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Lester Packer - One of the best experts on this subject based on the ideXlab platform.
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ascorbate dependent recycling of the vitamin e homologue trolox by Dihydrolipoate and glutathione in murine skin homogenates
Free Radical Biology and Medicine, 2000Co-Authors: Lester PackerAbstract:Abstract In the redox antioxidant network, Dihydrolipoate can synergistically enhance the ascorbate-dependent recycling of vitamin E. Since the major endogenous thiol antioxidant in biological systems is glutathione (GSH) it was of interest to compare the effects of Dihydrolipoate with GSH on ascorbate-dependent recycling of the water-soluble homologue of vitamin E, Trolox, by electron spin resonance (ESR). Trolox phenoxyl radicals were generated by a horseradish peroxidase (HRP)–hydrogen peroxide (H 2 O 2 ) oxidation system. In the presence of Dihydrolipoate, Trolox radicals were suppressed until both Dihydrolipoate and endogenous levels of ascorbate in skin homogenates were consumed. Similar experiments made in the presence of GSH revealed that Trolox radicals reappeared immediately after ascorbate was depleted and that GSH was not able to drive the ascorbate-dependent Trolox recycling reaction. However, at higher concentrations GSH was able to increase ascorbate-mediated Trolox regeneration from the Trolox radical. ESR and spectrophotometric measurements demonstrated the ability of Dihydrolipoate or GSH to react with dehydroascorbate, the two-electron oxidation product of ascorbate in this system. Dihydrolipoate regenerated greater amounts of ascorbate at a much faster rate than equivalent concentrations of GSH. Thus the marked difference between the rate and efficiency of ascorbate generation by Dihydrolipoate as compared with GSH appears to account for the different kinetics by which these thiol antioxidants influence ascorbate-dependent Trolox recycling.
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neuroprotection by the metabolic antioxidant α lipoic acid
Free Radical Biology and Medicine, 1997Co-Authors: Lester Packer, Hans Tritschler, Klaus WesselAbstract:Reactive oxygen species are thought to be involved in a number of types of acute and chronic pathologic conditions in the brain and neural tissue. The metabolic antioxidant alpha-lipoate (thioctic acid, 1, 2-dithiolane-3-pentanoic acid; 1, 2-dithiolane-3 valeric acid; and 6, 8-dithiooctanoic acid) is a low molecular weight substance that is absorbed from the diet and crosses the blood-brain barrier. alpha-Lipoate is taken up and reduced in cells and tissues to Dihydrolipoate, which is also exported to the extracellular medium; hence, protection is afforded to both intracellular and extracellular environments. Both alpha-lipoate and especially Dihydrolipoate have been shown to be potent antioxidants, to regenerate through redox cycling other antioxidants like vitamin C and vitamin E, and to raise intracellular glutathione levels. Thus, it would seem an ideal substance in the treatment of oxidative brain and neural disorders involving free radical processes. Examination of current research reveals protective effects of these compounds in cerebral ischemia-reperfusion, excitotoxic amino acid brain injury, mitochondrial dysfunction, diabetes and diabetic neuropathy, inborn errors of metabolism, and other causes of acute or chronic damage to brain or neural tissue. Very few neuropharmacological intervention strategies are currently available for the treatment of stroke and numerous other brain disorders involving free radical injury. We propose that the various metabolic antioxidant properties of alpha-lipoate relate to its possible therapeutic roles in a variety of brain and neuronal tissue pathologies: thiols are central to antioxidant defense in brain and other tissues. The most important thiol antioxidant, glutathione, cannot be directly administered, whereas alpha-lipoic acid can. In vitro, animal, and preliminary human studies indicate that alpha-lipoate may be effective in numerous neurodegenerative disorders.
