The effect of pluronics L61 and F68 containing hydrophobic poly(propylene oxide) blocks of the same length and hydrophilic poly(ethylene oxide) blocks of different lengths on the conductance of planar bilayer lipid membranes made of azolectine is investigated. The conductance of these membranes increases as the concentration of both pluronics increases. For the same concentration of pluronics in solution, the conductance is higher for L61. Based on the literature data, the concentration of pluronics bound with the bilayer is calculated. For the close concentration of membrane-bound pluronics, the conductance of membranes is also close. It is concluded that in the first approximation, the appearance of the same hydrophobic parts of pluronics L61 and F68 in a membrane is accompanied by the same increase in its conductance. The conductance vs. concentration curves are superlinear for L61 and sublinear for F68. In the presence of either of these pluronics, the conduction spikes with the amplitude from 10 to 300 pSm and higher are observed for approximately 40

The integral conductance of planar lipid bilayer membranes in the presence of two Poloxamers (Pluronics) L61 and F68 with the same lengths of hydrophobic poly(propylene oxide) blocks and the different lengths of hydrophilic poly(ethylene oxide) blocks increases with an increase in the concentration of both Pluronics; however, the shape of the conductance-concentration curves is super linear for L61 and sublinear for F68. In the presence of both Pluronics, rare discrete current jumps are observed against the background of continuous current. At high concentrations, the I–V curves of membranes with both L61 and F68 became nonlinear at sufficiently low voltages but differed significantly. At voltages greater than 50 mV, the conductance of membranes with L61 increased sharply and quantized jumps were observed toward higher conductance, which could be interpreted as the appearance of additional pores. On the contrary, the conductance of membranes with F68 decreased and quantized jumps to lower conductance were observed, which could be interpreted as blocking of already existing pores. We attributed the differences in the conductance-concentration and I–V curves of these two Pluronics to their different effects on the dynamics of membrane hydration and, accordingly, on the probability of formation of conducting pores.

The electrical conductivity of azolectine bilayer lipid membranes is observed to increase 10–40-fold with respect to its background value of 67 ± 13 pS/mm2 upon the addition of cubic CoFe2O4 nanoparticles with the main diagonal of 14 nm (MNP-14) and 27 nm (MNP-27). As the concentration of MNP-14 in the membrane solution increases from 50 to 450 µg/mL, the increase in the membrane conductivity with respect to its background value is nonlinear and can be approximated by the exponential dependence with exponent 2.75. Discrete current pulses are observed in the constant voltage mode for the MNP-14 concentration higher than 250 µg/mL and for all MNP-27 concentrations starting from 50 µg/mL, which points to the appearance of conducting lipid pores.

Abstract—The phenolic compound purpurogallin (PPG) is found in oak nutgalls and is a red pigment with a benzotropolone ring structure. PPG shows pronounced cytoprotective and anti-inflammatory activities. PPG might be effective in preventing and treating diverse systemic inflammatory diseases, affecting functional activities of various cell metabolic and signaling pathways that are associated with inflammation. A study was made to compare the antioxidant (free radical) properties for PPG, dihydroquercetin (DHQ), ascorbic acid, and trolox using two test systems, hemoglobin (Hb)–H2O2–luminol (LM) and 2,2'-azobis(2-methylpropionamidine) dihydrochloride (AAPH)–LM. PPG was additionally tested for its effect on the permeability of flat lipid bilayer membranes (LBMs). Moderate antioxidant activity was observed for PPG in the Hb–H2O2–LM system; its neutralizing potential towards hydroxyl and superoxide anions was comparable with that of ascorbic acid. The compounds were ranked according to the efficiency of their antioxidant activity in the system: DHQ > trolox > ascorbic acid > PPG. Interestingly, when the AAPH–LM system was used to test antioxidant activity, PPG did not show neutralizing activity towards peroxyl radicals formed in the system. PPG did not significantly change the permeability of flat LBMs in a dose range of 1.5–30 μM, suggesting lack of a primary membrane effect. Putative mechanisms and characteristics of cytoprotective, antioxidant, and anti-inflammatory activities of PPG are discussed.

