Effects of diesel exhaust particles (DEP), carbon black, and silica on macrophage responses to lipopolysaccharide: evidence of DEP suppression of macrophage activity

Revisiting Total Particle Number Measurements for Vehicle Exhaust Regulations

Road transport significantly contributes to air pollution in cities. Emission regulations have led to significantly reduced emissions in modern vehicles. Particle emissions are controlled by a particulate matter (PM) mass and a solid particle number (SPN) limit. There are concerns that the SPN limit does not effectively control all relevant particulate species and there are instances of semi-volatile particle emissions that are order of magnitudes higher than the SPN emission levels. This overview discusses whether a new metric (total particles, i.e., solids and volatiles) should be introduced for the effective regulation of vehicle emissions. Initially, it summarizes recent findings on the contribution of road transport to particle number concentration levels in cities. Then, both solid and total particle emission levels from modern vehicles are presented and the adverse health effects of solid and volatile particles are briefly discussed. Finally, the open issues regarding an appropriate methodology (sampling and instrumentation) in order to achieve representative and reproducible results are summarized. The main finding of this overview is that, even though total particle sampling and quantification is feasible, details for its realization in a regulatory context are lacking. It is important to define the methodology details (sampling and dilution, measurement instrumentation, relevant sizes, etc.) and conduct inter-laboratory exercises to determine the reproducibility of a proposed method. It is also necessary to monitor the vehicle emissions according to the new method to understand current and possible future levels. With better understanding of the instances of formation of nucleation mode particles it will be possible to identify its culprits (e.g., fuel, lubricant, combustion, or aftertreatment operation). Then the appropriate solutions can be enforced and the right decisions can be taken on the need for new regulatory initiatives, for example the addition of total particles in the tailpipe, decrease of specific organic precursors, better control of inorganic precursors (e.g., NH3, SOx), or revision of fuel and lubricant specifications.

Lung toxicity profile of inhaled copper-nickel welding fume in A/J mice

Objective: Stainless steel welding creates fumes rich in carcinogenic metals such as chromium (Cr). Welding consumables devoid of Cr are being produced in an attempt to limit worker exposures to toxic and carcinogenic metals. The study objective was to characterize a copper-nickel (Cu-Ni) fume generated using gas metal arc welding (GMAW) and determine the pulmonary deposition and toxicity of the fume in mice exposed by inhalation. Materials and Methods: Male A/J mice (6-8 weeks of age) were exposed to air or Cu-Ni welding fumes for 2 (low deposition) or 4 (high deposition) hours/day for 10 days. Mice were sacrificed, and bronchoalveolar lavage (BAL), macrophage function, and histopathological analyses were performed at different timepoints post-exposure to evaluate resolution. Results and Discussion: Characterization of the fume indicated that most of the particles were between 0.1 and 1 µm in diameter, with a mass median aerodynamic diameter of 0.43 µm. Metal content of the fume was Cu (∼76%) and Ni (∼12%). Post-exposure, BAL macrophages had a reduced ability to phagocytose E. coli, and lung cytotoxicity was evident and significant (>12%-19% fold change). Loss of body weight was also significant at the early timepoints. Lung inflammation, the predominant finding identified by histopathology, was observed as a subacute response early that progressively resolved by 28 days with only macrophage aggregates remaining late (84 days). Conclusions: Overall, there was high acute lung toxicity with a resolution of the response in mice which suggests that the Cu-Ni fume may not be ideal for reducing toxic and inflammatory lung effects.

Particulate matter air pollution and the expression of microRNAs and pro-inflammatory genes: Association and mediation among children in Jinan, China

Exposure to particulate matter (PM) has been associated with increased risk of various diseases, possibly through its effect on inflammatory response. MicroRNAs (miRNAs), an epigenetic mechanism regulating gene expression, can affect the expression of pro-inflammatory genes. However, few epidemiological studies have examined the impact of PM on inflammation-related miRNAs and their target mRNAs, especially among vulnerable population. We recruited 160 and 113 children from areas with different PM level in Jinan, China. We measured benzo[a]pyrene-r-7,t-8,t-9,c-10-tetrahydotetrol-albumin (BPDE-Alb) adducts in serum and the expression of 5 candidate miRNAs involved in inflammation regulation and 7 pro-inflammatory genes predicted to be their targets in leukocytes. Generally, children in the polluted area had higher miRNAs and lower mRNAs expression than those in the control area. An interquartile increase of BPDE-Alb adducts was associated with 12.66 %, 14.13 %, and 12.76 % higher of let-7a, miR-146a-5p, and miR-155-5p, as well as 21.61 %, 20.16 %, and 12.49 % lower of IL-6, CXCL8, and TLR2 mRNAs at false discovery rate<0.05, respectively. Additionally, let-7a, miR-146a-5p, and miR-155-5p were found to mediate the associations of BPDE-Alb adducts with IL-6 and/or TLR2 expression. Our findings suggested that PM exposure might attenuate inflammatory response among children in China, which was partly mediated by miRNAs regulating pro-inflammatory genes.

Pulmonary toxicity following acute coexposures to diesel particulate matter and α-quartz crystalline silica in the Sprague-Dawley rat

The effects of acute pulmonary coexposures to silica and diesel particulate matter (DPM), which may occur in various mining operations, were investigated in vivo. Rats were exposed by intratracheal instillation (IT) to silica (50 or 233 µg), DPM (7.89 or 50 µg) or silica and DPM combined in phosphate-buffered saline (PBS) or to PBS alone (control). At one day, one week, one month, two months and three months postexposure bronchoalveolar lavage and histopathology were performed to assess lung injury, inflammation and immune response. While higher doses of silica caused inflammation and injury at all time points, DPM exposure alone did not. DPM (50 µg) combined with silica (233 µg) increased inflammation at one week and one-month postexposure and caused an increase in the incidence of fibrosis at one month compared with exposure to silica alone. To assess susceptibility to lung infection following coexposure, rats were exposed by IT to 233 µg silica, 50 µg DPM, a combination of the two or PBS control one week before intratracheal inoculation with 5 × 105 Listeria monocytogenes. At 1, 3, 5, 7 and 14 days following infection, pulmonary immune response and bacterial clearance from the lung were evaluated. Coexposure to DPM and silica did not alter bacterial clearance from the lung compared to control. Although DPM and silica coexposure did not alter pulmonary susceptibility to infection in this model, the study showed that noninflammatory doses of DPM had the capacity to increase silica-induced lung injury, inflammation and onset/incidence of fibrosis.

Comparison of lung damage in mice exposed to black carbon particles and 1,4-naphthoquinone coated black carbon particles

Black carbon (BC) is a key component of atmospheric particles and has a significant effect on human health. BC can provide reactive sites and surfaces thus absorb quinones which were primarily generated from fossil fuel combustion and/or atmospheric photochemical conversions of PAHs. Oxidation could change the characteristics of BC and increase its toxicity. The comparison of lung damage in mice exposed to BC and 1,4-NQ-coated BC (1,4NQ-BC) particles is investigated in this study. Mice which were intratracheally instilled with particles have a higher expression of IL-1β, IL-6 and IL-33 in bronchoalveolar lavage fluid (BALF). Also, the IL-6, IL-33 mRNA expression in the lung tissue of mice instilled with 1,4NQ-BC were higher than that of mice instilled with BC. The pathology results showed that the lung tissue of mice instilled with 1,4NQ-BC particles have much more inflammatory cells infiltration than that of mice treated with BC. It is believed that the MAPK and PI3K-AKT pathway might be involved in the 1,4NQ-BC particles caused lung damage. Results indicated that 1,4NQ-BC particles in the atmosphere may cause more damage to health.

