A clonal cell line (BME-UV1) as a possible model to study bovine mammary epithelial metabolism: metabolism and cytotoxicity of aflatoxin B1

Despite the toxicological risks to which humans and animals are exposed due to the transfer of toxic xenobiotic metabolites into milk of domestic animals, studies on the metabolizing mechanisms occurring in ruminant mammary gland are totally lacking. To investigate the possible biotransformation capabilities of a bovine mammary epithelial cell line (BME-UV1), monolayers were exposed to aflatoxin B1 (AFB1 - 1.0-8.0 μM). Starting from 4 h of exposure, the hydroxylate metabolite aflatoxin M1 (AFM1) was detected in media by high performance liquid chromatography. AFM1 concentration increased linearly with time for 36-48 h and the percent biotransformation of AFB1 (2-4 μM) at 48 h was about 12-14%. Parallel cytotoxicity assays (neutral red uptake-NRU and MTT assays) were performed to investigate the possible interference of AFB1 cytotoxicity with cellular metabolism. MTT assay (from 24 h of cell exposure) and NRU assay (from 16 h of cell exposure) showed time-dependent and time/concentration-dependent decrease of cell viability, respectively, and the former assay being more successful at revealing cytotoxic effects (NRU: CC₅₀ at 48 h = 12.00 ± 2.66 μM; MTT: CC₅₀ at 72 h = 20.42 ± 7.30 μM). The results suggest that BME-UV1 cells express metabolizing enzymes having catalytic activity, thus representing a potential in vitro model for studying biotransformation in bovine mammary gland.