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

"Other Than NLRP3" Inflammasomes: Multiple Roles in Brain Disease

Human neuroinflammatory and neurodegenerative diseases, whose prevalence keeps rising, are still unsolved pathobiological/therapeutical problems. Among others, recent etiology hypotheses stressed as their main driver a chronic neuroinflammation, which is mediated by innate immunity-related protein oligomers: the inflammasomes. A panoply of exogenous and/or endogenous harmful agents activates inflammasomes' assembly, signaling, and IL-1β/IL-18 production and neural cells' pyroptotic death. The underlying concept is that inflammasomes' chronic activation advances neurodegeneration while their short-lasting operation restores tissue homeostasis. Hence, from a therapeutic standpoint, it is crucial to understand inflammasomes' regulatory mechanisms. About this, a deluge of recent studies focused on the NLRP3 inflammasome with suggestions that its pharmacologic block would hinder neurodegeneration. Yet hitherto no evidence proves this view. Moreover, known inflammasomes are numerous, and the mechanisms regulating their expression and function may vary with the involved animal species and strains, as well as organs and cells, and the harmful factors triggered as a result. Therefore, while presently leaving out some little-studied inflammasomes, this review focuses on the "other than NLRP3" inflammasomes that participate in neuroinflammation's complex mechanisms: NLRP1, NLRP2, NLRC4, and AIM2. Although human-specific data about them are relatively scant, we stress that only a holistic view including several human brain inflammasomes and other potential pathogenetic drivers will lead to successful therapies for neuroinflammatory and neurodegenerative diseases.

Activation of nucleotide-binding oligomerization domain-like receptor family pyrin domain containing 6 by Porphyromonas gingivalis regulates programmed cell death in epithelium

Background/purpose

Gingival epithelial cells form a physiological barrier against bacterial invasion. Programmed cell death (PCD) regulated by pathogen precognition receptors (PRRs) lead to tissue destruction and is closely related to inflammatory diseases. The purpose of this study was to investigate whether nucleotide-binding oligomerization domain-like receptor family pyrin domain containing 6 (NLRP6) expresses in periodontal epithelium and induces PCD of epithelial cells infected by Porphyromonas gingivalis (P. gingivalis), therefore involves in periodontitis.

Material and methods

The expression of NLRP6 was detected in periodontal epithelium from human gingival sections and HaCaT cells stimulated by P. gingivalis. NLRP6 was over-expressed by adenovirus infection in HaCaT or knocked down by siRNA in P. gingivalis infected HaCaT, and the cell death was observed by transmission electron microscopy and flow cytometry analysis. In addition, qPCR and Western blot were performed to determine the expression of NLRP6 and the pyroptosis excutors, caspase-1 and gasdermin D. Enzyme-linked immunosorbent assay were performed to detect the secretion of IL-1β and IL-18.

Results

NLRP6 was up-regulated in both gingival epithelium of patients with periodontitis and P. gingivalis infected HaCaT. Over-expression of NLRP6 in HaCaT led to caspase-1 dependent pyroptosis. Interestingly, knockdown of NLRP6 with siRNA followed by P. gingivalis stimulation inhibited pyroptosis and induced apoptosis.

Conclusion

Up-regulation of NLRP6 by P. gingivalis in HaCaT led to pyroptosis, while knocking down NLRP6 inhibited pyroptosis and induced apoptosis, which indicated this PRR may play a crucial role in periodontitis by regulating PCD in periodontal epithelium.

Portrayal of NLRP3 Inflammasome in Atherosclerosis: Current Knowledge and Therapeutic Targets

We are witnessing the globalization of a specific type of arteriosclerosis with rising prevalence, incidence and an overall cardiovascular disease burden. Currently, atherosclerosis increasingly affects the younger generation as compared to previous decades. While early preventive medicine has seen improvements, research advances in laboratory and clinical investigation promise to provide us with novel diagnosis tools. Given the physio-pathological complexity and epigenetic patterns of atherosclerosis and the discovery of new molecules involved, the therapeutic field of atherosclerosis has room for substantial growth. Thus, the scientific community is currently investigating the role of nucleotide-binding and oligomerization domain-like receptor family pyrin domain-containing 3 (NLRP3) inflammasome, a crucial component of the innate immune system in different inflammatory disorders. NLRP3 is activated by distinct factors and numerous cellular and molecular events which trigger NLRP3 inflammasome assembly with subsequent cleavage of pro-interleukin (IL)-1β and pro-IL-18 pathways via caspase-1 activation, eliciting endothelial dysfunction, promotion of oxidative stress and the inflammation process of atherosclerosis. In this review, we introduce the basic cellular and molecular mechanisms of NLRP3 inflammasome activation and its role in atherosclerosis. We also emphasize its promising therapeutic pharmaceutical potential.

Involvement of inflammasomes in tumor microenvironment and tumor therapies

Inflammasomes are macromolecular platforms formed in response to damage-associated molecular patterns (DAMPs) and pathogen-associated molecular patterns, whose formation would cause maturation of interleukin-1 (IL-1) family members and gasdermin D (GSDMD), leading to IL-1 secretion and pyroptosis respectively. Several kinds of inflammasomes detecting different types of dangers have been found. The activation of inflammasomes is regulated at both transcription and posttranscription levels, which is crucial in protecting the host from infections and sterile insults. Present findings have illustrated that inflammasomes are involved in not only infection but also the pathology of tumors implying an important link between inflammation and tumor development. Generally, inflammasomes participate in tumorigenesis, cell death, metastasis, immune evasion, chemotherapy, target therapy, and radiotherapy. Inflammasome components are upregulated in some tumors, and inflammasomes can be activated in cancer cells and other stromal cells by DAMPs, chemotherapy agents, and radiation. In some cases, inflammasomes inhibit tumor progression by initiating GSDMD-mediated pyroptosis in cancer cells and stimulating IL-1 signal-mediated anti-tumor immunity. However, IL-1 signal recruits immunosuppressive cell subsets in other cases. We discuss the conflicting results and propose some possible explanations. Additionally, we also summarize interventions targeting inflammasome pathways in both preclinical and clinical stages. Interventions targeting inflammasomes are promising for immunotherapy and combination therapy.

