Preparation of glucuronides using liver microsomes and their characterization by 1D/2D NMR spectroscopy and mass spectrometry: Application to fentanyl metabolites

A simple, low-cost method for preparing glucuronic acid-conjugated metabolites was developed using fentanyl, a potent synthetic opioid, as a model drug. Five glucuronic acid-conjugated metabolites of fentanyl were measured in the culture medium of fresh human hepatocytes incubated with fentanyl. These glucuronides were also formed by incubation of their corresponding substrates (e.g., 4'-hydroxy-fentanyl and β-hydroxy-fentanyl) with uridine 5'-diphosphoglucuronic acid and human liver microsomes (HLM). Experiments using liver microsomes of several animals revealed that significant species differences exist in the glucuronide formation patterns; fentanyl glucuronide was only formed in HLM, and 4'-hydroxy-fentanyl glucuronide was formed much more in rat liver microsomes (RLM) than HLM and dog liver microsomes. Furthermore, surprisingly, HLM and RLM showed opposite substrate selectivity for the enantiomers of β-hydroxy-fentanyl. Submilligram amounts of three of these metabolites, namely, 4'-hydroxy-fentanyl glucuronide and two glucuronides of β-hydroxy-fentanyl, were prepared by using HLM or RLM. The products were readily purified with a reversed-phase/anion-exchange mixed-mode solid-phase extraction cartridge, and then, their chemical structures were confirmed by 1D/2D nuclear magnetic resonance (NMR) spectroscopy and mass spectrometry data. In addition, the products were quantitated by quantitative NMR, and the yields were 3.6-69%.

A critical examination of human data for the biological activity of quercetin and its phase-2 conjugates

This critical review examines evidence for beneficial effects of quercetin phase-2 conjugates from clinical intervention studies, volunteer feeding trials, and in vitro work. Plasma concentrations of quercetin-3-O-glucuronide (Q3G) and 3'-methylquercetin-3-O-glucuronide (3'MQ3G) after supplementation may produce beneficial effects in macrophages and endothelial cells, respectively, especially if endogenous deglucuronidation occurs, and lower blood uric acid concentration via quercetin-3'-O-sulfate (Q3'S). Unsupplemented diets produce much lower concentrations (<50 nmol/l) rarely investigated in vitro. At 10 nmol/l, Q3'S and Q3G stimulate or suppress, respectively, angiogenesis in endothelial cells. Statistically significant effects have been reported at 100 nmol/l in breast cancer cells (Q3G), primary neuron cultures (Q3G), lymphocytes (Q3G and3'MQ3G) and HUVECs (QG/QS mixture), but it is unclear whether these translate to a health benefit in vivo. More sensitive and more precise methods to measure clinically significant endpoints are required before a conclusion can be drawn regarding effects at normal dietary concentrations. Future requirements include better understanding of inter-individual and temporal variation in plasma quercetin phase-2 conjugates, their mechanisms of action including deglucuronidation and desulfation both in vitro and in vivo, tissue accumulation and washout, as well as potential for synergy or antagonism with other quercetin metabolites and metabolites of other dietary phytochemicals.

Enzymatic Synthesis of α-Glucosyl-Baicalin through Transglucosylation via Cyclodextrin Glucanotransferase in Water

Baicalin is a biologically active flavone glucuronide with poor water solubility that can be enhanced via glucosylation. In this study, the transglucosylation of baicalin was successfully achieved with CGTases from Thermoanaerobacter sp. and Bacillus macerans using α-cyclodextrin as a glucosyl donor. The synthesis of baicalin glucosides was optimized with CGTase from Thermoanaerobacter sp. Enzymatically modified baicalin derivatives were α-glucosylated with 1 to 17 glucose moieties. The two main glucosides were identified as Baicalein-7-O-α-D-Glucuronidyl-(1→4')-O-α-D-Glucopyranoside (BG₁) and Baicalein-7-O-α-D-Glucuronidyl-(1→4')-O-α-D-Maltoside (BG₂), thereby confirming recent findings reporting that glucuronyl groups are acceptors of this CGTase. Optimized conditions allowed for the attainment of yields above 85% (with a total glucoside content higher than 30 mM). BG₁ and BG₂ were purified via centrifugal partition chromatography after an enrichment through deglucosylation with amyloglucosidase. Transglucosylation increased the water solubility of BG₁ by a factor of 188 in comparison to that of baicalin (molar concentrations), while the same value for BG₂ was increased by a factor of 320. Finally, BG₁ and BG₂ were evaluated using antioxidant and anti-glycation assays. Both glucosides presented antioxidant and anti-glycation properties in the same order of magnitude as that of baicalin, thereby indicating their potential biological activity.

Oxyresveratrol and Gnetol Glucuronide Metabolites: Chemical Production, Structural Identification, Metabolism by Human and Rat Liver Fractions, and In Vitro Anti-inflammatory Properties

Stilbene metabolites are attracting great interest because many of them exhibit similar or even stronger biological effects than their parent compounds. Furthermore, the metabolized forms are predominant in biological fluids; therefore, their study is highly relevant. After hemisynthesis production, isolation, and structural elucidation, three glucuronide metabolites for oxyresveratrol (ORV) were formed: trans-ORV-4'-O-glucuronide, trans-ORV-3-O-glucuronide, and trans-ORV-2'-O-glucuronide. In addition, two glucuronide metabolites were obtained for gnetol (GN): trans-GN-2'-O-glucuronide and trans-GN-3-O-glucuronide. When the metabolism of ORV and GN is studied in vitro by human and rat hepatic enzymes, four of the five hemisynthesized compounds were identified and quantified. Human enzymes glucuronidated preferably at the C-2' position, whereas rat enzymes do so at the C-3 position. In view of these kinetic findings, rat enzymes have a stronger metabolic capacity than human enzymes. Finally, ORV, GN, and their glucuronide metabolites (mainly at the C-3 position) decreased nitric oxide, reactive oxygen species, interleukin 1β, and tumor necrosis factor α production in lipopolysaccharide-stimulated macrophages.

Investigation of buprenorphine-related deaths using urinary metabolite concentrations

Quantitative analysis of postmortem urine, instead of blood, for buprenorphine and metabolites may provide additional evidence for the diagnosis of fatal buprenorphine poisoning. In this study, 247 autopsy urine samples, previously testing positive for buprenorphine or norbuprenorphine, were quantitatively reanalysed with a recently developed liquid chromatography-tandem mass spectrometry (LC-MS/MS) method for unconjugated buprenorphine (BUP), norbuprenorphine (NBUP), naloxone (NAL), and their respective conjugated metabolites, buprenorphine glucuronide (BUPG), norbuprenorphine glucuronide (NBUPG), and naloxone glucuronide (NALG). The cases were divided, according to medical examiners' decision, to buprenorphine poisonings and other causes of death. The groups were compared for urinary concentrations and metabolite concentration ratios of the six analytes. All median concentrations were higher in the buprenorphine poisoning group. The median concentration of BUPG was significantly higher and the median metabolite ratios NBUP/BUP, NBUPG/BUPG, and NBUPtotal/BUPtotal were significantly lower in poisonings than in other causes of death. Naloxone-related concentrations and ratios were not significantly different between the groups.

