Inhibitor Report for: 7-Methoxytacrine

Alzheimer s disease (AD) is a progressive neurodegenerative dementia which currently represents one of the biggest threats for the human kind. The cure is still unknown and various hypotheses (cholinergic, amyloidal, oxidative, vascular etc.) are investigated in order to understand the pathophysiology of the disease and on this basis find an effective treatment. Tacrine, the first approved drug for the AD disease treatment, has been reported to be a multitargeted drug, however it was withdrawn from the market particularly due to its hepatotoxicity. Its derivative 7-methoxytacrine (7- MEOTA) probably due to the different metabolization does not exert this side effect. The aim of our study was to compare these two cholinesterase inhibitors from various, mainly cholinergic, points of view relevant for a potential AD drug. We found that 7-MEOTA does not fall behind its more well-known parent compound - tacrine. Furthermore, we found, that 7-MEOTA exerts better properties in most of the tests related to a possible AD treatment. Only the pharmacokinetics and a higher acetylcholinesterase and butyrylcholinesterase inhibitory potency would slightly give advantages to tacrine over 7-MEOTA, but concerning its lower toxicity, better antioxidant properties, interaction with muscarinic and nicotinic receptors and "safer" metabolization provide strong evidence for reconsider 7-MEOTA and its derivatives as candidate molecules for the treatment of AD.

In vivo inhibition of blood acetylcholinesterase activity by 9-amino-1, 2, 3, 4-tetrahydroacridine, its 7-methoxy derivative and physostigmine was studied in rats. Changes of enzyme activity in the blood were continually registered using an automatic colorimeter Auto Analyzer system. The dependence of % enzyme inhibition upon time in semilogarithmic transformation was characterized by a two phase curve. The first phase reflected the increase in the concentration of inhibitors in the blood during their resorption; this was followed by a slow second phase of inhibition. The inhibitory effect decreased in the order: physostigmine greater than tacrine greater than 7-methoxytacrine. The relationship between the anticholinesterase and antipsychotomimetic action of the examined substances is discussed.

Alzheimer s disease (AD) is a progressive neurodegenerative dementia which currently represents one of the biggest threats for the human kind. The cure is still unknown and various hypotheses (cholinergic, amyloidal, oxidative, vascular etc.) are investigated in order to understand the pathophysiology of the disease and on this basis find an effective treatment. Tacrine, the first approved drug for the AD disease treatment, has been reported to be a multitargeted drug, however it was withdrawn from the market particularly due to its hepatotoxicity. Its derivative 7-methoxytacrine (7- MEOTA) probably due to the different metabolization does not exert this side effect. The aim of our study was to compare these two cholinesterase inhibitors from various, mainly cholinergic, points of view relevant for a potential AD drug. We found that 7-MEOTA does not fall behind its more well-known parent compound - tacrine. Furthermore, we found, that 7-MEOTA exerts better properties in most of the tests related to a possible AD treatment. Only the pharmacokinetics and a higher acetylcholinesterase and butyrylcholinesterase inhibitory potency would slightly give advantages to tacrine over 7-MEOTA, but concerning its lower toxicity, better antioxidant properties, interaction with muscarinic and nicotinic receptors and "safer" metabolization provide strong evidence for reconsider 7-MEOTA and its derivatives as candidate molecules for the treatment of AD.

The aim of this work is a comparison of single and repeated peroral administration of cyclosporine (CsA) and the interaction of repeated administration of CsA and 7-methoxytacrine (MEOTA) on the activity of acetylcholinesterase (AChE) in the frontal cortex, hippocampus, septum, and basal ganglia in rats. Both single and repeated administration of CsA diminished the activity of AChE in the frontal cortex, septum and basal ganglia, while the enzyme activity in the hippocampus was diminished only in the case of repeated CsA, as well as repeated CsA + MEOTA administration. Repeated administration of CsA led to a further augmentation of anticholinesterase activity only in the frontal cortex and--in a lesser extent--in the basal ganglia. No augmentation of AChE activity was observed in the hippocampus and septum.

Changes of choline acetyltransferase (ChAT) activity in the hippocampus and the basal ganglia were studied in rats treated i.p. with L-carnitine (CRT) and 7-methoxytacrine (7-MEOTA) (i.m.) separately or 3-days treated with L-carnitine and then with one administration of 7-MEOTA. Both compounds increased ChAT activity when administered separately. 3-day treatment of CRT followed by administration of 7-MEOTA normalized ChAT activity.

