Oxidized Phospholipid OxPAPC Activates TRPA1 and Contributes to Chronic Inflammatory Pain in Mice

Oxidation products of the naturally occurring phospholipid 1-palmitoyl-2-arachidonoyl-sn-glycerol-3-phosphatidylcholine (PAPC), which are known as OxPAPC, accumulate in atherosclerotic lesions and at other sites of inflammation in conditions such as septic inflammation and acute lung injury to exert pro- or anti-inflammatory effects. It is currently unknown whether OxPAPC also contributes to inflammatory pain and peripheral neuronal excitability in these conditions. Here, we observed that OxPAPC dose-dependently and selectively activated human TRPA1 nociceptive ion channels expressed in HEK293 cells in vitro, without any effect on other TRP channels, including TRPV1, TRPV4 and TRPM8. OxPAPC agonist activity was dependent on essential cysteine and lysine residues within the N-terminus of the TRPA1 channel protein. OxPAPC activated calcium influx into a subset of mouse sensory neurons which were also sensitive to the TRPA1 agonist mustard oil. Neuronal OxPAPC responses were largely abolished in neurons isolated from TRPA1-deficient mice. Intraplantar injection of OxPAPC into the mouse hind paw induced acute pain and persistent mechanical hyperalgesia and this effect was attenuated by the TRPA1 inhibitor, HC-030031. More importantly, we found levels of OxPAPC to be significantly increased in inflamed tissue in a mouse model of chronic inflammatory pain, identified by the binding of an OxPAPC-specific antibody. These findings suggest that TRPA1 is a molecular target for OxPAPC and OxPAPC may contribute to chronic inflammatory pain through TRPA1 activation. Targeting against OxPAPC and TRPA1 signaling pathway may be promising in inflammatory pain treatment.     

A role for VEGFR2 activation in endothelial responses caused by barrier disruptive OxPAPC concentrations

Introduction

Oxidation products of 1-palmitoyl-2-arachidonoyl-sn-glycero-3-phosphatidylcholine (OxPAPC) differentially modulate endothelial cell (EC) barrier function in a dose-dependent fashion. Vascular endothelial growth factor receptor-2 (VEGFR2) is involved in the OxPAPC-induced EC inflammatory activation. This study examined a role of VEGFR2 in barrier dysfunction caused by high concentrations of OxPAPC and evaluated downstream signaling mechanisms resulting from the effect of OxPAPC in EC from pulmonary and systemic circulation.

Methods

EC monolayer permeability in human pulmonary artery endothelial cells (HPAEC) and human aortic endothelial cells (HAEC) was monitored by changes in transendothelial electrical resistance (TER) across EC monolayers. Actin cytoskeleton was examined by immunostaining with Texas Red labeled phalloidin. Phosphorylation of myosin light chains (MLC) and VE-Cadherin was examined by Western blot and immunofluorescence techniques. The role of VEGFR2 in OxPAPC-induced permeability and cytoskeletal arrangement were determined using siRNA-induced VEGFR2 knockdown.

Results

Low OxPAPC concentrations (5–20 µg/ml) induced a barrier protective response in both HPAEC and HAEC, while high OxPAPC concentrations (50–100 µg/ml) caused a rapid increase in permeability ; actin stress fiber formation and increased MLC phosphorylation were observed as early as 30 min after treatment. VEGFR2 knockdown dramatically decreased the amount of MLC phosphorylation and stress fiber formation caused by high OxPAPC concentrations with modest effects on the amount of VE-cadherin phosphorylation at Y⁷³¹. We present evidence that activation of Rho is involved in the OxPAPC/VEGFR2 mechanism of EC permeability induced by high OxPAPC concentrations. Knockdown of VEGFR2 did not rescue the early drop in TER but prevented further development of OxPAPC-induced barrier dysfunction.

Conclusions

This study shows that VEGFR2 is involved in the delayed phase of EC barrier dysfunction caused by high OxPAPC concentrations and contributes to stress fiber formation and increased MLC phosphorylation.     

