Chirality Influence of Zaltoprofen Towards UDP‐Glucuronosyltransferases (UGTs) Inhibition Potential

Zaltoprofen (ZLT) is a nonsteroidal antiinflammation drug, and has been clinically employed to treat rheumatoid arthritis, osteoarthritis, and other chronic inflammatory pain conditions. The present study aims to investigate the chirality influence of zaltoprofen towards the inhibition potential towards UDP‐glucuronosyltransferases (UGTs) isoforms. In vitro a recombinant UGT isoforms‐catalyzed 4‐methylumbelliferone (4‐MU) glucuronidation incubation system was employed to investigate the inhibition of (R)‐zaltoprofen and (S)‐zaltoprofen towards UGT isoforms. The inhibition difference capability was observed for the inhibition of (R)‐zaltoprofen and (S)‐zaltoprofen towards UGT1A8 and UGT2B7, but not for other tested UGT isoforms. (R)‐zaltoprofen exhibited noncompetitive inhibition towards UGT1A8 and competitive inhibition towards UGT2B7. The inhibition kinetic parameters were calculated to be 35.3 μM and 19.2 μM for UGT1A8 and UGT2B7. (R)‐zaltoprofen and (S)‐zaltoprofen exhibited a different inhibition type towards UGT1A7. Based on the reported maximum plasma concentration of (R)‐zaltoprofen in vivo, a high drug–drug interaction between (R)‐zaltoprofen and the drugs mainly undergoing UGT1A7, UGT1A8, and UGT2B7‐catalyzed glucuronidation was indicated. Chirality 27:359–363, 2015. © 2015 Wiley Periodicals, Inc.     

Albumin's Influence on Carprofen Enantiomers–Hymecromone Interaction

Hymecromone is an important coumarin drug, and carprofen is one of the most important nonsteroidal antiinflammatory drugs (NSAIDs). The present study aims to determine the influence of bovine serum albumin (BSA) on the carprofen–hymecromone interaction. The inhibition of carprofen enantiomers on the UDP‐glucuronosyltransferase (UGT) 2B7‐catalyzed glucuronidation of hymecromone was investigated in the UGTs incubation system with and without BSA. The inhibition capability of increased by 20% (P < 0.001) of (R)‐carprofen after the addition of 0.5% BSA in the incubation mixture. In contrast, no significant difference was observed for the inhibition of (S)‐carprofen on UGT2B7 activity in the absence or presence of 0.5% BSA in the incubation system. The Lineweaver‐Burk plot showed that the intersection point was located in the vertical axis, indicating the competitive inhibition of (R)‐carprofen on UGT2B7 in the incubation system with BSA, which is consistent with the inhibition kinetic type of (R)‐carprofen on UGT2B7 in the incubation system without BSA. Furthermore, the second plot using the slopes from the Lineweaver‐Burk versus the concentrations of (R)‐carprofen showed that the fitting equation was y=39.997x+50. Using this equation, the inhibition kinetic parameter was calculated to be 1.3 μM. For (S)‐carprofen, the intersection point was located in the horizontal axis in the Lineweaver‐Burk plot for the incubation system with BSA, indicating the noncompetitive inhibition of (S)‐carprofen on the activity of UGT2B7. The fitting plot of the second plot was y=24.6x+180, and the inhibition kinetic parameter was 7.3 μM. In conclusion, the present study gives a short summary of BSA's influence on the carprofen enantiomers–hymecromone interaction, which will guide the clinical application of carprofen and hymecromone. Chirality 28:226–229, 2016. © 2015 Wiley Periodicals, Inc.     

Chiral Inhibition of Rivaroxaban Derivatives Towards UDP‐Glucuronosyltransferase (UGT) Isoforms

