Beata Skibska

Lipoic acid – biological activity and therapeutic potential

α-Lipoic acid (LA; 5-(1,2-dithiolan-3-yl)pentanoic acid) was originally isolated from bovine liver by Reed et al. in 1951. LA was once considered a vitamin. Subsequently, it was found that LA is not a vitamin and is synthesized by plants and animals. LA is covalently bound to the ε-amino group of lysine residues and functions as a cofactor for mitochondrial enzymes by catalyzing the oxidative decarboxylation of pyruvate, α-ketoglutarate and branched-chain α-keto acids. LA and its reduced form - dihydrolipoic acid (DHLA), meet all the criteria for an ideal antioxidant because they can easily quench radicals, can chelate metals, have an amphiphlic character and they do not exhibit any serious side effects. They interact with other antioxidants and can regenerate them. For this reason, LA is called an antioxidant of antioxidants. LA has an influence on the second messenger nuclear factor κB (NF-κB) and attenuates the release of free radicals and cytotoxic cytokines. The therapeutic action of LA is based on its antioxidant properties. Current studies support its use in the ancillary treatment of many diseases, such as diabetes, cardiovascular, neurodegenerative, autoimmune diseases, cancer and AIDS. This review was undertaken to gather the most recent information regarding the therapeutic properties of LA and its possible utility in disease treatment.

The NADPH oxidase family and its inhibitors.

The classical nicotinamide adenine dinucleotide phosphate (NADPH) oxidase was originally detected in neutrophils as a multicomponent enzyme that catalyzes the generation of superoxide from oxygen and the reduced form of NADPH. This enzyme is composed of two membrane-bound subunits (p22phox and gp91phox), three cytosolic subunits (p67phox, p47phox, and p40phox) and a small G-protein Rac (Rac1 and Rac2). Recently, it has been demonstrated that there are several isoforms of nonphagocytic NADPH oxidase. Endothelial cells, vascular smooth muscle cells or adventitial fibroblasts possess multiple isoforms of this enzyme. The new homologs, along with gp91phox are now designated the Nox family of NADPH oxidases and are key sources of reactive oxygen species in the vasculature. Reactive oxygen species play a significant role in regulating endothelial function and vascular tone. However, besides the participation in the processes of physiological cell, these enzymes can also be the perpetrator of oxidative stress that causes endothelial dysfunction. This review summarizes the current state of knowledge of the structure and functions of NADPH oxidase and NADPH oxidase inhibitors in the treatment of disorders with endothelial damage.

The Role of Endothelin-1 and Endothelin Receptor Antagonists in Inflammatory Response and Sepsis

Endothelin-1 (ET-1) is a potent endogenous vasoconstrictor, mainly secreted by endothelial cells. It acts through two types of receptors: ETA and ETB. Apart from a vasoconstrictive action, ET-1 causes fibrosis of the vascular cells and stimulates production of reactive oxygen species. It is claimed that ET-1 induces proinflammatory mechanisms, increasing superoxide anion production and cytokine secretion. A recent study has shown that ET-1 is involved in the activation of transcription factors such as NF-κB and expression of proinflammatory cytokines including TNF-α, IL-1, and IL-6. It has been also indicated that during endotoxaemia, the plasma level of ET-1 is increased in various animal species. Some authors indicate a clear correlation between endothelin plasma level and morbidity/mortality rate in septic patients. These pathological effects of ET-1 may be abrogated at least partly by endothelin receptor blockade. ET-1 receptor antagonists may be useful for prevention of various vascular diseases. This review summarises the current knowledge regarding endothelin receptor antagonists and the role of ET-1 in sepsis and inflammation.

Effects of lipoic acid on spleen oxidative stress after LPS administration

BACKGROUND Bacterial endotoxin (lipopolysaccharide - LPS) is a strong modulator of the immune system that plays a crucial role in the pathogenesis of endotoxic shock. The aim of the study was to investigate the effects of lipoic acid (LA) on oxidative stress markers in spleen homogenates obtained from LPS-induced endotoxic shock rats. METHODS The animals were treated with saline or lipoic acid (LA) (60 or 100 mg/kg b.w. iv) 30 min before or 30 min after LPS administration (30 mg/kg b.w. iv). Five hours after LPS, LA or saline administration, the animals were euthanized and their spleens were isolated for measurements. RESULTS The LPS-treated animals developed oxidative stress, indicated by a significant increase in thiobarbituric acid-reactive substances (TBARS) and hydrogen peroxide (H2O2) concentrations (p<0.001) as well as an insignificant decrease in the level of sulfhydryl groups (-SH groups) and the glutathione redox ratio [reduced glutathione (GSH) to oxidized glutathione (GSSG) ratio] (p<0.02) as compared with control group. Treatment with LA (60 or 100 mg/kg) before or after LPS administration resulted in an increase in -SH group content (p<0.01) and a decrease in TBARS and H2O2 concentration in the spleen as compared with LPS group (p<0.001). LA (60 or 100 mg/kg) before LPS administration decreased the level of GSSG (p<0.05) and increased the level of GSH in spleen homogenates (p<0.05), resulting in an increase in the GSH/GSSG ratio compared with the LPS group (p<0.01). It also improved the LPS-induced increase in the spleen weight (SW) to body weight (BW) ratio (p<0.001 vs. control). CONCLUSION The present results have shown that LA is endowed with antioxidant properties that are protective in the spleen against the deleterious actions of Gram-negative bacterial endotoxin.

