IL4I1 Is a Metabolic Immune Checkpoint that Activates the AHR and Promotes Tumor Progression.

Aryl hydrocarbon receptor (AHR) activation by tryptophan (Trp) catabolites enhances tumor malignancy and suppresses anti-tumor immunity. The context specificity of AHR target genes has so far impeded systematic investigation of AHR activity and its upstream enzymes across human cancers. A pan-tissue AHR signature, derived by natural language processing, revealed that across 32 tumor entities, interleukin-4-induced-1 (IL4I1) associates more frequently with AHR activity than IDO1 or TDO2, hitherto recognized as the main Trp-catabolic enzymes. IL4I1 activates the AHR through the generation of indole metabolites and kynurenic acid. It associates with reduced survival in glioma patients, promotes cancer cell motility, and suppresses adaptive immunity, thereby enhancing the progression of chronic lymphocytic leukemia (CLL) in mice. Immune checkpoint blockade (ICB) induces IDO1 and IL4I1. As IDO1 inhibitors do not block IL4I1, IL4I1 may explain the failure of clinical studies combining ICB with IDO1 inhibition. Taken together, IL4I1 blockade opens new avenues for cancer therapy.

Amino Chemoassay Profiling of Aromatic Aldehydes-Unraveling Drivers of Their Skin Sensitization Potency.

Aromatic aldehydes are ubiquitous in humans' everyday life. As aldehydes, they can form imines (Schiff bases) with amino groups of skin proteins, leading to immune response-triggered allergic contact dermatitis. Many known aromatic aldehydes are considered as weak or nonsensitizers, but others like atranol and chloratranol, two components of the fragrance oak moss absolute, show strong sensitization potency. This large discrepancy in potency and, in particular, the underlying reaction mechanisms are only little understood so far. To reduce this knowledge gap, our chemoassay employing glycine-para-nitroanilide (Gly-pNA) as an amino model nucleophile was applied to 23 aromatic aldehydes. The determined Gly-pNA second-order rate constants for imine formation (k1 ≤ 2.85 L·mol-1·min-1) and the imine stability constant (K ≤ 333 L·mol-1) are on the lower end of the known amino reactivity scale for aldehydes, confirming many aromatic aldehydes as less potent sensitizers in line with animal and human data. The substantially higher sensitization potency of atranol and chloratranol, in turn, is reflected by their unique reaction chemistry profiles, inter alia, identifying them as cross-linkers able to form thermodynamically more stable epitopes with skin proteins (despite low formation kinetics, k1). The discussion further includes a comparison of experimentally determined k1 values with computed reactivity data (Taft σ*), the impact of the substitution pattern of the aryl ring on the reactivity with Gly-pNA, and analytically determined adduct patterns. Overall, this work provides new insights into the reaction of aromatic aldehydes with amino groups under aqueous conditions and fosters a better understanding of the chemistry underlying skin sensitization.

Baseline Narcosis for the Glass-Vial 96-h Growth Inhibition of the Nematode C. elegans and Its Use for Identifying Electrophilic and Pro-Electrophilic Toxicity.

The nematode Caenorhabditis elegans has been widely used as a model organism for assessing chemical toxicity. So far, however, a respective baseline narcosis reference has been lacking to predict narcosis-level toxicity and to identify excess-toxic compounds and associated mechanisms of action. Employing 22 organic narcotics that cover 7.2 units of their log Kow (octanol/water partition coefficient) from -1.20 to 6.03, a baseline narcosis model has been derived for a glass-vial 96-h growth inhibition test with C. elegans, both without and with correction for compound loss through volatilization and sorption. The resultant effective concentrations yielding 50% growth inhibition, EC50, vary by 6.4 log units from 5.04 · 10-1 to 1.90 · 10-7 mol/L (exposure-corrected). Application of the new model is illustrated through sensing the toxicity enhancement (Te) of four Michael-acceptor carbonyls driven by their reactive mode of action. Moreover, narcosis-level predicted vs experimental EC50 of two α,ß-unsaturated alcohols demonstrate the biotransformation capability of C. elegans regarding ADH (alcohol dehydrogenase). The discussion includes narcosis-level and excess-toxicity doses (critical body burdens) as well as chemical activities A50 (at the EC50) as compared to fish, daphnids, ciliates, bacteria, zebrafish embryo, and cell lines. Overall, the presently introduced model for predicting C. elegans baseline narcosis enables generating respective pre-test expectations, enriches experimental results by mechanistic information, and may complement 3Rs (reduce, refine, replace) test batteries through its ADH metabolic capacity.

