The interaction of the factor VIII/von Willebrand factor complex with hematin.
Intravenous infusion of hematin, used in the treatment of acute porphyria, induces a decline in the plasma factor VIII/von Willebrand factor complex (VIII/ vWF) and thrombocytopenia. We investigated this problem by studying the interaction between hematin, purified VIII/ vWF, and platelets in vitro. Hematin was labeled with either 59Fe or 3H and characterized by gel chromatography. Hematin self-aggregated, forming a complex with an average molecular weight of approximately 10,000 daltons. When incubated with VIII/ vWF for 30 min at 37 degrees C and applied to Sepharose CL-4B, the hematin eluted with the VIII/ vWF in the void volume. Hematin inhibited the dissociation of factor VIII antigen (VIII:Ag) from the von Willebrand antigen (vWF:Ag) in 0.25 M CaCl2, and reversed the aggregation of VIII:Ag induced by 0.1 M 6-aminocaproic acid. Both hematin and the hematin-VIII/ vWF complex bound to washed normal platelets and to platelets from a patient with Bernard-Soulier syndrome. Thrombasthenic platelets were not aggregatable by hematin, and bound significantly less hematin-VIII/ vWF than normal platelets suggesting that hematin-induced platelet activation was required for binding. Likewise, binding was inhibited by PGE1 which also prevented aggregation. We conclude that hematin forms complexes with VIII/ vWF, alters the functional activity and dissociation of this compound, and participates in the binding of VIII/ vWF to platelets.[1]References
- The interaction of the factor VIII/von Willebrand factor complex with hematin. Green, D., Furby, F.H., Berndt, M.C. Thromb. Haemost. (1986) [Pubmed]
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