Biomedical subjects

Akira Tsuji

Publications and source records attributed to Akira Tsuji.

At least 19 recordsLinked to original sources

PubMed2006

Functional expression of stereoselective metabolism of cephalexin by exogenous transfection of oligopeptide transporter PEPT1.

Gastrointestinal absorption of the beta-lactam antibiotic cephalexin (CEX) is highly stereoselective: l- and d-CEX are both taken up by intestinal epithelial cells through the brush-border membrane, most likely via oligopeptide transporter PEPT1, but l-CEX is not found in serum or urine after administration p.o. because of its rapid intestinal metabolism, whereas d-CEX is well absorbed in the unchanged form. We examined the contribution of PEPT1 to the stereoselective uptake and metabolism of CEX. We observed stereoselective metabolism of CEX after exogenous transfection of PEPT1 alone into mammalian cell lines: l-CEX, but not d-CEX, was metabolized to 7-aminodesacetoxycephalosporanic acid (7-ADCA) in HeLa and human embryonic kidney 293 cells stably and transiently expressing human PEPT1, respectively, whereas such metabolism was minor in cells expressing the vector alone. The formation rate of 7-ADCA depended on the amount of PEPT1 cDNA transfected. l-CEX metabolism was rapid because only 7-ADCA was found inside and outside the cells during incubation with l-CEX. The characteristics of PEPT1-mediated metabolism of l-CEX were similar, but not identical, to those of PEPT1-mediated transport. PEPT1-mediated metabolism was also observed in permeabilized cells expressing PEPT1, in which PEPT1-mediated intracellular substrate accumulation was negligible, suggesting that the increase in l-CEX metabolism by PEPT1 transfection cannot be fully explained by an increase in uptake and subsequent exposure to intracellular hydrolases. The present findings show that stereoselectivity in CEX absorption can be fully explained in terms of PEPT1, implying that the l-CEX hydrolase is PEPT1 itself or is induced by PEPT1.

Anti-Bacterial Agents↗

PubMed2006

Characterization of the uptake mechanism for a novel loop diuretic, M17055, in Caco-2 cells: involvement of organic anion transporting polypeptide (OATP)-B.

PURPOSE: M17055 is under development as a novel loop diuretic for oral administration. To investigate the molecular mechanism of its gastrointestinal absorption, we initially aimed to clarify the mechanism of uptake of M17055 by Caco-2 cells, focusing on possible involvement of OATP-B (SLCO2B1), which is localized in the apical membranes of human intestinal epithelial cells. MATERIALS AND METHODS: The uptake of [14C]M17055 by Caco-2 cells cultured on multi-well dishes was measured after cultivation for 14 days. Uptake of [14C]M17055 by HEK293 cells stably expressing OATP-B (HEK293/OATP-B cells) was also examined. RESULTS: M17055 uptake by Caco-2 cells was saturable, and was inhibited by various organic anions, including other loop diuretics, and several bile acids. Uptake of M17055 by HEK293/OATP-B cells was much higher than that by mock cells. The inhibitory profiles of various organic anions and the estimated Km values for M17055 uptake were similar in Caco-2 and HEK293/OATP-B cells. Moreover, the values of inhibition constants of several inhibitors for M17055 uptake were comparable in the two cell lines. CONCLUSION: Our data suggest that OATP-B plays a major role in the uptake of the novel loop diuretic M17055 from apical membranes in Caco-2 cells.

Algorithms↗

PubMed2006

Impact of transporter-mediated drug absorption, distribution, elimination and drug interactions in antimicrobial chemotherapy.

A comprehensive list of drug transporters has recently become available as a result of extensive genome analysis. Membrane transporters play important roles in determining the pharmacokinetic aspects of intestinal absorption, tissue distribution, and the urinary and biliary excretions of a wide variety of therapeutic drugs. The identification and characterization of transporters responsible for the transfer of nutrients and xenobiotics, including drugs, is expected to provide a scientific basis for understanding drug disposition, as well as the molecular mechanisms of drug-drug/drug-food/drug-protein interactions and inter-individual/inter-species differences. This review focuses on the influence of transporters on the pharmacokinetics of beta-lactam antibiotics, new quinolones, and other antimicrobial agents, as well as focusing on the drug-drug interactions associated with transporter-mediated uptake from the small intestine and transporter-mediated elimination from the kidney and liver.

