Amino Group Of Phosphatidylethanolamine Research Articles

Free Radical Lipid Peroxidation Induced by Reactive Halogen Species.

The review is devoted to the mechanisms of free radical lipid peroxidation (LPO) initiated by reactive halogen species (RHS) produced in mammals, including humans, by heme peroxidase enzymes, primarily myeloperoxidase (MPO). It has been shown that RHS can participate in LPO both in the initiation and branching steps of the LPO chain reactions. The initiation step of RHS-induced LPO mainly involves formation of free radicals in the reactions of RHS with nitrite and/or with amino groups of phosphatidylethanolamine or Lys. The branching step of the oxidative chain is the reaction of RHS with lipid hydroperoxides, in which peroxyl and alkoxyl radicals are formed. The role of RHS-induced LPO in the development of human inflammatory diseases (cardiovascular and neurodegenerative diseases, cancer, diabetes, rheumatoid arthritis) is discussed in detail.

The oxysterol 3β-hydroxy-5-oxo-5,6-secocholestan-6-al changes the phase behavior and structure of phosphatidylethanolamine–phosphatidylcholine mixtures

An oxidized form of cholesterol, atheronal, is a form found in vivo that has been associated with human pathologies. We have studied mixtures of this oxidized sterol with the phospholipids phosphatidylethanolamine and phosphatidylcholine. We used phospholipids either with palmitoyl and oleoyl acyl chains on the C1 and C2 carbon atoms of glycerol or with both acyl chains being palmitoleoyl. We also compared the effects of atheronal on the curvature properties of these lipids with the action of cholesterol. We studied the bilayer to hexagonal phase transition temperature of mixtures of these lipids using differential scanning calorimetry as well as the dimensions of the hexagonal phase cylinders using X-ray diffraction. Disordering of the lamellar phase was also qualitatively assessed by the loss of sharp diffraction peaks. Our results demonstrate that the modulation of membrane curvature in these systems depends not only on the nature of the sterol, but also on the acyl chain composition of the phospholipids used. In addition, some of the effects of atheronal could be ascribed to reaction of the aldehyde and ketone groups of this oxidized sterol with the amino group of phosphatidylethanolamine.

LC-MS/MS analysis of carboxymethylated and carboxyethylated phosphatidylethanolamines in human erythrocytes and blood plasma

An amino group of phosphatidylethanolamine (PE) is considered as a target for nonenzymatic glycation, and the potential involvement of lipid glycation in the pathogenesis of diabetic complications has generated interest. However, unlike an early glycation product of PE (Amadori-PE), the occurrence and roles of advanced glycation end products of PE (AGE-PE) in vivo have been unclear. Here, we developed an LC-MS/MS method for the analysis of AGE-PE [carboxymethyl-PE (CM-PE) and carboxyethyl-PE (CE-PE)]. Collision-induced dissociation of CM-PE and CE-PE produced characteristic ions, permitting neutral loss scanning (NLS) and multiple reaction monitoring (MRM) of AGE-PE. By NLS analysis, a series of AGE-PE molecular species was detected in human erythrocytes and blood plasma. In LC-MS/MS analysis, MRM enabled the separation and determination of the predominant AGE-PE species. Between healthy subjects and diabetic patients, no significant differences were observed in AGE-PE concentrations in erythrocytes and plasma, whereas Amadori-PE concentrations were higher in diabetic patients. These results provide direct evidence for the presence of AGE-PE in human blood, and indicated that, compared with Amadori-PE, AGE-PE is less likely to be accumulated in diabetic blood. The presently developed LC-MS/MS method appears to be a powerful tool for understanding in vivo lipid glycation and its pathophysiological consequence.

