Beta-amyloid peptide fragment 31-35 induces apoptosis in cultured cortical neurons

Putative Pore Structures of Amyloid β 25-35 in Lipid Bilayers

The amyloid β peptide aggregates to form extracellular plaques in the brains of Alzheimer's disease patients. Certain of its fragments have been found to have similar properties to those of the full-length peptide. The best-studied of these is 25-35, which aggregates into fibrils, is toxic to neurons, and forms ion channels in synthetic lipid bilayers. Here, we investigate possible pore-forming structures of oligomers of this peptide in a POPC/POPG membrane. We consider octameric and decameric β-barrels of different topology, strand orientation, and shear, evaluate their stability in an implicit membrane model, and subject the best models to multimicrosecond all-atom molecular dynamics simulations. We find two decameric structures that are kinetically stable in membranes on this time scale: an imperfectly closed antiparallel β-barrel with K28 in the pore lumen and a short parallel β-barrel with K28 toward the membrane interface. Both structures exhibit dehydrated gaps in the pore lumen, which are larger for the antiparallel barrel. Based on these results, the experimental cation selectivity, the dependence of ion channel activity on voltage direction, and certain mutation data, the parallel model seems more compatible with experimental data.

Advances in Alzheimer's Disease-Associated Aβ Therapy Based on Peptide

Alzheimer's disease (AD) urgently needs innovative treatments due to the increasing aging population and lack of effective drugs and therapies. The amyloid fibrosis of AD-associated β-amyloid (Aβ) that could induce a series of cascades, such as oxidative stress and inflammation, is a critical factor in the progression of AD. Recently, peptide-based therapies for AD are expected to be great potential strategies for the high specificity to the targets, low toxicity, fast blood clearance, rapid cell and tissue permeability, and superior biochemical characteristics. Specifically, various chiral amino acids or peptide-modified interfaces draw much attention as effective manners to inhibit Aβ fibrillation. On the other hand, peptide-based inhibitors could be obtained through affinity screening such as phage display or by rational design based on the core sequence of Aβ fibrosis or by computer aided drug design based on the structure of Aβ. These peptide-based therapies can inhibit Aβ fibrillation and reduce cytotoxicity induced by Aβ aggregation and some have been shown to relieve cognition in AD model mice and reduce Aβ plaques in mice brains. This review summarizes the design method and characteristics of peptide inhibitors and their effect on the amyloid fibrosis of Aβ. We further describe some analysis methods for evaluating the inhibitory effect and point out the challenges in these areas, and possible directions for the design of AD drugs based on peptides, which lay the foundation for the development of new effective drugs in the future.

Two statins and cromolyn as possible drugs against the cytotoxicity of Aβ(31-35) and Aβ(25-35) peptides: a comparative study by advanced computer simulation methods

In this work, possible effective mechanisms of cromolyn, atorvastatin and lovastatin on the cytotoxicity of Aβ(31-35) and Aβ(25-35) peptides were investigated by classical molecular dynamics and well-tempered metadynamics simulations. The results demonstrate that all the drugs affect the behavior of the peptides, such as their ability to aggregate, and alter their secondary structures and their affinity to a particular drug. Our findings from the computed properties suggest that the best drug candidate is lovastatin. This medicine inhibits peptide aggregation, adsorbs the peptides on the surface of the drug clusters, changes the secondary structure and binds to MET₃₅, which has been seen as the reason for the toxicity of the studied peptide sequences. Moreover, lovastatin is the drug which previously has demonstrated the strongest ability to penetrate the blood-brain barrier and makes lovastatin the most promising medicine among the three investigated drugs. Atorvastatin is also seen as a potential candidate if its penetration through the blood-brain barrier could be improved. Otherwise, its properties are even better than the ones demonstrated by lovastatin. Cromolyn appears to be less interesting as an anti-aggregant from the computational data, in comparison to the two statins.

Aβ31-35 Decreases Neprilysin-Mediated Alzheimer's Amyloid-β Peptide Degradation

Alzheimer's disease is associated with the deposition of extracellular senile plaques, made primarily of amyloid-β (Aβ), particularly peptides Aβ_1-42 and Aβ_1-40. Neprilysin, or neutral endopeptidase (NEP), catalyzes proteolysis of the amyloid peptides (Aβ) and is recognized as one of the major regulators of the levels of these peptides in the brain, preventing Aβ accumulation and plaque formation. Here, we used a combination of techniques to elucidate the mechanism of Aβ binding and cleavage by NEP. Our findings indicate that the Aβ_31-X cleavage products remain bound to the neprilysin active site, reducing proteolytic activity. Interestingly, it was already shown that this Aβ_31-35 sequence is also critical for recognition of Aβ peptides by other targets, such as the serpin-enzyme complex receptor in neuronal cells.

Component of Cannabis, Cannabidiol, as a Possible Drug against the Cytotoxicity of Aβ(31-35) and Aβ(25-35) Peptides: An Investigation by Molecular Dynamics and Well-Tempered Metadynamics Simulations

In this work cannabidiol (CBD) was investigated as a possible drug against the cytotoxicity of Aβ(31-35) and Aβ(25-35) peptides with the help of atomistic molecular dynamics (MD) and well-tempered metadynamics simulations. Four interrelated mechanisms of possible actions of CBD are proposed from our computations. This implies that one mechanism can be a cause or/and a consequence of another. CBD is able to decrease the aggregation of peptides at certain concentrations of compounds in water. This particular action is more prominent for Aβ(25-35), since originally Aβ(31-35) did not exhibit aggregation properties in aqueous solutions. Interactions of CBD with the peptides affect secondary structures of the latter ones. Clusters of CBD are seen as possible adsorbents of Aβ(31-35) and Aβ(25-35) since peptides are tending to aggregate around them. And last but not least, CBD exhibits binding to MET35. All four mechanisms of actions can possibly inhibit the Aβ-cytotoxicity as discussed in this paper. Moreover, the amount of water also played a role in peptide clustering: with a growing concentration of peptides in water without a drug, the aggregation of both Aβ(31-35) and Aβ(25-35) increased. The number of hydrogen bonds between peptides and water was significantly higher for simulations with Aβ(25-35) at the higher concentration of peptides, while for Aβ(31-35) that difference was rather insignificant. The presence of CBD did not substantially affect the number of hydrogen bonds in the simulated systems.

A Novel scFv Anti-Aβ Antibody Reduces Pathological Impairments in APP/PS1 Transgenic Mice via Modulation of Inflammatory Cytokines and Aβ-related Enzymes

Immunotherapy for Alzheimer's disease (AD) remains promising in the improvement of cognition and memory via the clearing of amyloid-β protein (Aβ) in the AD brain, despite some side effects. Our previous studies demonstrated that the 31-35 sequence of the Aβ molecule was the shortest active center and that polyclonal anti-Aβ31-35 antibody reduced neuronal apoptosis and cognitive impairments induced with acute Aβ application. The present study designed a novel single-chain variable fragment (scFv) monoclonal anti-Aβ31-35 antibody (scFv17) that specifically recognized extracellular Aβ and observed protective effects of scFv17 on pathological impairments in APP/PS1 transgenic mice. We also investigated its cellular and molecular mechanisms and found that scFv17 and 6E10 (a positive control) exhibited similar Aβ-clearing ability and that scFv17 produced a stronger effect in clearing Aβ oligomers than 6E10. scFv17, but not 6E10, enhanced anti-inflammatory responses with significant increases in IL-10 and TGF-β. 6E10 decreased BACE1 levels, and scFv17 significantly increased the level of secreted amyloid precursor protein-α (sAPPα), which is an important physiological neurotrophin from APP generated by α-secretase. 6E10 and scFv17, especially the latter, dramatically down-regulated the expression of neprilysin, which is an enzyme expressed in proportion to Aβ concentration. Therefore, the present study demonstrated that the novel monoclonal anti-Aβ31-35 antibody scFv17 effectively reduced pathological impairments in APP/PS1 transgenic mice via modulation of inflammatory cytokines and Aβ-related enzymes, which supports scFv17 as a new alternative in the current immunotherapy of AD.