Amino Reactivity of Glutardialdehyde and Monoaldehydes─Chemoassay Profile vs Skin Sensitization Potency.

Chemoassay profiling of organic electrophiles through the direct peptide reactivity assay has become an OECD-accepted nonanimal component in the REACH evaluation of potential skin sensitizers. For aldehydes forming imines (Schiff bases), however, existing chemoassays yielded inconclusive results, indicating issues with their NH2 sensitivity and the reversibility of the reaction. In the present study, a new kinetic chemoassay employing the N terminus of glycine-para-nitroanilide, Gly-pNA, as a model nucleophile for protein NH2 groups is introduced and applied to nine aliphatic monoaldehydes and glutardialdehyde (1,5-pentanedial) that have log Kow (octanol/water partition coefficient) values from 0.63 to 3.99. The Gly-pNA second-order rate constants k1 range from 8.56 to 150 L·mol-1·min-1 for the monoaldehydes. Interestingly, glutardialdehyde with a k1 of 17 731 L·mol-1·min-1 is 170-fold more reactive than its monoaldehyde counterpart pentanal. This can be rationalized by hydration or tautomerization of the dialdehyde to monoaldehydic forms, now facilitating Schiff base formation through an intramolecular H bond. Comparison with murine local lymph node assay data from the literature reveals that adduct stability in terms of reaction thermodynamics (K = k1/k-1pseudo) rather than formation kinetics (k1) governs the skin sensitization potency of Schiff-base-forming aldehydes. The discussion includes analytically determined adduct patterns, and the impact of α- and ß-carbon substitution as well as hydrophobicity on aldehyde reactivity.

Glutathione Adduct Patterns of Michael-Acceptor Carbonyls.

Glutathione (GSH) has so far been considered to facilitate detoxification of soft organic electrophiles through covalent binding at its cysteine (Cys) thiol group, followed by stepwise catalyzed degradation and eventual elimination along the mercapturic acid pathway. Here we show that in contrast to expectation from HSAB theory, Michael-acceptor ketones, aldehydes and esters may form also single, double and triple adducts with GSH involving ß-carbon attack at the much harder N-terminus of the γ-glutamyl (Glu) unit of GSH. In particular, formation of the GSH-N single adduct contradicts the traditional view that S alkylation always forms the initial reaction of GSH with Michael-acceptor carbonyls. To this end, chemoassay analyses of the adduct formation of GSH with nine α,ß-unsaturated carbonyls employing high performance liquid chromatography and tandem mass spectrometry have been performed. Besides enriching the GSH adductome and potential biomarker applications, electrophilic N-terminus functionalization is likely to impair GSH homeostasis substantially through blocking the γ-glutamyl transferase catalysis of the first breakdown step of modified GSH, and thus its timely reconstitution. The discussion includes a comparison with cyclic adducts of GSH and furan metabolites as reported in literature, and quantum chemically calculated thermodynamics of hard-hard, hard-soft, and soft-soft adducts.

Chemoavailability of Organic Electrophiles: Impact of Hydrophobicity and Reactivity on Their Aquatic Excess Toxicity.

Organic electrophiles have been recognized as important components of the exposome that can be characterized as cumulative totality of exposure in the organism in response to environmental perturbation. For such compounds, chemical reactivity may contribute significantly to the toxicological profile through covalent attacks at nucleophilic sites of peptides such as glutathione (GSH), proteins, lipid components, and the DNA and RNA. Employing a Michael acceptor set of 58 α,ß-unsaturated carbonyls with 15 ketones, 18 aldehydes, and 25 esters, the hydrophobicity and reactivity contributions to their toxicity enhancement Te over baseline narcosis with the ciliates Tetrahymena pyriformis is analyzed through a conceptual model, featuring toxicokinetic phase transfer steps and the reactive molecular initiating event (MIE) at endogenous target sites exposed to water-rich or water-poor compartments. To this end, hydrophobicity was quantified by the octanol/water partition coefficient, Kow, electrophilic reactivity through second-order rate constants of reaction with GSH in a kinetic chemoassay, kGSH, and Te as the ratio of narcosis-level vs experimental concentration yielding 50% growth inhibition of the ciliates within 48 h of exposure. The observed decrease of log Te with increasing log Kow can be traced back to a rate-determining impact of the toxicant transfer from the membrane to the intracellular cytosol. Moreover, the recently introduced concept of chemoavailability is shown to enable, from knowledge of log Kow and log kGSH alone, a screening-level discrimination between reactive and hydrophobic MIEs triggering predominantly alone or in parallel respective adverse outcome pathways (AOPs) including the diffusion-control limit of reactive MIE saturation. As such, chemoavailability may aid in evaluating prevalent MIEs expected for a given organic electrophile and in assessing its toxicological profile within AOP schemes addressing aquatic toxicity.

