Amyloid beta protein-induced neuronal cell death: neurotoxic properties of aggregated amyloid beta protein

JAK2/STAT3 as a new potential target to manage neurodegenerative diseases: An interactive review

Neurodegenerative diseases (NDDs) are a collection of incapacitating disorders in which neuroinflammation and neuronal apoptosis are major pathological consequences due to oxidative stress. Neuroinflammation manifests in the impacted cerebral areas as a result of pro-inflammatory cytokines stimulating the Janus Kinase2 (JAK2)/Signal Transducers and Activators of Transcription3 (STAT3) pathway via neuronal cells. The pro-inflammatory cytokines bind to their respective receptor in the neuronal cells and allow activation of JAK2. Activated JAK2 phosphorylates tyrosines on the intracellular domains of the receptor which recruit the STAT3 transcription factor. The neuroinflammation issues are exacerbated by the active JAK2/STAT3 signaling pathway in conjunction with additional transcription factors like nuclear factor kappa B (NF-κB), and the mammalian target of rapamycin (mTOR). Neuronal apoptosis is a natural process made worse by persistent neuroinflammation and immunological responses via caspase-3 activation. The dysregulation of micro-RNA (miR) expression has been observed in the consequences of neuroinflammation and neuronal apoptosis. Neuroinflammation and neuronal apoptosis-associated gene amplification may be caused by dysregulated miR-mediated aberrant phosphorylation of JAK2/STAT3 signaling pathway components. Therefore, JAK2/STAT3 is an attractive therapeutic target for NDDs. Numerous synthetic and natural small molecules as JAK2/STAT3 inhibitors have therapeutic advances against a wide range of diseases, and many are now in human clinical studies. This review explored the interactive role of the JAK2/STAT3 signaling system with key pathological factors during the reinforcement of NDDs. Also, the clinical trial data provides reasoning evidence about the possible use of JAK2/STAT3 inhibitors to abate neuroinflammation and neuronal apoptosis in NDDs.

Neuroprotective effects of combined therapy with memantine, donepezil, and vitamin D in ovariectomized female mice subjected to dementia model

Women older than 60 have a higher risk of dementia, aging-related cognitive decline, and Alzheimer's Disease (AD) than the rest of the population. The main reason is hormonal senescence after menopause, a period characterized by a decline in estrogen levels. Since the effectiveness of drugs currently approved for the treatment of AD is limited, it is necessary to seek the development of new therapeutic strategies. Vitamin D deficiency is prevalent in AD patients and individuals with dementia in general. The supplementation of this vitamin in dementia patients might be an interesting approach for increasing the effectiveness of pre-existing medications for dementia treatment. Thus, the present study aims to investigate the effect of vitamin D treatment associated with memantine and donepezil in female mice submitted to ovariectomy (OVX) for five months and subjected to a dementia animal model induced by intracerebroventricular injection of aggregated amyloid βeta (Aβ_1-42). For this purpose, Balb/c mice were divided into five experimental groups, which received 17 days of combined therapy with vitamin D, donepezil, and memantine. Then, animals were subjected to behavioral tests. OVX groups exhibited reduced levels of estradiol (E2) in serum, which was not altered by the combined therapy. Higher levels of vitamin D3 were found in the OVX animals submitted to the triple-association treatment. Mice exposed to both OVX and the dementia animal model presented impairment in short and long-term spatial and habituation memories. Also, female mice exposed to Aβ and OVX exhibited a reduction in brain-derived neurotrophic factor (BDNF) and interleukin-4 (IL-4) levels, and an increase in tumor necrose factor-α (TNFα) levels in the hippocampus. Besides, increased levels of IL-1β in the hippocampus and cerebral cortex were observed, as well as a significant increase in immunoreactivity for glial fibrillary acidic protein (GFAP), an astrocytes marker, in the hippocampus. Notably, triple-association treatment reversed the effects of the exposition of mice to Aβ and OVX in the long-term spatial and habituation memories impairment, as well as reversed changes in TNFα, IL-1β, IL-4, and GFAP immunoreactivity levels in the hippocampus of treated animals. Our results indicate that the therapeutic association of vitamin D, memantine, and donepezil has beneficial effects on memory performance and attenuated the neuroinflammatory response in female mice subjected to OVX associated with a dementia animal model.

Molecular details of aluminium-amyloid β peptide interaction by nuclear magnetic resonance

Alzheimer's disease (AD) is a devastating neurodegenerative condition that poses major challenges to human health. Both amyloid β (Aβ) and metal ions such as aluminium are implicated in the development of AD. By the means of NMR, the interactions of Al³⁺ with Aβ_1-28 peptide as well as the Aβ_1-28 analogues were studied, and the key binding sites of Al³⁺ in Aβ determined. NMR data showed Al³⁺ interacts with Aβ_1-28 at the NH and αH of numerous residues by exhibiting upfield shifts. Using Aβ analogues where His6, His13 and His14 were individually replaced by alanine residue(s), including Aβ H6A, Aβ H13A, Aβ H14A, and Aβ H6,13,14A, the results demonstrated that the histidine residues (His6, His13 and His14) and N-terminal Asp1 were involved in the Al³⁺ coordination. These findings provide, for the first time, the details of the molecular interaction between Al³⁺ and Aβ, which points to the potential role of Al³⁺ in Aβ aggregation, hence in AD development.

α-Synuclein binding activity of the plant growth promoter asterubine

Preventing the aggregation of certain amyloid proteins has the potential to slow down the progression of diseases like Alzheimer's, Parkinson's, and type 2 diabetes mellitus. During a high-throughput screen of 300 Australian marine invertebrate extracts, the extract of the marine sponge Thorectandra sp. 4408 displayed binding activity to the Parkinson's disease-associated protein, α-synuclein. Isolation of the active component led to its identification as the known plant growth promoter asterubine (1). This molecule shares distinct structural similarities with potent amyloid beta aggregation inhibitors tramiprosate (homotaurine) and ALZ-801. Herein we report the isolation, NMR data acquired in DMSO and α-synuclein binding activity of asterubine (1).

Pathophysiological Roles of Intracellular Proteases in Neuronal Development and Neurological Diseases

Proteases are classified into six distinct classes (cysteine, serine, threonine, aspartic, glutamic, and metalloproteases) on the basis of catalytic mechanism. The cellular control of protein quality senses misfolded or damaged proteins principally by selective ubiquitin-proteasome pathway and non-selective autophagy-lysosome pathway. The two pathways do not only maintain cell homeostasis physiologically, but also mediate necrosis and apoptosis pathologically. Proteasomes are threonine proteases, whereas cathepsins are lysosomal aspartic proteases. Calpains are non-lysosomal cysteine proteases and calcium-dependent papain-like enzyme. Calpains and cathepsins are involved in the neuronal necrosis, which are accidental cell death. Necrosis is featured by the disruption of plasma membranes and lysosomes, the loss of ATP and ribosomes, the lysis of cell and nucleus, and the caspase-independent DNA fragmentation. On the other hand, caspases are cysteine endoproteases and mediate neuronal cell death such as apoptosis and pyroptosis, which are programmed cell death. In the central nervous system, necroptosis, ferroptosis and autophagic cell death are also classified into programmed cell death. Neuronal apoptosis is characterized by cell shrinkage, plasma membrane blebbing, karyorrhexis, chromatin condensation, and DNA fragmentation. Necroptosis and pyroptosis are necrotic and lytic forms of programmed cell death, respectively. Although autophagy is involved in cell survival, it fails to maintain cellular homeostasis, resulting in autophagic cell death. Ferroptosis is induced by reactive oxygen species in excitotoxicity of glutamate and ischemia-reperfusion. Apoptosis and pyroptosis are dependent on caspase-3 and caspase-1, respectively. Autophagic cell death and necroptosis are dependent on calpain and cathepsin, respectively, but independent of caspase. Although apoptosis has been defined by the absence of morphological features of necrosis, the two deaths are both parts of a continuum. The intracellular proteases do not only maintain cell homeostasis but also regulate neuronal maturation during the development of embryonic brain. Furthermore, neurodegenerative diseases are caused by the impairment of quality control mechanisms for a proper folding and function of protein.

