Oxidized phospholipids as potential novel drug targets

Impact of Truncated Oxidized Phosphatidylcholines on Phospholipase A2 Activity in Mono- and Polyunsaturated Biomimetic Vesicles

The interplay between inflammatory and redox processes is a ubiquitous and critical phenomenon in cell biology that involves numerous biological factors. Among them, secretory phospholipases A₂ (sPLA₂) that catalyze the hydrolysis of the sn-2 ester bond of phospholipids are key players. They can interact or be modulated by the presence of truncated oxidized phosphatidylcholines (OxPCs) produced under oxidative stress from phosphatidylcholine (PC) species. The present study examined this important, but rarely considered, sPLA₂ modulation induced by the changes in biophysical properties of PC vesicles comprising various OxPC ratios in mono- or poly-unsaturated PCs. Being the most physiologically active OxPCs, 1-palmitoyl-2-(5'-oxo-valeroyl)-sn-glycero-3-phosphocholine (POVPC) and 1-palmitoyl-2-glutaryl-sn-glycero-3-phosphocholine (PGPC) have been selected for our study. Using fluorescence spectroscopy methods, we compared the effect of OxPCs on the lipid order as well as sPLA₂ activity in large unilamellar vesicles (LUVs) made of the heteroacid PC, either monounsaturated [1-palmitoyl-2-oleoyl-sn-glycero-3-phosphocholine (POPC)], or polyunsaturated [1-palmitoyl-2-docosahexaenoyl-sn-glycero-3-phosphocholine (PDPC)] at a physiological temperature. The effect of OxPCs on vesicle size was also assessed in both the mono- and polyunsaturated PC matrices. Results: OxPCs decrease the membrane lipid order of POPC and PDPC mixtures with PGPC inducing a much larger decrease in comparison with POVPC, indicative that the difference takes place at the glycerol level. Compared with POPC, PDPC was able to inhibit sPLA₂ activity showing a protective effect of PDPC against enzyme hydrolysis. Furthermore, sPLA₂ activity on its PC substrates was modulated by the OxPC membrane content. POVPC down-regulated sPLA₂ activity, suggesting anti-inflammatory properties of this truncated oxidized lipid. Interestingly, PGPC had a dual and opposite effect, either inhibitory or enhancing on sPLA₂ activity, depending on the protocol of lipid mixing. This difference may result from the chemical properties of the shortened sn-2-acyl chain residues (aldehyde group for POVPC, and carboxyl for PGPC), being, respectively, zwitterionic or anionic under hydration at physiological conditions.

Lipid oxidation controls peptide self-assembly near membranes through a surface attraction mechanism

The self-assembly of peptides into supramolecular structures has been linked to neurodegenerative diseases but has also been observed in functional roles. Peptides are physiologically exposed to crowded environments of biomacromolecules, and particularly cellular membrane lipids. Previous research has shown that membranes can both accelerate and inhibit peptide self-assembly. Here, we studied the impact of membrane models that mimic cellular oxidative stress and compared this to mammalian and bacterial membranes. Using molecular dynamics simulations and experiments, we propose a model that explains how changes in peptide-membrane binding, electrostatics, and peptide secondary structure stabilization determine the nature of peptide self-assembly. We explored the influence of zwitterionic (POPC), anionic (POPG) and oxidized (PazePC) phospholipids, as well as cholesterol, and mixtures thereof, on the self-assembly kinetics of the amyloid β (1-40) peptide (Aβ40), linked to Alzheimer's disease, and the amyloid-forming antimicrobial peptide uperin 3.5 (U3.5). We show that the presence of an oxidized lipid had similar effects on peptide self-assembly as the bacterial mimetic membrane. While Aβ40 fibril formation was accelerated, U3.5 aggregation was inhibited by the same lipids at the same peptide-to-lipid ratio. We attribute these findings and peptide-specific effects to differences in peptide-membrane adsorption with U3.5 being more strongly bound to the membrane surface and stabilized in an α-helical conformation compared to Aβ40. Different peptide-to-lipid ratios resulted in different effects. We found that electrostatic interactions are a primary driving force for peptide-membrane interaction, enabling us to propose a model for predicting how cellular changes might impact peptide self-assembly in vivo.

