Study on the effect of blackcurrant extract - based preservative on model membranes and pathogenic bacteria.

In this work the cosmetic preservative based on a Ribes Nigrum (blackcurrant) plant extract (PhytoCide Black Currant Powder abbr. BCE) was investigated to evaluate its antibacterial effect and to gain an insight into its mechanism of action. The influence of this commercially available formulation on model Escherichia coli and Staphylococcus aureus lipid membranes was studied to analyze its interactions with membrane lipids at a molecular level. The mixed lipid monolayers and one component bacteria lipid films were used to investigate the effect of BCE on condensation and morphology of model systems and to study the ability of BCE components to penetrate into the lipid environment. The in vitro tests were also done on different bacteria species (E. coli, Enterococcus faecalis, S. aureus, Salmonella enterica, Pseudomonas aeruginosa) to compare antimicrobial potency of the studied formulation. As evidenced the in vitro studies BCE formulation exerts very similar antibacterial activity against E. coli and S. aureus. Moreover, based on the collected data it is impossible to indicate which bacteria: Gram-positive or Gram-negative are more susceptible to this formulation. Model membrane experiments evidenced that the studied preservative affects organization of both E. coli and S. aureus model system by decreasing their condensation and altering their morphology. BCE components are able to penetrate into the lipid systems. However, all these effects depend on the lipid composition and monolayer organization. The collected results were analyzed from the point of view of the mechanism of action of blackcurrant extract and the factors, which may determine the activity of this formulation.

Liposomes as Carriers of GHK-Cu Tripeptide for Cosmetic Application.

Liposomes are self-assembled spherical systems composed of amphiphilic phospholipids. They can be used as carriers of both hydrophobic and hydrophilic substances, such as the anti-aging and wound-healing copper-binding peptide, GHK-Cu (glycyl-L-histidyl-L-lysine). Anionic (AL) and cationic (CL) hydrogenated lecithin-based liposomes were obtained as GHK-Cu skin delivery systems using the thin-film hydration method combined with freeze-thaw cycles and the extrusion process. The influence of total lipid content, lipid composition and GHK-Cu concentration on the physicochemical properties of liposomes was studied. The lipid bilayer fluidity and the peptide encapsulation efficiency (EE) were also determined. Moreover, in vitro assays of tyrosinase and elastase inhibition were performed. Stable GHK-Cu-loaded liposome systems of small sizes (approx. 100 nm) were obtained. The bilayer fluidity was higher in the case of cationic liposomes. As the best carriers, 25 mg/cm3 CL and AL hydrated with 0.5 mg/cm3 GHK-Cu were selected with EE of 31.7 ± 0.9% and 20.0 ± 2.8%, respectively. The obtained results confirmed that the liposomes can be used as carriers for biomimetic peptides such as copper-binding peptide and that the GHK-Cu did not significantly affect the tyrosinase activity but led to 48.90 ± 2.50% elastase inhibition, thus reducing the rate of elastin degeneration and supporting the structural integrity of the skin.

The influence of Leucidal - eco-preservative from radish - on model lipid membranes and selected pathogenic bacteria.

In this work the effect of Leucidal - a natural preservative from radish dedicated to be used in cosmetics - on bacteria cells and model bacteria membranes was investigated. To get insight into the mechanism of action of this formulation the lipid Langmuir monolayers imitating Escherichia coli (E. coli) and Staphylococcus aureus (S. aureus) membranes were prepared. Then, the influence of Leucidal on model systems was investigated by means of the surface pressure/area measurements, penetration studies and Brewster Angle Microscopy (BAM) visualization. Similar experiments were done also for one component monolayers formed from the model membrane lipids. The in vitro tests were done on five different bacteria species (E. coli, Enterococcus faecalis, S. aureus, Salmonella enterica, Pseudomonas aeruginosa). Leucidal was found to decrease packing of the monolayers, however, it was excluded from the films at higher concentrations. Model membrane experiments evidenced also a stronger affinity of the components of this eco-preservative to E. coli vs S. aureus membrane. Among one component films, those formed from phosphatidylglycerols and cardiolipins were more sensitive to the presence of Leucidal. However, in vitro tests evidenced that Leucidal exerts stronger inhibitory effect against S. aureus bacteria as compared to E. coli strain. These findings were discussed from the point of view of the role of Leucidal components and the lipid membrane properties in the membrane - based mechanism of action of this preservative. The results allow one to suggest that the membrane may not be the main site of action of Leucidal on bacteria. Moreover, since high concentration of the tested preparation exerted antibacterial activity in relation to all tested bacteria, a low selectivity of Leucidal can be postulated, which may be problematic from the point of view of its effect on the skin microbiome.