Detergent effects on lipid bilayers of artificial and biological membranes at subsolubilizing concentrations are known to include the membrane permeabilization which manifests itself through both a flip-flop of detergent molecules from the outer monolayer to the inner monolayer and the membrane leakage of entrapped solutes. We have explored the current fluctuations occurring in planar BLM of asolectin in the presence of ionic detergent SDS at subsolubilizing concentration. Two groups of current fluctuations which the average duration differs by two orders of magnitude can be distinguished. We assume that these differences in the duration of current fluctuations are associated with a different number of SDS molecules in the walls of the putative toroidal hydrophilic pores. We associated short pulses with the formation of short-lived lipid hydrophilic pores. Impulses of greater duration (steps) were associated with the formation of hydrophilic pores, the walls of which contain detergent. Taking into account the characteristics of these pores, we estimated the pore energy, as well as the edge energy of these two kinds of pores. We believe that the flip-flop of SDS molecules in liposomes is provided by long-lived pores, and the contents of the liposome leakage occurs through all pores.

Luteolin, a water-insoluble 3′,4′,5,7-tetrahydroxyflavon, is one of the best-studied representatives of bioflavonoids. Luteolin is an essential food component for humans and other mammals that possesses a wide spectrum of biological activities by affecting the activities of various metabolic enzymes, target receptors, and signal transduction pathways. In this study, we conducted a comparative study of the antioxidant (free-radical scavenging) properties of luteolin in 2,2′-azobis(2-methylpropionamidine) dihydrochloride–luminol and hemoglobin–hydrogen peroxide–luminol systems and assessed its effect on the permeability of planar lipid bilayer membranes. Trolox was used as a reference antioxidant, while ascorbic acid and dihydroquercetin were taken as standards. Luteolin shows moderate antioxidant activity, exhibiting a higher antioxidant capacity than trolox and ascorbic acid, but it was less effective than dihydroquercetin in tests for antioxidant activity in the studied systems. The studied compounds can be ranked according to the effectiveness of their antioxidant action: dihydroquercetin > luteolin > trolox > ascorbic acid. It should be noted that the antioxidant activity of a water-soluble form of luteolin, luteolin disulfate, is comparable with that of luteolin. Luteolin does not cause significant changes in the permeability of planar bilayer membranes in the dose range from 1.5 to 30 μM. Our findings indicate the presence of a high level of free-radical scavenging activity and the absence of a primary membranotropic effect for luteolin. It can be assumed that the multiple pleiotropic nature of luteolin activity towards a variety of biological systems is associated not only with a neutralizing effect in regard to reactive oxygen species, but also with the ability of luteolin to block and modulate different cell-signaling processes and biochemical pathways. The presumed mechanisms of the biological activity of luteolin and luteolin disulfate are discussed.

Проведено сравнительное исследование антиоксидантных (радикалперехватывающих) свойств триптантрина (хиназолинового алкалоида, обладающего высокой противовоспалительной активностью и найденного во многих видах различных семейств высших растений и микроорганизмов, включая микробиом человека) в системах 2,2'-азобис(2-метилпропионамидин)дигидрохлорид-люминол и гемоглобин-пероксид водорода-люминол и оценено его влияние на проницаемость плоских бислойных липидных мембран. В качестве эталонного антиоксиданта был использован тролокс, а в качестве стандартов - аскорбиновая кислота и дигидрокверцетин. Показано, что триптантрин проявляет очень слабую антиоксидантную активность, заметно уступая эталонному и стандартным антиоксидантам в тестах по антиоксидантной активности в обеих исследованных системах. По эффективности антиоксидантного действия исследуемые вещества могут быть выстроены в следующий ряд: дигидрокверцетин > тролокс > аскорбиновая кислота > триптантрин. Антиоксидантный потенциал триптантрина приблизительно в 1000 и 3000 раз меньше, чем у тролокса и у биофлавоноида дигидрокверцетина соответственно. Триптантрин не вызывает достоверного изменения проницаемости плоских бислойных мембран в диапазоне доз от 0,5 до 10 мкг/мл. Полученные данные свидетельствуют об отсутствии у триптантрина значимой радикалперехватывающей и мембранотропной активности. Можно предположить, что отмеченная для триптантрина высокая противовоспалительная активность не связана с нейтрализующим действием в отношении активных форм кислорода и влиянием на проницаемость клеточных мембран. Предполагаемые механизмы биологической активности триптантрина обсуждаются

