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ABSTRACT: We have previously reported that bis(propyl)-cognitin (B3C), similar to memantine (MEM), is an uncompetitive N-methyl-D-aspartate receptor antagonist with fast off-rate property. In the current study, we further demonstrated that in primary cultures of rat cerebellar granule neurons (CGNs), 2 h pretreatment of B3C (IC(50), 0.45 μM) prevented glutamate-induced excitotoxicity 10 times more potently than memantine (IC(50), 4.58 μM), as evidenced by cell viability and lactate dehydrogenase release assays. Additionally, B3C pretreatment could inhibit the increase of intracellular nitric oxide (NO) and the activation of phosphorylated ERK, and reverse the suppression of phosphorylated Akt and GSK3β caused by glutamate. Furthermore, the neuroprotection of B3C was abolished by phosphatidylinositol 3-kinase (PI3-K) inhibitor LY294002. Meanwhile, pharmacological inhibition showed that neither the single specific inhibitors of nitric oxide synthase (L-NMMA), MEK1/2 (U0126) and GSK3β (SB415286 and LiCl) nor the combinations of any two of them could fully protect against glutamate-induced apoptosis. However, the co-application of these three inhibitors produced nearly 100% inhibition of glutamate-induced apoptosis. These results taken together suggest that B3C elicits neuroprotection against glutamate-induced neurotoxicity in CGNs via concurrent inhibition of NO, MAPK/ERK pathways and activation of PI3-K/Akt/GSK3β pathway. Combining these and our previous publications, it is conjectured that the dimer might be an ideal candidate drug in delaying the course of neurodegeneration related with Alzheimer's disease.
Neurochemistry International 01/2013; · 2.86 Impact Factor
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Jialie Luo,
Wenming Li,
Yuming Zhao,
Hongjun Fu,
Dik-Lung Ma,
Jing Tang,
Chaoying Li,
Robert W Peoples,
Fushun Li,
Qinwen Wang,
Pingbo Huang,
Jun Xia, Yuanping Pang,
Yifan Han
[show abstract]
[hide abstract]
ABSTRACT: Uncompetitive N-methyl-d-aspartate (NMDA) receptor antagonists with fast off-rate (UFO) may represent promising drug candidates for various neurodegenerative disorders. In this study, we report that bis(propyl)-cognitin, a novel dimeric acetylcholinesterase inhibitor and gamma-aminobutyric acid subtype A receptor antagonist, is such an antagonist of NMDA receptors. In cultured rat hippocampal neurons, we demonstrated that bis(propyl)-cognitin voltage-dependently, selectively, and moderately inhibited NMDA-activated currents. The inhibitory effects of bis(propyl)-cognitin increased with the rise in NMDA and glycine concentrations. Kinetics analysis showed that the inhibition was of fast onset and offset with an off-rate time constant of 1.9 s. Molecular docking simulations showed moderate hydrophobic interaction between bis(propyl)-cognitin and the MK-801 binding region in the ion channel pore of the NMDA receptor. Bis(propyl)-cognitin was further found to compete with [(3)H]MK-801 with a K(i) value of 0.27 mum, and the mutation of NR1(N616R) significantly reduced its inhibitory potency. Under glutamate-mediated pathological conditions, bis(propyl)-cognitin, in contrast to bis(heptyl)-cognitin, prevented excitotoxicity with increasing effectiveness against escalating levels of glutamate and much more effectively protected against middle cerebral artery occlusion-induced brain damage than did memantine. More interestingly, under NMDA receptor-mediated physiological conditions, bis(propyl)-cognitin enhanced long-term potentiation in hippocampal slices, whereas MK-801 reduced and memantine did not alter this process. These results suggest that bis(propyl)-cognitin is a UFO antagonist of NMDA receptors with moderate affinity, which may provide a pathologically activated therapy for various neurodegenerative disorders associated with NMDA receptor dysregulation.
