Carcinogen-protein complexes in liver during hepatocarcinogenesis by aflatoxin B1 (1)
Mainigi, K.D.; Sorof, S.
Cancer Research 37(12): 4304-4312
1977
ISSN/ISBN: 0008-5472 PMID: 922723 Document Number: 116511
To furnish a basis for evaluation of the roles of individual carcinogen-protein complexes in carcinogenesis, this study provides the initial description of the different kinds of aflatoxin-protein complexes that are present in liver throughout hepatocarcinogenesis by aflatoxin B1 (AFB1) in rats. The various classes of carcinogen-protein complexes were separated according to molecular size and charge, quantitated and characterized in part. Male rats were fed a diet containing AFB1 (1 mg/kg) for 0, 4, 8, 16 or 24 wk or the same diet without carcinogen (control) for 24 wk. The rats were then given a single intragastric dose of [3H]AFB1 and sacrificed 18 or 48 h later. The kinds and relative amounts of labeled aflatoxin-protein complexes present in liver cytosol were essentially unchanged throughout the period of carcinogen feeding. At least 8 macromolecular size classes of labeled complexes were separated by gel filtration, their amounts and modal molecular weights were determined. Three major and 1 minor weakly acidic classes and 2 weakly basic species of radioactive macromolecular complexes were resolved by chromatography involving ion exchange and molecular sieving. Direct incubation (2 h; 1-4.degree. C) of [3H]AFB1 at 1 .times. 10-7 M with nonradioactive liver cytosols of rats fed similarly the AFB1 diet produced 1 size class of labeled aflatoxin-protein complexes with a modal MW of 45,000-50,000 daltons, the molecular size like that of the class of complexes present in greatest amount in vivo. These in vitro-generated complexes, assumed to result from hydrophobic associations, were distributed over the entire charge-size profile. In addition to macromolecular aflatoxin complexes, liver cytosols labeled in vivo or in vitro also had a radioactive nonmacromolecular aflatoxin adduct with an estimated molecular weight of 500-5000 daltons. The ability of metabolites of AFB1 to interact in vivo with a wide variety of liver proteins as well as extensively with DNA and RNA suggests that metabolites of AFB1 react nonspecifically with liver macromolecules. It appears reasonable to speculate that the extraordinary carcinogenic potency of AFB1 may be due to its related capacity to inflict multiple molecular insults on target cells. The presence of multiple aflatoxin macromolecular adducts in liver undergoing carcinogenesis by AFB1 raises the level of complexity of the problem of determining which interactions between activated aflatoxins and target macromolecules are of importance in the oncogenic process.