title: Hypoglycemic effect of insulin-transferrin conjugate in streptozotocin-induced diabetic rats.
abstract: Transferrin (Tf) receptor-mediated transcytosis of insulin-transferrin conjugate (In-Tf) has been demonstrated in cultured human enterocyte-like Caco-2 cells. In the present report, oral delivery of insulin as a Tf conjugate in streptozotocin (STZ)-induced diabetic rats was investigated. Human insulin was conjugated at a 1:1 molar ratio to iron-loaded human Tf by a disulfide linkage. The stability of In-Tf and the free insulin released from In-Tf was studied in the presence of rat liver slices by using radioimmunoassay. The release of free insulin involved a disulfide reduction reaction that was inhibited by the pretreatment of the liver slice with a sulfhydryl-reactive reagent N-ethylmaleimide. A protease inhibitor cocktail also showed a partial inhibition of insulin degradation. The biological activity of the conjugate was tested in STZ-induced diabetic rats with s.c. administration, and the conjugate exhibited a slow but prolonged hypoglycemic effect compared with that of the native human insulin. In-Tf also displayed a slow but prolonged hypoglycemic effect after oral administration in fasted STZ-induced diabetic rats in a dose-dependent manner. Furthermore, In-Tf was detected in the serum of rats at 4 h after oral administration of the conjugate, indicating that In-Tf can overcome the barriers in the gastrointestinal tract and be absorbed as an intact conjugate. These results demonstrate that transepithelial transport via TfR-mediated transcytosis is a feasible approach for developing the oral delivery of insulin, as well as other peptide drugs.
authors.affiliation: Department of Pharmaceutical Sciences, School of Pharmacy, University of Southern California, Los Angeles, California, USA.
authors.forename: C Q
authors.initials: CQ
authors.lastname: Xia
authors.forename: J
authors.initials: J
authors.lastname: Wang
authors.forename: W C
authors.initials: WC
authors.lastname: Shen
mesh_terms: D000284:Administration, Oral; D000818:Animals; D001786:Blood Glucose / Q000187:drug effects / Q000378:metabolism; D002851:Chromatography, High Pressure Liquid; D003921:Diabetes Mellitus, Experimental / Q000097:blood / Q000188:drug therapy* / Q000378:metabolism; D004355:Drug Stability; D005260:Female; D006801:Humans; D007004:Hypoglycemic Agents / Q000008:administration & dosage* / Q000097:blood / Q000493:pharmacokinetics; D007279:Injections, Subcutaneous; D007328:Insulin / Q000008:administration & dosage* / Q000097:blood / Q000493:pharmacokinetics; D008099:Liver / Q000378:metabolism; D051381:Rats; D017207:Rats, Sprague-Dawley; D014168:Transferrin / Q000008:administration & dosage* / Q000378:metabolism / Q000493:pharmacokinetics
chemical_list: D001786:Blood Glucose; D007004:Hypoglycemic Agents; D007328:Insulin; D014168:Transferrin