Glucuronidation of N-acetylbenzidine by human liver

N-Glucuronidation is an important pathway in aromatic amine metabolism. This study assessed N-glucuronidation of N-acetylbenzidine by human liver slices and microsomes. With slices, considerable metabolism of [3H]N-acetylbenzidine (0.2 mM) was observed during a 2-hr incubation. N-Acetylbenzidine N&#...

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Published inDrug metabolism and disposition Vol. 22; no. 6; p. 922
Main Authors Babu, S R, Lakshmi, V M, Zenser, T V, Davis, B B
Format Journal Article
LanguageEnglish
Published United States 01.11.1994
Subjects
Aged
Benzidines - metabolism
Female
Glucuronates - metabolism
Glucuronosyltransferase - physiology
Humans
In Vitro Techniques
Liver - metabolism
Male
Middle Aged
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Summary:N-Glucuronidation is an important pathway in aromatic amine metabolism. This study assessed N-glucuronidation of N-acetylbenzidine by human liver slices and microsomes. With slices, considerable metabolism of [3H]N-acetylbenzidine (0.2 mM) was observed during a 2-hr incubation. N-Acetylbenzidine N'-glucuronide represented significant metabolism in four different human liver samples (6-33% of the total recovered radioactivity following HPLC). Benzidine (11-43%), benzidine N-glucuronide (8-11%), and N,N'-diacetylbenzidine (0-2%) were also formed. The kinetics of N-acetylbenzidine N'-glucuronide formation were investigated using Triton X-100-pretreated microsomes. Data were best described by a two-component Michaelis-Menten model composed of both high-affinity (low KM) and low-affinity (high KM) UDP-glucuronsyltranosferases. The high- and low-affinity KMs were 0.36 +/- 0.02 and 1.07 +/- 0.12 mM, respectively. To help identify the UDP-glucuronosyltransferases metabolizing N-acetylbenzidine, 23 transferase substrates were tested for their ability to inhibit glucuronidation. At 0.25 mM, bilirubin, estriol, and 17-epiestriol were good inhibitors (< 50% of control). Dose-response inhibition studies with estriol and 4-aminobiphenyl demonstrated that each agent reached a plateau as its concentration was increased. IC50 for estriol and 4-aminobiphenyl was 0.15 +/- 0.03 and 0.57 +/- 0.06 mM, respectively. Complimentary inhibition was observed when these agents were combined at maximal inhibitory concentrations. These results suggest that more than one UDP-glucuronosyltransferase metabolizes N-acetylbenzidine. N-Glucuronidation represents a major pathway for N-acetylbenzidine metabolism in humans.
ISSN:0090-9556