BACKGROUND/PURPOSE:Phototoxicity is a common adverse effect triggered by systemic or topical drug treatments. It is mainly caused by drug-induced sensitization to UVA radiation, arising from either the drug's inherent photosensitizing potential or its interference with the metabolism of endogenous photosensitizers. A potent endogenous UVA sensitizer is 6-formylindolo[3,2-b]carbazole (FICZ), a tryptophan photoproduct formed in UVB-irradiated epidermal cells. By sequentially activating the aryl hydrocarbon receptor signaling pathway and inducing cytochrome P450 (CYP) 1A1 expression, FICZ induces its own degradation. Recently, we reported that the BRAF inhibitor vemurafenib interferes with CYP1A1 activity and sensitizes keratinocytes to FICZ/UVA-induced phototoxicity. Herein, we screened 12 clinical drugs, known to exhibit phototoxicity in patients, for their potential to interfere with the metabolism of (exogenous) FICZ and sensitize HaCaT keratinocytes to UVA-induced phototoxicity. METHODS:The UV-VIS absorption of the drugs was determined, and their effect on CYP1A1 activity and FICZ/UVA-triggered apoptosis was assessed in immortalized and primary human keratinocytes using 7-ethoxyresorufin-O-deethylase (EROD) and caspase-3 activity assays. Moreover, the impact of the candidate drugs on the metabolic degradation of FICZ in cells (LC analysis) as well as on the generation of oxidative stress (MitoSOX assay, qPCR analyses) was investigated. RESULTS:We identified two drugs, erlotinib and leflunomide, to sensitize human keratinocytes to FICZ/UVA-induced apoptosis by inhibiting CYP1A1 activity. Moreover, both drugs attenuated the metabolic breakdown of FICZ, enhanced the FICZ/UVA-triggered formation of mitochondrial superoxide anions, and increased heme oxygenase-1 (HMOX1) transcript levels, indicative of antioxidant defense activation. CONCLUSION:Disruption of FICZ metabolism may contribute to the phototoxicity of drugs.

Exposure to airborne particulate matter (PM) is a substantial threat to public health, contributing to respiratory, cardiovascular, and skin-related diseases. Population-based studies strongly indicate that chronic exposure to airborne PM, especially combustion-derived PM2.5, accelerates skin aging and thus reduces the quality of life of those affected. There is increasing evidence that especially PM-bound polycyclic aromatic hydrocarbons (PAHs) critically contribute to the clinical manifestation of skin aging, i.e. the development of lentigines/pigment spots and coarse wrinkles. PAHs harm human skin primarily by activating the aryl hydrocarbon receptor (AHR), a ligand-activated transcription factor amongst others involved in orchestrating xenobiotic metabolism and immune responses. In this review, we summarize the available population-based data linking particulate air pollution exposure to skin aging. We explain in detail how PAH-rich PM induces the formation of oxidative stress, the release of pro-inflammatory mediators, the expression extracellular matrix degrading metalloproteases, and melanin synthesis, in an AHR-dependent manner, and how these events may culminate in the development of pigment spots and wrinkles, respectively. We also review the current data on the interaction of airborne PM with another factor of the skin aging exposome that exerts its deleterious effects in part through AHR-dependent signaling pathways, namely solar ultraviolet radiation.

A multidisciplinary platform is presented to address aryl hydrocarbon receptor (AhR) modulation. A rewired Yonemitsu multicomponent reaction with indole 2-carboxaldehydes and nucleophilic species was designed to access a family of 6-substituted indolocarbazoles. The conformational behavior of these compounds was examined to rationalize their axial chirality. In silico docking and molecular simulations highlighted key features implicated in their binding to AhR. Furthermore, the synthesis of linkable derivatives allowed the direct development of conjugated entities. Reporter gene and target gene expression analyses identified these novel structures as potent noncytotoxic activating AhR ligands, that can be extended to bifunctional molecules. The anti-inflammatory properties of these AhR agonists were assessed in interleukin-13 treated keratinocytes. Altogether, the synergistic research in synthetic and computational chemistry integrated with biological studies opens novel avenues toward understanding the biological roles of AhR and the development of targeted therapeutics.

