Interplay between lipoic acid and glutathione in the protection against microsomal lipid peroxidation

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.

Analysis of proteome and transcriptome of tumor necrosis factor ? stimulated vascular smooth muscle cells with or without alpha lipoic acid

Vascular smooth muscle cells (VSMCs) play an important role in the development and progression of atherosclerosis. Tumor necrosis factor alpha (TNFalpha), a cytokine secreted by VSMCs and macrophages in atherosclerotic lesions, regulates a variety of cellular functions of inflammatory cells and VSMCs by promoting cell growth and motility, which are critical for the initiation and progression of vascularlesions. Alpha lipoic acid (ALA), a well known antioxidant, acts as a pyruvate dehydrogenase cofactor in mitochondrial metabolism. Recently, we reported that ALA has many beneficial effects on vascular cells in atherosclerosis. The aim of the current study was to examine VSMCs, treated for 24 hours with TNFalpha (10 ng/mL) in the presence or absence of ALA (2 mM), for differential protein and genes expression using two-dimensional gel electrophoresis (2-DE) and DNA microarray analysis, respectively. Using 2-DE, we identified proteins whose expression changed by at least 2.5-fold after TNFalpha stimulation. Proteins up-regulated by TNFalpha that were subsequently down-regulated in the presence of ALA were identified by matrix-assisted laser desorption/ionization-time of flight mass spectrometry as plasminogen activator inhibitor-2, fetal liver LKB-interacting protein, osteoblast-specific factor 2, glucosidase II, cyclin-dependent kinase 3, endoplasmin precursor and glutathione synthetase. TNFalpha down-regulated proteins that were up-regulated in the presence of ALA were keratin 19, eukaryotic translation elongation factor and Rho GDP dissociation inhibitor alpha. Gene expression analysis using DNA microarray tools confirmed the up-regulation or down-regulation of some, but not all, of the proteins observed in ALA challenged, TNFalpha-treated cells. This data should provide valuable information about the underlying mechanisms of atherosclerosis.

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.

Pseudomonas aeruginosa‐induced production of free radicals by IFNγ plus TNFα‐activated human endothelial cells: mechanism of host defense or of bacterial pathogenesis?

We have previously shown that human umbilical vein endothelial cells (HUVEC) can be activated by IFNgamma plus TNFalpha to kill intracellular (IC) Pseudomonas aeruginosa through production of reactive oxygen intermediate, but the cumulative effects of cytokine activation and bacterial infection on host cells has not been extensively addressed. In this study we investigated the fate of IFNgamma plus TNFalpha-activated HUVEC that have harboured IC bacteria for up to 24 h. At 10 h, the endothelial cell killing of P. aeruginosa isolates exceeded 90%. IC bacteria enhanced the expression of inducible nitric oxide synthase (iNOS) and induced overproduction of NO and superoxide by infected HUVEC. P. aeruginosa IC infection also induced a slight decrease in the cellular level of reduced glutathione (GSH). Overproduction of NO correlated with a marked peroxidation of plasma membrane lipids and decline in HUVEC viability. Treatment of cells with the antioxidant alpha-lipoic acid significantly increased the survival of infected cells. Our data suggest that with the failure of adequate scavenger mechanisms, oxidant radicals overproduced in response to bacterial infection were highly toxic to host cells. Therefore, instead of contributing to defence against infectious agents, the upregulation of free radicals production by endothelial cells in response to cytokine activation would be detrimental to the host.

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 as a Potential First Agent for Protection from Mycotoxins and Treatment of Mycotoxicosis

Mycotoxins--toxic substances produced by fungi or molds--are ubiquitous in the environment and are capable of damaging multiple biochemical mechanisms, resulting in a variety of human symptoms referred to collectively as "mycotoxicosis." In fact, mycotoxins mimic multiple xenobiotics, not only with respect to their ultimate damage, but also in their routes of detoxification. This suggests potential therapeutic options for the challenging treatment of mycotoxicosis. In this brief review, the author examines the use of lipoic acid as an example of an inexpensive and available nutrient that has been shown to protect against, or reverse, the adverse health effects of mycotoxins.

Evaluation of the effect of lipoic acid administered along with gentamicin in rats rendered bacteremic

Gentamicin is an aminoglycosidic antibiotic widely used in the treatment of many gram-negative bacterial infections. The present study was designed to investigate the extent of nephrotoxicity and the degree of protection afforded by lipoic acid under E. coli infected conditions and to note its effect on the antimicrobial activity of gentamicin. The study was carried out with adult male albino rats of Wistar strain. Group I animals served as controls. Group II animals were injected intraperitoneally for 2 successive days with 0.2 ml inoculum containing 10(10)) colony forming units of E. coli. Group III animals were injected E. coli as those in group II, in addition gentamicin 100 mg kg(-1) was administered intraperitoneally for 10 successive days. Group IV animals received intraperitoneal injections of E. coli as above plus gentamicin and also received lipoic acid (25 mg kg(-1)) for 10 days by oral gavage. Rats subjected to E. coli administration showed a decline in the thiol content of the cell accompanied by high malondialdehyde levels along with lowered activities of catalase, superoxide dismutase and glutathione peroxidase with an added effect observed when gentamicin was administered along with it. The extent of nephrotoxicity induced by gentamicin was clearly evident with the decline in the activities of lactate dehydrogenase, alkaline phosphatase and N-acetyl-beta-D-glucosaminidase in the rat renal tissues. A significant decrease was also observed in the activities of the transmembrane enzymes upon gentamicin administration. Treatment with lipoic acid decreased lipid peroxidation thereby maintaining the antioxidant status of the cell. The activities of the renal and transmembrane enzymes were also restored on lipoic acid treatment. The study has highlighted the beneficial effects of lipoic acid against experimental aminoglycoside toxicity in rats rendered bacteremic.

