Thomas F. Slaughter

Characterization of prothrombin activation during cardiac surgery by hemostatic molecular markers.

BackgroundProthrombin activation represents the key regulatory step in the hemostatic process. Once formed, thrombin contributes to the generation of fibrin as well as the activation of platelets and fibrinolysis. Failure to suppress thrombin formation during cardiac surgery could result in disorders of hemostasis and thrombosis in the perioperative period. The aim of this study was to determine the time course for prothrombin activation during the perioperative period associated with cardiac surgery. MethotdsWe measured prothrombin activation during the perioperative period in 19 adult patients undergoing primary cardiac surgery using enzyme-linked immunosorbent assays for the detection of thrombin formation (prothrombin fragment 1.2 and thrombin-antithrombin III complex) and thrombin activity (fibrinopeptide A and fibrin monomer). Blood samples were obtained preoperatively; at 30-min intervals during cardiopulmonary bypass (CPB); and 1, 3, and 20 h after completion of CPB. ResultsDespite anticoagulation with heparin, plasma concentrations of prothrombin fragment 1.2, thrombin-antithrombin III complex, and fibrin monomer increased throughout CPB. Peak concentrations for all hemostatic markers occurred in the samples obtained 3 h after completion of CPB. By the morning after surgery, plasma prothrombin fragment 1.2 returned to preoperative concentrations; however, fibrinopeptide A and fibrin monomer concentrations remained significantly increased (P < 0.05) compared to preoperative values. ConclusionsThese data clearly demonstrate the occurrence of prothrombin activation and thrombin activity during CPB despite heparin concentrations adequate to maintain the activated clotting time greater than 400 s. Hemostatic markers for the activation of prothrombin demonstrated peak concentrations 3 h after completion of CPB with a return to baseline concentrations by the morning after surgery. Markers for thrombin activity, however, suggest the presence of active thrombin through the morning after surgery. Further investigations will be necessary to determine the role of hemostatic activation in thrombotic complications after cardiac surgery.

Regulation of Human Tissue Transglutaminase Function by Magnesium-Nucleotide Complexes IDENTIFICATION OF DISTINCT BINDING SITES FOR Mg-GTP AND Mg-ATP

Tissue transglutaminase (tTG) catalyzes a Ca2+-dependent transglutaminase (TGase) activity that stabilizes tissues and a GTP hydrolysis activity that regulates cell receptor signaling. The purpose of this study was to examine the true substrates for nucleotide hydrolysis and the effects of these substrates on modulating the dual enzymatic activities of tTG. We found that Mg-GTP and Mg-ATP are the true substrates of the hydrolysis reaction. tTG hydrolyzed Mg-GTP and Mg-ATP at similar rates and interacted with Mg-ATP (K m = 38 ± 10 μm) at a 3-fold greater steady-state affinity than with Mg-GTP (K m = 130 ± 35 μm). In addition, Mg-ATP inhibited GTP hydrolysis (IC50 = 24 μm), whereas 1 mm Mg-GTP reduced ATP hydrolysis by only 20%. Furthermore, the TGase activity of tTG was inhibited by Mg-GTP, Mg-GDP, and Mg-GMP, with IC50 values of 9, 9, and 400 μm, respectively, whereas the Mg-adenine nucleotides were ineffective. Kinetic analysis of the hydrolysis reaction demonstrates the presence of separate binding sites for Mg-GTP and Mg-ATP. Finally, we found that Mg-GTP protected tTG from proteolytic degradation by trypsin, whereas Mg-ATP was ineffective. In conclusion, we report that Mg-GTP and Mg-ATP can bind to distinct sites and serve as substrates for nucleotide hydrolysis. Furthermore, binding of Mg-GTP causes a conformational change and the inhibition of TGase activity, whereas Mg-ATP is ineffective. The implication of these findings in regulating the intracellular and extracellular function of tTG is discussed.

Cost-Benefit and Efficacy of Aprotinin Compared with ε-Aminocaproic Acid in Patients Having Repeated Cardiac Operations A Randomized, Blinded Clinical Trial

Background: Aprotinin and epsilon‐aminocaproic acid are routinely used to reduce bleeding during cardiac surgery. The marked difference in average wholesale cost between these two drug therapies (aprotinin,

C-terminal Deletion of Human Tissue Transglutaminase Enhances Magnesium-dependent GTP/ATPase Activity

1,080 vs. epsilon‐aminocaproic acid,

Thromboelastography as a perioperative measure of anticoagulation resulting from low molecular weight heparin : a comparison with anti-Xa concentrations

11) has generated significant controversy regarding their relative efficacies and costs. Methods: In a multicenter, randomized, prospective, blinded trial, patients having repeated cardiac surgery received either a high‐dose regimen of aprotinin (total dose, 6 x 106 kallikrein inactivator units) or epsilon‐aminocaproic acid (total dose, 270 mg/kg). Results: Two hundred four patients were studied. Overall (data are median [25th‐75th percentiles]), aprotinin‐treated patients had less postoperative thoracic drainage (511 ml [383–805 ml] vs. 655 ml [464–1,045 ml]; P = 0.016) and received fewer platelet transfusions (0 [range, 0–1] vs. 1 [range, 0–2]; P = 0.036). The surgical field was more likely to be considered free of bleeding in aprotinin‐treated patients (44% vs. 26%; P = 0.012). No differences, however, were seen in allogeneic erythrocyte transfusions or in the time required for chest closure. Overall, direct and indirect bleeding‐related costs were greater in aprotinin‐ than in epsilon‐aminocaproic acid‐treated patients (

The effects of epsilon-aminocaproic acid on fibrinolysis and thrombin generation during cardiac surgery.

1,813 [

Reversible shear-mediated platelet dysfunction during cardiac surgery as assessed by the PFA-100® platelet function analyzer

1,476–2,605] vs.

Antifibrinolytic drugs and perioperative hemostasis

1,088 [range,

Antiphospholipid syndrome and cardiac surgery: management of anticoagulation in two patients.

511–2,057]; P = 0.0001). This difference in cost per case varied in magnitude among sites but not in direction. Conclusions: Aprotinin was more effective than epsilon‐aminocaproic acid at decreasing bleeding and platelet transfusions. Epsilon‐aminocaproic acid, however, was the more cost‐effective therapy over a broad range of estimates for bleeding‐related costs in patients undergoing repeated cardiac surgery. A cost‐benefit analysis using the lower cost of half‐dose aprotinin (

Hemostatic effects of antithrombin III supplementation during cardiac surgery : results of a prospective randomized investigation

540) still resulted in a significant cost advantage using epsilon‐aminocaproic therapy (P = 0.022).