Freestanding lipid bilayers as substrates for electron cryomicroscopy of integral membrane proteins

Phospholipid bilayers, 40 Å thick, were generated as electron microscope substrates by submerging copper grids overlaid with holey plastic through a lipid monolayer on a water surface. Previously formed proteoliposomes containing single‐particle membrane proteins in their bilayers were then fused into the newly formed bilayer substrate. To demonstrate this methodology, multi‐drug resistance protein P‐glycoprotein was incorporated into these bilayers and imaged by fixed beam microscopy and scanning transmission electron microscopy.     

Effect of PEG lipid on fusion and fission of phospholipid vesicles in the process of freeze-thawing

The effects of freeze-thawing on the sizes and size distribution of egg yolk phosphatidylcholine (EggPC) liposomes in the presence of 0-40 mol% distearoylphosphatidylethanolamine-polyethyleneglycol 2000 (DSPE-PEG2000) prepared by detergent removal method were studied by quasielastic light scattering (QELS), gel exclusion chromatography, and freeze-fracture electron microscope. Especially, gel exclusion chromatography successfully provided the size distribution of polydisperse vesicle suspension. The mean diameters of the liposomes, which had originally large size, decreased with increase in the number of freeze-thawing cycles. On the contrary, the mean diameters of the liposomes, which had originally small size, increased with increase in the numbers of freeze-thawing cycles. After freeze-thawing over 10 times, the liposomal mean diameters fell into a range from 80 to 150 nm in spite of their original size. Gel exclusion chromatography showed that in the process of freeze-thawing of the liposomes containing DSPE-PEG 2000, two opponent events, one is fission and the other is fusion, occurred at the same time.     

脂质体与胶束体儿茶素对动物血清血脂的影响

本文探讨了脂质体和胶束体结合形式的儿茶素,经灌胃或静脉注射后对小白鼠血清血脂含量的影响。结果表明:无论是采用灌胃或静脉注射方法,儿茶素均有明显降低高脂血症小白鼠血清总胆固醇（TC）、甘油三酯（TG）、低密度脂蛋白（LDL-C）、升高高密度脂蛋白（HDL-C）的作用;脂质体儿茶素的作用效果略好于胶束体儿茶素（p<0.05）;胶束体儿茶素显著好于对照组（对照2组）（p<0.05）;静脉注射组的效果明显好于灌胃组（p<0.05）。     

A reversible colorimetric and fluorescent polydiacetylene vesicle sensor platform

A multi-functional liposome has been developed that demonstrates reversible changes in color and fluorescence intensity in response to changes in pH. Addition of a pendant tryptophan moiety gives the assembly the ability to detect Escherichia coli. The sensor platform is made from a polymerized vesicular assembly of hydrazide-terminated diacetylene lipids and a BO558 fluorescent dye. The polymer backbone is responsible for the color change, while the organization induced by hydrogen bonding of the terminal hydrazide groups permits the reversibility of the color change. Fluorescence quenching is due to internal rearrangement of the liposome and occurs in both polymerized and unpolymerized structures.     

IN-VITRO INTERACTION OF LIPOSOME ENCAPSULATED HEMOGLOBIN WITH BLOOD COMPONENTS

This study involves an in-vitro experimental approach that was designed to investigate the possible interaction between liposome encapsulated hemoglobin (LEH). Reverse micelle processing was used to produce LEH. The study presented here does not indicate any negative interaction between LEH formed by reverse micelle method and relevant blood cells, namely platelets and red blood cells. Liposomes encapsulated hemoglobin affected rheological properties of blood, and Newtonian behavior is observed as a result of mixing LEH with whole blood (WHB). Neither shear induced nor stagnant hemolyses were significant. Moreover, platelets do not seem to be activated as a result of mixing WHB with LEH.     

