Protective effects of idebenone and alpha-tocopherol on beta-amyloid-(1-42)-induced learning and memory deficits in rats: implication of oxidative stress in beta-amyloid-induced neurotoxicity in vivo

Synergistic effects of selegiline and donepezil on cognitive impairment induced by amyloid beta (25-35)

Selegiline, an irreversible inhibitor of monoamine oxidase B used in the treatment of Parkinson's disease, has been demonstrated to have a potential cognition-improving effect in patients with Alzheimer's disease (AD) undergoing treatment with an acetylcholinesterase inhibitor donepezil. To confirm such clinical events, we investigated whether co-administration of donepezil with selegiline had a synergistic cognition-improving effect in an animal model of AD. Intracerebroventricular injection of amyloid beta protein fragment 25-35 [Abeta(25-35)] induced impairment of learning and memory in a Y-maze, novel object recognition and contextual fear conditioning tests. Either donepezil or selegiline alone improved the cognitive impairments in the Y-maze and conditioned fear learning tasks in Abeta(25-35)-injected mice, whereas donepezil, but not selegiline, failed to improve the impairment in a novel object recognition task. Co-administration of donepezil with selegiline, at doses that do not exert efficacy individually, significantly improved the deficits in all three tests, indicating a synergistic cognition-improving effect. These alleviating effects were antagonized by pretreatment with a muscarinic receptor antagonist scopolamine and a dopamine receptor antagonist haloperidol. These results suggest that selegiline potentiates the effect of donepezil on the cognitive impairment, and that the synergistic effect may be mediated through both the cholinergic and dopaminergic systems.

Green tea catechins prevent cognitive deficits caused by Abeta1-40 in rats

Amyloid beta peptide (Abeta)-induced oxidative stress is involved in the pathogenesis of Alzheimer's disease (AD). In contrast, green tea catechins confer potent antioxidative defense to brain neurons. Therefore, we examined whether long-term administration of green tea catechins [Polyphenon E (PE): 63% of epigallocatechin-3-gallate, 11% of epicatechin, 6% of (-)-epigallocatechin and 6% of (-)-epicatechin-gallate] prevents cognitive impairment in an animal model of AD, rats infused with Abeta1-40 into the cerebral ventricle. Five-week-old male Wistar rats fed with an MF diet were randomly divided into two groups: 0.0% PE (rats administered with water only) and 0.5% PE (rats administered with 5 g/L of PE). Twenty weeks after the PE administration, the 0.0% PE group was divided into the Vehicle group (rats infused with the solvent used for dissolving Abeta) and the Abeta(1-40)-infused rat group (Abeta group), whereas the 0.5% PE group was divided into the PE+Vehicle group (PE-preadministered vehicle-infused rats) and the PE+Abeta group (PE-preadministered Abeta-infused rats). Abeta1-40 or vehicle was infused into the cerebral ventricle using a mini osmotic pump. Behavioral changes in the rats were assessed by an eight-arm radial maze. PE administration for 26 weeks significantly decreased the Abeta-induced increase in the number of reference and working memory errors, with a concomitant reduction of hippocampal lipid peroxide (LPO; 40%) and cortico-hippocampal reactive oxygen species (ROS; 42% and 50%, respectively). Significantly reduced levels of LPO in the plasma (24%) and hippocampus (25%) as well as those of ROS in the hippocampus (23%) and cortex (41%) were found in the PE+Vehicle group as compared with the Vehicle group. Furthermore, rats with preadministered PE had higher ferric-reducing antioxidation power of plasma as compared with the Vehicle group. Our results suggest that long-term administration of green tea catechins provides effective prophylactic benefits against Abeta-induced cognitive impairment by increasing antioxidative defenses.

Decreased nicotinic receptors and cognitive deficit in rats intracerebroventricularly injected with beta-amyloid peptide(1-42) and fed a high-cholesterol diet

To investigate whether the changes in nicotinic receptors (nAChRs) and in learning and memory associated with Alzheimer's disease (AD) are influenced by both beta-amyloid peptide (Abeta) and cholesterol in vivo, we examined the effects of intracerebroventricular injection of Abeta(1-42) and/or a high-cholesterol diet on brain levels of nAChRs and learning and memory in rats. The levels of nAChR subunit proteins and the corresponding mRNA were measured by Western blotting and RT-PCR, respectively; and learning and memory were evaluated with the Morris Water Maze examination. Injection of Abeta(1-42) resulted in deposition of this peptide, activation of astrocytes, decreased levels of the alpha7 and alpha4 protein subunits of the nAChR, and elevated expression of alpha7 mRNA, as well as impaired learning and spatial memory. A high-cholesterol diet activated astrocytes and, more importantly, potentiated the toxic effects of Abeta on nAChR subunit levels and on learning and memory. These findings may be highly relevant to the mechanisms underlying the cognitive deficits associated with AD.

