent manner action of chemically different inflammatory agonists such as OxPLs, LPS, and TNFα. Thus, AZ11645373 may be especially effective for treatment of inflammatory disorders due to a beneficial combination of P2X7 receptor-dependent effects (inhibition of inflammasome activation, antinociceptive effects) with P2X7-independent general anti-inflammatory action described in this paper.

Development of an Acrylate Derivative Targeting the NLRP3 Inflammasome for the Treatment of Inflammatory Bowel Disease

Pharmacological inhibition of NLRP3 inflammasome activation may offer a new option in the treatment of inflammatory bowel disease. In this work, we report the design, synthesis, and biological screening of a series of acrylate derivatives as NLRP3 inhibitors. The in vitro determination of reactivity, cytotoxicity, NLRP3 ATPase inhibition, and antipyroptotic properties allowed the selection of 11 (INF39), a nontoxic, irreversible NLRP3 inhibitor able to decrease interleukin-1β release from macrophages. Bioluminescence resonance energy transfer experiments proved that this compound was able to directly interfere with NLRP3 activation in cells. In vivo studies confirmed the ability of the selected lead to alleviate the effects of colitis induced by 2,4-dinitrobenzenesulfonic acid in rats after oral administration.

The NLRP3 and Pyrin Inflammasomes: Implications in the Pathophysiology of Autoinflammatory Diseases

Inflammasomes are multiprotein complexes that critically control different aspects of innate and adaptive immunity. Among them we could highlight the release of pro-inflammatory cytokines that induce and maintain the inflammatory response. Usually, inflammasomes result from oligomerization of a nucleotide-binding domain-like receptor (NLR) after sensing different pathogenic or endogenous sterile dangerous signals; however, other proteins such as absent in melanoma 2, retinoic acid-inducible gene I, or pyrin could also form inflammasome platforms. Inflammasome oligomerization leads to caspase-1 activation and the processing and release of the pro-inflammatory cytokines, such as interleukin (IL)-1β and IL-18. Mutations in different inflammasomes are causative for multiple periodic hereditary syndromes or autoinflammatory diseases, characterized by acute systemic inflammatory flares not associated with infections, tumors, or autoimmunity. This review focuses on germline mutations that have been described in cryopyrin-associated periodic syndrome (CAPS) for NLRP3 or in familial Mediterranean fever (FMF) and pyrin-associated autoinflammation with neutrophilic dermatosis (PAAND) for MEFV. Besides the implication of inflammasomes in autoinflammatory syndromes, these molecular platforms are involved in the pathophysiology of different illnesses, including chronic inflammatory diseases, degenerative processes, fibrosis, or metabolic diseases. Therefore, drug development targeting inflammasome activation is a promising field in expansion.

Canonical and Non-Canonical Activation of NLRP3 Inflammasome at the Crossroad between Immune Tolerance and Intestinal Inflammation

Several lines of evidence point out the relevance of nucleotide-binding oligomerization domain leucine rich repeat and pyrin domain-containing protein 3 (NLRP3) inflammasome as a pivotal player in regulating the integrity of intestinal homeostasis and shaping innate immune responses during bowel inflammation. Intensive research efforts are being made to achieve an integrated view about the protective/detrimental role of canonical and non-canonical NLRP3 inflammasome activation in the maintenance of intestinal microenvironment integrity. Evidence is also emerging that the pharmacological modulation of NLRP3 inflammasome could represent a promising molecular target for the therapeutic management of inflammatory immune-mediated gut diseases. The present review has been intended to provide a critical appraisal of the available knowledge about the role of canonical and non-canonical NLRP3 inflammasome activation in the dynamic interplay between microbiota, intestinal epithelium, and innate immune system, taken together as a whole integrated network regulating the maintenance/breakdown of intestinal homeostasis. Moreover, special attention has been paid to the pharmacological modulation of NLRP3 inflammasome, emphasizing the concept that this multiprotein complex could represent a suitable target for the management of inflammatory bowel diseases.

