Inhibition of the formation of benzo[a]pyrene adducts to DNA in A549 lung cells exposed to mixtures of polycyclic aromatic hydrocarbons

Genetic and epigenetic modulations in toxicity: The two-sided roles of heavy metals and polycyclic aromatic hydrocarbons from the environment

This study emphasizes the importance of considering the metabolic and toxicity mechanisms of environmental concern chemicals in real-life exposure scenarios. Furthermore, environmental chemicals may require metabolic activation to become toxic, and competition for binding sites on receptors can affect the severity of toxicity. The multicomplex process of chemical toxicity is reflected in the activation of multiple pathways during toxicity of which AhR activation is major. Real-life exposure to a mixture of concern chemicals is common, and the composition of these chemicals determines the severity of toxicity. Nutritional essential elements can mitigate the toxicity of toxic heavy metals, while the types and ratio of composition of PAH can either increase or decrease toxicity. The epigenetic mechanisms of heavy metals and PAH toxicity involves either down-regulation or up-regulation of some non-coding RNAs (ncRNAs) whereas specific small RNAs (sRNAs) may have dual role depending on the tissue and circumstance of expression. Similarly, decrease DNA methylation and histone modification are major players in heavy metals and PAH mediated toxicity and FLT1 hypermethylation is a major process in PAH induced carcinogenesis. Overall, this review provides the understanding of the metabolism of environmental concern chemicals, emphasizing the importance of considering mixed compositions and real-life exposure scenarios in assessing their potential effects on human health and diseases development as well as the dual mechanism of toxicity via genetic or epigenetic axis.

Sources, chemical components, and toxicological responses of size segregated urban air PM samples in high air pollution season in Guangzhou, China

The sources, sizes, components, and toxicological responses of particulate matter (PM) have demonstrated remarkable spatiotemporal variability. However, associations between components, sources, and toxicological effects in different-sized PM remain unclear. The purposes of this study were to 1) determine the sources of PM chemical components, 2) investigate the associations between components and toxicology of PM from Guangzhou high air pollution season. We collected size-segregated PM samples (PM_10-2.5, PM_2.5-1, PM_1-0.2, PM_0.2) from December 2017 to March 2018 in Guangzhou. PM sources and components were analyzed. RAW264.7 mouse macrophages were treated with PM samples for 24 h followed by measurements of toxicological responses. The concentrations of PM_10-2.5 and PM_1-0.2 were relatively high in all samples. Water-soluble ions and PAHs were more abundant in smaller-diameter PM, while metallic elements were more enriched in larger-diameter PM. Traffic exhaust, soil dust, and biomass burning/petrochemical were the most important sources of PAHs, metals and ions, respectively. The main contributions to PM were soil dust, coal combustion, and biomass burning/petrochemical. Exposure to PM_10-2.5 induced the most significant reduction of cell mitochondrial activity, oxidative stress and inflammatory response, whereas DNA damage, an increase of Sub G1/G0 population, and impaired cell membrane integrity were most evident with PM_1-0.2 exposure. There were moderate or strong correlations between most single chemicals and almost all toxicological endpoints as well as between various toxicological outcomes. Our findings highlight those various size-segregated PM-induced toxicological effects in cells, and identify chemical components and sources of PM that play the key role in adverse intracellular responses. Although fine and ultrafine PM have attracted much attention, the inflammatory damage caused by coarse PM cannot be ignored.

Polycyclic aromatic hydrocarbons (PAHs): Updated aspects of their determination, kinetics in the human body, and toxicity

