JC2-11, a benzylideneacetophenone derivative, attenuates inflammasome activation.

Dysregulation of inflammasome activation induces chronic and excess inflammation resulting in several disorders, such as metabolic disorders and cancers. Thus, screening for its regulator derived from natural materials has been conducted progressively. JC2-11 (JC) was designed to enhance the antioxidant activity based on a chalcone, which is abundant in edible plants and a precursor of flavonoids. This study examined the effects of JC on inflammasome activation in human and murine macrophages. JC inhibited the secretion of interleukin (IL)-1ß and lactate dehydrogenases, and the cleavage of caspase-1 and gasdermin D in response to the tested activators (i.e., NLRP3, NLRC4, AIM2, and non-canonical inflammasome triggers). In addition, JC attenuated IL-1ß secretion from lipopolysaccharide (LPS)-injected mice, an inflammasome-mediating disease model. Mechanistically, JC blocked the expression of the inflammasome components during the priming step of the inflammasome, and interrupted the production of mitochondrial reactive oxygen species. In addition, JC inhibited the activity of caspase-1. In conclusion, JC may be a candidate pan-inflammasome inhibitor.

Parabens disrupt non-canonical inflammasome activation.

Parabens are synthetic chemicals widely used as preservatives in cosmetics, pharmaceuticals, and foods. Although parabens, i.e., ethyl- and methyl-parabens, are considered relatively safe, study of possible health hazards has been undertaken due to the frequent exposure to parabens and their accumulation in the body. In this study, we elucidated the effect of parabens on inflammasome induction of inflammatory responses in innate immunity, such as interleukin (IL)-1ß maturation and gasdermin D (GSDMD)-mediating pyroptosis. Parabens attenuated the inflammatory responses to intracellular lipopolysaccharide (LPS) triggering of non-canonical (NC) inflammasome activation, but did not alter canonical inflammasome (i.e., NLRP3, NLRC4 and AIM2) responses. The NC inflammasome is assembled by the interaction of murine caspase (Casp)-11 (Casp4/5 in human) with cytosolic LPS, inducing endotoxin sepsis. Parabens selectively inhibited NC inflammasome activation in both human and murine macrophages and diminished the peritoneal IL-1ß production in LPS-injected mice. Parabens blocked the cleavage of GSDMD, Casp1, and Casp4, but did not change the expression of Casp11 or the activity of Casp1. Taken together, the results indicate that parabens could disrupt Gram-negative pathogen infection through the inhibition of NC inflammasome activation.

NLRP3 Triggers Attenuate Lipocalin-2 Expression Independent with Inflammasome Activation.

Lipocalin-2 (LCN2), a small secretory glycoprotein, is upregulated by toll-like receptor (TLR) signaling in various cells and tissues. LCN2 inhibits bacterial growth by iron sequestration and regulates the innate immune system. Inflammasome activates the inflammatory caspases leading to pyroptosis and cytokine maturation. This study examined the effects of inflammasome activation on LCN2 secretion in response to TLR signaling. The triggers of NLRP3 inflammasome activation attenuated LCN2 secretion while it induced interleukin-1ß in mouse macrophages. In mice, NLRP3 inflammasome activation inhibited TLR-mediated LCN2 secretion. The inhibition of NLRP3 triggers on LCN2 secretion was caused by the inhibited transcription and translation of LCN2. At the same time, no changes in the other cytokines and IκBζ, a well-known transcriptional factor of Lcn2 transcription, were observed. Overall, NLRP3 triggers are a regulator of LCN2 expression suggesting a new linkage of inflammasome activation and LCN2 secretion in the innate immunity.

Lower Temperatures Exacerbate NLRP3 Inflammasome Activation by Promoting Monosodium Urate Crystallization, Causing Gout.

