Hepatic EROD Activity Research Articles

Influence of UVA and UVB irradiation on hepatic and cutaneous P450 isoenzymes.

The influence of UVA and UVB irradiation of the skin for 1, 2 and 4 weeks on the activities of the hepatic and cutaneous P450 isoenzymes was investigated in female Wistar rats before and after systemic administration of hexachlorobenzene (HCB), a well-known porphyrogenic agent, which additionally induces P450 1A1 and P450 1A2 isoenzymes. UVA and UVB irradiation of the skin of controls and HCB-treated animals did not influence porphyrin metabolism. In the nonporphyric rats hepatic EROD (P450 1A1) activity was induced by UVB, but the activity of ADM (P450 2B) and EMDM (P450 3A) was either minimally or not affected. In the HCB-treated (porphyric) rats UVA and UVB irradiation resulted in a significant depression of HCB-induced EROD in the liver and in the skin. In both the nonporphyric and the porphyric rats UVA and UVB irradiation had no effect on hepatic ADM activity. In the liver of the nonporphyric animals EMDM activity remained unchanged after UVA and UVB irradiation, whereas in the HCB-treated animals the activity of this enzyme was increased. Finally, after UVA and UVB irradiation cutaneous EMDM activity was increased in the controls, whereas the HCB-induced increase of this enzyme in porphyric animals was decreased. In addition long-term (28 days) UVB irradiation decreased hepatic GSH content significantly in normal and porphyric rats. These experimental findings cannot be directly extrapolated to humans; however, they suggest that exposure of human skin to UV radiation may result in alterations in the activity of cutaneous hepatic and other extracutaneous P450 isoenzymes.

Interaction of nonylphenol and hepatic CYP1A in rats

Both estradiol and nonylphenol (NP) inhibited hepatic microsomal 7-ethoxyresorufin O-deethylase (EROD) activity of β-naphthoflavone-treated rats. Enzyme kinetic analyses (Lineweaver-Burk plots) using different estradiol and NP concentrations with graded increases in the concentrations of the substrate, ethoxyresorufin, showed that the inhibition was of a competitive nature at all concentrations of estradiol or NP used. Thus, the mechanism by which NP inhibits EROD activity is similar to that of estradiol. NP, however, was much less potent than estradiol. Young rats treated in vivo with 80 mg/kg body weight of NP demonstrated a slight but significant decrease in their hepatic microsomal EROD activity and CYP1A protein as measured by western blot analysis. In addition, treatment with NP led to a decrease in the steady-state levels of hepatic CYP1A mRNA in rats, suggesting that NP acted at the pre-translational level. The competitive nature of inhibition by NP on hepatic microsomal EROD activity indirectly suggests that this compound is a possible substrate of the CYP1A enzyme. Furthermore, NP had a moderate modulating effect on the expression of CYP1A in rat liver. BiocHEM pharmacol 52;6:885-889, 1996.

Low hepatic 7-ethoxyresorufin- O-deethylase (EROD) activity and minor alterations in retinoid and thyroid hormone levels in flounder ( Platichthys flesus) exposed to the polychlorinated biphenyl (PCB) mixture, Clophen A50

The effect of the polychlorinated biphenyl (PCB) mixture Clophen A50 on hepatic cytochrome P4501A1 dependent EROD (7-ethoxyresorufin- O-deethylase) activity, plasma thyroid hormone levels and plasma, kidney and liver retinoid concentrations of the euryhaline flatfish flounder ( Platichthys flesus) was determined 2 and 10 days after i.p. (intraperitoneal) injection with 20, 100 and 500 mg Clophen A50/kg body weight. No effect of Clophen A50 on total cytochrome P450 content in flounder liver was observed at both time points. A six-fold, dose-dependent, significant increase in EROD activity was found at exposure day 10 in flounder receiving 100 or 500 mg Clophen A50/kg body weight. Plasma retinol concentrations were not altered at both time points after Clophen A50 administration, whereas renal retinol levels showed a minor dose-related increase at day 2 and day 10 of exposure. Significant alterations in hepatic retinoid concentrations were observed, which were not dependent on the dose of PCB administered. In addition Clophen A50 administration did not result in a dose-related alteration of total T 4 concentrations in plasma. Total T 3 concentrations in plasma were only significantly increased at day 2 after exposure, whereas free T 4 concentrations were increased at both time points after Clophen A50 administration. These data indicate that with regard to the parameters investigated and in contrast to other fish species studied, the flounder is not a sensitive species to PCB exposure.

