Phospholipid composition of cultured human endothelial cells

The gluconeogenesis enzyme PCK2 has a non-enzymatic role in proteostasis in endothelial cells

Endothelial cells (ECs) are highly glycolytic, but whether they generate glycolytic intermediates via gluconeogenesis (GNG) in glucose-deprived conditions remains unknown. Here, we report that glucose-deprived ECs upregulate the GNG enzyme PCK2 and rely on a PCK2-dependent truncated GNG, whereby lactate and glutamine are used for the synthesis of lower glycolytic intermediates that enter the serine and glycerophospholipid biosynthesis pathways, which can play key roles in redox homeostasis and phospholipid synthesis, respectively. Unexpectedly, however, even in normal glucose conditions, and independent of its enzymatic activity, PCK2 silencing perturbs proteostasis, beyond its traditional GNG role. Indeed, PCK2-silenced ECs have an impaired unfolded protein response, leading to accumulation of misfolded proteins, which due to defective proteasomes and impaired autophagy, results in the accumulation of protein aggregates in lysosomes and EC demise. Ultimately, loss of PCK2 in ECs impaired vessel sprouting. This study identifies a role for PCK2 in proteostasis beyond GNG.

Dietary (poly)phenols as modulators of the biophysical properties in endothelial cell membranes: its impact on nitric oxide bioavailability in hypertension

Hypertension is a major contributor to premature death, owing to the associated increased risk of damage to the heart, brain and kidneys. Although hypertension is manageable by medication and lifestyle changes, the risk increases with age. In an increasingly aged society, the incidence of hypertension is escalating, and is expected to increase the prevalence of (cerebro)vascular events and their associated mortality. Adherence to plant-based diets improves blood pressure and vascular markers in individuals with hypertension. Food flavonoids have an inhibitory effect towards angiotensin-converting enzyme (ACE1) and although this effect is greatly diminished upon metabolization, their microbial metabolites have been found to improve endothelial nitric oxide synthase (eNOS) activity. Considering the transmembrane location of ACE1 and eNOS, the ability of (poly)phenols to interact with membrane lipids modulate the cell membrane's biophysical properties and impact on nitric oxide (· NO) synthesis and bioavailability, remain poorly studied. Herein, we provide an overview of the current knowledge on the lipid remodeling of endothelial membranes with age, its impact on the cell membrane's biophysical properties and · NO permeability across the endothelial barrier. We also discuss the potential of (poly)phenols and other plant-based compounds as key players in hypertension management, and address the caveats and challenges in adopted methodologies.

Myeloperoxidase-derived hypochlorous acid targets human airway epithelial plasmalogens liberating protein modifying electrophilic 2-chlorofatty aldehydes

Neutrophil and airway epithelial cell interactions are critical in the inflammatory response to viral infections including respiratory syncytial virus, Sendai virus, and SARS-CoV-2. Airway epithelial cell dysfunction during viral infections is likely mediated by the interaction of virus and recruited neutrophils at the airway epithelial barrier. Neutrophils are key early responders to viral infection. Neutrophil myeloperoxidase catalyzes the conversion of hydrogen peroxide to hypochlorous acid (HOCl). Previous studies have shown HOCl targets host neutrophil and endothelial cell plasmalogen lipids, resulting in the production of the chlorinated lipid, 2-chlorofatty aldehyde (2-ClFALD). We have previously shown that the oxidation product of 2-ClFALD, 2-chlorofatty acid (2-ClFA) is present in bronchoalveolar lavage fluid of Sendai virus-infected mice, which likely results from the attack of the epithelial plasmalogen by neutrophil-derived HOCl. Herein, we demonstrate small airway epithelial cells contain plasmalogens enriched with oleic acid at the sn-2 position unlike endothelial cells which contain arachidonic acid enrichment at the sn-2 position of plasmalogen. We also show neutrophil-derived HOCl targets epithelial cell plasmalogens to produce 2-ClFALD. Further, proteomics and over-representation analysis using the ω-alkyne analog of the 2-ClFALD molecular species, 2-chlorohexadecanal (2-ClHDyA) showed cell adhesion molecule binding and cell-cell junction enriched categories similar to that observed previously in endothelial cells. However, in contrast to endothelial cells, proteins in distinct metabolic pathways were enriched with 2-ClFALD modification, particularly pyruvate metabolism was enriched in epithelial cells and mitochondrial pyruvate respiration was reduced. Collectively, these studies demonstrate, for the first time, a novel plasmalogen molecular species distribution in airway epithelial cells that are targeted by myeloperoxidase-derived hypochlorous acid resulting in electrophilic 2-ClFALD, which potentially modifies epithelial physiology by modifying proteins.

Endothelial Cell Protein Targeting by Myeloperoxidase-Derived 2-Chlorofatty Aldehyde

Neutrophils are important cellular mediators of injury and repair in diseases including ischemic heart disease, atherosclerosis, and sepsis. Myeloperoxidase-derived (MPO)-oxidants released from neutrophils are potential mediators of endothelial injury in disease. MPO-derived HOCl attacks plasmalogen phospholipid to liberate 2-chlorofatty aldehyde (2-ClFALD). Both 2-ClFALD and its oxidation product, 2-chlorofatty acid (2-ClFA), are electrophilic lipids, and both probably react with proteins through several mechanisms. In the present study, we investigate protein modification specifically by 2-ClFALD under non-reducing conditions (e.g., without stabilizing Schiff base bonds), which likely reflects nucleophilic targeting of the electrophilic chlorinated carbon. Protein modification by the ω-alkyne analog of 2-chlorohexadecanal (2-ClHDA), 2-ClHDyA, was compared to that with the ω-alkyne analog of 2-chlorohexadecanoic acid (2-ClHA), 2-ClHyA, in multiple cell lines, which demonstrated 2-ClFALD preferentially modifies proteins compared to 2-ClFA. The 2-ClHDyA modified proteins from EA.hy926 cells and human lung microvascular endothelial cells analyzed by shotgun proteomics and over-representation analysis included adherens junction, cell adhesion molecule binding, and cell substrate junction enrichment categories. It is possible that proteins in these groups may have roles in previously described 2-ClFALD-elicited endothelial barrier dysfunction.

