Co-injection of beta-amyloid with ibotenic acid induces synergistic loss of rat hippocampal neurons

Sink or swim: Does a worm paralysis phenotype hold clues to neurodegenerative disease?

Receiving a neurodegenerative disease (NDD) diagnosis, such as Alzheimer's disease, Parkinson's disease, Huntington's disease, or amyotrophic lateral sclerosis, is devastating, particularly given the limited options for treatment. Advances in genetic technologies have allowed for efficient modeling of NDDs in animals and brought hope for new disease-modifying medications. The complexity of the mammalian brain and the costs and time needed to identify and develop therapeutic leads limits progress. Modeling NDDs in invertebrates, such as the fruit fly Drosophila melanogaster and the nematode Caenorhabditis elegans, offers orders of magnitude increases in speed of genetic analysis and manipulation, and can be pursued at substantially reduced cost, providing an important, platform complement and inform research with mammalian NDD models. In this review, we describe how our efforts to exploit C. elegans for the study of neural signaling and health led to the discovery of a paralytic phenotype (swimming-induced paralysis) associated with altered dopamine signaling and, surprisingly, to the discovery of a novel gene and pathway whose dysfunction in glial cells triggers neurodegeneration. Research to date on swip-10 and its putative mammalian ortholog MBLAC1, suggests that a tandem analysis will offer insights into NDD mechanisms and insights into novel, disease-modifying therapeutics.

Spontaneous and familial models of Alzheimer's disease: Challenges and advances in preclinical research

Alzheimer's disease (AD) is a debilitating neurodegenerative disorder that is progressive and irreversible in nature. Even after decades of dedicated research and paradigm-shifting hypotheses of AD etiology, very few well-founded credible improvements have been foreseen in understanding the actual underlying mechanisms involved in the development of the disorder. As for any disease to be well-comprehended, AD also requires optimal modelling strategies, which will then pave way for effective therapeutic interventions. Most of the clinical trials and research towards better treatment of AD fail in translation, due to the inefficacy of explored animal models to mimic the actual AD pathology, precisely. The majority of the existing AD models are developed based on the mutations found in the familial form of AD (fAD) which accounts for less than 5 % of the incidence of AD. Further, the investigations also face more challenges due to the additional complexities and lacunae found in etiology of sporadic form of AD (sAD), which accounts for 95 % of total AD. This review illustrates the gaps found in different models of AD, both sporadic and familial variants with additional focus on recent avenues for accurate simulation of AD pathology using in vitro and chimeric AD models.

Influence of amyloid beta on impulse spiking of isolated hippocampal neurons

One of the signs of Alzheimer's disease (AD) is the formation of β-amyloid plaques, which ultimately lead to the dysfunction of neurons with subsequent neurodegeneration. Although extensive researches have been conducted on the effects of different amyloid conformations such as oligomers and fibrils on neuronal function in isolated cells and circuits, the exact contribution of extracellular beta-amyloid on neurons remains incompletely comprehended. In our experiments, we studied the effect of β-amyloid peptide (Aβ1-42) on the action potential (APs) generation in isolated CA1 hippocampal neurons in perforated patch clamp conditions. Our findings demonstrate that Aβ1-42 affects the generation of APs differently in various hippocampal neurons, albeit with a shared effect of enhancing the firing response of the neurons within a minute of the start of Aβ1-42 application. In the first response type, there was a shift of 20-65% toward smaller values in the firing threshold of action potentials in response to inward current. Conversely, the firing threshold of action potentials was not affected in the second type of response to the application of Aβ1-42. In these neurons, Aβ1-42 caused a moderate increase in the frequency of spiking, up to 15%, with a relatively uniform increase in the frequency of action potentials generation regardless of the level of input current. Obtained data prove the absence of direct short-term negative effect of the Aβ1-42 on APs generation in neurons. Even with increasing the APs generation frequency and lowering the neurons' activation threshold, neurons were functional. Obtained data can suggest that only the long-acting presence of the Aβ1-42 in the cell environment can cause neuronal dysfunction due to a prolonged increase of APs firing and predisposition to this process.

Dimethyl Fumarate is a Potential Therapeutic Option for Alzheimer's Disease

BACKGROUND

Dimethyl fumarate (DMF) has been approved for clinical treatment of multiple sclerosis based on its antioxidant and anti-inflammatory effects by activating the Nrf2 pathway. Since both oxidative stress and inflammation are involved in Alzheimer's disease (AD), DMF is a potential therapeutic option for AD.

OBJECTIVE

This study aims to test the therapeutic effects of DMF on AD model mice and to reveal its underlying molecular mechanisms.

METHODS

Cell viability assay and in vitro immunofluorescence imaging were used to evaluate the antioxidant effect of DMF on embryonic mouse hippocampal neurons. Behavioral test and brain magnetic resonance imaging were used to assess the therapeutic effects of DMF on spatial learning and memory as well as hippocampal volume in AD model mice with and without Nrf2 knockdown. Western blotting was used to analyze the expression of antioxidant enzymes and molecules associated with AD-related pathological pathways.

RESULTS

DMF inhibits reactive oxygen species overproduction and protects neurons without Nrf2 knockdown from death. DMF reduces amyloid-β induced memory impairment and hippocampal atrophy in AD model mice rather than in Nrf2 knockdown AD mice. DMF delays the progression of AD by activating the Nrf2 pathway to enhance the expression of downstream antioxidant enzymes and inhibits lipid peroxidation, apoptosis, inflammation, mitochondrial dysfunction and amyloid-β deposition.

CONCLUSION

These results indicate that DMF is a potential therapeutic option for AD through its antioxidant, anti-inflammatory, anti-apoptotic, and other anti-AD effects by activating the Nrf2 pathway.

Preclinical Models of Alzheimer's Disease: Relevance and Translational Validity

The only drugs currently approved for the treatment of Alzheimer's Disease (AD) are four acetylcholinesterase inhibitors and the NMDA antagonist memantine. Apart from these drugs, which have minimal to no clinical benefit, the 40-year search for effective therapeutics to treat AD has resulted in a clinical failure rate of 100% not only for compounds that prevent brain amyloid deposition or remove existing amyloid plaques but also those acting by a variety of other putative disease-associated mechanisms. This indicates that the preclinical data generated from current AD targets to support the selection, optimization, and translation of new chemical entities (NCEs) and biologics to clinical trials is seriously compromised. While many of these failures reflect flawed hypotheses or a lack of adequate characterization of the preclinical pharmacodynamic and pharmacokinetic (PD/PK) properties of lead NCEs-including their bioavailability and toxicity-the conceptualization, validation, and interrogation of the current animal models of AD represent key limitations. The overwhelming majority of these AD models are transgenic, based on aspects of the amyloid hypothesis and the genetics of the familial form of the disease. As a result, these generally lack construct and predictive validity for the sporadic form of the human disease. The 170 or so transgenic models, perhaps the largest number ever focused on a single disease, use rodents, mainly mice, and in addition to amyloid also address aspects of tau causality with more complex multigene models including other presumed causative factors together with amyloid. This overview discusses the current animal models of AD in the context of both the controversies surrounding the causative role of amyloid in the disease and the need to develop validated models of cognitive function/dysfunction that more appropriately reflect the phenotype(s) of human aged-related dementias. © 2019 by John Wiley & Sons, Inc.

