Purification of NADPH-linked and NADH-linked quinone reductases from liver cytosol of sea bream, Pagrus major

Lack of increased oxidative stress in catechol-O-methyltransferase (COMT)-deficient mice

The effect of catechol-O-methyltransferase (COMT) deficiency on methamphetamine-induced hydroxyl radical production in the brain was assessed by the salicylate trapping method. Methamphetamine-induced hyperthermia was also studied. Furthermore, the effect of COMT deficiency on the activities of glutathione S-transferase, quinone reductase and liver mono-oxygenases was assessed with and without l-dopa challenge. Finally, two alternative pathways of l-dopa metabolism were evaluated. Methamphetamine increased 2,3-dihydroxybenzoic acid levels only slightly (n.s.) at the lowest dose level (2.5 mg/kg x 4 i.p.). This was accompanied by a simultaneous increase in salicylate levels so that the 2,3-dihydroxybenzoic acid/salicylate ratio decreased correspondingly. Most importantly, no COMT genotype-dependent changes were observed. However, hyperthermia was induced even at the lowest methamphetamine dose, the COMT-deficient mice being most sensitive. COMT deficiency did not significantly change the activities of liver glutathione S-transferase, quinone reductase or 7-ethoxyresorufin and 7-pentoxyresorufin O-dealkylation. In COMT-deficient female mice, l-dopa (30-80 mg/kg b.i.d. for 2 days) did not induce any significant changes in liver or brain glutathione S-transferase and quinone reductase activity or liver 7-ethoxyresorufin O-deethylation activity. The levels of l-dopa conjugates in urine were also negligible in COMT-deficient mice. Skin tyrosinase activity was increased in 7- to 8-day-old hairless COMT-deficient pups. The present results suggest that despite the increased hyperthermic response, COMT deficiency does not increase methamphetamine-induced hydroxyl radical production or change significantly the activity of certain enzymes involved in defense against reactive oxygen species. In conclusion, we found no evidence of increased oxidative stress in the liver or brain of adult mice lacking COMT activity.

Effects of 17-beta estradiol and 4-nonylphenol on phase II electrophilic detoxification pathways in largemouth bass (Micropterus salmoides) liver

The effects of in vivo exposure to a natural and synthetic estrogen upon three hepatic phase II enzyme pathways involved in cellular protection against reactive intermediates were investigated in the largemouth bass (Micropterus salmoides). The pathways analyzed included glutathione S-transferases (GST), glutathione (GSH) biosynthesis and NAD(P)H-dependent quinone reductase (QR). Following exposure to 17-beta estradiol (E2, a model natural estrogen; 2 mg/kg, i.p.) or 4-nonylphenol (NP, a model synthetic estrogen; 5 mg/kg and 50 mg/kg, i.p.), serum vitellogenin concentrations in male fish were markedly increased. Exposure to E2 did not affect steady-state GST-A mRNA expression, although GST catalytic activity toward 1-chloro 2,4-dinitrobenzene (CDNB) was elevated at 48 h post-injection. In addition, the rates of bass liver GST-4-hydroxy-2-nonenal (GST-4HNE) conjugation were elevated by E2 exposure at all timepoints. In contrast, exposure to NP decreased steady-state GST-A mRNA levels, but did not alter GST catalytic activities. Hepatic GSH levels were not significantly affected by exposure to either compound, although a trend towards increased GSH biosynthesis was observed with both compounds. Although bass liver quinone reductase catalyzed 2,6-dichloroindophenol (DCP) reduction, unlike in rodents, these catalytic activities were not inhibited by dicoumarol. Exposure to 5 mg/kg NP significantly increased hepatic QR activities. Collectively, our data suggest that exposure to E2 or NP alters the ability of largemouth bass to biotransform environmental chemicals through glutathione S-transferase and quinone reductase catalytic pathways.

Metabolism of 2-nitrofluorene, an environmental pollutant, by liver preparations of sea bream, Pagrus major

1. The in vitro metabolism of 2-nitrofluorene (NF), an environmental pollutant, was examined in fish, focusing on nitro-reduction followed by N-acylation and hydroxylation. 2. When NF was incubated with liver microsomes or cytosol of sea bream, Pagrus major, in the presence of NADPH or 2-hydroxypyrimidine, 2-aminofluorene (AF) was formed. 3. When AF was incubated with liver cytosol in the presence of acetyl-CoA or N-formyl-L-kynurenine, 2-acetylaminofluorene (AAF) or 2-formylaminofluorene (FAF) was formed, respectively. AAF and FAF thus formed were deacylated to the parent AF by the liver preparations. 4. AF, AAF and FAF were oxidized to 7-hydroxy or 5-hydroxy derivatives by the liver microsomes. 5. Nitro-reduction, N-acylation and ring-hydroxylation of NF and the metabolites were also observed in rat liver preparations. These activities in sea bream livers were lower than those of rat liver. However, the order of magnitude of these activities in fish was the same as in rat. 6. It is suggested that NF is effectively reduced to AF by the cytochrome P450 system or aldehyde oxidase, and the acylated metabolites, AAF and FAF, generated by arylamine acetyltransferase and formamidase were hydroxylated by the cytochrome P450 system in fish in the same way as in rat. Further, the acetylamino and formylamino derivatives were interconverted via amino derivatives in the fish.

Whole-body metabolism of the organophosphorus pesticide, fenthion, in goldfish, Carassius auratus

The in vivo metabolism of fenthion, an organophosphorus pesticide, and its sulfoxide (fenthion sulfoxide) was examined in goldfish (Carassius auratus). When goldfish were administered fenthion i.p. at a dose of 100 mg/kg, two metabolites were isolated from the tank water. They were identified as fenthion sulfoxide and fenthion oxon, in which > P = S of fenthion is transformed to > P = O, by comparing their mass and UV spectra, and their behavior in HPLC and TLC, with those of authentic standards. However, fenthion sulfone was not detected as a metabolite. The amounts of fenthion, fenthion sulfoxide and fenthion oxon excreted within 4 days were 2.7, 3.4 and 2.5%, of the initial dose of fenthion, respectively. Unchanged fenthion was detected in the body of the fish to the extent of 42-50% of the dose after 10 days, but fenthion sulfoxide and fenthion oxon showed very low concentrations. When fenthion sulfoxide was administered to the fish, about 70% of the dose was excreted unchanged into the tank water within 24 h, but little of the reduced compound, fenthion, was found. In contrast, fenthion was detected at 2.1% of dose in the body of goldfish as a metabolite of fenthion sulfoxide. The fact that fenthion is metabolized to the toxic oxon form in fish presumably has environmental and health implication for its use as a pesticide.