AhR agonists screening and identification in indoor dust based on non-target chemical analysis by GC-Q-TOFMS and biological effect evaluation referring to ToxCast/Tox21 database.

Numerous studies reported the concentration of agonists of aryl hydrocarbon receptor (AhR) in indoor dust by target chemical analysis or the biological effects of activating the AhR by indoor extracts, but the major AhR agonists identification in indoor dust were rarely researched. In the present study, the indoor dust samples were collected for 7-ethoxyresorufin O-deethylase (EROD) assay and both non-targeted and targeted chemical analysis for AhR agonists by gas chromatography quadrupole time-of-flight mass spectrometry and gas chromatography-mass spectrometry analysis. Coupled with non-targeted analysis and toxicity Forecaster (ToxCast)/Tox21 database, 104 ToxCast chemicals were screened to be able to induce EROD response. The combination of targeted chemical analyses and biological effects evaluation indicated that PAHs, dibutyl phthalate (DBP) and Cypermethrin might be the important AhR-agonists in different indoor dust and mainly contributed in 1.84%-97.56 % (median: 26.62%) of total observed biological effects through comparing toxic equivalency quotient derived from chemical analysis with biological equivalences derived from bioassay. DBP and cypermethrin seldom reported in the analysis of AhR agonists should raise great concern. In addition, the present results in experiment of synthetic solution of 4 selected AhR-agonists pointed out that some unidentified AhR agonists existed in indoor dust.

Targeting the Aryl Hydrocarbon Receptor to Address the Challenges of Atopic Dermatitis.

Atopic dermatitis (AD) is a chronic relapsing–remitting disease with a multifactorial etiology involving epidermal barrier and immunologic dysfunction. Topical therapies form the mainstay of AD treatment, but options are limited by adverse effects and restrictions on application site, duration, and extent of use. Tapinarof (VTAMA; Dermavant Sciences, Inc.) is a first-in-class, non-steroidal, topical aryl hydrocarbon receptor (AhR) agonist approved for the treatment of plaque psoriasis. AhR is a ligand-dependent transcription factor with wide-ranging roles, including regulation of homeostasis and immune response in skin cells. AhR expression and signaling are altered in many inflammatory skin diseases, and clinical trials with tapinarof have validated AhR as a therapeutic target capable of delivering significant efficacy. Tapinarof cream 1% once daily demonstrated efficacy versus vehicle in adults and adolescents with AD and is being investigated in the ADORING trials for the treatment of AD in adults and children down to 2 years of age. J Drugs Dermatol. 2024;23(2):23-28.  doi:10.36849/JDD.8026.

Structural Insights into the Activation of Human Aryl Hydrocarbon Receptor by the Environmental Contaminant Benzo[a]pyrene and Structurally Related Compounds.

The aryl hydrocarbon receptor (AHR) is a ligand-dependent transcription factor belonging to the bHLH/PAS protein family and responding to hundreds of natural and chemical substances. It is primarily involved in the defense against chemical insults and bacterial infections or in the adaptive immune response, but also in the development of pathological conditions ranging from inflammatory to neoplastic disorders. Despite its prominent roles in many (patho)physiological processes, the lack of high-resolution structural data has precluded for thirty years an in-depth understanding of the structural mechanisms underlying ligand-binding specificity, promiscuity and activation of AHR. We recently reported a cryogenic electron microscopy (cryo-EM) structure of human AHR bound to the natural ligand indirubin, the chaperone Hsp90 and the co-chaperone XAP2 that provided the first experimental visualization of its ligand-binding PAS-B domain. Here, we report a 2.75 Å resolution structure of the AHR complex bound to the environmental pollutant benzo[a]pyrene (B[a]P). The structure substantiates the existence of a bipartite PAS-B ligand-binding pocket with a geometrically constrained primary binding site controlling ligand binding specificity and affinity, and a secondary binding site contributing to the binding promiscuity of AHR. We also report a docking study of B[a]P congeners that validates the B[a]P-bound PAS-B structure as a suitable model for accurate computational ligand binding assessment. Finally, comparison of our agonist-bound complex with the recently reported structures of mouse and fruit fly AHR PAS-B in different activation states suggests a ligand-induced loop conformational change potentially involved in the regulation of AHR function.

Tapinarof cream 1% once daily for the treatment of adults with mild to severe plaque psoriasis: A novel topical therapy targeting the aryl hydrocarbon receptor.

