The interaction between factor VIII clotting antigen (VIIICAg) and phospholipid

Area of Science:

• Biochemistry
• Hematology
• Immunology

Background:

• Factor VIII clotting antigen (VIIICAg) is crucial for hemostasis.
• The interaction between VIIICAg and phospholipids (PL) is not fully understood.
• Previous studies suggest potential interactions affecting VIIICAg measurement.

Purpose of the Study:

• To investigate the interaction between VIIICAg and phospholipid (PL).
• To determine the effect of phospholipase-C (PL-C) on VIIICAg-PL complexes.
• To explore the presence and accessibility of VIIICAg in platelet-rich environments.

Main Methods:

• Utilized a two-site solid-phase immunoradiometric assay (IRMA) to measure VIIICAg.
• Incubated plasma, cryoprecipitate, and factor VIII concentrates with purified PLs and PL-C.
• Analyzed changes in VIIICAg, factor VIII related antigen (VIIIRAg), and factor VIII clotting activity (VIIIC) levels.
• Investigated VIIICAg-PL complexes in activated prothrombin complex and platelet lysates.

Main Results:

• Incubation with PL caused an 80-90% loss of measurable VIIICAg, without affecting VIIIC or VIIIRAg.
• Phosphatidylserine demonstrated the greatest reduction in VIIICAg.
• PL-C treatment increased VIIICAg levels by 25-30% in plasma and concentrates, and 70-80% recovery after PL preincubation.
• VIIICAg-PL complexes were confirmed in activated prothrombin complex and platelet lysates, with PL-C increasing VIIICAg by 14-fold in platelets.

Conclusions:

• VIIICAg interacts with phospholipids, forming complexes that reduce its measurable levels.
• Phospholipase-C can disrupt these complexes, restoring VIIICAg detectability.
• VIIICAg within platelets may be masked by VIIICAg-PL complexes, impacting its availability.