Liposomes with phosphatidylethanol as a carrier for oral delivery of insulin: studies in the rat.
In this study, phosphatidylethanol formed by phospholipase D catalysed transphosphatidylation of phosphatidylcholine was employed as a component for preparation of liposomal carrier for oral delivery of insulin. Thermotropic behaviour of liposomes from mixtures of dipalmitoyl phosphatidylcholine and dipalmitoyl phosphatidylethanol, and their resistance to pancreatic phospholipase A(2) catalysed hydrolysis were studied. Three kinds of liposomes with insulin were prepared to examine the pharmacological availability of liposomes with phosphatidylethanol: (i) dipalmitoyl phosphatidylcholine/dipalmitoyl phosphatidylethanol (1:1 w/w) liposomes; (ii) dipalmitoyl phosphatidylcholine/dipalmitoyl phosphatidylethanol/palmitoyl-stearoyl sucrose (1:1:0.2) liposomes; and (iii) liposomes composed of natural phosphatidylcholine and phosphatidylinositol (1:1). The resultant liposomes were orally administrated to rats with blood glucose concentration of 270 mg/100 ml in a dose of 12 IU/kg body weight. Blood samples were collected 0.5, 1.5, 3, 5, and 24 h after treatment. Oral administration of all liposomal species resulted in hyperinsulinemia. Hyperinsulinemia induced by liposomes containing dipalmitoyl phosphatidylethanol was attended by a decrease of blood glucose concentration. No correlation between insulin level and glucose concentration in the rat blood after oral administration of phosphatidylinositol-containing liposomes was observed.