Particulate matter properties and health effects: consistency of epidemiological and toxicological studies

Identifying the ambient particulate matter (PM) fractions or constituents, critically involved in eliciting adverse health effects, is crucial to the implementation of more cost-efficient abatement strategies to improve air quality. This review focuses on the importance of different particle properties for PM-induced effects, and whether there is consistency in the results from epidemiological and experimental studies. An evident problem for such comparisons is that epidemiological and experimental data on the effects of specific components of ambient PM are limited. Despite this, some conclusions can be drawn. With respect to the importance of the PM size-fractions, experimental and epidemiological studies are somewhat conflicting, but there seems to be a certain consistency in that the coarse fraction (PM10-2.5) has an effect that should not be neglected. Better exposure characterization may improve the consistency between the results from experimental and epidemiological studies, in particular for ultrafine particles. Experimental data indicate that surface area is an important metric, but composition may play an even greater role in eliciting effects. The consistency between epidemiological and experimental findings for specific PM-components appears most convincing for metals, which seem to be important for the development of both pulmonary and cardiovascular disease. Metals may also be involved in PM-induced allergic sensitization, but the epidemiological evidence for this is scarce. Soluble organic compounds appear to be implicated in PM-induced allergy and cancer, but the data from epidemiological studies are insufficient for any conclusions. The present review suggests that there may be a need for improvements in research designs. In particular, there is a need for better exposure assessments in epidemiological investigations, whereas experimental data would benefit from an improved comparability of studies. Combined experimental and epidemiological investigations may also help answer some of the unresolved issues.

Toxicology of ambient particulate matter

It is becoming increasingly clear that inhalation exposure to particulate matter (PM) can lead to or exacerbate various diseases, which are not limited to the lung but extend to the cardiovascular system and possibly other organs and tissues. Epidemiological studies have provided strong evidence for associations with chronic obstructive pulmonary disease (COPD), asthma, bronchitis and cardiovascular disease, while the evidence for a link with lung cancer is less strong. Novel research has provided first hints that exposure to PM might lead to diabetes and central nervous system (CNS) pathology. In the current review, an overview is presented of the toxicological basis for adverse health effects that have been linked to PM inhalation. Oxidative stress and inflammation are discussed as central processes driving adverse effects; in addition, profibrotic and allergic processes are implicated in PM-related diseases. Effects of PM on key cell types considered as regulators of inflammatory, fibrotic and allergic mechanisms are described.

Use of amniotic fluid for determining pregnancies at risk of preterm birth and for studying diseases of potential environmental etiology

Amniotic fluid (AF) is a biological medium uniquely suited for the study of early exposure of the human fetus to environmental contaminants acquired by the mother before and during pregnancy. Traditional diagnostic applications of AF have focused almost exclusively on the diagnosis of genetic aberrations such as Trisomy-21 and on heritable diseases in high-risk pregnancies. Since more than 50 anthropogenic compounds have been detected in AF, there is considerable potential in utilizing fetal protein biomarkers as indicators of health effects related to prenatal toxic exposure. Here, we focus on preterm birth (PTB) to illustrate opportunities and limitations of using AF as a diagnostic matrix. Representing a pervasive public health challenge worldwide, PTB cannot be managed simply by improving hygiene and broadening access to healthcare. This is illustrated by 15-year increases of PTB in the U.S. from 1989 to 2004. AF is uniquely suited as a matrix for early detection of the association between fetal exposures and PTB due to its fetal origin and the fact that it is sampled from women who are at higher risk of PTB. This critical review shows the occurrence in AF of a number of xenobiotics, including endocrine-disrupting compounds (EDCs), which are known or may reasonably be expected to shorten fetal gestation. It is not yet known whether EDCs, including bisphenol A, phytoestrogens, and polychlorinated biphenyls (PCBs), can affect the expression of proteins considered viable or potential biomarkers for the onset of PTB. As such, the diagnostic value of AF is broad and has not yet been fully explored for prenatal diagnosis of pregnancies at risk from toxic, environmental exposures and for the elucidation of mechanisms underlying important public health challenges including PTB.

Interactive effects of cerium oxide and diesel exhaust nanoparticles on inducing pulmonary fibrosis

Cerium compounds have been used as a fuel-borne catalyst to lower the generation of diesel exhaust particles (DEPs), but are emitted as cerium oxide nanoparticles (CeO2) along with DEP in the diesel exhaust. The present study investigates the effects of the combined exposure to DEP and CeO2 on the pulmonary system in a rat model. Specific pathogen-free male Sprague-Dawley rats were exposed to CeO2 and/or DEP via a single intratracheal instillation and were sacrificed at various time points post-exposure. This investigation demonstrated that CeO2 induces a sustained inflammatory response, whereas DEP elicits a switch of the pulmonary immune response from Th1 to Th2. Both CeO2 and DEP activated AM and lymphocyte secretion of the proinflammatory cytokines IL-12 and IFN-γ, respectively. However, only DEP enhanced the anti-inflammatory cytokine IL-10 production in response to ex vivo LPS or Concanavalin A challenge that was not affected by the presence of CeO2, suggesting that DEP suppresses host defense capability by inducing the Th2 immunity. The micrographs of lymph nodes show that the particle clumps in DEP+CeO2 were significantly larger than CeO2 or DEP, exhibiting dense clumps continuous throughout the lymph nodes. Morphometric analysis demonstrates that the localization of collagen in the lung tissue after DEP+CeO2 reflects the combination of DEP-exposure plus CeO2-exposure. At 4 weeks post-exposure, the histological features demonstrated that CeO2 induced lung phospholipidosis and fibrosis. DEP induced lung granulomas that were not significantly affected by the presence of CeO2 in the combined exposure. Using CeO2 as diesel fuel catalyst may cause health concerns.

Perturbation of pulmonary immune functions by carbon nanotubes and susceptibility to microbial infection

Occupational and environmental pulmonary exposure to carbon nanotubes (CNT) is considered to be a health risk with a very low threshold of tolerance as determined by the United States Center for Disease Control. Immortalized airway epithelial cells exposed to CNTs show a diverse range of effects including reduced viability, impaired proliferation, and elevated reactive oxygen species generation. Additionally, CNTs inhibit internalization of targets in multiple macrophage cell lines. Mice and rats exposed to CNTs often develop pulmonary granulomas and fibrosis. Furthermore, CNTs have immunomodulatory properties in these animal models. CNTs themselves are proinflammatory and can exacerbate the allergic response. However, CNTs may also be immunosuppressive, both locally and systemically. Studies that examined the relationship of CNT exposure prior to pulmonary infection have reached different conclusions. In some cases, pre-exposure either had no effect or enhanced clearance of infections while other studies showed CNTs inhibited clearance. Interestingly, most studies exploring this relationship use pathogens which are not considered primary pulmonary pathogens. Moreover, harmony across studies is difficult as different types of CNTs have dissimilar biological effects. We used Pseudomonas aeruginosa as model pathogen to study how helical multi-walled carbon nanotubes (HCNTs) affected internalization and clearance of the pulmonary pathogen. The results showed that, although HCNTs can inhibit internalization through multiple processes, bacterial clearance was not altered, which was attributed to an enhanced inflammatory response caused by pre-exposure to HCNTs. We compare and contrast our findings in relation to other studies to gauge the modulation of pulmonary immune response by CNTs.

Induction of pulmonary fibrosis by cerium oxide nanoparticles

Cerium compounds have been used as a diesel engine catalyst to lower the mass of diesel exhaust particles, but are emitted as cerium oxide (CeO(2)) nanoparticles in the diesel exhaust. In a previous study, we have demonstrated a wide range of CeO(2)-induced lung responses including sustained pulmonary inflammation and cellular signaling that could lead to pulmonary fibrosis. In this study, we investigated the fibrogenic responses induced by CeO(2) in a rat model at various time points up to 84 days post-exposure. Male Sprague Dawley rats were exposed to CeO(2) by a single intratracheal instillation. Alveolar macrophages (AM) were isolated by bronchial alveolar lavage (BAL). AM-mediated cellular responses, osteopontin (OPN) and transform growth factor (TGF)-β1 in the fibrotic process were investigated. The results showed that CeO(2) exposure significantly increased fibrotic cytokine TGF-β1 and OPN production by AM above controls. The collagen degradation enzymes, matrix metalloproteinase (MMP)-2 and -9 and the tissue inhibitor of MMP were markedly increased in the BAL fluid at 1 day- and subsequently declined at 28 days after exposure, but remained much higher than the controls. CeO(2) induced elevated phospholipids in BAL fluid and increased hydroxyproline content in lung tissue in a dose- and time-dependent manner. Immunohistochemical analysis showed MMP-2, MMP-9 and MMP-10 expressions in fibrotic regions. Morphological analysis noted increased collagen fibers in the lungs exposed to a single dose of 3.5mg/kg CeO(2) and euthanized at 28 days post-exposure. Collectively, our studies show that CeO(2) induced fibrotic lung injury in rats, suggesting it may cause potential health effects.

