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Lipoic and dihydrolipoic acids as antioxidants. A critical evaluation.

A detailed evaluation of the antioxidant and pro-oxidant properties of lipoic acid (LA) and dihydrolipoic acid (DHLA) was performed. Both compounds are powerful scavengers of hypochlorous acid, able to protect alpha 1-antiproteinase against inactivation by HOCl. LA was a powerful scavenger of hydroxyl radicals (OH.) and could inhibit both iron-dependent OH. generation and peroxidation of ox-brain phospholipid liposomes in the presence of FeCl3-ascorbate, presumably by binding iron ions and rendering them redox-inactive. By contrast, DHLA accelerated iron-dependent OH. generation and lipid peroxidation, probably by reducing Fe3+ to Fe2+. LA inhibited this pro-oxidant action of DHLA. However, DHLA did not accelerate DNA degradation by a ferric bleomycin complex and slightly inhibited peroxidation of arachidonic acid by the myoglobin-H2O2 system. Under certain circumstances, DHLA accelerated the loss of activity of alpha-antiproteinase exposed to ionizing radiation under a N2O/O2 atmosphere and also the loss of creatine kinase activity in human plasma exposed to gas-phase cigarette smoke. Neither LA nor DHLA reacted with superoxide radical (O.2-) or H2O2 at significant rates, but both were good scavengers of trichloromethylperoxyl radical (CCl3O2.). We conclude that LA and DHLA have powerful antioxidant properties. However, DHLA can also exert pro-oxidant properties, both by its iron ion-reducing ability and probably by its ability to generate reactive sulphur-containing radicals that can damage certain proteins, such as alpha 1-antiproteinase and creatine kinase.

Animals↗

LACTATE-DEGRADING SYSTEM IN BUTYRIBACTERIUM RETTGERI SUBJECT TO GLUCOSE REPRESSION.

Wittenberger, Charles L. (National Institute of Dental Research, U.S. Public Health Service, Bethesda, Md.), and Ann S. Haaf. Lactate-degrading system in Butyribacterium rettgeri subject to glucose repression. J. Bacteriol. 88:896-903. 1964.-The ability of Butyribacterium rettgeri to utilize lactate as the main energy source for growth requires the formation of a lactate-degrading system. The precise nature of this system is unknown, but preliminary evidence suggests that cellular acquisition of lactate-decomposing activity involves the formation of a nonpyridine nucleotide-linked lactic dehydrogenase. This enzyme, which can couple lactate oxidation to the reduction of ferricyanide [K(3)Fe(CN)(6)-lactic de-hydrogenase (LDH)], is absent from glucose-grown cells; this observation appears to account for the inability of such cells to decompose lactate even though they may form lactate from glucose. The formation of K(3)Fe(CN)(6)-LDH in growing cultures requires the addition of lipoic acid to the medium, and is repressed by glucose, pyruvate, or fructose. When any of the latter substrates are included in the growth medium with lactate, nicotinamide adenine dinucleotide-linked LDH activity is present in cells at markedly higher levels than it is in cells grown on lactate alone.

Culture Media↗

PYRUVATE FERMENTATION BY STREPTOCOCCUS FAECALIS.

Deibel, R. H. (American Meat Institute Foundation, Chicago, Ill.), and C. F. Niven, Jr. Pyruvate fermentation by Streptococcus faecalis. J. Bacteriol. 88:4-10. 1964.-Streptococcus faecalis, as opposed to S. faecium, utilizes pyruvate as an energy source for growth. The fermentation is adaptive, as demonstrated by growth experiments in a casein-hydrolysate medium and the fermentation of pyruvate by cell suspensions. The principal products of pyruvate catabolism were acetoin, CO(2), and lactic, acetic, and formic acids, although carbon recoveries were low due to the formation of slime. End-product analyses suggested that both the phosphoroclastic and dismutation systems were active in pyruvate breakdown. Studies with cell-free extracts indicated a thiamine diphosphate requirement for active pyruvate catabolism. The involvement of lipoic acid in the phosphoroclastic system was investigated, and, although inconclusive results were obtained, no association of this cofactor with phosphoroclastic activity could be made.

Acetates↗

Reactive oxygen species, antioxidants, and the mammalian thioredoxin system.

