Lung retention and metabolic fate of inhaled benzo(a)pyrene associated with diesel exhaust particles

Transcriptional and phenotypical alterations associated with a gradual benzo[a]pyrene-induced transition of human bronchial epithelial cells into mesenchymal-like cells

The role of benzo[a]pyrene (BaP), a prominent genotoxic carcinogen and aryl hydrocarbon receptor (AhR) ligand, in tumor progression remains poorly characterized. We investigated the impact of BaP on the process of epithelial-mesenchymal transition (EMT) in normal human bronchial epithelial HBEC-12KT cells. Early morphological changes after 2-week exposure were accompanied with induction of SERPINB2, IL1, CDKN1A/p21 (linked with cell cycle delay) and chemokine CXCL5. After 8-week exposure, induction of cell migration and EMT-related pattern of markers/regulators led to induction of further pro-inflammatory cytokines or non-canonical Wnt pathway ligand WNT5A. This trend of up-regulation of pro-inflammatory genes and non-canonical Wnt pathway constituents was observed also in the BaP-transformed HBEC-12KT-B1 cells. In general, transcriptional effects of BaP differed from those of TGFβ1, a prototypical EMT inducer, or a model non-genotoxic AhR ligand, TCDD. Carcinogenic polycyclic aromatic hydrocarbons could thus induce a unique set of molecular changes linked with EMT and cancer progression.

Patterns of Carbon-Bound Exogenous Compounds Impact Disease Pathophysiology in Lung Cancer Subtypes in Different Ways

Carbon-bound exogenous compounds, such as polycyclic aromatic hydrocarbons (PAHs), tobacco-specific nitrosamines, aromatic amines, and organohalogens, are known to affect both tumor characteristics and patient outcomes in lung squamous cell carcinoma (LUSC); however, the roles of these compounds in lung adenocarcinoma (LUAD) remain unclear. We analyzed 11 carbon-bound exogenous compounds in LUAD and LUSC samples using in situ high mass-resolution matrix-assisted laser desorption/ionization Fourier-transform ion cyclotron resonance mass spectrometry imaging and performed a cluster analysis to compare the patterns of carbon-bound exogenous compounds between these two lung cancer subtypes. Correlation analyses were conducted to investigate associations among exogenous compounds, endogenous metabolites, and clinical data, including patient survival outcomes and smoking behaviors. Additionally, we examined differences in exogenous compound patterns between normal and tumor tissues. Our analyses revealed that PAHs, aromatic amines, and organohalogens were more abundant in LUAD than in LUSC, whereas the tobacco-specific nitrosamine nicotine-derived nitrosamine ketone was more abundant in LUSC. Patients with LUAD and LUSC could be separated according to carbon-bound exogenous compound patterns detected in the tumor compartment. The same compounds had differential impacts on patient outcomes, depending on the cancer subtype. Correlation and network analyses indicated substantial differences between LUAD and LUSC metabolomes, associated with substantial differences in the patterns of the carbon-bound exogenous compounds. These data suggest that the contributions of these carcinogenic compounds to cancer biology may differ according to the cancer subtypes.

Patterns of carbon-bound exogenous compounds in lung cancer patients and association with disease pathophysiology

Asymptomatic anthracosis is the accumulation of black carbon particles in adult human lungs. It is a common occurrence, but the pathophysiological significance of anthracosis is debatable. Using in situ high mass resolution matrix-assisted laser desorption/ionization (MALDI) fourier-transform ion cyclotron resonance (FT-ICR) mass spectrometry imaging analysis, we discovered noxious carbon-bound exogenous compounds, such as polycyclic aromatic hydrocarbons (PAHs), tobacco-specific nitrosamines, or aromatic amines, in a series of 330 lung cancer patients in highly variable and unique patterns. The characteristic nature of carbon-bound exogenous compound had a strong association with patient outcome, tumor progression, the tumor immune microenvironment, PD-L1 expression, and DNA damage. Spatial correlation network analyses revealed substantial differences in the metabolome of tumor cells compared to tumor stroma depending on carbon-bound exogenous compounds. Overall, the bioactive pool of exogenous compounds is associated with several changes in lung cancer pathophysiology and correlates with patient outcome. Given the high prevalence of anthracosis in the lungs of adult humans, future work should investigate the role of carbon-bound exogenous compounds in lung carcinogenesis and lung cancer therapy.

Predicting lung dosimetry of inhaled particleborne benzo[a]pyrene using physiologically based pharmacokinetic modeling

Benzo[a]pyrene (BaP) is a by-product of incomplete combustion of fossil fuels and plant/wood products, including tobacco. A physiologically based pharmacokinetic (PBPK) model for BaP for the rat was extended to simulate inhalation exposures to BaP in rats and humans including particle deposition and dissolution of absorbed BaP and renal elimination of 3-hydroxy benzo[a]pyrene (3-OH BaP) in humans. The clearance of particle-associated BaP from lung based on existing data in rats and dogs suggest that the process is bi-phasic. An initial rapid clearance was represented by BaP released from particles followed by a slower first-order clearance that follows particle kinetics. Parameter values for BaP-particle dissociation were estimated using inhalation data from isolated/ventilated/perfused rat lungs and optimized in the extended inhalation model using available rat data. Simulations of acute inhalation exposures in rats identified specific data needs including systemic elimination of BaP metabolites, diffusion-limited transfer rates of BaP from lung tissue to blood and the quantitative role of macrophage-mediated and ciliated clearance mechanisms. The updated BaP model provides very good prediction of the urinary 3-OH BaP concentrations and the relative difference between measured 3-OH BaP in nonsmokers versus smokers. This PBPK model for inhaled BaP is a preliminary tool for quantifying lung BaP dosimetry in rat and humans and was used to prioritize data needs that would provide significant model refinement and robust internal dosimetry capabilities.

