Comparison of thermal effects of stilbenoid analogs in lipid bilayers using differential scanning calorimetry and molecular dynamics: correlation of thermal effects and topographical position with antioxidant activity

Trans-Resveratrol Decreases Membrane Water Permeability: A Study of Cholesterol-Dependent Interactions

Resveratrol (RSV), a biologically active plant phenol, has been extensively investigated for cancer prevention and treatment due to its ability to regulate intracellular targets and signaling pathways which affect cell growth and metastasis. The non-specific interactions between RSV and cell membranes can modulate physical properties of membranes, which in turn can affect the conformation of proteins and perturb membrane-hosted biological functions. This study examines non-specific interactions of RSV with model membranes having varying concentrations of cholesterol (Chol), mimicking normal and cancerous cells. The perturbation of the model membrane by RSV is sensed by changes in water permeability parameters, using Droplet Interface Bilayer (DIB) models, thermotropic properties from Differential Scanning Calorimetry, and structural properties from confocal Raman spectroscopy, all of which are techniques not complicated by the use of probes which may themselves perturb the membrane. The nature and extent of interactions greatly depend on the presence and absence of Chol as well as the concentration of RSV. Our results indicate that the presence of RSV decreases water permeability of lipid membranes composed of 1,2-dioleoyl-sn-glycero-3-phosphocholine (DOPC), indicating a capability for RSV in stiffening fluidic membranes. When Chol is present, however, (at 4:1 and 2:1 mol ratio DOPC to cholesterol), the addition of RSV has no significant effect upon the water permeability. DSC thermograms show that RSV interacts with DOPC and DOPC/Chol bilayers and influences their thermotropic phase behavior in a concentration-dependent manner, by decreasing the main phase transition temperature and enthalpy, with a phase separation shown at the higher concentrations of RSV. Raman spectroscopic studies indicate an ordering effect of RSV on DOPC supported bilayer, with a lesser extent of ordering in the presence of Chol. Combined results from these investigations highlight a differential effect of RSV on Chol-free and Chol-enriched membranes, respectively, which results constitute a bellwether for increased understanding and effective use of resveratrol in disease therapy including cancer.

Study of Resveratrol's Interaction with Planar Lipid Models: Insights into Its Location in Lipid Bilayers

Resveratrol, a polyphenolic molecule found in edible fruits and vegetables, shows a wide range of beneficial effects on human health, including anti-microbial, anti-inflammatory, anti-cancer, and anti-aging properties. Due to its poor water solubility and high liposome-water partition coefficient, the biomembrane seems to be the main target of resveratrol, although the mode of interaction with membrane lipids and its location within the cell membrane are still unclear. In this study, using electrophysiological measurements, we study the interaction of resveratrol with planar lipid membranes (PLMs) of different composition. We found that resveratrol incorporates into palmitoyl-oleoyl-phosphatidylcholine (POPC) and POPC:Ch PLMs and forms conductive units unlike those found in dioleoyl-phosphatidylserine (DOPS):dioleoyl-phosphatidylethanolamine (DOPE) PLMs. The variation of the biophysical parameters of PLMs in the presence of resveratrol provides information on its location within a lipid double layer, thus contributing to an understanding of its mechanism of action.

A Journey to the Conformational Analysis of T-Cell Epitope Peptides Involved in Multiple Sclerosis

Multiple sclerosis (MS) is a serious central nervous system (CNS) disease responsible for disability problems and deterioration of the quality of life. Several approaches have been applied to medications entering the market to treat this disease. However, no effective therapy currently exists, and the available drugs simply ameliorate the destructive disability effects of the disease. In this review article, we report on the efforts that have been conducted towards establishing the conformational properties of wild-type myelin basic protein (MBP), myelin proteolipid protein (PLP), myelin oligodendrocyte glycoprotein (MOG) epitopes or altered peptide ligands (ALPs). These efforts have led to the aim of discovering some non-peptide mimetics possessing considerable activity against the disease. These efforts have contributed also to unveiling the molecular basis of the molecular interactions implicated in the trimolecular complex, T-cell receptor (TCR)–peptide–major histocompatibility complex (MHC) or human leucocyte antigen (HLA).

