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Fujiwara R, Yokoi T, Nakajima M. Structure and Protein-Protein Interactions of Human UDP-Glucuronosyltransferases. Front Pharmacol 2016; 7:388. [PMID: 27822186 PMCID: PMC5075577 DOI: 10.3389/fphar.2016.00388] [Citation(s) in RCA: 36] [Impact Index Per Article: 4.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/15/2016] [Accepted: 10/05/2016] [Indexed: 12/11/2022] Open
Abstract
Mammalian UDP-glucuronosyltransferases (UGTs) catalyze the transfer of glucuronic acid from UDP-glucuronic acid to various xenobiotics and endobiotics. Since UGTs comprise rate-limiting enzymes for metabolism of various compounds, co-administration of UGT-inhibiting drugs and genetic deficiency of UGT genes can cause an increased blood concentration of these compounds. During the last few decades, extensive efforts have been made to advance the understanding of gene structure, function, substrate specificity, and inhibition/induction properties of UGTs. However, molecular mechanisms and physiological importance of the oligomerization and protein–protein interactions of UGTs are still largely unknown. While three-dimensional structures of human UGTs can be useful to reveal the details of oligomerization and protein–protein interactions of UGTs, little is known about the protein structures of human UGTs due to the difficulty in solving crystal structures of membrane-bound proteins. Meanwhile, soluble forms of plant and bacterial UGTs as well as a partial domain of human UGT2B7 have been crystallized and enabled us to predict three-dimensional structures of human UGTs using a homology-modeling technique. The homology-modeled structures of human UGTs do not only provide the detailed information about substrate binding or substrate specificity in human UGTs, but also contribute with unique knowledge on oligomerization and protein–protein interactions of UGTs. Furthermore, various in vitro approaches indicate that UGT-mediated glucuronidation is involved in cell death, apoptosis, and oxidative stress as well. In the present review article, recent understandings of UGT protein structures as well as physiological importance of the oligomerization and protein–protein interactions of human UGTs are discussed.
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Affiliation(s)
- Ryoichi Fujiwara
- Department of Pharmaceutics, School of Pharmacy, Kitasato University Tokyo, Japan
| | - Tsuyoshi Yokoi
- Department of Drug Safety Sciences, Division of Clinical Pharmacology, Nagoya University Graduate School of Medicine Nagoya, Japan
| | - Miki Nakajima
- Drug Metabolism and Toxicology, Faculty of Pharmaceutical Sciences, Kanazawa University Kanazawa, Japan
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Wlcek K, Hofstetter L, Stieger B. Transport of estradiol-17β-glucuronide, estrone-3-sulfate and taurocholate across the endoplasmic reticulum membrane: evidence for different transport systems. Biochem Pharmacol 2014; 88:106-18. [PMID: 24406246 PMCID: PMC3969151 DOI: 10.1016/j.bcp.2013.12.026] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/19/2013] [Revised: 12/23/2013] [Accepted: 12/23/2013] [Indexed: 11/06/2022]
Abstract
Important reactions of drug metabolism, including UGT mediated glucuronidation and steroidsulfatase mediated hydrolysis of sulfates, take place in the endoplasmic reticulum (ER) of hepatocytes. Consequently, UGT generated glucuronides, like estradiol-17β-glucuronide, have to be translocated back into the cytoplasm to reach their site of excretion. Also steroidsulfatase substrates, including estrone-3-sulfate, have to cross the ER membrane to reach their site of hydrolysis. Based on their physicochemical properties such compounds are not favored for passive diffusion and therefore likely necessitate transport system(s) to cross the ER membrane in either direction. The current study aims to investigate the transport of taurocholate, estradiol-17β-glucuronide, and estrone-3-sulfate in smooth (SER) and rough (RER) endoplasmic reticulum membrane vesicles isolated from Wistar and TR− rat liver. Time-dependent and bidirectional transport was demonstrated for taurocholate, showing higher uptake rates in SER than RER vesicles. For estradiol-17β-glucuronide a fast time-dependent efflux with similar efficiencies from SER and RER but no clear protein-mediated uptake was shown, indicating an asymmetric transport system for this substrate. Estrone-3-sulfate uptake was time-dependent and higher in SER than in RER vesicles. Inhibition of steroidsulfatase mediated estrone-3-sulfate hydrolysis decreased estrone-3-sulfate uptake but had no effect on taurocholate or estradiol-17β-glucuronide transport. Based on inhibition studies and transport characteristics, three different transport mechanisms are suggested to be involved in the transport of taurocholate, estrone-3-sulfate and estradiol-17β-glucuronide across the ER membrane.
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Affiliation(s)
- Katrin Wlcek
- Department of Clinical Pharmacology and Toxicology, University Hospital Zurich, Rämistrasse 100, 8091 Zurich, Switzerland.
| | - Lia Hofstetter
- Department of Clinical Pharmacology and Toxicology, University Hospital Zurich, Rämistrasse 100, 8091 Zurich, Switzerland.
| | - Bruno Stieger
- Department of Clinical Pharmacology and Toxicology, University Hospital Zurich, Rämistrasse 100, 8091 Zurich, Switzerland.