Stereoselective Covalent Adduct Formation of Acyl Glucuronide Metabolite of Nonsteroidal Anti-Inflammatory Drugs with UDP-Glucuronosyltransferase

A reactive metabolite of nonsteroidal anti-inflammatory drugs (NSAIDs), acyl-β-D-glucuronide (AG), covalently binds to endogenous proteins. The covalent adduct formation of NSAIDs-AG may lead to the dysfunction of target proteins. Therefore, it is important to clarify the detailed characterization of the formation of covalent protein adducts of NSAID-AG. UDP-glucuronosyltransferase (UGT) catalyzes the conversion of NSAIDs to NSAIDs-AG. The aim of this study was to perform a quantitative analysis of the covalent adduct formation of NSAIDs-AG with UGT. Diclofenac-AG and ketoprofen-AG formed covalent adducts with organelle proteins. Next, the number of covalent adducts formed between NSAIDs-AG and UGT isoforms (UGT1A1, UGT1A9, UGT2B4, and UGT2B9) was determined. The capacity of diclofenac-AG to form covalent adducts with UGT1A9 or UGT2B7 was approximately 10 times higher than that of mefenamic acid-AG. The amounts of covalent adducts of AG of propionic acid derivative NSAIDs with UGT2B were higher than those with UGT1A. Stereoselectivity was observed upon covalent binding to UGT. A significant negative correlation between the half-lives of NSAIDs-AG in phosphate buffers and the amount of covalent adduct with UGT2B7 was observed, suggesting the more labile NSAID-AG forms higher irreversible bindings to UGT. This report provides comprehensive information on the covalent adduct formation of NSAIDs-AGs with UGT.

Conjugated Metabolites of Hydroxytyrosol and Tyrosol Contribute to the Maintenance of Nitric Oxide Balance in Human Aortic Endothelial Cells at Physiologically Relevant Concentrations

Nitric oxide (NO) is an important signaling molecule involved in many pathophysiological processes. NO mediates vasodilation and blood flow in the arteries, and its action contributes to maintaining vascular homeostasis by inhibiting vascular smooth muscle contraction and growth, platelet aggregation, and leukocyte adhesion to the endothelium. Dietary antioxidants and their metabolites have been found to be directly and/or indirectly involved in the modulation of the intracellular signals that lead to the production of NO. The purpose of this study was to investigate the contribution of conjugated metabolites of hydroxytyrosol (HT) and tyrosol (TYR) to the release of NO at the vascular level, and the related mechanism of action, in comparison to their parental forms. Experiments were performed in human aortic endothelial cells (HAEC) to evaluate the superoxide production, the release of NO and production of cyclic guanosine monophosphate (cGMP), the activation of serine/threonine-protein kinase 1 (Akt1), and the activation state of endothelial nitric oxide synthase (eNOS). It was observed that the tested phenolic compounds enhanced NO and cGMP concentration, inhibiting its depletion caused by superoxide overproduction. Moreover, some of them enhanced the activation of Akt (TYR, HT metabolites) and eNOS (HT, HVA, TYR-S, HT-3S). Overall, the obtained data showed that these compounds promote NO production and availability, suggesting that HT and TYR conjugated metabolites may contribute to the effects of parental extra virgin olive oil (EVOO) phenolics in the prevention of cardiovascular diseases.

In Vitro and In Vivo Analysis of Ochratoxin A-Derived Glucuronides and Mercapturic Acids as Biomarkers of Exposure

Ochratoxin A (OTA) is a widespread food contaminant, with exposure estimated to range from 0.64 to 17.79 ng/kg body weight (bw) for average consumers and from 2.40 to 51.69 ng/kg bw per day for high consumers. Current exposure estimates are, however, associated with considerable uncertainty. While biomarker-based approaches may contribute to improved exposure assessment, there is yet insufficient data on urinary metabolites of OTA and their relation to external dose to allow reliable estimates of daily intake. This study was designed to assess potential species differences in phase II biotransformation in vitro and to establish a correlation between urinary OTA-derived glucuronides and mercapturic acids and external exposure in rats in vivo. In vitro analyses of OTA metabolism using the liver S9 of rats, humans, rabbits and minipigs confirmed formation of an OTA glucuronide but provided no evidence for the formation of OTA-derived mercapturic acids to support their use as biomarkers. Similarly, OTA-derived mercapturic acids were not detected in urine of rats repeatedly dosed with OTA, while indirect analysis using enzymatic hydrolysis of the urine samples prior to LC-MS/MS established a linear relationship between urinary glucuronide excretion and OTA exposure. These results support OTA-derived glucuronides but not mercapturic acids as metabolites suitable for biomonitoring.

A rapid ultra high performance liquid chromatography-tandem mass spectrometry method for the quantification of daidzein, its valine carbamate prodrug, and glucuronide in rat plasma samples: Comparison of the pharmacokinetic behavior of daidzine valine carbamate prodrugs

Two valine carbamate prodrugs of daidzein were designed to improve its bioavailability. To compare the pharmacokinetic behavior of these prodrugs with different protected phenolic hydroxyl groups of daidzein, a rapid and sensitive method for simultaneous quantification of daidzein, its valine carbamate prodrug, and daidzein-7-O-glucuronide in rat plasma was developed and validated in this study. The samples were processed using a fast one-step protein precipitation method with methanol added to 50 μL of plasma and were analyzed by ultra-high performance liquid chromatography with tandem mass spectrometry. To improve the selectivity, peak shape, and peak elution, several key factors, especially stationary phase and the composition of the mobile phase, were tested, and the analysis was performed using the Kinetex^® C18 column (100 × 2.1 mm, 2.6 μm) within only 2.6 min under optimal conditions. The established method exhibited good linearity over the concentration range of 2.0-1000 ng/mL for daidzein, and 8.0-4000 ng/mL for the prodrug and daidzein-7-O-glucuronide. The accuracy of the quality control samples was between 95.5 and 110.2% with satisfactory intra- and interday precision (relative standard deviation values < 10.85%), respectively. This sensitive, rapid, low-cost, and high-throughput method was successfully applied to compare the pharmacokinetic behavior of different daidzein carbamate prodrugs.

