The neuroprotective role of volatile oils: insights into chemical profiles, characteristics, neurochemical mechanisms, and preclinical studies in Alzheimer's disease.

Volatile oils (VOs), synonymously termed essential oils (EOs), are highly hydrophobic liquids obtained from aromatic plants, containing diverse organic compounds for example terpenes and terpenoids. These oils exhibit significant neuroprotective properties, containing antioxidant, anti-inflammatory, anti-apoptotic, glutamate activation, cholinesterase inhibitory action, and anti-protein aggregatory action, making them potential therapeutic agents in managing neurodegenerative diseases (NDs). VOs regulate glutamate activation, enhance synaptic plasticity, and inhibit oxidative stress through the stimulation of antioxidant enzymes. They also reduce inflammation by inhibiting key inflammatory mediators and enzymes. Furthermore, VOs prevent neuronal apoptosis by modulating apoptosis-related proteins and caspases. Their anti-protein aggregation potential helps mitigate the accumulation of misfolded proteins, a hallmark of neurodegenerative disorders. Additionally, VOs inhibit cholinesterase enzymes, increasing acetylcholine levels, and improving neuronal communication. In addition to their neuroprotective action, it also exerts some toxic effects, such as genotoxicity, hepatotoxicity, embryotoxicity, and hypersensitivity, which are most commonly caused by the presence of monoterpenes in the volatile oils. This review examines the diverse functions of vasoactive oxidants (VOs) in neuroprotection, underscoring their therapeutic promise for various neurological conditions, with a particular emphasis on Alzheimer's disease.