Atomically detailed lipid bilayer models for the interpretation of small angle neutron and X-ray scattering data

We present a new atom density profile (ADP) model and a statistical approach for extracting structural characteristics of lipid bilayers from X-ray and neutron scattering data. Models for five lipids with varying head and tail chemical composition in the fluid phase, 1,2-dioleoyl-sn-glycero-3-phosphatidylcholine (DOPC), 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphatidylcholine (POPC), 1,2-dipalmitoyl-sn-glycero-3-phosphatidylcholine (DPPC), 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphatidylserine (POPS), and 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphatidylglycerol (POPG), are optimized using a simplex based method to simultaneously reproduce both neutron and X-ray scattering data. Structural properties are determined using statistical analysis of multiple optimal model structures. The method and models presented make minimal assumptions regarding the atomic configuration, while taking into account the underlying physical properties of the system. The more general model and statistical approach yield data with well defined uncertainties, indicating the precision in determining density profiles, atomic locations, and bilayer structural characteristics. Resulting bilayer structures include regions exhibiting large conformational variation. Due to the increased detail in the model, the results demonstrate the possibility of a distinct hydration layer within the interfacial (backbone) region.     

Reversible sheet-turn conformational change of a cell-penetrating peptide in lipid bilayers studied by solid-state NMR

The membrane-bound conformation of a cell-penetrating peptide, penetratin, is investigated using solid-state NMR spectroscopy. The ¹³C chemical shifts of ¹³C, ¹⁵N-labeled residues in the peptide indicate a reversible conformational change from β-sheet at low temperature to coil-like at high temperature. This conformational change occurs for all residues examined between positions 3 and 13, at peptide/lipid molar ratios of 1:15 and 1:30, in membranes with 25-50% anionic lipids, and in both saturated DMPC/DMPG (1,2-dimyristoyl-sn-glycero-3-phosphatidylchloline/1,2-dimyristoyl-sn-glycero-3-phosphatidylglycerol) membranes and unsaturated POPC/POPG (1-palmitoyl-2-oleoyl-sn-glycero-3-phosphatidylcholine/1-palmitoyl-2-oleoyl-sn-glycero-3-phosphatidylglycerol) membranes. Thus, it is an intrinsic property of penetratin. The coil state of the peptide has C-H order parameters of 0.23-0.52 for C^α and C^β sites, indicating that the peptide backbone is unstructured. Moreover, chemical shift anisotropy lineshapes are uniaxially averaged, suggesting that the peptide backbone undergoes uniaxial rotation around the bilayer normal. These observations suggest that the dynamic state of penetratin at high temperature is a structured turn instead of an isotropic random coil. The thermodynamic parameters of this sheet-turn transition are extracted and compared to other membrane peptides reported to exhibit conformational changes. We suggest that the function of this turn conformation may be to reduce hydrophobic interactions with the lipid chains and facilitate penetratin translocation across the bilayer without causing permanent membrane damage.     

A Comparison of the Membrane Binding Properties of C1B Domains of PKCγ, PKCδ, and PKC?

The C1 domains of classical and novel PKCs mediate their diacylglycerol-dependent translocation. Using fluorescence resonance energy transfer, we studied the contribution of different negatively charged phospholipids and diacylglycerols to membrane binding. Three different C1B domains of PKCs were studied (the classical γ, and the novel δ and ?), together with different lipid mixtures containing three types of acidic phospholipids and three types of activating diacylglycerols. The results show that C1Bγ and C1B? exhibit a higher affinity to bind to vesicles containing 1-palmitoyl-2-oleoyl-sn-phosphatidic acid, 1-palmitoyl-2-oleoyl-sn-phoshatidylserine, or 1-palmitoyl-2-oleoyl-sn-phosphatidylglycerol, with C1B? being the most relevant case because its affinity for POPA-containing vesicles increased by almost two orders of magnitude. When the effect of the diacylglycerol fatty acid composition on membrane binding was studied, the C1B? domain showed the highest binding affinity to membranes containing 1-stearoyl-oleoyl-sn-glycerol or 1,2-sn-dioleoylglycerol with POPA as the acidic phospholipid. Of the three diacylglycerols used in this study, 1,2-sn-dioleoylglycerol and 1-stearoyl-oleoyl-sn-glycerol showed the highest affinities for each isoenzyme, whereas 1,2-sn-dipalmitoylglycerol; showed the lowest affinity. DSC experiments showed this to be a consequence of the nonfluid conditions of 1,2-sn-dipalmitoylglycerol;-containing systems.     

