Tacrine: a pharmacological review

Innovative approaches to Alzheimer's therapy: Harnessing the power of heterocycles, oxidative stress management, and nanomaterial drug delivery system

Alzheimer's disease (AD) presents a complex pathology involving amyloidogenic proteolysis, neuroinflammation, mitochondrial dysfunction, and cholinergic deficits. Oxidative stress exacerbates AD progression through pathways like macromolecular peroxidation, mitochondrial dysfunction, and metal ion redox potential alteration linked to amyloid-beta (Aβ). Despite limited approved medications, heterocyclic compounds have emerged as promising candidates in AD drug discovery. This review highlights recent advancements in synthetic heterocyclic compounds targeting oxidative stress, mitochondrial dysfunction, and neuroinflammation in AD. Additionally, it explores the potential of nanomaterial-based drug delivery systems to overcome challenges in AD treatment. Nanoparticles with heterocyclic scaffolds, like polysorbate 80-coated PLGA and Resveratrol-loaded nano-selenium, show improved brain transport and efficacy. Micellar CAPE and Melatonin-loaded nano-capsules exhibit enhanced antioxidant properties, while a tetra hydroacridine derivative (CHDA) combined with nano-radiogold particles demonstrates promising acetylcholinesterase inhibition without toxicity. This comprehensive review underscores the potential of nanotechnology-driven drug delivery for optimizing the therapeutic outcomes of novel synthetic heterocyclic compounds in AD management. Furthermore, the inclusion of various promising heterocyclic compounds with detailed ADMET (Absorption, Distribution, Metabolism, Excretion, and Toxicity) data provides valuable insights for planning the development of novel drug delivery treatments for AD.

Electrochemical Acetylcholinesterase Sensors for Anti-Alzheimer's Disease Drug Determination

Neurodegenerative diseases and Alzheimer's disease (AD), as one of the most common causes of dementia, result in progressive losses of cholinergic neurons and a reduction in the presynaptic markers of the cholinergic system. These consequences can be compensated by the inhibition of acetylcholinesterase (AChE) followed by a decrease in the rate of acetylcholine hydrolysis. For this reason, anticholinesterase drugs with reversible inhibition effects are applied for the administration of neurodegenerative diseases. Their overdosage, variation in efficiency and recommendation of an individual daily dose require simple and reliable measurement devices capable of the assessment of the drug concentration in biological fluids and medications. In this review, the performance of electrochemical biosensors utilizing immobilized cholinesterases is considered to show their advantages and drawbacks in the determination of anticholinesterase drugs. In addition, common drugs applied in treating neurodegenerative diseases are briefly characterized. The immobilization of enzymes, nature of the signal recorded and its dependence on the transducer modification are considered and the analytical characteristics of appropriate biosensors are summarized for donepezil, huperzine A, rivastigmine, eserine and galantamine as common anti-dementia drugs. Finally, the prospects for the application of AChE-based biosensors in clinical practice are discussed.

Advances in the Study of the Pathology and Treatment of Alzheimer's Disease and Its Association with Periodontitis

Alzheimer's disease (AD) has become one of the leading causes of health problems in the elderly, and studying its causes and treatments remains a serious challenge for researchers worldwide. The two main pathological features of Alzheimer's disease are the extracellular deposition of β-amyloid (Aβ) to form senile plaques and the intracellular aggregation of hyperphosphorylated Tau protein to form neurofibrillary tangles (NFTs). Researchers have proposed several hypotheses to elucidate the pathogenesis of AD, but due to the complexity of the pathophysiologic factors involved in the development of AD, no effective drugs have been found to stop the progression of the disease. Currently, the mainstay drugs used to treat AD can only alleviate the patient's symptoms and do not have a therapeutic effect. As researchers explore interactions among diseases, much evidence suggests that there is a close link between periodontitis and AD, and that periodontal pathogenic bacteria can exacerbate Aβ deposition and Tau protein hyperphosphorylation through neuroinflammatory mechanisms, thereby advancing the pathogenesis of AD. This article reviews recent advances in the pathogenesis of AD, available therapeutic agents, the relevance of periodontitis to AD, and mechanisms of action.

Thiadiazole – A promising structure in design and development of anti-Alzheimer agents

The design and development of effective multitargeted agents in treating Alzheimer disease (AD) has always been a hot topic in the field of drug discovery. Since AD is a multifactorial disorder, various key hidden players such as deficit of acetylcholine (ACh), tau-protein aggregation, and oxidative stress have been associated with the incidence and progress of AD. In pursuit of improving efficacy and expanding the range of pharmacological activities of current AD drugs, the molecular hybridization method is also used intensively. Five-membered heterocyclic systems such as thiadiazole scaffolds have previously been shown to have therapeutic activity. Thiadiazole analogs as an anti-oxidant compound have been known to include a wide range of biological activity from anti-cancer to anti-Alzheimer properties. The suitable pharmacokinetic and physicochemical properties of the thiadiazole scaffold have introduced it as a therapeutic target in medicinal chemistry. The current review portrays the critical role of the thiadiazole scaffold in the design of various compounds with potential effects in the treatment of Alzheimer's disease. Furthermore, the rationale used behind hybrid-based design strategies and the outcomes achieved through the hybridization of Thiadiazole analogs with various core structures have been discussed. In addition, the data in the present review may help researchers in the design of new multidrug combinations that may provide new options for the treatment of AD.

In silico study of tacrine and acetylcholine binding profile with human acetylcholinesterase: docking and electronic structure

Alzheimer disease (AD) is a neurodegenerative process, one of the most common and incident dementia in the population over 60 years. AD manifests the presence of complex biochemical processes involved in neuronal degeneration, such as the formation of senile plaques containing amyloid-β peptides, the development of intracellular neurofibrillary tangles, and the suppression of the acetylcholine neurotransmitter. In this way, we performed a set of theoretical tests of tacrine ligand and acetylcholine neurotransmitter against the human acetylcholinesterase enzyme. Molecular docking was used to understand the most important interactions of these molecules with the enzyme. Computational chemistry calculation was carried out using MP2, DFT, and semi-empirical methods, starting from molecular docking structures. We have also performed studies regarding the non-covalent interactions, electron localization function, molecular electrostatic potential and explicit water molecule influence. For Trp86 residue, we show two main interactions in accordance to the results of the literature for TcAChE. First, intermolecular interactions of the cation-π and sigma-π type were found. Second, close stacking interactions were stablished between THA+ and Trp86 residue on one side and with Tyr337 residue on the other side.