Adjuvanticity of stealth liposomes on the immunogenicity of synthetic gp41 epitope of HIV-1

Present study aims to enhance the efficacy of liposomes as an adjuvant by steric protection and strengthen the path of vaccine research. PEG grafted liposomes carrying epitopes on their surface showed enhanced adjuvanticity than liposomes carrying epitopes for elicitation and prolongation of immune response to an antigenic epitope of gp41, a transmembrane protein of HIV-1. The multiples of epitope were incorporated onto the surface of liposomes by conjugating them with phosphatidylethanolamine that was used in the formulation of liposomes at an optimized ratio. Furthermore, the liposomes carrying epitopes on their surface were sterically protected by shielding with methoxy-poly(ethylene glycol), mass 20 kDa. Methoxy-poly(ethylene glycol) was activated to its electrophilic N-succinimide carbonate derivative, methoxy-poly(ethylene glycol)-N-succinimide carbonate, that formed a urethane linkage with the amino group of phosphatidylethanolamine. The epitope was covalently coupled to phosphatidylethanolamine through an amide bond between the –COOH group of the epitope and –NH 2 group of phosphatidylethanolamine under the catalysis of 1-ethyl-3-(3-dimethylaminopropy-1)-carbodiimide. PEG grafted epitopes carrying liposomes showed about two times higher immune response and prolonged persistence of antibodies than that of liposomes carrying epitopes without PEG moieties.

Nonenymatic Browning, Fluorescence Development, and Formation of Pyrrole Derivatives in Phosphatidylethanolamine/ Ribose/Lysine Model Systems

ABSTRACTBrowning, fluorescence, and pyrrole formation were determined in 4 mixtures of phosphatidylethanolamine (PE), ribose (RI), and/or lysine (lys) incubated at 60°C to study the contribution of lipid oxidation to food browning when lipid oxidation products are formed in the presence of other food components. The 4 assayed systems (PE/lys, PE/RI, RI/lys, and PE/RI/lys) were also extracted with chloroform‐methanol (2:1) to distinguish between the nonenzymatic browning produced with the amino group of PE and that produced with the amino groups of lys. Under the assay conditions, both the RI and the oxidized products produced in the fatty acid chains of PE contributed to the development of browning in the assayed systems. However, RI and oxidation products of PE exhibited different reactivities for the different amino groups involved in these reactions. Thus, the oxidized lipids reacted with the amino group of PE with preference for the amino group of lys, and this preference was reversed for RI. These results suggest that the contribution of both carbohydrates and lipid oxidation products to food browning may be distinguished. In addition, determination of oxidized lipid/ethanolamine derivatives in phospholipids may be an alternative procedure to evaluate oxidative damage in foods.

Phospholipid oxidation and nonenzymatic browning development in phosphatidylethanolamine/ribose/lysine model systems

Fatty acid losses, lipid oxidation, pyrrole formation, and browning and fluorescence development were determined in four mixtures of phosphatidylethanolamine (PE), ribose (RI), and/or lysine (lys) incubated at 37 °C to study the influence of lipid oxidation on the Maillard reaction and vice versa. Under the conditions assayed, the amino group of PE was preferentially damaged compared with the amino group of lys. In addition, oxidized lipid/amino acid reactions produced more pyrrolization, browning and fluorescence than carbohydrate/amino acid reactions, but both oxidized lipid/amino acid and sugar/amino acid reactions were produced in the PE/RI/lys system and both of them were inhibited by the presence of the other. Thus, fewer RI/lys reaction products were produced in the PE/RI/lys system than in an analogous system with no PE added. All these results confirm that there is an interaction between lipid oxidation and the Maillard reaction, and both of them should be considered simultaneously to understand their consequences on foods when lipids, carbohydrates, and amino acids or proteins are present.

A ubiquitin-like system mediates protein lipidation

Autophagy is a dynamic membrane phenomenon for bulk protein degradation in the lysosome/vacuole. Apg8/Aut7 is an essential factor for autophagy in yeast. We previously found that the carboxy-terminal arginine of nascent Apg8 is removed by Apg4/Aut2 protease, leaving a glycine residue at the C terminus. Apg8 is then converted to a form (Apg8-X) that is tightly bound to the membrane. Here we report a new mode of protein lipidation. Apg8 is covalently conjugated to phosphatidylethanolamine through an amide bond between the C-terminal glycine and the amino group of phosphatidylethanolamine. This lipidation is mediated by a ubiquitination-like system. Apg8 is a ubiquitin-like protein that is activated by an E1 protein, Apg7 (refs 7, 8), and is transferred subsequently to the E2 enzymes Apg3/Aut1 (ref. 9). Apg7 activates two different ubiquitin-like proteins, Apg12 (ref. 10) and Apg8, and assigns them to specific E2 enzymes, Apg10 (ref. 11) and Apg3, respectively. These reactions are necessary for the formation of Apg8-phosphatidylethanolamine. This lipidation has an essential role in membrane dynamics during autophagy.