Animals↗

PubMed2006

Site-dependent contributions of P-glycoprotein and CYP3A to cyclosporin A absorption, and effect of dexamethasone in small intestine of mice.

We examined whether the oral bioavailability of cyclosporin A is controlled primarily by P-glycoprotein (P-gp) or CYP3A in the small intestine. In situ loop method was used to evaluate the uptake of cyclosporin A (40nmol) at the upper and lower intestine of wild-type and mdr1a/1b knockout mice treated or not treated with dexamethasone (75mg/kg/day, 7 days, i.p.). Expression of CYP3A mRNA in the control group was higher in the upper than the lower intestine, while that of the multidrug resistance-1a (mdr1a) mRNA was in the opposite order. Dexamethasone administration potently induced CYP3A and mdr1a mRNAs in the lower and upper intestine, respectively. At 45min after cyclosporin A administration into an upper intestinal loop of the control group of wild-type mice, the ratio of residual cyclosporin A to dose did not differ significantly from that of mdr1a/1b knockout mice, whereas in dexamethasone-treated wild-type mice, the residual ratio was increased significantly. The ratio of the cyclosporin A metabolite M17 to cyclosporin A in portal venous blood at an upper intestinal loop of mdr1a/1b knockout mice was much higher than that a lower intestinal loop. The M17/cyclosporin A ratio of portal venous blood at a lower intestinal loop in mdr1a/1b knockout mice was increased significantly by dexamethasone treatment. These results suggest that, under physiological conditions, the oral bioavailability of cyclosporin A is mainly controlled by CYP3A in the upper intestine, rather than liver, but when P-gp is induced by steroid, the intestinal absorption of cyclosporin A may be inhibited.

ATP Binding Cassette Transporter, Subfamily B↗

PubMed2006

PDZ adaptor protein PDZK2 stimulates transport activity of organic cation/carnitine transporter OCTN2 by modulating cell surface expression.

A part of the organic cation transporter families (OCT3, OCTN1, and OCTN2) has recently been identified to physically interact with PDZ (PSD95, Dlg, and ZO1) domain-containing proteins, although the physiological relevance of such interaction has not yet been fully examined. Here we have examined the stimulatory effect of PDZK2 [also named NaPi-Cap2 and intestinal and kidney-enriched PDZ protein (IKEPP)] on those cation transporters. In HEK293 cells, coexpression with PDZK2 increased the uptake of carnitine by OCTN2 with minimal effect on its substrate recognition specificity, but not for transport activity of OCT3 or OCTN1. The stimulatory effect of PDZK2 on OCTN2 was compatible with an approximately 2 times increase in transport capacity and can be accounted for by the increase in cell surface expression of OCTN2. Coexpression of PDZK2 did not affect carnitine transport activity of OCTN2 with deletion of the last four amino acids, which were found to be important for the interaction, suggesting involvement of physical interaction of the two proteins in the increase of cell surface expression of OCTN2. In mouse kidney, colocalization of PDZK2 and OCTN2 occurred predominantly in the region that was close to, but not the same as, the surface of apical membranes where OCTN2 alone was observed, suggesting the existence of OCTN2 in the subapical compartment that interacts with PDZK2. The present data have thus proposed an "intracellular pool" for OCTN2 that may be relevant to the stabilization of cell surface expression of OCTN2, thereby increasing transport activity for carnitine.

Adaptor Proteins, Signal Transducing↗

PubMed2006

Role of SLC xenobiotic transporters and their regulatory mechanisms PDZ proteins in drug delivery and disposition.