Gout is a recurrent and chronic form of arthritis caused by the deposition of monosodium urate (MSU) crystals in the joints. Macrophages intake MSU crystals, the trigger for NLRP3 inflammasome activation, which leads to the release of interleukin (IL)-1ß and results in the flaring of gout. The effects of temperature, an environmental factor for MSU crystallization, on IL-1ß secretion have not been well studied. This study examined the effects of temperature on inflammasome activation. Specific triggers activated canonical inflammasomes (NLRP3, NLRC4, and AIM2) in murine macrophages at various temperatures (25, 33, 37, 39, and 42 °C). The maturation of IL-1ß and caspase-1 was measured as an indicator for inflammasome activation. As expected, the optimal temperature of inflammasome activation was 37 °C. The MSU crystal-mediated activation of inflammasome increased at temperatures lower than 37 °C and decreased at higher temperatures. MSU crystals at lower temperatures enhanced IL-1ß secretion via the NLRP3 inflammasome pathway. A lower temperature promoted the formation of MSU crystals without changing phagocytosis. Overall, lower temperatures form more MSU crystals and enhance NLRP3 inflammasome activation. In light of these findings, it is possible that hyperthermia therapy may reduce gout flaring.

Characterization of equine inflammasomes and their regulation.

Inflammasome, a cytosolic multi-protein complex, assembly is a response to sensing intracellular pathogenic and endogenic danger signals followed by caspase-1 activation, which maturates precursor cytokines such as interleukin (IL)-1ß. Most inflammasome research has been undertaken in humans and rodents, and inflammasomes in veterinary species have not been well-characterized. In this study, we observed the effects of well-known inflammasome activators on equine peripheral blood monocytes (PBMCs). The NLRP3 inflammasome triggers include ATP, nigericin, aluminum crystals, and monosodium urate crystals, and NLRP3 activation induces IL-1ß secretion in a dose-dependent manner. Activators of NLRC4 and AIM2 inflammasomes include cytosolic flagellin and dsDNA, and their activation induces IL-1ß secretion. The bacterial inflammasome triggers Salmonella Typhimurium and Listeria monocytogenes also induce IL-ß releases. To elucidate the role of potassium efflux as an upstream signal of NLRP3 inflammasome activation, equine PBMCs were treated with blockers of potassium efflux in the presence of NLRP3 triggers. As a result, the IL-1ß secretion stemming from equine NLRP3 inflammasome activation was not completely attenuated by the inhibition of potassium efflux. Taken together, the results indicate that equine PBMCs normally secrete IL-1ß in response to well-known inflammasome activators, although equine NLRP3 inflammasome activation might not be dependent on potassium efflux.

IκBζ controls NLRP3 inflammasome activation via upregulation of the Nlrp3 gene.

Inflammasome activation induces the maturation and secretion of interleukin (IL)-1ß and -18, and is dependent on NF-κB signaling to induce the transcription of the inflammasome components, called the priming step. This study elucidated the role of IκBζ, an atypical IκBs (inhibitor of κB) and a coactivator of NF-κB target genes, on the activation of inflammasome. Bone marrow-derived macrophages (BMDMs) that originated from IκBζ-encoding Nfkbiz gene depletion mice presented a defect in NLRP3 inflammasome activation. In addition, the Nfkbiz+/- and Nfkbiz-/- mice significantly attenuated serum IL-1ß secretion in response to a monosodium urate injection, a NLRP3 trigger, when compared with Nfkbiz-+/+ mice. The lack of IκBζ in BMDMs produced a disability in the expression of Nlrp3 and pro-Il1ß mRNAs during the priming step. In addition, ectopic IκBζ expression enhanced the Nlrp3 promoter activity, and Nlrp3 and pro-Il1ß transcription. Overall, IκBζ controlled the activation of NLRP3 inflammasome by upregulating the Nlrp3 gene during the priming step.

Obovatol inhibits NLRP3, AIM2, and non-canonical inflammasome activation.

