[Possible mechanism of antioxidant action of dinitrosyl iron complexes]. / Vozmozhnyi mekhanizm antioksidantnogo deistviia dinitrozil'nykh kompleksov zheleza.

The antioxidant effect of dinitrosyl iron complexes (DNICs) was studied in various model systems. DNICs with glutathione ligands effectively inhibited Cu2+-induced peroxidation of low density lipoproteins (LDL). The antioxidant effect of DNICs with phosphate ligands and free reduced glutathione (GSH) was less pronounced. In addition, DNICs with glutathione suppressed the formation of reactive oxygen species during co-oxidation of lecithin liposomes and glucose. Free radical oxidation in this system was induced with a lipophilic azo initiator and evaluated by luminol-dependent chemiluminescence. NO sharply stimulated chemiluminescence during co-oxidation of glucose and liposomes, thus suggesting the formation of potent oxidants under these conditions. Glutathione DNICs scavenge the superoxide radical anion generated in the xanthine-xanthine oxidase system. Superoxide production was assessed by lucigenin-dependent chemiluminescence and electron paramagnetic resonance (EPR) spectroscopy. Chemiluminescence revealed the dose-dependent character of antiradical effect of glutathione DNICs; moreover, these complexes turned out to be more efficient than GSH. EPR spectra of the adducts of the DEPMPO spin trap with free radicals suggest that the interaction of glutathione DNICs and superoxide does not result in the formation of the thiyl radical of glutathione. Here we propose a mechanism of the antioxidant action of glutathione DNICs, suggesting that unstable intermediate complexes are formed upon their interaction with superoxide or lipid radicals. Further, as a result of intramolecular rearrangement, these intermediates decompose without the free radical as the by-products.

Changes in Transcriptional Regulation of Postnatal Morphogenesis of the Adrenal Zona Fasciculata Caused by Endocrine Disruptor Dichlorodiphenyltrichloroethane.

We studied the expression of transcriptional factors regulating postnatal morphogenesis of the adrenal zona fasciculata in rats after developmental exposure to endocrine disruptor DDT. It was found that tissue reparation after trophic disorders and cell death triggered by prenatal and postnatal exposure to DDT was accompanied by an increase in the number of Oct4- and Shh-expressing cells forming a pool located outside the regeneration zones and involved in the maintenance of tissue homeostasis in the zona fasciculata. DDT exposure also disrupted the expression of antiproliferative factor Hhex. The data showed that proliferation of fasciculata cells after termination of adrenal cortex growth was downregulated by inhibition of the expression of Oct4 and Shh and suppression of canonical Wnt signaling, i.e. due to a decrease in the reserve cell pool essential for physiological regeneration, which can reduce the reactive potential of the zona fasciculata.

The Enhancement of Metal-Binding Properties in Hemoglobin: The Role of Mild Damaging Factors.

X-ray studies revealed the considerable enhancement of metal-binding properties in human hemoglobin under exposure to mild damaging factors (in the presence of 0.09 M urea or upon heating for 30 min at 50 °C). Changes in the element composition of the hemoglobin monolayer, formed on the water subphase in the Langmuir trough, have been monitored in real time by the total external reflection X-ray fluorescence measurements. X-ray absorption spectroscopy has been applied to study the local environment of zinc ions bound on hemoglobin molecules. According to these data, each zinc ion is coordinated by four ligands, two of which are cysteine and histidine. The oxidative stress has been found to accelerate extensively the enhancement of metal-binding ability in protein. A two-stage mechanism has been proposed as a possible explanation of the observed phenomenon: First, in the presence of the mild damaging agents, protein molecules can undergo a transition from the native conformation to a more labile intermediate state that increases the accessibility of amino acid residues (in particular cysteine). At the second stage, oxidation of cysteine and the subsequent activation of cysteine SH groups can affect markedly the protein-metal interaction. The presented investigations provide a deeper insight into the pathogenesis of metabolic disorders that excessive concentrations of the endogenic toxicants might trigger in an organism.

