The effect of dl-α-lipoic acid on heavy-metal intoxication in mice and dogs

Alpha lipoic acid toxicosis in cats (2008-2016): Four cases

OBJECTIVE

To review clinical signs, treatments, and outcome of 4 cases in cats after ingestion of alpha lipoic acid.

CASE SERIES SUMMARY

Four cases with known alpha lipoic acid ingestions developed clinical signs. A consistent clinical sign in all cases was vomiting, while 2 of the 4 cases resulted in death.

NEW OR UNIQUE INFORMATION PROVIDED

This is the first reported case series of alpha lipoic acid ingestions in cats.

Alpha-Lipoic Acid Protects Co-Exposure to Lead and Zinc Oxide Nanoparticles Induced Neuro, Immuno and Male Reproductive Toxicity in Rats

We evaluated the neuro-, immuno-, and male reproductive toxicity of zinc oxide nanoparticles (ZnO NPs) alone and in combination with lead acetate. We also studied the therapeutic role of α-lipoic acid postexposure. Lead (10 mg/kg, body weight), ZnO NPs (100 mg/kg, bwt) alone, and their combination were administered orally in Wistar rats for 28 days, followed by the administration of α-lipoic acid (15 mg/kg, bwt) for the next 15 days. Our results demonstrated protective effects of α-lipoic acid on lead and ZnO NP-induced biochemical alterations in neurological, immunological, and male reproductive organs in rats. The altered levels of blood δ-aminolevulinic acid dehydratase (ALAD), immunoglobulins (IgA, IgG, IgM, and IgE), interleukins (IL-1β, IL-4, and IL-6), caspase-3, and tumor necrosis factor (TNF-α) were attenuated by lipoic acid treatment. Lead and ZnO NP-induced oxidative stress was decreased by lipoic acid treatment, while a moderate recovery in the normal histoarchitecture of the brain section (cortex and hippocampus) and testes further confirmed the neuro- and male reproductive toxicity of lead and ZnO NPs. We also observed a significant decrease in the blood metal content in the animals treated with lipoic acid compared to the lead-administered group, indicating the moderate chelating property of lipoic acid. It may thus be concluded that lipoic acid might be a promising protective agent against lead and ZnO NP-induced alterations in the neurological, immunological, and reproductive parameters.

Alpha-Lipoic Acid as a Nutritive Supplement for Humans and Animals: An Overview of Its Use in Dog Food

Simple Summary

A review of human and animal studies involving alpha-lipoic acid supplementation was conducted to determine the utility of alpha-lipoic acid in dog food. The present literature shows that alpha-lipoic acid has utility as a nutritive additive at concentrations of 2.7–4.94 mg/kg body weight/day and improves antioxidant capacity in dogs.

Abstract

Alpha-lipoic acid (a-LA) is used as a nutritive additive in dog food. Therefore, we performed a systematic review of studies published to date in PubMed, Google Scholar, Cochrane Library and MedlinePlus involving alpha-lipoic acid supplementation, which included human clinical trials as well as animal studies, to evaluate its utility as a supplement in foods for healthy, adult dogs. While an upper limit of alpha-lipoic acid intake in humans has not been conclusively determined, the levels for oral intake of a-LA have been better defined in animals, and distinct differences based on species have been described. The maximum tolerated oral dose of a-LA in dogs has been reported as 126 mg/kg body weight and the LD₅₀ as 400 to 500 mg/kg body weight. The antioxidant, anti-inflammatory and neuro-protective benefits of alpha-lipoic acid in dogs were observed at concentrations much lower than the maximum tolerated dose or proposed LD₅₀. At concentrations of 2.7–4.94 mg/kg body weight/day, alpha-lipoic acid is well tolerated and posed no health risks to dogs while providing improved antioxidant capacity. This review thereby supports the utility of alpha-lipoic acid as an effective nutritive additive in dog food.

Alpha-Lipoic Acid Is an Effective Nutritive Antioxidant for Healthy Adult Dogs

This study was designed to determine the effect of alpha-lipoic acid on the glutathione status in healthy adult dogs. Following a 15 month baseline period during which dogs were fed a food containing no alpha-lipoic acid, dogs were randomly allocated into four groups. Groups were then fed a nutritionally complete and balanced food with either 0, 75, 150 or 300 ppm of alpha-lipoic acid added for 6 months. Evaluations included physical examination, body weight, food intake, hematology, serum biochemistry profile and measurements of glutathione in plasma and erythrocyte lysates. Throughout, blood parameters remained within reference ranges, dogs were healthy and body weight did not change significantly. A significant increase of 0.05 ng/mL of total glutathione in red blood cell (RBC) lysate for each 1 mg/kg bodyweight/day increase in a-LA intake was observed. In addition, a significant increase was observed for GSH, GSSG and total glutathione in RBC lysate at Month 6. We conclude that alpha-lipoic acid, as part of a complete and balanced food, was associated with increasing glutathione activity in healthy adult dogs.