Liposomes incorporating hydrophobically modified glucose oxidase

Glucose oxidase (GOD) was hydrophobically modified by conjugating palmitic acids to the amino groups of the enzyme. The number of palmitic acid residues conjugated to GOD was determined by using trinitrobenzenesulfonic acid (TNBS). According to the result, six palmitic acids turned out to be covalently attached to one GOD molecule. The activity of the modified GOD was 75%–80% of that of the native one, and due to the conjugated alkyl chain, the modified GOD was more surface-active than the native one. The modified GOD was incorporated into the liposomal bilayer of dioleoylphosphatidylethanolamine (DOPE) and cholesteryl hemisuccinate (CHEMS) by a detergent removal method. According to the results of the pH-dependent release, no significant release was observed in 60 sec at pH 8.2. An appreciable amount of calcein released at pH 7.0. A marked amount released at pH 6.0. The degree of release became more extensive at pH 5.0 and pH 5.6. This is possibly because the liposome is disintegrated into hexagonal phases under acidic conditions.     

Chitosan-coated liposomes for enhanced skin permeation of resveratrol

In this study, chitosan-coated liposomes were investigated for use in enhanced transdermal delivery of resveratrol. Particle size, entrapment efficiency, stability, and skin-permeation efficiency were evaluated. The particle size was seen to increase on coating with chitosan, with higher concentrations of coating solution forming larger particles. The zeta potential of the liposomes also followed the same trend, i.e., it changed from a negative value for uncoated liposomes to increasingly positive values for the chitosan-coated ones. The chitosan coating was seen to increase the stability of the liposomes by preventing their aggregation. Transdermal delivery of uncoated and 0.1% chitosan-coated liposomes containing 0.1% resveratrol was investigated using Franz diffusion cells. The proportions of resveratrol that permeated the animal skin were 40.42% and 30.84% for the coated and uncoated liposomes, respectively. This increased skin-permeation efficiency with the coating could be explained by the tendency of positively charged liposomes to interact more strongly with the skin surface. These results indicate that chitosan-coated liposomes could be an effective transdermal delivery system for delaying skin aging using resveratrol.     

Structure and property changes in certain materials influenced by the external qi of qigong

 Temperature, time, pressure (or stress) are considered important factors in changing the Gibbs free energy and optimizing the structure and properties of materials during materials processing. The effects of some other variables, including the magnetic field, electrical field, electromagnetic and ultrasonic radiation, and chemical reactions have also been well characterized. These factors have been widely applied in materials processing, and their limitations have been discovered. Thus additional factors and innovative techniques are constantly being sought to overcome those limitations. This paper presents such an innovative technique called qigong. Three sets of materials-related experiments conducted by qigong doctor Yan and his collaborators are described in which for the first time the effects of qi on inanimate matter samples with no mechanical or electrical connection to the system are revealed on laboratory instruments. These experiments show that external qi of qigong produces significant structural changes in water and aqueous solutions, alters the phase behavior of dipalmitoyl phosphatidyl choline (DPPC) liposomes, and enables the growth of Fab protein crystals. These results demonstrate objective phenomena resulting from qigong and the potential of this ancient technology system, even in material processing. Important attributes of qi are summarized and the possible implications of these results from the materials perspective are discussed. Received: 26 October 1998/Reviewed and accepted: 3 November 1998     

The selective delivery of anticancer agents using target-sensitive liposomes

Target-sensitive (TG-S) liposomes having modified antibodies on their surface were employed to study the release of calcein and the selective delivery of the anticancer agents, doxorubicin (DOX) and methotrexate (MTX). The release of calcein from TG-S liposome occurred when the various target cells were contacted with liposomes and it was proportionally increased with the increase of antibody affinity to the target cells. Increasing the concentration of antigen molecules (major histocompatibility, MHC) on the surface of RMA-S, the release of calcein and drugs from TG-S liposomes contacting with RMA-S also rised. The destabilization of TG-S liposomes was only induced above a threshold density of surface antigen on the target cell membrane. The growth inhibition of specific target cells by the liposomal drugs was always stronger than that of the non-specific ones. For specific target cells, the IC₅₀ of liposomal DOX was about 2 times greater than that of free DOX, on the while, for non-specific target cells, more than 5 times. This indicates that the liposomal drugs were transferred preferentially to the specific target cells than the non-specific ones. Based on this phenomenon, the TG-S liposomal MTX were also applied for the selective elimination of the specific target cells in the mixed culture of specific and non-specific target cells.