Lubica Horakova

Natural and synthetic antioxidants: An updated overview

Abstract The current understanding of the complex role of ROS in the organism and pathological sequelae of oxidative stress points to the necessity of comprehensive studies of antioxidant reactivities and interactions with cellular constituents. Studies of antioxidants performed within the COST B-35 action has concerned the search for new natural antioxidants, synthesis of new antioxidant compounds and evaluation and elucidation of mechanisms of action of both natural and synthetic antioxidants. Representative studies presented in the review concern antioxidant properties of various kinds of tea, the search for new antioxidants of herbal origin, modification of tocopherols and their use in combination with selenium and properties of two promising groups of synthetic antioxidants: derivatives of stobadine and derivatives of 1,4-dihydropyridine.

Human Low Density Lipoprotein as a Target of Hypochlorite Generated by Myeloperoxidase

The aim of this study was to further clarify which part of human low density lipoprotein (LDL) is attacked by the MPO/H2O2/Cl- -system and which reactive oxygen species is responsible for the attack. Therefore the influence of this system on the modification of the lipid and protein moiety of LDL was studied in vitro. Using the monochlorodimedone assay it was found that HOCl is produced in micromolar quantities in the absence of LDL and is rapidly consumed by LDL in a concentration dependent manner. The consumption of HOCl was reflected in the formation of HOCl-specific epitopes on apo B-100 as determined by an antibody raised against HOCl-modified LDL. The absorbency at 234 nm was applied to measure continuously the extent of modification of LDL. The general kinetic pattern of the absorbency measurement consisted of a lag phase where no LDL modification was observed, followed by a rapid increase of absorbency and a plateau phase. Finally the absorbency decreased due to LDL precipitation. Time dependent absorption spectra indicated that this kinetic pattern is mainly caused by light scattering due to particle aggregation rather than by a specific absorption at 234 nm due to conjugated diene formation. In agreement with this finding a low rate of thiobarbituric acid reactive substances (TBArS) formation was observed after a lag phase. The aggregation of LDL occurs most likely by modification of apo B-100, which was determined fluorimetrically in terms of LDL-tryptophan destruction in presence of the MPO/H2O2/Cl(-)-system. The kinetic course of tryptophan fluorescence generally consisted of a rapid decrease leveling off into a low plateau phase. Gas chromatographic determinations of linoleic acid in LDL in presence of the MPO system showed that this polyunsaturated fatty acid (PUFA) is easily attacked by HOCl. Consistent with this finding NMR spectra of HOCl modified LDL indicated a complete disappearance of bis-allylic methylene groups. Since lipid peroxidation products only partially account for this loss of PUFAs, other reactions of HOCl with unsaturated lipids--probably chlorohydrin formation--must be involved. Summarizing, although the rate of lipid peroxidation is low, both the lipid and the protein moiety of LDL are readily modified by the MPO system. It appears that the immediate consequence of apo B-100 modification is its aggregation. It is concluded that MPO, which has been detected in atherosclerotic lesions, is able to contribute to the modification of LDL into a form recognizable for uncontrolled uptake by macrophages.

Exploring oxidative modifications of tyrosine: An update on mechanisms of formation, advances in analysis and biological consequences

Abstract Protein oxidation is increasingly recognised as an important modulator of biochemical pathways controlling both physiological and pathological processes. While much attention has focused on cysteine modifications in reversible redox signalling, there is increasing evidence that other protein residues are oxidised in vivo with impact on cellular homeostasis and redox signalling pathways. A notable example is tyrosine, which can undergo a number of oxidative post-translational modifications to form 3-hydroxy-tyrosine, tyrosine crosslinks, 3-nitrotyrosine and halogenated tyrosine, with different effects on cellular functions. Tyrosine oxidation has been studied extensively in vitro, and this has generated detailed information about the molecular mechanisms that may occur in vivo. An important aspect of studying tyrosine oxidation both in vitro and in biological systems is the ability to monitor the formation of oxidised derivatives, which depends on a variety of analytical techniques. While antibody-dependent techniques such as ELISAs are commonly used, these have limitations, and more specific assays based on spectroscopic or spectrometric techniques are required to provide information on the exact residues modified and the nature of the modification. These approaches have helped understanding of the consequences of tyrosine oxidation in biological systems, especially its effects on cell signalling and cell dysfunction, linking to roles in disease. There is mounting evidence that tyrosine oxidation processes are important in vivo and can contribute to cellular pathology.