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antioxidant and redox regulation of gene transcription
The FASEB Journal, 1996Co-Authors: Chandan K Sen, Lester PackerAbstract:Reactive oxygen species (ROS) are implicated in the pathogenesis of a wide variety of human diseases. Recent evidence suggests that at moderately high concentrations, certain forms of ROS such as H202 may act as signal transduction messengers. To develop a better understanding of the exact mechanisms that underlie ROS-dependent disorders in biological systems, recent studies have investigated the regulation of gene expression by oxidants, antioxidants, and other determinants of the intracellular reduction-oxidation (redox) state. At least two well-defined transcription factors, nuclear factor (NF) kappa B and activator protein (AP) -1 have been identified to be regulated by the intracellular redox state. The regulation of gene expression by oxidants, antioxidants, and the redox state has emerged as a novel subdiscipline in molecular biology that has promising therapeutic implications. Binding sites of the redox-regulated transcription factors NF-kappa B and AP-1 are located in the promoter region of a large variety of genes that are directly involved in the pathogenesis of diseases, e.g., AIDS, cancer, atherosclerosis and diabetic complications. Biochemical and clinical studies have indicated that antioxidant therapy may be useful in the treatment of disease. Critical steps in the signal transduction cascade are sensitive to oxidants and antioxidants. Many basic events of cell regulation such as protein phosphorylation and binding of transcription factors to consensus sites on DNA are driven by physiological oxidant-antioxidant homeostasis, especially by the thiol-disulfide balance. Endogenous glutathione and thioredoxin systems, and the exogenous lipoate-Dihydrolipoate couple may therefore be considered to be effective regulators of redox-sensitive gene expression. The efficacy of different antioxidants to favorably influence the molecular mechanisms implicated in human disease should be a critical determinant of its selection for clinical studies.
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modelling cortical cataractogenesis 17 in vitro effect of a lipoic acid on glucose induced lens membrane damage a model of diabetic cataractogenesis
Iubmb Life, 1995Co-Authors: Fusun Kilic, Lester Packer, Garry J Handelman, Elena Serbinova, Jason R. TrevithickAbstract:: The effect of R, S, and racemic forms of a-lipoic acid was tested on the formation of opacity in normal rat lenses incubated with 55.6 mM glucose, as a model for in vivo diabetic cataractogenesis. Control lenses, incubated 8 days with 5.56 mM glucose, did not develop opacities. Formation of lens opacities in vitro was correlated with lactate dehydrogenase (LDH) leakage into the incubation medium. Opacity formation and LDH leakage, resulting from incubation in medium containing 55.6 mM glucose to model diabetes, were both suppressed by the addition of 1 mM R-lipoic acid. Addition of 1 mM racemic lipoic acid reduces these damaging effects to the lens by one-half, while S-lipoic acid potentiated LDH leakage, consistent with the hypothesis that R-lipoic acid is the active form. Although HPLC analysis demonstrated that both stereoisomers of lipoic acid were reduced to Dihydrolipoate at comparable rates by the intact lens, the mitochondrial lipoamide dehydrogenase system is highly specific for reduction of exogenous R-lipoic to dihydrolipoic acid. Therefore, stereospecific protection against this opacity is consistent with specific reduction of R-lipoic acid in mitochondria of the vulnerable cells at the lens equator where the first globular degeneration is seen in glucose cataract.
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alpha lipoic acid as a biological antioxidant
Free Radical Biology and Medicine, 1995Co-Authors: Lester Packer, Eric Witt, Hans J. TritschlerAbstract:alpha-Lipoic acid, which plays an essential role in mitochondrial dehydrogenase reactions, has recently gained considerable attention as an antioxidant. Lipoate, or its reduced form, Dihydrolipoate, reacts with reactive oxygen species such as superoxide radicals, hydroxyl radicals, hypochlorous acid, peroxyl radicals, and singlet oxygen. It also protects membranes by interacting with vitamin C and glutathione, which may in turn recycle vitamin E. In addition to its antioxidant activities, Dihydrolipoate may exert prooxidant actions through reduction of iron. alpha-Lipoic acid administration has been shown to be beneficial in a number of oxidative stress models such as ischemia-reperfusion injury, diabetes (both alpha-lipoic acid and dihydrolipoic acid exhibit hydrophobic binding to proteins such as albumin, which can prevent glycation reactions), cataract formation, HIV activation, neurodegeneration, and radiation injury. Furthermore, lipoate can function as a redox regulator of proteins such as myoglobin, prolactin, thioredoxin and NF-kappa B transcription factor. We review the properties of lipoate in terms of (1) reactions with reactive oxygen species; (2) interactions with other antioxidants; (3) beneficial effects in oxidative stress models or clinical conditions.
