The hypotensive drug 2-hydroxyoleic acid modifies the structural properties of model membranes

Exploring pH-Triggered Lamellar to Cubic Phase Transition in 2-Hydroxyoleic Acid/Monoolein Nanodispersions: Insights into Membrane Physicochemical Properties

Self-assembled lipid nanoparticles (LNPs) are essential nanocarriers for drug delivery. Functionalization of LNPs with ionizable lipids creates pH-responsive nanoparticles that change structures under varying pH conditions, enabling pH-triggered drug release. Typically, bicontinuous cubic phase nanoparticles (Cubosomes) and lamellar structured vesicles (Liposomes) differ in lipid packing statuses, affecting drug release and cellular uptake. However, most research predominantly focuses on elucidating lattice structure changes of these LNPs without a deep investigation of lipid-membrane properties. Addressing this gap, our study delves into the lipid-membrane physicochemical property variations during the lamellar-to-cubic phase transition. Here, we prepared pH-responsive LNPs using 2-hydroxyoleic acid/monoolein (2-OHOA/MO) binary components. Small-angle X-ray scattering (SAXS) revealed a phase transition from lamellar vesicles (Lα) to cubosomes (Im3m/Pn3m) with pH reduction. Laurdan and 1,6-diphenyl-1,3,5-hexatriene (DPH) fluorescence probes tracked the lipid-water interfacial polarity and lipid-membrane fluidity variations during the phase transition. Raman spectroscopy provided further insights into lipid-membrane lipid chain packing and chain torsion. We observed that the changes in lipid-membrane properties coincided with the lamellar-to-cubic phase transition, emphasizing the interplay between the phase structure and lipid-membrane behaviors in the 2-OHOA/MO system. This study provides insights into the lipid-membrane properties variation during the pH-triggered phase transition in the 2-OHOA/MO system, guiding future research toward more effective and reliable pH-responsive drug delivery platforms.

Influence of Nitrosyl Iron Complex with Thiosulfate Ligands on Therapeutically Important Targets Related to Type 2 Diabetes Mellitus

The high prevalence of type 2 diabetes mellitus (T2DM), and the lack of effective therapy, determine the need for new treatment options. The present study is focused on the NO-donors drug class as effective antidiabetic agents. Since numerous biological systems are involved in the pathogenesis and progression of T2DM, the most promising approach to the development of effective drugs for the treatment of T2DM is the search for pharmacologically active compounds that are selective for a number of therapeutic targets for T2DM and its complications: oxidative stress, non-enzymatic protein glycation, polyol pathway. The nitrosyl iron complex with thiosulfate ligands was studied in this work. Binuclear iron nitrosyl complexes are synthetic analogues of [2Fe-2S] centers in the regulatory protein natural reservoirs of NO. Due to their ability to release NO without additional activation under physiological conditions, these compounds are of considerable interest for the development of potential drugs. The present study explores the effects of tetranitrosyl iron complex with thiosulfate ligands (TNIC-ThS) on T2DM and its complications regarding therapeutic targets in vitro, as well as its ability to bind liposomal membrane, inhibit lipid peroxidation (LPO), and non-enzymatic glycation of bovine serum albumin (BSA), as well as aldose reductase, the enzyme that catalyzes the reduction in glucose to sorbitol in the polyol pathway. Using the fluorescent probe method, it has been shown that TNIC-ThS molecules interact with both hydrophilic and hydrophobic regions of model membranes. TNIC-ThS inhibits lipid peroxidation, exhibiting antiradical activity due to releasing NO (IC50 = 21.5 ± 3.7 µM). TNIC-ThS was found to show non-competitive inhibition of aldose reductase with Ki value of 5.25 × 10^-4 M. In addition, TNIC-ThS was shown to be an effective inhibitor of the process of non-enzymatic protein glycation in vitro (IC50 = 47.4 ± 7.6 µM). Thus, TNIC-ThS may be considered to contribute significantly to the treatment of T2DM and diabetic complications.

The anti-tumor drug 2-hydroxyoleic acid regulates the oncogenic potassium channel Kv10.1

Background

2-hydroxyoleic acid (2OHOA) is a synthetic fatty acid with antitumor properties that alters membrane composition and structure, which in turn influences the functioning of membrane proteins and cell signaling. In this study, we propose a novel antitumoral mechanism of 2OHOA accomplished through the regulation of Kv10.1 channels. We evaluated the effects of 2OHOA on Kv10.1 channels expressed in HEK-293 cells by using electrophysiological techniques and a cell proliferation assay.

Results

2OHOA increased Kv10.1 channel currents in a voltage-dependent manner, shifted its conductance-voltage relationship towards negative potentials, and accelerated its activation kinetics. Moreover, 2OHOA reduced proliferation of cells that exogenously (HEK-293) and endogenously (MCF-7) expressed Kv10.1 channels. It is worth noting that the antiproliferative effect of 2OHOA was maintained in HEK-293 cells expressing a non-conducting mutant of Kv10.1 channel (Kv10.1-F456A), while it did not affect HEK-293 cells not expressing Kv10.1 channels, suggesting that 2OHOA interferes with a non-conducting function of Kv10.1 channels involved in cell proliferation. Finally, we found that 2OHOA can act synergistically with astemizole, a Kv10.1 channel blocker, to decrease cell proliferation more efficiently.

Conclusion

Our data suggest that 2OHOA decreases cell proliferation, at least in part, by regulating Kv10.1 channels.