Alpha lipoic acid changes iron uptake and storage in lens epithelial cells

Alpha lipoic acid (LA) is a cofactor in mitochondrial dehydrogenase complexes. Previous studies have shown that when administered exogenously LA has antioxidant properties, which include free radical scavenging, metal chelation and regeneration of other antioxidants. The cells convert LA into dihydroplipoic acid (DHLA), which in the presence of iron can act as a prooxidant. In vitro DHLA reduces Fe(+3) to Fe(+2) and removes iron from ferritin, increasing the risk of Fe catalyzed free radical formation. In the present study we examined the in vivo effects of lipoic acid treatment on Fe metabolism in cultured lens epithelial cells, and found that LA decreases Fe uptake from transferrin, increases Fe deposition into ferritin and increases the concentration of this protein. When administered together with ascorbic acid, lipoic acid changes the characteristic heavy to light chain ratio of ferritin makeup. The decreased Fe uptake and increased storage diminishes the size of the cytosolic highly reactive Fe pool (LIP). These changes are associated with increased cell resistance to H(2)O(2) challenge. Therefore, LA may reduce the risk of Fe induced oxidative damage and also might be useful as a treatment of Fe overload.

Interactions of lipoic acid radical cations with vitamins C and E analogue and hydroxycinnamic acid derivatives

As a powerful natural antioxidant, lipoic acid exerts significant antioxidant activities in vivo and in vitro by deactivation of reactive oxygen and nitrogen species. In this study we present a novel synergistic interaction of lipoic acid with other endogenous or exogenous antioxidants. Antioxidants vitamins C and E analogue (Trolox C) and hydroxycinnamic acid derivatives were found to recycle lipoic acid by donating electrons to lipoic acid radical cations, thereby increasing the antioxidant capacity of lipoic acid in vivo and in vitro. The rate constant of the electron transfer is in the order 10(9)dm(3)mol(-1)s(-1), close to the diffusion-controlled limit, and transfer quantum yield is above 95%.

The toxicity of antioxidants and their metabolites

Antioxidants are used on a very large scale to try to obtain and preserve optimal health. Nutraceuticals and food supplements frequently contain huge dosages of antioxidants. It is not generally recognised that high intake of antioxidants may also have adverse effects. Three antioxidants i.e. vitamin E, β-carotene and lipoic acid are used to illustrate general considerations on the toxicity of antioxidants. Based on the examples the following recommendations for the evaluation of the toxicity of antioxidants are made: (i) classical safety factors should not be used. (ii) Knowledge on the mechanism of the efficacy and toxicity of antioxidants should be increased. (iii) Bio-kinetic/bio-efficacy modelling might be of help to optimise dosage. (iv) When antioxidant supplementation changes into therapy, a more accurate risk/benefit analyses is warranted.

Mitigation of free radical toxicity in hyperoxaluric condition by a novel derivative eicosapentaenoate-lipoate

Lipoic acid (LA) and eicosapentaenoic acid (EPA) have been shown to ameliorate the changes associated with hyperoxaluria. This prompted us to study the effect of EPA-LA, a new derivative, in experimental urolithiatic condition. Foreign body implantation method followed by supplementation of ammonium oxalate was adopted to induce stone formation in the bladder. Significant depletion in the antioxidant status was observed in the kidney and bladder of stone-forming animals, associated with increased lipid peroxidation. The present observations provide supporting evidence to the hypothesis that free radicals might be involved in causing toxicity in hyperoxaluric condition. The three drugs, namely LA, EPA and EPA-LA had reversed the above changes, but the effect was more pronounced in EPA-LA-treated stone formers. These features highlight the beneficial effect of EPA-LA wherein the potency of two drugs has been combined. The practical outcome of these findings is that the cellular antioxidant defence can be increased by the supplementation of lipoate and its derivative EPA-LA.

Lipoic acid confers protection against oxidative injury in non-neuronal and neuronal tissue

In the past decade or so, a convincing link between oxidative stress and degenerative conditions has been made and with the knowledge that oxidatiye changes may actually trigger deterioration in cell function, a great deal of energy has focussed on identifying agents which may have possible therapeutic value in combating oxidative changes. One agent which has received attention, because of its powerful antioxidative effects, particularly in neuronal tissue, is lipoic acid.

Exploring the interest of 1,2-dithiolane ring system in peptide chemistry. Synthesis of a chemotactic tripeptide and x-ray crystal structure of a 4-amino-1,2-dithiolane-4-carboxylic acid derivative

Due to their relevant biological functions and specific chemical reactivity 1,2-dithiolanes (five-membered cyclic disulfides) represent an emerging class of heterocyclic compounds. However, despite the extensive research centered on lipoic acid and its analogues, only very few data are at the present available on peptides containing this ring system. We report here synthesis, conformation and bioactivity of a fMLF-OMe analogue, namely For-Met-Adt-Phe-OMe (7), in which the residue of the 4-amino-1,2-dithiolane-4-carboxylic acid (Adt) (4) replaces the central L-leucine. The crystal conformation of the synthetic intermediate Boc-Adt-OMe (5) is also described and compared to that of lipoic acid (R-1,2-dithiolane-3-pentanoic acid) (3) and asparagusic acid (1,2-dithiolane-4-carboxylic acid) (2).

Sulfur-centered radical formation from the antioxidant dihydrolipoic acid

Lipoic acid and its reduced form, dihydrolipoic acid, are thought to be strong antioxidants. There are also reports of dihydrolipoic acid acting as a pro-oxidant under certain circumstances. This article reports the direct observation by ESR spectrometry of the disulfide radical anion and the spin trapping of the primary thiyl radical formed from the oxidation of dihydrolipoic acid through thiol pumping with phenol and horseradish peroxidase. The disulfide radical anion reacts rapidly with oxygen to form the reactive radical superoxide, which is also trapped. The radical species formed show a potential for pro-oxidant activity of this compound. Although antioxidants, in general, have been shown to have pro-oxidant potential, the pro-oxidant chemistry of dihydrolipoic acid has not been well characterized.

