Brush-border Membrane (brush-border + membrane)

Distribution by Scientific Domains


Selected Abstracts


Site-specific contribution of proton-coupled folate transporter/haem carrier protein 1 in the intestinal absorption of methotrexate in rats

JOURNAL OF PHARMACY AND PHARMACOLOGY: AN INTERNATI ONAL JOURNAL OF PHARMACEUTICAL SCIENCE, Issue 7 2009
Tomoharu Yokooji
Abstract Objectives Methotrexate is reportedly a substrate for proton-coupled folate transporter/haem carrier protein 1 (PCFT/HCP1) and reduced folate carrier 1 (RFC1). In this study, we examined the contribution of PCFT/HCP1 and RFC1 in the intestinal absorption of methotrexate in rats. Methods Western blot analysis was carried out to evaluate the protein levels of PCFT/HCP1 and multidrug resistance-associated protein 2 in brush-border membrane of rat small intestine. Mucosal uptake of methotrexate was studied in the rat everted small intestine and an in-situ intestinal perfusion study of methotrexate was also carried out in rats. Key findings In transport studies using everted intestine, the mucosal methotrexate influx rate in proximal intestine at pH 5.5 was significantly greater than that at pH 7.4. Coadministration of folate or its analogues, such as folinate and 5-methyltetrahydrofolate, substrates for both PCFT/HCP1 and RFC1, significantly suppressed the methotrexate influx at pH 5.5, whereas thiamine pyrophosphate, an inhibitor for RFC1 alone, exerted no significant effect. Western blot analysis showed higher PCFT/HCP1 expression in proximal than distal small intestine. In distal small intestine, methotrexate influx rate was low and was not pH dependent. Also, folate and its analogues exerted no significant effect on methotrexate absorption. Conclusions Based on the present and our previous results, the site-specific contributions of various transporters including PCFT/HCP1 in methotrexate intestinal absorption were discussed. The variation in luminal pH and the involvement of multiple transporters in methotrexate absorption may cause variation in oral bioavailability among patients. [source]


Taurine uptake across the human intestinal brush-border membrane is via two transporters: H+ -coupled PAT1 (SLC36A1) and Na+ - and Cl, -dependent TauT (SLC6A6)

THE JOURNAL OF PHYSIOLOGY, Issue 4 2009
Catriona M. H. Anderson
Taurine is an essential amino acid in some mammals and is conditionally essential in humans. Taurine is an abundant component of meat and fish-based foods and has been used as an oral supplement in the treatment of disorders such as cystic fibrosis and hypertension. The purpose of this investigation was to identity the relative contributions of the solute transporters involved in taurine uptake across the luminal membrane of human enterocytes. Distinct transport characteristics were revealed following expression of the candidate solute transporters in Xenopus laevis oocytes: PAT1 (SLC36A1) is a H+ -coupled, pH-dependent, Na+ - and Cl, -independent, low-affinity, high-capacity transporter for taurine and ,-alanine; TauT (SLC6A6) is a Na+ - and Cl, -dependent, high-affinity, low-capacity transporter of taurine and ,-alanine; ATB0,+ (SLC6A14) is a Na+ - and Cl, -dependent, high-affinity, low-capacity transporter which accepts ,-alanine but not taurine. Taurine uptake across the brush-border membrane of human intestinal Caco-2 cell monolayers showed characteristics of both PAT1- and TauT-mediated transport. Under physiological conditions, Cl, -dependent TauT-mediated uptake predominates at low taurine concentrations, whereas at higher concentrations typical of diet, Cl, -independent PAT1-mediated uptake is the major absorptive mechanism. Real-time PCR analysis of human duodenal and ileal biopsy samples demonstrates that PAT1, TauT and ATB0,+ mRNA are expressed in each tissue but to varying degrees. In conclusion, this study is the first to demonstrate both taurine uptake via PAT1 and functional coexpression of PAT1 and TauT at the apical membrane of the human intestinal epithelium. PAT1 may be responsible for bulk taurine uptake during a meal whereas TauT may be important for taurine supply to the intestinal epithelium and for taurine capture between meals. [source]


