Background and aim Type 1 diabetes is an autoimmune disorder characterized by the destruction of pancreatic beta cells, leading to insulin deficiency and hyperglycemia. Regulatory T cells (Tregs), particularly type 1 regulatory T (Tr1) cells, play a crucial role in modulating autoimmune responses. Therefore, this study aimed to evaluate the frequency of Tr1 cells and their association with aryl hydrocarbon receptor (AHR) and interferon regulatory factor-4 (IRF4) gene expression levels in type 1 diabetes mellitus (T1DM) compared to the healthy controls. Method A case-control study design was used. The case group included patients diagnosed with T1DM, while the control group consisted of healthy individuals, matched for age and sex. Blood samples were collected, and peripheral blood mononuclear cells (PBMCs) were isolated. Serum interleukin 10 (IL-10) and interleukin 21 (IL-21) levels were measured using enzyme-linked immunosorbent assay (ELISA). The gene expression of AHR and IRF4 was analyzed using quantitative real-time polymerase chain reaction (qPCR), and Tr1 cell populations were determined using flow cytometry. Data were summarized with mean and standard error of the mean (SEM) for quantitative variables. Independent sample t-test, chi-square test, and the Mann-Whitney U test were used to compare groups. Statistical analyses were performed using SPSS version 25 (IBM SPSS Statistics, Armonk, NY), with significance levels set at p < 0.05. Figures were created using GraphPad Prism (GraphPad Software, San Diego, CA). Results A total of 45 cases were enrolled in the study, with 30 T1DM patients and 15 healthy controls. The mean IL-10 concentration was significantly higher in the patients (10.4 ± 1.1 pg/mL) compared to the healthy controls (5.1 ± 0.7 pg/mL), with a p-value of 0.001. There was no significant difference in IL-21 levels between the patients (76.1 ± 9.0 pg/mL) and healthy controls (88.2 ± 17.5 pg/mL), indicated by a p-value of 0.480. AHR gene expression was significantly lower in patients, with a p-value of 0.037. Although IRF4 gene expression was higher in patients, the difference was not statistically significant (p = 0.449). Tr1 cell frequency was significantly higher in T1DM patients (1.45% of cluster of differentiation 4+ {CD4+} T cells) compared to the healthy controls (0.40% of CD4+ T cells), with a p-value of 0.045. Conclusions The study demonstrated that T1DM is associated with higher IL-10 levels, decreased AHR gene expression, and a higher frequency of Tr1 cells. Policymakers should focus on developing targeted immunomodulatory therapies to address these immunological abnormalities. Healthcare providers should prioritize monitoring cytokine levels and gene expression in T1DM patients to tailor treatment plans effectively. Further research is needed to explore the therapeutic potential of modulating Tr1 cells and their related pathways in T1DM management.

The vast majority of gastric cancer (GC) cases are adenocarcinomas including intestinal and diffuse GC. The incidence of diffuse GC, often associated with poor overall survival, has constantly increased in Western countries. Epidemiological studies have reported increased mortality from GC after occupational exposure to pro-carcinogens that are metabolically activated by cytochrome P450 enzymes through aryl hydrocarbon receptor (AhR). However, little is known about the role of AhR and environmental AhR ligands in diffuse GC as compared to intestinal GC in Western patients. In a cohort of 29, we demonstrated a significant increase in AhR protein and mRNA expression levels in GCs independently of their subtypes and clinical parameters. AhR and RHOA mRNA expression were correlated in diffuse GC. Further, our study aimed to characterize in GC how AhR and the AhR-related genes cytochrome P450 1A1 (CYP1A1) and P450 1B1 (CYP1B1) affect the mRNA expression of a panel of genes involved in cancer development and progression. In diffuse GC, CYP1A1 expression correlated with genes involved in IGF signaling, epithelial-mesenchymal transition (Vimentin), and migration (MMP2). Using the poorly differentiated KATO III epithelial cell line, two well-known AhR pollutant ligands, namely 2-3-7-8 tetrachlorodibenzo-p-dioxin (TCDD) and benzo[a]pyrene (BaP), strongly increased the expression of CYP1A1 and Interleukin1β (IL1B), and to a lesser extend UGT1, NQO1, and AhR Repressor (AhRR). Moreover, the increased expression of CYP1B1 was seen in diffuse GC, and IHC staining indicated that CYP1B1 is mainly expressed in stromal cells. TCDD treatment increased CYP1B1 expression in KATO III cells, although at lower levels as compared to CYP1A1. In intestinal GC, CYP1B1 expression is inversely correlated with several cancer-related genes such as IDO1, a gene involved in the early steps of tryptophan metabolism that contributes to the endogenous AhR ligand kynurenine expression. Altogether, our data provide evidence for a major role of AhR in GC, as an environmental xenobiotic receptor, through different mechanisms and pathways in diffuse and intestinal GC. Our results support the continued efforts to clarify the identity of exogenous AhR ligands in diffuse GC in order to define new therapeutic strategies.

