Thioctic acid protects against ischemia-reperfusion injury in the isolated perfused Langendorff heart

Effects of Lipoic Acid on Ischemia-Reperfusion Injury

Ischemia-reperfusion (I/R) injury often occurred in some pathologies and surgeries. I/R injury not only harmed to physiological functions of corresponding organ and tissue but also induced multiple tissue or organ dysfunctions (even these in distant locations). Although the reperfusion of blood attenuated I/R injury to a certain degree, the risk of secondary damages was difficult to be controlled and it even caused failures of these tissues and organs. Lipoic acid (LA), as an endogenous active substance and a functional agent in food, owns better safety and effects in our body (e.g., enhancing antioxidant activity, improving cognition and dementia, controlling weight, and preventing multiple sclerosis, diabetes complication, and cancer). The literature searching was conducted in PubMed, Embase, Cochrane Library, Web of Science, and SCOPUS from inception to 20 May 2021. It had showed that endogenous LA was exhausted in the process of I/R, which further aggravated I/R injury. Thus, supplements with LA timely (especially pretreatments) may be the prospective way to prevent I/R injury. Recently, studies had demonstrated that LA supplements significantly attenuated I/R injuries of many organs, though clinic investigations were short at present. Hence, it was urgent to summarize these progresses about the effects of LA on different I/R organs as well as the potential mechanisms, which would enlighten further investigations and prepare for clinic applications in the future.

Protective effect of green tea against neuro-functional alterations in rats treated with MnO2 nanoparticles

BACKGROUND

Inhalation of manganese-containing metal fumes at workplaces can cause central nervous damage including a Parkinson-like syndrome. Oxidative stress is likely to be involved in the pathomechanism, due to the presence of nano-sized metal oxide particles with high biological and chemical activity. Oxidative damage of the nervous system could be prevented or ameliorated by properly applied antioxidants, preferably natural ones such as green tea, a popular drink. The aim of this work was to see if orally applied green tea brew could diminish the functional neurotoxicity of manganese dioxide nanoparticles introduced into the airways of rats.

RESULTS

Young adult male Wistar rats were treated intratracheally for 6 weeks with a suspension of synthetic MnO₂ nanoparticles (4 mg/kg body weight), and received green tea brew (1 g leaves 200 mL^-1 water) as drinking fluid. Reduced body weight gain, indicating general toxicity of the nanoparticles, was not influenced by green tea. However, in rats receiving green tea the nervous system effects - changes in the spontaneous and evoked cortical activity and peripheral nerve action potential - were diminished.

CONCLUSION

The use of green tea as a neuroprotective functional drink seems to be a viable approach. © 2016 Society of Chemical Industry.

Impact of acute Cd²⁺ exposure on the antioxidant defence systems in the skin and red blood cells of common carp (Cyprinus carpio)

Cd(2+)-induced oxidative stress and its effects on the expression of stress biomarkers and on macromolecule damage in the skin and blood of common carp were studied. Both tissues play important roles in the defence mechanisms against external hazards, serving as an anatomical barrier and as connecting tissue between the organs. In the skin, the production of peroxynitrite anion and hydrogen peroxide was almost doubled after exposure to 10 mg/L Cd(2+). The accumulation of these oxidant molecules suggests an intensive production of superoxide anion and nitrogen monoxide and the development of oxidative and/or nitrosative stress. Although the metallothioneins and the components of the glutathione redox system were activated in the skin, the accumulation of reactive intermediates led to the enhanced damage of lipid molecules after 24 h of metal exposure. In the blood, the basal levels of metallothionein messenger RNAs (mRNAs) were 2-2.5-fold of that measured in the skin. This high level of metallothionein expression could be the reason that the blood was less affected by an acute Cd(2+) challenge and the metallothionein and glutathione systems were not activated.

Alpha-lipoic acid protects cardiomyocytes against hypoxia/reoxygenation injury by inhibiting autophagy

Hypoxia/reoxygenation (H/R) is an important in vitro model for exploring the molecular mechanisms and functions of autophagy during myocardial ischemia/reperfusion (I/R). Alpha-lipoic acid (LA) plays an important role in the etiology of cardiovascular disease. Autophagy is widely implicated in myocardial I/R injury. We assessed the degree of autophagy by pretreatment with LA exposed to H/R in H9c2 cell based on the expression levels of Beclin-1, LC3II/LC3I, and green fluorescent protein-labeled LC3 fusion proteins. Autophagic vacuoles were confirmed in H9c2 cells exposed to H/R using transmission electron microscopy. Our findings indicated that pretreatment with LA inhibited the degree of autophagy in parallel to the enhanced cell survival and decreased total cell death in H9c2 cells exposed to H/R. We conclude that LA protects cardiomyocytes against H/R injury by inhibiting autophagy.

Major distinctions in the antioxidant responses in liver and kidney of Cd(2+)-treated common carp (Cyprinus carpio)

This study is related to the accumulation of Cd(2+), its effects on oxidative stress biomarkers and its role in macromolecule damage in liver and kidney of common carp. We present evidence of an increased ratio of reduced to oxidized glutathione (GSH/GSSG) in both organs after 10 mg/L Cd(2+) exposure, with different underlying biological mechanisms and consequences. In the liver, the expressions and/or activities of superoxide dismutase, catalase, glutathione reductase and glutathione peroxidase increased to cope with the Cd(2+)-generated toxic effects during the first 48 h of treatment. In contrast, none of these selected antioxidant markers was significantly altered in the kidney, whereas the expression of glutathione synthetase was upregulated. These results suggest that the major defense mechanism provoked by Cd(2+) exposure involves the regeneration of GSH in the liver, while its de novo synthesis predominates in the kidney. High levels of accumulation of Cd(2+) and peroxynitrite anion (ONOO(-)) were detected in the kidney; the major consequences of ONOO(-) toxicity were enhanced lipid peroxidation and GSH depletion. The accumulation of ONOO(-) in the kidney suggests intensive production of NO and the development of nitrosative stress. In the liver the level of hydrogen peroxide was elevated.

Anti-apoptotic and neuroprotective effects of α-lipoic acid on spinal cord ischemia-reperfusion injury in rabbits

PURPOSE

Radical oxygen species produced after injury counteracts antioxidant activity and frequently causes severe oxidative stress for the tissues. Alpha-lipoic acid is a powerful metabolic antioxidant with immunomodulatory effects which provides neuroprotection. The aim of this study is to investigate the neuroprotective and anti-apoptotic effects of alpha-lipoic acid on spinal cord ischemia-reperfusion.

