title: Heme binds to factor VIII and inhibits its interaction with activated factor IX.
abstract: BACKGROUND
  Heme is a redox active macrocyclic compound that is released upon tissue damage or hemorrhages. The extracellular release of large amounts of heme saturates scavenging heme-binding proteins. Free heme has been proposed to affect coagulation and has been co-purified with the factor VIII (FVIII)-von Willebrand factor (VWF) complex. The sites from which heme is released upon injury overlap with the sites to which FVIII is targeted for performing its hemostatic functions.
  
  
  OBJECTIVE
  To investigate the interaction of heme with FVIII and the consequence for the procoagulant activity of FVIII in vitro.
  
  
  RESULTS
  Heme bound to several sites on FVIII with high apparent affinity. Heme-binding inhibited FVIII procoagulant activity in a dose-dependent manner. FVIII inactivation in the presence of saturating amounts of heme implicated a reduced interaction of FVIII with activated FIX, as shown by ELISA, surface plasmon resonance and fluorescence quenching. Heme-mediated inactivation of FVIII was prevented by VWF, but not by human serum albumin, a heme-binding protein known for its protective activity in hemolytic conditions.
  
  
  CONCLUSIONS
  Our data identify FVIII as a novel heme-binding protein. Occupation of high affinity heme-binding sites on FVIII at low concentrations of free heme did not inactivate FVIII. Conversely, large molar excesses of heme over FVIII, which correspond to conditions of extensive heme release, inhibited FVIII activity in vitro. It remains to be demonstrated whether, under such conditions, heme-mediated modulation of the activity of FVIII plays some role in the regulation of coagulation.
authors.affiliation: INSERM, UMR S 872, Paris, France.
authors.forename: Y
authors.initials: Y
authors.lastname: Repessé
authors.forename: J D
authors.initials: JD
authors.lastname: Dimitrov
authors.forename: I
authors.initials: I
authors.lastname: Peyron
authors.forename: E
authors.initials: E
authors.lastname: Farrokhi Moshai
authors.forename: L
authors.initials: L
authors.lastname: Kiger
authors.forename: S
authors.initials: S
authors.lastname: Dasgupta
authors.forename: S
authors.initials: S
authors.lastname: Delignat
authors.forename: M C
authors.initials: MC
authors.lastname: Marden
authors.forename: S V
authors.initials: SV
authors.lastname: Kaveri
authors.forename: S
authors.initials: S
authors.lastname: Lacroix-Desmazes
mesh_terms: D001665:Binding Sites; D001667:Binding, Competitive; D001777:Blood Coagulation; D004797:Enzyme-Linked Immunosorbent Assay; D015949:Factor IXa / Q000378:metabolism*; D005169:Factor VIII / Q000378:metabolism*; D015944:Factor VIIIa / Q000378:metabolism; D006418:Heme / Q000378:metabolism*; D006427:Hemin / Q000378:metabolism; D006801:Humans; D054730:Protein Interaction Domains and Motifs; D025941:Protein Interaction Mapping; D011994:Recombinant Proteins / Q000378:metabolism; D013050:Spectrometry, Fluorescence; D020349:Surface Plasmon Resonance; D014841:von Willebrand Factor / Q000378:metabolism
chemical_list: D011994:Recombinant Proteins; D014841:von Willebrand Factor; D006418:Heme; D015944:Factor VIIIa; D006427:Hemin; D005169:Factor VIII; D015949:Factor IXa