Xenobiotic metabolism and accumulation of polychlorinated biphenyls in the rainbow trout and cod brain and pituitary

212

Abstracts

the major metabolites in fish and rat (70%). When inhibitors of drugmetabolizing enzymes were used (~-naphthoflavone for P450 and trichloropropeneoxide for epoxide hydrolase), the rate of formation of diols strongly decreased while the mutagenic activity of B(a)P was highly inhibited in rat and fish only. Tocopherol (radical scavenger) had a weak effect on B(a)P metabolite profile and B(a)P mutagenic activity in rat experiments. In fish, the mutagenicity of B(a)P was strongly reduced ( - 5 0 % ) whereas diol formation was increased (+35%). In mussel microsomes, quinone formation was strongly decreased ( - 8 0 % ) by addition of tocopherol. The results show that one-electron oxidation is a major route for B(a)P metabolism in mussel, whereas mixed-function oxidase is mainly involved for B(a)P activation in fish and rat. This work was supported by a grant from the 'Institut Franqais pour la Recherche et l'Exploitation de la Mer'.

Xenobiotic Metabolism and Accumulation of Polychlorinated Biphenyis in the Rainbow Trout and Cod Brain and Pituitary. TOMMY ANDERSSON,* ANDERS GOKSIOYR,++ KRISTIAN INGEBR1GTSEN,§ ~ K E BERGMAN:~ & INGVAR BRANDT.rl *Department of Zoophysiology,

University of GOteborg, Box 25059, S-400 31 Gdteborg, Sweden; ~Department o/ Biochemistry, University of Bergen, ,4rstadvejen 19, N-5000 Bergen, Norway; §Department of Pharmacology and Toxicology, The Norwegian College o[" Veterinary Medicine. Oslo, Norway; ~Environmental Chemistry, Wallenberg Laboratory, Stockholm University, Stockholm, Sweden & ItDepartment of Pharmacology and Toxicology, The Swedish University of Agricultural Science, Uppsala, Sweden. The level of radio-labeled PCBs in the brain displayed profound interspecies differences when the accumulation and distribution pattern was studied by tape-section autoradiography and liquid-scintillation counting. The level in cod was from six- to eight-fold higher in the cod brain than in the rainbow trout brain. Furthermore, in the cod, high levels of radioactive compounds could be seen in the cerebrospinal fluid, indicating formation of watersoluble compounds. To investigate the ability of the brain to biotransform lipid-soluble compounds to more water-soluble products, the activity of cytochrome P450 was measured in whole-tissue homogenates by two model substrates, 7-ethoxycoumarin and 7-ethoxyresorufin. The level of cytochrome P4501A1 was also specifically determined by an indirect ELISA. The cytochrome P450-dependent activities were generally low in the various brain parts and displayed activities below 1 pmol/mg protein per min. The only exception was the rainbow trout olfactory bulbs, which showed 7-

Abstracts

213

ethoxycoumarin-O-deethylase (ECOD) activities over 6pmol/mg protein per min. The pituitary gland from both cod and rainbow trout showed activities of 2-4 pmol/mg protein per min towards 7-ethoxycoumarin and 7ethoxyresorufin. The P450 system in cod and rainbow trout brain was found to be inducible to various extents. Treatment of rainbow trout with flnaphthoflavone (BNF) increased the 7-ethoxyresorufin-O-deethylase (EROD) activity from four- to eight-fold in the various brain parts whereas in the cod a significant induction (eight-fold) could be seen only in the olfactory bulbs. The ECOD activity was induced (from four- to five-fold) in the rainbow trout hypothalamus and the optic lobe, whereas no significant changes were seen in the cod brain by BNF treatment. The present study shows that the cod and rainbow trout brains contain an active cytochrome P450 system, which, at least in some parts of the tissue, could be induced. The toxicological consequences and physiological function of the brain P450 in fishes should be further investigated.

Metabolic Activation of Carcinogens by Three Marine Invertebrates. JANE W. MARSH,* JAMES K. C H I P M A N * & DAVID R. LIVINGSTONE.:~ * School of Biochemistry, University of Birmingham, Edgbaston, Birmingham, UK, BI5 2TT & ~Plymouth Marine Laboratory, Citadel Hill, Plymouth, UK, PL1 2PB. The ability of mussels (Mytilus edulis), shore crabs (Carcinus maenus), and common starfish (Asterias rubens) to convert 2-acetylaminofluorene (2AAF), 2-aminofluorene (2AF), N-hydroxy-2AAF, and benzo(a)pyrene (BP) to reactive and mutagenic products was compared. In a Salmonella typhimurium pre-incubation assay, with strain TA98, post-mitochondrial supernatants ($9) of crab hepatopancreas and mussel digestive gland converted 2AAF (1-100 #g/plate), 2AF (1-10/~g/plate), and N-hydroxy2AAF (0.1-1#g/plate) to products that were mutagenic. The mussel appeared to possess a soluble deacetylase (paraoxon inhibited mutagenicity by 96%) capable of converting 2AAF to 2AF, and an enzyme, similar to mammalian microsomal flavin-containing monooxygenase, which oxidized 2AF (methimazole inhibited activation by 69% but cytochrome P450 inhibitors, DPEA, ~-naphthoflavone, and metyrapone had no effect). Activation of 2AAF by the crab was also inhibited by paraoxon (88%) but the oxidative activation step was not inhibited by either methimazole or the above cytochrome P450 inhibitors. The starfish pyloric caeca $9 also activated 2AF and N-hydroxy-2AAF at the doses shown above but surprisingly did not convert 2AAF to mutagens (dose up to 500/~g/plate). The deacetylation and/or oxidation systems of the starfish, although