Anticancer drugs tamoxifen and 4hydroxytamoxifen as effectors of phosphatidylethanolamine lipid polymorphism

The interaction of tamoxifen (TMX) and its metabolite 4-hydroxytamoxifen (HTMX) with a biomimetic membrane model system composed of 1,2-dielaidoylphosphatidylethanolamine (DEPE) has been studied using a biophysical approach. Incorporation of TMX into DEPE bilayers gives rise to a progressive broadening of the L_β/L_α phase transition and a downward temperature shift. The L_β/L_α phase transition presents multiple endotherms, indicating a lateral segregation of TMX/DEPE domains within the plane of the bilayer. TMX and HTMX also widen and shift the L_α to hexagonal-H_II transition toward lower values, the phase diagrams showing that both compounds facilitate formation of the H_II phase. TMX increases motional disorder of DEPE acyl chains in the L_β, L_α and H_II phases, whereas the effect of HTMX is clearly different. In addition, neither TMX nor HTMX significantly perturb the hydration state of the polar headgroup region of DEPE. Molecular dynamics (MD) simulations indicate that these drugs do not affect membrane thickness, area per lipid, or the conformation of DEPE molecules. As a general rule, the interaction of HTMX with DEPE is qualitatively similar to TMX but less intense. However, a significant difference shown by MD is that HTMX is mainly placed around the center of each monolayer while TMX is located mainly at the center of the membrane, also having a greater tendency to cluster formation. These results are discussed to understand the modulation of phosphatidylethanolamine lipid polymorphism carried out by these drugs, which could be of relevance to explain their effects on enzyme activity or membrane permeabilization.

pH-Responsive Nano-Self-Assemblies of the Anticancer Drug 2-Hydroxyoleic Acid

pH-responsive lipid nanocarriers have the potential to selectively target the acidic extracellular pH environment of cancer tissues and may further improve the efficacy of chemotherapeutics by minimizing their toxic side-effects. Here, we present the design and characterization of pH-sensitive nano-self-assemblies of the poorly water-soluble anticancer drug 2-hydroxyoleic acid (2OHOA) with glycerol monooleate (GMO). pH-triggered nanostructural transformations from 2OHOA/GMO nanoparticles with an internal inverse hexagonal structure (hexosomes) at pH around 2.0-3.0, via nanocarriers with an internal inverse bicontinuous cubic structure (cubosomes) at pH 2.0-4.5, to vesicles at pH 4.5-7.4 were observed with synchrotron small-angle X-ray scattering, and cryogenic transmission electron microscopy. ζ-potential measurements highlight that the pH-driven deprotonation of the carboxylic group of 2OHOA, and the resulting charge-repulsions at the lipid-water interface account for these nanostructural alterations. The study provides detailed insight into the pH-dependent self-assembly of 2OHOA with GMO in excess buffer at physiologically relevant pH values, and discusses the effects of pH alterations on modulating their nanostructure. The results may guide the further development of pH-responsive anticancer nanocarriers for the targeted delivery of chemotherapeutics to the local microenvironment of tumor cells.

Membrane-lipid therapy: A historical perspective of membrane-targeted therapies - From lipid bilayer structure to the pathophysiological regulation of cells

Our current understanding of membrane lipid composition, structure and functions has led to the investigation of their role in cell signaling, both in healthy and pathological cells. As a consequence, therapies based on the regulation of membrane lipid composition and structure have been recently developed. This novel field, known as Membrane Lipid Therapy, is growing and evolving rapidly, providing treatments that are now in use or that are being studied for their application to oncological disorders, Alzheimer's disease, spinal cord injury, stroke, diabetes, obesity, and neuropathic pain. This field has arisen from relevant discoveries on the behavior of membranes in recent decades, and it paves the way to adopt new approaches in modern pharmacology and nutrition. This innovative area will promote further investigation into membranes and the development of new therapies with molecules that target the cell membrane. Due to the prominent roles of membranes in the cells' physiology and the paucity of therapeutic approaches based on the regulation of the lipids they contain, it is expected that membrane lipid therapy will provide new treatments for numerous pathologies. The first on-purpose rationally designed molecule in this field, minerval, is currently being tested in clinical trials and it is expected to enter the market around 2020. However, it seems feasible that during the next few decades other membrane regulators will also be marketed for the treatment of human pathologies. This article is part of a Special Issue entitled: Membrane Lipid Therapy: Drugs Targeting Biomembranes edited by Pablo V. Escribá.

WITHDRAWN: Membrane-lipid therapy: A historical perspective of membrane-targeted therapies-From lipid bilayer structure to the pathophysiological regulation of cells

The Publisher regrets that this article is an accidental duplication of an article that has already been published, http://dx.doi.org/10.1016/j.bbamem.2017.05.017. The duplicate article has therefore been withdrawn. The full Elsevier Policy on Article Withdrawal can be found at https://www.elsevier.com/about/our-business/policies/article-withdrawal.

Computational study on human sphingomyelin synthase 1 (hSMS1)

Human sphingomyelin synthase 1 (hSMS1) is the last enzyme for sphingomyelin (SM) biosynthesis. It has been discovered that in different human tumor tissues the SM levels are lower compared to normal tissues and the activation of hSMS1, to restore the normal levels of SM, inhibits cell cycle proliferation of cancer cells. Since the importance of SM and other lipid metabolism genes in the malignant transformation, we decided to explore the hSMS1 mechanism of action. Enzymes capable to regulate the formation of lipids are therefore of paramount importance. Here we present a computational study on sphingomyelin synthases hSMS1. The full structure of the enzyme was obtained by means of homology and ab initio techniques. Further molecular dynamics and docking studies permitted to identify putative binding sites and to identify the key residues for binding. This article is part of a Special Issue entitled: Membrane Lipid Therapy: Drugs Targeting Biomembranes edited by Pablo V. Escribá.

A comparative study on the effect of Curcumin and Chlorin-p6 on the transport of the LDS cation across a negatively charged POPG bilayer: Effect of pH

We report the use of interface selective Second Harmonic generation technique to investigate the transport of the LDS cation across POPG liposomes in the pH range of 4.0 to 8.0 in the presence and absence of two amphiphilic drugs, Curcumin and Chlorin-p₆ (Cp₆). Our results show that bilayer permeability of liposomes is significantly affected by the presence of the drugs and pH of the medium as evidenced by significant changes in the transport kinetics of the LDS. Studies carried out in the pH range 4.0-8.0 show that while Cp₆ significantly enhanced the transport of LDS at pH4.0, the transport of the cation was seen to increase with increasing pH, with maximum effect at pH7.4 for Curcumin. The pH dependent bilayer localization of both the drugs was investigated by conducting steady state FRET studies using DPH labeled lipids as donors. The FRET results and the relative population of the various ionic/nonionic species of the drugs at different pH suggest that distance dependent interaction between the various ionic species of the drugs and polar head groups of the lipid is responsible for the observed pH dependence enhancement of the drug induced membrane permeability. Another interesting observation was that the stability of Curcumin in presence of POPG liposomes was observed to degrade significantly near physiological pH (7.4 and 8.0). Although this degradation did not affect the liposome integrity, interestingly this was observed to enhance the transport of the LDS cation across the bilayer. That the degradation products of Curcumin are equally effective as the drug itself in enhancing the membrane permeability lends additional support to the current opinion that the bioactive degradation products of the drug may have a significant contribution to its observed pharmacological effects.

