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Lipid biosensors are molecular tools used both in vivo and in vitro applications, capable of selectively detecting specific types of lipids in biological membranes. However, despite their extensive use, there is a lack of systematic characterization of their binding properties in various membrane conditions. The purpose of this study was to investigate the impact of membrane properties, such as fluidity and membrane charge, on the sensitivity of two lipid biosensors, LactC2 and P4M, to their target lipids, phosphatidylserine (PS) or phosphatidylinositol 4-phosphate (PI4P), respectively. Dual-color fluorescence cross-correlation spectroscopy, employed in this study, provided a useful technique to investigate interactions of these recombinant fluorescent biosensors with liposomes of varying compositions. The results of the study demonstrate that the binding of the LactC2 biosensor to low levels of PS in the membrane is highly supported by the presence of anionic lipids or membrane fluidity. However, at high PS levels, the presence of anionic lipids does not further enhance binding of LactC2. In contrast, neither membrane charge, nor membrane fluidity significantly affect the binding affinity of P4M to PI4P. These findings provide valuable insights into the role of membrane properties on the binding properties of lipid biosensors. • Fluorescence cross-correlation reveals binding properties of lipid biosensors. • Lipid biosensors binding responses might be affected by bulk membrane properties. • LactC2 sensitivity to PS is influenced by membrane charge and fluidity. • P4M is not susceptible to various membrane conditions when recognizing PI4P. [ABSTRACT FROM AUTHOR]

The lipidome of cells and organelles is more complex than originally anticipated. It has become clear that biomembranes are active materials bearing a tremendous regulatory potential. Cells control the collective biophysical properties of their organelle membranes in order to maintain the organization and functionality of the membrane proteome. The concept of homeoviscous adaptation provided an intuitive interpretation for the changes of membrane compositions with temperature. However, the mechanistic relevance of membrane viscosity for many cellular processes including those regulating the lipid fatty acyl chain composition has been recently challenged. The crucial role of membrane compressibility and thickness in organizing the membrane proteome, however, has gained fresh emphasis. The transverse membrane compressibility of the endoplasmic reticulum (ER) membrane modulates crucial aspects of transmembrane protein biology including their bilayer insertion and extraction, their conformational dynamics and activity, as well as their sorting along the secretory pathway and inheritance from mother to daughter cells. The unfolded protein response (UPR) can sense aberrant ER membrane stiffening and surfaces as a prime candidate for balancing membrane lipid and protein production at the ER as a mechanism of biophysical membrane homeostasis during cellular stress. Biomembranes are complex materials composed of lipids and proteins that compartmentalize biochemistry. They are actively remodeled in response to physical and metabolic cues, as well as during cell differentiation and stress. The concept of homeoviscous adaptation has become a textbook example of membrane responsiveness. Here, we discuss limitations and common misconceptions revolving around it. By highlighting key moments in the life cycle of a transmembrane protein, we illustrate that membrane thickness and a finely regulated membrane compressibility are crucial to facilitate proper membrane protein insertion, function, sorting, and inheritance. We propose that the unfolded protein response (UPR) provides a mechanism for endoplasmic reticulum (ER) membrane homeostasis by sensing aberrant transverse membrane stiffening and triggering adaptive responses that re-establish membrane compressibility. [ABSTRACT FROM AUTHOR]

Lipophilic index (LI) has been introduced to assess the overall fatty acid lipophilicity and as a simple estimate of membrane fluidity. However, little is known on effect of diet on LI. We tested if Camelina sativa oil (CSO) high in ALA, fatty fish (FF) or lean fish (LF) affect LI as compared to control diet and, secondarily, if the LI is associated with HDL lipids and functionality and LDL lipidome. We used data from two randomized clinical trials. The AlfaFish intervention lasted 12 weeks and 79 subjects with impaired glucose tolerance were randomized to FF, LF, CSO or control group. In the Fish trial, 33 subjects with myocardial infarction or unstable ischemic heart attack were randomized to FF, LF or control group for 8 weeks. LI was calculated from erythrocyte membrane fatty acids in AlfaFish and from serum phospholipids in Fish trial. HDL lipids were measured using high-throughput proton nuclear magnetic resonance spectroscopy. There was a significant decrease in LI in the FF group in the AlfaFish (fold change 0.98 ± 0.03) and in the Fish trial (0.95 ± 0.04) and the decrease differed from that of control group in both trials and from CSO group in the AlfaFish study. There were no significant changes in LI in LF or CSO groups. The mean diameter of HDL particles and concentration of large HDL particles were inversely associated with LI. FF consumption decreased LI indicating better membrane fluidity in subjects with impaired glucose tolerance or coronary heart disease. • Low lipophilic index is considered as marker of better membrane fluidity. • Fatty fish consumption decreased lipophilic index. • Lower lipophilic index was associated with larger mean HDL size. [ABSTRACT FROM AUTHOR]

[Display omitted] Previously, we reported that the combined use of spermine (SPM) and sodium taurocholate (STC) (SPM–STC) significantly improves the oral absorption of rebamipide (BCS class IV) and pulmonary absorption of interferon-α without any harmful histopathological changes in the gastrointestinal tract and lungs, respectively. In the present study, we examined the effect of SPM–STC on the transport of fluorescein isothiocyanate-labeled dextrans (FDs) across Caco-2 cell monolayers and attempted to clarify the mechanisms underlying the transport enhancement caused by SPM–STC. SPM–STC were found to significantly enhance the transport of FDs, while the treatment with SPM–STC was not harmful, and the decrease in transepithelial electrical resistance was transient and reversible. The voltage-clamp study clearly indicated that the opening of the paracellular route could be mainly responsible for the enhanced transport of FD-4. As for the mechanisms, it was found that SPM–STC caused a significant increase in membrane fluidity, which would lead to the enhanced transport of small-molecule drugs such as rebamipide. Since SPM–STC increased intracellular Ca2+ via Ca2+ uptake through Ca2+ channels and Ca2+ release from the endoplasmic reticulum stimulated by the IP 3 pathway, the subsequent possible activation of the MLCK signaling pathway would have led to the contraction of the actin–myosin ring. The rearrangement of tight junction-constituting proteins induced through the MAPK pathway has also been suggested as a possible mechanism for opening tight junctions. Claudin-4, a key protein constituting the tight junction, merged with F-actin along with the plasma membrane, was significantly decreased, which would be at least partial structural evidence for the tight-junction opening. [ABSTRACT FROM AUTHOR]

EPR spectroscopy is a technique that provides direct information about free radicals in biological systems. So far, X-band EPR was seldomly used for in vivo studies as the small resonator size and high power used to detect EPR signals were unsuitable for living organisms. Here, we report new solutions which lift some limitations and make X-band EPR suitable for an in vivo detection of free radicals in zebrafish - a small laboratory animal that is often used as a model for various studies related to free radicals. We designed specially-shaped glass and quartz capillaries to ensure the zebrafish's safety during the experiments. The optimal EPR spectrometer parameters, safe for zebrafish embryos and sufficient to obtain EPR spectrum, were 4 scans by 20s, 100G sweep, and 0.8 mW power. Combining the specially-shaped capillary with a multi-harmonic analyzer for the EPR spectrometer allowed increasing the time up to 16 scans by 11s and lowering the power to 0.25 mW. As a proof of principle, we demonstrate the detection of melanin radicals and the 5-DSA spin probe in zebrafish larvae. As fish survive the EPR scans, the possibility of performing multiple measurements of free radicals in living zebrafish offers new tools for studies aiming to understand redox biology and membrane-dependent functions in both health and disease. [Display omitted] • Short exposure to low power X band EPR radiation is safe for zebrafish. • Specially shaped capillary ensures proper positioning of the sample and tuning of EPR. • Glass and quartz capillaries are both effective for the measurement of free radicals. • Melanin radical could be observed in vivo in zebrafish larvae with X band EPR. • Membrane fluidity changes could be observed in vivo in zebrafish larvae with X band EPR. [ABSTRACT FROM AUTHOR]

Carthamus tinctorius L. (Safflower) is extensively used as a functional food and herbal medicine, with its application closely associated with hydroxysafflor yellow A (HSYA). However, the low oral bioavailability of HSYA in safflower extract (SFE) limits its health benefits and application. Our study found that co-administration of 250, 330, and 400 mg/kg peach kernel oil (PKO) increased the oral bioavailability of HSYA in SFE by 1.99-, 2.11-, and 2.49-fold, respectively. The enhanced bioavailability is attributed to improved lipid solubility and intestinal permeability of HSYA in SFE due to PKO. PKO is believed to modify membrane fluidity and tight junctions, increase paracellular penetration, and inhibit the expression and function of P-glycoprotein, enhancing the transcellular transport of substrates. These mechanisms suggest that PKO is an effective absorption enhancer. Our findings provide valuable insights for developing functional foods with improved bioavailability. [Display omitted] • Peach kernel oil (PKO) enhance the oral bioavailability of hydroxysafflor yellow A in safflower • PKO increase the lipid solubility and membrane fluidity • PKO can temporarily and reversibly open tight junctions • PKO can inhibit the expression and function of P-gp [ABSTRACT FROM AUTHOR]

We investigated the influence of archaeal lipids (C 25,25) isolated from thermophilic archaeon Aeropyrum pernix K1 on physicochemical properties of liposomes comprised of egg sphingomyelin (SM) and cholesterol (CH) using fluorescence emission anisotropy, calcein release studies, dynamic light scattering, transmission electron microscopy and phase analysis light scattering. The 2 mol% addition of archaeal lipids enabled formation of small unilamellar vesicles by sonication while also having significant effect on reducing mean size, polydispersity index and zeta potential of C 25,25 /SM/CH vesicles. Increasing the ratio of C 25,25 lipids in mixture of C 25,25 /SM/CH decreased lipid ordering parameter in dose dependent manner at different temperatures. We also demonstrated that adding 15 mol% C 25,25 to SM/CH mixture will cause it to notably interact with fetal bovine serum which could make them a viable alternative adjuvant to synthetic ether-linked lipids in development of advanced liposomal vaccine delivery systems. The prospect of combining the proven strengths of SM/CH mixtures with the unique properties of C 25,25 opens exciting possibilities for advancing drug delivery technologies, promising to yield formulations that are both highly effective and adaptable to a range of therapeutic applications. [Display omitted] • Archaeal lipids in SM-CH liposomes enable formation of vesicles by sonication. • Archaeal lipids increase fluidity in SM-CH liposomes dose-dependently. • 2 mol% addition of archaeal lipids stabilizes the SM-CH liposomes. • Mixed liposomes show morphological stability and reduced calcein release. [ABSTRACT FROM AUTHOR]