A new capillary zone electrophoresis (CZE) method for the determination of tacrine (THA), 7-methoxytacrine (7-MTHA) and their basic metabolites (THAm, 7-MTHAm) in pharmaceutical and biological samples (urine and serum) was developed. Separation of all compounds by CZE was carried out using a 46.6 cm untreated fused-silica capillary applying 20 kV separation voltage using 50 mM phosphate buffer of pH 2.8 for THA and THAm and of pH 7.8 for 7-MTHA and 7-MTHAm as background electrolyte (BGE). Detection was carried out at 240 nm (THA and THAm) and 248 nm (7-MTHA and 7-MTHAm). THA and THAm were separated in less than 4 min while 7-MTHA and 7-MTHAm were separated in less than 7 min. The detection limits (SIN = 3) obtained were 3 ppb for THA and 4 ppb for 7-MTHA in aqueous solutions; 50 ppb for THA and 47 ppb for 7-MTHA for the determination in urine (diluted 1:10); 52 ppb for THA and 56 ppb for 7-MTHA, in deproteinized serum samples. The methods are suitable for therapeutic drug monitoring of the drugs.

The effects of 7-methoxytacrine (7-MEOTA), a less toxic derivative of tetrahydroaminoacridine, on the activity of acetylcholinesterase (AChE) molecular forms were investigated in vitro. AChE molecular forms were separated by sucrose gradient sedimentation from homogenates of the frontal cerebral cortex prepared with buffer containing Triton X-100 (soluble + membrane-bound enzyme). Two molecular forms, namely 10S and 4S corresponding to globular tetrameric (G4) and monomeric (G1) forms, respectively, were detected; their molecular weights were 220,000 and 54,000 Da. A significantly higher sensitivity to 7-MEOTA of G4 than of G1 forms was observed. The Ki values were 0.21 +/- 0.07 microM for the former and 0.70 +/- 0.15 microM for the latter. The differential inhibition of AChE molecular forms by 7-MEOTA is discussed in relation to its possible clinical application for treatment of disorders such as Alzheimer's disease, in which a reduction of brain cholinergic neurotransmission is believed to play a role.

The 7-metoxytacrine (7-MEOTA) is an original Czech cholinergic agent synthetized in the labs of the Military Medical Academy in Hradec Kralove. The treatment of tardive dyskinesias is one of the possible indications of the use of 7-MEOTA in clinical practice. The authors have summed up their experience from the first phase of clinical tests with 7-MEOTA in psychiatrical patients suffering from tardive dyskinesias in long-termed administration of cholinergic agents. The clinical efficiency and tolerance of 7-MEOTA have been evaluated after a single administration of 100 mg of 7-MEOTA per os in 19 patients. A reduction of dyskinesias was observed as early as 4 h following the testing dose. In 5 patients, viz. in 26% a reduction of dyskinesias was observed of more than 50% of the original value of the total score of the testing scale AIMS. Except for a slight decrease of the blood pressure and a mild somnolence in 3 patients no other undesirable effects have been observed. In some patients a slight euphorization effect of 7-MEOTA has been found.

The effects of tacrine (1,2,3,4-tetrahydro-9-aminoacridine) and 7-methoxytacrine on the metabolism of acetylcholine were investigated in experiments on prisms of rat cerebral cortex incubated in vitro in low-potassium (3 mmol/L K+) media; cholinesterases were inactivated by paraoxon to avoid any action of tacrine and methoxytacrine via their inhibition. Under "resting" conditions, tacrine and methoxytacrine increased the synthesis of unlabeled acetylcholine in the prisms; at the same time, they inhibited the uptake of [14C]choline from the medium and the synthesis of [14C]acetylcholine. The concentration of free choline was not increased by tacrine or methoxytacrine in either the tissue or the medium. The contradiction between the increased synthesis of unlabeled and the diminished synthesis of labeled acetylcholine indicates that the utilization of intracellular choline (which is presumably mobilized from intracellular choline esters) for the synthesis of acetylcholine is increased by tacrine and methoxytacrine. This conclusion is supported by the observation that the inhibition of acetylcholine synthesis during incubation with hemicholinium-3 (an inhibitor of choline transport into cholinergic nerve terminals) was overcome when tacrine was present simultaneously with hemicholinium-3. When the prisms were preincubated with [14C]choline and incubated with tacrine or methoxytacrine only after this, the amount of [14C]acetylcholine recovered in the tissue plus the medium was higher at the end of incubation with tacrine or methoxytacrine than without them, again suggesting that the drugs were able to increase the utilization of intracellular [14C]choline or its esters for acetylcholine synthesis.(ABSTRACT TRUNCATED AT 250 WORDS)

7-methoxy-tetrahydroaminoacridine (7-MEOTA) is a new reversible cholinesterase inhibitor. Forty-eight young male volunteers divided into six dosage groups were included into a single-dose pharmacokinetic study with either oral (p.o.) or intramuscular (i.m.) administration. The dose of 7-MEOTA was 2, 4 or 8 mg/kg body weight p.o. or 0.5, 1 or 2 mg/kg body weight i.m. in the respective six dosage groups. The plasma levels data were fitted to an open one-compartmental model. The compound showed cholinomimetic adverse effects in 2 subjects with the blood levels exceeding 1,500 micrograms/l. The red blood cells levels paralleled those in plasma and were 2.5 times higher. The tmax was 4 hours and 1 h, t1/2 8.7 +/- 3.9 hours and 6.5 +/- 5.8 hours in case of p.o. and i.m. administration, respectively. The apparent clearance (D/AUC) was 5 times higher following p.o. administration, reflecting the differences in bioavailability.