Various types of xenobiotic (or drug) transporters have been recently identified to play important roles as barriers against toxic compounds and influx pumps to take up nutrients into the body. Since those xenobiotic transporters generally have wide range of recognition specificity and accept various types of compounds as substrates, localization and functional expression of such transporters could be one of the critical factors that affect the disposition and subsequent biological activity of therapeutic agents. Identification and characterization of drug transporters have given us a scientific basis for understanding drug delivery and disposition, as well as the molecular mechanisms of drug interaction and inter-individual/inter-species differences. To precisely understand pharmacological roles of the transporters in the body, it is also important to clarify molecular mechanisms involved in regulation of the transporters. As a first step to clarify the regulatory mechanisms that govern cell-surface expression and/or function of these transporters, recent researches have focused on PDZ (PSD-95/Discs-large/ZO-1) binding motif localized on carboxylic terminus of several types of xenobiotic transporters. Most of the transporters showing direct interaction potential with the PDZ domain-containing proteins are expressed on apical membranes in epithelial cells of kidney and/or small intestine, implying that such protein-protein interaction may play a role in apical localization of the transporters. In this mini-review article, we summarize importance of transporters and their regulatory mechanisms in drug delivery and disposition, focusing on several aspects of transporter-mediated drug targeting.

ATP-Binding Cassette Transporters↗

PubMed2006

Organic cation/carnitine transporter OCTN2 (Slc22a5) is responsible for carnitine transport across apical membranes of small intestinal epithelial cells in mouse.

The organic cation/carnitine transporter OCTN2 is responsible for renal tubular reabsorption of its endogenous substrate, carnitine, although its physiological role in small intestine remains controversial. Here we present direct evidence for a predominant role of OCTN2 in small intestinal absorption of carnitine based on experiments with juvenile visceral steatosis (jvs) mice, which have a hereditary deficiency of the octn2 gene. Uptake of carnitine, assessed with an Ussing-type chamber system, from the apical surface of the small intestine was saturable and higher than that from the basal surface in wild-type mice, whereas carnitine uptake having these characteristics was almost absent in jvs mice. Saturable uptake of carnitine was also confirmed in isolated enterocytes obtained from wild-type mice, and the Km value obtained (approximately 20 microM) was close to that reported for carnitine uptake by human embryonic kidney 293 cells stably expressing mouse OCTN2 (Slc22a5). The carnitine uptake by enterocytes was decreased in the presence of various types of organic cations, and this inhibition profile was similar to that of mouse OCTN2, whereas uptake of carnitine was quite small and unsaturable in enterocytes obtained from jvs mice. Immunohistochemical and immunoprecipitation analyses suggested colocalization of OCTN2 with PDZK1, an adaptor protein that functionally regulates OCTN2. Immunoelectron microscopy visualized both OCTN2 and PDZK1 in microvilli of absorptive epithelial cells. These findings indicate that OCTN2 is predominantly responsible for the uptake of carnitine from the apical surface of mouse small intestinal epithelial cells, and it may therefore be a promising target for oral delivery of therapeutic agents that are OCTN2 substrates.

Animals↗

PubMed2006

Predominant contribution of organic anion transporting polypeptide OATP-B (OATP2B1) to apical uptake of estrone-3-sulfate by human intestinal Caco-2 cells.

Human organic anion transporting polypeptide OATP-B (OATP2B1) is a pH-sensitive transporter expressed in the apical membranes of small intestinal epithelial cells. In this study, we have examined the contribution of OATP-B to the uptake of [3H]estrone-3-sulfate in Caco-2 cells in comparison with those of its homologs OATP-D (OATP3A1) and OATP-E (OATP4A1). Immunocytochemical study revealed that OATP-B is expressed in the apical membranes of Caco-2 cells. The uptake of [3H]estrone-3-sulfate by Caco-2 cells was Na+-independent and inhibited by several organic anions. It showed biphasic saturation kinetics with Km values of 1.81 microM and 1.40 mM. The uptake of [3H]estrone-3-sulfate by human embryonic kidney (HEK) 293 cells stably expressing OATP-B (HEK293/OATP-B) was also Na+-independent and inhibited by several organic anions. The Km value for estrone-3-sulfate uptake by OATP-B (1.56 microM) was close to that for the high-affinity component observed in Caco-2 cells. The mRNA expression level of OATP-B was higher than that of OATP-D or OATP-E in Caco-2 cells and in human jejunum biopsies from healthy volunteers. The values of [3H]estrone-3-sulfate uptake normalized to OATP-B mRNA expression were similar in Caco-2 cells and HEK293/OATP-B cells. The specific activity of OATP-B per mRNA expression was much higher than that of OATP-D and OATP-E. [3H]Estrone-3-sulfate uptake by membrane vesicles prepared from HEK293/OATP-B cells exhibited an overshoot phenomenon in the presence of an inwardly directed H+ gradient, suggesting that an H+ gradient is the driving force of estrone-3-sulfate transport by OATP-B. These results suggest that OATP-B is predominantly responsible for the apical uptake of estrone-3-sulfate in Caco-2 cells.

