Inhibition of Recombinant Human Acetylcholinesterase Activity by Antipsychotics

<b><i>Background/Aims:</i></b> Extrapyramidal symptoms (EPS) are representative side effects of antipsychotics, caused by their inhibitory action on dopaminergic nerves in nigrostriatal pathways. EPS could be also caused by direct augmentation of cholinergic effects, for example, by acetylcholinesterase (AChE) inhibition. We investigated the potential inhibitory effects of 26 clinically available antipsychotics on the activity of recombinant human AChE (rhAChE) to predict the role of antipsychotic-induced AChE inhibition in EPS onset. <b><i>Method:</i></b> The degree of rhAChE activity inhibition was calculated using the 5,5′-dithio-bis-(2-nitrobenzoic acid) method. <b><i>Results:</i></b> At a concentration of 10^–5 mol/L, haloperidol, bromperidol, timiperone, nemonapride, pimozide, risperidone, blonanserin, aripiprazole, and brexpiprazole inhibited rhAChE activity by &#x3e;20%. Risperidone, aripiprazole, and brexpiprazole inhibited rhAChE activity in a concentration-dependent manner, and their effects were more potent than those of other antipsychotics. The inhibitory effects of these 3 drugs were evident from 10^–6 mol/L, and their pIC₅₀ values were 4.74 ± 0.04, 4.80 ± 0.04, and 4.93 ± 0.06, respectively. Notably, the concentration range in which aripiprazole inhibited rhAChE activity (≥10^–6 mol/L) overlapped with its clinically achievable blood levels. <b><i>Conclusion:</i></b> Aripiprazole may cause EPS at clinical dosages by augmenting cholinergic effects via AChE inhibition, in addition to its suppressive effect on dopaminergic neurons.