Postnatal development of cytochrome P4501A1 and 2B1 in rat lung and liver: effect of aged and diluted sidestream cigarette smoke.

Earlier studies have shown that both mainstream and sidestream cigarette smoke increase the activities of cytochrome P4501A1 and 2E1 in the lungs of adult animals; however, little information is available on the influence of ambient levels of sidestream cigarette smoke on cytochrome P450 monooxygenase activity in the developing lung. The present studies were conducted to define the developmental profiles of cytochrome P450 monooxygenases 1A1 and 2B1 in rat lung and liver and to assess the effects of aged and diluted sidestream cigarette smoke (ADSS) on the developmental profile of these two enzymes. Accordingly, pulmonary and hepatic microsomal P4501A1 and 2B1 activities were determined by measuring ethoxy- and pentoxyresorufin-O-delakylase (EROD and PROD, respectively) activity in animals exposed to filtered air or ADSS from birth to 7, 14, 21, 50, and 100 days of age. Pulmonary P4501A1 activity in control rats was not detected until 14 days of age. Activities increased threefold between 14 and 21 days of age and remained unchanged to 100 days of age. In animals exposed to ADSS from birth, pulmonary EROD activities were detected as early as 7 days postnatal and were elevated three- to fourfold above control at all other ages examined. Hepatic EROD activities were unaltered by ADSS exposure. Short-term (4-day) ADSS exposure was as effective in upregulating pulmonary microsomal EROD activities as 100-day exposures. Induction of pulmonary EROD activities and the associated increases in mRNA levels were dependent upon the particulate fraction. Stimulation of EROD activities in major and minor daughter subcompartments was three- to fourfold higher in ADSS-exposed animals compared to controls, while there was no induction in the trachea and less than a twofold increase in the parenchyma. Pulmonary PROD activities developed more slowly than EROD and did not reach adult levels until Day 50. ADSS did not alter pulmonary or hepatic PROD activities. These studies show that P4501A1 and 2B1 develop at different rates in rat lung and liver and that exposure to ADSS markedly increases P4501A1 activities in the lung at all ages examined.

Temporal studies of the impact of the braer oilspill on inshore feral fish from Shetland, Scotland

Activities of the petroleum-inducible mixed function oxygenase CYP1A (EROD) were measured in livers of inshore demersal fish species at various sites around the coast of Shetland to determine the sub-lethal impact of oil spilled after the wreck of the tanker M.V. Braer in January 1993. Visible coastal pollution by the oil was only apparent for some two weeks after the incident and tissue PAH levels in muscle of gadoid fish such as rockling from these areas were not elevated 3 months afterwards, while hepatic EROD activities were elevated some 7-to 9-fold. A 6.5-fold elevation was still observed 5 months afterwards; however, the levels had returned to those of fish from non-polluted environments 7 months after the incident and remained at baseline levels after the following winter's storm action. These data demonstrate the usefulness of enzymatic analysis as a sensitive method for assessing the temporal and spatial impact of an oil spill.

Cytochrome P4501A indices as biomarkers of contaminant exposure: results of a field study with plaice ( Pleuronectes platessa) and flounder ( Platichthys flesus) from the southern North Sea

