Final Report: Particulate Air Pollution and Initiation of Asthma

EPA Grant Number: R826779
Title: Particulate Air Pollution and Initiation of Asthma
Investigators: Kobzik, Lester , Gonzalez-Flecha, Beatriz , Shore, Stephanie , Koutrakis, Petros
Institution: Harvard University
EPA Project Officer: Chung, Serena
Project Period: October 1, 1998 through September 30, 2001
Project Amount: $557,340
RFA: Health Effects of Particulate Matter and Associated Air Pollutants (1998) RFA Text |  Recipients Lists
Research Category: Air Quality and Air Toxics , Health Effects , Air , Particulate Matter

Objective:

This research project had two specific aims. Specific Aim 1 sought to determine the effects of air pollution particulates on responses to inhaled antigen. In this aim, the response of developing mice (1-3 weeks old) to aerosolized antigen +/- exposure to inhaled oxidant air pollution was studied. The combustion source particulate, residual oil fly ash (ROFA), and concentrated ambient air particulates (CAPs) were primarily studied. For the latter, exposures in the Harvard ambient air concentrator were used to test unaltered "real-world" particulates. Physiologic (airway hyperresponsiveness), pathologic (airway inflammation), and immunologic (total and allergen specific IgE, IgG levels) features of the asthmatic phenotype were measured. Also, dose-response relationships for pollutant effects, age of susceptibility, and persistence of hypersensitivity were tested.

Specific Aim 2 sought to determine the role of oxidant injury in air pollution-mediated initiation of airway hypersensitivity. These experiments sought to test the hypothesis that oxidant-components of air pollution are critical for initiation of hypersensitivity to inhaled antigens. Oxidant stress in situ in the lungs of mice exposed to particulates have been measured. Also, this hypothesis was tested by use of pharmacologic interventions with in vivo administration of anti-oxidants (e.g., DMTU) to abrogate air pollution effects.

Summary/Accomplishments (Outputs/Outcomes):

The potential effects of air pollution on immune responses to inhaled allergens in developing lungs were sought by using very young mice. Neonatal mice were repeatedly exposed to aerosolized ovalbumin (3 percent OVA in PBS, 10 minutes/day, days 5-15 of age). Some mice also were exposed to leachate of residual oil fly ash (ROFA-s, a surrogate for ambient air particles; 30 minutes, on days 6, 8, and 10 of age). Repeated exposure of very young mice to allergen alone (OVA) or pollutant alone (ROFA-s) had no effect on airway hyperresponsiveness (AHR, measured as Penh by noninvasive plethysmography at day 16 of age) and did not cause inflammation or OVA-specific antibody production. Similar exposures of adult mice did result in AHR after either OVA alone or OVA + ROFA-s, without evidence of enhancement by combined exposure. In contrast, very young mice exposed to both OVA and ROFA-s showed significantly increased AHR (e.g., Penh, 50 mg/ml methacholine, OVA +ROFA-s vs. OVA alone: 2.6 + 0.4, 1.2 + 0.1, p < .01, n > 15) and produced OVA-specific IgE and IgG upon allergen challenge 1 week later. Immunostaining of airways from mice at day 11 showed a marked increase in Ia+ cells after OVA + ROFA-s exposure. It is concluded that exposure to pollutant aerosols can disrupt normal resistance to sensitization to inhaled allergens and thereby promote development of airway hypersensitivity in this neonatal/juvenile mouse model.

Further characterization was sought of the pulmonary effects of ROFA, an experimentally useful surrogate for combustion-derived particulates in ambient air. Mice were exposed to aerosols of ROFA-s. Physiologic testing of airway function (noninvasive plethysmography) showed increased Penh, an index of AHR in a time and dose-dependent manner after exposure to ROFA-s (see Figure 1). BAL analysis showed a minor influx of neutrophils, which was maximal 12 hours after exposure, and essentially resolved by the time point of maximal AHR (48 hours after exposure). The AHR caused by ROFA-s was reproduced by a mixture of its major metal components (Ni, V, Zn, Co, Mn, Cu), but not by any individual metal alone. Systemic pretreatment of mice with the antioxidant dimethylthiourea abrogated ROFA-s mediated AHR. Analysis of mice of varying ages showed that ROFA-s had no marked effect on airway responsiveness of 2-week old mice, in contrast to the AHR seen in 3- and 8-week old mice. ROFA-s-mediated AHR was unchanged in neurokinin 1 receptor knockout mice and mice treated with a neurokinin antagonist, arguing against a role for this mediator in ROFA-s mediated effects. Data indicate that ROFA-s mediates AHR in mice through anti-oxidant sensitive mechanisms that require multiple metal constituents. Maturational differences in susceptibility to ROFA-induced AHR may be useful for further studies of mechanisms of particle effects.

