Mixture Of Phospholipids Research Articles

Effects of lipid saturation on bicelle to vesicle transition of a binary phospholipid mixture: a molecular dynamics simulation study.

Controlling the transition from lipid bicelles to vesicles is essential for producing engineered vesicles. We perform coarse-grained molecular dynamics (CGMD) simulations of unsaturated/saturated lipid mixtures to clarify the effects of lipid unsaturation on vesiculation at the molecular scale. The results demonstrate that vesiculation depends on the concentration of unsaturated lipids and the degree of unsaturation. The probability of vesiculation increases linearly with the apparent unsaturated lipid concentration at a low degree of unsaturation. Higher degrees of unsaturation lead to phase segregation within the binary bicelles, reducing the probability of vesiculation. A comparison between CGMD simulations and the conventional theory of vesiculation shows that the theoretical predictions of binary lipid systems must explicitly include phase segregation effects. Furthermore, simulations with biased lipid distributions reveal that vesiculation is facilitated by the preconcentration of unsaturated lipids in the core region of the bicelle but is then temporally limited as the unsaturated lipids move to the bicelle edges. These findings advance theoretical and experimental studies on binary lipid systems and promote the development of tailor-made vesicles.

Dispersion of Titanium Oxide Nanoparticles Using Mixtures of Anionic Technol PG and Sodium Cholate

Titanium dioxide (TiO2) is widely used in cosmetics and self-cleaning materials because of its high refractive index and photocatalytic activity. In the present work, the surfaces of TiO2 nanoparticles were coated with sodium cholate and the commercially available anionic phospholipid mixture Technol PG. These surface-coated TiO2 nanoparticles could be homogeneously dispersed in water and subsequently produced films on glass substrates after drop casting.

Non-criteria antiphospholipid antibodies in antiphospholipid syndrome: Diagnostic value added.

Non-criteria antiphospholipid antibodies (aPLs) increase the diagnostic value for antiphospholipid syndrome (APS) and contribute to better recognition of seronegative APS (SNAPS). However, the clinical utility and the diagnostic value of non-criteria aPLs are inconsistent. This study aimed to investigate the prevalence and clinical significance of 7 non-criteria aPLs in a large APS cohort. Seven non-criteria aPLs, including anti-phosphatidylserine/prothrombin (aPS/PT) antibodies IgG/IgA/IgM, anti-phosphatidylethanolamine antibodies (aPE) IgG/IgA/IgM, anti-Annexin V antibodies (aAnnexinV) IgG/IgA/IgM, anti-phosphatidylserine antibodies (aPS) IgM, aPS IgG, antibodies directed againsta mixture of phospholipids(APhL) IgG, and APhL IgM were tested among 175 patients with APS, 122 patients with other autoimmune diseases (as disease controls), and 50 healthy controls. In the present study, the highest prevalence of non-criteria aPLs was seen in aAnnexinV (58.86%). APhL IgG and aPS IgM showed the highest specificity (95.35%) and aPS/PT showed the highest Youden index (0.3991) for the diagnostic value of APS. The aAnnexinV also showed the highest prevalence in SNAPS (43.3%), followed by APhL IgM (21.7%), aPE (16.7%) and aPS/PT (16.7%). APhL IgG, aPS/PT, and aPS IgG showed positive association with thrombotic events in APS patients [APhL IgG: odds ratio (OR) = 2.26, 95% confidence interval (CI) 1.18-4.34, p = 0.013; aPS/PT: OR = 2.48, 95% CI: 1.32-4.69, p = 0.004; aPS IgG: OR = 1.90, 95% CI 1.01-3.60, p = 0.046; respectively). The inclusion of the non-criteria aPLs increased the accuracy of APS diagnosis from 65.7% to 87.4%. Our data provide evidence that adding the non-criteria aPLs can improve the diagnostic accuracy in APS. APhL IgG, aPS/PT, and aPS IgG may be potential biomarkers to predict the risk of thrombosis in APS.

Dispersion of Cannabidiol Into Small-Sized Nanoparticles Using Technol PG

Cannabidiol (CBD) has been used for the treatment of neuronal disease. Herein CBD was mixed with sodium cholate and Technol PG, a commercially available mixture of anionic phospholipids, which allowed for effective dispersion of the CBD in water.

Novel Small Multilamellar Liposomes Containing Large Quantities of Peptide Nucleic Acid Selectively Kill Breast Cancer Cells.

