Disrupting membrane raft domains by alkylphospholipids

Unraveling Cholesterol-Dependent Interactions of Alkylphospholipids with Supported Lipid Bilayers

Alkylphospholipids are single-chain lipid amphiphiles that possess clinically relevant biological activities driven by membrane-destabilizing interactions. Subtle variations in alkylphospholipid structure can lead to significant differences in their biological effects, yet corresponding membrane interactions remain underexplored. Herein, we employed the quartz crystal microbalance-dissipation (QCM-D) technique to characterize the real-time membrane interactions of three alkylphospholipids-edelfosine, miltefosine, and perifosine-on supported lipid bilayers with varying cholesterol fractions. Our findings reveal that the tested alkylphospholipids had distinct membrane-interaction profiles: (1) edelfosine exhibited irreversible binding and caused weak membrane disruption; (2) miltefosine caused major disruption by affecting membrane packing; and (3) perifosine exhibited reversible binding while triggering structural rearrangements and modest disruption. Overall, alkylphospholipid micelles showed greater activity than monomers, and higher membrane cholesterol fractions resulted in more extensive disruption, highlighting the interplay between membrane stiffness and responsiveness. These results provide biophysical evidence that different alkylphospholipids have distinct membrane-interaction behaviors that align well with reported biological activities. Our supported lipid bilayer approach offers a valuable platform for designing and assessing alkylphospholipids with tailored membrane-interaction profiles.

Toxic Effects of Butanol in the Plane of the Cell Membrane

Solvent toxicity limits n-butanol fermentation titer, increasing the cost and energy consumption for subsequent separation processes and making biobased production more expensive and energy-intensive than petrochemical approaches. Amphiphilic solvents such as n-butanol partition into the cell membrane of fermenting microorganisms, thinning the transverse structure, and eventually causing a loss of membrane potential and cell death. In this work, we demonstrate the deleterious effects of n-butanol partitioning upon the lateral dimension of the membrane structure, called membrane domains or lipid rafts. Lipid rafts are regions of the cell membrane enriched with certain lipids, providing a reservoir of high melting temperature lipids and a platform for membrane protein partitioning and oligomerization. Neutron scattering experiments and molecular dynamics simulations revealed that n-butanol increased the size of the lipid domains in a model membrane system. The data showed that n-butanol partitions more into the disordered lipid regions than into the raft-like phase, leading to a differential thinning of these coexisting phases in the plane of the membrane and increasing the hydrophobic mismatch. The resulting increase in line tension at the interface favors domain coalescence to minimize the ratio of the interfacial length to domain area. A detailed computational investigation of the lipid domain interface identifies the boundary as a site of membrane disorder and thinning due to an accumulation of n-butanol. Solvent-induced changes to domain morphology and membrane instability at the domain interface are unrecognized modes of solvent-induced stress to fermenting microbes, representing targets for new solvent tolerance strategies to increase the n-butanol titer.

Molecular docking as a tool for the discovery of novel insight about the role of acid sphingomyelinase inhibitors in SARS- CoV-2 infectivity

Recently, COVID-19, caused by severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) and its variants, caused > 6 million deaths. Symptoms included respiratory strain and complications, leading to severe pneumonia. SARS-CoV-2 attaches to the ACE-2 receptor of the host cell membrane to enter. Targeting the SARS-CoV-2 entry may effectively inhibit infection. Acid sphingomyelinase (ASMase) is a lysosomal protein that catalyzes the conversion of sphingolipid (sphingomyelin) to ceramide. Ceramide molecules aggregate/assemble on the plasma membrane to form "platforms" that facilitate the viral intake into the cell. Impairing the ASMase activity will eventually disrupt viral entry into the cell. In this review, we identified the metabolism of sphingolipids, sphingolipids' role in cell signal transduction cascades, and viral infection mechanisms. Also, we outlined ASMase structure and underlying mechanisms inhibiting viral entry 40 with the aid of inhibitors of acid sphingomyelinase (FIASMAs). In silico molecular docking analyses of FIASMAs with inhibitors revealed that dilazep (S = - 12.58 kcal/mol), emetine (S = - 11.65 kcal/mol), pimozide (S = - 11.29 kcal/mol), carvedilol (S = - 11.28 kcal/mol), mebeverine (S = - 11.14 kcal/mol), cepharanthine (S = - 11.06 kcal/mol), hydroxyzin (S = - 10.96 kcal/mol), astemizole (S = - 10.81 kcal/mol), sertindole (S = - 10.55 kcal/mol), and bepridil (S = - 10.47 kcal/mol) have higher inhibition activity than the candidate drug amiodarone (S = - 10.43 kcal/mol), making them better options for inhibition.

