Curcumin Represses NLRP3 Inflammasome Activation via TLR4/MyD88/NF-κB and P2X7R Signaling in PMA-Induced Macrophages

HSP60 critically regulates endogenous IL-1β production in activated microglia by stimulating NLRP3 inflammasome pathway

Background

Interleukin-1β (IL-1β) is one of the most important cytokine secreted by activated microglia as it orchestrates the vicious cycle of inflammation by inducing the expression of various other pro-inflammatory cytokines along with its own production. Microglia-mediated IL-1β production is a tightly regulated mechanism which involves the activation of nucleotide-binding oligomerization domain leucine-rich repeat and pyrin domain-containing 3 (NLRP3) inflammasome pathway. Our previous study suggests the critical role of heat shock protein 60 (HSP60) in IL-1β-induced inflammation in microglia through TLR4-p38 MAPK axis. However, whether HSP60 regulates endogenous IL-1β production is not known. Therefore, to probe the underlying mechanism, we elucidate the role of HSP60 in endogenous IL-1β production.

Methods

We used in vitro (N9 murine microglial cells) and in vivo (BALB/c mouse) models for our study. HSP60 overexpression and knockdown experiment was done to elucidate the role of HSP60 in endogenous IL-1β production by microglia. Western blotting and quantitative real-time PCR was performed using N9 cells and BALB/c mice brain, to analyze various proteins and transcript levels. Reactive oxygen species levels and mitochondrial membrane depolarization in N9 cells were analyzed by flow cytometry. We also performed caspase-1 activity assay and enzyme-linked immunosorbent assay to assess caspase-1 activity and IL-1β production, respectively.

Results

HSP60 induces the phosphorylation and nuclear localization of NF-κB both in vitro and in vivo. It also induces perturbation in mitochondrial membrane potential and enhances reactive oxygen species (ROS) generation in microglia. HSP60 further activates NLRP3 inflammasome by elevating NLRP3 expression both at RNA and protein levels. Furthermore, HSP60 enhances caspase-1 activity and increases IL-1β secretion by microglia. Knockdown of HSP60 reduces the IL-1β-induced production of IL-1β both in vitro and in vivo. Also, we have shown for the first time that knockdown of HSP60 leads to decreased IL-1β production during Japanese encephalitis virus (JEV) infection, which eventually leads to decreased inflammation and increased survival of JEV-infected mice.

Conclusion

HSP60 mediates microglial IL-1β production by regulating NLRP3 inflammasome pathway and reduction of HSP60 leads to reduction of inflammation in JEV infection.

Electronic supplementary material

The online version of this article (10.1186/s12974-018-1214-5) contains supplementary material, which is available to authorized users.

Local administration of curcumin-loaded nanoparticles effectively inhibits inflammation and bone resorption associated with experimental periodontal disease

There is evidence indicating that curcumin has multiple biological activities, including anti-inflammatory properties. In vitro and in vivo studies demonstrate that curcumin may attenuate inflammation and the connective tissue destruction associated with periodontal disease. Most of these studies use systemic administration, and considering the site-specific nature of periodontal disease and also the poor pharmacodynamic properties of curcumin, we conducted this proof of principle study to assess the biological effect of the local administration of curcumin in a nanoparticle vehicle on experimental periodontal disease. We used 16 rats divided into two groups of 8 animals according to the induction of experimental periodontal disease by bilateral injections of LPS or of the vehicle control directly into the gingival tissues 3×/week for 4 weeks. The same volume of curcumin-loaded nanoparticles or of nanoparticle vehicle was injected into the same sites 2×/week. µCT analysis showed that local administration of curcumin resulted in a complete inhibition of inflammatory bone resorption and in a significant decrease of both osteoclast counts and of the inflammatory infiltrate; as well as a marked attenuation of p38 MAPK and NF-kB activation. We conclude that local administration of curcumin-loaded nanoparticles effectively inhibited inflammation and bone resorption associated with experimental periodontal disease.

