151
|
Thwaites DT, Kennedy DJ, Raldua D, Anderson CMH, Mendoza ME, Bladen CL, Simmons NL. H/dipeptide absorption across the human intestinal epithelium is controlled indirectly via a functional Na/H exchanger. Gastroenterology 2002; 122:1322-33. [PMID: 11984519 DOI: 10.1053/gast.2002.32992] [Citation(s) in RCA: 83] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 12/02/2022]
Abstract
BACKGROUND & AIMS For optimal nutrient absorption to occur, the enterocyte must express a range of specialist ion-driven carrier proteins that function cooperatively in a linked and mutually dependent fashion. Thus, absorption via the human intestinal H(+)-coupled di/tripeptide transporter (hPepT1) is dependent on maintenance of the trans-apical driving force (the H(+)-electrochemical gradient) established, in part, by brush-border Na(+)/H(+) exchanger (NHE3) activity. This study aimed to examine whether physiologic regulation of NHE3 activity can limit hPepT1 capacity and, therefore, protein absorption after a meal. METHODS hPepT1 and NHE3 activities were determined in intact human intestinal epithelial Caco-2 cell monolayers by measurements of [(14)C]glycylsarcosine transport and uptake, (22)Na(+)-influx, H(+)-influx, and H(+)-efflux. Expression of NHE regulatory factors was determined by reverse-transcriptase polymerase chain reaction. RESULTS Optimal dipeptide transport was observed in the presence of a transapical pH gradient and extracellular Na(+). At apical pH 6.5, and only in Na(+)-containing media, protein kinase A activation (by forskolin or vasoactive intestinal peptide) or selective NHE3 inhibition (by S1611) reduced transepithelial dipeptide transport and cellular accumulation by a reduction in the capacity (without effect on affinity) of dipeptide uptake. CONCLUSIONS Protein kinase A-mediated modulation of intestinal dipeptide absorption is indirect via effects on the apical Na(+)/H(+) exchanger.
Collapse
Affiliation(s)
- David T Thwaites
- Department of Physiological Sciences, Medical School, University of Newcastle upon Tyne, Newcastle upon Tyne, United Kingdom.
| | | | | | | | | | | | | |
Collapse
|
152
|
Groneberg DA, Döring F, Theis S, Nickolaus M, Fischer A, Daniel H. Peptide transport in the mammary gland: expression and distribution of PEPT2 mRNA and protein. Am J Physiol Endocrinol Metab 2002; 282:E1172-9. [PMID: 11934684 DOI: 10.1152/ajpendo.00381.2001] [Citation(s) in RCA: 64] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
The lactating mammary gland utilizes free plasma amino acids as well as those derived by hydrolysis from circulating short-chain peptides for protein synthesis. Apart from the major route of amino acid nitrogen delivery to the gland by the various transporters for free amino acids, it has been suggested that dipeptides may also be taken up in intact form to serve as a source of amino acids. The identification of peptide transporters in the mammary gland may therefore provide new insights into protein metabolism and secretion by the gland. The expression and distribution of the high-affinity type proton-coupled peptide transporter PEPT2 were investigated in rat lactating mammary gland as well as in human epithelial cells derived from breast milk. By use of RT-PCR, PEPT2 mRNA was detected in rat mammary gland extracts and human milk epithelial cells. The expression pattern of PEPT2 mRNA revealed a localization in epithelial cells of ducts and glands by nonisotopic high resolution in situ hybridization. In addition, immunohistochemistry was carried out and showed transporter immunoreactivity in the same epithelial cells of the glands and ducts. In addition, two-electrode voltage clamp recordings using PEPT2-expressing Xenopus laevis oocytes demonstrated positive inward currents induced by selected dipeptides that may play a role in aminonitrogen handling in mammalian mammary gland. Taken together, these data suggest that PEPT2 is expressed in mammary gland epithelia, in which it may contribute to the reuptake of short-chain peptides derived from hydrolysis of milk proteins secreted into the lumen. Whereas PEPT2 also transports a variety of drugs, such as selected beta-lactams, angiotensin-converting enzyme inhibitors, and antiviral and anticancer metabolites, their efficient reabsorption via PEPT2 may reduce the burden of xenobiotics in milk.
Collapse
Affiliation(s)
- David A Groneberg
- Dept. of Pediatric Pneumology and Immunology, Charité Campus-Virchow, Humboldt-University, D-13353 Berlin, Germany
| | | | | | | | | | | |
Collapse
|
153
|
Ashida K, Katsura T, Motohashi H, Saito H, Inui KI. Thyroid hormone regulates the activity and expression of the peptide transporter PEPT1 in Caco-2 cells. Am J Physiol Gastrointest Liver Physiol 2002; 282:G617-23. [PMID: 11897620 DOI: 10.1152/ajpgi.00344.2001] [Citation(s) in RCA: 46] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 01/31/2023]
Abstract
An oligopeptide transporter (PEPT1) in the small intestine plays an important role in the absorption of small peptides and peptide-like drugs. We examined the effect of thyroid hormone 3,5,3'-L-triiodothyronine (T(3)) on the activity and expression of PEPT1 in human intestinal Caco-2 cells. Treatment of Caco-2 cells with T(3) inhibited [(14)C]glycylsarcosine uptake in a time- and dose-dependent manner. [(14)C]glycylsarcosine uptake was reduced by pretreatment of the cells with 100 nM T(3) for 4 days (67% of control value), whereas methyl-alpha-D-[U-(14)C]glucopyranoside and [(3)H]threonine uptake were not decreased. Kinetic analysis showed that T(3) treatment significantly decreased the maximum uptake (V(max)) value for [(14)C]glycylsarcosine uptake but had no effect on the K(m) value. Moreover, T(3) treatment caused a significant decrease in the amount of PEPT1 mRNA (25% of the control). Western blotting indicated that the amount of PEPT1 protein in the apical membrane was decreased (70% of the control). These findings indicate that T(3) treatment inhibits the uptake of [(14)C]glycylsarcosine by decreasing the transcription and/or stability of PEPT1 mRNA.
Collapse
Affiliation(s)
- Kayoko Ashida
- Department of Pharmacy, Kyoto University Hospital, Faculty of Medicine, Kyoto University, Sakyo-ku, Kyoto 606-8507, Japan
| | | | | | | | | |
Collapse
|
154
|
Abstract
Transport proteins have critical physiological roles in nutrient transport and may be utilized as a mechanism to increase drug absorption. However, we have little understanding of these proteins at the molecular level due to the absence of high-resolution crystal structures. Numerous efforts have been made to characterize the P-glycoprotein efflux pump, the peptide transporter (PepT1) and the apical sodium-dependent transporter (ASBT) which are important not only for their native transporter function but also as drug targets to increase absorption and bioactivity. In vitro and computational approaches have been applied to gain some insight into these transporters with some success. This represents an opportunity for optimizing molecules as substrates for the solute transporters and providing a further screening system for drug discovery. Clearly the future growth in knowledge of transporter function will be led by integrated in vitro and in silico approaches.
Collapse
Affiliation(s)
- Eric Y Zhang
- Division of Pharmaceutics, The Ohio State University, 500 West 12th Avenue, Columbus, OH 43210-1291, USA
| | | | | | | | | |
Collapse
|
155
|
Chen H, Pan Y, Wong EA, Bloomquist JR, Webb KE. Molecular cloning and functional expression of a chicken intestinal peptide transporter (cPepT1) in Xenopus oocytes and Chinese hamster ovary cells. J Nutr 2002; 132:387-93. [PMID: 11880560 DOI: 10.1093/jn/132.3.387] [Citation(s) in RCA: 61] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/13/2022] Open
Abstract
To study peptide absorption in chickens, an intestinal peptide transporter cDNA (cPepT1) was isolated from a chicken duodenal cDNA library. The cDNA was 2914 bp long and encoded a protein of 714 amino acid residues with an estimated molecular size of 79.3 kDa and an isoelectric point of 7.48. cPepT1 protein is similar60% identical to PepT1 from rabbits, humans, mice, rats and sheep. Sixteen dipeptides, three tripeptides and four tetrapeptides that contained the essential amino acids Met, Lys and(or) Trp were used for functional analysis of cPepT1 in Xenopus oocytes and Chinese hamster ovary cells. For most di- and tripeptides tested, the substrate affinities were in the micromolar range, indicating that cPepT1 has high affinity for these peptides. Lys-Lys and Lys-Trp-Lys were exceptions, with substrate affinities in the millimolar range. Neither free amino acids nor tetrapeptides were transported by cPepT1. Northern blot analysis using a full-length cPepT1 cDNA as the probe demonstrated that cPepT1 is expressed strongly in the duodenum, jejunum and ileum, and at lower levels in kidney and ceca. The present study demonstrated for the first time the presence and functional characteristics of a peptide transport system from an avian species.
Collapse
Affiliation(s)
- Hong Chen
- Department of Animal and Poultry Sciences, Virginia Polytechnic Institute and State University, Blacksburg, VA 24061, USA
| | | | | | | | | |
Collapse
|
156
|
Theis S, Hartrodt B, Kottra G, Neubert K, Daniel H. Defining minimal structural features in substrates of the H(+)/peptide cotransporter PEPT2 using novel amino acid and dipeptide derivatives. Mol Pharmacol 2002; 61:214-21. [PMID: 11752223 DOI: 10.1124/mol.61.1.214] [Citation(s) in RCA: 34] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
The peptide transporter PEPT2, expressed in a variety of tissues, including kidney, lung, and the central nervous system, mediates the uphill transport of di- and tripeptides, as well as a variety of peptidomimetic drugs. To identify the essential molecular features of substrates that determine affinity and transport by PEPT2, we synthesized a series of amino acid derivatives as well as modified dipeptides. Kinetic constants for the interaction of test compounds with PEPT2 were obtained in a competition assay using Pichia pastoris yeast cells expressing mammalian PEPT2. The two-electrode voltage-clamp technique in Xenopus laevis oocytes was used to assess the substrate's electrogenic transport properties. Whereas omega bar-amino fatty acids showed no affinity for PEPT2, the introduction of a single carbonyl group into the backbone increased both affinity and transport currents more than 30-fold. omega bar-amino fatty acids, at their amino or carboxyl group coupled to an alanine residue, allowed us to determine the importance of the spatial position of functional groups within the molecule. Affinity and transport function declined by elongating the omega bar-amino acid chain when located in the N-terminal position, whereas the elongation in the carboxyl terminal with an N-terminal alanine caused less pronounced effects. The results clearly establish that a free N terminus, a correctly positioned backbone carbonyl group, and a carboxylic group that is in a suitable distance from the intramolecular carbonyl function and the amino terminal head group are the main features for substrate recognition and transport by PEPT2. This information provides the framework for a rational design of peptidomimetic drugs for delivery via PEPT2.