Multimodal strategy to counteract vasodilation in septic shock

Early initiation of a multimodal treatment strategy in the management of vasopressors during septic shock has been advocated to reduce delays in restoring adequate organ perfusion and to mitigate side effects associated with the administration of high-dose catecholamines. We provide a review that summarises the pathophysiology of vasodilation, the physiologic response to the vascular response, and the different drugs used in this situation, focusing on the need to combine early different vasopressors. Fluid loading being insufficient for counteracting vasoplegia, norepinephrine is usually the first-line vasopressor used to restore hemodynamics. Norepinephrine sparing is discussed in further detail through the concomitant use of adrenergic, vasopressinergic, and renin-angiotensin systems and the optimisation of endothelial reactivity with methylene blue. A blueprint for the construction of new studies is outlined to address the question of vasopressor selection and timing in septic shock.

Optical spectral diagnostics of the oxygenation level in periodontal tissues and photodynamic therapy using methylene blue in children with cerebral palsy

Dental diseases occur in children with cerebral palsy three times higher than in healthy children. Low values of the unstimulated salivation rate (<0.3 ml per minute), pH and buffer capacity, changes in enzyme activity and sialic acid concentration, as well as increased saliva osmolarity and total protein concentration, which indicates impaired hydration, are the factors in the development of a gingiva disease in case of cerebral palsy. This leads to increased bacterial agglutination and the formation of acquired pellicle and biofilm, leading to the formation of dental plaque. There is a tendency toward an increase in the concentration of hemoglobin and a decrease in the degree of hemoglobin oxygenation, as well as an increase in the generation of reactive oxygen and nitrogen species. Photodynamic therapy (PDT) with the use of photosensitizer methylene blue improves blood circulation and the degree of oxygenation in periodontal tissues, as well as eliminates a bacterial biofilm. Analysis of back diffuse reflection spectra makes it possible to conduct non-invasive monitoring determine tissue areas with a low level of hemoglobin oxygenation for precision photodynamic exposure.

Aim

To improve the effectiveness of phototheranostics methods using, namely PDT with simultaneous optical-spectral control, for the treatment of gingivitis in children with complex dental and somatic status (cerebral palsy).

Methods

The study involved 15 children (6-18 y.o.) with various forms of cerebral palsy, in particular, spastic diplegia and atonic-astatic form and with gingivitis. The degree of hemoglobin oxygenation was measured in tissues before PDT and on the 12th day. PDT was performed using laser radiation (λ = 660 nm) with a power density of 150 mW/cm² with a five-minute application of 0.01% MB. The total light dose was 45 ± 15 J/cm². For statistical evaluation of the results, a paired Student's t-test was used.

Results

The paper presents the results of phototheranostics using methylene blue in children with cerebral palsy. An increase in the level of hemoglobin oxygenation from 50 to 67% (p < 0.001) and a decrease in blood volume in the microcirculatory bed of periodontal tissues were shown.

Conclusion

Photodynamic therapy methods with application of methylene blue make it possible to assess the state of the gingival mucosa tissue diseases objectively in real time, and to provide effective targeted therapy for gingivitis in children with cerebral palsy. There is a prospect that they can become widely used clinical methods.

A Novel Approach of Combining Methylene Blue Photodynamic Inactivation, Photobiomodulation and Oral Ingested Methylene Blue in COVID-19 Management: A Pilot Clinical Study with 12-Month Follow-Up

Coronavirus disease 2019 (COVID-19) caused by SARS-CoV-2 virus was first recognized in late 2019 and remains a significant threat. We therefore assessed the use of local methylene blue photodynamic viral inactivation (MB-PDI) in the oral and nasal cavities, in combination with the systemic anti-viral, anti-inflammatory and antioxidant actions of orally ingested methylene blue (MB) and photobiomodulation (PBM) for COVID-19 disease. The proposed protocol leverages the separate and combined effects of MB and 660nm red light emitted diode (LED) to comprehensively address the pathophysiological sequelae of COVID-19. A total of eight pilot subjects with COVID-19 disease were treated in the Bahamas over the period June 2021-August 2021, using a remote care program that was developed for this purpose. Although not a pre-requisite for inclusion, none of the subjects had received any COVID-19 vaccination prior to commencing the study. Clinical outcome assessment tools included serial cycle threshold measurements as a surrogate estimate of viral load; serial online questionnaires to document symptom response and adverse effects; and a one-year follow-up survey to assess long-term outcomes. All subjects received MB-PDI to target the main sites of viral entry in the nose and mouth. This was the central component of the treatment protocol with the addition of orally ingested MB and/or PBM based on clinical requirements. The mucosal surfaces were irradiated with 660 nm LED in a continuous emission mode at energy density of 49 J/cm2 for PDI and 4.9 J/cm2 for PBM. Although our pilot subjects had significant co-morbidities, extremely high viral loads and moderately severe symptoms during the Delta phase of the pandemic, the response to treatment was highly encouraging. Rapid reductions in viral loads were observed and negative PCR tests were documented within a median of 4 days. These laboratory findings occurred in parallel with significant clinical improvement, mostly within 12-24 h of commencing the treatment protocol. There were no significant adverse effects and none of the subjects who completed the protocol required in-patient hospitalization. The outcomes were similarly encouraging at one-year follow-up with virtual absence of "long COVID" symptoms or of COVID-19 re-infection. Our results indicate that the protocols may be a safe and promising approach to challenging COVID-19 disease. Moreover, due its broad spectrum of activity, this approach has the potential to address the prevailing and future COVID-19 variants and other infections transmitted via the upper respiratory tract. Extensive studies with a large cohort are warranted to validate our results.

