A Comparative Study on Three Analytical Methods for the Determination of the Neurotoxin BMAA in Cyanobacteria

Abstract

The cyanobacterial neurotoxin β-N-methylamino-L-alanine (BMAA) has been considered a serious health threat because of its putative role in multiple neurodegenerative diseases. First reports on BMAA concentrations in cyanobacteria were alarming: nearly all cyanobacteria were assumed to contain high BMAA concentrations, implying ubiquitous exposure. Recent studies however question this presence of high BMAA concentrations in cyanobacteria. To assess the real risk of BMAA to human health, this discrepancy must be resolved. We therefore tested whether the differences found could be caused by the analytical methods used in different studies. Eight cyanobacterial samples and two control samples were analyzed by three commonly used methods: HPLC-FLD analysis and LC-MS/MS analysis of both derivatized and underivatized samples. In line with published results, HPLC-FLD detected relatively high BMAA concentrations in some cyanobacterial samples, while both LC-MS/MS methods only detected BMAA in the positive control (cycad seed sarcotesta). Because we could eliminate the use of different samples and treatments as causal factors, we demonstrate that the observed differences were caused by the analytical methods. We conclude that HPLC-FLD overestimated BMAA concentrations in some cyanobacterial samples due to its low selectivity and propose that BMAA might be present in (some) cyanobacteria, but in the low µg/g or ng/g range instead of the high µg/g range as sometimes reported before. We therefore recommend to use only selective and sensitive analytical methods like LC-MS/MS for BMAA analysis. Although possibly present in low concentrations in cyanobacteria, BMAA can still form a health risk. Recent evidence on BMAA accumulation in aquatic food chains suggests human exposure through consumption of fish and shellfish which expectedly exceeds exposure through cyanobacteria.

The neurotoxin BMAA in aquatic systems : analysis, occurrence and effects

“…This pre-column derivatisation has an additional advantage: the derivatised molecule is bigger and more hydrophobic, which facilitates reversed phase LC separation. A disadvantage of optical detection methods is that they are non-selective for BMAA, and therefore risk BMAA misidentification and overestimation [93]. In Box 1.1, the principles of the LC-FLD method using AQC derivatisation are explained.…”

“…When properly applied, LC-MS/MS is more selective than optical detection techniques [58,93]. Although pre-column derivatisation of BMAA is not required for LC-MS/MS analysis, it is often used to enhance reversed phase separation.…”

“…Total BMAA content, irrespective of its original form, is usually obtained by hydrolysis of the total sample (e.g. [93,94]). …”

“…At present, the cause of these differences in BMAA concentrations in cyanobacteria has not been identified yet, although it is very probable that studies that have used the unselective HPLC-FLD (e.g. [33,35,133]) have misidentified BMAA and/or overestimated its concentrations [93].…”

“…The analytical methods used for unambiguous identification of BMAA in the aquatic ecosystem should be sensitive, selective and robust [93,134]. Methods based on tandem mass spectrometry like liquid chromatography coupled to tandem mass-spectrometry (LC-MS/MS) meet these requirements, but these types of analysis require rather specialized and expensive equipment.…”