Mitochondrial Functionality Is Regulated by Alkylphospholipids in Human Colon Cancer Cells

Alkylphospholipids (APLs) have been studied as anticancer drugs that interfere with biological membranes without targeting DNA. Although their mechanism of action is not fully elucidated yet, it is known that they disrupt the intracellular trafficking of cholesterol and its metabolism. Here, we analyzed whether APLs could also interfere with mitochondrial function. For this purpose, we used HT29 colorectal cancer cells, derived from a primary tumor, and SW620 colorectal cancer cells, derived from a metastasis site. After treatment with the APLs miltefosine and perifosine, we analyzed various mitochondrial parameters, including mitochondrial mass, cardiolipin content, mitochondrial membrane potential, H2O2 production, the levels of oxidative phosphorylation (OXPHOS) complexes, metabolic enzymes activity, the oxygen consumption rate, and the levels of apoptosis and autophagy markers. APLs, especially perifosine, increased mitochondrial mass while OXPHOS complexes levels were decreased without affecting the total oxygen consumption rate. Additionally, we observed an increase in pyruvate dehydrogenase (PDH) and isocitrate dehydrogenase (IDH) levels and a decrease in lactate dehydrogenase (LDH) activity, suggesting a metabolic rewiring induced by perifosine. These alterations led to higher mitochondrial membrane potential, which was potentiated by decreased uncoupling protein 2 (UCP2) levels and increased reactive oxygen species (ROS) production. Consequently, perifosine induced an imbalance in mitochondrial function, resulting in higher ROS production that ultimately impacted cellular viability.

Lipid raft-disrupting miltefosine preferentially induces the death of colorectal cancer stem-like cells

BACKGROUND

Lipid rafts (LRs), cholesterol-enriched microdomains on cell membranes, are increasingly viewed as signalling platforms governing critical facets of cancer progression. The phenotype of cancer stem-like cells (CSCs) presents significant hurdles for successful cancer treatment, and the expression of several CSC markers is associated with LR integrity. However, LR implications in CSCs remain unclear.

METHODS

This study evaluated the biological and molecular functions of LRs in colorectal cancer (CRC) by using an LR-disrupting alkylphospholipid (APL) drug, miltefosine. The mechanistic role of miltefosine in CSC inhibition was examined through normal or tumour intestinal mouse organoid, human CRC cell, CRC xenograft and miltefosine treatment gene expression profile analyses.

RESULTS

Miltefosine suppresses CSC populations and their self-renewal activities in CRC cells, a CSC-targeting effect leading to irreversible disruption of tumour-initiating potential in vivo. Mechanistically, miltefosine reduced the expression of a set of genes, leading to stem cell death. Among them, miltefosine transcriptionally inhibited checkpoint kinase 1 (CHEK1), indicating that LR integrity is essential for CHEK1 expression regulation. In isolated CD44high CSCs, we found that CSCs exhibited stronger therapy resistance than non-CSC counterparts by preventing cell death through CHEK1-mediated cell cycle checkpoints. However, inhibition of the LR/CHEK1 axis by miltefosine released cell cycle checkpoints, forcing CSCs to enter inappropriate mitosis with accumulated DNA damage and resulting in catastrophic cell death.

CONCLUSION

Our findings underscore the therapeutic potential of LR-targeting APLs for CRC treatment that overcomes the therapy-resistant phenotype of CSCs, highlighting the importance of the LR/CHEK1 axis as a novel mechanism of APLs.

