Aquatic Toxicology 90 (2008) 172–181 Contents lists available at ScienceDirect Aquatic Toxicology journal homepage: www.elsevier.com/locate/aquatox Energy intake affects the biotransformation rate, scope for induction, and metabolite proﬁle of benzo[a]pyrene in rainbow trout Christopher J. Kennedy ∗ , Keith B. Tierney Department of Biological Sciences, Simon Fraser University, Burnaby, BC, Canada V5A 1S6 article info Article history: Received 12 July 2008 Received in revised form 12 August 2008 Accepted 13 August 2008 Keywords: Benzo[a]pyrene Rainbow trout Biotransformation Diet Fasting Hepatocytes abstract The metabolic conversion of benzo[a]pyrene (B[a]P) by rainbow trout (Oncorhynchus mykiss) hepatocytes was not signiﬁcantly different between any group of fed ﬁsh (fed one of three isoenergetic diets that varied in protein and lipid content at full satiation levels or half rations), however at 12 weeks, fasted ﬁsh exhib- ited signiﬁcantly reduced B[a]P biotransformation rates (by 58%). Alterations in metabolite proﬁles were also seen: fasted ﬁsh produced signiﬁcantly more Phase I metabolites, higher levels of both glucuronide and sulphate conjugates, and lower levels of presumptive glutathione conjugates, compared to fed ﬁsh. When ﬁsh were fasted, higher proportions of phenols were produced, with lower proportions of quinones, triols and tetrols. Inducing metabolism (using -naphthoﬂavone) increased metabolic scope for B[a]P by 2-fold, regardless of each diet’s baseline metabolic rate. However, the balance between Phase I and II reactions was altered with induction and fasting: higher proportions of Phase I metabolites were found, with lower glutathione conjugates and higher proportions of triols/tetrols. Fasting-mediated reductions in glutathione conjugation, and increased induction of oxidation vs. conjugating enzymes, can explain altered metabolite proﬁles. These results suggest that in contaminated habitats, where pollution-induced reductions in food quantity or quality are combined with the presence of toxic compounds and inducers, detoxiﬁcation rates can be diminished. © 2008 Elsevier B.V. All rights reserved. 1. Introduction Resistance to xenobiotics begins with the basic strategy of reducing cellular uptake and intracellular accumulations. The early evolution of systems capable of reducing xenobiotic accumula- tion highlights the signiﬁcance of cellular resistance systems and their ﬁtness advantages (Lage, 2003; Stegeman and Hahn, 1994). For example, it has been suggested that the evolution of the large number of P450 genes 400 million years ago corresponded with the advance of animals onto land where the ability to biotrans- form phytochemicals in terrestrial plants was selected for (Yang et al., 1992). With the more recent addition of synthetic xenobiotics to the existing natural chemical challenge, defense strategies have become ever more important, in fact, it is likely that human-derived contamination is now an evolutionary selection pressure. At least three major lines of xenobiotic defense exist in eukary- otic cells: (1) the efﬂux of moderately hydrophobic compounds (or metabolites) by the ABC-binding cassette P-glycoproteins, (2) the biotransformation (metabolism) of hydrophobic xenobiotics to more hydrophilic products mediated by Phase I (functionaliza- ∗ Corresponding author. Tel.: +1 778 782 5640; fax: +1 778 782 3496. E-mail address: ckennedy@sfu.ca (C.J. Kennedy). tion) and Phase II (conjugation) reactions, and (3) ABC-transporters (multidrug resistance-associated protein family) which mediate the efﬂux of conjugated metabolites (Phase II products) of xeno- biotics. The importance of biotransformation in reducing bioaccu- mulation and the toxicity of xenobiotics is well known. Although it has been intensively studied in teleosts, attempts at predicting metabolic transformation rates a priori has proven to be difﬁcult. An understanding of the signiﬁcant factors that can affect transfor- mation rates is therefore extremely important. Aside from factors which affect the concentrations of substrate at the enzyme level, there are a number of pharmacological, physiological, and envi- ronmental factors that can affect speciﬁc rates of biotransformation in ﬁsh: species and strain, age, sex, disease status, pre-exposure to xenobiotics, and water quality parameters such as temperature and salinity (Johnston et al., 1999; Seubert and Kennedy, 1997). Nutritional modulations can have both profound and subtle con- sequences on biotransformation through both direct and indirect effects. Both macronutrient and micronutrient content in mam- malian diets, as well as energy intake, are known to affect the levels and rates of xenobiotic biotransformation (Paine and McLean, 1973; Parke and Ioannides, 1981). When nutrients involved directly in biotransformation reactions are limiting, there are generally decreases in metabolism, however, indirect effects can also occur by altering the status of other nutrients, i.e. nutrient–nutrient or 0166-445X/$ – see front matter © 2008 Elsevier B.V. All rights reserved. doi:10.1016/j.aquatox.2008.08.016