Proarrhythmic Effect of Acetylcholine-Esterase Inhibitors Used in the Treatment of Alzheimer's Disease: Benefit of Rivastigmine in an Experimental Whole-Heart Model.

Several studies suggest QT prolongation and torsade de pointes with acetylcholine-esterase inhibitors. We therefore examined the electrophysiologic profile of donepezil, rivastigmine, and galantamine in a sensitive whole-heart model of proarrhythmia. 34 rabbit hearts were isolated and retrogradely perfused employing the Langendorff setup. Hearts were treated either with donepezil, rivastigmine, or galantamine in rising concentrations and electrophysiologic studies were performed. In the presence of donepezil and galantamine, spatial dispersion of repolarization was amplified. Cardiac repolarization (QT interval and action potential duration) was prolonged with donepezil but not with galantamine. Remarkably, both drugs induced triggered activity (early afterdepolarizations and torsade de pointes tachycardia). Despite a pronounced prolongation of repolarization with rivastigmine, no increase in spatial dispersion of repolarization and thus no triggered activity was observed. In the present study, donepezil and galantamine provoked triggered activity, whereas rivastigmine did not have proarrhythmic effects. Spatial dispersion of repolarization but not duration of cardiac repolarization was associated with increased risk of drug-induced proarrhythmia with acetylcholine-esterase inhibitors. Consequently, QT interval duration might be insufficient to estimate the risk of proarrhythmia with acetylcholine-esterase inhibitors. Our findings emphasize the need for further electrocardiographic risk predictors.

Synthesis of New Galanthamine-Peptide Derivatives Designed for Prevention and Treatment of Alzheimer's Disease.

BACKGROUND: Although no effective treatment for the Alzheimer's disease currently exist, some drugs acting as Acetylcholinesterase inhibitors, like galanthamine have positively affected such patients. ß- and/or γ-secretase inhibitors are another type of potential drugs. Here we report synthesis of new peptide-galanthamine derivatives, with expected inhibitory activity against both Acetylcholinesterase and ß-secretase. OBJECTIVES: The aim of this work is obtaining new peptide derivatives of galanthamine with decreased toxicity compared to galanthamine. METHODS: Syntheses were conducted in solution using fragment condensation approach. The new derivatives were characterized by melting points, angle of optical rotation, NMR and Mass spectra. Acute toxicity was determined on mice, according to a Standard protocol. All new compounds were tested in vitro for cytotoxic activity in a panel of human (HEP-G2, BV-173) and murine (Neuro-2a) tumor cell lines via a standard MTT-based colorimetric method. RESULTS: New derivatives of galanthamine containing shortened analogues of ß-secretase inhibitor (Boc- Asn-Leu-Ala-Val-OH) and either nicotinic or isonicotinic residue, both connected with a linker (L-Asp) to position 11 of galanthamine were obtained. In vivo toxicity of some new compounds was found up to 1000 mg/kg. Cell toxicity screening against the tumor cell lines showed negligible growth-inhibiting properties of the galanthamine derivatives. CONCLUSION: Synthesis of new galanthamine derivatives comprising peptide moiety and nicotinic acid or isonicotinic acid is reported. Acute toxicity studies reveal they are about 100 times less toxic than galanthamine. This effect is due to the peptide fragment. Cytotoxicity studies show good correlation with low toxicity results. These results are encouraging for the application of this class compounds as medicines.

Zebrafish biosensor for toxicant induced muscle hyperactivity.

Robust and sensitive detection systems are a crucial asset for risk management of chemicals, which are produced in increasing number and diversity. To establish an in vivo biosensor system with quantitative readout for potential toxicant effects on motor function, we generated a transgenic zebrafish line TgBAC(hspb11:GFP) which expresses a GFP reporter under the control of regulatory elements of the small heat shock protein hspb11. Spatiotemporal hspb11 transgene expression in the musculature and the notochord matched closely that of endogenous hspb11 expression. Exposure to substances that interfere with motor function induced a dose-dependent increase of GFP intensity beginning at sub-micromolar concentrations, while washout of the chemicals reduced the level of hspb11 transgene expression. Simultaneously, these toxicants induced muscle hyperactivity with increased calcium spike height and frequency. The hspb11 transgene up-regulation induced by either chemicals or heat shock was eliminated after co-application of the anaesthetic MS-222. TgBAC(hspb11:GFP) zebrafish embryos provide a quantitative measure of muscle hyperactivity and represent a robust whole organism system for detecting chemicals that affect motor function.

Deep brain stimulation of the subthalamic nucleus reverses oral tremor in pharmacological models of parkinsonism: interaction with the effects of adenosine A2A antagonism.