Plasmalogen Loss in Sepsis and SARS-CoV-2 Infection

Plasmalogens are plasma-borne antioxidant phospholipid species that provide protection as cellular lipid components during cellular oxidative stress. In this study we investigated plasma plasmalogen levels in human sepsis as well as in rodent models of infection. In humans, levels of multiple plasmenylethanolamine molecular species were decreased in septic patient plasma compared to control subject plasma as well as an age-aligned control subject cohort. Additionally, lysoplasmenylcholine levels were significantly decreased in septic patients compared to the control cohorts. In contrast, plasma diacyl phosphatidylethanolamine and phosphatidylcholine levels were elevated in septic patients. Lipid changes were also determined in rats subjected to cecal slurry sepsis. Plasma plasmenylcholine, plasmenylethanolamine, and lysoplasmenylcholine levels were decreased while diacyl phosphatidylethanolamine levels were increased in septic rats compared to control treated rats. Kidney levels of lysoplasmenylcholine as well as plasmenylethanolamine molecular species were decreased in septic rats. Interestingly, liver plasmenylcholine and plasmenylethanolamine levels were increased in septic rats. Since COVID-19 is associated with sepsis-like acute respiratory distress syndrome and oxidative stress, plasmalogen levels were also determined in a mouse model of COVID-19 (intranasal inoculation of K18 mice with SARS-CoV-2). 3 days following infection, lung infection was confirmed as well as cytokine expression in the lung. Multiple molecular species of lung plasmenylcholine and plasmenylethanolamine were decreased in infected mice. In contrast, the predominant lung phospholipid, dipalmitoyl phosphatidylcholine, was not decreased following SARS-CoV-2 infection. Additionally total plasmenylcholine levels were decreased in the plasma of SARS-CoV-2 infected mice. Collectively, these data demonstrate the loss of plasmalogens during both sepsis and SARS-CoV-2 infection. This study also indicates plasma plasmalogens should be considered in future studies as biomarkers of infection and as prognostic indicators for sepsis and COVID-19 outcomes.

Identification of novel neutrophil very long chain plasmalogen molecular species and their myeloperoxidase mediated oxidation products in human sepsis

Plasmalogens are a class of phospholipids containing vinyl ether linked aliphatic groups at the sn-1 position. Plasmalogens are known to contain 16- and 18-carbon aliphatic groups at the sn-1 position. Here, we reveal that the human neutrophil plasmenylethanolamine pool uniquely includes molecular species with very long carbon chain (VLC) aliphatic groups, including 20-, 22- and 24-carbon vinyl ether linked aliphatic groups at the sn-1 position. We identified these novel VLC plasmalogen species by electrospray ionization mass spectrometry methods. VLC plasmalogens were only found in the neutrophil plasmenylethanolamine pool. During neutrophil activation, VLC plasmenylethanolamines undergo myeloperoxidase-dependent oxidation to produce VLC 2-chlorofatty aldehyde and its oxidation product, 2-chlorofatty acid (2-ClFA). Furthermore, plasma concentrations of VLC 2-ClFA are elevated in human sepsis. These studies demonstrate for the first time VLC plasmenylethanolamine molecular species, their myeloperoxidase-mediated chlorolipid products and the presence of these chlorolipids in human sepsis.

How Tim proteins differentially exploit membrane features to attain robust target sensitivity

Immune surveillance cells such as T cells and phagocytes utilize integral plasma membrane receptors to recognize surface signatures on triggered and activated cells such as those in apoptosis. One such family of plasma membrane sensors, the transmembrane immunoglobulin and mucin domain (Tim) proteins, specifically recognize phosphatidylserine (PS) but elicit distinct immunological responses. The molecular basis for the recognition of lipid signals on target cell surfaces is not well understood. Previous results suggest that basic side chains present at the membrane interface on the Tim proteins might facilitate association with additional anionic lipids including but not necessarily limited to PS. We, therefore, performed a comparative quantitative analysis of the binding of the murine Tim1, Tim3, and Tim4, to synthetic anionic phospholipid membranes under physiologically relevant conditions. X-ray reflectivity and vesicle binding studies were used to compare the water-soluble domain of Tim3 with results previously obtained for Tim1 and Tim4. Although a calcium link was essential for all three proteins, the three homologs differed in how they balance the hydrophobic and electrostatic interactions driving membrane association. The proteins also varied in their sensing of phospholipid chain unsaturation and showed different degrees of cooperativity in their dependence on bilayer PS concentration. Surprisingly, trace amounts of anionic phosphatidic acid greatly strengthened the bilayer association of Tim3 and Tim4, but not Tim1. A novel mathematical model provided values for the binding parameters and illuminated the complex interplay among ligands. In conclusion, our results provide a quantitative description of the contrasting selectivity used by three Tim proteins in the recognition of phospholipids presented on target cell surfaces. This paradigm is generally applicable to the analysis of the binding of peripheral proteins to target membranes through the heterotropic cooperative interactions of multiple ligands.

Neutrophil Myeloperoxidase Derived Chlorolipid Production During Bacteria Exposure

Neutrophils are the most abundant white blood cells recruited to the sites of infection and inflammation. During neutrophil activation, myeloperoxidase (MPO) is released and converts hydrogen peroxide to hypochlorous acid (HOCl). HOCl reacts with plasmalogen phospholipids to liberate 2-chlorofatty aldehyde (2-ClFALD), which is metabolized to 2-chlorofatty acid (2-ClFA). 2-ClFA and 2-ClFALD are linked with inflammatory diseases and induce endothelial dysfunction, neutrophil extracellular trap formation (NETosis) and neutrophil chemotaxis. Here we examine the neutrophil-derived chlorolipid production in the presence of pathogenic E. coli strain CFT073 and non-pathogenic E. coli strain JM109. Neutrophils cocultured with CFT073 E. coli strain and JM109 E. coli strain resulted in 2-ClFALD production. 2-ClFA was elevated only in CFT073 coculture. NETosis is more prevalent in CFT073 cocultures with neutrophils compared to JM109 cocultures. 2-ClFA and 2-ClFALD were both shown to have significant bactericidal activity, which is more severe in JM109 E. coli. 2-ClFALD metabolic capacity was 1000-fold greater in neutrophils compared to either strain of E. coli. MPO inhibition reduced chlorolipid production as well as bacterial killing capacity. These findings indicate the chlorolipid profile is different in response to these two different strains of E. coli bacteria.