The Use of a Barley-Based Well to Define Cationic Betaglucan to Study Mammalian Cell Toxicity Associated with Interactions with Biological Structures.

Among potential macromolecule-based pharmaceuticals, polycations seem particularly interesting due to their proven antimicrobial properties and use as vectors in gene therapy. This makes an understanding of the mechanisms of these molecules' interaction with living structures important, so the goal of this paper was to propose and carry out experiments that will allow us to characterize these phenomena. Of particular importance is the question of toxicity of such structures to mammalian cells and, in the work presented here, two lines, normal fibroblasts 3T3-L1 and A549 lung cancer, were used to determine this. In this work, three well-defined cationic derivatives of barley-derived betaglucans obtained in a reaction with glycidyltrimethylammonium chloride (BBGGTMAC) with different degrees of cationization (50, 70, and 100% per one glucose unit) and electrostatic charge were studied. The studies address interactions of these polymers with proteins (bovine serum proteins and BSA), nucleic acids (DNA), glycosaminoglycans (heparin), and biological membranes. The results described in this study make it possible to indicate that toxicity is most strongly influenced by interactions with biological membranes and is closely related to the electrostatic charge of the macromolecule. The presentation of this observation was the goal of this publication. This paper also shows, using fluorescently labeled variants of polymers, the penetration and impact on cell structure (only for the polymer with the highest substitution binding to cell membranes is observed) by using confocal and SEM (for the polymer with the highest degree of substitution, and the appearance of additional structures on the surface of the cell membrane is observed). The labeled polymers are also tools used together with dynamic light scattering and calorimetric titration to study their interaction with other biopolymers. As for the interactions with biological membranes, lipid Langmuir monolayers as model membrane systems were used.

Preliminary Studies on the Mechanism of Antifungal Activity of New Cationic ß-Glucan Derivatives Obtained from Oats and Barley.

New chemical structures with antifungal properties are highly desirable from the point of view of modern pharmaceutical science, especially due to the increasingly widespread instances of drug resistance in the case of these diseases. One way to solve this problem is to use polymeric drugs, widely described as biocidal, positively charged macromolecules. In this work, we present the synthesis of new cationic ß-glucan derivatives that show selective antifungal activity and at the same time low toxicity toward animal and human cells. Two ß-glucans isolated from oats and barley and modified using glycidyltrimethylammonium chloride were obtained and evaluated for biocidal properties on the cells of mammals and pathogenic fungi and bacteria. These compounds were found to be nontoxic to fibroblast and bacterial cells but showed selective toxicity to certain species of filamentous fungi (Scopulariopsis brevicaulis) and yeasts (Cryptococcus neoformans). The most important aspect of this work is the attempt to explain the mechanisms of action of these compounds by studying their interaction with biological membranes. This was achieved by examining the interactions with model biological membranes representative of given families of microorganisms using Langmuir monolayers. The data obtained partly show correlations between the results for model systems and biological experiments and allow indicating that the selective antifungal activity of cationic ß-glucans is related to their interaction with fungal biological membranes and partly lack of such interaction toward cells of other organisms. In addition, the obtained macromolecules were characterized by spectral methods (Fourier transform infrared (FTIR) and 1H nuclear magnetic resonance (NMR) spectroscopies) to confirm that the desired structure was obtained, and their degree of modification and molecular weights were determined.

The effect of selected bisphenols on model erythrocyte membranes of different cholesterol content.

