Protamine sulfate down-regulates thrombin generation by inhibiting factor V activation

Abstract

Protamine sulfate is a positively charged polypeptide widely used to reverse heparininduced anticoagulation. Paradoxically, prospective randomized trials have shown that protamine administration for heparin neutralization is associated with increased bleeding, particularly after cardiothoracic surgery with cardiopulmonary bypass. The molecular mechanism(s) through which protamine mediates this anticoagulant effect has not been defined. In vivo administration of pharmacologic doses of protamine to BALB/c mice significantly reduced plasma thrombin generation and prolonged tail-bleeding time (from 120 to 199 seconds). Similarly, in pooled normal human plasma, protamine caused significant dose-dependent prolongations of both prothrombin time and activated partial thromboplastin time. Protamine also markedly attenuated tissue factor-initiated thrombin generation in human plasma, causing a significant decrease in endogenous thrombin potential (41% ؎ 7%). As expected, low-dose protamine effectively reversed the anticoagulant activity of unfractionated heparin in plasma. However, elevated protamine concentrations were associated with progressive dose-dependent reduction in thrombin generation. To assess the mechanism by which protamine mediates down-regulation of thrombin generation, the effect of protamine on factor V activation was assessed. Protamine was found to significantly reduce the rate of factor V activation by both thrombin and factor Xa. Protamine mediates its anticoagulant activity in plasma by downregulation of thrombin generation via a novel mechanism, specifically inhibition of factor V activation. (Blood. 2009;114: 1658-1665) IntroductionProtamine sulfate is a 5-kDa cationic polypeptide derived from salmon sperm that can bind negatively charged unfractionated heparin (UFH). 1 Although the mechanisms of the molecular interaction between protamine and heparin are not well defined, this binding serves to neutralize the antithrombin-mediated anticoagulant properties of heparin. Moreover, the resultant protamineheparin complex is rapidly cleared by the reticuloendothelial system. 2 Consequently, for more than 30 years, protamine has been widely used to reverse the anticoagulant effects of UFH. Protamine is considered the treatment of choice for patients who develop significant bleeding complications while on UFH. 3,4 Furthermore, protamine is routinely administered postoperatively to reverse the high concentrations of UFH required for patients undergoing cardiac surgery and cardiopulmonary bypass (CPB). 5 As a result, estimates suggest that more than 2 million heparinized patients are managed with protamine each year. 2 Clinical use of protamine is, however, associated with several important adverse side effects, including potentially life-threatening systemic arterial hypotension and pulmonary artery hypertension. 1 Paradoxically, in vitro studies have also suggested that protamine may possess intrinsic anticoagulant properties. [6][7][8] Administration of excess protamine in the neutralization of UFH has b...

Reducing transfusion requirements in liver transplantation

“…A small empirical dose of 50 mg protamine can be considered if there is profuse bleeding and a HLE on VET. At high doses protamine can exert a paradoxical anticoagulant effect by inhibiting Factor Ⅴ activation and impairing endogenous thrombin potential [114] .…”

Guideline on the management of bleeding in patients on antithrombotic agents

“…Patients at risk may be pre-treated with corticosteroids and antihistamines. At higher doses, protamine may have significant anticoagulant and antiplatelet effects (Ammar & Fisher, 1997;Ni Ainle et al, 2009).…”

Dynamic and Quantitative Assessment of Blood Coagulation Status with an Oscillatory Rheometer

“…A deficit and also a surplus of protamine lead to prolonged clotting time. This is due to the surplus of protamine exhibiting an anticoagulant activity itself by inhibiting factor V activation [26]. This phenomenon could be also observed within the oscillatory rheometer measurements, a surplus of protamine, led to a prolonged clotting time, the linear slopes and the viscous and elastic shear moduli were lower than in the control measurement.…”