methionine mitochondrial oxidative stress

1: Exp Eye Res. 2006 Nov;83(5):1281-6. Epub 2006 Aug 24. Related Articles, Links
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Silencing of the methionine sulfoxide reductase A gene results in loss of mitochondrial membrane potential and increased ROS production in human lens cells.

Marchetti MA, Lee W, Cowell TL, Wells TM, Weissbach H, Kantorow M.

Department of Biomedical Science, Florida Atlantic University, 777 Glades Road, PO Box 3091, Boca Raton, FL 33431-0991, USA.

Accumulation of methionine sulfoxide (Met(O)) is a significant feature of human cataract and previous studies have shown that methionine sulfoxide reductase A (MsrA), which acts to repair Met(O), can defend human lens cells against oxidative stress induced cell death. A key feature of oxidative stress is increased reactive oxygen species (ROS) in association with loss of mitochondrial function. Here, we sought to establish a potential role for MsrA in the accumulation of ROS in lens cells and the corresponding mitochondrial membrane potential in these cells. Targeted gene silencing was used to establish populations of lens cells expressing different levels of MsrA, and the mitochondrial membrane potential and ROS levels of these cell populations were monitored. Decreased MsrA levels were found to be associated with loss of cell viability, decreased mitochondrial membrane potential, and increased ROS levels in the absence of oxidative stress. These effects were augmented upon oxidative stress treatment. These results provide evidence that MsrA is a major determinant for accumulation of ROS in lens cells and that increased ROS levels in lens cells are associated with a corresponding decrease in mitochondrial membrane potential that is likely related to the requirement for MsrA in lens cell viability.

PMID: 16934804 [PubMed – in process]

2: Pharmacol Rep. 2006 May-Jun;58(3):381-92. Related Articles, Links
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Ebselen attenuates oxidative stress in ischemic astrocytes depleted of glutathione. Comparison with glutathione precursors.

Gabryel B, Malecki A.

Department of Pharmacology, Silesian Medical University, Medykow 18, PL 40-752 Karowice, Poland.

In this study, we investigated the protective effect of ebselen, a seleno-organic compound with antioxidant activity, towards astrocyte degeneration caused by exposure to simulated in vitro ischemic conditions and simultaneous depletion of glutathione (GSH).Depletion of GSH was induced by 24 h pretreatment with L-buthionine-(S,R)-sulfoximine (BSO). In this experimental paradigm, we examined the effects of ebselen (1-40 muM) on apoptosis, mitochondrial function, reactive oxygen species (ROS) production, intracellular GSH level and mitochondrial transmembrane potential (MTP). In addition, we also compared the antioxidant potential of ebselen with cystine and methionine as precursors of GSH synthesis as well as with GSH ethyl ester. Our study demonstrated that toxicity of simulated ischemia conditions was enhanced when intracellular GSH was depleted. Treatment with ebselen, especially at concentrations of 20 and 40 muM prevented ischemia-induced cytotoxicity. Our study has shown that antiapoptotic effect of ebselen is associated with its strong antioxidant properties, preservation of MTP and possibly conservation of mitochondrial GSH during cytoplasmatic GSH depletion caused by oxidative damage. Also, promoting GSH synthesis by the delivery of its substrates, like cystine or inhibition of the efflux by methionine may be a powerful strategy to minimize cell damage in the nervous tissue after ischemia.

PMID: 16845212 [PubMed – in process]

3: FASEB J. 2006 Jun;20(8):1064-73. Related Articles, Links
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Methionine restriction decreases mitochondrial oxygen radical generation and leak as well as oxidative damage to mitochondrial DNA and proteins.

Sanz A, Caro P, Ayala V, Portero-Otin M, Pamplona R, Barja G.

Department of Animal Physiology-II, Complutense University, Madrid, Spain.

