Molecular aspects of lipoic acid in the prevention of diabetes complications

Antioxidant strategies in the management of diabetic neuropathy

Chronic hyperglycaemia (an abnormally high glucose concentration in the blood) resulting from defects in insulin secretion/action, or both, is the major hallmark of diabetes in which it is known to be involved in the progression of the condition to different complications that include diabetic neuropathy. Diabetic neuropathy (diabetes-induced nerve damage) is the most common diabetic complication and can be devastating because it can lead to disability. There is an increasing body of evidence associating diabetic neuropathy with oxidative stress. Oxidative stress results from the production of oxygen free radicals in the body in excess of its ability to eliminate them by antioxidant activity. Antioxidants have different mechanisms and sites of actions by which they exert their biochemical effects and ameliorate nerve dysfunction in diabetes by acting directly against oxidative damage. This review will examine different strategies for managing diabetic neuropathy which rely on exogenous antioxidants.

Alpha-Lipoic Acid and Antioxidant Diet Help to Improve Endothelial Dysfunction in Adolescents with Type 1 Diabetes: A Pilot Trial

After evaluating the prevalence of early endothelial dysfunction, as measured by means of reactive hyperemia in adolescents with type 1 diabetes, we started a 6-month, double-blind, randomized trial to test the efficacy of an antioxidant diet (± alpha-lipoic acid supplementation) to improve endothelial dysfunction. Seventy-one children and adolescents, ages 17 ± 3.9 yrs, with type 1 diabetes since 9.5 ± 5.3 yrs, using intensified insulin therapy, were randomized into 3 arms: (a) antioxidant diet 10.000 ORAC + alpha-lipoic acid; (b) antioxidant diet 10.000 ORAC + placebo; (c) controls. BMI, blood pressure, fasting lipid profile, HbA1c, insulin requirement, dietary habits, and body composition were determined in each patient. An antioxidant diet significantly improved endothelial dysfunction when supplemented with alpha-lipoic acid, unlike diet with placebo or controls. A significant reduction in bolus insulin was also observed. We speculate that alpha-lipoic acid might have an antioxidant effect in pediatric diabetes patients by reducing insulin.

Spectroscopic studies of R(+)-α-lipoic acid--cyclodextrin complexes

α-Lipoic acid (ALA) has a chiral center at the C6 position, and exists as two enantiomers, R(+)-ALA (RALA) and S(−)-ALA (SALA). RALA is naturally occurring, and is a cofactor for mitochondrial enzymes, therefore playing a major role in energy metabolism. However, RALA cannot be used for pharmaceuticals or nutraceuticals because it readily polymerizes via a 1,2-dithiolane ring-opening when exposed to light or heat. So, it is highly desired to find out the method to stabilize RALA. The purpose of this study is to provide the spectroscopic information of stabilized RALA and SALA through complexation with cyclodextrins (CDs), α-CD, β-CD and γ-CD and to examine the physical characteristics of the resultant complexes in the solid state. The RALA-CD structures were elucidated based on the micro fourier transform infrared (FT-IR) and Raman analyses. The FT-IR results showed that the C=O stretching vibration of RALA appeared at 1717 cm⁻¹ and then shifted on formation of the RALA-CD complexes. The Raman spectra showed that the S–S and C–S stretching vibrations for RALA at 511 cm⁻¹ (S–S), 631 cm⁻¹ (C–S) and 675 cm⁻¹ (C–S) drastically weakened and almost disappeared upon complexation with CDs. Several peaks indicative of O–H vibrations also shifted or changed in intensity. These results indicate that RALA and CDs form host-guest complexes by interacting with one another.

Role of dietary and endogenous antioxidants in diabetes

Diabetes affects different people of all ages, race, and sex. This is a condition characterized by a state of chronic hyperglycaemia that leads to an increase of intracellular oxidative stress linked to the overproduction of free radicals. In the present review, we focus our attention on the molecular mechanisms leading to oxidative stress-mediates complications with particular regard to central nervous system (CNS). Furthermore, the present review reports the effects of different kind of antioxidants with enzymatic and nonenzymatic action that may significantly decrease the intracellular free radicals' overproduction and prevents the hyperglycaemia-mediated complications.

Antidiabetic effect of the α-lipoic acid γ-cyclodextrin complex

In recent years, the number of patients suffering from diabetes mellitus has been increasing worldwide. In particular, type 2 diabetes mellitus, a lifestyle-related disease, is recognized as a serious disease with various complications. Many types of pharmaceutics or specific health foods have been used for the management of diabetes mellitus. At the same time, the relationship between diabetes mellitus and α-lipoic acid has been recognized for many years. In this study, we found that the α-lipoic acid γ-cyclodextrin complex exhibited an HbA_1c lowering effect for treating type 2 diabetes mellitus in animal models. Moreover, in this study, we investigated the activation of phosphorylation of AMP-activated protein kinase, which plays a role in cellular energy homeostasis, in the liver of KKA^y mice by using α-lipoic acid and the α-lipoic acid γ-cyclodextrin complex. Our results show that the α-lipoic acid γ-cyclodextrin complex strongly induced the phosphorylation of AMP-activated protein kinase. Thus, we concluded that intake of the α-lipoic acid γ-cyclodextrin complex exerted an antidiabetic effect by suppressing the elevation of postprandial hyperglycemia as well as doing exercise.