Collapse
Affiliation(s)
- Stephan Theis
- Molecular Nutrition Unit, Institute of Nutritional Science, Technical University of Munich, Freising-Weihenstephan, Germany
| | | | | | | | | |
Collapse
|
157
|
Matthews JC, Anderson KJ. Recent advances in amino acid transporters and excitatory amino acid receptors. Curr Opin Clin Nutr Metab Care 2002; 5:77-84. [PMID: 11790954 DOI: 10.1097/00075197-200201000-00014] [Citation(s) in RCA: 18] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/26/2022]
Abstract
Complementary DNAs that encode proteins capable of biochemically defined system A-, N-, asc-, and T-like activities have been cloned. Functional expression and localization analyses of these proteins have revealed significant information about how transport is energized, what substrates are recognized, and where transporter messenger RNA or proteins are expressed. Still lacking, however, is definitive knowledge about transporter localization and how expression and function are coordinated with that of other transport proteins, enzymes, and receptors to support tissue physiology. Although the molecular identity of the physiologically relevant glutamate receptors has been known for nearly 10 years, work has progressed in the areas of molecular regulation, the localization of receptors to identified populations of neurons and glia, and the rate of turnover at the cell membrane. Collectively, these accomplishments enable the putative relationship between abnormal transporter or receptor functions to be correlated with the etiology of several diseases.
Collapse
Affiliation(s)
- James C Matthews
- Department of Animal Sciences, University of Kentucky, Lexington, KY 40456-0215, USA.
| | | |
Collapse
|
158
|
Chen H, Pan YX, Wong EA, Webb KE. Characterization and regulation of a cloned ovine gastrointestinal peptide transporter (oPepT1) expressed in a mammalian cell line. J Nutr 2002; 132:38-42. [PMID: 11773505 DOI: 10.1093/jn/132.1.38] [Citation(s) in RCA: 14] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
Abstract
To investigate the kinetics of peptide transport by the peptide transporter, PepT1, Chinese hamster ovary cells were transfected with an expression vector containing our cloned ovine PepT1 cDNA. Transport was assessed by uptake studies using the radiolabeled dipeptide, [(3)H]-Gly-Sar. Expression of oPepT1 was detected at 8-24 h post-transfection with an optimal time of 16-24 h. Uptake of Gly-Sar by oPepT1 was pH-dependent with an optimal pH of 5.5-6.0, concentration-dependent and saturable with an apparent K(m) value of 1.0 +/- 0.1 mmol/L and a maximum velocity of 14.3 +/- 0.4 nmol/(mg protein x 40 min). Competition studies with nonradiolabeled peptides and [(3)H]-Gly-Sar showed that all di- and tripeptides inhibited uptake of [(3)H]-Gly-Sar. In addition, three tetrapeptides (Met-Gly-Met-Met, Pro-Phe-Gly-Lys, and Val-Gly-Ser-Glu) also inhibited [(3)H]-Gly-Sar uptake. There was no inhibition of [(3)H]-Gly-Sar uptake detected in the presence of nonradiolabeled free amino acids. Treatment of the cells with staurosporine, an inhibitor of protein kinase C (PKC) significantly increased the transport system. This increase was specific and could be blocked if treatment was done in the presence of phorbol 12-myristate-13-acetate (PMA), an activator of PKC. The staurosporine- and PMA-induced changes in peptide transport activity were not affected by cotreatment with cycloheximide. These data demonstrate that the transport of peptide substrates by oPepT1 in transfected mammalian cells is similar to that in microinjected Xenopus oocytes and that PKC phosphorylation plays a regulatory role in oPepT1 function.
Collapse
Affiliation(s)
- Hong Chen
- Department of Animal and Poultry Sciences, Virginia Polytechnic Institute and State University, Blacksburg VA 24061, USA
| | | | | | | |
Collapse
|
159
|
Takahashi K, Masuda S, Nakamura N, Saito H, Futami T, Doi T, Inui K. Upregulation of H(+)-peptide cotransporter PEPT2 in rat remnant kidney. Am J Physiol Renal Physiol 2001; 281:F1109-16. [PMID: 11704562 DOI: 10.1152/ajprenal.0346.2000] [Citation(s) in RCA: 32] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
The progression of renal damage resulting from reduced nephron mass has been extensively studied in the 5/6 nephrectomized rat. However, reabsorption of small peptides and D-glucose across the renal proximal tubule in this model remains poorly understood. In this study, we examined the alterations of H(+)-peptide cotransporters (PEPT1 and PEPT2) and Na(+)-D-glucose cotransporters (SGLT1 and SGLT2) in chronic renal failure. Two weeks after surgery, H(+)-dependent [(14)C]glycylsarcosine uptake by the renal brush-border membrane vesicles isolated from 5/6 nephrectomized rats was significantly increased compared with that from sham-operated controls. Kinetic analysis revealed that the maximum velocity value for [(14)C]glycylsarcosine uptake by the high-affinity-type of peptide transporter was increased threefold by 5/6 nephrectomy, without significant changes in the apparent Michaelis-Menten constant value. Competitive PCR analyses indicated that the expression of PEPT2 mRNA was markedly increased in the remnant kidney, but PEPT1, SGLT1, and SGLT2 mRNA levels showed no significant changes. These findings indicated that the high-affinity-type H(+)-peptide cotransport activity is upregulated by 5/6 nephrectomy, accompanied by the increased expression of PEPT2. The upregulation of PEPT2 expression would result in an increase in reabsorption of small peptides and peptide-like drugs across the brush-border membranes in chronic renal failure.
Collapse
Affiliation(s)
- K Takahashi
- Department of Pharmacy, Kyoto University Hospital, Faculty of Medicine, Kyoto University, Kyoto 606-8507, Japan
| | | | | | | | | | | | | |
Collapse
|
160
|
Payne JW, Payne GM, Gupta S, Marshall NJ, Grail BM. Conformational limitations of glycylsarcosine as a prototypic substrate for peptide transporters. BIOCHIMICA ET BIOPHYSICA ACTA 2001; 1514:65-75. [PMID: 11513805 DOI: 10.1016/s0005-2736(01)00364-9] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 10/17/2022]
Abstract
Peptide transporters are present in all species to absorb the small peptides that occur ubiquitously as products of proteolysis. The broad substrate specificities of these systems allow them to be exploited therapeutically for delivery of peptidomimetic drugs in microbes and man. To this end, glycylsarcosine is currently used as a standard substrate for assaying peptidomimetic transport by peptide transporters. However, in this study we find it is unsuitable as a general substrate, based on assays of its transport by model bacterial peptide transporters and computer-based conformational analysis of its structure. Of the two generic transporters for di- and tripeptides, exemplified by Dpp and Tpp in Escherichia coli, only Dpp can transport glycylsarcosine. The explanation for this finding came from molecular modelling, which indicated that glycylsarcosine can adopt only a restricted range of conformers compared with typical dipeptides, and that of the conformers with a trans peptide bond, the majority have the specific psi and phi backbone torsion angles needed for molecular recognition and transport by Dpp but none possessed psi and phi torsions required for recognition by Tpp; moreover, 38% of its conformers have cis peptide bonds that are not substrates for any peptide transporter. Thus, using glycylsarcosine as substrate in competition assays with compounds that typically form conformers recognised by both types of peptide transporter will underestimate their transport. These findings have implications for assays of oral availability of peptidomimetic drugs such as beta-lactams, ACE inhibitors and anti-viral compounds, for which glycylsarcosine is routinely used.
Collapse
Affiliation(s)
- J W Payne
- School of Biological Sciences, University of Wales, Bangor, Gwynedd LL57 2UW, UK.
| | | | | | | | | |
Collapse
|
161
|
Motohashi H, Masuda S, Katsura T, Saito H, Sakamoto S, Uemoto S, Tanaka K, Inui KI. Expression of peptide transporter following intestinal transplantation in the rat. J Surg Res 2001; 99:294-300. [PMID: 11469900 DOI: 10.1006/jsre.2001.6163] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/27/2022]
Abstract
BACKGROUND The absorptive function of the intestinal graft is one of the most important factors for successful intestinal transplantation. To clarify whether the intestinal H(+)/peptide cotransporter (PEPT1) was expressed in the transplanted intestine, we examined the expression of PEPT1 in an experimental model of rat small intestinal transplantation in comparison with expression of Na(+)/glucose cotransporter (SGLT1). MATERIALS AND METHODS Heterotopic intestinal transplantation was performed in allogeneic and syngeneic rat strain combinations. An additional group of allogeneic recipients was treated with tacrolimus (1 mg/kg) prior to transplantation, then daily for 7 days. Intestinal grafts were examined for histopathology and PEPT1 and SGLT1 expression. RESULTS In the isografts, the levels of messenger RNA (mRNA) encoding both transporters were not changed, while the amount of SGLT1 protein was decreased and that of PEPT1 protein was increased. In the allografts, mRNA level and protein amount of both transporters and the amount of villin protein were decreased, and microscopic examination revealed histopathological features of rejection on day 7. Tacrolimus treatment ameliorated the histopathological features and prevented the decrease in villin protein expression. However, the decreases in PEPT1 and SGLT1 expression (both mRNA and protein) were partially prevented by tacrolimus treatment. CONCLUSION This study indicated that the expression of transporters should be determined to evaluate intestinal graft function in addition to histopathological examination of the mucosa and that the levels of mRNA encoding intestinal nutrient transporters in biopsy specimens may be useful for evaluating the intestinal graft function for intestinal transplant patients.
