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2-Hexadecenal (2-HD)-a biologically active long-chain fatty aldehyde formed in organism enzymatically or nonenzymatically in the reaction of free-radical destruction of sphingolipids under the action of hypochlorous acid, producing by myeloperoxidase. This research aimed to study 2-HD effects on polymorphonuclear leukocytes' (PMNLs) functions. It has been shown that at submicromolar concentrations, 2-HD causes an elevation in ROS production by PMNLs. It has been found that such effect is associated with signal transduction pathways modification and expressed in elevation of NADPH oxidase, MPO, and JNK-MAPK contributions to this process. At higher concentrations, 2-HD induces apoptosis, which correlates with a significant increase in free Ca 2+ in the cytoplasm, a decrease in ROS production, and a decline in mitochondrial potential. Both of these processes are accompanied by cytoskeleton reorganization., (© 2022. The Author(s), under exclusive licence to Springer Science+Business Media, LLC, part of Springer Nature.)

Vicinal diols and its derivatives can be exploited as model compounds for the investigation of radiation-induced free-radical transformations of hydroxyl-containing biomolecules such as carbohydrates, phospholipids, ribonucleotides, amino acids, and peptides. In this paper, for the first time, the prospects of isotope reinforcement approach in inhibiting free-radical transformations of hydroxyl-containing compounds in aqueous solutions are investigated on the example of radiolysis of 1,2-propanediol and 1,2-propanediol-2-d 1 aqueous solutions. At an absorbed dose rate of 0.110 ± 0.003 Gy·s -1 a profound kinetic isotope effect (KIE) is observed for the non-branched chain formation of acetone, which is a final dehydration product of predominant carbon-centred radicals CH 3 ·C(OH)CH 2 OH. In 0.1 and 1 M deaerated solutions at pH 7.00 ± 0.01, the values of KIE are 8.9 ± 1.7 and 15.3 ± 3.1, respectively. A rationale for the fact that a strong KIE takes place only in the case of chain processes, which may occur during free-radical transformations of vicinal diols, is also provided herein based on the results of 2-propanol and 2-propanol-2-d 1 indirect radiolysis. Lastly, the lack of KIE is shown in the case of 2-butanone formation from 2,3-butanediol or 2,3-butanediol-2,3-d 2 . This indicates that the type (primary, secondary) of the β-carbonyl radicals formed as a result of CH 3 ·C(OH)CH(OH)R (R = H, CH 3 ) dehydration determines the manifestation of the effect.

Thymoquinone (TQ) is a highly perspective chemotherapeutic agent against gliomas and glioblastomas because of its ability to cross the blood-brain barrier and its selective cytotoxicity for glioblastoma cells compared to primary astrocytes. Here, we tested the hypothesis that TQ-induced mild oxidative stress provokes C6 glioma cell apoptosis through redox-dependent alteration of MAPK proteins. We showed that low concentrations of TQ (20-50 μM) promoted cell-cycle arrest and induced hydrogen peroxide generation as a result of NADH-quinone oxidoreductase 1-catalyzed two-electron reduction of this quinone. Similarly, low concentrations of TQ efficiently conjugated intracellular GSH disturbing redox state of glioma cells and provoking mitochondrial dysfunction. We demonstrated that high concentrations of TQ (70-100 μM) induced reactive oxygen species generation due to its one-electron reduction. TQ provoked apoptosis in C6 glioma cells through mitochondrial potential dissipation and permeability transition pore opening. The identified TQ modes of action on C6 glioma cells open up the possibility of considering it as a promising agent to enhance the sensitivity of cancer cells to standard chemotherapeutic drugs.

Effects of quinones and azoles on the formation of steady-state radiolysis products in aqueous solutions of glycerol-1-phosphate and aqueous dispersions of 1,2-dimyristoyl-glycero-3-phosphatidyl-glycerol has been investigated. The data obtained by LC-MS-ESI and spectrophotometric measurements shows that the compounds having quinoid structures, including the antitumor agent doxorubicin, and azoles having nitro groups effectively inhibit free-radical fragmentation of glycerol-1-phosphate and 1,2-dimyristoyl-glycero-3-phosphatidyl-glycerol, decreasing the radiation-chemical yields of either inorganic phosphate or phosphatidic acid respectively. The observed effects of blocking free-radical processes are believed to be related to the ability of the tested compounds to oxidize α-hydroxyl-containing carbon-centered radicals of starting substrates, which give rise to fragmentation reaction. The possibility of using the discovered properties of quinones, doxorubicin and nitroazoles to provide practical solutions in oncological radiotherapy and pathophysiology is discussed., (Copyright © 2019 Elsevier B.V. All rights reserved.)