Minocycline reduces inflammatory parameters in the brain structures and serum and reverses memory impairment caused by the administration of amyloid β (1-42) in mice

Alzheimer's disease (AD) is a neurodegenerative disorder and the most common type of age-related dementia. Cognitive decline, beta-amyloid (Aβ) accumulation, neurofibrillary tangles, and neuroinflammation are the main pathophysiological characteristics of AD. Minocycline is a tetracycline derivative with anti-inflammatory properties that has a neuroprotective effect. The aim of this study was to evaluate the effect of minocycline on memory, neurotrophins and neuroinflammation in an animal model of AD induced by the administration of Aβ (1-42) oligomer. Male BALB/c mice were treated with minocycline (50mg/kg) via the oral route for a total of 17days, 24h after intracerebroventricular administration of Aβ (1-42) oligomer. At the end of this period, was performed the radial maze test, and 24h after the last minocycline administration, serum was collected and the cortex and hippocampus were dissected for biochemical analysis. The administration of minocycline reversed the memory impairment caused by Aβ (1-42). In the hippocampus, minocycline reversed the increases in the levels of interleukin (IL-1β), Tumor Necrosis Factor- alpha (TNF-α) and, IL-10 caused by Aβ (1-42). In the cortex, AD-like model increase the levels of IL-1β, TNF-α and, IL-4. Minocycline treatment reversed this. In the serum, Aβ (1-42) increased the levels of IL-1β and IL-4, and minocycline was able to reverse this action, but not to reverse the decrease of IL-10 levels. Minocycline also reversed the increase in the levels of Brain-derived neurotrophic factor (BDNF) in the hippocampus caused by Aβ (1-42), and reduced Nerve Growth Factor (NGF) increases in the total cortex. Therefore, our results indicate that minocycline causes improvements in the spatial memory, and cytokine levels were correlated with this effect in the brain it. Besides this, minocycline reduced BDNF and NGF levels, highlighting the promising effects of minocycline in treating AD-like dementia.

Lithium and memantine improve spatial memory impairment and neuroinflammation induced by β-amyloid 1-42 oligomers in rats

Alzheimer's disease (AD) is the most common cause of dementia in the elderly. The main hallmarks of this disease include progressive cognitive dysfunction and an accumulation of soluble oligomers of β-amyloid (Aβ) 1-42 peptide. In this research, we show the effects of lithium and memantine on spatial memory and neuroinflammation in an Aβ1-42 oligomers-induced animal model of dementia in rats. Aβ 1-42 oligomers were administered intrahippocampally to male wistar rats to induce dementia. Oral treatments with memantine (5mg/kg), lithium (5mg/kg), or both drugs in combination were performed over a period of 17days. 14days after the administration of the Aβ1-42 oligomers, the radial arm-maze task was performed. At the end of the test period, the animals were euthanized, and the frontal cortex and hippocampus were removed for use in our analysis. Our results showed that alone treatments with lithium or memantine ameliorate the spatial memory damage caused by Aβ1-42. The animals that received combined doses of lithium and memantine showed better cognitive performance in their latency time and total errors to find food when compared to the results from alone treatments. Moreover, in our study, lithium and/or memantine were able to reverse the decreases observed in the levels of interleukin (IL)-4 that were induced by Aβ1-42 in the frontal cortex. In the hippocampus, only memantine and the association of memantine and lithium were able to reverse this effect. Alone doses of lithium and memantine or the association of lithium and memantine caused reductions in the levels of IL-1β in the frontal cortex and hippocampus, and decreased the levels of TNF-α in the hippocampus. Taken together, these data suggest that lithium and memantine might be a potential therapy against cognitive impairment and neuroinflammation induced by Aβ1-42, and their association may be a promising alternative to be investigated in the treatment of AD-like dementia.

Gas1 Knockdown Increases the Neuroprotective Effect of Glial Cell-Derived Neurotrophic Factor Against Glutamate-Induced Cell Injury in Human SH-SY5Y Neuroblastoma Cells

Growth arrest-specific 1 (Gas1) protein acts as an inhibitor of cell growth and a mediator of cell death in nervous system during development and is also re-expressed in adult neurons during excitotoxic insult. Due to its structural similarity to the glial cell-derived neurotrophic factor family receptors α (GFRα), Gas1 is likely to interfere with the neuroprotective effect of GDNF. In the present study, we investigated the expression profile of Gas1 during glutamate insults in human SH-SY5Y neuroblastoma cells as well as the influence of Gas1 inhibition on the protective effect of GDNF against glutamate-induced cell injury. Our data showed that Gas1 expression was significantly increased with the treatment of glutamate in SH-SY5Y cells. The silencing of Gas1 by small interfering RNA promoted the protective effect of GDNF against glutamate-induced cytotoxicity as well as cell apoptosis, which effect was likely mediated through activating Akt/PI3 K-dependent cell survival signaling pathway and inhibiting mitochondrial-dependent cell apoptosis signaling pathway via Bad dephosphorylation blockade. In summary, this study showed the synergistic effect of Gas1 inhibition and GDNF against glutamate-induced cell injury in human SH-SY5Y neuroblastoma cells, which information might significantly contribute to better understanding the function of Gas1 in neuronal cells and form the basis of the therapeutic development of GDNF in treating human neurodegenerative diseases in the future.

Formation of a flavin-linked peptide

In a previous study, we showed that formylmethylflavin (FMF) can bind to cysteine. In this study, FMF was reacted with native peptides (CG and CKLVFF) containing an N-terminal cysteine. The formation of flavin-CG and flavin-CKLVFF was confirmed using HPLC and ESI-MS. Storage of flavin-CKLVFF in DMSO at −30 °C for 7 days resulted in no detectable deposition. In contrast, flavin-CKLVFF formed deposits when stored in water at −30 °C for 1 day, but no deposit was observed in the aqueous solution of flavin-CKLVFF after 7 days storage in the presence of 0.1% Triton X-100.

The role of secretory phospholipase A₂ in the central nervous system and neurological diseases

Secretory phospholipase A2 (sPLA2s) are small secreted proteins (14-18 kDa) and require submillimolar levels of Ca(2+) for liberating arachidonic acid from cell membrane lipids. In addition to the enzymatic function, sPLA2 can exert various biological responses by binding to specific receptors. Physiologically, sPLA2s play important roles on the neurotransmission in the central nervous system and the neuritogenesis in the peripheral nervous system. Pathologically, sPLA2s are involved in the neurodegenerative diseases (e.g., Alzheimer's disease) and cerebrovascular diseases (e.g., stoke). The common pathology (e.g., neuronal apoptosis) of Alzheimer's disease and stroke coexists in the mixed dementia, suggesting common pathogenic mechanisms of the two neurological diseases. Among mammalian sPLA2s, sPLA2-IB and sPLA2-IIA induce neuronal apoptosis in rat cortical neurons. The excess influx of calcium into neurons via L-type voltage-dependent Ca(2+) channels mediates the two sPLA2-induced apoptosis. The elevated concentration of intracellular calcium activates PKC, MAPK and cytosolic PLA2. Moreover, it is linked with the production of reactive oxygen species and apoptosis through activation of the superoxide producing enzyme NADPH oxidase. NADPH oxidase is involved in the neurotoxicity of amyloid β peptide, which impairs synaptic plasticity long before its deposition in the form of amyloid plaques of Alzheimer's disease. In turn, reactive oxygen species from NADPH oxidase can stimulate ERK1/2 phosphorylation and activation of cPLA2 and result in a release of arachidonic acid. sPLA2 is up-regulated in both Alzheimer's disease and cerebrovascular disease, suggesting the involvement of sPLA2 in the common pathogenic mechanisms of the two diseases. Thus, our review presents evidences for pathophysiological roles of sPLA2 in the central nervous system and neurological diseases.