Alpha-lipoic acid as a pleiotropic compound with potential therapeutic use in diabetes and other chronic diseases

Alpha-lipoic acid is a naturally occurring substance, essential for the function of different enzymes that take part in mitochondria's oxidative metabolism. It is believed that alpha-lipoic acid or its reduced form, dihydrolipoic acid have many biochemical functions acting as biological antioxidants, as metal chelators, reducers of the oxidized forms of other antioxidant agents such as vitamin C and E, and modulator of the signaling transduction of several pathways. These above-mentioned actions have been shown in experimental studies emphasizing the use of alpha-lipoic acid as a potential therapeutic agent for many chronic diseases with great epidemiological as well economic and social impact such as brain diseases and cognitive dysfunctions like Alzheimer disease, obesity, nonalcoholic fatty liver disease, burning mouth syndrome, cardiovascular disease, hypertension, some types of cancer, glaucoma and osteoporosis. Many conflicting data have been found concerning the clinical use of alpha-lipoic acid in the treatment of diabetes and of diabetes-related chronic complications such as retinopathy, nephropathy, neuropathy, wound healing and diabetic cardiovascular autonomic neuropathy. The most frequent clinical condition in which alpha-lipoic acid has been studied was in the management of diabetic peripheral neuropathy in patients with type 1 as well type 2 diabetes. Considering that oxidative stress, a imbalance between pro and antioxidants with excessive production of reactive oxygen species, is a factor in the development of many diseases and that alpha-lipoic acid, a natural thiol antioxidant, has been shown to have beneficial effects on oxidative stress parameters in various tissues we wrote this article in order to make an up-to-date review of current thinking regarding alpha-lipoic acid and its use as an antioxidant drug therapy for a myriad of diseases that could have potential benefits from its use.

Antioxidant and toxicological effects elicited by alpha-lipoic acid in aquatic organisms

Lipoic acid (LA) is a disulfide-containing compound derived from octanoic acid that is synthesized in mitochondria. This molecule acts as a co-factor for mitochondrial enzymes that catalyze oxidative decarboxylation reactions. Several antioxidant properties of LA enable it to be considered as an "ideal antioxidant", having diverse benefits that allow it to deal with environmental or biological stress. Some of the effects induced by LA in aquatic organisms render it suitable for use in aquaculture. However, it is necessary to determine the appropriate dose(s) to be used with different species and even organs to maximize the beneficial antioxidant and detoxifying effects and to minimize the pro-oxidant toxic effects. This review analyzes and compiles existing data from aquatic organisms in which both benefits and drawbacks of LA have been described.

The role of antioxidants and other agents in alleviating hyperglycemia mediated oxidative stress and injury in liver

Several antioxidants and agents having similar antioxidant effects are known to exert beneficial effects in ameliorating the injurious effects of hyperglycemia on liver in different diabetic in vitro and in vivo models. The review deals with some of the agents which have been shown to exert protective effects on liver against hyperglycemic insult and the various mechanisms involved. The different classes of agents which protect the diabetic liver or decrease the severity of hyperglycemia mediated injury include flavonoids, catechins, and other polyphenolic compounds, curcumin and its derivatives, certain vitamins, hormones and drugs, trace elements, prototypical antioxidants and amino acids. Some of the pronounced changes mediated by the antioxidants in liver exposed to hyperglycemia include decreased oxidative stress, and alterations in carbohydrate and lipid metabolism. Other mechanisms through which the agents ameliorate hyperglycemia mediated liver injury include decrease in oxidative DNA and protein damage, restoration of mitochondrial structural and functional integrity, decrease in inflammation and improved insulin signaling. Thus, antioxidants may prove to be an important mode of defense in maintaining normal hepatic functions in diabetes.

R-α lipoic acid γ-cyclodextrin complex increases energy expenditure: a 4-month feeding study in mice

OBJECTIVE

A high-fat diet (HFD) affects energy expenditure in laboratory rodents. R-α lipoic acid cyclodextrin (RALA-CD) complex is a stable form of lipoic acid (LA) and may improve energy expenditure. The aim of this study was to determine the effect of RALA-CD on energy expenditure and underlying molecular targets in female laboratory mice.

METHODS

Female C57BL/6J mice were fed a HFD containing 0.1% LA for about 16 wk. The effects on energy expenditure, gene and protein expression were assessed using indirect calorimetry, real-time reverse transcriptase polymerase chain reaction, and Western blot, respectively.

RESULTS

Supplementing mice with RALA-CD resulted in a significant increase in energy expenditure. However, both RALA per se (without γ-cyclodextrin) and S-α lipoic acid cyclodextrin did not significantly alter energy expenditure. Furthermore RALA-CD changed expression of genes encoding proteins centrally involved in energy metabolism. Transcriptional key regulators sirtuin 3 and peroxisome proliferator-activated receptor-γ, coactivator 1 alpha, as well as thyroid related enzyme type 2 iodothyronine deiodinase were up-regulated in brown adipose tissue (BAT) of RALA-CD-fed mice. Importantly, mRNA and/or protein expression of downstream effectors uncoupling protein (Ucp) 1 and 3 also were elevated in BAT from RALA-CD-supplemented mice.

CONCLUSION

Overall, present data suggest that RALA-CD is a regulator of energy expenditure in laboratory mice.

α-Lipoic acid prevents p53 degradation in colon cancer cells by blocking NF-κB induction of RPS6KA4

