Early oxidative DNA damages and late development of lung cancer in diesel exhaust-exposed rats

Ellagic Acid Prevents Particulate Matter-Induced Pulmonary Inflammation and Hyperactivity in Mice: A Pilot Study

The inhalation of fine particulate matter (PM) is a significant health-related environmental issue. Previously, we demonstrated that repeated PM exposure causes hyperlocomotive activity in mice, as well as inflammatory and hypoxic responses in their lungs. In this study, we evaluated the potential efficacy of ellagic acid (EA), a natural polyphenolic compound, against PM-induced pulmonary and behavioral abnormalities in mice. Four treatment groups were assigned in this study (n = 8): control (CON), particulate-matter-instilled (PMI), low-dose EA with PMI (EL + PMI), and high-dose EA with PMI (EH + PMI). EA (20 and 100 mg/kg body weight for low dose and high dose, respectively) was orally administered for 14 days in C57BL/6 mice, and after the eighth day, PM (5 mg/kg) was intratracheally instilled for 7 consecutive days. PM exposure induced inflammatory cell infiltration in the lungs following EA pretreatment. Moreover, PM exposure induced inflammatory protein expression in the bronchoalveolar lavage fluid and the expression of inflammatory (tumor necrosis factor alpha (Tnfα), interleukin (Il)-1b, and Il-6) and hypoxic (vascular endothelial growth factor alpha (Vegfα), ankyrin repeat domain 37 (Ankrd37)) response genes. However, EA pretreatment markedly prevented the induction of expression of inflammatory and hypoxic response genes in the lungs. Furthermore, PM exposure significantly triggered hyperactivity by increasing the total moving distance with an increase in moving speed in the open field test. On the contrary, EA pretreatment significantly prevented PM-induced hyperactivity. In conclusion, dietary intervention with EA may be a potential strategy to prevent PM-induced pathology and activity.

Concordance between sites of tumor development in humans and in experimental animals for 111 agents that are carcinogenic to humans

Since the inception of the IARC Monographs Programme in the early 1970s, this Programme has developed 119 Monograph Volumes on more than 1000 agents for which there exists some evidence of cancer risk to humans. Of these, 120 agents were found to meet the criteria for classification as carcinogenic to humans (Group 1). Volume 100 of the IARC Monographs, compiled in 2008-2009 and published in 2012, provided a review and update of the 107 Group 1 agents identified as of 2009. These agents were divided into six broad categories: (I) pharmaceuticals; (II) biological agents; (III) arsenic, metals, fibers and dusts; (IV) radiation; (V) personal habits and indoor combustions; and (VI) chemical agents and related occupations. The Group I agents reviewed in Volume 100, as well as five additional Group 1 agents defined in subsequent Volumes of the Monographs, were used to assess the degree of concordance between sites where tumors originate in humans and experimental animals including mice, rats, hamsters, dogs, and non-human primates using an anatomically based tumor nomenclature system, representing 39 tumor sites and 14 organ and tissue systems. This evaluation identified 91 Group 1 agents with sufficient evidence (82 agents) or limited evidence (9 agents) of carcinogenicity in animals. The most common tumors observed in both humans and animals were those of the respiratory system including larynx, lung, and lower respiratory tract. In humans, respiratory system tumors were noted for 31 of the 111 distinct Group 1 carcinogens identified up to and including Volume 109 of the IARC Monographs, comprising predominantly 14 chemical agents and related occupations in category VI; seven arsenic, metals, fibers, and dusts in category III, and five personal habits and indoor combustions in category V. Subsequent to respiratory system tumors, those in lymphoid and hematopoietic tissues (26 agents), the urothelium (18 agents), and the upper aerodigestive tract (16 agents) were most often seen in humans, while tumors in digestive organs (19 agents), skin (18 agents), and connective tissues (17 agents) were frequently seen in animals. Exposures to radiation, particularly X- and γ-radiation, and tobacco smoke were associated with tumors at multiple sites in humans. Although the IARC Monographs did not emphasize tumor site concordance between animals and humans, substantial concordance was detected for several organ and tissue systems, even under the stringent criteria for sufficient evidence of carcinogenicity used by IARC. Of the 60 agents for which at least one tumor site was identified in both humans and animals, 52 (87%) exhibited tumors in at least one of the same organ and tissue systems in humans and animals. It should be noted that some caution is needed in interpreting concordance at sites where sample size is particularly small. Although perfect (100%) concordance was noted for agents that induce tumors of the mesothelium, only two Group 1 agents that met the criteria for inclusion in the concordance analysis caused tumors at this site. Although the present analysis demonstrates good concordance between animals and humans for many, but not all, tumor sites, limitations of available data may result in underestimation of concordance.

Genotoxic and epigenotoxic effects in mice exposed to concentrated ambient fine particulate matter (PM2.5) from São Paulo city, Brazil

BACKGROUND

The Metropolitan Area of São Paulo has a unique composition of atmospheric pollutants, and positive correlations between exposure and the risk of diseases and mortality have been observed. Here we assessed the effects of ambient fine particulate matter (PM2.5) on genotoxic and global DNA methylation and hydroxymethylation changes, as well as the activities of antioxidant enzymes, in tissues of AJ mice exposed whole body to ambient air enriched in PM2.5, which was concentrated in a chamber near an avenue of intense traffic in São Paulo City, Brazil.

RESULTS

Mice exposed to concentrated ambient PM2.5 (1 h daily, 3 months) were compared to in situ ambient air exposed mice as the study control. The concentrated PM2.5 exposed group presented increased levels of the oxidized nucleoside 8-oxo-7,8-dihydro-2'-deoxyguanosine in lung and kidney DNA and increased levels of the etheno adducts 1,N6-etheno-2'-deoxyadenosine and 1,N2-etheno-2'-deoxyguanosine in kidney and liver DNA, respectively. Apart from the genotoxic effects, the exposure to PM2.5 led to decreased levels of the epigenetic mark 5-hydroxymethylcytosine (5-hmC) in lung and liver DNA. Changes in lung, liver, and erythrocyte antioxidant enzyme activities were also observed. Decreased glutathione reductase and increased superoxide dismutase (SOD) activities were observed in the lungs, while the liver presented increased glutathione S-transferase and decreased SOD activities. An increase in SOD activity was also observed in erythrocytes. These changes are consistent with the induction of local and systemic oxidative stress.

CONCLUSIONS

Mice exposed daily to PM2.5 at a concentration that mimics 24-h exposure to the mean concentration found in ambient air presented, after 3 months, increased levels of DNA lesions related to the occurrence of oxidative stress in the lungs, liver, and kidney, in parallel to decreased global levels of 5-hmC in lung and liver DNA. Genetic and epigenetic alterations induced by pollutants may affect the genes committed to cell cycle control, apoptosis, and cell differentiation, increasing the chance of cancer development, which merits further investigation.

