Metabolism and Lung Toxicity of Inhaled Naphthalene: Effects of Postnatal Age and Sex

Impact of aging and ergothioneine pre-treatment on naphthalene toxicity in lung

Aging increases susceptibility to lung disease, but the topic is understudied, especially in relation to environmental exposures with the bulk of rodent studies using young adults. This study aims to define the pulmonary toxicity of naphthalene (NA) and the impacts of a dietary antioxidant, ergothioneine (ET), in the liver and lungs of middle-aged mice. NA causes a well-characterized pattern of conducting airway epithelial injury in the lung in young adult mice, but NA's toxicity has not been characterized in middle-aged mice, aged 1-1.5 years. ET is a dietary antioxidant that is synthesized by bacteria and fungi. The ET transporter (ETT), SLC22A4, is upregulated in tissues that experience high levels of oxidative stress. In this study, middle-aged male and female C57BL/6 J mice, maintained on an ET-free synthetic diet from conception, were gavaged with 70 mg/kg of ET for five consecutive days. On day 8, the mice were exposed to a single intraperitoneal NA dose of 50, 100, 150, or 200 mg/kg. At 24 hours post NA injection samples were collected and analyzed for ET concentration and reduced (GSH) and oxidized glutathione (GSSG) concentrations. Histopathology, morphometry, and gene expression were examined. Histopathology of mice exposed to 100 mg/kg of NA suggests reduction in toxicity in the terminal airways of both male (p ≤ 0.001) and female (p ≤ 0.05) middle-aged mice by the ET pretreatment. Our findings in this study are the first to document the toxicity of NA in middle-aged mice and show some efficacy of ET in reducing NA toxicity.

Longitudinal association of polycyclic aromatic hydrocarbons and genetic risk with lung function

To quantify the association of polycyclic aromatic hydrocarbons (PAHs) and the polygenic risk score (PRS) with lung function decline, we developed a repeated-measures study with 4681 observations from baseline and 6-year follow-up of the Wuhan-Zhuhai cohort. Lung function and urinary monohydroxylated PAH metabolites (OH-PAHs) were measured for each observation. The PRS was derived from 246 lung function-associated genetic variants weighted by the effect size of the decreasing ratio of forced expiratory volume in 1 s by forced vital capacity (FEV1/FVC). Linear mixed models were used to estimate the longitudinal exposure-response relationships between OH-PAHs and lung function, and to evaluate the interactions between OH-PAHs and PRS on the longitudinal change of lung function. We found that each 1-unit increase in log-transformed values of 9-hydroxyfluorene, 2-hydroxyfluorene, 4-hydroxyphenanthrene, 9-hydroxyphenanthrene, 2-hydroxyphenanthrene, 1-hydroxyphenanthrene, 1-hydroxypyrene, low molecular weight OH-PAHs (ΣLMW-OH-PAHs), and total OH-PAHs (ΣOH-PAHs) was associated with an annual change in FEV1/FVC of -0.140, -0.112, -0.260, -0.300, -0.159, -0.220, -0.145, -0.156, and -0.177 %/year, respectively. Interactions on the annual decline of FEV1/FVC were detected between ΣLMW-OH-PAHs and PRS (-0.010 %/year, 95% confidence interval -0.018 to -0.001, Pint = 0.0228), and between ΣOH-PAHs and PRS (-0.010 %/year, -0.018 to -0.001, Pint = 0.0203). These results indicated that specific and total urinary OH-PAHs were associated with the longitudinal FEV1/FVC decline, and ΣLMW-OH-PAHs as well as ΣOH-PAHs interacted with PRS on the annual decline of FEV1/FVC.

