Improving insulin enteral absorption using water-in-oil-in-water emulsion

The purpose of this study was to evaluate the hypoglycemic effects of water-in-oil-in-water (W/O/W) insulin emulsions containing lipoidal absorption enhancer after enteral administration to rats. The hypoglycemic effects of insulin were examined using an in situ loop method in rats. The insulin emulsions prepared with soybean oil, triolein or trilinolein slightly but significantly decreased the serum glucose levels compared to the insulin solution. By addition of 3% limonene or 3% menthol to the triolein emulsion, the hypoglycemic effect of insulin was promoted in the ileum but not in the colon. Strong hypoglycemic effects were observed with the triolein emulsion containing 2% fatty acids such as oleic acid, linoleic acid and linolenic acid. The remarkable enhancing effects occurred more predominately in the colon than in the ileum. The effect of degree of unsaturation of fatty acids was not observed. No tissue damage was noted by light microscopic examination of both regions treated with triolein emulsion, triolein emulsion containing menthol or oleic acid. W/O/W emulsion containing unsaturated fatty acids are able to enhance the ileal and colonic absorption of insulin without tissue damage and may, therefore, be useful in dosage form in enteral delivery system for insulin. (C) 1998 Elsevier Science B.V. All rights reserved.