Identification of UDP-glucuronosyltransferases 1A1, 1A3 and 2B15 as the main contributors to glucuronidation of bakuchiol,a natural biologically active compound

1.?Bakuchiol, one of the main active compounds of Psoralea corylifolia, possesses a variety of pharmacological activities such as anti-tumor and anti-aging effects. Here, we aimed to characterize the glucuronidation of bakuchiol using human liver microsomes (HLM) and expressed UDP-glucuronosyltransferase (UGT) enzymes.

2.?The glucuronide of bakuchiol was confirmed by liquid chromatography–mass spectrometry (LC-MS) and β-glucuronidase hydrolysis assay. Glucuronidation rates and kinetic parameters were derived by enzymatic incubation and model fitting. Activity correlation analyses were performed to identify the main UGT isoforms contributing to hepatic metabolism of bakuchiol.

3.?Among the three UGT enzymes (i.e., UGT1A1, UGT1A3 and UGT2B15) capable of catalyzing bakuchiol glucuronidation, UGT2B15 showed the highest activity with a CL_int value of 100?μl/min/nmol. Bakuchiol glucuronidation was strongly correlated with glucuronidation of 5-hydroxyrofecoxib (r?=?0.933; p?r?=?0.719; p?r?=?0.594; p?4.?In conclusion, UGT1A1, UGT1A3 and UGT2B15 were identified as the main contributors to glucuronidation of bakuchiol.     

Raloxifene glucuronidation in liver and intestinal microsomes of humans and monkeys: contribution of UGT1A1, UGT1A8 and UGT1A9

1.?Raloxifene is an antiestrogen that has been marketed for the treatment of osteoporosis, and is metabolized into 6- and 4′-glucuronides by UDP-glucuronosyltransferase (UGT) enzymes. In this study, the in vitro glucuronidation of raloxifene in humans and monkeys was examined using liver and intestinal microsomes and recombinant UGT enzymes (UGT1A1, UGT1A8 and UGT1A9).

2.?Although the K_m and CL_int values for the 6-glucuronidation of liver and intestinal microsomes were similar between humans and monkeys, and species differences in V_max values (liver microsomes, humans?>?monkeys; intestinal microsomes, humans?<?monkeys) were observed, no significant differences were noted in the K_m or S₅₀, V_max and CL_int or CL_max values for the 4′-glucuronidation of liver and intestinal microsomes between humans and monkeys.

3.?The activities of 6-glucuronidation in recombinant UGT enzymes were UGT1A1?>?UGT1A8?>UGT1A9 for humans, and UGT1A8?>?UGT1A1?>?UGT1A9 for monkeys. The activities of 4′-glucuronidation were UGT1A8?>?UGT1A1?>?UGT1A9 in humans and monkeys.

4.?These results demonstrated that the profiles for the hepatic and intestinal glucuronidation of raloxifene by microsomes were moderately different between humans and monkeys.     

Glucuronidation of macelignan by human liver microsomes and expressed UGT enzymes: identification of UGT1A1 and 2B7 as the main contributing enzymes

Macelignan is a natural phenolic compound that possesses many types of health benefits such as antiinflammation. This study aimed to characterize the metabolism of macelignan via the glucuronidation pathway and to identify the main UGT enzymes involved in macelignan glucuronidation. The rates of glucuronidation were determined by incubating macelignan with UDPGA‐supplemented microsomes. Kinetic parameters were derived by fitting an appropriate model to the data. Reaction phenotyping, the relative activity factor (RAF) approach and activity correlation analysis were employed to identify the main UGT enzymes contributing to the hepatic metabolism of macelignan. Glucuronidation of macelignan in pooled human liver microsomes (pHLM) was rather efficient with a high CL_int (the intrinsic clearance) value of 13.90 ml/min/mg. All UGT enzymes, except UGT1A4, 1A6 and 2B10, showed metabolic activities toward macelignan. UGT1A1 and 2B7 were the enzymes with the highest activities; the CL_int values were 4.92 and 2.13 ml/min/mg, respectively. Further, macelignan glucuronidation was significantly correlated with 3‐O‐glucuronidation of β‐estradiol (r = 0.69; p < 0.01) and glucuronidation of zidovudine (r = 0.60; p < 0.05) in a bank of individual HLMs (n = 14). Based on the RAF approach, UGT1A1 and 2B7, respectively, contributed 55.40% and 32.20% of macelignan glucuronidation in pHLM. In conclusion, macelignan was efficiently metabolized via the glucuronidation pathway. It was also shown that UGT1A1 and 2B7 were probably the main contributors to the hepatic glucuronidation of macelignan. Copyright © 2014 John Wiley & Sons, Ltd.     

