In previous studies, artificial sunlight and
riboflavin synergistically increased acute
aflatoxin toxicity in rats. Three new experiments were designed to provide information on the interaction of
riboflavin,
aflatoxin, and light. In a study of
carcinogenesis, rats received low levels of
aflatoxin 5 days/wk for 3
wk; 30 min after each dosing, half of them were irradiated for 2 hr. In some, levels of
glucose-6-phosphatase and
acid phosphatase were determined 5 days after completion of treatment. Remaining rats were killed at 30 or 53 wk. All underwent complete necropsies and histopathologic examination. In the second experiment, rats were dosed with
riboflavin and divided into four groups: no further treatment;
aflatoxin (LD50); irradiation (1-2 hr); or
aflatoxin plus irradiation. Blood
riboflavin levels were determined at intervals following these treatments. In the third experiment, the chemical reactions of irradated
aflatoxin and/or
riboflavin were studied by uv spectroscopy and TLC. The 53-wk study showed clearly that light decreased the incidence of
aflatoxin-induced
cancer. The other results may provide an explanation.
Aflatoxin caused blood
riboflavin levels to decrease-an effect enhanced by irradiation, suggesting that photosensitized
riboflavin and
aflatoxin form a complex. This interpretation gains support from studies in vitro that showed that
riboflavin quenched
aflatoxin photodegradation, perhaps by complexing with
aflatoxin. Thus, low, carcinogenic doses of
aflatoxin may complex with endogenous, photosensitized
riboflavin, inhibiting its degradation into carcinogenic metabolites.