Effect of N-glucuronidation on urinary bladder genotoxicity of 4-aminobiphenyl in male and female mice

Urinary bladder cancer is the fourth most commonly diagnosed malignancy in men and the tenth most commonly diagnosed malignancy in women in the US. Arylamines have long been associated with bladder cancer and several studies documented that men exposed to arylamines (cigarette smokers, hairdressers, and workers of dye and textile industries) have several times increased risk compared to women. N-glucuronidation is an important phase II conjugation reaction that delivers the active metabolites of arylamines from the liver to the urinary bladder. In the current study, we found that male mice are more active in 4-ABP N-glucuronidation than female mice and this difference was statistically significant. In the in vivo experiments, male and female mice (strain C57BL/6) were treated with 4-ABP after modulating their 4-ABP N-glucuronidation using the plant steroid, hecogenin. The distribution of 4-ABP adducts in liver and bladder was then determined. In animals treated with 4-ABP only, males had statistically significant higher levels of DNA adducts in the bladder (p-value 0.0004) while females had statistically significant higher levels in the liver (p-value < 0.0001). Hecogenin co-treatment increased levels of DNA adducts in the liver in both males and females but this increase was statistically significant only in males (p-value 0.0024). There was a slight decrease in levels of DNA adducts in the bladder in both males and females co-treated with hecogenin, but this decrease was statistically insignificant. Using two-way ANOVA, we found that gender and hecogenin treatment both had a statistically significant effect on liver DNA adduct levels, whereas only gender had statistically significant effect on bladder adduct levels where males have about 2.2-fold higher DNA adducts than females. The current data suggests that N-glucuronidation of 4-ABP may have an important impact on the organ distribution of DNA damage. The fact that there was only a slight decrease in bladder adduct levels compared to the significant increase in the liver in groups co-treated with hecogenin indicates that besides N-glucuronidation, conjugation and metabolic activation by other enzymes may also contribute to the transport of the proximate metabolites of 4-ABP to the bladder.