Plaque psoriasis is a chronic, immunemediated skin disease characterized by scaly, erythematous, pruritic plaques. The effects of psoriasis are often debilitating and stigmatizing, significantly impacting patients' physical and psychological well-being and quality of life. Current guideline-recommended psoriasis therapies (topicals, oral systemics, and biologics) have substantial limitations that include overall efficacy, safety, tolerability, sites of application, disease severity, and duration and extent of body surface area treated. Due to these limitations, psoriasis treatment regimens often require combination therapy, especially for moderate to severe disease, leading to increased treatment burden. Psoriasis is also associated with increased indirect costs (eg, reduced work productivity), leading to greater total costs expenditures. Thus, more effective, safe, well-tolerated, and cost-effective therapeutic options are needed. Tapinarof cream 1% once daily is a first-in-class, nonsteroidal, topical aryl hydrocarbon receptor agonist approved by the US Food and Drug Administration in 2022 for the treatment of plaque psoriasis in adults. Tapinarof cream has been evaluated in plaque psoriasis, including 2 pivotal phase 3 trials (NCT03956355 and NCT03983980) and a long-term extension trial (NCT04053387). These trials demonstrated high rates of complete skin clearance with tapinarof cream, durable effects while on treatment (a lack of tachyphylaxis for up to 52 weeks), an approximately 4-month remittive effect off therapy after achieving complete clearance and stopping treatment (ie, duration during which psoriasis does not recur off therapy), and no rebound effects after cessation of therapy. According to the US Food and Drug Administration-approved prescribing information, tapinarof may be used to treat plaque psoriasis of any severity and in any location, has no restrictions on duration of use or extent of total body surface area treated, and has no contraindications, warnings, precautions, or drug-drug interactions. Tapinarof cream is thus an efficacious, well-tolerated, steroid-free topical option that addresses many of the limitations of current recommended therapies. Here we review current knowledge on the physical, psychological, and financial burdens of plaque psoriasis and identify how the clinical profile of tapinarof cream can address key treatment gaps important in the management of plaque psoriasis and patient quality of life. In this article, we aim to assist pharmacists and other managed care practitioners by providing an evidence-based overview of tapinarof cream to support patient-centric decision-making.

Activation of AHR by ITE improves cardiac remodelling and function in rats after myocardial infarction.

AIMS: Left ventricular remodelling subsequent to myocardial infarction (MI) constitutes a pivotal underlying cause of heart failure. Intervention with the nontoxic endogenous aryl hydrocarbon receptor (AHR) agonist 2-(1'H-indole-3'-carbonyl)-thiazole-4-carboxylic acid methyl ester (ITE) in the acute phase of MI has been shown to ameliorate cardiac function, but its role in the chronic phase remains obscured. This study explores the beneficial role of ITE in delaying the progression of heart failure in the chronic phase of MI. METHODS AND RESULTS: MI rats established by ligating the left anterior descending coronary artery were treated with the indicated concentration of the AHR agonist ITE or vehicle alone. Echocardiography was performed to determine cardiac structure and function; myocardial morphology and fibrosis were observed by haematoxylin and eosin and Masson's trichrome staining; serum biochemical indices, BNP, and inflammatory cytokine levels were detected by enzyme-linked immunosorbent assay; F4/80+ iNOS+ M1 macrophages and F4/80+ CD206+ M2 macrophages were detected by immunofluorescence; the terminal deoxynucleotidyl transferase-mediated dUTP nick end labelling assay was used to detect the apoptosis of cardiomyocytes; ultrastructural changes in myocardial tissue were observed by transmission electron microscopy; and Cyp1a1, Akt, P-Akt, p70S6K, P-p70S6K, Bcl-2, Bax, caspase-3, and cleaved caspase-3 protein levels were determined via Western blotting. We found that therapy with the AHR agonist ITE rescued cardiac remodelling and dysfunction in rats with MI and attenuated myocardial fibrosis, inflammation, and mitochondrial damage. Further studies confirmed that ITE dose-dependently improved myocardial cell apoptosis after MI, as demonstrated by reduced levels of the apoptosis-related proteins cleaved caspase-3 and Bax but increased expression levels of Bcl-2. These effects were attributed to ITE-induced activation of AHR receptors, leading to the down-regulation of Akt and p70S6K phosphorylation. CONCLUSIONS: The AHR agonist ITE alleviates cardiomyocyte apoptosis through the Akt/p70S6K signalling pathway, thereby rescuing left ventricular adverse remodelling and cardiac dysfunction after MI.

3, 3'-diindolylmethane, a natural aryl hydrocarbon receptor agonist, alleviates ulcerative colitis by enhancing "glycolysis-lactate-STAT3″ and TIP60 signals-mediated Treg differentiation.