Previous studies have consistently shown that caloric restriction (CR) decreases mitochondrial reactive oxygen species (ROS) (mitROS) generation and oxidative damage to mtDNA and mitochondrial proteins, and increases maximum longevity, although the mechanisms responsible for this are unknown. We recently found that protein restriction (PR) also produces these changes independent of energy restriction. Various facts link methionine to aging, and methionine restriction (MetR) without energy restriction increases, like CR, maximum longevity. We have thus hypothesized that MetR is responsible for the decrease in mitROS generation and oxidative stress in PR and CR. In this investigation we subjected male rats to exactly the same dietary protocol of MetR that is known to increase their longevity. We have found, for the first time, that MetR profoundly decreases mitROS production, decreases oxidative damage to mtDNA, lowers membrane unsaturation, and decreases all five markers of protein oxidation measured in rat heart and liver mitochondria. The concentration of complexes I and IV also decreases in MetR. The decrease in mitROS generation occurs in complexes I and III in liver and in complex I in heart mitochondria, and is due to an increase in efficiency of the respiratory chain in avoiding electron leak to oxygen. These changes are strikingly similar to those observed in CR and PR, suggesting that the decrease in methionine ingestion is responsible for the decrease in mitochondrial ROS production and oxidative stress, and possibly part of the decrease in aging rate, occurring during caloric restriction.

PMID: 16770005 [PubMed – indexed for MEDLINE]

4: Exp Gerontol. 2006 Jul;41(7):663-7. Epub 2006 May 4. Related Articles, Links
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Alterations in mitochondrial and cytosolic methionine sulfoxide reductase activity during cardiac ischemia and reperfusion.

Picot CR, Perichon M, Lundberg KC, Friguet B, Szweda LI, Petropoulos I.

Laboratoire de Biologie et Biochimie Cellulaire du Vieillissement, EA 3106/IFR 117, Universite Paris 7-Denis Diderot, 2 place Jussieu, Tour 33-23, 1er etage, CC 7128, 75251 Paris Cedex 05, France.

During cardiac ischemia/reperfusion, proteins are targets of reactive oxygen species produced by the mitochondrial respiratory chain resulting in the accumulation of oxidatively modified protein. Sulfur-containing amino acids are among the most sensitive to oxidation. Certain cysteine and methionine oxidation products can be reversed back to their reduced form within proteins by specific repair enzymes. Oxidation of methionine in protein produces methionine-S-sulfoxide and methionine-R-sulfoxide that can be catalytically reduced by two stereospecific enzymes, methionine sulfoxide reductases A and B, respectively. Due to the importance of the methionine sulfoxide reductase system in the maintenance of protein structure and function during conditions of oxidative stress, the fate of this system during ischemia/reperfusion was investigated. Mitochondrial and cytosolic methionine sulfoxide reductase activities are decreased during ischemia and at early times of reperfusion, respectively. Partial recovery of enzyme activity was observed upon extended periods of reperfusion. Evidence indicates that loss in activity is not due to a decrease in the level of MsrA but may involve structural modification of the enzyme.

PMID: 16677789 [PubMed – in process]

5: J Biol Chem. 2006 Jun 16;281(24):16551-62. Epub 2006 Apr 10. Related Articles, Links
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One single in-frame AUG codon is responsible for a diversity of subcellular localizations of glutaredoxin 2 in Saccharomyces cerevisiae.

Porras P, Padilla CA, Krayl M, Voos W, Barcena JA.

Department of Biochemistry and Molecular Biology, University of Cordoba, 14071 Cordoba, Spain.

