In vitro reactions of aflatoxin B1-adducted DNA

J. D. Groopman, R. G. Croy, G. N. Wogan

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The chemical stability of aflatoxin B1 bound to calf thymus DNA was studied over a 48-hour exposure to phosphate buffers at pH 6.8-8.0 (37°C). During this time, aliquots of the aflatoxin B1-modified DNA were acid-hydrolyzed and analyzed for the presence of r184w1.w2 =2,3-dihydroxy-2-(n5-formyl-2',5',6'-triamino-4'-oxo-n5-p yrimidyl-3-hydroxyaflatoxin r185w1 =2,3-dihydro-2-(8,9-dihydro-8-hydroxy-n7-guanyl)-3-hydroxy aflatoxin l atoxin B1 and 2,3-dihydro-2-(8.9-dihydro-8-hydroxy-N7-guanyl)-3-hydroxyaflatoxin B1. Initial experiments determined the stability of 2,3-dihydro-2(N7-guanyl)-3-hydroxyaflatoxin B1 in DNA at levels of modification of one residue per 60 and 1500 nucleotides. The acid-hydrolysis products obtained from these modified nucleic acids were qualitatively similar, but their proportional concentrations were different. These quantitative differences were dependent upon both pH and the initial level of modification of the DNA. During the first 6 hr of incubation, under all conditions examined, the formation of 2,3-dihydro-2,3-dihydroxyaflatoxin B1 was responsible for the initial decrease of the 2,3-dihydro-2-(N7-guanyl)-3-hydroxyaflatoxin B1 adduct in DNA. After 48 hr of incubation at pH 7.0 the major reaction of the modified DNA was depurination of the 2,3-dihydro-2-(N7-guanyl)-3-hydroxyaflatoxin B1 adduct. However, at pH 8.0, the predominant reaction product formed in 48hr was the putative 2,3-dihydro-2-(N5-formyl-2',5',6'-triamino-4'-oxo-N5-pyrimidyl)-3-hydroxy-aaflatoxin B1. The putative DNA-bound products resulting from the elimination of the positive charge in the imidazole ring of the aflatoxin-N7-guanine adduct [2,3-dihydro-2-(N5-formyl-2',5',6'-triamino-4'-oxo-N5-pyrimidyl)-3-hydroxy-aflatoxin r206w1 =2,3-dihydro-2-(8,9-dihydro-8-hydroxy-N7-guanyl)-3-hydroxy aflatoxin B1] B1 and 2,3-dihydro-2-(8.9-dihydro-8-hydroxy-N7-guanyl)-3-hydroxyaflatoxinB1] were found to be stable in DNA for at least 24 hr at both pH 6.8 and 7.4. Taken together with observed patterns of stability of aflatoxin B1 adduct in vivo, these observations strongly suggest the involvement of enzymatic repair processes in removal of the N7-guanyl adduct and also emphasize the possible biological significance of the stable imidazole ring-opened adduct.

Original languageEnglish (US)
Pages (from-to)5445-5449
Number of pages5
JournalProceedings of the National Academy of Sciences of the United States of America
Issue number9 II
StatePublished - 1982
Externally publishedYes

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