The role of lipoic acid in the regulation of the redox status of wheat irrigated with 20% sea water.

The effect of irrigation with 20% sea water was studied in 14 and 21-day-old seedlings of durum wheat (Triticum durum, cv. Ofanto). Comparisons between control (Hoagland's 2 solution) and treated (20% sea water in Hoagland's solution) plants included, besides HPLC determination of reduced (DHLA) and oxidised (LA) forms of lipoic acid, ascorbate and glutathione contents, their redox status, the activity of ascorbate peroxidase (APX, EC 1.11.1.11.) and glutathione reductase (GR, EC 1.6.4.2.). The results indicated a more relevant presence of lipoic acid in the roots in comparison to the shoots. An involvement of its reduced form in the regeneration of the reduced glutathione, at least at 14 days of treatment, suggested, besides its role as dehydrogenase enzyme cofactor, a role in the recycling of the other antioxidants. The amount of LA always increased with growth in shoots and decreased in roots, while DHLA remained constant in control and increased in treated plants. Besides, the oxidised form always decreased with sea water while the reduced form decreased in shoots and increased in roots. The ascorbate pool exerted its positive influence especially in the shoots, while APX and GR activities resulted differently modulated by the salinity level.     

Lipoic acid: a unique antioxidant in the detoxification of activated oxygen species

Lipoic acid (1,2-dithiolane-pentanoic acid) is a dithiol which is effective in affording protection against oxidative stress by virtue of its two sulphydryl moieties. It is present in all kinds of eukaryotic and prokaryotic cells. As lipoamide, it functions as a cofactor in the multienzyme complexes that catalyse the oxidative decarboxylation of α-keto acids such as pyruvate, α-ketoglutarate, and branched-chain α-keto acids. The complete enzyme pathway responsible for the de novo synthesis of lipoic acid has not yet been elucidated. Octanoic acid appears to be the precursor for the eight-carbon fatty acid chain, and cysteine the source of sulfur. Lipoic acid is unique, among antioxidants, because it retains powerful antioxidant properties in both its reduced (dihydrolipoic acid) and oxidised (lipoic acid) forms. Both lipoic and dihydrolipoic acids have metal-chelating ability and quench activated oxygen species either in the cytosol or in the hydrophobic domains. Dihydrolipoic acid has more antioxidant properties than lipoic acid, and it plays an important role in the recycling of other oxidised radical scavengers such as glutathione, ascorbate and tocopherol. However, dihydrolipoic acid can also exert pro-oxidant properties both by its iron-reducing ability and by its ability to generate sulfur-containing radicals that can damage proteins. There are few quantitative data on lipoic acid contents in vegetables. It has been found in asparagus, wheat and potatoes, and recently, the presence of both lipoic and dihydrolipoic acids in roots, leaves and in the stroma of wheat has been demonstrated.     

Altered gene and protein expression by Nm23-H1 in metastasis suppression

The aim of our work was to study (1) the antioxidant properties of lipoic acid (LA) and its reduced metabolite dihydrolipoic acid (DHLA) formed by reduction of LA and (2) the effects of treatment with LA and DHLA on (a) K(+) efflux from human red blood cells and (b) post-ischemic recovery and oxidative stress in isolated perfused rat hearts challenged with an ischemia-reperfusion (IR) sequence. In vitro, we used xanthine and xanthine oxidase to generate superoxide anion, which is not directly measurable by electron paramagnetic resonance (EPR), but specifically oxidizes the spin probe CPH into an EPR-detectable long lasting CP(*) nitroxide radical. While 5 mM of LA was ineffective in reducing the kinetics of CP(*) nitroxide formation, DHLA was shown to lessen this rate in a dose-dependent manner and at 30 mM was even more efficient than 300 UI/ml SOD. These results are in agreement with the fact that DHLA is able to directly scavenge superoxide anion. Red cells are a good model to investigate oxidative damage in biological membranes; hence, we used a suspension of erythrocytes incubated with 2,2(')-azobis(2-amidinopropane) hydrochloride (AAPH) which generates in vitro free radicals. DHLA provided more effective protection of red cells membranes than LA; DHLA was comparable to Trolox for its antioxidant potency. In vivo, treatment of rats (50 mg/kg/day i.p. for 7 days) with LA induced a slight increase in coronary flow (CF) in isolated perfused hearts, after 30 min of global total ischemia. This effect was not associated with an improvement in contractile function and reduction of myocardial oxidative stress. In conclusion, because of their ability to scavenge free radicals, LA and to an even greater degree DHLA were able to protect the membranes of red blood cells. This finding suggests that LA and DHLA might be useful in the treatment of diseases associated with oxidative stress such as diabetes.     