Assessing the enrichment of heavy metals in surface soil and plant (Digitaria eriantha) around coal-fired power plants in South Africa

Nine metals (Fe, Cu, Mn, Ni, Cd, Pb, Hg, Cr, and Zn) were determined in soil and Digitaria eriantha plants within the vicinity of three coal power plants (Matla, Lethabo, and Rooiwal), using ICP-OES and GFAAS. The total metal concentration in soil ranged from 0.05 ± 0.02 to 1836 ± 70 μg g(-1), 0.08 ± 0.05 to 1744 ± 29 μg g(-1), and 0.07 ± 0.04 to 1735 ± 91 μg g(-1) in Matla, Lethabo, and Rooiwal, respectively. Total metal concentration in the plant (D. eriantha) ranged from 0.005 ± 0.003 to 535 ± 43 μg g(-1) in Matla, 0.002 ± 0.001 to 400 ± 269 μg g(-1) in Lethabo, and 0.002 ± 0.001 to 4277 ± 201 μg g(-1) in Rooiwal. Accumulation factors (A) of less than 1 (i.e., 0.003 to 0.37) at all power plants indicate a low transfer of metal from soil to plant (excluder). Enrichment factor values obtained (2.4-5.0) indicate that the soils are moderately enriched with the exception of Pb that had significant enrichment of 20. Geo-accumulation index (I-geo) values of metals indicate that the soils are moderately polluted (0.005-0.65), except for Pb that showed moderate to strong pollution (1.74-2.53).

Nanoparticles and the cardiovascular system: a critical review

Nanoparticles (NPs) are tiny particles with a diameter of less than 100 nm. Traffic exhaust is a major source of combustion-derived NPs (CDNPs), which represent a significant component in urban air pollution. Epidemiological, panel and controlled human chamber studies clearly demonstrate that exposure to CDNPs is associated with multiple adverse cardiovascular effects in both healthy individuals and those with pre-existing cardiovascular disease. NPs are also manufactured from a large range of materials for industrial use in a vast array of products including for use as novel imaging agents for medical use. There is currently little information available on the impacts of manufactured NPs in humans, but experimental studies demonstrate similarities to the detrimental cardiovascular actions of CDNPs. This review describes the evidence for these cardiovascular effects and attempts to resolve the paradox between the adverse effects of the unintentional exposure of CDNPs and the intentional delivery of manufactured NPs for medical purposes.

The chemical biology of naphthoquinones and its environmental implications

Quinones are a group of highly reactive organic chemical species that interact with biological systems to promote inflammatory, anti-inflammatory, and anticancer actions and to induce toxicities. This review describes the chemistry, biochemistry, and cellular effects of 1,2- and 1,4-naphthoquinones and their derivatives. The naphthoquinones are of particular interest because of their prevalence as natural products and as environmental chemicals, present in the atmosphere as products of fuel and tobacco combustion. 1,2- and 1,4-naphthoquinones are also toxic metabolites of naphthalene, the major polynuclear aromatic hydrocarbon present in ambient air. Quinones exert their actions through two reactions: as prooxidants, reducing oxygen to reactive oxygen species; and as electrophiles, forming covalent bonds with tissue nucleophiles. The targets for these reactions include regulatory proteins such as protein tyrosine phosphatases; Kelch-like ECH-associated protein 1, the regulatory protein for NF-E2-related factor 2; and the glycolysis enzyme glyceraldehyde-3-phosphate dehydrogenase. Through their actions on regulatory proteins, quinones affect various cell signaling pathways that promote and protect against inflammatory responses and cell damage. These actions vary with the specific quinone and its concentration. Effects of exposure to naphthoquinones as environmental chemicals can vary with the physical state, i.e., whether the quinone is particle bound or is in the vapor state. The exacerbation of pulmonary diseases by air pollutants can, in part, be attributed to quinone action.

Polycyclic aromatic hydrocarbons (PAHs) from coal combustion: emissions, analysis, and toxicology

Coal may become more important as an energy source in the 21st century, and coal contains large quantities of organic and inorganic matter. When coal burns chemical and physical changes take place, and many toxic compounds are formed and emitted. Polycyclic aromatic hydrocarbons (PAHs) are among those compounds formed and are considered to pose potential health hazards because some PAHs are known carcinogens. Based on their toxicology, 16 PAHs are considered as priority pollutants by the USEPA. More attention must be given to the various methods of extraction and analysis of PAH from coal or coal products to accurately explain and determine the species of PAHs. The influences of the extraction time, solvents, and methods for PAH identification are important. In the future, more methods and influences will be studied more carefully and widely. PAHs are environmental pollutants, are highly lipid soluble, and can be absorbed by the lungs, gut, and skin of mammals because they are associated with fine particles from coal combustion. More attention is being given to PAHs because of their carcinogenic and mutagenic action. We suggest that when using a coal stove indoors, a chimney should be used; the particles and gas containing PAHs should be released outdoors to reduce the health hazard, especially in Southwest China. During coal utilization processes, such as coal combustion and pyrolysis, PAHs released may be divided into two categories according to their formation pathways: one pathway is derived from complex chemical reactions and the other is from free PAHs transferred from the original coal. The formation and emission of PAHs is a complex physical and chemical process that has received considerable attention in recent years. It is suggested that the formation mechanisms of PAHs will be an increasingly important topic for researchers to find methods for controlling emissions during coal combustion.

Mutations in the lungs of gpt delta transgenic mice following inhalation of diesel exhaust

Diesel exhaust (DE) is a major airborne pollutant of urban areas. It contains various polycyclic aromatic hydrocarbons (PAH) and nitrated PAHs. In this study, gpt delta mice were treated with inhalation of 1 or 3 mg m(-3) DE, or a single intratracheal instillation of diesel exhaust particles (DEP) or DEP extract. In the lungs of mice treated with inhalation of 3 mg m(-3) DE for 12 weeks, the mutant frequency (MF) was 3.2-fold higher than that of the control group (1.90 x 10(-5) and 0.59 x 10(-5), respectively). An instillation of DEP and DEP extract resulted in a significant dose-dependent linear increase in MF. In mice treated with 0.5 mg DEP and 0.2 mg DEP extract, the MFs were 3.0- and 2.7-fold higher than that of the control group, respectively. The mutagenic potency (MF mg(-1)) of DEP extract (5.6 x 10(-5)) was double that of DEP (2.7 x 10(-5)), suggesting that the mutagenicity of the latter is derived primarily from compounds in the extract, which itself is responsible for ca. 50% of the weight of DEP. G:C-->A:T transitions were the predominant gpt mutation induced by all three treatments and G:C-->T:A transversions were induced by DEP and DEP extract. Guanine bases centered in nucleotide sequences such as GGA, TGA, CGG, and CGT were the major mutation targets of all three treatments. Thus, our results suggest that the mutagens contained in DEP such as PAH and nitrated PAHs induce mutations and may be responsible for carcinogenesis caused by inhalation of DE.