Alpha-lipoic acid inhibits TNF-alpha-induced NF-kappaB activation and adhesion molecule expression in human aortic endothelial cells

Endothelial activation and monocyte adhesion are initiating steps in atherogenesis thought to be caused in part by oxidative stress. The metabolic thiol antioxidant alpha-lipoic acid has been suggested to be of therapeutic value in pathologies associated with redox imbalances. We investigated the role of (R)-alpha-lipoic acid (LA) vs. glutathione and ascorbic acid in tumor necrosis factor alpha (TNF-alpha) -induced adhesion molecule expression and nuclear factor kappaB (NF-kappaB) signaling in human aortic endothelial cells (HAEC). Preincubation of HAEC for 48 h with LA (0.05-1 mmol/l) dose-dependently inhibited TNF-alpha (10 U/ml) -induced adhesion of human monocytic THP-1 cells, as well as mRNA and protein expression of E-selectin, vascular cell adhesion molecule 1 and intercellular adhesion molecule 1. LA also strongly inhibited TNF-alpha-induced mRNA expression of monocyte chemoattractant protein-1 but did not affect expression of TNF-alpha receptor 1. Furthermore, LA dose-dependently inhibited TNF-alpha-induced IkappaB kinase activation, subsequent degradation of IkappaB, the cytoplasmic NF-kappaB inhibitor, and nuclear translocation of NF-kappaB. In contrast, TNF-alpha-induced NF-kappaB activation and adhesion molecule expression were not affected by ascorbic acid or by manipulating cellular glutathione status with l-2-oxo-4-thiazolidinecarboxylic acid, N-acetyl-l-cysteine, or d,l-buthionine-S,R-sulfoximine. Our data show that clinically relevant concentrations of LA, but neither vitamin C nor glutathione, inhibit adhesion molecule expression in HAEC and monocyte adhesion by inhibiting the IkappaB/NF-kappaB signaling pathway at the level, or upstream, of IkappaB kinase.

Monitoring diabetic antioxidant status: a role for in vitro methaemoglobin formation

Diabetes leads to premature organ and system failure and considerably shortens lifespan. Careful control of glucose levels may not be enough to prevent the onset of complications in most diabetics. Compared with non-diabetics, diabetic tissues must not only resist a much greater long-term threat from hyperglycaemia-mediated reactive species but also defend themselves with compromised antioxidant systems. Although antioxidant therapy is a logical step in the prevention of oxidant and carbonyl stresses in the face of intermittent hyperglycaemia, this approach is not yet universally accepted to be effective in preventing complications. Although there are many biochemical indices of oxidant stress, piecemeal elevations of individual markers may not necessarily reflect true diabetic cellular antioxidant status. A dynamic process such as in vitro methaemoglobin generation may provide an opportunity to compare the response of a diabetic erythrocyte with that of a non-diabetic before and after corrective antioxidant therapy. Due to compromised cellular antioxidant capacity, diabetic cells generate less methaemoglobin in the presence of aromatic amine hydroxylamines, 4-aminophenol and nitrite compared with non-diabetics. Agents such as dihydrolipoic acid have been shown to correct methaemoglobin formation-mediated thiol deficits during in vitro studies. It is hoped that the progress of antioxidant supplementation studies in diabetics can be monitored with the aid of in vitro methaemoglobin generation using agents such as hydroxylamines, 4-aminophenol and nitrite. The most appropriate antioxidants and dosages can thus be recommended to diabetics worldwide to attenuate the development of complications.

Use of in vitro methaemoglobin generation to study antioxidant status in the diabetic erythrocyte

Poor glycaemic control in diabetes and a combination of oxidative, metabolic, and carbonyl stresses are thought to lead to widespread non-enzymatic glycation and eventually to diabetic complications. Diabetic tissues can suffer both restriction in their supply of reducing power and excessive demand for reducing power. This contributes to compromised antioxidant status, particularly in the essential glutathione maintenance system. To study and ultimately correct deficiencies in diabetic glutathione maintenance, an experimental model would be desirable, which would provide in vitro a rapid, convenient, and dynamic reflection of the performance of diabetic GSH antioxidant capacity compared with that of non-diabetics. Xenobiotic-mediated in vitro methaemoglobin formation in erythrocytes drawn from diabetic volunteers is significantly lower than that in erythrocytes of non-diabetics. Aromatic hydroxylamine-mediated methaemoglobin formation is GSH-dependent and is indicative of the ability of an erythrocyte to maintain GSH levels during rapid thiol consumption. Although nitrite forms methaemoglobin through a complex GSH-independent pathway, it also reveals deficiencies in diabetic detoxification and antioxidant performance compared with non-diabetics. Together with efficient glycaemic monitoring, future therapy of diabetes may include trials of different antiglycation agents and antioxidant combinations. Equalization in vitro of diabetic methaemoglobin generation with that of age/sex-matched non-diabetic subjects might provide an early indication of diabetic antioxidant status improvement in these studies.

Differential regulation of MAP kinase signaling by pro- and antioxidant biothiols

Some biologically derived thiol-containing compounds have potential for health benefits whereas others elicit biochemical events leading to pathogenesis. Effects of two biothiols, alpha-lipoic acid (alpha LA), a therapeutic antioxidant, and homocysteine (Hcy), a risk factor for age-associated cardiovascular disease, on cell signaling events involving p44 and p42 MAP kinases (p44/42 MAPK) were evaluated in cell culture. Treatment of serum-deprived NIH/3T3 cells with Hcy (20 microM) resulted in the activation of p44/42 MAPK as determined by Western blot analysis using the phospho-specific p44/42 MAPK antibody. p44/42 MAPK phosphorylation was rapid and transient with maximal activation occurring at 10-30 min. Transient activation of p44/42 MAPK was also observed in response to treatment of serum-deprived cells with alpha LA. In cells grown in serum, serum-dependent p44/42 MAPK phosphorylation was transiently enhanced by Hcy or Hcy thiolactone, but inhibited by alpha LA. Thus, alpha LA and Hcy differentially influence signal transduction events depending on the state of cells. These observations may be important in understanding how some biothiols are associated with pathogenic events while others have potential as therapeutic agents.

Synthesis of benzylideneacetophenones and their inhibition of lipid peroxidation

A series of benzylideneacetophenone derivatives have been synthesized and found to show potent inhibition of the lipid peroxidation (LPO) in rat liver microsomes. All 19 compounds prepared in this series are LPO inhibitors. The highest activity was found in para hydroxy derivatives with two meta tert-butyl substituents.

