Binding of annexin V to membrane products of lipid peroxidation

Platelet-Derived Microparticles (MPs) and Thrombin Generation Velocity in Deep Vein Thrombosis (DVT): Results of a Case-Control Study

Introduction

The role of platelets (Ps) and platelet-derived microparticles (MPs) in venous thromboembolism (VTE) is still being debated.

Methods

We measured MPs, velocity of thrombin formation (PiCT) and phospholipid generation (PLPs) in 40 patients with unprovoked deep vein thrombosis (DVT), who were compared with 40 healthy controls.

Results

MPs were higher in DVT (7.12 nM; 25th–75th percentile 5.26–9.12) than in controls (5.45 nM; 25th–75th percentile 1.67–8.96) (p = 0.19). PiCT velocity was lower in DVT (1.87 sec; 25th–75th percentile 1.75–1.93 sec) compared with controls (1.95 sec; 25th–75th percentile 1.84–2.24 sec) (p = 0.04). PLPs were higher in DVT (77.03 µg/mL; 25th–75th percentile 72.12–103.59 µg/mL) compared with controls (68.65 µg/mL, 25th–75th percentile 55.31–78.20 µg/mL) (p = 0.02).

Discussion

We hypothesize that MPs could be integrated with the lab network assay in evaluating Ps’ role as an activated procoagulative condition. We encourage research on Ps and P-derived microvesicle pathways in patients with unprovoked DVT and not only in patients with cancer-induced DVT.

Insights into plant annexins function in abiotic and biotic stress tolerance

Crop productivity depends heavily on several biotic and abiotic factors. Plant annexins are a multigene family of calcium-dependent phospholipid-binding proteins that function in response to environmental stresses and signaling during growth and development of plants. We recently isolated and characterized a Triticum durum annexin, called TdANN12, which is upregulated by different abiotic stresses. Overexpression of TdANN12 in transgenic tobacco improves stress tolerance through ROS removal. This mini-review outlines the functional characterization of plant annexin genes and suggests how these features could be exploitated to improve stress tolerance in plants. Furthermore, transgenic overexpression of plant annexin genes in crops (tobacco, tomato, rice, alfalfa, cotton, and potato) will be discussed as a promising approach to acquire abiotic and biotic stress tolerance.

Avenues to molecular imaging of dying cells: Focus on cancer

Successful treatment of cancer patients requires balancing of the dose, timing, and type of therapeutic regimen. Detection of increased cell death may serve as a predictor of the eventual therapeutic success. Imaging of cell death may thus lead to early identification of treatment responders and nonresponders, and to “patient‐tailored therapy.” Cell death in organs and tissues of the human body can be visualized, using positron emission tomography or single‐photon emission computed tomography, although unsolved problems remain concerning target selection, tracer pharmacokinetics, target‐to‐nontarget ratio, and spatial and temporal resolution of the scans. Phosphatidylserine exposure by dying cells has been the most extensively studied imaging target. However, visualization of this process with radiolabeled Annexin A5 has not become routine in the clinical setting. Classification of death modes is no longer based only on cell morphology but also on biochemistry, and apoptosis is no longer found to be the preponderant mechanism of cell death after antitumor therapy, as was earlier believed. These conceptual changes have affected radiochemical efforts. Novel probes targeting changes in membrane permeability, cytoplasmic pH, mitochondrial membrane potential, or caspase activation have recently been explored. In this review, we discuss molecular changes in tumors which can be targeted to visualize cell death and we propose promising biomarkers for future exploration.

Printing-induced cell injury evaluation during laser printing of 3T3 mouse fibroblasts

Three-dimensional bioprinting has emerged as a promising solution for the freeform fabrication of living cellular constructs, which can be used for tissue/organ transplantation and tissue models. During bioprinting, some living cells are unavoidably injured and may become necrotic or apoptotic cells. This study aims to investigate the printing-induced cell injury and evaluates injury types of post-printing cells using the annexin V/7-aminoactinomycin D and FAM-DEVD-FMK/propidium iodide assays during laser printing of NIH 3T3 mouse fibroblasts. As observed, the percentage of post-printing early apoptotic mouse fibroblasts increases with the incubation time, indicating that post-printing apoptotic mouse fibroblasts have different initiation lag times of apoptosis due to different levels of mechanical stress exerted during laser printing. Post-printing necrotic mouse fibroblasts can be detected immediately after printing, while post-printing early apoptotic mouse fibroblasts need time to develop into a late apoptotic stage. The minimum time needed for post-printing early apoptotic mouse fibroblasts to complete their apoptosis pathway and transition into late apoptotic mouse fibroblasts is from 4 h to 5 h post-printing. The resulting knowledge of the evolution of different apoptotic post-printing mouse fibroblasts will help better design future experiments to quantitatively determine, model, and mitigate the post-printing cell injury based on molecular signal pathway modeling.

Peptide translocation through the plasma membrane of human cells: Can oxidative stress be exploited to gain better intracellular access?

Cell-penetrating peptides (CPPs) enter cells primarily by escaping from endosomal compartments or by directly translocating across the plasma membrane. Due to their capability of permeating into the cytosolic space of the cell, CPPs are utilized for the delivery of cell-impermeable molecules. However, the fundamental mechanisms and parameters associated with the penetration of CPPs and their cargos through the lipid bilayer have not been fully determined. This in turn has hampered their usage in biotechnological or therapeutic applications. We have recently reported that the cell penetration activity of poly-arginine CPPs (PACPPs) is dependent on the oxidation status of the plasma membrane of cells. Our data support a model where the positively-charged PACPP binds negatively-charged lipids exposed on the cell surface as a result of oxidative damage. The PACPP then crosses the membrane via formation of inverted micelles with these anionic lipids. This model provides a plausible explanation for the high variability in the cell delivery efficiency of a PACPP often observed in different settings. Notably, taking into account the current literature describing the effects of lipid oxidation, our data point to a highly complex and underappreciated interplay between PACPPs and oxidized membrane species. Overall, a better understanding of oxidation-dependent cell penetration might provide a fundamental basis for development of optimal cell permeable peptides (including cyclic peptides, stapled peptides, peptoids, etc…) and of robust delivery protocols.