Reactivity-based identification of oxygen containing functional groups of chemicals applied as potential classifier in non-target analysis.

In this work, we developed a reactivity-based strategy to identify functional groups of unknown analytes, which can be applied as classifier in non-target analysis with gas chromatography. The aim of this strategy is to reduce the number of potential candidate structures generated for a molecular formula determined by high resolution mass spectrometry. We selected an example of 18 isomers with the molecular formula C12H10O2 to test the performance of different derivatization reagents, whereas our aim was to select mild and fast reaction conditions. Based on the results for the isomers, we developed a four-step workflow for the identification of functional groups containing oxygen.

Predicting partitioning from low density polyethylene to blood and adipose tissue by linear solvation energy relationship models.

The variety of polymers utilized in medical devices demands for testing of extractables and leachables according to ISO 10993-18:2020 in combination with ISO 10993-1:2018. The extraction of the materials involves the use of organic solvents as well as aqueous buffers to cover a wide range of polarity and pH-values, respectively. To estimate patient exposure to chemicals leaching from a polymer in direct body contact, simulating solvents are applied to best mimic the solubilization and partitioning behavior of the related tissue or body fluid. Here we apply linear solvation energy relationship (LSER) models to predict blood/water and adipose tissue/water partition coefficients. We suggest this predictive approach to project levels of potential leachables, design extraction experiments, and to identify the optimal composition of simulating extraction solvents. We compare our predictions to LSER predictions for commonly applied surrogates like ethanol/water mixtures, butanol, and octanol as well as olive oil, butanone, 1,4-dioxane for blood and adipose tissue, respectively. We therefore selected a set of 26 experimentally determined blood/water partition coefficients and 33 adipose tissue/water partition coefficients, where we demonstrate that based on the root mean squared error rmse the LSER approach performs better than surrogates like octanol or butanol and equally well as 60:40 ethanol/water for blood. For adipose tissue/water partitioning, the experimentally determined octanol/water partition coefficient performs best but the rmse is at the same range as our LSER approach based on experimentally determined descriptors. Further, we applied our approach for 248 extractables where we calculated blood/low density polyethylene (LDPE) and adipose tissue/LDPE partition coefficients. By this approach, we successfully identified chemicals of potential interest to a toxicological evaluation based on the total risk score.

DNA adducts as link between in vitro and in vivo carcinogenicity - A case study with benzo[a]pyrene.

To reduce the need for animal tests, in vitro assays are often used as alternative methods. To derive toxic doses for higher tier organisms from in vitro assay results, quantitative in vitro-in vivo extrapolation (qIVIVE) based on physiological-based toxicokinetic (PBTK) models is typically the preferred approach. Such PBTK models require many input parameters to address the route from dose to target site concentration. However, respective data is very often not available. Hence, our aim is to call attention to an alternative way to build a link between animal (in vivo) and cell-derived (in vitro) toxicity data. To this end, we selected the carcinogenic chemical benzo[a]pyrene (BaP) for our study. Our approach relates both in vitro assay and in vivo data to a main intermediate marker structure for carcinogenicity on the subcellular level - the BaP-DNA adduct BaP-7,8-dihydrodiol-9,10-epoxide-deoxyguanosine. Thus, BaP dose is directly linked to a measure of the toxicity-initiating event. We used Syrian hamster embryo (SHE) and Balb/c 3T3 cell transformation assay as in vitro data and compared these data to outcomes of in vivo carcinogenicity tests in rodents. In vitro and in vivo DNA adduct levels range within three orders of magnitude. Especially metabolic saturation at higher doses and interspecies variabilities are identified and critically discussed as possible sources of errors in our simplified approach. Finally, our study points out possible routes to overcome limitations of the envisaged approach in order to allow for a reliable qIVIVE in the future.

Structural alerts for the excess toxicity of acrylates, methacrylates, and propiolates derived from their short-term and long-term bacterial toxicity.