Multiple approaches to evaluate the toxicity of the biomass fuel cow dung (kanda) smoke

Cow dung (Kanda) is a major source of energy in rural and urban population of developing countries and is burnt in traditional open stoves in confined space of kitchen without proper ventilation. In epidemiological studies, biomass fuel smoke has been reported to be responsible for several respiratory disorders in exposed population. In a laboratory experiment, female wistar rats were exposed to kanda smoke for 60 min/day over a period of 12 weeks. Chemical analysis of smoke showed the presence of PAHs. The increase in CYP1A1, GST-ya, GST-yc expression was found in 12 week exposed lung tissues as compared with controls. The exposure to smoke resulted in significant alteration in the BALF cells in the form of clustering of alveolar macrophages and giant cell formation with vacuolated cytoplasm. The macrophages also showed thickness and villi like projections on the cell surface thus reducing their phagocytic activities. Histopathological changes in lung tissue were manifested in the form of damage to bronchiolar epithelium, edema and thickening of alveolar septa and emphysema after 4 and 8 week of exposure. These findings suggest that exposure to kanda smoke increases pulmonary tissue damage and may result in various forms of respiratory infections in the exposed popultion.

Time-response relationship of nano and micro particle induced lung inflammation. Quartz as reference compound

An increasing number of engineered particles, including nanoparticles, are being manufactured, increasing the need for simple low-dose toxicological screening methods. This study aimed to investigate the kinetics of biomarkers related to acute and sub-chronic particle-induced lung inflammation of quartz. Mice were intratracheal instilled with 50 µg of microsized or nanosized quartz. Acute inflammation was assessed 1, 2, 4, 8, 16 or 48 hours post exposure, whereas sub-chronic inflammation was investigated 3 months after exposure. Markers of acute inflammation in the bronchoalveolar lavage fluid (BALF) were neutrophils (PMN), tumor necrosis factor-alpha (TNF-α), interleukin (IL)-1β, macrophage inflammatory protein-2 (MIP-2), keratinocyte derived chemokine (KC) and total protein, which were all close to maximum 16 hours post instillation. No major differences were seen in the time-response profiles of nano- and micro-sized particles. The potency of the two samples cannot be compared; during the milling process, a substantial part of the quartz was converted to amorphous silica and contaminated with corundum. For screening, BALF PMN, either TNF-α or IL-1β at 16 hours post instillation may be useful. At 3 months post instillation, KC, PMN and macrophages were elevated. Histology showed no interstitial inflammation three months post instillation. For screening of sub-chronic effects, KC, PMN, macrophages and histopathology is considered sufficient.

Signal transduction pathways linking the activation of alveolar macrophages with the recruitment of neutrophils to lungs in chronic obstructive pulmonary disease

Chronic obstructive pulmonary disease (COPD) is a major and increasing global health problem. It is predicted by the World Health Organization to become the third most common cause of death and the fifth most common cause of disability in the world by 2020. COPD is a complex inflammatory disease involving several types of inflammatory cells and multiple inflammatory mediators. Although abnormal numbers of inflammatory cells such as macrophages, dendritic cells, neutrophils, and T lymphocytes have been documented in COPD, the relationship between these cell types and the sequence of their appearance and persistence is largely unknown. Alveolar macrophages have been identified as one of the major cell types that plays a key role in orchestrating the inflammatory events associated with the pathophysiology of COPD. One of the major functions of macrophages is the secretion of chemotactic factors and this function is markedly increased on exposure to cigarette smoke (CS). This enhanced release of chemoattractants results in increased lung neutrophil infiltration, which is thought to be a key event in the development of COPD. The molecular basis for this amplified inflammatory response is not very clear, but it could be due to an alteration in signal transduction pathways within the macrophage. Based on existing literature, an attempt has been made to create a comprehensive review of the signal transduction pathways that link the activation of macrophages with the increased recruitment of neutrophils into the airways. Some of the major stimuli that activate macrophages and cause them to secrete chemotactic factors have been identified as CS, wood smoke, ozone, bacterial endotoxin, and proinflammatory cytokines such as interleukin (IL)-1beta and tumor necrosis factor (TNF)-alpha. These stimuli seem to activate mainly redox-sensitive transcription factors such as nuclear factor (NF)-kappa B and activator protein (AP)-1, both of which play a major role in the synthesis and secretion of chemotactic factors such as IL-8 and leukotriene B(4) (LTB(4)). The pathways involved in the synthesis and secretion of other factors such as macrophage chemotactic protein-1 (MCP-1) and growth-related oncogene-alpha (Gro-alpha) have also been reviewed.

The effects of ambient particulate matter on human alveolar macrophage oxidative and inflammatory responses

Epidemiologic and occupational studies demonstrated that ambient particulate matter (PM) and diesel exhaust particles (DEP) exert deleterious effects on human cardiopulmonary health, including exacerbation of pre-existing lung disease and development of respiratory infections. The effects of ambient PM on lung cell responsiveness are poorly defined. Human alveolar macrophages (AM) were exposed to SRM 1649 (Washington, DC, urban dust; UD), SRM 2975 (forklift diesel exhaust particles; DEP), and fine or coarse ambient PM collected in Chapel Hill, NC, during the late fall (November) and early summer (June) of 2001-2002. AM were subsequently incubated with lipopolysaccharide (LPS), phorbol myristate acetate (PMA), or calcium ionophore A23817 for 6 or 24 h after PM exposure. UD and DEP markedly suppressed O2- release 24 h post-PM exposure. UD exposure significantly inhibited tumor necrosis factor (TNF)-alpha, interleukin (IL)-6, and IL-8 release after exposure to 10 nanog/ml LPS. DEP significantly suppressed only TNF-alpha and IL-6 release. Suppressed cytokine release may also be produced by reduced cellular cytokine production. Data suggested that decreased cytokine release is not produced by the presence of benzo[a]pyrene (BaP), a polycyclic aromatic hydrocarbon. Comparison of TNF-alpha release after LPS, PMA, or A23817 revealed that suppressive effects of UD are LPS dependent, whereas inhibitory effects of DEP may work across multiple mechanistic pathways. November and June Chapel Hill PM exposure stimulated TNF-alpha and IL-8 release before LPS exposure. Fine and coarse November PM exposure markedly suppressed TNF-alpha release 6 h after LPS stimulation, but appeared to exert a stimulatory effect on IL-8 release 24 h after LPS exposure. June fine and coarse PM suppressed IL-8 release after LPS exposure. Data suggest that seasonal influences on PM composition affect AM inflammatory response before and after bacterial exposure. Overall, delayed or inhibited AM immune responses to LPS after PM exposure suggest human exposure to ambient PM may enhance pulmonary susceptibility to respiratory infections.

THE EFFECTS OF INHALATION OF DIESEL EXHAUST ON MURINE MYCOBACTERIAL INFECTION

The authors investigated the effects of inhalation of diesel exhaust (DE) on murine mycobacterial infection in vivo. Eight-week-old female BALB/c mice were exposed to DE (3 mg/m3 of diesel exhaust particles [DEPs]) for 1 month, 2 months, or 6 months (for 7 hours a day, 5 days a week). Control mice were housed in a clean room for the same periods. On the day following the last DE exposure, control mice and DE-exposed mice were aerially infected with Mycobacterium tuberculosis (1 x 10(6) colony-forming units (CFU), Kurono strain). At 7 weeks after mycobacterial infection, the authors examined the lung tissues for histopathological changes and performed reverse transcriptase-polymerase chain reaction (RT-PCR) to measure the messenger RNA (mRNA) expression of several proinflammatory cytokines and inducible nitric oxide synthase (iNOS). Then, the homogenates of lungs and spleens were cultured on 1% (v/v) Ogawa's egg slant medium, and after a 4-week incubation period at 37 degrees C, colonies on the medium were counted. After 1 month of DE exposure, the mycobacterial infection had slightly ameliorated. After 2 months of DE exposure, the expression levels of tumor necrosis factor (TNF)-alpha, interleukin (IL)-1beta, IL-12p40, interferon (IFN)-gamma, and iNOS mRNAs were slightly increased. However, after 6 months of DE exposure, the expression levels of IL-1beta , IL-12p40, IFN-gamma, and iNOS mRNAs were decreased, and the infection as measured by increased lung burden (CFU) actually increased. These results indicate that long-term DE exposure may increase pulmonary mycobacterial burden.

