In vivo effects of some tertiary alkylaminoethyl esters with choline acetyltransferase inhibitory properties

Intracortical AF64A: memory impairments and recovery from cholinergic hypofunction

The long-term effects of intracortical AF64A (ethylcholine mustard aziridinium ion) treatment on presynaptic cortical cholinergic markers and cognitive function in the rat were investigated. Two 1.0 microliter infusions of AF64A (1 nmole/microliter) or vehicle were placed bilaterally into the fronto-parietal cortex. At 3 weeks postinfusion, AF64A-treated animals were found to be deficient in passive avoidance memory retention. During weeks 4 through 10, AF64A-treated animals were markedly deficient in the extinction (memory) phase, but not the acquisition (learning) phase of 2-way active avoidance behavior. Cortical acetylcholine synthesis and high-affinity choline uptake were significantly decreased in AF64A-treated animals at 24 hours, 3 weeks, and 10 weeks following infusion. At 6 months after AF64A treatment, however, cortical cholinergic markers were not reduced compared to controls. These data indicate that memory deficits are observed during a period of cortical cholinergic hypofunction induced by cortical AF64A infusions and that a recovery from such hypofunction occurs by 6 months after these infusions.

Relationships between chemical structure and inhibition of choline acetyltransferase by 2-(alpha-naphthoyl)ethyltrimethylammonium and related compounds

A choline acetyltransferase (ChA) inhibitor with an optimum combination of properties of potency, stability and membrane permeability is required to study several functional aspects of acetylcholine in nervous and non-nervous tissues. Therefore, 2-(alpha-naphthoyl)ethyltrimethylammonium iodide (alpha-NETA), 2-(beta-naphthoyl)ethyltrimethylammonium iodide (beta-NETA), 2-(9'-anthroyl)ethyltrimethylammonium iodide (9'-AETA) and their corresponding tertiary dimethylamine hydrochloride analogs (alpha-NEDA, beta-NEDA, 9'-AEDA) were synthesized and tested for their ChA inhibitory activities. The quaternary ammonium compounds were more potent inhibitors (150 in microM: alpha-NETA, 9; beta-NETA, 76; 9'-AETA, 32) than the corresponding tertiary compounds (150 in microM: alpha-NEDA, 63; beta-NEDA, 1400; 9'-AEDA, 77). The alpha-naphthyl moiety was preferable to the beta-naphthyl- or 9'-anthryl moieties for alignment with the enzyme for inhibition. alpha-NETA and alpha-NEDA exhibited adequate ChA inhibitory potencies for further pharmacological studies and localization of membrane bound ChA. They exhibited fluorescent characteristics of the alpha-naphthyl moiety. Their ChA inhibition was not reversible by dialysis. They were considerably more potent for inhibiting ChA than cholinesterases and carnitine acetyltransferase.

Induction of cortical cholinergic hypofunction and memory retention deficits through intracortical AF64A infusions

Ethylcholine mustard aziridinium ion (AF64A), an irreversible inhibitor of high-affinity choline uptake on cholinergic nerve terminals, appears to selectively decrease presynaptic cholinergic markers after intracerebral injection. To restrict AF64A's action to cholinergic terminals within the frontoparietal (FP) cortex, the present study utilized multiple-site cortical infusions of the agent. Following an extensive histological analysis, a dose of 1 nmol AF64A/1 microliter was selected for determining AF64A's effects on acetylcholinesterase (AChE) staining, cortical cholinergic/non-cholinergic markers, and passive avoidance behavior. Adult rats given two infusions of AF64A into the right FP cortex had reduced AChE staining throughout 75% of the ipsilateral FP cortex at 10 days following infusion, thus suggesting an extensive cortical diffusion of the agent; minimal non-specific damage was seen (totalling only 4% of the ipsilateral FP cortex for both infusion sites) and no effects on AChE staining were observed in the striatum or hippocampus. Three weeks after bilateral AF64A infusions into the FP cortex (two injections on each side), significant frontal cortex deficits were observed in high-affinity choline uptake, acetylcholine synthesis, acetylcholine release, and hemicholinium-3 binding compared to vehicle-infused controls. However, choline acetyltransferase activity within the anterior cortex did not appear to be consistently affected by AF64A infusion. Cortical glutamic acid decarboxylase activity, as well as cortical monoaminergic markers, and neuropeptide levels were also unaffected. Moreover, animals that received bilateral AF64A infusions and were tested two weeks afterwards showed marked memory retention deficits during both the 24-h and 48-h postshock trials of passive avoidance testing. These results indicate that cortical AF64A infusion induces a specific, long-term cholinergic hypofunction of presynaptic markers within the cortex, resulting in a significant long-term memory impairment. Since the primary cholinergic innervation to the FP cortex, originating in the nucleus basalis of Meynert, appears to become dysfunctional (but not totally degenerative) in Alzheimer's disease, cortical AF64A infusions may closely reflect this cholinergic dysfunction by 'functionally' eliminating cortical cholinergic terminals.

Relationships between chemical structure and inhibition of human placental choline acetyltransferase by keto analogs of acetylcholine

Seven keto analogs of acetylcholine were synthesized and evaluated as inhibitors of human placental choline placental choline acetyltransferase. Their potencies for inhibition of horse serum cholinesterase and stimulation of cholinergic receptors in the longitudinal ileal muscle of the guinea pig were investigated. The most potent and selective inhibitor of choline acetyltransferase was (2-benzoylethyl)trimethylammonium chloride with an I50 of 3 X 10(-6) M. It exhibited considerably low activities at muscarinic and nicotinic receptors and cholinesterases. Its high potency for inhibiting choline acetyltransferase was atrributed to: (a) its cationic terminal, a site for an electron acceptor interaction; (b) an aryl moiety for hydrophobic and electron donor contributions; and (c) a positive charge on the carbon atom adjacent to the benzene ring due to the presence of the carbonyl group, which interacts with the nucleophilic residue on the enzyme.