Victoria I. Bunik - One of the best experts on this subject based on the ideXlab platform.
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increased catalytic performance of the 2 oxoacid dehydrogenase complexes in the presence of thioredoxin a thiol disulfide oxidoreductase
Journal of Molecular Catalysis B-enzymatic, 2000Co-Authors: Victoria I. BunikAbstract:Abstract Bacterial and mammalian pyruvate and 2-oxoglutarate dehydrogenase complexes undergo an irreversible inactivation upon accumulation of the Dihydrolipoate intermediate. The first component of the complexes, 2-oxoacid dehydrogenase, is affected. Addition of thioredoxin protects from this inactivation, increasing catalytic rates and limiting degrees of the substrate transformation to products, acyl-CoA and NADH. Although the redox active cysteines of thioredoxin are essential for its interplay with the complexes, the effects are observed with both dithiol and disulfide forms of the protein. This indicates that thioredoxin affects an SH/S–S component of the system, which is present in the two redox states. The complex-bound lipoate is concluded to be the thioredoxin target, since (i) both dithiol and disulfide forms of the residue are available during the catalytic cycle and (ii) the thioredoxin reaction with the essential SH/S–S group of the terminal component of the complex, dihydrolipoyl dehydrogenase, is excluded. Thus, the thioredoxin disulfide interacts with the Dihydrolipoate intermediate, while the thioredoxin dithiol reacts with the lipoate disulfide. Kinetic consequences of such interplay are consistent with the observed thioredoxin effects. Owing to the essential reactivity of the SH/S–S couple in thioredoxin, the thiol–disulfide exchange between thioredoxin and the lipoate residue is easy reversible, providing both protection (by the mixed disulfide formation) and catalysis (by the appropriate lipoate release). In contrast, non-protein SH/S–S compounds prevent the inactivatory action of Dihydrolipoate intermediate only at a high excess over the complex-bound lipoate. This interferes with the catalysis-required release of the residue from its mixed disulfide. Therefore, only thioredoxin is capable to `buffer' the steady-state concentration of the reactive dithiol. Such action represents a new thioredoxin function, which may be exploited to protect other enzymes with exposed redox-active thiol intermediates.
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Using lipoate enantiomers and thioredoxin to study the mechanism of the 2-oxoacid-dependent Dihydrolipoate production by the 2-oxoacid dehydrogenase complexes
FEBS Letters, 1995Co-Authors: Victoria I. Bunik, Hans Bisswanger, A. Shoubnikova, S. Loeffelhardt, H.o. Borbe, Hartmut FollmannAbstract:The thioredoxin-catalyzed insulin reduction by Dihydrolipoate was applied to study the 2-oxoacid:lipoate oxidoreductase activity of 2-oxoacid dehydrogenase complexes. The enzymatic and non-enzymatic mechanisms of the transfer of reducing equivalents from the complexes to free lipoic acid (α-lipoic acid, 6,8-thiooctic acid) were distinguished using the high stereoselectivity of the complex enzymes to the R-enantiomer of lipoate. Unlike these enzymes, thioredoxin from E. coli exibited no stereoselectivity upon reduction with chemically obtained Dihydrolipoate. However, coupled to the Dihydrolipoate production by dehydrogenase complexes, the process was essentially sensitive both to the enantiomer used and the dihydrolipoyl dehydrogenase activity of the complexes. These results indicated the involvement of the third complex component, dihydrolipoyl dehydrogenase, in the 2-oxoacid-dependent Dihydrolipoate formation. The implication of the investigated reaction for a connection between thioredoxin and the 2-oxoacid dehydrogenase complexes in the mitochondrial metabolism are discussed.