Particulate matter air pollution exposure: role in the development and exacerbation of chronic obstructive pulmonary disease

Due to the rapid urbanization of the world population, a better understanding of the detrimental effects of exposure to urban air pollution on chronic lung disease is necessary. Strong epidemiological evidence suggests that exposure to particulate matter (PM) air pollution causes exacerbations of pre-existing lung conditions, such as, chronic obstructive pulmonary disease (COPD) resulting in increased morbidity and mortality. However, little is known whether a chronic, low-grade exposure to ambient PM can cause the development and progression of COPD. The deposition of PM in the respiratory tract depends predominantly on the size of the particles, with larger particles deposited in the upper and larger airways and smaller particles penetrating deep into the alveolar spaces. Ineffective clearance of this PM from the airways could cause particle retention in lung tissues, resulting in a chronic, low-grade inflammatory response that may be pathogenetically important in both the exacerbation, as well as, the progression of lung disease. This review focuses on the adverse effects of exposure to ambient PM air pollution on the exacerbation, progression, and development of COPD.

Reactive oxygen species- and nitric oxide-mediated lung inflammation and mitochondrial dysfunction in wild-type and iNOS-deficient mice exposed to diesel exhaust particles

Pulmonary responses to diesel exhaust particles (DEP) exposure are mediated through enhanced production of reactive oxygen species (ROS) and nitric oxide (NO) by alveolar macrophages (AM). The current study examined the differential roles of ROS and NO in DEP-induced lung injury using C57B/6J wild-type (WT) and inducible NO synthase knockout (iNOS KO) mice. Mice exposed by pharyngeal aspiration to DEP or carbon black particles (CB) (35 mg/kg) showed an inflammatory profile that included neutrophil infiltration, increased lactate dehydrogenase (LDH) activity, and elevated albumin content in bronchoalveolar lavage fluid (BALF) at 1, 3, and 7 d postexposure. The organic extract of DEP (DEPE) did not induce an inflammatory response. Comparing WT to iNOS KO mice, the results show that NO enhanced DEP-induced neutrophils infiltration and plasma albumin content in BALF and upregulated the production of the pro-inflammatory cytokine interleukin 12 (IL-12) by AM. DEP-exposed AM from iNOS KO mice displayed diminished production of IL-12 and, in response to ex vivo lipopolysaccharide (LPS) challenge, decreased production of IL-12 but increased production of IL-10 when compared to cells from WT mice. DEP, CB, but not DEPE, induced DNA damage and mitochondria dysfunction in AM, however, that is independent of cellular production of NO. These results demonstrate that DEP-induced immune/inflammatory responses in mice are regulated by both ROS- and NO-mediated pathways. NO did not affect ROS-mediated mitochondrial dysfunction and DNA damage but upregulated IL-12 and provided a counterbalance to the ROS-mediated adaptive stress response that downregulates IL-12 and upregulates IL-10.

The generation of diesel exhaust particle aerosols from a bulk source in an aerodynamic size range similar to atmospheric particles

The influence of diesel exhaust particles (DEP) on the lungs and heart is currently a topic of great interest in inhalation toxicology. Epidemiological data and animal studies have implicated airborne particulate matter and DEP in increased morbidity and mortality due to a number of cardiopulmonary diseases including asthma, chronic obstructive pulmonary disorder, and lung cancer. The pathogeneses of these diseases are being studied using animal models and cell culture techniques. Real-time exposures to freshly combusted diesel fuel are complex and require significant infrastructure including engine operations, dilution air, and monitoring and control of gases. A method of generating DEP aerosols from a bulk source in an aerodynamic size range similar to atmospheric DEP would be a desirable and useful alternative. Metered dose inhaler technology was adopted to generate aerosols from suspensions of DEP in the propellant hydrofluoroalkane 134a. Inertial impaction data indicated that the particle size distributions of the generated aerosols were trimodal, with count median aerodynamic diameters less than 100 nm. Scanning electron microscopy of deposited particles showed tightly aggregated particles, as would be expected from an evaporative process. Chemical analysis indicated that there were no major changes in the mass proportion of 2 specific aromatic hydrocarbons (benzo[a]pyrene and benzo[k]fluoranthene) in the particles resulting from the aerosolization process.

Suppression of phagocytic and bactericidal functions of rat alveolar macrophages by the organic component of diesel exhaust particles

Exposure to diesel exhaust particles (DEP) was shown to increase the susceptibility of the lung to bacterial infection in rats. In this study, the effects of DEP on alveolar macrophage (AM) phagocytic and bactericidal functions and cytokine secretion by AM and lymphocytes in response to Listeria monocytogenes infection were investigated in vitro and the roles of different DEP components in these processes were compared. Exposure to DEP or the organic extracts of DEP (eDEP) significantly decreased the phagocytosis and killing of L. monocytogenes by AM obtained from normal rats. Washed DEP (wDEP) also decreased AM phagocytosis and bacterial killing to a lesser extent, whereas carbon black (CB) reduced AM phagocytosis but had no significant effect on AM bactericidal activity. DEP or eDEP concentration-dependently suppressed L. monocytogenes-induced secretion of tumor necrosis factor-alpha, interleukin (IL)-1beta, and IL-12 by AM and of IL-2 and interferon-gamma by lymphocytes obtained from L. monocytogenes-infected rats, but augmented the AM secretion of IL-10. wDEP or CB, however, exerted little or no effect on these L. monocytogenes-induced cytokines. These results provide direct evidence that DEP, through the actions of organic components, suppresses AM phagocytic and bactericidal functions in vitro. Inhibition of AM phagocytic function and alterations of AM and lymphocyte cytokine secretion by DEP and DEP organic compounds may be implicated in the diminished AM bactericidal activity and the lymphatic arm of the host immune system, thus resulting in an suppressed pulmonary clearance of L. monocytogenes and an increased susceptibility of the lung to bacterial infection.

Proteomic analysis of bronchoalveolar lavage fluid: effect of acute exposure to diesel exhaust particles in rats

BACKGROUND

Inhalation of diesel exhaust particles (DEPs) is characterized by lung injury and inflammation, with significant increases in the numbers of polymorphonuclear leukocytes and alveolar macrophages. This influx of cellular infiltrates is associated with the activation of multiple genes, including cytokines and chemokines, and the production of reactive oxygen species.

OBJECTIVE

The pathogenesis of the lung injury is not fully understood, but alterations in the presence or abundance of a number of proteins in the lung have been observed. Our objective in this study was to further characterize these changes and to ask whether additional changes could be discerned using modern proteomic techniques.

METHODS

The present study investigates global alterations in the proteome of bronchoalveolar lavage fluid taken from rats 1, 7, or 30 days after exposure to 5, 35, or 50 mg/kg of animal weight of DEPs.

RESULTS

Analysis by surface-enhanced laser desorption/ionization-time of flight mass spectrometry identified two distinct peaks that appeared as an acute response postexposure at all doses in all animals. We identified these two peaks, with mass to charge ratios (m/z) of 9,100 and 10,100, as anaphylatoxin C3a and calgranulin A by additional mass spectral investigation using liquid chromatography coupled to mass spectrometry.

CONCLUSIONS

With this approach, we found a number of inflammatory response proteins that may be associated with the early phases of inflammation in response to DEP exposure. Further studies are warranted to determine whether serum levels of these proteins could be markers of diesel exhaust exposure in workers.