BACKGROUND: Obovatol, a biphenolic chemical originating from Magnolia obovata, has been utilized as a traditional medicine for the treatment of inflammatory diseases. Inflammasome induces maturation of inflammatory cytokines in response to intracellular danger signals, and its dysregulation induces inflammatory diseases. PURPOSE: The effect of obovatol on inflammasome activation has not been reported, although its anti-inflammatory properties have been studied. STUDY DESIGN/METHODS: Obovatol was treated to macrophages with inflammasome triggers, and secretions of interleukin (IL)-1ß, IL-18, and caspase-1 were measured as readouts of inflammasome activation. In addition, Asc pyroptosome formation, caspase-1 activity, and mitochondrial reactive oxygen species (ROS) production were analyzed in mechanical studies. Anti-inflammasome properties of obovatol were confirmed in an animal model. RESULTS: Obovatol inhibited NLRP3, AIM2, and non-canonical inflammasomes through inhibition of Asc pyroptosome formation and mitochondrial ROS generation. In addition, obovatol disrupted the priming step of inflammasome activation and inhibited transcription of inflammatory cytokines. In mice, obovatol attenuated serum IL-1ß elevation in response to monosodium urate crystals. CONCLUSION: Obovatol is suggested as an inhibitor of NLRP3, AIM2, and non-canonical inflammasomes.

Mercury and arsenic attenuate canonical and non-canonical NLRP3 inflammasome activation.

Exposure to heavy metals can cause several diseases associated with the immune system. Although the effects of heavy metals on production of inflammatory cytokines have been previously studied, the role of heavy metals in inflammasome activation remains poorly studied. The inflammasome is an intracellular multi-protein complex that detects intracellular danger signals, resulting in inflammatory responses such as cytokine maturation and pyroptosis. In this study, we elucidated the effects of four heavy metals, including cadmium (Cd), mercury (Hg), arsenic (As), and lead (Pb), on the activation of NLRP3, NLRC4, and AIM2 inflammasomes. In our results, mercury and arsenic inhibited interleukin (IL)-1ß and IL-18 secretion resulting from canonical and non-canonical NLRP3 inflammasome activation in macrophages and attenuated elevation of serum IL-1ß in response to LPS treatment in mice. In the mechanical studies, mercury interrupted production of mitochondrial reactive oxygen species, release of mitochondrial DNA, and activity of recombinant caspase-1, whereas arsenic down-regulated expression of promyelocytic leukemia protein. Both mercury and arsenic inhibited Asc pyroptosome formation and gasdermin D cleavage. Thus, we suggest that exposure to mercury and/or arsenic could disrupt inflammasome-mediated inflammatory responses, which might cause unexpected side effects.

Triggers of NLRC4 and AIM2 inflammasomes induce porcine IL-1ß secretion.

Pigs are an important livestock and serve as a large animal model due to physiological and anatomical similarities with humans. Thus, components of the porcine immune system such as inflammasomes need to be characterized for disease control, vaccination, and translational research purposes. Previously, we and others elucidated porcine nucleotide-binding oligomerization domain (NOD)-like receptor (NLR) family Pyrin domain containing 3 (NLRP3) inflammasome activation. However, until now, porcine NLR family caspase recruitment domain (CARD)-containing 4 (NLRC4) and absent in melanoma 2 (AIM2) inflammasomes have been not well studied. In this study, we treated well defined NLRC4 and AIM2 inflammasome triggers to porcine peripheral blood mononuclear cells (PBMCs) and murine bone-marrow derived macrophages (BMDMs) and observed interleukin (IL)-1ß maturation as a readout of inflammasome activation. NLRC4 (flagellin) and AIM2 (dsDNA) triggers led to IL-1ß secretion in both porcine PBMCs and mice macrophages. In addition, porcine and mouse NLRC4 and AIM2 inflammasomes responded differently to NLRP3 inhibitors. Bacterial inflammasome triggers, Salmonella enterica serovar Typhimurium, Listeria monocytogenes, and Escherichia coli, also induced IL-1ß secretion in porcine PBMCs. Taken together, we suggest that known triggers of NLRC4 and AIM2 inflammasomes in mice induce IL-1ß secretion in porcine PBMCs.

Poly-gamma-glutamic acid from Bacillus subtilis upregulates pro-inflammatory cytokines while inhibiting NLRP3, NLRC4 and AIM2 inflammasome activation.

