Mixed-function oxygenase activity and benzo[a]pyrene metabolism in the barnacle Balanus eburneus (Crustacea: Cirripedia)

Cytochrome P450-dependent monooxygenase system mediated hydrocarbon metabolism and antioxidant enzyme responses in prawn, Macrobrachium malcolmsonii

We investigated the alteration of cytochrome P450-dependent monooxygenase enzymes and antioxidant enzymes in response to oil effluent in freshwater prawn, Macrobrachium malcolmsonii. The prawns were exposed to two sublethal (10% [0.91 ppt] and 25% [2.3 ppt] of 5-day median lethal concentration) concentrations of oil. After 30 days, treated prawns were transferred into untreated freshwater and depuration was followed for another 30 days. At 7-day intervals, hydrocarbons and detoxifying enzymes were analysed in the hepatopancreas. Accumulation of hydrocarbon in the tissues gradually increased when exposed to sublethal concentration of oil effluent associated with enhanced levels of cytochrome P450, NADPH cytochrome c reductase and cytochrome b(5). During depuration, the levels of accumulated hydrocarbons decreased due to the induction of these detoxifying enzymes. Oil derived hydrocarbon mediated oxyradical production would have occurred in M. malcolmsonii. This was confirmed by elevated levels of superoxide dismutase (SOD) and catalase (CAT). Thus, cytochrome P450-dependent monooxygenase enzymes and antioxidant enzymes in oil-exposed prawns demonstrate a well-established detoxifying mechanism in M. malcolmsonii.

Temperature-dependent disposition of [14C]benzo(a)pyrene in the spiny lobster, Panulirus argus

[14C]Benzo(a)pyrene (BP) (1 mg/kg) was administered by intracardiac injection to groups of spiny lobsters which were killed at various times up to 7 weeks after dosing. Tissues and fluids were evaluated for BP-derived radioactivity. Two studies were conducted in successive summer and winter seasons, when seawater temperatures throughout were 26.5 to 29.0 and 13.5 to 16.5 degrees C, respectively. Highest concentrations of BP-derived radioactivity were found in the hepatopancreas, stomach, intestine, intestinal contents, and the green gland. After an initial distribution phase, the dose was lost from the lobsters in a log linear manner. The elimination half-lives for overall elimination of BP-derived radioactivity were 1.11 weeks in the warmer (summer) and 2.25 weeks in the colder (winter) water. Similarly, for individual organs, elimination was more rapid in the warmer water. For the hepatopancreas, green gland, intestine, and tail muscle, respective t1/2 values (week) were 1.02, 1.26, 1.71, and 1.42 in the summer and 2.50, 1.50, 5.04, and 2.11 in the winter. There was no suggestion of tissue accumulation of BP-derived radioactivity. HPLC analysis of hepatopancreas samples showed that, in summer, unmetabolized BP concentrations fell rapidly, accounting for only 5% of the total label in the hepatopancreas by 3 days. The fall in unmetabolized BP was accompanied by approximately equal increases in the percentages of both polar metabolites and conjugates. Although the time curve for metabolism of BP in the hepatopancreas was not studied in winter, the metabolic capacity was such that, by 3 days after the dose, only 5% of the 14C present in hepatopancreas was unmetabolized BP. Thus, it appears that, for this dose of BP, the more rapid elimination of 14C in summer was due to a more rapid excretion of metabolites, and not to increased metabolism of BP.

Cytochrome P-450-dependent oxidation of progesterone, testosterone, and ecdysone in the spiny lobster, Panulirus argus

Experiments were performed to determine the ability of the cytochrome P-450 present in hepatopancreas microsomes from the spiny lobster, Panulirus argus, to catalyze oxidation of progesterone, testosterone, and ecdysone. Preparations of hepatopancreas microsomes fortified with NADPH cytochrome P-450 reductase from pig liver efficiently catalyzed NADPH-dependent 16 alpha- and 6 beta-hydroxylation of progesterone and testosterone, and 21-hydroxylation of progesterone. These products were also found if NADPH and NADPH cytochrome P-450 reductase were replaced by cumene hydroperoxide. Cytochrome P-450 purified from hepatopancreas microsomes catalyzed NADPH- and reductase-dependent 16 alpha-hydroxylation of progesterone and testosterone 10 times more rapidly than the original microsomal preparation. While ecdysone was not a substrate for the hepatopancreas microsomal cytochrome P-450, low ecdysone 20-monooxygenase activity was found in hepatopancreas mitochondria. Further studies showed that homogenates of green gland, ovaries, and testes had higher ecdysone monooxygenase activities than hepatopancreas, and that the activity in green gland was localized in mitochondria.

An aryl hydrocarbon hydroxylating hepatic cytochrome P-450 from the marine fish Stenotomus chrysops

Hepatic microsomal cytochrome P-450 from the untreated coastal marine fish scup, Stenotomus chrysops, was solubilized and resolved into five fractions by ion-exchange chromatography. The major fraction, cytochrome P-450E (Mr = 54,300), was further purified to a specific content of 11.7 nmol heme/mg protein and contained a chromophore absorbing at 447 nm in the CO-ligated, reduced difference spectrum. NH2-terminal sequence analysis of cytochrome P-450E by Edman degradation revealed no homology with any known cytochrome P-450 isozyme in the first nine residues. S. chrysops liver NADPH-cytochrome P-450 reductase, purified 225-fold (Mr = 82,600), had a specific activity of 45-60 U/mg with cytochrome c, contained both FAD and FMN, and was isolated as the one-electron reduced semiquinone. Purified cytochrome P-450E metabolized several substrates including 7-ethoxycoumarin, acetanilide, and benzo[a]pyrene when reconstituted with lipid and hepatic NADPH-cytochrome P-450 reductase from either S. chrysops or rat. The purified, reconstituted monooxygenase system was sensitive to inhibition by 100 microM 7,8-benzoflavone, and analysis of products in reconstitutions with purified rat epoxide hydrolase indicated a preference for oxidation on the benzo-ring of benzo[a]pyrene consistent with the primary features of benzo[a]pyrene metabolism in microsomes. Cytochrome P-450E is identical to the major microsomal aromatic hydrocarbon-inducible cytochrome P-450 by the criteria of molecular weight, optical properties, and catalytic profile. It is suggested that substantial quantities of this aromatic hydrocarbon-inducible isozyme exist in the hepatic microsomes of some untreated S. chrysops. The characterization of this aryl hydrocarbon hydroxylase extends our understanding of the metabolism patterns observed in hepatic microsomes isolated from untreated fish.