Interaction of neurotransmitters with a phospholipid bilayer: a molecular dynamics study

We have performed a series of molecular dynamics simulations to study the interactions between the neurotransmitters (NTs) γ-aminobutyrate (GABA), glycine (GLY), acetylcholine (ACH) and glutamate (GLU) as well as the amidated/acetylated γ-aminobutyrate (GABA(neu)) and the osmolyte molecule glycerol (GOL) with a dipalmitoylphosphatidylcholine (DPPC) bilayer. In agreement with previously published experimental data, we found the lowest membrane affinity for the charged molecules and a moderate affinity for zwitterionic and polar molecules. The affinity can be ranked as follows: ACH-GLU<<GABA<GLY<<GABA(neu)<<GOL. The latter three penetrated the bilayer at most with the deepest location being close to the glycerol backbone of the phospholipids. Even at that position, these solutes were noticeably hydrated and carried ∼30-80% of the bulk water along. The mobility of hydration water at the solute is also affected by the penetration into the bilayer. Two time scales of exchanging water molecules could be determined. In the bulk phase, the hydration layer contains ∼20% slow exchanging water molecules which increases 2-3 times as the solutes entered the bilayer. Our results indicate that there is no intermediate exchange of slow moving water molecules from the solutes to the lipid atoms and vice versa. Instead, the exchange relies on the reservoir of unbounded ("free") water molecules in the interfacial bilayer region. Results from the equilibrium simulations are in good agreement with the results from umbrella sampling simulations, which were conducted for the four naturally occurring NTs. Free energy profiles for ACH and GLU show a minimum of ∼2-3 kJ/mol close to the bilayer interface, while for GABA and GLY, a minimum of respectively ∼2 kJ/mol and ∼5 kJ/mol is observed when these NTs are located in the vicinity of the lipid glycerol backbone. The most important interaction of NTs with the bilayer is the charged amino group of NTs with the lipid phosphate group.

Regulation of the cancer cell membrane lipid composition by NaCHOleate: effects on cell signaling and therapeutical relevance in glioma

This review summarizes the cellular bases of the effects of NaCHOleate (2-hydroxyoleic acid; 2OHOA; Minerval) against glioma and other types of tumors. NaCHOleate, activates sphingomyelin synthase (SGMS) increasing the levels of cell membrane sphingomyelin (SM) and diacylglycerol (DAG) together with reductions of phosphatidylethanolamine (PE) and phosphatidylcholine (PC). The increases in the membrane levels of NaCHOleate itself and of DAG induce a translocation and overexpression of protein kinase C (PKC) and subsequent reductions of Cyclin D, cyclin-dependent kinases 4 and 6 (CDKs 4 and 6), hypophosphorylation of the retinoblastoma protein, inhibition of E2F1 and knockdown of dihydrofolate reductase (DHFR) impairing DNA synthesis. In addition in some cancer cells, the increases in SM are associated with Fas receptor (FasR) capping and ligand-free induction of apoptosis. In glioma cell lines, the increases in SM are associated with the inhibition of the Ras/MAPK and PI3K/Akt pathways, in association with p27Kip1 overexpression. Finally, an analysis of the Repository of Molecular Brain Neoplasia Data (REMBRANDT) database for glioma patient survival shows that the weight of SM-related metabolism gene expression in glioma patients' survival is similar to glioma-related genes. Due to its low toxicity and anti-tumoral effect in cell and animal models its status as an orphan drug for glioma treatment by the European Medicines Agency (EMA) was recently acknowledged and a phase 1/2A open label, non-randomized study was started in patients with advanced solid tumors including malignant glioma. This article is part of a Special Issue entitled: Membrane Structure and Function: Relevance in the Cell's Physiology, Pathology and Therapy.

The effect of hydroxylated fatty acid-containing phospholipids in the remodeling of lipid membranes

The synthetic fatty acid 2-hydroxyoleic acid (2OHOA) is an antitumor drug that regulates membrane lipid composition and structure. An important effect of this drug is the restoration of sphingomyelin (SM) levels in cancer cell membranes, where the SM concentration is lower than in non-tumor cells. It is well known that free fatty acid concentration in cell membranes is lower than 5%, and that fatty acid excess is rapidly incorporated into phospholipids. In a recent work, we have considered the effect of free 2OHOA in model membranes in liquid ordered (Lo) and liquid disordered (Ld) phases, by using all-atom molecular dynamics. This study concerns membranes that are modified upon incorporation of 2OHOA into different phospholipids. 2OHOA-containing phospholipids have a permanent effect on lipid membranes, making a Ld membrane surface more compact and less hydrated, whereas the opposite effect is observed in Lo domains. Moreover, the hydroxyl group of fatty acid chains increases the propensity of Ld model membranes to form hexagonal or other non-lamellar structures. This article is part of a Special Issue entitled: Membrane Structure and Function: Relevance in the Cell's Physiology, Pathology and Therapy.

Differential effect of 2-hydroxyoleic acid enantiomers on protein (sphingomyelin synthase) and lipid (membrane) targets

The complex dual mechanism of action of 2-hydroxyoleic acid (2OHOA), a potent anti-tumor compound used in membrane lipid therapy (MLT), has yet to be fully elucidated. It has been demonstrated that 2OHOA increases the sphingomyelin (SM) cell content via SM synthase (SGMS) activation. Its presence in membranes provokes changes in the membrane lipid structure that induce the translocation of PKC to the membrane and the subsequent overexpression of CDK inhibitor proteins (e.g., p21(Cip1)). In addition, 2OHOA also induces the translocation of Ras to the cytoplasm, provoking the silencing of MAPK and its related pathways. These two differential modes of action are triggered by the interactions of 2OHOA with either lipids or proteins. To investigate the molecular basis of the different interactions of 2OHOA with membrane lipids and proteins, we synthesized the R and S enantiomers of this compound. A molecular dynamics study indicated that both enantiomers interact similarly with lipid bilayers, which was further confirmed by X-ray diffraction studies. By contrast, only the S enantiomer was able to activate SMS in human glioma U118 cells. Moreover, the anti-tumor efficacy of the S enantiomer was greater than that of the R enantiomer, as the former can act through both MLT mechanisms. The present study provides additional information on this novel therapeutic approach and on the magnitude of the therapeutic effects of type-1 and type-2 MLT approaches. This article is part of a Special Issue entitled: Membrane Structure and Function: Relevance in the Cell's Physiology, Pathology and Therapy.

