The paper describes the pseudosugar 2 [Galβ1-3GalNAcβ1-4(NeuAcR2-3)DCCHD], a high affinity binder of cholera toxin (CT). The molecule was designed using molecular modeling techniques to mimic the natural CT membrane receptor, ganglioside GM1. The central residue of GM1, a 3,4-disubstituted galactose unit, was recognized as the ganglioside scaffold element and substituted with a conformationally locked cyclohexanediol (DCCHD). DCCHD was synthesized in enantiopure form using enantioselective Diels Alder methodology and regioselectively R-sialylation at the equatorial position. Glycosylation with a Galβ(1-3)-GalNAc donor completed the synthesis of 2. The solution structure of 2 and its binding ability to CT were found to be analogous to those of the GM1 oligosaccharide.

The solution structure of ganglioside G(M1) carbohydrate moiety at the surface of a 102-kDa lipid-modified-G(M1) micelle is investigated by high-resolution 1H-NMR in H2O. The micellar surface can be considered a cluster-like lateral distribution of the gangliosides, each single monomer being anchored in a carbohydrate-enriched model membrane matrix. 1H NOESY measurements at short mixing times reveal a rigid trisaccharide core -beta-GalNAc-(1-4)-[alpha-Neu5Ac-(2-3)]-beta-Gal- and a more flexible beta-Gal-(1-3)-beta-GalNAc- terminal glycosidic bond. In the lipid-modified G(M1) ganglioside micellar system, there is no evidence that intermolecular side-by-side carbohydrate interactions modulate, or alter in any way, the head-group spatial arrangement. Possible intermonomer interactions at the level of the branched trisaccharide portion were further investigated on mixed micelles of natural N-glycolyl- and N-acetylneuraminic acid containing G(M1) in D2O, taking advantage of the different NMR features of N-glycolyl- and N-acetylneuraminic acids, which allow discrimination between sialic acid ring proton signals. Measurements of the water/ganglioside-OH proton chemical exchange rates suggest hydroxyl group involvement at position 8 of sialic acid in strong intramolecular interaction processes.

We packaged condensed DNA/protamine particles in multicomponent envelope-type nanoparticle systems (MENS) combining different molar fractions of the cationic lipids 1,2-dioleoyl-3-trimethylammonium-propane (DOTAP) and 3β-[N-(N,N-dimethylaminoethane)-carbamoyl] cholesterol (DC-Chol) and the zwitterionic lipids dioleoylphosphocholine (DOPC) and dioleoylphosphatidylethanolamine (DOPE). Dynamic light scattering (DLS) and microelectrophoresis allowed us to identify the cationic lipid/DNA charge ratio at which MENS are small sized and positively charged, while synchrotron small-angle X-ray scattering (SAXS) and atomic force microscopy (AFM) revealed that MENS are well-shaped DNA/protamine particles covered by a lipid monobilayer. Transfection efficiency (TE) experiments indicate that a nanoparticle formulation, termed MENS-3, was not cytotoxic and highly efficient to transfect Chinese hamster ovary (CHO) cells. To rationalize TE, we performed a quantitative investigation of cell uptake, intracellular trafficking, endosomal escape, and final fate by laser scanning confocal microscopy (LSCM). We found that fluid-phase macropinocytosis is the only endocytosis pathway used by MENS-3. Once taken up by the cell, complexes that are actively transported by microtubules frequently fuse with lysosomes, while purely diffusing systems do not. Indeed, spatiotemporal image correlation spectroscopy (STICS) clarified that MENS-3 mostly exploit diffusion to move in the cytosol of CHO cells, thus explaining the high TE levels observed. Also, MENS-3 exhibited a marked endosomal rupture ability resulting in extraordinary DNA release. The lipid-dependent and structure-dependent TE boost suggests that efficient transfection requires both the membrane-fusogenic activity of the nanocarrier envelope and the employment of lipid species with intrinsic endosomal rupture ability.

Human cultured fibroblasts were fed with G,, ganglioside species isotopically labeled at C3 of C1 Ssphingosine, or at C3 of C18-sphinganine, or at the sialic acid acetyl group, and with C18-sphingosine and CIS-sphinganine, both labeled at C1. After a lipid pulse the cells were subjected until 7-day chase; measurements were then made of the radioactive products resulting from the administered long-chain base and ganglioside species catabolism and the salvage processes of catabolic fragments. From the data we drew the following conclusions.The G,, species differing in the long-chain base structure were taken up by the cells and metabolized. About 80% of the total catabolic CIS-sphingosine and C18-sphinganine were recycled for the biosynthesis of complex sphingolipids, the rest being degraded.Results obtained by administering ganglioside species of G,, containing radioactive sphingosine or the free radioactive sphingosine to fibroblasts suggested the existence in the cells of two quite separate pools of sphingosine. One pool was the direct result of either the catabolism of radioactive G,, highdensity microdomains or the diffusion of exogenous sphingosine into the cell; this pool was mainly used for the biosynthesis of the G,, species that contain palmitic and stearic acids. The other pool of sphingosine, the cell basal pool, came from the catabolism of radioactive sphingolipids in the recycling of sphingosine, and was used for the biosynthesis of the G,, species that mainly contain very long fatty acid chains, the main fibroblast endogenous species of GD3. Administration of the ganglioside species of G,, containing sphinganine or free sphinganine to fibroblasts yielded the G,, species containing mainly very long-chain fatty acids and sphingosine.These results show the possible existence of a pool of ganglioside-derived sphingosine, quite separate from the cell basal pool of sphingosine, suggesting that sphingosine derived from sphingolipid catabolism is reduced to sphinganine before entering the sphingolipid biosynthetic pathway.Keywords: ganglioside ; biosynthesis ; sphingosine ; sphinganine ; recycling.Gangliosides, sialic acid containing glycosphingolipids that are normal components of plasma membranes [I], are biosynthesized in the Golgi apparatus and degraded in the lysosomes [2] to fragments that are recycled for biosynthetic purposes [3-61. Among the ganglioside catabolic fragments, sphingosine has attracted scientific interest and increasing attention. It has been shown to act as an intracellular effector through the modulation of protein kinase C and other enzyme activities [7-91. Most of our present information arises from the administration of sphingosine to cells, but little is known about a potential role of a pool of sphingosine originated from ganglioside catabolism in modulating cell function.Catabolic sphingosine is partly recycled, but much of it is degraded [6, ; thus it is difficult to determine to what degree this recycling affects the overall sphingolipid turnover. Moreover, the de novo biosy...