Dietary neurotoxin linked with neurologic disease

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Researchers believe they now know how the neurotoxic amino acid BMAA, found in seeds of the cycad tree native to Guam, may eventually cause neurodegenerative disease in the native population after a long latent period.

The high rate of amyotrophic lateral sclerosis (also known as “Lou Gehrig’s disease") Parkinsonism dementia complex (ALS/PDC) among the Chamorro people of the Mariannas Islands has mystified researchers for over five decades,” Dr. Paul Alan Cox of the Institute for Ethnobotany at the National Tropical Botanical Gardens in Kalaheo, Hawaii, told Health News Online. 

Previously, he and his colleagues found that BMAA, as a free amino acid, is passed up the food chain in Guam.

“BMAA accumulates at high levels in cycad seeds, which are eaten by flying foxes, a traditional favorite of Chamorro feasts,” Dr. Cox noted. “BMAA concentrations increase 10,000-fold from cyanobacteria to flying foxes. So when the Chamorro people ate flying foxes, they unwittingly ingested massive quantities of BMAA.”

According to a report in the Early Edition of the Proceedings of the National Academy of Science, BMAA occurs not only as a free amino acid in the Guam ecosystem but also in a protein-bound form. In this form, it accumulates in living tissues and is subsequently released into brain tissues during digestion and protein metabolism.

The discovery that protein-bound neurotoxic BMAA “accumulates in the body as a neurotoxic reservoir, slowly trickling out over years and decades as proteins are metabolized...may account for the observed latency of ALS/PDC in Chamorro people,” Cox explained.

Last year in PNAS, his group reported finding BMAA in brain tissue of Chamorros who died of ALS/PDC but not in brain tissue of patients who did not eat a traditional Chamorro diet and who died of causes unrelated to neurodegeneration.

This week in PNAS, they report finding protein-bound BMAA in brain tissue from six Chamorro patients with neurological disease, one of two Chamorros who had not been diagnosed with neurodegenerative disease as well as in eight of nine brain tissue samples from Canadian patients with Alzheimer’s disease.

“At this point, our results in Alzheimer’s patients are really too preliminary and the sample size too small to say much other than more work is needed,” Cox emphasized.

He did say, however, that “prior to our work, BMAA was known to come only from cycads, so our finding that it is produced by cyanobacteria, which are global in their distribution suggests that there could be BMAA exposures outside of Guam.”

Proceedings of the National Academy of Science USA Early Edition 2004.

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