Aflatoxin toxicity in cultured human epidermal cells: stimulation by 2,3,7,8-tetrachlorodibenzo-p-dioxin.
Aflatoxin B1 (AFB1) at 1 microgram/ml was markedly toxic to human epidermal cells grown in the Rheinwald-Green 3T3 feeder layer system. At 0.1 microgram/ml, the toxicity was barely evident, as assessed by colony expansion during a 2 week exposure, but it was dramatically stimulated by 5 nM 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD), which was non-toxic alone. Neither AFB1-dihydrodiol nor AFB2 were toxic in the presence or absence of TCDD, indicating that metabolism to the 8,9-epoxide was responsible for the AFB1 toxicity. Stimulation of AFB1 epoxidation by TCDD was also indicated by the > 20-fold increase in DNA adduct formation in cultures exposed to [14C]AFB1 and TCDD for 4 days as compared to AFB1 alone. Analysis of free metabolites in culture medium by reverse-phase HPLC revealed that confluent epidermal cultures metabolized AFB1 to AFM1, AFB2a and aflatoxicol. In the presence of TCDD, the levels of AFM1 were higher (14 versus 3% of dose) as were those of AFB2a (3 versus 0.5% of dose), while aflatoxicol levels were lower (0.8 versus 2% of dose). In the absence of irradiated 3T3, the toxicities of AFB1, AFB2, AFM1 and aflatoxicol to cells in serum-free medium (0.15 mM Ca2+) were similar to those in the feeder layer system. Although this moderately low calcium concentration appeared quite satisfactory for observing toxicity, the response was attenuated at a lower calcium concentration (0.09 mM Ca2+).
Walsh
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Department of Environmental Toxicology, University of California, Davis 95616-8588.
Hsieh
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Rice
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D016604:Aflatoxin B1 / Q000737:chemistry / Q000378:metabolism / Q000633:toxicity*; D002118:Calcium / Q000494:pharmacology; D002478:Cells, Cultured; D002851:Chromatography, High Pressure Liquid; D003470:Culture Media / Q000494:pharmacology; D004247:DNA / Q000187:drug effects; D004249:DNA Damage; D004357:Drug Synergism; D000078404:Epidermal Cells; D004817:Epidermis / Q000187:drug effects*; D006801:Humans; D015394:Molecular Structure; D000072317:Polychlorinated Dibenzodioxins / Q000633:toxicity*
D003470:Culture Media; D000072317:Polychlorinated Dibenzodioxins; D004247:DNA; D016604:Aflatoxin B1; D002118:Calcium