Synthetic Artificial Apoptosis-Inducing Receptor for On-Demand Deactivation of Engineered Cells

The design of a fully synthetic, chemical "apoptosis-inducing receptor" (AIR) molecule is reported that is anchored into the lipid bilayer of cells, is activated by the incoming biological input, and responds with the release of a secondary messenger-a highly potent toxin for cell killing. The AIR molecule has four elements, namely, an exofacial trigger group, a bilayer anchor, a toxin as a secondary messenger, and a self-immolative scaffold as a mechanism for signal transduction. Receptor installation into cells is established via a robust protocol with minimal cell handling. The synthetic receptor remains dormant in the engineered cells, but is effectively triggered externally by the addition of an activating biomolecule (enzyme) or in a mixed cell population through interaction with the surrounding cells. In 3D cell culture (spheroids), receptor activation is accessible for at least 5 days, which compares favorably with other state of the art receptor designs.

Stanozolol-N-glucuronide metabolites in human urine samples as suitable targets in terms of routine anti-doping analysis

The exogenous anabolic-androgenic steroid (AAS) stanozolol stays one of the most detected substances in professional sports. Its detection is a fundamental part of doping analysis, and the analysis of this steroid has been intensively investigated for a long time. This contribution to the detection of stanozolol doping describes for the first time the unambiguous proof for the existence of 17-epistanozolol-1'N-glucuronide and 17-epistanozolol-2'N-glucuronide in stanozolol-positive human urine samples due to the access to high-quality reference standards. Examination of excretion study samples shows large detection windows for the phase-II metabolites stanozolol-1'N-glucuronide and 17-epistanozolol-1'N-glucuronide up to 12 days and respectively up to almost 28 days. In addition, we present appropriate validation parameters for the analysis of these metabolites using a fully automatic method online solid-phase extraction (SPE) method already published before. Limits of identification (LOIs) as low as 100 pg/ml and other validation parameters like accuracy, precision, sensitivity, robustness, and linearity are given.

Association of NQO2 With UDP-Glucuronosyltransferases Reduces Menadione Toxicity in Neuroblastoma Cells

The balance between detoxification and toxicity is linked to enzymes of the drug metabolism Phase I (cytochrome P450 or oxidoreductases) and phase II conjugating enzymes (such as the UGTs). After the reduction of quinones, the product of the reaction, the quinols-if not conjugated-re-oxidizes spontaneously to form the substrate quinone with the concomitant production of the toxic reactive oxygen species (ROS). Herein, we documented the modulation of the toxicity of the quinone menadione on a genetically modified neuroblastoma model cell line that expresses both the quinone oxidoreductase 2 (NQO2, E.C. 1.10.5.1) alone or together with the conjugation enzyme UDP-glucuronosyltransferase (UGT1A6, E.C. 2.4.1.17), one of the two UGT isoenzymes capable to conjugate menadione. As previously shown, NQO2 enzymatic activity is concomitant to massive ROS production, as previously shown. The quantification of ROS produced by the menadione metabolism was probed by electron-paramagnetic resonance (EPR) on cell homogenates, while the production of superoxide was measured by liquid chromatography coupled to mass spectrometry (LC-MS) on intact cells. In addition, the dysregulation of the redox homeostasis upon the cell exposure to menadione was studied by fluorescence measurements. Both EPR and LCMS studies confirmed a significant increase in the ROS production in the NQO2 overexpressing cells due to the fast reduction of quinone into quinol that can re-oxidize to form superoxide radicals. However, the effect of NQO2 inhibition was drastically different between cells overexpressing only NQO2 vs. both NQO2 and UGT. Whereas NQO2 inhibition decreases the amount of superoxide in the first case by decreasing the amount of quinol formed, it increased the toxicity of menadione in the cells co-expressing both enzymes. Moreover, for the cells co-expressing QR2 and UGT the homeostasis dysregulation was lower in presence of menadione than for the its counterpart expressing only QR2. Those results confirmed that the cooperation of the two enzymes plays a fundamental role during the cells' detoxification process. The fluorescence measurements of the variation of redox homeostasis of each cell line and the detection of a glucuronide form of menadiol in the cells co-expressing NQO2 and UGT1A6 enzymes further confirmed our findings.

Nanozymes and Glucuronides: Glucuronidase, Esterase, and/or Transferase Activity

Nanozymes are fundamentally interesting catalysts that are investigated as alternatives to fragile protein-enzymes for applications in biotechnology, for prodrug activation, and use in biomedicine, as well as the catalysts that contributed to the Origin of Life. However, until now, nanozymes mostly have been documented to exhibit activity as red/ox catalysts, whereas examples of activity outside this broad class of reactions are very few. Herein, activity of nanozymes on glucuronide prodrugs is investigated, specifically focusing on the mechanism of prodrug conversion reactions. The main finding of this work is that nanozymes exhibit glucuronide-like activity, but also catalyze prodrug conversion via esterase-like mechanism and facilitate group transfer reactions.

Equine uridine diphospho-glucuronosyltransferase 1A1, 2A1, 2B4, 2B31: cDNA cloning, expression and initial characterization of morphine metabolism

OBJECTIVE

Uridine diphospho-glucuronosyltransferases (UGTs) are membrane-bound enzymes that catalyze the conjugation of glucuronic acid onto a diverse set of xenobiotics. Horses efficiently and extensively glucuronidate a number of xenobiotics, including opioids, making UGTs an important group of drug-metabolizing enzymes for the clearance of drugs. Recombinant enzymes have allowed researchers to characterize the metabolism of a variety of drugs. The primary objective was to clone, express and characterize equine UGTs using drugs characterized as UGT substrates in other species. A secondary objective was to characterize the in vitro metabolism of morphine in horses.

STUDY DESIGN

In vitro drug metabolism study using liver microsomes and recombinant enzyme systems.

ANIMALS

Liver microsomes and RNA from tissue collected from two Thoroughbred mares euthanized for other reasons.

METHODS

Based on homology to the human UGT2B7, four equine UGT variants were expressed: UGT1A1, UGT2A1, UGT2B31 and UGT2B4. cDNA sequences were cloned and resulting protein expressed in a baculovirus expression system. Functionality of the enzymes was assessed using 4-methylumbelliferone, testosterone, diclofenac and ketoprofen. Recombinant enzyme, control cells, equine liver microsomes and human UGT2B7 supersomes were then incubated with morphine. Concentrations of metabolites were measured using liquid chromatography-tandem mass spectrometry and enzyme kinetics determined.

RESULTS

4-Methylumbelliferone was glucuronidated by all expressed equine UGTs. Testosterone glucuronide was not produced by any of the expressed enzymes, and diclofenac glucuronide and ketoprofen glucuronide were produced by UG2A1 and UGT1A1, respectively. UGT2B31 metabolized morphine to morphine-3-glucuronide and low concentrations of morphine-6-glucuronide.

