The effect of myeloperoxidase isoforms on biophysical properties of red blood cells

Myeloperoxidase (MPO), an oxidant-producing enzyme, stored in azurophilic granules of neutrophils has been recently shown to influence red blood cell (RBC) deformability leading to abnormalities in blood microcirculation. Native MPO is a homodimer, consisting of two identical protomers (monomeric MPO) connected by a single disulfide bond but in inflammatory foci as a result of disulfide cleavage monomeric MPO (hemi-MPO) can also be produced. This study investigated if two MPO isoforms have distinct effects on biophysical properties of RBCs. We have found that hemi-MPO, as well as the dimeric form, bind to the glycophorins A/B and band 3 protein on RBC's plasma membrane, that lead to reduced cell resistance to osmotic and acidic hemolysis, reduction in cell elasticity, significant changes in cell volume, morphology, and the conductance of RBC plasma membrane ion channels. Furthermore, we have shown for the first time that both dimeric and hemi-MPO lead to phosphatidylserine (PS) exposure on the outer leaflet of RBC membrane. However, the effects of hemi-MPO on the structural and functional properties of RBCs were lower compared to those of dimeric MPO. These findings suggest that the ability of MPO protein to influence RBC's biophysical properties depends on its conformation (dimeric or monomeric isoform). It is intriguing to speculate that hemi-MPO appearance in blood during inflammation can serve as a regulatory mechanism addressed to reduce abnormalities on RBC response, induced by dimeric MPO.

Protective Effect of Dinitrosyl Iron Complexes with Glutathione in Red Blood Cell Lysis Induced by Hypochlorous Acid

Hypochlorous acid (HOCl), one of the major precursors of free radicals in body cells and tissues, is endowed with strong prooxidant activity. In living systems, dinitrosyl iron complexes (DNIC) with glutathione ligands play the role of nitric oxide donors and possess a broad range of biological activities. At micromolar concentrations, DNIC effectively inhibit HOCl-induced lysis of red blood cells (RBCs) and manifest an ability to scavenge alkoxyl and alkylperoxyl radicals generated in the reaction of HOCl with tert-butyl hydroperoxide. DNIC proved to be more effective cytoprotective agents and organic free radical scavengers in comparison with reduced glutathione (GSH). At the same time, the kinetics of HOCl-induced oxidation of glutathione ligands in DNIC is slower than in the case of GSH. HOCl-induced oxidative conversions of thiolate ligands cause modification of DNIC, which manifests itself in inclusion of other ligands. It is suggested that the strong inhibiting effect of DNIC with glutathione on HOCl-induced lysis of RBCs is determined by their antioxidant and regulatory properties.

Enzymatic and bactericidal activity of myeloperoxidase in conditions of halogenative stress

Myeloperoxidase (MPO), found mainly in neutrophils, is released in inflammation. MPO produces reactive halogen species (RHS), which are bactericidal agents. However, RHS overproduction, i.e., halogenative stress, can also damage host biomolecules, and MPO itself may be targeted by RHS. Therefore, we examined the susceptibility of MPO to inactivation by its primary products (HOCl, HOBr, HOSCN) and secondary products such as taurine monochloramine (TauCl) and taurine monobromamine (TauBr). MPO was dose-dependently inhibited up to complete inactivity by treatment with HOCl or HOBr. TauBr diminished the activity but did not eliminate it. TauCl had no effect. MPO became inactivated when producing HOCl or HOBr but not HOSCN. Taurine protected MPO against inactivation when MPO was catalyzing oxidation of Cl− to HOCl, whereas taurine failed to prevent inactivation when MPO was working with Br−, either alone or in combination with Cl−. SCN− interfered with HOCl-mediated MPO inhibition. UV–vis spectra showed that heme degradation is involved in HOCl- and HOBr-mediated MPO inactivation. A negative linear correlation between the remaining chlorinating activity of HOCl- or HOBr-modified MPO and Escherichia coli survival upon incubation with MPO/H2O2/Cl− was found. This study elucidated the possibility of MPO downregulation by MPO-derived RHS, which could counteract halogenative stress.

Neutrophil activation in response to monomeric myeloperoxidase

Myeloperoxidase (MPO) is an oxidant-producing enzyme that can also regulate cellular functions via its nonenzymatic effects. Mature active MPO isolated from normal human neutrophils is a 145 kDa homodimer, which consists of 2 identical protomers, connected by a single disulfide bond. By binding to CD11b/CD18 integrin, dimeric MPO induces neutrophil activation and adhesion augmenting leukocyte accumulation at sites of inflammation. This study was performed to compare the potency of dimeric and monomeric MPO to elicit selected neutrophil responses. Monomeric MPO (hemi-MPO) was obtained by treating the dimeric MPO by reductive alkylation. Analysis of the crucial signal transducer, intracellular Ca2+, showed that dimeric MPO induces Ca2+ mobilization from the intracellular calcium stores of neutrophils and influx of extracellular Ca2+ whereas the effect of monomeric MPO on Ca2+ increase in neutrophils was less. It was also shown that monomeric MPO was less efficient than dimeric MPO at inducing actin cytoskeleton reorganization, cell survival, and neutrophil degranulation. Furthermore, we have detected monomeric MPO in the blood plasma of patients with acute inflammation. Our data suggest that the decomposition of dimeric MPO into monomers can serve as a regulatory mechanism that controls MPO-dependent activation of neutrophils and reduces the proinflammatory effects of MPO.