Dihydrolipoic acid inhibits 15-lipoxygenase-dependent lipid peroxidation

The potential antioxidant effects of the hydrophobic therapeutic agent lipoic acid (LA) and of its reduced form dihydrolipoic acid (DHLA) on the peroxidation of either linoleic acid or human non-HDL fraction catalyzed by soybean 15-lipoxygenase (SLO) and rabbit reticulocyte 15-lipoxygenase (RR15-LOX) were investigated. DHLA, but not LA, did inhibit SLO-dependent lipid peroxidation, showing an IC(50) of 15 microM with linoleic acid and 5 microM with the non-HDL fraction. In specific experiments performed with linoleic acid, inhibition of SLO activity by DHLA was irreversible and of a complete, noncompetitive type. In comparison with DHLA, the well-known lipoxygenase inhibitor nordihydroguaiaretic acid and the nonspecific iron reductant sodium dithionite inhibited SLO-dependent linoleic acid peroxidation with an IC(50) of 4 and 100 microM, respectively, while the hydrophilic thiol N-acetylcysteine, albeit possessing iron-reducing and radical-scavenging properties, was ineffective. Remarkably, DHLA, but not LA, was also able to inhibit the peroxidation of linoleic acid and of the non-HDL fraction catalyzed by RR15-LOX with an IC(50) of, respectively, 10 and 5 microM. Finally, DHLA, but once again not LA, could readily reduce simple ferric ions and scavenge efficiently the stable free radical 1,1-diphenyl-2-pycrylhydrazyl in ethanol; DHLA was considerably less effective against 2,2'-azobis(2-amidinopropane) dihydrochloride-mediated, peroxyl radical-induced non-HDL peroxidation, showing an IC(50) of 850 microM. Thus, DHLA, at therapeutically relevant concentrations, can counteract 15-lipoxygenase-dependent lipid peroxidation; this antioxidant effect may stem primarily from reduction of the active ferric 15-lipoxygenase form to the inactive ferrous state after DHLA-enzyme hydrophobic interaction and, possibly, from scavenging of fatty acid peroxyl radicals formed during lipoperoxidative processes. Inhibition of 15-lipoxygenase oxidative activity by DHLA could occur in the clinical setting, eventually resulting in specific antioxidant and antiatherogenic effects.     

Lipoic acid protects efficiently only against a specific form of peroxynitrite-induced damage