METHODS

Twenty-four adult, male, New Zealand rabbits were divided into sham (n = 8), control (n = 8), and treatment groups (n = 8). The abdominal aorta was clamped for 30 min by an aneurysm clip, approximately 1 cm below the renal artery and 1 cm above the iliac bifurcation in control and treatment groups. Only laparotomy was performed in the sham group. Twenty-five cubic centimeters of saline in control group and 100 mg/kg lipoic acid were administered intraperitoneally in the treatment group after closure of the incision. The animals were killed 48 h later. Spinal cord segments between L2 and S1 were harvested for analysis. Levels of nitric oxide, glutathione, malondialdehyde, advanced oxidation protein products, and superoxide dismutase were analyzed as markers of oxidative stress and inflammation. Caspase-3 activity was analyzed to detect the effect of lipoic acid on apoptosis.

RESULTS

In all measured parameters of oxidative stress, administration of lipoic acid significantly demonstrated favorable effects. Both plasma and tissue levels of nitric oxide, glutathione, malondialdehyde, and advanced oxidation protein products significantly changed in favor of antioxidant activity. There was no significant difference between the plasma superoxide dismutase levels of the groups. Histopathological evaluation of the tissues also demonstrated significant decrease in cellular degeneration and infiltration parameters after lipoic acid administration. However, lipoic acid has no effect on caspase-3 activity.

CONCLUSIONS

Although further studies considering different dose regimens and time intervals are required, the results of the present study prove that alpha-lipoic acid has favorable effects on experimental spinal cord ischemia-reperfusion injury.

Plasma protein oxidation in patients with brain tumors

OBJECTIVE

Proteins can undergo numerous covalent changes on exposure to oxidants. Oxidative modification of protein in vivo may affect a variety of cellular functions. Protein oxidation in vivo is a natural consequence of aerobic life. Oxygen radicals and other activated oxygen species generated as byproducts of cellular metabolism or from environmental sources cause modifications to the amino acids of proteins that generally result in loss of protein function/enzymatic activity. It is now well known that reactive oxygen species (ROS) play a key role in human cancer development. Moreover, the brain is especially vulnerable to ROS mediated injury.

METHOD

Therefore, in the present study, protein oxidation was assessed in the plasma of 17 patients with brain tumors and 16 age and gender-matched controls by measuring protein thiols and protein carbonyls spectrophotometrically.

RESULTS

There was a significant decrease in protein thiols and carbonyls in malignant cases of brain tumors when compared with the control group. No significant change in protein thiols was noted in benign cases compared to controls. A comparison of levels in benign and malignant cases for both the parameters also showed no significant difference.

DISCUSSION

Thus, free radical toxicity does lead to protein oxidation in patients with brain tumors.

Oxidative stress : relationship with exercise and training

Free radicals are reactive compounds that are naturally produced in the human body. They can exert positive effects (e.g. on the immune system) or negative effects (e.g. lipids, proteins or DNA oxidation). To limit these harmful effects, an organism requires complex protection - the antioxidant system. This system consists of antioxidant enzymes (catalase, glutathione peroxidase, superoxide dismutase) and non-enzymatic antioxidants (e.g. vitamin E [tocopherol], vitamin A [retinol], vitamin C [ascorbic acid], glutathione and uric acid). An imbalance between free radical production and antioxidant defence leads to an oxidative stress state, which may be involved in aging processes and even in some pathology (e.g. cancer and Parkinson's disease). Physical exercise also increases oxidative stress and causes disruptions of the homeostasis. Training can have positive or negative effects on oxidative stress depending on training load, training specificity and the basal level of training. Moreover, oxidative stress seems to be involved in muscular fatigue and may lead to overtraining.

Critical role of PI3-kinase/Akt activation in the PARP inhibitor induced heart function recovery during ischemia-reperfusion

Poly(ADP-ribose) polymerase (PARP) inhibitors protect hearts from ischemia-reperfusion (IR)-induced damages by limiting nicotinamide adenine dinucleotide (NAD+) and ATP depletion, and by other, not yet elucidated mechanisms. Our preliminary data suggested that PARP catalyzed ADP-ribosylations may affect signaling pathways in cardiomyocytes. To clarify this possibility, we studied the effect of a well-characterized (4-hydroxyquinazoline) and a novel (carboxaminobenzimidazol-derivative) PARP inhibitor on the activation of phosphatidylinositol-3-kinase (PI3-kinase)/Akt pathway in Langendorff-perfused hearts. PARP inhibitors promoted the restoration of myocardial energy metabolism (assessed by 31P nuclear magnetic resonance spectroscopy) and cardiac function compared to untreated hearts. PARP inhibitors also attenuated the infarct size and reduced the IR-induced lipid peroxidation, protein oxidation and total peroxide concentration. Moreover, PARP inhibitors facilitated Akt phosphorylation and activation, as well as the phosphorylation of its downstream target glycogen synthase kinase-3beta (GSK-3beta) in normoxia and, more robustly, during IR. Blocking PI3-kinase by wortmannin or LY294002 reduced the PARP inhibitor-elicited robust Akt and GSK-3beta phosphorylation upon ischemia-reperfusion, and significantly diminished the recovery of ATP and creatine phosphate showing the importance of Akt activation in the recovery of energy metabolism. In addition, inhibition of PI3-kinase/Akt pathway decreased the protective effect of PARP inhibitors on infarct size and the recovery of heart functions. All these data suggest that contrary to the original view, which considered preservation of NAD+ and consequently ATP pools as the exclusive underlying mechanism for the cytoprotective effect of PARP inhibitors, the activation of PI3-kinase/Akt pathway and related processes are at least equally important in the cardioprotective effects of PARP inhibitors during ischemia-reperfusion.

