The Entrapment of A Human Insulin-Deae Dextran Complex in Different Compound Liposomes

Abstract

Human insulin and a human insulin-DEAE (diethylaminoethyl) dextran complex entrapped in liposomes of various lipid compositions were studied. DMPC (dimyristoyl phosphatidylcholine) and E 200 H (Epikuron 200 H = hydrogenated soy lecithin) were the two phospholipids used and the liposome systems were phospholipid only, phospholipid/cholesterol compound in the molar ratios of 9:1, 8:2 and 7:3 as well as a positively charged liposome system of phospholipid/cholesterol/stearylamine compound in the molar ratio of 7:2:1. Liposomes were prepared by a chloroform film method and passed through a high pressure homogenizer. The percentage of entrapment of insulin in liposomes were determined by ultracentrifugation. Insulin was assayed by a modified Lowry method with protein precipitation. Positively charged liposomes gave the highest percentage of entrapment of approximately 76 and 58% with the uncomplexed human insulin system, and approximately 24 and 28% with the complexed human insulin system of the charged DMPC and E 200 H phospholipid liposomes respectively. In all cases, except the positively charged liposome system, the percentage of entrapment of the human insulin-DEAE dextran complex into liposomes was higher about 2–3% in a DMPC liposome system and about 2–8% in a E 200 H liposome system more than that of the uncomplexed insulin. Not only the increase of cholesterol contents in liposomes increased the percentage of entrapment of insulin, but also the homogenization of liposomes appears to increase the percentage of entrapment as well

The permeability kinetics of human insulin and human insulin-DEAE dextran complex from positively charged liposomes of both DMPC and E 200 H phospholipid was studied at 37°C in 0.067 M phosphate buffer, pH 7.4. All liposome systems appear to show a biphasic first order release kinetics of human insulin. The complexed human insulin system gave a release half life of about 2 times longer than the uncomplexed system in the first phase of DMPC liposomes and in the second phase of E 200 H liposomes. In the first phase of E 200 H liposomes, the complexed system showed a release half life of approximately 3 times longer than the uncomplexed insulin liposome system. However, in the second phase of DMPC liposomes, the release half life of the complexed and uncomplexed human insulin showed no significant differences. The human insulin-DEAE dextran complex liposomes showed about 14% and 7% human insulin bound to the liposome surface while the uncomplexed human insulin showed only 22% and 19% in DMPC and E 200 H liposome systems respectively