A University of Miami Miller School of Medicine neurotoxicologist has found that exposure to toxins from blue-green algae leads to neurodegeneration and increased expression of gene markers in dolphin brains, similar to the changes found in humans with Alzheimer’s disease and related dementia.
“Dolphins are well-regarded sentinels for toxin exposure,” said David A. Davis, Ph.D., research assistant professor of neurology and associate director of the Brain Endowment Bank at the Miller School. “They can accumulate both methylmercury and β-N-methylamino-l-alanine (BMAA), a toxin found in blue-green algae that has been linked to human neurodegenerative disease. In our latest study, both gene expression and the severity of neuropathology were amplified in dolphins with the highest toxin levels.”
Dr. Davis is the lead author of a collaborative study, “BMAA, Methylmercury, and Mechanisms of Neurodegeneration in Dolphins: A Natural Model of Toxin Exposure,” published recently in the journal Toxins. Miller School coauthors are Suzanna Garamszegi, manager, Research Laboratory; Patrick D. Dooley, HTL (ASCP), senior histotechnologist; Dylan W. McLean, undergraduate student; and Deborah C. Mash, Ph.D., professor emeritus of neurology and molecular and cellular pharmacology.
For the study, the Miller School researchers examined brain tissues from seven short-beaked common dolphins (Delphinus delphis) that were stranded and euthanized in Massachusetts in 2012. It follows a 2019 study led by Dr. Davis that showed that dolphins can accumulate neurotoxins in the brain. “We took the same set of dolphin brain tissues and did a more extensive analysis comparing the level of toxins to human Alzheimer’s brains with the same toxins,” he said. “We found the dolphin brains possessed hallmarks of Alzheimer’s disease, including far more neurofibrillary tangles and amyloid beta plaques, suggesting a possible association between toxin exposure and neuropathology.”
Humans can be exposed to both methylmercury and BMAA, said Dr. Davis. Methylmercury is found concentrated in large marine predators, such as swordfish, tuna and sharks, as well as dolphins. “When ingested with seafood, this toxin causes neurons to die and can lead to a form of dementia in humans,” he said.
Chronic dietary exposure to BMAA has been linked to a form of amyotrophic lateral sclerosis/Parkinson dementia complex (ALS/PDC) in indigenous residents of the Pacific island of Guam. Since BMAA has been documented in diverse ecosystems around the world, exposure of marine mammals and humans to this toxin is a global concern, he added.
“The links between chronic dietary exposure to environmental toxins and progressive neurodegenerative disease continue to accumulate,” Dr. Davis said. “This study indicates eating foods high in methylmercury and BMAA toxins may increase the risk for developing neurodegenerative disease.”