INTERACTIONS OF THE PYRETHROID INSECTICIDE ALLETHRIN WITH LIPOSOMES

The action of allethrin, a pyrethroid with an alkenylmethylcyclopenten olone group, on the thermotropic properties of lipid vesicles has been investigated. Application of turbidimetry and differential scanning c alorimetry to liposomes made with dimyristoyl- (DMPC), dipalmitoyl- (D PPC), and distearoyl- (DSPC) phosphatidylcholine, containing variable concentrations of allethrin, showed that the pyrethroid lowers the tem perature at which the phase transition of the phospholipid occurs. Fur thermore, allethrin produces a broadening of the peak which marks the gel to liquid-crystalline phase transition. The appearance of a second peak as the allethrin concentration in the membranes rises indicates a limited miscibility of the pyrethroid in lipids. Incorporation of al lethrin in carboxyfluorescein-trapped unilamellar liposomes, followed by incubation at several temperatures, enhances carboxyfluorescein rel ease in allethrin-containing vesicles. The results are discussed in te rms of a preferential localization of allethrin in an extended orienta tion in the bilayer with the carbonyl group of the alkenylmethylcyclop entenolone residue in the lipid mater interface and the cyclopropaneca rboxylate moiety between the hydrocarbon acyl chain of the phospholipi ds. (C) 1994 Academic Press, Inc.