Molecular Mechanism of Resveratrol's Lipid Membrane Protection

Resveratrol, a natural compound found in red wine and various vegetables, has drawn increasing interest due to its reported benefit in cardiovascular protection, neurodegenerative disorders, and cancer therapy. The mechanism by which resveratrol exerts such pleiotropic effects remains unclear. It remains as one of the most discussed polyphenol compounds in the debating "French Paradox". In this study, using molecular dynamics simulations of dipalmitoyl phosphatidylcholine (DPPC) bilayer with resveratrol, we generated a free energy map of resveratrol's location and orientation of inside the lipid bilayer. We found that resveratrol increases the surface area per lipid and decreases membrane thickness, which is the opposite effect of the well-studied cholesterol on liquid phase DPPC. Most importantly, based on the simulation observation that resveratrol has a high probability of forming hydrogen bonds with sn-1 and sn-2 ester groups, we discovered a new mechanism using experimental approach, in which resveratrol protects both sn-1 and sn-2 ester bonds of DPPC and distearoyl phosphatidylcholine (DSPC) from phospholipase A1 (PLA1) and phospholipase A2 (PLA2) cleavage. Our study elucidates the new molecular mechanism of potential health benefits of resveratrol and possibly other similar polyphenols and provides a new paradigm for drug design based on resveratrol and its analogs.

Experimental and theoretical studies of emodin interacting with a lipid bilayer of DMPC

Emodin is one of the most abundant anthraquinone derivatives found in nature. It is the active principle of some traditional herbal medicines with known biological activities. In this work, we combined experimental and theoretical studies to reveal information about location, orientation, interaction and perturbing effects of Emodin on lipid bilayers, where we have taken into account the neutral form of the Emodin (EMH) and its anionic/deprotonated form (EM^-). Using both UV/Visible spectrophotometric techniques and molecular dynamics (MD) simulations, we showed that both EMH and EM^- are located in a lipid membrane. Additionally, using MD simulations, we revealed that both forms of Emodin are very close to glycerol groups of the lipid molecules, with the EMH inserted more deeply into the bilayer and more disoriented relative to the normal of the membrane when compared with the EM^-, which is more exposed to interfacial water. Analysis of several structural properties of acyl chains of the lipids in a hydrated pure DMPC bilayer and in the presence of Emodin revealed that both EMH and EM^- affect the lipid bilayer, resulting in a remarkable disorder of the bilayer in the vicinity of the Emodin. However, the disorder caused by EMH is weaker than that caused by EM^-. Our results suggest that these disorders caused by Emodin might lead to distinct effects on lipid bilayers including its disruption which are reported in the literature.

Effects of resveratrol on the structure and fluidity of lipid bilayers: a membrane biophysical study

Resveratrol is a natural active compound which has been attracting increasing interest due to its several pharmacological effects in cancer prevention, cardiovascular protection and treatment of neurodegenerative disorders and diabetes. The current work investigates how resveratrol affects membrane order and structure, gathering information determined by X-ray scattering analysis, derivative spectrophotometry, fluorescence quenching and fluorescence anisotropy studies. The results indicate that resveratrol is able to be incorporated into DMPC liposome model systems, either fluidizing or stiffening the bilayer, which largely depends on the membrane fluidity state. These findings suggest that the effects of resveratrol resemble cholesterol action on biological membranes, thereby contributing to the regulation of cell membrane structure and fluidity, which may influence the activity of transmembrane proteins and hence control the cell signaling pathways. The regulation of a number of cellular functions, thus may contribute to the pharmacological and therapeutic activities of this compound, explaining its pleiotropic action.

Biological and computational evaluation of resveratrol inhibitors against Alzheimer's disease

It has been reported that beta amyloid induces production of radical oxygen species and oxidative stress in neuronal cells, which in turn upregulates β-secretase (BACE-1) expression and beta amyloid levels, thereby propagating oxidative stress and increasing neuronal injury. A series of resveratrol derivatives, known to be inhibitors of oxidative stress-induced neuronal cell death (oxytosis) were biologically evaluated against BACE-1 using homogeneous time-resolved fluorescence (TRF) assay. Correlation between oxytosis inhibitory and BACE-1 inhibitory activity of resveratrol derivatives was statistically significant, supporting the notion that BACE-1 may act as pivotal mediator of neuronal cell oxytosis. Four of the biologically evaluated resveratrol analogs demonstrated considerably higher activity than resveratrol in either assay. The discovery of some "hits" led us to initiate detailed docking studies associated with Molecular Dynamics in order to provide a plausible explanation for the experimental results and understand their molecular basis of action.