Carbon black particles increase reactive oxygen species formation in rat alveolar macrophages in vitro

Alveolar macrophages (AM) have an important role in clearing particles from the lungs. In response to different stimuli they can release reactive oxygen species (ROS) and inflammatory mediators and promote pulmonary inflammation. We exposed rat AM to carbon black (CB) particles (0.63-20 microg/ml) and measured the eneration of ROS by using the fluorescent probe 2',7'-dichlorofluorescein diacetate. Fluorescence was elevated in a concentration dependent manner in the AM exposed to CB. Follow-up experiments using a series of enzyme inhibitors indicate that the ERK MAP kinase pathway and the p38 MAP kinase pathway may be involved in the formation of ROS.

ROS scavenging effects of organic extract of diesel exhaust particles on human neutrophil granulocytes and rat alveolar macrophages

Diesel exhaust particles are major constituents of ambient air pollution, and are associated with respiratory and cardiovascular diseases and lung cancer. The organic part of the particles is heterogenic and complex, and seems to be responsible for many of the adverse effects. Increased formation of ROS is often connected to the adverse effects. We have therefore investigated the effect of an organic extract of diesel exhaust particles on the reactive oxygen species (ROS) status in human neutrophil granulocytes and rat alveolar macrophages in vitro. ROS formation were studied by three different assays namely the use of DCFH-DA, lucigenin and luminol. The organic extract increased ROS assayed with DCFH-DA, but it decreased the amount of ROS in cells stimulated by PMA in all three assays. The identities of the ROS affected were further studied in cell free systems. The cell free studies confirmed that the extract had scavenging effects against superoxide, hypochlorite and to a smaller extent against peroxynitrite, but not against the hydroxyl radical and nitric oxide. ROS take part in the intracellular signalling pathways as well as in the defence against invading microorganisms, and the possible effects of interference of the redox status in the cells are discussed.

Assessing exposure to diesel exhaust particles: a case study

The assessment of the vehicular contributions to urban pollution levels is of particular importance given the current interest in the possible adverse health effects. This study focused on human exposure to diesel-engine-derived particulate matter. Diesel vehicles are known to emit fine particulate matter (PM2.5) containing carcinogens such as polycyclic aromatic hydrocarbons (PAHs), and have therefore received considerable attention. In this study, the physical (mass and number concentration, and size distribution) and chemical (PAHs) properties were investigated at a major bus interchange in Singapore, influenced only by diesel exhausts. Number concentration and size distribution of particles were determined in real time, while the mass concentrations of PM2.5, and PAHs were measured during operating and nonoperating hours. The average mass concentrations of PM2.5 and PAHs increased by a factor of 2.34 and 5.18, respectively, during operating hours. The average number concentration was also elevated by a factor of 5.07 during operating hours. This increase in the concentration of PM2.5 particles and their chemical constituents during operating hours was attributable to diesel emissions from in-use buses based on the particle size analysis, correlation among PAHs, and the commonly used PAHs diagnostic ratios. To evaluate the potential health threat due inhalation of air pollutants released from diesel engines, the incremental lifetime cancer risk was also calculated for a maximally exposed individual. The findings indicate that the air quality at the bus interchange poses adverse health effects.

Environmental cardiology: studying mechanistic links between pollution and heart disease

Environmental factors are considered key determinants of cardiovascular disease. Although lifestyle choices such as smoking, diet, and exercise are viewed as major environmental influences, the contribution of pollutants and environmental chemicals is less clear. Accumulating evidence suggests that exposure to pollutants and chemicals could elevate the risk of cardiovascular disease. Many epidemiological studies report that exposure to fine particles present in ambient air is associated with an increase in cardiovascular mortality. Statistically significant relationships between particulate air pollution and ischemic heart disease, arrhythmias, and heart failure have been reported. Animal studies show that exposure to ambient air particles increases peripheral thrombosis and atherosclerotic lesion formation. Exposures to arsenic, lead, cadmium, pollutant gases, solvents, and pesticides have also been linked to increased incidence of cardiovascular disease. Mechanistically, these effects have been attributed to changes in the synthesis or reactivity of nitric oxide that may be caused by environmental oxidants or increased endogenous production of reactive oxygen species. Additional studies are urgently needed to: identify the contribution of individual pollutants to specific aspects of cardiovascular disease; establish causality; elucidate the underlying physiological and molecular mechanisms; estimate the relative susceptibility of diseased and healthy individuals and that of specific population groups; and determine whether pollutant exposure are risk correlates, that is, whether they influence major risk factors, such as hypertension, cholesterol, or diabetes, or whether they contribute to the absolute risk of heart disease. Collectively, these investigations could contribute to the emergent field of environmental cardiology.

Role of reactive oxygen species on diesel exhaust particle-induced cytotoxicity in rat cardiac myocytes

Exposure to air pollution containing diesel exhaust particles (DEP) is associated with an increase in mortality rate attributed to cardiovascular diseases, but the mechanisms by which DEP produces adverse cardiovascular effects at the cellular level are not elucidated. This study investigated the cytotoxic mechanisms underlying DEP-induced neonatal rat cardiac myocytes effects in vitro, focusing on the role of reactive oxygen species (ROS). DEP extracts (DEPE) damaged cells in a concentration- and a time-dependent manner. Lactate dehydrogenase activity leaked to medium was also increased in a concentration-dependent manner after 24 h of DEPE exposure. DEPE-induced cytotoxicity was markedly reduced by treatment with superoxide dismutase, catalase, and N-(2-mercaptopropionyl)-glycine. Furthermore, superoxide was produced from both DEPE and myocardial cells. These results suggest that ROS such as superoxide, hydrogen peroxide, and hydroxyl radical are involved in DEPE-induced cardiac cell damage.

Mechanistically identified suitable biomarkers of exposure, effect, and susceptibility for silicosis and coal-worker's pneumoconiosis: a comprehensive review

Clinical detection of silicosis is currently dependent on radiological and lung function abnormalities, both late manifestations of disease. Markers of prediction and early detection of pneumoconiosis are imperative for the implementation of timely intervention strategies. Understanding the underlying mechanisms of the etiology of coal workers pneumoconiosis (CWP) and silicosis was essential in proposing numerous biomarkers that have been evaluated to assess effects following exposure to crystalline silica and/or coal mine dust. Human validation studies have substantiated some of these proposed biomarkers and argued in favor of their use as biomarkers for crystalline silica- and CWP-induced pneumoconiosis. A number of "ideal" biological markers of effect were identified, namely, Clara cell protein-16 (CC16) (serum), tumor necrosis factor-alpha (TNF-alpha) (monocyte release), interleukin-8 (IL-8) (monocyte release), reactive oxygen species (ROS) measurement by chemiluminescence (neutrophil release), 8-isoprostanes (serum), total antioxidant levels measured by total equivalent antioxidant capacity (TEAC), glutathione, glutathione peroxidase activity, glutathione S-transferase activity, and platelet-derived growth factor (PDGF) (serum). TNF-alpha polymorphism (blood cellular DNA) was identified as a biomarker of susceptibility. Further studies are planned to test the validity and feasibility of these biomarkers to detect either high exposure to crystalline silica and early silicosis or susceptibility to silicosis in gold miners in South Africa.

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.

The immune system as a target for environmental chemicals: Xenoestrogens and other compounds

The immune system in higher organisms is under integrated control and has the capacity to rapidly respond to the environment. Recently, there has been a significant increase in the prevalence of allergic diseases. Environmental factors likely play a major role in the explosion of allergy. Although the "hygiene hypothesis" may explain the increase in allergic diseases which are prone to T helper 2 (Th2) immune responses, recent findings highlight the possible involvement of environmental xenobiotic chemicals which can modulate normal immune function. Interestingly, several reports suggest that the prevalence of systemic lupus erythematosus, a Th2-type autoimmune disease, is also increasing, although the development of high-sensitivity immunological tests may be a possible cause. The increased prevalence of autoimmune disease in women, the sexual dimorphism of the immune response, and the immunomodulatory effects of sex steroids, have focused attention on the role of chemicals which influence sex steroids in the development of immune diseases. Moreover, recent reports indicate that some environmental chemicals can work on nuclear hormone receptors, other than sex hormone receptors, and modulate immune reactions. This review focuses on the impact of environmental chemicals on immune system function and pathogenesis of immune diseases, including allergy and autoimmune diseases.

