Effects of fine and ultrafine sulfuric acid aerosols in guinea pigs: Alterations in alveolar macrophage function and intracellular pH

Abstract

Acidic sulfate is the most toxicologically important sulfur oxide which exists in the ambient air. To determine if particle size influences toxic effects of sulfuric acid, we investigated the effects of sulfuric acid aerosols of two different sizes on biochemical and cellular parameters of bronchoalveolar lavage fluid from exposed guinea pigs. Guinea pigs were exposed to fine (mass median diameter, 0.3 μm), and ultrafine (mass median diameter, 0.04 μm) sulfuric acid aerosols at 300 μg/m³ for 3 hr/day. The animals were euthanized immediately and 24 hr after 1 and 4 days of exposure and lungs were lavaged. Elevated β-glucuronidase, lactate dehydrogenase activities, and total protein concentration as well as decreased cell viability were observed in the lavage after a single exposure to sulfuric acid aerosols of both sizes. These alterations were small, though statistically significant, and transient. No alteration in these parameters was observed after 4 days of exposure to acid aerosols. In contrast, sulfuric acid-induced alterations in alveolar macrophage function were more pronounced and longer lasting. Immediately after a single exposure to fine acid, there was a 2.7-fold increase in the spontaneous tumor necrosis factor (TNF) release over that in the control group while endotoxin-stimulated TNF release was increased by 2.2-fold. In addition, acid aerosols of both sizes increased the TNF release from macrophages after 4 days of exposure, although there was no clear temporal pattern of induction or recovery. Furthermore, immediately after 4 days of exposure to either fine or ultrafine acid, the amount of H₂O₂ that could be induced from baseline production by alveolar macrophages was 2.2-fold higher than that of the controls. The phagocytic function of macrophages was also altered by exposure to sulfuric acid aerosols. Twenty-four hours after single or multiple exposure, fine acid enhanced (as high as 78% above control) the in vitro phagocytic activity of alveolar macrophages while ultrafine acid depressed the phagocytic capacity (as much as 50% below that in the control). In addition to these biochemical parameters and cellular functions, we also measured the intracellular pH (pH_i) of macrophages harvested after exposures to these acid aerosols using a pH-sensitive fluorescent dye. The resting pH_i was depressed after a single exposure to both acid aerosols. The depression in pH_i persisted 24 hr after ultrafine acid exposure. A similar depression of resting pH_i was observed 24 hr after 4 days of exposure to ultrafine acid while the resting pH_i of the groups of animals that were exposed to fine acid was not affected. We conclude that exposure to sulfuric acid can produce pronounced alterations in cellular function and intracellular pH of alveolar macrophages and that sulfuric acid of different particle size produces different patterns of changes in alveolar macrophages.