Downregulation of SLC7A7 Triggers an Inflammatory Phenotype in Human Macrophages and Airway Epithelial Cells

Lysinuric protein intolerance (LPI) is a recessively inherited aminoaciduria caused by mutations of SLC7A7, the gene encoding y+LAT1 light chain of system y⁺L for cationic amino acid transport. The pathogenesis of LPI is still unknown. In this study, we have utilized a gene silencing approach in macrophages and airway epithelial cells to investigate whether complications affecting lung and immune system are directly ascribable to the lack of SLC7A7 or, rather, mediated by an abnormal accumulation of arginine in mutated cells. When SLC7A7/y+LAT1 was silenced in human THP-1 macrophages and A549 airway epithelial cells by means of short interference RNA (siRNA), a significant induction of the expression and release of the inflammatory mediators IL1β and TNFα was observed, no matter the intracellular arginine availability. This effect was mainly regulated at transcriptional level through the activation of NFκB signaling pathway. Moreover, since respiratory epithelial cells are the important sources of chemokines in response to pro-inflammatory stimuli, the effect of IL1β has been addressed on SLC7A7 silenced A549 cells. Results obtained indicated that the downregulation of SLC7A7/y+LAT1 markedly strengthened the stimulatory effect of the cytokine on CCL5/RANTES expression and release without affecting the levels of CXCL8/IL8. Consistently, also the conditioned medium of silenced THP-1 macrophages activated airway epithelial cells in terms of CCL5/RANTES expression due to the presence of elevated amount of proinflammatory cytokines. In conclusion, our results point to a novel thus far unknown function of SLC7A7/y+LAT1, that, under physiological conditions, besides transporting arginine, may act as a brake to restrain inflammation.

DFMG attenuates the activation of macrophages induced by co‑culture with LPC‑injured HUVE‑12 cells via the TLR4/MyD88/NF‑κB signaling pathway

7‑difluoromethoxy‑5,4'‑dimethoxy‑genistein (DFMG) is a novel active chemical entity, which modulates the function and signal transduction of endothelial cells and macrophages (MPs), and is essential in the prevention of atherosclerosis. In the present study, the activity and molecular mechanism of DFMG on MPs was investigated using a Transwell assay to construct a non‑contact co‑culture model. Human umbilical vein endothelial cells (HUVE‑12), which were incubated with lysophosphatidylcholine (LPC), were seeded in the upper chambers, whereas PMA‑induced MPs were grown in the lower chambers. The generation of reactive oxygen species (ROS) and the release of lactate dehydrogenase (LDH) were measured using the corresponding assay kits. The proliferation and migration were assessed using 3‑(4,5‑dimethylthiazol‑2‑yl)‑2,5‑diphenyltetrazolium bromide and wound healing assays, respectively. Foam cell formation was examined using oil red O staining and a total cholesterol assay. The protein expression levels of Toll‑like receptor 4 (TLR4), myeloid differentiation factor 88 (MyD88) and nuclear factor (NF)‑κB p65 were detected by western immunoblotting. The secretion of interleukin (IL)‑1β was examined using an enzyme‑linked immunosorbent assay. It was found that LPC significantly increased the generation of ROS and the release of LDH in HUVE‑12 cells. The LPC‑injured HUVE‑12 cells activated MPs under co‑culture conditions and this process was inhibited by DFMG treatment. LPC upregulated the expression levels of TLR4, MyD88 and NF‑κB p65, and the secretion of IL‑1β in the supernatant of the co‑cultured HUVE‑12 cells and MPs. These effects were reversed by the application of DFMG. Furthermore, CLI‑095 and IL‑1Ra suppressed the activation of MPs that was induced by co‑culture with injured HUVE‑12 cells. These effects were further enhanced by co‑treatment with DFMG, and DFMG exhibited synergistic effects with a TLR4‑specific inhibitor. Take together, these findings revealed that DFMG attenuated the activation of MP induced by co‑culture with LPC‑injured HUVE‑12 cells. This process was mediated via inhibition of the TLR4/MyD88/NF‑κB signaling pathway in HUVE‑12 cells.

