Aryl Hydrocarbon Receptor Plays Protective Roles against High Fat Diet (HFD)-induced Hepatic Steatosis and the Subsequent Lipotoxicity via Direct Transcriptional Regulation of Socs3 Gene Expression

Indoxyl sulfate-induced TNF-α is regulated by crosstalk between the aryl hydrocarbon receptor, NF-κB, and SOCS2 in human macrophages

Indoxyl sulfate (IS) is a uremic toxin associated with increased prevalence of cardiovascular diseases (CVDs) in patients with chronic kidney disease. Despite the crucial role of uremia-related immune dysfunction, a majority of studies attempting to elucidate its pathogenic role in CVD have focused on IS-mediated endothelial dysfunction. Thus, we investigated the underlying molecular mechanisms involved in IS-induced production of TNF-α, a major cardiotoxic cytokine, by human macrophages. We found that crosstalk between the aryl hydrocarbon receptor (AhR), NF-κB, and the suppressor of cytokine signaling (SOCS)2 is important for TNF-α production in IS-stimulated human macrophages. IS-activated AhR rapidly associates with the p65 NF-κB subunit, resulting in mutual inhibition of AhR and NF-κB and inhibition of TNF-α production at an early time point. Later, this repression of TNF-α production is alleviated when SOCS2, a negative modulator of NF-κB, is directly induced by IS-activated AhR. In addition, once free of inhibition, activated AhR induces TNF-α expression by interacting with AhR binding sites in the TNF-α gene. Lastly, we confirmed decreased AhR and increased SOCS2 expression in monocytes of patients with end-stage renal disease, indicating the activation of AhR. Taken together, our results suggest that IS-induced TNF-α production in macrophages is regulated through a complicated mechanism involving interaction of AhR, NF-κB, and SOCS2.-Kim, H. Y., Yoo, T.-H., Cho, J.-Y., Kim, H. C., Lee, W.-W. Indoxyl sulfate-induced TNF-α is regulated by crosstalk between the aryl hydrocarbon receptor, NF-κB, and SOCS2 in human macrophages.

Aryl hydrocarbon receptor agonist indigo protects against obesity-related insulin resistance through modulation of intestinal and metabolic tissue immunity

Background/objectives

Low-grade chronic inflammation in visceral adipose tissue and the intestines are important drivers of obesity associated insulin resistance. Bioactive compounds derived from plants are an important source of potential novel therapies for the treatment of chronic diseases. In search for new immune based treatments of obesity associated insulin resistance, we screened for tissue relevant anti-inflammatory properties in 20 plant-based extracts.

Methods

We screened 20 plant-based extracts to assess for preferential production of IL-10 compared to TNFα, specifically targetting metabolic tissues, including the visceral adipose tissue. We assessed the therapeutic potential of the strongest anti-inflammatory compound, indigo, in the C57BL/6J diet-induced obesity mouse model with supplementation for up to 16 weeks by measuring changes in body weight, glucose and insulin tolerance, and gut barrier function. We also utilized flow cytometry, quantitative PCR, enzyme-linked immunosorbent assay (ELISA), and histology to measure changes to immune cells populations and cytokine profiles in the intestine, visceral adipose tissue (VAT), and liver. 16SrRNA sequencing was performed to examine gut microbial differences induced by indigo supplementation.

Results

We identifed indigo, an aryl hydrocarbon receptor (AhR) ligand agonist, as a potent inducer of IL-10 and IL-22, which protects against high-fat diet (HFD)-induced insulin resistance and fatty liver disease in the diet-induced obesity model. Therapeutic actions were mechanistically linked to decreased inflammatory immune cell tone in the intestine, VAT and liver. Specifically, indigo increased Lactobacillus bacteria and elicited IL-22 production in the gut, which improved intestinal barrier permeability and reduced endotoxemia. These changes were associated with increased IL-10 production by immune cells residing in liver and VAT.

Conclusions

Indigo is a naturally occurring AhR ligand with anti-inflammatory properties that effectively protects against HFD-induced glucose dysregulation. Compounds derived from indigo or those with similar properties could represent novel therapies for diseases associated with obesity-related metabolic tissue inflammation.