Early-life ozone exposure modulates region-specific gene expression in the developing rat lung

Early-life ozone exposure disrupts normal patterns of lung development, but the molecular determinants underlying these changes are not well understood. This study aimed to elucidate changes in gene expression following episodic ozone exposure to identify potential mechanisms of ozone-mediated impairments in lung development. Rat pups were exposed to either filtered air or ozone (0.5 ppm, 6 hr./day, 5 days/week) from postnatal day (PND) 7-28 (16 dams total with 8 pups each, 4 M & 4 F) and sacrificed at either PND 30-31 or PND 80-84. Lung microdissection isolated major regions for RNA-Seq analysis. Ozone modified inherent differences in gene expression between lung regions in both male and female rat pups, whereas statistically significant changes in gene expression directly attributed to ozone were only identified in females. The greatest number of differentially expressed genes was observed between the distal airways and the parenchyma of ozone-exposed juvenile female rats, with 355 genes being differentially expressed. Genes modulating epithelial-to-mesenchymal transition, cell growth, and adhesion were differentially expressed in the parenchyma of ozone exposed juvenile females, suggesting that episodic ozone exposure may affect branching morphogenesis and lung cell growth. Importantly, our study provides novel targets for future experiments investigating the impact of ozone on lung development.

Association between co-exposure of polycyclic aromatic hydrocarbons and chronic obstructive pulmonary disease among the US adults: results from the 2013-2016 National Health and Nutrition Examination Survey

Although existing epidemiological studies have reported the relationship between single polycyclic aromatic hydrocarbon (PAH) exposure and chronic obstructive pulmonary disease (COPD), little is known about the impact of PAH mixture exposure on COPD. Therefore, we aimed to evaluate the associations of single and mixed exposures to PAHs with COPD in US adults using data from NHANES 2013-2016 by fitting three statistical methods, including multiple logistic regression, Bayesian kernel machine regression (BKMR), and quantile-based g-computation (qgcomp) models. This study included 1836 participants aged 40 and older. Multiple logistic regression showed that 2-FLU, 1-PHE, 1-PYR, and 2&3-PHE increased the risk of COPD after adjusting for all covariates. The BKMR model identified positive trends between PAH mixture and the risk of COPD in all adults and males when all PAHs were at or above their 55th percentile compared to all PAHs at their 50th percentile. The qgcomp model suggested that PAH co-exposure increased the risk of COPD (OR:1.44, 95%CI:1.09, 1.90) when each quartile increased in PAH mixture concentration, with 2-FLU having the highest weight. The combined impact also be observed in men. In conclusion, PAHs co-exposure was associated with a higher risk of COPD, especially in males, with the positive impact of 2-FLU being the most important.

Naphthalene and its Derivatives: Efficient Fluorescence Probes for Detecting and Imaging Purposes

Naphthalene, white crystalline solid having polycyclic aromatic hydrocarbon with characteristic mothball order is naturally present in crucial oils of various plants. Naphthalene derivatives are extensive drug resources and are use as wetting agents, surfactants and as insecticides. These derivatives exhibit unique photo physical and chemical properties. These characteristics make them the most studied group of organic compounds. Naphthalene dyes have rigid plane and large π-electron conjugation. Therefor they have high quantum yield and excellent photostability. Naphthalene based fluorescence probes due to hydrophobic nature exhibit excellent sensing and selectivity properties towards anions and cations and also used as a part of target biomolecules. In conjugated probe system, introducing naphthalene moiety caused improvement in photo-stability. Therefore among various conjugated framework, naphthalene derivatives are considered excellent candidate for the construction of organic electronic appliances. These derivatives are useful for a variety of applications owing to their strong fluorescence, electroactivity and photostability. This article is based upon investigation of photophysical properties of naphthalene derivatives and fluorescence detecting probe of naphthalene. For photophysical properties the techniques under investigation are UV visible spectroscopy and fluorescence spectroscopy. Concentration dependent spectra and solvatochromic shifts on UV visible spectra are also part of discussion.

