Nickel induces interleukin-1β secretion via the NLRP3-ASC-caspase-1 pathway

HDAC6-Mediated NLRP3 Inflammasome Activation Is Involved in Nickel Nanoparticle-Induced Pulmonary Inflammation and Fibrosis

Nickel nanoparticles (Nano-Ni) are increasingly utilized in industrial and biomedical applications, drawing growing attention to their potential adverse health effects. Our previous studies have demonstrated that Nano-Ni exposure induces severe, widespread, and persistent pulmonary inflammation and fibrosis. However, the underlying mechanisms are still unclear. The NLRP3 inflammasome is a vital component of the innate immune system and inflammatory signaling. In this study, we investigated whether Nano-Ni exposure activated the NLRP3 inflammasome and also examined its role in Nano-Ni-induced pulmonary inflammation and fibrosis. Our findings demonstrated that intratracheal instillation of wild-type mice (C57BL/6J) with 50 μg Nano-Ni per mouse resulted in NLRP3 inflammasome activation, IL-1β production, and extensive pulmonary inflammation and fibrosis. In contrast, Nano-Ni exposure induced only mild pulmonary inflammation and fibrosis in Nlrp3-/- mice (lacking functional NLRP3 inflammasome) or Il-1r1-/- mice (unresponsive to IL-1), highlighting the critical role of NLRP3 inflammasome activation in Nano-Ni-induced pulmonary damage. Further investigations using mouse alveolar macrophages (MH-S) revealed that Nano-Ni acts as a secondary activation signal for the NLRP3 inflammasome, triggering its activation in LPS-primed but not unprimed cells. Moreover, siRNA-mediated knockdown experiments demonstrated that this activation depended on Nano-Ni-induced upregulation of HDAC6. These findings suggest that Nano-Ni activates the NLRP3 inflammasome via HDAC6 as a second activation signal, leading to IL-1β production and subsequent pulmonary inflammation and fibrosis.

Associations of Urinary Nickel with NAFLD and Liver Fibrosis in the USA: A Nationwide Cross‑Sectional Study

Despite the robust correlation between metabolic disorders and heavy metals, there has been limited research on the associations between nickel levels and non-alcoholic fatty liver disease (NAFLD) as well as liver fibrosis. This study aimed to examine the associations among urinary nickel, NAFLD, and liver fibrosis. The data utilized in this study were obtained from the National Health and Nutrition Examination Survey 2017-2020. A comprehensive screening process was conducted, resulting in the inclusion of a total of 3169 American adults in the analysis. The measurement of urinary nickel was conducted through inductively coupled-plasma mass spectrometry. Vibration-controlled transient elastography was employed to assess the controlled attenuation parameter and liver stiffness measurement as indicators for NAFLD and liver fibrosis, respectively. Multivariable logistic regression models were employed to evaluate the associations among urinary nickel, NAFLD, and liver fibrosis. Restricted cubic splines were employed to explored the nonlinear associations. After adjusting for all covariates, the correlation between the highest quartile of urinary nickel and NAFLD was found to be significant (OR = 1.65; 95% CI, 1.19-2.27). Subgroup analysis revealed that the correlation was significant only in men. A significant association occurred between the second quartile of urinary nickel and liver fibrosis (OR 1.88; 95% CI, 1.22-2.90). Restricted cubic spline showed that the relationship was linear between urinary nickel and NAFLD and non-monotonic, inverse U-shaped between urinary nickel and liver fibrosis. This cross-sectional study indicated that the risk of NAFLD is associated with urinary nickel, and this correlation was only present among males.

Repression of BRD4 mitigates NLRP3 inflammasome-mediated pyroptosis in Mycobacterium-infected macrophages by repressing endoplasmic reticulum stress

Tuberculosis (TB) is the leading cause of human death worldwide due to Mycobacterium tuberculosis (Mtb) infection. Multiple lines of evidences have illuminated the emerging role of NLRP3 inflammasome-mediated pyroptosis in the clearance of pathogenic infection. In the current study, we sought to investigate the functional role and feasible potential mechanism of BRD4 in Mtb-infected macrophages. We observed that BRD4 was distinctly ascended in THP-1 macrophages upon Mtb infection. Functionally, intervention of BRD4 or pretreated with JQ1 obviously restricted Mtb-triggered cell pyroptosis, as evidenced by declination of protein level of the specific pyroptosis markers including Cleaved Caspase 1, gasdermin D (GSDMD-N) and Cleaved-IL-1β. In the meanwhile, disruption of BRD4 or JQ1 application remarkably prohibited excessive inflammatory responses as characterized by reduce the production of the inflammatory factors such as IL-1β and IL-18. Concomitantly, disruption of BRD4 or administrated with JQ1 manifestly repressed Mtb-aroused Nod-like receptor family pyrindomain-containing 3 (NLRP3) inflammasome activation, as witnessed by attenuation of protein levels of NLRP3, Pro-Caspase1 and apoptosis-associated speck-like protein (ASC). The above findings clearly demonstrated that suppression of BRD4 exerted great influence on regulating Mtb-elicited inflammatory response by coordinating NLRP3 inflammasome-mediated pyroptosis. More importantly, perturbation of BRD4 or JQ1 employment notably restrained endoplasmic reticulum (ER) stress triggered by Mtb-infection, as reflected by noticeably lessened the levels of GRP78, CHOP and ATF6. In terms of mechanism, ER stress agonist tunicamycin profoundly abrogated the favorable effects of BRD4 inhibition on Mtb-triggered pyroptosis, inflammation reaction and inflammasome activation. Collectively, these preceding outcomes strongly illuminated that inhibition of BRD4 targeted ER stress to retard NLRP3 inflammasome activation and subsequent cell pyroptosis and prevention of inflammatory response in Mtb-infected macrophages, highlighting that blocking BRD4 might serve as a promising candidate for protection against Mtb-triggered inflammatory injury.

Neutrophil-derived oxidative stress contributes to skin inflammation and scratching in a mouse model of allergic contact dermatitis via triggering pro-inflammatory cytokine and pruritogen production in skin

Allergic contact dermatitis (ACD) is a common skin disease featured with skin inflammation and a mixed itch/pain sensation. The itch/pain causes the desire to scratch, affecting both physical and psychological aspects of patients. Nevertheless, the mechanisms underlying itch/pain sensation of ACD still remain elusive. Here, we found that oxidative stress and oxidation-related injury were remarkably increased in the inflamed skin of a mouse model of ACD. Reducing oxidative stress significantly attenuated itch/pain-related scratching, allokonesis and skin inflammation. RNA-Sequencing reveals oxidative stress contributes to a series of skin biological processes, including inflammation and immune response. Attenuating oxidative stress reduces overproduction of IL-1β and IL-33, two critical cytokines involved in inflammation and pain/itch, in the inflamed skin of model mice. Exogenously injecting H2O2 into the neck skin of naïve mice triggered IL-33 overproduction in skin keratinocytes and induced scratching, which was reduced in mice deficient in IL-33 receptor ST2. ACD model mice showed remarkable neutrophil infiltration in the inflamed skin. Blocking neutrophil infiltration reduced oxidative stress and attenuated scratching and skin inflammation. Therefore, our study reveals a critical contribution of neutrophil-derived oxidative stress to skin inflammation and itch/pain-related scratching of ACD model mice via mechanisms involving the triggering of IL-33 overproduction in skin keratinocytes. Targeting skin oxidative stress may represent an effective therapy for ameliorating ACD.