Cyclooxygenase (COX)-1 activity precedes the COX-2 induction in Aβ-induced neuroinflammation

Two different isoforms of cyclooxygenases, COX-1 and COX-2, are constitutively expressed under normal physiological conditions of the central nervous system, and accumulating data indicate that both isoforms may be involved in different pathological conditions. However, the distinct role of COX-1 and COX-2 and the probable interaction between them in neuroinflammatory conditions associated with Alzheimer's disease are conflicting issues. The aim of this study was to elucidate the comparable role of each COX isoform in neuroinflammatory response induced by β-amyloid peptide (Aβ). Using histological and biochemical methods, 13 days after stereotaxic injection of Aβ into the rat prefrontal cortex, hippocampal neuroinflammation and neuronal injury were confirmed by increased expression of tumor necrosis factor-alpha (TNF-α) and COX-2, elevated levels of prostaglandin E2 (PGE2), astrogliosis, activation of caspase-3, and neuronal cell loss. Selective COX-1 or COX-2 inhibitors, SC560 and NS398, respectively, were chronically used to explore the role of COX-1 and COX-2. Treatment with either COX-1 or COX-2 selective inhibitor or their combination equally decreased the level of TNF-α, PGE2, and cleaved caspase-3 and attenuated astrogliosis and neuronal cell loss. Interestingly, treatment with COX-1 selective inhibitor or the combined COX inhibitors prevented the induction of COX-2. These results indicate that the activity of both isoforms is detrimental in neuroinflammatory conditions associated with Aβ, but COX-1 activity is necessary for COX-2 induction and COX-2 activity seems to be the main source of PGE2 increment.

Cerebral arachidonate cascade in dementia: Alzheimer's disease and vascular dementia

Phospholipase A(2) (PLA(2)), cyclooxygenase (COX) and prostaglandin (PG) synthase are enzymes involved in arachidonate cascade. PLA(2) liberates arachidonic acid (AA) from cell membrane lipids. COX oxidizes AA to PGG(2) followed by an endoperoxidase reaction that converts PGG(2) into PGH(2). PGs are generated from astrocytes, microglial cells and neurons in the central nervous system, and are altered in the brain of demented patients. Dementia is principally diagnosed into Alzheimer's disease (AD) and vascular dementia (VaD). In older patients, the brain lesions associated with each pathological process often occur together. Regional brain microvascular abnormalities appear before cognitive decline and neurodegeneration. The coexistence of AD and VaD pathology is often termed mixed dementia. AD and VaD brain lesions interact in important ways to decline cognition, suggesting common pathways of the two neurological diseases. Arachidonate cascade is one of the converged intracellular signal transductions between AD and VaD. PLA(2) from mammalian sources are classified as secreted (sPLA(2)), Ca(2+)-dependent, cytosolic (cPLA(2)) and Ca(2+)-independent cytosolic PLA(2) (iPLA(2)). PLA(2) activity can be regulated by calcium, by phosphorylation, and by agonists binding to G-protein-coupled receptors. cPLA(2) is upregulalted in AD, but iPLA(2) is downregulated. On the other hand, sPLA(2) is increased in animal models for VaD. COX-2 is induced and PGD(2) are elevated in both AD and VaD. This review presents evidences for central roles of PLA(2)s, COXs and PGs in the dementia.

Tyk2/STAT3 signaling mediates beta-amyloid-induced neuronal cell death: implications in Alzheimer's disease

One of the pathological hallmarks of Alzheimer's disease (AD) is deposition of extracellular amyloid-beta (Abeta) peptide, which is generated from the cleavage of amyloid precursor protein (APP). Accumulation of Abeta is thought to associate with the progressive neuronal death observed in AD. However, the precise signaling mechanisms underlying the action of Abeta in AD pathophysiology are not completely understood. Here, we report the involvement of the transcription factor signal transducer and activator of transcription 3 (STAT3) in mediating Abeta-induced neuronal death. We find that tyrosine phosphorylation of STAT3 is elevated in the cortex and hippocampus of APP/PS1 transgenic mice. Treatment of cultured rat neurons with Abeta or intrahippocampal injection of mice with Abeta both induces tyrosine phosphorylation of STAT3 in neurons. Importantly, reduction of either the expression or activation of STAT3 markedly attenuates Abeta-induced neuronal apoptosis, suggesting that STAT3 activation contributes to neuronal death after Abeta exposure. We further identify Tyk2 as the tyrosine kinase that acts upstream of STAT3, as Abeta-induced activation of STAT3 and caspase-3-dependent neuronal death can be inhibited in tyk2(-/-) neurons. Finally, increased tyrosine phosphorylation of STAT3 is also observed in postmortem brains of AD patients. Our observations collectively reveal a novel role of STAT3 in Abeta-induced neuronal death and suggest the potential involvement of Tyk2/STAT3 signaling in AD pathophysiology.

Soluble fibrillar oligomer levels are elevated in Alzheimer's disease brain and correlate with cognitive dysfunction

Recent evidence has suggested a role for soluble oligomeric Abeta species in the pathology of Alzheimer's disease (AD). Fibrillar plaque deposits are present in non-demented individuals and levels of soluble Abeta correlate better with cognitive dysfunction in AD and transgenic mouse models. We have previously reported that there are at least two conformationally distinct types of Abeta oligomers: prefibrillar oligomers that are kinetic intermediates in fibril assembly reactions and are specifically recognized by A11 antibody and fibrillar oligomers that may represent fibril seeds or small pieces of fibrils and are recognized by a fibril specific antibody, OC. We have examined the levels of these two types of oligomers in the PBS soluble fraction of brain tissue from control cases, cases with senile degenerative changes (SDC) and AD patients. We found that the levels of soluble fibrillar oligomers detected by OC antibody are significantly elevated in multiple brain regions of AD patients. The elevated fibrillar oligomer levels were found not to be an artifact of tissue homogenization, nor a result of increased Abeta or APP levels. The concentration of fibrillar oligomers in adjacent brain regions of the same patient can vary widely and were not detected in post-mortem cerebrospinal fluid. In contrast, the level of prefibrillar oligomers are variable in both AD and age matched controls, indicating that they are not correlated with cognitive dysfunction and suggesting that they precede dementia in AD. Significant correlations were found between the levels of fibrillar oligomers and cognitive decline (MMSE scores) as well as the neuropathological hallmarks of AD. These results indicate that fibrillar oligomers may play a key role in the pathology of AD and may be a new target for diagnostic and therapeutic development.

Advanced glycation endproducts and their receptor RAGE in Alzheimer's disease

Alzheimer's disease (AD) is the most common dementing disorder of late life. Although there might be various different triggering events in the early stages of the disease, they seem to converge on a few characteristic final pathways in the late stages, characterized by inflammation and neurodegeneration. In this review, we revisit the hypothesis that advanced glycation endproducts (AGEs) and their receptor RAGE may play an important role in disease pathogenesis. Accumulation of AGEs in cells and tissues is a normal feature of aging, but is accelerated in AD. In AD, AGEs can be detected in pathological deposits such as amyloid plaques and neurofibrillary tangles. AGEs explain many of the neuropathological and biochemical features of AD such as extensive protein crosslinking, glial induction of oxidative stress and neuronal cell death. Oxidative stress and AGEs initiate a positive feedback loop, where normal age-related changes develop into a pathophysiological cascade. RAGE and its decoy receptor soluble RAGE, may contribute to or protect against AD pathogenesis by influencing transport of β-amyloid into the brain or by manipulating inflammatory mechanisms. Targeted pharmacological interventions using AGE-inhibitors, RAGE-antagonists, RAGE-antibodies, soluble RAGE or RAGE signalling inhibitors such as membrane-permeable antioxidants may be promising therapeutic strategies to slow down the progression of AD.

Beta-amyloid(1-42) induces neuronal death through the p75 neurotrophin receptor

Alzheimer's disease is characterized by the accumulation of neurotoxic amyloidogenic peptide Abeta, degeneration of the cholinergic innervation to the hippocampus (the septohippocampal pathway), and progressive impairment of cognitive function, particularly memory. Abeta is a ligand for the p75 neurotrophin receptor (p75(NTR)), which is best known for mediating neuronal death and has been consistently linked to the pathology of Alzheimer's disease. Here we examined whether p75(NTR) is required for Abeta-mediated effects. Treatment of wild-type but not p75(NTR)-deficient embryonic mouse hippocampal neurons with human Abeta(1-42) peptide induced significant cell death. Furthermore, injection of Abeta(1-42) into the hippocampus of adult mice resulted in significant degeneration of wild-type but not p75(NTR)-deficient cholinergic basal forebrain neurons, indicating that the latter are resistant to Abeta-induced toxicity. We also found that neuronal death correlated with Abeta(1-42) peptide-stimulated accumulation of the death-inducing p75(NTR) C-terminal fragment generated by extracellular metalloprotease cleavage of full-length p75(NTR). Although neuronal death was prevented in the presence of the metalloprotease inhibitor TAPI-2 (tumor necrosis factor-alpha protease inhibitor-2), Abeta(1-42)-induced accumulation of the C-terminal fragment resulted from inhibition of gamma-secretase activity. These results provide a novel mechanism to explain the early and characteristic loss of cholinergic neurons in the septohippocampal pathway that occurs in Alzheimer's disease.

