Aryl Hydrocarbon Receptor Modulates the Expression of TNF-α and IL-8 in Human Sebocytes via the MyD88-p65NF-κB/p38MAPK Signaling Pathways

A Review on the Extraction, Structural Characterization, Function, and Applications of Peptidoglycan

Peptidoglycan (PGN) is the primary component of bacterial cell walls, consisting of linear glycan chains formed by alternating linkages of N-acetylglucosamine (NAG) and N-acetylmuramic acid (NAM) through glycosidic bonds. It exhibits biological activity in various aspects, making it a biologically significant macromolecule with extensive industrial application. This review aims to explore the latest research advancements in the extraction techniques, structural characterization, functions, and applications of PGN. The review compares the advantages and limitations of traditional chemical lysis methods with modern mechanical-assisted and bio-assisted extraction techniques, discusses chemical composition analysis techniques and structural characterization methods of PGN. The review emphasizes the potential of PGN in immune modulation, specific recognition, and adsorption functions. Furthermore, the review examines potential applications of PGN in vaccine development, the livestock industry, the removal of harmful substances, and protein bioprocessing. In the end, based on the current development trend, future research directions for PGN are proposed, including in-depth studies on the mechanisms of PGN in different hosts and its immunomodulatory effects in various disease models. It is expected that a comprehensive reference framework for the research and application of PGN will be provided through this review, offering ideas and directions for further development and utilization.

Successful Treatment of Recalcitrant Chloracne With Adalimumab in an Older Man

This case report describes a man in his 60s with recalcitrant chloracne caused by chlorantraniliprole, a chlorinated pesticide, exposure successfully treated with adalimumab.

Unveiling the hidden potential: Above-ground parts of Paris yunnanensis Franch. Is promise as an anti-acne therapeutic beyond traditional medicinal sites

The dried rhizomes of Paris yunnanensis Franch. have been extensively utilized in traditional Chinese medicine as hemostatic, antitumor, and antimicrobial agents. An examination of classical texts and renowned Chinese medical formulations showcased its efficacy in acne treatment. Presently, there is a significant scarcity of Paris resources. Consider directing attention towards the non-medicinal parts of Paris to mitigate the strain on medicinal resources within this realm. To address these resource limitations, this study investigated the bioactivity and pharmacodynamics of the above-ground parts of Paris (AGPP). A synergistic approach integrating network pharmacology, molecular docking (in silico validation), and animal experimentation (in vivo validation) was employed to elucidate the potential mechanisms underlying the efficacy of AGPP against acne vulgaris in this study. The active constituents in AGPP extracts were identified via UHPLC-Q-Orbitrap HRMS analysis, with their targets extracted for network pharmacological analysis. KEGG pathway analysis unveiled potential therapeutic mechanisms, validated through molecular docking and rat auricular acne model experiments. Comprehensive chemical characterization revealed fifty constituents, including steroidal saponins, flavonoids, amino acids, organic acids, phytohormones, phenolic acids, and alkaloids. Diosgenin, Quercetin, Kaempferol, Ecdysone, and α-linolenic acid were identified as main constituents with acne-treating potential. Core targets included SRC, MAPK3, and MAPK1, with key signaling pathways implicated. Histologically, AGPP mitigated acne-induced follicular dilatation and inflammation, inhibiting inflammatory cytokine production (IL-6, IL-1β, TNF-α). This study offers insight into AGPP's mechanism for acne treatment, laying groundwork for Paris development and drug discovery.

