Sample characterization of automobile and forklift diesel exhaust particles and comparative pulmonary toxicity in mice

Disruption of microRNA expression in human airway cells by diesel exhaust particles is linked to tumorigenesis-associated pathways

BACKGROUND

Particulate matter (PM) is associated with adverse airway health effects; however, the underlying mechanism in disease initiation is still largely unknown. Recently, microRNAs (miRNAs; small noncoding RNAs) have been suggested to be important in maintaining the lung in a disease-free state through regulation of gene expression. Although many studies have shown aberrant miRNA expression patterns in diseased versus healthy tissue, little is known regarding whether environmental agents can induce such changes.

OBJECTIVES

We used diesel exhaust particles (DEP), the largest source of emitted airborne PM, to investigate pollutant-induced changes in miRNA expression in airway epithelial cells. We hypothesized that DEP exposure can lead to disruption of normal miRNA expression patterns, representing a plausible novel mechanism through which DEP can mediate disease initiation.

METHODS

Human bronchial epithelial cells were grown at air-liquid interface until they reached mucociliary differentiation. After treating the cells with 10 microg/cm(2) DEP for 24 hr, we analyzed total RNA for miRNA expression using microarray profile analysis and quantitative real-time polymerase chain reaction.

RESULTS

DEP exposure changed the miRNA expression profile in human airway epithelial cells. Specifically, 197 of 313 detectable miRNAs (62.9%) were either up-regulated or down-regulated by 1.5-fold. Molecular network analysis of putative targets of the 12 most altered miRNAs indicated that DEP exposure is associated with inflammatory responses pathways and a strong tumorigenic disease signature.

CONCLUSIONS

Alteration of miRNA expression profiles by environmental pollutants such as DEP can modify cellular processes by regulation of gene expression, which may lead to disease pathogenesis.

Exacerbation of allergic inflammation in mice exposed to diesel exhaust particles prior to viral infection

Background

Viral infections and exposure to oxidant air pollutants are two of the most important inducers of asthma exacerbation. Our previous studies have demonstrated that exposure to diesel exhaust increases the susceptibility to influenza virus infections both in epithelial cells in vitro and in mice in vivo. Therefore, we examined whether in the setting of allergic asthma, exposure to oxidant air pollutants enhances the susceptibility to respiratory virus infections, which in turn leads to increased virus-induced exacerbation of asthma. Ovalbumin-sensitized (OVA) male C57BL/6 mice were instilled with diesel exhaust particles (DEP) or saline and 24 hours later infected with influenza A/PR/8. Animals were sacrificed 24 hours post-infection and analyzed for markers of lung injury, allergic inflammation, and pro-inflammatory cytokine production.

Results

Exposure to DEP or infection with influenza alone had no significant effects on markers of injury or allergic inflammation. However, OVA-sensitized mice that were exposed to DEP and subsequently infected with influenza showed increased levels of eosinophils in lung lavage and tissue. In addition Th2-type cytokines, such as IL-4 and IL-13, and markers of eosinophil chemotaxis, such as CCL11 and CCR3, were increased in OVA-sensitized mice exposed to DEP prior to infection with influenza. These mice also showed increased levels of IL-1α, but not IL-10, RANTES, and MCP-1 in lung homogenates.

Conclusion

These data suggest that in the setting of allergic asthma, exposure to diesel exhaust could enhance virus-induced exacerbation of allergic inflammation.

Differential pulmonary retention of diesel exhaust particles in Wistar Kyoto and spontaneously hypertensive rats

Spontaneously hypertensive (SH) and normotensive Wistar Kyoto (WKY) rats have been used for understanding the mechanisms of variations in susceptibility to airborne pollutants. We examined the lung burden of diesel exhaust particles (DEP) following inhalation of diesel engine exhaust (DEE) in both strains. The kinetics of clearance was also examined after single intratracheal (IT) instillation of DEP. Lungs were analyzed for DEP elemental carbon (EC) after exposure to DEE (0, 500, or 2000 microg/m(3) 4 h/day, 5 days/week x 4 weeks). SH rats had 16% less DEP-EC at 500 and 32% less at 2000 microg/m(3) in the lungs, despite having 50% higher than the average minute volume. No strain-related differences were noted in number of alveolar macrophages or their average DEP load as evident from examining cells in bronchoalveolar lavage fluid (BALF). The kinetics of DEP clearance from lungs of male WKY and SH rats was studied following a single instillation at 0.0 or 8.33 mg/kg of DEP standard reference material (SRM 2975) from the National Institute of Standards Technology. SH rats cleared 60% DEP over 112 days while minimal clearance occurred from the lungs of WKY. The pattern of DEP-induced inflammatory response assessed by BALF analysis was similar in both strains, although the overall protein leak was slightly greater in SH rats. A time-dependent accumulation of DEP occurred in tracheal lymph nodes of both strains (SH > WKY). Thus, SH rats may clear DEP more efficiently from their lungs than normotensive WKY rats, with a small contribution of more effective lymphatic drainage.

Effects of native organic material and water on sorption properties of reference diesel soot

Soot has been considered as a potentially important sorbent for organic contaminants in soils, sediments, and aerosols. This paper demonstrates that native (authigenic) extractable organic material (EOM) and surface-covering water on soot may have a substantial influence on sorption properties of the soot. Sorption isotherms were determined for apolar and weakly polar sorbates (n-octane, cyclooctane, n-propylbenzene, naphthalene) from an aqueous solution to a standard reference material of diesel soot (SRM 2975) in the original state and after extraction with methanol. For all sorbates tested, removal of EOM from soot by methanol caused the sorption isotherms to be more nonlinear (decrease of Freundlich exponents by 0.19-0.25) compared to the untreated soot. The changes in the isotherms depend on both sorbate structure and sorbate concentration and can be accounted for by two opposing roles that EOM could have on the sorption properties of soot (i) enhancing the overall sorption by absorbing the sorbate into the EOM phase, and (ii) attenuating the sorbate adsorption to the soot carbon surface through sorption competition or site blockage. The n-alkane-to-cycloalkane sorption coefficient ratios (Kn/Kc) indicated that the removal of EOM altered the sorption mode for alkanes from absorption to adsorption. A comparison of the sorption isotherms measured in aqueous suspensions with the soot-air sorption coefficients reported for SRM 2975 in the literature showed that sorption to "soot in water" is significantly weaker than sorption to "soot in air", indicating that complete surface coverage with water suppresses the sorption by soot.

