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Jakobsen S, Nielsen CU. Exploring Amino Acid Transporters as Therapeutic Targets for Cancer: An Examination of Inhibitor Structures, Selectivity Issues, and Discovery Approaches. Pharmaceutics 2024; 16:197. [PMID: 38399253 PMCID: PMC10893028 DOI: 10.3390/pharmaceutics16020197] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/19/2023] [Revised: 01/18/2024] [Accepted: 01/28/2024] [Indexed: 02/25/2024] Open
Abstract
Amino acid transporters are abundant amongst the solute carrier family and have an important role in facilitating the transfer of amino acids across cell membranes. Because of their impact on cell nutrient distribution, they also appear to have an important role in the growth and development of cancer. Naturally, this has made amino acid transporters a novel target of interest for the development of new anticancer drugs. Many attempts have been made to develop inhibitors of amino acid transporters to slow down cancer cell growth, and some have even reached clinical trials. The purpose of this review is to help organize the available information on the efforts to discover amino acid transporter inhibitors by focusing on the amino acid transporters ASCT2 (SLC1A5), LAT1 (SLC7A5), xCT (SLC7A11), SNAT1 (SLC38A1), SNAT2 (SLC38A2), and PAT1 (SLC36A1). We discuss the function of the transporters, their implication in cancer, their known inhibitors, issues regarding selective inhibitors, and the efforts and strategies of discovering inhibitors. The goal is to encourage researchers to continue the search and development within the field of cancer treatment research targeting amino acid transporters.
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Affiliation(s)
- Sebastian Jakobsen
- Department of Physics, Chemistry and Pharmacy, University of Southern Denmark, Campusvej 55, DK-5230 Odense, Denmark
| | - Carsten Uhd Nielsen
- Department of Physics, Chemistry and Pharmacy, University of Southern Denmark, Campusvej 55, DK-5230 Odense, Denmark
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Walters DC, Jansen EEW, Salomons GS, Arning E, Ashcraft P, Bottiglieri T, Roullet JB, Gibson KM. Preferential accumulation of the active S-(+) isomer in murine retina highlights novel mechanisms of vigabatrin-associated retinal toxicity. Epilepsy Res 2020; 170:106536. [PMID: 33385945 DOI: 10.1016/j.eplepsyres.2020.106536] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/29/2020] [Revised: 11/27/2020] [Accepted: 12/15/2020] [Indexed: 11/17/2022]
Abstract
((S)-(+)/(R)-(-)) vigabatrin (SabrilR; γ-vinyl GABA), an antiepileptic irreversibly inactivating GABA-transaminase, was administered to male C57Bl6 J mice via continuous infusion (0, 40, 80 mg/kg/d) for 12 days. Our study design pooled retina, eye (minus retina), whole brain and plasma from n = 24 animals for each dose to provide n = 8 triplicates per treatment group. Hypothesizing that (S)-(+) VGB (active isomer) would preferentially accumulate in retina, we determined VGB isomers, comprehensive amino acids, and pharmacokinetic parameters. In brain, eye and plasma, the ((S)-(+)/(R)-(-)) ratio varied from 0.73 to 1.29 and 13.3 in retina, accompanied by a partition coefficient (tissue/plasma, ((S)-(+);(R)-(-))) of 5.8;0.34, 0.63;0.49, and 0.51;0.34 in retina, eye and brain, respectively. Racemic VGB (nmol/g; plasma, nmol/mL, range of means for dose) content was: retina, 25-36; eye (minus retina), 4.8-8.0; brain, 3.1-6.8 and plasma, 8.7-14.9. GABA tissue content (nmol/g) was 1246-3335, 18-64 and 2615-3200 as a function of VGB dose for retina, eye (minus retina) and brain, respectively. The retinal glial cell toxin 2-aminoadipic acid also increased with VGB dose (76-96 nmol/g). Partitioning of active (S)-(+) VGB to retina suggests the involvement of a stereospecific transporter, the identification of which could reveal new therapeutic paradigms that might mitigate VGB's well-known retinal toxicity and expand its clinical utility.
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Affiliation(s)
- Dana C Walters
- Department of Pharmacotherapy, College of Pharmacy and Pharmaceutical Sciences, Washington State University, Spokane, WA, USA
| | - Erwin E W Jansen
- Department of Clinical Chemistry, Metabolic Unit, VU University Medical Center & Amsterdam Neuroscience, Amsterdam, the Netherlands
| | - Gajja S Salomons
- Department of Clinical Chemistry, Metabolic Unit, VU University Medical Center & Amsterdam Neuroscience, Amsterdam, the Netherlands
| | - Erland Arning
- Baylor Scott & White Research Institute, Institute of Metabolic Disease, Dallas, TX, USA
| | - Paula Ashcraft
- Baylor Scott & White Research Institute, Institute of Metabolic Disease, Dallas, TX, USA
| | - Teodoro Bottiglieri
- Baylor Scott & White Research Institute, Institute of Metabolic Disease, Dallas, TX, USA
| | - Jean-Baptiste Roullet
- Department of Pharmacotherapy, College of Pharmacy and Pharmaceutical Sciences, Washington State University, Spokane, WA, USA
| | - K Michael Gibson
- Department of Pharmacotherapy, College of Pharmacy and Pharmaceutical Sciences, Washington State University, Spokane, WA, USA.
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Nielsen CU, Pedersen M, Müller S, Kæstel T, Bjerg M, Ulaganathan N, Nielsen S, Carlsen KL, Nøhr MK, Holm R. Inhibitory Effects of 17-α-Ethinyl-Estradiol and 17-β-Estradiol on Transport Via the Intestinal Proton-Coupled Amino Acid Transporter (PAT1) Investigated In Vitro and In Vivo. J Pharm Sci 2020; 110:354-364. [PMID: 32835702 DOI: 10.1016/j.xphs.2020.08.010] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/01/2020] [Revised: 08/12/2020] [Accepted: 08/18/2020] [Indexed: 11/24/2022]
Abstract
The proton-coupled amino acid transporter, PAT1, is known to be responsible for intestinal absorption drug substances such as gaboxadol and vigabatrin. The aim of the present study was to investigate, if 17-α-ethinyl-estradiol (E-E2) and 17-β-estradiol (E) inhibit PAT1-mediated intestinal absorption of proline and taurine in vitro in Caco-2 cells and in vivo using Sprague-Dawley rats to assess the potential for taurine-drug interactions. E and E-E2 inhibited the PAT1-mediated uptake of proline and taurine in Caco-2 cells with IC50 values of 10.0-50.0 μM without major effect on other solute carriers such as the taurine transporter (TauT), di/tri-peptide transporter (PEPT1), and serotonin transporter (SERT1). In PAT1-expressing oocytes E and E-E2 were non-translocated inhibitors. In Caco-2 cells, E and E-E2 lowered the maximal uptake capacity of PAT1 in a non-competitive manner. Likewise, the transepithelial permeability of proline and taurine was reduced in presence of E and E-E2. In male Sprague Dawley rats pre-dosed with E-E2 a decreased maximal plasma concentration (Cmax) of taurine and increased the time (tmax) to reach this was indicated, suggesting the possibility for an in vivo effect on the absorption of PAT1 substrates. In conclusion, 17-α-ethinyl-estradiol and 17-β-estradiol were identified as non-translocated and non-competitive inhibitors of PAT1.
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Affiliation(s)
- Carsten Uhd Nielsen
- Department of Physics, Chemistry and Pharmacy, University of Southern Denmark, Campusvej 55, DK-5230 Odense M, Denmark.
| | - Maria Pedersen
- Department of Physics, Chemistry and Pharmacy, University of Southern Denmark, Campusvej 55, DK-5230 Odense M, Denmark
| | - Stefanie Müller
- Department of Pharmacy, Faculty of Health and Medical Sciences, Universitetsparken 2, DK-2100 Copenhagen, Denmark
| | - Thea Kæstel
- Department of Pharmacy, Faculty of Health and Medical Sciences, Universitetsparken 2, DK-2100 Copenhagen, Denmark
| | - Maria Bjerg
- Department of Physics, Chemistry and Pharmacy, University of Southern Denmark, Campusvej 55, DK-5230 Odense M, Denmark
| | - Nithiya Ulaganathan
- Department of Physics, Chemistry and Pharmacy, University of Southern Denmark, Campusvej 55, DK-5230 Odense M, Denmark
| | - Salli Nielsen
- Department of Physics, Chemistry and Pharmacy, University of Southern Denmark, Campusvej 55, DK-5230 Odense M, Denmark
| | - Krestine Lundgaard Carlsen
- Department of Physics, Chemistry and Pharmacy, University of Southern Denmark, Campusvej 55, DK-5230 Odense M, Denmark
| | - Martha Kampp Nøhr
- Department of Pharmacy, Faculty of Health and Medical Sciences, Universitetsparken 2, DK-2100 Copenhagen, Denmark
| | - René Holm
- Drug Product Development, Janssen R&D, Johnson & Johnson, Turnhoutseweg 30, 2340 Beerse, Belgium; Department of Science and Environment, Roskilde University, 4000 Roskilde, Denmark
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Police A, Shankar VK, Murthy SN. Role of Taurine Transporter in the Retinal Uptake of Vigabatrin. AAPS PharmSciTech 2020; 21:196. [PMID: 32666325 DOI: 10.1208/s12249-020-01736-7] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/22/2020] [Accepted: 06/20/2020] [Indexed: 12/18/2022] Open
Abstract
Vigabatrin (VGB) is a first-line drug used for treatment of infantile spasms. On therapeutic dose, VGB accumulates in the retina causing permanent peripheral visual field constriction. The mechanism involved in retinal accumulation of VGB is ambiguous. In the present study, mechanism of VGB transport into retina was evaluated. VGB uptake into retina was studied in vitro using human adult retinal pigment epithelial (ARPE-19) cells as a model for outer blood retinal barrier. The VGB cell uptake studies demonstrated saturation kinetics with Km value of 13.1 mM and uptake was significantly increased at pH 7.4 and hyperosmolar conditions indicating involvement of carrier-mediated Na+-Cl--dependent transporter. In the presence of taurine transporter (TauT) substrates (taurine and GABA) and inhibitor guanidinoethyl sulfonate (GES), the uptake of VGB decreased significantly demonstrating contribution of TauT. The VGB retinal levels in rats were decreased by 1.5- and 1.3-folds on chronic administration of GES and taurine, respectively. In conclusion, this study demonstrated the TauT involvement in VGB uptake and accumulation in retina.