α-Lipoic acid (α-LA) is a biogenic antioxidant that has been used successfully in the treatment of diabetic polyneuropathy and its application to many oxidative stress-associated chronic diseases has increased. In this study, we investigated the effect of α-LA on colorectal cancer cell growth and its underlying mechanism. α-LA treatment resulted in a marked reduction in the growth of HCT116 colon cancer cells in a dose-dependent manner through the G1 arrest of the cell cycle and apoptosis induction. α-LA treatment significantly increased tumor cell response to various apoptotic stresses, such as etoposide, 5-fluorouracil, UVC, γ-irradiation, hypoxia, and tumor necrosis factor α (TNFα). Interestingly, α-LA increased p53 protein stability and its apoptosis-enhancing effect was more evident in wild-type p53-carrying cells compared with p53-deficient cells, suggesting that the proapoptotic role of α-LA is associated with its p53-stabilizing function. On the basis of our microarray data showing α-LA downregulation of the ribosomal protein p90S6K (RPS6KA4), which has been reported to inhibit p53 function, we tested whether α-LA regulation of RPS6KA4 is associated with its proapoptotic function. α-LA treatment led to a marked reduction in the RPS6KA4 mRNA level in multiple colorectal cancer cells and restoration of RPS6KA4 expression markedly attenuated α-LA induction of apoptosis in a p53-dependent manner. In addition, we observed that RPS6KA4 expression is activated by TNFα whereas both basal and TNFα induction of RPS6KA4 are inhibited by the nuclear factor-κB (NF-κB) inhibitor BAY11-7082 or transfection of a dominant-negative mutant of NF-κB, indicating that NF-κB plays a crucial role in RPS6KA4 gene expression. Finally, we found that α-LA exerts an inhibitory effect on the nuclear translocation of NF-κB triggered by TNFα. Collectively, our study shows that α-LA suppresses colorectal tumor cell growth at least partially by preventing RPS6KA4-mediated p53 inhibition through blockade of NF-κB signaling.

Lipoic acid analogs with enhanced pharmacological activity

Lipoic acid (1,2-dithiolane-3-pentanoic acid) is a pharmacophore with unique antioxidant and cytoprotective properties. We synthesized a library based upon the condensation of natural and unnatural amino acids with the carboxylic acid moiety of lipoic acid. SAR studies were conducted using a cardiac ischemia-reperfusion animal model. Cytoprotective efficacy was associated with the R-enantiomer of the dithiolane. Potency of library compounds was dictated by the acidic strength of the adduct. α-N-[(R)-1,2-dithiolane-3-pentanoyl]-L-glutamyl-L-alanine, designated CMX-2043, was chosen for further pharmacologic evaluation.

Total antioxidant intake in relation to prostate cancer incidence in the Health Professionals Follow-Up Study

Epidemiologic evidence on the association of antioxidant intake and prostate cancer incidence is inconsistent. Total antioxidant intake and prostate cancer incidence have not previously been examined. Using the ferric-reducing antioxidant potential (FRAP) assay, the total antioxidant content (TAC) of diet and supplements was assessed in relation to prostate cancer incidence. A prospective cohort of 47,896 men aged 40-75 years was followed from 1986 to 2008 for prostate cancer incidence (N = 5,656), and they completed food frequency questionnaires (FFQs) every 4 years. A FRAP value was assigned to each item in the FFQ, and for each individual, TAC scores for diet, supplements and both (total) were calculated. Major contributors of TAC intake at baseline were coffee (28%), fruit and vegetables (23%) and dietary supplements (23%). In multivariate analyses for dietary TAC a weak inverse association was observed [highest versus lowest quintiles: 0.91 (0.83-1.00, p-trend = 0.03) for total prostate cancer and 0.81 (0.64-1.01, p-trend = 0.04) for advanced prostate cancer]; this association was mainly due to coffee. No association of total TAC on prostate cancer incidence was observed. A positive association with lethal and advanced prostate cancers was observed in the highest quintile of supplemental TAC intake: 1.28 (0.98-1.65, p-trend < 0.01) and 1.15 (0.92-1.43, p-trend = 0.04). The weak association between dietary antioxidant intake and reduced prostate cancer incidence may be related to specific antioxidants in coffee, to nonantioxidant coffee compounds or other effects of drinking coffee. The indication of increased risk for lethal and advanced prostate cancers with high TAC intake from supplements warrants further investigation.

Dietary strategies to recover from exercise-induced muscle damage

Exhaustive or unaccustomed intense exercise can cause exercise-induced muscle damage (EIMD) and its undesirable consequences may decrease the ability to exercise and to adhere to a training programme. This review briefly summarises the muscle damage process, focusing predominantly on oxidative stress and inflammation as contributing factors, and describes how nutrition may be positively used to recover from EIMD. The combined intake of carbohydrates and proteins and the use of antioxidants and/or anti-inflammatory nutrients within physiological ranges are interventions that may assist the recovery process. Although the works studying food instead of nutritional supplements are very scarce, their results seem to indicate that food might be a favourable option as a recovery strategy. To date, the only tested foods were milk, cherries, blueberries and pomegranate with promising results. Other potential solutions are foods rich in protein, carbohydrates, antioxidants and/or anti-inflammatory nutrients.

Protective Effect of Alpha-Lipoic Acid on Cypermethrin-Induced Oxidative Stress in Wistar Rats

Cypermethrin (CY), a class II pyrethroid pesticide, is globally used to control insects in the household and in agriculture. Despite beneficial roles, its uncontrolled and repetitive application leads to unintended effects in non-target organisms. In light of the relevant anti-oxidant properties of alpha-lipoic acid (ALA), in the work described herein we tested the effect of a commercially available ALA formulation on cypermethrin (CY)-induced oxidative stress in Wistar rats. The rats were orally administered with 53.14 mg/kg of ALA and 35.71 mg/kg of CY for 60 days. The treatment with CY did not induce changes in either locomotor activities or in body weight. Differences were observed on superoxide dismutase (SOD), catalase (CAT) and lipid peroxidation that were re-established by ALA treatment at similar levels of the placebo group. Furthermore, ALA formulation increased glutathione (GSH) level and glutathione peroxidase (GPx) activity. Because of the widespread use of CY, higher amounts of pesticide residues are present in food, and a diet supplementation with ALA could be an active free radical scavenger protecting against diseases associated with oxidative stress.