Poly-gamma-glutamic acid (γ-PGA) is a natural, edible and non-toxic polymer synthesized by Bacillus subtilis and is suggested as a safe biomaterial for the use in hydrogels and vaccine adjuvants. However, the effect of γ-PGA on inflammasome activation has not yet been studied in macrophages. Inflammasomes, which are intracellular multi-protein complexes, promote acute and chronic inflammation via interleukin-1ß or interleukin-18 maturation, and they are known targets for metabolic syndromes and cancer. In this study, we observed that γ-PGA attenuated NLRP3, NLRC4 and AIM2 inflammasome activation, whereas it upregulated pro-inflammatory cytokine expression in human and murine macrophages. Although γ-PGA had conflicting effects on cytokine production and maturation, it clearly alleviated the severity of lipopolysaccharide-induced endotoxin shock in an animal model. Thus, we suggest γ-PGA as a candidate to control inflammasome-mediated disorders.

Methylene blue inhibits NLRP3, NLRC4, AIM2, and non-canonical inflammasome activation.

Methylene blue (MB), which has antioxidant, anti-inflammatory, neuroprotective, and mitochondria protective effects, has been widely used as a dye and medication. However, the effect of MB on inflammasome activation has not yet been studied. Inflammasomes are multi-protein complexes that induce maturation of interleukins (ILs)-1ß and -18 as well as caspase-1-mediated cell death, known as pyroptosis. Dysregulation of inflammasomes causes several diseases such as type 2 diabetes, Alzheimer's disease, and gout. In this study, we assess the effect of MB on inflammasome activation in macrophages. As the result, MB attenuated activation of canonical inflammasomes such as NLRP3, NLRC4, and AIM2 as well as non-canonical inflammasome activation. In addition, MB inhibited upstream signals such as inflammasome assembly, phagocytosis, and gene expression of inflammasome components via inhibition of NF-κB signaling. Furthermore, MB reduced the activity of caspase-1. The anti-inflammasome properties of MB were further confirmed in mice models. Thus, we suggest that MB is a broad-spectrum anti-inflammasome candidate molecule.

Lentinan from shiitake selectively attenuates AIM2 and non-canonical inflammasome activation while inducing pro-inflammatory cytokine production.

Lentinan extracted from shiitake (Lentinula edodes) is a ß-glucan that has been reported as an intravenous anti-tumor polysaccharide via enhancement of the host immune system. In this study, we determined the effect of lentinan on inflammasome activation, a multi-protein platform, in myeloid cells. Mouse bone marrow-derived macrophages were treated with lentinan with/without inflammasome triggers, and maturation of interleukin (IL)-1ß, IL-18, or caspase-1 was measured as a readout of inflammasome activation. As a result, lentinan selectively inhibited absent in melanoma 2 (AIM2) inflammasome activation. In addition, lentinan up-regulated pro-inflammatory cytokines and induced expression of inflammasome-related genes through toll-like receptor 4 signaling. Furthermore, we assessed the effect of lentinan on mice treated with Listeria monocytogenes or lipopolysaccharide as an AIM2 or non-canonical inflammasome-mediated model. Lentinan attenuated IL-1ß secretion resulting from Listeria-mediated AIM2 inflammasome activation and reduced endotoxin lethality via inhibition of non-canonical inflammasome activation. Thus, lentinan is suggested as an anti-AIM2 and anti-non-canonical inflammasome candidate despite its up-regulation of cytokine expression.

Isorhamnetin and hyperoside derived from water dropwort inhibits inflammasome activation.