Reactive oxygen species (ROS) are known mediators of intracellular signaling cascades. Excessive production of ROS may, however, lead to oxidative stress, loss of cell function, and ultimately apoptosis or necrosis. A balance between oxidant and antioxidant intracellular systems is hence vital for cell function, regulation, and adaptation to diverse growth conditions. Thioredoxin reductase (TrxR) in conjunction with thioredoxin (Trx) is a ubiquitous oxidoreductase system with antioxidant and redox regulatory roles. In mammals, extracellular forms of Trx also have cytokine-like effects. Mammalian TrxR has a highly reactive active site selenocysteine residue resulting in a profound reductive capacity, reducing several substrates in addition to Trx. Due to the reactivity of TrxR, the enzyme is inhibited by many clinically used electrophilic compounds including nitrosoureas, aurothioglucose, platinum compounds, and retinoic acid derivatives. The properties of TrxR in combination with the functions of Trx position this system at the core of cellular thiol redox control and antioxidant defense. In this review, we focus on the reactions of the Trx system with ROS molecules and different cellular antioxidant enzymes. We summarize the TrxR-catalyzed regeneration of several antioxidant compounds, including ascorbic acid (vitamin C), selenium-containing substances, lipoic acid, and ubiquinone (Q10). We also discuss the general cellular effects of TrxR inhibition. Dinitrohalobenzenes constitute a unique class of immunostimulatory TrxR inhibitors and we consider the immunomodulatory effects of dinitrohalobenzene compounds in view of their reactions with the Trx system.

Animals↗

Isolation and characterization of lipoylated and unlipoylated domains of the E2p subunit of the pyruvate dehydrogenase complex of Escherichia coli.

The dihydrolipoamide acetyltransferase subunit (E2p) of the pyruvate dehydrogenase complex of Escherichia coli has three highly conserved and tandemly repeated lipoyl domains, each containing approx. 80 amino acid residues. These domains are covalently modified with lipoyl groups bound in amide linkage to the N6-amino groups of specific lysine residues, and the cofactors perform essential roles in the formation and transfer of acetyl groups by the dehydrogenase (E1p) and acetyltransferase (E2p) subunits. A subgene encoding a hybrid lipoyl domain was previously shown to generate two products when overexpressed, whereas a mutant subgene, in which the lipoyl-lysine codon is replaced by a glutamine codon, expresses only one product. A method has been devised for purifying the three types of independently folded domain from crude extracts of E. coli, based on their pH-(and heat-)stabilities. The domains were characterized by: amino acid and N-terminal sequence analysis, lipoic acid content, acetylation by E1p, tryptic peptide analysis and immunochemical activity. This has shown that the two forms of domain expressed from the parental subgene are lipoylated (L203) and unlipoylated (U203) derivatives of the hybrid lipoyl domain, whereas the mutant subgene produces a single unlipoylatable domain (204) containing the Lys-244----Gln substitution.

Acetylation↗

T cell responses to the putative dominant autoepitope in primary biliary cirrhosis (PBC).

PBC is characterized by T cell-mediated destruction of the biliary epithelial cells lining the small intrahepatic bile ducts. The E2 and E3 binding protein (E3BP (protein X)) components of pyruvate dehydrogenase complex (PDC) are disease-specific autoantigens in PBC. Attempts to localize the T cell autoepitopes within PDC-E2 have, however, generated contradictory results. One study has suggested the presence of T cell epitopes throughout PDC-E2, whilst another has identified a single dominant 14 amino acid T cell epitope (p163) spanning the lipoic acid binding lysine residue in the inner lipoyl domain (ILD) of PDC-E2. The aim of the current study was to determine the prevalence of T cell responses to p163 and PDC-E2 ILD, and the role played by lipoylation of these antigens in their immunogenicity, in a UK PBC population. We found that the majority of the PBC patients showing a 6-day peripheral blood T cell proliferative response to native human PDC also responded, in a MHC class II-restricted fashion, to biochemically purified PDC-E2 and E3BP (which co-purify) (9/10 positive (SI > 2.76), mean SI 5.74 +/- 5.04 (PDC-E2/E3BP) versus 6.67 +/- 3.84 (PDC), P = NS), implying that the important PBC-specific T cell epitopes are contained within the PDC-E2 or E3BP components of PDC. Only a minority of patients responsive to PDC, however, responded to either lipoylated recombinant PDC-E2 ILD (4/10 positive, mean SI 1.98 +/- 1.24, P < 0.005 versus PDC response) or lipoylated p163 (4/12 positive, mean SI 1.90 +/- 1.58, P < 0.001). The lipoylation state did not affect the T cell response to either ILD or p163. Our findings suggest that in some UK patients with PBC there are immunodominant T cell autoepitopes within PDC-E2/E3BP which are outside the ILD of PDC-E2.