BACKGROUND: Aryl hydrocarbon receptor (AhR) plays an important role in the occurrence and development of ulcerative colitis (UC). In this study, the effect and mechanism of 3, 3'-diindolylmethane (DIM), the classical AhR agonist, on UC was investigated from the angle of recovering the balance of Th17/Treg. METHODS: The in vivo colitis model was established in mice by using dextran sulfate sodium, and CD4+ T cells were used to simulate the in vitro differentiation of Treg and Th17 cells. The proportions and related factors of Th17 and Treg cells were measured using flow cytometry, Q-PCR and western blotting. The glycolysis was evaluated by examining the glucose uptake, glucose consumption and lactate production using kits or immunofluorescence. The activation of AhR was detected by western blotting and the XRE-luciferase reporter gene. The co-immunoprecipitation, transfection or other methods were selected to investigate and identify the signaling molecular pathway. RESULTS: DIM significantly attenuated symptoms of colitis mice by rebuilding the balance of Th17/Treg in anoxic colons. In hypoxia, a more potent promotion of Treg differentiation was showed by DIM relative to normoxia, and siFoxp3 prevented DIM-suppressed Th17 differentiation. DIM repressed the excessive glycolysis in hypoxia evidenced by down-regulated glucose uptake, lactate production, Glut1 and HK2 levels. Interestingly, IL-10, the function-related factor of Treg cells, showed the feedback effect of DIM-suppressed glycolysis. Besides, 2-deoxy-D-glucose, HK2 plasmid and IL-10 antibody prevented increase of DIM on the expression of Foxp3 at the transcriptional level and subsequent Treg differentiation through the lactate-STAT3 pathway, and reasons for the direct improvement of DIM on Foxp3 protein was attributed to promoting the formation of HIF-1α/TIP60 complexes as well as subsequent acetylation and protein stability. Finally, AhR dependence and mechanisms for DIM-improved Treg differentiation in vitro and in vivo were well confirmed by using plasmids or inhibitors. CONCLUSIONS: DIM enhances activation of AhR and subsequent "glycolysis-lactate-STAT3″ and TIP60 signals-mediated Treg differentiation.

Role of ERK1/2 Signaling in Cinnabarinic Acid-Driven Stanniocalcin 2-Mediated Protection against Alcohol-Induced Apoptosis.

We have previously shown that a bona fide aryl hydrocarbon receptor (AhR) agonist, cinnabarinic acid (CA), protects against alcohol-induced hepatocyte apoptosis via activation of a novel AhR target gene, stanniocalcin 2 (Stc2). Stc2 translates to a secreted disulfide-linked hormone, STC2, known to function in cell development, calcium and phosphate regulation, angiogenesis, and antiapoptosis-albeit the comprehensive mechanism by which the CA-AhR-STC2 axis confers antiapoptosis is yet to be characterized. In this study, using RNA interference library screening, downstream antiapoptotic molecular signaling components involved in CA-induced STC2-mediated protection against ethanol-induced apoptosis were investigated. RNA interference library screening of kinases and phosphatases in Hepa1 cells and subsequent pathway analysis identified mitogen-activated protein kinase (MAPK) signaling as a critical molecular pathway involved in CA-mediated protection. Specifically, phosphorylation of ERK1/2 was induced in response to CA treatment without alterations in p38 and JNK signaling pathways. Silencing Stc2 in Hepa1 cells and in vivo experiments performed in Stc2-/- (Stc2 knockout) mice, which failed to confer CA-mediated protection against ethanol-induced apoptosis, showed abrogation of ERK1/2 activation, underlining the significance of ERK1/2 signaling in CA-STC2-mediated protection. In conclusion, activation of ERK1/2 signaling in CA-driven AhR-dependent Stc2-mediated protection represents a novel mechanism of protection against acute alcohol-induced apoptosis. SIGNIFICANCE STATEMENT: Previous studies have shown the role of stanniocalcin 2 (Stc2) in cinnabarinic acid (CA)-mediated protection against alcohol-induced apoptosis. Here, using RNA interference library screening and subsequent in vivo studies, the functional significance of ERK1/2 activation in CA-induced Stc2-mediated protection against acute ethanol-induced apoptosis was identified. This study is thus significant as it illustrates a comprehensive downstream mechanism by which CA-induced Stc2 protects against alcoholic liver disease.

Tapinarof, a Novel, First-in-Class, Topical Therapeutic Aryl Hydrocarbon Receptor Agonist for the Management of Psoriasis.

