Commentary on: Return of the cycad hypothesis - does the amyotrophic lateral sclerosis/parkinsonism dementia complex (ALS/PDC) of Guam have new implications for global health?

The biotoxin BMAA promotes dysfunction via distinct mechanisms in neuroblastoma and glioblastoma cells

Chronic exposure to the Cyanobacteria biotoxin Beta-methylamino-L-alanine (BMAA) has been associated with development of a sporadic form of ALS called Amyotrophic Lateral Sclerosis/Parkinsonism-Dementia Complex (ALS/PDC), as observed within certain Indigenous populations of Guam and Japan. Studies in primate models and cell culture have supported the association of BMAA with ALS/PDC, yet the pathological mechanisms at play remain incompletely characterized, effectively stalling the development of rationally-designed therapeutics or application of preventative measures for this disease. In this study we demonstrate for the first time that sub-excitotoxic doses of BMAA modulate the canonical Wnt signaling pathway to drive cellular defects in human neuroblastoma cells, suggesting a potential mechanism by which BMAA may promote neurological disease. Further, we demonstrate here that the effects of BMAA can be reversed in cell culture by use of pharmacological modulators of the Wnt pathway, revealing the potential value of targeting this pathway therapeutically. Interestingly, our results suggest the existence of a distinct Wnt-independent mechanism activated by BMAA in glioblastoma cells, highlighting the likelihood that neurological disease may result from the cumulative effects of distinct cell-type specific mechanisms of BMAA toxicity.

Presence of the neurotoxin BMAA in aquatic ecosystems: what do we really know?

The neurotoxin β-N-methylamino-l-alanine (BMAA) is suspected to play a role in the neurological diseases amyotrophic lateral sclerosis, Alzheimer’s disease, and Parkinson’s disease. BMAA production by cyanobacteria has been reported and contact with cyanobacteria infested waters or consumption of aquatic organisms are possible pathways to human exposure. However, there is little consensus regarding whether BMAA is present in cyanobacteria or not, and if so, at what concentrations. The aim of this review is to indicate the current state of knowledge on the presence of BMAA in aquatic ecosystems. Some studies have convincingly shown that BMAA can be present in aquatic samples at the µg/g dry weight level, which is around the detection limit of some equally credible studies in which no BMAA was detected. However, for the majority of the reviewed articles, it was unclear whether BMAA was correctly identified, either because inadequate analytical methods were used, or because poor reporting of analyses made it impossible to verify the results. Poor analysis, reporting and prolific errors have shaken the foundations of BMAA research. First steps towards estimation of human BMAA exposure are to develop and use selective, inter-laboratory validated methods and to correctly report the analytical work.

Animal models of BMAA neurotoxicity: a critical review

Of all the molecules reported to have toxicological effects, BMAA (beta-methylamino alanine) stands out as having the most checkered past. In the late 1960's it was reported to be a toxic component of the cycad flour consumed by Chamorros on Guam which caused the high incidence of amyotrophic lateral sclerosis (ALS) in Guam, that was associated with a Parkinson's disease-like dementia complex (ALS-PDC). However, because ALS-PDC is a slow onset disease, manifesting itself as long as 30 years following exposure to the putative neurotoxin, and only acute toxic effects of BMAA were observed in animal studies, interest in BMAA waned. A seminal study by Spencer et al., in 1987 showing neurological impairments with long-term BMAA-fed monkeys revived the hypothesis that BMAA could cause ALS-PDC. However, the amounts of BMAA used in that study were viewed as being the equivalent of a person consuming their body weight of cycad flour every day. Again, the BMAA hypothesis was discarded. Recently a third iteration of the BMAA hypothesis has been proposed. It is based on the discovery of a novel dietary source of BMAA via biomagnification of BMAA in flying foxes, once consumed in great amounts by Chamorros. Also, reports that BMAA can be incorporated into plant and animal proteins, a heretofore unrecognized dietary source of BMAA, further solidified this new hypothesis. However, once again this hypothesis has its detractors and it remains controversial. This manuscript critically evaluates in vivo studies directed at establishing an animal model of BMAA-induced ALS-PDC and their implications for this hypothesis.

Lack of behavioral and neuropathological effects of dietary beta-methylamino-L-alanine (BMAA) in mice

Beta-methylamino-L-alanine (BMAA) is an excitotoxin allegedly involved in ALS-parkinsonism-dementia complex (ALS-PDC), a neurological disorder found in Guam and its surrounding islands, in which motor neuron disease symptoms can present alone or can co-occur with parkinsonism and dementia. Although in vitro experiments have shown BMAA's neurotoxic properties, studies using adult animals and systemic administration which better model the case of environmentally-induced human neurodegenerative diseases have not supported the involvement of BMAA in these disorders. In order to better test the hypothesized role of BMAA in neurodegeneration, we fed adult mice BMAA at a dose (28 mg/kg body weight, daily for 30 days) that reproduces the natural levels and tested the animals with a battery of behavioural tests, the latter including the evaluation of motor coordination, motor neuron-mediated reflexes, locomotion, muscular strength and memory. We also assessed whether BMAA exposure triggers cell death in the central nervous system (CNS) of mice by examining neuronal numbers and glial response in the spinal cord and the brain. No motor, cognitive or neuropathological outcome resulted from this feeding paradigm. Our findings support neither the causal role of BMAA in neurodegeneration nor the specific involvement of this amino acid in ALS-PDC.