Endothelial dysfunction - a major mediator of diabetic vascular disease

The vascular endothelium is a multifunctional organ and is critically involved in modulating vascular tone and structure. Endothelial cells produce a wide range of factors that also regulate cellular adhesion, thromboresistance, smooth muscle cell proliferation, and vessel wall inflammation. Thus, endothelial function is important for the homeostasis of the body and its dysfunction is associated with several pathophysiological conditions, including atherosclerosis, hypertension and diabetes. Patients with diabetes invariably show an impairment of endothelium-dependent vasodilation. Therefore, understanding and treating endothelial dysfunction is a major focus in the prevention of vascular complications associated with all forms of diabetes mellitus. The mechanisms of endothelial dysfunction in diabetes may point to new management strategies for the prevention of cardiovascular disease in diabetes. This review will focus on the mechanisms and therapeutics that specifically target endothelial dysfunction in the context of a diabetic setting. Mechanisms including altered glucose metabolism, impaired insulin signaling, low-grade inflammatory state, and increased reactive oxygen species generation will be discussed. The importance of developing new pharmacological approaches that upregulate endothelium-derived nitric oxide synthesis and target key vascular ROS-producing enzymes will be highlighted and new strategies that might prove clinically relevant in preventing the development and/or retarding the progression of diabetes associated vascular complications.

Microvascular complications and diabetic retinopathy: recent advances and future implications

Retinal microvascular alterations have been observed during diabetic retinopathy (DR) due to the retinal susceptibility towards subtle pathological alterations. Therefore, retinal microvascular pathology is essential to understand the nature of retinal degenerations during DR. In this review, the role of retinal microvasculature complications during progression of DR, along with recent efforts to normalize such alterations for better therapeutic outcome, will be underlined. In addition, current therapeutics and future directions for advancement of standard treatment for DR patients will be discussed.

α-Lipoic acid enhances endogenous peroxisome-proliferator-activated receptor-γ to ameliorate experimental autoimmune encephalomyelitis in mice

ALA (α-lipoic acid) is a natural, endogenous antioxidant that acts as a PPAR-γ (peroxisome-proliferator-activated receptor-γ) agonist to counteract oxidative stress. Thus far, the antioxidative and immunomodulatory effects of ALA on EAE (experimental autoimmune encephalomyelitis) are not well understood. In this study, we found that ALA restricts the infiltration of inflammatory cells into the CNS (central nervous system) in MOG (myelin oligodendrocyte glycoprotein)-EAE mice, thus reducing the disease severity. In addition, we revealed that ALA significantly suppresses the number and percentage of encephalitogenic Th1 and Th17 cells and increases splenic Treg-cells (regulatory T-cells). Strikingly, we further demonstrated that ALA induces endogenous PPAR-γ centrally and peripherally but has no effect on HO-1 (haem oxygenase 1). Together, these data suggest that ALA can up-regulate endogenous systemic and central PPAR-γ and enhance systemic Treg-cells to inhibit the inflammatory response and ameliorate MOG-EAE. In conclusion, our data provide the first evidence that ALA can augment the production of PPAR-γ in vivo and modulate adaptive immunity both centrally and peripherally in EAE and may reveal further antioxidative and immunomodulatory mechanisms for the application of ALA in human MS (multiple sclerosis).

Lipoic acid lessens Th1-mediated inflammation in lipopolysaccharide-induced uveitis reducing selectively Th1 lymphocytes-related cytokines release

Inflammation results in the production of free radicals. We evaluated the anti-inflammatory and antioxidant capacity of lipoic acid in an experimental uveitis model upon a subcutaneous injection of endotoxin into Lewis rats. The role of oxidative stress in the endotoxin-induced uveitis model is well-known. Besides, the Th1 response classically performs a central part in the immunopathological process of experimental autoimmune uveitis. Exogenous sources of lipoic acid have been shown to exhibit antioxidant and anti-inflammatory properties. Our results show that lipoic acid treatment plays a preventive role in endotoxin-induced oxidative stress at 24 h post-administration and reduced Th1 lymphocytes-related cytokines by approximately 50-60%. Simultaneously, lipoic acid treatment caused a significant reduction in uveal histopathological grading and in the protein concentration in aqueous humors, but not in cellular infiltration.

The effect of lipoic acid and vitamin E therapies in individuals with the metabolic syndrome

The metabolic syndrome is associated with abnormal glucose and lipid metabolism, insulin resistance, increased oxidative stress and pro-inflammatory activity that increase the risk of type 2 diabetes and cardiovascular disease. The aim of this study was to investigate the effect of treatment with the antioxidant α-lipoic acid (ALA) with or without vitamin E supplementation, on markers of insulin resistance and systemic inflammation and plasma nonesterified fatty acid (NEFA) concentrations in individuals with the metabolic syndrome. In a randomized, double-blind, placebo-controlled trial, subjects with the metabolic syndrome received ALA (600 mg/day, n = 34), vitamin E (100 IU/day, n = 36), both ALA and vitamin E (n = 41), or matching placebo (n = 40) for 1 year. Fasting circulating concentrations of glucose and insulin were measure every 3 months and NEFA, markers of inflammation, adiponectin and vitamin E were measured at 6 monthly intervals. Plasma NEFA concentrations decreased [-10 (-18, 0)%] at a marginal level of significance (p = 0.05) in those who received ALA alone compared with placebo and decreased [-8 (-14, -1)% (95% CI)] significantly (P = 0.02) in participants who were randomised to ALA with and without vitamin E compared with those who did not receive ALA. Fasting glucose, insulin, homeostatic model assessment of insulin resistance, adiponectin, and markers of inflammation did not change significantly during the study. These data suggest that prolonged treatment with ALA may modestly reduce plasma NEFA concentrations but does not alter insulin or glucose levels in individuals with the metabolic syndrome.

Lipoic acid suppresses portal endotoxemia-induced steatohepatitis and pancreatic inflammation in rats

AIM: To examine the effect of α-lipoic acid (LA) on mild portal endotoxemia-induced steatohepatitis and associated pancreatic abnormalities in fructose-fed rats.