Polycyclic aromatic hydrocarbons (PAHs) are legacy pollutants of considerable public health concern. Polycyclic aromatic hydrocarbons arise from natural and anthropogenic sources and are ubiquitously present in the environment. Several PAHs are highly toxic to humans with associated carcinogenic and mutagenic properties. Further, more severe harmful effects on human- and environmental health have been attributed to the presence of high molecular weight (HMW) PAHs, that is PAHs with molecular mass greater than 300 Da. However, more research has been conducted using low molecular weight (LMW) PAHs). In addition, no HMW PAHs are on the priority pollutants list of the United States Environmental Protection Agency (US EPA), which is limited to only 16 PAHs. However, limited analytical methodologies for separating and determining HMW PAHs and their potential isomers and lack of readily available commercial standards make research with these compounds challenging. Since most of the PAH kinetic data originate from animal studies, our understanding of the effects of PAHs on humans is still minimal. In addition, current knowledge of toxic effects after exposure to PAHs may be underrepresented since most investigations focused on exposure to a single PAH. Currently, information on PAH mixtures is limited. Thus, this review aims to critically assess the current knowledge of PAH chemical properties, their kinetic disposition, and toxicity to humans. Further, future research needs to improve and provide the missing information and minimize PAH exposure to humans.

Winter and spring variation in sources, chemical components and toxicological responses of urban air particulate matter samples in Guangzhou, China

The sources and chemical components of urban air particles exhibit seasonal variations that may affect their hazardousness to human health. Our aims were to investigate winter and spring variation in particulate matter (PM) sources, components and toxicological responses of different PM size fractions from samples collected in Guangzhou, China. Four size-segregated PM samples (PM_10-2.5, PM_2.5-1, PM_1-0.2, and PM_0.2) were collected separately during winter (December 2017 and January 2018) and spring (March 2018). All PM samples were analyzed for chemical components and characterized by source. RAW 264.7 macrophages were exposed to four doses of PM samples for 24 h. Cytotoxicity, oxidation, cell cycle, genotoxicity and inflammatory parameters were tested. PM concentrations were higher in the winter samples and caused more severe cytotoxicity and oxidative damage than to PM in the spring samples. PM in winter and spring led to increases in cell cycle and genotoxicity. The trends of size-segregated PM components were consistent in winter and spring samples. Metallic elements and PAHs were found in the largest concentrations in winter PM, but ions were found in the largest concentrations in spring PM. metallic elements, PAHs and ions in size-segregated PM samples were associated with most toxicological endpoints. Soil dust and biomass burning were the main sources of PM in winter, whereas traffic exhaust and biomass burning was the main source with of spring PM. Our results suggest that the composition of PM samples from Guangzhou differed during winter and spring, which led to strong variations in toxicological responses. The results demonstrate the importance of examining a different particle sizes, compositions and sources across different seasons, for human risk assessment.

Black carbon toxicity dependence on particle coating: Measurements with a novel cell exposure method

Black carbon (BC) is a component of ambient particulate matter which originates from incomplete combustion emissions. BC is regarded as an important short-lived climate forcer, and a significant public health hazard. These two concerns have made BC a focus in aerosol science. Even though, the toxicity of BC particles is well recognized, the mechanism of toxicity for BC as a part of the total gas and particle emission mixture from combustion is still largely unknown and studies concerning it are scarce. In the present study, using a novel thermophoresis-based air-liquid interface (ALI) in vitro exposure system, we studied the toxicity of combustion-generated aerosols containing high levels of BC, diluted to atmospheric levels (1 to 10 μg/m³). Applying multiple different aerosol treatments, we simulated different sources and atmospheric aging processes, and utilizing several toxicological endpoints, we thoroughly examined emission toxicity. Our results revealed that an organic coating on the BC particles increased the toxicity, which was seen as larger genotoxicity and immunosuppression. Furthermore, aging of the aerosol also increased its toxicity. A deeper statistical analysis of the results supported our initial conclusions and additionally revealed that toxicity increased with decreasing particle size. These findings regarding BC toxicity can be applied to support policies and technologies to reduce the most hazardous compositions of BC emissions. Additionally, our study showed that the thermophoretic ALI system is both a suitable and useful tool for toxicological studies of emission aerosols.

