Transcriptional effects on glutathione S-transferases in first feeding Atlantic cod (Gadus morhua) larvae exposed to crude oil P.A. Olsvik a, * , T. Nordtug b , D. Altin c , K.K. Lie a , I. Overrein d , B.H. Hansen b a National Institute of Nutrition and Seafood Research, Nordnesboder 1-2, N-5005 Bergen, Norway b SINTEF, Materials and Chemistry, Marine Environmental Technology, N-7465 Trondheim, Norway c Biotrix, N-7022 Trondheim, Norway d SINTEF, Fisheries and Aquaculture, N-7465 Trondheim, Norway article info Article history: Received 15 January 2010 Received in revised form 3 March 2010 Accepted 14 March 2010 Available online 3 April 2010 Keywords: Atlantic cod Exposure Oil dispersion Water-soluble fraction of oil Glutathione S-transferase Transcription abstract Polycyclic aromatic hydrocarbons (PAHs) and other oil compounds are known to induce stress and impact health of marine organisms. Water-soluble fractions of oil contain components known to induce glutathione S-transferases (GSTs), one of the major classes of phase II detoxifying enzymes present in essentially all eukaryotic organisms. In this study, the transcriptional responses of six GSTs (GST pi, GST mu, GST omega, GST theta, GSY zeta and GST kappa) were examined in early larvae of Atlantic cod Gadus morhua exposed to five concentrations of dispersed oil (containing oil droplets and water-sol- uble fraction) and water-soluble fractions (WSF) of oil. When Atlantic cod larvae were exposed to WSF (containing 1.31 ± 0.31 lg P PAH/L for 4 days), expression of GSTM3 and GSTO1 was significantly increased, whereas no differences in GST expression were observed in larvae exposed to a corresponding 50% lower amount of dispersed oil (containing 0.36 ± 0.10 lg P PAH/L for 4 days). The study suggest that although the oil clearly had severe negative effects on the larvae (i.e. concentration-dependent lethality and growth reduction), only minor effects on GST transcription could be observed using RNA obtained from pooled whole-larvae homogenates. This result indicates that the expression of these important detoxification enzymes is only moderately inducible at such an early developmental stage either reflect- ing low tolerance of cod larvae to dispersed oil or alternatively that using whole-larvae homogenates may have masked tissue-specific mRNA induction. Ó 2010 Elsevier Ltd. All rights reserved. 1. Introduction The glutathione S-transferases (GSTs) (GSTs: EC 2.5.1.18) repre- sent a family of phase II enzymes that provide cellular protection against the toxic effects of a number of environmental toxicants. Mechanisms of detoxification by GSTs involve catalytic substrate conjugation and oxidant reduction with reduced glutathione (GSH). Advances in genomics have facilitated the identification and classification of multiple forms of fish GST, as has been true for other phase II drug-metabolizing enzymes (Blanchette et al., 2007; Schlenk et al., 2008). The GST super-family includes cytosolic and mitochondrial GSTs. Based on amino acid sequence similari- ties, seven classes of cytosolic GSTs are recognized in mammalian organisms, designated alpha, mu, pi, sigma, theta, omega, and zeta (Hayes et al., 2005). The kappa class GSTs are quite distinct from cytosolic GSTs, and they represent the mitochondrial GST isoen- zymes. Even though GSTs and uridine diphosphate glu- curonosyltransferases (UGTs), together with the sulfotransferases (SULTs), make up the main phase II detoxifying enzymes, involved in the biotransformation of many POPs, they are also considered to be important antioxidants, involved in antioxidant responsive ele- ment (ARE)-regulated gene expression and the protection of cells against reactive oxygen species. Relatively little is known about GST transcription in fish ex- posed to various toxicants (Schlenk et al., 2008). Typically, only modest alteration of overall GST activity has been reported under most conditions (2-fold or less) (Henson et al., 2001; Henson and Gallagher, 2004). For example, Hasselberg et al. (2004) reported a modest 1.3-fold reduced GST activity in first-spawning male Atlan- tic cod exposed to 0.02 ppm alkylphenol. Four classes of GSTs have previously been characterized in salmonids: pi, mu, theta and al- pha (Donham et al., 2005). Analysis of our Atlantic cod EST data (as of August 2009) suggests that these four isoforms also are pres- ent in this North-Atlantic species (unpublished data). Based upon studies from the plaice (Pleuronectes platessa), a unique fish GST class, Rho, has been designated (Schlenk et al., 2008). Trute et al. (2007) characterized GSTs in coho salmon (Oncorhynchus kisutch) and described two major isoforms in liver, the pi and theta- class GSTs, but noted that they might have a limited capacity to 0045-6535/$ - see front matter Ó 2010 Elsevier Ltd. All rights reserved. doi:10.1016/j.chemosphere.2010.03.026 * Corresponding author. E-mail address: pal.olsvik@nifes.no (P.A. Olsvik). Chemosphere 79 (2010) 905–913 Contents lists available at ScienceDirect Chemosphere journal homepage: www.elsevier.com/locate/chemosphere