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Fujiwara R, Itoh T. Extensive Protein-Protein Interactions Involving UDP-glucuronosyltransferase (UGT) 2B7 in Human Liver Microsomes. Drug Metab Pharmacokinet 2014; 29:259-65. [DOI: 10.2133/dmpk.dmpk-13-rg-096] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
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Révész K, Tóth B, Staines AG, Coughtrie MWH, Mandl J, Csala M. Luminal accumulation of newly synthesized morphine-3-glucuronide in rat liver microsomal vesicles. Biofactors 2013; 39:271-8. [PMID: 23281118 DOI: 10.1002/biof.1067] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 07/24/2012] [Accepted: 10/16/2012] [Indexed: 01/23/2023]
Abstract
Morphine is converted to morphine 3-β-D-glucuronide (M3G) by the UDP-glucuronosyltransferase Ugt2b1 in the endoplasmic reticulum (ER) of rat liver. Because of its luminal localization, UGT activity requires UDP-glucuronate import and glucuronide export across the ER membrane. The former transport is generally considered to be rate limiting and to explain the latency of UGT activities in intact microsomal vesicles. However, some observations indicate that the release of bulky glucuronides, such as M3G, might also be rate limiting for glucuronidation. This assumption was tested by characterizing the transport of M3G and its distribution between the intra- and extravesicular spaces during synthesis in rat liver microsomes. The amount of vesicle-associated M3G was measured using rapid filtration and LC-MS measurement. Our results reveal a remarkable accumulation of newly synthesized M3G in the microsomal lumen above the equilibrium. The transport showed a linear concentration-dependence in a wide range (5-200 μM). Therefore, the build-up of high (about 20 μM) luminal M3G concentration could adjust the rate of release to that of synthesis (44.85 ± 4.08 pmol/min/mg protein) during the conjugation of 100 μM morphine. These data can explain earlier findings indicative of separate intracellular pools of M3G in rat liver. Accumulation of bulky glucuronides in the ER lumen might also play an important role in their targeting and in the control of biliary excretion.
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Affiliation(s)
- Katalin Révész
- Department of Medical Chemistry, Molecular Biology and Pathobiochemistry, Semmelweis University, Budapest, Hungary
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Révész K, Tüttő A, Szelényi P, Konta L. Tea flavan-3-ols as modulating factors in endoplasmic reticulum function. Nutr Res 2011; 31:731-40. [DOI: 10.1016/j.nutres.2011.09.008] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/18/2011] [Revised: 09/07/2011] [Accepted: 09/15/2011] [Indexed: 01/04/2023]
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6
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Wu B, Kulkarni K, Basu S, Zhang S, Hu M. First-pass metabolism via UDP-glucuronosyltransferase: a barrier to oral bioavailability of phenolics. J Pharm Sci 2011; 100:3655-81. [PMID: 21484808 DOI: 10.1002/jps.22568] [Citation(s) in RCA: 204] [Impact Index Per Article: 15.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/10/2011] [Revised: 03/10/2011] [Accepted: 03/10/2011] [Indexed: 12/11/2022]
Abstract
Glucuronidation mediated by UDP-glucuronosyltransferases (UGTs) is a significant metabolic pathway that facilitates efficient elimination of numerous endobiotics and xenobiotics, including phenolics. UGT genetic deficiency and polymorphisms or inhibition of glucuronidation by concomitant use of drugs are associated with inherited physiological disorders or drug-induced toxicities. Moreover, extensive glucuronidation can be a barrier to oral bioavailability as the first-pass glucuronidation (or premature clearance by UGTs) of orally administered agents usually results in the poor oral bioavailability and lack of efficacies. This review focused on the first-pass glucuronidation of phenolics including natural polyphenols and pharmaceuticals. The complexity of UGT-mediated metabolism of phenolics is highlighted with species-, gender-, organ- and isoform-dependent specificity, as well as functional compensation between UGT1A and 2B subfamily. In addition, recent advances are discussed with respect to the mechanisms of enzymatic actions, including the important properties such as binding pocket size and phosphorylation requirements.
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Affiliation(s)
- Baojian Wu
- Department of Pharmacological and Pharmaceutical Sciences, College of Pharmacy, University of Houston, Houston, Texas 77030, USA
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García C, Barriga A, Díaz JC, Lagos M, Lagos N. Route of metabolization and detoxication of paralytic shellfish toxins in humans. Toxicon 2010; 55:135-44. [DOI: 10.1016/j.toxicon.2009.07.018] [Citation(s) in RCA: 36] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/11/2009] [Revised: 05/16/2009] [Accepted: 07/14/2009] [Indexed: 11/28/2022]
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Choi S, Sainz B, Corcoran P, Uprichard S, Jeong H. Characterization of increased drug metabolism activity in dimethyl sulfoxide (DMSO)-treated Huh7 hepatoma cells. Xenobiotica 2009; 39:205-17. [PMID: 19280519 DOI: 10.1080/00498250802613620] [Citation(s) in RCA: 81] [Impact Index Per Article: 5.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/28/2023]
Abstract
The objective of this study was to characterize Huh7 cells' baseline capacity to metabolize drugs and to investigate whether the drug metabolism was enhanced upon treatment with dimethyl sulfoxide (DMSO). The messenger RNA (mRNA) levels of major Phase I and Phase II enzymes were determined by quantitative real-time-polymerase chain reaction (RT-PCR), and activities of major drug-metabolizing enzymes were examined using probe drugs by analysing relevant metabolite production rates. The expression levels of drug-metabolizing enzymes in control Huh7 cells were generally very low, but DMSO treatment dramatically increased the mRNA levels of most drug-metabolizing enzymes as well as other liver-specific proteins. Importantly, functionality assays confirmed concomitant increases in drug-metabolizing enzyme activity. Additionally, treatment of the Huh7 cells with 3-methylcholanthrene induced cytochrome P450 (CYP) 1A1 expression. The results indicate that DMSO treatment of Huh7 cells profoundly enhances their differentiation state, thus improving the usefulness of this common cell line as an in vitro hepatocyte model.