Topical treatments remain the foundation of psoriasis management. Tapinarof (VTAMA®; Dermavant Sciences, Inc.) is a first-in-class, non-steroidal, topical, aryl hydrocarbon receptor (AhR) agonist approved by the US Food and Drug Administration for the treatment of plaque psoriasis in adults and is under investigation for the treatment of psoriasis in children, and atopic dermatitis in adults and children down to 2 years old. Here, we review the mechanism of action of tapinarof and the PSOARING phase 3 trial program in mild to severe psoriasis. AhR is a ligand-dependent transcription factor involved in maintaining skin homeostasis. Tapinarof specifically binds to AhR to decrease proinflammatory cytokines, decrease oxidative stress, and promote skin barrier normalization. In two identical, randomized, 12-week pivotal phase 3 trials, PSOARING 1 and 2, tapinarof cream 1% once daily (QD) demonstrated significant efficacy versus vehicle and was well tolerated in adults with mild to severe psoriasis. In the PSOARING 3 long-term extension trial of repeated, intermittent tapinarof cream in eligible patients completing the pivotal trials, a high rate of complete disease clearance (40.9%) and a remittive effect of approximately 4 months off therapy were demonstrated over 52 weeks, with no tachyphylaxis. The most common adverse event, folliculitis, was mostly mild or moderate and resulted in a low trial discontinuation rate in PSOARING 1 and 2 (≤1.8%). Tapinarof cream 1% QD provides a novel, non-steroidal, topical treatment option for patients with psoriasis and is highly effective and well tolerated with long-term use including when applied to sensitive and intertriginous skin. Bobonich M, Gorelick J, Aldredge L, et al. Tapinarof, a novel, first-in-class, topical therapeutic aryl hydrocarbon receptor agonist for the management of psoriasis. J Drugs Dermatol. 2023;22(8):779-784. doi:10.36849/JDD.7317.

Discovery of 5-((1H-indazol-3-yl) methylene)-2-thioxoimidazolidin-4-one derivatives as a new class of AHR agonists with anti-psoriasis activity in a mouse model.

Aryl hydrocarbon receptor (AHR) is a ligand dependent transcription factor and participates in the regulation of the immune balance of Th17/22 and Treg cells. It has been found to be widely expressed in the skin, and involved in the pathology of psoriasis. Therefore, AHR is thought as a potential intervention target for psoriasis. Here, we report the discovery of 5-((1H-indazol-3-yl) methylene)-2-thioxoimidazolidin-4-one derivatives as a new class of AHR agonists. Structure-activity relationship analyses led to the identification of the most active compound, 5- ((1H-indazol-3-yl)methylene) -3- (prop-2-yn-1-yl) -2-thiooimidazolidin-4-one (24e), which exhibited an EC50 value of 0.015 µM against AHR. Mechanism of action studies showed that 24e regulated the expression of CYP1A1 by activating the AHR pathway. Topical administration of 24e substantially alleviated imiquimod (IMQ)-induced psoriasis-like skin lesion. Overall, compound 24e could be a good lead compound for drug discovery against psoriasis, and hence deserving further in-depth studies.

AhR agonist tapinarof ameliorates lupus autoimmunity by suppressing Tfh cell differentiation via regulation of the JAK2-STAT3 signaling pathway.

BACKGROUND: The aryl hydrocarbon receptor (AhR) is a critical regulator of the pathogenesis of autoimmune disorders. We aimed to investigate the therapeutic effect of the AhR agonist tapinarof during the development of systemic lupus erythematosus (SLE). METHODS: MRL/lpr mice were intraperitoneally injected with 1 or 5 mg/kg tapinarof for 6 weeks. Kidney histopathology was evaluated using hematoxylin and eosin (H&E) and Periodic-Acid-Schiff (PAS) staining. Immunofluorescence microscopy was performed to detect immune complex renal depositions. Flow cytometry (FCM) analysis was carried out to determine the proportions of T and B cell subsets. Realtime qPCR was used to quantify the expression of Tfh cell-associated genes. We conducted an in vitro polarization experiment to observe the effect of tapinarof on Tfh differentiation. Western blotting was used to detect the expression of target proteins. RESULTS: We found that tapinarof treatment ameliorated lupus phenotypes, including splenomegaly, lymph node enlargement, kidney damages, immune complex deposition, and excessive secretion of antibodies. Additionally, we showed that Treg subpopulation frequencies significantly increased in MRL/lpr mice treated with tapinarof, while the proportion of Th1/Th2 cells was reduced after tapinarof administration. Moreover, tapinarof suppressed Tfh cell differentiation and germinal center (GC) reaction in vivo. The inhibitory effect of tapinarof on Tfh cells was further verified in the in vitro Tfh cell polarization experiment. Realtime qPCR revealed that tapinarof repressed the expression of Tfh signature genes. Mechanistically, tapinarof significantly inhibited the phosphorylation levels of JAK2 and STAT3. The capacity for Tfh differentiation was partially rescued by the STAT3 activator Colivelin TFA. Furthermore, our in vitro Tfh polarization experiments indicated that tapinarof suppressed Tfh cell development in SLE. CONCLUSIONS: Our data demonstrated that tapinarof modulated the JAK2-STAT3 pathway to suppress Tfh cell differentiation for the treatment of lupus symptoms in MRL/lpr mice.

