Phosphatidylethanolamine at the luminal endothelial surface--implications for hemostasis and thrombotic autoimmunity

A case of repeated in-stent restenosis of coronary artery as a primary manifestation of seronegative antiphospholipid antibody syndrome

BACKGROUND

Antiphospholipid antibody syndrome (APS) is a multisystemic autoimmune disorder which affects many organs or systems; however, coronary artery is relatively less frequently involved.

CASE PRESENTATION

A 65-year-old female with effort chest pain was hospitalized for unstable angina in Janurary, 2015. Coronary angiography revealed sub-total occlusion of proximal left anterior descending (LAD) coronary artery, where a drug-eluting stent was successfully deployed. The patient experienced multiple in-stent stenosis at LAD coronary artery and coronary artery bypass graft (CABG) surgery was advised. Subsequently, severe stenosis of left circumflex (LCX) coronary artery emerged, and the patient suffered persistent in-stent restenosis. Eventually, the patient was diagnosed with seronegative antiphospholipid antibody syndrome and salvaged by immunosuppressants.

CONCLUSIONS

Repeated in-stent restenosis could be a primary manifestation of seronegative antiphospholipid antibody syndrome, and suppression of autoimmune activity and inflammation other than purely coronary revascularization might be a better option.

Levels and avidities of antiphosphatidylethanolamine antibodies in patients with thrombotic events and immunologically-mediated diseases

AIMS

Antiphosphatidylethanolamine antibodies (aPE) represent one type of antiphospholipid antibody (aPL) directed against the neutral phospholipids - phosphatidylethanolamines. The aim of this study was to evaluate levels and avidities of aPE in several groups of patients and compare them with conventional aPLs.

METHODS

aPE were analysed in a cohort consisting of 68 hospitalized patients. The other cohort comprised 22 patients with immunologically-mediated diseases. The control group consisted of 20 healthy persons. ELISA methods were used for determination of aPL. Avidities of aPE were tested by modified ELISA with urea as a chaotropic agent.

RESULTS

aPE IgG/IgM were significantly higher in the group of patients with venous thromboembolism than those with non-thrombotic internal disorders (P=0.02 for both Ig classes). aPE IgG/IgM elevated above cut-off values were found in 10.8% of patients with venous thromboembolism and as a single aPL in 6.5%. Levels of aPE IgG higher than our limit (>6 U/mL) were detected in 29% of patients with immunologically-mediated diseases with other positive aPL. Low-, intermediate- and high-avidity aPE IgG were found in patients of both cohorts. The avidities of aPE IgG differed from those of anticardiolipin antibodies IgG. Neither aPE IgG levels nor avidity dynamics significantly changed during follow-up.

CONCLUSION

aPE may be related to venous thromboembolism and may be part of the repertoire of aPL in immunologically-mediated diseases. There are patients with thrombosis negative for conventional aPL but positive for aPE. aPE IgG may have different avidities.

Egg yolk lipids: separation, characterization, and utilization

Egg yolk contains very high levels of lipids, which comprise 33% of whole egg yolk. Although triglyceride is the main lipid, egg yolk is the richest source of phospholipids and cholesterol in nature. The egg yolk phospholipids have a unique composition with high levels of phosphatidylcholine followed by phosphatidylethanolamine, sphingomyelin, plasmalogen, and phosphatidylinositol. All the egg yolk lipids are embedded inside the HDL and LDL micelles or granular particles. Egg yolk lipids can be easily extracted using solvents or supercritical extraction methods but their commercial applications of egg yolk lipids are limited. Egg yolk lipids have excellent potential as a food ingredient or cosmeceutical, pharmaceutical, and nutraceutical agents because they have excellent functional and biological characteristics. This review summarizes the current knowledge on egg yolk lipids' extraction methods and functions and discusses their current and future use, which will be important to increase the use and value of the egg.

Egg Allergy in Children and Weaning Diet

Eggs are a fundamental food in the human diet, and together with cow’s milk, they are the most common food allergen. This work highlights the main nutritional characteristics of eggs to show how their absence from a child’s diet can constitute a serious deficiency. We then analyze the risk factors that facilitate the onset of egg allergy. The third part of the paper reports possible interventions to lower the appearance of food allergy that have been occurred in trials. The last part of the paper is a synthesis of this research study that has been taken from several of the latest guidelines or from position papers.

Is Oxidative Stress an Emerging Player in the Thrombosis of Patients with Anti-Phosphatidylethanolamine Autoantibodies?