CONCLUSIONS AND CLINICAL RELEVANCE

This is the first successful expression of functional recombinant equine UGTs. UGT2B31 contributes to the glucuronidation of morphine; however, it is probably not the main metabolizing enzyme. These results warrant further investigation of equine UGTs, including expression of additional enzymes and further characterization of UGT2B31 as a contributor to morphine metabolism.

Incomplete Hydrolysis of Curcumin Conjugates by β-Glucuronidase: Detection of Complex Conjugates in Plasma

SCOPE

The diphenol curcumin from turmeric is rapidly metabolized into phase II conjugates following oral administration, resulting in negligible plasma concentration of the free compound, which is considered the bioactive form. Total plasma concentration of curcumin is often quantified after treatment with β-glucuronidase to hydrolyze curcumin-glucuronide, the most abundant conjugate in vivo. The efficiency of enzymatic hydrolysis has not been tested.

METHODS AND RESULTS

Using liquid chromatography-mass spectrometry (LC-MS) analyses the efficiency of β-glucuronidase and sulfatase from Helix pomatia is compared to hydrolyze curcumin conjugates in human and mouse plasma after oral administration of turmeric. Both β-glucuronidase and sulfatase completely hydrolyze curcumin-glucuronide. Unexpectedly, β-glucuronidase hydrolysis is incomplete, affording a large amount of curcumin-sulfate, whereas sulfatase hydrolyzed both glucuronide and sulfate conjugates. With sulfatase, the concentration of free curcumin is doubled in human and increased in mouse plasma compared to β-glucuronidase treatment. Incomplete hydrolysis by β-glucuronidase suggests the presence of mixed glucuronide-sulfate conjugates. LC-MS based searches detect diglucuronide, disulfate, and mixed sulfate-glucuronide and sulfate-diglucuronide conjugates in plasma that likely contribute to the increase of free curcumin upon sulfatase treatment.

CONCLUSION

β-Glucuronidase incompletely hydrolyzes complex sulfate-containing conjugates that appear to be major metabolites, resulting in an underestimation of the total plasma concentration of curcumin.

Formation of (2R)- and (2S)-8-Prenylnaringenin Glucuronides by Human UDP-Glucuronosyltransferases

Occurring in hops (Humulus lupulus) and beer as a racemic mixture, (2R,2S)-8-prenylnaringenin (8-PN) is a potent phytoestrogen in hop dietary supplements used by women as alternatives to conventional hormone therapy. With a half-life exceeding 20 h, 8-PN is excreted primarily as 8-PN-7-O-glucuronide or 8-PN-4'-O-glucuronide. Human liver microsomes and 11 recombinant human UDP-glucuronosyltransferases (UGTs) were used to catalyze the formation of the two oxygen-linked glucuronides of purified (2R)-8-PN and (2S)-8-PN, which were subsequently identified using mass spectrometry and nuclear magnetic resonance spectroscopy. Formation of (2R)- and (2S)-8-PN-7-O-glucuronides predominated over the 8-PN-4'-O-glucuronides except for intestinal UGT1A10, which formed more (2S)-8-PN-4'-O-glucuronide. (2R)-8-PN was a better substrate for all 11 UGTs except for UGT1A1, which formed more of both (2S)-8-PN glucuronides than (2R)-8-PN glucuronides. Although several UGTs conjugated both enantiomers of 8-PN, some conjugated just one enantiomer, suggesting that human phenotypic variation might affect the routes of metabolism of this chiral estrogenic constituent of hops.

Identification of equol-7-glucuronide-4'-sulfate, monoglucuronides and monosulfates in human plasma of 2 equol producers after administration of kinako by LC-ESI-MS

Equol is a product formed during the biotransformation of the naturally occurring isoflavone daidzein by intestinal bacteria. The role of equol in the prevention of several hormone-dependent diseases such as prostate cancer and osteoporosis as well as vasomotor symptoms has been extensively investigated. Equol primarily occurs in the form of major metabolites such as glucuronides and sulfates, while intact equol has been detected at only ca. 1% in human plasma. However, to date, conjugated metabolites have been evaluated by measuring the free equol obtained after selective enzymatic hydrolysis. Thus, the precise types of conjugates circulating in vivo and the position(s) of the conjugation sites on the equol skeleton have yet to be clarified. Our study describes the identification of polar equol metabolites in the plasma of 2 equol-producers obtained at 8 hours after consuming 50 g of kinako (approximately 37 mg of daidzein). The structural identification of these conjugated metabolites in plasma was performed by comparison to the LC-ESI-MS n and 1H-NMR spectral data of the corresponding chemically synthesized compounds. The results of the LC-ESI-MS/MS analysis indicated that the main conjugated metabolite in plasma was (S)-equol-7-glucuronide-4'-sulfate along with lower amounts of 7- and 4'-monoglucuronides as well as 7- and 4'-monosulfates.

Predictability of human pharmacokinetics of diisononyl phthalate (DINP) using chimeric mice with humanized liver

1. In order to investigate the pharmacokinetics of diisononyl phthalate (DINP) in humans, we administered [phenyl-U-¹⁴C]DINP at a dose of 50.0 mg/kg orally to chimeric mice (humanized-liver mice) in which the liver of TK-NOG mice (control mice) was replaced with human hepatocytes. 2. The plasma radioactivity concentrations peaked (18.0 and 59.9 µg equivalent of DINP/mL, respectively) at 2 h after administration in control and humanized-liver mice. Concentrations rose again at 8 h in controls, but not in humanized-liver mice. 3. The cumulative excretion rates in urine and feces, respectively, were 58.1% and 37.3% of the doses in controls up to 48 h, but were 86.0% and 7.7% in humanized-liver mice. 4. The main circulating metabolites in control and humanized-liver mice were monoisononyl phthalate (MINP) and the glucuronide of oxidized MINP, respectively. The urinary excretion ratio of the glucuronide of oxidized MINP in control mice was one-third of that in humanized-liver mice. 5. The present results suggested that the oxidation rates of the primary metabolite of DINP and their excretion routes to urine/feces were different for control and humanized-liver mice. Species differences in liver activities could be a determinant factor in the in vivo metabolism and disposition of diallyl phthalates such as DINP.