Implication of scavenger receptors in the interactions between diesel exhaust particles and immature or mature dendritic cells

BACKGROUND

The exposure to pollutants such as diesel exhaust particles (DEP) is associated with an increased incidence of respiratory diseases. However, the mechanisms by which DEP have an effect on human health are not completely understood. In addition to their action on macrophages and airway epithelial cells, DEP also modulate the functions of dendritic cells (DC). These professional antigen-presenting cells are able to discriminate unmodified self from non-self thanks to pattern recognition receptors such as the Toll like Receptors (TLR) and Scavenger Receptors (SR). SR were originally identified by their ability to bind and internalize modified lipoproteins and microorganisms but also particles and TLR agonists. In this study, we assessed the implication of SR in the effects of DEP associated or not with TLR agonists on monocyte-derived DC (MDDC). For this, we studied the regulation of CD36, CXCL16, LOX-1, SR-A1 and SR-B1 expression on MDDC treated with DEP associated or not with TLR2, 3 and 4 ligands. Then, the capacity of SR ligands (dextran sulfate and maleylated-ovalbumin) to block the effects of DEP on the function of lipopolysaccharide (LPS)-activated DC has been evaluated.

RESULTS

Our data demonstrate that TLR2 agonists mainly augmented CXCL16, LOX-1 and SR-B1 expression whereas DEP alone had only a weak effect. Interestingly, DEP modulated the action of TLR2 and TLR4 ligands on the expression of LOX-1 and SR-B1. Pretreatment with the SR ligand maleylated-ovalbumin but not dextran sulfate inhibited the endocytosis of DEP by MDDC. Moreover, this SR ligand blocked the effect by DEP at low dose (1 mug/ml) on MDDC phenotype (a decrease of CD86 and HLA-DR expression) and on the secretion of CXCL10, IL-12 and TNF-alpha. In contrast, the decrease of IL-12 and CXCL10 secretion and the generation of oxygen metabolite induced by DEP at 10 mug/ml was not affected by SR ligands

CONCLUSION

Our results show for the first time that the modulation of DC functions by DEP implicates SR. TLR agonists upregulated SR expression in contrast to DEP. Interfering with the expression and/or the function of SR might be one way to limit the impact of DEP on lung immune response.

Diesel exhaust particles activate the matrix-metalloproteinase-1 gene in human bronchial epithelia in a beta-arrestin-dependent manner via activation of RAS

BACKGROUND

Diesel exhaust particles (DEPs) are globally relevant air pollutants that exert a detrimental human health impact. However, mechanisms of damage by DEP exposure to human respiratory health and human susceptibility factors are only partially known. Matrix metalloproteinase-1 (MMP-1) has been implied as an (etio)pathogenic factor in human lung and airway diseases such as emphysema, chronic obstructive pulmonary disease, chronic asthma, tuberculosis, and bronchial carcinoma and has been reported to be regulated by DEPs.

OBJECTIVE

We elucidated the molecular mechanisms of DEPs' up-regulation of MMP-1.

METHODS/RESULTS

Using permanent and primary human bronchial epithelial (HBE) cells at air-liquid interface, we show that DEPs activate the human MMP-1 gene via RAS and subsequent activation of RAF-MEK-ERK1/2 mitogen-activated protein kinase signaling, which can be scaffolded by beta-arrestins. Short interfering RNA mediated beta-arrestin1/2 knockout eliminated formation, subsequent nuclear trafficking of phosphorylated ERK1/2, and resulting MMP-1 transcriptional activation. Transcriptional regulation of the human MMP-1 promoter was strongly influenced by the presence of the -1607GG polymorphism, present in 60-80% of humans, which led to striking up-regulation of MMP-1 transcriptional activation.

CONCLUSION

Our results confirm up-regulation of MMP-1 in response to DEPs in HBE and provide new mechanistic insight into how these epithelia, the first line of protection against environmental insults, up-regulate MMP-1 in response to DEP inhalation. These mechanisms include a role for the human -1607GG polymorphism as a susceptibility factor for an accentuated response, which critically depends on the ability of beta-arrestin1/2 to generate scaffolding and nuclear trafficking of phosphorylated ERK1/2.

Comparison of allergic lung disease in three mouse strains after systemic or mucosal sensitization with ovalbumin antigen

Murine models of allergic lung disease have many similar traits to asthma in humans and can be used to investigate mechanisms of allergic sensitization and susceptibility factors associated with disease severity. The purpose of this study was to determine strain differences in allergic airway inflammation, immunoglobulin production, and changes in respiratory responses between systemic and mucosal sensitization routes in BALB/cJ, FVB/NJ, and C57BL/6J, and to provide correlations between immune and pathophysiological endpoints. After a single intranasal ovalbumin (OVA) challenge, all three strains of mice systemically sensitized with OVA and adjuvant exhibited higher airflow limitation than non-sensitized mice. No changes were seen in mice that were pre-sensitized via the nose with OVA. Systemic sensitization resulted in an elevated response to methacholine (MCH) in BALB/cJ and FVB/NJ mice and elevated total and OVA-specific IgE levels and pulmonary eosinophils in all three strains. The mucosal sensitization and challenge produced weaker responses in the same general pattern with the C57BL/6J strain producing less serum IgE, IL5, IL13, and eosinophils in lung fluid than the other two strains. The converse was found for IL6 where the C57BL/6J mice had more than twice the amount of this cytokine. The results show that the FVB/NJ and BALB/cJ mice are higher Th2-responders than the C57BL/6J mice and that the levels of pulmonary eosinophilia and cytokines did not fully track with MCH responsiveness. These differences illustrate the need to assess multiple endpoints to provide clearer associations between immune responses and type and severity of allergic lung disease.