Induction of heat shock proteins may combat insulin resistance

The molecular mechanism responsible for obesity-associated insulin resistance has been partially clarified: increased fatty acid levels in muscle fibers promote diacylglycerol synthesis, which activates certain isoforms of protein kinase C (PKC). This in turn triggers a kinase cascade which activates both IkappaB kinase-beta (IKK-beta) and c-Jun N-terminal kinase (JNK), each of which can phosphorylate a key serine residue in IRS-1, rendering it a poor substrate for the activated insulin receptor. Heat shock proteins Hsp27 and Hsp72 have the potential to prevent the activation of IKK-beta and JNK, respectively; this suggests that induction of heat shock proteins may blunt the adverse impact of fat overexposure on insulin function. Indeed, bimoclomol--a heat shock protein co-inducer being developed for treatment of diabetic neuropathy--and lipoic acid--suspected to be a heat shock protein inducer--have each demonstrated favorable effects on the insulin sensitivity of obese rodents, and parenteral lipoic acid is reported to improve the insulin sensitivity of type 2 diabetics. Moreover, there is reason to believe that heat shock protein induction may have a favorable impact on the microvascular complications of diabetes, and on the increased risk for macrovascular disease associated with diabetes and insulin resistance syndrome. Heat shock protein induction may also have potential for preventing or treating neurodegenerative disorders, controlling inflammation, and possibly even slowing the aging process. The possible complementarity of bimoclomol and lipoic acid for heat shock protein induction should be assessed, and further efforts to identify well-tolerated agents active in this regard are warranted.

alpha-Lipoic acid induces apoptosis in human colon cancer cells by increasing mitochondrial respiration with a concomitant O2-*-generation

The antioxidant alpha-lipoic acid (ALA) has been shown to affect a variety of biological processes associated with oxidative stress including cancer. We determined in HT-29 human colon cancer cells whether ALA is able to affect apoptosis, as an important parameter disregulated in tumour development. Exposure of cells to ALA or its reduced form dihydrolipoic acid (DHLA) for 24 h dose dependently increased caspase-3-like activity and was associated with DNA-fragmentation. DHLA but not ALA was able to scavenge cytosolic O2-* in HT-29 cells whereas both compounds increased O2-*-generation inside mitochondria. Increased mitochondrial O2-*-production was preceded by an increased influx of lactate or pyruvate into mitochondria and resulted in the down-regulation of the anti-apoptotic protein bcl-X(L). Mitochondrial O2-*-generation and apoptosis induced by ALA and DHLA could be prevented by the O2-*-scavenger benzoquinone. Moreover, when the lactate/pyruvate transporter was inhibited by 5-nitro-2-(3-phenylpropylamino) benzoate, ALA- and DHLA-induced mitochondrial ROS-production and apoptosis were blocked. In contrast to HT-29 cells, no apoptosis was observed in non-transformed human colonocytes in response to ALA or DHLA addition. In conclusion, our study provides evidence that ALA and DHLA can effectively induce apoptosis in human colon cancer cells by a prooxidant mechanism that is initiated by an increased uptake of oxidizable substrates into mitochondria.

The role of Akt and mitogen-activated protein kinase systems in the protective effect of poly(ADP-ribose) polymerase inhibition in Langendorff perfused and in isoproterenol-damaged rat hearts

Blocking poly(ADP-ribosyl)ation of nuclear proteins protects the heart from ischemia-reperfusion injury. In addition, activation of Akt and mitogen-activated protein kinase (MAPK) cascades also plays a pivotal role in the survival of cardiomyocytes during ischemia-reperfusion; however, the potential interplay between these pathways is yet to be elucidated. We therefore tested the hypothesis whether poly(ADP-ribose) polymerase (PARP) inhibition can modulate Akt and MAPK signaling of ischemic-reperfused rat hearts. A novel PARP inhibitor, L-2286 [2-[(2-piperidin-1-yletil)thio]quinazolin-4(3H)-one] was administered during ischemia-reperfusion in Langendorff perfused rat hearts and in isoproterenol-induced myocardial infarction. Thereafter, the cardiac energy metabolism, oxidative damage, and the phosphorylation state of Akt and MAPK cascades were monitored. L-2286 exerted significant protective effect against ischemia-reperfusion-induced myocardial injury in both experimental models. More importantly, L-2286 facilitated the ischemia-reperfusion-induced activation of Akt, extracellular signal-regulated kinase, and p38-MAPK in both isolated hearts and in vivo cardiac injury. By contrast, isoproterenol-induced rapid c-Jun N-termainal kinase activation was repressed by L-2286. Here, we provide evidence for the first time that PARP inhibition beneficially modulates the cardiac Akt and MAPK signaling in ex vivo and in vivo ischemia-reperfusion models. We therefore propose that this novel mechanism may contribute to the cardioprotective properties of PARP inhibitors.

Overexpression of wild-type heat shock protein 27 and a nonphosphorylatable heat shock protein 27 mutant protects against ischemia/reperfusion injury in a transgenic mouse model

BACKGROUND

The small heat shock protein 27 (hsp27) increases in expression with ischemia/reperfusion (I/R) insult in the heart. One feature of the small hsps is their ability to oligomerize and form intracellular aggregates. Oligomerization pattern is governed by the phosphorylation state of the protein that may influence their ability to protect against cellular stresses.

METHODS AND RESULTS

We generated transgenic (tg) mice that overexpress a wild-type human hsp27 (hsp27tg) protein or a mutant hsp27 protein (mut-hsp27tg), in which serine residues (aa15, aa78, and aa82) were replaced by alanine residues, rendering them incapable of phosphorylation. Using a Langendorff perfusion model and an intraventricular balloon, we subjected hearts to 20 minutes of ischemia followed by 1 hour of reperfusion. During reperfusion, negative and positive pressure derivatives as well as developed pressures were significantly higher in both hsp27tg and mut-hsp27tg compared with control (P<0.01) mice, with no significant difference between hsp27tg and mut-hsp27tg. Creatine kinase release during reperfusion was higher in control compared with both hsp27tg and mut-hsp27tg (P<0.05). Malondialdehyde content as well as protein oxidation products were lower in mut-hsp27tg compared with control (P<0.05). hsp27tg hearts possessed oligomers that ranged in size from small to large, whereas mut-hsp27tg hearts contained no small oligomers.

CONCLUSIONS

These results indicate that in a tg mouse model, overexpression of either wild-type hsp27 or a nonphosphorylatable hsp27 mutant was equally capable of protecting the heart from I/R injury. Furthermore, the phosphorylation status of hsp27 may influence its ability to decrease oxidative stress.