Biotransformation as a tool for remediation of polycyclic aromatic hydrocarbons from polluted environment - review on toxicity and treatment technologies

Polycyclic aromatic hydrocarbons, a prominent family of persistent organic molecules produced by both anthropogenic and natural processes, are widespread in terrestrial and aquatic environments owing to their hydrophobicity, electrochemical stability and low aqueous solubility. Phenanthrene and naphthalene belong to the group of polycyclic aromatic hydrocarbons whose occurrence are reported to be relatively higher. The bioremediation mode of removing the toxicities of these two compounds has been reported to be promising than other methods. Most of the microbial classes of bacterial, fungal and algal origin are reported to degrade the target pollutants into non-toxic compounds effectively. The review aims to give an overview on toxicological studies, identification and enrichment techniques of phenanthrene and naphthalene degrading microbes and the bioremediation technologies (microbial assisted reactors, microbial fuel cells and microbial assisted constructed wetlands) reported by various researchers. All the three modes of bioremediation techniques were proved to be promising on different perspectives. In the treatment of phenanthrene, a maximum recovery of 96% and 98% was achieved in an aerobic membrane reactor with Bacillus species and single chamber air cathode microbial fuel cell with Acidovorax and Aquamicrobium respectively were reported. With the constructed wetland configuration, 95.5% of removal was attained with manganese oxide based microbial constructed wetland. The maximum degradation efficiency reported for naphthalene are 99% in a reverse membrane bioreactor, 98.5% in a marine sediment microbial fuel cell and 92.8% with a low-cost sandy soil constructed wetland.

In vitro airway models from mice, rhesus macaques, and humans maintain species differences in xenobiotic metabolism and cellular responses to naphthalene

The translational value of high-throughput toxicity testing will depend on pharmacokinetic validation. Yet, popular in vitro airway epithelia models were optimized for structure and mucociliary function without considering the bioactivation or detoxification capabilities of lung-specific enzymes. This study evaluated xenobiotic metabolism maintenance within differentiated air-liquid interface (ALI) airway epithelial cell cultures (human bronchial; human, rhesus, and mouse tracheal), isolated airway epithelial cells (human, rhesus, and mouse tracheal; rhesus bronchial), and ex vivo microdissected airways (rhesus and mouse) by measuring gene expression, glutathione content, and naphthalene metabolism. Glutathione levels and detoxification gene transcripts were measured after 1-h exposure to 80 µM naphthalene (a bioactivated toxicant) or reactive naphthoquinone metabolites. Glutathione and glutathione-related enzyme transcript levels were maintained in ALI cultures from all species relative to source tissues, while cytochrome P450 monooxygenase gene expression declined. Notable species differences among the models included a 40-fold lower total glutathione content for mouse ALI trachea cells relative to human and rhesus; a higher rate of naphthalene metabolism in mouse ALI cultures for naphthalene-glutathione formation (100-fold over rhesus) and naphthalene-dihydrodiol production (10-fold over human); and opposite effects of 1,2-naphthoquinone exposure in some models-glutathione was depleted in rhesus tissue but rose in mouse ALI samples. The responses of an immortalized bronchial cell line to naphthalene and naphthoquinones were inconsistent with those of human ALI cultures. These findings of preserved species differences and the altered balance of phase I and phase II xenobiotic metabolism among the characterized in vitro models should be considered for future pulmonary toxicity testing.

Pesticide pollutants in the environment - A critical review on remediation techniques, mechanism and toxicological impact