One-month diesel exhaust inhalation produces hypertensive gene expression pattern in healthy rats

BACKGROUND

Exposure to diesel exhaust (DE) is linked to vasoconstriction, endothelial dysfunction, and myocardial ischemia in compromised individuals.

OBJECTIVE

We hypothesized that DE inhalation would cause greater inflammation, hematologic alterations, and cardiac molecular impairment in spontaneously hypertensive (SH) rats than in healthy Wistar Kyoto (WKY) rats.

METHODS AND RESULTS

Male rats (12-14 weeks of age) were exposed to air or DE from a 30-kW Deutz engine at 500 or 2,000 microg/m3, 4 hr/day, 5 days/week for 4 weeks. Neutrophilic influx was noted in the lung lavage fluid of both strains, but injury markers were minimally changed. Particle-laden macrophages were apparent histologically in DE-exposed rats. Lower baseline cardiac anti-oxidant enzyme activities were present in SH than in WKY rats; however, no DE effects were noted. Cardiac mitochondrial aconitase activity decreased after DE exposure in both strains. Electron microscopy indicated abnormalities in cardiac mitochondria of control SH but no DE effects. Gene expression profiling demonstrated alterations in 377 genes by DE in WKY but none in SH rats. The direction of DE-induced changes in WKY mimicked expression pattern of control SH rats without DE. Most genes affected by DE were down-regulated in WKY. The same genes were down-regulated in SH without DE producing a hypertensive-like expression pattern. The down-regulated genes included those that regulate compensatory response, matrix metabolism, mitochondrial function, and oxidative stress response. No up-regulation of inflammatory genes was noted.

CONCLUSIONS

We provide the evidence that DE inhalation produces a hypertensive-like cardiac gene expression pattern associated with mitochondrial oxidative stress in healthy rats.

Epidermal growth factor receptor activation by diesel particles is mediated by tyrosine phosphatase inhibition

Exposure to particulate matter (PM) is associated with increased cardiopulmonary morbidity and mortality. Diesel exhaust particles (DEP) are a major component of ambient PM and may contribute to PM-induced pulmonary inflammation. Proinflammatory signaling is mediated by phosphorylation-dependent signaling pathways whose activation is opposed by the activity of protein tyrosine phosphatases (PTPases) which thereby function to maintain signaling quiescence. PTPases contain an invariant catalytic cysteine that is susceptible to electrophilic attack. DEP contain electrophilic oxy-organic compounds that may contribute to the oxidant effects of PM. Therefore, we hypothesized that exposure to DEP impairs PTPase activity allowing for unopposed basal kinase activity. Here we report that exposure to 30 microg/cm(2) DEP for 4 h induces differential activation of signaling in primary cultures of human airway epithelial cells (HAEC), a primary target cell in PM inhalation. In-gel kinase activity assay of HAEC exposed to DEPs of low (L-DEP), intermediate (I-DEP) or high (H-DEP) organic content showed differential activation of intracellular kinases. Exposure to these DEP also induced varying levels of phosphorylation of the receptor tyrosine kinase EGFR in a manner that requires EGFR kinase activity but does not involve receptor dimerization. We demonstrate that treatment with DEP results in an impairment of total and EGFR-directed PTPase activity in HAEC with a potency that is independent of the organic content of these particles. These data show that DEP-induced EGFR phosphorylation in HAEC is the result of a loss of PTPase activities which normally function to dephosphorylate EGFR in opposition to baseline EGFR kinase activity.

Differential potentiation of allergic lung disease in mice exposed to chemically distinct diesel samples

Numerous studies have demonstrated that diesel exhaust particles (DEP) potentiate allergic immune responses, however the chemical components associated with this effect, and the underlying mechanisms are not well understood. This study characterized the composition of three chemically distinct DEP samples (N, C, and A-DEP), and compared post-sensitization and post-challenge inflammatory allergic phenotypes in BALB/c mice. Mice were instilled intranasally with saline or 150 microg of N-DEP, A-DEP, or C-DEP with or without 20 microg of ovalbumin (OVA) on days 0 and 13, and were subsequently challenged with 20 microg of OVA on days 23, 26, and 29. Mice were necropsied 18 h post-sensitization and 18 and 48 h post-challenge. N-DEP, A-DEP, and C-DEP contained 1.5, 68.6, and 18.9% extractable organic material (EOM) and 47, 431, and 522 microg of polycyclic aromatic hydrocarbons (PAHs), respectively. The post-challenge results showed that DEP given with OVA induced a gradation of adjuvancy as follows: C-DEP approximately A-DEP > N-DEP. The C- and A-DEP/OVA exposure groups had significant increases in eosinophils, OVA-specific IgG1, and airway hyperresponsiveness. In addition, the C-DEP/OVA exposure increased the T helper 2 (T(H)2) chemoattractant chemokine, thymus and activation-regulated chemokine and exhibited the most severe perivascular inflammation in the lung, whereas A-DEP/OVA increased interleukin (IL)-5 and IL-10. In contrast, N-DEP/OVA exposure only increased OVA-specific IgG1 post-challenge. Analysis of early signaling showed that C-DEP induced a greater number of T(H)2 cytokines compared with A-DEP and N-DEP. The results suggest that potentiation of allergic immune responses by DEP is associated with PAH content rather than the total amount of EOM.