An outline for the pharmacological effect of icariin in the nervous system

Icariin is a major active component of the traditional herb Epimedium, also known as Horny Goat Weed. It has been extensively studied throughout the past several years and is known to exert anti-oxidative, anti-neuroinflammatory, and anti-apoptotic effects. It is now being considered as a potential therapeutic agent for a wide variety of disorders, ranging from neoplasm to cardiovascular disease. More recent studies have shown that icariin exhibits potential preventive and/or therapeutic effects in the nervous system. For example, icariin can prevent the production of amyloid β (1-42) and inhibit the expression of amyloid precursor protein (APP) and β-site APP cleaving enzyme 1 (BACE-1) in animal models of Alzheimer's disease (AD). Icariin has been shown to mitigate pro-inflammatory responses of microglia in culture and in animal models of cerebral ischemia, depression, Parkinson's disease (PD), and multiple sclerosis (MS). Icariin also prevents the neurotoxicity induced by hydrogen peroxide (H₂O₂), endoplasmic reticulum (ER) stress, ibotenic acid, and homocysteine. In addition, icariin is implicated in facilitating learning and memory in both normal aging animals and disease models. To date, we still have no consolidated source of knowledge about the pharmacological effects of icariin in the nervous system, though its roles in other tissues have been reviewed in recent years. Here, we summarize the pharmacological development of icariin as well as its possible mechanisms in prevention and/or therapy of disorders afflicting the nervous system in hope of expanding the knowledge about the preventive and/or therapeutic effect of icariin in brain disorders.

Toxin-Induced Experimental Models of Learning and Memory Impairment

Animal models for learning and memory have significantly contributed to novel strategies for drug development and hence are an imperative part in the assessment of therapeutics. Learning and memory involve different stages including acquisition, consolidation, and retrieval and each stage can be characterized using specific toxin. Recent studies have postulated the molecular basis of these processes and have also demonstrated many signaling molecules that are involved in several stages of memory. Most insights into learning and memory impairment and to develop a novel compound stems from the investigations performed in experimental models, especially those produced by neurotoxins models. Several toxins have been utilized based on their mechanism of action for learning and memory impairment such as scopolamine, streptozotocin, quinolinic acid, and domoic acid. Further, some toxins like 6-hydroxy dopamine (6-OHDA), 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) and amyloid-β are known to cause specific learning and memory impairment which imitate the disease pathology of Parkinson's disease dementia and Alzheimer's disease dementia. Apart from these toxins, several other toxins come under a miscellaneous category like an environmental pollutant, snake venoms, botulinum, and lipopolysaccharide. This review will focus on the various classes of neurotoxin models for learning and memory impairment with their specific mechanism of action that could assist the process of drug discovery and development for dementia and cognitive disorders.

Hippocampal Injections of Oligomeric Amyloid β-peptide (1-42) Induce Selective Working Memory Deficits and Long-lasting Alterations of ERK Signaling Pathway

Increasing evidence suggests that abnormal brain accumulation of soluble rather than aggregated amyloid-β1-42 oligomers (Aβo(1-42)) plays a causal role in Alzheimer's disease (AD). However, as yet, animal's models of AD based on oligomeric amyloid-β1-42 injections in the brain have not investigated their long-lasting impacts on molecular and cognitive functions. In addition, the injections have been most often performed in ventricles, but not in the hippocampus, in spite of the fact that the hippocampus is importantly involved in memory processes and is strongly and precociously affected during the early stages of AD. Thus, in the present study, we investigated the long-lasting impacts of intra-hippocampal injections of oligomeric forms of Aβo(1-42) on working and spatial memory and on the related activation of ERK1/2. Indeed, the extracellular signal-regulated kinase (ERK) which is involved in memory function had been found to be activated by amyloid peptides. We found that repeated bilateral injections (1injection/day over 4 successive days) of oligomeric forms of Aβo(1-42) into the dorsal hippocampus lead to long-lasting impairments in two working memory tasks, these deficits being observed 7 days after the last injection, while spatial memory remained unaffected. Moreover, the working memory deficits were correlated with sustained impairments of ERK1/2 activation in the medial prefrontal cortex (mPFC) and the septum, two brain areas tightly connected with the hippocampus and involved in working memory. Thus, our study is first to evidence that sub-chronic injections of oligomeric forms of Aβo(1-42) into the dorsal hippocampus produces the main sign of cognitive impairments corresponding to the early stages of AD, via long-lasting alterations of an ERK/MAPK pathway in an interconnected brain networks.

Comparative study of the neuroprotective and nootropic activities of the carboxylate and amide forms of the HLDF-6 peptide in animal models of Alzheimer's disease

A comparative study of the neuroprotective and nootropic activities of two pharmaceutical substances, the HLDF-6 peptide (HLDF-6-OH) and its amide form (HLDF-6-NH2), was conducted. The study was performed in male rats using two models of a neurodegenerative disorder. Cognitive deficit in rats was induced by injection of the beta-amyloid fragment 25-35 (βA 25-35) into the giant-cell nucleus basalis of Meynert or by coinjection of βA 25-35 and ibotenic acid into the hippocampus. To evaluate cognitive functions in animals, three tests were used: the novel object recognition test, the conditioned passive avoidance task and the Morris maze. Comparative analysis of the data demonstrated that the neuroprotective activity of HLDF-6-NH2, evaluated by improvement of cognitive functions in animals, surpassed that of the native HLDF-6-OH peptide. The greater cognitive/ behavioral effects can be attributed to improved kinetic properties of the amide form of the peptide, such as the character of biodegradation and the half-life time. The effects of HLDF-6-NH2 are comparable to, or exceed, those of the reference compounds. Importantly, HLDF-6-NH2 exerts its effects at much lower doses than the reference compounds.

GM1-Modified Lipoprotein-like Nanoparticle: Multifunctional Nanoplatform for the Combination Therapy of Alzheimer's Disease

Alzheimer's disease (AD) exerts a heavy health burden for modern society and has a complicated pathological background. The accumulation of extracellular β-amyloid (Aβ) is crucial in AD pathogenesis, and Aβ-initiated secondary pathological processes could independently lead to neuronal degeneration and pathogenesis in AD. Thus, the development of combination therapeutics that can not only accelerate Aβ clearance but also simultaneously protect neurons or inhibit other subsequent pathological cascade represents a promising strategy for AD intervention. Here, we designed a nanostructure, monosialotetrahexosylganglioside (GM1)-modified reconstituted high density lipoprotein (GM1-rHDL), that possesses antibody-like high binding affinity to Aβ, facilitates Aβ degradation by microglia, and Aβ efflux across the blood-brain barrier (BBB), displays high brain biodistribution efficiency following intranasal administration, and simultaneously allows the efficient loading of a neuroprotective peptide, NAP, as a nanoparticulate drug delivery system for the combination therapy of AD. The resulting multifunctional nanostructure, αNAP-GM1-rHDL, was found to be able to protect neurons from Aβ(1-42) oligomer/glutamic acid-induced cell toxicity better than GM1-rHDL in vitro and reduced Aβ deposition, ameliorated neurologic changes, and rescued memory loss more efficiently than both αNAP solution and GM1-rHDL in AD model mice following intranasal administration with no observable cytotoxicity noted. Taken together, this work presents direct experimental evidence of the rational design of a biomimetic nanostructure to serve as a safe and efficient multifunctional nanoplatform for the combination therapy of AD.