Homeostatic activation of aryl hydrocarbon receptor by dietary ligands dampens cutaneous allergic responses by controlling Langerhans cells migration.

Dietary compounds can affect the development of inflammatory responses at distant sites. However, the mechanisms involved remain incompletely understood. Here, we addressed the influence on allergic responses of dietary agonists of aryl hydrocarbon receptor (AhR). In cutaneous papain-induced allergy, we found that lack of dietary AhR ligands exacerbates allergic responses. This phenomenon was tissue-specific as airway allergy was unaffected by the diet. In addition, lack of dietary AhR ligands worsened asthma-like allergy in a model of 'atopic march.' Mice deprived of dietary AhR ligands displayed impaired Langerhans cell migration, leading to exaggerated T cell responses. Mechanistically, dietary AhR ligands regulated the inflammatory profile of epidermal cells, without affecting barrier function. In particular, we evidenced TGF-ß hyperproduction in the skin of mice deprived of dietary AhR ligands, explaining Langerhans cell retention. Our work identifies an essential role for homeostatic activation of AhR by dietary ligands in the dampening of cutaneous allergic responses and uncovers the importance of the gut-skin axis in the development of allergic diseases.

Identification of Methylsulochrin as a Partial Agonist for Aryl Hydrocarbon Receptors and Its Antiviral and Anti-inflammatory Activities.

Although aryl hydrocarbon receptors (AhRs) are related to the metabolic pathway of xenobiotics, recent studies have revealed that this receptor is also associated with the life cycle of viruses and inflammatory reactions. For example, flutamide, used to treat prostate cancer, inhibits hepatitis C virus proliferation by acting as an AhR antagonist, and methylated-pelargonidin, an AhR agonist, suppresses pro-inflammatory cytokine production. To discover a novel class of AhR ligands, we screened 1000 compounds derived from fungal metabolites using a reporter assay and identified methylsulochrin as a partial agonist of the aryl hydrocarbon receptor. Methylsulochrin was found to inhibit the production of hepatitis C virus (HCV) in Huh-7.5.1 cells. Methylsulochrin also suppressed the production of interleukin-6 in RAW264.7 cells. Furthermore, a preliminary structure-activity relationship study using sulochrin derivatives was performed. Our findings suggest the use of methylsulochrin derivatives as anti-HCV compounds with anti-inflammatory activity.

Dietary tryptophan metabolite released by intratumoral Lactobacillus reuteri facilitates immune checkpoint inhibitor treatment.

The use of probiotics by cancer patients is increasing, including among those undergoing immune checkpoint inhibitor (ICI) treatment. Here, we elucidate a critical microbial-host crosstalk between probiotic-released aryl hydrocarbon receptor (AhR) agonist indole-3-aldehyde (I3A) and CD8 T cells within the tumor microenvironment that potently enhances antitumor immunity and facilitates ICI in preclinical melanoma. Our study reveals that probiotic Lactobacillus reuteri (Lr) translocates to, colonizes, and persists within melanoma, where via its released dietary tryptophan catabolite I3A, it locally promotes interferon-γ-producing CD8 T cells, thereby bolstering ICI. Moreover, Lr-secreted I3A was both necessary and sufficient to drive antitumor immunity, and loss of AhR signaling within CD8 T cells abrogated Lr's antitumor effects. Further, a tryptophan-enriched diet potentiated both Lr- and ICI-induced antitumor immunity, dependent on CD8 T cell AhR signaling. Finally, we provide evidence for a potential role of I3A in promoting ICI efficacy and survival in advanced melanoma patients.

AhR activation promotes Treg cell generation by enhancing Lkb1-mediated fatty acid oxidation via the Skp2/K63-ubiquitination pathway.