Determination of 252-302 Da and tentative identification of 316-376 Da polycyclic aromatic hydrocarbons in Standard Reference Materials 1649a Urban Dust and 1650b and 2975 Diesel Particulate Matter by accelerated solvent extraction-HPLC-GC-MS

We have assessed and compared the extraction recoveries of polycyclic aromatic hydrocarbons (PAHs) with molecular weights of 252, 276, 278, 300 and 302 from diesel particulate matter (PM) and urban air particles using ultrasonically assisted extraction and accelerated solvent extraction methods, and evaluated the effects of sample and treatment parameters. The results show that accelerated solvent extraction can extract PAHs more efficiently from diesel PM than ultrasonically assisted extraction. They also show that PAHs are more difficult to extract from diesel PM than from urban air particles. Using toluene and maximum instrumental settings (200 degrees C, 3,000 psi and five extraction cycles) with 30-min static extraction times > 85% of the analytes were estimated to be extracted from the diesel particles, but four extraction cycles with just 5-min static extraction times under these conditions seem to be sufficient to extract > 95% of the analytes from the urban air particles. The accelerated solvent extraction method was validated using the Standard Reference Materials (SRM) 1649a, Urban Dust, and SRM 2975 and SRM 1650a, Diesel Particulate Matter, from the US National Institute of Standards and Technology (NIST). PAH concentrations determined by on-line high-performance liquid chromatography-gas chromatography-mass spectrometry (HPLC-GC-MS) following the developed accelerated solvent extraction method were generally higher than the certified and reference NIST values and concentrations reported in the literature (e.g. the estimated concentration of benzo[a]pyrene in SRM 2975 was 15-fold higher than the NIST-certified value), probably because the extraction recoveries were higher than in previous studies. The developed accelerated solvent extraction method was used to analyse high molecular (HMW) weight PAHs (MW > 302) in the investigated SRMs, and more than 170 (SRM 1649a), 80 (SRM 1650b) and 60 (SRM 2975) potential high molecular weight PAHs were tentatively identified in them, with molecular weights (depending on the SRM sample analysed) of 316, 326, 328, 340, 342, 350, 352, 366, 374 and 376. This is, to our knowledge, the first study to tentatively report PAHs with molecular weights of 316, 326, 328, 342, 350, 352, 366 and 376 in diesel particulate matter. GC-MS chromatograms obtained in selected ion monitoring mode (extracted ions for the abovementioned m/z) and full-scan mass spectra of tentatively identified high molecular weight PAHs are shown in the Electronic supplementary material.

Diesel exhaust particles induce oxidative stress, proinflammatory signaling, and P-glycoprotein up-regulation at the blood-brain barrier

Here, we report that diesel exhaust particles (DEPs), a major constituent of urban air pollution, affect blood-brain barrier function at the tissue, cellular, and molecular levels. Isolated rat brain capillaries exposed to DEPs showed increased expression and transport activity of the key drug efflux transporter, P-glycoprotein (6 h EC(50) was approximately 5 microg/ml). Up-regulation of P-glycoprotein was abolished by blocking transcription or protein synthesis. Inhibition of NADPH oxidase or pretreatment of capillaries with radical scavengers ameliorated DEP-induced P-glycoprotein up-regulation, indicating a role for reactive oxygen species in signaling. DEP exposure also increased brain capillary tumor necrosis factor-alpha (TNF-alpha) levels. DEP-induced P-glycoprotein up-regulation was abolished when TNF-receptor 1 (TNF-R1) was blocked and was not evident in experiments with capillaries from TNF-R1 knockout mice. Inhibition of JNK, but not NF-kappaB, blocked DEP-induced P-glycoprotein up-regulation, indicating a role for AP-1 in the signaling pathway. Consistent with this, DEPs increased phosphorylation of c-jun. Together, our results show for the first time that a component of air pollution, DEPs, alters blood-brain barrier function through oxidative stress and proinflammatory cytokine production. These experiments disclose a novel blood-brain barrier signaling pathway, with clear implications for environmental toxicology, CNS pathology, and the pharmacotherapy of CNS disorders.

Isolation and quantitative estimation of diesel exhaust and carbon black particles ingested by lung epithelial cells and alveolar macrophages in vitro

A new procedure for isolating and estimating ingested carbonaceous diesel exhaust particles (DEP) or carbon black (CB) particles by lung epithelial cells and macrophages is described. Cells were incubated with DEP or CB to examine cell-particle interaction and ingestion. After various incubation periods, the cells were separated from free extracellular DEP or CB particles by Ficoll density gradient centrifugation and dissolved in hot sodium dodecyl sulfate detergent. Insoluble DEP or CB residues were isolated by high-speed centrifugation, and the elemental carbon (EC) concentrations in the pellets were estimated by a thermal-optical-transmittance method (i.e., carbon analysis). From the EC concentration, the amount of ingested DEP or CB could be calculated. The described technique allowed the determination of the kinetics and dose dependence of DEP uptake by LA4 lung epithelial cells and MHS alveolar macrophages. Both cell types ingested DEP to a similar degree; however, the MHS macrophages took up significantly more CB than the epithelial cells. Cytochalasin D, an agent that blocks actin polymerization in the cells, inhibited approximately 80% of DEP uptake by both cell types, indicating that the process was actin-dependent in a manner similar to phagocytosis. This technique can be applied to examine the interactions between cells and particles containing EC and to study the modulation of particle uptake in diseased tissue.