Sticholysin I (StI) is a pore-forming toxin (PFT) belonging to the actinoporin protein family characterized by high permeabilizing activity in membranes. StI readily associates with sphingomyelin (SM)-containing membranes originating pores that can lead to cell death. Binding and pore-formation are critically dependent on the physicochemical properties of membrane. 1-palmitoyl-2-oleoylphosphatidylcholine hydroperoxide (POPC–OOH) is an oxidized phospholipid (OxPL) containing an –OOH moiety in the unsaturated hydrocarbon chain which orientates towards the bilayer interface. This orientation causes an increase in the lipid molecular area, lateral expansion and decrease in bilayer thickness, elastic and bending modulus, as well as modification of lipid packing. Taking advantage of membrane structural changes promoted by POPC-OOH, we investigated its influence on the permeabilizing ability of StI. Here we report the action of StI on Giant Unilamellar Vesicles (GUVs) made of 1-palmitoyl-2-oleoylphosphatidylcholine (POPC) and SM containing increasing amount of POPC-OOH to assess vesicle permeability changes when compared to OxPL-lacking membranes. Inclusion of POPC-OOH in membranes did not promote spontaneous vesicle leaking but resulted in increased membrane permeability due to StI action. StI activity did not modify the fluid-gel phase coexistence boundaries neither in POPC:SM or POPC-OOH:SM membranes. However, the StI insertion mechanism in membrane seems to differ between POPC:SM and POPC-OOH:SM mixtures as suggested by changes in the time course of monolayer surface tension measurements, even though a preferable binding of the toxin to OxPL-containing systems could not be here demonstrated. In summary, modifications in the membrane imposed by lipid hydroperoxidation favor StI permeabilizing activity. • Membrane properties changes promoted by POPC-OOH increase StI pore-forming activity. • StI interaction with membranes does not modify fluid-gel phase coexistence boundaries. • The StI insertion mechanism in POPC-OOH:SM membrane differs from POPC:SM mixtures. [ABSTRACT FROM AUTHOR]

Protein phosphatase Z1 (Ppz1) has been shown to take part in important physiological functions in fungi including a contribution to virulence of Candida albicans. Although its involvement in the oxidative stress response has also been documented, the exact mechanism of action of its protective effect against oxidative damage remains unknown. By developing a pipeline to analyze the biophysical properties of the cell membrane in fungi, we demonstrate that the plasma membrane of Ppz1-KO Candida albicans displays increased sensitivity to tert-butyl-hydroperoxide-induced oxidative damage. In particular, the response to the oxidizing agent, characterized by increased lipid peroxidation, reduced lipid order, and inhibited lateral mobility of plasma membrane components, is significantly more pronounced in the Ppz1-KO C. albicans strain than in the wild-type counterpart. Remarkably, membrane constituents became almost completely immobile in the phosphatase deletion mutant exposed to oxidative stress. Furthermore, moderately elevated membrane lipid peroxidation accompanied by the aforementioned changes in the biophysical characteristics of the plasma membrane are already detectable in untreated Ppz1-KO cells indicating latent membrane damage even in the absence of oxidative stress. In conclusion, the hypersensitivity of cells lacking Ppz1 to oxidative damage establishes that potential Ppz1 inhibitors may synergize with oxidizing agents in prospective anti-fungal combination therapies. [Display omitted] • Membrane damage induced by the oxidizing agent tBOOH is exacerbated in PPZ1 KO Candida albicans. • This damage involves increased membrane hydration and lipid peroxidation as well as lower mobility of membrane components. • Similar biophysical changes can be detected in untreated KO cells implying latent oxidative damage in the KO strain. • The combined effect of the oxidizing agent and the KO genotype immobilized fluorescent lipid markers in the membrane. • Combination of prospective Ppz1 inhibitors with oxidative stress may tackle infections by drug-resistant Candida species. [ABSTRACT FROM AUTHOR]

• EPR is a powerful technique for monitoring lipid and protein dynamics in human hair. • Membrane fluidity in the hair cuticle is much lower than in the cortex region. • Lipid depletion and dehydration decrease membrane fluidity in hair. • Oleic acid and linalool hair softeners increase lipid fluidity in the cuticle region. Electron paramagnetic resonance (EPR) spectroscopy of a lipid spin label indicated that hair membrane fluidity is low in the cuticle region and high in the inner region comprising the cortex and medulla. This study evaluated the effect of hair treatments and dehydration on membrane fluidity and protein dynamics. In the cuticle region, treatment of hydrated hair with the ionic surfactants, sodium dodecyl sulfate (SDS, anionic), cetyltrimethylammonium chloride (cationic), and N-hexadecyl-N,N-dimethyl-3-ammonio-1-propanesulfonate (zwitterionic), as well as the non-ionic Tween 80, caused notable increases in fluidity, with the anionic surfactant SDS having a lesser effect. Furthermore, oleic acid and the monoterpene linalool increased fluidity, while propylene glycol (at 50 %) reduced fluidity and showed the ability to extract the lipid spin label from hair membranes. In the cortex and medulla region, where lipid fluidity is high, the treatments did not cause any changes. For dry hair, membrane fluidity was significantly reduced both in the cuticle and in the inner region. For lipid-depleted hair (containing only covalently bound lipids), the spin label found membranes of high rigidity both in the cuticle and inner regions. In addition, protein dynamics in the peripheral and inner regions of the hair was evaluated using a protein spin label covalently attached to sulfhydryl groups. Dehydration was found to decrease protein dynamics while treatments with oleic acid, linalool, and ethanol caused small increases in the dynamics. Lower molecular dynamics of hair lipids and proteins could be associated with dehydration, lipid depletion, and stiffness through EPR spectroscopy analysis, while the physical presence of softeners and hair cleansers, such as surfactants, leads to an increase in lipid dynamics. EPR spectroscopy has potential application in determining how the molecular dynamics of lipids and proteins are related to the external appearance of hair. [Display omitted] [ABSTRACT FROM AUTHOR]

Transition of Mycolicibacterium smegmatis (Msm) and Mycobacterium tuberculosis to dormancy in vitro is accompanied by an accumulation of free methylated forms of porphyrins (tetramethyl coproporphyrin – TMC) localized in the cell wall of dormant bacteria. A study of the fluorescence anisotropy of BODIPY based fluorescent probes on individual cell level using confocal microscope revealed significant changes in this parameter for BODIPY FL C16 from 0.05 to 0.22 for vegetative and dormant Msm cells correspondingly. Similarly, the increase of TMC concentration in vegetative Msm cells grown in the presence of 5-aminolevulinic acid (a known inducer of porphyrin synthesis) resulted in an increase of BODIPY FL C16 anisotropy. These changes in TMC concentration and membrane fluidity were accompanied by an inhibition of the activity of the respiratory chain measured by oxygen consumption and a reduction of the DCPIP redox acceptor. During the first 8 h of the reactivation of the dormant Msm cells, the porphyrin content and probe fluorescent anisotropy returned to the level for vegetative bacteria. We suggested that upon transition to dormancy, an accumulation of TMC in membranes leads to a decrease in membrane fluidity, resulting in an inhibition of the respiratory chain activity. However, direct interactions of TMC with membrane bound enzymes cannot also be excluded. This, in turn, may result in the down regulation of many metabolic energy-dependent reactions as a part of mechanisms accompanying the transition to a hypometabolic state of mycobacteria. [Display omitted] • Membrane fluidity decrease in dormant M. smegmatis cells in comparison with vegetative cells was detected. • The change in membrane fluidity correlates with the change in the concentration of methylated coproporphyrin. • The fluorescence anisotropy method for individual cell was applied for the first time for mycobacteria. [ABSTRACT FROM AUTHOR]

Drought induces alteration in membrane lipid composition in plants; however, still little is known about whether membrane lipid remodeling plays a role in plant drought acclimation, including both drought tolerance and recovery, especially in crops. Here, we imposed natural progressive drought and re-watering in 18 maize genotypes at the seedling stage, and analyzed the physiological responses, drought tolerance and drought acclimation capabilities, contents of lipids, and fatty acid compositions. The results showed that drought caused significant reductions in shoot dry weight, relative water content, Fv/Fm, total lipid content, and double bond index (DBI) in most genotypes, while re-watering partially recovered these reductions. Meanwhile, the total lipid content, fatty acid composition, and DBI were also changed obviously in response to drought and re-watering. In order to explore the relationship between membrane lipid change and plant drought response, we did a principal component analysis. The results showed that C18:3 fatty acid contributed greatly to drought tolerance, and C16:2 and C16:3 fatty acids were more responsible for drought recovery. Meanwhile, DBI showed significant positive correlations with shoot dry weight and relative water content, but a negative association with lipid peroxidation, and more importantly, DBI was important for both drought tolerance and recovery. These alterations in membrane lipid composition may facilitate increasing membrane fluidity and decreasing membrane damage, thus maintaining the high photosynthetic capability under drought. Our results suggest that lipid remodeling is important for drought tolerance and recovery in crops, and different fatty acid species have different roles in crop drought acclimation. • Lipid remodeling is an important pathway for drought acclimation in maize. • A high level of C18:3 fatty acid is beneficial to drought tolerance. • High levels of C16:2 and C16:3 fatty acids are more important for drought recovery. • DBI of the total lipid plays a crucial role in both drought tolerance and recovery. [ABSTRACT FROM AUTHOR]

