The anionic phospholipid-mediated membrane interaction of the anti-cancer drug doxorubicin is enhanced by phosphatidylethanolamine compared to other zwitterionic phospholipids

Anthracyclins Increase PUFAs: Potential Implications in ER Stress and Cell Death

Metabolic and personalized interventions in cancer treatment require a better understanding of the relationship between the induction of cell death and metabolism. Consequently, we treated three primary liver cancer cell lines with two anthracyclins (doxorubicin and idarubin) and studied the changes in the lipidome. We found that both anthracyclins in the three cell lines increased the levels of polyunsaturated fatty acids (PUFAs) and alkylacylglycerophosphoethanolamines (etherPEs) with PUFAs. As PUFAs and alkylacylglycerophospholipids with PUFAs are fundamental in lipid peroxidation during ferroptotic cell death, our results suggest supplementation with PUFAs and/or etherPEs with PUFAs as a potential general adjuvant of anthracyclins. In contrast, neither the markers of de novo lipogenesis nor cholesterol lipids presented the same trend in all cell lines and treatments. In agreement with previous research, this suggests that modulation of the metabolism of cholesterol could be considered a specific adjuvant of anthracyclins depending on the type of tumor and the individual. Finally, in agreement with previous research, we found a relationship across the different cell types between: (i) the change in endoplasmic reticulum (ER) stress, and (ii) the imbalance between PUFAs and cholesterol and saturated lipids. In the light of previous research, this imbalance partially explains the sensitivity to anthracyclins of the different cells. In conclusion, our results suggest that the modulation of different lipid metabolic pathways may be considered for generalized and personalized metabochemotherapies.

The relevance of the supramolecular arrangements of the respiratory chain complexes in human diseases and aging

Mitochondrial dysfunction, a common factor in several diseases is accompanied with reactive oxygen species (ROS) production. These molecules react with proteins and lipids at their site of generation, establishing a vicious cycle which might result in further mitochondrial injury. It is well established that mitochondrial respiratory complexes can be organized into supramolecular structures called supercomplexes (SCs) or respirasomes; yet, the physiological/pathological relevance of these structures remains unresolved. Changes in their stabilization and content have been documented in Barth's syndrome, degenerative diseases such as Parkinson's and Alzheimer, cardiovascular diseases including heart failure and ischemia-reperfusion damage, as well as in aging. Under pathological conditions, SCs stability could have relevant biomedical implications or might be used as a reliable marker of mitochondrial damage. The purpose of this review is to recapitulate the current state of the significance on mitochondrial bioenergetics of these structures and their possible role in pathophysiologies related with ROS increase.

Liposomal Co-Encapsulation of Two Novel Europium Complexes and Doxorubicin: Fluorescence Study

The present study was undertaken to design the novel liposomal drug formulation containing doxorubicin and europium coordination complexes. It was shown that co-encapsulation of the drugs facilitates the partitioning and permeation of lanthanides into the lipid bilayer. The obtained results suggest that new drug platform may have potential application in the design of novel antitumor agents.

C8-glycosphingolipids preferentially insert into tumor cell membranes and promote chemotherapeutic drug uptake

Insufficient drug delivery into tumor cells limits the therapeutic efficacy of chemotherapy. Co-delivery of liposome-encapsulated drug and synthetic short-chain glycosphingolipids (SC-GSLs) significantly improved drug bioavailability by enhancing intracellular drug uptake. Investigating the mechanisms underlying this SC-GSL-mediated drug uptake enhancement is the aim of this study. Fluorescence microscopy was used to visualize the cell membrane lipid transfer intracellular fate of fluorescently labeled C6-NBD-GalCer incorporated in liposomes in tumor and non-tumor cells. Additionally click chemistry was applied to image and quantify native SC-GSLs in tumor and non-tumor cell membranes. SC-GSL-mediated flip-flop was investigated in model membranes to confirm membrane-incorporation of SC-GSL and its effect on membrane remodeling. SC-GSL enriched liposomes containing doxorubicin (Dox) were incubated at 4°C and 37°C and intracellular drug uptake was studied in comparison to standard liposomes and free Dox. SC-GSL transfer to the cell membrane was independent of liposomal uptake and the majority of the transferred lipid remained in the plasma membrane. The transfer of SC-GSL was tumor cell-specific and induced membrane rearrangement as evidenced by a transbilayer flip-flop of pyrene-SM. However, pore formation was measured, as leakage of hydrophilic fluorescent probes was not observed. Moreover, drug uptake appeared to be mediated by SC-GSLs. SC-GSLs enhanced the interaction of doxorubicin (Dox) with the outer leaflet of the plasma membrane of tumor cells at 4°C. Our results demonstrate that SC-GSLs preferentially insert into tumor cell plasma membranes enhancing cell intrinsic capacity to translocate amphiphilic drugs such as Dox across the membrane via a biophysical process.