The Protective Effect of Lipoic Acid on Selected Cardiovascular Diseases Caused by Age-Related Oxidative Stress

Oxidative stress is considered to be the primary cause of many cardiovascular diseases, including endothelial dysfunction in atherosclerosis and ischemic heart disease, hypertension, and heart failure. Oxidative stress increases during the aging process, resulting in either increased reactive oxygen species (ROS) production or decreased antioxidant defense. The increase in the incidence of cardiovascular disease is directly related to age. Aging is also associated with oxidative stress, which in turn leads to accelerated cellular senescence and organ dysfunction. Antioxidants may help lower the incidence of some pathologies of cardiovascular diseases and have antiaging properties. Lipoic acid (LA) is a natural antioxidant which is believed to have a beneficial effect on oxidative stress parameters in relation to diseases of the cardiovascular system.

ET-1 mediates the release of reactive oxygen species and TNF-α in lung tissue by protein kinase C α and β1

BACKGROUND The aim of this study was to determine the involvement of protein kinase C (PKC) in the ET-1 induced generation of reactive oxygen species and TNF-α in rat lungs. METHODS Experiments were performed on 6 groups of rats: Group I: saline-treated control; Group II: saline followed by endothelin-1 (ET-1) (3μg/kg); Group III: saline followed by selective PKC αβ1 inhibitor (Gö6976) (2μg/kg); Group IV: Gö6976 (2μg/kg) administered 30min before ET-1 (3μg/kg); Group V: saline followed by the PKC activator phorbol 12-myristate 13-acetate (PMA) (50μg/kg); Group VI: Gö6976 (2μg/kg) administered 30min before PMA (50μg/kg). After 5h, the animals were euthanized and their lungs were isolated for measurements. RESULTS ET-1 resulted in increase in thiobarbituric acid reactive substances (TBARS) and hydrogen peroxide (H2O2) levels and lung edema, as well as a decrease in GSH/GSSG ratio compared to the controls. The level of TNF-α also was elevated in the presence of ET-1. Administration of Gö6976 30min before ET-1 injection significantly decreased lung edema, as well as the concentrations of TBARS, H2O2 and TNF-α, but increased the GSH/GSSG redox ratio compared to ET-1. Conversely, PMA elevated lung edema and TBARS, H2O2 and TNF-α concentrations, but decreased the GSH/GSSG redox ratio compared to the control group. Treatment with Gö6976 significantly ameliorated the PMA-induced oxidative stress parameters, decreased tissue TNF-α level, and lung edema. CONCLUSION Endothelin-1 induces ROS generation, increases TNF-α level and lung edema via activation of PKC αβ1.

Anti-oxidative and anti-inflammatory effects of lipoic acid in rat liver.

INTRODUCTION Lipopolysaccharide (LPS) is a key inflammatory component of Gram-negative bacteria, which after entering the systemic circulation contributes to the development of septic hepatic failure. AIM The aim of this study was to evaluate the effects of alpha lipoic acid (LA) on oxidative stress parameters and inflammation in endotoxemic rat liver. MATERIAL/METHODS Male Wistar rats were divided into 4 groups, each group consisting of 8 animals. Group I received saline and served as a control, Group II received a single dose of LA (60 mg/kg i.v.), Group III received lipopolysaccharide (LPS) (15 mg/kg i.v.), and Group IV received LPS (15 mg/kg i.v.) and 30 min later received LA (60 mg/kg i.v.). Five hours after LPS or LA administration, the animals were sacrificed and the liver was isolated for measurements of levels of thiobarbituric acid reactive substances (TBARS), hydrogen peroxide (H2O2), total sulfhydryl groups (-SH), total glutathione (tGSH) and reduced glutathione (GSH). RESULTS Injection of LPS caused a significant increase in liver TBARS and H2O2 levels and a significant decrease in levels of -SH groups, tGSH and GSH. LPS-treated rats also showed an increase in TNF-α and IL-6 levels and edema in the liver. The administration of LA to endotoxemic rats significantly reduced TBARS, H2O2, TNF-α, and IL-6 levels and reduced edema in the liver when compared to the LPS group. This antioxidant also resulted in an increase in -SH groups and tGSH and GSH levels and ameliorated the glutathione redox status when compared to the LPS group. CONCLUSIONS The results indicated that LA administered 30 min following LPS infusion may effectively prevent oxidative stress and inflammation in the liver. Thus LA is a potent antioxidant that can be useful in rebuilding LPS-induced damaged liver tissue.

Estimate of antioxidant capacity and lipid peroxidation in plasma of healthy subjects

Serum contains various antioxidant molecules that may provide important protection against free radical attack. The aim of this work was to assess the total antioxidant capacity of plasma and a marker of lipid per oxidation [(thiobarbituric acid-reactive substances (TBARS)] in plasma of healthy smoking and non-smoking young and elderly subjects. In addition, we investigated plasma concentrations of α-tocopherol, β-carotene, and ascorbic acid. In in vitro experiments, the effects of exogenous compounds (ascorbic acid, uric acid, Trolox) on total ferric-reducing activity of plasma (FRAP) were also tested. We demonstrated that total antioxidant capacity of plasma obtained from healthy non-smoking young subjects was significantly higher than plasma antioxidant capacity of smoking elderly subjects. The concentration of TBARS in young non-smoking volunteers was lower than that in young smokers. The concentration of TBARS in elderly non-smoking volunteers was lower than in elderly smokers. Plasma concentrations of alpha-tocopherol, beta-carotene and ascorbic acid were significantly lower in elderly smoker than in elderly non-smokers of the same age. No difference in the plasma levels of alpha-tocopherol, beta-carotene and ascorbic acid were found in 22-year-old smoking and non-smoking subjects. In vitro addition of ascorbic acid, uric acid, or Trolox to plasma samples significantly increased their total antioxidant capacity. Decrease of FRAP values and increase of TBARS concentrations is a significant physiologic condition of the aging process. Supplementation of antioxidants could be useful for the enhancement of antioxidant screen in plasma.