Generating local amyloidosis in mice by the subcutaneous injection of human insulin amyloid fibrils

Localized deposits of amyloid structures are observed in various pathological conditions. One example of when local amyloidosis occurs is following repeated insulin injections in diabetic patients. The present study aimed to simulate the same condition in mice. To obtain the amyloid structures, regular insulin was incubated at 57°C for 24 h. The subsequently formed amyloid fibrils were analyzed using the Congo red absorbance test, as well as transmission electron microscopy images, and then injected into mice once per day for 21 consecutive days. Firm waxy masses were developed following this period, which were excised, prepared as thin sections and stained with hematoxylin and eosin, Congo red and Sudan black. Histological examination revealed that these masses contained adipose cells and connective tissue, in which amyloid deposition was visible. Thus, localized amyloidosis was obtained by the subcutaneous injection of insulin fibrils. The present results may be of further use in the development of models of amyloid tumors.

Spontaneous and induced nontransgenic animal models of AD: modeling AD using combinatorial approach

Alzheimer's disease (AD), the most common neurodegenerative and dementing disorder, is characterized by extracellular amyloid deposition, intracellular neurofibrillary tangle formation, and neuronal loss. We are still behind in AD research in terms of knowledge regarding understanding its pathophysiology and designing therapeutics because of the lack of an accurate animal model for AD. A complete animal model of AD should imitate all the cognitive, behavioral, and neuropathological features of the disease. Partial models are currently in use, which only mimic specific and not all of the components of AD pathology. Currently the transgenic animals are the popular models for AD research, but different genetic backgrounds of these transgenic animals remain a major confounding factor. This review attempts to summarize the current literature on nontransgenic animal models of AD and to highlight the potential of exploiting spontaneous and induced animal models for neuropathological, neurochemical, neurobehavioral, and neuroprotective studies of AD.

Lactoferrin-modified PEG-co-PCL nanoparticles for enhanced brain delivery of NAP peptide following intranasal administration

Development of effective non-invasive drug delivery systems is of great importance to the treatment of Alzheimer's diseases and has made great progress in recent years. In this work, lactoferrin (Lf), a natural iron binding protein, whose receptor is highly expressed in both respiratory epithelial cells and neurons is here utilized to facilitate the nose-to-brain drug delivery of neuroprotection peptides. The Lf-conjugated PEG-PCL nanoparticle (Lf-NP) was constructed via a maleimide-thiol reaction with the Lf conjugation confirmed by CBQCA Protein Quantitation and XPS analysis. Other important parameters such as particle size distribution, zeta potential and in vitro release of fluorescent probes were also characterized. Compared with unmodified nanoparticles (NP), Lf-NP exhibited a significantly enhanced cellular accumulation in 16HBE14o-cells through both caveolae-/clathrin-mediated endocytosis and direct translocation. Following intranasal administration, Lf-NP facilitated the brain distribution of the coumarin-6 incorporated with the AUC0-8h in rat cerebrum (with hippocampus removed), cerebellum, olfactory tract, olfactory bulb and hippocampus 1.36, 1.53, 1.70, 1.57 and 1.23 times higher than that of coumarin-6 carried by NP, respectively. Using a neuroprotective peptide - NAPVSIPQ (NAP) as the model drug, the neuroprotective and memory improvement effect of Lf-NP was observed even at lower dose than that of NP in a Morris water maze experiment, which was also confirmed by the evaluation of acetylcholinesterase, choline acetyltransferase activity and neuronal degeneration in the mice hippocampus. In conclusion, Lf-NP may serve as a promising nose-to-brain drug delivery carrier especially for peptides and proteins.

Mitochondrial ferritin attenuates β-amyloid-induced neurotoxicity: reduction in oxidative damage through the Erk/P38 mitogen-activated protein kinase pathways

AIMS

Mitochondrial ferritin (MtFt), which was recently discovered, plays an important role in preventing neuronal damage in 6-hydroxydopamine-induced Parkinsonism by maintaining mitochondrial iron homeostasis. Disruption of iron regulation also plays a key role in the etiology of Alzheimer's disease (AD). To explore the potential neuroprotective roles of MtFt, rats and cells were treated with Aβ(25-35) to establish an AD model.

RESULTS

We report that knockdown of MtFt expression significantly enhanced Aβ(25-35)-induced neurotoxicity as shown by dysregulation of iron homeostasis, enhanced oxidative stress, and increased cell apoptosis. Opposite results were obtained when MtFt was overexpressed in SH-SY5Y cells prior to treatment with Aβ(25-35). Further, MtFt inhibited Aβ(25-35)-induced P38 mitogen-activated protein kinase and activated extracellular signal-regulated kinase (Erk) signaling.

INNOVATION

MtFt attenuated Aβ(25-35)-induced neurotoxicity and reduced oxidative damage through Erk/P38 kinase signaling.

CONCLUSION

Our results show a protective role of MtFt in AD and suggest that regulation of MtFt expression in neuronal cells may provide a new neuroprotective strategy for AD.

Enhancement of nose-to-brain delivery of basic fibroblast growth factor for improving rat memory impairments induced by co-injection of β-amyloid and ibotenic acid into the bilateral hippocampus

Basic fibroblast growth factor (bFGF) delivery to the brain of animals appears to be an emerging potential therapeutic approach to neurodegenerative diseases, such as Alzheimer's disease (AD). The intranasal route of administration could provide an alternative to intracerebroventricular infusion. A nasal spray of bFGF had been developed previously and the objective of the present study was to investigate whether bFGF nasal spray could enhance brain uptake of bFGF and ameliorate memory impairment induced by co-injection of β-amyloid(25-35) and ibotenic acid into bilateral hippocampus of rats. The results of brain uptake study showed that the AUC(0-12h) of bFGF nasal spray in olfactory bulb, cerebrum, cerebellum and hippocampus was respectively 2.47, 2.38, 2.56 and 2.19 times that of intravenous bFGF solution, and 1.11, 1.95, 1.40 and 1.93 times that of intranasal bFGF solution, indicating that intranasal administration of bFGF nasal spray was an effective means of delivering bFGF to the brain, especially to cerebrum and hippocampus. In Morris water maze tasks, intravenous administration of bFGF solution at high dose (40 μg/kg) showed little improvement on spatial memory impairment. In contrast, bFGF solution of the same dose following intranasal administration could significantly ameliorate spatial memory impairment. bFGF nasal spray obviously improved spatial memory impairment even at a dose half (20 μg/kg) of bFGF solution, recovered their acetylcholinesterase and choline acetyltransferase activity to the sham control level, and alleviated neuronal degeneration in rat hippocampus, indicating neuroprotective effects on the central nerve system. In a word, bFGF nasal spray may be a new formulation of great potential for treating AD.

