Use of liposomes to aid intestinal absorption of entrapped insulin in normal and diabetic dogs

The effectiveness of liposomes in aiding intestinal absorption of entrapped insulin was studied in normal and diabetic dogs. Intraduodenal administration of free insulin (490 and 1630 U) or free insulin (88 U) plus empty liposomes to normal conscious dogs produced no change in plasma immunoreactive insulin or glucose Administration of 40–80 U insulin entrapped in liposomes composed of either phosphatidylcholine, distearoylphosphatidylcholine, or dipalmitoylphosphatidylcholine with cholesterol and dicetylphosophate ( in the ratio 10:2:1 by weight) to normal dogs produced substantial rises in peripheral plasma immunoreactive insulin after 45–60 min. However, the magnitude of these rises was neither reproducible nor dose-dependent. No fall in plasma glucose was observed. Intraduodenal administration of 50–100 U insulin entrapped in liposomes to diabetic dogs also produced rises in plasma immunoreactive insulin levels after 45–60 min but again these rises were not dose-related. However, unlike the results in normal dogs, a small fall in plasma glucose followed the plasma immunoreactive insulin rise in diabetic dogs. This glucose fall was not dose-dependent nor was it related to the magnitude of the rise in plasma immunoreactive insulin. In conclusion, it seems that administration of insulin in liposomes may allow absorption of partially degraded insulin into the circulation but the rise in plasma immunoreactive insulin observed in normal and diabetic dogs and the fall in plasma glucose in diabetic dogs are not influenced by the dose of insulin entrapped nor the lipid composition of the liposomes.