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Nepomuceno DB, Paim RMM, Araújo RN, Pereira MH, Pessoa GCD, Koerich LB, Sant'Anna MRV, Gontijo NF. The role of LuloPAT amino acid/proton symporters in midgut alkalinization in the sandfly Lutzomyia longipalpis (Diptera - Psychodidae). JOURNAL OF INSECT PHYSIOLOGY 2020; 120:103973. [PMID: 31715141 DOI: 10.1016/j.jinsphys.2019.103973] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 05/27/2019] [Revised: 11/07/2019] [Accepted: 11/08/2019] [Indexed: 06/10/2023]
Abstract
In Lutzomyia longipalpis females, which are the main vectors of Leishmania infantum in the Americas, hematophagy is crucial for ovary development. The control of pH in the midgut during blood digestion is important to the functioning of the digestive enzymes, which release amino acids in the luminal compartment that are then transported through the enterocytes to the hemolymph for delivery to the ovary and other organs. In the present work, we investigated transport systems known as LuloPATs that are present in the midgut of L. longipalpis but not in other organs. These transporters achieve symport of amino acids with H+ ions, and one of them (LuloPAT1) is orthologous to a transporter described in Aedes aegypti. According to our results, the transcription levels of LuloPAT1 increased significantly immediately after a blood meal. Based on the variation of the fluorescence of fluorescein with the pH of the medium, we developed a technique that shows the acidification of the cytoplasm of gut cells when amino acids are cotransported with H+ from the lumen into the enterocytes. In our experiments, the midguts of the sandflies were dissected and opened longitudinally so that added amino acids could enter the enterocytes via the lumen (PAT carriers are apical). LuloPAT1 transporters are part of a complex of mechanisms that act synergistically to promote gut alkalinization as soon as blood intake by the vector occurs. In dissected but not longitudinally opened midguts, added amino acids could only enter through the basolateral region of enterocytes. However, alkalinization of the lumen was observed because the entry of some amino acids into the cytoplasm of enterocytes triggers a luminal alkalinization mechanism independent of LuloPATs. These findings provide new perspectives that will enable the characterization of the set of signaling pathways involved in pH regulation within the L. longipalpis midgut.
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Affiliation(s)
- Denise Barguil Nepomuceno
- Laboratório de Fisiologia de Insetos Hematófagos, Departamento de Parasitologia/ICB, Universidade Federal de Minas Gerais, Caixa Postal 486, 31270-901 Belo Horizonte, MG, Brazil
| | - Rafaela Magalhães Macedo Paim
- Laboratório de Fisiologia de Insetos Hematófagos, Departamento de Parasitologia/ICB, Universidade Federal de Minas Gerais, Caixa Postal 486, 31270-901 Belo Horizonte, MG, Brazil
| | - Ricardo Nascimento Araújo
- Laboratório de Fisiologia de Insetos Hematófagos, Departamento de Parasitologia/ICB, Universidade Federal de Minas Gerais, Caixa Postal 486, 31270-901 Belo Horizonte, MG, Brazil
| | - Marcos Horácio Pereira
- Laboratório de Fisiologia de Insetos Hematófagos, Departamento de Parasitologia/ICB, Universidade Federal de Minas Gerais, Caixa Postal 486, 31270-901 Belo Horizonte, MG, Brazil.
| | - Grasielle Caldas D'Ávila Pessoa
- Laboratório de Fisiologia de Insetos Hematófagos, Departamento de Parasitologia/ICB, Universidade Federal de Minas Gerais, Caixa Postal 486, 31270-901 Belo Horizonte, MG, Brazil
| | - Leonardo Barbosa Koerich
- Laboratório de Fisiologia de Insetos Hematófagos, Departamento de Parasitologia/ICB, Universidade Federal de Minas Gerais, Caixa Postal 486, 31270-901 Belo Horizonte, MG, Brazil
| | - Mauricio Roberto Viana Sant'Anna
- Laboratório de Fisiologia de Insetos Hematófagos, Departamento de Parasitologia/ICB, Universidade Federal de Minas Gerais, Caixa Postal 486, 31270-901 Belo Horizonte, MG, Brazil
| | - Nelder Figueiredo Gontijo
- Laboratório de Fisiologia de Insetos Hematófagos, Departamento de Parasitologia/ICB, Universidade Federal de Minas Gerais, Caixa Postal 486, 31270-901 Belo Horizonte, MG, Brazil.
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Henze LJ, Koehl NJ, O'Shea JP, Kostewicz ES, Holm R, Griffin BT. The pig as a preclinical model for predicting oral bioavailability and in vivo performance of pharmaceutical oral dosage forms: a PEARRL review. ACTA ACUST UNITED AC 2018; 71:581-602. [PMID: 29635685 DOI: 10.1111/jphp.12912] [Citation(s) in RCA: 46] [Impact Index Per Article: 7.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/03/2017] [Accepted: 03/03/2018] [Indexed: 12/21/2022]
Abstract
OBJECTIVES In pharmaceutical drug development, preclinical tests in animal models are essential to demonstrate whether the new drug is orally bioavailable and to gain a first insight into in vivo pharmacokinetic parameters that can subsequently be used to predict human values. Despite significant advances in the development of bio-predictive in vitro models and increasing ethical expectations for reducing the number of animals used for research purposes, there is still a need for appropriately selected pre-clinical in vivo testing to provide guidance on the decision to progress to testing in humans. The selection of the appropriate animal models is essential both to maximise the learning that can be obtained from such experiments and to avoid unnecessary testing in a range of species. KEY FINDINGS The present review, provides an insight into the suitability of the pig model for predicting oral bioavailability in humans, by comparing the conditions in the GIT. It also contains a comparison between the bioavailability of compounds dosed to both humans and pigs, to provide an insight into the relative correlation and examples on why a lack of correlation may be observed. SUMMARY While there is a general trend towards predicting human bioavailability from pig data, there is considerable variability in the data set, most likely reflecting species specific differences in individual drug metabolism. Nonetheless, the correlation between pigs vs. humans was comparable to that reported for dogs vs. humans. The presented data demonstrate the suitability of the pig as a preclinical model to predict bioavailability in human.
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Affiliation(s)
- Laura J Henze
- School of Pharmacy, University College Cork, Cork, Ireland
| | - Niklas J Koehl
- School of Pharmacy, University College Cork, Cork, Ireland
| | | | - Edmund S Kostewicz
- Institute of Pharmaceutical Technology, Goethe University, Frankfurt am Main, Germany
| | - René Holm
- Drug Product Development, Janssen Research and Development, Johnson & Johnson, Beerse, Belgium
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Spelbrink EM, Mabud TS, Reimer R, Porter BE. Plasma taurine levels are not affected by vigabatrin in pediatric patients. Epilepsia 2016; 57:e168-72. [PMID: 27344989 DOI: 10.1111/epi.13447] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 05/26/2016] [Indexed: 11/29/2022]
Abstract
Vigabatrin is a highly effective antiseizure medication, but its use is limited due to concerns about retinal toxicity. One proposed mechanism for this toxicity is vigabatrin-mediated reduction of taurine. Herein we assess plasma taurine levels in a retrospective cohort of children with epilepsy, including a subset receiving vigabatrin. All children who underwent a plasma amino acid analysis as part of their clinical evaluation between 2006 and 2015 at Stanford Children's Health were included in the analysis. There were no significant differences in plasma taurine levels between children taking vigabatrin (n = 16), children taking other anti-seizure medications, and children not taking any anti-seizure medication (n = 556) (analysis of variance [ANOVA] p = 0.841). There were, however, age-dependent decreases in plasma taurine levels. Multiple linear regression revealed no significant association between vigabatrin use and plasma taurine level (p = 0.87) when controlling for age. These results suggest that children taking vigabatrin maintain normal plasma taurine levels, although they leave unanswered whether taurine supplementation is necessary or sufficient to prevent vigabatrin-associated visual field loss. They also indicate that age should be taken into consideration when evaluating taurine levels in young children.