A comparative study of curcuminoids to measure their effect on inflammatory and apoptotic gene expression in an Aβ plus ibotenic acid-infused rat model of Alzheimer's disease

Alzheimer's disease (AD) is a neurodegenerative disorder, which depicts features of chronic inflammatory conditions resulting in cellular death and has limited therapeutic options. We aimed to explore the effect of a curcuminoid mixture and its individual components on inflammatory and apoptotic genes expression in AD using an Aβ+ibotenic acid-infused rat model. After 5 days of treatment with demethoxycurcumin, hippocampal IL-1β levels were decreased to 118.54 ± 47.48 and 136.67 ± 31.96% respectively at 30 and 10mg/kg, compared with the amyloid treated group (373.99 ± 15.28%). After 5 days of treatment, the curcuminoid mixture and demethoxycurcumin effectively decreased GFAP levels in the hippocampus. When studied for their effect on apoptotic genes expression, the curcuminoid mixture and bisdemethoxycurcumin effectively decreased caspase-3 level in the hippocampus after 20 days of treatment, where bisdemethoxycurcumin showed a maximal rescuing effect (92.35 ± 3.07%) at 3mg/kg. The curcuminoid mixture at 30 mg/kg decreased hippocampal FasL level to 70.56 ± 3.36% after 5 days of treatment and 19.01 ± 2.03% after 20 days. In the case of Fas receptor levels, demethoxycurcumin decreased levels after 5 days of treatment with all three doses showing a maximal effect (189.76 ± 15.01%) at 10mg/kg. Each compound was effective after 20 days in reducing Fas receptor levels in the hippocampus. This study revealed the important effect of curcuminoids on genes expression, showing that, each component of the curcuminoid mixture distinctly affects gene expression, thus highlighting the therapeutic potential of curcuminoids in AD.

[Identification in the rat olfactory epithelium new subgroup YM-1 chitinase-like protein]

Novel protein with a molecular mass of ~43 kDa from rat olfactory epithelium in pathophysiological conditions was discovered. Its amino acid sequence and affiliation with the family 18 glycohydrolase subgroup of chitinase-like proteins YM-1 were determined.

Curcuminoids enhance memory in an amyloid-infused rat model of Alzheimer's disease

Alzheimer's disease (AD) is a neurodegenerative disease. There are a limited number of therapeutic options available for the treatment of AD. Curcuminoids (a mixture of bisdemethoxycurcumin, demethoxycurcumin and curcumin) is the main chemical constituent found in turmeric, a well known curry spice, having potential in the treatment of AD. The objective of this study was to investigate the effects of curcuminoid mixture and individual constituents on spatial learning and memory in an amyloid-beta (Abeta) peptide-infused rat model of AD and on the expression of PSD-95, synaptophysin and camkIV. Curcuminoid mixture showed a memory-enhancing effect in rats displaying AD-like neuronal loss only at 30 mg/kg, whereas individual components were effective at 3-30 mg/kg. A shorter duration treatment with test compounds showed that the curcuminoid mixture and bisdemethoxycurcumin increased PSD-95 expression in the hippocampus at 3-30 mg/kg, with maximum effect at a lower dose (3 mg/kg) with respective values of 470.5 and 587.9%. However, after a longer duration treatment, two other compounds (demethoxycurcumin and curcumin) also increased PSD-95 to 331.7 and 226.2% respectively at 30 mg/kg. When studied for their effect on synaptophysin in the hippocampus after the longer duration treatment, the curcuminoid mixture and all three individual constituents increased synaptophysin expression. Of these, demethoxycurcumin was the most effective showing a 350.1% increase (P<0.01) at 30 mg/kg compared to the neurotoxin group. When studied for their effect on camkIV expression after longer treatment in the hippocampus, only demethoxycurcumin at 30 mg/kg increased levels to 421.2%. These compounds salvaged PSD-95, synaptophysin and camkIV expression levels in the hippocampus in the rat AD model, which suggests multiple target sites with the potential of curcuminoids in spatial memory enhancing and disease modifying in AD.

TGF-β1 pathway as a new target for neuroprotection in Alzheimer's disease

Alzheimer's disease (AD) is a neurodegenerative disorder that affects more than 37 million people worldwide. Current drugs for AD are only symptomatic, but do not interfere with the underlying pathogenic mechanisms of the disease. AD is characterized by the presence of ß-amyloid (Aβ) plaques, neurofibrillary tangles, and neuronal loss. The identification of the molecular determinants underlying AD pathogenesis is a fundamental step to design new disease-modifying drugs. Recently, a specific impairment of transforming-growth-factor-β1 (TGF-β1) signaling pathway has been demonstrated in AD brain. The deficiency of TGF-β1 signaling has been shown to increase both Aβ accumulation and Aβ-induced neurodegeneration in AD models. The loss of function of TGF-ß1 pathway seems also to contribute to tau pathology and neurofibrillary tangle formation. Growing evidence suggests a neuroprotective role for TGF-β1 against Aβ toxicity both in vitro and in vivo models of AD. Different drugs, such as lithium or group II mGlu receptor agonists are able to increase TGF-β1 levels in the central nervous system (CNS), and might be considered as new neuroprotective tools against Aβ-induced neurodegeneration. In the present review, we examine the evidence for a neuroprotective role of TGF-β1 in AD, and discuss the TGF-β1 signaling pathway as a new pharmacological target for the treatment of AD.

BEHAVIORAL AND NEUROCHEMICAL EFFECTS OF THE INTRAHIPPOCAMPAL CO-INJECTION OF ß-AMYLOID PROTEIN1-40 AND IBOTENIC ACID IN RATS

The authors investigated the effects of bilateral intrahippocampal co-injection of Abeta1-40 (4 microg for each side) with ibotenic acid (Ibo, 2 microg for each side) on rats' performance in the open field behavior, Y-maze, and passive avoidance task, and also examined some neurochemical changes in hippocampus two weeks after the co-injection. The results showed that the co-injection of Abeta1-40 with Ibo induced a decrease in exploratory activity and a significant decline in learning-memory ability of the tested rats (p < .01). The neurochemistry changes induced by the co-injection included a significant decreased in membrane fluidity of hippocampal mitochondria (p < .01), a significant decrease in the activity of SOD (p < .01), and a remarkable increase in the content of MDA (p < .01). These results suggest that the co-injection of Abeta1-40 with Ibo may induce an increase of hippocampal damage by peroxidation, and a serious learning and memory impairment of the rats. The results also suggest that the co-injection of Abeta1-40 with Ibo may provide a useful animal model for Alzheimer's disease (AD) research.