A novel compound, maltolyl p-coumarate, attenuates cognitive deficits and shows neuroprotective effects in vitro and in vivo dementia models

To develop a novel and effective drug that could enhance cognitive function and neuroprotection, we newly synthesized maltolyl p-coumarate by the esterification of maltol and p-coumaric acid. In the present study, we investigated whether maltolyl p-coumarate could improve cognitive decline in scopolamine-injected rats and in amyloid beta peptide(1-42)-infused rats. Maltolyl p-coumarate was found to attenuate cognitive deficits in both rat models using passive avoidance test and to reduce apoptotic cell death observed in the hippocampus of the amyloid beta peptide(1-42)-infused rats. We also examined the neuroprotective effects of maltolyl p-coumarate in vitro using SH-SY5Y cells. Cells were pretreated with maltolyl p-coumarate, before exposed to amyloid beta peptide(1-42), glutamate or H2O2. We found that maltolyl p-coumarate significantly decreased apoptotic cell death and reduced reactive oxygen species, cytochrome c release, and caspase 3 activation. Taking these in vitro and in vivo results together, our study suggests that maltolyl p-coumarate is a potentially effective candidate against Alzheimer's disease that is characterized by wide spread neuronal death and progressive decline of cognitive function.

Ferulic acid attenuated cognitive deficits and increase in carbonyl proteins induced by buthionine-sulfoximine in mice

beta-Amyloid peptide (Abeta), the major constituent of the senile plaques observed in the brains of Alzheimer's disease patients, is cytotoxic to neurons and plays a central role in the pathogenesis of this disease. Previous studies have suggested that oxidative stress is involved in the mechanisms of Abeta-induced neurotoxicity in vivo. Here, we used a mouse model of brain dysfunction induced by dl-buthionine-(S,R)-sulfoximine (BSO: 3micromol/3microL/mouse, i.c.v.), an inhibitor of glutathione synthesis. In the novel object recognition test, we found impairments of exploratory preference in the retention trial but not the training trial 24h after BSO treatment, suggesting that BSO produces cognitive dysfunction in mice. In the forebrain of this model, we observed increase in carbonyl protein levels, an index of biochemical oxidative damage of proteins, compared to vehicle-treated mice. Pretreatment with ferulic acid (5mg/kg, s.c.) once a day for 6 days inhibited the induction of deficits in memory and increase in carbonyl protein levels by BSO. These findings suggest that pretreatment with FA may attenuate the memory deficits and increase the carbonyl protein levels induced by BSO in mice.

Pre-treatment and post-treatment with α-tocopherol attenuates hippocampal neuronal damage in experimental cerebral hypoperfusion

Alpha-tocopherol, a potent antioxidant, has been widely investigated as a dietary supplement with which to reduce the risk of atherosclerosis, and has recently been considered as a potential supplement to moderate oxidative neuronal damage in Alzheimer's disease patients. Since alpha-tocopherol appears beneficial in vascular and neurodegenerative disorders, we set out to identify its neuroprotective action in a rat model of chronic cerebral hypoperfusion-induced brain injury. The bilateral common carotid arteries of male Wistar rats were permanently occluded (2VO). Sham-operated animals served as controls. Half of the animals were pre- or post-treated repeatedly with alpha-tocopherol (5x100 mg/kg daily, i.p.), the other half receiving only soybean oil, the alpha-tocopherol vehicle. One week after the onset of 2VO, the spatial learning capacity of the animals was assessed in the Morris water maze. After testing, hippocampal slices were stained with cresyl violet in order to examine the pyramidal cell layer integrity. The density of microtubule-associated protein-2 (MAP-2)-positive dendrites and the OX-42-labeled microglial activation level were determined immunocytochemically. Finally, alpha-tocopherol was determined in the peripheral tissues, blood and brain. Alpha-tocopherol moderated the 2VO-induced learning impairment. The various forms of alpha-tocopherol treatment, and particularly the post-treatment, prevented the 2VO-induced pyramidal cell death and the activation of microglia in the hippocampus CA1 region, and the degeneration of MAP-2-positive dendrites in the CA3 region. The alpha-tocopherol concentration was elevated in the peripheral tissues and the blood, but not in the brain. The data indicate that alpha-tocopherol, particularly when administered as post-treatment, is neuroprotective in chronic cerebral hypoperfusion.