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Affiliation(s)
- S Choi
- Center for Pharmaceutical Biotechnology,University of Illinois at Chicago, 833 S. Wood Street, Chicago, IL 60612, USA
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Bock KW, Köhle C. Topological aspects of oligomeric UDP-glucuronosyltransferases in endoplasmic reticulum membranes: Advances and open questions. Biochem Pharmacol 2009; 77:1458-65. [DOI: 10.1016/j.bcp.2008.12.004] [Citation(s) in RCA: 26] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/27/2008] [Revised: 12/04/2008] [Accepted: 12/09/2008] [Indexed: 11/24/2022]
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Margittai E, Bánhegyi G. Isocitrate dehydrogenase: A NADPH-generating enzyme in the lumen of the endoplasmic reticulum. Arch Biochem Biophys 2008; 471:184-90. [PMID: 18201546 DOI: 10.1016/j.abb.2007.12.017] [Citation(s) in RCA: 36] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/04/2007] [Revised: 12/21/2007] [Accepted: 12/30/2007] [Indexed: 11/26/2022]
Abstract
The aim of the present study was the investigation of the occurrence of NADPH-generating pathways in the endoplasmic reticulum others then hexose-6-phosphate dehydrogenase. A significant isocitrate and a moderate malate-dependent NADP+ reduction were observed in endoplasmic reticulum-derived rat liver microsomes. The isocitrate-dependent activity was very likely attributable to the appearance of the cytosolic isocitrate dehydrogenase isozyme in the lumen. The isocitrate dehydrogenase activity of microsomes was present in the luminal fraction; it showed a strong preference towards NADP+ versus NAD+, and it was almost completely latent. Antibodies against the cytosolic isoform of isocitrate dehydrogenase immunorevealed a microsomal protein of identical molecular weight; the microsomal enzyme showed similar kinetic parameters and oxalomalate inhibition as the cytosolic one. Measurable luminal isocitrate dehydrogenase activity was also present in microsomes from rat epididymal fat. The results suggest that isocitrate dehydrogenase is an important NADPH-generating enzyme in the endoplasmic reticulum.
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Affiliation(s)
- Eva Margittai
- Department of Medical Chemistry, Molecular Biology and Pathobiochemistry, Semmelweis University, Pathobiochemistry Research Group of The Hungarian Academy of Sciences, 1444 Budapest, P.O. Box 260, Budapest, Hungary
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Révész K, Tüttô A, Konta L. [Effect of green tea flavonols on the function of the endoplasmic reticulum]. Orv Hetil 2007; 148:1903-7. [PMID: 17905686 DOI: 10.1556/oh.2007.28173] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/02/2023]
Abstract
The various (e.g. anti-tumor and anti-diabetic) health effects of green tea attributed to its flavonols, primarily to epigallocatechin-gallate, got into the focus of interest. The endoplasmic reticulum, which plays key role in the metabolism of carcinogens, in the synthesis of secreted or cell surface proteins as well as in the glucose production, might be a potential target for anti-tumor and anti-diabetic agents. Therefore, it is an important question how the flavonols affect its functions. Experiments carried out in microsomes and hepatoma cells revealed that flavonols inhibit glucuronide transport in the endoplasmic reticulum, which may reduce the reactivation of carcinogens; they inhibit glucosidase II, which may cause endoplasmic reticulum stress and apoptosis in hepatoma cells; and they hinder glucose efflux, which may decrease hepatic glucose production and blood glucose level. These observations are useful for further investigation of the relevant transport processes and transporters and also contribute to the better understanding of the mechanisms of flavanol effects.
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Affiliation(s)
- Katalin Révész
- Semmelweis Egyetem, Orvosi Vegytani, Molekuláris Biológiai és Patobiokémiai Intézet Budapest.
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Iyanagi T. Molecular mechanism of phase I and phase II drug-metabolizing enzymes: implications for detoxification. ACTA ACUST UNITED AC 2007; 260:35-112. [PMID: 17482904 DOI: 10.1016/s0074-7696(06)60002-8] [Citation(s) in RCA: 154] [Impact Index Per Article: 9.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/08/2023]
Abstract
Enzymes that catalyze the biotransformation of drugs and xenobiotics are generally referred to as drug-metabolizing enzymes (DMEs). DMEs can be classified into two main groups: oxidative or conjugative. The NADPH-cytochrome P450 reductase (P450R)/cytochrome P450 (P450) electron transfer systems are oxidative enzymes that mediate phase I reactions, whereas the UDP-glucuronosyltransferases (UGTs) are conjugative enzymes that mediate phase II enzymes. Both enzyme systems are localized to the endoplasmic reticulum (ER) where a number of drugs are sequentially metabolized. DMEs, including P450s and UGTs, generally have a highly plastic active site that can accommodate a wide variety of substrates. The P450 and UGT genes constitute a supergene family, in which UGT proteins are encoded by distinct genes and a complex gene. Both the P450 and UGT genes have evolved to diversify their functions. This chapter reviews advances in understanding the structure and function of the P450R/P450 and UGT enzyme systems. In particular, the coordinate biotransformation of xenobiotics by phase I and II enzymes in the ER membrane is examined.
