Identification of Acid Hydrolysis Metabolites of the Pimelea Toxin Simplexin for Targeted UPLC-MS/MS Analysis

Toxins (Basel). 2023 Sep 5;15(9):551. doi: 10.3390/toxins15090551.

Abstract

Pimelea poisoning of cattle is a unique Australian toxic condition caused by the daphnane orthoester simplexin present in native Pimelea pasture plants. Rumen microorganisms have been proposed to metabolise simplexin by enzymatic reactions, likely at the orthoester and epoxide moieties of simplexin, but a metabolic pathway has not been confirmed. This study aimed to investigate this metabolic pathway through the analysis of putative simplexin metabolites. Purified simplexin was hydrolysed with aqueous hydrochloric acid and sulfuric acid to produce target metabolites for UPLC-MS/MS analysis of fermentation fluid samples, bacterial isolate samples, and other biological samples. UPLC-MS/MS analysis identified predicted hydrolysed products from both acid hydrolysis procedures with MS breakdown of these putative products sharing high-resolution accurate mass (HRAM) fragmentation ions with simplexin. However, targeted UPLC-MS/MS analysis of the biological samples failed to detect the H2SO4 degradation products, suggesting that the rumen microorganisms were unable to produce similar simplexin degradation products at detectable levels, or that metabolites, once formed, were further metabolised. Overall, in vitro acid hydrolysis was able to hydrolyse simplexin at the orthoester and epoxide functionalities, but targeted UPLC-MS/MS analysis of biological samples did not detect any of the identified simplexin hydrolysis products.

Keywords: Pimelea; acid hydrolysis; fermentation; mass spectrometry; metabolite; plant toxin; rumen; simplexin.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Animals
  • Australia
  • Cattle
  • Chromatography, High Pressure Liquid
  • Chromatography, Liquid / methods
  • Hydrolysis
  • Tandem Mass Spectrometry / methods
  • Thymelaeaceae*
  • Toxins, Biological*

Substances

  • simplexin
  • Toxins, Biological

Grants and funding

This research was funded by Meat & Livestock Australia (MLA), grant number B.GBP.0023—Improving beef production through management of plant toxins. Pimelea plant material used in simplexin isolation was collected during MLA Donor Company (MDC) grant number P.PSH.0900: Pimelea toxicity—finding potential solutions for managing cattle poisoning. Z.H.L. received financial support from an Australian Government Research Training Program (RTP) Scholarship. Portions of this work were presented and published in thesis form in fulfillment of the requirements for the PhD for Z.H.L. from The University of Queensland.