Synthesis of N-glucuronides of carcinogenic N-hydroxyarylamines

Glucuronide conjugates of 4-aminobiphenyl and its N-hydroxy metabolites. pH stability and synthesis by human and dog liver

Glucuronide conjugates of arylamines are thought to be important in the carcinogenic process. This study investigated the pH stability and synthesis of glucuronide conjugates of 4-aminobiphenyl and its N-hydroxy metabolites by human and dog liver. Both dog and human liver slices incubated with 0.06 mM [3H]-4-aminobiphenyl produced the N-glucuronide of 4-aminobiphenyl as the major product. After 2 hr of incubation, the N-glucuronide of 4-aminobiphenyl represented 52 and 27% of the total radioactivity recovered by HPLC in dog and human, respectively. When 4-aminobiphenyl, N-hydroxy-4-aminobiphenyl, or N-hydroxy-N-acetyl-4-aminobiphenyl was added to human microsomes containing [14C]UDP-glucuronic acid, a new product peak was detected by HPLC. At 0.5 mM, the rate of glucuronidation was N-hydroxy-N-acetyl-4-aminobiphenyl > N-hydroxy-4-aminobiphenyl > 4-aminobiphenyl. The rate of formation of the N-glucuronide of 4-aminobiphenyl was similar to that observed with benzidine and N-acetylbenzidine. The glucuronides of 4-aminobiphenyl and N-hydroxy-4-aminobiphenyl were both acid labile with T1/2 values of 10.5 and 32 min, respectively, at pH 5.5. The glucuronide of N-hydroxy-N-acetyl-4-aminobiphenyl was not acid labile with T1/2 values at pH 5.5 and 7.4 of 55 and 68 min, respectively. The glucuronide of 4-aminobiphenyl was the most acid labile conjugate examined. Thus, the glucuronide of 4-aminobiphenyl is a major product of dog and human liver slice metabolism and likely to play an important role in the carcinogenic process.

Genetic toxicity of 2-acetylaminofluorene, 2-aminofluorene and some of their metabolites and model metabolites

2-Acetylaminofluorene and 2-aminofluorene are among the most intensively studied of all chemical mutagens and carcinogens. Fundamental research findings concerning the metabolism of 2-acetylaminofluorene to electrophilic derivatives, the interaction of these derivatives with DNA, and the carcinogenic and mutagenic responses that are associated with the resulting DNA damage have formed the foundation upon which much of genetic toxicity testing is based. The parent compounds and their proximate and ultimate mutagenic and carcinogenic derivatives have been evaluated in a variety of prokaryotic and eukaryotic assays for mutagenesis and DNA damage. The reactive derivatives are active in virtually all systems, while 2-acetylaminofluorene and 2-aminofluorene are active in most systems that provide adequate metabolic activation. Knowledge of the structures of the DNA adducts formed by 2-acetylaminofluorene and 2-aminofluorene, the effects of the adducts on DNA conformation and synthesis, adduct distribution in tissues, cells and DNA, and adduct repair have been used to develop hypotheses to understand the genotoxic and carcinogenic effects of these compounds. Molecular analysis of mutations produced in cell-free, bacterial, in vitro mammalian, and intact animal systems have recently been used to extend these hypotheses.

Lack of carcinogenicity of 2-aminofluorene, its glucuronide and the glucuronide of N-hydroxy-2-acetylaminofluorene in heterotopic bladder of the rat

The role of 2-aminofluorene and its N-glucuronide and the O-glucuronide of N-hydroxy-2-acetylaminofluorene in the bladder carcinogenesis by 2-aminofluorene were investigated. These compounds were injected into heterotopically transplanted bladders of male rats at a weekly dose of 1 mumol for 20 weeks. The experiment was terminated at the end of 50 weeks. The results showed that none of these compounds were carcinogenic in the heterotopically transplanted bladder. The O-glucuronide was not carcinogenic even when it was administered in a phosphate saline (pH 8.0), that favors the activation of this compound. The N-glucuronide of N-hydroxy-2-aminofluorene, a positive control, produced urothelial tumors. These results are consistent with the hypothesis that the N-glucuronides of hydroxylamines, but not the O-glucuronides of hydroxamic acids, are responsible for bladder carcinogenesis by arylamines.

A review of the methods of chemical synthesis of sulphate and glucuronide conjugates

1. Methods for the synthesis of drug conjugates with sulphuric acid have been reviewed. 2. Some analytical methods are presented for the analysis of sulphate conjugates. 3. The synthesis of several types of N, O and C beta-D-glucuronides is reviewed. Different beta-coupling reactions of protected glucuronides are presented. 4. Application of n.m.r. and mass spectrometry to the analysis of beta-D-glucuronides is discussed.

Glucuronidation of carcinogenic arylamine metabolites by rat liver microsomes

Since 2-acetylaminofluorene (2-AAF), 4-acetylaminobiphenyl (4-AABP) and 2-aminonaphthalene (2-AN) display varying degrees of carcinogenicity in the rat, which is capable of N-acetylating arylamines, an attempt was made to correlate the difference in carcinogenicity of these compounds with the ease of O-glucuronidation of their hydroxamic acids by rat hepatic microsomes, a reaction believed to be a detoxification mechanism. UDP-glucuronosyltransferase activity of rat hepatic microsomes was activated by Triton X-100. Glucuronidation by Triton X-100 activated microsomes of the N-hydroxy derivative of 2-AN was approximately 1.5 and 1.8 times faster than the corresponding derivatives of 2-aminofluorene (2-AF) and 4-aminobiphenyl (4-ABP) respectively. However, glucuronidation of the N-hydroxy-N-acetyl derivative of 2-AN was 40 and 17 times faster than the corresponding derivatives of 2-AF and 4-ABP respectively. Aroclor 1254 and 3-methylcholanthrene, but not phenobarbital, acetanilide and butylated hydroxytoluene, induced the enzyme for the glucuronidation of 2-AN derivatives. The present study (1) demonstrates an inverse relationship between the carcinogenicity of 2-AN, 4-AABP and 2-AAF and the ease of glucuronidation of their hydroxamic acid derivatives, and (2) suggests that, in addition to N- and C-hydroxylation, glucuronidation may play an important role in determining the carcinogenicity of arylamines and arylacetamides in the rat.