Comparative study of diesel and biodiesel exhausts on lung oxidative stress and genotoxicity in rats

The contribution of diesel exhaust to atmospheric pollution is a major concern for public health, especially in terms of occurrence of lung cancers. The present study aimed at addressing the toxic effects of a repeated exposure to these emissions in an animal study performed under strictly controlled conditions. Rats were repeatedly exposed to the exhaust of diesel engine. Parameters such as the presence of a particle filter or the use of gasoil containing rapeseed methyl ester were investigated. Various biological parameters were monitored in the lungs to assess the toxic and genotoxic effects of the exposure. First, a transcriptomic analysis showed that some pathways related to DNA repair and cell cycle were affected to a limited extent by diesel but even less by biodiesel. In agreement with occurrence of a limited genotoxic stress in the lungs of diesel-exposed animals, small induction of γ-H2AX and acrolein adducts was observed but not of bulky adducts and 8-oxodGuo. Unexpected results were obtained in the study of the effect of the particle filter. Indeed, exhausts collected downstream of the particle filter led to a slightly higher induction of a series of genes than those collected upstream. This result was in agreement with the formation of acrolein adducts and γH2AX. On the contrary, induction of oxidative stress remained very limited since only SOD was found to be induced and only when rats were exposed to biodiesel exhaust collected upstream of the particle filter. Parameters related to telomeres were identical in all groups. In summary, our results point to a limited accumulation of damage in lungs following repeated exposure to diesel exhausts when modern engines and relevant fuels are used. Yet, a few significant effects are still observed, mostly after the particle filter, suggesting a remaining toxicity associated with the gaseous or nano-particular phases.

Telomere tracking from birth to adulthood and residential traffic exposure

BACKGROUND

Telomere attrition is extremely rapid during the first years of life, while lifestyle during adulthood exerts a minor impact. This suggests that early life is an important period in the determination of telomere length. We investigated the importance of the early-life environment on both telomere tracking and adult telomere length.

METHODS

Among 184 twins of the East Flanders Prospective Twin Survey, telomere length in placental tissue and in buccal cells in young adulthood was measured. Residential addresses at birth and in young adulthood were geocoded and residential traffic and greenness exposure was determined.

RESULTS

We investigated individual telomere tracking from birth over a 20 year period (mean age (SD), 22.6 (3.1) years) in association with residential exposure to traffic and greenness. Telomere length in placental tissue and in buccal cells in young adulthood correlated positively (r = 0.31, P < 0.0001). Persons with higher placental telomere length at birth were more likely to have a stronger downward shift in telomere ranking over life (P < 0.0001). Maternal residential traffic exposure correlated inversely with telomere length at birth. Independent of birth placental telomere length, telomere ranking between birth and young adulthood was negatively and significantly associated with residential traffic exposure at the birth address, while traffic exposure at the residential address at adult age was not associated with telomere length.

CONCLUSIONS

Longitudinal evidence of telomere length tracking from birth to adulthood shows inverse associations of residential traffic exposure in association with telomere length at birth as well as accelerated telomere shortening in the first two decades of life.

Occupational exposure to diesel motor exhaust and risk of lung cancer by histological subtype: a population-based case-control study in Swedish men

We investigated occupational exposure to diesel motor exhaust (DME) and the risk of lung cancer by histological subtype among men, using elemental carbon (EC) as a marker of DME exposure. 993 cases and 2359 controls frequency-matched on age and year of study inclusion were analyzed by unconditional logistic regression in this Swedish case-control study. Work and smoking histories were collected by a questionnaire and telephone interviews. DME was assessed by a job-exposure matrix. We adjusted for age, year of study inclusion, smoking, occupational exposure to asbestos and combustion products (other than motor exhaust), residential exposure to radon and exposure to air pollution from road traffic. The OR for lung cancer for ever vs. never exposure to DME was 1.15 (95% CI 0.94-1.41). The risk was higher for squamous and large cell, anaplastic or mixed cell carcinoma than for alveolar cell cancer, adenocarcinoma and small cell carcinoma. The OR in the highest quartile of exposure duration (≥34 years) vs. never exposed was 1.66 (95% CI 1.08-2.56; p for trend over all quartiles: 0.027) for lung cancer overall, 1.73 (95% CI 1.00-3.00; p: 0.040) for squamous cell carcinoma and 2.89 (95% CI 1.37-6.11; p: 0.005) for the group of undifferentiated, large cell, anaplastic and mixed cell carcinomas. We found no convincing association between exposure intensity and lung cancer risk. Long-term DME exposure was associated with an increased risk of lung cancer, particularly to squamous cell carcinoma and the group of undifferentiated, large cell, anaplastic or mixed carcinomas.

The Toxicological Mechanisms of Environmental Soot (Black Carbon) and Carbon Black: Focus on Oxidative Stress and Inflammatory Pathways

The environmental soot and carbon blacks (CBs) cause many diseases in humans, but their underlying mechanisms of toxicity are still poorly understood. Both are formed after the incomplete combustion of hydrocarbons but differ in their constituents and percent carbon contents. For the first time, “Sir Percival Pott” described soot as a carcinogen, which was subsequently confirmed by many others. The existing data suggest three main types of diseases due to soot and CB exposures: cancer, respiratory diseases, and cardiovascular dysfunctions. Experimental models revealed the involvement of oxidative stress, DNA methylation, formation of DNA adducts, and Aryl hydrocarbon receptor activation as the key mechanisms of soot- and CB-induced cancers. Metals including Si, Fe, Mn, Ti, and Co in soot also contribute in the reactive oxygen species (ROS)-mediated DNA damage. Mechanistically, ROS-induced DNA damage is further enhanced by eosinophils and neutrophils via halide (Cl⁻ and Br⁻) dependent DNA adducts formation. The activation of pulmonary dendritic cells, T helper type 2 cells, and mast cells is crucial mediators in the pathology of soot- or CB-induced respiratory disease. Polyunsaturated fatty acids (PUFAs) were also found to modulate T cells functions in respiratory diseases. Particularly, telomerase reverse transcriptase was found to play the critical role in soot- and CB-induced cardiovascular dysfunctions. In this review, we propose integrated mechanisms of soot- and CB-induced toxicity emphasizing the role of inflammatory mediators and oxidative stress. We also suggest use of antioxidants and PUFAs as protective strategies against soot- and CB-induced disorders.

Biochemical and physiological effects from exhaust emissions. A review of the relevant literature

Exhaust emissions are to date ranked among the most frequent causes of premature deaths worldwide. The combustion of fuels such as diesel, gasoline, and bio-blends provokes a series of pathophysiological responses in exposed subjects, which are associated with biochemical and immunological triggering. It is critical to understand these mechanisms, which are directly related to the levels of aerosol, liquid and gaseous components in fuel exhaust (e.g. nanoparticles, particulate matter, volatile compounds), so to cast attention on their toxicity and gradually minimize their use. This review reports findings in the recent literature concerning the biochemical and cellular pathways triggered during intoxication by exhaust emissions, and links these findings to pathophysiological responses such as inflammation and vasoconstriction. This study provides critical in vitro and in vivo data for the reduction of emissions in urban centers, with an emphasis on the prevention of exposure of groups such as children, the elderly, and other affected groups, and shows how the exposure to exhaust emissions induces mechanisms of pathogenesis related to cardiopulmonary pathologies and long-term diseases such as asthma, allergies, and cancer. This review summarizes the cellular and physiological responses of humans to exhaust emissions in a comprehensive fashion, and is important for legislative developments in fuel politics.

Workplace exposure to diesel and gasoline engine exhausts and the risk of colorectal cancer in Canadian men

BACKGROUND

The International Agency for Research on Cancer (IARC) classified diesel exhaust as carcinogenic to humans (Group 1) and gasoline exhaust as a possible carcinogen (Group 2B) based studies of lung cancer, however the evidence for other sites is limited. We addressed this question by investigating exposure to diesel and gasoline emissions with respect to risk of colorectal cancer in men.