Mutagenicity and DNA adduct formation of PAH, nitro-PAH, and oxy-PAH fractions of atmospheric particulate matter from São Paulo, Brazil

Urban particulate matter (UPM) contributes to lung cancer incidence. Here, we have studied the mutagenic activity and DNA adduct-forming ability of fractionated UPM extractable organic matter (EOM). UPM was collected with a high-volume sampler in June 2004 at two sites, one at street level adjacent to a roadway and the other inside a park within the urban area of the city of São Paulo, Brazil. UPM was extracted using dichloromethane, and the resulting EOM was separated by HPLC to obtain PAH, nitro-PAH, and oxy-PAH fractions which were tested for mutagenicity with the Salmonella strains TA98 and YG1041 with and without S9 metabolic activation. The PAH fraction from both sites showed negligible mutagenic activity in both strains. The highest mutagenic activity was found for the nitro-PAH fraction using YG1041 without metabolic activation; however, results were comparable for both sites. The nitro-PAH and oxy-PAH fractions were incubated with calf thymus DNA under reductive conditions appropriate for the activation of nitro aromatic compounds, then DNA adduct patterns and levels were determined with thin-layer chromatography (TLC) 32P-postlabeling method using two enrichment procedures-nuclease P1 digestion and butanol extraction. Reductively activated fractions from both sites produced diagonal radioactive zones (DRZ) of putative aromatic DNA adducts on thin layer plates with both enrichment procedures. No such DRZ were observed in control experiments using fractions from unexposed filters or from incubations without activating system. Total adduct levels produced by the nitro-PAH fractions were similar for both sites ranging from 30 to 45 adducts per 10(8) normal nucleotides. In contrast, the DNA binding of reductively activated oxy-PAH fractions was three times higher and the adduct pattern consisted of multiple discrete spots along the diagonal line on the thin layer plates. However, DNA adduct levels were not significantly different between the sampling sites. Both samples presented the same levels of mutagenic activity. The response in the Salmonella assay was typical of nitroaromatics. Although, more mutagenic activity was related to the nitro-PAH fraction in the Salmonella assay, the oxy-PAH fractions showed the highest DNA adduct levels. More studies are needed to elucidate the nature of the genotoxicants occurring in São Paulo atmospheric samples.

Diesel exhaust enhanced susceptibility to influenza infection is associated with decreased surfactant protein expression

We have previously shown that exposure of respiratory epithelial cells to diesel exhaust (DE) enhances susceptibility to influenza infection and increases the production of interleukin (IL)-6 and interferon (IFN)-beta. The purpose of this study was to confirm and expand upon these in vitro results by assessing the effects of DE exposure on the progression of influenza infection and on development of associated pulmonary immune and inflammatory responses in vivo. BALB/c mice were exposed to air or to DE containing particulate matter at concentrations of 0.5 or 2 mg/m(3) for 4 h/day for 5 days and subsequently instilled with influenza A/Bangkok/1/79 virus. Exposure to 0.5 mg/m(3) (but not the higher 2-mg/m(3) dose) of DE increased susceptibility to influenza infection as demonstrated by a significant increase in hemagglutinin (HA) mRNA levels, a marker of influenza copies, and greater immunohistochemical staining for influenza virus protein in the lung. The enhanced susceptibility to infection observed in mice exposed to 0.5 mg/m(3) of DE was associated with a significant increase in the expression of IL-6, while antiviral lung IFN levels were unaffected. Analysis of the expression and production of surfactant proteins A and D, which are components of the interferon-independent antiviral defenses, showed that these factors were decreased following exposure to 0.5 mg/m(3) of DE but not to the higher 2-mg/m(3) concentration. Taken together, the results demonstrate that exposure to DE enhances the susceptibility to respiratory viral infections by reducing the expression and production of antimicrobial surfactant proteins.

Comparative toxicity of size-fractionated airborne particulate matter obtained from different cities in the United States

Hundreds of epidemiological studies have shown that exposure to ambient particulate matter (PM) is associated with dose-dependent increases in morbidity and mortality. While early reports focused on PM less than 10 microm (PM10), numerous studies have since shown that the effects can occur with PM stratified into ultrafine (UF), fine (FI), and coarse (CO) size modes despite the fact that these materials differ significantly in both evolution and chemistry. Furthermore the chemical makeup of these different size fractions can vary tremendously depending on location, meteorology, and source profile. For this reason, high-volume three-stage particle impactors with the capacity to collect UF, FI, and CO particles were deployed to four different locations in the United States (Seattle, WA; Salt Lake City, UT; Sterling Forest and South Bronx, NY), and weekly samples were collected for 1 mo in each place. The particles were extracted, assayed for a standardized battery of chemical components, and instilled into mouse lungs (female BALB/c) at doses of 25 and 100 microg. Eighteen hours later animals were euthanized and parameters of injury and inflammation were monitored in the bronchoalveolar lavage fluid and plasma. Of the four locations, the South Bronx coarse fraction was the most potent sample in both pulmonary and systemic biomarkers, with a strong increase in lung inflammatory cells as well as elevated levels of creatine kinase in the plasma. These effects did not correlate with lipopolysaccharide (LPS) or total zinc or sulfate content, but were associated with total iron. Receptor source modeling on the PM2.5 samples showed that the South Bronx sample was heavily influenced by emissions from coal fired power plants (31%) and mobile sources (22%). Further studies will assess how source profiles correlate with the observed effects for all locations and size fractions.

The complexities of air pollution regulation: the need for an integrated research and regulatory perspective

The Clean Air Act mandates the U.S. Environmental Protection Agency to periodically reassess existing and new science that underlie the regulation of major ambient pollutants -- particulate matter (PM) and tropospheric ozone being most notable. While toxic effects have been ascribed individually to these and other pollutants in the air, it is clear that mixtures of these contaminants have the potential to interact and thereby influence their overall toxic outcomes. It follows that a more comprehensive assessment of the potential health effects of the air pollution complex might better protect human health; however, traditional regulatory drivers and funding constraints have impeded progress to such a goal. Despite difficulties in empirically conducting studies of complex mixtures of air pollutants and acquiring relevant exposure data, there remains a need to develop integrated, interdisciplinary research and analytical strategies to provide more comprehensive (and relevant) assessments of associated health outcomes and risks. The research and assessment communities are endeavoring to dissect this complexity using varied approaches Here we present five interdisciplinary perspectives of this evolving line of thought among researchers and those who use such data in assessment: (1) analyses that coordinate air quality-health analyses utilizing representative polluted U.S. air sheds to apportion source and component-specific health risks; (2) novel approaches to characterize air quality in terms of emission sources and how emission reduction strategies might effectively impact pollutant levels; (3) insights from present-day studies of effects of single ambient pollutants in animal and controlled clinical toxicology studies and how these are evolving to address air pollution; (4) refinements in epidemiologic health assessments that take advantage of the complexities of existent air quality conditions; and (5) new approaches to integrative analyses to establish the criteria for regulation of PM and other criteria pollutants. As these examples illustrate, implementing multidisciplined and integrative strategies offer the promise of more realistic and relevant science, greater reductions in uncertainty, and improved overall air pollution assessment. The regulatory mandate may lag behind the science, but real gains both in public health benefit and the science to dissect complex problems will result.