Ferritin oxidation and proteasomal degradation: protection by antioxidants.

The accumulation of oxidatively damaged proteins is a well-known hallmark of aging and several neurodegenerative diseases including Alzheimers, Parkinsons and Huntigtons diseases. These highly oxidized protein aggregates are in general not degradable by the main intracellular proteolytic machinery, the proteasomal system. One possible strategy to reduce the accumulation of such oxidized protein aggregates is the prevention of the formation of oxidized protein derivatives or to reduce the protein oxidation to a degree that can be handled by the proteasome. To do so an antioxidative strategy might be successful. Therefore, we undertook the present study to test whether antioxidants are able to prevent the protein oxidation and to influence the proteasomal degradation of moderate oxidized proteins. As a model protein we choose ferritin. H2O2 induced a concentration dependent increase of protein oxidation accompanied by an increased proteolytic susceptibility. This increase of proteolytic susceptibility is limited to moderate hydrogen peroxide concentrations, whereas higher concentrations are accompanied by protein aggregate formation. Protective effects of the vitamin E derivative Trolox, the pyridoindole derivative Stobadine and of the standardized extracts of flavonoids from bark of Pinus Pinaster Pycnogenol® and from leaves of Ginkgo biloba (EGb 761) were studied on moderate damaged ferritin.

Antioxidant action of stobadine.

Abstract The above-mentioned physicochemical, chemical, as well as pharmacological properties including successful results of Phase I and II clinical testing of stobadine as an antianginal agent permit us to consider this compound as potential drug in prevention and/or treatment of tissue injuries caused by oxidative stress.

Antioxidant activity of the pyridoindole stobadine in liposomal and microsomal lipid peroxidation

Stobadine, a pyridoindole derivative, is an efficient inhibitor of lipid peroxidation in phosphatidylcholine liposomes and in rat liver microsomes treated with iron/ADP/NADPH as pro-oxidant. Accumulation of thiobarbituric acid-reactive substances (TBARS) or low-level chemiluminescence were taken as a measure of lipid peroxidation and 5 microM stobadine doubled the duration of the lag phase preceding the onset of rapidly increasing chemiluminescence. Inhibition of lipid peroxidation was not observed with tocopherol-deficient microsomes, suggesting that the antioxidant effect of stobadine depends on vitamin E in the membrane. The cis(-) isomer was most effective, with the cis(+) and trans(rac) as well as dehydro- or acetyl derivatives being less active. In liposomes, the presence of reductant (NADPH or ascorbate) protects from the loss of stobadine.

Effect of high glucose concentrations on human erythrocytes in vitro

Exposure to high glucose concentrations in vitro is often employed as a model for understanding erythrocyte modifications in diabetes. However, effects of such experiments may be affected by glucose consumption during prolonged incubation and changes of cellular parameters conditioned by impaired energy balance. The aim of this study was to compare alterations in various red cell parameters in this type of experiment to differentiate between those affected by glycoxidation and those affected by energy imbalance. Erythrocytes were incubated with 5, 45 or 100 mM glucose for up to 72 h. High glucose concentrations intensified lipid peroxidation and loss of activities of erythrocyte enzymes (glutathione S-transferase and glutathione reductase). On the other hand, hemolysis, eryptosis, calcium accumulation, loss of glutathione and increase in the GSSG/GSH ratio were attenuated by high glucose apparently due to maintenance of energy supply to the cells. Loss of plasma membrane Ca2+-ATPase activity and decrease in superoxide production were not affected by glucose concentration, being seemingly determined by processes independent of both glycoxidation and energy depletion. These results point to the necessity of careful interpretation of data obtained in experiments, in which erythrocytes are subject to treatment with high glucose concentrations in vitro.