Nasal Lavage Fluid as a Biomedical Sample for Verification of Chlorine Exposure

Chlorine is a toxic chemical that has been used as a chemical warfare agent in recent armed conflicts. There is an urgent need for methods to verify alleged uses of chlorine, and phospholipid chlorohydrins (PL-HOCl) derived from the pulmonary surfactant of exposed victims have previously been proposed as biomarkers of chlorine exposure. Here we describe an improved protocol for the chemical analysis of these biomarkers and its applicability to biomedical samples from chlorine-exposed animals. By the use of a polymeric solid phase-supported transesterification of PL-HOCl using ethanolamine, a common biomarker; oleoyl ethanolamide chlorohydrin (OEA-HOCl), was derived from all the diverse oleoyl PL-HOCl that may be formed by chlorine exposure. Compared to native lipid biomarkers, OEA-HOCl represents a larger biomarker pool and is better suited for nano-liquid chromatography tandem mass spectrometry (nLC-MS/MS analysis), generating 3 amol LOD and a reduced sample carry-over. With the improved protocol, significantly elevated levels of OEA-HOCl was identified in broncho-alveolar lavage fluid (BALF) of chlorine exposed rats, 2-48 hours after exposure. The difficulty of BALF sampling from humans limits the methods usefulness as a verification tool of chlorine exposure. Conversely, nasal lavage fluid (NLF) is readily collected without advanced equipment. In NLF from chlorine-exposed rats, PL-HOCl were identified and significantly elevated levels of the OEA-HOCl biomarker was detected 2- 24 hours after exposure. In order to test the potential of NLF as a biomedical sample for verification of human exposure to chlorine, in-vitro chlorination of human NLF samples was performed. All human in-vitro chlorinated NLF samples exhibited elevated OEA-HOCl biomarker levels, following sample derivatization. This data indicates the potential of human NLF as a biomedical sample for the verification of chlorine exposure but further work is required to develop and validate the method for the use on real-world samples.

Molecular dynamics simulations of Piezo1 channel opening by increases in membrane tension

Piezo1 is a mechanosensitive channel involved in many cellular functions and responsible for sensing shear stress and pressure forces in cells. Piezo1 has a unique trilobed topology with a curved membrane region in the closed state. It has been suggested that upon activation Piezo1 adopts a flattened conformation, but the molecular and structural changes underpinning the Piezo1 gating and opening mechanisms and how the channel senses forces in the membrane remain elusive. Here, we used molecular dynamics simulations to reveal the structural rearrangements that occur when Piezo1 moves from a closed to an open state in response to increased mechanical tension applied to a model membrane. We find that membrane stretching causes Piezo1 to flatten and expand its blade region, resulting in tilting and lateral movement of the pore-lining transmembrane helices 37 and 38. This is associated with the opening of the channel and movement of lipids out of the pore region. Our results reveal that because of the rather loose packing of Piezo1 pore region, movement of the lipids outside the pore region is critical for the opening of the pore. Our simulations also suggest synchronous flattening of the Piezo1 blades during Piezo1 activation. The flattened structure lifts the C-terminal extracellular domain up, exposing it more to the extracellular space. Our studies support the idea that it is the blade region of Piezo1 that senses tension in the membrane because pore opening failed in the absence of the blades. Additionally, our simulations reveal that upon opening, water molecules occupy lateral fenestrations in the cytosolic region of Piezo1, which might be likely paths for ion permeation. Our results provide a model for how mechanical force opens the Piezo1 channel and thus how it might couple mechanical force to biological response.

Modeling of full-length Piezo1 suggests importance of the proximal N-terminus for dome structure

Piezo1 forms a mechanically activated calcium-permeable nonselective cation channel that is functionally important in many cell types. Structural data exist for C-terminal regions, but we lack information about N-terminal regions and how the entire channel interacts with the lipid bilayer. Here, we use computational approaches to predict the three-dimensional structure of the full-length Piezo1 and simulate it in an asymmetric membrane. A number of novel insights are suggested by the model: 1) Piezo1 creates a trilobed dome in the membrane that extends beyond the radius of the protein, 2) Piezo1 changes the lipid environment in its vicinity via preferential interactions with cholesterol and phosphatidylinositol 4,5-bisphosphate (PIP₂) molecules, and 3) cholesterol changes the depth of the dome and PIP₂ binding preference. In vitro alteration of cholesterol concentration inhibits Piezo1 activity in a manner complementing some of our computational findings. The data suggest the importance of N-terminal regions of Piezo1 for dome structure and membrane cholesterol and PIP₂ interactions.

2-Chlorofatty Aldehyde Elicits Endothelial Cell Activation

Endothelial activation and dysfunction are hallmarks of inflammation. Neutrophil-vascular endothelium interactions have significant effects on vascular wall physiology and pathology. Myeloperoxidase (MPO)-derived products released from activated neutrophils can mediate the inflammatory response and contribute to endothelial dysfunction. 2-Chlorofatty aldehyde (2-ClFALD) is the direct oxidation product of MPO-derived hypochlorous acid (HOCl) targeting plasmalogen phospholipids. The role of 2-ClFALD in endothelial dysfunction is poorly understood and may be dependent on the vascular bed. This study compared the role of 2-ClFALD in eliciting endothelial dysfunction in human coronary artery endothelial cells (HCAEC), human lung microvascular endothelial cells (HLMVEC), and human kidney endothelial cells (HKEC). Profound increases in selectin surface expression as well as ICAM-1 and VCAM-1 surface expression were observed in HCAEC and HLMVEC. The surface expression of these adherence molecules resulted in robust adherence of neutrophils and platelets to 2-ClFALD treated endothelial cells. In contrast to HCAEC and HLMVEC, 2-ClFALD-treated HKEC had substantially reduced adherence molecule surface expression with no resulting increase in platelet adherence. 2-ClFALD-treated HKEC did have an increase in neutrophil adherence. All three endothelial cell lines treated with 2-ClFALD displayed a time-dependent loss of barrier function. Further studies revealed 2-ClHDyA localizes to ER and Golgi when using a synthetic alkyne analog of 2-ClFALD in HCAEC and HLMVEC. These findings indicate 2-ClFALDs promote endothelial cell dysfunction with disparate degrees of responsiveness depending on the vascular bed of origin.

Single-Cell RNA Sequencing Maps Endothelial Metabolic Plasticity in Pathological Angiogenesis

Endothelial cell (EC) metabolism is an emerging target for anti-angiogenic therapy in tumor angiogenesis and choroidal neovascularization (CNV), but little is known about individual EC metabolic transcriptomes. By single-cell RNA sequencing 28,337 murine choroidal ECs (CECs) and sprouting CNV-ECs, we constructed a taxonomy to characterize their heterogeneity. Comparison with murine lung tumor ECs (TECs) revealed congruent marker gene expression by distinct EC phenotypes across tissues and diseases, suggesting similar angiogenic mechanisms. Trajectory inference predicted that differentiation of venous to angiogenic ECs was accompanied by metabolic transcriptome plasticity. ECs displayed metabolic transcriptome heterogeneity during cell-cycle progression and in quiescence. Hypothesizing that conserved genes are important, we used an integrated analysis, based on congruent transcriptome analysis, CEC-tailored genome-scale metabolic modeling, and gene expression meta-analysis in cross-species datasets, followed by in vitro and in vivo validation, to identify SQLE and ALDH18A1 as previously unknown metabolic angiogenic targets.

