DNA binding and adduct formation of aflatoxin B1 in cultured human and animal tracheobronchial and bladder tissues

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Abstract
DNA binding and adduct formation of aflatoxin B1 (AFB1) was studied in cultured bladder and tracheobronchial explants from human, monkey, dog, hamster and rat. Explants were exposed to [3H]AFB1 (1 μM final concentration) in PFMR-4 medium (pH 7.4) without serum for 24 h, after which epithetial cell DNA was isolated by hydroxylapatite chromatography. Binding (μmol AFB1/mol deoxyribo-nucledetide, mean ± SD) was higher in tracheobronchial tissues (human, 2.2 ± 2.4; rat, 5.7 ± 2.4; dog, 10.6 ± 6.6; hamster 134.6 ± 44.6) than in bladder tissues (human, 1.5 ± 2.3; monkey, 2.5 ± 1.1; rat, 3.8 ± 1.1; dog, 5.2 ± 2.3; hamster, 26.2 ± 13.3). These binding levels were not correlated with the relative susceptibilities of these species to AFB1 hepatocarcinogenesis, in that the hamster and the dog are insensitive, but exhibited the highest binding, while the susceptible species, the rat and the monkey, had lower binding. After acid hydrolysis of the isolated DNA, the [3H]AFB1-DNA adducts were separated by h.p.l.c. In all cases, almost all of the [3H]AFB1-DNA represented addition of AFB1 to the N7 atom of guanine, the major adduct (40–79% of the total) being 8, 9-dihydro-8-(N5-formyl-2', 5', 6' -triamino-4' -oxo-N5-pyrimidyl)-9-hydroxyAFB1, with minor amounts (7–28%) of 8,9-dihydro-8-(N7-guanyl)-9-hydroxyAFB1. In some cases small amounts (0–8%) of unknown, polar adducts could be detected. It is concluded that, qualitatively, AFB1-DNA adduct formation by human and animal bladder and tracheobronchilal explants is similar to that found in other in vitro and in vivo extrahepatic and hepatic systems, but that in vitro binding data of AFB1 to extrahepatic animal tissues can probably not be used to predict the susceptibility of the human to AFB1-related cardnogenesis in these tissues.