Relationship between redox activity and chemical speciation of size-fractionated particulate matter

BACKGROUND

Although the mechanisms of airborne particulate matter (PM) related health effects remain incompletely understood, one emerging hypothesis is that these adverse effects derive from oxidative stress, initiated by the formation of reactive oxygen species (ROS) within affected cells. Typically, ROS are formed in cells through the reduction of oxygen by biological reducing agents, with the catalytic assistance of electron transfer enzymes and redox active chemical species such as redox active organic chemicals and metals. The purpose of this study was to relate the electron transfer ability, or redox activity, of the PM samples to their content in polycyclic aromatic hydrocarbons and various inorganic species. The redox activity of the samples has been shown to correlate with the induction of the stress protein, hemeoxygenase-1.

RESULTS

Size-fractionated (i.e. < 0.15; < 2.5 and 2.5 - 10 microm in diameter) ambient PM samples were collected from four different locations in the period from June 2003 to July 2005, and were chemically analyzed for elemental and organic carbon, ions, elements and trace metals and polycyclic aromatic hydrocarbons. The redox activity of the samples was evaluated by means of the dithiothreitol activity assay and was related to their chemical speciation by means of correlation analysis. Our analysis indicated a higher redox activity on a per PM mass basis for ultrafine (< 0.15 microm) particles compared to those of larger sizes. The PM redox activity was highly correlated with the organic carbon (OC) content of PM as well as the mass fractions of species such as polycyclic aromatic hydrocarbons (PAH), and selected metals.

CONCLUSION

The results of this work demonstrate the utility of the dithiothreitol assay for quantitatively assessing the redox potential of airborne particulate matter from a wide range of sources. Studies to characterize the redox activity of PM from various sources throughout the Los Angeles basin are currently underway.

Bioavailability and risk assessment of orally ingested polycyclic aromatic hydrocarbons

Polycyclic aromatic hydrocarbons (PAHs) are a family of toxicants that are ubiquitous in the environment. These contaminants generate considerable interest, because some of them are highly carcinogenic in laboratory animals and have been implicated in breast, lung, and colon cancers in humans. These chemicals commonly enter the human body through inhalation of cigarette smoke or consumption of contaminated food. Of these two pathways, dietary intake of PAHs constitutes a major source of exposure in humans. Although many reviews and books on PAHs have been published, factors affecting the accumulation of PAHs in the diet, their absorption following ingestion, and strategies to assess risk from exposure to these hydrocarbons following ingestion have received much less attention. This review, therefore, focuses on concentrations of PAHs in widely consumed dietary ingredients along with gastrointestinal absorption rates in humans. Metabolism and bioavailability of PAHs in animal models and the processes, which influence the disposition of these chemicals, are discussed. The utilitarian value of structure and metabolism in predicting PAH toxicity and carcinogenesis is also emphasized. Finally, based on intake, disposition, and tumorigenesis data, the exposure risk to PAHs from diet, and contaminated soil is presented. This information is expected to provide a framework for refinements in risk assessment of PAHs from a multimedia exposure perspective.

Approaches to carcinogenic risk assessment for polycyclic aromatic hydrocarbons: a UK perspective

This paper reviews the approaches to carcinogenic risk assessment of polycyclic aromatic hydrocarbons (PAHs) in air pollution with emphasis on high potency PAHs such as dibenzo[a,l]pyrene (DB[a,l]P). The potency of DB[a,l]P may be 100-fold greater than benzo[a]pyrene (B[a]P); thus the B[a]P surrogate approach currently used to monitor for compliance with UK air pollution standards may not be appropriate. It is suggested that an approach based on potency equivalency factors (PEFs) could be developed to include highly potent PAHs provided an appropriate reference data set for relevant PAHs using a route acceptable for inhalation risk assessment is selected. Available data suggest that intratracheal administration of low doses of PAHs to rats is likely to simulate the kinetics of inhalation exposure to PAHs in a feasible manner. The use of a measure of total DNA adducts as an endpoint, which correlates well with lung tumourigenicity, would provide surrogate data for setting PEFs without the need for long-term bioassays in rodents. Further, dose-response studies using intratracheal administration of a range of PAHs singly and in combination to assess additivity are required to develop a PEF system for inhalation PEFs derived from DNA adduct measurements.

Inhaled particles and lung cancer. Part A: Mechanisms

Both occupational and environmental exposure to particles is associated with an increased risk of lung cancer. Particles are thought to impact on genotoxicity as well as on cell proliferation via their ability to generate oxidants such as reactive oxygen species (ROS) and reactive nitrogen species (RNS). For mechanistic purposes, one should discriminate between a) the oxidant-generating properties of particles themselves (i.e., acellular), which are mostly determined by the physicochemical characteristics of the particle surface, and b) the ability of particles to stimulate cellular oxidant generation. Cellular ROS/RNS can be generated by various mechanisms, including particle-related mitochondrial activation or NAD(P)H-oxidase enzymes. In addition, since particles can induce an inflammatory response, a further subdivision needs to be made between primary (i.e., particle-driven) and secondary (i.e., inflammation-driven) formation of oxidants. Particles may also affect genotoxicity by their ability to carry surface-adsorbed carcinogenic components into the lung. Each of these pathways can impact on genotoxicity and proliferation, as well as on feedback mechanisms involving DNA repair or apoptosis. Although abundant evidence suggests that ROS/RNS mediate particle-induced genotoxicity and mutagenesis, little information is available towards the subsequent steps leading to neoplastic changes. Additionally, since most of the proposed molecular mechanisms underlying particle-related carcinogenesis have been derived from in vitro studies, there is a need for future studies that evaluate the implication of these mechanisms for in vivo lung cancer development. In this respect, transgenic and gene knockout animal models may provide a useful tool. Such studies should also include further assessment of the relative contributions of primary (inflammation-independent) and secondary (inflammation-driven) pathways.