[Exocytosis of myeloperoxidase from activated neutrophils in the presence of heparin]

Exocytosis of myeloperoxidase (MPO) from activated neutrophils in the presence of the anionic polysaccharide heparin was studied. It was determined that the optimal concentration of heparin (0.1 u/ml), at which there is no additional activation of cells (absence of amplification of exocytosis of lysozyme contained in specific and azurophilic granules). It was found that after preincubation of cells with heparin (0.1 u/ml) the exocytosis of MPO from neutrophils activated by various stimulants (fMLP, PMA, plant lectins CABA and PHA-L) increased compared to that under the action of activators alone. In addition, it was shown that heparin in the range of concentrations 0.1-50 u/ml did not affect on the peroxidase activity of the MPO isolated from leukocytes. Thus, the use of heparin at a concentration of 0.1 u/ml avoids the artifact caused by the "loss" of MPO in a result of its binding to neutrophils, and increases the accuracy of the method of registration the degranulation of azurophilic granules of neutrophils based on determination of the concentration or peroxidase activity of MPO in cell supernatants.

Myeloperoxidase Stimulates Neutrophil Degranulation

Myeloperoxidase, heme enzyme of azurophilic granules in neutrophils, is released into the extracellular space in the inflammation foci. In neutrophils, it stimulates a dose-dependent release of lactoferrin (a protein of specific granules), lysozyme (a protein of specific and azurophilic granules), and elastase (a protein of azurophilic granules). 4-Aminobenzoic acid hydrazide, a potent inhibitor of peroxidase activity of myeloperoxidase, produced no effect on neutrophil degranulation. Using signal transduction inhibitors (genistein, methoxyverapamil, wortmannin, and NiCl2), we demonstrated that myeloperoxidase-induced degranulation of neutrophils resulted from enzyme interaction with the plasma membrane and depends on activation of tyrosine kinases, phosphatidylinositol 3-kinases (PI3K), and calcium signaling. Myeloperoxidase modified by oxidative/halogenation stress (chlorinated and monomeric forms of the enzyme) lost the potency to activate neutrophil degranulation.

[Myeloperoxidase activity in blood plasma as a criterion of therapy for patients with cardiovascular disease]

A significant increase in the myeloperoxidase (MPO) activity has been found in plasma of patients with stable angina and with acute coronary syndrome (ACS) in comparison with the control group. MPO concentration was significantly increased in plasma of ACS patients. Reduced MPO activity in the treated ACS patients correlated with a favorable outcome of the disease. Generally, changes in plasma MPO concentration coincided with changes in lactoferrin concentration thus confirming the role of neutrophil degranulation in the increase of plasma concentrations of these proteins. The increase in MPO activity was obviously determined by modification of the MPO protein caused by reactive oxygen species and halogen in the molar ratio of 1 : 25 and 1 : 50. The decrease in plasma MPO activity may be associated with increased plasma concentrations of the physiological inhibitor of its activity, ceruloplasmin, and also with modification of the MPO protein with reactive oxygen species and halogen at their molar ratio of 1 : 100 and higher. Thus, MPO activity may be used for evaluation of effectiveness of the treatment of cardiovascular diseases.

[Phenolic antioxidant TS-13 regulating ARE-dependent genes induces tumor cell death by mitochondria-dependent pathway]

Effects of water-soluble phenolic antioxidant sodium 3-(3'-tret-butyl-4'-hydroxyphenyl)-propyl thiosulfonate (TS-13), potassium 3,5-dimethyl-4-hydroxybenzyl thioetanoate (BEP-11-K) and potassium 3-(3',5'-ditretbutyl-4'-hydroxyphenyl)-propionate (potassium phenosan) on tumor cells proliferative activity and the role of redox-dependent and calcium-dependent signaling mechanisms in realization of tumor cell response to the antioxidant action were studied. Potassium phenosan and BEP-11-K were found to stimulate proliferation and ARE-inducing phenolic antioxidant TS-13 was found to inhibit tumor cell growth in culture. The tumor cell growth rate depended on the rate of intracellular reactive oxygen species production and was decreased by apocynin (a NADPH-oxidase inhibitor) and antimycin A (an ubiquinol-cytochrome c oxidoreductase inhibitor). TS-13 action on tumor cells was accompanied by a transient increase in intracellular reactive oxygen species production and the intracellular calcium concentration, whereas cell incubation with potassium phenosan and BEP-11-K did not influence the reactive oxygen species level and intracellular calcium ions. Cyclosporine A blocked the inhibitory effect of TS-13. Thus, it can be reasonably speculated that phenolic antioxidant TS-13 starts mitochondria-dependent apoptosis in tumor cells by the opening of permeability transition pores.

Hypohalous acid-modified human serum albumin induces neutrophil NADPH oxidase activation, degranulation, and shape change

Halogenated lipids, proteins, and lipoproteins formed in reactions with myeloperoxidase (MPO)-derived hypochlorous acid (HOCl) and hypobromous acid (HOBr) can contribute to the regulation of functional activity of cells and serve as mediators of inflammation. Human serum albumin (HSA) is the major plasma protein target of hypohalous acids. This study was performed to assess the potency of HSA modified by HOCl (HSA-Cl) and HOBr (HSA-Br) to elicit selected neutrophil responses. HSA-Cl/Br were found to induce neutrophil degranulation, generation of reactive oxygen intermediates, shape change, and actin cytoskeleton reorganization. Thus HSA-Cl/Br can initially act as a switch and then as a feeder of the "inflammatory loop" under oxidative stress. In HSA-Cl/Br-treated neutrophils, monoclonal antibodies against CD18, the β subunit of β2 integrins, reduced the production of superoxide anion radicals and hydrogen peroxide as well as MPO exocytosis, suggesting that CD18 contributed to neutrophil activation. HSA-Cl/Br-induced neutrophil responses were also inhibited by genistein, a broad-specificity tyrosine kinase inhibitor, and wortmannin, a phosphoinositide 3-kinase (PI3K) inhibitor, supporting the notion that activation of both tyrosine kinase and PI3K may play a role in neutrophil activation by HSA modified in MPO-dependent reactions. These results confirm the hypothesis that halogenated molecules formed in vivo via MPO-dependent reactions can be considered as a new class of biologically active substances potentially able to contribute to activation of myeloid cells in sites of inflammation and serve as inflammatory response modulators.