Exposure to combustion-derived airborne polycyclic aromatic hydrocarbons (PAHs) may harm human skin, exacerbate cutaneous inflammatory diseases and accelerate skin aging. The toxicity of PAHs is unleashed upon their metabolic activation by cytochrome P450 (CYP) 1 monooxygenases, resulting in the formation of reactive intermediates that form mutagenic DNA adducts. Moreover, PAHs cause oxidative stress, which is primarily due to aldo-keto reductases (AKRs), such as AKR1C3, which convert CYP1-derived PAH-trans-diols to PAH-catechols. The catechols undergo autooxidation leading to the formation of reactive oxygen species (ROS) and PAH-quinones. The latter are highly reactive, mitotoxic and are reduced back to PAH-catechols, thus facilitating redox cycling. As AKR1C expression is inducible by other NRF2-stimulating chemicals, we tested the hypothesis that co-exposure of HaCaT keratinocytes to skin sensitizers and the PAH benzo[a]pyrene (BaP) enhances ROS formation. We observed a synergistic effect of the skin sensitizers on the BaP-induced expression of the NRF2 target genes heme oxygenase-1, sulfiredoxin-1 and AKR1C3. In fact, co-exposure to the skin sensitizers also enhanced the BaP-induced formation of superoxide anions. Intriguingly, the co-exposure-related ROS formation was abolished upon inhibition of either CYP1A1 or AKR1C3. Testing of additional skin-sensitizing compounds, differing in their mode of action, indicated that especially potent Michael acceptors enhance the toxicity of BaP by increasing AKR1C3 expression and, presumably, downstream BaP-quinone formation. Our study reveals potential health risks associated with the simultaneous exposure to common skin-sensitizing substances and ubiquitous PAHs, and implies a role for NRF2 in mediating PAH toxicity.

The aryl hydrocarbon receptor (AHR) is a ligand-dependent transcription factor regulating adaptive and maladaptive responses toward exogenous and endogenous signals. Research from various biomedical disciplines has provided compelling evidence that the AHR is critically involved in the pathogenesis of a variety of diseases and disorders, including autoimmunity, inflammatory diseases, endocrine disruption, premature aging and cancer. Accordingly, AHR is considered an attractive target for the development of novel preventive and therapeutic measures. However, the ligand-based targeting of AHR is considerably complicated by the fact that the receptor does not always follow the beaten track, i.e. the canonical AHR/ARNT signaling pathway. Instead, AHR might team up with other transcription factors and signaling molecules to shape gene expression patterns and associated physiological or pathophysiological functions in a ligand-, cell- and micromilieu-dependent manner. Herein, we provide an overview about some of the most important non-canonical functions of AHR, including crosstalk with major signaling pathways involved in controlling cell fate and function, immune responses, adaptation to low oxygen levels and oxidative stress, ubiquitination and proteasomal degradation. Further research on these diverse and exciting yet often ambivalent facets of AHR biology is urgently needed in order to exploit the full potential of AHR modulation for disease prevention and treatment.

A rewired Yonemitsu multicomponent reaction was designed to readily synthesize a family of 6-substituted indolocarbazoles. In this approach, indole 2-carboxaldehyde and nucleophilic species directly yield the final adducts through a domino reaction. The scope of the new process was analyzed, and the range of the indole aldehydes and nucleophiles was established. Comparative studies with analogous compounds reveal important details on the reaction mechanism. Experimental and computational studies address the conformational behavior of representative adducts, determining their potential chirality. These novel structures are potent activating ligands of the human aryl hydrocarbon receptor, importantly being non-toxic. Furthermore, the scaffold may be included in a 2-step synthesis of (homo)-PROTACs that efficiently and specifically degrade the receptor. Our approach allows the control of this important target in biomedicine through a designed new chemistry.