Overexpression of Arabidopsis AnnAt8 Alleviates Abiotic Stress in Transgenic Arabidopsis and Tobacco

Abiotic stress results in massive loss of crop productivity throughout the world. Because of our limited knowledge of the plant defense mechanisms, it is very difficult to exploit the plant genetic resources for manipulation of traits that could benefit multiple stress tolerance in plants. To achieve this, we need a deeper understanding of the plant gene regulatory mechanisms involved in stress responses. Understanding the roles of different members of plant gene families involved in different stress responses, would be a step in this direction. Arabidopsis, which served as a model system for the plant research, is also the most suitable system for the functional characterization of plant gene families. Annexin family in Arabidopsis also is one gene family which has not been fully explored. Eight annexin genes have been reported in the genome of Arabidopsis thaliana. Expression studies of different Arabidopsis annexins revealed their differential regulation under various abiotic stress conditions. AnnAt8 (At5g12380), a member of this family has been shown to exhibit ~433 and ~175 fold increase in transcript levels under NaCl and dehydration stress respectively. To characterize Annexin8 (AnnAt8) further, we have generated transgenic Arabidopsis and tobacco plants constitutively expressing AnnAt8, which were evaluated under different abiotic stress conditions. AnnAt8 overexpressing transgenic plants exhibited higher seed germination rates, better plant growth, and higher chlorophyll retention when compared to wild type plants under abiotic stress treatments. Under stress conditions transgenic plants showed comparatively higher levels of proline and lower levels of malondialdehyde compared to the wild-type plants. Real-Time PCR analyses revealed that the expression of several stress-regulated genes was altered in AnnAt8 over-expressing transgenic tobacco plants, and the enhanced tolerance exhibited by the transgenic plants can be correlated with altered expressions of these stress-regulated genes. Our findings suggest a role for AnnAt8 in enhancing abiotic stress tolerance at different stages of plant growth and development.

Annexin-Mediated Calcium Signalling in Plants

Calcium-permeable channels underpin elevations of free calcium that encode specific signals in stress adaptation, development and immunity. Identifying the genes encoding these channels remains a central goal of plant signalling research. Evidence now suggests that members of the plant annexin family function as unconventional calcium-permeable channels, with roles in development and stress signalling. Arabidopsis annexin 1 mediates a plasma membrane calcium-permeable conductance in roots that is activated by reactive oxygen species. Recombinant annexin 1 forms a very similar conductance in planar lipid bilayers, indicating that this protein could facilitate the in vivo conductance directly. The annexin 1 mutant is impaired in salinity-induced calcium signalling. Protein-protein interactions, post-translational modification and dynamic association with membranes could all influence annexin-mediated calcium signalling and are reviewed here. The prospect of annexins playing roles in calcium signalling events in symbiosis and immunity are considered.

Calcium-phosphate microprecipitates mimic microparticles when examined with flow cytometry

There are increased levels of circulating microparticles (MPs) in several disease states. Flow cytometry is a common method to examine MPs, but their small size necessitates the use of markers to distinguish specifically MPs from artifact. Annexin V, which binds phosphatidylserine, is a commonly used marker for MP detection. Annexin V requires millimolar calcium ion for optimum binding. Ca(++) can precipitate with phosphate in phosphate-buffered saline (PBS). Calcium-phosphate microprecipitates were formed by titrating Ca(++) into PBS and examined using flow cytometry. Calcium-phosphate microprecipitates were compared with MPs derived from aged donor blood units. Microprecipitates were ∼0.7-0.9 μm in diameter compared with standard beads of known size. The microprecipitates disappeared with the addition of Ca(++) chelator. When we added fluorescently labeled antibodies to microprecipitates, the median fluorescent signal increased with increasing Ca(++) concentration regardless of specificity of the antibody. When repeated with a biological sample, there was an apparent increase in the fluorescent signal that returned to baseline after Ca(++) chelation. The flow cytometry signal of calcium-phosphate microprecipitates overlaps with the MP signal. Since Ca(++) is essential for annexin V binding, it is essential to avoid artifacts from calcium-phosphate microprecipitates when using any buffer or biological fluid containing phosphate. This also highlights the potential utility of flow cytometry for the analysis of crystals in biological fluids.

Identification of novel bioactive aldehyde-modified phosphatidylethanolamines formed by lipid peroxidation

Lipid aldehydes generated by lipid peroxidation induce cell damage and inflammation. Recent evidence indicates that γ-ketoaldehydes (isolevuglandins, IsoLGs) form inflammatory mediators by modifying the ethanolamine headgroup of phosphatidylethanolamines (PEs). To determine if other species of aldehyde-modified PEs (al-PEs) with inflammatory bioactivity were generated by lipid peroxidation, we oxidized liposomes containing arachidonic acid and characterized the resulting products. We detected PE modified by IsoLGs, malondialdehyde (MDA), and 4-hydroxynonenal (HNE), as well as a novel series of N-acyl-PEs and N-carboxyacyl-PEs in these oxidized liposomes. These al-PEs were also detected in high-density lipoproteins exposed to myeloperoxidase. When we tested the ability of al-PEs to induce THP-1 monocyte adhesion to cultured endothelial cells, we found that PEs modified by MDA, HNE, and 4-oxononenal induced adhesion with potencies similar to those of PEs modified by IsoLGs (∼2μM). A commercially available medium-chain N-carboxyacyl-PE (C11:0CAPE) also stimulated adhesion, whereas C4:0CAPE and N-acyl-PEs did not. PEs modified by acrolein or by glucose were only partial agonists for adhesion. These studies indicate that lipid peroxidation generates a large family of al-PEs, many of which have the potential to drive inflammation.

