Aflatoxin-DNA adduct formation in chronically dosed rats fed a choline-deficient diet

Abstract

Nutritional modulation of male Fischer rats by a choline-deficient/methionine-low diet dramatically increases hepatocarcinogenesis and reduces time to first tumors induced by aflatoxin B1 (AFB1). The effect of this diet on hepatic aflatoxin-DNA adduct burden in male Fischer rats dosed with a carcinogenic regimen of AFB1 was examined in this study. After 3 weeks of ingestion of a choline-deficient/methionine-low diet or control semi-purified diet, rats were administered a carcinogenic regimen of 25 micrograms [3H]AFB1 for 5 days a week over 2 weeks. Six choline-deficient and four control diet rats were killed 2 h after each dose, and liver DNA isolated. In addition, hepatic DNA was isolated from animals 1, 2, 3, and 11 days after the last [3H]AFB1 administration. At all time points HPLC analysis of aflatoxin-DNA adducts was performed to confirm radiometric determinations of DNA binding levels. No significant quantitative differences in AFB1-DNA adduct formation between the dietary groups were observed following the first exposure to [3H]AFB1; however, total aflatoxin-DNA adduct levels in the choline-deficient animals were significantly increased during the multiple dose schedule. When total aflatoxin-DNA adduct levels were integrated over the 10 day dose period, a 41% increase in adduct burden was determined for the choline-deficient animals. While this increase in DNA damage is consistent with the hypothesis that DNA damage is related to tumor outcome, the biochemical basis for this effect still needs to be elucidated.

Dissimilarity in aflatoxin dose-response relationships between DNA adduct formation and development of preneoplastic foci in rat liver

“…Prior exposure to high levels (250-350 µg/kg/day) of AFB reduced by about two-thirds adducts formed by the last dose compared to the first. Schrager et al [25] measured AFB-N 7 -guanine adducts after ten doses of about 200-250 µg/kg/ day and found about a 50% decrease in accumulated adducts compared to adduct levels after a single dose.…”

Risk Assessment for Aflatoxin: I. Metabolism of Aflatoxin B1 by Different Species

“…(148) Choline deficiency in the diet increases the incidence of AFB,-induced tumors in DNA adduct levels followed different kinetics in animals maintained on this diet for 3 weeks prior to exposure and during multiple exposures to AFB, (five daily exposures per week for 2 weeks) compared with animals maintained on the control diet. (150) In particular, AFB,-DNA binding in animals fed the choline-deficient diet was maximal in the middle of each exposure week, compared with no significant peak in adduct levels in control animals. Between the peaks, however, adduct levels in animals fed the test diet returned to control levels.…”

Cholineʼs role in maintaining liver function

“…This suggests that the underlying mechanisms for this response to low choline are intrinsic to the hepatocytes. Choline–methionine deficiency also sensitizes rodents to liver carcinogens such as aflatoxin B1 [24]. For example, the dose of aflatoxin B1 needed to induce hepatocarcinomas was greatly reduced in rats fed low-choline–methionine diet [24].…”

“…Choline–methionine deficiency also sensitizes rodents to liver carcinogens such as aflatoxin B1 [24]. For example, the dose of aflatoxin B1 needed to induce hepatocarcinomas was greatly reduced in rats fed low-choline–methionine diet [24]. Thus, choline–methionine deficiency acts as an initiator and as a promoter of carcinogenesis.…”