A pyrenylated fluorogenic probe has been designed that can detect heavy metal pollutants exclusively at the bilayer interface. The compound, due to extensive self-aggregation, showed no interaction with metal ions in the bulk solution phase. However, effective, nanomolar level detection of multiple metal ions, such as Cu2+, Hg2+, and Ni2+, etc. was achieved exclusively in vesicular aggregates. The optical response towards metal ions, including selectivity and sensitivity, largely depends on the microenvironment around the probe molecules, governed by the nature of the bilayer membrane (polarity, order, interfacial hydration, etc). In zwitterionic membranes, like DPPC, Hg2+-induced fluorescence quenching was witnessed along with red-shifted emission maxima. On the contrary, turn-off responses along with blue-shifted in maxima were noted upon addition of both Cu2+ and Ni2+ ions in the anionic phospholipid vesicle, DPPA. Moreover, an improvement in sensitivity was witnessed when the probe was embedded into phospholipid vesicles with a fluid-like liquid crystalline phase. The larger mobility of the probe molecules on the bilayer membrane, resulting in ease of reorganization, might be the probable reason for this. [Display omitted] • Multiple metal ion sensing at lipid-water interface. • Microenvironment-Dependent modulation in analytical performance. • Protonation at anionic interface due to acidic local pH. • Fluidity-dependent reorganization of probe molecules on bilayer surface. [ABSTRACT FROM AUTHOR]

• LQFM332 causes cell membrane rigidity, as detected by EPR spectroscopy. • Membrane rigidity was associated with antileishmanial activity. • EPR spectra suggest that chalcone derivatives cause oxidation in membrane proteins. Novel chalcone-like compounds, LQFM332 (4), LQFM333 (5), and LQFM341 (6), were synthesized and their activity against Leishmania (L.) amazonensis was evaluated and compared. Compound 4 was synthesized from the molecular hybridization of vanillin (9) and butylated hydroxytoluene (BHT), forming a chalcone scaffold. BHT was replaced by another apocynin to give compound 5, while for compound 6 the Michael acceptor double bond from compound 4 was reduced. The IC 50 values for compounds 4, 5, and 6 against the Leishmania parasite were 7, 20, and 16 µM for the promastigote form, and 19, 11, and 1 µM for the amastigote form inside infected macrophages, respectively. Electron paramagnetic resonance (EPR) spectroscopy of a lipid spin label incorporated into the parasite plasma membrane demonstrated that treatment with these compounds in culture medium causes membrane rigidity in a concentration-dependent manner, owing to oxidative processes. From the IC 50 values with different cell concentrations, the membrane-water partition coefficient (K M/W) of the compounds could be estimated, as well as their concentrations in the membrane (c m50) and in the aqueous culture medium (c w50) that reduce antiproliferative activity by 50%. Values for these biophysical parameters were similar to those reported for the antileishmanial drug, miltefosine. K M/W values indicated that the compounds have high affinity for the parasite membrane, with the compound containing the BHT group having the highest affinity. Compound 5, which contained a two 4-OH-3-methoxybenzene scaffold, showed the lowest values of c w50 and c m50. Compound 6 showed that the reduction of the double bond decreased the membrane affinity and the c w50 value, but maintained the c m50 , demonstrating the same activity as compound 4 for assays with higher concentration of cells. As cytotoxic activities were modulated by effects on the cell membrane, our results suggest that the primary action of the compounds is on the parasite membrane. [ABSTRACT FROM AUTHOR]

Glucocerebroside (GlcCer) is a group of compounds consisting of β-linked glucose and ceramide with various chain lengths, some of which possess anti-tumor activity and improve skin barrier function for atopic patients when administered orally. The amphiphilic GlcCer molecules are generally easy to aggregate in aqueous solution and result in low absorption in the gut, which can be improved by forming a liposome. With a recognition that a relatively large amount of GlcCer is contained in the starfish and is being discarded, we prepared a liposome consisting mainly of GlcCer (over 95%) with 100 nm in diameter. The adsorption efficiency of the liposome into cultured Caco-2 cells was investigated by live-cell imaging using fluorescently labeled liposomes. We found an immediate internalization of GlcCer-liposome on exposure without significant accumulation on the plasma membrane. The membrane fluidity was transiently affected as evidenced by fluorescence recovery after photobleaching (FRAP) experiments without no significant cellular damage, which indicates a liposome with high content of GlcCer might be useful as the carrier of dietary and/or drug molecules. A liposome consisting mainly of glucocerebroside (GlcCer) isolated from a starfish A. amurensis with its diameter approximately 100 nm was prepared, and its internalization process and the effects on membrane fluidity were investigated using cultured Caco-2 cells. It was found that the liposome was rapidly taken up by the cell without apparent cellular damage but with slight membrane fluidity changes. [Display omitted] • Liposomes consisting of over 95% glucosyl cerebroside (GlcCer) from A. amurensis were prepared with approximately 100 nm in diameter. • Cellular uptake efficiency of GlcCer-liposome was visualized by using fluorescently labeled GlcCer-liposome containing BODIPY-carrying Glc-sphingoid base (Sph). • The membrane fluidity changes after the addition of GlcCer-liposome were investigated by FRAP using LactosylSphBODIPY–BSA complex as a membrane probe. • Rapid internalization of the GlcCer liposome without cellular damages was found. [ABSTRACT FROM AUTHOR]

Cells are constantly adapting to maintain their identity in response to the surrounding media's temporal and spatial heterogeneity. The plasma membrane, which participates in the transduction of external signals, plays a crucial role in this adaptation. Studies suggest that nano and micrometer areas with different fluidities at the plasma membrane change their distribution in response to external mechanical signals. However, investigations linking fluidity domains with mechanical stimuli, specifically matrix stiffness, are still in progress. This report tests the hypothesis that the stiffness of the extracellular matrix can modify the equilibrium of areas with different order in the plasma membrane, resulting in changes in overall membrane fluidity distribution. We studied the effect of matrix stiffness on the distribution of membrane lipid domains in NIH-3 T3 cells immersed in matrices of varying concentrations of collagen type I, for 24 or 72 h. The stiffness and viscoelastic properties of the collagen matrices were characterized by rheometry, fiber sizes were measured by Scanning Electron Microscopy (SEM) and the volume occupied by the fibers by second harmonic generation imaging (SHG). Membrane fluidity was measured using the fluorescent dye LAURDAN and spectral phasor analysis. The results demonstrate that an increase in collagen stiffness alters the distribution of membrane fluidity, leading to an increasing amount of the LAURDAN fraction with a high degree of packing. These findings suggest that changes in the equilibrium of fluidity domains could represent a versatile and refined component of the signal transduction mechanism for cells to respond to the highly heterogeneous matrix structural composition. Overall, this study sheds light on the importance of the plasma membrane's role in adapting to the extracellular matrix's mechanical cues. [Display omitted] • Matrix stiffness induced changes in membrane fluidity. • Matrix stiffness as low as 95 Pa induced changes in membrane fluidity. • Matrix stiffness increased areas with high degree of packing in the membrane. • Cells in 2D and 3D configuration showed different distributions of fluidity regions in the membrane. [ABSTRACT FROM AUTHOR]

• The zwitterionic compounds miltefosine and HPS showed similar results in this study. • SDS was the least effective compound for increasing membrane protein dynamics. • SDS demonstrated the lowest hemolytic effect among the compounds studied. For miltefosine (MIL), a zwitterionic alkylphospholipid approved for leishmaniasis treatment, the mechanism of action is not well established. Electron paramagnetic resonance (EPR) spectroscopy has indicated that the interaction of MIL with membrane proteins has similarities to that of ionic surfactants. A general concern about leishmanicides is their high hemolytic potential, so we decided to compare the interactions of MIL and three ionic surfactants with the erythrocyte membrane. Measurements with two different spin labels indicated that the surfactants sodium dodecyl sulfate (SDS, anionic), cetyltrimethylammonium chloride (CTAC, cationic) and N-hexadecyl-N,N-dimethyl-3-ammonio-1-propanesulfonate (HPS, zwitterionic) as well as MIL increase the dynamics of erythrocyte membrane proteins in a concentration-dependent manner. SDS produced the smallest increases in protein dynamics and was also the least hemolytic for measurements in PBS and in whole blood. Spin label EPR measurements performed directly in the blood plasma detected increased albumin stiffness caused by 2.5 mM SDS due to electrostatic/hydrophobic interactions. For 10 mM concentrations of the compounds, the EPR spectra showed a fraction of albumin with greater mobility and another with the same as that of the untreated plasma. The zwitterionic compounds MIL and HPS did not present significant differences in this study. [ABSTRACT FROM AUTHOR]

• Drug-membrane interactions are crucial to understand the mechanisms of Alzheimer's. • Liposomes are suitable for the study of drug–membrane interactions. • Cholesterol hampers the interaction of natural compounds with membranes. • Tannic acid has a significant higher affinity than caffeine and gallic acid. • Tannic acid may interact with extracellular Aβ fibrils and intracellular oligomers. Natural compounds such as caffeine (CA), gallic acid (GA) and tannic acid (TA) have been reported to be useful for Alzheimer's disease (AD) therapy. It was proved that some natural compounds inhibit the formation of senil plaques composed by beta-amyloid peptide (A β), a hallmark of AD. Evidences suggest that the therapeutic activity of compounds depends of their interaction with biological membranes. To understand why these compounds fail in vivo and in clinical trials, it is important to evaluate their pharmacokinetics properties. Thus, a biophysical approach to study drug-membrane interactions is essential to understand the mechanisms by which the drugs interact with the cellular membranes and affect the A β production, aggregation and clearance pathways. 1,2-dimyristoyl-sn-glycero-3-phosphocholine (DMPC) and cholesterol (chol) were used to mimic the biophysical properties of cell membranes and study their interactions with these compounds. The partition coefficient, influence on membrane fluidity and location within the bilayer of the drugs were studied by derivative spectrophotometry, dynamic light scattering and fluorescence quenching, respectively. The results suggest that TA exhibited a significant higher partition than CA and GA and a preferential location near to the polar head of bilayer. The obtained results may explain the therapeutic mechanisms reported for these natural compounds. [ABSTRACT FROM AUTHOR]