Rivaroxaban is an oral direct factor Xa (FXa) inhibitor clinically used to prevent and treat thromboembolic disorders. Drug–drug interaction (DDI) exist for rivaroxaban and the inhibitors of CYP3A4/5. This study aims to investigate the inhibition of rivaroxaban and its derivatives with a chiral center towards UDP‐glucuronosyltransferases (UGTs). Chemical synthesis was performed to obtain rivaroxaban derivatives with different chiral centers. UGTs supersomes‐catalyzed 4‐methylumbelliferone (4‐MU) glucuronidation was employed to evaluate the inhibition potential towards various UGT isoforms. A significant influence of rivaroxaban derivatives towards UGT1A3 was observed. Chiral centers produce different effects towards the effect of four pairs of rivaroxaban derivatives towards UGT1A3 activity, with stronger inhibition potential of S1 than R1, but stronger inhibition capability of R2, R3, R4 than S2, S3, and S4. Competitive inhibition of R3 and R4 towards UGT1A3 was demonstrated by Dixon and Lineweaver‐Burk plots. In conclusion, the significant influence of rivaroxaban derivatives towards UGT1A3's activity was demonstrated in the present study. The chirality centers highly affected the inhibition behavior of rivaroxaban derivatives towards UGT1A3. Chirality 27:936–943, 2015. © 2015 Wiley Periodicals, Inc.     

Albumin Supplement Affects the Metabolism and Metabolism‐Related Drug–Drug Interaction of Fenoprofen Enantiomers

The influence of albumin towards the metabolism behavior of fenoprofen enantiomers and relevant drug–drug interaction was investigated in the present study. The metabolic behavior of fenoprofen enantiomers was compared in a phase II metabolic incubation system with and without bovine serum albumin (BSA). BSA supplement increased the binding affinity parameter (Km) of (R)‐fenoprofen towards human liver microsomes (HLMs) from 148.3 to 214.4 μM. In contrast, BSA supplement decreased the Km of (S)‐fenoprofen towards HLMs from 218.2 to 123.5 μM. For maximum reaction velocity (Vmax), the addition of BSA increased the Vmax of (R)‐fenoprofen from 1.3 to 1.6 nmol/min/mg protein. In the contrast, BSA supplement decreased the Vmax value from 3.3 to 1.5 nmol/min/mg protein. Andrographolide–fenoprofen interaction was used as an example to investigate the influence of BSA supplement towards fenoprofen‐relevant drug–drug interaction. The addition of 0.2% BSA in the incubation system significantly decreased the inhibition potential of andrographolide towards (R)‐fenoprofen metabolism (P < 0.001). Different from (R)‐fenoprofen, the addition of BSA significantly increased the inhibition potential of andrographolide towards the metabolism of (S)‐fenoprofen. BSA supplement also changed the inhibition kinetic type and parameter of andrographolide towards the metabolism of (S)‐fenoprofen. In conclusion, albumin supplement changes the metabolic behavior of fenoprofen enantiomers and the fenoprofen–andrographolide interaction. Chirality 27:436–440, 2015. © 2015 Wiley Periodicals, Inc.     

Selective and potent inhibition of different hepatic UDP-glucuronosyltransferase activities by omega,omega,omega-triphenylalcohols and UDP derivatives.

A homologous series of omega,omega,omega-triphenylalcohols and corresponding omega,omega,omega-triphenylalkyl-UDP derivatives was synthesized and tested as inhibitors of UDP-glucuronosyltransferase (UGT) activity in rat liver microsomes, with 1-naphthol, testosterone and bilirubin as substrates. Introduction of the UDP moiety in the triphenylalcohols increased their inhibition potency markedly toward the isoforms which glucuronidate 1-naphthol and testosterone, but strongly decreased that toward bilirubin. The inhibiting potency of the UDP-derivatives increased as a function of the length of the hydrocarbon chain. The best inhibitor 7,7,7-triphenylheptyl-UDP showed an I50 of 30 and 10 microM for 1-naphthol and testosterone glucuronidation, respectively; even a 1 mM concentration of the compound had little, if any, effect on bilirubin glucuronidation. The inhibition by 7,7,7-triphenylheptyl-UDP was mixed-type toward 1-naphthol, and non competitive toward testosterone (apparent K(i) 30 microM and 1.7 microM, respectively); on the other hand, the inhibition was competitive toward the common substrate UDP-glucuronic acid (apparent K(i) 1.9-1.2 microM). In addition, 7,7,7-triphenylheptyl-UDP (0.25-0.50 mM) almost inhibited glucuronidation of 1-naphthol and testosterone catalyzed by the recombinant rat liver UGT-2B1 and human liver UGT-1A1, whose cDNA has been expressed in V79 cells. In conclusion, the data indicate that 7,7,7-triphenyheptyl-UDP interacted competitively with the UDP binding site of UGT. The results also indicate that it is possible to design transition state analogue inhibitors with specificity for different UGT forms.     

