High-performance liquid chromatographic assay for acetaminophen glucuronide in human liver microsomes

Characterisation of UDP-glucuronosyltransferase activity in sea turtle Chelonia mydas

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 V_max (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.

Fentanyl Assay Derived from Intermolecular Interaction-Enabled Small Molecule Recognition (iMSR) with Differential Impedance Analysis for Point-of-Care Testing

Rapid and effective differentiation and quantification of a small molecule drug, such as fentanyl, in bodily fluids are major challenges for diagnosis and personal medication. However, the current toxicology methods used to measure drug concentration and metabolites require laboratory-based testing, which is not an efficient or cost-effective way to treat patients in a timely manner. Here, we show an assay for monitoring fentanyl levels by combining the intermolecular interaction-enabled small molecule recognition (iMSR) with differential impedance analysis of conjugated polymers. The differential interactions with the designed anchor interface were transduced through the perturbance of the electric status of the flexible conducting polymer. This assay showed excellent fentanyl selectivity against common interferences, as well as in variable body fluids through either testing strips or skin patches. Directly using the patient blood, the sensor provided 1%-5% of the average deviation compared to the "gold" standard method LC-MS results in the medically relevant fentanyl range of 20-90 nM. The superior sensing properties, in conjunction with mechanical flexibility and compatibility, enabled point-of-care detection and provided a promising avenue for applications beyond the scope of biomarker detection.

Evidence-based strategies for the characterisation of human drug and chemical glucuronidation in vitro and UDP-glucuronosyltransferase reaction phenotyping

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.

Degradation of Paracetamol and Its Oxidation Products in Surface Water by Electrochemical Oxidation

Paracetamol and its toxic transformation products have been found in surface water, wastewater, and drinking water. Effective methods to degrade these products must be found to reduce their detrimental effects on microorganisms in aquatic systems and minimize the concern on human health. Thus, this study looked into the electrochemical oxidation of paracetamol and its oxidation products on surface water, and results were compared with those of paracetamol synthetic solution oxidation. Degradation of paracetamol was conducted using a stainless steel electrode cell, a pH of 3, and direct current densities of 5.7 mA/cm² (6 V) and 7.6 mA/cm² (12 V). For both current densities applied, the pharmaceutical and its oxidation products observed by high-performance liquid chromatography with diode-array detection (HPLC-DAD) at 254 nm were totally degraded. Faster degradation of paracetamol was observed at a higher current density. Indeed, 95% of paracetamol was oxidized in only 15 min at the 7.6 mA/cm² current density. In comparison to the paracetamol synthetic solution's oxidation, degradation of paracetamol was faster in the surface water than the synthetic solution, at 5.7 mA/cm². Nevertheless, at 7.6 mA/cm², total degradation of paracetamol in surface water was delayed up to 40 min, versus 7.5 min in the synthetic solution. Three oxidation products, observed by HPLC-DAD at 254 nm, were fully oxidized. In comparison with the paracetamol synthetic solution, degradation of the oxidation products in surface water was faster than in synthetic solutions for both current densities. Furthermore, the 7.6 mA/cm² current density resulted in faster degradation of oxidation products. Results obtained from this work are promising for practical applications because short reaction times and low current densities are needed for degradation of paracetamol and its oxidation products. These densities can be potentially supplied by photovoltaic cells.

Point-of-Care Determination of Acetaminophen Levels with Multi-Hydrogen Bond Manipulated Single-Molecule Recognition (eMuHSiR)

This work aims to face the challenge of monitoring small molecule drugs accurately and rapidly for point-of-care (POC) diagnosis in current clinical settings. Overdose of acetaminophen (AP), a commonly used over the counter (OTC) analgesic drug, has been determined to be a major cause of acute liver failure in the US and the UK. However, there is no rapid and accurate detection method available for this drug in the emergency room. The present study examined an AP sensing strategy that relies on a previously unexplored strong interaction between AP and the arginine (Arg) molecule. It was found that as many as 4 hydrogen bonds can be formed between one Arg molecule and one AP molecule. By taking advantages of this structural selectivity and high tenability of hydrogen bonds, Arg, immobilized on a graphene surface via electrostatic interactions, was utilized to structurally capture AP. Interestingly, bonded AP still remained the perfect electrochemical activities. The extent of Arg-AP bonds was quantified using a newly designed electrochemical (EC) sensor. To verify the feasibility of this novel assay, based on multihydrogen bond manipulated single-molecule recognition (eMuHSiR), both pharmaceutical and serum sample were examined. In commercial tablet measurement, no significant difference was seen between the results of eMuHSiR and other standard methods. For measuring AP concentration in the mice blood, the substances in serum, such as sugars and fats, would not bring any interference to the eMuHSiR in a wide concentration range. This eMuHSiR method opens the way for future development of small molecule detection for the POC testing.