The ability of the sulfur-containing compounds glutathione (GSH), glutathione disulphide (GSSG), S-methylglutathione (GSMe), lipoic acid (LA), and dihydrolipoic acid (DHLA) to protect against hypochlorous acid (HOCl)-mediated damage and peroxynitrite (ONOOH)-induced damage has been compared. Protective activity was assessed in competition assays by monitoring several detectors, i.e. dihydrorhodamine-123 (DHR-123) oxidation, alpha(1)-antiproteinase (alpha(1)-AP) inactivation, and glutathione S-transferase P1-1 (GST-P1-1) inactivation. In addition, nitration of tyrosine was measured to assess protection of the sulfur-containing compounds against ONOOH. For protection against HOCl, the efficacy of the antioxidant was controlled by the ratio of the reaction rates of the antioxidant and the detector molecule with the oxidant. The rank order of the activity of the antioxidants (GSH > DHLA approximately LA approximately GSMe > GSSG) appeared to be independent of the detector used. However, the rank order of the antioxidants against ONOOH-induced damage is strongly dependent on the detector. LA was 40 times less active than GSH in the inhibition of ONOOH-induced DHR-123 oxidation, whereas LA was 20 times more active than GSH in preventing the inhibition of GST-P1-1 by ONOOH. This points to different molecular mechanisms of ONOOH damage to DHR-123 compared with ONOOH damage to GST-P1-1. LA is a poor antioxidant in protecting against the form of ONOOH damage involved in DHR-123 oxidation. In the form of ONOOH toxicity involved in GST-P1-1 inhibition, LA is the most potent sulfur-containing antioxidant in our series. It is proposed that an intermediate product in which both sulfur atoms of LA have reacted is involved in the reaction of ONOOH with LA. The high potency of LA to protect GST-P1-1 against ONOOH might be of therapeutic interest.     

Effects of oxidative stress caused by NaCl or Na2SO4 excess on lipoic acid and tocopherols in Genovese and Fine basil (Ocimum basilicum)

With this investigation, we aimed to study more deeply the antioxidative response to moderate doses of NaCl or Na₂SO₄ in two cultivars of basil differentially sensitive to salinity. Tolerance to salinity was previously evaluated by the extent of growth inhibition whereas the antioxidant response was assessed studying the changes in the activities of superoxide dismutase (SOD) and catalase as well as in the amounts of tocopherols and lipoic acid. To make possible the comparison of the responses of basil cv. Genovese and cv. Fine to different salts, the experiment was carried out with equimolar concentrations of Na⁺. The results showed that changes caused by salinity were dependent on cultivar and exposure time. In particular, cv. Genovese was more sensitive to Na₂SO₄ excess than cv. Fine whereas both of them had higher SOD activity under NaCl salinity. Generally, Fine basil withstood salinity better than Genovese, being endowed with higher constitutive levels of reduced lipoic acid [dihydrolipoic acid (DHLA)] as well as of α‐ and γ‐tocopherols. Moreover, cv. Fine showed the ability to utilise DHLA and to synthesise tocopherols during stressful conditions. Thus, more than one mechanism was involved in basil in the detoxification of reactive oxygen species during salt stress. In fact, when lipoic acid did not participate in the regeneration of reduced ascorbate and glutathione form, high amounts of tocopherols were present, likely protecting cell membranes from oxidative damage and making basil tolerant to moderate salinity.     

Lipoic acid plays a role in scleroderma: insights obtained from scleroderma dermal fibroblasts

Introduction

Systemic sclerosis (SSc) is a connective tissue disease characterized by fibrosis of the skin and organs. Increase in oxidative stress and platelet-derived growth factor receptor (PDGFR) activation promote type I collagen (Col I) production, leading to fibrosis in SSc. Lipoic acid (LA) and its active metabolite dihydrolipoic acid (DHLA) are naturally occurring thiols that act as cofactors and antioxidants and are produced by lipoic acid synthetase (LIAS). Our goals in this study were to examine whether LA and LIAS were deficient in SSc patients and to determine the effect of DHLA on the phenotype of SSc dermal fibroblasts. N-acetylcysteine (NAC), a commonly used thiol antioxidant, was included as a comparison.

Methods

Dermal fibroblasts were isolated from healthy subjects and patients with diffuse cutaneous SSc. Matrix metalloproteinase (MMPs), tissue inhibitors of MMPs (TIMP), plasminogen activator inhibitor 1 (PAI-1) and LIAS were measured by enzyme-linked immunosorbent assay. The expression of Col I was measured by immunofluorescence, hydroxyproline assay and quantitative PCR. PDGFR phosphorylation and α-smooth muscle actin (αSMA) were measured by Western blotting. Student’s t-tests were performed for statistical analysis, and P-values less than 0.05 with two-tailed analysis were considered statistically significant.