Hartmut Follmann - One of the best experts on this subject based on the ideXlab platform.
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Using lipoate enantiomers and thioredoxin to study the mechanism of the 2-oxoacid-dependent Dihydrolipoate production by the 2-oxoacid dehydrogenase complexes
FEBS Letters, 1995Co-Authors: Victoria I. Bunik, Hans Bisswanger, A. Shoubnikova, S. Loeffelhardt, H.o. Borbe, Hartmut FollmannAbstract:The thioredoxin-catalyzed insulin reduction by Dihydrolipoate was applied to study the 2-oxoacid:lipoate oxidoreductase activity of 2-oxoacid dehydrogenase complexes. The enzymatic and non-enzymatic mechanisms of the transfer of reducing equivalents from the complexes to free lipoic acid (α-lipoic acid, 6,8-thiooctic acid) were distinguished using the high stereoselectivity of the complex enzymes to the R-enantiomer of lipoate. Unlike these enzymes, thioredoxin from E. coli exibited no stereoselectivity upon reduction with chemically obtained Dihydrolipoate. However, coupled to the Dihydrolipoate production by dehydrogenase complexes, the process was essentially sensitive both to the enantiomer used and the dihydrolipoyl dehydrogenase activity of the complexes. These results indicated the involvement of the third complex component, dihydrolipoyl dehydrogenase, in the 2-oxoacid-dependent Dihydrolipoate formation. The implication of the investigated reaction for a connection between thioredoxin and the 2-oxoacid dehydrogenase complexes in the mitochondrial metabolism are discussed.
Hans J. Tritschler - One of the best experts on this subject based on the ideXlab platform.
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alpha lipoic acid as a biological antioxidant
Free Radical Biology and Medicine, 1995Co-Authors: Lester Packer, Eric Witt, Hans J. TritschlerAbstract:alpha-Lipoic acid, which plays an essential role in mitochondrial dehydrogenase reactions, has recently gained considerable attention as an antioxidant. Lipoate, or its reduced form, Dihydrolipoate, reacts with reactive oxygen species such as superoxide radicals, hydroxyl radicals, hypochlorous acid, peroxyl radicals, and singlet oxygen. It also protects membranes by interacting with vitamin C and glutathione, which may in turn recycle vitamin E. In addition to its antioxidant activities, Dihydrolipoate may exert prooxidant actions through reduction of iron. alpha-Lipoic acid administration has been shown to be beneficial in a number of oxidative stress models such as ischemia-reperfusion injury, diabetes (both alpha-lipoic acid and dihydrolipoic acid exhibit hydrophobic binding to proteins such as albumin, which can prevent glycation reactions), cataract formation, HIV activation, neurodegeneration, and radiation injury. Furthermore, lipoate can function as a redox regulator of proteins such as myoglobin, prolactin, thioredoxin and NF-kappa B transcription factor. We review the properties of lipoate in terms of (1) reactions with reactive oxygen species; (2) interactions with other antioxidants; (3) beneficial effects in oxidative stress models or clinical conditions.