Contribution of UDP-glucuronosyltransferases 1A9 and 2B7 to the glucuronidation of indomethacin in the human liver

Objective We characterized the kinetics of indomethacin glucuronidation by recombinant UDP-glucuronosyltransferase (UGT) isozymes and human liver microsomes (HLM) and identified the human UGT isozymes involved. Methods Indomethacin glucuronidation was investigated using HLM and recombinant human UGT isozymes. Human UGTs involved in indomethacin glucuronidation were assessed in kinetic studies, chemical inhibition studies, and correlation studies. Results Among the UGT isozymes investigated, UGT1A1, 1A3, 1A9, and 2B7 showed glucuronidation activity for indomethacin, with UGT1A9 possessing the highest activity, followed by UGT2B7. Glucuronidation of indomethacin by recombinant UGT1A9 and 2B7 showed substrate inhibition kinetics with K _m values of 35 and 32 μM, respectively. The glucuronidation of indomethacin was significantly correlated with morphine 3OH-glucuronidation (r = 0.69, p < 0.05) and 3′-azido-3′-deoxythymidine glucuronidation (r = 0.82, p < 0.05), a reaction mainly catalyzed by UGT2B7. Propofol inhibited indomethacin glucuronidation in HLM with an IC₅₀ value of 248 μM, which is between the IC₅₀ value in recombinant UGT1A9 (106 μM) and UGT2B7 (> 400 μM). Conclusions These findings suggest that UGT2B7 plays a predominant role in indomethacin glucuronidation in the human liver and that UGT1A9 is partially involved.     

Mutual inhibition between carvedilol enantiomers during racemate glucuronidation mediated by human liver and intestinal microsomes

Carvedilol is administered orally as a racemic mixture of R(+)- and S(-)-enantiomers for treatment of angina pectoris, hypertension and chronic heart failure. We have reported that enzyme kinetic parameters for carvedilol glucuronidation by human liver microsomes (HLM) differed greatly depending on the substrate form, namely, racemic carvedilol and each enantiomer. These phenomena were thought to be caused by mutual inhibition between carvedilol enantiomers during racemate glucuronidation. The aim of this study was to clarify the mechanism of these phenomena in HLM and human intestinal microsomes (HIM) and its relevance to uridine 5'-diphosphate (UDP)-glucuronosyl transferase (UGT) 1A1, UGT2B4 and UGT2B7, which mainly metabolize carvedilol directly in phase II enzymes. HLM apparently preferred metabolizing (S)-carvedilol to (R)-carvedilol in the racemate, but true activities of HLM for both glucuronidation were approximately equal. By determination of the inhibitory effects of (S)-carvedilol on (R)-carvedilol glucuronidation and vice versa, it was shown that (R)-carvedilol glucuronidation was more easily inhibited than was (S)-carvedilol glucuronidation. UGT2B7 was responsible for (S)-carvedilol glucuronidation in HLM. Ratios of contribution to (R)-carvedilol glucuronidation were approximately equal among UGT1A1, UGT2B4 and UGT2B7. However, enzyme kinetic parameters were different between the two lots of HLM used in this study, depending on the contribution ratio of UGT2B4, in which (R)-glucuronidation was much more easily inhibited by (S)-carvedilol than was (S)-glucuronidation by (R)-carvedilol. Meanwhile, HIM preferred metabolizing (R)-carvedilol, and this tendency was not different between the kinds of substrate form.     

Identification of UDP-glucuronosyltransferase isoforms responsible for leonurine glucuronidation in human liver and intestinal microsomes

Abstract

1.?Leonurine is a potent component of herbal medicine Herba leonuri. The detail information on leonurine metabolism in human has not been revealed so far.

2.?Two primary metabolites, leonurine O-glucuronide and demethylated leonurine, were observed and identified in pooled human liver microsomes (HLMs) and O-glucuronide is the predominant one.

