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Dias VHV, Mattos JJ, Bastolla CLV, Lüchmann KH, Bainy ACD. Characterisation of UDP-glucuronosyltransferase activity in sea turtle Chelonia mydas. Xenobiotica 2022; 52:1011-1019. [PMID: 36594659 DOI: 10.1080/00498254.2022.2164750] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/04/2023]
Abstract
Uridine diphosphate glucuronosyltransferase (UGT) enzymes conjugate many lipophilic chemicals, such as drugs, environmental contaminants, and endogenous compounds, promoting their excretion. The complexity of UGT kinetics, and the location of enzyme active site in endoplasmic reticulum lumen, requires an accurate optimisation of enzyme assays.In the present study, we characterised UGT activity in liver microsomes of green turtles (Chelonia mydas), an endangered species. The conditions for measuring UGT activity were standardised through spectrofluorimetric methods, using the substrates 4-methylumbelliferone (4-MU) and uridine diphosphate glucuronic acid (UDPGA) at 30 °C and pH 7.4.The green turtles showed UGT activity at the saturating concentrations of substrates of 250 µM to 4-MU and 7 mM to UDPGA. The alamethicin, Brij®58, bovine serum albumin (BSA), and magnesium increased UGT activity. The assay using alamethicin (22 µg per mg of protein), magnesium (1 mM), and BSA (0.25%) reached the highest Vmax (1203 pmol·min-1mg·protein-1). Lithocholic acid and diclofenac inhibited UGT activity in green turtles.This study is the first report of UGT activity in the liver of green turtles and provides a base for future studies to understand the mechanisms of toxicity by exposure to contaminants in this charismatic species.
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Affiliation(s)
- Vera Helena V Dias
- Laboratory of Biomarkers of Aquatic Contamination and Immunochemistry-LABCAI, Federal University of Santa Catarina, Florianópolis, Brazil
| | - Jacó J Mattos
- Aquaculture Pathology Research Center-NEPAQ, Federal University of Santa Catarina, Florianópolis, Brazil
| | - Camila L V Bastolla
- Laboratory of Biomarkers of Aquatic Contamination and Immunochemistry-LABCAI, Federal University of Santa Catarina, Florianópolis, Brazil
| | - Karim H Lüchmann
- Department of Scientific and Technological Education, Santa Catarina State University, Florianópolis, Brazil
| | - Afonso C D Bainy
- Laboratory of Biomarkers of Aquatic Contamination and Immunochemistry-LABCAI, Federal University of Santa Catarina, Florianópolis, Brazil
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2
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Miners JO, Rowland A, Novak JJ, Lapham K, Goosen TC. Evidence-based strategies for the characterisation of human drug and chemical glucuronidation in vitro and UDP-glucuronosyltransferase reaction phenotyping. Pharmacol Ther 2020; 218:107689. [PMID: 32980440 DOI: 10.1016/j.pharmthera.2020.107689] [Citation(s) in RCA: 22] [Impact Index Per Article: 5.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/04/2020] [Revised: 09/17/2020] [Accepted: 09/18/2020] [Indexed: 12/26/2022]
Abstract
Enzymes of the UDP-glucuronosyltransferase (UGT) superfamily contribute to the elimination of drugs from almost all therapeutic classes. Awareness of the importance of glucuronidation as a drug clearance mechanism along with increased knowledge of the enzymology of drug and chemical metabolism has stimulated interest in the development and application of approaches for the characterisation of human drug glucuronidation in vitro, in particular reaction phenotyping (the fractional contribution of the individual UGT enzymes responsible for the glucuronidation of a given drug), assessment of metabolic stability, and UGT enzyme inhibition by drugs and other xenobiotics. In turn, this has permitted the implementation of in vitro - in vivo extrapolation approaches for the prediction of drug metabolic clearance, intestinal availability, and drug-drug interaction liability, all of which are of considerable importance in pre-clinical drug development. Indeed, regulatory agencies (FDA and EMA) require UGT reaction phenotyping for new chemical entities if glucuronidation accounts for ≥25% of total metabolism. In vitro studies are most commonly performed with recombinant UGT enzymes and human liver microsomes (HLM) as the enzyme sources. Despite the widespread use of in vitro approaches for the characterisation of drug and chemical glucuronidation by HLM and recombinant enzymes, evidence-based guidelines relating to experimental approaches are lacking. Here we present evidence-based strategies for the characterisation of drug and chemical glucuronidation in vitro, and for UGT reaction phenotyping. We anticipate that the strategies will inform practice, encourage development of standardised experimental procedures where feasible, and guide ongoing research in the field.
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Affiliation(s)
- John O Miners
- Department of Clinical Pharmacology and Flinders Centre for Innovation in Cancer, College of Medicine and Public Health, Flinders University, Adelaide, Australia.
| | - Andrew Rowland
- Department of Clinical Pharmacology and Flinders Centre for Innovation in Cancer, College of Medicine and Public Health, Flinders University, Adelaide, Australia
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3
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Hyndman L, McKee S, Mottram NJ, Singh B, Webb SD, McGinty S. Mathematical modelling of fluid flow and solute transport to define operating parameters for in vitro perfusion cell culture systems. Interface Focus 2020; 10:20190045. [PMID: 32194930 PMCID: PMC7061945 DOI: 10.1098/rsfs.2019.0045] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/14/2019] [Accepted: 11/14/2019] [Indexed: 01/20/2023] Open
Abstract
In recent years, there has been a move away from the use of static in vitro two-dimensional cell culture models for testing the chemical safety and efficacy of drugs. Such models are increasingly being replaced by more physiologically relevant cell culture systems featuring dynamic flow and/or three-dimensional structures of cells. While it is acknowledged that such systems provide a more realistic environment within which to test drugs, progress is being hindered by a lack of understanding of the physical and chemical environment that the cells are exposed to. Mathematical and computational modelling may be exploited in this regard to unravel the dependency of the cell response on spatio-temporal differences in chemical and mechanical cues, thereby assisting with the understanding and design of these systems. In this paper, we present a mathematical modelling framework that characterizes the fluid flow and solute transport in perfusion bioreactors featuring an inlet and an outlet. To demonstrate the utility of our model, we simulated the fluid dynamics and solute concentration profiles for a variety of different flow rates, inlet solute concentrations and cell types within a specific commercial bioreactor chamber. Our subsequent analysis has elucidated the basic relationship between inlet flow rate and cell surface flow speed, shear stress and solute concentrations, allowing us to derive simple but useful relationships that enable prediction of the behaviour of the system under a variety of experimental conditions, prior to experimentation. We describe how the model may used by experimentalists to define operating parameters for their particular perfusion cell culture systems and highlight some operating conditions that should be avoided. Finally, we critically comment on the limitations of mathematical and computational modelling in this field, and the challenges associated with the adoption of such methods.
