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

Liver ethoxyresorufin-O-deethylase and brain acetylcholinesterase in two freshwater fish species of South America; the effects of seasonal variability on study design for biomonitoring

Responses at low levels of biological organization to evaluate environmental changes and water quality have been used for many years. South America is no different, and recently biochemical endpoints in fish have been used to assess the impacts of industrial and sewage effluents on wild fish populations. For Chilean native freshwater fish, basic biological data is scarce and data on 7-ethoxyresorufin-O-deethylase (EROD) and Acetylcholinesterase (AChE) activity is practically absent. Moreover, extensive variation in these two biochemical endpoints exists among species and seasons. In this article we evaluate seasonal variation in liver EROD and brain AChE activities in Trichomycterus areolatus and Percilia gillissi, two widely distributed native freshwater fish species in central Chile. We observed a marked seasonality in hepatic EROD activity in both species, with maximums for P. gillissi during winter months and sex differences in February, July, August and December. T. areolatus showed no sex differences, and peaks in EROD activity in the middle of summer, winter and late spring. Species differences in EROD activity were observed with activity being 1-2 orders of magnitude higher in P. gillissi compared to T. areolatus. Scarce seasonal variation and no sex related differences in brain AChE for both species were observed. Multivariate analysis (PCA) indicated that physical water quality parameters had some degree of responsibility for the seasonal responses found. The seasonal variability data of these biochemical endpoints were used to optimize study design for future monitoring programs, planning timing of sampling, increasing statistical power by collecting specific sample sizes required.

Molecular mechanisms of cold-induced CYP1A activation in rat liver microsomes

Cytochrome P4501A (the CYP1A1 and CYP1A2 enzymes) is known to metabolize anthropogenic xenobiotics to carcinogenic and mutagenic compounds. CYP1A1 transcriptional activation is regulated via the aryl hydrocarbon receptor (AhR)-dependent signal transduction pathway. CYP1A2 activation may occur through the AhR-dependent or AhR-independent signal transduction pathways. We used male Wistar rats to explore possible mechanisms of CYP1A activation induced by exposure to cold and the effects of the protein-tyrosine kinase inhibitors genistein, herbimycin A, and geldanamycin on the properties of hepatic CYP1A1 and CYP1A2 proteins following exposure to cold and to classic CYP1A inducers. The molecular mechanisms of cold-induced CYP1A1 and CYP1A2 activation are different. The CYP1A2 activation apparently occurs at the post-transcriptional level. The CYP1A1 activation, whether caused by exposure to cold or by classic CYP1A inducers, is AhR-dependent and occurs at the transcriptional level. Protein tyrosine kinase inhibitors have no effect on benzo(a)pyrene-induced CYP1A expression but alter cold-induced CYP1A1 activity and the CYP1A1 mRNA level. Thus, treatment with herbimycin A or geldanamycin leads to an increase in CYP1A1 activity, while treatment with genistein increases CYP1A1 mRNA expression and decreases CYP1A2 activity. These data elucidate the molecular mechanisms of cold-induced CYP1A activation and the role of protein kinases in the regulation of CYP1A during exposure to cold. Our results can also help identify the differences between the molecular mechanisms underlying the effects of the classic CYP1A inducers and the effects of cooling.

Toxic effects of waterborne polychlorinated biphenyls and sex differences in an endangered goodeid fish (Girardinichthys viviparus)

Polychlorinated biphenyls (PCBs) elicit toxic effects in different species. PCBs undergo biotransformation by enzymes associated with the mixed functional oxidase system, such as cytochrome P450 (cyt P450), this biotransformation being sex-dependent. No other metabolic pathways are known, however, in connection with this process. Thus, the present study aims to evaluate the effects of waterborne PCBs at sublethal nominal concentrations (0.92 mg PCBs/L) on the black-fin goodeid Girardinichthys viviparus, an endangered fish native to the Valley of Mexico, as well as any sex differences related to PCB biotransformation. Eight-month-old adult fish born in the laboratory were exposed for 1, 2, 4, 8 and 16 days to half the LC(0) (calculated concentration at which no deaths occurred after 96 h) determined by an acute toxicity test. Specimens were sacrificed following exposure and the liver was used to evaluate different biomarkers: cyt P450 concentration and alcohol dehydrogenase (ADH) and ethoxyresorufin O-deethylase (EROD) activities. Results show sexual differentiation with regard to all biomarkers in both the control group and PCB-treated fish, with higher values found in males. The induction rate of cyt P450 remained constant throughout the study in males. In females, induction peaked on day 4, coinciding with maximum EROD activity, and fell significantly thereafter. EROD was lower in PCB-treated males than in the control group, but was greater in magnitude. ADH was significantly induced in both sexes from day 2 to day 16 of exposure. The highest response as compared to the control group occurred on day 8 in females. A correlation was found between ADH activity and exposure to PCBs. Three possible action mechanisms, operating either individually or concurrently, are proposed.