2-Hexadecenal (2HD) formation in the organism occurs via irreversible enzymatic degradation of sphingosine-1-phosphate or nonenzymatic γ-, UV-, or HOCl-induced destruction of a number of sphingolipids including S1P. The current research focuses on the study of 2HD effects on C6 glioma cells growth. The results obtained show that 2HD causes a dose-dependent decrease in proliferative and mitotic indices. The change in the mitotic index is due to the redistribution of cells in the different phases of mitosis. These processes are accompanied by cytoskeleton rearrangement and changes in cell morphology, which are expressed in F-actin redistribution, change in the number and type of filopodia and fibrils, leading to cell shape changes, decrease in intercellular contacts and monolayer rarefaction. Cells treatment with 2HD leads to apoptosis induction and signalling pathways modification, including activation of JNK, p38, and ERK1/2 MAPK but not PI3K. The effects observed are not related to the cytotoxicity of 2HD. Significance of the study: 2HD-an unsaturated aldehyde, which level can rise under conditions of oxidative stress as a result of nonenzymatic sphingolipids' destruction. The mechanisms of 2HD action on various cell types have not been sufficiently studied. Therefore, the study on functional role of this aldehyde in different cell types that may be its target is relevant. This study demonstrated that 2HD inhibits growth of C6 glioma cells due to modification of intracellular processes of signal transduction, cytoskeleton rearrangement, change in the mitotic regimen and apoptosis induction., (© 2019 John Wiley & Sons, Ltd.)

Cytochrome c (cyt c ) is a small hemoprotein involved in electron shuttling in the mitochondrial respiratory chain and is now also recognized as an important mediator of apoptotic cell death. Its role in inducing programmed cell death is closely associated with the formation of a complex with the mitochondrion-specific phospholipid cardiolipin (CL), leading to a gain of peroxidase activity. However, the molecular mechanisms behind this gain and eventual cyt c autoinactivation via its release from mitochondrial membranes remain largely unknown. Here, we examined the kinetics of the H 2 O 2 -mediated peroxidase activity of cyt c both in the presence and absence of tetraoleoyl cardiolipin (TOCL)- and tetralinoleoyl cardiolipin (TLCL)-containing liposomes to evaluate the role of cyt c -CL complex formation in the induction and stimulation of cyt c peroxidase activity. Moreover, we examined peroxide-mediated cyt c heme degradation to gain insights into the mechanisms by which cyt c self-limits its peroxidase activity. Bottom-up proteomics revealed >50 oxidative modifications on cyt c upon peroxide reduction. Of note, one of these by-products was the Tyr-based "cofactor" trihydroxyphenylalanine quinone (TPQ) capable of inducing deamination of Lys ϵ-amino groups and formation of the carbonylated product aminoadipic semialdehyde. In view of these results, we propose that autoinduced carbonylation, and thus removal of a positive charge in Lys, abrogates binding of cyt c to negatively charged CL. The proposed mechanism may be responsible for release of cyt c from mitochondrial membranes and ensuing inactivation of its peroxidase activity., (© 2019 Barayeu et al.)

Effects of tryptophan, 5-hydroxytryptophan, serotonin, and melatonin on final product formation during radiolysis of deaerated and oxygen-saturated ethanol and aqueous 1M ethanol solutions were studied. The named amino acids were found to be capable of adding α-hydroxyethyl radicals, thereby suppressing recombination reactions of these species. Unlike melatonin, tryptophan, 5-hydroxytryptophan, and serotonin were able to reduce oxygen-centered radicals being formed on radiation-chemical oxidation of ethanol in the presence of oxygen via electron transfer from the amine nitrogen lone pair.

A possibility of a novel photodestruction process has been shown for sphingolipids and their low-molecular analogues, including the stage of Norrish Type-I decomposition of excited molecules of the starting compounds followed by fragmentation of nitrogen-centered radicals via rupture of the C-C and O-H bonds. Realization of such transformation during photolysis of ceramide, sphingomyelin and galactocerebroside results in formation of 2-hexadecenal, which possess a wide spectrum of biological activity., (© 2012 Wiley Periodicals, Inc. Photochemistry and Photobiology © 2012 The American Society of Photobiology.)

The inhibition efficiency (antioxidant activity) of hydroxy derivatives of coumarin, such as esculetin, dicumarol, and fraxetin, was studied in the methemalbumin-H2O2-tetramethylbenzidine (TMB) pseudoperoxidase system at 20 degrees C in a buffered physiological solution (pH 7.4) containing 6% DMF and 0.25% DMSO. The inhibitor's efficiency was quantitatively characterized by the inhibition constants (K(i), microM) and the inhibition degree (%). The K(i) values for esculetin, dicumarol, and fraxetin were 9.5, 15, and 26 microM, respectively. Esculetin and fraxetin inhibited pseudoperoxidase oxidation of TMB in a noncompetitive manner; dicumarol, in a mixed manner. The inhibiting activity ofesculetin in peroxidase-catalyzed TMB oxidation at pH 6.4 is characterized by a K(i) value equal to 1.15 microM, and the inhibition process is competitive. Esculetin was found to be the most effective antioxidant of plant origin among all derivatives previously studied in model biochemical systems.

The ability of ascorbic acid and a number of its derivatives to suppress replication of Herpes simplex virus type I was investigated in human rhabdomyosarcoma cell line. In parallel, interaction of the test compounds with carbon- and oxygen-centered radicals formed on radiolysis of hydroxyl-containing organic compounds was studied using the steady state radiolysis method. It has been shown that 2-O-glycoside of ascorbic acid, displaying marked antiviral properties against Herpes simplex virus type I, is also capable of inhibiting fragmentation and recombination reactions of α-hydroxyl-containing carbon-centered radicals while not affecting processes involving oxygen-centered radicals., (Copyright © 2012 Elsevier Ltd. All rights reserved.)

