Inhalation Coexposure to Carbon Black and Acrolein Suppresses Alveolar Macrophage Phagocytosis and Tnf-α Release and Modulates Peritoneal Macrophage Phagocytosis

Inhaled particle-bound sulfate: effects on pulmonary inflammatory responses and alveolar macrophage function

Acid sulfate-coated solid particles are a significant environmental hazard produced primarily by the combustion of fossil fuels. We have previously described a system for the nascent generation of carbonaceous particles surface coated with approximately 140 microg/m(3) acid sulfate [cpSO(4)(2-); 10 mg/m(3) carbon black (CB) and 10 ppm sulfur dioxide (SO(2)) at 85% relative humidity (RH)]. The effects of inhaled cpSO(4)(2-) on pulmonary host defenses are assessed in the present work. Mice were acutely exposed (4 h) to either 10 mg/m(3) CB, 10 ppm SO(2), or their combination at 10% or 85% RH in a nose-only inhalation chamber. No evidence of an inflammatory response was found following any of the exposures as assessed by total cell counts and differential cell counts from bronchoalveolar lavage fluid. However, alveolar macrophage Fc receptor-mediated phagocytosis decreased only following exposure to 140 microg cpSO(4)(2-), significant suppression occurred after 24 h, maximal suppression occurred at 3 days postexposure, and recovery to preexposure levels required 7-14 days. Intrapulmonary bactericidal activity (IBA) was also suppressed only after exposure to 140 microg cpSO(4)(2-); suppression was maximal at 1 day postexposure and recovered by day 7. To assess the effects of lower cpSO(4)(2-) concentrations, mice were repeatedly exposed to 1 mg/m(3) CB and 1 ppm SO(2) at 85% RH ( approximately 20 microg/m(3) cpSO(4)(2-) for 4 h/day) for up to 6 days. A significant decrement in IBA was observed following 5 and 6 days of exposure. These studies indicated that acute or repeated exposure to cpSO(4)(2-) could alter pulmonary host defense mechanisms.

Interstrain variation in murine susceptibility to inhaled acid-coated particles

Epidemiologic studies have demonstrated a positive correlation between concentration of acid aerosol and increased morbidity and mortality in many urban environments. To determine whether genetic background is an important risk factor for susceptibility to the toxic effects of inhaled particles, we studied the interstrain (genetic) and intrastrain (environmental) variance of lung responses to acid-coated particle (ACP) aerosol in nine strains of inbred mice. A flow-past nose-only inhalation system was used to expose mice to ACPs produced by the cogeneration of a carbon black aerosol-sulfur dioxide (SO(2)) mixture at high humidity. Three days after a single 4-h exposure to ACPs or filtered air, mice underwent bronchoalveolar lavage, and cell differentials and total protein were determined as indexes of inflammation and epithelial permeability, respectively. To determine the effect of ACPs on alveolar macrophage (AM) function, lavaged AMs were isolated from exposed animals and Fc receptor-mediated phagocytosis was evaluated. Compared with air-exposed animals, there was a slight but significant exposure effect of ACPs on the mean number of lavageable polymorphonuclear leukocytes in C3H/HeJ and C3H/HeOuJ mice. ACP exposure also caused a significant decrease in AM phagocytosis. Relative to respective air-exposed animals, Fc receptor-mediated phagocytosis was suppressed in eight of nine strains. The order of strain-specific effect of ACPs on phagocytosis was C57BL/6J > 129/J > SJL/J > BALB/cJ > C3H/HeOuJ > A/J > SWR/J > AKR/J. There was no effect of ACP exposure on AM phagocytosis in C3H/HeJ mice. The significant interstrain variation in AM response to particle challenge indicates that genetic background has an important role in susceptibility. The effects of ACPs on AM function, inflammation, and epithelial hyperpermeability were not correlated (i.e., no cosegregation). This model may have important implications concerning interindividual variation in particle-induced compromise of host defense.

