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The glutaredoxin GLRX-21 functions to prevent selenium-induced oxidative stress in Caenorhabditis elegans.

Morgan KL, Estevez AO, Mueller CL, Cacho-Valadez B, Miranda-Vizuete A, Szewczyk NJ, Estevez M - Toxicol. Sci. (2010)

Bottom Line: The C elegans glrx-21 gene belongs to the family of glutaredoxins (glutathione-dependent oxidoreductases) and the glrx-21(tm2921) allele is a mutation that renders animals hypersensitive for the selenium-induced motility impairment, but not lethality.In addition, the lethality of animals with the tm2921 mutation exposed to selenium was unaffected by the addition of reduced glutathione, suggesting that GLRX-21 is required for glutathione to moderate this selenium-induced lethality.Our findings provide the first description of selenium-induced toxicity in C elegans and support its use as a model for elucidating the mechanisms of selenium toxicity.

View Article: PubMed Central - PubMed

Affiliation: Department of Neurology, Veterans Affairs Pittsburgh Healthcare System, Research and Development (151U), University Drive C, Pittsburgh, Pennsylvania 15240, USA.

ABSTRACT
Selenium is an essential micronutrient that functions as an antioxidant. Yet, at higher concentrations, selenium is pro-oxidant and toxic. In extreme cases, exposures to excess selenium can lead to death or selenosis, a syndrome characterized by teeth, hair and nail loss, and nervous system alterations. Recent interest in selenium as an anti- tumorigenic agent has reemphasized the need to understand the mechanisms underlying the cellular consequences of increased selenium exposure. We show here, that in the nematode, Caenorhabditis elegans, selenium has a concentration range in which it functions as an antioxidant, but beyond this range it exhibits a dose- and time-dependent lethality. Oxidation-induced fluorescence emitted by the dye, carboxy-H(2)DCFDA, indicative of reactive oxygen species formation was significantly higher in animals after a brief exposure to 5mM sodium selenite. Longer-term exposures lead to a progressive selenium-induced motility impairment that could be partially prevented by coincident exposure to the cellular antioxidant-reduced glutathione. The C elegans glrx-21 gene belongs to the family of glutaredoxins (glutathione-dependent oxidoreductases) and the glrx-21(tm2921) allele is a mutation that renders animals hypersensitive for the selenium-induced motility impairment, but not lethality. In addition, the lethality of animals with the tm2921 mutation exposed to selenium was unaffected by the addition of reduced glutathione, suggesting that GLRX-21 is required for glutathione to moderate this selenium-induced lethality. Our findings provide the first description of selenium-induced toxicity in C elegans and support its use as a model for elucidating the mechanisms of selenium toxicity.

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Chronic exposure to selenium results in a progression of behavioral phenotypes leading to lethality. (A) Populations of adult animals placed continuously on NGM agar plates supplemented with 5mM Na2SeO3 were scored at 24-h intervals to determine the percentages of animals with each behavioral phenotype (normal, backing [impaired], paralyzed) and for lethality (dead). The percentages of all phenotypes for each time point (0, 24, 48, 72, and 96 h) equal 100%. Each dataset represents six plates with 20 animals per plate and is presented as the mean percentage of animals with each phenotype ± SD. * p < 0.05, compared with normal at the same time point. **p < 0.001, compared with normal at the same time point. # p < 0.05, compared with 24-h within phenotype. ## p < 0.001, compared with 24-h within phenotype. (B) Individual animals were grown singularly on 5mM Na2SeO3 plates for a total of 48 h. The behavioral phenotype of each individual animal was assessed every 6 h. A total of 20 individual animals were observed. N = normal (light gray), B = backing (white), P = paralyzed (dark gray), D = dead (black).
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fig6: Chronic exposure to selenium results in a progression of behavioral phenotypes leading to lethality. (A) Populations of adult animals placed continuously on NGM agar plates supplemented with 5mM Na2SeO3 were scored at 24-h intervals to determine the percentages of animals with each behavioral phenotype (normal, backing [impaired], paralyzed) and for lethality (dead). The percentages of all phenotypes for each time point (0, 24, 48, 72, and 96 h) equal 100%. Each dataset represents six plates with 20 animals per plate and is presented as the mean percentage of animals with each phenotype ± SD. * p < 0.05, compared with normal at the same time point. **p < 0.001, compared with normal at the same time point. # p < 0.05, compared with 24-h within phenotype. ## p < 0.001, compared with 24-h within phenotype. (B) Individual animals were grown singularly on 5mM Na2SeO3 plates for a total of 48 h. The behavioral phenotype of each individual animal was assessed every 6 h. A total of 20 individual animals were observed. N = normal (light gray), B = backing (white), P = paralyzed (dark gray), D = dead (black).

Mentions: For the initial studies, plates containing 10 ml of agar that had previously been seeded with bacteria had 0.5 ml of either a Na2SeO3 (Fig. 4A) or SeMet (Supplementary fig. 2A) stock solution added such that the final concentrations in the agar were as listed (0.5, 1, 5, 10, 20mM). Control plates (0mM) to which 0.5 ml of carrier solution (dH20) was added were included in all behavioral assays. A final concentration of 5mM Na2SeO3 per agar plate was used in all additional studies beyond the initial assays (Figs. 5B and 5C, 6 and 7); this concentration and source of selenium was chosen because it produced a standard dose-response curve in which the animals showed a time-dependent decrease in the percentage of “motile” animals within each given population studied over the course of the 96-h exposure period (Figure 5A).