Simple SummaryWe present, for the first time, the preparation of small (60–90 nm in diameter) liposomes containing extremely large amounts (~8000 molecules per vesicle) of short, cytosine-rich peptide nucleic acid. The outer surface of liposomes wasfunctionalized with scaffold molecules specific to tumor-associated antigen overexpressing in breast cancer. We have shown that targeted liposomesspecifically interact with cancer cells and reduce their viability in sub-nanomolar concentrations. The results presented here can be widely used in cancer therapy based on cytosine-rich PNA oligonucleotides.Peptide nucleic acid (PNA) may be used in various biomedical applications; however, these are currently limited, due to its low solubility in aqueous solutions. In this study, a methodology to overcome this limitation is demonstrated, as well as the effect of PNA on cell viability. We show that extruding a mixture of natural phospholipids and short (6–22 bases), cytosine-rich PNA through a 100 nm pore size membrane under mild acidic conditions resulted in the formation of small (60–90 nm in diameter) multilamellar vesicles (SMVs) comprising several (3–5) concentric lipid membranes. The PNA molecules, being positively charged under acidic conditions (due to protonation of cytosine bases in the sequence), bind electrostatically to negatively charged phospholipid membranes. The large membrane surface area allowed the encapsulation of thousands of PNA molecules in the vesicle. SMVs were conjugated with the designed ankyrin repeat protein (DARPin_9-29), which interacts with human epidermal growth factor receptor 2 (HER2), overexpressed in human breast cancer. The conjugate was shown to enter HER2-overexpressing cells by receptor-mediated endocytosis. PNA molecules, released from lysosomes, aggregate in the cytoplasm into micron-sized particles, which interfere with normal cell functioning, causing cell death. The ability of DARPin-functionalized SMVs to specifically deliver large quantities of PNA to cancer cells opens a new promising avenue for cancer therapy.

Molecular interactions of hesperidin with DMPC/cholesterol bilayers

Since cell membranes are complex systems, the use of model lipid bilayers is quite important for the study of their interactions with bioactive molecules. Mammalian cell membranes require cholesterol (CHOL) for their structure and function. For this reason, the mixtures of phospholipid and cholesterol are necessary to use in model membrane studies to better simulate the real systems. In the present study, we investigated the effect of the incorporation of hesperidin in model membranes consisting of dimyristoylphosphatidylcholine (DMPC) and CHOL by using differential scanning calorimetry (DSC), attenuated total reflection Fourier transform infrared (ATR-FTIR) spectroscopy, and atomic force microscopy (AFM). ATR-FTIR results demonstrated that hesperidin increases the fluidity of the DMPC/CHOL binary system. DSC findings indicated that the presence of 5 mol% hesperidin induces a broadening of the main phase transition consisting of three overlapping components. AFM experiments showed that hesperidin increases the thickness of DMPC/CHOL lipid bilayer model membranes. In addition to experimental results, molecular docking studies were conducted with hesperidin and human lanosterol synthase (LS), which is an enzyme found in the final step of cholesterol synthesis, to characterize hesperidin's interactions with its surrounding via its hydroxyl and oxygen groups. Then, hesperidin's ADME/Tox (absorption, distribution, metabolism, excretion and toxicity) profile was computed to see the potential impact on living system. In conclusion, considering the data obtained from experimental studies, this work ensures molecular insights in the interaction between a flavonoid, as an antioxidant drug model, and lipids mimicking those found in mammalian membranes. Moreover, computational studies demonstrated that hesperidin may be a great potential for use as a therapeutic agent for hypercholesterolemia due to its antioxidant property.

Bioconversion of lignocellulosic wastes to zwitterionic biosurfactants by an alkaliphilic bacterium: Process development and product characterization

The bioconversion of lignocellulosic wastes to value-added biosurfactants was investigated using a single flask to carry out both substrate pretreatment and biosurfactant production. Lignocellulosic wastes were added to an alkaline medium and autoclaved, which led to a combined alkaline and hydrothermal pretreatment. For biosurfactant production, alkaliphilic Brevibacterium casei NK8 was added to the medium without pH neutralization. Among several lignocellulosic wastes, the media with corn husk, coconut oil cake, and defatted rice bran gave the highest biosurfactant concentrations (1.14–1.32 g L−1). These wastes provided a relatively high concentration of soluble substrates in the pretreated liquid, while solid residues swelled. The bacterium could use the pretreated liquid and solid residues for growth and biosurfactant production. The produced biosurfactants in cell-free broth could be applied directly or after lignin removal. The residual lignin decreased biosurfactant performance in terms of surface tension, contact angle, and oil displacement; conversely, lignin enhanced the biosurfactant emulsification capacity. Cell-free broths with and without lignin were appropriate for different tasks. Biosurfactants synthesized from different lignocellulosic wastes were similar and were identified as a mixture of zwitterionic lipopeptides and phospholipids. The surface tension of the crude biosurfactant solution was extremely low, ranging between 25.9 and 27.6 mN m−1 over a wide range of pH values (1–11), salinities (2–10% NaCl), and temperatures (4–121 °C). In addition, biosurfactants as crude solution and cell-free broth with lignin showed lower phytotoxicity than the commercial surfactant Tween 80. These findings suggest a convenient method for manufacturing biosurfactants from lignocellulosic wastes.