For eight acrylates, three methacrylates, and three propiolates as three subclasses of α,ß-unsaturated esters, short-term and long-term bacterial toxicity with Vibrio fischeri was determined in terms of EC(50) (effective concentration 50%) values for the 30-min bioluminescence and 24-h growth inhibition. To this end, experimental exposure concentrations were corrected for volatilization through a thermodynamic model based on Henry's law constant of the compounds. Moreover, toxicity enhancements T(e) as the ratio of narcosis-predicted over actual EC(50) were determined and discussed in terms of underlying mechanisms of reaction of the electrophiles with endogenous nucleophiles such as glutathione (GSH) and proteins. Overall, log EC(50) [M] ranges from -2.28 to -3.70 (30 min) and from -2.80 to -5.28 (24 h), respectively, indicating a significantly larger sensitivity of the growth inhibition bioassay for the reactive toxicity of these Michael acceptors. The latter is also reflected in the observed toxicity enhancements, where log T(e) > 1 was obtained for only 5 of 14 30-min EC(50) values but for 11 of 13 24-h EC(50) values. Moreover, the average long-term to short-term difference in log T(e) is 1 unit for the acrylates and 0.7 units for both methacrylates and propiolates. Methacrylates exert narcosis-level toxicity except for the methyl derivative in the long-term assay. The log EC(50) (24 h) of a subset of 10 mostly excess-toxic acrylates and a propiolate correlates with their logarithmic rate constants of reaction with GSH, log k(GSH), significantly more than with log K(ow) (r(2) 0.76 vs 0.47), yielding a respective regression rms of 0.34 log units. For allyl and propargyl acrylate as well as propargyl methacrylate, the observed excess toxicity is likely caused by initial enzymatic hydrolysis and subsequent oxidation of the α,ß-unsaturated alcohols to the respective carbonyls. The latter shows that in the context of nonanimal testing schemes such as for REACH, the metabolic capacity of in vitro screens requires attention.

Chemoassay screening of DNA-reactive mutagenicity with 4-(4-nitrobenzyl)pyridine - application to epoxides, oxetanes, and sulfur heterocycles.

Organic electrophiles have the potential to covalently attack DNA bases, and thus initiate mutagenic and carcinogenic processes. In this context, aromatic nitrogen sites of the DNA bases are often particularly nucleophilic, with guanine N7 being one of the most favored sites of adduct formation with electrophilic xenobiotics. Employing 4-(4-nitrobenzyl)pyridine (NBP) as model nucleophile with a respective aromatic ═N- unit, a new kinetic variant of a photometric chemoassay for sensing the DNA reactivity of organic compounds is introduced and applied to 21 three- and four-membered oxygen and sulfur heterocycles (15 epoxides, two thiiranes, three oxetanes, and one thietane). Besides six unreactive compounds (oxetanes, thietane, and aliphatic epoxides with six or more side-chain carbons), second-order rate constants of the electrophile-NBP reaction, k(NBP), were obtained for 15 compounds, ranging from (1.16 ± 0.05)·10⁻³ to (36.5 ± 0.6)·10⁻³ L mol⁻¹ min⁻¹ in a methanol/tris-HCl buffer (16/84 v/v) reaction medium. Solvolysis as confounding factor was addressed by determining respective first-order rate constants k(solv). Analysis of the k(NBP) values resulted in structure-reactivity relationships, and comparison with literature data from the Ames test bacterial strains TA100, TA1535, and TA97 (Salmonella typhimurium) as well as from WP2 uvrA (Escherichia coli) revealed significant log-log relationships between the mutagenic potency of the heterocycles and their reactivity toward NBP. The latter demonstrates the potential of the NBP chemoassay as a nonanimal component of integrated testing strategies for REACH, enabling an efficient screening of organic electrophiles with respect to their DNA reactivity and associated mutagenicity and carcinogenicity.

Thiol reactivity and its impact on the ciliate toxicity of α,ß-unsaturated aldehydes, ketones, and esters.

