The TIR/BB-loop mimetic AS-1 prevents non-alcoholic steatohepatitis and hepatic insulin resistance by inhibiting NLRP3-ASC inflammasome activation

Pharmacological targeting of adaptor proteins in chronic inflammation

BACKGROUND

Inflammation, a biological response of the immune system, can be triggered by various factors such as pathogens, damaged cells, and toxic compounds. These factors can lead to chronic inflammatory responses, potentially causing tissue damage or disease. Both infectious and non-infectious agents, as well as cell damage, activate inflammatory cells and trigger common inflammatory signalling pathways, including NF-κB, MAPK, and JAK-STAT pathways. These pathways are activated through adaptor proteins, which possess distinct protein binding domains that connect corresponding interacting molecules to facilitate downstream signalling. Adaptor molecules have gained widespread attention in recent years due to their key role in chronic inflammatory diseases.

METHODS

In this review, we explore potential pharmacological agents that can be used to target adaptor molecules in chronic inflammatory responses. A comprehensive analysis of published studies was performed to obtain information on pharmacological agents.

CONCLUSION

This review highlights the therapeutic strategies involving small molecule inhibitors, antisense oligonucleotide therapy, and traditional medicinal compounds that have been found to inhibit the inflammatory response and pro-inflammatory cytokine production. These strategies primarily block the protein-protein interactions in the inflammatory signaling cascade. Nevertheless, extensive preclinical studies and risk assessment methodologies are necessary to ensure their safety.

Compound c17 alleviates inflammatory cardiomyopathy in streptozotocin-induced diabetic mice by targeting MyD88

BACKGROUND

Diabetic cardiomyopathy (DCM) is a common complication of diabetes mellitus and is associated with increased morbidity and mortality due to cardiac dysfunction. Chronic inflammation plays a significant role in the development of DCM, making it a promising target for novel pharmacological strategies. Our previous study has synthesized a novel compound, c17, which exhibited strong anti-inflammatory activity by specifically targeting to myeloid differentiation primary response 88 (MyD88). In this study, we evaluated the therapeutic effect of c17 in DCM.

METHODS

The small molecular selective MyD88 inhibitor, c17, was used to evaluate the effect of MyD88 on DCM in both high concentration of glucose- and palmitic acid-stimulated macrophages and streptozotocin (STZ)-induced type 1 diabetes mellitus (T1DM) mice.

RESULTS

The treatment of c17 in T1DM mice resulted in improved heart function and reduced cardiac hypertrophy, inflammation and fibrogenesis. RNA sequencing analysis of the heart tissues revealed that c17 effectively suppressed the inflammatory response by regulating the MyD88-dependent pathway. Co-immunoprecipitation experiments further confirmed that c17 disrupted the interaction between MyD88 and Toll-like receptor 4 (TLR4), consequently inhibiting downstream NF-κB activation. In vitro studies demonstrated that c17 exhibited similar anti-inflammatory activity by targeting MyD88 in macrophages, which are the primary regulators of cardiac inflammation. Furthermore, conditioned medium derived from c17-treated macrophages showed reduced capacity to induce hypertrophy, pro-fibrotic reactions, and secondary inflammation in cardiomyocytes.

CONCLUSIONS

In conclusion, the small-molecule MyD88 inhibitor, c17, effectively combated the inflammatory DCM, therefore could be a potential candidate for the treatment of this disease.

The CYP2E1 inhibitor Q11 ameliorates LPS-induced sepsis in mice by suppressing oxidative stress and NLRP3 activation

