The fraction of recombinant factor VIII:Ag unable to bind von Willebrand factor has no FVIII coagulant activity: studies in vitro.
A fraction of FVIII:Ag in commercial recombinant FVIII (rFVIII) cannot bind VWF whereas all the FVIII:Ag in plasma-derived FVIII (pd-FVIII) concentrates does. To compare the FVIII:C activities of the fractions of rFVIII:Ag that can and cannot bind VWF. The FVIII:Ag contents of the rFVIII Kogenate, and Advate and a pd-FVIII-pd-VWF (Fanhdi) were measured by ELISA. The FX activation was initiated by adding 1.0 IU of FVIII:C of each FVIII-containing product to a coagulant phospholipids suspension containing 1.0 nm FIXa, 100 nm FX, 1 μm hirudin and 2 mm calcium chloride and measured after 1, 5 and 10 min. The same approach was followed after adding 2.0 IU of pd-VWF to 1.0 IU of FVIII:C of Kogenate or Advate. The FVIII:Ag content/IU of FVIII:C of Kogenate, Advate and Fanhdi were 1.80 ± 0.05, 1.31 ± 0.9 and 0.84 ± 1.5 IU respectively. Only Kogenate and Advate effectively enhanced FX activation 1 min after adding each FVIII:C to the coagulant suspension containing FIXa and FX. Thus, the FXa initially generated by FIXa readily activated FVIII:C in control Kogenate and Advate to thereby effectively enhance FX activation while the VWF in Fanhdi continued to suppress FX activation for up to 10 min. Addition of pd-VWF to Kogenate or Advate effectively decreased their enhancements of FX activation to the same level as Fanhdi over 10 min. The FVIII:Ag fraction in Kogenate and Advate that cannot bind VWF appears to be inactive as it has no measureable FVIII:C activity in the presence of added VWF in vitro.
Department of Pathology and Molecular Medicine, McMaster University, Hamilton, ON, Canada. ofosuf@mcmaster.ca
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D001780:Blood Coagulation Tests; D004797:Enzyme-Linked Immunosorbent Assay; D015949:Factor IXa / Q000378:metabolism; D005169:Factor VIII / Q000378:metabolism*; D015951:Factor Xa / Q000378:metabolism; D011485:Protein Binding; D014841:von Willebrand Factor / Q000378:metabolism*
D014841:von Willebrand Factor; C078147:F8 protein, human; D005169:Factor VIII; D015949:Factor IXa; D015951:Factor Xa