Abstract Cells maintain physicochemical characteristics of membranes in order to allow for proper function of membrane-associated cellular processes, such as endocytosis and exocytosis. To investigate the interplay between membrane properties and biological processes, we applied lipid engineering approaches that allowed for systematic manipulation of fatty acid unsaturation and sterol biosynthesis, the main regulators of membrane fluidity. In combination with electrophysiological membrane capacitance measurements, we were able to study the dependence of the endo- and exocytic activity of Saccharomyces cerevisiae on membrane lipid composition in vivo. We found that a strong decrease in the cell's total ergosterol content leads to a severely reduced frequency of vesicle fission (endocytosis), whereas the exocytic activity remained largely unaffected. In contrast, increased lipid saturation lowered both endocytic and the exocytic activity, with the former being more severely affected. We were able to correlate the decreased ratio of endocytic/exocytic frequencies (f endo / f exo) upon lipid perturbation with the growth of yeast protoplasts, which is based on a surface enlargement resulting from a net excess of exocytic over endocytic flux. Experiments using clathrin-deficient mutants confirm a correlation between reduced endocytic activity and increased size of intact walled cells, as well as accelerated protoplast growth. These data show that lipid composition is intimately tied to membrane trafficking in yeast cells and suggest that endocytosis is particularly dependent on the lipid-defined properties of cell membrane. Graphical abstract Unlabelled Image Highlights • A titratable promoter is used to manipulate the cellular ergosterol content in budding yeast by regulating expression of ERG9 • Ergosterol depleted cells show strongly reduced endocytic activity but largely unaffected exocytic activity • Low lipid unsaturation results in moderate decline of exocytic, but strong decline of endocytic activity • A decreased ratio of endocytic/exocytic frequencies upon lipid perturbation leads to faster growth of yeast protoplasts [ABSTRACT FROM AUTHOR]

Bacterial membranes are complex mixtures of lipids and proteins, the combination of which confers biophysical properties that allows cells to respond to environmental conditions. Carotenoids are sterol analogs that are important for regulating membrane dynamics. The membrane of Pantoea sp. YR343 is characterized by the presence of the carotenoid zeaxanthin, and a carotenoid-deficient mutant, Δ crtB, displays defects in root colonization, reduced secretion of indole-3-acetic acid, and defects in biofilm formation. Here we demonstrate that the loss of carotenoids results in changes to the membrane lipid composition in Pantoea sp. YR343, including increased amounts of unsaturated fatty acids in the Δ crtB mutant membranes. These mutant cells displayed less fluid membranes in comparison to wild type cells as measured by fluorescence anisotropy of whole cells. Studies with artificial systems, however, have shown that carotenoids impart membrane rigidifying properties. Thus, we examined membrane fluidity using spheroplasts and vesicles composed of lipids extracted from either wild type or mutant cells. Interestingly, with the removal of the cell wall and membrane proteins, Δ crtB vesicles were more fluid than vesicles made from lipids extracted from wild type cells. In addition, carotenoids appeared to stabilize membrane fluidity during rapidly changing temperatures. Taken together, these results suggest that Pantoea sp. YR343 compensates for the loss of carotenoids by changing lipid composition, which together with membrane proteins, results in reduced membrane fluidity. These changes may influence the abundance or function of membrane proteins that are responsible for the physiological changes observed in the Δ crtB mutant cells. Unlabelled Image • Pantoea sp. YR343 membranes contain the carotenoid zeaxanthin. • Loss of carotenoids from Pantoea results in changes in lipid profiles and membrane fluidity • Membrane fluidity is modulated by a combination of membrane lipids, proteins, and carotenoids [ABSTRACT FROM AUTHOR]

Zinc has a strong influence on the function of the immune system and is a driving factor for immune cell development. In this regard, studies revealed cell type specific effects of zinc. During zinc deficiency for example, development and activity of myeloid cells seems to be prioritized at the cost of cells from the lymphoid lineage. In T-cells, the altered proliferation was found to be due to zinc's effect on IL-2-induced signaling processes, but in contrast to lymphoid cells, effects of zinc homeostasis on growth-factor-induced signaling in myeloid cells have not been investigated yet. The granulocyte-macrophage colony-stimulating factor (GM-CSF) is one of the major factors inducing monopoiesis. Considering the structural similarities between the GM-CSF receptor and those of the IL-receptor family as well as a similar set of signaling molecules involved, an impact of zinc on the GM-CSF signaling seems to be likely. Therefore, the effect of zinc on GM-CSF-induced signaling molecules was investigated here, using U937 cells as a model myeloid cell line. GM-CSF stimulation significantly increased STAT5 phosphorylation which was prevented completely by pre-incubation with zinc and pyrithione. U937 cells showed a strong pre-activation regarding c-Raf, which was significantly decreased by zinc and pyrithione incubation, independently from GM-CSF stimulation. As current literature was not sufficient to explain the observed effects, we hypothesized an altered receptor-complex assembly. As membrane composition and plasticity, subsumed under the term of membrane fluidity, was found to affect receptor multimerization, the impact of zinc on membrane fluidity was considered as a completely novel approach. Indeed, addition of zinc also decreased GM-CSFR expression on the cell surface and most interestingly altered membrane fluidity. In conclusion, we hypothesize that the incubation with zinc causes an alteration of membrane fluidity that hinders efficient receptor assembly as well as phosphorylation of signal molecules and therefore signal transduction. [ABSTRACT FROM AUTHOR]

The sesquiterpene nerolidol is a membrane-active compound that has demonstrated antitumor, antibacterial, antifungal and antiparasitic activities. In this study, we used electron paramagnetic resonance (EPR) spectroscopy and biophysical parameters determined via cell culture assays to study the mechanisms underlying the in vitro antileishmanial activity of nerolidol. The EPR spectra of a spin-labeled stearic acid indicated notable interactions of nerolidol with the cell membrane of Leishmania amazonensis amastigotes. The nerolidol IC 50 values in L. amazonensis amastigotes and promastigotes were found to depend on the cell concentration used in the assay. This dependence was described by an equation that considers various cell suspension parameters, such as the 50% inhibitory concentrations of nerolidol in the cell membrane (c m50) and the aqueous phase (c w50) and the membrane-water partition coefficient of nerolidol (K M/W). Via cytotoxicity (CC 50) and hemolytic potential (HC 50) data, these parameters were also determined for nerolidol in macrophages and erythrocytes. With a c w50 of 125 μM, macrophages were less sensitive to nerolidol than amastigotes and promastigotes, which had mean c w50 values of 56 and 74 μM, respectively. The estimated c m50 values of nerolidol for amastigotes and promastigotes and macrophages were between 2.6 and 3.0 M, indicating substantial accumulation of nerolidol in the cell membrane. In addition, the spin-label EPR data indicated that membrane dynamic changes occurred in L. amazonensis amastigotes at concentrations similar to the nerolidol IC 50 value. Unlabelled Image • Nerolidol accumulates in the Leishmania plasma membrane in very large quantities. • Spin-label EPR spectra detected parasite membrane alterations at 1× IC 50 nerolidol. • The hemolytic potential of nerolidol in whole blood is relatively low. [ABSTRACT FROM AUTHOR]

Membrane fluidity, a broad term adopted to describe the thermodynamic phase state of biological membranes, can be altered by local pressure variations caused by ultrasound exposure. The alterations in lipid spatial configuration and dynamics can modify their interactions with membrane proteins and activate signal transduction pathways, thus regulating several cellular functions. Here fluidity maps of murine fibroblast cells are generated at a sub-micrometric scale during ultrasound stimulation with an intensity and frequency typical of medical applications. Ultrasound induces a phase separation characterized by two-step kinetics leading to a time-dependent decrease in fluidity. First, nucleation of liquid crystallin domains with an average dimension of ∼1 μm occurs. Then, these domains condense into larger clusters with an average dimension of ∼1.5 μm. The induced phase separation could be an important driving force critical for the cellular response connecting the ultrasound-induced mechanical stress and signal transduction. [ABSTRACT FROM AUTHOR]

Abstract The anaerobic digestion (AD) has become an important part of the wastewater treatment plants that regulates the sustainable management of organic wastes with simultaneous production of bioenergy. AD at low temperatures using psychrophilic anaerobes with optimum growth temperatures < 20 °C has gained significant attention for improvement of biogas productivity in cold regions. The present review discusses the detailed characteristics of psychrophilic anaerobes, and how the properties of those particular psychrophiles can be utilized towards the cost-effective production of methane at cold environment. The different challenges for AD at low temperature have been described thoroughly. The various strategies such as (a) adaptation of microbial community, (b) optimization of operational parameters, (c) utilization of specialized biodigester design, and (d) modification of downstream process to improve the AD and biomethane production in cold environments have also been summarized. The present review proposes the future technological developments which should be aimed at effective performance of anaerobic digesters to improve biomethanation in cold regions. Graphical abstract fx1 Highlights • Psychrophilic AD is an energy efficient process for biomethanation in cold regions. • Alterations of cellular physiology increases the adaptive response in psychrophiles. • Cold adaptation of inoculum and process optimization could improve psychrophilic AD. [ABSTRACT FROM AUTHOR]

Abstract Vibrio splendidus is a marine bacterium often considered as a threat in aquaculture hatcheries where it is responsible for mass mortality events, notably of bivalves' larvae. This bacterium is highly adapted to dynamic salty ecosystems where it has become an opportunistic and resistant species. To characterize their membranes as a first and necessary step toward studying bacterial interactions with diverse molecules, we established a labelling protocol for in vivo 2H solid-state nuclear magnetic resonance (SS-NMR) analysis of V. splendidus. 2H SS-NMR is a useful tool to study the organization and dynamics of phospholipids at the molecular level, and its application to intact bacteria is further advantageous as it allows probing acyl chains in their natural environment and study membrane interactions. In this study, we showed that V. splendidus can be labelled using deuterated palmitic acid, and demonstrated the importance of surfactant choice in the labelling protocol. Moreover, we assessed the impact of lipid deuteration on the general fitness of the bacteria, as well as the saturated-to-unsaturated fatty acid chains ratio and its impact on the membrane properties. We further characterize the evolution of V. splendidus membrane fluidity during different growth stages and relate it to fatty acid chain composition. Our results show larger membrane fluidity during the stationary growth phase compared to the exponential growth phase under labelling conditions - an information to take into account for future in vivo SS-NMR studies. Our lipid deuteration protocol optimized for V. splendidus is likely applicable other microorganisms for in vivo NMR studies. Graphical abstract Unlabelled Image Highlights • Marine bacteria are studied by in vivo solid-state NMR for the first time. • 2H isotopic labelling of marine bacteria membranes is optimized. • Membrane fluidity measured by NMR changes with bacterial growth time. • Fatty acid analysis shows bacterial adaptation to labelling conditions. • Labelled bacteria harvested in the late exponential phase are in a native state. [ABSTRACT FROM AUTHOR]