Use of two biomarkers (CYP450 and acetylcholinesterase) in zebra mussel for the biomonitoring of Lake Maggiore (northern Italy)

The use of zebra mussel Dreissena polymorpha as a bioaccumulator for lipophilic compounds is nowadays standardized, but its employment in early warning systems by the biomarker approach is much less frequent. One of the main problems with the biomarker approach is due to natural variation of abiotic factors such as temperature that influence the activity of several enzymes. In this study, we investigated the influence of this environmental parameter on the activities of two different biomarkers: acetylcholinesterase (AChE) (inhibited by organophosphorus compounds) and CYP450 (inversely influenced by planar compounds and heavy metals). We used these two biomarkers to evaluate the environmental pollution of Lake Maggiore (northern Italy). Results showed a strong AChE inhibition in mussel specimens collected in some sampling sites of the lake, indicating heavy pollution by neurotoxic compounds. We also found a twofold effect on CYP450 activity, probably due to the activating effect of planar compounds and the inhibiting effect of trace metals.

Fish bioaccumulation and biomarkers in environmental risk assessment: a review

In this review, a wide array of bioaccumulation markers and biomarkers, used to demonstrate exposure to and effects of environmental contaminants, has been discussed in relation to their feasibility in environmental risk assessment (ERA). Fish bioaccumulation markers may be applied in order to elucidate the aquatic behavior of environmental contaminants, as bioconcentrators to identify certain substances with low water levels and to assess exposure of aquatic organisms. Since it is virtually impossible to predict the fate of xenobiotic substances with simple partitioning models, the complexity of bioaccumulation should be considered, including toxicokinetics, metabolism, biota-sediment accumulation factors (BSAFs), organ-specific bioaccumulation and bound residues. Since it remains hard to accurately predict bioaccumulation in fish, even with highly sophisticated models, analyses of tissue levels are required. The most promising fish bioaccumulation markers are body burdens of persistent organic pollutants, like PCBs and DDTs. Since PCDD and PCDF levels in fish tissues are very low as compared with the sediment levels, their value as bioaccumulation markers remains questionable. Easily biodegradable compounds, such as PAHs and chlorinated phenols, do not tend to accumulate in fish tissues in quantities that reflect the exposure. Semipermeable membrane devices (SPMDs) have been successfully used to mimic bioaccumulation of hydrophobic organic substances in aquatic organisms. In order to assess exposure to or effects of environmental pollutants on aquatic ecosystems, the following suite of fish biomarkers may be examined: biotransformation enzymes (phase I and II), oxidative stress parameters, biotransformation products, stress proteins, metallothioneins (MTs), MXR proteins, hematological parameters, immunological parameters, reproductive and endocrine parameters, genotoxic parameters, neuromuscular parameters, physiological, histological and morphological parameters. All fish biomarkers are evaluated for their potential use in ERA programs, based upon six criteria that have been proposed in the present paper. This evaluation demonstrates that phase I enzymes (e.g. hepatic EROD and CYP1A), biotransformation products (e.g. biliary PAH metabolites), reproductive parameters (e.g. plasma VTG) and genotoxic parameters (e.g. hepatic DNA adducts) are currently the most valuable fish biomarkers for ERA. The use of biomonitoring methods in the control strategies for chemical pollution has several advantages over chemical monitoring. Many of the biological measurements form the only way of integrating effects on a large number of individual and interactive processes in aquatic organisms. Moreover, biological and biochemical effects may link the bioavailability of the compounds of interest with their concentration at target organs and intrinsic toxicity. The limitations of biomonitoring, such as confounding factors that are not related to pollution, should be carefully considered when interpreting biomarker data. Based upon this overview there is little doubt that measurements of bioaccumulation and biomarker responses in fish from contaminated sites offer great promises for providing information that can contribute to environmental monitoring programs designed for various aspects of ERA.