Effects of salinity acclimation on the expression and activity of Phase I enzymes (CYP450 and FMOs) in coho salmon (Oncorhynchus kisutch)
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Phase I biotransformation enzymes are critically important in the disposition of xenobiotics within biota and are regulated by multiple environmental cues, particularly in anadromous fish species. Given the importance of these enzyme systems in xenobiotic/endogenous chemical bioactivation and detoxification, the current study was designed to better characterize the expression of Phase I biotransformation enzymes in coho salmon (Oncorhynchus kisutch) and the effects of salinity acclimation on those enzymes. Livers, gills, and olfactory tissues were collected from coho salmon (O. kisutch) after they had undergone acclimation from freshwater to various salinity regimes of seawater (8, 16 and 32 g/L). Using immunoblot techniques coupled with testosterone hydroxylase catalytic activities, 4 orthologs of cytochrome P450 (CYP1A, CYP2K1, CYP2M1, and CYP3A27) were measured in each tissue. Also, the expression of 2 transcripts of flavin-containing monooxygenases (FMO A and B) and associated activities were measured. With the exception of CYP1A, which was down-regulated in liver, protein expression of the other 3 enzymes was induced at higher salinity, with the greatest increase observed in CYP2M1 from olfactory tissues. In liver and gills, 6β- and 16β-hydroxylation of testosterone was also significantly increased after hypersaline acclimation. Similarly, FMO A was up-regulated in all 3 tissues in a salinity-dependent pattern, whereas FMO B mRNA was down-regulated. FMO-catalyzed benzydamine N-oxygenase and methyl p-tolyl sulfoxidation were significantly induced in liver and gills by hypersalinity, but was either unchanged or not detected in olfactory tissues. These data demonstrate that environmental conditions may significantly alter the toxicity of environmental chemicals in salmon during freshwater/saltwater acclimation.
KeywordsSalmonids Salinity acclimation Pesticide biotransformation CYP450 FMO
The authors appreciated Prof. Dr. Margarita Curras-Collazo for her help with plasma osmolality measurements. The authors would like to thank Dr. D. R. Buhler from Oregon State University for the anti-CYP2M1 and anti-CYP2K1 antibodies and Dr. Malin Celander from University of Goteborg, Sweden, for the anti-CYP3A27 antibodies. This work was supported from funds of the University of Washington Superfund Basic Research Program (NIEHS P42ES04696).
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