Aryl hydrocarbon receptor role in chronic inflammatory skin diseases: a narrative review

The aryl hydrocarbon receptor (AHR) is a ligand-activated transcription factor that has gained increasing attention in the field of dermatology due to its multifaceted role in skin health and disease. This review provides a comprehensive overview of the current state of knowledge regarding the AHR and its implications in dermatological conditions. The AHR is well known for its involvement in xenobiotic metabolism, particularly in response to polycyclic aromatic hydrocarbons and dioxins. However, recent research has unveiled its pivotal role in the skin immune response, barrier function, and homeostasis. The AHR signalling pathway is intricately linked to various dermatological disorders, including psoriasis, atopic dermatitis, acne and hidradenitis suppurativa. In this review, we delve into the molecular mechanisms through which AHR activation influences skin physiology and highlight how dysregulation can lead to pathological conditions. Moreover, we discuss the emerging therapeutic potential of AHR modulators in the treatment of skin diseases. In conclusion, the AHR is a pivotal player in dermatology, with a multifaceted role in skin physiology and pathology. Understanding the intricacies of AHR signalling in the skin offers promising avenues for the development of novel therapies and preventive strategies for various dermatological conditions. Further research is warranted to elucidate the full scope of AHR's contributions to dermatology and its potential as a therapeutic target.

Unlocking the potential of N-acetylcysteine: Improving hepatopancreas inflammation, antioxidant capacity and health in common carp (Cyprinus carpio) via the MAPK/NF-κB/Nrf2 signalling pathway

N-acetylcysteine (NAC) positively contributes to enhancing animal health, regulating inflammation and reducing stress by participating in the synthesis of cysteine, glutathione, and taurine in the body. The present study aims to investigate the effects of dietary different levels of NAC on the morphology, function and physiological state of hepatopancreas in juvenile common carp (Cyprinus carpio). 450 common carps were randomly divided into 5 groups: N1 (basal diet), N2 (1.5 g/kg NAC diet), N3 (3.0 g/kg NAC diet), N4 (4.5 g/kg NAC diet) and N5 (6.0 g/kg NAC diet), and fed for 8 weeks. The results indicated that dietary 3.0-6.0 g/kg NAC reduced hepatopancreas lipid vacuoles and nuclear translocation, and inhibited apoptosis in common carp. Simultaneously, the activities of hepatopancreas alanine aminotransferase and aspartate aminotransferase progressively increased with rising dietary NAC levels. Dietary NAC enhanced the non-specific immune function of common carp, and exerted anti-inflammatory effects by inhibiting the MAPK/NF-κB signaling pathway. Additionally, dietary 3.0-6.0 g/kg NAC significantly improved the antioxidant capacity of common carp, which was associated with enhanced glutathione metabolism, clearance of ROS and the activation of Nrf2 signaling pathway. In summary, NAC has the potential to alleviate inflammation, mitigate oxidative stress and inhibit apoptosis via the MAPK/NF-κB/Nrf2 signaling pathway, thereby improving hepatopancreas function and health of common carp. The current findings provide a theoretical basis for promoting the application of NAC in aquaculture and ecological cultivation of aquatic animals.

The updates and implications of cutaneous microbiota in acne

Acne is a chronic inflammatory skin disorder that profoundly impacts the quality of life of patients worldwide. While it is predominantly observed in adolescents, it can affect individuals across all age groups. Acne pathogenesis is believed to be a result of various endogenous and exogenous factors, but the precise mechanisms remain elusive. Recent studies suggest that dysbiosis of the skin microbiota significantly contributes to acne development. Specifically, Cutibacterium acnes, the dominant resident bacterial species implicated in acne, plays a critical role in disease progression. Various treatments, including topical benzoyl peroxide, systemic antibiotics, and photodynamic therapy, have demonstrated beneficial effects on the skin microbiota composition in acne patients. Of particular interest is the therapeutic potential of probiotics in acne, given its direct influence on the skin microbiota. This review summarizes the alterations in skin microbiota associated with acne, provides insight into its pathogenic role in acne, and emphasizes the potential of therapeutic interventions aimed at restoring microbial homeostasis for acne management.

