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Biomarkers of Oxidative Status: Missing Tools in Conservation Physiology

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Biomarkers of Oxidative Status: Missing Tools in Conservation Physiology

Michaël Beaulieu et al. Conserv Physiol.

Abstract

Recent ecological studies have shown that oxidative status could have a significant impact on fitness components in wild animals. Not only can oxidative status reflect the environmental conditions that animals experience, but it can also predict their chances of reproduction and survival in the future in their natural habitat. Such important characteristics make markers of oxidative status informative tools to evaluate a priori individual perspectives of reproduction and survival as well as to assess a posteriori the effect of human activities on the fitness of species of conservation concern and wildlife in general. Markers of oxidative status may therefore help conservation practitioners to identify conservation threats to animal populations and to maximize the success of wildlife management. Despite these potential benefits for animal conservation programmes, up to now markers of oxidative status have only been reported anecdotally in conservation studies. The aim of this review is therefore to raise awareness by conservation practitioners of the use of markers of oxidative status. Towards this end, we first describe how environmental disruptions due to human activities can translate into variation in oxidative status. Second, we show how individual and population variation in oxidative status may contribute to the success or the failure of reintroduction or translocation programmes. Finally, we emphasize the technical features specific to the measurement of markers of oxidative status in conservation programmes, which may help investigators with the interpretation of their results. Such prior knowledge about markers of oxidative status may encourage conservation physiologists to use them in order to enhance the success of conservation programmes and wildlife management.

Keywords: Biomarker; conservation; ecophysiology; environmental disruption; oxidative stress; stress.

Figures

Figure 1:
Figure 1:
Number of studies including immunity parameters (orange), glucocorticoids (blue) or markers of oxidative stress (green) in view of conservation issues. The research was done in January 2014 by using Web of Knowledge and entering the following keywords: (i) “animal conservation” AND “animal population*” AND “immunity* OR immune*”; (ii) “animal conservation” AND “animal population*” AND “glucocorticoid* OR cortisol* OR corticosterone”; and (iii) “animal conservation” AND “animal population*” AND “oxidative stress* OR antioxidants*”. The upper panel represents the number of publications in each year, while the lower panel represents the relative contribution of each type of study.
Figure 2:
Figure 2:
Theoretical scenarios regarding alteration of the oxidative balance [antioxidant defences (AO) and oxidative damage] of animals subjected to an environmental disruption. Mobilization is considered with a broad meaning, i.e. the mobilization of exogenous antioxidants and/or the up-regulation of endogenous antioxidants. Note that oxidative damage may also decrease following environmental disruptions, presumably because of a reduction in metabolism associated with low body reserves or because of increased mitochondrial uncoupling. Given that this scenario has been reported rarely following environmental disruption (e.g. Beaulieu et al., 2013) and in order to keep the figure as clear as possible, it is not represented here.
Figure 3:
Figure 3:
Schematic diagram showing the environmental disruptions due to human activities that are likely to affect the oxidative balance of animals. An arrow between two factors indicates a causal relationship.
Figure 4:
Figure 4:
Schematic and simplified representation of molecular interactions among some of the most common biomarkers of oxidative damage and antioxidant defences. Oxidation of fatty acids gives rise to early derivatives of oxidative damage called hydroperoxides; these are precursors of end-products of lipid peroxidation, such as malondialdehyde (MDA), 4-hydroxy-2-nonenal (HNE) and isoprostanes. In turn, MDA and HNE can form adducts with proteins, generating protein carbonyls. Protein carbonyls can also be generated by direct oxidation of proteins caused by reactive species (RS). Note that other peroxidation pathways can also lead to formation of MDA, HNE and isoprostanes. Hydroperoxides are reduced to alcohols by the enzyme glutathione peroxidase, which uses glutathione as a cofactor to do so. Glutathione is consequently oxidized, but the enzyme glutathione reductase reduces glutathione back to the reduced form. The action of reactive oxygen species (ROS) and of other RS is neutralized by several antioxidants, such as superoxide dismutase, catalase, glutathione, vitamins C and E, carotenoids and polyphenols. The action of non-enzymatic antioxidants (vitamins C and E, carotenoids and polyphenols) can be quantified using in vitro assays of antioxidant capacity. Finally, assays are also available to quantify the activity of enzymes used by the organism to repair damage to DNA, RNA or telomeres. Dashed lines indicate the fatty acid peroxidation chain. 8-OHG, 8-hydroxyguanosine; 8-OHdG, 8-hydroxy-2′-deoxyguanosine. Key: green, substrates that can be oxidized; grey, radical and non-radical reactive species; pink, antioxidant molecules (including damage repair enzymes); and red, oxidative damage compounds.

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