Pulmonary surfactant phosphatidylcholines induce immunological adaptation of alveolar macrophages

Pulmonary surfactant plays an important role in lung surface tension, defense against invading pathogens, and immune response. Furthermore, alveolar macrophages (AM) that comprise the front line of immune defense against inhaled microorganisms are covered by a layer of pulmonary fluid. Phosphatidylcholines (PCs), including unsaturated lipids such as 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphocholine (POPC), are the most prevalent phospholipids in pulmonary surfactant. POPC reacts with ozone to produce 1-palmitoyl-2-(9-oxo-nonanoyl)-sn-glycero-3-phosphocholine (PONPC), a soluble mediator that initiates an inflammatory reaction in the lungs. However, the modulatory effects of POPC and PONPC on biology and activity of AM remain inconclusive. The exposure of AM (cell line AMJ2-C11) to POPC and PONPC was not directly related to the production of inflammatory mediators. However, AM, pre-incubated with POPC or PONPC, showed enhanced response after lipopolysaccharide (LPS) stimulation, and increased the production of nitric oxide and cytokines. This phenomenon was also observed for classical-polarized macrophages (M1). This increment on the production of inflammatory mediators was not associated with macrophage polarization, but with up-regulation of Tlr4 and Myd88 gene expression, which was in accordance with the adaptation of immune cells. This observation was confirmed by the histone acetylation epigenetic pathway. In contrast to the priming effect of POPC on AM activity, a harmful immune response, induced on incubation with PONPC, improved prostaglandin E2 (PGE2) formation, resulting in diminished bacterial phagocytosis. Additionally, PONPC induced production of CXCL1/KC, which potentially mediates neutrophil recruitment and enhances tissue inflammation. These results disclosed another dynamic mechanism by which pulmonary surfactant lipids (natural or oxidized) primed macrophage activity, thus affecting lung host defense.

Integrated approaches to unravel the impact of protein lipoxidation on macromolecular interactions

Protein modification by lipid derived reactive species, or lipoxidation, is increased during oxidative stress, a common feature observed in many pathological conditions. Biochemical and functional consequences of lipoxidation include changes in the conformation and assembly of the target proteins, altered recognition of ligands and/or cofactors, changes in the interactions with DNA or in protein-protein interactions, modifications in membrane partitioning and binding and/or subcellular localization. These changes may impact, directly or indirectly, signaling pathways involved in the activation of cell defense mechanisms, but when these are overwhelmed they may lead to pathological outcomes. Mass spectrometry provides state of the art approaches for the identification and characterization of lipoxidized proteins/residues and the modifying species. Nevertheless, understanding the complexity of the functional effects of protein lipoxidation requires the use of additional methodologies. Herein, biochemical and biophysical methods used to detect and measure functional effects of protein lipoxidation at different levels of complexity, from in vitro and reconstituted cell-like systems to cells, are reviewed, focusing especially on macromolecular interactions. Knowledge generated through innovative and complementary technologies will contribute to comprehend the role of lipoxidation in pathophysiology and, ultimately, its potential as target for therapeutic intervention.

Oxidative Phospholipidomics in health and disease: Achievements, challenges and hopes

Phospholipid peroxidation products are recognized as important bioactive lipid mediators playing an active role as modulators in signalling events in inflammation, immunity and infection. The biochemical responses are determined by the oxidation structural features present in oxPL modulating biophysical and biological properties in model membranes and lipoproteins. In spite of the extensive work conducted with model systems over the last 20 years, the study of oxPL in biological systems has virtually stagnated. In fact, very little is known concerning the predominant oxPL in fluids and tissues, their basal levels, and any variations introduced with age, gender and ethnicity in health and disease. In consequence, knowledge on oxPL has not yet translated into clinical diagnostic, in the early and timely diagnosis of "silent" diseases such as atherosclerosis and cardiovascular diseases, or as prognosis tools in disease stratification and particularly useful in the context of multimorbidities. Their use as therapeutic solutions or the development of innovative functional biomaterials remains to be explored. This review summarizes the achievements made in the identification of oxPL revealing an enormous structural diversity. A brief overview of the challenges associated with the analysis of such diverse array of products is given and a critical evaluation on key aspects in the analysis pipeline that need to be addressed. Once these issues are addressed, Oxidative Phospholipidomics will hopefully lead to major breakthrough discoveries in biochemistry, pharmaceutical, and clinical areas for the upcoming 20 years. This article is part of Special Issue entitled 4-Hydroxynonenal and Related Lipid Oxidation Products.

