Effects of methylmercury exposure on glutathione metabolism, oxidative stress, and chromosomal damage in captive-reared common loon (Gavia immer) chicks

U.S. Geological Survey, Upper Midwest Environmental Sciences Center, 2630 Fanta Reed Road, La Crosse, WI 54603, USA.
Environmental Pollution (Impact Factor: 4.14). 12/2008; 156(3):732-8. DOI: 10.1016/j.envpol.2008.06.009
Source: PubMed


We quantified the level of dietary mercury (Hg), delivered as methylmercury chloride (CH3HgCl), associated with negative effects on organ and plasma biochemistries related to glutathione (GSH) metabolism and oxidative stress, and chromosomal damage in captive-reared common loon (Gavia immer) chicks reared from hatch to 105 days. Mercury-associated effects related to oxidative stress and altered glutathione metabolism occurred at 1.2 microg Hg/g and 0.4 microg Hg/g, an ecologically relevant dietary mercury level, but not at 0.08 microg Hg/g. Among the variables that contributed most to dissimilarities in tissue chemistries between control and treatment groups were increased levels of oxidized glutathione (GSSG), GSH peroxidase, and the ratio of GSSG to GSH in brain tissue; increased levels of hepatic GSH; and decreased levels of hepatic glucose-6-phosphate dehydrogenase (G-6-PDH). Our results also suggest that chronic exposure to environmentally relevant dietary Hg levels did not result in statistically significant somatic chromosomal damage in common loon chicks.