NLRP3 inflammasome activation in response to metals

Implant surgery is followed by a series of inflammatory reactions that directly affect its postoperative results. The inflammasome plays a vital role in the inflammatory response by inducing pyroptosis and producing interleukin-1β, which plays a critical role in inflammation and tissue damage. Therefore, it is essential to study the activation of the inflammasome in the bone healing process after implant surgery. As metals are the primary implant materials, metal-induced local inflammatory reactions have received significant attention, and there has been more and more research on the activation of the NLRP3 (NOD-like receptor protein-3) inflammasome caused by these metals. In this review, we consolidate the basic knowledge on the NLRP3 inflammasome structures, the present knowledge on the mechanisms of NLRP3 inflammasome activation, and the studies of metal-induced NLRP3 inflammasome activation.

Autophagy involvement in T lymphocyte signalling induced by nickel with quantitative phosphoproteomic analysis

Nickel-induced allergic contact dermatitis (ACD) is a common skin disease. The mechanism by which nickel causes ACD is not clear. There is no treatment for it, only symptomatic therapy. However, due to the lifetime sensitization characteristics, the recurrence rate in patients is high. T lymphocytes play a key role in nickel-induced ACD. Elucidating the potential mechanism underlying nickel-induced T lymphocyte signalling might make it possible to achieve targeted treatment of nickel-induced ACD. In our study, a phosphoproteomic approach based on tandem mass tag (TMT) labelling and LCMS/MS analyses was employed. An animal model of nickel allergy was established. Splenic T lymphocytes were purified for quantitative phosphoproteomic analysis. The numbers of phosphoproteins, phosphopeptides and phosphosites identified in this study were 3072, 7977 and 10,200, respectively. Comprehensive gene ontology (GO) analysis combined with Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway enrichment analysis revealed that nickel can significantly affect the phosphorylation of the mTOR signalling pathway in T lymphocytes. Western blotting analysis was used to detect changes in the expression of autophagy-related proteins (Beclin 1, LC3II, and p62). Nickel allergy changed autophagy-related protein expression (p < 0.05). It has been demonstrated that nickel causes autophagy of T lymphocytes in the spleen. Using autophagy inhibitors to intervene, it was found that Th1 differentiation was inhibited, and the expression of Th1-related inflammatory factors was downregulated. Overall, the identification of relevant signalling pathways yielded new insights into the molecular mechanisms underlying nickel allergy and might help in the discovery and development of mechanism-based drugs.

Prenatal exposure to nickel and atopic dermatitis at age 3 years: a birth cohort study with cytokine profiles

BACKGROUND

Nickel, the fifth most common element on Earth, is the leading inducer of contact allergies in humans, with potent immunological effects. Nickel-induced contact allergies predominantly affect females. Maternal exposure to nickel has been associated with several developmental abnormalities. However, how a maternal nickel exposure affects the development of atopic diathesis and immune abnormalities in children has never been addressed.

OBJECTIVES

We aimed to determine whether maternal Ni exposure affects the development of atopic dermatitis and immune abnormalities in their children.

METHODS

Using a birth cohort study, we analysed 140 mother-child pairs recruited in 2012-2015 from central Taiwan. Maternal exposure to nickel was estimated using urinary nickel levels measured by inductively coupled plasma mass spectrometry (ICP-MS). The serum levels of 65 analytes and IgE in 3-year-old children were profiled with a multiplex ELISA. The correlation between the maternal urinary nickel concentration and serum analyte levels was assessed using Spearmen's correlation. Multivariant regression analysis was performed to evaluate the association between maternal urinary nickel levels and serum analyte concentrations in their children.

RESULTS

The geometric means of the maternal urinary nickel and the children's serum IgE levels were 2.27 μg/L and 69.71 IU/ml, respectively. The maternal nickel exposure was associated with increased serum levels of IL-1β, IL-2, TNF-α, and leukaemia inhibitory factor (LIF) but with decreased serum levels of matrix metalloproteinase-1 (MMP-1), IL-2R, and eotaxin-1 in the children. In addition, the development of childhood atopic dermatitis at 3 years old was significantly associated with the child's serum levels of IgE and IL-2R, but it was negatively associated with the maternal nickel exposure.

CONCLUSIONS

This is the first study showing the potential immunological effects of maternal nickel exposure in their children at an early developmental stage.

Immunological Mechanisms of Metal Allergies and the Nickel-Specific TCR-pMHC Interface

Besides having physiological functions and general toxic effects, many metal ions can cause allergic reactions in humans. We here review the immune events involved in the mediation of metal allergies. We focus on nickel (Ni), cobalt (Co) and palladium (Pd), because these allergens are among the most prevalent sensitizers (Ni, Co) and immediate neighbors in the periodic table of the chemical elements. Co-sensitization between Ni and the other two metals is frequent while the knowledge on a possible immunological cross-reactivity using in vivo and in vitro approaches remains limited. At the center of an allergic reaction lies the capability of a metal allergen to form T cell epitopes that are recognized by specific T cell receptors (TCR). Technological advances such as activation-induced marker assays and TCR high-throughput sequencing recently provided new insights into the interaction of Ni2+ with the αβ TCR-peptide-major histocompatibility complex (pMHC) interface. Ni2+ functionally binds to the TCR gene segment TRAV9-2 or a histidine in the complementarity determining region 3 (CDR3), the main antigen binding region. Thus, we overview known, newly identified and hypothesized mechanisms of metal-specific T cell activation and discuss current knowledge on cross-reactivity.

The Keratinocyte as a Crucial Cell in the Predisposition, Onset, Progression, Therapy and Study of the Atopic Dermatitis

The keratinocyte (KC) is the main functional and structural component of the epidermis, the most external layer of the skin that is highly specialized in defense against external agents, prevention of leakage of body fluids and retention of internal water within the cells. Altered epidermal barrier and aberrant KC differentiation are involved in the pathophysiology of several skin diseases, such as atopic dermatitis (AD). AD is a chronic inflammatory disease characterized by cutaneous and systemic immune dysregulation and skin microbiota dysbiosis. Nevertheless, the pathological mechanisms of this complex disease remain largely unknown. In this review, we summarize current knowledge about the participation of the KC in different aspects of the AD. We provide an overview of the genetic predisposing and environmental factors, inflammatory molecules and signaling pathways of the KC that participate in the physiopathology of the AD. We also analyze the link among the KC, the microbiota and the inflammatory response underlying acute and chronic skin AD lesions.

Topical inflammasome inhibition with disulfiram prevents irritant contact dermatitis

BACKGROUND

The pathogenesis of contact dermatitis, a common inflammatory skin disease with limited treatment options, is held to be driven by inflammasome activation induced by allergens and irritants. We here aim to identify inflammasome-targeting treatment strategies for irritant contact dermatitis.

METHODS

A high content screen with 41,184 small molecules was performed using fluorescent Apoptosis associated speck-like protein containing a CARD (ASC) speck formation as a readout for inflammasome activation. Hit compounds were validated for inhibition of interleukin (IL)-1β secretion. Of these, the approved thiuramdisulfide derivative disulfiram was selected and tested in a patch test model of irritant contact dermatitis in 25 healthy volunteers. Topical application of disulfiram, mometasone or vehicle was followed by application of sodiumdodecylsulfate (SDS) for 24 h each. Eczema induction was quantified by mexameter and laser speckle imaging. Corneocyte sampling of lesional skin was performed to assess inflammasome-mediated cytokines IL-1β and IL-18.

RESULTS

Disulfiram induced a dose-dependent inhibition of ASC speck formation and IL-1β release in cellular assays in vitro. In vivo, treatment with disulfiram, but not with vehicle and less mometasone, inhibited SDS-induced eczema. This was demonstrated by significantly lower erythema and total perfusion values assessed by mexameter and laser speckle imaging for disulfiram compared to vehicle (p < 0.001) and/or mometasone (p < 0.001). Also, corneocyte IL-18 levels were significantly reduced after application of disulfiram compared to vehicle (p < 0.001).