Structure and Interaction of Ceramide-Containing Liposomes with Gold Nanoparticles as Characterized by SERS and Cryo-EM.

Due to the great potential of surface-enhanced Raman scattering (SERS) as local vibrational probe of lipid-nanostructure interaction in lipid bilayers, it is important to characterize these interactions in detail. The interpretation of SERS data of lipids in living cells requires an understanding of how the molecules interact with gold nanostructures and how intermolecular interactions influence the proximity and contact between lipids and nanoparticles. Ceramide, a sphingolipid that acts as important structural component and regulator of biological function, therefore of interest to probing, lacks a phosphocholine head group that is common to many lipids used in liposome models. SERS spectra of liposomes of a mixture of ceramide, phosphatidic acid, and phosphatidylcholine, as well as of pure ceramide and of the phospholipid mixture are reported. Distinct groups of SERS spectra represent varied contributions of the choline, sphingosine, and phosphate head groups and the structures of the acyl chains. Spectral bands related to the state of order of the membrane and moreover to the amide function of the sphingosine head groups indicate that the gold nanoparticles interact with molecules involved in different intermolecular relations. While cryogenic electron microscopy shows the formation of bilayer liposomes in all preparations, pure ceramide was found to also form supramolecular, concentric stacked and densely packed lamellar, nonliposomal structures. That the formation of such supramolecular assemblies supports the intermolecular interactions of ceramide is indicated by the SERS data. The unique spectral features that are assigned to the ceramide-containing lipid model systems here enable an identification of these molecules in biological systems and allow us to obtain information on their structure and interaction by SERS.

The Use of Sea Buckthorn Processing Products in the Creation of a Functional Biologically Active Food Emulsion.

The current trend in dietary supplements and functional foods is the use of lipophilic bioactive compounds. The sea buckthorn (Hippóphae rhamnoídes) contains some such compounds: polyunsaturated fatty acids, tocopherols, and carotenoids. Lipophilic components are best distributed using oil-in-water emulsions, which ensures their high bioavailability. A significant property of emulsions is colloidal and oxidative stability, so the choice of emulsifiers that have both surface-active properties and antioxidant activity is an important area of research for making new types of food emulsions. The purpose of this study is the development and refinement of an emulsified biologically active food additive containing sea buckthorn products (pulp, juice, and oil) and stabilized with soy phospholipids. We studied the fruits of Chuyskaya, Orange, and Prevoskhodnaya sea buckthorn varieties growing in the Altai Territory. As we analyzed their composition, we chose the Chuyskaya variety for making the emulsion. The fruits contain 5.30 ± 0.1% of lipids including 16.8 ± 0.5 mg/100 g of carotenoids and 10.5 ± 0.5 mg/100 g of tocopherols. To choose the emulsifier we studied the fractional and fatty acid composition of the soy and sunflower phospholipids with different hydrophilic-lipophilic balances (HLB). We made the emulsions containing sea buckthorn oil and pulp of its different layers, soybean oil, and phospholipids by dispersion using an HG-15D homogenizer. The study of the colloidal stability showed that the most stable (99.5%) are the emulsions containing a mixture of hydrolyzed soybean phospholipids (HLB = 7) and fractionated soybean phospholipids (HLB = 3). The best ratio is 40:60. We examined the oxidative stability of the emulsions by provoking accelerated oxidation. The emulsions containing 1.5% of a soy phospholipids mixture showed the best oxidative stability. The resulting direct oil-in-water fine emulsion contains polyunsaturated fatty acids (PUFAs), tocopherols, β-carotene, and essential phospholipids. For this reason, the emulsion can be used to make biologically active food supplements (also encapsulated) and as part of special nutrients.