Journal of Biological Chemistry 06/2010; 285(26):19947-58. · 4.77 Impact Factor
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ABSTRACT: Alzheimer’s disease (AD) is a progressive, degenerative disorder of the brain and the most common form of dementia among the
elderly. The neuropathological hallmarks of AD are senile plaques, which are extracellular deposits predominantly composed
of fibrillar amyloid β peptide (Aβ), and intracellular neurofibrillary tangles composed of filamentous aggregates called paired
helical filaments of hyperphosphorylated tau protein. Aβ is proposed to play a key role in the pathogenesis of AD. Therefore,
treatments targeting the biosynthesis, oligomerization/ aggregation, and toxicity of Aβ are likely to be the promising disease-modifying
therapeutics. Bis(7)-Cognitin, one of our promising anti-Alzheimer’s dimers, has previously been shown to possess potent acetylcholinesterase
(AChE) inhibition, memory-enhancement, and neuroprotection against several stimuli that go beyond the inhibition of AChE.
Our recent studies have further demonstrated that bis(7)-Cognitin exerts profound neuroprotective effects by targeting the
multiple stages of the Aβ pathological cascade of AD, i.e. the biosynthesis, oligomerization/aggregation and toxicity of Aβ.
These findings may offer not only a new and clinically significant modality as to how the agent exerts neuroprotective effects,
but also a novel direction to rationally develop one-compound-multi-targets drugs for the prevention and treatment of AD,
even of other neurodegenerative diseases.
KeywordsAlzheimer’s disease-Aβ-APP processing-Bis(7)-Cognitin-Disease modification
12/2009: pages 165-183;
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Hongjun Fu,
Juan Dou,
Wenming Li,
Wei Cui,
Shinghung Mak,
Qiansheng Hu,
Jialie Luo,
Colin S C Lam, Yuanping Pang,
Moussa B H Youdim,
Yifan Han
[show abstract]
[hide abstract]
ABSTRACT: We have recently demonstrated that bis(7)-Cognitin, a promising multifunctional anti-Alzheimer's dimer, can remarkably reduce the generation of amyloid beta peptide (Abeta) by inhibiting beta-secretase (BACE-1) and activating alpha-secretase activity. In this study, the mechanism(s) underlying bis(7)-Cognitin's regulation of the activity of these two proteases was further investigated. In N2a cells stably expressing human amyloid precursor protein with the Swedish mutation (APPswe), the reduction in Abeta production induced by 1microM bis(7)-Cognitin was not altered by the co-pretreatment of muscarinic and nicotinic cholinergic receptor antagonists, indicating that the regulation of APP processing by this dimer is independent of cholinergic transmission. Furthermore, bis(7)-Cognitin (0.1-3microM) significantly increased protein kinase C (PKC) activity in cells and in vitro in a concentration-dependent manner. Administration of a PKC activator, phorbol 12-myristate 13-acetate (PMA), concentration-dependently increased the alpha-secretase cleavage products, and reduced the BACE-1 cleavage products. In addition, the inhibition of PKC prevented PMA- or bis(7)-Cognitin-induced alterations in alpha-secretase and BACE-1 activities, eliminating reductions in Abeta production seen with PMA or the dimer. These results strongly suggest that bis(7)-Cognitin may reduce the biosynthesis of Abeta by inhibiting BACE-1 and activating alpha-secretase concurrently through the direct activation of PKC. Combined with previous findings of direct inhibition of AChE and BACE-1 by this dimer, this work indicates that strategy may have potential to provide new insights into designing novel drugs that target multiple steps of aberrant APP processing to treat Alzheimer's disease.
European journal of pharmacology 09/2009; 623(1-3):14-21. · 2.59 Impact Factor
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ABSTRACT: Alzheimer's disease (AD) is a progressive and degenerative brain disorder that has emerged as one of the major public health problems in adults. Unfortunately, its molecular pathology and therapeutic strategies remain elusive. Because there are multiple factors closely indicated in the pathogenesis of AD, multiple drug therapy will be required to address the varied pathological aspects of this disease. Existing pharmacological approaches with one-molecule-one-target are limited in their ability to modify the pathology of AD. Novel therapeutics strategies comprise multifunctional compounds specifically designed to target concurrently on different sites at multifactorial etiopathogenesis of AD, thereby providing greater therapeutic efficacy. Over the past decade, our group has developed several series of dimeric acetylcholinesterase (AChE) inhibitors derived from tacrine and huperzine A, a unique anti-Alzheimer's drug originally discovered from a traditional Chinese medicinal plant. Bis(7)-Cognitin, one of our novel dimers, through inhibition of AChE, N-methyl-D-aspartate receptor, nitric oxide synthase, and amyloid precursor protein/beta-amyloid cascade concurrently, possesses remarkable neuroprotective activities. More importantly, the synergism between these targets might serve as one of the most effective therapeutic strategies to arrest/modify pathological process of AD in addition to improving the cognitive functions for AD.