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Glutathione reductase and lipoamide dehydrogenase have opposite stereospecificities for α-lipoic acid enantiomers
Biochemical and biophysical research communications, 1995Co-Authors: Uri Pick, Hans J. Tritschler, N. Haramaki, A. Constantinescu, G.j. Handelman, Lester PackerAbstract:Abstract The reduction of exogenous α-lipoic acid to Dihydrolipoate by mammalian cells and tissues confers additional antioxidant protection to the cell. Both (R+) and (S−) isomers of α-lipoic acid were analyzed as substrates with glutathione reductase from several sources and with mammalian lipoamide dehydrogenase. Mammalian glutathione reductase catalyzed faster reduction of (S)-lipoic acid (1.4-2.4-fold greater activity) than of (R)-lipoic acid, whereas lipoamide dehydrogenase had a very marked preference for (R)-lipoic acid (18-fold greater activity) over (S)-lipoic acid. Mammalian glutathione reductase showed better affinity for (S)-lipoic acid substrate; Km values were 3.5 mM for (S)-lipoic acid and and 7 mM for (R)-lipoic acid. Glutathione reductase from yeast reduced lipoic acid less efficiently than the mammalian enymes, had a Km for both stereoisomers of about 10 mM, and showed little stereospecificity. Although (S)-lipoic acid is not formed in nature, these findings indicate that exogenous (S)-lipoic acid may have a useful role as an antioxidant for mammalian systems.
Helmut Sies - One of the best experts on this subject based on the ideXlab platform.
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vitamins e and c beta carotene and other carotenoids as antioxidants
The American Journal of Clinical Nutrition, 1995Co-Authors: Helmut Sies, Wilhelm StahlAbstract:Tocopherols and tocotrienols (vitamin E), ascorbic acid (vitamin C), and the carotenoids react with free radicals, notably peroxyl radicals, and with singlet molecular oxygen ( 1 O 2 ), which is the basis for their function as antioxidants. RRR-α-Tocopherol is the major peroxyl radical scavenger in biological lipid phases such as membranes or low-density lipoproteins. Ascorbic acid is present in aqueous compartments (eg, cytosol, plasma, and other body fluids) and can reduce the tocopheroxyl radical ; it also has several metabolically important cofactor functions in enzyme reactions, especially hydroxylations. These micronutrients need to be regenerated on oxidation in the biological setting, hence the need for further coupling to nonradical reducing systems such as glutathione-glutathione disulfide, Dihydrolipoate-lipoate, or NADPH-NADP + and NADH-NAD + . Carotenoids, such as β-carotene, lycopene, and some oxycarotenoids, eg, zeaxanthin and lutein, exert antioxidant functions in lipid phases by quenching 1 O 2 or free radicals. There are pronounced differences in tissue carotenoid patterns, extending also to the distribution between the all-trans and various cis isomers of the respective carotenoids. Physical quenching leaves the structure intact, so that in this mode the carotenoids do not require a regeneration reaction.
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Ebselen, a selenoorganic compound as glutathione peroxidase mimic.
Free radical biology & medicine, 1993Co-Authors: Helmut SiesAbstract:Abstract The selenoorganic compound ebselen, 2-phenyl-1,2-benzisoselenazol-3(2H)-one, exhibits activity as an enzyme mimic. The reaction catalyzed is that of a glutationed (GSH) peroxidase (i.e., the reduction of a hydroperoxide at the expense of thil). The specificity for substances ranges from hydrogen peroxide and smaller organic hydroperoxides to membrane-bound phospholipid and cholesterol hydroperoxides. In addition to glutatione, the thiol reductant cosubstrate can be dithioerythritol, N-acetylcysteine or Dihydrolipoate, or other suitable thiol compounds. Ebselen also has properties such as free radical and singlet oxygen quenching. Model experiments in vitro with liposomes, microsomes, isolated cells, and organs show that the protection against oxidative challenge afforded by ebselen can be explained largely by the activity ad GSH peroxidase mimic. Whether this also explains the known preliminary results in clinical settings is yet open. The metabolism and disposition of ebselen is presented in thsi review. The main point is that the selenium is not bioavailable, explaining the extremely low toxicity observed in animals studies. The occurrence of natural GPx mimics, ovothiol and related compounds, is briefly mentioned.