Myeloperoxidase modulates human platelet aggregation via actin cytoskeleton reorganization and store-operated calcium entry

Myeloperoxidase (MPO) is a heme-containing enzyme released from activated leukocytes into the extracellular space during inflammation. Its main function is the production of hypohalous acids that are potent oxidants. MPO can also modulate cell signaling and inflammatory responses independently of its enzymatic activity. Because MPO is regarded as an important risk factor for cardiovascular diseases associated with increased platelet activity, we studied the effects of MPO on human platelet functional properties. Laser scanning confocal microscopy was used to reveal carbohydrate-independent MPO binding to human platelet membrane. Adding MPO to platelets did not activate their aggregation under basal conditions (without agonist). In contrast, MPO augmented agonist-induced platelet aggregation, which was not prevented by MPO enzymatic activity inhibitors. It was found that exposure of platelets to MPO leads to actin cytoskeleton reorganization and an increase in their elasticity. Furthermore, MPO evoked a rise in cytosolic Ca²⁺ through enhancement of store-operated Ca²⁺ entry (SOCE). Together, these findings indicate that MPO is not a direct agonist but rather a mediator that binds to human platelets, induces actin cytoskeleton reorganization and affects the mechanical stiffness of human platelets, resulting in potentiating SOCE and agonist-induced human platelet aggregation. Therefore, an increased activity of platelets in vascular disease can, at least partly, be provided by MPO elevated concentrations.

[Human serum albumin modified under oxidative/halogenative stress enhances luminol-dependent chemiluminescence of human neutrophils]

It is shown that human serum albumin, previously treated with HOCl (HSA-Cl), enhances luminol-dependent chemiluminescence of neutrophils activated by phorbol-12-myristate-13-acetate (PMA). The enzyme-linked immunosorbent assay revealed that addition of HSA-Cl to neutrophils promotes exocytosis of myeloperoxidase. Inhibitor of myeloperoxidase--4-aminobenzoic acid hydrazide, without any effect on lucigenin-dependent chemiluminescence of neutrophils stimulated with PMA, effectively suppressed luminol-dependent chemiluminescence (IC50 = 20 microM) under the same conditions. The transfer of the cells from medium with HSA-Cl and myeloperoxidase to fresh medium abolished an increase in PMA-induced luminol-dependent chemiluminescence, but not the ability of neutrophils to respond to re-addition of HSA-Cl. A direct and significant (r = 0.75, p) correlation was observed between the intensity of PMA stimulated neutrophil chemiluminescence response and myeloperoxidase activity in the cell-free media after chemiluminescence measurements. These results suggest the involvement of myeloperoxidase in the increase of neutrophil PMA-stimulated chemiluminescence response in the presence of HSA-Cl. A significant positive correlation was found between myeloperoxidase activity in blood plasma of children with severe burns and the enhancing effects of albumin fraction of the same plasma on luminol-dependent chemiluminescence of PMA-stimulated donor neutrophils. These results support a hypothesis that proteins modified in reactions involving myeloperoxidase under oxidative/halogenative stress, stimulate neutrophils, leading to exocytosis of myeloperoxidase, a key element of halogenative stress, and to closing a "vicious circle" of neutrophil activation at the inflammatory site.

Functional activity of neutrophils in diabetes mellitus and coronary heart disease: role of myeloperoxidase in the development of oxidative stress

We performed a comparative analysis of functional activity of neutrophils in patients with type 2 diabetes mellitus with and without symptoms of CHD. Enhanced H2O2 production by neutrophils in response to N-formyl-Met-Leu-Phe (fMLP) was found in patients with type 2 diabetes mellitus. In patients with type 2 diabetes mellitus associated with CHD, fMLP-induced release of myeloperoxidase from azurophilic granules of neutrophils was reduced and plasma myeloperoxidase level was elevated. Increased peroxidase activity of myeloperoxidase, reduced plasma catalase activity, and increased levels of TBA-reactive lipid peroxidation products and oxidized glutathione were detected in patients of both groups. Since myeloperoxidase is an important neutrophilic mediator of oxidative stress, its increased activity in the blood can be an additional marker of oxidative stress and cardiovascular risk in patients with diabetes mellitus.

[Increased myelopepoxidase activity is a risk factor for ishemic heart disease in patients with diabetes mellitus]

Using previously developed spectro-photonmetrical method (Bioorg. Khim. 2009. V. 35. pp. 629-639), a significant increase of myeloperoxidase (MPO) activity was found in blood plasma of patients with type 2 diabetes mellitus (DM2) without of cardiovascular complications, as well as with ischemic heart disease (IHD). Plasma MPO concentration measured by an enzyme-linked immunosorbent assay was significantly higher only in blood plasma of patient with DM2 and IHD. A direct and significant correlation between MPO activity and MPO concentration was observed only in blood plasma samples from healthy donors. Increased MPO activity did not correlate with MPO concentration in blood plasma of patients with DM2 and DM2 with IHD. Taken together, these results highlight the necessity for studying of the MPO role in the development of pathological processes to determine both the amount of enzyme and its peroxidase activity in the blood. The proposed approach gives comprehensive information about the relationship between MPO activity and MPO concentration in patient blood. Since the high concentration of MPO is a diagnostically significant parameter in the prediction of endothelial dysfunction and cardiovascular disease development, the obtained results evidence the contribution of MPO-dependent reactions in cardiovascular complications associated with diabetes. MPO activity may serve as an additional diagnostic criterion for determination of risk of IHD in DM patients.

[Glutathione-dependent regulation of platelet aggregation with neutrophils and tumor cells]

It is shown that in the presence of reduced glutathione at low concentrations (1-5 microM) the extent of platelet aggregation with neutrophils increases and the lag period of platelet aggregation induced by tumor cells decreases. At the same time in the presence of reduced glutathione at high concentration (3 mM) the extent of platelet aggregation with neutrophils decreases, and the lag period of platelet aggregation induced by tumor cells increases. It is established that glutathione-dependent regulation of the intercellular contact formation between platelets and neutrophils depends on the ratio of glutathione oxidized and reduced forms: at fixed total glutathione concentration of 5 microM, increase of glutathione redox potential from -175 mV to 0 mV led to reduction in platelet aggregation with neutrophils. Thus, it is shown for the first time, that GSH has priming effect on the platelet aggregation with neutrophils and tumor cells, which may contribute to the regulation of inflammatory diseases and cancer.