METHODS: Rats were randomly assigned into two groups with a regular or 60% fructose-enriched diet for 8 wk. After fructose feeding for 4 wk, rats were further divided into four subgroups: with intraportal saline (F_PV), with intraportal saline plus administration of LA (F_{PV + LA}), with lipopolysaccharide (LPS) infusion (F_PLPS), and with LPS infusion plus administration of LA (F_{PLPS + LA}). Rats were treated with LPS using intraportal infusion while LA was administered orally. Metabolite levels, superoxide levels, inflammatory markers, malondialdehyde content, glutathione content and toll-like receptor 4 (TLR4) gene expression were all measured using standard biochemical techniques. Pancreatic insulin secretion was evaluated by a hyperglycemic clamp technique. Histology of liver and pancreas tissues were evaluated using hematoxylin and eosin staining and immunohistochemistry.

RESULTS: Fructose-induced elevation in plasma C-reactive protein, amylase, superoxide, white blood cell count as well as in hepatic and pancreatic contents of malondialdehyde, tumor necrosis factor alpha and interleukin-6 were increased in animals treated with LPS and reversed with LA administration. The augmented hepatic gene expression of TLR4 in fructose-fed rats was further increased in those with intraportal LPS infusion, which was partially reversed by LA administration. Pathological examination showed inflammatory changes and leukocyte infiltration in hepatic and pancreatic islets of animals treated with LPS but were rarely observed in those with LA treatment. In addition to affects on the liver, impaired pancreatic insulin secretion seen in fructose-fed rats was deteriorated in with LPS treatment and partially reversed with LA administration.

CONCLUSION: These data suggest LA could significantly suppress mild portal-endotoxemia but not fructose-induced liver and pancreatic abnormalities in a rodent model for metabolic syndrome.

From clinical description, to in vitro and animal studies, and backward to patients: oxidative stress and mitochondrial dysfunction in Fanconi anemia

Fanconi anemia (FA) is a rare genetic disease associated with deficiencies in DNA repair pathways. A body of literature points to a pro-oxidant state in FA patients, along with evidence for oxidative stress (OS) in the FA phenotype reported by in vitro, molecular, and animal studies. A highlight arises from the detection of mitochondrial dysfunction (MDF) in FA cell lines of complementation groups A, C, D2, and G. As yet lacking, in vivo studies should focus on FA-associated MDF, which may help in the understanding of the mitochondrial basis of OS detected in cells and body fluids from FA patients. Beyond the in vitro and animal databases, the available analytical devices may prompt the direct observation of metabolic and mitochondrial alterations in FA patients. These studies should evaluate a set of MDF-related endpoints, to be related to OS endpoints. The working hypothesis is raised that, parallel to OS, nitrosative stress might be another, so far unexplored, hallmark of the FA phenotype. The expected results may shed light on the FA pathogenesis and might provide grounds for pilot chemoprevention trials using mitochondrial nutrients.

α-lipoic acid protects dopaminergic neurons against MPP+-induced apoptosis by attenuating reactive oxygen species formation

Reactive oxygen species (ROS) elicited by oxidative stress are widely recognized as a major initiator in the dege-neration of dopaminergic neurons distinctive of Parkinson's disease (PD). The interaction of ROS with mitochondria triggers sequential events in the mitochondrial cell death pathway, which is thought to be responsible for ROS-mediated neurodegeneration in PD. α-lipoic acid (LA) is a pleiotropic compound with potential pharmacotherapeutic value against a range of pathophysiological insults. Its protective actions against oxidative damage by scavenging ROS and reducing production of free radicals have been reported in various in vitro and in vivo systems. This study analyzed the ability of LA to protect PC12 neuronal cells from toxicity of 1-methyl-4-phenylpyridinium (MPP+), the neurotoxic metabolite of 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) which is known to kill dopaminergic neurons selectively and to cause severe parkinsonism-like symptoms in humans and primate animals. Our results demonstrate that the apoptosis of PC12 cells elicited by MPP+ could be significantly prevented by pretreatment with LA for 1 h. In addition, LA inhibits intercellular ROS levels and the mitochondrial transmembrane permeability, the key players in the pathogenesis of PD, thereby protecting dopaminergic neuronal cells against oxidative damage.

New concepts in diabetic embryopathy

Diabetes mellitus is responsible for nearly 10% of fetal anomalies in diabetic pregnancies. Although aggressive perinatal care and glycemic control are available in developed countries, the birth defect rate in diabetic pregnancies remains higher than that in the general population. Major cellular activities (ie, proliferation and apoptosis) and intracellular metabolic conditions (ie, nitrosative, oxidative, and endoplasmic reticulum stress) have been shown to be associated with diabetic embryopathy using animal models. Translating advances made in animal studies into clinical applications in humans requires collaborative efforts across the basic research, preclinical, and clinical communities.

α-Lipoic acid-induced inhibition of proliferation and met phosphorylation in human non-small cell lung cancer cells

α-Lipoic acid (α-LA), a naturally occurring anti-oxidant and co-factor for metabolic enzymes, suppresses the growth of different types of tumor cells. The mechanisms that are responsible for these results, however, remain to be elucidated. In the present study, we investigated the effects of α-LA on the proliferation and activation status of definitive receptor tyrosine kinases, epidermal growth factor receptor (EGFR) and Met/hepatocyte growth factor (HGF) receptor, in gefitinib-sensitive human non-small cell lung cancer cells harboring EGFRs with an activating mutation. The enantiomers R-α-LA and S-α-LA suppressed cell proliferation and increased the level of reactive oxygen species in HCC-827 and PC-9 human non-small cell lung cancer cells in an indistinguishable dose-dependent fashion. A phospho-receptor tyrosine kinase array and cell cycle analysis indicated that α-LA decreased tyrosine phosphorylation levels of EGFR, ErbB2, and Met, and this was associated with an inhibition in the cell-cycle transition from the G1 phase to the S phase without inducing apoptosis. Gefitinib, an inhibitor for EGFR tyrosine kinase, inhibited EGFR tyrosine phosphorylation/activation and proliferation of the cells. Instead, the addition of HGF induced Met tyrosine phosphorylation, and this was associated with a resistance to gefitinib-induced growth inhibition, which meant a gain in proliferative ability. In the presence of gefitinib and HGF, the addition of α-LA suppressed Met tyrosine phosphorylation, and this was associated with an inhibition in cell growth. These results suggest that the suppression of tyrosine phosphorylation/activation of growth factor receptors that is critical for the proliferation of human non-small cell lung cancer cells is a mechanism by which α-LA exerts growth inhibition for cancer cells.

