Syntheses of DNA adducts of two heterocyclic amines, 2-amino-3-methyl-9H-pyrido[2,3-b]indole (MeAαC) and 2-amino-9H-pyrido[2,3-b]indole (AαC) and identification of DNA adducts in organs from rats dosed with MeAαC

Abstract

2-Amino-3-methyl-9H-pyrido[2,3-b]indole (MeAαC) and 2-amino-3-methyl-9H-pyrido[2,3-b]indole (AαC) are mutagenic and carcinogenic heterocyclic amines formed during ordinary cooking. MeAαC and AαC are activated to mutagenic metabolites by cytochrome P450-mediated N-oxidation to the corresponding N2-OH derivatives. The proximate mutagenic N2-OH derivatives of MeAαC and AαC did not react with deoxynucleosides or DNA. However, upon acetylation with acetic anhydride both reacted with 2′-deoxyguannosine and 3′-phospho-2′-deoxyguanosine, resulting in one adduct each, but not with other nucleosides or nucleotides. The adducts were identified as N2-(2′-deoxyguanosin-8-yl)-MeAαC, N2-(2′-deoxyguanosin-8-yl)-AαC, N2-(3′-phospho-2′-deoxyguanosin-8-yl)-MeAαC and N2-(3′-phospho-2′-deoxyguanosin-8-yl) -AαC by comparison with adducts of known structure obtained by reaction of the parent amines with acetylated guanine N3-oxide. N2-OH-MeAαC and N2-OH-AαC reacted with calf thymus DNA after addition of acetic anhydride. 32P-postlabelling analysis of modified DNA showed one major adduct co-migrating with N2-(3′,5′-diphospho-2′-deoxyguanosin-8-yl -MeAαC and N2-(3′,5′-diphospho-2′ -deoxyguanosin-8-yl-AαC, respectively. Some minor adducts presumed to be undigested oligomers were also detected . 32P-postlabelling analysis of DNA from several organs of rats dosed orally with MeAαC showed that in vivo N2-(2′-deoxyguanosin-8-yl)-MeAαC also was the major adduct formed. Relative adduct level in DNA isolated from the liver of the rats was about 50.40 adducts/109 nt. The adduct levels were ∼4-fold lower in the colon and the heart and ∼12-fold lower in the kidney of the rats. © Oxford University Press 2004; all rights reserved.