Phosphatidylcholine Molecules Research Articles

Phytosomes:An Overview

Phytosome is a patented technology that incorporates standardized plant extracts into phospholipids to create lipid-soluble molecular complexes with improved bioavailability and absorption. These phyto-constituents are increasingly important due to their nutritional and medicinal properties, but their bioavailability remains poor. Phytosome drug delivery is a method developed to enhance their bioavailability and is compatible in-vivo. Preparation methods are easy and can be characterized using techniques like FTIR, PXRD, DSC, SEM, TEM, and HNMR. Phytosomes can be used to augment the bioavailability of plant constituents and treat incurable diseases with less side effects. Phytosomes are formed by reacting a stoichiometric amount of phospholipid with standardized herbal extract or polyphenolic constituents in an aprotic solvent. Phosphatidylcholine molecules in phytosomes have hepatoprotective activity and nutritional value. In this article, we are going to keep an eye on Phytosomes Overview.

LPGAT1/LPLAT7 regulates acyl chain profiles at the sn-1 position of phospholipids in murine skeletal muscles

Skeletal muscle consists of both fast- and slow-twitch fibers. Phospholipids are important structural components of cellular membranes, and the diversity of their fatty acid composition affects membrane characteristics. Although some studies have shown that acyl chain species in phospholipids differ among various muscle fiber types, the mechanisms underlying these differences are unclear. To investigate this, we analyzed phosphatidylcholine (PC) and phosphatidylethanolamine (PE) molecules in the murine extensor digitorum longus (EDL; fast-twitch) and soleus (slow-twitch) muscles. In the EDL muscle, the vast majority (93.6%) of PC molecules was palmitate-containing PC (16:0-PC), whereas in the soleus muscle, in addition to 16:0-PC, 27.9% of PC molecules was stearate-containing PC (18:0-PC). Most palmitate and stearate were bound at the sn-1 position of 16:0- and 18:0-PC, respectively, and 18:0-PC was found in type I and IIa fibers. The amount of 18:0-PE was higher in the soleus than in the EDL muscle. Peroxisome proliferator-activated receptor γ coactivator-1α (PGC-1α) increased the amount of 18:0-PC in the EDL. Lysophosphatidylglycerol acyltransferase 1 (LPGAT1) was highly expressed in the soleus compared with that in the EDL muscle and was upregulated by PGC-1α. LPGAT1 knockout decreased the incorporation of stearate into PC and PE invitro and exvivo and the amount of 18:0-PC and 18:0-PE in murine skeletal muscle with an increase in the level of 16:0-PC and 16:0-PE. Moreover, knocking out LPGAT1 decreased the amount of stearate-containing phosphatidylserine (18:0-PS), suggesting that LPGAT1 regulated the acyl chain profiles of phospholipids, namely, PC, PE, and PS, in the skeletal muscle.

Phosphatidylcholine in the tear film of the eye: Enhanced topical delivery of fluorometholone to the eye

In this study, the ability of the phosphatidylcholine (PC) molecule, which is in the tear films in human eyes, to release the fluorometholone (FLU) drug from the sulfobutylether-β-cyclodextrin (SBE-β-CD) carrier, is investigated. The binding energy obtained from the density functional theory (DFT) calculations shows that the PC molecule affinity to bind with the SBE-β-CD is higher than that of the FLU molecule. In addition, the results of molecular dynamic (MD) simulations revealed that PC couldinteractwith the carrier through both coulombic and L-J interactions (Ecoul = ∼−206 and EL-J = ∼−190 kJ/mol), while FLU interaction with SBE-β-CD is mainly via van der Waals interactions (Ecoul = ∼−49 and EL-J = ∼−125 kJ/mol). The obtained results show that in both studied systems, H-bond formation is the driving force in stabilizing these structures. The results confirmed that the Phosphatidylcholine could replace the fluorometholone in the carrier cavity and release the drug in the target site. Overall, our findings demonstrate that SBE-β-CD&FLU complex can be a suitable alternative for treating inflammatory disorders of the eye over the conventional delivery systems.

