The biotransformation of [14C]phenol in some freshwater fish

Effects of phenol in antioxidant metabolism in matrinxã, Brycon amazonicus (Teleostei; Characidae)

Parameters of the antioxidant defense systems of Brycon amazonicus (matrinxã--a neotropical fish) exposed to phenol for 96 h plus the recovery over 1 and 2 weeks were studied in erythrocytes and liver. Hematocrit increase was observed during phenol exposure and recovery for 1 week. Total superoxide dismutases (SOD), glutathione peroxidase (GPx) and reduced glutathione (GSH) did not change during phenol exposure. Erythrocyte glucose-6-phosphate dehydrogenase (G6PDH) increased during that period while catalase (CAT) activity decreased during phenol exposure and recovery for 2 weeks. In the liver, SOD and CAT did not change, whereas GPx increased in the first week of recovery and decreased after 2 weeks. A late response was observed for G6PDH activity which increased only at the second week. Ascorbate concentration in the brain decreased during phenol exposure and increased over recovery. From our results it appears that the oxidative stress was limited in matrinxã exposed to phenol, but seemed to occur during the recovery period.

Residues of the lampricides 3-trifluoromethyl-4-nitrophenol and niclosamide in muscle tissue of rainbow trout

Rainbow trout (Oncorhyncus mykiss) were exposed to the (14)C-labeled lampricide 3-trifluoromethyl-4-nitrophenol (TFM) (2.1 mg/L) or niclosamide (0.055 mg/L) in an aerated static water bath for 24 h. Fish were sacrificed immediately after exposure. Subsamples of skin-on muscle tissue were analyzed for residues of the lampricides. The primary residues in muscle tissue from fish exposed to TFM were parent TFM (1.08 +/- 0.82 nmol/g) and TFM-glucuronide (0.44 +/- 0.24 nmol/g). Muscle tissue from fish exposed to niclosamide contained niclosamide (1.42 +/- 0.51 nmol/g), niclosamide-glucuronide (0.0644 +/- 0.0276 nmol/g), and a metabolite not previously reported, niclosamide sulfate ester (1.12 +/- 0.33 nmol/g).

Rate and capacity of hepatic microsomal ring-hydroxylation of phenol to hydroquinone and catechol in rainbow trout (Oncorhynchus mykiss)

Rainbow trout (Oncorhynchus mykiss) liver microsomes were used to study the rate of ring-hydroxylation of phenol at 11 and 25 degrees C by directly measuring the production of two potentially toxic metabolites, hydroquinone (HQ) and catechol (CAT). An HPLC method with integrated ultraviolet and electrochemical detection was used for metabolite identification and quantification at low (pmol) formation rates found in fish. The Michaelis-Menten saturation kinetics for the production of HQ and CAT over a range of phenol concentrations were determined at trout physiological pH. The apparent Km's for the production of HQ and CAT at 11 degrees C were 14+/-1 and 10+/-1 mM, respectively, with Vmax's of 552+/-71 and 161+/-15 pmol/min per mg protein. The kinetic parameters for HQ and CAT at 25 degrees C were 22+/-1 and 32+/-3 mM (Km) and 1752+/-175 and 940+/-73 pmol/min per mg protein (Vmax), respectively. The calculated increase in metabolic rate per 10 degrees C temperature rise (Q(10)) was 2.28 for HQ and 3.53 for CAT production. These experiments assess the potential for metabolic bioactivation in fish through direct quantification of putative reactive metabolites at the low, but toxicologically significant, chemical concentrations found in aquatic organisms. This work initiates a series of studies to compare activation pathway, rate, and capacity across fish species, providing a basis for development of biologically-based dose response models in diverse species.