Neurotherapeutics 02/2009; 6(1):187-201. · 6.01 Impact Factor
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[show abstract]
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ABSTRACT: Bis(7)-tacrine, a promising anti-Alzheimer's dimer, has been shown to have multiple neuroprotective activities in vitro. Here, we investigate whether bis(7)-tacrine attenuates focal cerebral ischemic impairment in vivo. Cerebral ischemia was induced in Sprague-Dawley rats by transient (2h) middle cerebral artery occlusion (MCAO) followed by 24h of reperfusion. Bis(7)-tacrine administered intraperitoneally 15 min after ischemia dose-dependently improved neurological behavior deficits and reduced both cerebral infarct volume and edema. The TUNEL staining assay showed that bis(7)-tacrine attenuated neuronal apoptosis in the penumbral region. Compared with that for memantine, a moderately effective N-methyl-d-aspartate (NMDA) receptor antagonist with a similar affinity and potency to bis(7)-tacrine in blocking NMDA receptors, the therapeutic window for bis(7)-tacrine was wider and lasted up to 6h after the onset of ischemia. Bis(7)-tacrine did not affect physiological parameters or regional cerebral blood flow during either the occlusion period or the early reperfusion stage. In conclusion, bis(7)-tacrine dose- and time-dependently protected against acute focal cerebral ischemic insults, possibly through the drug's anti-apoptotic effects during multiple events in the ischemic cascade.
Neuroscience Letters 08/2008; 439(2):160-4. · 2.11 Impact Factor
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[show abstract]
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ABSTRACT: The regulation of alpha-, beta-, (BACE-1), and gamma-secretase activities to alter beta-amyloid (Abeta) generation is considered to be one of the most promising disease-modifying therapeutics for Alzheimer's disease. In this study, the effect and mechanisms of bis(7)-tacrine (a promising anti-Alzheimer's dimer) on Abeta generation were investigated. Bis(7)-tacrine (0.1-3muM) substantially reduced the amounts of both secreted and intracellular Abeta in Neuro2a APPswe cells without altering the expression of APP. sAPPalpha and CTFalpha increased, while sAPPbeta and CTFbeta decreased significantly in Neuro2a APPswe cells following the treatment with bis(7)-tacrine, indicating that bis(7)-tacrine might activate alpha-secretase and/or inhibit BACE-1 activity. Furthermore, bis(7)-tacrine concentration-dependently inhibited BACE-1 activity in cultured cells, and also in recombinant human BACE-1 in a non-competitive manner with an IC(50) of 7.5muM, but did not directly affect activities of BACE-2, Cathepsin D, alpha- or gamma-secretase. Taken together, our results not only suggest that bis(7)-tacrine may reduce the biosynthesis of Abeta mainly by directly inhibiting BACE-1 activity, but also provide new insights into the rational design of novel anti-Alzheimer's dimers that might have disease-modifying properties.
Biochemical and Biophysical Research Communications 03/2008; 366(3):631-6. · 2.48 Impact Factor
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Jialie Luo,
Wenming Li,
Yuwei Liu,
Wei Zhang,
Hongjun Fu,
Nelson T K Lee,
Hua Yu, Yuanping Pang,
Pingbo Huang,
Jun Xia,
Zhi-Wang Li,
Chaoying Li,
Yifan Han
[show abstract]
[hide abstract]
ABSTRACT: Bis(7)-tacrine has been shown to prevent glutamate-induced neuronal apoptosis by blocking NMDA receptors. However, the characteristics of the inhibition have not been fully elucidated. In this study, we further characterize the features of bis(7)-tacrine inhibition of NMDA-activated current in cultured rat hippocampal neurons. The results show that with the increase of extracellular pH, the inhibitory effect decreases dramatically. At pH 8.0, the concentration-response curve of bis(7)-tacrine is shifted rightwards with the IC(50) value increased from 0.19+/-0.03 microM to 0.41+/-0.04 microM. In addition, bis(7)-tacrine shifts the proton inhibition curve rightwards. Furthermore, the inhibitory effect of bis(7)-tacrine is not altered by the presence of the NMDA receptor proton sensor shield spermidine. These results indicate that bis(7)-tacrine inhibits NMDA-activated current in a pH-dependent manner by sensitizing NMDA receptors to proton inhibition, rendering it potentially beneficial therapeutic effects under acidic conditions associated with stroke and ischemia.