Effects of curcumin and related compounds on product formation in radiolysis of aerated and deaerated ethanol were studied. Ab initio calculations of enthalpy values relating to O-H bond dissociation and H-atom addition to > C = O bonds of the compounds under study have been performed. The obtained data allowed the conclusion that the presence of a 7-carbon chain containing conjugated > C = C < and > C = O bonds in the structures of curcumin and its analogues makes these compounds capable of inhibiting the reactions involving α-hydroxyl-containing carbon-centered radicals. This finding broadens the existing views concerning radical-regulating properties of curcuminoids, and it should be taken into account when practical use of these compounds is envisaged.

Inhibition efficiency (antioxidant activity) of 26 oxygen-containing aromatic compounds was studied in methemalbumin-H202-o-phenylenediamine (PDA) or tetramethylbenzidine (TMB) pseudoperoxidase system at 20 degrees C in buffered physiological solution (pH 7.4) containing 6% DM F and 0.25% DMSO. The inhibitor's efficiency was quantitatively characterized by the inhibition constants (Ki, microM) or the inhibition degree (%). Ki values varied in the range of4 to 500 microM and were influenced by a substrate, the structure of an inhibitor, hydroxyl groups, electron-donating substituents in aromatic ring, and steric hindrances. The type of inhibition at cooxidation of eight pairs was noncompetitive, and that of five pairs was mixed and determined by the substrate nature and the inhibitor structure. Lignin phenolic compounds ofguaiacyl and syringal series exhibited high antioxidant activity (Ki in the range of 10-300 microM), and their efficiency decreased in the following order: caffeic acid > synapaldehyde > syringic acid > coniferyl aldehyde > para-hydroxycou maric acid.

Data have been obtained showing regularities in product formation following radiolysis of serinol, lysosphingomyelin and photolysis of N-(2-hydroxypropyl)hexanamide, sphingomyelin, which point to the possibility of photo- and radiation-induced destruction of the named substrates via a C-C bond rupture. The key stage of this process is the formation and decomposition of N-centered radicals generated from the starting compounds.

A highly effective test-system for quantitative characterization of the total antioxidant activity (TAA) of human blood serum (HBS), including methemalbumin (MetHa) as biocatalyst, H2O2 as the oxidant, o-phenylenediamine (PDA) as the acceptor of radicals and 2,2,5,7,8-pentamethylchroman-6-ol (PMC) as the inhibitor-calibrator, has been developed and proved under the laboratory environments. The test-system has been optimized for the concentrations of all the components, the reaction conditions and the PDA consumption monitoring at 37 degrees C in the medium of buffered physiological solution, pH 7.4 containing 5% DMFA and 0.5% DMSO. Under strongly standardized conditions by a comparison of the inhibiting action of the HBS and the calibrator PMC at 37 degrees C, the quantitative parameters of the HBS TAA were determined in microg of PMC, equivalent to 1 mg of HBS, or as a reverse value in mg of HBS, equivalent to the action of 1 microg of PMC. The values of the HBS TAA significantly varied for the group of healthy individuals and essentially decreased for the group of patients with thyroid gland pathologies. This underlies necessity of antioxidant therapy in these patients.

Effects of ascorbic acid and 5,6-O-isopropylidene-2,3-O-dimethylascorbic acid on final product formation in radiolysis of ethanol, aqueous solutions of ethanol, ethylene glycol, alpha-methylglycoside, maltose, alpha-glycerophosphate, and alpha-glucose phosphate were studied. It was found that ascorbic acid is able to suppress reactions involving various alpha-hydroxyl-containing carbon-centered radicals and depending on the experimental conditions can either oxidize or reduce alpha-hydroxyethyl radicals.

Mitochondria are an important intracellular source of ROS as well as a sensitive target for oxidative damage under certain pathological conditions such as iron or copper overload. Mitochondrial membranes are rich in the tetraacyl phospholipid cardiolipin. Its integrity is important for efficient oxidative phosphorylation. Mouse liver mitochondria were subjected to oxidative stress by the Cu(2+)(Fe(2+))/H(2)O(2)/ascorbate system. Phosphatidic acid was detected in oxidized mitochondria, but not in unperturbed mitochondria. The Cu(2+)/H(2)O(2)/and (or not) ascorbate system caused the formation of phosphatidic acid and phosphatidylhydroxyacetone in cardiolipin liposomes. These products proceed via an HO*-radical induced fragmentation taking place in the polar moiety of cardiolipin. Mass spectrometry analysis of phosphatidic acid newly formed in mitochondria revealed that it has been derived from fragmentation of cardiolipin. Thus, free-radical fragmentation of cardiolipin in its polar part with the formation of phosphatidic acid is a likely mechanism that damages mitochondria under conditions of oxidative stress.

