Potentiation effects of (±)huprine X, a new acetylcholinesterase inhibitor, on nicotinic receptors in rat cortical synaptosomes

Clock/Sleep-Dependent Learning and Memory in Male 3xTg-AD Mice at Advanced Disease Stages and Extrinsic Effects of Huprine X and the Novel Multitarget Agent AVCRI104P3

A new hypothesis highlights sleep-dependent learning/memory consolidation and regards the sleep-wake cycle as a modulator of β-amyloid and tau Alzheimer's disease (AD) pathologies. Sundowning behavior is a common neuropsychiatric symptom (NPS) associated with dementia. Sleep fragmentation resulting from disturbances in sleep and circadian rhythms in AD may have important consequences on memory processes and exacerbate the other AD-NPS. The present work studied the effect of training time schedules on 12-month-old male 3xTg-AD mice modeling advanced disease stages. Their performance in two paradigms of the Morris water maze for spatial-reference and visual-perceptual learning and memory were found impaired at midday, after 4 h of non-active phase. In contrast, early-morning trained littermates, slowing down from their active phase, exhibited better performance and used goal-directed strategies and non-search navigation described for normal aging. The novel multitarget anticholinesterasic compound AVCRI104P3 (0.6 µmol·kg^-1, 21 days i.p.) exerted stronger cognitive benefits than its in vitro equipotent dose of AChEI huprine X (0.12 μmol·kg^-1, 21 days i.p.). Both compounds showed streamlined drug effectiveness, independently of the schedule. Their effects on anxiety-like behaviors were moderate. The results open a question of how time schedules modulate the capacity to respond to task demands and to assess/elucidate new drug effectiveness.

Protective Effects of Pinus halepensis Bark Extract and Nicotine on Cigarette Smoke-induced Oxidative Stress in Keratinocytes

BACKGROUND/AIM

Cigarette smoke (CS) is a major environmental health threat. The oxidative stress induced by CS on keratinocytes and the possible protective effect of nicotine, its receptor inhibitors, and Pinus halepensis bark extract in relation to known antioxidants were investigated.

MATERIALS AND METHODS

Primary mouse keratinocytes were exposed to cigarette smoke in the presence and absence of Pinus halepensis bark extract (1 μg/ml), rutin (50 μM) and ascorbic acid (250 μM), nicotine (1 μM) with or without mecamylamine (5 μM) and α-bungarotoxin (0.1 μM). Keratinocyte viability and oxidative stress were evaluated by MTT and fluorescence assays.

RESULTS

Pinus halepensis bark extract decreased the oxidative stress and increased the viability of keratinocytes, and moreover, these effects were more pronounced compared to the mixture of rutin and L-ascorbic acid. Nicotine significantly enhanced the viability potentiation of the beneficial effect induced by Pinus halepensis bark extract. Mecamylamine and α-bungarotoxin showed no specific effect.

CONCLUSION

Pinus halepensis bark extract in combination with nicotine may successfully reverse skin damage induced by cigarette smoke.

Neuroprotective Effects of the Multitarget Agent AVCRI104P3 in Brain of Middle-Aged Mice

Molecular factors involved in neuroprotection are key in the design of novel multitarget drugs in aging and neurodegeneration. AVCRI104P3 is a huprine derivative that exhibits potent inhibitory effects on human AChE, BuChE, and BACE-1 activities, as well as on AChE-induced and self-induced Aβ aggregation. More recently, cognitive protection and anxiolytic-like effects have also been reported in mice treated with this compound. Now, we have assessed the ability of AVCRI104P3 (0.43 mg/kg, 21 days) to modulate the levels of some proteins involved in the anti-apoptotic/apoptotic processes (pAkt1, Bcl2, pGSK3β, p25/p35), inflammation (GFAP and Iba1) and neurogenesis in C57BL/6 mice. The effects of AVCRI104P3 on AChE-R/AChE-S isoforms have been also determined. We have observed that chronic treatment of C57BL/6 male mice with AVCRI104P3 results in neuroprotective effects, increasing significantly the levels of pAkt1 and pGSK3β in the hippocampus and Bcl2 in both hippocampus and cortex, but slightly decreasing synaptophysin levels. Astrogliosis and neurogenic markers GFAP and DCX remained unchanged after AVCRI104P3 treatment, whereas microgliosis was found to be significantly decreased pointing out the involvement of this compound in inflammatory processes. These results suggest that the neuroprotective mechanisms that are behind the cognitive and anxiolytic effects of AVCRI104P3 could be partly related to the potentiation of some anti-apoptotic and anti-inflammatory proteins and support the potential of AVCRI104P3 for the treatment of brain dysfunction associated with aging and/or dementia.