Rodrigues K, Pinz MP, Biondi JV, Becker NP, Blodorn E, Domingues WB, Larroza A, Campos VF, Alves D, Wilhelm EA, Luchese C. Prospecting for a quinoline containing selenium for comorbidities depression and memory impairment induced by restriction stress in mice

RATIONALE

Depression is often associated with memory impairment, a clinical feature of Alzheimer's disease (AD), but no effective treatment is available. 7-Chloro-4-(phenylselanyl) quinoline (4-PSQ) has been studied in experimental models of diseases that affect the central nervous system.

OBJECTIVES

The pharmacological activity of 4-PSQ in depressive-like behavior associated with memory impairment induced by acute restraint stress (ARS) in male Swiss mice was evaluated.

METHODS

ARS is an unavoidable stress model that was applied for a period of 240 min. Ten minutes after ARS, animals were intragastrically treated with canola oil (10 ml/kg) or 4-PSQ (10 mg/kg) or positive controls (paroxetine or donepezil) (10 mg/kg). Then, after 30 min, mice were submitted to behavioral tests. Corticosterone levels were evaluated in plasma and oxidative stress parameters; monoamine oxidase (MAO)-A and MAO -B isoform activity; mRNA expression levels of kappa nuclear factor B (NF-κB); interleukin (IL)-1β, IL-18, and IL-33; phosphatidylinositol-se-kinase (PI3K); protein kinase B (AKT2), as well as acetylcholinesterase activity were evaluated in the prefrontal cortex and hippocampus.

RESULTS

4-PSQ attenuated the depressive-like behavior, self-care, and memory impairment caused by ARS. Based on the evidence, we believe that effects of 4-PSQ may be associated, at least in part, with the attenuation of HPA axis activation, attenuation of alterations in the monoaminergic system, modulation of oxidative stress, reestablishment of AChE activity, modulation of the PI3K/AKT2 pathway, and reduction of neuroinflammation.

CONCLUSIONS

These results suggested that 4-PSQ exhibited an antidepressant-like effect and attenuated the memory impairment induced by ARS, and it is a promising molecule to treat these comorbidities.

Differential Inhibition of the Brain Acetylcholinesterase Molecular Forms Following Sarin, Soman and VX Intoxication in Laboratory Rats

The female Wistar rats were intoxicated (i.m.) with sarin, soman and VX in doses equal to 1xLD50 and pontomedullar areas of the brain were prepared, homogenized, centrifuged and in these samples, acetylcholinesterase (AChE, EC 3.1.1.7) activities were determined. In the same samples, AChE was separated using polyacrylamide gel electrophoresis and AChE molecular forms were detected and densitometrically evaluated. In control animals, AChE was separated into four forms differing in their electrophoretic mobility and their quantitative content in the sample. The form with lowest electrophoretic mobility represent the main part of AChE activity constituting the whole enzymatic activity. Following intoxication with the nerve agents mentioned, the whole AChE activity in the pontomedullar area of the brain was decreasing in intervals of ten minutes (soman and sarin) or one hour (VX). The AChE activity at the time of death (or terminal stage) was represented 5-30 % of controls. Molecular forms of AChE were inhibited in different extent: the form with lowest electrophoretic mobility was diminished to zero level while the form with the highest mobility was practically unaffected, independently on the type of nerve agent. From quantitative expression of percentage content of the forms vs their activity we can imply that values of the total AChE activity represent the ãmeanÒ activity of the forms determined.

N-alkylated Tacrine Derivatives as Potential Agents in Alzheimer's Disease Therapy

BACKGROUND

Based on the prevalence studies, the number of people suffering from dementia will almost double every 20 years, to 65.7 million in 2030 and 115.4 million in 2050, assuming no changes in mortality, effective preventative measures, definitive diagnostic guidelines or curative treatment. From the abovementioned epidemiological data, it is obvious that dementia constitutes a major public health problem not only at present, but unfortunately also in the future.

OBJECTIVES AND METHODS

Several N-alkylated tacrine (THA) derivatives have already been synthesized by Pomponi et al., in 1997. However, these compounds were tested for their anti-AChE activity using enzyme isolated from Electrophorus electricus. For this reason, we have decided to extend the previously reported series of THA derivatives and consequently test them in the battery of experiments, the results of which have served to more relevant evaluation of these compounds from the perspective of Alzeimer´s disease compared to that published by Pomponi.

RESULTS AND CONCLUSION

In summary, all compounds of interest effectively inhibited ChEs in vitro. One of the most promising derivatives 8 bearing an N-octyl chain showed 2.5-fold higher AChE inhibitory activity in relation to tacrine. With respect to blood-brain barrier (BBB) penetration, it can be claimed that synthesized analogues are presumably able to cross the BBB. From the point of view of hepatotoxicity, selected Nalkylated tacrine derivatives exerted worse results compared to tacrine. However, in vitro results are only illustrative, therefore, only in vivo experiments could determine the real value of selected N-alkylated THA derivatives.

Cholinesterase Inhibitors for Alzheimer's Disease: Multitargeting Strategy Based on Anti-Alzheimer's Drugs Repositioning

In the brain, acetylcholine (ACh) is regarded as one of the major neurotransmitters. During the advancement of Alzheimer's disease (AD) cholinergic deficits occur and this can lead to extensive cognitive dysfunction and decline. Acetylcholinesterase (AChE) remains a highly feasible target for the symptomatic improvement of AD. Acetylcholinesterase (AChE) remains a highly viable target for the symptomatic improvement in AD because cholinergic deficit is a consistent and early finding in AD. The treatment approach of inhibiting peripheral AChE for myasthenia gravis had effectively proven that AChE inhibition was a reachable therapeutic target. Subsequently tacrine, donepezil, rivastigmine, and galantamine were developed and approved for the symptomatic treatment of AD. Since then, multiple cholinesterase inhibitors (ChEIs) have been continued to be developed. These include newer ChEIs, naturally derived ChEIs, hybrids, and synthetic analogues. In this paper, we summarize the different types of ChEIs which are under development and their respective mechanisms of actions.