Co(II) and Ni(II) complexes with 4,6-di-tert-butyl-3-[(2-hydroxyethyl)thio]benzene-1,2-diol (L) have been synthesized and characterized by means of elemental analysis, TG/DTA, FT-IR, ESR, UV-vis, XRD, magnetic susceptibility, cyclic voltammetry and conductance measurements. According to the data obtained the organic compound acts as a bidentate O,S-coordinated ligand and yields Co(II) and Ni(II) complexes of the stoichiometry ML(2) which is characterized by square planar geometry. Antifungal and anti-HIV activities of the ligand and its metal(II) complexes were found to decrease in the sequence CuL(2)>CoL(2) ~ NiL(2)>HL, along with their reducing ability (determined electrochemically).

The coenzymes Q and Vitamin K(3), as well as their synthetic analogues, have been found to inhibit free-radical processes of fragmentation of hydroxyl-containing organic compounds and oxidation of the latter by molecular oxygen. It has been established that the observed effects are due to the ability of quinones to oxidize the alpha-hydroxyl-containing carbon-centered radicals formed from the starting compounds.

A comparative kinetic study of ortho-phenylenediamine (PDA) oxidation in the "pseudoperoxidase" system Methemalbumin-H2O2 in the presence of 2-amino-4-tret-butylphenol (ATBP), 2-amino-4,6-di-tret-butylphenol (ADTBP) and its four N-acyl derivates, as well as flavonoids (quercetin, morin, silibin, hesperidin and naringin) has been carried out under standart conditions at 20 degrees C in phosphate buffered saline, pH 7.4, containing 5.25% ethanol and DMFA. ATBP, ADTBP and two its N-acyl-derivatives as well as all five flavonoids inhibited with different efficiency the PDA oxidation characterized in terms of the inhibition constants, K(i), M, or the percent of inhibition degree at the maximal taking concentrations of these inhibitors. Most effective antioxidants were quercetin (K(i) = 7.7x10(-5) M) and ATBP (K(i) = 1.26x10(-4) M). Using these characteristics and other necessary criteria, the pairs PDA-quercetin and PDA-ATBP were proposed for a practical application in the test-systems for total antioxidant activity of biological objects.

Cu(II) complexes with 4,6-di(tert-butyl)-2-aminophenol (I) and 2-anilino-4,6-di(tert-butyl)phenol (II) have been synthesized and characterized by means of elemental analysis, TG/DTA, FT-IR, UV-vis, ESR, and conductance measurements. The compounds I and II can coordinate in their singly deprotonated forms and behave as bidentate O,N-coordinated ligands; their CuL(2) complexes are characterized by CuN(2)O(2) coordination modes and square planar geometry. In vitro antimicrobial screening against Gram-positive and Gram-negative bacteria, yeasts, and moulds indicated that the compound I and its Cu(II) complex were more active than Questiomycin B, the compound II, and its Cu(II) complex.

It has been established that vitamins B1, K3 and C, coenzyme Q0 and amino acids cysteine and histidine effectively inhibit reactions of homolytic cleavage of the O-glycoside bond, which are responsible for the destruction of di- and polysaccharides on gamma-irradiation or the action of other reactive radical initiators. This effect was shown to originate from either oxidation or reduction of the radicals of carbohydrates undergoing destruction.

Effects of alpha-tocopherol, PMC, and a number of the respective sulfur-containing analogues on reactions involving various organic radicals were studied. The test compounds were found to interact with alkyl radicals more effectively than with peroxyl radicals. The presence of a sulfur atom in structures of the respective analogues did not produce significant effects on reactivity. Derivatives of 5-hydroxy-1,3-benzoxathiol-2-one and 6-hydroxy-1,4-benzoxathiin-2(3H)-one displayed a high reactivity toward alpha-hydroxyalkyl radicals.

It has been found that flavonoids (FL) are able to reduce, add or oxidize alpha-hydroxyethyl radicals (HER). The probability of these processes to occur depends on the structure of the FL under study. Namely, to cause reduction of HER, the presence of hydroxyl groups is necessary, and to effect oxidation or addition of HER, the presence of a carbonyl group at C4 and a C2-C3 double bond in the C ring is required.

The formation of products resulting from the O-glycoside bond cleavage following radiolysis of aqueous solutions of methyl-alpha-D-glucopyranoside (I), 3-O-methyl-alpha-D-glucopyranose (II), maltose, lactose, gentiobiose and cellobiose were studied. Radiation-induced destruction yields were also determined for dextran, laminarin and trimethylcelulose upon irradiation of their aqueous solutions. Oxygen, quinones and compounds capable of forming quinoid structures were found to inhibit radiation-induced homolytic destruction processes taking place in glycosides, di- and polysaccharides. The data obtained in this study enabled the authors to demonstrate an important role played by the fragmentation reaction of C-2 radicals which were generated from the starting substances in the formation of final radiolysis products.

Effects of vitamins B1, B2, B6, and pyridoxal phosphate (PPh) on final product formation in radiolysis of aqueous solutions of ethanol, ethylene glycol, alpha-methylglycoside, and maltose were studied. It has been found that vitamin B2 and PPh effectively oxidize R*CHOH species, while suppressing their recombination and fragmentation reactions, thereby increasing the yields of the respective oxidation products. Vitamins B1 and B2 are capable of reducing alcohol radicals to the respective initial molecules, decreasing the yields of the radical transformation products.