Preparation of T-2-glucoronide with Rat Hepatic Microsomes and Its Use along with T-2 for Activation of the JAK/STAT Signaling Pathway in RAW264.7 Cells

T-2 toxin (T-2), one of the most toxic trichothecene A-type mycotoxins, is biotransformed in animal tissues to modified T-2s (mT-2s) including T-2-glucuronide (T-2-GlcA). In this study, the optimal conditions for T-2-GlcA synthesis were established, and the JAK/STAT pathway in RAW264.7 cells was used to study the toxicity of T-2-GlcA. Because many mT-2 standards are not readily available, optimal conditions for T-2-GlcA synthesis in vitro were established by incubating T-2 with rat liver microsomes, UDPGA, and 0.2% Triton X-100 for 90 min. qRT-PCR and Western blot results showed 21- and 760-fold increases in IL-6 mRNA expression induced by T-2-GlcA and T-2, respectively. Similar differences were observed in JAK3, SOCS2/3, and CIS mRNA expression. T-2-GlcA induced a dose-responsive decrease in STAT1 mRNA expression, whereas the result with T-2 was the opposite. Moreover, the phosphorylation of STAT3 induced by T-2-GlcA was higher than that by T-2, whereas the phosphorylation of STAT1 was to the contrary. Overall, the results show that T-2-GlcA was somewhat toxic, but activation of the JAK/STAT pathway in RAW264.7 was higher by T-2.

Alamethicin for using in bioavailability studies? - Re-evaluation of its effect

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.

Enzyme kinetics of uridine diphosphate glucuronosyltransferases (UGTs)

Glucuronidation, catalyzed by uridine diphosphate glucuronosyltransferases (UGTs), is an important process for the metabolism and clearance of many lipophilic chemicals, including drugs, environmental chemicals, and endogenous compounds. Glucuronidation is a bi-substrate reaction that requires the aglycone and a cofactor, UDPGA. Accumulating evidence suggests that the bi-substrate reaction follows a compulsory-order ternary mechanism. To simplify the kinetic modelling of glucuronidation reactions in vitro, UDPGA is usually added to incubations in large excess. Many factors have been shown to influence UGT activity and kinetics in vitro, and these must be accounted for in experimental design and data interpretation. Assessing drug-drug interactions (DDIs) involving UGT inhibition remains challenging. However, the increasing availability of UGT enzyme-specific substrate and inhibitor "probes" provides the prospect for more reliable reaction phenotyping and assessment of DDI potential. Although extrapolation of the in vitro intrinsic clearance of a glucuronidated drug often under-predicts in vivo clearance, careful selection of in vitro experimental conditions and inclusion of extrahepatic glucuronidation may improve the predictivity of in vitro-in vivo extrapolation (IVIVE).

UDP-glucuronosyltransferase expression in mouse liver is increased in obesity- and fasting-induced steatosis