Involvement of P2X7 receptor in neuronal degeneration triggered by traumatic injury

Axonal injury is a common feature of central nervous system insults that culminates with the death of the affected neurons, and an irreversible loss of function. Inflammation is an important component of the neurodegenerative process, where the microglia plays an important role by releasing proinflammatory factors as well as clearing the death neurons by phagocytosis. Here we have identified the purinergic signaling through the P2X7 receptor as an important component for the neuronal death in a model of optic nerve axotomy. We have found that in P2X7 receptor deficient mice there is a delayed loss of retinal ganglion cells and a decrease of phagocytic microglia at early times points after axotomy. In contralateral to the axotomy retinas, P2X7 receptor controlled the numbers of phagocytic microglia, suggesting that extracellular ATP could act as a danger signal activating the P2X7 receptor in mediating the loss of neurons in contralateral retinas. Finally, we show that intravitreal administration of the selective P2X7 receptor antagonist A438079 also delays axotomy-induced retinal ganglion cell death in retinas from wild type mice. Thus, our work demonstrates that P2X7 receptor signaling is involved in neuronal cell death after axonal injury, being P2X7 receptor antagonism a potential therapeutic strategy.

Inflammasomes and Natural Ingredients towards New Anti-Inflammatory Agents

Inflammasomes are a family of proteins in charge of the initiation of inflammatory process during innate immune response. They are now considered major actors in many chronic inflammatory diseases. However, no major drug focusing on this target is currently on the market. Among the various approaches aiming to control this major metabolic pathway, compounds aiming to modify the intracellular antioxidant profile appear to be promising. This can be obtained by “light” antioxidants able to induce natural antioxidant response of the cell itself. This review will give an overview of the current available information on this promising pharmacology approach.

Danggui Buxue Tang Attenuates Tubulointerstitial Fibrosis via Suppressing NLRP3 Inflammasome in a Rat Model of Unilateral Ureteral Obstruction

Inflammation significantly contributes to the progression of chronic kidney disease (CKD). This study aimed to characterize Danggui Buxue Tang (DBT) renoprotection and relationship with NOD-like receptors family pyrin domain-containing 3 (NLRP3) inflammasome expression in rats with unilateral ureteral obstruction (UUO). Sprague-Dawley rats were subjected to UUO and randomly assigned to untreated UUO, enalapril-treated (10 mg/kg/day), and DBT-treated (9 g/kg/day) groups. Sham-operated rats served as controls, with 8 rats in each group. All rats were sacrificed for blood and renal specimen collection at 14 days after UUO. Untreated UUO rats exhibited azotemia, intense tubulointerstitial collagen deposition, upregulations of tubulointerstitial injury index, augmentation levels of collagen I (Col I), α-smooth muscle actin (α-SMA), NLRP3, apoptosis-associated speck-like protein containing a caspase recruitment domain (ASC), pro-caspase-1, caspase-1, IL-1β, and pro-IL-1β. DBT treatment significantly attenuated interstitial collagen deposition and tubulointerstitial injury, lowering Col I and α-SMA levels. Synchronous expressions of NLRP3, ASC, pro-caspase-1, caspase-1, pro-IL-1β, and IL-1β decreased in renal tissue. In comparison to enalapril, DBT significantly reduced tubulointerstitial injury, interstitial collagen deposition, and expressions of Col I and IL-1β. Thus, DBT offers renoprotection in UUO rats, which was associated with suppressing NLRP3 inflammasome expression and following reduction of the secretion of cytokine IL-1β. The mechanisms of multitargets of traditional Chinese medicine can be better used for antifibrotic treatment.

Obesity-associated NLRC4 inflammasome activation drives breast cancer progression

Obesity is associated with an increased risk of developing breast cancer and is also associated with worse clinical prognosis. The mechanistic link between obesity and breast cancer progression remains unclear, and there has been no development of specific treatments to improve the outcome of obese cancer patients. Here we show that obesity-associated NLRC4 inflammasome activation/ interleukin (IL)-1 signalling promotes breast cancer progression. The tumour microenvironment in the context of obesity induces an increase in tumour-infiltrating myeloid cells with an activated NLRC4 inflammasome that in turn activates IL-1β, which drives disease progression through adipocyte-mediated vascular endothelial growth factor A (VEGFA) expression and angiogenesis. Further studies show that treatment of mice with metformin inhibits obesity-associated tumour progression associated with a marked decrease in angiogenesis. This report provides a causal mechanism by which obesity promotes breast cancer progression and lays out a foundation to block NLRC4 inflammasome activation or IL-1β signalling transduction that may be useful for the treatment of obese cancer patients.

NLR-regulated pathways in cancer: opportunities and obstacles for therapeutic interventions

NLRs (nucleotide-binding domain, leucine-rich repeat containing receptors) are pattern recognition receptors associated with immunity and inflammation in response to endogenous and exogenous pathogen and damage associated molecular patterns (PAMPs and DAMPs respectively). Dysregulated NLR function is associated with several diseases including cancers, metabolic diseases, autoimmune disorders and autoinflammatory syndromes. In the last decade, distinct cell and organ specific roles for NLRs have been identified however; their roles in cancer initiation, development and progression remain controversial. This review summarizes the emerging role of NLRs in cancer and their possible future as targets for cancer therapeutics.