Supramolecular Optimization of Sensory Function of a Hemicurcuminoid through Its Incorporation into Phospholipid and Polymeric Polydiacetylenic Vesicles: Experimental and Computational Insight.

This work presents the synthesis of a new representative of hemicurcuminoids with a nonyloxy substituent (HCur) as a fluorescent amphiphilic structural element of vesicular aggregates based on phosphatidylcholine (PC), phosphatidylserine (PS), and 10,12-pentacosadiynoic acid (PCDA). Both X-ray diffraction analysis of the single crystal and 1H NMR spectra of HCur in organic solvents indicate the predominance of the enol-tautomer of HCur. DFT calculations show the predominance of the enol tautomer HCur in supramolecular assemblies with PC, PS, and PCDA molecules. The results of the molecular modeling show that HCur molecules are surrounded by PC and PS with a rather weak exposure to water molecules, while an exposure of HCur molecules to water is enhanced under its supramolecular assembly with PCDA molecules. This is in good agreement with the higher loading of HCur into PC(PS) vesicles compared to PCDA vesicles converted into polydiacetylene (PDA) ones by photopolymerization. HCur molecules incorporated into HCur-PDA vesicles exhibit greater planarity distortion and hydration effect in comparison with HCur-PC(PS) ones. HCur-PDA is presented as a dual fluorescence-chromatic nanosensor responsive to a change in pH within 7.5-9.5, heavy metal ions and polylysine, and the concentration-dependent fluorescent response is more sensitive than the chromatic one. Thus, the fluorescent response of HCur-PDA allows for the distinguishing between Cd2+ and Pb2+ ions in the concentration range 0-0.01 mM, while the chromatic response allows for the selective sensing of Pb2+ over Cd2+ ions at their concentrations above 0.03 mM.

Mass spectrometric based analysis of whole eggs dissolved in formic acid

We have developed a method for complete dissolution of whole eggs in formic acid that provides a new approach to analyzing egg biomolecules. As expected from prior work with extracted lipids, phosphatidylcholine represents the most abundant 31P NMR signal. A simplified methanol/chloroform partitioning method for separating the dissolved egg solution into metabolites, lipids and protein was performed and after ultra-high mass resolution and tandem MS fragmentation analyses several phosphatidylcholine molecules containing different fatty acid chain lengths as well as number and position of double bonds was detected. The MS based proteomic analysis further revealed 6 Gallus sequences annotated as 'uncharacterized' because they show no sequence homology with any other protein found in nature and thus, may represent proteins uniquely evolved to perform functions specific to chickens. Overall, this procedure is a rapid and facile means of characterizing in a high throughput and comprehensive manner, the molecular components of whole eggs.

Genetic Variants in One-Carbon Metabolism and Their Effects on DHA Biomarkers in Pregnant Women: A Post-Hoc Analysis.

The delivery of docosahexanoic acid (DHA) to the fetus is dependent on maternal one-carbon metabolism, as the latter supports the hepatic synthesis and export of a DHA-enriched phosphatidylcholine molecule via the phosphatidylethanolamine N-methyltransferase (PEMT) pathway. The following is a post-hoc analysis of a choline intervention study that sought to investigate whether common variants in one-carbon metabolizing genes associate with maternal and/or fetal blood biomarkers of DHA status. Pregnant women entering their second trimester were randomized to consume, until delivery, either 25 (n = 15) or 550 (n = 15) mg choline/d, and the effects of genetic variants in the PEMT, BHMT, MTHFD1, and MTHFR genes on DHA status were examined. Variant (vs. non-variant) maternal PEMT rs4646343 genotypes tended to have lower maternal RBC DHA (% total fatty acids) throughout gestation (6.9% vs. 7.4%; main effect, p = 0.08) and lower cord RBC DHA at delivery (7.6% vs. 8.4%; main effect, p = 0.09). Conversely, variant (vs. non-variant) maternal MTHFD1 rs2235226 genotypes exhibited higher cord RBC DHA (8.3% vs. 7.3%; main effect, p = 0.0003) and higher cord plasma DHA (55 vs. 41 μg/mL; main effect, p = 0.05). Genotype tended to interact with maternal choline intake (p < 0.1) to influence newborn DHA status for PEMT rs4646343 and PEMT rs7946. These data support the need to consider variants in one-carbon metabolic genes in studies assessing DHA status and requirements during pregnancy.