Bisphenols belong to the group of environmental pollutants with proven harmful impact on human red blood cells. However, the exact effect of these substances may vary depending on the lipid composition of the cell membrane, since this structure is the first barrier between the cell interior and the external environment. The aim of this work was to analyze the influence of bisphenol A (BPA), bisphenol S (BPS) and their 1:1 mixture on model human erythrocyte membranes, composed of sphingomyelin (SM), phospatidylcholine (PC) and cholesterol (Chol). Due to the postulated correlation between the content of cholesterol in biomembranes and the toxic effect of bisphenols the model systems of different sterol concentrations (10, 20 and 40 mol% of Chol) were used in the studies. In the experiments, Langmuir monolayer technique accompanied with Brewster Angle Microscopy were applied and liposome properties were investigated. The obtained findings reveal that, in the investigated range of the sterol content, the effect of BPA, namely the changes of the organization and stability of model membranes and weakening of the attractive lipid-lipid interactions, is strongly dependent on the concentration of Chol in the system. The higher the sterol content, the stronger the BPA-induced alterations in membrane properties. However taking into account the results reported previously for the system containing 33.3% of cholesterol, it seems that the relationship between the effect of BPA and the amount of Chol is not linear for higher sterol concentrations. In contrast, BPS shows a much weaker influence on model erythrocyte membranes and does not act selectively on the systems studied. The effect of a mixture of BPA and BPS is intermediate between that of BPA and BPS used separately, however, the observed effects appear to be determined only by the presence of BPA in the system. Thus, the concentration of cholesterol in human erythrocyte membranes, which depends on factors such as age or health status, may play a key role in the toxic effects of BPA but not BPS.

The influence of ergosterol on the action of the hop oil and its major terpenes on model fungi membranes. Towards understanding the mechanism of action of phytocompounds for food and plant protection.

The aim of this work was to find the correlation between the content of ergosterol in fungi membrane and the action of the hop essential oil, myrcene and humulene on its properties. To reach this goal, the monolayers and bilayers composed of phosphatidylcholine, phosphatidyethanol amine and ergosterol, differing in the concentration of sterol, were used as model membrane systems. The impact of the essential oil and its major terpenes on one component ergosterol film was also investigated. It was found that pure isolated terpenes, in contrast to the hop oil being the mixture of them, do not incorporate into pure ergosterol membrane, however, they cause the loss of monolayer material from the interface. These results are in contrast to the effect of these terpenes on phospholipid films reported previously and they may suggest a strong effect of ergosterol on the behavior of terpenes in the mixed systems. Surprisingly, for model membranes, the effect of myrcene was qualitatively similar to the effect of the hop oil and ergosterol was found to regulate the incorporation of both these substances into the film. In contrast, very strong correlation between ergosterol content and the action of humulene was found. Namely, the ability of humulene to change model membrane properties was found to increase with ergosterol concentration. Additionally, the differentiating effect of ergosterol on humulene action in membranes was much more pronounced than for myrcene or the hop oil. Interestingly, at the highest ergosterol level the influence of humulene was even stronger than the effect of the hop oil. This is very important finding suggesting that ergosterol may regulate the sensitivity of particular membrane to the impact of humulene. Summarizing, ergosterol substantially differentiates the effect of the hop oil, myrcene and humulene on the lipid systems and it can be the molecule important for antifungal effect of the essential oil and terpenes.

The influence of cationic lipoid - 1-palmitoyl-2-oleoyl-sn-glycero-3-ethylphosphocholine - on model lipid membranes.

The triesters of phosphatidylcholine as the derivatives of natural phosphatidylcholines are less cytotoxic than the other cationic lipoids, therefore they can be applied in lipofection and in drug delivery. However, a successful and effective use of these compounds requires detailed information of their mechanism of action, which is probably highly complex and multi-stages. However, the first barrier in the way to cell and thus the first side of action of these compounds is the cellular membrane. The aim of this work was to investigate the effect of one cationic lipoid, namely 1-palmitoyl-2-oleoyl-sn-glycero-3-ethylphosphocholine (EPOPC) on model POPC/SM/Chol = 1:1:1 membranes. The experiments were performed on monolayer and bilayer systems and they involved the surface pressure measurements, Brewster angle microscopy studies, dynamic light scattering and zeta potential measurements and the experiments with the surfactant solution and steady-state fluorescence anisotropy of DPH and TMA-DPH. Moreover, to perform the studies systematically also the properties of the binary (POPC/EPOPC, SM/EPOPC, Chol/EPOPC) and ternary (POPC/Chol/EPOPC, SM/Chol/EPOPC) model systems were investigated. The obtained results indicated that even low concentration of EPOPC alters properties and organization of model membranes. Namely, EPOPC makes the interactions in model membrane weaker and increases fluidity and permeability of the lipid system. Finally, based on these data it can be proposed that the mechanism of action of EPOPC in lipofection/drug delivery involves the modifications in membrane organization, which facilitates the incorporation of drug or other material into the cell.