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Available from: John Bickham, Oct 02, 2015
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    • "In birds, MeHg penetrates the blood–brain barrier and is transported to eggs (Heinz, 1996; Wolfe et al., 1998; Scheuhammer et al., 2007; Kenow et al., 2008; Frederick and Jayasena, 2011). Elevated MeHg causes a variety of adverse effects in birds, such as disturbances in blood chemistry, neurochemistry, hormones, chromosome and mitochondria structures, as well as documented aberrant behavior , reduction in reproductive success and survival. "
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    ABSTRACT: Although the relationship between mercury (Hg) and selenium (Se) has been studied in wild birds in areas with sufficient or excessive Se levels, little is known about this relationship in areas where the supply of Se is limited. As Hg detoxification is based on the production of biologically inactive Hg–Se complexes, the aim of this study was to investigate the relationships between the concentrations of total mercury (THg), methylmercury (MeHg), inorganic mercury (InHg=THg−MeHg), percent MeHg of THg, Se and molar ratios (THg:Se, MeHg:Se, InHg:Se) in the breast muscle (n=16) of the piscivorous common mergansers (Mergus merganser) from a Se-deficient and moderately Hg-polluted area in Poland. Mergansers were divided into two groups differing in condition (A—very good condition; C—moderate condition). Concentrations of THg, MeHg and Se were determined by atomic absorption spectrometry, modified gas chromatography atomic fluorescence spectroscopy, and spectrofluorometric methods, respectively. In all studied mergansers, mean concentrations of THg, MeHg, InHg, and Se in muscle were 2.63, 1.92, 0.46, and 0.54 µg g−1 dw, respectively. THg and MeHg concentrations in the muscle of group A mergansers were greater than in group C. The ratio of THg:Se was higher in group A than in group C (2.32 vs 1.36; p<0.01), as well as the molar ratio of MeHg:Se (A vs C: 1.98 vs 1.03; p<0.05). Comparisons between mergansers from Poland and Canada showed similar THg and percent MeHg in the muscle, but mergansers from Poland had several times lower Se levels and higher THg:Se ratios (>2.0) than the Canadian mergansers and other European and North American waterbirds. We found statistically significant positive correlations (MeHg–THg, percent MeHg/THg–MeHg, percent InHg/THg–InHg, THg:Se–THg, MeHg:Se–THg, THg:Se–MeHg, MeHg:Se–MeHg, InHg:Se–InHg, MeHg:Se–THg:Se) and some negative correlations (percent InHg/THg–MeHg, percent MeHg/THg–InHg, THg:Se–Se, MeHg:Se–Se). As THg and percent MeHg in the studied mergansers were similar to populations living in non-Se-deficient areas, it is likely that different mechanisms of muscle Hg detoxification have evolved in mergansers populations living in Se-deficient areas.
    Ecotoxicology and Environmental Safety 03/2014; 101(1):107–115. DOI:10.1016/j.ecoenv.2013.12.019 · 2.76 Impact Factor
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    • "included in these studies (Ji et al., 2006; Kenow et al., 2008; Bonisoli- Alquati et al., 2009). Little information is available about neither the antioxidant system of adults nor chicks of some of the most abundant seabird species on the northern hemisphere. "
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    ABSTRACT: The efficiency of antioxidant defenses and relationship with body burden of metal and organic contaminants has not been previously investigated in arctic seabirds, neither in chicks nor in adults. The objective of this study was to compare such defenses in chicks from three species, Black-legged kittiwake (Rissa tridactyla), Northern fulmar (Fulmarus glacialis), and Herring gull (Larus argentatus), and the relationship with tissue concentrations of essential metals such as selenium and iron and halogenated organic compounds, represented by polychlorinated biphenyl (PCB). The results showed significant species-specific differences in the antioxidant responses which also corresponded with metal and PCB levels in different ways. The capability to neutralize hydroxyl radicals (TOSC-HO•) and the activities of catalase and Se-dependent glutathione peroxidases (GPX) clearly increased in species with the higher levels of metals and PCBs, while the opposite trend was observed for Se-independent GPX, TOSC against peroxyl radicals (ROO•) and peroxynitrite (ONOOH). Less clear relationships were obtained for glutathione levels, GSH/GSSG ratio, glutathione reductase and superoxide dismutase. The results showed differences in antioxidant efficiency between the species, and some of these defenses exhibited dose-response-like relationships with measured levels of selenium, iron and ΣPCBs. PCBs, selenium and iron levels were positively related to the responses of antioxidants with potential to reduce HO•/H₂O₂ (Se-dependent GPX, CAT and TOSC against HO•). However, direct causal relationships between antioxidant responses and contaminant concentrations could not be shown on individual level. Varying levels of metals and contaminants due to different diet and age were probably the main explanations for the species differences in antioxidant defense.
    Comparative Biochemistry and Physiology Part C Toxicology & Pharmacology 03/2011; 154(1):28-35. DOI:10.1016/j.cbpc.2011.02.008 · 2.30 Impact Factor
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    • "Isaksson et al. 2005; Berglund et al. 2007) or intoxication experiments (e.g. Kenow et al. 2008; Ansari et al. 2009), which enable us to interpret the variation in the markers of OS in association with pathological processes. Another promising research perspective is the study of the effects of OS on ornamental traits. "
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    ABSTRACT: 1. Reactive oxygen and nitrogen species can damage biomolecules if these lack sufficient antioxidant protection. Maintaining and up-regulating antioxidant defenses and repair of the damaged molecules require resources that could potentially be allocated to other functions, including life-history and signal traits. 2. Identifying the physiological mechanisms causing and counteracting oxidative damage may help to understand evolution of oxidative balance systems from molecular to macroevolutionary levels. This review addresses methodological and statistical problems of measuring and interpreting biomarkers of oxidative stress or damage. 3. A major methodological problem is distinguishing between controlled and uncontrolled processes that can lead either to shifts in dynamic balance of redox potential or cause pathological damage. An ultimate solution to this problem requires establishing links between biomarkers of antioxidant defenses and oxidative damage and components of fitness. 4. Biomarkers of redox balance must correspond to strict technical criteria, most importantly to validated measurement technology. Validation criteria include intrinsic qualities such as specificity, sensitivity, assessment of measurement precision, and knowledge of confounding and modifying factors. 5. The complexity of oxidative balance systems requires that assay choice be informed by statistical analyses incorporating context at biochemical, ecological and evolutionary levels. We review proper application of statistical methods, such as principal components analysis and structural equation modelling, that should help to account for these contexts and isolate the variation of interest across multiple biomarkers simultaneously.
    Functional Ecology 10/2010; 24(5):960-970. DOI:10.2307/40863627 · 4.83 Impact Factor
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