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Affiliation(s)
- Takashi Iyanagi
- Biometal Science Laboratory, RIKEN SPring-8 Center, Harima Institute, Hyogo 679-5148, Japan
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Hrebícek M, Jirásek T, Hartmannová H, Nosková L, Stránecký V, Ivánek R, Kmoch S, Cebecauerová D, Vítek L, Mikulecký M, Subhanová I, Hozák P, Jirsa M. Rotor-type hyperbilirubinaemia has no defect in the canalicular bilirubin export pump. Liver Int 2007; 27:485-91. [PMID: 17403188 DOI: 10.1111/j.1478-3231.2007.01446.x] [Citation(s) in RCA: 20] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 02/13/2023]
Abstract
BACKGROUND The cause of Rotor syndrome (RS), a rare-familial conjugated hyperbilirubinaemia with normal liver histology, is unclear. We hypothesized that RS can be an allelic variant of Dubin-Johnson syndrome, caused by mutation in ABCC2, and investigated ABCC2 (gene) and ABCC2 (protein) in two patients with RS. METHODS A 57-year-old male presented with a 5-year history of predominantly conjugated hyperbilirubinaemia (170 micromol/l). Urinary porphyrin excretion was increased; cholescintigraphy revealed no chromoexcretion. A 68-year-old male presented with lifelong conjugated hyperbilirubinaemia (85 micromol/l). Bromosulfophthalein elimination was typical for RS. Both patients had histologically normal liver, without pigment. ABCC2 expression was investigated by confocal fluorescence microscopy. ABCC2 was sequenced from genomic DNA and cDNA, and exon deletions/duplications were sought by comparative genomic hybridization on a custom micro-array. RESULTS In both patients, ABCC2 was expressed unremarkably at the apical membrane of hepatocytes and no sequence alterations were found in 32 exons, adjacent intronic regions and the promoter region of ABCC2. CONCLUSIONS Rotor-type hyperbilirubinaemia is not an allelic variant of ABCC2 deficiency.
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Affiliation(s)
- Martin Hrebícek
- Institute of Inherited Metabolic Diseases, Charles University 1st Faculty of Medicine, Prague, Czech Republic
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Csala M, Marcolongo P, Lizák B, Senesi S, Margittai E, Fulceri R, Magyar JE, Benedetti A, Bánhegyi G. Transport and transporters in the endoplasmic reticulum. BIOCHIMICA ET BIOPHYSICA ACTA-BIOMEMBRANES 2007; 1768:1325-41. [PMID: 17466261 DOI: 10.1016/j.bbamem.2007.03.009] [Citation(s) in RCA: 36] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 12/28/2006] [Revised: 03/08/2007] [Accepted: 03/15/2007] [Indexed: 12/12/2022]
Abstract
Enzyme activities localized in the luminal compartment of the endoplasmic reticulum are integrated into the cellular metabolism by transmembrane fluxes of their substrates, products and/or cofactors. Most compounds involved are bulky, polar or even charged; hence, they cannot be expected to diffuse through lipid bilayers. Accordingly, transport processes investigated so far have been found protein-mediated. The selective and often rate-limiting transport processes greatly influence the activity, kinetic features and substrate specificity of the corresponding luminal enzymes. Therefore, the phenomenological characterization of endoplasmic reticulum transport contributes largely to the understanding of the metabolic functions of this organelle. Attempts to identify the transporter proteins have only been successful in a few cases, but recent development in molecular biology promises a better progress in this field.
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Affiliation(s)
- Miklós Csala
- Department of Medical Chemistry, Molecular Biology and Pathobiochemistry, Semmelweis University, Budapest, Hungary
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van der Heide SM, Joosten BJLJ, Dragt BS, Everts ME, Klaren PHM. A physiological role for glucuronidated thyroid hormones: preferential uptake by H9c2(2-1) myotubes. Mol Cell Endocrinol 2007; 264:109-17. [PMID: 17118529 DOI: 10.1016/j.mce.2006.10.012] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 08/14/2006] [Revised: 10/12/2006] [Accepted: 10/13/2006] [Indexed: 02/07/2023]
Abstract
Conjugation reactions are important pathways in the peripheral metabolism of thyroid hormones. Rat cardiac fibroblasts produce and secrete glucuronidated thyroxine (T4G) and 3,3',5-triiodothyronine (T3G). We here show that, compared to fibroblasts from other anatomical locations, the capacity of cardiofibroblasts to secrete T4G and T3G is highest. H9c2(2-1) myotubes, a model system for cardiomyocytes, take up T4G and T3G at a rate that is 10-15 times higher than that for the unconjugated thyroid hormones. T3 and T4, and their glucuronides, stimulate H9c2(2-1) myoblast-to-myotube differentiation. A substantial beta-glucuronidase activity was measured in H9c2(2-1) myotubes, and this confers a deconjugating capacity to these cells, via which native thyroid hormones can be regenerated from glucuronidated precursors. This indicates that the stimulatory effects on myoblast differentiation are exerted by the native hormones. We suggest that glucuronidation represents a mechanism to uncouple local thyroid hormone action in the heart from that in other peripheral tissues and in the systemic circulation. This could represent a mechanism for the local fine-tuning of cardiac thyroid hormone action.
