Effect of a topical corticosteroid on airway hyperresponsiveness and eosinophilic inflammation induced by trimellitic anhydride exposure in sensitized guinea pigs

Background: Topical corticosteroids are effective in the treatment of asthma by improving bronchial hyperresponsiveness and reducing airway inflammation. Methods: We assessed the effect of a nebulized corticosteroid, budesonide, on airway hyperresponsiveness and inflammatory response provoked by inhalation of trimellitic anhydride (TMA) dust, a known cause of occupational asthma in human beings, in guinea pigs sensitized to the free hapten. Male Dunkin-Hartley guinea pigs ( n = 24) were injected intradermally with 0.1 ml of 0.3% TMA in corn oil, followed by exposure 21 to 28 days later to five consecutive doses of budesonide aerosol (0.5 mg/ml) or saline solution, administered for 10 minutes every 12 hours. They were then exposed (noses only) to TMA dust (8 mg/m 3) or air for 1 hour (four groups, n = 6 in each). Airway responsiveness to acetylcholine, defined as the concentration needed to cause a 200% increase in lung resistance (PC 200), was measured 8 hours later. Results: In saline-treated guinea pigs exposed to TMA, mean PC 200 was 0.094 mmol/L (geometric SEM, 1.4 mmol/L) compared with 0.31 mmol/L (geometric SEM, 1.3 mmol/L, p < 0.05) in those guinea pigs pretreated with budesonide. In sham-exposed sensitized guinea pigs, PC 200 was 0.35 mmol/L (geometric SEM, 1.2 mmol/L), which was not significantly different from the budesonide-treated group (0.36 mmol/L; geometric SEM, 1.3 mmol/L). There was a significant increase in the number of eosinophils in the subepithelium of guinea pigs further exposed to TMA dust (71.5 ± 6.8 cells/unit area [mean ± SEM]) compared with those exposed to air (22.7 ± 6.7, p < 0.01). Budesonide did not inhibit the number of subepithelial eosinophils of guinea pigs exposed to TMA dust (54.0 ± 3.7cells/unit area) or in those exposed to air (24.3 ± 6.7 cells/unit area) and did not affect the increase in eosinophlis found in bronchoalveolar fluid. Conclusions: Budesonide significantly inhibited the increase in airway responsiveness but not the eosinophilic inflammation induced by exposure to TMA dust in sensitized guinea pigs.