Indexed on: 03 Feb '09Published on: 03 Feb '09Published in: Journal of toxicology and environmental health. Part A
The mechanisms by which the biocide tributyltin (TBT) and its metabolites affect the hormonal and xenobiotic biotransformation pathways in aquatic species are not well understood. In this study hepatocytes isolated from salmon were used to evaluate the mechanistical effects of TBT on fish hormonal and xenobiotic biotransformation pathways. Cells were exposed to 0.01, 0.1, 1, or 5 microM TBT and samples were collected at 0, 12, 24, or 48 h following exposure. Gene expression patterns were evaluated using quantitative polymerase chain reaction (PCR), and cytochrome P-450 (CYP)-mediated enzyme activities were evaluated by ethoxyresorufin, benzyloxyresorufin, and pentoxyresorufin O-deethylase (EROD, BROD, and PROD, respectively) activity assays. Generally, exposure of hepatocytes to 1 microM (at 48 h) and 5 microM TBT (at 12, 24, and 48 h) consistently produced reductions in all mRNA species investigated. TBT produced significant decreases of vitellogen (Vtg) expression at 48 h and modified the expression patterns of estrogen receptors (ERalpha and ERbeta) and androgen receptor-beta (ARbeta) that were dependent on time and TBT concentration. In the xenobiotic biotransformation pathway, TBT produced differential expression patterns that were dependent on exposure time and concentration for all salmonid AhR2 isoforms (AhR2alpha, AhR2beta, AhR2delta, and AhR2gamma). For CYP1A1, CYP3A, AhRR, and Arnt mRNA, TBT produced exposure- and time-specific modulations. Catalytic CYP activities showed that BROD activity increased in an apparent concentration-specific manner in cells exposed to TBT for 12 h. Interestingly, EROD activity showed a TBT concentration-dependent increase at 24 h and PROD at 12 and 48 h of exposure. In general our data show that TBT differentially modulated hormonal and biotransformation responses in the salmon in vitro system. The apparent and consistent decrease of the studied responses with time in 1 and 5 microM exposed hepatocytes suggest a possible transcription inhibitory effect of TBT.