A novel antibody targeting sequence 31-35 in amyloid β protein attenuates Alzheimer's disease-related neuronal damage

Amyloid β protein (Aβ) plays a critical role in pathogenesis of Alzheimer's disease (AD). Our previous studies indicated that the sequence 31-35 in Aβ molecule is an effective active center responsible for Aβ neurotoxicity in vivo and in vitro. In the present study, we prepared a novel antibody specifically targeting the sequence 31-35 of amyloid β protein, and investigated the neuroprotection of the anti-Aβ_31-35 antibody against Aβ_1-42 -induced impairments in neuronal viability, spatial memory, and hippocampal synaptic plasticity in rats. The results showed that the anti-Aβ_31-35 antibody almost equally bound to both Aβ_31-35 and Aβ_1-42 , and pretreatment with the antibody dose-dependently prevented Aβ_1-42 -induced cytotoxicity on cultured primary cortical neurons. In behavioral study, intracerebroventricular (i.c.v.) injection of anti-Aβ_31-35 antibody efficiently attenuated Aβ_1-42 -induced impairments in spatial learning and memory of rats. In vivo electrophysiological experiments further indicated that Aβ_1-42 -induced suppression of hippocampal synaptic plasticity was effectively reversed by the antibody. These results demonstrated that the sequence 31-35 of Aβ may be a new therapeutic target, and the anti-Aβ_31-35 antibody could be a novel immunotheraputic approach for the treatment of AD. © 2016 Wiley Periodicals, Inc.

Lixisenatide attenuates the detrimental effects of amyloid β protein on spatial working memory and hippocampal neurons in rats

Type 2 diabetes mellitus(T2DM) is a risk factor of Alzheimer's disease (AD), which is most likely linked to impairments of insulin signaling in the brain. Hence, drugs enhancing insulin signaling may have therapeutic potential for AD. Lixisenatide, a novel long-lasting glucagon-like peptide 1 (GLP-1) analogue, facilitates insulin signaling and has neuroprotective properties. We previously reported the protective effects of lixisenatide on memory formation and synaptic plasticity. Here, we describe additional key neuroprotective properties of lixisenatide and its possible molecular and cellular mechanisms against AD-related impairments in rats. The results show that lixisenatide effectively alleviated amyloid β protein (Aβ) 25-35-induced working memory impairment, reversed Aβ25-35-triggered cytotoxicity on hippocampal cell cultures, and prevented against Aβ25-35-induced suppression of the Akt-MEK1/2 signaling pathway. Lixisenatide also reduced the Aβ25-35 acute application induced intracellular calcium overload, which was abolished by U0126, a specific MEK1/2 inhibitor. These results further confirmed the neuroprotective and cytoprotective action of lixisenatide against Aβ-induced impairments, suggesting that the protective effects of lixisenatide may involve the activation of the Akt-MEK1/2 signaling pathway and the regulation of intracellular calcium homeostasis.

Inhibition of beta-amyloid-induced neurotoxicity by pinocembrin through Nrf2/HO-1 pathway in SH-SY5Y cells

Amyloid beta peptide (Aβ) can cause neurotoxicity in Alzheimer's disease (AD). It evokes a cascade of oxidative damage to neurons. Pinocembrin (PCB), the most abundant flavonoid in propolis, has been proven to have neuroprotective effects in vivo and in vitro. In the present study, we investigated the neuroprotective effects of PCB on Aβ25-35-induced neurotoxicity. Exposure of SH-SY5Y cells to 25μM Aβ25-35 for 24h caused viability loss, apoptotic increase and reactive oxygen species (ROS) increase, pre-treatment with PCB for 4h significantly reduced the viability loss, apoptotic rate and attenuated Aβ-mediated ROS production. PCB strikingly inhibited Aβ25-35-induced mitochondrial dysfunctions, including lowered membrane potential, decreased Bcl-2/Bax ratio. In addition, PCB suppressed the release of cytochrome c and the cleavage of caspase-3. PCB treatment also resulted in an increase in Nrf2 protein levels and subsequent induction of heme oxygenase-1(HO-1) expression in SH-SY5Y cells. RNA interference-mediated knockdown of Nrf2 expression suppressed the PCB-induced HO-1 expression. Notably, we found that the HO-1 inhibitor zinc protoporphyrin IX (ZnPP) markedly diminished the neuroprotective effect of PCB against Aβ-mediated neurotoxicity. Taken together, these results indicated that PCB protects SH-SY5Y cells from Aβ25-35-induced neurotoxicity through activation of Nrf2/HO-1 pathways. Thus, activation of Nrf2/HO-1 pathways and inhibition of mitochondria-dependent apoptosis together may protect cells from Aβ25-35-induceded neurotoxicity.

[Gly14]-Humanin Protects Against Amyloid β Peptide-Induced Impairment of Spatial Learning and Memory in Rats

Alzheimer disease (AD), a progressive neurodegenerative disorder, is characterized by cognitive decline and the accumulation of senile plaques in the brain. Amyloid β protein (Aβ) in the plaques is thought to be responsible for the memory loss in AD patients. [Gly14]-humanin (HNG), a derivative of humanin (HN), has much stronger neuroprotective effects than natural HN in vitro. However, clarification of the Aβ active center and the neuroprotective mechanism of HN still need in vivo evidence. The present study first compared the in vivo biological effects of three Aβ fragments (1-42, 31-35, and 35-31) on spatial memory in rats, and investigated the neuroprotective effects and molecular mechanisms of HNG. The results showed that intrahippocampal injection of Aβ1-42 and Aβ31-35 almost equally impaired spatial learning and memory, but the reversed sequence Aβ35-31 did not have any effect; a high dose of Aβ31-35 (20 nmol) produced a more detrimental response than a low dose (2 nmol); Aβ31-35 injection also disrupted gene and protein expression in the hippocampus, with up-regulation of caspase3 and down-regulation of STAT3; pretreatment with HNG not only protected spatial memory but also rescued STAT3 from Aβ-induced disruption; and the neuroprotective effects of HNG were effectively counteracted by genistein, a specific tyrosine kinase inhibitor. These results clearly show that sequence 31-35 in Aβ is the shortest active center responsible for the neurotoxicity of Aβ from molecule to behavior; and HNG protects spatial learning and memory in rats against Aβ-induced insults; and probably involves the activation of tyrosine kinases and subsequent beneficial modulation of STAT3 and caspase3.

Effects of amyloid β-peptide fragment 31-35 on the BK channel-mediated K⁺ current and intracellular free Ca²⁺ concentration of hippocampal CA1 neurons

The present study characterizes the effects of Aβ31-35, a short active fragment of amyloid β-peptide (Aβ), upon the BK channel-mediated K⁺ current and intracellular free Ca²⁺ concentration ([Ca²⁺]i) of freshly dissociated pyramidal cells from rat CA1 hippocampus by using whole-cell patch-clamp recording and single cell Ca²⁺ imaging techniques. The results show that: (1) in the presence of voltage- and ATP-gated K⁺ channel blockers application of 5.0 μM Aβ31-35 significantly diminished transient outward K⁺ current amplitudes at clamped voltages between 0 and 45mV; (2) under the same conditions [Ca²⁺]i was minimally affected by 5.0 μM but significantly increased by 12.5 μM and 25 μM Aβ31-35; and (3) when 25 μM of a larger fragment of the amyloid β-peptide, Aβ25-35, was applied, the results were similar to those obtained with the same concentration of Aβ31-35. These results indicate that Aβ31-35 is likely to be the shortest active fragment of the full Aβ sequence, and can be as effectively as the full-length Aβ peptide in suppressing BK-channel mediated K⁺ currents and significantly elevating [Ca²⁺]i in hippocampal CA1 neurons.