Pathophysiology and aetiology of hypoglycaemic crises

Hypoglycaemia is a common, life-threatening complication that occurs as a component of a wide variety of disease processes. Despite its frequent occurrence, information concerning the aetiology, characteristics and outcomes of hypoglycaemic crises in veterinary medicine is limited. This review summarises the current understanding of the pathophysiology of hypoglycaemia, the body's counter-regulatory response, underlying aetiologies, diagnosis and treatment. Disease mechanisms are discussed and published evidence in veterinary literature regarding prognostic indicators, prevalence, diagnosis and treatment is examined for hypoglycaemia-related disease processes including insulinoma, glucose-lowering toxins and medications.

Arsenic-induced oxidative stress and its reversibility

This review summarizes the literature describing the molecular mechanisms of arsenic-induced oxidative stress, its relevant biomarkers, and its relation to various diseases, including preventive and therapeutic strategies. Arsenic alters multiple cellular pathways including expression of growth factors, suppression of cell cycle checkpoint proteins, promotion of and resistance to apoptosis, inhibition of DNA repair, alterations in DNA methylation, decreased immunosurveillance, and increased oxidative stress, by disturbing the pro/antioxidant balance. These alterations play prominent roles in disease manifestation, such as carcinogenicity, genotoxicity, diabetes, cardiovascular and nervous systems disorders. The exact molecular and cellular mechanisms involved in arsenic toxicity are rather unrevealed. Arsenic alters cellular glutathione levels either by utilizing this electron donor for the conversion of pentavalent to trivalent arsenicals or directly binding with it or by oxidizing glutathione via arsenic-induced free radical generation. Arsenic forms oxygen-based radicals (OH(•), O(2)(•-)) under physiological conditions by directly binding with critical thiols. As a carcinogen, it acts through epigenetic mechanisms rather than as a classical mutagen. The carcinogenic potential of arsenic may be attributed to activation of redox-sensitive transcription factors and other signaling pathways involving nuclear factor κB, activator protein-1, and p53. Modulation of cellular thiols for protection against reactive oxygen species has been used as a therapeutic strategy against arsenic. N-acetylcysteine, α-lipoic acid, vitamin E, quercetin, and a few herbal extracts show prophylactic activity against the majority of arsenic-mediated injuries in both in vitro and in vivo models. This review also updates the reader on recent advances in chelation therapy and newer therapeutic strategies suggested to treat arsenic-induced oxidative damage.

The role of thiols, dithiols, nutritional factors and interacting ligands in the toxicology of mercury

Mercury has been a known as a toxic substance for centuries. Whilst the clinical features of acute mercury poisoning have been well described, chronic low dose exposure to mercury remains poorly characterised and its potential role in various chronic disease states remains controversial. Low molecular weight thiols, i.e. sulfhydryl containing molecules such as cysteine, are emerging as important factors in the transport and distribution of mercury throughout the body due to the phenomenon of "Molecular Mimicry" and its role in the molecular transport of mercury. Chelation agents such as the dithiols sodium 2,3-dimercaptopropanesulfate (DMPS) and meso-2,3-dimercaptosuccinic acid (DMSA) are the treatments of choice for mercury toxicity. Alpha-lipoic acid (ALA), a disulfide, and its metabolite dihydrolipoic acid (DHLA), a dithiol, have also been shown to have chelation properties when used in an appropriate manner. Whilst N-acetyl-cysteine (NAC) and glutathione (GSH) have been recommended in the treatment of mercury toxicity in the past, an examination of available evidence suggests these agents may in fact be counterproductive. Zinc and selenium have also been shown to exert protective effects against mercury toxicity, most likely mediated by induction of the metal binding proteins metallothionein and selenoprotein-P. Evidence suggests however that the co-administration of selenium and dithiol chelation agents during treatment may also be counter-productive. Finally, the issue of diagnostic testing for chronic, historical or low dose mercury poisoning is considered including an analysis of the influence of ligand interactions and nutritional factors upon the accuracy of "chelation challenge" tests.