Prenatal choline supplementation improves biomarkers of maternal docosahexaenoic acid (DHA) status among pregnant participants consuming supplemental DHA: a randomized controlled trial

ABSTRACTBackgroundDietary methyl donors (e.g., choline) support the activity of the phosphatidylethanolamine N-methyltransferase (PEMT) pathway, which generates phosphatidylcholine (PC) molecules enriched in DHA that are exported from the liver and made available to extrahepatic tissues.ObjectivesThis study investigated the effect of prenatal choline supplementation on biomarkers of DHA status among pregnant participants consuming supplemental DHA.MethodsPregnant participants (n = 30) were randomly assigned to receive supplemental choline intakes of 550 mg/d [500 mg/d d0-choline + 50 mg/d deuterium-labeled choline (d9-choline); intervention] or 25 mg/d (25 mg/d d9-choline; control) from gestational week (GW) 12–16 until delivery. All participants received a daily 200-mg DHA supplement and consumed self-selected diets. Fasting blood samples were obtained at baseline, GW 20–24, and GW 28–32; maternal/cord blood was obtained at delivery. Mixed-effects linear models were used to assess the impact of prenatal choline supplementation on maternal and newborn DHA status.ResultsCholine supplementation (550 vs. 25 mg/d) did not achieve a statistically significant intervention × time interaction for RBC PC-DHA (P = 0.11); a significant interaction was observed for plasma PC-DHA and RBC total DHA, with choline supplementation yielding higher levels (+32–38% and +8–11%, respectively) at GW 28–32 (P < 0.05) and delivery (P < 0.005). A main effect of choline supplementation on plasma total DHA was also observed (P = 0.018); its interaction with time was not significant (P = 0.068). Compared with controls, the intervention group exhibited higher (P = 0.007; main effect) plasma enrichment of d3-PC (d3-PC/total PC). Moreover, the ratio of d3-PC to d9-PC was higher (+50–67%; P < 0.001) in the choline intervention arm (vs. control) at GW 20–24, GW 28–32, and delivery.ConclusionsPrenatal choline supplementation improves hepatic DHA export and biomarkers of DHA status by bolstering methyl group supply for PEMT activity among pregnant participants consuming supplemental DHA. This trial is registered at www.clinicaltrials.gov as NCT03194659.

Molecular substructure of the liquid-ordered phase formed by sphingomyelin and cholesterol: sphingomyelin clusters forming nano-subdomains are a characteristic feature.

As a model of lipid rafts, the liquid-ordered (Lo) phase formed by sphingomyelin (SM) and cholesterol (Cho) in bilayer membranes has long attracted the attention of biophysics researchers. New approaches and methodologies have led to a better understanding of the molecular basis of the Lo domain structure. This review summarizes studies on model membrane systems consisting of SM/unsaturated phospholipid/Cho implying that the Lo phase contains SM-based nanodomains (or nano-subdomains). Some of the Lo phase properties may be attributed to these nanodomains. Several studies suggest that the nanodomains contain clustered SM molecules packed densely to form gel-phase-like subdomains of single-digit nanometer size at physiological temperatures. Cho and unsaturated lipids located in the Lo phase are likely to be concentrated at the boundaries between the subdomains. These subdomains are not readily detected in the Lo phase formed by saturated phosphatidylcholine (PC) molecules, suggesting that they are strongly stabilized by homophilic interactions specific to SM, e.g., between SM amide groups. This model for the Lo phase is supported by experiments using dihydro-SM, which is thought to have stronger homophilic interactions than SM, as well as by studies using the enantiomer of SM having opposite stereochemistry to SM at the 2 and 3 positions and by some molecular dynamics (MD) simulations of lipid bilayers containing Lo-lipids. Nanosized gel subdomains seem to play an important role in controlling membrane organization and function in biological membranes.