Glucuronidation of haloperidol by rat liver microsomes: involvement of family 2 UDP-glucuronosyltransferases

The purposes of this study were to develop a HPLC method to assay for haloperidol glucuronide (HALG); to apply this assay method to the in vitro determination of haloperidol (HAL) UDP-glucuronosyltransferase (UGT) enzyme kinetics in rat liver microsomes (RLM); and to identify the UGT isoforms catalyzing glucuronidation of HAL in rats. Incubation of Brij-activated RLM with HAL and UDP-glucuronic acid (UDPGA) in TRIS pH 7.4 buffer resulted in the formation of a single peak in the HPLC chromatogram at 270 nm. The identity of this peak was confirmed to be that of HALG by 1) β-glucuronidase hydrolysis; 2) incubation without UDPGA; 3) UV spectral analysis; and 4) LC/MS/MS to yield the expected mass of 552.1. Enzyme kinetic studies using single enzyme Michaelis-Menton model showed an apparent V_max = 271.9 ± 10.1 pmoles min⁻¹ mg protein⁻¹ and K_m = 61 ± 7.2 μM. Glucuronidation activity in homozygous Gunn (j/j) rats was approximately 80% as compared to Sprague-Dawley RLM. HALG formation was approximately doubled in PB-induced RLM. There was no increase in glucuronidation activities in 3MC-induced RLM. The Gunn rat and the PB-induced RLM data suggest predominant but not exclusive involvement of the UGT2B family in the formation of HALG. Because the UGTs exhibit overlapping substrate specificities and most substrates are glucuronidated by more than one isoform, inhibition studies with UGT2B1 substrate probe testosterone and the UGT2B12 substrate probe borneol were conducted. UGT2B1 and UGT2B12 exhibited 40% and 90% inhibition of HAL glucuronidation, respectively. Thus, UGT2B12 and UGT 2B1 isoforms are responsible for catalyzing HAL glucuronidation in rats. Our HPLC assay provides a specific and sensitive technique for the measurement of in vitro HAL-UGT activity.     

Stereoselective metabolism of propranolol glucuronidation by human UDP‐glucuronosyltransferases 2B7 and 1A9

Stereoselective metabolism of propranolol side‐chain glucuronidation was studied for two recombinant human uridine diphosphate glucuronosyltransferases (UGTs), UGT1A9 and UGT2B7. The S‐ and R‐propranolol side‐chain glucuronides produced in the incubation mixtures were assayed simultaneously by RP‐HPLC with fluorescent detector. The excitation and emission wavelengths were set at 310 nm and 339 nm, respectively. UGT1A9 prefers catalyzing S‐enantiomer to R‐enantiomer and the intrinsic clearance (CL_int) ratios of S‐enantiomer to R‐enantiomer are 3.8 times and 6.5times for racemic propranolol and individual enantiomers, respectively. UGT2B7, however, catalyzes slightly less S‐enantiomer than R‐enantiomer and the CL_int ratio of S‐enantiomer to R‐enantiomer is 0.8 times. The high concentration of racemic propranolol (>0.57 mmol/l) and individual enantiomers (>0.69 mmol/l) exhibited substrate inhibition of glucuronidation for UGT2B7, but only the S‐enantiomer (>0.44 mmol/l) in racemic propranolol exhibited substrate inhibition for UGT1A9. The substrate inhibition constants (K_si) were all similar (P > 0.05). Drug–drug interactions were also found between S‐ and R‐enantiomer glucuronidation metabolisms by UGT1A9 and UGT2B7. Chirality 2010. © 2009 Wiley‐Liss, Inc.     