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Affiliation(s)
- Lauren Hyndman
- Division of Biomedical Engineering, University of Glasgow, Glasgow G12 8QQ, UK
| | - Sean McKee
- Department of Mathematics and Statistics, University of Strathclyde, Glasgow G1 1XH, UK
| | - Nigel J. Mottram
- Department of Mathematics and Statistics, University of Strathclyde, Glasgow G1 1XH, UK
| | - Bhumika Singh
- Kirkstall Ltd, York House, Outgang Lane, Osbaldwick, York YO19 5UP, UK
| | - Steven D. Webb
- Department of Applied Mathematics, Liverpool John Moores University, Liverpool L3 5UA, UK
| | - Sean McGinty
- Division of Biomedical Engineering, University of Glasgow, Glasgow G12 8QQ, UK
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4
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Vollmer M, Klingebiel M, Rohn S, Maul R. Alamethicin for using in bioavailability studies? - Re-evaluation of its effect. Toxicol In Vitro 2016; 39:111-118. [PMID: 27940284 DOI: 10.1016/j.tiv.2016.11.015] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/17/2016] [Revised: 11/25/2016] [Accepted: 11/29/2016] [Indexed: 11/24/2022]
Abstract
A major pathway for the elimination of drugs is the biliary and renal excretion following the formation of more hydrophilic secondary metabolites such as glucuronides. For in vitro investigations of the phase II metabolism, hepatic microsomes are commonly used in the combination with the pore-forming peptide alamethicin, also to give estimates for the in vivo situation. Thus, alamethicin may represent a neglected parameter in the characterization of microsomal in vitro assays. In the present study, the influence of varying alamethicin concentrations on glucuronide formation of selected phenolic compounds was investigated systematically. A correlation between the alamethicin impact and the lipophilicity of the investigated substrates was analyzed as well. Lipophilicity was determined by the logarithm of the octanol-water partition coefficient. For every substrate, a distinct alamethicin concentration could be detected leading to a maximal glucuronidation activity. Further increase of the alamethicin application led to negative effects. The differences between the maximum depletion rates with and without alamethicin addition varied between 2.7% and 18.2% depending on the substrate. A dependence on the lipophilicity could not be confirmed. Calculation of the apparent intrinsic clearance led to a more than 2-fold increase using the most effective alamethicin concentration compared to the alamethicin free control.
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Affiliation(s)
- Maren Vollmer
- Institute of Food Chemistry, Hamburg School of Food Science, University of Hamburg, Grindelallee 117, 20146 Hamburg, Germany.
| | - Mirko Klingebiel
- Institute of Food Chemistry, Hamburg School of Food Science, University of Hamburg, Grindelallee 117, 20146 Hamburg, Germany.
| | - Sascha Rohn
- Institute of Food Chemistry, Hamburg School of Food Science, University of Hamburg, Grindelallee 117, 20146 Hamburg, Germany.
| | - Ronald Maul
- Institute of Food Chemistry, Hamburg School of Food Science, University of Hamburg, Grindelallee 117, 20146 Hamburg, Germany.
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Ge S, Tu Y, Hu M. Challenges and Opportunities with Predicting in Vivo Phase II Metabolism via Glucuronidation from in Vitro Data. ACTA ACUST UNITED AC 2016; 2:326-338. [PMID: 28966903 DOI: 10.1007/s40495-016-0076-8] [Citation(s) in RCA: 23] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/19/2022]
Abstract
Glucuronidation is the most important phase II metabolic pathway which is responsible for the clearance of many endogenous and exogenous compounds. To better understand the elimination process for compounds undergoing glucuronidation and identify compounds with desirable in vivo pharmacokinetic properties, many efforts have been made to predict in vivo glucuronidation using in vitro data. In this article, we reviewed typical approaches used in previous predictions. The problems and challenges in prediction of glucuronidation were discussed. Besides that different incubation conditions can affect the prediction accuracy, other factors including efflux / uptake transporters, enterohepatic recycling, and deglucuronidation reactions also contribute to the disposition of glucuronides and make the prediction more difficult. PBPK modeling, which can describe more complicated process in vivo, is a promising prediction strategy which may greatly improve the prediction of glucuronidation and potential DDIs involving glucuronidation. Based on previous studies, we proposed a transport-glucuronidation classification system, which was built based on the kinetics of both glucuronidation and transport of the glucuronide. This system could be a very useful tool to achieve better in vivo predictions.
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Affiliation(s)
- Shufan Ge
- Department of Pharmacological and Pharmaceutical Sciences, College of Pharmacy, The University of Houston, 1441 Moursund Street, Houston, TX, 77030, USA
| | - Yifan Tu
- Department of Pharmacological and Pharmaceutical Sciences, College of Pharmacy, The University of Houston, 1441 Moursund Street, Houston, TX, 77030, USA
| | - Ming Hu
- Department of Pharmacological and Pharmaceutical Sciences, College of Pharmacy, The University of Houston, 1441 Moursund Street, Houston, TX, 77030, USA
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James MO, Ambadapadi S. Interactions of cytosolic sulfotransferases with xenobiotics. Drug Metab Rev 2014; 45:401-14. [PMID: 24188364 DOI: 10.3109/03602532.2013.835613] [Citation(s) in RCA: 76] [Impact Index Per Article: 7.6] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/10/2023]
Abstract
Cytosolic sulfotransferases are a superfamily of enzymes that catalyze the transfer of the sulfonic group from 3'-phosphoadenosine-5'-phosphosulfate to hydroxy or amine groups in substrate molecules. The human cytosolic sulfotransferases that have been most studied, namely SULT1A1, SULT1A3, SULT1B1, SULT1E1 and SULT2A1, are expressed in different tissues of the body, including liver, intestine, adrenal, brain and skin. These sulfotransferases play important roles in the sulfonation of endogenous molecules such as steroid hormones and neurotransmitters, and in the elimination of xenobiotic molecules such as drugs, environmental chemicals and natural products. There is often overlapping substrate selectivity among the sulfotransferases, although one isoform may exhibit greater enzyme efficiency than other isoforms. Similarly, inhibitors or enhancers of one isoform often affect other isoforms, but typically with different potency. This means that if the activity of one form of sulfotransferase is altered (either inhibited or enhanced) by the presence of a xenobiotic, the sulfonation of endogenous and xenobiotic substrates for other isoforms may well be affected. There are more examples of inhibitors than enhancers of sulfonation. Modulators of sulfotransferase enzymes include natural products ingested as part of the human diet as well as environmental chemicals and drugs. This review will discuss recent work on such interactions.
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Affiliation(s)
- Margaret O James
- Department of Medicinal Chemistry, University of Florida, Gainesville , FL , USA
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7
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The pharmacokinetic profile of intravenous paracetamol in adult patients undergoing major abdominal surgery. Ther Drug Monit 2013; 34:713-21. [PMID: 23149443 DOI: 10.1097/ftd.0b013e31826a70ea] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/29/2022]
Abstract
BACKGROUND Intravenous (IV) paracetamol is commonly used in the postoperative period for the treatment of mild to moderate pain. The main pathways for paracetamol metabolism are glucuronidation, sulfation, and oxidation, accounting for approximately 55%, 30%, and 10% of urinary metabolites, respectively. The aim of this study was to describe the pharmacokinetics of IV paracetamol and its metabolites in adult patients after major abdominal surgery. METHODS Twenty patients were given 1 g of paracetamol by IV infusion at induction of anesthesia (Interval 1) and every 6 hours thereafter, with the final dose given at 48-72 hours (Interval 2). Plasma and urine samples were collected for up to 8 hours after infusion for both intervals. The samples were analyzed by high-performance liquid chromatography to determine the amount of paracetamol and its metabolites. The data were modeled in Phoenix WinNonlin using a user-defined ASCII parent-metabolite model with linear disposition, to obtain the estimates for volume of distribution, metabolic and urinary clearance. RESULTS Mean (95% confidence interval) metabolic clearance to paracetamol glucuronide increased from 0.06 (0.05-0.08) to 0.14 (0.11-0.18) L · h⁻¹ · kg⁻¹, P value <0.001 and urinary clearance increased from 0.08 (0.07-0.09) to 0.14 (0.10-0.17) L · h⁻¹ · kg⁻¹, P value 0.002. The mean (95% confidence interval) volume of distribution of paracetamol increased from 0.17 (0.12-0.21) to 0.43 (0.27-0.59) L · kg⁻¹, P value 0.032. CONCLUSIONS After major abdominal surgery, there were apparent increases in the metabolic conversion to paracetamol glucuronide and its urinary clearance suggesting potential induction of paracetamol glucuronidation.