Molecular basis of caspase-1 polymerization and its inhibition by a new capping mechanism

Inflammasomes are cytosolic caspase-1-activation complexes that sense intrinsic and extrinsic danger signals, and trigger inflammatory responses and pyroptotic cell death. Homotypic interactions among Pyrin domains and caspase recruitment domains (CARDs) in inflammasome-complex components mediate oligomerization into filamentous assemblies. Several cytosolic proteins consisting of only interaction domains exert inhibitory effects on inflammasome assembly. In this study, we determined the structure of the human caspase-1 CARD domain (caspase-1(CARD)) filament by cryo-electron microscopy and investigated the biophysical properties of two caspase-1-like CARD-only proteins: human inhibitor of CARD (INCA or CARD17) and ICEBERG (CARD18). Our results reveal that INCA caps caspase-1 filaments, thereby exerting potent inhibition with low-nanomolar Ki on caspase-1(CARD) polymerization in vitro and inflammasome activation in cells. Whereas caspase-1(CARD) uses six complementary surfaces of three types for filament assembly, INCA is defective in two of the six interfaces and thus terminates the caspase-1 filament.

Elevated caspase‑1 activity and IL‑1β expression are associated with the IPAF inflammasome in an experimental model of allergy

Previous studies have indicated that interleukin (IL)‑1β has an important role in the development of allergic diseases. Therefore, the present study aimed to investigate the upstream pathway underlying IL‑1β production in an experimental model of allergy. BALB/c mice (female, 6‑8 weeks old) were sensitized to recombinant (r)Che a 2 by intraperitoneal injection of rChe a 2 adsorbed onto an alum gel suspension on days 0, 7, 14 and 21. In the control group, mice received an injection of 20 mM phosphate‑buffered saline absorbed onto alum via the same route. The allergic status of the mice was confirmed serologically by measuring allergen‑specific immunoglobulin (Ig)E levels. The protein expression levels of IL‑1β and the mRNA expression levels of inflammasome compartments were measured by enzyme‑linked immunosorbent assay and semi‑quantitative reverse transcription polymerase chain reaction, respectively. In addition, caspase‑1 activity was determined by fluorometric assay. Sensitized mice exhibited significantly increased levels of specific IgE (P<0.05). IL‑1β production and caspase‑1 activity were significantly higher in the sensitized mice compared with the control group. In addition, no significant differences were observed between the control and sensitized mice in the expression of genes associated with the inflammasome, including NLR family, pyrin domain containing 3; apoptosis‑associated speck‑like protein; and NLR family, apoptosis inhibitory protein 5. However, IL‑1β converting enzyme protease‑activating factor (IPAF) expression was significantly increased in sensitized mice compared with in the control group (P<0.05). These data indicate that caspase‑1 activation and IL‑1β expression are associated with the IPAF inflammasome. Therefore, based on this association, the IPAF inflammasome may be considered for IL‑1β production in the experimental model of allergy.

Targeting Cell Death and Sterile Inflammation Loop for the Treatment of Nonalcoholic Steatohepatitis

Nonalcoholic fatty liver disease represents a wide spectrum of conditions and is currently the most common form of chronic liver disease affecting both adults and children in the United States and many other parts of the world. Great effort has been focused on the development of novel therapies for those patients with the more advanced forms of the disease, in particular those with nonalcoholic steatohepatitis (NASH) and liver fibrosis that can be associated with significant morbidity and mortality. In this review, the authors focus on the role of cell death and sterile inflammatory pathways as well as the self-perpetuating deleterious cycle they may trigger as novel therapeutic targets for the treatment of fibrotic NASH.

P2X ion channel receptors and inflammation

Neuroinflammation limits tissue damage in response to pathogens or injury and promotes repair. There are two stages of inflammation, initiation and resolution. P2X receptors are gaining attention in relation to immunology and inflammation. The P2X7 receptor in particular appears to be an essential immunomodulatory receptor, although P2X1 and P2X4 receptors also appear to be involved. ATP released from damaged or infected cells causes inflammation by release of inflammatory cytokines via P2X7 receptors and acts as a danger signal by occupying upregulated P2X receptors on immune cells to increase immune responses. The purinergic involvement in inflammation is being explored for the development of novel therapeutic strategies.