A comparative study of antioxidant (radical-interceptor) properties of tryptanthrin (quinazoline alkaloid shows a high anti-inflammatory activity and it is found in many types of different families of higher plants and microorganisms, including the human microbiome) in the systems of 2,2'-azo-bis(2-methylpropionamidin)dihydrochloride-luminol and hemoglobin-hydrogen peroxide-luminol has been conducted and the influence on the permeability of planar bilayer lipid membranes is evaluated. Trolox was used as a reference antioxidant, and ascorbic acid and dihydroquercetin were taken as standards. Tryptanthrin exhibits very weak antioxidant activity, being markedly inferior to the reference standard and antioxidants while testing antioxidant activity in both studied systems. By the efficacy of antioxidative action the substrates in the systems studied can be arranged in the following order: dihydroquercetin > trolox > ascorbic acid > tryptanthrin. Antioxidant potential of tryptanthrin is approximately 1000 and 3000 times lower than that of trolox and bioflavonoid dihydroquercetine, respectively. Tryptanthrin causes no significant changes in the permeability of planar bilayer membranes in a dose range of 0.5 to. 10 μg/ml. Our data show that tryptanthrin displays no significant radical-interceptor and membranotropic activities. It can be assumed that the observed high anti-inflammatory activity of tryptanthrin is not related to the neutralizing effect against reactive oxygen species and the influence on the permeability of cell membranes. The anticipated mechanisms of biological activity of tryptanthrin are discussed.

A comparative study of antioxidant (radical-scavenging) properties of triptantrin, which is a quinazoline alkaloid with anti-inflammatory activity that occurs in many species of higher plants and microorganisms, including the human microbiome, in systems containing 2,2’-azobis (2-methylpropionamidin) dihydrochloride and luminol, or hemoglobin, hydrogen peroxide, and luminol was performed and the impact of the alkaloid on the permeability of planar bilayer lipid membranes was assessed. Trolox was used as a reference antioxidant, and ascorbic acid and dihydroquercetin were used as standards. The antioxidant activity of triptantrin in both systems was much lower than that of the reference and standard antioxidants. The substances formed the following series according to antioxidant activity: dihydroquercetin > trolox > ascorbic acid > triptantrin, with the antioxidant potential of the latter being 1000 times lower than that of trolox and 3000 times lower than that of the bioflavonoid dihydroquercetin. Triptantrin did not cause significant changes in permeability of planar bilayer membranes when applied at concentrations of 0.5–10 μg/mL. The data show that triptantrin lacks considerable radical-scavenging and membranotropic activities; therefore one can assume that the high antiinflammatory activity that has been reported for triptantrin is neither related to an ability to neutralize reactive oxygen species nor to effects on cell membrane permeability. The putative mechanisms that underlie the biological effects of triptantrin are discussed.

The release of cytochrome c (cyt c) from mitochondria is responsible for initiation of cell apoptosis. Although extramitochondrial proteins are thought to initiate this release, the exact mechanism remains unclear. Cyt c binds to and penetrates lipid bilayer membranes of specific phospholipid cardiolipin (CL) contained in mitochondria. We present here the experimental results of monitoring planar BLM (pBLM) from mixtures of azolectin and of CL (4/1 by moles) by triangle voltage pulses of 100 mV in amplitude and frequency of 2 Hz. The BLM were modified by a successive addition of cyt c and of H2O2 in water solution. It is shown that the addition of cyt c alone leads to a stepwise increase in the ionic conductance of the pBLM, indicating the appearance of transmembrane pores. Pore lifetimes then reached several seconds at an average pore diameter of ~2 nm. Current–voltage characteristics were then linear and passed through the origin which is characteristic for broad, nonselective ion pores. Subsequent addition of H2O2 caused a dramatic increase in transmembrane current at retention of average pore size constant. Observed increase in membrane current is due to growth of a number of pores in an open state. We suggest that hydrogen peroxide in the presence of cyt c promotes a peroxidation of membrane phospholipids to form lysolipids, the embedding of which stabilizes the edge of the pore and the surface of lipid bilayer.

