ALPHA(1)-ANTITRYPSIN PITTSBURGH (MET(358)-]ARG) INHIBITS THE CONTACT PATHWAY OF INTRINSIC COAGULATION AND ALTERS THE RELEASE OF HUMAN NEUTROPHIL ELASTASE DURING SIMULATED EXTRACORPOREAL-CIRCULATION

Cardiopulmonary bypass prolongs bleeding time, increases postoperative brood loss, and triggers activation of plasma proteolytic enzyme syst ems and blood cells referred to as the ''whole body inflammatory respo nse'', Contact of blood with synthetic surfaces leads to qualitative a nd quantitative alterations in platelets, neutrophils, contact and com plement systems. Contact and complement pathway proteins both induce n eutrophil activation. alpha(1)-antitrypsin Pittsburgh (MET(358) --> Ar g), a mutant of alpha(1)-antitrypsin, is a potent inhibitor of plasma kallikrein and thrombin. We investigated whether this recombinant muta nt protein inhibited platelet activation, as well as contact and/or co mplement-induced neutrophil activation during simulated extracorporeal circulation. Arg(358) alpha(1)-antitrypsin did not prevent the 34% dr op in platelet count at 5 min of recirculation, did not block the 50% decrease in ADP-induced platelet aggregation at 120 min of recirculati on, nor inhibit the release of 6.06 +/- 1.07 mu g/ml beta-thromboglobu lin at 120 min of recirculation suggesting that the inhibitor had litt le effect on platelet activation. However, Arg(358) alpha(1)-antitryps in totally blocked kallikrein-C ($) over bar 1-inhibitor complex forma tion but not C ($) over bar 1-C ($) over bar 1-inhibitor complex forma tion. Most importantly, Arg(358) alpha(1)-antitrypsin decreased the re lease of 1.11 +/- 0.16 mu g/ml human neutrophil elastase by 43%. The a ttenuation of neutrophil activation in the absence of an effect on com plement activation via the classical pathway, supports the concept tha t kallikrein is a major mediator of neutrophil degranulation during ca rdiopulmonary bypass.