TGF-beta 1 protects against Abeta-neurotoxicity via the phosphatidylinositol-3-kinase pathway

beta-Amyloid (A beta) injection into the rat dorsal hippocampus had a small neurotoxic effect that was amplified by i.c.v. injection of SB431542, a selective inhibitor of transforming growth factor-beta (TGF-beta) receptor. This suggested that TGF-beta acts as a factor limiting A beta toxicity. We examined the neuroprotective activity of TGF-beta1 in pure cultures of rat cortical neurons challenged with A beta. Neuronal death triggered by A beta is known to proceed along an aberrant re-activation of the cell cycle, and involves late beta-catenin degradation and tau hyperphosphorylation. TGF-beta1 was equally protective when added either in combination with, or 6 h after A beta. Co-added TGF-beta1 prevented A beta-induced cell cycle reactivation, whereas lately added TGF-beta1 had no effect on the cell cycle, but rescued the late beta-catenin degradation and tau hyperphosphorylation. The phosphatidylinositol-3-kinase (PI-3-K) inhibitor, LY294402, abrogated all effects. Thus, TGF-beta1 blocks the whole cascade of events leading to A beta neurotoxicity by activating the PI-3-K pathway.

The effects of chronic estradiol treatment on working memory deficits induced by combined infusion of beta-amyloid (1-42) and ibotenic acid

Estrogen limits in vitro neuron death induced by application of beta-amyloid, the cytotoxic peptide linked to Alzheimer's disease. However, the ability of estrogen to protect neurons and preserve cognitive function in vivo following exposure to beta-amyloid has not been demonstrated. Our objective was to evaluate the potential of estrogen to reduce spatial working memory deficits in female rats induced by administration of a neurotoxic form of beta-amyloid in combination with the excitotoxin, ibotenic acid. The interaction of beta-amyloid with excitotoxic factors may underlie cognitive deficits associated with Alzheimer's disease. Therefore, to create an experimental model typical of early Alzheimer's disease a low dose of ibotenic acid was administered with beta-amyloid into the dorsal hippocampus. Ovariectomized rats were implanted subcutaneously with Silastic capsules that produce physiological levels of 17beta-estradiol 10 days before bilateral intrahippocampal injections of aggregated beta-amyloid (1-42) and ibotenic acid. Capsules remained in situ throughout behavioral testing. When tested 3-10 weeks after neurotoxin treatment, females without estrogen capsules exhibited delay-dependent impairments in working memory performance on a water maze and a radial arm maze. Females treated with estrogen and combined neurotoxins displayed working memory performance comparable to unlesioned females on both tasks. Neurotoxin treatment increased immunoreactivity for glial fibrillary acidic protein but this measure was unaffected by estradiol treatment indicating that estrogen did not limit glial proliferation. Results indicate that estrogen prevented deficits in spatial working memory induced by neurotoxin treatments intended to mimic the pathology of early Alzheimer's disease.

Amyloid beta-protein potentiates tunicamycin-induced neuronal death in organotypic hippocampal slice cultures

We have assessed amyloid beta protein (Abeta)-induced neurotoxicity, with and without added tunicamycin (TM), an inhibitor of N-glycosylation in the endoplasmic reticulum (ER), in rat organotypic hippocampal slice cultures (OHCs). In the rat OHCs cultured for 3 weeks, there was little neurotoxicity after treatment with Abeta(25-35) (25 microM) alone for 48 h. However, with TM alone, concentration-dependent neuronal death was observed at concentrations between 20 and 80 microg/mL. When amyloid-beta protein was combined with tunicamycin (Abeta+TM), cell death was more acute than with TM alone. Western blot analysis revealed that calpain activity and the active forms of caspase-12 and caspase-3 was increased after exposure to Abeta+TM as compared with exposure to TM alone. In contrast, the levels of glucose regulated protein (GRP)94, GRP78 and C/EBP homologous protein (CHOP) were not changed in the presence of Abeta. Abeta potentiation of TM neurotoxicity was reversibly blocked by S-allyl-L-cysteine (SAC), an organosulfur compound purified from aged garlic extract, and the L-type calcium channel blocker, nifedipine, in a restricted neuronal area of the OHCs. Simultaneously applied SAC also reversed the increases in calpain activity and the active forms of caspase-12 and caspase-3 by Abeta+TM with no change in the increased levels of GRP94, GRP78 and CHOP. These data indicate that Abeta facilitates the calpain-caspase-12-caspase-3 pathway, thus potentiating TM-induced neuronal death in the hippocampus.

Suppressive Effects of Melatonin on Amyloid-β-induced Glial Activation in Rat Hippocampus

BACKGROUND

Growing evidence indicates that activated glia, as a result of chronic inflammation, are associated with amyloid-beta peptide (Abeta) deposits in the brain of Alzheimer's disease (AD) patients. The purpose of the present study was to investigate, in vivo, the effects of melatonin on glia activation, which may contribute to improved learning and memory in amnesic rats induced by amyloid-beta peptide 25-35 (Abeta25-35).

METHODS

We examined cognitive function using the Morris water maze test. Expression of interleukin 1alpha (IL-1alpha) or complement 1q (C1q) in rat hippocampal tissue was determined by immunohistochemistry.

RESULTS

It was found that Abeta25-35 injected into rat hippocampus induced an impairment in learning and memory and a marked increase of positive glial cells expressing IL-1alpha and C1q in hippocampus, compared with the controls. This suggests that glial activation triggered by Abeta25-35 parallels the dysfunction of learning and memory. Melatonin, at doses of 0.01, 0.1, and 1 mg/kg (i.g. for 10 days), improved learning and memory of rats treated with Abeta25-35. Cells expressing IL-1alpha and C1q were significantly decreased in hippocampus by pretreatment with melatonin at doses of 0.1 mg/kg and 1 mg/kg, but not at the dose of 0.01 mg/kg.

CONCLUSIONS

Our data indicate that melatonin inhibited expressions of proinflammatory factors, which may contribute to improvement of learning and memory function in AD.

Protective effects and mechanism of total coptis alkaloids on A β25–35 induced learning and memory dysfunction in rats

OBJECTIVE

To observe the effect of total coptis alkaloids (TCA) on beta -amyloid peptide (A beta 25-35) induced learning and memory dysfunction in rats, and to explore its mechanism.

METHODS

Forty male Wistar rats were randomly divided into four groups: the control group, the model group, the TCA low dose (60 mg/kg) group and the TCA high dose (120 mg/kg) group, 10 in each. A beta 25-35 (5microl, 2 microg/microl) was injected into bilateral hippocampi of each rat to induce learning and memory dysfunction. TCA were administered through intragavage for consecutive 15 days. Morris Water Maze test was used to assess the impairment of learning and memory; concentration of malondialdehyde (MDA) in cerebral cortex was determined by thiobarbituric acid reactive substance to indicate the level of lipid peroxidation in brain tissues; activity of manganese-superoxide dismutase (Mn-SOD) in cerebral cortex was determined by xanthine-oxidase to indicate the activity of the enzyme; and NF- kappa B protein expression in cerebral cortex was measured by SP immunohistochemistry.