Results

The expression of LA and LIAS in SSc dermal fibroblasts was lower than normal fibroblasts; however, LIAS was significantly higher in SSc plasma and appeared to be released from monocytes. DHLA lowered cellular oxidative stress and decreased PDGFR phosphorylation, Col I, PAI-1 and αSMA expression in SSc dermal fibroblasts. It also restored the activities of phosphatases that inactivated the PDGFR. SSc fibroblasts produced lower levels of MMP-1 and MMP-3, and DHLA increased them. In contrast, TIMP-1 levels were higher in SSc, but DHLA had a minimal effect. Both DHLA and NAC increased MMP-1 activity when SSc cells were stimulated with PDGF. In general, DHLA showed better efficacy than NAC in most cases.

Conclusions

DHLA acts not only as an antioxidant but also as an antifibrotic because it has the ability to reverse the profibrotic phenotype of SSc dermal fibroblasts. Our study suggests that thiol antioxidants, including NAC, LA, or DHLA, could be beneficial for patients with SSc.

Electronic supplementary material

The online version of this article (doi:10.1186/s13075-014-0411-6) contains supplementary material, which is available to authorized users.     

Dihydrolipoic acid lowers the redox activity of transition metal ions but does not remove them from the active site of enzymes

Alpha-lipoic acid (LA) and its reduced form, dihydrolipoic acid (DHLA), have been suggested to chelate transition metal ions and, hence, mitigate iron- and copper-mediated oxidative stress in biological systems. However, it remains unclear whether LA and DHLA chelate transition metal ions in a redox-inactive form, and whether they remove metal ions from the active site of enzymes. Therefore, we investigated the effects of LA and DHLA on iron- or copper-catalyzed oxidation of ascorbate, a sensitive assay for the redox activity of these metal ions. We found that DHLA, but not LA, significantly inhibited ascorbate oxidation mediated by Fe(III)-citrate, suggesting that reduced thiols are required for iron binding. DHLA also strongly inhibited Cu(II)(histidine)(2)-mediated ascorbate oxidation in a concentration-dependent manner, with complete inhibition at a DHLA:Cu(II) molar ratio of 3:1. In contrast, no inhibition of copper-catalyzed ascorbate oxidation was observed with LA. To investigate whether LA and DHLA remove copper or iron from the active site of enzymes, Cu,Zn superoxide dismutase and the iron-containing enzyme aconitase were used. We found that neither LA nor DHLA, even at high, millimolar concentrations, altered the activity of these enzymes. Our results suggest that DHLA chelates and inactivates redox-active transition metal ions in small-molecular, biological complexes without affecting iron- or copper-dependent enzyme activities.     

Comparison of antioxidant effectiveness of lipoic acid and dihydrolipoic acid

The abilities of dihydrolipoic acid (DHLA) to scavenge peroxynitrite (ONOO^?), galvinoxyl radical, 2,2′‐azinobis(3‐ethylbenzothiazoline‐6‐sulfonate) cation radical (ABTS^+?), and 2,2′‐diphenyl‐1‐picrylhydrazyl radical (DPPH) were higher than those of lipoic acid (LA). The effectiveness of DHLA to protect methyl linoleate against 2,2′‐azobis(2‐amidinopropane hydrochloride) (AAPH)‐induced oxidation was about 2.2‐fold higher than that of LA, and DHLA can retard the autoxidation of linoleic acid (LH) in the β‐carotene‐bleaching test. DHLA can also trap ～0.6 radicals in AAPH‐induced oxidation of LH. Moreover, DHLA can scavenge ～2.0 radicals in AAPH‐induced oxidation of DNA and AAPH‐induced hemolysis of erythrocytes, whereas LA can scavenge ～1.5 radicals at the same experimental conditions. DHLA can protect erythrocytes against hemin‐induced hemolysis, but accelerate the degradation of DNA in the presence of Cu²⁺. Therefore, the antioxidant capacity of –SH in DHLA is higher than S‐S in LA. © 2010 Wiley Periodicals, Inc. J Biochem Mol Toxicol 25:216–223, 2011; View this article online at wileyonlinelibrary.com . DOI 10.1002/jbt.20378     

R-alpha-lipoic acid action on cell redox status, the insulin receptor, and glucose uptake in 3T3-L1 adipocytes.

