Bulky DNA adducts, microRNA profiles, and lipid biomarkers in Norwegian tunnel finishing workers occupationally exposed to diesel exhaust

Lung cancer associated with combustion particles and fine particulate matter (PM2.5) - The roles of polycyclic aromatic hydrocarbons (PAHs) and the aryl hydrocarbon receptor (AhR)

Air pollution is the leading cause of lung cancer after tobacco smoking, contributing to 20% of all lung cancer deaths. Increased risk associated with living near trafficked roads, occupational exposure to diesel exhaust, indoor coal combustion and cigarette smoking, suggest that combustion components in ambient fine particulate matter (PM2.5), such as polycyclic aromatic hydrocarbons (PAHs), may be central drivers of lung cancer. Activation of the aryl hydrocarbon receptor (AhR) induces expression of xenobiotic-metabolizing enzymes (XMEs) and increase PAH metabolism, formation of reactive metabolites, oxidative stress, DNA damage and mutagenesis. Lung cancer tissues from smokers and workers exposed to high combustion PM levels contain mutagenic signatures derived from PAHs. However, recent findings suggest that ambient air PM2.5 exposure primarily induces lung cancer development through tumor promotion of cells harboring naturally acquired oncogenic mutations, thus lacking typical PAH-induced mutations. On this background, we discuss the role of AhR and PAHs in lung cancer development caused by air pollution focusing on the tumor promoting properties including metabolism, immune system, cell proliferation and survival, tumor microenvironment, cell-to-cell communication, tumor growth and metastasis. We suggest that the dichotomy in lung cancer patterns observed between smoking and outdoor air PM2.5 represent the two ends of a dose-response continuum of combustion PM exposure, where tumor promotion in the peripheral lung appears to be the driving factor at the relatively low-dose exposures from ambient air PM2.5, whereas genotoxicity in the central airways becomes increasingly more important at the higher combustion PM levels encountered through smoking and occupational exposure.

Diesel exhaust particles exposure induces liver dysfunction: Exploring predictive potential of human circulating microRNAs signature relevant to liver injury risk

Diesel exhaust particles (DEP) pollution should be taken seriously because it is an extensive environmental and occupational health concern. Exploring early effect biomarkers is crucial for monitoring and managing DEP-associated health risk assessment. Here, we found that serum levels of 67 miRNAs were dysregulated in DEP exposure group. Notably, 20 miRNAs were identified as each having a significant dose-response relationship with the internal exposure level of DEP. Further, we revealed that the DEP exposure could affect the liver function of subjects and that 7 miRNAs (including the well-known liver injury indicator, miR-122-5p) could serve as the novel epigenetic-biomarkers (epi-biomarkers) to reflect the liver-specific response to the DEP exposure. Importantly, an unprecedented prediction model using these 7 miRNAs was established for the assessment of DEP-induced liver injury risk. Finally, bioinformatic analysis indicated that the unique set of miRNA panel in serum might also contribute to the molecular mechanism of DEP exposure-induced liver damage. These results broaden our understanding of the adverse health outcomes of DEP exposure. Noteworthy, we believe this study could shed light on roles and functions of epigenetic biomarkers from environmental exposure to health outcomes by revealing the full chain of exposure-miRNAs-molecular pathways-disease evidence.

Biodiesel feedstock determines exhaust toxicity in 20% biodiesel: 80% mineral diesel blends

To address climate change concerns, and reduce the carbon footprint caused by fossil fuel use, it is likely that blend ratios of renewable biodiesel with commercial mineral diesel fuel will steadily increase, resulting in biodiesel use becoming more widespread. Exhaust toxicity of unblended biodiesels changes depending on feedstock type, however the effect of feedstock on blended fuels is less well known. The aim of this study was to assess the impact of biodiesel feedstock on exhaust toxicity of 20% blended biodiesel fuels (B20). Primary human airway epithelial cells were exposed to exhaust diluted 1/15 with air from an engine running on conventional ultra-low sulfur diesel (ULSD) or 20% blends of soy, canola, waste cooking oil (WCO), tallow, palm or cottonseed biodiesel in diesel. Physico-chemical exhaust properties were compared between fuels and the post-exposure effect of exhaust on cellular viability and media release was assessed 24 h later. Exhaust properties changed significantly between all fuels with cottonseed B20 being the most different to both ULSD and its respective unblended biodiesel. Exposure to palm B20 resulted in significantly decreased cellular viability (96.3 ± 1.7%; p < 0.01) whereas exposure to soy B20 generated the greatest number of changes in mediator release (including IL-6, IL-8 and TNF-α, p < 0.05) when compared to air exposed controls, with palm B20 and tallow B20 closely following. In contrast, canola B20 and WCO B20 were the least toxic with only mediators G-CSF and TNF-α being significantly increased. Therefore, exposure to palm B20, soy B20 and tallow B20 were found to be the most toxic and exposure to canola B20 and WCO B20 the least. The top three most toxic and the bottom three least toxic B20 fuels are consistent with their unblended counterparts, suggesting that feedstock type greatly impacts exhaust toxicity, even when biodiesel only comprises 20% of the fuel.