CONCLUSION

We show that disulfiram is a dose-dependent inhibitor of inflammasome pathway activation in vitro and inhibitor of SDS-induced eczema in vivo. Topical application of disulfiram represents a potential treatment option for irritant contact dermatitis.

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

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

Morin Protects LPS-Induced Mastitis via Inhibiting NLRP3 Inflammasome and NF-κB Signaling Pathways

Mastitis is one of the most common diseases that both affects human and animals. Morin is derived from the member of Moraceae family, which has been used in the treatment of many inflammatory diseases. The purpose of this study was to test the protective effect of morin on LPS-induced mastitis and to clarify the possible mechanism. In vivo, the mastitis model was established by lipopolysaccharide (LPS), and morin was treated 1 h before stimulation of LPS. In vitro, peritoneal macrophages were used to test the regulation mechanisms of morin on mastitis. The inflammatory cytokines (TNF-α, IL-1β, and IL-6) was tested by ELISA. Myeloperoxidase (MPO) activity was measured by MPO kit. The expression of NLRP3 inflammasome and NF-κB signaling pathway proteins were detected by western blotting. The results showed that morin alleviated the pathological damage of mammary gland tissues, MPO activity, and the production of TNF-α, IL-1β, and IL-6 in mammary gland tissues. In vitro, morin significantly suppressed the production of inflammatory cytokines. In addition, it also inhibited the activation of NLRP3 inflammasome and NF-κB signaling pathway induced by LPS. In conclusion, the present study suggested that the protective effect of morin against LPS-induced mastitis may be due to its ability to inhibit NLRP3 inflammasome expression and NF-κB signaling pathway.

Contact dermatitis

Contact dermatitis (CD) is among the most common inflammatory dermatological conditions and includes allergic CD, photoallergic CD, irritant CD, photoirritant CD (also called phototoxic CD) and protein CD. Occupational CD can be of any type and is the most prevalent occupational skin disease. Each CD type is characterized by different immunological mechanisms and/or requisite exposures. Clinical manifestations of CD vary widely and multiple subtypes may occur simultaneously. The diagnosis relies on clinical presentation, thorough exposure assessment and evaluation with techniques such as patch testing and skin-prick testing. Management is based on patient education, avoidance strategies of specific substances, and topical treatments; in severe or recalcitrant cases, which can negatively affect the quality of life of patients, systemic medications may be needed.

Mast Cells as a Double Edged Sword in Immunity: Disorders of Mast Cell Activation and Therapeutic Management. Second of Two Parts

Mast cells (MCs) bear many receptors that allow them to respond to a variety of exogenous and endogenous stimuli. However, MC function is dual since they can initiate pathological events or protect the host against infectious challenges. The role of MCs in disease will be analyzed in a broad sense, describing cellular and molecular mechanisms related to their involvement in auto-inflammatory diseases, asthma, autoimmune diseases and cancer. On the other hand, their protective role in the course of bacterial, fungal and parasitic infections will also be illustrated. As far as treatment of MC-derived diseases is concerned, allergen immunotherapy as well as other attempts to reduce MC-activation will be outlined according to the recent data. Finally, in agreement with current literature and our own data polyphenols have been demonstrated to attenuate type I allergic reactions and contact dermatitis in response to nickel. The use of polyphenols in these diseases will be discussed also in view of MC involvement.

Ni and TiO2 nanoparticles cause adhesion and cytoskeletal changes in human osteoblasts

Titanium-based alloys have established a crucial role in implantology. As material deteriorates overtime, nanoparticles of TiO₂ and Ni are released. This study is focused on the impact of TiO₂ and Ni nanoparticles with size of 100 nm on cytoskeletal and adhesive changes in human physiological and osteoarthritic osteoblasts. The impact of nanoparticles with concentration of 1.5 ng/mL on actin and tubulin expression and gene expression of FAK and ICAM-1 was studied. The cell size and actin expression of physiological osteoblasts decreased in presence of Ni nanoparticles, while TiO₂ nanoparticles caused increase in cell size and actin expression. Both cell lines expressed more FAK as a response to TiO₂ nanoparticles. ICAM-1 gene was overexpressed in both cell lines as a reaction to both types of nanoparticles. The presented study shows a crucial role of Ni and TiO₂ nanoparticles in human osteoblast cytoskeletal and adhesive changes, especially connected with the osteoarthritic cells. Graphical abstract.

Emerging role of mitochondria in airborne particulate matter-induced immunotoxicity

The immune system is one of the primary targets of airborne particulate matter. Recent evidence suggests that mitochondria lie at the center of particulate matter-induced immunotoxicity. Particulate matter can directly interact with mitochondrial components (proteins, lipids, and nucleic acids) and impairs the vital mitochondrial processes including redox mechanisms, fusion-fission, autophagy, and metabolic pathways. These disturbances impede different mitochondrial functions including ATP production, which acts as an important platform to regulate immunity and inflammatory responses. Moreover, the mitochondrial DNA released into the cytosol or in the extracellular milieu acts as a danger-associated molecular pattern and triggers the signaling pathways, involving cGAS-STING, TLR9, and NLRP3. In the present review, we discuss the emerging role of mitochondria in airborne particulate matter-induced immunotoxicity and its myriad biological consequences in health and disease.

Update of the risk assessment of nickel in food and drinking water

The European Commission asked EFSA to update its previous Opinion on nickel in food and drinking water, taking into account new occurrence data, the updated benchmark dose (BMD) Guidance and newly available scientific information. More than 47,000 analytical results on the occurrence of nickel were used for calculating chronic and acute dietary exposure. An increased incidence of post-implantation loss in rats was identified as the critical effect for the risk characterisation of chronic oral exposure and a BMDL 10 of 1.3 mg Ni/kg body weight (bw) per day was selected as the reference point for the establishment of a tolerable daily intake (TDI) of 13 μg/kg bw. Eczematous flare-up reactions in the skin elicited in nickel-sensitised humans, a condition known as systemic contact dermatitis, was identified as the critical effect for the risk characterisation of acute oral exposure. A BMDL could not be derived, and therefore, the lowest-observed-adverse-effect-level of 4.3 μg Ni/kg bw was selected as the reference point. The margin of exposure (MOE) approach was applied and an MOE of 30 or higher was considered as being indicative of a low health concern. The mean lower bound (LB)/upper bound (UB) chronic dietary exposure was below or at the level of the TDI. The 95th percentile LB/UB chronic dietary exposure was below the TDI in adolescents and in all adult age groups, but generally exceeded the TDI in toddlers and in other children, as well as in infants in some surveys. This may raise a health concern in these young age groups. The MOE values for the mean UB acute dietary exposure and for the 95th percentile UB raises a health concern for nickel-sensitised individuals. The MOE values for an acute scenario regarding consumption of a glass of water on an empty stomach do not raise a health concern.