Antioxidant lipoate and tissue antioxidants in aged rats

Oxidative metabolism produces free radicals that must be removed from the cellular environment for the cell to survive. The levels of nonenzymic antioxidants involved in the elimination of free radicals were investigated in an attempt to correlate any changes in the levels of enzymic antioxidants during aging with changes in free radical mediated cellular damage. Antioxidants were measured in liver and kidney of young and aged rats with respect to DL-alpha-lipoic acid supplemented rats. In both organs lipid peroxidation damage (a marker of free radical mediated damage) increased with age, and a significant decrease in antioxidant systems was observed. Moreover, DL-alpha-lipoic acid treated aged rats showed a decrease in the level of lipid peroxides and an increase in the antioxidant status. The results of this study provide evidence that DL-alpha-lipoic acid treatment can improve antioxidants during aging and minimize the age-associated disorders in which free radicals are the major cause.

Effects of oxidised alpha-lipoic acid and alpha-tocopherol on xenobiotic-mediated methaemoglobin formation in diabetic and non-diabetic human erythrocytes in-vitro

The effects of oxidised alpha-lipoic acid and alpha-tocopherol were investigated on a human erythrocytic in vitro model of diabetic metabolic stress. Preincubation of non-diabetic and diabetic erythrocytes with oxidised alpha-lipoic acid or alpha-tocopherol resulted in marked increases in nitrite-mediated methaemoglobin formation. In contrast, oxidised alpha-lipoic acid resulted in considerable reductions in 4-aminophenol-mediated methaemoglobin formation in both diabetic and non-diabetic cells. alpha-Tocopherol showed an increase only in diabetic cells, at one time point. Monoacetyl dapsone hydroxylamine (MADDS-NHOH)-mediated methaemoglobin formation was reduced by oxidised alpha-lipoic acid in non-diabetic and diabetic cells at all three time points, although alpha-tocopherol had no effect with MADDS-NHOH. In diabetic cells only, alpha-tocopherol incubation caused a reduction in GSH levels compared with non-diabetic cells. As the agents showed pro- as well as anti-oxidant effects in this study, further studies are required to demonstrate potential diabetic benefit from alpha-lipoic acid adminstration.

Activities of glucose-metabolizing enzymes in experimental neurotoxic models with lipoate as an alleviator

Acrylamide (35 mg kg(-1) body wt, i.p.) and mercuric chloride (1 mg kg(-1)body wt, i.m.) were administered as specific and non-specific toxins, respectively, to induce neurotoxicity in rats for a period of 10 days. Two different concentrations (35 and 70 mg kg(-1) body wt, i.p.) of lipoic acid were given as prophylactic therapy to mitigate the toxic neuropathies. Homogenates of cerebrum, cerebellum and sciatic nerves were used for the determination of the activities of glyceraldehyde-3-phosphate dehydrogenase (GAPDH), neuron-specific enolase (NSE), hexokinase, phosphoglucoisomerase, aldolase and glucose-6-phosphatase. Inhibition of the activities of these glucose-metabolizing enzymes by the neurotoxins emphasizes the reduction in glucose utilization by the neural tissues to impart its normal function. The degree of inhibition of the enzymes varies with both of the toxins. Acrylamide seems to be a specific inhibitor of GAPDH and NSE, whereas the inhibition caused by HgCl(2) on the enzymes was more general. Enhanced activities of the enzymes indicate increased glucose utility on lipoate administration. This result may be due to the detoxifying potency and possibly due to the cofactor vitality of lipoate.

Attenuation of aminoglycoside-induced cochlear damage with the metabolic antioxidant alpha-lipoic acid

Free radical generation is increasingly implicated in a variety of pathological processes, including drug toxicity. Recently, a number of studies have demonstrated the ability of gentamicin to facilitate the generation of radical species both in vivo and in vitro, which suggests that this process plays an important role in aminoglycoside-induced ototoxicity. Free radical scavengers are compounds capable of inactivating free radicals, thereby attenuating their tissue damaging capacity. In this study we have determined the ability of the powerful free radical scavenger alpha-lipoic acid (100 mg/kg/day) to attenuate the cochlear damage induced by a highly ototoxic regimen of the aminoglycoside amikacin (450 mg/kg/day, i.m.). Experiments were carried out on pigmented guinea pigs initially weighing 200-250 g. Changes in cochlear function were characterized as shifts in compound action potential (CAP) thresholds, estimated every 5 days, by use of chronic indwelling electrodes implanted at the round window, vertex, and contralateral mastoid. Results showed that animals receiving alpha-lipoic acid in combination with amikacin demonstrated a significantly less severe elevation in CAP thresholds compared with animals receiving amikacin alone (P < 0.001; t-test). These results provide further evidence of the recently reported intrinsic role of free radical generation in aminoglycoside ototoxicity, and highlight a potential clinical therapeutic use of alpha-lipoic acid in the management of patients undergoing aminoglycoside treatment.

Homocysteine and alpha-lipoic acid regulate p44/42 MAP kinase phosphorylation in NIH/3T3 cells

Biological thiols can regulate cell signal transduction. The effects of two biothiols, homocysteine (Hcy), a risk factor for cardiovascular disease, and alpha-lipoic acid (alphaLA), a therapeutic antioxidant, on p44/42 mitogen-activated protein kinases (MAPK) phosphorylation were examined in NIH/3T3 fibroblasts. Cells grown in serum-containing media had constitutive levels of MAPK phosphorylation as determined by Western blot analysis using the phospho-specific MAPK antibody. Treatment of cells with 20 microM Hcy for 0-60 min resulted in a transient enhancement of MAPK phosphorylation. In contrast, 20 microM alphaLA inhibited serum-mediated phosphorylation of MAPK. The differential effects of these two thiols are not due to their redox states as oxidized Hcy (Hcy thiolactone) enhanced MAPK phosphorylation. The effect of alphaLA appears to be serum-dependent because Hcy or alphaLA treatment of serum-deprived cells activated MAPK phosphorylation. Thus, alphaLA and Hcy can either induce common signal transduction pathways or differentially modulate MAPK phosphorylation, depending on the state of the cell. This relationship may be important to understand how some biothiols are associated with pathogenic events while others offer potential as therapeutic agents.