Partitioning of liquid-ordered/liquid-disordered membrane microdomains induced by the fluidifying effect of 2-hydroxylated fatty acid derivatives

Cellular functions are usually associated with the activity of proteins and nucleic acids. Recent studies have shown that lipids modulate the localization and activity of key membrane-associated signal transduction proteins, thus regulating the cell's physiology. Membrane Lipid Therapy aims to reverse cell dysfunctions (i.e., diseases) by modulating the activity of membrane signaling proteins through regulation of the lipid bilayer structure. The present work shows the ability of a series of 2-hydroxyfatty acid (2OHFA) derivatives, varying in the acyl chain length and degree of unsaturation, to regulate the membrane lipid structure. These molecules have shown greater therapeutic potential than their natural non-hydroxylated counterparts. We demonstrated that both 2OHFA and natural FAs induced reorganization of lipid domains in model membranes of POPC:SM:PE:Cho, modulating the liquid-ordered/liquid-disordered structures ratio and the microdomain lipid composition. Fluorescence spectroscopy, confocal microscopy, Fourier transform infrared spectroscopy and differential detergent solubilization experiments showed a destabilization of the membranes upon addition of the 2OHFAs and FAs which correlated with the observed disordering effect. The changes produced by these synthetic fatty acids on the lipid structure may constitute part of their mechanism of action, leading to changes in the localization/activity of membrane proteins involved in signaling cascades, and therefore modulating cell responses.

Sustained activation of sphingomyelin synthase by 2-hydroxyoleic acid induces sphingolipidosis in tumor cells

The mechanism of action of 2-hydroxyoleic acid (2OHOA), a potent antitumor drug, involves the rapid and specific activation of sphingomyelin synthase (SMS), leading to a 4-fold increase in SM mass in tumor cells. In the present study, we investigated the source of the ceramides required to sustain this dramatic increase in SM. Through radioactive and fluorescent labeling, we demonstrated that sphingolipid metabolism was altered by a 24 h exposure to 2OHOA, and we observed a consistent increase in the number of lysosomes and the presence of unidentified storage materials in treated cells. Mass spectroscopy revealed that different sphingolipid classes accumulated in human glioma U118 cells after exposure to 2OHOA, demonstrating a specific effect on C16-, C20-, and C22-containing sphingolipids. Based on these findings, we propose that the demand for ceramides required to sustain the SMS activation (ca. 200-fold higher than the basal level) profoundly modifies both sphingolipid and phospholipid metabolism. As the treatment is prolonged, tumor cells fail to adequately metabolize sphingolipids, leading to a situation resembling sphingolipidosis, whereby cell viability is compromised.

The role of membrane fatty acid remodeling in the antitumor mechanism of action of 2-hydroxyoleic acid

The synthetic fatty acid 2-hydroxyoleic acid (2OHOA) is a potent antitumor drug that we rationally designed to regulate the membrane lipid composition and structure. The lipid modifications caused by 2OHOA treatments induce important signaling changes that end up with cell death (Terés et al., 2012 [1]). One of these regulatory effects is restoration of sphingomyelin levels, which are markedly lower in cancer cells compared to normal cells (Barceló-Coblijn et al., 2011 [2]). In this study, we report another important regulatory effect of 2OHOA on cancer cell membrane composition: a large increase in 2OHOA levels, accounting for ~15% of the fatty acids present in membrane phospholipids, in human glioma (SF767 and U118) and lung cancer (A549) cells. Concomitantly, we observed marked reductions in oleic acid levels and inhibition of stearoyl-CoA desaturase. The impact of these changes on the biophysical properties of the lipid bilayer was evaluated in liposomes reconstituted from cancer cell membrane lipid extracts. Thus, 2OHOA increased the packing of ordered domains and decreased the global order of the membrane. The present results further support and extend the knowledge about the mechanism of action for 2OHOA, based on the regulation of the membrane lipid composition and structure and subsequent modulation of membrane protein-associated signaling.

2-Hydroxyoleic acid induces ER stress and autophagy in various human glioma cell lines

Background

2-Hydroxyoleic acid is a synthetic fatty acid with potent anti-cancer activity which does not induce undesired side effects. However, the molecular and cellular mechanisms by which this compound selectively kills human glioma cancer cells without killing normal cells is not fully understood. The present study was designed to determine the molecular bases underlying the potency against 1321N1, SF-767 and U118 human glioma cell lines growth without affecting non cancer MRC-5 cells.

Methodology/Principal Findings

The cellular levels of endoplasmic reticulum (ER) stress, unfolded protein response (UPR) and autophagy markers were determined by quantitative RT-PCR and immunoblotting on 1321N1, SF-767 and U118 human glioma cells and non-tumor MRC-5 cells incubated in the presence or absence of 2OHOA or the ER stress/autophagy inducer, palmitate. The cellular response to these agents was evaluated by fluorescence microscopy, electron microscopy and flow cytometry. We have observed that 2OHOA treatments induced augments in the expression of important ER stress/UPR markers, such as phosphorylated eIF2α, IRE1α, CHOP, ATF4 and the spliced form of XBP1 in human glioma cells. Concomitantly, 2OHOA led to the arrest of 1321N1 cells in the G₂/M phase of the cell cycle, with down-regulation of cyclin B1 and Cdk1/Cdc2 proteins in the three glioma cell lines studied. Finally, 2OHOA induced autophagy in 1321N1, SF-767 and U118 cells, with the appearance of autophagic vesicles and the up-regulation of LC3BI, LC3BII and ATG7 in 1321N1 cells, increases of LC3BI, LC3BII and ATG5 in SF-767 cells and up-regulation of LC3BI and LC3BII in U118 cells. Importantly, 2OHOA failed to induce such changes in non-tumor MRC-5 cells.

