Preparation of Asymmetric Vesicles with Trapped CsCl Avoids Osmotic Imbalance, Non-Physiological External Solutions, and Minimizes Leakage

The natural asymmetry of cellular membranes influences their properties. In recent years, methodologies for preparing asymmetric vesicles have been developed that rely on the methyl-α-cyclodextrin catalyzed exchange of lipids between donor lipid multilamellar vesicles and acceptor lipid unilamellar vesicles, and the subsequent separation of the, now asymmetric, acceptor vesicles from the donors. Isolation is accomplished by pre-loading acceptor vesicles with a high concentration of sucrose, typically 25% (w/w), and separating from donor and cyclodextrin by sucrose gradient centrifugation. We found that when the asymmetric vesicles were dispersed under hypotonic conditions using physiological salt solutions, there was enhanced leakage of an entrapped probe, 6-carboxyfluorescein. Studies with symmetric vesicles showed this was due to osmotic pressure and was specific to hypotonic solutions. Inclusion of cholesterol partly reduced leakage but did not completely eliminate it. To avoid having to use hypotonic conditions or to suspend vesicles at non-physiological solute concentrations to minimize leakage, a method for preparing asymmetric vesicles using acceptor vesicle-entrapped CsCl at a physiological salt concentration (100 mM) was developed. Asymmetric vesicles prepared with the entrapped CsCl protocol were highly resistant to 6-carboxyfluorescein.

Polypeptide-participating complex nanoparticles with improved salt-tolerance as excellent candidates for intelligent insulin delivery

The strategy of introducing synthetic polypeptides with hierarchical ordered structures into glucose-responsive materials is reported in this study to achieve self-regulated release of insulin under physiological salt concentration.

A Protease-Resistant 61-Residue Prion Peptide Causes Neurodegeneration in Transgenic Mice

ABSTRACT An abridged prion protein (PrP) molecule of 106 amino acids, designated PrP106, is capable of forming infectious miniprions in transgenic mice (S. Supattapone, P. Bosque, T. Muramoto, H. Wille, C. Aagaard, D. Peretz, H.-O. B. Nguyen, C. Heinrich, M. Torchia, J. Safar, F. E. Cohen, S. J. DeArmond, S. B. Prusiner, and M. Scott, Cell 96:869–878, 1999). We removed additional sequences from PrP106 and identified a 61-residue peptide, designated PrP61, that spontaneously adopted a protease-resistant conformation in neuroblastoma cells. Synthetic PrP61 bearing a carboxy-terminal lipid moiety polymerized into protease-resistant, β-sheet-enriched amyloid fibrils at a physiological salt concentration. Transgenic mice expressing low levels of PrP61 died spontaneously with ataxia. Neuropathological examination revealed accumulation of protease-resistant PrP61 within neuronal dendrites and cell bodies, apparently causing apoptosis. PrP61 may be a useful model for deciphering the mechanism by which PrP molecules acquire protease resistance and become neurotoxic.

Salt Effects in Mucin Lubrication

Animal joints are lubricated by two complementary mechanisms. Weeping lubrication carries most of the joint load hydrostatically, leaving only a small fraction of the total to be carried by rubbing of the solid “skeletons” of the two cartilages. This rubbing is, in turn, lubricated by the synovial mucin; i.e., by long chain polymer molecules dissolved in the joint fluid. There is good evidence that the mucin molecules adsorb to the surfaces and provide boundary lubrication. In this paper we examine further this adsorption processs using a bearing whose two surfaces are rubber and glass, respectively. It is found that the lubricating ability of the mucin is good if it is applied to the bearing in a solution with about physiological salt concentration. At higher salt concentrations the lubrication is comparatively poor, while at zero salt concentration it is very bad indeed. If, on the other hand, the mucin is applied at physiological salt concentration, and then the salt and unadsorbed mucin are washed away with distilled water the lubrication remains good, and has, on occasion, even improved. Once the mucin has been adsorbed the entire range of salt concentration can be explored, with the lubrication becoming worse at high salt concentration and then recovering in greater or lesser degree when the salt is washed off. It seems, then, that the salt concentration affects lubrication in two ways. It can upset the adsorption of the lubricating film, and it can change the lubricating effectiveness of the film once it is adsorbed.