Raman studies of lipid interactions at the bilayer interface: phosphatidyl choline--cholesterol

Unravelling the success of transferosomes against skin cancer: Journey so far and road ahead

Skin cancer remains one of the most prominent types of cancer. Melanoma and non-melanoma skin cancer are commonly found together, with melanoma being the more deadly type. Skin cancer can be effectively treated with chemotherapy, which mostly uses small molecular medicines, phytoceuticals, and biomacromolecules. Topical delivery of these therapeutics is a non-invasive way that might be useful in effectively managing skin cancer. Different skin barriers, however, presented a major obstacle to topical cargo administration. Transferosomes have demonstrated significant potential in topical delivery by improving cargo penetration through the circumvention of diverse skin barriers. Additionally, the transferosome-based gel can prolong the residence of drug on the skin, lowering the frequency of doses and their associated side effects. However, the choice of appropriate transferosome compositions, such as phospholipids and edge activators, and fabrication technique are crucial for achieving improved entrapment efficiency, penetration, and regulated particle size. The present review discusses skin cancer overview, current treatment strategies for skin cancer and their drawbacks. Topical drug delivery against skin cancer is also covered, along with the difficulties associated with it and the importance of transferosomes in avoiding these difficulties. Additionally, a summary of transferosome compositions and fabrication methods is provided. Furthermore, topical delivery of small molecular drugs, phytoceuticals, and biomacromolecules using transferosomes and transferosomes-based gel in treating skin cancer is discussed. Thus, transferosomes can be a significant option in the topical delivery of drugs to manage skin cancer efficiently.

Structural dynamics of chlorpromazine (CPZ) drug with dipalmitoylphosphatidylcholine (DPPC) lipid: a potential drug for SARS-CoV-2

There is an urgent requirement for drug discovery and more importantly drug repositioning due to infectious new Severe Acute Respiratory Syndrome coronavirus 2. As per the recent report published in the journal L'Encéphale in May 2020, there is a planned ReCoVery Study examining the repurposing the chlorpromazine for the treatment of COVID-19. Here, we apply a combined Raman microspectroscopy and DFT-MD approach to investigate the structural dynamics of the Chlorpromazine (CPZ) drug with dipalmitoylphosphatidylcholine (DPPC) lipid bilayer, identifying the specific position of the drug in the DPPC lipid bilayer. The intensity ratios of the Raman peaks I2935/I2880, I1097/I1064 and I1097/I1129 are representative of the interaction of drugs with lipid alkyl chains and furnish conformation of lipid alkyl chains. Raman imaging microscopy for the study of the distribution of CPZ inside the lipid vesicles is reported. We also investigated the influence of order and disorder ratio in the CPZ on the DPPC liposomes prepared on phase transition temperature. HIGHLIGHTSDrug-membrane interactions using micromolar concentrations of both lipid and drugs.Neuroleptic drug and DPPC vesicles composed of DPPC/drug mixtures reveal qualitative differences between the Raman spectraThe temperature-controlled Raman microspectroscopic study has demonstrated that below phase-transition temperature, the fatty acid chains of the phospholipids are stiff and packed in a highly ordered array.DFT and MD simulations to understand molecular interactions, structural dynamics, and Raman spectra.Above phase-transition temperature, the chains are disordered and possess more motional freedom. Communicated by Ramaswamy H. Sarma.

A manual and an automatic TERS based virus discrimination

Rapid techniques for virus identification are more relevant today than ever. Conventional virus detection and identification strategies generally rest upon various microbiological methods and genomic approaches, which are not suited for the analysis of single virus particles. In contrast, the highly sensitive spectroscopic technique tip-enhanced Raman spectroscopy (TERS) allows the characterisation of biological nano-structures like virions on a single-particle level. In this study, the feasibility of TERS in combination with chemometrics to discriminate two pathogenic viruses, Varicella-zoster virus (VZV) and Porcine teschovirus (PTV), was investigated. In a first step, chemometric methods transformed the spectral data in such a way that a rapid visual discrimination of the two examined viruses was enabled. In a further step, these methods were utilised to perform an automatic quality rating of the measured spectra. Spectra that passed this test were eventually used to calculate a classification model, through which a successful discrimination of the two viral species based on TERS spectra of single virus particles was also realised with a classification accuracy of 91%.