Glutaredoxins belong to a family of small proteins with glutathione-dependent disulfide oxidoreductase activity involved in cellular defense against oxidative stress. The product of the yeast GRX2 gene is a protein that is localized both in the cytosol and mitochondria. To throw light onto the mechanism responsible for the dual subcellular distribution of Grx2 we analyzed mutant constructs containing different targeting information. By altering amino acid residues around the two in-frame translation initiation start sites of the GRX2 gene, we could demonstrate that the cytosolic isoform of Grx2 was synthesized from the second AUG, lacking an N-terminal extension. Translation from the first AUG resulted in a long isoform carrying a mitochondrial targeting presequence. The mitochondrial targeting properties of the presequence and the influence of the mature part of Grx2 were analyzed by the characterization of the import kinetics of specific fusion proteins. Import of the mitochondrial isoform is relatively inefficient and results in the accumulation of a substantial amount of unprocessed form in the mitochondrial outer membrane. Substitution of Met(35), the second translation start site, to Val resulted in an exclusive targeting to the mitochondrial matrix. Our results show that a plethora of Grx2 subcellular localizations could spread its antioxidant functions all over the cell, but one single Ala to Gly mutation converts Grx2 into a typical protein of the mitochondrial matrix.

PMID: 16606613 [PubMed – indexed for MEDLINE]

6: Biochim Biophys Acta. 2006 May-Jun;1757(5-6):496-508. Epub 2006 Feb 24. Related Articles, Links
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Mitochondrial oxidative stress, aging and caloric restriction: the protein and methionine connection.

Pamplona R, Barja G.

Department of Basic Medical Sciences, University of Lleida, Lleida 25008, Spain.

Caloric restriction (CR) decreases aging rate and mitochondrial ROS (MitROS) production and oxidative stress in rat postmitotic tissues. Low levels of these parameters are also typical traits of long-lived mammals and birds. However, it is not known what dietary components are responsible for these changes during CR. It was recently observed that 40% protein restriction without strong CR also decreases MitROS generation and oxidative stress. This is interesting because protein restriction also increases maximum longevity (although to a lower extent than CR) and is a much more practicable intervention for humans than CR. Moreover, it was recently found that 80% methionine restriction substituting it for l-glutamate in the diet also decreases MitROS generation in rat liver. Thus, methionine restriction seems to be responsible for the decrease in ROS production observed in caloric restriction. This is interesting because it is known that exactly that procedure of methionine restriction also increases maximum longevity. Moreover, recent data show that methionine levels in tissue proteins negatively correlate with maximum longevity in mammals and birds. All these suggest that lowering of methionine levels is involved in the control of mitochondrial oxidative stress and vertebrate longevity by at least two different mechanisms: decreasing the sensitivity of proteins to oxidative damage, and lowering of the rate of ROS generation at mitochondria.

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PMID: 16574059 [PubMed – indexed for MEDLINE]

7: BMC Mol Biol. 2006 Mar 16;7:11. Related Articles, Links
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Alternative first exon splicing regulates subcellular distribution of methionine sulfoxide reductases.

Kim HY, Gladyshev VN.

Department of Biochemistry, University of Nebraska, Lincoln, Nebraska 68588, USA.

BACKGROUND: Methionine sulfoxide reduction is an important protein repair pathway that protects against oxidative stress, controls protein function and has a role in regulation of aging. There are two enzymes that reduce stereospecifically oxidized methionine residues: MsrA (methionine-S-sulfoxide reductase) and MsrB (methionine-R-sulfoxide reductase). In many organisms, these enzymes are targeted to various cellular compartments. In mammals, a single MsrA gene is known, however, its product is present in cytosol, nucleus, and mitochondria. In contrast, three mammalian MsrB genes have been identified whose products are located in different cellular compartments. RESULTS: In the present study, we identified and characterized alternatively spliced forms of mammalian MsrA. In addition to the previously known variant containing an N-terminal mitochondrial signal peptide and distributed between mitochondria and cytosol, a second mouse and human form was detected in silico. This form, MsrA(S), was generated using an alternative first exon. MsrA(S) was enzymatically active and was present in cytosol and nucleus in transfected cells, but occurred below detection limits in tested mouse tissues. The third alternative form lacked the active site and could not be functional. In addition, we found that mitochondrial and cytosolic forms of both MsrA and MsrB in Drosophila could be generated by alternative first exon splicing. CONCLUSION: Our data suggest conservation of alternative splicing to regulate subcellular distribution of methionine sulfoxide reductases.