Chromatographic analysis of lipoic acid and related compounds

The analysis of lipoic acid and related compounds, such as its reduced form dihydrolipoic acid, its amide form lipoamide and other analogues, in biological and food samples is important in biochemistry, nutritional and clinical chemistry. This review summarizes the chromatographic methods for the determination of lipoic acid and related compounds, and their applications to various samples such as bacteria, tissues, drugs and food. Gas chromatographic methods with flame ionization detection and flame photometric detection are commonly used for the quantification of lipoic acid present as its protein-bound form, after acid or base hydrolysis of these samples. High-performance liquid chromatographic methods with ultraviolet, fluorescence and electrochemical detection are mainly used for the determination of free lipoic acid and related compounds, such as dihydrolipoic acid, lipoamide and other analogues. Moreover, gas chromatography-mass spectrometry and capillary electrophoresis methods are also developed.

Rickettsia rickettsii infection of the EA.hy 926 endothelial cell line: morphological response to infection and evidence for oxidative injury

EA.hy 926 is a permanent human cell line that expresses highly differentiated functions characteristic of human vascular endothelium. Rickettsia rickettsii can efficiently infect and cause a cytopathic effect in EA.hy 926 cells. R. rickettsii produced visible lytic plaques in EA.hy 926 cells at 10 d post-infection (p.i.) following application of a secondary agarose overlay containing 2 micrograms emetine ml-1 and 40 micrograms NaF ml-1 on day 2. Rickettsial growth in EA.hy 926 cells had a similar profile to that occurring in human umbilical vein endothelial cells (HUVEC) and rickettsiae catalysed polymerization of actin tails. Intracellular multiplication of R. rickettsii resulted in significant changes in the internal morphology of EA.hy 926 cells, most notably extensive dilatation of the membranes of the endoplasmic reticulum and outer nuclear envelope by 72 h p.i. These events correlated with significant alterations in the host-cell antioxidant system, including decreased levels of intracellular reduced glutathione and glutathione peroxidase activity and increased amounts of intracellular peroxide through to 96 h of infection. These findings are similar to the changes described previously for R. rickettsii-infected HUVEC and suggest that common mechanisms associated with rickettsia-induced oxidative injury occur in the two cell lines. EA.hy 926 cells were also used to investigate the influence of the antioxidant alpha-lipoic acid on rickettsial infection. Overnight pretreatment with 1-500 microM alpha-lipoic acid did not prevent cells from being destroyed following infection with rickettsiae. Supplementation of the culture medium with 1 and 10 microM alpha-lipoic acid 2 h after rickettsial inoculation also did not provide any protective effect. However, 100, 200 and 500 microM alpha-lipoic acid increased the viability of infected cells at 96 h to 45, 51 and 70%, respectively compared with 26% for untreated, infected samples. Thiol levels and glutathione peroxidase activity in treated, infected cells increased and peroxide content decreased proportionally to increasing alpha-lipoic acid concentrations. Furthermore, treatment with 500 microM alpha-lipoic acid for 72 h p.i. completely prevented ultrastructural changes in infected cells. In conclusion, the permanent endothelial cell line EA.hy 926 is susceptible to injury induced by R. rickettsii infection. Although the cellular changes resulting from infection are not identical in all aspects to that demonstrated previously in HUVEC, the increased reproducibility and convenience of EA.hy 926 cells make them suitable for biochemical and morphological studies.

Specific reduction of insulin disulfides by macrophage migration inhibitory factor (MIF) with glutathione and dihydrolipoamide: potential role in cellular redox processes

The molecular mechanism of action of MIF, a cytokine that plays a critical role in the host immune and inflammatory response, has not yet been identified. We recently demonstrated that MIF is an enzyme that exhibits oxidoreductase activity by a cysteine thiol-mediated mechanism. Here we further investigated this function by examining the reduction of insulin disulfides by wild-type human MIF (wtMIF) using various substrates, namely glutathione (GSH), dihydrolipoamide, L-cysteine, beta-mercaptoethanol and dithiothreitol. The activity of wtMIF was compared to that of the relevant cysteine mutants of MIF and to two carboxy-truncated mutants. Only GSH and dihydrolipoamide were found to serve as reductants, whereas the other substrates were not utilized by MIF. Reduction of insulin disulfides by MIF was closely dependent on the presence of the Cys57-Ala-Leu-Cys60 (CALC) motif-forming cysteines C57 and C60, whereas C81 was not involved (activities: 51+/-13%, 14+/-5%, and 70+/-12% of wtMIF, respectively, and 20+/-3% for the double mutant C57S/C60S). Confirming the notion that the activity of MIF was dependent on the CALC motif in the central region of the MIF sequence, the C-terminal deletion mutants MIF(1-105) and MIF(1-110) were found to be fully active. The favored use of GSH and dihydrolipoamide indicated that MIF may be involved in the regulation of cellular redox processes and was supported further by the finding that MIF expression by the cell lines COS-1 and RAW 264.7 was significantly induced upon treatment with the oxidant hydrogen peroxide.

Effects of the antioxidant alpha-lipoic acid on human umbilical vein endothelial cells infected with Rickettsia rickettsii