Inflammatory targets of therapy in sickle cell disease

Sickle cell disease (SCD) is a monogenic globin disorder characterized by the production of a structurally abnormal hemoglobin (Hb) variant Hb S, which causes severe hemolytic anemia, episodic painful vaso-occlusion, and ultimately end-organ damage. The primary disease pathophysiology is intracellular Hb S polymerization and consequent sickling of erythrocytes. It has become evident for more than several decades that a more complex disease process contributes to the myriad of clinical complications seen in patients with SCD with inflammation playing a central role. Drugs targeting specific inflammatory pathways therefore offer an attractive therapeutic strategy to ameliorate many of the clinical events in SCD. In addition, they are useful tools to dissect the molecular and cellular mechanisms that promote individual clinical events and for developing improved therapeutics to address more challenging clinical dilemmas such as refractoriness to opioids or hyperalgesia. Here, we discuss the prospect of targeting multiple inflammatory pathways implicated in the pathogenesis of SCD with a focus on new therapeutics, striving to link the actions of the anti-inflammatory agents to a defined pathobiology, and specific clinical manifestations of SCD. We also review the anti-inflammatory attributes and the cognate inflammatory targets of hydroxyurea, the only Food and Drug Administration-approved drug for SCD.

Genipin inhibits NLRP3 and NLRC4 inflammasome activation via autophagy suppression

Inflammasomes are cytoplasmic, multiprotein complexes that trigger caspase-1 activation and IL-1β maturation in response to diverse stimuli. Although inflammasomes play important roles in host defense against microbial infection, overactive inflammasomes are deleterious and lead to various autoinflammatory diseases. In the current study, we demonstrated that genipin inhibits the induction of IL-1β production and caspase-1 activation by NLRP3 and NLRC4 inflammasomes. Furthermore, genipin specifically prevented NLRP3-mediated, but not NLRC4-mediated, ASC oligomerization. Notably, genipin inhibited autophagy, leading to NLRP3 and NLRC4 inflammasome inhibition. UCP2-ROS signaling may be involved in inflammasome suppression by genipin. In vivo, we showed that genipin inhibited NLRP3-dependent IL-1β production and neutrophil flux in LPS- and alum-induced murine peritonitis. Additionally, genipin provided protection against flagellin-induced lung inflammation by reducing IL-1β production and neutrophil recruitment. Collectively, our results revealed a novel role in inhibition of inflammatory diseases for genipin that has been used as therapeutics for centuries in herb medicine.

IL-1α Gene Deletion Protects Oligodendrocytes after Spinal Cord Injury through Upregulation of the Survival Factor Tox3

Spinal cord injury (SCI) causes the release of danger signals by stressed and dying cells, a process that leads to neuroinflammation. Evidence suggests that inflammation plays a role in both the damage and repair of injured neural tissue. We show that microglia at sites of SCI rapidly express the alarmin interleukin (IL)-1α, and that infiltrating neutrophils and macrophages subsequently produce IL-1β. Infiltration of these cells is dramatically reduced in both IL-1α(-/-) and IL-1β(-/-) mice, but only IL-1α(-/-) mice showed rapid (at day 1) and persistent improvements in locomotion associated with reduced lesion volume. Similarly, intrathecal administration of the IL-1 receptor antagonist anakinra restored locomotor function post-SCI. Transcriptome analysis of SCI tissue at day 1 identified the survival factor Tox3 as being differentially regulated exclusively in IL-1α(-/-) mice compared with IL-1β(-/-) and wild-type mice. Accordingly, IL-1α(-/-) mice have markedly increased Tox3 levels in their oligodendrocytes, beginning at postnatal day 10 (P10) and persisting through adulthood. At P10, the spinal cord of IL-1α(-/-) mice showed a transient increase in mature oligodendrocyte numbers, coinciding with increased IL-1α expression in wild-type animals. In adult mice, IL-1α deletion is accompanied by increased oligodendrocyte survival after SCI. TOX3 overexpression in human oligodendrocytes reduced cellular death under conditions mimicking SCI. These results suggest that IL-1α-mediated Tox3 suppression during the early phase of CNS insult plays a crucial role in secondary degeneration.