Purification and characterization of hepatic and intestinal phenol sulfotransferase with high affinity for benzo[a]pyrene phenols from channel catfish, Ictalurus punctatus

Cytosol from channel catfish liver and intestinal mucosa has high sulfotransferase activity with low concentrations of 3-, 7-, or 9-hydroxybenzo[a]pyrene. To further investigate this conjugation pathway, sulfotransferase activity toward 9-hydroxybenzo[a]pyrene was isolated from catfish intestinal and hepatic cytosol by chromatography on anion exchange and PAP-agarose affinity columns. SDS-PAGE of the active fractions showed that one major band with molecular size of about 41,000 Da was isolated from intestine, while two bands of about 41,000 and 31,000 Da were obtained from liver. Antibodies against human phenol-sulfating sulfotransferase cross-reacted strongly with the 41,000-Da bands from liver and intestine, but weakly with the hepatic 31,000-Da protein. N-Terminal sequence information could not be obtained from the pure proteins. Following digestion, an internal sequence of 20 amino acid residues was obtained from the hepatic 41,000-Da protein, which matched a sequence found in several mammalian sulfotransferases. No fish sulfotransferase sequences were available for comparison. The identity of the hepatic 31,000-Da protein was not established. The purified 41,000-Da proteins had very high activities with 3-, 7-, or 9-hydroxybenzo[a]pyrene, with K(m) values in the 40-100 nM range and V(max) 125-300 nmol/min/mg of protein. Substrate inhibition was observed when the concentrations of hydroxylated benzo[a]pyrenes were above 0.5 microM. As well as benzo[a]pyrene phenols, the purified 41,000-Da sulfotransferases catalyzed sulfation of 2-naphthol, 4-nitrophenol, 4-methylumbelliferone, 7-(hydroxymethyl)-12-methylbenz[a]anthracene, dehydroepiandrosterone, estrone, and 17beta-estradiol. Phenolic compounds were the preferred substrates for the purified enzymes.

Metabolites of 2-chlorosyringaldehyde in fish bile: indicator of exposure to bleached hardwood effluent

1. 2-Chlorosyringaldehyde (2-CSA) is the major chlorinated phenol produced by the 100% chlorine dioxide bleaching of eucalypt pulp and is found in other bleached hardwood effluents. Almost nothing is known of the environmental or metabolic fates of this chemical. 2. Sand flathead (Platycephalus bassensis) was given 2-CSA by intraperitoneal injection at 0.15, 1.5, 15 and 75 mg/kg doses and, 4 days later, bile was collected and solvent extracted before and after enzymatic cleavage of conjugates. The acetate derivatives of bile extracts were analysed by gas chromatography/mass spectrometry. 3. The major metabolite 4 days after administration was the glucuronide or sulphate conjugate of 2-chloro-4-hydroxy-3,5-dimethoxy-benzylalcohol (2-CB-alcohol). The identity of 2-CB-alcohol was confirmed by chemical synthesis. 4. The quantity of 2-CB-alcohol in the bile was linearly related to dose of 2-CSA and was detected at all dose levels. Minor metabolites identified were conjugated 2-CSA, unchanged 2-CSA and 2-chloro-4-hydroxy-3,5-dimethoxy-benzoic acid. 5. The amount of 2-CB-alcohol in bile has the potential to be a sensitive and specific indicator of fish exposure or bleached hardwood effluent.

Metabolism of pentachlorophenol by fish

1. Interspecies variability in the metabolism of pentachlorophenol (PCP) was investigated by exposing rainbow trout, fathead minnows, sheepshead minnow, firemouth, and goldfish to water-borne 14C-PCP for 64 h. 2. The amounts of metabolites in bile and exposure water were species-dependent; all of the metabolites excreted into the water were sulphate conjugates while bile was enriched in glucuronide conjugates. 3. Biliary excretion accounted for less than 30% of the total PCP metabolites. 4. Biliary metabolites alone were a poor indication of the metabolites produced and of the major routes of elimination.