3.?Among 12 recombinant human UDP-glucuronosyltransferases (UGTs), UGT1A1, UGT1A8, UGT1A9, and UGT1A10 showed catalyzing activity toward leonurine glucuronidation. The intrinsic clearance (CL_int) of UGT1A1 was approximately 15-to 20-fold higher than that of UGT1A8, UGT1A9, and UGT1A10, respectively. Both chemical inhibition study and correlation study demonstrated that leonurine glucuronidation activities in HLMs had significant relationship with UGT1A1 activities.

4.?Leonurine glucuronide was the major metabolite in human liver microsomes. UGT1A1 was principal enzyme that responsible for leonurine glucuronidation in human liver and intestine microsomes.     

Differential modulation of UDP-glucuronosyltransferase 1A1 (UGT1A1)-catalyzed estradiol-3-glucuronidation by the addition of UGT1A1 substrates and other compounds to human liver microsomes.

Previous results demonstrating homotropic activation of human UDP-glucuronosyltransferase (UGT) 1A1-catalyzed estradiol-3-glucuronidation led us to investigate the effects of 16 compounds on estradiol glucuronidation by human liver microsomes (HLM). In confirmation of previous work using alamethicin-treated HLM pooled from four livers, UGT1A1-catalyzed estradiol-3-glucuronidation demonstrated homotropic activation kinetics (S(50) = 22 microM, Hill coefficient, n = 1.9) whereas estradiol-17-glucuronidation (catalyzed by other UGT enzymes) followed Michaelis-Menten kinetics (K(m) = 7 microM). Modulatory effects of the following compounds were investigated: bilirubin, eight flavonoids, 17alpha-ethynylestradiol (17alpha-EE), estriol, 2-amino-1-methyl-6-phenylimidazo [4,5-b]pyridine (PhIP), anthraflavic acid, retinoic acid, morphine, and ibuprofen. Although the classic UGT1A1 substrate bilirubin was a weak competitive inhibitor of estradiol-3-glucuronidation, the estrogens and anthraflavic acid activated or inhibited estradiol-3-glucuronidation dependent on substrate and effector concentrations. For example, at substrate concentrations of 5 and 10 microM, estradiol-3-glucuronidation activity was stimulated by as much as 80% by low concentrations of 17alpha-EE but was unaltered by flavanone. However, at higher substrate concentrations (25-100 microM) estradiol-3-glucuronidation was inhibited by about 55% by both compounds. Anthraflavic acid and PhIP were also stimulators of estradiol 3-glucuronidation at low substrate concentrations. The most potent inhibitor of estradiol 3-glucuronidation was the flavonoid tangeretin. The UGT2B7 substrates morphine and ibuprofen had no effect on estradiol 3-glucuronidation, whereas retinoic acid was slightly inhibitory. Estradiol-17-glucuronidation was inhibited by 17alpha-EE, estriol, and naringenin but was not activated by any compound. This study demonstrates that the interactions of substrates and inhibitors at the active site of UGT1A1 are complex, yielding both activation and competitive inhibition kinetics.     

Identification and characterization of human UDP-glucuronosyltransferases responsible for xanthotoxol glucuronidation

1.?Xanthotoxol is a furanocoumarin that possesses many pharmacological activities and in this study its in vitro glucuronidation was studied.

2.?Xanthotoxol can be rapidly metabolized to a mono-glucuronide in both human intestine microsomes (HIM) and human liver microsomes (HLM); the structure of the metabolite was confirmed by NMR spectroscopy.

3.?Reaction phenotyping with 12 commercial recombinant human UGTs, as well as with the Helsinki laboratory UGT1A10 that carry a C-terminal His-tag (UGT1A10-H), revealed that UGT1A10-H catalyzes xanthotoxol glucuronidation at the highest rate, followed by UGT1A8. The other enzymes, namely UGT1A3, UGT1A1, UGT1A6, UGT1A10 (commercial), and UGT2B7 displayed moderate-to-low reaction rates.

4.?In kinetic analyses, HIM exhibited much higher affinity for xanthotoxol, along with high V_max and mild substrate inhibition, whereas the kinetics in HLM was biphasic. UGT1A1 (high K_m value), UGT1A10-H (low K_m value), and UGT1A8 exhibited mild substrate inhibition.

5.?Considering the above findings and the current knowledge on UGTs expression in HIM, it is likely that UGT1A10 is mainly responsible for xanthotoxol glucuronidation in the human small intestine, with some contribution from UGT1A1. In the liver, this reaction is mainly catalyzed by UGT1A1 and UGT2B7.