Nonsteroidal anti-inflammatory drugs and phenols glucuronidation in Caco-2 cells: identification of the UDP-glucuronosyltransferases UGT1A6, 1A3 and 2B7

Glucuronidation of phenols (1-naphthol, 4-methylumbelliferone) and nonsteroidal anti-inflammatory drugs (NSAIDs) such as ketoprofen, naproxen and carprofen was investigated in human colon carcinoma Caco-2 cell clones. Glucuronidation of these substances was highly effective in microsomes of the clones PD-7 and TC-7, but much lower in the PF-11 clone. The activity increased up to a maximum after 21 days of culture. RT-PCR experiments indicated that the PD-7 and TC-7 clones expressed the UDP-glucuronosyltransferase (UGT) isoforms UGT1A6, UGT1A3 and UGT2B7, which could account for the glucuronidation of phenols and carboxylic acids observed. Beta-naphthoflavone stimulated by 2-fold the enzyme activity toward 1-naphthol in PD-7 and TC-7 clones, but not in PF-11 cells. This increase was parallel to that of the UGT1A6 mRNA level. Glucuronidation of ketoprofen was also sensitive to the inducing effect of beta-naphthoflavone. Actinomycin D and cycloheximide did not affect the induction of UGT1A6 by beta-naphthoflavone, but suppressed that of ketoprofen UGT. The UGT1A3 mRNA content was enhanced by beta-naphthoflavone; by contrast, that of UGT2B7 was insensitive to the inducer. In conclusion, several UGT isoforms of both families 1 and 2, which glucuronidate phenols and carboxylic NSAIDs, have been identified in Caco-2 cells. They are differently sensitive to beta-naphthoflavone.     

Differential glucuronidation of bile acids, androgens and estrogens by human UGT1A3 and 2B7.

In this work, UDP-glucuronosyltransferases (UGTs), UGT1A3, 2B7(H268) and 2B7(Y268), stably expressed in human embryonic kidney cells (HK293) were used to assess glucuronidation activities with a variety of steroid hormone and bile acid substrates. The rate of synthesis of carboxyl- and hydroxyl-linked glucuronides was determined under optimal reaction conditions. Expressed UGT1A3 catalyzed bile acid glucuronidation at high rates exclusively at the carboxyl moiety for all compounds tested. In contrast, UGT1A4 catalyzed bile acid glucuronidation at very low rates exclusively at the 3alpha-hydroxyl function. Both UGT2B7 allelic variants glucuronidated the bile acid substrates at both carboxyl and hydroxyl moieties, however, the 3alpha-hydroxyl position was preferentially conjugated compared to the carboxyl function. Similarly, androsterone, a 3alpha-hydroxylated androgenic steroid, was glucuronidated at very high rates by expressed UGT2B7. Of the estrogenic compounds tested, UGT2B7 catalyzed the glucuronidation of estriol at rates comparable to those determined for androsterone. Other structural discrimination was found with UGT2B7 which had activity toward estriol and estradiol exclusively at the 17beta-OH position, yielding the cholestatic steroid D-ring glucuronides.     

The inhibition study of human UDP-glucuronosyltransferases with cytochrome P450 selective substrates and inhibitors

Human uridine-5'-diphosphoglucuronosyltransferases (UGTs) are the major phase II metabolizing enzymes. In the present study, five human UGTs (UGT1A1, 1A4, 1A6, 2B7, and 2B10) were individually expressed and used to examine the inhibition IC(50) values of 20 selective substrates and inhibitors of major cytochromes P450 (CYPs). The inhibition kinetics of UGT1A1 was also analyzed. The results showed that some compounds like α-naphthoflavone, paclitaxel, midazolam, cyclosporine A, and ketoconazole displayed strong inhibitions on UGT activities with their IC(50) values in a range of 4.1-26 μM. Especially, the IC(50) values were 4.1?±?0.8 μM for ketoconazole in inhibiting UGT1A1-mediated β-estradiol-3-glucuronidation, and 4.9?±?0.3 μM for paclitaxel towards UGT1A4-mediated midazolam-N-glucuronidation. Additionally, the IC(50) values of bupropion, tolbutamide, and testosterone in inhibiting UGT-mediated metabolisms were similar with the K(m) values of respective CYPs. Some kinetic behaviours of UGTs were following Michaelis-Menten kinetics, while some were not.     

