Menthol Aroma as a Therapeutic Agent for Improving Cognitive Abilities in Alzheimer’s

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Alzheimer’s disease is a progressive neurodegenerative disorder characterized by the accumulation of beta-amyloid plaques and tau protein tangles in the brain. The accumulation of these protein deposits leads to the death of neurons, resulting in cognitive and memory impairments. One of the key inflammatory cytokines involved in Alzheimer’s disease pathogenesis is interleukin-1-beta (IL-1b). High levels of IL-1b are observed in the brains of Alzheimer’s patients, and they are associated with disease progression. Hence, reducing the levels of IL-1b in the brain is a promising therapeutic approach for Alzheimer’s disease.

Aromatherapy is a complementary therapy that involves the use of essential oils derived from plants for therapeutic purposes. The essential oils are obtained by distillation, and they contain a complex mixture of volatile compounds with pharmacological properties. Several studies have shown that some essential oils possess anti-inflammatory properties, which can help reduce the levels of IL-1b in the brain.

One of the essential oils that have been extensively studied for its anti-inflammatory properties is lavender oil. Lavender oil is derived from the flowers of the lavender plant, and it has been shown to possess potent anti-inflammatory effects. A study published in the journal Life Sciences demonstrated that inhalation of lavender oil reduced the levels of IL-1b in the brain of rats. The study also showed that lavender oil reduced the expression of genes involved in inflammation and oxidative stress.

Another essential oil that has been shown to possess anti-inflammatory properties is frankincense oil. Frankincense oil is derived from the resin of the Boswellia tree, and it has been used for centuries in traditional medicine for its anti-inflammatory and analgesic properties. A study published in the Journal of Ethnopharmacology demonstrated that frankincense oil reduced the levels of IL-1b in the brain of mice. The study also showed that frankincense oil reduced the activation of microglial cells, which are immune cells involved in neuroinflammation.

In addition to lavender and frankincense oil, several other essential oils have been shown to possess anti-inflammatory properties, including peppermint oil, eucalyptus oil, and ginger oil. These oils have been shown to reduce the levels of IL-1b in vitro and in animal models of inflammation.

While the anti-inflammatory properties of essential oils are promising, more research is needed to determine their efficacy in humans. Clinical trials are needed to evaluate the safety and effectiveness of aromatherapy in reducing the levels of IL-1b in the brain of Alzheimer’s patients. Moreover, it is important to note that aromatherapy should not be used as a standalone therapy for Alzheimer’s disease, but rather as a complementary therapy to conventional treatments.

A new research ….

The physiological homeostasis of the brain relies on the complex interactions among various immune cells, including microglia and astrocytes, peripheral immune cells such as T cells, natural killer (NK) cells, and macrophages, as well as neurons and neural precursor cells.

Activation of the immune system, triggered by infections or chronic stressful conditions, can have direct effects on memory, neural plasticity, and neurogenesis.

While inflammation initially leads to sickness behavior and infiltration of peripheral immune cells into the central nervous system (CNS), accumulating research suggests that neuroimmune interactions primarily serve beneficial functions in maintaining nervous system homeostasis. This research investigates the potential role of the olfactory system in the immune system and its impact on cognitive function.

Previous studies have reported the immunomodulatory and neurological effects of odorants. In a preliminary experiment, menthol was identified as an immunostimulatory odor in mice. Further confirmation of this finding revealed that exposure to menthol enhances the cognitive capacity of healthy young mice.

Conversely, impairment of olfaction induced by MTZ treatment had a negative impact on cognitive capacity, as measured by fear conditioning tests.

The study also observed that the cognitive improvement induced by menthol was associated with a reduction in the expression of pro-inflammatory cytokines IL-6 and IL-1β, as well as CD3 mRNA in the brain cortex. On the other hand, MTZ treatment had the opposite effect.

The role of cytokines such as IL-1β and IL-6 in learning and memory is still debated, with evidence supporting both negative and positive effects. Impairment of cognitive tasks in mice deficient in IL-1R1, IL-6, or TNFR2 underscores the importance of cytokine signaling in maintaining homeostatic behavior.

Interestingly, IL-1β and IL-6 are upregulated in neurodegenerative disorders like Alzheimer’s disease (AD) and are associated with cognitive decline.

Inhibitors targeting IL-1R1, IL-1β, or IL-6 have shown promise as therapeutic options in CNS diseases. Treatment with anakinra, an IL-1β inhibitor, improved cognitive capacity in healthy mice and demonstrated significant improvement in cognitive capacity in AD mouse models.

Similar observations were made in a previous study using an anti–IL-1R blocking mAb in another AD mouse model. These findings suggest that IL-1β inhibitors or treatments modulating its expression may have beneficial effects in CNS diseases like AD. Additionally, other cytokines, including IFN-γ, may play a crucial role in cognition and behavior, making them potential targets for modulation in cognitive decline.

The study also highlighted the connection between the immune system and cognitive capacity by demonstrating impaired fear-conditioning learning in highly immunosuppressed NSG mice. Depletion of regulatory T cells (Treg) resulted in improved cognitive capacity in healthy young mice, associated with changes in CD3 expression and reduced IL-1β levels.

Treg cells have shown both beneficial and detrimental influences in CNS pathologies, including AD. Their exact contribution remains complex and unclear. However, studies have reported both aggravation and reversal of cognitive decline in AD animal models after Treg depletion. Treg depletion in this study improved memory capacity in a mouse model of AD and was associated with reduced levels of IL-1β and IL-6 in the pre-frontal brain cortex and choroid plexus.

The findings suggest that disruption of immune system functioning leads to impairments in cognition and neurogenesis. Immunostimulation may have a beneficial role in brain fitness, presenting a therapeutic opportunity for CNS-related diseases. The repeated exposure to menthol during the long process of cognitive impairment development in the APP/PS1 model further supports this hypothesis.

The correlation between anosmia (loss of olfaction) and a faster rate of cognitive decline preceding the onset of Alzheimer’s disease symptoms is noteworthy. Further investigation is required to determine whether the loss of olfaction predicts or contributes to neurodegenerative changes associated with AD.

If olfactory deficits are found to be a contributing factor, strategies aimed at improving olfactory function in patients could be evaluated. Intensive olfactory training has shown promising results in improving olfactory function and inducing structural changes in the brain regions involved in olfactory processing.

In summary, the findings of this study suggest that immunomodulatory strategies capable of modulating cytokine expression, particularly IL-1β, may have an impact on cognitive function. These results highlight the potential therapeutic value of odorants and other immunomodulators in CNS-related diseases.

The observations made in the APP/PS1 murine model, although requiring further in-depth studies, offer new avenues for developing therapies based on olfactory system stimulation and training to prevent or alleviate the effects of devastating CNS diseases such as Alzheimer’s disease.

Overall, this research sheds light on the complex interactions between brain cells with immune functions, peripheral immune cells, neurons, and neural precursor cells in maintaining brain homeostasis. It highlights the role of the olfactory system in the immune system and its potential impact on cognitive function and CNS diseases.

Further investigations are warranted to validate these findings and explore the underlying mechanisms, but the study provides valuable insights into the therapeutic opportunities for immunomodulatory approaches in CNS-related disorders.


reference link: https://www.frontiersin.org/articles/10.3389/fimmu.2023.1130044/full

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