Collapse
Affiliation(s)
- H Motohashi
- Department of Pharmacy, Faculty of Medicine, Kyoto University Hospital, Sakyo-ku, Kyoto 606-8507, USA
| | | | | | | | | | | | | | | |
Collapse
|
162
|
Abstract
Mammalian peptide transporters (PEPT1 and PEPT2) play a pivotal role in the absorption of small peptides from the intestine and kidney, respectively, and in the disposition and targeting of peptide or mimetic drugs. However, there are few reports on the molecular basis of their regulation, especially in the young. The aim of this study was to determine the developmental expression of intestinal and renal oligopeptide transporters in rats from embryonic to adult ages. Intestinal segments were collected (i.e. duodenum, jejunum, ileum, and colon) along with whole kidney, and their mRNA and protein levels were measured. Expression levels of PEPT1 were maximal 3-5 d after birth in the duodenum, jejunum, and ileum, and then declined rapidly. Expression was increased transiently at d 24, most notably in the ileum. Adult protein levels were approximately 70% of that observed on d 3-5. Significant PEPT1 expression was observed in colon during the first week of life, but levels were undetectable shortly thereafter through adulthood. PEPT1 and PEPT2 expression is less regulated in rat kidney and more pronounced in older animals. Peptide transporters were also present as early as d 20 of fetal life for all tissues tested. These results are unique in providing the developmental expression of peptide transporter mRNA and protein in distinct regions of the small intestine, colon, and kidney in rat. Our findings suggest that intestinal expression of PEPT1 is induced postpartum, possibly by suckling, and again at the time of weaning, and that the colon may participate in peptide transport early in life.
Collapse
Affiliation(s)
- H Shen
- College of Pharmacy and Upjohn Center for Clinical Pharmacology, The University of Michigan, Ann Arbor, Michigan 48109, USA
| | | | | |
Collapse
|
163
|
Abstract
PURPOSE The peptide transporter PEPT2 was recently shown to be functionally active in rat choroid plexus, suggesting that it may play a role in neuropeptide homeostasis in the cerebrospinal fluid. This study, therefore, examined the role of PEPT2 in mediating neuropeptide uptake into choroid plexus. METHODS Whole-tissue rat choroid plexus uptake studies were performed on GlySar in the absence and presence of neuropeptides and on carnosine. RESULTS The neuropeptides NAAG, CysGly, GlyGln, kyotorphin, and carnosine inhibited the uptake of radiolabeled GlySar at 1.0 mM concentrations. In contrast, TRH, [D-Arg2]-kyotorphin, glutathione, and homocarnosine did not inhibit GlySar uptake. Kyotorphin, an analgesic, was a competitive inhibitor of GlySar with a Ki of 8.0 microM. The direct uptake of carnosine was also shown to be mediated by PEPT2 in isolated choroid plexus (Km = 39.3 microM; Vmax = 73.9 pmol/mg/min). Radiolabeled carnosine uptake was inhibited by 1.0 mM concentrations of GlySar or carnosine but not homocarnosine, L-histidine, or beta-alanine. CONCLUSIONS These findings indicate that PEPT2 mediates the uptake of a diverse group of neuropeptides in choroid plexus, and suggests a role for PEPT2 in the regulation of neuropeptides, peptide fragments, and peptidomimetics in cerebrospinal fluid.
Collapse
Affiliation(s)
- N S Teuscher
- College of Pharmacy and Upjohn Center for Clinical Pharmacology, The University of Michigan, Ann Arbor 48109, USA
| | | | | |
Collapse
|
164
|
Motohashi H, Katsura T, Saito H, Inui K. Effects of tacrolimus and cyclosporin A on peptide transporter PEPT1 in Caco-2 cells. Pharm Res 2001; 18:713-7. [PMID: 11465431 DOI: 10.1023/a:1011006015593] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022]
Affiliation(s)
- H Motohashi
- Department of Pharmacy, Kyoto University Hospital, Faculty of Medicine, Kyoto University, Japan
| | | | | | | |
Collapse
|
165
|
Knütter I, Theis S, Hartrodt B, Born I, Brandsch M, Daniel H, Neubert K. A novel inhibitor of the mammalian peptide transporter PEPT1. Biochemistry 2001; 40:4454-8. [PMID: 11284702 DOI: 10.1021/bi0026371] [Citation(s) in RCA: 46] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
This study was initiated to develop inhibitors of the intestinal H(+)/peptide symporter. We provide evidence that the dipeptide derivative Lys[Z(NO(2))]-Pro is an effective competitive inhibitor of mammalian PEPT1 with an apparent binding affinity of 5-10 microM. Characterization of the interaction of Lys[Z(NO(2))]-Pro with the substrate binding domain of PEPT1 has been performed in (a) monolayer cultures of human Caco-2 cells expressing PEPT1, (b) transgenic Pichia pastoris cells expressing PEPT1, and (c) Xenopus laevis oocytes expressing PEPT1. By competitive uptake studies with radiolabeled dipeptides, HPLC analysis of Lys[Z(NO(2))]-Pro in cells, and electrophysiological techniques, we unequivocally show that Lys[Z(NO(2))]-Pro binds with high affinity to PEPT1, competes competitively with various dipeptides for uptake into cells, but is not transported itself. Lack of transport was substantiated by the absence of Lys[Z(NO(2))]-Pro in Caco-2 cell extracts as determined by HPLC analysis, and by the absence of any positive inward currents in oocytes when exposed to the inhibitor. The fact that Lys[Z(NO(2))]-Pro can bind to PEPT1 from the extracellular as well as the intracellular site was shown in the oocyte expression system by a strong inhibition of dipeptide-induced currents under voltage clamp conditions. Our findings serve as a starting point for the identification of the substrate binding domain in the PEPT1 protein as well as for studies on the physiological and pharmacological role of PEPT1.
Collapse
Affiliation(s)
- I Knütter
- Institute of Biochemistry, Department of Biochemistry/Biotechnology, and Biozentrum, Martin-Luther-University Halle-Wittenberg, Halle, Germany
| | | | | | | | | | | | | |
Collapse
|
166
|
Gao J, Sudoh M, Aubé J, Borchardt RT. Transport characteristics of peptides and peptidomimetics: I. N-methylated peptides as substrates for the oligopeptide transporter and P-glycoprotein in the intestinal mucosa. THE JOURNAL OF PEPTIDE RESEARCH : OFFICIAL JOURNAL OF THE AMERICAN PEPTIDE SOCIETY 2001; 57:316-29. [PMID: 11328489 DOI: 10.1046/j.1397-002x.2001.00000.x] [Citation(s) in RCA: 23] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
Abstract
Peptides and peptidomimetics often exhibit poor oral bioavailability due to their metabolic instability and low permeation across the intestinal mucosa. N-Methylation has been used successfully in peptide-based drug design in an attempt to improve the metabolic stability of a peptide-based lead compound. However, the effect of N-methylation on the absorption of peptides through the intestinal mucosa is not well understood, particularly when transporters, i.e. the oligopeptide transporter (OPT) and P-glycoprotein (P-gp), modulate the passive diffusion of these types of molecules. To examine this, terminally free and terminally modified (N-acetylated and C-amidated) analogs of H-Ala-Phe-Ala-OH with N-methyl groups on either the Ala-Phe or Phe-Ala peptide bond were synthesized. Transport studies using Caco-2 cell monolayers, an in vitro model of the intestinal mucosa, showed that N-methylation of the Ala-Phe peptide bond of H-Ala-Phe-Ala-OH stabilized the molecule to protease degradation, and the resulting analog exhibited significant substrate activity for OPT. However, N-methylation of the Phe-Ala peptide bond of H-Ala-Phe-Ala-OH did not stabilize the molecule to protease degradation, and the substrate activity of the resulting molecule for OPT could not be determined. Interestingly, N-methylation of the Phe-Ala peptide bond of the terminally modified tripeptide Ac-Ala-Phe-Ala-NH2 decreased the substrate activity of the molecule for the efflux transporter P-gp. In contrast, N-methylation of the Ala-Phe peptide bond of the terminally modified tripeptide Ac-Ala-Phe-Ala-NH2 increased the substrate activity of the molecule for P-gp.
Collapse
Affiliation(s)
- J Gao
- Department of Pharmaceutical Chemistry, The University of Kansas, Lawrence 66047, USA
| | | | | | | |
Collapse
|
167
|
Pan Y, Wong EA, Bloomquist JR, Webb KE. Expression of a cloned ovine gastrointestinal peptide transporter (oPepT1) in Xenopus oocytes induces uptake of oligopeptides in vitro. J Nutr 2001; 131:1264-70. [PMID: 11285336 DOI: 10.1093/jn/131.4.1264] [Citation(s) in RCA: 42] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
Abstract
We determined the primary structure, tissue distribution and in vitro functional characterization of a peptide transporter, oPepT1, from ovine intestine. Ovine PepT1 (oPepT1) cDNA was 2829-bp long, encoding a protein of 707 amino acid residues with an estimated molecular size of 78 kDa and an isoelectric point (pI) of 6.57. Transport function of oPepT1 was assessed by expressing oPepT1 in Xenopus oocytes using a two-electrode voltage-clamp technique. The transport process was electrogenic and pH dependent, but independent of Na+, Cl- and Ca2+. The oPepT1 displayed a broad substrate specificity for transport of neutral and charged dipeptides and tripeptides. All dipeptides and tripeptides examined evoked inward currents in a saturable manner, with an affinity constant (Kt) ranging from 27 micromol/L to 3.0 mmol/L. No responses were detected from tetrapeptides or free amino acids. Northern blot analysis demonstrated that oPepT1 was expressed in the small intestine, omasum and rumen, but was not expressed in liver and kidney. The presence of the peptide transporter in the forestomach at such levels could provide nutritionally important amino acid nitrogen to ruminants.
Collapse
Affiliation(s)
- Y Pan
- Department of Animal and Poultry Sciences, Virginia Polytechnic Institute and State University, Blacksburg, VA 24061, USA
| | | | | | | |
Collapse
|
168
|
Sams-Nielsen A, Orskov C, Jansen-Olesen I. Pharmacological evidence for CGRP uptake into perivascular capsaicin sensitive nerve terminals. Br J Pharmacol 2001; 132:1145-53. [PMID: 11226146 PMCID: PMC1572649 DOI: 10.1038/sj.bjp.0703910] [Citation(s) in RCA: 28] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022] Open
Abstract
Specific mechanisms, providing reuptake of cathecholamine and amino acid neurotransmitters (e.g. serotonin and glutamate) into cells of the central nervous system are well known, whereas neuronal uptake of neuropeptide transmitters have not previously been reported. In the present study we present evidence for uptake of the 37 amino acid neuropeptide, calcitonin gene-related peptide (CGRP) into perivascular terminals of capsaicin sensitive nerve fibres, innervating the guinea-pig basilar artery. Release of CGRP from perivascular nerve terminals was obtained by capsaicin-induced vanilloid receptor-stimulation and detected as CGRP receptor-mediated dilation of isolated segments of the guinea-pig basilar artery. Following three repeated capsaicin challenges, CGRP-depleted segments were incubated with CGRP. This caused significant reappearance of capsaicin-induced vasodilatory responses. These responses were dependent on duration and concentration of the preceding CGRP incubation and were inhibited by the CGRP receptor antagonist, CGRP(8 - 37). The CGRP-re-depletion was significantly reduced when CGRP(8 - 37) was present during the preceding CGRP incubation. Thus, presynaptic CGRP receptors are likely to be involved in neuronal CGRP uptake. Incubating the artery segments with (125)I-CGRP allowed subsequent detection of capsaicin-induced (125)I-release. Immunohistochemical experiments showed that only terminal CGRP is subject to capsaicin-induced depletion in vitro, whereas CGRP-immunoreactivity endures in the nerve fibres.
