Fish bioaccumulation and biomarkers in environmental risk assessment: a review

Environmentally induced oxidative stress in aquatic animals

Contaminant-stimulated reactive oxygen species production and oxidative damage in aquatic organisms

Molecular biomarkers of oxidative stress in aquatic organisms in relation to toxic environmental pollutants.

Oxidative stress-the production and accumulation of reduced oxygen intermediates such as superoxide radicals, singlet oxygen, hydrogen peroxide, and hydroxyl radicals-can damage lipids, proteins, and DNA. Many disease processes of clinical interest and the aging process involve oxidative stress in their underlying etiology. The production of reactive oxygen species is also prevalent in the world's oceans, and oxidative stress is an important component of the stress response in marine organisms exposed to a variety of insults as a result of changes in environmental conditions such as thermal stress, exposure to ultraviolet radiation, or exposure to pollution. As in the clinical setting, reactive oxygen species are also important signal transduction molecules and mediators of damage in cellular processes, such as apoptosis and cell necrosis, for marine organisms. This review brings together the voluminous literature on the biochemistry and physiology of oxidative stress from the clinical and plant physiology disciplines with the fast-increasing interest in oxidative stress in marine environments.

Oxidative stress in marine environments: biochemistry and physiological ecology.

Metals and organic contaminants, present in the water-column, sediment or food, are readily accumulated by aquatic organisms Exposure to and toxic effects of contaminants can be measured in terms of the biochemical responses of the organisms—so-called molecular biomarkers The applications, advantages and limitations of such diagnostic and prognostic tests are discussed The hepatic biotransformation enzyme cytochrome P4501A in fish and other vertebrates is specifically induced by organic contaminants such as aromatic hydrocarbons, PCBs and dioxins, and is used as a biomarker of exposure to organic pollution Its induction is involved in chemical carcinogenesis via catalysis of the covalent binding of organic contaminants to DNA (DNA-adducts) P4501A-induction, measured as enzyme activity, enzyme amount, or mRNA, has been successively used in many field studies, involving some 27 fish species, in USA and Europe Metallothioneins (MTs) bind and are specifically induced by metals such as Cd, Hg, Ag and Cu, and are used in both vertebrates and invertebrates as a biomarker for metal exposure Bulky, hydrophobic DNA-adducts are used as a biomarker for organic contaminant damage MTs (measured at protein and mRNA levels) and DNA-adducts (32P-postlabelling method) have been applied less extensively in the field than P4501A, but the results are similarly encouraging Biomarkers should be used as part of an integrated programme of pollution monitoring, involving also general measurements of biological damage and animal health, and analysis of chemical contaminants in the biota and environment Commercial availability of antibodies and mRNA probes will accelerate the widespread application of these molecular biomarkers

Biotechnology and pollution monitoring: Use of molecular biomarkers in the aquatic environment

Since their heterotrophic origin, animals have been faced with a continual input of foreign compounds, so-called xenobiotics, from their food sources, e.g. polybromomethanes and alkyl halides in seaweeds (Gschwend et al. 1985) and defensive toxins in other animals (Bakus and Kawaguchi 1984); and from the attacks of predators, e.g. venoms of certain gastropods and cephalopods (Fange 1984). For example, “animal-plant warfare” is considered to be a major selective pressure in driving the evolution of some of the gene families of the biotransformation enzyme, cytochrome P-450 (Nebert et al. 1989b). Over time, additional sources of xenobiotics have included erosion of hydrocarbon-containing shales, and oil seepage from natural reservoirs (started at least 100,000 years ago) (Farrington 1985), hostile environments such as the high sulphide levels around deep sea hydrothermal vents (Vetter et al. 1987), and, in more recent years, man’s multifarious industrial and other activities (Mix 1984). Central to the defense against such an enormous and diverse number of potentially toxic compounds is an impressive array of enzymes, which function ideally to detoxify and eliminate xenobiotics from an organism. The biological significance of biotransformation enzymes is increased by the inducibility of some of them by xenobiotics, and by their metabolism of certain xenobiotics to molecular species more toxic, mutagenic or carcinogenic than the parent compound. Elaboration of the qualitative and quantitative aspects of organic xenobiotic metabolism in marine invertebrates, and the function and regulation of the enzymes involved, is important for several reasons, viz. predicting and modelling the fate and toxicity of xenobiotics in marine organisms and ecosystems (e.g. Harris et al. 1984); development of specific indices of biological effect for use in pollution monitoring and impact assessment (e.g. Malins et al. 1985; Kleinow et al. 1987; Payne et al. 1987; Bayne et al. 1988); and understanding the evolutionary relationships of the biotransformation pathways in different phylogenetic groups, and the use of the pathways in invading, or exploiting, ecological time and space to create new niches.

Organic Xenobiotic Metabolism in Marine Invertebrates

Antioxidant enzymes function to remove deleterious reactive oxygen species, including the superoxide anion radical and H2O2. Subcellular distributions and optimal and other properties of catalase (EC. 1.11.1.6), superoxide dismutase (SOD; EC. 1.15.1.1), selenium-dependent glutathione peroxidase (Se-GPX; EC. 1.11.1.9) and total glutathione peroxidase (GPX) activities were determined in the digestive gland of the common musselMytilus edulis L. by spectrophotometric and cytochemical/electron microscopic (catalase) techniques. Assay conditions for Se-GPX and total GPX activities were determined which optimized the difference between the non-enzymic and enzymic rates of reaction. General peroxidase activity (guaiacol as substrate) (EC. 1.11.1.7) was not detectable in any subcellular fraction. Catalase was largely, if not totally, peroxisomal, whereas SOD and GPX activities were mainly cytosolic. Distinct mitochondrial (Mn-SOD) and cytosolic (CuZn-SOD) SOD forms were indicated. Catalase properties were consistent with a catalase, rather than a catalase-peroxidase. The pH-dependence and temperature-dependence of GPX activity were different with H2O2 or CHP as substrate, and these and other observations indicate the existence of a distinct Se-GPX. Under saturating or optimal (GPX) assay conditions, the apparent Michaelis constantsKm (mM) were: catalase, 48 to 68 (substrate, H2O2); Se-GPX, 0.11 (H2O2) and 2.0 (glutathione); and total GPX, 2.2 (eumene hydroperoxide) and 1.2 (glutathione). Calculated catalase activity was 2 to 4 orders of magnitude greater than Se-GPX activity over an [H2O2] of 1 to 1000 μM. The results are discussed in relation to theoretical calculations of in vivo oxyradical production and phylogenetic differences in antioxidant enzyme activities.

David R. Livingstone

Papers

Biotechnology and pollution monitoring: Use of molecular biomarkers in the aquatic environment

Organic Xenobiotic Metabolism in Marine Invertebrates

Antioxidant enzymes in the digestive gland of the common mussel Mytilus edulis

Physiological and biochemical responses of bivalve molluscs to exposure to air

Detection of DNA Strand Breaks in Isolated Mussel (Mytilus edulisL.) Digestive Gland Cells Using the “Comet” Assay