Graphical abstract Abstract Temozolomide (TMZ) is the first-line treatment for Glioblastoma Multiforme (GBM). After administration, TMZ is rapidly converted into its active metabolite (MTIC). However, its pharmacological activity is reduced due MTIC low bioavailability in the brain. Since drugs' permeability through biological barriers and tumor cell membranes affects its bioavailability, the ability of MTIC to interact with the biological membranes presents a major contribution on its pharmacological properties and activity. Biomembrane models mimic the physiological conditions, allowing to predict the drug's behavior at biological membranes and its effects on drug biodistribution profiles. In this work, lipid bilayer models using liposomes were applied for the drug-membrane interaction studies. The zwitterionic phospholipid, 1,2-dimyristoyl-sn-glycero-3-phosphocholine (DMPC), and cholesterol were chosen for the composition of the model, since they represent the major components of the membranes of GBM cells and brain capillary endothelial cell. Thus, the molecular interactions between MTIC and these models were studied by the evaluation of the partition of the drug into the phospholipid's membrane, its location within the bilayer and its effect on the fluidity of the membrane. The attained results suggest that the composition of membranes affects drugs partition, showing that drug biodistribution depends not only on its physicochemical features, but also depends on the characteristics of the membrane such as the packing of the lipid molecules. Also, MTIC exhibited low affinity to biological membranes, explaining its low bioavailability on the target cells. [ABSTRACT FROM AUTHOR]

Background: Chronic stress, an important factor in the development of depressive disorders, leads to an increased formation of cortisol, which causes a hyperactivity of the hypothalamic-pituitary-adrenal (HPA) axis. In addition, cortisol mediates an adaptive effect on plasma membrane fluidity which may affect signal transduction of membrane-bound receptors and contribute to pathophysiological changes.Methods: Membrane fluidity was measured by fluorescence anisotropy using DPH (1,6-diphenyl-1,3,5-hexatriene) and TMA-DPH (1-(4-(trimethylamino)phenyl)-6-phenylhexa-1,3,5-triene). Changes in cellular content of phosphatidylcholine species was determined by pulse-chase experiments using deuterated choline and mass spectrometry. Single molecule tracking was used to examine the lateral mobility of β1-adrenoceptors and changes in cAMP formation were measured by ELISA.Results: Chronic exposure (6 - 8 days) of C6 cells to cortisol dose-dependently decreased DPH and TMA-DPH fluorescence anisotropy, reflecting increased membrane fluidity. In contrast, cells pretreated with St. John's wort extract Ze117 showed increased DPH and TMA-DPH fluorescence anisotropy values, indicating a membrane rigidification effect which was mediated at least by the constituents hypericin, hyperforin, quercetin, amentoflavone and biapigenin. The observed membrane fluidizing effect of cortisol could be reversed by cotreatment with Ze117. The membrane rigidification of Ze117 was in line with the in parallel observed decrease in the phosphatidylcholine/phosphatidylethanolamine ratio determined in whole cell lipid extracts. Interestingly, pulse-chase experiments demonstrated, that Ze117 inhibited the incorporation of choline-D9 in phosphatidylcholine species with saturated or monounsaturated fatty acids compared to control cells, while the synthesis of phosphatidylcholine species with polyunsaturated fatty acids was not affected. C6 cells whose membranes have become more rigid by Ze117 showed altered lateral mobility of β1-adrenoceptors as well as reduced cAMP formation after stimulation with the β1-adrenoceptor agonist dobutamine.Conclusion: Obviously, the signaling of β1-adrenoceptors depends on the nature of the membrane environment. It can therefore be assumed that Ze117 has a normalizing effect not only on the membrane fluidity of "stressed" cells, but also on lateral mobility and subsequently on the signal transduction of membrane-associated receptors. [ABSTRACT FROM AUTHOR]

Abstract In this work the influence of growth temperature (10–42 °C) on Staphylococcus aureus heat resistance was studied, and its relationship with the ability of cells to repair sublethal damages and with membrane fluidity was evaluated. Non-linear, convex from above survival curves were obtained, and therefore a special case of the Baranyi model was used to fit them. For exponential phase cells, heat resistance did not change with growth temperature in the range between 10 and 37 °C, but cells grown at 42 °C were significantly more resistant, showing D 58 and shoulder length (sl 58) values 2.5 and 4 times greater than the others, respectively. For stationary growth phase cells, an increase in growth temperature above 20 °C resulted in an increase in D 58 values, and cells grown at 42 °C also displayed the highest D 58 and sl 58 values. The increased heat resistance at 58 °C of stationary growth phase cells grown at higher temperatures was coincident with the appearance of a higher proportion of sublethally damaged cells capable of recovery and outgrowth in non-selective medium. Membrane fluidity was measured at treatment temperatures, and it was observed that those cells with more rigid membranes displayed greater heat resistance (Pearson coefficient = 0.969***). Additionally, S. aureus cells whose membrane was fluidized through exposure to benzyl alcohol were notably sensitized against the action of heat, in a concentration-dependent manner. Results obtained in this research indicate that membrane physical state could be an important factor determining the survival capacity of bacterial cells to a heat treatment. Highlights • S. aureus heat resistance proved to be growth temperature and phase dependent. • Heat resistance of stationary growth phase cells increased when cells were grown over 20 °C. • Conversely, for exponential phase cells only those grown at 42 °C were more heat resistant. • Benzyl alcohol fluidized S. aureus membranes and sensitized cells against heat. • A relationship between membrane fluidity, heat resistance and damage repair ability was found. [ABSTRACT FROM AUTHOR]

Abstract The effect of lyophilization and rehydration medium on a liposome system for conjugated linoleic acid (CLA) delivery was studied. Liposomes were prepared by ethanol injection method employing soy phosphatidylcholine and CLA isomers 9c, 11t and 10t, 12c. Two rehydration media were assessed: a food simulant (distilled water) and the original medium used for liposome preparation (ethanol: water 1:9). Rehydrated liposomes were characterized in size, morphology, CLA encapsulation efficiency and membrane fluidity, at 3 and 30 days of cold storage. CLA loaded liposomes presented better stability and lower size than control liposomes without CLA through storage time, regardless of the rehydration medium. These facts could be related with spin label EPR measurements: CLA disordered the outer part of the lipid bilayer increasing fluidity, and ordered the inner part of the bilayer decreasing fluidity, which indicates a more packed membrane in the hydrophobic region. In all cases Transmission Electronic Microscopy images showed nanometric sized and oligo-lamellar vesicles. Liposomes preserved CLA isomers with high encapsulation efficiency: no differences were noticed between fresh and lyophilized samples. No influence of rehydration medium was noticed for the majority of the studied parameters. We have successfully developed efficient liposomal systems for bioactive compounds delivery in food applications. Highlights • Food grade liposomes with soy PC and CLA were studied. • Ethanol injection technique was successfully employed. • CLA loaded liposomes resisted lyophilization without cryoprotectants. • Fresh and lyophilized liposomes had similar encapsulation functional efficiency. • CLA influenced membrane fluidity in fresh and lyophilized vesicles. [ABSTRACT FROM AUTHOR]

Abstract Triterpenoids have multiple biological properties, although little information is available regarding their toxicity. The present study evaluates the toxicity of two new synthetic lupane derivatives using distinct biological models including synthetic lipids membranes, isolated liver and heart mitochondria fractions, and cell lines in culture. The two novel triterpenoids caused perturbations in the organization of synthetic lipid bilayers, leading to changes in membrane fluidity. Inhibition of cell proliferation and mitochondrial and nuclear morphological alterations were also identified. Inhibition of mitochondrial oxygen consumption, transmembrane electric potential depolarization and induction of the mitochondrial permeability transition pore was observed, although effects on isolated mitochondrial fractions were tissue-dependent (e.g. liver vs. heart). The size and length of hydrocarbon chains in the two molecules appear to be determinant for the degree of interaction with mitochondria, especially in the whole cell environment, where more barriers for diffusion exist. The results suggest that the positively charged triterpenoids target mitochondria and disrupt bioenergetics. Highlights • The present lupane triterpenoids molecules possess anticancer activity. • The lupane triterpenoids molecules positively charge are preferencial accumulated in mitochondria. • The optimal activity of the lupane triterpenoids will depend on the lipid composition of the target. [ABSTRACT FROM AUTHOR]

Abstract In cholesterol/DSPE-PEG 2000 /DPPC systems, nano-disks could evolve between liposomes and spherical micelles in a certain range of PEG-lipids. How cholesterol or drug influences this evolution and what about the properties of discoidal micelles as drug carrier are still not clear. Aiming at this, nanocarriers with different contents of cholesterol and DSPE-PEG 2000 were prepared by thin-film-hydration method. Firstly, the bilayer fluidity of nanocarriers was investigated and proved to decrease with the increase of cholesterol, and the cooperative degree between phospholipids was also related to cholesterol content in an order of 30 > 40 > 15 > 0 mol%. Then three different levels of cholesterol were chosen to study its effect on DSPE-PEG 2000 limit used to form discoidal micelles. For transition from liposomes to disks, the limit of DSPE-PEG 2000 employed is above 0.5 mol% at 0 mol% cholesterol, above 15 mol% at 30 mol% cholesterol and above 5 mol% at 40 mol% cholesterol observed from TEM images, indicating that nanocarriers with 30 mol% cholesterol formed discoidal micelles most difficultly due to the strongest interaction between phospholipids. However, membrane fluidity seems to have little responsibility for the different morphologies. And imatinib (IM) could promote the formation of discoidal micelles, resulting from the interaction between IM and polar headgroups of phospholipid demonstrated by DSC. The relative reduction of entrapment efficiency for three agents with different dissolving properties showed that lipophilic drugs were the most suitable drug that could be loaded into discoidal micelles. In addition, the discoidal micelle formulations tested could readily change to other morphologies after 80 days' storage. In conclusion, both the cholesterol content and IM could affect the formation of discoidal micelles by probably influencing the interaction between phospholipids, also the discoidal structure was not stable enough and only suitable for lipophilic drug loading. We hope this study could help to design the formula and choose the proper drugs that may retain the discoidal morphology. Graphical abstract Unlabelled Image [ABSTRACT FROM AUTHOR]