We next tested whether exposure to CAPs also would promote initiation of an asthma-like phenotype, as observed with exposure to ROFA (OVA/ROFA-s). Using a similar protocol, cohorts of very young mice were exposed to inhaled ovalbumin allergen for 10 consecutive days (ages 5-15 days after birth). One group (OVA/CAPs) also was exposed to CAPs (5 hours/day, days 6, 8, and 10 of life, average concentration ~250 µg/m3), while the other group was exposed only to filtered air (OVA/AIR). On day 16, pulmonary function testing was performed, followed by analysis of pulmonary inflammation by bronchoalveolar lavage.

Figure 1
Figure 1.

In contrast to the results seen with co-exposure to ROFA leachate, no effect of CAPs exposure was found on development of allergic sensitization to aerosolized ovalbumin (n>12 each group). Both groups showed similar and minimal responsiveness to increasing concentrations of methacholine. BAL analysis showed absence of inflammatory cells in both groups (e.g, percent eosinophils: OVA/AIR = 1.4+0.6; OVA CAPs = 0.6+0.3). These negative findings were repeated in multiple cohorts (litters). It is concluded that exposure to CAPs under these conditions does not promote initiation of the asthma phenotype in this mouse model.

As part of these studies, it was investigated whether co-exposure to inhaled ambient particles and ozone affects airway responsiveness (AR, measured as enhanced pause, Penh) and allergic inflammation (AI) in a murine model of asthma. Ovalbumin-sensitized mice were challenged with either ovalbumin ("asthmatic") or PBS aerosols for 3 successive days. Immediately after daily challenge, mice were exposed for 5 hours to CAPs, 0.3 ppm ozone, both, or neither (n>61/group, 12 experiments). Exposure to CAPs alone or co-exposure to CAPs + O3 caused an increase in Penh in both normal and "asthmatic" mice. These responses were transient and small, increasing approximately 0.9 percent per 100 g/m3 increase in CAPs. Analysis of the effects of particle composition on AR revealed an association between the AlSi particle fraction and increased AR in "asthmatic" mice exposed to ozone and particles. No effects of pollutants on AI were noted. It is concluded that: (1) particle exposure causes an immediate, short-lived (< 24 hour) increase in AR in mice; (2) these responses are small; and (3) changes in AR may be correlated with specific elements within the particle mixture. The small magnitude of changes seen in these experiments are consistent with the lack of effect seen in the initiation experiments described above.

The research findings support two major conclusions. First, inhalation of toxicologic levels of pollutant (e.g., leachate of ROFA) can indeed promote initiation of allergic sensitization to inhaled allergen in young mice. Second, similar episodes of inhalation of arguably more realistic and less toxic amounts of concentrated air particles does not promote initiation of the allergic sensitization in this model.


Journal Articles on this Report : 4 Displayed | Download in RIS Format

Other project views: All 4 publications 4 publications in selected types All 4 journal articles
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Journal Article Goldsmith C-AW, Ning YY, Qin G, Imrich A, Lawrence J, Murthy GGK, Catalano PJ, Kobzik L. Combined air pollution particle and ozone exposure increases airway responsiveness in mice. Inhalation Toxicology 2002;14(4):325-347. R826779 (Final)
R824790 (Final)
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  • Journal Article Hamada K, Goldsmith C-A, Kobzik L. Increased airway hyperresponsiveness and inflammation in a juvenile mouse model of asthma exposed to air-pollutant aerosol. Journal of Toxicology And Environmental Health-Part A 1999;58(3):129-143. R826779 (Final)
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  • Journal Article Hamada K, Goldsmith C-A, Goldman A, Kobzik L. Resistance of very young mice to inhaled allergen sensitization is overcome by coexposure to an air-pollutant aerosol. American Journal of Respiratory and Critical Care Medicine 2000;161(4):1285-1293. R826779 (Final)
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  • Journal Article Hamada K, Goldsmith C-A, Suzaki Y, Goldman A, Kobzik L. Airway hyperresponsiveness caused by aerosol exposure to residual oil fly ash leachate in mice. Journal of Toxicology and Environmental Health-Part A 2002;65(18):1351-1365. R826779 (Final)
    R825702 (Final)
    R827353 (Final)
    R827353C014 (Final)
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  • Supplemental Keywords:

    sensitive populations, children, infants, human health., RFA, Health, Scientific Discipline, Air, particulate matter, Toxicology, Environmental Chemistry, Health Risk Assessment, Risk Assessments, Susceptibility/Sensitive Population/Genetic Susceptibility, Allergens/Asthma, Children's Health, genetic susceptability, ambient air quality, asthma, particulates, sensitive populations, co-factors, cytokine production, adolescence, air toxics, copollutants, infants, morbidity, PM 2.5, airway disease, allergic airway, exposure, respiratory problems, air pollution, children, Human Health Risk Assessment, laboratory animals, susceptible subpopulations, asthmatic phenotype, airborne pollutants, chronic health effects, human exposure, inhalation, susceptibility, children's vulnerablity, assessment of exposure, childhood respiratory disease, Acute health effects, environmental toxicant, inhaled, sensitive subgroups, environmentally caused disease, human susceptibility, acute exposure, human health risk, hypersensitive people, metals, respiratory, oxidant stress

    Progress and Final Reports:

    Original Abstract
  • 1999
  • 2000