Elsevier

Aquatic Toxicology

Volume 78, Supplement, 1 June 2006, Pages S73-S78
Aquatic Toxicology

Effects of North Sea oil and alkylphenols on biomarker responses in juvenile Atlantic cod (Gadus morhua)

https://doi.org/10.1016/j.aquatox.2006.02.019Get rights and content

Abstract

A consequence of oil drilling at sea is the release of produced water contaminated with e.g. polycyclic aromatic hydrocarbons (PAH) and alkylphenols. In the present study, juvenile Atlantic cod were exposed to North Sea oil, nonylphenol and a combination of the North Sea oil and an alkylphenol mixture in a flow-through system. A suite of hepatic biomarkers were analysed. Exposure to North Sea oil resulted in strong induction of CYP1A protein levels and EROD activities. Exposure to nonylphenol, on the other hand, resulted in decreased CYP1A levels and EROD activities. Thus, nonylphenol appears to down-regulate CYP1A expression in Atlantic cod. Combined exposure to North Sea oil with an alkylphenol mixture resulted in lower EROD induction, compared to that in fish exposed to North Sea oil alone. This difference was not statistically significant, but still we believe that the alkylphenols have inhibited CYP1A activities in the fish which may have compromised CYP1A mediated metabolism of other xenobiotics, including PAH. CYP3A protein levels were lower, compared to controls, in fish exposed to nonylphenol and the combination of North Sea oil and alkylphenol mixture. In contrast, the oil alone had no effect on CYP3A protein content. North Sea oil exposure, alone or in combination with alkylphenols, caused oxidative stress observed as elevated levels of GSSG content and GR and CAT activities. Interestingly, exposure to nonylphenol resulted in a marked depletion of total glutathione levels. This apparent depletion may be a consequence of increased conjugation of glutathione to nonylphenol followed by excretion. An increase in conjugation enzyme GST activity was observed in the nonylphenol exposed group, although the difference was not significant. No sign of oxidative damage, measured as lipid peroxidation, was observed in any of the exposures experiments. This study suggests that North Sea oil may lead to oxidative stress and altered CYP1A and CYP3A expression. Alkylphenols, present in produced water, resulted in decreased CYP1A and CYP3A protein expression in Atlantic cod.

Introduction

A major part of the oil consumed globally derives from off shore oil fields. A consequence of oil drilling at sea is the formation of produced water, and this formation increases considerably with age of the oil field. The produced water contains large amounts of pollutants including polycyclic aromatic hydrocarbons (PAH) and alkylphenols (Brendehaug et al., 1992, Stephens et al., 2000). Several PAH have been found to have cytotoxic, immunotoxic, mutagenic and/or carcinogenic effects in aquatic organisms (Aas et al., 2000, Reichert et al., 1998, Vogelbein, 2003). PAH are primarily metabolized, and thereby detoxified, by enzymes in the cytochrome P450 system, mainly CYP1A (Goksøyr and Förlin, 1992). CYP1A levels are strongly up regulated by planar aromatic compounds, such as PAH and planar polychlorinated biphenyls and this is demonstrated by an increase in ethoxyresorufin-O-deethylase (EROD) activities (Förlin et al., 1994). It has been shown that CYP1A activity is inhibited by alkylphenols in several fish species (Arukwe et al., 1997, Hasselberg et al., 2004b, Navas and Segner, 2001). This inhibition may have consequences in clearance of xenobiotics. This may result in increased accumulation of harmful compounds including PAH (Levine et al., 1997).

In addition to detoxifying function, CYP1A mediated metabolism of PAH can also lead to the formation of reactive oxygen species (ROS) through the formation of redox labile metabolites. Benzo[a]pyrene, for example, can be metabolized by CYP1A to benzo[a]pyrene diones that have the ability to form ROS through the process of redox cycling (Lemaire et al., 1994). Exposure to several PAH can lead to a state of oxidative stress in aquatic organisms (Livingstone, 2001, Winston and Di Giulio, 1991). It has also been shown in Atlantic cod that exposure to alkylphenols results in elevated glutathione reductase activities and total glutathione levels, possibly as a result of oxidative stress (Hasselberg et al., 2004a).

Although acute toxicity for produced water from oil drilling is low, mainly due to the high dilution (Stephens et al., 2000) it is still of great interest to study sublethal effects in marine organisms since very little is known about the fate of alkylphenols in the marine environment (Roe, 1998). The aim of the present study was to investigate the effects of alkylphenols and North Sea oil, alone or in combination, on CYP1A and CYP3A protein expression in juvenile Atlantic cod (Gadus morhua). The composition of the alkylphenol mixture reflects the composition that can be observed in produced water. One group of fish were also exposed to nonylphenol. In addition, the effects on the phase II enzyme glutathione S-transferase (GST), the antioxidant enzymes glutathione reductase (GR) and catalase (CAT) and levels of total and oxidized glutathione (GSH and GSSG) were analysed. Oxidative damage was estimated as levels of lipid peroxidation measured as thiobarbituric acid reactive substances (TBARS).

Section snippets

Chemicals

GSH, GSSG, GR (3664), 5-sulfosalicylic acid, 5,5′-dithiobis(2-nitrobenzoic acid) (DTNB), β-nicotinamide adenine di-nucleotide phosphate (NADPH), 1-chloro-2,4-dinitrobenzene (CDNB), 2-thiobarbituric acid, butylated hydroxytoluene, phosphoric acid, 2-vinylpyridine, 7-ethoxyresorufin and bovine serum albumin were obtained from Sigma (St. Louis, USA). Ethylenedinitrilotetraacetic acid, rodamin B and hydrogen peroxide were purchased from Merck. Ready gels (12% continuous acrylamide in Tris–HCl) and

EROD activity

Exposure to nonylphenol led to a significant decrease in EROD activities in juvenile Atlantic cod (Fig. 1). North Sea oil exposure, on the other hand, resulted in a significant increase in EROD activities (Fig. 1). An increase in EROD activity was also observed in the fish exposed to a combination of the oil and alkylphenols, although the increase was not significant compared to control fish (Fig. 1).

CYP1A and CYP3A protein expression

Exposure to nonylphenol decreased both CYP1A- and CYP3A-protein expression in juvenile cod (

Discussion

The present study demonstrates that ecological relevant concentrations of North Sea oil and alkylphenols lead to biochemical changes in juvenile Atlantic cod. Exposure to this oil resulted in an increase in the levels of CYP1A and also CYP1A mediated EROD activities. This confirms previous studies that have reported increased EROD activities in Atlantic cod and turbot (Scophthalmus maximus) exposed to North Sea oil (Aas et al., 2000, Stephens et al., 2000). Exposure to nonylphenol, on the other

Acknowledgements

This study was supported by the European Union BEEP project (Biological Effects of Environmental Pollution in marine coastal ecosystems). The authors also wish to express their gratitude to Dr. Odd Ketil Andersen and the people at IRIS—International Research Institute of Stavanger AS and Akvamiljø a/s, for organizing the experiment and the exposure of the fish. Linda Hasselberg and Malin Celander were supported by grants from the Swedish EPA (Reprosafe).

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