Retention of the cyanobacterial neurotoxin beta-N-methylamino-l-alanine in melanin and neuromelanin-containing cells--a possible link between Parkinson-dementia complex and pigmentary retinopathy.

beta-N-methylamino-l-alanine (BMAA), a neurotoxic amino acid produced by cyanobacteria, has been suggested to be involved in the etiology of a neurodegenerative disease complex which includes Parkinson-dementia complex (PDC). In PDC, neuromelanin-containing neurons in substantia nigra are degenerated. Many PDC patients also have an uncommon pigmentary retinopathy. The aim of this study was to investigate the distribution of (3)H-BMAA in mice and frogs, with emphasis on pigment-containing tissues. Using autoradiography, a distinct retention of (3)H-BMAA was observed in melanin-containing tissues such as the eye and neuromelanin-containing neurons in frog brain. Analysis of the binding of (3)H-BMAA to Sepia melanin in vitro demonstrated two apparent binding sites. In vitro-studies with synthetic melanin revealed a stronger interaction of (3)H-BMAA with melanin during synthesis than the binding to preformed melanin. Long-term exposure to BMAA may lead to bioaccumulation in melanin- and neuromelanin-containing cells causing high intracellular levels, and potentially changed melanin characteristics via incorporation of BMAA into the melanin polymer. Interaction of BMAA with melanin may be a possible link between PDC and pigmentary retinopathy.