Amnesia-ameliorative effect of a quinoline derivative through regulation of oxidative/cholinergic systems and Na+/K+-ATPase activity in mice

The present study evaluated the anti-amnesic activity of 1-(7-chloroquinolin-4-yl)-5-methyl-N-phenyl-1H-1,2,3-triazole-4-carboxamide (QTCA-1) against scopolamine (SCO)-induced amnesia in mice. It was evaluated cholinergic dysfunction, oxidative stress and Na⁺/K⁺-ATPase activity in cerebral cortex and hippocampus of mice. Male Swiss mice were treated with QTCA-1 (10 mg/kg, intragastrically (i.g.), daily) for nine days. Thirty minutes after the treatment with compound, the animals received a injection of SCO (0.4 mg/kg, intraperitoneally (i.p.)). Mice were submitted to the behavioral tasks 30 min after injection of SCO (Barnes maze, open-field, object recognition and location, and step-down inhibitory avoidance tasks) during nine days. In day 9, cerebral cortex and hippocampus of mice were removed to determine the thiobarbituric acid reactive species (TBARS) levels, and catalase (CAT), Na⁺/K⁺-ATPase and acetylcholinesterase (AChE) activities. SCO caused amnesia in mice for changing in step-down inhibitory avoidance, Barnes maze, and object recognition and object location tasks. QTCA-1 treatment attenuated the behavioral changes caused by SCO. Moreover, SCO increased AChE and CAT activities, decreased Na⁺/K⁺-ATPase activity and increased TBARS levels in the cerebral structures of mice. QTCA-1 protected against these brain changes. In conclusion, QTCA-1 had anti-amnesic action in the experimental model used in the present study, through the anticholinesterase effect, modulation of Na⁺/K⁺-ATPase activity and antioxidant action.

Alonso S, Prieto MJ. Combined Therapy for Alzheimer's Disease: Tacrine and PAMAM Dendrimers Co-Administration Reduces the Side Effects of the Drug without Modifying its Activity

Alzheimer's disease has become a public health priority, so an investigation of new therapies is required. Tacrine (TAC) was licensed for treatments; however, its oral administration caused hepatotoxicity, so it is essential to reduce the side effects. PAMAM dendrimer generation 4.0 and 4.5 (DG4.0 and DG4.5) can be used as drug delivery systems and as nanodrugs per se. Our work aims to propose a combined therapy based on TAC and PAMAM dendrimer co-administration. TAC and dendrimer interactions were studied by in vitro drug release, drug stability, and FTIR. The toxicity profile of co-administration was evaluated in human red blood cells, in Neuro-2a cell culture, and in zebrafish larvae. Also, the anti-acetylcholinesterase activity was studied in cell culture. It was possible to obtain DG4.0-TAC and DG4.5-TAC suspensions, without reducing the drug solubility and stability. FTIR and in vitro release studies confirmed that interaction between TAC and DG4.5 was of the electrostatic type. No toxicity effects on human red blood cells were observed, whereas the co-administration with DG4.5 reduced cytotoxicity of TAC on the Neuro-2a cell line. Moreover, in vivo co-administration of both DG4.0-TAC and DG4.5-TAC reduced the morphological and hepatotoxic effects of TAC in zebrafish larvae. The reduction of TAC toxicity was not accompanied by a reduction in its activity since the anti-acetylcholinesterase activity remains when it is co-administrated with dendrimers. In conclusion, the co-administration of TAC with both DG4.0 and DG4.5 is a novel therapy since it was less-toxic, was more biocompatible, and has the same effectiveness than the free drug. Graphical abstract.

Tacrine modulates Kv2.1 channel gene expression and cell proliferation

Purpose/Aim: Besides as a cholinesterase (ChE) inhibitor, tacrine is able to act on multiple targets such as nicotinic receptors (nAChRs) and voltage-gated K⁺ (Kv) channels. Kv2.1, a Kv channel subunit underlying delayed rectifier currents with slow kinetics of inactivation, is highly expressed in the mammalian brain, especially in the hippocampus. Nevertheless, limited data are available concerning the relationship between tacrine and Kv2.1 channels. In the present study, we explore the possible effects of tacrine on Kv2.1 channels in heterologous expression systems and N2A cells.Materials and methods: The change of expression and currents of Kv2.1 after treatment with tacrine was detected by PCR and whole-cell recordings, respectively. WST-8 experiments were performed to reveal the effects of tacrine on cell proliferation.Results: Incubation with tacrine induced a significant reduction of the mRNA level of Kv2.1 channels in HEK293 cells. The decline of corresponding currents carried by Kv2.1 was also observed. Moreover, the proliferation rates of HEK293 cells with Kv2.1 channel were substantially enhanced after treatment with this chemical for 24 h. Similar results were also detected after exposure to tacrine in N2A cells with native expression of Kv2.1 channels.Conclusion: These lines of evidence indicate that application of tacrine downregulates the expression of Kv2.1 channels and increase cell proliferation. The effect of tacrine on Kv2.1 channels may provide an alternative explanation for its neuroprotective action.

Dual-Acting Cholinesterase-Human Cannabinoid Receptor 2 Ligands Show Pronounced Neuroprotection in Vitro and Overadditive and Disease-Modifying Neuroprotective Effects in Vivo

We have designed and synthesized a series of 14 hybrid molecules out of the cholinesterase (ChE) inhibitor tacrine and a benzimidazole-based human cannabinoid receptor subtype 2 (hCB2R) agonist and investigated them in vitro and in vivo. The compounds are potent ChE inhibitors, and for the most promising hybrids, the mechanism of human acetylcholinesterase (hAChE) inhibition as well as their ability to interfere with AChE-induced aggregation of β-amyloid (Aβ), and Aβ self-aggregation was assessed. All hybrids were evaluated for affinity and selectivity for hCB1R and hCB2R. To ensure that the hybrids retained their agonist character, the expression of cAMP-regulated genes was quantified, and potency and efficacy were determined. Additionally, the effects of the hybrids on microglia activation and neuroprotection on HT-22 cells were investigated. The most promising in vitro hybrids showed pronounced neuroprotection in an Alzheimer's mouse model at low dosage (0.1 mg/kg, i.p.), lacking hepatotoxicity even at high dose (3 mg/kg, i.p.).