Revealing Sex and Alzheimer’s Disease‐related Changes in the Spatial Localization of Brain Lipids in Mice using Mass Spectrometry Imaging

Lipids are essential biomolecules in the brain, as they have important roles in signaling and structural integrity. Of note, the central nervous system has a high concentration of lipids, second only to adipose tissue. Recently, it has been shown that abnormalities in lipid levels play a critical role in the onset of neurodegenerative diseases including Alzheimer’s disease (AD). AD is a progressive and severe neurodegenerative disease and the leading cause for dementia, affecting millions worldwide. However, the spatial localization of individual lipid molecules in normal brain tissues, as well as region‐specific lipid alterations during AD are yet to be explored. Additionally, current understanding of potential sexual dimorphisms in lipid localization in brain is incomplete. With these in mind, we employed high‐resolution matrix‐assisted laser desorption/ionization mass spectrometry imaging (MALDI MSI) coupled to ion mobility mass spectrometry to characterize region‐specific lipid distribution in brain obtained from age‐ and sex‐matched wild type and AD mice (18‐month‐old female C57BL/6J and 3xTg‐AD mice, which exhibits both amyloid and tau pathology, n=3 per group). Additionally, the spatial distributions of lipids were investigated in male and female mice within two different age groups (4 and 12‐week‐old, n=3 per group). From these experiments, we were able to detect more than one thousand ions in brain tissue sections. Following detection, we annotated an approximate 100 lipid molecules with high confidence. Tissue imaging results revealed region‐specific distributions of specific lipids representing a range of classes including phosphatidylcholines, lysophosphatidylcholines, phosphatidylethanolamines, ceramide phosphates, sphingomyelins, sulfated hexosyl ceramides, and ceramide phosphoinositols across male and female mice. Interestingly, ceramide phosphate (30:7), lysophosphatidylcholine (16:0), and phosphatidylcholine (36:5) molecules exhibited sex‐specific localization patterns restricted to the cerebellum in 4‐week‐old male mice. Further, ceramide phosphoinositol (42:6) was localized to the cerebellum region of 12‐week‐old male and female mice whereas 4‐week‐old male and female mice showed relative homogeneous spatial distribution. Notably, we observed region‐specific alterations in the spatial localization of several lipid molecules including phosphatidylcholine [(40:6), and (40:7)] and sulfated hexosyl ceramide [(16:1;2O/22:2;O), (24:2;2O/12:1;O), and (19:0;2O/15:0;O)] in AD mice as compared to age‐ and sex‐matched controls. These observed changes occurred in the hippocampus region and were further confirmed using receiver operating characteristic analysis. Taken together, the above results reveal highly localized patterns of alterations in lipid molecules across male and female mice, as well as during AD.

Two Pathways Diverge: Glycerophosphocholine Impacts Both Phosphate and Lipid Metabolism in Candida albicans

