Evaluation of selected mushroom extracts, dispiropiperazine and dispiropyrrolizidine derivatives on acetylcholinesterase activity

Acetylcholinesterase is a hydrolase enzyme known for its major role in neurotransmission regulation by breaking down the neurotransmitter acetylcholine at the synapse after every electrochemical signal is successfully relayed between two adjacent neurons. In a healthy human brain, it retains itself on the extracellular surface of neurons, concordantly paints up an artistic beautiful web of an intricate neural network upon staining. However, in an aging human brain experiencing neurodegeneration, the network collapses into plaques that are neurotoxic to the brain. At the center of these individual plaques are heavily aggregated amyloid-beta peptides and fibers enveloping the neurons. This is most often one of the specific traits of Alzheimer’s and Parkinson’s disease, two most common neurodegenerative diseases. Many studies have provided experimental evidences of stable co-localization and fiber growth promotion existing between the amyloid-beta peptides and acetylcholinesterase. Nevertheless, the specific chemistry and mechanism of how the relationship between the amyloid-beta peptides and acetylcholinesterase is formed and maintained, still remains tentative to date. Most neurodegenerative diseases remain incurable, and most of the available medical treatments focus on alleviating the symptoms and mitigating the disease progression, for instance through the use of acetylcholinesterase inhibitors. But with drawbacks related to treatment effectiveness and undesirable side effects of the current available acetylcholinesterase inhibitors, the continued search for more effective acetylcholinesterase inhibitors has never ceased. The objectives of this in vitro study were to examine four small molecules and twenty-one mushroom extracts for their ability to inhibit acetylcholinesterase activity. To perform the screen, an enzyme assay using Ellman’s reagent DTNB was used. The assay utilizes thiocholine produced from the hydrolysis of acetylthiocholine by acetylcholinesterase to reduce DTNB into TNB2-, a colorimetric product that can be used to monitor the changes in the acetylcholinesterase activity level in the presence or absence of inhibitors. Using the established acetylcholinesterase assay, none of the four small molecules showed any inhibitory effect on acetylcholinesterase activity. On the contrary, eight of the mushroom extracts were found to inhibit the acetylcholinesterase activity. These eight extracts were prepared from five mushroom species that have not been extensively researched nor reported for acetylcholinesterase inhibition. Surprisingly, for the remaining thirteen mushroom extracts that did not show inhibition, they were found to enhance the acetylcholinesterase activity. Albeit the unexpected irrelevance to the focus of the study, these thirteen extracts could be useful as biological tools in the general research of regeneration, as acetylcholinesterase has been reported to act as a mediator promoting cell proliferation and regeneration.