D. Shah et Wc. Shen, TRANSCELLULAR DELIVERY OF AN INSULIN-TRANSFERRIN CONJUGATE IN ENTEROCYTE-LIKE CACO-2 CELLS, Journal of pharmaceutical sciences, 85(12), 1996, pp. 1306-1311
Insulin, acylated with dimethylmaleic anhydride, was conjugated to tra
nsferrin (Tf) via a disulfide linkage. The molar insulin: Tf ratio in
the conjugate was 3:1. The insulin-Tf conjugate (insulin-Tf) was teste
d for the transport of insulin across enterocyte-like Caco-2 cell mono
layers by the process of transferrin receptor (TfR)-mediated transcyto
sis. The uptake of insulin-Tf in Caco-2 cells was TfR-mediated but not
insulin receptor-mediated. Transport studies showed that insulin-Tf t
ransport was 5- to 15-fold higher than free insulin transport across C
aco-2 cells in both apical-to-basal and basal-to-apical directions. Br
efeldin A (BFA), an agent that we have previously shown to cause an in
crease in TfR transcytosis, further enhanced the transport of the conj
ugated insulin three-fold in both directions; thus, a combination of t
he conjugate and BFA can cause a net 45-fold increase in the apical-to
-basolateral transport of insulin across Caco-2 cell monolayers. The t
ransported conjugate was intact as indicated by elution on a Sephadex
G-50 column. Insulin in the transcytosed conjugate, unlike the origina
l dimethylmaleyl insulin, was capable of binding to anti-insulin antib
odies, indicating that free amino groups of insulin were regenerated e
ither during or after the transcytotic process. Because Caco-2 cell mo
nolayers provide a good model for intestinal epithelium, the insulin-T
f conjugate in combination with BFA can be a rational approach to incr
ease the oral absorption of insulin in vivo.