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Affiliation(s)
- Emily M Spelbrink
- Department of Neurology, Stanford University School of Medicine, Stanford, California, U.S.A.,Department of Neurology, Stanford Children's Health, Palo Alto, California, U.S.A
| | - Tarub S Mabud
- Department of Neurology, Stanford University School of Medicine, Stanford, California, U.S.A
| | - Richard Reimer
- Department of Neurology, Stanford University School of Medicine, Stanford, California, U.S.A
| | - Brenda E Porter
- Department of Neurology, Stanford University School of Medicine, Stanford, California, U.S.A.,Department of Neurology, Stanford Children's Health, Palo Alto, California, U.S.A
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Rasmussen RN, Lagunas C, Plum J, Holm R, Nielsen CU. Interaction of GABA-mimetics with the taurine transporter (TauT, Slc6a6) in hyperosmotic treated Caco-2, LLC-PK1 and rat renal SKPT cells. Eur J Pharm Sci 2015; 82:138-46. [PMID: 26631583 DOI: 10.1016/j.ejps.2015.11.020] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/01/2015] [Revised: 11/11/2015] [Accepted: 11/25/2015] [Indexed: 10/22/2022]
Abstract
The aim of the present study was to investigate if basic GABA-mimetics interact with the taurine transporter (TauT, Slc6a6), and to find a suitable cell based model that is robust towards extracellular changes in osmolality during uptake studies. Taurine uptake was measured in human Caco-2 cells, porcine LLC-PK1 cells, and rat SKPT cells using radiolabelled taurine. Hyperosmotic conditions were obtained by incubation with raffinose (final osmolality of 500mOsm) for 24h prior to the uptake experiments. Expression of the taurine transporter, TauT, was investigated at the mRNA level by real-time PCR. Uptake of the GABA-mimetics gaboxadol and vigabatrin was investigated in SKPT cells, and quantified by liquid scintillation or HPLC-MS/MS analysis, respectively. The uptake rate of [(3)H]-taurine was Na(+) and Cl(-) and concentration dependent with taurine with an apparent Vmax of 6.3±1.6pmolcm(-2)min(-1) and a Km of 24.9±15.0μM. β-alanine, nipecotic acid, gaboxadol, GABA, vigabatrin, δ-ALA and guvacine inhibited the taurine uptake rate in a concentration dependent manner. The order of affinity for TauT was β-alanine>GABA>nipecotic acid>guvacine>δ-ALA>vigabatrin>gaboxadol with IC50-values of 0.04, 1.07, 2.02, 4.19, 4.94, 31.4 and 39.9mM, respectively. In conclusion, GABA mimetics inhibited taurine uptake in hyperosmotic rat renal SKPT cells. SKPT cells, which seem to be a useful model for investigating taurine transport in the short-term presence of high concentrations of osmolytes. Furthermore, analogues of β-alanine appear to have higher affinities for TauT than GABA-analogues.
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Affiliation(s)
- Rune Nørgaard Rasmussen
- Department of Physics, Chemistry and Pharmacy, University of Southern Denmark, Campusvej 55, DK 5230 Odense M, Denmark
| | - Candela Lagunas
- Drug Transporters in ADME, Department of Pharmacy, Faculty of Health and Medical Sciences, Universitetsparken 2, DK 2100, Copenhagen, Denmark
| | - Jakob Plum
- Drug Transporters in ADME, Department of Pharmacy, Faculty of Health and Medical Sciences, Universitetsparken 2, DK 2100, Copenhagen, Denmark
| | - René Holm
- Pharmaceutical Science and CMC Biologics, H. Lundbeck A/S, DK 2500, Valby, Denmark
| | - Carsten Uhd Nielsen
- Department of Physics, Chemistry and Pharmacy, University of Southern Denmark, Campusvej 55, DK 5230 Odense M, Denmark.
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Nøhr M, Juul R, Thale Z, Holm R, Kreilgaard M, Nielsen C. Is oral absorption of vigabatrin carrier-mediated? Eur J Pharm Sci 2015; 69:10-8. [DOI: 10.1016/j.ejps.2014.12.018] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/03/2014] [Revised: 12/17/2014] [Accepted: 12/25/2014] [Indexed: 01/28/2023]
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Nøhr MK, Thale ZI, Brodin B, Hansen SH, Holm R, Nielsen CU. Intestinal absorption of the antiepileptic drug substance vigabatrin is altered by infant formula in vitro and in vivo. Pharmacol Res Perspect 2014; 2:e00036. [PMID: 25505585 PMCID: PMC4184708 DOI: 10.1002/prp2.36] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/21/2014] [Accepted: 02/25/2014] [Indexed: 11/25/2022] Open
Abstract
Vigabatrin is an antiepileptic drug substance mainly used in pediatric treatment of infantile spasms. The main source of nutrition for infants is breast milk and/or infant formula. Our hypothesis was that infant formula may affect the intestinal absorption of vigabatrin. The aim was therefore to investigate the potential effect of coadministration of infant formula with vigabatrin on the oral absorption in vitro and in vivo. The effect of vigabatrin given with an infant formula on the oral uptake and transepithelial transport was investigated in vitro in Caco-2 cells. In vivo effects of infant formula and selected amino acids on the pharmacokinetic profile of vigabatrin was investigated after oral coadministration to male Sprague–Dawley rats using acetaminophen as a marker for gastric emptying. The presence of infant formula significantly reduced the uptake rate and permeability of vigabatrin in Caco-2 cells. Oral coadministration of vigabatrin and infant formula significantly reduced Cmax and prolonged tmax of vigabatrin absorption. Ligands for the proton-coupled amino acid transporter PAT1, sarcosine, and proline/l-tryptophan had similar effects on the pharmacokinetic profile of vigabatrin. The infant formula decreased the rate of gastric emptying. Here we provide experimental evidence for an in vivo role of PAT1 in the intestinal absorption of vigabatrin. The effect of infant formula on the oral absorption of vigabatrin was found to be due to delayed gastric emptying, however, it seems reasonable that infant formula may also directly affect the intestinal absorption rate of vigabatrin possibly via PAT1.
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Affiliation(s)
- Martha Kampp Nøhr
- Department of Pharmacy, Faculty of Health and Medical Sciences, University of Copenhagen DK-2100, Copenhagen, Denmark
| | - Zia I Thale
- Department of Bioanalysis, H. Lundbeck A/S DK-2500, Valby, Denmark
| | - Birger Brodin
- Department of Pharmacy, Faculty of Health and Medical Sciences, University of Copenhagen DK-2100, Copenhagen, Denmark
| | - Steen H Hansen
- Department of Pharmacy, Faculty of Health and Medical Sciences, University of Copenhagen DK-2100, Copenhagen, Denmark
| | - René Holm
- Department of Pharmacy, Faculty of Health and Medical Sciences, University of Copenhagen DK-2100, Copenhagen, Denmark ; Biologics and Pharmaceutical Science, H. Lundbeck A/S DK-2500, Valby, Denmark
| | - Carsten Uhd Nielsen
- Department of Pharmacy, Faculty of Health and Medical Sciences, University of Copenhagen DK-2100, Copenhagen, Denmark
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Plum J, Nøhr MK, Hansen SH, Holm R, Nielsen CU. The anti-epileptic drug substance vigabatrin inhibits taurine transport in intestinal and renal cell culture models. Int J Pharm 2014; 473:395-7. [PMID: 25062867 DOI: 10.1016/j.ijpharm.2014.07.023] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/07/2014] [Accepted: 07/17/2014] [Indexed: 10/25/2022]
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Nielsen CU, Frølund S, Abdulhadi S, Sari H, Langthaler L, Nøhr MK, Kall MA, Brodin B, Holm R. Sertraline inhibits the transport of PAT1 substrates in vivo and in vitro. Br J Pharmacol 2014; 170:1041-52. [PMID: 23962042 DOI: 10.1111/bph.12341] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/06/2013] [Revised: 07/02/2013] [Accepted: 08/03/2013] [Indexed: 01/16/2023] Open
Abstract
BACKGROUND AND PURPOSE Intestinal nutrient transporters may mediate the uptake of drugs. The aim of this study was to investigate whether sertraline interacts with the intestinal proton-coupled amino acid transporter 1 PAT1 (SLC36A1). EXPERIMENTAL APPROACH In vitro investigations of interactions between sertraline and human (h)PAT1, hSGLT1 (sodium-glucose linked transporter 1) and hPepT1 (proton-coupled di-/tri-peptide transporter 1) were conducted in Caco-2 cells using radiolabelled substrates. In vivo pharmacokinetic investigations were conducted in male Sprague-Dawley rats using gaboxadol (10 mg·kg(-1), p.o.) as a PAT1 substrate and sertraline (0-30.6 mg·kg(-1)). Gaboxadol was quantified by hydrophilic interaction chromatography followed by MS/MS detection. KEY RESULTS Sertraline inhibited hPAT1-mediated L-[(3)H]-Pro uptake in Caco-2 cells. This interaction between sertraline and PAT1 appeared to be non-competitive. The uptake of the hSGLT1 substrate [(14)C]-α-methyl-D-glycopyranoside and the hPepT1 substrate [(14)C]-Gly-Sar in Caco-2 cells was also decreased in the presence of 0.3 mM sertraline. In rats, the administration of sertraline (0.1-10 mM, corresponding to 0.3-30.6 mg·kg(-1), p.o.) significantly reduced the maximal gaboxadol plasma concentration and AUC after its administration p.o. CONCLUSIONS AND IMPLICATIONS Sertraline is an apparent non-competitive inhibitor of hPAT1-mediated transport in vitro. This inhibitory effect of sertraline is not specific to hPAT1 as substrate transport via hPepT1 and hSGLT1 was also reduced in the presence of sertraline. In vivo, sertraline reduced the amount of gaboxadol absorbed, suggesting that the inhibitory effect of sertraline on PAT1 occurs both in vitro and in vivo. Hence, sertraline could alter the bioavailability of drugs absorbed via PAT1.
