Polysorbate 20 vesicles as oral delivery system: in vitro characterization

Non-phospholipid vesicles made with non-ionic surfactants represent a promising alternative to the more widely studied liposomes. The main aim of the present work is to evaluate if vesicles of polysorbate 20 may be used as delivery systems for oral administration of drugs. Then in vitro stability and mucoadhesion studies in simulated gastrointestinal fluids were carried out. The colloidal stability of the surfactant vesicles was determined by size and fluorescence-dequenching assay, while their mucoadhesive properties were evaluated by light-scattering and protein assay. The results of in vitro stability demonstrated that the pHs and enzymes (pepsin and/or pancreatin) of the gastrointestinal fluids had not influence on surfactant vesicle stability. However, in presence of bile salts the nanosize vesicles showed a release of fluorescent marker (about 11% at 2 h and 28% at 4 h), whereas they were stable in size as confirmed by the light scattering experiments. Finally, the in vitro mucoadhesive experiments showed that the capacity of nanovesicles to adsorb mucin was higher at neutral pH than at acidic pH. As a conclusion of these preliminary studies, the surfactant vesicles could be considered a versatile tool for the oral delivery of drugs with poor stability in gastrointestinal tract and low permeability. Nevertheless, further work is required in order to examine the interaction with and/or the transport route through the epithelial cells of the gastrointestinal wall.