Deep brain stimulation (DBS) of the subthalamic nucleus is increasingly being employed as a treatment for parkinsonian symptoms, including tremor. The present studies used tremulous jaw movements, a pharmacological model of tremor in rodents, to investigate the tremorolytic effects of subthalamic DBS in rats. Subthalamic DBS reduced the tremulous jaw movements induced by the dopamine D2 family antagonist pimozide and the D1 family antagonist ecopipam, as well as the cholinomimetics pilocarpine and galantamine. The ability of DBS to suppress tremulous jaw movements was dependent on the neuroanatomical locus being stimulated (subthalamic nucleus vs. a striatal control site), as well as the frequency and intensity of stimulation used. Importantly, administration of the adenosine A2A receptor antagonist MSX-3 reduced the frequency and intensity parameters needed to attenuate tremulous jaw movements. These results have implications for the clinical use of DBS, and future studies should determine whether adenosine A2A antagonism could be used to enhance the tremorolytic efficacy of subthalamic DBS at low frequencies and intensities in human patients.

Galantamine (Reminyl) delays cardiac ventricular repolarization and prolongs the QT interval by blocking the HERG current.

Galantamine is a reversible inhibitor of acetylcholinesterase and an allosteric-potentiating ligand of the nicotinic acetylcholine receptors. It is used for treating mild-to-moderate Alzheimer's disease. Interestingly, QT interval prolongation on the electrocardiogram (ECG), malignant ventricular arrhythmias and syncope have been reported with galantamine. Our objective was to evaluate the effects of galantamine on cardiac ventricular repolarization. Three sets of experiments were undertaken: 1) Whole cell patch-clamp experiments: HERG- or KCNQ1+KCNE1-transfected cells were exposed to galantamine 0.1-1000 µmol/l (n=25 cells, total) to assess drug effect on HERG and KCNQ1+KCNE1 currents. 2) Langendorff perfusion experiments: Isolated hearts from male Hartley guinea pigs (n=9) were exposed to galantamine 1 µmol/l to assess drug-induced prolongation of monophasic action potential duration measured at 90% repolarization (MAPD(90)). 3) Cardiac telemetry experiments: Guinea pigs (n=7) implanted with wireless transmitters were injected a single intraperitoneal (i.p.) dose of galantamine 3mg/kg and 24h ECG recordings were made. 1) The estimated IC(50) for galantamine on HERG current was 760.2 µmol/l. Moreover, galantamine 10 µmol/l had a small inhibiting effect on KCNQ1+KCNE1 current (12.17 ± 2.19% inhibition, n=10 cells). 2) While pacing at cycle lengths of 150, 200 or 250 ms, galantamine 1 µmol/l prolonged MAPD(90) by respectively 5.1 ± 1.6 ms, 9.4 ± 1.9 ms and 12.1 ± 2.1 ms. 3) Galantamine 3 mg/kgi.p. caused a maximal 11.9 ± 2.7 ms prolongation of the corrected QT (QTc). Galantamine is a weak HERG blocker. This contributes to its mild QT-prolonging effect. Patients could be at risk of cardiac proarrhythmia during drug overdosage or interactions involving cytochrome 2D6 drug-metabolizing enzyme.

Oral tremor induced by galantamine in rats: a model of the parkinsonian side effects of cholinomimetics used to treat Alzheimer's disease.

Anticholinesterases are the most common treatment for Alzheimer's disease, and, in recent years, a new group of cholinesterase inhibitors (i.e. rivastigmine, galantamine, and donepezil) has become available. Although these drugs improve cognitive symptoms, they also can induce or exacerbate parkinsonian symptoms, including tremor. The present studies were conducted to determine if galantamine induces tremulous jaw movements, a rodent model of parkinsonian tremor, and to investigate whether these oral motor impairments can be reversed by co-administration of adenosine A(2A) antagonists. The first experiment demonstrated that systemic injections of galantamine (0.75-6.0 mg/kg I.P.) induced a dose-related increase in tremulous jaw movements in rats. In a second study, co-administration of the muscarinic antagonist scopolamine (0.0156-0.25 mg/kg I.P.) produced a dose dependent suppression of tremulous jaw movements induced by a 3.0 mg/kg dose of galantamine, indicating that galantamine induces these tremulous oral movements through actions on muscarinic acetylcholine receptors. In two additional studies, analyses of freeze-frame video and electromyographic activity recorded from the lateral temporalis muscle indicated that the local frequency of these galantamine-induced jaw movements occurs in the 3-7 Hz frequency range that is characteristic of parkinsonian tremor. In the final experiment, the adenosine A(2A) antagonist MSX-3 significantly attenuated the tremulous jaw movements induced by the 3.0mg/kg dose of galantamine, which is consistent with the hypothesis that co-administration of adenosine A(2A) antagonists may be beneficial in reducing parkinsonian motor impairments induced by anticholinesterase treatment.

A single in vivo application of cholinesterase inhibitors has neuron type-specific effects on nicotinic receptor activity in guinea pig hippocampus.

