Aminoheterocycles are important environmental carcinogens. They are abundant in cooked foods, cigarette smoke and ambient air. The long-term goal of this project is to better understand the mechanisms of human urinary bladder carcinogenesis. The immediate intent is to investigate the carcinogenic potential for human urinary bladder of this class of compounds. These amines are N-hydroxylated and conjugated with glucuronic acid in the liver, then excreted as N-hydroxy-N-glucuronide metabolites (N-OH-N-Gl) through biliary and urinary routes. These metabolites can be activated, following deconjugation, by esterification to yield electrophiles that covalently bind predominantly to the deoxyguanosine residues of DNA. Since humans are constantly exposed to these amines and excrete their N-OH-N-Gl metabolites, these amines may be potential carcinogens for human intestine and urinary bladder. Since bladder epithelial cells cannot absorb N-OH-N-Gl metabolites and urine is deficient in beta-glucuronidase activity that converts these glucuronides to absorbable N-OH metabolites, it appears that only those aminoheterocycles whose N-OH-N-Gls are hydrolyzable in urine may be carcinogenic for urinary bladder.
The specific aims of this project are to answer the questions: (1) Are the N-OH-N-Gl metabolites of these aminoheterocycles hydrolyzable in neutral solution or susceptible to cleavage by beta-glucuronidase? (2) Are their N-OH metabolites activated by urothelial cells of human and other species? (3) Do their N-OH-N-Gl metabolites induce urothelial tumors in rat and human urothelial tissue? Are only those hydrolyzable in neutral solution carcinogenic for urinary bladder? Experimentally, the N-OH and N-OH-N-Gl metabolites of eight aminoheterocycles reported to be present in both cooked foods and cigarette smoke, and structurally similar to the strong bladder carcinogen 2-acetylaminofluorene will be synthesized. The hydrolysis of these glucuronides in aqueous solution, with or without the presence of beta-glucuronidase, will be determined. The abilities of these N-OH and N-OH-N-Gl derivatives to produce DNA adducts and elicit unscheduled DNA synthesis (UDS) in primary cultures of urothelial cells of human and other species will be investigated. The N-OH-N-Gl will be tested for carcinogenicity in rat bladders transplanted in syngeneic rats. To explore the carcinogenic potential for human urinary bladder, the compounds that are most carcinogenic for rat bladder will be tested in human ureters implanted in athymic nude rats. The relationship between the stabilities of N-OH-N-Gls, and their abilities to induce UDS and urothelial tumors will be evaluated. This project may provide insight into the genotoxic potential of an important class of compounds to which humans are exposed. Moreover, it may also provide a unique opportunity for tumor induction in a human organ outside the human body.