Candida albicans (C. albicans)is a leading source of fungal infections in humans, resulting in over 250,000 deaths annually. C. albicanscolonizes multiple host niches and causes invasive disease, requiring its adaptation to wide variations in nutrient availability. Phosphate is an essential nutrient, and several genes associated with phosphate acquisition are differentially expressed during infection. In addition to inorganic phosphate (Pi), C. albicans utilizes the abundant lipid metabolite, glycerophosphocholine (GPC), as a phosphate source. GPC is transported into the cell via the Git3 and Git4 transporters. The Git transporters are required for full virulence in a mouse model of disseminated candidiasis, but the mechanism for that virulence defect is unknown. Here, we probe the importance of GPC uptake to cellular metabolism by examining two aspects of its metabolic fate: i) its catabolism to liberate Pi), and ii) its potential conversion to phosphatidylcholine (PC) via reacylation. To query its role in phosphate homeostasis, we employed a knockout strain of the high affinity phosphate transporter, Pho84. Cells lacking Pho84 display sensitivity to several host‐related stressors and decreased virulence. Our results show that provision of cells with GPC as phosphate source alleviates hypersensitivity of pho84∆/∆ mutants to osmotic, oxidative, and cell wall stress. The rate at which GPC and Pi are transported into the cell varies depending upon the total level of phosphate provided, with Pitransport exceeding GPC transport by a maximum of two‐fold at 500 µM total phosphate. The effect of exogenous GPC on induction of the PHO regulon, the cellular system of phosphate homeostasis, is complex and concentration dependent. Beyond its role in phosphate metabolism, GPC has other physiologically relevant metabolic fates, namely its reacylation to form a phosphatidylcholine (PC) molecule. In Saccharomyces cerevisiae, the first step of this novel reacylation pathway is catalyzed by the acyltransferase, Gpc1, which converts GPC to lyso‐PC. Initial in vivo labeling studies under phosphate replete conditions indicate that the C. albicans homolog of Gpc1 is a GPC acyltransferase and that the reacylation pathway is functional in C. albicans. In vitro assays in strains lacking or containing Gpc1 are underway. Taken together, our results indicate that C. albicans can utilize the abundant lipid metabolite, GPC, via at least two metabolic pathways to promote its growth and survival in the human host.

Lipidomics of Thalassiosira pseudonana as a function of valve SDV synthesis

Silica polycondensation occurring in diatom organelles called silica deposition vesicles (SDVs) leads to valve and girdle band formation to complete the biosilica cell wall after cell division. As SDVs have as yet not successfully been isolated, the role of SDV membranes in silica biogenesis is still largely unexplored. Here we used the possibility of synchronizing the diatom Thalassiosira pseudonana to produce two synchronized cultures in different cell cycle stages that differ in their valve SDV production. Lipid subclass fold changes between valve SDV-enriched samples and cells in the G1 state are interpreted as indications for SDV-relevant membrane lipids. The lipid classes phosphatidylcholine (PC), phosphatidylethanolamine (PE), phosphatidic acid (PA), and lysophosphatidylcholine (LPC) were found to be elevated in valve SDV-enriched cells, also showing accumulation of the very long-chain polyunsaturated fatty acids eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA). It is conceivable that PA and LPC are preferentially found in SDV regions with high membrane curvature like the rims of the pancake-shaped valve SDV, while PC and PE molecules are presumably found in the planar regions of the SDVs. In addition, DHA-enriched phospholipids are known to form highly disordered membrane domains, which might be involved in membrane protein localization, possibly used for cytoskeleton-mediated positioning of the SDV.

Perspective: Estrogen and the Risk of Cognitive Decline: A Missing Choline(rgic) Link?

ABSTRACTFactors that influence the risk of neurocognitive decline and Alzheimer's disease (AD) may provide insight into therapies for both disease treatment and prevention. Although age is the most striking risk factor for AD, it is notable that the prevalence of AD is higher in women, representing two-thirds of cases. To explore potential underlying biological underpinnings of this observation, the intent of this article is to explore the interplay between cognitive aging and sex hormones, the cholinergic system, and novel hypotheses related to the essential nutrient choline. Mechanistic evidence points toward estrogen's neuroprotective effects being strongly dependent on its interactions with the cholinergic system, a modulator of attentional functioning, learning, and memory. Estrogen has been shown to attenuate anticholinergic-induced impairments in verbal memory and normalize patterns of frontal and occipital cortex activation, resulting in a more “young adult” phenotype. However, similar to estrogen replacement's effect in cardiovascular diseases, its putative protective effects may be restricted to early postmenopausal women only, a finding supportive of the “critical window hypothesis.” Estrogen's impact on the cholinergic system may act both locally in the brain but also through peripheral tissues. Estrogen is critical for inducing endogenous choline synthesis via the phosphatidylethanolamine N-methyltransferase (PEMT) gene–mediated pathway of phosphatidylcholine (PC) synthesis. PEMT is dramatically induced in response to estrogen, producing not only a PC molecule and source of choline for the brain but also a key source of the long-chain ω-3 fatty acid, DHA. Herein, we highlight novel hypotheses related to hormone replacement therapy and nutrient metabolism aimed at directing future preclinical and clinical investigation.