Molecular Mechanisms of the Neuroprotective Effect of Methylene Blue

Methylene blue (MB) is the first fully synthetic compound that had found its way into medicine over 120 years ago as a treatment against malaria. MB has been approved for the treatment of methemoglobinemia, but there are premises for its repurposing as a neuroprotective agent based on the efficacy of this compound demonstrated in the models of Alzheimer's, Parkinson's, and Huntington's diseases, traumatic brain injury, amyotrophic lateral sclerosis, depressive disorders, etc. However, the goal of this review was not so much to focus on the therapeutic effects of MB in the treatment of various neurodegeneration diseases, but to delve into the mechanisms of direct or indirect effect of this drug on the signaling pathways. MB can act as an alternative electron carrier in the mitochondrial respiratory chain in the case of dysfunctional electron transport chain. It also displays the anti-inflammatory and anti-apoptotic effects, inhibits monoamine oxidase (MAO) and nitric oxide synthase (NOS), activates signaling pathways involved in the mitochondrial pool renewal (mitochondrial biogenesis and autophagy), and prevents aggregation of misfolded proteins. Comprehensive understanding of all aspects of direct and indirect influence of MB, and not just some of its effects, can help in further research of this compound, including its clinical applications.

The NLRP3 Inflammasome Pathway: A Review of Mechanisms and Inhibitors for the Treatment of Inflammatory Diseases

The NLRP3 inflammasome is a multiprotein complex that plays a pivotal role in regulating the innate immune system and inflammatory signaling. Upon activation by PAMPs and DAMPs, NLRP3 oligomerizes and activates caspase-1 which initiates the processing and release of pro-inflammatory cytokines IL-1β and IL-18. NLRP3 is the most extensively studied inflammasome to date due to its array of activators and aberrant activation in several inflammatory diseases. Studies using small molecules and biologics targeting the NLRP3 inflammasome pathway have shown positive outcomes in treating various disease pathologies by blocking chronic inflammation. In this review, we discuss the recent advances in understanding the NLRP3 mechanism, its role in disease pathology, and provide a broad review of therapeutics discovered to target the NLRP3 pathway and their challenges.

Inflammatory Response to Regulated Cell Death in Gout and Its Functional Implications

Gout, a chronic inflammatory arthritis disease, is characterized by hyperuricemia and caused by interactions between genetic, epigenetic, and metabolic factors. Acute gout symptoms are triggered by the inflammatory response to monosodium urate crystals, which is mediated by the innate immune system and immune cells (e.g., macrophages and neutrophils), the NACHT, LRR, and PYD domains-containing protein 3 (NLRP3) inflammasome activation, and pro-inflammatory cytokine (e.g., IL-1β) release. Recent studies have indicated that the multiple programmed cell death pathways involved in the inflammatory response include pyroptosis, NETosis, necroptosis, and apoptosis, which initiate inflammatory reactions. In this review, we explore the correlation and interactions among these factors and their roles in the pathogenesis of gout to provide future research directions and possibilities for identifying potential novel therapeutic targets and enhancing our understanding of gout pathogenesis.

Establishment of tumor inflammasome clusters with distinct immunogenomic landscape aids immunotherapy

Inflammasome signaling is a reaction cascade that influences immune response and cell death. Although the inflammasomes participate in tumorigenesis, their role as an oncogenic booster or a tumor suppresser is still controversial. Therefore, it is important to comprehensively investigate the inflammasome signaling status across various cancers to clarify its clinical and therapeutic significance.

Methods: A total of 9881 patients across 33 tumor types from The Cancer Genome Atlas database were included in this study. Five gene sets were identified to step-wisely profile inflammasome signaling. Unsupervised clustering was used for sample classification based on gene set enrichment. Machine learning and in vitro and in vivo experiments were used to confirm the implications of inflammasome classification.

Results: A hundred and forty-one inflammasome-signaling-related genes were identified to construct five gene sets representing the sensing, activation, and termination steps of the inflammasome signaling. Six inflammasome clusters were robustly established with distinct molecular, biological, clinical, and therapeutic features. Importantly, clusters with inflammasome signaling activation were found to be immunosuppressive and resistant to ICB treatment. Inflammasome inhibition reverted the therapeutic failure of ICB in inflammasome-activated tumors. Moreover, based on the proposed classification and therapeutic implications, an open website was established to provide tumor patients with comprehensive information on inflammasome signaling.

Conclusions: Our study conducted a systematical investigation on inflammasome signaling in various tumor types. These findings highlight the importance of inflammasome evaluation in tumor classification and provide a foundation for improving relevant therapeutic regimens.

Optimal Isolation Protocols for Examining and Interrogating Mononuclear Phagocytes From Human Intestinal Tissue

The human intestine contains numerous mononuclear phagocytes (MNP), including subsets of conventional dendritic cells (cDC), macrophages (Mf) and monocytes, each playing their own unique role within the intestinal immune system and homeostasis. The ability to isolate and interrogate MNPs from fresh human tissue is crucial if we are to understand the role of these cells in homeostasis, disease settings and immunotherapies. However, liberating these cells from tissue is problematic as many of the key surface identification markers they express are susceptible to enzymatic cleavage and they are highly susceptible to cell death. In addition, the extraction process triggers immunological activation/maturation which alters their functional phenotype. Identifying the evolving, complex and highly heterogenous repertoire of MNPs by flow cytometry therefore requires careful selection of digestive enzyme blends that liberate viable cells and preserve recognition epitopes involving careful selection of antibody clones to enable analysis and sorting for functional assays. Here we describe a method for the anatomical separation of mucosa and submucosa as well as isolating lymphoid follicles from human jejunum, ileum and colon. We also describe in detail the optimised enzyme digestion methods needed to acquire functionally immature and biologically functional intestinal MNPs. A comprehensive list of screened antibody clones is also presented which allows for the development of high parameter flow cytometry panels to discriminate all currently identified human tissue MNP subsets including pDCs, cDC1, cDC2 (langerin⁺ and langerin^-), newly described DC3, monocytes, Mf1, Mf2, Mf3 and Mf4. We also present a novel method to account for autofluorescent signal from tissue macrophages. Finally, we demonstrate that these methods can successfully be used to sort functional, immature intestinal DCs that can be used for functional assays such as cytokine production assays.