Transport of di- and tripeptides in teleost fish intestine

AQUACULTURE RESEARCH, Issue 5 2010
Tiziano Verri
Abstract The initial observation of peptide absorption in fish intestine dates back to 1981, when, in rainbow trout (Oncorhynchus mykiss), the rate of intestinal absorption of the dipeptide glycylglycine (Gly-Gly) was compared in vivo with the rate of absorption of its component amino acid glycine (Gly). The description of the identification of the underlying mechanisms that allow di- and tripeptide transport across the plasma membranes in fish was provided in 1991, when the first evidence of peptide transport activity was reported in brush-border membrane vesicles of intestinal epithelial cells of Mozambique tilapia (Oreochromis mossambicus) by monitoring uptake of radiolabelled glycyl- l -phenylalanine (Gly- l -Phe). Since then, the existence of a carrier-mediated, H+ -dependent transport of di- and tripeptides (H+/peptide cotransport) in the brush-border membrane of fish enterocytes has been confirmed in many teleost species by a variety of biochemical approaches, providing basic kinetics and substrate specificities of the transport activity. In 2003, the first peptide transporter from a teleost fish, i.e. the zebrafish (Danio rerio) PEPtide transporter 1 (PEPT1), was cloned and functionally characterized in the Xenopus laevis oocyte expression system as a low-affinity/high-capacity system. PEPT1 is the protein in brush-border membranes responsible for translocation of intact di- and tripeptides released from dietary protein by luminal and membrane-bound proteases and peptidases. The transporter possesses affinities for the peptide substrates in the 0.1,10 mM range, depending on the structure and physicochemical nature of the substrates. After the molecular and functional characterization of the zebrafish transporter, the interest in PEPT1 in teleost fish has increased and approaches for cloning and functional characterization of PEPT1 orthologues from other fish species, some of them of the highest commercial value, are now underway. In this paper, we provide a brief overview of the transport of di- and tripeptides in teleost fish intestine by recalling the bulk of biochemical, biophysical and physiological observations collected in the pre-cloning era and by recapitulating the more recent molecular and functional data. [source]


The World of , - and , -Peptides Comprised of Homologated Proteinogenic Amino Acids and Other Components

CHEMISTRY & BIODIVERSITY, Issue 8 2004
Dieter Seebach
The origins of our nearly ten-year research program of chemical and biological investigations into peptides based on homologated proteinogenic amino acids are described. The road from the biopolymer poly[ethyl (R)-3-hydroxybutanoate] to the , -peptides was primarily a step from organic synthesis methodology (the preparation of enantiomerically pure compounds (EPCs)) to supramolecular chemistry (higher-order structures maintained through non-covalent interactions). The performing of biochemical and biological tests on the , - and , -peptides, which differ from natural peptides/proteins by a single or two additional CH2 groups per amino acid, then led into bioorganic chemistry and medicinal chemistry. The individual chapters of this review article begin with descriptions of work on , -amino acids, , -peptides, and polymers (Nylon-3) that dates back to the 1960s, even to the times of Emil Fischer, but did not yield insights into structures or biological properties. The numerous, often highly physiologically active, or even toxic, natural products containing ,- and ,-amino acid moieties are then presented. Chapters on the preparation of homologated amino acids with proteinogenic side chains, their coupling to provide the corresponding peptides, both in solution (including thioligation) and on the solid phase, their isolation by preparative HPLC, and their characterization by mass spectrometry (HR-MS and MS sequencing) follow. After that, their structures, predominantly determined by NMR spectroscopy in methanolic solution, are described: helices, pleated sheets, and turns, together with stack-, crankshaft-, paddlewheel-, and staircase-like patterns. The presence of the additional CC bonds in the backbones of the new peptides did not give rise to a chaotic increase in their secondary structures as many protein specialists might have expected: while there are indeed more structure types than are observed in the , -peptide realm , three different helices (10/12 -, 12 -, and 14 -helix) if we include oligomers of trans -2-aminocyclopentanecarboxylic acid, for example , the structures are already observable with chains made up of only four components, and, having now undergone a learning process, we are able to construct them by design. The structures of the shorter , -peptides can also be reliably determined by molecular-dynamics calculations (in solution; GROMOS program package). Unlike in the case of the natural helices, these compounds' folding into secondary structures is not cooperative. In , - and , -peptides, it is possible to introduce heteroatom substituents (such as halogen or OH) onto the backbones or to incorporate heteroatoms (NH, O) directly into the chain, and, thanks to this, it has been possible to study effects unobservable in the world of the , -peptides. Tests with proteolytic enzymes of all types (from mammals, microorganisms, yeasts) and in vivo examination (mice, rats, insects, plants) showed , - and , -peptides to be completely stable towards proteolysis and, as demonstrated for two , -peptides, extraordinarily stable towards metabolism, even when bearing functionalized side chains (such as those of Thr, Tyr, Trp, Lys, or Arg). The , -peptides so far examined also normally display no or only very weak cytotoxic, antiproliferative, antimicrobial, hemolytic, immunogenic, or inflammatory properties either in cell cultures or in vivo. Even biological degradation by microbial colonies of the types found in sewage-treatment plants or in soil is very slow. That there are indeed interactions of ,- and ,-peptides with biological systems, however, can be seen in the following findings: i) organ-specific distribution takes place after intravenous (i.v.) administration in rats, ii) transport through the intestines of rodents has been observed, iii) , -peptides with positively charged side chains (Arg and Lys) settle on cell surfaces, are able to enter into mammalian cells (fibroplasts, keratinocytes, HeLa cells), and migrate into their cell nuclei (and nucleoli), and iv) in one case, it has already been established that a , -peptide derivative can up- and down-regulate gene expression rates. Besides these less sharply definable interactions, it has also been possible to construct , - and , -peptide agonists of naturally occurring peptide hormones, MHC-binding , -peptides, or amphipathic , -peptide inhibitors of membrane-bound proteins in a controlled fashion. Examples include somatostatin mimics and the suppression of cholesterol transport through the intestinal brush-border membrane (by the SR-BI-protein). The results so far obtained from investigations into peptides made up of homologues of the proteinogenic amino acids also represent a contribution to deepening of our knowledge of the natural peptides/proteins, while potential for biomedicinal application of this new class of substances has also been suggested. [source]