The health relevance of ambient particulate matter characteristics: coherence of toxicological and epidemiological inferences

The aim of this article is to review progress toward integration of toxicological and epidemiological research results concerning the role of specific physicochemical properties, and associated sources, in the adverse impact of ambient particulate matter (PM) on public health. Contemporary knowledge about atmospheric aerosols indicates their complex and variable nature. This knowledge has influenced toxicological assessments, pointing to several possible properties of concern, including particle size and specific inorganic and organic chemical constituents. However, results from controlled exposure laboratory studies are difficult to relate to actual community health results because of ambiguities in simulated PM mixtures, inconsistent concentration measurements, and the wide range of different biological endpoints. The use of concentrated ambient particulates (CAPs) coupled with factor analysis has provided an improved understanding of biological effects from more realistic laboratory-based exposure studies. Epidemiological studies have provided information concerning sources of potentially toxic particles or components, adding insight into the significance of exposure to secondary particles, such as sulfate, compared with primary emissions, such as elemental and organic carbon from transportation sources. Recent epidemiological approaches incorporate experimental designs that take advantage of broadened speciation monitoring, multiple monitoring stations, source proximity designs, and emission intervention. However, there continue to be major gaps in knowledge about the relative toxicity of particles from various sources, and the relationship between toxicity and particle physicochemical properties. Advancing knowledge could be facilitated with cooperative toxicological and epidemiological study designs, with the support of findings from atmospheric chemistry.

Diesel exhaust particles induce endothelial dysfunction in apoE−/− mice

BACKGROUND

Particulate air pollution can aggravate cardiovascular disease by mechanisms suggested to involve translocation of particles to the bloodstream and impairment of endothelial function, possibly dependent on present atherosclerosis.

AIM

We investigated the effects of exposure to diesel exhaust particles (DEP) in vivo and ex vivo on vasomotor functions in aorta from apoE(-/-) mice with slight atherosclerosis and from normal apoE(+/+) mice.

METHODS

DEP 0, 0.5 or 5 mg/kg bodyweight in saline was administered i.p. The mice were sacrificed 1 h later and aorta ring segments were mounted on wire myographs. Segments from unexposed mice were also incubated ex vivo with 0, 10 and 100 microg DEP/ml before measurement of vasomotor functions.

RESULTS

Exposure to 0.5 mg/kg DEP in vivo caused a decrease in the endothelium-dependent acetylcholine elicited vasorelaxation in apoE(-/-) mice, whereas the response was enhanced in apoE(+/+) mice. No significant change was observed after administration of 5 mg/kg DEP. In vivo DEP exposure did not affect constriction induced by K(+) or phenylephrine. In vitro exposure to 100 microg DEP/ml enhanced acetylcholine-induced relaxation and attenuated phenylephrine-induced constriction. Vasodilation induced by sodium nitroprusside was not affected by any DEP exposure.

CONCLUSION

Exposure to DEP has acute effect on vascular functions. Endothelial dysfunction possibly due to decreased NO production as suggested by decreased acetylcholine-induced vasorelaxation and unchanged sodium nitroprusside response can be induced by DEP in vivo only in vessels of mice with some atherosclerosis.

Oropharyngeal aspiration of a silica suspension produces a superior model of silicosis in the mouse when compared to intratracheal instillation

Instillation of crystalline silica into the lungs of mice is a common experimental model of pulmonary fibrosis. Typically, a suspension of silica in saline is injected into the trachea via intubation or surgical tracheostomy. These techniques require a high degree of technical skill, have a lengthy training period, and can suffer from a high failure rate. In oropharyngeal aspiration, a droplet of liquid is placed in the animal's mouth while simultaneously holding its tongue (to block the swallow reflex) and pinching its nose shut, forcing it to breathe through its mouth, aspirating the liquid. To determine whether oropharyngeal aspiration (OA) could replace intratracheal instillation (IT) in a model of silica-induced fibrosis, a comparison was performed. Crystalline silica was introduced into the lungs of male C57BL/6 mice by the IT or OA procedure, and the resulting inflammation and fibrosis was assessed after 3 weeks. IT and OA instillation of silica both resulted in neutrophilic inflammation and fibrotic changes, including interstitial fibrosis and dense fibrotic foci. Mice treated via IT demonstrated a few large lesions proximal to conducting airways with little involvement of the distal parenchyma and large interanimal variability. In contrast, OA resulted in a diffuse pathology with numerous fibrotic foci distributed throughout the lung parenchyma, which is more representative of human fibrotic lung disease. OA- but not IT-treated mice exhibited significantly increased lung collagen content. Furthermore, the interanimal variability within the OA group was significantly less than in the IT group. Oropharyngeal aspiration should be considered as an alternative to intratracheal instillation of silica and other particulates in studies of respiratory toxicity and lung disease.

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.