Spectroscopic Measurement of Methylene Blue Distribution in Organs and Tissues of Hamadryas Baboons during Oral Administration

New research on Methylene Blue (MB), carried out in 2020, shows that it can be an effective antiviral drug as part of COVID-19 treatment. According to the research findings, MB has potential as a direct antiviral drug for the prevention and treatment of COVID-19 in the first stages of the disease. However, the MB accumulation by various types of tissues, as well as by immune cells, has not been previously studied. Therefore, the objective of this study was to obtain spectral data on the interstitial distribution of the administered drug in endothelial tissues in primates. The data on interstitial MB distribution obtained by spectroscopic measurement at both macro- and microlevels during oral administration to Hamadryas baboon individuals demonstrate that MB accumulates in mucous membranes of gastrointestinal tract and the tissues of the respiratory, cardiovascular, immune, and nervous systems. Additionally, it was found that MB was present in lung and brain myeloid cells in significant concentrations, which makes it potentially useful for protection from autoimmune response (cytokine storm) and as a tool for the correction of immunocompetent cells’ functional state during laser irradiation. Since the cytokine storm starts from monocytic cells during SARS-CoV-2 cellular damage and since tumor-associated macrophages can significantly alter tumor metabolism, accumulation of MB in these cells provides a reason to conclude that the immune response correction in COVID-19 patients and change in macrophages phenotype can be achieved by deactivation of inflammatory macrophages in tissues with MB using laser radiation of red spectral range.

Methylene Blue Application to Lessen Pain: Its Analgesic Effect and Mechanism

Methylene blue (MB) is a cationic thiazine dye, widely used as a biological stain and chemical indicator. Growing evidence have revealed that MB functions to restore abnormal vasodilation and notably it is implicated even in pain relief. Physicians began to inject MB into degenerated disks to relieve pain in patients with chronic discogenic low back pain (CDLBP), and some of them achieved remarkable outcomes. For osteoarthritis and colitis, MB abates inflammation by suppressing nitric oxide production, and ultimately relieves pain. However, despite this clinical efficacy, MB has not attracted much public attention in terms of pain relief. Accordingly, this review focuses on how MB lessens pain, noting three major actions of this dye: anti-inflammation, sodium current reduction, and denervation. Moreover, we showed controversies over the efficacy of MB on CDLBP and raised also toxicity issues to look into the limitation of MB application. This analysis is the first attempt to illustrate its analgesic effects, which may offer a novel insight into MB as a pain-relief dye.

Role of pyroptosis in diabetic retinopathy and its therapeutic implications

Pyroptosis has recently been established as a term of programmed-inflammatory cell death. Pyroptosis is mainly divided into two molecular signaling pathways, including caspase-1-dependent canonical and caspase-4/5/11-dependent non-canonical inflammasome pathways. Extensive investigations have reported inflammasome activation facilitates the maturation and secretion of the inflammatory factors interleukin-1β/18 (IL-1β/18), cleavage of gasdermin D (GSDMD), and leading to the stimulation of pyroptosis-mediated cell death. Furthermore, accumulating studies report NLRP3 inflammasome activation plays a significant role in triggering the pyroptosis-mediated cell death and promotes the pathogenesis of diabetic retinopathy (DR). Our current review elaborates on the molecular mechanisms of pyroptosis-signaling pathways and their potential roles in the pathogenesis and impact of DR development. We also emphasize several investigational molecules regulating key steps in pyroptotic-cell death to create new comprehensions and findings to explore the pathogenesis of DR advancement. Our narrative review concisely suggests these potential pharmacological agents could be promising therapies to treat and manage DR in the future.

Rod Photoreceptor Neuroprotection in Dark-Reared Pde6brd10 Mice

Purpose

The purpose of this study was to test the hypothesis that anti-oxidant and / or anti-inflammation drugs that suppress rod death in cyclic light-reared Pde6brd10 mice are also effective in dark-reared Pde6brd10 mice.

Methods

In untreated dark-reared Pde6brd10 mice at post-natal (P) days 23 to 24, we measured the outer nuclear layer (ONL) thickness (histology) and dark-light thickness difference in external limiting membrane-retinal pigment epithelium (ELM-RPE) (optical coherence tomography [OCT]), retina layer oxidative stress (QUEnch-assiSTed [QUEST] magnetic resonance imaging [MRI]); and microglia/macrophage-driven inflammation (immunohistology). In dark-reared P50 Pde6brd10 mice, ONL thickness was measured (OCT) in groups given normal chow or chow admixed with methylene blue (MB) + Norgestrel (anti-oxidant, anti-inflammatory), or MB or Norgestrel separately.

Results

P24 Pde6brd10 mice showed no significant dark-light ELM-RPE response in superior and inferior retina consistent with high cGMP levels. Norgestrel did not significantly suppress the oxidative stress of Pde6brd10 mice that is only found in superior central outer retina of males at P23. Overt rod degeneration with microglia/macrophage activation was observed but only in the far peripheral superior retina in male and female P23 Pde6brd10 mice. Significant rod protection was measured in female P50 Pde6brd10 mice given 5 mg/kg/day MB + Norgestrel diet; no significant benefit was seen with MB chow or Norgestrel chow alone, nor in similarly treated male mice.