Lixisenatide rescues spatial memory and synaptic plasticity from amyloid β protein-induced impairments in rats

Alzheimer's disease (AD) is a progressive and degenerative disorder accompanied by cognitive impairment, but effective strategies against AD are currently not available. Interestingly, glucagon-like peptide-1 (GLP-1) used in type 2 diabetes mellitus (T2DM) has shown neuroprotective effects in preclinical studies of AD. Lixisenatide, an effective GLP-1 receptor (GLP-1R) agonist with much longer half life than GLP-1, has been licensed in the EU as a treatment for T2DM. However, the neuroprotective effects of lixisenatide in the brain remain to be clarified. In the present study, we report for the first time the effects of lixisenatide on the amyloid β (Aβ) protein-induced impairments in spatial learning and memory of rats, and investigated its electrophysiological and molecular mechanisms. We found that: (1) bilateral intrahippocampal injection of Aβ25-35 resulted in a significant decline in spatial learning and memory of rats, as well as a suppression of in vivo hippocampal long-term potentiation (LTP); (2) lixisenatide treatment effectively prevented the Aβ25-35-induced impairments; (3) lixisenatide inhibited the Aβ25-35 injection-induced activation of glycogen synthase kinase 3β (GSK3β), with a significant increase in the phosphorylation of ser9 and a significant decrease in the phosphorylation of Y216. These results indicate that lixisenatide, by affecting the PI3K-Akt-GSK3β pathway, can prevent Aβ-related impairments in synaptic plasticity and spatial memory of rats, suggesting that lixisenatide may be a novel and effective treatment for AD.

The neuroprotection of Rattin against amyloid β peptide in spatial memory and synaptic plasticity of rats

Rattin, a specific derivative of humanin in rats, shares the ability with HN to protect neurons against amyloid β (Aβ) peptide-induced cellular toxicity. However, it is still unclear whether Rattin can protect against Aβ-induced deficits in cognition and synaptic plasticity in rats. In the present study, we observed the effects of Rattin and Aβ31-35 on the spatial reference memory and in vivo hippocampal Long-term potentiation of rats by using Morris water maze test and hippocampal field potential recording. Furthermore, the probable molecular mechanism underlying the neuroprotective roles of Rattin was investigated. We showed that intra-hippocampal injection of Rattin effectively prevented the Aβ31-35-induced spatial memory deficits and hippocampal LTP suppression in rats; the Aβ31-35-induced activation of Caspase-3 and inhibition of STAT3 in the hippocampus were also prevented by Rattin treatment. These findings indicate that Rattin treatment can protect spatial memory and synaptic plasticity of rats against Aβ31-35-induced impairments, and the underlying protective mechanism of Rattin may be involved in STAT3 and Caspases-3 pathways. Therefore, application of Rattin or activation of its signaling pathways in the brain might be beneficial to the prevention of Aβ-related cognitive deficits.

Melatonin protects against amyloid-β-induced impairments of hippocampal LTP and spatial learning in rats

Alzheimer's disease (AD), the most prevalent neurodegenerative disease in the elderly, leads to progressive loss of memory and cognitive deficits. Amyloid-β protein (Aβ) in the brain is thought to be the main cause of memory loss in AD. Melatonin, an indole hormone secreted by the pineal gland, has been reported to produce neuroprotective effects. We examined whether melatonin could protect Aβ-induced impairments of hippocampal synaptic plasticity, neuronal cooperative activity, and learning and memory. Rats received bilateral intrahippocampal injection of Aβ1-42 or Aβ31-35 followed by intraperitoneal application of melatonin for 10 days, and the effects of chronic melatonin treatment on in vivo hippocampal long-term potentiation (LTP) and theta rhythm and Morris water maze performance were examined. We showed that intrahippocampal injection of Aβ1-42 or Aβ31-35 impaired hippocampal LTP in vivo, while chronic melatonin treatment reversed Aβ1-42- or Aβ31-35-induced impairments in LTP induction. Intrahippocampal injection of Aβ31-35 impaired spatial learning and decreased the power of theta rhythm in the CA1 region induced by tail pinch, and these synaptic, circuit, and learning deficits were rescued by chronic melatonin treatment. These results provide evidence for the neuroprotective action of melatonin against Aβ insults and suggest a strategy for alleviating cognition deficits of AD.

Amyloid β-protein suppressed nicotinic acetylcholine receptor-mediated currents in acutely isolated rat hippocampal CA1 pyramidal neurons

Amyloid β protein (Aβ) is responsible for the deficits of learning and memory in Alzheimer's disease (AD). The high affinity between Aβ and nicotinic acetylcholine receptors (nAChRs) suggests that the impairment of cognitive function in AD might be involved in the Aβ-induced damage of nAChRs. This study investigated the effects of Aβ fragments on nAChR-mediated membrane currents in acutely isolated rat hippocampal pyramidal neurons by using whole-cell patch clamp technique. The results showed that: (1) nonspecific nAChR agonist nicotine, selective α7 nAChR agonist choline, and α4β2 nAChR agonist epibatidine all effectively evoked inward currents in CA1 neurons at normal resting membrane potential, with different desensitization characteristics; (2) acute application of different concentrations (pM-μM) of Aβ25-35, Aβ31-35, or Aβ35-31 alone did not trigger any membrane current, but pretreatment with 1 μM Aβ25-35 and Aβ31-35 similarly and reversibly suppressed the nicotine-induced currents; (3) further, choline- and epibatidine-induced currents were also reversibly suppressed by the Aβ pretreatment, but more prominent for the choline-induced response. These results demonstrate that the functional activity of both α7 and α4β2 nAChRs in the membrane of acutely isolated hippocampal neurons was significantly downregulated by Aβ treatment, suggesting that nAChRs, especially α7 nAChRs, in the brain may be the important biological targets of neurotoxic Aβ in AD. In addition, the similar suppression of nAChR currents by Aβ25-35 and Aβ31-35 suggests that the sequence 31-35 in Aβ molecule may be a shorter active center responsible for the neurotoxicity of Aβ in AD.

Liraglutide protects against amyloid-β protein-induced impairment of spatial learning and memory in rats

Type 2 diabetes mellitus is a risk factor of Alzheimer's disease (AD), most likely linked to an impairment of insulin signaling in the brain. Liraglutide, a novel long-lasting glucagon-like peptide 1 (GLP-1) analog, facilitates insulin signaling and shows neuroprotective properties. In the present study, we analyzed the effects of liraglutide on the impairment of learning and memory formation induced by amyloid-β protein (Aβ), and the probable underlying electrophysiological and molecular mechanisms. We found that (1) bilateral intrahippocampal injection of Aβ(25-35) resulted in a significant decline of spatial learning and memory of rats in water maze tests, together with a serious depression of in vivo hippocampal late-phase long-term potentiation (L-LTP) in CA1 region of rats; (2) pretreatment with liraglutide effectively and dose-dependently protected against the Aβ(25-35)-induced impairment of spatial memory and deficit of L-LTP; (3) liraglutide injection also activated cAMP signal pathway in the brain, with a nearly doubled increase in the cAMP contents compared with control. These results strongly suggest that upregulation of GLP-1 signaling in the brain, such as application of liraglutide, may be a novel and promising strategy to ameliorate the learning and memory impairment seen in AD.

Peptides for therapy and diagnosis of Alzheimer's disease

Alzheimer's disease (AD) is a progressive neurodegenerative disorder with devastating effects. The greatest risk factor to develop AD is age. Today, only symptomatic therapies are available. Additionally, AD can be diagnosed with certainty only post mortem, whereas the diagnosis "probable AD" can be established earliest when severe clinical symptoms appear. Specific neuropathological changes like neurofibrillary tangles and amyloid plaques define AD. Amyloid plaques are mainly composed of the amyloid-βpeptide (Aβ). Several lines of evidence suggest that the progressive concentration and subsequent aggregation and accumulation of Aβ play a fundamental role in the disease progress. Therefore, substances which bind to Aβ and influence aggregation thereof are of great interest. An enormous number of organic substances for therapeutic purposes are described. This review focuses on peptides developed for diagnosis and therapy of AD and discusses the pre- and disadvantages of peptide drugs.