The insulin signaling pathway has been reported to mediate R-alpha-lipoic acid- (R-LA-)-stimulated glucose uptake into 3T3-L1 adipocytes and L6 myotubes. We investigated the role of the thiol antioxidant dihydrolipoic acid (DHLA) and intracellular glutathione (GSH) in R-LA-stimulated glucose transport and explored the hypothesis that R-LA could increase glucose uptake into 3T3-L1 adipocytes in an oxidant-mimetic manner. R-LA pretreatment of 3T3-L1 cells stimulated glucose transport at early time points (30 min - 6 h), whereas it inhibited glucose uptake at later time points. Analysis of the oxidized and reduced content of LA in cells and medium showed that >90% of lipoic acid present was in its oxidized form. Furthermore, all oxidized forms of LA (S-, R-, and racemic LA) stimulated glucose uptake, whereas the reduced form, dihydrolipoic acid, was ineffective. Intracellular GSH levels were not changed at the early time points (before 12 h), while longer preincubation (24 - 48 h) of cells with R-LA significantly increased intracellular GSH. Pretreatment of adipocytes with R-LA increased intracellular peroxide levels at early time points (30 min - 6 h), after which it was decreased (12 - 48 h). R-LA also increased tyrosine phosphorylation of immunoprecipitated insulin receptors from 3T3-L1 adipocytes. These results indicate that (i) 3T3-L1 adipocytes have a low capacity to reduce R-LA and the oxidized form of lipoic acid is responsible for stimulating glucose uptake, (ii) R-LA modulates glucose uptake by changing the intracellular redox status, and (iii) the insulin receptor is a potential cellular target for R-LA action.     

Biodegradation of polychlorinated dibenzo-p-dioxins by recombinant yeast expressing rat CYP1A subfamily

Thiols represent preferential targets of peroxynitrite in biological systems. In this work, we investigated the mechanisms and kinetics of the reaction of peroxynitrite with the dithiol dihydrolipoic acid (DHLA) and its oxidized form, lipoic acid (LA). Peroxynitrite reacted with DHLA being oxidation yields higher at alkaline pH. The stoichiometry for the reaction was two thiols oxidized per peroxynitrite. LA formation accounted for approximately 50% DHLA consumption at pH 7.4, probably reflecting secondary reactions between LA and peroxynitrite. Indeed, peroxynitrous acid reacted with LA with an apparent second-order rate constant (k(2app)) of 1400 M(-1) s(-1) at pH 7.4 and 37 degrees C. Nitrite and LA-thiosufinate were formed as reaction products. Surprisingly, the k(2app) for peroxynitrite-dependent DHLA oxidation was only 250 M(-1) s(-1) per thiol, at pH 7.4 and 37 degrees C. Testing various low-molecular-weight thiols, we found that an increase in the thiol pK (pK(SH)) value correlated with a decrease of k(2app) for the reaction with peroxynitrite at pH 7.4. The pK(SH) for DHLA is 10.7, in agreement with its modest reactivity with peroxynitrite.     

Peroxynitrite-derived carbonate and nitrogen dioxide radicals readily react with lipoic and dihydrolipoic acid