Phospholipidome of endothelial cells shows a different adaptation response upon oxidative, glycative and lipoxidative stress

Endothelial dysfunction has been widely associated with oxidative stress, glucotoxicity and lipotoxicity and underlies the development of cardiovascular diseases (CVDs), atherosclerosis and diabetes. In such pathological conditions, lipids are emerging as mediators of signalling pathways evoking key cellular responses as expression of proinflammatory genes, proliferation and apoptosis. Hence, the assessment of lipid profiles in endothelial cells (EC) can provide valuable information on the molecular alterations underlying CVDs, atherosclerosis and diabetes. We performed a lipidomic approach based on hydrophilic interaction liquid chromatography-tandem mass spectrometry (HILIC-MS/MS) for the analysis of the phospholipidome of bovine aortic EC (BAEC) exposed to oxidative (H₂O₂), glycative (glucose), or lipoxidative (4-hydroxynonenal, HNE) stress. The phospholipid (PL) profile was evaluated for the classes PC, PE, PS, PG, PI, SM, LPC and CL. H₂O₂ induced a more acute adaptation of the PL profile than glucose or HNE. Unsaturated PL molecular species were up-regulated after 24 h incubation with H₂O₂, while an opposite trend was observed in glucose- and HNE-treated cells. This study compared, for the first time, the adaptation of the phospholipidome of BAEC upon different induced biochemical stresses. Although further biological studies will be necessary, our results unveil specific lipid signatures in response to characteristic types of stress.

The chlorinated lipidome originating from myeloperoxidase-derived HOCl targeting plasmalogens: Metabolism, clearance, and biological properties

Myeloperoxidase produces the two-electron oxidant HOCl, which targets plasmalogen phospholipids liberating 2-chlorofatty aldehyde. 2-Chlorofatty aldehyde has four known fates: 1) oxidation to 2-chlorofatty acid; 2) reduction to 2-chlorofatty alcohol; 3) Schiff base adduct formation with proteins and amines; and 4) reactivity with glutathione through nucleophilic attack of the α-chlorinated carbon. 2-Chlorofatty acid does not undergo conventional fatty acid β-oxidation due to the presence of the α-chlorinated carbon; however, 2-chlorofatty acid does undergo sequential ω-oxidation and β-oxidation from the ω-end, ultimately resulting in 2-chloroadipic acid urinary excretion. Recent studies have demonstrated that 2-chlorofatty acid clearance is increased by treatment with the PPAR-α agonist WY14643, which increases the enzymatic machinery responsible for hepatic ω-oxidation. Furthermore, 2-chlorofatty acid has been shown to be a PPAR-α agonist, and thus accelerates its own clearance. The roles of 2-chlorofatty aldehyde and 2-chlorofatty acid on leukocyte and endothelial function have been explored by several groups, suggesting that chlorinated lipids induce endothelial cell dysfunction, neutrophil chemotaxis, monocyte apoptosis, and alterations in vascular tone. Thus, the chlorinated lipidome, produced in response to leukocyte activation, is a potential biomarker and therapeutic target to modulate host response in inflammatory diseases.

2-Chlorofatty acids induce Weibel-Palade body mobilization

Endothelial dysfunction is a hallmark of multiple inflammatory diseases. Leukocyte interactions with the endothelium have significant effects on vascular wall biology and pathophysiology. Myeloperoxidase (MPO)-derived oxidant products released from leukocytes are potential mediators of inflammation and endothelial dysfunction. 2-Chlorofatty acids (2-ClFAs) are produced as a result of MPO-derived HOCl targeting plasmalogen phospholipids. Chlorinated lipids have been shown to be associated with multiple inflammatory diseases, but their impact on surrounding endothelial cells has not been examined. This study tested the biological properties of the 2-ClFA molecular species 2-chlorohexadecanoic acid (2-ClHA) on endothelial cells. A synthetic alkyne analog of 2-ClHA, 2-chlorohexadec-15-ynoic acid (2-ClHyA), was used to examine the subcellular localization of 2-ClFA in human coronary artery endothelial cells. Click chemistry experiments revealed that 2-ClHyA localizes to Weibel-Palade bodies. 2-ClHA and 2-ClHyA promote the release of P-selectin, von Willebrand factor, and angiopoietin-2 from endothelial cells. Functionally, 2-ClHA and 2-ClHyA cause neutrophils to adhere to and platelets to aggregate on the endothelium, as well as increase permeability of the endothelial barrier which has been tied to the release of angiopoietin-2. These findings suggest that 2-ClFAs promote endothelial cell dysfunction, which may lead to broad implications in inflammation, thrombosis, and blood vessel stability.

Myeloperoxidase-derived 2-chlorofatty acids contribute to human sepsis mortality via acute respiratory distress syndrome

Sepsis-associated acute respiratory distress syndrome (ARDS) is characterized by neutrophilic inflammation and poor survival. Since neutrophil myeloperoxidase (MPO) activity leads to increased plasma 2-chlorofatty acid (2-ClFA) levels, we hypothesized that plasma concentrations of 2-ClFAs would associate with ARDS and mortality in subjects with sepsis. In sequential consenting patients with sepsis, free 2-ClFA levels were significantly associated with ARDS, and with 30-day mortality, for each log increase in free 2-chlorostearic acid. Plasma MPO was not associated with either ARDS or 30-day mortality but was correlated with 2-ClFA levels. Addition of plasma 2-ClFA levels to the APACHE III score improved prediction for ARDS. Plasma 2-ClFA levels correlated with plasma levels of angiopoietin-2, E selectin, and soluble thrombomodulin. Endothelial cells treated with 2-ClFA responded with increased adhesion molecule surface expression, increased angiopoietin-2 release, and dose-dependent endothelial permeability. Our results suggest that 2-ClFAs derived from neutrophil MPO-catalyzed oxidation contribute to pulmonary endothelial injury and have prognostic utility in sepsis-associated ARDS.

Endothelial nitric oxide synthase oxygenase on lipid nanodiscs: A nano-assembly reflecting native-like function of eNOS

Endothelial nitric oxide synthase (eNOS) is a membrane-anchored enzyme. To highlight the potential role and effect of membrane phospholipids on the structure and activity of eNOS, we have incorporated the recombinant oxygenase subunit of eNOS into lipid nanodiscs. Two different size distribution modes were detected by multi-angle dynamic light scattering both for empty nanodiscs, and nanodiscs-bound eNOS_oxy. The calculated hydrodynamic diameter for mode 1 species was 9.0 nm for empty nanodiscs and 9.8 nm for nanodisc bound eNOS_oxy. Spectroscopic Griess assay was used to measure the enzymatic activity. Remarkably, the specific activity of nanodisc-bound eNOS_oxy is ∼65% lower than the activity of free enzyme. The data shows that the nano-membrane environment affects the catalytic properties of eNOS heme domain.