Understanding sterol-membrane interactions, part II: complete 1H and 13C assignments by solid-state NMR spectroscopy and determination of the hydrogen-bonding partners of cholesterol in a lipid bilayer

The complete assignment of cholesterol 1H and 13C NMR resonances in a lipid bilayer environment (Lalpha-dimyristoylphosphatidylcholine/cholesterol 2:1) has been obtained by a combination of 1D and 2D MAS NMR experiments: 13C spectral editing, ge-HSQC, dipolar HETCOR and J-based HETCOR. Specific chemical shift variations have been observed for the C1-C6 atoms of cholesterol measured in CCl4 solution and in the membrane. Based on previous work (F. Jolibois, O. Soubias, V. Reat, A. Milon, Chem. Eur. J. 2004, 10, preceding paper in this issue: DOI: 10.1002/chem.200400245) these variations were attributed to local changes around the cholesterol hydroxy group, such as the three major rotameric states of the C3-O3 bond and different hydrogen bonding partners (water molecules, carboxy and phosphodiester groups of phosphatidylcholine). Comparison of the experimental and theoretical chemical shifts obtained from quantum-chemistry calculations of various transient molecular complexes has allowed the distributions of hydrogen bonding partners and hydroxy rotameric states to be determined. This is the first time that the probability of hydrogen bonding occurring between cholesterol's hydroxy group and phosphatidylcholine's phosphodiester has been determined experimentally.

Interactions between cholesterol and lipids in bilayer membranes. Role of lipid headgroup and hydrocarbon chain-backbone linkage

We have employed four lipids in the present study, of which two are cationic and two bear phosphatidylcholine (PC) headgroups. Unlike dipalmitoylphosphatidylcholine, the other lipids employed herein do not have any ester linkage between the hydrocarbon chains and the respective lipid backbones. Small unilamellar vesicles formed from each of the PC and cationic lipids with or without varying amounts of cholesterol have been examined using the steady-state fluorescence anisotropy method as a function of temperature. The anisotropy data clearly indicate that the order in the lipid bilayer packing is strongly affected upon inclusion of cholesterol. This effect is similar irrespective of the electrostatic character of the lipid employed. The influence of cholesterol inclusion on multi-lamellar lipid dispersions has also been examined by 1H-nuclear magnetic resonance spectroscopy above the phase transition temperatures. With all the lipids, the line widths of (CH2)n protons of hydrocarbon chains in the NMR spectra respond to the addition of cholesterol to membranes. The influence on the bilayer widths of various lipids upon inclusion of cholesterol was determined from X-ray diffraction studies of the cast films of the lipid-cholesterol coaggregates in water. The effect of cholesterol on the efflux rates of entrapped carboxyfluorescein (CF) from the phospholipid vesicles was determined. Upon incremental incorporation of cholesterol into the phospholipid vesicles, the CF leakage rates were progressively reduced. Independent experiments measuring transmembrane OH- ion permeation rates from cholesterol-doped cationic lipid vesicles using entrapped dye riboflavin also demonstrated that the addition of cholesterol into the cationic lipid vesicles reduced the leakage rates irrespective of lipid molecular structure. It was found that the cholesterol induced changes on the membrane properties such as lipid order, linewidth broadening, efflux rates, bilayer widths, etc., did not depend on the ability of the lipids to participate in the hydrogen bonding interactions with the 3beta-OH of cholesterol. These findings emphasize the importance of hydrophobic interaction between lipid and cholesterol and demonstrate that it is not necessary to explain the observed cholesterol induced effects on the basis of the presence of hydrogen bonding between the 3beta-OH of cholesterol and the lipid chain-backbone linkage region or headgroup region.

Cholesterol effects on the phosphatidylcholine bilayer polar region: a molecular simulation study

A molecular dynamics (MD) simulation of a fully hydrated, liquid-crystalline dimyristoylphosphatidylcholine (DMPC)-Chol bilayer membrane containing approximately 22 mol% Chol was carried out for 4.3 ns. The bilayer reached thermal equilibrium after 2.3 ns of MD simulation. A 2.0-ns trajectory generated during 2.3-4.3 ns of MD simulation was used for analyses to determine the effects of Chol on the membrane/water interfacial region. In this region, 70% of Chol molecules are linked to DMPC molecules via short-distance interactions, where the Chol hydroxyl group (OH-Chol) is 1) charge paired to methyl groups of the DMPC choline moiety ( approximately 34%), via the hydroxyl oxygen atom (Och); 2) water bridged to carbonyl ( approximately 19%) and nonester phosphate ( approximately 14%) oxygen atoms, via both Och and the hydroxyl hydrogen atom (Hch); and 3) directly hydrogen (H) bonded to carbonyl ( approximately 11%) and nonester phosphate ( approximately 5%) oxygen atoms, via Hch ( approximately 17% of DMPC-Chol links are multiple). DMPC's gamma-chain carbonyl oxygen atom is involved in 44% of water bridges and 51% of direct H bonds formed between DMPC and Chol. On average, a Chol molecule forms 0.9 links with DMPC molecules, while a DMPC molecule forms 2.2 and 0.3 links with DMPC and Chol molecules, respectively. OH-Chol makes hydrogen bonds with 1.1 water molecules, preferentially via Hch. The average number of water molecules H bonded to the DMPC headgroup is increased by 7% in the presence of Chol. These results indicate that inclusion of Chol decreases interlipid links and increases hydration in the polar region of the membrane.

