beta-Methylamino-L-alanine

beta-Methylamino-L-alanine

Names
IUPAC names (2S)-2-Amino-3-(methylamino)propanoic acid[1]
Other names 2-Amino-3-methylaminopropanoic acid
Identifiers
CAS Registry Number	15920-93-1 Y
ChEBI	CHEBI:73169 N
ChEMBL	ChEMBL11488 N
ChemSpider	94816 N
InChI InChI=1S/C4H10N2O2/c1-6-2-3(5)4(7)8/h3,6H,2,5H2,1H3,(H,7,8)/t3-/m0/s1 N Key: UJVHVMNGOZXSOZ-VKHMYHEASA-N N
Jmol-3D images	Image
KEGG	C08291 N
MeSH	alpha-amino-beta-methylaminopropionate
PubChem	105089
SMILES CNC[C@@H](C(=O)O)N
Properties
Molecular formula	C4H10N2O2
Molar mass	118.13 g·mol−1
log P	−0.1
Acidity (pKa)	1.883
Basicity (pKb)	12.114
Related compounds
Related alkanoic acids	Sarcosine Dimethylglycine Glycocyamine Creatine N-Methyl-D-aspartic acid Guanidinopropionic acid Arginine
Related compounds	Dimethylacetamide
Except where noted otherwise, data is given for materials in their standard state (at 25 °C (77 °F), 100 kPa)
N verify (what is: Y/N?)
Infobox references

β-Methylamino-L-alanine, or BMAA, is a non-proteinogenic amino acid produced by cyanobacteria.

Structure and properties

BMAA is a derivative of the amino acid alanine with an aminomethyl group on the side chain. This non-proteinogenic amino acid is classified as a polar base.

Sources and detection

BMAA is produced by cyanobacteria in marine, freshwater and terrestrial environments.^[2][3] In cultured non-nitrogen-fixing cyanobacteria, BMAA production increases in nitrogen depleted medium.^[4] BMAA has been found in aquatic organisms and in plants with cyanobacterial symbionts such as certain lichens, the floating fern Azolla, the leaf petioles of the tropical flowering plant Gunnera, cycads as well as in animals that eat the fleshy covering of cycad seeds, including flying foxes.^[5][6][7][8]

High concentrations of BMAA are present in shark fins.^[9] Consumption of shark fin soup and cartilage pills may therefore pose a health risk.^[10] The toxin can be detected via several laboratory methods, including liquid chromatography, high-performance liquid chromatography, mass spectrometry, amino acid analyzer, capillary electrophoresis and NMR spectroscopy.^[11]

Neurotoxicity

Mechanisms

Although the mechanisms by which BMAA causes motor neuron dysfunction and death are not entirely understood, current research suggests that there are multiple mechanisms of action. Acutely, BMAA can act as an excitotoxin on glutamate receptors such as NMDA, calcium dependent AMPA and kainite receptors.^[12][13] The activation of the metabotropic glutamate receptor 5 is believed to induce oxidative stress in the neuron by depletion of glutathione.^[14]

BMAA may also misincorporate into nascent proteins in place of L-serine, possibly causing protein misfolding and aggregation, both hallmarks of tangle diseases, including Alzheimer's disease, Parkinson's disease, Amyotrophic lateral sclerosis (ALS), progressive supranuclear palsy (PSP), and Lewy body disease. In vitro research has shown that protein association of BMAA can be inhibited in presence of excess L-serine.^[15]

Effects

Degenerative loco-motor diseases have been described in animals grazing on cycad species, fueling interest in a possible link between the plant and the etiology of ALS/PDC. Subsequent laboratory investigations discovered the presence of BMAA. BMAA induced severe neurotoxicity in rhesus macaques, including.^[16]

• limb muscle atrophy
• nonreactive degeneration of anterior horn cells
• degeneration and partial loss of pyramidal neurons of the motor cortex
• behavioral dysfunction
• conduction deficits in the central motor pathway
• neuropathological changes of motor cortex Betz cells

There are reports that low BMAA concentrations can selectively kill cultured motor neurons from mouse spinal cords and produce reactive oxygen species.^[13][17]

Scientists have also found that newborn rats treated with BMAA show a progressive neurodegeneration in hippocampus, including fibril formation, and impaired learning and memory as adults.^[18][19][20] In addition BMAA has been reported to be excreted into rodent breast milk, and subsequently transferred to the suckling offspring, suggesting mothers and cows milk might be other possible exposure routes. ^[19]

Human cases

BMAA is considered a possible cause of the amyotrophic lateral sclerosis/parkinsonism–dementia complex (ALS/PDC) that had an extremely high rate of incidence among the Chamorro people of Guam.^[21] The Chamorro call the condition lytico-bodig.^[22] In the 1950s, ALS/PDC prevalence ratios and death rates for Chamorro residents of Guam and Rota were 50–100 times that of developed countries, including the United States.^[22] No demonstrable heritable or viral factors were found for the disease, and a subsequent decline of ALS/PDC after 1963 on Guam led to the search for responsible environmental agents.^[23] The use of cycad (Cycas micronesica^[24]) seeds in food decreased as that plant became rarer and the Chamorro population became more Americanized following World War II.^[25]

In addition to eating the seeds directly, BMAA may be ingested by humans through biomagnification. Flying foxes, a Chamorro delicacy, may feed on cycad seeds and concentrate the toxin in their flesh. Twenty-four specimens of flying foxes from museum collections were tested for BMAA and BMAA was found in large concentrations in the flying foxes from Guam.^[26]

Studies on human brain tissue of ALS/PDC, ALS, Alzheimer's disease, Parkinson's disease, Huntington's disease and neurological controls indicated that BMAA is present in non-genetic progressive neurodegenerative disease but not in controls or genetic-based Huntington's disease.^{[27][28][29][30]}

There is currently ongoing research into the role of BMAA as an environmental factor in neurodegenerative disease.^[31][32]

Clinical trials

Studying safe and effective ways of reducing levels of BMAA in ALS patients have been goals of clinical trials sponsored by Phoenix Neurological Associates and the Institute for Ethnomedicine.^[33][34]

See also

• Oxalyldiaminopropionic acid, a related toxin

References