Time-course and regional analyses of the physiopathological changes induced after cerebral injection of an amyloid β fragment in rats

Alzheimer's disease (AD) is a neurodegenerative pathology characterized by the presence of senile plaques and neurofibrillary tangles, accompanied by synaptic and neuronal loss. The major component of senile plaques is an amyloid β protein (Aβ) formed by pathological processing of the Aβ precursor protein. We assessed the time-course and regional effects of a single intracerebroventricular injection of aggregated Aβ fragment 25-35 (Aβ(25-35)) in rats. Using a combined biochemical, behavioral, and morphological approach, we analyzed the peptide effects after 1, 2, and 3 weeks in the hippocampus, cortex, amygdala, and hypothalamus. The scrambled Aβ(25-35) peptide was used as negative control. The aggregated forms of Aβ peptides were first characterized using electron microscopy, infrared spectroscopy, and Congo Red staining. Intracerebroventricular injection of Aβ(25-35) decreased body weight, induced short- and long-term memory impairments, increased endocrine stress, cerebral oxidative and cellular stress, neuroinflammation, and neuroprotective reactions, and modified endogenous amyloid processing, with specific time-course and regional responses. Moreover, Aβ(25-35), the presence of which was shown in the different brain structures and over 3 weeks, provoked a rapid glial activation, acetylcholine homeostasis perturbation, and hippocampal morphological alterations. In conclusion, the acute intracerebroventricular Aβ(25-35) injection induced substantial central modifications in rats, highly reminiscent of the human physiopathology, that could contribute to physiological and cognitive deficits observed in AD.

Abeta(31-35)-induced neuronal apoptosis is mediated by JNK-dependent extrinsic apoptosis pathway

OBJECTIVE

To investigate whether JNK-caspase-dependent apoptotic pathway is involved in Abeta(31-35)-induced apoptosis of cultured cortical neurons.

METHODS

Cultured cortical neurons were treated with Abeta(31-35) (25 micromol/L) for 4 h, 8 h, 16 h and 24 h, respectively. Caspase activities were measured using a spectrophotometer. Levels of c-Jun phosphorylation (p-c-Jun) and Fas ligand (FasL) expression were assessed by immunocytochemistry method and quantified using Image-pro plus11.0 image processing and analysis software.

RESULTS

Treatment with Abeta(31-35) (25 micromol/L) for 24 h induced significant increases in the activities of caspase-3 and caspase-8 in the cortical neurons. Besides, Abeta(31-35) could time-dependently enhance the expression of p-c-Jun protein. Moreover, SP600125 application (100 nmol/L) could completely abolish Abeta(31-35) neurotoxicity. The increase in FasL expression was detected at 8 h, 16 h and 24 h after Abeta(31-35) treatment, and SP600125 (100 nmol/L) significantly inhibited FasL expression.

CONCLUSION

JNK-c-Jun-FasL-caspase-dependent extrinsic apoptotic pathway plays a critical role in mediating Abeta(31-35)-induced apoptosis of cultured neurons.

[Gly(14)]-humanin rescues long-term potentiation from amyloid beta protein-induced impairment in the rat hippocampal CA1 region in vivo

The novel neuroprotective action of Humanin (HN), especially its derivative [Gly(14)]-humanin (HNG), against Alzheimer's disease (AD)-related insults has been reported. However, it is still short of electrophysiological evidence for the protection of HN on synaptic plasticity, and the molecular mechanisms that underlie the neuroprotective function of HN remain largely unknown. The present study examined the effects of intracerebroventricular (i.c.v.) injection of HNG on amyloid beta (Abeta), a main constituent of senile plaques in the AD brain, induced suppression of long-term potentiation (LTP) in the rat hippocampal CA1 region in vivo and investigated the possible mechanism of HNG in LTP protection. We found that application of Abeta fragments 25-35 (Abeta25-35) and 31-35 (Abeta31-35) significantly inhibited high frequency stimulation-induced LTP, while HNG effectively prevented the suppression of LTP induced by Abeta fragments in a dose-dependent manner. After pretreatment with Genistein, a tyrosine kinase inhibitor, the protective action of HNG on LTP was nearly completely abolished. Therefore, the present study demonstrated for the first time that HNG could protect against the neurotoxic Abeta-induced hippocampal LTP impairment and the tyrosine kinase pathway was involved in the neuroprotective action of HNG, suggesting that HNG might be one of the promising candidates for the treatment of AD in the future.

Protective effect of pyrroloquinoline quinone against Abeta-induced neurotoxicity in human neuroblastoma SH-SY5Y cells

The neurotoxicity of aggregated beta-amyloid (Abeta) has been implicated as a critical cause in the pathogenesis of Alzheimer's disease (AD). It can cause neurotoxicity in AD by evoking a cascade of oxidative damage-dependent apoptosis to neurons. In the present study, we for the first time investigated the protective effect of pyrroloquinoline quinone (PQQ), an anionic, water soluble compound that acts as a redox cofactor of bacterial dehydrogenases, on Abeta-induced SH-SY5Y cytotoxicity. Abeta(25-35) significantly reduced cell viability, increased the number of apoptotic-like cells, and increased ROS production. All of these phenotypes induced by Abeta(25-35) were markedly reversed by PQQ. PQQ pretreatment recovered cells from Abeta(25-35)-induced cell death, prevented Abeta(25-35)-induced apoptosis, and decreased ROS production. PQQ strikingly decreased Bax/Bcl-2 ratio, and suppressed the cleavage of caspase-3. These results indicated that PQQ could protect SH-SY5Y cells against beta-amyloid induced neurotoxicity.

Activation of group III metabotropic glutamate receptor reduces intracellular calcium in beta-amyloid peptide [31-35]-treated cortical neurons

It is unknown whether amyloid beta-protein 31-35 (Abeta[31-35]) has effects similar to Abeta[1-40] and Abeta[25-35] on the intracellular calcium ([Ca(2+)]i) to induce a disruption of calcium homeostasis. In this study, we investigated the effects of Abeta[31-35] on [Ca(2+)]i in primary cultured cortical neurons using real time fluorescence imaging technique and the Ca(2+)-sensitive dye Furo-2/AM. It was found that Abeta[31-35] (25 microM) could induce a significant elevation in [Ca(2+)]i and a decrease in the average latency in the cortical neurons in a dose-dependent manner. To examine whether the activation of group III mGluRs could block the changes in [Ca(2+)]i and protect neurons from apoptosis induced by Abeta[31-35], we then investigated the effects of L: -serine-O-phosphate (L: -SOP) and (R,S)-4-phosphonophenylglycine ((R,S)-PPG), the selective agonists of group III metabotropic glutamate receptors (mGluRs), on [Ca(2+)]i and apoptosis in neurons treated by Abeta[31-35]. We demonstrated that L: -SOP or (R,S)-PPG (100 microM) treatment suppresses significantly the elevation of [Ca(2+)]i induced by Abeta[31-35] and also induces an almost complete recovery of both the fluorescence intensity and apoptotic cells (%) to the control level in the neurons. These results suggest that Abeta[31-35] may be the shortest sequence responsible for the neuronal toxicity of Abeta protein and that the neuroprotective role of the activation of group III mGluRs from the apoptosis induced by Abeta[31-35] might be partly due to its ability to inhibit the increased calcium influx, which results from Abeta[31-35].

Amyloid beta-protein fragments 25-35 and 31-35 potentiate long-term depression in hippocampal CA1 region of rats in vivo

Amyloid beta-protein (Abeta) is thought to be responsible for the deficit of learning and memory in Alzheimer's disease (AD), possibly through interfering with synaptic plasticity in the brain. It has been reported that Abeta fragments suppress the long-term potentiation (LTP) of synaptic transmission. However, it is unclear whether Abeta fragments can regulate long-term depression (LTD), an equally important form of synaptic plasticity in the brain. The present study investigates the effects of Abeta fragments on LTD induced by low frequency stimulation (LFS) in the hippocampus in vivo. Our results showed that (1) prolonged 1-10 Hz of LFS all effectively elicited LTD, which could persist for at least 2 h and be reversed by high frequency stimulation (HFS); (2) the effectiveness of LTD induction depended mainly on the number of pulses but not the frequency of LFS; (3) pretreatment with Abeta fragment 25-35 (Abeta(25-35), 12.5 and 25 nmol) did not change baseline field excitatory postsynaptic potentials but dose-dependently potentiated LTD; (4) Abeta fragment 31-35 (Abeta(31-35)), a shorter Abeta fragment than Abeta(25-35), also dose-dependently strengthened LFS-induced hippocampal LTD. Thus, the present study demonstrates the enhancement of hippocampal LTD by Abeta in in vivo condition. We propose that Abeta-induced potentiation of LTD, together with the suppression of LTP, will result in the impairment of cognitive function of the brain.

