1-O-Alkylglycerol vesicles (Algosomes): their formation and characterization.

1-O-alkylglycerols (ALKG) have exhibited several biological activities and a prominent effect on blood-brain barrier permeability. They have markedly improved brain uptake of cancerostatic agents. Since ALKG are amphiphilic, we explored their tendency to assemble into bilayer vesicles, which can be applied as carriers for drugs. Vesicles (Algosomes) were formed by film hydration method using ALKG (tetra-, penta-, hexa-, hepta-, octa- or nona-decylglycerols) in combination with cholesterol (CHOL) and dicetyl phosphate (DCP) (1-O-alkylglycerol:CHOL:DCP in 45:45:10 molar ratio). On microscopic examination, the algosomes were found to be conspicuously spherical and the dispersion was a mixture of multi-lamellar and small-unilamellar vesicles. Phase transition temperatures of 1-O-hexadecylglycerol (HXDG) and CHOL mixtures were tested by differential scanning calorimetry (DSC). The changes in phase transition temperatures indicate the vesicle forming tendency of ALKG in presence of CHOL. Alkyl chain length dependent variations in vesicle size, zeta-potential (ZP) and capture volume (CV) could not be observed. Vesicles of 1-O-tetradecylglycerol (TTDG) showed improvement in CV with increase in CHOL content from 15 to 55 mol%. However the vesicle size decreased. On challenging algosomes with hypertonic salt solution [potassium iodide (KI) in water], vesicle size decreased and thus algosomes were found to be osmotically sensitive. Algosome dispersions on addition of higher concentrations of KI (40-100 mM) brought about increases in vesicle size and at concentrations 60 mM and above showed aggregation. All vesicular dispersions were stable for only a few days.