A role for neutral sphingomyelinase activation in the inhibition of LPS action by phospholipid oxidation products

Previous studies from our laboratory and others presented evidence that oxidized 1-palmitoyl-2-arachidonyl-sn-glycero-3-phosphatidylcholine (OxPAPC) and oxidized 1-palmitoyl-2-arachidonyl-sn-glycero-3-phosphatidylethanolamine can inhibit lipopolysaccharide (LPS)-mediated induction of interleukin-8 (IL-8) in endothelial cells. Using synthetic derivatives of phosphatidylethanolamine, we now demonstrate that phospholipid oxidation products containing alpha,beta-unsaturated carboxylic acids are the most active inhibitors we examined. 5-Keto-6-octendioic acid ester of 2-phosphatidylcholine (KOdiA-PC) was 500-fold more inhibitory than OxPAPC, being active in the nanomolar range. Our studies in human aortic endothelial cells identify one important mechanism of the inhibitory response as involving the activation of neutral sphingomyelinase. There is evidence that Toll-like receptor-4 and other members of the LPS receptor complex must be colocalized to the caveolar/lipid raft region of the cell, where sphingomyelin is enriched, for effective LPS signaling. Previous work from our laboratory suggested that OxPAPC could disrupt this caveolar fraction. These studies present evidence that OxPAPC activates sphingomyelinase, increasing the levels of 16:0, 22:0, and 24:0 ceramide and that the neutral sphingomyelinase inhibitor GW4869 reduces the inhibitory effect of OxPAPC and KOdiA-PC. We also show that cell-permeant C6 ceramide, like OxPAPC, causes the inhibition of LPS-induced IL-8 synthesis and alters caveolin distribution similar to OxPAPC. Together, these data identify a new pathway by which oxidized phospholipids inhibit LPS action involving the activation of neutral sphingomyelinase, resulting in a change in caveolin distribution. Furthermore, we identify specific oxidized phospholipids responsible for this inhibition.     

Biosynthesis of prostaglandin 15dPGJ2 -glutathione and 15dPGJ2-cysteine conjugates in macrophages and mast cells via MGST3

Inhibition of microsomal prostaglandin E synthase-1 (mPGES-1) results in decreased production of proinflammatory PGE₂ and can lead to shunting of PGH₂ into the prostaglandin D₂ (PGD₂)/15-deoxy-Δ^12,14-prostaglandin J₂ (15dPGJ₂) pathway. 15dPGJ₂ forms Michael adducts with thiol-containing biomolecules such as GSH or cysteine residues on target proteins and is thought to promote resolution of inflammation. We aimed to elucidate the biosynthesis and metabolism of 15dPGJ₂ via conjugation with GSH, to form 15dPGJ₂-glutathione (15dPGJ₂-GS) and 15dPGJ₂-cysteine (15dPGJ₂-Cys) conjugates and to characterize the effects of mPGES-1 inhibition on the PGD₂/15dPGJ₂ pathway in mouse and human immune cells. Our results demonstrate the formation of PGD₂, 15dPGJ₂, 15dPGJ₂-GS, and 15dPGJ₂-Cys in RAW264.7 cells after lipopolysaccharide stimulation. Moreover, 15dPGJ₂-Cys was found in lipopolysaccharide-activated primary murine macrophages as well as in human mast cells following stimulation of the IgE-receptor. Our results also suggest that the microsomal glutathione S-transferase 3 is essential for the formation of 15dPGJ₂ conjugates. In contrast to inhibition of cyclooxygenase, which leads to blockage of the PGD₂/15dPGJ₂ pathway, we found that inhibition of mPGES-1 preserves PGD₂ and its metabolites. Collectively, this study highlights the formation of 15dPGJ₂-GS and 15dPGJ₂-Cys in mouse and human immune cells, the involvement of microsomal glutathione S-transferase 3 in their biosynthesis, and their unchanged formation following inhibition of mPGES-1. The results encourage further research on their roles as bioactive lipid mediators.     