Conclusions

In early rod degeneration in dark-reared Pde6brd10 mice, little evidence is found in central retina for spatial associations among biomarkers of the PDE6B mutation, oxidative stress, and rod death; neuroprotection at P50 was limited to a combination of anti-oxidant/anti-inflammation treatment in a sex-specific manner.

Mitochondrial Dysfunction and Mitophagy Closely Cooperate in Neurological Deficits Associated with Alzheimer's Disease and Type 2 Diabetes

Alzheimer's disease (AD) and type 2 diabetes (T2D) are known to be correlated in terms of their epidemiology, histopathology, and molecular and biochemical characteristics. The prevalence of T2D leading to AD is approximately 50-70%. Moreover, AD is often considered type III diabetes because of the common risk factors. Uncontrolled T2D may affect the brain, leading to memory and learning deficits in patients. In addition, metabolic disorders and impaired oxidative phosphorylation in AD and T2D patients suggest that mitochondrial dysfunction is involved in both diseases. The dysregulation of pathways involved in maintaining mitochondrial dynamics, biogenesis and mitophagy are responsible for exacerbating the impact of hyperglycemia on the brain and neurodegeneration under T2D conditions. The first section of this review describes the recent views on mitochondrial dysfunction that connect these two disease conditions, as the pathways are observed to overlap. The second section of the review highlights the importance of different mitochondrial miRNAs (mitomiRs) involved in the regulation of mitochondrial dynamics and their association with the pathogenesis of T2D and AD. Therefore, targeting mitochondrial biogenesis and mitophagy pathways, along with the use of mitomiRs, could be a potent therapeutic strategy for T2D-related AD. The last section of the review highlights the known drugs targeting mitochondrial function for the treatment of both disease conditions.

Korean Red Ginseng attenuates ultraviolet-mediated inflammasome activation in keratinocytes

Background

Keratinocytes form a physical barrier and act as an innate immune cell in skin. Keratinocytes secrete pro-inflammatory cytokines, such as interleukin (IL)-1β, resulting from inflammasome activation when exposed to ultraviolet (UV) irradiation. Korean Red Ginseng extracts (RGE) have been well-studied as modulators of inflammasome activation in immune cells, such as macrophages. In the study, we elucidated the role of RGE on the UV-mediated inflammasome activation in keratinocytes compared with that in macrophages.

Methods

Human skin keratinocyte cells (HaCaT), human epidermal keratinocytes (HEK), human monocyte-like cells (THP-1), and mouse macrophages were treated with RGE or a saponin fraction (SF) or non-saponin fraction (NS) of RGE before and after UV irradiation. The secretion levels of IL-1β, as an indicator of inflammasome activation, were analyzed.

Results

The treatment of RGE or SF in macrophages after UV irradiation inhibited IL-1β secretion, but similar treatment in HaCaT cells did not. However, the treatment of RGE or SF in HaCaT cells in the presence of poly I:C, a toll-like receptor (TLR) 3 ligand, before UV exposure elicited the inhibition of the IL-1β secretion. The inhibition was caused by the disruption by RGE or SF of the TLR mediating up-regulation of the pro-IL-1β and NLRP3 genes during the priming step.

Conclusion

RGE and its saponins inhibit IL-1β secretion in response to UV exposure in both keratinocytes and macrophages. In particular, RGE treatment interrupted only the priming step in keratinocytes, although it did attenuate both the priming and activation steps in macrophages.

Methylene blue induces an analgesic effect by significantly decreasing neural firing rates and improves pain behaviors in rats

Methylene blue (MB) is a blue cationic thiazine dye and currently used in different medical settings. Notably, there have been several attempts to introduce MB for attenuating pain in the last decade. Some clinical studies reported remarkable results, which, however, have been much debated. In addition, accumulating evidence have revealed that MB diminishes voltage-gated sodium channel currents. Accordingly, in the present study, we conducted in vivo experiments, including in vivo single nerve recording and behavioral test, to investigate whether MB dampens neural firing rates and ultimately contributes to pain relief. As a result, neural firing rates significantly decreased and finally converged to zero after MB administration. This event lasted longer than that of lidocaine and was dose-dependently modulated. Furthermore, there was a marked improvement in pain behaviors. The withdrawal threshold and latency of hind paws significantly rose post-MB administration. Therefore, these results demonstrate that MB lessens pain by significantly weakening neural excitability, which implies a strong possibility that this dye may be developed as a pain-relieving medication in the future. This is the first in vivo study to elucidate the effect of MB on nerves and pain relief.

Riboflavin, vitamin B2, attenuates NLRP3, NLRC4, AIM2, and non-canonical inflammasomes by the inhibition of caspase-1 activity

Riboflavin is commonly taken as a nutritional supplement, and it converts to coenzymes during the process of energy production from carbohydrates, fats, and proteins. Although riboflavin is considered to be an anti-inflammatory vitamin because of its antioxidant properties, the effects of riboflavin on inflammasome have been not reported. Inflammasome, a cytosolic surveillance protein complex, leads to the activation of caspase-1, cytokine maturation, and pyroptosis. In the present study, riboflavin attenuated the indicators of NLRP3 inflammasome activation in macrophages, such as the maturation and secretion of interleukin (IL)-1β, IL-18, and caspase-1; the formation of Asc pyroptosome; and the cleavage of gasdermin D. In addition, the oral and peritoneal administration of riboflavin inhibited the peritoneal production of IL-1β and IL-18 in a mouse model. Mechanistically, riboflavin prevented mitochondrial perturbations, such as mitochondrial ROS production and mitochondrial DNA release, which trigger the NLRP3 inflammasome assembly. Riboflavin was further confirmed to disrupt the activity of caspase-1, and it also inhibited the AIM2, NLRC4, and non-canonical inflammasomes. Therefore, riboflavin has both an antioxidant effect and an anti-inflammasome property that regulates the inflammatory response.