Biochemical and Biophysical Research Communications 10/2007; 361(2):505-9. · 2.48 Impact Factor
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Hongjun Fu,
Wenming Li,
Yulin Liu,
Yuanzhi Lao,
Wei Liu,
Cheng Chen,
Hua Yu,
Nelson T K Lee,
Donald C Chang,
Peng Li, Yuanping Pang,
Karl W K Tsim,
Mingtao Li,
Yifan Han
[show abstract]
[hide abstract]
ABSTRACT: Increasing evidence supports that the mitochondrial dysfunction, mainly caused by abnormal changes in mitochondrial proteins, plays a pivotal role in glutamate-induced excitotoxicity, which is closely associated with the pathogenesis of acute and chronic neurodegenerative disorders, such as stroke and Alzheimer's disease. In this study, post-treatment of cerebellar granule neurons with bis(7)-tacrine significantly reversed declines in mitochondrial membrane potential, ATP production, and neuronal cell death induced by glutamate. Moreover, this reversal was independent of NMDA antagonism, acetylcholinesterase inhibition, and cholinergic pathways. Using two-dimensional differential in-gel electrophoresis, we conducted a comparative analysis of mitochondrial protein patterns. In all, 29 proteins exhibiting significant differences in their abundances were identified in the glutamate-treated group when compared with the control. The expression patterns in 22 out of these proteins could be reversed by post-treatment with bis(7)-tacrine. Most of the differentially expressed proteins are involved in energy metabolism, oxidative stress, and apoptosis. In particular, the altered patterns of four of these proteins were further validated by Western blot analysis. Our findings suggest that multiple signaling pathways initiated by the altered mitochondrial proteins may mediate glutamate-induced excitotoxicity and also offer potentially useful intracellular targets for the neuroprotection provided by bis(7)-tacrine.
Journal of Proteome Research 08/2007; 6(7):2435-46. · 5.11 Impact Factor
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Wenming Li,
Jian Xue,
Chunying Niu,
Hongjun Fu,
Colin S C Lam,
Jialie Luo,
Hugh H N Chan,
Huaiguo Xue,
Kelvin K W Kan,
Nelson T K Lee,
Chaoying Li, Yuanping Pang,
Mingtao Li,
Karl W K Tsim,
Hualiang Jiang,
Kaixian Chen,
Xiaoyuan Li,
Yifan Han
[show abstract]
[hide abstract]
ABSTRACT: The excessive activation of the N-methyl-D-aspartate receptor (NMDAR)/nitric oxide (NO) pathway has been proposed to be involved in the neuropathology of various neurodegenerative disorders. In this study, NO was found to mediate glutamate-induced excitotoxicity in primary cultured neurons. Compared with the NO synthase (NOS) inhibitor, N(G)-monomethyl-L-arginine (L-NMMA), and the NMDAR antagonist memantine, bis(7)-tacrine was found to be more potent in reducing NO-mediated excitotoxicity and the release of NO caused by glutamate. Moreover, like L-NMMA but not like 5H-dibenzo[a,d]cyclohepten-5,10-imine (MK-801) and memantine, bis(7)-tacrine showed greater neuroprotection and inhibition on NO release when neurons were pretreated for a prolonged time between 0 and 24 h and remained quite potent even when neurons were post-treated 1 h after the glutamate challenge. Bis(7)-tacrine was additionally found to be as moderately potent as memantine in competing with [(3)H]MK-801, inhibiting NMDA-evoked currents and reducing glutamate-triggered calcium influx, which eventually reduced neuronal NOS activity. More importantly, at neuroprotective concentrations, bis(7)-tacrine substantially reversed the overactivation of neuronal NOS caused by glutamate without interfering with the basal activity of NOS. Furthermore, in vitro pattern analysis demonstrated that bis(7)-tacrine competitively inhibited both purified neuronal and inducible NOS with IC(50) values at 2.9 and 9.3 microM but not endothelial NOS. This result was further supported by molecular docking simulations that showed hydrophobic interactions between bis(7)-tacrine and three NOS isozymes. Taken together, these results strongly suggest that the substantial neuroprotection against glutamate by bis(7)-tacrine might be mediated synergistically through the moderate blockade of NMDAR and selective inhibition of neuronal NOS.