Effects of vitamins B, C, E, K and P, as well as coenzymes Q, on formation of final products of radiation-induced free-radical transformations of ethanol, ethylene glycol, alpha-methylglycoside and glucose in aqueous solutions were studied. Based on the obtained results, it can be concluded that there are substances among vitamins and coenzymes that effectively interact with alpha-hydroxyl-containing radicals. In the presence of these substances, recombination reactions of alpha-hydroxyalkyl radicals and fragmentation of alpha-hydroxy-beta-substituted organic radicals are suppressed. It has been established that the observed effects are due to the ability of the vitamins and coenzymes under study to either oxidize alpha-hydroxyl-containing radicals yielding the respective carbonyl compounds or reduce them into the initial molecules.

Peroxidase-catalyzed oxidation of 3,3 ,5,5 -tetramethylbenzidine (TMB) was inhibited by o-aminophenol (AP), 2-amino-4-tert-butylphenol (ATBP), 2-amino-4,6-di-tert-butylphenol (ADTBP), and 4-tert-butylpyrocatechol (TBP). Inhibitors were characterized by inhibition constant K(i) and stoichiometric coefficient f, the number of radicals terminated by one inhibitor molecule. The most efficient inhibitor is ADTBP characterized by K(i) = 36 microM in 0.015 M phosphate citrate buffer, pH 6.0, at 20 degrees C. According to their antiradical efficiency, the studied inhibitors can be arranged as follows: ADTBP > ATBP > AP > TBP. The role of the NH(2) group in the inhibitory capacity of aminophenols is discussed. Using gas-liquid chromatography, kinetics of consumption of the initial components and accumulation of the reaction products on peroxidase-catalyzed oxidation of the TMB-TBP pair was studied; the data clarify the stages of a complex process of co-oxidation of amines and phenols.

Based on product yield data on radiolysis of hexane, ethanol and 3 M aqueous ethylene glycol solutions, the ability of a number of arylamine, aminophenol and quinonimine derivatives to affect processes involving peroxyl, alkyl or alpha-hydroxyalkyl radicals was assessed. It has been shown that the introduction of a hydroxyl group into aromatic amine structure enhances its antioxidant performance and makes it significantly more reactive with respect to carbon-centered organic radicals. Replacement of the hydrogen atom of a hydroxyl group by a methyl group decreases the anti-radical activity of aminophenols drastically. Compounds containing (or capable of forming) a quinonimine moiety interact with alkyl or alpha-hydroxyalkyl radicals most effectively, suppressing recombination and fragmentation reactions of the latter. In the sequence: aromatic amines--aminophenols--quinonimines, a trend towards enhancement of the ability of the compounds studied to react with carbon-centered radicals was noted. Also, this study presents for the first time evidence of riboflavin reactivity with respect to organic radicals.

A comparative kinetic study of the peroxidase oxidation of three chromogenic substrates--2,2'-azino-bis(3-ethyl-2,3-dihydrobenzothiazoline-6-sulfonic acid), o-phenylenediamine (PDA), and 3,3',5,5'-tetramethylbenzidine--inhibited by trimethylhydroquinone and six tert-butylated pyrocatechols (InH) was carried out at 20 degrees C in 0.015 M phosphate-citrate buffer (pH 6.0) containing organic cosolvents (0-10% ethanol or DMF). The inhibitors were quantitatively characterized by the inhibition constants (Ki), the duration of the lag period in the oxidation product formation (delta tau), and the stoichiometric coefficient of inhibition that specifies the number of radicals terminated by one InH molecule (f). The inhibition could be competitive, noncompetitive, mixed, or uncompetitive, which depended on the nature and structure of the chromogenic substrate-diatomic phenol pair. Various substrate-diatomic phenol pairs exhibited Ki values within the range of 11-240 microM and f values from 0.7 to 2.6. The absence of a lag period was characteristic of oxidation of the substituted o-phenylenediamine-substituted pyrocatechol. The total kinetic parameters and properties of the components allowed us to suggest six chromogenic substrate-substituted diatomic phenol pairs for use in test systems for the determination of antioxidant activity in human body fluids, natural biological preparations, and food. The English version of the paper: Russian Journal of Bioorganic Chemistry, 2004, vol. 30, no. 5; see also http: // www.maik.ru.

A series of novel phenolic antioxidants of amphiphilic structure has been synthesized. Investigations into the influence of aliphatic spacer length and nature of a hydrophilic anchor on the antioxidant activity allowed elucidating certain structure requirements for the membrane-addressed antioxidant designing.

Purpose: To obtain evidence for the possibility of free-radical fragmentation of cardiolipin under the action of ionizing radiation as measured by its aqueous dispersion from liposomes., Materials and Methods: Liposomes of tetramyristoylcardiolipin (TMCL) were exposed to gamma-rays from 60Co or 137Cs sources at doses between 1 and 24kGy. Fragmentation products were identified using thin-layer chromatography and matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF MS)., Results: Using MALDI-TOF MS and thin-layer chromatography, it was shown that gamma-irradiation of liposomes consisting of TMCL was accompanied by free-radical fragmentation of the lipid to form dimiristoylphosphatidic acid and dimiristoylphosphatidyl hydroxyacetone. The yields of dimiristoylphosphatidic acid were greater than those of dimiristoylphosphatidyl hydroxyacetone, and formation of the named compounds was inhibited by dissolved oxygen., Conclusion: It is shown for the first time that on gamma-irradiation, cardiolipin can undergo free-radical fragmentation in its polar component.