Ribavirin-induced externalization of phosphatidylserine in erythrocytes is predominantly caused by inhibition of aminophospholipid translocase activity

Ribavirin in combination with interferon-α is the standard treatment for chronic hepatitis C, but often induces severe anemia forcing discontinuation of the therapy. Whereas suppression of bone marrow by interferon may impact on the production of erythrocytes, it has been suggested that accumulation of ribavirin in erythrocytes induces alterations causing an early removal of these cells by the mononuclear phagocytic system. Externalization of phosphatidylserine, which is exclusively present in the cytoplasmic leaflet of the plasma membrane, is a recognition signal for phagocytosis in particular of apoptotic cells. Here, we demonstrate that surface exposure of phosphatidylserine upon prolonged treatment of erythrocytes with ribavirin results mainly from inactivation of the aminophospholipid translocase, an ATP-dependent lipid pump, which specifically transports phosphatidylserine from the outer to the inner leaflet of the plasma membrane. Inactivation is due to severe ATP depletion, although competitive inhibition by ribavirin or its phosphorylated derivatives cannot be excluded. Phospholipid scramblase, responsible for collapse of lipid asymmetry, appears to be of minor importance as erythrocytes of patients with the Scott syndrome, lacking Ca(2+)-induced lipid scrambling, are equally sensitive to ribavirin treatment. Neither the antioxidant N-acetylcysteine nor the pan-caspase inhibitor Q-VD-OPH did affect ribavirin-induced phosphatidylserine exposure, suggesting that oxidative stress or apoptotic-related mechanisms are not involved in this process. In conclusion, we propose that spontaneous loss of lipid asymmetry, not corrected by aminophospholipid translocase activity, is the mechanism for ribavirin-induced phosphatidylserine exposure that may contribute to ribavirin-induced anemia.

Beyond annexin V: fluorescence response of cellular membranes to apoptosis

Dramatic changes in the structure of cell membranes on apoptosis allow easy, sensitive and non-destructive analysis of this process with the application of fluorescence methods. The strong plasma membrane asymmetry is present in living cells, and its loss on apoptosis is commonly detected with the probes interacting strongly and specifically with phosphatidylserine (PS). This phospholipid becomes exposed to the cell surface, and the application of annexin V labeled with fluorescent dye is presently the most popular tool for its detection. Several methods have been suggested recently that offer important advantages over annexin V assay with the ability to study apoptosis by spectroscopy of cell suspensions, flow cytometry and confocal or two-photon microscopy. The PS exposure marks the integrated changes in the outer leaflet of cell membrane that involve electrostatic potential and hydration, and the attempts are being made to provide direct probing of these changes. This review describes the basic mechanisms underlying the loss of membrane asymmetry during apoptosis and discusses, in comparison with the annexin V-binding assay, the novel fluorescence techniques of detecting apoptosis on cellular membrane level. In more detail we describe the detection method based on smart fluorescent dye F2N12S incorporated into outer leaflet of cell membrane and reporting on apoptotic cell transformation by easily detectable change of the spectral distribution of fluorescent emission. It can be adapted to any assay format.

Phosphatidylethanolamines modified by γ-ketoaldehyde (γKA) induce endoplasmic reticulum stress and endothelial activation

Peroxidation of plasma lipoproteins has been implicated in the endothelial cell activation and monocyte adhesion that initiate atherosclerosis, but the exact mechanisms underlying this activation remain unclear. Lipid peroxidation generates lipid aldehydes, including the γ-ketoaldehydes (γKA), also termed isoketals or isolevuglandins, that readily modify the amine headgroup of phosphatidylethanolamine (PE). We hypothesized that aldehyde modification of PE could mediate some of the proinflammatory effects of lipid peroxidation. We found that PE modified by γKA (γKA-PE) induced THP-1 monocyte adhesion to human umbilical cord endothelial cells. γKA-PE also induced expression of adhesion molecules and increased MCP-1 and IL-8 mRNA in human umbilical cord endothelial cells. To determine the structural requirements for γKA-PE activity, we tested several related compounds. PE modified by 4-oxo-pentanal induced THP-1 adhesion, but N-glutaroyl-PE and C(18:0)N-acyl-PE did not, suggesting that an N-pyrrole moiety was essential for cellular activity. As the N-pyrrole headgroup might distort the membrane, we tested the effect of the pyrrole-PEs on membrane parameters. γKA-PE and 4-oxo-pentanal significantly reduced the temperature for the liquid crystalline to hexagonal phase transition in artificial bilayers, suggesting that these pyrrole-PE markedly altered membrane curvature. Additionally, fluorescently labeled γKA-PE rapidly internalized to the endoplasmic reticulum (ER); γKA-PE induced C/EBP homologous protein CHOP and BiP expression and p38 MAPK activity, and inhibitors of ER stress reduced γKA-PE-induced C/EBP homologous protein CHOP and BiP expression as well as EC activation, consistent with γKA-PE inducing ER stress responses that have been previously linked to inflammatory chemokine expression. Thus, γKA-PE is a potential mediator of the inflammation induced by lipid peroxidation.

The antioxidant effect of erythropoietin on thalassemic blood cells

Because of its stimulating effect on RBC production, erythropoietin (Epo) is used to treat anemia, for example, in patients on dialysis or on chemotherapy. In β-thalassemia, where Epo levels are low relative to the degree of anemia, Epo treatment improves the anemia state. Since RBC and platelets of these patients are under oxidative stress, which may be involved in anemia and thromboembolic complications, we investigated Epo as an antioxidant. Using flow-cytometry technology, we found that in vitro treatment with Epo of blood cells from these patients increased their glutathione content and reduced their reactive oxygen species, membrane lipid peroxides, and external phosphatidylserine. This resulted in reduced susceptibility of RBC to undergo hemolysis and phagocytosis. Injection of Epo into heterozygous (Hbb(th3/+)) β-thalassemic mice reduced the oxidative markers within 3 hours. Our results suggest that, in addition to stimulating RBC and fetal hemoglobin production, Epo might alleviate symptoms of hemolytic anemias as an antioxidant.