Changes of plasmalogen phospholipid levels during differentiation of induced pluripotent stem cells 409B2 to endothelial phenotype cells

Endothelial cells (EC) are involved in regulating several aspects of lipid metabolism, with recent research revealing the clinicopathological significance of interactions between EC and lipids. Induced pluripotent stem cells (iPSC) have various possible medical uses, so understanding the metabolism of these cells is important. In this study, endothelial phenotype cells generated from human iPSC formed cell networks in co-culture with fibroblasts. Changes of plasmalogen lipids and sphingomyelins in endothelial phenotype cells generated from human iPSC were investigated by reverse-phase ultra-high-pressure liquid chromatography mass spectrometry (UHPLC-MS/MS) analysis. The levels of plasmalogen phosphatidylethanolamines (38:5) and (38:4) increased during differentiation of EC, while sphingomyelin levels decreased transiently. These changes of plasmalogen lipids and sphingomyelins may have physiological significance for EC and could be used as markers of differentiation.

Direct visualization of the arterial wall water permeability barrier using CARS microscopy

The artery wall is equipped with a water permeation barrier that allows blood to flow at high pressure without significant water leak. The precise location of this barrier is unknown despite its importance in vascular function and its contribution to many vascular complications when it is compromised. Herein we map the water permeability in intact arteries, using coherent anti-Stokes Raman scattering (CARS) microscopy and isotopic perfusion experiments. Generation of the CARS signal is optimized for water imaging with broadband excitation. We identify the water permeation barrier as the endothelial basolateral membrane and show that the apical membrane is highly permeable. This is confirmed by the distribution of the AQP1 water channel within endothelial membranes. These results indicate that arterial pressure equilibrates within the endothelium and is transmitted to the supporting basement membrane and internal elastic lamina macromolecules with minimal deformation of the sensitive endothelial cell. Disruption of this pressure transmission could contribute to endothelial cell dysfunction in various pathologies.

Peroxisome proliferator-activated receptor-α accelerates α-chlorofatty acid catabolism

α-Chlorofatty aldehydes are generated from myeloperoxidase-derived HOCl targeting plasmalogens, and are subsequently oxidized to α-chlorofatty acids (α-ClFAs). The catabolic pathway for α-ClFA is initiated by ω-oxidation. Here, we examine PPAR-α activation as a mechanism to increase α-ClFA catabolism. Pretreating both HepG2 cells and primary mouse hepatocytes with the PPAR-α agonist, pirinixic acid (Wy 14643), increased the production of α-chlorodicarboxylic acids (α-ClDCAs) in cells treated with exogenous α-ClFA. Additionally, α-ClDCA production in Wy 14643-pretreated wild-type mouse hepatocytes was accompanied by a reduction in cellular free α-ClFA. The dependence of PPAR-α-accelerated α-ClFA catabolism was further demonstrated by both impaired metabolism in mouse PPAR-α^-/- hepatocytes and decreased clearance of plasma α-ClFA in PPAR-α^-/- mice. Furthermore, Wy 14643 treatments decreased plasma 2-chlorohexadecanoic acid levels in wild-type mice. Additional studies showed that α-ClFA increases PPAR-α, PPAR-δ, and PPAR-γ activities, as well as mRNA expression of the PPAR-α target genes, CD36, CPT1a, Cyp4a10, and CIDEC. Collectively, these results indicate that PPAR-α accelerates important pathways for the clearance of α-ClFA, and α-ClFA may, in part, accelerate its catabolism by serving as a ligand for PPAR-α.

Identification of glutathione adducts of α-chlorofatty aldehydes produced in activated neutrophils

α-Chlorofatty aldehydes (α-ClFALDs) are produced by hypochlorous acid targeting plasmalogens during neutrophil activation. This study investigated the reaction of the α-chlorinated carbon of α-ClFALD with the nucleophile, GSH. Utilizing ESI/MS/MS, the reaction product of GSH and the 16-carbon α-ClFALD, 2-chlorohexadecanal (2-ClHDA), was characterized. The resulting conjugate of 2-ClHDA and GSH (HDA-GSH) has an intact free aldehyde, and the chlorine at the α-carbon is ejected. Stable isotope-labeled [d4]HDA-GSH was synthesized, which further confirmed the structure, and was used to quantify natural α-ClFALD conjugates of GSH (FALD-GSH) using reverse-phase LC with detection by ESI/MS/MS using selected reaction monitoring. HDA-GSH is elevated in RAW 264.7 cells treated with physiologically relevant concentrations of exogenous 2-ClHDA. Furthermore, PMA-treated primary human neutrophils have elevated levels of HDA-GSH and the conjugate of 2-chlorooctadecanal (2-ClODA) and GSH (ODA-GSH), as well as elevated levels of 2-ClHDA and 2-ClODA. Production of both conjugates in PMA-stimulated neutrophils was reduced by 3-aminotriazole pretreatment, which also blocks endogenous α-ClFALD production. Additionally, plasma FALD-GSH levels were elevated in the K/BxN mouse arthritis model. Taken together, these studies demonstrate novel peptidoaldehydes derived from GSH and α-ClFALD in activated human neutrophils and in vivo in K/BxN mice.

Eicosapentaenoic acid (EPA) reduces cardiovascular events: relationship with the EPA/arachidonic acid ratio

The clinical efficacy of fish oil and high-purity eicosapentaenoic acid ethyl ester (hp-EPA-E) for treating cardiovascular disease (CVD) has been reported. Fish oil contains saturated and monounsaturated fatty acids that have pharmacological effects opposite to those of ω3 fatty acids (ω3). Moreover, ω3, such as EPA and docosahexaenoic acid (DHA), do not necessarily have the same metabolic and biological actions. This has obscured the clinical efficacy of ω3. Recently, the Japan EPA Lipid Intervention Study (JELIS) of hp-EPA-E established the clinical efficacy of EPA for CVD, and higher levels of blood EPA, not DHA, were found to be associated with a lower incidence of major coronary events. A significant reduction in the risk of coronary events was observed when the ratio of EPA to arachidonic acid (AA) (EPA/AA) was > 0.75. Furthermore, the ratio of prostaglandin (PG) I3 and PGI2 to thromboxane A2 (TXA2) ([PGI2 + PGI3]/TXA2) was determined to have a linear relationship with the EPA/AA ratio as follows: (PGI2 + PGI3)/TXA2 =λ + π＊ (EPA/AA). Like PGI2, PGI3 not only inhibits platelet aggregation and vasoconstriction, but also is assumed to reduce cardiac ischemic injury and arteriosclerosis and promote angiogenesis. Thus, the effects of EPA in reducing the risk of CVD could be mediated by biological action of PGI3 in addition to hypotriglyceridemic action of EPA. Compared with DHA, EPA administration increases the EPA/AA ratio and the (PGI2 + PGI3)/TXA2 balance to a state that inhibits the onset and/or progression of CVD.

