DPPC Model Membranes Research Articles

Understanding the Transepithelial Transport and Transbilayer Diffusion of the Antihypertensive Peptide Asn-Cys-Trp: Insights from Caco-2 Cell Monolayers and the DPPC Model Membrane.

Understanding the transport mechanism of the peptide Asn-Cys-Trp (NCW) is crucial to improving its intestinal absorption and bioavailability. This study investigated the absorption of NCW through Caco-2 cell monolayers and its interaction with the DPPC bilayers. Results revealed that after a 3 h incubation, the Papp (AP-BL) and Papp (BL-AP) values of NCW at a concentration of 5 mmol/L were (22.24 ± 4.52) × 10-7 and (6.63 ± 2.31) × 10-7 cm/s, respectively, with the transport rates of 1.59 ± 0.32 and 0.62 ± 0.20%, indicating its moderate absorption. NCW was found to be transported via PepT1 and paracellular transport pathways, as evidenced by the significant impact of Gly-Pro and cytochalasin D on the Papp values. Moreover, NCW upregulated ZO-1 mRNA expression. Further investigation of the ZO-1-mediated interaction between NCW and tight junction proteins will contribute to a better understanding of the paracellular transport mechanism of NCW. The interaction between NCW and the DPPC bilayers was predominantly driven by entropy. NCW permeated the bilayers through electrostatic, hydrogen bonding, and hydrophobic interactions, resulting in increased fluidity, flexibility, and disorder as well as phase transition and phase separation of the bilayers.

The investigation of the interaction of Armodafinil with membrane lipids by using DPPC model membrane system

The investigation of the interaction of Armodafinil with membrane lipids by using DPPC model membrane system

Interaction of Phenylalanine with DPPC Model Membranes: More Than a Hydrophobic Interaction.

The negative free energy previously reported is explained by the stabilization of a PC-Phe (phosphocholine-phenylalanine) complex in the presence of water shown by the decrease in the symmetric stretching frequency of the phosphate group of the lipid (PO2(-)). An entropic contribution due to the disruption of the water network around the phenyl and in the membrane defect may be invoked. The dipole potential decrease is explained by the orientation of the carboxylate opposing to the CO of the lipids with oxygen moiety toward the low hydrated hydrocarbon core. The symmetric bending frequency of NH3(+) group of Phe, decreases in 5.2 cm(-1) in relation to water congruent with zeta potential shift to positive values. The Phe to DPPC dissociation constant is Kd = 2.23 ± 0.09 mM, from which the free energy change is about -4.54 kcal/mol at 25 °C. This may be due to hydrophobic contributions and two hydrogen bonds.

Effects of oxyethylated glycerol cryoprotectants on phase transitions of DPPC model membranes

Effects of oxyethylated glycerol cryoprotectants on phase transitions of DPPC model membranes

The Interaction of Resveratrol with DPPC Bilayers - a Biophysical Contribution on the Mediterranean Diet

Resveratrol, contained in the skin of grape and accordingly in red wine, exhibits a wide range of health effects such as cardioprotection and anti-oxidation. Biophysical studies on the unspecific interaction of resveratrol with lipid membranes are rare so far. Here we present results from a series of investigations on the interaction of resveratrol with DPPC model membranes, combining structural (neutron reflectometry) and thermodynamic methods (measurement of partition coefficient, Langmuir isotherm and differential scanning calorimetry (DSC)).The details of the partitioning and the neutron experiments report on the localization of resveratrol within the membrane headgroup layer, close to the interface between the hydrophilic headgroup region and the hydrophobic core. Its presence decreases the tilt angle of the headgroups with respect to the membrane surface normal, as compared to the control (pure DPPC). At the same time, the projected area per headgroup drops, and the bilayer is more condensed.The analysis of the thermograms confirms these findings. DSC measurements on SUVs of pure DPPC (0.05°C/min) exhibit a complex characteristics of the main transition, revealing three peaks. We attribute them to a contribution of the headgroups and a bending dependent contribution of the chains, different for the two leaflets. With resveratrol, the headgroup transition exhibits a freezing point depression together with a loss in cooperativity. The chain condensation makes the corresponding transition more uniform. We conjecture a compensating effect of resveratrol: extrusion allows for an asymmetric distribution among the two leaflets that partially counteracts the curvature induced packing gradient in the core region.The findings in summary yield a more comprehensive view on the passive impact of resveratrol in model membranes that will hopefully contribute to a better understanding of the biophysical mechanisms behind the Mediterranean diet.