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Affiliation(s)
- C U Nielsen
- Department of Pharmacy, Faculty of Health and Medical Sciences, University of Copenhagen, Copenhagen, Denmark
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Pharmacokinetic aspects of the anti-epileptic drug substance vigabatrin: focus on transporter interactions. Ther Deliv 2014; 5:927-42. [DOI: 10.4155/tde.14.55] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/16/2023] Open
Abstract
Drug transporters in various tissues, such as intestine, kidney, liver and brain, are recognized as important mediators of absorption, distribution, metabolism and excretion of drug substances. This review gives a current status on the transporter(s) mediating the absorption, distribution, metabolism and excretion properties of the anti-epileptic drug substance vigabatrin. For orally administered drugs, like vigabatrin, the absorption from the intestine is a prerequisite for the bioavailability. Therefore, transporter(s) involved in the intestinal absorption of vigabatrin in vitro and in vivo are discussed in detail. Special focus is on the contribution of the proton-coupled amino acid transporter 1 (PAT1) for intestinal vigabatrin absorption. Furthermore, the review gives an overview of the pharmacokinetic parameters of vigabatrin across different species and drug–food and drug–drug interactions involving vigabatrin.
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14
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Nøhr MK, Holm R, Thale ZI, Nielsen CU. Intestinal absorption of the antiepileptic drug substance vigabatrin in Göttingen mini-pigs is unaffected by co-administration of amino acids. Int J Pharm 2014; 466:18-20. [DOI: 10.1016/j.ijpharm.2014.03.004] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/18/2013] [Revised: 02/28/2014] [Accepted: 03/01/2014] [Indexed: 01/21/2023]
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15
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McIntyre CM, Monk HM. Medication absorption considerations in patients with postpyloric enteral feeding tubes. Am J Health Syst Pharm 2014; 71:549-56. [DOI: 10.2146/ajhp130597] [Citation(s) in RCA: 22] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/23/2022] Open
Affiliation(s)
| | - Heather M. Monk
- Neonatology, Department of Pharmacy, Children’s Hospital of Philadelphia, Philadelphia, PA
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16
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PAT4 is abundantly expressed in excitatory and inhibitory neurons as well as epithelial cells. Brain Res 2014; 1557:12-25. [PMID: 24530433 DOI: 10.1016/j.brainres.2014.02.014] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/09/2014] [Accepted: 02/05/2014] [Indexed: 11/23/2022]
Abstract
PAT4, the fourth member of the SLC36/proton dependent amino acid transporter (PAT) family, is a high-affinity, low capacity electroneutral transporter of neutral amino acids like proline and tryptophan. It has also been associated with the function of mTORC1, a complex in the mammalian target of rapamycin (mTOR) pathway. We performed in situ hybridization and immunohistological analysis to determine the expression profile of PAT4, as well as an RT-PCR study on tissue from mice exposed to leucine. We performed a phylogenetic analysis to determine the evolutionary origin of PAT4. The in situ hybridization and the immunohistochemistry on mouse brain sections and hypothalamic cells showed abundant PAT4 expression in the mouse brain intracellularly in both inhibitory and excitatory neurons, partially co-localizing with lysosomal markers and epithelial cells lining the ventricles. Its location in epithelial cells around the ventricles indicates a transport of substrates across the blood brain barrier. Phylogenetic analysis showed that PAT4 belongs to an evolutionary old family most likely predating animals, and PAT4 is the oldest member of that family.
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Nøhr MK, Hansen SH, Brodin B, Holm R, Nielsen CU. The absorptive flux of the anti-epileptic drug substance vigabatrin is carrier-mediated across Caco-2 cell monolayers. Eur J Pharm Sci 2014; 51:1-10. [DOI: 10.1016/j.ejps.2013.08.034] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/27/2013] [Revised: 08/19/2013] [Accepted: 08/25/2013] [Indexed: 01/10/2023]
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Alexander SPH, Benson HE, Faccenda E, Pawson AJ, Sharman JL, Spedding M, Peters JA, Harmar AJ. The Concise Guide to PHARMACOLOGY 2013/14: transporters. Br J Pharmacol 2013; 170:1706-96. [PMID: 24528242 PMCID: PMC3892292 DOI: 10.1111/bph.12450] [Citation(s) in RCA: 120] [Impact Index Per Article: 10.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/11/2022] Open
Abstract
The Concise Guide to PHARMACOLOGY 2013/14 provides concise overviews of the key properties of over 2000 human drug targets with their pharmacology, plus links to an open access knowledgebase of drug targets and their ligands (www.guidetopharmacology.org), which provides more detailed views of target and ligand properties. The full contents can be found at http://onlinelibrary.wiley.com/doi/10.1111/bph.12444/full. Transporters are one of the seven major pharmacological targets into which the Guide is divided, with the others being G protein-coupled receptors, ligand-gated ion channels, ion channels, catalytic receptors, nuclear hormone receptors and enzymes. These are presented with nomenclature guidance and summary information on the best available pharmacological tools, alongside key references and suggestions for further reading. A new landscape format has easy to use tables comparing related targets. It is a condensed version of material contemporary to late 2013, which is presented in greater detail and constantly updated on the website www.guidetopharmacology.org, superseding data presented in previous Guides to Receptors and Channels. It is produced in conjunction with NC-IUPHAR and provides the official IUPHAR classification and nomenclature for human drug targets, where appropriate. It consolidates information previously curated and displayed separately in IUPHAR-DB and the Guide to Receptors and Channels, providing a permanent, citable, point-in-time record that will survive database updates.
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Affiliation(s)
- Stephen PH Alexander
- School of Life Sciences, University of Nottingham Medical SchoolNottingham, NG7 2UH, UK
| | - Helen E Benson
- The University/BHF Centre for Cardiovascular Science, University of EdinburghEdinburgh, EH16 4TJ, UK
| | - Elena Faccenda
- The University/BHF Centre for Cardiovascular Science, University of EdinburghEdinburgh, EH16 4TJ, UK
| | - Adam J Pawson
- The University/BHF Centre for Cardiovascular Science, University of EdinburghEdinburgh, EH16 4TJ, UK
| | - Joanna L Sharman
- The University/BHF Centre for Cardiovascular Science, University of EdinburghEdinburgh, EH16 4TJ, UK
| | | | - John A Peters
- Neuroscience Division, Medical Education Institute, Ninewells Hospital and Medical School, University of DundeeDundee, DD1 9SY, UK
| | - Anthony J Harmar
- The University/BHF Centre for Cardiovascular Science, University of EdinburghEdinburgh, EH16 4TJ, UK
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Frølund S, Nøhr M, Holm R, Brodin B, Nielsen C. Potential involvement of the proton-coupled amino acid transporter PAT1 (SLC36A1) in the delivery of pharmaceutical agents. J Drug Deliv Sci Technol 2013. [DOI: 10.1016/s1773-2247(13)50046-3] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/16/2022]
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20
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Voigt V, Laug L, Zebisch K, Thondorf I, Markwardt F, Brandsch M. Transport of the areca nut alkaloid arecaidine by the human proton-coupled amino acid transporter 1 (hPAT1). J Pharm Pharmacol 2012; 65:582-90. [DOI: 10.1111/jphp.12006] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/20/2012] [Accepted: 10/18/2012] [Indexed: 11/27/2022]
Abstract
Abstract
Objectives
The pyridine alkaloid arecaidine is an ingredient of areca nut preparations. It is responsible for many physiological effects observed during areca nut chewing. However, the mechanism underlying its oral bioavailability has not yet been studied. We investigated whether the H+-coupled amino acid transporter 1 (PAT1, SLC36A1), which is expressed in the intestinal epithelium, accepts arecaidine, arecoline, isoguvacine and other derivatives as substrates.
Methods
Inhibition of l-[3H]proline uptake by arecaidine and derivatives was determined in Caco-2 cells expressing hPAT1 constitutively and in HeLa cells transiently transfected with hPAT1-cDNA. Transmembrane transport of arecaidine and derivatives was measured electrophysiologically in Xenopus laevis oocytes.