The excessive and unorganised utilisation of pesticides have posed negative impacts on soil and water at higher levels. Pesticides are a major class of persistent organic compounds with high resistance to natural biodegradation and enhanced tendency to bio accumulate. The severe health hazards imposed on the living organisms hinder the ecosystem and lead to chronic and irreversible health issues. Photocatalytic method is reported as a potential alternative with a variety of techniques and materials that are safer, easier, durable, cost-effective and efficient. Nanomaterials play a key role in this domain due to their versatility. In particular, nanostructured materials of organized shapes and morphological properties have gained enormous attention in research and real-time applications. Specifically, nanomaterials like nanotubes, nanorods and nanowires have unique properties and anisotropic structure that make them more suitable for treating pesticide wastes with photocatalysis. Variety of tuning methods and materials are emerging to enhance the activity of titanium and zinc based nanocatalysts in remediation methods. In the present article, four pesticides, namely, atrazine, chlorpyrifos, paraquat and naphthalene are chosen due to their common occurrence and usage in agricultural applications. These pesticides are highly toxic and need special attention to explore appropriate remediation methods. The report also details the latest innovations reported by several research studies in exploring the potential of specially synthesised nanoparticles for photocatalytic removal of pesticide pollutants from environment. For zinc-based hybrid nanomaterials, the maximum disintegration reported were 99%, 98%, 73.3% and 92.3% for atrazine, chlorpyrifos, paraquat and naphthalene, respectively.

Evaluation of cytokines in exhaled breath condensate in an occupationally exposed population to pneumotoxic pollutants

The quarrying is considered a precarious occupation with high toxicity, is an informal economic activity that employs low technology, limited protection, and poses a risk to workers and their families. In quarrying, silica dust is generated and there is also occupational exposure to significant mixtures of pneumotoxic pollutants, including mineral dust (crystalline silica, carbon or cement, polycyclic aromatic hydrocarbons (PAHs), solvents, and others, which are aggravated by the lack of use of protective equipment, causing irreversible damage to the worker's respiratory health. Thus, the objective of this work focused on the evaluation of the respiratory health of artisan stonemasons in San Luis Potosí, Mexico through the study of exhaled breath condensate (EBC) (pH, pro-inflammatory cytokines) as well as the study of the exposure to pollutants present in the work area (PAHs, toluene, and 2.5 µm particulate matter) through biomarkers of exposure (hippuric acid and hydroxylated metabolites of PAHs). The results show the presence of crystalline SiO₂ in 100% of the samples analyzed; the PM_2.5 concentrations were 5 to 10 times the permitted levels. Regarding exposure to PAHs, all the stonemasons presented urine concentrations of at least 5 of the OH-PAHs evaluated; 9-OH-FLU occurred at higher concentrations of 171.2 (122.7-279.4) µg L^-1; hippuric acid, which was present in 100% of the workers evaluated in concentrations of 283.4 (27.72-1119) mg L^-1, 100% of which were above the values established for occupational scenarios. The pH values obtained for the EBC samples were presented at an average of 7.07 (6.33-7.66). Pro-inflammatory cytokines were present in 86.1% of the study population. The cytokine that was found in higher concentrations was IL-2, with a mean of 178.01 pg mL^-1 and 3124.01 pg mL^-1 for the pH < 7 and pH > 7 groups, respectively. Some correlations between the cytokines and the exposure biomarkers were presented. Stonemasons are highly exposed to pneumotoxic pollutants and markers of inflammation at the pulmonary level; in addition, a high risk of developing silicosis. Quarrying should be addressed as a carcinogenic activity, which would imply the design of monitoring and control strategies for these pollutants that our country currently lacks, particularly in precarious occupations. It is necessary to develop strategies to protect the health of precarious workers.

Genome-wide gene-bisphenol A, F and triclosan interaction analyses on urinary oxidative stress markers

BACKGROUND

Bisphenols and triclosan (TCS) are common endocrine disrupters (EDCs) that may induce oxidative stress. However, there is limited information as to whether these EDCs interact with genetic variants to modify the levels of oxidative stress on a genome-wide scale.

METHODS

We first performed a genome-wide scan among a Chinese population and also measured three urinary EDCs, including bisphenol A (BPA), bisphenol F (BPF) and TCS, and three urinary oxidative stress markers [4-hydroxy-2-nonenal-mercapturic acid (HNE-MA), 8-iso-prostaglandin-F_2α (8-isoPGF_2α) and 8-hydroxy-deoxyguanosine (8-OHdG)]. Subsequently, we examined interactions between three urinary EDCs and nearly 4.6 million genetic variants for three urinary oxidative stress markers by the general linear model.

