THROMBIN AND HUMAN PLASMA KALLIKREIN INHIBITION DURING SIMULATED EXTRACORPOREAL-CIRCULATION BLOCK PLATELET AND NEUTROPHIL ACTIVATION

Cardiopulmonary bypass causes hemorrhagic complications, and initiates a chemical and cellular inflammatory response. Contact of blood with synthetic surfaces leads to qualitative and quantitative alterations i n platelets, neutrophils, complement, and contact systems. Despite the fact that cardiopulmonary bypass is carried out in the presence of hi gh doses of heparin, there is significant activation of both platelets and neutrophils. Thrombin is protected on cell and fibrin surfaces fr om antithrombin, even in the presence of high doses of heparin (simila r to 5 U/ml). We therefore studied the effect of a small (Mr = 497), h ighly effective (Ki = 41 pM), reversible tripeptide inhibitor of throm bin, DUP 714 (1 mu M), in a well characterized model of simulated extr acorporeal circulation. ln the absence of DUP 714, platelet counts dec reased by 75% 5 min after the start of extracorporeal bypass and incre ased to 48% at 120 min of recirculation. DUP 714 significantly preserv ed platelet counts, decreased plasma levels of platelet beta-thrombogl obulin levels, but did not prevent a decrease in sensitivity of platel ets to adenosine diphosphate. Kallikrein-C1-inhibitor and C1-C1-inhibi tor complexes increased progressively from 0.32 U/ml to 0.67 U/ml and from 4.45 U/ml to 7.25 U/ml, respectively, during 120 min of recircula tion without DUP 714. Addition of DUP 714 significantly inhibited kall ikrein-C1-inhibitor complex formation but did not affect C1-C1-inhibit or complexes. In the absence of DUP 714, human neutrophil elastase lev els rose from a baseline of 0.01 +/- 0.00 mu g/ml to 1.18 +/- 0.21 mu g/ml during 120 min of recirculation. Human neutrophil elastase releas e at 120 min was significantly inhibited in the presence of DUP 714 to 37% of the value with heparin alone. These results indicated that add ition of this novel thrombin (and kallikrein) inhibitor to heparin pre served platelet counts, decreased platelet secretion, and provided the additional benefit of partially blocking neutrophil activation during simulated extracorporeal circulation.