Table of Contents

  • Assessment of health risks connected with exposure to naturally occurring toxicants in foodstuffs has become an important area for NNT in the recent years. A series of Nordic reports based on the work performed by the Nordic project group on inherent natural toxicants in food plants and mushrooms has been published

  • Since the 1940’s the cause of the highly raised incidence of amyotrophic lateral sclerosis (ALS) and Parkinsons dementia complex (PDC) within the local Chamorro population of Guam and neighboring islands of the south-west Pacific Ocean has been searched for. Even though the incidence now has decreased from its peak in the 1950’s (179/100 000 for men and 61/100 000 for women) to numbers that compared to incidence in the Western world in the 1990s (1.9/100 000) are only a few times greater, the search for the main causative factor is still ongoing. Factors hypothesised and discarded after analysis with scientific scrutiny include hereditary causes, environmental causes, infectious agents, prions, and micronutrient deficiency. None of these have been thought to give the whole answer. The traditional diet was the only factor identified in epidemiological studies to be linked to the disease complex. In particular, the use of flour prepared form cycad seeds as a staple food by the Chamorro population became a topic of discussion in the 1960’s. Since then it has been clearly demonstrated that there is a connection between dietary exposure to cycad and high incidence of ALS-PDC on Guam.

  • Is it possible that the cause of degenerative neurological disease such as amyotrophic lateral sclerosis (ALS), Parkinson dementia and Alzheimers disease could be a dietary exposure to an amino acid not known to occur in proteins? This is a question that has to be tackled by authorities after a suggestion in 2005 that the potentially neurotoxic amino acid BMAA might occur in drinking water.

  • In the aftermath of World War II, U.S. Army physicians assigned to Guam, found the local Chamorro people to be afflicted with a progressive neurodegenerative disease described as amyotrophic lateral sclerosis (ALS) or an ALS-like condition appearing hand-in-hand with an unusual form of Parkinson dementia (PD). The incidence of amyotrophic lateral sclerosis-Parkinson dementia complex (ALS-PDC) was estimated to be 50 to 100 times higher than elsewhere in the world (Zimmerman, 1945; Koerner, 1952; Arnold et al., 1954, Kurland and Mulder, 1954; Hirano et al., 1961a). After recognizing the high incidence of ALS-PDC on Guam, the US National Institute of Neurological Disorders established a registry for cases of motor neuron disease and Parkinson dementia complex on the island Guam in 1956. This registry has been a goldmine for epidemiological studies of the disease. Epidemiological studies focusing on ALSPDC on Guam are summarised in Annex 1 of this report.

  • Because of its content of powerful emetic, teratogenic, and hepatotoxic agents, the raw female gametophyte tissue of cycads can not be consumed. The consumption of only a few unprocessed cycad seeds at one sitting has been reported to result in acute gastrointestinal disturbances (Kurland, 1988). In addition, there are effects of chronic exposure to the raw cycad seeds. As a consequence, the Chamorro people have learnt that the seeds have to be detoxified before they are used.

  • As mentioned in the previous chapters, cycads contain several bioactive compounds that may be responsible alone or in combination for the adverse effects reported in humans and animals consuming cycad plant tissues or products derived thereof. As outlined in chapter 2, cycacin and its active metabolite methylazoxymethanol, was early deleted from the list of candidates responsible for the neurodegenerative disease on Guam. The search for other toxins than cycasin in cycads was succesfull 1967, when BMAA was isolated and described (Vega and Bell, 1967). The neurotoxic activity of this compound was confirmed by administering BMAA to chickens and young rats. In this study only the L-isomer produced toxic effects (Vega et al, 1968). As a consequence of BMAA being identified in cycad seeds, the hypothesis that this compound was responsible for the high incidence of ALS-PDC in Guam was presented, and this hypothesis stimulated further studies on BMAA. Annex 2 summarizes the in vivo toxicity studies conducted with BMAA.

  • BMAA, or ß-N-methylamino-L-alanine (Figure 5), is an amino acid with a secondary amine in the side chain. The substance is also called a- amino-ß-methylamino propionic acid. Figure 5, in addition to BMAA, presents some amino acids similar in structure to BMAA.