Protective Effects of Aryl Hydrocarbon Receptor Signaling in Celiac Disease Mucosa and in Poly I:C-Induced Small Intestinal Atrophy Mouse Model

Aryl hydrocarbon receptor (AhR), a transcription factor activated by a large number of natural and synthetic agents, modulates the activity of immune cells in the gut and represents an important link between the environment and immune-mediated pathologies. In this study, we investigated the role of AhR in celiac disease (CD), a gluten-driven enteropathy. AhR expression was evaluated in intestinal biopsies taken from patients with CD and controls by real-time polymerase chain reaction (PCR), immunohistochemistry and flow cytometry. AhR was also analyzed in ex vivo organ cultures of duodenal biopsies taken from inactive CD patients incubated in presence or absence of peptic-tryptic digest of gliadin. IFN-γ, TNF-α, granzyme B, and perforin expression was evaluated in anti-CD3/CD28-activated intestinal lamina propria mononuclear cells (LPMC) and intestinal intra-epithelial cells (IEL) of active CD patients cultured in the presence or absence of the AhR agonist 6-formylindolo(3, 2-b)carbazole (Ficz). Finally, the protective role of AhR was evaluated in a mouse model of poly I:C-driven small intestine damage. AhR RNA transcripts were reduced in active CD samples as compared to inactive CD and normal controls. Flow cytometry confirmed such results and showed a reduction of AhR in both IEL and LPMC of active CD patients. The addition of a peptic-tryptic digest of gliadin to ex vivo organ cultures of duodenal biopsies taken from inactive CD patients reduced AhR expression. Treatment of CD IEL and LPMC with Ficz reduced the levels of inflammatory cytokines, granzyme B and perforin. Mice injected with Ficz were protected against poly I:C-induced intestinal lesions. Our findings suggest that defective AhR-driven signals could contribute to amplify pathogenic responses in the gut of CD patients.

Impaired Aryl Hydrocarbon Receptor Ligand Production by the Gut Microbiota Is a Key Factor in Metabolic Syndrome

The extent to which microbiota alterations define or influence the outcome of metabolic diseases is still unclear, but the byproducts of microbiota metabolism are known to have an important role in mediating the host-microbiota interaction. Here, we identify that in both pre-clinical and clinical settings, metabolic syndrome is associated with the reduced capacity of the microbiota to metabolize tryptophan into derivatives that are able to activate the aryl hydrocarbon receptor. This alteration is not merely an effect of the disease as supplementation with AhR agonist or a Lactobacillus strain, with a high AhR ligand-production capacity, leads to improvement of both dietary- and genetic-induced metabolic impairments, particularly glucose dysmetabolism and liver steatosis, through improvement of intestinal barrier function and secretion of the incretin hormone GLP-1. These results highlight the role of gut microbiota-derived metabolites as a biomarker and as a basis for novel preventative or therapeutic interventions for metabolic disorders.

The aryl hydrocarbon receptor-cytochrome P450 1A1 pathway controls lipid accumulation and enhances the permissiveness for hepatitis C virus assembly

Viruses hijack and modify host cell functions to maximize viral proliferation. Hepatitis C virus (HCV) reorganizes host cell metabolism to produce specialized membrane structures and to modify organelles such as double-membrane vesicles and enlarged lipid droplets (LDs), thereby enabling virus replication and assembly. However, the molecular bases of these host-HCV interactions are largely unknown. Here, using a chemical screen, we demonstrate that the benzamide derivative flutamide reduces the host capacity to produce infectious HCV. Flutamide disrupted the formation of enlarged LDs in HCV-infected cells, thereby abolishing HCV assembly. We also report that aryl hydrocarbon receptor (AhR), a known flutamide target, plays a key role in mediating LD accumulation and HCV production. This AhR function in lipid production was also observed in HCV-uninfected Huh-7 cells and primary human hepatocytes, suggesting that AhR signaling regulates lipid accumulation independently of HCV infection. We further observed that a downstream activity, that of cytochrome P450 1A1 (CYP1A1), was the primary regulator of AhR-mediated lipid production. Specifically, blockade of AhR-induced CYP1A1 up-regulation counteracted LD overproduction, and overproduction of CYP1A1, but not of CYP1B1, in AhR-inactivated cells restored lipid accumulation. Of note, HCV infection up-regulated the AhR-CYP1A1 pathway, resulting in the accumulation of enlarged LDs. In conclusion, we demonstrate that the AhR-CYP1A1 pathway has a significant role in lipid accumulation, a hallmark of HCV infection that maximizes progeny virus production. Our chemical-genetic analysis reveals a new strategy and lead compounds to control hepatic lipid accumulation as well as HCV infection.

