There is evidence that the response of CYP
There is evidence that the response of CYP450 activity to DEX is species-specific. CYP1A and CYP3A expressions were strongly induced by DEX in porcine hepatocytes (Rasmussen et al., 2014) and in rat and human, but not minipig or beagle dog hepatocytes (Lu and Li, 2001). Within fish, there are also species-specific differences. Thus, in the same study, the effects of DEX were observed in rainbow trout but not in killifish (Smith and Wilson, 2010). Additionally, DEX induced CYP3A activity (induction of aminopyrine N-demethylase and erythromycin N-demethylase) in two grass carp cell lines (Li et al., 2008). Given that DEX is a well-known inducer of mammalian CYP3A, we included two catalyzed reactions (BFCOD and BQOD) to evaluate CYP3A activity. Both affected rainbow trout in similar ways, and induction followed 21d exposure. In mammals, DEX can initiate moclobemide mg of CYP2E1 (Sampol et al., 1997). The CYP2E1-like protein activity has also been identified in fish (Kaplan et al., 1999, Wall and Crivello, 1999, Zamaratskaia and Zlabek, 2011). To date, there are no reports on the in vivo effect of DEX on PNPH activity. In vitro, DEX did not modify PNPH activity in rainbow trout (Burkina et al., 2013); however, we found that PNPH activity was induced by DEX after 21d exposure. Compared to mammals, the regulation of CYP2E1 in fish is less investigated and requires further study. The molecular mechanisms by which DEX regulates PNPH activity appear to be similar to those of other studied CYP450-mediated reactions in fish liver. At 3000ngL−1, DEX did not affect our investigated parameters, suggesting that DEX is regulated by CYP450 in a biphasic way, a response to xenobiotics that is not uncommon (Heinrichs et al., 1994). These data might also suggest that fish adapted to DEX exposure. It was previously shown that, depending on concentration, DEX might act as either a permissive or suppressive factor in enzyme induction (Ringel et al., 2002). We found that CYP1A1, CYP2E1-like and CYP3A-like enzyme activities increased in the presence of environmentally relevant concentrations of DEX, but not in the presence of the highest tested concentration (3000ngL−1) when activities were calculated per nmol total CYP450 content. No effect was observed when the activities were calculated relative to total protein content. Differences in the CYP450 responses to DEX depended on the calculation, either relative to total protein or to total CYP450 content. This is an important observation. Activities of CYP450-mediated reactions expressed relative to total protein content more closely reflected an in vivo situation, suggesting that overall DEX did not alter measured CYP450 activities. Nevertheless, an increase in the activities of CYP1A, CYP3A and CYP2E1-like proteins, expressed relative to total CYP450 content, suggest an eventual increase in the protein content of individual CYP450 isoforms. In studies using mammals, significant differences in enzyme catalytic activities were also found only after calculation of enzyme catalytic activity per total CYP450 (Wandel et al., 1998, Anzenbacherova et al., 2008). This means that the estimation of enzyme activity, expressed relative to total CYP450, is another way to illustrate a complete picture of the effects of various pharmaceutical drugs other than by calculation per milligram of protein. To further test this concept, protein expressions of CYP1A and CYP3A were measured in the same sample. Samples from fish exposed to DEX for 21d were used because no effect was observed after 42d. Previous studies showed diverse evidence in the regulation of CYP1A and CYP3A proteins in fish and fish cell cultures. For example, DEX down regulated CYP1A1 in trout hepatocytes (Dasmahapatra and Lee, 1993), but did not affect CYP3A in rainbow trout (Lee et al., 1993). Moreover, in combination with beta-naphthoflavone (a known AhR activator), DEX increased CYP1A1 protein levels in the P. lucida hepatocellular carcinoma cell line (Celander et al., 1997).