Several aryl hydrocarbon receptor (AhR) agonists have been reported to promote the generation of regulatory T cells (Treg cells), and the action mechanisms need to be identified. In this study, we addressed the underlying mechanism of AhR activation to induce the generation of Treg cells in the view of cellular metabolism. Naïve CD4+ T cells were purified with mouse CD4+ CD62L+ T Cells Isolation Kits. The proportions of Treg cells were detected by flow cytometry. The value of oxygen consumption rate (OCR) of CD4+ T cells was detected by the Seahorse XFe 96 analyzer. The activation of fatty acid oxidation (FAO)-related metabolic pathways was detected by Western blotting. Intracellular localization of Lkb1 was detected by immunofluorescence. The Strad-Mo25-Lkb1 complex formation and K63 chain ubiquitination modification of Lkb1 were detected by co-immunoprecipitation. The binding of AhR to the Skp2 promoter was detected by constructing luciferase reporter gene. AhR or carnitine palmitoyltransferases 1 was knockdown in dextran sulphate sodium (DSS)-induced colitis or collagen-induced arthritis (CIA) mice by infecting mice with adeno-associated virus via the tail vein injection. Compared to the control group, exogenous and endogenous AhR agonists 3,3'-diindolylmethane (DIM) and 2-(1'H-indole-3'-carbonyl)-thiazole-4-carboxylic acid methyl ester (ITE) were shown to preferentially upregulate the mRNA expression of FAO-related enzymes and the value of OCR. Consistently, pharmacological or genetic inhibition of FAO markedly diminished the induction of DIM and ITE on the differentiation of Treg cells. DIM and ITE functioned mainly through activating the liver kinase B1 (Lkb1)-AMPK pathway via promotion of Lkb1-Strad-Mo25 complex formation and Lkb1 K63 ubiquitination. DIM and ITE were also shown to upregulate the mRNA expression of Skp2, a ubiquitination-related enzyme, and facilitate the binding of AhR to the xenobiotic responsive element of Skp2 promoter region by luciferase reporter gene assay. Furthermore, the contribution of Skp2/K63 ubiquitination/Lkb1/FAO axis was verified in (DSS)-induced colitis or CIA mice. In summary, these findings indicate that AhR activation promotes Treg cell generation by enhancing Lkb1-mediated FAO via the Skp2/K63-ubiquitination pathway, and AhR agonists may be used as inducers of Treg cells to prevent and treat autoimmune diseases.

Astrocytic aryl hydrocarbon receptor mediates chronic kidney disease-associated mental disorders involving GLT1 hypofunction and neuronal activity enhancement in the mouse brain.

Chronic kidney disease (CKD)-associated mental disorders have been attributed to the excessive accumulation of hemodialysis-resistant indoxyl-3-sulfate (I3S) in the brain. I3S not only induces oxidative stress but is also a potent endogenous agonist of the aryl hydrocarbon receptor (AhR). Here, we investigated the role of AhR in CKD-induced brain disorders using a 5/6 nephrectomy-induced CKD mouse model, which showed increased I3S concentration in both blood and brain, anxiety and impaired novelty recognition, and AhR activation in the anterior cortex. GFAP+ reactive astrocytes were increased accompanied with the reduction of glutamate transporter 1 (GLT1) on perineuronal astrocytic processes (PAPs) in the anterior cingulate cortex (ACC) in CKD mice, and these alterations were attenuated in both neural lineage-specific and astrocyte-specific Ahr conditional knockout mice (nAhrCKO and aAhrCKO). By using chronic I3S treatment in primary astrocytes and glia-neuron (GN) mix cultures to mimic the CKD brain microenvironment, we also found significant reduction of GLT1 expression and activity in an AhR-dependent manner. Chronic I3S treatment induced AhR-dependent pro-oxidant Nox1 and AhR-independent anti-oxidant HO-1 expressions. Notably, AhR mediates chronic I3S-induced neuronal activity enhancement and synaptotoxicity in GN mix, not neuron-enriched cortical culture. In CKD mice, neuronal activity enhancement was observed in ACC and hippocampal CA1, and these responses were abrogated by both nAhrCKO and aAhrCKO. Finally, intranasal AhR antagonist CH-223191 administration significantly ameliorated the GLT1/PAPs reduction, increase in c-Fos+ neurons, and memory impairment in the CKD mice. Thus, astrocytic AhR plays a crucial role in the CKD-induced disturbance of neuron-astrocyte interaction and mental disorders.

