Improved quantification of the cyanobacteria metabolite, β-methylamino-l-alanine (BMAA) using HPLC-MS/MS detection of its dansyl chloride derivative referenced to a 15N-labeled internal standard

Analytical Methods Pub Date: 2019-05-22 DOI: 10.1039/C9AY00284G

Abstract

Environmental exposure to the cyanotoxin, β-N-methylamino-L-alanine (BMAA), has been implicated as the etiological agent of a human neurodegenerative disease possessing the combined neuropathologies of amyotrophic lateral sclerosis/parkinsonism-dementia complex (ALS/PDC). However, the hypothesis linking dietary exposure to BMAA in isolated populations to their elevated incidence of ALS/PDC has been criticized due to methodological issues that include a failure to separate BMAA from co-eluting and/or isobaric compounds during quantification. We developed an improved HPLC-MS/MS quantification method for the total fraction of the dansyl chloride (DNS) derivatives of BMAA, 2,4-diaminobutyric acid (DAB), and N-(2-aminoethyl)glycine (AEG). The use of 15N-labelled BMAA as a stable isotope-labeled (SIL) internal standard (15N-BMAA) provides a direct comparison for quantification of total BMAA, and generates a more robust (>20?:?1 peak area) and stable (25.8% vs. 68.2% mean deviation of peak area) MS quantification transition as compared to the deuterated analogue, 2H3-BMAA, used in prior studies. Partial method validation using 15N-BMAA as a SIL internal standard provided high accuracy and precision (R2 > 0.999; S = 0.004) over a wide range of L-BMAA concentrations (0–100 μg g?1 lyophilized material), with improved lower limits of quantification (LLOQ) and detection (LOD) of 22.9 and 2.8 ng g?1 lyophilized material, respectively. BMAA was detected at several sites in the Lower Columbia River (USA) above the LOD, and at concentrations ranging from 23.5 ± 4.5 to 63.3 ± 18.1 ng g?1 lyophilized-material. Use of dansyl chloride derivatization provides a comparable alternative to 6-aminoquinolyl-N-hydroxysccinimidyl carbamate (AQC)-based methods. We note that the use of deuterated SIL standard variants and the derivatization buffer pH used in prior BMAA quantification studies, based on data-dependent acquisition/tandem mass spectrometry methods, may have led to false-negative results, and therefore contributed to the historic disagreement regarding the prevalence and abundance of BMAA.

Graphical abstract: Improved quantification of the cyanobacteria metabolite, β-methylamino-l-alanine (BMAA) using HPLC-MS/MS detection of its dansyl chloride derivative referenced to a 15N-labeled internal standard
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