6.?Glucuronidation appears to be the major metabolic pathway of xanthotoxol in human.     

Glucuronidation of etoposide in human liver microsomes is specifically catalyzed by UDP-glucuronosyltransferase 1A1.

A metabolite formed by incubation of human liver microsomes, etoposide, and UDP-glucuronic acid was identified as etoposide glucuronide by liquid chromatography-tandem mass spectrometry analysis. According to the derivatization with trimethylsilylimidazole (Tri-Sil-Z), it was confirmed that the glucuronic acid is linked to an alcoholic hydroxyl group of etoposide and not to a phenolic group. Among nine recombinant human UGT isoforms (UGT1A1, UGT1A3, UGT1A4, UGT1A6, UGT1A8, UGT1A9. UGT1A10, UGT2B7, and UGT2B15), only UGT1A1 exhibited the catalytic activity of etoposide glucuronidation. The enzyme kinetics in pooled human liver microsomes and recombinant UGT1A1 microsomes showed a typical Michaelis-Menten plot. The kinetic parameters of etoposide glucuronidation were K(m) = 439.6 +/- 70.7 microM and V(max) = 255.6 +/- 19.2 pmol/min/mg of protein in human liver microsomes and K(m) = 503.2 +/- 110.2 microM and V(max) = was 266.5 +/- 28.6 pmol/min/mg of protein in recombinant UGT1A1. The etoposide glucuronidation in pooled human liver microsomes was inhibited by bilirubin (IC(50) = 31.7 microM) and estradiol (IC(50) = 34 microM) as typical substrates for UGT1A1. The inhibitory effects of 4-nitrophenol (IC(50) = 121.0 microM) as a typical substrate for UGT1A6 and UGT1A9, imipramine (IC(50) = 393.8 microM) as a typical substrate for UGT1A3 and UGT1A4, and morphine (IC(50) = 109.3 microM) as a typical substrate for UGT2B7 were relatively weak. The interindividual difference in etoposide glucuronidation in 13 human liver microsomes was 78.5-fold (1.4-109.9 pmol/min/mg of protein). The etoposide glucuronidation in 10 to 13 human liver microsomes was significantly correlated with beta-estradiol-3-glucuronidation (r = 0.841, p < 0.01), bilirubin glucuronidation (r = 0.935, p < 0.01), and the immunoquantified UGT1A1 protein content (r = 0.800, p < 0.01). These results demonstrate that etoposide glucuronidation in human liver microsomes is specifically catalyzed by UGT1A1.     

A high throughput assay for the glucuronidation of 7-hydroxy-4-trifluoromethylcoumarin by recombinant human UDP-glucuronosyltransferases and liver microsomes

Abstract

1.?UDP-glucuronosyltransferases (UGTs) are versatile and important conjugation enzymes in the metabolism of drugs and other xenobiotics.

2.?We have developed a convenient quantitative multi-well plate assay to measure the glucuronidation rate of 7-hydroxy-4-trifluoromethylcoumarin (HFC) for several UGTs.

3.?We have used this method to screen 11 recombinant human UGTs for HFC glucuronidation activity and studied the reaction kinetics with the most active enzymes. We have also examined the HFC glucuronidation activity of liver microsomes from human, pig, rabbit and rat.

4.?At a substrate concentration of 20?µM, the most active HFC glucuronidation catalysts were UGT1A10 followed by UGT1A6 >UGT1A7 >UGT2A1, whereas at 300?µM UGT1A6 was about 10 times better catalyst than the other recombinant UGTs. The activities of UGTs 1A3, 1A8, 1A9, 2B4 and 2B7 were low, whereas UGT1A1 and UGT2B17 exhibited no HFC glucuronidation activity. UGT1A6 exhibited a significantly higher V_max and Km values toward both HFC and UDP-glucuronic acid than the other UGTs.

5.?Human, pig and rabbit, but not rat liver microsomes, catalyzed HFC glucuronidation at high rates.

6.?This new method is particularly suitable for fast activity screenings of UGTs 1A6, 1A7, 1A10 and 2A1 and HFC glucuronidation activity determination from various samples.     