PMID: 16542431 [PubMed – indexed for MEDLINE]

2: J Cell Biochem. 2005 Nov 1;96(4):665-71. Related Articles, Links
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Mitochondrial mechanism of oxidative stress and systemic hypertension in hyperhomocysteinemia.

Tyagi N, Moshal KS, Ovechkin AV, Rodriguez W, Steed M, Henderson B, Roberts AM, Joshua IG, Tyagi SC.

Department of Physiology and Biophysics, University of Louisville School of Medicine, Louisville, Kentucky 40202, USA.

Formation of homocysteine (Hcy) is the constitutive process of gene methylation. Hcy is primarily synthesized by de-methylation of methionine, in which s-adenosyl-methionine (SAM) is converted to s-adenosyl-homocysteine (SAH) by methyltransferase (MT). SAH is then hydrolyzed to Hcy and adenosine by SAH-hydrolase (SAHH). The accumulation of Hcy leads to increased cellular oxidative stress in which mitochondrial thioredoxin, and peroxiredoxin are decreased and NADH oxidase activity is increased. In this process, Ca2+-dependent mitochondrial nitric oxide synthase (mtNOS) and calpain are induced which lead to cytoskeletal de-arrangement and cellular remodeling. This process generates peroxinitrite and nitrotyrosine in contractile proteins which causes vascular dysfunction. Chronic exposure to Hcy instigates endothelial and vascular dysfunction and increases vascular resistance causing systemic hypertension. To compensate, the heart increases its load which creates adverse cardiac remodeling in which the elastin/collagen ratio is reduced, causing cardiac stiffness and diastolic heart failure in hyperhomocysteinemia. Copyright 2005 Wiley-Liss, Inc.

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PMID: 16149054 [PubMed – indexed for MEDLINE]
7: Semin Liver Dis. 1998;18(4):389-401. Related Articles, Links
Mitochondrial glutathione: importance and transport.

Fernandez-Checa JC, Kaplowitz N, Garcia-Ruiz C, Colell A.

Department of Medicine, Hospital Clinic i Provincial and Instituto Investigaciones Biomedicas August Pi i Sunyer, Consejo Superior Investigaciones Cientificas, Barcelona, Spain.

Accumulating evidence pointing to mitochondria as critical participants in the control of apoptotic and necrotic cell death and in the development of specific disease states has led to a renaissance on the study of these organelles. Because mitochondria are the major consumers of molecular oxygen within cells, they stand as one of the most important generators of reactive oxygen species and therefore constitute potential targets of therapeutic intervention in pathologic states in which oxidative stress originates from these organelles. In this regard, mitochondria are specific targets of ethanol intoxication, thereby leading to reported morphologic and functional alterations of mitochondria. Because mitochondria are also indispensable for the maintenance of cell functions, their dysfunction induced by ethanol may be a key event in the development of alcoholic liver disease. Indeed, chronic ethanol feeding in experimental animals has been reported to cause a selective deficiency in the availability of reduced glutathione (GSH) in mitochondria due to the impaired functioning of the specific mitochondrial carrier that translocates GSH from cytosol into the mitochondrial matrix. Such a selective depletion sensitizes hepatocytes from chronic ethanol-fed animals to the oxidative effects of cytokines, e.g., tumor necrosis factor (TNF). Restoration of mitochondrial GSH by the in vivo administration of S-adenosyl-L-methionine or the in vitro use of GSH ethyl ester prevents the susceptibility of hepatocytes to TNF. Although the nature of this specific carrier has not yet been uncovered, the elucidation of the mechanisms whereby ethanol leads to its impaired activity may provide important clues as to its function and mechanism of action, which in turn may be useful toward the definitive characterization and identification of this important carrier.

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PMID: 9875556 [PubMed – indexed for MEDLINE]


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