 
         
         Summary
         
         Liposomes with a covalently bound synthetic peptide containing the dodecapeptide sequence
            HHLGGAKQAGDV, the putative platelet interaction site at γ400-411 of fibrinogen (dodecapeptide-liposomes), were prepared. These liposomes enhanced
            platelet aggregation and specifically adhered to platelets activated on the collagen
            surface. Dodecapeptide-liposomes released encapsulated materials upon interacting
            with platelets activated on the collagen surface.The rate of content release was dependent
            on the peptide surface density, indicating that the interaction between the dodecapeptide-liposomes
            and platelets activated on the collagen surface induces clustering of the surfacecoupled
            ligands at the binding site on the receptor matrix to facilitate release of the internal
            contents through the liposome membranes. The level of lipid mixing between the dodecapeptide-liposomes
            and platelets activated on the collagen surface was relatively low, however it was
            increased in liposome preparations containing octa-arginine, the (R)8GDV sequence, while content release was maintained at the same level as that of the
            dodecapeptide-liposomes. The level of content release and lipid mixing for liposome
            preparations containing the RGD sequence as a ligand (RGD-liposomes) upon interacting
            with platelets activated on the collagen surface was extremely low. Both the level
            of the content release and lipid mixing, however, were enhanced in liposome preparations
            containing octa-arginine, the (R)8RGD sequence. Dodecapeptide-liposomes and RGD-liposomes were not internalized by activated
            platelets. On the other hand, liposomes containing (R)8PPQ, (R)8RGD, or (R)8GDV were internalized by activated platelets, and the extent of internalization was
            inversely related to ligand affinity to the target.
         
         Keywords
Liposome-platelet interaction - peptide-conjugated liposome - platelet substitute
            - dodecapeptide - octa-arginine