The impact of toxic bisphenols on model human erythrocyte membranes.

Bisphenols are the environmental pollution of a highly harmful, but different in their magnitude, influence on the living organisms. Among various aspects of the toxicity of these compounds their effect on the red blood cells is intensively investigated. The aim of this work was to compare the effect of bisphenol A (BPA), bisphenol S (BPS) and bisphenol F (BPF) on model erythrocyte membranes and to get insight into the origin of the differences in the harmful effect of these substances on cells. Thus, the influence of bisphenols on multicomponent Langmuir films imitating the outer leaflet of erythrocyte membrane was thoroughly analyzed. An important step of the experiments were the studies on the effect of bisphenols on the films composed from particular erythrocyte membrane lipids. It was confirmed that both BPA and BPF affect model lipid systems more strongly than BPS, by changing their condensation, ordering, stability and morphology. However, the most essential conclusion was that BPA acts on the erythrocyte lipids more selectively than BPS and BPF and the influence exerted by this molecule is more strongly determined by the membrane composition. It was also suggested that cholesterol may act as the molecule of a decisive role from the point of view of the magnitude of the incorporation and the effect of BPA and BPF on membrane. Thus, the level of bisphenols toxicity to erythrocytes may depend on the concentration of cholesterol in their membranes.

The influence of terpinen-4-ol and eucalyptol - The essential oil components - on fungi and plant sterol monolayers.

Antifungal and herbicidal activity of terpenes, being the components of the essential oils, is directly related to the incorporation of these compounds into cellular membranes. Thus, the differences in the lipid composition of various pathogenic membranes may be the factor determining the activity of these molecules. One of the class of lipids, which form the membrane environment are sterols. The aim of this work was to compare the effect of two terpenes: terpinen-4-ol and eucalyptol on the monolayers formed by ergosterol and ß - sitosterol, which are the components of fungi and plant membranes, respectively. The modifications in the sterol monolayer properties were investigated in the surface pressure-area measurements and penetration studies as well as in a micrometer scale (Brewster angle microscopy experiments) and in nanoscale (GIXD technique). It was evidenced that although at higher surface pressure the terpene molecules are in part removed from the interface, they are able to substantially modify the condensation, morphology and molecular organization of the sterol film. It was also found that the incorporation of terpenes into sterol films is comparable for both sterols, however, ß - sitosterol monolayers properties are affected more strongly than ergosterol films. Finally, the analysis of the results of the studies performed on model membrane systems and the results of antimicrobial studies reported in literature, enabled us to suggest that the activity of terpenes depends on the membrane composition and that the sterol concentration may be important from the point of view of antifungal effect of terpinen-4-ol and eucalyptol.

The influence of the essential oil extracted from hops on monolayers and bilayers imitating plant pathogen bacteria membranes.

Many plant-derived compounds possess antimicrobial, antioxidant and even anticancer activities. Therefore, they are considered as substances that can be used instead of synthetic compounds in various applications. In this work, the essential oil from hop cones was extracted and analyzed, and then its effects on model bacteria membranes were studied to verify whether the hop essential oils could be used as ecological pesticides. The experiments involved surface pressure-area measurements, penetration studies and Brewster angle microscopy (BAM) imaging of lipid monolayers as well as hydrodynamic diameter, zeta potential, steady-state fluorescence anisotropy and Cryo-Transmission Electron Microscopy (cryo-TEM) measurements of liposomes. Finally the bactericidal tests on plant pathogen bacteria Pseudomonas syringae pv. lachrymans PCM 1410 were performed. The obtained results showed that the components of the essential oils from hop cones incorporate into lipid monolayers and bilayers and alter their fluidity. However, the observed effect is determined by the system composition, its condensation and the oil concentration. Interestingly, at a given dose, the effect of the essential oil on membranes was found to stabilize. Moreover, BAM images proved that hop oil prevents the formation of a large fraction of a condensed phase at the interface. Both the studies on model membranes as well as the in vitro tests allow one to conclude that the hop essential oil could likely be considered as the candidate to be used in agriculture as a natural pesticide.