P-Hydroxyphenylacetaldehyde, an Aldehyde Generated by Myeloperoxidase, Modifies Phospholipid Amino Groups of Low Density Lipoprotein in Human Atherosclerotic Intima

Oxidation of low density lipoprotein (LDL) may be of critical importance in the pathogenesis of atherosclerosis. Recent studies suggest that oxidized phospholipids render LDL atherogenic. However, both the structures and the physiologically relevant pathways for the formation of modified phospholipids in oxidized LDL remain poorly understood. We previously showed that p-hydroxyphenylacetaldehyde (pHA) is the major product of L-tyrosine oxidation by the myeloperoxidase/hydrogen peroxide/chloride system of phagocytes. In the current studies, we demonstrate that this reactive aldehyde targets the aminophospholipids of LDL in vitro and in vivo. Activated human neutrophils generated pHA-ethanolamine, the reduced adduct of pHA with the amino group of phosphatidylethanolamine, on LDL phospholipids by a reaction that required myeloperoxidase, H(2)O(2), and L-tyrosine. The cellular system could be replaced by HOCl and L-tyrosine but not by a wide variety of other oxidation systems, indicating that pHA-ethanolamine is a specific marker for covalent modification of aminophospholipids by myeloperoxidase. To determine whether aldehydes modify aminophospholipids in vivo, we quantified levels of pHA-ethanolamine in acid hydrolysates of reduced lipid extracts through isotope dilution gas chromatography/mass spectrometry. Circulating LDL contained undetectable levels of pHA-modified phospholipid (<0.1 mmol/mol). In contrast, the concentration of pHA-ethanolamine in LDL isolated from human atherosclerotic lesions was strikingly elevated (4.5 mmol/mol). Collectively, these results demonstrate a novel, myeloperoxidase-based mechanism for modifying the amino group of LDL phospholipids. They also offer the first evidence that myeloperoxidase may damage LDL lipids in vivo, raising the possibility that aldehyde-modified aminophospholipids play a role in inflammation and vascular disease.

Long-lifetime lipid rhenium metal–ligand complex for probing membrane dynamics on the microsecond timescale

We report the luminescence and spectral properties of a phospholipid analogue containing a long-lifetime luminescent rhenium metal–ligand complex (MLC) covalently linked to the amino group of phosphatidyl ethanolamine. When incorporated into synthetic membranes, this lipid probe displays intensity decay times near 3 μs. Importantly, the probe displays highly polarized emission with a maximal fundamental anisotropy of 0.33. This probe is expected to have numerous applications for studies of microsecond diffusion and dynamics of membranes.

Long-lifetime lipid probe containing a luminescent metal-ligand complex

We describe the chemical synthesis and spectral properties of a long-life- time luminescent probe for membranes. A ruthenium metal-ligand complex was cova- lently coupled to the amino group of phosphatidyl ethanolamine. When incorporated into model membranes, this probe displays decay times near 500 ns. Importantly, the probe displays polarized emission and can be used to study membrane motions on the microsecond timescale. q 1997 John Wiley & Sons, Inc. Biospect 3: 155-159, 1997

Proton/hydroxide conductance through lipid bilayer membranes.

A simple method of measuring proton/hydroxide conductance (GH/OH) through planar lipid bilayer membranes is described. First the total conductance (Gm) is measured electrically. Then the H+/OH- transference number (TH/OH) is estimated from the diffusion potential (Vm) produced by a transmembrane pH gradient. The pH gradient is produced by a pair of buffered solutions which have identical concentrations of all ions except H+ and OH-. Thus, Vm is due entirely to H+/OH- diffusion and GH/OH can be calculated from the relations, Vm = TH/OHEH/OH and GH/OH = TH/OHGm, where EH/OH is the equilibrium potential for H+ and OH-. In bilayers made from bacterial phosphatidylethanolamine (PE) in n-decane, GH/OH is nearly independent of pH, ranging from about 10(-9) S cm-2 at pH 1.6 to 10(-8) S cm-2 at pH 10.5. Because GH/OH is nearly independent of pH, the calculated permeability coefficients to H+ and/or OH- are extremely pH dependent, which partly explains the wide range of values reported for phospholipid vesicles and biological membranes. GH/OH appears to be independent of the membrane surface charge, because titrating either the phosphate or the amino group of PE has little effect on GH/OH. GH/OH is reduced about 10-fold when the water activity is reduced 33% by replacement with glycerol. Although the mechanism of H+/OH- conductance is not known, the relation between GH/OH and water activity suggests that several water molecules are involved in the H+/OH- transport process.