Auranofin Attenuates Non-Alcoholic Fatty Liver Disease by Suppressing Lipid Accumulation and NLRP3 Inflammasome-Mediated Hepatic Inflammation In Vivo and In Vitro

Non-alcoholic fatty liver disease (NAFLD) causes liver dysfunction and is associated with obesity and type 2 diabetes. Chronic inflammation is associated not only with the development of NAFLD, but also with hepatic diseases, including steatohepatitis, cirrhosis, and hepatocellular carcinoma. Auranofin is a treatment for rheumatoid arthritis and has recently been reported to have potential effects against a variety of diseases, including inflammation, cancer, and viral infection. In this study, auranofin may be considered as a new treatment for the management of metabolic syndrome, as well as in the treatment of NAFLD through immunomodulation. To determine the effect of auranofin on NAFLD, C57BL/6 mice were randomly grouped, fed a regular diet or a high fat diet (HFD), and injected with normal saline or auranofin for 8 weeks. Auranofin significantly decreased the body weight, epididymal fat weight, serum aspartate aminotransferase (AST), and glucose, as well as the serum triglyceride, cholesterol, and low-density lipoprotein cholesterol levels as compared to the HFD group. We also observed that hepatic steatosis was increased in the HFD group and was suppressed by auranofin treatment. In addition, auranofin suppressed the expressions of interleukin (IL)-1β, IL-18, caspase-1, and the NOD-like receptor family pyrin domain containing 3 (NLRP3) in the liver tissue. Furthermore, the expression of NADPH oxidase 4 and peroxisome proliferator-activated receptor γ (PPARγ), which are a major source of oxidative stress and a regulator of adipogenesis, respectively, were also decreased by auranofin. In addition, primary mouse hepatocytes were incubated with lipopolysaccharide (LPS) and palmitic acid (PA) to induce lipid accumulation and hepatic inflammation for an in vitro model. Auranofin could significantly inhibit LPS- and PA-induced inflammatory activity including nitric oxide and NLRP3 inflammasome-mediated cytokines. The results of this study demonstrate that auranofin treatment inhibits the characteristics of NAFLD through the inhibition of NLRP3 inflammasome. Therefore, auranofin may have potential as a candidate for improving NAFLD symptoms.

Immunotoxicity of nickel: Pathological and toxicological effects

Nickel (Ni) is a widely distributed metal in the environment and an important pollutant because of its many industrial applications. With increasing incidences of Ni contamination, Ni toxicity has become a global public health concern and recent evidence suggests that Ni adversely affects the immune system. Hence, this paper reviews the literature on immune-related effects of Ni exposure, the immunotoxicological effects of Ni, and the underlying mechanism of Ni immunotoxicity. The main focus was on the effect of Ni on the development of organs of immune system, lymphocyte subpopulations, cytokines, immunoglobulins, natural killer (NK) cells, and macrophages. Moreover, Ni toxicity also induces inflammation and several studies demonstrated that Ni could induce immunotoxicity. Excessive Ni exposure can inhibit the development of immune organs by excessively inducing apoptosis and inhibiting proliferation. Furthermore, Ni can decrease T and B lymphocytes, the specific mechanism of which requires further research. The effects of Ni on immunoglobulin A (IgA), IgG, and IgM remain unknown and while Ni inhibited IgA, IgG, and IgM levels in an animal experiment, the opposite result was found in research on humans. Ni inhibits the production of cytokines in non-inflammatory responses. Cytokine levels increased in Ni-induced inflammation responses, and Ni activates inflammation through toll like (TL)4-mediated nuclear factor-κB (NF-κB) and signal transduction cascades mitogen-activated protein kinase (MAPK) pathways. Ni has been indicated to inactivate NK cells and macrophages both in vitro and in vivo. Identifying the mechanisms underlying the Ni-induced immunotoxicity may help to explain the growing risk of infections and cancers in human populations that have been exposed to Ni for a long time. Such knowledge may also help to prevent and treat Ni-related carcinogenicity and toxicology.

Cadmium exposure induces pyroptosis of lymphocytes in carp pronephros and spleens by activating NLRP3

Cadmium (Cd) is a type of toxic metal, in most cases, coming from fuel burning and aquatic plants. The cells of organisms can be caused serious damage, including pyroptosis, exposure to low concentrations of Cd in long-term. Pyroptosis is a recently discovered Caspase-1-mediated cell death. In this study, lymphocytes were extracted from the pronephros and spleens in carps, respectively. After treating cells with low concentration of Cd, the mRNA and protein expression levels of pyroptosis-related genes, NLRP3, Caspase-1, and pro-inflammatory cytokines, increased obviously. And the content of reactive oxygen species (ROS) and mitochondria reactive oxygen species (mtROS) increased significantly, we also found the activities of CAT, GSH-px and T-SOD reduce significantly, and the content of MDA have a clear upward trend. We then added NLRP3 inhibitor, Glyburide, to the Cd-treated group, further confirming that NLRP3 is a key gene in pyroptosis pathways by detecting the mRNA and protein expression levels. Besides, the rupture of the cell membrane was also confirmed by Hoechst/PI double staining, red fluorescence increased obviously in the Cd treatment group. The experiment revealed that Cd exposure induces pyroptosis of lymphocytes in carp pronephros and spleens by activating NLRP3. Inhibition of NLRP3 activity can slow down the degree of lymphocytes pyroptosis. Thus, the above information provides a new avenue toward understanding the partial mechanism of Cd exposure-induced pyroptosis.

NLRP3 Inflammasome and Allergic Contact Dermatitis: A Connection to Demystify

Allergic contact dermatitis is a common occupational disease that manifests as a cell-mediated hypersensitivity reaction following skin exposure to small reactive chemicals termed haptens. Haptens penetrate the stratum corneum and covalently modify proteins in the epidermis, inducing intracellular stress, which further leads to the release of damage-associated molecular patterns (DAMPs), such as uric acid, reactive oxygen species, hyaluronic acid fragments and extracellular adenosine triphosphate (ATP). These DAMPs are recognized by pattern recognition receptors (PRRs) in innate immune cells, namely dendritic cells (DCs), leading to their maturation and migration to the draining lymph nodes where they activate naïve T lymphocytes. Among all PRRs, several studies emphasize the role of NOD-, LRR- and pyrin domain-containing protein 3 (NLRP3) inflammasome on the allergic contact dermatitis (ACD) sensitization phase. However, skin allergens-danger signals-NLRP3 inflammasome axis is yet to be completely elucidated. Therefore, in this review, we sought to discuss the molecular mechanisms underlying DAMPs release and NLRP3 inflammasome activation triggered by skin allergens. The elucidation of these key events might help to identify novel therapeutic strategies for ACD, as well as the development of nonanimal alternative methods for the identification and potency categorization of skin sensitizers.

Proinflammatory and regulatory mechanisms in allergic contact dermatitis caused by methylchloroisothiazolinone and methylisothiazolinone

BACKGROUND

Methylchloroisothiazolinone (MCI) and methylisothiazolinone (MI) are the cause of an increasing number of contact allergies. Understanding the mechanisms by which MCI/MI induces proinflammatory and regulatory factors production is necessary to understand the outcome of allergic contact dermatitis (ACD).

OBJECTIVES

To evaluate the dysfunction of proinflammatory cytokines and regulatory factors in the positive MCI/MI patch test at the transcriptional and protein expression levels. Moreover, to analyse the cytokines production induced by MI in peripheral blood mononuclear cells (PBMCs).

MATERIALS AND METHODS

The selected patients had positive MCI/MI patch test results. The expression of proinflammatory factors was evaluated by q-PCR and immunochemistry at 48 hours of positive MCI/MI patch test. The MCI/MI- or MI- induced secretion of IL-1β, TNF and IL-6 by PBMC was analysed by flow cytometry.

RESULTS

The results showed a decreased TLR4 expression with upregulated IL6, FOXP3, IL10 and TGFβ mRNA expression as assessed by q-PCR at the site of the MCI/MI skin reaction. We detected increased protein levels of TLR4, FOXP3 and IL-10 in the dermis layer in the ACD reaction by immunocitochemistry. Moreover, MCI/MI induced proinflammatory cytokine production by PBMC through the NF-κB signalling pathway.

CONCLUSION

Considering the altered innate immune response triggered by MCI/MI sensitization, these findings indicate that the regulatory process at the induction phase of ACD is a crucial mechanism. Given the increase in occupational and domestic exposure to MCI/MI, the underlying immunological mechanisms should be understood.