Activation of the kynurenine-aryl hydrocarbon receptor axis impairs the chondrogenic and chondroprotective effects of human umbilical cord-derived mesenchymal stromal cells in osteoarthritis rats.

It has been proven that intra-articular injection of mesenchymal stromal cells (MSCs) can alleviate cartilage damage in osteoarthritis (OA) by differentiating into chondrocytes and protecting inherent cartilage. However, the mechanism by which the OA articular microenvironment affects MSCs' therapeutic efficiency is yet to be fully elucidated. The aryl hydrocarbon receptor (AHR) is a ligand-activated transcription factor involved in various cellular processes, such as osteogenesis and immune regulation. Tryptophan (Trp) metabolites, most of which are endogenous ligand for AHR, are abnormally increased in synovial fluid (SF) of OA and rheumatoid arthritis (RA) patients. In this study, the effects of kynurenine (KYN), one of the most important metabolites of Trp, were evaluated on the chondrogenic and chondroprotective effects of human umbilical cord-derived mesenchymal stromal cells (hUC-MSCs). hUC-MSCs were cultured in conditioned medium containing different proportions of OA/RA SF, or stimulated with KYN directly, and then, AHR activation, proliferation, and chondrogenesis of hUC-MSCs were measured. Moreover, the chondroprotective efficiency of short hairpin-AHR-UC-MSC (shAHR-UC-MSC) was determined in a rat surgical OA model (right hind joint). OA SF could activate AHR signaling in hUC-MSCs in a concentration-dependent manner and inhibit the chondrogenic differentiation and proliferation ability of hUC-MSCs. Similar results were observed in hUC-MSCs stimulated with KYN in vitro. Notably, shAHR-UC-MSC exhibited superior therapeutic efficiency in OA rat upon intra-articular injection. Taken together, this study indicates that OA articular microenvironment is not conducive to the therapeutic effect of hUC-MSCs, which is related to the activation of the AHR pathway by tryptophan metabolites, and thus impairs the chondrogenic and chondroprotective effects of hUC-MSCs. AHR might be a promising modification target for further improving the therapeutic efficacy of hUC-MSCs on treatment of cartilage-related diseases such as OA.

Insights into the toxicities of UV-328, UV-329, UV-P in HepG2 cells and their roles in AHR-mediated pathway.

The widespread high concentrations of benzotriazole ultraviolet stabilizers (BUVSs) in many biotic and abiotic samples have raised urgent concerns of their adverse effects on environmental and human health. In this study, we investigated the toxicity of three typical BUVSs (UV-328, UV-329, UV-P) with HepG2 cells in vitro. Results indicated that the three BUVSs showed weak cytotoxicity in HepG2 cells at concentrations lower than 50 µM. Transcriptional analysis indicated that the toxic effects of the three chemicals followed the order of UV-P > UV-329 > UV-328. UV-P and UV-329 may act as potential environmental diabetogens by significantly enriching several diabetic related items in both GO and KEGG analysis. Moreover, UV-P and UV-329 significantly upregulated the expression of AHR target genes (CYP1A1, CYP1A2, UGT1A1, etc.), and increased the ethoxyresorufin-O-deethylase (EROD) activity and exhibited agonistic activity toward AHR in the XRE-mediated luciferase reporter gene assay. Molecular docking assay also indicated that UV-329 and UV-P had higher binding affinities to AHR-LBD than UV-328. In brief, our findings indicated that UV-P and UV-329 were potential agonist of AHR ligand, and may exert more toxicity than UV-328 in inducing liver toxicity.

Association between altered tryptophan metabolism, plasma aryl hydrocarbon receptor agonists, and inflammatory Chagas disease.