Wavelengths and temporal effects on the response of mammalian cells to UV radiation: Limitations of action spectra illustrated by genotoxicity

All photobiological events depend on the wavelength of the incident radiation. In real-life situations and in the vast majority of laboratory experiments, exposure always involves sources with various emission spectra spreading over a wide wavelength range. Action spectra are often used to describe the efficiency of a process at different wavelengths and to predict the effects of a given light source by summation of the individual effects at each wavelength. However, a full understanding of the biological effects of complex sources requires more than considering these concomitant events at each specific wavelength. Indeed, photons of different energies may not have additive but synergistic or inhibitory effects on photochemical processes and cellular responses. The evolution of a photobiological response with post-irradiation time must also be considered. These two aspects may represent some limitations to the use of action spectra. The present review, focused on mammalian cells, illustrates the concept of action spectrum and discusses its drawbacks using theoretical considerations and examples taken from the literature. Emphasis is placed on genotoxicity for which wavelength effects have been extensively studied. Other effects of UV exposure are also mentioned.

Combustion-derived particles from biomass sources differently promote epithelial-to-mesenchymal transition on A549 cells

Combustion-derived particles (CDPs), due to the presence in their composition of several toxic and carcinogenic chemical compounds, such as polycyclic aromatic hydrocarbons (PAHs) and metals, are linked to several respiratory diseases, including lung cancer. Epithelial-to-mesenchymal transition (EMT) is a crucial step in lung cancer progression, involving several morphological and phenotypical changes. The study aims to investigate how exposure to CDPs from different biomass sources might be involved in cancer development, focusing mainly on the effects linked to EMT and invasion on human A549 lung cells. Biomass combustion-derived particles (BCDPs) were collected from a stove fuelled with pellet, charcoal or wood, respectively. A time course and dose response evaluation on cell viability and pro-inflammatory response was performed to select the optimal conditions for EMT-related studies. A significant release of IL-8 was found after 72 h of exposure to 2.5 μg/cm² BCDPs. The EMT activation was then examined by evaluating the expression of some typical markers, such as E-cadherin and N-cadherin, and the possible enhanced migration and invasiveness. Sub-acute exposure revealed that BCDPs differentially modulated cell viability, migration and invasion, as well as the expression of proteins linked to EMT. Results showed a reduction in the epithelial marker E-cadherin and a parallel increase in the mesenchymal markers N-cadherin, mainly after exposure to charcoal and wood. Migration and invasion were also increased. In conclusion, our results suggest that BCDPs with a higher content of organic compounds (e.g. PAHs) in their chemical composition might play a crucial role in inducing pro-carcinogenic effects on epithelial cells.

Metabolism and genotoxicity of polycyclic aromatic hydrocarbons in human skin explants: mixture effects and modulation by sunlight

Cutaneous exposure to carcinogenic polycyclic aromatic hydrocarbons (PAH) occurs frequently in the industrialized workplace. In the present study, we addressed this topic in a series of experiments using human skin explants and organic extracts of relevant industrial products. PAH mixtures were applied topically in volumes containing either 10 or 1 nmol B[a]P. We first observed that although mixtures were very efficient at inducing expression of CYP450 1A1, 1A2, and 1B1, formation of adducts of PAH metabolites to DNA, like those of benzo[a]pyrene diol epoxide (BPDE), was drastically reduced as the complexity of the surrounding matrix increased. Interestingly, observation of a nonlinear, dose-dependent response with the least complex mixture suggested the existence of a threshold for this inhibitory effect. We then investigated the impact of simulated sunlight (SSL) on the effects of PAH in skin. SSL was found to decrease the expression of CYP450 genes when applied either after or more efficiently before PAH treatment. Accordingly, the level of DNA-BPDE adducts was reduced in skin samples exposed to both PAH and SSL. The main conclusion of our work is that both increasing chemical complexity of the mixtures and co-exposure to UV radiation decreased the production of adducts between DNA and PAH metabolites. Such results must be taken into account in risk management.