Nasal responses in asthmatic and nonasthmatic subjects following exposure to diesel exhaust particles

Asthma rates have been increasing worldwide, and exposure to diesel exhaust particles (DEP) may be implicated in this increase. DEP may also play a role in the increased morbidity and mortality associated with ambient airborne particulate matter (PM) exposure. Two types of nasal responses have been reported for human subjects nasally instilled with one type of DEP: alterations in cytokines responses, and an increase in immunoglobulin E (IgE) production. Since DEP composition can vary depending on several factors, including fuel composition and engine load, the ability of another DEP particle and ozone-treated DEP to alter nasal IgE and cytokine production was examined. Nonasthmatic and asthmatic subjects were intranasally instilled with 300 microg NIST 1650 DEP per nostril, NIST 1650 DEP previously exposed to ozone (ozDEP; 300 microg/nostril), or vehicle. Subjects underwent nasal lavage before DEP exposure, and 4 and 96 h after exposure. Nasal cell populations and soluble mediators in the nasal lavage fluid were characterized. Total cell number, cell types, cell viability, concentrations of soluble mediators (including interleukin [IL]-8, IL-6, IgE, and granulocyte-macrophage colony-stimulating factor [GM-CSF]) were not altered by either DEP or ozDEP exposure. NO levels were not altered by either particle exposure. These findings suggest that DEP can be relatively noninflammatory and nontoxic, and that the physicochemical characteristics of DEP need to be considered when assessing the health effects of exposure to diesel exhaust.

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.

Components of diesel exhaust particles differentially affect Th1/Th2 response in a murine model of allergic airway inflammation

BACKGROUND

Diesel exhaust particles (DEP) can enhance various respiratory diseases. However, it is unclear as to which components in DEP are associated with the enhancement. We investigated the effects of DEP components on antigen-related airway inflammation, using residual carbonaceous nuclei of DEP after extraction (washed DEP), extracted organic chemicals (OC) in DEP (DEP-OC), and DEP-OC plus washed DEP (whole DEP) in the presence or absence of ovalbumin (OVA).

METHODS

Male ICR mice were intratracheally administrated with OVA and/or DEP components. We examined the cellular profile of bronchoalveolar lavage (BAL) fluid, histological changes, lung expression of inflammatory molecules, and antigen-specific production of IgG1 in the serum.

RESULTS

DEP-OC, rather than washed DEP, enhanced infiltration of inflammatory cells into BAL fluid, magnitude of airway inflammation, and proliferation of goblet cells in the airway epithelium in the presence of OVA, which was paralleled by the enhanced lung expression of eotaxin and IL-5 as well as the elevated concentration of OVA-specific IgG1. In contrast, washed DEP with OVA showed less change and increased the lung expression of IFN-gamma. The combination of whole DEP and OVA caused the most remarkable changes in the entire enhancement, which was also accompanied by the enhanced expression of IL-13 and macrophage inflammatory protein-1 alpha.

CONCLUSION

DEP-OC, rather than washed DEP, exaggerated allergic airway inflammation through the enhancement of T-helper type 2 responses. The coexistence of OC with carbonaceous nuclei caused the most remarkable aggravation. DEP components might diversely affect various types of respiratory diseases, while whole DEP might mostly aggravate respiratory diseases.

Cytokine expression in mice exposed to diesel exhaust particles by inhalation. Role of tumor necrosis factor

Background

Particulate air pollution has been associated with lung and cardiovascular disease, for which lung inflammation may be a driving mechanism. The pro-inflammatory cytokine, tumor necrosis factor (TNF) has been suggested to have a key-role in particle-induced inflammation.

We studied the time course of gene expression of inflammatory markers in the lungs of wild type mice and Tnf-/- mice after exposure to diesel exhaust particles (DEPs). Mice were exposed to either a single or multiple doses of DEP by inhalation. We measured the mRNA level of the cytokines Tnf and interleukin-6 (Il-6) and the chemokines, monocyte chemoattractant protein (Mcp-1), macrophage inflammatory protein-2 (Mip-2) and keratinocyte derived chemokine (Kc) in the lung tissue at different time points after exposure.

Results

Tnf mRNA expression levels increased late after DEP-inhalation, whereas the expression levels of Il-6, Mcp-1 and Kc increased early. The expression of Mip-2 was independent of TNF if the dose was above a certain level. The expression levels of the cytokines Kc, Mcp-1 and Il-6, were increased in the absence of TNF.

Conclusion

Our data demonstrate that Tnf is not important in early DEP induced inflammation and rather exerts negative influence on Mcp-1 and Kc mRNA levels. This suggests that other signalling pathways are important, a candidate being one involving Mcp-1.

Physicochemical characterisation of combustion particles from vehicle exhaust and residential wood smoke

Background

Exposure to ambient particulate matter has been associated with a number of adverse health effects. Particle characteristics such as size, surface area and chemistry seem to influence the negative effects of particles. In this study, combustion particles from vehicle exhaust and wood smoke, currently used in biological experiments, were analysed with respect to microstructure and chemistry.

Methods

Vehicle exhaust particles were collected in a road tunnel during two seasons, with and without use of studded tires, whereas wood smoke was collected from a stove with single-stage combustion. Additionally, a reference diesel sample (SRM 2975) was analysed. The samples were characterised using transmission electron microscopy techniques (TEM/HRTEM, EELS and SAED). Furthermore, the elemental and organic carbon fractions were quantified using thermal optical transmission analysis and the content of selected PAHs was determined by gas chromatography-mass spectrometry.

Results

Carbon aggregates, consisting of tens to thousands of spherical primary particles, were the only combustion particles identified in all samples using TEM. The tunnel samples also contained mineral particles originating from road abrasion. The geometric diameters of primary carbon particles from vehicle exhaust were found to be significantly smaller (24 ± 6 nm) than for wood smoke (31 ± 7 nm). Furthermore, HRTEM showed that primary particles from both sources exhibited a turbostratic microstructure, consisting of concentric carbon layers surrounding several nuclei in vehicle exhaust or a single nucleus in wood smoke. However, no differences were detected in the graphitic character of primary particles from the two sources using SAED and EELS. The total PAH content was higher for combustion particles from wood smoke as compared to vehicle exhaust, whereas no source difference was found for the ratio of organic to total carbon.

Conclusion

Combustion particles from vehicle exhaust and residential wood smoke differ in primary particle diameter, microstructure, and PAH content. Furthermore, the analysed samples seem suitable for assessing the influence of physicochemical characteristics of particles on biological responses.