RESULTS

Urinary BPA, BPF and TCS were positively associated with HNE-MA, 8-isoPGF_2α and 8-OHdG. Significant rs6855040 (4p15.32/between SNORA75B and QDPR)-BPA, rs1112943 (4q35.1/SNX25)-TCS interactions were associated with the 8-isoPGF_2α levels (all P < 5 × 10^-8). In addition, rs4656116 (1p22.3/CACL1), rs16958760 (17p11.2/between USP43 and DHRS7C) and rs11651078 (17p11.2/LOC339260) showed significant gene-TCS interactions with 8-OHdG (all P < 5 × 10^-8). The gene-level analysis found significant interaction between SNX25 and TCS for 8-isoPGF_2α levels (P < 2.12 × 10^-6).

CONCLUSION

Our results identify several gene-EDCs interactions for oxidative stress, highlighting that EDCs may modify the effect of genetic variants on oxidative stress.

Indoor Air Pollution Increases the Risk of Lung Cancer

(1) Background: Cooking and burning incense are important sources of indoor air pollutants. No studies have provided biological evidence of air pollutants in the lungs to support this association. Analysis of pleural fluid may be used to measure the internal exposure dose of air pollutants in the lung. The objective of this study was to provide biological evidence of indoor air pollutants and estimate their risk of lung cancer. (2) Methods: We analyzed 14 common air pollutants in the pleural fluid of 39 cases of lung adenocarcinoma and 40 nonmalignant controls by gas chromatography-mass spectrometry. (3) Results: When we excluded the current smokers and adjusted for age, the adjusted odds ratios (ORs) were 2.22 (95% confidence interval CI = 0.77-6.44) for habitual cooking at home and 3.05 (95% CI = 1.06-8.84) for indoor incense burning. In females, the adjusted ORs were 5.39 (95% CI = 1.11-26.20) for habitual cooking at home and 6.01 (95% CI = 1.14-31.66) for indoor incense burning. In pleural fluid, the most important exposure biomarkers for lung cancer were naphthalene, ethylbenzene, and o-xylene. (4) Conclusions: Habitual cooking and indoor incense burning increased the risk of lung adenocarcinoma.

Metabolomics of Lung Microdissections Reveals Region- and Sex-Specific Metabolic Effects of Acute Naphthalene Exposure in Mice

Naphthalene is a ubiquitous environmental contaminant produced by combustion of fossil fuels and is a primary constituent of both mainstream and side stream tobacco smoke. Naphthalene elicits region-specific toxicity in airway club cells through cytochrome P450 (P450)-mediated bioactivation, resulting in depletion of glutathione and subsequent cytotoxicity. Although effects of naphthalene in mice have been extensively studied, few experiments have characterized global metabolomic changes in the lung. In individual lung regions, we found metabolomic changes in microdissected mouse lung conducting airways and parenchyma obtained from animals sacrificed at 3 timepoints following naphthalene treatment. Data on 577 unique identified metabolites were acquired by accurate mass spectrometry-based assays focusing on lipidomics and nontargeted metabolomics of hydrophilic compounds. Statistical analyses revealed distinct metabolite profiles between the 2 lung regions. Additionally, the number and magnitude of statistically significant exposure-induced changes in metabolite abundance were different between airways and parenchyma for unsaturated lysophosphatidylcholines, dipeptides, purines, pyrimidines, and amino acids. Importantly, temporal changes were found to be highly distinct for male and female mice with males exhibiting predominant treatment-specific changes only at 2 h postexposure. In females, metabolomic changes persisted until 6 h postnaphthalene treatment, which may explain the previously characterized higher susceptibility of female mice to naphthalene toxicity. In both males and females, treatment-specific changes corresponding to lung remodeling, oxidative stress response, and DNA damage were observed. Overall, this study provides insights into potential mechanisms contributing to naphthalene toxicity and presents a novel approach for lung metabolomic analysis that distinguishes responses of major lung regions.