2,3,7,8-Tetrachlorodibenzo-p-dioxin (TCDD) is a persistent environmental contaminant that disrupts hepatic function leading to steatotic liver disease (SLD)-like pathologies, such as steatosis, steatohepatitis, and fibrosis. These effects are mediated by the aryl hydrocarbon receptor following changes in gene expression. Although diverse cell types are involved, initial cell-specific changes in gene expression have not been reported. In this study, differential gene expression in hepatic cell types was examined in male C57BL/6 mice gavaged with 30 µg/kg of TCDD using single-nuclei RNA-sequencing. Ten liver cell types were identified with the proportions of most cell types remaining unchanged, except for neutrophils which increased at 72 h. Gene expression suggests TCDD induced genes related to oxidative stress in hepatocytes as early as 2 h. Lipid homeostasis was disrupted in hepatocytes, macrophages, B cells, and T cells, characterized by the induction of genes associated with lipid transport, steroid hormone biosynthesis, and the suppression of β-oxidation, while linoleic acid metabolism was altered in hepatic stellate cells (HSCs), B cells, portal fibroblasts, and plasmacytoid dendritic cells. Pro-fibrogenic processes were also enriched, including the induction retinol metabolism genes in HSCs and the early induction of anti-fibrolysis genes in hepatocytes, endothelial cells, HSCs, and macrophages. Hepatocytes also had gene expression changes consistent with hepatocellular carcinoma. Collectively, these findings underscore the effects of TCDD in initiating SLD-like phenotypes and identified cell-specific gene expression changes related to oxidative stress, steatosis, fibrosis, cell proliferation and the development of HCC.

OBJECTIVE: In this in vitro study, we investigated the effects of polychlorinated biphenyls (PCBs) on human thyrocytes, with a focus on the involvement of AhR, a key player in xenobiotic response, and the anti-oxidant Nrf-2/HO-1 pathway.
METHODS: Primary cultured thyrocytes were exposed to the dioxin-like congeners PCB118 and PCB126 at 2.5 and 5 µM concentrations. mRNA expression was assessed by real-time PCR, and protein expression by Western Blot and ELISA, while protein quantification was assessed by densitometric analysis.
RESULTS: In cultured thyrocytes, PCB118 and PCB126 induced a significant (P < 0.01) increase of mRNA and protein levels of the pro-inflammatory cytokines IL-1beta and IL-6, while reducing those of thyroglobulin (TG) and NIS (p < 0.05), indicating down-regulation of these thyroid-specific genes in PCB-induced inflammation. ROS production also increased (p < 0.001). mRNA levels of AhR and the downstream molecules cytochrome P4501A, Nrf-2/HO-1 increased (p < 0.001), as well as related protein levels (p < 0.01), suggesting the activation of AhR and Nrf-2 pathways in response to PCBs exposure. AhR silencing decreased AhR-related gene expression and restored NIS and TG expression, while reducing inflammatory cytokines and oxidative stress markers (p < 0.05).
CONCLUSIONS: Dioxin-like PCBs (PCB118 and PCB126) may promote inflammation and oxidative stress in thyrocytes, impairing the expression of genes that are key players of thyroid function. These effects can be partially attributed to the activation of the AhR and Nrf-2 pathways. These data may contribute to explain the mechanisms underlying thyroid toxicity of PCBs, highlighting the potential role of these pollutants as a trigger of autoimmune thyroid inflammation and damage.