Properties of sonicated vesicles of three synthetic phospholipids

The following synthetic phospholipids were prepared, and the structures that were formed by ultrasonic irradiation in aqueous solution were studied: 1,2-di(10-bromo stearoyl)-3-sn-phosphatidylcholine (DBrPC), 1,2-di(10-methyl stearoyl)-3-sn-phosphatidylcholine (DMePC), and 1-palmitoyl-2-oleyl-3-sn-phosphatidylcholine (POPC). Uniform populations of small, unilamellar vesicles were obtained in all cases by gel filtration on Sepharose 4B. Hydrodynamic and trapped volume measurements show that POPC is nearly identical in size and shape to vesicles of egg phosphatidylcholine whereas DBrPC and DMePC appear to have a non-spherical shape. Fluorescence depolarization measurements show that vesicles from all three lipids are in the liquid crystalline state between 5 and 50°C.The partial specific volume of DMePC is larger than that of egg PC, whereas the partial specific volume of DBrPC is considerably lower; these lipids should therefore be useful in studies requiring the separation of vesicle populations. POPC, being virtually identical in size, shape and bilayer fluidity to egg PC, should be an excellent model of a ‘natural’ lecithin with a defined fatty acid composition.     

GRP78 is a novel receptor initiating a vascular barrier protective response to oxidized phospholipids

Vascular integrity and the maintenance of blood vessel continuity are fundamental features of the circulatory system maintained through endothelial cell–cell junctions. Defects in the endothelial barrier become an initiating factor in several pathologies, including ischemia/reperfusion, tumor angiogenesis, pulmonary edema, sepsis, and acute lung injury. Better understanding of mechanisms stimulating endothelial barrier enhancement may provide novel therapeutic strategies. We previously reported that oxidized phospholipids (oxidized 1-palmitoyl-2-arachidonoyl-sn-glycero-3-phosphocholine [OxPAPC]) promote endothelial cell (EC) barrier enhancement both in vitro and in vivo. This study examines the initiating mechanistic events triggered by OxPAPC to increase vascular integrity. Our data demonstrate that OxPAPC directly binds the cell membrane–localized chaperone protein, GRP78, associated with its cofactor, HTJ-1. OxPAPC binding to plasma membrane–localized GRP78 leads to GRP78 trafficking to caveolin-enriched microdomains (CEMs) on the cell surface and consequent activation of sphingosine 1-phosphate receptor 1, Src and Fyn tyrosine kinases, and Rac1 GTPase, processes essential for cytoskeletal reorganization and EC barrier enhancement. Using animal models of acute lung injury with vascular hyperpermeability, we observed that HTJ-1 knockdown blocked OxPAPC protection from interleukin-6 and ventilator-induced lung injury. Our data indicate for the first time an essential role of GRP78 and HTJ-1 in OxPAPC-mediated CEM dynamics and enhancement of vascular integrity.     

Labelling of glycerolipids in the cotyledons of developing oilseeds by [1-14C]acetate and [2-3H]glycerol