Collapse
Affiliation(s)
- A Sams-Nielsen
- Department of Pharmacology, The Royal Danish School of Pharmacy, Universitetsparken 2, DK-2100 Copenhagen Ø, Denmark.
| | | | | |
Collapse
|
169
|
Abstract
Although a large number of plasma cell nutrient transport proteins has been cloned in the last couple of years, much remains to be learned about their structure-function relationships, membrane topology, posttranslational regulation, and bioenergetics of transport. Major progress in the study of the human and animal transporters has come from heterologous expression systems, which offer the benefits of ease of genetic selection and manipulation, short generation time of the organisms in which transporters are expressed, and comparatively high levels of expression of the recombinant proteins. Because our main focus is mammalian peptide transporters, the intestinal peptide transporter, PEPT1, and its renal counterpart, PEPT2, will serve here as models for the analysis of their structure and function when they are heterologously expressed in different cell systems.
Collapse
Affiliation(s)
- H Daniel
- Institute of Nutritional Sciences, Technical University of Munich, Hochfeldweg 2, 85350 Freising-Weihenstephan, Germany.
| |
Collapse
|
170
|
Xiao G, Wang J, Tangen T, Giacomini KM. A novel proton-dependent nucleoside transporter, CeCNT3, from Caenorhabditis elegans. Mol Pharmacol 2001; 59:339-48. [PMID: 11160871 DOI: 10.1124/mol.59.2.339] [Citation(s) in RCA: 26] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
In this study, we describe the cloning and characterization of a proton-dependent, broadly selective nucleoside transporter from Caenorhabditis elegans. Recently, we constructed a broadly selective nucleoside transporter which accepts both purine and pyrimidine nucleosides. Based on these studies, we hypothesized that CNTs with novel substrate selectivities exist in nature and that a CNT homolog in the C. elegans genomic database may function as a broadly selective nucleoside transporter. We cloned the cDNA for this transporter, termed CeCNT3 because of its broad selectivity, using polymerase chain reaction-based methods. CeCNT3 is predicted to have 575 amino acid residues (63.4 kDa) with 11 to 14 putative transmembrane domains and exhibits approximately 30% identity to members of the mammalian CNT family. This transporter exhibits a novel substrate selectivity, transporting a wide range of purine and pyrimidine nucleosides (inosine, guanosine, adenosine, uridine, and thymidine) but not cytidine. The apparent Km values for inosine and thymidine are 15.2 +/- 5.3 microM and 11.0 +/- 2.4 microM, respectively. Kinetic studies demonstrate that purine and pyrimidine nucleosides share a common recognition site in the transporter. In contrast to all known members of the mammalian CNT family, CeCNT3-mediated transport of nucleosides is proton-, but not sodium-, dependent. Mutation of tyrosine 332 in CeCNT3 decreased both the maximum uptake rate and apparent Km of thymidine, suggesting that this residue is in the domain of nucleoside recognition and translocation. The broad nucleoside specificity of CeCNT3 may be explained by this and other residues that restrict purine and pyrimidine nucleoside uptake and that discriminate among pyrimidine nucleosides.
Collapse
Affiliation(s)
- G Xiao
- Department of Biopharmaceutical Sciences, School of Pharmacy, University of California, San Francisco, San Francisco, California, USA
| | | | | | | |
Collapse
|
171
|
Suzuki H, Sugiyama Y. Role of metabolic enzymes and efflux transporters in the absorption of drugs from the small intestine. Eur J Pharm Sci 2000; 12:3-12. [PMID: 11121729 DOI: 10.1016/s0928-0987(00)00178-0] [Citation(s) in RCA: 228] [Impact Index Per Article: 9.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/19/2022]
Abstract
It has been established that the absorption of many drugs from the small intestine is hindered by the detoxification systems which are present in this epithelial tissue. In this article, we will summarize the significant role of small intestine in reducing the oral bioavailability of drugs, particularly focusing on the role of metabolic enzymes and efflux transporters. Since the role of cytochrome P450 3A (CYP3A) and MDR1 P-glycoprotein (P-gp) in intestinal drug disposition has been highlighted, the disposition of CYP3A substrates, P-gp substrates and CYP3A/P-gp bisubstrates are summarized. Moreover, it is plausible that conjugative enzymes and/or carboxyesterases act synergistically with efflux transporters of organic anions, affecting the intestinal availability, i.e. many xenobiotics and ester-type prodrugs are metabolized to the corresponding glucuronide and sulfate conjugates and carboxylates (active drugs), respectively, followed by cellular extrusion. The characteristics of the efflux transporters of organic anions across the apical and basal membrane of enterocytes and Caco-2 cells are also summarized from this point of view.
Collapse
Affiliation(s)
- H Suzuki
- Graduate School of Pharmaceutical Sciences, The University of Tokyo and Core Research for Evolutional Science and Technology, Japan Science and Technology Corporation, Hongo, Bunkyo-ku, 113-0033, Tokyo, Japan.
| | | |
Collapse
|
172
|
Terada T, Sawada K, Ito T, Saito H, Hashimoto Y, Inui K. Functional expression of novel peptide transporter in renal basolateral membranes. Am J Physiol Renal Physiol 2000; 279:F851-7. [PMID: 11053045 DOI: 10.1152/ajprenal.2000.279.5.f851] [Citation(s) in RCA: 31] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
We examined the peptide transport activity in renal basolateral membranes. [(14)C]glycylsarcosine (Gly-Sar) uptake in rat renal cortical slices was saturable and inhibited by excess dipeptide and aminocephalosporin cefadroxil. When several renal cell lines were screened for the basolateral peptide transport activity, Madin-Darby canine kidney (MDCK) cells were demonstrated to have the greatest transport activity. [(14)C]Gly-Sar uptake across the basolateral membranes of MDCK cells was inhibited by di- and tripeptide and decreased with decreases in extracellular pH from 7.4 to 5.0. The Michaelis-Menten constant value of [(14)C]Gly-Sar uptake across the basolateral membranes of MDCK cells was 71 microM. The basolateral peptide transporter in MDCK cells showed several different [(14)C]Gly-Sar transport characteristics in growth dependence, pH profile, substrate affinity, and sensitivities to chemical modifiers from those of the apical H(+)-peptide cotransporter of MDCK cells. The findings of the present investigation indicated that the peptide transporter was expressed in the renal basolateral membranes. In addition, from the functional characteristics, the renal basolateral peptide transporter was suggested to be distinguishable from known peptide transporters, i.e., H(+)-peptide cotransporters (PEPT1 and PEPT2) and the intestinal basolateral peptide transporter.
Collapse
Affiliation(s)
- T Terada
- Department of Pharmacy, Kyoto University Hospital, Faculty of Medicine, Kyoto University, Kyoto 606 - 8507, Japan
| | | | | | | | | | | |
Collapse
|
173
|
Abstract
The kidney plays an important role in the elimination of numerous hydrophilic xenobiotics, including drugs, toxins, and endogenous compounds. It has developed high-capacity transport systems to prevent urinary loss of filtered nutrients, as well as electrolytes, and simultaneously to facilitate tubular secretion of a wide range of organic ions. Transport systems for organic anions and cations are primarily involved in the secretion of drugs in renal tubules. The identification and characterization of organic anion and cation transporters have been progressing at the molecular level. To date, many members of the organic anion transporter (OAT), organic cation transporter (OCT), and organic anion-transporting polypeptide (oatp) gene families have been found to mediate the transport of diverse organic anions and cations. It has also been suggested that ATP-dependent primary active transporters such as MDR1/P-glycoprotein and the multidrug resistance-associated protein (MRP) gene family function as efflux pumps of renal tubular cells for more hydrophobic molecules and anionic conjugates. Tubular reabsorption of peptide-like drugs such as beta-lactam antibiotics across the brush-border membranes appears to be mediated by two distinct H+/peptide cotransporters: PEPT1 and PEPT2. Renal disposition of drugs is the consequence of interaction and/or transport via these diverse secretory and absorptive transporters in renal tubules. Studies of the functional characteristics, such as substrate specificity and transport mechanisms, and of the localization of cloned drug transporters could provide information regarding the cellular network involved in renal handling of drugs. Detailed information concerning molecular and cellular aspects of drug transporters expressed in the kidney has facilitated studies of the mechanisms underlying renal disposition as well as transporter-mediated drug interactions.
Collapse
Affiliation(s)
- K I Inui
- Department of Pharmacy, Kyoto University Hospital, Faculty of Medicine, Kyoto University, Sakyo-ku, Kyoto, Japan.
| | | | | |
Collapse
|
174
|
Saier MH. Families of transmembrane transporters selective for amino acids and their derivatives. MICROBIOLOGY (READING, ENGLAND) 2000; 146 ( Pt 8):1775-1795. [PMID: 10931885 DOI: 10.1099/00221287-146-8-1775] [Citation(s) in RCA: 135] [Impact Index Per Article: 5.6] [Reference Citation Analysis] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/18/2022]
Affiliation(s)
- Milton H Saier
- Department of Biology, University of California at San Diego, La Jolla, CA 92093-0116, USA1
| |
Collapse
|
175
|
Van Aubel RA, Masereeuw R, Russel FG. Molecular pharmacology of renal organic anion transporters. Am J Physiol Renal Physiol 2000; 279:F216-32. [PMID: 10919840 DOI: 10.1152/ajprenal.2000.279.2.f216] [Citation(s) in RCA: 106] [Impact Index Per Article: 4.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/17/2023] Open
Abstract
Renal organic anion transport systems play an important role in the elimination of drugs, toxic compounds, and their metabolites, many of which are potentially harmful to the body. The renal proximal tubule is the primary site of carrier-mediated transport from blood to urine of a wide variety of anionic substrates. Recent studies have shown that organic anion secretion in renal proximal tubule is mediated by distinct sodium-dependent and sodium-independent transport systems. Knowledge of the molecular identity of these transporters and their substrate specificity has increased considerably in the past few years by cloning of various carrier proteins. However, a number of fundamental questions still have to be answered to elucidate the participation of the cloned transporters in the overall tubular secretion of anionic xenobiotics. This review summarizes the latest knowledge on molecular and pharmacological properties of renal organic anion transporters and homologs, with special reference to their nephron and plasma membrane localization, transport characteristics, and substrate and inhibitor specificity. A number of the recently cloned transporters, such as the p-aminohippurate/dicarboxylate exchanger OAT1, the anion/sulfate exchanger SAT1, the peptide transporters PEPT1 and PEPT2, and the nucleoside transporters CNT1 and CNT2, are key proteins in organic anion handling that possess the same characteristics as has been predicted from previous physiological studies. The role of other cloned transporters, such as MRP1, MRP2, OATP1, OAT-K1, and OAT-K2, is still poorly characterized, whereas the only information that is available on the homologs OAT2, OAT3, OATP3, and MRP3-6 is that they are expressed in the kidney, but their localization, not to mention their function, remains to be elucidated.
