U18666A, a cholesterol-inhibition agent, modulates human neuronal nicotinic acetylcholine receptors heterologously expressed in SH-EP1 cell line.

In this study, we evaluate the effects of (3beta)-3-[2-(diethylamino)ethoxy]androst-5-en-17-one dihydrochloride (U18666A), a cholesterol synthesis/transporter inhibitor, on selected human neuronal nicotinic acetylcholine receptors (nAChRs) heterologously expressed in the SH-EP1 cell line using whole-cell patch-clamp recordings. The results indicate that with 2-min pretreatment, U18666A inhibited different nAChR subtypes with a rank-order of potency (IC(50) of whole-cell peak current): alpha4beta2 (8.0 +/- 3.0 nM) > alpha3beta2 (1.7 +/- 0.4 microM) > alpha4beta4 (26 +/- 7.2 microM) > alpha7 (> 100 microM), suggesting this compound is more selective to alpha4beta2-nAChRs. Thus, the pharmacological profiles and mechanisms of U18666A acting on alpha4beta2-nAChRs were investigated in detail. U18666A suppresses both peak and steady state components of whole-cell currents mediated by human alpha4beta2-nAChRs in response to nicotine. In nicotine-induced concentration-response curves, U18666A reduces nicotine-induced current at maximally effective agonist concentrations without influencing nicotine's EC(50) value, suggesting a non-competitive inhibition. U18666A-induced inhibition of nAChR function is concentration-, voltage-, and use-dependent, suggesting an open channel block. Taken into consideration of approximately 10 000-fold enhancement of the potency of U18666A after 2-min pre-treatment, this compound also likely inhibits alpha4beta2-nAChRs through a close channel block. In addition, the U18666A-induced inhibition in alpha4beta2-nAChRs is not mediated by either increased receptor endocytosis or altered cell cholesterol. These data indicate that U18666A is a potent antagonist of alpha4beta2-nAChRs and may be useful as a tool in the functional characterization and pharmacological profiling of nAChRs, as well as a potential candidate for smoking cessation.