Brain regional responses in antioxidant system to α-lipoic acid in arsenic intoxicated rat

Impaired antioxidant defense mechanisms and oxidative stress are implicated in the pathogenesis of arsenic toxicity. Our study was designed to determine whether alpha-lipoic acid, which has been shown to have substantial antioxidant properties, when administered (70 mg/kg body weight) once daily for 60 days along with arsenic (100 ppm sodium arsenite mixed in drinking water) would prevent arsenic-induced changes in antioxidant defense system, superoxide dismutase (SOD-total SOD, Mn SOD, Cu/Zn SOD), catalase (CAT) and glutathione peroxidase (GSH-PX) in rat brain regions such as cortex, hypothalamus, striatum, cerebellum and hippocampus. The present study also examined the effect of alpha-lipoic acid over arsenic-induced oxidant production and lipid peroxidation level (LPO) in discrete brain regions of rats. The cortex, striatum and hippocampus showed greater decreases in GSH-Px enzyme activity than cerebellum and hypothalamus with arsenic exposure. Striatum had the greatest percentage of decreased activities of total SOD and Mn SOD, whereas cortex had the greatest percentage decrease in the activity of Cu/Zn SOD in arsenic-alone treated rats. Hypothalamus and cerebellum exhibited the lowest catalase activity among all tested regions in arsenic-only treated rats. Rate of dichlorofluorescin oxidation, an indication of reactive oxygen species and other intracellular oxidants production was increased with arsenic exposure in all brain regions studied. Cortex, hippocampus and striatum exhibited greater increase of LPO levels than cerebellum and hypothalamus. SOD, CAT, GSH-Px activities were upregulated in arsenic plus lipoic acid treated versus arsenic-only treated rats. Also, simultaneous lipoic acid treatment along with arsenic proved to be sufficient in reducing oxidant production and LPO level in all rat brain regions. Our results demonstrate that arsenic-induced deficits in antioxidant enzyme activities and increase in oxidant production and lipid peroxidation level in brain regions can be overcome through simultaneous treatment with lipoic acid.

Biotin biochemistry and human requirements

Human biotin turnover and requirements can be estimated on the basis of (1) concentrations of biotin and metabolites in body fluids, (2) activities of biotin-dependent carboxylases, and (3) the urinary excretion of organic acids that are formed at increased rates if carboxylase activities are reduced. Recent studies suggest that the urinary excretions of biotin and its metabolite bisnorbiotin, activities of propionyl-CoA carboxylase and beta-methylcrotonyl-CoA carboxylase in lymphocytes, and urinary excretion of 3-hydroxyisovaleric acid are good indicators of marginal biotin deficiency. On the basis of studies using these indicators of biotin deficiency, an adequate intake of 30 microg (123 nmoles) of biotin per day is currently recommended for adults. The dietary biotin intake in Western populations has been estimated to be 35 to 70 microg/d (143-287 nmol/d). Recent studies suggest that humans absorb biotin nearly completely. Conditions that may increase biotin requirements in humans include pregnancy, lactation, and therapy with anticonvulsants or lipoic acid.

Therapeutic efficacy of lipoic acid in combination with dimercaptosuccinic acid against lead-induced renal tubular defects and on isolated brush-border enzyme activities

The combined therapeutic potentials of lipoic acid and dimercaptosuccinic acid were compared against their sole administrations in restoring the altered lead sensitive indices in urine and isolated renal brush-border preparations. Toxicity was induced in male albino rats (Wistar strain) by administering lead acetate (0.2%) in drinking water for 5 weeks, followed by therapy comprising lipoic acid (25 mg/kg body weight) and dimercaptosuccinic acid (20 mg/kg body weight) solely as well as combined during the 6th week. Changes in kidney weights encountered upon lead administration improved after therapy with lipoic acid and dimercaptosuccinic acid. Renal integrity was assessed by measuring the activities of alkaline phosphatase, acid phosphatase, lactate dehydrogenase, leucine aminopeptidase, N-acetyl-beta-D-glucosaminidase, gamma-glutamyl transferase and beta-glucuronidase in urine along with some urinary constituents (urea, uric acid, creatinine, protein and phosphorous). The effects of lead were also studied on isolated brush-border enzymes (alkaline phosphatase, acid phosphatase, gamma-glutamyl transferase and beta-glucuronidase) that showed a decline upon its administration. Increased activities of urinary enzymes were accompanied by increase in the urinary constituents. Increase in renal lead content was paralleled by a drastic fall in the renal delta-aminolevulinic acid dehydratase and a rise in urinary lead levels. Relative to the administration of lead, the combined therapy showed betterment on the renal integrity with respect to the functional parameters assessed, thereby indicating its efficacy over the monotherapies.

