Analysis of swainsonine and swainsonine N-oxide as trimethylsilyl derivatives by Liquid Chromatography-Mass Spectrometry and their relative occurrence in plants toxic to livestock

Authors: Gardner, Dale; Cook, Daniel

Submitted to: Journal of Agricultural and Food Chemistry
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 7/20/2016
Publication Date: 7/20/2016
Publication URL: http://handle.nal.usda.gov/10113/5399135
Citation: Gardner, D.R., Cook, D. 2016. Analysis of swainsonine and swainsonine N-oxide as trimethylsilyl derivatives by Liquid Chromatography-Mass Spectrometry and their relative occurrence in plants toxic to livestock. Journal of Agricultural and Food Chemistry. 64(31):6156-6162.

Interpretive Summary: The locoweeds (Astragalus and Oxytropis species) found in the western United States as well as number of other plants species found worldwide contain a toxic alkaloid known as swainsonine. These plants result in significant livestock loses do due chronic intoxication and the resulting wasting disease or locoisim. The toxic alkaloid can exist as the free base alkaloid or in an oxidized form known as swainsonine-N-oxide. Although previously identified as occurring in swainsonine containing plants, the relative amounts of swainsonine and its N-oxide has not been previously determined, thus leaving a question as to the potential importance of the N-oxide in the overall toxicity of the plant. Therefore, a liquid chromatography-mass spectrometry method was developed for the analysis of both swainsonine and its N-oxide and then applied to the analysis of representative samples from a variety of plant species previously known to contain swainsonine. In addition two endophytic isolates that produce swainsonine were also analyzed. The ratio of N-oxide to free base ranged from zero to 0.18 in the samples analyzed. It was concluded that because of the low concentration of swainsonine-N-oxide relative to swainsonine that it likely does not affect the overall toxicity of the various plant samples.

Technical Abstract: A liquid chromatography-mass spectrometry method was developed for the analysis of the indolizidine alkaloid swainsonine and its N-oxide. The method is based on a one step solvent partitioning extraction procedure followed by trimethylsilylation of the dried extract and subsequent detection and quantitation using reversed phase high pressure liquid chromatography-mass spectrometry. There are limited data in the literature concerning the occurrence of swainsonine-N-oxide in plants known to contain swainsonine, and its relative impact on toxicity of the plant material. Thus the concentrations of each were measured in several swainsonine-containing taxa as well as two endophytic isolates that produce swainsonine. In all vegetative samples, swainsonine-N-oxide was detected along with swainsonine. The ratio of N-oxide to free base ranged from 0.009 to 0.18. In seed samples the N-oxide to free base ratio ranged from zero to 0.10. With an expected increased water solubility and rapid elimination in vivo, the low concentration of swainsonine-N-oxide relative to swainsonine indicates that it likely does not affect the overall toxicity of the various plant samples.