The habenula prevents helpless behavior in larval zebrafish

Animals quickly learn to avoid predictable danger. However, if pre-exposed to a strong stressor, they do not display avoidance even if this causes continued contact with painful stimuli [1, 2]. In rodents, lesioning the habenula, an epithalamic structure that regulates the monoaminergic system, has been reported to reduce avoidance deficits caused by inescapable shock [3]. This is consistent with findings that inability to overcome a stressor is accompanied by an increase in serotonin levels [4]. However, other studies conclude that habenula lesions cause avoidance deficits [5, 6]. These contradictory results may be caused by lesions affecting unintended regions [6]. To clarify the role of the habenula, we used larval zebrafish, whose transparency and amenability to genetic manipulation enables more precise disruption of cells. We show that larval zebrafish learn to avoid a light that has been paired with a mild shock but fail to do so when pre-exposed to inescapable shock. Photobleaching of habenula afferents expressing the photosensitizer KillerRed causes a similar failure in avoidance. Expression of tetanus toxin in dorsal habenula neurons is sufficient to prevent avoidance. We suggest that this region may signal the ability to control a stressor, and that its disruption could contribute to anxiety disorders.

Measurement of annexin V uptake and lactadherin labeling for the quantification of apoptosis in adherent Tca8113 and ACC-2 cells

Phosphatidylserine (PS) exposure occurs during the cell death program and fluorescein-labeled lactadherin permits the detection of PS exposure earlier than annexin V in suspended cell lines. Adherent cell lines were studied for this apoptosis-associated phenomenon to determine if PS probing methods are reliable because specific membrane damage may occur during harvesting. Apoptosis was induced in the human tongue squamous carcinoma cell line (Tca8113) and the adenoid cystic carcinoma cell line (ACC-2) by arsenic trioxide. Cells were harvested with a modified procedure and labeled with lactadherin and/or annexin V. PS exposure was localized by confocal microscopy and apoptosis was quantified by flow cytometry. The detachment procedure without trypsinization did not induce cell damage. In competition binding experiments, phospholipid vesicles competed for more than 95 and 90% of lactadherin but only about 75 and 70% of annexin V binding to Tca8113 and ACC-2 cells. These data indicate that PS exposure occurs in three stages during the cell death program and that fluorescein-labeled lactadherin permitted the detection of early PS exposure. A similar pattern of PS exposure has been observed in two malignant cell lines with different adherence, suggesting that this pattern of PS exposure is common in adherent cells. Both lactadherin and annexin V could be used in adherent Tca8113 and ACC-2 cell lines when an appropriate harvesting procedure was used. Lactadherin is more sensitive than annexin V for the detection of PS exposure as the physical structure of PS in these blebs and condensed apoptotic cell surface may be more conducive to binding lactadherin than annexin V.

Oxidative burst assessment and neutrophil-platelet complexes in unlysed whole blood

BACKGROUND

Methods currently employed for measuring reactive oxygen species production can lead to both cellular depletion and in artifactual activation. The objective of this study was to design a methodology allowing the measurement of oxidative burst (OB) with minimal sample manipulation.

METHODS

To that purpose a flow cytometry technique developed in our laboratory, based on nucleic acid staining to discriminate erythrocytes and debris, was employed. DRAQ5 dye and PECy5-CD45 monoclonal antibody (MoAb) were simultaneously used in FL3 to identify the leukocyte population and the PE-CD14 MoAb emission was detected in FL2 for monocytes. OB was measured by using the fluorogenic probe dihydrorhodamine 123, a marker of hydrogen peroxide production. Phorbol myristate acetate (PMA), Opsonized Zymosan (OZ), fMLP and calcium ionophore A23187 activators were also used in this study. For OB assays, dose-response curves were performed for each activator. In addition, the effect of activator concentration on annexin V binding, as a measure of phosphatidylserine translocation, was evaluated.

RESULTS

With this method no-lysis and no-wash steps are required, thus avoiding an unwanted damage to leukocytes. PMA and Zymosan produced an increase in annexin V binding, while fMLP and calcium ionophore did not.

CONCLUSIONS

This study reports a feasible and reproducible new flow cytometry assay for assessing OB of neutrophils and monocytes with minimal sample manipulation. In addition, under PMA and OZ conditions, the number of neutrophils showing annexin V binding was strikingly increased. This effect is not related with a phagocytic overstimulation, but with an increased neutrophil-platelet complexes formation.

Effects of apoptosis and lipid peroxidation on T-lymphoblastoid phospholipid-dependent procoagulant activity

BACKGROUND

Coagulation has an absolute requirement for macromolecular complexes to be assembled on a negatively charged phospholipid (PL) surface. Previously, we reported that malignant T-lymphoblastoid cells have the ability to support procoagulant activity (PCA) independently of tissue factor by providing such a surface.

OBJECTIVE

To explore the effect of two pathophysiologic processes, apoptosis and lipid peroxidation (LP), on this PL-dependent PCA.

METHODS

Three different assays for PL-dependent PCA (factor IXa-initiated FXa and thrombin generation and prothrombinase activity) were used to investigate this PCA after exposing three T-lymphoblastoid cell lines to either apoptotic stimuli (1 microM staurosporine) or oxidative stress (4 mm H(2)O(2) and 40 microM CuSO(4)). Surface exposure of anionic PL was measured by flow cytometry using annexin A5(FITC) and an antibody (3G4) specific for native, but not oxidized, phosphatidylserine (PS).

RESULTS AND CONCLUSIONS

Both apoptosis and LP significantly enhanced the PCA of cells, to a level that was greater than that observed following calcium ionophore treatment, suggesting that the increased activity was not solely due to anionic PL exposure. Whereas cells undergoing apoptosis bound both annexin A5(FITC) and 3G4, only annexin A5(FITC) bound to cells undergoing LP. This implies that apoptosis increases PCA by causing the translocation of oxidized/native PS to the outer membrane, whereas LP appears to increase the PCA, possibly due to malondialdehyde adducts altering the net charge on the cell surface, which allows PLs other than PS to participate in thrombin generation.