The metabolic damages and inflammatory diseases are closely connected with high increase of the contents of the reactive oxygen species (ROS) and lipid peroxidation products in organism. In connection with this natural antioxidants are actively used for efficient fight with oxidative stress. In current work we have estimated an antioxidative potential of rosmarinic acid (RA), which is broadly wide-spread amongst plants and possesses the useful spectrum of biological activities. It has been shown that RA noticeably exceeded known antioxidants in test on antioxidant activities in Hb-H2O2-luminol and 2,2'-azo bis (2-methylpropionamidine) dihydrochloride-luminol systems, as well as on inhibition of linoleic acid peroxidation. On antioxidant activities the investigated substances can be arranged in the following order: RA > dihydroquercetin > trolox > ascorbic acid. RA molecules are localized mainly in the lipid bilayer of polar groups, but have no significant effect on its structural and functional properties: RA does not cause significant changes in permeability of planar bilayer membranes in a dose range of 0.5 to 10 microg/ml. Spontaneous incorporating of 1 mol% of RA into the lipid bilayer is sufficient for the complete prevention of lipid peroxidation. Thus, the antioxidant activity of RA is based on its ability to inhibit the initiation stage of free radical reactions of lipid peroxidation, largely caused by the formation of ROS. In this regard RA, as a powerful and effective inhibitor of ROS and lipid peroxidation, has great potential for wide use not only in medicine but also in the food industry to preserve the quality of perishable food products.

Interaction of cytochrome c with cardiolipin in the presence of hydrogen peroxide induces peroxidase activity in cytochrome c and the ability to oxidize membrane lipids. These cytochrome c properties play a substantial role in the cytochrome c-mediated apoptotic reactions. In the present study the electric properties (specific capacitance and integral conductance) of the cardiolipin-containing asolectin planar bilayer lipid membranes (pBLM) in the presence of cytochrome c and hydrogen peroxide were studied. Cytochrome c interaction with cardiolipin-containing pBLM in the presence of hydrogen peroxide resulted in the dramatic increase of the conductance, pore production, their growth up to 3.5 nm diameter and subsequent membrane destruction. In the absence of hydrogen peroxide cytochrome c demonstrated almost no effect on the membrane capacitance and conductance. The data obtained prove the pivotal role of cytochrome c and membrane lipids in the permeabilization of pBLM. Correlation of apoptotic reactions and cytochrome c-mediated membrane permeability is discussed.

Rosmarinic acid is found in many species of different families of higher plants and its chemical structure is phenol propanoid with various biological activity. In this paper, we conducted a comparative study of antioxidant (radical-scavenging) properties of rosmarinic acid in systems of 2,2tāzo-bis(2-methylpropionamidin)dihydrochloride-luminol and hemoglobin-hydrogen peroxide-luminol, determined its protective potential in preventing peroxidation of linoleic acid, and evaluated the effect on the permeability of planar bilayer lipid membranes. Linoleic acid peroxidation was assessed by iron-thiocyanate method. In these studies, trolox was used as a reference antioxidant, and ascorbic acid, and dihydroquercetin were taken as standards. Rosmarinic acid is significantly superior to trolox, ascorbic acid and dihydroquercetin in the tests for antioxidant activity in the systems studied, as well as in inhibition of linoleic acid peroxidation. According to their activity the investigated substances can be arranged in the following order: rosmarinic acid > dihydroquercetin trolox > ascorbic acid. Rosmarinic acid does not cause significant changes in the permeability of planar bilayer membranes in a dose range of 0.5 to 10 μg/mL. Antioxidant activity of rosmarinic acid is due to the neutralization of reactive oxygen species and/or luminol radicals generated in model systems. The observed features of the antioxidant and membrane activity of rosmarinic acid, which may underlie the previously mentioned pharmacological effects are discussed.