Collapse
Affiliation(s)
- R A Van Aubel
- Department of Pharmacology and Toxicology, Institute of Cellular Signaling, University of Nijmegen, The Netherlands
| | | | | |
Collapse
|
176
|
Fei YJ, Sugawara M, Liu JC, Li HW, Ganapathy V, Ganapathy ME, Leibach FH. cDNA structure, genomic organization, and promoter analysis of the mouse intestinal peptide transporter PEPT1. BIOCHIMICA ET BIOPHYSICA ACTA 2000; 1492:145-54. [PMID: 11004485 DOI: 10.1016/s0167-4781(00)00101-9] [Citation(s) in RCA: 77] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
We describe in this report the cDNA structure, functional characteristics, genomic organization, and promoter analysis of the mouse H(+)-coupled low-affinity peptide transporter PEPT1. The mouse PEPT1 cDNA cloned from a kidney cDNA library is approximately 3.1 kb long and encodes a protein of 709 amino acids. When expressed heterologously in mammalian cells and in Xenopus laevis oocytes, mouse PEPT1 mediates H(+)-coupled electrogenic transport of the dipeptide glycylsarcosine. The mouse pept1 gene, cloned from a genomic DNA library in bacterial artificial chromosome, is approximately 38 kb long and consists of 23 exons and 22 introns. 5'-Rapid amplification of cDNA ends with poly(A)(+) RNA from mouse intestine has identified the transcription start site that lies 31 bp upstream of the translation start site. The promoter region upstream of the transcription start site does not contain the TATA box but possesses three GC boxes which are the binding sites for the transcription activator SP1. Functional analysis of the promoter region using the luciferase reporter assay in Caco-2 cells (a human intestinal cell line that express PEPT1 constitutively) and five different 5'-deletion fragments of the promoter has shown that essential promoter/enhancer elements are present within 1140 bp upstream of the transcription start site.
Collapse
Affiliation(s)
- Y J Fei
- Department of Biochemistry and Molecular Biology, Medical College of Georgia, Augusta, 30912, USA
| | | | | | | | | | | | | |
Collapse
|
177
|
Chen XZ, Steel A, Hediger MA. Functional roles of histidine and tyrosine residues in the H(+)-peptide transporter PepT1. Biochem Biophys Res Commun 2000; 272:726-30. [PMID: 10860823 DOI: 10.1006/bbrc.2000.2851] [Citation(s) in RCA: 76] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/13/2023]
Abstract
Histidyl residues in peptide transporters PepT1 and PepT2 are believed to participate in proton and substrate binding and to be crucial to the transporters' functional activities. In the present study, we performed mutagenesis of rabbit PepT1. We mutated three histidine residues (H57, H111, and H121) predicted to reside in transmembrane segments, as well as tyrosine residues adjacent to H57. Functional analysis of wild-type and mutant PepT1 expressed in Xenopus oocytes, using both the radiotracer methods and two-microelectrode voltage-clamping, revealed that not only the H57 but also the aromatic residues near H57 were essential for the normal function of PepT1, in agreement with the concept that aromatic residues stabilize the charge on H(+) when interacting with H57. While mutagenesis at H111 did not significantly affect the activity of PepT1, mutagenesis at H121 had profound implications. The substrate affinities for H121 mutants were decreased depending both on the charge of the substrate and the charge on the substituted residues at position 121. We propose that H57 and H121 are intimately involved in the binding of the coupling ion H(+) and the recognition of transportable peptide substrates, respectively.
Collapse
Affiliation(s)
- X Z Chen
- Membrane Biology Program and Renal Division, Brigham & Women's Hospital, Harvard Medical School, Boston, MA 02115, USA
| | | | | |
Collapse
|
178
|
Affiliation(s)
- K Inui
- Department of Pharmacy, Kyoto University Hospital, Japan
| | | |
Collapse
|
179
|
Sugawara M, Huang W, Fei YJ, Leibach FH, Ganapathy V, Ganapathy ME. Transport of valganciclovir, a ganciclovir prodrug, via peptide transporters PEPT1 and PEPT2. J Pharm Sci 2000; 89:781-9. [PMID: 10824137 DOI: 10.1002/(sici)1520-6017(200006)89:6<781::aid-jps10>3.0.co;2-7] [Citation(s) in RCA: 226] [Impact Index Per Article: 9.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/07/2022]
Abstract
In clinical trials, valganciclovir, the valyl ester of ganciclovir, has been shown to enhance the bioavailability of ganciclovir when taken orally by patients with cytomegalovirus infection. We investigated the role of the intestinal peptide transporter PEPT1 in this process by comparing the interaction of ganciclovir and valganciclovir with the transporter in different experimental systems. We also studied the interaction of these two compounds with the renal peptide transporter PEPT2. In cell culture model systems using Caco-2 cells for PEPT1 and SKPT cells for PEPT2, valganciclovir inhibited glycylsarcosine transport mediated by PEPT1 and PEPT2 with K(i) values (inhibition constant) of 1.68+/-0.30 and 0.043+/- 0.005 mM, respectively. The inhibition by valganciclovir was competitive in both cases. Ganciclovir did not interact with either transporter. Similar studies done with cloned PEPT1 and PEPT2 in heterologous expression systems yielded comparable results. The transport of valganciclovir via PEPT1 was investigated directly in PEPT1-expressing Xenopus laevis oocytes with an electrophysiological approach. Valganciclovir, but not ganciclovir, induced inward currents in PEPT1-expressing oocytes. These results demonstrate that the increased bioavailability of valganciclovir is related to its recognition as a substrate by the intestinal peptide transporter PEPT1. This prodrug is also recognized by the renal peptide transporter PEPT2 with high affinity.
Collapse
Affiliation(s)
- M Sugawara
- Department of Biochemistry and Molecular Biology, Medical College of Georgia, Augusta, Georgia 30912, USA
| | | | | | | | | | | |
Collapse
|
180
|
Zhu T, Chen XZ, Steel A, Hediger MA, Smith DE. Differential recognition of ACE inhibitors in Xenopus laevis oocytes expressing rat PEPT1 and PEPT2. Pharm Res 2000; 17:526-32. [PMID: 10888303 DOI: 10.1023/a:1007556630189] [Citation(s) in RCA: 80] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022]
Abstract
PURPOSE To examine the mechanism of inhibition of glycylsarcosine (GlySar) transport by quinapril and enalapril, and whether or not angiotensin converting enzyme (ACE) inhibitors are transported by PEPT2 as well as by PEPT1. METHODS Xenopus laevis oocytes were cRNA-injected with rat PEPT1 or PEPT2 and the transport kinetics of radiolabeled GlySar were studied in the absence and presence of quinapril and enalapril. The two-microelectrode voltage-clamp technique was also performed to probe the electrogenic uptake of captopril, quinapril and enalapril. RESULTS Kinetic analyses demonstrated that quinapril inhibited the uptake of GlySar in a noncompetitive manner in Xenopus oocytes injected with PEPT1 or PEPT2 (Ki = 0.8 or 0.4 mM, respectively). In contrast, a competitive interaction was observed between GlySar and enalapril (Ki = 10.8 mM for PEPT1 or 4.3 mM for PEPT2). Most significantly, captopril and enalapril, but not quinapril, induced inwardly-directed currents in both PEPT1- and PEPT2-expressed oocytes. CONCLUSIONS These results are unique in providing direct evidence for the substrate recognition and transport of some ACE inhibitors by the high- and low-affinity oligopeptide transporters. Our findings point to differences between PEPT1 and PEPT2 in their affinity to, rather than in their specificity for, ACE inhibitors.
Collapse
Affiliation(s)
- T Zhu
- College of Pharmacy and Upjohn Center for Clinical Pharmacology, The University of Michigan, Ann Arbor 48109-0504, USA
| | | | | | | | | |
Collapse
|
181
|
Tribolo S, Maroux S, Massey-Harroche D. Kidney proximal tubule cells: Epithelial cells without EGTA-extractable annexins? Biochem Cell Biol 2000. [DOI: 10.1139/o00-061] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
The expression and the subcellular localizations of annexins I, II, IV, VI, and XIII in renal epithelial cells were investigated, using immunological techniques with specific monoclonal antibodies. Upon performing Western blotting experiments, no annexins VI and XIII were detected in kidney, whereas annexins I, II, and IV were. Immunofluorescence labelling procedure performed on thin frozen renal sections showed the presence of these three annexins along the plasma membrane of the collecting duct cells with a restricted expression of annexin I at principal cells. Annexin I was also found present in some glomerular cells. None of these annexins, however, were detected in the proximal tubular cells upon performing immunofluorescence labelling and electrophoretic analysis on an EGTA (ethylenebis(oxyethylenenitrilo)tetraacetic acid)-extractable annexin fraction prepared from freshly isolated cells. This is the first time a mammalian epithelial cell has been found to express non-typical annexin (at least partly solubilized with EGTA). However, when these cells were grown in primary culture, they were found to express annexins I, II, IV, and V. As well as being located along the basolateral membrane, annexins I and II are also present on vesicles, which suggests that these annexins may be involved in vesicular traffic under cell culture conditions.Key words: annexin, kidney, proximal tubule, primary culture.