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Moyer AM, Fridley BL, Jenkins GD, Batzler AJ, Pelleymounter LL, Kalari KR, Ji Y, Chai Y, Nordgren KKS, Weinshilboum RM. Acetaminophen-NAPQI hepatotoxicity: a cell line model system genome-wide association study. Toxicol Sci 2010; 120:33-41. [PMID: 21177773 DOI: 10.1093/toxsci/kfq375] [Citation(s) in RCA: 49] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/07/2023] Open
Abstract
Acetaminophen is the leading cause of acute hepatic failure in many developed nations. Acetaminophen hepatotoxicity is mediated by the reactive metabolite N-acetyl-p-benzoquinonimine (NAPQI). We performed a "discovery" genome-wide association study using a cell line-based model system to study the possible contribution of genomics to NAPQI-induced cytotoxicity. A total of 176 lymphoblastoid cell lines from healthy subjects were treated with increasing concentrations of NAPQI. Inhibiting concentration 50 values were determined and were associated with "glutathione pathway" gene single nucleotide polymorphisms (SNPs) and genome-wide basal messenger RNA expression, as well as with 1.3 million genome-wide SNPs. A group of SNPs in linkage disequilibrium on chromosome 3 was highly associated with NAPQI toxicity. The p value for rs2880961, the SNP with the lowest p value, was 1.88 × 10(-7). This group of SNPs mapped to a "gene desert," but chromatin immunoprecipitation assays demonstrated binding of several transcription factor proteins including heat shock factor 1 (HSF1) and HSF2, at or near rs2880961. These chromosome 3 SNPs were not significantly associated with variation in basal expression for any of the genome-wide genes represented on the Affymetrix U133 Plus 2.0 GeneChip. We have used a cell line-based model system to identify a SNP signal associated with NAPQI cytotoxicity. If these observations are validated in future clinical studies, this SNP signal might represent a potential biomarker for risk of acetaminophen hepatotoxicity. The mechanisms responsible for this association remain unclear.
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Affiliation(s)
- Ann M Moyer
- Division of Clinical Pharmacology, Department of Molecular Pharmacology and Experimental Therapeutics, Mayo Clinic, Rochester, Minnesota 55905, USA
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9
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Riches Z, Bloomer J, Patel A, Nolan A, Coughtrie M. Assessment of cryopreserved human hepatocytes as a model system to investigate sulfation and glucuronidation and to evaluate inhibitors of drug conjugation. Xenobiotica 2010; 39:374-81. [PMID: 19280384 DOI: 10.1080/00498250902763440] [Citation(s) in RCA: 25] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/21/2022]
Abstract
Cultured cryopreserved human hepatocytes are extensively used as a model system for studying drug metabolism, although they remain poorly characterized in respect of the major conjugation reactions glucuronidation and sulfation. Using paracetamol (acetaminophen), we assessed eleven samples of cryopreserved human hepatocytes for their suitability to investigate the simultaneous glucuronidation and sulfation of xenobiotics and evaluated inhibitors of conjugation. Kinetic characterization showed broadly similar values for paracetamol conjugation by hepatocytes (as reported in the literature for in vitro systems), with Km values of approximately 6 mM and 0.3 mM for glucuronidation and sulfation, respectively. Substantial interindividual differences were observed. The hepatocytes demonstrated a strong dose-dependent switch from a preponderance of sulfation at low concentrations of paracetamol to glucuronidation at higher doses, consistent with routes of clearance in vivo. A number of drugs, some of which such as probenecid and sulfinpyrazone are known to interact with paracetamol in vivo, were demonstrated to inhibit the sulfation and/or glucuronidation of paracetamol in hepatocytes, demonstrating the potential application of this model system for studying drug-drug interactions involving conjugation.
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Affiliation(s)
- Z Riches
- Division of Medical Sciences, University of Dundee, Ninewells Hospital & Medical School, Dundee, UK
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Reith D, Medlicott NJ, Kumara De Silva R, Yang L, Hickling J, Zacharias M. SIMULTANEOUS MODELLING OF THE MICHAELIS-MENTEN KINETICS OF PARACETAMOL SULPHATION AND GLUCURONIDATION. Clin Exp Pharmacol Physiol 2009; 36:35-42. [DOI: 10.1111/j.1440-1681.2008.05029.x] [Citation(s) in RCA: 28] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
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Miners JO, Knights KM, Houston JB, Mackenzie PI. In vitro–in vivo correlation for drugs and other compounds eliminated by glucuronidation in humans: Pitfalls and promises. Biochem Pharmacol 2006; 71:1531-9. [PMID: 16455060 DOI: 10.1016/j.bcp.2005.12.019] [Citation(s) in RCA: 152] [Impact Index Per Article: 8.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/17/2005] [Revised: 12/13/2005] [Accepted: 12/14/2005] [Indexed: 10/25/2022]
Abstract
Enzymes of the UDP-glucuronosyltransferase (UGT) superfamily are responsible for the metabolism of many drugs, environmental chemicals and endogenous compounds. Identification of the UGT(s) involved in the metabolism of a given compound ('reaction phenotyping') currently relies on multiple confirmatory approaches, which may be confounded by the dependence of UGT activity on enzyme source, incubation conditions, and the occurrence of atypical glucuronidation kinetics. However, the increasing availability of substrate and inhibitor 'probes' for the individual UGTs provides the prospect for reliable phenotyping of glucuronidation reactions using human liver microsomes or hepatocytes, thereby providing data directly relevant to drug metabolism in humans. While the feasibility of computational prediction of UGT substrate selectivity has been demonstrated, the development of easily interpretable and generalisable models requires further improvement in the datasets available for analysis. Quantitative prediction of the hepatic clearance of glucuronidated drugs and the magnitude of inhibitory interactions based on in vitro kinetic data is more problematic. Intrinsic clearance (CL(int)) values generated using human liver microsomes under-predict in vivo hepatic clearance, typically by an order of magnitude. In vivo clearances of glucuronidated drugs are also generally under-predicted by CL(int) values from human hepatocytes, but to a lesser extent than observed with the microsomal model. While it is anticipated that systematic analysis of the potential causes of under-prediction may provide more reliable in vitro-in vivo scaling strategies, mechanistic interpretation of in vitro-in vivo correlation more broadly awaits further advances in our understanding of the structural and cellular determinants of UGT activity.
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Affiliation(s)
- John O Miners
- Department of Clinical Pharmacology, Flinders University and Flinders Medical Centre, Adelaide, Australia.