Molecular Pharmacology 06/2007; 71(5):1258-67. · 4.88 Impact Factor
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Chaoying Li,
Paul R Carlier,
Hong Ren,
Kelvin K W Kan,
Kwokmin Hui,
Hong Wang,
Wenming Li,
Zhiwang Li,
Keming Xiong,
Ella Chow Clement,
Hong Xue,
Xiangou Liu,
Mingtao Li, Yuanping Pang,
Yifan Han
[show abstract]
[hide abstract]
ABSTRACT: Bis(7)-tacrine was previously demonstrated as an antagonist of gamma-aminobutyric acid type A (GABA(A)) receptors. In this study, the effects of a series of alkylene-linked tacrine dimers on GABA(A) receptors were examined. In radioligand binding assay, the analogues differed in binding affinity for GABA(A) receptors, and potency monotonically increased as the tether was shortened from nine to two methylenes. Bis(2)-tacrine, the shortest tacrine dimer, could displace [(3)H]muscimol from rat brain membranes with an IC(50) of 0.48 microM, which was 11, 13 and 525 times more potent than the GABA(A) receptor antagonist (+)-bicuculline, bis(7)-tacrine and tacrine, respectively. In whole-cell patch-clamp recordings, these dimeric tacrine analogues competitively antagonized GABA-induced inward current with a rank order of potency of bis(2)-tacrine>bicuculline>bis(7)-tacrine>bis(9)-tacrine>tacrine, and the potency of bis(2)-tacrine was 11, 18 and 487 times higher than that of (+)-bicuculline, bis(7)-tacrine and tacrine, respectively. Bis(2)-tacrine shifted the GABA concentration-response curve to the right in a parallel manner, and the inhibition was voltage-independent between -80 and +20 mV. It can be concluded that the shorter the alkylene linkage in tacrine dimers the stronger the binding affinity and higher the antagonistic effect on the GABA(A) receptor will be.
Neuropharmacology 03/2007; 52(2):436-43. · 4.81 Impact Factor
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Hongjun Fu,
Wenming Li,
Yuanzhi Lao,
Jialie Luo,
Nelson T K Lee,
Kelvin K W Kan,
Hing Wai Tsang,
Karl W K Tsim, Yuanping Pang,
Zhiwang Li,
Donald C Chang,
Mingtao Li,
Yifan Han
[show abstract]
[hide abstract]
ABSTRACT: Beta amyloid protein (Abeta) and acetylcholinesterase (AChE) have been shown to be closely implicated in the pathogenesis of Alzheimer's disease. In the current study, we investigated the effects of bis(7)-tacrine, a novel dimeric AChE inhibitor, on Abeta-induced neurotoxicity in primary cortical neurons. Bis(7)-tacrine, but not other AChE inhibitors, elicited a marked reduction of both fibrillar and soluble oligomeric forms of Abeta-induced apoptosis as evidenced by chromatin condensation and DNA specific fragmentation. Both nicotinic and muscarinic receptor antagonists failed to block the effects of bis(7)-tacrine. Instead, nimodipine, a blocker of L-type voltage-dependent Ca2+ channels (VDCCs), attenuated Abeta neurotoxicity, whereas N-, P/Q- or R-type VDCCs blockers and ionotropic glutamate receptor antagonists did not. Fluorescence Ca2+ imaging assay revealed that, similar to nimodipine, bis(7)-tacrine reversed Abeta-triggered intracellular Ca2+ increase, which was mainly contributed by the extracellular Ca2+ instead of endoplasmic reticulum and mitochondria Ca2+. Concurrently, using whole cell patch-clamping technique, it was found that bis(7)-tacrine significantly reduced the augmentation of high voltage-activated inward calcium currents induced by Abeta. These results suggest that bis(7)-tacrine attenuates Abeta-induced neuronal apoptosis by regulating L-type VDCCs, offers a novel modality as to how the agent exerts neuroprotective effects.
