Influence of environmental temperature on the induction of xenobiotic metabolism by beta-naphthoflavone in rainbow trout, Salmo gairdneri

Measurement of Xenobiotic Metabolising Enzyme Activities in Primary Monolayer Cultures of Immature Rainbow Trout Hepatocytes at Two Acclimatisation Temperatures

Rainbow trout hepatocytes with a high viability were isolated by two-step collagenase perfusion through the portal vein. The yield was 1-2.5 x 106cells/g body weight. Culture conditions were defined for providing enhanced attachment and long-term cell survival at 7 ± 0.5°C and 15 ± 0.5°C, respectively. The hepatocytes, attached to Primaria™ plastic and cultured in Leibowitz L-15 medium with 9% fetal calf serum, were maintained as monolayers for 6–7 days. The activities in hepatocytes from immature trout of the biotransformation enzymes ethoxyresorufin-O-deethylase (EROD), aldrine epoxidase (AEPOX), NADPH-cytochrome c reductase (NCR), glutathione-S-transferase (GST) and UDP-glucuronosyltransferase (UDPGT), were all stable during the culture period. Differences in enzyme stability and activity (particularly the activity of EROD) between hepatocytes from different fish were observed at both temperatures. The temperature did not influence the activities of EROD or NCR, whereas AEPOX showed metabolic compensation. Both GST and UDPGT exhibited inverse temperature compensation. Hepatocyte monolayers, cultured from immature trout, may provide a useful system in pharmacological and toxicological research for investigating drug metabolism.

Cumulative effects of cadmium and natural stressors (temperature and parasite infection) on molecular and biochemical responses of juvenile rainbow trout

The simultaneous presence of natural and anthropogenic stressors in aquatic ecosystems can challenge the identification of factors causing decline in fish populations. These stressors include chemical mixtures and natural abiotic and biotic factors such as water temperature and parasitism. Effects of cumulative stressors may vary from antagonism to synergism at the organismal or population levels and may not be predicted from exposure to individual stressors. This study aimed to evaluate the combined effects of chronic exposure to cadmium (Cd) and elevated water temperature (23 °C) or parasite infection in juvenile rainbow trout (Oncorhynchus mykiss) using a multi-level biological approach, including RNA-sequencing. Fish were exposed to diet-borne Cd (6 μg Cd/g wet feed), individually and in combination with thermal (23 °C) or parasitic stressors, for 28 days. The parasite challenge consisted of a single exposure to glochidia (larvae) of the freshwater mussel (Strophitus undulatus), which encysts in fish gills, fins and skin. Results indicated lower fish length, weight, and relative growth rate in fish exposed to a higher water temperature (23 °C). Body condition and hepatosomatic index of trout were, however, higher in the 23 °C temperature treatment compared to the control fish kept at 15 °C. Exposure to thermal stress or parasitism did not influence tissue Cd bioaccumulation. More than 700 genes were differentially transcribed in fish exposed to the individual thermal stress treatment. However, neither Cd exposure nor parasite infection affected the number of differentially transcribed genes, compared to controls. The highest number of differentially transcribed genes (969 genes) was observed in trout exposed to combined Cd and high temperature stressors; these genes were mainly related to stress response, protein folding, calcium metabolism, bone growth, energy metabolism, and immune system; functions overlapped with responses found in fish solely exposed to higher water temperature. Only 40 genes were differentially transcribed when fish were exposed to Cd and glochidia and were related to the immune system, apoptosis process, energy metabolism and malignant tumor. These results suggest that dietary Cd may exacerbate the temperature stress and, to a lesser extent, parasitic infection stress on trout transcriptomic responses. Changes in the concentrations of liver ethoxyresorufin-o-deethylase, heat shock protein 70 and thiobarbituric acid reactive substances coupled to changes in the activities of cellular glutathione S-transferase and glucose-6-phosphate dehydrogenase were also observed at the cellular level. This study may help understand effects of freshwater fish exposure to cumulative stressors in a changing environment.