In vitro metabolism of the anti-inflammatory clerodane diterpenoid polyandric acid A and its hydrolysis product by human liver microsomes and recombinant cytochrome P450 and UDP-glucuronosyltransferase enzymes

1.?The metabolism of the anti-inflammatory diterpenoid polyandric acid A (PAA), a constituent of the Australian Aboriginal medicinal plant Dodonaea polyandra, and its de-esterified alcohol metabolite, hydrolysed polyandric acid A (PAAH) was studied in vitro using human liver microsomes (HLM) and recombinant UDP-glucuronosyltransferase (UGT) and cytochrome P450 (CYP) enzymes.

2.?Hydrolysis of PAA to yield PAAH occurred upon incubation with HLM. Further incubations of PAAH with HLM in the presence of UGT and CYP cofactors resulted in significant depletion, with UGT-mediated depletion as the major pathway.

3.?Reaction phenotyping utilising selective enzyme inhibitors and recombinant human UGT and CYP enzymes revealed UGT2B7 and UGT1A1, and CYP2C9 and CYP3A4 as the major enzymes involved in the metabolism of PAAH.

4.?Analysis of incubations of PAAH with UDP-glucuronic acid-supplemented HLM and recombinant enzymes by UPLC/MS/MS identified three glucuronide metabolites. The metabolites were further characterised by β-glucuronidase and mild alkaline hydrolysis. The acyl glucuronide of PAAH was shown to be the major metabolite.

5.?This study demonstrates the in vitro metabolism of PAA and PAAH and represents the first systematic study of the metabolism of an active constituent of an Australian Aboriginal medicinal plant.     

Cis-resveratrol glucuronidation kinetics in human and recombinant UGT1A sources

1. It was hypothesized that cis-resveratrol glucuronidation contributes to a greater extent to in-vitro disposition of total resveratrol than previously assumed. To this end, the kinetic data for cis-resveratrol glucuronidation are reported.

2. Glucuronidation assays were conducted in human liver and intestinal microsomes and in uridine diphosphate-glucuronosyltransferases (UGTs) UGT1A1, UGT1A6, UGT1A9, and UGT1A10. Kinetic parameters were estimated for the major cis-resveratrol-3-O-glucuronide (cis-R3G). Substrate inhibition was observed with apparent V_max, K_m and K_i of 6.1?±?0.3/27.2?±?1.2 nmol min^?1 mg^?1, 415?±?48.1/989.9?±?92.8 and 789.6?±?76.3/1012?±?55.9?μM in human intestinal microsomes (HIMs) and UGT1A6, respectively (estimate?±?standard error (SE)). Biphasic kinetics were observed in human liver microsomes (HLMs), while sigmoidal kinetics were seen in UGT1A9 (V_max?=?11.92?±?0.2 nmol min^?1 mg^?1; K_m?=?360?μM; n?=?1.27?±?0.07). The 4′-O-glucuronide (cis-R4′G) exhibited atypical kinetics in HLM, HIM, UGT1A1, and UGT1A10. UGT1A9 catalysed cis-R4′G formation at high substrate concentrations (V_max?=?0.33?±?0.015 nmol min^?1 mg^?1; K_m?=?537.8?±?67.8?μM).

3. In conclusion, although the rates of formation of cis-R3G in HLM and UGT1A9 were higher than those for trans-R3G, the contribution to total resveratrol disposition could not be determined fully due to atypical kinetics observed.

     

Characterization of bropirimine O-glucuronidation in human liver microsomes

1. The antitumour agent bropirimine undergoes significant Phase II conjugation in vivo. Incubation of [¹⁴C]bropirimine with human liver microsomes resulted in the formation of a single product peak (M1) using high-performance liquid chromatography with radiochemical detection and was tentatively assigned as bropirimine glucuronide based on sensitivity to β-glucuronidase and by obtaining the expected mass of 442/444 amu with liquid chromatography/mass spectrometry. Following metabolite isolation, the structure of M1 was established as bropirimine O-glucuronide by ¹H-nuclear magnetic spectroscopy.

2. Studies aimed at identifying the human liver UDP-glucuronosyltransferase (UGT) enzyme(s) involved in the glucuronidation of bropirimine were carried out using recombinant human UGTs and it was determined that glucuronidation of bropirimine was catalysed by UGT1A1, UGT1A3 and UGT1A9. Bropirimine O-glucuronidation followed Michaelis–Menten kinetics and the K_m and V_max (mean ± SD; n?=?3) were 1217 ± 205?μM and 667 ± 188?pmol?min^?1 mg^?1, respectively.