Anti-inflammation of hydrogenated isoflavones in LPS-stimulated RAW264.7 cells via inhibition of NF-κB and MAPK signaling pathways

Isoflavones are commonly found in diets, such as soybean and clover. Their anti-inflammatory effects are due to the inhibition of the transcriptional regulation of NF-κB. Hydrogenated isoflavones are metabolites of isoflavones with higher bioavailability, however, there have been few studies on their anti-inflammatory effects. In this work, by using the LPS-stimulated RAW264.7 cell model, we investigated the anti-inflammatory effect and the underlying mechanism of hydrogenated isoflavones. Hydrogenated isoflavones reduced the production of LPS-stimulated pro-inflammatory mediators and enzymes, including TNF-α, IL-6, NO, iNOS and COX-2. The level of ROS was also diminished in LPS-stimulated RAW264.7 cells. Further mechanistic studies showcase that hydrogenated isoflavones block NF-κB and MAPK pathways via attenuation of p65 nuclear translocation and JNK, ERK, and p38 phosphorylation, respectively. In addition, we found that hydrogenated isoflavones display anti-proliferation effect in human colon cancer cells with wild-type p53. Together, hydrogenated isoflavones could be used as an adjuvant for the treatment of inflammation and cancer.

Aging in the sebaceous gland

Sebaceous glands (SGs) originate from hair follicular stem cells and secrete lipids to lubricate the skin. The coordinated effects of intrinsic and extrinsic aging factors generate degradation of SGs at a late age. Senescence of SGs could be a mirror of the late aging of both the human body and skin. The procedure of SG aging goes over an initial SG hyperplasia at light-exposed skin areas to end with SG atrophy, decreased sebum secretion, and altered sebum composition, which is related to skin dryness, lack of brightness, xerosis, roughness, desquamation, and pruritus. During differentiation and aging of SGs, many signaling pathways, such as Wnt/β-catenin, c-Myc, aryl hydrocarbon receptor (AhR), and p53 pathways, are involved. Random processes lead to random cell and DNA damage due to the production of free radicals during the lifespan and neuroendocrine system alterations. Extrinsic factors include sunlight exposure (photoaging), environmental pollution, and cigarette smoking, which can directly activate signaling pathways, such as Wnt/β-catenin, Notch, AhR, and p53 pathways, and are probably associated with the de-differentiation and hyperplasia of SGs, or indirectly activate the abovementioned signaling pathways by elevating the inflammation level. The production of ROS during intrinsic SG aging is less, the signaling pathways are activated slowly and mildly, and sebocytes are still differentiated, yet terminal differentiation is not completed. With extrinsic factors, relevant signaling pathways are activated rapidly and fiercely, thus inhibiting the differentiation of progenitor sebocytes and even inducing the differentiation of progenitor sebocytes into keratinocytes. The management of SG aging is also mentioned.

Potential roles of gut microbial tryptophan metabolites in the complex pathogenesis of acne vulgaris

Acne vulgaris is a chronic inflammatory skin disease in which the influence of gut microbiota has been implicated but without clarification of mechanisms. Gut microbiota may exert such an influence via metabolites, particularly those of tryptophan. End metabolites of tryptophan activate receptors, including aryl hydrocarbon, G protein-coupled, and pregnane X receptors to stabilize the immune microenvironment and intestinal mucosal homeostasis. Any impact on the pathogenesis of acne vulgaris remains unclear. The current review collates recent advances concerning potential roles of tryptophan metabolism in mediating skin inflammation, follicular sebaceous gland function and intestinal permeability, all of which influence the pathogenesis of acne vulgaris. The aim was to improve understanding of the pathogenesis of acne vulgaris and to expose therapeutic opportunities.

Explore the Anti-Acne Mechanism of Licorice Flavonoids Based on Metabonomics and Microbiome

Acne vulgaris is one of the most common inflammatory dermatoses in dermatological practice and can affect any gender or ethnic group. Although in previous studies, we had found that licorice flavonoids (LCF) play an anti-acne role by inhibiting PI3K-Akt signaling pathways and mitochondrial activity, the mechanism of LCF regulating skin metabolism, serum metabolism and skin microbes is still unclear. Here, we performed a full spectrum analysis of metabolites in the skin and serum using UHPLC-Triple TOF-MS. The results showed that LCF could treat acne by regulating the metabolic balance of amino acids, lipids and fatty acids in serum and skin. Similarly, we performed Illumina Hiseq sequencing of DNA from the skin microbes using 16S ribosomal DNA identification techniques. The results showed that LCF could treat acne by regulating the skin microbes to interfere with acne and make the microecology close to the normal skin state of rats. In summary, this study confirmed the anti-acne mechanism of LCF, namely by regulating metabolic balance and microbial balance. Therefore, this discovery will provide theoretical guidance for the preparation development and clinical application of the drug.