Cholinesterase inhibitor tacrine (1,2,3,4-tetrahydro-9-aminoacridine) is known to interfere with the binding of specific ligands to muscarinic receptors with unusually steep binding inhibition curves. We investigated whether the concentration dependence of the inhibition of binding is associated with the inhibitory effect of tacrine on the activity of cholinesterases, and compared the effect of tacrine with that of 7-methoxytacrine. Tacrine was found to inhibit the specific binding of [3H]quinuclidinyl benzilate (QNB) in rat brain cortex with IC50 values of 11 microM both in the absence and in the presence of 100 microM eserine, which had been added to ensure complete inhibition of cholinesterases at all concentrations of tacrine; in the cerebellum, the IC50 value was 10 microM in the absence and 14 microM in the presence of eserine; Hill slope factors (nH) were in the range of 1.55-1.79 and were not significantly affected by the presence of eserine. 7-Methoxytacrine inhibited the binding of [3H]QNB with an IC50 value of 2.3 microM in the cortex and of 2.6 microM in the cerebellum. The results indicate that the degree and the steep course of the inhibition of [3H]QNB binding to M1 and M2 muscarinic receptors by tacrine do not depend on its inhibitory effect on cholinesterases, and that 7-methoxytacrine is likely to interfere with the function of muscarinic receptors 4-5 times more strongly than tacrine.

The effects of tacrine (1,2,3,4-tetrahydro-9-aminoacridine) and 7-methoxytacrine on the metabolism of brain acetylcholine were investigated in experiments in which acetylcholine turnover was stimulated by tissue depolarization or by 4-aminopyridine. Rat cerebrocortical prisms were preincubated under "resting" conditions (Krebs-Ringer buffer with 3 mmol/L K+ and with paraoxon to inhibit cholinesterases) and then incubated in the presence of tacrine or methoxytacrine and of 50 mmol/L K+. Both drugs diminished the amount of acetylcholine released by depolarization and the amount of acetylcholine synthesized during incubation; in experiments in which [14C]choline was present in the incubation medium simultaneously with tacrine or methoxytacrine, the drugs diminished the uptake of [14C]choline by the tissue and the amount of [14C]-acetylcholine synthesized and released into the medium. In these experiments, it was not possible to distinguish whether the inhibitory effects of tacrine and methoxytacrine were primarily on the process of acetylcholine synthesis (particularly on the uptake of choline), or whether the drugs also acted directly on the process of neurotransmitter release. In subsequent experiments the prisms were preincubated with [14C]choline and only then subjected to a short depolarization in the presence of hemicholinium-3 and tacrine or methoxytacrine. Both drugs severely inhibited the release of preformed [14C]acetylcholine and prevented the diminution of tissue [14C]acetylcholine stores. Methoxytacrine was also found to diminish the release of acetylcholine induced by 4-aminopyridine while increasing the content of acetylcholine in the tissue. Tacrine and methoxytacrine had no effect on the activity of choline acetyltransferase (EC 2.3.1.6).(ABSTRACT TRUNCATED AT 250 WORDS)

1. The influence of 7-methoxytacrine (7-MEOTA) on the non epileptic myoclonus of the Papio papio baboon was studied in 5 animals. 2. This type of myoclonus is thought to depend on a cholinergic system dysfunction since it can be induced by atropine and blocked by physostigmine. 3. 7-MEOTA, a tacrine derivative, is believed to display a conspicuous anticholinesterase activity but, surprisingly, it here potentiated the non epileptic myoclonus occuring either spontaneously or induced by atropine. 4. In baboons not spontaneously presenting the non epileptic myoclonus, 7-MEOTA induced the myoclonus in a fashion similar to atropine; such a myoclonus was blocked by physostigmine. 5. These data indicate a possible antagonist action of tacrine on the muscarinic acetylcholine receptor. From these data, it is suggested that caution is necessary when introducing a tacrine derivative in clinical practice.

In vivo inhibition of blood acetylcholinesterase activity by 9-amino-1, 2, 3, 4-tetrahydroacridine, its 7-methoxy derivative and physostigmine was studied in rats. Changes of enzyme activity in the blood were continually registered using an automatic colorimeter Auto Analyzer system. The dependence of % enzyme inhibition upon time in semilogarithmic transformation was characterized by a two phase curve. The first phase reflected the increase in the concentration of inhibitors in the blood during their resorption; this was followed by a slow second phase of inhibition. The inhibitory effect decreased in the order: physostigmine greater than tacrine greater than 7-methoxytacrine. The relationship between the anticholinesterase and antipsychotomimetic action of the examined substances is discussed.