Substrate specificity of the human UDP-glucuronosyltransferase UGT2B4 and UGT2B7. Identification of a critical aromatic amino acid residue at position 33

The human UDP-glucuronosyltransferase (UGT) isoforms UGT2B4 and UGT2B7 play a major role in the detoxification of bile acids, steroids and phenols. These two isoforms present distinct but overlapping substrate specificity, sharing common substrates such as the bile acid hyodeoxycholic acid (HDCA) and catechol-estrogens. Here, we show that in UGT2B4, substitution of phenylalanine 33 by leucine suppressed the activity towards HDCA, and impaired the glucuronidation of several substrates, including 4-hydroxyestrone and 17-epiestriol. On the other hand, the substrate specificity of the mutant UGT2B4F33Y, in which phenylalanine was replaced by tyrosine, as found at position 33 of UGT2B7, was similar to wild-type UGT2B4. In the case of UGT2B7, replacement of tyrosine 33 by leucine strongly reduced the activity towards all the tested substrates, with the exception of 17-epiestriol. In contrast, mutation of tyrosine 33 by phenylalanine exhibited similar or even somewhat higher activities than wild-type UGT2B7. Hence, the results strongly indicated that the presence of an aromatic residue at position 33 is important for the activity and substrate specificity of both UGT2B4 and UGT2B7.     

UDP-glucuronosyltransferases 1A6 and 1A10 catalyze reduced menadione glucuronidation

Menadione (2-methyl-1,4-naphthoquine), also known as vitamin K3, has been widely used as a model compound in the field of oxidative stress-related research. The metabolism of menadione has been studied, and it is known that menadione undergoes a two-electron reduction by NAD(P)H:Quinone oxidoreductase 1 (NQO1) after which the reduced form of menadione (2-methyl-1,4-naphthalenediol, menadiol) is glucuronidated and excreted in urine. To investigate which human UDP-glucuronosyltransferase (UGT) isoforms participate in the glucuronidation of menadiol reduced by NQO1 from menadione, we first constructed heterologously expressed NQO1 in Sf9 cells and tested the menadiol glucuronidating activity of 16 human recombinant UGT isoforms. Of the 16 UGT isoforms, UGTs 1A6, 1A7, 1A8, 1A9, and 1A10 catalyzed menadiol glucuronidation, and, of these, UGTs 1A6 and 1A10 catalyzed menadiol glucuronidation at much higher rates than the other UGTs. Menadiol was regioselectively glucuronidated in the manner of 4-position > 1-position by UGTs 1A7, 1A8, 1A9, and 1A10. In contrast to these UGTs, only UGT1A6 exhibited 1-menadiol-preferential glucuronidating activity. The results suggest possible detoxification pathways for quinones via NQO1 reduction followed by UGT glucuronidation.     

Glucuronidation of the steroid enantiomers ent-17β-estradiol, ent-androsterone and ent-etiocholanolone by the human UDP-glucuronosyltransferases

Steroids enantiomers are interesting compounds for detailed exploration of drug metabolizing enzymes, such as the UDP-glucuronosyltransferases (UGTs). We have now studied the glucuronidation of the enantiomers of estradiol, androsterone and etiocholanolone by the 19 human UGTs of subfamilies 1A, 2A and 2B. The results reveal that the pattern of human UGTs of subfamily 2B that glucuronidate ent-17β-estradiol, particularly 2B15 and 2B17, resembles the glucuronidation of epiestradiol (17α-estradiol) rather than 17β-estradiol, the main physiological estrogen. The UGTs of subfamilies 1A and 2A exhibit higher degree of regioselectivity than enantioselectivity in the conjugation of these estradiols, regardless of whether the activity is primarily toward the non-chiral site, 3-OH (UGT1A1, UGT1A3, UGT1A7, UGT1A8 and, above all, UGT1A10), or the 17-OH (UGT1A4). In the cases of etiocholanolone and androsterone, glucuronidation of the ent-androgens, like the conjugation of the natural androgens, is mainly catalyzed by UGTs of subfamilies 2A and 2B. Nevertheless, the glucuronidation of ent-etiocholanolone and ent-androsterone by both UGT2B7 and UGT2B17 differs considerably from their respective activity toward the corresponding endogenous androgens, whereas UGT2A1-catalyzed conjugation is much less affected by the stereochemistry differences. Kinetic analyses reveal that the K(m) value of UGT2A1 for ent-estradiol is much higher than the corresponding value in the other two high activity enzymes, UGT1A10 and UGT2B7. Taken together, the results highlight large enantioselectivity differences between individual UGTs, particularly those of subfamily 2B.     