A conservative triple antioxidant approach to the treatment of hepatitis C. Combination of alpha lipoic acid (thioctic acid), silymarin, and selenium: three case histories

BACKGROUND

There has been an increase in the number of adults seeking liver transplantation for hepatitis C in the last few years and the count is going up rapidly. There is no reliable and effective therapy for chronic hepatitis C since interferon and antivirals work no more than 30% of the time, and liver transplant surgery is uncertain and tentative over the long run. This is because, ultimately, residual hepatitis C viremia infects the new liver. Furthermore, liver transplantation can be painful, disabling and extremely costly.

TREATMENT PROGRAM

The author describes a low cost and efficacious treatment program in 3 patients with cirrhosis, portal hypertension and esophageal varices secondary to chronic hepatitis C infection. This effective and conservative regimen combines 3 potent antioxidants (alpha-lipoic acid [thioctic acid], silymarin, and selenium) that possess antiviral, free radical quenching and immune boosting qualities.

CONCLUSION

There are no remarkably effective treatments for chronic hepatitis C in general use. Interferon and antivirals have less than a 30% response rate and because of the residual viremia, a newly transplanted liver usually becomes infected again. The triple antioxidant combination of alpha-lipoic acid, silymarin and selenium was chosen for a conservative treatment of hepatitis C because these substances protect the liver from free radical damage, increase the levels of other fundamental antioxidants, and interfere with viral proliferation. The 3 patients presented in this paper followed the triple antioxidant program and recovered quickly and their laboratory values remarkably improved. Furthermore, liver transplantation was avoided and the patients are back at work, carrying out their normal activities, and feeling healthy. The author offers a more conservative approach to the treatment of hepatitis C, that is exceedingly less expensive. One year of the triple antioxidant therapy described in this paper costs less than $2,000, as compared to mor than $300,000 a year for liver transplant surgery. It appears reasonable, that prior to liver transplant surgery evaluation, or during the transplant evaluation process, the conservative triple antioxidant treatment approach should be considered. If these is a significant betterment in the patient's condition, liver transplant surgery may be avoided.

The effect of alpha-lipoic acid on the neurovascular reflex arc in patients with diabetic neuropathy assessed by capillary microscopy

Patients with diabetic polyneuropathy are known to have an impaired neurovascular reflex arc compared to healthy controls. This is seen in a delayed decrease in microcirculation of the ipsilateral hand after cooling of the contralateral hand. The aim of this pilot study was to investigate whether intravenous alpha-lipoic acid (ALA) (Thioctacid, Asta Medica) therapy might be able to improve this impaired neurovascular reflex arc in patients with diabetic neuropathy. In addition, clinical effects were evaluated with the aid of the neuropathy symptom score (NSS) and the neuropathy disability score (NDS). Ten patients with diabetes mellitus and polyneuropathy (5 females, 5 males, 2 smokers, 5 IDDM, 5 NIDDM, body mass index 26.1 +/- 1.0 kg/m2, age 58.3 +/- 9.5 years, diabetes duration 15.7 +/- 11.2 years, Hb A1c 6.8 +/- 0.3%) were investigated by nail-fold capillaroscopy after contralateral cooling before and after intravenous therapy with 600 mg alpha-lipoic acid per day over 3 weeks. Cardiac autonomic neuropathy was excluded by beat-to-beat variation analysis. Symptoms of diabetic neuropathy were evaluated before and after therapy with the aid of the NSS and NDS. Capillary blood cell velocity (CBV) of the hand was determined before, during, and for the following 30 min after cooling (3 min at 15 degrees C) of the contralateral hand. Blood pressure, heart rate, and local skin temperature were monitored at 2-min intervals. ALA therapy resulted in a significant improvement of the microcirculatory response to cooling, as seen by an immediate decrease in CBV of 12. 3% (P < 0.02 vs before treatment), which was absent before therapy. Blood pressure, heart rate, and local skin temperature were not different between investigations. There was a significant improvement of the NSS after therapy (5.4 +/- 1.1 vs 8.6 +/- 1.1 points, P < 0.01). These results demonstrate that intravenous therapy with ALA has a positive influence on the impaired neurovascular reflex arc in patients with diabetic neuropathy.