Interactions of doxorubicin with organized interfacial assemblies. 1. Electrochemical characterization

Doxorubicin is an anthracycline that has found wide use as a chemotherapeutic agent, with the primary target of its action being nuclear DNA. Despite the large body of knowledge on this family of compounds, the mechanism of doxorubicin penetration through the cellular or nuclear membrane remains understood to a limited extent. The plasma membrane acts as a barrier to the permeation of polar molecules, and this effect is mainly due to the hydrophobicity of membrane interior. The partitioning of DOX molecules into the lipid bilayer must thus be the basis for its passive transport across the biological membrane and therefore a key area of research activity lies in understanding how the structure of the anthracycline influences its interactions with amphiphilic interfaces. We have studied interactions between doxorubicin and Langmuir/Langmuir-Blodgett monomolecular films of octadecylamine (C18NH2), dihexadecylphosphate (DHP) and 1,2-dimyristoyl-sn-glycero-3-phosphocholine (DMPC), and DMPC bilayer films (Langmuir-Schaeffer) on a polycrystalline gold surface using ellipsometry, cyclic voltammetry, electrochemical impedance spectroscopy, and quartz crystal microbalance measurements. For all biomimetic films there is a substantial interaction between doxorubicin and the interface, and the extent of this interaction depends on the hydrophobic/hydrophilic properties of the film formed and its organization.

Interactions of doxorubicin with self-assembled monolayer-modified electrodes: electrochemical, surface plasmon resonance (SPR), and gravimetric studies

We present the results on the partitioning of doxorubicin (DOX), a potent anticancer drug, through the model membrane system, self-assembled monolayers (SAMs) on gold electrodes. The monolayers were formed from alkanethiols of comparable length with different ω-terminal groups facing the aqueous electrolyte: the hydrophobic -CH(3) groups for the case of dodecanethiol SAMs or hydrophilic -OH groups of mercaptoundecanol SAMs. The electrochemical experiments combined with the surface plasmon resonance (SPR) and gravimetric studies show that doxorubicin is likely adsorbed onto the surface of hydrophilic monolayer, while for the case of the hydrophobic one the drug mostly penetrates the monolayer moiety. The adsorption of the drug hinders further penetration of doxorubicin into the monolayer moiety.

On the role of anionic lipids in charged protein interactions with membranes

We investigate the role of anionic lipids in the binding to, and subsequent movement of charged protein groups in lipid membranes, to help understand the role of membrane composition in all membrane-active protein sequences. We demonstrate a small effect of phosphatidylglycerol (PG) lipids on the ability of an arginine (Arg) side chain to bind to, and cross a lipid membrane, despite possessing a neutralizing charge. We observe similar membrane deformations in lipid bilayers composed of phosphatidylcholine (PC) and PC/PG mixtures, with comparable numbers of water and lipid head groups pulled into the bilayer hydrocarbon core, and prohibitively large ~20 kcal/mol barriers for Arg transfer across each bilayer, dropping by just 2-3 kcal/mol due to the binding of PG lipids. We explore the causes of this small effect of introducing PG lipids and offer an explanation in terms of the limited membrane interaction for the choline groups of PC lipids bound to the translocating ion. Our calculations reveal a surprising lack of preference for Arg binding to PG lipids themselves, but a small increase in interfacial binding affinity for lipid bilayers containing PG lipids. These results help to explain the nature of competitive lipid binding to charged protein sequences, with implications for a wide range of membrane binding domains and cell perturbing peptides.

Actin-induced perturbation of PS lipid-cholesterol interaction: A possible mechanism of cytoskeleton-based regulation of membrane organization

To obtain insight into the potential role of the cytoskeleton on lipid mixing behavior in plasma membranes, the current study explores the influence of physisorbed actin filaments (F-actin) on lipid-lipid phase separations in planar model membrane systems containing raft-mimicking lipid mixtures of well-defined compositions using a complementary experimental approach of epifluorescence microscopy, fluorescence anisotropy, wide-field single molecule fluorescence microscopy, and interfacial rheometry. In particular, we have explored the impact of F-actin on cholesterol (CHOL)-phospholipid interactions, which are considered important for the formation of CHOL-enriched lipid raft domains. By using epifluorescence microscopy, we show that physisorbed filamentous actin (F-actin) alters the domain size of lipid-lipid phase separations in the presence of 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphatidylserine (POPS) and cholesterol (CHOL). In contrast, no actin-induced modification in lipid-lipid phase separations is observed in the absence of POPS or when POPS is replaced by another anionic lipid, 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphatidylglycerol (POPG). Wide-field single molecule fluorescence microscopy on binary lipid mixtures indicate that PS and PG lipids show similar electrostatic interactions with physisorbed actin filaments. Complementary fluorescence anisotropy experiments on binary PS lipid-containing lipid mixtures are provided to illustrate the actin-induced segregation of anionic lipids. The similarity of electrostatic interactions between actin and both anionic lipids suggests that the observed differences in actin-mediated perturbations of lipid phase separations are caused by distinct PS lipid-CHOL versus PG lipid-CHOL interactions. We hypothesize that the actin cytoskeleton and some peripheral membrane proteins may alter lipid-lipid phase separations in plasma membranes in a similar way by interacting with PS lipids.