Key findings
Arecaidine, guvacine and isoguvacine but not arecoline strongly inhibited the uptake of l-[3H]proline into Caco-2 cells. Kinetic analyses revealed the competitive manner of l-proline uptake inhibition by arecaidine. In HeLa cells transfected with hPAT1-cDNA an affinity constant of 3.8 mm was obtained for arecaidine. Electrophysiological measurements at hPAT1-expressing X. laevis oocytes demonstrated that arecaidine, guvacine and isoguvacine are transported by hPAT1 in an electrogenic manner.
Conclusion
We conclude that hPAT1 transports arecaidine, guvacine and isoguvacine across the apical membrane of enterocytes and that hPAT1 might be responsible for the intestinal absorption of these drug candidates.
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Affiliation(s)
- Valerie Voigt
- Biozentrum of the Martin-Luther-University Halle-Wittenberg, Halle, Germany
| | - Linda Laug
- Biozentrum of the Martin-Luther-University Halle-Wittenberg, Halle, Germany
| | - Katja Zebisch
- Biozentrum of the Martin-Luther-University Halle-Wittenberg, Halle, Germany
| | - Iris Thondorf
- Institute of Biochemistry and Biotechnology, Martin-Luther-University Halle-Wittenberg, Halle, Germany
| | - Fritz Markwardt
- Julius-Bernstein-Institute for Physiology, Martin-Luther-University Halle-Wittenberg, Halle, Germany
| | - Matthias Brandsch
- Biozentrum of the Martin-Luther-University Halle-Wittenberg, Halle, Germany
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21
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Broberg ML, Holm R, Tønsberg H, Frølund S, Ewon KB, Nielsen AL, Brodin B, Jensen A, Kall MA, Christensen KV, Nielsen CU. Function and expression of the proton-coupled amino acid transporter PAT1 along the rat gastrointestinal tract: implications for intestinal absorption of gaboxadol. Br J Pharmacol 2012; 167:654-65. [PMID: 22577815 PMCID: PMC3449268 DOI: 10.1111/j.1476-5381.2012.02030.x] [Citation(s) in RCA: 27] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/13/2011] [Revised: 04/12/2012] [Accepted: 05/02/2012] [Indexed: 12/29/2022] Open
Abstract
BACKGROUND AND PURPOSE Intestinal absorption via membrane transporters may determine the pharmacokinetics of drug compounds. The hypothesis is that oral absorption of gaboxadol (4,5,6,7-tetrahydroisoxazolo [5,4-c] pyridine-3-ol) in rats occurs via the proton-coupled amino acid transporter, rPAT1 (encoded by the gene rSlc36a1). Consequently, we aimed to elucidate the in vivo role of rPAT1 in the absorption of gaboxadol from various intestinal segments obtained from Sprague-Dawley rats. EXPERIMENTAL APPROACH The absorption of gaboxadol was investigated following its administration into four different intestinal segments. The intestinal expression of rSlc36a1 mRNA was measured by quantitative real-time PCR. Furthermore, the hPAT1-/rPAT1-mediated transport of gaboxadol or L-proline was studied in hPAT1-expressing Xenopus laevis oocytes, Caco-2 cell monolayers and excised segments of the rat intestine. KEY RESULTS The absorption fraction of gaboxadol was high (81.3-91.3%) following its administration into the stomach, duodenum and jejunum, but low (4.2%) after administration into the colon. The pharmacokinetics of gaboxadol were modified by the co-administration of L-tryptophan (an hPAT1 inhibitor) and L-proline (an hPAT1 substrate). The in vitro carrier-mediated uptake rate of L-proline in the excised intestinal segments was highest in the mid jejunum and lowest in the colon. The in vitro uptake and the in vivo absorption correlated with the expression of rSlc36a1 mRNA along the rat intestine. CONCLUSIONS AND IMPLICATIONS These results suggest that PAT1 mediates the intestinal absorption of gaboxadol and therefore determines its oral bioavailability. This has implications for the in vivo role of PAT1 and may have an influence on the design of pharmaceutical formulations of PAT1 substrates.
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Affiliation(s)
- M l Broberg
- Department of Pharmacy, Faculty of Health and Medical Sciences, University of Copenhagen, Denmark
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22
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Frølund S, Langthaler L, Kall MA, Holm R, Nielsen CU. Intestinal Drug Transport via the Proton-Coupled Amino Acid Transporter PAT1 (SLC36A1) Is Inhibited by Gly-Xaa Dipeptides. Mol Pharm 2012; 9:2761-9. [DOI: 10.1021/mp300345e] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Affiliation(s)
- Sidsel Frølund
- Department of Pharmacy, Faculty
of Health and Medical Sciences, University of Copenhagen, Universitetsparken 2, DK-2100 Copenhagen, Denmark
| | - Louise Langthaler
- Department of Pharmacy, Faculty
of Health and Medical Sciences, University of Copenhagen, Universitetsparken 2, DK-2100 Copenhagen, Denmark
- Department of Preformulation, H. Lundbeck A/S, Ottiliavej 9, DK-2500 Valby, Denmark
| | - Morten A. Kall
- Department of Bioanalysis, H. Lundbeck A/S, Ottiliavej 9, DK-2500 Valby, Denmark
| | - René Holm
- Department of Pharmacy, Faculty
of Health and Medical Sciences, University of Copenhagen, Universitetsparken 2, DK-2100 Copenhagen, Denmark
- Department of Preformulation, H. Lundbeck A/S, Ottiliavej 9, DK-2500 Valby, Denmark
| | - Carsten Uhd Nielsen
- Department of Pharmacy, Faculty
of Health and Medical Sciences, University of Copenhagen, Universitetsparken 2, DK-2100 Copenhagen, Denmark
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23
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Thwaites DT, Anderson CMH. The SLC36 family of proton-coupled amino acid transporters and their potential role in drug transport. Br J Pharmacol 2012; 164:1802-16. [PMID: 21501141 DOI: 10.1111/j.1476-5381.2011.01438.x] [Citation(s) in RCA: 105] [Impact Index Per Article: 8.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/23/2022] Open
Abstract
Members of the solute carrier (SLC) 36 family are involved in transmembrane movement of amino acids and derivatives. SLC36 consists of four members. SLC36A1 and SLC36A2 both function as H(+) -coupled amino acid symporters. SLC36A1 is expressed at the luminal surface of the small intestine but is also commonly found in lysosomes in many cell types (including neurones), suggesting that it is a multipurpose carrier with distinct roles in different cells including absorption in the small intestine and as an efflux pathway following intralysosomal protein breakdown. SLC36A1 has a relatively low affinity (K(m) 1-10 mM) for its substrates, which include zwitterionic amino and imino acids, heterocyclic amino acids and amino acid-based drugs and derivatives used experimentally and/or clinically to treat epilepsy, schizophrenia, bacterial infections, hyperglycaemia and cancer. SLC36A2 is expressed at the apical surface of the human renal proximal tubule where it functions in the reabsorption of glycine, proline and hydroxyproline. SLC36A2 also transports amino acid derivatives but has a narrower substrate selectivity and higher affinity (K(m) 0.1-0.7 mM) than SLC36A1. Mutations in SLC36A2 lead to hyperglycinuria and iminoglycinuria. SLC36A3 is expressed only in testes and is an orphan transporter with no known function. SLC36A4 is widely distributed at the mRNA level and is a high-affinity (K(m) 2-3 µM) transporter for proline and tryptophan. We have much to learn about this family of transporters, but from current knowledge, it seems likely that their function will influence the pharmacokinetic profiles of amino acid-based drugs by mediating transport in both the small intestine and kidney.
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Affiliation(s)
- David T Thwaites
- Epithelial Research Group, Institute for Cell & Molecular Biosciences, Faculty of Medical Sciences, Newcastle University, Newcastle upon Tyne, UK.
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24
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Rectal Absorption of Vigabatrin, a Substrate of the Proton Coupled Amino Acid Transporter (PAT1, Slc36a1), in Rats. Pharm Res 2012; 29:1134-42. [DOI: 10.1007/s11095-012-0673-0] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/11/2011] [Accepted: 01/03/2012] [Indexed: 01/16/2023]
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25
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Thondorf I, Voigt V, Schäfer S, Gebauer S, Zebisch K, Laug L, Brandsch M. Three-dimensional quantitative structure–activity relationship analyses of substrates of the human proton-coupled amino acid transporter 1 (hPAT1). Bioorg Med Chem 2011; 19:6409-18. [DOI: 10.1016/j.bmc.2011.08.058] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/16/2011] [Revised: 08/22/2011] [Accepted: 08/28/2011] [Indexed: 10/17/2022]
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26
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Anderson CMH, Thwaites DT. Hijacking solute carriers for proton-coupled drug transport. Physiology (Bethesda) 2011; 25:364-77. [PMID: 21186281 DOI: 10.1152/physiol.00027.2010] [Citation(s) in RCA: 46] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/31/2022] Open
Abstract
The physiological role of mammalian solute carrier (SLC) proteins is to mediate transmembrane movement of electrolytes, nutrients, micronutrients, vitamins, and endogenous metabolites from one cellular compartment to another. Many transporters in the small intestine, kidney, and solid tumors are H(+)-coupled, driven by local H(+)-electrochemical gradients, and transport numerous drugs. These transporters include PepT1 and PepT2 (SLC15A1/2), PCFT (SLC46A1), PAT1 (SLC36A1), OAT10 (SLC22A13), OATP2B1 (SLCO2B1), MCT1 (SLC16A1), and MATE1 and MATE2-K (SLC47A1/2).