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Affiliation(s)
- Sabine M van der Heide
- Department of Pathobiology, Faculty of Veterinary Medicine, Utrecht University, Utrecht, The Netherlands
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Révész K, Tütto A, Margittai E, Bánhegyi G, Magyar JE, Mandl J, Csala M. Glucuronide transport across the endoplasmic reticulum membrane is inhibited by epigallocatechin gallate and other green tea polyphenols. Int J Biochem Cell Biol 2007; 39:922-30. [PMID: 17317271 DOI: 10.1016/j.biocel.2007.01.010] [Citation(s) in RCA: 18] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/22/2006] [Revised: 01/03/2007] [Accepted: 01/08/2007] [Indexed: 11/22/2022]
Abstract
Toxic endogenous or exogenous compounds can be inactivated by various conjugation reactions. Glucuronidation (i.e. conjugation with glucuronate) is especially important due to the large number of drugs and chemical carcinogens that are detoxified through this pathway. Stable and harmless glucuronides can be reactivated by enzymatic hydrolysis thus inhibitors of glucuronidase activity reduce the risk of chemical carcinogenesis. The aim of this study was to reveal whether this mechanism contributes to the anti-cancer effect of green tea flavanols, which has been shown in various animal models. Therefore, we investigated the effect of these polyphenols on deglucuronidation in rat liver microsomes and in Hepa 1c1c7 mouse hepatoma cells, using 4-methylumbelliferyl glucuronide as model substrate. Tea flavanols inhibited beta-glucuronidase in intact vesicles, where glucuronide transport across the microsomal membrane is rate-limiting, but were almost ineffective in permeabilized vesicles. Epigallocatechin gallate, the major green tea flavanol was shown to have a concentration-dependent inhibitory effect on both beta-glucuronidase activity and glucuronide transport in native vesicles. Epigallocatechin gallate also inhibited beta-glucuronidase activity in native Hepa 1c1c7 mouse hepatoma cells, while failed to affect the enzyme in alamethicin-permeabilized cells, where the endoplasmic membrane barrier was eliminated. Our findings indicate that tea flavanols inhibit deglucuronidation in the endoplasmic reticulum at the glucuronide transport stage. This phenomenon might potentially contribute to the cancer-preventing dietary or pharmacological effect attributed to these catechins.
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Affiliation(s)
- Katalin Révész
- Department of Medical Chemistry, Molecular Biology and Pathobiochemistry, Endoplasmic Reticulum Research Group of The Hungarian Academy of Sciences, Semmelweis University, H-1444 Budapest, P.O. Box 260, Hungary
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Kobayashi T, Sleeman J, Coughtrie M, Burchell B. Molecular and functional characterization of microsomal UDP-glucuronic acid uptake by members of the nucleotide sugar transporter (NST) family. Biochem J 2006; 400:281-9. [PMID: 16965264 PMCID: PMC1652819 DOI: 10.1042/bj20060429] [Citation(s) in RCA: 28] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/17/2022]
Abstract
Transport of the co-substrate UDPGA (UDP-glucuronic acid) into the lumen of the endoplasmic reticulum is an essential step in glucuronidation reactions due to the intraluminal location of the catalytic site of the enzyme UGT (UDP-glucuronosyltransferase). In the present study, we have characterized the function of several NSTs (nucleotide sugar transporters) and UGTs as potential carriers of UDPGA for glucuronidation reactions. UDPGlcNAc (UDP-N-acetylglucosamine)-dependent UDPGA uptake was found both in rat liver microsomes and in microsomes prepared from the rat hepatoma cell line H4IIE. The latency of UGT activity in microsomes derived from rat liver and V79 cells expressing UGT1A6 correlated well with mannose-6-phosphatase latency, confirming the UGT in the recombinant cells retained a physiology similar to rat liver microsomes. In the present study, four cDNAs coding for NSTs were obtained; two were previously reported (UGTrel1 and UGTrel7) and two newly identified (huYEA4 and huYEA4S). Localization of NSTs within the human genome sequence revealed that huYEA4S is an alternatively spliced form of huYEA4. All the cloned NSTs were stably expressed in V79 (Chinese hamster fibroblast) cells, and were able to transport UDPGA after preloading of isolated microsomal vesicles with UDPGlcNAc. The highest uptake was seen with UGTrel7, which displayed a V(max) approx. 1% of rat liver microsomes. Treatment of H4IIE cells with beta-naphthoflavone induced UGT protein expression but did not affect the rate of UDPGA uptake. Furthermore, microsomes from UGT1-deficient Gunn rat liver showed UDPGA uptake similar to those from control rats. These data show that NSTs can act as UDPGA transporters for glucuronidation reactions, and indicate that UGTs of the 1A family do not function as UDPGA carriers in microsomes. The cell line H4IIE is a useful model for the study of UDPGA transporters for glucuronidation reactions.
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Affiliation(s)
- Tsutomu Kobayashi
- Division of Pathology and Neuroscience, University of Dundee, Ninewells Hospital and Medical School, DUNDEE DD1 9SY, Scotland, U.K
| | - Judith E. Sleeman
- Division of Pathology and Neuroscience, University of Dundee, Ninewells Hospital and Medical School, DUNDEE DD1 9SY, Scotland, U.K
| | - Michael W. H. Coughtrie
- Division of Pathology and Neuroscience, University of Dundee, Ninewells Hospital and Medical School, DUNDEE DD1 9SY, Scotland, U.K
- To whom correspondence should be addressed (email )
| | - Brian Burchell
- Division of Pathology and Neuroscience, University of Dundee, Ninewells Hospital and Medical School, DUNDEE DD1 9SY, Scotland, U.K
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Tamura A, Ozawa K, Ohya T, Tsuyama N, Eyring EM, Masujima T. Nanokinetics of drug molecule transport into a single cell. Nanomedicine (Lond) 2006; 1:345-50. [PMID: 17716164 DOI: 10.2217/17435889.1.3.345] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022] Open
Abstract
Aims: To analyze drug transport at a single cell level, a mast cell line, RBL-2H3, was treated with cell-permeable fluorescent compounds, such as quinacrine, and was monitored by a fluorescence video microscope. Methods: Small areas in the video that corresponded to granules and part of the cytosol in a cell were chosen and the signal intensity in these areas was monitored sequentially. Results: The initial rate of quinacrine uptake through the cell membrane calculated from the fluorescent signal was correlated with quinacrine concentration, and it decreased at a lower temperature, showing that the transport was an energy-requiring process, such as active transport. The kinetics of the transport through the microgranular membrane did not depend on the temperature but the pH in the cytosol, therefore this process should be passive transport by pH gradient. Conclusion: These data indicate that the observation of video microscope-mediated drug transport using fluorescent dye is useful in kinetic analysis at the nanometer scale.