Anti-dementia drugs and hippocampal-dependent memory in rodents

Abnormalities in hippocampal structure and function are characteristics of early Alzheimer's disease (AD). Behavioral tests measuring hippocampal-dependent memory in rodents are often used to evaluate novel treatments for AD and other dementias. In this study, we review the effects of drugs marketed for the treatment of AD, such as the acetylcholinesterase inhibitors, donepezil, rivastigmine, galantamine and the N-methyl-D-aspartic acid antagonist, memantine, in rodent models of memory impairment. We also briefly describe the effects of novel treatments for cognitive impairment in rodent models of memory impairment, and discuss issues concerning the selection of the animal model and behavioral tests. Suggestions for future research are offered.

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.

Involvement of the sigma1 (sigma1) receptor in the anti-amnesic, but not antidepressant-like, effects of the aminotetrahydrofuran derivative ANAVEX1-41

BACKGROUND AND PURPOSE

Tetrahydro-N, N-dimethyl-5, 5-diphenyl-3-furanmethanamine hydrochloride (ANAVEX1-41) is a potent muscarinic and sigma(1) (sigma (1)) receptor ligand. The sigma (1) receptor modulates glutamatergic and cholinergic responses in the forebrain and selective agonists are potent anti-amnesic and antidepressant DRUGS. WE HAVE HERE ANALYSED THE SIGMA (1) COMPONENT IN THE BEHAVIOURAL EFFECTS OF ANAVEX1-41.

EXPERIMENTAL APPROACH

Binding of ANAVEX1-41 to muscarinic and sigma (1) receptors were measured using cell membranes. Behavioural effects of ANAVEX1-41 were tested in mice using memory (spontaneous alternation, passive avoidance, water-maze) and antidepressant-like activity (forced swimming) procedures.

KEY RESULTS

In vitro, ANAVEX1-41 was a potent muscarinic (M(1)>M(3), M(4)>M(2) with K(i) ranging from 18 to 114 nM) and selective sigma (1) ligand (sigma (1), K(i)=44 nM; sigma (2), K(i)=4 microM). In mice, ANAVEX1-41 failed to affect learning when injected alone (0.03-1 mg kg(-1)), but attenuated scopolamine-induced amnesia with a bell-shaped dose response (maximum at 0.1 mg kg(-1)). The sigma (1) antagonist BD1047 blocked the anti-amnesic effect of ANAVEX1-41 on both short- and long-term memories. Pretreatment with a sigma (1) receptor-directed antisense oligodeoxynucleotide prevented effects of ANAVEX1-41 only in the passive avoidance procedure, measuring long-term memory. ANAVEX1-41 reduced behavioural despair at 30 and 60 mg kg(-1), without involving the sigma (1) receptor, as it was not blocked by BD1047 or the antisense oligodeoxynucleotide.

CONCLUSIONS AND IMPLICATIONS

ANAVEX1-41 is a potent anti-amnesic drug, acting through muscarinic and sigma (1) receptors. The latter component may be involved in the enhancing effects of the drug on long-term memory processes.

Ameliorative effects of a neuroprotective agent, T-817MA, on place learning deficits induced by continuous infusion of amyloid-beta peptide (1-40) in rats

Alzheimer's disease (AD) is a neurodegenerative disease characterized by cognitive decline due to neuronal loss and neural network dysfunction. It has been postulated that progressive neuronal loss in AD is consequence of the neurotoxic properties of the amyloid-beta peptide (Abeta). In the present study, we investigated the effect of T-817MA (1-{3-[2-(1-benzothiophen-5-yl)ethoxy] propyl}-3-azetidinol maleate), a newly synthesized neurotrophic compound, on place learning deficits in rats with hippocampal damages. To induce granule cell loss in the dentate gyrus (DG) of the hippocampus, Abeta (1-40) was continuously infused (300 pmol/day) into the cerebral ventricle using a mini-osmotic pump for 5 weeks. Three weeks after the Abeta infusion, the rats were tested in a place learning task, which required them to alternatively visit two diametrically opposed areas in an open field to obtain intracranial self-stimulation reward. The results indicated that the Abeta-infused rats without treatment of T-817MA displayed learning impairment in the task; their performance level was significantly inferior to that of the vehicle rats. Treatment of T-817MA (8.4 mg/kg/day, p.o.) significantly improved the task performance of the Abeta-infused rats. Furthermore, T-817MA prevented granule cell loss due to Abeta-infusion, which was correlated to task performance of the rats. However, other cognitive enhancer, an acetylcholinesterase inhibitor, had no such effects. The results demonstrated that T-817MA ameliorated learning deficits induced by Abeta infusion, which might be attributed to neuroprotection in the hippocampus.

