Coating of negatively charged liposomes by polylysine: drug release study.

The present work describes surface coating of carboxyfluorescein(CF)-loaded liposomes with poly-l-lysine (PLL) and liposome membrane permeability. The vesicles were prepared from synthetic or natural lipids. Interaction between PLL and the liposomes leads to the formation of complexes - either single PLL-coated vesicles or vesicle aggregates. Formation of the complexes is strongly affected by PLL/lipid molar ratio and the molecular mass of the PLL chains. Liposome permeability depends strongly on the lipid phase state - vesicles in the solid state retained the entrapped dye for a long time, but continuous CF release was registered for "fluid" vesicles. Crossing the transition temperature leads to intensive dye leakage because of the appearance of leaky interfacial domains between the coexisting solid and liquid phases and also because of a reversible change in the vesicle size upon the solid-liquid state phase transition. PLL coverage does not cause permeabilization of "solid" liposomes, but increases the permeability of "fluid" vesicles. At the same time, the results of differential scanning calorimetry and vesicle fusion suggest that PLL adsorption occurs exclusively on the vesicular surface and that the lipidic organization is not significantly disturbed. Moreover, PLL does not prevent lipid exchange between vesicles induced by temperature change.