Behavioural effects of novel multitarget anticholinesterasic derivatives in Alzheimer's disease

The current pharmacological approach to Alzheimer's disease (AD) treatment, mostly based on acetylcholinesterase inhibitors (AChEIs), is being revisited, especially in terms of the temporal frames and the potential benefits of their noncanonic actions, raising the question of whether inhibitors of AChE might also act in a disease-modifying manner. Besides, in the last decades, the pharmacophoric moieties of known AChEIs have been covalently linked to other pharmacophores in the pursuit of multitarget hybrid molecules that are expected to induce long-lasting amelioration of impaired neurotransmission and clinical symptoms but also to exert disease-modifying effects. Our research consortium has synthesized and defined the pharmacological profile of new AChEIs derivatives of potential interest for the treatment of AD. Among these, huprines and derivatives have been characterized successfully. Huprine X, a reversible AChE inhibitor, designed by molecular hybridization of tacrine and huperzine A, has been shown to affect the amyloidogenic process in vitro, and the AD-related neuropathology in vivo in mice models of the disease. More recently, we have shown that a group of donepezil-huprine heterodimers exerts a highly potent and selective inhibitory action on AChE both in vitro and ex vivo, simultaneously interacting with both peripheral and catalytic binding sites, and inhibiting the β-amyloid aggregation, whereas some levetiracetam-huprine hybrids have been shown to reduce epileptiform activity, neuroinflammation and amyloid burden in an animal model of AD. Here, we summarize the behavioural correlates of these noncanonic actions as assessed in three distinct biological scenarios: middle-age, cognitive deficits associated with ageing and AD-like phenotype in mice. Besides the improvement in the hallmark cognitive symptomatology without inducing side effects, these drugs have shown to be able to modulate emotional and anxiety-like behaviours or to reduce spontaneous seizures, all of them related to the so-called 'behavioural and psychological symptoms of dementia'. Overall, the studies show that these novel multitarget anticholinesterasics exert noncanonic actions providing symptomatic and disease-modifying benefits of potential interest for the management of AD.

Huprine X Attenuates The Neurotoxicity Induced by Kainic Acid, Especially Brain Inflammation

Huprine X (HX) is a synthetic anticholinesterasic compound that exerts a potent inhibitory action on acetylcholinesterase (AChE) activity, an agonist effect on cholinergic receptors, neuroprotective activity in different neurotoxicity models in vivo and in vitro and cognition enhancing effects in non-transgenic (C57BL/6) and transgenic (3xTg-AD, APPswe) mice. In this study, we assessed the ability of HX (0.8 mg/kg, 21 days) to prevent the damage induced by kainic acid (KA; 28 mg/kg) regarding apoptosis, glia reactivity and neurogenesis in mouse brain. KA administration significantly modified the levels of pAkt1, Bcl2, pGSK3β, p25/p35, increased the glial cell markers and reduced the neurogenesis process. We also observed that pre-treatment with HX significantly reduced the p25/p35 ratio and increased synaptophysin levels, which suggests a protective effect against apoptosis and an improvement of neuroplasticity. The increase in GFAP (88%) and Iba-1 (72%) induced by KA was totally prevented by HX pre-treatment, underlying a relevant anti-inflammatory action of the anticholinesterasic drug. Our findings highlight the potential of HX, in particular, and of AChEIs, in general, to treat a number of diseases that course with both cognitive deficits and chronic inflammatory processes.