METHODS: Chalcones are widely present in most plants and have various health beneficial functions. This study investigates the suppressive effect of 13 natural and synthetic chalcones on transformation of aryl hydrocarbon receptor (AhR) induced by 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) and 3-methylcholanthrene (3-MC) in a cell-free system, Hepa-1c1c7 cells, and liver of ICR mice.
RESULTS: In the cell-free system, cardamonin dose-dependently inhibits AhR transformation. Chalcones with substitution on 2\' and/or 6\' position is important for the suppressive effect, while the substitution on 4\' position is negatively for the effect. Moreover, cardamonin and 2\'-hydroxychalcone competitively inhibit the binding of [3H]-3-MC to the AhR. In Hepa-1c1c7 cells, cardamonin inhibits AhR transformation and expression of cytochrome P4501A1 (CYP1A1) in a dose-dependent manner through suppressing TCDD-induced phosphorylation of both AhR and AhR nuclear translocator, heterodimerization of them, and nuclear translocation of AhR. In the liver of mice, oral administered cardamonin also inhibits 3-MC-induced AhR translocation and expression of CYP1A1.
CONCLUSIONS: Among used chalcones, a natural chalcone cardamonin competitively binds to AhR and suppresses its transformation. Thus, cardamonin is an effective food factor for suppression of the dioxin-caused biochemical alterations and toxicities.

Microbial tryptophan (Trp) metabolites acting as aryl hydrocarbon receptor (AhR) ligands are shown to effectively improve metabolic diseases via regulating microbial community. However, the underlying mechanisms by which Trp metabolites ameliorate bone loss via gut-bone crosstalk are largely unknown. In this study, supplementation with Trp metabolites, indole acetic acid (IAA), and indole-3-propionic acid (IPA), markedly ameliorate bone loss by repairing intestinal barrier integrity in ovariectomy (OVX)-induced postmenopausal osteoporosis mice in an AhR-dependent manner. Mechanistically, intestinal AhR activation by Trp metabolites, especially IAA, effectively repairs intestinal barrier function by stimulating Wnt/β-catenin signaling pathway. Consequently, enhanced M2 macrophage by supplementation with IAA and IPA secrete large amount of IL-10 that expands from intestinal lamina propria to bone marrow, thereby simultaneously promoting osteoblastogenesis and inhibiting osteoclastogenesis in vivo and in vitro. Interestingly, supplementation with Trp metabolites exhibit negligible ameliorative effects on both gut homeostasis and bone loss of OVX mice with intestinal AhR knockout (VillinCreAhrfl/fl). These findings suggest that microbial Trp metabolites may be potential therapeutic candidates against osteoporosis via regulating AhR-mediated gut-bone axis.

Aryl Hydrocarbon Receptor (AHR) ligands, upon binding, induce distinct gene expression profiles orchestrated by the AHR, leading to a spectrum of pro- or anti-inflammatory effects. In this study, we designed, synthesized and evaluated three indole-containing potential AHR ligands (FluoAHRL: AGT-4, AGT-5 and AGT-6). All synthesized compounds were shown to emit fluorescence in the near-infrared. Their AHR agonist activity was first predicted using in silico docking studies, and then confirmed using AHR luciferase reporter cell lines. FluoAHRLs were tested in vitro using mouse peritoneal macrophages and T lymphocytes to assess their immunomodulatory properties. We then focused on AGT-5, as it illustrated the predominant anti-inflammatory effects. Notably, AGT-5 demonstrated the ability to foster anti-inflammatory regulatory T cells (Treg) while suppressing pro-inflammatory T helper (Th)17 cells in vitro. AGT-5 actively induced Treg differentiation from naïve CD4+ cells, and promoted Treg proliferation, cytotoxic T-lymphocyte-associated antigen 4 (CTLA-4) expression and interleukin-10 (IL-10) production. The increase in IL-10 correlated with an upregulation of Signal Transducer and Activator of Transcription 3 (STAT3) expression. Importantly, the Treg-inducing effect of AGT-5 was also observed in human tonsil cells in vitro. AGT-5 showed no toxicity when applied to zebrafish embryos and was therefore considered safe for animal studies. Following oral administration to C57BL/6 mice, AGT-5 significantly upregulated Treg while downregulating pro-inflammatory Th1 cells in the mesenteric lymph nodes. Due to its fluorescent properties, AGT-5 could be visualized both in vitro (during uptake by macrophages) and ex vivo (within the lamina propria of the small intestine). These findings make AGT-5 a promising candidate for further exploration in the treatment of inflammatory and autoimmune diseases.