Lipid composition, membrane structure relationships in lens and muscle sarcoplasmic reticulum membranes

Membrane lipid composition varies in different tissues and species. Since a defined lipid composition is essential to the function of many membranes, the relationship between membrane lipid composition and structure was determined using infrared and Raman spectroscopy in four membranes containing a calcium pump: rabbit fast and slow twitch muscle sarcoplasmic reticulum and human and bovine lens fiber cell membranes. We found that membrane sphingolipid and phosphatidylcholine content were correlated to a decrease and increase, respectively, in the infrared lipid CH2 symmetric stretching band frequency. We interpret the change in frequency as a change in lipid hydrocarbon chain structural order. This was confirmed by Raman order parameters. The high degree of hydrocarbon chain saturation found in the variable amide chains of sphingolipids is likely to account for this correlation. Lipid phase transition temperature and cooperativity also correlated to sphingolipid and phosphatidylcholine content, and are the forces defining the order in at physiological temperature in the samples studied. Ca(2+)-ATPase caused an increase in the CH2 symmetric stretching frequency in fast twitch muscle sarcoplasmic reticulum (interpreted as an increase in hydrocarbon chain disorder), but had no effect on slow twitch muscle sarcoplasmic reticulum lipid hydrocarbon chain structure. In the natural systems studied, we find that it is the lipid hydrocarbon chain saturation that defines lipid hydrocarbon chain order.

Ether lipids in biomembranes

Plasmalogens (1-O-1'-alkenyl-2-acylglycerophospholipids) and to a lesser extent the 1-O-alkyl analogs are ubiquitous and in some cases major constituents of mammalian cellular membranes and of anaerobic bacteria. In archaebacteria polar lipids of the cell envelope are either diphytanylglycerolipids or bipolar macrocyclic tetraether lipids capable of forming covalently linked 'bilayers'. Information on the possible role of ether lipids as membrane constituents has been obtained from studies on the biophysical properties of model membranes consisting of these lipids. In addition, effects of modified ether lipid content on properties of biological membranes have been investigated using microorganisms or mammalian cells which carry genetic defects in ether lipid biosynthesis. Differential utilization of ether glycerophospholipids by specific phospholipases might play a role in the generation of lipid mediators that are involved in signal transduction. A possible function of plasmalogens as antioxidants has been demonstrated with cultured cells and might play a role in serum lipoproteins. Synthetic ether lipid analogs exert cytostatic effects, most likely by interfering with membrane structure and by specific interaction with components of signal transmission pathways, such as phospholipase C and protein kinase C.

Raman structural characterization of clear human lens lipid membranes

Raman spectroscopy was used for the first time to characterize the structure of lipid membranes prepared from the nuclear and cortical regions of 48 and 69 year old clear human lenses. The interface region carbonyl band appears as a doublet at 1742 and 1728 cm-1. The lower frequency band is characteristic of a hydrogen bonded carbonyl group, perhaps to bilayer water. From the intensity of the curve fit bands, we calculate that 43% of the carbonyl groups are hydrogen bonded. Our data show that the hydrocarbon chains of the nuclear lipids are 1.4 times more saturated than those of the cortical lipids. The molar ratio of phospholipid CH2/= C-H groups was calculated to be 13 and 18 for cortical and nuclear lipids, respectively. Hydrocarbon chain disorder was estimated to be 72 and 58% (+/- 8% disorder) for the cortical and the nuclear lipids, respectively. Raman spectroscopy is sensitive to structural differences in various regions of the lipid bilayer and could be an effective tool to explore lipid and protein interactions in terms of lens region, age and opacity.