It was found that the incorporation of anionic dipalmitoyl phosphatidic acid (DPPA) into phosphatidylcholine (PC) liposomes up to 15 mol % was accompanied by the intensification of accumulation of diene conjugates (DC), which are primary products of lipid peroxidation (LPO), if the LPO was initiated by gamma-irradiation of a 137Cs source. Monoethyl ester of DPPA, phosphatidylethanol (DPPEt), exerted a lesser influence at the same concentrations. Ca2+ ions inhibited the DC production not only in liposomes consisting of lipid mixture but in lipid membranes of PC alone as well. It was assumed that the electrostatic repulsion of negatively charged DPPA and DPPEt resulted in the loosening of polarside region of membrane hydrophobic layer and in consequence the access of hydroxyl radicals to hydrocarbon chains of PC. This assumption is in good agreement with the results of osmotic behavior of liposomes in hypertonic urea solution.

Investigation of effects produced by 26 various phenol and diphenol derivatives, including industrial and natural antioxidants (ionol, bis-phenol 2246, alpha-tocopherol), on final product yields of radiation-induced free-radical processes involving peroxyl, alkyl, alpha-hydroxyalkyl and alpha,beta-dihydroxyalkyl radicals has been performed. Ionol and bis-phenol 2246 have been shown to be more effective than alpha-tocopherol or diphenol derivatives in suppressing hydrocarbon oxidation processes. At the same time, alpha-tocopherol and its water-soluble analogues, as well as diphenol-based substances, are more effective than phenol derivatives in regulating various homolytic processes involving carbon-centered radicals. This fact can be accounted for by taking into consideration the contribution to formation of the final product set and the respective yields made by semiquinone radicals and compounds with quinoid structure arising in the course of homolytic transformations in systems containing diphenol derivatives.

Peroxidase-catalyzed oxidation of o-phenylene diamine (OPD) was competitively inhibited by trimethylhydroquinone (TMHQ), 4-tert-butylpyrocatechol (In5), and 4,6-di-tert-butyl-3-sulfanyl-1,2-dihydroxybenzene (In6). In6 was the most efficient inhibitor (Ki = 11 microM at 20 degrees C in 0.015 M phosphate-citrate buffer, pH 6.0). The effects of In5 and In6 were not preceded by periods of induction of OPD oxidation products (contrary to TMHQ). Peroxidase-catalyzed oxidation of tetramethylbenzidine (TMB) was non-competitively inhibited by In6 and 3-(2-hydroxyethylthio)-4,6-di-tert-butylpyrocatechol (In4), whereas o-aminophenol (OAP) acted as a mixed-type inhibitor. The effects of all three inhibitors were preceded by an induction period, during which TMB oxidation products were formed. Again, In6 was the most efficient inhibitor (Ki = 16 microM at 20 degrees C in 0.015 M phosphate-citrate buffer supplemented with 5% ethanol, pH 6.0). Judging by the characteristics of the inhibitors, taken in aggregate, it is advisable to use the pairs OPD-In5 and OPD-In6 in systems for testing the total antioxidant activity of biological fluids of humans.

Purpose: To investigate regularities observed in the course of reactions involving cleavage of C-N bonds on the radiolysis of amino-containing organic compounds and their derivatives in aqueous solutions., Materials and Methods: Aqueous solutions of amino-containing compounds, saturated with Ar or O(2), were exposed to gamma-radiation from a (137)Cs source. The absorbed dose-rate was 0.33 Gy s(-1), the absorbed dose range was 0.1-7.5 kGy. Analyses for ammonia and amino-containing organic compounds were performed using an amino acid analyser, and analyses for other radiolysis products were made by gas-liquid chromatography., Results: The presence of a hydroxyl group in the beta-position to the amino group promotes deamination of amino alcohols, amino acids, di- and tripeptides, these processes being associated with the possible occurrence of monomolecular fragmentation of the respective radicals. Oxygen inhibits the deamination of alpha,beta-amino alcohols and hydroxyl-containing amino acids. The presence of alkyl substituents in the amino group favours C-N bond cleavage on the radiolysis of amino alcohols, whereas the presence of an acyl group sharply suppresses this process. Replacement of the hydroxyl group in molecules of the initial amino alcohols by a hydrogen atom (i.e. a changeover to alkylamines) or by a methoxy group decreases the efficiency of deamination sharply. The presence of hydroxyl groups in side residues of di- and tripeptides promotes destruction of the peptide chain with formation of amides of amino acids, while suppression of deamination and main chain destruction processes in these compounds is observed in the presence of oxygen., Conclusions: The most effective processes leading to the C-N bond cleavage on the radiolysis of aqueous solutions of amino-containing organic compounds are those in which the key role is played by reactions of monomolecular decomposition of radicals of the initial compounds.