Air pollution and daily mortality in the Coachella Valley, California: a study of PM10 dominated by coarse particles

Many epidemiological studies provide evidence of an association between airborne particles, measured as PM10 (particulate matter less than 10 microm in diameter), and daily morbidity and mortality. Most of these studies have been conducted in urban areas where PM10 consists primarily of fine particles (<2.5 microm in diameter). Few studies have investigated impacts associated with coarse mode particles (>2.5 microm in diameter). We investigated associations between PM10 and daily mortality in the Coachella Valley, a desert resort and retirement area east of Los Angeles, where coarse particles of geologic origin typically comprise approximately 50-60% of PM10 and can exceed 90% during wind events. Our analysis utilized daily data on mortality from 1989 through 1992 as well as several pollutant and meteorological variables, including PM10, nitrates, sulfates, ozone, nitrogen dioxide, carbon monoxide, temperature, and relative humidity. Outcome variables included several measures of daily mortality, including all-cause, cardiovascular and respiratory mortality, and counts of deaths for those above age 50. Multivariate Poisson regression models were used to explain these health endpoints, controlling for temperature, humidity, day of the week, season, and time, using locally weighted smoothing techniques. The analysis indicated statistically significant associations between PM10 (2- or 3-day lags) and each measure of mortality. The results were robust to various model specifications, correction for autocorrelation and overdispersion, and analysis of influential observations. A 10 microg/m3 change in daily PM10 was associated with an approximately 1% increase in mortality, which is of similar magnitude to particle-associated impacts identified in urban areas. Thus, our findings provide evidence for a mortality effect of PM10 in an area where the particulate mass is dominated by coarse particles.

Monocyte inflammation augments acrolein-induced Muc5ac expression in mouse lung

Acrolein, an unsaturated aldehyde found in smog and tobacco smoke, can induce airway hyperreactivity, inflammation, and mucus hypersecretion. To determine whether changes in steady-state mucin gene expression (Muc2 and Muc5ac) are associated with inflammatory cell accumulation and neutrophil elastase activity, FVB/N mice were exposed to acrolein (3.0 parts/million; 6 h/day, 5 days/wk for 3 wk). The levels of Muc2 and Muc5ac mRNA were determined by RT-PCR, and the presence of Muc5ac protein was detected by immunohistochemistry. Total and differential cell counts were determined from bronchoalveolar lavage (BAL) fluid, and neutrophil elastase activity was measured in the BAL fluid supernatant. Lung Muc5ac mRNA was increased on days 12 and 19, and Muc5ac protein was detected in mucous granules and on the surface of the epithelium on day 19. Lung Muc2 mRNA was not detected at measurable levels in either control or exposed mice. Acrolein exposure caused a significant and persistent increase in macrophages and a rapid but transient increase in neutrophils in BAL fluid. Recoverable neutrophil elastase activity was not significantly altered at any time after acrolein exposure. To further examine the role of macrophage accumulation in mucin gene expression, additional strains of mice (including a strain genetically deficient in macrophage metalloelastase) were exposed to acrolein for 3 wk, and Muc5ac mRNA levels and macrophage accumulation were measured. The magnitude of macrophage accumulation coincided with increased Muc5ac mRNA levels, indicating that excessive macrophage accumulation augments acrolein-induced Muc5ac synthesis and secretion after repeated exposure. These findings support a role for chronic monocytic inflammation in the pathogenesis of mucus hypersecretion observed in chronic bronchitis.

Urban air particulate inhalation alters pulmonary function and induces pulmonary inflammation in a rodent model of chronic bronchitis

