Human CYP1A1-activated aneugenicity of aflatoxin B1 in mammalian cells and its combined effect with benzo(a)pyrene.

Aflatoxin B1 (AFB1) is the most toxic mycotoxin and a proven human carcinogen that requires metabolic activation, known by cytochrome P450 (CYP) 1A2 and 3A4. Previous evidence showed that AFB1 is activated by human recombinant CYP1A1 expressed in budding yeast. Yet, the toxicity, in particular the genotoxicity of the reactive metabolites formed from AFB1 remains unclear. Humans could be exposed to both AFB1 and benzo(a)pyrene (BaP) simultaneously, thus we were interested in their combined genotoxic effects subsequent to metabolic activation by CYP1A1. In this study, molecular docking of AFB1 to human CYP1A1 indicated that AFB1 is valid as a substrate. In the incubations with AFB1 in human CYP1A1-expressed microsomes, AFM1 as a marking metabolite of AFB1 was detected. Moreover, AFB1 induced micronucleus formation in a Chinese hamster V79-derived cell line and in a human lung epithelial BEAS-2B cell line, both expressing recombinant human CYP1A1, V79-hCYP1A1 and 2B-hCYP1A1 cells, respectively. Immunofluorescence of centromere protein B stained micronuclei was dominant in AFB1-treated BEAS-2B cells exposed to AFB1, suggesting an aneugenic effect. Moreover, AFB1 elevated the levels of ROS, 8-OHdG, AFB1-DNA adduct, and DNA breaks in 2B-hCYP1A1 cells, compared with those in the parental BEAS-2B cells. Meanwhile, AFB1 increased CYP1A1, RAD51, and γ-H2AX protein levels in 2B-hCYP1A1 cells, which were attenuated by the CYP1A1 inhibitor bergamottin. Co-exposure of AFB1 with BaP increased 8-OHdG, RAD51, and γ-H2AX levels (indicating DNA damage). In conclusion, AFB1 could be activated by human CYP1A1 for potent aneugenicity, which may be further enhanced by co-exposure to BaP.