Suppression of aberrant choroidal neovascularization through activation of the aryl hydrocarbon receptor

The aryl hydrocarbon receptor (AhR) is a ligand activated transcription factor, initially discovered for its role in regulating xenobiotic metabolism. There is extensive evidence supporting a multi-faceted role for AhR, modulating physiological pathways important in cell health and disease. Recently we demonstrated that the AhR plays a role in the pathogenesis of age-related macular degeneration (AMD), the leading cause of vision loss in the elderly. We found that loss of AhR exacerbates choroidal neovascular (CNV) lesion formation in a murine model. Herein we tested the therapeutic impact of AhR activation on CNV lesion formation and factors associated with aberrant neovascularization. We screened a panel of synthetic drugs and endogenous AhR ligands, assessed their ability to activate AhR in choroidal endothelial cells, and inhibit angiogenesis in vitro. Drugs with an anti-angiogenic profile were then administered to a murine model of CNV. Two compounds, leflunomide and flutamide, significantly inhibited CNV formation concurrent with positive modifying effects on angiogenesis, inflammation, extracellular matrix remodeling, and fibrosis. These results validate the role of the AhR pathway in regulating CNV pathogenesis, identify mechanisms of AhR-based therapies in the eye, and argue in favor of developing AhR as a drug target for the treatment of neovascular AMD.

Chronic exposure of 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) induces an obesogenic effect in C57BL/6J mice fed a high fat diet

Contaminant involvement in the pathophysiology of obesity is widely recognized. It has been shown that low dose and chronic exposure to endocrine disruptor compounds (EDCs) potentiated diet- induced obesity. High and acute exposure to 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD), a persistent organic pollutant (POP) and an EDC with anti-estrogenic property, causes wasting syndrome . However at lower doses, the TCDD metabolic effects remain poorly understood. We investigated the obesogenic effect during chronic exposure of TCDD at 1μg/kg body weight (bw)/week in adult C57BL/6J mice fed with a high fat diet (HFD) and exposed from 10 to 42 weeks old to TCDD or equal volume of vehicle by intragastric gavage. Under these conditions, TCDD was obesogenic in adult mice (7% in males and 8% in females), which was linked to fat mass. A sex effect was observed in the fat mass distribution in adipose tissue and in the hepatic triglyceride content evolution. In visceral fat pad weight, we observed a decrease (11%) in males and an increase (14%) in females. The hepatic triglyceride content increase (41%) in females only. TCDD failed to induce any change in plasma parameters regarding glucose and lipid homeostasis. Messenger ribonucleic acid (mRNA) levels involved in adipose tissue and hepatic metabolism, inflammation, xenobiotic metabolism and endocrine disruption were differently regulated between males and females. In conclusion, these results provide new evidence that dioxin, a POP and EDC can be obesogenic for adult mice with multi-organ effects.