RESULTS

(1) Morris Water Maze test showed that, during the 4 consecutive days of acquisition trials, the rats in the model group took longer latency and searching distance than those in the control group (P<0.01), which could be shortened by high dose TCA (P<0.05); during the spatial probe trial on the fifth day, the rats in the model group took shorter searching time and distance on the previous flat area than those in the control group (P<0.01), which could be prolonged after TCA treatment (for low dose group, P<0.05; for high dose group, P<0.01). (2) Analysis of cerebral cortical tissues showed that, compared with the control group, MDA level got significantly increased and Mn-SOD activity decreased in the model group (both P<0.01). After having been treated with TCA, the MDA level got significantly decreased (P<0.05 and P<0.01 respectively for low and high dose group), while relative increase of Mn-SOD activity only appeared in high dose group (P<0.05). (3) Immunohistochemistry analysis showed the protein expression of NF- kappa B got significantly increased after modeling, while high dose TCA can significantly inhibit it.

CONCLUSION

TCA could improve A beta 25-35 induced dysfunction of learning and memory in rats, and its protective mechanism is associated with its actions in decreasing MDA level, increasing Mn-SOD activity and inhibiting the expression of NF-kappa B in cerebral cortex.

Cognitive dysfunction induced by sequential injection of amyloid-β and ibotenate into the bilateral hippocampus; protection by memantine and MK-801

Aggregated 40-residue amyloid-beta peptide (beta40, 4 microg/microl), and 2 days later, ibotenate (NMDA receptor agonist, 0.3 microg/0.5 microl), were bilaterally injected into the hippocampus of rats. Five to six weeks after the beta40 injection, the rats showed learning deficits in the Morris water maze task and neuronal damage in the hippocampus, although the injection of beta40 or ibotenate alone did not result in cognitive deficits and hippocampal damage. Memantine (10, 20 mg/kg/day s.c. infusion for 6 weeks starting 24 h before the beta40 injection) significantly prevented learning deficits as measured for 4 days from 5 weeks after the beta40 injection, while a lower dose of memantine (5 mg/kg/day) and MK-801 (0.312, 0.624 mg/kg/day) did not have inhibitory effects on the learning deficits. The neuronal damage in the hippocampus, assessed as an elevation of the levels of the peripheral-type benzodiazepine-binding site (a gliosis marker for neuronal damage) produced by sequential intra-hippocampal injections of beta40 and ibotenate, at 6 weeks (39 days) after the beta40 injection, was significantly attenuated by memantine (10, 20 mg/kg/day) and MK-801 (0.624 mg/kg/day). These protective effects were also confirmed by histochemical examination (Cresyl violet staining of brain slices). In naive rats, MK-801 produced a significant learning impairment in the water maze task at a dose of 0.624 mg/kg/day, while memantine (20 mg/kg/day s.c. infusion) did not, although the beta40 plus ibotenate-induced hippocampal damage was lessened by both treatments. These results suggest that memantine and MK-801 exert protective effects on progressive neuronal damage, but that only memantine prevents memory impairment in hippocampal-lesioned rats, and that memantine may be a beneficial agent for the treatment of progressive cognitive dysfunction including Alzheimer's disease-type dementia.

Role of oxidative stress on beta-amyloid neurotoxicity elicited during impairment of energy metabolism in the hippocampus: protection by antioxidants

Age-associated oxidative stress has been implicated in neuronal damage linked with Alzheimer's disease (AD). In addition to the role of beta-amyloid peptide (Abeta) in the pathogenesis of AD, reduced glucose oxidative metabolism and decreased mitochondrial activity have been suggested as associated factors. However, the relationship between Abeta toxicity, metabolic impairment, and oxidative stress is far from being understood. In vivo neurotoxicity of Abeta25-35 peptide has been conflicting. However, in previous studies, we have shown that Abeta25-35 consistently induces synaptic toxicity and neuronal death in the hippocampus in vivo, when administered during moderate glycolytic or mitochondrial inhibition. In the present study, we have investigated whether enhancement of Abeta neurotoxicity during these conditions involves oxidative stress. Results show increased lipoperoxidation (LPO) when Abeta is administered in the hippocampus of rats previously treated with the glycolysis inhibitor, iodoacetate. Neuronal damage and LPO are efficiently prevented by vitamin E, while the spin trapper, alpha-phenyl-N-tert-butyl nitrone, shows partial protection. Abeta stimulates LPO in synaptosomes, but toxicity is only observed in the presence of metabolic inhibitors. Damage and LPO are efficiently prevented by vitamin E. The present results suggest an interaction between oxidative stress and metabolic impairment in the Abeta neurotoxic cascade.

A new approach to the pharmacological regulation of memory: Sarsasapogenin improves memory by elevating the low muscarinic acetylcholine receptor density in brains of memory-deficit rat models

The purpose of this paper is to study the basic pharmacological action of sarsasapogenin, a sapogenin from the Chinese medicinal herb Rhizoma Anemarrhenae, (abbreviated as ZMS in this paper), on learning ability and memory of three animal models: aged rats and two neurodegeneration models produced either by single unilateral injection of beta-amyloid 1-40 (Abeta1-40) plus ibotenic acid (Ibot A) or by bilateral injection of Ibot A alone into nucleus basalis magnocellularis. Y-maze test and step-through test revealed that learning ability and memory were impaired in the three models and were improved by oral administration of ZMS. ZMS did not inhibit acetylcholinesterase nor did it occupy the binding sites of muscarinic acetylcholine receptor (M receptor), hence it is neither an cholinesterase inhibitor nor an agonist or antagonist of M receptors. On the other hand, the densities of total M receptor and its M1 subtype in the brain of the three models were significantly lower than control rats, and ZMS significantly raised the densities of total M receptors and its M1 subtype. Linear regression revealed significant correlation between the learning ability/memory and the density of either total M receptor or its M1 subtype. Autoradiographic study with 3H-pirenzipine showed that the M1 subtype density was significantly lowered in cortex, hippocampus and striatum of aged rats, and ZMS could reverse these changes towards normal control level. Interestingly, the M1 receptor density after ZMS administration only approached but did not exceed that of normal young control rats. Therefore, ZMS seems to represent a new approach to the pharmacological regulation of learning and memory and appears to be not simply palliative but may modify the progression of the disease.

Galantamine modulates nicotinic receptor and blocks Abeta-enhanced glutamate toxicity

Galantamine is a plant alkaloid that is used in the treatment of Alzheimer's disease. We have studied the effects of galantamine on beta-amyloid-enhanced glutamate toxicity using primary rat cultured cortical neurons. Nicotine and galantamine alone, and in combination, protected neurons against this neurotoxicity. The protection was not blocked by alpha4beta2 nicotinic acetylcholine receptor (nAChR) antagonists, but was partially blocked by alpha7 nAChR antagonists. Galantamine induced phosphorylation of Akt, an effector of phosphatidylinositol 3-kinase (PI3K), while PI3K inhibitors blocked the protective effect and Akt phosphorylation. The antibody FK1, which selectively blocks the allosterically potentiating ligand site on nAChR, significantly reduced the galantamine-induced protection and Akt phosphorylation. Furthermore, suppression of alpha7 nAChR using an RNA interference technique reduced Akt phosphorylation induced by galantamine. Our data suggest that neuroprotection by galantamine is mediated, at least in part, by alpha7 nAChR-PI3K cascade.