Bisdemethoxycurcumin and Its Cyclized Pyrazole Analogue Differentially Disrupt Lipopolysaccharide Signalling in Human Monocyte-Derived Macrophages

Several studies suggest that curcumin and related compounds possess antioxidant and anti-inflammatory properties including modulation of lipopolysaccharide- (LPS-) mediated signalling in macrophage cell models. We here investigated the effects of curcumin and the two structurally unrelated analogues GG6 and GG9 in primary human blood-derived macrophages as well as the signalling pathways involved. Macrophages differentiated from peripheral blood monocytes for 7 days were activated with LPS or selective Toll-like receptor agonists for 24 h. The effects of test compounds on cytokine production and immunophenotypes evaluated as CD80⁺/CCR2⁺ and CD206⁺/CD163⁺ subsets were examined by ELISA and flow cytometry. Signalling pathways were probed by Western blot. Curcumin (2.5–10 μM) failed to suppress LPS-induced inflammatory responses. While GG6 reduced LPS-induced IκB-α degradation and showed a trend towards reduced interleukin-1β release, GG9 prevented the increase in proinflammatory CD80⁺ macrophage subset, downregulation of the anti-inflammatory CD206⁺/CD163⁺ subset, increase in p38 phosphorylation, and increase in cell-bound and secreted interleukin-1β stimulated by LPS, at least in part through signalling pathways not involving Toll-like receptor 4 and nuclear factor-κB. Thus, the curcumin analogue GG9 attenuated the LPS-induced inflammatory response in human blood-derived macrophages and may therefore represent an attractive chemical template for macrophage pharmacological targeting.

Curcumin Protects against Atherosclerosis in Apolipoprotein E-Knockout Mice by Inhibiting Toll-like Receptor 4 Expression

Toll-like receptor 4 (TLR4) has been reported to play a critical role in the pathogenesis of atherosclerosis, the current study aimed to investigate whether curcumin suppresses atherosclerosis development in ApoE-knockout (ApoE^-/-) mice by inhibiting TLR4 expression. ApoE^-/- mice were fed a high-fat diet supplemented with or without curcumin (0.1% w/w) for 16 weeks. Curcumin supplementation significantly reduced TLR4 expression and macrophage infiltration in atherosclerotic plaques. Curcumin also reduced aortic interleukin-1β (IL-1β), tumor necrosis factor-α (TNF-α), vascular cell adhesion molecule-1 (VCAM-1) and intercellular adhesion molecule-1 (ICAM-1) expression, nuclear factor-κB (NF-κB) activity, and plasma IL-1β, TNF-α, soluble VCAM-1 and ICAM-1 levels. In addition, aortic sinus sections revealed that curcumin treatment reduced the extent of atherosclerotic lesions and inhibited atherosclerosis development. In vitro, curcumin inhibited NF-κB activation in macrophages and reduced TLR4 expression induced by lipopolysaccharide. Our results indicate that curcumin protects against atherosclerosis at least partially by inhibiting TLR4 expression and its related inflammatory reaction.

Inhibiting Inflammasomes with Small Molecules

Modulation of inflammasomes has tremendous therapeutic potential and is hotly pursued by industry and academia alike. Indeed a growing number of patents are emerging to protect the intellectual property in valuable compound classes. This chapter focusses specifically on the suite of small-molecule NLRP3 inflammasome inhibitors published, as specific modulation of other inflammasomes is not yet well established. Synthetic molecules, known drugs and natural product NLRP3 modulators will be detailed. Some of the molecular classes discussed have been extensively characterised through cell-based screening, pharmacokinetic profiling and therapeutic proof of concept animal models. However, many inhibitors lack rigorous studies and/or have multiple activities of which NLRP3 modulation is only one. While this is not intended as an exhaustive list, it should give an impression of the range of structures and strategies that are being used, alongside challenges encountered, in an effort to exploit the significant therapeutic benefits of targeting inflammasomes.