Diversity of ESI-MS Based Phosphatidylcholine Profiles in Basidiomycetes.

Phosphatidylcholines (PC) are the main membrane lipid constituents comprising more than 50% of total glycerophospholipids. They coordinate a number of cell functions, particularly cell growth, homeostasis, secretion, recognition and communication. In basidial fungi PC are synthesized via the Kennedy pathway as well as through methylation of phosphatidylethanolamines (PE) and then undergo remodeling in Lands cycle that replaces fatty acids in PC molecules. The molecular profile of PC is determined by the genetic features that are characteristic for every species and depend on the environment. Here we present the results of ESI-MS based analyses of PC profiles of 38 species of basidiomycetes belonging to Agaricales (12), Polyporales (17), Russulales (5), Gleophyllales (2), Cantharellales (1), Auriculariales (1), Phallales (1). Although the variety of PC molecular species of basidiomycetes is rather diverse (20–38 molecular species in every profile), only 1–3 main molecular species represent 70–90% of total PC content. The most abundant of them are C36:4 and C36:3, followed by C34:1, C34:2, C36:5, C36:2. In the majority of basidiomycetes, C36:4 reaches up to 50–70% of total PC molecular species. Based on the results of hierarchical cluster analysis four main types of PC profiles which characterized the studied fungi independently from their taxonomic position, ecology, trophic status, and hyphal differentiation have been revealed. Comparative analyses of studied fungi using PCA method have shown that species of Polyporales differ from those of Agaricales by higher variability of PC profiles.

Evaluation of the Physico-Chemical Properties of Liposomes Assembled from Bioconjugates of Anisic Acid with Phosphatidylcholine.

The aim of this work was the evaluation of the physico-chemical properties of a new type of liposomes that are composed of DPPC and bioconjugates of anisic acid with phosphatidylcholine. In particular, the impact of modified anisic acid phospholipids on the thermotropic parameters of liposomes was determined, which is crucial for using them as potential carriers of active substances in cancer therapies. Their properties were determined using three biophysical methods, namely differential scanning calorimetry (DSC), steady-state fluorimetry and attenuated total reflectance Fourier transform infrared spectroscopy (ATR-FTIR). Moreover, temperature studies of liposomes composed of DPPC and bioconjugates of anisic acid with phosphatidylcholine provided information about the phase transition, fluidity regarding chain order, hydration and dynamics. The DSC results show that the main phase transition peak for conjugates of anisic acid with phosphatidylcholine molecules was broadened and shifted to a lower temperature in a concentration- and structure-dependent manner. The ATR-FTIR results and the results of measurements conducted using fluorescent probes located at different regions in the lipid bilayer are in line with DSC. The results show that the new bioconjugates with phosphatidylcholine have a significant impact on the physico-chemical properties of a membrane and cause a decrease in the temperature of the main phase transition. The consequence of this is greater fluidity of the lipid bilayer.