Simultaneous collection of the portal and superior vena cava blood in conscious rats defined that intestinal epithelium is the major site of glucuronidation, but not sulfation and methylation, of quercetin

Quercetin is a flavonoid with many physiological effects. Absorbed quercetin is rapidly conjugated in the intestinal epithelium and liver. Different positional isomers of quercetin conjugates have different physiological properties. However, the mechanisms of quercetin conjugation in the intestine are not fully clarified. We examined the regioselective quercetin conjugate formation in the intestine after oral administration of quercetin glycosides, by simultaneous sampling of blood from the portal vein and superior vena cava, and quantifying various positional isomers of quercetin glucuronides and sulfates in conscious rats. Concentrations of quercetin glucuronides were higher in blood from the portal vein than the superior vena cava, showing that glucuronidation mainly occurred in the intestine. Such differences were not observed for quercetin sulfates. Regioselectivity of the intestinal glucuronidation in quercetin hydroxyl groups were 7- >3'- >3- >4'-OH. Quercetin was mainly sulfated on 3'-OH at 30 min, but on 4'-OH at 240 min.

Inhibition of Methotrexate Uptake via Organic Anion Transporters OAT1 and OAT3 by Glucuronides of Nonsteroidal Anti-inflammatory Drugs

Combination therapy of non-steroidal anti-inflammatory drugs (NSAIDs) and methotrexate (MTX) sometimes triggers adverse effects, such as liver injury, renal failure, gastrointestinal disorders, and myelosuppression, owing to the reduction of MTX clearance. Previous reports have suggested that NSAIDs inhibit renal MTX uptake via organic anion transporters (OATs) and reduced folate transporter (RFC)-1 and efflux via multidrug resistance-associated proteins (MRPs). Recently, our laboratory found inhibitory effects of NSAIDs-glucuronide (NSAIDs-Glu), a major metabolite of NSAIDs, on MRP-mediated MTX transport as a new site of interaction between MTX and NSAIDs. However, it remains unclear that whether NSAIDs-Glu inhibit renal uptake of MTX. Therefore, the present study aimed to evaluate inhibitory effects of several NSAIDs-Glu (diclofenac, R- and S-ibuprofen, R- and S-flurbiprofen, and R- and S-naproxen) on human OAT1 and OAT3-mediated MTX transport. In this study, [³H]MTX uptake was observed by using human OAT1 and OAT3-overexpressing HEK293 cells in the presence or absence of NSAIDs-Glu. All examined NSAIDs-Glu exhibited concentration-dependent inhibitory effects on MTX uptake via OAT1 and OAT3. Our results indicated that NSAIDs-Glu are more potent (5- to 15-fold) inhibitors of OAT3 than OAT1. Moreover, stereoselective inhibitory effects of NSAIDs-Glu on OATs-mediated MTX uptake were not observed, unlike on MRPs-mediated transport. These findings suggest that inhibition of OAT1 and OAT3-mediated renal uptake of MTX by plasma NSAIDs-Glu may be one of the competitive sites underlying complex drug interaction between MTX and NSAIDs.

Glucuronidated Flavonoids in Neurological Protection: Structural Analysis and Approaches for Chemical and Biological Synthesis

Both plant and mammalian cells express glucuronosyltransferases that catalyze glucuronidation of polyphenols such as flavonoids and other small molecules. Oral administration of select polyphenolic compounds leads to the accumulation of the corresponding glucuronidated metabolites at μM and sub-μM concentrations in the brain, associated with amelioration of a range of neurological symptoms. Determining the mechanisms whereby botanical extracts impact cognitive wellbeing and psychological resiliency will require investigation of the modes of action of the brain-targeted metabolites. Unfortunately, many of these compounds are not commercially available. This article describes the latest approaches for the analysis and synthesis of glucuronidated flavonoids. Synthetic schemes include both standard organic synthesis, semisynthesis, enzymatic synthesis and use of synthetic biology utilizing heterologous enzymes in microbial platform organisms.

Concentration of Sulfate and Glucuronide Conjugates of Ritodrine in Twin Pregnancy

Ritodrine, a drug for the treatment of threatened premature labor, is a highly selective beta-2 agonist with the major metabolites of sulfate and glucuronide conjugates. This study investigated the continuous evaluation of the concentration of ritodrine conjugates in relation to the clinical course in twin pregnancy. The subjects were 9 twin-pregnancy mothers who delivered after receiving ritodrine treatment between April 2012 and December 2013. Serum ritodrine sulfate and glucuronide conjugates were deconjugated using their specific enzymes. Ritodrine concentration was measured by liquid chromatography-tandem mass spectrometry. The continuous infusion rate of ritodrine was 2.66±0.67 (0.8-3.54) µg/min/kg, and the average concentration of unchanged ritodrine was 118.8±33.2 (63.8-194.0) ng/mL. During the study period between week 32 and week 36 of gestation, the average ratio of unchanged ritodrine concentration and sulfate ritodrine conjugate concentration for weeks 32, 33, 34, 35, and 36 were 1.7, 1.9, 1.5, 1.7, and 1.7 not significant (N.S.), respectively. The average ratio of unchanged ritodrine concentration and glucuronide ritodrine conjugate concentration were 1.8, 2.2, 1.9, 1.8, and 2.1 (N.S.), respectively. No statistical difference was identified in the ratios of unchanged ritodrine concentration and sulfate or glucuronide ritodrine conjugate concentrations. Large individual differences were shown in the concentration of sulfate and glucuronide during the gestational period. No change in the ratio of the formation of ritodrine metabolites was identified as the gestational age progressed.

Use of liquid chromatography hybrid triple-quadrupole mass spectrometry for the detection of emodin metabolites in rat bile and urine

Emodin is the representative form of rhubarb, which is widely used in traditional Chinese medicine for the treatment of purgative, anti-inflammatory, antioxidative and antiviral, etc. Previous reports demonstrated that emodin glucuronide was the major metabolite in plasma. Owing to the extensive conjugation reactions of polyphenols, the aim of this study was to identify the metabolites of emodin in rat bile and urine. Neutral loss and precursor ion scan methods of triple-quadrupole mass spectrometer revealed 13 conjugated metabolites in rat bile and 22 metabolites in rat urine, which included four phase I and 18 phase II metabolites. The major metabolites in rat biosamples were emodin glucuronoconjugates. Moreover, rhein monoglucuronide, chrysophanol monoglucuronide and rhein sulfate were proposed for the first time after oral administration of emodin. Overall, liquid chromatography hybrid triple-quadrupole mass spectrometry analysis leads to the discovery of several novel emodin metabolites in rat bile and urine and underscores that conjugated with glucuronic acid is the main metabolic pathway.