Neurotoxicity induced by amyloid beta-peptide and ibotenic acid in organotypic hippocampal cultures: protection by S-allyl-L-cysteine, a garlic compound

We have assessed amyloid-beta (Abeta)-induced neurotoxicity, with and without added ibotenic acid (IBO), a potent N-methyl-D-aspartate (NMDA) agonist, in an organotypic hippocampal slice culture (OHC). In the OHC, there was little neurotoxicity after treatment with Abeta(25-35) (25 or 50 microM) alone for 48 h. However, with IBO alone neuronal death was observed in the pyramidal cell layer at low concentrations, and there was dramatic neuronal death at concentrations of 65 microM or more. When Abeta was combined with IBO (Abeta+IBO) there was more intense cell death than with IBO alone. S-Allyl-L-cysteine (SAC), one of the organosulfur compounds having a thioallyl group in aged garlic extract, was shown to protect the hippocampal neurons in the CA3 area and the dentate gyrus (DG) from the cell death induced by Abeta+IBO with no change in the CA1 area. Although L-glutamate (500 microM) potentiated the degree of IBO-induced neuronal death, it attenuated the Abeta+IBO-induced neuronal death in both the CA3 area and the DG with no obvious effect on the CA1 area. These results suggest that Abeta+IBO induces extensive neuronal death, and that SAC and L-glutamate protect cells from death in specific areas of the hippocampus. In addition, inhibition using a pan-caspase inhibitor, z-VAD-fmk, only provided partial protection from Abeta+IBO-induced toxicity for the neurons in the CA3 area. These results suggest that multiple mechanisms may be involved in Abeta+IBO-induced neuronal death in the OHC.

Single intracerebroventricular administration of amyloid-beta (25-35) peptide induces impairment in short-term rather than long-term memory in rats

Ample experimental evidence indicates that intracerebral injection or infusion of amyloid-beta peptides (Abeta) to rodents induces learning and memory impairments as well as neurodegeneration in brain areas related to cognitive function. In the present study, we assessed the effects of a single intracerebroventricular (i.c.v.) injection of aggregated Abeta fragment (25-35) at a dose of 15nmol/rat on short-term and long-term memory in rats during the 6-month post-surgery period. The results demonstrate that Abeta(25-35)-induced memory impairments in spontaneous alternation behavior in a Y-maze at 17, 36, and 180 days after the surgery as well as in a social recognition task 110 days post-surgery. Abeta(25-35) also impaired spatial memory in an 8-arm radial maze, but did not influence performance of the step-down passive avoidance task. These results suggest that Abeta(25-35) preferably induces impairments of spatial and non-spatial short-term (working) memory rather than long-term memory in rats.

Kainate exacerbates beta-amyloid toxicity in rat hippocampus

We have previously shown that beta-amyloid (Abeta) increased the excitotoxicity of ibotenate, an N-methyl-D-aspartate (NMDA) receptor agonist, to hippocampal neurons of rats. In this report, non-toxic amounts of kainate were co-injected with Abeta into rat hippocampus. Nissl-stained brain sections revealed that Abeta/kainate co-injection exerted synergistic neuronal degeneration in the hippocampus as well as that by Abeta/ibotenate co-injection. MK-801, an NMDA receptor antagonist, blocked the neuronal loss induced by Abeta/ibotenate co-injection, but not by Abeta/kainate co-injection. On the other hand, 6-cyano-7-nitroquinoxaline-2, 3-dione, a kainate receptor antagonist, suppressed the neuronal loss induced by the Abeta/kainate co-injection, but not that by the Abeta/ibotenate co-injection. This suggests that Abeta increases the sensitivity of both the NMDA receptor and the kainate receptor.

Beta-amyloid racemized at the Ser26 residue in the brains of patients with Alzheimer disease: implications in the pathogenesis of Alzheimer disease

Oligomeric and fibrillar beta-amyloid (Abeta) may be toxic in Alzheimer disease (AD), especially after post-translation modification cumulative over time. Racemization of Ser and Asp residues of Abeta in senile plaques (SPs) occurs as an age-dependent process in AD. We previously reported that Abeta1-40 racemized at Ser26 is soluble and susceptible to proteolysis yielding toxic [D-Ser26]Abeta25-35/40 fragments in vitro and in vivo. Here, we focus on the localization of racemized Ser26 residues in AD brains within the limbic system, the earliest site of AD histopathology. We developed antisera (20.1 and 22.7). each with epitopes within [D-Ser26]Abeta25-40. Two forms of truncated [D-Ser26]Abeta were detected either in SPs or within neurons in all 11 AD-affected brains, but not in age-matched controls. [D-Ser26]Abeta25/26-35 (detected by 20.1) was localized to plaque cores, extracellular neurofibrillary "ghost" tangles and vascular amyloid deposits. In contrast, [D-Ser26]Abeta25-40 (detected by 22.7) was observed in most neurons containing intracellular neurofibrillary tangles, but not in SPs. These results suggest [D-Ser26]Abeta]1-40, formed during aging, becomes soluble and diffuses from SPs. It is then proteolyzed to [D-Ser26]Abeta25-35/40, which is toxic and may contribute to the neurodegeneration. This hypothesis may explain the long lag between SP formation and neurofibrillary degeneration in AD brains.

In vivo conversion of racemized beta-amyloid ([D-Ser 26]A beta 1-40) to truncated and toxic fragments ([D-Ser 26]A beta 25-35/40) and fragment presence in the brains of Alzheimer's patients

The lag between beta-amyloid (A beta) deposition and neurodegeneration in Alzheimer's disease (AD) suggests that age-dependent factors are involved in the pathogenesis. Racemization of Ser and Asp in A beta is a typical age-dependent modification in AD. We have shown recently that A beta1-40 racemized at Ser(26) ([D-Ser(26)]A beta 1-40) is soluble and non-toxic to neuronal cells, but is easily converted by brain proteases to truncated toxic fragments, [D-Ser(26)]A beta 25-35/40. Furthermore, [D-Ser(26)]A beta1-40 in vivo, produced a drastic and synergistic neuronal loss by enhancing the excitotoxicity when co-injected into rat hippocampus with ibotenic acid, an excitatory amino acid, suggesting an in vivo conversion of non-toxic [D-Ser(26)]A beta1-40 to toxic fragments including [D-Ser(26)]A beta 25-35/40. In this study, we further investigated the mechanism behind the in vivo neuronal loss by [D-Ser(26)]A beta1-40 and ibotenic acid in rats, and also searched for the presence of [D-Ser(26)]A beta 25-35/40 antigens in AD brains. Quantitative analyses of the damaged area indicate clearly that non-toxic [D-Ser(26)]A beta 1-40 caused as much neurodegeneration as toxic [D-Ser(26)]A beta 25-35/40. MK-801, an NMDA receptor antagonist, completely inhibited the neurodegeneration. The immunohistochemical analyses using anti-[D-Ser(26)]A beta 25-35/40-specific antibodies demonstrated the presence of [D-Ser(26)]A beta 25-35/40 antigens in senile plaques and in degenerating hippocampal CA1 neurons in AD brains, but not in age-matched control brains. These results strengthen our hypothesis that soluble [D-Ser(26)]A beta1-40, possibly produced during aging, is released from plaques and converted by proteolysis to toxic [D-Ser(26)]A beta 25-35/40, which damage hippocampal CA1 neurons by enhancing excitotoxicity in AD. This may account for the lag between A beta deposition and neurodegeneration in AD.

