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

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.

Ultrafast protein digestion using an immobilized enzyme reactor following high-resolution mass spectrometry analysis for rapid identification of abrin toxin

“…The identification of abrin protein relies on either antigen recognition using antibodies, such as enzyme-linked immunosorbent assay (ELISA), 12,13 immunochromatography assay (ICA), 14 and electrochemiluminescence (ECL), 15 or sequence characterization by mass spectrometry (MS). 16,17 Antibodybased methods have high sensitivity, but poor specificity and do not discern closely related toxin variants. 18 In contrast, MSbased methods provide direct measurements and characterization of the protein sequence for unambiguous differentiation of toxin types or variants.…”

“…18 In contrast, MSbased methods provide direct measurements and characterization of the protein sequence for unambiguous differentiation of toxin types or variants. A typical MS-based proteomic identification of abrin workflow involves protein hydrolysis and the subsequent detection of resulting peptides by MS. 16,17,19 Enzymatic-based tryptic digestion, which is the most widely used method for protein hydrolysis, has some barriers including the lengthy digestion time, as well as limited availability of free enzymes due to their high costs, poor stability, enzyme auto-digestion, and weak reusability.…”

Introduction to the Toxins Special Issue: “Antibodies for Toxins: From Detection to Therapeutics”

“…As an example, an immunocapture method combined with mass spectrometry detection (MALDI-Tof) has been developed by Livet et al for the detection of abrin in food matrices [ 6 ]. Abrin is a toxin from Abrus precatorius , which is close to ricin in its mechanism of action.…”