Molecular and cellular effects of temperature in oysters Crassostrea brasiliana exposed to phenanthrene

Exposure of aquatic organisms to polycyclic aromatic hydrocarbons (PAH), such as phenanthrene (PHE), may increase the production of reactive oxygen species (ROS) and cause changes in the biotransformation systems. In addition, changes in water temperature can cause adverse effects in the organisms. Estuarine species, like the oyster Crassostrea brasiliana, can adapt and tolerate temperature variation. To evaluate the influence of temperature on biological responses of C. brasiliana exposed to PHE, oysters were maintained at three temperatures (18, 24 and 32 °C) for 15 days and co-exposed afterwards to 100 μg.L^-1 of PHE for 24 and 96 h. Levels of PHE in the water and oyster tissues were determined, respectively after 24 and 96 h. In addition, thermal stress, biotransformation and oxidative stress-related genes were analyzed in oyster gills, together with the activity of superoxide dismutase (SOD), catalase (CAT), glutathione peroxidase (GPx), glutathione-S-transferases (GST) and levels of lipid peroxidation. Oyster accumulated significant levels of PHE. HSP70-like transcripts were affected by PHE exposure only at 32 °C. Transcript levels of cytochrome P450 isoforms (CYP2-like2 and CYP2AU1) were down-regulated in oysters exposed to PHE for 24 h at 32 °C. GSTΩ-like transcript levels were also down-regulated in the PHE-exposed group at 32 °C. After 96 h, CYP2-like2 transcripts were higher in the PHE exposed groups at 32 °C. Oysters kept at 18 °C showed higher levels of SOD-like transcripts, together with higher GST, GPx and G6PDH activities, associated to lower levels of lipoperoxidation. In general the biological responses evaluated were more affected by temperature, than by co-exposure to PHE.

Genotoxic damage of benzo[a]pyrene in cultured sea bream (Sparus aurata L.) hepatocytes: harmful effects of chronic exposure

The large majority of studies on the genotoxic hazard of PAHs polluted water widely applied the ENA assay as versatile tool in large number of wild and farmed aquatic species. Nuclear abnormalities are commonly considered to be a direct consequence of genotoxic lesions in DNA macromolecule, and such evaluation might be helpful in identifying the genotoxic damage induced by the most harmful PAHs such as B[a]P. Regarding at the fish species subjected to aquaculture, most of the toxicological data come from wild fish and mainly focus on freshwater fish, but very little is known for other marine major aquacultured species. The gilthead sea bream (Sparus aurata L.) is the most economically important sparid species cultured along the Mediterranean costs, and it has been proved a very sensitive species to acute B[a]P exposure. However, further investigation is needed on several other types of genotoxic assessments, especially for chronic effects. This work was totally based on an in vitro model for chronic toxicity, using long-term S. aurata hepatocytes in primary culture, continuously exposed to low levels of BaP, over a prolonged period of time, to provide evidences for latent toxicity response. We aimed to investigate the kind of nuclear damage in gilthead sea bream hepatocytes continuously exposed to B[a]P sublethal doses. Cells were exposed to several B[a]P concentrations (10 μg/mL, 1 μg/mL, 1 ng/mL, 1 pg/mL) for two exposure times (24 and 72 h), and then tested both for apoptosis induction and for nuclear abnormalities by immunofluorescence analysis. The presence of severe nuclear damage, revealed cells progressing towards abnormal genotypes, due to a series of aberrant mitosis followed by unequal distribution of chromosomal content. The nuclear atypia (NA) more frequently observed were: a) micronuclei (MN); b) nuclear buds or blebs (NBUDs); c) notched nuclei; d) lobed nuclei; e) nuclei with nucleoplasmic bridge (NPBs); f) nuclei squashed, with a residual nuclear membrane; g) open nuclei, with membrane tape unrolled; and h) apoptotic bodies. Our results showed at medium-low doses a sustained genotoxic response, whose potency increased with the exposure time, becoming apparent as apoptosis induction, both by cell surface and nuclear changes. At the lowest doses, the longer was B[a]P exposure, greater was the involvement on masses of replicating cells, establishing the connection between the escape from apoptosis and the selection of tumoral cell evolution. In view of these results, there is no evidence of a threshold dose below which B[a]P was found not to be genotoxic in sea bream cultured hepatocytes.

The influence of water temperature on induced liver EROD activity in Atlantic cod (Gadus morhua) exposed to crude oil and oil dispersants

Juvenile Atlantic cod were exposed to either the water-accommodated fraction (WAF) or the chemically enhanced water-accommodated fraction (CEWAF) of Mediterranean South American (MESA), a medium grade crude oil at three different temperatures. Two concentrations of each mixture were tested, 0.2% and 1.0% (v/v) at 2, 7 and 10°C. Corexit 9500 was the chemical dispersant tested. The liver enzyme ethoxyresorufin-O-deethylase (EROD) was measured during a 72-h exposure. The WAF of oil had significant (P<0.05) effect on enzyme activity compared to controls at only one sampling time: 48 h at 10°C. Exposure of CEWAF of oil resulted in significantly (P<0.05) elevated EROD activity compared to controls. The level of EROD induction was temperature related with higher induction being observed in cod exposed to CEWAF at higher temperatures. Total polycyclic aromatic hydrocarbon (PAH) concentrations in exposure water were significantly higher in chemically dispersed mixtures. While PAH concentrations were lower in the 2°C water compared to 7 or 10°C (8.7 vs 11.9 μg mL(-1)), the level of EROD induction was approximately 9 and 12 times lower at 2°C compared to 7 or 10°C, respectively, suggesting the metabolic rate of the cod plays a role in the enzyme response. These data suggest the risk of negative impacts associated with exposure to chemically dispersed oil may be affected by water temperature and that risk assessment of potential effects of WAF or CEWAF should consider the effects of water temperature on the physiology of the fish as well as the effectiveness of dispersants.