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.

The redox chemistry of the Alzheimer's disease amyloid beta peptide

There is a growing body of evidence to support a role for oxidative stress in Alzheimer's disease (AD), with increased levels of lipid peroxidation, DNA and protein oxidation products (HNE, 8-HO-guanidine and protein carbonyls respectively) in AD brains. The brain is a highly oxidative organ consuming 20% of the body's oxygen despite accounting for only 2% of the total body weight. With normal ageing the brain accumulates metals ions such iron (Fe), zinc (Zn) and copper (Cu). Consequently the brain is abundant in antioxidants to control and prevent the detrimental formation of reactive oxygen species (ROS) generated via Fenton chemistry involving redox active metal ion reduction and activation of molecular oxygen. In AD there is an over accumulation of the Amyloid beta peptide (Abeta), this is the result of either an elevated generation from amyloid precursor protein (APP) or inefficient clearance of Abeta from the brain. Abeta can efficiently generate reactive oxygen species in the presence of the transition metals copper and iron in vitro. Under oxidative conditions Abeta will form stable dityrosine cross-linked dimers which are generated from free radical attack on the tyrosine residue at position 10. There are elevated levels of urea and SDS resistant stable linked Abeta oligomers as well as dityrosine cross-linked peptides and proteins in AD brain. Since soluble Abeta levels correlate best with the degree of degeneration [C.A. McLean, R.A. Cherny, F.W. Fraser, S.J. Fuller, M.J. Smith, K. Beyreuther, A.I. Bush, C.L. Masters, Soluble pool of Abeta amyloid as a determinant of severity of neurodegeneration in Alzheimer's disease, Ann. Neurol. 46 (1999) 860-866] we suggest that the toxic Abeta species corresponds to a soluble dityrosine cross-linked oligomer. Current therapeutic strategies using metal chelators such as clioquinol and desferrioxamine have had some success in altering the progression of AD symptoms. Similarly, natural antioxidants curcumin and ginkgo extract have modest but positive effects in slowing AD development. Therefore, drugs that target the oxidative pathways in AD could have genuine therapeutic efficacy.

Cu(II) potentiation of Alzheimer Abeta1-40 cytotoxicity and transition on its secondary structure

Mounting evidence has shown that dyshomeostasis of the redox-active biometals such as Cu and Fe can lead to oxidative stress, which plays a key role in the neuropathology of Alzheimer' disease (AD). Here we demonstrate that with the formation of Cu(II).beta1-40 complexes, copper markedly potentiates the neurotoxicity exhibited by beta-amyloid peptide (Ab). A greater amount of hydrogen peroxide was released when Cu(II).beta1-40 complexes was added to the xanthine oxidase/xanthine system detected by potassium iodide spectrophotometry. Copper bound to Abeta1-40 was observed by electron paramagnetic resonance (EPR) spectroscopy. Circular dichroism (CD) studies indicated that copper chelation could cause a structural transition of Abeta. The addition of copper to Ab introduced an increase on beta-sheet as well as alpha-helix, which may be responsible for the aggregation of Abeta. We hypothesized that Abeta aggregation induced by copper may be responsible for local injury in AD. The interaction between Cu(2+) and Ab also provides a possible mechanism for the enrichment of metal ions in amyloid plaques in the AD brain.

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.

Different dendrite and dendritic spine alterations in basal and apical arbors in mutant human amyloid precursor protein transgenic mice

The extracellular deposition of amyloid-beta peptide (Abeta) in brain parenchyma is one of the characteristic features of Alzheimer's disease and is suggested to induce reactive and degenerative changes in neuronal cell bodies, axons and dendritic processes. In particular, within and in close proximity to amyloid plaques, distinctive morphological alterations have been observed, including changes in neurite trajectory and decreases in dendritic diameter and in spine density. Apart from these plaque-associated focal aberrations, little is known regarding modifications of the global dendritic morphology including the detailed and comparative quantitative analysis of apical and basal arbors. The objective of the present study was to investigate the effects of amyloid plaque deposition and elevated soluble Abeta on neuronal morphology in mutant human amyloid precursor protein (hAPP) transgenic mice (line Tg2576; [K. Hsiao, P. Chapman, S. Nilsen, C. Eckman, Y. Harigaya, S. Younkin, F. Yang, G. Cole, Correlative memory deficits, Abeta elevation, and amyloid plaques in transgenic mice, Science 274 (1996) 99-102]). Retrogradelly labeled callosal-projecting pyramidal cells in the primary somatosensory cortex were three-dimensionally analyzed. Although basal dendrites remained unaffected, analysis of apical trees revealed a number of unambiguous morphological changes. Thus, in TG2576 mice, the apical arbors were shortened in total length and less branched. Furthermore, the diameter of proximal dendritic segments was increased whereas that of distal segments was reduced. Analysis of spine numbers and distribution on basal and apical trees demonstrated a significant reduction in spine densities along the whole course of dendrites. The findings suggest that Abeta-related pathology induces morphological aberrations in basal and apical arbors to different degrees which are unrelated to direct plaque-associated changes.

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.

The influence of phospholipid membranes on bovine calcitonin peptide's secondary structure and induced neurotoxic effects

The peptide hormone, calcitonin, which is associated with medullary carcinoma of the thyroid, has a marked tendency to form amyloid fibrils and may be a useful model in probing the role of peptide-membrane interactions in beta-sheet and amyloid formation and amyloid neurotoxicity. Using bovine calcitonin, we found that, like other amyloids, the peptide was toxic only when in a beta-sheet-rich, amyloid form, but was non-toxic, when it lacked an amyloid structure. We found that the peptide bound with significant affinity to membranes that contained either cholesterol and gangliosides. In addition, incubation of calcitonin with cholesterol-rich and ganglioside-containing membranes resulted in significant changes in peptide structure yielding a peptide enriched in beta-sheet and amyloid content. Because the cholesterol- and ganglioside-rich phospholipid systems enhanced the calcitonin beta-sheet and amyloid contents, and peptide amyloid content was associated with neurotoxicity, we then investigated whether depleting cellular cholesterol and gangliosides affected calcitonin neurotoxicity. We found that cholesterol and ganglioside removal significantly reduced the calcitonin-induced PC12 cell neurotoxicity. Similar results have been observed with other amyloid-forming peptides such as beta-amyloid (A beta) of Alzheimer's disease and suggest that modulation of membrane composition and peptide-membrane interactions may prove useful in the control of amyloid formation and amyloid neurotoxicity.

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.

Phosphorylated amyloid-beta: the toxic intermediate in alzheimer's disease neurodegeneration

Phosphorylated Amyloid-beta (Abeta) was identified in Alzheimer's disease (AD) brain. Using an anti-sense peptide approach the human cyclin-dependent kinase-1 (CDK-1) was identified as being responsible for Abeta phosphorylation. The phosphorylated Abeta peptide showed increased neurotoxicity and reduced ability to form Congo red-positive fibrils. Mutation of the serine 26 residue and inhibition of Abeta phosphorylation by the CDK-1 inhibitor olomoucine prevented Abeta toxicity, suggesting that the phosphorylated Abeta peptide represents a toxic intermediate. Cannabinoids prevented phosphorylated Abeta toxicity. The results from this study suggest that Abeta phosphorylation could play a role in AD pathology and represent a novel therapeutic target.

