Enhanced Transepithelial Transport of Peptides by Conjugation to Cholic Acid

Abstract

The potential of the intestinal bile acid transporter to serve as a shuttle for small peptide molecules was investigated. Eleven peptides with a 2-6 amino acid backbone were conjugated to the 24-position of 3 alpha, 7 alpha, 12 alpha-trihydroxy-5 beta-cholan-24-oic acid (cholic acid) via an amide bond using an automated peptide synthesizer. In a human intestinal cell line (CaCo-2), cholic acid-peptide conjugates were able to inhibit the transepithelial transport of [3H]taurocholic acid, a natural substrate for the bile acid carrier, at a 100:1 conjugate/substrate ratio. Affinity for the carrier decreased significantly when the conjugate in the 24-position increased from 1 to 2 amino acids. Further increase in the amino acid chain length caused only minor decrease in affinity. A tetrapeptide-bile acid conjugate, [3H]-ChEAAA (Ch = cholic acid), was transported by the bile acid transporter, showing markedly higher apical (AP)-to-basolateral (BL) compared to BL-to-AP transport and inhibition by a 100-fold excess taurocholic acid. Another conjugate with 6 amino acids (ChEASASA) was transported by a passive diffusion pathway but still showed higher transport rates than the passive permeability marker mannitol, suggesting the possibility that the cholic acid moiety aids the passive membrane transfer of peptide molecules by increasing its lipophilicity. Metabolism of bile acid-peptide conjugates in CaCo-2 cells was 3% over 3 h. In conclusion, these studies show that the coupling of peptides to the 24-position of the sterol nucleus in cholic acid results in a combination of decreased metabolism and increased intestinal absorption, either by a carrier-mediated pathway or by accelerated passive diffusion.

Investigations into the absorption of insulin and insulin derivatives from the small intestine of the anaesthetised rat

“…This, however, was successful only for peptides of up to ten amino acids [75]. Conjugation has also been undertaken at the C 24 carboxyl group via a γ glutamyl link, though uptake was limited to tetrapeptides and hexapeptides [76].…”

Inhibition of hepatitis C virus RNA translation by antisense bile acid conjugated phosphorothioate modified oligodeoxynucleotides (ODN)

“…Conjugation of drugs as well as small peptide molecules and ODN by bile acid carriers has been described to augment uptake and selectivity of drug action, specifically in the liver (33,34). Conjugation of a drug to a bile acid has also the theoretical advantage of improving delivery from the gut to the liver due to enterohepatic circulation.…”

Apical Sodium Dependent Bile Acid Transporter (ASBT, SLC10A2): A Potential Prodrug Target

“…Similarly, the absorption of the C-24 dipeptide bile acid conjugate cholylglycyltyrosine was low compared to taurocholic acid 58 . Swaan et al evaluated the transport of peptides of varying length that were conjugated at the 24-position of cholic acid via an amide linkage 59 . While conjugation of peptides to bile acids did not directly enhance absorption via hASBT-mediated transport, it lead to lower metabolic lability 54,59 .…”