Arginine vasopressin prevents amyloid beta protein-induced impairment of long-term potentiation in rat hippocampus in vivo

Amyloid beta protein (Abeta) is thought to be responsible for the loss of memory in Alzheimer's disease (AD). A significant decrease in [Arg(8)]-vasopressin (AVP) in the AD brain has been found. However, it is unclear whether the decrease in AVP is involved in Abeta-induced impairment of memory and whether AVP can protect against Abeta-induced neurotoxicity. The present study examines the effects of intracerebroventricular (i.c.v.) injection of AVP on hippocampal long-term potentiation (LTP), a synaptic model of memory, and investigates the potential protective function of AVP in Abeta-induced LTP impairment. The results showed that (1) i.c.v. injection of different concentrations of AVP or Abeta(25-35) did not affect the baseline field excitatory postsynaptic potentials (fEPSPs); (2) AVP administration alone induced a significant increase in HFS-induced LTP, while Abeta(25-35) significantly suppressed HFS-induced LTP; (3) Abeta(25-35)-induced LTP suppression was significantly prevented by the pretreatment with AVP; (4) paired-pulse facilitation did not change after separate application or co-application of AVP and Abeta(25-35). These results indicate that AVP can potentiate hippocampal synaptic plasticity and dose-dependently prevent Abeta(25-35)-induced LTP impairment. Thus, the present study provides further insight into the mechanisms by which Abeta impairs synaptic plasticity and suggests an important approach in the treatment of AD.

Alpha4beta2 nicotinic acetylcholine receptors are required for the amyloid beta protein-induced suppression of long-term potentiation in rat hippocampal CA1 region in vivo

Amyloid beta protein (Abeta) is thought to be responsible for the deficit of learning and memory in Alzheimer's disease (AD), possibly through interfering with synaptic plasticity such as hippocampal long-term potentiation (LTP). Nicotinic acetylcholine receptors (nAChRs) participate in various cognitive brain functions. However, it is unclear whether nAChRs, especially alpha4beta2 subtype nAChRs, are involved in Abeta-induced impairment of hippocampal LTP. The present study investigates a possible role of nAChRs during the impairment of LTP by Abeta. Our results showed that: (1) intracerebroventricular injection of Abeta(1-40), Abeta(25-35) or Abeta(31-35) significantly suppressed high-frequency stimulation-induced LTP, while Abeta(35-31), a reversed sequence of Abeta(31-35), have no effect on the LTP; (2) epibatidine, a specific agonist of alpha4beta2 subtype of nAChRs, dose-dependently suppressed the induction of LTP; (3) co-injection of epibatidine together with Abeta(31-35) did not further enhance the suppression of LTP induced by Abeta(31-35) or epibatidine alone; (4) dihydro-beta-erythroidine, a selective antagonist against alpha4beta2 subtype of nAChRs, showed no effect on the induction of LTP, but significantly reversed Abeta(31-35)-induced LTP impairment. These results indicate that: (1) sequence 31-35 in Abeta molecule might be a shorter active center responsible for the neurotoxicity of full length of Abeta; (2) alpha4beta2 subtype of nAChRs is required for the suppressive action of Abeta on the hippocampal LTP in vivo. Thus, the present study provides further insight into the mechanisms by which Abeta impairs synaptic plasticity and cognitive function in the AD brain.

Amyloid beta-peptide 31-35-induced neuronal apoptosis is mediated by caspase-dependent pathways via cAMP-dependent protein kinase A activation

This study aims to investigate the roles of the protein kinase A (PKA)- and caspase-dependent pathways in amyloid beta-peptide 31-35 (Abeta[31-35])-induced apoptosis, and the mechanisms of neuroprotection by group III metabotropic glutamate receptor (mGluR) activation against apoptosis induced by Abeta[31-35] in cortical neurons. We demonstrated that Abeta[31-35] induces neuronal apoptosis as well as a significant increase in caspase-3, -8 and -9. Activation of group III mGluRs by l-serine-O-phosphate and (R,S)-4-phosphonophenylglycine (two group III mGluR agonists), which attenuate the effects of Abeta[31-35], provides neuroprotection to the cortical neurons subjected to Abeta[31-35]. We also showed that Rp-cAMP, an inhibitor of cAMP-dependent PKA, has the ability to protect neurons from Abeta[31-35]-induced apoptosis and to reverse almost completely the effects of Abeta[31-35] on the activities of caspase-3. Further, we found that Sp-cAMP, an activator of cAMP-dependent PKA, can significantly abolish the l-serine-O-phosphate- and (R,S)-4-phosphonophenylglycine-induced neuroprotection against apoptosis, and decrease caspase-3, -8 and -9 in the Abeta[31-35]-treated neurons. Our findings suggest that neuronal apoptosis induced by Abeta[31-35] is mediated by the PKA-dependent pathway as well as the caspase-dependent intrinsic and extrinsic apoptotic pathways. Activation of group III mGluRs protects neurons from Abeta[31-35]-induced apoptosis by blocking the caspase-dependent pathways. Inhibition of the PKA-dependent pathway might also protect neurons from Abeta[31-35]-induced apoptosis by blocking the caspase-dependent pathways. Taken together, our observations suggest that Abeta[31-35] might have the ability to activate PKA, which in turn activates the caspase-dependent intrinsic and extrinsic apoptotic pathways, inducing apoptosis in the cortical neurons.

3,4-Dihydroxybenzoic acid from Smilacis chinae rhizome protects amyloid β protein (25–35)-induced neurotoxicity in cultured rat cortical neurons

The neuroprotective effect of 3,4-dihydroxybenzoic acid (3,4-DHBA) isolated from Smilacis chinae rhizome against Abeta (25-35)-induced neurotoxicity on cultured rat cortical neurons was found in this study. The protective effect of 3,4-DHBA against Abeta (25-35)-induced neuronal cell death was investigated by measuring cell viability via a 3-[4,5-dimethylthiazol-2-yl]-2,5-diphenyl-tetrazolium bromide (MTT) assay and Hoechst 33342 staining. 3,4-DHBA (1 and 10 microM) concentration-dependently inhibited 10 microM Abeta (25-35)-induced neuronal apoptotic death. 3,4-DHBA (1 and 10 microM) inhibited 10 microM Abeta (25-35)-induced elevation of cytosolic Ca(2+) concentration ([Ca(2+)](c)), which was measured by a fluorescent dye, Fluo-4 AM. 3,4-DHBA also inhibited glutamate release into medium, reactive oxygen species (ROS) generation, and caspase-3 activation, which were induced by 10 microM Abeta (25-35). These results suggest that 3,4-DHBA prevents Abeta (25-35)-induced neuronal cell damage by interfering with the increase of [Ca(2+)](c), and then by inhibiting glutamate release, generation of ROS and caspase-3 activity.

