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An investigation whether phospholipid transfer protein (PLTP) and cholesteryl ester transfer protein (CETP) are present in human tear fluid is conducted, in order to gain insight into the formation of tear film. The results suggest that PLTP may play role in the formation of the tear film by supporting phospholipid transfer.

The distribution, orientation, and dynamics of 1,6-diphenyl-1,3,5-hexatriene (DPH) fluorescence probes in a dipalmitoylphosphatidylcholine (DPPC) bilayer were studied using 50 ns molecular dynamics. The results indicated that DPH did not prefer to be embedded in the membrane center where free volume was largest.

A novel approach is described, which studies enzymatic reactions and allows manipulating giant vesicles as well as cultured cells in a spatially controlled manner. The study shows that the enzymatic catalysis can be restrained topically to the site of contact between the vesicle and the derivatized microsphere.

The physicochemical properties of sphingolipids in a 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphatidylcholine (POPC) matrix were investigated. To this end, the behaviors of two chemically well-defined sphingolipids, N-palmitoyl-sphingomyelin and the corresponding ceramide, were compared. Experimental results showed that the enzymatic generation of ceramide from sphingomyelin stimulates microdomain formation in LUVs, although the reorganization of ceramide into microdomains within the bilayer took a significantly longer time.

A synthetic peptide, corresponding to 1 to 42 amino acid residue of amyloid beta-peptide (A-Beta(sub 1-42)), enhances the hydrolysis of the pyrene-labeled acidic phospholipid analog 1-palmitoyl-2-((pyren-1-yl))hexanoyl-sn-glycero-3-phosphoglycerol by porcine pancreatic phospholipase A(sub 2). Ca2+, at higher concentrations, abolishes the enhancing effect of A-Beta(sub 1-42), which is found in senile plaques in Alzheimer's disease (AD). Brain samples of AD patients show decreased levels of phosphatidylcholine. Activation of lipolytic enzyme by amyloid beta peptide indicates a direct involvement of the peptide in neuronal cell death in AD afflicted brain tissue.

Biochemical studies are conducted to identify proteins in retinal cell extracts that interact with RP2 in order to define the role of RP2 in the retina and X-linked retinitis pigmentosa (XLRP). The studies have shown that RP2, in addition to serving as a regulator of ADP ribosylation factor-like 3 (Arl3), has interacted with N-ethylmaleimide sensitive factor (NSF) and the complex has played a vital role in membrane protein trafficking in photoreceptors and other cells of the retina.

The interfacial properties of phospholipid transfer protein (PLTP) are studied using Langmuir phospholipid monolayers and asymmetrical flow field--flow fractionation (AsFIFFF) to follow the transfer of [super 14]C-labeled phospholipids and {[super 35]S}PLTP between lipid vesicles and high-density lipoprotein particles. It is observed that high activity-PLTP (HA-PLTP) can transfer lipids by a shuttle mechanism and phospholipid transfer can take place in the absence of formation of ternary complex between PLTP, acceptor and donor particles.

The influence of pyrene-labeled phospholipids on the structural properties of a fluid dipalmitoylphosphatidylcholine lipid membrane is elucidated. The pyrene labeling is found to perturb the membrane structure significantly in the vicinity of the probe, the correlation length in the bilayer plane being about 1.0-1.5 nm.

The structural dynamics of the main phase transition of large unilamellar dipalmitoylphosphocholine (DPPC) vesicles were studied using differential scanning calorimetry (DSC) with steady-state and time-resolved fluorescence spectroscopy. It indicates the possibility that there is an intermediate phase of strongly fluctuating lattice of fluidlike and gel-like lipids.

In circulation the phospholipid transfer protein (PLTP) facilitates the transfer of phospholipid-rich surface components from postlipolytic chylomicrons and very low density lipoproteins (VLDL) to HDL and thereby regulates plasma HDL levels. To study the molecular mechanisms involved in PLTP-mediated lipid transfer, we studied the interfacial properties of PLTP using Langmuir phospholipid monolayers and asymmetrical flow field-flow fractionation (AsFlFFF) to follow the transfer of 14C-labeled phospholipids and [35S]PLTP between lipid vesicles and HDL particles. The AsFlFFF method was also used to determine the sizes of spherical and discoidal HDL particles and small unilamellar lipid vesicles. In Langmuir monolayer studies high-activity (HA) and low-activity (LA) forms of PLTP associated with fluid phosphatidylcholine monolayers spread at the air/buffer interphase. Both forms also mediated desorption of [14C]dipalmitoylphosphatidylcholine (DPPC) from the phospholipid monolayer into the buffer phase, even when it contained no physiological acceptor such as HDL. After the addition of HDL3 to the buffer, HA-PLTP caused enhanced lipid transfer to them. The particle diameter of HA-PLTP was and that of HDL3 ~8 nm as determined by AsFlFFF analysis. Using this method, it could be demonstrated that in the presence of HA-PLTP, but not LA-FLIP, [14C]DPPC was transferred from small unilamellar vesicles (SUV) to acceptor HDL3 molecules. Concomitantly, [35S]-HA-PLTP was transferred from the donor to acceptor, and this transfer was not observed for its low-activity counterpart. These observations suggest that HA-PLTP is capable of transferring lipids by a shuttle mechanism and that formation of a ternary complex between PLTP, acceptor, and donor particles is not necessary for phospholipid transfer. [ABSTRACT FROM AUTHOR]

