A potent inhibitor of α-mannosidase was isolated from Swainsona canescens. The inhibitor was shown to be an indolizidinetriol by spectroscopic techniques and the relative stereochemistry was defined as 8aβ-indolizidine-lα,2α,8β-triol.

An indolizidine alkaloid (swainsonine) was isolated from the plant Swainsona canescens. Swainsonine is a specific and potent inhibitor of alpha-mannosidase (EC 3.2.1.24) and when administered to animals produces a phenocopy of the genetically based lysosomal storage disease, mannosidosis. Evidence is presented to suggest that swainsonine is a reversible active site-directed inhibitor of lysosomal alpha-mannosidase.

Swainsonine, an indolizidine alkaloid, inhibits the processing ofasparagine-linked glycoproteins in both cell-free extracts and animal cells in culture. Thus, in a liver particulate enzyme preparation, swainsonine at 0.1-1.0 FM inhibited the mannosidase that releases [3H]mannose from a high mannose glycopeptide but only slightly inhibited the release of glucose from a glucose-labeled glycopeptide. MDCK and Chinese hamster ovary cells in culture incorporate [2-3H]mannose and [6-3H]-glucosamine into both high mannose and complex types ofoligosaccharides. When these cells were incubated with swainsonine and then labeled with mannose or glucosamine, there was a dramatic decrease in the amount oflabel in the complex type ofglycopeptide and a substantial increase in the radioactivity in the high mannose type. This change was monitored by the increase in radioactivity that became susceptible to digestion by endoglucosaminidase H with increasing concentrations of swainosine. The endoglucosaminidase H-released oligosaccharide(s) from swainsonine-treated cells was larger and more homogenous than that from controls and eluted from Bio-Gel P4 at the position of Man9GlcNAc. Several tissue culture cell lines were grown in the presence of swainsonine to determine its effect on cell surface glycoproteins. Cells grown in the alkaloid showed an increased capacity to bind Escherichia coli B886, a bacterium that binds to high mannose glycoproteins. These cells also showed an increasing binding of [3H]concanavalinA.During the synthesis of the oligosaccharide portion of asparagine-linked glycoproteins, a Glc3Man9GlcNAc2 oligosaccharide is transferred from its dolichol derivative to the protein (1). This newly formed glycoprotein is apparently the precursor of both the high mannose and the complex types ofoligosaccharide and undergoes a number ofprocessing or trimming reactions to form these oligosaccharides. These reactions result in the removal of all three glucose residues and a number of mannose units (3). Several enzymes having glucosidase and mannosidase activity have been described in various membrane fractions (4-9). While the mannose residues are being removed, the sugars that characterize the complex oligosaccharides are added from the appropriate sugar nucleotide donors to form the trisaccharide structures, NeuNAc -* galactose --GlcNAc, linked to the mannose core (10).In this paper, we describe a new inhibitor, swainsonine, that blocks the processing of asparagine-linked glycoproteins. Swainsonine is an indolizidine alkaloid isolated from the plant Swainsona canescens (11). The compound has been shown to inhibit lysosomal a-mannosidase and to produce symptoms of a-mannosidosis in cattle that eat the plant (12). We also show that this alkaloid inhibits the a-mannosidase involved in glycoprotein processing and therefore leads to an increase in high mannose oligosaccharides and a decrease in complex types at the cell surface.EXPERIMENTAL PROCEDURES Studies in Cell-Free Systems. The effect of swainsonine on neutral a-m...

Ingestion of Swainsona spp. by grazing livestock results in a chronic disease characterized by neurological disturbances and intense vacuolation of cells in most organs. Experiments were carried out using Swainsona canescens and evidence is presented to show that tissues from affected animals contain high levels of mannose-rich oligosaccharides and that the plant contains an inhibitor of lysosomal alpha-mannosidase. It is concluded that ingestion of Swainsona induces a lysosomal storage disease, biochemically and morphologically similar to genetically determined mannosidosis. The role of this process in relation to Swainsona toxicosis is discussed.

The glucuronic acid analogue of 1‐deoxynojirimycin, 2(S)‐carboxy‐3(R), 4(R), 5(S)‐trihydroxypiperidine, recently isolated from seeds of Baphia racemosa, is a novel specific inhibitor of human liver β‐D‐glucuronidase and α‐L‐iduronidase. No other glycosidases are inhibited. The inhibition of β‐D‐glucuronidase is competitive, with a K i of 8 × 10−5 M and is pH‐dependent. This inhibitor may be useful to induce a mucopolysaccharidosis or to investigate the function of microsomal β‐D‐glucoronidase.