Expression and anti-inflammatory role of activin receptor-interacting protein 2 in lipopolysaccharide-activated macrophages

The bacterial endotoxin lipopolysaccharide (LPS), a key pathogenic stimulator, can induce the activation of macrophages. Activin receptor-interacting protein 2 (ARIP2), an intracellular signaling protein, has a wide histological distribution, however, whether ARIP2 is involved in regulation of activation of macrophages was not well characterized. Here, by immunocytochemical staining, we found that ARIP2 protein existed in monocyte-macrophage cell line RAW264.7 cells and peritoneal macrophages of mouse, and ARIP2 expression in RAW264.7 cells was up-regulated by LPS. Furthermore, the results revealed that ARIP2 overexpression in the LPS-activated RAW264.7 cells inhibited the productions of IL-1β and TNFα, phagocytic activities and CD14 expression, whereas did not alter expressions of MyD88, TLR2 and TLR4. Additionally, in vivo ARIP2 overexpression also reduced the productions of IL-1β and TNFα from the LPS-stimulated peritoneal macrophages of mouse. These data suggest that ARIP2 may play an anti-inflammatory role in macrophages via inhibiting CD14 expression.

The NLPR3 inflammasome and obesity-related kidney disease

Over the past decade, the prevalence of obesity has increased, accompanied by a parallel increase in the prevalence of chronic kidney disease (CKD). Mounting evidence suggests that high body mass index (BMI) and obesity are important risk factors for CKD, but little is known about the mechanisms of obesity‐related kidney disease (ORKD). The NLRP3 inflammasome is a polyprotein complex that plays a crucial role in the inflammatory process, and numerous recent studies suggest that the NLRP3 inflammasome is involved in ORKD development and may serve as a key modulator of ORKD. Moreover, inhibiting activation of the NLRP3 inflammasome has been shown to attenuate ORKD. In this review, we summarize recent progress in understanding the link between the NLRP3 inflammasome and ORKD and discuss targeting the NLRP3 inflammasome as a novel therapeutic approach for ORKD.

α7 nicotinic acetylcholine receptor agonist inhibits the damage of rat hippocampal neurons by TLR4/Myd88/NF‑κB signaling pathway during cardiopulmonary bypass

The present study aimed to investigate the effect of α7 nicotinic acetylcholine receptor (α7nAChR) agonist on the damage of hippocampal neurons and the expression of toll like receptor 4 (TLR4)/myeloid differentiation primary response 88 (Myd88)/nuclear factor (NF)‑κB signal pathway‑associated factors in cardiopulmonary bypass (CPB). Sprague Dawley rats were randomly divided into five groups: Sham operation (Sham); CPB; CPB + α7nAChR agonist PHA568487 (PHA); CPB + α7nAChR inhibitor MLA (MLA); and CPB + PHA568487 + TLR4 antagonist (CPT). Blood and brain tissue samples were harvested at 12 h following the withdrawal of CPB. Levels of serum inflammatory factors [interleukin (IL)‑1β, IL‑6 and tumor necrosis factor (TNF)‑α] and brain injury markers [S‑100β and neuron‑specific enolase (NSE)] were measured using ELISA. In addition, pathological histology and apoptosis changes were observed using hematoxylin and eosin staining, and Tunnel assays. Quantitative polymerase chain reaction and western blot assays were used to determine the expression of TLR4, Myd88 and NF‑κB mRNA, and protein in the hippocampus. The morphology of hippocampal pyramidal cells in the Sham group was observed to be normal. Pyramidal cells in the CPB, MLA and CPT groups were loosely arranged, and the baselines had disappeared, with clear nucleus pyknosis and neuronal apoptosis. Furthermore, the cells in the PHA group were slightly damaged. IL‑1β, IL‑6, TNF‑α, S‑100β and NSE expression levels in the CPB, MLA, and CPT groups were significantly higher compared with that in the Sham group (P<0.05). Compared with CPB group, the expression of inflammatory cytokines in the PHA group was significantly lower (P<0.05). The expression of TLR4, Myd88 and NF‑κB mRNA, and protein in the hippocampus of CPB, MLA and CPT groups were significantly higher compared with that in the Sham group, and the PHA group expression was significantly lower compared with the CPB group (P<0.05). α7nAChRs agonist can inhibit the apoptosis of rat brain neurons induced by CPB, and may protect against brain injury through the TLR4/Myd88/NF‑κB signaling pathway.