Neuroprotective effect of oxyresveratrol from smilacis chinae rhizome on amyloid Beta protein (25-35)-induced neurotoxicity in cultured rat cortical neurons

We previously reported that Smilacis chinae rhizome inhibits amyloid beta protein (25-35) (Abeta (25-35))-induced neurotoxicity in cultured rat cortical neurons. The present study evaluated the neuroprotective effect of oxyresveratrol isolated from Smilacis chinae rhizome against Abeta (25-35)-induced neurotoxicity on cultured rat cortical neurons. Oxyresveratrol over the concentration range of 1-10 microM significantly inhibited 10 microM Abeta (25-35)-induced neuronal cell death, which was measured by a 3-[4,5-dimethylthiazol-2-yl]-2,5-diphenyl-tetrazolium bromide (MTT) assay and Hoechst 33342 staining. Oxyresveratrol (10 microM) inhibited 10 microM Abeta (25-35)-induced elevation of cytosolic calcium concentration ([Ca2+]c), which was measured by a fluorescent dye, Fluo-4 AM. Oxyresveratrol (1, 10 microM) also inhibited glutamate release into medium and reactive oxygen species (ROS) generation induced by 10 microM Abeta (25-35). These results suggest that oxyresveratrol prevents Abeta (25-35)-induced neuronal cell damage by interfering with the increase of [Ca2+]c, and then by inhibiting glutamate release and ROS generation. Furthermore, these effects of oxyresveratrol may be associated with the neuroprotective effect of Smilacis chinae rhizome.

Fragment 31–35 of β-amyloid peptide induces neurodegeneration in rat cerebellar granule cells via bax gene expression and caspase-3 activation

The amyloid beta-peptide (AbetaP) is the major protein component of brain senile plaques in Alzheimer's disease. The redox state of methionine-35 residue plays a critical role in peptide neurotoxic actions. We used the fragment 31-35 of AbetaP [AbetaP(31-35)], containing a single methionine-35 residue (Met-35), to investigate the relationship between the oxidative state of Met-35 and neurotoxic and pro-apoptotic actions induced by the peptide; in rat cerebellar granule cells (CGC), we compared the effects of AbetaP(31-35), in which the Met-35 is present in the reduced state, with those of a modified peptide with oxidized Met-35 [AbetaP(31-35)Met-35(OX)](,) as well as an AbetaP-derivative with Met-35 substituted by norleucine [AbetaP(31-35)Nle-35]. AbetaP(31-35) induced a time-dependent decrease in cell viability. AbetaP(31-35)Met-35(OX) was significantly less potent, but still induced a significant decrease in cell viability compared to control. No toxic effects were observed after treatment with AbetaP(31-35)Nle-35. AbetaP(31-35) induced a 2-fold increase in bax mRNA levels after 4h, whereas AbetaP(31-35)Met-35(OX) raised bax mRNA levels by 41% and AbetaP(31-35)Nle-35 had no effect. Finally, AbetaP(31-35) caused a 43% increase in caspase-3 activity after 24h; AbetaP(31-35)Met-35(OX) caused only a 18% increase, and AbetaP(31-35)Nle-35 had no effect. These findings suggest that AbetaP(31-35)-induced neurodegeneration in CGC is mediated by a selective early increase in bax mRNA levels followed by delayed caspase-3 activation; the redox state of the single Met-35 residue is crucial in the occurrence and extent of the above phenomena.

Catechin and epicatechin from Smilacis chinae rhizome protect cultured rat cortical neurons against amyloid beta protein (25-35)-induced neurotoxicity through inhibition of cytosolic calcium elevation

We previously reported that the Smilacis chinae rhizome inhibits amyloid beta protein (25-35) (Abeta (25-35))-induced neurotoxicity in cultured rat cortical neurons. Here, we isolated catechin and epicatechin from S. chinae rhizome and also studied their neuroprotective effects on Abeta (25-35)-induced neurotoxicity in cultured rat cortical neurons. Catechin and epicatechin inhibited 10 microM Abeta (25-35)-induced neuronal cell death at a concentration of 10 microM, which was measured by a 3-[4,5-dimethylthiazol-2-yl]-2,5-diphenyl-tetrazolium bromide (MTT) assay and Hoechst 33342 staining. Catechin and epicatechin inhibited 10 microM Abeta (25-35)-induced elevation of cytosolic calcium concentration ([Ca2+]c), which was measured by a fluorescent dye, Fluo-4 AM. Catechin and epicatechin also inhibited glutamate release into medium induced by 10 microM Abeta (25-35), which was measured by HPLC, generation of reactive oxygen species (ROS) and activation of caspase-3. These results suggest that catechin and epicatechin prevent Abeta (25-35)-induced neuronal cell damage by interfering with the increase of [Ca2+]c, and then by inhibiting glutamate release, generation of ROS and caspase-3 activity. Furthermore, these effects of catechin and epicatechin may be associated with the neuroprotective effect of the S. chinae rhizome.

Protection of amyloid beta protein (25-35)-induced neurotoxicity by methanol extract of Smilacis chinae rhizome in cultured rat cortical neurons

Smilax has various pharmacological effects including antiinflammatory, anticancer and antioxidant activity. The present study aims to investigate the effect of the methanol extract of Smilacis chinae rhizome (SCR) from Smilax china L. (Liliaceae) on amyloid beta protein (Abeta) (25-35), a synthetic 25-35 amyloid peptide, -induced neurotoxicity in cultured rat cerebral cortical neurons. Abeta (25-35) (10 microM) produced a reduction of cell viability, which was significantly reduced by (5R,10S)-(+)-5-methyl-10,11-dihydro-5H-dibenzo[a,d]cyclohepten-5,10-imine (MK-801), an N-methyl-D-aspartate (NMDA) receptor antagonist, verapamil, an L-type Ca2+ channel blocker, and NG-nitro-L-arginine methyl ester (L-NAME), a nitric oxide synthase inhibitor. SCR, over a concentration range of 10-50 microg/ml, inhibited 10 microM Abeta (25-35)-induced neuronal cell death, which was measured by a 3-[4,5-dimethylthiazol-2-yl]-2,5-diphenyl-tetrazolium bromide (MTT) assay and Hoechst 33342 staining. SCR (50 microg/ml) inhibited 10 microM Abeta (25-35)-induced elevation of cytosolic calcium concentration ([Ca2+]c), which was measured by a fluorescent dye, Fluo-4 AM. Pretreatment of SCR (10 and 50 microg/ml) also inhibited glutamate release into medium induced by 10 microM Abeta (25-35), which was measured by HPLC, generation of reactive oxygen species and activation of caspase-3. These results suggest that SCR prevents Abeta (25-35)-induced neuronal cell damage in vitro.

Alzheimer's amyloid beta-peptide (1-42) induces cell death in human neuroblastoma via bax/bcl-2 ratio increase: an intriguing role for methionine 35

The beta amyloid (Abeta), the major protein component of brain senile plaques in Alzheimer's disease, is known to be directly responsible for the production of free radicals toxic to brain tissue and the redox state of Met-35 residue seems to play a particular and critical role in peptide's neurotoxic actions. In this study, we investigated, in human neuroblastoma cells (IMR-32), the relationship between the oxidative state of methionine, and both neurotoxic and pro-apoptotic actions induced by Abeta-peptide, comparing the effects of native peptide, in which the Met-35 is present in the reduced state, with those of a modified peptide with oxidized Met-35 (Abeta(1-42)(35Met-ox)), as well as an Abeta-derivative with Met-35 substituted with norleucine (Abeta(1-42)(35Nle)). The obtained results show that Abeta induces a time-dependent decrease in cell viability; Abeta(1-42)(35Met-ox) was significantly less potent, though inducing a remarkable decrease in cell viability compared to control. On the contrary, no toxic effects were observed after treatment with Abeta(1-42)(35Nle). Abeta-peptide as well as the amyloid modified peptide with oxidized Met-35 induced the pro-apoptotic gene bax over-expression after 24 h, whereas Abeta(1-42)(35Nle) had no effect. Conversely, bcl-2, an anti-apoptotic gene, became highly down-regulated by Abeta peptide treatment, in contrast to that evidenced by the Abeta(1-42)(35Met-ox) peptide. Finally, Abeta caused an increase in caspase-3 activity to be higher with respect to that shown by Abeta(1-42)(35Met-ox) while Abeta(1-42)(35Nle) had no effect. These results support the hypothesis that Abeta-induced neurotoxicity occurs via bax over-expression, bcl-2 down-regulation, and caspase-3 activation, first indicating that methionine 35 redox state may alter this cell death pathway.