Autoantigens↗

Antioxidants reduce cone cell death in a model of retinitis pigmentosa.

Retinitis pigmentosa (RP) is a label for a group of diseases caused by a large number of mutations that result in rod photoreceptor cell death followed by gradual death of cones. The mechanism of cone cell death is uncertain. Rods are a major source of oxygen utilization in the retina and, after rods die, the level of oxygen in the outer retina is increased. In this study, we used the rd1 mouse model of RP to test the hypothesis that cones die from oxidative damage. A mixture of antioxidants was selected to try to maximize protection against oxidative damage achievable by exogenous supplements; alpha-tocopherol (200 mg/kg), ascorbic acid (250 mg/kg), Mn(III)tetrakis (4-benzoic acid) porphyrin (10 mg/kg), and alpha-lipoic acid (100 mg/kg). Mice were treated with daily injections of the mixture or each component alone between postnatal day (P)18 and P35. Between P18 and P35, there was an increase in two biomarkers of oxidative damage, carbonyl adducts measured by ELISA and immunohistochemical staining for acrolein, in the retinas of rd1 mice. The staining for acrolein in remaining cones at P35 was eliminated in antioxidant-treated rd1 mice, confirming that the treatment markedly reduced oxidative damage in cones; this was accompanied by a 2-fold increase in cone cell density and a 50% increase in medium-wavelength cone opsin mRNA. Antioxidants also caused some preservation of cone function based upon photopic electroretinograms. These data support the hypothesis that gradual cone cell death after rod cell death in RP is due to oxidative damage, and that antioxidant therapy may provide benefit.

Animals↗

The cosmetic treatment of wrinkles.

Wrinkles now have a greater social impact because people live longer. Science and hedonism overlap in the search for causes, treatments and prevention of wrinkles. The cosmetic approach to wrinkles includes: i Cleansing ii Photoprotection iii Active ingredients Active ingredients go well beyond simple moisturisers and exert a more complex activity in protecting skin from external injuries, nourishing it and removing its superficial layers. Transport systems and excipients are increasingly effective. Functional agents currently include alpha hydroxy acids (AHAs), poly-AHAs, complex poly-AHAs, retinoids, fish polysaccharides, anti-enzymatic agents, antioxidants (including ascorbic acid, pycnogenol, ursolic acid, vegetable isoflavones, vitamin E, coenzyme Q10, lipoic acid, resveratorol, l-carnosine and taurine) as well as agaricic acid and various plant extracts. All are reviewed in this text. Most are topical, some can be given by mouth, even as food supplements. Cosmetics are becoming closer to drugs in preventing and treating wrinkles. Included amongst the cosmeceuticals are the anti-wrinkle agents described herein.

Journal Article↗

Nutritional and botanical interventions to assist with the adaptation to stress.

Prolonged stress, whether a result of mental/emotional upset or due to physical factors such as malnutrition, surgery, chemical exposure, excessive exercise, sleep deprivation, or a host of other environmental causes, results in predictable systemic effects. The systemic effects of stress include increased levels of stress hormones such as cortisol, a decline in certain aspects of immune system function such as natural killer cell cytotoxicity or secretory-IgA levels, and a disruption of gastrointestinal microflora balance. These systemic changes might be a substantial contributor to many of the stress-associated declines in health. Based on human and animal research, it appears a variety of nutritional and botanical substances - such as adaptogenic herbs, specific vitamins including ascorbic acid, vitamins B1 and B6, the coenzyme forms of vitamin B5 (pantethine) and B12 (methylcobalamin), the amino acid tyrosine, and other nutrients such as lipoic acid, phosphatidylserine, and plant sterol/sterolin combinations - may allow individuals to sustain an adaptive response and minimize some of the systemic effects of stress.