Alpha-lipoic acid (LA) and dihydrolipoic acid (DHLA) may have a role as antioxidants against nitric oxide-derived oxidants. We previously reported that peroxynitrite reacts with LA and DHLA with second-order rate constants of 1400 and 500 M(-1) s(-1), respectively, but indicated that these direct reactions are not fast enough to protect against peroxynitrite-mediated damage in vivo. Moreover, the mechanism of the reaction of peroxynitrite with LA has been recently challenged (J. Biol. Chem.279:9693-9697; 2004). Pulse radiolysis studies indicate that LA and DHLA react with peroxynitrite-derived nitrogen dioxide (*NO2) (k2 = 1.3 x 10(6) and 2.9 x 10(7) M(-1) s(-1), respectively) and carbonate radicals (CO(3-)) (k2 = 1.6 x 10(9) and 1.7 x 10(8) M(-1) s(-1), respectively). Carbonate radical-mediated oxidation of LA led to the formation of the potent one-electron oxidant LA radical cation. LA inhibited peroxynitrite-mediated nitration of tyrosine and of a hydrophobic tyrosine analog, N-t-BOC L-tyrosine tert-butyl ester (BTBE), incorporated into liposomes but enhanced tyrosine dimerization. Moreover, while LA competitively inhibited the direct oxidation of glutathione by peroxynitrite, it was poorly effective against the radical-mediated thiol oxidation. The mechanisms of reaction defined herein allow to rationalize the biochemistry of peroxynitrite based on direct and free radical-mediated processes and contribute to the understanding of the antioxidant actions of LA and DHLA.     

Is alpha-lipoic acid a scavenger of reactive oxygen species in vivo? Evidence for its initiation of stress signaling pathways that promote endogenous antioxidant capacity

The chemical reduction and oxidation (redox) properties of alpha-lipoic acid (LA) suggest that it may have potent antioxidant potential. A significant number of studies now show that LA and its reduced form, dihydrolipoic acid (DHLA), directly scavenge reactive oxygen species (ROS) and reactive nitrogen species (RNS) species and protect cells against a host of insults where oxidative stress is part of the underlying etiology. However, owing to its limited and transient accumulation in tissues following oral intake, the efficacy of nonprotein-bound LA to function as a physiological antioxidant has been questioned. Herein, we review the evidence that the micronutrient functions of LA may be more as an effector of important cellular stress response pathways that ultimately influence endogenous cellular antioxidant levels and reduce proinflammatory mechanisms. This would promote a sustained improvement in cellular resistance to pathologies where oxidative stress is involved, which would not be forthcoming if LA solely acted as a transient ROS scavenger.     

Antioxidant response to cadmium in Phragmites australis plants

Phragmites (Phragmites australis Cav. (Trin.) ex Steud) plants exposed to a high concentration of CdSO₄ (50 μM) for 21 d were analysed with respect to the distribution of metal, its effects on antioxidants, the antioxidant enzymes and the redox status in leaves, roots and stolons. The highest accumulation of Cd²⁺ occurred in roots followed by leaves, and it was not significant in the stolons when compared with the control plants. In particular, in roots from Cd-treated plants, both the high amount of GSH and the parallel increase of glutathione-S-transferase (EC 2.5.1.18; GST) activity seemed to be associated with an induction of the detoxification processes in response to the high cadmium concentration. Superoxide dismutase (EC 1.15.1.1; SOD), ascorbate peroxidase (EC 1.11.1.11; APX), glutathione reductase (EC 1.6.4.2; GR) and catalase (EC 1.11.1.6; CAT) activities as well as reduced and oxidised glutathione contents in all samples of leaves, roots and stolons were increased in the presence of Cd²⁺ when compared to control plants. Despite the fact that Cd²⁺ has a redox characteristic not compatible with the Fenton-type chemistry that produces active oxygen species, the antioxidant response is widespread and generic. Increased activities of antioxidant enzymes in Cd-treated plants suggest that metal tolerance in Phragmites plants might be associated to the efficiency of these mechanisms.     

Is dihydrolipoic acid among the reductive activators of parasite CysHis proteases?