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Affiliation(s)
- Atsushi Tamura
- Analytical Molecular Medicine and Devices Laboratory, Graduate School of Medical Sciences, Hiroshima University, Kasumi, Minami-ku, Hiroshima, Japan
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19
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Lizák B, Czegle I, Csala M, Benedetti A, Mandl J, Bánhegyi G. Translocon pores in the endoplasmic reticulum are permeable to small anions. Am J Physiol Cell Physiol 2006; 291:C511-7. [PMID: 16611737 DOI: 10.1152/ajpcell.00274.2005] [Citation(s) in RCA: 28] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
Contribution of translocon peptide channels to the permeation of low molecular mass anions was investigated in rat liver microsomes. Puromycin, which purges translocon pores of nascent polypeptides, creating additional empty pores, raised the microsomal uptake of radiolabeled UDP-glucuronic acid, while it did not increase the uptake of glucose-6-phosphate or glutathione. The role of translocon pores in the transport of small anions was also investigated by measuring the effect of puromycin on the activity of microsomal enzymes with intraluminal active sites. The mannose-6-phosphatase activity of glucose-6-phosphatase and the activity of UDP-glucuronosyltransferase were elevated upon addition of puromycin, but glucose-6-phosphatase and beta-glucuronidase activities were not changed. The increase in enzyme activities was due to a better access of the substrates to the luminal compartment rather than to activation of the enzymes. Antibody against Sec61 translocon component decreased the activity of UDP-glucuronosyltransferase and antagonized the effect of puromycin. Similarly, the addition of the puromycin antagonist anisomycin or treatments of microsomes, resulting in the release of attached ribosomes, prevented the puromycin-dependent increase in the activity. Mannose-6-phosphatase and UDP-glucuronosyltransferase activities of smooth microsomal vesicles showed higher basal latencies that were not affected by puromycin. In conclusion, translationally inactive, ribosome-bound translocons allow small anions to cross the endoplasmic reticulum membrane. This pathway can contribute to the nonspecific substrate supply of enzymes with intraluminal active centers.
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Affiliation(s)
- Beáta Lizák
- Department of Medical Chemistry, Molecular Biology and Pathobiochemistry, Semmelweis University, PO Box 260, 1444 Budapest, Hungary
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20
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Csala M, Bánhegyi G, Benedetti A. Endoplasmic reticulum: a metabolic compartment. FEBS Lett 2006; 580:2160-5. [PMID: 16580671 DOI: 10.1016/j.febslet.2006.03.050] [Citation(s) in RCA: 81] [Impact Index Per Article: 4.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/03/2006] [Revised: 03/07/2006] [Accepted: 03/15/2006] [Indexed: 01/12/2023]
Abstract
Several biochemical reactions and processes of cell biology are compartmentalized in the endoplasmic reticulum (ER). The view that the ER membrane is basically a scaffold for ER proteins, which is permeable to small molecules, is inconsistent with recent findings. The luminal micro-environment is characteristically different from the cytosol; its protein and glutathione thiols are remarkably more oxidized, and it contains a separate pyridine nucleotide pool. The substrate specificity and activity of certain luminal enzymes are dependent on selective transport of possible substrates and co-factors from the cytosol. Abundant biochemical, pharmacological, clinical and genetic data indicate that the barrier function of the lipid bilayer and specific transport activities in the membrane make the ER a separate metabolic compartment.
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Affiliation(s)
- Miklós Csala
- Department of Medical Chemistry, Semmelweis University and Endoplasmic Reticulum Research Group of the Hungarian Academy of Sciences, 1444 Budapest, Hungary
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21
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Piccirella S, Czegle I, Lizák B, Margittai E, Senesi S, Papp E, Csala M, Fulceri R, Csermely P, Mandl J, Benedetti A, Bánhegyi G. Uncoupled redox systems in the lumen of the endoplasmic reticulum. Pyridine nucleotides stay reduced in an oxidative environment. J Biol Chem 2005; 281:4671-7. [PMID: 16373343 DOI: 10.1074/jbc.m509406200] [Citation(s) in RCA: 70] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/13/2022] Open
Abstract
The redox state of the intraluminal pyridine nucleotide pool was investigated in rat liver microsomal vesicles. The vesicles showed cortisone reductase activity in the absence of added reductants, which was dependent on the integrity of the membrane. The intraluminal pyridine nucleotide pool could be oxidized by the addition of cortisone or metyrapone but not of glutathione. On the other hand, intraluminal pyridine nucleotides were slightly reduced by cortisol or glucose 6-phosphate, although glutathione was completely ineffective. Redox state of microsomal protein thiols/disulfides was not altered either by manipulations affecting the redox state of pyridine nucleotides or by the addition of NAD(P)+ or NAD(P)H. The uncoupling of the thiol/disulfide and NAD(P)+/NAD(P)H redox couples was not because of their subcompartmentation, because enzymes responsible for the intraluminal oxidoreduction of pyridine nucleotides were distributed equally in smooth and rough microsomal subfractions. Instead, the phenomenon can be explained by the negligible representation of glutathione reductase in the endoplasmic reticulum lumen. The results demonstrated the separate existence of two redox systems in the endoplasmic reticulum lumen, which explains the contemporary functioning of oxidative folding and of powerful reductive reactions.
