BENZIDINE GLUCURONIDATION IN DOG LIVER

Dog is an animal model for assessing aromatic amine-induced bladder ca ncer, and hepatic N-glucuronidation is proposed as an important pathwa y leading to initiation of carcinogenesis. Therefore, benzidine N-gluc uronidation was evaluated with dog liver microsomes and slices. Micros omal benzidine UDP-glucuronosyltransferase activity was increased with a variety of detergents. For kinetic analysis, native microsomal prep arations were separated into treated (detergent treated, not centrifug ed) or soluble (detergent treated, centrifuged) fractions. The deterge nts Triton X-100, Lubrol PX, Emulgen 911 and CHAPS increased the speci fic activity of treated fractions relative to the native microsomes 3- to 6-fold. The specific activities of the soluble fractions were high est with Emulgen 911 and CHAPS at a detergent-to-protein ratio of 1. S ubsequent studies used Emulgen 911 or CHAPS. Similar results were obse rved with either preparation. For treated preparations, the K(m) and V (max) values were 0.142 +/- 0.006 mM and 0.65 +/- 0.1 nmol/mg protein/ min respectively. A variety of chemicals were tested for their effect on benzidine N-glucuronide formation. At 0.1 mM, the only effective in hibitors (<50% of control) were 2-aminofluorene, estriol, 17-epiestrio l, 2-OH-estrone, and 4-OH-estrone. With Emulgen-treated microsomes, th e K(i) values for 2-aminofluorene, 4-aminobiphenyl and estriol were 0. 114 +/- 0.014, 0.347 +/- 0.032 and 0.047 +/- 0.003 mM respectively. 2- Aminofluorene and estriol were noncompetitive inhibitors, while 4-amin obiphenyl was a competitive inhibitor. Slices incubated with these che micals exhibited an inhibition profile similar to that observed with m icrosomes. Thus, N-glucuronidation of benzidine may be an important me tabolic pathway in dog. Inhibition of benzidine N-glucuronidation by e striol and catechol estrones may be important in vivo events in aromat ic amine-induced carcinogenesis.