Measurement of Polynuclear Aromatic Hydrocarbons in Canine Lung after Alkaline Decomposition

An alkaline decomposition method employing a KOH/alcohol solution was studied, and polynuclear aromatic hydrocarbons (PAHs) contained in particles remaining in canine lung were measured. As a result, BaA, BkF, BaP, and BghiP were found. By this method, PAHs extracted from the lungs of 32 dogs were 13.0-166.0 ng (mean, 63.0 ng) for BaA, 6.6-90.2 ng (mean, 27.4 ng) for BkF, 9.8-167.4 ng (mean 47.2 ng) for BaP, and 10.8-206.0 ng (mean, 61.8 ng) for BghiP. The results showed no correlation between the age and the concentration of PAHs in the lung, but some correlation was found between the age and the lung weight (p<0.01). There were significant correlations among the concentrations of the compounds in the lung (p<0.01). These results suggest that dogs, like humans, are affected by automobile exhaust and other common generation sources of such substances.

Effects of fluoranthene, a polycyclic aromatic hydrocarbon, on cAMP-dependent anion secretion in human airway epithelia

The human respiratory tract is constantly exposed to polycyclic aromatic hydrocarbons (PAHs) through inhalation of atmospheric pollutants. We examined the effects of three PAHs (benzo[a]pyrene, anthracene, and fluoranthene) on the airway ion transport, which is essential for lung defense and normal airway function, using human airway epithelia (Calu-3). These three PAHs had no significant effect on the basal short-circuit current (I(sc)). However, fluoranthene (1-100 microM) applied in the apical compartment potentiated I(sc) in response to cAMP-related agents (isoproterenol, forskolin, and 8-bromo-cAMP). The effects of fluoranthene were unaffected by ellipticine, a PAH receptor antagonist. Estimation of the anionic composition of I(sc) revealed that isoproterenol increased both HCO(3)(-) and Cl(-) transport in the control, whereas it potentiated only Cl(-) transport in the presence of fluoranthene. The fluoranthene-induced modulations of these anion transporters were counteracted by charybdotoxin (ChTx, a hIK-1 channel blocker). Fluoranthene gradually augmented the ChTx-sensitive K(+) current (I(K)) across the basolateral membrane, accompanied by a sustained increase in the cytosolic Ca(2+) concentration ([Ca(2+)](i)). In the presence of fluoranthene, however, a much larger hIK-1-dependent I(K) was identified by the application of 8-bromo-cAMP without concomitant elevation of [Ca(2+)](i). These results suggest that fluoranthene switches from cAMP-dependent HCO(3)(-) secretion to Cl(-) secretion through the hIK-1 channel, whose sensitivity to protein kinase A may be up-regulated by the sustained [Ca(2+)](i) elevation produced by this chemical.

Benzo[a]pyrene diones are produced by photochemical and enzymatic oxidation and induce concentration-dependent decreases in the proliferative state of human pulmonary epithelial cells

Organic components within mixtures of combustion-derived materials may play an important role in the correlation between air pollution and adverse cardio/respiratory health. One class of these organic components, polycyclic aromatic hydrocarbons (PAHs), has been shown to produce a wide variety of adverse health effects. An air toxic and a model PAH, benzo[a]pyrene (BaP), is a component of combustion-derived particulate matter (PM). Although most biological effects associated with BaP have been attributed to the cytochrome P-450 derived BaP 7,8-diol 9,10-epoxide, many other BaP oxidation products are formed in atmospheric and biological reactions and may contribute to PAH-induced adverse health effects. In an ambient environment, BaP and other PAHs undergo oxidation in the presence of ultraviolet light, O(2), O(3), NO(2), or OH(*). Biological peroxidase- and P-450 mediated conversion of BaP produces an extensive metabolic profile of BaP oxidation products that significantly outnumber the 7,8-diol/diol epoxide. The data herein show that in addition to near-ultraviolet light and P-450 isozymes, lactoperoxidase (airway peroxidase) converted BaP into a mixture of three diones, the 1,6-, 3,6-, and 6,12-BaP dione (BPD). In addition, it was found that low concentrations of BPDs induced a concentration-dependent decrease in the proliferation state of human pulmonary epithelial cells in vitro. Nanomolar concentrations of BPDs mediated cell growth inhibition, which was partially reversed by co-incubation with N-acetyl-L-cysteine and ascorbate. BPDs induced the formation of reactive oxygen species as measured by the fluorophore 2,7-dichloro-fluorescein. Together, these results may indicate a role for PAH oxidation products (PAH diones) in the adverse health effects associated with combustion-derived PM and semivolatile organic compounds.

Chemical carcinogens as foreign bodies and some pitfalls regarding cancer immune surveillance

Interferon-gamma-receptor (IFN-gammaR)-deficient mice are more susceptible to tumor induction by methylcholanthrene (MCA) in comparison to control littermates. The cellular source of IFNgamma is not known, but the absence of T cells does not significantly increase the incidence of MCA-induced tumors. However, it appears that the presence of T cells in combination with unknown, perhaps environmental, factors can decrease MCA-induced tumor incidence, indicating that IFN-gamma of unknown origin contributes to the protective response. The current knowledge of cancer biology, immune regulation, and tumor-promoting effects of inflammation are difficult to reconcile with the concept of immune surveillance against non-virus-associated cancer. Analysis of the primary MCA-treated mouse indicates, as one protective mechanism, a tissue repair response against MCA-induced damage, in the course of which MCA is encapsulated and persists for long time in tumor-free mice, termed foreign-body reaction. The protection from DNA damage could simultaneously diminish tissue injury and malignant transformation. We argue that inhibition of MCA-induced carcinogenesis is mechanistically different from tumor transplantation immunity and that a longer latency in MCA-treated mice is unlikely due to T cell-mediated tumor recognition and selection of less immunogenic variants. We discuss that the IFNgammaR-dependent mechanism against MCA is unrelated to the original concept of T cell-mediated immune surveillance and that the increased spontaneous tumor incidence observed in some immune-deficient mice is likely to be explained by opportunistic infection and tumor-promoting chronic inflammation.

