Responses of hepatic biotransformation and antioxidant enzymes to CYP1A-inducers (3-methylcholanthrene, β-naphthoflavone) in sea bass ( Dicentrarchus labrax), dab ( Limanda limanda) and rainbow trout ( Oncorhynchus mykiss)

Abstract

The time-course responses of hepatic biotransformation and antioxidant enzymes to cytochrome P4501A-inducers in fish were examined using marine and freshwater species, viz. respectively, sea bass ( Dicentrarchus labrax) and dab ( Limanda limanda) exposed up to 5 to 11 days to 3-methylcholanthrene (3MC; intraperitoneal (i.p.) 20 mg kg −1), and rainbow trout ( Oncorhynchus mykiss) exposed up to 15 days to β-naphthoflavone (BNF; i.p. 5 mg kg −1). The enzymes included those which are part of the mammalian [ Ah]-gene locus, viz. cytochrome P4501A (CYP1A), DT-diaphorase (DTD; EC 1.6.99.2), aldehyde dehydrogenase (ADH; EC 1.2.1.3), glutathione S-transferase (GST; EC 2.5.1.18) and UDP-glucuronyltransferase (UDPGT). DTD was assayed as dicoumarol-inhibitable menadione reductase, dicoumarol-inhibitable dichlorophenolindophenol (DCPIP) reductase and resorufin reductase activities; and ADH as benzaldehyde dehydrogenase (BADH) and propionaldehyde dehydrogenase (PADH) activities. The responses varied considerably with enzyme, species and treatment. CYP1A-dependent 7-ethoxyresorufin O-deethylase (EROD) activity was markedly inducible, more so in BNF-treated O. mykiss (maximal 284-fold increase after 2 days) than the 3MC-treated species (maximal 24–30-fold). Modest increases (up to 2-fold) and/or inhibition were seen in UDPGT and GST activities. DTD activities increased about 2-fold after 8 to 15 days in BNF-treated O. mykiss, but were not elevated in the other species. Changes in dicoumarol-inhibitable DCPIP and menadione reductase activities were more similar than resorufin reductase activity. No marked increases were evident in BADH, PADH, superoxide dismutase (SOD; EC 1.15.1.1), catalase (EC 1.11.1.6) and glutathione peroxidase (GPX; EC 1.11.1.9) activities in any species. Overall, some co-induction of CYP1A and DTD, over different time-courses, was indicated for BNF-treated O. mykiss.