Humans↗

Iron-molybdenum cofactor from nitrogenase. Modified extraction methods as probes for composition.

Five modifications of the preparative procedure for isolating iron-molybdenum cofactor (FeMoco) from the molybdenum-iron (MoFe) protein of Azotobacter vinelandii nitrogenase have been developed. This variety of isolation methods has established that no single component of the original isolation protocol, i.e. Tris, Cl-, citrate, HPO4(2-), N,N-dimethylformamide, and N-methylformamide, is essential for the effective isolation and/or structural stability of FeMoco, although any of them may act as ligands to FeMoco when present. The acid-bse status (effective pH) of the extracting solvent is a key adjustable parameter in the isolation procedure. The new procedures produced FeMoco with yields, metal analysis, charge, EPR spectrum, and specific activity (after reconstituting crude extracts from A. vinelandii UW45 mutant cells) essentially identical with FeMoco isolated by the original procedure. After purification, FeMoco apparently contains molybdenum, iron, and sulfide in a 1:7:4 ratio with N-methylformamide as a ligand but no amino acid residues, common sugars, coenzyme A, or lipoic acid. Reaction with o-phenanthroline allows quantitation of both adventitious and FeMoco-associated iron. Correlations of total activity after UW45 reconstitution with molybdenum, total iron, and o-phenanthroline-resistant iron contents show that only the last gives a consistent relationship of 35 +/- 5 nmol of C2H4/min/ng atom of Fe. Both o-phenanthroline and EDTA interact with FeMoco to abolish its EPR signal in reactions reversible by additions of Fe2+ or Zn2+, respectively. These and related reactions point against the presence of an endogenous organic component in FeMoco and toward the presence of exogenous ligands and imply a relatively labile coordination sphere whose nature may be determinable by a systematic investigation.

Amino Acids↗

In vitro neuroprotection against oxidative stress by pre-treatment with a combination of dihydrolipoic acid and phenyl-butyl nitrones.

One consequence of trauma to the CNS is the production and liberation, from damaged tissue, of large amounts of oxygen-centered free radicals or reactive oxygen species (ROS). An excessive production of ROS can overwhelm the endogenous antioxidant defense system resulting in lipid peroxidation, DNA strand breaks, protein denaturation and cross-linking. The brain is particularly vulnerable to oxidative injury, because it contains high concentrations of readily oxidizable poly-unsaturated fatty acids, has a high rate of oxygen consumption per unit mass, and has only a relatively modest antioxidant defense system. We have conducted studies in vitro to determine the feasibility of reducing ROS-mediated damage in neurons by bolstering endogenous neuronal antioxidant defenses. Primary cultures of neurons derived from embryonic rat forebrain were pre-treated with the free radical scavenger dihydrolipoic acid (DHLA), the reduced form of Alpha-lipoic acid (ALA), and then subjected to H(2)O(2)-mediated oxidative stress. Neuroprotection was determined using the colorimetric MTT reduction assay. As has been reported by others, pre-treatment of neurons with DHLA (4 h) provided dose-dependent neuroprotection against a subsequent exposure to H(2)O(2). The addition of spin trapping nitrones N-tert-butyl-Alpha-phenyl-nitrone (PBN) or its sulfonated analog N-tert-butyl-Alpha(2-sulfophenyl)-nitrone (SPBN) to the pre-treatment cocktail enhanced neuroprotection at every dihydrolipoate concentration. Greater therapeutic efficacy in antioxidant treatment might be realized by employing combinations of complementary antioxidants.

Animals↗

Effect of selenolipoic acid on peroxynitrite-dependent inactivation of NADPH-cytochrome P450 reductase.

Seleno-organic compounds are known as efficient "scavengers" of peroxynitrite (PN). Here we studied the protective effect of selenolipoic acid (SeLA), the seleno-containing analogue of lipoic acid, on peroxynitrite-dependent inactivation of NADPH-cytochrome P450 reductase. 3-Morpholinosydnonimine hydrochloride (SIN-1) was used as a source of peroxynitrite. The reductase was irreversibly inactivated by PN generated from SIN-1. The inactivation occurred with the rate constant of about 3 x 10(4) M-1 s-1. The presence of SeLA at low concentration (0.5 microM) led to synergistic increase of the reductase inactivation by PN. Our results suggest the formation of a reactive derivative of SeLA in the reaction of SeLA with PN, probably selenolseleninate, that mediates the aggravation of reductase inactivation. In the presence of SeLA, the inactivation was reversible under the action of thiols, allowing us to conclude that the observed action of SeLA may be considered as protective.