Contribution of Pulmonary CYP-mediated Bioactivation of Naphthalene to Airway Epithelial Injury in the Lung

Previous studies have established that cytochrome P450 enzymes (CYPs) in both liver and lung are capable of bioactivating naphthalene (NA), an omnipresent air pollutant and possible human carcinogen, in vitro and in vivo. The aim of this study was to examine the specific contribution of pulmonary CYPs in airway epithelial cells to NA-induced airway toxicity. We used a lung-Cpr-null mouse model, which undergoes doxycycline-induced, Cre-mediated deletion of the Cpr (a redox partner of all microsomal CYPs) gene specifically in airway epithelial cells. In 2-month-old lung-Cpr-null mice, Cpr deletion occurred in 75%-82% of epithelial cells of conducting airways. The extent of NA-induced acute lung toxicity (as indicated by total protein concentration and lactate dehydrogenase activity in bronchoalveolar lavage fluid collected at 24-h after initiation of a 4-h, nose-only, 10-ppm NA inhalation exposure) was substantially lower (by 37%-39%) in lung-Cpr-null mice, compared with control littermates. Moreover, the extent of cellular proliferation (as indicated by 5-bromo-2'-deoxyuridine incorporation) was noticeably lower in both proximal and distal airways (by 59% and 65%, respectively) of NA-treated lung-Cpr-null mice, compared with control littermates, at 2-day post-NA inhalation exposure. A similar genotype-related difference in the extent of postexposure cell proliferation was also observed in mice exposed to NA via intraperitoneal injection at 200 mg/kg. These results directly validate the hypothesis that microsomal CYP enzymes in airway epithelial cells play a large role in causing injury to airway epithelia following exposure to NA via either inhalation or intraperitoneal route.

Health Effects of Naphthalene Exposure: A Systematic Evidence Map and Analysis of Potential Considerations for Dose-Response Evaluation

BACKGROUND

Naphthalene is a polycyclic aromatic hydrocarbon that has been associated with health effects, including cancer. As the state of the science on naphthalene toxicity continues to evolve, updated toxicity reference value(s) may be required to support human health risk assessment.

OBJECTIVES

We present a systematic evidence map of studies that could be used to derive toxicity reference value(s) for naphthalene.

METHODS

Human and animal health effect studies and physiologically based pharmacokinetic (PBPK) models were identified from a literature search based on populations, exposures, comparators, and outcomes (PECO) criteria. Human and animal studies meeting PECO criteria were refined to a smaller subset considered most informative for deriving chronic reference value(s), which are preferred for assessing risk to the general public. This subset was evaluated for risk of bias and sensitivity, and the suitability of each study for dose-response analysis was qualitatively assessed. Lowest observed adverse effect levels (LOAELs) were extracted and summarized. Other potentially relevant studies (e.g., mechanistic and toxicokinetic studies) were tracked as supplemental information but not evaluated further. Existing reference values for naphthalene are also summarized.

RESULTS

We identified 26 epidemiology studies and 16 animal studies that were considered most informative for further analysis. Eleven PBPK models were identified. The available epidemiology studies generally had significant risk of bias and/or sensitivity concerns and were mostly found to have low suitability for dose-response analysis due to the nature of the exposure measurements. The animal studies had fewer risk of bias and sensitivity concerns and were mostly found to be suitable for dose-response analysis.

CONCLUSION

Although both epidemiological and animal studies of naphthalene provide weight of evidence for hazard identification, the available animal studies appear more suitable for reference value derivation. PBPK models and mechanistic and toxicokinetic data can be applied to extrapolate these animal data to humans, considering mode of action and interspecies metabolic differences. https://doi.org/10.1289/EHP7381.