Fluorescence monitoring of the effect of oxidized lipids on the process of protein fibrillization

The kinetics of lysozyme and insulin amyloid formation in the presence of the oxidized phospholipids (oxPLs) was investigated using Thioflavin T fluorescence assay. The kinetic parameters of fibrillization process (lag time and apparent rate constant) have been determined upon varying the following experimental parameters: the type of lipid assemblies (premicellar aggregates and lipid bilayer vesicles), pH, temperature and lipid-to-protein molar ratio. It was found that oxPLs premicellar aggregates induced the more pronounced increase of the maximum Thioflavin T fluorescence, which is proportional to the extent of fibril formation, compared to the vesicles composed of the oxidized and unoxidized lipids. In contrast, the oxPLs, used as dispersions or included into vesicles, inhibited fibril nucleation and elongation under near-physiological conditions in vitro compared to liposomes containing unoxidized lipids. The results obtained provide deeper insight into the molecular mechanisms of the oxidative stress-modulated conformational diseases, and could be employed for the anti-amyloid drug development.

Acyl Chain Disorder and Azelaoyl Orientation in Lipid Membranes Containing Oxidized Lipids

Oxidized phospholipids occur naturally in conditions of oxidative stress and have been suggested to play an important role in a number of pathological conditions due to their effects on a lipid membrane acyl chain orientation, ordering, and permeability. Here we investigate the effect of the oxidized phospholipid 1-palmitoyl-2-azelaoyl-sn-glycero-3-phosphocholine (PazePC) on a model membrane of 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphocholine (POPC) using a combination of (13)C-(1)H dipolar-recoupling nuclear magnetic resonance (NMR) experiments and united-atom molecular dynamics (MD) simulations. The obtained experimental order parameter SCH profiles show that the presence of 30 mol % PazePC in the bilayer significantly increases the gauche content of the POPC acyl chains, therefore decreasing the thickness of the bilayer, although with no stable bilayer pore formation. The MD simulations reproduce the disordering effect and indicate that the orientation of the azelaoyl chain is highly dependent on its protonation state with acyl chain reversal for fully deprotonated states and a parallel orientation along the interfacial plane for fully protonated states, deprotonated and protonated azelaoyl chains having negative and positive SCH profiles, respectively. Only fully or nearly fully protonated azelaoyl chain are observed in the (13)C-(1)H dipolar-recoupling NMR experiments. The experiments show positive SCH values for the azelaoyl segments confirming for the first time that oxidized chains with polar termini adopt a parallel orientation to the bilayer plane as predicted in MD simulations.

Interactions and dynamics of two extended conformation adapting phosphatidylcholines in model biomembranes

In order to obtain molecular level insight into the biophysics of the apoptosis promoting phospholipid 1-palmitoyl-2-azelaoyl-sn-glycero-3-phosphocholine (PazePC) we studied its partitioning into different lipid phases by isothermal titration calorimetry (ITC). To aid the interpretation of these data for PazePC, we additionally characterized by both ITC and fluorescence spectroscopy the fluorescent phospholipid analog 1-palmitoyl-2-{6-[(7-nitro-2-1,3-benzoxadiazol-4-yl)amino]hexanoyl}-sn-glycero-3-phosphocholine (NBD-C6-PC), which similarly to PazePC can adopt extended conformation in lipid bilayers. With the NBD-hexanoyl chain reversing its direction and extending into the aqueous space out of the bilayer, 7-nitro-2,1,3-benzoxadiazol-4-yl (NBD) becomes accessible to the water soluble dithionite, which reduces to non-fluorescent product. Our results suggest that these phospholipid derivatives first partition and penetrate into the outer bilayer leaflet of liquid disordered phase liposomes composed of unsaturated 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphocholine (POPC). Upon increase up to 2 mol% PazePC and NBD-C6-PC of the overall content, flip-flop from the outer into the inner bilayer leaflet commences. Interestingly, the presence of 40 mol% cholesterol in POPC liposomes did not abrogate the partitioning of PazePC into the liquid ordered phase. In contrast, only insignificant partitioning of PazePC and NBD-C6-PC into sphingomyelin/cholesterol liposomes was evident, highlighting a specific membrane permeability barrier function of this particular lipid composition against oxidatively truncated PazePC, thus emphasizing the importance of detailed characterization of the biophysical properties of membranes found in different cellular organelles, in terms of providing barriers for lipid-mediated cellular signals in processes such as apoptosis. Our data suggest NBD-C6-PC to represent useful fluorescent probe to study the cellular dynamics of oxidized phospholipid species, such as PazePC.

