Alzheimer’s is a progressive disease that impairs memory and other brain functions. The most common form of dementia, it currently affects some 6 million Americans, with that number expected to rise to nearly 13 million by 2050. It’s responsible for about 33% of senior deaths each year, more than breast and prostate cancers combined. And it costs the country about $345 billion annually, with that number expected to rise to over $1 trillion by 2050.
While there is no known cure for Alzheimer’s, scientists in Pamplona, Spain who were researching the link between the olfactory system and immunity may have discovered a promising new therapy. “We have focused on the olfactory system’s role in the immune and central nervous systems, and we have confirmed that menthol is an immunostimulatory odor in animal models. But surprisingly, we observed that short exposures to this substance for six months prevented cognitive decline in mice with Alzheimer’s,” says Dr. Juan José Lasarte, director of the Immunology and Immunotherapy Program at Cima University of Navarra and the study’s principal author.
Several previous studies have noted the immunomodulatory and neurological effects of different odorants, and other research has shown a correlation between the loss of the sense of smell and the appearance of the first symptoms of Alzheimer’s disease. With those results in mind, the team from Cima University tested the effects of regular exposure to menthol on several groups of mice, including young, healthy mice and mice that had been bred to have recognized equivalents of Alzheimer’s disease.
The mice were exposed to vaporized menthol for eight cycles of 15 minutes of inhalation (one cycle every three hours) per day over periods from one week to six months. The scientists then evaluated the cognitive effects on the mice in several ways, including contextual fear conditioning and direct examinations of brain tissue.
Their results showed that repeated short exposures to menthol odor prevented the cognitive deterioration typical of Alzheimer’s disease. When analyzing exactly how it was able to do this, the researchers observed that when smelling this aroma, the mice saw reduced levels of interleukin-1-beta (IL-1b), a critical protein mediating the inflammatory response that may be related to cognitive decline. And when researchers also inhibited this protein with a drug approved for the treatment of some autoimmune diseases, they were again able to improve cognitive ability in the diseased mice.
“This study is an important step toward understanding the connection between the immune system, the central nervous system, and smell, as the results suggest that odors and immune modulators may play an important role in the prevention and treatment of Alzheimer’s,” said Dr. Noelia Casares, another of the study’s authors.
In their conclusion, the team from Cima University noted that while their results need to be confirmed by further research, this study opens the door to developing promising new therapies based on stimulating and training the olfactory system to prevent or alleviate the symptoms of Alzheimer’s and other diseases of the central nervous system.