Adult↗

PubMed2006

Regulation of drug transporters by PDZ adaptor proteins and nuclear receptors.

Drug transporters have been suggested to be involved in various aspects of pharmacokinetics. Identification and characterization of drug transporters have given us a scientific basis for understanding drug disposition, as well as the molecular mechanisms of drug interaction and inter-individual/inter-species differences. On the other hand, regulatory mechanisms of drug transporters are still poorly understood, and information is limited to induction and down-regulation of drug transporters by various microsomal enzyme inducers. Little is known about the molecular machinery that directly interacts with the drug transporters. As a first step to clarify such molecular mechanisms, recent studies have identified PDZ (PSD-95/Discs-large/ZO-1) domain-containing proteins that directly interact with the so-called PDZ binding motif located at the C-terminus of drug transporters. Some of the PDZ proteins have been suggested to regulate transporters via at least two pathways, i.e. stabilization at the cell-surface and direct modulation of transporter function. Therefore, it is possible that membrane transport of therapeutic agents is not only governed by the drug transporters themselves, but also indirectly by PDZ proteins. The PDZ proteins are classified as a family, the members of which are thought to have distinct, but also redundant physiological roles. The purpose of this review article is to summarize the available knowledge on protein interactions and functional modulation of drug transporters.

Adaptor Proteins, Signal Transducing↗

PubMed2006

Carrier-mediated hepatic uptake of a novel nonrenal excretion type uric acid generation inhibitor, Y-700.

Y-700, a novel xanthine oxidase inhibitor, was recently developed for the treatment of hyperuricemia and gout. Since the major elimination route of this compound is hepatic metabolism and excretion, the aim of the present study was to characterize the uptake mechanism of Y-700 in the liver, which is also the pharmacological target of Y-700. Efficient uptake of Y-700 was observed both in the liver in vivo and in isolated rat hepatocytes. The uptake was Na(+)-dependent, saturable and inhibited both by ATP-depressants and various organic anions. Indomethacin competitively inhibited Y-700 uptake, whereas the inhibitory effect of organic cations and nucleosides was not so remarkable. Saturable and Na(+)-dependent uptake of Y-700 was also observed in freshly isolated human hepatocytes. Uptake of Y-700 by sinusoidal membrane transporters, such as organic anion transporter (Oat) 2 and organic anion transporting polypeptide (OATP)-B, OATP-C, OATP-8, and Oatp1, could not be detected although uptake of Y-700 in the oocytes expressing sodium/taurocholate cotransporting polypeptide (NTCP) was slightly observed. In conclusion, active transport system(s), which specifically recognize certain types of anionic compounds, are involved in the hepatic uptake of Y-700 and, at least partially, relevant to its elimination from the circulation as well as delivery to pharmacological target.

Animals↗

PubMed2006

Mutation in an adaptor protein PDZK1 affects transport activity of organic cation transporter OCTNs and oligopeptide transporter PEPT2.