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12
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Boase S, Miners JO. In vitro-in vivo correlations for drugs eliminated by glucuronidation: investigations with the model substrate zidovudine. Br J Clin Pharmacol 2002; 54:493-503. [PMID: 12445028 PMCID: PMC1874472 DOI: 10.1046/j.1365-2125.2002.01669.x] [Citation(s) in RCA: 98] [Impact Index Per Article: 4.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/28/2022] Open
Abstract
AIMS To investigate the effects of incubation conditions on the kinetic constants for zidovudine (AZT) glucuronidation by human liver microsomes, and whether microsomal intrinsic clearance (CLint) derived for the various conditions predicted hepatic AZT clearance by glucuronidation (CLH) in vivo. METHODS The effects of incubation constituents, particularly buffer type (phosphate, Tris) and activators (Brij58, alamethacin, UDP-N-acetylglucosamine (UDP-NAcG)), on the kinetics of AZT glucuronidation by human liver microsomes was investigated. AZT glucuronide (AZTG) formation by microsomal incubations was quantified by h.p.l.c. Microsomal CLint values determined for the various experimental conditions were extrapolated to a whole organ CLint and these data were used to calculate in vivo CLH using the well-stirred, parallel tube and dispersion models. RESULTS Mean CLint values for Brij58 activated microsomes in both phosphate (3.66 +/- 1.40 micro l min-1 mg-1, 95% CI 1.92, 5.39) and Tris (3.79 +/- 0.74 micro l min-1 mg-1, 95% CI 2.87, 4.71) buffers were higher (P < 0.05) than the respective values for native microsomes (1.04 +/- 0.42, 95% CI 0.53, 1.56 and 1.37 +/- 0.30 micro l min-1 mg-1, 95% CI 1.00, 1.73). Extrapolation of the microsomal data to a whole organ CLint and substitution of these values in the expressions for the well-stirred, parallel tube and dispersion models underestimated the known in vivo blood AZT clearance by glucuronidation by 6.5- to 23-fold (3.61-12.71 l h-1vs 82 l h-1). There was no significant difference in the CLH predicted by each of the models for each set of conditions. A wide range of incubation constituents and conditions were subsequently investigated to assess their effects on GAZT formation, including alamethacin, UDP-NAcG, MgCl2, d-saccharic acid 1,4-lactone, ATP, GTP, and buffer pH and ionic strength. Of these, only decreasing the phosphate buffer concentration from 0.1 m to 0.02 m for Brij58 activated microsomes substantially increased the rate of GAZT formation, but the extrapolated CLH determined for this condition still underestimated known AZT glucuronidation clearance by more than 4-fold. AZT was shown not to bind nonspecifically to microsomes. Analysis of published data for other glucuronidated drugs confirmed a trend for microsomal CLint to underestimate in vivo CLH. CONCLUSIONS AZT glucuronidation kinetics by human liver microsomes are markedly dependent on incubation conditions, and there is a need for interlaboratory standardization. Extrapolation of in vitro CLint underestimates in vivo hepatic clearance of drugs eliminated by glucuronidation.
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Affiliation(s)
- Sam Boase
- Department of Clinical Pharmacology, Medical Centre, Flinders University of South Australia, Bedford Park, Adelaide, SA, Australia
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13
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Alkharfy KM, Frye RF. High-performance liquid chromatographic assay for acetaminophen glucuronide in human liver microsomes. JOURNAL OF CHROMATOGRAPHY. B, BIOMEDICAL SCIENCES AND APPLICATIONS 2001; 753:303-8. [PMID: 11334344 DOI: 10.1016/s0378-4347(00)00566-1] [Citation(s) in RCA: 37] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/16/2022]
Abstract
A rapid and specific high-performance liquid chromatographic assay was developed for the determination of acetaminophen glucuronide formed by human liver microsomes. In addition, incubation conditions were systematically evaluated. Conditions that yielded the optimal rate of acetaminophen glucuronide formation over various concentrations of acetaminophen (0.15-30 mM) consisted of the following: 0.1 M potassium phosphate buffer, 1 mM magnesium chloride, 30 microg/mg alamethicin, 4 mM uridine 5'-diphosphoglucuronic acid at a pH of 7.1. Alamethicin produced higher and more consistent APAPG formation rates compared to Brij-58. Adding saccharolactone to the incubation medium reduced the velocity of the reaction. Acetaminophen glucuronide, acetaminophen, and the internal standard (paraxanthine), were analyzed on a C18 column with UV detection at 250 nm. The mean correlation coefficient (r2) of the standard curves for acetaminophen glucuronide was >0.99 over the range of 0.1-25 nmol. The intra- and inter-day coefficients of variation were <4%. This method is suitable for in vitro studies using acetaminophen glucuronide formation as an index reaction for UGT activity.
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Affiliation(s)
- K M Alkharfy
- Department of Pharmaceutical Sciences, School of Pharmacy, University of Pittsburgh, PA 15261, USA
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14
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Dennis GC, Soni D, Dehkordi O, Millis RM, James H, West WL, Taylor RE. Analgesic responses to intrathecal morphine in relation to CSF concentrations of morphine-3,beta-glucuronide and morphine-6,beta-glucuronide. Life Sci 1999; 64:1725-31. [PMID: 10353626 DOI: 10.1016/s0024-3205(99)00110-1] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/01/2022]
Abstract
This study was performed to determine whether variations in analgesic responses to intrathecal morphine could be explained by cerebrospinal fluid (CSF) concentrations of morphine metabolites. Twenty-four CSF samples were collected at the beginning, middle and end of treatment periods in seven cancer patients with pain of malignant origin. CSF concentrations of morphine-3,beta-glucuronide (M3G) and morphine-6,beta-glucuronide (M6G) metabolites were measured by gas chromatography/mass spectrometry. Analgesic responses to morphine were estimated concurrent with CSF collection using a visual analog scale representing percentages of pain relief. Effective analgesia was defined as > or = 75% pain relief. CSF concentration of M3G and M6G in the 24 samples were 722 +/- 116 ng/ml and 699 +/- 158 ng/ml, respectively. CSF samples were categorized into two groups: (1) those collected during effective analgesia (N=14), and (2) those collected during ineffective analgesia (N=10). M6G levels detected in group 1 samples (effective analgesia) were significantly greater than those found in group 2 samples (ineffective analgesia) (978 +/- 243 ng/ml vs 309 +/- 68 ng/ml, P<0.05). Intergroup differences in CSF M3G concentrations and M3G/M6G ratios were not significant. It is concluded that CSF M6G may be indicative of effectiveness of analgesia in cancer patients subjected to intrathecal morphine.
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Affiliation(s)
- G C Dennis
- Department of Surgery, Howard University Hospital, Washington, DC 20060, USA
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15
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Villar D, Furusawa N, Monshouwer M, Van Miert AS. Novobiocin inhibits both UDP-glucuronosyltransferase and cytochrome P450-mediated enzyme activities in pig liver microsomes. Vet Res Commun 1998; 22:405-14. [PMID: 9810637 DOI: 10.1023/a:1006101530107] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022]
Abstract
The effects of novobiocin (range 0.0125-2 mmol/L) on the hydroxylation of testosterone, the N-demethylation of erythromycin, and the glucuronidation of alpha-naphthol and paracetamol were studied using pig hepatic microsomes, pooled from five animals. The final concentrations of these substrates in the incubation mixtures were selected to meet Vmax conditions. Novobiocin caused a concentration-dependent inhibition of the glucuronidation of paracetamol; the formation of alpha-naphthol-glucuronide was reduced to a lesser degree. These results confirm and extend earlier findings in laboratory animal species that novobiocin inhibits UDP-glucuronosyltransferases (UDPGTs). Moreover, novobiocin strongly inhibited 6 beta-hydroxylation of testosterone. The microsomal N-demethylation of erythromycin and hydroxylation of testosterone at the 15 alpha position were less affected by novobiocin. These results suggest that novobiocin inhibits not only UDPGTs, but also cytochrome P450 (CYP) enzyme activities, probably those belonging to the CYP3A subfamily. More research is needed to reveal which CYPs and UDPGTs are affected by novobiocin in vivo, in order to improve the understanding the probably the predictability of potential drug interactions with this antibiotic.