Neuronal apoptosis in neurodegeneration

Apoptosis mediates the precise and programmed natural death of neurons and is a physiologically important process in neurogenesis during maturation of the central nervous system. However, premature apoptosis and/or an aberration in apoptosis regulation is implicated in the pathogenesis of neurodegeneration, a multifaceted process that leads to various chronic disease states, such as Alzheimer's (AD), Parkinson's (PD), Huntington's (HD) diseases, amyotrophic lateral sclerosis (ALS), spinal muscular atrophy (SMA), and diabetic encephalopathy. The current review focuses on two major areas (a) the fundamentals of apoptosis, which includes elements of the apoptotic machinery, apoptosis inducers, and emerging concepts in apoptosis research, and (b) apoptotic involvement in neurodegenerative disorders, neuroprotective treatment strategies/modalities, and the mechanisms of, and signaling in, neuronal apoptosis. Current and new experimental models for apoptosis research in neurodegenerative diseases are also discussed.

Antioxidant vitamins and Alzheimer’s disease: a review of the epidemiological literature

Identifying ways to prevent Alzheimer’s disease is becoming increasingly critical in our aging population. Antioxidant vitamins hold promise for lowering the risk of Alzheimer’s disease and cognitive decline in older persons. In animal models and cell lines, these vitamins, such as vitamins E and C, prevent neuronal damage caused by free radicals, delaying brain aging and, perhaps, memory loss. However, epidemiological data on antioxidant vitamins and cognition are conflicting and are not conclusive. This report reviews current research, in particular, the large, prospective, observational studies and randomized, controlled trials to assess the evidence regarding the relation of antioxidant vitamins to dementia or cognitive decline.

Cognitive effects of SL65.0155, a serotonin 5-HT4 receptor partial agonist, in animal models of amnesia

Given that several data suggest the involvement of serotonergic (5-HT) system, particularly the serotonin 5-HT(4) receptors, in memory processes; this study was undertaken to investigate the role of serotonin 5-HT(4) receptors in different experimental models of amnesia in male Swiss mice or in male Sprague-Dawley rats, tested in learning and memory tasks. Amnesia was induced in mice by intracerebroventricular (i.c.v.) injection of beta-amyloid 1-42 fragment (BAP 1-42; 400 pmol/mouse) or of galanin (GAL) 1-29 (3 microg/mouse). Another group of animals was exposed to carbon monoxide (CO). Treatments were made 14 days, 15 min or 8 days prior to the learning trial of a step-through passive avoidance paradigm, respectively. Latency to re-enter the dark box appeared to be reduced in all treatment groups. Intraperitoneal (i.p.) administration of SL65.0155 (5-(8-amino-7-chloro-2,3-dihydro-1,4-benzodioxin-5-yl)-3-[1-(2-phenylethyl)-4-piperidinyl]-1,3,4-oxadiazol-2(3H)-one-monohydrochloride), a serotonin 5-HT(4) receptor partial agonist (1 mg/kg/day), for 7 days prior to the learning trial, inhibited the amnesic effect of both peptides increasing the latency to re-enter the dark box also in mice exposed to CO. In rats with ibotenate-induced lesions of the nucleus basalis magnocellularis (NBM) or prenatally exposed to methylazoxymethanol (MAM), SL65.0155 (1 mg/kg/day, i.p.) administered for 7 days, improved the learning and memory capacity in animals tested in shuttle-box active avoidance and radial maze tests. These findings give further support to the hypothesis of SL65.0155 cognition-enhancing activity across a range of tasks.