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.

Lipoic acid reduces the activities of biotin-dependent carboxylases in rat liver

In the past, lipoic acid has been administered to patients and test animals as therapy for diabetic neuropathy and various intoxications. Lipoic acid and the vitamin biotin have structural similarities. We sought to determine whether the chronic administration of lipoic acid affects the activities of biotin-dependent carboxylases. For 28 d, rats received daily intraperitoneal injections of one of the following: 1) a small dose of lipoic acid [4.3 micromol/( kg.d)]; 2) a large dose of lipoic acid [15.6 micromol/(kg.d)]; or 3) a large dose of lipoic acid plus biotin [15.6 and 2.0 micromol/(kg.d), respectively]. Another group received n-hexanoic acid [14.5 micromol/(kg.d)], which has structural similarities to lipoic acid and biotin and thus served as a control for the specificity of lipoic acid. A fifth group received phosphatidylcholine in saline injections and served as the vehicle control. The rat livers were assayed for the activities of acetyl-CoA carboxylase, pyruvate carboxylase, propionyl-CoA carboxylase, and beta-methylcrotonyl-CoA carboxylase. Urine was analyzed for lipoic acid; serum was analyzed for indicators of liver damage and metabolic aberrations. The mean activities of pyruvate carboxylase and beta-methylcrotonyl-CoA carboxylase were 28-36% lower in the lipoic acid-treated rats compared with vehicle controls (P < 0.05). Rats treated with lipoic acid plus biotin had normal carboxylase activities. Carboxylase activities in livers of n-hexanoic acid-treated rats were normal despite some evidence of liver injury. Propionyl-CoA carboxylase and acetyl-CoA carboxylase were not significantly affected by administration of lipoic acid. This study provides evidence consistent with the hypothesis that chronic administration of lipoic acid lowers the activities of pyruvate carboxylase and beta-methylcrotonyl-CoA carboxylase in vivo by competing with biotin.

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.

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.

Thioctic (lipoic) acid: a therapeutic metal-chelating antioxidant?

Thioctic (alpha-lipoic) acid (TA) is a drug used for the treatment of diabetic polyneuropathy in Germany. It has been proposed that TA acts as an antioxidant and interferes with the pathogenesis of diabetic polyneuropathy. We suggest that one component of its antioxidant activity requiring study is the direct transition metal-chelating activity of the drug. We found that TA had a profound dose-dependent inhibitory effect upon Cu(2+)-catalysed ascorbic acid oxidation (monitored by O2 uptake and spectrophotometrically at 265 nm) and also increased the partition of Cu2+ into n-octanol from an aqueous solution suggesting that TA forms a lipophilic complex with Cu2+. TA also inhibited Cu(2+)-catalysed liposomal peroxidation. Furthermore, TA inhibited intracellular H2O2 production in erythrocytes challenged with ascorbate, a process thought to be mediated by loosely chelated Cu2+ within the erythrocyte. These data, taken together, suggest that prior intracellular reduction of TA to dihydrolipoic acid is not an obligatory mechanism for an antioxidant effect of the drug, which may also operate via Cu(2+)-chelation. The R-enantiomer and racemic mixture of the drug (alpha-TA) generally seemed more effective than the S-enantiomer in these assays of metal chelation.

Analysis of lipoic acid in biological samples by gas chromatography with flame photometric detection

A selective and sensitive gas chromatographic method for the analysis of lipoic acid in biological samples has been developed. After base hydrolysis of the sample, the liberated lipoic acid was converted into its S,S-diethoxycarbonyl methyl ester derivative and measured by gas chromatography using a DB-210 capillary column and a flame photometric detector. The calibration curve was linear in the range 20-500 ng, and the detection limit was ca. 50 pg injected. The best hydrolysis conditions for the biological samples were obtained by using 2 M potassium hydroxide containing 4% bovine serum albumin at 110 degrees C for 3 h. Using this method, lipoic acid in the hydrolysate could be selectively determined without any interference from matrix substances. Analytical results for the determination of lipoic acid in the mouse tissue and bacterial cell samples are presented.