Acute effects of benzo[a]pyrene on liver phase I and II enzymes, and DNA damage on sea bream Sparus aurata

In the present study biotransformation and detoxification responses to acute exposure to the polycyclic aromatic hydrocarbons benzo[a]pyrene (B[a]P) were investigated in the liver of Sparus aurata (sea bream). Sexually immature gilthead sea bream were treated by intraperitoneal injection of B[a]P (20 mg kg(-1)) for 6, 12, 24, and 48 h. B[a]P accumulation was quantified in sea bream liver by mean of gas phase chromatography (GPC-MS) after the various exposure periods. The following biological responses were measured: (1) ethoxyresorufin-O-deethylase (EROD) activity, as a phase I biotransformation parameter; (2) liver glutathione S-transferase (GST) activity as a phase II conjugation enzyme. DNA damage was assessed over time using the single-cell gel electrophoresis comet assay. B[a]P bioaccumulation in the liver resulted in a biphasic curve with an increasing uptake up to 5.55 +/- 0.67 microg g(-1) dry weight after only 6 h exposure and 4.67 +/- 0.68 microg g(-1) dry weight after 48 h exposure. EROD activity showed a nonsymmetrical bell-shaped kinetic with a maximum at 24 h and lower but significant activities at 12 and 48 h with respect to control animals. Hepatic GST activities were only significant after 48 h exposure. Comet assay showed an increase in liver cells DNA damage with a maximum after 48 h exposure reaching up to 12.17 % DNA in the tail.

Energy intake affects the biotransformation rate, scope for induction, and metabolite profile of benzo[a]pyrene in rainbow trout

The metabolic conversion of benzo[a]pyrene (B[a]P) by rainbow trout (Oncorhynchus mykiss) hepatocytes was not significantly different between any group of fed fish (fed one of three isoenergetic diets that varied in protein and lipid content at full satiation levels or half rations), however at 12 weeks, fasted fish exhibited significantly reduced B[a]P biotransformation rates (by 58%). Alterations in metabolite profiles were also seen: fasted fish produced significantly more Phase I metabolites, higher levels of both glucuronide and sulphate conjugates, and lower levels of presumptive glutathione conjugates, compared to fed fish. When fish were fasted, higher proportions of phenols were produced, with lower proportions of quinones, triols and tetrols. Inducing metabolism (using beta-naphthoflavone) increased metabolic scope for B[a]P by 2-fold, regardless of each diet's baseline metabolic rate. However, the balance between Phase I and II reactions was altered with induction and fasting: higher proportions of Phase I metabolites were found, with lower glutathione conjugates and higher proportions of triols/tetrols. Fasting-mediated reductions in glutathione conjugation, and increased induction of oxidation vs. conjugating enzymes, can explain altered metabolite profiles. These results suggest that in contaminated habitats, where pollution-induced reductions in food quantity or quality are combined with the presence of toxic compounds and inducers, detoxification rates can be diminished.

Monitoring contaminants from oil production at sea by measuring gill EROD activity in Atlantic cod (Gadus morhua)

An ex vivo gill EROD assay was applied in Atlantic cod (Gadus morhua) as a biomarker for waterborne CYP1A-inducing compounds derived from oil production at sea. Exposure to nominal concentrations of 1 ppm or 10 ppm North Sea crude oil in a static water system for 24 h caused a concentration-dependent gill EROD induction. Further, exposure of cod for 14 days to environmentally relevant concentrations of produced water (PW, diluted 1:200 or 1:1000) from a platform in the North Sea using a flow-through system resulted in a concentration-dependent induction of gill EROD. Crude oil (0.2 ppm) from the same oil field also proved to induce EROD. Finally, gill EROD activity in cod caged for 6 weeks at 500-10 000 m from two platforms outside Norway was measured. The activities in these fish were very low and did not differ from those in fish caged at reference sites.