Conclusion/Significance

The present results demonstrate that 2OHOA induces ER stress/UPR and autophagy in human glioma (1321N1, SF-767 and U118 cell lines) but not normal (MRC-5) cells, unraveling the molecular bases underlying the efficacy and lack of toxicity of this compound.

Self-assembled nanostructures of fully hydrated monoelaidin-elaidic acid and monoelaidin-oleic acid systems

In recent years, there has been a surge of interest in exploring the effect of trans-fatty acids (TFAs) on biological membrane properties. The research studies are motivated by an increasing body of evidence suggesting that the consumption of TFAs increases the risk of developing negative health effects such as coronary heart disease and cancer. The ultimate goal of studying the lipid-fatty acid interactions at the molecular level is to predict the biological role of fatty acids in cells. In this regard, it is interesting to elucidate the effect of loading TFAs and their counterpart cis-fatty acids (CFAs) on the physical properties of lipid model membranes. Here, the present study focuses on discussing the following: (1) the effect of mixing monoelaidin (ME, TFA-containing lipid) with its counterpart monoolein (MO, CFA-containing lipid) on modulating the fully hydrated self-assembled structure, and (2) the influence of solubilizing oleic acid (OA) and its trans counterpart elaidic acid (EA) on the fully hydrated ME system. The ME model membrane was selected due to its sensitivity to variations in lipid composition and temperature. Synchrotron small-angle X-ray scattering (SAXS) was applied for studying the temperature-dependent structural behavior of the fully hydrated ME/MO-based system prepared with an equal ME/MO weight ratio and also for characterizing the fully hydrated OA- and EA-loaded ME systems. Wide-angle X-ray (WAXS) experiments were also performed for characterizing the formed crystalline lamellar phases at ambient temperatures. The results demonstrate the significant influence of the partial replacement of ME by MO on the phase behavior. The addition of MO induces the lamellar-nonlamellar phase transitions at ambient temperatures and promotes the formation of the inverted type hexagonal (H(2)) phase above 72 °C. The fully hydrated ME/EA and ME/OA systems with their rich polymorphism exhibit an interesting temperature-dependent complex behavior. The experimental findings show that the temperature-induced phase transitions are dictated by the solubilized fatty acid concentration and its configuration. Both EA and OA have a significant impact on the fully hydrated ME system. Similar to previous published studies, OA induces a significantly stronger mean negative membrane curvature as compared to EA. The two phase diagrams are discussed in terms of water-lipid and lipid-fatty acid interactions, membrane bending, and lipid packing concepts. A newly observed interesting epitaxial relationship for the lamellar-hexagonal phase transition in the EA-loaded ME system is illustrated and discussed in detail.

2-Hydroxyoleate, a nontoxic membrane binding anticancer drug, induces glioma cell differentiation and autophagy

Despite recent advances in the development of new cancer therapies, the treatment options for glioma remain limited, and the survival rate of patients has changed little over the past three decades. Here, we show that 2-hydroxyoleic acid (2OHOA) induces differentiation and autophagy of human glioma cells. Compared to the current reference drug for this condition, temozolomide (TMZ), 2OHOA combated glioma more efficiently and, unlike TMZ, tumor relapse was not observed following 2OHOA treatment. The novel mechanism of action of 2OHOA is associated with important changes in membrane-lipid composition, primarily a recovery of sphingomyelin (SM) levels, which is markedly low in glioma cells before treatment. Parallel to membrane-lipid regulation, treatment with 2OHOA induced a dramatic translocation of Ras from the membrane to the cytoplasm, which inhibited the MAP kinase pathway, reduced activity of the PI3K/Akt pathway, and downregulated Cyclin D-CDK4/6 proteins followed by hypophosphorylation of the retinoblastoma protein (RB). These regulatory effects were associated with induction of glioma cell differentiation into mature glial cells followed by autophagic cell death. Given its high efficacy, low toxicity, ease of oral administration, and good distribution to the brain, 2OHOA constitutes a new and potentially valuable therapeutic tool for glioma patients.

Sphingomyelin and sphingomyelin synthase (SMS) in the malignant transformation of glioma cells and in 2-hydroxyoleic acid therapy

The mechanism of action of 2-hydroxyoleic acid (2OHOA), a potent antitumor compound, has not yet been fully elucidated. Here, we show that human cancer cells have markedly lower levels of sphingomyelin (SM) than nontumor (MRC-5) cells. In this context, 2OHOA treatment strongly augments SM mass (4.6-fold), restoring the levels found in MRC-5 cells, while a loss of phosphatidylethanolamine and phosphatidylcholine is observed (57 and 30%, respectively). The increased SM mass was due to a rapid and highly specific activation of SM synthases (SMS). This effect appeared to be specific against cancer cells as it did not affect nontumor MRC-5 cells. Therefore, low SM levels are associated with the tumorigenic transformation that produces cancer cells. SM accumulation occurred at the plasma membrane and caused an increase in membrane global order and lipid raft packing in model membranes. These modifications would account for the observed alteration by 2OHOA in the localization of proteins involved in cell apoptosis (Fas receptor) or differentiation (Ras). Importantly, SMS inhibition by D609 diminished 2OHOA effect on cell cycle. Therefore, we propose that the regulation of SMS activity in tumor cells is a critical upstream event in 2OHOA antitumor mechanism, which also explains its specificity for cancer cells, its potency, and the lack of undesired side effects. Finally, the specific activation of SMS explains the ability of this compound to trigger cell cycle arrest, cell differentiation, and autophagy or apoptosis in cancer cells.

Biophysical interactions with model lipid membranes: applications in drug discovery and drug delivery

The transport of drugs or drug delivery systems across the cell membrane is a complex biological process, often difficult to understand because of its dynamic nature. In this regard, model lipid membranes, which mimic many aspects of cell-membrane lipids, have been very useful in helping investigators to discern the roles of lipids in cellular interactions. One can use drug-lipid interactions to predict pharmacokinetic properties of drugs, such as their transport, biodistribution, accumulation, and hence efficacy. These interactions can also be used to study the mechanisms of transport, based on the structure and hydrophilicity/hydrophobicity of drug molecules. In recent years, model lipid membranes have also been explored to understand their mechanisms of interactions with peptides, polymers, and nanocarriers. These interaction studies can be used to design and develop efficient drug delivery systems. Changes in the lipid composition of cells and tissue in certain disease conditions may alter biophysical interactions, which could be explored to develop target-specific drugs and drug delivery systems. In this review, we discuss different model membranes, drug-lipid interactions and their significance, studies of model membrane interactions with nanocarriers, and how biophysical interaction studies with lipid model membranes could play an important role in drug discovery and drug delivery.

