Vincenzo Carelli

Choline pivaloyl esters improve in rats cognitive and memory performances impaired by scopolamine treatment or lesions of the nucleus basalis of Meynert.

The effects of two choline pivaloyl esters, [2-(2,2-dimethylpropionyloxy)ethyl]trimethylammonium iodide (1) and [2-(2,2-dimethylpropionyloxy)ethyl]trimethylammonium 2,2-dimethylpropionate (2), on learning and memory impairments induced in rats by scopolamine or lesions of nucleus basalis magnocellularis (NBM) have been evaluated by object recognition and Morris water maze tests in comparison with Tacrine (THA). Both 1 and 2 restored discrimination in object recognition test for assessing working-episodic memory and improved spatial memory in scopolamine or NBM-lesioned rats as well. The positive effects produced by 1 and 2 on cognitive and memory deficits were well comparable with those evoked by THA, used as reference compound.

New systems for the specific delivery and sustained release of dopamine to the brain

Abstract The present paper reports the synthesis of the chemical delivery system 5 and dopamine (DA) prodrug 6 as well as their application for the specific delivery and sustained release of DA to the rat brain. The ability of 5 and 6 to penetrate the blood-brain barrier (BBB) and release DA into the central nervous system (CNS) was assessed by comparing, on a molar basis, the behavioural effects produced by DA itself and the above compounds, when centrally or peripherally administered in conscious rats. When intravenously injected, both derivatives 5 and 6 elicited vacuous chewing behaviours comparable with those induced by intracerebroventricular (icv) injection of the parent drug. These results suggest that 5 and 6 are able to cross the BBB and enter the CNS, releasing DA. Furthermore, a long lasting effect was observed for the tripivaloyl-derivative 6, likely due to a slower release of DA following from an increased resistance of the sterically hindered pivaloylamide group to enzymatic hydrolysis. It must be pointed out that the α-adrenergic effect (piloerection) observed after DA was peripherally injected was not observed after systemic administration of the compounds 5 and 6. This finding may indicate that neither the chemical delivery system 5 nor the prodrug 6 release free DA at bioactive concentrations at a peripheral level.

On the structure of intermediate adducts arising from dithionite reduction of pyridinium salts: a novel class of derivatives of the parent sulfinic acid

Abstract 13C and 17O NMR spectroscopy show that adducts arising from dithionite reduction of 3- or 3,5-cyano- or carbamoyl-substituted pyridinium salts to the corresponding 1,4-dihydropyridines, are S-anions of esters of the simplest parent sulfinic acid. A pathway for formation of the 1,4-dihydropyridines, involving an intramolecular hydride transfer, is suggested.

Photocatalyzed oxidation of NAD dimers

Abstract A mixture of dimers of nicotinamide adenine dinucleotide, largely 4,4−-linked, obtained by electrochemical reduction of NAD + , can be photooxidized back to NAD + in the presence of oxygen. Oxygen is consumed during the photooxidation process with the production of hydrogen peroxide. The oxidation is almost pH independent and is stimulated by light whose wavelength exceeds 300 nm. Lactate dehydrogenase and alcohol dehydrogenase added to the solutions under irradiation increased the oxygen uptake by the NAD dimers in a concentration-dependent way. These observations suggest that light induces the homolytic cleavage of NAD dimers to NAD radicals which in turn are oxidized to NAD + by oxygen.

Evidence for binding of NAD dimers to NAD-dependent dehydrogenases.

The binding of dimers of nicotinamide adenine dinucleotide, (NAD)2, to lactate, malate and alcohol dehydrogenase has been studied by the fluorescence quenching technique. While the alcohol dehydrogenase shows a low binding ability, malate and lactate dehydrogenases have been found to bind (NAD)2 in a specific way with high affinity. Malate dehydrogenase binds (NAD)2 more than NADH. All three dehydrogenases are inhibited by (NAD)2, which behaves as a competitive inhibitor with respect to both NAD+ and NADH. The results show that (NAD)2 is bound to the nucleotide-specific binding site of the dehydrogenases. (NAD)2 was found to stoichiometrically react with ferricyanide at variance with NADH. The specific interactions with the NAD-dependent dehydrogenases and the ability to enter in monoelectronic redox cycles suggest possible physiological roles for (NAD)2.

Choline pivaloyl ester strengthened the benefit effects of Tacrine and Galantamine on electroencephalographic and cognitive performances in nucleus basalis magnocellularis-lesioned and aged rats.

The aim of the present work was the assessment of the effects produced on the electroencephalographic (EEG) activity and the cognitive and memory performances of nucleus basalis magnocellularis (NBM)-lesioned or aged rats by the combined treatment with [2-(2,2-dimethylpropionyloxy)ethyl]trimethylammonium 2,2-dimethylpropionate (choline pivaloyl ester) (CPE) and the Cholinesterase inhibitors (ChEIs) Tacrine (THA) and Galantamine (GAL). Intraperitoneal administration of CPE combined with THA or GAL to both NBM-lesioned or aged rats, produced EEG desynchronisation, and a significant decrease in the energy of the total EEG spectrum and the lower frequency bands (delta 0.25-3 and theta 4-7 Hz) lasting many minutes. Furthermore, drug associations reversed in aged rats the scopolamine (0.2 mg/kg, i.p.)-induced increase in EEG power, slow waves and high-voltage spindle (HVS). Furthermore, the combined administration of CPE and Cholinesterase inhibitors in both NBM-lesioned or aged animals, improved performances in all behavioural tasks, enhancing object discrimination, increasing locomotory activity and alternation choice in T-maze, ameliorating retention in passive avoidance and decreasing escape latency in Morris water maze. In all test, AChEIs and CPE combinations proved to be more effective than CPE, THA or GAL given alone. In conclusion, the present work shows the ability of choline pivaloyl ester in strengthening the positive cerebral activity of THA and GAL.