Significance of cytochrome P450 system responses and levels of bile fluorescent aromatic compounds in marine wildlife following oil spills

The relationships among cytochrome P450 induction in marine wildlife species, levels of fluorescent aromatic compounds (FAC) in their bile, the chemical composition of the inducing compounds, the significance of the exposure pathway, and any resulting injury, as a consequence of exposure to crude oil following a spill, are reviewed. Fish collected after oil spills often show increases in cytochrome P450 system activity, cytochrome P4501A (CYP1A) and bile fluorescent aromatic compounds (FAC), that are correlated with exposure to polycyclic aromatic hydrocarbons (PAH) in the oil. There is also some evidence for increases in bile FAC and induction of cytochrome P450 in marine birds and mammals after oil spills. However, when observed, increases in these exposure indicators are transitory and generally decrease to background levels within one year after the exposure. Laboratory studies have shown induction of cytochrome P450 systems occurs after exposure of fish to crude oil in water, sediment or food. Most of the PAH found in crude oil (dominantly 2- and 3-ring PAH) are not strong inducers of cytochrome P450. Exposure to the 4-ring chrysenes or the photooxidized products of the PAH may account for the cytochrome P450 responses in fish collected from oil-spill sites. The contribution of non-spill background PAH, particularly combustion-derived (pyrogenic) PAH, to bile FAC and cytochrome P450 system responses can be confounding and needs to be considered when evaluating oil spill effects. The ubiquity of pyrogenic PAH makes it important to fully characterize all sources of PAH, including PAH from natural resources, e.g. retene, in oil spill studies. In addition, such parameters as species, sex, age, ambient temperature and season need to be taken into account. While increases in fish bile FAC and cytochrome P450 system responses, can together, be sensitive general indicators of PAH exposure after an oil spill, there is little unequivocal evidence to suggest a linkage to higher order biological effects, e.g. toxicity, lesions, reproductive failure.

Ethoxyresorufin-O-deethylase (EROD) activity in fish as a biomarker of chemical exposure

This review compiles and evaluates existing scientific information on the use, limitations, and procedural considerations for EROD activity (a catalytic measurement of cytochrome P4501A induction) as a biomarker in fish. A multitude of chemicals induce EROD activity in a variety of fish species, the most potent inducers being structural analogs of 2,3,7,8-tetracholordibenzo-p-dioxin. Although certain chemicals may inhibit EROD induction/activity, this interference is generally not a drawback to the use of EROD induction as a biomarker. The various methods of EROD analysis currently in use yield comparable results, particularly when data are expressed as relative rates of EROD activity. EROD induction in fish is well characterized, the most important modifying factors being fish species, reproductive status and age, all of which can be controlled through proper study design. Good candidate species for biomonitoring should have a wide range between basal and induced EROD activity (e.g., common carp, channel catfish, and mummichog). EROD activity has proven value as a biomarker in a number of field investigations of bleached kraft mill and industrial effluents, contaminated sediments, and chemical spills. Research on mechanisms of CYP1A-induced toxicity suggests that EROD activity may not only indicate chemical exposure, but also may also precede effects at various levels of biological organization. A current research need is the development of chemical exposure-response relationships for EROD activity in fish. In addition, routine reporting in the literature of EROD activity in standard positive and negative control material will enhance confidence in comparing results from different studies using this biomarker.

Effects of food deprivation and handling stress on head kidney 17alpha-hydroxyprogesterone 21-hydroxylase activity, plasma cortisol and the activities of liver detoxification enzymes in rainbow trout

The 21-hydroxylation of 17alpha-hydroxyprogesterone is one step in the biosynthesis of corticosteroids. Both 7 days of handling-induced stress and 7 weeks of food deprivation significantly elevated head kidney microsomal 17alpha-hydroxyprogesterone 21-hydroxylase activity in juvenile rainbow trout. The increased 21-hydroxylase activity was not paralleled by changes in plasma cortisol levels induced by handling stress whereas food deprivation for 3 and 7 weeks increased both 21-hydroxylase activity and plasma cortisol levels significantly. Food deprivation in rainbow trout affected detoxification enzyme activities, namely glutathione-S-transferase (GST), uridine-di-phosphate glucuronosyltransferase (UGT) and glutathione reductase (GR) activities in the liver. Together our observations suggest that experimental conditions can affect experimental results, especially the values of parameters like GST, UGT and GR. Furthermore, alterations in the metabolic state of the liver caused by stress or food deprivation can alter the balance between detoxification enzymes in rainbow trout liver.