METHODS

We used data from a population-based case-control study with incident cases of colon (n = 931) and rectal (n = 840) cancer and 1360 controls from 7 Canadian provinces conducted in 1994-1997. Lifetime occupational history and information on other risk factors was collected. Occupational hygienists, blinded to case-control status, assigned exposures to each job for 3 dimensions: concentration, frequency, and reliability. Logistic regression was used to estimate odds ratios (OR) and their 95 % confidence intervals (CI), adjusted for age, province, use of proxy respondents, smoking, body-mass index, physical activity, intake of alcohol, processed meats, and occupational exposure to asbestos and aromatic amines.

RESULTS

Among CRC cases, 638 (36 %) were exposed to diesel and 814 (46 %) were exposed to gasoline emissions. Relative to the unexposed, elevated risks were observed among subjects ever exposed to high concentration levels of diesel emissions for colorectal cancer (OR = 1.65, 95 % CI = 0.98-2.80) and rectal cancer (OR = 1.98, 95 % CI = 1.09-3.60), but not colon cancer. Prolonged (>10 years) exposure at high concentrations was also associated with high risks of rectal cancer (OR = 2.33 95 % CI = 0.94-5.78; p-trend = 0.02). No statistically significant associations were observed for gasoline emissions.

CONCLUSIONS

Our findings suggest that sustained high-level exposure diesel emissions may increase the risk of rectal cancer.

Lower placental telomere length may be attributed to maternal residential traffic exposure; a twin study

BACKGROUND

High variation in telomere length between individuals is already present before birth and is as wide among newborns as in adults. Environmental exposures likely have an impact on this observation, but remain largely unidentified. We hypothesize that placental telomere length in twins is associated with residential traffic exposure, an important environmental source of free radicals that might accelerate aging. Next, we intend to unravel the nature-nurture contribution to placental telomere length by estimating the heritability of placental telomere length.

METHODS

We measured the telomere length in placental tissues of 211 twins in the East Flanders Prospective Twin Survey. Maternal traffic exposure was determined using a geographic information system. Additionally, we estimated the relative importance of genetic and environmental sources of variance.

RESULTS

In this twin study, a variation in telomere length in the placental tissue was mainly determined by the common environment. Maternal residential proximity to a major road was associated with placental telomere length: a doubling in the distance to the nearest major road was associated with a 5.32% (95% CI: 1.90 to 8.86%; p=0.003) longer placental telomere length at birth. In addition, an interquartile increase (22%) in maternal residential surrounding greenness (5 km buffer) was associated with an increase of 3.62% (95% CI: 0.20 to 7.15%; p=0.04) in placental telomere length.

CONCLUSIONS

In conclusion, we showed that maternal residential proximity to traffic and lower residential surrounding greenness is associated with shorter placental telomere length at birth. This may explain a significant proportion of air pollution-related adverse health outcomes starting from early life, since shortened telomeres accelerate the progression of many diseases.

Cell injury and repair resulting from sleep loss and sleep recovery in laboratory rats

STUDY OBJECTIVES

Increased cell injury would provide the type of change in constitution that would underlie sleep disruption as a risk factor for multiple diseases. The current study was undertaken to investigate cell injury and altered cell fate as consequences of sleep deprivation, which were predicted from systemic clues.

DESIGN

Partial (35% sleep reduction) and total sleep deprivation were produced in rats for 10 days, which was tolerated and without overtly deteriorated health. Recovery rats were similarly sleep deprived for 10 days, then allowed undisturbed sleep for 2 days. The plasma, liver, lung, intestine, heart, and spleen were analyzed and compared to control values for damage to DNA, proteins, and lipids; apoptotic cell signaling and death; cell proliferation; and concentrations of glutathione peroxidase and catalase.

MEASUREMENTS AND RESULTS

Oxidative DNA damage in totally sleep deprived rats was 139% of control values, with organ-specific effects in the liver (247%), lung (166%), and small intestine (145%). Overall and organ-specific DNA damage was also increased in partially sleep deprived rats. In the intestinal epithelium, total sleep deprivation resulted in 5.3-fold increases in dying cells and 1.5-fold increases in proliferating cells, compared with control. Recovery sleep restored the balance between DNA damage and repair, and resulted in normal or below-normal metabolic burdens and oxidative damage.

CONCLUSIONS

These findings provide physical evidence that sleep loss causes cell damage, and in a manner expected to predispose to replication errors and metabolic abnormalities; thereby providing linkage between sleep loss and disease risk observed in epidemiological findings. Properties of recovery sleep include biochemical and molecular events that restore balance and decrease cell injury.

Oxidatively damaged DNA in animals exposed to particles

Exposure to combustion-derived particles, quartz and asbestos is associated with increased levels of oxidized and mutagenic DNA lesions. The aim of this survey was to critically assess the measurements of oxidatively damaged DNA as marker of particle-induced genotoxicity in animal tissues. Publications based on non-optimal assays of 8-oxo-7,8-dihydroguanine by antibodies and/or unrealistically high levels of 8-oxo-7,8-dihydroguanine (suggesting experimental problems due to spurious oxidation of DNA) reported more induction of DNA damage after exposure to particles than did the publications based on optimal methods. The majority of studies have used single intracavitary administration or inhalation with dose rates exceeding the pulmonary overload threshold, resulting in cytotoxicity and inflammation. It is unclear whether this is relevant for the much lower human exposure levels. Still, there was linear dose-response relationship for 8-oxo-7,8-dihydroguanine in lung tissue without obvious signs of a threshold. The dose-response function was also dependent on chemical composition and other characteristics of the administered particles, whereas dependence on species and strain could not be equivocally determined. Roles of cytotoxicity or inflammation for oxidatively induced DNA damage could not be documented or refuted. Studies on exposure to particles in the gastrointestinal tract showed consistently increased levels of 8-oxo-7,8-dihydroguanine in the liver. Collectively, there is evidence from animal experimental models that both pulmonary and gastrointestinal tract exposure to particles are associated with elevated levels of oxidatively damaged DNA in the lung and internal organs. However, there is a paucity of studies on pulmonary exposure to low doses of particles that are relevant for hazard/risk assessment.

Evaluation of oxidative stress and DNA damage in traffic policemen exposed to vehicle exhaust

OBJECTIVE

We aimed to study the genotoxic effects in traffic police who are occupationally exposed due to higher free radical generation.

METHODS

Ambient and breathing zone air samples were analyzed blood samples were collected for analysis of antioxidant enzymes Superoxide Dismutase (SOD), Glutathione Peroxidase (GPx) and free radicals - nitric oxide (NO) and malondialdehyde (MDA) levels using a spectrophotometer. DNA damage was measured with the comet assay.

RESULTS

Higher levels of benzene (BZ), toluene (TOL), carbon monoxide (CO), benzo([a])pyrene (BaP) and sulfur dioxide (SO2) was observed in traffic police. Elevated levels of NO, MDA and comet tail length and lower SOD and GPx levels observed in traffic police.

CONCLUSION

The studied biomarkers, related to oxidative stress and DNA damage positively correlated in traffic police exposed to environmental air pollutants.

