Preparation and Properties of Vesicles Formed from Phospholipid Analogues of N-(Phosphonoacetyl)-L-aspartate (PALA) by Sonication or Extrusion: Transition Temperature, Particle Size, Glucose Entrapment, and 31P NMR

Abstract

We characterize here the ability of new amphiphilic compounds to form vesicles that could potentially be used as vectors for therapeutical applications. These compounds are derived from N-phosphonoacetyl-L-aspartate (PALA), a potential antitumoral agent. Vesicular dispersions of phospholipid analogues of PALA with different alkyl chain lengths (diC12-, diC14-, diC16-, and diC18-PALA), which had been previously synthesized, are tested from different points of view. Two kinds of preparation methods are compared: sonication; extrusion. The two preparation methods resulted in important differences in the properties of the dispersions which confirmed the conclusions of a previous investigation from cryo-TEM imaging. The results of fluorescence polarization experiments, performed either with the pure compounds or their mixtures with lecithins or cholesterol, indicated that the transition temperature Tm can be modulated if it is required for the applications. The sonicated particles showed smaller size and much lower glucose encapsulation than the extruded particles. In both cases these properties are only weakly depending on the amphiphile alkyl chain lengths. The glucose permeability has appeared to considerably increase (lower encapsulation) at T > Tm. The effect of Mn2+ on the 31P NMR signal intensity suggested that unilamellar vesicles are coexisting with other types of particle in case of extrusion, whereas in case of sonication only few and less stable vesicles are present, in agreement with the preceding observations.