Protein Radical Formation during Lactoperoxidase-mediated Oxidation of the Suicide Substrate Glutathione

A novel anti-5,5-dimethyl-1-pyrroline N-oxide (DMPO) polyclonal antiserum that specifically recognizes protein radical-derived DMPO nitrone adducts has been developed. In this study, we employed this new approach, which combines the specificity of spin trapping and the sensitivity of antigen-antibody interactions, to investigate protein radical formation from lactoperoxidase (LPO). When LPO reacted with GSH in the presence of DMPO, we detected an LPO radical-derived DMPO nitrone adduct using enzyme-linked immunosorbent assay and Western blotting. The formation of this nitrone adduct depended on the concentrations of GSH, LPO, and DMPO as well as pH values, and GSH could not be replaced by H(2)O(2). The level of this nitrone adduct was decreased significantly by azide, catalase, ascorbate, iodide, thiocyanate, phenol, or nitrite. However, its formation was unaffected by chemical modification of free cysteine, tyrosine, and tryptophan residues on LPO. ESR spectra showed that a glutathiyl radical was formed from the LPO/GSH/DMPO system, but no protein radical adduct could be detected by ESR. Its formation was decreased by azide, catalase, ascorbate, iodide, or thiocyanate, whereas phenol or nitrite increased it. GSH caused marked changes in the spectrum of compound II of LPO, indicating that GSH binds to the heme of compound II, whereas phenol or nitrite prevented these changes and reduced compound II back to the native enzyme. GSH also dose-dependently inhibited the peroxidase activity of LPO as determined by measuring 2,2'-azino-bis(3-ethylbenzothiazoline-6-sulfonic acid) oxidation. Taken together, these results demonstrate that the GSH-dependent LPO radical formation is mediated by the glutathiyl radical, possibly via the reaction of the glutathiyl radical with the heme of compound II to form a heme-centered radical trapped by DMPO.

Akt activation induced by an antioxidant compound during ischemia-reperfusion

Molecular mechanisms of cardioprotection afforded by modified mexiletine compounds were investigated during ischemia-reperfusion (IR) in Langendorff perfused hearts. Rat hearts were subjected to a global 25 min ischemia followed by reperfusion, either untreated or treated with mexiletine, or three substituted mexiletine derivates (5 muM). A modified mexiletine derivative (H-2693) promoted best the recovery of myocardial energy metabolism (assessed by (31)P NMR spectroscopy) compared to untreated and mexiletine-treated hearts. H-2693 also preserved cardiac contractile function and attenuated the IR-induced lipid peroxidation (TBARS formation) and protein oxidation (carbonyl content). Western blot revealed that H-2693 propagated the phosphorylation of Akt (activation) and its downstream substrate glycogen synthase kinase-3beta (GSK-3beta, inactivation) compared to untreated IR. Parallel treatment with the phosphatidylinositol-3-kinase (upstream activator of Akt) inhibitor wortmannin (100 nM) abolished the beneficial effects of H-2693 on energetics and function, and reduced Akt and GSK-3beta phosphorylation. As a result of the antiapoptotic impacts of Akt activation, H-2693 decreased caspase-3 activity, which was neutralized by wortmannin. Here we first demonstrated that a free radical-entrapping compound could activate the prosurvival Akt pathway beyond its proven ability to scavenge reactive oxygen species. In conclusion, the favorable influence of H-2693 on signaling events during IR may have considerably contributed to its cardioprotective effect.

Protective role of DLalpha-lipoic acid against adriamycin-induced cardiac lipid peroxidation

The cytoprotective activity of alpha-lipoic acid against free radical toxicity manifested during adriamycin (ADR)-induced cardiotoxicity has been investigated. ADR is a potent antitumour drug known to cause severe cardiotoxicity. Although ADR generates free radicals, the role of these radicals in the development of cardiac toxicity is still not well understood. In the present study, we evaluated the influence of chronic ADR treatment on the cellular defence mechanism against free radicals and the effect of alpha-lipoic acid supplementation on ADR-induced cardiotoxicity in male Wistar rats. The increase in lipid peroxidation (LPO) and activities of serum myocardial enzymes, namely lactate dehydrogenase (LDH) and creatinephosphokinase, associated with the decrease in activities of enzymatic (SOD, CAT, GPx, G6PD and GR) and non-enzymatic (GSH, Vit C and Vit E) antioxidants levels were the salient features observed in ADR-induced cardiotoxicity. Lipoic acid pretreated groups showed significant increase in activities of both enzymatic and non-enzymatic antioxidant levels. These observations highlight the antioxidant property of alpha-lipoic acid and its cytoprotective action against ADR-induced cardiotoxicity.

Modifications and oxidation of lipids and proteins in human serum detected by thermochemiluminescence

Detection of electronically excited species (EES) in body fluids may constitute an important diagnostic tool in various pathologies. Examples of such products are triplet excited carbonyls (TEC), which can be a source for photon emission in the 400-550 nm range. The aim of the present study was to determine the actual contribution of lipid and protein components (protein carbonyls) to photon emission generated by thermochemiluminescence (TCL) during the heating of biological fluids. In this study, a new TCL Photometer device, designed by Lumitest Ltd, Israel, was used. Samples were heated to a constant temperature of 80 +/- 0.5 degrees C for 280 s and photon emission was measured at several time points. In order to compare the results of TCL measurements to conventional methods of detecting lipid and protein oxidation, each examined sample was also heated in a waterbath at 80 degrees C for 10-280 s. Lipid and protein oxidation were subsequently measured using conventional methods. The TCL of four polyunsaturated fatty acids (PUFA) with three to six double bonds was measured. The elevation of the PUFA TCL amplitude correlated with the increase in the number of double bonds of PUFA. A correlation between the increase in TCL intensity and protein carbonyl generation in bovine serum albumin (BSA) was also observed. In the venous blood serum, our study showed that an increase of TCL intensity during heating reflected the cleavage of TEC of lipid origin. Our study suggests that biological molecules such as proteins, lipids and other molecules, which may become unstable during heating, are capable of generating EES. We demonstrated that a TCL curve can be used as a kinetic model for measuring oxidative processes, which reflects modifications of different molecules involved in the oxidative stress phenomena.

Effect of poly(ADP-ribose) polymerase inhibitors on the ischemia-reperfusion-induced oxidative cell damage and mitochondrial metabolism in Langendorff heart perfusion system

Ischemia-reperfusion induces reactive oxygen species (ROS) formation, and ROS lead to cardiac dysfunction, in part, via the activation of the nuclear poly(ADP-ribose) polymerase (PARP, called also PARS and ADP-RT). ROS and peroxynitrite induce single-strand DNA break formation and PARP activation, resulting in NAD(+) and ATP depletion, which can lead to cell death. Although protection of cardiac muscle by PARP inhibitors can be explained by their attenuating effect on NAD(+) and ATP depletion, there are data indicating that PARP inhibitors also protect mitochondria from oxidant-induced injury. Studying cardiac energy metabolism in Langendorff heart perfusion system by (31)P NMR, we found that PARP inhibitors (3-aminobenzamide, nicotinamide, BGP-15, and 4-hydroxyquinazoline) improved the recovery of high-energy phosphates (ATP, creatine phosphate) and accelerated the reutilization of inorganic phosphate formed during the ischemic period, showing that PARP inhibitors facilitate the faster and more complete recovery of the energy production. Furthermore, PARP inhibitors significantly decrease the ischemia-reperfusion-induced increase of lipid peroxidation, protein oxidation, single-strand DNA breaks, and the inactivation of respiratory complexes, which indicate a decreased mitochondrial ROS production in the reperfusion period. Surprisingly, PARP inhibitors, but not the chemically similar 3-aminobenzoic acid, prevented the H(2)O(2)-induced inactivation of cytochrome oxidase in isolated heart mitochondria, suggesting the presence of an additional mitochondrial target for PARP inhibitors. Therefore, PARP inhibitors, in addition to their important primary effect of decreasing the activity of nuclear PARP and decreasing NAD(+) and ATP consumption, reduce ischemia-reperfusion-induced endogenous ROS production and protect the respiratory complexes from ROS induced inactivation, providing an additional mechanism by which they can protect heart from oxidative damages.

