Synthesis and in vitro evaluation of N-alkyl-7-methoxytacrine hydrochlorides as potential cholinesterase inhibitors in Alzheimer disease

All approved drugs for Alzheimer disease (AD) in clinical practice ameliorate the symptoms of the disease. Among them, acetylcholinesterase inhibitors (AChEIs) are used to increase the cholinergic activity. Among new AChEI, tacrine compounds were found to be more toxic compared to 7-MEOTA (9-amino-7-methoxy-1,2,3,4-tetrahydroacridine). In this Letter, series of 7-MEOTA analogues (N-alkyl-7-methoxytacrine) were synthesized. Their inhibitory ability was evaluated on recombinant human acetylcholinesterase (AChE) and plasmatic human butyrylcholinesterase (BChE). Three novel compounds showed promising results towards hAChE better to THA or 7-MEOTA. Three compounds resulted as potent inhibitors of hBChE. The SAR findings highlighted the C₆–C₇ N-alkyl chains for cholinesterase inhibition.     

Synthesis and biological activity of derivatives of tetrahydroacridine as acetylcholinesterase inhibitors

Current state of medical sciences does not allow to treatment neurodegenerative diseases such as Alzheimer’s disease (AD). At present treatment of AD is severely restricted. The main class of medicines which are applied in AD is acetylcholinesterase inhibitors (AChEIs) like tacrine, donepezil, galantamine and rivastigmine that do not contribute to significant and long-term improvement in cognitive and behavioural functions.In this work, we report synthesis and biological evaluation of new hybrids of tacrine-6-hydrazinonicotinamide. The synthesis was based on the condensation reaction between tacrine derivatives and the hydrazine nicotinate moiety (HYNIC). All obtained compounds present affinity for both cholinesterases and are characterized by high selectivity in relation to butyrylcholinesterase (BChE).     

Increased levels of tau protein in SH-SY5Y cells after treatment with cholinesterase inhibitors and nicotinic agonists

Several cholinesterase inhibitors used in the treatment of Alzheimer's disease (AD) have been shown to interact with an allosteric site on the nicotinic acetylcholine receptor (nAChR). A possible linkage between the phosphorylation state of tau, the major component of paired helical filaments found in AD brain, and stimulation of nAChRs by cholinesterase inhibitors and nicotinic agonists was investigated. Western blot analysis showed that treatment of SH-SY5Y cells for 72 h with the cholinesterase inhibitors tacrine (10(-5) M), donepezil (10(-5) M), and galanthamine (10(-5) M), nicotine (10(-5) M), and epibatidine (10(-7) M) increased tau levels as detected with Tau-1, AT 8, and AT 270 monoclonal antibodies and binding of [3H]epibatidine. The increase in tau immunoreactivity induced by nicotine, epibatidine, and tacrine, but not the up-regulation of nAChRs, was prevented by the antagonists d-tubocurarine and mecamylamine. Both antagonists were synergistic with the nicotinic agonists in causing up-regulation, but only d-tubocurarine showed a synergistic effect with tacrine. The increased tau immunoreactivity induced by tacrine was not prevented by atropine, indicating that in terms of cholinergic receptors, tacrine modulates tau levels mainly through interactions with nAChRs and not with muscarinic receptors. Additional work is needed to determine the exact mechanism by which cholinesterase inhibitors and nicotinic agonists modulate phosphorylation and levels of tau protein.     

O-Hydroxyl- or o-amino benzylamine-tacrine hybrids: Multifunctional biometals chelators,antioxidants, and inhibitors of cholinesterase activity and amyloid-β aggregation

In an effort to identify novel multifunctional drug candidates for the treatment of Alzheimer’s disease (AD), a series of hybrid molecules were synthesised by reacting N-(aminoalkyl)tacrine with salicylic aldehyde or derivatives of 2-aminobenzaldehyde. These compounds were then evaluated as multifunctional anti-Alzheimer’s disease agents. All of the hybrids are potential biometal chelators, and in addition, most of them were better antioxidants and inhibitors of cholinesterases and amyloid-β (Aβ) aggregation than the lead compound tacrine. Compound 7c has the potential to be a candidate for AD therapy: it is a much better inhibitor of acetylcholinesterase (AChE) than tacrine (IC₅₀: 0.55 nM vs 109 nM), has good biometal chelation ability, is able to inhibit Aβ aggregation and has moderate antioxidant activity (1.22 Trolox equivalents).     

