A swainsonine survey of North American Astragalus and Oxytropis taxa implicated as locoweeds

Abstract

Swainsonine, an indolizidine alkaloid with significant physiological activity, is an α-mannosidase and mannosidase II inhibitor that causes lysosomal storage disease and alters glycoprotein processing. Swainsonine is found in a number of plant species worldwide, and causes severe toxicosis in livestock grazing these plants, leading to a chronic wasting disease characterized by weight loss, depression, altered behavior, decreased libido, infertility, and death. Swainsonine has been detected in 19 Astragalus and 2 Oxytropis species in North America by thin layer chromatography, gas chromatography-mass spectrometry, liquid chromatography-mass spectrometry and a jack bean α-mannosidase inhibition assay. In addition, 5 species in North America are presumed to contain swainsonine based upon reports from field cases. Many of these plant species have not been analyzed for swainsonine using modern instrumentation such as gas or liquid chromatography coupled with mass spectrometry. To provide clarification, 22 Astragalus species representing 93 taxa and 4 Oxytropis species representing 18 taxa were screened for swainsonine using both liquid chromatography-mass spectrometry and gas chromatography-mass spectrometry. Swainsonine was detected in 48 Astragalus taxa representing 13 species and 5 Oxytropis taxa representing 4 species. Forty of the fifty-three swainsonine-positive taxa had not been determined to contain swainsonine previously using liquid or gas chromatography coupled with mass spectrometry. The list of swainsonine-containing taxa reported here will serve as a reference for risk assessment and diagnostic purposes.

A Screen for Swainsonine in Select North American Astragalus Species

“…Previously we reported that swainsonine was detected in 13 North American Astragalus species of which eight belong to four taxonomic sections, the Densifolii , Diphysi , Inflati , and Trichopodi ( Table ) . An additional 31 species represented by 38 taxa belonging to these four taxonomic sections were screened for swainsonine.…”

“…Swainsonine concentrations in locoweeds have been shown to vary among species, varieties, and populations . Some species may or may not contain swainsonine simply due to the presence or absence of the endophyte .…”

“…), an indolizidine alkaloid, was first identified as the bioactive principle of a neurologic disease in Swainsona canescens , a legume native to Australia . Swainsonine was later identified as the active principle in Astragalus lentiginosus in the United States and subsequently other Astragalus and Oxytropis species . Locoweeds are Astragalus and Oxytropis s pecies that cause locoism and contain swainsonine.…”

“…Rupert Barneby 's taxonomic treatment, Atlas of North American Astragalus , divided over 350 Astragalus species into 93 different sections based upon morphological characters . Swainsonine has been detected in 13 North American Astragalus species of which eight belong to taxa in four taxonomic sections, the Densifolii , Diphysi , Inflati , and Trichopodi ( Table ). These sections belong to two larger groups representing several morphologically related species, the Pacific Piptolobi and the small flowered Piptolobi.…”

“…Herbarium specimens provide a well curated resource to quickly screen several specimens of multiple species and have been successfully used in screening other Astragalus and Oxytropis species for the alkaloid swainsonine . A modified swainsonine extraction method that allows for the rapid extraction of hundreds of samples simultaneously has been reported .…”