Undifferentiated and differentiated PC12 cells protected by huprines against injury induced by hydrogen peroxide

Oxidative stress is implicated in the pathogenesis of neurodegenerative disorders and hydrogen peroxide (H₂O₂) plays a central role in the stress. Huprines, a group of potent acetylcholinesterase inhibitors (AChEIs), have shown a broad cholinergic pharmacological profile. Recently, it has been observed that huprine X (HX) improves cognition in non transgenic middle aged mice and shows a neuroprotective activity (increased synaptophysin expression) in 3xTg-AD mice. Consequently, in the present experiments the potential neuroprotective effect of huprines (HX, HY, HZ) has been analyzed in two different in vitro conditions: undifferentiated and NGF-differentiated PC12 cells. Cells were subjected to oxidative insult (H₂O₂, 200 µM) and the protective effects of HX, HY and HZ (0.01 µM–1 µM) were analyzed after a pre-incubation period of 24 and 48 hours. All huprines showed protective effects in both undifferentiated and NGF-differentiated cells, however only in differentiated cells the effect was dependent on cholinergic receptors as atropine (muscarinic antagonist, 0.1 µM) and mecamylamine (nicotinic antagonist, 100 µM) reverted the neuroprotection action of huprines. The decrease in SOD activity observed after oxidative insult was overcome in the presence of huprines and this effect was not mediated by muscarinic or nicotinic receptors. In conclusion, huprines displayed neuroprotective properties as previously observed in in vivo studies. In addition, these effects were mediated by cholinergic receptors only in differentiated cells. However, a non-cholinergic mechanism, probably through an increase in SOD activity, seems to be also involved in the neuroprotective effects of huprines.

Huprine X and huperzine A improve cognition and regulate some neurochemical processes related with Alzheimer's disease in triple transgenic mice (3xTg-AD)

BACKGROUND

Different studies have established that cholinergic neurodegeneration could be a major pathological feature of Alzheimer's disease (AD). Thus, enhancement of the central cholinergic neurotransmission has been regarded as one of the most promising strategies for the symptomatic treatment of AD, mainly by means of reversible acetylcholinesterase inhibitors (AChEIs). The cognitive-enhancing properties of both huprine X, a new AChEI, and the structurally related huperzine A, as well as their effects on the regulation of several neurochemical processes related to AD have been studied in triple transgenic mice (3xTg-AD).

METHODS

Seven-month-old homozygous 3xTg-AD male mice, which received chronic intraperitoneal treatment with either saline, huprine X (0.12 µmol·kg(-1)) or huperzine A (0.8 µmol·kg(-1)) were subjected to a battery of behavioural tests after 3 weeks of treatment and thereafter the brains were dissected to study the neurochemical effects induced by the two AChEIs.

RESULTS

Treatments with huprine X and huperzine A improved learning and memory in the Morris water maze and some indicators of emotionality without inducing important adverse effects. Moreover, huprine X and huperzine A activate protein kinase C/mitogen-activated protein kinase pathway signalling, α-secretases (ADAM 10 and TACE) and increase the fraction of phospho-glycogen synthase kinase 3-β.

CONCLUSION

Results obtained herein using a sample of 3xTg-AD animals strongly suggest that the treatment with the two AChEIs not only improves the cognitive performance of the animals but also induces some neurochemical changes that could contribute to the beneficial effects observed.