Within the framework of the Integrated North Sea Programme (INP), samples of two flatfish species, flounder, Platichthys flesus, and plaice, Pleuronectes platessa, were collected during August/September 1991 and May/June 1992 in the southern North Sea. The aim of the study was to examine the induction of hepatic cytochrome P4501A (CYP1A) in both species when exposed to environmental PCBs and PAHs. Plaice and flounder occupy different but partly overlapping habitats. Flounder live mainly in estuaries and coastal areas whereas plaice can be found throughout the North Sea. CYP1A was measured by a semiquantitative immunochemical ELISA technique and also by the activity of its catalyst, 7-ethoxyresorufm O-deethylase (EROD). In plaice, both hepatic CYP1A protein level and EROD activity were significantly higher at offshore sampling locations than at coastal locations, by a factor of 1.5 to 2. In flounder, which were only collected at coastal locations, the range of values of EROD activity was much greater than in plaice, but the response in the ELISA test using polyclonal trout CYP1A1 antibodies was comparable in both species. Multiple regression analysis of data from plaice and flounder did not show any significant correlation between CYP1A indices, water temperature and contaminant concentrations in fish tissues. CYP1A indices also appeared to be unrelated to food type, as determined by visual screening of fish intestines. One possible explanation for the lack of correlation between CYP1A indices and indices of exposure to pollution could be the influence of additional modifying factors (biological, physical or chemical), which might mask CYP1A induction by PCBs and PAHs in this area. However, the low statistical power of the tests used, related to difficulties in collecting sufficiently large sample sizes, should also be borne in mind. It can be concluded that the induction of CYP1A in plaice and flounder from the southern North Sea is not related in a simple manner to exposure to PCBs and PAHs, two groups of chemicals that cause induction in the laboratory. Apparently, other unknown modifying factors also have a considerable influence. From the point of view of use as a biomarker, the measurement of CYP1A protein level and EROD activity in plaice and flounder from the open North Sea cannot be applied straightforwardly for monitoring exposure to PCBs and/or PAHs in the absence of more knowledge about the mentioned modifying factors.

Seasonal variation of hepatic EROD activity in flounder ( Platichthys flesus) in the Dutch Wadden Sea

The use of hepatic 7-ethoxyresorufin O-deethylase (EROD) activity in flounder ( Platichthys flesus) as a potential biomarker of marine pollution by organic chemicals (as indicated by hepatic PCB-153 concentration) was investigated in the Dutch Wadden Sea in 1989 and 1990. Particular attention was paid to the seasonal variation. The results indicate that EROD activity was reasonably stable during the year, except for a period in January–February when a marked peak occurred. This peak coincided with the absence of mature flounder from the sampling area probably due to the spawning migration. Generally a good relationship existed between hepatic EROD activity and PCB-153 concentration, with one exception. During the period January–April 1990 a peak in PCB-153 concentration occurred immediately after the observed peak in EROD activity. It is concluded that the best period for monitoring EROD activity in flounder is the summer, corresponding to the non-migratory period of the species.

Effects of PCDDs, PCDFs and PCBs in common tern (sterna hirundo) breeding in estuarine and coastal colonies in the netherlands and belgium

AbstractIn 1991, eggs of the common tern (Sterna hirundo) were collected at eight different locations and incubated artificially. The residual yolk sacs of the hatchlings from the highly polluted colonies, located in the main sedimentation area of the Rhine and Meuse rivers, contained on average 16 ng TEQ (toxicity equivalency) per gram lipid, which was fivefold higher than the concentrations in the reference colony. The hepatic EROD activity was induced fourfold compared to the reference colony (p < 0.005). At the individual level, a significant relationship was found between log TEQ and both log EROD and log PROD (r = 0.568, p < 0.05 and r = 0.661, p < 0.02, respectively). Average TEQ concentration in chicks that hatched after 23 d of incubation were twice the concentration of those that hatched after 21 d (p < 0.05). No concentration‐related effects on morphology and physiology were found. The non‐ortho‐ and mono‐ortho‐PCBs were predominant regarding the total TEQ, while the PCDDs and PCDFs contributed less than 10%. The PCB patterns were highly similar among the individual birds and among different locations. In contrast, PCDD and PCDF patterns were not similar at all locations, and two distinct patterns could be recognized and related to sediments that were deposited during different time periods.

Studies of the inducibility of P450 1A in perch from the PCB-contaminated Lake Järnsjön in Sweden

Comparatively low levels of hepatic EROD activities were observed in feral perch caught in Lake Järnsjön, heavily contaminated with polychlorinated biphenyls (PCBs) when compared to reference sites. On the other hand rainbow trout, caged in Lake Järnsjön, exhibited elevated EROD activities, P450 1A1 protein and CYP1A1 mRNA levels. The feral perch from the PCB area were non-responsive towards model P450 1A system inducers. These results suggest a possible pollutant-induced suppression or inactivation of the P450 1A system in feral perch in Lake Järnsjön.