P2X7 receptor antagonism modulates IL-1β and MMP9 in human atherosclerotic vessels

In atherosclerosis, matrix metallopeptidases (MMPs) contribute to plaque rupture through weakening of the fibrous cap. Pleiotropic P2X purinoceptor 7 (P2X7), expressed in the carotid plaque (PL), is involved in interleukin 1 beta (IL-1β) release that may influence MMP9 generation, thus their possible modulation through acting on P2X7 was investigated. P2X7-related machinery was characterized and the effects of P2X7 antagonists (A740003, KN62) and MMPs inhibitors (Batimastat, Ro28-2653) were studied in ex-vivo tissue cultures of human PL’s vs. non-atherosclerotic internal mammary artery (IMA) by using molecular biology, immune-biochemical and microscopy methodologies. We highlighted atherosclerosis-related differences between PLs and IMAs molecular patterns, and their responsivity to P2X7 antagonism. High IL-1β tissue content was associated with PLs morphology and instability/vulnerability. We demonstrated that A740003, but not KN62, decreased IL-1β and MMP9 independently from NLR family pyrin domain containing 3, but in relationship with patient’s smoking status. Acting downstream P2X7 by MMPs inhibitors, diminished IL-1β mRNA without transcriptional effect at MMP9, possibly because the assumption of statin by patients. These data firstly demonstrated A740003 suitability as a specific tool to decrease inflammatory status in human vessels and might support the design of studies applying P2X7 antagonists for the local targeting and tailored therapy of atherosclerosis.

Curcumin attenuates lipopolysaccharide/d-galactosamine-induced acute liver injury by activating Nrf2 nuclear translocation and inhibiting NF-kB activation

Curcumin, a polyphenol in curry spice isolated from the rhizome of turmeric, has been reported to possess versatile biological properties including anti-inflammatory, anti-oxidant, antifibrotic, and anticancer activities. In this study, the hepatoprotective effect of curcumin was investigated in lipopolysaccharide (LPS)/d-galactosamine (d-GalN)-induced acute liver injury (ALI) in rats. Experimental ALI was induced with an intraperitoneal (ip) injection of sterile 0.9% sodium chloride (NaCl) solution containing 8μg LPS and 800mg/kg d-GalN. Curcumin was administered once daily starting three days prior to LPS/d-GalN treatment. Results indicated that curcumin could attenuate hepatic pathological damage, decrease serum ALT and AST levels, and reduce malondialdehyde (MDA) content in experimental ALI rats. Moreover, higher dosages of curcumin pretreatment inhibited NF-κB activation and reduced serum TNF-α and liver TNF-α levels induced by LPS/d-GalN ip injection. Furthermore, we found that curcumin up-regulated the expression of nuclear Nrf2 and Nrf2-dependent antioxidant defense genes including heme oxygenase-1 (HO-1), glutamate-cysteine ligase (GCLC), NAD(P)H dehydrogenase, and quinone (NQO-1) in a dose-dependent manner. Our results showed that curcumin protected experimental animals against LPS/d-GalN-induced ALI through activation of Nrf2 nuclear translocation and inhibition of NF-κB activation.

Potential of IL-1, IL-18 and Inflammasome Inhibition for the Treatment of Inflammatory Skin Diseases