S-Glucuronidation of 7-mercapto-4-methylcoumarin by human UDP glycosyltransferases in genetically engineered fission yeast cells

Human UDP glycosyltransferases (UGTs) play an important role in xenobiotic detoxification. They increase the solubility of their substrates by adding a sugar moiety (such as glucuronic acid) to different functional entities (such as hydroxyl groups). The aim of this study was to investigate how glucuronidation of a standard substrate is affected by a change of the hetero-atom at the conjugation site. For this purpose, we compared the in vitro glucuronidation rates of 4-methylumbelliferone and 7-mercapto-4-methylcoumarin, respectively. Human liver microsomes catalyzed the S-glucuronidation of 7-mercapto-4--methylcoumarin almost as efficient as the O-glucuronidation of 4-methylumbelliferone. When testing isoenzyme specificity by whole cell biotransformation with fission yeast strains that recombinantly express all 19 human members of the UGT1 and UGT2 families, it was found that 13 isoenzymes were able to glucuronidate 7-mercapto-4-methylcoumarin, with five of them being specific for this substrate and the other eight also converting 4-methylumbelliferone under these conditions. The remaining six UGTs did not accept either substrate. Out of the eight isoenzymes that glucuronidated both substrates, four catalyzed both reactions approximately to the same extent, while three displayed higher conversion rates towards 4-methylumbelliferone and one preferred 7-mercapto-4-methylcoumarin. These data suggest that 7-mercapto-4-methylcoumarin is a convenient new standard substrate for monitoring S-glucuronidation.     

Carboxyl nonsteroidal anti-inflammatory drugs are efficiently glucuronidated by microsomes of the human gastrointestinal tract

Limited studies have been carried out on the biotransformation of carboxyl nonsteroidal anti-inflammatory drugs (NSAIDs) in the liver. However, the role of the intestine in NSAID metabolism has not been investigated. In this report, the contribution of UDP-glucuronosyltransferases (UGTs) in the human gastrointestinal (GI) tract from five donors to the glucuronidation of the NSAIDs, RS-ketoprofen, S-naproxen, RS- and S-etodolac, was investigated. UGT activity and, for some donors, mRNA levels were evaluated. All NSAIDs were glucuronidated throughout the GI tract; however, glucuronidation was low in stomach and duodenum as compared to the remainder of the intestine. RT-PCR analysis demonstrated that the UGT1A isoforms, UGT1A3, 1A8, and 1A10, and UGT2B7 were expressed in the GI tract. Human recombinant UGT1A3, 1A9, 1A10 and 2B7 were actively involved in the glucuronidation of all NSAIDs while UGT1A7 and the intestine-specific UGT1A8 had no glucuronidating activity towards those compounds. Despite interindividual variations in both the levels of mRNA and the distribution of activity through the intestine, UGTs in the GI tract may contribute significantly to the first pass metabolism of orally administered NSAIDs.     

Glucuronidation of carboxylic acid containing compounds by UDP-glucuronosyltransferase isoforms

Glucuronide conjugation of xenobiotics containing a carboxylic acid moiety represents an important metabolic pathway for these compounds in humans. Several human UDP-glucuronosyltransferases (UGTs) have been shown to catalyze the formation of acyl-glucuronides, including UGT2B7, UGT1A3, and UGT1A9. In this study, recombinant expressed UGT isoforms were investigated with many structurally related carboxylic acid analogues, and the UGT rank order for catalyzing the glucuronidation of carboxylic acids was UGT2B7?UGT1A3 approximately UGT1A9. Despite being a poor substrate with UGT1A3, coumarin-3-carboxylic acid was not a substrate for any other UGT isoform tested in this study, suggesting that it could be a specific substrate for UGT1A3. Interestingly, UGT1A7 and UGT1A10 also react with several carboxylic acid aglycones. Kinetic analysis showed that UGT2B7 exhibits much higher glucuronidation efficiency (Vmax/Km) with ibuprofen, ketoprofen, and others, compared to UGT1A3. These data indicate that UGT2B7 could be the major isoform involved in the glucuronidation of carboxylic acid compounds in humans.     