Sepsis is an infection-induced, multi-organ system failure with a pathophysiology related to inflammation and oxidative stress. Increasing evidence indicates that cytochrome P450 2E1 (CYP2E1) is involved in the incidence and development of inflammatory diseases. However, a role for CYP2E1 in lipopolysaccharide (LPS)-induced sepsis has not been completely explored. Here we use Cyp2e1 knockout (cyp2e1-/-) mice to determine if CYP2E1 could be a therapeutic target for sepsis. We also evaluated the ability of Q11, a new specific CYP2E1 inhibitor, to prevent and ameliorate LPS-induced sepsis in mice and in LPS-treated J774A.1 and RAW264.7 cells. Cyp2e1 deletion significantly reduced hypothermia, multi-organ dysfunction and histological abnormalities in LPS-treated mice; consistent with this finding, the CYP2E1 inhibitor Q11 significantly prolonged the survival time of septic mice and ameliorated multi-organ injury induced by LPS. CYP2E1 activity in liver correlated with indicators of multi-organ injury, such as the level of lactate dehydrogenase (LDH) and blood urea nitrogen (BUN) (P<0.05). Q11 significantly suppressed the expression of NLRP3 in tissues after LPS injection; in vitro studies revealed that activation of NLRP3 signaling and increase of ROS was attenuated by Q11 in LPS-stimulated macrophages, which was reflected by reduced expression of caspase-1 and formation of ASC specks. Overall, our results indicate that Q11 improves the survival of mice with LPS-induced sepsis and attenuates sepsis-induced multiple-organ injury, suggesting that CYP2E1 could be a therapeutic target for sepsis.

Salidroside alleviates hepatic ischemia-reperfusion injury during liver transplant in rat through regulating TLR-4/NF-κB/NLRP3 inflammatory pathway

Salidroside has anti-inflammatory, antioxidant and hepatoprotective properties. However, its effect on hepatic ischemia–reperfusion injury (IRI), an unavoidable side effect associated with liver transplantation, remains undefined. Here, we aimed to determine whether salidroside alleviates hepatic IRI and elucidate its potential mechanisms. We used both in vivo and in vitro assays to assess the effect and mechanisms of salidroside on hepatic IRI. Hepatic IRI rat models were pretreated with salidroside (5, 10 or 20 mg/kg/day) for 7 days following liver transplantation while hypoxia/reoxygenation (H/R) model of RAW 264.7 macrophages were pretreated with salidroside (1, 10 or 50 μM). The effect of salidroside on hepatic IRI was assessed using hematoxylin–eosin staining, terminal deoxynucleotidyl transferase dUTP nick-end labeling staining, qRT-PCR, immunosorbent assay and western blotting. Our in vivo assays showed that salidroside significantly reduced pathological liver damage, serum aminotransferase levels and serum levels of IL-1, IL-18 and TNF-α. Besides, salidroside reduced the expression of TLR-4/NF-κB/NLRP3 inflammatory pathway associated proteins (TLR-4, MyD88, p-IKKα, p-IKKβ, p-IKK, p-IκBα, p-P65, NLRP3, ASC, Cleaved caspase-1, IL-1β, IL-18, TNF-α and IL-6) in rats after liver transplantation. On the other hand, data from the in vitro analysis demonstrated that salidroside blocks expression of TLR-4/NF-κB/NLRP3 inflammatory pathway related proteins in the RAW264.7 cells treated with H/R. The salidroside-specific anti-inflammatory effects were partially inhibited by the TLR-4 agonist lipopolysaccharide. Taken together, our study showed that salidroside inhibits hepatic IRI following liver transplantation by modulating the TLR-4/NF-κB/NLRP3 inflammatory pathway.

Inflammasomes and Pyroptosis of Liver Cells in Liver Fibrosis

Inflammasomes are multiprotein complexes that can sense danger signals and activate caspase-1 to mediate pro-inflammatory cytokines release and pyroptotic cell death. There are two main canonical and non-canonical signaling pathways that trigger inflammasome activation. Inflammasomes are expressed and assembled in parenchymal and nonparenchymal cells in response to liver injury in the liver. Additionally, the hepatocytes, biliary epithelial cells (cholangiocytes), hepatic stellate cells (HSCs), hepatic macrophages, and liver sinusoidal endothelial cells (LSECs) contribute to liver fibrosis via different mechanisms. However, the underlying mechanism of the inflammasome and pyroptosis in these liver cells in liver fibrosis remains elusive. This review summarizes the activation and function of inflammasome complexes and then discusses the association between inflammasomes, pyroptosis, and liver fibrosis. Unlike other similar reviewers, we will focus on the effect of inflammasome activation and pyroptosis in the various liver cells during the development of liver fibrosis. We will also highlight the latest progress of pharmacological intervention in inflammasome-mediated liver fibrosis.