Thermal modulation of the toxicokinetics of benzo[a]pyrene in isolated hepatocytes of sablefish (Anoplopoma fimbria), black rockfish (Sebastes melanops), and chub mackerel (Scomber japonicus)

Hepatocytes from sablefish (Anoplopoma fimbria), black rockfish (Sebastes melanops) and chub mackerel (Scomber japonicus) were isolated from 11 degrees C acclimated animals. The uptake, metabolism, and excretion of benzo[a]pyrene (B[a]P) in hepatocytes was measured at 6, 11 and 19 degrees C. Chub mackerel hepatocyte uptake rates were significantly lower (0.012 +/- 0.003 microg/s per g cell) at 11 degrees C than black rockfish (0.028 +/- 0.009 microg/s per g cell) or sablefish (0.032 +/- 0.012 microg/s per g cell) hepatocytes at all temperatures. Hepatocytes metabolized B[a]P to phase I (1-8%) and phase II (92-99%) metabolites. Accumulation of phase II metabolites was lower in chub mackerel hepatocytes (0.016 +/- 0.004 microg/h per g cell), than black rockfish (0.052 +/- 0.012 microg/h per g cell), or sablefish hepatocytes (0.060 +/- 0.015 microg/h per g cell). Phase II metabolite accumulation increased greatest with temperature in chub mackerel hepatocytes (Q10 = 1.94 +/- 0.30), followed by sablefish (Q10 = 1.65 +/- 0.30), and rockfish (Q10 = 1.38 +/- 0.30). Sablefish hepatocytes had higher excretion rates of phase II metabolites (0.010 +/- 0.0023 microg/h per g cell), than mackerel (0.0046 +/- 0.0009 microg/h per g cell) or rockfish hepatocytes (0.0029 +/- 0.0008 microg/h per g cell). Phase II metabolite excretion rates increased with temperature only in sablefish hepatocytes (Q1O = 1.67 +/- 0.76). These differences in toxicokinetics may indicate distinct consequences for various species exposed to xenobiotics.

Rainbow trout cytochrome P450s: purification, molecular aspects, metabolic activity, induction and role in environmental monitoring

Cytochromes P450 (P450s or CYPs) constitute a superfamily of heme-thiolate proteins that play important roles in oxidative metabolism of endogenous and exogenous compounds. This review provides some limited history but addresses mainly the research progress on the cytochrome P450s in rainbow trout (Oncorhynchus mykiss), their purification, structures at the primary level, role in metabolism, responses to chemicals and environmental pollutants, application to biomonitoring and the effect of various factors on their expression or activities. Information obtained to date suggests that the rainbow trout P450 systems are as complex as those seen in mammals. Fourteen P450s have been purified from liver or trunk kidney to relatively high specific content. cDNAs belonging to seven different P450 families have been documented from trout liver, kidney and ovary. Two CYP1A genes, nine cDNAs containing open reading frames, and a cDNA fragment were entered into GenBank. Among them, CYP2K1, CYP2K3, CYP2K4, CYP2M1, CYP3A27 and CYP4T1 are the most recently described forms. CYP2K1, CYP2M1 and CYP4T1 represent newly identified P450 subfamilies first described in the rainbow trout. In many cases, the cloned rainbow trout P450s have subsequently been expressed in heterologous expressions systems such as COS-7 cells, yeast and baculovirus infected insect cells. Some of the overexpressed P450 isoforms have been partially characterized. Potential future research directions are discussed.

Laboratory and field-caging studies on hepatic enzymatic activities in European eel and rainbow trout

Caging field experiments were conducted on young European eel (Anguilla anguilla) and on rainbow trout (Onchorynchus mykiss) for the determination of a biomonitoring protocol of freshwater streams. Hepatic monooxygenase and conjugation enzyme activities were measured as biomarkers of exposure to some organic pollutants. Laboratory studies were performed to compare the responsiveness of these two species concerning their enzymatic activities. The induction of monooxygenase activity, measured as the deethylation of 7-ethoxyresorufin (EROD activity) was examined by beta-naphtoflavone (beta-NF) treatment. Dose-response study revealed that EROD activity increased significantly from 1 mg beta-NF/kg bw and was on a plateau at 50 mg beta-NF/kg bw for both species. No significant effect on glutathione S-transferase (GST) activity was observed. During a time-course study, EROD activity increased, starting from the second day for both species. In European eel, this enzymatic activity decreased significantly from the seventh day, whereas no significant decrease was observed for rainbow trout after 14 days. During a 2-week field study, EROD and GST activities were measured in fish held in cages upstream and downstream of a polluted area. For both species, the induction of EROD activity was observed in the polluted site after 14 days of caging; GST activity was not significantly affected. Monooxygenase activity appeared to be a sensitive tool for biomonitoring freshwater streams for both species.