Genetic polymorphisms in xenobiotic transporters have recently been clarified to be associated with change in drug distribution and disposition. To expand on recent identification of direct interaction and functional regulation of several transporters by a PDZ (PSD95, Dlg and ZO1) domain containing protein PDZK1, the effect of mutation in PDZK1 on transport activity and subcellular localization of organic cation/carnitine transporters OCTN1 and OCTN2, and oligopeptide transporter PEPT2 was examined in the present study. HEK293 cells stably expressing a mutant transcript PDZK1-E195K (HEK293/PDZK1-E195K) were constructed, followed by transient transfection of cDNA for each transporter. Uptake of tetraethylammonium by OCTN1 was much higher in HEK293/PDZK1 cells, compared with that in the parent HEK293 cells, the uptake in HEK293/PDZK1-E195K cells showing middle range between the two values. Such difference in transport activity was accounted for the difference in transport capacity, with minimal change in affinity of OCTN1 to the substrate or other compounds. The similar difference among HEK293/PDZK1, HEK293/PDZK1-E195K and HEK293 cells was also observed in transport property of OCTN2 and PEPT2, whereas the difference was not so remarkable in each transporter with the last four amino acids deleted, that has much lower interaction potential with PDZK1. Immunohistochemical analysis indicated that OCTN1 was colocalized with PDZK1 on cell-surface, whereas colocalization with PDZK1-E195K was partially observed in cytoplasmic region. These results suggest a novel hypothesis that mutation in PDZK1 potentially changes transport property of various types of xenobiotic transporters by affecting their subcellular localization, possibly leading to change in disposition of various types of substrate drugs.

Adaptor Protein Complex gamma Subunits↗

PubMed2005

Contributions of intestinal P-glycoprotein and CYP3A to oral bioavailability of cyclosporin A in mice treated with or without dexamethasone.

The contributions of P-glycoprotein (P-gp) and CYP3A to the oral bioavailability (BA) of cyclosporin A (CyA) were separately evaluated by using wild-type and mdr1a/1b knockout mice treated with dexamethasone (DEX). Mice were treated with DEX (1 or 75 mg/kg/day, i.p.) daily for 7 days, and the blood concentrations of CyA were measured after an i.v. or p.o. dose of CyA (10mg/kg) at 1.5h after the last DEX treatment. The BA values of CyA in wild-type and mdr1a/1b knockout mice were similar, 0.25 and 0.287, respectively. As regards expression of mdr1a and CYP3A mRNAs, expression of mdr1a mRNA was weakest in the duodenum, the main absorption site of CyA, along the whole intestine of wild-type mice, while expression of CYP3A was strongest in the duodenum of both types of mice. After treatment with 1 and 75 mg/kg DEX, the BA values decreased to 43 and 25% of the control in wild-type mice, respectively, and to 89 and 73% of the control in mdr1a/1b knockout mice, respectively. Expression of mdr1a mRNA in duodenum of wild-type mice was potently induced by DEX treatment. The expression of CYP3A mRNA in liver and duodenum of both strains was enhanced only by high-DEX treatment. These results suggest that P-glycoprotein plays only a small role in the absorption of CyA under physiological conditions, but the protein is readily induced by DEX and then functions as a more substantial absorption barrier to CyA than does CYP3A in the intestine.

ATP Binding Cassette Transporter, Subfamily B↗

PubMed2005

Characterization of the transdermal transport of flurbiprofen and indomethacin.

Transdermal permeation of two types of NSAIDs, [(3)H] flurbiprofen and [(14)C] indomethacin, was examined by use of the Ussing-type chamber method. We found that the transdermal permeability in the absorptive direction (P(abs)) of [(3)H] flurbiprofen was significantly higher than that of [(14)C] indomethacin. A lower pH (5.0) on the epidermal side increased the accumulation and the P(abs) of [(3)H] flurbiprofen (18-fold and 50-fold, respectively) and [(14)C] indomethacin (18-fold and 22-fold, respectively), compared with pH 7.4. Coadministration of unlabeled flurbiprofen and indomethacin increased P(abs) of [(3)H] flurbiprofen and [(14)C] indomethacin, respectively, in a concentration-dependent manner. Similar high-affinity transport was also observed in the uptake of [(3)H] flurbiprofen by human epidermal keratinocytes (HEK001 cells). RT-PCR analysis revealed the expression of mRNA of numerous transporters including MRP, OATP, MCT and OCTN family members in hairless mouse skin, human skin and HEK001 cells. These findings support the novel hypothesis that transdermal permeation of NSAIDs is mediated by saturable transport mechanisms, which may be candidates as targets for transdermal delivery of drugs.

