NLRP3 Inflammasome Inhibitor OLT1177 Suppresses Onset of Inflammation in Mice with Dextran Sulfate Sodium-Induced Colitis

New Insights on NLRP3 Inflammasome: Mechanisms of Activation, Inhibition, and Epigenetic Regulation

Inflammasomes are important modulators of inflammation. Dysregulation of inflammasomes can enhance vulnerability to conditions such as neurodegenerative diseases, autoinflammatory diseases, and metabolic disorders. Among various inflammasomes, Nucleotide-binding oligomerization domain leucine-rich repeat and pyrin domain-containing protein 3 (NLRP3) is the best-characterized inflammasome related to inflammatory and neurodegenerative diseases. NLRP3 is an intracellular sensor that recognizes pathogen-associated molecular patterns and damage-associated patterns resulting in the assembly and activation of NLRP3 inflammasome. The NLRP3 inflammasome includes sensor NLRP3, adaptor apoptosis-associated speck-like protein (ASC), and effector cysteine protease procaspase-1 that plays an imperative role in caspase-1 stimulation which further initiates a secondary inflammatory response. Regulation of NLRP3 inflammasome ameliorates NLRP3-mediated diseases. Much effort has been invested in studying the activation, and exploration of specific inhibitors and epigenetic mechanisms controlling NLRP3 inflammasome. This review gives an overview of the established NLRP3 inflammasome assembly, its brief molecular mechanistic activations as well as a current update on specific and non-specific NLRP3 inhibitors that could be used in NLRP3-mediated diseases. We also focused on the recently discovered epigenetic mechanisms mediated by DNA methylation, histone alterations, and microRNAs in regulating the activation and expression of NLRP3 inflammasome, which has resulted in a novel method of gaining insight into the mechanisms that modulate NLRP3 inflammasome activity and introducing potential therapeutic strategies for CNS disorders.

Antagonizing interleukin-5 receptor ameliorates dextran sulfate sodium-induced experimental colitis in mice through reducing NLRP3 inflammasome activation

Inflammatory bowel disease (IBD) is a condition characterized by inflammation in the gastrointestinal tract. Reducing intestinal inflammation is a promising approach for treating IBD. The nucleotide-binding oligomerization domain-like receptor family pyrin domain-containing protein 3 (NLRP3) inflammasome, a critical component of the innate immune system, is implicated in the pathogenesis of IBD. Therefore, inhibiting NLRP3 inflammasome activation is a potential therapeutic strategy for IBD. In this study, we investigated the effects of the interleukin-5 (IL-5) receptor antagonist YM-90709 on dextran sulfate sodium-induced experimental colitis in mice. We found that YM-90709 reduced the expressions of IL-1β and caspase-1 p20 in the colon and ameliorated colitis. Furthermore, we identified YM-90709 as an effective agent for inhibiting NLRP3 inflammasome activation. Knockdown of IL-5 receptor or using an inhibitor of STAT5, a key transcription factor downstream of the IL-5/IL-5 receptor signal pathway, also reduced NLRP3 inflammasome-dependent IL-1β release and ASC speck formation. Our study is the first to demonstrate that the NLRP3 inflammasome may be a downstream signal of IL-5/IL-5 receptor and that YM-90709 protects against IBD by inhibiting IL-5 receptor. These findings suggest a new strategy for regulating intestinal inflammation and managing IBD.