Pharmacokinetic Characterization and Bioavailability of Strawberry Anthocyanins Relative to Meal Intake

Plasma strawberry anthocyanins were characterized in overweight (BMI: 26 ± 2 kg/m(2)) adults (n = 14) on the basis of meal timing. At each visit, subjects ingested three study drinks: two control and one strawberry drink. A strawberry drink was given at either 2 h before the breakfast meal (BM), with the meal (WM), or 2 h after the meal (AM), and control drinks were given at the alternative time points. Plasma anthocyanins and their metabolic conjugates were assessed hourly for 10 h using a triple-quadrupole liquid chromatography mass spectrometer. Maximum concentrations (Cmax), area under the curve (AUC), and bioavailability of pelargonidin-based anthocyanins determined from the main conjugated metabolite (pelargonidin glucuronide) were greater when a strawberry drink was consumed 2 h before the meal (BM) compared to consumption WM or AM (p < 0.05). Our results indicate that the timing of strawberry consumption relative to a meal impacts anthocyanin pharmacokinetic variables.

Hesperetin glucuronides induce adipocyte differentiation via activation and expression of peroxisome proliferator-activated receptor-γ

In previous reports, hesperidin, a flavonoid glucoside from citrus fruit, is hydrolyzed to hesperetin, an aglycone of hesperidin, and converted to the hesperetin glucuronides (H7-OG and H3'-OG) in vivo and depresses blood glucose levels. But there are no reports on the activity of hesperetin glucuronides. To determine the activity of hesperetin glucuronides, H7-OG and H3'-OG were synthesized and peroxisome proliferator-activated receptor-γ (PPARγ) agonist activity was observed at 250 μM. These glucuronides accelerated the differentiation of 3T3-L1 cells into adipocytes at 10 μM. Furthermore, H7-OG showed additive effects in reporter gene assays and caused noncompetitive reactions in time-resolved fluorescence resonance energy transfer assays with a thiazolidinedione derivative. Our results indicated that hesperetin glucuronides activated PPARγ, accelerated adipocyte differentiation.

β-Glucuronidase activity and mitochondrial dysfunction: the sites where flavonoid glucuronides act as anti-inflammatory agents

Epidemiological and experimental studies suggest that the consumption of flavonoid-rich diets decreases the risk of various chronic diseases such as cardiovascular diseases. Although studies on the bioavailability of flavonoids have been well-characterized, the tissue and cellular localizations underlying their biological mechanisms are largely unknown. The development and application of novel monoclonal antibodies revealed that macrophages could be the major target of dietary flavonoids in vivo. Using macrophage-like cell lines in vitro, we examined the molecular basis of the interaction between the macrophages and flavonoids, especially the glucuronide metabolites. We have found that extracellular β-glucuronidase secreted from macrophages is essential for the bioactivation of the glucuronide conjugates into the aglycone, and that the enzymatic activity, which requires an acidic pH, is promoted by the increased secretion of lactate in response to the mitochondrial dysfunction. This review describes our recent findings indicating the molecular mechanisms responsible for the anti-inflammatory activity of dietary flavonoids within the inflammation sites. We propose that the extracellular activity of β-glucuronidase associated with the status of the mitochondrial function in the target cells might be important biomarkers for the specific sites where the glucuronides of dietary flavonoids can act as anti-atherosclerotic and anti-inflammatory agents in vivo.

Quantitative determination of common urinary odorants and their glucuronide conjugates in human urine

Our previous study on the identification of common odorants and their conjugates in human urine demonstrated that this substance fraction is a little-understood but nonetheless a promising medium for analysis and diagnostics in this easily accessible physiological medium. Smell as an indicator for diseases, or volatile excretion in the course of dietary processes bares high potential for a series of physiological insights. Still, little is known today about the quantitative composition of odorous or volatile targets, as well as their non-volatile conjugates, both with regard to their common occurrence in urine of healthy subjects, as well as in that of individuals suffering from diseases or other physiological misbalancing. Accordingly, the aim of our study was to develop a highly sensitive and selective approach to determine the common quantitative composition of selected odorant markers in healthy human subjects, as well as their corresponding glucuronide conjugates. We used one- and two-dimensional high resolution gas chromatography-mass spectrometry in combination with stable isotope dilution assays to quantify commonly occurring and potent odorants in human urine. The studies were carried out on both native urine and on urine that had been treated by glucuronidase assays, with analysis of the liberated odor-active compounds using the same techniques. Analytical data are discussed with regard to their potential translation as future diagnostic tool.

Synthesis and stability study of a new major metabolite of γ-hydroxybutyric acid

γ-Hydroxybutanoic acid (GHB) is used as a date-rape drug, which renders the victims unconscious and defenceless. Intoxications are very difficult to detect for forensic scientists due to rapid metabolism to endogenous levels of GHB. We recently discovered a new major metabolite, 2, of GHB (1) that could potentially extend the analytical detection window for GHB intoxications. Herein we disclose synthetic procedures based on a Koenigs-Knorr glucuronidation approach that provides GHB glucuronide 2 and a deuterium-labelled analogue d 4-2 of high purity suitable for analytical chemistry. In addition, we have assessed the stability of GHB glucuronide 2 by mimicking the natural pH range for urine, which is of importance in the development of new analytical methods. Using NMR we show that GHB glucuronide 2 is highly stable towards aqueous hydrolysis within the pH range normally observed for urine even at elevated temperature.

Acetaminophen glucuronide and plasma glucose report identical estimates of gluconeogenesis and glycogenolysis for healthy and prediabetic subjects using the deuterated water method

Plasma glucose (2) H-enrichment in positions 5 ((2) H5) and 2 ((2) H2) from deuterated water ((2) H2 O) provides a measure of the gluconeogenic contribution to endogenous glucose production. Urinary glucuronide analysis can circumvent blood sampling but it is not known if glucuronide and glucose enrichments are equal. Thirteen subjects with impaired fasting glucose/impaired glucose tolerance and 11 subjects with normal fasting glucose and normal glucose tolerance ingested (2) H2 O to ∼0.5% body water and acetaminophen. Glucose and glucuronide (2) H5 and (2) H2 were measured by (2) H NMR spectroscopy of monoacetone glucose. For normal fasting glucose/normal glucose tolerance, (2) H5 was 0.23 ± 0.02% and 0.25 ± 0.02% for glucose and glucuronide, respectively, whereas (2) H2 was 0.47 ± 0.01% and 0.49 ± 0.02%, respectively. For impaired fasting glucose/impaired glucose tolerance, (2) H5 was 0.22 ± 0.01% and 0.26 ± 0.02% for glucose and glucuronide, respectively, whereas (2) H2 was 0.46 ± 0.01% and 0.49 ± 0.02%, respectively. The gluconeogenic contribution to endogenous glucose production measured from glucose and glucuronide were identical for both normal fasting glucose/normal glucose tolerance (48 ± 4 vs. 51 ± 3%) and impaired fasting glucose/impaired glucose tolerance (48 ± 2 vs. 53 ± 3%).