Administration, Cutaneous↗

PubMed2005

Carnitine/xenobiotics transporters in the human mammary gland epithelia, MCF12A.

The barrier function of the human mammary gland collapses if challenged with cationic drugs, causing their accumulation in milk. However, underlying molecular mechanisms are not well understood. To gain insight into the mechanism, we characterized transport of organic cations in the MCF12A human mammary gland epithelial cells, using carnitine and tetraethylammonium (TEA) as representative nutrient and xenobiotics probes, respectively. Our results show that the mammary gland cells express mRNA and proteins of human (h) novel organic cation transporters (OCTN) 1 and hOCTN2 (a Na+-dependent carnitine carrier with Na+-independent xenobiotics transport function), which belong to the solute carrier superfamily (SLC) of transporters. Other SLC OCTs such as hOCT1 and extraneuronal monoamine transporter (EMT)/hOCT3 are also expressed at mRNA levels, but hOCT2 was undetectable. We further showed mRNA expression of ATB0+ (an amino acid transporter with a Na+/Cl(-)-dependent carnitine transport activity), and Fly-like putative transporter 2/OCT6 (a splice variant of carnitine transporter 2: a testis-specific Na+-dependent carnitine transporter). TEA uptake was pH dependent. Carnitine uptake was dependent on Na+, and partly on Cl-, compatible with hOCTN2 and ATB0+ function. Modeling analyses predicted multiplicity of the uptake mechanisms with the high-affinity systems characterized by K(m) of 5.1 microM for carnitine and 1.6 mM for TEA, apparently similar to the reported hOCTN2 parameter for carnitine, and that of EMT/hOCT3 for TEA. Verapamil, cimetidine, carbamazepine, quinidine, and desipramine inhibited the carnitine uptake but required supratherapeutic concentrations, suggesting robustness of the carnitine uptake systems against xenobiotic challenge. Our findings suggest functional roles of a network of multiple SLC organic cation/nutrient transporters in human mammary gland drug transfer.

Carnitine↗

PubMed2005

Suppression of cell proliferation by inhibition of estrone-3-sulfate transporter in estrogen-dependent breast cancer cells.

PURPOSE: The aim of the study is to suppress the progress of estrogen-dependent breast cancer by inhibiting the membrane transporter, which mediates the internalization of estrone-3-sulfate as estrogen precursor in the cancer cells. METHODS: The uptake of estrone-3-sulfate by estrogen-dependent breast cancer MCF-7 cells was measured, and inhibitory study using various organic anions on estrone-3-sulfate uptake by MCF-7 cells was conducted. The effects of the inhibitor on the transcription of reporter gene and cell proliferation induced by estrone-3-sulfate were examined. RESULTS: The uptake of estrone-3-sulfate by MCF-7 cells was saturable with Km value of 2.32 microM. The uptake was Na+-independent and was inhibited by several anionic compounds such as bromosulfophthalein. Bromosulfophthalein also significantly inhibited the transcription of reporter gene via estrogen response element and cell proliferation induced by estrone-3-sulfate. However, the transcriptional activation or cell proliferation induced by estrone was not inhibited by bromosulfophthalein. Reverse transcription-polymerase chain reaction analysis revealed the expression of mRNA of organic anion transporting polypeptide (OATP)-D and OATP-E as possible candidates to transport estrone-3-sulfate. CONCLUSIONS: The uptake of estrone-3-sulfate is mediated by Na+-independent transporter(s). Inhibitor of estrone-3-sulfate transporter suppressed the transcription and cell proliferation induced by estrone-3-sulfate in MCF-7 cells. The results provide the basis of a novel strategy for breast cancer treatment by focusing on the transporter responsible for the uptake of estrone-3-sulfate.