3. The activity of bropirimine O-glucuronidation by human liver microsomes was inhibited by bilirubin (40%) and with mefenamic acid (80%). Although buprenorphine extensively inhibited the activity of bropirimine O-glucuronidation by UGT1A3, the inhibition profile did not parallel that observed in HLMs.

4. The results demonstrate that UGT1A9 and to a lesser extent UGT1A1 are responsible for the majority of bropirimine O-glucuronidation in man.     

Udp-glucuronosyltransferase 2b7 is the major enzyme responsible for gemcabene glucuronidation in human liver microsomes.

The predominant metabolic pathway of gemcabene in humans is glucuronidation. The principal human UDP-glucuronosyltransferases (UGTs) involved in the glucuronidation of gemcabene were determined in this study. Glucuronidation of gemcabene was catalyzed by recombinant UGT1A3, recombinant UGT2B7, and recombinant UGT2B17, as well as by human liver microsomes (HLM). Gemcabene glucuronidation in recombinant UGTs and HLM followed non-Michaelis-Menten kinetics consistent with homotropic activation, but pharmacokinetics in humans were linear over the dose range tested (total plasma C(max), 0.06-0.88 mM). Gemcabene showed similar affinity (S(50)) for recombinant UGTs (0.92-1.45 mM) and HLM (1.37 mM). S-Flurbiprofen was identified as a more selective inhibitor of recombinant UGT2B7-catalyzed gemcabene glucuronidation (>23-fold lower IC(50)) when compared with recombinant UGT1A3- or recombinant UGT2B17-catalyzed gemcabene glucuronidation. The IC(50) for S-flurbiprofen inhibition of gemcabene glucuronidation was similar in HLM (60.6 microM) compared with recombinant UGT2B7 (27.4 microM), consistent with a major role for UGT2B7 in gemcabene glucuronidation in HLM. In addition, 5,6,7,3',4',5'-hexamethoxyflavone inhibited recombinant UGT1A3 and recombinant UGT2B17-catalyzed gemcabene glucuronidation (with 4-fold greater potency for recombinant UGT1A3) but did not inhibit gemcabene glucuronidation in HLM, suggesting that UGT1A3 and UGT2B17 do not contribute significantly to gemcabene glucuronidation. Reaction rates for gemcabene glucuronidation from a human liver bank correlated well (r(2)=0.722, P<0.0001; n=24) with rates of glucuronidation of the UGT2B7 probe substrate 3'-azido-3'-deoxythymidine. In conclusion, using the three independent experimental approaches typically used for cytochrome P450 reaction phenotyping, UGT2B7 is the major enzyme contributing to gemcabene glucuronidation in human liver microsomes.     

Characterization of fimasartan metabolites in human liver microsomes and human plasma

1.?The metabolites of fimasartan (FMS), a new angiotensin II receptor antagonist, were characterized in human liver microsomes (HLM) and human subjects.

2.?We developed a method for a simultaneous quantitative and qualitative analysis using predictive multiple reaction monitoring information-dependent acquisition-enhanced product ion scanning. To characterize metabolic reactions, FMS metabolites were analyzed using quadrupole-time of flight mass spectrometer in full-scan mode.

3.?The structures of metabolites were confirmed by comparison of chromatographic retention times and mass spectra with those of authentic metabolite standards.

4.?In the cofactor-dependent microsomal metabolism study, the half-lives of FMS were 56.7, 247.9 and 53.3?min in the presence of NADPH, UDPGA and NADPH?+?UDPGA, respectively.

5.?The main metabolic routes in HLM were S-oxidation, oxidative desulfuration, n-butyl hydroxylation and N-glucuronidation.

6.?In humans orally administered with 120?mg FMS daily for 7 days, the prominent metabolites were FMS S-oxide and FMS N-glucuronide in the 0–8-h pooled plasma sample of each subject.

7.?This study characterizes, for the first time, the metabolites of FMS in humans to provide information for its safe use in clinical medicine.     