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Affiliation(s)
- D Villar
- MaCaulay Land Use Research Institute, Aberdeen, UK
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16
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Kirkwood LC, Nation RL, Somogyi AA. Glucuronidation of dihydrocodeine by human liver microsomes and the effect of inhibitors. Clin Exp Pharmacol Physiol 1998; 25:266-70. [PMID: 9590580 DOI: 10.1111/j.1440-1681.1998.t01-19-.x] [Citation(s) in RCA: 20] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
1. Glucuronidation is the major route of metabolism of dihydrocodeine (DHC) and accounts for 25-30% of an oral dose in urine. The kinetics of DHC-6-glucuronide formation in liver microsomes from five human donors and the effect of a number of potential inhibitor drugs were examined using a newly developed and validated HPLC assay. 2. The formation of DHC-6-glucuronide exhibited atypical kinetics that conformed to the Hill equation. The mean intrinsic dissociation constant (Ks) and maximum velocity (Vmax) values were 1566 micromol/L and 0.043 micromol/min per g, respectively. The Ks and Vmax values varied 1.5- and 3.5-fold, respectively. 3. Seven drugs were tested for inhibitory effects on DHC glucuronidation at low (50 micromol/L) and high (500 micromol/L) concentrations. At 50 micromol/L, only diclofenac produced greater than 50% inhibition, while at concentrations of 500 micromol/L inhibition was greater than 35% for diclofenac, amitriptyline, oxazepam, naproxen, chloramphenicol and probenecid, but not paracetamol. 4. The present study found little interindividual variation in the activity of human liver microsomes for glucuronidation of DHC. Comparison of the results from the inhibition studies with those reported previously for codeine and morphine suggest that the UDP-glucuronosyltransferase isoform UGT2B7 is involved in the glucuronidation of DHC.
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Affiliation(s)
- L C Kirkwood
- Centre for Pharmaceutical Research, School of Pharmacy and Medical Sciences, University of South Australia, Adelaide, Australia
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17
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Tingle MD, Mahmud R, Maggs JL, Hawley S, Coleman MD, Ward SA, Park BK. The effect of 2,2'-substitution on the metabolism and toxicity of dapsone in vitro and in vivo. ENVIRONMENTAL TOXICOLOGY AND PHARMACOLOGY 1998; 5:145-153. [PMID: 21781861 DOI: 10.1016/s1382-6689(97)10070-9] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 07/08/1997] [Revised: 11/13/1997] [Accepted: 11/18/1997] [Indexed: 05/31/2023]
Abstract
The effect of 2,2'-substitution with fluorine, methyl or trifluoromethyl groups on the toxicity, metabolism and pharmacological activity of dapsone has been investigated in vitro and in vivo. There was marked inter-species variation in the bioactivation (N-hydroxylation) of the compounds, as determined by methemoglobin formation. However, the inclusion of fluorine significantly (P<0.01) reduced methemoglobin formation compared with dapsone in all species studied. All three analogs resulted in significantly (P<0.001) less methemoglobinemia than dapsone when given either intraperitoneally or intravenously to the male Wistar rat. Rapid plasma clearance of the analogs through increased lipophilicity and enhanced N-glucuronidation may account for the low toxicity compared with dapsone. Although trifluoromethyl substitution resulted in a loss of activity against respiratory burst in human neutrophils in an in vitro model, all three analogs retained pharmacological activity against Plasmodium berghei malaria in an in vivo mouse model.
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Affiliation(s)
- M D Tingle
- Department of Pharmacology and Therapeutics, University of Liverpool, P.O. Box 147, Liverpool, L69 3BX, UK
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18
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Firdaous I, Verbeeck RK, Hassoun A, Langrehr JM, Wallemacq PE. Excretion of tacrolimus glucuronides in human bile. Eur J Drug Metab Pharmacokinet 1997; 22:217-21. [PMID: 9358202 DOI: 10.1007/bf03189810] [Citation(s) in RCA: 13] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/05/2023]
Abstract
Tacrolimus is extensively metabolized by the cytochrome P-450 system. Hepatic metabolic phase I reactions of tacrolimus include mainly demethylation and/or hydroxylation. No valid data have been published on phase II pathways (glucuronide- or sulfo-conjugation). In order to investigate these pathways, different beta-glucuronidase/sulfatase enzyme preparations were used to hydrolyse the conjugates potentially present in human bile extracts. Two analytical methods were used: a non-specific method, MEIA, and a specific combined HPLC/MEIA method. The influence of the extraction pH was investigated. After beta-glucuronidase hydrolysis and extraction at pH 5, tacrolimus concentrations, obtained either from HPLC-MEIA or MEIA, always appeared significantly higher, suggesting the presence of glucuronides in the bile. When the extraction was performed at pH 1.5, only the HPLC-MEIA concentrations appeared higher after hydrolysis. MEIA concentrations obtained before and after hydrolysis were similar. These data are consistent with the fact that glucuronides are extracted at pH 1.5 but not at pH 5 and suggest first that, without hydrolysis, the extracted glucuronides are separated from the tacrolimus fraction in the HPLC-MEIA procedure, and second, that the glucuronides are cross-detected by the monoclonal antibody in the immunoassay. From these data, it is concluded that clues have been found, suggesting the presence in human bile of tacrolimus glucuronides, which cross-react with the monoclonal antibody, provided they are extracted in the sample tested.
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Affiliation(s)
- I Firdaous
- Department of Clinical Chemistry, University Hospital St Luc, Catholic University of Louvain, Brussels, Belgium
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19
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Court MH, Greenblatt DJ. Molecular basis for deficient acetaminophen glucuronidation in cats. An interspecies comparison of enzyme kinetics in liver microsomes. Biochem Pharmacol 1997; 53:1041-7. [PMID: 9174118 DOI: 10.1016/s0006-2952(97)00072-5] [Citation(s) in RCA: 140] [Impact Index Per Article: 5.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/04/2023]
Abstract
Cats are highly susceptible to acetaminophen toxicity because of deficient glucuronidation of this drug in vivo. The enzyme kinetic basis for this defect is unknown. Therefore, the kinetic properties of acetaminophen UDP-glucuronosyltransferase (acetaminophen-UGT) were investigated, using hepatic microsomes from cats (N = 4) compared with those of species that are less sensitive to acetaminophen intoxication including dogs (N = 4), humans (N = 4), and six other mammalian species (one liver from each). Gunn rats were also studied, since they express defective UGT family 1 isoenzymes and are also prone to acetaminophen toxicity. Acetaminophen kinetics were biphasic in all instances with distinct high and low affinity components. Km values for the high affinity activity in cat microsomes (0.31 +/- 0.1 mM; mean +/- SEM) were intermediate between those of dogs (0.11 +/- 0.02 mM) and humans (0.60 +/- 0.06 mM) and other species (0.22 to 6.7 mM; range). On the other hand, high affinity Vmax values were over 10-fold less in cat microsomes (0.025 +/- 0.006 nmol/min/mg) than in dogs (0.92 +/- 0.09 nmol/min/mg) and humans (0.27 +/- 0.09 nmol/min/mg); and over 5-fold less compared with microsomes from other species (range 0.13 to 7.63 nmol/min/mg). Gunn rat microsomes showed a similar 10-fold difference in high affinity Vmax values between the homozygous mutant (0.67 nmol/min/mg) and homozygous normal (6.75 nmol/min/mg) animals. These results demonstrate that, relative to a number of other species, cats have remarkably low hepatic levels of a high affinity acetaminophen-UGT. This difference is sufficient enough to explain poor glucuronidation of acetaminophen in vivo and susceptibility to acetaminophen intoxication.