The pathogenesis of atopic dermatitis (AD) involves an impairment of the skin barrier by an interplay of genetic and environmental factors. The resulting inappropriate defense against allergens, microbes, and pollutants results in a chronic, mainly T-helper (Th) 2 cell-driven skin inflammation.1 Environmental factors that may increase the risk for AD are airborne particulate matter (PM) and commonly associated polycyclic aromatic hydrocarbons (PAHs).1, 2 However, the available epidemiological data provide a heterogeneous picture. While some studies found a significant association between PM exposure and AD symptoms, in particular in children, other studies reported null associations.1, 2 This data inconsistency in airborne PM exposure-related AD may depend on interindividual genetic susceptibilities.3 A gene that is highly expressed in lesional AD skin4 and upregulated in PAH-exposed keratinocytes in an aryl hydrocarbon receptor-dependent manner5 encodes aldo-keto reductase (AKR)1C3. AKR1C3 reduces prostaglandin (PG)D2 to 9α,11β-PGF2, a metabolically stable stimulator of Th2 cells that serves as a systemic biomarker for allergen-induced mast cell activation.6 Herein, we demonstrate the functional and clinical relevance of the AKR1C3 gene variant rs12529 for the PM exposure-associated development of AD. Study individuals enrolled in the GINIplus/LISA birth cohort were restricted to 457 participants (49.5% male; age: mean = 15.1 years, sd = 0.2; BMI: mean = 21.2, sd = 3.3) with available AD diagnosis at the 15-year follow-up examination, air pollution, and genetic data. AD, defined as ever diagnosed by a physician, was present in 174 individuals. Median chronic exposures to PMs with interquartile ranges were for PM2.5 17.3 μg/m3 (0.9), for PM10 25.2 μg/m3 (1.5), for PM2.5 absorbance 1.16 10−5/m (0.2), and for PMcoarse 8.4 μg/m3 (0.6). The single nucleotide polymorphism (SNP) rs12529 was genotyped with sufficient quality (estimated R2 = 0.997), and the minor/effect allele frequency (EAF) was G: 0.400. We found consistent effects for all PM exposures showing a higher chance for adolescent carriers of the rs12529 effect allele (G) to develop AD as compared to rs12529 major allele (C) carriers under constant airborne PM exposure (Figure 1). With the increase per one effect allele, the odds ratio for developing AD significantly increases by 38% (PM10, PM2.5, PM2.5 absorbance) and 37% (PMcoarse), respectively. Next, we investigated whether the rs12529 effect allele, causing an amino acid exchange in codon 5 from His to Gln, affects the catalytic activity of AKR1C3. In comparison with the major allele variant, the overexpression of an effect allele-resembling AKR1C3 variant in CRISPR/Cas9-generated AKR1C3-knockout (HaCaT-AKR1C3-KO) keratinocytes (Figure S1A–C) resulted in an enhanced 11-ketoreduction of PGD2 to 9α,11β-PGF2 (Figure 2A). However, after normalization of the LC–MS data to the protein level, this effect was diminished (Figure 2B,C), indicating that the rs12529 effect allele affects AKR1C3 enzyme activity indirectly by enhancing its protein stability. Accordingly, treatment of transfected HaCaT-AKR1C3-KO cells with the translation blocker cycloheximide revealed a delayed degradation of the effect allele-resembling AKR1C3 enzyme over time (Figure 2D), indicating that the SNP-related amino acid exchange indeed enhances protein stability. Importantly, AKR1C3 expression is not only inducible by PAHs, such as benzo[a]pyrene, but also by PAH-rich PM. In fact, treatment of HaCaT keratinocytes with an organic extract of PM2.5 collected from traffic-related air pollution and a repetitive topical exposure of human ex vivo skin with diesel exhaust particles increased the expression of AKR1C3 (Figure 2E, Figure S2A) and the prototypic aryl hydrocarbon receptor target gene cytochrome P450 (CYP)1A1 (Figure S2). Taken together, our data show that under constant chronic PM exposure, the increase per one AKR1C3 SNP rs12529 effect allele increases the chance to develop AD significantly by approx. 