Beneficial effect of Toona sinensis Roemor on improving cognitive performance and brain degeneration in senescence-accelerated mice

The purpose of the present study was to examine the effects of Toona sinensis Roemor extracts on antioxidative activities, brain morphological changes and cognitive ability. In an in vitro study, the antioxidant capacities of water extracts from Toona sinensis Roemor leaf (TSL), root (TSR) and bark (TSB) were evaluated by an alpha,alpha-diphenyl-beta-pricryl-hydrazyl radical-scavenging test. The results showed that the scavenging activities of all Toona sinensis Roemor extracts were over 80% at a concentration of 0.625 mg/ml. In an in vivo study, 3-month-old male senescence-accelerated-prone 8 mice were used as the tested subjects and fed four different diets: casein diet or casein diet supplemented with 1% TSL, TSR or TSB extract for 12 weeks. The results showed that the mice supplemented with Toona sinensis Roemor extracts demonstrated significantly less amyloid beta-protein deposition and lower levels of thiobarbituric acid-reactive substances than the control group. All Toona sinensis Roemor diet groups also showed better active shuttle avoidance responses, and higher superoxide dismutase, catalase and glutathione peroxidase activities, than the control group. It can thus be concluded that supplementation with either TSL, TSR or TSB extract could not only reduce the incidence of ss-amyloid plaques, but also improve learning and memory ability in senescence-accelerated-prone 8 mice. This might be due to the beneficial effects of Toona sinensis Roemor extracts on promoting the antioxidative defence system.

Dietary chelators as antioxidant enzyme mimetics: implications for dietary intervention in neurodegenerative diseases

Following recent reviews on the role of metal ions in oxidative stress and neurodegenerative diseases, this article reports advances in the study of dietary components for the control of these conditions. Poor metal ion homeostasis is credited with pathological roles in the progression of a number of disorders including Alzheimer's disease, Parkinson's disease and multiple sclerosis. Synthetic metal ion chelators continue to show promise as a new therapeutic approach for neurodegenerative disorders. Dietary chelators, unlike most vitamins, are, however, capable of negating or even reversing the roles of metal ions by: (i) decorporation of metal ions, (ii) redox silencing, (iii) dissolution of deposits, and (iv) generation of an antioxidant enzyme mimetic. This review gives a critical evaluation of recent progress in, and potential for, dietary control of neurodegeneration on the basis of the formation of antioxidant enzyme mimetics.

Effects of memantine and donepezil on amyloid beta-induced memory impairment in a delayed-matching to position task in rats

We investigated the effects of memantine and donepezil on amyloid beta (Abeta)-induced memory impairment in rats, which was assessed by a delayed-matching to position (DMPT) paradigm in three-lever operant chambers. Aggregated Abeta1-40 was microinjected bilaterally (1 nmol/side) into both CA1 and CA3 subfields of the hippocampus in rats that had previously performed the DMTP task. Memantine (20 mg/(kg day), s.c.) was continuously infused by an osmotic minipump for 4 weeks from 3 days before the microinjection of Abeta. Donepezil (2.5 mg/kg, p.o.) was administered 60 min before the DMTP test session. Bilateral microinjections of Abeta1-40 into the hippocampus resulted in a delayed, but persistent impairment of DMTP performance, which appeared more than 50 days after the injection. Memantine prevented the development of Abeta-induced memory impairment, while donepezil symptomatically alleviated the deficits. Because of a ceiling effect, the combination of donepezil with memantine failed to produce any additive or synergic effects. These results support the clinical data showing that memantine and donepezil are effective for the treatment of Alzheimer's disease. Moreover, it is suggested that memantine is effective for preventing Abeta-induced short-term memory impairment.

Effects of a novel cognitive enhancer, spiro[imidazo-[1,2-a]pyridine-3,2-indan]-2(3H)-one (ZSET1446), on learning impairments induced by amyloid-beta1-40 in the rat