Transient receptor potential vanilloid subtype 1 depletion mediates mechanical allodynia through cellular signal alterations in small-fiber neuropathy

Transient receptor potential vanilloid subtype 1 (TRPV1) is a polymodal nociceptor that monitors noxious thermal sensations. Few studies have addressed the role of TRPV1 in mechanical allodynia in small-fiber neuropathy (SFN) caused by sensory nerve damage. Accordingly, this article reviews the putative mechanisms of TRPV1 depletion that mediates mechanical allodynia in SFN. The intraepidermal nerve fibers (IENFs) degeneration and sensory neuronal injury are the primary characteristics of SFN. Intraepidermal nerve fibers are mainly C-polymodal nociceptors and Aδ-fibers, which mediated allodynic pain after neuronal sensitization. TRPV1 depletion by highly potent neurotoxins induces the upregulation of activating transcription factor 3 and IENFs degeneration which mimics SFN. TRPV1 is predominately expressed by the peptidergic than nonpeptidergic nociceptors, and these neurochemical discrepancies provided the basis of the distinct pathways of thermal analgesia and mechanical allodynia. The depletion of peptidergic nociceptors and their IENFs cause thermal analgesia and sensitized nonpeptidergic nociceptors respond to mechanical allodynia. These distinct pathways of noxious stimuli suggested determined by the neurochemical-dependent neurotrophin cognate receptors such as TrkA and Ret receptors. The neurogenic inflammation after TRPV1 depletion also sensitized Ret receptors which results in mechanical allodynia. The activation of spinal TRPV1(+) neurons may contribute to mechanical allodynia. Also, an imbalance in adenosinergic analgesic signaling in sensory neurons such as the downregulation of prostatic acid phosphatase and adenosine A1 receptors, which colocalized with TRPV1 as a membrane microdomain also correlated with the development of mechanical allodynia. Collectively, TRPV1 depletion-induced mechanical allodynia involves a complicated cascade of cellular signaling alterations.

Interaction of drugs with lipid raft membrane domains as a possible target

Introduction

Plasma membranes are not the homogeneous bilayers of uniformly distributed lipids but the lipid complex with laterally separated lipid raft membrane domains, which provide receptor, ion channel and enzyme proteins with a platform. The aim of this article is to review the mechanistic interaction of drugs with membrane lipid rafts and address the question whether drugs induce physicochemical changes in raft-constituting and raft-surrounding membranes.

Methods

Literature searches of PubMed/MEDLINE and Google Scholar databases from 2000 to 2020 were conducted to include articles published in English in internationally recognized journals. Collected articles were independently reviewed by title, abstract and text for relevance.

Results

The literature search indicated that pharmacologically diverse drugs interact with raft model membranes and cellular membrane lipid rafts. They could physicochemically modify functional protein-localizing membrane lipid rafts and the membranes surrounding such domains, affecting the raft organizational integrity with the resultant exhibition of pharmacological activity. Raft-acting drugs were characterized as ones to decrease membrane fluidity, induce liquid-ordered phase or order plasma membranes, leading to lipid raft formation; and ones to increase membrane fluidity, induce liquid-disordered phase or reduce phase transition temperature, leading to lipid raft disruption.

Conclusion

Targeting lipid raft membrane domains would open a new way for drug design and development. Since angiotensin-converting enzyme 2 receptors which are a cell-specific target of and responsible for the cellular entry of novel coronavirus are localized in lipid rafts, agents that specifically disrupt the relevant rafts may be a drug against coronavirus disease 2019.

New Insights Into Targeting Membrane Lipids for Cancer Therapy

Modulation of membrane lipid composition and organization is currently developing as an effective therapeutic strategy against a wide range of diseases, including cancer. This field, known as membrane-lipid therapy, has risen from new discoveries on the complex organization of lipids and between lipids and proteins in the plasma membranes. Membrane microdomains present in the membrane of all eukaryotic cells, known as lipid rafts, have been recognized as an important concentrating platform for protein receptors involved in the regulation of intracellular signaling, apoptosis, redox balance and immune response. The difference in lipid composition between the cellular membranes of healthy cells and tumor cells allows for the development of novel therapies based on targeting membrane lipids in cancer cells to increase sensitivity to chemotherapeutic agents and consequently defeat multidrug resistance. In the current manuscript strategies based on influencing cholesterol/sphingolipids content will be presented together with innovative ones, more focused in changing biophysical properties of the membrane bilayer without affecting the composition of its constituents.