Inhibition of methylcholanthrene-induced carcinogenesis by an interferon gamma receptor-dependent foreign body reaction

The foreign body reaction is one of the oldest host defense mechanisms against tissue damage which involves inflammation, scarring, and encapsulation. The chemical carcinogen methylcholanthrene (MCA) induces fibrosarcoma and tissue damage in parallel at the injection site. Tumor development induced by MCA but not due to p53-deficiency is increased in interferon-gamma receptor (IFN-gammaR)-deficient mice. In the absence of IFN-gammaR, MCA diffusion and DNA damage of surrounding cells is increased. Locally produced IFN-gamma induces the formation of a fibrotic capsule. Encapsulated MCA can persist virtually life-long in mice without inducing tumors. Together, the foreign body reaction against MCA prevents malignant transformation, probably by reducing DNA damage. This mechanism is more efficient in the presence of IFN-gammaR. Our results indicates that inflammation and scarring, both suspected to contribute to malignancy, prevent cancer in certain situations.

Toxicokinetics of inhaled benzo[a]pyrene: plasma and lung bioavailability

Bioavailability and toxicokinetic studies are essential in order to establish dose-response relationships of widely distributed environmental toxicants such as benzo[a]pyrene (BaP), a polycyclic aromatic hydrocarbon. Fischer 344 rats were exposed for 4 h (via nose-only inhalation) to aerosol exposure concentrations of 0.1, 1.0, and 2.5 mg/m(3) of BaP absorbed onto carbon black particles using a state-of-the-art model aerosol generation system. Nominal and chamber concentrations of the particulate aerosol were determined gravimetrically with a seven-stage cascade impactor. The average aerosol for the 3 exposure concentrations used in this study exhibited a trimodal distribution with 93% cumulative mass less than 15.85 microm, 89% cumulative mass less than 10 microm, 55.3% cumulative mass less than 2.5 microm, and 38% less than 1 microm. Fifty-five percent of the aerosol had a cumulative mass less than PM(2.5) and the mass median aerodynamic diameter (MMAD) -/+ geometric standard deviation (GSD) for this mode was 1.7 -/+ 0.085 microm. Plasma and lung samples were collected at 30, 60, 120, and 240 min postexposure. The concentrations of BaP parent compound and metabolites were determined by high-performance liquid chromatography. The toxicokinetic parameters were computed from the time course of plasma BaP concentration. The bioavailability of BaP increased as a function of exposure concentration, and toxicokinetic analysis indicates first-order pharmacokinetics for BaP. However, some toxicokinetic parameters such as clearance and volume of distribution remained constant throughout the duration of the postexposure period. BaP and its metabolite concentrations in plasma peaked at 1 h postexposure. At 240 min postexposure, only trace levels of BaP remained in the plasma. The BaP metabolites in the lung showed an identical trend where no parent compound was detected. Among the metabolites detected, BaP 4,5-, 7,8-, and 9,10-dihydrodiols, 3-OH-BaP, and 9-OH-BaP were predominant.

Modulation in the developmental expression profile of Sp1 subsequent to transplacental exposure of fetal rats to desorbed benzo[a]pyrene following maternal inhalation

Any alteration of the critical sequence of genes that are required to coordinate the differentiation of cells, the promotion of migration, dendritic arborization, synapse formation, and myelination in the developing nervous system would be expected to have deleterious consequences. The focus of this article is a molecular evaluation of the neurotoxicological effects that result subsequent to the transplacental exposure of fetal rats to desorbed benzo(a)pyrene (BaP) following maternal inhalation. A state-of-the-art, newly designed, fabricated, and tested model aerosol generation system was utilized in these studies. Timed-pregnant Sprague Dawley rats were exposed for 4 h on gestation day 15 of a 21-day gestation period to an acute dose of BaP:carbon black aerosol (100 microg/m(3)). Controls received carbon black only. Nominal and chamber concentrations of the particulate aerosol were determined gravimetrically with a seven-stage cascade impactor. The aerosol exhibited a trimodal distribution with 95% cumulative mass less than 15.85 microm, 90% cumulative mass less than 10 microm, 67. 5% cumulative mass less than 2.5 microm and 66.2% cumulative mass less than 1.0 microm. Time-course bioavailability results indicated that greater than 95% of the parent compound is cleared from blood 240 min postexposure. An Sp1 transcription factor consensus sequence was examined by electrophoretic mobility shift analysis of nuclear extracts from various brain regions of resulting pups on postnatal days 3, 5, 7, 10, and 15. It revealed perturbations in the developmental expression profile of Sp1 abundance as a result of nose-only particulate aerosol exposure to the timed-pregnant dam. The data obtained on the temporal and spatial regulation of gene expression in the brain indicate that (1) Sp1 DNA-binding is developmentally regulated and expressed very highly in actively developing brain regions, and (2) a consequence of the transplacental deposition of desorbed BaP to the fetus is in utero neurotoxicity.

DNA methylation and expression of p16(INK4A) gene in pulmonary adenocarcinoma and anthracosis in background lung

The p16 (CDKN2/MTS-1/INK4A) tumor-suppressor gene is frequently inactivated by DNA methylation in lung carcinomas. To clarify whether background anthracosis may play a role in DNA methylation and inactivation of the p16 gene, we examined DNA methylation of the p16-promoter region by methylation-specific polymerase chain reaction, and p16 expression immunohistochemically, and compared the results with the level of background anthracosis which was measured by an original quantitative method. At autopsy, DNA methylation of the p16 gene was observed in 6/19 tumors (32%) from patients who had died of pulmonary adenocarcinoma. The degree of background anthracosis (the effect of extrinsic carcinogenic factors) (mean absorbance value, A = 0.715) of the cases with p16-gene methylation was significantly higher than that without methylation (mean A value = 0.298). p16 expression was inactivated in all tumors with p16-gene methylation. The mean A value of black dust matter deposition in cases with normal expression of p16 (A = 0.151) was significantly lower than cases with abnormal expression of p16 (A = 0.531). These results indicate that the level of background anthracosis is closely associated with inactivation of p16 expression and also DNA methylation of the p16-gene promoter region in pulmonary adenocarcinogenesis. Int. J. Cancer (Pred. Oncol.) 84:609-613, 1999.