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Affiliation(s)
- Simona Piccirella
- Department of Medical Chemistry, Molecular Biology, and Pathobiochemistry, Semmelweis University, Budapest, Hungary
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22
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Csala M, Senesi S, Bánhegyi G, Mandl J, Benedetti A. Characterization of sulfate transport in the hepatic endoplasmic reticulum. Arch Biochem Biophys 2005; 440:173-80. [PMID: 16055076 DOI: 10.1016/j.abb.2005.06.017] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/22/2005] [Revised: 06/21/2005] [Accepted: 06/22/2005] [Indexed: 10/25/2022]
Abstract
The transport of sulfate ion across the endoplasmic reticulum membrane was investigated using rapid filtration and light scattering assays. We found a protein-mediated, bi-directional, low-affinity, and high-capacity, facilitative sulfate transport in rat liver microsomes, which could be inhibited by the prototypical anion transport inhibitor, 4,4'-diisothiocyanatostilbene-2,2'-disulfonic acid. It was resistant to various phosphate transport inhibitors and was not influenced by high concentration of phosphate or pyrophosphate, which is contradictory to involvement of phosphate transporters. It was sensitive to S3483 that has been reported to inhibit the glucose 6-phosphate transporter (G6PT), but the weak competition between sulfate and glucose 6-phosphate did not confirm the participation of this transporter. Moreover, the comparison of the activity and S3483 sensitivity of sulfate transport in microsomes prepared from G6PT-overexpressing or wild type COS-7 cells did not show any significant difference. Our results indicate that sulfate fluxes in the endoplasmic reticulum are mediated by a novel, S3483-sensitive transport pathway(s).
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Affiliation(s)
- Miklós Csala
- Department of Medical Chemistry, Molecular Biology and Pathobiochemistry, Semmelweis University, Endoplasmic Reticulum Research Group of The Hungarian Academy of Sciences, H-1444, Budapest, P.O. Box 260, Hungary
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23
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Lengyel G, Veres Z, Szabó P, Vereczkey L, Jemnitz K. CANALICULAR AND SINUSOIDAL DISPOSITION OF BILIRUBIN MONO- AND DIGLUCURONIDES IN SANDWICH-CULTURED HUMAN AND RAT PRIMARY HEPATOCYTES. Drug Metab Dispos 2005; 33:1355-60. [PMID: 15951449 DOI: 10.1124/dmd.105.004481] [Citation(s) in RCA: 21] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
Due to cholestasis or adverse drug effects, the excretion of bilirubin conjugates can decrease; therefore, the level of bilirubin (B) and bilirubin glucuronides (BGs) increases in the serum with the concomitant shift of bilirubin diversus monoglucuronide (BDG/BMG) equilibrium. The aim of this study was to utilize the collagen-sandwich culture of hepatocytes as an in vitro model for studying B conjugation and canalicular versus sinusoidal disposition of BGs. Canalicular and sinusoidal efflux of BMG and BDG obtained in sandwich-cultured rat primary hepatocytes was compared with that measured in human hepatocyte cultures. The BMG and BDG were separated by high-performance liquid chromatography and identified by mass spectrometry. The biliary excretion index (BEI) was estimated by measuring disposition of BGs into standard and Ca(2+), Mg(2+)-free medium. Significantly more BGs were excreted into the canalicular networks than into the medium in 96-h sandwich culture of both human and rat hepatocytes (BEI, 62.5 and 80.6, respectively). The BDG/BMG ratio in the medium versus that in the canalicular networks was 0.55/1.48, which is similar to the serum/bile values (0.6/1.5) observed in vivo by Mesa et al. [Mesa VA, De Vos R, and Fevery J (1997) J Hepatol 27:912-916]. In contrast, the BEI for p-nitrophenol glucuronide was 5.2. The low BEI value is in agreement with empirical observations, which suggest that molecules with low molecular weight are preferably excreted by the kidney. In conclusion, sandwich-cultured primary hepatocytes provide a useful in vitro method to differentiate between sinusoidal and canalicular disposition of BGs. Since the normal BDG/BMG ratio changes in hyperbilirubinemia, this model could be used to predict drug effects leading to hyperbilirubinemia.
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Affiliation(s)
- György Lengyel
- Institute of Biomolecular Chemistry, Chemical Research Center, Hungarian Academy of Sciences, Budapest, Hungary
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24
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Staines A, Sindelar P, Coughtrie M, Burchell B. Farnesol is glucuronidated in human liver, kidney and intestine in vitro, and is a novel substrate for UGT2B7 and UGT1A1. Biochem J 2005; 384:637-45. [PMID: 15320866 PMCID: PMC1134150 DOI: 10.1042/bj20040997] [Citation(s) in RCA: 34] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/11/2023]
Abstract
Farnesol is an isoprenoid found in many aromatic plants and is also produced in humans, where it acts on numerous nuclear receptors and has received considerable attention due to its apparent anticancer properties. Although farnesol has been studied for over 30 years, its metabolism has not been well characterized. Recently, farnesol was shown to be metabolized by cytochromes P450 in rabbit; however, neither farnesol hydroxylation nor glucuronidation in humans have been reported to date. In the present paper, we show for the first time that farnesol is metabolized to farnesyl glucuronide, hydroxyfarnesol and hydroxyfarnesyl glucuronide by human tissue microsomes, and we identify the specific human UGTs (uridine diphosphoglucuronosyltransferases) involved. Farnesol metabolism was examined by a sensitive LC (liquid chromatography)-MS/MS method. Results indicate that farnesol is a good substrate for glucuronidation in human liver, kidney and intestine microsomes (values in nmol/min per mg). Initial analysis using expressed human UGTs indicated that UGTs 1A1 and 2B7 were primarily responsible for glucuronidation in vitro, with significantly lower activity for all the other UGTs tested (UGTs 1A3, 1A4, 1A6, 1A9 and 2B4). Kinetic analysis and inhibition experiments indicate that, in liver microsomes, UGT1A1 is primarily responsible for farnesol glucuronidation; however, in intestine microsomes, UGT2B7 is probably the major isoform involved, with a very-low-micromolar K(m). We also show the first direct evidence that farnesol can be metabolized to hydroxyfarnesol by human liver microsomes and that hydroxyfarnesol is metabolized further to hydroxyfarnesyl glucuronide. Thus glucuronidation may modulate the physiological and/or pharmacological properties of this potent signalling molecule.