Conjugation of organic pollutants in aquatic species

Aquatic organisms can take up organic pollutants from their environment and subsequently excrete the pollutant or its biotransformation products (metabolites). Phase II (conjugation) biotransformation products are almost always less toxic than the unmetabolized organic pollutant. For many organic pollutants, the extent to which conjugates are formed is extremely important in determining the rate of excretion of the pollutant. This is because most conjugates (glycosides, sulfates, amino acid conjugates, mercapturic acids) are organic anions which are readily water-soluble and are rapidly excreted by fish (and probably higher invertebrates) by a combination of glomerular filtration and tubular transport. In this paper, each major conjugation pathway is discussed with respect to what is known about its occurrence in fish and aquatic invertebrates, both from in vivo and in vitro data. Although limited data are available, this paper also considers what is known about how each conjugation reaction affects the toxicity and potential for renal and biliary excretion of organic xenobiotic substrates.

Hydroxylation and conjugation of phenol by the frog Rana temporaria

Frogs injected with phenol excrete 67-95% of dose in 15 h; 32-87% of dose are metabolites. Metabolites identified were phenyl sulphate (15-44% of dose), phenyl glucuronide (10-25% of dose), catechol sulphate (up to 7% of dose), quinol sulphate (1-25% of dose), resorcinol and catechol (traces).

The biotransformation of three 14C-labelled phenolic compounds in twelve species of freshwater fish

1. The urinary and biliary excretion of 14C-labelled m-cresol, 1-naphthol and o-chlorophenol were investigated in 12 species of freshwater fish (bitterling, Rhodeus sericeus amarus; bream, Abramis brama; crucian carp, Carassius carassius; goldfish, Carassius auratus; gudgeon, Gobio gobio; guppy, Poecilia reticulata; minnow, Phoximus phoximus; perch, Perca fluviatilis; roach, Rutilus rutilus; rudd, Scardinius erythropthalmus; three-spined stickleback, Gasterosteus aculeatus; tench, Tinca tinca) when immersed in sub-lethal concentrations of the compounds in the aquarium water for 48 h. 2. The sulphate and glucuronic acid conjugates of 1-naphthol and o-chlorophenol were detected in both the aquarium water and the bile of all the fish species. 3. The oxidation product of m-cresol, m-hydroxybenzoic acid, and the sulphate conjugate of the phenol, were excreted into the aquarium water of all species except the guppy, which did not excrete m-hydroxybenzoic acid. In addition to these two metabolites, the glucuronic acid conjugate of m-cresol was found in the bile of all species, except for guppies whose small size precluded study of biliary excretion.

Quinol sulphate, a new conjugate of phenol in goldfish

1. Metabolism of phenol in goldfish yielded the known phenyl conjugates in fish--phenyl sulphate and phenyl glucuronide. Additionally, quinol sulphate, a new conjugate of phenol in fish, was detected.

Species differences, influence of dose and application on biotransformation of phenol in fish

1. The metabolism of phenol in goldfish (Carassius auratus), rainbow trout (Salmo gairdneri) and goldenorfe ide (Leuciscus ideus melanotus) was compared. All three species produced phenyl sulphate, quinol sulphate and phenyl glucuronide. 2. The dose dependence of metabolism of phenol in goldfish was investigated. When the concn. of phenol was increased from 0.2 to 2 mg/l medium, that glucuronylated increased from 7 to 16% and that sulphated decreased from 63 to 47%. 3. The influence of mode of exposure on metabolism of phenol in goldfish was examined. Dietary exposure and uptake from medium was compared with i.p. injection. There was less metabolism in the order: dietary exposure greater than uptake from medium greater than injection.

Hydrolysis of the biliary glucuronic acid conjugate of phenol by the intestinal mucus/flora of goldfish (Carassius auratus)

1. An investigation was carried out on the hydrolytic activity of the intestinal mucus/flora on phenylglucuronide in the bile of goldfish. 2. Approximately 79% of the total phenylglucuronide (3.4 mumol) in the bile was hydrolysed after 16 h incubation with the intestinal mucus/flora. 3. Of the total phenol in the aquarium water of goldfish exposed previously to phenol for 48 h, 41% was found to be phenylglucuronide when fish were placed in a phenol-free medium and were dosed hourly for 8 h with D-saccharic acid 1,4-lactone to inhibit beta-glucuronidase activity in the intestine.