Relationship between radical generation by urban ambient particulate matter and pulmonary function of school children

The mechanisms by which particulate matter (PM) produces adverse effects on the respiratory system, such as pulmonary dysfunction in children, are largely unknown. However, oxidative stress is thought to play an important role. Various chemical compounds in ambient particulate matter, including transition metals and aromatic organic compounds, may contribute to adverse effects through intrinsic generation of reactive oxygen species (ROS). It was hypothesized that ROS generation by PM, as determined through electron spin resonance (ESR) spectroscopy, may be negatively associated with pulmonary function in school children. PM(2.5), PM(10), and total suspended particulates (TSP) were sampled at the playgrounds of six elementary schools in the city of Maastricht, the Netherlands. All children (8-13 yr) from the six schools were asked to undergo spirometry. Multivariate linear regression models were constructed to evaluate associations between oxygen radical formation by PM and lung function. The radical-generating capacity per microgram PM correlated negatively to forced expiratory volume in 1 s (FEV(1)) and forced expiratory flow at 50% (FEF(50%)) of forced vital capacity (FVC). The data indicate that chemical features that contribute to intrinsic generation of ROS may be relevant for PM risk assessment.

Diesel exhaust enhances virus- and poly(I:C)-induced Toll-like receptor 3 expression and signaling in respiratory epithelial cells

Prior exposure of respiratory epithelial cells to an aqueous-trapped solution of diesel exhaust (DE(as)) enhances the susceptibility to influenza infections. Here, we examined the effect of DE(as) on the Toll-like receptor 3 (TLR3) pathway, which is responsible for the recognition of and response to viruses and double-stranded RNA. Flow cytometric and confocal microscopy analyses showed that TLR3 is predominantly expressed in the cytoplasm of respiratory epithelial cells. To examine the effect of DE on TLR3 expression and function, differentiated human bronchial or nasal epithelial cells as well as A549 cells were exposed to DE(as) and then infected with influenza A or treated with polyriboinosinic acid-polyribocytidylic acid [poly(I:C)], a synthetic form of double-stranded RNA. Exposure to DE(as) before infection with influenza or stimulation with poly(I:C) significantly upregulated the expression of TLR3. Additionally, preexposure to DE(as) significantly increased the poly(I:C)-induced expression of IL-6. Overexpression of a dominant-negative mutant form of TNF receptor-associated factor 6 reversed the effects of DE(as) on poly(I:C)-induced IL-6 expression, suggesting that the response was TLR3 dependent. Similarly, preexposure to DE(as) significantly increased nuclear levels of interferon regulatory factor 3 and the expression of IFN-beta in response to poly(I:C). Pretreatment with wortmannin, a specific inhibitor of phosphatidylinositol 3-kinase, was able to abate the effect of DE(as) on poly(I:C)-induced IFN-beta expression. Together, these results indicate that exposure of respiratory epithelial cells to DE(as) could potentially alter the response to viral infections by increasing the expression and function of TLR3.

Effect of composition and different fractions of hay dust suspension on inflammation in lungs of heaves-affected horses: MMP-9 and MMP-2 as indicators of tissue destruction

REASONS FOR PERFORMING STUDY

Airway matrix metalloproteinases (MMPs) increase following inhalation of organic dust. The relative contribution of dust components to this elevation is unknown.

OBJECTIVE

To identify components of organic dust responsible for elevated MMP levels in equine airways.

METHODS

Bronchoalveolar lavage (BALF) from 7 heaves-susceptible horses, collected 6 h following inhalation challenges with saline, 2 different hay dust suspensions (HDS-1 and -2) and soluble and particulate fractions of HDS-1, were analysed for MMP-2 and -9 using SDS-page gelatin zymography.

RESULTS

HDS-1 challenge increased BALF proMMP-9 and total MMP-9. HDS-1 fractions, or the particulate fraction with added lipopolysaccharide, increased BALF proMMP-9 and total MMP-9 in combination, but not when inhaled separately. HDS-2 inhalation elevated BALF complex forms, proMMP-9, active MMP-9, total MMP-9 and total MMP-2.

CONCLUSIONS

The results suggest synergistic action of soluble and particulate organic dust components. The fact that HDS-1 and HDS-2 had different glucan concentrations supports a role for moulds in the activation of MMP-9.

POTENTIAL RELEVANCE

Activation and release of MMPs in response to inhaled moulds are involved in the aetiopathogenesis of heaves. Endotoxin contributes to the synergistic action of the dust components, but the overall MMP response to organic dust inhalation in heaves-susceptible horses largely reflects the mould content of the dust. In the future, inhibition of MMP production and release may offer therapeutic means for treatment and prevention of heaves and recommendations for acceptable dust levels can be given.

Exposure of Brown Norway Rats to Diesel Exhaust Particles Prior to Ovalbumin (OVA) Sensitization Elicits IgE Adjuvant Activity but Attenuates OVA-Induced Airway Inflammation

Exposure to diesel exhaust particles (DEP) during the sensitization process has been shown to increase antigen-specific IgE production and aggravate allergic airway inflammation in human and animal models. In this study, we evaluated the effect of short-term DEP exposure on ovalbumin (OVA)-mediated responses using a post-sensitization model. Brown Norway rats were first exposed to filtered air or DEP (20.6 +/- 2.7 mg/m3) for 4 h/day for five consecutive days. One day after the final air or DEP exposure (day 1), rats were sensitized with aerosolized OVA (40.5 +/- 6.3 mg/m3), and then again on days 8 and 15, challenged with OVA on day 29, and sacrificed on days 9 or 30, 24 h after the second OVA exposure or the final OVA challenge, respectively. Control animals received aerosolized saline instead of OVA. DEP were shown to elicit an adjuvant effect on the production of antigen-specific IgE and IgG on day 30. At both time points, no significant airway inflammatory responses and lung injury were found for DEP exposure alone. However, the OVA-induced inflammatory cell infiltration, acellular lactate dehydrogenase activity and albumin content in bronchoalveolar lavage (BAL) fluid, and numbers of T cells and their CD4+ and CD8+ subsets in lung-draining lymph nodes were markedly reduced by DEP on day 30 compared with the air-plus-OVA exposure group. The OVA-induced nitric oxide (NO) in the BAL fluid and production of NO, interleukin (IL)-10, and IL-12 by alveolar macrophages (AM) were also significantly lowered by DEP on day 30 as well as day 9. DEP or OVA alone decreased intracellular glutathione (GSH) in AM and lymphocytes on days 9 and 30. The combined DEP and OVA exposure resulted in further depletion of GSH in both cell types. These results show that short-term DEP exposure prior to sensitization had a delayed effect on enhancement of the sensitization in terms of allergen-specific IgE and IgG production, but caused an attenuation of the allergen-induced airway inflammatory responses.

Sustained effect of inhaled diesel exhaust particles on T-lymphocyte-mediated immune responses against Listeria monocytogenes

Studies have shown that exposure to diesel exhaust particles (DEP) suppresses pulmonary host defense against bacterial infection. The present study was carried out to characterize whether DEP exposure exerts a sustained effect in which inhaled DEP increase the susceptibility of the lung to bacterial infection occurring at a later time. Brown Norway rats were exposed to filtered air or DEP by inhalation at a dose of 21.2 +/- 2.3 mg/m3, 4 h/day for 5 days, and intratracheally instilled with saline or 100,000 Listeria monocytogenes (Listeria) 7 days after the final DEP exposure. Bacterial growth and cellular responses to DEP and Listeria exposures were examined at 3 and 7 days post-infection. The results showed that inhaled DEP prolonged the growth of bacteria, administered 7 days post DEP exposure, in the lung as compared to the air-exposed controls. Pulmonary responses to Listeria infection were characterized by increased production of interleukin (IL)-1beta, tumor necrosis factor (TNF)-alpha, IL-12, and IL-10 by alveolar macrophages (AM) and increased presence of T lymphocytes and their CD4+ and CD8+ subsets in lung draining lymph nodes that secreted elevated levels of IL-2, IL-6, IL-10, and interferon (IFN)-gamma. Diesel exhaust particles were found to inhibit Listeria-induced production of IL-1beta and TNF-alpha, which are responsible for the innate immunity, and IL-12, which initiates the development of T helper (Th)1 responses, but enhance Listeria-induced AM production of IL-10, which prolongs Listeria survival in these phagocytes. The dual action of DEP on AM production of IL-12 and IL-10 correlated with an inhibition of the development of bacteria-specific T lymphocytes by DEP. Cytokine production by lymphocytes from DEP- and Listeria-exposed rats showed a marked decrease in the production of IL-2, IL-10, and IFN-gamma compared to Listeria infection alone, suggesting either that DEP inhibit the production of cytokines by lymphocytes or that these lymphocytes contained T-cell subsets that are different from those of Listeria infection alone and less effective in mediating Th1 immune responses. This study demonstrates that inhaled DEP, after a 7-day resting period, increase the susceptibility of the lung to bacterial infection occurring at a later time by inhibiting macrophage immune function and suppressing the development of T-cell-mediated immune responses. The results support the epidemiological observations that exposure to DEP may be responsible for the pulmonary health effects on humans.