Studies on the interactions of anticancer drug - Minerval - with membrane lipids in binary and ternary Langmuir monolayers.

2-Hydroxyoleic acid (2OHOA, Minerval), a derivative of oleic acid, is the lipid used in Membrane Lipid Therapy. This compound is of confirmed anticancer effect, however its exact mechanism of action has not been fully elucidated. In this work the interactions of 2OHOA with cholesterol, sphingomyelin and phosphatidylcholine in Langmuir films were investigated. Moreover, the influence of this drug on SM/Chol and POPC/Chol films was studied. The collected results evidenced that 2OHOA substantially increases fluidity of lipid monolayers and modifies membrane organization, however, its influence depends on drug concentration and membrane properties. It was found that the condensation of model membrane is a critical factor determining the effect of 2OHOA. Moreover, the drug molecules added into SM/Chol film treated as model raft system drastically decrease molecular packing, weaken the interactions between raft components, destabilize the system and alter its morphology. This allows one to suggest that alterations made directly in membrane and microdomains architecture can be treated as one of the areas of Minerval activity.

Influence of Cationic Phosphatidylcholine Derivative on Monolayer and Bilayer Artificial Bacterial Membranes.

An increasing number of bacterial infections and the rise in antibiotic resistance of a number of bacteria species forces one to search for new antibacterial compounds. The latter facts motivate the investigations presented herein and are aimed at studying the influence of a cationic lipid, 1-palmitoyl-2-oleoyl- sn-glycero-3-ethylphosphocholine (EPOPC), on model (mono- and bilayer) membranes. The monolayer experiments involved the analysis of the interactions of EPOPC with bacterial membrane lipids in one component and mixed systems as well as Brewster angle microcopy studies. The properties of liposomes were analyzed based on the results of dynamic light scattering (DLS) and zeta potential measurements as well as on the experiments concerning the release of calcein entrapped in liposomes after titration with surfactant solution and steady-state fluorescence anisotropy of DPH. The obtained results evidenced that EPOPC, even at low concentrations, strongly changes organization of model systems making them less condensed. Moreover, EPOPC decreases the hydrodynamic diameter of liposomes, increases their zeta potential, and destabilizes model membranes, increasing their fluidity and permeability. Also, the in vitro tests performed on Escherichia coli (Gram-negative) and Staphylococcus aureus (Gram-positive) strains prove that EPOPC has some bacteriostatic properties which seem to be stronger toward Gram-negative than Gram-positive bacteria. All these findings allow one to conclude that EPOPC mode of action may be directly connected with the interactions of EPOPC molecules with bacterial membranes.

Studies on the Behavior of Eucalyptol and Terpinen-4-ol-Natural Food Additives and Ecological Pesticides-in Model Lipid Membranes.

Effective application of the essential oils requires detailed exploration of their mechanism of action and the origin of diverse activity of their components. In this work, the influence of eucalyptol and terpinen-4-ol on artificial membranes was studied to verify whether the differences in the activity of these compounds are related to their effect on membranes. The properties of monolayers formed from structurally different lipids in the presence of terpenes were examined based on the results of the surface pressure-area measurements, penetration studies, and Brewster angle microscopy experiments. Both compounds were able to incorporate into the membrane and alter lipid/lipid interactions, making the monolayer less stable and more fluid. These effects were determined by monolayer composition (but not by its condensation per se) and the resulting rheological properties and were stronger in the presence of terpinen-4-ol. These findings confirm the hypothesis that differences in the antimicrobial potency of these terpenes are membrane-related, and membrane composition may determine their selectivity.

Essential oils as food eco-preservatives: Model system studies on the effect of temperature on limonene antibacterial activity.