Air pollution: An environmental factor contributing to intestinal disease

The health impacts of air pollution have received much attention and have recently been subject to extensive study. Exposure to air pollutants such as particulate matter (PM) has been linked to lung and cardiovascular disease and increases in both hospital admissions and mortality. However, little attention has been given to the effects of air pollution on the intestine. The recent discovery of genes linked to susceptibility to inflammatory bowel diseases (IBD) explains only a fraction of the hereditary variance for these diseases. This, together with evidence of increases in incidence of IBD in the past few decades of enhanced industrialization, suggests that environmental factors could contribute to disease pathogenesis. Despite this, little research has examined the potential contribution of air pollution and its components to intestinal disease. Exposure of the bowel to air pollutants occurs via mucociliary clearance of PM from the lungs as well as ingestion via food and water sources. Gaseous pollutants may also induce systemic effects. Plausible mechanisms mediating the effects of air pollutants on the bowel could include direct effects on epithelial cells, systemic inflammation and immune activation, and modulation of the intestinal microbiota. Although there is limited epidemiologic evidence to confirm this, we suggest that a link between air pollution and intestinal disease exists and warrants further study. This link may explain, at least in part, how environmental factors impact on IBD epidemiology and disease pathogenesis.

Oxidative stress and DNA damage responses in rat and mouse lung to inhaled carbon nanoparticles

We have investigated whether short-term nose-only inhalation exposure to electric spark discharge-generated carbon nanoparticles (∼60 nm) causes oxidative stress and DNA damage responses in the lungs of rats (152 μg/m(3); 4 h) and mice (142 μg/m(3); 4 h, or three times 4 h). In both species, no pulmonary inflammation and toxicity were detected by bronchoalveolar lavage or mRNA expression analyses. Oxidative DNA damage (measured by fpg-comet assay), was also not increased in mouse whole lung tissue or isolated lung epithelial cells from rat. In addition, the mRNA expressions of the DNA base excision repair genes OGG1, DNA Polβ and XRCC1 were not altered. However, in the lung epithelial cells isolated from the nanoparticle-exposed rats a small but significant increase in APE-1 mRNA expression was measured. Thus, short-term inhalation of carbon nanoparticles under the applied exposure regimen, does not cause oxidative stress and DNA damage in the lungs of healthy mice and rats.

Role of oxidative damage in toxicity of particulates

Particulates are small particles of solid or liquid suspended in liquid or air. In vitro studies show that particles generate reactive oxygen species, deplete endogenous antioxidants, alter mitochondrial function and produce oxidative damage to lipids and DNA. Surface area, reactivity and chemical composition play important roles in the oxidative potential of particulates. Studies in animal models indicate that particles from combustion processes (generated by combustion of wood or diesel oil), silicate, titanium dioxide and nanoparticles (C60 fullerenes and carbon nanotubes) produce elevated levels of lipid peroxidation products and oxidatively damaged DNA. Biomonitoring studies in humans have shown associations between exposure to air pollution and wood smoke particulates and oxidative damage to DNA, deoxynucleotides and lipids measured in leukocytes, plasma, urine and/or exhaled breath. The results indicate that oxidative stress and elevated levels of oxidatively altered biomolecules are important intermediate endpoints that may be useful markers in hazard characterization of particulates.

DNA damage and cytotoxicity in type II lung epithelial (A549) cell cultures after exposure to diesel exhaust and urban street particles

Background

Exposure to air pollution particles has been acknowledged to be associated with excess generation of oxidative damage to DNA in experimental model systems and humans. The use of standard reference material (SRM), such as SRM1650 and SRM2975, is advantageous because experiments can be reproduced independently, but exposure to such samples may not mimic the effects observed after exposure to authentic air pollution particles. This study was designed to compare the DNA oxidizing effects of authentic street particles with SRM1650 and SRM2975. The authentic street particles were collected at a traffic intensive road in Copenhagen, Denmark.

Results

All of the particles generated strand breaks and oxidized purines in A549 lung epithelial cells in a dose-dependent manner and there were no overt differences in their potency. The exposures also yielded dose-dependent increase of cytotoxicity (as lactate dehydrogenase release) and reduced colony forming ability with slightly stronger cytotoxicity of SRM1650 than of the other particles. In contrast, only the authentic street particles were able to generate 8-oxo-7,8-dihydro-2'-deoxyguanosine (8-oxodG) in calf thymus DNA, which might be due to the much higher level of transition metals.

Conclusion

Authentic street particles and SRMs differ in their ability to oxidize DNA in a cell-free environment, whereas cell culture experiments indicate that the particle preparations elicit a similar alteration of the level of DNA damage and small differences in cytotoxicity. Although it cannot be ruled out that SRMs and authentic street particles might elicit different effects in animal experimental models, this study indicates that on the cellular level, SRM1650 and SRM2975 are suitable surrogate samples for the study of authentic street particles.

Air pollution, oxidative damage to DNA, and carcinogenesis

There is growing concern that air pollution exposure increases the risk of lung cancer. The mechanism of action is related to particle-induced oxidative stress and oxidation of DNA. Humans exposed to urban air with vehicle emissions have elevated levels of oxidized guanine bases in blood cells and urine. Animal experimental studies show that pulmonary and gastrointestinal exposure is associated with elevated levels of oxidized guanines in the lung and other organs. Collectively, there is evidence indicating that exposure to traffic-related air pollution particles is associated with oxidative damage to DNA and this might be associated with increased risk of cancer.

Combustion-derived nanoparticles: mechanisms of pulmonary toxicity

1. The general term 'nanoparticle' (NP) is used to define any particle less than 100 nm in at least one dimension and NPs are generally classified as natural, anthropogenic or engineered in origin. Anthropogenic, also referred to as 'ultrafine' particles (UFPs), are predominately combustion derived and are characterized by having an equivalent spherical diameter less than 100 nm. 2. These particles, considered to be 'combustion-derived nanoparticles' (CDNPs), are of toxicological interest given their nanosized dimensions, with properties not displayed by their macroscopic counterparts. 3. The pulmonary deposition efficiency of inhaled UFPs, along with their large surface areas and bound transition metals, is considered important in driving the emerging health effects linked to respiratory toxicity. 4. The toxicology of CDNPs is currently used to predict the health outcomes in humans following exposure to manufactured NPs. Their similar physicochemistry would suggest similar adverse health effects (i.e. pulmonary (and perhaps cardiac) toxicity). As such, it is essential to fully understand CDNP nanotoxicology in order to minimize occupational and environmental exposure.

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.

DNA damage in rats after a single oral exposure to diesel exhaust particles

The gastrointestinal route of exposure to particulate matter is important because particles are ingested via contaminated foods and inhaled particles are swallowed when removed from the airways by the mucociliary clearance system. We investigated the effect of an intragastric administration by oral gavage of diesel exhaust particles (DEP) in terms of DNA damage, oxidative stress and DNA repair in colon epithelial cells, liver, and lung of rats. Eight rats per group were exposed to Standard Reference Material 2975 at 0.064 or 0.64 mg/kg bodyweight for 6 and 24 h. Increased levels of 8-oxo-7,8-dihydro-2'-deoxyguanosine lesions were observed at the highest dose after 6 and 24 h in all three organs. 8-Oxo-7,8-dihydro-2'-deoxyguanosine is repaired by oxoguanine DNA glycosylase 1 (OGG1); upregulation of this repair system was observed as elevated pulmonary OGG1 mRNA levels after 24 h at both doses of DEP, but not in the colon and liver. A general response of the antioxidant defence system is further indicated by elevated levels of heme oxygenase 1 mRNA in the liver and lung 24 h after administration. The level of bulky DNA adducts was increased in liver and lung at both doses after 6 and 24h (DNA adducts in colon epithelium were not investigated). In summary, DEP administered via the gastrointestinal tract at low doses relative to ambient exposure generates DNA damage and increase the expression of defence mechanisms in organs such as the lung and liver. The oral exposure route should be taken into account in risk assessment of particulate matter.