New performance of biosensor technology for Alzheimer's disease drugs: in vitro comparison of tacrine and 7-methoxytacrine

Two drugs were tested using electrochemical biosensor with immobilized acetylcholinesterase (AChE). The first was commercialized drug tacrine (known also as Cognex) used for treatment of cognitive manifestation of Alzheimer\'s disease (AD). The second one was its 7-methoxy derivate (7-MEOTA) that has not been marketed. We determined the IC50 (6.67+/-0.92)x10-7 M for tacrine and (1.66+/-1.43)x10-9 M for 7-MEOTA. In this in vitro study, 7-MEOTA acts as stronger inhibitor of AChE and in this way could be more favorable for treatment of cognitive manifestation of AD. Our study shows that biosensor technology could be used as a quick and cheap tool for testing of promising AChE inhibitors (AD drug candidates).     

Therapy for Alzheimer's disease

Therapeutic strategies aimed to treat Alzheimer's disease (AD) may either produce an attenuation of symptoms or slowdown deterioration by attenuating progression of the disease. Presently, cholinesterase inhibitors (ChEI) have shown the most promising therapeutic effects. The best documented clinical efficacy of ChEI are studies of THA (tacrine, tetrahydroaminoacridine). The results of five recent studies in a total of 1,242 patients are discussed. Based on differences from placebo in scoring, a gain of 2–12 (MMSE) or 5–6 (ADAS) in deterioration can be seen for a THA treatment of 2–3 mo duration. This suggests that if treatment with THA will be extended to a longer period, the drug effect may not be only a symptomatic improvement but also a slowdown of disease course. A similarity of THA's effect in AD withl-deprenyl effects in Parkinson's is suggested.     

Effects of a memory enhancing peptide on cognitive abilities of brain-lesioned mice: additivity with huperzine A and relative potency to tacrine.

Alzheimer's disease (AD) and related dementing disorders having cognitive manifestations represent an increasing threat to public health. In the present study, the effects of a memory enhancing NLPR tetra-peptide (MEP), huperzine A (Hup A), or a combination of the two on the cognitive abilities of brain-lesioned mice were evaluated and compared with tacrine in the passive avoidance and Y-water maze tests for the acquisition and retention aspects of cognitive functions. MEP at microg kg(-1) doses, and Hup A or tacrine at mg kg(-1) doses significantly reversed the cognition deficits induced by scopolamine. For acquisition ability, it was observed that mice administered with MEP (4.0 microg kg(-1)) spent less time escaping onto the platform in the water maze than those treated with tacrine (1.5 mg kg(-1)); whereas for memory retention, tacrine-administration resulted in a higher step-through latency in mice at the tested dose regime. In addition, co-administration of MEP (2.0 microg kg(-1)) and Hup A (0.1 mg kg(-1)) exhibited an additive effect resulting in considerable improvements in both acquisition and retention abilities of brain-lesioned mice. The results demonstrated that MEP was highly efficient in the rescue of cognitive abilities of brain-lesioned mice and in particular, the effective doses of MEP were about two orders of magnitude lower than that of tacrine, a therapeutic currently used in the treatment of AD. Moreover, MEP and Hup A were effective at reduced doses when the two were co-administered, providing a rationale for their combined usage in the treatment of cognitive deficits.     

Syntheses of coumarin–tacrine hybrids as dual-site acetylcholinesterase inhibitors and their activity against butylcholinesterase,Aβ aggregation,and β-secretase

Exploring small-molecule acetylcholinesterase (AChE) inhibitors to slow the breakdown of acetylcholine (Ach) represents the mainstream direction for Alzheimer’s disease (AD) therapy. As the first acetylcholinesterase inhibitor approved for the clinical treatment of AD, tacrine has been widely used as a pharmacophore to design hybrid compounds in order to combine its potent AChE inhibition with other multi-target profiles. In present study, a series of novel tacrine–coumarin hybrids were designed, synthesized and evaluated as potent dual-site AChE inhibitors. Moreover, compound 1g was identified as the most potent candidate with about 2-fold higher potency (K_i = 16.7 nM) against human AChE and about 2-fold lower potency (K_i = 16.1 nM) against BChE than tacrine (K_i = 35.7 nM for AChE, K_i = 8.7 nM for BChE), respectively. In addition, some of the tacrine–coumarin hybrids showed simultaneous inhibitory effects against both Aβ aggregation and β-secretase. We therefore conclude that tacrine–coumarin hybrid is an interesting multifunctional lead for the AD drug discovery.     