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Affiliation(s)
- M H Court
- Department of Pharmacology and Experimental Therapeutics, Tufts University School of Medicine, Boston, MA 02111, U.S.A
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20
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Court MH, Greenblatt DJ. Biochemical basis for deficient paracetamol glucuronidation in cats: an interspecies comparison of enzyme constraint in liver microsomes. J Pharm Pharmacol 1997; 49:446-9. [PMID: 9232546 DOI: 10.1111/j.2042-7158.1997.tb06822.x] [Citation(s) in RCA: 40] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/04/2023]
Abstract
Unlike most other mammalian species, domestic cats glucuronidate phenolic compounds poorly and are therefore highly susceptible to the toxic side effects of many drugs, including paracetamol. In this study, we evaluated the role of enzyme constraint, a characteristic that limits the activity of all uridine 5'-diphosphoglucuronosyltransferase (UGT) enzymes, in the aetiology of this species-dependent defect of drug metabolism. Detergent activation experiments were performed using hepatic microsomes from cats (4), dogs (4), man (4), and 6 other mammalian species (1 liver each). In addition, we used microsomes from Gunn rats which are sensitive to paracetamol toxicity because of a genetic defect affecting all family 1 UGTs. Increase in paracetamol-UGT activity at optimum concentrations of detergent was used as an index of enzyme constraint. Native activity (measured in the absence of detergent) was less than one-sixth in cats compared with other species. Optimum detergent treatment tended to enhance rather than abolish this difference, however, indicating relatively lower levels of constraint of paracetamol-UGT in cats compared with other species. Similarly, detergent treatment failed to reduce the native activity difference between homozygous mutant and normal Gunn rats. Initially CHAPS (3-(3-cholamidopropyl)-dimethylammonio-1-propanesulphonic acid) was used as the detergent activator; in 3 of 4 microsomal preparations from man, however, inhibition rather than activation was observed at all detergent concentrations used. Studies were repeated using the non-ionic detergent, Brij 58 (polyoxyethylene 20-cetyl ether), which resulted in similar although more profound activation and no inhibition. We conclude that deficient paracetamol glucuronidation in cats does not result from increased paracetamol-UGT constraint in this species compared with other mammalian species. Other causes, such as differences in enzyme protein concentration or substrate affinity might be responsible.
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Affiliation(s)
- M H Court
- Department of Pharmacology and Experimental Therapeutics, Tufts University School of Medicine, Boston, MA 02111, USA
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21
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Le Guellec C, Lacarelle B, Villard PH, Point H, Catalin J, Durand A. Glucuronidation of Propofol in Microsomal Fractions from Various Tissues and Species Including Humans. Anesth Analg 1995. [DOI: 10.1213/00000539-199510000-00034] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/05/2022]
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22
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Le Guellec C, Lacarelle B, Villard PH, Point H, Catalin J, Durand A. Glucuronidation of propofol in microsomal fractions from various tissues and species including humans: effect of different drugs. Anesth Analg 1995; 81:855-61. [PMID: 7574023 DOI: 10.1097/00000539-199510000-00034] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/26/2023]
Abstract
This in vitro study was conducted to evaluate propofol glucuronidation and the effect of concomitantly administered drugs in various species. Propofol glucuronidation was studied in microsomal fractions from rat, rabbit, and human livers. Extrahepatic metabolism was investigated using lung and kidney microsomes. The propofol-uridine diphosphate-glucuronosyltransferase (UGT) activity measured in liver microsomes was higher in rabbit than in rat. Among the three tested species, human livers exhibited the highest activity, with only small variability in the three samples studied. Animal kidney, but not lung (animal or human), microsomes were able to glucuronidate propofol, meaning that extrahepatic metabolism of propofol exists, at least in the kidney, in the tested species (rat and rabbit). Since metabolic interactions are potential sources of prolonged drug effect or overdose, we screened the effect of 21 compounds (known substrates of various UGT or potentially coadministered drugs) on the glucuronidation of propofol by human liver microsomes. Inhibitions obtained with chemicals or drugs glucuronidated by either UGT1 or UGT2 families (1-naphtol, 4-hydroxybiphenyl, carvacrol, n-propylgallate, ketoprofen, chloramphenicol, acetylsalicylic acid) indicated that at least two UGT isoforms are involved in propofol glucuronidation. Inhibition was observed with several drugs potentially coadministered during pre-, per, or postoperative periods (e.g., acetylsalicyclic acid, ketoprofen, oxazepam, fentanyl). Although not directly transposable to the in vivo situation, these results indicate that such interactions are theoretically possible.(ABSTRACT TRUNCATED AT 250 WORDS)
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Affiliation(s)
- C Le Guellec
- Laboratoire de Pharmacocinétique et Toxicocinétique, Faculté de Pharmacie, Marseille, France
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23
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Glazier AP, Kokwaro GO, Ismail S, Edwards G. Effect of an experimental malaria infection on the metabolism of phenacetin in the rat isolated perfused liver. Xenobiotica 1994; 24:785-93. [PMID: 7839701 DOI: 10.3109/00498259409043278] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/27/2023]
Abstract
1. The effect of infection with the rodent malaria parasite Plasmodium berghei on the metabolism of phenacetin has been investigated in a rat isolated perfused liver preparation. 2. A bolus dose of phenacetin (10 mg) was introduced into the perfusate reservoir of both control (n = 4) and malaria-infected (n = 4) liver preparations, and samples of bile and perfusate were collected (0-4 h) for hplc analysis of phenacetin, paracetamol and its phase II metabolites. 3. Whereas malaria had no effect on the hepatic clearance of phenacetin (control: 0.64 +/- 0.15 versus malaria: 0.66 +/- 0.14 ml min-1), there was a significant reduction in the hepatic clearance of generated paracetamol (control: 1.22 +/- 0.15 versus malaria: 0.41 +/- 0.08 ml min-1) and the total recovery in bile and perfusate of paracetamol glucuronide (control: 1.18 +/- 0.44 versus malaria: 0.29 +/- 0.20 mg). There was no significant change during malaria infection in the total recovery of either phenacetin (control: 1.30 +/- 0.73 versus malaria: 0.79 +/- 0.36 mg) or paracetamol sulphate (control: 0.81 +/- 0.25 versus malaria: 0.74 +/- 0.16 mg),
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Affiliation(s)
- A P Glazier
- Department of Pharmacology and Therapeutics, University of Liverpool, UK
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24
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Monshouwer M, Witkamp RF, Pijpers A, Verheijden JH, van Miert AS. Dose-dependent pharmacokinetic interaction between antipyrine and paracetamol in vivo and in vitro when administered as a cocktail in pig. Xenobiotica 1994; 24:347-55. [PMID: 8059538 DOI: 10.3109/00498259409045898] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/28/2023]
Abstract
1. The pharmacokinetic interactions between paracetamol (PA) and antipyrine (AP) were studied in pigs in order to investigate the usefulness of this combination for the simultaneous assessment of oxidative and conjugative metabolism. 2. When both drugs were given at a dose of 5 mg/kg, AP plasma clearance was reduced from 2.22 to 0.96 lh-1 kg-1. PA clearance was not changed in comparison with control values. 3. At a dose of 2 mg/kg no pharmacokinetic interaction between the two drugs was observed. 4. The only oxidative AP metabolite found in urine was 4-hydroxyantipyrine (4-OHA). It accounted for 80% of the dose and, like PA, it was completely glucuronidated. 5. The glucuronidation of PA has been studied in vitro in pig liver microsomes. The apparent Km value for PA glucuronidation was 40 mM with a Vmax = 54 nmol min-1 mg protein-1. To determine if 4-OHA and PA competed for the same UDP-glucuronosyl-transferase, the effect of 4-OHA and AP on PA glucuronidation was studied. It appeared that 4-OHA was a competitive inhibitor with a Ki app = 0.07 microM, whereas AP had no effect. 5. Results suggest a dose-dependent interaction between AP and PA, which may be due to competition at the level of glucuronidation. Therefore, the usefulness of AP and PA in vivo in a cocktail for metabolism studies is limited.