Chronic nose-only inhalation study in rats, comparing room-aged sidestream cigarette smoke and diesel engine exhaust

Nose-only exposure of male and female Wistar rats to a surrogate for environmental tobacco smoke, termed room-aged sidestream smoke (RASS), to diesel engine exhaust (DEE), or to filtered, fresh air (sham) was performed 6 hours/day, 7 days/week for 2 years, followed by a 6-month post-exposure period. The particulate concentrations were 3 and 10 mg/m3. Markers of inflammation in bronchoalveolar lavage showed that DEE (but not RASS) produced a dose-related and persistent inflammatory response. Lung weights were increased markedly in the DEE (but not RASS) groups and did not decrease during the 6-month post-exposure period. Bulky lung DNA adducts increased in the RASS groups, but not in the DEE groups. Cell proliferation in the lungs was unaffected by either experimental treatment. Histopathological responses in the RASS groups were minimal and almost completely reversible; lung tumors were similar in number to those seen in the sham-exposed groups. Rats exposed to DEE showed a panoply of dose-related histopathological responses: largely irreversible and in some cases progressive. Malignant and multiple tumors were seen only in the DEE groups; after 30 months, the tumor incidence (predominantly bronchiolo-alveolar adenomas) was 2% in the sham-exposed groups, 5%in the high RASS groups, and 46% in the high DEE groups (sexes combined). Our results suggest that in rats exposed to DEE, but not to RASS, the following series of events occurs: particle deposition in lungs --> lung "overload" --> pulmonary inflammation --> tumorigenesis, without a significant modifying role of cell proliferation or DNA adduct formation.

Cooperation of the inducible nitric oxide synthase and cytochrome P450 1A1 in mediating lung inflammation and mutagenicity induced by diesel exhaust particles

Diesel exhaust particles (DEPs) have been shown to activate oxidant generation by alveolar macrophages (AMs), alter xenobiotic metabolic pathways, and modify the balance of pro-antiinflammatory cytokines. In this study we investigated the role of nitric oxide (NO) in DEP-mediated and DEP organic extract (DEPE) -mediated inflammatory responses and evaluated the interaction of inducible NO synthase (iNOS) and cytochrome P450 1A1 (CYP1A1). Male Sprague-Dawley rats were intratracheally (IT) instilled with saline, DEPs (35 mg/kg), or DEPEs (equivalent to 35 mg DEP/kg), with or without further treatment with an iNOS inhibitor, aminoguanidine (AG; 100 mg/kg), by intraperitoneal injection 30 min before and 3, 6, and 9 hr after IT exposure. At 1 day postexposure, both DEPs and DEPEs induced iNOS expression and NO production by AMs. AG significantly lowered DEP- and DEPE-induced iNOS activity but not the protein level while attenuating DEPE- but not DEP-mediated pulmonary inflammation, airway damage, and oxidant generation by AMs. DEP or DEPE exposure resulted in elevated secretion of both interleukin (IL) -12 and IL-10 by AMs. AG significantly reduced DEP- and DEPE-activated AMs in IL-12 production. In comparison, AG inhibited IL-10 production by DEPE-exposed AMs but markedly increased its production by DEP-exposed AMs, suggesting that NO differentially regulates the pro- and antiinflammatory cytokine balance in the lung. Both DEPs and DEPEs induced CYP1A1 expression. AG strongly inhibited CYP1A1 activity and lung S9 activity-dependent 2-aminoanthracene mutagenicity. These studies show that NO plays a major role in DEPE-induced lung inflammation and CYP-dependent mutagen activation but a lesser role in particulate-induced inflammatory damage.

Reduction of alachlor-induced olfactory mucosal neoplasms by the matrix metalloproteinase inhibitor Ro 28-2653

Chronic exposure to the chloracetanilide herbicide alachlor has been shown to cause olfactory mucosal neoplasms. Genomic analysis of olfactory mucosa from rats given alachlor (126 mg/kg/d) for from 1 day to 18 mo suggested that matrix metalloproteinases MMP-2 and MMP-9 were upregulated in the month following initiation of treatment. The present studies were designed to confirm this latter finding and to explore the potential role of MMPs in alachlor-induced olfactory carcinogenesis. Zymographic analysis of olfactory mucosal extracts confirmed that MMP-2 activity is higher in the olfactory mucosa of alachlor-treated rats. Therefore, rats were fed alachlor (126 mg/kg/d in the diet for 1 year) either with or without the MMP-2/MMP-9 inhibitor Ro 28-2653 (100 mg/kg daily by gavage for the first 2 months of alachlor treatment). The number of olfactory mucosal neoplasms was reduced by 25% after 1 year of alachlor treatment in rats that received both alachlor and Ro 28-2653. The morphology of alachlor-induced olfactory tumors was similar whether or not Ro 28-2653 had been given; the MMP inhibitor itself had no impact on olfactory mucosal histology. These data confirm that olfactory mucosal MMP-2 activity is increased following short-term alachlor exposure and show that administration of an MMP-2/9 inhibitor reduced the incidence of olfactory neoplasms in alachlor-treated rats, thereby implicating MMP-2 activity as a mediator of alachlor-induced carcinogenicity.

Lung Cancer Risk Assessment in Relation With Personal Exposure to Airborne Particles in Four French Metropolitan Areas

OBJECTIVE

The objective of this study was to quantify the total number of lung cancer deaths attributable to chronic exposure to fine particles (pm2.5) among adult populations of four French urban populations (Grenoble, Rouen, Paris, and Strasbourg).

METHODS

A geographic information system (GIS) was used to extrapolate personal average exposures to the total population of each metropolitan area across three sectors contrasted in terms of local sources of pollutants. We followed a health impact assessment approach by using the risk estimates in the CSP II study.

RESULTS

The annual number of lung cancer cases attributable to pm2.5 chronic exposure ranged from 12 to 404 according to the city. Among these deaths, up to 60% occurred, in the Paris metropolitan area in the urban sector most exposed to traffic emissions.

CONCLUSIONS

The health impact of chronic exposures to urban air pollution in metropolitan areas of developed countries warrants further efforts to abate sources of toxicants and to reduce exposure. Traffic emissions still contribute significantly to the total lung cancer burden in France.

Combustion-derived nanoparticles: a review of their toxicology following inhalation exposure

This review considers the molecular toxicology of combustion-derived nanoparticles (CDNP) following inhalation exposure. CDNP originate from a number of sources and in this review we consider diesel soot, welding fume, carbon black and coal fly ash. A substantial literature demonstrates that these pose a hazard to the lungs through their potential to cause oxidative stress, inflammation and cancer; they also have the potential to redistribute to other organs following pulmonary deposition. These different CDNP show considerable heterogeneity in composition and solubility, meaning that oxidative stress may originate from different components depending on the particle under consideration. Key CDNP-associated properties of large surface area and the presence of metals and organics all have the potential to produce oxidative stress. CDNP may also exert genotoxic effects, depending on their composition. CDNP and their components also have the potential to translocate to the brain and also the blood, and thereby reach other targets such as the cardiovascular system, spleen and liver. CDNP therefore can be seen as a group of particulate toxins unified by a common mechanism of injury and properties of translocation which have the potential to mediate a range of adverse effects in the lungs and other organs and warrant further research.