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Affiliation(s)
- Catriona M H Anderson
- Epithelial Research Group, Institute for Cell & Molecular Biosciences, Faculty of Medical Sciences, Newcastle University, Newcastle upon Tyne, United Kingdom
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27
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Frølund S, Rapin N, Nielsen CU. Gaboxadol has affinity for the proton-coupled amino acid transporter 1, SLC36A1 (hPAT1)—A modelling approach to determine IC50 values of the three ionic species of gaboxadol. Eur J Pharm Sci 2011; 42:192-8. [DOI: 10.1016/j.ejps.2010.11.009] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/04/2010] [Revised: 10/20/2010] [Accepted: 11/18/2010] [Indexed: 10/18/2022]
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28
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Frølund S, Holm R, Brodin B, Nielsen CU. The proton-coupled amino acid transporter, SLC36A1 (hPAT1), transports Gly-Gly, Gly-Sar and other Gly-Gly mimetics. Br J Pharmacol 2011; 161:589-600. [PMID: 20880398 DOI: 10.1111/j.1476-5381.2010.00888.x] [Citation(s) in RCA: 23] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022] Open
Abstract
BACKGROUND AND PURPOSE The intestinal proton-coupled amino acid transporter, SLC36A1, transports zwitterionic α-amino acids and drugs such as vigabatrin, gaboxadol and δ-aminolevulinic acid. We hypothesize that SLC36A1 might also transport some dipeptides. The aim of the present study was to investigate SLC36A1-mediated transport of Gly-Gly and Gly-Gly mimetics, and to investigate Gly-Sar transport via SLC36A1 and the proton-coupled dipeptide/tripeptide transporter, SLC15A1 in Caco-2 cells. EXPERIMENTAL APPROACH Transport of a compound via SLC36A1 was determined by its ability to induce an increase in the inward current of two-electrode voltage clamped SLC36A1 cRNA-injected Xenopus laevis oocytes. SLC36A1-mediated L-[³H]Pro uptake in Caco-2 cells was measured in the absence and presence of Gly-Gly or Gly-Sar. In addition, apical [¹⁴C]Gly-Sar uptake was measured in the absence and presence of the SLC36A1 inhibitor 5-hydroxy-L-tryptophan (5-HTP) or the SLC15A1 inhibitor L-4,4'-biphenylalanyl-L-proline (Bip-Pro). KEY RESULTS In SLC36A1-expressing oocytes, an inward current was induced by Gly-Sar, Gly-Gly, δ-aminolevulinic acid, β-aminoethylglycine, δ-aminopentanoic acid, GABA, Gly and Pro, whereas Val, Leu, mannitol, 5-HTP and the dipeptides Gly-Ala, Gly-Pro and Gly-Phe did not evoke currents. In Caco-2 cell monolayers, the apical uptake of 30 mM Gly-Sar was inhibited by 20 and 22% in the presence of 5-HTP or Bip-Pro, respectively, and by 48% in the presence of both. CONCLUSION AND IMPLICATIONS Our results suggest that whereas Gly-Gly amid bond bioisosteres are widely accepted by the hPAT1 carrier, dipeptides in general are not; and therefore, Gly-Sar might structurally define the size limit of dipeptide transport via SLC36A1.
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Affiliation(s)
- S Frølund
- Department of Pharmaceutics and Analytical Chemistry, Faculty of Pharmaceutical Sciences, University of Copenhagen, Copenhagen, Denmark
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29
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Pillai SM, Meredith D. SLC36A4 (hPAT4) is a high affinity amino acid transporter when expressed in Xenopus laevis oocytes. J Biol Chem 2010; 286:2455-60. [PMID: 21097500 DOI: 10.1074/jbc.m110.172403] [Citation(s) in RCA: 32] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
The SLC36 family of transporters consists of four genes, two of which, SLC36A1 and SLC36A2, have been demonstrated to code for human proton-coupled amino acid transporters or hPATs. Here we report the characterization of the fourth member of the family, SLC36A4 or hPAT4, which when expressed in Xenopus laevis oocytes also encodes a plasma membrane amino acid transporter, but one that is not proton-coupled and has a very high substrate affinity for the amino acids proline and tryptophan. hPAT4 in Xenopus oocytes mediated sodium-independent, electroneutral uptake of [(3)H]proline, with the highest rate of uptake when the uptake medium pH was 7.4 and an affinity of 3.13 μM. Tryptophan was also an excellently transported substrate with a similarly high affinity (1.72 μM). Other amino acids that inhibited [(3)H]proline were isoleucine (K(i) 0.23 mM), glutamine (0.43 mM), methionine (0.44 mM), and alanine (1.48 mM), and with lower affinity, glycine, threonine, and cysteine (K(i) >5 mM for all). Of the amino acids directly tested for transport, only proline, tryptophan, and alanine showed significant uptake, whereas glycine and cysteine did not. Of the non-proteogenic amino acids and drugs tested, only sarcosine produced inhibition (K(i) 1.09 mM), whereas γ-aminobutyric acid (GABA), β-alanine, L-Dopa, D-serine, and δ-aminolevulinic acid were without effect on [(3)H]proline uptake. This characterization of hPAT4 as a very high affinity/low capacity non-proton-coupled amino acid transporter raises questions about its physiological role, especially as the transport characteristics of hPAT4 are very similar to the Drosophila orthologue PATH, an amino acid "transceptor" that plays a role in nutrient sensing.
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30
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Edwards N, Anderson CMH, Gatfield KM, Jevons MP, Ganapathy V, Thwaites DT. Amino acid derivatives are substrates or non-transported inhibitors of the amino acid transporter PAT2 (slc36a2). BIOCHIMICA ET BIOPHYSICA ACTA-BIOMEMBRANES 2010; 1808:260-70. [PMID: 20691150 PMCID: PMC3000476 DOI: 10.1016/j.bbamem.2010.07.032] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Figures] [Subscribe] [Scholar Register] [Received: 06/02/2010] [Revised: 07/13/2010] [Accepted: 07/28/2010] [Indexed: 11/21/2022]
Abstract
The H+-coupled amino acid transporter PAT2 (SLC36A2) transports the amino acids proline, glycine, alanine and hydroxyproline. A physiological role played by PAT2 in amino acid reabsorption in the renal proximal tubule is demonstrated by mutations in SLC36A2 that lead to an iminoglycinuric phenotype (imino acid and glycine uria) in humans. A number of proline, GABA and tryptophan derivatives were examined to determine if they function either as transported substrates or non-transported inhibitors of PAT2. The compounds were investigated following heterologous expression of rat PAT2 in Xenopus laevis oocytes. PAT2 function was characterised by: radiotracer uptake and competition (cis-inhibition) studies; radiotracer efflux and trans-stimulation; and measurement of substrate-induced positive inward current by two-electrode voltage-clamp. In general, the proline derivatives appeared to be transported substrates and the relative ability to induce current flow was closely related to the inhibitory effects on PAT2-mediated l-[3H]proline uptake. In contrast, certain heterocyclic GABA derivatives (e.g. l-pipecolic acid) were translocated only slowly. Finally, the tryptophan derivatives inhibited PAT2 function but did not undergo transport. l-Proline uptake was inhibited by 5-hydroxy-l-tryptophan (IC50 1.6 ± 0.4 mM), α-methyl-d,l-tryptophan (3.5 ± 1.5 mM), l-tryptophan, 1-methyl-l-tryptophan and indole-3-propionic acid. Although neither 5-hydroxy-l-tryptophan nor α-methyl-d,l-tryptophan were able to elicit inward current in PAT2-expressing oocytes both reduced the current evoked by l-proline. 5-Hydroxy-l-tryptophan and α-methyl-d,l-tryptophan were unable to trans-stimulate l-proline efflux from PAT2-expressing oocytes, confirming that the two compounds act as non-transported blockers of PAT2. These two tryptophan derivatives should prove valuable experimental tools in future investigations of the physiological roles of PAT2.