1. 3-sn-Phosphatidylcholine was identified as the major lipid in cotyledons from the developing seeds of soya bean, linseed and safflower when tissue was steamed before lipid extraction. The proportion of oleate in this lipid decreased markedly and that of the polyunsaturated C₁₈ fatty acids increased when detached developing cotyledons were incubated for up to 3h. Similar but less pronounced changes occurred in diacylglycerol, which had a fatty acid composition resembling that of the 3-sn-phosphatidylcholine from cotyledons of the same species. 2. [1-¹⁴C]Acetate supplied to detached cotyledons was incorporated into the acyl moieties of mainly 3-sn-phosphatidylcholine, 1,2-diacylglycerol and triacylglycerol. Initially label was predominantly in oleate, but subsequently entered at accelerating rates the linoleoyl moieties of the above lipids in soya-bean and safflower cotyledons and the linoleoyl and linolenyl moieties of these lipids in linseed cotyledons. In pulse–chase experiments label was rapidly lost from the oleate of 3-sn-phosphatidylcholine and accumulated in the linoleoyl and linolenoyl moieties of this phospholipid and of the di- and tri-acylglycerols. 3. [2-³H]Glycerol was incorporated into the glycerol moieties of mainly 3-sn-phosphatidylcholine and di- and tri-acylglycerols of developing linseed and soya-bean cotyledons. The label entered the phospholipid and diacylglycerol at rates essentially linear with time from the moment the substrate was supplied, and entered the triacylglycerol at an accelerating rate. With linseed cotyledons the labelled glycerol was incorporated initially mainly into species of 3-sn-phosphatidylcholine and diacylglycerol that contained oleate, but accumulated with time in more highly unsaturated species. In pulse–chase experiments with linseed cotyledons, label was lost from both 3-sn-phosphatidylcholine and diacylglycerol, preferentially from the dioleoyl species, and accumulated in triacylglycerol, mainly in species containing two molecules of linolenate. 4. The results suggest a rapid turnover of 3-sn-phosphatidylcholine during triacylglycerol accumulation in developing oilseeds, and are consistent with the operation of a biosynthetic route whereby oleate initially esterified to the phospholipid is first desaturated, then polyunsaturated fatty acids transferred to triacylglycerol, via diacylglycerol. The possible role of oleoyl phosphatidylcholine as a substrate for oleate desaturation is discussed.     

Hydrolysis of 1-palmitoyl-2-[6-(pyren-1-yl)]hexanoyl-sn-glycero-3-phospholipids by phospholipase A2: effect of the polar head-group

The effect of the phospholipid polar head-group on the porcine pancreatic phospholipase A₂ (phosphatidylcholine 2-acylhydrolase, EC 3.1.1.4) reaction was studied using 1-palmitoyl-2-[6-(pyren-1-yl)]hexanoyl-sn-glycero-3-phosphatidylcholine,-ethanolamine, -glycerol, -monomethylester and -serine as substrates. Except for the monomethylester analogue, which was maximally activated by 3.5 mM CaCl₂, maximal enhancement of hydrolysis of the other pyrenephospholipids was obtained at 2 mM Ca₂₊. Sodium cholate inhibited hydrolysis of the ethanolamine and serine lipids, whereas a slight (1.4–2.0-fold) activation was observed for the -choline, -glycerol and -monomethylester derivatives. Arrhenius plots of hydrolysis of pyrenephospholipids by porcine pancreatic phospholipase A₂ revealed no discontinuities, thus indicating the absence of phase transition for these lipids in the temperature range 15–45°C. Specific activities of porcine and bovine pancreatic, porcine intestinal and snake venom (Crotalus atrox) phospholipases A₂ towards pyrenephospholipid liposomes were then compared. Whereas the snake venom phospholipase A₂ preferred phosphatidylcholine as a substrate, the other phospholipases A₂ preferred acidic phospholipids in the order monomethylester ⩾ glycerol ⩾ serine.     

Molecular dynamics study of 4-OH-phenylacetyl-D-Y(Me)FQNRPR-NH2 selectivity to V1a receptor

G protein-coupled receptors relay diverse extracellular signals into cells via a common mechanism, involving activation of cytosol G proteins. The mechanism underlies the actions of ~50% of all drugs. In this work, we focus on simulating three protein–ligand complexes of the neurohypophyseal hormone analog 4-OH-phenylacetyl-D-Y(Me)FQNRPR-NH₂ (I) with the human V1a, V2 and oxytocin receptors. The peptide I is a potent selective V1a receptor antagonist. To obtain relaxed models of the complexes, the following techniques were used: docking of I into the vasopressin V1a, V2 and oxytocin receptor models, optimization of the geometry of the resulting complexes and molecular dynamics in a fully hydrated 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphatidylcholine lipid bilayer. The results of the simulations allow us to draw some conclusions about the ligand selectivity to V1aR.     

