Factor VII binding to tissue factor in plasma from warfarin-treated individuals

Area of Science:

• Biochemistry
• Hematology

Background:

• Warfarin therapy can affect coagulation factor levels and activity.
• Factor VII (FVII) plays a crucial role in the extrinsic coagulation pathway.
• The gamma-carboxyglutamic acid (Gla)-domain of FVII is essential for its interaction with phospholipids and tissue factor (TF).

Purpose of the Study:

• To investigate the impact of Gla-domain removal on FVII's ability to bind TF.
• To assess the relationship between FVII clotting activity (FVII:c), FVII antigen (FVII:ag), and FVII-TF binding in warfarin-treated patients.

Main Methods:

• Enzyme immunoassay was used to measure FVII-TF binding.
• Artificial Gla-domainless-FVII was generated by digesting purified FVII with cathepsin G.
• Plasma samples from 44 warfarin-treated patients were analyzed for FVII:c, FVII:ag, and FVII-TF binding before and after Al(OH)3 adsorption.

Main Results:

• Digestion with cathepsin G rendered FVII Gla-domainless, causing a loss of both FVII-TF binding and clotting activity.
• In warfarin patients, FVII:c was significantly lower than FVII:ag.
• FVII-TF binding correlated better with FVII:ag than with FVII:c, and was significantly higher than FVII:c but not FVII:ag.

Conclusions:

• Artificial Gla-domainless-FVII loses its TF binding capacity.
• The reduced specific activity of FVII in warfarin patients may not be solely attributed to diminished FVII-TF binding.
• PIVKA-VII (protein induced by vitamin K absence or antagonist-II) exhibits TF binding but lacks clotting activity.