Cholinergic interactions between donepezil and prucalopride in human colon: potential to treat severe intestinal dysmotility

Abstract

Background and purpose: Cholinesterase inhibitors such as neostigmine are used for acute colonic pseudo-obstruction, but cardio-bronchial side-effects limit use. To minimize side-effects, lower doses could be combined with a 5-HT4 receptor agonist, which also facilitates intestinal cholinergic activity. However, safety concerns, especially in the elderly, require drugs with good selectivity of action. These include the AChE inhibitor donepezil (used for Alzheimer's disease, with reduced cardio-bronchial liability) and prucalopride, the first selective, clinically available 5-HT4 receptor agonist. This study examined their individual and potential synergistic activities in human colon.

Experimental approach: Neuronally mediated muscle contractions and relaxations of human colon were evoked by electrical field stimulation (EFS) and defined phenotypically as cholinergic, nitrergic or tachykinergic using pharmacological tools; the effects of drugs were determined as changes in 'area under the curve'.

Key results: Prucalopride increased cholinergically mediated contractions (EC50 855 nM; 33% maximum increase), consistent with its ability to stimulate intestinal motility; donepezil (477%) and neostigmine (2326%) had greater efficacy. Concentrations of donepezil (30-100 nM) found in venous plasma after therapeutic doses had minimal ability to enhance cholinergic activity. However, donepezil (30 nM) together with prucalopride (3, 10 μM) markedly increased EFS-evoked contractions compared with prucalopride alone (P = 0.04). For example, the increases observed with donepezil and prucalopride 10 μM together or alone were, respectively, 105 ± 35%, 4 ± 6% and 35 ± 21% (n = 3-7, each concentration).

Conclusions and implications: Potential synergy between prucalopride and donepezil activity calls for exploration of this combination as a safer, more effective treatment of colonic pseudo-obstruction.

Keywords: colon; donepezil; elderly; human; neostigmine; prucalopride; pseudo-obstruction.

© 2013 The British Pharmacological Society.

Figures

Figure 1

Representative traces illustrating muscle relaxations and contractions to EFS in circular muscle from human isolated colon. (A) Trace showing effects of different frequencies of EFS (1, 2, 5, 10, 15 and 20 Hz, 50 V, 0.5 ms bipolar pulse duration) applied for 10 s every 1 min. The horizontal bar indicates the period of EFS, with the response generated during this time usually followed by an ‘after-contraction’ on termination of EFS. Contractions and relaxations during 5 Hz EFS were prevented, respectively, by (B) 1 μM atropine and (C) by 300 μM L-NAME. The enlarged sections of tracing show the ability of atropine to prevent contractions during EFS (revealing muscle relaxation) and greatly reduce the large after-contractions, which followed termination of EFS. Similarly, muscle relaxation was prevented by L-NAME and the resultant contraction became monophasic.

Figure 2

Effects of donepezil and neostigmine on cholinergically mediated contractions evoked by (EFS of human isolated colon circular muscle. Typical traces are shown in the upper panels (A, C), with the graphs below each trace showing the mean (±SEM) increase in EFS-evoked AUC at increasing concentrations of donepezil (B) and neostigmine (D) (n = 3–4 and 4–5 patients for each data point, respectively); note the different g-tension scales for the traces shown. EFS (50 V, 0.5 ms bipolar pulse duration, 5 Hz) was given for 10 s, every 1 min.

Figure 3

Effects of prucalopride on cholinergically mediated contractions evoked by EFS of the human isolated colon circular muscle. Typical traces are shown in the upper panels in the absence (A) and presence (B) of L-NAME 300 μM; the enlarged section of tracing obtained in the absence of L-NAME shows the ability of prucalopride to act mostly by increasing muscle contractions during EFS. The graph below (C) shows the concentration-response curve for prucalopride in the absence of L-NAME, measuring the mean (±SEM) increase in EFS-evoked AUC. EFS (50 V, 0.5 ms bipolar pulse duration, 5 Hz) was given for 10 s, every 1 min (n = 3–6 patients for each data point).

Figure 4

Facilitation by donepezil, in the absence and presence of prucalopride, of cholinergically mediated contractions evoked by EFS in human colonic circular muscle. (A) Trace showing the large increase in EFS-evoked contractions after application of donepezil together with prucalopride. (B) Bars showing the mean (±SEM) facilitation of EFS-evoked AUC caused by donepezil 30 nM alone (n = 3) and in the presence of prucalopride 3 and 10 μM (respectively, n = 6 each for 3 μM in the absence and presence of donepezil, and 7 and 8 for 10 μM). EFS (50 V, 0.5 ms bipolar pulse duration, 5 Hz) was given for 10 s, every 1 min (n = 3–7 patients for each data point). P = 0.04 (two-way anova) when the effects of donepezil on both concentrations of prucalopride were assessed together.