Some Possibilities to Study New Prophylactics against Nerve Agents

Nerve agents belong to the most dangerous chemical warfare agents and can be/were misused by terrorists. Effective prophylaxis and treatment is necessary to diminish their effect. General principles of prophylaxis are summarized (protection against acetylcholinesterase inhibition, detoxification, treatment "in advance" and use of different drugs). They are based on the knowledge of mechanism of action of nerve agents. Among different examinations, it is necessary to test prophylactic effectivity in vivo and compare the results with protection in vitro. Chemical and biological approaches to the development of new prophylactics would be applied simultaneously during this research. Though the number of possible prophylactics is relatively high, the only four drugs were introduced into military medical practice. At present, pyridostigmine seems to be common prophylactic antidote; prophylactics panpal (tablets with pyridostigmine, trihexyphenidyl and benactyzine), transant (transdermal patch containing HI-6) are other means introduced into different armies as prophylactics. Scavenger commercionally available is Protexia®. Future development will be focused on scavengers, and on other drugs either reversible cholinesterase inhibitors (e.g., huperzine A, gallantamine, physostigmine, acridine derivatives) or other compounds.

Tacrine and its 7-methoxy derivate; time-change concentration in plasma and brain tissue and basic toxicological profile in rats

The search for tacrine derivatives, as potential Alzheimer´s disease treatment, is still being at the forefront of scientific efforts. 7-MEOTA was found to be a potent, centrally active acetylcholinesterase inhibitor free of the serious side effects observed for tacrine. Unfortunately, a relevant argumentation about pharmacokinetics and potential toxicity is incomplete; information about tacrine derivatives absorption and especially CNS penetration are still rare as well as detailed toxicological profile in vivo. Although the structural changes between these compounds are not so distinctive, differences in plasma profile and CNS targeting were found. The maximum plasma concentration were attained at 18^th min (tacrine; 38.20 ± 3.91 ng/ml and 7-MEOTA; 88.22 ± 15.19 ng/ml) after i.m. application in rats. Although the brain profiles seem to be similar; tacrine achieved 19.34 ± 0.71 ng/ml in 27 min and 7-MEOTA 15.80 ± 1.13 ng/ml in 22 min; the tacrine Kp (AUC_brain/AUC_plasma) fit 1.20 and was significantly higher than 7-MEOTA Kp 0.10. Administration of tacrine and 7-MEOTA showed only mild elevation of some biochemical markers following single p.o. application in 24 hours and 7 days. Also histopathology revealed only mild-to-moderate changes following repeated p.o. administration for 14 days. It seems that small change in tacrine molecule leads to lower ability to penetrate through the biological barriers. The explanation that lower p.o. acute toxicity of 7-MEOTA depends only on differences in metabolic pathways may be now revised to newly described differences in pharmacokinetic and toxicological profiles.

Complex View on Poisoning with Nerve Agents and Organophosphates

OP/nerve agents are still considered as important chemicals acting on living organisms and widely used in human practice. Nerve agents are the most lethal chemical warfare agents. They are characterized according to their action as compounds influencing cholinergic nerve transmission via inhibition of AChE. The symptoms of intoxication comprise nicotinic, muscarinic and central symptoms, for some OP/nerve agents, a delayed neurotoxicity is observed. Cholinesterases (AChE and BuChE) are characterized as the main enzymes involved in the toxic effect of these compounds including their molecular forms. The activity of both enzymes (and molecular forms) is influenced by inhibitors and other factors such as pathological states. There are different methods for cholinesterase determination, however, the most frequent is the method based on the hydrolysis of thiocholine esters and following detection of free SH-group of the released thiocholine. The diagnosis of OP/nerve agents poisoning is based on anamnesis, the clinical status of the intoxicated organism and on cholinesterase determination in the blood. Some principles of prophylaxis against OP/nerve agents poisoning comprising the administration of reversible cholinesterase inhibitors such as pyridostigmine (alone or in combination with other drugs), scavengers such as preparations of cholinesterases, some therapeutic drugs and possible combinations are given. Basic principles of the treatment of nerve agents/OP poisoning are described. New drugs for the treatment are under experimental study based on new approaches to the mechanism of action.

Increasing Polarity in Tacrine and Huprine Derivatives: Potent Anticholinesterase Agents for the Treatment of Myasthenia Gravis

Symptomatic treatment of myasthenia gravis is based on the use of peripherally-acting acetylcholinesterase (AChE) inhibitors that, in some cases, must be discontinued due to the occurrence of a number of side-effects. Thus, new AChE inhibitors are being developed and investigated for their potential use against this disease. Here, we have explored two alternative approaches to get access to peripherally-acting AChE inhibitors as new agents against myasthenia gravis, by structural modification of the brain permeable anti-Alzheimer AChE inhibitors tacrine, 6-chlorotacrine, and huprine Y. Both quaternization upon methylation of the quinoline nitrogen atom, and tethering of a triazole ring, with, in some cases, the additional incorporation of a polyphenol-like moiety, result in more polar compounds with higher inhibitory activity against human AChE (up to 190-fold) and butyrylcholinesterase (up to 40-fold) than pyridostigmine, the standard drug for symptomatic treatment of myasthenia gravis. The novel compounds are furthermore devoid of brain permeability, thereby emerging as interesting leads against myasthenia gravis.

The pharmacology of tacrine at N-methyl-d-aspartate receptors

The mechanism of tacrine as a precognitive drug has been considered to be complex and not fully understood. It has been reported to involve a wide spectrum of targets involving cholinergic, gabaergic, nitrinergic and glutamatergic pathways. Here, we review the effect of tacrine and its derivatives on the NMDA receptors (NMDAR) with a focus on the mechanism of action and biological consequences related to the Alzheimer's disease treatment. Our findings indicate that effect of tacrine on glutamatergic neurons is both direct and indirect. Direct NMDAR antagonistic effect is often reported by in vitro studies; however, it is achieved by high tacrine concentrations which are not likely to occur under clinical conditions. The impact on memory and behavioral testing can be ascribed to indirect effects of tacrine caused by influencing the NMDAR-mediated currents via M1 receptor activation, which leads to inhibition of Ca²⁺-activated potassium channels. Such inhibition prevents membrane repolarization leading to prolonged NMDAR activation and subsequently to long term potentiation. Considering these findings, we can conclude that tacrine-derivatives with dual cholinesterase and NMDARs modulating activity may represent a promising approach in the drug development for diseases associated with cognitive dysfunction, such as the Alzheimer disease.

