In vitro response of the brown bullhead catfish (BB) and rainbow trout (RTG-2) cell lines to benzo[a]pyrene

Established cell lines from rainbow trout (RTG-2) and brown bullhead catfis h (BB) were evaluated as bioindicators of benzo[a]pyrene (B[a]P) toxicity w ith 3-(4,5-dimethyltiazol-2-yl)-2,5-diphenyl tetrazolium bromide (MTT) redu ction and neutral red (NR) uptake assays. Cytochrome P450 1A1 (CYP1A1) enzy matic activity was also evaluated, and taken as a biological indicator of t he B[a]P induction power by ethoxyresorufin O-deethylase (EROD) and ethoxyc oumarin O-deethylase (ECOD) assays. The BE and RTG-2 cells were compared af ter 1 and 6 days of exposure to Bra]P. The photoactivation of the compound (B[a]PUV) was another parameter taken into consideration. Cytotoxicity was not observed after 1 day of incubation with B[a]P in both cell lines, altho ugh the enzymatic activities of ECOD and EROD presented an induction. Appar ently, after 1 day, cells did not metabolise sufficient amounts of B[a]P to cytotoxic metabolites. After 6 days of exposure to this compound a signifi cant reduction in cell viability was observed, this reduction being superio r to 50% at the highest B[a]P concentrations for the RTG-2 cell line. These results are in agreement with the values observed for the ECOD and EROD in duction. The B[a]P cytotoxicity determined in both cell lines could be ascr ibed to the significant increase of EROD activity by 6 days of exposure. Th e photoactivation of B[a]P showed marked differences in both cytotoxic assa ys and CYP1A1 enzymatic activities, for both cell lines. After 1 day of exp osure there was a significant reduction in cell viability, superior to 50% for the RTG-2 cell line. However, it was observed that no induction occurre d but rather a decrease in ECOD and EROD activities. Six days of incubation with B[a]PUV showed a decrease in cell viability at the highest concentrat ions for the BE cells and at the lowest concentrations for the RTG-2 cell l ine, and the CYP1A1 enzymatic activity presented a significant induction. T hese results and those observed after 1 day of exposure suggest that B[a]PU V acts as a direct-acting toxicant as well as a metabolism-mediated toxican t-like B[a]P. The RTG-2 cells were more sensitive to B[a]P and its toxic me tabolites as well as to the photoactivation of the compound, in both exposu re times tested. The finding that the cell lines responded to the CYP1A1 in duction in a very efficient way gives proof of the applicability of this sy stem to environmental biomonitoring and toxicology. (C) 2000 Elsevier Scien ce B.V. All rights reserved.