Acute neuroinflammation exacerbates excitotoxicity in rat hippocampus in vivo

Accumulating evidence suggests that inflammation may play an important part in neurodegenerative diseases such as Alzheimer's disease. Inflammation itself, however, is insufficient to produce acute neurodegeneration in vivo. In this report, we determined whether inflammation increases excitotoxicity in hippocampal neurons. A proinflammagen, bacterial endotoxin lipopolysaccharide, was coinjected with ibotenate, an N-methyl-D-aspartate receptor agonist, into rat hippocampus. One week after coinjection, significant neuronal degeneration and severe tissue collapse were observed in the hippocampus. Astroglial and microglial infiltration were also detected. The neurodegeneration was suppressed by dizocilpine maleate, an N-methyl-D-aspartate receptor antagonist. We then examined whether microglial activation takes part in synergistic neuronal loss. One day after the lipopolysaccharide injection into the rat hippocampus, substantial microglial activation and induction of inducible nitric oxide synthase were observed, while neither neuronal nor astrocytic changes were detected. On the other hand, ibotenate injection at the same place 1 day after lipopolysaccharide injection in the hippocampus produced significant neuronal degeneration and gross microglial activation. These results suggest that inflammation by lipopolysaccharide might play an important role in ibotenate/lipopolysaccharide neurotoxicity.

beta-Amyloid neurotoxicity is exacerbated during glycolysis inhibition and mitochondrial impairment in the rat hippocampus in vivo and in isolated nerve terminals: implications for Alzheimer's disease

Senile plaques composed mainly by beta-amyloid (Abeta) protein are one of the pathological hallmarks of Alzheimer's disease (AD). In vitro, Abeta and its active fragment 25-35 have been shown either to be directly neurotoxic or to exacerbate the damaging effect of other neurotoxic insults. However, the attempts to replicate Abeta neurotoxicity in vivo have yielded conflicting results. One of the most consistent alterations in AD is a reduced resting glucose utilization. Important evidence suggests that impairment of brain energy metabolism can lead to neuronal damage or facilitate the deleterious effects of some neurotoxic agents. In the present study we have investigated the influence of glycolysis inhibition induced by iodoacetate, and mitochondrial impairment induced by 3-nitropropionic acid (3-NP), in the toxicity of Abeta. We have studied Abeta neurotoxicity during energy deficiency both in vivo in the dentate gyrus of the hippocampal formation and in presynaptic terminals isolated from neocortex and hippocampus. Results show that during metabolic inhibition an enhanced vulnerability of hippocampal neurons to Abeta peptide toxicity occurs, probably resulting from decreased glucose metabolism and mitochondrial ATP production. Synaptosomal response to energy impairment and Abeta toxicity was evaluated by the MTT assay. Results suggest that synapses may be particularly sensitive to metabolic perturbation, which in turn exacerbates Abeta toxicity. The present data provide experimental support to the hypothesis that certain risk factors such as metabolic dysfunction and amyloid accumulation may interact to exacerbate AD, and that metabolic substrates such as pyruvate may play a role as a therapeutic tool.

Evolution of beta-amyloid induced neuropathology: magnetic resonance imaging and anatomical comparisons in the rodent hippocampus

Alzheimer's disease (AD) is characterized by the anatomical appearance of beta-amyloid (betaA) plaques and neurofibrillary tangles. These changes are also associated with cyclical inflammation, oxidative damage and, as inferred from the autopsied brains of patients, progressive injury to neurons. Here, we report the short-term effects of an intrahippocampal injection of the toxic betaA peptide fragment 25-35 in rats using quantitative magnetic resonance imaging (MRI) methods. Physiological changes within the cornu ammonis 1 (CA1) region of the hippocampus were monitored using a 1.5 T scanner at time points of 0.25, 1 and 24 h, and 7 and 14 days post injection. Spin echo T2-weighted (T2W) and diffusion weighted (DW) images were sequentially acquired. Apparent diffusion coefficients (ADC) were calculated and compared with histological alterations. A significant elevation in mean ADC values (17%) was observed in the ipsilateral CA1 at 14 days. The ADC changes were associated with disrupted pyramidal cells and nuclear lysis observed in histological sections. The contralateral CA1 exhibited a significant decrease in mean ADC of 15% at 14 days post treatment. Histological changes in the contralateral hippocampus suggested decreased neuronal density. T2W maps revealed no significant differences between the active betaA 25-35 fragment and its non-active analog, betaA 35-25. In conclusion, these results, based on changes in hippocampal ADC, demonstrate that the betaA 25-35 treatment induced pathology consistent with edema and cellular necrosis. This is the first report describing the evolution of AD-like pathology in an animal model using DW imaging.

The protective effects of melatonin from oxidative damage induced by amyloid beta-peptide 25-35 in middle-aged rats

This work investigated the ability of melatonin to prevent oxidative damage in brain tissue induced by injection of beta-amyloid peptide 25-35 (Abeta25-35) in middle-aged rats. The Morris water maze was used to evaluate the cognitive function of the rats. Thiobarbituric acid-reactive substances and antioxidative enzymes (superoxide dismutase and glutathione peroxidase) activities were measured. It was found that injection of (Abeta25-35) (20 microg) into the rat hippocampus caused an increase in the latency (the time to find the platform), the total swimming distance to the platform, and the starting angles in (Abeta25-35)-treated rats. Furthermore, a significant rise in lipid peroxidation and decrease in antioxidative enzyme activities in brain tissue were found. Melatonin (0.1, 1, and 10 mg/kg, i.g. x 10 days) improved the spatial resolution of amnesic rats in the Morris water maze test. Meanwhile, melatonin antagonized the lipid peroxidation in both the mitochondria (P < 0.01) at the doses of 0.1, 1.0, and 10 mg/kg and in the cytoplasm at the doses of 0.1 and 1.0 mg/kg. Also in the amnesic rats, melatonin (0.1, 1.0, and 10 mg/kg. i.g. x 10 days) stimulated the antioxidative enzyme activities. The results show that melatonin effectively reduced lipid peroxidation and enhanced the antioxidative enzyme activities in Abeta(25-35)-treated rats, which may contribute to the improvement of rats' learning and memory impaired by Abeta(25-35).

Glutamate exacerbates amyloid beta1-42-induced impairment of long-term potentiation in rat hippocampal slices

Amyloid beta (A beta) is the principal constituent of senile plaques in Alzheimer's disease patients. We investigated whether A beta and glutamate affect long-term potentiation (LTP) in rat hippocampal slices. Pretreatment with 1 microM A beta1-42 alone for 3 h slightly inhibited LTP; however, the potentiation was maintained for 60 min. Although the impairment was not observed by pretreatment with 30 microM glutamate alone for 3 h, pretreatment with A beta1-42 and glutamate impaired LTP significantly. These results raise the possibility that neurotoxicity of A beta is exacerbated by the enhancement of susceptibility to excitatory amino acids.