Multi-target therapeutics for neuropsychiatric and neurodegenerative disorders

Historically, neuropsychiatric and neurodegenerative disease treatments focused on the 'magic bullet' concept; however multi-targeted strategies are increasingly attractive gauging from the escalating research in this area. Because these diseases are typically co-morbid, multi-targeted drugs capable of interacting with multiple targets will expand treatment to the co-morbid disease condition. Despite their theoretical efficacy, there are significant impediments to clinical success (e.g., difficulty titrating individual aspects of the drug and inconclusive pathophysiological mechanisms). The new and revised diagnostic frameworks along with studies detailing the endophenotypic characteristics of the diseases promise to provide the foundation for the circumvention of these impediments. This review serves to evaluate the various marketed and nonmarketed multi-targeted drugs with particular emphasis on their design strategy.

A critical review of cholinesterase inhibitors as a treatment modality in Alzheimer's disease

Early research into Alzheimer's disease launched the cholinergic hypothesis, based on the correlation between central cholinergic deficiency and clinical measures of cognitive decline. This was epitomized in therapeutic strategies employing a variety of procholinergic agents, of which only the inhibitors of cholinesterase (ChE), the enzyme thai hydrolyzes acetylcholine in the synaptic cleft, have been proven clinically viable. Five such agents are reviewed: tacrine and donepezil, which act at the ionic subsite of acetylcholinesterase (AChE), and rivastigmine, galantamine, and metrifonate, which act at its catalytic esteratic subsite. Despite statistical evidence of efficacy from numerous well-controlled multicenter trials, important clinical utility issues remain outstanding: (i) number-needed-to-treat (NNT) analyses, quantifying the number of patients needing to be treated for one patient to show benefit, find values of 3 to 20; (ii) the pivotal trials themselves were conducted in nonrepreseniative populations, largely comprised of physically healthy outpatients with mildto-moderate Alzheimer's disease and a mean age of 72 years (thereby excluding over 30% of typical Alzheimer patients in State of California-funded clinics), treated for up to 6 months; and (Hi) tolerability is underreported and characterized by a positive correlation between dose, effect and cholinergic side effects - potentially serious adverse events include bradycardia, anorexia, weight loss and myasthenia with respiratory depression. Therapies thus require titration and constant monitoring. Nevertheless, acetylcholinesterase inhibitors (AChEls) constitute the first class of effective agents and are likely to remain so in the continuing absence of viable alternatives.

Effects of novel tacripyrines ITH12117 and ITH12118 on rat vas deferens contractions, calcium transients and cholinesterase activity

We have recently synthesized a new series of hybrid compounds having the moieties of tacrine, a potent inhibitor of brain and peripheral acetylcholinesterase (AChE), and nimodipine, a blocker of L-type voltage-dependent calcium channels (VDCCs). These compounds were designed to target AChE and L calcium channels in the brain, as potential therapeutic agents in Alzheimer's disease. We performed the present study to determine the main peripheral side effects of two of these compounds, ITH12117 and ITH12118. We have here shown that in rat vas deferens these compounds inhibited AChE with a potency about 1000-fold lower than that of physostigmine or tacrine. Furthermore, the hybrid compounds enhanced contractions evoked by acetylcholine, with a potency about 100-fold lower than that of physostigmine or tacrine. Additionally, contractions induced by Ca2+ on depolarized vas deferens were blocked by nimodipine with greater efficacy, compared with ITH12117 and ITH12118. Compound ITH12118 (1 μM) caused a pronounced inhibition of the tonic (but not phasic) contraction elicited by electrical field stimulation. Furthermore, the same dose of nimodipine and ITH12118 blocked by 75% cytosolic Ca2+ elevations produced by acetylcholine, noradrenaline, or ATP. As a matter of comparison, we showed that rat brain cortex AChE was inhibited by ITH12118 with a potency 10 to 20-fold higher than that for vas deferens. This study shows that ITH12118 could be a paradigmatic multitarget compound having selective brain effects with smaller peripheral side effects. This may help to orient the search of new neuroprotective compounds with potential therapeutic application in Alzheimer's disease.

Mechanism of action of cholinesterase inhibitors in Alzheimer's disease

Cholinesterase inhibitors, such as physostigmine and tacrine, have lately gained interest as potential drugs in the treatment of Alzheimer's disease. Already in the 1950s, it was discovered that physostigmine and tacrine were potent inhibitors of acetylcholinesterase and butyrylcholinesterase. However, later studies have shown that cholinesterase inhibitors also interact with cholinergic receptors, with sodium and potassium ion channels and effect the uptake, synthesis and release of neurotransmitters. In summary, cholinesterase inhibitors are drugs with many modes of action, which may be of advantage in the treatment of a complex disorder such as Alzheimer's disease.

Significant delivery of tacrine into the brain using magnetic chitosan microparticles for treating Alzheimer's disease

Alzheimer's disease (AD) is a progressive degenerative disorder of the brain characterized by a slow, progressive decline in cognitive function and behavior. As the disease advances, persons have a tough time with daily tasks like using the phone, cooking, handling money or driving the car. AD affects 15 million people worldwide and it has been estimated that AD affects 4.5 million Americans. Tacrine is a reversible cholinesterase inhibitor used for treating mild to moderate AD. In the present study, an attempt was made to target the anti-Alzheimer's drug tacrine in the brain by using magnetic chitosan microparticles. The magnetic chitosan microparticles were prepared by emulsion cross-linking. The formulated microparticles were characterized for process yield, drug loading capacity, particle size, in vitro release, release kinetics and magnetite content. The particle size was analyzed by scanning electron microscope. The magnetite content of the microparticles was determined by atomic absorption spectroscopy. For animal testing, the microparticles were injected intravenously after keeping a suitable magnet at the target region. The concentrations of tacrine at the target and non-target organs were analyzed by HPLC. The magnetic chitosan microparticles significantly increased the concentration of tacrine in the brain in comparison with the free drug.