Cytochrome P450IA induction by a coplanar PCB, a PAH mixture, and PCB-contaminated sediment extracts following microinjection of rainbow trout sac-fry

The 7-ethoxyresorufin- O-deethylase (EROD)-inducing potencies of a coplanar polychlorinated biphenyl (PCB) (3,3′,4,4′,5-pentachlorobiphenyl, IUPAC No. 126), a mixture of five polycyclic aromatic hydrocarbons (benzo(k)fluoranthene, benz(a)anthracene, benzo(a)pyrene, indeno(1,2,3-cd)pyrene and chrysene), and lipophilic compounds extracted from the sediments in a PCB-contaminated lake and from sediments in lakes up- and downstream, were studied in rainbow trout sac-fry in a 43-day study. The compounds/extracts were injected into the yolk sacs of newly hatched sac-fry and hepatic EROD activities and mortality rates were measured at various times after the injections. Five livers from each group were also examined by transmission electron microscopy. All the compounds/extracts induced hepatic EROD activities in the sac-fry. Ten days after injection the EROD activity caused by PCB No. 126 (1.3 ng per embryo) was 40-fold compared to the control activity. This was the highest induction rate observed in the experiment. For the sediment extracts, the highest induction rates were observed at the first sampling occasion, which for these groups was on day 24. The extract from the Lake Järnsjön sediment was more potent as an EROD inducer than the extracts of sediments from the lakes up- and downstream from Lake Järnsjön. None of the sediment extracts caused any significant mortality. In sac-fry injected with the PAH mixture, EROD was only slightly induced. The highest dose of PAHs (10 μg per embryo) caused about 90% mortality by 24 days after injection. When the livers were examined by transmission electron microscopy, morphological alterations (e.g. hepatocyte degeneration and hypertrophy) were seen in the groups injected with Lake Järnsjön sediment extract, PCB No. 126 and the highest dose of the PAH mixture (10 μg per embryo).

Effects of polyhalogenated aromatic hydrocarbons (PHAHs) on biochemical parameters in chicks of the common tern ( Sterna hirundo)

Common tern ( Sterna hirundo) eggs were collected from eight breeding colonies that differed in degree of polyhalogenated aromatic hydrocarbon (PHAH) pollution. The eggs were artificially incubated and the chicks sacrificed within 12 hours after hatching. Plasma thyroid hormones (total thyroxine (TT4), free thyroxine (FT4) and triiodothyronine (TT3)), hepatic T4-glucuronyltransferase (T4-UGT) activity, plasma retinol and yolksac retinoid levels were measured and compared with yolksac PHAH residues and hepatic ethoxyresorufin- and pentoxyresorufin- O-deethylase (EROD and PROD) activities. The yolksac PHAH residues measured were polychlorinated biphenyl (PCB), polychlorinated dibenzofuran (PCDF) and polychlorinated dibenzo- p-dioxin (PCDD). No significant differences were observed between colony average levels of plasma thyroid hormones (TT4, FT4 and TT3) nor plasma retinol levels and T4-UGT activities that could be related to colony average PHAH levels. However, average colony yolksac retinyl ester levels did show significant differences. When correlated for individual terns, significant correlations between all these parameters and PHAH levels or EROD or PROD activities were found. The correlation between hepatic T4-UGT and EROD and PROD activities was very strong, suggesting a concomitant induction of these drug metabolizing enzymes. The PHAH levels were expressed as dioxin equivalents (TEQs) based on toxic equivalence factors (TEFs) as proposed by Safe (1990, 1994). In addition to plasma retinol, another retinoid was found which resembles 3,4-didehydro-retinol (vitamin A2) in chromatographic and spectroscopic behaviour. This putative plasma vitamin A2 was significantly positive correlated with the yolksac TEQs and with the hepatic EROD activity. Esters of both retinol and putative vitamin A2 were detected in the yolksac. The average yolksac vitamin A2 levels of the cleanest Zeewolde colony were significantly higher than the average levels in the other colonies.

Exposure of fish to biologically treated bleached‐kraft effluent. 2. Induction of hepatic cytochrome P4501A in mountain whitefish (Prosopium williamsoni) and other species