The detection of anti-phosphatidylethanolamine autoantibodies (aPEs) has been proposed to improve the diagnosis and management of patients presenting clinical manifestations of antiphospholipid syndrome (APS), such as thrombosis, and who are persistently negative for conventional markers. After selecting the most specific ELISA for their detection, we evidenced the interest of aPEs in the exploration of thrombosis when APS conventional markers were negative through a 1-year retrospective study including 1131 consecutive patients routinely tested for aPEs. To validate this result, we assessed aPEs in a newly selected population of 77 patients with unexplained deep vein thrombosis (DVT). With a total prevalence of 19.5%, we confirmed the interest of aPE detection in patients with unexplained DVT who were devoid of other aPLs markers. Since endosomal compartment, a source of ROS production, has been recently identified as the cellular target of aPEs in vitro, we then investigated an association between aPE positivity and reactive oxygen species (ROS) production by measuring the production of thiobarbituric acid-reactive substances. We showed, for the first time, a significant association between aPE positivity and systemic ROS production in patients which led us to hypothesize a new mechanism of action of aPEs in thrombosis through a signaling related to oxidative stress.

Development of Duramycin-Based Molecular Probes for Cell Death Imaging

Cell death is involved in numerous pathological conditions such as cardiovascular disorders, ischemic stroke and organ transplant rejection, and plays a critical role in the treatment of cancer. Cell death imaging can serve as a noninvasive means to detect the severity of tissue damage, monitor the progression of diseases, and evaluate the effectiveness of treatments, which help to provide prognostic information and guide the formulation of individualized treatment plans. The high abundance of phosphatidylethanolamine (PE), which is predominantly confined to the inner leaflet of the lipid bilayer membrane in healthy mammalian cells, becomes exposed on the cell surface in the early stages of apoptosis or accessible to the extracellular milieu when the cell suffers from necrosis, thus representing an attractive target for cell death imaging. Duramycin is a tetracyclic polypeptide that contains 19 amino acids and can bind to PE with excellent affinity and specificity. Additionally, this peptide has several favorable structural traits including relatively low molecular weight, stability to enzymatic hydrolysis, and ease of conjugation and labeling. All these highlight the potential of duramycin as a candidate ligand for developing PE-specific molecular probes. By far, a couple of duramycin-based molecular probes such as Tc-99 m-, F-18-, or Ga-68-labeled duramycin have been developed to target exposed PE for in vivo noninvasive imaging of cell death in different animal models. In this review article, we describe the state of the art with respect to in vivo imaging of cell death using duramycin-based molecular probes, as validated by immunohistopathology.

Constitutive oxidants from hepatocytes of male iPLA2β-null mice increases the externalization of phosphatidylethanolamine on plasma membrane

We have found that group VIA calcium-independent phospholipase A2 (iPLA2β) has specificity for hydrolysis of phosphatidylethanolamine (PE) in mouse livers. Phospholipids (PLs) are transported to plasma membrane and some PLs including PE are externalized to maintain membrane PL asymmetry. Here we demonstrated that hepatocytes of iPLA2β-null (KO) mice showed an increase in PE containing palmitate and oleate. We aimed to examine whether externalization of PE on the outer leaflets could be affected by iPLA2β deficiency and its modulation by reactive oxygen species (ROS) or apoptosis. As duramycin has high affinity to PE, we used duramycin conjugated with biotin (DLB) and streptavidin 488 as a probe for detection of externalized PE. Compared to WT, naïve KO hepatocytes showed an increase in both PE externalization and ROS generation. These events were observed in male but not in female KO mice. Hydrogen peroxide or menadione treatment enhanced PE externalization to the same extent for both male/female WT and KO hepatocytes. By indirect immunofluorescence, DLB-streptavidin staining was observed as small punctuated spots on the cell surface of menadione-treated KO hepatocytes. Unlike the reported PS externalization, CD95/FasL treatment did not lead to any increase in PE externalization, and iPLA2β deficiency-dependent PE externalization was also not correlated with apoptosis. Thus, constitutive (but not induced) ROS generation in iPLA2β-deficient hepatocytes leads to PE externalization observed only in male mice. Such PE externalization may imply detrimental effects regarding further oxidation of PE fatty acids and the binding with pathogens on the outer leaflets of hepatocyte plasma membrane.

Thromboses in tuberculosis are linked to antiphosphatidylethanolamine antibodies levels: A cross-sectional study

Venous thromboses have been associated with tuberculosis, but the relationship with circulating anticoagulant has not been studied yet. In a cohort of 48 patients with tuberculosis, 22.9% of them presented with venous thromboses significantly associated with dose dependent level of antiphosphophatidyl-ethanolamine antibodies.