Micro-Current Stimulation Suppresses Inflammatory Responses in Peptidoglycan-Treated Raw 264.7 Macrophages and Propionibacterium acnes-Induced Skin Inflammation via TLR2/NF-κB Signaling Pathway

Acne is a common inflammatory disorder of the human skin and a multifactorial disease caused by the sebaceous gland and Propionibacterium acnes (P. acnes). This study aimed to evaluate the anti-inflammatory effect of micro-current stimulation (MC) on peptidoglycan (PGN)-treated raw 264.7 macrophages and P. acnes-induced skin inflammation. To specify the intensity with anti-inflammatory effects, nitric oxide (NO) production was compared according to various levels of MC. As the lowest NO production was shown at an intensity of 50 μA, subsequent experiments used this intensity. The changes of expression of the proteins related to TLR2/NF-κB signaling were examined by immunoblotting. Also, immunofluorescence analysis was performed for observing NF-κB p65 localization. All of the expression levels of proteins regarding TLR2/NF-κB signaling were decreased by the application of MC. Moreover, the application of MC to PGN-treated raw 264.7 cells showed a significant decrease in the amount of nuclear p65-protein. In the case of animal models with P. acnes-induced skin inflammation, various pro-inflammatory cytokines and mediators significantly decreased in MC-applied mice. In particular, the concentration of IL-1β in serum decreased, and the area of acne lesions, decreased from the histological analysis. We suggest for the first time that MC can be a novel treatment for acne.

Peptidoglycan-based immunomodulation

Peptidoglycan (PGN) is a unique component in the cytoderm of prokaryotes which can be recognized by different pathogen-associated molecular patterns (PAMPs) in eukaryotes, followed by a cascade of immune responses via different pathways. This review outlined the basic structure of PGN, its immunologic functions. The immunomodulation pathways mediated by PGN were elaborated. PGN induces specific immunity through stimulating different cytokine release and Th1/Th2-dominated immune responses during humoral/cellular immune response. The nonspecific immunity activation by PGN involves immunomodulation by different pattern recognition receptors (PRRs) including PGN recognition proteins (PGRPs), nucleotide oligomerization domain (NOD)-like receptors (NLRs), Toll-like receptors (TLRs), and C-type lectin receptors (CLRs). The sources and classification of PGRPs were summarized. In view of the stimulating activities of PGN and its monomers, the potential application of PGN as vaccine or adjuvant was prospected. This review provides systematic information on PGN functionalities from the point of immunoregulation, which might be useful in the deep exploitation of PGN.Key points. The immunological functions of PGN were illustrated. Cellular and humoral immunomodulation by PGN were outlined. The use of PGN as vaccine or adjuvant was prospected.

Role of Aryl Hydrocarbon Receptor Activation in Inflammatory Chronic Skin Diseases

Aryl Hydrocarbon Receptor (AhR) is an evolutionary transcription factor which acts as a crucial sensor of different exogenous and endogenous molecules Recent data indicate that AhR is implicated in several physiological processes such as cell physiology, host defense, proliferation and differentiation of immune cells, and detoxification. Moreover, AhR involvement has been reported in the development and maintenance of several pathological conditions. In recent years, an increasing number of studies have accumulated highlighting the regulatory role of AhR in the physiology of the skin. However, there is evidence of both beneficial and harmful effects of AHR signaling. At present, most of the evidence concerns inflammatory skin diseases, in particular atopic dermatitis, psoriasis, acne, and hidradenitis suppurativa. This review exam-ines the role of AhR in skin homeostasis and the therapeutic implication of its pharmacological modulation in these cutaneous inflammatory diseases.