The electrical capacity of planar bilayer lipid membranes (BLM) from natural hydrogenated egg lecithin (HEL) in n-decane at a temperature of phase transition was measured. The temperature of phase transition was determined calorimetrically to be 51degreesC. The data obtained revealed a phase separation of HEL in BLM into two fractions, one freezing at 42-44degreesC and one that is converted to a liquid-crystal state at 51-59degreesC. It was assumed that the first fraction is rich in dipalmitoyl lecithin, and the second fraction is rich in distearoyl lecithin. Freezing and the transition to the liquid-crystal state were accompanied by an increase and decrease in membrane thickness, respectively, in part due to a displacement of the solvent from the torus to the planar part of the bilayer. The displacement of the solvent is explained by changes in the disjoining pressure in BLM, which arises across the lipid bilayer due to van der Waals forces of attraction between water layers on both sides of the BLM.

The electrical capacity of planar bilayer lipid membranes (BLM) from natural hydrogenated egg lecithin (HEL) in n-decane at a temperature of phase transition was measured. The temperature of phase transition was determined calorimetrically to be 51 degrees C. The data obtained revealed a phase separation of HEL in BLM into two fractions, one freezing at 42-44 degrees C and one that is converted to a liquid-crystal state at 51-59 degrees C. It was assumed that the first fraction is rich in dipalmitoyl lecithin, and the second fraction is rich in distearoyl lecithin. Freezing and the transition to the liquid-crystal state were accompanied by an increase and decrease in membrane thickness, respectively, in part due to a displacement of the solvent from the torus to the planar part of the bilayer. The displacement of the solvent is explained by changes in the disjoining pressure in BLM, which arises across the lipid bilayer due to van der Waals forces of attraction between water layers on both sides of the BLM.

Polymyxin B in micromolar concentrations induces current fluctuations in liquid crystalline bilayer lipid membranes from dipalmitoylphosphatidic acid identified as ion channels. The appearance of ion channels correlates with phase separation of the lipid in the presence of peptide polycations detected by differential scanning calorimetry. Ca2+ also induces the formation of ion channels in liquid crystalline bilayer lipid membranes from dipalmitoylphosphatidic acid followed by the phase transition of the phospholipid. The capacitive current, which indicates the possibility of structural transformations of bilayer-non-bilayer type (hexagonal phase II), precedes the formation of Ca(2+)-induced channels in bilayer lipid membranes from dipalmitoylphosphatidic acid.

Polymyxin B in micromolar concentrations induces current fluctuations in liquid crystalline bilayer lipid membranes from dipalmitoylphosphatidic acid identified as ion channels. The appearance of ion channels correlates with phase separation of the lipid in the presence of peptide polycations detected by differential scanning calorimetry. Ca2+ also induces the formation of ion channels in liquid crystalline bilayer lipid membranes from dipalmitoylphosphatidic acid followed by the phase transition of the phospholipid. The capacitive current, which indicates the possibility of structural transformations of bilayer - non-bilayer type (hexagonal phase II), precedes the formation of Ca2+-induced channels in bilayer lipid membranes from dipalmitoylphosphatidic acid.

The effect of the synthetic polycation VMII-DEMA (a potential antiheparin agent) on the ion transport through erythrocyte membranes was studied using ion-selective electrodes. We found that the passive ionic permeability of erythrocyte membranes in the presence of VMII-DEMA noticeably increased after the pretreatment of erythrocytes with long-chain fatty acids. When used separately, neither polycation nor fatty acids changed the membrane permeability at the same concentrations. The efficiency of the combined action of the polycation and fatty acids correlated with the length of the fatty acid (C9-C18) and the number of double bonds in it. The fatty acids C12:0, C13:0 and C18:2 were the most efficient. We suggest that in pathologies accompanied with deteriorations in lipid metabolism, polycations used for the correction of blood coagulation may damage the erythrocyte membrane.