Gene expression in mouse muscle over time after nickel pellet implantation

The transition metal nickel is used in a wide variety of alloys and medical devices. Nickel can cause a range of toxicities from allergy in humans to tumors when implanted in animals. Several microarray studies have examined nickel toxicity, but so far none have comprehensively profiled expression over an extended period. In this work, male mice were implanted with a single nickel pellet in the muscle of the right leg with the left leg used as a control. At 3 week intervals up to 12 months, nickel concentrations in bioflulids and microarrays of surrounding tissue were used to track gene expression patterns. Pellet biocorrosion resulted in varying levels of systemic nickel over time, with peaks of 600 μg L-1 in serum, while global gene expression was cyclical in nature with immune related genes topping the list of overexpressed genes. IPA and KEGG pathway analyses was used to attribute overall biological function to changes in gene expression levels, supported by GO enrichment analysis. IPA pathways identified sirtuin, mitochondria, and oxidative phosphorylation as top pathways, based predominantly on downregulated genes, whereas immune processes were associated with upregulated genes. Top KEGG pathways identified were lysosome, osteoclast differentiation, and phasgosome. Both pathway approaches identified common immune responses, as well as hypoxia, toll like receptor, and matrix metalloproteinases. Overall, pathway analysis identified a negative impact on energy metabolism, and a positive impact on immune function, in particular the acute phase response. Inside the cell the impacts were on mitochondria and lysosome. New pathways and genes responsive to nickel were identified from the large dataset in this study which represents the first long-term analysis of the effects of chronic nickel exposure on global gene expression.

Shifting Paradigms in Allergic Contact Dermatitis: The Role of Innate Immunity

The role of the innate immune system in allergic contact dermatitis (ACD) has traditionally been confined to the initial antigen sensitization phase. However, more recent findings have shown the role of innate immunity in additional aspects of ACD, including the effector phase of the classic type IV hypersensitivity reaction. As a result, the precise immunologic mechanisms mediating ACD are more complex than previously believed. The aim of this review is to provide insight into recent advances in understanding the role of the innate immune system in the pathogenesis of ACD, including novel mechanistic roles for macrophages, innate lymphoid cells, natural killer cells, innate γδ T cells, and other signaling molecules. These insights provide new opportunities for therapeutic intervention in ACD.

Nickel induces inflammatory activation via NF-κB, MAPKs, IRF3 and NLRP3 inflammasome signaling pathways in macrophages

Nickel (Ni), an environmental hazard, widely causes allergic contact hypersensitivity worldwide. Despite that Ni-stimulated pro-inflammatory response is vital in allergy, the underlying molecular mechanisms remain largely unclear. Here, we demonstrated that NiCl₂ activated nuclear factor kappa B (NF-κB), mitogen-activated protein kinases (MAPKs) and interferon regulatory factor 3 (IRF3) signaling pathways in primary bone marrow-derived macrophages (BMDMs), leading to the altered transcription levels of interleukin-1β (IL-1β), -6, -8, -18, tumor necrosis factor-α (TNF-α) and interferon β (INF-β). We also found that nickel chloride (NiCl₂) activated Nod-like receptor 3 (NLRP3) inflammasome pathway, resulting in the proteolytic cleavage and release of IL-1β. NiCl₂ induced the accumulation of mitochondrial reactive oxygen species (mtROS) and the release of mitochondrial DNA (mtDNA), thus activating NLRP3 inflammasome pathway. Additionally, NiCl₂-induced apoptosis was dependent on the generation of mtROS, and caspase-1 activation might also partly contribute to the apoptotic process. Altogether, abovementioned results indicate that NiCl₂ induces inflammatory activation in BMDMs via NF-κB, MAPKs, IRF3 signaling pathways as well as NLRP3 inflammasome pathway, which provides a mechanism to improve the efficiency of treatment against Ni-induced allergic reactions.

Impact of Heavy Metals on Host Cells: Special Focus on Nickel-Mediated Pathologies and Novel Interventional Approaches

BACKGROUND

Heavy metals [arsenic, aluminium, cadmium, chromium, cobalt, lead, nickel (Ni), palladium and titanium] are environmental contaminants able to impact with host human cells, thus, leading to severe damage.

OBJECTIVE

In this review, the detrimental effects of several heavy metals on human organs will be discussed and special emphasis will be placed on Ni. In particular, Ni is able to interact with Toll-like receptor-4 on immune and non-immune cells, thus, triggering the cascade of pro-inflammatory cytokines. Then, inflammatory and allergic reactions mediated by Ni will be illustrated within different organs, even including the central nervous system, airways and the gastrointestinal system.

DISCUSSION

Different therapeutic strategies have been adopted to mitigate Ni-induced inflammatoryallergic reactions. In this context, the ability of polyphenols to counteract the inflammatory pathway induced by Ni on peripheral blood leukocytes from Ni-sensitized patients will be outlined. In particular, polyphenols are able to decrease serum levels of interleukin (IL)-17, while increasing levels of IL- 10. These data suggest that the equilibrium between T regulatory cells and T helper 17 cells is recovered with IL-10 acting as an anti-inflammatory cytokine. In the same context, polyphenols reduced elevated serum levels of nitric oxide, thus, expressing their anti-oxidant potential. Finally, the carcinogenic potential of heavy metals, even including Ni, will be highlighted.

CONCLUSION

Heavy metals, particularly Ni, are spread in the environment. Nutritional approaches seem to represent a novel option in the treatment of Ni-induced damage and, among them, polyphenols should be taken into consideration for their anti-oxidant and anti-inflammatory activities.

NLRP inflammasome as a key role player in the pathogenesis of environmental toxicants

Exposure to environmental toxicants (ET) results in specific organ damage and auto-immune diseases, mostly mediated by inflammatory responses. The NLRP3 inflammasome has been found to be the major initiator of the associated pathologic inflammation. It has been found that ETs can trigger all the signals required for an NLRP3-mediated response. The exaggerated activation of the NLRP3 inflammasome and its end product IL-1β, is responsible for the pathogenesis caused by many ETs including pesticides, organic pollutants, heavy metals, and crystalline compounds. Therefore, an extensive study of these chemicals and their mechanisms of inflammasome (INF) activation may provide the scientific evidence for possible targeting of this pathway by proposing possible protective agents that have been previously shown to affect INF compartments and its activation. Melatonin and polyunsaturated fatty acids (PUFA) are among the safest and the most studied of these agents, which affect a wide variety of cellular and physiological processes. These molecules have been shown to suppress the NLRP3 inflammasome mostly through the regulation of cellular redox status and the nuclear factor-κB (NF-κB) pathway, rendering them potential promising compounds to overcome ET-mediated organ damage. In the present review, we have made an effort to extensively review the ETs that exert their pathogenesis via the stimulation of inflammation, their precise mechanisms of action and the possible protective agents that could be potentially used to protect against such toxicants.

Calpain silencing alleviates myocardial ischemia-reperfusion injury through the NLRP3/ASC/Caspase-1 axis in mice

AIMS

Prior to reperfusion, Calpains remain inactive due to the acidic pH and elevated ionic strength in the ischemic myocardium; but Calpain is activated during myocardial reperfusion. The underlying mechanism of Calpain activation in the ischemia-reperfusion (I/R) is yet to be determined. Therefore, the present study aims to investigate the mechanism of Calpain in I/R-induced mice.

MAIN METHODS

In order to detect the function of Calpain and the NLRP3/ASC/Caspase-1 axis in cardiomyocyte pyroptosis, endoplasmic reticulum (ER) stress and myocardial function, the cardiomyocytes were treated with hypoxia-reoxygenation (H/R), and NLRP3 were silenced, Calpain was overexpressed and Caspase-1 inhibitors were used to determine cardiomyocyte pyroptosis. The results obtained from the cell experiments were then verified with an animal experiment in I/R mice.