Effect of stobadine on Cu++-mediated oxidation of low-density lipoprotein☆

The pyridoindole derivative stobadine [(-)-cis-2,8-dimethyl-2,3,4,4a,5,9b-hexahydro-1H-pyrido(4,3b) indole] has been described as a drug with antihypoxic and antiarrhythmic cardioprotective properties. The antioxidative properties of this compound were studied during Cu(++)-mediated low-density lipoprotein (LDL) oxidation. Stobadine (concentration 0-5 microM) prolonged the lag phase (in min produced by one molecule antioxidant per LDL particle) as measured by diene formation more effectively than did ascorbate, trolox, or alpha-tocopherol. It also has the ability to decrease the rate of diene formation during the propagation phase very efficiently. Diene formation, Trp destruction, and alpha-tocopherol consumption were measured in the presence and absence of stobadine. Stobadine (10 microM) did not influence tocopherol consumption during oxidation and the Trp fluorescence quenching of Cu++ was not influenced by this compound. From these results, as well as polarographic measurements, we conclude that the antioxidative effect of stobadine is not simply a result of Cu(++)-ion complexation. In contrast to ascorbate, this compound is stable in the presence of Cu++. Stobadine inhibits the oxidation of LDL-Trp residues very efficiently via its radical scavenging properties, and may even have the ability to reduce Trp radicals to tryptophan. The concentration of stobadine used for LDL oxidation was in the range found in plasma (stobadine given p.o. in human and rats results in plasma concentrations between 0.2-3.9 microM.

Modulation of sarcoplasmic/endoplasmic reticulum Ca2+-ATPase activity and oxidative modification during the development of adjuvant arthritis

Adjuvant arthritis (AA) was induced by intradermal administration of Mycobacterium butyricum to the tail of Lewis rats. In sarcoplasmic reticulum (SR) of skeletal muscles, we investigated the development of AA. SR Ca(2+)-ATPase (SERCA) activity decreased on day 21, suggesting possible conformational changes in the transmembrane part of the enzyme, especially at the site of the calcium binding transmembrane part. These events were associated with an increased level of protein carbonyls, a decrease in cysteine SH groups, and alterations in SR membrane fluidity. There was no alteration in the nucleotide binding site at any time point of AA, as detected by a FITC fluorescence marker. Some changes observed on day 21 appeared to be reversible, as indicated by SERCA activity, cysteine SH groups, SR membrane fluidity, protein carbonyl content and fluorescence of an NCD-4 marker specific for the calcium binding site. The reversibility may represent adaptive mechanisms of AA, induced by higher relative expression of SERCA, oxidation of cysteine, nitration of tyrosine and presence of acidic phospholipids such as phosphatidic acid. Nitric oxide may regulate cytoplasmic Ca(2+) level through conformational alterations of SERCA, and decreasing levels of calsequestrin in SR may also play regulatory role in SERCA activity and expression.

Free Radicals in Rabbit Spinal Cord Ischemia: Electron Spin Resonance Spectroscopy and Correlation with SOD Activity

Abstract1. In nonanesthetized rabbits temporal occlusion of the abdominal aorta was used to induce oxidative stress in the lower part of the body including distal segments of the spinal cord.2. Spinal cord samples were taken from the animals exposed to 25-min aortic occlusion (AO ) or to occlusion followed by 1- or 2-hr reperfusion (AO/R1 or AO/R2, respectively) or from sham-operated animals (C). The presence of free radicals (FR) in the spinal cord samples frozen in liquid N2 was assessed by ESR spectroscopy without spin trapping. Moreover, superoxide dismutase (SOD) activity and conjugated diene (CD) levels were measured in the samples.3. In the AO group FR were detected in the spinal cord regions close to the occlusion (lower thoracic and distal segments) along with a decrease in SOD activity. The calculated g value (g = 2.0291) indicated that the paramagnetic signal recorded might be attributed to superoxide radicals. FR were absent in the AO/R1 group. Concurrently, the SOD activity revealed a significant tendency to return to the control level. FR appeared again in the AO/R2 group, mostly in the upper and middle lumbar regions, along with a decrease in SOD activity. No sample from the C group revealed FR. A significant increase in CD levels was observed in the thoracolumbar region only in the AO/R2 group. The temporary absence of FR in the AO/R1 group suggests activation of defense antioxidant mechanisms (e.g., specific enzymatic systems such as SOD), which might have been exhausted later.4. Changes in SOD activity similar to those observed in the thoracolumbar region, though less noticeable, occurred in the obviously noncompromised tissue (upper cervical region). This points to a kind of generalized reponse of the animal to aortic occlusion.5. Direct ESR spectroscopy revealed the presence of FR as well as their time course in the spinal cord during the early phase of ischemia/reperfusion injury and the inverse relationship between FR and SOD activity.