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Affiliation(s)
- M Monshouwer
- Department of Veterinary Basic Sciences, University of Utrecht, The Netherlands
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25
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Goucke RC, Hackett PL, Ilett KF. Concentrations of morphine, morphine-6-glucuronide and morphine-3-glucuronide in serum and cerebrospinal fluid following morphine administration to patients with morphine-resistant pain. Pain 1994; 56:145-149. [PMID: 8008404 DOI: 10.1016/0304-3959(94)90088-4] [Citation(s) in RCA: 64] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/28/2023]
Abstract
Recent studies have suggested that morphine-3-glucuronide (M3G) may antagonize the analgesic effects of morphine and morphine-6-glucuronide (M6G). To investigate this hypothesis, steady-state concentrations of morphine, M6G and M3G in serum and cerebrospinal fluid (CSF) were measured in 11 patients receiving chronic morphine therapy (9 orally and 2 subcutaneously) for treatment of cancer-related pain. All patients appeared to have morphine-resistant pain and had elected to proceed to intrathecal bupivacaine or percutaneous cordotomy. Morphine, M6G and M3G concentrations were measured by high-performance liquid chromatography. The concentrations (median and range) for morphine, M6G and M3G in serum were 193 (14-1086) nmol/l, 847 (210-4113) nmol/l and 4553 (1324-24035) nmol/l, respectively, while in CSF concentrations of morphine, M6G and M3G were 200 (21-1461) nmol/l, 115 (30-427) nmol/l and 719 (249-3252) nmol/l, respectively. Median molar ratios of M6G/morphine and M3G/morphine in serum were 3.79 and 22.1, respectively, while in CSF the same ratios were 0.42 and 2.39, respectively. Median molar ratios of M3G/M6G in serum and CSF were 5.84 and 6.61, respectively. The median molar ratios for CSF/serum distribution of morphine, M6G and M3G were 1.23, 0.12 and 0.14, respectively. Thus, despite their relatively poor ability to penetrate into the CSF, the high serum concentrations of M6G and M3G resulted in substantial concentrations of these metabolites in the CSF. Nevertheless, M3G/M6G ratios in our morphine-resistant patients were similar to published values in patients with well-controlled pain, suggesting that the hypothesis that M3G plays a major role in morphine-resistance is not correct.
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Affiliation(s)
- Roger C Goucke
- Department of Pain Management, Sir Charles Gairdner Hospital, Nedlands 6009 Australia Combined Unit in Clinical Pharmacology and Toxicology, State Health Laboratories/University of Western Australia, Nedlands 6009 Australia
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26
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Bock KW, Forster A, Gschaidmeier H, Brück M, Münzel P, Schareck W, Fournel-Gigleux S, Burchell B. Paracetamol glucuronidation by recombinant rat and human phenol UDP-glucuronosyltransferases. Biochem Pharmacol 1993; 45:1809-14. [PMID: 8494539 DOI: 10.1016/0006-2952(93)90437-2] [Citation(s) in RCA: 109] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/31/2023]
Abstract
Stably expressed human and rat phenol UDP-glucuronosyltransferases (UGTs) of the UGT1 complex (HlugP1, HlugP4 and 3-methylcholanthrene-inducible rat UGT1A1, the latter considered to be an orthologous enzyme to HlugP1) have been used to investigate the role of UGTs in paracetamol glucuronidation. Kinetic analysis of recombinant UGTs was compared to that of total UGT activities in liver microsomes. Paracetamol was found to be an overlapping substrate of several UGTs. It shows higher affinity for HlugP1 and rat UGT1A1 (apparent Km values of 2 and 3 mM, respectively) than for HlugP4 (Km = 50 mM) and other UGTs present in liver microsomes (Km values of > 12 mM). Glucuronidation of paracetamol with HlugP1 contrasts with that of 6-hydroxychrysene and of 4-methylumbelliferone, which are conjugated with higher affinity by HlugP4 than by HlugP1. Due to the wide tissue distribution of rat UGT1A1, paracetamol glucuronidation was also investigated in extrahepatic rat and human tissues. Paracetamol UGT activity was present and inducible by 2,3,7,8-tetrachlorodibenzo-p-dioxin in rat kidney, lung and spleen. It was also detected in human kidney. A selective cDNA probe for exon 1 of HlugP1 cross-reacted with mRNA from both human liver and kidney. The results demonstrate that paracetamol is conjugated by HlugP1 and its rat orthologue UGT1A1 with higher affinity than by HlugP4 and other UGTs.
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Affiliation(s)
- K W Bock
- Institute of Toxicology, University of Tübingen, Germany
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27
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Kokwaro GO, Glazier AP, Ward SA, Breckenridge AM, Edwards G. Effect of malaria infection and endotoxin-induced fever on phenacetin O-deethylation by rat liver microsomes. Biochem Pharmacol 1993; 45:1235-41. [PMID: 8466544 DOI: 10.1016/0006-2952(93)90275-2] [Citation(s) in RCA: 20] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/30/2023]
Abstract
We have investigated the effect of malaria infection with the rodent parasite Plasmodium berghei and fever induced by Escherichia coli endotoxin on the metabolism of phenacetin to paracetamol by rat liver microsomes from young (4 weeks old) male Wistar rats (N = 5 in control and fever groups; N = 10 in malaria-infected group). Following determination of % parasitaemia, the malaria-infected group was divided into a low parasitaemia subgroup (N = 5; mean % parasitaemia = 9.87 +/- 2.6) and a high parasitaemia subgroup (N = 5; mean % parasitaemia = 36.6 +/- 8.1). The control group received normal saline. Total microsomal protein was not significantly affected by fever or malaria infection while cytochrome P450 levels were reduced by approximately 50% in the high parasitaemia subgroup, 20% in the low parasitaemia subgroup and 20% in the endotoxin-treated group. Phenacetin-O-deethylation kinetics were biphasic in both control and malaria-infected rats, but monophasic in endotoxin-treated rats. Total apparent intrinsic clearance (CL(int),total; calculated as Vmax/Km; Vmax is maximum velocity, Km is Michaelis constant) of phenacetin was reduced approximately 6-fold in low parasitaemia, 30-fold in high parasitaemia and 35-fold in fever. There was a poor correlation between CL(int),total and % parasitaemia (r = -0.6). However, log CL(int),total correlated inversely with % parasitaemia (r = -0.9), suggesting that Cl(int),total decreased exponentially with an increase in % parasitaemia. Phenacetin O-deethylation is a marker for cytochrome P4501A2 activity and the results of the present study suggest that both malaria infection and fever might specifically reduce P4501A2 activity in the rat.