The new approach in development of anti-Alzheimer's disease drugs via the cholinergic hypothesis

A wide range of evidences show that cholinesterase (ChE) inhibitors can interfere with the progression of Alzheimer's disease (AD). The earliest known ChE inhibitors, namely, physostigmine and tacrine, showed modest improvement in the cognitive function of AD patients. However, clinical studies show that physostigmine has poor oral activity, brain penetration and pharmacokinetic parameters while tacrine has hepatotoxic liability. Studies were then focused on finding a new type of acetylcholinesterase (AChE) inhibitor that would overcome the disadvantages of these two compounds. During the study, by chance we found a seed compound. We then conducted a structure-activity relationship (SAR) study of this compound. After four years of exploratory research, we found donepezil hydrochloride (donepezil). Recently, acetylcholinesterase inhibitors (AChEIs) have been studied for other mechanisms of action, such as neuroprotective action and lowering of beta-amyloid (beta-amyloid). Donepezil also reduced beta-amyloid plaque in in vitro. The amyloid hypothesis is believed to be the most promising approach in the development of anti-AD drugs. We speculate the mechanism of lowering beta-amyloid by donepezil implicate alpha-secretase (alpha-secretase) enhancer.     

Long-lasting acetylcholinesterase splice variations in anticholinesterase-treated Alzheimer's disease patients

Protein levels of different acetylcholinesterase (AChE) splice variants were explored by a combination of immunoblot techniques, using two different antibodies, directed against the C-terminus of the AChE-R splice variant or the core domain common to all variants. Both AChE-R and AChE-S splice variants as well as several heavier AChE complexes were detected in brain homogenates from the parietal cortex of patients with or without Alzheimer's disease (AD) as well as the cerebrospinal fluid (CSF) of AD patients, compatible with the assumption that CSF AChEs might originate from CNS neurons. Long-term changes in the composition of CSF AChE variants were further pursued in AD patients treated with rivastigmine (n = 11) or tacrine (n = 17) in comparison to untreated AD patients (n = 5). In untreated patients, AChE-R was markedly reduced as compared with the baseline level (37%), whereas the medium size AChE-S complex was increased by 32%. Intriguingly, tacrine produced a general and profound up-regulation of all detected AChE variants (up to 117%), whereas rivastigmine treatment caused a mild and selective up-regulation of AChE-R ( approximately 10%, p < 0.05). Moreover, the change in the ratio of AChE-R to AChE-S (R/S-ratio) strongly and positively correlated with sustained cognition at 12 months (p < 0.0001). Thus, evaluation of changes in the composition of CSF AChE variants may yield important information referring to the therapeutic efficacy and/or development of drug tolerance in AD patients treated with anti-cholinesterases.     

Mushroom Species Stereum hirsutum as Natural Source of Phenolics and Fatty Acids as Antioxidants and Acetylcholinesterase Inhibitors

Many lignicolous mushroom species are used as a food supplement and may represent an alternative treatment of Alzheimer's disease (AD). This study aimed to evaluate acetylcholinesterase inhibition (AChEI) of Stereum hirsutum together with antioxidant activity (AO) and cytotoxic activity against HepG2 cells. Different extracts (water, ethanol, methanol, polysaccharide) were analyzed, with respect to their mineral composition and chemical content. Ethanol extract was the most potent in AChEI (98.44 %) and demonstrated cytotoxic activity (91.96 % at 900.00 μg/mL), while the highest AO was demonstrated for polar extracts (methanol and water) as well. These activities may be attributed to determined phenolics (hydroxybenzoic and quinic acid) and fatty acids (FA), while biflavonoid amentoflavone may be responsible for cytotoxic activity. The most prevalent FA was linoleic (40.00 %) and the domination of unsaturated FA (UFA) (71.91 %) over saturated (26.96 %) was observed. This is the first report of AChEI of S. hirsutum extracts and first detection of amentoflavone. Due to high amount of UFA and well-expressed AChEI, this species can be considered as a potent food supplement in the palliative therapy of AD.     

Characterization of the interactions between coumarin-derivatives and acetylcholinesterase: Examination by NMR and docking simulations

Alzheimer’s disease (AD) is one of the most common forms of dementia and a significant threat to the elderly populations, especially in the Western world. The rapid hydrolysis of the principal neurotransmitter into choline and acetate by acetylcholinesterase (AChE) at synapses causes the loss of cognitive response that becomes the real cause of AD. Therefore, inhibition of AChE is the most fundamental therapy among currently available treatments for AD. In this context, we designed and performed molecular recognitions studies of coumarin-based inhibitors towards AChE. STD NMR and Tr-NOESY applications were utilized to evaluate the binding epitope, the dissociation constant (K_D) and bound conformations of these inhibitors within this inhibitor-AChE complex. Compound 1, which has a similar inhibition activity to tacrine (a current drug) led in this study as a stronger binder with K_D?=?30 μM ,even greater than tacrine (K_D?=?140 μM). Moreover, docking simulations mimic NMR results and provided evidence of synchronizing binding of compound 1 with three sites; the peripheral anionic site, the bottom of the gorge, and the catalytic site. Therefore, we envisioned from our experimental and theoretical results that coumarin-based inhibitors containing a piperidinyl scaffold might be a potential drug candidates for AD in the future.     