The implication of anthracosis in the development of pulmonary adenocarcinoma

The relationship between anthracosis, which is the deposition of black dust matter in the lung parenchyma, and the development of pulmonary adenocarcinoma has not been fully characterized. In order to clarify whether background black dust matter deposition could be implicated in the development of pulmonary adenocarcinoma, we measured the level of anthracosis at autopsy in 47 patients who had died of pulmonary adenocarcinoma. Both lungs of all 47 cadavers were examined. Twenty-micrometer sections were cut from formalin-fixed, paraffin-embedded blocks of the largest cut surface of each lung. Black dust matter was extracted from the sections and blotted onto a nitrocellulose membrane. The density of the blotted black dust matter was then analyzed using an imaging densitometer. There were no significant differences in the density of black dust matter deposition between lungs affected by pulmonary adenocarcinoma and control lungs. However, well differentiated adenocarcinomas tended to develop more frequently than poorly differentiated ones in lungs showing less deposition. We found a very strong correlation between the degree of black dust matter deposition and smoking history. Patients with severe anthracosis tended to have a poorer prognosis than those with mild anthracosis.

1-Nitropyrene as a marker for the mutagenicity of diesel exhaust-derived particulate matter in workplace atmospheres

The use of 1-nitropyrene (1-NP) as a marker for the occupational exposure to diesel exhaust (DE) mutagens was investigated in workplace atmospheres contaminated with DE from a variety of emission sources, such as power supplies, forklifts, trucks, caterpillar vehicles, trains, ships' engines, and vehicles in city traffic. Total suspended particulate matter was collected by area sampling. The 1-NP content of acetone extracts of these samples as determined by gas chromatography-high resolution mass spectrometry varied from 0.080 to 17 micrograms/g acetone extractable matter, corresponding to air concentrations of 0.012 to 1.2 ng/m3. A sample collected in a rural area contained 0.0017 ng/m3 1-NP. The mutagenicity of the extracts was tested in the Salmonella typhimurium strains TA98 and TA1538, using the microsuspension assay with and without metabolic activation by an exogeneous metabolizing system (rat liver S9-fraction). In addition, the S. typhimurium strains YG1021 and YG1024 were used because of their high sensitivity towards the mutagenicity of nitro polycyclic aromatic hydrocarbons. When plotting the mutagenic potency of the air sample extracts as determined in the absence of liver S9 versus the particle-associated 1-NP level, a relatively high correlation (r = 0.80-0.91) was observed in all of the S. typhimurium strains. High correlations (r = 0.80-0.93) were also observed when plotting the results of mutagenicity testing after activation by S9 versus the outcome of chemical analysis. These results show that the 1-NP content of workplace air samples is associated with their mutagenic potency, suggesting that 1-NP may be used as a marker for occupational exposure to DE-derived particle-associated mutagens.

The significance of an across-shift decrease in vital capacity--a re-analysis of a study on subjects exposed to diesel exhaust

Occupational exposure to diesel exhaust may develop acute as well as chronic lung function impairment. In this study, data from an earlier study on a group of subjects working at tunnel construction site were analyzed. The aim of the analysis was to examine the significance of an across-shift decrease in vital capacity with concern to other lung physiological measurements. There were no statistically significant differences, either in the average age, time of employment, vital capacity before a working shift after two days of no exposure, or the distributions of smoking habits and respiratory symptoms, between the eight workers who had an across-shift decrease in vital capacity and the five workers who had not. Subjects with an across-shift decrease in vital capacity had a significantly greater across-shift decrease in residual volume and total lung capacity than subjects without an across-shift decrease in vital capacity. The pathophysiological mechanisms for this across-shift decrease in residual volume is not fully understood. However, an altered defence mechanism in the lung may play a role for a prolonged retention time for the particles in the inhaled diesel exhaust, resulting in the across-shift decrease in residual volume. The results thus suggest that measurements of across-shift vital capacity is of importance in identifying susceptible subjects with occupational exposure to diesel exhaust.

Pharmacokinetics of inhaled pyrene in rats

Male Wistar rats were exposed to micronized aerosol concentrations of a 14C-labeled model polycyclic aromatic hydrocarbon (pyrene) at 200, 500, and 800 mg/m3 for a period of 95 min. Both the 14C label and free pyrene were monitored in the blood, urine, and feces. At the termination of the blood sampling, three of the six rats per dose group were killed and the distribution of [14C]pyrene to eight major tissues was analyzed. The analysis of blood concentration data using a one-compartment pharmacokinetic model revealed that the uptake and elimination kinetic parameters were dose dependent, for both total radioactivity (pyrene plus metabolites) and for pyrene per se, over the range of exposures used in this study. The ratio of the percent excreted via the urinary and fecal routes, collected over a 5-d period postexposure was about 1.0 at each exposure level.

Determination of polycyclic aromatic hydrocarbons in the lung

Polycyclic aromatic hydrocarbons (PAHs) accumulated in human lung samples from men (n = 236) and women (n = 128) were determined by high-performance liquid chromatography (HPLC) to examine their association with lung cancer. The mean values for benzo[a]pyrene (BaP), benzo[k]fluoranthene (BkF), and benzo[g,h,i]perylene (BghiP) in lungs (ng/g dry lung) of Japanese autopsied patients were 0.54, 0.44, and 0.87, respectively. The modal values were 0.3, 0.3 and 0.5, respectively. Each of the PAH concentrations was highly correlated with the others (r > 0.83). PAH concentrations in the lungs showed age-related increases with low correlation-coefficient values. BaP, BkF and BghiP concentrations in lungs of various subgroups were in the following order: male > female; and lung cancer > all cancers > non-cancer among male not female group. Only BghiP concentration in the lungs of the male smoker group is significantly higher (P < 0.10) than that of the male non-smoker group. Even among non-smoker groups, PAH concentrations in the lungs of male group were significantly higher than those of female group. In the male population, excess exposure to PAHs together with fine carbon particles, such as tobacco smoke or diesel exhaust, correlated with increased prevalence of lung cancer.