Rickettsia rickettsii infection of endothelial cells is manifested in very distinctive changes in cell morphology, consisting of extensive dilatation of the membranes of the endoplasmic reticulum and outer nuclear envelope and blebbing of the plasma membrane, as seen by transmission electron microscopy (D. J. Silverman, Infect. Immun. 44:545-553, 1984). These changes in cellular architecture are thought to be due to oxidant-mediated cell injury, since their occurrence correlates with dramatic alterations in cellular metabolism, particularly with regard to antioxidant systems. In this study, it was shown that R. rickettsii infection of human umbilical vein endothelial cells resulted in a significant depletion of intracellular reduced glutathione (thiol) content at 72 and 96 h and decreased glutathione peroxidase activity at 72 h postinfection. Infected cells displayed a dramatic increase in the concentration of intracellular peroxides by 72 h. Supplementation of the cell culture medium with 100, 200, or 500 microM alpha-lipoic acid, a metabolic antioxidant, after inoculation with R. rickettsii restored the intracellular levels of thiols and glutathione peroxidase and reduced the intracellular peroxide levels in infected cells. These effects were dose dependent. Treated infected monolayers maintained better viability at 96 h after inoculation with R. rickettsii than did untreated infected cells. Moreover, supplementation of the cell culture medium with 100 microM alpha-lipoic acid for 72 h after infection prevented the occurrence of morphological changes in the infected cells. The presence of 100 or 200 microM alpha-lipoic acid did not influence rickettsial growth in endothelial cells, nor did it affect the ability of R. rickettsii to form lytic plaques in Vero cells. Treatment with 500 microM alpha-lipoic acid decreased by 50% both the number and size of lytic plaques in Vero cells, and it also decreased the recovery of viable rickettsiae from endothelial cells. However, under all treatment conditions, a significant number of rickettsiae could be detected microscopically. Furthermore, the rickettsiae apparently retained their capacity for intracellular movement, since they possessed long polymerized actin tails after 72 and 96 h of treatment regardless of the concentration of alpha-lipoic acid used. Since alpha-lipoic acid does not seem to exhibit direct antirickettsial activity except with long-term exposure at very high concentrations, the mechanism of its protective activity for endothelial cells infected with rickettsiae may involve complex changes in cellular metabolism that only indirectly affect rickettsiae.

alpha-Lipoic acid: a metabolic antioxidant which regulates NF-kappa B signal transduction and protects against oxidative injury

Although the metabolic role of alpha-lipoic acid has been known for over 40 years, it is only recently that its effects when supplied exogenously have become known. Exogenous alpha-lipoic acid is reduced intracellularly by at least two and possibly three enzymes, and through the actions of its reduced form, it influences a number of cell process. These include direct radical scavenging, recycling of other antioxidants, accelerating GSH synthesis, and modulating transcription factor activity, especially that of NF-kappa B (Fig. 12). These mechanisms may account for the sometimes dramatic effects of alpha-lipoic acid in oxidative stress conditions (e.g., brain ischemia-reperfusion), and point the way toward its therapeutic use.

Assay of protein-bound lipoic acid in tissues by a new enzymatic method

A new enzymatic method for the determination of protein-bound lipoic acid was established. Bound lipoyl groups were liberated in the form of lipoyllysine by protease digestion and assayed by lipoamide dehydrogenase (NADH:lipoamide oxidoreductase, EC 1.8.1.4)-mediated NADH oxidation. NADH oxidation was coupled to reduction of the lipoyl disulfide group. Fluorescence kinetics of NADH oxidation were markedly enhanced by the addition of glutathione disulfide, recycling the enzyme-mediated lipoyl/dihydrolipoyl conversion. In the presence of a large excess of glutathione disulfide, NADH oxidation follows pseudo-first-order kinetics in terms of lipoyllysine concentration. A good linear correlation is obtained between the oxidation rate and lipoyllysine concentration up to 5 microM and the calibration curve indicates that the detection limit could be 100 nM lipoyllysine. The method was applied to protease lysates of bovine, rat, and rabbit tissues to determine lipoyllysine levels. Kidney and liver were found to have the highest content of lipoyllysine in the range of 3.9 to 4.6 nmol/g rat or rabbit wet tissue or 11.6 to 13.1 nmol/g bovine acetone powder.

The b-wave of the electroretinogram as an index of retinal ischemia

1. The b-wave of the electroretinogram (ERG) is a particularly sensitive index of retinal ischemia. The present paper summarizes the changes in the b-wave observed in five in vivo models of retinal ischemia. 2. Although the amount of reduction in b-wave amplitude during ischemia corresponds to the severity of the insult, the degree of recovery of the b-wave during reperfusion depends on the duration of ischemia. 3. A massive release of glutamate, intracellular overload with calcium and enhanced production of free radicals are suggested to be three major pathophysiological processes that contribute to retinal ischemic damage. The b-wave of the ERG represents a functional measure for potential therapeutic efficacy of drugs interacting with these pathophysiological processes. 4. Several glutamate antagonists, such as MK-801, memantine, flupirtine or GYKI 52466, along with the free radical scavengers vitamin E, lipoate, superoxide dismutase and catalase, all reduce the depression of the b-wave during ischemia or accelerate the recovery of the b-wave during reperfusion or both. The calcium channel antagonists nimodipine and levemopamil exert only a slight beneficial effect on the recovery of the amplitude of the b-wave during reperfusion, provided that the blood pressure is not potently reduced.

The lipoic acid analogue 1,2-diselenolane-3-pentanoic acid protects human low density lipoprotein against oxidative modification mediated by copper ion

1,2-Diselenolane-3-pentanoic acid, in which the sulfur atoms of alpha-lipoic acid are replaced with selenium, displayed markedly different antioxidant properties when compared to alpha-lipoic acid. 1,2-Diselenolane-3-pentanoic acid was unable to inhibit protein oxidative modification of human low density lipoprotein (LDL) and bovine serum albumin induced by copper ion or hydroxyl radical, whereas alpha-lipoic acid showed significant protection. However, 1,2-diselenolane-3-pentanoic acid was able to inhibit the formation of lipid peroxidation products in LDL after oxidation by copper, while alpha-lipoic acid did not. Hence the diselenium compound exerts its effects in a lipophilic environment whilst lipoic acid exerts its effects in a hydrophilic environment. These differences in antioxidant activities of the two compounds may be explained, at least in part, by their differing partition coefficients.