Interactions of fatty acids with phosphatidylethanolamine membranes: X-ray diffraction and molecular dynamics studies

An experimental and theoretical study on 1,2-dielaidoyl-sn-glycero-3-phosphoethanolamine (DEPE) membranes containing fatty acids (FAs) was performed by means of X-ray diffraction analysis and molecular dynamics (MD) simulations. The study was aimed at understanding the interactions of several structurally related FAs with biomembranes, which is necessary for further rational lipid drug design in membrane-lipid therapy. The main effect of FAs was to promote the formation of a H(II) phase, despite a stabilization of the coexisting L(alpha) + H(II) phases. Derivatives of OA exhibited a specific density profile in the direction perpendicular to the bilayer that reflects differences in the relative localization of the carboxylate group within the polar region of the membrane as well as in the degree of membrane penetration of the FA acyl chain. Hydroxyl and methyl substituents at carbon-2 in the FA acyl chain were identified as effective modulators of the position of carboxylate group in the lipid bilayer. Our data highlight the specific potential of each FA in modulating the membrane structure properties.

Pivotal role of dihydrofolate reductase knockdown in the anticancer activity of 2-hydroxyoleic acid

alpha-Hydroxy-9-cis-octadecenoic acid, a synthetic fatty acid that modifies the composition and structure of lipid membranes. 2-Hydroxyoleic acid (HOA) generated interest due to its potent, yet nontoxic, anticancer activity. It induces cell cycle arrest in human lung cancer (A549) cells and apoptosis in human leukemia (Jurkat) cells. These two pathways may explain how HOA induces regression of a variety of cancers. We showed that HOA repressed the expression of dihydrofolate reductase (DHFR), the enzyme responsible for tetrahydrofolate (THF) synthesis. Folinic acid, which readily produces THF without the participation of DHFR, reverses the antitumor effects of HOA in A549 and Jurkat cells, as well as the inhibitory influence on cyclin D and cdk2 in A549 cells, and on DNA and PARP degradation in Jurkat cells. This effect was very specific, because either elaidic acid (an analog of HOA) or other lipids, failed to alter A549 or Jurkat cell growth. THF is a cofactor necessary for DNA synthesis. Thus, impairment of DNA synthesis appears to be a common mechanism involved in the different responses elicited by cancer cells following treatment with HOA, namely cell cycle arrest or apoptosis. Compared with other antifolates, such as methotrexate, HOA did not directly inhibit DHFR but rather, it repressed its expression, a mode of action that offers certain therapeutic advantages. These results not only demonstrate the effect of a fatty acid on the expression of DHFR, but also emphasize the potential of HOA to be used as a wide-spectrum drug against cancer.

Farnesol and geranylgeraniol modulate the structural properties of phosphatidylethanolamine model membranes

The biological activity of farnesol (FN) and geranylgeraniol (GG) and their isoprenyl groups is related to membrane-associated processes. We have studied the interactions of FN and GG with 1,2-dielaidoyl-sn-glycero-3-phosphoethanolamine (DEPE) membranes using DSC and X-ray diffraction. Storage of samples at low temperature for a long time favors a multidomain system formed by a lamellar crystalline (Lc) phase and isoprenoids (ISPs) aggregates. We demonstrate that ISPs alter the thermotropic behavior of DEPE, thereby promoting a HII growth in a lamellar Lc phase with a reduced degree of hydration. The HII phase occurs with the same repeat distance (dHII=5.4 nm) as the Lc phase and upon heating it expands considerably (deltad/deltaT approximately 0.22 nm/ degrees C). The dimensional stabilization of this HII phase coincides with the transition temperature of the Lc to Lalpha phase. Thereafter, the system DEPE/ISP will progress by increasing the nonlamellar-forming propensity and reaching a single HII phase at high temperature. The cooling scan followed a similar structural path, except that the system went into a stable gel phase Lbeta with a repeat distance, dLbeta=6.5 nm, in co-existence with a HII phase. The formation of ISP microdomains in model PE membranes substantiates the importance of the isoprenyl group in the binding of isoprenylated proteins to membranes and in lipid-lipid interactions through modulation of the membrane structure.

Minerval induces apoptosis in Jurkat and other cancer cells

Minerval is an oleic acid synthetic analogue that impairs lung cancer (A549) cell proliferation upon modulation of the plasma membrane lipid structure and subsequent regulation of protein kinase C localization and activity. However, this mechanism does not fully explain the regression of tumours induced by this drug in animal models of cancer. Here we show that Minerval also induced apoptosis in Jurkat T-lymphoblastic leukaemia and other cancer cells. Minerval inhibited proliferation of Jurkat cells, concomitant with a decrease of cyclin D3 and cdk2 (cyclin-dependent kinase2). In addition, the changes that induced on Jurkat cell membrane organization caused clustering (capping) of the death receptor Fas (CD95), caspase-8 activation and initiation of the extrinsic apoptosis pathway, which finally resulted in programmed cell death. The present results suggest that the intrinsic pathway (associated with caspase-9 function) was activated downstream by caspase-8. In a xenograft model of human leukaemia, Minerval also inhibited tumour progression and induced tumour cell death. Studies carried out in a wide variety of cancer cell types demonstrated that apoptosis was the main molecular mechanism triggered by Minerval. This is the first report on the pro-apoptotic activity of Minerval, and in part explains the effectiveness of this non-toxic anticancer drug and its wide spectrum against different types of cancer.

