The inhibition of AChE and BuChE has been broadly established as a first-line treatment for symptoms of neurodegenerative conditions, such as AD (Zabuski & Kufniewski, 2016). Three AChE inhibitors have been approved by the U.S. Food and Drug Administration for the treatment of AD: donepezil, rivastigmine, and galantamine. However, these drugs are known to have limitations for clinical use due to their short half-lives and/or unfavorable side effects (Benamar et al., 2010). The development of interventions that substantially delay the onset or progression of AD is currently ongoing. Therefore, the search for new AChE inhibitors is of great interest.
The potential use of natural products has been successfully demonstrated in the field of AD (Wszelaki et al., 2010). Naturally occurring compounds from plants are considered prime sources of new inhibitors and has led to the discovery of an important number of secondary metabolites in plant extracts that are able to inhibit AChE, which, according to the cholinergic hypothesis, increases the levels of ACh in the brain, improves cholinergic function in patients with AD, and alleviates symptoms of this neurological disorder (Orhan et al., 2004).
A great deal of attention has been focused on herbs and spices as sources of drugs. While the scientific evidence for the use of common herbs and spices is lacking, the beneficial effects observed from their use are generally encouraging (Mirmosayyeb et al., 2017). There is a need for a more comprehensive understanding of the health-promoting and protective properties of herbs and spices. A spice is a dried seed, fruit, root, bark, or flower of a plant used in small quantities in food for flavor, color, or as a preservative. Spices have been evaluated by researchers for the treatment of many diseases far removed from their traditional uses (Dini, ?2018). The present study was undertaken to evaluate the anticholinesterase activity of a number of common Jordanian spices to provide science-based evidence for their use as preventive and therapeutic agents for AD.
We investigated 30 spices from 17 families for their ability to inhibit AChE and BuChE using a TLC bioautographic assay and Ellman’s spectrophotometric method. Among the 30 screened extracts, 11 had AChE and/or BuChE. The anti-cholinesterase activities of these spices are summarized in Table 3. However, most of the cited studies focused on the inhibition of AChE but not BuChE. BuChE plays an equally important role to that of AChE, as the sole inhibition of AChE leads to a compensatory mechanism by which the activity of BuChE is increased. Five of the active spice extracts were screened for their ability to inhibit BuChE, supporting their roles as preventive and therapeutic agents for AD with dual inhibitory activities. To the best of our knowledge, we report for the first time that fennel seed extract is able to inhibit both AChE and BuChE.