Environmental, inflammatory, and anti-inflammatory squad in acne vulgaris pathogenesis: AhR, IL-36, and IL-38

BACKGROUND

Acne vulgaris (AV) is an extraordinarily common skin condition. The high prevalence of AV is linked to the exposure factors, as environmental pollutants and climatic factors, occupational, psychosocial, and lifestyle factors. The AhR plays a critical part in environmental toxic action. The AhR expression and imbalance in the IL-36 & 38 expression may have a role in inflammation and AV pathogenesis.

AIMS

To detect possible links between environmental, inflammatory, and anti-inflammatory factors in AV pathogenesis through measuring AhR, IL-36, and IL-38 mRNA gene expression levels.

PATIENTS AND METHODS

Total of 100 subjects (70 AV patients and 30 apparently healthy control subjects) were tested for AhR, IL-36γ, and IL-38 mRNA levels by quantitative real-time PCR.

RESULTS

The median levels of AhR and IL-36 mRNA gene expression were considerably greater, while that of IL-38 was essentially lower in AV than healthy subjects (p < 0.001, 0.021 and 0.002, respectively). The AhR and IL-36 mRNA gene expression levels increased, while IL-38 decreased significantly with higher grades of severity (p < 0.001, 0.001, and <0.001, respectively). ROC curve showed that AhR mRNA gene expression level had the best AUC for diagnosis of AV, with better sensitivity and specificity than IL-36 and IL-38.

CONCLUSIONS

Higher levels of AhR, IL-36, and lower levels of IL-38 gene expression were significantly associated with AV patients and higher grades of severity. AhR had better diagnostic ability than IL-38 and IL-36.

AhR Regulates Peptidoglycan-Induced Inflammatory Gene Expression in Human Keratinocytes

Bacterial peptidoglycan (PGN) stimulates toll-like receptor 2 (TLR2) on the surface of keratinocytes (KCs), triggering signaling pathways that promote an innate immune response. However, excessive TLR2 activation can lead to inappropriate inflammation, which contributes to skin conditions such as rosacea. To better treat these conditions, there is a need to understand the molecular mechanisms that regulate the cellular response to TLR2 activation in the skin. Aryl hydrocarbon receptor (AhR) is a transcription factor that modulates the immune response in KCs and is a promising therapeutic target for inflammatory skin diseases. Here, we investigated the role of the AhR in regulating the transcriptional response of human KCs to PGN. We performed whole-transcriptome sequencing in wild-type and AhR-depleted KCs after PGN stimulation. AhR depletion altered the expression of 72 genes in response to PGN, leading to increased expression of 48 genes and repression of 24 genes, including interleukin (IL)-1β. Chromatin immunoprecipitation showed that PGN stimulation resulted in AhR binding the promoters of IL-1β and IL-6 to activate them. More broadly, AhR promoted inflammatory gene expression by increasing JNK/mitogen-activated protein kinase signaling and FosB expression. Finally, we observed that AhR depletion increased TLR2 expression itself, raising the hypothesis that AhR may serve to restrain TLR2-mediated inflammation in KCs through negative feedback. Viewed together, our findings demonstrate a significant and complex role for AhR in modulating the expression of inflammatory genes in KCs in response to PGN.

Resveratrol ameliorates lipid accumulation and inflammation in human SZ95 sebocytes via the AMPK signaling pathways in vitro

BACKGROUND

Acne vulgaris is a prevalent skin disease lacking effective and well-tolerated treatment. An earlier study indicated that resveratrol (RVT) has therapeutic effects in acne patients through unknown mechanisms.

OBJECTIVES

To evaluate the effects of RVT on linoleic acid (LA)-induced lipogenesis and peptidoglycan (PGN)-induced inflammation in cultured SZ95 sebocytes in vitro, and to investigate the underlying mechanisms.

METHODS

RNA-sequencing was used to analyze the whole transcriptome. Nile red staining was used to detect intracellular neutral lipids, whereas lipidomics was used to investigate changes in the lipid profile in sebocytes. Interleukin (IL)-1β and IL-6 mRNA and protein levels were assessed through quantitative real-time PCR and Enzyme-linked immunosorbent assay, respectively. Western blot was used to evaluate the expression of lipogenesis-related proteins, the inflammatory signaling pathway, and the AMP-activated protein kinase (AMPK) pathway. Further, specific small interfering RNA (siRNA) was used to knockdown sirtuin-1 (SIRT1) expression.