Melanogenesis and antioxidant defense system in normal human melanocytes cultured in the presence of chlorpromazine

Chlorpromazine is used in the treatment of schizophrenia and psychotic disorders and belongs to phenothiazine class of neuroleptic drugs. It shows severe side effects such as extrapyramidal symptoms as well as ocular and skin disorders, but the mechanism is still not fully established. The aim of this study was to examine the effect of chlorpromazine on cell viability, melanogenesis and antioxidant defense system in normal human melanocytes. It has been demonstrated that chlorpromazine induces concentration dependent loss in cell viability. The value of EC(50) was calculated to be 2.53 μM. Chlorpromazine in lower concentrations (0.0001, 0.001 and 0.01 μM) increased the melanin and microphthalmia-associated transcription factor (MITF) content and tyrosinase activity, while changes of antioxidant enzymes activity were not observed. It suggests that long-term chlorpromazine therapy, even with low drug doses, may lead to hyperpigmentation disorders in skin and/or eye. The use of the analyzed drug in higher concentrations (0.1 and 1.0 μM) caused significant alterations of antioxidant enzymes activity in normal melanocytes, what may explain a potential role of chlorpromazine in the depletion of cellular antioxidant status leading to other adverse effects associated with the high-dose and/or long-term therapy.

Effect of thioridazine on antioxidant status of HEMn-DP melanocytes

Thioridazine as an antipsychotic agent was extensively used to treat various psychotic disorders, e.g. schizophrenia. However, the therapy with this drug can induce serious side effects such as extrapyramidal symptoms or ocular and skin disorders, which mechanisms are still not fully established. To gain inside the molecular mechanisms underlying thioridazine toxicity, we examined the effect of this drug on cell viability, antioxidant defence system as well as melanogenesis in normal human melanocytes. It was demonstrated that thioridazine induces concentration-dependent loss in cell viability. The value of EC₅₀ was calculated to be 2.24 μM. To study the effect of thioridazine on antioxidant defence system in melanocytes, the level of hydrogen peroxide and the activities of antioxidant enzymes superoxide dismutase, catalase and glutathione peroxidase were determined. The drug in concentrations of 0.1, 0.25, 1.0 and 2.5 μM caused changes in cellular antioxidant defence system indicating the induction of oxidative stress. It was also shown that the analysed neuroleptic in concentrations of 1.0 and 2.5 μM significantly inhibited melanogenesis. The observed changes in cell viability, antioxidant defence system and melanization in normal human melanocytes after thioridazine treatment may explain an important role of reactive oxygen species as well as melanin in mechanisms involved in this drug side effects directed on pigmented tissues.

EPR spectroscopy of chlorpromazine-induced free radical formation in normal human melanocytes

The purpose of this study was to estimate the effect of chlorpromazine on free radical concentration in HEMn-DP melanocytes using electron paramagnetic resonance (EPR) spectroscopy. It was found that chlorpromazine at concentrations of 1 × 10(-7) and 1 × 10(-6) M contributed to the formation of free radicals (g values ~2) in a dose-dependent manner. The increase in free radical formation was accompanied by an increase in cytotoxicity, as shown by a tetrazolium assay. Homogeneous broadening of EPR lines, slow spin-lattice relaxation processes, and strong dipolar interactions characterized all the tested cellular samples. The performed examination of free radical formation in cells exposed to different chlorpromazine concentrations confirmed the usefulness of electron paramagnetic resonance spectroscopy to determine the effect of a drug on free radical production in a cellular model system in vitro.

