title: Transcellular delivery of an insulin-transferrin conjugate in enterocyte-like Caco-2 cells.
abstract: Insulin, acylated with dimethylmaleic anhydride, was conjugated to transferrin (Tf) via a disulfide linkage. The molar insulin: Tf ratio in the conjugate was 3:1. The insulin-Tf conjugate (insulin-Tf) was tested for the transport of insulin across enterocyte-like Caco-2 cell monolayers by the process of transferrin receptor (TfR)-mediated transcytosis. The uptake of insulin-Tf in Caco-2 cells was TfR-mediated but no insulin receptor-mediated. Transport studies showed that insulin-Tf transport was 5- to 15-fold higher than free insulin transport across Caco-2 cells in both apical-to-basal and basal-to-apical directions. Brefeldin A (BFA), an agent that we have previously shown to cause an increase in TfR transcytosis, further enhanced the transport of the conjugated insulin three-fold in both directions; thus, a combination of the conjugate and BFA can cause a net 45-fold increase in the apical-to-basolateral transport of insulin across Caco-2 cell monolayers. The transported conjugate was intact as indicated by elution on a Sephadex G-50 column. Insulin in the transcytosed conjugate, unlike the original dimethylmaleyl insulin, was capable of binding to anti-insulin antibodies, indicating that free amino groups of insulin were regenerated either during or after the transcytotic process. Because Caco-2 cell monolayers provide a good model for intestinal epithelium, the insulin-Tf conjugate in combination with BFA can be a rational approach to increase the oral absorption of insulin in vivo.
authors.affiliation: Department of Pharmaceutical Sciences, School of Pharmacy, University of Southern California, Los Angeles 90033, USA.
authors.forename: D
authors.initials: D
authors.lastname: Shah
authors.forename: W C
authors.initials: WC
authors.lastname: Shen
mesh_terms: D001692:Biological Transport; D020126:Brefeldin A; D018938:Caco-2 Cells / Q000378:metabolism; D003517:Cyclopentanes / Q000494:pharmacology; D006801:Humans; D007328:Insulin / Q000493:pharmacokinetics*; D007330:Insulin Antibodies / Q000276:immunology; D011990:Receptors, Transferrin / Q000502:physiology; D014168:Transferrin / Q000493:pharmacokinetics*
chemical_list: D003517:Cyclopentanes; D007328:Insulin; D007330:Insulin Antibodies; D011990:Receptors, Transferrin; D014168:Transferrin; D020126:Brefeldin A