Monoselenolipoic acid may be an outstanding pharmaceutical antioxidant with direct thioredoxin-like activity

Owing to the low pKa of its selenohydryl group, reduced monoselenolipoic acid (MSL) can be expected to be a very versatile antioxidant with direct thioredoxin-like activity. Since MSL supports the growth of lipoate-dependent bacteria, it can be anticipated that MSL will be susceptible to reversible reduction by one or more of the enzymes that reduces lipoic acid - thus greatly potentiating MSL's utility as an antioxidant. If it is not metabolized to release toxic free selenide, MSL may have interesting pharmaceutical potential.

Indicators of oxidative injury and alterations of the cell membrane in the skeletal muscle of rats submitted to ischemia and reperfusion

BACKGROUND

Oxygen free radicals are considered to be important components involved in the physiopathological tissue alterations observed during ischemia and reperfusion. The objective of the present study was to investigate oxidative stress based on indicators of oxygen free radical activity and on the changes in behavior of the lipoprotein membrane (O-phosphoserine) in the skeletal muscle of rats.

MATERIAL AND METHODS

Twenty Wistar rats were divided into two groups of 10. One group was submitted to 3 h of total ischemia by applying a tourniquet to the hind limb and the contralateral hind limb was used as control. The second group was submitted to the same procedure and was reperfused for 45 min after 3 h of ischemia by removing the tourniquet, where the contralateral hind limb of the same animal was used as control. Muscle biopsies were taken after ischemia and reperfusion and the parameters indicating oxidative stress (reduced and oxidized glutathione, malondialdehyde, glutamine synthetase, protein carbonyl) and O-phosphoserine (OPS) alterations were analyzed.

RESULTS

The following results display control versus experimental hindlimbs groups obtained from the same animal. The skeletal muscle of rats submitted to total ischemia of 3 h duration showed increased OPS release (2.69 +/- 4.52 vs 8.03 +/- 7.20; n = 10; P = 0.024) and no change in reduced and oxidized glutathione, glutamine synthetase, protein carbonyl, or malondialdehyde. After 45 min of reperfusion there was an increase in oxidized glutathione levels (0.30 +/- 0.06 vs 0.39 +/- 0.09; n = 8; P = 0.02) and malondialdehyde levels (154. 78 +/- 26.13 vs 206.30 +/- 47.30; n = 9; P = 0.008), a fall in glutamine synthetase (21.80 +/- 3.61 vs 13.52 +/- 6.78; n = 9; P = 0. 004), and a return of OPS to levels close to the initial ones. No changes in reduced glutathione or protein carbonyl were observed in the two groups studied.

CONCLUSIONS

After a total ischemia duration of 3 h there were signs of damage to the phospholipid membrane of the rat skeletal muscle, as demonstrated by the elevation of OPS and the few or no oxidative changes in the cell. After 45 min of reperfusion, oxidative damage to the lipoprotein components of the cell membrane was observed, characterized by elevations of oxidized glutathione and malondialdehyde levels and a fall in glutamine synthetase levels.

Neurobehavioral aspects of antioxidants in aging

Both aging and age-associated neurodegenerative diseases are associated with various degrees of behavioral impairments, and among the prime candidates responsible for producing the neuronal changes mediating these behavioral deficits appear to be free radicals and the oxidative stress they generate. Therefore, there have been a number of studies which have examined the putative positive benefits of antioxidants in altering, reversing, or forestalling these neuronal/behavioral decrements, with varying degrees of success. Additional experiments have examined the effects of diets rich in fruits and vegetables or herbal extracts in reducing certain types of cancer and cardiovascular diseases, and evidence emerging from such experiments suggests that these kinds of dietary modifications may be beneficial in altering neuronal/behavioral deficits in aging, as well. These kinds of diets are particularly rich in antioxidants such as vitamins A, C, E, and bioflavonoids (such as flavones, tannins, and anthocyanins), and thus, there may be synergistic effects among them. The present paper will review studies concerning the influence of dietary and synthetic antioxidants on normal, pathological age-related, and reactive oxygen species-induced behavioral changes in human and animal subjects. The antioxidants reviewed are vitamin E, alpha-lipoic acid, and the phytochemicals contained in herbals, fruits and vegetables.

BGP-15, a nicotinic amidoxime derivate protecting heart from ischemia reperfusion injury through modulation of poly(ADP-ribose) polymerase

The protective effect of O-(3-piperidino-2-hydroxy-1-propyl)nicotinic amidoxime (BGP-15) against ischemia-reperfusion-induced injury was studied in the Langendorff heart perfusion system. To understand the molecular mechanism of the cardioprotection, the effect of BGP-15 on ischemic-reperfusion-induced reactive oxygen species (ROS) formation, lipid peroxidation single-strand DNA break formation, NAD(+) catabolism, and endogenous ADP-ribosylation reactions were investigated. These studies showed that BGP-15 significantly decreased leakage of lactate dehydrogenase, creatine kinase, and aspartate aminotransferase in reperfused hearts, and reduced the rate of NAD(+) catabolism. In addition, BGP-15 dramatically decreased the ischemia-reperfusion-induced self-ADP-ribosylation of nuclear poly(ADP-ribose) polymerase(PARP) and the mono-ADP-ribosylation of an endoplasmic reticulum chaperone GRP78. These data raise the possibility that BGP-15 may have a direct inhibitory effect on PARP. This hypothesis was tested on isolated enzyme, and kinetic analysis showed a mixed-type (noncompetitive) inhibition with a K(i) = 57 +/- 6 microM. Furthermore, BGP-15 decreased levels of ROS, lipid peroxidation, and single-strand DNA breaks in reperfused hearts. These data suggest that PARP may be an important molecular target of BGP-15 and that BGP-15 decreases ROS levels and cell injury during ischemia-reperfusion in the heart by inhibiting PARP activity.