Time course of gene expression of inflammatory mediators in rat lung after diesel exhaust particle exposure

Diesel exhaust particles (DEPs) at three concentrations (5, 35, and 50 mg/kg body weight) were instilled into rats intratracheally. We studied gene expression at 1, 7, and 30 days postexposure in cells obtained by bronchoalveolar lavage (BAL) and in lung tissue. Using real-time reverse transcriptase-polymerase chain reaction (RT-PCR), we measured the mRNA levels of eight genes [interleukin (IL)-1beta, IL-6, IL-10, iNOS (inducible nitric oxide synthase), MCP-1 (monocyte chemoattractant protein-1), MIP-2 (macrophage inflammatory protein-2), TGF-beta1 (transforming growth factor-beta1), and TNF-alpha (tumor necrosis factor-alpha )] in BAL cells and four genes [IL-6, ICAM-1 (intercellular adhesion molecule-1), GM-CSF (granulocyte/macrophage-colony stimulating factor), and RANTES (regulated upon activation normal T cell expressed and secreted)] in lung tissue. In BAL cells on day 1, high-dose exposure induced a significant up-regulation of IL-1beta, iNOS, MCP-1, and MIP-2 but no change in IL-6, IL-10, TGF-beta1, and TNF-alpha mRNA levels. There was no change in the mRNA levels of IL-6, RANTES, ICAM-1, and GM-CSF in lung tissue. Nitric oxide production and levels of MCP-1 and MIP-2 were increased in the 24-hr culture media of alveolar macrophages (AMs) obtained on day 1. IL-6, MCP-1, and MIP-2 levels were also elevated in the BAL fluid. BAL fluid also showed increases in albumin and lactate dehydrogenase. The cellular content in BAL fluid increased at all doses and at all time periods, mainly due to an increase in polymorphonuclear leukocytes. In vitro studies in AMs and cultured lung fibroblasts showed that lung fibroblasts are a significant source of IL-6 and MCP-1 in the lung.

Tumor necrosis factor is not required for particle-induced genotoxicity and pulmonary inflammation

Particle-induced carcinogenicity is not well understood, but might involve inflammation. The proinflammatory cytokine tumor necrosis factor (TNF) is considered to be an important mediator in inflammation. We investigated its role in particle-induced inflammation and DNA damage in mice with and without TNF signaling. TNF-/- mice and TNF+/+ mice were exposed by inhalation to 20 mg m(-3) carbon black (CB), 20 mg m(-3) diesel exhaust particles (DEP), or filtered air for 90 min on each of four consecutive days. DEP, but not CB particles, induced infiltration of neutrophilic granulocutes into the lung lining fluid (by the cellular fraction in the bronchoalveolar lavage fluid), and both particle types induced interleukin-6 mRNA in the lung tissue. Surprisingly, TNF-/- mice were intact in these inflammatory responses. There were more DNA strand breaks in the BAL cells of DEP-exposed TNF-/- mice and CB-exposed mice compared with the air-exposed mice. Thus, the CB-induced DNA damage in BAL-cells was independent of neutrophil infiltration. The data indicate that an inflammatory response was not a prerequisite for DNA damage, and TNF was not required for the induction of inflammation by DEP and CB particles.

Heating of indoor dust causes reduction in its ability to stimulate release of IL-8 and TNFalpha in vitro compared to non-heated dust

Dust is a major contaminant of the indoor air environment and may affect human health. Indoor dust accumulates on surfaces including heaters and light fixtures, and will be heated when these devices are used. Heat treatment of the dust may change its biologic properties and in this study we simulated the heat treatment with a dust-heating model (50-250 degrees C). The residual and the non-heated dust from seven samples were tested in cultures of fresh peripheral blood mononuclear cells and in A549 cell culture using the release of TNFalpha and IL-8, respectively, as effect indicators. The endotoxin-content and the particle size distribution of the residual and the non-heated dust suspensions were determined for some of the samples. We found that the residual dust had less ability to induce the release of TNFalpha and IL-8. The cytokine decline pattern was similar for all the dust tested and could partly be explained by the reduction in endotoxin content or possibly by inhibitory decomposition products. No correlation was found between the measured particle size distribution and the decreased cytokine levels. The results in this study suggest that the residual dust promotes reduced cytokine response and thereby a possibly lower inflammation reaction in the airways if suspended and inhaled compared with the non-heated dust.

PRACTICAL IMPLICATIONS

Accumulation of indoor dust on electric heaters and light fixtures may produce a bad odor when switched on in the cold season and some people claim respiratory distress during such events. To investigate to what extent the residuals of heated indoor dust represent a health hazard, we measured the effect in cell cultures before and after heat treatment of the dust. The in vitro results imply that the residual dust will cause a lower proinflammatory response in the airways if suspended and inhaled compared with non-heated dust. This is partly explained by heat destruction of inflammatory components in the dust.

Emissions from indoor dust inhibit proliferation of A549 cells and TNFalpha release from stimulated PBMCs

Dust accumulating on hot indoor surfaces, e.g., heaters and light fixtures, are likely to emit chemicals when heated. Using in vitro techniques we have investigated biological effects of extracts from such emissions from three indoor and two outdoor dust samples heated at 50-250 degrees C. The cell cultures were a lung epithelial cell line (A549) and primary immune cells [peripheral blood mononuclear cell (PBMCs)]. We found that a 24-h incubation with extracts generated at 200 degrees C or higher inhibit both proliferation and mitochondrial activity of the epithelial cells. At non-cytotoxic concentrations, the extracts generated at 100 degrees C or higher inhibit the release of the pro-inflammatory cytokine tumor necrosis factor-alpha (TNFalpha) from lipopolysaccharide-stimulated PBMCs. The results imply that temperatures relevant for surfaces of equipment in the indoor environment cause emissions from dust that may have an impact on indoor air quality and affect the respiratory health of building occupants.

A review of experimental studies on diesel exhaust particles and nasal epithelium alterations

The aim of the present review is to summarize biological events in nasal epithelium after short-term exposure to diesel exhaust particles (DEP). Therefore human, animal, and in vitro studies carried out since 1987 are reviewed. Short-term exposure results included qualitative alterations characterized by immediate nasal hyperresponsiveness, antioxidant responses, marked epithelial inflammation, and a specific humoral response. In addition, studies on combined DEP/allergen challenge reported that, besides their intrinsic deleterious properties, DEP produced adjuvant-like effects on the immediate and late-phase response to allergen challenge, since they are able to mimic effects occurring after allergen challenge. DEP act deeply in nasal epithelium by (1) directing cytokine gene expression toward a Th2 profile, (2) enhancing local antigen-specific immunoglobulin E (IgE) production, and (3) driving in vivo isotype switch to IgE. Furthermore, DEP can induce in allergic subjects sensitization to a neoallergen, sensitization that did not occur with exposure to the neoantigen alone. Particulate pollutants such as DEP, encountered in urban areas, are therefore thought to be contributing causal factors to the exaggerated sensitization to allergens in subjects with appropriate genetic predisposition, sensitization that they might not otherwise have experienced. These findings add weight to the hypothesis that DEP are involved in the increased prevalence of airway allergic diseases.