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Affiliation(s)
- Noel Edwards
- Epithelial Research Group, Institute for Cell & Molecular Biosciences, Faculty of Medical Sciences, Newcastle University, Framlington Place, Newcastle upon Tyne, NE2 4HH, UK
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31
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Frølund S, Marquez OC, Larsen M, Brodin B, Nielsen CU. Delta-aminolevulinic acid is a substrate for the amino acid transporter SLC36A1 (hPAT1). Br J Pharmacol 2010; 159:1339-53. [PMID: 20128809 DOI: 10.1111/j.1476-5381.2009.00620.x] [Citation(s) in RCA: 41] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/27/2022] Open
Abstract
BACKGROUND AND PURPOSE delta-Aminolevulinic acid (ALA) is used in cancer patients for photodynamic diagnosis or therapy. Oral administration of ALA has been used in patients with prostate and bladder cancer. The present aim was to investigate the mechanism of intestinal absorption of ALA and its transport via the amino acid transporter SLC36A1. EXPERIMENTAL APPROACH In vitro investigations of ALA affinity for and uptake via SLC36A1 and SLC15A1 were performed in Caco-2 cell monolayers. Interaction of ALA with SLC15A1 was investigated in MDCK/SLC15A1 cells, whereas interactions with SLC36A1 were investigated in COS-7 cells transiently expressing SLC36A1. KEY RESULTS ALA inhibited SLC36A1-mediated L-[(3)H]Pro and SLC15A1-mediated [(14)C]Gly-Sar uptake in Caco-2 cell monolayers with IC(50) values of 11.3 and 2.1 mM respectively. In SLC36A1-expressing COS-7 cells, the uptake of [(14)C]ALA was saturable with a K(m) value of 6.8 +/- 3.0 mM and a V(max) of 96 +/- 13 pmol x cm(-2) x min(-1). Uptake of [(14)C]ALA was pH and concentration dependent, and could be inhibited by glycine, proline and GABA. In a membrane potential assay, translocation of ALA via SLC36A1 was concentration dependent, with a K(m) value of 3.8 +/- 1.0 mM. ALA is thus a substrate for SLC36A1. In Caco-2 cells, apical [(14)C]ALA uptake was pH dependent, but Na(+) independent, and completely inhibited by 5-hydroxy-L-tryptophan and L-4,4'-biphenylalanyl-l-proline. CONCLUSIONS AND IMPLICATIONS. ALA was a substrate for SLC36A1, and the apical absorption in Caco-2 cell was only mediated by SLC36A1 and SLC15A1. This advances our understanding of intestinal absorption mechanisms of ALA, as well as its potential for drug interactions.
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Affiliation(s)
- S Frølund
- Department of Pharmaceutics and Analytical Chemistry, Faculty of Pharmaceutical Sciences, University of Copenhagen, Universitetsparken 2, DK-2100 Copenhagen, Denmark
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Evans AM, Aimanova KG, Gill SS. Characterization of a blood-meal-responsive proton-dependent amino acid transporter in the disease vector, Aedes aegypti. ACTA ACUST UNITED AC 2009; 212:3263-71. [PMID: 19801431 DOI: 10.1242/jeb.029553] [Citation(s) in RCA: 25] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
Abstract
After anautogenous mosquitoes ingest the required blood meal, proteins in it are rapidly cleaved, yielding a large pool of amino acids. Transport of these amino acids into gut epithelial cells and their subsequent translocation into other tissues is critical for oogenesis and other physiological processes. We have identified a proton amino acid transporter (PAT) in Aedes aegypti (AaePAT1, AAEL007191) which facilitates this transport and is expressed in epithelial cell membranes of larval caecae and the adult midgut. AaePAT1 encodes a 475 amino acid protein showing high similarity to Anopheles gambiae AGAP009896, Culex pipiens CPIJ011438 and Drosophila melanogaster CG7888. When expressed in Xenopus oocytes the transport kinetics showed AaePAT1 is a low affinity transporter with low substrate specificity, having Km and Vmax values of about 7.2 mmol l(-1) and 69 pmol oocyte(-1) min(-1), respectively, for glutamine. A number of other amino acids are also transported by this PAT. In female adult midgut, AaePAT1 transcript levels were induced after ingestion of a blood meal.
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Affiliation(s)
- Amy M Evans
- Department of Cell Biology and Neuroscience, University of California, Riverside, CA 92521, USA
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Anderson CMH, Jevons M, Thangaraju M, Edwards N, Conlon NJ, Woods S, Ganapathy V, Thwaites DT. Transport of the photodynamic therapy agent 5-aminolevulinic acid by distinct H+-coupled nutrient carriers coexpressed in the small intestine. J Pharmacol Exp Ther 2009; 332:220-8. [PMID: 19789362 DOI: 10.1124/jpet.109.159822] [Citation(s) in RCA: 39] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/13/2022] Open
Abstract
5-Aminolevulinic acid (ALA) is a prodrug used in photodynamic therapy, fluorescent diagnosis, and fluorescent-guided resection because it leads to accumulation of the photosensitizer protoporphyrin IX (PpIX) in tumor tissues. ALA has good oral bioavailability, but high oral doses are required to obtain selective PpIX accumulation in colonic tumors because accumulation is also observed in normal gut mucosa. Structural similarities between ALA and GABA led us to test the hypothesis that the H(+)-coupled amino acid transporter PAT1 (SLC36A1) will contribute to luminal ALA uptake. Radiolabel uptake and electrophysiological measurements identified PAT1-mediated H(+)-coupled ALA symport after heterologous expression in Xenopus oocytes. The selectivity of the nontransported inhibitors 5-hydroxytryptophan and 4-aminomethylbenzoic acid for, respectively, PAT1 and the H(+)-coupled di/tripeptide transporter PepT1 (SLC15A1) were examined. 5-Hydroxytryptophan selectively inhibited PAT1-mediated amino acid uptake across the brush-border membrane of the human intestinal (Caco-2) epithelium whereas 4-aminomethylbenzoic acid selectively inhibited PepT1-mediated dipeptide uptake. The inhibitory effects of 5-hydroxytryptophan and 4-aminomethylbenzoic acid were additive, demonstrating that both PAT1 and PepT1 contribute to intestinal transport of ALA. This is the first demonstration of overlap in substrate specificity between these distinct transporters for amino acids and dipeptides. PAT1 and PepT1 expression was monitored by reverse transcriptase-polymerase chain reaction using paired samples of normal and cancer tissue from human colon. mRNA for both transporters was detected. PepT1 mRNA was increased 2.3-fold in cancer tissues. Thus, increased PepT1 expression in colonic cancer could contribute to the increased PpIX accumulation observed. Selective inhibition of PAT1 could enhance PpIX loading in tumor tissue relative to that in normal tissue.
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Affiliation(s)
- Catriona M H Anderson
- Epithelial Research Group, Institute for Cell and Molecular Biosciences, Faculty of Medical Sciences, Framlington Place, Newcastle University, Newcastle upon Tyne, UK
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Larsen M, Holm R, Jensen KG, Brodin B, Nielsen CU. Intestinal gaboxadol absorption via PAT1 (SLC36A1): modified absorption in vivo following co-administration of L-tryptophan. Br J Pharmacol 2009; 157:1380-9. [PMID: 19594759 DOI: 10.1111/j.1476-5381.2009.00253.x] [Citation(s) in RCA: 32] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/11/2023] Open
Abstract
BACKGROUND AND PURPOSE Gaboxadol has been in development for treatment of chronic pain and insomnia. The clinical use of gaboxadol has revealed that adverse effects seem related to peak serum concentrations. The aim of this study was to investigate the mechanism of intestinal absorption of gaboxadol in vitro and in vivo. EXPERIMENTAL APPROACH In vitro transport investigations were performed in Caco-2 cell monolayers. In vivo pharmacokinetic investigations were conducted in beagle dogs. Gaboxadol doses of 2.5 mg.kg(-1) were given either as an intravenous injection (1.0 mL.kg(-1)) or as an oral solution (5.0 mL.kg(-1)). KEY RESULTS Gaboxadol may be a substrate of the human proton-coupled amino acid transporter, hPAT1 and it inhibited the hPAT1-mediated L-[(3)H]proline uptake in Caco-2 cell monolayers with an inhibition constant K(i) of 6.6 mmol.L(-1). The transepithelial transport of gaboxadol was polarized in the apical to basolateral direction, and was dependent on gaboxadol concentration and pH of the apical buffer solution. In beagle dogs, the absorption of gaboxadol was almost complete (absolute bioavailability, F(a), of 85.3%) and T(max) was 0.46 h. Oral co-administration with 2.5-150 mg.kg(-1) of the PAT1 inhibitor, L-tryptophan, significantly decreased the absorption rate constant, k(a), and C(max), and increased T(max) of gaboxadol, whereas the area under the curve and clearance of gaboxadol were constant. CONCLUSIONS AND IMPLICATIONS The absorption of gaboxadol across the luminal membrane of the small intestinal enterocytes is probably mediated by PAT1. This knowledge is useful for reducing gaboxadol absorption rates in order to decrease peak plasma concentrations.