AbstractInduction of the hepatic detoxification enzyme cytochrome P4501A has been observed in fish exposed to bleached‐kraft mill effluents (BKME). P4501A content was examined in three species of wild fish exposed to BKME in a western Canadian river as part of an extensive program that included chemical monitoring, fish population studies, and other fish biochemical and physiological measurements. The Rocky Mountain whitefish Prosopium williamsoni exhibited marked induction of P4501A compared to reference whitefish, as measured by both catalytic activity and immunoreactive protein content. Similar P4501A induction was observed 4 d after reference fish were treated with 20 mg/kg β‐naphthoflavone. Whitefish P4501A levels have declined from a peak in spring 1991, following mill process modifications and concurrent with reductions in body burdens of hydrophobic compounds. Whitefish collected near the mill, moved upstream of effluent discharges, and held for 8 d showed no significant loss of hepatic P4501A‐related (ethoxyresorufin O‐deethylase, EROD) enzyme activity or P4501A protein levels. For spring 1991, correlations were found between EROD activity and measures of chronic exposure to BKME (e.g., muscle 2,3,7,8‐tetrachlorodibenzo‐p‐dioxin content), but not between EROD and measures of acute exposure (e.g., bile content of resin acids or chlorophenolic metabolites). These and other lines of evidence indicate that the P4501A‐inducing agent(s) at this site may be neither waterborne nor rapidly eliminated. A second species, longnose sucker (Catostomus catostomus), collected near the mill exhibited modest (two‐ to threefold) P4501A induction. For both species, no significant correlations between P4501A induction and trends in other biological responses were found, as described in a companion paper. Burbot (Lota lota) had hepatic EROD activities generally in the range of reference values, despite substantial exposure to mill‐related compounds. In contrast to studies at historically degraded pulp mill sites, P4501A induction is the only major biological response observed to date at this site. As P4501A induction is not related to adverse effects, it could be best classified as an indicator of exposure to BKME.

Effect of 2,3,7,8-tetrachlorodibenzoy- p-dioxin on the hepatic 7-ethoxyresorufin O-deethylase activity in four rodent species

Temporal and dose-related effects of 2,3,7,8-tetrachlorodibenzo- p-dioxin (TCDD) on hepatic 7-ethoxyresorufin O-deethylase (EROD) activity were investigated in young male Hartley guinea pigs, Sprague-Dawley rats, C57B1/6 mice, DBA/2 mice and Golden Syrian hamsters. Animals were terminated 1, 7, 14, 28, 56 and 112 days after the administration of a single i.p. dose of TCDD. The maximal induction of EROD activity, at doses producing a similar toxic and limited lethal effect in all species/strains, was 42-, 18-, 7- and 3-fold in rats, DBA/2 mice, C57B1/6 mice and guinea pigs, respectively. No treatment-related induction of EROD activity was observed in hamsters. Generally, maximal induction occurred 1–4 weeks after injection in all species. The guinea pig alone maintained the same magnitude of induction of EROD activity throughout the study. Observed toxic effects, i.e., lethality, loss of body weight gain, liver enlargement and thymic atrophy, did not correlate with the TCDD-induced hepatic EROD activity. The obtained results suggest that the fold induction of cytochrome P450 1A1 activity is not a critical event for the expression of the lethal effect of TCDD inrodents.

Appendix J: Polychlorinated dibenzo p-dioxins and polychlorinated dibenzofurans

The site of the 2000 Olympic Games (Sydney Olympic Park (SOP), Sydney, Australia) was contaminated by persistent organic pollutants (POPs) prior to remediation in the 1990s. This study investigates the bioactivity of POPs in the sediment and water of wetlands across SOP by in vitro 2,3,7,8-TCDD equivalence (TCDDeq) measurement (H4IIE cell line bioassay). Further, it examines whether disturbance of these sediments is likely to mobilise ligands for this receptor into the water column. Exposure to aryl hydrocarbon receptor (AhR) ligands was measured in vivo using hepatic cytochrome P4501A (CYP1A) induction (EROD) in the mosquitofish (Gambusia holbrooki). Aqueous TCDDeq ranged from 0.013 to 0.057 pM in SOP wetlands which was significantly (p < 0.05) less that in urban reference sites. These concentrations were not correlated to physical or chemical characteristics of the wetlands. In the sediments, TCDDeq ranged from 0.0016 to 7.06 µg/kg and these were not significantly (p ≥ 0.05) different to that measured in urban reference sites. Simulated disturbance of small quantities of sediment in water samples significantly (p < 0.05) increased the levels of TCDDeq measured in the water. Sediment TCDDeq was correlated to sediment ΣPAH concentration in 2006 and sediment ΣPCB, ΣDDT concentrations and fine sediment grain size in 2005. While fish at one SOP wetland had hepatic EROD activity elevated above the estimated basal level for this species, these were at the lower end of the range measured in urban impacted, non-remediated wetlands. EROD activity was positively correlated with both the sediment ΣPCB load and aqueous TCDDeq. Increased catchment size was correlated with increased EROD activity suggesting an even spread of POPs throughout the residential areas of the Sydney metropolitan area. The concentration of bioactive POPs in the wetlands of SOP is therefore low relative to urban reference sites demonstrating the ongoing success of the remediation program.

