POLYMER-INDUCED FUSION AND LEAKAGE OF SMALL UNILAMELLAR PHOSPHOLIPID-VESICLES - EFFECT OF SURFACE GRAFTED POLYETHYLENE-GLYCOL IN THE PRESENCE OF FREE PEG

We investigated the effect of surface grafted polyethylene glycol (PEG ) in the presence of free PEG on leakage and fusion of small unilamell ar vesicles. High concentrations of free PEG (MW 2000) caused leakage and fusion of small unilamellar vesicles. Addition of distearoyl phosp hatidylethanolamine-polyethylene glycol (DSPE-PEG), a lipid containing a covalently bonded PEG at the headgroup, to the membrane forming sol ution reduced leakage and fusion induced by free PEG drastically. The inhibitory effect of this surface grafted PEG was a function of the co ncentration of DSPE-PEG in the lipid mixtures and increased continuous ly up to 10 mol%, at which leakage or fusion almost vanished. From our studies we concluded that surface grafted PEG acts as a steric barrie r inhibiting the close approach of liposomes which is necessary for fu sion. (C) 1997 Elsevier Science Ireland Ltd.