Inhibition of Gabrp reduces the differentiation of airway epithelial progenitor cells into goblet cells

Bronchial asthma is an intractable pulmonary disease that affects millions of individuals worldwide, with the overproduction of mucus contributing to high morbidity and mortality. Gamma-aminobutyric acid (GABA) is associated with goblet cell hyperplasia in the lungs of primate models and Club cells serve as airway epithelial progenitor cells that may differentiate into goblet and ciliated cells. In the present study, it was investigated whether the GABAA receptor pi (Gabrp) is essential for Club cell proliferation and differentiation in mice. Validation of microarray analysis results by reverse transcription-quantitative PCR (RT-qPCR) demonstrated that Gabrp is highly expressed in mouse Club cells. Predominant expression of Gabrp in mouse Club cells was further confirmed based on naphthalene-induced Club cell injury in mice, with organoid cultures indicating significant reductions in the organoid-forming ability of mouse Club cells in the presence of Gabrp antagonist bicuculline methiodide (BMI). Furthermore, the RT-qPCR results indicated that the mRNA levels of chloride channel accessory 3, pseudogene (Clca3p), mucin (Muc)5Ac and Muc5B were significantly decreased in BMI organoid cultures. These results suggested that blocking GABA signaling through Gabrp inhibits mouse Club cell proliferation, as well as differentiation into goblet cells. Therefore, targeting GABA/Gabrp signaling may represent a promising strategy for treating goblet cell hyperplasia in bronchial asthma.

Backward modeling of urinary test reliability for assessing PAH health risks: An approximation solution for naphthalene

Urine sample tests are one of the most common methods of estimating human exposure to polycyclic aromatic hydrocarbons (PAHs) and assessing population health risks. To evaluate the reliability of the urine test and the impact of other PAH elimination routes on the health risk estimated by this test, we proposed a backward modeling framework integrating other common elimination routes of PAH metabolites to calculate the overall intake rate of the parent PAH based on the levels of corresponding main metabolites in urine. Due to limited biotransformation data, we selected naphthalene as an example to evaluate model performance and collected urine samples from 234 random adults in Shenzhen. The overall intake rates of naphthalene were then simulated and compared to current literature data. The simulated intake rates of naphthalene ranged from 3.70 × 10-3 mg d-1 to 1.95 mg d-1 and followed a lognormal distribution with a median value of 6.51 × 10-2 mg d-1. The results indicated that, if naphthalene exposure occurred only via food for the population of Shenzhen, the literature data fell within the most frequent interval [3.70 × 10-3, 4.45 × 10-2] but were lower than the simulated median value. However, if other exposure routes were considered, the allocation factor-adjusted literature data were close to the simulated median values. In addition, under normal physiological conditions, the simulated results were more sensitive to 1-hydroxynaphthalene (1-OHN) and 2-hydroxynaphthalene (2-OHN) levels in urine than other biometric variables, which is due to the limited load of 1-OHN and 2-OHN in human elimination routes. Furthermore, the suggested safety levels of 1-OHN and 2-OHN in urine to protect 99% of the general population of Shenzhen were 6.40 × 10-6 and 3.75 × 10-5 mg L-1, which could be used as regulatory indicators based on the high reliability of the model.

