Elastase-mediated fibrinogenolysis by chemoattractant-stimulated neutrophils occurs in the presence of physiologic concentrations of antiproteinases.

Plasma levels of the HNE-derived fibrinopeptide A alpha 1-21 reflect in vivo enzyme activity. To provide a possible explanation for the presence of circulating A alpha 1-21 in individuals with normal plasma antiproteinase concentrations we investigated whether PMN-associated HNE is more resistant to inhibition than the free enzyme. PMN were stimulated to migrate across 125I-fibrinogen-coated nitrocellulose filters in response to 10(-7) M FMLP, and the extent of fibrinogenolysis was determined by measuring release of A alpha 1-21 and 125I-labeled fibrinogen degradation products. The fibrinogenolytic activity of migrating PMN was then compared with that of free HNE present in PMN lysates or secreted by PMN stimulated with FMLP. Whereas the fibrinogenolytic activity of soluble HNE was completely inhibited by low concentrations (1%) of plasma or serum and macromolecular antiproteinase (alpha 1 proteinase-inhibitor and soybean trypsin-inhibitor), even in the presence of undiluted plasma or serum the activity of the migrating PMN was incompletely blocked (81-85%). Further, concentrations of alpha 1 proteinase-inhibitor and soybean trypsin-inhibitor that totally inhibited free HNE activity also incompletely blocked (88-89%) the fibrinogenolytic activity of migrating PMN, indicating that FMLP-stimulated PMN demonstrate significant fibrinogenolytic activity in the presence of antiproteinases as small as 20,000 mol wt. A specific low molecular weight HNE inhibitor (MeO-Suc-Ala2-Pro-ValCH2Cl), however, totally blocked PMN-mediated fibrinogenolysis without affecting intracellular HNE activity, HNE secretion from PMN, or PMN migration in response to FMLP. These findings support the hypothesis that PMN migrating on a fibrinogen-coated surface form zones of close contact with fibrinogen, thus preventing access of plasma antiproteinases to HNE released at the cell-substrate interface. The occurrence of this phenomenon in vivo would explain the presence of circulating A alpha 1-21 in individuals with normal antiproteinase concentrations.

Development of an assay for in vivo human neutrophil elastase activity. Increased elastase activity in patients with alpha 1-proteinase inhibitor deficiency.

Leukocyte extracts contain enzymes that digest fibrinogen and release a fibrinopeptide A-containing fragment. This study was undertaken to identify the responsible proteinase and to characterize the fibrinopeptide A-containing fragment so that it could be used as an index of enzyme activity. Both the fibrinogenolytic activity and the release of the fibrinopeptide A-containing fragment mediated by the leukocyte extracts were shown to be due to human neutrophil elastase (HNE) by the following criteria: activity was completely blocked by a specific HNE inhibitor or by adsorbing HNE from the extracts with a monospecific antibody and reconstitution with purified HNE restored the ability to release the fibrinopeptide A-containing fragment. This fragment was not released by a variety of other proteinases or by HNE-inhibitor complexes indicating that, at least with respect to the enzymes tested, it is a specific product of HNE and its release requires the free enzyme. By separating the products of HNE digestion of fibrinogen using high performance liquid chromatography, identifying the immunoreactive fractions and subjecting them to amino acid analysis, the fragment was identified as A alpha 1-21, indicating an HNE cleavage site at the Val(A alpha 21)-Glu(A alpha 22) bond. The mean plasma A alpha 1-21 level was markedly higher in patients with alpha 1-proteinase inhibitor deficiency as compared to healthy controls (0.2 nM vs. 7.9 nM; P less than 0.0001), consistent with increased in vivo HNE activity in these individuals.

Development of a radioimmunoassay for the fibrinogen-derived peptide B beta 1-42.

The peptide B beta 1-42 is the initial cleavage product of plasmin-mediated proteolysis of the NH2-terminal region of fibrinogen or fibrin I, while beta 15-42 is the major fragment released by plasmin degradation of fibrin II. Numerous studies have described the measurement of plasma B beta 1-42 levels as an index of plasmin activity. Previous assays were indirect and included quantitation of thrombin-increasable fibrinopeptide B immunoreactivity (TIFPB) or measurement of beta 15-42 with an antiserum (132) which cross-reacted with B beta 1-42. We report on a new antiserum (R142) directed against B beta 1-42 which does not cross-react with beta 15-42 or fibrinopeptide B. Employing this antiserum, a specific assay for B beta 1-42 was developed. This assay was used to measure plasmin-mediated B beta 1-42 release from fibrinogen and its subsequent proteolysis by thrombin. The selectivity constant (Kcat/Km) for thrombin cleavage of the B beta 14-15 bond of B beta 1-42 was 10(5)-fold less than that for proteolysis of the same bond in the intact fibrinogen molecule, thus explaining the stability of this peptide in the presence of thrombin activity in the blood. Similarly, the selectivity constant for plasmin cleavage of the B beta 21-22 bond of B beta 1-42 was 140-fold less than that for proteolysis of the B beta 42-43 bond of fibrinogen, indicating that secondary plasmin attack of the B beta 1-42 molecule is not physiologically important. The specific B beta 1-42 assay provided excellent recovery of peptide added to blood or plasma. Comparison of B beta 1-42 levels with TIFPB values in 37 patient samples yielded good correlation over a wide range of levels (r2 = 0.91). The median plasma B beta 1-42 level in 15 normal individuals was 1.2 pmol/mL. This is similar to the previously reported normal range for TIFPB (1 to 4 pmol/mL) but is higher than the normal level of 0.4 pmol/mL reported with the assay employing antiserum 132. This discrepancy reflects rapid removal of Arg (B beta 42) by plasma carboxypeptidase activity resulting in 50% loss of B beta 1-42 immunoreactivity with antiserum 132 but no loss with R142. To circumvent this problem, we have developed a beta 15-42 antiserum (R154) which, like antiserum 132, cross-reacts with B beta 1-42. However, B beta 1-42/beta 15-42 immunoreactivity with R154 is stable in the presence of carboxypeptidase activity.(ABSTRACT TRUNCATED AT 400 WORDS)

Increased neutrophil elastase activity in cigarette smokers.

We compared plasma levels of the neutrophil elastase-derived fibrinopeptide A-alpha-1-21 in healthy cigarette smokers with those in nonsmokers. The mean A-alpha-1-21 concentration was fivefold higher (95% confidence interval [CI], 3.0 to 9.6) in ten cigarette smokers than in 20 healthy nonsmokers (2.0 nmol/L compared with 0.4 nmol/L; p less than 0.0001). To evaluate the acute effect of smoking on enzyme activity, a second group of ten smokers was studied. After refraining from smoking for 12 hours, each person smoked three cigarettes. The mean A-alpha-1-21 level in the second group of smokers was not different from that in the first group of smokers (1.8 nmol/L compared with 2.0 nmol/L) but was fivefold higher (95% CI, 2.6 to 8.7) than that in the nonsmokers (1.8 nmol/L compared with 0.4 nmol/L; p less than 0.0001). After smoking three cigarettes, subjects had a twofold elevation (95% CI, 1.6 to 3.5) in the mean A-alpha-1-21 concentration (from 1.8 nmol/L to 4.1 nmol/L; p = 0.002). Our data show that cigarette smoking perturbs the in-vivo elastase-antielastase balance and thus may produce lung disease through this mechanism.