Mechanisms of diabetic complications

It is increasingly apparent that not only is a cure for the current worldwide diabetes epidemic required, but also for its major complications, affecting both small and large blood vessels. These complications occur in the majority of individuals with both type 1 and type 2 diabetes. Among the most prevalent microvascular complications are kidney disease, blindness, and amputations, with current therapies only slowing disease progression. Impaired kidney function, exhibited as a reduced glomerular filtration rate, is also a major risk factor for macrovascular complications, such as heart attacks and strokes. There have been a large number of new therapies tested in clinical trials for diabetic complications, with, in general, rather disappointing results. Indeed, it remains to be fully defined as to which pathways in diabetic complications are essentially protective rather than pathological, in terms of their effects on the underlying disease process. Furthermore, seemingly independent pathways are also showing significant interactions with each other to exacerbate pathology. Interestingly, some of these pathways may not only play key roles in complications but also in the development of diabetes per se. This review aims to comprehensively discuss the well validated, as well as putative mechanisms involved in the development of diabetic complications. In addition, new fields of research, which warrant further investigation as potential therapeutic targets of the future, will be highlighted.

Analysis of the enhanced stability of r(+)-alpha lipoic Acid by the complex formation with cyclodextrins

R(+)-alpha lipoic acid (RALA) is one of the cofactors for mitochondrial enzymes and, therefore, plays a central role in energy metabolism. RALA is unstable when exposed to low pH or heat, and therefore, it is difficult to use enantiopure RALA as a pharma- and nutra-ceutical. In this study, we have aimed to stabilize RALA through complex formation with cyclodextrins (CDs). α-CD, β-CD and γ-CD were used for the formation of these RALA-CD complexes. We confirmed the complex formation using differential scanning calorimetry and showed by using HPLC analysis that complexed RALA is more stable than free RALA when subjected to humidity and high temperature or acidic pH conditions. Scanning electron microscopy studies showed that the particle size and shape differed depending on the cyclodextrin used for complexation. Further, the complexes of CD and RALA showed a different particle size distribution pattern compared with that of CD itself or that of the physical mixture of RALA and CD.

Effects of alpha lipoic acid and its R+ enantiomer supplemented to hyperbaric oxygen therapy on interleukin-6, TNF-α and EGF production in chronic leg wound healing

CONTEXT

Lipoic acid (LA) and hyperbaric oxygenation therapy (HBOT) improve chronic wound healing.

OBJECTIVE

We compared the effects of LA or its enantiomer R-(+)-lipoic acid (RLA) on wound healing.

MATERIALS AND METHODS

Groups LA + HBOT (L), RLA + HBOT (R) and placebo + HBOT (P). Lesion areas measured before treatment and on 20th and 40th day. The biopsies and plasma were harvested before treatment and on 7th and 14th (measurements of VEGF, vascular endothelial growth factor; EGF, epidermal growth factor, TNF-α and IL-6).

RESULTS

Ulcers improved more on RLA. In both L and R groups, EGF and VEFG increased in time. RLA decreased IL-6 on T7 and T14, which did not happen with LA. TNF-α levels decreased on T14 in both LA and RLA.

DISCUSSION

The improved wound healing is associated with increased EGF and VEGF and reduced plasma TNF-α and IL-6.

CONCLUSION

RLA may be more effective than LA in improving chronic wound healing in patients undergoing HBO therapy.

Decreased O-GlcNAcylation of the key proteins in kinase and redox signalling pathways is a novel mechanism of the beneficial effect of α-lipoic acid in diabetic liver

The present study aimed to investigate the effects of the treatment with a-lipoic acid (LA), a naturally occurring compound possessing antioxidant activity, on liver oxidant stress in a rat model of streptozotocin (STZ)-induced diabetes by examining potential mechanistic points that influence changes in the expression of antioxidant enzymes such as catalase (CAT) and CuZn/Mn superoxide dismutase(s) (SOD). LA was administered for 4 weeks by daily intraperitoneal injections (10 mg/kg) to STZ-induced diabetic rats, starting from the last STZ treatment. LA administration practically normalised the activities of the indicators of hepatocellular injury, alanine and aspartate aminotransferases, and lowered oxidative stress, as observed by the thiobarbituric acid-reactive substance assay, restored the reduced glutathione:glutathione disulphide ratio and increased the protein sulfhydryl group content. The lower level of DNA damage detected by the comet assay revealed that LA reduced cytotoxic signalling, exerting a hepatoprotective effect. The LA-treated diabetic rats displayed restored specific enzymatic activities of CAT, CuZnSOD and MnSOD. Quantitative real-time PCR analysis showed that LA restored CAT gene expression to its physiological level and increased CuZnSOD gene expression, but the gene expression of MnSOD remained at the diabetic level. Although the amounts of CAT and CuZnSOD protein expression returned to the control levels, the protein expression of MnSOD was elevated. These results suggested that LA administration affected CAT and CuZnSOD expression mainly at the transcriptional level, and MnSOD expression at the post-transcriptional level. The observed LA-promoted decrease in the O-GlcNAcylation of extracellular signal-regulated kinase, protein 38 kinase, NF-kB, CCAAT/enhancer-binding protein and the antioxidative enzymes themselves in diabetic rats suggests that the regulatory mechanisms that supported the changes in antioxidative enzyme expression were also influenced by post-translational mechanisms.

