Differences in oxidative susceptibilities between glycerophosphocholine and glycerophosphoethanolamine in dried scallop (Argopecten irradians) adductor muscle during storage: an oxidation kinetic assessment.

BACKGROUND: Phospholipids, the main lipid component in marine shellfish, mainly comprise glycerophosphocholine (GPC) and glycerophosphoethanolamine (GPE). GPC and GPE in marine shellfish, especially scallop, carry n-3 long-chain polyunsaturated fatty acids, such as eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA), although different types of glycerophospholipids (GP) have different health benefits on human health. Moreover, different GP subclasses such as GPC and GPE have different oxidative susceptibilities in complex food systems. The present study compared the oxidative susceptibilities of GPC and GPE in dried scallop during storage by high-performance liquid chromatography-tandem mass spectrometry and kinetic models, and also investigated the effects of natural phenolic antioxidant on their susceptibilities. RESULTS: The results showed that GPC and GPE molecular species (carrying EPA or DHA) contents in samples continuously reduced during storage at two different temperatures. The first-order kinetic model better reflected the changes of GPC and GPE molecular species (carrying EPA or DHA) in samples than the zero-order kinetic model during storage. According to the oxidation rate (k) obtained from first-order kinetic models, GPE possessed a greater oxidation rate than GPC during storage. Moreover, the results showed that antioxidants of bamboo leaves (AOB, polar polyphenolic antioxidants) significantly decreased the oxidation rates of GPC and GPE molecular species (carrying EPA or DHA) in samples during storage, and GPC could be more effectively protected by AOB compared to GPE. CONCLUSION: The present study provides a practical method for accurately evaluating the oxidative susceptibility of different phospholipid classes in complex food systems. © 2020 Society of Chemical Industry.

FRET Detects the Size of Nanodomains for Coexisting Liquid-Disordered and Liquid-Ordered Phases.

Biomembranes with as few as three lipid components can form coexisting liquid-disordered (Ld) and liquid-ordered (Lo) phases. In the coexistence region of Ld and Lo phases, the lipid mixtures 1,2-distearoyl-sn-glycero-3-phosphocholine (DSPC)/1,2-dioleoyl-sn-glycero-3-phosphocholine (DOPC)/chol or brain sphingomyelin (bSM)/DOPC/chol form micron-scale domains that are easily visualized with light microscopy. Although large domains are not observed in the mixtures DSPC/1-palmitoyl-2-oleoyl-sn-glycero-3-phosphocholine (POPC)/chol and bSM/POPC/chol, lateral heterogeneity is nevertheless detected using techniques with nanometer-scale spatial resolution. We propose a simple and accessible method to measure domain sizes below optical resolution (∼200 nm). We measured nanodomain size for the latter two mixtures by combining experimental Förster resonance energy transfer data with a Monte-Carlo-based analysis. We found a domain radius of 7.5-10 nm for DSPC/POPC/chol, similar to values obtained previously by neutron scattering, and ∼5 nm for bSM/POPC/chol, slightly smaller than measurable by neutron scattering. These analyses also detect the domain-size transition that is observed by fluorescence microscopy in the four-component lipid mixture bSM/DOPC/POPC/chol. Accurate measurements of fluorescent-probe partition coefficients are especially important for the analysis; therefore, we exploit three different methods to measure the partition coefficient of fluorescent molecules between Ld and Lo phases.

Perturbations of Native Membrane Protein Structure in Alkyl Phosphocholine Detergents: A Critical Assessment of NMR and Biophysical Studies.

Membrane proteins perform a host of vital cellular functions. Deciphering the molecular mechanisms whereby they fulfill these functions requires detailed biophysical and structural investigations. Detergents have proven pivotal to extract the protein from its native surroundings. Yet, they provide a milieu that departs significantly from that of the biological membrane, to the extent that the structure, the dynamics, and the interactions of membrane proteins in detergents may considerably vary, as compared to the native environment. Understanding the impact of detergents on membrane proteins is, therefore, crucial to assess the biological relevance of results obtained in detergents. Here, we review the strengths and weaknesses of alkyl phosphocholines (or foscholines), the most widely used detergent in solution-NMR studies of membrane proteins. While this class of detergents is often successful for membrane protein solubilization, a growing list of examples points to destabilizing and denaturing properties, in particular for α-helical membrane proteins. Our comprehensive analysis stresses the importance of stringent controls when working with this class of detergents and when analyzing the structure and dynamics of membrane proteins in alkyl phosphocholine detergents.