UDP-glucuronosyltransferases (Ugt) catalyze phase II conjugation reactions with glucuronic acid, which enhances chemical polarity and the elimination from the body. Few studies have addressed whether Ugt expression and activity are affected by liver disease, such as steatosis. The purpose of this study was to determine whether steatosis induced by obesity or fasting could affect liver Ugt mRNA expression and activity. Male C57BL/6J and Lep(ob/ob) (ob/ob) mice were fed ad libitum or food was withheld for 24 h. In steatotic livers of ob/ob mice, Ugt1a1, -1a6, -1a9, -2a3, -3a1, and -3a2 mRNA expression increased. Fasting, which also induced steatosis, increased hepatic Ugt1a1, -1a6, -1a7, -1a9, -2b1, -2b5, -2a3, -3a1, and -3a2 mRNA expression in mouse liver. Likewise, acetaminophen glucuronidation increased by 47% in hepatic microsomes from ob/ob mice compared with that in C57BL/6J mice, but not after fasting. In both steatosis models, Ugt induction was accompanied by increased aryl hydrocarbon receptor, constitutive androstane receptor (CAR), peroxisome proliferator-activated receptor (PPAR)-α, pregnane X receptor, nuclear factor (erythroid-derived 2)-like 2 (Nrf2), and peroxisome proliferator-activated receptor-γ coactivator-1α mRNA expression. In addition, fasting increased CAR, PPAR, and Nrf2 binding activity. The work points to hepatic triglyceride concentrations corresponding with nuclear receptor and Ugt expression. The findings indicate that steatosis significantly alters hepatic Ugt expression and activity, which could have a significant impact on determining circulating hormone levels, drug efficacy, and environmental chemical clearance.

Inhibition of paracetamol glucuronidation by tyrosine kinase inhibitors

WHAT IS ALREADY KNOWN ABOUT THIS SUBJECT

• Clinical cases reported that fatal acute liver failure occurred when paracetamol (acetaminophen) was co-administrated with some tyrosine kinase inhibitors (TKIs). The direct inhibition of UDP-glucuronosyltransferase activities has been identified as a mechanism of potentiation of paracetamol hepatotoxicity. However, the effects of TKIs on paracetamol glucuronidation are not known.

WHAT THIS STUDY ADDS

• The TKIs, sorafenib, dasatinib and imatinib exhibited potent mixed inhibition against paracetamol glucuronidation in pooled human liver microsomes, implying a possible increase in paracetamol hepatotoxicity when they are co-administrated with paracetamol. AIMS We aimed to investigate the effects of tyrosine kinase inhibitors (TKIs) on paracetamol (acetaminophen) glucuronidation.

METHODS

The inhibition of nine small molecule TKIs on paracetamol glucuronidation was investigated in human liver microsomes (HLMs) and recombinant human UDP-glucuronosyltransferases (UGTs).

RESULTS

Sorafenib, dasatinib and imatinib exhibited mixed inhibition against paracetamol glucuronidation in pooled HLMs, and potent inhibition in UGT1A9 and UGT2B15. Dasatinib and imatinib also inhibited UGT1A1-mediated paracetamol glucuronidation. Axitinib, erlotinib, gefitinib, lapatinib, nilotinib and vandetanib exhibited weak inhibition of paracetamol glucuronidation activity in HLMs.

CONCLUSIONS

The inhibition of paracetamol glucuronidation by TKIs might be of particular concern when they are co-administered.

Effect of the beta-glucuronidase inhibitor saccharolactone on glucuronidation by human tissue microsomes and recombinant UDP-glucuronosyltransferases

Glucuronidation studies using microsomes and recombinant uridine diphosphoglucuronosyltransferases (UGTs) can be complicated by the presence of endogenous beta-glucuronidases, leading to underestimation of glucuronide formation rates. Saccharolactone is the most frequently used beta-glucuronidase inhibitor, although it is not clear whether this reagent should be added routinely to glucuronidation incubations. Here we have determined the effect of saccharolactone on eight different UGT probe activities using pooled human liver microsomes (pHLMs) and recombinant UGTs (rUGTs). Despite the use of buffered incubation solutions, it was necessary to adjust the pH of saccharolactone solutions to avoid effects (enhancement or inhibition) of lowered pH on UGT activity. Saccharolactone at concentrations ranging from 1 to 20 mM did not enhance any of the glucuronidation activities evaluated that could be considered consistent with inhibition of beta-glucuronidase. However, for most activities, higher saccharolactone concentrations resulted in a modest degree of inhibition. The greatest inhibitory effect was observed for glucuronidation of 5-hydroxytryptamine and estradiol by pHLMs, with a 35% decrease at 20 mM saccharolactone concentration. Endogenous beta-glucuronidase activities were also measured using various human tissue microsomes and rUGTs with estradiol-3-glucuronide and estradiol-17-glucuronide as substrates. Glucuronide hydrolysis was observed for pHLMs, lung microsomes and insect-cell expressed rUGTs, but not for kidney, intestinal or human embryonic kidney HEK293 microsomes. However, the extent of hydrolysis was relatively small, representing only 9-19% of the glucuronide formation rate measured in the same preparations. Consequently, these data do not support the routine inclusion of saccharolactone in glucuronidation incubations. If saccharolactone is used, concentrations should be titrated to achieve activity enhancement without inhibition.

