Excessive neutrophil elastase in bronchoalveolar lavage fluid in subclinical emphysema

In an attempt to further evaluate the role of neutrophil elastase (NE) in the development of emphysema, we examined the immunologic quantity of NE bound to α₁-protease inhibitor (PI), the NE inhibitory activity, and the molecular pattern of α₁-PI in unconcentrated bronchoalveolar lavage fluid (BALF) supernatant from 36 community-based older volunteers. They were classified into three groups: 10 current smokers with low attenuation areas (LAAs) on the lung computed tomography (CT) scans who were considered to have subclinical emphysema, 13 current smokers who had a comparable smoking history but no LAA, and 13 noncurrent smokers without LAA. The concentration of NE-α₁-PI complex was significantly increased in the subjects with subclinical emphysema when compared not only with the noncurrent smokers (0.52 ± 0.10 versus 0.21 ± 0.03 SEM μg/mg albumin, p < 0.01) but also with the LAA(-) current smokers (0.52 ± 0.10 versus 0.23 ± 0.07 SEM μg/mg albumin, p < 0.01). NE inhibitory activity measured by a spectrophotometric method using methoxysuccinyl-alanyl-alanyl-prolyl-valyl-paranitroanilide did not show any significant difference between the two groups of current smokers. There was no difference in the pattern or density of native and proteolysed α₁-PI bands between the three groups by Western blotting. We conclude that NE-α₁-PI complex in BALF is a factor that may differentiate smokers who are potentially developing emphysema from those who are not.