Interaction of 7,7,8,8-tetracyanoquinodimethane with diacylphosphatidylcholines and -phosphatidylglycerols. A photoacoustic Fourier transform infrared study

7,7,8,8-Tetracyanoquinodimethane (TCNQ) was incorporated in fully hydrated liposomes of the following pyrene-containing as well as non-labelled phospholipids: 1-palmitoyl-2-[10-(pyren-1-yl)decanoyl]-sn-glycero-3-phosphatid ylc holine (PPDPC), 1-palmitoyl-2-[10-(pyren-1-yl)decanoyl]-sn-glycero-3-phosphatidyl- rac'- glycerol (rac'-PPDPG), 1-palmitoyl-2-[10-(pyren-1-yl)decanoyl]-sn-glycero-3-phosphatidyl- sn-3'- glycerol (3'-PPDPG), 1-[10-(pyren-1-yl)decanoyl]-2-palmitoyl-sn-glycero-3-phosphatidyl- sn-3'- glycerol (3'-PDPPG), 1-[10-pyren-1-yl)decanoyl]-2-palmitoyl-sn-glycero-3-phosphatidyl-s n-1'- glycerol (1'-PDPPG), 1,2-dipalmitoyl-sn-glycero-3-phosphatidylcholine (DPPC) and 1,2-dipalmitoyl-sn-glycero-3-phosphatidyl-rac'-glycerol (rac'-DPPG). Lyophilized charge-transfer (CT) complexes of TCNQ with phospholipids were examined by Fourier transform infrared photoacoustic spectroscopy (FTIR-PAS). Due to the spectral changes observed in the vibrational bands originating from the CH2 and C = O stretching vibrations, and the bands associated with the polar headgroup of the phospholipids it is evident that TCNQ has only a minor perturbing effect on the hydrocarbon chains. However, the molecular interaction between TCNQ and phospholipids is seen in the polar headgroup region. The donated electrons are most likely located on the oxygens of the phosphate group in the polar head. As judged from the present infrared data interactions of TCNQ with phosphatidylcholines (PC) and phosphatidylglycerols (PG) differ. For PG the complex formation produces a second strong C = O stretching band at approx. 1710 cm-1 in addition to the band at approx. 1735 cm-1 indicating a specific molecular interaction in the interfacial region.

Hydrogen bonding between anhydrous cholesterol and phosphatidylcholines: an infrared spectroscopic study

Fourier transform infrared spectroscopy performed with a high pressure diamond anvil cell was used to study hydrogen bonding between anhydrous phosphatidylcholines and cholesterol at the molar ratio 4:1. The hydroxyl group of cholesterol which acts as a proton donor, engages in strong hydrogen bonding to the sn-2 chain carbonyl group of DMPC, DPPC and HPPC and in weak hydrogen bonding to the phosphate group of all these phospholipids. No evidence of hydrogen bonding between cholesterol and the sn-1 chain carbonyl group of DMPC and DPPC was found. From a comparison of the relative hydrogen-bond strengths between cholesterol or water and the sn-2 chain carbonyl and phosphate groups of all these phospholipids, it is predicted that in aqueous dispersions of cholesterol containing phospholipids, the hydrogen bond of cholesterol to the phosphate group would be replaced by that of water, while the hydrogen bond of cholesterol to the sn-2 chain carbonyl group would remain intact.

Cholesterol and the cell membrane

Recent studies concerning cholesterol, its behavior and its roles in cell growth provide important new clues to the role of this fascinating molecule in normal and pathological states.

Influence of cholesterol on bilayers of ester- and ether-linked phospholipids. Permeability and 13C-nuclear magnetic resonance measurements