Effect of valerian, valerian/hops extracts, and valerenic acid on glucuronidation in vitro

Valerian preparations alone or in combination with hops are popular over-the-counter products used for sleep disturbances or anxiety. Therefore, it is important to characterize the effect of these products on the activity of human drug-metabolizing enzymes. The inhibitory effects of valerian and valerian/hops extracts as well as valerenic acid (a major constituent of valerian) on glucuronidation were evaluated in human liver microsomes and with expressed uridine 5'-diphosphate (UDP)-glucuronosyltransferases (UGT). Methanolic extracts of two herbal preparations caused significant reductions in the rate of formation of acetaminophen, oestradiol, morphine, and testosterone glucuronides. Oestradiol glucuronidation at the 3-hydroxy position was inhibited by nearly 87% in microsomal incubations. In addition, marked reductions in UGT1A1 and UGT2B7 activities were observed in the presence of the herbal extracts using oestradiol and morphine as probe substrates, respectively. Valerenic acid also demonstrated significant inhibitory effects on the glucuronidation of acetaminophen, oestradiol, and morphine with both microsomes and expressed UGTs. The relatively low IC50 values obtained for valerenic acid in microsomal incubations may indicate that this essential oil contributes to the effects observed with herbal extracts in inhibiting glucuronidation in vitro. Overall, these findings suggest that valerian-containing products may interfere with the glucuronidation of endo- and xenobiotics.

Glucuronidation in the chimpanzee (Pan troglodytes): studies with acetaminophen, oestradiol and morphine

The chimpanzee has recently been characterized as a surrogate for oxidative drug metabolism in humans and as a pharmacokinetic model for the selection of drug candidates. In the current study, the glucuronidation of acetaminophen, morphine and oestradiol was evaluated in the chimpanzee to extend the characterization of this important animal model. Following oral administration of acetaminophen (600 mg) to chimpanzees (n=2), pharmacokinetics were comparable with previously reported human values, namely mean oral clearance 0.91 vs. 0.62+/-0.05 l h-1 kg-1, apparent volume of distribution 2.29 vs. 1.65+/-0.25 l kg-1, and half-life 1.86 vs. 1.89+/-7h, for chimpanzee vs. human, respectively. Urinary excretions (percentage of dose) of acetaminophen, acetaminophen glucuronide and acetaminophen sulfate were also similar between chimpanzees and humans, namely 2.3 vs. 5.0, 63.1 vs. 54.7, and 25.0 vs. 32.3%, respectively. Acetaminophen, oestradiol and morphine glucuronide formation kinetics were investigated using chimpanzee (n=2) and pooled human liver microsomes (n=10). V(max) (app) and K(m)(app) (or S(50)(app)) for acetaminophen glucuronide, morphine 3- and 6-glucuronide, and oestradiol 3- and 17-glucuronide formation were comparable in both species. Eadie-Hofstee plots of oestradiol 3-glucuronide formation in chimpanzee microsomes were characteristic of autoactivation kinetics. Western immunoblot analysis of chimpanzee liver microsomes revealed a single immunoreactive band when probed with anti-human UGT1A1, anti-human UGT1A6, and anti-human UGT2B7. Taken collectively, these data demonstrate similar glucuronidation characteristics in chimpanzees and humans.