Amyloid beta protein impairs motor function via thromboxane A2 in the rat striatum

Amyloid beta protein (Abeta) deposits are found in the striatum of patients with Alzheimer disease (AD) showing extrapyramidal motor dysfunction, but neuronal cell loss has not yet been detected. To clarify how Abeta impairs motor function, we analyzed intrastriatally Abeta-injected rats. Unilateral injection of Abeta(25-35) enhanced apomorphine-induced circling in an ipsilateral direction, indicating ipsilateral dysfunction of dopaminergic nigrostriatal pathways. Volumes of lesion in the Abeta(25-35)-injected striata were significantly higher than those in the saline-injected ones. The correlation between lesion volume and circling behavior was close to significance, but slightly too low, suggesting the possible involvement of other factors in the striatal dysfunction. Abeta(25-35) significantly elevated the level of thromboxane A2 (TXA2). A stable TXA2 agonist, U46619, enhanced circling behavior, and TXA2 receptor antagonists attenuated U46619- and Abeta(25-35)-enhanced circling behavior. This study demonstrated that Abeta(25-35) impairs the motor function of dopaminergic neurons via neuronal cell loss and TXA2. It also sheds light on the therapeutic potential of TXA2 receptor blockers for the neurotoxicity of Abeta.

The effect of cholesterol and monosialoganglioside (GM1) on the release and aggregation of amyloid beta-peptide from liposomes prepared from brain membrane-like lipids

In order to investigate the influence of cholesterol (Ch) and monosialoganglioside (GM1) on the release and subsequent deposition/aggregation of amyloid beta peptide (Abeta)-(1-40) and Abeta-(1-42), we have examined Abeta peptide model membrane interactions by circular dichroism, turbidity measurements, and transmission electron microscopy (TEM). Model liposomes containing Abeta peptide and a lipid mixture composition similar to that found in the cerebral cortex membranes (CCM-lipid) have been prepared. In all, four Abeta-containing liposomes were investigated: CCM-lipid; liposomes with no GM1 (GM1-free lipid); those with no cholesterol (Ch-free lipid); liposomes with neither cholesterol nor GM1 (Ch-GM1-free lipid). In CCM liposomes, Abeta was rapidly released from membranes to form a well defined fibril structure. However, for the GM1-free lipid, Abeta was first released to yield a fibril structure about the membrane surface, then the membrane became disrupted resulting in the formation of small vesicles. In Ch-free lipid, a fibril structure with a phospholipid membrane-like shadow formed, but this differed from the well defined fibril structure seen for CCM-lipid. In Ch-GM1-free lipid, no fibril structure formed, possibly because of membrane solubilization by Abeta. The absence of fibril structure was noted at physiological extracellular pH (7.4) and also at liposomal/endosomal pH (5.5). Our results suggest a possible role for both Ch and GM1 in the membrane release of Abeta from brain lipid bilayers.

Novel binding sites of 15-deoxy-Delta12,14-prostaglandin J2 in plasma membranes from primary rat cortical neurons

15-Deoxy-Delta12,14-prostaglandin J2 (15d-Delta12,14-PGJ2) is an endogenous ligand for a nuclear peroxysome proliferator activated receptor-gamma (PPAR). We found novel binding sites of 15d-Delta12,14-PGJ2 in the neuronal plasma membranes of the cerebral cortex. The binding sites of [3H]15d-Delta12,14-PGJ2 were displaced by 15d-Delta12,14-PGJ2 with a half-maximal concentration of 1.6 microM. PGD2 and its metabolites also inhibited the binding of [3H]15d-Delta12,14-PGJ2. Affinities for the novel binding sites were 15d-Delta12,14-PGJ2 > Delta12-PGJ2 > PGJ2 > PGD2. Other eicosanoids and PPAR agonists did not alter the binding of [3H]15d-Delta12,14-PGJ2. In primary cultures of rat cortical neurons, we examined the pathophysiologic roles of the novel binding sites. 15d-Delta12,14-PGJ2 triggered neuronal cell death in a concentration-dependent manner, with a half-maximal concentration of 1.1 microM. The neurotoxic potency of PGD2 and its metabolites was also 15d-Delta12,14-PGJ2 > Delta12-PGJ2 > PGJ2 > PGD2. The morphologic and ultrastructural characteristics of 15d-Delta12,14-PGJ2-induced neuronal cell death were apoptotic, as evidenced by condensed chromatin and fragmented DNA. On the other hand, we detected little neurotoxicity of other eicosanoids and PPAR agonists. In conclusion, we demonstrated that novel binding sites of 15d-Delta12,14-PGJ2 exist in the plasma membrane. The present study suggests that the novel binding sites might be involved in 15d-Delta12,14-PGJ2-induced neuronal apoptosis.

Effect of Gas6 on secretory phospholipase A(2)-IIA-induced apoptosis in cortical neurons

Gas6, a product of the growth-arrest-specific gene 6, protects cortical neurons from amyloid beta protein (Abeta)-induced apoptosis. Neuronal apoptosis is also caused by human group IIA secretory phospholipase A(2) (sPLA(2)-IIA), which is expressed in the cerebral cortex after brain ischemia. sPLA(2)-IIA induces Ca(2+) influx via L-type voltage-sensitive calcium channels (L-VSCCs), leading to its neurotoxicity. In the present study, we investigated effects of Gas6 on sPLA(2)-IIA-induced cell death in primary cultures of rat cortical neurons. sPLA(2)-IIA caused neuronal cell death in a concentration- and time-dependent manner. Gas6 significantly prevented neurons from sPLA(2)-IIA-induced cell death. Gas6 suppressed sPLA(2)-IIA-induced apoptotic features such as the condensation of chromatin and the fragmentation of DNA. Prior to cell death, sPLA(2)-IIA increased the influx of Ca(2+) into neurons through L-VSCCs. Gas6 significantly inhibited the sPLA(2)-IIA-induced Ca(2+) influx. The blocker of L-VSCCs also suppressed sPLA(2)-IIA-induced neuronal cell death. The cortical cultures contained few non-neuronal cells, indicating that Gas6 affected the survival of neurons directly, but not indirectly via non-neuronal cells. In conclusion, we demonstrate that Gas6 rescues cortical neurons from sPLA(2)-IIA-induced apoptosis. Furthermore, the present study indicates that inhibition of L-VSCC contributes to the neuroprotective effect of Gas6.

Identification of a mutant amyloid peptide that predominantly forms neurotoxic protofibrillar aggregates

The amyloid peptide (Abeta), derived from the proteolytic cleavage of the amyloid precursor protein (APP) by beta- and gamma-secretases, undergoes multistage assemblies to fibrillar depositions in the Alzheimer's brains. Abeta protofibrils were previously identified as an intermediate preceding insoluble fibrils. While characterizing a synthetic Abeta variant named EV40 that has mutations in the first two amino acids (D1E/A2V), we discerned unusual aggregation profiles of this variant. In comparison of the fibrillogenesis and cellular toxicity of EV40 to the wild-type Abeta peptide (Abeta40), we found that Abeta40 formed long fibrillar aggregates while EV40 formed only protofibrillar aggregates under the same in vitro incubation conditions. Cellular toxicity assays indicated that EV40 was slightly more toxic than Abeta40 to human neuroblastoma SHEP cells, rat primary cortical, and hippocampal neurons. Like Abeta40, the neurotoxicity of the protofibrillar EV40 could be partially attributed to apoptosis since multiple caspases such as caspase-9 were activated after SHEP cells were challenged with toxic concentrations of EV40. This suggested that apoptosis-induced neuronal loss might occur before extensive depositions of long amyloid fibrils in AD brains. This study has been the first to show that a mutated Abeta peptide formed only protofibrillar species and mutations of the amyloid peptide at the N-terminal side affect the dynamic amyloid fibrillogenesis. Thus, the identification of EV40 may lead to further understanding of the structural perturbation of Abeta to its fibrillation.

Human group IIA secretory phospholipase A2 potentiates Ca2+ influx through L-type voltage-sensitive Ca2+ channels in cultured rat cortical neurons

Mammalian group IIA secretory phospholipase A2 (sPLA2-IIA) generates prostaglandin D2 (PGD2) and triggers apoptosis in cortical neurons. However, mechanisms of PGD2 generation and apoptosis have not yet been established. Therefore, we examined how second messengers are involved in the sPLA2-IIA-induced neuronal apoptosis in primary cultures of rat cortical neurons. sPLA2-IIA potentiated a marked influx of Ca2+ into neurons before apoptosis. A calcium chelator and a blocker of the L-type voltage-sensitive Ca2+ channel (L-VSCC) prevented neurons from sPLA2-IIA-induced neuronal cell death in a concentration-dependent manner. Furthermore, the L-VSCC blocker ameliorated sPLA2-IIA-induced morphologic alterations and apoptotic features such as condensed chromatin and fragmented DNA. Other blockers of VSCCs such as N type and P/Q types did not affect the neurotoxicity of sPLA2-IIA. Blockers of L-VSCC significantly suppressed sPLA2-IIA-enhanced Ca2+ influx into neurons. Moreover, reactive oxygen species (ROS) were generated prior to apoptosis. Radical scavengers reduced not only ROS generation, but also the sPLA2-IIA-induced Ca2+ influx and apoptosis. In conclusion, we demonstrated that sPLA2-IIA potentiates the influx of Ca2+ into neurons via L-VSCC. Furthermore, the present study suggested that eicosanoids and ROS generated during arachidonic acid oxidative metabolism are involved in sPLA2-IIA-induced apoptosis in cooperation with Ca2+.