Acute aflatoxin B1 - Induced hepatotoxicity alters gene expression and disrupts lipid and lipoprotein metabolism in rats

In this study, alterations in lipid metabolism associated with acute aflatoxin B1 (AFB1) induced hepatotoxicity and gene expression changes underlying these effects were investigated. Rats were orally administered three doses (0.25 mg/kg, 0.5 mg/kg and 1.0 mg/kg) of AFB1 for seven days; after which blood was collected and liver excised. Lipid profiles of plasma and liver were determined spectrophotometrically while the expression of genes associated with lipid and lipoprotein metabolism was assayed by reverse transcriptase polymerase chain reaction. Acute exposure to AFB1 increased the levels of plasma and liver cholesterol, triglycerides and phospholipids. AFB1 at 0.5 mg/kg and 1.0 mg/kg resulted in a dose-dependent (1.2 and 1.5 fold, respectively) downregulation of hepatic Cpt1a with a concomitant 1.2 and 1.5 fold increase in the level of plasma FFA, respectively. A similar observation of 1.2 and 1.3 fold increase was also observed in plasma triglyceride concentration, at both respective doses. AFB1 also decreased the relative expression of Ahr, Lipc and Lcat whereas, it upregulated Scarb1 in a dose dependent manner. AFB1-induced dysregulation of the expression of lipid and lipoprotein metabolizing genes may be one mechanism linking AFB1 to altered lipid metabolism and ultimately risk for coronary heart disease.

Acute aflatoxin B1 - Induced hepatotoxicity alters gene expression and disrupts lipid and lipoprotein metabolism in rats

In this study, alterations in lipid metabolism associated with acute aflatoxin B1 (AFB1) induced hepatotoxicity and gene expression changes underlying these effects were investigated. Rats were orally administered three doses (0.25 mg/kg, 0.5 mg/kg and 1.0 mg/kg) of AFB1 for seven days; after which blood was collected and liver excised. Lipid profiles of plasma and liver were determined spectrophotometrically while the expression of genes associated with lipid and lipoprotein metabolism was assayed by reverse transcriptase polymerase chain reaction. Acute exposure to AFB1 increased the levels of plasma and liver cholesterol, triglycerides and phospholipids. AFB1 at 0.5 mg/kg and 1.0 mg/kg resulted in a dose-dependent (1.2 and 1.5 fold, respectively) downregulation of hepatic Cpt1a with a concomitant 1.2 and 1.5 fold increase in the level of plasma FFA, respectively. A similar observation of 1.2 and 1.3 fold increase was also observed in plasma triglyceride concentration, at both respective doses. AFB1 also decreased the relative expression of Ahr, Lipc and Lcat whereas, it upregulated Scarb1 in a dose dependent manner. AFB1-induced dysregulation of the expression of lipid and lipoprotein metabolizing genes may be one mechanism linking AFB1 to altered lipid metabolism and ultimately risk for coronary heart disease.

Habitual coffee consumption and risk of type 2 diabetes, ischemic heart disease, depression and Alzheimer's disease: a Mendelian randomization study

Observationally, coffee is inversely associated with type 2 diabetes mellitus (T2DM), depression and Alzheimer’s disease, but not ischemic heart disease (IHD). Coffee features as possibly protective in the 2015 Dietary Guidelines for Americans. Short-term trials suggest coffee has neutral effect on most glycemic traits, but raises lipids and adiponectin. To clarify we compared T2DM, depression, Alzheimer’s disease, and IHD and its risk factors by genetically predicted coffee consumption using two-sample Mendelian randomization applied to large extensively genotyped case-control and cross-sectional studies. Childhood cognition was used as a negative control outcome. Genetically predicted coffee consumption was not associated with T2DM (odds ratio (OR) 1.02, 95% confidence interval (CI) 0.76 to 1.36), depression (0.89, 95% CI 0.66 to 1.21), Alzheimer’s disease (1.17, 95% CI 0.96 to 1.43), IHD (0.96, 95% CI 0.80 to 1.14), lipids, glycemic traits, adiposity or adiponectin. Coffee was unrelated to childhood cognition. Consistent with observational studies, coffee was unrelated to IHD, and, as expected, childhood cognition. However, contrary to observational findings, coffee may not have beneficial effects on T2DM, depression or Alzheimer’s disease. These findings clarify the role of coffee with relevance to dietary guidelines and suggest interventions to prevent these complex chronic diseases should be sought elsewhere.