Approaches for the analysis of chlorinated lipids

Leukocytes are key cellular mediators of human diseases through their role in inflammation. Identifying unique molecules produced by leukocytes may provide new biomarkers and mechanistic insights into the role of leukocytes in disease. Chlorinated lipids are generated as a result of myeloperoxidase-containing leukocyte-derived hypochlorous acid targeting the vinyl ether bond of plasmalogens. The initial product of this reaction is α-chlorofatty aldehyde. α-Chlorofatty aldehyde is both oxidized to α-chlorofatty acid and reduced to α-chlorofatty alcohol by cellular metabolism. This review focuses on the separation techniques and quantitative analysis for these chlorinated lipids. For α-chlorofatty acid, the negative charge of carboxylic acids is exploited to detect the chlorinated lipid species of these acids by electrospray ionization mass spectrometry in the negative ion mode. In contrast, α-chlorofatty aldehyde and α-chlorofatty alcohol are converted to pentafluorobenzyl oxime and pentafluorobenzoyl ester derivatives, which are detected by negative ion chemical ionization mass spectrometry. These two detection methods coupled with the use of stable isotope internal standards and either liquid chromatography or gas chromatography provide highly sensitive analytical approaches to measure these novel lipids.

Strategies for the analysis of chlorinated lipids in biological systems

Myeloperoxidase-derived HOCl reacts with the vinyl ether bond of plasmalogens yielding α-chlorofatty aldehydes. These chlorinated aldehydes can be purified using thin-layer chromatography, which is essential for subsequent analysis of extracts from some tissues such as myocardium. The α-chlorofatty aldehyde 2-chlorohexadecanal (2-ClHDA) is quantified after conversion to its pentafluorobenzyl oxime derivative using gas chromatography-mass spectrometry and negative-ion chemical ionization detection. 2-ClHDA accumulates in activated human neutrophils and monocytes, as well as in atherosclerotic lesions and infarcted myocardium. Metabolites of 2-ClHDA have also been identified, including the oxidation product, 2-chlorohexadecanoic acid (2-ClHA), and the reduction product, 2-chlorohexadecanol. 2-ClHA can be quantified using LC-MS with selected reaction monitoring (SRM) detection. 2-ClHA can be ω-oxidized by hepatocytes and subsequently β-oxidized from the ω-end, leading to the production of the dicarboxylic acid, 2-chloroadipic acid. This dicarboxylic acid is excreted in the urine and can also be quantified using LC-MS methods with SRM detection. Quantitative analyses of these novel chlorinated lipids are essential to identify the role of these lipids in leukocyte-mediated injury and disease.

Lipid metabolism in human endothelial cells

Although lipids are largely involved in cardiovascular physiopathology, the lipid metabolism in endothelial cells remains largely unknown. Human umbilical vein endothelial cells (HUVECs) were used to investigate the metabolism of complex lipids. The membrane phospholipid homeostasis results from both de novo synthesis and remodelling that ensures the fine tuning of the phospholipid fatty acid composition. Using [(3)H]-glycerol and phosphoderivatives we showed the efficiency of glycerolipid synthesis from glycerol (0.9 nmol h(-1) mg proteins(-1)), but not from its phosphorylated form suggesting the requirement of a functional glycerol kinase in HUVECs. Conversely, the synthesis of triacylglycerols was very low (less than 5% of phospholipid synthesis). The incorporation rate of fatty acids into phospholipids showed that there is a specific fate for each fatty acid in respect to its chain length and saturation level. Moreover in steady state condition, increasing the long chain omega3 polyunsaturated fatty acids in the medium resulted in an increased polyunsaturated/saturated ratio in phospholipids (from 0.42 to 0.63). [(14)C]O(2) was produced form either [(14)C]-glucose or [(14)C]-palmitate indicating the functionality of the oxidation pathways, although beta-oxidation was less efficient than glucose oxidation. The endothelial cell lipid metabolism involves conventional pathways, with functional rates largely slower than in hepatocytes or in cardiomyocytes.

Neutrophil-mediated accumulation of 2-ClHDA during myocardial infarction: 2-ClHDA-mediated myocardial injury

The pathophysiological sequelae of myocardial infarction include neutrophil infiltration into the infarct zone that contributes to additional damage to viable tissue and removal of cellular debris from necrosed tissue. Reactive chlorinating species produced by myeloperoxidase amplify the oxidant capacity of activated neutrophils. Plasmalogens are a major phospholipid subclass of both endothelial cells and cardiac myocytes. Recent studies have shown that plasmalogens are targeted by neutrophil-derived reactive chlorinating species that lead to the production of alpha-chloro fatty aldehydes. Results herein demonstrate that the alpha-chloro fatty aldehyde 2-chlorohexadecanal (2-ClHDA) accumulates in rat hearts subjected to left anterior descending coronary artery occlusion. Myocardia from rats subjected to surgical infarction had increased 2-ClHDA and neutrophil infiltration levels compared with myocardia from rats subjected to sham surgery. Additionally, infarcted myocardia from rats rendered neutropenic by treatments with an anti-neutrophil antibody had diminished 2-ClHDA and neutrophil infiltration levels compared with infarcted myocardia from normopenic rats; 2-ClHDA was shown to elicit myocardial damage as determined by lactate dehydrogenase release in isolated perfused rat hearts. Additionally, 2-ClHDA treatment of hearts resulted in decreased heart rate and ventricular performance. Taken together, the present results demonstrate a novel neutrophil-dependent myeloperoxidase-based mechanism that results in 2-ClHDA production in response to regional myocardial infarction that may also contribute to cardiac dysfunction.

