Effect of polymeric surfactants on the release of encapsulated marker from large unilamellar vesicles

Abstract

Large unilamellar vesicles (LUV) of lecithin, radioactively labeled in the membranes and in the aqueous interior, were used as membrane models to measure the stabilizing effect of different polymeric surfactants on the membrane integrity upon addition of sodium cholate as a detergent. Parameters for the membrane damage were the release of encapsulated [³H]inulin, indicating larger membrane defects and the release of [¹⁴C]dipalmitoylphosphatidylcholine, representing membrane dissolution. The polymeric surfactants were block copolymers of the type

with triethylene glycol monomethyl ether and hexyl alcohol as hydrophilic and lipophilic side-chains coupled to poly(methacrylic acid) by ester bonds. All polymers had a molecular weight of 30000 and differed in the mass ratio of hydrophilic to lipophilic parts: 100/0 (A), 90/10 (B), 60/40 (C) and 50/50 (D). It was found that the addition of these compounds in a concentration range from the critical micellar concentration (c.m.c.) to 100 times the c.m.c. to liposomes had no measurable membrane-destabilizing effect, in contrast to monomeric surfactants of low molecular weight such as cholate. Furthermore, the more lipophilic polymers C and D even show a more pronounced membrane-stabilizing effect than the hydrophilic compounds against cholate attack.