The brain’s balance relies on interactions between nerve, immune, and stem cells. Studies suggest that certain smells can influence brain function and immunity. Research has also linked losing the sense of smell to early signs of Alzheimer’s disease.
A new study aims to investigate the connection between an immunostimulatory odorant, such as menthol, and its impact on the immune system and cognitive capacity in healthy and Alzheimer’s Disease Mouse Models.
Initially, repeated short exposures to menthol odor enhanced the immune response following immunization with ovalbumin. In animal models of Alzheimer’s disease, inhaling menthol has been shown to improve cognitive function.
Brief exposure to this substance can help regulate the immune system and prevent cognitive decline in neurodegenerative diseases. Researchers have found that smelling the aroma reduces levels of IL-1β, a key protein involved in inflammation. Blocking this protein with an existing drug also improved cognitive function in affected mice.
The key cellular mechanism driving Alzheimer’s disease unraveled
Dr. Juan José Lasarte, the director of the Program of Immunology and Immunotherapy at Cima and principal author of the investigation, said, “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 the mice with Alzheimer’s and, what is most interesting, also improved the cognitive ability of healthy young mice.”
In addition, researchers found that blocking T regulatory cells, which suppress immune activity, improved cognitive function in mice with Alzheimer’s. Interestingly, this also boosted cognitive ability in healthy young mice.
Exposure to menthol and blocking T regulatory cells reduced IL-1β, a protein linked to cognitive decline in these models. Additionally, a drug that targets this protein—already approved for use in autoimmune diseases—enhanced cognitive function in both healthy mice and those with Alzheimer’s.
Cognitive function: The power of scent
Dr Noelia Casares, also a researcher at the Immunology and Immunotherapy Program and the first author of the article, said, “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 and other diseases related to the central nervous system.”
Journal Reference:
- Noelia Casares, María Alfaro, Mar Cuadrado-Tejedor, Aritz Lasarte-Cia, Flor Navarro, Isabel Vivas, María Espelosin, Paz Cartas-Cejudo, Joaquín Fernández-Irigoyen, Enrique Santamaría, Ana García-Osta, Juan José Lasarte. Improvement of cognitive function in wild-type and Alzheimer’s disease mouse models by the immunomodulatory properties of menthol inhalation or by depletion of T regulatory cells. Front. Immunol. DOI: 10.3389/fimmu.2023.1130044