Aurantio-obtusin induces hepatotoxicity through activation of NLRP3 inflammasome signaling

Aurantio-obtusin (AO) is a major anthraquinone (AQ) compound derived from Cassiae semen (CS). Although pharmacological studies have shown that the CS extracts can serve as effective agents in preclinical and clinical practice, AQ-induced hepatotoxicity in humans has attracted widespread attention. To explore whether AO induces hepatotoxicity and its underlying mechanisms, we exposed larval zebrafish and mice to AO. We found that AO delayed yolk sac absorption, and increased liver area and inflammation in the larval zebrafish. This inflammation was manifested as an increase in liver neutrophils and the up-regulated mRNA expression of interleukin-6 (Il-6) and tumor necrosis factor-α (Tnf-α) in the larval zebrafish. Furthermore, a pharmacokinetics study showed that AO was quickly absorbed into the blood and rapidly metabolized in the mice. Of note, AO induced hepatotoxicity in a gender-dependent manner, characterized by liver dysfunction, increased hepatocyte necrosis with inflammatory infiltration, and up-regulated mRNAs of Il-6, Tnf-α and monocyte chemotactic protein 1(Mcp1) in the female mice after 28-day oral administration. It also highlighted that AO triggered NOD-like receptor protein (NLRP) signaling in the female mice, as evidenced by the increased NLRP3, Caspase-1, pro-IL-1β, IL-1β and IL-18. Finally, we found that AO led to a significant increase in potassium calcium-activated channel, subfamily N, member 4 (KCNN4) and reactive oxygen species (ROS) levels, along with decreased nuclear factor kappa B p65 (NF-κB p65), in the female mouse livers. In conclusion, AO induced hepatotoxicity by activating NLRP3 inflammasome signaling, at least in part, through increased KCNN4 and ROS production, and NF-κB inhibition.

Protective roles of the TIR/BB-loop mimetic AS-1 in alkali-induced corneal neovascularization by inhibiting ERK phosphorylation

Hydrocinnamoyl-L-valylpyrrolidine (AS-1), a synthetic low-molecule mimetic of myeloid differentiation primary response gene 88 (MyD88), inhibits inflammation by disrupting the interaction between the interleukin-1 receptor (IL-1R) and MyD88. Here, we describe the effects of AS-1 on injury-induced increases in inflammation and neovascularization in mouse corneas. Mice were administered a subconjunctival injection of 8 μL AS-1 diluent before or after corneal alkali burn, followed by evaluation of corneal resurfacing and corneal neovascularization (CNV) by slit-lamp biomicroscopy and clinical assessment. Corneal inflammation was assessed by whole-mount CD45⁺ immunofluorescence staining, and corneal hemangiogenesis and lymphangiogenesis following injury were evaluated by immunostaining for the vascular markers isolectin B4 (IB4) and the lymphatic vascularized marker lymphatic vessel endothelial hyaluronan receptor 1 (LYVE1), respectively. Additionally, corneal tissues were collected to determine the expression of 35 cytokines, and we detected activation of IL-1RI, MyD88, and mitogen-activated protein kinase (MAPK). The results showed that alkali conditions increased the number of CD45⁺ cells and expression of vascular endothelial growth factor (VEGF)-A, VEGF-C, and LYVE1 in corneas, with these levels decreased in the AS-1-treated group. Moreover, AS-1 effectively prevented alkali-induced cytokine production, blocked interactions between IL-1RI and MyD88, and inhibited MAPK activation post-alkali burn. These results indicated that AS-1 prevented alkali-induced corneal hemangiogenesis and lymphangiogenesis by blocking IL-1RI-MyD88 interaction, as well as extracellular signal-regulated kinase phosphorylation, and could be efficacious for the prevention and treatment of corneal alkali burn.