  • As pointed out earlier in this report, BMAA was originally detected in cycads when the investigators searched for other toxic non-protein amino acids. In subsequent studies, Dossaji and Bell (1973) noted that slightly higher amounts of BMAA could be found in cycad seeds and leaves when the materials were hydrolysed before extraction and analysis, possibly indicating that the compound might occur both in free and bound form. However, these possibilities were not seriously explored until thirty years later when Murch et al. (2004a) actually claimed that the compound occur also in bound form. As pointed out in Chapter 5, the analytical techniques used in these studies may be questioned. If BMAA is confirmed to occur bound to proteins, there is no proof that it is incorporated into proteins. Its appearance in proteins may also be the result of postsynthetic modification of protein amino acids already built into the polypeptides. However, no alanine-methylating activity has been identified in cycads.

  • Because of the difficulty to explain a “slow toxin”-action of watersoluble free BMAA molecules on the neurological system, Murch et al. (2004a) investigated the possibility of biomagnification of BMAA and leakage from bound forms of BMAA. They found that axenic cultures of cyanobacteria, initially isolated from collaroid cycad roots, contained approximately 240 times more bound BMAA than free BMAA, 72 as compared to 0.3 mg/kg bacteria. Collaroid roots of the cycad Cycas micronesica contained 2 mg BMAA per kg root in bound form. As noncollaroid roots had no symbiosis with cyanobacteria and contain no BMAA, it seems as though BMAA has to leak out from the cyanobacteria and be taken up by the collaroid cycad roots. When other cycad tissues were investigated the results pointed to that leaf tissue contained 738 mg BMAA per kg tissue, outer seed layers 48 mg BMAA per kg tissue, the sarcotesta 89 mg per kg tissue, and the female gametophyte 81 mg BMAA per kg tissue. These observations do not only suggest that the total BMAA exposure may be higher than that indicated by the amount of free BMAA, but also that the amount of BMAA found may increase going from cyanobacteria to cycads.

  • In 2003 Cox and coworkers found BMAA to be present in cyanobacteria of the strain Nostoc, which live in symbiosis with the coralloid roots of the cycad (Cox et al, 2003). Pursuing this line of research they continued to analyse presence of BMAA in 30 different species or strains of freeliving cyanobacteria and concluded that BMAA was present in free form in 27 of these species or strains in amounts varying from 3 – 6478 microg/ g dry weight, and in bound form in 24 species or strains in amounts varying from 4- 5415 microg/g dry weight (Cox et al, 2005). According to Cox (2005) the presence of BMAA in cycads could be explained by the symbiosis these plants have with cyanobacteria. It was proposed that BMAA is produced by cyanobacteria infecting the coralloid roots of cycad trees as symbionts. BMAA is then transferred to the cycad where higher concentrations can be reached. The accumulation when going from one trophic level to another could be 100-fold. The biomagnification of BMAA through the chain cyanobacteria – cycads – flying foxes – humans could be the explanation for the high incidence of ALS-PDC on Guam and neighboring islands, according to Cox et al. (2005).

  • A review of information available in published literature supports a true connection between cycad exposure and the development of ALS-PDC on the island of Guam. However, it is not clear which the compound(s) in the cycad is that is responsible for the development of neurological disease.

  • To be able to draw conclusions on the possible connection between BMAA and the development of degenerative neurological disease we have the following recommendations

  • Steele and Guzman (1987) observed that the ALS/PD complex only occurred where cycad trees grow and where people use its seeds for food and medicine. They provided an explanation for the rarity of the disease on the island of Saipan. During Spanish and German administrations, before 1914, cycad trees were abundant and people used cycad flour in the same way as the people of Guam and Rota did. When the Japanese occupied Saipan in 1914 they cleared large parts of the island for sugar plantation and by the 1920s most of the cycad forests had been cut down. When neurological surveillance teams visited Saipan in the 1950s cycad flour had not been used on the island for 30 years. At that time ALS was less common there than on Guam or Rota, and Saipanese people that suffered the disease were born before 1917. Another fact that is related is that the disease was not seen in Filipinos who arrived on Guam after 1950, when the flour ceased to be a staple food. Interwievs that Steele and Guzman conducted suggested that familial aggregation of patients could relate to differences between families in the method of preparing the cycad seeds. There appeared to be considerable differences in regard to the soaking process and the number of water changes between families (Steele and Guzman, 1987).

  • Annex 2 includes summaries of in vivo toxicological studies performed with preparations of cycad, in Annex 2 table 1, and with BMAA, in Annex 2 table 2