KEY FINDINGS

There was an overexpression in Calpain, ASC, NLRP3, GRP78 and C/EBP homologous protein (CHOP) in cardiomyocytes following H/R. A significant increase was witnessed in lactic acid dehydrogenase (LDH) activity, cardiomyocyte pyroptosis rate, Calpain activity, reactive oxygen species (ROS) concentration, as well as activation of ER stress in cardiomyocytes after H/R. However, opposing results were observed in H/R cardiomyocytes that received siRNA Calpain, siRNA NLRP3 or Caspase-1 inhibitor treatment. Overall, the results obtained from the animal experiment were consistent with the results from the cell experiment.

SIGNIFICANCE

The silencing of Calpain suppresses the activation of the NLRP3/ASC/Caspase-1 axis, thus inhibiting ER stress in mice and improving myocardial dysfunction induced by I/R, providing a novel therapeutic pathway for I/R.

Nrf2 Involvement in Chemical-Induced Skin Innate Immunity

Exposure to certain chemicals disturbs skin homeostasis. In particular, protein-reactive chemical contact sensitizers trigger an inflammatory immune response resulting in eczema and allergic contact dermatitis. Chemical sensitizers activate innate immune cells which orchestrate the skin immune response. This involves oxidative and inflammatory pathways. In parallel, the Nrf2/Keap1 pathway, a major ubiquitous regulator of cellular oxidative and electrophilic stress is activated in the different skin innate immune cells including epidermal Langerhans cells and dermal dendritic cells, but also in keratinocytes. In this context, Nrf2 shows a strong protective capacity through the downregulation of both the oxidative stress and inflammatory pathways. In this review we highlight the important role of Nrf2 in the control of the innate immune response of the skin to chemical sensitizers.

The role of lysosomal cysteine cathepsins in NLRP3 inflammasome activation

Lysosomal cysteine cathepsins are a family of proteases that are involved in a myriad of cellular processes from proteolytic degradation in the lysosome to bone resorption. These proteins mature following the cleavage of a pro-domain in the lysosome to become either exo- or endo-peptidases. The cathepsins B, C, L, S and Z have been implicated in NLRP3 inflammasome activation following their activation with ATP, monosodium urate, silica crystals, or bacterial components, among others. These five cathepsins have both compensatory and independent functions in NLRP3 inflammasome activation. There is much evidence in the literature to support the release of cathepsin B following lysosomal membrane degradation which leads to NLRP3 inflammasome activation. This is likely due to a hitherto unidentified role of this protein in the cytoplasm, although other interactions with autophagy proteins and within lysosomes have been proposed. Cathepsin C is involved in the processing of neutrophil IL-1β through processing of upstream proteases. Cathepsin Z is non-redundantly required for NLRP3 inflammasome activation following nigericin, ATP and monosodium urate activation. Lysosomal cysteine cathepsins are members of a diverse and complementary family, and likely share both overlapping and independent functions in NLRP3 inflammasome activation.

Effects of cobalt and chromium ions on oxidative stress and energy metabolism in macrophages in vitro

Cobalt and chromium ions released from cobalt-chromium-molybdenum (CoCrMo)-based implants are a potential health concern, especially since both ions have been shown to induce oxidative stress in macrophages, the predominant immune cells in periprosthetic tissues. Ions of other transition metals (Cd, Ni) have been reported to inhibit the activity of mitochondrial enzymes in the electron transport chain. However, the effects of Co and Cr ions on the energy metabolism of macrophages remain largely unknown. The objective of the present study was to analyze the effects of Co²⁺ and Cr³⁺ on oxidative stress and energy metabolism in macrophages in vitro. RAW 264.7 murine macrophages were exposed to 6-18 ppm Co²⁺ or 50-150 ppm Cr³⁺ . Results showed a significant increase in two markers of oxidative stress, reactive oxygen species level and protein carbonyl content, with increasing concentrations of Co²⁺ , but not with Cr³⁺ . In addition, oxygen consumption rates (OCR; measured using an extracellular flux analyzer) showed significant decreases in both mitochondrial respiration and non-mitochondrial oxygen consumption with increasing concentrations of Co²⁺ , but not with Cr³⁺ . OCR results further showed that Co²⁺ , but not Cr³⁺ , induced mitochondrial dysfunction, including a decrease in oxidative phosphorylation capacity. Overall, this study suggests that mitochondrial dysfunction may contribute to Co²⁺ -induced oxidative stress in macrophages, and thereby to the inflammatory response observed in periprosthetic tissues. © 2018 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 36:3178-3187, 2018.

Emodin attenuated severe acute pancreatitis via the P2X ligand‑gated ion channel 7/NOD‑like receptor protein 3 signaling pathway

Acute pancreatitis (AP) is an aseptic inflammation characterized with an annual incidence rate, and ~20% patients progressing to severe AP (SAP) with a high mortality rate. Although Qingyi decoction has been frequently used for SAP treatment over the past 3 decades in clinic, the actual mechanism of its protective effects remains unknown. As the major active ingredient of Qingyi decoction, emodin was selected in the present study to investigate the effect of emodin against severe acute pancreatitis (SAP) in rats through NOD-like receptor protein 3 (NLRP3) inflammasomes. The rats were randomly divided into a sham operation group, an SAP model group induced by a standard retrograde infusion of 5.0% sodium taurocholate into the biliopancreatic duct, and low-dose (30 mg/kg) and high-dose (60 mg/kg) emodin-treated groups. At 12 h after the event, the plasma amylase, lipase, interleukin (IL)-1β, IL-18 and myeloperoxidase (MPO) activities were examined. Furthermore, the pathological scores of pancreases were evaluated by hematoxylin and eosin staining. The expression levels of P2X ligand-gated ion channel 7 (P2X7), NLRP3, apoptosis-associated speck-like protein containing a C-terminal caspase recruitment domain and caspase-1 were also analyzed by western blot analysis. The data demonstrated that, compared with the SAP group, emodin could significantly relieve the pancreatic histopathology and acinar cellular structure injury, and notably downregulate the plasma amylase and lipase levels, as well as the MPO activities in pancreatic tissues, in a dose-dependent manner. Furthermore, emodin inhibited the P2X7/NLRP3 signaling pathway followed by the decrease of pro-inflammatory factors, and the latter is beneficial for the recovery of SAP. Collectively, the data indicated that emodin may be an efficient candidate natural product for SAP treatment.

Danger-Associated Molecular Patterns (DAMPs): the Derivatives and Triggers of Inflammation

PURPOSE OF REVIEW

Allergen is an umbrella term for irritants of diverse origin. Along with other offenders such as pathogens, mutagens, xenobiotics, and pollutants, allergens can be grouped as inflammatory agents. Danger-associated molecular patterns (DAMPs) are altered metabolism products of necrotic or stressed cells, which are deemed as alarm signals by the innate immune system. Like inflammation, DAMPs play a role in correcting the altered physiological state, but in excess, they can be lethal due to their signal transduction roles. In a vicious loop, inflammatory agents are DAMP generators and DAMPs create a pro-inflammatory state. Only a handful of DAMPs such as uric acid, mtDNA, extracellular ATP, HSPs, amyloid β, S100, HMGB1, and ECM proteins have been studied till now. A large number of DAMPs are still obscure, in need to be unveiled. The identification and functional characterization of those DAMPs in inflammation pathways can be insightful.

RECENT FINDINGS

As inflammation and immune activation have been implicated in almost all pathologies, studies on them have been intensified in recent times. Consequently, the pathologic mechanisms of various DAMPs have emerged. Following PRR ligation, the activation of inflammasome, MAPK, and NF-kB is some of the common pathways. The limited number of recognized DAMPs are only a fraction of the vast array of other DAMPs. In fact, any misplaced or abnormal level of metabolite can be a DAMP. Sophisticated analysis studies can reveal the full profile of the DAMPs. Lowering the level of DAMPs is useful therapeutic intervention but certainly not as effective as avoiding the DAMP generators, i.e., the inflammatory agents. So, rather than mitigating DAMPs, efforts should be focused on the elimination of inflammatory agents.