Oxidized phosphatidylcholines in membrane-level cellular signaling: from biophysics to physiology and molecular pathology

The oxidation of lipids has been shown to impact virtually all cellular processes. The paradigm has been that this involvement is due to interference with the functions of membrane-associated proteins. It is only recently that methodological advances in molecular-level detection and identification have begun to provide insights into oxidative lipid modification and its involvement in cell signaling as well as in major diseases and inflammation. Extensive evidence suggests a correlation between lipid peroxidation and degenerative neurological diseases such as Parkinson's and Alzheimer's, as well as type 2 diabetes and cancer. Despite the obvious relevance of understanding the molecular basis of the above ailments, the exact modes of action of oxidized lipids have remained elusive. In this minireview, we summarize recent findings on the biophysical characteristics of biomembranes following oxidative derivatization of their lipids, and how these altered properties are involved in both physiological processes and major pathological conditions. Lipid-bearing, oxidatively truncated and functionalized acyl chains are known to modify membrane bulk physical properties, such as thermal phase behavior, bilayer thickness, hydration and polarity profiles, as manifest in the altered structural dynamics of lipid bilayers, leading to augmented membrane permeability, fast lipid transbilayer diffusion (flip-flop), loss of lipid asymmetry (scrambling) and phase segregation (the formation of 'rafts'). These changes, together with the generated reactive lipid derivatives, can be further expected to interfere with lipid-protein interactions, influencing metabolic pathways, causing inflammation, the execution phase in apoptosis and initiating pathological processes.

Fusogenicity of Naja naja atra cardiotoxin-like basic protein on sphingomyelin vesicles containing oxidized phosphatidylcholine and cholesterol

This study investigated the effect of oxidized phosphatidylcholine (oxPC) and cholesterol (Chol) on Naja naja atra cardiotoxin-like basic protein (CLBP)-induced fusion and leakage in sphingomyelin (SM) vesicles. Compared with those on PC/SM/Chol vesicles, CLBP showed a lower activity to induce membrane permeability but a higher fusogenicity on oxPC/SM/Chol vesicles. A reduction in inner-leaflet fusion elucidated that CLBP fusogenicity was not in parallel to its membrane-leakage activity on oxPC/SM/Chol vesicles. The lipid domain formed by Chol and SM supported CLBP fusogenicity on oxPC/SM/Chol vesicles, while oxPC altered the interacted mode of CLBP with oxPC/SM/Chol vesicles as evidenced by Fourier transform infrared spectra analyses and colorimetric phospholipid/polydiacetylene membrane assay. Although CLBP showed similar binding affinity with PC/SM/Chol and oxPC/SM/Chol vesicles, the binding capability of CLBP with PC/SM/Chol and oxPC/SM/Chol vesicles was affected differently by NaCl. This emphasized that CLBP adopted different membrane interaction modes upon binding with PC/SM/Chol and oxPC/SM/Chol vesicles. CLBP induced fusion in vesicles containing oxPC bearing the aldehyde group, and aldehyde scavenger methoxyamine abrogated the CLBP ability to induce oxPC/SM/Chol fusion. Taken together, our data indicate that Chol and oxPC bearing aldehyde group alter the CLBP membrane-binding mode, leading to fusogenicity promotion while reducing the membrane-damaging activity of CLBP.

Oxidized phospholipid based pH sensitive micelles for delivery of anthracyclines to resistant leukemia cells in vitro

A self-assembled micelle drug delivery system was constructed with an oxidized phospholipid for anthracycline anti-cancer drug delivery. An oxidized phospholipid, 1-palmitoyl-2-azelaoyl-sn-glycero-3-phosphocholine (PazPC), was chosen to fabricate micelles via both electrostatic and hydrophobic interactions for delivery of doxorubicin (DOX) and idarubicin (IDA). The formation of ion-pair complexes between PazPC and DOX was first investigated under different pH conditions. Drug-loaded PazPC micelles at a 5:1 molar ratio of lipid/drug at pH 7.0 were then prepared by the solvent evaporation method. The empty and drug-loaded PazPC micelles exhibited a small particle size (∼10 nm) and high encapsulation efficiency. In vitro stability and release profile indicated that the micelles were stable at physiological conditions, but exhibited pH-sensitive behavior with accelerated release of DOX or IDA in an acidic endosome environment. Finally, in vitro uptake and cytotoxicity were evaluated for leukemia P388 and its resistant subline P388/ADR. The drug-loaded PazPC micelles enhanced drug uptake and exhibited higher cytotoxicity in both leukemia cells in comparison to free drugs. In conclusion, we developed a novel pH sensitive oxidized phospholipid-based micellar formulation which could potentially be useful in delivering anthracycline anti-cancer drugs and provide a novel strategy for increasing the therapeutic index while overcoming multidrug resistance for leukemia treatment.