Eosinophil peroxidase-derived reactive brominating species target the vinyl ether bond of plasmalogens generating a novel chemoattractant, alpha-bromo fatty aldehyde

Plasmalogens are a subclass of glycerophospholipids that are enriched in the plasma membrane of many mammalian cells. The vinyl ether bond of plasmalogens renders them susceptible to oxidation. Accordingly, it was hypothesized that reactive brominating species, a unique oxidant formed at the sites of eosinophil activation, such as in asthma, might selectively target plasmalogens for oxidation. Here we show that reactive brominating species produced by the eosinophil peroxidase system of activated eosinophils attack the vinyl ether bond of plasmalogens. Reactive brominating species produced by eosinophil peroxidase target the vinyl ether bond of plasmalogens resulting in the production of a neutral lipid and lysophosphatidylcholine. Chromatographic and mass spectrometric analyses of this neutral lipid demonstrated that it was 2-bromohexadecanal (2-BrHDA). Reactive brominating species produced by eosinophil peroxidase attacked the plasmalogen vinyl ether bond at acidic pH. Bromide was the preferred substrate for eosinophil peroxidase, and chloride was not appreciably used even at a 1000-fold molar excess. Furthermore, 2-BrHDA production elicited by eosinophil peroxidase-derived reactive brominating species in the presence of 100 microM NaBr doubled with the addition of 100 mM NaCl. The potential physiological significance of this pathway was suggested by the demonstration that 2-BrHDA was produced by phorbol myristate acetate-stimulated eosinophils and by the demonstration that 2-BrHDA is a phagocyte chemoattractant. Taken together, the present studies demonstrate the targeting of the vinyl ether bond of plasmalogens by the reactive brominating species produced by eosinophil peroxidase and by activated eosinophils, resulting in the production of brominated fatty aldehydes.

Separate myocardial ethanolamine phosphotransferase activities responsible for plasmenylethanolamine and phosphatidylethanolamine synthesis

Ethanolamine phosphotransferase (EPT) is a key enzyme responsible for the synthesis of ethanolamine glycerophospholipids. Plasmenylethanolamine is a predominant molecular subclass of ethanolamine glycerophospholipids in the heart. The present study was designed to identify the selective use of 1-O-alk-1'-enyl-2-acyl-sn-glycerol as a substrate for EPT as a mechanism responsible for the predominance of plasmenylethanolamine in the rabbit heart. EPT activity in rabbit myocardial membranes using 1,2-diacyl-sn-glycerol as substrate is activated by Mn2+, inhibited by dithiobisnitrobenzoic acid (DTNB) and is unaffected by Ca2+. In contrast, ethanolamine phosphotransferase activity using 1-O-alk-1'-enyl-2-acyl-sn-glycerol as substrate is inhibited by Mn2+ and Ca2+, but is activated by DTNB. Additionally, ethanolamine phosphotransferase activity using 1-O-alk-1'-enyl-2-acyl-sn-glycerol substrate was more sensitive to thermal denaturation compared with that of 1,2-diacyl-sn-glycerol. Taken together, these results suggest that separate ethanolamine phosphotransferase activities are present in heart membranes that are responsible for the synthesis of phosphatidylethanolamine and plasmenylethanolamine.

Increasing plasmalogen levels protects human endothelial cells during hypoxia

Supplementation of cultured human pulmonary arterial endothelial cells (PAEC) with sn-1-O-hexadecylglycerol (HG) resulted in an approximately twofold increase in cellular levels of plasmalogens, a subclass of phospholipids known to have antioxidant properties; this was due, primarily, to a fourfold increase in the choline plasmalogens. Exposure of unsupplemented human PAEC to hypoxia (PO(2) = 20-25 mmHg) caused an increase in cellular reactive oxygen species (ROS) over a period of 5 days with a coincident decrease in viability. In contrast, HG-supplemented cells survived for at least 2 wk under these conditions with no evidence of increased ROS. Hypoxia resulted in a selective increase in the turnover of the plasmalogen plasmenylethanolamine. Human PAEC with elevated plasmalogen levels were also more resistant to H(2)O(2), hyperoxia, and the superoxide generator plumbagin. This protection was seemingly specific to cellular stresses in which significant ROS were generated because the sensitivity to lethal heat shock or glucose deprivation was not altered in HG-treated human PAEC. HG, by itself, was not sufficient for protection; HG supplementation of bovine PAEC had no effect upon plasmalogen levels and did not rescue these cells from the cytotoxic effects of hypoxia. This is the initial demonstration that plasmalogen content can be substantially enhanced in a normal cell. These data also demonstrate that HG can protect cells during hypoxia and other ROS-mediated stress, likely due to the resulting increase in these antioxidant phospholipids.

Development of lentiviral vectors for antiangiogenic gene delivery

Growth and metastasis of malignant tumors requires angiogenesis. Inhibition of tumor-induced angiogenesis may represent an effective cytostatic strategy. We have constructed recombinant self-inactivating lentiviral vectors expressing angiostatin and endostatin, and have tested their antiangiogenic activities. As VSV-G-pseudotyped lentiviral vectors showed low relative transduction titers on bovine aortic and human umbilical vein endothelial cells, it was difficult to achieve significant inhibition of endothelial cell growth by lentivirus-mediated antiangiogenic gene transfer directly to endothelial cells without concomitant vector-associated cytotoxicity. However, lentivirus vectors could efficiently and stably transduce T24 human bladder cancer cells that are relatively resistant to adenovirus infection due to loss of coxsackievirus-adenovirus receptor expression. Long-term expression and secretion of angiostatin and endostatin from lentivirus-transduced T24 cells resulted in significant inhibition of cellular proliferation on coculture with endothelial cells. This report represents the first use of lentivirus-based vectors to deliver the antiangiogenic factors, angiostatin and endostatin, and suggests the potential utility of antiangiogenic gene therapy with lentiviral vectors for the treatment of cancer.

Platelet-activating factor and related lipid mediators

Platelet-activating factor (PAF) is a phospholipid with potent, diverse physiological actions, particularly as a mediator of inflammation. The synthesis, transport, and degradation of PAF are tightly regulated, and the biochemical basis for many of these processes has been elucidated in recent years. Many of the actions of PAF can be mimicked by structurally related phospholipids that are derived from nonenzymatic oxidation, because such compounds can bind to the PAF receptor. This process circumvents much of the biochemical control and presumably is regulated primarily by the rate of degradation, which is catalyzed by PAF acetylhydrolase. The isolation of cDNA clones encoding most of the key proteins involved in regulating PAF has allowed substantial recent progress and will facilitate studies to determine the structural basis for substrate specificity and the precise role of PAF in physiological events.

