Effects of concentrated ambient particles and diesel engine exhaust on allergic airway disease in Brown Norway rats

Abstract

Increased concentrations of airborne fine particulate matter (PM2.5; particulate matter with an aerodynamic diameter < or = 2.5 microm) are associated with increases in emergency room visits and hospitalizations of asthmatic patients. Emissions from local stationary combustion sources (e.g., coal-burning power plants) or mobile motor vehicles (e.g., diesel-powered trucks) have been identified as potential contributors to the development or exacerbation of allergic airway disease. In the present study, a rodent model of allergic airway disease was used to study the effects of concentrated ambient particles (CAPs) or diesel engine exhaust (DEE) on the development of allergic airway disease in rats sensitized to the allergen ovalbumin (OVA). The overall objective of our project was to understand the effects of PM2.5 on the development of OVA-induced allergic airway disease. Our specific aims were to test the following hypotheses: (1) exposure to CAPs during OVA challenge enhances epithelial remodeling of the airway and inflammation in rats previously sensitized to the allergen; and (2) exposure to DEE during OVA sensitization, or during OVA challenge, exacerbates epithelial remodeling of the airway and inflammation in rats. In the DEE studies, Brown Norway (BN) rats were sensitized with three daily intranasal (IN) instillations of 0.5% OVA, and then two weeks later were challenged with IN OVA or saline for 3 consecutive days. Rats were exposed to DEE diluted to mass concentrations of 30 or 300 microg/m3 diesel exhaust particles (DEPs) or to filtered air during either the sensitization or challenge periods. For the CAPs studies, the same OVA sensitization and challenge rat model was used but exposures to Detroit, Michigan, CAPs were limited to the OVA challenge period. Two separate 3-day CAPs exposures were conducted (week 1, high mean mass concentration = 595 microg/m3; week 2, low mean mass concentration = 356 microg/m3) during OVA challenge. In both the DEE and CAPs studies, rats were killed 24 hours after the last OVA challenge, bronchoalveolar lavage fluid (BALF) was collected and analyzed for cellularity and secreted mediators, and lungs and nose were processed for histopathologic examination and morphometric analysis of intraepithelial mucosubstances (IM). The results of our animal inhalation studies in the southwest (SW) Detroit community, an area with elevated ambient PM2.5 concentrations, suggested that, during allergen challenge, exposure to CAPs that were predominantly associated with emissions from combustion sources markedly enhanced the OVA-induced allergic airway disease, which was characterized by an increased infiltration in the lungs of eosinophilic and lymphocytic inflammation, increased IM in conducting airways, and increased concentrations in BALF of mucin-specific proteins and inflammatory cytokines. These findings suggest that urban airborne PM2.5 derived from stationary combustion sources (e.g., refineries, coal-burning power plants, waste-treatment plants) may enhance the development of human allergic airway diseases like childhood asthma. Previous animal inhalation studies in this community have also suggested that these fine, ambient combustion-derived particles may also exacerbate preexisting allergic airway disease. In contrast to our CAPs studies in Detroit, the controlled DEE exposures of allergen-sensitized BN rats, during either allergen sensitization or challenge periods, caused only a few mild modifications in the character of the allergen-induced disease. This finding contrasts with other reported studies that indicate that DEPs at relatively higher exposure doses do enhance allergic airway disease in some rodent models. The reasons for these disparities between studies likely reflect differences in exposure dose, animal models, the timing of exposures to the allergens and DEP exposures, the methods of allergen sensitization and challenge, or physicochemical differences among DEEs.