Evaluation of the Bile Acid Transporter in Enhancing Intestinal Permeability to Renin-Inhibitory Peptides

Abstract

To evaluate the bile acid transporter as a means of enhancing the ability of renin-inhibitory peptides (RIPs) to penetrate the intestinal mucosa, two RIP-cholic acid conjugates and an RIP-taurocholic acid conjugate were synthesized. Conjugation was through the N-terminus of an RIP and the 3-position of the bile acid, via a six-carbon spacer. An RIP derivative containing the spacer without the bile acid moiety was also synthesized. The bile acid-RIP conjugates and the RIP derivative were shown to be potent inhibitors of human renin in vivo and to have in vivo hypotensive activity equivalent to that of the parent RIP (ditekiren) in a human renin-infused rat model. The ability of these RIP derivatives to bind to the bile acid transporter and be transported across an epithelial cell monolayer was evaluated in an in vitro model of the intestinal mucosa consisting of Caco-2 cell monolayers grown on microporous membranes. One of the RIP-cholic acid conjugate (KI = 60 +/- 10 microM) and the RIP-taurocholic acid conjugate (KI = 19 +/- 5 microM), but not the RIP derivative, were shown to be potent inhibitors of the apical (AP) to basolateral (BL) transport of [14C]-taurocholic acid ([14C]-TA). At concentrations up to 250 microM these RIP-bile acid conjugates had no effect on the diffusion of [3H]-PEG (800-1000), which is a marker of the paracellular pathway. The permeability coefficients of the RIP-bile acid conjugates, determined using Caco-2 cell monolayers, were shown to be six times less than that of [3H]-PEG (800-1000). In addition, the transport of one of the RIP-cholic acid conjugates was investigated in perfused rat ileum in which the mesenteric vein was cannulated. The conjugate was not detected in blood samples taken from the mesenteric vein, while its concentration in intestinal perfusate remained almost constant during the perfusion experiment. These results suggest that while the peptide-bile acid conjugates retain binding affinity for the intestinal bile acid transporter, the molecules are not themselves transported.

Electrical charge on protein regulates its absorption from the rat small intestine

“…Although some reports have suggested involvement of these mechanisms in the transport of glycosylated macromolecules (12,23), no improved absorption was observed for glycosylated Lyz derivatives. Kim et al (19) reported that bile acid-conjugated small peptides could bind to intestinal bile acid transporters without being transported.…”

Structural Biology and Function of Solute Transporters: Implications for Identifying and Designing Substrates

“…These studies prove that the coupling of drug entities to bile acids does not cause a loss of affinity for the hepatic bile acid carrier. Apart from the necessity of a negatively charged group around the C-24 position, Kim et al [165] have shown that some size restrictions apply when compounds are coupled to the C-3 position. Both the 3 and the 24 positions appear to be usable coupling points for a prodrug stratagem.…”

A Tribute to Ronald T. Borchardt—Teacher, Mentor, Scientist, Colleague, Leader, Friend, and Family Man

“…161 Then, Ron's laboratory and collaborators at The Upjohn Company (Kalamazoo, MI) used the Caco-2 cell model to evaluate whether the bile acid transporter can enhance the ability of renin-inhibitory peptides to penetrate the intestinal mucosa by synthesizing and testing peptide-cholic acid conjugates. 162 A similar "one-two punch" was used by exploiting the functional expression of a biotin (vitamin H) transporter, now known to be the sodium-dependent multivitamin transporter (SMVT or SLC5A6), in Caco-2 cells and the intestine to assess whether oral absorption of peptidic HIV-1 protease inhibitors could be enhanced through biotin-peptide conjugation. 163,164 Such studies led to many subsequent applications of the Caco-2 cell and BBMEC models in Ron's laboratory to elucidate the structural features of peptides and peptidomimetics influencing their ability to cross cell membranes.…”