Influence of calcium on phosphatidylethanolamine. An investigation of the structure at high pH

The influence of calcium on the structure of 1,2-dihexadecyl- sn-glycero-3-phosphoethanolamine was investigated at pH 8 and 12 by differential scanning calorimetry and by X-ray diffraction. At pH 12, where the amino group of phosphatidylethanolamine is partly deprotonated, two separate lamellar phases are observed at 60°C in the presence of CaCl 2; one phase is metastable and the other is present in a crystalline structure. At high temperature (90°C), the small-angle diffraction lines indicate the existence of a hexagonal phase at pH 8. At pH 12 a hexagonal phase is detected only in the presence of calcium.

Nonenzymic browning. X. Kinetics of the oxidative browning of phosphatidylethanolamine

The formation of brown pigments produced by autoxidation of egg phosphatidylethanolamine in thin films in the temperature range of 20-100°C proceeds in three steps: (a) very rapid transformation of polyunsaturated fatty acids into conjugated hydroperoxides (a first order reaction); (b) reaction of hydroperoxide decomposition products (various aldehydic cleavage products) with the primary amino group of phosphatidylethanolamine resulting in the formation of nearly colourless Schiff bases (a zeroth-order reaction, slow at 30-60°C., fast at higher temperatures); (c) transformation of intermediary Schiff bases into brown pigments by further polycondensation reactions (a first order reaction). The activation energies of the three reactions were calculated.

The catabolism of phosphatidylethanolamine by the rumen protozoon Entodinium caudatum and its conversion into the N-(1-carboxyethyl) derivative.

1. The N-(2-hydroxyethyl)alanine esterified to phosphatidic acid in anaerobic ciliate rumen protozoa has the l configuration. 2. Labelling experiments with Entodinium caudatum cultures using [(32)P]P(i) [2-(14)C]ethanolamine and (32)P- and (14)C-labelled phosphatidylethanolamine show that phosphatidylethanolamine is the direct lipid precursor of the N-(2-hydroxyethyl)alanine-containing phospholipid. 3. Labelling experiments with [(14)C]starch, [(14)C]lactate and [(14)C]pyruvate with E. caudatum cultures indicate that a three-carbon glycolytic intermediate is probably the precursor of the N-(1-carboxyethyl) grouping which substitutes on the amino group of phosphatidylethanolamine. 4. [(32)P]phosphatidylethanolamine is catabolized by E. caudatum forming initially glycerylphosphorylethanolamine and subsequently glycerophosphate and P(i). A little phosphorylethanolamine formed may possibly arise from bacterial enzymes ingested by the protozoa.

On the biochemical mechanism of the visual process

Evidence is presented supporting an ionic mechanism for the stimulation of the photoreceptor by light. Illumination of a rhodopsin monolayer at an air-water interface causes expansion of the layer, which can be interpreted as the result of penetration of the monolayer by retinal. Illumination of a rod outer segment suspension causes efflux of K ions and an equivalent influx of Na ions. The same effect, qualitatively and quantitatively, occurs upon addition of all-trans retinal to the suspension. All-trans retinal added to artificial phosphatidyl-ethanolamine membranes greatly increases cation leakage through these micelles, but has no effect on lecithin micelles. All-trans retinol has a small effect on both types of micelles. These findings are interpreted as suggesting that upon photolysis of rhodopsin all-trans retinal would be transferred from opsin to a Schiff base link with the amino group of phosphatidylethanolamine or phosphatidylserine present in the rod sac membrane. Blocking of the amino group would make the membrane more negatively charged and thus more cation-permeable. The resulting cation exchange would cause a depolarizing current stimulating the synapse with the bipolar cell.