Oleic acid content is responsible for the reduction in blood pressure induced by olive oil

Numerous studies have shown that high olive oil intake reduces blood pressure (BP). These positive effects of olive oil have frequently been ascribed to its minor components, such as alpha-tocopherol, polyphenols, and other phenolic compounds that are not present in other oils. However, in this study we demonstrate that the hypotensive effect of olive oil is caused by its high oleic acid (OA) content (approximately 70-80%). We propose that olive oil intake increases OA levels in membranes, which regulates membrane lipid structure (H(II) phase propensity) in such a way as to control G protein-mediated signaling, causing a reduction in BP. This effect is in part caused by its regulatory action on G protein-associated cascades that regulate adenylyl cyclase and phospholipase C. In turn, the OA analogues, elaidic and stearic acids, had no hypotensive activity, indicating that the molecular mechanisms that link membrane lipid structure and BP regulation are very specific. Similarly, soybean oil (with low OA content) did not reduce BP. This study demonstrates that olive oil induces its hypotensive effects through the action of OA.

Effects of 2-hydroxyoleic acid on the structural properties of biological and model plasma membranes

Genetic hypertension is associated with alterations in lipid metabolism, membrane lipid composition and membrane-protein function. 2-Hydroxyoleic acid (2OHOA) is a new antihypertensive molecule that regulates the structure of model membranes and their interaction with certain peripheral signalling proteins in vitro. While the effect of 2OHOA on elevated blood pressure is thought to arise through its influence on signalling proteins, its effects on membrane lipid composition remain to be assessed. 2OHOA administration altered the lipid membrane composition of hypertensive and normotensive rat plasma membranes, and increased the fluidity of reconstituted liver membranes from hypertensive rats. In spontaneously hypertensive rats (SHR), treatment with 2OHOA increased the cholesterol and sphingomyelin content while decreasing that of phosphatidylserine-phosphatidylinositol lipids. In addition, monounsaturated fatty acid levels increased as well as the propensity of reconstituted membranes to form HII-phases. These data suggest that 2OHOA regulates lipid metabolism that is altered in hypertensive animals, and that it affects the structural properties of liver plasma membranes in SHR. These changes in the structural properties of the plasma membrane may modulate the activity of signalling proteins that associate with the cell membrane such as the Galphaq/11 protein and hence, signal transduction.

2-hydroxyoleic acid affects cardiomyocyte [Ca2+]i transient and contractility in a region-dependent manner

Monounsaturated fatty acids such as oleic acid are cardioprotective, modify the physicochemical properties of cardiomyocyte membranes, and affect the electrical stability of these cells by regulating the conductance of ion channels. We have designed a nonhydrolysable oleic acid derivative, 2-hydroxyoleic acid (2-OHOA), which regulates membrane lipid structure and cell signaling, resulting in beneficial cardiovascular effects. We previously demonstrated that 2-OHOA induces PKA activation and PKCalpha translocation to the membrane; both pathways are thought to regulate transient outward K(+) current (I(to)) depending on the stimulus and the species used. This study was designed to investigate the effect of 2-OHOA on isolated cardiomyocytes. We examined the dose- and time-dependent effect of 2-OHOA on cytosolic Ca(2+) concentration ([Ca(2+)](i)) transient and contraction of myocytes isolated from different parts of the rat ventricular myocardium. Although this drug had no effect on [Ca(2+)](i) transient and cell shortening in myocytes isolated from the septum, it increased (up to 95%) [Ca(2+)](i) transient and cell shortening in subpopulations of myocytes from the right and left ventricles. The pattern of the effects of 2-OHOA was similar to that observed following the application of the I(to) blocker 4-aminopyridine, suggesting that the drug may act on this channel. Unlike the effect of 2-OHOA on [Ca(2+)](i) transient and cell shortening, PKCalpha translocation to membranes was not region specific. Thus 2-OHOA-induced effects on [Ca(2+)](i) transients and cell shortening are likely related to reductions in I(to) function, but PKCalpha translocation does not seem to play a role. The present results indicate that 2-OHOA selectively increases myocyte inotropic responsiveness, which could underlie its beneficial cardiovascular effects.

Tetracaine-membrane interactions: effects of lipid composition and phase on drug partitioning, location, and ionization

Interactions of the local anesthetic tetracaine with unilamellar vesicles made of dimyristoyl or dipalmitoyl phosphatidylcholine (DMPC or DPPC), the latter without or with cholesterol, were examined by following changes in the drug's fluorescent properties. Tetracaine's location within the membrane (as indicated by the equivalent dielectric constant around the aromatic fluorophore), its membrane:buffer partition coefficients for protonated and base forms, and its apparent pK(a) when adsorbed to the membrane were determined by measuring, respectively, the saturating blue shifts of fluorescence emission at high lipid:tetracaine, the corresponding increases in fluorescence intensity at this lower wavelength with increasing lipid, and the dependence of fluorescence intensity of membrane-bound tetracaine (TTC) on solution pH. Results show that partition coefficients were greater for liquid-crystalline than solid-gel phase membranes, whether the phase was set by temperature or lipid composition, and were decreased by cholesterol; neutral TTC partitioned into membranes more strongly than the protonated species (TTCH(+)). Tetracaine's location in the membrane placed the drug's tertiary amine near the phosphate of the headgroup, its ester bond in the region of the lipids' ester bonds, and associated dipole field and the aromatic moiety near fatty acyl carbons 2-5; importantly, this location was unaffected by cholesterol and was the same for neutral and protonated tetracaine, showing that the dipole-dipole and hydrophobic interactions are the critical determinants of tetracaine's location. Tetracaine's effective pK(a) was reduced by 0.3-0.4 pH units from the solution pK(a) upon adsorption to these neutral bilayers, regardless of physical state or composition. We propose that the partitioning of tetracaine into solid-gel membranes is determined primarily by its steric accommodation between lipids, whereas in the liquid-crystalline membrane, in which the distance between lipid molecules is larger and steric hindrance is less important, hydrophobic and ionic interactions between tetracaine and lipid molecules predominate.

Membrane-lipid therapy: a new approach in molecular medicine

Although most drugs bind to proteins and regulate their activity, some drugs act through a new therapeutic approach called membrane-lipid therapy and bind to lipids, thus modulating the structure of membranes. Most cellular functions are highly dependent on the lipid environment because they are controlled by proteins in or around membranes. The wide variety of cell and organelle membranes and the existence of special lipid regions (e.g. microvilli) and domains (e.g. lipid rafts) support the possibility of designing specific lipid therapies. Indeed, recent evidence suggests that lipid therapy might have potential for the treatment of cancer, cardiovascular pathologies, neurodegenerative processes, obesity, metabolic disorders, inflammation, and infectious and autoimmune diseases.