The effect of binding of spider-derived antimicrobial peptides, oxyopinins, on lipid membranes

Oxyopinins (Oxki1 and Oxki2) are antimicrobial peptides isolated from the crude venom of the wolf spider Oxyopes kitabensis. The effect of oxyopinins on lipid bilayers was investigated using high-sensitivity titration calorimetry and ³¹P solid-state NMR spectroscopy. High-sensitivity titration calorimetry experiments showed that the binding of oxyopinins was exothermic, and the binding enthalpies (ΔH) to 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphatidylcholine (POPC) small unilamellar vesicles (SUVs) were − 18.1 kcal/mol and − 15.0 kcal/mol for Oxki1 and Oxki2, respectively, and peptide partition coefficient (K_p) was found to be 3.9 × 10³ M^− 1. ³¹P NMR spectra of 1,2-dielaidoyl-sn-glycero-3-phosphoethanolamine (DEPE) membranes in the presence of oxyopinins indicated that they induced a positive curvature in lipid bilayers. The induced positive curvature was stronger in the presence of Oxki2 than in the presence of Oxki1. ³¹P NMR spectra of phosphaditylcholine (PC) membranes in the presence of Oxki2 showed that Oxki2 produced micellization of membranes at low peptide concentrations, but unsaturated PC membranes or acidic phospholipids prevented micellization from occurring. Furthermore, ³¹P NMR spectra using membrane lipids from E. coli suggested that Oxki1 was more disruptive to bacterial membranes than Oxki2. These results strongly correlate to the known biological activity of the oxyopinins.     

Barotropic and thermotropic bilayer phase behavior of positional isomers of unsaturated mixed-chain phosphatidylcholines

The bilayer phase transitions of six kinds of mixed-chain phosphatidylcholines (PCs) with an unsaturated acyl chain in the sn-1 or sn-2 position, 1-oleoyl-2-stearoyl- (OSPC), 1-stearoyl-2-oleoyl- (SOPC), 1-oleoyl-2-palmitoyl- (OPPC), 1-palmitoyl-2-oleoyl- (POPC), 1-oleoyl-2-myristoyl- (OMPC) and 1-myristoyl-2-oleoyl-sn-glycero-3-phosphocholine (MOPC), were observed by means of differential scanning calorimetry (DSC) and high-pressure light transmittance measurements. Bilayer membranes of SOPC, POPC and MOPC with an unsaturated acyl chain in the sn-2 position exhibited only one phase transition, which was identified as the main transition between the lamellar gel (L_β) and liquid crystalline (L_α) phases. On the other hand, the bilayer membranes of OSPC, OPPC and OMPC with an unsaturated acyl chain in the sn-1 position exhibited not only the main transition but also a transition from the lamellar crystal (L_c) to the L_β (or L_α) phase. The stability of their gel phases was markedly affected by pressure and chain length of the saturated acyl chain in the sn-2 position. Considering the effective chain lengths of unsaturated mixed-chain PCs, the difference in the effective chain length between the sn-1 and sn-2 acyl chains was proven to be closely related to the temperature difference of the main transition. That is, a mismatch of the effective chain length promotes a temperature difference of the main transition between the positional isomers. Anomalously small volume changes of the L_c/L_α transition for the OPPC and OMPC bilayers were found despite their large enthalpy changes. This behavior is attributable to the existence of a cis double bond and to significant inequivalence between the sn-1 and sn-2 acyl chains, which brings about a small volume change for chain melting due to loose chain packing, corresponding to a large partial molar volume, even in the L_c phase. Further, the bilayer behavior of unsaturated mixed-chain PCs containing an unsaturated acyl chain in the sn-1 or sn-2 position was well explained by the chemical-potential diagram of a lipid in each phase.     