Activities of mature CysHis proteases depend upon relative rates of oxidations vs. reductions of catalytic sulfur by multiple enzymatic and non-enzymatic reactions. CysHis peptidolysis is inhibited by Fe3+ but not Fe2+. Others report the paradox that malarial parasites require exogenous free lipoic acid (LA) from human host, although the apicoplast organelle produces it. Extra-cellular LA disulfide can be taken up and reduced to dihydrolipoic acid (DHLA) by reductases of any cell type. Here, the opposing effects of DHLA vs. Fe3+ on the falcipain-2 hemoglobinase were investigated employing Z-Phe-Arg-AMC substrate. Despite limited solubility, non-regenerated DHLA (10 microM, threshold 2 microM) was found to be the most potent activator of the air-inactivated (sulfoxygenated) protease discovered thus far. Activation was preemptively opposed by Fe3+, but not Fe2+. However, cruzain from T. cruzi, and cathepsin B from mammal were indistinguishable in their responsiveness to DHLA and Fe redox. Thus, DHLA activation vs. Fe3+ inhibition is not unique to falcipain-2 or apicomplexans but is rather a primordial feature of CysHis peptidolysis. Free LA and/or unassociated lipoylated enzyme subunits could be among multiple pathways shuttling reducing equivalents to reduction of proteins, including CysHis proteases. It is discussed that opposing DHLA-Fe3+ modification of plasmodial proteolysis might be a specialized adaptation to intra-erythrocytic growth.     

Antioxidant role of alpha-lipoic acid in lead toxicity.

The assumption of oxidative stress as a mechanism in lead toxicity suggests that antioxidants might play a role in the treatment of lead poisoning. The present study was designed to investigate the efficacy of lipoic acid (LA) in rebalancing the increased prooxidant/antioxidant ratio in lead-exposed Chinese hamster ovary (CHO) cells and Fischer 344 rats. Furthermore, LA's ability to decrease lead levels in the blood and tissues of lead-treated rats was examined. LA administration resulted in a significant improvement in the thiol capacity of cells via increasing glutathione levels and reducing malondialdehyde levels in the lead-exposed cells and animals, indicating a strong antioxidant shift on lead-induced oxidative stress. Furthermore, administration of LA after lead treatment significantly decreased catalase and red blood cell glucose-6-phosphate dehydrogenase activity. In vitro administration of LA to cultures of CHO cells significantly increased cell survival, that was inhibited by lead treatment in a concentration-dependent manner. Administration of LA was not effective in decreasing blood or tissue lead levels compared to a well-known chelator, succimer, that was able to reduce them to control levels. Hence, LA seems to be a good candidate for therapeutic intervention of lead poisoning, in combination with a chelator, rather than as a sole agent.     

Neuroprotective role of lipoic acid against acute toxicity of N-acetylaspartic acid

N-Acetylaspartic acid (NAA) accumulates in Canavan disease, a severe inherited neurometabolic disorder clinically characterized by mental retardation, hypotonia, macrocephaly, and seizures. The mechanisms of brain damage in this disease remain poorly understood. Recent studies developed by our research group showed that NAA induces oxidative stress in vitro and in vivo in cerebral cortex of rats. Lipoic acid is considered as an efficient antioxidant which can easily cross the blood–brain barrier. Considering the absence of specific treatment to Canavan disease, this study evaluates the possible prevention of the oxidative stress promoted by NAA in vivo by the antioxidant lipoic acid to preliminarily evaluate lipoic acid efficacy against pro-oxidative effects of NAA. Fourteen-day-old Wistar rats received an acute administration of 0.6 mmol NAA/g body weight with or without lipoic acid (40 mg/kg body weight). Catalase (CAT), glutathione peroxidase (GPx), and glucose 6-phosphate dehydrogenase activities, hydrogen peroxide content, thiobarbituric acid-reactive substances (TBA-RS), spontaneous chemiluminescence, protein carbonyl content, total antioxidant potential, and DNA–protein cross-links were assayed in the cerebral cortex of rats. CAT, GPx activities, and total antioxidant potential were significantly reduced, while hydrogen peroxide content, TBA-RS, spontaneous chemiluminescence, and protein carbonyl content were significantly enhanced by acute administration of NAA. Those effects were all prevented by lipoic acid pretreatment. Our results clearly show that lipoic acid may protect against the oxidative stress promoted by NAA. This could represent a new therapeutic approach to the patients affected by Canavan disease.     

