Effect Of Cholesterol On The Process Of Gene Delivery By PAMAM

Polyamidoamine (PAMAM), with unique molecular architectures and properties, can interact electrostatically with DNA and condense it, protect it from degradation. Recently, it has been widely used as non-viral gene vector, but compared with viral vectors; the transfection efficiency is still low because of different barriers during gene delivery. A well description to the mechanism of PAMAM interaction with and enterance to cell membrane will find an avaliable way to overcome the membrane barrier and help us enhance transfection efficiency.In this thesis, different liposomes were prepared as mimic membranes using phosphatidycholine and cholesterol with different concentrations, the mechanism of PAMAM/DNA complex interacting with liposome membrane and effect of cholesterol during this process was investigated by isothermal titration microcalorimetry, zeta potential measurement and transmission electron microscope.Isothermal titration microcalorimetry studies showed that PAMAM/DNA complex binding both to liposome containing cholesterol as to liposome devoid of it was through electrostatic interaction and driven by enthalpy. The existence of cholesterol helped PAMAM/DNA complex which was binding to the surface of liposome insert into the bilayer of liposomes, which caused the increase of enthalpy and entropy, even aggregate of lipsome. When the charge ratio of PAMAM and DNA was over 1, zeta potential of liposomes decreased with addition of PAMAM/DNA complex, which also indicated that PAMAM/DNA complex was binding to liposome by electrostatic interaction. PAMAM/DNA complex combined to the surface of liposome devoid of cholesterol, but insert into the liposome containing cholesterol resulting in diameter increase which was observed by TEM. The whole data indicated that PAMAM/DNA complex interact with liposome by electrostatics but inserting into mimic membrane was significantly affected by cholesterol.