In 2002, intracellular protein complexes known as the inflammasomes were discovered and were shown to have a crucial role in the sensing of intracellular pathogen- and danger-associated molecular patterns (PAMPs and DAMPs). Activation of the inflammasomes results in the processing and subsequent secretion of the pro-inflammatory cytokines IL-1β and IL-18. Several autoinflammatory disorders such as cryopyrin-associated periodic syndromes and Familial Mediterranean Fever have been associated with mutations of genes encoding inflammasome components. Moreover, the importance of IL-1 has been reported for an increasing number of autoinflammatory skin diseases including but not limited to deficiency of IL-1 receptor antagonist, mevalonate kinase deficiency and PAPA syndrome. Recent findings have revealed that excessive IL-1 release induced by harmful stimuli likely contributes to the pathogenesis of common dermatological diseases such as acne vulgaris or seborrheic dermatitis. A key pathogenic feature of these diseases is IL-1β-induced neutrophil recruitment to the skin. IL-1β blockade may therefore represent a promising therapeutic approach. Several case reports and clinical trials have demonstrated the efficacy of IL-1 inhibition in the treatment of these skin disorders. Next to the recombinant IL-1 receptor antagonist (IL-1Ra) Anakinra and the soluble decoy Rilonacept, the anti-IL-1α monoclonal antibody MABp1 and anti-IL-1β Canakinumab but also Gevokizumab, LY2189102 and P2D7KK, offer valid alternatives to target IL-1. Although less thoroughly investigated, an involvement of IL-18 in the development of cutaneous inflammatory disorders is also suspected. The present review describes the role of IL-1 in diseases with skin involvement and gives an overview of the relevant studies discussing the therapeutic potential of modulating the secretion and activity of IL-1 and IL-18 in such diseases.

The acute airway inflammation induced by PM2.5 exposure and the treatment of essential oils in Balb/c mice

PM2.5 is the main particulate air pollutant whose aerodynamic diameter is less than 2.5 micron. The inflammation of various respiratory diseases are associated with PM2.5 inhalation. Pro-inflammatory cytokine IL-1β generated from effected cells usually plays a crucial role in many kinds of lung inflammatory reactions. The exacerbation of Th immune responses are identified in some PM2.5 related diseases. To elucidate the underlying mechanism of PM2.5-induced acute lung inflammation, we exposed Balb/c mice to PM2.5 intratracheally and established a mice model. Acute lung inflammation and increased IL-1β expression was observed after PM2.5 instillation. Regulatory factors of IL-1β (TLR4/MyD88 signaling pathway and NLRP3 inflammasome) participated in this lung inflammatory response as well. Treatment with compound essential oils (CEOs) substantially attenuated PM2.5-induced acute lung inflammation. The decreased IL-1β and Th immune responses after CEOs treatment were significant. PM2.5 may increase the secretion of IL-1β through TLR4/MyD88 and NLRP3 pathway resulting in murine airway inflammation. CEOs could attenuate the lung inflammation by reducing IL-1β and Th immune responses in this model. This study describes a potentially important mechanism of PM2.5-induced acute lung inflammation and that may bring about novel therapies for the inflammatory diseases associated with PM2.5 inhalation.

Curcumin Attenuates Titanium Particle-Induced Inflammation by Regulating Macrophage Polarization In Vitro and In Vivo

Periprosthetic inflammatory osteolysis and subsequent aseptic loosening are commonly observed in total joint arthroplasty. Other than revision surgery, few approved treatments are available for this complication. Wear particle-induced inflammation and macrophage polarization state play critical roles in periprosthetic osteolysis. We investigated the effects of curcumin, a polyphenol extracted from Curcuma longa, on titanium (Ti) particle-induced inflammation and macrophage polarization in vitro using the murine cell line RAW 264.7 and in vivo using a murine air pouch model. The expression of specific macrophage markers was qualitatively analyzed by immunofluorescence (inducible nitric oxide synthase and CD206) and quantitatively analyzed by flow cytometry (CCR7 and CD206), representing M1 and M2 macrophages, respectively. Our results show that curcumin induced a higher percentage of M2 macrophages together with a higher concentration of anti-inflammatory cytokine IL-10, and a lower percentage of M1 macrophages with a lower concentration of pro-inflammatory cytokines (TNF-α and IL-6). The genes encoding CD86 (M1) and CD163 (M2), two additional markers, were shifted by curcumin toward an M2 phenotype. C57BL/J6 mice were injected with air and Ti particles to establish an air pouch model. Curcumin reduced cell infiltration in the pouch membrane and decreased membrane thickness. The analysis of exudates obtained from pouches demonstrated that the effects of curcumin on macrophage polarization and cytokine production were similar to those observed in vitro. These results prove that curcumin suppresses Ti particle-induced inflammation by regulating macrophage polarization. Thus, curcumin could be developed as a new therapeutic candidate for the prevention and treatment of inflammatory osteolysis and aseptic loosening.