Dose-related effects of the acetylcholinesterase inhibitor tacrine on cocaine and food self-administration in rats

RATIONALE

Acetylcholine (ACh) is involved in brain reward and learning functions and contributes to opiate- and psychostimulant-motivated behaviors. Tacrine is a centrally acting, reversible cholinesterase inhibitor that also inhibits monoamine oxidase (MAO) and blocks reuptake of dopamine (DA) and serotonin.

OBJECTIVES

To determine the effects of pretreatment with tacrine on self-administration of cocaine and nondrug reinforcers.

MATERIALS AND METHODS

Male Wistar rats were trained to self-administer cocaine under a fixed-ratio-5 (FR-5) schedule during 2-h multiple-component sessions in which 0.1, 0.2, and 0.4 mg/kg per injection of cocaine were each available for 40 min. Other animals self-administered 45 mg food pellets under FR-30 or 20% Ensure (liquid food) under FR-5 in amounts of 30, 60, or 120 microl. Vehicle or tacrine was administered as single intravenous doses 20 min before self-administration of cocaine, food pellets, or liquid food.

RESULTS

Although pretreatment with 0.032 mg/kg of tacrine increased self-administration of food pellets, pretreatment with higher doses of tacrine attenuated self-administration of cocaine, food pellets, or liquid food. Tacrine's ED50 value for attenuating self-administration of 0.1 mg/kg per injection of cocaine was more than sixfold lower than values for attenuating liquid food- or food pellet-reinforced behavior. However, ED50 values for attenuating self-administration of higher doses of cocaine were similar to those observed for 30 or 60 microl of liquid food.

CONCLUSIONS

Tacrine can selectively attenuate self-administration of low-dose cocaine, but its effects on higher doses of cocaine are similar to its ability to decrease self-administration of nondrug reinforcers.

Changes of cholinesterase activities in the plasma and some tissues following administration of L-carnitine and galanthamine to rats

Changes of acetylcholinesterase (AChE) activities in the hypophysis and brain (frontal cortex, hippocampus, medial septum and basal ganglia), and butyrylcholinesterase in plasma and liver following galanthamine (GAL) administration were studied in rats pretreated with L-carnitine (CAR). Following only GAL administration (10 mg/kg, i.m.), both cholinesterases (without clinical symptoms of GAL overdosage) were significantly inhibited. Pretreatment with CAR (3 consecutive days, 250 mg/kg, p.o.) followed by GAL administration showed higher AChE inhibition in comparison with single GAL administration. However, a statistically significant difference was observed for AChE in the hippocampus only. The activity of peripheral cholinesterases was not influenced by CAR pretreatment. Thus, pretreatment with CAR enhanced AChE inhibition in some brain parts of the rat following GAL administration.

Alzheimer Disease and Its Management

Alzheimer disease is a progressive degenerative disorder of the brain characterized by a slow, progressive decline in cognitive function and behavior. As the disease advances, persons with Alzheimer disease have tough time with daily usage of things like using the phone, cooking, handling money, or driving the car. The disease is more common in elder population. It is estimated that Alzheimer disease affects 15 million people worldwide and approximately 4 million Americans. The clinical features of Alzheimer disease overlaps with common signs of aging, and other types of dementia, hence the diagnosis remains difficult. The neuropathologic hallmarks of the disorder are amyloid-rich senile plaques, neurofibrillary tangles, and neuronal degeneration. Drugs approved for treating Alzheimer disease include acetylcholinesterase inhibitors and N-methyl-D-aspartate (NMDA) receptor antagonist. Caregivers not getting adequate information about Alzheimer disease may believe that nothing can be done to manage its symptoms. Understanding the extent of Alzheimer disease related knowledge can assist disease management that result in improved disease management and reduced care costs. This article attempts to focus on some of the important recent developments in understanding and management of Alzheimer disease.

Protective effects of compound FLZ on beta-amyloid peptide-(25-35)-induced mouse hippocampal injury and learning and memory impairment

AIM

To study the protective effects of compound FLZ, a novel synthetic analogue of natural squamosamide, on learning and memory impairment and lesions of the hippocampus caused by icv injection of beta-amyloid(25-35)(Abeta(25-35)) in mice.

METHODS

Mice were icv injected with the Abeta(25-35) (15 nmol/mouse), and then treated with oral administration of 75 mg/kg or 150 mg/kg of FLZ once daily for 16 consecutive days. The impairment of learning and memory in mice were tested using step-down test and Morris water maze test. The content of malondialdehyde (MDA) and the expressions of acetylcholinesterase (AChE), Bax, and Bcl-2 in the CA1 region of the mouse hippocampus were measured by biochemical and immunohistochemical analysis, respectively. The pathological damages of hippocampus were observed using a microscope.

RESULTS

FLZ (75 mg/kg, 150 mg/kg) significantly attenuated Abeta(25-35)-induced impairment of learning and memory in the step-down test and Morris water maze test. FLZ also reduced pathological damages to the hippocampus induced by Abeta(25-35). Furthermore, FLZ prevented the increase of AChE and Bax, and the decrease of Bcl-2 immunoreactive cells in the CA1 region of the hippocampus, and reduced the increase of MDA content in the hippocampus in mice injected with Abeta(25-35).

CONCLUSION

FLZ has protective action against the impairment of learning and memory and pathological damage to the hippocampus induced by icv injection of Abeta(25-35) in mice.

Structural basis for inhibition of histamine N-methyltransferase by diverse drugs

In mammals, histamine action is terminated through metabolic inactivation by histamine N-methyltransferase (HNMT) and diamine oxidase. In addition to three well-studied pharmacological functions, smooth muscle contraction, increased vascular permeability, and stimulation of gastric acid secretion, histamine plays important roles in neurotransmission, immunomodulation, and regulation of cell proliferation. The histamine receptor H1 antagonist diphenhydramine, the antimalarial drug amodiaquine, the antifolate drug metoprine, and the anticholinesterase drug tacrine (an early drug for Alzheimer's disease) are surprisingly all potent HNMT inhibitors, having inhibition constants in the range of 10-100nM. We have determined the structural mode of interaction of these four inhibitors with HNMT. Despite their structural diversity, they all occupy the histamine-binding site, thus blocking access to the enzyme's active site. Near the N terminus of HNMT, several aromatic residues (Phe9, Tyr15, and Phe19) adopt different rotamer conformations or become disordered in the enzyme-inhibitor complexes, accommodating the diverse, rigid hydrophobic groups of the inhibitors. The maximized shape complementarity between the protein aromatic side-chains and aromatic ring(s) of the inhibitors are responsible for the tight binding of these varied inhibitors.