The 'speck'-tacular oversight of the NLRP3-pyroptosis pathway on gastrointestinal inflammatory diseases and tumorigenesis

The NLRP3 inflammasome is an intracellular sensor and an essential component of the innate immune system involved in danger recognition. An important hallmark of inflammasome activation is the formation of a single supramolecular punctum, known as a speck, per cell, which is the site where the pro-inflammatory cytokines IL-1β and IL-18 are converted into their bioactive form. Speck also provides the platform for gasdermin D protein activation, whose N-terminus domain perforates the plasma membrane, allowing the release of mature cytokines alongside with a highly inflammatory form of cell death, namely pyroptosis. Although controlled NLRP3 inflammasome-pyroptosis pathway activation preserves mucosal immunity homeostasis and contributes to host defense, a prolonged trigger is deleterious and could lead, in genetically predisposed subjects, to the onset of inflammatory bowel disease, including Crohn's disease and ulcerative colitis, as well as to gastrointestinal cancer. Experimental evidence shows that the NLRP3 inflammasome has both protective and pathogenic abilities. In this review we highlight the impact of the NLRP3-pyroptosis axis on the pathophysiology of the gastrointestinal tract at molecular level, focusing on newly discovered features bearing pro- and anti-inflammatory and neoplastic activity, and on targeted therapies tested in preclinical and clinical trials.

Taurodeoxycholate ameliorates DSS-induced colitis in mice

BACKGROUND

Inflammatory bowel disease (IBD) is typically managed using medications such as 5-aminosalicylic acid (5-ASA), glucocorticoids, anti-TNFα Ab, or anti-IL-12/23 Ab. However, some patients do not respond well to these treatments or frequently experience relapses. Therefore, alternative therapeutic options are needed. Since the activation of the inflammasome is crucial to the pathogenesis of IBD, inhibiting the inflammasome may be beneficial for patients.

MATERIALS AND METHODS

We tested the efficacy of taurodeoxycholate (TDCA), which is a known G-protein coupled receptor 19 (GPCR19) agonist, in a mouse colitis model induced by dextran sodium sulfate (DSS).

RESULTS

In the mouse colitis model, TDCA prevented loss of body weight, shortening of the colon, production of pro-inflammatory cytokines, infiltration of pro-inflammatory cells, and mucosal ulceration in the colon. In vitro, TDCA inhibited the activation of NF-κB in bone marrow-derived macrophages (BMDMs) by activating the cAMP-PKA axis. TDCA downregulated the expression of purinergic receptor P2X7 (P2X7R) and enhanced the colocalization of P2X7R with GPCR19, and inhibited the Ca2+ mobilization of BMDMs when stimulated with ATP or BzATP, which plays a pivotal role in activating the NLRP3 inflammasome (N3I) via P2X7R. TDCA inhibited the oligomerization of NLRP3-ASC and downregulated the expression of NLRP3 and ASC, as well as suppressed the maturation of pro-caspase-1 and pro-IL-1β. TDCA also increased the percentage of M2 macrophages while decreasing the number of M1 macrophages, Th1, Th2, and Th17 cells in the colon.

CONCLUSION

TDCA ameliorated DSS-induced colitis in mice, possibly by inhibiting both the priming phase (via the GPCR19-cAMP-PKA-NF-κB axis) and the activation phase (via the GPCR19-P2X7R-NLRP3-Caspase 1-IL-1β axis) of N3I signaling.

Therapeutic Potential of Targeting the NLRP3 Inflammasome in Rheumatoid Arthritis

NOD-like receptor family pyrin domain-containing 3 (NLRP3) inflammasome is a cytoplasmic multiprotein complex composed of the innate immune receptor protein NLRP3, the adapter protein apoptosis-associate speck-like protein containing a caspase recruitment domain (ASC), and the inflammatory protease cysteine-1. Pathogen-associated molecular patterns (PAMPs) or other endogenous danger-associated molecular patterns (DAMPs) activate the NLRP3 inflammasome. As part of the innate immune response, activated NLRP3 promotes GSDMD-dependent pyroptosis, and IL-1β and IL-18 are released during inflammation. Aberrantly activated NLRP3 is deeply involved in various inflammatory diseases. Due to its interaction with adaptive immunity. NLRP3 inflammation has increasingly received attention in autoimmune diseases. Rheumatoid arthritis (RA) is a classic autoimmune disease, which mainly causes bone and cartilage damage. Elevated levels of NLRP3 can be detected in the synovium of RA patients. NLRP3 overactivation is strongly associated with RA activity. Mouse models of spontaneous arthritis has shown that NLRP3/IL-1β axis is implicated in periarticular inflammation in RA. In this review, we describe the current understanding of NLRP3 activation in RA pathogenesis and dissect its impact on innate and adaptive immunity. We also discuss the potential application of specific inhibitors of NLRP3 to provide new therapeutic strategies for treating RA.