Based on the membrane addressing concept, designing and synthesis of 11-(3,5-di-tert-butyl-2-hydroxyphenylcarbamoyl)undecanoic acid have been carried out. Antioxidant properties of the prepared compound were investigated in comparison with its non-amphiphilic analogues.

Effects of a number of quinones and diphenols of various structures on free-radical fragmentation processes taking place in alpha-diols, glycerol, 2-aminoethanol, glycero-1-phosphate, ethylene glycol monobutyrate, maltose, and some lipids were investigated. Quinone additions have been found to change the direction of free-radical transformations of the compounds cited above by inhibiting formation of the respective fragmentation products owing to oxidation of radicals of the starting compounds. The results obtained and literature data available allow a suggestion to be made that the system quinone/diphenol is able to not only deactivate or generate such active species as O2.- but also control the realization probability of free-radical processes of peroxidation and fragmentation in biologically important molecules.

Purpose: To ascertain the possibility of fragmentation processes in lipid membranes when acted upon with gamma-radiation under various conditions, and to evaluate fragmentation processes quantitatively in comparison with the lipid peroxidation processes., Materials and Methods: Phospholipids as components of multilamellar liposomes exposed to 137Cs gamma-rays at dose-rates of 0.06 and 0.33 Gy s-1 in the dose range 0-18 kGy. Peroxidation products were determined spectrophotometrically and fragmentation products were analysed using thin-layer chromatography and GLC methods., Results: Phosphatidylglycerol containing unsaturated fatty acid residues and free hydroxyl groups underwent both peroxidation and fragmentation when its aqueous dispersions were treated with ionizing radiation. gamma-Radiolysis of multilamellar liposomes led to the formation of peroxidation products, as well as phosphatidic acid and hydroxyacetone, fragmentation products of the initial lipid. Comparable radiation-chemical yields of conjugated-diene products and phosphatidic acid indicate that the probabilities of oxidation and fragmentation processes to occur are approximately equal in this case. In contrast to lipid peroxidation, lipid fragmentation is not accelerated but suppressed by oxygen and appears to be a prevailing process in de-aerated solutions. The phosphatidic acid formed as a result of phosphatidylglycerol fragmentation can intensify the lipid peroxidation., Conclusions: Treatment of lipid membranes with ionizing radiation leads to the destructive processes within both hydrophobic and hydrophilic moiety of lipids.

The effect of lysophosphatidylcholine (LPC) on the lipid peroxidation process (LPO) in liposomes of rat liver phosphatidylcholine initiated by irradiation of 137Cs source was studied. The formation of diene conjugates (DC) is shown to increase dramatically on incorporation of more than 10% LPC into liposomes. The dependence of DC proportion on the irradiation dose is practically linear in the range of 0 to 5 kGy. The DC concentration in the liposomes without LPC grows at least to dose of 3.3 kGy and is unchanged on further irradiation. The malonic dialdehide accumulation follows the similar dependence. The LPC effect is neutralized by the incorporation of cholesterol into liposomes. The product of free radical fragmentation of LPC, palmitoxyacetone, practically has no influence on the DC concentration. The reasons of LPC effect on the irradiation initiated LPO in liposomes is discussed.

A comparative kinetic study on the poly(gallic acid disulfide) (poly(DSGA)) inhibition of the iodide ion oxidation and on the 2-hydroxy-3,5-di-tert-butyl-N-phenylaniline (butaminophene) inhibition of 3,3',5,5'-tetramethylbenzidine (TMB) oxidation involving human thyroid peroxidase (hTPO) and horseradish peroxidase (HRP) was performed. The inhibition processes were characterized with the inhibition constants Ki and stoichiometric inhibition coefficients f, indicating the number of radical particles perishing on one inhibitor molecule. In the case of poly(DSGA), the Ki values for the I- oxidation were 0.60 and 0.04 microM, and the coefficients f were 13.6 and 16.5 for hTPO and HRP, respectively, which evidences the regeneration and high effectiveness of the polymeric inhibitor. In the case of butaminophene, the Ki values for TMB oxidation were 38 and 46 microM for hTPO and HRP, respectively. The coefficients f were 1.33 and 1.47, respectively, to reveal that butaminophene does not regenerate. The inhibition mechanisms for I- and TMB oxidation involving the two peroxidases are discussed.

The regularities of accumulation of conjugated dienes and thiobarbituric acid (TBA)-reactive substances under gamma-irradiation of liposomes from rat liver phosphatidylcholine (PC) and its mixtures with the resistant to lipid peroxidation saturated phospholipids and bovine brain sphingomyelin (SM) were studied. It was established that the incorporation of negatively charged dipalmitoylphosphatidylglycerol (DPPG) and dipalmitoylphosphatidylethanol (DPPET) into lipid bilayer resulted in the increase of primary and secondary products of LPO, whereas neutral dipalmitoylphosphatidylcholine (DPPC) and SM involving in the phospholipid mixtures inhibited the peroxidation of PC. For anionic phospholipids, DPPG had more profound activating action on LPO, amongst the neutral phospholipids SM was more potent inhibitor of the reaction. Unlike DPPET and DPPC, DPPG and SM were subjected to free radical fragmentation on gamma-radiation. It is suggested that the intermediates and products of free radical fragmentation may modulate the progress of LPO.

