Formation and characterization of phosphatidylethanolamine/lysophosphatidylcholine mixed vesicles

An Updated Review of Pro- and Anti-Inflammatory Properties of Plasma Lysophosphatidylcholines in the Vascular System

Lysophosphatidylcholines are a group of bioactive lipids heavily investigated in the context of inflammation and atherosclerosis development. While present in plasma during physiological conditions, their concentration can drastically increase in certain inflammatory states. Lysophosphatidylcholines are widely regarded as potent pro-inflammatory and deleterious mediators, but an increasing number of more recent studies show multiple beneficial properties under various pathological conditions. Many of the discrepancies in the published studies are due to the investigation of different species or mixtures of lysophatidylcholines and the use of supra-physiological concentrations in the absence of serum or other carrier proteins. Furthermore, interpretation of the results is complicated by the rapid metabolism of lysophosphatidylcholine (LPC) in cells and tissues to pro-inflammatory lysophosphatidic acid. Interestingly, most of the recent studies, in contrast to older studies, found lower LPC plasma levels associated with unfavorable disease outcomes. Being the most abundant lysophospholipid in plasma, it is of utmost importance to understand its physiological functions and shed light on the discordant literature connected to its research. LPCs should be recognized as important homeostatic mediators involved in all stages of vascular inflammation. In this review, we want to point out potential pro- and anti-inflammatory activities of lysophospholipids in the vascular system and highlight recent discoveries about the effect of lysophosphatidylcholines on immune cells at the endothelial vascular interface. We will also look at their potential clinical application as biomarkers.

MFN2 mutations in Charcot-Marie-Tooth disease alter mitochondria-associated ER membrane function but do not impair bioenergetics

Charcot-Marie-Tooth disease (CMT) type 2A is a form of peripheral neuropathy, due almost exclusively to dominant mutations in the nuclear gene encoding the mitochondrial protein mitofusin-2 (MFN2). However, there is no understanding of the relationship of clinical phenotype to genotype. MFN2 has two functions: it promotes inter-mitochondrial fusion and mediates endoplasmic reticulum (ER)-mitochondrial tethering at mitochondria-associated ER membranes (MAM). MAM regulates a number of key cellular functions, including lipid and calcium homeostasis, and mitochondrial behavior. To date, no studies have been performed to address whether mutations in MFN2 in CMT2A patient cells affect MAM function, which might provide insight into pathogenesis. Using fibroblasts from three CMT2AMFN2 patients with different mutations in MFN2, we found that some, but not all, examined aspects of ER-mitochondrial connectivity and of MAM function were indeed altered, and correlated with disease severity. Notably, however, respiratory chain function in those cells was unimpaired. Our results suggest that CMT2AMFN2 is a MAM-related disorder but is not a respiratory chain-deficiency disease. The alterations in MAM function described here could also provide insight into the pathogenesis of other forms of CMT.

[World constructed by self-organization of some amphiphils--with a focus on vesicle formation--]

The world constructed by self-organization of some amphiphils was discussed on the basis of micelle formation, vesicle formation, and oriented-nano-wire formation. First, the micelle formation of a both water- and oil- soluble surfactant, Aerosol OT, was discussed. Solution states of micelles and monomer were discussed on the basis of thermodinamic and NMR spectroscopic analyses of micelle formation. Next, micelle-vesicle transition was discussed. It was proposed that the phospholipid LUV formation by removing detergents and destruction by adding detergents occurred via 4 stages. The 4 stage model instead of the 3 stage model could not only elucidate the complicated phenomena observed during micelle-vesicle transition, but predicted the size and properties of the vesicles formed by detergent removal from mixed micelles. Next, the vesicle formation of a fatty acid with a single hydrophobic chain different from phospholipid, which has two hydorophobic chains, was discussed. The vesicle formation was strongly affected by the presence of preformed vesicles and the size was biased on the preformed vesicles. It was shown there exist two pass ways in the process of micelle-vesicle transition by pH jump. One is fission of the preformed vesicles after transfer of monomers from newly added oleate micelles and the other is transition from the mixed micelles after partial solubilization by the oreate micelles. Then, the vesicle formation of HCO-10, which has 3 hydrophobic chains, the mixed vesicle formation of phosphatidylethanolamine and lysophosphtidylcholine, which can not form vesicles, and the phospholipid vesicle formation and destruction by removing and adding PEG-lipid, were discussed. Lastly, oriented nano wire formation of mulamyldipeptid-conjugated lipids with ca 5 nm of diameter was discussed.

