Development and Evaluation of an Immuno-MALDI-TOF Mass Spectrometry Approach for Quantification of the Abrin Toxin in Complex Food Matrices.

Sandrine Livet,François Becher,Martin B Dorner,Sylvia Worbs,Brigitte G Dorner,Hervé Volland,Stéphanie Simon,François Fenaille

doi:10.3390/toxins13010052

Abstract

The toxin abrin found in the seeds of Abrus precatorius has attracted much attention regarding criminal and terroristic misuse over the past decade. Progress in analytical methods for a rapid and unambiguous identification of low abrin concentrations in complex matrices is essential. Here, we report on the development and evaluation of a MALDI-TOF mass spectrometry approach for the fast, sensitive and robust abrin isolectin identification, differentiation and quantification in complex food matrices. The method combines immunoaffinity-enrichment with specific abrin antibodies, accelerated trypsin digestion and the subsequent MALDI-TOF analysis of abrin peptides using labeled peptides for quantification purposes. Following the optimization of the workflow, common and isoform-specific peptides were detected resulting in a ~38% sequence coverage of abrin when testing ng-amounts of the toxin. The lower limit of detection was established at 40 ng/mL in milk and apple juice. Isotope-labeled versions of abundant peptides with high ionization efficiency were added. The quantitative evaluation demonstrated an assay variability at or below 22% with a linear range up to 800 ng/mL. MALDI-TOF mass spectrometry allows for a simple and fast (<5 min) analysis of abrin peptides, without a time-consuming peptide chromatographic separation, thus constituting a relevant alternative to liquid chromatography-tandem mass spectrometry.

Highlights

Abrin is a protein toxin contained in the seeds of the plant Abrus precatorius, found in tropical regions [1]
The objective of this work was to widen the scope of the application of the LC-ESIMS/HRMS assay previously reported by our group for abrin identification and quantification in complex matrices [5], taking advantage of matrix-assisted laser desorption/ionization (MALDI)-TOF mass spectrometry (MS)’s simplicity, time efficiency and broader availability
Rapid on-beads trypsin digestion combined with LC-electrospray ionization (ESI)-MS/HRMS was found to be efficient for the release of unique peptides of the toxin following enrichment [13,20]

Summary

Introduction

Abrin is a protein toxin contained in the seeds of the plant Abrus precatorius, found in tropical regions [1]. Abrin and ricin toxins are both composed of A and B-polypeptide chains, which are approximately 30–32 kDa each, resulting in a molecular weight of approximately 60–64 kDa with several N-glycosylation sites Both toxins occur in many isoforms in plants, e.g., abrin-a, abrin-b, abrin-c and abrin-d (sequence similarity ≈78%) or ricin D and ricin E (sequence similarity ≈97%), respectively [4,5]. Liquid chromatography coupled with ESI and tandem mass spectrometry (LC-ESI-MS/MS) was mostly reported for ricin, enabling the identification in several environmental or food matrices at low ng/mL concentrations [8,9,10,11,12,13,14] Along this line, abrin detection and quantification by tandem mass spectrometry at high resolution (LC-ESI-MS/HRMS) was recently reported by our group [5]. Only few MALDI-TOF MS assays have been described for ricin [12,15,16,17], and none for abrin

Objectives

Methods

Results

Conclusion