Alkaline Phosphatase↗

PubMed2005

Multidrug resistance-associated protein 1 functions as an efflux pump of xenobiotics in the skin.

PURPOSE: Recent research has identified gene expression of several types of xenobiotic transporters in the skin. The aim of this study was to investigate whether multidrug resistance-associated protein 1 (MRP1) functions in the skin. METHODS: The distribution of [14C]grepafloxacin in vivo and the transport of 1-[2-amino-5-(2,7-dichloro-6-hydroxy-3-oxo-9-xanthenyl)phenoxy]-2-(2-amino-5-methylphenoxy)ethane-N,N,N',N'-tetraacetic acid (fluo 3) were examined in the skin of Mrp1 knockout mice [FVB/Mrp1(-/-)] and normal mice [FVB/Mrp1(+/+)]. RESULTS: The tissue-to-plasma concentration ratio of [14C]grepafloxacin was higher in the skin of FVB/Mrp1(-/-) mice than that of FVB/Mrp1(+/+) mice. In skin slices of hairless mouse incubated with fluo 3 pentaacetoxymethyl ester, the accumulation of fluo 3 was significantly increased in the presence of probenecid (2 mM) and carbonyl cyanide p-trifluoromethoxyphenylhydrazone (5 muM) in a time-dependent manner but did not change in the presence of tetraethylammonium (2 mM). In FVB/Mrp1(-/-) mouse skin, the accumulation of fluo 3 increased time-dependently, while no increase was observed in FVB/Mrp1(+/+) mouse skin. CONCLUSIONS: These findings suggest that Mrp1 is involved in the efflux of [14C]grepafloxacin and fluo 3 in the skin, possibly acting as part of a barrier system against xenobiotic compounds.

Aniline Compounds↗

PubMed2005

Transport mechanism for aluminum citrate at the blood-brain barrier: kinetic evidence implies involvement of system Xc- in immortalized rat brain endothelial cells.

Although accumulation of aluminum (Al) in the brain is known to cause neurodegenerative disorders and to be regulated mainly by the blood-brain barrier (BBB), the mechanism responsible for Al transport at the BBB has not been clarified yet. In this study, we investigated what kind of transporter is involved in the transport of Al citrate, which is the major species of Al in the brain, at the BBB using a rat immortalized brain endothelial cell line (RBEC1), focusing on the glutamate transporter family. The uptake of Al citrate showed temperature- and concentration-dependency, and did not require an inwardly directed Na+-gradient as a driving force, ruling out the involvement of Na+-dependent glutamate transporters in its transport. By RT-PCR, in RBEC1, there were mRNAs for the components of a Na+-independent glutamate transporter, system Xc-. L-Glutamate and L-cystine, representative ligands for system Xc-, significantly inhibited the uptake of Al citrate, and loading of them into the cells resulted in stimulation of its uptake in RBEC1. These results demonstrated that Al citrate is taken up into RBEC1 via system Xc-, and that this system might play an important role in Al citrate transport at the BBB.

Amino Acid Transport System X-AG↗

PubMed2005

Determination of 2-methylisoborneol and geosmin in aqueous samples by static headspace-gas chromatography-mass spectrometry with ramped inlet pressure.

A method for determining the earthy and musty odors 2-methylisoborneol (2-MIB) and geosmin in drinking water using static headspace-GC-MS is described. To achieve lower detection limits, split ratio was optimized with ramped inlet pressure for large headspace sampling volume. The ramped inlet pressure, which held higher pressure (higher column flow rate) only during injection, allowed us to inject 3-mL volume to GC with very low split ratio (2:1). Although sequential analysis with a stainless steel ion source often changed the mass spectrum of 2-MIB, this spectral change was eliminated by using an inert ion source with a 6 mm drawout plate. The detection limits of this method were 0.36 and 0.14 ng/L, respectively, for 2-MIB and geosmin. The repeatabilities (n = 30) were 6.6 and 4.8%, respectively, at 1 ng/L for 2-MIB and geosmin.

Journal Article↗