Reduction of mutagenicity and toxicity of aflatoxin B1 by chlorine gas treatment.

Chlorine gas was used to treat aflatoxin B1 (AFB1). The time-related exposure study showed that 4 ml (15 mg) pure chlorine gas caused about 90% destruction of 100 micrograms AFB1 within 10 min, at standard temperature and pressure. Four fluorescent reaction products were produced, two of which were identified as 8,9-dichloro-AFB1 and 8,9-dihydroxy-AFB1 (diol). The use of [14C]AFB1 confirmed the 90% destruction of the compound by chlorine gas. An increased destruction of AFB1 also occurred when an increased amount of chlorine gas was used. The mutagenic activity of the AFB1 sample treated for 10 min was reduced to about 5% of the untreated control using the Salmonella typhimurium strain TA98 in the presence of a rat-liver S-9 mix. A similar time-related reduction in AFB1 toxicity after chlorine treatment was also achieved using the chicken embryo toxicity assay.

Dietary protein level and aflatoxin B1-induced preneoplastic hepatic lesions in the rat.

Previous studies have shown that the development in rats of aflatoxin B1 (AFB1)-induced gamma-glutamyl transpeptidase-positive (GGT+) foci, indicators of early preneoplastic liver lesions, was markedly greater when a 20% casein diet was fed than when a 5% casein diet was fed during the postinitiation period. In the present study, the dose-response relationship between dietary protein level (dose) and emergence of AFB1-induced GGT+ foci (response) in livers of rats was determined. Male Fischer-344 rats fed a 20% casein diet were orally administered AFB1 at a dose level of 250 micrograms/(kg X d) (10 doses over 12 d). One week after the last dose, the animals were divided into eight groups and fed isoenergetic diets containing either 4, 6, 8, 10, 12, 15, 20 or 30% dietary casein for the remaining 12 wk of the study. The development of GGT+ foci, as measured by number and percent of liver volume occupied, displayed a response with three discrete phases. The lowest dietary protein levels, 4, 6, 8 and 10% casein, were associated with a minimal level of GGT+ foci development. Between 10 and 12% dietary casein, the development of GGT+ foci sharply increased, up to the 15-30% dietary casein level. The sudden increase in the formation of GGT+ foci at 10-12% dietary casein was just above the level of dietary casein (6-8%) required for maximum body weight gain. These results in this animal model suggest that protein intake in excess of that required to sustain maximum growth rate may enhance AFB1-induced cancer development.

Relative contribution of dietary protein level and aflatoxin B1 dose in generation of presumptive preneoplastic foci in rat liver.

Male weanling F344 rats were orally gavaged with aflatoxin B1 (AFB1) in daily doses of 200, 235, 270, 300, and 350 micrograms/kg/day for a total of 10 doses over a 12-day period, and then 1 week after the last dose they were fed diets of varying protein (casein) content to compare the contribution of AFB1 dose and dietary protein level on the development of presumptive preneoplastic gamma-glutamyltransferase-positive (GGT+) foci in rat liver. All animals were fed the same 20% dietary casein level during the dosing period. One week after the end of the dosing period, one-half of the animals in each dose group were then continued on the 20% casein diet for the entire 12-week foci-development period; the remaining half in each dose group were fed lower levels of dietary casein during the foci-development period for the increasing AFB1 dose groups (20, 16, 12, 8, and 4% casein for the 235-, 250-, 270-, 300-, and 350-micrograms/kg/day groups, respectively). The AFB1 dose groups used were determined in a preliminary experiment. In this previous experiment, a clearly discernible threshold dose at about 100-150 micrograms AFB1/kg/day (below which no GGT+ foci were observed) and a steep slope between 150 and 400 micrograms/kg/day were produced. In the second experiment, while the expected positive slope of (AFB1) dose versus (GGT+ foci) response relationship was found for animals fed the 20% casein diet, the dose response for the animals fed the lower levels of casein was eliminated, providing evidence that nutrient intake during the postdosing foci development is more rate limiting toward the development of these preneoplastic lesions than is the carcinogen dose.