Examination of the pharmacokinetics of active ingredients of ginger in humans

Ginger extracts have been studied in various clinical trials for different indications. However, the pharmacokinetics of the ginger active constituents in human biological matrices is not well investigated. This study aims to develop a LC-MS/MS method for simultaneous measurement of 6-, 8-, and 10-gingerols and 6-shogaol and study their pharmacokinetics in human plasma and colon tissues. A sensitive LC-MS/MS method was established and validated with a low limit of quantification of 2-5 ng/mL. The intra- and inter-day accuracy ranged from -7.3% to 10.4% and from -9.4% to 9.8%, respectively. The intra- and inter-day precision ranged from 0.9% to 10.9% and from 2.0% to 12.4%, respectively. The glucuronide and sulfate metabolites of 6-, 8-, and 10-gingerols and 6-shogaol in plasma and colon tissues were quantified after hydrolysis with β-glucuronidase and sulfatase. After oral dosing of 2.0 g ginger extracts in human, free 10-gingerol and 6-shogaol were detected in plasma with peak concentrations (9.5 ± 2.2 and 13.6 ± 6.9 ng/mL, respectively) at 1 h after oral administration, but no free 6-gingerol and 8-gingerol were detected in plasma from 0.25 to 24 h. The peak concentrations of glucuronide metabolites of 6-, 8-, and 10-gingerols and 6-shogaol were 0.47 ± 0.31, 0.17 ± 0.14, 0.37 ± 0.19, and 0.73 ± 0.54 μg/mL at 1 h, respectively. The peak concentrations of the sulfate metabolites of 6-, 8-, and 10-gingerols and 6-shogaol were 0.28 ± 0.15, 0.027 ± 0.018, 0.018 ± 0.006, and 0.047 ± 0.035 μg/mL at 1 h, respectively. Very low concentrations (2-3 ng/mL) of 10-gingerol glucuronide and sulfate were found in colon tissues. Pharmacokinetic analysis showed that half-lives of these four analytes and their metabolites were 1-3 h in human plasma. No accumulation was observed for 6-, 8-, and 10-gingerols and 6-shogaol and their metabolites in both plasma and colon tissues after multiple daily dosing.

Inhibitory Effects of Conjugated Epicatechin Metabolites on Peroxynitrite-mediated Nitrotyrosine Formation

Previously, we identified four metabolites of (−)-epicatechin in blood and urine: (−)-epicatechin-3'-O-glucuronide (E3'G), 4'-O-methyl-(−)-epicatechin-3'-O-glucuronide (4'ME3'G), (−)-epicatechin-7-O-glucuronide (E7G), and 3'-O-methyl-(−)-epicatechin-7-O-glucuronide (3'ME7G) (Natsume et al. Free Radical Biol. Med. 34, 840-849, 2003). The aim of the current study was to compare the antioxidative activities of these metabolites with that of their parent compound. After oral administration of (−)-epicatechin, E3'G and 4'ME3'G were isolated from human urine, and E7G and 3'ME7G isolated from rat urine. We found that these compounds inhibited peroxynitrite-mediated tyrosine nitration, in the following order of potency: E3'G > (−)-epicatechin > E7G = 3'ME7G. = 4'ME3'G. These results demonstrate that the metabolites of (−)-epicatechin retain antioxidative activity on peroxynitrite-induced oxidative damages to some extent.

UGT2B10 genotype influences nicotine glucuronidation, oxidation, and consumption

BACKGROUND

Tobacco exposure is routinely assessed by quantifying nicotine metabolites in plasma or urine. On average, 80% of nicotine undergoes C-oxidation to cotinine. However, interindividual variation in nicotine glucuronidation is substantial, and glucuronidation accounts for from 0% to 40% of total nicotine metabolism. We report here the effect of a polymorphism in a UDP-glucuronsyltransferase, UGT2B10, on nicotine metabolism and consumption.

METHODS

Nicotine, cotinine, their N-glucuronide conjugates, and total trans-3'-hydroxycotinine were quantified in the urine (n = 327) and plasma (n = 115) of smokers. Urinary nicotine N-oxide was quantified in 105 smokers. Nicotine equivalents, the sum of nicotine and all major metabolites, were calculated for each smoker. The relationship of the UGT2B10 Asp67Tyr allele to nicotine equivalents, N-glucuronidation, and C-oxidation was determined.

RESULTS

Individuals heterozygous for the Asp67Tyr allele excreted less nicotine or cotinine as their glucuronide conjugates than did wild-type, resulting in a 60% lower ratio of cotinine glucuronide to cotinine, a 50% lower ratio of nicotine glucuronide to nicotine, and increased cotinine and trans-3'-hydroxycotinine. Nicotine equivalents, a robust biomarker of nicotine intake, were lower among Asp67Tyr heterozygotes compared with individuals without this allele: 58.2 (95% confidence interval, 48.9-68.2) versus 69.2 nmol/mL (95% confidence interval, 64.3-74.5).

CONCLUSIONS

Individuals heterozygous for UGT2B10 Asp67Tyr consume less nicotine than do wild-type smokers. This striking observation suggests that variations in nicotine N-glucuronidation, as reported for nicotine C-oxidation, may influence smoking behavior.

IMPACT

UGT2B10 genotype influences nicotine metabolism and should be taken into account when characterizing the role of nicotine metabolism on smoking.

Enzymes and inhibitors in neonicotinoid insecticide metabolism

Neonicotinoid insecticide metabolism involves considerable substrate specificity and regioselectivity of the relevant CYP450, aldehyde oxidase, and phase II enzymes. Human CYP450 recombinant enzymes carry out the following conversions: CYP3A4, 2C19, and 2B6 for thiamethoxam (TMX) to clothianidin (CLO); 3A4, 2C19, and 2A6 for CLO to desmethyl-CLO; 2C19 for TMX to desmethyl-TMX. Human liver aldehyde oxidase reduces the nitro substituent of CLO to nitroso much more rapidly than it does that of TMX. Imidacloprid (IMI), CLO, and several of their metabolites do not give detectable N-glucuronides but 5-hydroxy-IMI, 4,5-diol-IMI, and 4-hydroxythiacloprid are converted to O-glucuronides in vitro with mouse liver microsomes and UDP-glucuronic acid or in vivo in mice. Mouse liver cytosol with S-adenosylmethionine converts desmethyl-CLO to CLO but not desmethyl-TMX to TMX. Two organophosphorus CYP450 inhibitors partially block IMI, thiacloprid, and CLO metabolism in vivo in mice, elevating brain and liver levels of the parent compounds while reducing amounts of the hydroxylated metabolites.