Annexins: multifunctional components of growth and adaptation

Plant annexins are ubiquitous, soluble proteins capable of Ca(2+)-dependent and Ca(2+)-independent binding to endomembranes and the plasma membrane. Some members of this multigene family are capable of binding to F-actin, hydrolysing ATP and GTP, acting as peroxidases or cation channels. These multifunctional proteins are distributed throughout the plant and throughout the life cycle. Their expression and intracellular localization are under developmental and environmental control. The in vitro properties of annexins and their known, dynamic distribution patterns suggest that they could be central regulators or effectors of plant growth and stress signalling. Potentially, they could operate in signalling pathways involving cytosolic free calcium and reactive oxygen species.

Regulation of protein C inhibitor (PCI) activity by specific oxidized and negatively charged phospholipids

Protein C inhibitor (PCI) is a serpin with affinity for heparin and phosphatidylethanolamine (PE). We analyzed the interaction of PCI with different phospholipids and their oxidized forms. PCI bound to oxidized PE (OxPE), and oxidized and unoxidized phosphatidylserine (PS) immobilized on microtiter plates and in aqueous suspension. Binding to OxPE and PS was competed by heparin, but not by the aminophospholipid-binding protein annexin V or the PCI-binding lipid retinoic acid. PS and OxPE stimulated the inhibition of activated protein C (aPC) by PCI in a Ca++-dependent manner, indicating that binding of both, aPC (Ca++ dependent) and PCI (Ca++ independent), to phospholipids is necessary. A peptide corresponding to the heparin-binding site of PCI abolished the stimulatory effect of PS on aPC inhibition. No stimulatory effect of phospholipids on aPC inhibition was seen with a PCI mutant lacking the heparin-binding site. A heparin-like effect of phospholipids (OxPE) was not seen with antithrombin III, another heparin-binding serpin, suggesting that it is specific for PCI. PCI and annexin V were found to be endogenously colocalized in atherosclerotic plaques, supporting the hypothesis that exposure of oxidized PE and/or PS may be important for the local regulation of PCI activity in vivo.

Annexins: putative linkers in dynamic membrane-cytoskeleton interactions in plant cells

The plasma membrane, the most external cellular structure, is at the forefront between the plant cell and its environment. Hence, it is naturally adapted to function in detection of external signals, their transduction throughout the cell, and finally, in cell reactions. Membrane lipids and the cytoskeleton, once regarded as simple and static structures, have recently been recognized as significant players in signal transduction. Proteins involved in signal detection and transduction are organised in specific domains at the plasma membrane. Their aggregation allows to bring together and orient the downstream and upstream members of signalling pathways. The cortical cytoskeleton provides a structural framework for rapid signal transduction from the cell periphery into the nucleus. It leads to intracellular reorganisation and wide-scale modulation of cellular metabolism which results in accumulation of newly synthesised proteins and/or secondary metabolites which, in turn, have to be distributed to the appropriate cell compartments. And again, in plant cells, the secretory vesicles that govern polar cellular transport are delivered to their target membranes by interaction with actin microfilaments. In search for factors that could govern subsequent steps of the cell response delineated above we focused on an evolutionary conserved protein family, the annexins, that bind in a calcium-dependent manner to membrane phospholipids. Annexins were proposed to regulate dynamic changes in membrane architecture and to organise the interface between secretory vesicles and the membrane. Certain proteins from this family were also identified as actin binding, making them ideal mediators in cell membrane and cytoskeleton interactions.

Lactadherin binding and phosphatidylserine expression on cell surface-comparison with annexin A5

BACKGROUND

Transbilayer movement of anionic phospholipids from the inner to the outer leaflet of the plasma membrane occurs during platelet activation, red cell senescence, and apoptosis. The anionic phospholipid-binding protein, annexin A5, has been used to detect the presence of phosphatidylserine on the outer leaflet of the cell membrane. Lactadherin, a glycoprotein secreted by macrophages, binds to phosphatidylserine on apoptotic cells and promote their clearance by macrophages.

METHODS

The authors isolated and labeled lactadherin and annexin A5 with FITC and compared their ability to detect phosphatidylserine expression by flow cytometry.

RESULTS

FITC-lactadherin induced greater shift in the histogram and a higher mean fluorescence intensity than FITC-annexin A5 when platelets were activated with thrombin (0.1 unit/mL) or Ca(2+) ionophore A23187 (1 microM). Similarly, lactadherin was more sensitive in detecting phosphatidylserine in red cells induced to express phosphatidylserine. Also, in HL 60 cells undergoing apoptosis, lactadherin detected phosphatidylserine expression earlier than annexin A5. In patients with disseminated intravascular coagulation, lactadherin detected phosphatidylserine-expressing platelets in most patients, whereas under similar conditions, FITC-annexin A5 could not.

CONCLUSIONS

The authors' studies show that FITC-lactadherin is a better probe than annexin A5 in detecting phosphatidylserine-expressing activated platelets, red cells, and apoptotic cells.

Protection against amyloid beta-peptide (1–42)-induced loss of phospholipid asymmetry in synaptosomal membranes by tricyclodecan-9-xanthogenate (D609) and ferulic acid ethyl ester: Implications for Alzheimer's disease