In Vitro Antithrombotic Properties of Salmon (Salmo salar) Phospholipids in a Novel Food-Grade Extract

Marine and salmon polar lipids (PLs) extracted by conventional extractions with non-food-grade solvents (CE-salmon-PLs) possess antithrombotic bioactivities against platelet-activating factor (PAF) and thrombin. Similar effects of food-grade-extracted (FGE) marine PLs have not yet been reported. In this study, food-grade solvents were used to extract PLs from Irish organic farmed salmon (Salmo salar) fillets (FGE-salmon-PLs), while their antithrombotic bioactivities were assessed in human platelets induced by platelet aggregation agonists (PAF/thrombin). FGE-salmon-PLs were further separated by thin layer chromatography (TLC) into lipid subclasses, and the antithrombotic bioactivities of each subclass were also assessed. LC-MS was utilized to elucidate the structure-activity relationships. FGE-salmon-PLs strongly inhibited PAF-induced platelet aggregation, while their relevant anti-thrombin effects were at least three times more potent than the previously reported activities of CE-salmon-PLs. TLC-derived lipid fractions corresponding to phosphatidylcholines (PC) and phosphatidylethanolamines (PE) were the most bioactive lipid subclasses obtained, especially against thrombin. Their LC-MS analysis elucidated that they are diacyl- or alkyl-acyl- PC and PE moieties baring ω3 polyunsaturated fatty acids (PUFA) at their sn-2 position, such as eicosapentaenoic acid (EPA) or docosahexaenoic acid (DHA). Our results concerning the potent antithrombotic effects of FGE-salmon-PLs against both PAF and thrombin pathways strongly suggest that such food-grade extracts are putative candidates for the development of novel cardioprotective supplements and nutraceuticals.

How Can the Value and Use of Egg Yolk Be Increased?

The major driving force for the egg consumption in the United States over the past few decades was processed egg. However, the consumption of egg through the processed egg reached the plateau in recent years because of the imbalance in the demands between the egg white and yolk products. The consumer demands for egg white products are very high while those for the egg yolk, the co-product of dried egg white, are low because of the negative perceptions on egg yolk. Two key approaches that can be used to increase the value and use of egg yolk are: (1) developing new commodity products by fractionating egg yolk and apply them in various food processing, and (2) separating functional proteins and lipids from yolk and use them as is or further develop functional peptides and functional lipids and use them as pharmaceutical, nutraceutical, and cosmeceutical agents. These approaches can diversify the use of egg yolk, which eventually will help increase the consumption of egg. This review (1) discusses the current use of egg yolk products and the development of new functional commodity products from egg yolk, (2) review the important functional components in egg yolk and overview the current separation methods and their applications, (3) discuss the production of functional peptides and lipids using the separated egg proteins and lipids, and (4) suggest the future directions for the best use of egg yolk components. Development of scale-up production methods, which is vital for the practical applications, is discussed when appropriate.

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.

Early endosome as a pathogenic target for antiphosphatidylethanolamine antibodies

Phosphatidylethanolamine (PE) is a major phospholipid species with important roles in membrane trafficking and reorganization. Accumulating clinical data indicate that the presence of circulating antibodies against PE is positively correlated with the symptoms of antiphospholipid syndromes (APS), including thrombosis and repeated pregnancy loss. However, PE is generally sequestered inside a normal resting cell, and the mechanism by which circulating anti-PE antibodies access cellular PE remains unknown. The studies presented here were conducted with synthetic PE-binding agents, plasma samples from patients with anti-PE autoimmunity, and purified anti-PE antibodies. The results suggest that the cellular vulnerability to anti-PE antibodies may be mediated by the binding of PE molecules in the membrane of the early endosome. Endosomal PE binding led to functional changes in endothelial cells, including declines in proliferation and increases in the production of reactive oxygen species, as well as the expression of inflammatory molecules. Collectively, our findings provide insight into the etiology of anti-PE autoimmunity and, because endosomes are of central importance in almost all types of cells, could have important implications for a wide range of biological processes.

Duramycin-induced calcium release in cancer cells

Duramycin, through binding with phosphatidylethanolamine (PE), has shown potential to be an effective antitumour agent. However, its mode of action in relation to tumour cells is not fully understood. PE expression on the surface of a panel of cancer cell lines was analysed using duramycin and subsequent antibody labelling, and then analysed by flow cytometry. Cell viability was also assessed by flow cytometry using annexin V and propidium iodide. Calcium ion (Ca) release by tumour cells in response to duramycin was determined by spectrofluorometry following incubation with Fluo-3, AM. Confocal microscopy was performed on the cancer cell line AsPC-1 to assess real-time cell response to duramycin treatment. Duramycin could detect cell surface PE expression on all 15 cancer cell lines screened, which was shown to be duramycin concentration dependent. However, higher concentrations induced necrotic cell death. Duramycin induced calcium ion (Ca) release from the cancer cell lines also in a concentration-dependent and time-dependent manner. Confocal microscopy showed an influx of propidium iodide into the cells over time and induced morphological changes. Duramycin induces Ca release from cancer cell lines in a time-dependent and concentration-dependent manner.

