Glucuronidation of N-hydroxy metabolites of N-acetylbenzidine
36
Citation
0
Reference
10
Related Paper
Citation Trend
Abstract:
Glucuronidation of N-hydroxy arylamines is thought to be a necessary step in their initiation of bladder cancer. This was evaluated for the N-hydroxy metabolites of N-acetylbenzidine (ABZ). N'-Hydroxy-N-acetylbenzidine (N'-HA), N-hydroxy-N-acetylbenzidine (N-HA) and N-hydroxy- N,N'-diacetylbenzidine (N-HDA) were synthesized. Except for N'-HA, these compounds were quite stable. Ascorbic acid and/or acidic pH increased the stability of N'-HA. When each N-hydroxy compound was added to reaction mixtures containing [14C]UDP-glucuronic acid, 3 mM ascorbic acid and human liver microsomes a new product was detected by HPLC. Emulgen 911 was a better detergent than Triton X-100 for expressing microsomal activity, with maximal glucuronidation observed with 0.3% Emulgen 911. At 0.125 mM amine the rate of glucuronidation was N-HDA >> N'-HA = benzidine > ABZ > N-HA. In contrast, at 0.5 mM amine the rate of glucuronidation of N-HA was only exceeded by N-HDA. At pH 5.5 and 37 degrees C the t1/2 for the enzymatically prepared glucuronide conjugates of ABZ, N'-HA and N-HA were 7.5 min and 3.5 and 1.8 h respectively. For N-HDA > 90% of this glucuronide remained after 24 h. At pH 7.4 and 37 degrees C the t1/2 for the glucuronide conjugates of ABZ and N-HA were 2.3 and 2 h respectively, with the amounts remaining after 24 h for N'-HA and N-HDA being 75 and 90% respectively. At pH 6.5 the t1/2 for N'-HA was 14 h. Thus only glucuronides of ABZ and N'-HA exhibit pH-dependent changes in t1/2. Compared with ABZ, glucuronides the N-hydroxy metabolites are more stable at acidic pH. Acidic urine would be more likely to hydrolyze the glucuronide conjugate of ABZ than those of its N-hydroxy metabolites. Because these results are different from that hypothesized for arylmonoamines, a new model was developed to explain the role of N-oxidation, N-glucuronidation and N-acetylation in the carcinogenesis of benzidine, an aryldiamine.Keywords:
Glucuronide
Cite
Citations (7)
HMR1098, a novel KATP-blocking agent, is metabolized to form an S-glucuronide in rat and dog bile. Synthesis of the S-glucuronide metabolite was studied in human liver and kidney microsomes. Recombinant UPD-glucuronosyltransferases (UGTs) were screened for activity, and kinetic analysis was performed to identify the isoform or isoforms responsible for the formation of this novel S-glucuronide in humans. S-Glucuronidation is relatively rare, but from this study it appears that S-glucuronides are not generated exclusively by a single UGT isoform. From the panel of recombinant isoforms used, both UGT1A1 and UGT1A9 catalyzed the glucuronidation of HMR1098. The Vmax values in both instances were similar, but the Km for UGT1A1 was substantially lower than that measured for UGT1A9, 82 μM compared with 233 μM, respectively. Liver and kidney microsomes displayed similar Km values, but the Vmax in kidney was more than 20-fold less than in liver microsomes, which is suggestive of a significant role for the bilirubin UGT in catalysis of HMR1098, although other UGTs may play a secondary role.
Glucuronide
Microsoma
UGT2B7
Cite
Citations (23)
Use of the immunosuppressant mycophenolic acid ( MPA ) in cats is limited because MPA elimination depends on glucuronidation, which is deficient in cats. We evaluated formation of major (phenol glucuronide) and minor (acyl glucuronide, phenol glucoside, and acyl glucoside) MPA metabolites using liver microsomes from 16 cats, 26 dogs, and 48 humans. All MPA metabolites were formed by human liver microsomes, while dog and cat liver microsomes formed both MPA glucuronides, but only one MPA glucoside (phenol glucoside). Intrinsic clearance ( CL int) of MPA for phenol glucuronidation by cat liver microsomes was only 15–17% that of dog and human liver microsomes. However, CL int for acyl glucuronide and phenol glucoside formation in cat liver microsomes was similar to or greater than that for dog and human liver microsomes. While total MPA conjugation CL int was generally similar for cat liver microsomes compared with dog and human liver microsomes, relative contributions of each pathway varied between species with phenol glucuronidation predominating in dog and human liver microsomes and phenol glucosidation predominating in cat liver microsomes. MPA conjugation variation between cat liver microsomes was threefold for total conjugation and for phenol glucosidation, sixfold for phenol glucuronidation, and 11‐fold for acyl glucuronidation. Our results indicate that total MPA conjugation is quantitatively similar between liver microsomes from cats, dogs, and humans despite large differences in the conjugation pathways that are utilized by these species.