Melatonin Counteracts Cholesterol's Effects on Lipid Membrane Structure

The cell membrane plays an important role in amyloid toxicity in relation to Alzheimer's disease. The membrane's composition and the inclusion of small molecules, such as melatonin and cholesterol, may alter the membrane's structure and physical properties, affecting its interaction with amyloid peptides. Both melatonin and cholesterol have been linked to amyloid toxicity. Melatonin has been shown to have a protective role against amyloid toxicity, while the underlying molecular mechanism of this protection is still not well understood. Here we have studied the non-specific interaction of melatonin and cholesterol with a model lipid membrane. We used small-angle neutron diffraction (SAND) from oriented lipid multilayers and small-angle neutron scattering (SANS) from unilamellar vesicles experiments to elucidate the structure of DOPC and DPPC model membrane in order to determine the effects of melatonin and cholesterol. From the present study we conclude that cholesterol and melatonin affect the lipid membrane differentially. Specifically, the incorporation of melatonin results in membrane thinning, in stark contrast to the increase in membrane thickness induced by cholesterol. This very different response of membrane thickness to cholesterol and melatonin may help to understand their relation to amyloid toxicity.

Polymer-capped magnetite nanoparticles change the 2D structure of DPPC model membranes

The interaction of biocompatible and stimuli-responsive Fe3O4 nanoparticles (NPs) with DPPC model membranes was studied at the air–water interface. The pure NPs, pure DPPC and mixed DPPC–NP Langmuir layers have been characterized in situ by compression–expansion isotherms, infrared reflection–absorption spectrometry (IRRAS), grazing incidence X-ray diffraction (GIXD), total reflection X-ray fluorescence (TRXF), Brewster angle microscopy, and by atomic force microscopy after transfer onto a solid support. When dispersed in aqueous solution, the NPs are able to penetrate the phospholipid monolayer and to occupy a certain part of the interface defined by their own surface activity. The study reveals a largely phase separated system which actually masks an important interplay between the two compounds. Detailed GIXD measurements prove that the NPs are able to change the DPPC monolayer structure in a highly cooperative way by inducing a tighter in-plane packing. As IRRAS additionally supports, the effective size of the phospholipid polar head group is reduced due to partial dehydration and reorientation. The most surprising observation is the rigidification of the DPPC–NPs composite in a large range of surface pressures. Above the critical pressure, the phase separated NPs are squeezed out but the ones interacting with the DPPC molecules stay in the layer up to much higher lateral pressures. The interactions between NPs and DPPC stabilize the NPs at the interface. Only at very high pressures, all NPs are squeezed out. The amount of NPs in the monolayer has been quantified by TRXF. The desorption process is kinetically hindered.

Interaction of quercetin with DPPC model membrane Molecular dynamic simulation, DSC and multinuclear NMR studies

Interaction of quercetin with DPPC model membrane Molecular dynamic simulation, DSC and multinuclear NMR studies

Membrane Interactions and Conformational Preferences of Human and Avian Prion N-Terminal Tandem Repeats: The Role of Copper(II) Ions, pH, and Membrane Mimicking Environments

The flexible N-terminal domain of the prion protein (PrP(c)) is believed to play a pivotal role in both trafficking of the protein through the cell membrane and its pathogenic conversion into the β sheet-rich scrapie isoform (PrP(sc)). Unlike mammalian PrP(c), avian prion proteins are not known to undergo any pathogenic conformational conversions. Consequently, some critical advances in our understanding of the molecular mechanisms underlying prion pathogenesis are expected from comparative studies of the biophysical properties of the N-terminal domains of the two proteins. The present study addresses the role played by different environmental factors, i.e., copper(II), pH, and membrane-mimicking environments, in assisting the conformational preferences of huPrP60-91 and chPrP53-76, two soluble peptides encompassing the N-terminal copper(II) binding domains of the human and chicken prion proteins, respectively. Moreover, the membrane interactions of huPrP60-91, chPrP53-76, and their copper(II) complexes were evaluated by Trp fluorescence in conjunction with measurements of the variation in thermotropic properties of 1,2-dipalmitoyl-sn-glycero-3-phosphocholine (DPPC) unilamellar vesicles. Circular dichroism experiments revealed that huPrP60-91 adopts a predominant polyproline II conformation in aqueous solution that is destabilized at basic pH or in the presence of trifluoroethanol (TFE). Unlike anionic sodium dodecyl sulfate (SDS), which seems to stabilize the polyproline II conformation further, zwitterionic dodecylphosphocholine (DPC) micelles do not affect the peptide structure. On the contrary, copper(II) promptly promotes an increase in β-turn-rich structures. Differential scanning calorimetry (DSC) and Trp fluorescence assays carried out on DPPC model membranes after incubation with huPrP60-91 showed a marked tendency of the peptide to slowly penetrate the lipid bilayer with a concomitant conformational transition toward an extended β-sheet-like structure. Such an event, which was ascribed to the hydrophobic Trp side chain residues, was shown to also depend on the level of copper(II) occupancy along the peptide. Conversely, the CD spectra of chPrP53-76 aqueous solutions indicated the presence of a mixture of random-coil/β-turn-like structures whose resulting equilibrium was influenced by SDS and copper(II) addition. Furthermore, chPrP53-76 did not exhibit any tendency to interact with model membranes in either the presence or absence of copper(II). The results reported here provide evidence of the different roles played by environmental factors in affecting the conformation and membrane activity of human and avian prion N-terminal domains.

