Contribution of complement system on destabilization of liposomes composed of hydrogenated egg phosphatidylcholine in rat fresh plasma.

Large multilamellar vesicles (MLV) composed of hydrogenated egg phosphatidylcholine (HEPC), cholesterol (CH), and dicetyl phosphate (DCP) rapidly release part of an entrapped aqueous marker when incubated with fresh rat plasma and thus have severely limited usefulness as drug carriers. The mechanisms causing the instability of liposomes in plasma were investigated in this study. The leakage of liposomal constituents was completely inhibited by pre-heating at 56 degrees C for 30 min with plasma or by treating with EDTA, K-76COOH, or anti-C3 antiserum but was not inhibited with EGTA/MgCl2. These results indicated that the destabilization of liposomes in fresh rat plasma was induced by activation of the alternative complement pathway (ACP). Furthermore, the complement third component (C3) was detected from the liposomes incubated with fresh plasma by SDS-PAGE followed by Western blotting and immune detection. The C3b deposited on the liposomal surface via ACP was rapidly cleaved to iC3b. The results obtained in the present study suggest a possibility that the liposomes composed of HEPC (without any surface modification) may be effective carriers for macrophages because C3b and its degradative products, iC3b are related to the opsonic function on phagocytosis of foreign particles by macrophages.