Porcine pancreatic group IB secretory phospholipase A2 potentiates Ca2+ influx through L-type voltage-sensitive Ca2+ channels

Secretory phospholipase A(2) (sPLA(2)) exhibits neurotoxicity in the central nervous system. There are high-affinity binding sites of the porcine pancreatic group IB sPLA(2) (sPLA(2)-IB) in the brain. sPLA(2)-IB causes neuronal cell death via apoptosis in the rat cerebral cortex. Although apoptosis is triggered by an influx of Ca(2+) into neurons, it has not yet been ascertained whether the Ca(2+) influx is associated with the neurotoxicity of sPLA(2)-IB. We thus examined the possible involvement of Ca(2+) in the neurotoxicity of sPLA(2)-IB in the primary culture of rat cortical neurons. sPLA(2)-IB induced neuronal cell death in a concentration- and time-dependent manner. This death was accompanied by condensed chromatin and fragmented DNA, exhibiting apoptotic features. Before apoptosis, sPLA(2)-IB markedly enhanced the influx of Ca(2+) into neurons. A calcium chelator suppressed neurons from sPLA(2)-IB-induced neuronal cell death in a concentration-dependent manner. An L-type voltage-sensitive Ca(2+) channel (L-VSCC) blocker significantly protected the sPLA(2)-IB-potentiated influx of Ca(2+). On the other hand, blockers of N-VSCC and P/Q-VSCC did not. An L-VSCC blocker protected neurons from sPLA(2)-IB-induced neuronal cell death. In addition, the L-VSCC blocker ameliorated the apoptotic features of sPLA(2)-IB-treated neurons. Neither an N-VSCC blocker nor P/Q-VSCC blockers affected the neurotoxicity of the enzyme. In conclusion, these findings demonstrate that the influx of Ca(2+) into neurons play an important role in the neurotoxicity of sPLA(2)-IB. Furthermore, the present study suggests that L-VSCC contribute to the sPLA(2)-IB-potentiated influx of Ca(2+) into neurons.

Prostaglandin E2 rescues cortical neurons from amyloid beta protein-induced apoptosis

Cerebrospinal fluid prostaglandin E(2) (PGE(2)) levels are elevated in patients with Alzheimer's disease (AD), suggesting an involvement of PGE(2) in the neurodegeneration. AD is characterized by deposits of amyloid beta protein (Abeta) in various regions of the brain, e.g. the cerebral cortex. In the present study, we investigated the effects of PGE(2) on neuronal survival in primary cultures of rat cortical neurons. PGE(2) had no effect on neuronal cell viability or its morphology. Therefore, we examined the synergistic effects of PGE(2) with Abeta, a neurotoxin. Abeta caused neuronal cell death via apoptosis. PGE(2) significantly suppressed Abeta neurotoxicity, but did not promote the neurotoxicity. Furthermore, PGE(2) ameliorated Abeta-induced apoptotic features such as the condensation of chromatin and the fragmentation of DNA. Abeta increased the influx of Ca(2+) into neurons before cell death. Nimodipine, an inhibitor of the L-type voltage-sensitive calcium channel (L-VSCC), significantly reduced Abeta-potentiated Ca(2+) uptake. On the other hand, there was no effect on the Abeta-induced Ca(2+) influx by an N-VSCC blocker or P/Q-VSCC blockers. Moreover, the inhibitor of L-VSCC suppressed Abeta-induced neuronal cell death, whereas neither an N-VSCC blocker nor P/Q-VSCC blockers affected the neurotoxicity of Abeta. PGE(2) also suppressed the Abeta-induced Ca(2+) influx in a concentration-dependent manner. This study demonstrated that PGE(2) rescues cortical neurons from Abeta-induced apoptosis by reducing Ca(2+) influx in the primary culture. Furthermore, the present study suggested that the inhibition of L-VSCC contributes to the neuroprotective effect of PGE(2).

Synthesis of (-)-5,8-dihydroxy-3R-methyl-2R-(dipropylamino)-1,2,3,4-tetrahydronaphthalene: an inhibitor of beta-amyloid(1-42) aggregation

A concise synthesis of the beta-amyloid(1-42 )aggregation inhibitor (-)-5,8-dihydroxy-3R-methyl-2R-(dipropylamino)-1,2,3,4-tetrahydronaphthalene [(-)-2] has been developed. The key step is a regio- and diastereoselective hydroboration-amination sequence to convert alkene into amine. Enantiomeric resolution was achieved by recrystallization of amine as the dibenzoyl-D-tartaric acid salt. Hydroquinone is a potent inhibitor of the fibrillar aggregation of beta-amyloid as determined in two different assay systems.

Effects of endothelin B receptor agonists on amyloid beta protein (25-35)-induced neuronal cell death

Endothelin (ET), a vasoconstrictive peptide, acts as an anti-apoptotic factor, and endothelin receptor B (ET(B) receptor) is associated with neuronal survival in the brain. In the Alzheimer's disease (AD) brain, accumulation of amyloid beta protein (Abeta) is thought to cause neuronal cell death via apoptosis. In the present study, we investigated effects of ET(B) receptor agonists on Abeta-induced neuronal cell death. In primary cultures of rat cortical neurons, Abeta(25-35) caused neuronal cell death in a concentration- and time-dependent manner. Abeta(25-35)-induced neuronal cell death was accompanied by chromatin condensation and DNA fragmentation, exhibiting apoptotic features. ET-3 and IRL-1620, ET(B) receptor agonists, significantly prevented neurons from undergoing Abeta(25-35)-induced cell death. Prior to cell death, Abeta increased concentration of intracellular Ca(2+) ([Ca(2+)](i)). Nimodipine, an L-type voltage-sensitive Ca(2+) channel (L-VSCC) blocker, suppressed the Abeta-induced Ca(2) influx, and attenuated Abeta-induced neuronal apoptosis. On the other hand, omega-conotoxin GIVA, an N-type VSCC blocker and omega-conotoxin MVIIC and omega-agatoxin IVA, P/Q-type VSCC blockers, had no effect. ET-3 and IRL-1620 significantly blocked Abeta(25-35)-induced Ca(2) influx. Furthermore, BQ788, an ET(B) receptor antagonist, inhibited both an anti-apoptotic effect and an L-VSCC-inactivating effect of ET(B) receptor agonists. In conclusion, ET(B) receptor agonists exhibit a protective effect against neurotoxicity of Abeta. Furthermore, these agonists appear to act as anti-apoptotic factors by blocking of L-VSCCs.

Pro-domain removal in ASP-2 and the cleavage of the amyloid precursor are influenced by pH

BACKGROUND

One of the signatures of Alzheimer's disease is the accumulation of aggregated amyloid protein, Abeta, in the brain. Abeta arises from cleavage of the Amyloid Precursor protein by beta and gamma secretases, which present attractive candidates for therapeutic targeting. Two beta-secretase candidates, ASP-1 and ASP-2, were identified as aspartic proteases, both of which cleave the amyloid precursor at the beta-site. These are produced as immature transmembrane proteins containing a pro-segment.

RESULTS

ASP-2 expressed in HEK293-cells cleaved the Swedish mutant amyloid precursor at different beta-sites at different pHs in vitro. Recent reports show that furin cleaves the pro-peptide of ASP-2, whereas ASP-1 undergoes auto-catalysis. We show that purified recombinant ASP-2 cleaves its own pro-peptide at ph 5 but not pH 8.5 as seen by mass spectrometry, electrophoresis and N-terminal sequencing.

