IN-VITRO INTERACTION OF ZINC(II)-PHTHALOCYANINE-CONTAINING LIPOSOMES AND PLASMA-LIPOPROTEINS

We have studied the interaction of small unilamellar liposomes contain ing zinc(II)-phthalocyanine (Zn-Pc) with human plasma lipoproteins. Hi gh-, low- and very low-density lipoproteins (HDL, LDL and VLDL) were p urified from plasma and combined in amounts reflecting their natural a bundance in plasma. After short periods of incubation at 37 degrees C, the bulk of Zn-Pe was incorporated into HDL and LDL; very little C-14 -labelled palmitoyl oleoyl phosphocholine, the most abundant phospholi pid in the formulation, was associated with lipoproteins. When liposom es were incubated in pooled plasma, 73%-85% of Zn-Pc and 27%-34% of ra diolabelled phospholipid were recovered with HDL and LDL, indicating a possible role for plasma lipid transfer proteins in the incorporation of phospholipid into lipoproteins. Some Zn-Pc was also found in assoc iation with VLDL. The buoyant density of Zn-Pc liposomes increased in a dose-dependent fashion when the particles were incubated with plasma , and it is suggested that this was due, at least in part, to opsoniza tion of liposomes by plasma proteins.