[Redox regulation of cellular processes: a biophysical model and experiment]

A model for the redox regulation of the functional state of the cell has been constructed on the basis of representation of electron transfer processes by equivalent electric circuits. The mechanism of action of redox active molecules on biosystems has been discussed in terms of circuit theory. A method for determining the parameters of cellular redox sensors has been proposed. It has been established that the concentration and redox potential of compounds entering the cell are the main regulatory parameters of redox signals for the cell. It has been experimentally shown that the calcium response to hydrogen peroxide in rat C6 glioma cells and human FL amnion cells depends on the redox buffer capacity of cells.

[Regulation of the functional and mechanical properties of platelet and red blood cells by nitric oxide donors]

The effect of NO donors (sodium nitroprusside, S-nitrosoglutathione, dinitrosyl-iron complexes) on the functional and mechanical properties of human platelets and red blood cells has been investigated. It has been established by atomic force microscopy that NO donor-induced platelet disaggregation is accompanied by changes in the elastic properties of cells. It has been shown that, in the presence of NO donors, the detergent-induced hemolysis of red blood cells is delayed, and the elasticity modulus of these cells decreases. The results obtained indicate that NO donors regulate the structural and functional properties of platelets and red blood cells.

Redox regulation of morphology, cell stiffness, and lectin-induced aggregation of human platelets

Redox regulation and carbohydrate recognition are potent molecular mechanisms which can contribute to platelet aggregation in response to various stimuli. The purpose of this study is to investigate the relationship between these mechanisms and to examine whether cell surface glycocalyx and cell stiffness of human platelets are sensitive to the redox potential formed by glutathione. To this end, human platelets were treated with different concentrations (0.05 μM to 6 mM) and ratios of reduced or oxidized glutathione (GSH or GSSG), and platelet morphological, mechanical, and functional properties were determined using conventional light microscopy, atomic force microscopy, and lectin-induced cell aggregation analysis. It was found that lowering the glutathione redox potential changed platelet morphology and increased platelet stiffness as well as modulated nonuniformly platelet aggregation in response to plant lectins with different carbohydrate-binding specificity including wheat germ agglutinin, Sambucus nigra agglutinin, and Canavalia ensiformis agglutinin. Extracellular redox potential and redox buffering capacity of the GSSG/2GSH couple were shown to control the availability of specific lectin-binding glycoligands on the cell surface, while the intracellular glutathione redox state affected the general functional ability of platelets to be aggregated independently of the type of lectins. Our data provide the first experimental evidence that glutathione as a redox molecule can affect the mechanical stiffness of human platelets and induce changes of the cell surface glycocalyx, which may represent a new mechanism of redox regulation of intercellular contacts.

Modification of redox processes in astroglial cells induced by microbial and viral infections

BACKGROUND

The authors hypothesized that the cell redox state might be modified during microbial and viral infections. To detect and evaluate changes in astroglial cell redox state, rat C6 glioma cells after exposure to lipopolysaccharide (LPS) or after herpes simplex virus type 1 (HSV-1) inoculation were used. Redox state modification of glioma cells was determined by the change in menadione-induced superoxide yield.

MATERIAL/METHODS

Menadione-induced superoxide formation was registered by the lucigenin-enhanced chemiluminescence (CL) method.

RESULTS

The results demonstrate that exposure of C6 glioma cells to LPS for 24 hours resulted in a dose-dependent increase in the mitotic index and integral intensity of menadione-induced lucigenin-enhanced CL. Menadione-induced ROS generation in C6 cells during HSV-1 infection changed depending on the time after HSV-1 inoculation.

CONCLUSIONS

The redox state of astroglial cells is modified during microbial and viral infections. The use of redox-active quinones is an informative model for determining cell redox state change and analyzing cells' functional state.

[Vitamin K3-induced activation of molecular oxygen in glioma cells]

It has been shown by the method of fluorescent analysis that the rate of hydrogen peroxide generation in human U251 glioma cells under the effect of lipophilic (menadione) or hydrophilic (vikasol) analogues of vitamin K3 was different. Analyzing experimental data we can conclude that menadione underwent one- and two-electron reduction by intracellular reductases in glioma cells. Reduced forms of menadione interact with molecular oxygen leading to reactive oxygen species (ROS) generation. The theoretical model of ROS generation including two competitive processes of one- and two-electron reduction of menadione has been proposed. Rate constants of ROS generation mediated by one-electron reduction process have been estimated.

[Role of hydrogen ions in the regulation of the redox state of erythrocytes]

The parameters of the acid-base state and redox state of erythrocytes have been studied with the use of the fluorescent probes 2',7'-bis(2-carboxyethyl)-5(6)-carboxyfluorescein and 2',7'-dichlorodihydrofluorescein. It has been found that the value of redox state parameters in erythrocytes depends both on the extracellular and intracellular concentrations of hydrogen ions. It has been shown that hydrogen peroxide induces a decrease in the value of the intracellular pH. The interrelation of cellular homeostasis parameters characterizing the acid-base and redox states of erythrocytes has been theoretically and experimentally substantiated.

Effects of ascorbic acid on calcium signaling in tumor cells

Effects of ascorbic acid on calcium homeostasis of human laryngeal carcinoma cells were studied. Intracellular concentration of free calcium and intracellular pH were measured by fluorescent analysis. Ascorbic acid in concentrations of 3-10 mM caused pH drop and sharply increased concentrations of free Ca ions in HEp-2 cells. Intracellular concentration of free Ca ions resulted from Ca ion release from the thapsigargin-sensitive Ca depots.

