Effects of Eugenol on the Central Nervous System: Its Possible Application to Treatment of Alzheimer's Disease, Depression, and Parkinson's Disease

Eugenol (4-allyl-2-methoxyphenol) is a fragrant compound that is commonly contained in various sorts of plants, especially in spices and medicinal herbs. Eugenol has been used for dental analgesic, which also has anticonvulsive and anti-microbial activities. Besides, anti-inflammatory and antioxidative activities of eugenol are known. A body of evidence suggests that eugenol can be used as a drug for treatment of Alzheimer's disease (AD). According to recent reports, the extract of a medicinal plant Rhizoma Acori Graminei (RAG) alleviates neurotoxicity induced by amyloid beta peptides (Aβ) in vitro and the active constituent of RAG is eugenol. Eugenol inhibits Aβ-induced excessive influx of calcium ion into neurons that causes neuronal death. Moreover, eugenol possesses an antidepressant-like activity. Eugenol, like other antidepressants, increases expression of brain-derived neurotrophic factor (BDNF) gene in the hippocampus, which is necessary for an antidepressant to exhibit its activity. Furthermore, eugenol inhibits monoamine oxidase A (MAO-A) and may restore monoamines that are decreased in the brain of patients with depression. Thus, eugenol can be a good medicine for AD and depression. Here we suggest that eugenol and its analogs can be used also for other diseases of the central nervous system (CNS) including Parkinson's disease (PD). This article reviews the previous investigations concerning effects of eugenol including its analogs on the CNS and describes perspectives of this highly potential compound.