Chemical Imaging of Lipid Segregation: Determining Different Length Scales of Heterogeneity with Compressive-Sensing Sum Frequency Generation Microscopy and Brewster Angle Microscopy

Membranes of various phospholipids may separate into different domains at micrometer length scales at the air-water interface. A significant challenge is to visualize the molecular organization and obtain chemical information on this surface. Langmuir-Blodgett monolayers of 1,2-distearoyl-sn-glycero-3-phosphocholine (DSPC) and 1,2-dilauroyl-sn-glycero-3-phosphocholine (DLPC) on fused silica were investigated with compressive sensing sum frequency generation (SFG) microscopy. Before and after mixing, SFG spectra for DSPC and DLPC revealed significant differences, indicating a structural change. Brewster angle microscopy images show phase separations that directly correlate the morphology of phospholipid mixtures with SFG images. Exploiting vibrational contrast in SFG images, exchange between the two phases was discovered, and quantitative thermodynamic analysis of lipid compositions in liquid-condensed and liquid-expanded (LE) phases was provided. Local SFG spectra reveal significant differences from one another, indicating the heterogeneity resulting from domain areas with distinct molecular orientation and conformation. Further heterogeneity across the domain boundary was presented on a finer scale, revealing an effect on DLPC due to the condensed phase DSPC, and the terminal methyl of DLPC perturbs the ordering of DSPC in the LE phase. This work demonstrates the heterogeneity of a two-dimensional binary lipid system mainly due to the aliphatic chain length and transition temperature difference.

Electrostatic interactions between single arginine and phospholipids modulate physiological properties of sarcoplasmic reticulum Ca2+-ATPase

Arg324 of sarcoplasmic reticulum Ca2+-ATPase forms electrostatic interactions with the phosphate moiety of phospholipids in most reaction states, and a hydrogen bond with Tyr122 in other states. Using site-directed mutagenesis, we explored the functional roles of Arg324 interactions, especially those with lipids, which at first glance might seem too weak to modulate the function of such a large membrane protein. The hydrogen bond forms transiently and facilitates Ca2+ binding from the cytoplasmic side. The contributions of the electrostatic interactions to the reaction steps were quantified using a rate vs activity coefficient plot. We found that the interaction between Arg324 and lipids decreases the affinity for luminal Ca2+. The transformation rate of the phosphoenzyme intermediate is facilitated by the electrostatic interactions, and the function of these interactions depends not only on the type but also on the composition of the phospholipids. The properties observed in microsomes could not be reproduced with any single phospholipid, but with a mixture of phospholipids that mimics the native membrane. These results suggest the importance of swapping of the lipid partners of different headgroups in the reaction step. This study shows that Arg324 plays a role in the reaction cycle via complex intra-protein and protein-lipid interactions.

Development of low-cost cage-like particles to formulate veterinary vaccines

Low-cost adjuvants are urgently needed for the development of veterinary vaccines able to trigger strong immune responses. In this work, we describe a method to obtain a low-cost cage-like particles (ISCOMATRIX-like) adjuvant useful to formulate veterinary vaccines candidates. The main components to form the particles are lipids and saponins, which were obtained from egg yolk by ethanolic extraction and by dialyzing a non-refined saponins extract, respectively. Lipids were fully characterized by thin layer chromatography (TLC) and gas-chromatography (GC) and enzymatic methods, and saponins were characterized by TLC, HPLC and MALDI-TOF. Cage-like particles were prepared with these components or with commercial inputs. Both particles and the traditional Alum used in veterinary vaccines were compared by immunizing mice with Ovalbumin (OVA) formulated with these adjuvants and assessing IgG1, IgG2a anti OVA antibodies and specific Delayed-type Hypersensitivity (DTH). In the yolk extract, a mixture of phospholipids, cholesterol and minor components of the extract (e.g. lyso-phospholipids) with suitable proportions to generate cage-like particles was obtained. Also, semi-purified saponins with similar features to those of the QuilA® were obtained. Cage-like particles prepared with these components have 40–50 nm and triggers similar levels of Anti-OVA IgG1 and DTH than with commercial inputs but higher specific-IgG2a. Both adjuvants largely increased the levels of IgG1, IgG2a and DTH in relation to the formulation with Alum. The methods described to extract lipids from egg yolk and saponins from non-refined extract allowed us to obtain an inexpensive and highly effective adjuvant.