Prostaglandin E2 promotes pathological retinal neovascularisation via EP4R-EGFR-Gab1-AKT signaling pathway

Proliferative retinopathies, such as proliferative diabetic retinopathy (PDR) and retinopathy of prematurity (ROP) are major causes of visual impairment and blindness in industrialized countries. Prostaglandin E2 (PGE2) is implicated in cellular proliferation and migration via E-prostanoid receptor (EP4R). The aim of this study was to investigate the role of PGE2/EP4R signaling in the promotion of retinal neovascularisation. In a streptozotocin (STZ)-induced diabetic model and an oxygen-induced retinopathy (OIR) model, rats received an intravitreal injection of PGE2, cay10598 (an EP4R agonist) or AH23848 (an EP4R antagonist). Optical coherence tomography, retinal histology and biochemical markers were assessed. Treatment with PGE2 or cay10598 accelerated pathological retinal angiogenesis in STZ and OIR-induced rat retina, which was ameliorated in rats pretreated with AH23848. Serum VEGF-A was upregulated in the PGE2-treated diabetic rats vs non-treated diabetic rats and significantly downregulated in AH23848-treated diabetic rats. PGE2 or cay10598 treatment also significantly accelerated endothelial tip-cell formation in new-born rat retina. In addition, AH23848 treatment attenuated PGE2-or cay10598-induced proliferation and migration by repressing the EGF receptor (EGFR)/Growth factor receptor bound protein 2-associated binder protein 1 (Gab1)/Akt/NF-κB/VEGF-A signaling network in human retinal microvascular endothelial cells (hRMECs). PGE2/EP4R signaling network is thus a potential therapeutic target for pathological intraocular angiogenesis.

Arsenic induces hepatic insulin resistance via mtROS-NLRP3 inflammasome pathway

Hepatic insulin resistance (IR) is the key event for arsenic-caused type 2 diabetes (T2D). However, the unequivocal mechanism of arsenic-induced hepatic IR remains unclear. The current study determined the role of NOD-like receptor family pyrin domain-containing 3 (NLRP3) inflammasome activation in arsenic-induced IR and revealed the underlying mechanism. Three-month NaAsO₂ gavage led to glucose intolerance and insulin insensitivity, impaired hepatic insulin signaling. Additionally, NaAsO₂ upregulated the level of oxidized mitochondrial DNA (ox-mtDNA) and mitophagy, thereby activating the NLRP3 inflammasome in SD rat liver. In vitro, we demonstrated that NaAsO₂-induced IR depended upon the NLRP3 inflammasome activation. Moreover, inhibiting mitophagy mitigated the NLRP3 inflammasome activation and impaired insulin signaling induced by NaAsO₂. Furthermore, mitochondrial reactive oxygen species (mtROS) scavenger alleviated the upregulated ox-mtDNA and mitophagy, thereby inhibiting the NLRP3 inflammasome activation, and improving insulin signaling. Taken together, these data demonstrated that mtROS-triggered ox-mtDNA, mitophagy, and the activation of NLRP3 inflammasome was involved in arsenic-induced hepatic IR.

Cannabinoid Receptor 1/miR-30b-5p Axis Governs Macrophage NLRP3 Expression and Inflammasome Activation in Liver Inflammatory Disease

Nod-like receptor (NLR) family pyrin domain containing 3 (NLRP3) has been regarded as an important initiator or promoter in multiple inflammatory diseases. However, the relationship between cannabinoid receptor 1 (CB1) and macrophage NLRP3 inflammasome and the corresponding molecular mechanism in liver inflammation remain unclear. Mouse liver injury models were induced by carbon tetrachloride (CCl₄) or methionine-choline-deficient and high fat (MCDHF) diet. Human liver tissues were obtained from patients with different chronic liver diseases. CB1 expression was increased in liver tissue and macrophages of CCl₄- and MCDHF-treated mice, positively correlated with NLRP3. CB1 agonist ACEA (Arachiodonyl-2’-Chloroethylamide) promoted NLRP3 expression and NLRP3 inflammasome activation in macrophages. CB1 blockade with its antagonist AM281 reduced NLRP3 expression, inflammasome activation, and liver inflammation in CCl₄- and MCDHF-treated mice. MicroRNA-30b-5p (miR-30b-5p), screened by the intersection of bioinformatics databases and downregulated miRNAs in injured liver, negatively correlated with NLRP3 in mouse and human liver. miR-30b-5p was involved in CB1-mediated activation of NLRP3 inflammasome in macrophages by directly targeting NLRP3. Importantly, administration of miR-30b-5p agomir targeted NLRP3 and attenuated liver inflammation in the injured liver. Altogether, CB1/miR-30b-5p axis modulates NLRP3 expression and NLPR3 inflammasome activation in macrophages during liver inflammation, which provides a potential target for liver disease.

