A new study reports something strange: When mice with Alzheimer’s disease inhale menthol, their cognitive skills improve. It appears that the chemical compound may stop some of the brain damage commonly associated with the disease.
Notably, researchers noticed a reduction in the interleukin-1-beta (IL-1β) protein, which helps regulate the body’s inflammatory response — a response that may provide natural protection but leads to harm if not properly controlled.
The team behind the study says it shows the possibility that certain scents could be used as therapies for Alzheimer’s disease. If we can identify which odors trigger which brain and immune system responses, we can use them to improve health.
“We focused on the role of the olfactory system in the immune system and central nervous system, and we confirmed that menthol is an immunostimulatory odorant in animal models,” say immunologist Juan José Lasarte of the Center for Applied Medical Research (CIMA) in Spain.
“But surprisingly, we found that brief exposure to this compound over six months prevented cognitive decline in mice with Alzheimer’s disease and, most interestingly, also improved cognitive ability in healthy young mice.”
To have previously observed menthol inhalation boosting the immune response of mice, here the team showed it could also improve the animals’ cognitive abilities, as observed in a series of hands-on tests in the lab.
In mice with Alzheimer’s disease, the course of menthol for a period of six months was sufficient to prevent the mice’s cognitive skills and memory from deteriorating. In addition, menthol seems to push the IL-1β protein back to safe levels in the brain.
When researchers artificially reduced the number of T-regulatory (Treg) cells — known to help control the immune system — some of the same effects were observed, opening up a possible route that future treatments could take.
“Both menthol exposure and Treg cell blockade caused a decrease in IL-1β, a protein that may be behind the cognitive decline seen in these models,” say neuroscientist Ana Garcia-Osta, of CIMA.
“In addition, the specific blockade of this protein with a drug used in the treatment of some autoimmune diseases also improved the cognitive capacity of healthy mice and mice with Alzheimer’s disease.”
Scientists have already made numerous connections between smells and our immune and nervous systems. These relationships are difficult to fully understand, but we know that our olfactory system can strongly influence the brain. Certain smells can trigger certain reactions in the brain, leading to chemical reactions that affect memory, emotion and more.
Indeed, diseases related to the central nervous system – such as Alzheimer’s, Parkinson’s and schizophrenia – are common with loss of smell. This new study adds some promising data, but much more is needed in both humans and mice.
“This study is an important step toward understanding the connection between the immune system, central nervous system and smell,” say immunologist Noelia Casares of CIMA.
“The results suggest that odors and immune modulators may play an important role in the prevention and treatment of Alzheimer’s disease and other diseases related to the central nervous system.”
The research has been published in Frontiers in immunology.