The comparison of protein-entrapped liposomes and lipoparticles: preparation, characterization, and efficacy of cellular uptake

Abstract

Fluorescein isothiocyanate-conjugated bovine serum albumin(FITC-BSA)-loaded polyethylene glycol (PEG)-modified liposomes andlipoparticles with high protein entrapment were developed. The lipidformula of the liposomes contained PEGylated lipids and unsaturatedfatty acids for enhancing membrane fluidity and effective delivery intocells. The preparation techniques, lipid content, and PEG-modifiedlipoparticle ratios were evaluated. The PEG-modified lipoparticlesprepared by ethanol injection extrusion (100 nm pore size) achieve apopulation of blank liposomes with a mean size of 125 +/- 2.3 nm and azeta potential of -12.4 +/- 1.5 mV. The average particle size of thePEG-modified lipoparticles was 133.7 +/- 8.6 nm with a zeta potential of+13.3 mV. Lipoparticle conformation was determined using transmissionelectron microscopy and field-emission scanning electron microscopy. TheFITC-BSA encapsulation efficiency was dramatically increased from 19.0%for liposomes to 59.7% for lipoparticles. Sodium dodecyl sulfatepolyacrylamide gel electrophoresis (SDS-PAGE) results confirmed thepreparation process, and an 8-hour leaching test did not harm theprotein structure. Once prepared, the physical and chemical stability ofthe PEG-modified lipoparticle formulations was satisfactory over 90days. In vitro retention tests indicated that the 50% retention timefor the protein-containing lipoparticles was 7.9 hours, substantiallylonger than the liposomes at 3.3 hours. A Caco-2 cell model was used forevaluating the cytotoxicity and cell uptake efficiency of thePEG-modified lipoparticles. At a lipid content below 0.25 mM, neitherthe liposomes nor the lipoparticles caused significant cellularcytotoxicity (P < 0.01) and FITC-BSA was significantly taken up intocells within 60 minutes (P < 0.01).