[Pteridine-dependent oxygen activation in neutrophils]

We investigated the influence ofneopterin and 7, 8-dihydroneopterin on the activity and secretory degranulation of myeloperoxidase in neutrophils and the ability of pteridines to interact with the main substrate of this enzyme, hydrogen peroxide, and with the intermediate product of halogenation cycle--hypochlorous acid. It was shown that neopterin and 7, 8-dihydroneopterin while being a redox-pair regulated the process of oxygen activation in neutrophils by functioning of myeloperoxidase. Depending on concentration, pteridines can influence the secretion of myeloperoxidase into intracellular medium and decrease the level of hydrogen peroxide and hypochlorous acid that are a substrate and an intermediate product of the enzyme respectively. It was shown that 7, 8-dihydroneopterin in micromolar concentration appeared to be noncompetitive inhibitor of myeloperoxidase. We suppose that myeloperoxidase assists 7, 8-dihydroneopterin oxidation by hypochlorous acid that leads to neopterin concentration increase. These changes modify the concentration of reactive oxygen species in intracellular and extracellular media.

[Quantitative characteristic of the redox state of erythrocytes]

The introduction of the parameters characterizing the redox state of the cell, such as the effective redox potential and the redox buffer capacity has been theoretically substantiated. A comparative study of the parameters of the redox state of erythrocytes from healthy donors and patients with diabetes and acute coronary syndrome has been performed. It was found that the redox buffer capacity in erythrocytes from patients with diabetes and acute coronary syndrome was reduced by 30-40% in comparison with the redox buffer capacity of erythrocytes from healthy donors. The largest change in the effective redox potential was observed for erythrocytes from patients with diabetes, which indicates a more expressed oxidative stress in this pathology.

[Redox-homeostasis of cells]

Recent achievements of biophysics and physiology resulted to remarkable progress in the understanding of role of redox processes in cell vital function. It was established that oxidizing and reducing agents participate in processes of differentiation, proliferation and apoptosis. Representations about an existence of definite balance between oxidation and reduction processes in cells or a redox homeostasis were formed. Recent data about mechanisms of regulation of redox homeostasis were considered in the review. The correlation between redox homeostasis and metabolism were in detail analyzed. The special interest is given to a problem of quantitative description of redox phenomena in biological systems.

[The formation of stable aggrregates of human platelets induced by lectin from Solanum tuberosum]

It has been demonstrated for the first time that GlcNAc-specific lectin from Solanum tuberosum induces the formation of haptenic sugar-resistant intercellular contacts (HSR-contacts) in platelet aggregation and does not induce stable neutrophil and lymphocyte aggregation. The formation of HSR-contacts in platelets was significantly impaired by the inhibitors of cAMP phosphodiesterase (papaverine) and arachidonic acid methabolism (indomethacin, aristolochic acid, and MK-886) as well as by the sulfhydryl reagent N-ethylmaleimide. The results obtained indicate that STA can be used to study the mechanisms of stable platelet aggregation, to screen drugs with potential antithrombotic activity, and to develop new cell engineering techniques.

[Effect of hydrogen peroxide on ability of neutrophils to generate the reactive oxygen and chlorine species and secrete myeloperoxidase in vitro]

The influence of H2O2 at concentrations of 10(-8)--10(-2) mol/l on neutrophil ability to generate the reactive oxygen and chlorine species (ROCS) and secrete myeloperoxidase (MPO) was studied, and H202 injurious effect on neutrophils was also investigated in this work. It was revealed that H2O2 at concentrations of 2 x 10(-3)--2 x 10(-2) mol/l induced disturbance of the neutrophil membrane barrier properties and lactate dehydrogenase release. The incubation of the neutrophils with the addition of 10(-4)--10(-7) mol/l H2O2 led to an increase in the cell ability to generate ROCS during phagocytosis and decreased neutrophil ability to secrete MPO and ROCS in extracellular medium during adhesion. The mechanisms of H2O2 effect are coupled with arachidonic acid metabolism. Inhibition of metabolic pathways of 5-lipoxygenase or cyclooxygenase increased the destructive effect of H2O2 on the cells. Five-lipoxygenase way prohibition led to cancellation of H2O2 influence on MPO and ROCS secretion and to enhancement of H2O2 effect on neutrophil ability to generate ROCS during phagocytosis. The data obtained testify to the high neutrophil resistance to destructive effect of H2O2 and confirm the regulatory role of H2O2 with respect to the neutrophil functions.

Effects of peroxynitrite and lipopolysaccharide on mitotic activity of C6 glioma cells

Peroxynitrite is one of the most potent neurotoxic agents with multiple targets in neurons and glial cells. This study addressed a question of whether peroxynitrite-mediated cytotoxicity can be prevented by Escherichia coli lypopolisaccharide (LPS) due to its mitogenic activity towards C6 glioma cells. A number of characteristic morphological changes (processes impairments, nuclei modifications, cytoplasm vacuolization) and apoptotic cells were observed in the cell culture after 24-h treatment with 3-morpholinosyndnonimine (SIN-1), a well-known donor of peroxynitrite. These morphological changes were clearly associated with a SIN-1 dose-dependent increase in the number of pathological mitoses as well as with SIN-1 inhibition of the menadione-induced, lucigenin-enhanced chemiluminescence of C6 glioma cells, an independent indicator of mitotic activity of these cells. The mitotic index of C6 glioma cells increased in response to LPS and underwent non-uniform changes depending on SIN-1 concentrations. At a mitogenic concentration of 100 ng/ml, LPS reduced significantly the toxicity of SIN-1 determined as the accumulation of pathological mitoses, thus acting as a protective agent. Taken together, our findings indicate that SIN-1 specifically impairs the mitotic process in C6 glioma cells, and provide the first evidence that antimitotic effects of peroxynitrite can be restored by LPS.