Cholesterol slows down the lateral mobility of an oxidized phospholipid in a supported lipid bilayer

We investigated the mobility and phase-partitioning of the fluorescent oxidized phospholipid analogue 1-palmitoyl-2-glutaroyl-sn-glycero-3-phospho-N-Alexa647-ethanolamine (PGPE-Alexa647) in supported lipid bilayers. Compared to the conventional phospholipid dihexadecanoylphosphoethanolamine (DHPE)-Bodipy we found consistently higher diffusion constants. The effect became dramatic when immobile obstacles were inserted into the bilayer, which essentially blocked the diffusion of DHPE-Bodipy but hardly influenced the movements of PGPE-Alexa647. In a supported lipid bilayer made of 1,2-dioleoyl-sn-glycero-3-phosphocholine (DOPC), the differences in probe mobility leveled off with increasing cholesterol content. Using coarse-grained molecular dynamics simulations, we could ascribe this effect to increased interactions between the oxidized phospholipid and the membrane matrix, concomitant with a translation in the headgroup position of the oxidized phospholipid: at zero cholesterol content, its headgroup is shifted to the outside of the DOPC headgroup region, whereas increasing cholesterol concentrations pulls the headgroup into the bilayer plane.

Screening for the drug-phospholipid interaction: correlation to phospholipidosis

Phospholipid bilayers represent a complex, anisotropic environment fundamentally different from bulk oil or octanol, for instance. Even "simple" drug association to phospholipid bilayers can only be fully understood if the slab-of-hydrocarbon approach is abandoned and the complex, anisotropic properties of lipid bilayers reflecting the chemical structures and organization of the constituent phospholipids are considered. The interactions of drugs with phospholipids are important in various processes, such as drug absorption, tissue distribution, and subcellular distribution. In addition, drug-lipid interactions may lead to changes in lipid-dependent protein activities, and further, to functional and morphological changes in cells, a prominent example being the phospholipidosis (PLD) induced by cationic amphiphilic drugs. Herein we briefly review drug-lipid interactions in general and the significance of these interactions in PLD in particular. We also focus on a potential causal connection between drug-induced PLD and steatohepatitis, which is induced by some cationic amphiphilic drugs.

Lipid gymnastics: evidence of complete acyl chain reversal in oxidized phospholipids from molecular simulations

In oxidative environments, biomembranes contain oxidized lipids with short, polar acyl chains. Two stable lipid oxidation products are PoxnoPC and PazePC. PoxnoPC has a carbonyl group, and PazePC has an anionic carboxyl group pendant at the end of the short, oxidized acyl chain. We have used MD simulations to explore the possibility of complete chain reversal in OXPLs in POPC-OXPL mixtures. The polar AZ chain of PazePC undergoes chain reversal without compromising the lipid bilayer integrity at concentrations up to 25% OXPL, and the carboxyl group points into the aqueous phase. Counterintuitively, the perturbation of overall membrane structural and dynamic properties is stronger for PoxnoPC than for PazePC. This is because of the overall condensing and ordering effect of sodium ions bound strongly to the lipids in the PazePC simulations. The reorientation of AZ chain is similar for two different lipid force fields. This work provides the first molecular evidence of the "extended lipid conformation" in phospholipid membranes. The chain reversal of PazePC lipids decorates the membrane interface with reactive, negatively charged functional groups. Such chain reversal is likely to exert a profound influence on the structure and dynamics of biological membranes, and on membrane-associated biological processes.

High-affinity small molecule-phospholipid complex formation: binding of siramesine to phosphatidic acid

Siramesine (SRM) is a sigma-2 receptor agonist which has been recently shown to inhibit growth of cancer cells. Fluorescence spectroscopy experiments revealed two distinct binding sites for this drug in phospholipid membranes. More specifically, acidic phospholipids retain siramesine on the bilayer surface due to a high-affinity interaction, reaching saturation at an apparent 1:1 drug-acidic phospholipid stoichiometry, where after the drug penetrates into the hydrocarbon core of the membrane. This behavior was confirmed using Langmuir films. Of the anionic phospholipids, the highest affinity, comparable to the affinities for the binding of small molecule ligands to proteins, was measured for phosphatidic acid (PA, mole fraction of X(PA) = 0.2 in phosphatidylcholine vesicles), yielding a molecular partition coefficient of 240 +/- 80 x 10(6). An MD simulation on the siramesine:PA interaction was in agreement with the above data. Taking into account the key role of PA as a signaling molecule promoting cell growth our results suggest a new paradigm for the development of anticancer drugs, viz. design of small molecules specifically scavenging phospholipids involved in the signaling cascades controlling cell behavior.