The effect of gamma-radiation on aqueous solutions of saturated phospholipids, 1,2-dipalmitoyl-sn-glycero-3-phosphocholine (DPPC), 1,2-dipalmitoyl-sn-glycero-3-phosphoglycerol (DPPG), 1-palmitoyl-2-lyso-sn-glycero-3-phosphocholine (lysoPC), and bovine brain sphingomyelin (SM) has been investigated. It is shown that the phospholipids with an OH group in beta-position to the P-O bond (DPPG and lysoPC), or to the amide bond (SM), undergo a free radical fragmentation. As a result of such fragmentation, stearoylamide, palmitoxyacetone and phosphatidic acid are formed from SM, lysoPC and DPPG, respectively. In parallel with the formation of hydrophobic fragments, an accumulation of hydrophilic species such as oxyacetone and phosphocholine in the irradiated DPPG and lysoPC dispersions was observed. On the basis of the data obtained for free radical transformation of phospholipids and their simplest analogs, such as glycero-1-phosphate, triacetin and 1,2-isopropylidene glycerol, it is suggested that the fragmentation of the radicals derived from the above compounds proceed by a concerted mechanism through a five-membered transition state. The accumulation of hydrophobic fragments in phospholipid membranes is shown to influence the temperature and co-operativity of the 'gel-to-liquid crystal' phase transition. An assumption is made that the fragmentation of phospholipids caused by free radical attack on the hydrophilic moiety, along with lipid peroxidation, may constitute principal mechanisms of radiation-induced damage of biological membranes.

The bioantioxidant activity of the synthesized by us on the base of the diatomic phenol compound--3,5-di-t-butylpyrocatechol--has been studied. It was shown that this substance exhibits more pronounced antioxidant properties than tocopherol on the lipid peroxidation process in the rat brain homogenate appears in concentrations right up to 10(-8)-10(-7) M. Antioxidant effect of 3,5-di-t-butylpyrocatechol protecting action correlation has been found in the simulation of such pathological organism states as hypoxia, inflammation, burn, pain. All above mentioned results confirms the expedience of search for new drugs based on diatomic phenols.

The substituted pyrocatechols sodium (2,3-dihydroxy-4,6-di-tert-butyl-phenyl)-S-thiosulfate (InH1) and 3-(S-glutathionyl)-4,6-di-tert-butyl-pyrocatechol (InH2) effectively inhibited oxidation of o-phenyle-nediamine and tetramethylbenzidine (TMB) catalyzed by hemin or its complex with BSA (methemalbumin). The method of competitive reactions of aromatic amines (PDA, TMB) and pyrocatechols (InH1, InH2) with active radicals was used for the quantitative determination of rates of radical initiation in systems containing hemin (methemalbumin) and H2O2 (TBHP). The use of the inhibitor method for heme-protein-peroxide systems is complicated by heterogeneity of the radicals generated (HO., RO., HO2., RO2., peroxide-like compounds I and II), formation of complexes of the inhibitors with protein component, and possible interaction of active radicals with organic co-solvents (DMF or DMSO). The system hemin (methemalbumin)-H2O2 (TBHP)-aromatic amines can be used for testing the efficacy of potential bioantioxidants.

Phospholipase A2 hydrolysis of dioleoylphosphatidylcholine, dimyristoylphosphatidylcholine or their equimolar mixture with sphingomyelin in liposomes exposed to gamma-radiation has been investigated. Stabilization of the gamma-irradiated lipid bilayer to hydrolysis by sphingomyelin has been shown.

Amphiphilic membrane-addressed antioxidants differing in their hydrophobic-hydrophilic balance, 3,5-di-tert-butyl-2-hydroxyphenyl phosphate, (3,5-di-tert-butyl-2-hydroxyphenyl)hexadecyl phosphate, and (3,5-di-tert-butyl-2-hydroxyphenyl)-5-cholesten-3 beta-yl phosphate, were synthesized starting from 3,5-di-tert-butyl-o-quinone. Even at 10(-8) M concentration, 3,5-di-tert-butyl-2-hydroxyphenyl phosphate and (3,5-di-tert-butyl-2-hydroxyphenyl)hexadecyl phosphate inhibit formation of malonic aldehyde during peroxidation of lipids from rat brain homogenate initiated with a Fe(2+)-ascorbate system. At 10(-4) M and higher concentrations of antioxidants in the brain homogenate, the formation of malonic aldehyde is inhibited more efficiently than with tocopherol at the same concentrations.

The effect of gamma-irradiated solutions of carbohydrates, mainly glucose, upon Na+, K(+)-ATPase and lipid peroxidation in rat brain synaptosomal membranes was studied. The membrane damage by irradiated glucose was enhanced in the presence of Fe2+ and was diminished when a free-radical scavenger (BHT) or metal chelators (EDTA, EGTA) were present. It is suggested that a key element in the free-radical membrane damage by irradiated carbohydrates is an Fe(2+)-complex of some species of the radiolysis products. Participation of radiotoxins of carbohydrate origin in radiobiological effects is discussed.