Combustion of diesel fuel from a toxicological perspective. II. Toxicity

Epidemiological data and results of toxicity studies in experimental animals indicate the possible health risk of diesel exhaust exposure. Acute effects of this exposure include odor, eye irritations, lung function decrements, cardiovascular symptoms, and some non-specific effects. Most of these effects are reported among persons highly exposed to diesel exhaust. Lung function decrements are reported as chronic effects. Another chronic effect that has been studied extensively among occupationally exposed persons in lung cancer. In addition to lung cancer, but at a less frequent rate, an enhanced incidence of bladder cancer is reported. The carcinogenic action of diesel exhaust exposure is ascribed to effects of the soot particles, particle-associated organics, and/or gas phase compounds. Direct effects of the particle load may include retardation of lung clearance, inflammation, and increased cell proliferation. These effects were all demonstrated in rodents. The particles may also prolong the residence time of particulate organics or induce the generation of reactive oxygen species. These compounds are known to react with macromolecules, causing lipid peroxidation, DNA damage, and/or activation of other genotoxic substances such as polycyclic aromatic hydrocarbons (PAHs). However, these results have not yet been confirmed in mammals in vivo. A direct interaction of particles with lung tissue is also suggested as a cause of cancer but a mechanism for this interaction has not yet been proposed. Organics associated with the particles are known to contain genotoxic properties attributable to PAHs and their derivatives. A number of these compounds are also identified as carcinogens in animal studies. However, it is not clear whether parent PAHs, their nitro-, oxy-, alkylated, or heterocyclic derivatives, or possibly other compounds are principally responsible for inducing tumors in the lungs of animals after diesel exhaust exposure. Furthermore, the mechanism of the bioavailability of these organics is not completely understood. The effects of gas phase constituents on the carcinogenic properties of the particles and/or particle-associated organics either have not been investigated or the findings have been inconclusive.

Bioavailability in vivo of benzo[a]pyrene adsorbed to diesel particulate

To evaluate health risks associated with exposure to particulates in the environment, it is necessary to quantify the bioavailability of carcinogens associated with the particulates. Direct analysis of bioavailability in vivo is most readily accomplished by adsorbing a radiolabeled form of the carcinogen to the particulate. A sample of native diesel particulate collected from an Oldsmobile diesel engine that contained 1.03 micrograms benzo[a]pyrene (BaP)/g particulate was supplemented with exogenous [3H]-BaP to produce a particulate containing 2.62 micrograms BaP/g. To insure that elution of BaP from native and [3H]-BaP-supplemented particulate was similar, in vitro analyses were performed. When using phospholipid vesicles composed of dimyristoylphosphatidylcholine (DMPC), 1.52% of total BaP was eluted from native particulate into the vesicles in 18 hrs; from [3H]-BaP supplemented particulate, 1.68% was eluted. Using toluene as eluent, 2.55% was eluted from native particulate, and 8.25% from supplemented particulate, in 6 hrs. Supplemented particulate was then instilled intratracheally into male Sprague-Dawley rats and distribution of radioactivity was analyzed at selected times over 3 days. About 50% of radioactivity remained in lungs at 3 days following instillation, with 30% being excreted into feces and the remainder distributed throughout the organs of the rats. To estimate the amount of radioactivity that entered feces through swallowing of a portion of the instilled dose, [3H]-BaP-supplemented particulate was instilled intratracheally into rats that had a cannula surgically implanted in the bile duct. Rate of elimination of radioactivity into bile was monitored; 10.6% of radioactivity was recovered in 6 hr, an amount slightly lower than the 12.8% excreted in 6 hrs into feces of animals with intact bile ducts. Our studies provide a quantitative description of the distribution of BaP and its metabolites following intratracheal instillation of diesel particulate. Because rates of elution of BaP in vitro are similar for native diesel particulate and particulate with supplemental [3H]-BaP, our results provide a reasonable estimate of the bioavailability in vivo of BaP associated with diesel particulate.

The retention of polycyclic aromatic hydrocarbons in the bronchial airways and in the alveolar region--a theoretical comparison

Several experiments indicate that physical transport phenomena such as molecular diffusion and partitioning between aqueous and lipid phases have a profound influence on the pulmonary retention of polycyclic aromatic hydrocarbons (PAHs). Because the average distance of diffusion between the air interface and the capillary blood is only about 0.5 microm in the alveoli, whereas in the bronchi it probably exceeds 50 microm, there should be a fundamental difference between the bronchial airways and the alveolar region in the retention of PAHs. A theoretical model was developed to simulate the retention of lipophilic substances in the two regions of the lung. Results show that a substance like benzo[a]pyrene, a PAH, may be retained for hours in the bronchi, compared to less than 1 min in the alveoli. This predicted dramatic difference in retention could explain the characteristic, biphasic pattern in the pulmonary clearance of PAHs observed in many animal experiments, but more importantly, it could also explain the fact that human lung cancers occur predominantly in the bronchi, although only a small fraction of inhaled particles carrying PAHs are deposited there.

Lung retention and binding of [14C]-1-nitropyrene when inhaled by F344 rats as a pure aerosol or adsorbed to carbon black particles

1-Nitropyrene (NP), as found in the environment, is more typically associated with carbonaceous particles than found as an aerosol of the pure compound. To determine whether (and why) an association with particles resulted in prolonged lung retention of NP, rats were exposed to 14C-NP as a pure aerosol or adsorbed on carbon black particles. Total 14C retained in the lung was greater at all times from 0.5 h to 30 d after exposure to 14C-NP adsorbed to carbon black particles than after exposure to pure 14C-NP (p less than .05). The fraction of total 14C in lung bound to carbon black particles decreased steadily with time after exposure, indicating in vivo removal of NP from the particles. At 0.5 h after exposure, the fraction of the estimated deposited 14C that was covalently bound to lung macromolecules was twofold greater for NP adsorbed on carbon black than for pure NP. Covalently bound 14C in lungs increased with time after exposure to 14C-NP adsorbed to carbon black, reaching levels of approximately 1% of the deposited radioactivity at 7-30 d after exposure, whereas levels of covalently bound 14C declined with time after exposure to pure NP. Thus, at 30 d after exposure, the amount of 14C covalently bound to lung macromolecules was approximately 10-fold greater (p less than .05) in rats that inhaled 14C-NP adsorbed on carbon black particles than in rats that inhaled pure 14C-NP aerosols. These results suggest that association of NP with carbon black particles augments the interaction of reactive metabolites of NP with target macromolecules. This phenomenon is thought to be related to the slow release of NP from carbon black particles, and may augment the biological effects of inhaled NP when adsorbed on carbon black or similar particles in the environment.

