Role of Heparin Induced Tissue Factor Pathway Inhibitor Release in Attenuation of Tissue Factor-Dependent Thrombin Generation During Cardiopulmonary Bypass

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Background: Administration of high doses of heparin causes massive release of tissue factor pathway inhibitor (TFPI) from vascular endothelial cells. However, it is unclear whether TFPI sufficiently attenuates thrombin generation triggered by tissue factor (TF) during cardiopulmonary bypass (CPB). In this study, we purposed to provide evidence to clarify the role of TFPI in attenuation of TF-dependent thrombin generation during and after simulated CPB and primate CPB using Cynomolgus monkeys (Macaca fascicularis) which may provide high or normal plasma level of TEPI by various pharmacological settings.Methods: Simulated CPB was established by recirculating 250 mL of donor blood for 120 minutes in an oxygenator and a roller pump. Three protocols were evaluated: control (heparin 3. 75 U/mL); TF (heparin + recombinant human TF 1000 pg/mL); and TF plus induced TFPI (heparin + TF, using pre-heparinized donor blood, n=7 fot each group). In the third group, 50 U/kg of heparin was administered … More intravenously five minutes before donation to cause TFPI release. Total plasma TEPI, thrombin antithrombin complex and F_ (1+2) were measured using enzyme immunoassay before and during CPB. For a primate CPB model, we used Cynomolgus monkeys (Macaca fascicularis) for 120 minutes of normothermic CPB. Plasma TFPI was enhanced by pre-heparinization for monkeys, and levels of thrombin generation were compared with control animals. Soluble TF, total plasma TFPI, thrombin antithrombin complex and F_ (1+2) were measured using enzyme immunoassay before and during CPB.Results: In the simulated CPB, significant thrombin generation was observed in all three groups and TF enhanced the generation of F_ (1+ 2). In the TF plus induced TFPI group, pre-heparinization resulted in a 3-fold increase in total TFPI, and thrombin generation was significantly reduced to the control levels during CPB despite the administration of TF. In the primate CPB model, plasma TFPI was enhanced by pre-heparinization for monkeys, and levels of thrombin generation were reduced by inhibition of extrinsic pathway when compared with control group.Conclusions: Although TF enhances thrombin generation in CPB, it is likely that contact and intrinsic pathways still play a considerable role in the thrombin generation. Massive release of plasma TFPI induced by early heparin administration may attenuate TF-dependent thrombin generation during clinical CPB. Less