Differential metabolic and hepatic transcriptome responses of two miniature pig breeds to high dietary cholesterol

AIMS

Pigs are increasingly used as human metabolic disease models; however, there is insufficient research on breed-related genetic background differences. This study aimed to investigate the differential metabolic responses to high-fat and high-cholesterol (HFC) diet-induced non-alcoholic fatty liver disease (NAFLD) of two miniature pig breeds and explore the molecular mechanisms involved.

MAIN METHODS

Male Wuzhishan (WZSP) and Tibetan pigs (TP) were randomly fed either a standard or an HFC diet for 24 weeks. Weight, serum lipids, bile acid, insulin resistance, liver function, liver histology, and hepatic lipid deposition were determined. RNA-Seq was used to detect the hepatic gene expression profiles. Western blot, immunohistochemistry, and qRT-PCR were used to detect the lipid and glucose metabolism-related gene expressions.

KEY FINDINGS

The HFC diet caused obesity, hypertension, severe hypercholesterolemia, liver injury, increased hepatocellular steatosis and inflammation, and significantly increased serum insulin levels in both pig breeds. This diet led to higher serum and hepatic cholesterol level concentrations in WZSP and elevated fasting glucose levels in TP. Transcriptome analysis revealed that the genes controlling hepatic cholesterol metabolism and the inflammatory response were consistently regulated; lipid metabolism and insulin signaling related genes were uniquely regulated by the HFC diet in the WZSP and TP, respectively.

SIGNIFICANCE

Our study demonstrated that the genetic background affects profoundly pigs' metabolic and hepatic responses to an HFC diet. These results deepened our understanding of the molecular mechanisms of HFC diet-induced NAFLD and provided a foundation for selecting the appropriate pig breeds for metabolic studies in the future.

The TIR/BB-loop mimetic AS-1 prevents Ang II-induced hypertensive cardiac hypertrophy via NF-κB dependent downregulation of miRNA-143

Untreated pathological cardiac hypertrophy, which can be caused by sustained systemic hypertension, may lead to heart failure. In the present study, we investigated whether AS-1 had attenuating effects on hypertension-induced cardiac hypertrophy, and whether this process was mediated by the regulation of miRNA-143. To induce the hypertrophic response in vitro, cardiomyocytes were stimulated with Ang II for 24hs. AS-1 administration strongly attenuated Ang II-induced hypertrophic response of cardiomyocytes. Chronical infusion of Ang II via implanted osmotic mini-pump induced increased blood pressure and cardiac hypertrophy in vivo. AS-1 administration attenuated hypertension-induced cardiac hypertrophy by, at least in part, inhibin of MAPK signaling. We observed, for the first time, upregulated expression of miRNA-143 in Ang II-induced cardiomyocytes, and inhibition of miRNA-143 significantly reduced the Ang II-induced hypertrophic responses. Importantly, AS-1 administration diminished the Ang II-induced upregulation of miRNA-143. Overexpression of miRNA-143 abolished the attenuating effects of AS-1 on Ang II-induced hypertrophic response of cardiomyocytes. Additionally, AS-1 administration abrogates Ang II-induced nuclear translocation of p50 NF-κB subunit in hypertrophic cardiomyocytes. Application of NF-κB inhibitor significantly suppressed Ang II-induced upregulation of miRNA-143. Our data suggest a novel mechanism by which AS-1 attenuates Ang II-induced hypertrophic response through downregulation miRNA-143 expression in a NF-κB-dependent manner.