Oxidants downstream from superoxide inhibit nitric oxide production by vascular endothelium--a key role for selenium-dependent enzymes in vascular health

Although superoxide can directly quench endothelium-generated nitric oxide (NO), there is considerable evidence that oxidants derived from superoxide--notably peroxides and their further derivatives--can also impair NO bioactivity. In part, this reflects inhibition of NO synthase activity, perhaps mediated by the oxidation of labile sulfhydryl groups, as well as the activation of protein kinase C. Selenium deficiency exacerbates these effects, presumably owing to the crucial role of selenium-dependent thioredoxin reductase and glutathione peroxidases in preventing and reversing oxidant damage to proteins. High-normal homocyst(e)ine levels may induce an 'effective selenium deficiency' by suppressing glutathione peroxidase transcription in endothelial cells. Considerable epidemiology, primarily of European origin, points to mediocre selenium nutrition as a significant vascular risk factor; the risk associated with elevated plasma homocyst(e)ine levels is now well established. In addition to preventing LDL oxidation, vitamin E can be expected to minimize the contribution of lipid peroxides to endothelial dysfunction. Lipoic acid, which can function in vivo as a versatile antioxidant and sulfhydryl reductant, may have particular value for protecting endothelium from oxidants; its clinical utility in diabetic neuropathy may reflect this benefit. Good selenium status, as well as supra-nutritional intakes of lipoic acid, may down-regulate cytokine-mediated endothelial activation by helping to maintain the proper structure of oxidant-labile proteins--such as tyrosine phosphatases--that modulate this signaling. It can be concluded that a number of supplemental nutrients--including selenium, vitamin E, lipoic acid, and the vitamins that promote catabolism of homocysteine--have the potential to promote vascular health by mitigating the adverse impact of superoxide-derived oxidants on endothelial function.

The reported clinical utility of taurine in ischemic disorders may reflect a down-regulation of neutrophil activation and adhesion

The first publications regarding clinical use of taurine were Italian reports claiming therapeutic efficacy in angina, intermittent claudication and symptomatic cerebral arteriosclerosis. A down-regulation of neutrophil activation and endothelial adhesion might plausibly account for these observations. Endothelial platelet-activating factor (PAF) is a crucial stimulus to neutrophil adhesion and activation, whereas endothelial nitric oxide (NO) suppresses PAF production and acts in various other ways to antagonize binding and activation of neutrophils. Hypochlorous acid (HOCl), a neutrophil product which avidly oxidizes many sulfhydryl-dependent proteins, can be expected to inhibit NO synthase while up-regulating PAF generation; thus, a vicious circle can be postulated whereby HOCl released by marginating neutrophils acts on capillary or venular endothelium to promote further neutrophil adhesion and activation. Taurine is the natural detoxicant of HOCl, and thus has the potential to intervene in this vicious circle, promoting a less adhesive endothelium and restraining excessive neutrophil activation. Agents which inhibit the action of PAF on neutrophils, such as ginkgolides and pentoxifylline, have documented utility in ischemic disorders and presumably would complement the efficacy of taurine in this regard. Fish oil, which inhibits endothelial expression of various adhesion factors and probably PAF as well, and which suppresses neutrophil leukotriene production, may likewise be useful in ischemia. These agents may additionally constitute a non-toxic strategy for treating inflammatory disorders in which activated neutrophils play a prominent pathogenic role. Double-blind studies to confirm the efficacy of taurine in symptomatic chronic ischemia are needed.

Protein carbonyl formation on mucosal proteins in vitro and in dextran sulfate-induced colitis

Reactive oxygen and nitrogen species have been implicated as mediators of mucosal injury in inflammatory bowel disease, but few studies have investigated protein oxidation in the inflamed mucosa. In this study, protein carbonyl formation on colonic mucosal proteins from mice was investigated following in vitro exposure of homogenates to iron/ascorbate, hydrogen peroxide, hypochloric acid (HOCl), or nitric oxide (*NO). Total carbonyl content was measured spectrophotometrically by derivatization with dinitrophenylhydrazine (DNPH), and oxidation of component proteins within the tissue was examined by Western blotting for DNPH-derivatized proteins using anti-dinitrophenyl DNP antibodies. These results were compared with protein carbonyl formation found in the acutely inflamed mucosa from mice with colitis induced by dextran sulfate sodium (DSS) administered at 5% w/v in the drinking water for 7 d. In vitro, carbonyl formation was observed after exposure to iron/ascorbate, HOCl and *NO. Iron/ascorbate (20 microM/20 mM) exposure for 5 h increased carbonyl groups by 80%, particularly on proteins of 48, 75-100, 116, 131, and 142 kDa. Oxidation by 0.1 and 0.5 mM HOCl did not increase total carbonyl levels, but Western blotting revealed carbonyl formation on many proteins, particularly in the 49-95 kDa region. After exposure to 1-10 mM HOCl, total carbonyl levels were increased by 0.5 to 12 times control levels with extensive cross-linking and fragmentation of proteins rich in carbonyl groups observed by Western blotting. In mice with acute colitis induced by DSS, protein carbonyl content of the inflamed mucosa was not significantly different from control mucosa, (7.80 +/- 1.05 vs. 8.43 +/- 0.59 nmo/mg protein respectively, p = .16 n = 8, 10); however, Western blotting analysis indicated several proteins of molecular weight 48, 79, 95, and 131 kDa that exhibited increased carbonyl content in the inflamed mucosa. These proteins corresponded to those observed after in vitro oxidation of normal intestinal mucosa with iron/ ascorbate and HOCl, suggesting that both HOCl and metal ions may be involved in protein oxidation in DSS-induced colitis. Identification and further analysis of the mucosal proteins susceptible to carbonyl modification may lead to a better understanding of the contribution of oxidants to the colonic mucosa tissue injury in inflammatory bowel disease.

Mammalian small stress proteins protect against oxidative stress through their ability to increase glucose-6-phosphate dehydrogenase activity and by maintaining optimal cellular detoxifying machinery

The protective activity of small stress proteins (sHsp) against H2O2-mediated cell death in the highly sensitive murine L929 fibroblast has been analyzed. We report here that the human Hsp27- and murine Hsp25-mediated rise in glutathione (GSH) levels as well as the maintenance of this redox modulator in its reduced form was directly responsible for the protection observed at the level of cell morphology and mitochondrial membrane potential. sHsp expression also buffered the increase in protein oxidation following H2O2 treatment and protected several key enzymes against inactivation. In this case, however, the protection necessitated both an increase in GSH and the presence of sHsp per se since the pattern of protection against protein oxidation mediated by a simple GSH increase was different from that induced by sHsp expression. Among the enzymes analyzed, we noticed that sHsp significantly increased glucose-6-phosphate dehydrogenase (G6PD) activity and to a lesser extent glutathione reductase and glutathione transferase activities. Moreover, an increased GSH level was observed in G6PD-overexpressing L929 cell clones. Taken together our results suggest that sHsp protect against oxidative stress through a G6PD-dependent ability to increase and uphold GSH in its reduced form and by using this redox modulator as an essential parameter of their in vivo chaperone activity against oxidized proteins.