The coumarin scopoletin potentiates acetylcholine release from synaptosomes, amplifies hippocampal long-term potentiation and ameliorates anticholinergic- and age-impaired memory

In a previous study the simple, naturally derived coumarin scopoletin (SCT) was identified as an inhibitor of acetylcholinesterase (AChE), using a pharmacophore-based virtual screening approach. In this study the potential of SCT as procholinergic and cognition-enhancing therapeutic was investigated in a more detailed way, using different experimental approaches like measuring newly synthesized acetylcholine (ACh) in synaptosomes, long-term potentiation (LTP) experiments in hippocampal slices, and behavior studies. SCT enhanced the K⁺-stimulated release of ACh from rat frontal cortex synaptosomes, showing a bell-shaped dose effect curve (E_max: 4 μM). This effect was blocked by the nicotinic ACh receptor (nAChR) antagonists mecamylamine (MEC) and dihydro-β-erythroidine (DHE). The nAChR agonist (and AChE inhibitor) galantamine induced a similar increase in ACh release (E_max: 1 μM). SCT potentiated LTP in hippocampal slices of rat brain. The high-frequency stimulation (HFS)-induced, N-methyl-D-aspartate (NMDA) receptor dependent LTP of field excitatory postsynaptic potentials at CA3-CA1 synapses was greatly enhanced by pre-HFS application of SCT (4 μM for 4 min). This effect was mimicked by nicotine (2 μM) and abolished by MEC, suggesting an effect on nAChRs. SCT did not restore the total inhibition of LTP by NMDA receptor antagonist d, l-2-amino-5-phosphonopentanoic acid (AP-5). SCT (2 μg, i.c.v.) increased T-maze alternation and ameliorated novel object recognition of mice with scopolamine-induced cholinergic deficit. It also reduced age-associated deficits in object memory of 15–18-month-old mice (2 mg/kg sc). Our findings suggest that SCT possesses memory-improving properties, which are based on its direct nAChR agonistic activity. Therefore, SCT might be able to rescue impaired cholinergic functions by enhancing nAChR-mediated release of neurotransmitters and promoting neural plasticity in hippocampus.

Bis(12)-hupyridone, a novel multifunctional dimer, promotes neuronal differentiation more potently than its monomeric natural analog huperzine A possibly through α7 nAChR

The cause of many neurodegenerative disorders can be ascribed to the loss of functional neurons, and thus agents capable of promoting neuronal differentiation may have therapeutic benefits to patients of these disorders. In this study, the effects and underlying mechanisms of bis(12)-hupyridone (B12H), a novel dimeric acetylcholinesterase inhibitor modified from huperzine A (HA), on neuronal differentiation were investigated using both the rat PC12 pheochromocytoma cell line and adult rat hippocampus neural stem cells. B12H (3-30 μM), characterized by morphological changes and expression of GAP-43, induced neurite outgrowth in a concentration- and time-dependent manner, with almost 3-fold higher efficacy than that of HA in PC12 cells. Furthermore, B12H (2.5-10 μM), but not HA, promoted neuronal differentiation as shown by the percentage increase of βIII-tubulin positive neurons in neural stem cells. The activities of extracellular signal-regulated kinase (ERK), as well as its downstream transcription factors Elk-1 and cAMP response element-binding protein (CREB) were elevated in the B12H-treated PC12 cells. Mitogen-activated protein kinase kinase inhibitors and alpha7-nicotinic acetylcholine receptor (α7nAChR) antagonist blocked the neurite outgrowth and the activation of ERK induced by B12H. All these findings suggest that B12H potently induces pro-neuronal cells into differentiated neurons by activating the ERK pathway possibly via regulating α7nAChR. These findings support the recent proposition that α7nAChR is required for the neuronal dendritic arborization and differentiation in the adult mice hippocampus, and provide insights into the possible therapeutic potential of B12H in treating neurodegenerative disorders.

Pharmacological aspects of the acetylcholinesterase inhibitor galantamine

Several lines of evidence suggest that cholinergic deficits may contribute to the pathophysiology of psychiatric disorders as well as Alzheimer's disease. There is growing clinical evidence that galantamine, currently used for the treatment of Alzheimer's disease, may improve cognitive dysfunction and psychiatric illness in schizophrenia, major depression, bipolar disorder, and alcohol abuse. Since galantamine is a rather weak acetylcholinesterase inhibitor, but has additional allosteric potentiating effects at nicotinic receptors, it affects not only cholinergic transmission but also other neurotransmitter systems such as monoamines, glutamate, and γ-aminobutyric acid (GABA) through its allosteric mechanism. It is likely that these effects may result in more beneficial effects. To understand the underlying mechanism for the clinical effectiveness of galantamine, neuropharmacological studies have been performed in animal models of several psychiatric disorders. These studies suggest that not only the nicotinic receptor-modulating properties but also the muscarinic receptor activation contribute to the antipsychotic effect and improvement of cognitive dysfunction by galantamine. This review summaries the current status on the pharmacology of galantamine, focusing on its effect on neurotransmitter release and pharmacological studies in animal models of psychiatric disorders.

