How the Neurotoxin β-N-Methylamino-l-Alanine Accumulates in Bivalves: Distribution of the Different Accumulation Fractions among Organs.

Alexandra Lepoutre,Miquel Lürling,Alain Geffard,A J Zweers,Elisabeth J Faassen,Emilie Lance

doi:10.3390/toxins12020061

Abstract

The environmental neurotoxin β-methylamino-l-alanine (BMAA) may represent a risk for human health. BMAA accumulates in freshwater and marine organisms consumed by humans. However, few data are available about the kinetics of BMAA accumulation and detoxification in exposed organisms, as well as the organ distribution and the fractions in which BMAA is present in tissues (free, soluble bound or precipitated bound cellular fractions). Here, we exposed the bivalve mussel Dreissena polymorpha to 7.5 µg of dissolved BMAA/mussel/3 days for 21 days, followed by 21 days of depuration in clear water. At 1, 3, 8, 14 and 21 days of exposure and depuration, the hemolymph and organs (digestive gland, the gills, the mantle, the gonad and muscles/foot) were sampled. Total BMAA as well as free BMAA, soluble bound and precipitated bound BMAA were quantified by tandem mass spectrometry. Free and soluble bound BMAA spread throughout all tissues from the first day of exposure to the last day of depuration, without a specific target organ. However, precipitated bound BMAA was detected only in muscles and foot from the last day of exposure to day 8 of depuration, at a lower concentration compared to free and soluble bound BMAA. In soft tissues (digestive gland, gonad, gills, mantle and muscles/foot), BMAA mostly accumulated as a free molecule and in the soluble bound fraction, with variations occurring between the two fractions among tissues and over time. The results suggest that the assessment of bivalve contamination by BMAA may require the quantification of total BMAA in whole individuals when possible.

Highlights

The environmental toxin β-Methylamino-l-alanine (BMAA) is a non-protein amino acid that may be involved in the development of neuro-degenerative pathologies such as the ALS-PDC syndrome [1,2,3]
In soft tissues, no organ appeared to stand out from the others in terms of BMAA concentration during the exposure or the depuration, as no significant differences in total BMAA concentration were observed between tissues during both periods (Kruskal–Wallis test, p > 0.05)
The study of the BMAA organ distribution within D. polymorpha and of the dynamics of its different accumulation fractions showed that BMAA was found in all tissues from the first day of exposure to the 21st day of depuration, without any specific target organ

Summary

Introduction

The environmental toxin β-Methylamino-l-alanine (BMAA) is a non-protein amino acid that may be involved in the development of neuro-degenerative pathologies such as the ALS-PDC syndrome (amyotrophic lateral sclerosis-parkinsonism-dementia) [1,2,3]. This environmental toxin is able to induce: (i) excitotoxicity by interacting with glutamate receptors in presence of bicarbonate at physiological concentrations, (ii) a dysregulation of the cellular protein homeostasis, and (iii) an inhibition of the cysteine/glutamate antiporter, leading to a potential oxidative stress [4]. The neurotoxin may be biomagnified in marine [16] and continental food webs [17]

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Conclusion