Statistical analysis of cyprinid ethoxyresorufin-O-deethylase data in a large French watershed

A comparison of ethoxyresorufin-O-deethylase (EROD) data collected in 1995 in various sites in the Rhône watershed (France) was carried out to quantify the influence of factors such as contamination and biological parameters on EROD levels and within-group variabilities. Three species of cyprinids were collected and fish chemical contamination was measured. A log transformation of EROD data provided both normalization and homogeneity of variances. The influence of female sexual maturation on the variability and EROD dimorphism was quantified. A relationship with contaminant bioaccumulation was observed. A comparison with EROD data collected during previous studies by the same laboratory was made to validate the results.

Temporal induction pattern of hepatic cytochrome P450 1A in thermally acclimated dab (Limanda limanda) treated with 3,3',4,4'-tetrachlorobiphenyl (CB77)

Mature male dab (Limanda limanda) acclimated at 10 degrees and 16 degrees C were orally administered a single dose of 0.5 mg/kg 3,3',4,4'-tetrachlorobiphenyl (CB77). At both temperatures, levels of cytochrome P450 1A (CYP1A) protein and 7-ethoxyresorufin O-deethylase (EROD) activity showed a two to six fold induction 40 days after CB77 treatment compared to control groups. Maximum responses of both EROD activity and CYP1A protein for the warm-acclimated fish were observed at 5 days after treatment. For the cold-acclimated fish a slow, progressive elevation for both EROD activity and CYP1A protein was observed and maximum responses were measured 40 days after treatment. Absolute EROD activity and CYP1A protein levels of fish from both temperatures were equally high at 40 days after treatment. Since in the control groups EROD activity and CYP1A protein levels were higher in the cold-acclimated fish, the magnitude of induction was higher in the warm acclimated ones. The highest concentrations of CB77 in muscle of fish from both temperatures were found at 5 and 10 days after treatment. The liver somatic index (LSI) showed 1.5 fold significantly higher values for the fish acclimated at 10 degrees C.

beta-Naphthoflavone-inducible cytochrome P4501A1 activity in liver microsomes of the marine safi fish (Siganus canaliculatus)

The cytochrome P450-dependent metabolism of benzo(a)pyrene and other xenobiotics has been investigated in liver microsomes prepared from a local marine safi fish, Siganus canaliculatus. The safi fish was found to have a well-developed microsomal monooxygenase system consisting of cytochrome P450, cytochrome b5 and NADPH-cytochrome c reductase. The fish microsomal enzyme system was able to metabolize benzo(a)pyrene, 7-ethoxycoumarin and 7-ethoxyresorufin. Male fish were found to exhibit a higher monooxygenase activity than female fish. Treatment of fish with beta-naphthoflavone was found to induce (2- to 4-fold) the activities of aryl hydrocarbon hydroxylase, ethoxycoumarin O-deethylase and ethoxyresorufin O-deethylase. HPLC analysis of the metabolites produced by incubation of benzo(a)pyrene with the liver microsomal preparation showed a predominant formation of 3-OH and 9-OH benzo(a)pyrene. There was an increased formation of benzo(a)pyrene 7,8-diol and benzo(a)pyrene 7,8,9,10-tetrol in liver microsomes prepared from beta-naphthoflavone-treated fish. Western immunoblot analysis of liver microsomes from beta-naphthoflavone-treated fish using an antibody to rat liver cytochrome P4501A1 (CYP1A1) suggested the presence of an inducible cytochrome P450 enzyme that was comparable with that of rat liver enzyme. Our results suggest that liver microsomes from the safi fish have multiple forms of cytochrome P450 with a specific beta-naphthoflavone-inducible CYP1A1 homologous protein that can metabolize a variety of substrates.

Erod measurement using post mitochondrial supernatant (pms) in roach (Rutilus rutilus L.), a possible biomonitor for PAH contamination in the freshwater environment

The use of hepatic post-mitochondrial supernatant (pms) as a source of monooxygenase activity in roach following intra peritoneal injection of beta-naphthoflavone was investigated. Pms was found to be three times less active than microsomes although the level of induction was similar (9 fold). No effect of dicumarol on Ethoxyresorufin O-deethylase (EROD) measurement using pms was recorded. EROD induction in roach peaked 2-4 days post treatment with beta-naphthoflavone. Given the ubiquitous nature and pollution tolerance of roach, their hepatic pms may serve as a convenient biomonitor of PAH contamination in the freshwater environment. Field studies are now underway to investigate this further.