Amyloid-beta (1-42) [Abeta (1-42)] deposition in the brain is a hallmark of Alzheimer's disease (AD) and has been shown to induce apoptosis and disrupt cellular ion homeostasis. Abeta (1-42) induces membrane lipid peroxidation, and 4-hydroxynonenal (HNE) and 2-propenal (acrolein) are the two reactive products of lipid peroxidation, which structurally modify proteins by covalent interaction and inhibit enzyme function. Phosphatidylserine (PS), an aminophospholipid, is sequestered in the inner leaflet of the plasma membrane in nonstimulated cells. An early signal of synaptosomal apoptosis is the loss of phospholipid asymmetry and the appearance of phosphatidylserine in the outer leaflet of the membrane. The ATP-requiring enzyme, flippase, maintains phospholipid asymmetry of PS. Here, we have investigated the inactivation of the transmembrane enzyme aminophospholipid-translocase (or flippase) by Abeta (1-42). Flippase activity depends on a critical cysteine residue, a putative site of covalent modification by the Abeta (1-42)-induced lipid peroxidation products, HNE or acrolein. The present study is aimed to investigate the protective effects of tricyclodecan-9-xanthogenate (D609) and ferulic acid ethyl ester (FAEE) on Abeta (1-42) induced modulation in phospholipid asymmetry in the synaptosomal membranes. Pretreatment of synaptosomes with D609 and FAEE significantly protected Abeta (1-42)-induced loss of phospholipid asymmetry in synaptosomal membranes. Our results suggest that D609 and FAEE exert protective effects against Abeta (1-42) induced apoptosis. The increase in intracellular Ca(2+) might not be the sole cause for the loss of flippase activity. Rather, other mechanisms that could modulate the function of flippase might be important in the modulation of phospholipid asymmetry. The results of this study are discussed with relevance to neuronal loss in the AD brain.

Recruitment of beta-2-glycoprotein 1 to cell surfaces in extrinsic and intrinsic apoptosis

Apoptotic cells and phagocytes have developed a diverse array of distinct ligand-receptor systems that drive the recognition and uptake of dying cells. Phagocytes recognize apoptotic cells either directly, by binding to specific ligands at their cell surface, or indirectly, by binding to bridging proteins that bind these ligands. Previous observations showed that the plasma bridging protein beta2GP1, binds PS containing vesicles, and enhances their binding and engulfment by phagocytes in vitro. In this study we show that apoptotic cells injected intravenously and intraperitonealy into syngeneic mice recruited the PS binding protein, beta2GP1. Examination of peritoneal exudates and spleen thin sections showed that only the injected apoptotic cells picked up endogenous beta2GP1. Recovery of cells from the peritoneum showed that apoptotic cells bearing beta2GP1 were clustered around host peritoneal phagocytes. In addition, tissue sections from mice injected with Fas antibody showed colocalization of beta2GP1 with TUNEL-positive apoptotic cells. These results provide evidence that endogenous beta2GP1 binds apoptotic cells in vivo, suggesting that the protein plays an important physiologic role in the recognition of dying cells.

Binding of cationic liposomes to apoptotic cells

One of the most prominent hallmarks of apoptotic cells is the altered characteristics of their plasma membrane, with its blebbing and exposure of the anionic phospholipid, phosphatidylserine (PS), in the outer leaflet of the lipid bilayer. The latter feature provides the basis of distinguishing apoptotic cells from most normal cells due to staining with fluorescently labeled annexin V, binding specifically to PS. In this article, we report on the binding to apoptotic leukemic T cells (Jurkat cell line, treated with different apoptotic inducers) of cationic liposomes (CLs) composed of the cationic gemini surfactant SS-1 ((2S,3S)-2,3-dimethoxy-1,4-bis(N-hexadecyl-N,N-dimethylammonium)butane dibromide), the fluorescent lipid analog DOPRho (1,2-dioleoyl-sn-glycero-3-phosphoethanolamine-N-(lissamine rhodamine B sulfonyl)), and POPC (1-palmitoyl-2-oleoyl-sn-glycero-3-phosphocholine). Control cells showed negligible and irregular binding patterns of CLs, whereas apoptotic cells revealed a strongly augmented staining of their plasma membrane. Morphological observations and comparison with standard procedures for detecting apoptotic cells further demonstrated the binding of CLs to be intense for cells undergoing apoptosis. In addition, some apoptotic cells with higher caspase-3 activity also revealed more pronounced staining by CLs. Our data suggest that the binding of CLs to apoptotic cells is mediated through an electrostatic interaction between the positively charged head group of SS-1 and the translocated anionic phospholipid PS in the plasma membrane. Because the fluorescent lipid tracer can be freely selected, this approach provides convenient and versatile means for the fluorescence detection of apoptotic cells.

Evaluation of the sensitivity of red blood cell markers to detect photodynamic membrane damage

BACKGROUND

Photodynamic dyes have been used to investigate pathogen reduction methods in RBC suspensions, but treatment with sensitizers and light can produce unwanted membrane damage during routine blood bank storage. This study compares the relative sensitivity of three assays for detecting RBC membrane damage.

STUDY DESIGN AND METHODS

RBCs were treated with dimethylmethylene blue and red light-emitting diode light under four conditions differing in photodynamic stringency and subsequently stored under refrigerated conditions for up to 42 days. Hemolysis, potassium release, and the apoptosis marker annexin V binding were assayed immediately after phototreatment and following storage.

RESULTS

In terms of increasing sensitivity for detecting photodynamic RBC membrane damage was enhanced ion leakage >> hemolysis > annexin V binding.

CONCLUSION

Although very stringent photodynamic treatment conditions generate annexin V-positive RBCs, the assay will not detect more subtle membrane damage that is readily detected by other well-established methods. In addition, many RBCs destined for photo-induced hemolysis later in storage are annexin V-negative throughout the storage period, suggesting that the two measures are not directly related.

Aminophospholipid asymmetry: A matter of life and death

Maintenance of membrane lipid asymmetry is a dynamic process that influences many events over the lifespan of the cell. With few exceptions, most cells restrict the bulk of the aminophospholipids to the inner membrane leaflet by means of specific transporters. Working in concert with each other, these proteins correct for sporadic incursions of the aminophospholipids to the outer membrane leaflet as a result of bilayer imbalances created by various cellular events. A shift in the relative contribution in each of these activities can result in sustained exposure of the aminophospholipids at the cell surface, which allows capture of the cells by phagocytes before the integrity of the plasma membrane is compromised. The absence of an efficient recognition and elimination mechanism can result in uncontrolled and persistent presentation of self-antigens to the immune system, with development of autoimmune syndromes. To prevent this, phagocytes have developed a diverse array of distinct and redundant receptor systems that drive the postphagocytic events along pathways that facilitate cross-talk between the homeostatic and the immune systems. In this work, we review the basis for the proposed mechanism(s) by which apoptotic ligands appear on the target cell surface and the phagocyte receptors that recognize these moieties.