Evidence for the involvement of central serotonergic mechanisms in cholinergic tremor induced by tacrine in Balb/c mice

Tacrine is a potent and reversible inhibitor of acetylcholinesterase (AChE) in the brain. It produces tremor in animals, which is believed to be due to an increase in the brain acetylcholine level following AChE inhibition. The present study was undertaken to investigate the involvement, if any, of biogenic amines in the genesis of this motor dysfunction. Administration of tacrine (10-20 mg/kg, i.p.) produced dose- and time-dependent tremor in Balb/c mice. While in vivo inhibition of striatal AChE activity was observed only for the highest dose of tacrine, a dose-dependent increase in striatal choline acetyltransferase activity was obtained. Serotonin (5-HT) levels, as assayed following a sensitive HPLC-electrochemical procedure, were significantly increased in nucleus caudatus putamen, nucleus accumbens, substantia nigra, nucleus raphe dorsalis, olivary nucleus and the cerebellum. However, dopamine or norepinephrine levels remained unaltered in these areas of the brain. In animals treated with p-chlorophenylalanine, a specific tryptophan hydroxylase inhibitor and 5-HT depletor, tacrine failed to elevate the levels of 5-HT in the brain regions, and significantly attenuated tremor response to the drug. Tacrine-induced tremor was also significantly (83%) attenuated by 5-HT(2A/2C) receptor antagonist mianserin (5 mg/kg, i.p.), but methysergide (5 mg/kg, i.v.) could block tacrine-induced tremor only by 20%. Atropine (5 mg/kg, i.p.) antagonized tacrine-induced tremor by about 53%, but a combination of atropine and mianserin completely blocked the tremor response. These results indicate that the cholinergic tremor produced by tacrine in Balb/c mice is mediated via central serotonergic mechanisms, and stimulation of 5-HT(2A/2C) receptors plays a pivotal role in this motor dysfunction.

Organophosphates/nerve agent poisoning: mechanism of action, diagnosis, prophylaxis, and treatment

OP/nerve agents are still considered as important chemicals acting on living organisms and are widely used. They are characterized according to their action as compounds influencing cholinergic nerve transmission via inhibition of AChE. Modeling of this action and extrapolation of experimental data from animals to humans is more possible for highly toxic agents than for the OP. The symptoms of intoxication comprise nicotinic, muscarinic, and central symptoms; for some OP/nerve agents, a delayed neurotoxicity is observed. Cholinesterases (AChE and BuChE) are characterized as the main enzymes involved in the toxic effect of these compounds, including molecular forms. The activity of both enzymes (and molecular forms) is influenced by inhibitors (reversible, irreversible, and allosteric) and other factors, such as pathological states. There are different methods for cholinesterase determination; however, the most frequent is the method based on the hydrolysis of thiocholine esters and subsequent detection of free SH-group of the released thiocholine. The diagnosis of OP/nerve agent poisoning is based on anamnesis, the clinical status of the intoxicated organism, and on cholinesterase determination in the blood. For nerve agent intoxication, AChE in the red blood cell is more diagnostically important than BuChE activity in the plasma. This enzyme is a good diagnostic marker for intoxication with OP pesticides. Some other biochemical examinations are recommended, especially arterial blood gas, blood pH, minerals, and some other specialized parameters usually not available in all clinical laboratories. These special examinations are important for prognosis of the intoxication, for effective treatment, and for retrospective analysis of the agent used for exposure. Some principles of prophylaxis against OP/nerve agent poisoning comprising the administration of reversible cholinesterase inhibitors such as pyridostigmine (alone or in combination with other drugs), scavengers such as preparations of cholinesterases, some therapeutic drugs, and possible combinations are given. Basic principles of the treatment of nerve agent OP poisoning are described. They are based on the administration of anticholinergics (mostly atropine but some other anticholinergics can be recommended) as a symptomatic treatment, cholinesterase reactivators as a causal treatment (different types but without a universal reactivator against all OP/nerve agents) as the first aid and medical treatment, and anticonvulsants, preferably diazepam though some other effective benzodiazepines are available. New drugs for the treatment are under experimental study based on new approaches to the mechanism of action. Future trends in the complex research of these compounds, which is important not only for the treatment of intoxication but also for the quantitative and qualitative increase of our knowledge of toxicology, neurochemistry, neuropharmacology, clinical biochemistry, and analytical chemistry in general, are characterized.

Disclosure of a pro-apoptotic glyceraldehyde-3-phosphate dehydrogenase promoter: anti-dementia drugs depress its activation in apoptosis

Overexpression and subsequent nuclear accumulation of glyceraldehyde-3-phosphate dehydrogenase (GAPDH) is involved in neuronal apoptosis induced by several stimuli in which GAPDH antisense oligonucleotides specifically block the increment (2 approximately 3 fold) of GAPDH mRNA contents occurring prior to neuronal death. However, these agents do not affect the basal, constitutive mRNA contents. This suggests that there may be distinct gene regulations for GAPDH mRNA expression. Herein, we cloned two types of promoter regions upstream of this gene; viz., #104 (1.02-kb) and #302 (2.46-kb). These fragments were inserted into the pGL3 luciferase reporter system and transiently transfected into cultured cerebellar neurons undergoing cytosine arabinonucleoside-induced apoptosis. The functional analysis of these constructs revealed that #104, but not #302, increased luciferase activity in response to the apoptotic stimulus. Deletion and replacement mutation analysis of the #104 fragment disclosed the promoter core harbored between the 154-bp and 84-bp domains (3.5-fold activity of the control). Furthermore, anti-dementia drugs (such as Cognex and Aricept) markedly depress the expression of this pro-apoptotic GAPDH promoter activity. Interestingly, immunocytochemical examination of human post-mortem materials from patients with Alzheimer's disease revealed nuclear aggregated GAPDH in neurons of the affected brain regions, implying an association with apoptotic cell death. The current findings indicate that induction of the pro-apoptotic protein GAPDH is genetically regulated at the level of promoter activation, and this protein may be an important molecular target for developing anti-apoptotic therapeutic agents in certain neurological illnesses.