We have previously shown that intracerebroventricular (i.c.v.) infusion of amyloid-beta (Abeta)1-40 produces oxidative stress and cholinergic dysfunction, as well as learning and memory deficits, in rats. In the present study, effects of a newly synthesized azaindolizinone derivative, spiro[imidazo[1,2-a]pyridine-3,2-indan]-2(3H)-one (ZSET1446), were assessed in rats with learning deficits induced by Abeta1-40 or scopolamine. The i.c.v. infusion of Abeta1-40 caused impairments in spontaneous alternation behavior in a Y-maze task, spatial reference and short-term memory in a water-maze task, and retention of passive-avoidance learning. Abeta1-40-infused rats also showed reduction in choline acetyltransferase (ChAT) activity in the medial septum and hippocampus, but not in the basal forebrain and cortex, and a decrease in glutathione S-transferase (GST)-like immunoreactivity in the cortex. Nicotine-stimulated acetylcholine (ACh) release in Abeta1-40-infused rats was lower than that in vehicle-infused rats. Oral administration of ZSET1446 at the dose range of 0.01 to 1 mg/kg ameliorated Abeta1-40-induced learning impairment in Y-maze, water-maze, and passive-avoidance tasks. ZSET1446 reversed the decrease of ChAT activity in the medial septum and hippocampus, GST-like immunoreactivity in the cortex, and nicotine-stimulated ACh release of Abeta1-40-treated rats to the levels of vehicle-infused control rats. Furthermore, 0.001 to 0.1 mg/kg ZSET1446 showed ameliorative effects on learning impairments caused by scopolamine in a passive-avoidance task. These results suggest that ZSET1446 may be a potential candidate for development as a therapeutic agent to manage cognitive impairment associated with conditions such as Alzheimer's disease.

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.

Inhibition of neprilysin by infusion of thiorphan into the hippocampus causes an accumulation of amyloid Beta and impairment of learning and memory

An imbalance between anabolism and catabolism causes an accumulation of amyloid beta-peptide (Abeta), which is a proposed trigger of the onset of Alzheimer's disease. Neprilysin is a rate-limiting peptidase that participates in the catabolism of Abeta in the brain. We examined whether rats continuously infused with thiorphan, a specific neprilysin inhibitor, into the hippocampus develop cognitive impairments through accumulation of Abeta. Thiorphan infusion elevated hippocampal Abeta40 and Abeta42 levels in the insoluble but not the soluble fraction. Thiorphan-infused rats displayed cognitive impairments in the ability to discriminate in the object recognition test, associative learning in the conditioned fear learning test, and spatial memory in the water maze test, tasks that depend on the hippocampus. These cognitive abilities in the battery of behavioral tasks inversely correlated with insoluble Abeta contents in the hippocampus. The nicotine-stimulated release of acetylcholine in the hippocampus of thiorphan-infused rats was significantly lower than that in vehicle-infused rats. These results indicate that continuous infusion of thiorphan into the hippocampus causes cognitive dysfunction and reduces cholinergic activity by raising the level of Abeta in the hippocampus and suggest that a reduction of neprilysin activity contributes to the deposition of Abeta and development of Alzheimer's disease.

Protective effect of Polygonum multiflorum Thunb on amyloid beta-peptide 25-35 induced cognitive deficits in mice

Amyloid beta protein (Abeta) may be neurotoxic during the progression of Alzheimer's disease by eliciting oxidative stress. This study was designed to determine the effect of Polygonum multiflorum Thunb water extract (PWE) on Abeta25-35-induced cognitive deficits and oxidative stress in mice. Mice were fed experimental diets comprising either 0.5 or 1% PWE for 4 weeks, and then received a single intracerebroventricular (i.c.v.) injection of Abeta25-35 (10 microg/mouse). Behavioral changes in the mice were evaluated using passive avoidance and water-maze tests. The consumption of PWE significantly ameliorated the cognitive deficits caused by i.c.v. injection of Abeta25-35. The Abeta25-35 treatment accelerated the lipid peroxidation, and PWE attenuated the Abeta-induced increase in brain levels of thiobarbituric acid reactive substances. There was an increase in glutathione peroxidase activity in PWE-treated groups. The acetylcholinesterase activity in the brain and serum was lower in PWE supplemented groups than in the only Abeta-injected group. These findings suggest that PWE exerts a preventive effect against cognitive deficits induced by Abeta25-35 accumulation in Alzheimer's disease, and that this effect is mediated by the antioxidant properties of PWE.

Protective effect of Rosa laevigata against amyloid beta peptide-induced oxidative stress

The amyloid beta (Abeta) peptide is known to increase free radical production in nerve cells, leading to cell death. To investigate the effect of Rosa laevigata against Abeta-induced oxidative damage, in vitro assays and in vivo behavioral tests were performed. R. laevigata showed cell protective effects against oxidative stress-induced cytotoxicity. MTT (3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyl tetrazolium bromide) reduction assay exhibited significant increase in cell viability when rat pheochromocytoma (PC 12) cells were treated with R. laevigata extracts. Administration of R. laevigata extracts to mice significantly reversed the Abeta-induced learning and memory impairment in in vivo behavioral tests. These results suggest that R. laevigata extracts can reduce the cytotoxicity of Abeta in PC 12 cells, possibly by the reduction of oxidative stress, and these extracts may be useful in the prevention of Alzheimer's disease.

