A model for evaluation of the peroral insulin therapy: short-term treatment of alloxan diabetic rats with oral water-in-oil-in-water insulin emulsions

Effect of bioadhesive polymers, sodium salicylate, polyoxyethylene-9-lauryl ether, and method of preparation on the relative hypoglycemia produced by insulin enteric-coated capsules in diabetic beagle dogs

The hypoglycemic effect of oral insulin capsules coated with pH-dependent Eudragit S100 and containing various absorption promoters was studied in hyperglycemic beagle dogs. The absorption enhancers used were bioadhesive polymers, sodium salicylate, and non-ionic surfactants. A comparative study of the bioadhesive polymers, polycarbophil (PC), hydroxypropyl methylcellulose (HPMC), and carbopol 934 in insulin-coated capsules revealed no significant difference between the insulin capsules containing these polymers, giving relative hypoglycemia (RH) values ranging from 4.3 +/- 2.3% to 6.5 +/- 5.1%. It was also found that the method of preparation of the mixture of the bioadhesive polymer with insulin either by physical mixing or freeze-drying did not affect the RH values obtained. Sodium salicylate, when used in insulin enteric-coated capsules (50 mg) mixed with insulin as a physical mixture, or prepared by wet granulation using 10% polyvinyl pyrollidone (PVP), or by freeze-drying, produced RH values ranging from 7.3 +/- 2.9% to 9.4 +/- 3.7%. When sodium salicylate (100 mg) was used with insulin in freeze-dried granules an RH value of 10 +/- 2.6% was produced. As the dose of insulin increased from 6 to 9 U/kg, the area under curve (AUC) of the enteric-coated capsules containing 50 mg sodium salicylate increased from 73.2 +/- 27.8% to 121.4 +/- 102.7% reduction, but the RH did not change significantly. Insulin capsules containing polyoxyethylene-9-lauryl ether (POELE) used in its optimum concentration (2%), found in these experiments, produced RH of 9.5 +/- 6.8% when prepared as granules by wetting with a few drops of absolute alcohol in the presence of PC (50 mg). Insulin capsules containing lower (1%) or higher (3%) concentrations of POELE and prepared with PC, 50 mg by wet granulation produced lower RH of about 6%. The enteric-coated oral insulin capsules containing insulin (6 or 9 U/kg) and sodium salicylate (50 mg) as an absorption promoter, together with the bioadhesive polymer polycarbophil (50 mg), and prepared either by wet granulation using ethanol or by freeze-drying, are the best formulations to be used. They achieved a reduction in plasma glucose levels of about 25-30% and RH of about 10%. Also insulin (9 U/kg) capsules containing 2% POELE produced a 28% reduction in plasma glucose levels and RH of 9.6 +/- 6.8%.

Insulin in w/o/w multiple emulsions: preparation characterization and determination of stability towards proteases in vitro

In this work two w/o/w multiple emulsions composed of soybean oil or medium-chain triglycerides and containing insulin were studied. These emulsions were prepared by means of two-step emulsification procedure. The w/o/w emulsions obtained were stable for at least 6 months of storage at 4-6 degrees C. The yield of encapsulation of insulin was > 95%. The main release mechanism is a swelling-breakdown phenomenon. In vitro, the two w/o/w multiple emulsions were able to protect insulin against enzymatic degradation. These results indicate that multiple emulsions have potential as a carrier of insulin for oral administration.

Insulin in w/o/w multiple emulsions: biological activity after oral administration in normal and diabetic rats

In this work the biological effects of two w/o/w multiple emulsions composed of the soybean oil (EHS) or medium-chain triglycerides (ETCM), containing insulin, were studied. The release mechanism of insulin from multiple emulsions proposed in our previous in-vitro investigations was confirmed by subcutaneous administration. This mechanism is the swelling-breakdown phenomenon which occurs when the emulsions are diluted under hypo-osmotic condition. The biological effect after oral administration, evaluated in two experimental protocols, single administration in normal and diabetic rats and short-term treatment in diabetic rats, shows that in diabetic rats small amounts of biologically active insulin were absorbed from these emulsions. In these experiments no significant difference between EHS and ETCM was found.

The stability of liposomes in vitro to pH, bile salts and pancreatic lipase

If liposomes are to be effective as carriers for the oral administration of insulin they must be able to withstand passage through the stomach and small intestine. Multilamellar liposomes, some identical in composition to those used in reported in vivo studies on the uptake of orally administered insulin, were tested in vitro for their stability in the presence of bile salts, pancreatic lipase, and variations in pH. While low or high pH had little effect on most liposomes, 10 mM bile salts caused the release of over 80% of entrapped marker from all liposomes tested except those composed of distearoyl phosphatidylcholine/cholesterol and those composed of dipalmitoyl phosphatidylethanolamine/cholesterol/dicetylphosphate. However, the latter were unstable at low pH. The distearoyl phosphatidylcholine/cholesterol liposomes were also resistant to pancreatic lipase, and therefore may be suitable for use in the oral administration of therapeutic agents.

Effects of bile salts on the structural integrity of liposomes

The effects of the bile salts, sodium taurocholate and sodium glycocholate on the structural integrity of liposomes of different lipid compositions were studied. The bile salt concentrations were in the range encountered in the human intestine and the incubations were conducted at 37 degrees C. Two measures of liposome integrity were used: (a) changes in their light-scattering properties; and (b) release of entrapped potassium chromate. The results show that "fluid" liposomes, i.e., those prepared from phospholipids whose phase transition temperatures are below 37 degrees C, were totally disrupted in the presence of 10 mM bile salts at pH 7.4, and their entire contents were released. In the case of liposomes prepared from phospholipids with phase transition temperatures above 37 degrees C, the effect of the bile salts became less pronounced as the phase transition temperature increased. Nevertheless, a considerable proportion of the entrapped marker compound was released from liposomes with phase transition temperatures as high as 60 degrees C. The relevance of these results to the reported liposome-mediated gastrointestinal uptake of insulin is discussed.