Investigation by mass spectrometry and 32P post-labelling of DNA adducts formation from 1,2-naphthoquinone, an oxydated metabolite of naphthalene

Naphthalene is the simplest representative of polycyclic aromatic hydrocarbons (PAHs). It is detected as major pollutant in the different compartments of the environment. This compound is considered by the international agency for research on cancer (IARC), the specialized cancer agency of the World Health Organisation (WHO), as a possible carcinogenic (group 2B) since 2002, mainly based on studies on chronic inhalation in rodent by the national toxicology program of the U.S. department of health and human services. In humans, its main metabolites correspond to derivatives substituted in position and 1 and 2 as 1,2-naphthoquinone (1,2-NphQ). Based on previous studies, 1,2-NphQ is supposed to react with DNA to form mostly depurinating adducts, a possible initiating step of carcinogenicity. To confirm this potentiality, adducts were synthetized by the reaction of 1,2-NphQ with 2'-deoxyguanosine (2'-dG) in N,N-dimethylformamide (DMF), water and calf thymus DNA. 2'-dG adducts were analyzed by ³²P post-labelling, HPLC with ultra-violet detection and ultra-performance liquid chromatography coupled to tandem mass spectrometry (UHPLC-MS/MS). We found stable DNA adducts detected in DNA. We proposed a formation mechanism by a 1,4-Michael addition with 2'-dG. Adducts with 2'-deoxyxanthosine are formed after a spontaneous deamination of 2'-dG. These adducts are good candidates as biomarkers allowing evaluation of exposure to naphthalene and its derivatives in the development of pathologies such as cancer.

Comparison of acute respiratory epithelial toxicity for 4-Methylimidazole and naphthalene administered by oral gavage in B6C3F1 mice

4-Methylimidazole (4MEI) is a contaminant in food and consumer products. Pulmonary toxicity and carcinogenicity following chronic dietary exposures to 4MEI is a regulatory concern based on previous rodent studies. This study examined acute pulmonary toxicity in B6C3F1 mice from 6 h to 5 days after oral gavage with a single dose of 150 mg/kg 4MEI, a double dose delivered 6 h apart, or vehicle controls. Oral gavage of 150 mg/kg naphthalene, a prototypical Club cell toxicant, was used as a positive control. Intrapulmonary conducting airway cytotoxicity was assessed in fixed-pressure inflated lungs using qualitative histopathology scoring, quantitative morphometric measurement of vacuolated and exfoliating epithelial cells, and immunohistochemistry. 4MEI treatment did not change markers of cytotoxicity including the mass of vacuolated epithelium, the thickness of the epithelium, or the distributions of epithelial proteins: secretoglobin 1A1, proliferating cell nuclear antigen, calcitonin gene-related peptide, and myeloperoxidase. 4MEI and vehicle controls caused slight cytotoxicity with rare vacuolization of the epithelium relative to the severe bronchiolar epithelial cell toxicity found in the naphthalene exposed mice at terminal bronchioles, intrapulmonary airways, or airway bifurcations. In summary, 4MEI caused minimal airway epithelial toxicity without characteristic Club Cell toxicity when compared to naphthalene, a canonical Club Cell toxicant.

Inhalation Toxicology of Vaping Products and Implications for Pulmonary Health

E-cigarettes have a liquid that may contain flavors, solvents, and nicotine. Heating this liquid generates an aerosol that is inhaled into the lungs in a process commonly referred to as vaping. E-cigarette devices can also contain cannabis-based products including tetrahydrocannabinol (THC), the psychoactive component of cannabis (marijuana). E-cigarette use has rapidly increased among current and former smokers as well as youth who have never smoked. The long-term health effects are unknown, and emerging preclinical and clinical studies suggest that e-cigarettes may not be harmless and can cause cellular alterations analogous to traditional tobacco smoke. Here, we review the historical context and the components of e-cigarettes and discuss toxicological similarities and differences between cigarette smoke and e-cigarette aerosol, with specific reference to adverse respiratory outcomes. Finally, we outline possible clinical disorders associated with vaping on pulmonary health and the recent escalation of acute lung injuries, which led to the declaration of the vaping product use-associated lung injury (EVALI) outbreak. It is clear there is much about vaping that is not understood. Consequently, until more is known about the health effects of vaping, individual factors that need to be taken into consideration include age, current and prior use of combustible tobacco products, and whether the user has preexisting lung conditions such as asthma and chronic obstructive pulmonary disease (COPD).