Survey of receiving‐water environmental impacts associated with discharges from pulp mills: 2. Gonad size, liver size, hepatic erod activity and plasma sex steroid levels in white sucker

AbstractFish collected from the receiving areas of 12 Canadian pulp mills were examined, including sites receiving effluent from kraft mills using chlorine as well as sulfite mills. Field collections included sampling of receiving water for chemistry and toxicity testing, and sampling of local fish for organ weights, hepatic MFO (ethoxyresorufin‐O‐deethylase, EROD) activity, plasma steroid levels, and levels of liver dioxins. The main objectives of this study were to determine whether the discharge of effluent from pulp mills to sites other than Jackfish Bay was associated with physiological or biochemical disruptions in wild fish, whether there was any correlation between waste treatment and the presence of biological responses in wild fish, and whether there was any association between the use of chlorine as a bleaching agent and these responses. Although white sucker collected near bleached‐kraft mills exhibited the highest EROD induction and dioxin levels, elevated enzyme activity was observed in fish from sites that did not use chlorine, and depressions in plasma sex steroid levels was not correlated with the level of EROD activity. The absence of chlorine bleaching or the presence of secondary treatment did not eliminate responses in fish, including decreased circulating levels of sex steroids, decreased gonadal size, and increased liver size. This survey has shown that (a) induction of hepatic EROD enzymes and depressions of plasma sex steroid levels during gonadal growth are found downstream of several pulp mills; (b) these changes are seen at some mills without chlorine bleaching and at mills that have secondary treatment; (c) substantial dilutions of nontoxic effluent do not appear to remove these responses; (d) the dominant factor determining the presence or absence of responses appeared to be dilution level; and (e) lab toxicity tests on invertebrates, rainbow trout, and fathead minnows could not predict the presence of these responses in wild fish.

MFO activity in carp (Cyprinus carpio) exposed to treated pulp and paper mill effluent in lake coleman, Victoria, Australia, in relation to AOX, EOX, and muscle PCDD/PCDF

AbstractEuropean carp (Cyprinus carpio) exposed to highly treated pulp mill effluent in Lake Coleman, a shallow‐water lake in southern Victoria, Australia, had significantly elevated hepatic microsomal EROD levels relative to reference fish from a nearby unexposed water body (Dowds and Heart morasses). Mean hepatic microsomal EROD activity appeared to be correlated with site adsorbable organic halogen (AOX) levels, with a simple linear regression yielding the equation Y = 0.059X+ 1.415 (r2 = 0.93, n = 5), where Y is mean EROD activity in nanomoles per minute per milligram and X is mean AOX concentration in micrograms per liter. Mean liver EROD activity was poorly related with fish muscle‐tissue extractable organic halogen (EOX) and sediment EOX concentrations. Hepatic microsomal EROD activity also appeared to be correlated with the low levels of PCDD/PCDFs measured in carp muscle (1.0‐4.0 ppt TCDD international toxic equivalents (TEs) in effluent‐exposed fish muscle compared to 0.48‐0.64 ppt TEs in reference fish muscle). Simple linear regression of mean EROD activity in carp liver with the mean fish muscle dioxin content yielded the equation Y= 6.514X+ 5.754 (n = 4, r2 = 0.88), where Y is mean EROD activity in nanomoles per minute per milligram and X is mean dioxin concentration in ppt of TCDD TEs. Hepatic microsomal ECOD activity, however, was not significantly different at any exposure site from the reference sites. Overall, Lake Coleman contained between 4.5 and 9.3 times the water AOX levels, 0.8 and 13.7 times the sediment EOX levels, 1.5 and 2.2 times the carp muscle‐fat EOX levels, 5.0 and 5.3 times the carp whole‐muscle TCDD toxic equivalents, and 6.5 times the carp fat TCDD toxic equivalents, compared to the Dowds and Heart morass reference samples. Within Lake Coleman, mean liver microsomal EROD activity levels were 2.3 to 6.3 times higher than the Dowds and Heart reference sites, respectively. Tissue concentrations of PCDD/PCDF and water AOX levels reduced with increasing distance from the effluent point source. Carp liver microsomal EROD represented a good biomarker of exposure to low levels of organochlorine contaminants from well‐treated pulp mill effluent.

