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- Title
Trapping of Nicotinic Acetylcholine Receptor Ligands Assayed by In Vitro Cellular Studies and In Vivo PET Imaging.
- Authors
Zhang, Hannah J.; Zammit, Matthew; Chien-Min Kao; Govind, Anitha P.; Mitchell, Samuel; Holderman, Nathanial; Bhuiyan, Mohammed; Freifelder, Richard; Kucharski, Anna; Xiaoxi Zhuang; Mukherjee, Jogeshwar; Chin-Tu Chen; Green, William N.
- Abstract
A question relevant to nicotine addiction is how nicotine and other nicotinic receptor membrane-permeant ligands, such as the antismoking drug varenicline (Chantix), distribute in brain. Ligands, like varenicline, with high pKa and high affinity for a4b2-type nicotinic receptors (a4b2Rs) are trapped in intracellular acidic vesicles containing a4b2Rs in vitro. Nicotine, with lower pKa and a4b2R affinity, is not trapped. Here, we extend our results by imaging nicotinic PET ligands in vivo in male and female mouse brain and identifying the trapping brain organelle in vitro as Golgi satellites (GSats). Two PET 18F-labeled imaging ligands were chosen: [18F]2- FA85380 (2-FA) with varenicline-like pKa and affinity and [18F]Nifene with nicotine-like pKa and affinity. [18F]2-FA PET-imaging kinetics were very slow consistent with 2-FA trapping in a4b2R-containing GSats. In contrast, [18F]Nifene kinetics were rapid, consistent with its binding to a4b2Rs but no trapping. Specific [18F]2-FA and [18F]Nifene signals were eliminated in b2 subunit knock-out (KO) mice or by acute nicotine (AN) injections demonstrating binding to sites on b2-containing receptors. Chloroquine (CQ), which dissipates GSat pH gradients, reduced [18F]2-FA distributions while having little effect on [18F]Nifene distributions in vivo consistent with only [18F]2-FA trapping in GSats. These results are further supported by in vitro findings where dissipation of GSat pH gradients blocks 2-FA trapping in GSats without affecting Nifene. By combining in vitro and in vivo imaging, we mapped both the brain-wide and subcellular distributions of weak-base nicotinic receptor ligands. We conclude that ligands, such as varenicline, are trapped in neurons in a4b2R-containing GSats, which results in very slow release long after nicotine is gone after smoking.
- Subjects
NICOTINIC acetylcholine receptors; POSITRON emission tomography; NICOTINIC receptors; LIGANDS (Biochemistry); BINDING sites; SMOKING statistics; NEUROMUSCULAR transmission
- Publication
Journal of Neuroscience, 2023, Vol 43, Issue 1, p2
- ISSN
0270-6474
- Publication type
Article
- DOI
10.1523/JNEUROSCI.2484-21.2022