Intestinal Drug Transport via the Proton-Coupled Amino Acid Transporter PAT1 (SLC36A1) Is Inhibited by Gly-X_aa Dipeptides

Abstract

The oral absorption of some drug substances is mediated by nutrient transporters. As a consequence, nutrients and drugs may compete for available transporters, and interactions at the level of intestinal absorption are possible. Recently, we have identified δ-aminolevulinic acid, Gly-Gly, and Gly-Sar as substrates of the amino acid transporter PAT1. The aim of the present study is to investigate if other Gly-containing dipeptides interact with PAT1, and whether they can inhibit PAT1 mediated drug absorption, in vitro and in vivo. The in vitro methods included two-electrode voltage clamp measurements on hPAT1 expressing Xenopus laevis oocytes, which were used to investigate the PAT1-mediated transport of 17 different Gly-containing dipeptides (Gly-X(aa) or X(aa)-Gly). Also, the transepithelial transport of the PAT1 substrate gaboxadol was investigated across Caco-2 cell monolayers in the presence of different dipeptides. The in vivo part consisted of a pharmacokinetic study in rats following oral administration of gaboxadol and preadministration of 200 mg/kg dipeptide. The results showed that in hPAT1 expressing oocytes Gly-Tyr, Gly-Pro, and Gly-Phe inhibited currents induced by drug substances. In Caco-2 cell monolayers, Gly-Gly, Gly-Sar, and Gly-Pro significantly inhibited the PAT1 mediated absorptive transepithelial transport of gaboxadol; however, when orally administered to rats, Gly-Gly, Gly-Sar, Gly-Pro, or Gly-Tyr did not alter the pharmacokinetic profile of gaboxadol. In conclusion, the present study identifies selected dipeptides as inhibitors of PAT1 mediated drug absorption in various in vitro models.

Intestinal absorption of the antiepileptic drug substance vigabatrin is altered by infant formula in vitro and in vivo.

“…Moreover, some dipeptides have been shown to reduce gaboxadol and vigabatrin transport in PAT1 expressing Xenopus Laevis oocytes (Frolund et al. ). Since most low‐immunogenic infant formula contains extensively hydrolyzed protein that is amino acid and small peptides, we hypothesize that these infant formulas could interfere with vigabatrin absorption in the intestine.…”

PAT1 (SLC36A1) shows nuclear localization and affects growth of smooth muscle cells from rats

“…The last exon encodes the COOH terminus of the protein as well as a large 3=-untranslated region (7). Transport of proline, alanine, glycine, and GABA via PAT1 is proton coupled and sodium independent (30 -32) and may be inhibited by tryptophan and 5-hydroxytryptophan (5-HTP) and some dipeptides (13,19). Attempts to map modifications and amino acids in PAT1 with influence on transport activity has led to identification of an extracellular disulfide bridge (10) and a histidine residue probably localized within the protein binding site involved in the proton-coupled PAT1-mediated transport (20).…”

Sertraline inhibits the transport of PAT1 substrates in vivo and in vitro

“…Normally, PAT1 substrates have affinities in the range of 1–20 mM (Thwaites and Anderson, ). Inhibitors containing an indole group have affinities in the range of 1–6 mM (Metzner et al ., ; Larsen et al ., ), whereas dipeptide inhibitors have lower affinities (Frolund et al ., ). Our investigation of the mechanism of sertraline‐induced inhibition of hPAT1‐mediated transport in Caco‐2 cells revealed a non‐competitive type of inhibition.…”

“…X. laevis oocytes were obtained and treated as previously described (Frolund et al ., ). L‐[ 3 H]‐Pro uptake (40 μM, 3 μCi·mL −1 ) was measured in Ringer's solution (in mM: NaCl, 115; KCl, 2.5; CaCl 2 , 1.8; MgCl 2 , 0.1; MES, 10), pH adjusted to 6.0, in the absence and presence of 10 mM L‐Pro or 1–1000 μM sertraline.…”

“…Animals devoid of the slc36a1 gene are currently not available, therefore, in vivo investigations rely on the use of inhibitors of PAT1-mediated transport. The inhibitors identified so far fall into two very different categories, that is, dipeptides and indole derivatives (Metzner et al, 2005;Frolund et al, 2012). The dipeptides have a relatively poor affinity for hPAT1, whereas indole-containing amino acids and amines, such as 5-hydroxy-tryptamine (5-HT), L-tryptophan, 5-hydroxy-L-tryptophan (5-HTP) and tryptamine, have high affinities for hPAT1 of approximately 1-6 mM (Metzner et al, 2005).…”