Two for the Price of One: PAMAM-Dendrimers with Mixed Phosphoryl Choline and Oligomeric Poly(Caprolactone) Surfaces.

The application of dendrimers for biological and medical purposes is highly dependent on the type of surface group in relation to cytotoxicity. Since amine terminated PAMAM dendrimers have been shown to have toxic properties and thereby limited applications in the medical field, the discovery of a new nontoxic surface coating is of great interest. In the present work, amine terminated DAB-PAMAM dendrimers from generation zero to four have been coated with statistical surface functionalization giving a dendrimer surface consisting of an approximately 1:1 mixture of zwitterionic phosphoryl choline hexanamide and 6-((6-hydroxyhexanoyl)oxy)hexanamide. The cytotoxic properties of generation two to four were tested on three different human cancer cell lines, SKBR3 human breast cancer cells, HeLa human cervical cancer cells, and Hep G2 human hepatocellular liver carcinoma cells and compared to the toxicity of amine terminated PAMAM dendrimers. In addition to lower cytotoxicity than observed for amine terminated dendrimers, the coated dendrimers showed minor cytotoxicity against all three human cell lines, negligible influence on ROS generation and mitochondrial membrane potential. These observations support the conclusion that the analyzed group of phosphorylcholine dendrimers may be suitable for medical applications.

Current analytical strategies for C-reactive protein quantification in blood.

The measurement of serum C-reactive protein (CRP) levels has been given particular interest as a marker of inflammation associated with cardiovascular diseases. CRP belongs to the pentraxin family of proteins and the routine clinical analysis of CRP in blood samples is used as an important factor in primary prevention programmes together with causative and predisposing factors. This review focuses on the most representative methodologies and strategies for CRP detection and quantification that have been recently proposed, as well as reviewing those that are currently being developed for the specific, sensitive, inexpensive and high-throughput blood analysis of this protein.

Characterization and identification of suspected counterfeit miltefosine capsules.

Recently, it was revealed that generic miltefosine capsules for the treatment of visceral leishmaniasis, a fatal parasitic disease, were possibly counterfeit products. Here we report on the methods to characterize and identify miltefosine in pharmaceutical products and the procedures that were used to assess the quality of these suspected counterfeit products. Characterization and identification of miltefosine were done with liquid chromatography coupled to tandem mass spectrometry (LC-MS/MS), Fourier transform infrared (FT-IR) spectroscopy and near-infrared (NIR) spectroscopy. Moreover, a simple, rapid and inexpensive colorimetric test was developed and evaluated for the detection of miltefosine in pharmaceutical products that can be used in the field. The complementary analytical techniques presented here were able to determine qualitatively or (semi-)quantitatively the presence or absence of miltefosine in pharmaceutical preparations and could identify suspected counterfeit miltefosine capsules. This finding of a suspected counterfeit drug intended to treat a neglected disease in a resource-poor country emphasizes the urgent need to develop more simple inexpensive assays to evaluate drug quality for use in the field.

Molecular simulation studies of protein interactions with zwitterionic phosphorylcholine self-assembled monolayers in the presence of water.

Molecular simulations were performed to study the interactions between a protein (lysozyme, LYZ) and phosphorylcholine-terminated self-assembled monolayers (PC-SAMs) in the presence of explicit water molecules and ions. The results show that the water molecules above the PC-SAM surface create a strong repulsive force on the protein as it approaches the surface. The structural and dynamic properties of the water molecules above the PC-SAM surface were analyzed to provide information regarding the role of hydration in surface resistance to protein adsorption. It can be seen from residence time dynamics that the water molecules immediately above the PC-SAM surface are significantly slowed down as compared to bulk water, suggesting that the PC-SAM surface generates a tightly bound, structured water layer around its head groups. Moreover, the orientational distribution and reorientational dynamics of the interfacial water molecules near the PC-SAM surface were found to have the ionic solvation nature of the PC head groups. These properties were also compared to those obtained previously for an oligo(ethylene glycol) (OEG) SAM system and bulk water.

In vitro and in vivo confocal Raman study of human skin hydration: assessment of a new moisturizing agent, pMPC.

