Humans and other mammals exhibit a genetic polymorphism in acetylation capacity that affects susceptibility to cancers related to arylamine chemicals. Various acetyl transfer steps have been identified in the metabolic activation and deactivation of arylamines to their ultimate carcinogenic forms. Enzymatic capacity for N- and O-acetylation catalysis may be controlled at a single and common structural gene locus encoding a single acetyltransferase isozyme capable of catalyzing both reactions. To test that hypothesis, homozygous rapid acetylator congenic inbred hamster strains, Bio. 82.73/H/Pat-rr and Bio. 1.51HIPat-rr, were constructed, isogenic to the Bio. 82.73/H/Pat-ss and Bio. 1.51HIPat-ss homozygous slow acetylator inbred hamster strains, respectively, except for a small segment (0.025%) of the hamster genome containing the locus coding for N-acetyltransferase. Consequently, one objective in the current proposal is to make direct comparisons in the expression and inheritance of the metabolic activation of N-hydroxy-arylamines to DNA adducts (via O-acetylation) between the homozygous rapid acetylator congenic strains and their corresponding homozygous slow acetylator progenitor strains. N-hydroxylation of arylamines to their N-hydroxy derivatives is an obligatory step in the metabolic activation to ultimate electrophiles. One hypothesis is that N-acetylation of arylamines is essentially a detoxication mechanism specifically by competition with the N-hydroxylation of arylamines. Moreover, a related hypothesis is that this detoxication mechanism is important not only in liver but also in target organs where the tumors are expressed, such as the bladder and colon. Thus, rapid acetylators should have higher levels of arylamides but lower levels of N-hydroxy-arylamines than slow acetylators, and the genetic toxicology and other toxic manifestations resulting from the metabolic activation of arylamines to N-hydroxy arylamines should be greater in slow acetylators. These hypotheses will be tested both in vitro and in vivo through direct comparisons between homozygous rapid and slow acetylator congenic inbred hamsters and in human tissues. Studies will center upon the oxidation and acetylation of the arylamine carcinogens, 2-aminofluorene (AF) and 3.2'-dimethyl-4-aminobiphenyl (DMABP) and metabolites. The in vitro studies will be carried out in tissues derived from homozygous rapid and slow acetylator congenic inbred hamster strains. In addition, companion studies will utilize human tissues from organ donors. The levels of arylamine metabolic activation will be compared between rapid and slow acetylators by measurement of key metabolites and by quantitating the levels of covalent arylamine-DNA adducts formed. The in vivo studies will make direct comparisons between congenic homozygous rapid and slow acetylator inbred hamsters in the metabolic activation of AF and DMABP by quantitating the serum and urinary levels of Salmonella mutagens, and the levels of covalently bound arylamine-hemoglobin adducts in blood and arylamine-DNA adducts in bladder. Chronic DMABP tumorigenesis studies in the homozygous rapid and slow acetylator congenic strains are also proposed to assess directly the role of acetylator genotype on the site, incidence, and severity of tumors. The long term objective of this program is to understand the metabolic basis for the relationship of acetylator genotype to increased risk of arylamine-induced bladder cancer.
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