37%–38%. PM exposure induces AKR1C3 expression in human skin; therefore, this observation might be due to an enhanced protein level and corresponding catalytic activity of AKR1C3. The allele frequency of rs12529 varies markedly across continental populations.7 Hence, we speculate that due to a higher rs12529 EAF, some populations (e.g., Asians, EAF = 0.861) might be more susceptible to PM/PAH exposure-induced or -exacerbated AD than others (e.g., Europeans, EAF = 0.405). FH was supported by the Jürgen Manchot Foundation. CFAV was supported by the National Institute of Environmental Health Sciences and the National Institutes of Health under Award Numbers R01ES029126 and R01ES032827. GINIplus/LISA birth cohort: The authors thank all the families for their participation in the GINIplus study. Furthermore, we thank all members of the GINIplus Study Group for their excellent work. The GINIplus Study group consists of the following: Institute of Epidemiology, Helmholtz Zentrum München, German Research Center for Environmental Health, Neuherberg (Heinrich J, Brüske I, Schulz H, Flexeder C, Zeller C, Standl M, Schnappinger M, Ferland M, Thiering E, Tiesler C); Department of Pediatrics, Marien-Hospital, Wesel (Berdel D, von Berg A); Ludwig-Maximilians-University of Munich, Dr von Hauner Children's Hospital (Koletzko S); Child and Adolescent Medicine, University Hospital rechts der Isar of the Technical University Munich (Bauer CP, Hoffmann U); IUF- Environmental Health Research Institute, Düsseldorf (Schikowski T, Link E, Klümper C, Krämer U, Sugiri D). The authors thank all the families for their participation in the LISA study. Furthermore, we thank all members of the LISA Study Group for their excellent work. The LISA Study group consists of the following: Helmholtz Zentrum München, German Research Center for Environmental Health, Institute of Epidemiology, Munich (Heinrich J, Schnappinger M, Brüske I, Ferland M, Schulz H, Zeller C, Standl M, Thiering E, Tiesler C, Flexeder C); Department of Pediatrics, Municipal Hospital “St. Georg”, Leipzig (Borte M, Diez U, Dorn C, Braun E); Marien-Hospital Wesel, Department of Pediatrics, Wesel (von Berg A, Berdel D, Stiers G, Maas B); Pediatric Practice, Bad Honnef (Schaaf B); Helmholtz Centre of Environmental Research—UFZ, Department of Environmental Immunology/Core Facility Studies, Leipzig (Lehmann I, Bauer M, Röder S, Schilde M, Nowak M, Herberth G, Müller J); Technical University Munich, Department of Pediatrics, Munich (Hoffmann U, Paschke M, Marra S); Clinical Research Group Molecular Dermatology, Department of Dermatology and Allergy, Technische Universität München (TUM), Munich (Ollert M, J. Grosch). Open Access funding enabled and organized by Projekt DEAL. The GINIplus study was mainly supported for the first 3 years of the Federal Ministry for Education, Science, Research and Technology (interventional arm) and Helmholtz Zentrum Munich (former GSF) (observational arm). The 4-year, 6-year, 10-year, and 15-year follow-up examinations of the GINIplus study were covered from the respective budgets of the 5 study centres (Helmholtz Zentrum Munich (former GSF), Research Institute at Marien-Hospital Wesel, LMU Munich, TU Munich, and from 6 years onwards also from IUF—Leibniz Research Institute for Environmental Medicine at the University of Düsseldorf), and a grant from the Federal Ministry for Environment (IUF Düsseldorf, FKZ 20462296). Further, the 15-year follow-up examination of the GINIplus study was supported by the Commission of the European Communities, the 7th Framework Program: MeDALL project, and as well by the companies Mead Johnson and Nestlé. The LISA study was mainly supported by grants from the Federal Ministry for Education, Science, Research and Technology and in addition from Helmholtz Zentrum Munich (former GSF), Helmholtz Centre for Environmental Research—UFZ, Leipzig, and Research Institute at Marien-Hospital Wesel, Pediatric Practice, Bad Honnef for the first 2 years. The 4-year, 6-year, 10-year, and 15-year follow-up examinations of the LISA study were covered from the respective budgets of the involved partners (Helmholtz Zentrum Munich (former GSF), Helmholtz Centre for Environmental Research—UFZ, Leipzig, Research Institute at Marien-Hospital Wesel, Pediatric Practice, Bad Honnef, IUF—Leibniz Research Institute for Environmental Medicine at the University of Düsseldorf) and in addition by a grant from the Federal Ministry for Environment (IUF Düsseldorf, FKZ 20462296). Further, the 15-year follow-up examination of the LISA study was supported by the Commission of the European Communities, the 7th Framework Program: MeDALL project. The research leading to the ESCAPE results has received funding from the European Community's Seventh Framework Program (FP7/2007–2011) under grant agreement number: 211250. The authors declare that they have no conflicts of interest. Appendix S1 Figure S1 Please note: The publisher is not responsible for the content or functionality of any supporting information supplied by the authors. Any queries (other than missing content) should be directed to the corresponding author for the article.