Epidemiological studies have reported increased morbidity in human populations following inhalation of elevated levels of urban particulate matter. These responses are especially prevalent in populations with chronic obstructive pulmonary diseases, including chronic bronchitis. Toxicological studies have reported altered pulmonary function and increased pulmonary inflammation following particulate inhalation in the laboratory setting. However, most of these studies have utilized artificial particles that may not accurately mimic outdoor air pollutant conditions. Few studies have utilized actual urban air particle samples in inhalation studies. In the present study, the effects of inhaled concentrated urban air particulates on pulmonary function and pulmonary inflammation are addressed. Normal rats and rats with chronic bronchitis induced by approximately 200 ppm SO(2) for 6 wk were subsequently subjected to filtered air or concentrated air particles (CAPs). Twelve rats per group in 4 groups (48 rats total) were exposed for 5 h/day for 3 consecutive days. The CAPs aerosol levels were 206, 733, and 607 microg/m(3) (MMAD = 0.18 microm, sigma(g) = 2.9) on days 1, 2, and 3, respectively. Following the final day of exposure, pulmonary function parameters, including peak expiratory flow (PEF), tidal volume (TV), respiratory frequency (RF), and minute volume (MV), were measured and compared to preexposure baseline levels. Twenty-four hours following the final day of exposure, bronchoalveolar lavage was performed for total cell counts, differential cell counts, and total lavage protein levels. Pulmonary responses to CAPs in chronic bronchitic animals indicated a significant increase in tidal volume as well as peak expiratory flow. In CAPs-exposed animals without underlying bronchitis, significantly increased tidal volume was observed. Significant pulmonary inflammation was observed in the CAPs-exposed animals, particularly those with chronic bronchitis. Significant increases in neutrophils, lymphocytes, and total lavage protein were observed. These results suggest two distinct mechanistic responses to inhaled particles: a stress-type pulmonary function response marked by increases in flow and volume, that is, deeper breathing; and acute pulmonary inflammation marked by cellular influx, particularly neutrophils. From these data it is concluded that inhaled urban air particles alter pulmonary breathing parameters and increase pulmonary inflammation.

Toxicology of chemical mixtures: international perspective

This paper reviews major activities outside the United States on human health issues related to chemical mixtures. In Europe an international study group on combination effects has been formed and has started by defining synergism and antagonism. Successful research programs in Europe include the development and application of statistically designed experiments combined with multivariate data analysis and modeling in vitro and in vivo studies on a wide variety of chemicals such as petroleum hydrocarbons, aldehydes, food contaminants, industrial solvents, and mycotoxins. Other major activities focus on the development of safety evaluation strategies for mixtures such as the use of toxic equivalence factors or alternatives such as the question-and-answer approach, fractionation followed by recombination of the mixture in combination with a mixture design, and quantitative structure-activity relationship analysis combined with lumping analysis and physiologically based pharmacokinetic/pharmacodynamic modeling for studying complex mixtures. A scheme for hazard identification and risk assessment of complex mixtures and a consistent way to generate total volatile organic compound values for indoor air have also been developed. Examples of other activities are carcinogenicity studies on complex mixtures (petroleum middle distillates, foundry fumes, pesticides, heterocyclic amines, diesel exhaust, solid particles), neurotoxicity studies of mixtures of solvents alone or in combination with exposure to physical factors, and toxicity studies of outdoor air pollutants, focusing on particulates. Outside the United States, toxicologists and regulators clearly have a growing interest in the toxicology and risk assessment of chemical mixtures.

Concomitant exposure to carbon black particulates enhances ozone-induced lung inflammation and suppression of alveolar macrophage phagocytosis

The goal of this study was to investigate whether coexposures to carbon black and O3 result in a toxicologic interaction in the lungs as quantitated by the inflammatory response and alveolar macrophage (AM) phagocytosis. This aim was accomplished through inhalation coexposures of Swiss mice for 4 h to target concentrations of 10 mg/m3 of carbon black and 1.5 ppm O3, or exposure to either agent alone. As a control for the coexposure experiments, mice were also exposed for 4 h to carbon black, followed immediately thereafter by exposure for 4 h to O3, or vice versa. At 24 h after exposure, the lungs of the animals were lavaged for quantitation of total and differential cell counts and assessment of AM Fc-receptor-mediated phagocytosis. Exposure to carbon black did not result in an inflammatory response, nor had it any effect on AM phagocytosis. Ozone exposure resulted in an inflammatory response in the lungs and suppression of AM phagocytosis. Both biologic parameters were significantly enhanced following combined exposure to the particle and the gas. Carbon black exposure either before or after O3 had no significant effect on AM phagocytosis as compared to O3 exposure alone. These data demonstrate the toxicologic interaction of coexposures to an inert particle and O3 on well-accepted biologic markers pulmonary toxicity. The mechanism for the enhanced biologic effect may be that the carbon black particle acts as a carrier mechanism for O3 to areas in the distal lung not accessible to O3 in the gaseous phase or that O3 alters the physicochemistry of the particulate from a nontoxic to a toxic form.