Journal of Neurochemistry 10/2006; 98(5):1400-10. · 4.06 Impact Factor
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[show abstract]
[hide abstract]
ABSTRACT: Here we report that bis(7)-tacrine, a novel acetylcholinesterase inhibitor, exerts neuroprotective effects by inhibition of nitric oxide synthase. In cortical neurons at 12 days in vitro, bis(7)-tacrine concentration-dependently reduced cell death induced by glutamate, beta-amyloid and L-arginine, but not by nitric sodium nitroprusside. N-monomethyl-L-arginine, a nitric oxide synthase inhibitor, also prevented the former three types but not the last type of the cytotoxicity; however, nitric oxide scavengers blocked all of these insults, indicating that nitric oxide mediated these neuronal injuries. Furthermore, with nitric oxide synthase activity assays, it was found that bis(7)-tacrine not only suppressed the activation of nitric oxide synthase caused by glutamate in cortical neurons, but also directly inhibited the activity of nitric oxide synthase in vitro.
Neuroreport 05/2006; 17(5):471-4. · 1.66 Impact Factor
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Wenming Li,
Rongbiao Pi,
Hugh H N Chan,
Hongjun Fu,
Nelson T K Lee,
Hing Wai Tsang,
Yongmei Pu,
Donald C Chang,
Chaoying Li,
Jialie Luo,
Keming Xiong,
Zhiwang Li,
Hong Xue,
Paul R Carlier, Yuanping Pang,
Karl W K Tsim,
Mingtao Li,
Yifan Han
[show abstract]
[hide abstract]
ABSTRACT: The neuroprotective properties of bis(7)-tacrine, a novel dimeric acetylcholinesterase (AChE) inhibitor, on glutamate-induced excitotoxicity were investigated in primary cultured cerebellar granule neurons (CGNs). Exposure of CGNs to 75 mum glutamate resulted in neuronal apoptosis as demonstrated by Hoechst staining, TUNEL, and DNA fragmentation assays. The bis(7)-tacrine treatment (0.01-1 mum) on CGNs markedly reduced glutamate-induced apoptosis in dose- and time-dependent manners. However, donepezil and other AChE inhibitors, even at concentrations of inhibiting AChE to the similar extents as 1 mum bis(7)-tacrine, failed to prevent glutamate-induced excitotoxicity in CGNs; moreover, both atropine and dihydro-beta-erythroidine, the cholinoreceptor antagonists, did not affect the anti-apoptotic properties of bis(7)-tacrine, suggesting that the neuroprotection of bis(7)-tacrine appears to be independent of inhibiting AChE and cholinergic transmission. In addition, ERK1/2 and p38 pathways, downstream signals of N-methyl-d-aspartate (NMDA) receptors, were rapidly activated after the exposure of glutamate to CGNs. Bis(7)-tacrine inhibited the apoptosis and the activation of these two signals with the same efficacy as the coapplication of PD98059 and SB203580. Furthermore, using fluorescence Ca(2+) imaging, patch clamp, and receptor-ligand binding techniques, bis(7)-tacrine was found effectively to buffer the intracellular Ca(2+) increase triggered by glutamate, to reduce NMDA-activated currents and to compete with [(3)H]MK-801 with an IC(50) value of 0.763 mum in rat cerebellar cortex membranes. These findings strongly suggest that bis(7)-tacrine prevents glutamate-induced neuronal apoptosis through directly blocking NMDA receptors at the MK-801-binding site, which offers a new and clinically significant modality as to how the agent exerts neuroprotective effects.