Dietary green and white teas suppress UDP-glucuronosyltransferase UGT2B17 mediated testosterone glucuronidation

The anabolic steroid testosterone can be used by athletes to enhance athletic performance and muscle growth. UDP-glucuronosyltransferase (UGT2B17) is the key enzyme involved in the glucuronidation of testosterone to testosterone glucuronide, which also serves as a marker for the testosterone/epitestosterone (T/E) ratio used to detect testosterone abuse in sport. Inhibitors of testosterone glucuronidation could have an impact on circulating testosterone levels, thus aiding performance, as well as potentially affecting the urinary T/E ratio and therefore masking testosterone abuse. Previous reports have revealed that non-steroidal, anti-inflammatory drugs, diclofenac and ibuprofen, inhibit the UGT2B17 enzyme. The aim of this study is to analyse dietary tea samples for inhibition of testosterone glucuronidation and, where inhibition is present, to identify the active compounds. Analysis of testosterone glucuronidation was conducted by performing UGT2B17 assays with detection of un-glucuronidated testosterone using high performance liquid chromatography. The results from this study showed that testosterone glucuronidation was inhibited by the green and white tea extracts, along with specific catechin compounds, notably: epicatechin, epigallocatechin gallate (EGCG) and catechin gallate. The IC50 inhibition value for EGCG was determined, using a Dixon plot, to be 64 μM, equalling the most active NSAID inhibitor diclofenac. Thus, common foodstuffs and their constituents, for the first time, have been identified as inhibitors of a key enzyme involved in testosterone glucuronidation. Whilst these common compounds are not substrates of the UGT2B17 enzyme, we showed that they inhibit testosterone glucuronidation which may have implications on current doping control in sport.     

Identification of UGT2B9*2 and UGT2B33 isolated from female rhesus monkey liver

Two UDP-glucuronosyltransferases (UGT2B9(*)2 and UGT2B33) have been isolated from female rhesus monkey liver. Microsomal preparations of the cell lines expressing the UGTs catalyzed the glucuronidation of the general substrate 7-hydroxy-4-(trifluoromethyl)coumarin in addition to selected estrogens (beta-estradiol and estriol) and opioids (morphine, naloxone, and naltrexone). UGT2B9(*)2 displayed highest efficiency for beta-estradiol-17-glucuronide production and did not catalyze the glucuronidation of naltrexone. UGT2B33 displayed highest efficiency for estriol and did not catalyze the glucuronidation of beta-estradiol. UGT2B9(*)2 was found also to catalyze the glucuronidation of 4-hydroxyestrone, 16-epiestriol, and hyodeoxycholic acid, while UGT2B33 was capable of conjugating 4-hydroxyestrone, androsterone, diclofenac, and hyodeoxycholic acid. Three glucocorticoids (cortisone, cortisol, and corticosterone) were not substrates for glucuronidation by liver or kidney microsomes or any expressed UGTs. Our current data suggest the use of beta-estradiol-3-glucuronidation, beta-estradiol-17-glucuronidation, and estriol-17-glucuronidation to assay UGT1A01, UGT2B9(*)2, and UGT2B33 activity in rhesus liver microsomes, respectively.     

Glucuronidation of oxidized fatty acids and prostaglandins B1 and E2 by human hepatic and recombinant UDP-glucuronosyltransferases

Arachidonic acid (AA) can be metabolized to various metabolites, which can act as mediators of cellular processes. The objective of this work was to identify whether AA, prostaglandin (PG) B1 and E2, and 15- and 20-hydroxyeicosatetraenoic acids (15- and 20-HETE) are metabolized via glucuronidation. Assays with human recombinant UDP-glucuronosyltransferase 1A (UGT1A) isoforms revealed that AA and 15-HETE were glucuronidated by UGT1A1, 1A3, 1A4, 1A9, and 1A10, whereas 20-HETE was glucuronidated by UGT1A1 and 1A4 and PGB1 was glucuronidated by UGT1A1, 1A9, and 1A10. All substrates were glucuronidated by recombinant UGT2B7, with AA and 20-HETE being the best substrates. Kinetic analysis of UGT1A1 and 1A9 with AA resulted in Km values of 37.9 and 45.8 microM, respectively. PGB1 was glucuronidated by UGT1A1 with a Km of 26.3 microM. The Km values for all substrates with UGT2B7 were significantly higher than with the UGT1A isoforms. Liquid chromatography-mass spectrometry of glucuronides biosynthesized from PGB1 and 15-HETE showed that hydroxyl groups were the major target of glucuronidation. This work demonstrates a novel metabolic pathway for HETEs and PGs and the role of UGT1A isoforms in this process. These results indicate that glucuronidation may play a significant role in modulation of the availability of these fatty acid derivatives for cellular processes.