Manipulation of the L-arginine-nitric oxide pathway in airway inflammation induced by diesel exhaust particles in mice

The role of the L-arginine-nitric oxide (NO) pathway in branchial asthma that is characterized by eosinophilic airway inflammation has not yet been established. We investigated the effects of three different agents on eosinophilic airway inflammation induced by the intratracheal instillation of diesel exhaust particles (DEP) in mice: L-Arginine, the substrate for NO synthases; L-N-G-nitro-L-arginine methyl eater (L-NAME), a relatively selective inhibitor of constitutive NO synthase; and aminoguanidine, a relatively selective inhibitor of inducible NO synthase. The mice received drinking water with or without added drug far a continuous period of 9 weeks plus 4 days. Lung histology showed that airway inflammation with goblet cell proliferation induced by DEP was aggravated by the administration of L-arginine or L-NAME, whereas it was reduced by aminoguanidine. The numbers of neutrophils around the airways in animals that received plain drinking water, L-arginine, L-NAME, and aminoguanidine were 0.98 +/- 0.26, 3.66 +/- 0.81, 1.64 +/- 0.31, and 0.12 +/- 0.04 (number/mm basement membrane), respectively. The numbers of eosinophils around the airways were 0.37 +/- 0.08, 16.1 +/- 6.47, 11.1 +/- 3.59, and 0.21 +/- 0.11, respectively. The numbers of goblet cells in the branchial epithelium were 1.67 +/- 0.80, 16.5 +/- 7.33, 19.0 +/- 3.40, and 0.86 +/- 0.41, respectively. The cellular profiles of the bronchoalveolar lavage fluid also showed that airway inflammation induced by DEP was aggravated by the administration of L-arginine or L-NAME, whereas it was reduced by aminoguanidine. These results suggest that NO produced from inducible NO synthase may have a detrimental effect on the DEP-induced airway inflammation. A relatively selective inhibition of inducible NO synthase by aminoguanidine may have therapeutic value in the inhalant injury. NO derived from constitutive NO synthase may afford protection against the airway inflammation induced by DEP. (C) 1999 Elsevier Science Ireland Ltd. All rights reserved.