FT-IR spectroscopy in diagnosis of diabetes in rat animal model

JOURNAL OF BIOPHOTONICS, Issue 8-9 2010
Feride Severcan
Abstract In recent years, Fourier Transform Infrared (FT-IR) spectroscopy has had an increasingly important role in the field of pathology and diagnosis of disease states. In the current study, FT-IR spectroscopy together with cluster analysis were used as a diagnostic tool in the discrimination of diabetic samples from control ones in rat kidney plasma membrane apical sides (brush-border membranes), liver microsomal membranes and Extensor digitorum longus (EDL) and Soleus (SOL) skeletal muscle tissues. A variety of alterations in the spectral parameters, such as frequency and signal intensity/area was observed in diabetic tissues and membranes compared to the control samples. Based on these spectral variations, using cluster analysis successful differentiation between diabetic and control groups was obtained in different spectral regions. The results of this current study further revealed the power and sensitivity of FT-IR spectroscopy in precise and automated diagnosis of diabetes. ( 2010 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]


Transport of di- and tripeptides in teleost fish intestine

AQUACULTURE RESEARCH, Issue 5 2010
Tiziano Verri
Abstract The initial observation of peptide absorption in fish intestine dates back to 1981, when, in rainbow trout (Oncorhynchus mykiss), the rate of intestinal absorption of the dipeptide glycylglycine (Gly-Gly) was compared in vivo with the rate of absorption of its component amino acid glycine (Gly). The description of the identification of the underlying mechanisms that allow di- and tripeptide transport across the plasma membranes in fish was provided in 1991, when the first evidence of peptide transport activity was reported in brush-border membrane vesicles of intestinal epithelial cells of Mozambique tilapia (Oreochromis mossambicus) by monitoring uptake of radiolabelled glycyl- l -phenylalanine (Gly- l -Phe). Since then, the existence of a carrier-mediated, H+ -dependent transport of di- and tripeptides (H+/peptide cotransport) in the brush-border membrane of fish enterocytes has been confirmed in many teleost species by a variety of biochemical approaches, providing basic kinetics and substrate specificities of the transport activity. In 2003, the first peptide transporter from a teleost fish, i.e. the zebrafish (Danio rerio) PEPtide transporter 1 (PEPT1), was cloned and functionally characterized in the Xenopus laevis oocyte expression system as a low-affinity/high-capacity system. PEPT1 is the protein in brush-border membranes responsible for translocation of intact di- and tripeptides released from dietary protein by luminal and membrane-bound proteases and peptidases. The transporter possesses affinities for the peptide substrates in the 0.1,10 mM range, depending on the structure and physicochemical nature of the substrates. After the molecular and functional characterization of the zebrafish transporter, the interest in PEPT1 in teleost fish has increased and approaches for cloning and functional characterization of PEPT1 orthologues from other fish species, some of them of the highest commercial value, are now underway. In this paper, we provide a brief overview of the transport of di- and tripeptides in teleost fish intestine by recalling the bulk of biochemical, biophysical and physiological observations collected in the pre-cloning era and by recapitulating the more recent molecular and functional data. [source]