Chronic dietary alpha-lipoic acid reduces deficits in hippocampal memory of aged Tg2576 mice

Oxidative stress may play a key role in Alzheimer's disease (AD) neuropathology. Here, the effects of the antioxidant, alpha-lipoic acid (ALA) were tested on the Tg2576 mouse, a transgenic model of cerebral amyloidosis associated with AD. Ten-month old Tg2576 and wild type mice were fed an ALA-containing diet (0.1%) or control diet for 6 months and then assessed for the influence of diet on memory and neuropathology. ALA-treated Tg2576 mice exhibited significantly improved learning, and memory retention in the Morris water maze task compared to untreated Tg2576 mice. Twenty-four hours after contextual fear conditioning, untreated Tg2576 mice exhibited significantly impaired context-dependent freezing. ALA-treated Tg2576 mice exhibited significantly more context freezing than the untreated Tg2576 mice. Assessment of brain soluble and insoluble beta-amyloid levels revealed no differences between ALA-treated and untreated Tg2576 mice. Brain levels of nitrotyrosine, a marker of nitrative stress, were elevated in Tg2576 mice, while F2 isoprostanes and neuroprostanes, oxidative stress markers, were not elevated in the Tg2576 mice relative to wild type. These data indicate that chronic dietary ALA can reduce hippocampal-dependent memory deficits of Tg2576 mice without affecting beta-amyloid levels or plaque deposition.

Beta-Amyloid and Oxidative Stress Jointly Induce Neuronal Death, Amyloid Deposits, Gliosis, and Memory Impairment in the Rat Brain

Infusion of Fe2+, Abeta42, and buthionine-sulfoximine (FAB), but not Abeta42 alone or in combination with Fe2+, into the left cerebral ventricle of Long-Evans rats for 4 weeks induced memory impairment that was accompanied by increased hyperphosphorylated Tau protein levels in the CSF. FAB-infused animals displayed thioflavin-S-positive amyloid deposits, hyperphosphorylated Tau protein, neuronal loss, and gliosis. Animals treated with Abeta42, Fe2+, or buthionine-sulfoximine alone or in combination failed to show the histological modifications seen with FAB. This data suggests that Abeta42 is not sufficient to induce an Alzheimer's disease-like symptomatology, and it supports a model whereby a decrease in the brain's antioxidant defense system leads to the Abeta42-independent oxidative stress necessary for the peptide to induce histopathological changes and memory loss.

Implanted cannula-mediated repetitive administration of Aβ25–35 into the mouse cerebral ventricle effectively impairs spatial working memory

Amyloid beta (Abeta) is closely related to the onset of Alzheimer's disease (AD). To construct AD animal models, a bolus administration of a large dose of toxic Abeta into the cerebral ventricles of rodents has been performed in earlier studies. In parallel, a continuous infusion system via an osmotic pump into the cerebral ventricle has been developed to make a rat AD model. In this study, we developed a mouse AD model by repetitive administration of Abeta25-35 via a cannula implanted into the cerebral ventricle. Using this administration system, we reproducibly constructed a mouse with impaired spatial working memory. In accordance with the occurrence of the abnormal mouse behavior, we found that the number of choline acetyltransferase (ChAT)-positive neurons was reduced in paraventricular regions of brains of Abeta25-35-administered mice in a dose-dependent manner. Considering that the repetitive administration of a small dose of toxic Abeta via an implanted cannula leads to a brain status more resembling that of the AD patients than a bolus injection of a large dose of Abeta, and therapeutic as well as toxic agents are able to be repeatedly and reliably administered via an implanted cannula, we concluded that the implanted cannula-bearing AD mouse model is useful for development of new AD therapy.

Parenteral antioxidant treatment preserves temporal discrimination following intrahippocampal aggregated Aβ(1–42) injections

There is evidence that oxidative stress may play a role in the neuropathology of Alzheimer's disease (AD). This study used an aggregated beta-amyloid (Abeta) injection model of AD in the rat, and a recycling conjunctive schedule of food reinforcement to examine the effects of bilateral intrahippocampal injections of aggregated Abeta(1-42) (5.0 microl/side) on temporal discrimination, and the efficacy of the antioxidant alpha-tocopherol (150 mg/kg daily p.o.) in alleviating these effects. The results indicated that bilateral intrahippocampal injections of aggregated Abeta(1-42) detrimentally affected temporal discrimination from five-day block 31-35 post-injections until the end of the study (90 days post-injections). Daily treatment with alpha-tocopherol improved temporal discrimination under the recycling conjunctive schedule following aggregated Abeta(1-42) injections from the five-day block 61-65 days until the end of the study.