A recently introduced chemoassay has been used to determine second-order rate constants of the electrophile-nucleophile reaction of 15 α,ß-unsaturated aldehydes with glutathione. The respective kGSH values vary for more than 3 orders of magnitude, and are within the range determined previously for 31 α,ß-unsaturated ketones and esters. Structure-reactivity analyses yield distinct relationships between kGSH and structural features of the compounds. Moreover, increasing kGSH increases the aldehyde toxicity toward ciliates in terms of 48 h-EC50 values (effective concentration yielding 50% growth inhibition of Tetrahymena pyriformis within 48 h). A respective log-log regression equation including both kGSH and the octanol/water partition coefficient, Kow, yields a squared correlation coefficient of 0.96. Comparative analysis with corresponding data for 15 ketones and 16 esters reveals systematic differences between the three compound classes with regard to the individual contributions of hydrophobicity and electrophilic reactivity to aquatic toxicity. The former is particularly pronounced for aldehydes, while the ester toxicity is largely governed by reactivity, with ketones showing an intermediate pattern that is more similar to the one of esters than of aldehydes. It follows that within the Michael acceptor domain of α,ß-unsaturated carbonyls, a distinction between aldehydes and nonaldehydic derivatives appears necessary when employing electrophilic reactivity as a component for the quantitative prediction of their reactive toxicity toward aquatic organisms.

Kinetic glutathione chemoassay to quantify thiol reactivity of organic electrophiles--application to alpha,beta-unsaturated ketones, acrylates, and propiolates.

Glutathione (GSH) is a soft nucleophile and, as such, can be used to sense the reactivity of electrophilic agents toward the thiol group and other electron-rich sites of molecular structures. A new kinetic GSH chemoassay is introduced that employs a photometric method to quantify GSH loss and enables an efficient determination of second-order rate constants, k(GSH), of the reaction between electrophilic substances and GSH. Comparison with an existing 2 h static assay shows that the new kinetic variant is superior with respect to the detectable range of electrophilic reactivity and to confounding factors such as additional GSH loss due to oxidation. Analysis of the chemoassay degradation kinetics provides insight into the characteristic reaction times and the contributions of GSH-electrophile Michael addition and GSH oxidation to the overall GSH loss. For 15 alpha,beta-unsaturated ketones, nine acrylates, and two propiolates acting as Michael acceptors, the measured k(GSH) values span ca. 5 orders of magnitude. Moreover, log k(GSH) correlates with the compounds' toxicity toward the ciliates Tetrahymena pyriformis in terms of 48 h log EC(50) (50% growth inhibition) values, yielding a squared correlation coefficient (r(2)) of 0.91 and a root-mean-square error of 0.30 log units. It shows that for these and related compounds, aquatic toxicity is driven by electrophilic reactivity. The findings demonstrate that the kinetic GSH chemoassay can be used as an efficient tool to analyze, interpret, and predict correspondingly reactive toxicity in the context of qualitative and quantitative structure-activity relationship studies and as a nonanimal tool of integrated testing strategies for REACH to screen compounds for excess toxicity.

Perfluoroalkyl acids in aqueous samples from Germany and Kenya.

Continuous monitoring of chemicals in the environment is important to control their fate and to protect human health, flora, and fauna. Perfluoroalkyl acids (PFAAs) have been detected frequently in different environmental compartments during the last 15 years and have drawn much attention because of their environmental persistence, omnipresence, and bioaccumulation potential. Water is an important source of their transport. In the present study, distributions of PFAAs in river water, wastewater treatment plant (WWTP) effluent, and tap water from eastern part of Germany and western part of Kenya were investigated. Eleven perfluorocarboxylic acids (PFCAs) and five perfluorosulfonic acids (PFSAs) were analyzed using liquid chromatography/tandem mass spectrometry. Sum of mean concentrations of eight PFAAs detected in drinking tap water from Leipzig was 11.5 ng L-1, dominated by perfluorooctanoic acid (PFOA, 6.2 ng L-1). Sums of mean riverine concentrations of PFAAs detected in Pleiße/White Elster, Saale, and Elbe (Germany) were 24.8, 54.3, and 26.8 ng L-1, respectively. Annual flux of PFAAs from River Saale was estimated to be 164 ± 23 kg a-1. The effluent of WWTP in Halle was found to contain four times higher levels of PFAAs than river water and was dominated by perfluorobutane sulfonate (PFBS) with 32 times higher concentration than the riverine level. It advocates that WWTPs are the point source of contaminating water bodies with PFAAs, and short-chain PFAAs are substituting long-chain homologues. Sums of mean riverine concentrations of PFAAs in Sosiani (Kenya) in samples from sparsely populated and densely populated areas were 58.8 and 109.4 ng L-1, respectively, indicating that population directly affected the emissions of PFAAs to surface waters. The discussion includes thorough review and comparison of recently published literature reporting occurrence of PFAAs in aqueous matrices. Graphical abstract Perfluoroalkyl acids in aqueous matrices.

From the exposome to mechanistic understanding of chemical-induced adverse effects.