Animals↗

Screening of potential cancer preventing chemicals as antioxidants in an in vitro assay.

We used an azo-initiated fluorescence assay to rank a series of antioxidants, with the objective of selecting compounds for further evaluation as chemopreventive agents. Trolox was the positive control for the assay and, with an IC50 of 0.50 microM, was more active than any of the other 16 compounds examined. Three compounds, U83836E, glutathione, and purpurgallin, were only slightly less active with IC50's in the 1-3 microM range. Four other compounds were almost as active: protochatechuic acid, N-acetyl-L-cysteine, U74389G, and lipoic acid (reduced). This fluorescence-based assay for antioxidant activity is a rapid, economical way of ranking antioxidants for further development in the National Cancer Institute's chemoprevention program.

Anticarcinogenic Agents↗

Protection against radiation-induced oxidative stress in cultured human epithelial cells by treatment with antioxidant agents.

PURPOSE: To evaluate the protective effects of antioxidant agents against space radiation-induced oxidative stress in cultured human epithelial cells. METHODS AND MATERIALS: The effects of selected concentrations of N-acetylcysteine, ascorbic acid, sodium ascorbate, co-enzyme Q10, alpha-lipoic acid, l-selenomethionine, and vitamin E succinate on radiation-induced oxidative stress were evaluated in MCF10 human breast epithelial cells exposed to radiation with X-rays, gamma-rays, protons, or high mass, high atomic number, and high energy particles using a dichlorofluorescein assay. RESULTS: The results demonstrated that these antioxidants are effective in protecting against radiation-induced oxidative stress and complete or nearly complete protection was achieved by treating the cells with a combination of these agents before and during the radiation exposure. CONCLUSION: The combination of antioxidants evaluated in this study is likely be a promising countermeasure for protection against space radiation-induced adverse biologic effects.

Acetylcysteine↗

Reactivity of primary biliary cirrhosis sera with Escherichia coli dihydrolipoamide acetyltransferase (E2p): characterization of the main immunogenic region.

Primary biliary cirrhosis (PBC) is a chronic cholestatic liver disease characterized by the presence of antimitochondrial autoantibodies in the serum. The major antigens recognized by the antibodies are the E2 components of the 2-oxo acid dehydrogenase complexes, all of which possess covalently attached lipoic acid cofactors. A bacterial etiology has been proposed for the disease, and patients' antibodies are known to recognize the E2 subunits (E2p) of both mammalian and bacterial pyruvate dehydrogenase complexes. Immunoblotting and ELISA inhibition techniques using extracts of Escherichia coli deletion strains, genetically restructured E2 polypeptides, and isolated lipoyl domains demonstrate that (i) the E2o subunit of the E. coli 2-oxoglutarate dehydrogenase complex is recognized by patients' antibodies; (ii) the main immunogenic region of E2p lies within the lipoly domains; (iii) the presence of a lipoly residue within the domain is crucial for effective recognition by the antibodies; and (iv) octanoylated E2p, octanoylated E2o, and octanoylated lipoyl domain, produced by a mutant deficient in lipoate biosynthesis, are recognized by patients' antibodies but not as effectively as their lipoylated counterparts. These findings indicate that antibodies in PBC patients' sera bind to a unique peptide-cofactor conformation within the lipoyl domains of the E2 polypeptides and that this epitope is partially mimicked by substituting the lipoyl cofactor with an octanoyl group.

Acetyltransferases↗

Attenuation of oxidative stress in HL-1 cardiomyocytes improves mitochondrial function and stabilizes Hif-1alpha.