Although our skin is not the primary visual organ in humans, it acts as a light sensor, playing a significant role in maintaining our health and overall well-being. Thanks to the presence of a complex and sophisticated optotransduction system, the skin interacts with the visible part of the electromagnetic spectrum and with ultraviolet (UV) radiation. Following a brief overview describing the main photosensitive molecules that detect specific electromagnetic radiation and their associated cell pathways, we analyze their impact on physiological functions such as melanogenesis, immune response, circadian rhythms, and mood regulation. In this paper, we focus on 6-formylindolo[3,2-b]carbazole (FICZ), a photo oxidation derivative of the essential amino acid tryptophan (Trp). This molecule is the best endogenous agonist of the Aryl hydrocarbon Receptor (AhR), an evolutionarily conserved transcription factor, traditionally recognized as a signal transducer of both exogenous and endogenous chemical signals. Increasing evidence indicates that AhR is also involved in light sensing within the skin, primarily due to its ligand FICZ, which acts as both a chromophore and a photosensitizer. The biochemical reactions triggered by their interaction impact diverse functions and convey crucial data to our body, thus adding a piece to the complex puzzle of pathways that allow us to decode and elaborate environmental stimuli.

The etiology of major depressive disorder (MDD) remains poorly understood. Our previous studies suggest a role for the aryl hydrocarbon receptor (AhR) in depression. 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) is a toxic environmental contaminant, with a high AhR binding affinity, and an established benchmark for assessing AhR activity. Therefore, this study examined the effect of TCDD on depression-like behaviors. Female mice were fed standard chow or a high-fat diet (HFD) for 11 weeks, and their weight was recorded. Subsequently, they were tested for baseline sucrose preference and splash test grooming. Then, TCDD (0.1 µg/kg/day) or vehicle was administered orally for 28 days, and mice were examined for their sucrose preference and performances in the splash test, forced swim test (FST), and Morris water maze (MWM) task. TCDD significantly decreased sucrose preference, increased FST immobility time, and decreased groom time in chow-fed mice. HFD itself significantly reduced sucrose preference. However, TCDD significantly increased FST immobility time and decreased groom time in HFD-fed mice. A small decrease in bodyweight was observed only at the fourth week of daily TCDD administration in chow-fed mice, and no significant effects of TCDD on bodyweights were observed in HFD-fed mice. TCDD did not have a significant effect on spatial learning in the MWM. Thus, this study demonstrated that TCDD induces a depression-like state, and the effects were not due to gross lethal toxicity. This study further suggests that more studies should examine a possible role for AhR and AhR-active environmental pollutants in precipitating or worsening MDD.

Massive evidence shows that intestinal tryptophan metabolites affected by intestinal flora can modulate the progression of rheumatoid arthritis (RA). However, the effects and mechanisms of intestinal tryptophan metabolites on RA are not yet detailed. Herein, we investigated the protective effects of intestinal tryptophan metabolites on RA and its detailed mechanisms. In this study, the collagen-induced arthritis (CIA) rat model was established. Based on metabolomics analysis, the contents of β-indole-3-acetic acid (IAA), indolylpropionic acid, and indole-3-β-acrylic acid in the sera of CIA rats were significantly less compared with those of the normal rats. Under the condition of Treg or Th17 cell differentiation, IAA significantly promoted the differentiation and activation of Treg cells instead of Th17 cells. Intestinal tryptophan metabolites are well-known endogenic ligands of aryl hydrocarbon receptor (AhR). Not surprisingly, IAA increased the level of Foxp3 through activating the AhR pathway. Interestingly, IAA had little impact on the level of Foxp3 mRNA, but reducing the ubiquitination and degradation of Foxp3. Mechanically, IAA reduced the expression of the transcriptional coactivator TAZ, which was almost completely reversed by either AhR antagonist CH223191 or siRNA. In vitro, IAA decreased the combination of TAZ and the histone acetyltransferase Tip60, while it increased the combination of Tip60 and Foxp3. In CIA rats, oral administration of IAA increased the number of Treg cells and relieved the inflammation. A combined use with CH223191 almost abolished the effect of IAA. Taken together, IAA attenuated CIA by promoting the differentiation of Treg cells through reducing the ubiquitination of Foxp3 via the AhR-TAZ-Tip60 pathway.