Inhibition of ethoxyresorufin-O-deethylase (EROD) activity in mixtures of 2,3,7,8-tetrachlorodibenzo-p-dioxin and polychlorinated biphenyls : EROD acitivity as biomarker in TCDD and PCB risk assessment

Integrative multi-biomarker approach on caged rainbow trout: A biomonitoring tool for wastewater treatment plant effluents toxicity assessment

The complex mixtures of contaminants released in wastewater treatment plant (WWTP) effluents are a major source of pollution for aquatic ecosystems. The present work aimed to assess the environmental risk posed by WWTP effluents by applying a multi-biomarker approach on caged rainbow trout (Oncorhynchus mykiss) juveniles. Fish were caged upstream and downstream of a WWTP for 21 days. To evaluate fish health, biomarkers representing immune, reproductive, nervous, detoxification, and antioxidant functions were assayed. Biomarker responses were then synthesized using an Integrated Biomarker Response (IBR) index. The IBR highlighted similar response patterns for the upstream and downstream sites. Caged juvenile females showed increased activities of innate immune parameters (lysozyme and complement), histological lesions and reduced glycogen content in the hepatic tissue, and higher muscle cholinergic metabolism. However, the intensity of the observed effects was more severe downstream of the WWTP. The present results suggest that the constitutive pollution level of the Meuse River measured upstream from the studied WWTP can have deleterious effects on fish health condition, which are exacerbated by the exposure to WWTP effluents. Our results infer that the application of IBR index is a promising tool to apply with active biomonitoring approaches as it provides comprehensive information about the biological effects caused by point source pollution such as WWTP, but also by the constitutive pollutions levels encountered in the receiving environment.

Evaluation of the Effects of the Enriched-Organic Diets Composition on European Sea Bass Welfare through a Multi-Parametric Approach

Three groups of European sea bass (Dicentrarchus labrax) were fed for seven months, with either a conventional diet or two different organic diets, which contain organic vegetables and a natural antioxidant compound. The two organic diets differed themselves in terms of raw proteins, fish oil, and lipid contents. Sea bass welfare condition was assessed in relation to these three diets, using 16 different indicators. These were: swimming activity (recovery test, muscle activity), haematological and serological stress indicators (haematocrit, haemoglobin, red-blood-cell count, cortisol, glucose, lactate), aspecific immunity parameter (lysozyme), indicators of exposure to organic contaminants (7-ethoxyresorufin-O-deethylase and glutathione-S-transferase), and growth parameters (weight gain, specific growth rate, feed conversion ratio, protein efficiency ratio, and hepato-somatic index). Most of these parameters individually did not give consistent responses, but their integration can provide an accurate evaluation of the fish welfare conditions among the three diet experimental groups. The multiparametric approach outlined a comprehensive picture of sea bass physiological state. The principal component analysis and the multi-criteria-decision-analysis were found to be useful tools for an integrated fish welfare assessment, highlighting that the best welfare condition was achieved in the experimental group fed with the protein-rich organic diet.

Comparative study of dioxin contamination from forest soil samples (BZE II) by mass spectrometry and EROD bioassay

Dioxins and dioxin-like compounds can be analyzed by bioanalytical screening methods to evaluate their biotoxicity. In vitro bioassays, based on 7-ethoxyresorufin-O-deethylase (EROD) and the activity of cytochrome P450 1A1 and the aryl hydrogen receptor (AhR) pathway, are employed for the evaluation of bioanalytical equivalents (BEQ) of polychlorinated dibenzo-p-dioxins (PCDDs), polychlorinated dibenzofurans (PCDFs), and polychlorinated biphenyls (PCBs) from a wide variety of sample matrices. Here, we present the evaluation of 11 humic soil samples derived from forest stands across Germany and a comparison of the BEQ values against toxic equivalents (TEQ, PCDD/Fs+PCBs) derived by chemical analysis. BEQ values ranged from 8.8 to 34.1 while TEQ values from 13.9 to 60.5 pg/g dry weight. Additional two subsequent mineral layers were analyzed to identify the BEQ/TEQ gradient vertically, showing a TEQ decrease of 85.1 and 93.8 % from the humic to the first and second mineral layers, respectively. For BEQ values, a decrease as well as an increase was detected. BEQ measurements were performed with and without sample clean-up. Omitting clean-up revealed about 20 times increased BEQ values presumably due to non-persistent bioactive compounds not detected by chemical analysis. The results we present suggest that the EROD assay can be used for the screening of large sample quantities for the identification of samples showing dioxin and dioxin-like contaminations even at low levels, which can then be further analyzed by chemical analysis to identify the congener composition. The study also shows that EROD results give a qualitative image of the contamination. EROD seems to be interfered with cross-contaminants specifically for soils with high biological activity as forest layers.

Assessment of cytotoxicity, genotoxicity and 7-ethoxyresorufin-O-deethylase (EROD) induction in sediment extracts from New Zealand urban estuaries

Sediments represent a major sink for contaminants resulting from industrial and agricultural activities - especially lipophilic substances. This study exclusively used in vitro methodologies to characterize specific toxicity effects of contaminants in sediment extracts from two urban New Zealand estuaries. Sediment extracts were prepared and tested for a range of biological endpoints. The micronucleus and comet assays in V79 cells were used to assess genotoxicity. Induction of 7-ethoxyresorufin-O-deethylase in piscine RTL-W1 cells was determined to estimate dioxin-like toxicity. Cytotoxic potentials were analyzed by neutral red uptake and MTT reduction. There was evidence of strong dioxin-like toxicity and moderate cytotoxicity. Genotoxicity was distinct in the micronucleus assay, but low in the comet assay. The results indicate the presence of chemicals in the sediments with the potential to pose a risk through multiple mechanisms of toxicity, the identities and amounts of which will be disclosed in a parallel study alongside with in vivo toxicity data.