Photosensitizers attenuate LPS-induced inflammation: implications in dentistry and general health

Antimicrobial photodynamic therapy (aPDT) is a complementary therapeutic modality for periodontal and endodontic diseases, in which Gram-negative bacteria are directly involved. Currently, there are few evidences regarding the effects of aPDT on bacterial components such as lipopolysaccharide (LPS) and it would represent a major step forward in the clinical use of this therapy. In this context, this study aimed to evaluate the efficacy of different photosensitizers (PSs) used in aPDT in LPS inhibition. Four PSs were used in this study: methylene blue (MB), toluidine blue (TBO), new methylene blue (NMB), and curcumin (CUR). Different approaches to evaluate LPS interaction with PSs were used, such as spectrophotometry, Limulus amebocyte lysate (LAL) test, functional assays using mouse macrophages, and an in vivo model of LPS injection. Spectrophotometry showed that LPS decreased the absorbance of all PSs used, indicating interactions between the two species. LAL assay revealed significant differences in LPS concentrations upon pre-incubation with the different PSs. Interestingly, the inflammatory potential of LPS decreased after previous treatment with the four PSs, resulting in decreased secretion of inflammatory cytokines by macrophages. In vivo, pre-incubating curcumin with LPS prevented animals from undergoing septic shock within the established time. Using relevant models to study the inflammatory activity of LPS, we found that all PSs used in this work decreased LPS-induced inflammation, with a more striking effect observed for NMB and curcumin. These data advance the understanding of the mechanisms of LPS inhibition by PSs.

Fructose-arginine, a non-saponin molecule of Korean Red Ginseng, attenuates AIM2 inflammasome activation

Background

Korean Red Ginseng extract (RGE) has been reported to act as an inflammasome modulator. Ginsenosides, saponin molecules of RGE, selectively inhibit activation of NLRP3 and AIM2 inflammasomes, while non-saponin molecules of RGE upregulate inflammasome components associated with the initiation of NLRP3 inflammasome activation. In this study, we investigated the effect of non-saponin components of RGE on AIM2 inflammasome activation.

Methods

The role of non-saponins of RGE on AIM2 inflammasomes was tested in mouse bone marrow-derived macrophages, a human monocyte-like cell line, and a mouse animal model. Cells or mice were transfected with dsDNA or inoculated with Listeria monocytogenes to activate AIM2 inflammasomes. Several indices of inflammasome activation were examined via immunoblot or ELISA analysis.

Results

The non-saponin fraction and saponin-eliminating fraction (SEF) of RGE selectively attenuated the activation of AIM2 inflammasomes, but not that of NLRP3 or NLRC4 inflammasomes. Fructose-arginine, an amino-sugar, was shown to be effective against AIM2 inflammasome activation.

Conclusion

Non-saponins of RGE, such as fructose-arginine, might be effective in regulating infectious and autoimmune diseases resulting from AIM2 inflammasome activation.

Summary-Based Methylome-Wide Association Analyses Suggest Potential Genetically Driven Epigenetic Heterogeneity of Alzheimer's Disease

Alzheimer’s disease (AD) is a progressive neurodegenerative disorder with no curative treatment available. Exploring the genetic and non-genetic contributors to AD pathogenesis is essential to better understand its underlying biological mechanisms, and to develop novel preventive and therapeutic strategies. We investigated potential genetically driven epigenetic heterogeneity of AD through summary data-based Mendelian randomization (SMR), which combined results from our previous genome-wide association analyses with those from two publicly available methylation quantitative trait loci studies of blood and brain tissue samples. We found that 152 probes corresponding to 113 genes were epigenetically associated with AD at a Bonferroni-adjusted significance level of 5.49E-07. Of these, 10 genes had significant probes in both brain-specific and blood-based analyses. Comparing males vs. females and hypertensive vs. non-hypertensive subjects, we found that 22 and 79 probes had group-specific associations with AD, respectively, suggesting a potential role for such epigenetic modifications in the heterogeneous nature of AD. Our analyses provided stronger evidence for possible roles of four genes (i.e., AIM2, C16orf80, DGUOK, and ST14) in AD pathogenesis as they were also transcriptionally associated with AD. The identified associations suggest a list of prioritized genes for follow-up functional studies and advance our understanding of AD pathogenesis.

Characterization of equine inflammasomes and their regulation

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

Caspases in Cell Death, Inflammation, and Pyroptosis

Caspases are a family of conserved cysteine proteases that play key roles in programmed cell death and inflammation. In multicellular organisms, caspases are activated via macromolecular signaling complexes that bring inactive procaspases together and promote their proximity-induced autoactivation and proteolytic processing. Activation of caspases ultimately results in programmed execution of cell death, and the nature of this cell death is determined by the specific caspases involved. Pioneering new research has unraveled distinct roles and cross talk of caspases in the regulation of programmed cell death, inflammation, and innate immune responses. In-depth understanding of these mechanisms is essential to foster the development of precise therapeutic targets to treat autoinflammatory disorders, infectious diseases, and cancer. This review focuses on mechanisms governing caspase activation and programmed cell death with special emphasis on the recent progress in caspase cross talk and caspase-driven gasdermin D-induced pyroptosis.

IκBζ controls NLRP3 inflammasome activation via upregulation of the Nlrp3 gene

Inflammasome activation induces the maturation and secretion of interleukin (IL)-1β and -18, and is dependent on NF-κB signaling to induce the transcription of the inflammasome components, called the priming step. This study elucidated the role of IκBζ, an atypical IκBs (inhibitor of κB) and a coactivator of NF-κB target genes, on the activation of inflammasome. Bone marrow-derived macrophages (BMDMs) that originated from IκBζ-encoding Nfkbiz gene depletion mice presented a defect in NLRP3 inflammasome activation. In addition, the Nfkbiz^+/- and Nfkbiz^-/- mice significantly attenuated serum IL-1β secretion in response to a monosodium urate injection, a NLRP3 trigger, when compared with Nfkbiz^-+/+ mice. The lack of IκBζ in BMDMs produced a disability in the expression of Nlrp3 and pro-Il1β mRNAs during the priming step. In addition, ectopic IκBζ expression enhanced the Nlrp3 promoter activity, and Nlrp3 and pro-Il1β transcription. Overall, IκBζ controlled the activation of NLRP3 inflammasome by upregulating the Nlrp3 gene during the priming step.