Collapse
|
182
|
Abstract
Classical prodrug design often represents a nonspecific chemical approach to mask undesirable drug properties such as limited bioavailability, lack of site specificity, and chemical instability. On the other hand, targeted prodrug design represents a new strategy for directed and efficient drug delivery. Particularly, targeting the prodrugs to a specific enzyme or a specific membrane transporter, or both, has potential as a selective drug delivery system in cancer chemotherapy or as an efficient oral drug delivery system. Site-selective targeting with prodrugs can be further enhanced by the simultaneous use of gene delivery to express the requisite enzymes or transporters. This review highlights evolving strategies in targeted prodrug design, including antibody-directed enzyme prodrug therapy, gene-directed enzyme prodrug therapy, and peptide transporter-associated prodrug therapy.
Collapse
Affiliation(s)
- Hyo-Kyung Han
- Parke-Davis Pharmaceutical Research, Division of Warner-Lambert, Department of Pharmacokinetics, Dynamics and Metabolism, 2800 Plymouth Road, 48105 Ann Arbor, Michigan USA
| | - Gordon L. Amidon
- College of Pharmacy, The University of Michigan, 48109-1065 Ann Arbor, MI
| |
Collapse
|
183
|
Rajan DP, Kekuda R, Huang W, Devoe LD, Leibach FH, Prasad PD, Ganapathy V. Cloning and functional characterization of a Na(+)-independent, broad-specific neutral amino acid transporter from mammalian intestine. BIOCHIMICA ET BIOPHYSICA ACTA 2000; 1463:6-14. [PMID: 10631289 DOI: 10.1016/s0005-2736(99)00224-2] [Citation(s) in RCA: 73] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
We have isolated a cDNA from a rabbit intestinal cDNA library which, when co-expressed with the heavy chain of the human 4F2 antigen (4F2hc) in mammalian cells, induces system L-like amino acid transport activity. This protein, called LAT2, consists of 535 amino acids and is distinct from LAT1 which also interacts with 4F2hc to induce system L-like amino acid transport activity. LAT2 does not interact with rBAT, a protein with a significant structural similarity to 4F2hc. The 4F2hc/LAT2-mediated transport process differs from the 4F2hc/LAT1-mediated transport in substrate specificity, substrate affinity, tissue distribution, interaction with D-amino acids, and pH-dependence. The 4F2hc/LAT2-associated transport process has a broad specificity towards neutral amino acids with K(t) values in the range of 100-1000 microM, does not interact with D-amino acids to any significant extent, and is stimulated by acidic pH. In contrast, the 4F2hc/LAT1-associated transport process has a narrower specificity towards neutral amino acids, but with comparatively higher affinity (K(t) values in the range of 10-20 microM), interacts with some D-amino acids with high affinity, and is not influenced by pH. LAT2 is expressed primarily in the small intestine and kidney, whereas LAT1 exhibits a much broader tissue distribution.
Collapse
Affiliation(s)
- D P Rajan
- Department of Biochemistry and Molecular Biology, Medical College of Georgia, Augusta, GA 30912-2100, USA
| | | | | | | | | | | | | |
Collapse
|
184
|
Abstract
This paper reviews the recent literature concerning the importance of the gut in extraintestinal protein metabolism. A growing body of evidence suggests that the gut modulates amino acid flux and inter-organ relationships in various metabolic states. This may be particularly true during the absorptive period, when the gut: (1) controls amino acid absorption; (2) may modulate catabolism and uptake for synthesis of absorbed amino acid; and (3) consequently influences the availability of liver and extrasplanchnic amino acids, as well as their pattern and kinetics through portal flow delivery.
Collapse
Affiliation(s)
- F Mariotti
- INRA Unité Nutrition Humaine et Physiologie Intestinale, Institut National Agronomique Paris-Grignon, Paris, France
| | | | | | | |
Collapse
|
185
|
Ganapathy V, Ganapathy ME, Leibach FH. Chapter 10 Intestinal transport of peptides and amino acids. CURRENT TOPICS IN MEMBRANES 2000. [DOI: 10.1016/s1063-5823(00)50012-x] [Citation(s) in RCA: 15] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 02/05/2023]
|
186
|
Ferruzza S, Scarino ML, Rotilio G, Ciriolo MR, Santaroni P, Muda AO, Sambuy Y. Copper treatment alters the permeability of tight junctions in cultured human intestinal Caco-2 cells. THE AMERICAN JOURNAL OF PHYSIOLOGY 1999; 277:G1138-48. [PMID: 10600810 DOI: 10.1152/ajpgi.1999.277.6.g1138] [Citation(s) in RCA: 17] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/07/2022]
Abstract
The effects of copper on tight-junction permeability were investigated in human intestinal Caco-2 cells, monitoring transepithelial electrical resistance and transepithelial passage of mannitol. Apical treatment of Caco-2 cells with 10-100 microM CuCl(2) (up to 3 h) produced a time- and concentration-dependent increase in tight-junction permeability, reversible after 24 h in complete medium in the absence of added copper. These effects were not observed in cells treated with copper complexed to L-histidine [Cu(His)(2)]. The copper-induced increase in tight-junction permeability was affected by the pH of the apical medium, as was the apical uptake of (64)CuCl(2), both exhibiting a maximum at pH 6.0. Treatment with CuCl(2) produced a concentration-dependent reduction in the staining of F actin but not of the junctional proteins zonula occludens-1, occludin, and E-cadherin and produced ultrastructural alterations to microvilli and tight junctions that were not observed after treatment with up to 200 microM Cu(His)(2) for 3 h. Overall, these data point to an intracellular effect of copper on tight junctions, mediated by perturbations of the F actin cytoskeleton.
Collapse
Affiliation(s)
- S Ferruzza
- Istituto Nazionale della Nutrizione, 00178 Rome, Università di Roma Tor Vergata, 00133 Rome, Italy
| | | | | | | | | | | | | |
Collapse
|
187
|
Sawada K, Terada T, Saito H, Hashimoto Y, Inui K. Effects of glibenclamide on glycylsarcosine transport by the rat peptide transporters PEPT1 and PEPT2. Br J Pharmacol 1999; 128:1159-64. [PMID: 10578127 PMCID: PMC1571742 DOI: 10.1038/sj.bjp.0702895] [Citation(s) in RCA: 25] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022] Open
Abstract
1 Glibenclamide is a widely used sulphonylurea for the treatment of non-insulin-dependent diabetes mellitus (NIDDM). This agent has been reported to inhibit the activities of various ion channels and transporters. In the present study, we examined the effects of glibenclamide on the function of the H+/peptide cotransporters PEPT1 and PEPT2 by using stable transfectants. 2 Uptake of [14C]-glycylsarcosine, a typical substrate for peptide transporters, by PEPT1- or PEPT2-expressing transfectant was inhibited by glibenclamide as well as other sulphonylureas including tolbutamide. 3 Kinetic analysis revealed that the inhibition by glibenclamide was noncompetitive. Dixon plot analyses showed that the Ki values of this agent were 25 and 7.8 microM for PEPT1 and PEPT2, respectively. 4 Glibenclamide did not inhibit Na+-coupled alanine and alpha-methyl-D-glucoside transport, suggesting that the inhibitory effects of glibenclamide on peptide transporters were not due to nonspecific interactions. 5 There was little uptake of [3H]-glibenclamide by PEPT-expressing transfectants as compared to mock-transfected cells, suggesting that glibenclamide was not a substrate for these peptide transporters. 6 In summary, glibenclamide inhibited the [14C]-glycylsarcosine transport by PEPT1 and PEPT2 in a noncompetitive fashion, although glibenclamide per se was not transported through these transporters. These findings would provide important information for clinical, physiological and biochemical aspects of peptide transporters.
Collapse
Affiliation(s)
- K Sawada
- Department of Pharmacy, Kyoto University Hospital, Faculty of Medicine, Kyoto University, Kyoto 606-8507, Japan
| | | | | | | | | |
Collapse
|
188
|
Hsu CP, Walter E, Merkle HP, Rothen-Rutishauser B, Wunderli-Allenspach H, Hilfinger JM, Amidon GL. Function and immunolocalization of overexpressed human intestinal H+/peptide cotransporter in adenovirus-transduced Caco-2 cells. AAPS PHARMSCI 1999; 1:E12. [PMID: 11741208 PMCID: PMC2761126 DOI: 10.1208/ps010312] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/13/2023]
Abstract
PURPOSE To determine the localization of the human intestinal H+/peptide cotransporter (hPepT1) and its function in intestinal epithelial cells after adenoviral transduction. METHODS Caco-2 cells grown on Transwell membrane filters were transduced with a recombinant replication-deficient adenovirus carrying the hPepT1 gene. The transport of Gly-Sar across both apical and basolateral membranes was measured after adenoviral transduction as a function of pH, temperature, inhibitors, and substrate concentration. The localization of hPepT1 was examined by immunocytochemistry using confocal laser scanning microscopy. RESULTS The apical-to-basolateral and basolateral-to-apical transport of Gly-Sar in Caco-2 cells after viral transduction was increased 3.3 and 3.5-fold, respectively. The similar magnitude of Gly-Sar permeability from either direction indicates involvement of identical transport pathways in both membranes. This was further confirmed by immunocytochemistry showing that hPepT1 was localized in the apical and basolateral membrane of Caco-2 cells after adenoviral transduction. In both directions, Gly-Sar transport was enhanced in the presence of a pH gradient. In addition, the basolateral-to-apical Gly-Sar transport was dependent on temperature, multiplicity of infection (MOI), and Gly-Sar concentration. It was inhibited in the presence of excess Gly-Pro and cephalexin. CONCLUSIONS Caco-2 cell monolayers represent an appropriate model to study gene expression in intestinal epithelial cells. Transport characteristics of Gly-Sar from the basolateral to the apical side in adenovirus-transduced Caco-2 cells are in agreement with those from the apical to the basolateral side, indicating that hPepT1 is also expressed in the basolateral membrane and displays a similar level of transport enhancement after adenovirus mediated hPepT1 gene expression.