Effects of metal ions on caspase-1 activation and interleukin-1β release in murine bone marrow-derived macrophages

Ions released from metal implants have been associated with adverse tissue reactions and are therefore a major concern. Studies with macrophages have shown that cobalt, chromium, and nickel ions can activate the NLRP3 inflammasome, a multiprotein complex responsible for the activation of caspase-1 (a proteolytic enzyme converting pro-interleukin [IL]-1β to mature IL-1β). However, the mechanism(s) of inflammasome activation by metal ions remain largely unknown. The objectives of the present study were to determine if, in macrophages: 1. caspase-1 activation and IL-1β release induced by metal ions are oxidative stress-dependent; and 2. IL-1β release induced by metal ions is NF-κB signaling pathway-dependent. Lipopolysaccharide (LPS)-primed murine bone marrow-derived macrophages (BMDM) were exposed to Co2+ (6-48 ppm), Cr3+ (100-500 ppm), or Ni2+ (12-96 ppm), in the presence or absence of a caspase-1 inhibitor (Z-WEHD-FMK), an antioxidant (L-ascorbic acid [L-AA]), or an NF-κB inhibitor (JSH-23). Culture supernatants were analyzed for caspase-1 by western blotting and/or IL-1β release by ELISA. Immunoblotting revealed the presence of caspase-1 (p20 subunit) in supernatants of BMDM incubated with Cr3+, but not with Ni2+ or Co2+. When L-AA (2 mM) was present with Cr3+, the caspase-1 p20 subunit was undetectable and IL-1β release decreased down to the level of the negative control, thereby demonstrating that caspase-1 activation and IL-1β release induced by Cr3+ was oxidative stress-dependent. ELISA demonstrated that Cr3+ induced the highest release of IL-1β, while Co2+ had no or limited effects. In the presence of Ni2+, the addition of L-AA (2 mM) also decreased IL-1β release, below the level of the negative control, suggesting that IL-1β release induced by Ni2+ was also oxidative stress-dependent. Finally, when present during both priming with LPS and activation with Cr3+, JSH-23 blocked IL-1β release, demonstrating NF-κB involvement. Overall, this study showed that while both Cr3+ and Ni2+ may be inducing inflammasome activation, Cr3+ is likely a more potent activator, acting through oxidative stress and the NF-κB signaling pathway.

NLRP3 inflammasome: A likely target for the treatment of allergic diseases

Allergic diseases, such as asthma, rhinitis, dermatitis, conjunctivitis, and anaphylaxis, have recently become a global public health concern. According to previous studies, the NLRP3 inflammasome is a multi-protein complex known to be associated with many inflammatory conditions. In response to allergens or allergen/damage-associated molecular signals, NLRP3 changes its conformation to allow the assembly of the NLRP3 inflammasome complex and activates caspase-1, which is an evolutionarily conserved enzyme that proteolytically cleaves other proteins, such as the precursors of the inflammatory cytokines IL-1β and IL-18. Subsequently, active caspase-1 cleaves pro-IL-1 and pro-IL-18. Recently, accumulating human and mouse experimental evidence has demonstrated that the NLRP3 inflammasome, IL-1β, and IL-18 are critically involved in the development of allergic diseases. Furthermore, the application of specific NLRP3 inflammasome inhibitors has been demonstrated in animal models. Therefore, these inhibitors may represent potential therapeutic methods for the management of clinical allergic disorders. This review summarizes findings related to the NLRP3 inflammasome and its related factors and concludes that specific NLRP3 inflammasome inhibitors may be potential therapeutic agents for allergic diseases.

Recent advances in understanding and managing contact dermatitis

About 20% of the general population is contact-sensitized to common haptens such as fragrances, preservatives, and metals. Many also develop allergic contact dermatitis (ACD), the clinical manifestation of contact sensitization. ACD represents a common health issue and is also one of the most important occupational diseases. Although this inflammatory skin disease is mediated predominantly by memory T lymphocytes recognizing low-molecular-weight chemicals after skin contact, the innate immune system also plays an important role. Along that line, the presence of irritants may increase the risk of ACD and therefore ACD is often seen in the context of irritant contact dermatitis. In this review article, we discuss recent progress in basic research that has dramatically increased our understanding of the pathomechanisms of ACD and provides a basis for the development of novel diagnostic and therapeutic measures. Current methods for diagnosis as well as treatment options of ACD are also discussed.

Nickel chloride (NiCl2) in hepatic toxicity: apoptosis, G2/M cell cycle arrest and inflammatory response

Up to now, the precise mechanism of Ni toxicology is still indistinct. Our aim was to test the apoptosis, cell cycle arrest and inflammatory response mechanism induced by NiCl₂ in the liver of broiler chickens. NiCl₂ significantly increased hepatic apoptosis. NiCl₂ activated mitochondria-mediated apoptotic pathway by decreasing Bcl-2, Bcl-xL, Mcl-1, and increasing Bax, Bak, caspase-3, caspase-9 and PARP mRNA expression. In the Fas-mediated apoptotic pathway, mRNA expression levels of Fas, FasL, caspase-8 were increased. Also, NiCl₂ induced ER stress apoptotic pathway by increasing GRP78 and GRP94 mRNA expressions. The ER stress was activated through PERK, IRE1 and ATF6 pathways, which were characterized by increasing eIF2α, ATF4, IRE1, XBP1 and ATF6 mRNA expressions. And, NiCl₂ arrested G₂/M phase cell cycle by increasing p53, p21 and decreasing cdc2, cyclin B mRNA expressions. Simultaneously, NiCl₂ increased TNF-α, IL-1β, IL-6, IL-8 mRNA expressions through NF-κB activation. In conclusion, NiCl₂ induces apoptosis through mitochondria, Fas and ER stress-mediated apoptotic pathways and causes cell cycle G₂/M phase arrest via p53-dependent pathway and generates inflammatory response by activating NF-κB pathway.

Inflammasomes, the cardinal pathology mediators are activated by pathogens, allergens and mutagens: A critical review with focus on NLRP3

Inflammation is a pivotal defense system of body. Unfortunately, when homeostasis falters, the same inflammatory mechanism acts as a double-edged sword, and turns offensive, paving the path for a broad array of pathologies. A multi-protein complex termed as inflammasome perceives the PAMPs (pathogen associated molecular patterns) and DAMPs (danger associated molecular patterns), executing immune responses. This activation predominantly encompasses the elaboration of effector cytokines IL-1β, IL-18, and the cysteine proteases (caspase 1 and 11). Extensive study on an inflammasome NLRP3 has revealed its role in the onset and progression of pathogenic, metabolic, autoimmune, neural, and geriatric diseases. In this regard, this inflammasome's immune activation mechanisms and inhibition strategies have been discussed. Through this rigorous literature analysis, the superficial diversity between pathogens/allergens and mutagens, and NLRP3 activity towards them has been emphasized. Though there is a scope for inhibition of aberrant inflammasomes, including that of NLRP3, given their complexity and unpredictability, prevention of their activation by lifestyle correction has been suggested.