CONCLUSION

We suggest that ASP-2 processing as well as activity are influenced by pH, and hence the cellular localisation of the protein may have profound effects on the production of Abeta. These factors should be taken into consideration in the design of potential inhibitors for these enzymes.

Apolipoprotein E4 potentiates amyloid beta peptide-induced lysosomal leakage and apoptosis in neuronal cells

We assessed the isoform-specific effects of apolipoprotein (apo) E on the response of Neuro-2a cells to the amyloid beta peptide (Abeta1-42). As determined by the intracellular staining pattern and the release of beta-hexosaminidase into the cytosol, apoE4-transfected cells treated with aggregated Abeta1-42 showed a greater tendency toward lysosomal leakage than neo- or apoE3-transfected cells. Abeta1-42 caused significantly greater cell death and more than 2-fold greater DNA fragmentation in apoE4-secreting than in apoE3-secreting or control cells. H2O2 or staurosporine enhanced cell death and apoptosis in apoE4-transfected cells but not in apoE3-transfected cells. A caspase-9 inhibitor abolished the potentiation of Abeta1-42-induced apoptosis by apoE4. Similar results were obtained with conditioned medium from cells secreting apoE3 or apoE4. Cells preincubated for 4 h with a source of apoE3 or apoE4, followed by removal of apoE from the medium and from the cell surface, still exhibited the isoform-specific response to Abeta1-42, indicating that the potentiation of apoptosis required intracellular apoE, presumably in the endosomes or lysosomes. Studies of phospholipid (dimyristoylphosphatidylcholine) bilayer vesicles encapsulating 5-(and-6)-carboxyfluorescein dye showed that apoE4 remodeled and disrupted the phospholipid vesicles to a greater extent than apoE3 or apoE2. In response to Abeta1-42, vesicles containing apoE4 were disrupted to a greater extent than those containing apoE3. These findings are consistent with apoE4 forming a reactive molecular intermediate that avidly binds phospholipid and may insert into the lysosomal membrane, destabilizing it and causing lysosomal leakage and apoptosis in response to Abeta1-42.

Divergent pathways account for two distinct effects of amyloid beta peptides on exocytosis and Ca(2+) currents: involvement of ROS and NF-kappaB

Amyloid peptides (AbetaPs) are implicated in neuronal death associated with Alzheimer's disease. Their toxicity involves disruption cellular Ca(2+) homeostasis, leading to activation of caspases and cell death. Antioxidants can prevent such cell death and show beneficial clinical effects in Alzheimer's disease patients. Using the model neurosecretory cell line, PC12, we have shown that AbetaPs cause enhancement of evoked exocytosis via formation of a Cd(2+) -resistant Ca(2+) influx pathway, and also cause selective, functional up-regulation of current through L-type Ca(2+) channels. The involvement of reactive oxygen species (ROS) in these effects were investigated by examining the ability of various antioxidants to interfere with these responses. Both melatonin and ascorbic acid fully blocked the enhancement of catecholamine secretion caused by application of AbetaP((1-40)), as monitored in real time amperometrically, but inhibition of the transcriptional regulator NF-kappaB with SN-50 did not affect secretion. Enhanced immunofluorescence, observed in AbetaP-treated cells using a monoclonal antibody raised against the N-terminus of AbetaP, was also suppressed by melatonin. Ascorbic acid, melatonin and ebselen also fully prevented augmentation of whole-cell Ca(2+) currents caused by application of AbetaP((1-40)). By contrast, inhibitors of NF-kappaB (sulfasalazine and SN-50) were able to prevent AbetaP induced Ca(2+) channel current enhancement, whilst inhibitors of mitogen-activated protein kinase and protein kinase C could not. Our results indicate that augmentation or induction by AbetaPs of two important, distinct factors regulating Ca(2+) homeostasis is mediated by increased ROS production, but only one of these (up-regulation of native Ca(2+) channels) requires activation of NF-kappaB.

Oral and subcutaneous administration of the glycosaminoglycan C3 attenuates Abeta(25-35)-induced abnormal tau protein immunoreactivity in rat brain

High molecular weight glycosaminoglycans (GAG) and proteoglycans (PG) affect pathological changes of the brain in Alzheimer's disease (AD). PG stimulate the processing and aggregation of amyloid-beta (Abeta), protect the protein from proteolysis, and increase the formation of neurofibrillary tangles by inducing the hyperphosphorylation of tau protein. These effects may be competitively inhibited by GAG. We have studied the effects of orally (by gavage) and subcutaneously (s.c.) administered low molecular weight heparin, C3 (4-10 oligosaccharides; MW = 2.1 kDa; USP value = 12 U/mg), on abnormal tau-2 protein immunoreactivity in the rat hippocampus following a single, unilateral intra-amygdaloid administration of Abeta(25-35). Oral administration of C3 (25 mg/kg; once daily) was initiated 3 days prior to Abeta(25-35) administration, and was continued daily for an additional 14 days. S.c. administration of C3 (2.5 mg/kg, twice daily), was started 3 days prior to, and was continued for 32 days after, Abeta(25-35) administration. Animal brains were subsequently processed for tau-2, ChAT-immunoreactivity, choline acetyltransferase (ChAT) activity and acetylcholinesterase (AChE) activity. Both oral and s.c. administration of C3 attenuated Abeta(25-35) induced appearance of tau-2-immunoreactive (IR) perikarya in the ipsilateral hippocampus (P < 0.05). Hippocampal cholinergic enzyme activity in C3 treated animals was not significantly different from control animals. The present findings suggest that C3 might be used successfully to prevent abnormal tau protein formation in chronic neurologic diseases, such as AD. Moreover, our data demonstrate that the mechanism of this effect does not appear to influence the cholinergic system of the brain.

Effects of S-2474, a novel nonsteroidal anti-inflammatory drug, on amyloid beta protein-induced neuronal cell death

1. The accumulation of amyloid beta protein (Abeta) in the brain is a characteristic feature of Alzheimer's disease (AD). Clinical trials of AD patients with nonsteroidal anti-inflammatory drugs (NSAIDs) indicate a clinical benefit. NSAIDs are presumed to act by suppressing inhibiting chronic inflammation in the brain of AD patients. 2. In the present study, we investigated effects of S-2474 on Abeta-induced cell death in primary cultures of rat cortical neurons. 3. S-2474 is a novel NSAID, which inhibits cyclo-oxygenase-2 (COX-2) and contains the di-tert-butylphenol antioxidant moiety. S-2474 significantly prevented neurons from Abeta(25 - 35)- and Abeta(1 - 40)-induced cell death. S-2474 ameliorated Abeta-induced apoptotic features such as the condensation of chromatin and the fragmentation of DNA completely. 4. Prior to cell death, Abeta(25 - 35) generated prostaglandin D(2) (PGD(2)) and free radicals from neurons. PGD(2) is a product of cyclo-oxygenase (COX), and caused neuronal cell death. 5. S-2474 significantly inhibited the Abeta(25 - 35)-induced generation of PGD(2) and free radicals. 6. The present cortical cultures contained little non-neuronal cells, indicating that S-2474 affected neuronal survival directly, but not indirectly via non-neuronal cells. Both an inhibitory effect of COX-2 and an antioxidant effect might contribute to the neuroprotective effects of S-2474. 7. In conclusion, S-2474 exhibits protective effects against neurotoxicity of Abeta. Furthermore, the present study suggests that S-2474 may possess therapeutic potential for AD via ameliorating degeneration in neurons as well as suppressing chronic inflammation in non-neuronal cells.