Journal of Biological Chemistry 06/2005; 280(18):18179-88. · 4.77 Impact Factor
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[show abstract]
[hide abstract]
ABSTRACT: The regulation of α-, β-, (BACE-1), and γ-secretase activities to alter β-amyloid (Aβ) generation is considered to be one of the most promising disease-modifying therapeutics for Alzheimer’s disease. In this study, the effect and mechanisms of bis(7)-tacrine (a promising anti-Alzheimer’s dimer) on Aβ generation were investigated. Bis(7)-tacrine (0.1–3 μM) substantially reduced the amounts of both secreted and intracellular Aβ in Neuro2a APPswe cells without altering the expression of APP. sAPPα and CTFα increased, while sAPPβ and CTFβ decreased significantly in Neuro2a APPswe cells following the treatment with bis(7)-tacrine, indicating that bis(7)-tacrine might activate α-secretase and/or inhibit BACE-1 activity. Furthermore, bis(7)-tacrine concentration-dependently inhibited BACE-1 activity in cultured cells, and also in recombinant human BACE-1 in a non-competitive manner with an IC50 of 7.5 μM, but did not directly affect activities of BACE-2, Cathepsin D, α- or γ-secretase. Taken together, our results not only suggest that bis(7)-tacrine may reduce the biosynthesis of Aβ mainly by directly inhibiting BACE-1 activity, but also provide new insights into the rational design of novel anti-Alzheimer’s dimers that might have disease-modifying properties.
Biochemical and Biophysical Research Communications.
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Jialie Luo,
Wenming Li,
Yuwei Liu,
Wei Zhang,
Hongjun Fu,
Nelson T.K. Lee,
Hua Yu, Yuanping Pang,
Pingbo Huang,
Jun Xia,
Zhi-Wang Li,
Chaoying Li,
Yifan Han
[show abstract]
[hide abstract]
ABSTRACT: Bis(7)-tacrine has been shown to prevent glutamate-induced neuronal apoptosis by blocking NMDA receptors. However, the characteristics of the inhibition have not been fully elucidated. In this study, we further characterize the features of bis(7)-tacrine inhibition of NMDA-activated current in cultured rat hippocampal neurons. The results show that with the increase of extracellular pH, the inhibitory effect decreases dramatically. At pH 8.0, the concentration–response curve of bis(7)-tacrine is shifted rightwards with the IC50 value increased from 0.19 ± 0.03 μM to 0.41 ± 0.04 μM. In addition, bis(7)-tacrine shifts the proton inhibition curve rightwards. Furthermore, the inhibitory effect of bis(7)-tacrine is not altered by the presence of the NMDA receptor proton sensor shield spermidine. These results indicate that bis(7)-tacrine inhibits NMDA-activated current in a pH-dependent manner by sensitizing NMDA receptors to proton inhibition, rendering it potentially beneficial therapeutic effects under acidic conditions associated with stroke and ischemia.
Biochemical and Biophysical Research Communications.
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Chaoying Li,
Paul R. Carlier,
Hong Ren,
Kelvin K.W. Kan,
Kwokmin Hui,
Hong Wang,
Wenming Li,
Zhiwang Li,
Keming Xiong,
Ella Chow Clement,
Hong Xue,
Xiangou Liu,
Mingtao Li, Yuanping Pang,
Yifan Han
[show abstract]
[hide abstract]
ABSTRACT: Bis(7)-tacrine was previously demonstrated as an antagonist of γ-aminobutyric acid type A (GABAA) receptors. In this study, the effects of a series of alkylene-linked tacrine dimers on GABAA receptors were examined. In radioligand binding assay, the analogues differed in binding affinity for GABAA receptors, and potency monotonically increased as the tether was shortened from nine to two methylenes. Bis(2)-tacrine, the shortest tacrine dimer, could displace [3H]muscimol from rat brain membranes with an IC50 of 0.48 μM, which was 11, 13 and 525 times more potent than the GABAA receptor antagonist (+)-bicuculline, bis(7)-tacrine and tacrine, respectively. In whole-cell patch-clamp recordings, these dimeric tacrine analogues competitively antagonized GABA-induced inward current with a rank order of potency of bis(2)-tacrine > bicuculline > bis(7)-tacrine > bis(9)-tacrine > tacrine, and the potency of bis(2)-tacrine was 11, 18 and 487 times higher than that of (+)-bicuculline, bis(7)-tacrine and tacrine, respectively. Bis(2)-tacrine shifted the GABA concentration–response curve to the right in a parallel manner, and the inhibition was voltage-independent between −80 and +20 mV. It can be concluded that the shorter the alkylene linkage in tacrine dimers the stronger the binding affinity and higher the antagonistic effect on the GABAA receptor will be.
Neuropharmacology.