The pharmacology of the antioxidant lipoic acid

1. Lipoic acid is an example of an existing drug whose therapeutic effect has been related to its antioxidant activity. 2. Antioxidant activity is a relative concept: it depends on the kind of oxidative stress and the kind of oxidizable substrate (e.g., DNA, lipid, protein). 3. In vitro, the final antioxidant activity of lipoic acid is determined by its concentration and by its antioxidant properties. Four antioxidant properties of lipoic acid have been studied: its metal chelating capacity, its ability to scavenge reactive oxygen species (ROS), its ability to regenerate endogenous antioxidants and its ability to repair oxidative damage. 4. Dihydrolipoic acid (DHLA), formed by reduction of lipoic acid, has more antioxidant properties than does lipoic acid. Both DHLA and lipoic acid have metal-chelating capacity and scavenge ROS, whereas only DHLA is able to regenerate endogenous antioxidants and to repair oxidative damage. 5. As a metal chelator, lipoic acid was shown to provide antioxidant activity by chelating Fe2+ and Cu2+; DHLA can do so by chelating Cd2+. 6. As scavengers of ROS, lipoic acid and DHLA display antioxidant activity in most experiments, whereas, in particular cases, pro-oxidant activity has been observed. However, lipoic acid can act as an antioxidant against the pro-oxidant activity produced by DHLA. 7. DHLA has the capacity to regenerate the endogenous antioxidants vitamin E, vitamin C and glutathione. 8. DHLA can provide peptide methionine sulfoxide reductase with reducing equivalents. This enhances the repair of oxidatively damaged proteins such as alpha-1 antiprotease. 9. Through the lipoamide dehydrogenase-dependent reduction of lipoic acid, the cell can draw on its NADH pool for antioxidant activity additionally to its NADPH pool, which is usually consumed during oxidative stress. 10. Within drug-related antioxidant pharmacology, lipoic acid is a model compound that enhances understanding of the mode of action of antioxidants in drug therapy.

Lipoic acid reduces glycemia and increases muscle GLUT4 content in streptozotocin-diabetic rats

Alpha lipoic acid (lipoate [LA]), a cofactor of alpha-ketodehydrogenase, exhibits unique antioxidant properties. Recent studies suggest a direct effect of LA on glucose metabolism in both human and experimental diabetes. This study examines the possibility that LA positively affects glucose homeostasis in streptozotocin (STZ)-induced diabetic rats by altering skeletal muscle glucose utilization. Blood glucose concentration in STZ-diabetic rats following 10 days of intraperitoneal (i.p.) injection of LA 30 mg/kg was reduced compared with that in vehicle-treated diabetic rats (495 +/- 131 v 641 +/- 125 mg/dL in fed state, P = .003, and 189 +/- 48 v 341 +/- 36 mg/dL after 12-hour fast, P = .001). No effect of LA on plasma insulin was observed. Gastrocnemius muscle crude membrane GLUT4 protein was elevated both in control and in diabetic rats treated with LA by 1.5- and 2.8-fold, respectively, without significant changes in GLUT4 mRNA levels. Gastrocnemius lactic acid was increased in diabetic rats (19.9 +/- 5.5 v 10.4 +/- 2.8 mumol/g muscle, P < .05 v nondiabetic rats), and was normal in LA-treated diabetic rats (9.1 +/- 5.0 mumol/g muscle). Insulin-stimulated 2-deoxyglucose (2 DG) uptake into isolated soleus muscle was reduced in diabetic rats compared with the control group (474 +/- 15 v 568 +/- 52 pmol/mg muscle 30 min, respectively, P = .05). LA treatment prevented this reduction, resulting in insulin-stimulated glucose uptake comparable to that of nondiabetic animals. These results suggest that daily LA treatment may reduce blood glucose concentrations in STZ-diabetic rats by enhancing muscle GLUT4 protein content and by increasing muscle glucose utilization.

Neuroprotection by the metabolic antioxidant alpha-lipoic acid

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.

Cytosolic and mitochondrial systems for NADH- and NADPH-dependent reduction of alpha-lipoic acid

In cellular, tissue, and organismal systems, exogenously supplied alpha-lipoic acid (thioctic acid) has a variety of significant effects, including direct radical scavenging, redox modulation of cell metabolism, and potential to inhibit oxidatively-induced injury. Because reduction of lipoate to dihydrolipoate is a crucial step in many of these processes, we investigated mechanisms of its reduction. The mitochondrial NADH-dependent dihydrolipoamide dehydrogenase exhibits a marked preference for R(+)-lipoate, whereas NADPH-dependent glutathione reductase shows slightly greater activity toward the S(-)-lipoate stereoisomer. Rat liver mitochondria also reduced exogenous lipoic acid. The rate of reduction was stimulated by substrates which increased the NADH content of the mitochondria, and was inhibited by methoxyindole-2-carboxylic acid, a dihydrolipoamide dehydrogenase inhibitor. In rat liver cytosol, NADPH-dependent reduction was greater than NADH, and lipoate reduction was inhibited by glutathione disulfide. In rat heart, kidney, and brain whole cell-soluble fractions, NADH contributed more to reduction (70-90%) than NADPH, whereas with liver, NADH and NADPH were about equally active. An intact organ, the isolated perfused rat heart, reduced R-lipoate six to eight times more rapidly than S-lipoate, consistent with high mitochondrial dihydrolipoamide dehydrogenase activity and results with isolated cardiac mitochondria. On the other hand, erythrocytes, which lack mitochondria, somewhat more actively reduced S- than R-lipoate. These results demonstrate differing stereospecific reduction by intact cells and tissues. Thus, mechanisms of reduction of alpha-lipoate are highly tissue-specific and effects of exogenously supplied alpha-lipoate are determined by tissue glutathione reductase and dihydrolipoamide dehydrogenase activity.

The isomers of thioctic acid alter C-deoxyglucose incorporation in rat basal ganglia

Nigral cell death in Parkinson's disease is associated with decreased reduced glutathione (GSH) levels, impaired complex I activity and inhibition of alpha-ketoglutarate dehydrogenase (alpha-KGDH) in substantia nigra. Thioctic acid exerts antioxidant activity through a thiol-disulphide redox couple and is an essential cofactor for alpha-KGDH. However, it is not known whether or not thioctic acid enters basal ganglia or exerts beneficial effects in Parkinson's disease. As a global measure of altered cerebral function, the effect of R- and S-thioctic acid on 14C-2-deoxyglucose (14C-2DG) incorporation was investigated in rats. Rats were treated with either R- or S-thioctic acid (50 mg/kg IP) or 0.9% saline acutely or for 5 days and 14C-2DG incorporation in basal ganglia was assessed. Following acute administration, R- but not S-thioctic acid caused an overall increase in 14C-2DG incorporation that was significant in both substantia nigra zona compacta and zona reticulata. R-thioctic acid also increased the incorporation of 14C-2DG in the medial forebrain bundle, thalamus, and red nucleus. S-thioctic acid decreased 14C-2DG incorporation in the subthalamic nucleus, but increased it in the red nucleus. Following repeated administration, R-thioctic acid no longer increased 14C-2DG incorporation in either zona compacta or zona reticulata of substantia nigra. However, both R- and S-thioctic acid now decreased 14C-2DG incorporation in the subthalamic nucleus. The data suggest that thioctic acid does enter the brain can alter neuronal activity in areas of the basal ganglia intimately associated with the motor deficits exhibited in Parkinson's disease.