A REVIEW ON THE RELATION BETWEEN THE BRAIN-SERUM CONCENTRATION RATIO OF DRUGS AND THE INFLUENCE OF P-GLYCOPROTEIN

This overview on the brain-serum relationship for drugs illustrates the importance of the drug transporter P-glycoprotein at the blood-brain barrier. Generally, an inverse relationship exists between the magnitude of the brain-serum ratio and the influence of P-glycoprotein. Concerning the pharmacogenomics of P-glycoprotein, no clear effect of single nucleotide polymorphisms (SNPs) has been demonstrated in humans.

Transport of anthracyclines and mitoxantrone across membranes by a flip-flop mechanism

The objectives of the present work are to characterize the transport of mitoxantrone and three anthracyclines in terms of binding to the membrane surface, flip-flop across the lipid core of the membrane, and release into the medium. Mitoxantrone and anthracyclines are positively charged amphipathic molecules, and as such are located at the surface of membranes among the headgroups of the phospholipids. Therefore, their transport across membranes occurs by a flip-flop mechanism, rather than by diffusion down a continuous concentration gradient located in the lipid core of the membrane. Flip-flop rates have been estimated with liposomes labeled at their surface with 7-nitrobenzo-2-oxa-1,3-diazol-4-yl (NBD) moiety attached to the headgroup of phosphatidylethanolamine. Flip-flop of mitoxantrone, doxorubicin, daunorubicin, and idarubicin occurred with half-lives of 6, 0.7, 0.15, and 0.1min, respectively. Partition of the drugs into the membrane occurred with lipid phase/aqueous medium coefficients of 230,000, 8600, 23,000, and 40,000 for mitoxantrone, doxorubicin, daunorubicin, and idarubicin, respectively, which are much higher than their corresponding octanol/aqueous medium values. There was no direct correlation between the lipophilicity of the drugs and their lipid phase/aqueous medium partition coefficient or their flip-flop rate. Mitoxantrone exhibited the highest affinity toward liposome membranes, but the slowest flip-flop across the lipid core of the membranes. Simulation of drug uptake into liposomes revealed that transmembrane movement of the mitoxantrone and anthracyclines is determined by their flip-flop rate and affinity toward membranes.

N-hexanoyl-sphingomyelin potentiates in vitro doxorubicin cytotoxicity by enhancing its cellular influx

Anticancer drugs generally have intracellular targets, implicating transport over the plasma membrane. For amphiphilic agents, such as the anthracycline doxorubicin, this occurs by passive diffusion. We investigated whether exogenous membrane-permeable lipid analogues improve this drug influx. Combinations of drugs and lipid analogues were coadministered to cultured endothelial cells and various tumour cell lines, and subsequent drug accumulation in cells was quantified. We identified N-hexanoyl-sphingomyelin (SM) as a potent enhancer of drug uptake. Low micromolar amounts of this short-chain sphingolipid, being not toxic itself, enhanced the uptake of doxorubicin up to 300% and decreased its EC₅₀ toxicity values seven- to 14-fold. N-hexanoyl SM acts at the level of the plasma membrane, but was found not incorporated in (isolated) lipid rafts, and artificial disruption or elimination of raft constituents did not affect its drug uptake-enhancing effect. Further, any mechanistic role of the endocytic machinery, membrane leakage or ABC-transporter-mediated efflux could be excluded. Finally, a correlation was established between the degree of drug lipophilicity, as defined by partitioning in a two-phase octanol–water system, and the susceptibility of the drug towards the uptake-enhancing effect of the sphingolipid. A clear optimum was found for amphiphilic drugs, such as doxorubicin, epirubicin and topotecan, indicating that N-hexanoyl-SM might act by modulating the average degree of plasma membrane lipophilicity, in turn facilitating transbilayer drug diffusion. The concept of short-chain sphingolipids as amphiphilic drug potentiators provides novel opportunities for improving drug delivery technologies.