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Affiliation(s)
- G O Kokwaro
- Department of Pharmacology and Therapeutics, University of Liverpool, U.K
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28
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von Moltke LL, Manis M, Harmatz JS, Poorman R, Greenblatt DJ. Inhibition of acetaminophen and lorazepam glucuronidation in vitro by probenecid. Biopharm Drug Dispos 1993; 14:119-30. [PMID: 8453022 DOI: 10.1002/bdd.2510140204] [Citation(s) in RCA: 21] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/30/2023]
Abstract
The effect of probenecid on glucuronidation of acetaminophen and lorazepam in hepatic microsomes from various species was studied to see if in vitro results were consistent with previous in vivo observations. Mouse, rat, and human microsomes were incubated with acetaminophen and probenecid while monkey microsomes were incubated with lorazepam and probenecid. Glucuronidation rates in all species varied with substrate, protein, and detergent concentrations. Mice exhibited faster rates of glucuronidation than rats or humans. All species showed inhibition of glucuronidation of acetaminophen or lorazepam when probenecid was added. Analysis suggested competitive inhibition. Thus, in vitro studies support in vivo results and confirm that the inhibition takes place at the hepatic level.
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Affiliation(s)
- L L von Moltke
- Division of Clinical Pharmacology, Tufts University School of Medicine, Boston, Massachusetts 02111
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29
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Ismail S, Back DJ, Edwards G. The effect of malaria infection on 3'-azido-3'-deoxythymidine and paracetamol glucuronidation in rat liver microsomes. Biochem Pharmacol 1992; 44:1879-82. [PMID: 1449539 DOI: 10.1016/0006-2952(92)90084-v] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/27/2022]
Abstract
The effect of malaria infection on UDP-glucuronosyltransferase (UDPGT) activity was investigated in rat liver microsomes using 3'-azido-3'-deoxythymidine and paracetamol. The Michaelis-Menten parameters, Km and Vmax were calculated and intrinsic clearance values were estimated for normal and infected livers. The results show that malaria infection alters the activity of UDPGT.
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Affiliation(s)
- S Ismail
- Department of Pharmacology and Therapeutics, University of Liverpool, U.K
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30
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Lear L, Nation RL, Stupans I. Influence of morphine concentration on detergent activation of rat liver morphine-UDP-glucuronosyltransferase. Biochem Pharmacol 1991; 42 Suppl:S55-60. [PMID: 1768286 DOI: 10.1016/0006-2952(91)90392-i] [Citation(s) in RCA: 15] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/28/2022]
Abstract
The effect of two detergents, Triton X-100 and Brij 58, on the production rate of morphine-3-glucuronide by rat hepatic microsomes has been investigated over a range of detergent and substrate concentrations, using a specific HPLC assay. Activation of morphine-UDP-glucuronosyltransferase (morphine-UDPGT) by Triton X-100 was more complex than that shown by Brij 58. At the optimal concentration of Triton X-100 (0.1-0.125 mg Triton X-100/mg microsomal protein), relative metabolic activity (activity of morphine-UDPGT in the activated state/activity of morphine-UDPGT in the native state; RMA) was 0.9, 1.3 and 2.5 at morphine concentrations of 0.05, 0.5 and 2.5 mM, respectively. Analysis of results from six individual rats in the native and maximally activated state (0.125 mg Triton X-100/mg microsomal protein) showed that RMA was highly dependent upon substrate concentration (P less than 0.0001). Activation produced by the optimal concentration of Brij 58 (0.15 mg Brij 58/mg microsomal protein) was also dependent upon substrate concentration with values for RMA of 3.3, 6.4 and 9.3 at morphine concentrations of 0.05, 0.5 and 2.5 mM, respectively. Analysis of kinetic data is complicated by substrate concentration-dependent detergent activation. It is proposed that factors contributing to substrate concentration-dependent variable activation may include micellar solubilization of substrate by detergent and/or the presence of at least two enzyme forms capable of glucuronidating morphine with differential effects of detergents on these forms.
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Affiliation(s)
- L Lear
- School of Pharmacy, University of South Australia, Adelaide
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Somogyi A, Bochner F, Chen ZR. Lack of effect of paracetamol on the pharmacokinetics and metabolism of codeine in man. Eur J Clin Pharmacol 1991; 41:379-82. [PMID: 1804656 DOI: 10.1007/bf00314972] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/28/2022]
Abstract
Plasma and urine concentrations of codeine and its measurable metabolites were determined by HPLC in six healthy subjects after a single 30 mg oral dose of codeine either alone or after 7 doses of 1 g paracetamol 8 hourly. After codeine alone, the t1/2 (h), AUC (mumol.l-1.h) and CLR (ml.min-1) for codeine were 2.2, 0.81, and 252 respectively. These were not significantly altered by paracetamol: 2.2, 0.84, and 291 respectively. For codeine-6-glucuronide the values were 2.4, 22.0, and 29.7 respectively. These were not significantly different from those after codeine plus paracetamol: 2.4, 21.9, and 39.6. There were no significant differences between the two treatments in the apparent partial clearances (ml.min-1) of codeine to morphine (88 codeine alone, 70 codeine plus paracetamol), to norcodeine (71 codeine alone, 88 codeine plus paracetamol), and to codeine-6-glucuronide (820 codeine alone, 1022 codeine plus paracetamol). The urinary excretion of codeine-6-glucuronide, morphine, norcodeine, and codeine were not significantly different between the two treatments.
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Affiliation(s)
- A Somogyi
- Department of Clinical Pharmacology, Royal Adelaide Hospital, Australia
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Miners JO, Lillywhite KJ. Assessment of the drug inhibitor specificity of the human liver 4-methylumbelliferone UDP-glucuronosyltransferase activity. Biochem Pharmacol 1991; 41:838-41. [PMID: 1900159 DOI: 10.1016/0006-2952(91)90090-r] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/29/2022]
Abstract
The data suggest that the 4MU-UDPGT activity of human liver microsomes probably contributes to the glucuronidation of a limited number of clinically used drugs. However, confirmation of this ultimately requires studies to be performed with purified isozymes, cDNAs expressed in cell culture, or specific inhibitory antibodies.
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Affiliation(s)
- J O Miners
- Department of Clinical Pharmacology, Flinders Medical Centre, Bedford Park, Adelaide, Australia
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Abstract
Glucuronidation is a major metabolic pathway for a large number of drugs in humans. Conjugation of drugs and other chemicals with glucuronic acid is catalyzed by the multigene UDP-glucuronosyltransferase family. It is believed that a number (unspecified at present) of glucuronosyltransferase isozymes, which probably differ in terms of substrate specificity and regulation, contribute to drug glucuronidation. Factors known to influence the pharmacokinetics of glucuronidated drugs in man, presumably via an effect on specific glucuronosyltransferases, include age (especially the neonatal period), cigarette smoking, diet, certain disease states, coadministered drugs, ethnicity, genetics and hormonal effects.
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Affiliation(s)
- J O Miners
- Department of Clinical Pharmacology, Flinders Medical Centre, Adelaide, South Australia
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