The exposome encompasses an individual's exposure to exogenous chemicals, as well as endogenous chemicals that are produced or altered in response to external stressors. While the exposome concept has been established for human health, its principles can be extended to include broader ecological issues. The assessment of exposure is tightly interlinked with hazard assessment. Here, we explore if mechanistic understanding of the causal links between exposure and adverse effects on human health and the environment can be improved by integrating the exposome approach with the adverse outcome pathway (AOP) concept that structures and organizes the sequence of biological events from an initial molecular interaction of a chemical with a biological target to an adverse outcome. Complementing exposome research with the AOP concept may facilitate a mechanistic understanding of stress-induced adverse effects, examine the relative contributions from various components of the exposome, determine the primary risk drivers in complex mixtures, and promote an integrative assessment of chemical risks for both human and environmental health.

Volatile organic compounds enhance allergic airway inflammation in an experimental mouse model.

BACKGROUND: Epidemiological studies suggest an association between exposure to volatile organic compounds (VOCs) and adverse allergic and respiratory symptoms. However, whether VOCs exhibit a causal role as adjuvants in asthma development remains unclear. METHODS: To investigate the effect of VOC exposure on the development of allergic airway inflammation Balb/c mice were exposed to VOCs emitted by new polyvinylchloride (PVC) flooring, sensitized with ovalbumin (OVA) and characterized in acute and chronic murine asthma models. Furthermore, prevalent evaporated VOCs were analyzed and mice were exposed to selected single VOCs. RESULTS: Exposure of mice to PVC flooring increased eosinophilic lung inflammation and OVA-specific IgE serum levels compared to un-exposed control mice. The increased inflammation was associated with elevated levels of Th2-cytokines. Long-term exposure to PVC flooring exacerbated chronic airway inflammation. VOCs with the highest concentrations emitted by new PVC flooring were N-methyl-2-pyrrolidone (NMP) and 2,2,4-trimethyl-1,3-pentanediol diisobutyrate (TXIB). Exposure to NMP or TXIB also increased the allergic immune response in OVA-sensitized mice. In vitro or in vivo exposure to NMP or TXIB reduced IL-12 production in maturing dendritic cells (DCs) and enhanced airway inflammation after adoptive DC transfer into Balb/c mice. At higher concentrations both VOCs induced oxidative stress demonstrated by increased isoprostane and glutathione-S-transferase-pi1 protein levels in the lung of non-sensitized mice. Treatment of PVC flooring-exposed mice with N-acetylcysteine prevented the VOC-induced increase of airway inflammation. CONCLUSIONS: Our results demonstrate that exposure to VOCs may increase the allergic immune response by interfering with DC function and by inducing oxidative stress and has therefore to be considerate as risk factor for the development of allergic diseases.

The aromatic volatile organic compounds toluene, benzene and styrene induce COX-2 and prostaglandins in human lung epithelial cells via oxidative stress and p38 MAPK activation.

Toluene, benzene and styrene are volatile organic compounds (VOCs) widely distributed in the environment. Tobacco smoke, traffic exposure and solvents used for paints, rubber and adhesives are known sources for these compounds. The aim of the present study was to investigate whether toluene, benzene and styrene can induce inflammatory reactions in lung cells and to characterize possible underlying mechanisms. A previous study gave evidence that expression of cyclooxygenase-2 (COX-2) is upregulated following exposure to the aromatic VOC chlorobenzene. Here, we investigated the effects of the aromatics toluene, benzene and styrene on human lung cells, with emphasis on COX-2, the rate-limiting enzyme of the prostaglandin pathway. In addition, we studied the potential role of oxidative stress and p38 MAPK activation in the toluene/benzene/styrene-dependent COX-2 induction. Following exposure to the aromatic compounds the expression level of COX-2 increased markedly. In addition, prostaglandin E(2) (PGE(2)) and prostaglandin F(2α) (PGF(2α)), major products of the COX enzyme, were found to be upregulated in response to toluene, benzene or styrene exposure. Furthermore, we observed an activation of p38 MAPK resulting from aromatic VOC exposure. Treatment of the cells with a specific p38 inhibitor (SB203580) or the antioxidant N-acetylcysteine (NAC) was able to prevent the toluene/benzene/styrene-dependent COX-2 activation, and subsequent increased PGE(2) and PGF(2α) secretion. These results suggest that toluene, benzene and styrene induce production and secretion of PGE(2) and PGF(2α) in lung epithelial cells via p38 MAPK and COX-2 activation in a redox sensitive manner.