Seasonal Variation in the Biological Effects of PM2.5 from Greater Cairo

Greater Cairo (Egypt) is a megalopolis where the studies of the air pollution events are of extremely high relevance, for the geographical-climatological aspects, the anthropogenic emissions and the health impact. While preliminary studies on the particulate matter (PM) chemical composition in Greater Cairo have been performed, no data are yet available on the PM’s toxicity. In this work, the in vitro toxicity of the fine PM (PM_2.5) sampled in an urban area of Greater Cairo during 2017–2018 was studied. The PM_2.5 samples collected during spring, summer, autumn and winter were preliminary characterized to determine the concentrations of ionic species, elements and organic PM (Polycyclic Aromatic Hydrocarbons, PAHs). After particle extraction from filters, the cytotoxic and pro-inflammatory effects were evaluated in human lung A549 cells. The results showed that particles collected during the colder seasons mainly induced the xenobiotic metabolizing system and the consequent antioxidant and pro-inflammatory cytokine release responses. Biological events positively correlated to PAHs and metals representative of a combustion-derived pollution. PM_2.5 from the warmer seasons displayed a direct effect on cell cycle progression, suggesting possible genotoxic effects. In conclusion, a correlation between the biological effects and PM_2.5 physico-chemical properties in the area of study might be useful for planning future strategies aiming to improve air quality and lower health hazards.

Lung cancer risk assessment for workers exposed to polycyclic aromatic hydrocarbons in various industries

BACKGROUND

Millions of workers are exposed to carcinogenic polycyclic aromatic hydrocarbon (PAH) mixtures. The toxicity of PAH mixtures is variable and depends on the composition of the mixture, which is related to the emission sources. Although several indicators exist, the cancer risk estimation associated with occupational exposure to PAHs is poorly known.

OBJECTIVES

To assess the risk of lung cancer associated with PAHs in several industries using the atmospheric concentrations of benzo[a]pyrene (BaP) as a proxy.

METHODS

A total of 93 exposure groups belonging to 9 industries were investigated. Eight indicators found in the literature were compared to assess risks. A consensual indicator was used to estimate lung cancer risks.

RESULTS

Approximately 30% of the exposure groups were above the maximal risk level of the European Union (10^-4). The risk probabilities were >10^-3 for coke and silicon production; >10^-4 for the manufacturing of carbon products and aluminum production; >10^-5 for foundries and combustion processes; >10^-6 for the use of lubricating oils and engine exhaust emissions; and >10^-7 for bitumen. The risk probabilities were highly variable within industries (from 1 to 1000 likelihood). A total of 27 (95% CI: 0.1-54) contemporary additional lung cancer cases could be expected per year in the French exposed population based on estimations using published data.

CONCLUSION

This study provides an overview of cancer risk estimation in many industries. Despite efforts and changes that had been made to decrease risks, PAHs remain a sanitary threat for people exposed to these pollutants in occupational environments.

In vitro lung toxicity of indoor PM10 from a stove fueled with different biomasses

Biomass combustion significantly contributes to indoor and outdoor air pollution and to the adverse health effects observed in the exposed populations. Besides, the contribution to toxicity of the particles derived from combustion of different biomass sources (pellet, wood, charcoal), as well as their biological mode of action, are still poorly understood. In the present study, we investigate the toxicological properties of PM10 particles emitted indoor from a stove fueled with different biomasses. PM10 was sampled by gravimetric methods and particles were chemically analyzed for Polycyclic Aromatic Hydrocarbons (PAHs) and elemental content. Human lung A549 cells were exposed for 24 h to 1-10 μg/cm² PM and different biological endpoints were evaluated to comparatively estimate the cytotoxic, genotoxic and pro-inflammatory effects of the different PMs. Pellet PM decreased cell viability, inducing necrosis, while charcoal and wood ones mainly induced apoptosis. Oxidative stress-related response and cytochrome P450 enzymes activation were observed after exposure to all the biomasses tested. Furthermore, after pellet exposure, DNA lesions and cell cycle arrest were also observed. The severe genotoxic and pro-necrotic effects observed after pellet exposure were likely the consequence of the high metal content. By administering the chelating agent TPEN, the genotoxic effects were indeed rescued. The higher content in PAHs measured in wood and charcoal PMs was likely the reason of the enhanced expression of metabolizing and oxidative stress-related enzymes, like CYP1B1 and HO-1, and the consequent increase in apoptotic cell death. These data suggest that combustion particles from different biomass sources may impact on lung cells according to different pathways, finally producing different toxicities. This is strictly related to the PM chemical composition, which reflects the quality of the combustion and the fuel in particular. Further studies are needed to clarify the role of particle dimension and the molecular mechanisms behind the harmful effects observed.