Highlights • Daptomycin forms cation-selective, octameric pores in membranes containing PG. • Pore formation is inhibited by phospholipids with acyl chains longer than 14 carbons. • Inhibition occurs even if the acyl chains are part of the "bulk" lipid, not of PG. • Inhibition is observed with low percentages (10%) of inhibitory phospholipid. • When inhibitory lipids are present, daptomycin forms tetramers rather than octamers. Abstract Daptomycin is a lipopeptide antibiotic that binds and permeabilizes the cell membranes of Gram-positive bacteria. Membrane permeabilization requires both calcium and phosphatidylglycerol (PG) in the target membrane, and it correlates with the formation of an oligomer that likely comprises eight subunits, which are evenly distributed between the two membrane leaflets. In both bacterial cells and model membranes, changes in the fatty acyl composition of the membrane phospholipids can prevent permeabilization. We here used liposomes to study the effect of phospholipids containing oleoyl and other fatty acyl residues on daptomycin activity, and made the following observations: (1) Oleic acid residues inhibited permeabilization when part not only of PG, but also of other phospholipids (PC or cardiolipin). (2) When included in an otherwise daptomycin-susceptible lipid mixture, even 10% of dioleoyl lipid (DOPC) can strongly inhibit permeabilization. (3) The inhibitory effect of fatty acyl residues appears to correlate more with their chain length than with unsaturation. (4) Under all conditions tested, permeabilization coincided with octamer formation, whereas tetramers were observed on membranes that were not permeabilized. Overall, our findings further support the notion that the octamer is indeed the functional transmembrane pore, and that fatty acyl residues may prevent pore formation by preventing the alignment of tetramers across the two membrane leaflets. [ABSTRACT FROM AUTHOR]

Abstract Background Amphipathic cationic antimicrobial peptides (AMPs) TC19 and TC84, derived from the major AMPs of human blood platelets, thrombocidins, and Bactericidal Peptide 2 (BP2), a synthetic designer peptide showed to perturb the membrane of Bacillus subtilis. We aimed to determine the means by which the three AMPs cause membrane perturbation in vivo using B. subtilis and to evaluate whether the membrane alterations are dependent on the phospholipid composition of the membrane. Methods Physiological analysis was employed using Alexa Fluor 488 labelled TC84, various fluorescence dyes, fluorescent microscopy techniques and structured illumination microscopy. Results TC19, TC84 and BP2 created extensive fluidity domains in the membrane that are permeable, thus facilitating the entering of the peptides and the leakage of the cytosol. The direct interaction of the peptides with the bilayer create the fluid domains. The changes caused in the packing of the phospholipids lead to the delocalization of membrane bound proteins, thus contributing to the cell's destruction. The changes made to the membrane appeared to be not dependent on the composition of the phospholipid bilayer. Conclusions The distortion caused to the fluidity of the membrane by the AMPs is sufficient to facilitate the entering of the peptides and leakage of the cytosol. General significance Here we show in vivo that cationic AMPs cause "membrane leaks" at the site of membrane insertion by altering the organization and fluidity of the membrane. Our findings thus contribute to the understanding of the membrane perturbation characteristic of cationic AMPs. Graphical abstract Unlabelled Image Highlights • Amphipathic cationic peptides rapidly create fluid domains in a rigid bulk membrane. • Direct insertion of the amphipathic cationic peptides creates the fluid domains. • Interaction of the amphipathic peptides only requires the presence of anionic phospholipids. [ABSTRACT FROM AUTHOR]

In this study, the potential toxicity of non-functionalized polystyrene nanoparticles (PS-NPs) in human erythrocytes has been assessed. The effect of PS-NPs with different diameters (∼30 nm, ∼45 nm, ∼70 nm) on fluidity of erythrocytes membrane, red blood cells shape, as well as haemolysis of these cells has been investigated. Erythrocytes were incubated for 24 h with non-functionalized PS-NPs in concentrations ranging from 0.001 to 200 μg/mL in order to study haemolysis and from 0.001 to 10 μg/mL to determine other parameters. Fluidity was estimated by electron paramagnetic resonance (EPR) and the fluorimetric method. It has been shown that PS-NPs induced haemolysis, caused changes in the fluidity of red blood cells membrane, and altered their shape. Non-functionalized PS-NPs increased the membrane stiffness in the hydrophobic region of hydrocarbon chains of fatty acids. The observed changes in haemolysis and morphology were dependent on the size of the nanoparticles. The smallest PS-NPs of ∼30 nm (with the smallest absolute value of the negative zeta potential −29.68 mV) induced the greatest haemolysis, while the largest PS-NPs of ∼70 nm (with the highest absolute value of the negative zeta potential −42.00 mV) caused the greatest changes in erythrocyte shape and stomatocytes formation. • Polystyrene nanoparticles induced in high concentrations hemolysis in human erythrocytes. • The smallest PS-NPs induced the greatest changes in hemolysis. • Nanoparticles caused changes in the fluidity of the erythrocyte membrane. • PS-NPs increased the membrane stiffness in hydrophobic region of hydrocarbon chains of fatty acids. • The largest PS-NPs caused the greatest changes in erythrocyte shape and stomatocyte formation. [ABSTRACT FROM AUTHOR]

Role of plant nsLTP in biotic stress is well reported; however, their role during abiotic stress is far from clear. This study comprises genome-wide identification of LTPs and characterizes the regulation and function of two Triticum aestivum lipid transfer proteins, TaLTP40 and TaLTP75, under stresses that influence membrane fluidity. A total of 105 LTP gene family members have been identified. The selected LTPs for functional validation were highly expressed during salt, cold and drought stress. Further, selected LTPs showed differential expression thermotolerant and thermosusceptible wheat cultivars. Higher expression of many TaLTPs was observed under different abiotic stresses in thermotolerant wheat cultivars as compared to thermosusceptible cultivars. TaLTPs regulation was correlated with light energy distribution studies under similar stress conditions. Cellular localization revealed localization of different TaLTPs to the tonoplast membrane along with the organelles involved in the secretory pathway. Induction of TaLTPs was observed upon treatment with dimethylsulphoxide. TaLTP40 and TaLTP75 overexpressing transgenic Arabidopsis showed a constitutively enhanced salt tolerance. Both the TaLTP40 and TaLTP75 overexpressing lines performed better in terms of chlorophyll a fluorescence, total chlorophyll content, membrane injury index, total biomass, percentage germination, percentage survival and relative growth rate. Hence, our analyses indicate that TaLTPs expression might be driven by change in membrane fluidity and could be involved in transferring membrane lipids to the biological membranes thus imparting tolerance to various abiotic stresses. [ABSTRACT FROM AUTHOR]

Highlights • Methylene blue uptake by Leishmania amazonensis promastigotes depends on its concentration but not on incubation time. • The lowest MB concentration and the lowest optical power promote higher inactivation of L. amazonensis cells. • MB-mediated PDT modifies membrane permeability and promotes depolarization of mitochondrial membrane potential. • MB-mediated PDT causes drastic ultrastructural changes on L. amazonensis. • Apoptosis is involved in parasite death following MB-mediated PDT. Abstract Antiparasitic photodynamic therapy (ApPDT) is an emerging approach to manage cutaneous leishmaniasis (CL) since no side effects, contraindications and parasite resistance have been reported. In addition, methylene blue (MB) is a suitable photosensitizer to mediate ApPDT on CL. In this study we aimed to look for the best parameters to eradicate Leishmania amazonensis and investigated the cell death pathways involved in MB-mediated ApPDT. MB uptake by parasites was determined using different MB concentrations (50, 100, 250 and 500 μM) and incubation times (10, 30 and 60 min). L. amazonensis promastigotes were cultured and submitted to ApPDT using different concentrations of MB (50, 100 and 250 μM) combined to a red LED emitting at 645 ± 10 nm. The pre-irradiation time was 10 min. Two optical powers (100 mW and 250 mW) were tested and cells were exposed to 60 and 300 s of MB-mediated ApPDT delivering energies of 6, 15, 30 and 75 J and fluences of 21.2, 53.1, 106.2 and 265.4 J/cm2, respectively. Following ApPDT, cells were prepared for flow cytometry and transmission electron microscopy to unravel the mechanisms of cell death. Our results showed the lowest MB concentration (50 μM) and the lowest optical power (100 mW) promoted the highest percentage of cell decrease. ApPDT caused alterations on cell membrane permeability as well depolarization of mitochondrial membrane potential. We also observed ultrastructural changes of the parasites such as cell shrinkage, intense vacuolization of the cytoplasm, enlargement of mitochondrion-kinetoplast complex, and small blebs on parasite flagella and cell membrane after MB-mediated ApPDT. Taken together, our findings ratify that ApPDT parameters play a pivotal role in cell susceptibility and suggest that apoptosis is involved in parasite death regardless MB-mediated ApPDT protocol. [ABSTRACT FROM AUTHOR]

