Aggregation of human platelets by bovine or human factor VIII: role of carbohydrate side chains

Bovine factor VIII has been shown to aggregate human platelets. The present study suggests that this action is dependent on the carbohydrate side chains containing galactose, but not terminated by sialic acid, found in bovine factor VIII. These side chains bind with sialyl transferase located on the platelet membrane and form a substrate - enzyme complex, presumably just as collagen and platelets interact to produce platelet aggregation. Exposure of bovine factor VIII to galactose oxidase abolished the aggregating property. Human factor VIII does not aggregate platelets, unless preincubated with neuraminidase, thereby exposing galactose containing side chains not terminated by sialic acid. Exposure to galactose oxidase also inhibits this reaction. The authors suggest that the defective platelet adhesiveness of Von Willebrand's disease may be related to the lack of available factor VIII seen in this disease. (Slyck - Detroit, Mich.)