The Fabrication of Oleophobic Coating and Its Application in Particulates Filtration

The stir-frying process in Chinese cooking has produced serious emissions of oily particles, which are an important source of urban air pollution. In particular, the complex composition of fine particulate may pose a threat to human respiratory and immune systems. However, current filtration methods for oily particulate fumes have low filtration efficiency, high resistance, and high equipment costs. In polypropylene (PP) electret filters, efficiency rapidly decreases and pressure drop (wind resistance) sharply increases after the adsorption of oily particles, due to the oleophilic properties of the PP fibre. We addressed this issue of filter performance degradation by fabricating a sodium perfluorooctanoate (SPFO) oleophobic coating on polyvinylidene fluoride (PVDF) fibre membranes for oily particle filtration. The SPFO coating showed a promising oleophobic effect even at low concentrations, which suggests it has oleophobic properties for different oil types and can be modified for different substrates. This fabricated oleophobic coating is thermostable and the oleophobic effect is unaffected by temperatures from 0 to 100 °C. By modifying the SPFO coating on the PVDF membrane, a high filtration efficiency (89.43%) and low wind resistance (69 Pa) was achieved without oil adhesion, so the proposed coating can be applied in the filtration and purification of oily fine particles and offers a potential strategy for preventing atmospheric oil pollution.

'Omics in environmental epidemiological studies of chemical exposures: A systematic evidence map

BACKGROUND

Systematic evidence maps are increasingly used to develop chemical risk assessments. These maps can provide an overview of available studies and relevant study information to be used for various research objectives and applications. Environmental epidemiological studies that examine the impact of chemical exposures on various 'omic profiles in human populations provide relevant mechanistic information and can be used for benchmark dose modeling to derive potential human health reference values.

OBJECTIVES

To create a systematic evidence map of environmental epidemiological studies examining environmental contaminant exposures with 'omics in order to characterize the extent of available studies for future research needs.

METHODS

Systematic review methods were used to search and screen the literature and included the use of machine learning methods to facilitate screening studies. The Populations, Exposures, Comparators and Outcomes (PECO) criteria were developed to identify and screen relevant studies. Studies that met the PECO criteria after full-text review were summarized with information such as study population, study design, sample size, exposure measurement, and 'omics analysis.

RESULTS

Over 10,000 studies were identified from scientific databases. Screening processes were used to identify 84 studies considered PECO-relevant after full-text review. Various contaminants (e.g. phthalate, benzene, arsenic, etc.) were investigated in epidemiological studies that used one or more of the four 'omics of interest: epigenomics, transcriptomics, proteomics, and metabolomics . The epidemiological study designs that were used to explore single or integrated 'omic research questions with contaminant exposures were cohort studies, controlled trials, cross-sectional, and case-control studies. An interactive web-based systematic evidence map was created to display more study-related information.

CONCLUSIONS

This systematic evidence map is a novel tool to visually characterize the available environmental epidemiological studies investigating contaminants and biological effects using 'omics technology and serves as a resource for investigators and allows for a range of applications in chemical research and risk assessment needs.

Epigenetic alterations induced by genotoxic occupational and environmental human chemical carcinogens: An update of a systematic literature review

Epigenetic alterations, such as changes in DNA methylation, histones/chromatin structure, nucleosome positioning, and expression of non-coding RNAs, are recognized among key characteristics of carcinogens; they may occur independently or concomitantly with genotoxic effects. While data on genotoxicity are collected through standardized guideline tests, data collected on epigenetic effects is far less uniform. In 2016, we conducted a systematic review of published studies of genotoxic carcinogens that reported epigenetic endpoints to better understand the evidence for epigenetic alterations of human carcinogens, and the potential association with genotoxic endpoints. Since then, the number of studies of epigenetic effects of chemicals has nearly doubled. This review stands as an update on epigenetic alterations induced by occupational and environmental human carcinogens that were previously and recently classified as Group 1 by the International Agency for Research on Cancer. We found that the evidence of epigenetic effects remains uneven across agents. Studies of DNA methylation are most abundant, while reports concerning effects on non-coding RNA have increased over the past 5 years. By contrast, mechanistic toxicology studies of histone modifications and chromatin state alterations remain few. We found that most publications of epigenetic effects of carcinogens were studies in exposed humans or human cells. Studies in rodents represent the second most common species used for epigenetic studies in toxicology, in vivo exposures being the most predominant. Future studies should incorporate dose- and time-dependent study designs and also investigate the persistence of effects following cessation of exposure, considering the dynamic nature of most epigenetic alterations.