Carcinogenicity studies of diesel engine exhausts in laboratory animals: a review of past studies and a discussion of future research needs

Diesel engines play a vital role in world economy, especially in transportation. Exhaust from traditional diesel engines using high-sulfur fuel contains high concentrations of respirable carbonaceous particles with absorbed organic compounds. Recognition that some of these compounds are mutagenic has raised concern for the cancer-causing potential of diesel exhaust exposure. Extensive research addressing this issue has been conducted during the last three decades. This critical review is offered to facilitate an updated assessment of the carcinogenicity of diesel exhaust and to provide a rationale for future animal research of new diesel technology. Life-span bioassays in rats, mice, and Syrian hamsters demonstrated that chronic inhalation of high concentrations of diesel exhaust caused lung tumors in rats but not in mice or Syrian hamsters. In 1989, the International Agency for Research on Cancer (IARC) characterized the rat findings as "sufficient evidence of animal carcinogenicity," and, with "limited" evidence from epidemiological studies, classified diesel exhaust Category 2A, a "probable human carcinogen." Subsequent research has shown that similar chronic high concentration exposure to particulate matter generally considered innocuous (such as carbon black and titanium dioxide) also caused lung tumors in rats. Thus, in 2002, the U.S. Environmental Protection Agency (EPA) concluded that the findings in the rats should not be used to characterize the cancer hazard or quantify the cancer risk of diesel exhaust. Concurrent with the conduct of the health effects studies, progressively more stringent standards have been promulgated for diesel exhaust particles and NOx. Engine manufacturers have responded with new technology diesel (improved engines, fuel injection, fuels, lubricants, and exhaust treatments) to meet the standards. This review concludes with an outline of research to evaluate the health effects of the new technology, research that is consistent with recommendations included in the U.S. EPA 2002 health assessment document. When this research has been completed, it will be appropriate for IARC to evaluate the potential cancer hazard of the new technology diesel.

Air pollution and cancer: biomarker studies in human populations

Large cohort studies in the U.S. and in Europe suggest that air pollution may increase lung cancer risk. Biomarkers can be useful to understand the mechanisms and to characterize high-risk groups. Here we describe biomarkers of exposure, in particular DNA adducts as well as markers of early damage, including mutagenicity, other endpoints of genotoxicity and molecular biomarkers of cancer. Several studies found an association between external measures of exposure to air pollution and increased levels of DNA adducts, with an apparent levelling-off of the dose-response relationship. Also, numerous experimental studies in vitro and in vivo have provided unambiguous evidence for genotoxicity of air pollution. In addition, due to the organic extracts of particulate matter [especially various polycyclic aromatic hydrocarbon (PAH) compounds], particulate air pollution induces oxidative damage to DNA. The experimental work, combined with the data on frequent oxidative DNA damage in lymphocytes in people exposed to urban air pollution, suggests 8-oxo-dG as one of the important promutagenic lesions. Lung cancer develops through a series of progressive pathological changes occurring in the respiratory epithelium. Molecular alterations such as loss of heterozygosity, gene mutations and aberrant gene promoter methylation have emerged as potentially promising molecular biomarkers of lung carcinogenesis. Data from such studies relevant for emissions rich in PAHs are also summarized, although the exposure circumstances are not directly relevant to outdoor air pollution, in order to shed light on potential mechanisms of air pollution-related carcinogenesis.

Oxidative stress-induced DNA damage by particulate air pollution

Exposure to ambient air particulate matter (PM) is associated with pulmonary and cardiovascular diseases and cancer. The mechanisms of PM-induced health effects are believed to involve inflammation and oxidative stress. The oxidative stress mediated by PM may arise from direct generation of reactive oxygen species from the surface of particles, soluble compounds such as transition metals or organic compounds, altered function of mitochondria or NADPH-oxidase, and activation of inflammatory cells capable of generating ROS and reactive nitrogen species. Resulting oxidative DNA damage may be implicated in cancer risk and may serve as marker for oxidative stress relevant for other ailments caused by particulate air pollution. There is overwhelming evidence from animal experimental models, cell culture experiments, and cell free systems that exposure to diesel exhaust and diesel exhaust particles causes oxidative DNA damage. Similarly, various preparations of ambient air PM induce oxidative DNA damage in in vitro systems, whereas in vivo studies are scarce. Studies with various model/surrogate particle preparations, such as carbon black, suggest that the surface area is the most important determinant of effect for ultrafine particles (diameter less than 100 nm), whereas chemical composition may be more important for larger particles. The knowledge concerning mechanisms of action of PM has prompted the use of markers of oxidative stress and DNA damage for human biomonitoring in relation to ambient air. By means of personal monitoring and biomarkers a few studies have attempted to characterize individual exposure, explore mechanisms and identify significant sources to size fractions of ambient air PM with respect to relevant biological effects. In these studies guanine oxidation in DNA has been correlated with exposure to PM(2.5) and ultrafine particles outdoor and indoor. Oxidative stress-induced DNA damage appears to an important mechanism of action of urban particulate air pollution. Related biomarkers and personal monitoring may be useful tools for risk characterization.

Diesel exhaust particles cause increased levels of DNA deletions after transplacental exposure in mice

Diesel exhaust particles (DEP) are a major source of air-borne pollution and are linked to increased risk of disease including lung cancer. Here we investigated effects of exposure to DEP on the frequency of DNA deletions, levels of oxidative DNA damage and DNA adduct formation during embryonic development in mice. Pregnant dams were orally exposed to various doses of DEP (500, 250, 125, 62.5, 31.25 mg/kg/day) at embryonic days 10.5-15.5. We determined the frequency of 70 kb DNA deletions spanning exons 6-18 at the p(un) allele that results in black-pigmented spots in the unpigmented retinal pigment epithelium in the eyes of p(un)/p(un) offspring mice. DEP caused a significant increase in the frequency of DNA deletions. Levels of 8-OH deoxyguanosine indicating oxidative DNA damage were within the limits of the unexposed mouse embryos. 33P post-labeling analysis revealed very low levels of DNA adducts in the embryo tissue. Thus, transplacental exposure to DEP resulted in a significant increase in the frequency of DNA deletions in the mouse fetus and such genetic alterations in the offspring may have pathological consequences later in life.

Genotoxicity of airborne particulate matter: the role of cell-particle interaction and of substances with adduct-forming and oxidizing capacity

Exposure to particulate matter (PM) is associated with several health effects including lung cancer. However, the mechanisms of particle-induced carcinogenesis are not fully understood. The main aim of this study was to investigate the genotoxicity of PM in relation to particle-cell interactions and to study the effect of removal of DNA-damaging substances by extraction of PM with different solvents. Genotoxicity was analyzed by means of the comet assay after exposure of cultured human fibroblasts to urban dust particles (SRM 1649). It was found that PM induced DNA damage in a dose-dependent manner and that cells interacting with PM suffered more DNA single-strand breaks relative to other cells. The genotoxicity of PM was significantly reduced after extraction with dichloromethane (DCM), dimethyl sulfoxide (DMSO) and water, but not with acetone and hexane. However, the insoluble particle core still induced DNA single-strand breaks. The extracts were further investigated in cell-free systems. Analysis of aromatic DNA adducts with 32P-HPLC showed that the DMSO and DCM extracts contained most of the DNA-reactive polyaromatic compounds (PACs). Further, the formation of 8-oxo-2'-deoxyguanosine (8-oxodG) upon incubation of the extracts with 2'-deoxyguanosine (dG) showed that the water extract contained most of the oxidizing substances. Thus, the genotoxicity of PM was caused both by adduct-forming PACs and oxidizing substances as well as the insoluble particle-core. This study showed that all these factors together contribute to explaining the mechanisms of PM genotoxicity.

