On The Nature Of The Activated Prothrombin Complex

Abstract

Prothrombin complex concentrates containing FVIII bypassing activity have been employed effectively in the management of patients with factor VIII and IX inhibitors. The active component has not been identified although the protease forms of factor IX and X, as well as VII exist in variable concentrations in these products.As a means of establishing the role of each factor in the concentrates, monospecific antibodies to prothrombin, FX and FVII were coupled to Sepharose 4B by means of cross linking reagent cyanogen bromide. These insol- ubilized antibodies were used to selectively remove all prothrombin FX or FVII from the therapeutic concentrate, Autoplex (570 u/vial) supplied by Hyland Labs, Costa Mesa, by batch adsorption. A control was prepared by reacting the concentrate with cyanogen bromide treated beads whose active sites had been blocked with ethanolamine. Successful removal of specific factors from concentrates was evaluated by immunodiffusion assays and by standard clotting assays using substrate deficient plasma. Thrombin was not found to be present in any of the products following extraction. Thrombogenicity was tested in an animal model. Concentrates reacted with cyanogen bromide beads as a control and those lacking prothrombin were found to shorten clotting time of FVIII deficient plasma and to trigger intravascular coagulation in the animals (D.I.C.). Removal of FVII produced a concentrate that was more active than the control with respect to FVIII correction and induction of D.I.C. Concentrates depleted of FX, on the other hand, lost their capacity to correct FVIII deficient plasma and to initiate D.I.C. Our findings would suggest that the content of FX and its active form FXa plays a major role in the concentrates FVIII correcting activity and most likely is responsible for its thrombogenic characteristics.