Fullerene Nanoparticles Using Technol PG for Inexpensive Preparation

Fullerene has attracted much attention for applications in biomaterials because of its high antioxidant activity. In this study, C60 and C70 fullerenes were mixed with a commercially available anionic phospholipid mixture, Technol PG, and sodium cholate, resulting in effective dispersion of the fullerenes to give small-sized fullerene nanoparticles.

Homogeneous hybrid droplet interface bilayers assembled from binary mixtures of DPhPC phospholipids and PB-b-PEO diblock copolymers

Hybrid membranes built from phospholipids and amphiphilic block copolymers seek to capitalize on the benefits of both constituents for constructing biomimetic interfaces with improved performance. However, hybrid membranes have not been formed or studied using the droplet interface bilayer (DIB) method, an approach that offers advantages for revealing nanoscale changes in membrane structure and mechanics and offers a path toward assembling higher-order tissues. We report on hybrid droplet interface bilayers (hDIBs) formed in hexadecane from binary mixtures of synthetic diphytanoyl phosphatidylcholine (DPhPC) lipids and low molecular weight 1,2 polybutadiene-b-polyethylene oxide (PBPEO) amphiphilic block copolymers and use electrophysiology measurements and imaging to assess the effects of PBPEO in the membrane. This work reveals that hDIBs containing up to 15 mol% PBPEO plus DPhPC are homogeneously mixtures of lipids and polymers, remain highly resistive to ion transport, and are stable—including under applied voltage. Moreover, they exhibit hydrophobic thicknesses similar to DPhPC-only bilayers, but also have significantly lower values of membrane tension. These characteristics coincide with reduced energy of adhesion between droplets and the formation of alamethicin ion channels at significantly lower threshold voltages, demonstrating that even moderate amounts of amphiphilic block copolymers in a lipid bilayer provide a route for tuning the physical properties of a biomimetic membrane.

The E. coli outer membrane: what have we learned from molecular simulations?

Gram-negative bacteria have two membranes, the external environment-facing outer membrane and the cytoplasm-facing inner membrane. They differ in terms of both their lipidic and protein compositions. The inner membrane contains a mixture of phospholipids and proteins with transmembrane domains that are helical in architecture (single helices and multiple, in contrast the outer membrane contains beta barrel (monomers or multimers) proteins and phospholipids in the inner leaflet and lipopolysaccharide in the outer leaflet.

Hydrophobic Chitosan Nanoparticles Loaded with Carvacrol against Pseudomonas aeruginosa Biofilms.

Pseudomonas aeruginosa infections have become more challenging to treat and eradicate due to their ability to form biofilms. This study aimed to produce hydrophobic nanoparticles by grafting 11-carbon and three-carbon alkyl chains to a chitosan polymer as a platform to carry and deliver carvacrol for improving its antibacterial and antibiofilm properties. Carvacrol–chitosan nanoparticles showed ζ potential values of 10.5–14.4 mV, a size of 140.3–166.6 nm, and an encapsulation efficiency of 25.1–68.8%. Hydrophobic nanoparticles reduced 46–53% of the biomass and viable cells (7–25%) within P. aeruginosa biofilms. Diffusion of nanoparticles through the bacterial biofilm showed a higher penetration of nanoparticles created with 11-carbon chain chitosan than those formulated with unmodified chitosan. The interaction of nanoparticles with a 50:50 w/w phospholipid mixture at the air–water interface was studied, and values suggested that viscoelasticity and fluidity properties were modified. The modified nanoparticles significantly reduced viable P. aeruginosa in biofilms (0.078–2.0 log CFU·cm−2) and swarming motility (40–60%). Furthermore, the formulated nanoparticles reduced the quorum sensing in Chromobacterium violaceum. This study revealed that modifying the chitosan polarity to synthesize more hydrophobic nanoparticles could be an effective treatment against P. aeruginosa biofilms to decrease its virulence and pathogenicity, mainly by increasing their ability to interact with the membrane phospholipids and penetrate preformed biofilms.

Membrane model as key tool in the study of glutathione-s-transferase mediated anticancer drug resistance

Glutathione-s-transferase is believed to be involved in the resistance to chemotherapeutic drugs, which depends on the interaction with the cell membranes. In this study, we employed Langmuir monolayers of a mixture of phospholipids and cholesterol (MIX) as models for tumor cell membranes and investigated their interaction with the anticancer drugs cisplatin (CDDP) and doxorubicin (DOX). We found that both DOX and CDDP expand and affect the elasticity of MIX monolayers, but these effects are hindered when glutathione-s-transferase (GST) and its cofactor glutathione (GSH) are incorporated. Changes are induced by DOX or CDDP on the polarization-modulated infrared reflection absorption spectroscopy (PM-IRRAS) data for MIX/GST/GSH monolayers, thus denoting some degree of interaction that is not sufficient to alter the monolayer mechanical properties. Overall, the results presented here give support to the hypothesis of the inactivation of DOX and CDDP by GST and point to possible directions to detect and fight drug resistance.