Can we use fixed ambient air monitors to estimate population long-term exposure to air pollutants? The case of spatial variability in the Genotox ER study

Associations between average total personal exposures to PM2.5, PM10, and NO2 and concomitant outdoor concentrations were assessed within the framework of the Genotox ER study. It was carried out in four French metropolitan areas (Grenoble, Paris, Rouen, and Strasbourg) with the participation, in each site, of 60-90 nonsmoking volunteers composed of two groups of equal size (adults and children) who carried the personal Harvard Chempass multipollutant sampler during 48 h along two different seasons ("hot" and "cold"). In each center, volunteers were selected so as to live (home and work/school) in three different urban sectors contrasted in terms of air pollution (one highly exposed to traffic emissions, one influenced by local industrial sources, and a background urban environment). In parallel to personal exposure measurements, a fixed ambient air monitoring station surveyed the same pollutants in each local sector. A linear regression model was accommodated where the dependent pollutant-specific variable was the difference, for each subject, between the average ambient air concentrations over 48 h and the personal exposure over the same period. The explanatory variables were the metropolitan areas, the three urban sectors, season, and age group. While average exposures to particles were underestimated by outdoor monitors, in almost all cities, seasons, and age groups, differences were lower for NO2 and, in general, in the other direction. Relationships between average total personal exposures and ambient air levels varied across metropolitan areas and local urban sectors. These results suggest that using ambient air concentrations to assess average exposure of populations, in epidemiological studies of long-term effects or in a risk assessment setting, calls for some caution. Comparison of personal exposures to PM or NO2 with ambient air levels is inherently disturbed by indoor sources and activities patterns. Discrepancies between measurement devices and local and regional sources of pollution may also strongly influence how the ambient air concentrations relate to population exposure. Much attention should be given to the selection of the most appropriate monitoring sites according to the study objectives.

Inflammatory and genotoxic effects of diesel particles in vitro and in vivo

Recent studies have identified an indirect genotoxicity pathway involving inflammation as one of the mechanisms underlying the carcinogenic effects of air pollution/diesel exhaust particles (DEP). We investigated the short-term effects of DEP on markers of inflammation and genotoxicity in vitro and in vivo. DEP induced an increase in the mRNA level of pro-inflammatory cytokines and a higher level of DNA strand breaks in the human lung epithelial cell line A549 in vitro. For the in vivo study, mice were exposed by inhalation to 20 or 80 mg/m3 DEP either as a single 90-min exposure or as four repeated 90-min exposures (5 or 20 mg/m3) and the effects in broncho-alveolar lavage (BAL) cells and/or lung tissue were characterized. Inhalation of DEP induced a dose-dependent inflammatory response with infiltration of macrophages and neutrophils and elevated gene expression of IL-6 in the lungs of mice. The inflammatory response was accompanied by DNA strand breaks in BAL cells and oxidative DNA damage and increased levels of bulky DNA adducts in lung tissue, the latter indicative of direct genotoxicity. The effect of a large single dose of DEP was more pronounced and sustained on IL-6 expression and oxidative DNA damage in the lung tissue than the effect of the same dose administered over four days, whereas the reverse pattern was seen in BAL cells. Our results suggest that the effects of DEP depend on the rate of delivery of the particle dose. The mutation frequency (MF), after DEP exposure, was determined using the transgenic Muta Mouse and a similar exposure regimen. No increase was observed in MF in lung tissue 28-days after exposure. In conclusion, short-term exposure to DEP resulted in DNA strand breaks in BAL cells, oxidative DNA damage and DNA adducts in lungs; and suggested that DNA damage in part is a consequence of inflammatory processes. The response was not associated with increased MF, indicating that the host defence mechanisms were sufficient to counteract the adverse effects of inflammation. Thus, there may be thresholds for the inflammation-associated genotoxic effects of DEP inhalation.

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.

Antioxidant perturbations in the olfactory mucosa of alachlor-treated rats

The chloracetanilide herbicide alachlor (2-chloro-2',6'-diethyl-N-(methoxymethyl)acetanilide) induces olfactory mucosal tumors in rats following chronic dietary exposure. Previous reports demonstrated that alachlor exposure was associated with depletion of glutathione (GSH) in liver in vivo and in vitro, but did not address this issue in the target tissue for the carcinogenic response. In this study we investigated a potential oxidative stress pathway in olfactory tissue by examining perturbations in olfactory mucosal antioxidants. Male Long-Evans rats were fed alachlor for up to 10 days (10-126 mg/kg per day), and intracellular reduced GSH and ascorbate levels were measured in olfactory mucosa. Both GSH and ascorbate rapidly decreased in olfactory mucosa following alachlor exposure, with a subsequent increase in both antioxidants to approximately 160% of control levels in the high dose group, and recovery of GSH to control levels in all groups by 10 days. Using Western blot analysis, we found that the modifier subunit of the rate-limiting enzyme in GSH synthesis, glutamate-cysteine ligase, increased in olfactory mucosa and remained elevated (126 mg/kg per day group). Two ascorbate transporters were detected by RT-PCR in olfactory mucosa, but neither appeared to be upregulated by alachlor exposure, and ascorbate synthesis was not stimulated in olfactory mucosa by alachlor treatment. Dietary exposure to alachlor depletes olfactory mucosa antioxidants, which may contribute to DNA damage and tissue-specific tumor formation.

Aerosol organic-mass-to-organic-carbon ratio measurements

The ratio of organic-mass-to-organic-carbon, typically taken to be between 1.4 and 1.7, has an uncertainty higher than 50%, but this value is used in every measurement to date of the organic fraction of atmospheric particles. A recently developed technique with errors reduced to between 9% and 33% provides measurements of this ratio that show its large variability for samples measured in northeastern Asia and the Caribbean. The technique uses functional groups measured by FTIR spectroscopy to estimate composite organic carbon from the number of carbon bonds present and organic mass from the molecular mass of each functional group associated with the measured bond type. The molecular masses associated with each functional group are not unique and do not account for highly branched organic compositions. For the organic mixtures described by the less than 20% of atmospheric organic mass that has been speciated by GCMS, the theoretical discrepancy in the composite organic-mass-to-organic-carbon ratio is less than 5%. The measured ratios for submicron particle samples are skewed: over 90% of the measurements collected lie between 1.2 and 1.6, with mean values just below 1.4. This variability highlights the importance of measured organic-mass-to-organic-carbon ratios to reduce the uncertainty associated with atmospheric organic aerosol.

Oxidative DNA damage in vitamin C-supplemented guinea pigs after intratracheal instillation of diesel exhaust particles

The health effects of diesel exhaust particles (DEP) are thought to involve oxidative damage. We have investigated the effect of intratracheal DEP instillation to guinea pigs in three groups of 12 animals each given 0, 0.7, or 2.1 mg. Five days later guinea pigs exposed to DEP had increased levels of oxidized amino acids (gamma-glutamyl semialdehyde), DNA strand breaks, and 7-hydro-8-oxo-2'-deoxyguanosine (8-oxodG) in the lung. Bulky DNA ad- ducts were not significantly elevated in the lung. The antioxidant enzyme activity of glutathione reductase was increased in the lung of DEP-exposed guinea pigs, whereas glutathione peroxidase and superoxide dismutase enzyme activities were unaltered. There was no difference in DNA strand breaks in lymphocytes or urinary excretion of 8-oxodG at the two doses tested. Protein oxidations in plasma and in erythrocytes were not altered by DEP exposure. The concentrations of ascorbate in liver, lung, and plasma were unaltered by the DEP exposure. The results indicate that in guinea pigs DEP causes oxidative DNA damage rather than bulky DNA adducts in the lung. Guinea pigs, which are similar to humans with respect to vitamin C metabolism, may serve as a new model for the study of oxidative damage induced by particulate matter.