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

BACKGROUND

Obovatol, a biphenolic chemical originating from Magnolia obovata, has been utilized as a traditional medicine for the treatment of inflammatory diseases. Inflammasome induces maturation of inflammatory cytokines in response to intracellular danger signals, and its dysregulation induces inflammatory diseases.

PURPOSE

The effect of obovatol on inflammasome activation has not been reported, although its anti-inflammatory properties have been studied.

STUDY DESIGN/METHODS

Obovatol was treated to macrophages with inflammasome triggers, and secretions of interleukin (IL)-1β, IL-18, and caspase-1 were measured as readouts of inflammasome activation. In addition, Asc pyroptosome formation, caspase-1 activity, and mitochondrial reactive oxygen species (ROS) production were analyzed in mechanical studies. Anti-inflammasome properties of obovatol were confirmed in an animal model.

RESULTS

Obovatol inhibited NLRP3, AIM2, and non-canonical inflammasomes through inhibition of Asc pyroptosome formation and mitochondrial ROS generation. In addition, obovatol disrupted the priming step of inflammasome activation and inhibited transcription of inflammatory cytokines. In mice, obovatol attenuated serum IL-1β elevation in response to monosodium urate crystals.

CONCLUSION

Obovatol is suggested as an inhibitor of NLRP3, AIM2, and non-canonical inflammasomes.

Methylene Blue in the Treatment of Neuropsychiatric Disorders

Methylene blue is a long-established drug with complex pharmacology and multiple clinical indications. Its diverse mechanisms of action are most likely responsible for the large variety of its clinical effects. Of interest to psychiatrists, methylene blue has antidepressant, anxiolytic, and neuroprotective properties documented by both animal and human studies. Its stabilizing effect on mitochondrial function and dose-dependent effect on the generation of reactive oxygen species are of significant heuristic value. For these reasons, methylene blue holds promise as a proof-of-concept treatment of organic/neurodegenerative disorders and as a neuroprotective agent in general. In psychiatry, methylene blue has been used for over a century. It was tried successfully in the treatment of psychotic and mood disorders and as a memory enhancer in fear-extinction training. Particularly promising results have been obtained in both short- and long-term treatment of bipolar disorder. In these studies, methylene blue produced an antidepressant and anxiolytic effect without risk of a switch into mania. Long-term use of methylene blue in bipolar disorder led to a better stabilization and a reduction in residual symptoms of the illness. It is usually well tolerated, but caution is needed in the light of its inhibitory effect on monoamine oxidase A.

Diverging inflammasome signals in tumorigenesis and potential targeting

Inflammasomes are molecular platforms that assemble upon sensing various intracellular stimuli. Inflammasome assembly leads to activation of caspase 1, thereby promoting the secretion of bioactive interleukin-1β (IL-1β) and IL-18 and inducing an inflammatory cell death called pyroptosis. Effectors of the inflammasome efficiently drive an immune response, primarily providing protection against microbial infections and mediating control over sterile insults. However, aberrant inflammasome signalling is associated with pathogenesis of inflammatory and metabolic diseases, neurodegeneration and malignancies. Chronic inflammation perpetuated by inflammasome activation plays a central role in all stages of tumorigenesis, including immunosuppression, proliferation, angiogenesis and metastasis. Conversely, inflammasome signalling also contributes to tumour suppression by maintaining intestinal barrier integrity, which portrays the diverse roles of inflammasomes in tumorigenesis. Studies have underscored the importance of environmental factors, such as diet and gut microbiota, in inflammasome signalling, which in turn influences tumorigenesis. In this Review, we deliver an overview of the interplay between inflammasomes and tumorigenesis and discuss their potential as therapeutic targets.

Cytoplasmic and Mitochondrial NADPH-Coupled Redox Systems in the Regulation of Aging

The reduced form of nicotinamide adenine dinucleotide phosphate (NADPH) protects against redox stress by providing reducing equivalents to antioxidants such as glutathione and thioredoxin. NADPH levels decline with aging in several tissues, but whether this is a major driving force for the aging process has not been well established. Global or neural overexpression of several cytoplasmic enzymes that synthesize NADPH have been shown to extend lifespan in model organisms such as Drosophila suggesting a positive relationship between cytoplasmic NADPH levels and longevity. Mitochondrial NADPH plays an important role in the protection against redox stress and cell death and mitochondrial NADPH-utilizing thioredoxin reductase 2 levels correlate with species longevity in cells from rodents and primates. Mitochondrial NADPH shuttles allow for some NADPH flux between the cytoplasm and mitochondria. Since a decline of nicotinamide adenine dinucleotide (NAD⁺) is linked with aging and because NADP⁺ is exclusively synthesized from NAD⁺ by cytoplasmic and mitochondrial NAD⁺ kinases, a decline in the cytoplasmic or mitochondrial NADPH pool may also contribute to the aging process. Therefore pro-longevity therapies should aim to maintain the levels of both NAD⁺ and NADPH in aging tissues.