New insights on how metals disrupt amyloid beta-aggregation and their effects on amyloid-beta cytotoxicity

Amyloid-beta protein (A beta) aggregates in the brain to form senile plaques. By using thioflavin T, a dye that specifically binds to fibrillar structures, we found that metals such as Zn(II) and Cu(II) normally inhibit amyloid beta-aggregation. Another method for detecting A beta, which does not distinguish the types of aggregates, showed that these metals induce a non-beta-sheeted aggregation, as reported previously. Secondary structural analysis and microscopic studies revealed that metals induced A beta to make non-fibrillar aggregates by disrupting beta-sheet formation. These non-fibrillar A beta aggregates displayed much weaker Congo Red birefringence, and in separate cell culture experiments, were less toxic than self beta-aggregates, as demonstrated by 3-[4,5-dimethylthiazol-2-yl]-2,5-diphenyltetrazolium bromide assay. The toxicity of soluble A beta was enhanced in the presence of Cu(II), which suggests the previously hypothesized role of A beta in generating oxidative stress. Finally, under an acidic condition, similar to that in the inflammation associated with senile plaques, beta-aggregation was robustly facilitated at one specific concentration of Zn(II) in the presence of heparin. However, because a higher concentration of Zn(II) virtually abolished this abnormal phenomenon, and at normal pH any concentrations strongly inhibit beta-aggregation and its associated cytotoxicity, including its anti-oxidative nature we suggest that Zn(II) has an overall protective effect against beta-amyloid toxicity.

Detection of beta-amyloid peptide aggregation using DNA electrophoresis

DNA could readily associate with the aggregated forms of the beta-amyloid peptides beta(1-40) and beta(25-35), giving rise to a shift in the electrophoretic mobility of DNA. As a result, DNA was retained at the top of a 1% agarose gel. In contrast, the electrophoretic mobility of DNA was little influenced by the monomeric forms of beta(1-40) and beta(25-30). DNA from different sources such as lambda phage, Escherichia coli plasmid, and human gene showed similar results. However, the electrophoretic mobility of RNA was shifted by the monomeric beta(1-40) and beta(25-35) as well as by the aggregated beta(1-40) and beta(25-35). The association of DNA with the aggregated beta-amyloid peptides could occur at pH 4-9. The inhibitory action of hemin on beta-amyloid aggregation could be confirmed using the DNA mobility shift assay. These results indicate that the DNA mobility shift assay is useful for kinetic study of beta-amyloid aggregation as well as for testing of agents that might modulate beta-amyloid aggregation.

Approaches to discovery and characterization of inhibitors of amyloid beta-peptide polymerization

Polymerization of the amyloid beta-peptide (Abeta) has been identified as a major feature of the pathogenesis of Alzheimer's disease (AD). Inhibition of the formation of these toxic polymers of Abeta has thus emerged as an approach to developing therapeutics for AD. Techniques for studying Abeta polymerization include the use of fibril nucleation and extension assays in a variety of formats. Detection of polymeric forms of Abeta has been achieved using turbidity, dye binding, light scattering and toxicity among other methods. Direct and indirect methods have been described for the measurement of binding affinities for Abeta fibrils. Imaging techniques include electron microscopy, X-ray diffraction and atomic force microscopy. These techniques have been used to characterize different classes of compounds that inhibit the formation of Abeta polymers. These compounds include dyes such as Congo Red, the antibiotic rifampicin, the anthracycline 4'-iodo-4'-deoxydoxorubicin, and a large variety of Abeta-derived peptides and modified peptides, among other reported inhibitors.

Inositol stereoisomers stabilize an oligomeric aggregate of Alzheimer amyloid beta peptide and inhibit abeta -induced toxicity

Inositol has 8 stereoisomers, four of which are physiologically active. myo-Inositol is the most abundant isomer in the brain and more recently shown that epi- and scyllo-inositol are also present. myo-Inositol complexes with Abeta42 in vitro to form a small stable micelle. The ability of inositol stereoisomers to interact with and stabilize small Abeta complexes was addressed. Circular dichroism spectroscopy demonstrated that epi- and scyllo- but not chiro-inositol were able to induce a structural transition from random to beta-structure in Abeta42. Alternatively, none of the stereoisomers were able to induce a structural transition in Abeta40. Electron microscopy demonstrated that inositol stabilizes small aggregates of Abeta42. We demonstrate that inositol-Abeta interactions result in a complex that is non-toxic to nerve growth factor-differentiated PC-12 cells and primary human neuronal cultures. The attenuation of toxicity is the result of Abeta-inositol interaction, as inositol uptake inhibitors had no effect on neuronal survival. The use of inositol stereoisomers allowed us to elucidate an important structure-activity relationship between Abeta and inositol. Inositol stereoisomers are naturally occurring molecules that readily cross the blood-brain barrier and may represent a viable treatment for AD through the complexation of Abeta and attenuation of Abeta neurotoxic effects.

Beta-amyloid-induced apoptosis of cerebellar granule cells and cortical neurons: exacerbation by selective inhibition of group I metabotropic glutamate receptors

Administration of beta-amyloid fragment 25-35 (Abeta25-35) to cultured rat cerebellar granule cells (CGC) or cortical neurons caused cell death that was characterized by morphological and nuclear changes consistent with apoptosis. Inhibition of NMDA receptors produced a mild exacerbation of Abeta25-35 toxicity in cortical neurons; a similar effect was induced by AMPA/kainate receptor inhibition in CGC. Selective activation of group I metabotropic glutamate receptors (mGluR) by dihyroxyphenylglycine (DHPG) had no effect on Abeta25-35-induced apoptosis in either cell type, and was unaffected by blockade of ionotropic glutamate receptors. In contrast, selective inhibition of group I mGluR by (RS)-1-aminoindan-1,5-dicarboxylic acid (AIDA) exacerbated Abeta toxicity in cortical neurons, whereas this treatment was without effect on CGC. However, AIDA significantly increased Abeta-induced apoptosis in CGC in the presence of either NMDA or AMPA/kainate receptor inhibition; blockade of both ionotropic glutamate receptor classes further increased the exacerbation of apoptosis following treatment with AIDA. These findings suggest that Abeta25-35-induced neuronal injury leads to activation of group I mGluR, which attenuates the resulting apoptosis.

Both oxidative stress-dependent and independent effects of amyloid beta protein are detected by 3-(4,5-dimethylthiazol-2-yl)-2, 5-diphenyltetrazolium bromide (MTT) reduction assay

3-(4,5-Dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) reduction assay has been widely used for evaluating amyloid beta protein (Abeta) toxicity. However, the potency of Abeta in inhibiting cellular MTT reduction and the underlying mechanism have been reported with some discrepancies among researchers. To understand what makes such discrepancies, the effect of Abeta detected by MTT reduction assay was re-examined in detail by using cultured rat hippocampal neurons. Micromolar concentrations (>10 microM) of Abeta caused a decrease in cell viability, which resulted in a decrease in MTT reduction per well regardless of assay time. The micromolar Abeta-induced decrease of cellular MTT reduction was significantly attenuated by antioxidants (catalase, propyl gallate or Trolox). On the other hand, nanomolar Abeta did not affect cellular MTT reduction activity at an initial stage of assay (<1 h), and decreased the total production of MTT formazan by accelerating the exocytosis of MTT formazan when MTT assay was performed for a longer time (>2 h). The assay time-dependent, nanomolar Abeta-induced decrease of cellular MTT reduction was not at all affected by antioxidants. Furthermore, subtoxic concentration of H2O2 failed to mimic the effect of nanomolar Abeta on MTT reduction. These results indicate that micromolar Abeta-induced, oxidative cell death is detected by MTT assay regardless of assay time, whereas nanomolar Abeta-induced acceleration of MTT formazan exocytosis is not mediated by oxidative stress and detected only when MTT assay is performed for a longer time. The time of MTT assay should be properly chosen depending on the purpose of the study.

Abnormalities of protein kinases in neurodegenerative diseases

In neurodegenerative diseases such as ALS and AD there is evidence for abnormal regulation of protein kinases. In these diseases, altered activities and protein levels of several specific kinases suggest that abnormal phosphorylation is present and this aberrant phosphorylation may be involved in the pathogenesis of these diseases. The observation that regulation of the NMDA receptor ion channel is altered in tissue from ALS patients may arise from the abnormal phosphorylation state of the protein kinase regulating NMDA receptor function. Whether the abnormalities of these protein kinases is a primary event leading to altered receptor regulation or vice versa is still poorly understood. The seemingly multiple pathogenic mechanisms of ALS and AD create complexity in assessing a primary cause that may lead to cell death. The mechanisms causing cell death (apoptosis or necrosis) may be overlapping with integrated events among the components interacting and contributing to a final pathway for neuron death. Thus, evidence of impairment in protein kinase signalling in these diseases may be a primary cause, a secondary event, or a compensatory mechanism. To further study this issue, different model systems could be beneficial to obtain a better understanding of these diseases.