Role of N-glucuronidation in benzidine-induced bladder cancer in dog.
The mechanism by which benzidine induces bladder cancer in dog was evaluated by assessing metabolism of [3H]benzidine by dog liver slices and microsomes. Slices incubated with 0.05 mM [3H]benzidine exhibited a 32.5 min incubated with 0.05 mM [3H]benzidine exhibited a 32.5 min peak, which was also produced when microsomal incubations were supplemented with UDP-glucuronic acid. In contrast to microsomes, very little of the 32.5 min peak was produced with the 100,000 g supernatant fraction. Microsomal metabolism was increased 5-fold by pretreatment with Triton X-100. Very little activity was observed with rat microsomes in either the presence or absence of Triton X-100. This metabolite was also generated by incubating benzidine with glucuronic acid at 4 degrees C for 3 days. Thermospray MS identified this metabolite as benzidine N-glucuronide. At 37 degrees C, the t1/2 stability of purified N-glucuronide was 99, 25 and 3 min in dog urine adjusted to pH 7.3, 6.3 and 5.3 respectively. The N-glucuronide was quite stable at pH 9.3, in dog plasma, and in aprotic solvents for 4 h at 37 degrees C. Relative to benzidine, its N-glucuronide is weakly bound to plasma proteins but not more reactive with DNA. Thus, detoxification by liver provides a mechanism for accumulation of benzidine in acidic urine, uptake of benzidine into bladder epithelium, and activation of benzidine in bladder. The liver and N-glucuronidation play a potentially important role in the species specificity of benzidine carcinogenesis.
Babu
S R
SR
VA Medical Center, St Louis, MO.
Lakshmi
V M
VM
Hsu
F F
FF
Zenser
T V
TV
Davis
B B
BB
D000818:Animals; D001560:Benzidines / Q000138:chemical synthesis / Q000302:isolation & purification / Q000378:metabolism* / Q000633:toxicity*; D004247:DNA / Q000378:metabolism*; D004285:Dogs; D005965:Glucuronates / Q000138:chemical synthesis / Q000302:isolation & purification / Q000378:metabolism*; D014453:Glucuronosyltransferase / Q000378:metabolism*; D066298:In Vitro Techniques; D008099:Liver / Q000378:metabolism*; D013058:Mass Spectrometry; D008862:Microsomes, Liver / Q000378:metabolism*; D014535:Uridine Diphosphate Glucuronic Acid / Q000378:metabolism*; D001749:Urinary Bladder Neoplasms / Q000139:chemically induced* / Q000378:metabolism
D001560:Benzidines; D005965:Glucuronates; D014535:Uridine Diphosphate Glucuronic Acid; C029876:benzidine; C075855:benzidine N-glucuronide; D004247:DNA; D014453:Glucuronosyltransferase