Alpha-lipoic--dihydrolipoic acids--active bioantioxidant and bioregulatory system

alpha-Lipoic (LA) acid (thioctic acid) is an intramolecular disulfide that may be simply endogenically turned into dithiol. Dihydrolipoic acid (DHLA)/ LA and DHLA are bioantioxidants. They are synthesized in the body and taken with diet. Water- and lipide-soluble LA is highly-effective against the reactive oxygen species. LA (DHLA) protect the biomembranes, mitochondria from oxidative stresses of various kinds. LA, DHLA and lipoamide function as cofactors of polyenzyme mitochondrial complexes of 2-oxoacid dehydrogenases, of glycin decarboxylases and of some other enzymes. LA (DHLA) is ubiquinone reactivator and synergist by vitamin A, C, E. LA optimizes glucose metabolism, it is effective in insulin-resistant diabetes and its complications, in neutopathies and neurodegenerative diseases.     

Combined efficacies of lipoic acid and 2,3-dimercaptosuccinic acid against lead-induced lipid peroxidation in rat liver

Oxidative stress with subsequent lipid peroxidation has been postulated as one mechanism for lead toxicity. Hence in assessing the protective effects of lipoic acid (LA) and meso 2,3-dimercaptosuccinic acid (DMSA) on lead toxicity, they were tested either separately or in combination for their effects on selected indices of hepatic oxidative stress. Elevated levels of lipid peroxides were accompanied by altered antioxidant defense systems. Lead acetate (Pb - 0.2%) was administered in drinking water for five weeks to induce toxicity. LA (25 mg kg(-1) body wt. day(-1) i.p) and DMSA (20 mg kg(-1) body wt. day(-1) i.p) were administered individually and also in combination during the sixth week. Lead damage to the liver was evident in the decreases in hepatic enzymes alanine transaminase (-38%), aspartate transaminase (-42%) and alkaline phosphatase (-43%); increases in lipid peroxidation (+38%); decreases in the antioxidant enzymes catalase (-45%), superoxide dismutase (-40%), glutathione peroxidase (-46%) and decreases in glutathione (-43%) and decreases in glutathione metabolizing enzymes, glutathione reductase (-59%), glucose-6-phosphate dehydrogenase (-27%) and glutathione-S-transferase (-42%). In combination LA and DMSA completely ameliorated the lead induced oxidative damage. Either compound alone was however only partially protective against lead damage.     

Dose‐response effects of the antioxidant α‐lipoic acid in the liver and brain of pompano Trachinotus marginatus (Pisces,Carangidae)

This study evaluated the effect of different doses of the antioxidant α‐lipoic acid (LA) administered by intraperitoneal injection on the detoxifying capacity (activity of glutathione‐S‐transferase, GST) and oxidative damage (lipids and proteins) in the pompano, Trachinotus marginatus. The plasma glucose levels showed that there were no differences between the treatments (P > 0.05). In the brain, GST activity was significantly higher (P < 0.05) in fish injected with 40 mg LA kg^?1 when compared with the control group. In the muscle, GST activity was not influenced by LA treatment (P > 0.05). In the liver, fish injected with 20 mg LA kg^?1 showed higher GST activity than the control group (P < 0.05); however, higher doses (40 and 60 mg LA kg^?1) led to a reduction of GST activity in the liver, which was comparable to that observed in the control group (P > 0.05). The two highest LA doses (40 and 60 mg kg^?1) had opposite effects, depending on the tissue examined: LA was an antioxidant in the brain, reducing lipid peroxidation (P < 0.05), and a pro‐oxidant in the liver, augmenting oxidative lipid damage (P < 0.05). The latter effect was accompanied by an increase in the free iron concentration in the liver at higher LA doses. These results indicate the need to thoroughly evaluate the antioxidant effects on aquatic organisms, since at some doses and/or in some organs their beneficial effects can be lost.