Antimicrobial properties of essential oils predestine these substances to be used as ecological food preservatives. However, their activity is determined by variety of factors among which external conditions and food properties are highly important. Herein the influence of limonene on artificial membranes was studied to verify the effect of temperature on the incorporation of this compound into model bacterial membrane. The investigations were done on lipid monolayers and the experiments involved the surface pressure-area measurements, penetration studies and Brewster Angle Microscopy analysis. It was found that limonene incorporates into lipid monolayers causing their fluidization. However, the magnitude of alterations depends on limonene concentration, model membrane composition and, for a given composition, on system condensation. Moreover, the influence of limonene is stronger at lower temperatures and, in the light of collected data, this may be a consequence of strong volatility and evaporation of limonene increasing with temperature.

Effect of Cd2+ and Cd2+/auxin mixtures on lipid monolayers - Model membrane studies on the role of auxins in phytoremediation of metal ions from contaminated environment.

In this work Langmuir monolayer experiments were performed to analyze the effect of Cd2+ ions and their mixtures with synthetic auxin (1-naphthaleneacetic acid - NAA) on lipid films. These investigations were motivated by the fact that auxins act effectively as the agents improving the removal of metal ions from contaminated water and soil by plants (phytoextraction), and although their mechanism of action in this area is still unclear, it was suggested that it can be membrane-related. The experiments were done for one component (1,2-dipalmitoyl-sn-glycero-3-phosphocholine - DPPC; 1,2-dioleoyl-sn-glycero-3-phosphocholine - DOPC; 1,2-dipalmitoyl-sn-glycero-3-phospho-(1'-rac-glycerol) (sodium salt) - DPPG) monolayers and mixed (DPPG/DOPC and DPPG/DPPC) films treated as model of plant leaves membranes. The monolayer properties were analyzed based on the surface pressure-area isotherms obtained during film compression, stability measurements and Brewster angle microcopy studies. The collected results together with the data presented in literature evidenced that both metal ions and auxins modify lipid system properties and by using them in a combination it is possible to weaken the influence of sole metal ions on membrane organization. This seems to be in agreement with the hypothesis that the role of plant growth regulators in increasing phytoextraction effectiveness may be membrane-related. However, further experiments are required to find possible correlations between the type and concentration of metal ion, composition of membrane or structural elements in auxin molecule and observed alterations in membrane properties.

The influence of environmentally friendly pesticide - Eucalyptol - alone and in combination with terpinen-4-ol - on model bacterial membranes.

Eucalyptus oil is known from antimicrobial properties and due to natural origin and low toxicity it can be applied as a green pesticide. This plant extract is a mixture of compounds among which Eucalyptol prevails strongly over the number of minor components including terpinen-4-ol. However, antimicrobial effect of total extract is stronger than the effect of its major component. The mechanism of action of essential oils involves their incorporation into membrane of pathogenic cell. To investigate the effect of eucalyptus oil components on bacterial membrane in this work the influence of Eucalyptol on model lipid systems of various compositions was studied and then compared with the effect induced by the mixture of Eucalyptol and terpinen-4-ol. The analysis of the lipid monolayer properties modified by the presence of the essential oils evidenced that Eucalyptol reduces the lipids packing and decreases membrane rigidity, however, its influence is determined both by the concentration of this terpene and by the composition of lipid film. As indicated the results of calculation of the surface excess values Eucalyptol molecules tend to adsorb at the interface, however, at higher concentration in the subphase, the molecules undergo desorption at membrane-related surface pressure. By mixing of Eucalyptol and terpinen-4-ol stronger monolayer fluidization and destabilization can be achieved as well as stronger adsorption, even at higher surface pressures, occurs. However, these effects are also determined by the composition of model system. The collected data suggest that these compounds may act by penetrating bacterial membrane. Moreover, it can be proposed that although Eucalyptol is a major component of the Eucalyptus oil the antimicrobial effect of total extract is generated also by a minor component. This may explain stronger antimicrobial effect of Eucalyptus oil as compared to sole Eucalyptol confirmed in biological studies.

The impact of auxins used in assisted phytoextraction of metals from the contaminated environment on the alterations caused by lead(II) ions in the organization of model lipid membranes.