Rational design and synthesis of highly potent anti-acetylcholinesterase activity huperzine A derivatives

By targeting multi-active sites of acetylcholinesterase (AChE), a series of huperzine A (Hup A) derivatives with various aromatic ring groups were designed and synthesized by Schiff reaction. They were evaluated as AChE and butyrylcholinesterase (BChE) inhibitors. Results showed very significant specificity that the group of imine derivatives could inhibit TcAChE and hAChE, but no inhibitory effect on hBChE was detected. The experiment was explained by a docking study. In the docking model, we confirmed that aromatic ring of Hup A derivatives played the pi-pi stacking against aminophenol residues of AChE, and the structure-activity relationship (SAR) was discussed.

Nicotinic-receptor potentiator drugs, huprine X and galantamine, increase ACh release by blocking AChE activity but not acting on nicotinic receptors

The main goal of the present study was to analyse the effects of (+/-)-huprine X ((+/-)-HX) and galantamine (GAL), with potentiating action on nicotinic receptors, and huperzine A (HPA), devoid of nicotinic activity, on [3H]-acetylcholine ([3H]-ACh) release in striatal slices of rat brain. All compounds are non-covalent and reversible inhibitors of AChE. Addition of (+/-)-HX (0.01 microM), GAL (10 microM) and HPA (0.1 microM) to the superfusion medium decreased the release of the ACh neurotransmitter to a similar extent: 36%, 30% and 34%, respectively (P<0.01). This effect was reverted in the presence of atropine (ATR; 0.1 microM), which blocks the pre-synaptic muscarinic M2 receptor. After that, a wide range of concentrations of drugs, concomitantly with ATR (0.1 microM), was studied in the presence of haloperidol (HAL; 0.01 microM), a dopamine D2 antagonist. In these conditions, a dose-dependent increase of [3H]-ACh release was observed in the presence of (+/-)-HX, GAL and HPA. To test the role of nicotinic receptors in the drugs' effects on [3H]-ACh release, mecamylamine (MEC) 100 microM was used to block such receptors. MEC alone significantly decreased neurotransmitter release by 18% (P<0.05), but no change was obtained in the presence of both ATR and MEC. Under these conditions, (+/-)-HX, GAL and HPA increased the release of [3H]-ACh by 37%, 25% and 38%, respectively (P<0.01). Taking into account all of these data, the present results suggest that the effects induced by (+/-)-HX and GAL nicotinic-receptor potentiators seem to be mainly due to their ability in inhibiting acetylcholinesterase activity, but not by interaction on the nicotinic receptors.

Effects of (±)-huprine Y and (±)-huprine Z, two new anticholinesterasic drugs, on muscarinic receptors

The cholinergic profile of (+/-)-huprine Y and (+/-)-huprine Z on muscarinic receptors has been determined. Displacement of [3H]-pirenzepine and [3H]-QNB plus pirenzepine was performed in rat hippocampus. Both compounds showed a higher degree of affinity to M1 muscarinic receptors (P < 0.01) than to M2 muscarinic receptors. To determine the M1 agonist or antagonist role of the two huprines, studies of inositol phosphates (IP) production were performed. Both huprines significantly stimulated IP accumulation in a concentration-dependent manner. The reversion of this effect by different antagonists showed that M1 muscarinic receptors were activated by (+/-)-huprine Y and (+/-)-huprine Z, but some other mechanisms, such as alpha1-adrenoceptors or nicotinic receptors, were involved.