Proapoptotic protein glyceraldehyde-3-phosphate dehydrogenase: a possible site of action of antiapoptotic drugs

Glyceraldehyde-3-phosphate dehydrogenase (GAPDH) has long been recognized as a classical glycolytic protein and has been used as a "housekeeping" gene in studies of genetic expression and regulation. However, recent advances reveal that GAPDH displays diverse nonglycolytic functions depending on its subcellular localization. Among those functions, one of the most intriguing is likely to be the induction of apoptosis. Previous works by our group and others have demonstrated that the overexpression of GAPDH and its subsequent nuclear translocation appear to be implicated in the initiation of one or more apoptotic cascades and also in the etiology of some neurological diseases. This review addresses new data demonstrating that a protein, referred to as proapoptotic protein GAPDH, with a quite mundane function in healthy cells behaves very differently during cell suicide, and summarizes emphatically the importance of this protein as a putative molecular target in developing antiapoptotic therapeutic agents for the treatment of certain neurodegenerative disorders.

Current pharmacologic options for patients with Alzheimer's disease

BACKGROUND: The aim of the current study was to provide general practitioners with an overview of the available treatment options for Alzheimer's disease (AD). Since general practitioners provide the majority of medical care for AD patients, they should be well versed in treatment options that can improve function and slow the progression of symptoms. DESIGN: Biomedical literature related to acetylcholinesterase inhibitors (AChEIs) was surveyed. In the United States, there are four AChEIs approved for the treatment of AD: tacrine, donepezil, rivastigmine, and galantamine. There are other agents under investigation, but at present, AChEIs are the only approved drug category for AD treatment. MEASUREMENTS AND MAIN RESULTS: AD is becoming a major public health concern and underdiagnosis is a significant problem (with only about half of AD patients being diagnosed and only half of those diagnosed actually being treated). Clinical trials have demonstrated that patients with AD who do not receive active treatment decline at more rapid rates than those who do. CONCLUSIONS: Given that untreated AD patients show decline in three major areas (cognition, behavior, and functional ability), if drug treatment is able to improve performance, maintain baseline performance over the long term, or allow for a slower rate of decline in performance, each of these outcomes should be viewed a treatment success.

Huperzine A inhibits the sustained potassium current in rat dissociated hippocampal neurons

The actions of huperzine A (HupA), a novel cholinesterase inhibitor, on the sustained potassium current were investigated in acutely dissociated hippocampal neurons of rat. HupA inhibited the current (IC(50) = 856 +/- 1 microM) with voltage-dependency. The effect was insensitive to 3 microM atropine. Tacrine (IC(50) = 43 +/- 3 microM) was 20 times more potent than HupA. HupA hyperpolarized the activation curve of the current by 16 mV, and markedly prolonged the decay time constant tau(2). HupA affected neither the steady-state inactivation of the current, nor its recovery from inactivation. The potential relevance of the inhibitory effect of HupA on the current to the treatment of Alzheimer's disease is discussed.

Presence or absence of at least one epsilon 4 allele and gender are not predictive for the response to donepezil treatment in Alzheimer's disease

The objective was to evaluate the effects of the apolipoprotein E (ApoE) genotype and gender on the response to donepezil treatment in Alzheimer's disease. ApoE genotyping was performed on 117 patients with mild to moderate Alzheimer's disease who were included in a 36-week open label trial of donepezil therapy. Of these 117 patients, who constituted the intent-to-treat population (ITT), 80 completed the trial, and constituted the evaluable population. Patients were treated blindly in relation to ApoE genotype. Outcome measures were Alzheimer's disease Assessment Scale-Cognitive Component (ADAS-Cog), the Mini Mental State Examination, Instrumental Activities of Daily Living, and the Caregiver-rated Clinical Global Impression of Change. ITT analysis did not reveal significant differences between the responses of epsilon 4- and epsilon 4+ carriers according to the ADAS-Cog (P = 0.28). No differences were found either between the responses of men and women (P = 0.81), and there was no significant interaction between genotype and gender (P = 0.09). Other outcome measures all exhibited similar patterns of change to those seen using the ADAS-Cog. Consequently, these results do not support the hypothesis that the ApoE phenotype and gender are predictors of the response to donepezil in Alzheimer's disease patients.

Development of a new class of nonimidazole histamine H(3) receptor ligands with combined inhibitory histamine N-methyltransferase activity

In search of novel ways to enhance histaminergic neurotransmission in the central nervous system, a new class of nonimidazole histamine H(3) receptor ligands were developed that simultaneously possess strong inhibitory activity on the main histamine metabolizing enzyme, histamine N-methyltransferase (HMT). The novel compounds contain an aminoquinoline moiety, which is an important structural feature for HMT inhibitory activity, connected by different spacers to a piperidino group (for H(3) receptor antagonism). Variation of the spacer structure provides two different series of compounds. One series, having only an alkylene spacer between the basic centers, led to highly potent HMT inhibitors with moderate to high affinity at human histamine H(3) receptors. The second series possesses a p-phenoxypropyl spacer, which may be extended by another alkylene chain. This latter series also showed strong inhibitory activity on HMT, and in most cases, the H(3) receptor affinity even surpassed that of the first series. One of the most potent compounds with this dual mode of action is 4-(4-(3-piperidinopropoxy)phenylamino)quinoline (34) (hH(3), K(i) = 0.09 nM; HMT, IC(50) = 51 nM). This class of compounds showed high antagonist potency and good H(3) receptor selectivity in functional assays in guinea pig on H(1), H(2), and H(3) receptors. Because of low or missing in vivo activity of two selected compounds, the proof of concept of these valuable pharmacological tools for the supposed superior overall enhancing effect on histaminergic neurotransmission failed to appear hitherto.

Novel and potent tacrine-related hetero- and homobivalent ligands for acetylcholinesterase and butyrylcholinesterase

Based upon synthetic and biochemical results, a novel and potent tacrine analogue and heterobivalent analogues of tacrine, were designed. The role played by the amino groups of homo- and heterobivalent ligands in the interaction with the peripheral and catalytic sites of AChE and BuChE were investigated. The syntheses of these materials together with the results of AChE/BuChE inhibition assays are detailed.