[Regulation of morphologicaland functional properties of astroglial cells by hydrogen peroxide]

Effects of hydrogen peroxide on morphological characteristics, proliferation index, menadione-dependent lucigenin-enhanced chemiluminescence of C6 glioma cells were studied. It was established that H2O2 at 1 x 10(-8) - 5 x 10(-7) M concentrations acts as a regulator of morphological and functional properties of astrocytes by inducing their reactivation that is manifested as a cell body hypertrophy and an increase of proliferative activity and of menadione-dependent production of superoxide (O2- ). Cytodestructive action of hydrogen peroxide at a concentration higher than 1 microM on C6 glioma cells shows itself as a decrease of their proliferation index and the ability to generate O2- under menadione action. Using lipopolysaccharide B as a functional stimulator it has been shown that H2O2 modifies signaling pathways leading to the increase of mitotic activity of C6 glioma cells and decreases the yield of lucigenin-enhanced chemiluminescence of astrocytes under menadione action to the level of control values.

[Formation of reactive oxygen species in monocytes at adhesion to glass]

Processes of oxygen activation in monocytes stimulated with adhesion to glass were studied by methods of luminol-dependent and lucigen-independent chemiluminescence. It was shown that monocyte chemiluminescence was caused by cell adhesion to glass surface. Generation of reactive oxygen species at monocyte adhesion to glass was dependent on calcium ion concentration in the medium. The increase in the level of cytosolic calcium, as the extracellular calcium concentration elevated, was accompanied by the activation of phospholipase A2, 5-lypoxygenase and cycloxygenases. Magnesium ions exerted no influence on oxygen activation by cells. Incubation of cells in glucose-free medium, or the addition of glycolysis blocker (2-deoxy-D-glucose) to cell suspension led to a decrease in chemiluminescence intensity. By means of inhibitory analysis, it has been established that processes of oxygen activation are related to arachidonic acid metabolism, and depend on the activity of phospholipase A2.

[Consumption of intracellular hydrogen peroxide in epithelial human amnion cells]

The method for determination of intracellular oxidants content has been proposed. The method is based on the analysis of changes of 2,7-dichlorodihydrofluorescein oxidation. The theoretical model of hydrogen peroxide diffusion and its consumption in the cell and quantitative determination of hydrogen peroxide gradient through the cellular membrane has been built taking into account the experimental data. The coefficient for H2O2 permeability through the plasma membrane of human amnion cells is (2.1 +/- 0.1) x 10(-4) cm x c(-1).

Intracellular redox state: towards quantitative description

Redox state is a widely used term for the description of redox phenomena in biological systems. The regulating mechanisms responsible for maintaining the redox state are not yet fully known. But it was shown that changes in the redox state might lead to a cascade of intracellular events, beneficial or deleterious to the cell. There are several methods for the description of the intracellular redox state. These methods are based on using measured intracellular concentrations of reduced and oxidized glutathione in the Nernst equation. However, glutathione is not always a basic redox component in biological fluids, organelles, cells or tissues. As a result, changes in the intracellular redox state are not always accompanied by considerable changes of glutathione concentration. In this work it was proposed to use the concept of effective reduction potential for the quantitative characteristic of the intracellular redox state. The effective reduction potential was substantiated on the basis of a thermodynamic description. A new equation for the calculation of the effective reduction potential was derived. This equation summarizes the contribution of different oxidizing and reducing agents in the formation of an effective redox potential. The theoretical estimation of the effective reduction potential values for the different biological fluids and cells was carried out with the use of a method developed.

Influence of neopterin on the generation of reactive oxygen species in human neutrophils

Neopterin is synthesized by human monocyte-derived macrophages primarily upon stimulation with the cytokine interferon-gamma. We studied the influence of neopterin on the generation of reactive oxygen species (ROS) in human peripheral blood neutrophils. Radical formation was measured using a biochemiluminometer. Neutrophils were isolated from peripheral blood of healthy donors. The generation of ROS by neutrophils suspended in Earl's solution (pH=7.4) at 37 degrees C was investigated by monitoring of chemiluminescence using luminol and lucigenin as light emitters. Neopterin induced chemiluminescence in suspensions of neutrophils in the presence of luminol, but not of lucigenin. Neopterin affected only adhesive cells. Addition of neopterin into the suspension of the cells involving D-mannitol, L-histidine and diazabicyclo[2.2.2]octane (DABCO) decreased luminol-dependent chemiluminescence (LDCL) of the neutrophils. The action of superoxide dismutase (SOD) and 2-phenyl-4,4,5,5-tetramethylimidazoline-1-oxyl-3-oxide (PTIO) reduced neopterin-induced LDCL of neutrophils. Data suggest that neutrophils respond on exposure to neopterin with additional generation of singlet oxygen, hydroxyl radical and nitric oxide by nicotinamide adenine dinucleotide phosphate (NADPH)-independent pathways.

[Regulation of the neurite growth]

Recent achievement of molecular biology and neurophysiology resulting in remarkable progress in the understanding of processes of neurodifferentiation, playing the relevant role both in an ontogenesis and working of adult brain. New representations have been formed about a role of cytoskeletal proteins in mechanisms of neurites growth. In the review we discussed recent data regarding mechanisms of neuronal differentiation regulation. The special interest is given to a problem of influence of electrical fields on neuronal growth and differentiation. The mechanisms of signal transduction from a cell surface to nuclear are in detail analyzed. The classification of the physical and chemical factors of growth neurites regulation is given.

[Damage to erythrocytes caused by the interaction of nitrite-ions with hemoglobin]

The formation of two hemoglobin forms (methemoglobin and nitrite methemoglobin) in native human erythrocytes in the presence of sodium nitrite in suspension was shown. In normal erythrocytes, the interaction of intracellular oxyhemoglobin with nitrite ions results in the formation of methemoglobin, whereas in metabolically exhausted erythrocytes, this leads predominantly to the formation of nitrite methemoglobin. The nitrite methemoglobin reacts with hydrogen peroxide to form reactive intermediates (e.g. peroxynitrous acid) and the products of hemoglobin destruction. During the storage of erythrocyte suspensions containing methemoglobin and modified nitrite methemoglobin, differences in the forms of erythrocytes and the degree of their hemolysis were revealed. It is assumed that the formation of methemoglobin leads to the destruction of erythrocytes.