A study of cobalt (II) complexes involved in marine biogeochemical processes: Co(II)-1,10-Phenanthroline and Co(II)-1,10-Phenanthroline-L-α-Phosphatidylcholine

The cell membrane is structured so that the surface layer is composed of lipid molecules with selective permeability for micronutrients and organic ligands. Binding of Co (II) to natural lipid phosphatidylcholine (PC) has been studied to identify a possible mechanism of Co (II) entry through the cell membrane of the biota in detail, by voltammetry followed by checking the system at the air–water boundary, by Langmuir method. Binding of cobalt (II) ions to the PC molecules was enabled by the Co(II)-1,10-Phenanthroline (Phen) complex formation as an intermediate. Co(II)-Phen-PC complex reduction was recorded in the pH range from 5 to 9.5. The reduction was identified as a two-electron irreversible reaction at about −1.5 V, with the reactant adsorption followed dissociation (EC mechanism). The Co(II)-Phen-PC complex electrode surface concentration (Γ) was calculated to be (1.45 ± 0.12) × 10-10 mol.cm−2. Conditional stability constants log KCo(II)Phen2PC = 23.02 ± 0.26 and log KCo(II)Phen2PC2 = 29.31 ± 0.17 (Ic = 0.55) were calculated by CLE/ACSV method. Pressure-area (π-A) isotherms obtained at water–air interface by Langmuir monolayer technique indicated penetration of Co(II)-Phen into the PC monolayer, supporting electrochemical results. The equilibrium constants of the Co (II)-PC system (1:1) at the air–water interface was calculated to be K1 = 2.4 × 10-2 m3 mol−1, while for Co(II)-Phen-PC K2 = 4.86 × 1010 m2 mol−1.

Hydrophobicity and Charge Distribution Effects in the Formation of Bioorganoclays

Interactions of bioorganic moieties with clay minerals have attracted attention not only from the perspective of novel bioclay materials but also because they play a crucial role in our understanding of physical and chemical processes in soils. The aim of the present article is to explore the interactions responsible for the formation of a phosphatidylcholine-kaolinite bioclay by employing a series of classical molecular dynamic simulations. Detailed analysis of the structure and energies of the resulting bioclays reveals that the phosphatidylcholine molecules bind to the kaolinite surface either via their zwitterionic heads or hydrophobic aliphatic tails, depending on the kaolinite surface characteristics and the density of organic coating. The phosphatidylcholine molecules have a tendency to form irregular layers with a preferred parallel orientation of molecules with respect to the kaolinite surface. The tails exhibit varying degrees of flexibility and disorder depending on their distance from the surface and the density of surface coating. Significant differences in the binding can be spotted with respect to the two types of kaolinite basal surfaces, i.e., the hydrophobic siloxane surface, which possesses a considerable dispersion character, and the hydrophilic alumina surface, polarized by the surface hydroxyl groups.

Phosphatidylcholine-Engineered Exosomes for Enhanced Tumor Cell Uptake and Intracellular Antitumor Drug Delivery.

Exosomes derived from non-tumor cells hold great potential as drug delivery vehicles because of their good biosafety and natural transference of bioactive cargo between cells. However, compared to tumor-derived exosomes, efficient delivery is limited by their weak interactions with tumor cells. It is essential to engineer exosomes that improve tumor cellular internalization efficiency. A simple and effective strategy to enhance tumor cell uptake by engineering the exosome membrane lipids can be established by drawing on the role of lipids in tumor exosomes interacting with tumor cells. Amphiphilic phosphatidylcholine (PC) molecules are inserted into the membrane lipid layer of reticulocyte-derived exosomes (Exos) by simple incubation to construct PC-engineered exosomes (PC-Exos). It is demonstrated that PC-Exos showed significantly enhanced tumor cell internalization and uptake rate compared to native Exos, up to a twofold increase. After therapeutic agent loading, PC-Exos remarkably promotes intracellular drug or RNA accumulation in cancer cells, thus showing enhanced in vitro anti-tumor activity. This work demonstrates the crucial role of engineering exosomal lipids in modulating cancer cellular uptake, which may shed light on the design of high-efficiency exosome-based drug delivery carriers.

