Abstract Number: PB0229
Meeting: ISTH 2020 Congress
Background: Protamine is a mixture of basic, arginine-rich peptides used clinically to neutralize the anticoagulant effect of negatively charged heparin. Paradoxically, protamine can elicit an anticoagulant effect. Previous studies have shown that protamine inhibits factor V (FV) activation; yet mechanistic insights are lacking. FV is activated to FVa through removal of its B-domain and destabilizing interactions between acidic region 2 (AR2; 1493-1538) and the basic region (BR; 964-1008) which are responsible for keeping FV inactive. FV species that lack BR but retain AR2 (FVAR; e.g. FV-short and platelet-FV) are active, but sensitive to inhibition following the addition of BR in trans. Here, we hypothesize that protamine mimics FV-BR and inhibits cofactor function of FVAR species.
Aims: To examine how protamine interacts with FV species.
Methods: We used biochemical assays to characterize the interaction between protamine and FV species in a purified system and examined protamine’s effects in plasma with or without heparin.
Results: We found that protamine bound tightly to FV-short and inhibited cofactor function (Ki = 2 nM), caused a dose-dependent anticoagulant response on thrombin generation (TG) and impaired the proteolytic processing of FV species by thrombin or FXa. Importantly, no effects were observed in assays employing FVa (lacks AR2). Low concentrations of protamine restored TG in heparinized normal human plasma (NHP) and FV deficient plasma reconstituted with FV-short or FVa. However, high concentrations resulted in the progressive reduction of TG in NHP and FV-deficient plasma reconstituted with FV-short. Similar results were obtained using Poly-Arginine, however other basic molecules (e.g. histone H3, Poly-Lysine or platelet Factor 4) failed to replicate protamine’s effects.
Conclusions: These results suggest protamine exerts its anticoagulant effect by interacting with physiological relevant FVAR species. The interaction of protamine is specific and similar to how the endogenous FV-BR keeps FV inactive or how TFPIα blocks the procoagulant effects of FVAR.
To cite this abstract in AMA style:Petrillo T, Remick BC, Camire RM. The Anticoagulant Effect of Protamine – A Stabilizer of the Factor V Procofactor State [abstract]. Res Pract Thromb Haemost. 2020; 4 (Suppl 1). https://abstracts.isth.org/abstract/the-anticoagulant-effect-of-protamine-a-stabilizer-of-the-factor-v-procofactor-state/. Accessed October 1, 2023.
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