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

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

Inhibiting the NLRP3 Inflammasome With Methylene Blue as Treatment Adjunct in Myelodysplasia

Myelodysplasia refers to a group of clonal hematopoietic neoplasms characterized by genetic heterogeneity, different clinical behaviors and prognoses. Some of this group of bone marrow failure conditions have known external causes, some are of unknown origin. Within marrow, intracellular, and extracellular elements of the innate immune system are activated and contribute to creation of multiple cytogenetic abnormalities and are central to the mode of hematopoietic cell failure. Basiorka et al. showed that NLRP3 inflammasome activity is essential to the innate immune system's destruction of marrow hematopoietic cells commonly in myelodysplasia. In April 2018 Hao et al. reported that methylene blue inhibits rat NLRP3 inflammasome function. Methylene blue has been in continuous use in humans for over a century. It is associated with an eminently benign side effect profile in human use. If as in rodents, methylene blue also inhibits NLRP3 inflammasome function in human myelodysplasia a trial of adjunctive methylene blue treatment in transfusion dependent, low risk myelodysplasia where marrow inflammation and apoptosis predominates, would be worth trying.

HIGHLIGHTS

- Cytogenetic abnormalities and innate immune activation are seen in myelodysplasia

- The NLRP3 inflammasome is a core element generating marrow failure of myelodysplasia

- In April 2018 methylene blue was reported to potently inhibit NLRP3 inflammasome function

- Methylene blue has benign side effects and has been in human use for a century

- Study of methylene blue treatment of myelodysplasia would be a low-risk intervention

NLRP6 Induces Pyroptosis by Activation of Caspase-1 in Gingival Fibroblasts

NLRP6, a member of the nucleotide-binding domain, leucine-rich repeat-containing (NLR) innate immune receptor family, has been reported to participate in inflammasome formation. Activation of inflammasome triggers a caspase-1-dependent programming cell death called pyroptosis. However, whether NLRP6 induces pyroptosis has not been investigated. In this study, we showed that NLRP6 overexpression activated caspase-1 and gasdermin-D and then induced pyroptosis of human gingival fibroblasts, resulting in release of proinflammatory mediators interleukin (IL)-1β and IL-18. Moreover, NLRP6 was highly expressed in gingival tissue of periodontitis compared with healthy controls. Porphyromonas gingivalis, which is a commensal bacterium and has periodontopathic potential, induced pyroptosis of gingival fibroblasts by activation of NLRP6. Together, we, for the first time, identified that NLRP6 could induce pyroptosis of gingival fibroblasts by activation of caspase-1 and may play a role in periodontitis.

Methylene Blue Attenuates Diabetic Retinopathy by Inhibiting NLRP3 Inflammasome Activation in STZ-Induced Diabetic Rats

Purpose: This study aimed to investigate the regulatory effects of methylene blue (MB) on diabetic retinopathy (DR) and explored the molecular mechanisms of MB as a retina protection agent. Methods: The thicknesses of retinal layers and permeability of the blood-retinal barrier (BRB) were measured by histology analysis, and the expression levels of NLRP3, ASC, procaspase-1, caspase-1, IL-1β, and IL-18 were measured by western blotting. Lentivirus-based knockdown of NLRP3 gene was used to confirm the role of NLRP3 inflammasome. Results: MB treatment attenuates DR supported by the increase of relative thicknesses of retinal layers and the reduction of BRB permeability when compared with the untreated diabetic group. Further, MB significantly downregulated the levels of all detected inflammation mediators and showed inhibition on NLRP3 inflammasome activation similar to NLRP3 gene silencing. Conclusions: This study revealed a novel mechanism underlying the protection role of MB in the pathogenesis of DR.

Role of inflammasome regulation on immune modulators

Inflammatory responses are essential in eliminating harmful substrates from damaged tissue and inducing recovery. Several cytokines participate in and facilitate this response. Certain cytokines such as interleukin (IL)-1β and IL-18 are initially produced in precursor form in response to toll-like receptor (TLR) ligands and undergo maturation by inflammasomes, which are cytosolic multi-protein complexes containing nucleotide-binding oligomerization domain (NOD)-containing protein 2-like receptors (NLRs). Immune modulators targeting inflammasomes have been investigated to control inflammatory diseases such as metabolic syndrome. However, most immune modulators possessing anti-inflammasome properties attenuate production of other cytokines, which are essential for host defense. In this review, we analyzed the effect of anti-inflammasome agents on the production of cytokines which are not regulated by inflammasome and involving in initial immune responses. As a result, the inflammasome inhibitors are put into three categories: non-effector, stimulator, or inhibitor of cytokine production. Even the stimulator of cytokine production ameliorated symptoms resulting from inflammasome activation in mouse models. Thus, we suggest ideal immune modulators targeting inflammasomes in order to enhance cytokine production while inhibiting cytokine maturation.

Methylene Blue Mitigates Acute Neuroinflammation after Spinal Cord Injury through Inhibiting NLRP3 Inflammasome Activation in Microglia

The spinal cord injury (SCI) is a detrimental neurological disease involving the primary mechanical injury and secondary inflammatory damage. Curtailing the detrimental neuroinflammation would be beneficial for spinal cord function recovery. Microglia reside in the spinal cord and actively participate in the onset, progression and perhaps resolution of post-SCI neuroinflammation. In the current study, we tested the effects of methylene blue on microglia both in vitro and in a rat SCI model. We found that methylene blue inhibited the protein levels of IL-1β and IL-18 rather than their mRNA levels in activated microglia. Further investigation indicated that methylene blue deceased the activation of NLRP3 inflammasome and NLRC4 inflammasome in microglia in vitro. Moreover, in the rat SCI model, the similar effect of methylene blue on post-SCI microglia was also observed, except that the activation of NLRC4 inflammasome was not seen. The inhibition of microglia NLRP3 inflammasome was associated with down-regulation of intracellular reactive oxygen species (ROS). The administration of methylene blue mitigated the overall post-SCI neuroinflammation, demonstrated by decreased pro-inflammatory cytokine production and leukocyte infiltrates. Consequently, the neuronal apoptosis was partially inhibited and the hind limb locomotor function was ameliorated by methylene blue treatment. Our research highlights the role of methylene blue in inhibiting post-SCI neuroinflammation, and suggests that methylene blue might be used for SCI therapy.