Auxins are successfully used to improve phytoextraction efficiency of metal ions from the contaminated environment, however, the mechanism of their activity in this field is not explained. Auxins are known to exert various biochemical alterations in the plant membranes and cells, but their activity involves also direct interactions with lipids leading to changes in membrane organization. Following the suggestion that the auxins-induced modifications in membrane properties alleviate toxic effect of metal ions in this paper we have undertaken the comparative studies on the effect of metal ions and metal ions/auxins mixtures on model membrane systems. The experiments were done on lipid monolayers differing in their composition spread on water subphase and on Pb(2+), Indole-3-acetic acid (IAA), 1-Naphthaleneacetic acid (NAA) and Pb(2+)/IAA and Pb(2+)/NAA water solutions. The analysis of the collected data suggests that metal ions and auxins can change fluidity of the lipid systems and weaken the interactions between monolayer components. This manifested in the increase of the mean area per molecule and the excess area per molecule values for the films on Pb(2+), auxins as well as Pb(2+)/auxin solutions as compared to the values on pure water subphase. However, the presence of auxin in the mixture with lead(II) ions makes the alterations induced by sole metal ions weaker. This effect was more pronounced for the membranes of a higher packing. Thus it was proposed that auxins may enhance phytoextraction of metal ions by weakening their destabilizing effect on membrane.

Crucial Role of the Double Bond Isomerism in the Steroid B-Ring on the Membrane Properties of Sterols. Grazing Incidence X-Ray Diffraction and Brewster Angle Microscopy Studies.

Three cholesterol precursors-desmosterol, zymosterol, and lanosterol-were comprehensively characterized in monolayers formed at the air/water interface. The studies were based on registration of the surface pressure (π)-area (A) isotherms complemented with in situ analysis performed with application of modern physicochemical techniques: grazing incidence X-ray diffraction (GIXD) and Brewster angle microscopy (BAM). In this approach we were interested in the correlation between molecular structures of the studied sterols found in the cholesterol biosynthetic pathway and their membrane properties. Our results revealed that only desmosterol behaves in Langmuir monolayers comparably to cholesterol, the molecules of which arrange in the monolayers into a hexagonal lattice, while the two remaining sterols possess extremely different properties. We found that molecules of both zymosterol and lanosterol are organized on the water surface in the two-dimensional oblique unit cells despite the fact that they are oriented perpendicular to the monolayer plane. The comparison of chemical structures of the investigated sterols leads to the conclusion that the only structural motive that can be responsible for such unusual behavior is the double bond in the B sterol ring, which is located in desmosterol in a different position from in the other two sterols. This issue, which was neglected in the scientific literature, seems to have crucial importance for sterol activity in biomembranes. We showed that this structural modification in sterol molecules is directly responsible for their adaptation to proper functioning in biomembranes.

Antagonistic effects of α-tocopherol and ursolic acid on model bacterial membranes.

α-tocopherol (Toc), the most active component of vitamin E can exert antagonistic effects disabling the therapy of cancers and bacterial infections. Such antagonisms were observed also between Toc and bioactive pentacyclic triterpenes (PT) exhibiting anticancer and antibacterial properties. Both Toc and PT are water-insoluble membrane active substances. Thus, our idea was to emulate their interactions with model Escherichia coli membranes. E. coli inner membranes were selected for the experiments because their lipid composition is quite simple and well characterized and the two main components are phosphatidylethanolamine and phosphatidylglycerol. As a model of E. coli membranes we applied Langmuir monolayers formed by the E. coli total extract of polar lipids (Etotal) as well as by the main lipid components: phosphatidylethanolamine (POPE) and phosphatidylglycerol (ECPG). The antagonistic effects of ursolic acid (Urs) and Toc were investigated with the application of ternary Langmuir monolayers formed by Urs, Toc and one of the phospholipids POPE or ECPG. Our studies indicated that the affinities of Urs and Toc towards the POPE molecule are comparable; whereas there are profound differences in the interactions of Urs and Toc with ECPG. Thus, the model experiments prove that in the case of E. coli membrane, the differences in the interactions between Urs and Toc with the anionic bacterial phosphatidylglycerol can be the key factor responsible for the antagonistic effects observed between PT and Toc in vivo.