Fluorescently labeled neomycin as a probe of phosphatidylinositol-4, 5-bisphosphate in membranes

Phosphatidylinositol-4,5-bisphosphate (PI(4,5)P(2)), a minor component of the plasma membrane, is important in signal transduction, exocytosis, and ion channel activation. Thus fluorescent probes suitable for monitoring the PI(4,5)P(2) distribution in living cells are valuable tools for cell biologists. We report here three experiments that show neomycin labeled with either fluorescein or coumarin can be used to detect PI(4,5)P(2) in model phospholipid membranes. First, addition of physiological concentrations of PI(4,5)P(2) (2%) to lipid vesicles formed from mixtures of phosphatidylcholine (PC) and phosphatidylserine (PS) enhances the binding of labeled neomycin significantly (40-fold for 5:1 PC/PS vesicles). Second, physiological concentrations of inositol-1,4,5-trisphosphate (10 microM I(1,4,5)P(3)) cause little translocation of neomycin from PC/PS/PI(4,5)P(2) membranes to the aqueous phase, whereas the same concentrations of I(1,4,5)P(3) cause significant translocation of the green fluorescent protein/phospholipase C-delta pleckstrin homology (GFP-PH) constructs from membranes (Hirose et al., Science, 284 (1999) 1527). Third, fluorescence microscopy observations confirm that one can distinguish between PC/PS vesicles containing either 0 or 2% PI(4, 5)P(2) by exposing a mixture of the vesicles to labeled neomycin. Thus fluorescently labeled neomycin could complement GFP-PH constructs to investigate the location of PI(4,5)P(2) in cell membranes.

Lipid composition of cultured endothelial cells in relation to their growth

Human endothelial cells in culture were examined in different growth conditions. The human endothelial cell line, EA.hy 926 cell line, was used and cells were studied either in exponential growth phase, at confluence, or growth-arrested by serum deprivation. Phospholipids were separated and analyzed by high-performance thin-layer chromatography, and their fatty acids were quantified by gas-liquid chromatography. No significant differences in the phospholipid distributions were found between exponentially growing and confluent endothelial cells in which phosphatidylcholine (PC) represented the major phospholipid. In comparison, serum-deprived cells exhibited higher proportions of sphingomyelin and lower content of PC. We also found that among the total lipids, cholesterol level for dividing endothelial cells was lower than for cells growth-arrested either by serum deprivation or by contact inhibition at confluence. The global fatty acid distribution was not affected by the growth conditions. Thus, oleate (18:1 n-9 and 18:1 n-7), palmitate (C16:0), and stearate (C18:0) were the main components of endothelial cell membranes. However, the fatty acid distributions obtained from each phospholipid species differed with the growth status. Altogether, the data indicated that subtle modulations of endothelial cell metabolism appear upon cell growth. The resulting membrane-dependent cellular functions such as cholesterol transport and receptor activities can be expected to be relevant for lipid trafficking within the vessel wall in vitro and in vivo.

Phosphatidylcholine synthesis-related enzyme activities of bovine brain microvessels exhibit susceptibility to peroxidation

In microvessels isolated from bovine brain, microsomal enzyme activities involved in phosphatidylcholine biosynthesis and degradation were determined. The microvessels possessed acyl-CoA:1-acyl-sn-glycero-3-phosphocholine (AT) and glycerophosphocholine phosphodiesterase (GroPChoPDE) activity at a higher level compared with bovine and rat brain or rat liver microsomes whereas they expressed CTP:phosphocholine cytidylyltransferase (CT) and choline phosphotransferase (CPT) activity at a lower level. Each enzyme has been characterized in terms of response to inhibitors or activators revealing properties very similar to those in brain and liver microsomes. In the homogenate prepared from t-butylhydroperoxide-treated microvessels (10 min exposure to 10 microM up to 1 mM concentrations), AT and CPT activities exhibited a significant dose-dependent inhibition. In contrast, GroPChoPDE activity was unaffected. CT was inhibited only at 1 mM concentration. Short treatment of microvessels with Fe2+ (20 microM)-ascorbate (0.25 mM) or 100 microM linoleate hydroperoxide did not have any effect on the activity of the four enzymes. Strong inhibition of all enzymes was noted when the linoleate hydroperoxide system was fortified by Fe2+ ions (100 microM). AT inactivation was also found when oxidized low density lipoprotein was preincubated with microvessels. On the other hand, oxidized LDL left unchanged CPT and GroPChoPDE activities whereas it promoted a slight stimulation of cytidylyltransferase activity. Overall, the results suggest a link between oxygen radical generation and the perturbation of the microvessel membrane structure in which the four enzymes are incorporated, coupled to a direct sulfhydryl protein modification.

Acidic hydrolysis of plasmalogens followed by high-performance liquid chromatography

A simple, quantitative method for determining the plasmalogen content of small samples is reported here. The method uses the different susceptibility to acid-catalyzed hydrolysis of the alkyl, alkenyl and acyl linkages to separate the plasmalogen subclass from the other two non-labile subclasses. Hydrolysis of plasmenylethanolamine and plasmenylcholine was complete after 4 and 1 min of acid treatment, respectively. The acid-catalyzed hydrolysis did not alter the phospholipid fatty acid composition, making this method useful for fatty acid compositional analysis of the plasmalogen subclass. High-performance liquid chromatography was used for separations, and phospholipids were quantitated by assay of lipid phosphorus or by direct quantitation of peak area. Using this method, small amounts (10 nmol) of ethanolamine glycerophospholipid and choline glycerophospholipid are subjected to acid-catalyzed hydrolysis and subsequent separation of the resulting lysocompounds obtained from plasmalogens from the more acid-stable alkylacyl and diacyl glycerophospholipid fractions. Our values for plasmalogens from commercial preparations of choline and ethanolamine glycerophospholipids agree with literature values. The usefulness of the method is demonstrated for small glycerophospholipid samples that are equivalent to samples from cultured neural cells.

A model for compression trauma: pressure-induced injury in cell cultures

An increase in pressure up to 15 atm was used to condense the cellular membrane of cells in culture thereby eliciting a mechanical-like trauma. This trauma is similar to a compression-like spinal cord injury or brain injury. The cells used in this study were ROC-1 oligodendroglia, N1E-115 neuroblastoma, and human umbilical vein endothelial (HUVE) cells. Total fatty acid (FA) release and release of lactate dehydrogenase (LDH) into the extracellular medium were used as indices of cellular trauma. Pressure-induced FA release, dependent on pressure and pressure duration, occurred with all cell types. The level of pressure needed to cause the greatest increase in FA levels was 10 atm for ROC-1 cells (3 min duration), 15 atm for N1E-115 cells (3 min duration), and 15 atm for HUVE cells (10 min duration). With each cell type, the released FA were reacylated or metabolized between 10 and 30 min of recovery. Following a 12- to 24-h recovery period, N1E-115 and HUVE cells release more FA, indicating that the initial perturbation of the membrane was not fully reversible. LDH levels were significantly increased in both the N1E-115 and HUVE cultures following 24 h of recovery. This efflux of LDH indicates irreversible membrane damage, suggesting that the trauma may be irreversible at longer recovery times.