The effects of lobeline on α4β2* nicotinic acetylcholine receptor binding and uptake of [18F]nifene in rats

Lobeline is a potential smoking cessation drug with affinity for the α4β2 nicotinic acetylcholine receptor and may inhibit the blood–brain barrier (BBB) amine transporter. The goal of this work was to use PET imaging to evaluate the effects of lobeline on the kinetic properties of [18F]nifene in the rat brain. Methods: Direct α4β2* competition of lobeline with [18F]nifene was evaluated using imaging experiments with both displacing and blocking doses of lobeline (1 mg/kg, i.v.) given between two injections of [18F]nifene separated by 50 min. Inhibition of the BBB amine transporter was examined using a separate imaging protocol with three injections of [18F]nifene, first at baseline, then following (−)nicotine blocking, and finally following lobeline blocking. Results: Rapid displacement of [18F]nifene was observed in the α4β2*-rich thalamus following lobeline administration, suggesting direct competition of the drug at α4β2* sites. Slight decreases in BBB transport of [18F]nifene were observed when the α4β2* system was first saturated with (−)nicotine and then given lobeline. This perturbation may be due to inhibition of the BBB amine transporter by lobeline or reductions in blood flow. Significant cerebellar displacement of [18F]nifene was found following the administration of both lobeline and (−)nicotine, indicating detectable specific binding in the rat cerebellum. Conclusion: The competition of lobeline with [18F]nifene is largely dominated at the α4β2* binding site and only small perturbations in BBB transport of [18F]nifene are seen at the 1 mg/kg dose. Similar experiments could be used to study other drugs as therapeutic agents for smoking cessation with PET.

► Lobeline interacts with α4β2* nAChRs and the BBB amine transporter.
► PET imaging in rats assessed the interaction of lobeline with [18F]nifene in vivo.
► Lobeline competes strongly with [18F]nifene at the α4β2* site.
► The cerebellum is not a valid reference region for [18F]nifene in the rat.
► Small decreases in [18F]nifene BBB transport rates were observed due to lobeline.