Fullerenols (polyhydroxylated fullerene C 60 ) are nanomaterial with potentially broad applicability in biomedical sciences with high antioxidant ability, thus, we investigated the radioprotecting potential of fullerenol C 60 (OH) 36 on human erythrocytes irradiated by high-energy electrons of 6 MeV. The results demonstrate that C 60 (OH) 36 at concentration of 150 μg/mL protects the erythrocytes against the radiation-induced hemolysis (comparing to non-protected cells, we observed 30% and 39% protection for 0.65 and 1.3 kGy irradiation doses, respectively). The protecting effect was confirmed by 32% decreased release of potassium cations comparing to the cells irradiated without C 60 (OH) 36 . Measurements of the amount of lactate dehydrogenase (LDH) released from the irradiated erythrocytes showed that the size of the pores formed by irradiation was not sufficient to release LDH across the erythrocyte membranes. We also report a significant decrease of the affinity of acetylcholinesterase (AChE) for the substrate in the presence of fullerenol, indicating the relatively strong adsorption of C 60 (OH) 36 to components of plasma membrane. Changes in membrane fluidity detected by fluorescence spectroscopy and conformational changes in membrane proteins detected by spin labeling suggest the dose-dependent formation of disulfide groups as an effect of oxidation and this process was inhibited by C 60 (OH) 36. We suppose that scavenging the ROS as well as adsorption of fullerenol to membrane proteins and steric protection of -SH groups against oxidation are responsible for the observed effects. [ABSTRACT FROM AUTHOR]

γ-Aminobutyric-acid receptor (GABA A -R), a membrane intrinsic protein, is activated by GABA and modulated by a wide variety of recognized drugs. GABA A -R is also target for several insecticides which act by recognition of a non-competitive blocking site. Mentha oil is rich in several ketones with established activity against various insects/pests. Considering that mint ketones are highly lipophilic, their action mechanism could involve, at least in part, a non-specific receptor modulation by interacting with the surrounding lipids. In the present work, we studied in detail the effect on membranes of five cyclic ketones present in mint plants, with demonstrated insecticide and gabaergic activity. Particularly, we have explored their effect on the organization and dynamics of the membrane, by using Molecular Dynamics (MD) Simulation studies in a bilayer model of DPPC. We performed free diffusion MD and obtained spatially resolved free energy profiles of ketones partition into bilayers based on umbrella sampling. The most favored location of ketones in the membrane corresponded to the lower region of the carbonyl groups. Both hydrocarbon chains were slightly affected by the presence of ketones, presenting an ordering effect for the methylene groups closer to the carbonyl. MD simulations results were also contrasted with experimental data from fluorescence anisotropy studies which evaluate changes in membrane fluidity. In agreement, these assays indicated that the presence of ketones between lipid molecules induced an enhancement of the intermolecular interaction, increasing the molecular order throughout the bilayer thickness. [ABSTRACT FROM AUTHOR]

We evaluate the behavior of the membrane of Bradyrhizobium sp. SEMIA6144 during adaptation to polyethylene glycol (PEG). A dehydrating effect on the morphology of the cell surface, as well as a fluidizing effect on the membrane was observed 10 min after PEG shock; however, the bacteria were able to restore optimal membrane fluidity. Shock for 1 h caused an increase of lysophosphatidylethanolamine in the outer membrane at the expense of phosphatidylcholine and phosphatidylethanolamine (PE), through an increase in phospholipase activity. The amount of lysophosphatidylethanolamine did not remain constant during PEG shock, but after 24 h the outer membrane was composed of large amounts of phosphatidylcholine and less amount of lysophosphatidylethanolamine similar to the control. The inner membrane composition was also modified after 1 h of shock, observing an increase of phosphatidylcholine at the expense of PE, the proportions of these phospholipids were then modified to reach 24 h of shock values similar to the control. Vesicles prepared with the lipids of cells exposed to 1 h shock presented higher rigidity compared to the control, indicating that changes in the composition of phospholipids after 1 h of shock restoring fluidity after the PEG effect and would allow cells to maintain surface morphology. [ABSTRACT FROM AUTHOR]

There has been growing interest in the use of particles coated with lipids for applications ranging from drug delivery, gene delivery, and diagnostic imaging to immunoengineering. To date, almost all particles with lipid coatings have been spherical despite emerging evidence that non-spherical shapes can provide important advantages including reduced non-specific elimination and increased target-specific binding. We combine control of core particle geometry with control of particle surface functionality by developing anisotropic, biodegradable ellipsoidal particles with lipid coatings. We demonstrate that these lipid coated ellipsoidal particles maintain advantageous properties of lipid polymer hybrid particles, such as the ability for modular protein conjugation to the particle surface using versatile bioorthogonal ligation reactions. In addition, they exhibit biomimetic membrane fluidity and demonstrate lateral diffusive properties characteristic of natural membrane proteins. These ellipsoidal particles simultaneously provide benefits of non-spherical particles in terms of stability and resistance to non-specific phagocytosis by macrophages as well as enhanced targeted binding. These biomaterials provide a novel and flexible platform for numerous biomedical applications. Statement of significance The research reported here documents the ability of non-spherical polymeric particles to be coated with lipids to form anisotropic biomimetic particles. In addition, we demonstrate that these lipid-coated biodegradable polymeric particles can be conjugated to a wide variety of biological molecules in a “click-like” fashion. This is of interest due to the multiple types of cellular mimicry enabled by this biomaterial based technology. These features include mimicry of the highly anisotropic shape exhibited by cells, surface presentation of membrane bound protein mimetics, and lateral diffusivity of membrane bound substrates comparable to that of a plasma membrane. This platform is demonstrated to facilitate targeted cell binding while being resistant to non-specific cellular uptake. Such a platform could allow for investigations into how physical parameters of a particle and its surface affect the interface between biomaterials and cells, as well as provide biomimetic technology platforms for drug delivery and cellular engineering. [ABSTRACT FROM AUTHOR]

In the face of the serious problem of antimicrobial resistance and the global dissemination of multidrug-resistant (MDR) bacteria, it is relevant to deeply study such bacteria both genetically and phenotypically. It is well known that bacteria have the ability to modify the biophysical properties of their cytoplasmic membranes, namely fluidity, in order to survive and thrive in hostile environments. The aim of this study was to assess and compare the membrane fluidity among multidrug-resistant (MDR) isolates of Escherichia coli and Staphylococcus aureus in absence and in presence of antibiotics (ceftazidime or ciprofloxacin). The membrane fluidity was monitored at 24-h intervals up to three days and at the sixth day, by measuring the anisotropy of 1,6-diphenyl-1,3,5-hexatriene (DPH) and the generalized polarization (GP) of Laurdan (6-dodecanoyl-2-dimethylaminonaphthalene). The anisotropy values as well as the Laurdan excitation GP (GP exc ) values obtained from all three E. coli strains (two MDR isolates and one susceptible reference strain) were quite similar and indicative of a very alike membrane phospholipid composition, regardless harboring or not resistance to multiple antimicrobials. Nonetheless, in the case of S. aureus , the anisotropy values were more increased in methicillin-resistant S. aureus (MRSA) isolates in comparison to the reference strain, meaning they have a less fluid membrane. Equally, GP exc values were statistically different among the three S. aureus strains and showed that the two MRSA isolates had more rigid membranes than the susceptible strain. The exposition of MDR isolates of S. aureus to subinhibitory concentrations of ciprofloxacin did not affect neither the anisotropy values nor the GP exc values, therefore, not altering membrane fluidity. Membrane integrity, assessed by the Live/Dead staining, of all strains and conditions studied was maintained over the six days. Thus, these preliminary studies on membrane properties of MDR isolates demonstrate that i) MRSA seem to have a more rigid membrane that susceptible S. aureus and ii) the presence of subinhibitory concentrations of antibiotics does not significantly alter the membrane fluidity of S. aureus , regardless being MDR or susceptible, but slightly affect the membrane fluidity of E. coli . [ABSTRACT FROM AUTHOR]

After cold shock, the Bacillus subtilis desaturase Des introduces double bonds into the fatty acids of existing membrane phospholipids. The synthesis of Des is regulated exclusively by the two-component system DesK/DesR; DesK serves as a sensor of the state of the membrane and triggers Des synthesis after a decrease in membrane fluidity. The aim of our work is to investigate the biophysical changes in the membrane that are able to affect the DesK signalling state. Using linear alcohols (ethanol, propanol, butanol, hexanol, octanol) and benzyl alcohol, we were able to suppress Des synthesis after a temperature downshift. The changes in the biophysical properties of the membrane caused by alcohol addition were followed using membrane fluorescent probes and differential scanning calorimetry. We found that the membrane fluidization induced by alcohols was reflected in an increased hydration at the lipid-water interface. This is associated with a decrease in DesK activity. The addition of alcohol mimics a temperature increase, which can be measured isothermically by fluorescence anisotropy. The effect of alcohols on the membrane periphery is in line with the concept of the mechanism by which two hydrophilic motifs located at opposite ends of the transmembrane region of DesK, which work as a molecular caliper, sense temperature-dependent variations in membrane properties. [ABSTRACT FROM AUTHOR]

We have recently reported the beneficial modulation of metabolic abnormalities and oxidative stress in diabetic rats by dietary fenugreek seeds and onion. This investigation evaluated the protective influence of dietary fenugreek seeds (100 g kg −1 ) and onion (30 g kg −1 ) on erythrocytes of streptozotocin-induced diabetic rats, through modulation of reduced haematological indices and antisickling potency. This study also evaluated the altered erythrocyte membrane lipid profile and beneficial countering of increased lipid peroxidation, osmotic fragility, along with reduced membrane fluidity and deformability, nitric oxide production and echinocyte formation. Dietary fenugreek seeds and onion appeared to counter the deformity and fragility of erythrocytes partially in diabetic rats by their antioxidant potential and hypocholesterolemic property. The antisickling potency of these spices was accomplished by a substantial decrease in echinocyte population and AGEs in diabetic rats. Further insight into the factors that might have reduced the fluidity of erythrocytes in diabetic rats revealed changes in the cholesterol: phospholipid ratio, fatty acid profile, and activities of membrane-bound enzymes. Dietary fenugreek seeds and onion offered a beneficial protective effect to the red blood cells, the effect being higher with fenugreek + onion. This is the first report on the hemato-protective influence of a nutraceutical food component in diabetic situation. [ABSTRACT FROM AUTHOR]