Genomic analysis of alachlor-induced oncogenesis in rat olfactory mucosa

Alachlor induces olfactory mucosal tumors in rats in a highly ordered temporal process. We used GeneChip analysis to test the hypothesis that histological progression and oncogenic transformation are accompanied by gene expression changes that might yield clues as to the molecular pathogenesis of tumor formation. Acute alachlor exposure caused upregulation of matrix metalloproteinases (MMP)-2 and -9, tissue inhibitor of metalloproteinase-1, carboxypeptidase Z, and other genes related to extracellular matrix homeostasis. Heme oxygenase was upregulated acutely and maintained elevated expression. Expression of ebnerin, related to the putative human tumor suppressor gene DMBT1, progressively increased in alachlor-treated olfactory mucosa. Progression from adenomas to adenocarcinoma was correlated with upregulation of genes in the wnt signaling pathway. Activated wnt signaling was confirmed by immunohistochemical localization of beta-catenin to nuclei of adenocarcinomas, but not earlier lesions. These observations suggest that initiation and progression of alachlor-induced olfactory mucosal tumors is associated with alterations in extracellular matrix components, induction of oxidative stress, upregulation of ebnerin, and final transformation to a malignant state by wnt pathway activation.

Progression of alachlor-induced olfactory mucosal tumours

Alachlor is an herbicide used primarily in the production of corn (maize), peanuts, and soybeans and is associated with cancer of the nasal cavity, thyroid, and stomach in rats. Previous work from our laboratory demonstrated that the nasal cavity tumours originate from the olfactory mucosa, and that neoplasms were present following 6 months of exposure (126 mg/kg/day in the diet). The studies presented herein were conducted to determine more precisely the earliest time point at which alachlor-induced tumours were present, and to describe the histological changes that occur en route to tumour formation. We determined that dramatic histological changes, including respiratory metaplasia of the olfactory mucosa, were present following 3 months of exposure, and the earliest alachlor-induced olfactory mucosal tumours were detected following 5 months of treatment. Because alachlor is positive in short-term mutagenicity assays with olfactory mucosal activation, and because of the relatively short time-to-tumour formation observed with alachlor, we also conducted a 'stop' study in which rats were treated with alachlor for 1 month and then held without further treatment for an additional 5 months. This study demonstrated that abbreviated alachlor exposure did not result in subsequent tumour formation within the 6-month observation period.

The dual effect of the particulate and organic components of diesel exhaust particles on the alteration of pulmonary immune/inflammatory responses and metabolic enzymes

Exposure to diesel exhaust particles (DEP) is an environmental and occupational health concern. This review examines the cellular actions of the organic and the particulate components of DEP in the development of various lung diseases. Both the organic and the particulate components cause oxidant lung injury. The particulate component is known to induce alveolar epithelial damage, alter thiol levels in alveolar macrophages (AM) and lymphocytes, and activate AM in the production of reactive oxygen species (ROS) and pro-inflammatory cytokines. The organic component, on the other hand, is shown to generate intracellular ROS, leading to a variety of cellular responses including apoptosis. There are a number of differences between the biological actions exerted by these two components. The organic component is responsible for DEP induction of cytochrome P450 family 1 enzymes that are critical to the polycyclic aromatic hydrocarbons (PAH) and nitro-PAH metabolism in the lung as well as in the liver. The particulate component, on the other hand, causes a sustained down-regulation of CYP2B1 in the rat lung. The significance of this effect on pulmonary metabolism of xenobiotics and endobiotics remains to be seen, but may prove to be an important factor governing the interplay of the pulmonary metabolic and inflammatory systems. Long-term exposures to various particles including DEP, carbon black (CB), TiO2, and washed DEP devoid of the organic content, have been shown to produce similar tumorigenic responses in rodents. There is a lack of correlation between tumor development and DEP chemical-derived DNA adduct formation. But the organic component has been shown to generate ROS that produce 8-hydroxydeoxyguanosine (8-OHdG) in cell culture. The organic, but not the particulate, component of DEP suppresses the production of pro-inflammatory cytokines by AM and the development of Th1 cell-mediated immunity. The mechanism for this effect is not yet clear, but may involve the induction of heme oxygenase-1 (HO-1), a cellular genetic response to oxidative stress. Both the organic and the particulate components of DEP enhance respiratory allergic sensitization. Part of the DEP effects may be due to a depletion of glutathione in lymphocytes. The organic component, which is shown to induce IL-4 and IL-10 productions, may skew the immunity toward Th2 response, whereas the particulate component may stimulate both the Th1 and Th2 responses. In conclusion, the literature shows that the particulate and organic components of DEP exhibit different biological actions but both involve the induction of cellular oxidative stress. Together, these effects inhibit cell-mediated immunity toward infectious agents, exacerbate respiratory allergy, cause DNA damage, and under long-term exposure, induce the development of lung tumors.

Effect of diet on cancer development: is oxidative DNA damage a biomarker?

Free radicals and other reactive species are generated in vivo and many of them can cause oxidative damage to DNA. Although there are methodological uncertainties about accurate quantitation of oxidative DNA damage, the levels of such damage that escape immediate repair and persist in DNA appear to be in the range that could contribute significantly to mutation rates in vivo. The observation that diets rich in fruits and vegetables can decrease both oxidative DNA damage and cancer incidence is consistent with this. By contrast, agents increasing oxidative DNA damage usually increase risk of cancer development. Such agents include cigarette smoke, several other carcinogens, and chronic inflammation. Rheumatoid arthritis and diabetes are accompanied by increased oxidative DNA damage but the pattern of increased cancer risk seems unusual. Other uncertainties are the location of oxidative DNA damage within the genome and the variation in rate and level of oxidative damage between different body tissues. In well-nourished human volunteers, fruits and vegetables have been shown to decrease oxidative DNA damage in several studies, but data from short-term human intervention studies suggest that the protective agents are not vitamin C, vitamin E, beta-carotene, or flavonoids.

Aberrant CpG island methylation of the p16(INK4a) and estrogen receptor genes in rat lung tumors induced by particulate carcinogens

Recent studies by our laboratory indicate that the p16(INK4a) gene is frequently methylated in lung tumors induced by genotoxic carcinogens and that the frequency for methylation of the estrogen receptor alpha (ER) gene varies as a function of carcinogenic exposure. The purpose of the current investigation was to define the role of these two genes in lung tumors induced by the particulate carcinogens carbon black (CB), diesel exhaust (DE) or beryllium metal. Methylation of p16 was observed in 59 and 46% of DE and CB tumors, respectively. In contrast, the ER gene was inactivated in only 15% of DE or CB tumors. Methylation of the p16 and ER genes was very common (80 and 50%, respectively) in beryllium-induced lung tumors; both genes were methylated in 40% of the tumors. Bisulfite sequencing revealed dense methylation throughout exon 1 of the ER gene. The inhibitory effect of methylation on gene transcription was confirmed through RT-PCR expression studies in which p16 gene expression was 30-60-fold lower in methylated than unmethylated tumors. Residual expression in methylated tumors was consistent with contamination by stromal and inflammatory cells. Results indicate that tumors induced by these particulate carcinogens arise, in part, through inactivation of the p16 and ER genes. Furthermore, the inactivation of the p16 gene by these carcinogenic exposures supports a possible role for oxidative stress and inflammation in the etiology of human lung cancer.