Asiatic Acid Protects Dopaminergic Neurons from Neuroinflammation by Suppressing Mitochondrial Ros Production

This study sought to evaluate the effects of Asiatic acid in LPS-induced BV2 microglia cells and 1-methyl-4-phenyl-pyridine (MPP⁺)-induced SH-SY5Y cells, to investigate the potential anti-inflammatory mechanisms of Asiatic acid in Parkinson’s disease (PD). SH-SY5Y cells were induced using MPP⁺ to establish as an in vitro model of PD, so that the effects of Asiatic acid on dopaminergic neurons could be examined. The NLRP3 inflammasome was activated in BV2 microglia cells to explore potential mechanisms for the neuroprotective effects of Asiatic acid. We showed that Asiatic acid reduced intracellular production of mitochondrial reactive oxygen species and altered the mitochondrial membrane potential to regulate mitochondrial dysfunction, and suppressed the NLRP3 inflammasome in microglia cells. We additionally found that treatment with Asiatic acid directly improved SH-SY5Y cell viability and mitochondrial dysfunction induced by MPP⁺. These data demonstrate that Asiatic acid both inhibits the activation of the NLRP3 inflammasome by downregulating mitochondrial reactive oxygen species directly to protect dopaminergic neurons from, and improves mitochondrial dysfunction in SH-SY5Y cells, which were established as a model of Parkinson’s disease. Our finding reveals that Asiatic acid protects dopaminergic neurons from neuroinflammation by suppressing NLRP3 inflammasome activation in microglia cells as well as protecting dopaminergic neurons directly. This suggests a promising clinical use of Asiatic acid for PD therapy.

Prostaglandin E2/EP2 receptor signalling pathway promotes diabetic retinopathy in a rat model of diabetes

AIMS/HYPOTHESIS

Diabetic retinopathy is a common microvascular complication of diabetes mellitus and is initiated by inflammation and apoptosis-associated retinal endothelial cell damage. Prostaglandin E₂ (PGE₂) has emerged as a critical regulator of these biological processes. We hypothesised that modulating PGE₂ and its E-prostanoid receptor (EP₂R) would prevent diabetes mellitus-induced inflammation and microvascular dysfunction.

METHODS

In a streptozotocin (STZ)-induced rat model of diabetes, rats received intravitreal injection of PGE₂, butaprost (a PGE₂/EP₂R agonist) or AH6809 (an EP₂R antagonist). Retinal histology, optical coherence tomography, ultrastructure of the retinal vascular and biochemical markers were assessed.

RESULTS

Intravitreal injection of PGE₂ and butaprost significantly accelerated retinal vascular leakage, leucostasis and endothelial cell apoptosis in STZ-induced diabetic rats. This response was ameliorated in diabetic rats pre-treated with AH6809. In addition, pre-treatment of human retinal microvascular endothelial cells with AH6809 attenuated PGE₂- and butaprost-induced activation of caspase 1, activation of the complex containing nucleotide-binding domain and leucine rich repeat containing family, pyrin domain containing 3 (NLRP3) and apoptosis-associated speck-like protein containing a C-terminal caspase-activation and recruitment domain (ASC), and activation of the EP₂R-coupled cAMP/protein kinase A/cAMP response element-binding protein signalling pathway.

CONCLUSIONS/INTERPRETATION

The PGE₂/EP₂R signalling pathway is involved in STZ-induced diabetic retinopathy and could be considered as a potential target for diabetic retinopathy prevention and treatment.

A long-acting FGF21 alleviates hepatic steatosis and inflammation in a mouse model of non-alcoholic steatohepatitis partly through an FGF21-adiponectin-IL17A pathway

BACKGROUND AND PURPOSE

Non-alcoholic steatohepatitis (NASH) is the most severe form of non-alcoholic fatty liver disease and is a serious public health problem around the world. There are currently no approved treatments for NASH. FGF21 has recently emerged as a promising drug candidate for metabolic diseases. However, the disadvantages of FGF21 as a clinically useful medicine include its short plasma half-life and poor drug-like properties. Here, we have explored the effects of PsTag600-FGF21, an engineered long-acting FGF21 fusion protein, in mice with NASH and describe some of the underlying mechanisms.

EXPERIMENTAL APPROACH

A long-acting FGF21 was prepared by genetic fusion with a 600 residues polypeptide (PsTag600). We used a choline-deficient high-fat diet-induced model of NASH in mice. The effects on body weight, insulin sensitivity, inflammation and levels of hormones and metabolites were studied first. We further investigated whether PsTag600-FGF21 attenuated inflammation through the Th17-IL17A axis and the associated mechanisms.