A visual test for hepatic EROD activity as a marker for exposure to aromatic and halogenated aromatic hydrocarbons

The kinetic, spectrophotometric method for determining 7-ethoxyresorufin O-deethylase activity in fish was further devleoped into a quick-test to be used in situations with poor laboratory facilities e.g. during field experiments. The method, developed for sample screening and monitoring, could precede and indicate whether further analysis is required. The assay can be conducted with microsomes, postmitochondrial supernatant or directly with whole homogenate, and without spectrophotometer.

Protein kinase C and CYP1A1 induction in rainbow trout (Oncorhynchus mykiss) hepatocyte culture.

1. The role of protein kinase C (PKC) in B-naphthoflavone (BNF) induction of CYP1A1 in rainbow trout hepatocytes was investigated. 2. Primary cultures of rainbow trout hepatocytes treated with BNF for 24 hr showed an increase in microsomal 7-ethyoxyresorufin-O-deethylase (EROD) activity compared to cells treated with vehicle (DMSO) only. 3. Increases in EROD activities were proportional to increased concentrations of BNF from 1 to 10 nM reaching a plateau at higher concentrations (20-100 nM) of BNF. 4. Western blot analysis using specific antibody (LM4b) against CYP1A1 showed that changes in microsomal CYP1A1 protein paralleled that of EROD activity. 5. The induction of EROD activity by BNF required both protein and RNA synthesis since the process was blocked by both cycloheximide and actinomycin D. 6. Pretreatment of hepatocytes with 12-O-tetradecanoyl-phorbol-13-acetate (TPA) led to a dose dependent suppression of BNF-induced EROD activity and CYP1A1 content. TPA alone had no effect on hepatic EROD activity and CYP1A1 protein level. 7. Pretreatment with sn-1,2 didecanoylglycerol, a PKC activator, had no effect on BNF-induced EROD activity in these cells. 8. Pretreatment of cells with staurosporine, a PKC inhibitor, effectively blocked BNF-induced EROD activity. 9. PKC may play a role in the induction of CYP1A1 gene expression in fish liver by BNF.

Occurrence and effects of PCBs, PCDDs and PCDFs in hatchlings of the common tern ( Sterna hirundo)

From eight common tern ( Sterna hirundo) colonies eggs were collected for laboratory incubation. Significant differences between colonies were found for yolk sac concentrations of polychlorinated biphenyls (PCBs), polychlorinated dibenzofurans (PCDFs) and polychlorinated dibenzo- p-dioxins (PCDDs). Corresponding differences were observed for hepatic EROD and PROD activities. No differences between the colonies were observed regarding embryonic O 2 CO 2 exchange, egg weight, eggshell thickness, hatchling weight or liver weight/body weight ratio. It is concluded that hepatic EROD activity is usable as a relative sensitive biochemical indicator for early exposure to planar halogenated polyaromatics in the early life stage of the common tern.

Induction of 7-ethoxyresorufin-O-deethylase (EROD) activity in mice foetuses by the PCB-congener 3,3',4,4'-tetrachlorobiphenyl.

1. 3,3',4,4'-Tetrachlorobiphenyl (TCB) induces liver microsomal 7-ethoxyresorufin-O-deethylase (EROD) activity, and this P450 isoform, i.e. CYP 1, is involved in the metabolism of TCB. 2. TCB administered i.p. to pregnant mice (5-25 mg/kg) induced foetal as well as maternal hepatic EROD activity; in all cases the maternal induced activity was higher than the foetal activity. EROD activity of TCB-induced foetuses increased with developmental age, but decreased with the length of time after treatment. 3. Strain differences were seen; in control mice and TCB-treated dams NMRI > C57BL in EROD activity, but in transplacentally TCB-treated foetuses, C57BL > NMRI. EROD activity in non-pregnant control C57BL mice was higher than in pregnant ones, whereas no activity was seen in control foetuses. 4. Results indicate that TCB at a certain dose can induce foetal metabolism, but that earlier observed foetal accumulation at lower TCB doses is probably a consequence of transplacental transport of maternally-produced metabolites.