Metabolism of the olive oil phenols hydroxytyrosol, tyrosol, and hydroxytyrosyl acetate by human hepatoma HepG2 cells

To study the potential hepatic metabolism of olive oil phenols, human hepatoma HepG2 cells were incubated for 2 and 18 h with hydroxytyrosol, tyrosol, and hydroxytyrosyl acetate, three phenolic constituents of olive oil. After incubation, culture media and cell lysates were hydrolyzed with beta-glucuronidase and sulfatase and analyzed by LC-MS. In vitro methylation, glucuronidation, and sulfation of pure phenols were also performed. Methylated and glucuronidated forms of hydroxytyrosol were detected at 18 h of incubation, together with methylglucuronidated metabolites. Hydroxytyrosyl acetate was largely converted into free hydroxytyrosol and subsequently metabolized, yet small amounts of glucuronidated hydroxytyrosyl acetate were detected. Tyrosol was poorly metabolized, with <10% of the phenol glucuronidated after 18 h. Minor amounts of free or conjugated phenols were detected in cell lysates. No sulfated metabolites were found. In conclusion, olive oil phenols can be metabolized by the liver as suggested by the results obtained using HepG2 cells as a hepatic model system.

Isoform‐Selective Probe Substrates for In Vitro Studies of Human UDP‐Glucuronosyltransferases

The majority of UDP-glucuronosyltransferases (UGT), like other drug-metabolizing enzymes, display broad and often overlapping substrate specificities, complicating evaluation of the function of individual UGT isoforms within human tissues. Despite this, there have been recent advances in identifying UGT-selective probes--UGT substrates that are primarily glucuronidated by a single isoform. Such probes can be used to (1) facilitate identification of UGT isoforms mediating a particular glucuronidation activity in human liver through activity correlation analysis; (2) evaluate the role of particular UGTs in drug-drug interactions through either enzyme induction or inhibition; and (3) elucidate the functional significance of genetic polymorphisms associated with the gene encoding the UGT of interest. UGT-selective probes currently being used in our laboratory for the evaluation of glucuronidation activities in human liver tissues include estradiol (3OH-glucuronidation; UGT1A1), trifluoperazine (UGT1A4) serotonin (UGT1A6), propofol (UGT1A9), 3'-azidothymidine (UGT2B7), and S-oxazepam (UGT2B15). In vitro incubation protocols and the HPLC analysis methods used to determine each of these activities are described in detail. Future work is needed to elucidate more highly selective probes than those in current usage, as well as probes for the extrahepatic UGT isoforms.

Altered Brain Penetration of Diclofenac and Mefenamic Acid, but Not Acetaminophen, in Shiga-Like Toxin II-Treated Mice

It is well accepted that bacterial and virus infections elevate the levels of cytokines in serum and cerebrospinal fluids. Such high levels of cytokines might alter the integrity of the blood-brain barrier (BBB) and/or blood-cerebrospinal fluid barrier (BCSFB), subsequently affecting brain penetration of drugs. However, few reports have addressed this issue. Thus, we investigated brain penetration of cyclooxygenase (COX) inhibitors, commonly used as antipyretics, in mice treated with Shiga-like toxin II (SLT-II) derived from E. coli O157:H7, which significantly elevates cytokine levels. As antipyretics, we used diclofenac, mefenamic acid, and acetaminophen. We found that SLT-II significantly increased the brain-to-plasma concentration ratio (Kp) of diclofenac and mefenamic acid, but not of acetaminophen. Moreover, the Kp of diclofenac and mefenamic acid was increased by probenecid, an anionic compound. These results suggest that efflux anion transporters might be involved in the transport of diclofenac and mefenamic acid. Western blot analysis revealed that SLT-II decreased the expression of organic anion transporter-3, an efflux transporter located on the BBB and/or BCSFB. Taken together, these results suggest that SLT-II and/or SLT-II-stimulated cytokines might change brain penetration of drugs and could possibly increase the risk of their side-effects by altering the expression of transporters.