Hydrophobic tail length, degree of fluorination and headgroup stereochemistry are determinants of the biocompatibility of (fluorinated) carbohydrate surfactants

A series of hydrocarbon and fluorocarbon carbohydrate surfactants with different headgroups (i.e., gluco-, galacto- and maltopyranoside) and (fluorinated) alkyl tails (i.e., C 7 and C 14 to C 19) was synthesized to investigate trends in their cytotoxicity and haemolytic activity, and how surfactant–lipid interactions of selected surfactants contribute to these two measures of biocompatibility. All surfactants displayed low cytotoxicity (EC 50 = 25 to >250 μM) and low haemolytic activity (EC 50 = 0.2 to >3.3 mM), with headgroup structure, tail length and degree of fluorination being important structural determinants for both endpoints. The EC 50 values of hydrocarbon and fluorocarbon glucopyranoside surfactants displayed a “cut-off” effect (i.e., a maximum with respect to the chain length). According to steady-state fluorescence anisotropy studies, short chain (C 7) surfactants partitioned less readily into model membranes, which explains their low cytotoxicity and haemolytic activity. Interestingly, galactopyranosides were less toxic compared to glucopyranosides with the same hydrophobic tail. Although both surfactant types only differ in the stereochemistry of the 4-OH group, hexadecyl gluco- and galactopyranoside surfactants had similar apparent membrane partition coefficients, but differed in their overall effect on the phase behaviour of DPPC model membranes, as assessed using steady-state fluorescence anisotropy studies. These observations suggest that highly selective surfactant–lipid interactions may be responsible for the differential cytotoxicity and, possible, haemolytic activity of hydrocarbon and fluorocarbon carbohydrate surfactants intended for a variety of pharmaceutical and biomedical applications.

Environmental Effects on a Prion's Helix II Domain: Copper(II) and Membrane Interactions with PrP180–193 and Its Analogues

An abnormal interaction between copper and the prion protein is believed to play a pivotal role in the pathogenesis of prion diseases. Copper binding has been mainly attributed to the N-terminal domain of the prion protein, but this hypothesis has recently been challenged in some papers which suggest that the C-terminal domain might also compete for metal anchoring. In particular, the segment corresponding to the helix II region of the prion protein, namely PrP180-193, has been shown both to bind copper and to exhibit a copper-enhanced cytotoxicity, as well as to interact with artificial membranes. The present work is aimed at extending these results by choosing the most representative model of this domain and by determining its copper affinity. With this aim, the different role played by the electrostatic properties of the C- and N-termini of PrP180-193 (VNITIKQHTVTTTT) in determining its conformational behaviour, copper coordination and ability to perturb model membranes was investigated. Owing to the low solubility of PrP180-193, its copper affinity was evaluated by using the shorter PrPAc184-188NH2 (IKQHT) analogue as a model. ESI-MS, ESR, UV/Vis, and CD measurements were carried out on the copper(II)/PrPAc184-188NH2 and copper(II)/PrP180-193NH2 systems, and showed that PrPAc184-188NH2 is a reliable model for the metal interaction with the helix II domain. The affinity of copper(II) for the helix II fragment is higher than that for the octarepeat and PrP106-126 peptides. Finally, the different ability of PrP180-193 analogues to perturb the DPPC model membrane was assessed by DSC measurements. The possible biological consequences of these findings are also discussed briefly.

Interactions of amphotericin B derivative of low toxicity with biological membrane components—the Langmuir monolayer approach

Amphotericin B (AmB)–a polyene macrolide antibiotic–exhibits strong antifungal activity, however, is known to be very toxic to mammalian cells. In order to decrease AmB toxicity, a number of its derivatives have been synthesized. Basing on in vitro and in vivo research, it was evidenced that one of AmB derivatives, namely N-methyl- N- d-fructopyranosylamphotericin B methyl ester (in short MF-AME) retained most of the antifungal activity of the parent antibiotic, however, exhibited dramatically lower animal toxicity. Therefore, MF-AME seems to be a very promising modification product of AmB. However, further development of this derivative as potential new antifungal drug requires the elucidation of its molecular mechanism of reduced toxicity, which was the aim of the present investigations. Our studies were based on examining the binding energies by determining the strength of interaction between MF-AME and membrane sterols (ergosterol-fungi sterol, and cholesterol-mammalian sterol) and DPPC (model membrane phospholipid) using the Langmuir monolayer technique, which serves as a model of cellular membrane. Our results revealed that at low concentration the affinity of MF-AME to ergosterol is considerably stronger as compared to cholesterol, which correlates with the improved selective toxicity of this drug. It is of importance that the presence of phospholipids is essential since–due to very strong interactions between MF-AME and DPPC–the antibiotic used in higher concentration is “immobilized” by DPPC molecules, which reduces the concentration of free antibiotic, thus enabling it to selectively interact with both sterols.

