Investigating Cosolvent Effects on Cholinesterases to Aid in Drug Solubility

Changes in activities of two major classes of cholinesterases, acetylcholinesterase (AChE) and butyrylcholinesterase (BChE), are suggested to lead to a depletion of neurotransmitter acetylcholine, contributing to neurodegenerative diseases. This creates a strong interest in developing selective inhibitors to regulate their activities, thus relieving symptoms and delaying progression of these diseases. For individuals with Alzheimer's disease, AChE activity is found to remain unchanged or decrease while BChE activity increases, and this observation has led to the design of BChE‐specific inhibitors. In modern day drug screening methods, cosolvents are often needed to aid in drugs solubility, however for AChE and BChE, the potential interactions between the enzymes and the cosolvents have not been examined closely. Although the overall AChE and BChE structures are essentially superimposable, previous studies reported that at low concentrations, DMSO, a common organic solvent used in drug discovery methods, affected AChE activity, however BChE activity was not changed. Building on this observation, we hypothesized that BChE activity was less sensitive to organic cosolvents and our model suggests that enzymes of similar overall structures may elicit different responses when exposed to different cosolvents. We conducted a series of UV‐Vis spectroscopy experiments to evaluate the effects of organic cosolvents on enzyme activity. Surveying a series of cosolvents showed that at low cosolvent concentrations of 2% and 5%, AChE activity was diminished, but BChE activity essentially unchanged. Indeed, using methanol and ethylene glycol as cosolvents required concentrations up to 50% before a decrease in BChE activity was observed. Evaluating Michaelis‐Menten kinetics showed that while changes in cosolvents have small effects on enzymatic activity ( k cat ), K M values increased, suggesting that changes in their activities are affected by the substrate binding. The observed behaviors support the previous findings in that BChE demonstrates more robustness in changes to its cosolvent environment compared to AChE, and we are now using fluorescence spectroscopy to evaluate the effects of the cosolvents on enzyme structure. Considering the purpose of cosolvents in drug discovery methods, it is essential to investigate cosolvent effects on enzyme activity to evaluate effects of the cosolvent on not only the enzyme of interest. Dissecting the energetic interactions between the enzymes' structures and their environment enables better prediction of what cosolvents can be used for drug solubility and will allow us to select more ideal conditions to evaluate the potency of inhibitors for therapeutic applications. Support or Funding Information Research reported in this publication was supported by the National Institute Of General Medical Sciences of the National Institutes of Health under Award Numbers RL5GM118978 and R25GM071638. The content is solely the responsibility of the authors and does not necessarily represent the official views of the National Institutes of Health. This abstract is from the Experimental Biology 2019 Meeting. There is no full text article associated with this abstract published in The FASEB Journal .