Collapse
Affiliation(s)
- C P Hsu
- Johnson & Johnson, Drug Metabolism, Route 202, P.O. Box 300, Raritan, NJ 08869, USA.
| | | | | | | | | | | | | |
Collapse
|
189
|
Metzger R, Bohle RM, Pauls K, Eichner G, Alhenc-Gelas F, Danilov SM, Franke FE. Angiotensin-converting enzyme in non-neoplastic kidney diseases. Kidney Int 1999; 56:1442-54. [PMID: 10504496 DOI: 10.1046/j.1523-1755.1999.00660.x] [Citation(s) in RCA: 76] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/14/2022]
Abstract
BACKGROUND The angiotensin I-converting enzyme (ACE, CD143, kininase II) plays a critical role in controlling the level of vasoactive peptides such as angiotensins and kinins in the local circulations and tissue interstitium. Because recent work has documented a vessel-, organ-, and species-specific pattern of endothelial ACE expression in the vascular system, we have analyzed whether or not changes of this pattern occur in vessels, tubules, and interstitium of the human kidney that is affected by different non-neoplastic diseases. METHODS Using a set of well-characterized monoclonal antibodies (mAbs), ACE was assessed on renal tissue of 135 patients by immunohistochemistry, including an additional analysis at the ultrastructural level. A semiquantitative evaluation allowed the estimation and comparison of ACE content in different renal compartments. These data were compared with several clinical findings, diagnosis, therapeutic modalities, and histological features. RESULTS In contrast to the normal human kidney, where ACE is abundant in the brush border of the proximal tubule but is usually absent in endothelial cells of any vessel type, an endothelial neoexpression of ACE was observed in different diseases. In general, this neoexpression was associated with histological sites of interstitial fibrosis and showed some selectivity for glomerular endothelial cells in diabetes mellitus and chronic arterial hypertension. There was also a loss of epithelial ACE in the proximal tubule in certain pathological conditions, for example, in chronic fibroplastic processes, acute pyelonephritis, and different stages of acute renal failure. CONCLUSIONS Neoexpression of ACE by renal endothelial cells, as well as changes of the tubular ACE content, is a common finding in diseased human kidneys. As associated with certain tissue sites, clinical and/or morphological features, these changes may be involved in parenchymal remodeling and renal pathophysiology.
Collapse
Affiliation(s)
- R Metzger
- Department of Pediatric Surgery, Ludwig-Maximilians-University of Munich, Germany
| | | | | | | | | | | | | |
Collapse
|
190
|
Ogihara H, Suzuki T, Nagamachi Y, Inui K, Takata K. Peptide transporter in the rat small intestine: ultrastructural localization and the effect of starvation and administration of amino acids. THE HISTOCHEMICAL JOURNAL 1999. [PMID: 10421416 DOI: 10.1023/a: 1003515413550] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.0] [Reference Citation Analysis] [Abstract] [Subscribe] [Scholar Register] [Indexed: 12/28/2022]
Abstract
Peptide transporter-1 is a H+/peptide cotransporter responsible for the uptake of small peptides and peptide-like drugs, and is present in the absorptive epithelial cells of the villi in the small intestine (duodenum, jejunum, and ileum). It has been localized to the apical microvillous plasma membrane of the absorptive epithelial cells of the rat small intestine using the immunogold electron microscopic technique. Digital image analysis of the jejunum revealed that the transporter protein was abundant at the tip of the villus and that the amount decreased from the tip of the villus to its base. The effect of dietary administration of amino acids and starvation on the expression of PepT1 in the jejunum was examined by immunoblotting and image analysis of immunofluorescence. Starvation markedly increased the amount of peptide transporter present, whereas dietary administration of amino acids reduced it. The gradient of the transporter protein along the crypt-villus axis was maintained under either condition. These observations show that it is specific to the microvillous plasma membrane and that its expression is regulated by the nutritional condition.
Collapse
Affiliation(s)
- H Ogihara
- First Department of Surgery, Gunma University School of Medicine, Maebashi, Japan
| | | | | | | | | |
Collapse
|
191
|
Thwaites DT, Ford D, Glanville M, Simmons NL. H(+)/solute-induced intracellular acidification leads to selective activation of apical Na(+)/H(+) exchange in human intestinal epithelial cells. J Clin Invest 1999; 104:629-35. [PMID: 10487777 PMCID: PMC408543 DOI: 10.1172/jci7192] [Citation(s) in RCA: 60] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/17/2022] Open
Abstract
The intestinal absorption of many nutrients and drug molecules is mediated by ion-driven transport mechanisms in the intestinal enterocyte plasma membrane. Clearly, the establishment and maintenance of the driving forces - transepithelial ion gradients - are vital for maximum nutrient absorption. The purpose of this study was to determine the nature of intracellular pH (pH(i)) regulation in response to H(+)-coupled transport at the apical membrane of human intestinal epithelial Caco-2 cells. Using isoform-specific primers, mRNA transcripts of the Na(+)/H(+) exchangers NHE1, NHE2, and NHE3 were detected by RT-PCR, and identities were confirmed by sequencing. The functional profile of Na(+)/H(+) exchange was determined by a combination of pH(i), (22)Na(+) influx, and EIPA inhibition experiments. Functional NHE1 and NHE3 activities were identified at the basolateral and apical membranes, respectively. H(+)/solute-induced acidification (using glycylsarcosine or beta-alanine) led to Na(+)-dependent, EIPA-inhibitable pH(i) recovery or EIPA-inhibitable (22)Na(+) influx at the apical membrane only. Selective activation of apical (but not basolateral) Na(+)/H(+) exchange by H(+)/solute cotransport demonstrates that coordinated activity of H(+)/solute symport with apical Na(+)/H(+) exchange optimizes the efficient absorption of nutrients and Na(+), while maintaining pH(i) and the ion gradients involved in driving transport.
Collapse
Affiliation(s)
- D T Thwaites
- Department of Physiological Sciences, Medical School, University of Newcastle upon Tyne, Newcastle upon Tyne NE2 4HH, United Kingdom.
| | | | | | | |
Collapse
|
192
|
Fujita T, Kishida T, Okada N, Ganapathy V, Leibach FH, Yamamoto A. Interaction of kyotorphin and brain peptide transporter in synaptosomes prepared from rat cerebellum: implication of high affinity type H+/peptide transporter PEPT2 mediated transport system. Neurosci Lett 1999; 271:117-20. [PMID: 10477116 DOI: 10.1016/s0304-3940(99)00540-6] [Citation(s) in RCA: 27] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/26/2022]
Abstract
High-affinity type H+/peptide cotransporter PEPT2 is preferentially expressed in the kidney, and is responsible for reabsorption of di- and tripeptides in epithelial tubules. Interestingly, PEPT2 has been recently cloned from rat brain. However, there is very little information available on the peptide transporter activity in the brain. In the present study, we investigated the interaction of kyotorphin (L-tyrosyl-L-arginine) with the peptide transporter using synaptosomes prepared from rat cerebellum. The activity of the peptide transporter was assessed by measuring the uptake of radiolabeled glycyl-sarcosine (Gly-Sar), which is a prototypical substrate for the peptide transporter, in the presence of H+-gradient. Kyotorphin competitively inhibited the uptake of Gly-Sar with an inhibitory constant (Ki) of 30 +/- 4 microM in rat cerebellum synaptosomes. This uptake property is very close to that of PEPT2. Carnosine (beta-alanyl-L-histidine) also inhibited the uptake of Gly-Sar, on the other hand, TRH did not interact with the peptide transporter. RT-PCR using specific primers revealed that PEPT2 mRNA exists in cerebellum in rat. Taken collectively, these results indicate that the functional peptide transport system in rat cerebellum might be the high affinity transporter PEPT2.
Collapse
Affiliation(s)
- T Fujita
- Department of Biopharmaceutical Sciences, Kyoto Pharmaceutical University, Japan.
| | | | | | | | | | | |
Collapse
|
193
|
Terada T, Sawada K, Saito H, Hashimoto Y, Inui K. Functional characteristics of basolateral peptide transporter in the human intestinal cell line Caco-2. THE AMERICAN JOURNAL OF PHYSIOLOGY 1999; 276:G1435-41. [PMID: 10362647 DOI: 10.1152/ajpgi.1999.276.6.g1435] [Citation(s) in RCA: 36] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/11/2023]
Abstract
The apical H+-coupled peptide transporter (PEPT1) and basolateral peptide transporter in human intestinal Caco-2 cells were functionally compared by the characterization of [14C]glycylsarcosine transport. The glycylsarcosine uptake via the basolateral peptide transporter was less sensitive to medium pH than uptake via PEPT1 and was not transported against the concentration gradient. Kinetic analysis indicated that glycylsarcosine uptake across the basolateral membranes was apparently mediated by a single peptide transporter. Small peptides and beta-lactam antibiotics inhibited glycylsarcosine uptake by the basolateral peptide transporter, and these inhibitions were revealed to be competitive. Comparison of the inhibition constant values of various beta-lactam antibiotics between PEPT1 and the basolateral peptide transporter suggested that the former had a higher affinity than the latter. A histidine residue modifier, diethyl pyrocarbonate, inhibited glycylsarcosine uptake by both transporters, although the inhibitory effect was greater on PEPT1. These findings suggest that a single facilitative peptide transporter is expressed at the basolateral membranes of Caco-2 cells and that PEPT1 and the basolateral peptide transporter cooperate in the efficient transepithelial transport of small peptides and peptidelike drugs.
Collapse
Affiliation(s)
- T Terada
- Department of Pharmacy, Kyoto University Hospital, Faculty of Medicine, Kyoto University, Kyoto 606-8507, Japan
| | | | | | | | | |
Collapse
|
194
|
Fei YJ, Nara E, Liu JC, Boyd CA, Ganapathy V, Leibach FH. Preferential recognition of zwitterionic dipeptides as transportable substrates by the high-affinity peptide transporter PEPT2. BIOCHIMICA ET BIOPHYSICA ACTA 1999; 1418:344-51. [PMID: 10320685 DOI: 10.1016/s0005-2736(99)00046-2] [Citation(s) in RCA: 13] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/16/2022]
Abstract
We investigated the interaction of rat PEPT2, a high-affinity peptide transporter, with neutral, anionic, and cationic dipeptides using electrophysiological approaches as well as tracer uptake methods. D-Phe-L-Gln (neutral), D-Phe-L-Glu (anionic), and D-Phe-L-Lys (cationic) were used as representative, non-hydrolyzable, dipeptides. All three dipeptides induced H+-dependent inward currents in Xenopus laevis oocytes heterologously expressing rat PEPT2. The H+:peptide stoichiometry was 1:1 in each case. A simultaneous measurement of radiolabeled dipeptide influx and charge transfer in the same oocyte indicated a transfer of one net positive charge into the oocyte per transfer of one peptide molecule irrespective of the charged nature of the peptide. We conclude that the zwitterionic peptides are preferentially recognized by PEPT2 as transportable substrates and that the proton/peptide stoichiometry is 1 for the transport process.