Macrophage recognition of externalized phosphatidylserine and phagocytosis of apoptotic Jurkat cells--existence of a threshold

Phosphatidylserine (PS) is predominantly confined to the inner leaflet of plasma membrane in cells, but it is externalized on the cell surface during apoptosis. This externalized PS is required for effective phagocytosis of apoptotic cells by macrophages. Because PS trans-bilayer asymmetry is not absolute in different types of nonapoptotic cells, we hypothesized that the amounts of externalized PS may be critical for macrophage discrimination between apoptotic and nonapoptotic cells. We developed a sensitive electron paramagnetic resonance method to quantify the amounts of externalized PS based on specific binding of paramagnetic annexin V-microbead conjugates with PS on cell surfaces. Using this technique, we found that nonapoptotic Jurkat cells externalize 0.9 pmol of endogenous PS/10(6) Jurkat cells. For cells with different amounts of integrated exogenous PS on their surface, no phagocytic response was observed at PS levels <5 pmol/10(6) Jurkat cells; at higher PS concentrations, phagocytosis increased in a concentration-dependent manner. Apoptosis in Jurkat cells caused externalization of approximately 240 pmol PS/10(6) Jurkat cells; these amounts of externalized PS are manyfold higher than the threshold amounts of PS required for phagocytosis. Thus, macrophages have a sensitivity threshold for PS externalized on the cell surface that provides for reliable recognition and distinction between normal cells with low contents of externalized PS and apoptotic cells with remarkably elevated PS levels.

Mechanisms of anemia in SHP-1 protein tyrosine phosphatase-deficient "viable motheaten" mice

OBJECTIVE

Viable motheaten mice (abbreviated gene symbol me(v)) are deficient in SHP-1, a critical negative regulator of signal transduction in hematopoietic cells. These mice exhibit severe immune dysfunction accompanied by hyperproliferation of myeloid cells, widespread inflammatory lesions, and regenerative anemia. The aim of this study was to investigate the mechanisms underlying anemia in me(v)/me(v) mice.

MATERIALS AND METHODS

Multiple hematologic parameters, osmotic fragility, and erythropoietin levels were measured to characterize the anemia in me(v)/me(v) mice. B-cell-deficient me(v)/me(v) Igh-6(null) mice were generated to assess the role of anti-erythrocyte antibodies. Coombs assays and flow cytometry were carried out for detection of anti-erythrocyte antibodies. Oxidant production by macrophages, glutathione levels, and lipid peroxidation products in erythrocytes were measured, as was the impact of oxidant on the ultrastructure of me(v)/me(v) erythrocytes. Erythroid maturation and erythrocyte plasma membrane integrity were assessed with flow cytometry by evaluating CD71 expression and annexin V labeling.

RESULTS

The regenerative anemia of me(v)/me(v) mice was associated with erythrocyte changes that were independent of the presence of anti-erythrocyte antibodies. Erythrocytes from me(v)/me(v) mice had increased fragility and heightened susceptibility to oxidant damage. Macrophages from me(v)/me(v) mice demonstrated a higher basal level of oxidant production and enhanced production after stimulation. Oxidant damage in me(v)/me(v) erythrocytes was evidenced by a significant elevation of lipid peroxidation and diminished levels of glutathione.

CONCLUSION

Our results support the hypothesis that as a consequence of severe inflammatory disease, me(v)/me(v) erythrocytes are subject to exceptionally high oxidative stress resulting in oxidation of phospholipids in the erythrocyte membrane with subsequent hemolysis.

NADPH oxidase-dependent oxidation and externalization of phosphatidylserine during apoptosis in Me2SO-differentiated HL-60 cells. Role in phagocytic clearance

Resolution of inflammation requires clearance of activated neutrophils by phagocytes in a manner that protects adjacent tissues from injury. Mechanisms governing apoptosis and clearance of activated neutrophils from inflamed areas are still poorly understood. We used dimethylsulfoxide-differentiated HL-60 cells showing inducible oxidase activity to study NADPH oxidase-induced apoptosis pathways typical of neutrophils. Activation of the NADPH oxidase by phorbol myristate acetate caused oxidative stress as shown by production of superoxide and hydrogen peroxide, depletion of intracellular glutathione, and peroxidation of all three major classes of membrane phospholipids, phosphatidylcholine, phosphatidylethanolamine, and phosphatidylserine. In addition, phorbol myristate acetate stimulation of the NADPH oxidase caused apoptosis, as evidenced by apoptosis-specific phosphatidylserine externalization, increased caspase-3 activity, chromatin condensation, and nuclear fragmentation. Furthermore, phorbol myristate acetate stimulation of the NADPH oxidase caused recognition and ingestion of dimethylsulfoxide-differentiated HL-60 cells by J774A.1 macrophages. To reveal the apoptosis-related component of oxidative stress in the phorbol myristate acetate-induced response, we pretreated cells with a pancaspase inhibitor, benzyloxycarbonyl-Val-Ala-Asp-fluoromethyl ketone (z-VAD-fmk), and found that it caused partial inhibition of hydrogen peroxide formation as well as selective protection of only phosphatidylserine, whereas more abundant phospholipids, phosphatidylcholine and phosphatidylethanolamine, were oxidized to the same extent in the absence or presence of z-VAD-fmk. In contrast, inhibitors of NADPH oxidase activity, diphenylene iodonium and staurosporine, as well as antioxidant enzymes, superoxide dismutase/catalase, completely protected all phospholipids against peroxidation, inhibited expression of apoptotic biomarkers and externalization of phosphatidylserine, and reduced phagocytosis of differentiated HL-60 cells by J774A.1 macrophages. Similarly, zymosan-induced activation of the NADPH oxidase resulted in the production of superoxide and oxidation of different classes of phospholipids of which only phosphatidylserine was protected by z-VAD-fmk. Accordingly, zymosan caused apoptosis in differentiated HL-60 cells, as evidenced by caspase-3 activation and phosphatidylserine externalization. Finally, zymosan triggered caspase-3 activation and extensive SOD/catalase-inhibitable phosphatidylserine exposure in human neutrophils. Overall, our results indicate that NADPH oxidase-induced oxidative stress in neutrophil-like cells triggers apoptosis and subsequent recognition and removal of these cells through pathways dependent on oxidation and externalization of phosphatidylserine.

