1-3-dimethylthiourea and Bronchial-Hyperreactivity

A prior airway exposure to wood smoke induces a tachykinin-dependent increase in airway responsiveness to the subsequent smoke inhalation in guinea pigs (Life Sci. 63: 1513, 1998). To further investigate the time course of, and the contribution of other chemical mediators to, this smoke-induced airway hyperresponsiveness (SIAHR), two smoke challenges (each 10 ml) separated by 30 min were delivered into the lungs of anesthetized guinea pigs by a respirator. In the control animals, the SIAHR was evidenced by the bronchoconstrictive response to the second smoke challenge (SM2) which was approximately 5.2-fold greater than that to the first challenge (SM1). This SIAHR was alleviated by shortening the elapsed time between SM1 and SM2 to 10 min or by extending it to 60 min, and was abolished by extending it to 120 min. This SIAHR was reduced by pretreatment with either MK-571 (a leukotriene D4-receptor antagonist) or dimethylthiourea (a hydroxyl radical scavenger), but was not affected by pretreatment with either pyrilamine (a histamine H1-receptor antagonist) or indomethacin (a cyclooxygenase inhibitor). The smoke-induced reduction in the neutral endopeptidase activity (a major enzyme for tachykinin degradation) measured in airway tissues excised 30 min post SM1 was largely prevented by pretreatment with dimethylthiourea. However, this reduction was not seen in airway tissues excised 120 min post SM1. These results suggest that 1) the SIAHR to inhaled wood smoke has a rapid onset time following smoke inhalation and lasts for less than two hours, 2) leukotrienes and hydroxyl radical may play contributory roles in the development of this SIAHR, and 3) hydroxyl radical is the major factor responsible for the smoke-induced inactivation of airway neutral endopeptidase, which may possibly participate in the development of this SIAHR.

Topics: Animals; Bronchial Hyperreactivity; Bronchodilator Agents; Guinea Pigs; Hydroxyl Radical; Leukotriene Antagonists; Leukotrienes; Male; Neprilysin; Propionates; Quinolines; Smoke; Thiourea; Wood

Asthma and its exacerbation by air pollution are major public health problems. This investigation sought to more precisely model this disorder, which primarily affects children, by using very young mice. The study first attempted to create allergic airway hypersensitivity in neonatal mice and to determine if physiologic testing of airway function was possible in these small animals. Neonatal mice were sensitized by i.p. injection of ovalbumin (OVA, 5 microg) and alum (1 mg) at 3 and 7 d of age. One week later, mice were challenged by allergen nebulization (3% OVA in PBS, 10 min/d, d 14-16). OVA-exposed mice showed: (1) increased airway hyperresponsiveness (AHR) to methacholine by whole-body plethysmography; (2) eosinophilia in bronchoalveolar lavage (BAL) fluid; (3) airway inflammation using histopathology techniques; and (4) elevated serum anti-OVA immunoglobulin E. Hence, these neonatal mice were successfully sensitized and manifested "asthmatic" responses after allergen challenge. Experiments were conducted to investigate the effect of one surrogate for ambient air particles, residual oil fly ash (ROFA), on this juvenile asthma model. Aerosolized ROFA leachate (supernatant of 50 mg/ml, 30 min, on d 15) had no marked effect alone, but caused a significant increase in AHR and airway inflammation in OVA-sensitized and challenged mice. This synergistic effect was abrogated by the antioxidant dimethylthiourea (DMTU, 3 mg/kg mouse, i.p.). This model may be useful to study air pollution-mediated exacerbation of asthma in children.

Topics: Aerosols; Air Pollutants; Allergens; Animals; Animals, Newborn; Asthma; Bronchial Hyperreactivity; Bronchitis; Carbon; Coal Ash; Enzyme-Linked Immunosorbent Assay; Free Radical Scavengers; Immunoglobulin E; Mice; Mice, Inbred BALB C; Ovalbumin; Particulate Matter; Phenotype; Plethysmography; Serine Proteinase Inhibitors; Thiourea