Human liver glucuronidation of benzidine.
Although glucuronidation is considered an important pathway in aromatic amine-induced bladder cancer, benzidine glucuronidation has not been assessed in humans. Glucuronidation of benzidine was assessed with human liver microsomes and slices. Emulgen 911-treated microsomes exhibited a Km for benzidine of 0.8 +/- 0.06 mM and a Vmax of 4.2 +/- 0.7 nmol/mg protein/min. A variety of agents were tested for their ability to inhibit benzidine N-glucuronide formation. At 0.25 mM, estriol, 17-epiestriol, bilirubin, hyodeoxycholic acid and cyproheptadine were good inhibitors (< 50% of control). Dose-dependent inhibition studies with estriol, testosterone and 4-aminobiphenyl demonstrated that each agent reached a plateau as its concentration was increased. When these agents were combined at maximal inhibitory concentrations, additive inhibition was observed. These results suggest that more than one UDP-glucuronosyltransferase metabolizes benzidine. The cDNA clones pUDPGTh-1 and -2 encode transferases which metabolize hyodeoxycholic acid and estrogen derivatives, but neither transferase catalyzed benzidine glucuronidation. Slices were used to assess metabolism by intact tissue and converted [3H]benzidine (0.09 mM) to N-acetyl-benzidine. N-Glucuronides of both benzidine and N-acetylbenzidine were observed and represented 14-37% of the total recovered radioactivity. The amount of N-acetylbenzidine N'-glucuronide observed was proportional to the amount of N-acetylbenzidine produced. Thus, N-glucuronidation appears to represent a major pathway for metabolism of benzidine in humans. The extent of N-acetylation affects the proportion of benzidine and N-acetylbenzidine glucuronidated by human liver slices.
Babu
S R
SR
VA Medical Center, Department of Biochemistry, St. Louis, MO.
Lakshmi
V M
VM
Owens
I S
IS
Zenser
T V
TV
Davis
B B
BB
D000368:Aged; D001560:Benzidines / Q000378:metabolism*; D006528:Carcinoma, Hepatocellular / Q000378:metabolism / Q000556:secondary; D003110:Colonic Neoplasms / Q000378:metabolism / Q000473:pathology; D005260:Female; D005965:Glucuronates / Q000378:metabolism*; D014453:Glucuronosyltransferase / Q000037:antagonists & inhibitors / Q000378:metabolism; D006801:Humans; D007700:Kinetics; D008099:Liver / Q000201:enzymology / Q000378:metabolism*; D008113:Liver Neoplasms / Q000378:metabolism / Q000556:secondary; D008297:Male; D008862:Microsomes, Liver / Q000201:enzymology / Q000378:metabolism; D008875:Middle Aged; D013045:Species Specificity; D014316:Tritium
D001560:Benzidines; D005965:Glucuronates; D014316:Tritium; C029876:benzidine; C075855:benzidine N-glucuronide; D014453:Glucuronosyltransferase