1-Cys peroxiredoxin overexpression protects cells against phospholipid peroxidation-mediated membrane damage

1-Cys peroxiredoxin (1-cysPrx) is a novel antioxidant enzyme able to reduce phospholipid hydroperoxides in vitro by using glutathione as a reductant. This enzyme is widely expressed and is enriched in lungs. A fusion protein of green fluorescent protein with 1-cysPrx was stably expressed in a lung-derived cell line (NCI-H441) lacking endogenous enzyme. Overexpressing cells (C17 or C48) degraded H(2)O(2) and t-butylhydroperoxide more rapidly and showed decreased sensitivity to oxidant stress as measured by (51)Cr release. On exposure to (*)OH generated by Cu(2+)-ascorbate (Asc), overexpressing cells compared with H441 showed less increase in thiobarbituric acid-reactive substance and phosphatidylcholine hydroperoxide content. This effect was reversed by depletion of cellular glutathione. Diphenyl-1-pyrenoylphosphonium fluorescence, used as a real-time probe of membrane phospholipid peroxidation, increased immediately on exposure to Cu(2+)-Asc and was abolished by preincubation of cells with Trolox (a soluble vitamin E) or Tempol (a radical scavenger). The rate of diphenyl-1-pyrenoylphosphonium fluorescence increase with Cu(2+)-Asc exposure was markedly attenuated in C17 and C48 cells as compared with H441. Annexin V-Cy3 was used to detect phosphatidylserine translocation from the inner to outer leaflet of the plasma membrane. Cu(2+)-Asc treatment induced phosphatidylserine translocation within 2 h in H441 cells but none was observed in C48 cells up to 24 h. These results indicate that 1-cysPrx can scavenge peroxides but in addition can reduce peroxidized membrane phospholipids. Thus, the enzyme can protect cells against oxidant-induced plasma membrane damage, thereby playing an important role in cellular defense against oxidant stress.

Fatty acid oxidation and signaling in apoptosis

It is well established that fatty acid metabolites of cyclooxygenase, lipoxygenase (LOX), and cytochrome P450 are implicated in essential aspects of cellular signaling including the induction of programmed cell death. Here we review the roles of enzymatic and non-enzymatic products of polyunsaturated fatty acids in controlling cell growth and apoptosis. Also, the spontaneous oxidation of polyunsaturated fatty acids yields reactive aldehydes and other products of lipid peroxidation that are potentially toxic to cells and may also signal apoptosis. Significant conflicting data in terms of the role of LOX enzymes are highlighted, prompting a re-evaluation of the relationship between LOX and prostate cancer cell survival. We include new data showing that LNCaP, PC3, and Du145 cells express much lower levels of 5-LOX mRNA and protein compared with normal prostate epithelial cells (NHP2) and primary prostate carcinoma cells (TP1). Although the 5-LOX activating protein inhibitor MK886 killed these cells, another 5-LOX inhibitor AA861 hardly showed any effect. These observations suggest that 5-LOX is unlikely to be a prostate cancer cell survival factor, implying that the mechanisms by which LOX inhibitors induce apoptosis are more complex than expected. This review also suggests several mechanisms involving peroxisome proliferator activated receptor activation, BCL proteins, thiol regulation, and mitochondrial and kinase signaling by which cell death may be produced in response to changes in non-esterified and non-protein bound fatty acid levels. Overall, this review provides a context within which the effects of fatty acids and fatty acid oxidation products on signal transduction pathways, particularly those involved in apoptosis, can be considered in terms of their overall importance relative to the much better studied protein or peptide signaling factors.

Caspase 3 regulates phosphatidylserine externalization and phagocytosis of oxidatively stressed erythrocytes

The appearance of phosphatidylserine (PS) on the outer surface of red cells is an important signal for their uptake by macrophages. We report for the first time that procaspase 3 present in the anucleated mature human erythrocyte is activated under oxidative stress induced by t-butylhydroperoxide leading to impairment of the aminophospholipid translocase, PS externalization and increased erythrophagocytosis. This is the first report linking caspase 3 activation to inhibition of flippase activity and uptake of red cells by macrophages.

Acrolein-induced cell death: a caspase-influenced decision between apoptosis and oncosis/necrosis

Due to the dominating roles that caspases play in the apoptotic cascade, their activities appear to be a primary factor in the death pathway (apoptosis versus oncosis/necrosis) decision. In murine FL5.12 proB lymphocytes, the cellular consequences of acrolein treatment included a lack of typical apoptotic features in preference to oncosis/necrosis. Oncosis/necrosis was apparent by detection of a reduction in intracellular ATP concentration, increased plasma membrane leakage (measured by LDH release and flow cytometric detection of propidium iodide uptake) and morphological criteria. Analysis of acrolein-treated cell lysates or recombinant caspase enzymes showed overall dose-dependent decreases in caspase-3, -8 and -9 activities. In addition to acrolein's effect on intracellular caspases, it was also able to alter caspase-dependent apoptosis induced by secondary treatment with etoposide or following cytokine withdrawal. Acrolein at doses > or =20 microM circumvented etoposide or interleukin-3 withdrawal induced apoptosis. When acrolein was combined with mechlorethamine, another alkylating agent not dependent on caspases for its cell death signaling, necrosis was increased in a dose-dependent manner. Overall, these data suggest that caspase inhibition plays an important role in the cell death pathway decision, particularly with treatments dependent on the caspase cascade to induce apoptosis.