Vigabatrin transport across the human intestinal epithelial (Caco‐2) brush‐border membrane is via the H⁺‐coupled amino‐acid transporter hPAT1

Abstract

The aim of this investigation was to determine if the human proton-coupled amino-acid transporter 1 (hPAT1 or SLC36A1) is responsible for the intestinal uptake of the orally-administered antiepileptic agent 4-amino-5-hexanoic acid (vigabatrin). The Caco-2 cell line was used as a model of the human small intestinal epithelium. Competition experiments demonstrate that [3H]GABA uptake across the apical membrane was inhibited by vigabatrin and the GABA analogues trans-4-aminocrotonic acid (TACA) and guvacine, whereas 1-(aminomethyl)cyclohexaneacetic acid (gabapentin) had no affect. Experiments with 2',7'-bis(2-carboxyethyl)-5(6)-carboxyfluorescein (BCECF)-loaded Caco-2 cells demonstrate that apical exposure to vigabatrin and TACA induce comparable levels of intracellular acidification (due to H+/amino-acid symport) to that generated by GABA, suggesting that they are substrates for a H+ -coupled absorptive transporter such as hPAT1. In hPAT1 and mPAT1-expressing Xenopus laevis oocytes [3H]GABA uptake was inhibited by vigabatrin, TACA and guvacine, whereas gabapentin failed to inhibit [3H]GABA uptake. In Na+ -free conditions, vigabatrin and TACA evoked similar current responses (due to H+/amino-acid symport) in hPAT1-expressing oocytes under voltage-clamp conditions to that induced by GABA (whereas no current was observed in water-injected oocytes) consistent with the ability of these GABA analogues to inhibit [3H]GABA uptake. This study demonstrates that hPAT1 is the carrier responsible for the uptake of vigabatrin across the brush-border membrane of the small intestine and emphasises the therapeutic potential of hPAT1 as a delivery route for orally administered, clinically significant GABA-related compounds.

Characterization of a blood-meal-responsive proton-dependent amino acid transporter in the disease vector, Aedes aegypti

“…The activity of this family of transporters is independent of Na + , K + and Cl -, but demonstrates dependence on pH, with amino acid uptake resulting in acidification of the cell (Abbot et al, 2006;Boll et al, 2002). Several PATs have been identified in vertebrates, and they fall into four PAT subclasses, but only PAT1 and PAT2 subclasses from human, mouse and rat have been characterized (Boll et al, 2003a;Boll et al, 2002;Chen et al, 2003a;Chen et al, 2003b;Kennedy et al, 2005;Sagne et al, 2001).…”

Hijacking Solute Carriers for Proton-Coupled Drug Transport

“…PAT1 is a high-capacity, low-affinity (K m ϳ0.5-10 mM) transporter of small neutral amino/imino acids and naturally occurring analogs including glycine, alanine, proline, hydroxy-proline, the neurotransmitter GABA, and the osmolytes taurine and betaine (Table 1) The relatively high capacity of PAT1 makes it an attractive target for oral delivery of hydrophilic, amino acid-like therapeutics. To date, PAT1 has been identified as the principal brush-border membrane transporter for D-serine (used in schizophrenia), the antibiotic D-cycloserine, the anti-hyperglycemic ␤-guanidinopropionic acid, and a number of therapeutic GABA analogs such as the anti-seizure drug vigabatrin (FIGURE 1A) (1,54,67,109,110,115). Recently, PAT1 (along with PepT1) has been identified as a transporter of 5-aminolevulinic acid, an orally delivered drug used widely in photodynamic therapy and imaging of cancer (5).…”

Transport of the Photodynamic Therapy Agent 5-Aminolevulinic Acid by Distinct H+-Coupled Nutrient Carriers Coexpressed in the Small Intestine

“…The H ϩ -coupled amino acid transporter PAT1 acts as a high-capacity, absorptive route for small neutral amino acids, such as GABA, and many orally active analogs across the brush-border membrane of the small intestine (Thwaites et al, 2000;Chen et al, 2003;Anderson et al, 2004;Abbot et al, 2006;Metzner et al, 2006;Thwaites and Anderson, 2007a;Larsen et al, 2009). PAT1 can also be considered a novel intestinal transporter of the heme precursor ALA, which is used extensively in photodynamic therapy.…”

“…PAT1 mediates uptake of GABA, other small neutral amino acids (e.g., proline, glycine, and taurine), and a large number of related amino acid analogs across the apical membrane of intestinal epithelial cells (Thwaites et al, 1995(Thwaites et al, , 2000Anderson et al, 2004;Metzner et al, 2006;Thwaites and Anderson, 2007a). PAT1 can also transport therapeutic GABA analogs such as vigabatrin and gaboxadol (Abbot et al, 2006;Larsen et al, 2009), which may account for the excellent bioavailability of these drugs when given orally. PAT1 transport, like that of PepT1, is driven by the H ϩ electrochemical gradient that exists because of an area of low pH adjacent to the intestinal luminal surface, called the acid microclimate (McEwan et al, 1988;Thwaites and Anderson, 2007b).…”