Effects of diesel exhaust particles on human alveolar macrophage ability to secrete inflammatory mediators in response to lipopolysaccharide

Ambient particulate matter (PM) has been shown to be associated with mortality and morbidity. Diesel exhaust particles (DEP) contribute to ambient PM. Alveolar macrophages (AM) are important targets for PM effects in the lung. The effects of DEP exposure on human AM response to lipopolysachharide (LPS; from gram-negative bacteria) challenge in vitro were determined by monitoring the production of interleukin 8 (IL-8), tumor necrosis factor-alpha (TNF-alpha) and prostaglandin E(2) (PGE(2)). The roles of organic compounds and carbonaceous core of DEP in response to LPS were evaluated by comparing the DEPs effect to that of carbon black (CB), a carbonaceous particle with few adsorbed organic compounds. AMs were exposed in vitro to Standard Reference Material (SRM) DEP 2975, SRM DEP 1650, SRM 1975 (a dichloromethane extract of SRM DEP 2975) and CB particles for 24 h. DEPs induced a decreased secretion of IL-8, TNF-alpha and PGE(2) in response to a subsequent LPS stimulation. DEPs also show suppressive effect on the release of inflammatory mediators when stimulated with lipoteichoic acid, a product of gram positive bacteria. In summary, in vitro exposure of human AM to DEPs significantly suppress AM responsiveness to gram-negative and positive bacterial products, which may be a contributing factor to the impairment of pulmonary defense.

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.

The genotoxicity of ambient outdoor air, a review: Salmonella mutagenicity

Mutagens in urban air pollution come from anthropogenic sources (especially combustion sources) and are products of airborne chemical reactions. Bacterial mutation tests have been used for large, multi-site, and/or time series studies, for bioassay-directed fractionation studies, for identifying the presence of specific classes of mutagens, and for doing site- or source-comparisons for relative levels of airborne mutagens. Early research recognized that although carcinogenic PAHs were present in air samples they could not account for the majority of the mutagenic activity detected. The mutagenicity of airborne particulate organics is due to at least 500 identified compounds from varying chemical classes. Bioassay-directed fractionation studies for identifying toxicants are difficult to compare because they do not identify all of the mutagens present, and both the analytical and bioassay protocols vary from study to study. However, these studies show that the majority of mutagenicity is usually associated with moderately polar/highly polar classes of compounds that tend to contain nitroaromatic compounds, aromatic amines, and aromatic ketones. Smog chamber studies have shown that mutagenic aliphatic and aromatic nitrogen-containing compounds are produced in the atmosphere when organic compounds (even non-mutagenic compounds) are exposed to nitrogen oxides and sunlight. Reactions that occur in the atmosphere, therefore, can have a profound effect on the genotoxic burden of ambient air. This review illustrates that the mutagenesis protocol and tester strains should be selected based on the design and purpose of the study and that the correlation with animal cancer bioassay results depends upon chemical class. Future emphasis needs to be placed on volatile and semi-volatile genotoxicants, and on multi-national studies that identify, quantify, and apportion mutagenicity. Initial efforts at replacing the Salmonella assay for ambient air studies with some emerging technology should be initiated.

A tale of two diesels

Two different samples of diesel exhaust particles (DEP) have been used by toxicologists interested primarily in cancer/genotoxicity or noncancer--such as pulmonary inflammation and asthma exacerbation--health end points. These are, respectively, a standard reference material, SRM 2975, from a heavy-duty diesel engine, and a sample collected by researchers at the Japanese National Institute for Environmental Studies from an automobile diesel engine. In this issue of Environmental Health Perspectives companion papers appear, by David DeMarini and co-workers and by Pramila Singh and co-workers, characterizing these samples and contrasting their Salmonella mutagenicity and pulmonary toxicity in mice. This commentary is a plea from an atmospheric chemist for more cooperation among toxicologists, analytical chemists, atmospheric chemists, and automotive and combustion engineers to provide a comprehensive assessment of health risks to humans exposed to contemporary diesel emissions and for greater quantities and more diverse types of DEP and ambient samples (i.e., SRMs) that can be shared and exhaustively characterized. This needs to be a continuing process as diesel engines, fuels, and exhaust components evolve in response to control regulations.

Bioassay-directed fractionation and salmonella mutagenicity of automobile and forklift diesel exhaust particles

Many pulmonary toxicity studies of diesel exhaust particles (DEPs) have used an automobile-generated sample (A-DEPs) whose mutagenicity has not been reported. In contrast, many mutagenicity studies of DEPs have used a forklift-generated sample (SRM 2975) that has been evaluated in only a few pulmonary toxicity studies. Therefore, we evaluated the mutagenicity of both DEPs in Salmonella coupled to a bioassay-directed fractionation. The percentage of extractable organic material (EOM) was 26.3% for A-DEPs and 2% for SRM 2975. Most of the A-EOM (~55%) eluted in the hexane fraction, reflecting the presence of alkanes and alkenes, typical of uncombusted fuel. In contrast, most of the SRM 2975 EOM (~58%) eluted in the polar methanol fraction, indicative of oxygenated and/or nitrated organics derived from combustion. Most of the direct-acting, base-substitution activity of the A-EOM eluted in the hexane/dichloromethane (DCM) fraction, but this activity eluted in the polar methanol fraction for the SRM 2975 EOM. The direct-acting frameshift mutagenicity eluted across fractions of A-EOM, whereas > 80% eluted only in the DCM fraction of SRM 2975 EOM. The A-DEPs were more mutagenic than SRM 2975 per mass of particle, having 227 times more polycyclic aromatic hydrocarbon-type and 8-45 more nitroarene-type mutagenic activity. These differences were associated with the different conditions under which the two DEP samples were generated and collected. A comprehensive understanding of the mechanisms responsible for the health effects of DEPs requires the evaluation of DEP standards for a variety of end points, and our results highlight the need for multidisciplinary studies on a variety of representative samples of DEPs.