Identification of enzymes responsible for the N-oxidation of darexaban glucuronide, the pharmacologically active metabolite of darexaban, and the glucuronidation of darexaban N-oxides in human liver microsomes

Darexaban maleate is a novel oral direct factor Xa inhibitor. Darexaban glucuronide (YM-222714) was the major component in plasma after oral administration of darexaban to humans and is the pharmacologically active metabolite. Additionally, YM-222714 N-oxides were detected as minor metabolites in human plasma and urine. It is possible that YM-222714 N-oxides are formed by the N-oxidation of YM-222714 and/or the glucuronidation of darexaban N-oxides (YM-542845) in vivo. The former reaction is the pharmacological inactivation process. In this study, we identified the human enzymes responsible for YM-222714 N-oxidation and the uridine 5'-diphosphate (UDP)-glucuronosyltransferase (UGT) isoforms involved in YM-542845 glucuronidation in vitro. YM-222714 N-oxidation activity was detected in human liver microsomes (HLM), but not in human intestinal microsomes. In HLM, YM-222714 N-oxidation activities were significantly correlated with flavin-containing monooxygenase (FMO) marker enzyme activities (p<0.001) and inhibited by methimazole, a typical inhibitor of FMOs. Recombinant human FMO3 and FMO1 were capable of efficiently catalyzing YM-222714 N-oxidation, but not FMO5 or any recombinant human cytochrome P450 (CYP) isoforms. Considering the mRNA expression levels of FMO isoforms in human liver, these results strongly suggest that YM-222714 N-oxidation in HLM is mainly catalyzed by FMO3. In HLM, YM-542845 glucuronidation was strongly inhibited by typical substrates for UGT1A8, UGT1A9, and UGT1A10. Recombinant human UGT1A7, UGT1A8, UGT1A9, and UGT1A10 were capable of catalyzing YM-542845 glucuronidation, and UGT1A9 exhibited the highest intrinsic clearance. Considered together with the expression levels of UGT isoforms in human liver, these results strongly suggest that YM-542845 glucuronidation in HLM is mainly catalyzed by UGT1A9.     

Assessment of UDP-glucuronosyltransferase catalyzed formation of Picroside II glucuronide in microsomes of different species and recombinant UGTs

1. This study compared the hepatic glucuronidation of Picroside II in different species and characterized the glucuronidation activities of human intestinal microsomes (HIMs) and recombinant human UDP-glucuronosyltransferases (UGTs) for Picroside II.

2. The rank order of hepatic microsomal glucuronidation activity of Picroside II was rat > mouse > human > dog. The intrinsic clearance of Picroside II hepatic glucuronidation in rat, mouse and dog was about 10.6-, 6.0- and 2.3-fold of that in human, respectively.

3. Among the 12 recombinant human UGTs, UGT1A7, UGT1A8, UGT1A9 and UGT1A10 catalyzed the glucuronidation. UGT1A10, which are expressed in extrahepatic tissues, showed the highest activity of Picroside II glucuronidation (K_m?=?45.1 μM, V_max?=?831.9 pmol/min/mg protein). UGT1A9 played a primary role in glucuronidation in human liver microsomes (HLM; K_m?=?81.3 μM, V_max?=?242.2 pmol/min/mg protein). In addition, both mycophenolic acid (substrate of UGT1A9) and emodin (substrate of UGT1A8 and UGT1A10) could inhibit the glucuronidation of Picroside II with the half maximal inhibitory concentration (IC₅₀) values of 173.6 and 76.2 μM, respectively.

4. Enzyme kinetics was also performed in HIMs. The K_m value of Picroside II glucuronidation was close to that in recombinant human UGT1A10 (K_m?=?58.6 μM, V_max?=?721.4 pmol/min/mg protein). The intrinsic clearance was 5.4-fold of HLMs. Intestinal UGT enzymes play an important role in Picroside II glucuronidation in human.

     

Structure- and isoform-specific glucuronidation of six curcumin analogs

1.?In the present study, we aimed to characterize the glucuronidation of six curcumin analogs (i.e. RAO-3, RAO-8, RAO-9, RAO-18, RAO-19, and RAO-23) derived from galangal using human liver microsomes (HLM) and twelve expressed UGT enzymes.

2.?Formation of glucuronide was confirmed using high-resolution mass spectrometry. Single glucuronide metabolite was generated from each of six curcumin analogs. The fragmentation patterns were analyzed and were found to differ significantly between alcoholic and phenolic glucuronides.

3.?All six curcumin analogs except one (RAO-23) underwent significant glucuronidation in HLM and expressed UGT enzymes. In general, the methoxy group (close to the phenolic hydroxyl group) enhanced the glucuronidation liability of the curcumin analogs.