This investigation was undertaken to study the inactivation of Enterococcus faecium ATCC 49624 by pulsed electric fields (PEF) treatments after exposure to sublethal acid and cold stresses. Cells were grown in Brain Heart Infusion (BHI) buffered to pH 7.4 (non-acid-adapted cells) and BHI acidified to pH 5.4 with acetic, ascorbic, citric, lactic, malic and hydrochloric acids (acid-adapted cells). Fresh and refrigerated cultures (kept at 4 °C for up to 1 month) were treated by PEF at 37 kV/cm in citrate-phosphate buffer of different pH (4.0, 5.5 and 7.0), at specific energies ranging from 79 to 1580 kJ/kg. Results demonstrated that acid adaptation exerted a different effect on the PEF resistance of E . faecium depending on the pH of the treatment medium. Thus, when treated in a medium of pH 7.0, previous acid adaptation, regardless of the type of acidulant used, reduced the calculated δ values (specific energies required to inactivate the first log 10 cycle of the population) by approximately two-fold. By contrast, in a medium of pH 4.0, acid-adapted cells showed a higher PEF resistance than non-adapted cells. On the other hand, exposure to 4 °C reduced the PEF resistance of acid-adapted cells, but not that of non-acid-adapted cells. Results obtained in this study suggested that, after the same PEF treatments, the number of electroporated cells was lower for non-acid-adapted cells, but that acid-adapted cells displayed a superior ability to repair sublethal damages caused by PEF. Nevertheless, exposure to refrigeration conditions would significantly reduce this damage repair ability. Finally, FT-IR spectroscopy measurements indicated that growth of E . faecium cells under acid conditions caused an increase in membrane fluidity. It was also observed that refrigerated storage resulted in a significant ( p < 0.05) reduction in membrane fluidity for acid-adapted cells but not for non-acid-adapted cells, with a potential impact on PEF resistance. Industrial relevance Given the inability of PEF to inactivate spores, pasteurization of acid products such as fruit juices appears as one of the more feasible applications for this technology. Microbial cells present in these products would have, very likely, undergone a process of adaptation to this acid pH; however, the impact of this phenomenon on microbial PEF resistance has only been scarcely investigated. Thus, the objective of this work was to study the inactivation of Enterococcus faecium by PEF treatments after sequential exposure to sublethal acid and cold stresses. This work will provide very valuable data for process design to further develop PEF application and improve understanding of microbial inactivation. [ABSTRACT FROM AUTHOR]

In this work, modifications of cell membrane fluidity, fatty acid composition and fatty acid biosynthesis-associated genes of Escherichia coli ATCC 25922 ( E. coli ) and Staphylococcus aureus ATCC 6538 ( S. aureus ), during growth in the presence of naringenin (NAR), one of the natural antibacterial components in citrus plants, was investigated. Compared to E. coli , the growth of S. aureus was significantly inhibited by NAR in low concentrations. Combination of gas chromatography–mass spectrometry with fluorescence polarization analysis revealed that E. coli and S. aureus cells increased membrane fluidity by altering the composition of membrane fatty acids after exposure to NAR. For example, E. coli cells produced more unsaturated fatty acids (from 18.5% to 43.3%) at the expense of both cyclopropane and saturated fatty acids after growth in the concentrations of NAR from 0 to 2.20 mM. For S. aureus grown with NAR at 0 to 1.47 mM, the relative proportions of anteiso-branched chain fatty acids increased from 37.2% to 54.4%, whereas iso-branched and straight chain fatty acids decreased from 30.0% and 33.1% to 21.6% and 23.7%, respectively. Real time q-PCR analysis showed that NAR at higher concentrations induced a significant down-regulation of fatty acid biosynthesis-associated genes in the bacteria, with the exception of an increased expression of fabA gene. The minimum inhibitory concentration (MIC) of NAR against these two bacteria was determined, and both of bacteria underwent morphological changes after exposure to 1.0 and 2.0 MIC. [ABSTRACT FROM AUTHOR]

Background Altered cholesterol levels in body fluids and brain tissues have been shown to be associated with suicidal behaviour, violence and aggression. But the biological underpinnings of this association in the pathophysiology of suicide are not clear. Cholesterol plays a crucial role in maintaining the cellular membrane fluidity and alterations in cellular membrane fluidity may impair serotonergic neurotransmission in the central nervous system. Methods We measured plasma esterified cholesterol and platelet membrane fluidity using fluorescence anisotropy and estimated flow activation energy which is a measure of order of membrane lipid bilayer in patients with recent suicidal attempt and compared with age and gender matched controls. Results The plasma esterified cholesterol, platelet membrane fluidity and flow activation energy was found to be significantly lower in patients with recent suicidal attempts compared to controls. Conclusion Altered levels of plasma esterified cholesterol which is in equilibrium with membrane cholesterol might have resulted in decreased membrane fluidity and an increase in the order of membrane lipid bilayer. This might impair the serotonergic neurotransmission, which has been implicated in the pathophysiology of suicide. [ABSTRACT FROM AUTHOR]

Curcumin is known to possess a wide range of pharmacological activities for the treatment of chronic or inflammatory diseases, Alzheimer’s disease, and various cancers. However, the therapeutic efficacy of curcumin is restricted by its poor bioavailability after oral administration. In this study, the effects of various cyclodextrins on the intestinal absorption of curcumin were evaluated in rat intestine by an in situ closed-loop method. Among the tested cyclodextrins, 50 mM α-cyclodextrin significantly enhanced the absorption of curcumin without inducing any intestinal toxicity. The analysis of cellular transport across Caco-2 cell monolayers showed that 50 mM α-cyclodextrin reduced the transepithelial electrical resistance value of cell monolayers and improved the permeability of 5(6)-carboxyfluorescein, a poorly absorbable drug, which is mainly transported via a paracellular pathway. Furthermore, the western blotting analysis showed that α-cyclodextrin decreased the expression of claudin-4, a tight junction-associated protein, in brush border membrane vesicles. Additionally, α-cyclodextrin increased the membrane fluidity of lipid bilayers in brush border membrane vesicles and may also have promoted the permeation of drug molecules via a transcellular pathway. These results suggested that α-cyclodextrin might enhance the intestinal absorption of curcumin via both paracellular and transcellular pathways. [ABSTRACT FROM AUTHOR]

Elevated levels of the essential trace metals cobalt and nickel are associated with a variety of toxic effects, which are not well-understood, and may involve interactions with the lipid membrane. Fluidity changes of biomimetic lipid membranes upon exposure to CoCl 2 and NiCl 2 were studied using the fluorescent probe Laurdan, which senses changes in environment polarity. Liposomes were prepared by extrusion in 20 mM HEPES + 100 mM NaCl at pH 7.4. Additionally, dynamic light scattering was used to monitor metal induced size changes of liposomes composed of: phosphatidic acid (PA), cardiolipin (CL), phosphatidylglycerol (PG), phosphatidylserine (PS), and phosphatidylcholine (PC), with saturated and unsaturated acyl chains. Micromolar concentrations of both metals significantly rigidify negatively-charged liposomes and generally increase the melting temperature. Saturated acyl chains showed stronger metal effects in PS and PG, while no clear acyl chain preference was observed in CL and PA systems. The strength of the effect appears to be influenced greatly by both the head group and acyl chain. The rigidifying effects of cobalt were almost always much larger than those of nickel. In addition, size changes and aggregation by both metals was detected in PS or PA liposomes at molar metal/lipid ratios as low as 1/10. [ABSTRACT FROM AUTHOR]

The study of surfactant and bio membranes interaction is particularly complex due to the diversity in lipid composition and the presence of proteins in natural membranes. Even more difficult is the study of this interaction in vivo since cellular damage may complicate the interpretation of the results, therefore for most of the studies in this field either artificial or model systems are used. One of the model system most used to study biomembranes are erythrocytes due to their relatively simple structure (they lack nuclei and organelles having only the plasma membrane), their convenient experimental manipulation and availability. In this context, we used rabbit erythrocytes as a model membrane and Laurdan (6-lauroyl-2-dimethylaminonaphthalene) as the fluorescent probe to study changes promoted in the membrane by the interaction with the sucrose monoester of myristic acid, β- d -fructofuranosyl-6- O -myristoyl-α- d -glucopyranoside (MMS). Surfactant and erythrocytes interaction was studied by measuring hemoglobin release and the changes in water content in the membrane sensed by Laurdan. Using two-photon excitation, three types of measurements were performed: Generalized Polarization (analyzed as average GP values), Fluorescence Lifetime Imaging, FLIM (analyzed using phasor plots) and Spectral imaging (analyzed using spectral phasor). Our data indicate that at sublytical concentration of surfactant (20 μM MMS), there is a decrease of about 35% in erythrocytes size, without changes in Laurdan lifetime or emission spectra. We also demonstrate that as hemolysis progress, Laurdan lifetime increased due to the decrease in hemoglobin (strong quencher of Laurdan emission) content inside the erythrocytes. Under these conditions, Laurdan spectral phasor analyses can extract the information on the water content in the membrane in the presence of hemoglobin. Our results indicate an increase in membrane fluidity in presence of MMS. [ABSTRACT FROM AUTHOR]

Bisphenols are massively used in the industry, and thus the exposure of biota including humans to these substances has been noted. In this study we have assessed the effect of BPA and its selected analogs, i.e. BPS, BPF and BPAF on membrane of human red blood cells, which is the first barrier that must be overcome by xenobiotics penetrating the cell, and is commonly utilized as a model in the investigation of the effect of different xenobiotics on various cell types. Red blood cells were incubated with BPA and its analogs in the concentrations ranging from 0.1 to 250 μg/ml for 4 h and 24 h. We have noted that the compounds studied altered membrane fluidity at its hydrophobic region, increased internal viscosity and osmotic fragility of the erythrocytes and altered conformational state of membrane proteins. Moreover, bisphenols examined increased thiol groups level, caused oxidative damage to membrane proteins, decreased ATP level, depleted the activity of Na+/K + ATPase and changed the activity of AChE in human red blood cells. It has been shown that the strongest changes were noted in cells treated with BPAF, while BPS caused the weakest (or none) alterations in the parameters studied. [ABSTRACT FROM AUTHOR]