Improving the in vitro ethoxyresorufin-O-deethylase (EROD) assay with RTL-W1 by metabolic normalization and use of β-naphthoflavone as the reference substance

The ethoxyresorufin-O-deethylase (EROD) assay is a widely applied method for the evaluation of the dioxin-like activity of single substances and environmental samples. As for most enzyme assays, the specific activity is normally related to total protein contents, the determination of which has clear limitations in high-throughput assays. EROD induction potentials are usually expressed as 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) equivalents, a substance highly toxic to humans. In order to compensate for these shortcomings, two modifications of the EROD protocol are proposed: (1) EROD activity is normalized to the metabolic activity of the cells as determined by a modified thiazolyl blue tetrazolium (MTT) assay and expressed as metabolic cell equivalents (MCE) based on MTT data rather than to protein contents. Via MCE data, cytotoxicity information can always be reported in parallel to EROD data; with the protocol presented here, MTT and EROD data are collected simultaneously. (2) Among several reference substances tested (2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD), β-naphthoflavone and benzo[a]pyrene), β-naphthoflavone proved to be the most suitable reference for the routine in vitro EROD assay, although TCDD has generally been preferred for purely scientific reasons.

Hepatic monooxygenase (CYP1A and CYP3A) and UDPGT enzymatic activities as biomarkers for long-term carbofuran exposure in tench (Tinca tinca L)

The effect of a long-term exposure of tenchs to different concentrations (10 and 100 micro g/L) of the pesticide carbofuran has been evaluated. Microsomal hepatic cytochrome P450 subfamily 1A (CYP1A) and 3A (CYP3A) activities, as well as the phase II enzyme uridine diphospho-glucuronosyltransferase (UDPGT) activity were evaluated as adequate biomarkers of fish exposure to environmentally relevant concentrations of the pesticide carbofuran in freshwater ecosystems. A clear time-dependent inhibition of both CYP1A and UDPGT activities was observed in fish exposed to the highest dose of carbofuran with respect to controls, whereas in the case of CYP3A activity, values of exposed animals did not show a clear pattern of alteration during the experiment. The results of the present study demonstrated that hepatic CYP1A and UDPGT activities from tench could be considered as sensitive biomarkers for carbamate pesticides in polluted water, thus allowing future and ecologically relevant biomonitoring studies with this species.

Structure dependent induction of CYP1A by polychlorinated biphenyls in hepatocytes of male castrated pigs

Hepatocytes cultures prepared from castrated pig hepatocytes (Great Yorkshire x Dutch Landrace), as a model for human liver, were used to study the effect of twenty polychlorinated biphenyls (PCBs) on CYP1A activity, measured as the dealkylation of either ethoxyresorufin or methoxyresorufin. The selection of the PCBs was based on their differences in physico-chemical properties. The non-ortho and mono-ortho substituted PCBs were the most potent CYP1A inducers in pig hepatocytes. In addition, several multiple-ortho substituted congeners, with five or more chlorine atoms, were inducers of CYP1A activity as well. Their relative effect potencies (REP) were proximately 10,000 times lower than the most potent congener, 3,3',4,4',5 PeCB (PCB#126). Using partial least-squares (PLS) modeling, predictions of CYP1A activity could be made for all tetra to hepta substituted congeners. Several multiple-ortho substituted PCBs, which are highly abundant in the biotic and abiotic environment, have been found to induce CYP1A activity in pig hepatocytes. Because induction of CYP1A activity is used as biomarker for Ah-receptor mediated responses, it is suggested to include these congeners in future risk assessment.

Structure-dependent induction of CYP1A by polychlorinated biphenyls in hepatocytes of cynomolgus monkeys (Macaca fascicularis)

Until now structure-activity relationships (SARs) for in vitro or in vivo CYP1A induction by polychlorinated biphenyls (PCBs) have only been determined in rodents and birds. This study describes the first development of such a SAR in a primate species by using hepatocyte cultures of cynomolgus monkey (Macaca fascicularis). Hepatocyte cultures of primate species might be a more suitable model for humans than those of rodents. For 20 PCBs, the in vitro induction of CYP1A activity was determined by measuring dealkylation of either methoxyresorufin or ethoxyresorufin. Selection of PCBs was based on multivariate physical-chemical characterization of all tetra- through heptachlorinated congeners. The non-ortho-substituted congeners were found to be the most potent inducers, followed by the mono-ortho-substituted PCBs. Multiple-ortho-substituted congeners, with more than five chlorine atoms, were inducers of CYP1A activity in monkey hepatocytes as well, with EC50 values approximately 10,000 times higher than 3,3',4,4',5 PeCB (PCB 126), the most potent congener. Using partial least-squares (PLS) modeling, predictions of CYP1A activity were established for all other tetra- to hepta-substituted congeners. Several congeners, which are abundant in the (a)biotic environment, were predicted to have CYP1A activity in cynomolgus monkey hepatocytes. Because induction of CYP1A activity is generally used as an early and sensitive biomarker for the Ah-receptor-mediated potential of a chemical, further studies are recommended to determine the possible risks of these multiple-ortho PCBs to humans.