4.?UGT1A9 and UGT2B7 were primarily responsible for the glucuronidation of two alcoholic analogs (RAO-3 and RAO-18). By contrast, UGT1A9 and four UGT2Bs (UGT2B4, 2B7, 2B15 and 2B17) played important roles in conjugating three phenolic analogs (RAO-8, RAO-9, and RAO-19). Interestingly, the conjugated double bonds system (in the aliphatic chain) was crucial to the substrate selectivity of gastrointestinal UGTs (i.e. UGT1A7, 1A8 and 1A10).

5.?In conclusion, glucuronidation of six curcumin analogs from galangal were structure- and isoform-specific. The knowledge should be useful in identifying a curcumin analog with improved metabolic property.     

Metabolism of the anthelmintic drug niclosamide by cytochrome P450 enzymes and UDP-glucuronosyltransferases: metabolite elucidation and main contributions from CYP1A2 and UGT1A1

1. Niclosamide is an old anthelmintic drug that shows potential in fighting against cancers. Here, we characterized the metabolism of niclosamide by cytochrome P450 enzymes (CYPs) and UDP-glucuronosyltransferases (UGTs) using human liver microsomes (HLM) and expressed enzymes.

2. NADPH-supplemented HLM (and liver microsomes from various animal species) generated one hydroxylated metabolite (M1) from niclosamide; and UDPGA-supplemented liver microsomes generated one mono-O-glucuronide (M2). The chemical structures of M1 (3-hydroxy niclosamide) and M2 (niclosamide-2-O-glucuronide) were determined through LC–MS/MS and/or NMR analyses.

3. Reaction phenotyping revealed that CYP1A2 was the main enzyme responsible for M1 formation. The important role of CYP1A2 in niclosamide metabolism was further confirmed by activity correlation analyses as well as inhibition experiments using specific inhibitors.

4. Although seven UGT enzymes were able to catalyze glucuronidation of niclosamide, UGT1A1 and 1A3 were the enzymes showed the highest metabolic activities. Activity correlation analyses demonstrated that UGT1A1 played a predominant role in hepatic glucuronidation of niclosamide, whereas the role of UGT1A3 was negligible.

5. In conclusion, niclosamide was subjected to efficient metabolic reactions hydroxylation and glucuronidation, wherein CYP1A2 and UGT1A1 were the main contributing enzymes, respectively.     

Evaluation of 3'-azido-3'-deoxythymidine, morphine, and codeine as probe substrates for UDP-glucuronosyltransferase 2B7 (UGT2B7) in human liver microsomes: specificity and influence of the UGT2B7*2 polymorphism.

UDP-glucuronosyltransferase 2B7 (UGT2B7) is involved in the glucuronidation of a wide array of clinically important drugs and endogenous compounds in humans. The aim of this study was to identify an isoform-selective probe substrate that could be used to investigate genetic and environmental influences on glucuronidation mediated by UGT2B7. Three potential probe substrates [3'-azido-3'-deoxythymidine (AZT), morphine, and codeine], were evaluated using recombinant UGTs and human liver microsomes (HLMs; n = 54). Of 11 different UGTs screened, UGT2B7 was the principal isoform mediating AZT glucuronidation, morphine-3-glucuronidation, and morphine-6-glucuronidation. Codeine was glucuronidated equally well by UGT2B4 and UGT2B7. Enzyme kinetic analysis of these activities typically showed higher apparent Km values for HLMs (pooled and individual) compared with UGT2B7. This difference was least (less than 2-fold higher Km) for AZT glucuronidation and greatest (3- to 6-fold higher Km) for codeine glucuronidation. Microsomal UGT2B7 protein content correlated well with AZT glucuronidation (rs = 0.77), to a lesser extent with morphine-3-glucuronidation (rs = 0.50) and morphine-6-glucuronidation (rs = 0.51), but very weakly with codeine glucuronidation (rs = 0.33). Livers were also genotyped for the UGT2B7*2 (H268Y) polymorphism. No effect of genotype on microsomal glucuronidation or UGT2B7 protein content was observed. In conclusion, although both AZT and morphine can serve as in vitro probe substrates for UGT2B7, AZT appears to be more selective than morphine. Codeine is not a useful UGT2B7 probe substrate because of significant glucuronidation by UGT2B4. The UGT2B7*2 polymorphism is not a determinant of glucuronidation of AZT, morphine, or codeine in HLMs.