Reports that amyloid beta-peptides (ABP) are centrally involved in pathogenesis of Alzheimer's disease. Correlation of disease severity with extent of ABP accumulation; Composition of ABP found in cerebral amyloid deposits; Variations of C-terminal residues in series of peptides.

The tear film lipid layer (TFLL) is considered to act as an evaporation barrier and to maintain the tear film intact between blinks. In vitro methods have, however, failed to reproduce this evaporation-retarding effect. Wax esters (WEs) are a major component of the TFLL. Close to their bulk melting temperature, WEs have been found to retard the evaporation of water, but the nature of this mechanism has remained unclear. We studied the interfacial organization of WE films by measuring their isochors and isotherms and evaporation-retarding effect, and we imaged these films by Brewster angle microscopy (BAM). Behenyl palmitoleate (BP) was used as a representative WE because it resembles the WEs found in meibum. At low temperatures, BP forms solid monolayer crystals in which the molecules are organized in a bulk-like extended conformation. Within approximately 3 °C below the bulk melting temperature, these solid monolayer domains coexist with a fluid monolayer film. At temperatures above the bulk melting temperature, BP forms a completely fluid monolayer in which the molecules are in a hairpin conformation. A fluid hairpin monolayer of BP does not significantly retard evaporation, whereas a solid monolayer decreases evaporation by >50%. The results provide a molecular-level rationale for the evaporation-retarding properties of WEs close to their melting temperature.

Tear fluid lipid layer (TFLL) residing at the air-water interface of tears has been recognized to play an important role in the development of dry eye syndrome. Yet, the composition, structure, and mechanical properties of TFLL are only partly known. Here, we report results of coarse-grained simulations of a lipid layer comprising phospholipids, free fatty acids, cholesteryl esters, and triglycerides at the air-water interface to shed light on the properties of TFLL. We consider structural as well as dynamical properties of the lipid layer as a function of surface pressure. Simulations revealed that neutral lipids reside heterogeneously between phospholipids at relatively low pressures but form a separate hydrophobic phase with increasing surface pressure, transforming the initial lipid monolayer to a two-layered structure. When the model of TFLL was compared to a one-component phospholipid monolayer system, we found drastic differences in both structural and dynamical properties that explain the prominent role of neutral lipids as stabilizers of the TFLL. Based on our results, we suggest that neutral lipids are able to increase the stability of the TFLL by modulating its dynamical and structural behavior, which is important for the proper function of tear film.

In cells, one of the main roles of ceramide-enriched membrane domains is to recruit or exclude intracellular signaling molecules and receptors, thereby facilitating signal transduction cascades. Accordingly, in model membranes, even low contents of ceramide segregate into lateral domains. The impact of the N-acyl chain on this segregation and on the morphology of the domains remains to be explored. Using Langmuir monolayers, we have systematically studied binary mixtures of 1,2-dimyristoyl-sn-glycero-3-phosphocholine (DMPC) and ceramide (2:1, molar ratio) and varied the N-acyl chain length of ceramide from 2 to 24 carbon atoms (Cer2 to Cer24). Fluid Cer2, Cer6, and Cer8/DMPC mixtures were miscible at all surface pressures. Longer ceramides, however, formed surface pressure-dependent immiscible mixtures with DMPC. The domain morphology under fluorescence microscopy after including a trace amount of fluorescent NBD-phosphatidylcholine into DMPC/Cer mixtures was found to be very sensitive to the N-acyl chain length. Shorter ceramides (Cer10-Cer14) formed flower-like (seaweed) domains, whereas longer ceramides (N-acyl chain length>14 carbon atoms) formed round and regular domains. We attribute the formation of the flower patterns to diffusive morphological instabilities during domain growth.