Nicotinic acetylcholinergic receptors (nAChR's) have been implicated in several brain disorders, including addiction, Parkinson's disease, Alzheimer's disease and schizophrenia. Here we report in vitro selectivity and functional properties, toxicity in rats, in vivo evaluation in humans, and comparison across species of [ 18 F]Nifene, a fast acting PET imaging agent for a4b2* nAChRs. Nifene had subnanomolar affinities for ha2b2 (0.34 nM), ha3b2 (0.80 nM) and ha4b2 (0.83 nM) nAChR but weaker (27-219 nM) for hb4 nAChR subtypes and 169 nM for ha7 nAChR. In functional assays, Nifene (100 lM) exhibited 14% agonist and >50% antagonist characteristics. In 14-day acute toxicity in rats, the maximum tolerated dose (MTD) and the no observed adverse effect level
Nicotinic acetylcholine α4β2 receptors (nAChRs) are implicated in various neurodegenerative diseases and smoking addiction. Imaging of brain high-affinity α4β2 nAChRs at the cellular and subcellular levels would greatly enhance our understanding of their functional role. Since better resolution could be achieved with fluorescent probes, using our previously developed positron emission tomography (PET) imaging agent [F]nifrolidine, we report here design, synthesis and evaluation of two fluorescent probes, nifrodansyl and nifrofam for imaging α4β2 nAChRs. The nifrodansyl and nifrofam exhibited nanomolar affinities for the α4β2 nAChRs in [H]cytisine-radiolabeled rat brain slices. Nifrofam labeling was observed in α4β2 nAChR-expressing HEK cells and was upregulated by nicotine exposure. Nifrofam co-labeled cell-surface α4β2 nAChRs, labeled with antibodies specific for a β2 subunit extracellular epitope indicating that nifrofam labels α4β2 nAChR high-affinity binding sites. Mouse brain slices exhibited discrete binding of nifrofam in the auditory cortex showing promise for examining cellular distribution of α4β2 nAChRs in brain regions.
Alzheimer's disease (AD) affects 10% of people older than 65 and is characterized by a progressive loss of cognitive function with an abnormal accumulation of amyloid β (Aβ ) plaques and neurofibrillary tangles (NFT) in the brain. Efforts to reduce brain Aβ plaques continue to be investigated as a therapeutic approach for AD. We report here development of dual targeting agents with affinity for Aβ plaque/P-glycoprotein (Pgp) and Aβ plaque/α4β 2* nicotinic acetylcholine receptors (nAChR). These novel dual agents may be able to efflux Aβ plaques via the paravascular (glymphatic) pathways. Ferulic acid (FA), ferulic acid ethyl ester (FAEE), and curcumin (CUR) were used for Aβ plaques, fexofenadine (FEX) was used as substrate for Pgp and nifrolidine (NIF) was used for α4β 2* nAChRs. Aβ plaque/α4β 2* nAChR dual agent, FA-NIF (GKS-007) exhibited IC = 3-6 nM for α4β 2* nAChRs in [H]cytisine-radiolabeled thalamus and frontal cortex in rat brain slices. In postmortem human AD frontal cortex, Aβ plaques labeled with [H]PIB, FEX-CUR showed a 35% reduction in gray matter (GM)/white matter (WM) [H]PIB binding, while CUR alone showed a 50% reduction. In vivo biodistribution studies are required of the Aβ-Pgp and Aβ-α4β 2* nAChRs dual targeting agents in order to evaluate their potential as therapeutic approaches for reducing brain Aβ plaques.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.