Neuroprotective effects of alpha-lipoic acid and its enantiomers demonstrated in rodent models of focal cerebral ischemia

The purpose of this study was to investigate whether alpha-lipoic acid (LA), the oxidized form of the radical scavenger dihydrolipoic acid (DLA), protected brain tissue against ischemic damage and whether there were differences in the neuroprotective potencies between its enantiomers. We used the models of focal cerebral ischemia in mice and rats. The infarct area on the mouse brain surface and the infarct volume of the rat brain were determined by means of an image analyzing system. The LA was capable of reducing the infarct area only when it was administered subcutaneously, but not when it was administered intraperitoneally or into the cisterna magna. Both the R- and the S-enantiomer of LA protected brain tissue against ischemic damage, but their protective activities seemed to be related to the time period of pretreatment. In mice, both enantiomers revealed a similar neuroprotective potency when they were administered subcutaneously 1 or 2 hr before occlusion of the middle cerebral artery (MCA), whereas a longer time period of pretreatment (4 or 6 hr) failed to exert neuroprotection. In rats, subcutaneous pretreatment with R- or S-LA for 2 hr before ischemia significantly diminished the infarct volume. We assume that LA has to be reduced to DLA which finally causes neuroprotection.

Reduction of lipoic acid by lipoamide dehydrogenase

Racemic lipoic acid is therapeutically applied in pathologies in which free radicals are involved. The in vivo reduction of lipoic acid may play an essential role in its antioxidant effect. It was found that mitochondrial lipoamide dehydrogenase (LipDH, EC 1.8.1.4.) reduces the R-enantiomer 28 times faster than the S-enantiomer of lipoic acid. Moreover, it was observed that the metabolites of lipoic acid, bisnor-, tetranor-, and beta-lipoic acid are poor substrates of LipDH. S-lipoic acid inhibits the reduction of the R enantiomer only at relatively high concentrations. The reduction of R-lipoic acid by mitochondria-rich tissues may proceed smoothly, even if the racemic mixture is applied. This is of importance in elucidating the molecular mechanism of the pharmacotherapeutic effect of lipoic acid.

Alpha-lipoic acid: antioxidant potency against lipid peroxidation of neural tissues in vitro and implications for diabetic neuropathy

Nerve lipid peroxidation is increased in experimental diabetic neuropathy, and alpha-lipoic acid will prevent the deficits in nerve blood flow, oxidative stress, and distal sensory conduction. Because these alterations can occur by mechanisms other than augmenting lipid peroxidation in vivo, and because both pro-oxidant and antioxidant effects of the agent have been reported, we undertook studies of in vitro lipid peroxidation of brain and sciatic nerve using an in vitro lipid peroxidation model with an ascorbate-iron-EDTA system. We evaluated the effectiveness of the R(+)-, S(-)-enantiomers, and racemate of alpha-lipoic acid in reducing thiobarbituric acid reactive substances (TBARS) generation in rat brain and sciatic nerve. Studies were also done in an incubation medium containing 20 mM glucose, which increased lipid peroxidation up to fourfold. A dose-dependent and statistically significant reduction in lipid peroxidation was seen with both tissues with similar potencies for both enantiomers. This effect was unassociated with any reduction in the loss of alpha-tocopherol.

Oxidative processes and free radical scavengers in ischaemia-reperfusion injury in adipocutaneous flaps: in vitro lipid peroxidation assessment

An in vitro lipid peroxidation study measuring Schiff base and TBAR formation in homogenates of the fat and skin fractions of epigastric free flaps of DA-rats was performed to determine the role of oxygen-derived free radicals (ODFRs) in the aetiology of ischaemic injury and of ischaemia and reperfusion injury following cold (0-1 degree C) storage. The storage intervals were 0, 48, 72, 96 and 120 h in the study on ischaemic injury and 72 and 96 h in the study on combined ischaemia and reperfusion injury. Reperfusion was accomplished by anastomosing the pedicle vessels of the flap to the femoral vessels of a recipient; the reperfusion period was 15 min. In addition to a control group (C), three experimental groups were created to test the benefit of a preischaemic single passage perfusion with a hypertonic citrate solution (HCA), a pre- and postischaemic treatment with desferrioxamine (DFX) and a pre- and postischaemic treatment with lipoic acid (LA). The susceptibility of homogenates of skin and fat fractions of epigastric free flaps in DA-rats for lipid peroxidation increased significantly whenever the cold (0-1 degree C) ischaemic interval was prolonged from 0 to 72 h. These findings offer circumstantial evidence for the role of ODFRs in the aetiology of ischaemic injury. Following a short reperfusion period after extended periods of cold (0-1 degree C) ischaemia, no significant increase in susceptibility for lipid peroxidation could be found. Furthermore, no unequivocal role in the prevention of ischaemia and/or reperfusion injury by the use of either HCA, or DFX or LA could be found. The exact role of ODFRs in the aetiology of ischaemia-reperfusion injury in this setting remains unclear.

The free radical scavenger, alpha-lipoic acid, protects against cerebral ischemia-reperfusion injury in gerbils

alpha-Lipoic acid (thioctic acid) was tested for its neuroprotective activity in a Mongolian gerbil model of forebrain ischemia/reperfusion. Adult gerbils were treated for 7 days with two intraperitoneal injections per day of alpha-lipoic acid (20 mg/kg), vehicle or saline and on the 7th day the animals were subjected to 5 min of forebrain ischemia. Ischemic injury was assessed by monitoring the increases in locomotor activity and from the extent of damage to the CA1 hippocampal pyramidal cell layer after 5 days of recovery. By both criteria, alpha-lipoic acid was neuroprotective against ischemia/reperfusion evoked cerebral injury.