Collapse
Affiliation(s)
- Y J Fei
- Department of Biochemistry and Molecular Biology, Medical College of Georgia, Augusta, GA 30912-2100, USA
| | | | | | | | | | | |
Collapse
|
195
|
Lin CJ, Smith DE. Glycylsarcosine uptake in rabbit renal brush border membrane vesicles isolated from outer cortex or outer medulla: evidence for heterogeneous distribution of oligopeptide transporters. AAPS PHARMSCI 1999; 1:E1. [PMID: 11741198 PMCID: PMC2761116 DOI: 10.1208/ps010201] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/29/2022]
Abstract
Studies were initially performed in rabbit brush border membrane vesicles (BBMV) prepared from whole cortex plus outer medulla. In these studies using combined tissues, two distinct peptide/H+transport systems were found for glycylsarcosine (GlySar) uptake, with one representing a low-affinity/high-capacity system (Vm1 = 974 pmol/mg/10 sec and Km1 = 4819 microM) and the other a high-affinity/low-capacity system (Vm2 = 220 pmol/mg/10 sec and Km2 = 96 microM). Thus, under linear conditions, the high-affinity transporter accounted for about 92% of the total transport of dipeptide. To better define the regional heterogeneity of peptide transporter activity in kidney, subsequent studies were performed in vesicles prepared from separately harvested outer cortical and outer medullary tissue. In BBMV studies prepared from outer cortex, two saturable components were revealed for GlySar transport (low-affinity/high-capacity transport system: Vm1 = 1921 pmol/mg/10 sec and Km1 = 11714 microM; high-affinity/low-capacity transport system: Vm2 = 143 pmol/mg/10 sec and Km2= 138 microM). However, in BBMV studies prepared from outer medulla, only one saturable component was revealed for GlySar transport (high-affinity/low-capacity transport system:Vm2= 168 pmol/mg/10 sec and Km2 = 230 microM). Overall, these studies support the contention that peptides are handled sequentially in kidney (ie, first by low-affinity transporter PEPT1, and then by high-affinity transporter PEPT2) and that PEPT2 is primarily responsible for the renal reabsorption of peptides and peptidomimetics.
Collapse
Affiliation(s)
- Chun-Jung Lin
- College of Pharmacy and Upjohn Center for Clinical Pharmacology, The University of Michigan, 48109-0504 Ann Arbor, Michigan
| | - David E. Smith
- College of Pharmacy and Upjohn Center for Clinical Pharmacology, The University of Michigan, 48109-0504 Ann Arbor, Michigan
| |
Collapse
|
196
|
Lin CJ, Akarawut W, Smith DE. Competitive inhibition of glycylsarcosine transport by enalapril in rabbit renal brush border membrane vesicles: interaction of ACE inhibitors with high-affinity H+/peptide symporter. Pharm Res 1999; 16:609-15. [PMID: 10350000 DOI: 10.1023/a:1018847818766] [Citation(s) in RCA: 27] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022]
Abstract
PURPOSE To examine the inhibitory potential of enalapril [and other angiotensin converting enzyme (ACE) inhibitors] on glycylsarcosine (GlySar) transport by the high-affinity renal peptide transporter. METHODS Studies were performed in rabbit renal brush border membrane vesicles in which the uptake of radiolabeled GlySar was examined in the absence and presence of captopril, enalapril, enalaprilat, fosinopril, lisinopril, quinapril, quinaprilat, ramipril and zofenopril. RESULTS Kinetic analyses demonstrated that enalapril inhibited the uptake of GlySar in a competitive manner (Ki approximately 6 mM). Fosinopril and zofenopril had the greatest inhibitory potency (IC50 values of 55 and 81 microM, respectively) while the other ACE inhibitors exhibited low-affinity interactions with the renal peptide transporter. With respect to structure-function, ACE inhibitor affinity was strongly correlated with drug lipophilicity (r = 0.944, p < 0.001 for all ACE inhibitors; r = 0.983, p < 0.001 without enalaprilat, quinaprilat and quinapril). CONCLUSIONS The data suggest that enalapril and GlySar compete for the same substrate-binding site on the high-affinity peptide transporter in kidney, and that ACE inhibitors can interact with the renal carrier and inhibit dipeptide transport.
Collapse
Affiliation(s)
- C J Lin
- College of Pharmacy and Upjohn Center for Clinical Pharmacology, The University of Michigan, Ann Arbor 48109, USA
| | | | | |
Collapse
|
197
|
Shen H, Smith DE, Yang T, Huang YG, Schnermann JB, Brosius FC. Localization of PEPT1 and PEPT2 proton-coupled oligopeptide transporter mRNA and protein in rat kidney. THE AMERICAN JOURNAL OF PHYSIOLOGY 1999; 276:F658-65. [PMID: 10330047 DOI: 10.1152/ajprenal.1999.276.5.f658] [Citation(s) in RCA: 86] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
To determine the renal localization of oligopeptide transporters, Northern blot analyses were performed and polyclonal antisera were generated against PEPT1 and PEPT2, the two cloned rat H+/peptide transporters. Under high-stringency conditions, a 3.0-kb mRNA transcript of rat PEPT1 was expressed primarily in superficial cortex, whereas a 3.5-kb mRNA transcript of PEPT2 was expressed primarily in deep cortex/outer stripe of outer medulla. PEPT1 antisera detected a specific band on immunoblots of renal and intestinal brush-border membrane vesicles (BBMV) with an apparent mobility of approximately 90 kDa. PEPT2 antisera detected a specific broad band of approximately 85 kDa in renal but not in intestinal BBMV. PEPT1 immunolocalization experiments showed detection of a brush border antigen in S1 segments of the proximal tubule and in the brush border of villi from all segments of the small intestine. In contrast, PEPT2 immunolocalization was primarily confined to the brush border of S3 segments of the proximal tubule. All other nephron segments in rat were negative for PEPT1 and PEPT2 staining. Overall, our results conclusively demonstrate that although PEPT1 is expressed in early regions of the proximal tubule (pars convoluta), PEPT2 is specific for the latter regions of proximal tubule (pars recta).
Collapse
Affiliation(s)
- H Shen
- College of Pharmacy and Upjohn Center for Clinical Pharmacology, Department of Internal Medicine, University of Michigan, Ann Arbor Michigan 48109, USA
| | | | | | | | | | | |
Collapse
|
198
|
Ogihara H, Suzuki T, Nagamachi Y, Inui K, Takata K. Peptide transporter in the rat small intestine: ultrastructural localization and the effect of starvation and administration of amino acids. THE HISTOCHEMICAL JOURNAL 1999; 31:169-74. [PMID: 10421416 DOI: 10.1023/a:1003515413550] [Citation(s) in RCA: 95] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/13/2023]
Abstract
Peptide transporter-1 is a H+/peptide cotransporter responsible for the uptake of small peptides and peptide-like drugs, and is present in the absorptive epithelial cells of the villi in the small intestine (duodenum, jejunum, and ileum). It has been localized to the apical microvillous plasma membrane of the absorptive epithelial cells of the rat small intestine using the immunogold electron microscopic technique. Digital image analysis of the jejunum revealed that the transporter protein was abundant at the tip of the villus and that the amount decreased from the tip of the villus to its base. The effect of dietary administration of amino acids and starvation on the expression of PepT1 in the jejunum was examined by immunoblotting and image analysis of immunofluorescence. Starvation markedly increased the amount of peptide transporter present, whereas dietary administration of amino acids reduced it. The gradient of the transporter protein along the crypt-villus axis was maintained under either condition. These observations show that it is specific to the microvillous plasma membrane and that its expression is regulated by the nutritional condition.
Collapse
Affiliation(s)
- H Ogihara
- First Department of Surgery, Gunma University School of Medicine, Maebashi, Japan
| | | | | | | | | |
Collapse
|
199
|
Ghishan FK. Nutritional management of pediatric gastrointestinal disorders. Pediatr Ann 1999; 28:123-8. [PMID: 10036688 DOI: 10.3928/0090-4481-19990201-09] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
Affiliation(s)
- F K Ghishan
- Department of Pediatrics, Steele Memorial Children's Research Center, University of Arizona Health Sciences Center, Tucson 85724-5070, USA
| |
Collapse
|
200
|
Bretschneider B, Brandsch M, Neubert R. Intestinal transport of beta-lactam antibiotics: analysis of the affinity at the H+/peptide symporter (PEPT1), the uptake into Caco-2 cell monolayers and the transepithelial flux. Pharm Res 1999; 16:55-61. [PMID: 9950279 DOI: 10.1023/a:1018814627484] [Citation(s) in RCA: 169] [Impact Index Per Article: 6.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022]
Abstract
PURPOSE This study on the intestinal transport of beta-lactam antibiotics was undertaken to investigate the correlation between cellular transport parameters and the bioavailability. METHODS Transport of 23 beta-lactam antibiotics was characterized by measuring their ability to inhibit the uptake of glycylsarcosine into Caco-2 cells, their uptake into the cells and their total flux across the cell monolayers. RESULTS Ceftibuten and cyclacillin were recognized by PEPT1 with affinity constants comparable to those of natural dipeptides (K(i) = 0.3 and 0.5 mM, respectively). Cefadroxil, cefamandole, cephradine, cefaclor, cefuroxime-axetil, cefixime, cephalotin, cephalexin and ampicillin also interacted with PEPTI (K(i) = 7-14 mM). In contrast, cefapirin, cefodizime, cefuroxime, cefmetazole, ceftazidime, benzyl-penicillin, ceftriaxone, cefpirome, cefotaxime, cefepime, cephaloridine and cefsulodin displayed no affinity to the transport system (K(i) > 20 mM). The uptake into the cells and the transepithelial flux was highest for those beta-lactam antibiotics, which showed the strongest inhibition of [14C]Gly-Sar transport (p < 0.0001). Exceptions were cefuroximaxetil and cephalotin. CONCLUSIONS The probability of oral bioavailability for beta-lactam antibiotics is mainly determined by their affinity to PEPTI. A threshold K(i) value of 14 mM with respect to Gly-Sar uptake is required.
Collapse
Affiliation(s)
- B Bretschneider
- Department of Pharmacy, Institute of Pharmaceutics and Biopharmaceutics, Martin-Luther-University Halle-Wittenberg, Halle, Germany
| | | | | |
Collapse
|