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Affiliation(s)
- Adam G. Staines
- *Division of Pathology and Neuroscience, Ninewells Hospital and Medical School, University of Dundee, Dundee DD1 9SY, Scotland, U.K
| | - Pavel Sindelar
- †Department of Biochemistry and Biophysics, The Arrhenius Laboratories for Natural Sciences, Stockholm University, SE-10691 Stockholm, Sweden
- ‡Department of Molecular Medicine, Karolinska Institutet, SE-17176 Stockholm, Sweden
| | - Michael W. H. Coughtrie
- *Division of Pathology and Neuroscience, Ninewells Hospital and Medical School, University of Dundee, Dundee DD1 9SY, Scotland, U.K
- To whom correspondence should be addressed (email )
| | - Brian Burchell
- *Division of Pathology and Neuroscience, Ninewells Hospital and Medical School, University of Dundee, Dundee DD1 9SY, Scotland, U.K
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Uesawa Y, Staines AG, O'Sullivan A, Mohri K, Burchell B. IDENTIFICATION OF THE RABBIT LIVER UDP-GLUCURONOSYLTRANSFERASE CATALYZING THE GLUCURONIDATION OF 4-ETHOXYPHENYLUREA (DULCIN). Drug Metab Dispos 2004; 32:1476-81. [PMID: 15448114 DOI: 10.1124/dmd.104.001206] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
Dulcin (DL), 4-ethoxyphenylurea, a synthetic chemical about 200 times as sweet as sucrose, has been proposed for use as an artificial sweetener. DL is excreted as a urinary ureido-N-glucuronide after oral administration to rabbits. The phenylurea N-glucuronide is the only ureido conjugate with glucuronic acid known at present; therefore, DL is interesting as a probe to search for new functions of UDP-glucuronosyltransferases (UGTs). Seven UGT isoforms (UGT1A3, UGT1A4, UGT1A6, UGT1A7, UGT2B13, UGT2B14, and UGT2B16) have been identified from rabbit liver, but these UGTs have not been investigated using DL as a substrate. In this work, the identities of UGT isoforms catalyzing the formation of DL glucuronide were investigated using rabbit liver microsomes (RabLM) and cloned/expressed as rabbit UGT isoforms. DL-N-glucuronide (DNG) production was determined quantitatively in RabLM and homogenates of COS-7 cells expressing each UGT isoform by using electrospray liquid chromatography-tandem mass spectrometry. Analysis of DNG formation using RabLM, by Eadie-Hofstee plot, gave a Vmax of 0.911 nmol/min/mg protein and the Km of 1.66 mM. DNG formation was catalyzed only by cloned expressed rabbit UGT1A7 and UGT2B16 (Vmax of 3.98 and 1.16 pmol/min/mg protein and a Km of 1.23 and 1.69 mM, respectively). Substrate inhibition of UGT1A7 by octylgallate confirmed the significant contribution of UGT1A7 to the formation of DNG. Octylgallate was further shown to competitively inhibit DNG production by RabLM (Ki = 0.149 mM). These results demonstrate that UGT1A7 is the major isoform catalyzing the N-glucuronidation of DL in RabLM.
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Affiliation(s)
- Yoshihiro Uesawa
- Clinical Pharmaceutics Laboratory, Department of Pharmaceutics, Meiji Pharmaceutical University, 2-522-1 Noshio, Kiyose, Tokyo 204-8588, Japan.
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Staines AG, Coughtrie MWH, Burchell B. N-Glucuronidation of Carbamazepine in Human Tissues Is Mediated by UGT2B7. J Pharmacol Exp Ther 2004; 311:1131-7. [PMID: 15292462 DOI: 10.1124/jpet.104.073114] [Citation(s) in RCA: 67] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
Carbamazepine (CBZ) is one of the most widely prescribed anticonvulsants despite a high incidence of idiosyncratic side effects. Metabolism of CBZ is complex, and of the more than 30 metabolites identified, one of the most abundant is CBZ N-glucuronide. To date the uridine diphosphate glucuronosyltransferase (UGT) isoform responsible for the N-glucuronidation of CBZ has not been identified. We have developed a sensitive liquid chromatography/mass spectrometry assay to quantify CBZ glucuronidation, and we report that CBZ is specifically glucuronidated by human UGT2B7. Kinetics of CBZ glucuronidation in human liver, kidney, and intestine microsomes were consistent with those of recombinant UGT2B7, which displayed a Km value of 214 microM and Vmax value of 0.79 pmol/mg/min. In addition to revealing the isoform responsible for CBZ glucuronidation, this is the first example of primary amine glucuronidation by UGT2B7.
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Affiliation(s)
- Adam G Staines
- Division of Pathology and Neuroscience, Ninewells Hospital and Medical School, University of Dundee, Dundee DD1 9SY, Scotland, UK
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