Phosphatidylethanolamine is externalized at the surface of microparticles

Microparticles (MPs) are membrane-bound vesicles shed normally or as a result of various (pathological) stimuli. MPs contain a wealth of bio-active macromolecules. Aminophospholipid phosphatidylserine (PS) is present on the surface of many MPs. As PS and phosphatidylethanolamine (PE) are related, yet distinct aminophospholipids, the purpose of this study was to systematically and directly assess PE exposure on MPs. We examined MPs from various human cellular sources (human breast cancer, endothelial, red and white blood cells) by flow cytometry using a PE-specific probe, duramycin, and two PS-specific probes, annexin V and lactadherin. PS and PE exposure percentage was comparable on vascular and blood cell-derived MPs (80-90% of MP-gated events). However, the percentage of malignant breast cancer MPs exposing PE (~90%) was significantly higher than PS (~50%). Thus, while PS and PE exposure can result from a general loss of membrane asymmetry, there may also be distinct mechanisms of PE and PS exposure on MPs that vary by cellular source.

A single-step kit formulation for the (99m)Tc-labeling of HYNIC-Duramycin

INTRODUCTION

(99m)Tc-Duramycin is a unique radiopharmaceutical that binds specifically to phosphatidylethanolamine (PE). The current effort is to develop a single-step kit formulation for the (99m)Tc labeling of HYNIC-Duramycin.

METHODS

A titration series of Tricine/TPPTS coligand systems were tested for an optimal formulation to produce (99m)Tc-Duramycin with high radiochemical purity and specific activity. The radiopharmaceutical prepared using the kit formulation was tested for PE binding specificity using polystyrene microbeads coated with different phospholipid species. Radiochemical performance of the kits was assessed after storage at -20°C, room temperature and 37°C. Biodistribution profile of kit-prepared (99m)Tc-Duramycin was characterized in healthy rats at 3, 10, 20, 60 and 180min after intravenous injection. Binding studies were performed using the rat aortic arch and a rat model of myocardial ischemia/reperfusion, which represent scenarios of physiological and pathological PE externalization.

RESULTS

A Tricine/TPPTS ratio of 10:1 led to a consistent production of (99m)Tc-Duramycin with high radiochemical purity (> 90%), whereas a higher ratio at 40:1 produced radiopharmaceuticals with incomplete substitution of Tricine coligand. (99m)Tc-Duramycin prepared using the single-step kit formulation retained PE-binding specificity. The kits are stable over long-term storage. The biodistribution profile of kit-prepared (99m)Tc-Duramycin is consistent with HPLC purified radiopharmaceutical from prior studies. Binding studies on a tissue level indicate that the radiopharmaceutical is suitable for studying biological processes that involve PE distribution and redistribution in various physiological and pathological conditions.

CONCLUSION

A single-step kit formulation is developed for (99m)Tc-labeling of HYNIC-Duramycin. The radiopharmaceutical has high radiochemical purity and specific activity, retained PE binding activities, amiable to long-term storage, and is injection-ready for in vivo applications.

Lantibiotics as probes for phosphatidylethanolamine

Phosphatidylethanolamine (PE) is a major component in the mammalian plasma membrane. It is present mainly in the inner leaflet of the membrane bilayer in a viable, typical mammalian cell. However, accumulating evidence indicates that a number of biological events involve PE externalization. For instance, PE is concentrated at the surface of cleavage furrow between mitotic daughter cells and is correlated with the dynamics of contractile ring. In apoptotic cells, PE is exposed to the cell surface, thus providing a molecular marker for detection. In addition, PE is a cofactor in the anticoagulant mechanism, and a distinct distribution profile of PE has been documented at the blood-endothelium interface. These recent discoveries were made possible using PE-specific probes derived from duramycin and cinnamycin, which are members of type B lantibiotics. This review provides an account on the features of these PE-specific lantibiotics in the context of molecular probes for the characterization of PE on a cellular and tissue level. According to the existing data, PE is likely a versatile chemical species that plays a role in the regulation of defined biological and physiological activities. The utilities of lantibiotic-based molecular probes will help accelerate the characterization of PE as an abundant, yet elusive membrane component.