Differential potency of two crosslinking plant lectins to induce formation of haptenic-sugar-resistant aggregates of rat thymocytes by post-binding signaling

To evaluate the significance of post-binding events for stable aggregate formation, the aggregation/dissociation of rat thymocytes initiated by two crosslinking plant lectins, namely concanavalin A (Con A) and Solanum tuberosum agglutinin (STA), were comparatively studied. Despite intimate cell contacts in the aggregates only Con A led to establishment of haptenic-sugar-resistant (HSR) complexes. The presence of inhibitor II of diacylglycerol kinase, a dual calmodulin antagonist/protein kinase C inhibitor (trifluoperazine), and a sulfhydryl group reagent (N-ethylmaleimide) impaired this process. The obtained results indicate that the formation of HSR cellular contacts is not an automatic response to lectin-dependent cell association. In contrast to STA, Con A binding elicits this reaction with involvement of diacylglycerol kinase, protein kinase C and/or calmodulin as well as thiol level perturbation, as inferred by the application of target-selective inhibitors.

[Lectin-reactive immune complexes in plasma in ENT diseases]

The content of circulating immune complexes (IC) interacting with plant lectins from Canavalia ensiformis (Con A), phaseolus vulgaris (PHA) and wheat germ (WGA) was examined in blood plasma of healthy donors and patients with ENT diseases (n = 36). It was found that the level of PHA- and WGA-reactive IC in patients with laryngeal carcinoma was significantly higher than in control, whereas only the level of WGA-reactive IC was elevated in patients with scleroma. The level of ConA-reactive IC was statistically uniform in control and both ENT diseases.

[Relationship between the oxidation-reduction system of astrocytes with production of active forms of oxygen]

Cells of neuroglia--the astrocytes are of interest from the point of view of their participation in phagocytosis. Phagocyte ability to generate active oxygen forms (AOF) as used as the basic criterion of the estimation of their functional activity. For the purpose to clear up molecular and cellular mechanisms of phagocytosis a study of astrocyte redox-systems, participating in production of AOF, was undertaken. Registration of AOF in astrocytes was carried out using a method of luminol-dependent chemiluminescence. Primary culture of guinea pig astrocytes was used. Spontaneous chemiluminescence of low intensity was found for the astrocytes at the presence of luminol. The destruction of the cells was accompanied by a significant growth of the intensity of spontaneous chemiluminescence. Suspension of endocutosis inductors, particle of latex and phytohemagglutinin, added to astrocytes did not result in formation of AOF, characteristic for other cells, possessing phagocytosis. It was established, that addition of hydrogen peroxide destroys astrocytes at the presence of luminol and gives rise to the emission. Chemiluminescence was not observed in similar experiments with intact cells. A conclusion was made that inside astrocytes there are structures, which show peroxidase-like activity.

Metabolic inhibitors as tools to delineate participation of distinct intracellular pathways in enhancement of lactose-induced dissociation of neutrophil and thymocyte aggregates formed by mediation of a plant lectin

Signaling processes in the course of the formation of the lectin-mediated aggregates may partake in conveying enhanced stability to the cell clusters. To prove the validity of this reasoning in a model, we have studied the impact of addition of three metabolic inhibitors (N-ethylmaleimide, nordihydroguaiaretic acid, and trifluoperazine) on lactose-dependent dissociation of cell aggregates, formed in the presence of the galactoside-binding mistletoe lectin. Using both human neutrophils and rat thymocytes to avoid measurement of responses restricted to a single cell type, an enhanced dissociation of lectin-formed cell aggregates was observed, when lactose and an inhibitor were present. Among the tested inhibitors, nordihydroguaiaretic acid and N-ethylmaleimide were more potent enhancers of cell dissociation than trifluoperazine. These results suggest that biosignalling pathways connected with lipoxygenase activity as well as the level of intracellular sulfhydryl groups confer further stability to lectin-dependent cell aggregates. The systematic evaluation of inhibitors for defined activities is thus suggested as a tool to disclose the nature and the contribution of individual signaling mechanisms to post-binding effects following lectin-initiated cell contact formation.

Effects of metabolic inhibitors and lectins on the menadione-dependent generation of H2O2 by rat thymocytes

The capacity of oxidative metabolism and its regulation is an important factor in disease control. Using scopoletin as a fluorescent substrate of peroxidase the extent of menadione-dependent production of H2O2 by rat thymocytes was determined. The reaction was inhibited by 2,4-dinitrophenol, papaverine, nordihydroguaiaretic acid and iodacetamide. The membrane-penetrating SH reagent N-ethylmaleimide primed the reaction, probably due to an inhibition of glutathione peroxidase. To delineate an influence of cell-surface protein-carbohydrate interactions by exogenous lectins, the impact of cell binding was analyzed for several plant lectins, namely concanavalin A, phytohemagglutinin, the lectins from Triticum vulgaris and from Sambucus nigra. Except for the alpha-NeuNAc(2-6)gal/galNAc-binding agglutinin, the other three plant proteins with specificities to different parts of N-linked oligosaccharides primed the reaction. This activity of lectins did not coincide with their ability to aggregate cells. The given results indicate that biosignaling pathways triggered by lectins are involved in the regulation of the intracellular reduction of menadione.

[H2O2 generation and human neutrophil aggregation as affected by lectins]

The effects of eight plant lectins on human neutrophils aggregation and H2O2 release were studied. Both processes were stimulated by lectins from Viscum album, Triticum vulgaris, Phaseolus vulgaris and Canavalia ensiformis while lectins from Solanum tuberosum, Sambucus nigra and Glycine mas displayed only aggregating activity and Arachis hypogaea lectin was not effective. Heating (46 degrees C) and UV-radiation during 4-5 min were found to suppress completely H2O2 release from neutrophils keeping the capacity of cells to be aggregated. The findings indicate that lectin-induced human neutrophils aggregation is necessary but not sufficient condition of respiratory burst of cells. The comparison of the aggregating activity of lectins with their ability to induce the H2O2 release is supposed to be the basis of screening of lectins with antitumor and immunomodulatory activity.