Amyloid β-protein fragment 31–35 suppresses long-term potentiation in hippocampal CA1 region of rats in vivo

Effects of fragment 31-35 of amyloid beta-protein (AbetaP31-35) on the baseline synaptic transmission, shown as fEPSPs, and the long-term potentiation (LTP) induced by high-frequency stimuli (HFS) were investigated in vivo in the hippocampal CA1 region of rats; a longer fragment of AbetaP, i.e., AbetaP25-35, which had been generally accepted as the active center in AbetaP, was also tested comparatively along with AbetaP31-35. The results showed that: (1) the baseline fEPSPs induced by test stimuli were not changed by i.c.v. injection of AbetaP31-35, while application of either AbetaP31-35 or AbetaP25-35 with the same molar concentration (50 nmol) significantly and similarly suppressed the HFS-induced LTP; (2) higher concentration of AbetaP31-35 or longer time of AbetaP exposure exhibited stronger suppression on LTP, indicating a dose- and time-dependent trends; (3) no significant effects could be found on the paired-pulse facilitation (PPF) following AbetaP31-35 injection; (4) pretreatment with verapamil (2.5 mg/kg, i.p., 1 h prior to HFS), a blocker of L-type Ca2+ channels, did not affect the baseline fEPSPs, while it exhibited a significant suppression on LTP induced by HFS; and (5) surprisingly enough, coapplication with verapamil and AbetaP31-35 exhibited a similar suppression on LTP just as both of these two agents were used alone. These results indicate that: (1) AbetaP31-35, similar to AbetaP25-35, possesses potent suppressive effects on hippocampal LTP in vivo, supporting our proposal that the fragment AbetaP31-35 might be to date the shortest active sequence in full-length of AbetaP molecule; (2) AbetaP31-35-induced LTP suppression is not mediated by affecting the presynaptic processes; and (3) L-type Ca2+ channels might be one of the main pathways by which AbetaP31-35 insults LTP.

Blockade of 5-HT3 receptor with MDL72222 and Y25130 reduces β-amyloid protein (25–35)-induced neurotoxicity in cultured rat cortical neurons

The present study was performed to examine neuroprotective effects of 5-hydroxytryptamine (5-HT)(3) receptor antagonists against beta-amyloid protein (25--35)-, a synthetic 25--35 amyloid peptide, induced neurotoxicity using cultured rat cortical neurons. beta-Amyloid protein (25--35) produced a concentration-dependent reduction of cell viability, which was significantly reduced by (5R,10S)-(+)-5-methyl-10,11-dihydro-5H-dibenzo[a,d] cyclohepten-5,10-imine (MK-801), an N-methyl-d-aspartate (NMDA) receptor antagonist, verapamil, an L-type Ca(2+) channel blocker, and N(G)-nitro-L-arginine methyl ester (L-NAME), a nitric oxide synthase inhibitor. The 5-HT(3) receptor antagonists, tropanyl-3,5-dichlorobenzoate (MDL-72222, 0.1--10 microM) and N-(1-azabicyclo[2.2.2.]oct-3-yl)-6-chloro-4-ethyl-3-oxo-3,4-dihydro-2H-1,4-benzoxazine-8-carboxamide hydrochloride (Y 25130, 0.05--5 microM), decreased the beta-amyloid protein (25--35) (10 microM)-induced neuronal cell death as assessed by a colorimetric 3-[4,5-dimethylthiazol-2-yl]-2,5-diphenyltetrazolium bromide (MTT) assay and the number of apoptotic nuclei, evidenced by Hoechst 33342 staining. MDL 72222 and Y 25130 inhibited the beta-amyloid protein (25--35) (10 microM)-induced elevation of cytosolic Ca(2+) concentration ([Ca(2+)](c)) and glutamate release, generation of reactive oxygen species, and caspase-3 activity. These neuroprotective effects of MDL 72222 (10 microM) and Y 25130 (5 microM) were completely blocked by the simultaneous treatment with 100 microM 1-phenylbiguanide, a 5-HT(3) receptor agonist, indicating that the protective effects of these compounds were due to 5-HT(3) receptor blockade. These results suggest that the activation of the 5-HT(3) receptor may be partially involved in beta-amyloid protein-induced neurotoxicity, by membrane depolarization for Ca(2+) influx. Therefore, the blockade of 5-HT(3) receptor with MDL 72222 and Y 25130, may ameliorate the beta-amyloid protein-induced neurotoxicity by interfering with the increase of [Ca(2+)](c), and then by inhibiting glutamate release, generation of reactive oxygen species and caspase-3 activity.

Chronic stimulation of GABAA receptor with muscimol reduces amyloid β protein (25–35)-induced neurotoxicity in cultured rat cortical cells

The present study was performed to examine how the stimulation of gamma-aminobutyric acid (GABA) receptor affects amyloid beta protein (25-35) (Abeta (25-35)), a synthetic 25-35 amyloid peptide, -induced neurotoxicity using cultured rat cortical neurons. Abeta (25-35) produced a concentration-dependent reduction of cell viability, which was significantly reduced by (5R,10S)-(+)-5-methyl-10,11-dihydro-5H-dibenzo[a,d] cyclohepten-5,10-imine (MK-801), an N-methyl-d-aspartate (NMDA) receptor antagonist, verapamil, an L-type Ca(2+) channel blocker, and N(G)-nitro-l-arginine methyl ester (l-NAME), a nitric oxide synthase inhibitor. Pretreatment with muscimol, a GABAA receptor agonist, over a concentration range of 0.1-10microM 24h before the treatment with 10microM Abeta (25-35) showed concentration-dependent inhibition on the Abeta (25-35)-induced neuronal apoptotic death. However, baclofen (1 and 10microM), a GABAB receptor agonist, failed to inhibit the Abeta (25-35)-induced neuronal death. In addition, pretreatment with muscimol (1microM) for 24h inhibited the Abeta (25-35) (10microM)-induced elevation of cytosolic Ca(2+) concentration ([Ca(2+)]c) and glutamate release, generation of reactive oxygen species (ROS), and caspase-3 activity in cultured neurons. These neuroprotective effects of muscimol (1microM) were completely blocked by the simultaneous treatment with 10microM bicuculline, a GABAA receptor antagonist, indicating that the protective effects of muscimol were due to GABAA receptor stimulation. When, however, treated just 15min before the treatment with Abeta (25-35), muscimol (1microM) did not show any protective effect against Abeta (25-35) (10microM)-induced neurotoxicity in cultured neurons. These results suggest that the chronic activation of GABAA receptor may ameliorate Abeta-induced neurotoxicity by interfering with the increase of [Ca(2+)]c, and then by inhibiting glutamate release, generation of ROS and caspase-3 activity.

Aβ(31-35) and Aβ(25-35) fragments of amyloid beta-protein induce cellular death through apoptotic signals: Role of the redox state of methionine-35

In order to clarify the basis of neuronal toxicity exerted by the shortest active peptides of amyloid beta-protein (Abeta), the toxic effects of Abeta(31-35) and Abeta(25-35) peptides on isolated rat brain mitochondria were investigated. The results show that exposure of isolated rat brain mitochondria to Abeta(31-35) and Abeta(25-35) peptides determines: (i) release of cytochrome c; (ii) mitochondrial swelling and (iii) a significant reduction in mitochondrial oxygen consumption. In contrast, the amplitude of these events resulted attenuated in isolated brain mitochondria exposed to the Abeta(31-35)Met35(OX) in which methionine-35 was oxidized to methionine sulfoxide. The Abeta peptide derivative with norleucine substituting Met-35, i.e., Abeta(31-35)Nle-35, had not effect on any of the biochemical parameters tested. We have further characterized the action of Abeta(31-35) and Abeta(25-35) peptides on neuronal cells. Taken together our result indicate that Abeta(31-35) and Abeta(25-35) peptides in non-aggregated form, i.e., predominantly monomeric, are strongly neurotoxic, having the ability to enter within the cells, determining mitochondrial damage with an evident trigger of apoptotic signals. Such a mechanism of toxicity seems to be dependent by the redox state of methionine-35.