The hydration capacities of a biomimetic polymer, 2-methacryloyloxethylphosphorylcholine polymer (pMPC), alone and microencapsulated, in association with another well known hydrating polymer, Hyaluronic acid, were investigated in vitro on skin models and in vivo on volunteers by using confocal Raman microspectroscopy. The hydration impact and the relative water content in the Stratum corneum were calculated from the Raman spectra using the OH (water)/CH3 (protein) ratio. Moreover, the follow-up of the presence of pMPC through the Stratum corneum was possible with confocal Raman microspectroscopy, using a characteristic vibration of pMPC, different from that of the encapsulating material. From our in vitro measurements, the improved hydration of the Stratum corneum was confirmed by the use of the encapsulated form of pMPC, which was higher when combined with Hyaluronic acid. On the basis of these in vitro findings, we validated this trend in in vivo measurements on 26 volunteers, and found a good correlation with the in vitro results. Mechanical and ultrastructural studies have been carried out to demonstrate the positive effects of the pMPC on the Stratum corneum function, namely the interaction with lamellar lipids and the plasticizing effects, which are both supposed to spell out the moisturizing effect. This study demonstrates the efficiency of a original hydrating agent, pMPC, entrapped with Hyaluronic acid in a new type of microcapsules by the use of a novel tool developed for both in vitro and in vivo approaches. This indicates a new step to evaluate and improve new moisturizers in response to the cosmetics or dermatologic demands.

Dynamic assessment of bilayer thickness by varying phospholipid and hydraphile synthetic channel chain lengths.

A library of "hydraphile" synthetic ion channel analogues that differ in overall length from approximately 28-58 A has been prepared. A new and convenient ion-selective electrode (ISE) method was used to assay Na(+) release. Liposomes were formed from three different phospholipids: 1,2-dimyristoleoyl-sn-glycero-3-phosphocholine (DMPC), 1,2-dioleoyl-sn-glycero-3-phosphocholine (DOPC), and 1,2-dierucoyl-sn-glycero-3-phosphocholine (DEPC). The acyl chains of the lipids comprise cis-unsaturated 14:1, 18:1, or 22:1 residues, respectively. Sodium release was measured for each liposome system with each of the synthetic channels. Peak activity was observed for shorter channels in liposomes formed from DMPC and for longer channels in DEPC. A separate study was then conducted in DMPC liposomes in the presence of the putative membrane-thickening agents cholesterol and decane. Peak activity was clearly shifted to longer channel lengths upon addition of 20 or 40 mol % cholesterol or n-decane to the liposome preparation.

Interactions of the M2delta segment of the acetylcholine receptor with lipid bilayers: a continuum-solvent model study.

M2delta, one of the transmembrane segments of the nicotinic acetylcholine receptor, is a 23-amino-acid peptide, frequently used as a model for peptide-membrane interactions. In this and the companion article we describe studies of M2delta-membrane interactions, using two different computational approaches. In the present work, we used continuum-solvent model calculations to investigate key thermodynamic aspects of its interactions with lipid bilayers. M2delta was represented in atomic detail and the bilayer was represented as a hydrophobic slab embedded in a structureless aqueous phase. Our calculations show that the transmembrane orientation is the most favorable orientation of the peptide in the bilayer, in good agreement with both experimental and computational data. Moreover, our calculations produced the free energy of association of M2delta with the lipid bilayer, which, to our knowledge, has not been reported to date. The calculations included 10 structures of M2delta, determined by nuclear magnetic resonance in dodecylphosphocholine micelles. All the structures were found to be stable inside the lipid bilayer, although their water-to-membrane transfer free energies differed by as much as 12 kT. Although most of the structures were roughly linear, a single structure had a kink in its central region. Interestingly, this structure was found to be the most stable inside the lipid bilayer, in agreement with molecular dynamics simulations of the peptide and with the recently determined structure of the intact receptor. Our analysis showed that the kink reduced the polarity of the peptide in its central region by allowing the electrostatic masking of the Gln13 side chain in that area. Our calculations also showed a tendency for the membrane to deform in response to peptide insertion, as has been previously found for the membrane-active peptides alamethicin and gramicidin. The results are compared to Monte Carlo simulations of the peptide-membrane system, as presented in the accompanying article.