Primary and secondary pyrrolic metabolites of pyrrolizidine alkaloids form DNA adducts in human A549 cells

Humans and animals can be exposed to carcinogenic pyrrolizidine alkaloids (PAs) through consumption of plants commonly found in many parts of the world. Although the liver is the primary target organ for carcinogenic PAs, they have also induced lung tumors in rodents. Hepatic cytochrome P450 activity converts PAs into dehydro-PAs that can be hydrolyzed to dehydropyrrolizidine (DHP); these reactive pyrrolic metabolites can produce four characteristic DNA adducts associated with PA-induced liver tumor initiation in laboratory animals. We reported recently that these four DNA adducts are also formed when 7-glutathione-DHP (7-GS-DHP) or 7-cysteine-DHP is incubated with calf thymus DNA. Here we showed that the four characteristic DNA adducts were formed when human A549 brochoalveolar carcinoma cells were treated with three dehydro-PAs (dehydroriddelliine, dehydromonocrotaline, or dehydroretronecine) or with 7-GS-DHP or 7-cysteine-DHP. For comparison, two parent PAs (riddelliine and monocrotaline) and 7,9-di-glutathionine-DHP were studied. No DHP-DNA adducts were detected with these incubations, confirming that A549 lung carcinoma cells do not express cytochrome P450 enzymes required for metabolic activation of PAs. Our results show that primary and secondary pyrrolic metabolites of carcinogenic PAs produce characteristic DHP-containing DNA adducts in A549 lung cancer cells, suggesting that they are DNA reactive metabolites.

Emissions and atmospheric processes influence the chemical composition and toxicological properties of urban air particulate matter in Nanjing, China

Ambient inhalable particulate matter (PM) is a serious health concern worldwide, but especially so in China where high PM concentrations affect huge populations. Atmospheric processes and emission sources cause spatial and temporal variations in PM concentration and chemical composition, but their influence on the toxicological characteristics of PM are still inadequately understood. In this study, we report an extensive chemical and toxicological characterization of size-segregated urban air inhalable PM collected in August and October 2013 from Nanjing, and assess the effects of atmospheric processes and likely emission sources. A549 human alveolar epithelial cells were exposed to day- and nighttime PM samples (25, 75, 150, 200, 300 μg/ml) followed by analyses of cytotoxicity, genotoxicity, cell cycle, and inflammatory response. PM_10-2.5 and PM_0.2 caused the greatest toxicological responses for different endpoints, illustrating that particles with differing size and chemical composition activate distinct toxicological pathways in A549 cells. PM_10-2.5 displayed the greatest oxidative stress and genotoxic responses; both were higher for the August samples compared with October. In contrast, PM_0.2 and PM_2.5-1.0 samples displayed high cytotoxicity and substantially disrupted cell cycle; August samples were more cytotoxic whereas October samples displayed higher cell cycle disruption. Several components associated with combustion, traffic, and industrial emissions displayed strong correlations with these toxicological responses. The lower responses for PM_1.0-0.2 compared to PM_0.2 and PM_2.5-1.0 indicate diminished toxicological effects likely due to aerosol aging and lower proportion of fresh emission particles rich in highly reactive chemical components in the PM_1.0-0.2 fraction. Different emission sources and atmospheric processes caused variations in the chemical composition and toxicological responses between PM fractions, sampling campaigns, and day and night. The results indicate different toxicological pathways for coarse-mode particles compared to the smaller particle fractions with typically higher content of combustion-derived components. The variable responses inside PM fractions demonstrate that differences in chemical composition influence the induced toxicological responses.

