Effect of Phospholipid Bilayer Phase Asymmetry on Phospholipase D Reaction-Induced Vesicle Rupture

Synthesis of Phospholipids Under Plausible Prebiotic Conditions and Analogies with Phospholipid Biochemistry for Origin of Life Studies

Phospholipids are essential components of biological membranes and are involved in cell signalization, in several enzymatic reactions, and in energy metabolism. In addition, phospholipids represent an evolutionary and non-negligible step in life emergence. Progress in the past decades has led to a deeper understanding of these unique hydrophobic molecules and their most pertinent functions in cell biology. Today, a growing interest in "prebiotic lipidomics" calls for a new assessment of these relevant biomolecules.

Racemic Phospholipids for Origin of Life Studies

Although prebiotic condensations of glycerol, phosphate and fatty acids produce phospholipid esters with a racemic backbone, most experimental studies on vesicles intended as protocell models have been carried out by employing commercial enantiopure phospholipids. Current experimental research on realistic protocell models urgently requires racemic phospholipids and efficient synthetic routes for their production. Here we propose three synthetic pathways starting from glycerol or from racemic solketal (α,β-isopropylidene-dl-glycerol) for the gram-scale production (up to 4 g) of racemic phospholipid ester precursors. We describe and compare these synthetic pathways with literature data. Racemic phosphatidylcholines and phosphatidylethanolamines were obtained in good yields and high purity from 1,2-diacylglycerols. Racemic POPC (rac-POPC, (R,S)-1-palmitoyl-2-oleoyl-3-phosphocholine), was used as a model compound for the preparation of giant vesicles (GVs). Confocal laser scanning fluorescence microscopy was used to compare GVs prepared from enantiopure (R)-POPC), racemic POPC (rac-POPC) and a scalemic mixture (scal-POPC) of (R)-POPC enriched with rac-POPC. Vesicle morphology and size distribution were similar among the different (R)-POPC, rac-POPC and scal-POPC, while calcein entrapments in (R)-POPC and in scal-POPC were significantly distinct by about 10%.

Mangiferin improves hepatic damage-associated molecular patterns, lipid metabolic disorder and mitochondrial dysfunction in alcohol hepatitis rats

This study was conducted to investigate the beneficial effects and possible mechanism of action of mangiferin (MF) in alcohol hepatitis (AH) rats. Building on our previous study, the damage-associated molecular patterns (DAMPs), lipid metabolic disorder and mitochondrial dysfunction were investigated. MF effectively regulated the abnormal liver function, the levels of alcohol, FFAs and metal elements in serum. More importantly, MF improved the expression levels of mRNA and protein of PPAR-γ, OPA-1, Cav-1, EB1, NF-κB p65, NLRP3, Cas-1 and IL-1β, and decreased the positive protein expression rates of HSP90, HMGB1, SYK, CCL20, C-CAS-3, C-PARP and STARD1. Additionally, MF decreased the levels of fumarate, cAMP, xanthurenic acid and d-glucurone-6,3-lactone, and increased the levels of hippuric acid and phenylacetylglycine, and then adjusted the changes of phenylalanine metabolism, TCA cycle and ascorbate and aldarate metabolic pathways. The above results suggested that MF can effectively prevent AH by modulating specific AH-associated genes, potential biomarkers and metabolic pathways in AH rats, etc.

Correlation between composition of the outer layer and phase asymmetry for vesicles ruptured by phospholipase D

Spherical phospholipid bilayers, vesicles, were prepared by using the layer-by-layer double emulsion technique, which allows individual layers to be formed asymmetrically. Phases of the layers were adjusted by selecting the lipid tail group. The head group composition of the vesicle outer layer varied 0-100 % of phosphatidylcholine (PC) by 10 % under the condition that the diameter of the vesicle was kept constant. On the outer layer of the vesicle, the phospholipase D (PLD) reacted to convert PC to phosphatidic acid. The reaction induced a curvature change of the vesicles, which eventually led them to rupture. Response time from the PLD injection to the rupture was measured against the different compositions of the outer layer at each phase (solid and liquid) using the fluorescence intensity change of pH-sensitive dye encapsulated in the vesicles. From this measurement, the rupture caused by the PLD reaction was analyzed with respect to the phase asymmetry of the layers and the composition of the outer layer. These results were interpreted with the lipid density and stability of the layers. It was observed that the solid phase of the outer layer had a variance in response time according to the phase of the inner layer, whereas the liquid phase did not. Additionally, the response of the solid phase of the outer layer at the liquid phase of the inner layer was faster than at the solid phase of the inner layer as a result of its stability.

Effect of mixed-phospholipid layer on phospholipase D reaction-induced vesicle rupture

Spherical phospholipid bilayers, or vesicles, were prepared layer by layer using a double-emulsion technique, which allows the outer layer of the vesicles to be formed with two phospholipids that have different head groups: phosphatidylcholine (PC) and phosphatidylethanolamine. At the outer layer of the vesicles, the phospholipase D (PLD) catalyzed for the conversion of PC to phosphatidic acid. The reaction caused by PLD induced the curvature change of the vesicles, which eventually led to the rupture of the vesicles. Before the investigation, the ratio of dioleoylphosphatidylethanolamine to oleoylhydroxyphosphatidylethanolamine was found as a condition such that the vesicles made with the mixed lipids were as stable as those made with pure dioleoylphosphatidylcholine. Response time from the PLD injection to vesicle rupture was monitored by the composition of the outer layer by the fluorescence intensity change of pH-sensitive dye encapsulated in the vesicles. The response time began to be slowed at approximately 30 % PC. The response times for the compositions were associated with the surface density of PC at the outer layer. These results also seem to be determined by the size of PLD, specifically the PLD active site.