Ononin alleviates DSS-induced colitis through inhibiting NLRP3 inflammasome via triggering mitophagy

BACKGROUND

Ononin, a flavonoid isolated from Astragalus membranaceus root, is the active ingredient of A. membranaceus and has potential anti-inflammatory properties, but its effect on colitis is unclear.

AIMS

This study aimed to explore the anticolitis effect of Ononin by establishing a colitis model in mice induced by dextran sulfate sodium (DSS).

METHODS

Male C57BL/6 mice were provided DSS, then treated with Ononin (10, 20, 40 mg/kg) or 5-ASA (40 mg/kg). The colitis symptoms were observed, the disease activity index (DAI) score were recorded daily, and colonic inflammation was evaluted by histopathological scoring. The expression of cytokines, inflammatory mediators, and mitophagy/NLRP3 inflammasome-related proteins were measured.

RESULTS

Ononin significantly alleviated weight loss and colon shortening in mice with colitis (p < .01). Moreover, Ononin decreased the production of inflammatory cytokines and mediators associated with colitis (p < .05). In addition, Ononin inhibited macrophages infiltration and reduced caspase-1 activation in colitis mice. Caspase-1 activation is closely related to the NLRP3 inflammasome. Therefore, we investigated the effect of Ononin on NLRP3 inflammasome in vitro. The relevant results confirmed that Ononin inhibited NLRP3 inflammasome activation and inhibited mitochondrial damage (p < .05). Further studies revealed that Ononin inhibited mitochondrial damage through triggering mitophagy (p < .05).

CONCLUSION

Ononin alleviates DSS-induced colitis by activating mitophagy to inhibit NLRP3 inflammasome.

NLRP3: A Promising Therapeutic Target for Inflammatory Bowel Disease

Inflammatory bowel disease (IBD), which includes Crohn's disease and ulcerative colitis, is an intestinal disease with complicated pathological mechanisms. The incidence of IBD has been increasing in recent years, which has a significant negative impact on the lives of patients. Therefore, it is particularly important to find new therapeutic targets and innovative drugs for the development of IBD. Recent studies have revealed that NLRP3 inflammatory vesicles can play an important role in maintaining intestinal homeostasis and sustaining the intestinal immune response in IBD. On the one hand, aberrant activation of NLRP3 inflammatory vesicles may cause excessive immune response by converting caspase-1, proIL-18, and proIL-1β to their active forms and releasing pro-inflammatory cytokines to stimulate the development and progression of IBD, and we can improve IBD by targeting blockade of NLRP3 activation. On the other hand, NLRP3 may also play an enter protective role by maintaining the homeostasis of the intestinal immune system. In this paper, we reviewed the activation mechanism of NLRP3 inflammasome, and the effects of NLRP3 inflammasome activation on IBD are discussed from two different perspectives: pathology and protection. At the same time, we listed the effects of direct inhibitors, indirect inhibitors, and natural inhibitors of NLRP3 inflammasome on IBD in combination with cutting-edge advances and clinical practice results, providing new targets and new ideas for the clinical treatment of IBD.