Biological Response-Enhancing Activity with Antigens in A549 Cells Exposed to Representative Polycyclic Aromatic Hydrocarbons

The question of what kinds of airborne particles, including diesel exhaust particles and their adherent chemical constituents, exacerbate the activity of allergic and inflammatory respiratory diseases has not been elucidated in detail. Therefore, chemicals that have amplifying actions on Dermatophagoides farinae (Df) body extract-induced IL-8, the inflammatory cytokines of the innate immune system, were comprehensively examined using commonly used human alveolar epithelial cells, A549, as simple screening for 17 polycyclic aromatic hydrocarbons (PAHs), which are representative organic constituents in atmospheric samples. The significant amplifying actions of two PAHs, dibenzo[a,l]pyrene (DB[a,l]P) at 50 nM and dibenzo[a,i]pyrene (DB[a,i]P) at 2 μM for 48 h, for IL-8 protein release induced by mite antigens in epithelial cells were observed for the first time. In contrast, the enhancement of IL-8 was not observed in protein levels for these PAHs without the antigens. Meanwhile, the significant synergistic amplifying effect of DB[a,l]P at 50 nM on proinflammatory actions was measured in gene expression (i.e., IL-8, IL-6, ICAM-1, and TNF-α) levels in the experimental setting; for the results, the induction of TNF-α may have been the essential factor that enhanced the amplifying activity of DB[a,l]P for IL-8 gene expression and protein release. Examining the exacerbating effect on allergic pathophysiological states for DB[a,l]P is planned for further study.

microRNAs expression in relation to particulate matter exposure: A systematic review

MicroRNAs (miRNAs) are a class of small, non-coding RNAs with a post-transcriptional regulatory function on gene expression and cell processes, including proliferation, apoptosis and differentiation. In recent decades, miRNAs have attracted increasing interest to explore the role of epigenetics in response to air pollution. Air pollution, which always contains kinds of particulate matters, are able to reach respiratory tract and blood circulation and then causing epigenetics changes. In addition, extensive studies have illustrated that miRNAs serve as a bridge between particulate matter exposure and health-related effects, like inflammatory cytokines, blood pressure, vascular condition and lung function. The purpose of this review is to summarize the present knowledge about the expression of miRNAs in response to particulate matter exposure. Epidemiological and experimental studies were reviewed in two parts according to the size and source of particles. In this review, we also discussed various functions of the altered miRNAs and predicted potential biological mechanism participated in particulate matter-induced health effects. More rigorous studies are worth conducting to understand contribution of particulate matter on miRNAs alteration and the etiology between environmental exposure and disease development.

Activation of NLRP3 in microglia exacerbates diesel exhaust particles-induced impairment in learning and memory in mice

BACKGROUND

The major components of traffic pollution particulate matter, diesel exhaust particles (DEPs), are airborne ultrafine particles (UFPs). DEPs can enter the central nervous system (CNS), where they may cause neurotoxicity.

METHODS

We established murine models with intranasal DEPs instillation in male C57BL/6 and Nlrp3 knock-out (Nlrp3^-/-) mice to investigate the effects of DEPs exposure on murine neurobehaviors and related mechanisms. Morris water maze (MWM) tests were performed to evaluate the learning and memory behaviors of mice following DEPs instillation. Metabolomics were assessed using an gas chromatography system coupled to a mass spectrometer. Real-time PCR and immunohistochemistry assays were used to analyze the mRNA and protein expression levels of target genes. Murine microglia, BV2 cells were employed to assay the effects of DEPs exposure in vitro.

RESULTS

Intranasal administration of DEPs in mice led to impairment in hippocampal-dependent learning and memory. Moreover, this phenotype was linked to increased number of Iba-1⁺ microglia and NLRP3 inflammasome, as well as suppression of mitochondrial gene expression in the hippocampus of mice exposed to DEPs. Nlrp3^-/- mice were resistant to DEPs-induced learning and memory impairment, concomitant with protection against the suppression of mitochondrial gene expression. Murine microglia cells (BV2) were exposed to DEPs in vitro and taurine was identified as one of the significantly suppressed metabolites in DEPs-treated microglia by metabolomics analysis. Supplementation with taurine efficiently rescued learning, memory and mitochondrial gene expression levels in the hippocampus of DEPs-exposed mice.

CONCLUSIONS

Mechanistically, our study revealed that microglia-mediated NLRP3 inflammasome activation plays a deleterious role in DEPs-induced neurotoxicity by inhibiting mitochondrial gene expression. These results shed novel light on the potential value of nutritional supplementation against DEPs-induced neurotoxicity in individuals exposed to severe airborne traffic-related air pollutions.

Recent Studies on DNA Adducts Resulting from Human Exposure to Tobacco Smoke

DNA adducts are believed to play a central role in the induction of cancer in cigarette smokers and are proposed as being potential biomarkers of cancer risk. We have summarized research conducted since 2012 on DNA adduct formation in smokers. A variety of DNA adducts derived from various classes of carcinogens, including aromatic amines, polycyclic aromatic hydrocarbons, tobacco-specific nitrosamines, alkylating agents, aldehydes, volatile carcinogens, as well as oxidative damage have been reported. The results are discussed with particular attention to the analytical methods used in those studies. Mass spectrometry-based methods that have higher selectivity and specificity compared to 32P-postlabeling or immunochemical approaches are preferred. Multiple DNA adducts specific to tobacco constituents have also been characterized for the first time in vitro or detected in vivo since 2012, and descriptions of those adducts are included. We also discuss common issues related to measuring DNA adducts in humans, including the development and validation of analytical methods and prevention of artifact formation.