BACKGROUND: Water dropwort (Oenanthe javanica), an umbelliferous plant, has been reported as hypolipidemic, antiplatelet, antitumor, or immune-stimulating agents and it has been suggested to cure cardiovascular disease and cancer. PURPOSE: Present study aimed to evaluate the effect of the extracts of water dropwort (EWD) and its pharmacological molecules, hyperoside and isorhamnetin, on inflammatory response, especially inflammasome activation. STUDY DESIGN/METHODS: The anti-inflammasome properties of EWD, isorhamnetin, and hyperoside were elucidated by human and mouse macrophages. RESULTS: EWD attenuated secretion of interleukin (IL)-1ß and formation of Asc pyroptosome resulting from NLRP3, NLRC4, and AIM2 inflammasome activation without interruption of cytokine transcription. Isorhamnetin selectively inhibited NLRP3 and AIM2 inflammasome activation and down-regulated expression of pro-inflammatory cytokines. Hyperoside selectively interrupted NLRC4 and AIM2 inflammasome activation but did not alter cytokine expression. In addition, EWD, isorhamnetin, and hyperoside inhibited caspase-1. CONCLUSION: Isorhamnetin and hyperoside, a key molecule of water dropwort, have been suggested as candidates to attenuate inflammasome inhibition.

Sulforaphane attenuates activation of NLRP3 and NLRC4 inflammasomes but not AIM2 inflammasome.

Sulforaphane (SFN), a compound within the isothiocyanate group of organosulfur compounds originating from cruciferous vegetables, has gained attention for its antioxidant, anti-inflammatory, and cancer chemopreventive properties. However, the effects of SFN on inflammasomes, which are multi-protein complexes that induce maturation of interleukin (IL)-1ß, have been poorly studied. In this study, we investigated the effects of SFN on the assembly of NLRP3, NLRC4, and AIM2 inflammasomes as well as on the priming step of NLRP3 inflammasome in murine macrophages. In our results, SFN attenuated activation of NLRP3 and NLRC4 inflammasomes but not AIM2 inflammasome. In addition, SFN blocked expression of the NLRP3 gene and pro-IL-1ß during the priming step. SFN further attenuated IL-1ß secretion of monosodium uric acid-induced peritonitis in mice. Lastly, SFN inhibited generation of mitochondrial reactive oxygen species, which trigger NLRP3 inflammasome activation. Thus, SFN is suggested as an anti-inflammasome molecule for NLRP3 and NLRC4 inflammasome activation.

Methylsulfonylmethane inhibits NLRP3 inflammasome activation.

Methylsulfonylmethane (MSM) is an organosulfur compound and the health benefits associated with MSM include inflammation. Although MSM has been shown to have various physiological effects, no study has yet focused on inflammasome activation. The inflammasome is a multiprotein complex that serves as a platform for caspase 1-dependent proteolytic maturation and secretion of interleukin-1ß (IL-1ß). In this study, we tested the effect of MSM on inflammasome activation using mouse and human macrophages. In our results, MSM significantly attenuated NLRP3 inflammasome activation in lipopolysaccharide-primed macrophages, although it had no effect on NLCR4 or AIM2 inflammasome activation. Extracts of MSM-enriched vegetables presented the same inhibitory effect on NLRP3 inflammasome activation as MSM. MSM also attenuated the transcriptional expression of IL-1α, IL-1ß, IL-6, and NLRP3. Taken together, these results show that MSM has anti-inflammatory characteristics, interrupts NLRP3 inflammasome activation, and inhibits pro-cytokine expression. We further confirmed the intracellular mechanism of MSM in relation to NLRP3 inflammasome activation, followed by comparison with that of DMSO. Both chemicals showed a synergic effect on anti-NLRP3 activation and attenuated production of mitochondrial reactive oxygen species (ROS). Thus, MSM is a selective inhibitor of NLRP3 inflammasome activation and can be developed as a supplement to control several metabolic disorders.

Generation of liver-specific TGF-α and c-Myc-overexpressing fibroblasts for future creation of a liver cancer porcine model.

Liver cancer is one of the most serious life-threatening diseases in the world. Although the rodent model of hepatocellar carcinoma (HCC) is commonly used, it is limited when considering preclinical applications, including transarterial chemoembolization. The pig is a more appropriate model for applying preclinical procedures as it has similar anatomical and physiological characteristics to humans. In the current study, transgenic fibroblasts were generated that overexpressed two proto-oncogenes specifically in hepatocytes. Porcine TGF-α and c-myc genes were isolated and these were linked with the porcine albumin promoter, which has exhibited selective activity in liver cells. Targeting vectors were introduced into the porcine fibroblasts using a liposome-mediated delivery system and the transgenic cell line was screened with 3 weeks of G-418 treatment. Selected vector­positive colonies were further confirmed with polymerase chain reaction-based genotyping. Thus, the transgenic cell lines created in the current study should induce liver cancer in pig models following somatic cell nuclear transfer.