Electrophilic Signaling: The Role of Reactive Carbonyl Compounds.

Reactive carbonyl compounds (RCC) are a group of compounds with clearly pronounced electrophilic properties that facilitate their spontaneous reactions with numerous nucleophilic reaction sites in proteins, lipids, and nucleic acids. The biological functions of RCC are determined by their concentration and governed by the hormesis (biphasic reaction) principle. At low concentrations, RCC act as signaling molecules activating defense systems against xenobiotics and oxidizers, and at high concentrations, they exhibit the cytotoxic effect. RCC participate in the formation of cell adaptive response via intracellular signaling pathways involving regulation of gene expression and cytoplasmic mechanisms related to the structure-functional rearrangements of proteins. Special attention in this review is given to the functioning of electrophiles as mediators of cell general adaption syndrome manifested as the biphasic response. The hypothesis is proposed that electrophilic signaling can be a proto-signaling system.

Alternate and Additional Functions of Erythrocyte Hemoglobin.

The review discusses pleiotropic effects of erythrocytic hemoglobin (Hb) and their significance for human health. Hemoglobin is mostly known as an oxygen carrier, but its biochemical functions are not limited to this. The following aspects of Hb functioning are examined: (i) catalytic functions of the heme component (nitrite reductase, NO dioxygenase, monooxygenase, alkylhydroperoxidase) and of the apoprotein (esterase, lipoxygenase); (ii) participation in nitric oxide metabolism; (iii) formation of membrane-bound Hb and its role in the regulation of erythrocyte metabolism; (iv) physiological functions of Hb catabolic products (iron, CO, bilirubin, peptides). Special attention is given to Hb participation in signal transduction in erythrocytes. The relationships between various erythrocyte metabolic parameters, such as oxygen status, ATP formation, pH regulation, redox balance, and state of the cytoskeleton are discussed with regard to Hb. Hb polyfunctionality can be considered as a manifestation of the principle of biochemical economy.

Carbonyl Stress in Bacteria: Causes and Consequences.

Pathways of synthesis of the α-reactive carbonyl compound methylglyoxal (MG) in prokaryotes are described in this review. Accumulation of MG leads to development of carbonyl stress. Some pathways of MG formation are similar for both pro- and eukaryotes, but there are reactions specific for prokaryotes, e.g. the methylglyoxal synthase reaction. This reaction and the glyoxalase system constitute an alternative pathway of glucose catabolism - the MG shunt not associated with the synthesis of ATP. In violation of the regulation of metabolism, the cell uses MG shunt as well as other glycolysis shunting pathways and futile cycles enabling stabilization of its energetic status. MG was first examined as a biologically active metabolic factor participating in the formation of phenotypic polymorphism and hyperpersistent potential of bacterial populations. The study of carbonyl stress is interesting for evolutionary biology and can be useful for constructing highly effective producer strains.

Measurement of plasma hemoglobin peroxidase activity.

We described a spectrophotometric method for measuring hemoglobin peroxidase activity in human plasma using o-dianisidine (o-DA) as the substrate and myeloperoxidase specific inhibitor 4-aminobensoic acid hydrazide (ruling out the probable contribution of myeloperoxidase to the measured parameter value). The optimal conditions (pH 5.5; 2 mM H2O2) have been determined, at which hemoglobin makes the main contribution to plasma oxidation of o-DA. A significant positive correlation between hemoglobin peroxidase activity measured by the spectrophotometric method and hemoglobin level measured by the pyridine hemochromogenic method has been detected (r=0.624; p<0.01) in plasma specimens from 16 donors. Plasma hemoglobin peroxidase activities were measured in healthy individuals and patients with type 2 diabetes mellitus and coronary heart disease. High plasma hemoglobin peroxidase activities in both groups of patients indicates disorders in the mechanisms of clearance of hemoglobin and its highly reactive derivatives and can serve as specific markers of diseases associated with oxidative stress.