Introduction: Chagas disease causes a cardiac illness characterized by immunoinflammatory reactions leading to myocardial fibrosis and remodeling. The development of Chronic Chagas Cardiomyopathy (CCC) in some patients while others remain asymptomatic is not fully understood, but dysregulated inflammatory responses are implicated. The Aryl hydrocarbon receptor (AhR) plays a crucial role in regulating inflammation. Certain tryptophan (Trp) metabolites have been identified as AhR ligands with regulatory functions. Methods results and discussion: We investigated AhR expression, agonist response, ligand production, and AhR-dependent responses, such as IDO activation and regulatory T (Treg) cells induction, in two T. cruzi-infected mouse strains (B6 and Balb/c) showing different polymorphisms in AhR. Furthermore, we assessed the metabolic profile of Trp catabolites and AhR agonistic activity levels in plasma samples from patients with chronic Chagas disease (CCD) and healthy donors (HD) using a luciferase reporter assay and liquid chromatography-mass spectrophotometry (LC-MS) analysis. T. cruzi-infected B6 mice showed impaired AhR-dependent responses compared to Balb/c mice, including reduced IDO activity, kynurenine levels, Treg cell induction, CYP1A1 up-regulation, and AhR expression following agonist activation. Additionally, B6 mice exhibited no detectable AhR agonist activity in plasma and displayed lower CYP1A1 up-regulation and AhR expression upon agonist activation. Similarly, CCC patients had decreased AhR agonistic activity in plasma compared to HD patients and exhibited dysregulation in Trp metabolic pathways, resulting in altered plasma metabolite profiles. Notably, patients with severe CCC specifically showed increased N-acetylserotonin levels in their plasma. The methods and findings presented here contribute to a better understanding of CCC development mechanisms and may identify potential specific biomarkers for T. cruzi infection and the severity of associated heart disease. These insights could be valuable in designing new therapeutic strategies. Ultimately, this research aims to establish the AhR agonistic activity and Trp metabolic profile in plasma as an innovative, non-invasive predictor of prognosis for chronic Chagas disease.

Dermal Safety of Tapinarof Cream 1%: Results From 4 Phase 1 Trials.

BACKGROUND: Tapinarof (VTAMA®; Dermavant Sciences, Inc.) is a novel, non-steroidal, topical, aryl hydrocarbon receptor agonist, FDA approved for psoriasis treatment and under investigation for atopic dermatitis treatment as a 1% cream formulation for once-daily (QD) application. OBJECTIVE: Evaluate cumulative skin irritation, sensitization, and photoallergic and phototoxic potential of tapinarof cream 1% across a range of dosing frequencies and conditions. METHODS: We conducted 4 randomized, controlled, phase 1 trials of topical tapinarof cream 1% vs vehicle or other appropriate controls in healthy adults. Cumulative skin irritation was assessed following QD application for 21 days under fully occlusive patch conditions. Contact sensitization, photoallergenicity, and phototoxicity were assessed under semi-occlusive patch conditions. The contact sensitization and photoallergenicity trials used an induction phase of repeated applications followed by a 2-week rest period and a 1-time challenge, with rechallenge if responses indicated sensitization/photosensitization; the phototoxicity trial comprised a single application. Ultraviolet A and B irradiation was used to assess photoallergenicity/toxicity. RESULTS: 376 participants were randomized across the 4 trials. In the cumulative irritation trial, tapinarof cream 1% QD was classified as having a slight potential for very mild cumulative irritation under the exaggerated test conditions of repeated dosing for 21 days. There was no evidence of sensitization, photosensitization, or phototoxicity. Tapinarof was well tolerated and there was a low discontinuation rate across all trials. CONCLUSIONS: Tapinarof cream 1% was well tolerated, non-sensitizing, non-phototoxic, and non-photoallergic, with no evidence of clinically meaningful cumulative skin irritation in 4 dermal safety trials in healthy adults. TRIAL REGISTRATION: IND 104601 J Drugs Dermatol. 2022;21(10):1084-1090. doi:10.36849/JDD.6627R1.

Carbidopa suppresses estrogen receptor-positive breast cancer via AhR-mediated proteasomal degradation of ERα.

Estrogen receptor-α (ERα) promotes breast cancer, and ER-positive cancer accounts for ~ 80% of breast cancers. This subtype responds positively to hormone/endocrine therapies involving either inhibition of estrogen synthesis or blockade of estrogen action. Carbidopa, a drug used to potentiate the therapeutic efficacy of L-DOPA in Parkinson's disease, is an agonist for aryl hydrocarbon receptor (AhR). Pharmacotherapy in Parkinson's disease decreases the risk for cancers, including breast cancer. The effects of carbidopa on ER-positive breast cancer were evaluated in cell culture and in mouse xenografts. The assays included cell proliferation, apoptosis, cell migration/invasion, subcellular localization of AhR, proteasomal degradation, and tumor growth in xenografts. Carbidopa decreased proliferation and migration of ER-positive human breast cancer cells in vitro with no significant effect on ER-negative breast cancer cells. Treatment of ER-positive cells with carbidopa promoted nuclear localization of AhR and expression of AhR target genes; it also decreased cellular levels of ERα via proteasomal degradation in an AhR-dependent manner. In vivo, carbidopa suppressed the growth of ER-positive breast cancer cells in mouse xenografts; this was associated with increased apoptosis and decreased cell proliferation. Carbidopa has therapeutic potential for ER-positive breast cancer either as a single agent or in combination with other standard chemotherapies.