Effect of Erufosine on Membrane Lipid Order in Breast Cancer Cell Models

Alkylphospholipids are a novel class of antineoplastic drugs showing remarkable therapeutic potential. Among them, erufosine (EPC3) is a promising drug for the treatment of several types of tumors. While EPC3 is supposed to exert its function by interacting with lipid membranes, the exact molecular mechanisms involved are not known yet. In this work, we applied a combination of several fluorescence microscopy and analytical chemistry approaches (i.e., scanning fluorescence correlation spectroscopy, line-scan fluorescence correlation spectroscopy, generalized polarization imaging, as well as thin layer and gas chromatography) to quantify the effect of EPC3 in biophysical models of the plasma membrane, as well as in cancer cell lines. Our results indicate that EPC3 affects lipid-lipid interactions in cellular membranes by decreasing lipid packing and increasing membrane disorder and fluidity. As a consequence of these alterations in the lateral organization of lipid bilayers, the diffusive dynamics of membrane proteins are also significantly increased. Taken together, these findings suggest that the mechanism of action of EPC3 could be linked to its effects on fundamental biophysical properties of lipid membranes, as well as on lipid metabolism in cancer cells.

Lipids and Membrane Microdomains: The Glycerolipid and Alkylphosphocholine Class of Cancer Chemotherapeutic Drugs

Synthetic antitumor lipids are metabolically stable lysophosphatidylcholine derivatives, encompassing a class of non-mutagenic drugs that selectively target cancerous cells. In this chapter we review the literature as relates to the clinical efficacy of these antitumor lipid drugs and how our understanding of their mode of action has evolved alongside key advances in our knowledge of membrane structure, organization, and function. First, the history of the development of this class of drugs is described, providing a summary of clinical outcomes of key members including edelfosine, miltefosine, perifosine, erufosine, and erucylphosphocholine. A detailed description of the biophysical properties of these drugs and specific drug-lipid interactions which may contribute to the selectivity of the antitumor lipids for cancer cells follows. An updated model on the mode of action of these lipid drugs as membrane disorganizing agents is presented. Membrane domain organization as opposed to targeting specific proteins on membranes is discussed. By altering membranes, these antitumor lipids inhibit many survival pathways while activating pro-apoptotic signals leading to cell demise.

Treatment with methyl-β-cyclodextrin prevents mechanical allodynia in resiniferatoxin neuropathy in a mouse model

Specialized microdomains which have cholesterol-rich membrane regions contain transient receptor potential vanilloid subtype 1 (TRPV1) are involved in pain development. Our previous studies have demonstrated that the depletion of prostatic acid phosphatase (PAP) – a membrane-bound ectonucleotidase ­– and disordered adenosine signaling reduce the antinociceptive effect. The role of membrane integrity in the PAP-mediated antinociceptive effect in small-fiber neuropathy remains unclear, especially with respect to whether TRPV1 and PAP are colocalized in the same microdomain which is responsible for PAP-mediated antinociception. Immunohistochemistry was conducted on the dorsal root ganglion to identify the membrane compositions, and pharmacological interventions were conducted using methyl-β-cyclodextrin (MβC) – a membrane integrity disruptor that works by depleting cholesterol – in pure small-fiber neuropathy with resiniferatoxin (RTX). Immunohistochemical evidence indicated that TRPV1 and PAP were highly colocalized with flotillin 1 (66.7%±9.7%) and flotillin 2 (73.7%±6.0%), which reside in part in the microdomain. MβC mildly depleted PAP, which maintained the ability to hydrolyze phosphatidylinositol 4,5-bisphosphate [PI(4,5)P2] and delayed the development of mechanical allodynia. MβC treatment had no role in thermal transduction and neuronal injury following RTX neuropathy. In summary, this study demonstrated the following: (1) membrane cholesterol depletion preserves PAP-mediated antinociception through PI(4,5)P2 hydrolysis and (2) pain hypersensitivity that develops after TRPV1(+) neuron depletion-mediated neurodegeneration following RTX neuropathy is attributable to the downregulation of PAP analgesic signaling.

Summary: The role and mechanism of cholesterol-rich membrane integrity in pain development for small-fiber neuropathy remains unclear. Depletion of membrane cholesterol contents preserves functional PAP profiles and the antinociceptive effect after RTX neuropathy.

