Paulina Kleniewska

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 Influence of Probiotic Lactobacillus casei in Combination with Prebiotic Inulin on the Antioxidant Capacity of Human Plasma

The aim of the present study was to assess whether probiotic bacteria Lactobacillus casei (4 × 108 CFU) influences the antioxidant properties of human plasma when combined with prebiotic Inulin (400 mg). Experiments were carried out on healthy volunteers (n = 32). Volunteers were divided according to sex (16 male and 16 female) and randomly assigned to synbiotic and control groups. Blood samples were collected before synbiotic supplementation and after 7 weeks, at the end of the study. Catalase (CAT), superoxide dismutase (SOD), glutathione peroxidase (GPx) activity, and the ferric reducing ability of plasma (FRAP) in human plasma were examined. The administration of synbiotics containing L. casei plus Inulin resulted in a significant increase in FRAP values (p = 0.00008) and CAT activity (p = 0.02) and an insignificant increase in SOD and GPx activity compared to controls. Synbiotics containing L. casei (4 × 108 CFU) with prebiotic Inulin (400 mg) may have a positive influence on human plasma antioxidant capacity and the activity of selected antioxidant enzymes.

Influence of block of NF-kappa B signaling pathway on oxidative stress in the liver homogenates.

The aim of the present study was to assess whether BAY 11-7082, a nuclear factor-kappaB (NF-κB) inhibitor, influences the level of reactive oxygen species (ROS), tumor necrosis factor alpha (TNF-α), and NF-κB related signaling pathways in the liver. The animals were divided into 4 groups: I: saline; II: saline + endothelin-1 (ET-1) (1.25 μg/kg b.w., i.v.); III: saline + ET-1 (12.5 μg/kg b.w., i.v.); and IV: BAY 11-7082 (10 mg/kg b.w., i.v.) + ET-1 (12.5 μg/kg b.w., i.v.). Injection of ET-1 alone at a dose of 12.5 μg/kg b.w. showed a significant (P < 0.001) increase in thiobarbituric acid reactive substances (TBARS) and hydrogen peroxide (H2O2) level and decrease (P < 0.01) in GSH level (vs. control). ET-1 administration slightly downregulated gene expression of p65 of NF-κB but potently and in a dose-dependent way downregulated p21-cip gene expression in the liver. BAY 11-7082 significantly decreased TBARS (P < 0.001), H2O2 (P < 0.01) and improved the redox status (P < 0.05), compared to ET-1 group. The concentration of TNF-α was increased in the presence of ET-1 (P < 0.05), while BAY 11-7082 decreased TNF-α concentration (P < 0.01). Inhibition of IkBα before ET-1 administration downregulated gene expression of p21-cip but had no effect on p65.

The participation of oxidative stress in the pathogenesis of bronchial asthma

Reactive oxygen species are produced during oxygen reduction and are characterized by high reactivity. They participate in many important physiological processes, but if produced in high concentrations they lead to oxidative stress development and disturb pro-oxidative/anti-oxidative balance towards the oxidation reaction - leading to damage of lipids, proteins, carbohydrates or nucleic acids. Asthma is a chronic inflammatory disease of the airways of various pathogenesis and clinical symptoms, prevalence in recent years has increased significantly. Recently published literature point out the involvement of reactive oxygen species in the pathogenesis of asthma. Changes in the protein and lipid oxidation lead, among others, to pathological changes in the respiratory epithelial cells, an increase in vascular permeability, mucus overproduction, smooth muscle contraction or airway hyperresponsiveness (AHR). The aim of this study is to present the current state of knowledge on the influence of oxidative stress parameters on asthma development.

The influence of ETA and ETB receptor blockers on LPS-induced oxidative stress and NF-κB signaling pathway in heart.

The aim of this study was to assess whether an endothelin-A receptor (ETA-R) blocker, BQ123, or an endothelin-B (ETB-R) receptor blocker, BQ788, influences nuclear factor kappa beta (NF-κB) pathway, free radical generation, tumor necrosis factor-alpha (TNF-α) concentration, and glutathione redox system in hearts obtained from lipopolysaccharide (LPS)-induced endotoxic rats. The study was performed on rats divided into groups: 1) saline, 2) saline + LPS (15 mg/kg), 3) BQ123 (1 mg/kg b.w.) + LPS, 4) BQ123 (0.5 mg/kg b.w.) + LPS, 5) BQ788 (3 mg/kg b.w.) + LPS. The ETA-R and ETB-R antagonists were injected i.v. 30 min before LPS administration. In rats, BQ123 caused a significant decrease in TBARS (p < 0.05) but not in H2O2 concentration. It also decreased tissue protein level and improved tissue redox status (p < 0.01). Only a dose of 1 mg/kg decreased TNF-α concentration (p < 0.05). BQ788 lowered TBARS, H2O2 and protein concentration (p < 0.05; p < 0.02; p < 0.001, respectively), however, it did not affect TNF-α concentration. Neither ETA-R nor ETB-R blockers influenced LPS-induced increase in p65 subunit level and activation of NF-κB pathway. Our results demonstrated that ETA-R blockage is more effective in inhibiting free radical generation and improving heart antioxidant properties than ETB-R blockage under oxidative stress. NF-κB pathway is not incorporated in ETA-R and ETB-R influence on ROS production.

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.

Influence of NADPH oxidase inhibition on oxidative stress parameters in rat hearts

BACKGROUND The aim of this study was to assess whether apocynin, an nicotinamide adenine dinucleotide phosphate (NADPH) oxidase blocker, influences lipid peroxidation TBARS, hydrogen peroxide (H2O2) content, protein level, heart edema, tumor necrosis factor α (TNF-α) concentration or the glutathione redox system in heart homogenates obtained from endothelin 1 (ET-1)-induced oxidative stress rats. METHODS Experiments were carried out on adult male Wistar-Kyoto rats. The animals were divided into 4 groups: Group I: saline-treated control; Group II: saline followed by ET-1 (3 μg/kg b.w., iv); Group III: apocynin (5 mg/kg b.w., iv) administered half an hour before saline; Group IV: apocynin (5 mg/kg b.w., iv) administered half an hour before ET-1 (3 μg/kg b.w., iv). RESULTS Injection of ET-1 alone showed a significant (p < 0.001) increase in thiobarbituric acid reactive substances (TBARS) and the hydrogen peroxide level (p < 0.01) vs. control, as well as a decrease (p < 0.001) in the GSH level. Apocynin significantly decreased TBARS (p < 0.001) and H2O2 (p < 0.05) level (vs. control) as well as improved protein level (p < 0.001) in the heart. Apocynin also prevented ET-1-induced heart edema (p < 0.05). The presence of ET-1 increased the concentration of TNF-α (p < 0.05) while apocynin decreased it (p < 0.05). Our results indicate that ET-1 may induce oxidative stress in heart tissue by reducing the GSH/GSSG ratio, stimulating lipid peroxidation and increasing TNF-α concentration. Apocynin diminished these measures of oxidative stress and TNF-α. CONCLUSION ET-1-induced formation of ROS in the heart is at least partially regulated via NADPH oxidase.