Galantamine is not a positive allosteric modulator of human α4β2 or α7 nicotinic acetylcholine receptors.

Abstract

The alkaloid galantamine was originally isolated from the green snowdrop Galanthus woronowii and is currently marketed as a drug for treatment of mild to moderate dementia in patients with Alzheimer's disease. In addition to a well-documented proficiency to inhibit acetylcholinesterase, galantamine has been reported to increase neuronal nicotinic ACh (nACh) receptor function by acting as a positive allosteric modulator. Yet there remains controversy regarding these findings in the literature. To resolve this conundrum, we evaluated galantamine actions at α4β2 and α7, which represent the nACh receptors most commonly associated with mammalian cognitive domains. α4β2 [in (α4)3 (β2)2 and (α4)2 (β2)3 stoichiometries] and α7 nACh receptors were expressed in Xenopus laevis oocytes and subjected to two-electrode voltage-clamp electrophysiological experiments. Galantamine (10nM to 100μM) was evaluated for direct agonist effects and for positive modulation by co-application with sub-maximally efficacious concentrations of ACh. In addition, similar experiments were performed with α7 nACh receptors stably expressed in HEK293 cells using patch-clamp electrophysiology. In concentrations ranging from 10nM to 1μM, galantamine did not display direct agonism nor positive modulatory effects at any receptor combination tested. At concentrations from 10μM and above, galantamine inhibited the activity with a mechanism of action consistent with open-channel pore blockade at all receptor types. Based on our data, we conclude that galantamine is not a positive allosteric modulator of α7 or α4β2 receptors, which represent the majority of nACh receptors in mammalian brain.