Glucuronide
Microsoma
Cite
Citations (25)
AIM To investigate the gender-related differences in the metabolism of trans tramadol (trans T) enantiomers and the glucuronidation of trans O-demethyltramadol (M1) enantiomers. METHODS In vitro, trans T or M1 were separately incubated with liver microsomes of male or female rats. The concentrations of the enantiomers of trans T and M1 were determined by an HPCE method. RESULTS Compared with (+)-enantiomers, (-)-trans T was preferentially metabolized, and (-)-M1 was produced faster in rat liver microsomes. (+)-M1 and (-)-M1 were preferentially glucuronidated in the liver microsomes of male and female rats, respectively. Compared with those in male rat liver microsomes, the enantiomeric ratios of CLint for M1 formation and M1 glucuronidation were more deviated from 1 in female rat liver microsomes. CONCLUSION In vitro, trans T metabolism, M1 formation and M1 glucuronidation were found to be stereoselective in rat liver microsomes. There were gender-related differences in the stereoselectivity in M1 formation and M1 glucuronidation, with a larger extent in female rat liver microsomes.
Microsoma
Cite
Citations (1)
The glucuronidation of 3'-azido-3'-deoxythymidine (AZT) by rat and human liver microsomes has been studied in vitro. The AZT-glucuronide was preliminarily identified through specific hydrolysis by beta-glucuronidase and rigorous product identification was performed by high-field proton nuclear magnetic resonance and fast-atom-bombardment mass spectrometry. A beta-linked 5'-O-glucuronide was the exclusive product formed in liver microsomes. Rat and human liver microsomal uridine 5'-diphosphoglucuronyltransferase activities toward AZT were investigated. These studies revealed that AZT had a lower Km and a 5-6-fold higher relative catalytic efficiency for uridine 5'-diphosphoglucuronyltransferase in human as compared to rat liver microsomes which may play a role in the quantitative differences observed in the degree of AZT glucuronidation between rat and human.
Glucuronide
Microsoma
Cite
Citations (28)
Wushanicaritin, a natural polyphenol compound, exerts many biological activities. This study aimed to characterize wushanicaritin glucuronidation by pooled human liver microsomes (HLM), human intestine microsomes and individual uridine diphosphate-glucuronosyltransferase (UGT) enzyme. Glucuronidation rates were determined by incubating wushanicaritin with uridine diphosphoglucuronic acid-supplemented microsomes. Kinetic parameters were derived by appropriate model fitting. Reaction phenotyping, the relative activity factor (RAF) and activity correlation analysis were performed to identify the main UGT isoforms. Wushanicaritin glucuronidation in HLM was efficient with a high CLint (intrinsic clearance) value of 1.25 and 0.69 mL/min/mg for G1 and G2, respectively. UGT1A1 and 1A7 showed the highest activities with the intrinsic clearance (CLint) values of 1.16 and 0.38 mL/min/mg for G1 and G2, respectively. In addition, G1 was significantly correlated with β-estradiol glucuronidation (r = 0.847; p = 0.0005), while G2 was also correlated with chenodeoxycholic acid glucuronidation (r = 0.638, p = 0.026) in a bank of individual HLMs (n = 12). Based on the RAF approach, UGT1A1 contributed 51.2% for G1, and UGT1A3 contributed 26.0% for G2 in HLM. Moreover, glucuronidation of wushanicaritin by liver microsomes showed marked species difference. Taken together, UGT1A1, 1A3, 1A7, 1A8, 1A9 and 2B7 were identified as the main UGT contributors responsible for wushanicaritin glucuronidation.
Uridine diphosphate
Glucuronosyltransferase
Microsoma
Cite
Citations (18)
Microsoma
Cite
Citations (9)
Objective:To compare the glucuronidation stereoselectivities of propranolol in rat hepatic microsome and study the influence of inducer PB on the glucuronidation of propranolol enantiomers.Methods:Rat hepatic microsome from control and PB induced rats were prepared for glucuronidation reaction.A RP HPLC method was used to determine propranolol concentrations in microsome incubations.Results:Stereoselectivities were observed in enzymatic affinity(Km),maximum reaction speed(Vmax) and intrinsic clearance (Clint).PB induction singnificantly increased Vmax and Clint of R(+) propranolol( P 0.01 or 0.001),and Km and Vmax of S(-)propranolol( P 0.001);but Clint of S(-) propranolol was significantly lowed( P 0.05).The glucuronidation of propranolol in rat hepatic microsome has stereoselectivity of S(-) propranolol,and the induction of PB reduced the difference between R(+) and S(-) propranolol glucuronidation in rat hepatic microsome.Conclusion:The PB induction changed the catalysis abilities of rat hepatic microsome to propranolol glucuronidation and still remained the stereoselectivity of S(-) propranolol.
Phenobarbital
Microsoma
Cite
Citations (0)
The glucuronidation of o-aminophenol is unaffected by p-nitrophenyl gluronide when native microsomal fractions are the source of UDP-glucuronyltransferase. When microsomal fractions treated with Lubrol detergent are the source of the enzyme, however, p-nitrophenyl glucuronide exhibits competitive inhibition of o-aminophenol glucuronidation. In addition, the apparent K1 for p-nitrophenyl glucuronide is the same whether o-aminophenol or p-nitrophenol is the acceptor substrate. The data suggest that UDP-glucuronyltransferase has one binding site for the two phenols and that the absence of inhibition observed in native microsomal fractions is dependent on an intact microsomal membrane.
Glucuronide
Microsoma
Product inhibition
Cite
Citations (0)
Glucuronide
Xenobiotic
Cite
Citations (39)