The effects of maternal dietary treatments with natural PPAR ligands on lipid metabolism in fetuses from control and diabetic rats

Maternal diabetes impairs fetal development and growth. We studied the effects of maternal diets enriched in unsaturated fatty acids capable of activating peroxisome proliferator-activated receptors (PPARs) on the concentrations of 15deoxyΔ^12,14PGJ₂ (15dPGJ₂), lipid mass, and the de novo lipid synthesis in 13.5-day fetuses from control and diabetic rats. Diabetes was induced by neonatal streptozotocin administration (90 mg/kg). Rats were treated with a standard diet supplemented or not with 6% olive oil or 6% safflower oil from days 0.5 to 13.5 of gestation. Fetuses from diabetic rats fed with the standard diet showed reduced 15dPGJ₂ concentrations, whereas maternal treatments with olive and safflower oils increased 15dPGJ₂ concentrations. Fetuses from diabetic rats showed increased concentrations of phospholipids and increased synthesis of triglycerides, phospholipids, cholesterol and free fatty acids. Diabetic rat treatments with olive and safflower oils reduced phospholipids, cholesterol, and free fatty acid concentrations and the de novo lipid synthesis in the fetuses. These effects were different from those observed in fetuses from control rats, and seem not to involve PPARγ activation. In conclusion, olive oil- and safflower oil-supplemented diets provide beneficial effects in maternal diabetes, as they prevent fetal impairments in 15dPGJ₂ concentrations, lipid synthesis and lipid accumulation.     

31P NMR study of head group behavior in sonicated phosphatidylcholine liposomes in the gel and in the liquid state

We measured the ³¹P[¹H] Nuclear Overhauser Effect (NOE) as a function of temperature and of ¹H irradiation frequency, the linewidth $\text{Δν}{}_{\mathrm{<mtext>1</mtext><mtext>2</mtext>}}$ as a function of temperature and the relaxation time T₁ above and below the thermal transition temperature, of the ³¹P-NMR signal in sonicated liposomes of 1,2-dimiristoyl-3-sn-phosphatidylcholine (DMPC), 1,2-dipalmitoyl-3-sn-phosphatidylcholine (DPPC) and 1,2-dimiristoyl-3-sn-phosphatidylcholine (DSPC). The same measurements were repeated in the presence of high molecular weight dextrans. They strongly reduce the NOE and produce longer relaxation times T₁. According to the current models, we were able to evaluate, in the different situations, the correlation time of the internal motion τ_G and the distance r between interacting groups in the region of the polar head groups. While the first parameter changes abruptly through the phase transition and under the effect of dextrans, the latter does not appear modified in any case. These results are discussed in terms of a conformational change of the phosphocholine head groups.     

Validation of all-atom phosphatidylcholine lipid force fields in the tensionless NPT ensemble

A recently defined charge set, to be used in conjunction with the all-atom CHARMM27r force field, has been validated for a series of phosphatidylcholine lipids. The work of Sonne et al. successfully replicated experimental bulk membrane behaviour for dipalmitoylphosphatidylcholine (DPPC) under the isothermal-isobaric (NPT) ensemble. Previous studies using the defined CHARMM27r charge set have resulted in lateral membrane contraction when used in the tensionless NPT ensemble, forcing the lipids to adopt a more ordered conformation than predicted experimentally. The current study has extended the newly defined charge set to 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphatidylcholine (POPC) and 1-palmitoyl-2-docosahexaenoyl-sn-glycero-3-phosphatidylcholine (PDPC). Molecular dynamics simulations were run for each of the lipids (including DPPC) using both the CHARMM27r charge set and the newly defined modified charge set. In all three cases a significant improvement was seen in both bulk membrane properties and individual atomistic effects. Membrane width, area per lipid and the depth of water penetration were all seen to converge to experimental values. Deuterium order parameters generated with the new charge set showed increased disorder across the width of the bilayer and reflected both results from experiment and similar simulations run with united atom models. These newly validated models can now find use in mixed biological simulations under the tensionless ensemble without concern for lateral contraction.