The acyltransferase, Gpc1, is regulated by the unfolded protein response in Saccharomyces cerevisiae

The unfolded protein response (UPR) is a proteostatic process is in which unfolded and misfolded proteins are degraded or modified. The UPR is initiated by abnormal proteins binding to the membrane protein Ire1, which dimerizes to become active and then splices the transcription factor Hac1. Spliced Hac1 produces a transcriptional response in downstream genes related to protein folding, secretion, and degradation. In addition, studies show that the UPR can be activated by endoplasmic reticulum (ER) membrane stress and can impact the expression of genes involved in lipid metabolism. Membrane abberancies that can activate the UPR include altered lipid composition and membrane fluidity. We have identified a glycerophosphocholine acyltransferase, Gpc1, that contributes to phosphatidylcholine (PC) synthesis in Saccharomyces cerevisiae and impacts PC species saturation. Gpc1 participates in the PC Deacylation-Reacylation Pathway (PC-DRP). In PC-DRP, PC is first completely deacylated by type B phospholipases, yielding glycerophosphocholine, which is then reacylated by Gpc1 to form lysophosphotidylcholine. Finally, a second acylation by Ale1 generates a PC molecule. Notably, our data demonstrate that Gpc1 produces more saturated PC species, potentially impacting membrane fluidity. Here, we report that GPC1 expressionis upregulated by UPR inducers such as tunicamycin and that loss of Gpc1 leads to increased sensitivity to tunicamycin. Additionally, loss of GPC1 is shown to activate the UPR based on expression of KAR2, a known UPR target. Ongoing studies include an examination of other constituents of PC-DRP are their relationship to the UPR.

Toward Bridging a Gap Between Model and Natural Membranes for Biophysical Studies

To study their lipid interactions or obtain valuable structural information, membrane peptides or proteins need to be maintained in a lipid system as close as possible to their natural environment. Model membranes are employed in a variety of biophysical techniques such as nuclear magnetic resonance (NMR). However, developing a method that could allow peptide extraction and reconstitution in a native or near-native membrane would be an asset. In this work, we propose an approach inspired by bicelles, which can orient in the magnetic field. We prepared magnetically-orientable phosphatidylcholine (PC) liposomes using the membrane softening detergent Tween80 (polyoxyethylene sorbitan monooleate) which is also used to extract soluble and membrane-bound proteins. Our 31P and 2H solid-state NMR results show that TWeen80 mixed to DMPC and DPPC bilayers leads to elongated oriented structures which align over a wide range of lipid-to-detergent molar ratios (2<q<13) and temperatures (25-80oC). This can be ascribed to the miscibility of Tween80 and PC molecules, as shown by the thermotropic behavior of these mixture in infrared spectroscopy. We show that the orientation with respect to the magnetic field direction can be flipped from parallel to perpendicular by addition of lanthanides ions. Using a 15N-labeled model KALP transmembrane peptide, 15N solid-state NMR spectra showed that Tween80-based PC membranes can reveal a peptide orientation, thus providing valuable data for structural determination. Altogether, our work shows that Tween80 could be exploited for membrane protein extraction, reconstitution and structural studies without requiring to a detergent removal step. This approach has the potentiel to be used with more complex membrane bilayers including native bological membranes.

Lipid molecular timeline profiling reveals diurnal crosstalk between the liver and circulation

Diurnal regulation of whole-body lipid metabolism plays a vital role in metabolic health. Although changes in lipid levels across the diurnal cycle have been investigated, the system-wide molecular responses to both short-acting fasting-feeding transitions and longer-timescale circadian rhythms have not been explored in parallel. Here, we perform time-series multi-omics analyses of liver and plasma revealing that the majority of molecular oscillations are entrained by adaptations to fasting, food intake, and the postprandial state. By developing algorithms for lipid structure enrichment analysis and lipid molecular crosstalk between tissues, we find that the hepatic phosphatidylethanolamine (PE) methylation pathway is diurnally regulated, giving rise to two pools of oscillating phosphatidylcholine (PC) molecules in the circulation, which are coupled to secretion of either very low-density lipoprotein (VLDL) or high-density lipoprotein (HDL) particles. Our work demonstrates that lipid molecular timeline profiling across tissues is key to disentangling complex metabolic processes and provides a critical resource for the study of whole-body lipid metabolism.