The effects of temperature on the uptake and metabolism of benzo[a]pyrene in isolated gill cells of the gulf toadfish, Opsanus beta

The effects of acclimation temperature and acute temperature change on the uptake and metabolism of the procarcinogen benzo[a]pyrene (BaP) by gill cells of the gulf toadfish, Opsanus beta, were examined. BaP was rapidly accumulated by isolated gill cells and uptake rates were directly proportional to BaP concentration in the medium (1 to 100 μg/ml). Uptake rates were higher in cells isolated from fish acclimated to 18°C when compared to cells from 28°C acclimated fish at all incubation temperatures. When cells were exposed to BaP at the respective acclimation temperatures of the fish, uptake rates were similar (0.14 ± 0.01 at 18°C and 0.12 ± 0.01 μg BaP/s/10 mg cells at 28°C). This finding is discussed in view of results which showed a partial compensation of membrane fluidity in plasma membranes isolated from fish from the two acclimation temperatures. At higher incubation temperatures, cells from fish acclimated to 18°C metabolized BaP at a greater rate than those at 28°C (49.6 ± 1.92 and 43.0 ± 2.24 μg/g/8h, respectively, at 23°C). Low but detectable activities of common biotransformation enzymes (aryl hydrocarbon hydroxylase, glutathione-S-transferase) and cytochrome P-450 content were found, however, no significant differences were evident between cells from fish acclimated to different temperatures.

Preexposure temperature acclimation and diet as modifying factors for the tolerance of golden ide (Leuciscus idus melanotus) to short-term exposure to 4-chloroaniline

The influence of different temperature and nutrition regimes on the acute toxicity of 4-chloroaniline to golden ide (Leuciscus idus melanotus) was investigated. Acute toxicity was determined over 48 hr at 20 degrees C without feeding after a 2-day acclimation period. In an attempt to reveal underlying mechanisms accounting for diet- and temperature-related differences in the toxicant resistance of golden ide, biochemical and quantitative morphological parameters of the liver, a central organ in the xenobiotic metabolism of fish, were recorded throughout the 12-week acclimation period. In cold-acclimated fish, acute toxicity of 4-chloroaniline was 40% higher than in fish acclimated to 20 degrees C. If compared to 20 degrees C, preacclimation to 14 degrees C was characterized by a lower specific growth rate, an increase of hepatic glycogen, and a decrease of body and liver lipid deposits. The organelle composition of hepatocytes was not significantly altered by temperature acclimation. For the nutrition experiment, commercially available diets A and B of similar crude composition were used. Acute toxicity of 4-chloroaniline was 60% lower with diet B than with diet A. If compared to diet B, diet A induced a higher specific growth rate and increased hepatocellular volume of endoplasmic reticulum and Golgi fields, whereas glycogen and lipid of the liver as well as body lipid contents were reduced. The toxicity of 4-chloroaniline was correlated with the development of the endoplasmic reticulum, the major site of biotransformation enzymes. A consistent correlation with lipid contents could not be established. Results illustrate not only that assay conditions during the actual test may profoundly interact with results of toxicity studies, but also that maintenance conditions before the test can have significant consequences on results. In order to improve reproducibility of the results of acute toxicity tests, more consideration should be given to the standardization of pretest maintenance conditions of fish.

Xenobiotic metabolizing enzymes in rainbow trout exposed to river water

1. Juvenile rainbow trout were exposed to river water in a flow-through system. After 15 days of exposure, hepatic biotransformation activities and related parameters were measured and compared to those of the control group organisms that were maintained in tap water under identical experimental conditions. 2. Liver somatic index (LSI), microsomal protein and cytochrome P-450 contents, benzo[a]pyrene hydroxylase (AHH), ethoxyresorufin-O-deethylase (EROD) and UDP glucuronyl transferase activities were not significantly affected. 3. Aminopyrine-N-demethylase (APD) activity showed a slight yet significant increase in exposed trout.

1,2-Dibromoethane and chloroform in the rainbow trout (Salmo gairdneri): studies on the distribution of nonvolatile and irreversibly bound metabolites

The disposition of metabolites from 14C-labeled 1,2-dibromoethane (DBE) and chloroform (CF) in juvenile rainbow trout was studied by autoradiography and quantitation of tissue radioactivity. Whole-body autoradiography of heated tissue sections showed a considerable level of nonvolatile metabolites of DBE and CF in the liver and certain areas of the body kidney. A lower level of metabolites appeared in the gills, intestinal mucosa, and olfactory rosettes in trouts exposed to DBE- or CF-containing water. Unlike previous studies in rodents, no specific uptake or binding of DBE or CF occurred in the surface epithelia of the upper alimentary tract. Microautoradiography and exhaustive tissue extraction confirmed a high irreversible binding of DBE metabolites in the liver and in a proximal tubular segment of the body kidney in fish exposed to DBE-containing water. A high level of radioactivity in the bile indicated fecal excretion of metabolites from both compounds. The results suggest that there is marked metabolism of DBE and CF in the liver and kidney, whereas the metabolism in the surface epithelia is low. The liver and kidney are proposed to be target organs of toxicity in fish.

