A method for the differential determination of plasma antithrombins

α-1-antitrypsin variants and the proteinase/antiproteinase imbalance in chronic obstructive pulmonary disease

The excessive activities of the serine proteinases neutrophil elastase and proteinase 3 are associated with tissue damage in chronic obstructive pulmonary disease. Reduced concentrations and/or inhibitory efficiency of the main circulating serine proteinase inhibitor α-1-antitrypsin result from point mutations in its gene. In addition, α-2-macroglobulin competes with α-1-antitrypsin for proteinases, and the α-2-macroglobulin-sequestered enzyme can retain its catalytic activity. We have studied how serine proteinases partition between these inhibitors and the effects of α-1-antitrypsin mutations on this partitioning. Subsequently, we have developed a three-dimensional reaction-diffusion model to describe events occurring in the lung interstitium when serine proteinases diffuse from the neutrophil azurophil granule following degranulation and subsequently bind to either α-1-antitrypsin or α-2-macroglobulin. We found that the proteinases remained uninhibited on the order of 0.1 s after release and diffused on the order of 10 μm into the tissue before becoming sequestered. We have shown that proteinases sequestered to α-2-macroglobulin retain their proteolytic activity and that neutrophil elastase complexes with α-2-macroglobulin are able to degrade elastin. Although neutrophil elastase is implicated in the pathophysiology of emphysema, our results highlight a potentially important role for proteinase 3 because of its greater concentration in azurophil granules, its reduced association rate constant with all α-1-antitrypsin variants studied here, its greater diffusion distance, time spent uninhibited following degranulation, and its greater propensity to partition to α-2-macroglobulin where it retains proteolytic activity.

The significance of the F variant of alpha-1-antitrypsin and unique case report of a PiFF homozygote

Background

Inheritance of the F variant of alpha-1-antitrypsin is associated with normal circulating protein levels, but it is believed to be dysfunctional in its ability to inhibit neutrophil elastase and therefore has been implicated as a susceptibility factor for the development of emphysema. In this study, its functional characteristics were determined following the identification of a unique patient with the PiFF phenotype, and the implications as a susceptibility factor for emphysema are considered both in homozygotes and heterozygotes.

Methods

Second order association rate constants were measured for M, Z, S and F variants of alpha-1-antitrypsin with neutrophil elastase and proteinase 3. Clinical characteristics of the PiFF homozygote and six PiFZ heterozygote subjects were studied.

Results

The F variant had a reduced association rate constant with neutrophil elastase (5.60 ± 0.83 × 10⁶ M^-1 s^-1) compared to the normal M variant (1.45 ± 0.02 × 10⁷ M^-1 s^-1), indicating an increased time to inhibition that was comparable to that of the Z variant (7.34 ± 0.03 × 10⁶ M^-1 s^-1). The association rate constant for the F variant and proteinase 3 (1.06 ± 0.22 × 10⁶ M^-1 s^-1) was reduced compared to that with neutrophil elastase, but was similar to that of other alpha-1-antitrypsin variants. Of the six PiFZ heterozygotes, five had airflow obstruction and radiological evidence of emphysema. The PiFF homozygote had airflow obstruction but no emphysema. None of the patients had clinical evidence of liver disease.

Conclusions

The F variant may increase susceptibility to elastase-induced lung damage but not emphysema, whereas co-inheritance with the Z deficiency allele may predispose to emphysema despite reasonable plasma concentrations of alpha-1-antitrypsin.

Selective determination of alpha 2-plasmin inhibitor activity in plasma using chromogenic substrate

In determination of antiplasmin activity of alpha 2-plasmin inhibitor (alpha 2 PI) using an amidolytic method, alpha 2-macroglobulin (alpha 2 M) in concentrations present in normal plasma inhibits the cleavage of chromogenic substrates by plasmin even if the reaction time between alpha 2M and plasmin is shortened as much as possible. The purpose of this study was to develop a new method to assay alpha 2 PI selectively with the chromogenic substrate S-2251 using an end-point method. The antiplasmin activity of alpha 2 M was destroyed by the addition of methylamine hydrochloride. In a case of congenital alpha 2 PI deficiency, antiplasmin activity determined with the previous method without the addition of methylamine was 20% of normal plasma, whereas the results obtained using this newly developed method was 5%. A statistically significant correlation between alpha 2 PI levels determined with this method and with a single radial immunodiffusion method was observed in plasma samples collected from 40 healthy subjects and 11 patients with disseminated intravascular coagulation (DIC). In two cases of DIC, in which markedly depleted levels of alpha 2 PI and normal concentrations of alpha 2 M were observed, antiplasmin activities measured without the addition of methylamine were higher than the ones measured immunologically, whereas the results obtained with the method described here were in accordance with the antigenicities of alpha 2 PI.