Viscum album agglutinin-induced aggregation of blood cells and the lectin effects on neutrophil function

Extracts from mistletoe enjoy a large popularity in central Europe as an unconventional treatment modality for cancer, warranting scientific efforts with defined components to delineate any potential benefit. The galactose-specific lectin from Viscum album (VAA), known to exhibit immunomodulatory and ensuing antitumoral capacities in animal model systems, was shown to aggregate human blood cells in the following order: neutrophils, mononuclear cells--thrombocytes and erythrocytes. To contribute to the analysis of lectin effects on individual aspects of the host defence system, two parameters of neutrophils were quantitatively assessed, namely the aggregating activity of VAA as a measure of strength of interaction with cell surface ligands and the effect of lectin on oxidative metabolism (H2O2 release) of these cells. It was found that whole lectin and its carbohydrate-binding B-subunit possessed the capacity to induce cell aggregation and H2O2 release, which were blocked by D-galactose and lactose. Both effects displayed similar dependence on the lectin concentration in the range 0.1-25 micrograms/ml. The toxic A-subunit displayed detectable activity only in high doses (50 micrograms/ml) while the bovine heart galaptin (14 kDa; galectin-1) failed to affect neutrophils. The role of oxidative metabolism in regulation of neutrophil aggregation induced by VAA was studied using metabolic inhibitors and controlled heating at 46 degrees C leading to inhibition of plasma membrane NADPH-oxidase system. Trifluoperazine and menadione inhibited the neutrophil aggregation in a dose-dependent manner in comparison with such inhibitors as amiloride and theophylline.(ABSTRACT TRUNCATED AT 250 WORDS)

[The effect of hyperthermia (45 C) on lymphoid cell aggregation]

Hyperthermia (45 degrees C) has found to decrease the rate of rat thymocytes as well as splenocytes aggregation induced by lectins (concanavalin A, wheat germ agglutinin) and sulphated polysaccharides (heparin, dextran sulphate-500) and to increase those induced by cationic dye alcian blue. Shedding of plasma membrane glycoproteins and changes of surface charge are supposed to affect the aggregation.

[Aggregation of neutrophils and their generation of active forms of oxygen as affected by lectins]

It was shown that neutrophil aggregation is caused by all lectins with different specificity for carbohydrates but generation of active oxygen forms is induced only by some lectins. Polyspecific lectins-erythroagglutinin and phytohemagglutinins have the greatest activity in relation to both processes.

[The effect of metabolic inhibitors on resistance of mannose-specific contacts of Escherichia coli K12 and human neutrophils]

Human neutrophil aggregation induced by Escherichia coli K12 cells has been studied. D-mannose has been found to inhibit the process in the dose-dependent way causing the full blockage at 10 mM concentration. The process of disaggregation induced by the concentration is significantly higher at 10 degrees C than at 37 degrees C. The inhibitors of cellular oxygenation such as N-ethylmaleimide, nordihydroguaiaretic acid, trifluoperazine, and colchicine did not affect the aggregation process. Cellular aggregation was concomitant with production of H2O2, and this reaction was also blocked by D-mannose and depended on the number of bacteria present. The nordihydroguaiaretic acid and N-ethylmaleimide inhibited production of H2O2, while sodium azide enhanced the process. The results show the mannose-specific contact of bacteria and neutrophils to depend on the functional activity of phagocytes including their ability to produce H2O2.

[The effect of recombinant interleukin-1 beta on concanavalin A-induced lymphocyte reactions]

As revealed by investigations made by the use of the method of luminol-dependent chemiluminescence and light dispersion, the addition of concanavalin A (ConA) to the suspension of human peripheral blood lymphocytes and subsequent incubation with recombinant interleukin-1 beta leads to a sharp increase in the yield of chemiluminescence and the rate of cell aggregation in comparison with similar parameters obtained for cells, not treated with interleukin-1 beta. The study revealed the potentiating action of recombinant interleukin-1 beta on ConA-induced proliferative response of thymocytes in the culture. The mechanisms of the priming action of recombinant interleukin-1 beta on ConA-induced reaction of lymphocytes are discussed.

[The free-radical mechanisms of the cytotoxic action of 1,2-benzoquinone derivatives]

The authors examined the interaction of 1,2-benzoquinone derivatives with HeLa cell cultures and ascite Ehrlich's cancer cells. 4-N (anilino)-5-methoxy-1,2-benzoquinone was found to produce a marked toxic effects against tumor cells. The cytotoxic effect is oxygen dependent and associated with the formation of oxygen radicals in quinone's redox cyclization reactions. The inhibitory analysis was used to show that the major mediators of the toxic action of the agent are superoxide radical-anion and hydrogen peroxide. It is concluded that the interaction of highly toxic oxygen radicals, which are generated in quinone redox cyclization, with plasma membrane cells is likely to be the mechanism responsible for cellular destruction when quinones act on tumor cells.

[A comparative study of the reactions of the peripheral blood neutrophils from donors and from lymphogranulomatosis patients to arachidonate stimulation of the cells]

Arachidonate-induced aggregation and generalization of active oxygen forms (OAF) by peripheral blood neutrophils in donors were studied in donors and Hodgkin's disease patients. Leukocytes of the latter had incomplete ability to produce AOF in response to cell stimulation with arachidonic acid. The study of arachidonate-induced aggregation of neutrophils indicated no differences in the speed of the process in the patients and donors. AOF catchers did not act on the rate of leukocyte aggregation in the patients though accelerated the process in the donors. It is inferred that Hodgkin's disease is associated with dysfunction of oxygen activation by neutrophils. The findings suggest that defects in leukocytes ability to activate oxygen in Hodgkin's disease may entail deranged regulation of other processes essential for functional activity of polymorphonuclear leukocytes.