Studies on the efficacy of lipoate and dihydrolipoate in the alteration of cadmium2+ toxicity in isolated hepatocytes

Lipoate (thioctic acid) is presently used in therapy of a variety of diseases such as liver and neurological disorders. However, nothing is known about the efficacy of lipoate and its reduced form dihydrolipoate in acute cadmium (Cd2+) toxicity which involves severe liver disturbances. Therefore, we investigated the effects of these redox compounds on Cd2(+)-induced injuries in isolated rat hepatocytes. The cells were coincubated with 150 microM Cd2+ and either 1.5-6.0 mM lipoate or 17-89 microM dihydrolipoate for up to 90 min and Cd2+ uptake as well as viability criteria were monitored. Both exposure regimens diminished Cd2+ uptake in correspondence to time and concentration. They also ameliorated Cd2(+)-induced cell deterioration as reflected by the decrease in Cd2(+)-induced membrane damage (leakage of aspartate aminotransferase), by the lessening of the Cd2(+)-stimulated lipid peroxidation (TBA-reactants) and by the increase in Cd2(+)-depleted cellular glutathione (GSH + 2 GSSG). Half-maximal protection was achieved at molar ratios of 9.9 to 19 (lipoate vs. Cd2+) and 0.25 to 0.74 (dihydrolipoate vs. Cd2+), indicating a 19.5 to 50.6 lower protective efficacy of lipoate as compared to dihydrolipoate. Lipoate induced an increase in extracellular acid-soluble thiols different from glutathione. It is suggested that dihydrolipoate primarily protects cells by extracellular chelation of Cd2+, whereas intracellular reduction of lipoate to the dihydro-compound followed by complexation of both intra- and extracellular Cd2+ contributes to the amelioration provided by lipoate.

Protective effects of DL-alpha-lipoic acid on cadmium-induced deterioration of rat hepatocytes

The suitability of DL-alpha-lipoic acid (LA) to serve as an antidote in cadmium (Cd) toxicity in rat hepatocytes was investigated. Isolated hepatocytes were exposed to 200 and 450 microM Cd in the presence of 0.2, 1.0 and 5.0 mM LA, respectively. After 30 min of incubation various criteria of cell viability were monitored. Lipoic acid markedly diminished Cd uptake. Concomitantly, Cd-induced membrane injury, as reflected by the leakage of aspartate aminotransferase and sorbitol dehydrogenase (SDH) was decreased. Moreover, LA protected against intracellular toxic responses to Cd, such as a decrease in cellular SDH activity, a decrease in cellular acid soluble thiols, especially in total glutathione, a decrease in cellular urea and an increase in thiobarbituric acid (TBA) reactants, as a measure of lipid peroxidation. Most protective effects were seen in hepatocytes challenged with the lower Cd concentration and coincubated with 5 mM LA. In contrast, at 450 microM Cd even the highest LA concentration applied either did only reverse Cd-effects incompletely (SDH-response, TBA-reactants) or did not protect at all (Cd uptake, enzyme leakage, loss of glutathione). The data indicate that DL-alpha-lipoic acid serves as a protective tool against Cd-induced membrane damage and cell dysfunction in hepatocytes. This stands as long as Cd exposure is low enough to permit interaction with LA prior to interaction with cell structures.

The reversal of phenylarsenoxide inhibition of keto acid oxidation in mitochondrial and bacterial suspensions by lipoic acid and other disulphides

1. Inhibition of pyruvate oxidation in suspensions of Aerobacter aerogenes cells and of isolated mitochondria from rat heart and liver by phenylarsenoxide is prevented by an excess of lipoic acid, whereas inhibition due to certain bivalent cations is not. 2. In both systems inhibition persists when the bacteria and mitochondria are recovered and resuspended in fresh media in the absence of the inhibitor. Persistent inhibition due to preincubation with phenylarsenoxide, but not with the metal ions, is reversed by lipoic acid and by certain other disulphides. 3. 2,3-Dimercaptopropan-1-ol prevents the inhibition of pyruvate oxidation by phenylarsenoxide and by bivalent cations in both mitochondria and bacterial cells. 4. In aerobic suspensions of mitochondria and bacteria disulphides such as lipoic acid are reduced rapidly to dithiols. Reduction is inhibited by Co(2+), Ni(2+), Cd(2+) and Zn(2+), but not by phenylarsenoxide. 5. It is concluded that the inability of lipoic acid to prevent the action of the metal ions on pyruvate oxidation is due to the inhibition of its reduction to the effective dithiol.