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.     

Antioxidant and acetylcholinesterase inhibitory activity of selected southern African medicinal plants

Alzheimer's disease (AD) is the most common type of dementia in the aging population. Enhancement of acetylcholine levels in the brain is one means of treating the disease. However, the drugs presently used in the management of the disease have various drawbacks. New treatments are required and in this study, extracts of Salvia tiliifolia Vahl. (whole plant), Chamaecrista mimosoides L. Greene (roots), Buddleja salviifolia (L.) Lam. (whole plant) and Schotia brachypetala Sond. (root and bark) were evaluated to determine their polyphenolic content, antioxidant and acetylcholinesterase inhibitory (AChEI) activity. The DPPH and ABTS assays were used to determine antioxidant activity and Ellman colorimetric method to quantify AChEI activity. Although all four plants showed activity in both assays, the organic extracts of C. mimosoides root was found to contain the highest AChEI activity (IC₅₀ = 0.03 ± 0.08 mg/ml) and B. salviifolia whole plant had the highest antioxidant activity (ABTS; IC₅₀ = 0.14 ± 0.08 mg/ml and DPPH; IC₅₀ = 0.23 ± 0.01 mg/ml). The results suggest that the tested plant species may provide a substantial source of secondary metabolites, which act as natural antioxidants and acetylcholinesterase inhibitors, and may be beneficial in the treatment of AD.     

Acetylcholinesterase‐Inhibitory Activities of the Extracts from Sponges Collected in Mauritius Waters

Patients diagnosed with Alzheimer's disease (AD) show a characteristic neurochemical deficit of acetylcholine, especially in the basal forebrains. The use of acetylcholinesterase (AChE) inhibitors to retard the hydrolysis of acetylcholine has been suggested as a promising strategy for AD treatment. In this study, we evaluated the acetylcholinesterase inhibitory (AChEI) activities of 134 extracts obtained from 45 species of marine sponges. Thin‐layer chromatography (TLC) and microplate assays reveal potent acetylcholinsterase inhibitory activities of two AcOEt extracts from the sponges Pericharax heteroraphis and Amphimedon navalis Pulitzer‐Finali . We further investigated the inhibitory kinetics of the extracts and found them to display mixed competitive/noncompetitive inhibition and associated their inhibitory activity partly to terpenoids. Acetylcholinesterase inhibitors from marine organisms have been rarely studied, and this study demonstrated the potential of marine sponges as a source of pharmaceutical leads against neurodegenerative diseases.     

Investigation of the role of linker moieties in bifunctional tacrine hybrids

Alzheimer’s disease (AD) is a complex neurological disorder with multiple inter-connected factors playing roles in the onset and progression of the disease. One strategy currently being explored for the development of new therapeutics for AD involves linking tacrine, a known acetylcholinesterase (AChE) inhibitor, to another drug to create bifunctional hybrids. The role and influence on activity of the linker moiety in these hybrids remains ill-defined. In this study, three series of 6-chlorotacrine with linkers varying in terminal functional group and length were synthesized, evaluated for AChE inhibition, and compared to tacrine and 6-chlorotacrine–mefenamic acid hybrids. Out of the compounds with terminal amine, methyl, and hydroxyl moieties tested, several highly potent molecules (low nanomolar IC₅₀ values) comprised of linkers with terminal amines were identified. These 6-chlorotacrine with linkers were significantly more potent than tacrine alone and were often more potent than similar 6-chlorotacrine–mefenamic acid hybrids.     

The role of caspases in Alzheimer’s disease; potential novel therapeutic opportunities

Although apoptosis plays a critical role in molding the CNS into its final appearance and function, inappropriate activation of this pathway in the aging brain may contribute to neurodegeneration. In Alzheimer’s disease (AD), an overwhelming body of evidence supports the activation of apoptosis in general, and caspases specifically as an early event that may not only contribute to neurodegeneration but also promote the underlying pathology associated with this disease. Therefore, caspase inhibitors may provide an effective strategy for treating AD. However, despite the compelling evidence indicating a role for caspases in disease progression, chronic treatment with caspase inhibitors in animal models of AD has never been undertaken. In this review the role of caspases in AD will be addressed, including recent studies utilizing in vivo transgenic mouse models of tauopathies. In addition, a discussion of the therapeutic value and dangers of targeting caspase inhibition in the treatment of AD using caspase inhibitors such as Q-VD-OPh will be evaluated.     