The present study was designed to test the hypothesis that an acute in vivo treatment with reversible or irreversible acetylcholinesterase (AChE) inhibitors modifies the activities of nicotinic receptors (nAChRs) in hippocampal neurons. Here, whole-cell nicotinic responses were recorded from CA1 interneurons in hippocampal slices obtained from male guinea pigs at 1, 7, or 14 days after treatment with the irreversible AChE inhibitor, soman (1x LD(50) s.c.), and/or the reversible AChE inhibitor, galantamine (8 mg/kg i.m.). Naive animals were used as controls. Three types of nAChR responses, namely types IA, II, and III, which were mediated by alpha 7, alpha 4 beta 2, and alpha 3 beta 2 beta 4 nAChRs, respectively, could be recorded from the interneurons. The magnitude of alpha 7 nAChR currents was neuron-type dependent. Stratum radiatum interneurons (SRIs) with thick initial dendrites had the largest alpha 7 nAChR currents. Acute challenge with soman caused sustained reduction of type IA current amplitudes recorded from stratum oriens interneurons and increased the ratio of acetylcholine- to choline-evoked current amplitudes recorded from SRIs. In guinea pigs that developed long-lasting convulsions after the soman challenge, there was a sustained reduction of alpha 3 beta 2 beta 4 nAChR responses. Acute treatment with galantamine had no effect on type IA or III responses, whereas it decreased the incidence of type II currents. Pretreatment of the guinea pigs with galantamine prevented the suppressive effect of soman on type III responses. The neuron type-specific changes in nAChR activity induced by soman, some of which could be prevented by galantamine, may contribute to the maintenance of pathological rhythms in the hippocampal neuronal network.

Analyses of mortality risk in patients with dementia treated with galantamine.

OBJECTIVE: To analyze mortality data from patients with Alzheimer's disease (AD), Alzheimer's plus cerebrovascular disease (AD + CVD) or vascular dementia (VaD). METHODS: (1) Meta-analysis of mortality data from double-blind, placebo-controlled, randomized trials; and (2) recontact study to collect additional longer term mortality data from previous galantamine trial participants. RESULTS (META-ANALYSIS): Across 12 trials (< or =6 months duration), there was no increased risk of mortality associated with the use of galantamine (n = 4116) compared with that of placebo (n = 2386) (OR galantamine/placebo: 0.67, 95% CI 0.41-1.10). RESULTS (RECONTACT STUDY): Median survival was 79 months for patients with AD (n = 478) and 59 months for patients with AD + CVD (n = 180) or VaD (n = 145). Prolonged galantamine treatment (> vs < or =6 months) was not associated with decreased survival time (75 vs 61 months respectively; P = 0.02). Cox regression analyses were consistent with the Kaplan-Meier analyses. CONCLUSIONS: We found no short-term or longer term evidence of increased risk of mortality associated with the use of galantamine in patients with AD, AD + CVD or VaD.

Study of PMS777, a new type of acetylcholinesterase inhibitor, in human HepG2 cells. Comparison with tacrine and galanthamine on oxidative stress and mitochondrial impairment.

Acetylcholinesterase inhibitors are commonly used as cognitive enhancers for dementia in aged people. Among them, tacrine (THA) but not galanthamine, was shown to exhibit hepatotoxicity which reduces its clinical use. PMS777, both a PAF antagonist and a new potent acetylcholinesterase inhibitor was recently demonstrated to reverse scopolamine-induced amnesia in mice without toxicity. In the present study, the effects of THA, galanthamine and PMS777 were compared in HepG2 cells on the oxidative parameters involved in the reported hepatotoxicity of THA. THA (> or = 10 microM) induced an oxidative stress as shown by elevated ROS and MDA production and by a decrease in GSH level. Moreover, mitochondrial membrane potential and redox status were decreased. At low concentrations (< or =10 microM), there was no significant disturbance. None of the oxidative stress markers was affected by PMS777 up to the maximum concentration tested and it is suggested that PMS777 is not cytotoxic for HepG2 cells. Galanthamine was also without cytotoxicity. Our results suggest that the toxic effect of THA above 10 microM may be caused by drug-induced mitochondrial energization impairment and destabilisation of membrane phospholipids associated with an oxidative stress. In contrast by preventing these dysfunctions, PMS777 could be safer than THA.

[Mechanism of the effect of diazepam on acetylcholine concentration in mouse brain]. / Issledovanie mekhanizma vliianiia diazepama na soderzhanie atsetilkholina v golovnom mozge myshei.

Intraperitoneal injection of diazepam (20 mg/kg) caused an increase of free and bound acetylcholine in the mouse brain. Diazepam pretreatment (20 mg/kg) increased galanthamine anticholinesterase activity and its toxicity; as to physostigmine, armine, and paraoxon toxicity--it remained unchanged. It is supposed that diazepam blocks the release of aetylcholine from the cholinergic nerve terminals which should result in a decrease of functional acetylcholine concentrations in the synapse.