RELATION OF FACTOR VIII CONCENTRATES ACTIVATED BY THROMBIN TO THE POTENCY

It has been indicated the highly purified factor VIII concentrates may be activated through the purification process. For the purpose of examining the activation in the factor VIII concentrates, the relation of factor VIII activated by thrombin to the potency in plasma-derived factor VIII (Hemofi1M) and recombinant factor VIII (BL-160, Baxter). The potency was measured by one stage clotting assay (VIIIC) and amidolytic assay (VIIIam), and then VIIIam/VIIIC ratio was calculated. At same time, factor VIII proteins were monitored by immunoblotting assay. Before thrombin activation, the ratio was 1.0 approximately, but it became 0.2-0.1 after the activation. The ratio of both products (3 lots) was within a range of normal plasma (n=30). L chain cleavage of BL-160 by thrombin was slower than Hemofi1M. But L chain was cleaved more rapidly, when vWF was added to BL-160. These results suggest that the ratio may be useful as a parameter to estimate the degree of activation in factor VIII concentrates. In addition it is assumed that vWF contributes to the cleavage of L chain, and that vWF, when added to BL-160, gives higher potency by VIIIC.