Methionine 35 oxidation reduces toxic effects of the amyloid beta-protein fragment (31-35) on human red blood cell

Amyloid beta-peptide, the central constituent of senile plaques in Alzheimer's disease brain, has been shown to be a source of free radical oxidative stress that may lead to neurodegeneration. In particular, it is well known that oxidation of methionine 35, is strongly related to the pathogenesis of Alzheimer's disease, since it represents the residue in the beta-amyloid peptide most susceptible to oxidation "in vivo". In this study, the fragment 31-35 of the beta-amyloid peptide, which has a single methionine at residue 35, was used to investigate the influence of the oxidation state of methionine-35 on the beta-amyloid peptide (31-35) mediated cytotoxic effects. Because no extensive studies have yet addressed whether amyloid beta peptides-mediated toxic effects can occur in the absence of mitochondria, human red blood cells were used as cell model. Exposure of intact red blood cells to beta-amyloid peptide (31-35) induced a marked stimulation (approximately 45%) of the pentose phosphate pathway and a significant inhibition of the red cell enzyme catalase, compared with the results observed in control red blood cells. In contrast, exposure of red blood cells to the beta-amyloid peptide (31-35)-Met35OX i.e. in which the sulfur of methionine is oxidised to sulfoxide, induced a slight activation of PPP (approximately 19%), and an inhibition of catalase activity lower with respect to the results observed in beta-amyloid peptide (31-35)-treated red blood cells. Since the activities of red cell phosphofructokinase, glucose-6-phosphate dehydrogenase, glutathione peroxidase, glutathione reductase and the functionality of hemoglobin were not modified within the red cell following to beta-amyloid peptides exposure, it is likely that beta-amyloid (31-35)-catalase interaction may represent a selective toxic event. Together, these results support the hypothesis that Abeta peptide and the oxidative state of Met-35 may be involved in the mechanisms responsible of neurodegeneration in Alzheimer's disease.

Beta-amyloid-derived pentapeptide RIIGLa inhibits Abeta(1-42) aggregation and toxicity

Pr-IIGL(a), a derivative of the tetrapeptide beta-amyloid 31-34 (Abeta(31-34)), exerts controversial effects: it is toxic in a neuroblastoma culture, but it protects glial cells from the cytotoxic action of Abeta(1-42). For an understanding of this phenomenon, a new pentapeptide, RIIGL(a) was synthetized, and both compounds were studied by different physicochemical and biological methods. Transmission electron microscopic (TEM) studies revealed that Pr-IIGL(a) forms fibrillar aggregates, whereas RIIGL(a) does not form fibrils. Congo red binding studies furnished the same results. Aggregated Pr-IIGL(a) acts as a cytotoxic agent in neuroblastoma cultures, but RIIGL(a) does not display inherent toxicity. RIIGL(a) co-incubated with Abeta(1-42) inhibits the formation of mature amyloid fibres (TEM studies) and reduces the cytotoxic effect of fibrillar Abeta(1-42). These results indicate that RIIGL(a) is an effective inhibitor of both the aggregation and the toxic effects of Abeta(1-42) and can serve as a lead compound for the design of novel neuroprotective peptidomimetics.

Methionine 35 oxidation reduces toxic and pro-apoptotic effects of the amyloid beta-protein fragment (31-35) on isolated brain mitochondria

Amyloid beta-peptide (AbetaP), the central constituent of senile plaques in Alzheimer's disease (AD) brain, has been shown to be a source of free radical oxidative stress that may lead to neurodegeneration. In particular, it is well known that oxidation of methionine 35, is strongly related to the pathogenesis of AD, since it represents the residue in AbetaP most susceptible to oxidation in vivo. In the present study, we used the fragment 31-35 of AbetaP, which has a single methionine at residue 35, in order to investigate the influence of the oxidation state of methionine-35 on the toxic and pro-apoptotic effects induced by Abeta(31-35) on isolated brain mitochondria. The obtained results show that exposure of isolated mitochondria from rat brain to AbetaP(31-35) determines (i) a large release of cytochrome c (ii) a significant reduction in mitochondrial respiration and (iii) a slight drop in the mitochondrial membrane potential (deltapsi). In contrast, the amplitude of these events resulted attenuated or completely abrogated in isolated brain mitochondria exposed to the AbetaP(31-35)Met35OX, in which methionine 35 was oxidized to methionine sulfoxide. We have further characterized the action of AbetaP(31-35) and Abeta(31-35)Met35OX peptide on PC12 cells. Although these two peptides, compromised mitochondrial function at a different extent as assessed by MTT reduction, neither one of them decreased cell viability as measured by Trypan Blue exclusion assay. The results obtained in this study support the hypothesis that the oxidative state of Met-35 may play a critical role in the mechanisms responsible of neurotoxicity exerted by this peptide.

Glutamate and amyloid beta-protein rapidly inhibit fast axonal transport in cultured rat hippocampal neurons by different mechanisms

Impairment of axonal transport leads to neurodegeneration and synapse loss. Glutamate and amyloid beta-protein (Abeta) have critical roles in the pathogenesis of Alzheimer's disease (AD). Here we show that both agents rapidly inhibit fast axonal transport in cultured rat hippocampal neurons. The effect of glutamate (100 microm), but not of Abeta25-35 (20 microm), was reversible, was mimicked by NMDA or AMPA, and was blocked by NMDA and AMPA antagonists and by removal of extracellular Ca2+. The effect of Abeta25-35 was progressive and irreversible, was prevented by the actin-depolymerizing agent latrunculin B, and was mimicked by the actin-polymerizing agent jasplakinolide. Abeta25-35 induced intracellular actin aggregation, which was prevented by latrunculin B. Abeta31-35 but not Abeta15-20 exerted effects similar to those of Abeta25-35. Full-length Abeta1-42 incubated for 7 d, which specifically contained 30-100 kDa molecular weight assemblies, also caused an inhibition of axonal transport associated with intracellular actin aggregation, whereas freshly dissolved Abeta1-40, incubated Abeta1-40, and fresh Abeta1-42 had no effect. These results suggest that glutamate inhibits axonal transport via activation of NMDA and AMPA receptors and Ca2+ influx, whereas Abeta exerts its inhibitory effect via actin polymerization and aggregation. The ability of Abeta to inhibit axonal transport seems to require active amino acid residues, which is probably present in the 31-35 sequence. Full-length Abeta may be effective when it represents a structure in which these active residues can access the cell membrane. Our results may provide insight into the early pathogenetic mechanisms of AD.

Progressive degeneration of nonphosphorylated neurofilament protein-enriched pyramidal neurons predicts cognitive impairment in Alzheimer's disease: stereologic analysis of prefrontal cortex area 9

We performed a stereologic analysis of a subset of pyramidal neurons known to be vulnerable in Alzheimer's disease (AD) and characterized by particularly high somatodendritic levels of nonphosphorylated neurofilament protein. In the neocortex, these large pyramidal neurons reside in the deep part of layer III (layer IIIc) and the superficial part of layer V (layer Va). We focused on prefrontal cortex area 9 in elderly control cases in comparison to cases with different degrees of cognitive dysfunction. The results confirmed that these neurons are preferentially vulnerable in AD, as their numbers decrease dramatically in cases with definite dementia, correlating strongly with the severity of the disease, to a nearly complete loss (>90%) in the endstages of AD. Furthermore, a triple-labeling experimental paradigm revealed that these particular neurons are far more likely to develop neurofibrillary tangles (NFT) and do so at a faster rate than other pyramidal cells. Nonphosphorylated neurofilament protein-rich neurons also shrink considerably during formation of NFT and the largest among them are preferentially affected. Laminar differences in the severity of these effects were observed, layer Va being more severely affected, possibly correlating with the involvement of specific cortical projections. These data reveal that different populations of neurons prone to NFT formation are lost at different rates in AD, and that nonphosphorylated neurofilament protein-enriched neurons emerge as a strikingly vulnerable subpopulation of neurons. Their preferential involvement suggests that neurons providing specific corticocortical connections between association areas are at high risk for degeneration in AD.