Anti-tumour activity and toxicity of the new prodrug 9-aminocamptothecin glucuronide (9ACG) in mice

Cancer chemotherapy is limited by the modest therapeutic index of most antineoplastic drugs. Some glucuronide prodrugs may display selective anti-tumour activity against tumours that accumulate beta-glucuronidase. We examined the toxicity and anti-tumour activity of 9-aminocamptothecin glucuronide, a new glucuronide prodrug of 9-aminocamptothecin, to evaluate its potential clinical utility. 9-aminocamptothecin glucuronide was 25-60 times less toxic than 9-aminocamptothecin to five human cancer cell lines. Beta-glucuronidase activated 9-aminocamptothecin glucuronide to produce similar cell killing as 9-aminocamptothecin or topotecan. The in vivo toxicity of 9-aminocamptothecin glucuronide in BALB/c mice was dose-, route-, sex- and age-dependent. 9-aminocamptothecin glucuronide was significantly less toxic to female than to male mice but the difference decreased with age. 9-aminocamptothecin glucuronide and 9-aminocamptothecin produced similar inhibition (approximately 80%) of LS174T human colorectal carcinoma tumours. 9-aminocamptothecin glucuronide cured a high percentage of CL1-5 human lung cancer xenografts with efficacy that was similar to or greater than 9-aminocamptothecin, irinotecan and topotecan. The potent anti-tumour activity of 9-aminocamptothecin glucuronide suggests that this prodrug should be further evaluated for cancer treatment.

A fully human anti-Ep-CAM scFv-beta-glucuronidase fusion protein for selective chemotherapy with a glucuronide prodrug

Monoclonal antibodies against tumour-associated antigens could be useful to deliver enzymes selectively to the site of a tumour for activation of a non-toxic prodrug. A completely human fusion protein may be advantageous for repeated administration, as host immune responses may be avoided. We have constructed a fusion protein consisting of a human single chain Fv antibody, C28, against the epithelial cell adhesion molecule and the human enzyme beta-glucuronidase. The sequences encoding C28 and human enzyme beta-glucuronidase were joined by a sequence encoding a flexible linker, and were preceded by the IgGkappa signal sequence for secretion of the fusion protein. A CHO cell line was engineered to secrete C28-beta-glucuronidase fusion protein. Antibody specificity and enzyme activity were retained in the secreted fusion protein that had an apparent molecular mass of 100 kDa under denaturing conditions. The fusion protein was able to convert a non-toxic prodrug of doxorubicin, N-[4-doxorubicin-N-carbonyl(oxymethyl)phenyl]-O-beta-glucuronyl carbamate to doxorubicin, resulting in cytotoxicity. A bystander effect was demonstrated, as doxorubicin was detected in all cells after N-[4-doxorubicin-N-carbonyl(oxymethyl)phenyl]-O-beta-glucuronyl carbamate administration when only 10% of the cells expressed the fusion protein. This is the first fully human and functional fusion protein consisting of an scFv against epithelial cell adhesion molecule and human enzyme beta-glucuronidase for future use in tumour-specific activation of a non-toxic glucuronide prodrug.

A novel doxorubicin-glucuronide prodrug DOX-GA3 for tumour-selective chemotherapy: distribution and efficacy in experimental human ovarian cancer

The doxorubicin (DOX) prodrug N-[4-doxorubicin-N-carbonyl (oxymethyl) phenyl] O-beta-glucuronyl carbamate (DOX-GA3) was synthesised for specific activation by human beta-glucuronidase, which is released in necrotic areas of tumour lesions. This novel prodrug was completely activated to the parent drug by human beta-glucuronidase with V(max)= 25.0 micromol x min(-1) x mg(-1) and K(m) = 1100 microM. The pharmacokinetics and distribution of DOX-GA3 in nude mice bearing human ovarian cancer xenografts (OVCAR-3) were determined and compared with DOX. Administration of DOX at 8 mg x kg(-1) i.v. (maximum tolerated dose, MTD) to OVCAR-3-bearing mice resulted in a peak plasma concentration of the drug of 16.4 microM (t = 1 min). A 7.6-times lower peak plasma concentration of DOX was measured after injection of DOX-GA3 at 250 mg x kg(-1) i.v. (50% of MTD). In normal tissues the prodrug showed peak DOX concentrations that were up to 5-fold (heart) lower than those found after DOX administration. DOX-GA3 activation by beta-glucuronidase in the tumour yielded an almost 5-fold higher DOX peak concentration of 9.57 nmol x g(-1) (P< 0.05) than the peak concentration of only 2.14 nmol x g(-1) observed after DOX. As a consequence, the area under the curve of DOX calculated in tumour tissue after DOX-GA3 (13.1 micromol x min(-1) x g(-1)) was 10-fold higher than after DOX (1.31 micromol x min(-1) x g(-1)). The anti-tumour effects of DOX-GA3 and DOX were compared at equitoxic doses in OVCAR-3 xenografts at a mean tumour size of 125 mm(3). The prodrug given i.v. at 500 mg x kg(-1) weekly x 2 resulted in a maximum tumour growth inhibition of 87%, while the standard treatment with DOX at a dose of 8 mg x kg(-1) i.v. weekly x 2 resulted in a maximum tumour growth inhibition of only 56%. Treatment with DOX-GA3 was also given to mice with larger tumours containing more necrosis. For tumours with a mean size of 400 mm(3) the specific growth delay by DOX-GA3 increased from 2.7 to 3.9. Our data indicate that DOX-GA3 is more effective than DOX and suggest that the prodrug will be specifically advantageous for treatment of advanced disease.

Morphine-6 beta-glucuronide has a higher efficacy than morphine as a mu-opioid receptor agonist in the rat locus coeruleus

1. The pharmacological properties of the active morphine metabolite, morphine-6 beta-D-glucuronide (M6G), and the parent compound were compared in rat locus coeruleus neurons by electrophysiological recording in brain slices. 2. M6G and morphine activated potassium currents in voltage clamped neurons, which were blocked by the opioid receptor antagonist naloxone. 3. Both M6G and morphine behaved as partial agonists that produced maximal responses smaller than the system maximum, which was measured using [Met(5)]-enkephalin. M6G produced a larger maximal response (78%) than morphine (62%), which we estimated was due to a 2 - 4 fold difference in the relative efficacy of the agonists. 4. 3-O-methoxynaltrexone, which has been reported to behave as a selective antagonist of a M6G preferring receptor, was equally effective at blocking currents produced by M6G and the selective mu-opioid receptor agonist DAMGO. 5. M6G currents were occluded by a prior application of morphine, and were reduced when mu-opioid receptors were desensitized by using [Met(5)]-enkephalin. 6. Morphine-3 beta-D-glucuronide did not affect action potential firing or membrane currents in locus coeruleus neurons and had no effect on currents produced by M6G. 7. These results show that the relative efficacy of M6G is higher than morphine in locus coeruleus neurons, contrary to what has been shown using mu-opioid receptors expressed in cell clones.