SIGNIFICANCE STATEMENT

The mechanisms underlying bystander degeneration of neurons and oligodendrocytes after CNS injury are ill defined. We show that microglia at sites of spinal cord injury (SCI) rapidly produce the danger signal interleukin (IL)-1α, which triggers neuroinflammation and locomotor defects. We uncovered that IL-1α(-/-) mice have markedly increased levels of the survival factor Tox3 in their oligodendrocytes, which correlates with the protection of this cell population, and reduced lesion volume, resulting in unprecedented speed, level, and persistence of functional recovery after SCI. Our data suggest that central inhibition of IL-1α or Tox3 overexpression during the acute phase of a CNS insult may be an effective means for preventing the loss of neurological function in SCI, or other acute injuries such as ischemia and traumatic brain injuries.

Resveratrol inhibits NLRP3 inflammasome activation by preserving mitochondrial integrity and augmenting autophagy

The NLRP3 inflammasome is a caspase-1-containing multi-protein complex that controls the release of IL-1β and plays important roles in the development of inflammatory disease. Here, we report that resveratrol, a polyphenolic compound naturally produced by plants, inhibits NLRP3 inflammasome-derived IL-1β secretion and pyroptosis in macrophages. Resveratrol inhibits the activation step of the NLRP3 inflammasome by suppressing mitochondrial damage. Resveratrol also induces autophagy by activating p38, and macrophages treated with an autophagy inhibitor are resistant to the suppressive effects of resveratrol. In addition, resveratrol administration mitigates glomerular proliferation, glomerular sclerosis, and glomerular inflammation in a mouse model of progressive IgA nephropathy. These findings were associated with decreased renal mononuclear leukocyte infiltration, reduced renal superoxide anion levels, and inhibited renal NLRP3 inflammasome activation. Our data indicate that resveratrol suppresses NLRP3 inflammasome activation by preserving mitochondrial integrity and by augmenting autophagy.

NLRP3 Inflammasome Mediates Chronic Mild Stress-Induced Depression in Mice via Neuroinflammation

BACKGROUND

Evidence from both clinical and experimental research indicates that the immune-brain interaction plays a pivotal role in the pathophysiology of depression. A multi-protein complex of the innate immune system, the NLRP3 inflammasome regulates cleavage and secretion of proinflammatory cytokine interleukin-1β. The inflammasome detects various pathogen-associated molecule patterns and damage-associated molecule patterns, which then leads to a series of immune-inflammatory reactions.

METHODS

To explore the role of inflammasome activation in the underlying biological mechanisms of depression, we established a mouse model of depression with unpredictable chronic mild stress.

RESULTS

Mice subjected to chronic mild stress for 4 weeks had significantly higher serum corticosterone levels, serum interleukin-1β levels, and hippocampal active interleukin-1β protein levels. They also displayed depressive-like symptoms, including decreased sucrose preference and increased immobility time. Moreover, the hippocampi of chronic mild stress-exposed mice had significantly higher activity of caspase-1, which accompanied by higher protein levels of NLRP3 and the apoptotic speck-containing protein with a card. Pretreatment with the NLRP3 inflammasome inhibitor VX-765 decreased serum and hippocampal levels of interleukin-1β protein and significantly moderated the depressive-like behaviors induced by chronic mild stress.

CONCLUSIONS

These data suggest the NLRP3 inflammasome mediates stress-induced depression via immune activation. Future procedures targeting the NLRP3 inflammasome may have promising effects in the prevention and treatment of depression.

A small-molecule inhibitor of the NLRP3 inflammasome for the treatment of inflammatory diseases

The NOD-like receptor (NLR) family, pyrin domain-containing protein 3 (NLRP3) inflammasome is a component of the inflammatory process, and its aberrant activation is pathogenic in inherited disorders such as cryopyrin-associated periodic syndrome (CAPS) and complex diseases such as multiple sclerosis, type 2 diabetes, Alzheimer's disease and atherosclerosis. We describe the development of MCC950, a potent, selective, small-molecule inhibitor of NLRP3. MCC950 blocked canonical and noncanonical NLRP3 activation at nanomolar concentrations. MCC950 specifically inhibited activation of NLRP3 but not the AIM2, NLRC4 or NLRP1 inflammasomes. MCC950 reduced interleukin-1β (IL-1β) production in vivo and attenuated the severity of experimental autoimmune encephalomyelitis (EAE), a disease model of multiple sclerosis. Furthermore, MCC950 treatment rescued neonatal lethality in a mouse model of CAPS and was active in ex vivo samples from individuals with Muckle-Wells syndrome. MCC950 is thus a potential therapeutic for NLRP3-associated syndromes, including autoinflammatory and autoimmune diseases, and a tool for further study of the NLRP3 inflammasome in human health and disease.