Physical activity and alpha-lipoic acid modulate inflammatory response through changes in thiol redox status

α-Lipoic acid (αLA), as an inductor of hydrogen peroxide (H2O2) and nitrogen oxide (NO) generation and modulator of thiol redox status, plays an important role in cell signalling pathways. The study was designed to observe the effect of αLA on inflammatory response through changes in H2O2 and NO levels as well as thiol redox status. Sixteen physically active males were randomly assigned to one of two groups: placebo or αLA (1,200 mg d(-1) for 10 days prior to exercise). The exercise trial involved a 90-min run at 65% VO2max (0% gradient) followed by 15-min eccentric phase at 65% VO2max (-10% gradient). Blood samples were collected before the exercise trial and then again 20 min, 24, and 48 h after. αLA significantly elevated H2O2 but reduced NO generation before or after exercise. Thiol redox status (GSHtotal-2GSSG/GSSG) increased by >50% after αLA and exercise (ANOVA, P < 0.05) and correlated with changes in cytokines interleukin-6 (IL-6) (r = -0.478, P < 0.05) and IL-10 (r = -0.455, P < 0.05). This was caused by strong effect of αLA on GSSG concentration. αLA elevated IL-6 and IL-10 levels at 20 min after exercise and decreased in interleukin-1β and tumor necrosis factor α before and after exercise. This enhanced the regeneration of injured muscles. Creatine kinase activity tended to lower values after αLA intake. The study suggests that the combination of intense exercise with α-lipoic acid intake might be useful to improve the skeletal muscle regeneration through changes in inflammatory response which are associated with H2O2 and NO generation as well as thiol redox status.

Micronutrient modulation of NF-κB in oral keratinocytes exposed to periodontal bacteria

Chronic periodontal diseases are characterised by a dysregulated and exaggerated inflammatory/immune response to plaque bacteria. We have demonstrated previously that oral keratinocytes up-regulate key molecular markers of inflammation, including NF-κB and cytokine signalling, when exposed to the periodontal bacteria Porphyromonas gingivalis and Fusobacterium nucleatum in vitro. The purpose of the current study was to investigate whether α-lipoic acid was able to abrogate bacterially-induced pro-inflammatory changes in the H400 oral epithelial cell line. Initial studies indicated that α-lipoic acid supplementation (1-4 mM) significantly reduced cell attachment; lower concentrations (<0.5 mM) enabled >85% cell adhesion at 24 h. While a pro-inflammatory response, demonstrable by NF-κB translocation, gene expression and protein production was evident in H400 cells following exposure to P. gingivalis and F. nucleatum, pre-incubation of cells with 0.5 mM α-lipoic acid modulated this response. α-Lipoic acid pre-treatment significantly decreased levels of bacterially-induced NF-κB activation and IL-8 protein production, and differentially modulated transcript levels for IL-8, IL-1β, TNF-α and GM-CSF, TLR2, 4, 9, S100A8, S100A9, lysyl oxidase, NF-κB1, HMOX, and SOD2. Overall, the data indicate that α-lipoic acid exerts an anti-inflammatory effect on oral epithelial cells exposed to periodontal bacteria and thus may provide a novel adjunctive treatment for periodontal diseases.

Effects of lipoic acid on AMPK and adiponectin in adipose tissue of low- and high-fat-fed rats

BACKGROUND

Lipoic acid (LA) is an antioxidant with antiobesity and antidiabetic properties. Adiponectin is an adipokine with potent anti-inflammatory and insulin-sensitizing properties. AMP-activated protein kinase (AMPK) is a key enzyme involved in cellular energy homeostasis. Activation of AMPK has been considered as a target to reverse the metabolic abnormalities associated with obesity and type 2 diabetes.

AIM OF THE STUDY

The aim of this study was to determine the effects of LA on AMPK phosphorylation and adiponectin production in adipose tissue of low-fat (control diet) and high-fat diet-fed rats.

RESULTS

Dietary supplementation with LA reduced body weight and adiposity in control and high-fat-fed rats. LA also reduced basal hyperinsulinemia as well as the homeostasis model assessment (HOMA) levels, an index of insulin resistance, in high-fat-fed rats, which was in part independent of their food intake lowering actions. Furthermore, AMPK phosphorylation was increased in white adipose tissue (WAT) from LA-treated rats as compared with pair-fed animals. Dietary supplementation with LA also upregulated adiponectin gene expression in WAT, while a negative correlation between adiposity-corrected adiponectin levels and HOMA index was found. Our present data suggest that the ability of LA supplementation to prevent insulin resistance in high-fat diet-fed rats might be related in part to the stimulation of AMPK and adiponectin in WAT.

A combination of lipoic acid plus coenzyme Q10 induces PGC1α, a master switch of energy metabolism, improves stress response, and increases cellular glutathione levels in cultured C2C12 skeletal muscle cells

Skeletal muscle function largely depend on intact energy metabolism, stress response, and antioxidant defense mechanisms. In this study, we tested the effect of a combined supplementation of α-lipoic acid (LA) plus coenzyme Q10 (Q10) on PPARγ-coactivator α (PGC1α) activity, expression of glutathione-related phase II enzymes and glutathione (GSH) levels in cultured C2C12 myotubes. Supplementation of myotubes with 250 μmol/L LA plus 100 μmol/L Q10 significantly increased nuclear levels of PGC1α, a master switch of energy metabolism and mitochondrial biogenesis. The increase of nuclear PGC1α was accompanied by an increase in PPARγ transactivation, a downstream target of PGC1α, and an increase in mitochondrial transcription factor A mRNA centrally involved in mitochondrial replication and transcription. Furthermore, supplementation of myotubes with LA plus Q10 resulted in an increase of genes encoding proteins involved in stress response, GSH synthesis, and its recycling. In LA-plus-Q10-treated myotubes a significant 4-fold increase in GSH was evident. This increase in GSH was accompanied by increased nuclear Nrf2 protein levels, partly regulating γGCS and GST gene expression. Present data suggest that the combined supplementation of skeletal muscle cells with LA plus Q10 may improve energy homeostasis, stress response, and antioxidant defense mechanisms.