The interaction of a peptide with a scrambled hydrophobic/hydrophilic sequence (Pro-Asp-Ala-Asp-Ala-His-Ala-His-Ala-His-Ala-Ala-Ala-His-Gly) (PADH) with DPPC model membranes: a DSC study

Depending on their hydrophobicity, peptides can interact differently with lipid membranes inducing dramatic modifications into their host systems. In the present paper, the interaction of a synthetic peptide with a scrambled hydrophobic/hydrophilic sequence (Pro-Asp-Ala-Asp-Ala-His-Ala-His-Ala-His-Ala-Ala-Ala-His-Gly) (PADH) with 1,2-dipalmitoyl-sn-glycero-3-phosphocholine (DPPC) model membranes has been investigated by differential scanning calorimetry (DSC), adopting three different experimental approaches. In the first, the peptide is forced to be included into the hydrocarbon region of the lipid bilayer, by codissolving it with the lipid giving rise to mixed multilamellar vesicles–peptide systems; in the second, this system is passed through an extruder, thus producing large unilamellar vesicles–peptide systems; in the third, it is allowed to interact with the external surface of the membrane. The whole of the DSC results obtained have shown that the incorporation of the peptide into the lipid bilayer by means of the first method induces a decrease in the enthalpy of the gel–liquid crystal transition of the membrane and a shift of the transition to the lower temperatures, thus resembling, in spite of its prevalently hydrophilic nature, the behavior of transbilayer hydrophobic peptides. The extrusion of these systems creates unilamellar vesicles free of peptides but of smaller size as evidenced by the decreased cooperativity of the transition. The peptide, added externally to the DPPC model membrane, has no effect on the phase behavior of the bilayer. These findings suggest that the effect of the interaction of scrambled hydrophobic/hydrophilic peptides into lipid bilayers strongly affects the thermotropic behavior of the host membrane depending on the preparation method of the lipid/peptide systems. The whole of the results obtained in the present paper can be useful in approaching studies of bioactive peptides/lipids systems.

Effect of the Esters of Gallic Acid on Model and Human Blood Platelet Membranes Studied by Fourier Transform Infrared Spectroscopy

Gallic acid is one of the components of Chinese herbal drug Radix paeoniae used for promoting blood circulation to remove blood stasis. This paper studied the effects of gallic acid and its esters (e.g. ethyl, propyl, isobutyl and butyl gallate) on model and human blood platelet membranes by FTIR which was used for monitoring the physical state of the acyl chain, interfacial and head group region of the membrane lipid bilayer. From the experimental results it can be seen that the gallic acid and its esters have the modifying function on the pure and cholesterol-containing DPPC model membranes, and have the quantity-effective and structural-effective relationships. In addition, it is discovered that these esters have the modifying effect on the structure of human blood platelet membrane and can reverse the effect of ADP. That the effect of the esters of gallic acid counteracts the effect of cholesterol and ADP on human blood platelet perhaps provides a new explanation of the mechanism of Chinese herbal drugs used for promoting blood circulation to remove blood stasis.

Effect of the fungicides tributyltin acetate and tributyltin chloride on multilamellar liposomes: fluorescence studies

The influence of tri- n-butyltin acetate (TBTA) and tri- n-butyltin chloride (TBTC) on the physico-chemical state of charged and neutral phospholipids was investigated using multilamellar liposomes. The thermal dependence of steady state fluorescence polarization of DPH and its charged derivative TMA-DPH was recorded. The two fungicides lowered DPPC phase transition temperature and broadened the temperature range of the transition in different ways. The effects were concentration-dependent. The results show that TBTC interacts more effectively with DPPC model membranes rather than TBTA. Moreover, TBTC broadens and shifts the main phase transition ( T m) more effectively in DPPC rather than in DMPC liposomes. Below T m, TBTC decreases fluorescence polarization (P) in all phospholipids used. Above T m P is almost constant in phospholipids with saturated acyl chains, except for DMPG. In fact, an increase of P is detectable in this lipid as in PLs with unsaturated acyl chains. It is suggested that the effects of TBT on liposomal membranes are dependent on the anion moiety and phospholipids characteristics.