title: Inhibiting the intrinsic pathway of coagulation with a factor XII-targeting RNA aptamer.
abstract: BACKGROUND
  Exposure of the plasma protein factor XII (FXII) to an anionic surface generates activated FXII that not only triggers the intrinsic pathway of blood coagulation through the activation of FXI but also mediates various vascular responses through activation of the plasma contact system. While deficiencies of FXII are not associated with excessive bleeding, thrombosis models in factor-deficient animals have suggested that this protein contributes to stable thrombus formation. Therefore, FXII has emerged as an attractive therapeutic target to treat or prevent pathological thrombosis formation without increasing the risk for hemorrhage.
  
  
  OBJECTIVE
  Using an in vitro directed evolution and chemical biology approach, we sought to isolate a nuclease-resistant RNA aptamer that binds specifically to FXII and directly inhibits FXII coagulant function.
  
  
  RESULTS
  We describe the isolation and characterization of a high-affinity RNA aptamer targeting FXII/activated FXII (FXIIa) that dose dependently prolongs fibrin clot formation and thrombin generation in clinical coagulation assays. This aptamer functions as a potent anticoagulant by inhibiting the autoactivation of FXII, as well as inhibiting intrinsic pathway activation (FXI activation). However, the aptamer does not affect the FXIIa-mediated activation of the proinflammatory kallikrein-kinin system (plasma kallikrein activation).
  
  
  CONCLUSIONS
  We have generated a specific and potent FXII/FXIIa aptamer anticoagulant that offers targeted inhibition of discrete macromolecular interactions involved in the activation of the intrinsic pathway of blood coagulation.
authors.affiliation: Department of Surgery, Duke University Medical Center, Durham, NC 27710, USA.
authors.forename: R S
authors.initials: RS
authors.lastname: Woodruff
authors.forename: Y
authors.initials: Y
authors.lastname: Xu
authors.forename: J
authors.initials: J
authors.lastname: Layzer
authors.forename: W
authors.initials: W
authors.lastname: Wu
authors.forename: M L
authors.initials: ML
authors.lastname: Ogletree
authors.forename: B A
authors.initials: BA
authors.lastname: Sullenger
mesh_terms: D000925:Anticoagulants / Q000494:pharmacology*; D052157:Aptamers, Nucleotide / Q000494:pharmacology*; D001777:Blood Coagulation / Q000187:drug effects*; D001780:Blood Coagulation Tests; D004305:Dose-Response Relationship, Drug; D005174:Factor XII / Q000037:antagonists & inhibitors* / Q000378:metabolism; D015956:Factor XIIa / Q000037:antagonists & inhibitors / Q000378:metabolism; D005337:Fibrin / Q000378:metabolism; D006801:Humans; D007700:Kinetics; D052156:SELEX Aptamer Technique; D013917:Thrombin / Q000378:metabolism
chemical_list: D000925:Anticoagulants; D052157:Aptamers, Nucleotide; D005174:Factor XII; D005337:Fibrin; D015956:Factor XIIa; D013917:Thrombin
keywords: RNA aptamers; anticoagulant agents; blood coagulation; factor XII; factor XIIa