Probing the position of resveratrol in lipid bilayers: A neutron reflectivity study

The effect of the natural antioxidant resveratrol on the structure of solid supported di-palmitoyl-phosphatidyl-choline (DPPC) bilayers in their fluid state was investigated by neutron reflectometry. Results reveal an accumulation of resveratrol (up to 25%, mol/mol) inside the headgroups and they exclude its presence in the hydrophobic core. The presence of resveratrol induces an increase of the average thickness and of the interfacial roughness of the headgroup layer. This may be due to a change of the tilt angle of the phosphocholine headgroups residing next to the resveratrol to a more upright orientation and leading to a reduction of the projected area per headgroup. This effect is propagated into the hydrophobic core, where the chain packing is modified despite the absence of resveratrol. When interacting with a DPPC/cholesterol membrane, resveratrol has a similar effect on the neighboring PC headgroups as in the cholesterol free membrane. The almost precise 1:1 insertion ratio (resveratrol:cholesterol) suggests that resveratrol is most probably inserted on top of the hydroxyl group of the cholesterol in between the PC headgroups. The ordering effect of cholesterol on the hydrophobic core is absent when both cholesterol and resveratrol are present. Most probably, the interaction of resveratrol with lipid membranes is non-specific.

Effect of resveratrol-related stilbenoids on biomembrane models

The interactions of the two resveratrol analogues 2-hydroxy-3,5,3',5'-tetramethoxystilbene (4) and 2-hydroxy-3,5,3',4'-tetramethoxystilbene (5) with model biomembranes were studied. The aim of this investigation was to highlight possible differences in the interactions with such biomembranes related to the minimal structural differences between these isomeric stilbenoids. In particular, different experiments on stilbenoid/biomembrane model systems using both differential scanning calorimetry (DSC) and Langmuir-Blodgett techniques were carried out to evaluate stilbenoid/multilamellar vesicle and stilbenoid/phospholipid monolayer interactions, respectively. Dimyristoylphosphatidylcholine was used as constituent of the biomembrane models and permitted the experiments to be carried out at 37 °C, close to body temperature. Kinetic studies were also run by DSC to evaluate the uptake of the resveratrol derivatives by the biomembrane model in an aqueous medium and when transported by a lipophilic carrier. The results indicated that both of the resveratrol analogues influenced the behavior of multilamellar vesicles and monolayers, biomembrane models, with 4 producing a larger effect than 5. These results are useful for better understanding the mechanism of action of these compounds. Moreover, the kinetic results could be of importance for future design of lipophilic delivery systems for these stilbenoids.

Conformational analysis of the ΜΒΡ83-99 (Phe91) and ΜΒΡ83-99 (Tyr91) peptide analogues and study of their interactions with the HLA-DR2 and human TCR receptors by using molecular dynamics

The two new synthetic analogues of the MBP(83-99) epitope substituted at Lys(91) (primary TCR contact) with Phe [MBP(83-99) (Phe(91))] or Tyr [MBP(83-99) (Tyr(91))], have been structurally elucidated using 1D and 2D high resolution NMR studies. The conformational analysis of the two altered peptide ligands (APLs) has been performed and showed that they adopt a linear and extended conformation which is in agreement with the structural requirements of the peptides that interact with the HLA-DR2 and TCR receptors. In addition, Molecular Dynamics (MD) simulations of the two analogues in complex with HLA-DR2 (DRA, DRB1*1501) and TCR were performed. Similarities and differences of the binding motif of the two analogues were observed which provide a possible explanation of their biological activity. Their differences in the binding mode in comparison with the MBP(83-99) epitope may also explain their antagonistic versus agonistic activity. The obtained results clearly indicate that substitutions in crucial amino acids (TCR contacts) in combination with the specific conformational characteristics of the MBP(83-99) immunodominant epitope lead to an alteration of their biological activity. These results make the rational drug design intriguing since the biological activity is very sensitive to the substitution and conformation of the mutated MBP epitopes.