Alpha-lipoic acid provides neuroprotection from ischemia-reperfusion injury of peripheral nerve

BACKGROUND

Reperfusion aggravates nerve ischemic fiber degeneration, likely by the generation of reduced oxygen species. We therefore evaluated if racemic alpha-lipoic acid (LA), a potent antioxidant, will protect peripheral nerve from reperfusion injury, using our established model of ischemia-reperfusion injury.

METHODS

We used male SD rats, 300+/-5 g. Ischemia was produced by the ligature of each of the supplying arteries to the sciatic-tibial nerve of the right hind-limb for predetermined periods of time (either 3 or 5 h), followed by the release of the ligatures, resulting in reperfusion. LA was given intraperitoneally daily for 3 days for both pre- and post-surgery. Animals received either LA, 100 mg/kg/day, or the same volume of saline intraperitoneally. Clinical behavioral score and electrophysiology of motor and sensory nerves were obtained at 1 week after ischemia-reperfusion. After electrophysiological examination, the sciatic-tibial nerve was fixed in situ and embedded in epon. We evaluated for ischemic fiber degeneration (IFD) and edema, as we described previously.

RESULTS

Distal sensory conduction (amplitude of sensory action potential and sensory conduction velocity (SCV) of digital nerve) was significantly improved in the 3-h ischemia group, treated with LA (P<0.05). LA also improved IFD of the mid tibial nerve (P=0.0522). LA failed to show favorable effects if the duration of ischemia was longer (5-h ischemia).

CONCLUSION

These results suggest that alpha-lipoic acid is efficacious for moderate ischemia-reperfusion, especially on distal sensory nerves.

Gel electrophoretic quantitation of protein carbonyls derivatized with tritiated sodium borohydride

A method for the quantitation of protein carbonyls, which have been widely employed as markers of protein oxidative damage, is described. Protein carbonyls were derivatized with tritiated sodium borohydride and the tritiated proteins were separated on SDS-PAGE. Protein bands, visualized by Coomassie blue staining, were then excised and incubated in 30% H2O2 at 60 degrees C for 48 h. Tritium, incorporated into the proteins, was quantitated by liquid scintillation counting after gel solubilization by H2O2. This method can be applied to the measurement of carbonylation of specific proteins as it employs SDS-PAGE and has the advantage that unreacted NaB3H4 in the labeling reaction mixture need not be removed. The present method, when combined with immunochemical detection of protein carbonyls, should be very useful in the quantitation of oxidative damage to individual proteins.

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.

Networking antioxidants in the isolated rat heart are selectively depleted by ischemia-reperfusion

Although cardiac endogenous antioxidants have been reported to be oxidized and decreased by ischemia-reperfusion, little is known whether the changes in these antioxidants are correlated with each other in a systematic relationship. In this study, isolated rat hearts were subjected to various periods of ischemia-reperfusion using the Langendorff method, and the content and/or redox status of tissue antioxidants were analyzed. Significant losses in the tissue hydrophilic antioxidants, ascorbate, and glutathione were observed. These losses were dependent on the duration of the reperfusion period (between 0-40 min) but not of ischemia (20-60 min). Marked increases of dehydroascorbate and glutathione disulfide, the oxidized forms of ascorbate and glutathione, respectively, were found during reperfusion, but these changes were not observed during ischemia. These findings indicate that the tissue hydrophilic antioxidants are easily oxidized and may be the first line of antioxidant defenses during reperfusion. Lipophilic antioxidants, like ubiquinol 9 and vitamin E, were not decreased during ischemia-reperfusion using regular buffer; however, if oxidative stress was induced by addition of H2O2 to the buffer solution during reperfusion after 20 min of ischemia, decreases in both the hydrophilic and hydrophobic antioxidants were noticeable. With 100 microM H2O2, the tissue antioxidant decreases were ubiquinol 9 (39%), vitamin E (3%), glutathione (44%) and ascorbate (58%). Only with 500 microM H2O2 treatment were marked decreases in tissue vitamin E (65%) observed; this was associated with almost complete depletion of tissue ubiquinol 9 (95%). These results suggest that prior to the consumption of vitamin E, other antioxidants are depleted and that vitamin E may serve as the ultimate antioxidant, protecting the integrity of cellular membranes. Thus, in this work, cardiac antioxidants were demonstrated to change in a systematically organized relationship under ischemia-reperfusion. This graded utilization of antioxidants supports the redox based antioxidant network concept, found to be present in other biological systems.

Macromolecular carbonyls in human stratum corneum: a biomarker for environmental oxidant exposure?

The presence of stratum corneum carbonyls may serve as an intrinsic dosimeter for environmental oxidative damage to skin. To investigate the accumulation of carbonyls in human stratum corneum, skin was tape-stripped, then tapes were sequentially incubated with 2,4-dinitrophenyl hydrazine (DNPH), rat anti-DNP, mouse anti-rat IgG conjugated with alkaline phosphatase, p-nitrophenyl phosphate and absorbance (405 nm) measured and carbonyls estimated. Stratum corneum exposed in vitro to oxidants: hypochlorous acid (1, 10, 100 mM), ozone (0, 1, 5, 10 ppm for 2 h) or UV light (280-400 nm; 0, 4, 88, or 24 J/cm2) contained increased carbonyls. Furthermore, stratum corneum carbonyls were elevated in tanned compared with untanned sites: dorsal hand (0.43 +/- 0.06 nmol/cm2) vs. lower arm (0.32 +/- 0.04, mean +/- S.E.M., n = 11; P < 0.003) and lower back (0.26 +/- 0.02) vs. buttock (0.21 +/- 0.02; n = 6, P < 0.01) indicating in vivo oxidative damage.