Effects of lipids on the interaction of SecA with model membranes

The effects of nonlamellar-prone lipids, diacylglycerol and phosphatidylethanolamine (PE), on the kinetic association of SecA with model membranes were examined by measuring changes in the intrinsic emission fluorescence with a stopped-flow apparatus. Upon interaction with standard liposomes composed of 50 mol% dioleolyphosphatidylcholine (DOPC) and 50 mol% of dioleoylphosphatidylglycerol (DOPG), the intrinsic fluorescence intensity of SecA was decreased after a lapse of time with a rate constant of 0.0049 s(-1). When the DOPC of the standard vesicles was gradually replaced with either dioeloyl PE (DOPE) or Escherichia coli (E. coli) PE, the rate constant increased appreciably as a function of PE concentration, in the order DOPE > E. coli PE. In addition, when the PE of E. coli PE/DOPG (50/50) vesicles was replaced with more than 5 mol% dioleoylglycerol (DOG), the rate constant further increased by 40%. The incorporation of nonlamellar-prone lipids in the vesicles also enhanced the binding of SecA to model membranes in the order DOPE > or = E. coli PE/DOG > E. coli PE > DOPC. These results provide the first kinetic evidence for the importance of nonlamellar-prone phospholipids for the association rate of SecA with membranes.

Phosphatidic acid-phosphatidylethanolamine interaction and apocytochrome c translocation across model membranes

The translocation of apocytochrome c (apocyt.c) across large unilamellar vesicles (LUVs) constructed from mixtures of anionic and zwitterionic phospholipids, phosphatidylethanolamine (PE) and phosphatidylcholine (PC), has been studied. It was shown that the import ratio of horse heart apocyt.c in LUVs composed of phosphatidic acid (PA) combined with PE and PC (62+/-10%) was much higher than that in LUVs made of PE and PC plus any other acidic phospholipid species (20+/-5%). This feature was shared by tuna heart and chicken heart apocyt.c. In addition, the greater efficiency of the PA/PE/PC system versus others in facilitating apocyt.c translocation was maintained using synthetic anionic phospholipids with the same acyl chains. Besides, apocyt.c induces more leakage of entrapped fluorescein sulphonate (FS) from the interior of PA/PC/PE vesicles compared with phosphatidylglycerol (PG)/PC/PE ones. By measuring the intrinsic fluorescence emission spectrum and the accessibility of the preprotein to the fluorescence quencher, acrylamide, differences could be detected in the conformational changes of apocyt.c as a consequence of its interaction with PA/PE/PC and PG/PE/PC vesicles, respectively. Particularly notable is that PE is indispensable for the PA/PE/PC system to most efficiently facilitate apocyt.c translocation across the model membranes. With the fraction of PE increasing from 0 to 30 mol%, the translocation efficiency of apocyt.c as well as its ability to induce FS efflux was significantly enhanced in PA-containing LUVs, whereas this was not observed in the case of replacement of PA by PG or phosphatidylserine. It is also interesting to note that in LUVs containing PA, dioleoyl-PE, but not dielaidoyl-PE, can exert such influences, indicative of the role of non-bilayer formation propensity. On the basis of these results it is postulated that PA might increase the bilayer-destabilizing effects of PE, and hence increase the translocation efficiency of apocyt.c and its leakage-induction ability.

Phosphatidylethanolamine mediates insertion of the catalytic domain of leader peptidase in membranes

Leader peptidase is an integral membrane protein of E. coli and it catalyses the removal of most signal peptides from translocated precursor proteins. In this study it is shown that when the transmembrane anchors are removed in vivo, the remaining catalytic domain can bind to inner and outer membranes of E. coli. Furthermore, the purified catalytic domain binds to inner membrane vesicles and vesicles composed of purified inner membrane lipids with comparable efficiency. It is shown that the interaction is caused by penetration of a part of the catalytic domain between the lipids. Penetration is mediated by phosphatidylethanolamine, the most abundant lipid in E. coli, and does not seem to depend on electrostatic interactions. A hydrophobic segment around the catalytically important residue serine 90 is required for the interaction with membranes.

Lipid polymorphism and biomembrane function

In recent years, several major developments have taken place in the biology, physical chemistry and technology of polymorphism of membrane lipids. These include the identification of polymorphic regulation of membrane lipid composition in Escherichia coli, the importance of nonbilayer lipids for protein functioning, the special packing properties of bilayers containing these lipids, and the crystallization of a membrane protein out of three dimensional bilayer networks (lipid cubic phases). These exciting developments bring us closer to understanding the paradox of the lipid bilayer structure of biomembranes and the molecular basis of membrane protein structure and function.