Attenuation of neuroblastoma cell growth by nisin is mediated by modulation of phase behavior and enhanced cell membrane fluidity

Antimicrobial peptide mediated fluidization of cancer membrane reduces cancer cell growth.

Contrasting roles of oxidized lipids in modulating membrane microdomains

Lipid rafts display a lateral heterogeneity forming membrane microdomains that hold a fundamental role on biological membranes and are indispensable to physiological functions of cells. Oxidative stress in cellular environments may cause lipid oxidation, changing membrane composition and organization, thus implying in effects in cell signaling and even loss of homeostasis. The individual contribution of oxidized lipid species to the formation or disruption of lipid rafts in membranes still remains unknown. Here, we investigate the role of different structures of oxidized phospholipids on rafts microdomains by carefully controlling the membrane composition. Our experimental approach based on fluorescence microscopy of giant unilamellar vesicles (GUV) enables the direct visualization of the impact of hydroperoxidized POPC lipid (referred to as POPCOOH) and shortened chain lipid PazePC (1-palmitoyl-2-azelaoyl-sn-glycero-3-phosphocholine) on phase separation. We found that the molecular structure of oxidized lipid is of paramount importance on lipid mixing and/or demixing. The hydrophobic mismatch promoted by POPCOOH coupled to its cylindrical molecular shape favor microdomains formation. In contrast, the conical shape of PazePC causes disarrangement of lipid 2D organized platforms. Our findings contribute to better unraveling how oxidized phospholipids can trigger formation or disruption of lipid rafts. As a consequence, phospholipid oxidation may indirectly affect association or dissociation of key biomolecules in the rafts thus altering cell signaling and homeostasis.

Perturbing the Dynamics and Organization of Cell Membrane Components: A New Paradigm for Cancer-Targeted Therapies

Cancer is a multi-process disease where different mechanisms exist in parallel to ensure cell survival and constant adaptation to the extracellular environment. To adapt rapidly, cancer cells re-arrange their plasma membranes to sustain proliferation, avoid apoptosis and resist anticancer drugs. In this review, we discuss novel approaches based on the modifications and manipulations that new classes of molecules can exert in the plasma membrane lateral organization and order of cancer cells, affecting growth factor signaling, invasiveness, and drug resistance. Furthermore, we present azurin, an anticancer protein from bacterial origin, as a new approach in the development of therapeutic strategies that target the cell membrane to improve the existing standard therapies.

Attenuating Staphylococcus aureus Virulence by Targeting Flotillin Protein Scaffold Activity

Scaffold proteins are ubiquitous chaperones that bind proteins and facilitate physical interaction of multi-enzyme complexes. Here we used a biochemical approach to dissect the scaffold activity of the flotillin-homolog protein FloA of the multi-drug-resistant human pathogen Staphylococcus aureus. We show that FloA promotes oligomerization of membrane protein complexes, such as the membrane-associated RNase Rny, which forms part of the RNA-degradation machinery called the degradosome. Cells lacking FloA had reduced Rny function and a consequent increase in the targeted sRNA transcripts that negatively regulate S. aureus toxin expression. Small molecules that altered FloA oligomerization also reduced Rny function and decreased the virulence potential of S. aureus in vitro, as well as in vivo, using invertebrate and murine infection models. Our results suggest that flotillin assists in the assembly of protein complexes involved in S. aureus virulence, and could thus be an attractive target for the development of new antimicrobial therapies.

The influence of an antitumor lipid - erucylphosphocholine - on artificial lipid raft system modeled as Langmuir monolayer

