Plasma levels of elastase-specific fibrinopeptides correlate with proteinase inhibitor phenotype: Evidence for increased elastase activity in subjects with homozygous and heterozygous deficiency of α,-proteinase inhibitor

Abstract

There is indirect evidence that unopposed human neutrophil elastase (HNE) is responsible for emphysema in patients with α1-proteinase inhibitor (Pi) deficiency. To directly explore this possibility, we developed an assay for fibrinopeptide Aα1-21 and its degradation products and used it to measure HNE activity in 128 subjects of known Pi phenotype. The mean elastase-specific fibrinopeptide (ESF) level in 49 deficient PiZ individuals is significantly higher than that in 56 PiMZ heterozygotes (4.5 and 1.5 nM, respectively; P < 0.01), while the mean ESF value in heterozygotes is significantly elevated over that in 23 normal PiM subjects (1.5 and 0.6 nM, respectively; P < 0.01), consistent with increased HNE activity in those deficient in the major regulator of the enzyme. These results are not due to differences in smoking history because after correction for pack-years of smoking, ESF values in PiZ subjects are fourfold higher than those in PiMZ individuals (P = 0.005), while the ESF levels in heterozygotes are threefold higher than those in PiM subjects (P = 0.02). In addition, this analysis suggests that cigarette smoking and α1-proteinase inhibitor deficiency have additive effects on ESF levels thereby explaining why PiZ and some PiMZ individuals are at especially high risk for the development of lung disease if they smoke. Finally, the observation that ESF levels in nonsmoking PiZ subjects are inversely related to the percent of predicted forced expiratory volume in 1 s (FEV1%) provides direct support for the concept that unregulated HNE activity causes alveolar septal destruction in patients with α1-proteinase inhibitor deficiency.