Identification of the Glycosidase Inhibitors Swainsonine and Calystegine B₂ in Weir Vine (Ipomoea sp. Q6 {aff. calobra}) and Correlation with Toxicity

Abstract

The polyhydroxy alkaloid glycosidase inhibitors swainsonine [1] and calystegine B2 [6] have been identified as constituents of the seeds of the Australian plant Ipomoea sp. Q6 [aff. calobra] (Weir vine) by gas chromatography-mass spectrometry and by their biological activity as inhibitors of specific glycosidases. This plant, which is known only from a small area of southern Queensland, has been reported to produce a neurological disorder when consumed by livestock. The extract of the seeds showed inhibition of alpha-mannosidase, beta-glucosidase, and alpha-galactosidase, consistent with the presence of 1 and alkaloids of the calystegine class. Histological examination of brain tissue from field cases of sheep and cattle poisoned by Weir vine showed lesions similar to those observed in animals poisoned by the swainsonine-containing poison peas (Swainsona spp.) of Australia and locoweeds (Astragalus and Oxytropis spp.) of North America. These results indicate that Weir vine poisoning is an additional manifestation of the induced lysosomal storage disease, mannosidosis, possibly exacerbated by inhibition of the enzymes beta-glucosidase and alpha-galactosidase by calystegine B2. This is the first reported example of a single plant species capable of producing structurally distinct glycosidase inhibitors, namely, alkaloids of the indolizidine and nortropane classes.

Experimental swainsonine poisoning in goats ingesting Ipomoea sericophylla and Ipomoea riedelii (Convolvulaceae)

“…The presence of swainsonine was verified using gas chromatography-mass spectrometry after a portion of the aqueous extract was dried and the residue derivatized by addition of N,O-bis(trimethylsilyl)trifluoroacetamide (BSTFA) and pyridine to convert swainsonine to its timethylsilyl ether derivative. Calystegines were analyzed by gas chromatography-mass spectrometry by the method of Molyneux et al (1995). Dried, ground leaves (1g) were extracted with methanol (MeOH) for 16 hours in a Soxhlet apparatus, and the alkaloidal fraction was purified by ionexchange chromatography on a 5 x 0.5cm column of Dowex 50WX8 (NH 4 + form).…”

Alpha-mannosidosis in goats caused by the swainsonine-containing plant Ipomoea verbascoidea

“…A conservative approach suggests that levels exceeding 0.001% of dry matter are most likely toxic. 23 In the experiments reported herein, it can be estimated that the goat that ingested the dry plant (10 g/kg body weight), with a concentration of 0.017% of swainsonine, ingested 1.7 mg of swainsonine daily. 2,3,7 The toxic effects of calystegines in animals were not determined, but calystegines are inhibitors of glycosides, mainly β-glucosidase, and α-galactosidase.…”

Histopathological lesions in central nervous system of goats poisoned by Ipomoea carnea

“…These results suggest that plant toxicity varies according to the time of the year; it has also been reported by other authors 4 . According to some researchers, levels of swansonine and calystegine superior to 0,001% would be probably toxic 15 . The illness also occurred in goats after consumption of 5 g of green plant per kg body weight per day for 5-107 trial days 2,18,19 .…”