Outer layer of cellular membrane contains ordered domains enriched in cholesterol and sphingolipids, called 'lipid rafts', which play various biological roles, i.e., are involved in the induction of cell death by apoptosis. Recent studies have shown that these domains may constitute binding sites for selected drugs. For example alkylphosphocholines (APCs), which are new-generation antitumor agents characterized by high selectivity and broad spectrum of activity, are known to have their molecular targets located at cellular membrane and their selective accumulation in tumor cells has been hypothesized to be linked with the alternation of biophysical properties of lipid rafts. To get a deeper insight into this issue, interactions between representative APC: erucylphosphocholine, and artificial lipid raft system, modeled as Langmuir monolayer (composed of cholesterol and sphingomyelin mixed in 1:2 proportion) were investigated. The Langmuir monolayer experiments, based on recording surface pressure-area isotherms, were complemented with Brewster angle microscopy results, which enabled direct visualization of the monolayers structure. In addition, the investigated monolayers were transferred onto solid supports and studied with AFM. The interactions between model raft system and erucylphosphocholine were analyzed qualitatively (with mean molecular area values) as well as quantitatively (with ΔG(exc) function). The obtained results indicate that erucylphosphocholine introduced to raft-mimicking model membrane causes fluidizing effect and weakens the interactions between cholesterol and sphingomyelin, which results in phase separation at high surface pressures. This leads to the redistribution of cholesterol molecules in model raft, which confirms the results observed in biological studies.

Antitumor Lipids--Structure, Functions, and Medical Applications

Cell proliferation and metastasis are considered hallmarks of tumor progression. Therefore, efforts have been made to develop novel anticancer drugs that inhibit both the proliferation and the motility of tumor cells. Synthetic antitumor lipids (ATLs), which are chemically divided into two main classes, comprise (i) alkylphospholipids (APLs) and (ii) alkylphosphocholines (APCs). They represent a new entity of drugs with distinct antiproliferative properties in tumor cells. These compounds do not interfere with the DNA or mitotic spindle apparatus of the cell, instead, they incorporate into cell membranes, where they accumulate and interfere with lipid metabolism and lipid-dependent signaling pathways. Recently, it has been shown that the most commonly studied APLs inhibit proliferation by inducing apoptosis in malignant cells while leaving normal cells unaffected and are potent sensitizers of conventional chemo- and radiotherapy, as well as of electrical field therapy. APLs resist catabolic degradation to a large extent, therefore accumulate in the cell and interfere with lipid-dependent survival signaling pathways, notably PI3K-Akt and Raf-Erk1/2, and de novo phospholipid biosynthesis. They are internalized in the cell membrane via raft domains and cause downstream reactions as inhibition of cell growth and migration, cell cycle arrest, actin stress fibers collapse, and apoptosis. This review summarizes the in vitro, in vivo, and clinical trials of most common ATLs and their mode of action at molecular and biochemical levels.

Understanding Miltefosine-Membrane Interactions Using Molecular Dynamics Simulations

Coarse-grained molecular dynamics simulations are used to calculate the free energies of transfer of miltefosine, an alkylphosphocholine anticancer agent, from water to lipid bilayers to study its mechanism of interaction with biological membranes. We consider bilayers containing lipids with different degrees of unsaturation: dipalmitoylphosphatidylcholine (DPPC, saturated, containing 0%, 10%, and 30% cholesterol), dioleoylphosphatidylcholine (DOPC, diunsaturated), palmitoyloleoylphosphatidylcholine (POPC, monounsaturated), diarachidonoylphosphatidylcholine (DAPC, polyunsaturated), and dilinoleylphosphatidylcholine (DUPC, polyunsaturated). These free energies, calculated using umbrella sampling, were used to compute the partition coefficients (K) of miltefosine between water and the lipid bilayers. The K values for the bilayers relative to that of pure DPPC were found to be 5.3 (DOPC), 7.0 (POPC), 1.0 (DAPC), 2.2 (DUPC), 14.9 (10% cholesterol), and 76.2 (30% cholesterol). Additionally, we calculated the free energy of formation of miltefosine-cholesterol complexes by pulling the surfactant laterally in the DPPC + 30% cholesterol system. The free energy profile that we obtained provides further evidence that miltefosine tends to associate with cholesterol and has a propensity to partition into lipid rafts. We also quantified the kinetics of the transport of miltefosine through the various bilayers by computing permeance values. The highest permeance was observed in DUPC bilayers (2.28 × 10(-2) m/s) and the lowest permeance in the DPPC bilayer with 30% cholesterol (1.10 × 10(-7) m/s). Our simulation results show that miltefosine does indeed interact with lipid rafts, has a higher permeability in polyunsaturated, loosely organized bilayers, and has higher flip-flop rates in specific regions of cellular membranes.