Curcumin--from molecule to biological function

Turmeric is traditionally used as a spice and coloring in foods. It is an important ingredient in curry and gives curry powder its characteristic yellow color. As a consequence of its intense yellow color, turmeric, or curcumin (food additive E100), is used as a food coloring (e.g. mustard). Turmeric contains the curcuminoids curcumin, demethoxycurcumin, and bisdemethoxycurcumin. Recently, the health properties (neuroprotection, chemo-, and cancer prevention) of curcuminoids have gained increasing attention. Curcuminoids induce endogenous antioxidant defense mechanisms in the organism and have anti-inflammatory activity. Curcuminoids influence gene expression as well as epigenetic mechanisms. Synthetic curcumin analogues also exhibit biological activity. This Review describes the development of curcumin from a "traditional" spice and food coloring to a "modern" biological regulator.

alpha-lipoic acid prevents the induction of iNOS gene expression through destabilization of its mRNA in proinflammatory cytokine-stimulated hepatocytes

BACKGROUND/AIMS

α-Lipoic acid (α-LA) has been reported to reduce ischemia-reperfusion injury (IRI). Proinflammatory cytokines stimulate the induction of inducible nitric oxide synthase (iNOS) gene expression, leading to excess production of NO and resulting in liver injury including IRI. We hypothesized that inhibition of iNOS induction underlies the protective effects of α-LA on the liver. The objective was to investigate whether α-LA directly influences iNOS induction in cultured hepatocytes, which is used as a simple in vitro injury model, and the mechanism involved.

METHODS

Primary cultured rat hepatocytes were treated with interleukin (IL)-1β in the presence or absence of α-LA. The induction of iNOS and NO production and its signal were analyzed.

RESULTS

α-LA inhibited the expression of iNOS mRNA and protein dose- and time-dependently, resulting in decreases in NO production. α-LA had no effects on the degradation of IκB proteins and activation of NF-κB. In contrast, α-LA inhibited the upregulation of type I IL-1 receptor stimulated by IL-1β, although α-LA had no effect on Akt activation. Transfection experiments with iNOS promoter-luciferase constructs revealed that α-LA had no effect on the transactivation of the iNOS promoter, but decreased the stabilization of iNOS mRNA. Further, α-LA inhibited the expression of an iNOS gene antisense-transcript, which is involved in iNOS mRNA stability.

CONCLUSIONS

Results indicate that α-LA inhibits the induction of iNOS gene expression at a posttranscriptional step via iNOS mRNA stabilization, rather than promoter activation. It may provide useful therapeutic effects through the suppression of iNOS induction involved in liver injury.

Structure of the inclusion complex of β-cyclodextrin with lipoic acid from laboratory powder diffraction data

The crystal structure of the inclusion complex of β-cyclodextrin with lipoic acid was determined from laboratory powder diffraction data. Thermogravimetric data was used to estimate the number of water molecules in the crystal structure. Lipoic acid is included in β-cyclodextrin through its primary face with the five-membered ring reaching the center plane of the cyclodextrin cavity and its fatty acid chain adopting a bent conformation. Lipoic acid and β-cyclodextrin form a channel-like packing which is stabilized by guest–host hydrogen bonding and close contacts, host–host intermolecular interactions and hydrogen bonding involving the water molecules.

Ginsenoside Re attenuates diabetes-associated cognitive deficits in rats

OBJECTIVE

This study was designed to investigate the effect of ginsenoside Re (Re) on cognitive functions, oxidative stress and inflammation in streptozotocin-induced diabetic rats.

RESEARCH DESIGN AND METHOD

Diabetic rats were treated with Re (40mg/kg) for 8weeks, blood glucose and body weight were measured monthly and weekly, respectively. Cognitive performances were evaluated with Morris water maze. Brain was obtained for measurements of TNF-α and malondialdehyde (MDA) contents in both temporal cortex and hippocampus, blood was collected for assays of TNF-α, MDA and reduced glutathione (GSH) levels.

RESULTS

Learning and memory abilities were significantly (both P<0.01) impaired in diabetic rats, accompanied by the marked (all P<0.01) elevations of TNF-α and MDA levels in temporal cortex and hippocampus. Increment of MDA and decrement of GSH in serum also occurred with significant differences (both P<0.01). Chronic treatment with Re markedly (P<0.05) improved the cognition of diabetic rats, evidenced by the decreased escape latency and the increased percentage of time spent in the target quadrant. Furthermore, Re treatment remarkably (P<0.05) reduced the levels of TNF-α and MDA in both brain areas of diabetic rats. Decline of MDA level and elevation of GSH level in serum were also seen in Re-treated diabetic rats, coupled with decrease in serum glucose level, all with statistically significant differences.

CONCLUSIONS

Our findings firstly provide the first evidence that ginsenoside Re can remarkably attenuate diabetes-associated cognitive decline, secondly confirm the involvement of oxidative stress and inflammation in the development of cognitive impairment caused by diabetes, finally point toward the potential of ginsenoside Re as an adjuvant therapy to conventional anti-hyperglycemic regimens as well as diabetes-associated cognitive decline.