Characterization of porcine NLRP3 inflammasome activation and its upstream mechanism.

Inflammasomes, which are intracellular sensors of endogenous or exogenous danger signals, activate caspase-1, resulting in interleukin (IL)-1ß maturation. Although most studies on inflammasomes have been performed in human and/or mouse-derived macrophages, porcine inflammasome activation has not been elucidated even though pigs are considered one of the best animal models for translational and preclinical investigations. In this study, we optimized detection of porcine IL-1ß secretion, which is the most well established indicator of inflammasome activation, and compared inflammasome activation between miniature and domestic pigs as well as between porcine and murine macrophages. In our results, anti-sera against murine IL-1ß had higher affinity to porcine IL-1ß than anti-sera against human IL-1ß, even though the amino acid sequence of porcine IL-1ß was more similar to that of human IL-1ß. In addition, there was no significant difference in inflammasome activation between miniature and domestic pigs. Furthermore, well established inflammasome triggers (ATP, nigericin, and crystals) in humans and mice had similar effects on porcine NLRP3 inflammasome activation. We further elucidated the upstream signaling pathway of porcine inflammasome activation using pharmacological inhibitors. Similar to the mechanisms of inflammasome activation in humans and mice, potassium efflux and reactive oxygen species generation were confirmed as key pathways in porcine inflammasome activation. Thus, inflammasome activation in pigs is not different from that in humans or mice.

Dimethyl sulfoxide inhibits NLRP3 inflammasome activation.

Dimethyl sulfoxide (DMSO) is an amphipathic molecule that is commonly/widely used as a solvent for biological compounds. In addition, DMSO has been studied as a medication for the treatment of inflammation, cystitis, and arthritis. Based on the anti-inflammatory characteristics of DMSO, we elucidated the effects of DMSO on activation of inflammasomes, which are cytoplasmic multi-protein complexes that mediate the maturation of interleukin (IL)-1ß by activating caspase-1 (Casp1). In the present study, we prove that DMSO attenuated IL-1ß maturation, Casp1 activity, and ASC pyroptosome formation via NLRP3 inflammasome activators. Further, NLRC4 and AIM2 inflammasome activity were not affected, suggesting that DMSO is a selective inhibitor of the NLRP3 inflammasomes. The anti-inflammatory effect of DMSO was further confirmed in animal, LPS-endotoxin sepsis and inflammatory bowel disease models. In addition, DMSO inhibited LPS-mediating IL-1s transcription. Taken together, DMSO shows anti-inflammatory characteristics, attenuates NLRP3 inflammasome activation, and mediates inhibition of IL-1s transcription.

Korean red ginseng extracts inhibit NLRP3 and AIM2 inflammasome activation.

Korean red ginseng extract (RGE) is one of the most popular natural herbs modulating the immune system. Although the effects of RGE on immunity have been reported, its effects on inflammasomes, multi-protein complexes that activate caspase-1 to induce maturation of interleukin (IL)-1ß, have not been studied yet. In this study, we elucidated the effect of RGE on inflammasome activation using mouse and human macrophages. In our results, RGE inhibited IL-1ß maturation resulting from NLRP3 inflammasome activation in both in vitro and in vivo models. In addition, RGE strongly attenuated IL-1ß secretion as well as pathogen clearance via pyroptotic cell death by macrophages through inhibition of AIM2 inflammasome activation. Ginsenosides Rg1 and Rh3 were suggested as inhibitors of the inflammasome activation. Thus, we demonstrated that RGE inhibits both NLRP3 and AIM2 inflammasome activation, with predominant involvement of the AIM2 inflammasome.