Solar simulated light exposure alters metabolization and genotoxicity induced by benzo[a]pyrene in human skin

Skin is a major barrier against external insults and is exposed to combinations of chemical and/or physical toxic agents. Co-exposure to the carcinogenic benzo[a]pyrene (B[a]P) and solar UV radiation is highly relevant in human health, especially in occupational safety. In vitro studies have suggested that UVB enhances B[a]P genotoxicity by activating the AhR pathway and overexpressing the cytochrome P450 enzymes responsible for the conversion of B[a]P into DNA damaging metabolites. Our present work involved more realistic conditions, namely ex vivo human skin explants and simulated sunlight (SSL) as a UV source. We found that topically applied B[a]P strongly induced expression of cutaneous cytochrome P450 genes and formation of DNA adducts. However, gene induction was significantly reduced when B[a]P was combined with SSL. Consequently, formation of BPDE-adducts was also reduced when B[a]P was associated with SSL. Similar results were obtained with primary cultures of human keratinocytes. These results indicate that UV significantly impairs B[a]P metabolism, and decreases rather than increases immediate toxicity. However, it cannot be ruled out that decreased metabolism leads to accumulation of B[a]P and delayed genotoxicity.

Pharmacokinetics of [14C]-Benzo[a]pyrene (BaP) in humans: Impact of Co-Administration of smoked salmon and BaP dietary restriction

Benzo[a]pyrene (BaP), a polycyclic aromatic hydrocarbon (PAH), is a known human carcinogen. In non-smoking adults greater than 95% of BaP exposure is through diet. The carcinogenicity of BaP is utilized by the U.S. EPA to assess relative potency of complex PAH mixtures. PAH relative potency factors (RPFs, BaP = 1) are determined from high dose animal data. We employed accelerator mass spectrometry (AMS) to determine pharmacokinetics of [¹⁴C]-BaP in humans following dosing with 46 ng (an order of magnitude lower than human dietary daily exposure and million-fold lower than animal cancer models). To assess the impact of co-administration of food with a complex PAH mixture, humans were dosed with 46 ng of [¹⁴C]-BaP with or without smoked salmon. Subjects were asked to avoid high BaP-containing diets and a 3-day dietary questionnaire given to assess dietary exposure prior to dosing and three days post-dosing with [¹⁴C]-BaP. Co-administration of smoked salmon, containing a complex mixture of PAHs with an RPF of 460 ng BaP_eq, reduced and delayed absorption. Administration of canned commercial salmon, containing very low amounts of PAHs, showed the impacts on pharmacokinetics were not due to high amounts of PAHs but rather a food matrix effect.

Carbon Nanotubes Disrupt Iron Homeostasis and Induce Anemia of Inflammation through Inflammatory Pathway as a Secondary Effect Distant to Their Portal-of-Entry

Although numerous toxicological studies have been performed on carbon nanotubes (CNTs), a few studies have investigated their secondary and indirect effects beyond the primary target tissues/organs. Here, a cascade of events are investigated: the initiating event and the subsequent key events necessary for the development of phenotypes, namely CNT-induced pro-inflammatory effects on iron homeostasis and red blood cell formation, which are linked to anemia of inflammation (AI). A panel of CNTs are prepared including pristine multiwall CNTs (P-MWCNTs), aminated MWCNTs (MWCNTs-NH₂ ), polyethylene glycol MWCNTs (MWCNTs-PEG), polyethyleneimine MWCNTs (MWCNTs-PEI), and carboxylated MWCNTs (MWCNTs-COOH). It has been demonstrated that all CNT materials provoke inflammatory cytokine interleukin-6 (IL-6) production and stimulate hepcidin induction, associated with disordered iron homeostasis, irrespective of exposure routes including intratracheal, intravenous, and intraperitoneal administration. Meanwhile, PEG and COOH modifications can ameliorate the activation of IL-6-hepcidin signaling. Long-term exposure of MWCNTs results in AI and extramedullary erythropoiesis. Thus, an adverse outcome pathway is identified: MWCNT exposure leads to inflammation, hepatic hepcidin induction, and disordered iron metabolism. Together, the combined data depict the hazardous secondary toxicity of CNTs in incurring anemia through inflammatory pathway. This study will also open a new avenue for future investigations on CNT-induced indirect and secondary adverse effects.