Inflammasomes and dermatology

Inflammasomes are intracellular multiprotein complexes that comprise part of the innate immune response. Since their definition, inflammasome disorders have been linked to an increasing number of diseases. Autoinflammatory diseases refer to disorders in which local factors lead to the activation of innate immune cells, causing tissue damage when in the absence of autoantigens and autoantibodies. Skin symptoms include the main features of monogenic inflammasomopathies, such as Cryopyrin-Associated Periodic Syndromes (CAPS), Familial Mediterranean Fever (FMF), Schnitzler Syndrome, Hyper-IgD Syndrome (HIDS), PAPA Syndrome, and Deficiency of IL-1 Receptor Antagonist (DIRA). Concepts from other pathologies have also been reviewed in recent years, such as psoriasis, after the recognition of a combined contribution of innate and adaptive immunity in its pathogenesis. Inflammasomes are also involved in the response to various infections, malignancies, such as melanoma, autoimmune diseases, including vitiligo and lupus erythematosus, atopic and contact dermatitis, acne, hidradenitis suppurativa, among others. Inhibition of the inflammasome pathway may be a target for future therapies, as already occurs in the handling of CAPS, through the introduction of IL-1 inhibitors. This study presents a literature review focusing on the participation of inflammasomes in skin diseases.

Induced histamine regulates Ni elution from an implanted Ni wire in mice by downregulating neutrophil migration

Histamine regulates various inflammatory reactions. We have reported that the expression of histidine decarboxylase (HDC) was induced by subcutaneous implantation of nickel (Ni) wire. However, the source and functions of histamine in Ni elution and Ni wire-induced inflammation have not been completely studied. We aimed to elucidate the effects of de novo synthesized histamine on leucocyte infiltration and Ni elution. Implantation of Ni wire induced an increase in the Ni ion content of the surrounding tissues and serum and in the mRNA levels of HDC, a histamine-producing enzyme, macrophage inflammatory protein-2 (MIP-2), a chemoattractant for neutrophils, and monocyte chemoattractant protein-1 (MCP-1), a chemoattractant for monocytes. The Ni wire induced HDC expression even in mast cell-deficient WBB6F1-W/W^V mice. In HDC knockout (HDC KO) mice, the Ni wire-induced increase in MIP-2 mRNA expression was significantly higher than that in wild-type mice but not MCP-1. MIP-2 expression was enhanced in histamine H2 receptor knockout (H2R KO) mice but not in WBB6F1-W/W^V mice. Histamine inhibited NiCl₂ -induced MIP-2 mRNA expression in mouse bone marrow-derived macrophages (BMDMs) obtained from wild-type mice; this inhibition was not observed in BMDMs from H2R KO mice. Ni elution increased in HDC KO mice, in which leucocyte infiltration also increased, and was suppressed in mice treated with neutrophil-specific antibody. These results suggest that the Ni wire induced HDC expression in non-mast cells and that, in the chronic phase of inflammation, endogenous histamine reduced Ni elution, probably through regulation of MIP-2 expression and neutrophil migration.

Orientin Ameliorates LPS-Induced Inflammatory Responses through the Inhibitory of the NF-κB Pathway and NLRP3 Inflammasome

Inflammation is a complex response to diverse pathological conditions, resulting in negative rather than protective effects when uncontrolled. Orientin (Ori), a flavonoid component isolated from natural plants, possesses abundant properties. Thus, we aimed to discover the potential therapeutic effects of orientin on lipopolysaccharide- (LPS-) induced inflammation in RAW 264.7 cells and the underlying mechanisms. In our studies, we evaluated the effects of Ori on proinflammatory mediator production stimulated by LPS, including tumor necrosis factor- (TNF-) α, interleukin- (IL-) 6, IL-18, and IL-1β, along with prostaglandin E₂ (PGE₂) and NO. Our data indicated that orientin dramatically inhibited the levels of these mediators. Consistent with these results, the expression levels of cyclooxygenase-2 (COX-2) and inducible nitric oxide synthase (iNOS) were also reduced. Further study demonstrated that such inhibitory effects of Ori were due to suppression of the nuclear factor-kappa B (NF-κB) pathway and nucleotide-binding domain- (NOD-) like receptor protein 3 (NLRP3) inflammasome activation, which may contribute to its anti-inflammatory effects. Together, these findings show that Ori may be an effective candidate for ameliorating LPS-induced inflammatory responses.

Allergy-Inducing Chromium Compounds Trigger Potent Innate Immune Stimulation Via ROS-Dependent Inflammasome Activation

Chromium allergy is a common occupational skin disease mediated by chromium (VI)-specific T cells that induce delayed-type hypersensitivity in sensitized individuals. Additionally, chromium (VI) can act as an irritant. Both responses critically require innate immune activation, but if and how chromium (VI) elicits this signal is currently unclear. Using human monocytes, primary human keratinocytes, and murine dendritic cells we show that chromium (VI) compounds fail to trigger direct proinflammatory activation but potently induce processing and secretion of IL-1β. IL-1β release required priming by phorbol-ester or toll-like receptor stimulation and was prevented by inhibition of K⁺ efflux, NLRP3 depletion or caspase-1 inhibition, identifying chromium (VI) as a hapten activator of the NLRP3 inflammasome. Inflammasome activation was initiated by mitochondrial reactive oxygen species production triggered by chromium (VI), as indicated by sensitivity to treatment with the ROS scavenger N-acetyl cysteine and a coinciding failure of K⁺ efflux, caspase-1, or NLRP3 inhibition to prevent mitochondrial reactive oxygen species accumulation. IL-1β release further correlated with cytotoxicity that was secondary to reactive oxygen species, K⁺ efflux, and NLRP3 activation. Trivalent chromium was unable to induce mitochondrial reactive oxygen species production, inflammasome activation, and cytotoxicity, suggesting that oxidation state-specific differences in mitochondrial reactivity may determine inflammasome activation and allergic/irritant capacity of different chromium compounds.

Oxidative stress and inflammatory responses involved in dietary nickel chloride (NiCl2)-induced pulmonary toxicity in broiler chickens

The respiratory system is the primary target of nickel or nickel compound toxicity after inhalation exposure. There are no reports on the effects of nickel or nickel compounds on the lung via dietary administration at present. This study aimed to investigate pulmonary toxicity induced by dietary NiCl₂ in broiler chickens by using histopathology, qRT-PCR, and ELISA. In comparison with the control group, NiCl₂ intake induced oxidative damage to DNA (upregulation of 8-OHdG) and lipid peroxidation (upregulation of MDA), which was associated with the upregulation of NO and the downregulation of the expression levels and activities of pulmonary CuZn-SOD, Mn-SOD, CAT, GSH-Px, GR and GST mRNA. Also, the T-AOC activity, GSH content, ability to inhibit the generation of hydroxyl radicals, and ratio of GSH/GSSG were decreased in the groups treated with NiCl₂. Concurrently, the mRNA expression levels of iNOS, TNF-α, COX-2, IL-1β, IL-6, IL-8, IL-18 and IFN-γ were increased via the activation of NF-κB, and the mRNA expression levels of anti-inflammatory mediators including IL-2, IL-4 and IL-13 were decreased in the groups treated with NiCl₂. The above-mentioned results were the first to demonstrate that NiCl₂ intake induced pulmonary oxidative stress and inflammatory responses via the dietary pathway, which subsequently contributed to histopathological lesions and dysfunction.

Interplay of innate and adaptive immunity in metal-induced hypersensitivity

Metal-induced hypersensitivity is driven by T cell sensitization to metal ions. Recent advances in our understanding of the complex interactions between innate and adaptive immunity have expanded our knowledge of the pathogenesis of these diseases. Metals activate the innate immune system through direct binding to pathogen recognition receptors, activation of the inflammasome, or the induction of cellular death and release of alarmins. Certain metals can serve as adjuvants, promoting dendritic cell activation and migration as well as antigen presentation to metal-specific T cells. These T cells can recognize metals as haptens or as altered MHC-peptide complexes. The ability of metals to create these neoantigens emphasizes the similarity between metal-induced hypersensitivity and autoimmunity.