In vitro response of the brown bullhead catfish BB/ and rainbow trout RTG-2/ cell lines to benzowaxpyrene

Established cell lines from rainbow trout RTG-2. and brown bullhead catfish BB. were evaluated as bioindicators of benzowaxpyrene BwaxP. toxicity with 3- 4,5-dimethyltiazol-2-yl.-2,5-diphenyl tetrazolium bromide MTT. reduction and neutral red NR. uptake assays. Cytochrome P450 1A1 CYP1A1. enzymatic activity was also evaluated, and taken as a biological indicator of the BwaxP induction power by ethoxyresorufin O-deethylase EROD. and ethoxycoumarin O-deethylase ECOD. assays. The BB and RTG-2 cells were compared after 1 and 6 days of exposure to BwaxP. The photoactivation of the compound BwaxPUV. was another parameter taken into consideration. Cytotoxicity was not observed after 1 day of incubation with BwaxP in both cell lines, although the enzymatic activities of ECOD and EROD presented an induction. Apparently, after 1 day, cells did not metabolise sufficient amounts of BwaxP to cytotoxic metabolites. After 6 days of exposure to this compound a significant reduction in cell viability was observed, this reduction being superior to 50% at the highest BwaxP concentrations for the RTG-2 cell line. These results are in agreement with the values observed for the ECOD and EROD induction. The BwaxP cytotoxicity determined in both cell lines could be ascribed to the significant increase of EROD activity by 6 days of exposure. The photoactivation of BwaxP showed marked differences in both cytotoxic assays and CYP1A1 enzymatic activities, for both cell lines. After 1 day of exposure there was a significant reduction in cell viability, superior to 50% for the RTG-2 cell line. However, it was observed that no induction occurred but rather a decrease in ECOD and EROD activities. Six days of incubation with BwaxPUV showed a decrease in cell viability at the highest concentrations for the BB cells and at the lowest concentrations for the RTG-2 cell line, and the CYP1A1 enzymatic activity presented a significant induction. These results and those observed after 1 day of exposure suggest that BwaxPUV acts as a direct-acting toxicant as well as a metabolism-mediated toxicant-like BwaxP. The RTG-2 cells were more sensitive to BwaxP and its toxic metabolites as well as to the photoactivation of the compound, in both exposure times tested. The finding that the cell lines responded to the CYP1A1 induction in a very efficient way gives proof of the applicability of this system to environmental biomonitoring and toxicology.