A high pressure liquid chromatography study on the removal of DNA-bound aflatoxin B¹ in rat liver and in vitro

Following intraperitoneal administration of [³H] aflatoxin B¹ (AFB¹) to young adult male rats, there is rapid uptake of the carcinogen by the liver, the target organ for carcinogenesis, leading to DNA covalent binding. Acid hydrolysis of this DNA shows that after 2h, the major DNA adduct is trans 8, 9-dihydro-8-(7-guanyl)-9-hydroxy AFB¹ (AFB¹-gua). By 24h after AFB¹administration the major DNA adduct is no longer AFB¹-gua but a product with the identical retention time on h.p.l.c. to 8, 9-dihydro-8-(N⁵-formyl-2', 5', 6' triamino-4' oxo-N⁵-pyrimidyl)-9-hydroxy AFB¹ (AFBrtriamino-Py). 48h after carcinogen administration, only a small amount of AFB¹-gua remains and the major product is AFB¹-triamino-Py. The half-life of removal of AFB¹gua is 22h, while AFB¹-triamino-Py is much more persistent. In vitro incubation studies on DNA isolated from rats treated 2h previously with [³H] AFB¹ show that at pH 7.4 AFBi-gua is the major product released from the DNA with some release of 8, 9-dihydro-8, 9-dihydroxy AFB¹, (AFB¹-diol). If more extensively reacted AFB¹DNA is used than that obtained from in vivo administration, then the rate of AFB¹-diol release is enhanced while that of AFB¹gua is reduced. It would appear, therefore, that much of the release of AFB¹ from DNA in vivo within the first 24h is probably not through a DNA repair process but through chemical release arising from the positively charged N⁷-guanine. There is considerable conversion of AFB¹-gua to AFBi-triamino-Py onin vitro incubation of DNA as well as AFB¹-gua and AFB¹-diol release. By 24h approximately 66% of the bound AFB¹ is in the form of AFB¹-triamino-Py and after 48h the conversion is complete. The complex pattern of AFB¹release fromDNA may have important consequences in both the induction of mutations and in tumour initiation.