High-performance liquid chromatography analysis of ganglioside carbohydrates at the picomole level after ceramide glycanase digestion and fluorescent labeling with 2-aminobenzamide.

The functional importance of glycolipids has emphasized the need for more sensitive methods of detection, characterization, and quantification than has often been possible using traditional thin-layer chromatographic techniques. We describe the use of ceramide glycanase and HPLC to identify and quantify gangliosides in which the carbohydrate is in Glcbeta1--> linkage with ceramide. Detection of released carbohydrate was by fluorescent labeling with 2-aminobenzamide at the reducing terminal prior to HPLC analysis. Under the conditions described, ceramide glycanase hydrolyzed all of the common gangliosides studied, offering a broad spectrum of specificity. Release and detection of carbohydrate were linear over a wide range (over two orders of magnitude) of micromolar glycolipid substrate concentrations. Use of an N-linked glycan as an internal standard allowed accurate quantification and a recovery of 93% was achieved. The method additionally maintained the sensitivity (chromatographic peaks containing 1 pmol were readily detected from tissue samples) and comparable resolution to related assays. This was shown by the separation, not only of isomeric carbohydrates from the "a" and "b" series, but also of ganglioside carbohydrate differing only by the presence of either N-acetyl- or N-glycolylneuraminic acid. Application of the method to neutral glycosphingolipids and to tissue samples, including 10-microl quantities of plasma, is illustrated. Glycan structures were confirmed by exoglycosidase digestion and/or matrix-assisted laser desorption/ionization mass spectrometry.

Extensive glycosphingolipid depletion in the liver and lymphoid organs of mice treated with N-butyldeoxynojirimycin.

The imino sugar N-butyldeoxynojirimycin is an inhibitor of the ceramide-specific glucosyltransferase that catalyzes the first step in glycosphingolipid biosynthesis. It results in extensive glycosphingolipid depletion in cells treated in vitro, without causing toxicity. However, we currently do not know the degree to which glycosphingolipids can be depleted in vivo in a mammalian species. We have therefore administered N-butyldeoxynojirimycin long term to young mice and have found that glycosphingolipid levels are reduced (50-70%) in all tissues examined, without resulting in any overt pathology. When the lymphoid tissues from these mice were examined, they were found to be 50% acellular relative to non-lymphoid tissues. These data implicate a role for glycosphingolipids in the biology of the immune system or indicate an additional as yet unknown activity of N-butyldeoxynojirimycin. Extensive glycosphingolipid depletion resulting from N-butyldeoxynojirimycin administration is therefore well tolerated in adult mice, and this compound may be in an invaluable tool for probing glycosphingolipid functions in vivo. In addition, this drug may be effective in clinical situations where glycosphingolipid depletion would be desirable, such as the in the treatment of the human glycosphingolipidoses.

The solution NMR structure of glucosylated N-glycans involved in the early stages of glycoprotein biosynthesis and folding.

Glucosylated oligomannose N-linked oligosaccharides (Glc(x)Man9GlcNAc2 where x = 1-3) are not normally found on mature glycoproteins but are involved in the early stages of glycoprotein biosynthesis and folding as (i) recognition elements during protein N-glycosylation and chaperone recognition and (ii) substrates in the initial steps of N-glycan processing. By inhibiting the first steps of glycan processing in CHO cells using the alpha-glucosidase inhibitor N-butyl-deoxynojirimycin, we have produced sufficient Glc3Man7GlcNAc2 for structural analysis by nuclear magnetic resonance (NMR) spectroscopy. Our results show the glucosyl cap to have a single, well-defined conformation independent of the rest of the saccharide. Comparison with the conformation of Man9GlcNAc2, previously determined by NMR and molecular dynamics, shows the mannose residues to be largely unaffected by the presence of the glucosyl cap. Sequential enzymatic cleavage of the glucose residues does not affect the conformation of the remaining saccharide. Modelling of the Glc3Man9GlcNAc2, Glc2Man9GlcNAc2 and Glc1Man9GlcNAc2 conformations shows the glucose residues to be fully accessible for recognition. A more detailed analysis of the conformations allows potential recognition epitopes on the glycans to be identified and can form the basis for understanding the specificity of the glucosidases and chaperones (such as calnexin) that recognize these glycans, with implications for their mechanisms of action.

Prevention of lysosomal storage in Tay-Sachs mice treated with N-butyldeoxynojirimycin.

The glycosphingolipid (GSL) lysosomal storage diseases result from the inheritance of defects in the genes encoding the enzymes required for catabolism of GSLs within lysosomes. A strategy for the treatment of these diseases, based on an inhibitor of GSL biosynthesis N-butyldeoxynojirimycin, was evaluated in a mouse model of Tay-Sachs disease. When Tay-Sachs mice were treated with N-butyldeoxynojirimycin, the accumulation of GM2 in the brain was prevented, with the number of storage neurons and the quantity of ganglioside stored per cell markedly reduced. Thus, limiting the biosynthesis of the substrate (GM2) for the defective enzyme (beta-hexosaminidase A) prevents GSL accumulation and the neuropathology associated with its lysosomal storage.