fibrinopeptide-a and Asthma

Previously we isolated a new trypsin-like enzyme designated human airway trypsin-like protease (HAT) from human sputum. In this study, we examined in vitro whether HAT was related to the prevention of fibrin deposition in the airway lumen by cleaving fibrinogen. In mucoid sputum samples from patients with chronic airway diseases, the concentration of fibrinogen, as measured by ELISA, was in the range of 2-20 micrograms/ml, and trypsin-like activity, as measured by spectrofluorometry was in the range of 10-50 milliunits (mU)/ml. We showed by gel filtration that the trypsin-like activity of mucoid sputum was mainly due to HAT. We examined the effects of HAT on human fibrinogen at pH 7.4 and 8.6. Fibrinogen was used at concentrations of 4-2,000 micrograms/ml and HAT purified from sputum at concentrations of 0.6-10 mU/ml. As shown by SDS-polyacrylamide gel electrophoresis, HAT cleaved fibrinogen, especially its alpha-chain, regardless of the concentration of fibrinogen. Pretreatment of fibrinogen with HAT resulted in a decrease or complete loss of its thrombin-induced clotting capacity, depending on the duration of pretreatment with HAT and the concentration of HAT. From these results we postulated that HAT may participate in the anticoagulation process within the airway, especially at the level of the mucous membrane, by cleaving fibrinogen transported from the blood stream.

Topics: Albumins; Asthma; Chromatography, Gel; Fibrinogen; Fibrinopeptide A; Humans; Lung Diseases, Obstructive; Pancreatic Elastase; Serine Endopeptidases; Sputum; Thrombin

There have been several reports on alterations of platelet function and raised plasma heparin levels in symptom-free atopic subjects. Either of these can affect formation of thrombin in vivo. In 25 symptom-free atopic patients and 32 healthy volunteers we studied the generation of thrombin in blood emerging from a standardized skin microvasculature injury, which also served to determine bleeding time. Generation of thrombin was delayed in atopics. They produced significantly less thrombin (P less than 0.01) during the early and central phase of haemostasis. The amount of thrombin generated was inversely correlated to bleeding time, which in atopics was on average 50 sec longer than in controls (P = 0.055). Two hours after ingestion of 500 mg aspirin, this difference increased up to 150 sec, although the individual responses varied markedly (P = 0.08), while the generation of thrombin became strongly depressed in both groups. The possible clinical relevance of the delayed formation of thrombin in atopy awaits further studies.

Topics: Aspirin; Asthma; Bleeding Time; Fibrinopeptide A; Hemostasis; Humans; Rhinitis, Allergic, Seasonal; Thrombin