Tacrine and its analogues impair mitochondrial function and bioenergetics: a lipidomic analysis in rat brain

Tacrine is an acetylcholinesterase (AChE) inhibitor used as a cognitive enhancer in the treatment of Alzheimer's disease (AD). However, its low therapeutic efficiency and a high incidence of side effects have limited its clinical use. In this study, the molecular mechanisms underlying the impact on brain activity of tacrine and two novel tacrine analogues (T1, T2) were approached by focusing on three aspects: (i) their effects on brain cholinesterase activity; (ii) perturbations on electron transport chain enzymes activities of non-synaptic brain mitochondria; and (iii) the role of mitochondrial lipidome changes induced by these compounds on mitochondrial bioenergetics. Brain effects were evaluated 18 h after the administration of a single dose (75.6 μmol/kg) of tacrine or tacrine analogues. The three compounds promoted a significant reduction in brain AChE and butyrylcholinesterase (BuChE) activities. Additionally, tacrine was shown to be more efficient in brain AChE inhibition than T2 tacrine analogue and less active than T1 tacrine analogue, whereas BuChE inhibition followed the order: T1 > T2 > tacrine. The studies using non-synaptic brain mitochondria show that all the compounds studied disturbed brain mitochondrial bioenergetics mainly via the inhibition of complex I activity. Furthermore, the activity of complex IV is also affected by tacrine and T1 treatments while FoF(1) -ATPase is only affected by tacrine. Therefore, the compounds' toxicity as regards brain mitochondria, which follows the order: tacrine > T1 > T2, does not correlate with their ability to inhibit brain cholinesterase enzymes. Lipidomics approaches show that phosphatidylethanolamine (PE) is the most abundant phospholipids (PL) class in non-synaptic brain mitochondria and cardiolipin (CL) present the greatest diversity of molecular species. Tacrine induced significant perturbations in the mitochondrial PL profile, which were detected by means of changes in the relative abundance of phosphatidylcholine (PC), PE, phosphatidylinositol (PI) and CL and by the presence of oxidized phosphatidylserines. Additionally, in both the T1 and T2 groups, the lipid content and molecular composition of brain mitochondria PL are perturbed to a lesser extent than in the tacrine group. Abnormalities in CL content and the amount of oxidized phosphatidylserines were associated with significant reductions in mitochondrial enzymes activities, mainly complex I. These results indicate that tacrine and its analogues impair mitochondrial function and bioenergetics, thus compromising the activity of brain cells.     

Dual functional cholinesterase and PDE4D inhibitors for the treatment of Alzheimer’s disease: Design,synthesis and evaluation of tacrine-pyrazolo[3,4-b]pyridine hybrids

A series of tacrine-pyrazolo[3,4-b]pyridine hybrids were synthesised and evaluated as dual cholinesterase (ChE) and phosphodiesterase 4D (PDE4D) inhibitors for the treatment of Alzheimer’s disease (AD). Compound 10j, which is tacrine linked with pyrazolo[3,4-b]pyridine moiety by a six-carbon spacer, was the most potent acetylcholinesterase (AChE) with IC₅₀ value of 0.125 μM. Moreover, compound 10j provided a desired balance of AChE and butylcholinesterase (BuChE) and PDE4D inhibition activities, with IC₅₀ value of 0.449 and 0.271 μM, respectively. The above results indicated that this hybrid was a promising dual functional agent for the treatment of AD.     

Syntheses of benzoquinolizidine and benzoindolizidine derivatives as anti-amnesic agents.

Tacrine, one of the drugs available for Alzheimer's disease based on the cholinergic approach, suffers from considerable toxicity. Many analogues of tacrine have been prepared which retain the pharmacologically rich aminopyridine or aminoquinoline motifs. The current research was undertaken to produce an acetylcholinesterase inhibitor by employing 11-aminobenzoquinolizidines (4) and 10-aminobenzoindolizidines (5) as templates. Thus, we aimed to achieve three goals relative to tacrine: eliminate the pyridine and quinoline moieties and render the molecule less flat. Overall, the compounds we prepared were poorer inhibitors of acetylcholinesterase compared to tacrine. The single exception was compound 6f which exhibited an effect comparable to that of tacrine, but only at a dose of the order of 10(-3) M. However, despite the poor acetylcholinesterase inhibition by 6b, this compound proved to be an effective anti-amnesic agent at 45 mg/kg dose.