HL-1 cardiomyocytes were subjected to simulated hypoxia, in the presence of cobalt chloride, which resulted in reduction of cell viability and induction of DNA laddering, indicating the activation of the apoptotic cascade. In the presence of trolox, ascorbic acid, melatonin and the hybrid compound of trolox and lipoic acid (LaT 3a), cell viability was increased, with LaT 3a exhibiting the best effect. Antioxidant treatment restored ATP levels, abolished laddering of DNA, abrogated MPTP opening, Bax translocation to the mitochondria and cytochrome c release to the cytoplasm. Moreover, severe hypoxia, was found to destabilize hypoxia inducible factor-1alpha (Hif-1alpha) mRNA. Reduction of oxidative stress attenuated this effect, implying a possible anti-apoptotic action of the master regulator of hypoxia response. Our data suggest that antioxidants can maintain cell function and survival by inhibiting the mitochondrial apoptotic pathway and stabilizing Hif-1alpha.

Adenosine Triphosphate↗

Futile cycling of intermediates of fatty acid biosynthesis toward peroxisomal beta-oxidation in Saccharomyces cerevisiae.

The flux of fatty acids toward beta-oxidation was analyzed in Saccharomyces cerevisiae by monitoring polyhydroxyalkanoate synthesis in the peroxisome from the polymerization, by a bacterial polyhydroxyalkanoate synthase, of the beta-oxidation intermediates 3-hydroxyacyl-CoAs. Synthesis of polyhydroxyalkanoate was dependent on the beta-oxidation enzymes acyl-CoA oxidase and enoyl-CoA hydratase/3-hydroxyacyl-CoA dehydrogenase multifunctional protein, which are involved in generating 3-hydroxyacyl-CoAs, and on the peroxin PEX5, which is involved in the import of proteins into the peroxisome. In wild type cells grown in media containing fatty acids, the polyhydroxyalkanoate monomer composition was largely influenced by the nature of the external fatty acid, such that even-chain monomers are generated from oleic acid and odd-chain monomers are generated from heptadecenoic acid. In contrast, polyhydroxyalkanoate containing predominantly 3-hydroxyoctanoate, 3-hydroxydecanoate, and 3-hydroxydodecanoate was synthesized in a mutant deficient in the peroxisomal 3-ketothiolase (fox3 Delta 0) growing either on oleic acid or heptadecenoic acid as well as in wild type and fox3 Delta 0 mutants grown on glucose or raffinose, indicating that 3-hydroxyacyl-CoAs used for polyhydroxyalkanoate synthesis were generated from the degradation of intracellular short- and medium-chain fatty acids by the beta-oxidation cycle. Inhibition of fatty acid biosynthesis with cerulenin blocked the synthesis of polyhydroxyalkanoate from intracellular fatty acids but still enabled the use of extracellular fatty acids for polymer production. Mutants affected in the synthesis of lipoic acid showed normal polyhydroxyalkanoate synthesis capacity. Together, these results uncovered the existence of a substantial futile cycle whereby short- and medium-chain intermediates of the cytoplasmic fatty acid biosynthetic pathway are directed toward the peroxisomal beta-oxidation pathway.

3-Hydroxyacyl CoA Dehydrogenases↗

Hepatic and biliary autoantigens.

Chronic active hepatitis (CAH) and primary biliary cirrhosis (PBC) are two enigmatic liver diseases in which autoimmunity is implicated. Provisional criteria to separate the autoimmune type of CAH (A-CAH) from others are specified. Western immunoblotting using disease sera and antibody screening of a rat liver gene expression library were used to identify hepatic and biliary autoantigens relevant to the pathogenesis of A-CAH or PBC. With all reported putative liver-specific autoantigen preparations, serum reactivity in A-CAH and CAH due to infection with hepatitis B virus tends to be similar. In A-CAH, immunoblotting showed multiple reactivities with all liver preparations used, including hepatocyte membrane. In PBC, immunoblotting showed two disease-specific polypeptide antigens of MW 70 and 45 kD. A cDNA clone derived from a rat liver gene expression library was shown to encode the antigenic site of the 70 kD polypeptide. Recently published work in two other laboratories has established that the 70 kD autoantigen is the E2 component of the pyruvate dehydrogenase enzyme (PDH), and a proposed antibody-binding site (autoepitope) is a conserved decapeptide, corresponding to residues 83-92 of the deduced amino acid sequence of M2, which is the binding site of lipoic acid to the E2 component of PDH.

Autoantigens↗