KEY RESULTS

PsTag600-FGF21 dose-dependently reduced body weight, blood glucose, and insulin and lipid levels and reversed hepatic steatosis. PsTag600-FGF21 enhanced fatty acid activation and mitochondrial β-oxidation in the liver. The profound reduction in hepatic inflammation in NASH mice following PsTag600-FGF21 was associated with inhibition of IL17A expression in Th17 cells. Furthermore, PsTag600-FGF21 depended on adiponectin to exert its suppression of Th17 cell differentiation and IL17A expression.

CONCLUSIONS AND IMPLICATIONS

Our data have uncovered some of the mechanisms by which PsTag600-FGF21 suppresses hepatic inflammation and further suggest that PsTag600-FGF21 could be an effective approach in NASH treatment.

MyD88 as a therapeutic target for inflammatory lung diseases

INTRODUCTION

Myeloid differentiation primary response protein 88 (MyD88) is a critical adaptor protein involved in Toll-like and IL-1 receptor family signaling controlling innate immune responses and inflammation. Genetic deletion of MyD88 function results in profound suppression of inflammation and reduced resistance of the host to pathogens indicating non-redundant roles of MyD88. The TIR domain is critical for MyD88 dimerization and signaling for TLR and IL-1R family receptor. Areas covered: Emerging evidence suggests that chemical disruption of the TIR domain attenuates cell activation and inhibits in vivo MyD88-dependent inflammation. We review the development of MyD88 dimerization disruptors as a novel therapeutic approach of respiratory diseases with a focus on COPD. Expert opinion: There is a proof of concept that therapeutic targeting of MyD88 is feasible and first preclinical data are highly promising. This opens a great opportunity to treat exacerbations of COPD and other chronic respiratory diseases. However, extensive preclinical investigations and risk analyses are required with carefully evaluation of reduced host resistance and opportunistic infections.

The TIR/BB-loop mimetic AS-1 prevents non-alcoholic steatohepatitis and hepatic insulin resistance by inhibiting NLRP3-ASC inflammasome activation

BACKGROUND AND PURPOSE

Non-alcoholic steatohepatitis (NASH) is characterized by excessive intracellular lipid accumulation, inflammation and hepatic insulin resistance. As the incidence of NASH is increasing worldwide, there is an urgent need to find novel interventional approaches. The pro-inflammatory cytokine IL-1β, generated and released from Kupffer cells, is considered to initiate the development of NASH. AS-1, a synthetic low-molecule mimetic of myeloid differentiation primary response gene 88 (MyD88), disrupts the interaction between the IL-1 receptor and MyD88. Here, we investigated whether AS-1 could attenuate the pathogenesis of NASH with an emphasis on hepatic insulin resistance.

EXPERIMENTAL APPROACH

Eight-week-old db/db mice were fed a control diet or a methionine- and choline-deficient (MCD) diet. AS-1 (50 mg·kg^-1 ) or vehicle was administered i.p.

KEY RESULTS

AS-1 administration significantly ameliorated NASH as evidenced by alanine aminotransferase levels and CD68 levels in livers of MCD-fed mice. AS-1 inhibited the MCD diet-induced activation of caspase 1 and the NLRP3-ASC inflammasome, and also reduced the enhanced levels of ROS, malondialdehyde, 3-nitrotyrosine, NADPH oxidase complex and CYP reductase-associated cytochrome p450 2E1 (CYP2E1) expression in the liver. In addition, AS-1 decreased ROS, inflammasome activation and IL-1β production in free fatty acid-LPS-treated Kupffer cells. Finally, pretreatment with AS-1 significantly ameliorated gluconeogenesis and insulin desensitization induced by IL-1β, probably by blocking the interaction between MyD88 and the IL-1 receptor.

CONCLUSIONS AND IMPLICATIONS

Our results indicate that AS-1 can ameliorate NASH and hepatic insulin resistance and could be considered as a potential strategy for the prevention and treatment of NASH.