Acute effect of nitrogen dioxide exposure on the functional activity of alpha-1-protease inhibitor in bronchoalveolar lavage fluid of normal subjects.

Nitrogen dioxide is one form of an oxidizing free radical that is sufficiently stable to exist in relatively high concentrations in ambient air and cigarette smoke. We examined the effect of NO2 exposure on the functional activity against pancreatic elastase of alpha-1-protease inhibitor (alpha 1PI) in bronchoalveolar lavage (BAL) fluid of nonsmoking subjects. Ten nonsmokers (mean age, 25 +/- 2 SE yr) were exposed to NO2 (3 or 4 ppm) for 3 h with intermittent exercise. Seven nonsmokers (mean age, 24 +/- 2 SE yr) underwent a similar protocol but were exposed to NO2-free air and served as control subjects. Bronchoalveolar lavage was performed 3.5 to 4 h after the end of exposure. Exposure to NO2 caused a 45% decrease in functional activity of alpha 1PI in BAL. There was no significant difference in immunoreactive alpha 1PI between the groups whether expressed as micrograms per 100 ml of recovered fluid or per milligram of albumin. This inactivation of alpha 1PI was not associated with any neutrophil migration into the air spaces of the lung. The "elastaselike" activity of BAL using synthetic elastinlike chromophore substrate succinyl-trialanine-nitroanilide showed no significant difference between the NO2-exposed group (221 +/- 39 SE ng/dl BAL) and the control group (196 +/- 61 SE ng/dl BAL). Assay for human leukocyte elastase (HLE) in concentrated BAL using the synthetic substrate Methoxysuc-Ala3-Pro-Val-aminomethylcoumarin did not detect any HLE activity in the BAL. These results showed that nonsmoking subjects exposed to relatively low concentrations of NO2 for a short time have a significant inactivation of alpha 1PI in the lower respiratory tract fluid than did nonsmoking control subjects.