The temporal relationships between P450E protein content, catalytic activity, and mRNA levels in the teleost Fundulus heteroclitus following treatment with beta-naphthoflavone

P450 induction occurs in some marine organisms following chemical exposure. The mode of 3-methylcholanthrene (MC)-type induction was evaluated by examining hepatic isozyme P450E content, catalytic activity, and mRNA levels in the marine teleost Fundulus heteroclitus after exposure to a single dose of beta-naphthoflavone (BNF). P450E is the major teleost P450 induced by MC-type compounds and is the catalyst for aryl hydrocarbon hydroxylase (AHH) and ethoxyresorufin O-deethylase (EROD) activities. In a 20-day experiment, EROD activity was elevated in BNF-treated animals from Day 4 through Day 20. Increases in immunodetectable P450E showed the same trend as EROD activity, with consistently low control values and at least a 19-fold increase in the BNF-treated fish. Precipitation of liver RNA in vitro translation products with anti-P450E antibody gave no detectable signal from control fish, while the BNF-treated animals showed incorporation of [3H]leucine in a single 6,000 Mr band. In a shorter term experiment, EROD activity and P450E levels were again coordinately increased in response to BNF treatment, and immunoprecipitation of translation products from these fish showed a clear trend of increased P450E mRNA levels for all time points 6 h or more post-treatment. Hybridization of RNA from BNF-treated Fundulus with a trout P450IA1 cDNA also showed increases in a single band with time. The increases in P450E mRNA preceded increases in P450E protein and enzyme activity by about 25 h. However, P450E mRNA declined rapidly, reaching control levels by 5 days, while protein levels remained elevated for at least 13 days. The results support a hypothesis that transcriptional enhancement is involved in induction of MC-inducible P450s in fish, but indicate that P450E induction is also under other forms of regulatory control.

Localization of cytochrome P-450 in the head and trunk kidney of rainbow trout (Salmo gairdneri)

Mature, untreated rainbow trout display a marked sex difference in the level and activity of the P-450-dependent mixed-function oxidase system with males demonstrating higher levels than females. This difference is accentuated in the trunk kidney, is specific for endogenous substrates such as lauric acid and sex steroids, and is correlated with greater levels of the constitutive cytochrome P-450 isozyme, LM2. Using an immunohistochemical technique, the cellular localization of P-450 LM2 and P-450 LM4b, the major beta-naphthoflavone inducible isozyme, in the head and trunk kidney of male, female, and juvenile trout has been demonstrated. Immunostaining for P-450 LM2 was observed in the cytoplasm of cells in the second portion (P2) of the proximal tubules of both male and female trout. In male fish, staining appeared to be more intense and involved most of the P2 segments in a tissue section. In female fish, P2 staining was moderate and involved fewer segments. Low staining intensity for P-450 LM4b was observed in the cytoplasm of cells both in the first portion of the proximal tubules and in P2 of male and female fish. Sexual dimorphism was not apparent. The finding of greater amounts of P-450 LM2 in males and low levels of P-450 LM4b in untreated male and female trout confirms previous biochemical studies. Localization of P-450 isozymes in the proximal tubules is consistent with findings in mammalian species. Moderate immunostaining by anti-P-450 LM4b IgG also was observed in the interrenal cells of the head kidney of male, female, and juvenile trout.

Induction of cytochrome P-450 mediated mono-oxygenase reactions and conjugation activities in freshwater crayfish (Astacus astacus)

The inducibility of the freshwater crayfish (Astacus astacus) biotransformation enzymes with model inducers (Aroclor 1254, beta-Naphthoflavone, Phenobarbital) were investigated three days after intra cephalothoracic injection in the fasting crayfish at 5 degrees C. Of the monooxygenase activities, 7-ethoxycoumar in O-deethylase increased in the hepatopancreas significantly (p less than 0.05) after beta-naphthoflavone administration. Benzo(a)pyrene hydroxylase did not change. Aroclor 1254 and phenobarbital injection elevated hepatopancreatic glutathione S-transferase activity (p less than 0.05).