Effect of diesel exhaust particulate (DEP) on immune responses: contributions of particulate versus organic soluble components

The effect of diesel exhaust particulate (DEP) exposure on innate, cellular and humoral pulmonary immunity was studied using high-dose, acute-exposure rat, mouse, and cell culture models. DEP consists of a complex mixture of petrochemical-derived organics adsorbed onto elemental carbon particles. DEP is a major component of particulate urban air pollution and a health concern in both urban and occupational environments. The alveolar macrophage is considered a key cellular component in pulmonary innate immunity. DEP and DEP organic extracts have been found to suppress alveolar macrophage function as demonstrated by reduced production of cytokines (interleukin-1 [IL-1], tumor necrosis factor- alpha [TNF- alpha]) and reactive oxygen species (ROS) in response to a variety of agents, including lipopolysaccharide (LPS), interferon- gamma (IFN- gamma), and bacteria. Fractionation of DEP organic extract suggests that this activity was predominately in polyaromatic-containing and more polar (resin) fractions. Organic-stripped DEP did not alter these innate pulmonary immune responses. DEP also depressed pulmonary clearance of Listeria monocytogenes and Bacillus Calmette-Guerin (BCG). The contribution of the organic component of DEP is less well defined with respect to acquired and humoral immunity. Indeed, both DEP and carbon black enhanced humoral immune responses (specific immunoglobulin [Ig] E and IgG) in an ovalbumin-sensitized rat model. It is concluded that both the particulate and adsorbed organics may contribute to DEP-mediated immune alterations.

In vitro relative toxicity screening of combined particulate and semivolatile organic fractions of gasoline and diesel engine emissions

Engine technology modifications designed to reduce engine emissions are likely to alter the physicochemical characteristics of the emissions. These changes may alter the biological effects of the emissions, but these effects cannot currently be predicted from the physical and chemical properties. Rapid in vitro toxicity screening techniques to compare the biological effects of emission samples would be useful as preliminary guides to assess the relative health impact of modified technology. Here, we demonstrate that selected responses of cultured human lung epithelial cells and rat alveolar macrophages can discriminate among combined particulate matter (PM) and semivolatile organic compound (SVOO fractions of emissions collected from normal- and high-emitter, in-use gasoline and diesel vehicles. Macrophages were more susceptible to cytotoxicity than epithelial cells. Samples from gasoline vehicles (except a vehicle that produced visible white smoke) generally caused greater effects than the diesel engine samples. However, low concentrations of diesel emission samples were more potent stimulators of peroxide production than gasoline emission samples. The same rank order of potency applied to suppression of this response at high concentrations. A diesel PM fraction was much less toxic to both types of cells than the combined PM +SVOC fractions, consistent with a role for the SVOC fraction in cytotoxicity. However, the rank order of potency from the in vitro assays in general did not correspond with the previous rankings from in vivo comparisons of the same samples. Thus, while the in vitro assays may provide mechanistic information, revealing cell type-specific responses, they did not accurately reflect in vivo comparative toxicity in their current form.

Inhaled endotoxin and organic dust particulates have synergistic proinflammatory effects in equine heaves (organic dust-induced asthma)

BACKGROUND

Equine heaves is a naturally occurring organic dust-induced asthma characterized by airway neutrophilia, mucus hypersecretion and obstructive lung dysfunction. However, the relative role of different dust components in disease severity remains unclear.

OBJECTIVE

This study investigated the relative contribution of inhaled endotoxin and organic dust particulates (mainly mould spores) in inducing heaves in heaves-susceptible horses.

METHODS

Control and heaves-susceptible horses received inhalation challenges with hay dust suspension (HDS) before and after lipopolysaccharide (LPS) depletion. Heaves-susceptible horses also received inhalation challenge with HDS particulates with and without the addition of LPS and were housed in two separate dusty environments during which mould and endotoxin exposure was measured. The airway inflammatory and functional response to each challenge was measured.

RESULTS

Depletion of endotoxin from HDS attenuated the airway neutrophilia and abrogated the airway dysfunction induced in heaves horses by inhaled HDS. The airway response was re-established by adding back LPS to the depleted HDS, confirming that the attenuation in airway response was due specifically to endotoxin depletion. Interestingly, the magnitude of alteration in airway response following endotoxin depletion and add-back was greater than that which could be attributed solely to endotoxin per se, indicating that the LPS activity was enhanced by the other dust components. Consistent with this possibility, washed particulates harvested from HDS enhanced the airway response to inhaled LPS in heaves horses. Heaves horses given two different hay/straw challenges had a significantly different severity of airway inflammation and dysfunction, despite airborne dust and endotoxin concentrations in the horses' breathing zones being similar.

CONCLUSION

Although inhaled endotoxin appears not to be the only determinant of disease severity in heaves, it does contribute significantly to the induction of airway inflammation and dysfunction. This contribution is largely via the synergistic action of inhaled endotoxin and organic dust particulates, although other soluble dust components also contribute to a lesser degree.

Increased susceptibility to RSV infection by exposure to inhaled diesel engine emissions

Although epidemiologic data strongly suggest a role for inhaled environmental pollutants in modulating the susceptibility to respiratory infection in humans, the underlying cellular and molecular mechanisms have not been well studied in experimental systems. The current study assessed the impact of inhaled diesel engine emissions (DEE) on the host response in vivo to a common pediatric respiratory pathogen, respiratory syncytial virus (RSV). Using a relatively resistant mouse model of RSV infection, prior exposure to either 30 microg/m3 particulate matter (PM) or 1,000 microg/m3 PM of inhaled DEE (6 h/d for seven consecutive days) increased lung inflammation to RSV infection as compared with air-exposed RSV-infected C57Bl/6 mice. Inflammatory cells in bronchoalveolar lavage fluid were increased in a dose-dependent manner with regard to the level of DEE exposure, concomitant with increased levels of inflammatory mediators. Lung histology analysis indicated pronounced peribronchial and peribronchiolar inflammation concordant with the level of DEE exposure during infection. Mucous cell metaplasia was markedly increased in the airway epithelium of DEE-exposed mice following RSV infection. Interestingly, both airway and alveolar host defense and immunomodulatory proteins were attenuated during RSV infection by prior DEE exposure. DEE-induced changes in inflammatory and lung epithelial responses to infection were associated with increased RSV gene expression in the lungs following DEE exposure. These findings are consistent with the concept that DEE exposure modulates the lung host defense to respiratory viral infections and may alter the susceptibility to respiratory infections leading to increased lung disease.

Inflammatory mediators induced by coarse (PM2.5-10) and fine (PM2.5) urban air particles in RAW 264.7 cells

Increased incidence of mortality and morbidity due to cardiopulmonary complications has been found to associate with elevated levels of urban air particles with an aerodynamic diameter <10 micron, PM10 and <2.5 micron, PM2.5. Respirable particles reach the lower respiratory tract where they are phagocytized by alveolar macrophages. Depending on particle composition, exposed macrophages may produce inflammatory mediators. A cascade impactor sampler was used to collect size-fractionated urban air particles. Particulate matter from the city of Rome (Italy) were collected onto stainless steel plates, and recovered using alcohol. The murine monocytic/macrophagic RAW 264.7 cell line was used to compare the ability of PM2.5-10, PM2.5 and carbon black to cause cell injury, such as arachidonic acid (AA) release, tumour necrosis factor alpha (TNF alpha) and interleukin (IL)-6 production. All test particles have been used at the same concentrations 30 and 120 microg/ml. Treatment with PM2.5-10 and PM2.5 induced significant AA release after 5 h of exposure at both concentrations, while carbon black was effective only at the higher concentration. After 5 h of incubation, PM2.5-10 and PM2.5 at 120 microg/ml induced 10 times the amount of TNF alpha than carbon black particles. The urban air particles-stimulated TNF alpha production decreased after 24 h of incubation while carbon black-stimulated TNF alpha was not. IL-6 production was induced by PM2.5 and by PM2.5-10 but not by carbon black. Carbon black was consistently less effective than the urban particles, suggesting that, the contaminants adsorbed on the particles are responsible for the release of inflammatory mediators.