Absorption of insulin using water-in-oil-in-water emulsion from an enteral loop in rats

The present work was undertaken to prepare water-in-oil-in-water (W/O/W) emulsions as a carrier for insulin via the enteral route. The emulsions were prepared by a two-step procedure using a homogenizer. To avoid insulin escape from the inner aqueous phase, 3, 5, or 10% gelatin was added in the inner phase. The oily phase was composed of 5% lecithin, 20% Span 80 and 75% soybean oil. The purified water containing 3% Tween 80 was used for the outer aqueous phase. In addition, these emulsions were filtered with a membrane filter (0.45 micron) to obtain smaller emulsion particles. The stability of the emulsions was evaluated by a turbidity measurement method and photomicrographic observation. By the addition of gelatin to the inner aqueous phase and storage at 4 degrees C, the stability of the emulsions could be improved. The hypoglycemic effects of insulin after administration of emulsion to the stomach, the duodenum, the jejunum, the ileum and the colon were examined using an in situ loop method in rats. A significant hypoglycemic effect was observed at the ileum and colon loops after administration of the filtered emulsions containing 5% gelatin in the inner phase. These findings suggest that the W/O/W multiple emulsions stabilized by gelatin can improve ileal and colonic absorption of insulin.