The role of phospholipid oxidation products in inflammatory and autoimmune diseases: evidence from animal models and in humans

Since the discovery of oxidized phospholipids (OxPL) and their implication as modulators of inflammation in cardiovascular disease, roles for these lipid oxidation products have been suggested in many other disease settings. Lipid oxidation products accumulate in inflamed and oxidatively damaged tissue, where they are derived from oxidative modification of lipoproteins, but also from membranes of cells undergoing apoptosis. Thus, increased oxidative stress as well as decreased clearance of apoptotic cells has been implied to contribute to accumulation of OxPL in chronically inflamed tissues.A central role for OxPL in disease states associated with dyslipedemia, including atherosclerosis, diabetes and its complications, metabolic syndrome, and renal insufficiency, as well as general prothrombotic states, has been proposed. In addition, in organs which are constantly exposed to oxidative stress, including lung, skin, and eyes, increased levels of OxPL are suggested to contribute to inflammatory conditions. Moreover, accumulation of OxPL causes general immunmodulation and may lead to autoimmune diseases. Evidence is accumulating that OxPL play a role in lupus erythematosus, antiphospholipid syndrome, and rheumatoid arthritis. Last but not least, a role for OxPL in neurological disorders including multiple sclerosis (MS), Alzheimer's and Parkinson's disease has been suggested.This chapter will summarize recent findings obtained in animal models and from studies in humans that indicate that formation of OxPL represents a general mechanism that may play a major role in chronic inflammatory and autoimmune diseases.

Oxidized phospholipids: emerging lipid mediators in pathophysiology

PURPOSE OF REVIEW

Oxidized phospholipids are biologically active agents that are generated by lipid peroxidation. They are associated with inflammation, oxidative stress and several diseased states as described by an increasing number of reports. In addition, information about the interaction partners, the binding sites, the intracellular signalling and the metabolizing enzymes of these compounds is rapidly increasing. This review will briefly summarize recent findings and focus on mechanisms with potential pathophysiological relevance.

RECENT FINDINGS

Reports reviewed here provide interesting insights into the involvement of oxidized phospholipids in interleukin transcription, phenotype switching of smooth muscle cells and apoptotic mechanisms of the modified phospholipids as well as the identification of metabolizing enzymes.

SUMMARY

Recent studies shed some light on oxidized phospholipid-induced signalling with regard to apoptosis, gene expression and receptor-mediated events. They support the notion that the bioactivities of these natural agents detrimentally contribute to the pathological alteration of basic mechanisms to states recognized in numerous medical conditions. Advances in the knowledge of signalling pathways and interaction partners of oxidized phospholipids will increase our understanding of inflammatory processes and molecular mechanisms of various diseases including atherosclerosis and may play an important role in the development of future therapeutic options or diagnostics.

Oxidized phospholipids as potential molecular targets for antimicrobial peptides

The effects of oxidatively modified phospholipids on the association with model biomembranes of four antimicrobial peptides (AMPs), temporin B and L, indolicidin, and LL-37(F27W) were studied by Langmuir balance and fluorescence spectroscopy. In keeping with previous reports the negatively charged phospholipid phosphatidylglycerol (PG) enhanced the intercalation of all four peptides into lipid monolayers and liposomal bilayers under low ionic strength conditions. Interestingly, similar effect was observed for 1-palmitoyl-2-(9'-oxo-nonanoyl)-sn-glycero-3-phosphocholine (PoxnoPC), a zwitterionic oxidized phospholipid bearing an aldehyde function at the end of its truncated sn-2 acyl chain. Instead, the structurally similar 1-palmitoyl-2-azelaoyl-sn-glycero-3-phosphocholine (PazePC) containing a carboxylic moiety was less efficient in promoting the membrane association of these peptides. Physiological saline reduced the binding of the above peptides to membranes containing PG, whereas interactions with PoxnoPC were found to be insensitive to ionic strength. Notably, membrane intercalation of temporin L, the most surface active of the above peptides could be into PoxnoPC containing monolayers was strongly attenuated by methoxyamine, suggesting the importance of Schiff base formation between peptide amino groups and the lipid aldehyde function. PoxnoPC and similar aldehyde bearing oxidatively modified phospholipids could represent novel molecular targets for AMPs.