RESULTS

RVT inhibited the lipogenesis-related pathway and nuclear factor-kappa B (NF-κB) signaling pathway in SZ95 sebocytes. It also downregulated LA-induced lipogenesis, the expression of lipid-related proteins, and the contents of unsaturated fatty acids. Besides, RVT promoted SIRT1 expression and deacetylation of the NF-κB p65 subunit, thereby lowering IL-1β and IL-6 secretion under PGN induction. Furthermore, pretreatment with AMPK inhibitor Compound C abolished RVT-mediated sebosuppressive and anti-inflammation effects. Meanwhile,SIRT1 silencing abrogated the anti-inflammatory potential of RVT.

CONCLUSION

In human SZ95 sebocytes, RVT exhibits sebosuppressive and anti-inflammatory effects partially through the AMPK pathway, which may justify the role of RVT treatment in acne vulgaris.

Anti-Inflammatory and Pro-Differentiating Properties of the Aryl Hydrocarbon Receptor Ligands NPD-0614-13 and NPD-0614-24: Potential Therapeutic Benefits in Psoriasis

The aryl hydrocarbon receptor (AhR), a ligand-activated transcription factor expressed in all skin cell types, plays a key role in physiological and pathological processes. Several studies have shown that this receptor is involved in the prevention of inflammatory skin diseases, e.g., psoriasis, atopic dermatitis, representing a potential therapeutic target. We tested the safety profile and the biological activity of NPD-0614-13 and NPD-0614-24, two new synthetic AhR ligands structurally related to the natural agonist FICZ, known to be effective in psoriasis. NPD-0614-13 and NPD-0614-24 did not alter per se the physiological functions of the different skin cell populations involved in the pathogenesis of inflammatory skin diseases. In human primary keratinocytes stimulated with tumor necrosis factor-α or lipopolysaccharide the compounds were able to counteract the altered proliferation and to dampen inflammatory signaling by reducing the activation of p38MAPK, c-Jun, NF-kBp65, and the release of cytokines. Furthermore, the molecules were tested for their beneficial effects in human epidermal and full-thickness reconstituted skin models of psoriasis. NPD-0614-13 and NPD-0614-24 recovered the psoriasis skin phenotype exerting pro-differentiating activity and reducing the expression of pro-inflammatory cytokines and antimicrobial peptides. These data provide a rationale for considering NPD-0614-13 and NPD-0614-24 in the management of psoriasis.

Myricetin: A review of the most recent research

Myricetin(MYR) is a flavonoid compound widely found in many natural plants including bayberry. So far, MYR has been proven to have multiple biological functions and it is a natural compound with promising research and development prospects. This review comprehensively retrieved and collected the latest pharmacological abstracts on MYR, and discussed the potential molecular mechanisms of its effects. The results of our review indicated that MYR has a therapeutic effect on many diseases, including tumors of different types, inflammatory diseases, atherosclerosis, thrombosis, cerebral ischemia, diabetes, Alzheimer's disease and pathogenic microbial infections. Furthermore, it regulates the expression of Hippo, MAPK, GSK-3β, PI3K/AKT/mTOR, STAT3, TLR, IκB/NF-κB, Nrf2/HO-1, ACE, eNOS / NO, AChE and BrdU/NeuN. MYR also enhances the immunomodulatory functions, suppresses cytokine storms, improves cardiac dysfunction, possesses an antiviral potential, can be used as an adjuvant treatment against cancer, cardiovascular injury and nervous system diseases, and it may be a potential drug against COVID-19 and other viral infections. Generally, this article provides a theoretical basis for the clinical application of MYR and a reference for its further use.

