CYP contributes to the metabolism
CYP450 contributes to the metabolism of more than 90% of currently available drugs (Shapiro and Shear, 2002). Currently, CYP1A is the most studied xenobiotic-metabolizing isoform in fish and is often used as a biomarker for early effects of pollutants in aquatic organisms (Havelkova et al., 2007). The CYP3A Angiotensin 1/2 (1-9) synthesis represent the family responsible for metabolism of 50% of currently prescribed drugs (Hasler et al., 1999). Presence of a CYP3A protein has been detected in Atlantic cod (Gadus morhua l.) (Husoy et al., 1994) and fathead minnow (Pimephales promelas) (Christen et al., 2010). Other isoforms may play a major role in metabolism of pharmaceutical compounds. The ethanol-inducible CYP2E1 contributes to oxidative and/or reductive metabolism of a broad range of toxicologically important compounds (Caro and Cederbaum, 2004). P-nitrophenol hydroxylation (PNPH) is a CYP2E1-catalyzed reaction in mammals and often used as a marker to estimate mammalian CYP2E1 activity. P-nitrophenol hydroxylation activity has also been detected in fish (Geter et al., 2003, Zlabek and Zamaratskaia, 2012).
The presence of pharmaceuticals in the aquatic environment can induce and/or inhibit CYP450 activity in fish and thus modify enzymatic pathways mediated by CYP450 and cause unfavorable physiological effects and toxicity (Laville et al., 2004). Clotrimazole (CLO) and dexamethasone (DEX) have been detected in the aquatic environment at ngL−1 level (Peschka et al., 2007, Liu et al., 2011, Kugathas et al., 2012). Fish can serve as sensitive bioindicators for exposure of aquatic organisms to chemical pollutants (van der Oost et al., 2003).
Clotrimazole belongs to the imidazole group, often used for treatment of fungal infections. It decreases fungal growth by inhibiting CYP51 conversion of lanosterol to ergosterol, an essential component of fungal cell membranes (Rozman and Waterman, 1998). As CLO acts via the inhibition of the CYP51-mediated sterol 14α-demethylase activity, there is a potential for interaction with other crucial CYP mediated reactions. For example, CLO has unwanted side effects through the inhibition of aromatase activity (CYP19), a key steroidal enzyme involved in the synthesis of androgens to estrogens, as shown in vitro in humans (Trosken et al., 2006) and in fish (Monod et al., 1993, Hinfray et al., 2006; Cheshenko et al., 2008).
Recent studies have indicated that short-term exposure of zebrafish to CLO results in induction of several steroidogenic enzymes and increased expression of testicular genes related to steroidogenesis (Hinfray et al., 2011, Baudiffier et al., 2012). Other reports on fish show that CLO acts as an inhibitor of CYP1A (Levine et al., 1999), CYP2K1, CYP3A27 (Miranda et al., 1998) and as inducer of CYP1A (Navas et al., 2004).
Dexamethasone is a potent synthetic member of the glucocorticoid class of steroid drugs (Hockey et al., 2009). Glucocorticosteroids have inhibitory action on inflammatory mediators of both the cyclo-oxygenase and lipoxygenase pathways of arachidonic acid metabolism (Vane and Botting, 1987).
The metabolite profile of DEX in human liver microsomes has been described by Tomlinson et al. (1997). DEX influences induction of CYP2B, CYP2A, CYP3A, and probably also CYP2C11 activity in rat (Ringel et al., 2002) and induction of CYP3A in human (Lu and Li, 2001) primary hepatocytes. There is limited information about the elimination pathway of DEX in fish. Studies on trout have suggested DEX induction of 3-cyano-7-ethoxycoumarin metabolism, a reaction used to estimate mammalian CYP1A2 activity, but have not shown it to significantly affect CYP450-mediated reactions in killifish (Fundulus heteroclitus) (Smith and Wilson, 2010) and grass carp (Ctenopharyngodon idellus) (Li et al., 2008). These results were explained by significant differences in the regulation of CYP induction via the pregnane X receptor in mammals and fish.
Materials and methods
Discussion There are a large number of studies of the inhibition of CYP450 by pharmaceuticals in mammalian in vitro models. In contrast, limited information is available for fish CYP450. This study evaluated in vitro inhibition potency of human drugs CLO and DEX on selected CYP450-mediated reactions in hepatic microsomes from juvenile rainbow trout. Both CLO and DEX are known to inhibit mammalian CYP450 (Ayub and Levell, 1988; Relling et al., 1993).