Polycyclic aromatic hydrocarbons (PAHs), dioxin-like compounds (DLCs) and structurally-related environmental pollutants may contribute to the pathogenesis of various diseases and disorders, primarily by activating the aryl hydrocarbon receptor (AHR) and modulating downstream cellular responses. Accordingly, AHR is considered an attractive molecular target for preventive and therapeutic measures. However, toxicological risk assessment of AHR-modulating compounds as well as drug development is complicated by the fact that different ligands elicit remarkably different AHR responses. By elucidating the differential effects of PAHs and DLCs on aldo-keto reductase 1C3 expression and associated prostaglandin D2 metabolism, we here provide evidence that the epidermal growth factor receptor (EGFR) substantially shapes AHR ligand-induced responses in human epithelial cells, i.e. primary and immortalized keratinocytes and breast cancer cells. Exposure to benzo[a]pyrene (B[a]P) and dioxin-like polychlorinated biphenyl (PCB) 126 resulted in a rapid c-Src-mediated phosphorylation of EGFR. Moreover, both AHR agonists stimulated protein kinase C activity and enhanced the ectodomain shedding of cell surface-bound EGFR ligands. However, only upon B[a]P treatment, this process resulted in an auto-/paracrine activation of EGFR and a subsequent induction of aldo-keto reductase 1C3 and 11-ketoreduction of prostaglandin D2. Receptor binding and internalization assays, docking analyses and mutational amino acid exchange confirmed that DLCs, but not B[a]P, bind to the EGFR extracellular domain, thereby blocking EGFR activation by growth factors. Finally, nanopore long-read RNA-seq revealed hundreds of genes, whose expression is regulated by B[a]P, but not by PCB126, and sensitive towards pharmacological EGFR inhibition. Our data provide novel mechanistic insights into the ligand response of AHR signaling and identify EGFR as an effector of environmental chemicals.

The participation of reactants undergoing a polarity inversion along a multicomponent reaction allows the continuation of the transformation with productive domino processes. Thus, indole aldehydes in Groebke-Blackburn-Bienaymé reactions lead to an initial adduct which spontaneously triggers a series of events leading to the discovery of novel reaction pathways together with direct access to a variety of linked, fused, and bridged polyheterocyclic scaffolds. Indole 3- and 4-carbaldehydes with suitable isocyanides and aminoazines afford fused adducts through oxidative Pictet-Spengler processes, whereas indole 2-carbaldehyde yields linked indolocarbazoles under mild conditions, and a bridged macrocycle at high temperature. These novel structures are potent activators of the human aryl hydrocarbon receptor signaling pathway.

An entry from the Cambridge Structural Database, the world’s repository for small molecule crystal structures. The entry contains experimental data from a crystal diffraction study. The deposited dataset for this entry is freely available from the CCDC and typically includes 3D coordinates, cell parameters, space group, experimental conditions and quality measures.