Putative Genes and Pathways Involved in the Acne Treatment of Isotretinoin via Microarray Data Analyses

Acne is the eighth most common disease worldwide. Disease burden of acne such as anxiety, reduced self-esteem, and facial scarring lowers the life quality of acne patients. Isotretinoin is the most potent treatment for moderate-severe acne. However, the adverse events of isotretinoin especially teratogenicity limit its use. This study aims at investigating the therapeutical mechanisms of isotretinoin using bioinformatics analysis. Differentially expressed genes (DEGs) were filtered from microarray datasets GSE10432, GSE10433, and GSE11792. Functional and pathway enrichment analyses of DEGs were performed. Protein–protein interaction (PPI) network and module analyses were also conducted based on DEGs. Using isotretinoin for 1 week, LCN2, PTGES, and GDF15 were upregulated and might mediate sebocytes apoptosis and thus decreased sebum production; CCL2 originated from activated TNF signaling pathway and S100A7 could be related with “acne-flare”. While treating with isotretinoin for 8 weeks, key genes were downregulated, including HMGCS1, HMGCR, FDFT1, MVD, IDI1, and FDPS, which may be associated with decreased sebum synthesis; HMGCS1, HMGCR, and FDFT1 also probably associated with apoptosis of sebocytes. There were only two common genes including ACSBG1 and BCAT2 which worked in both 1 week and 8 weeks and could associate with decreased sebum synthesis and apoptosis of sebocytes, respectively. These results indicate potential therapeutics and side effect mechanisms of isotretinoin in the acne treatment and provide a research direction to further investigate the therapeutic mechanism of isotretinoin and thus develop retinoid-like compounds with similar curative effect and without teratogenicity.

Quercetin induces an immunoregulatory phenotype in maturing human dendritic cells

The aryl hydrocarbon receptor (AhR) is an environmental sensor and ligand-activated transcription factor that is critically involved in the regulation of inflammatory responses and the induction of tolerance by modulating immune cells. As dendritic cells (DCs) express high AhR levels, they are efficient to induce immunomodulatory effects after being exposed to AhR-activating compounds derived from the environment or diet. To gain new insights into the molecular targets following AhR-activation in human monocyte-derived (mo)DCs, we investigated whether the natural AhR ligand quercetin or the synthetic ligand 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) modulates the function of human moDCs regarding their capability to prime naïve T cells or to migrate. As only quercetin, but not TCDD, impaired T cell activation and migration of LPS-matured DCs (LPS-DCs), we analyzed the mode of action of quercetin on moDCs in more detail. Here, we found a specific down-regulation of the immunomodulatory molecule CD83 through the direct binding of the activated AhR to the CD83 promoter. Furthermore, treatment of LPS-DCs with quercetin resulted in a reduced production of the pro-inflammatory cytokine IL-12p70 and in an increased expression of the immunoregulatory molecules disabled adaptor protein (Dab) 2, immunoglobulin-like transcript (ILT)-3, ILT4, ILT5 as well as ectonucleotidases CD39 and CD73, thereby inducing a tolerogenic phenotype in quercetin-treated maturing DCs. Overall, these data demonstrate that quercetin represents a potent immunomodulatory agent to alter human DC phenotype and function, shifting the immune balance from inflammation to resolution.

Chloracne and Hyperpigmentation Caused by Exposure to Hazardous Aryl Hydrocarbon Receptor Ligands

Dioxins and dioxin-like compounds are environmental pollutants that are hazardous to human skin. They can be present in contaminated soil, water, and air particles (such as ambient PM_2.5). Exposure to a high concentration of dioxins induces chloracne and hyperpigmentation. These chemicals exert their toxic effects by activating the aryl hydrocarbon receptor (AHR) which is abundantly expressed in skin cells, such as keratinocytes, sebocytes, and melanocytes. Ligation of AHR by dioxins induces exaggerated acceleration of epidermal terminal differentiation (keratinization) and converts sebocytes toward keratinocyte differentiation, which results in chloracne formation. AHR activation potently upregulates melanogenesis in melanocytes by upregulating the expression of melanogenic enzymes, which results in hyperpigmentation. Because AHR-mediated oxidative stress contributes to these hazardous effects, antioxidative agents may be potentially therapeutic for chloracne and hyperpigmentation.