Reconstitution of Membrane-associated Components of a G-protein Signaling Pathway on Membrane-coated Nanoparticles (Lipobeads).

G-protein coupled signaling pathways are organized into multi-protein complexes called signalosomes that are located within and on cellular membranes. We describe the use of silica nanoparticles coated with a unilamellar phospholipid bilayer (lipobeads) to reconstitute the activated photoreceptor G-protein α-subunit (Gtα*) with its cognate effector (phosphodiesterase-6; PDE6) for biochemical and structural studies of the activation mechanism regulating this GPCR signaling pathway. Lipobeads are prepared by resuspending dried-down phospholipid mixtures with monodisperse 70 nm silica particles, followed by extrusion through a 100 nm membrane filter. This uniform and supported liposomal preparation is easily sedimented, permitting the separation of soluble from membrane-associated proteins. Upon loading lipobeads with Gtα* and PDE6, we find that activation of PDE6 catalysis by Gtα* occurs much more efficiently than in the absence of membranes. Chemical cross-linking of membrane-confined proteins allows detection of changes in protein-protein interactions, resulting from G-protein activation of PDE6. The advantages of using lipobeads over partially purified membrane preparations or traditional liposomal preparations are generally applicable to the study of other membrane-confined signal transduction pathways.

Assessment of Amentoflavone Loaded Sub-Micron Particle Preparation using Supercritical Antisolvent for its Antitumor Activity.

The amentoflavone (AMF) loaded polymeric sub-micron particles were prepared using supercritical antisolvent (SAS) technology with the aim of improving the anticancer activity of AMF. Zein and phospholipid mixtures composed of Hydrogenated Phosphatidylcholine (HPC) and egg lecithin (EPC) were used as carrier materials and, the effects of carrier composition on the product morphology and drug release behavior were investigated. When the mass ratio of Zein/HPC/ EPC was 7/2/1, the AMF loaded particles were spherical shape and sub-micron sized around 400 nm, with a drug load of 4.3±0.3 w% and entrapment efficacy of 87.8±1.8%. The in vitro drug release assay showed that adding EPC in the wall materials could improve the dispersion stability of the released AMF in an aqueous medium, and the introduction of HPC could accelerate the drug release speed. MTT assay demonstrated that AMF-loaded micron particles have an improved inhibitory effect on A375 cells, whose IC50 was 37.39μg/ml, compared with that of free AMF(130.2μg/ml). It proved that the AMF loaded sub-micron particles prepared by SAS were a prospective strategy to improve the antitumor activity of AMF, and possibly promote the clinical use of AMF preparations.

Dynamic response on a nanometer scale of binary phospholipid-cholesterol vesicles: Low-frequency Raman scattering insight.

Low-frequency Raman spectroscopy was used to study the dynamic response on a nanometer scale of aqueous suspensions of two-component lipid vesicles. Binary mixtures of saturated phospholipid (1,2-dipalmitoyl-sn-glycero-3-phosphocholine, DPPC) and cholesterol are interesting for possible coexistence of solidlike and liquid-ordered phases, while the phase coexistence was not reported for unsaturated phospholipid (1,2-dioleoyl-sn-glycero-3-phosphocholine, DOPC) and cholesterol mixtures. The DOPC-DPPC mixtures represent the well-documented case of coexisting domains of solidlike and liquid-disordered phases. These three series of lipid mixtures are studied here. A broad peak with the maximum in the range of 30-50cm^{-1} and a narrow peak near 10cm^{-1} are observed in the Raman susceptibility of the binary mixtures and attributed to the acousticlike vibrational density of states and layer modes, respectively. Parameters of the broad and narrow peaks are sensitive to lateral and conformational hydrocarbon chain ordering. It was also demonstrated that the low-frequency Raman susceptibility of multicomponent lipid bilayers allows one to determine the phase state of lipid bilayers and distinguish the homogeneous distribution of molecular complexes from coexisting domains with sizes above several nanometers. Thus, the low-frequency Raman spectroscopy provides unique information in studying phase coexistence in lipid bilayers.