13C-NMR and permeability studies are described for sonicated vesicles of phosphatidylcholines bearing two 16-carbon saturated hydrocarbon chains with (a) one ether linkage at carbon 1 (3) or 2 of glycerol and one ester linkage at carbon 2 or 1 (3) of glycerol; (b) two ether linkages and (c) two ester linkages at carbons 1 (3) and 2 of glycerol. The results of 13C-NMR relaxation enhancement measurements using cholesterol enriched with 13C at the 4 position indicate that no significant relocation of the cholesterol molecules takes place in the bilayer when a methylene group is substituted for a carbonyl group in phosphatidylcholine. The 4-13C atom of cholesterol undergoes similar fast anisotropic motions in diester- and diether -phosphatidylcholine bilayers, as judged by spin-lattice relaxation time measurements in the liquid-crystalline phase; although the fast motions are unaltered, linewidth and spin-spin relaxation time measurements suggested some restriction of the slow motions of cholesterol molecules in bilayers from phosphatidylcholines containing an O-alkyl linkage at the sn-2 position instead of an acyl linkage. At temperatures above the gel to liquid-crystal phase transition, the kinetics of ionophore A23187-mediated 45Ca2+ efflux from vesicles prepared from each type of phosphatidylcholine molecule were the same; the kinetics of spontaneous carboxyfluorescein diffusion from diester- and diether -phosphatidylcholine vesicles were the same, whereas mixed ether/ester phosphatidylcholine molecules gave bilayers which are less permeable. The rate constants were reduced on cholesterol incorporation into the bilayers of each type of phosphatidylcholine molecule. The reductions were not statistically significant for 45Ca2+ release. The rate constants for carboxyfluorescein release were also reduced by cholesterol to the same extent in vesicles from diester-, diether -, and 1-ether, and 1-ether-2-ester-phosphatidylcholines; however, a smaller reduction was noted in bilayers from the 1-ester-2-ether analog. The results provide further evidence that there are no highly specific requirements for ester or ether linkages in phosphatidylcholine for cholesterol to reduce bilayer permeability. This is a reflection of the fact that in both diester- and diether -phosphatidylcholine bilayers, the 4-13C atom of cholesterol is located in the region of the acyl carboxyl group or the glyceryl ether oxygen atom.

Cholesterol-phospholipid interaction in membranes. 2. Stoichiometry and molecular packing of cholesterol-rich domains

A model for the molecular interaction between cholesterol and phospholipid in bilayer membranes is presented. We propose that cholesterol forms associations with phospholipids with stoichiometries of both 1:1 and 1:2. A hydrogen bond between the beta-OH of cholesterol and the glycerol ester oxygen of a phospholipid is suggested as a likely mechanism for tight binding in a 1:1 complex. A second phospholipid molecule is loosely associated with the complex to form domains of 1:2 stoichiometry, which may coexist with pure phospholipid domains. Interfacial boundary phospholipid separates these two domains. Under conditions in which interfacial phospholipid is maximal, the perturbed phospholipid assumes a composition of 20 mol % cholesterol. To account for the phase behavior and surface properties of cholesterol-lipid membranes, we propose a molecular packing model for linear arrays within the cholesterol-rich domains. In this arrangement, two rows of 1:1 complex run antiparallel with loosely associated phospholipid intercalated between them. The loosely associated phospholipid can pack in the nearly hexagonal manner in which pure crystalline phospholipid is known to pack. The model provides maximal van der Waals contact in the hydrocarbon region of the bilayer and can maintain phospholipids as cholesterol's nearest neighbors at all concentrations up to 50 mol % cholesterol. The model is compatible with the diverse experimental observations compiled by many investigators over the past decade.

Raman scattering in bilayers of saturated phosphatidylcholines and cholesterol. Experiment and theory

Raman spectroscopy has been applied to a model biomembrane structure in order to obtain information about the effect of cholesterol upon phospholipid hydrocarbon chain ordering. The intensity of the 1130-cm-1 Raman line obtained from a dipalmitoylphosphatidylcholine (DPPC) coarse aqueous dispersion was measured as a function of temperature for two concentrations, c, of cholesterol: c=0.15 and c = 0.35. The contribution of cholesterol to this line was deduced. Intensities of all lines were taken as peak areas. By use of a theory for assigning raman intensities to chain conformations as well as a model of lipid bilayers containing cholesterol, the temperature and concentration dependence of the 1130-cm-1 line was calculated. Good agreement with DPPC experimental data was obtained, and predictions are made for dimyristoylphosphatidylcholine. The experimental results are interpreted in terms of a DPPC-cholesterol phase diagram and the average number of gauche bonds per DPPC molecule.

ACTH stimulation on cholesterol side chain cleavage activity of adrenocortical mitochondria. Transfer of the stimulus from plasma membrane to mitochondria

Adrenocortical mitochondrial cholesterol side chain cleavage reactions are regulated by the influence of pituitary ACTH. The mechanism of the stimulation involves adenyl cyclase, cAMP-dependent protein kinase, cholesterol esterase, and ribosomal labile protein synthesis. Through these reactions the stimulus reaches the mitochondrial side chain cleavage enzyme system. In this review article, the current implications on the stimulus transfer from the plasma membrane to the mitochondrial inner membrane are summarized. In particular the availability of cholesterol to P-450scc was discussed in terms of the distribution of cholesterol molecules in the membranes.