Process of destruction of large unilamellar vesicles by a zwitterionic detergent, CHAPS: partition behavior between membrane and water phases

The process of vesicle destruction by zwitterionic detergent, 3-[(3-cholamidopropyl)dimethylammonio]-1-propanesulfonate (CHAPS), was examined to clarify the vesicle-micelle transition mechanism. The physicochemical properties including turbidity, apparent particle size, Cl(-) permeability, electron spin resonance (ESR) spectroscopic parameters, and freeze-fracture electron microscopy were investigated. The concentration of CHAPS was analyzed using HPLC to determine the partition coefficient during the solubilization process. The data obtained revealed that maximum turbidity and apparent particle size were found at the effective ratio (R(e)) of 0.21 and 0.49, respectively. With a further increase in CHAPS concentration, turbidity and particle size abruptly decreased, suggesting the formation of mixed micelles. The partition coefficient changed throughout the solubilization process. In the presence of low concentrations of CHAPS, CHAPS partitioned into vesicles without destruction of membrane bilayers. When the R(e)<0.04, the partition coefficient was independent of the detergent concentration with value of 24 M(-1). At R(e) greater than 0.05, the membrane barrier abruptly decreased. At 0.04</=R(e)<0.21, the gradual increase in the partition coefficient accounted for the occurrence of larger vesicles. In range of 0.21</=R(e)<0.52, the abrupt increase in the partition behavior was possibly attributed to the structural change of mixed vesicles to mixed micelles. Furthermore, the ESR results showed that the incorporation of CHAPS into vesicles led to an increase in membrane fluidity near the polar head, and a decrease near the end of the acyl chain. ESR spectra of 5-doxylstearic acid in CHAPS-containing micelles were anisotropic, indicating that the steroidal structure of CHAPS was responsible for the micelles possessing an orderly arrangement of hydrocarbon chains.

Membrane properties of cationic liposomes composed of dipalmitoylphosphatidylcholine and dipalmityldimethylammonium bromide

Cationic liposomes composed of dipalmitoylphosphatidylcholine (DPPC) and dipalmityldimethylammmonium bromide (DPAB) were prepared by the Bangham method and the effect of DPAB on the membrane properties was examined in terms of liposomal shape, particle size, trapping efficiency, surface potential and dispersibility. The dispersibility of the mixed DPPC/DPAB liposomes (the mole fraction of DPAB (XDPAB)>==0.05) was excellent and the dispersibility was maintained for 6 months, since the zeta-potential of the mixed liposomes was approximately +40 mV. The trapping efficiency of the mixed DPPC/DPAB liposomes (XDPAB=0.05) was 10 times greater than that of the DPPC liposomes, and the value was largest among the mixed liposomes (XDPAB=0-1.0). Freeze-fracture electron micrographs indicated that the shape of the mixed DPPC/DPAB liposomes (XDPAB=0.05) was that of large unilamellar vesicles (LUVs) with a diameter of approximately 2 microm, while the shape of the DPPC liposomes was that of multilamellar vesicles (MLVs). The mixed liposomes had, therefore, a high trapping efficiency. Furthermore, the shape of the mixed DPPC/DPAB liposomes (XDPAB=0.75) was also that of LUVs with a diameter of approximately 2 microm and these had a high trapping efficiency. Whereas, the particle size (500 nm) of the mixed DPPC/DPAB liposomes (XDPAB=0.25) was smaller than that of the former and had the minimum trapping efficiency. The phase transition temperature of the liposomal bilayer membranes indicated a maximum value at 0.25-0.30 mole fractions of DPAB. These facts were considered to be due to the fact that DPPC and DPAB, whose molar ratio was 7.5:2.5, were tightly packed in the liposomal bilayer membranes and that the curvature of the liposomal particle was resultantly large. Nevertheless, LUVs having a high trapping efficiency were easily obtained by mixing a small amount of DPAB with the DPPC.

Molecular Dynamics Simulation of the Formation, Structure, and Dynamics of Small Phospholipid Vesicles

Here, we use coarse grained molecular dynamics (MD) simulations to study the spontaneous aggregation of dipalmitoylphosphatidylcholine (DPPC) lipids into small unilamellar vesicles. We show that the aggregation process occurs on a nanosecond time scale, with bicelles and cuplike vesicles formed at intermediate stages. Formation of hemifused vesicles is also observed at higher lipid concentration. With either 25% dipalmitoylphosphatidylethanolamine (DPPE) or lysoPC mixed into the system, the final stages of the aggregation process occur significantly faster. The structure of the spontaneously formed vesicles is analyzed in detail. Microsecond simulations of isolated vesicles reveal significant differences in the packing of the lipids between the inner and outer monolayers, and between PC, PE, and lysoPC. Due to the small size of the vesicles they remain almost perfectly spherical, undergoing very limited shape fluctuations or bilayer undulations. The lipid lateral diffusion rate is found to be faster in the outer than in the inner monolayer. The water permeability coefficient of the pure DPPC vesicles is of the order of 10(-)(3) cm s(-)(1), in agreement with experimental measurements.