Receptor site and stereospecifity of dihydrolipoamide dehydrogenase for R- and S-lipoamide: a molecular modeling study

The binding of the substrate R-dihydrolipoamide to the active site of dihydrolipoamide dehydrogenase has been investigated by molecular modeling and energy-minimization studies on the basis of the resolved 3-dimensional structure of the enzyme from Azotobacter vinelandii (PDB entry 3LAD) which was determined without its bound substrate. The binding model is used as a template for a FIELD-FIT docking procedure for the inactive S-enantiomer of dihydrolipoamide which is an inhibitor of the enzyme. Results show that only the active R-enantiomer is able to form direct contacts with the reactive thiol groups and imidazol base at the active site, whereas with the S-enantiomer the SH-group at C6 points away from the His450* base. Evaluation of the binding energy to the receptor site yields nearly the same value for both enantiomers. This is in accordance with experimental results which show that the stereospecifity of dihydrolipoamide dehydrogenase occurs more at the level of catalysis than of binding. The substrate/receptor model is extended to the binding of lipoyllysine, the substrate of dihydrolipoamide dehydrogenase, when the enzyme is integrated into the pyruvate dehydrogenase complex. The penetration-site of the lipoyllysine arm into the structure of dihydrolipoamide dehydrogenase could be identified. The consequences for the interaction of dihydrolipoamide dehydrogenase with the lipoyl domain of the alpha-oxoacid dehydrogenase complexes are discussed.

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 increases de novo synthesis of cellular glutathione by improving cystine utilization

Lipoic acid (thiotic acid) is being used as a dietary supplement, and as a therapeutic agent, and is reported to have beneficial effects in disorders associated with oxidative stress, but its mechanism of action remains unclear. We present evidence that lipoic acid induces a substantial increase in cellular reduced glutathione in cultured human Jurkat T cells human erythrocytes, C6 glial cells, NB41A3 neuroblastoma cells, and peripheral blood lymphocytes. The effect depends on metabolic reduction of lipoic acid to dihydrolipoic acid. Dihydrolipoic acid is released into the culture medium where it reduces cystine. Cysteine thus formed is readily taken up by the neutral amino acid transport system and utilized for glutathione synthesis. By this mechanism lipoic acid enables cystine to bypass the xc- transport system, which is weakly expressed in lymphocytes and inhibited by glutamate. Thereby lipoic acid enables the key enzyme of glutathione synthesis, gamma-glutamylcysteine synthetase, which is regulated by uptake-limited cysteine supply, to work at optimum conditions. Flow cytometric analysis of freshly prepared human peripheral blood lymphocytes, using monobromobimane labeling of cellular thiols, reveals that lipoic acid acts mainly to normalize a subpopulation of cells severely compromised in thiol status rather than to increase thiol content beyond physiological levels. Hence lipoic acid may have clinical relevance in restoration of severely glutathione deficient cells.

alpha-Lipoic acid as a biological antioxidant

alpha-Lipoic acid, which plays an essential role in mitochondrial dehydrogenase reactions, has recently gained considerable attention as an antioxidant. Lipoate, or its reduced form, dihydrolipoate, reacts with reactive oxygen species such as superoxide radicals, hydroxyl radicals, hypochlorous acid, peroxyl radicals, and singlet oxygen. It also protects membranes by interacting with vitamin C and glutathione, which may in turn recycle vitamin E. In addition to its antioxidant activities, dihydrolipoate may exert prooxidant actions through reduction of iron. alpha-Lipoic acid administration has been shown to be beneficial in a number of oxidative stress models such as ischemia-reperfusion injury, diabetes (both alpha-lipoic acid and dihydrolipoic acid exhibit hydrophobic binding to proteins such as albumin, which can prevent glycation reactions), cataract formation, HIV activation, neurodegeneration, and radiation injury. Furthermore, lipoate can function as a redox regulator of proteins such as myoglobin, prolactin, thioredoxin and NF-kappa B transcription factor. We review the properties of lipoate in terms of (1) reactions with reactive oxygen species; (2) interactions with other antioxidants; (3) beneficial effects in oxidative stress models or clinical conditions.

Effect of alpha-lipoic acid and dihydrolipoic acid on ischemia/reperfusion injury of the heart and heart mitochondria

The aim of the present study was to evaluate a possible interference of alpha-lipoic acid (LA) or its reduced form (dithiol dihydrolipoic acid = DHLA) in the cardiac ischemia/reperfusion injury both at the level of the intact organ and at the subcellular level of mitochondria. In order to follow the effect of LA on the ischemia/reperfusion injury of the heart the isolated perfused organ was subjected to total global ischemia and reperfusion in the presence and absence of different concentrations of LA. Treatment with 0.5 microM LA improved the recovery of hemodynamic parameters; electrophysiological parameters were not influenced. However, application of 10 microM LA to rat hearts further impaired the recovery of hemodynamic functions and prolonged the duration of severe rhythm disturbances in comparison to reperfusion of control hearts. Treatment of isolated mitochondria with any concentration of DHLA could not prevent the impairment of respiratory-linked energy conservation caused by the exposure of mitochondria to 'reperfusion' conditions. However, DHLA was effective in decreasing the formation and the existence of mitochondrial superoxide radicals (O2.-). Apart from its direct O(2.-)-scavenging activities DHLA was also found to control mitochondrial O2.- formation indirectly by regulating redox-cycling ubiquinone. It is suggested that impairment of this mitochondrial O2.- generator mitigates postischemic oxidative stress which in turn reduces damage to hemodynamic heart function.

Alpha-lipoic acid prevents buthionine sulfoximine-induced cataract formation in newborn rats

We investigated the effect of alpha-lipoic acid, a powerful antioxidant, on cataract formation in L-buthionine(S,R)-sulfoximine (BSO)-treated newborn rats and found that a dose of 25 mg/kg b.w. protected 60% of animals from cataract formation. L-buthionine(S,R)-sulfoximine is an inhibitor of glutathione synthesis, whose administration to newborn animals leads to the development of cataracts; this is a potential model for studying the role of therapeutic antioxidants in protecting animals from cataract formation. Major biochemical changes in the lens associated with the protective effect of alpha-lipoic acid were increases in glutathione, ascorbate, and vitamin E levels, loss of which are effects of BSO administration. Treatment with alpha-lipoic acid also restored the activities of glutathione peroxidase, catalase, and ascorbate free radical reductase in lenses of L-buthionine(S,R)-sulfoximine-treated animals but did not affect glutathione reductase or superoxide dismutase activity. We conclude that alpha-lipoic acid may take over some of the functions of glutathione (e.g., maintaining the higher level of ascorbate, indirect participation in vitamin E recycling); the increase of glutathione level in lens tissue mediated by lipoate could be also due to a direct protection of protein thiols. Thus, alpha-lipoic acid could be of potential therapeutic use in preventing cataracts and their complications.