The glutaredoxin GLRX-21 functions to prevent selenium-induced oxidative stress in Caenorhabditis elegans.

Morgan KL, Estevez AO, Mueller CL, Cacho-Valadez B, Miranda-Vizuete A, Szewczyk NJ, Estevez M - Toxicol. Sci. (2010)

Chronic exposure to selenium results in a progression of behavioral phenotypes leading to lethality. (A) Populations of adult animals placed continuously on NGM agar plates supplemented with 5mM Na2SeO3 were scored at 24-h intervals to determine the percentages of animals with each behavioral phenotype (normal, backing [impaired], paralyzed) and for lethality (dead). The percentages of all phenotypes for each time point (0, 24, 48, 72, and 96 h) equal 100%. Each dataset represents six plates with 20 animals per plate and is presented as the mean percentage of animals with each phenotype ± SD. * p < 0.05, compared with normal at the same time point. **p < 0.001, compared with normal at the same time point. # p < 0.05, compared with 24-h within phenotype. ## p < 0.001, compared with 24-h within phenotype. (B) Individual animals were grown singularly on 5mM Na2SeO3 plates for a total of 48 h. The behavioral phenotype of each individual animal was assessed every 6 h. A total of 20 individual animals were observed. N = normal (light gray), B = backing (white), P = paralyzed (dark gray), D = dead (black).
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC2984526&req=5

fig6: Chronic exposure to selenium results in a progression of behavioral phenotypes leading to lethality. (A) Populations of adult animals placed continuously on NGM agar plates supplemented with 5mM Na2SeO3 were scored at 24-h intervals to determine the percentages of animals with each behavioral phenotype (normal, backing [impaired], paralyzed) and for lethality (dead). The percentages of all phenotypes for each time point (0, 24, 48, 72, and 96 h) equal 100%. Each dataset represents six plates with 20 animals per plate and is presented as the mean percentage of animals with each phenotype ± SD. * p < 0.05, compared with normal at the same time point. **p < 0.001, compared with normal at the same time point. # p < 0.05, compared with 24-h within phenotype. ## p < 0.001, compared with 24-h within phenotype. (B) Individual animals were grown singularly on 5mM Na2SeO3 plates for a total of 48 h. The behavioral phenotype of each individual animal was assessed every 6 h. A total of 20 individual animals were observed. N = normal (light gray), B = backing (white), P = paralyzed (dark gray), D = dead (black).
Mentions: For the initial studies, plates containing 10 ml of agar that had previously been seeded with bacteria had 0.5 ml of either a Na2SeO3 (Fig. 4A) or SeMet (Supplementary fig. 2A) stock solution added such that the final concentrations in the agar were as listed (0.5, 1, 5, 10, 20mM). Control plates (0mM) to which 0.5 ml of carrier solution (dH20) was added were included in all behavioral assays. A final concentration of 5mM Na2SeO3 per agar plate was used in all additional studies beyond the initial assays (Figs. 5B and 5C, 6 and 7); this concentration and source of selenium was chosen because it produced a standard dose-response curve in which the animals showed a time-dependent decrease in the percentage of “motile” animals within each given population studied over the course of the 96-h exposure period (Figure 5A).

Bottom Line: The C elegans glrx-21 gene belongs to the family of glutaredoxins (glutathione-dependent oxidoreductases) and the glrx-21(tm2921) allele is a mutation that renders animals hypersensitive for the selenium-induced motility impairment, but not lethality.In addition, the lethality of animals with the tm2921 mutation exposed to selenium was unaffected by the addition of reduced glutathione, suggesting that GLRX-21 is required for glutathione to moderate this selenium-induced lethality.Our findings provide the first description of selenium-induced toxicity in C elegans and support its use as a model for elucidating the mechanisms of selenium toxicity.

View Article: PubMed Central - PubMed

Affiliation: Department of Neurology, Veterans Affairs Pittsburgh Healthcare System, Research and Development (151U), University Drive C, Pittsburgh, Pennsylvania 15240, USA.

ABSTRACT
Selenium is an essential micronutrient that functions as an antioxidant. Yet, at higher concentrations, selenium is pro-oxidant and toxic. In extreme cases, exposures to excess selenium can lead to death or selenosis, a syndrome characterized by teeth, hair and nail loss, and nervous system alterations. Recent interest in selenium as an anti- tumorigenic agent has reemphasized the need to understand the mechanisms underlying the cellular consequences of increased selenium exposure. We show here, that in the nematode, Caenorhabditis elegans, selenium has a concentration range in which it functions as an antioxidant, but beyond this range it exhibits a dose- and time-dependent lethality. Oxidation-induced fluorescence emitted by the dye, carboxy-H(2)DCFDA, indicative of reactive oxygen species formation was significantly higher in animals after a brief exposure to 5mM sodium selenite. Longer-term exposures lead to a progressive selenium-induced motility impairment that could be partially prevented by coincident exposure to the cellular antioxidant-reduced glutathione. The C elegans glrx-21 gene belongs to the family of glutaredoxins (glutathione-dependent oxidoreductases) and the glrx-21(tm2921) allele is a mutation that renders animals hypersensitive for the selenium-induced motility impairment, but not lethality. In addition, the lethality of animals with the tm2921 mutation exposed to selenium was unaffected by the addition of reduced glutathione, suggesting that GLRX-21 is required for glutathione to moderate this selenium-induced lethality. Our findings provide the first description of selenium-induced toxicity in C elegans and support its use as a model for elucidating the mechanisms of selenium toxicity.

Show MeSH
Related in: MedlinePlus