The significance of lipid composition for membrane activity: New concepts and ways of assessing function

In the last decade or so, it has been realised that membranes do not just have a lipid-bilayer structure in which proteins are embedded or with which they associate. Structures are dynamic and contain areas of heterogeneity which are vital for their formation. In this review, we discuss some of the ways in which these dynamic and heterogeneous structures have implications during stress and in relation to certain human diseases. A particular stress is that of temperature which may instigate adaptation in poikilotherms or appropriate defensive responses during fever in mammals. Recent data emphasise the role of membranes in sensing temperature changes and in controlling a regulatory loop with chaperone proteins. This loop seems to need the existence of specific membrane microdomains and also includes association of chaperone (heat stress) proteins with the membrane. The role of microdomains is then discussed further in relation to various human pathologies such as cardiovascular disease, cancer and neurodegenerative diseases. The concept of modifying membrane lipids (lipid therapy) as a means for treating such pathologies is then introduced. Examples are given when such methods have been shown to have benefit. In order to study membrane microheterogeneity in detail and to elucidate possible molecular mechanisms that account for alteration in membrane function, new methods are needed. In the second part of the review, we discuss ultra-sensitive and ultra-resolution imaging techniques. These include atomic force microscopy, single particle tracking, single particle tracing and various modern fluorescence methods. Finally, we deal with computing simulation of membrane systems. Such methods include coarse-grain techniques and Monte Carlo which offer further advances into molecular dynamics. As computational methods advance they will have more application by revealing the very subtle interactions that take place between the lipid and protein components of membranes - and which are so essential to their function.

The repression of E2F-1 is critical for the activity of Minerval against cancer

The recently discovered anticancer drug Minerval (2-hydroxy-9-cis-octadecenoic acid) is a synthetic fatty acid that modifies the structure of the membrane. This restructuring facilitates the recruitment of protein kinase C (PKC) alpha to membranes and is associated with the antineoplastic activity of Minerval in cellular and animal models of cancer. Minerval is a derivative of oleic acid (OA) with an enhanced antiproliferative activity in human cancer cells and animal models of cancer, which is associated with PKCalpha activation and p21(CIP) overexpression. However, the signaling cascades involved in its pharmacological activity remain largely unknown. Here, we showed that this drug induced cell cycle arrest before entry into S phase, human lung adenocarcinoma (A549) cells accumulating in the G0/G1 phase. This cell cycle arrest was associated with a marked decrease in the expression of E2F-1. This transcription factor activates several cell cycle-related genes, and, accordingly, the expression of certain cyclins and cyclin-dependent kinases (cdks) was markedly lower upon exposure to Minerval. The reduced availability of these kinase heterodimers was associated with reduced phosphorylation of the retinoblastoma protein (pRb) observed after drug treatment. Significantly, hypophosphorylated pRb remains bound to E2F-1 and maintains this transcription factor inactive. The modulation of these antiproliferative mechanisms by Minerval explains its anticancer potency, through a new therapeutic strategy that can be used to develop new antitumor drugs. On the other hand, apoptosis did not seem to be involved in its pharmacological mechanism. Interestingly, whereas the changes induced by OA were only modest, they may reflect the beneficial effects of high olive oil intake against cancer.

Influence of the Membrane Lipid Structure on Signal Processing via G Protein-Coupled Receptors

We have recently reported that lipid structure regulates the interaction with membranes, recruitment to membranes, and distribution to membrane domains of heterotrimeric Galphabetagamma proteins, Galpha subunits, and Gbetagamma dimers (J Biol Chem 279:36540-36545, 2004). Here, we demonstrate that modulation of the membrane structure not only determines G protein localization but also regulates the function of G proteins and related signaling proteins. In this context, the antitumor drug daunorubicin (daunomycin) and oleic acid changed the membrane structure and inhibited G protein activity in biological membranes. They also induced marked changes in the activity of the alpha(2A/D)-adrenergic receptor and adenylyl cyclase. In contrast, elaidic and stearic acid did not change the activity of the above-mentioned proteins. These fatty acids are chemical but not structural analogs of oleic acid, supporting the structural basis of the modulation of membrane lipid organization and subsequent regulation of G protein-coupled receptor signaling. In addition, oleic acid (and also daunorubicin) did not alter G protein activity in a membrane-free system, further demonstrating the involvement of membrane structure in this signal modulation. The present work also unravels in part the molecular bases involved in the antihypertensive (Hypertension 43:249-254, 2004) and anticancer (Mol Pharmacol 67:531-540, 2005) activities of synthetic oleic acid derivatives (e.g., 2-hydroxyoleic acid) as well as the molecular bases of the effects of diet fats on human health.

Membrane structure modulation, protein kinase C alpha activation, and anticancer activity of minerval

Most drugs currently used for human therapy interact with proteins, altering their activity to modulate the pathological cell physiology. In contrast, 2-hydroxy-9-cis-octadecenoic acid (Minerval) was designed to modify the lipid organization of the membrane. Its structure was deduced following the guidelines of the mechanism of action previously proposed by us for certain antitumor drugs. The antiproliferative activity of Minerval supports the above-mentioned hypothesis. This molecule augments the propensity of membrane lipids to organize into nonlamellar (hexagonal H(II)) phases, promoting the subsequent recruitment of protein kinase C (PKC) to the cell membrane. The binding of the enzyme to membranes was marked and significantly elevated by Minerval in model (liposomes) and cell (A549) membranes and in heart membranes from animals treated with this drug. In addition, Minerval induced increased PKCalpha expression (mRNA and protein levels) in A549 cells. This drug also induced PKC activation, which led to a p53-independent increase in p21(CIP) expression, followed by a decrease in the cellular concentrations of cyclins A, B, and D3 and cdk2. These molecular changes impaired the cell cycle progression of A549 cells. At the cellular and physiological level, administration of Minerval inhibited the growth of cancer cells and exerted antitumor effects in animal models of cancer without apparent histological toxicity. The present results support the potential use of Minerval and related compounds in the treatment of tumor pathologies.