1H-NMR study and structure determination of 4,4- and 4,6-dimers from electrochemical reduction of NADP+

The products arising from one-electron electrochemical reduction of the coenzyme nicotinamide adenine dinucleotide phosphate (NADP+) have been studied by HPLC chromatography and 1H-NMR spectroscopy. HPLC and NMR analyses have shown seven dimeric species, the most abundant of which (40%) has been isolated and has resulted to be an NADP 4,4-linked dimer. The other two diastereoisomeric 4,4-dimers present for the 25% and 10%, respectively, have been detected in the crude reaction mixture, but have not been isolated. The 4,4-tetrahydrobipyridine structure and the stereochemistry at the ring-ring junction for these three isomers have been determined on the basis of their NMR parameters. Preparative HPLC chromatography also led to two fractions enriched in another four dimers, present in the crude mixture, which turned out to have a 4,6-tetrahydrobipyridine structure. All the chemical shifts and the H,H coupling constants of the 4,4- and 4,6-tetrahydrobipyridine systems have been obtained for the seven compounds. For the most abundant among the 4,4-dimers the NMR analysis also gave the coupling constant values of the ribose-diphosphate chain.

Choline pivaloyl ester enhances brain expression of both nerve growth factor and high-affinity receptor TrkA, and reverses memory and cognitive deficits, in rats with excitotoxic lesion of nucleus basalis magnocellularis

The aim of present work was the evaluation of the effects on brain levels of nerve growth factor (NGF) and of its high-affinity tyrosine kinase A receptor (TrkA), induced in rats unilaterally lesioned at nucleus basalis magnocellularis (NBM), by treatment with choline pivaloyl ester (CPE). CPE was daily administered (60 micromol/Kg ip) during 3 weeks to rats selectively lesioned by AMPA infusion into right NBM; the intact left NBM serving as control. NGF levels were determined in cerebral cortex and hippocampus by Elisa assay. TrkA receptor expression was evaluated in right NBM by Western blotting analysis. CPE treatment significantly increased NGF levels in both hippocampus and neocortex in right NBM, compared with intact left counter-part and controls. Western blotting showed an evident enhancement in TrkA receptor expression in lesioned right NBM in comparison with intact left counter-part and controls. CPE treatment was also able to restore, in bilaterally NBM-lesioned rats, the disrupted cortical EEG and HVS activities as well as to reverse deficits in learning and memory in spatial navigation and probe trials, and cognitive capacities in object recognition task.

Electroencephalographic effects induced by choline pivaloyl esters in scopolamine-treated or nucleus basalis magnocellularis lesioned rats

The electroencephalographic (EEG) effects of two choline pivaloyl esters, [2-(2,2-dimethylpropionyloxy)ethyl]trimethylammonium iodide (1) and [2-(2,2-dimethylpropionyloxy)ethyl]trimethylammonium 2,2-dimethylpropionate (2), were evaluated in scopolamine-treated or nucleus basalis magnocellularis (NBM) lesioned rats. In scopolamine-treated animals, Compounds 1 and 2 prevented or reduced EEG effects, such as increased amplitude of total spectra and high-voltage spindle (HVS) activity as well. Furthermore, choline esters showed a noticeable effectiveness in reversing the EEG changes produced in rats by AMPA-induced lesion of NBM. Indeed, Compounds 1 and 2 were able to induce EEG desynchronisation, a significant decrease in the total EEG power (0.25-16 Hz) and in the lower frequency delta and theta bands (0.25-3 and 3-6 Hz, respectively). The EEG effects produced by Compounds 1 and 2 were well comparable with that evoked by Tacrine, used as a reference compound. The results of the present work allow us to put forward the hypothesis that the EEG effects observed are most likely mediated through the stimulation of the cholinergic neurotransmission ensuing from enhanced cerebral levels of acetylcholine (ACh) consequent upon acetylcholinesterase (AChE) inhibition by choline pivaloyl esters.

Structure of the dimers arising from one-electron electrochemical reduction of pyridinium salts 3,5-disubstituted with electron-withdrawing groups

One-electron electrochemical reduction of the salts 1-benzyl-3,5-bis(methylcarbamoyl)pyridinium bromide 3a and 1-benzyl-3,5-dicarbamoylpyridinium bromide 3b yields mixtures of four isomeric dimers, as shown by HPLC analysis and mass spectrometry. 1H and 13C NMR spectrometry allows us to determine the structures of the mixture components. In both mixtures, the two most abundant products are identified as 4,4′- and 2,4′-tetrahydrobipyridines (5a, 5b and 6a, 6b, respectively), while minor amounts of a pair of diastereomeric 2,2′-linked dimers are also detected in (7a, 8a and 7b, 8b respectively). Therefore, the NMR studies lead to the conclusion that the structure assignment of conformers of 5a, made previously for 6a and 7a, is not correct. All the 2,2′- and 2,4′-linked dimers undergo photochemical dissociation into two pyridinyl radicals which recombine to yield 4,4′-linked dimers.