NLRP3 inflammasome in digestive diseases: From mechanism to therapy

Digestive system diseases remain a formidable challenge to human health. NOD-like receptor family pyrin domain containing 3 (NLRP3) inflammasome is the most characteristic multimeric protein complex and is involved in a wide range of digestive diseases as intracellular innate immune sensors. It has emerged as a research hotspot in recent years. In this context, we provide a comprehensive review of NLRP3 inflammasome priming and activation in the pathogenesis of digestive diseases, including clinical and preclinical studies. Moreover, the scientific evidence of small-molecule chemical drugs, biologics, and phytochemicals, which acts on different steps of the NLRP3 inflammasome, is reviewed. Above all, deep interrogation of the NLRP3 inflammasome is a better insight of the pathomechanism of digestive diseases. We believe that the NLRP3 inflammasome will hold promise as a novel valuable target and research direction for treating digestive disorders.

IL-38 Gene Deletion Worsens Murine Colitis

IL-38 is a recently discovered cytokine and member of the IL-1 Family. In the IL-1 Family, IL-38 is unique because the cytokine is primarily a B lymphocyte product and functions to suppress inflammation. Studies in humans with inflammatory bowel disease (IBD) suggest that IL-38 may be protective for ulcerative colitis or Crohn’s disease, and that IL-38 acts to maintain homeostasis in the intestinal tract. Here we investigated the role of endogenous IL-38 in experimental colitis in mice deficient in IL-38 by deletion of exons 1-4 in C57 BL/6 mice. Compared to WT mice, IL-38 deficient mice subjected to dextran sulfate sodium (DSS) showed greater severity of disease, more weight loss, increased intestinal permeability, and a worse histological phenotype including increased neutrophil influx in the colon. Mice lacking IL-38 exhibited elevated colonic Nlrp3 mRNA and protein levels, increased caspase-1 activation, and the concomitant increased processing of IL-1β precursor into active IL-1β. Expression of IL-1α, an exacerbator of IBD, was also upregulated. Colonic myleloperoxidase protein and Il17a, and Il17f mRNA levels were higher in the IL-38 deficient mice. Daily treatment of IL-38 deficient mice with an NLRP3 inhibitor attenuated diarrhea and weight loss during the recovery phase. These data implicate endogenous IL-38 as an anti-inflammatory cytokine that reduces DSS colitis severity. We propose that a relative deficiency of IL-38 contributes to IBD by disinhibition of the NLRP3 inflammasome.

NLRP3 and pyroptosis blockers for treating inflammatory diseases

The nucleotide-binding oligomerization domain, leucine-rich repeat and pyrin domain-containing protein 3 (NLRP3) inflammasome has emerged as a key mediator of pathological inflammation in many diseases and is an exciting drug target. Here, we review the molecular basis of NLRP3 inhibition by drug-like small molecules under development as novel therapeutics. We also summarize recent strategies to block pyroptosis as a novel approach to suppress chronic inflammation. Major recent developments in this area include the elucidation of mechanisms of action (MoAs) by which small molecules block NLRP3 inflammasome assembly and gasdermin D (GSDMD)-induced pyroptosis. We also discuss the status of clinical trials using agents that block specific components of the NLRP3 pathway, including their potential clinical applications for the treatment of many diseases.

Inflammasomes in Cancer Progression and Anti-Tumor Immunity

The inflammasomes are critical regulators of innate immunity, inflammation and cell death and have emerged as important regulators of cancer development and control. Inflammasomes are assembled by pattern recognition receptors (PRR) following the sensing of microbial- or danger-associated molecular patterns (MAMPs/DAMPs) and elicit inflammation through the oligomerization and activation of inflammatory caspases. These cysteinyl-aspartate proteases cleave the proinflammatory cytokines IL-1β and IL-18 into their biologically active mature form. The roles of the inflammasomes and associated pro-inflammatory cytokines vary greatly depending on the cancer type. Here we discuss recent studies highlighting contrasting roles of the inflammasome pathway in curbing versus promoting tumorigenesis. On one hand, the inflammasomes participate in stimulating anti-tumor immunity, but they have also been shown to contribute to immunosuppression or to directly promote tumor cell survival, proliferation, and metastasis. A better understanding of inflammasome functions in different cancers is thus critical for the design of novel cancer immunotherapies.