Metformin and Its Sulfenamide Prodrugs Inhibit Human Cholinesterase Activity

Abstract

The results of epidemiological and pathophysiological studies suggest that type 2 diabetes mellitus (T2DM) may predispose to Alzheimer's disease (AD). The two conditions present similar glucose levels, insulin resistance, and biochemical etiologies such as inflammation and oxidative stress. The diabetic state also contributes to increased acetylcholinesterase (AChE) activity, which is one of the factors leading to neurodegeneration in AD. The aim of this study was to assess in vitro the effects of metformin, phenformin, and metformin sulfenamide prodrugs on the activity of human AChE and butyrylcholinesterase (BuChE) and establish the type of inhibition. Metformin inhibited 50% of the AChE activity at micromolar concentrations (2.35 μmol/mL, mixed type of inhibition) and seemed to be selective towards AChE since it presented low anti-BuChE activity. The tested metformin prodrugs inhibited cholinesterases (ChE) at nanomolar range and thus were more active than metformin or phenformin. The cyclohexyl sulfenamide prodrug demonstrated the highest activity towards both AChE (IC50 = 890 nmol/mL, noncompetitive inhibition) and BuChE (IC50 = 28 nmol/mL, mixed type inhibition), while the octyl sulfenamide prodrug did not present anti-AChE activity, but exhibited mixed inhibition towards BuChE (IC50 = 184 nmol/mL). Therefore, these two bulkier prodrugs were concluded to be the most selective compounds for BuChE over AChE. In conclusion, it was demonstrated that biguanides present a novel class of inhibitors for AChE and BuChE and encourages further studies of these compounds for developing both selective and nonselective inhibitors of ChEs in the future.

Metformin and its sulphonamide derivative simultaneously potentiateanti-cholinesterase activity of donepezil and inhibit beta-amyloid aggregation

“…Donepezil, the approved drug for the treatment of AD reversibly inactivating the ChEs, and metformin were used to compare the obtained results 4 , 25 . Regarding AChE inhibition derivative 5 presented the highest activity of the tested compounds (IC 50 = 212.5 ± 48.3 µmol/L); however, this activity is much lower than that of donepezil (0.025 ± 0.004 µmol/L).…”

“…The activity of both cholinesterases (AChE and BuChE) were conducted using a spectrophotometric method developed by Ellman with previously described modifications 25 , 30 . The experiments were performed in Semi-Micro cuvettes (Medlab Products, Raszyn, Poland), by means of a Cecil CE 2021 spectrophotometer (CECIL Instruments Limited, Cambridge, UK) with circulating thermostated water (37 °C) and a magnetic stirrer (Electronic Stirrer Model 300; Rank Brothers Ltd, Cambridge, England).…”

“…To determine the potential synergistic effects of metformin derivatives on ChE inhibition binary-mixtures trials were performed. The effects of mixtures of metformin derivatives and donepezil on both ChEs activity were determined using a modified method of Ellman 25 . In brief, the samples (470 µL) were preincubated with a mixture (20 µL) of donepezil and biguanide (metformin, phenformin, or compound 5 ), before substrate addition (ATC or BTC at the final concentration of 0.75 µmol/mL) for 15 min.…”

“…Individual in vivo studies conducted on animals imply that chronic treatment with metformin might improve cognitive performance, reduce oxidative stress and ChE activity 23 , 24 . In our previous study 25 it was reported that metformin inhibited 50% of the AChE activity at milimolar concentrations (2350 µmol/L), in a mixed inhibition manner and seemed to be selective towards AChE since it presented low anti-BuChE activity. Phenformin was shown to be less active towards AChE in comparison with metformin (IC 50 = 4940 µmol/L), but it was also found to inhibit BuChE competitively (IC 50 = 259.0 µmol/L) 25 .…”

“…In our previous study 25 it was reported that metformin inhibited 50% of the AChE activity at milimolar concentrations (2350 µmol/L), in a mixed inhibition manner and seemed to be selective towards AChE since it presented low anti-BuChE activity. Phenformin was shown to be less active towards AChE in comparison with metformin (IC 50 = 4940 µmol/L), but it was also found to inhibit BuChE competitively (IC 50 = 259.0 µmol/L) 25 . The obtained results suggest that biguanides might act as a novel class of inhibitors for AChE and BuChE and encourage us to undertake further studies for the development of both selective and non-selective inhibitors of ChEs.…”