Membrane changes under oxidative stress: the impact of oxidized lipids

Studying photosensitized oxidation of unsaturated phospholipids is of importance for understanding the basic processes underlying photodynamic therapy, photoaging and many other biological dysfunctions. In this review we show that the giant unilamellar vesicle, when used as a simplified model of biological membranes, is a powerful tool to investigate how in situ photogenerated oxidative species impact the phospholipid bilayer. The extent of membrane damage can be modulated by choosing a specific photosensitizer (PS) which is activated by light irradiation and can react by either type I and or type II mechanism. We will show that type II PS generates only singlet oxygen which reacts to the phospholipid acyl double bond. The byproduct thus formed is a lipid hydroperoxide which accumulates in the membrane as a function of singlet oxygen production and induces an increase in its area without significantly affecting membrane permeability. The presence of a lipid hydroperoxide can also play an important role in the formation of the lipid domain for mimetic plasma membranes. Lipid hydroperoxides can be also transformed in shortened chain compounds, such as aldehydes and carboxylic acids, in the presence of a PS that reacts via the type I mechanism. The presence of such byproducts may form hydrophilic pores in the membrane for moderate oxidative stress or promote membrane disruption for massive oxidation. Our results provide a new tool to explore membrane response to an oxidative stress and may have implications in biological signaling of redox misbalance.

Cholesterol as a factor regulating the influence of natural (PAF and lysoPAF) vs synthetic (ED) ether lipids on model lipid membranes

In this work we have performed a comparative study on the effect of antineoplastic ether lipid-edelfosine (ED), its natural analogs - Platelet Activating Factor (PAF) and its precursor (lyso-PAF), both lacking anticancer properties, on cholesterol/phosphatidylcholine (Chol/PC) monolayers, serving as model membranes. Since all the above ether lipids are membrane active, it can be expected that their effect on membranes may differentiate their biological activity. Our investigations were aimed at studying potential relationship of the effect of ED, PAF and lyso-PAF on model membranes, differing in condensation. We have modified molecular packing of Chol/PC model systems either by increasing the level of sterol in the system or changing the structure of PC, while keeping the same sterol content. Additionally, we have performed a detailed comparison of the miscibility of ED, PAF and lyso-PAF with various membrane lipids. The collected data evidenced that all the investigated ether lipids influence Chol/PC films in the same way; however, in a different magnitude. Moreover, the interactions of ED, PAF and lyso-PAF with model membranes were the strongest at the highest level of sterol in the system. A thorough analysis of the obtained results has proved that the effect of the investigated ether lipids on membranes is not dependent on the condensation of the system, but it is strongly determined by the concentration of cholesterol. Since ED was found to interact with model membranes stronger than PAF and lyso-PAF, we have suggested that this fact may contribute to differences in cytotoxicity of these compounds.

Edelfosine and miltefosine effects on lipid raft properties: membrane biophysics in cell death by antitumor lipids

Edelfosine (1-O-octadecyl-2-O-methyl-sn-glycero-phosphocholine) and miltefosine (hexadecylphosphocholine) are synthetic alkylphospholipids (ALPs) that are reported to selectively accumulate in tumor cell membranes, inducing Fas clustering and activation on lipid rafts, triggering apoptosis. However, the exact mechanism by which these lipids elicit these events is still not fully understood. Recent studies propose that their mode of action might be related with alterations of lipid rafts biophysical properties caused by these lipid drugs. To achieve a clear understanding of this mechanism, we studied the effects of pharmacologically relevant amounts of edelfosine and miltefosine in the properties of model and cellular membranes. The influence of these molecules on membrane order, lateral organization, and lipid rafts molar fraction and size were studied by steady-state and time-resolved fluorescence methods, Förster resonance energy transfer (FRET), confocal and fluorescence lifetime imaging microscopy (FLIM). We found that the global membrane and lipid rafts biophysical properties of both model and cellular membranes were not significantly affected by both the ALPs. Nonetheless, in model membranes, a mild increase in membrane fluidity induced by both alkyl lipids was detected, although this effect was more noticeable for edelfosine than miltefosine. This absence of drastic alterations shows for the first time that ALPs mode of action is unlikely to be directly linked to alterations of lipid rafts biophysical properties caused by these drugs. The biological implications of this result are discussed in the context of ALPs effects on lipid metabolism, mitochondria homeostasis modulation, and their relationship with tumor cell death.