title: Protamine sulfate down-regulates thrombin generation by inhibiting factor V activation.
abstract: Protamine sulfate is a positively charged polypeptide widely used to reverse heparin-induced 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 down-regulation of thrombin generation via a novel mechanism, specifically inhibition of factor V activation.
authors.affiliation: Haemostasis Research Group, St James's Hospital, Dublin, Republic of Ireland.
authors.forename: Fionnuala
authors.initials: F
authors.lastname: Ni Ainle
authors.forename: Roger J S
authors.initials: RJ
authors.lastname: Preston
authors.forename: P Vincent
authors.initials: PV
authors.lastname: Jenkins
authors.forename: Hendrik J
authors.initials: HJ
authors.lastname: Nel
authors.forename: Jennifer A
authors.initials: JA
authors.lastname: Johnson
authors.forename: Owen P
authors.initials: OP
authors.lastname: Smith
authors.forename: Barry
authors.initials: B
authors.lastname: White
authors.forename: Padraic G
authors.initials: PG
authors.lastname: Fallon
authors.forename: James S
authors.initials: JS
authors.lastname: O'Donnell
mesh_terms: D000818:Animals; D000925:Anticoagulants / Q000494:pharmacology; D001760:Bleeding Time; D001777:Blood Coagulation / Q000187:drug effects; D004305:Dose-Response Relationship, Drug; D015536:Down-Regulation / Q000187:drug effects; D004353:Drug Evaluation, Preclinical; D004357:Drug Synergism; D005165:Factor V / Q000037:antagonists & inhibitors* / Q000378:metabolism; D015944:Factor VIIIa / Q000378:metabolism; D006493:Heparin / Q000494:pharmacology; D051379:Mice; D008807:Mice, Inbred BALB C; D011479:Protamines / Q000494:pharmacology*; D011486:Protein C / Q000378:metabolism / Q000502:physiology; D011499:Protein Processing, Post-Translational / Q000187:drug effects; D013917:Thrombin / Q000378:metabolism*
chemical_list: D000925:Anticoagulants; D011479:Protamines; D011486:Protein C; D015944:Factor VIIIa; D005165:Factor V; D006493:Heparin; D013917:Thrombin