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Affiliation(s)
- M Larsen
- Department of Pharmaceutics and Analytical Chemistry, Faculty of Pharmaceutical Sciences, University of Copenhagen, Universitetsparken, Copenhagen, Denmark
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Metzner L, Dorn M, Markwardt F, Brandsch M. The Orally Active Antihyperglycemic Drug β-Guanidinopropionic Acid Is Transported by the Human Proton-Coupled Amino Acid Transporter hPAT1. Mol Pharm 2009; 6:1006-11. [DOI: 10.1021/mp9000684] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Affiliation(s)
- Linda Metzner
- Membrane Transport Group, Biozentrum, Martin Luther University Halle-Wittenberg, Halle (Saale), Germany, and Julius Bernstein Institute for Physiology, Martin Luther University Halle-Wittenberg, Halle (Saale), Germany
| | - Madlen Dorn
- Membrane Transport Group, Biozentrum, Martin Luther University Halle-Wittenberg, Halle (Saale), Germany, and Julius Bernstein Institute for Physiology, Martin Luther University Halle-Wittenberg, Halle (Saale), Germany
| | - Fritz Markwardt
- Membrane Transport Group, Biozentrum, Martin Luther University Halle-Wittenberg, Halle (Saale), Germany, and Julius Bernstein Institute for Physiology, Martin Luther University Halle-Wittenberg, Halle (Saale), Germany
| | - Matthias Brandsch
- Membrane Transport Group, Biozentrum, Martin Luther University Halle-Wittenberg, Halle (Saale), Germany, and Julius Bernstein Institute for Physiology, Martin Luther University Halle-Wittenberg, Halle (Saale), Germany
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Larsen M, Larsen BB, Frølund B, Nielsen CU. Transport of amino acids and GABA analogues via the human proton-coupled amino acid transporter, hPAT1: Characterization of conditions for affinity and transport experiments in Caco-2 cells. Eur J Pharm Sci 2008; 35:86-95. [DOI: 10.1016/j.ejps.2008.06.007] [Citation(s) in RCA: 26] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/29/2008] [Revised: 06/13/2008] [Accepted: 06/15/2008] [Indexed: 10/21/2022]
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Abstract
Epilepsy is the most common serious chronic neurological disorder. Treatment consists mainly of antiepileptic drugs (AEDs), with more than 15 different molecules available. However, AED treatment is often problematic because of unpredictability of drug response, adverse drug reactions and optimal dosing in individual patients. Moreover, up to one in three patients with epilepsy are refractory to currently available AEDs. Pharmacogenetic studies explore the contribution of genetic variants to interindividual differences in drug response. An increasing number of pharmacogenetic association studies in epilepsy are being reported. Nevertheless, at present only one association is firmly established, namely that of the HLA-B*1502 allele with severe cutaneous adverse drug reactions on carbamazepine therapy in the Han Chinese population. It is likely that large collaborations looking at multiple genes encoding entire drug pathways, or even the entire human genome, together with new pharmacogenetic strategies will result in the discovery of other genetic variants involved in AED response. Although several challenges remain, it is hoped that, ultimately, these findings will lead to the development of predictive tests, resulting in a more efficacious and safer AED treatment, and to the development of new AEDs with novel mechanisms of action, particularly aimed at patients with drug-refractory epilepsy.
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Affiliation(s)
- Chantal Depondt
- Université Libre de Bruxelles, Service de Neurologie, Hôpital Erasme, 808 Route de Lennik, 1070 Bruxelles, Belgium.
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Thwaites DT, Anderson CMH. H+-coupled nutrient, micronutrient and drug transporters in the mammalian small intestine. Exp Physiol 2007; 92:603-19. [PMID: 17468205 PMCID: PMC2803310 DOI: 10.1113/expphysiol.2005.029959] [Citation(s) in RCA: 151] [Impact Index Per Article: 8.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/11/2023]
Abstract
The H(+)-electrochemical gradient was originally considered as a driving force for solute transport only across cellular membranes of bacteria, plants and yeast. However, in the mammalian small intestine, a H(+)-electrochemical gradient is present at the epithelial brush-border membrane in the form of an acid microclimate. Over recent years, a large number of H(+)-coupled cotransport mechanisms have been identified at the luminal membrane of the mammalian small intestine. These transporters are responsible for the initial stage in absorption of a remarkable variety of essential and non-essential nutrients and micronutrients, including protein digestion products (di/tripeptides and amino acids), vitamins, short-chain fatty acids and divalent metal ions. Proton-coupled cotransporters expressed at the mammalian small intestinal brush-border membrane include: the di/tripeptide transporter PepT1 (SLC15A1); the proton-coupled amino-acid transporter PAT1 (SLC36A1); the divalent metal transporter DMT1 (SLC11A2); the organic anion transporting polypeptide OATP2B1 (SLC02B1); the monocarboxylate transporter MCT1 (SLC16A1); the proton-coupled folate transporter PCFT (SLC46A1); the sodium-glucose linked cotransporter SGLT1 (SLC5A1); and the excitatory amino acid carrier EAAC1 (SLC1A1). Emerging research demonstrates that the optimal intestinal absorptive capacity of certain H(+)-coupled cotransporters (PepT1 and PAT1) is dependent upon function of the brush-border Na(+)-H(+) exchanger NHE3 (SLC9A3). The high oral bioavailability of a large number of pharmaceutical compounds results, in part, from absorptive transport via the same H(+)-coupled cotransporters. Drugs undergoing H(+)-coupled cotransport across the intestinal brush-border membrane include those used to treat bacterial infections, hypercholesterolaemia, hypertension, hyperglycaemia, viral infections, allergies, epilepsy, schizophrenia, rheumatoid arthritis and cancer.
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Affiliation(s)
- David T Thwaites
- Epithelial Research Group, Institute for Cell & Molecular Biosciences, Faculty of Medical Sciences, Framlington Place, University of Newcastle upon Tyne, Newcastle upon Tyne NE2 4HH, UK.
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Anderson CMH, Thwaites DT. Regulation of intestinal hPepT1 (SLC15A1) activity by phosphodiesterase inhibitors is via inhibition of NHE3 (SLC9A3). BIOCHIMICA ET BIOPHYSICA ACTA-BIOMEMBRANES 2007; 1768:1822-9. [PMID: 17498647 PMCID: PMC2428106 DOI: 10.1016/j.bbamem.2007.04.006] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Figures] [Subscribe] [Scholar Register] [Received: 01/19/2007] [Revised: 03/19/2007] [Accepted: 04/06/2007] [Indexed: 11/26/2022]
Abstract
The H+-coupled transporter hPepT1 (SLC15A1) mediates the transport of di/tripeptides and many orally-active drugs across the brush-border membrane of the small intestinal epithelium. Incubation of Caco-2 cell monolayers (15 min) with the dietary phosphodiesterase inhibitors caffeine and theophylline inhibited Gly–Sar uptake across the apical membrane. Pentoxifylline, a phosphodiesterase inhibitor given orally to treat intermittent claudication, also decreased Gly–Sar uptake through a reduction in capacity (Vmax) without any effect on affinity (Km). The reduction in dipeptide transport was dependent upon both extracellular Na+ and apical pH but was not observed in the presence of the selective Na+/H+ exchanger NHE3 (SLC9A3) inhibitor S1611. Measurement of intracellular pH confirmed that caffeine was not directly inhibiting hPepT1 but rather having an indirect effect through inhibition of NHE3 activity. NHE3 maintains the H+-electrochemical gradient which, in turn, acts as the driving force for H+-coupled solute transport. Uptake of β-alanine, a substrate for the H+-coupled amino acid transporter hPAT1 (SLC36A1), was also inhibited by caffeine. The regulation of NHE3 by non-nutrient components of diet or orally-delivered drugs may alter the function of any solute carrier dependent upon the H+-electrochemical gradient and may, therefore, be a site for both nutrient–drug and drug–drug interactions in the small intestine.
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Affiliation(s)
- Catriona M H Anderson
- Epithelial Research Group, Institute for Cell and Molecular Biosciences, Faculty of Medical Sciences, University of Newcastle upon Tyne, Newcastle upon Tyne, NE2 4HH, UK.
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Thwaites DT, Anderson CMH. Deciphering the mechanisms of intestinal imino (and amino) acid transport: The redemption of SLC36A1. BIOCHIMICA ET BIOPHYSICA ACTA-BIOMEMBRANES 2007; 1768:179-97. [PMID: 17123464 DOI: 10.1016/j.bbamem.2006.10.001] [Citation(s) in RCA: 51] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 07/28/2006] [Revised: 09/26/2006] [Accepted: 10/02/2006] [Indexed: 11/23/2022]
Abstract
The absorption of zwitterionic imino and amino acids, and related drugs, is an essential function of the small intestinal epithelium. This review focuses on the physiological roles of transporters recently identified at the molecular level, in particular SLC36A1, by identifying how they relate to the classical epithelial imino and amino acid transporters characterised in mammalian small intestine in the 1960s-1990s. SLC36A1 transports a number of D- and L-imino and amino acids, beta- and gamma-amino acids and orally-active neuromodulatory and antibacterial agents. SLC36A1 (or PAT1) functions as a proton-coupled imino and amino acid symporter in cooperation with the Na+/H+ exchanger NHE3 (SLC9A3) to produce the imino acid carrier identified in rat small intestine in the 1960s but subsequently ignored because of confusion with the IMINO transporter. However, it is the sodium/imino and amino acid cotransporter SLC6A20 which corresponds to the betaine carrier (identified in hamster, 1960s) and IMINO transporter (identified in rabbit and guinea pig, 1980s). This review summarises evidence for expression of SLC36A1 and SLC6A20 in human small intestine, highlights the differences in functional characteristics of the imino acid carrier and IMINO transporter, and explains the confusion surrounding these two distinct transport systems.
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Affiliation(s)
- David T Thwaites
- Epithelial Research Group, Institute for Cell and Molecular Biosciences, Faculty of Medical Sciences, Framlington Place, University of Newcastle upon Tyne, Newcastle upon Tyne NE2 4HH, UK.
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