Effects of adsorption of benzo[a]pyrene onto carbon black particles on levels of DNA adducts in lungs of rats exposed by inhalation

Exposure of rodents to benzo[a]pyrene (BaP) associated with particles has previously been shown to result in increased retention of BaP and metabolites in lungs. To determine if DNA damage might be enhanced, DNA adducts were measured in lungs of F344 rats following inhalation of pure BaP aerosols or BaP absorbed on carbon black particles. Groups of rats were exposed nose only to filtered air, [14C]BaP (2 mg/m3), or [14C]BaP (2 mg/m3) adsorbed on carbon black (97 mg/m3) (BaP/CB) for 4 hr/day, 1 day/week, for 12 weeks. Groups of rats were terminated at 4, 8, 12, 16, 20, and 24 weeks after the beginning of the 12-week exposure period. Retention of total 14C in lungs was used as an indicator of total reactive metabolites. DNA isolated from lungs was analyzed for adducts using a 32P-postlabeling assay. Inhalation of BaP/CB resulted in 100-fold higher levels of 14C in lungs at the end of the 12-week exposure than did inhalation of pure BaP. The halftime for the decline in 14C levels was 34 +/- 3 weeks (mean +/- SE) for rats exposed to BaP/CB and 6 +/- 2 weeks for rats exposed to pure BaP. At the end of 12 weeks of exposure, DNA adducts in lungs of rats exposed to pure BaP ranged from 2-15 adducts per 10(9) bases (mean = 7, n = 4) and in rats exposed to pure BaP absorbed on carbon black ranged from 10-12 adducts per 10(9) bases (mean = 11, n = 4); DNA adducts in lungs of sham-exposed rats ranged from 0-2 adducts per 10(9) bases (mean = 1, n = 4). The halftimes for the decline in DNA adducts in lungs were 3 +/- 1 weeks (mean +/- SE) for the rats exposed to BaP/CB and 5 +/- 2 weeks for the rats exposed to BaP. One of the DNA adducts found following exposure to both BaP and BaP/CB was tentatively identified as the BaP diol epoxide deoxyguanosine (BPDE) adduct. Levels of both total and BPDE DNA adducts were significantly increased (p less than 0.05) in lungs of rats exposed to both BaP and BaP/CB compared to levels in lungs of sham-exposed rats. There were no significant differences in levels of DNA adducts in lungs of rats exposed to BaP or BaP/CB, although the pattern of adducts was different between the two exposure modes.(ABSTRACT TRUNCATED AT 400 WORDS)

Studies on the ability of rat lung and liver microsomes to facilitate transfer and metabolism of benzo[a]pyrene from diesel particles

Little is known about the bioavailability of inhaled organic compounds that are associated with particles. It is known that certain particle-associated organic compounds, such as polycyclic aromatic hydrocarbons (PAH) adsorbed on diesel soot particles, are retained in the lung longer than PAH inhaled in pure form. If such particle-associated compounds are available for tissue interaction, their prolonged retention may result in an increased potential for a toxic effect. To determine the factors affecting the bioavailability of particle-associated PAH, we have studied the ability of microsomes to facilitate transfer of benzo[a]pyrene (B[a]P) adsorbed on the surface of diesel exhaust soot particles to the microsomes and the ability of the microsomes to metabolize the transferred B[a]P. Our results indicate that rat lung and liver microsomes were able to facilitate the transfer of small amounts of B[a]P from diesel particles (less than 3%), but only a fraction of the amount transferred (1-2%) was metabolized. Under the same incubation conditions without soot, free B[a]P was extensively metabolized by microsomes, principally to B[a]P-9,10-diol. Lung microsomes were about twice as effective as liver microsomes for the transfer of the B[a]P. The ability to transfer B[a]P to the microsomes was independent of metabolism or the presence of protein, but was related to the lipid content of the microsomal fraction. There was no metabolism of the B[a]P coated on diesel particles as analyzed by high-performance liquid chromatography. These findings suggest that microsomes are able to enhance the slow transfer of only a small amount of B[a]P from diesel particles in a form that can be metabolized. However, over a long period of time, this slow release might be significant.

Health effects of diesel exhaust. A contemporary air pollution issue

Extracts of diesel exhaust particles are mutagenic in bacterial and mammalian cell assays; they contain hundreds of identifiable organic compounds, some of which are known mutagens and carcinogens. The particles are readily respired and about 20% to 30% of them are deposited in the pulmonary region, where they are retained for long periods. At low diesel exhaust concentrations, typical of those likely for human exposure, particle deposition and clearance rates are essentially normal and particle concentrations in the pulmonary region are expected to remain quite low. At very high concentrations of diesel exhaust, clearance processes may be overwhelmed and lung burdens of particles may continue to increase over long periods. Evidence from laboratory animals suggests that pulmonary injury and reduced respiratory function would occur in humans at these high concentrations. Epidemiologic data and laboratory studies appear to indicate that the human lung cancer risk from exposure to diesel exhaust would be quite low, even if use of diesel vehicles increased substantially.

Dog pulmonary macrophage metabolism of free and particle-associated [14C]benzo[a]pyrene

Pulmonary macrophages (PM) are involved in the clearance of inhaled particulate matter from the lung. PM also are capable of metabolizing xenobiotics such as benzo[a]pyrene (BaP). The objective of this investigation was to measure the ability of PM isolated from dogs to metabolize BaP coated onto diesel exhaust particles and to compare this metabolism with that of BaP in solution. PM were isolated from male beagle dogs and incubated with 1 microM [14C]BaP (solution or diesel particle coated) for select times up to 48 h. After incubation of PM with [14C]BaP, both the cells and the media were individually analyzed for [14C]BaP metabolites by high-performance liquid chromatography. Total quantities of [14C]BaP metabolites in both the media (125 pmol/10(6) cells) and cells (45 pmol/10(6) cells) increased with incubation time for up to 48 h. BaP-9,10-diol and BaP-7,8-diol were the major metabolites in organic extracts from the culture media, whereas BaP-7,8-diol and BaP-4,5-diol were the major metabolites in extracts of cells. Small quantities of BaP phenols and BaP quinones were detected in both the cells and media. Total quantities of BaP metabolites (20-30 pmol/10(6) cells) were not significantly different when PM were incubated for 24 h with either [14C]BaP in solution or [14C]BaP coated on diesel particles. The data suggest that particles retained in lungs are capable of being acted upon by PM metabolizing enzymes and that the ensuing metabolism may play an important role in the metabolic fate of organic material inhaled on particulate matter.