GLUCURONIDATION OF THE OXIDATIVE CYTOCHROME P450-MEDIATED PHENOLIC METABOLITES OF THE ENDOCRINE DISRUPTOR PESTICIDE: METHOXYCHLOR BY HUMAN HEPATIC UDP-GLUCURONOSYL TRANSFERASES

Methoxychlor, a currently used pesticide, is a proestrogen exhibiting estrogenic activity in mammals in vivo. Methoxychlor undergoes oxidative metabolism by cytochromes P450, yielding 1,1,1-trichloro-2-(4-hydroxyphenyl)-2-(4-methoxyphenyl)ethane (mono-OH-M) and 1,1,1-trichloro-2,2-bis(4-hydroxyphenyl)ethane (bis-OH-M) as main metabolites. Since humans may be exposed to these estrogenic metabolites, which are potential substrates of UDP-glucuronosyltransferases (UGTs), their glucuronide conjugation was investigated with human liver preparations and individual UGTs. Incubation of both mono-OH-M and bis-OH-M with human liver microsomes formed monoglucuronides. The structures of the glucuronides were identified by liquid chromatography/tandem mass spectometry. Examination of cDNA-expressed recombinant human hepatic UGTs revealed that several catalyze glucuronidation of both compounds. Among the cDNA-expressed UGT1A enzymes, UGT1A9 seemed to be the main catalyst of formation of mono-OH-M-glucuronide, whereas UGT1A3 seemed to be the most active in bis-OH-M-glucuronide formation. Furthermore, the chiral selectivity of mono-OH-M glucuronidation was examined. The results of the incubation of single enantiomers generally agreed with the chiral analyses of mono-OH-M derived from the glucuronidase digestion of the glucuronides of the racemic mono-OH-M. There was a relatively slight but consistent enantioselective preference of individual UGT1A1, UGT1A3, UGT1A9, and UGT2B15 enzymes for glucuronidation of the S- over the R-mono-OH-M, whereas in human liver microsomes differences were observed among donors in generating the respective R/S-mono-OH-M ratio. Since it was previously shown that human liver microsomes demethylate methoxychlor mainly into S-mono-OH-M, the observation that UGT1A isoforms preferentially glucuronidate the S-mono-OH-M suggests a suitable mechanism for eliminating this major enantiomer. This enantiomeric preference, however, is not extended to all samples of human liver microsomes that we tested.

Analysis of acetaminophen glucuronide conjugate accompanied by adduct ion production by liquid chromatography-atmospheric pressure chemical ionization-mass spectrometry

Liquid chromatography-mass spectrometry (LC-MS) is an effective method for the analysis of polar compounds. A coupling of LC-MS, which is used under conventional conditions, and atmospheric-pressure chemical ionization (APCI), which applies mild ionization for the analysis of water-soluble drug conjugates, would offer a very convenient method. The APCI method is effective for ionizing low- and medium-polarized compounds, but not for highly polarized compounds. In this study, we have tried derivatization of carboxyl group of glucuronic acid, to which direct ionization is difficult to apply under the APCI method, was conducted using glucuronides. Methyl ester derivatives were found to be effectively ionized. Furthermore, acetaminophen glucuronide conjugate was investigated in detail. Methyl ester derivatives of acetaminophen glucuronide conjugate (ACEG) were detected at m/z 373 as O(2) adduct ion [M+O(2)](-) in the negative mode, and p-nitrophenyl beta-D-glucuronide (PNPG) demonstrated ionization behaviors very similar to ACEG. Quantitation of ACEG was examined using PNPG as an internal standard, and satisfactory results were obtained for the recovery test and quantification.

Sensitive liquid chromatographic method using fluorescence detection for the determination of estradiol 3- and 17-glucuronides in rat and human liver microsomal incubations: formation kinetics

We have developed a sensitive and specific HPLC-fluorescence assay for the determination of estradiol-3-glucuronide and estradiol-17-glucuronide in human and rat liver microsomal incubations. The method utilizes a mobile phase comprised of acetonitrile and 50 mM ammonium phosphate buffer (35:65, v/v) that is pumped though a phenyl column at 1 ml/min; the run time is less than 15 min. Calibration curves for both metabolites were linear over the range 20-4000 pmol. The intra- and inter-day coefficients of variation were <6%. In both rat and human liver microsomes, the formation of estradiol-3-glucuronide displayed atypical kinetics (consistent with activation), while estradiol-17-glucuronide formation was consistent with classical Michaelis-Menten kinetics. Overall, the assay described is a sensitive and reproducible method for the determination of estradiol glucuronides in liver microsomal preparations.