Gene expression profile of amyloid beta protein-injected mouse model for Alzheimer disease

AIM

To investigate the gene expression profile changes in the cerebral cortex of mice injected icv with amyloid beta-protein (Abeta) fragment 25-35 using cDNA microarray.

METHODS

Balb/c mice were randomly divided into a control group and Abeta-treated group. The Morris water maze test was performed to detect the effect of Abeta-injection on the learning and memory of mice. Atlas Mouse 1.2 Expression Arrays containing 1176 genes were used to investigate the gene expression pattern of each group.

RESULTS

The gene expression profiles showed that 19 genes including TBX1, NF-kB, AP-1/c-Jun, cadherin, integrin, erb-B2, and FGFR1 were up-regulated after 2 weeks of icv administration of Abeta; while 12 genes were down-regulated, including NGF, glucose phosphate isomerase 1, AT motif binding factor 1, Na+/K+-ATPase, and Akt.

CONCLUSIONS

The results provide important leads for pursuing a more complete understanding of the molecular events of Abeta-injection into mice with Alzheimer disease.

Chronic administration of docosahexaenoic acid ameliorates the impairment of spatial cognition learning ability in amyloid beta-infused rats

We investigated whether administration of docosahexaenoic acid (DHA), a major (n-3) fatty acid of the brain, ameliorates the impairment of learning ability in an animal model of Alzheimer's disease (AD), rats infused with amyloid-beta (Abeta) peptide (1-40) into the cerebral ventricle. Inbred 3rd generation male rats (20 wk old) fed a fish oil-deficient diet were randomly divided into 4 groups: a vehicle group, an Abeta peptide-infused group (Abeta group), a DHA group, and an Abeta + DHA group. A mini-osmotic pump filled with Abeta peptide or vehicle was implanted in the rats, and they were tested for learning ability-related reference and working memory in an 8-arm radial maze. The rats were then orally fed DHA dissolved in 5% gum Arabic solution at 300 mg/(kg . d) (DHA and Abeta + DHA groups) or vehicle alone (vehicle and Abeta groups) and tested again for learning ability. DHA administered for 12 wk significantly reduced the increase in the number of reference and working memory errors in the Abeta-infused rats, and increased both the cortico-hippocampal level of DHA and the molar ratio of DHA/arachidonic acid, suggesting an amelioration of the impaired spatial cognition learning ability. Furthermore, DHA suppressed the increases in the levels of lipid peroxide and reactive oxygen species in the cerebral cortex and the hippocampus of Abeta-infused rats, suggesting that DHA increases antioxidative defenses. DHA is thus a possible therapeutic agent for ameliorating learning deficiencies due to Alzheimer's disease.

Attenuation by a sigma1 (sigma1) receptor agonist of the learning and memory deficits induced by a prenatal restraint stress in juvenile rats

1. Stress during pregnancy results in complex neurochemical and behavioral alterations throughout the offspring lifetime. We here examined the impact of prenatal stress (PS) on memory functions in male and female offspring and report the efficacy of a selective sigma(1) (sigma(1)) receptor agonist, igmesine, in alleviating the observed deficits. 2. Dams received an unpredictable 90-min duration restraint stress from gestational day E17 to E20. Learning was examined in offspring between day P24 and P36 using spontaneous alternation in the Y-maze, delayed alternation in the T-maze, water-maze learning and passive avoidance. 3. Both male and female PS rats showed impairments of spontaneous and delayed alternation performances. Acquisition of a fixed platform position in the water-maze was unchanged in PS rats, but the probe test revealed a diminution of time spent in the training quadrant. Acquisition of a daily changing platform position demonstrated impaired working memory for male and female PS rats. Finally, passive avoidance deficits were observed. 4. Pretreatment with the selective sigma(1) agonist igmesine (1-10 mg x kg(-1) i.p.) reversed the PS-induced learning deficits in offspring rats for each test. The sigma(1) antagonist BD1063 failed to affect performances alone but blocked the igmesine effect, confirming the involvement of the sigma(1) receptor. 5. PS thus induces delayed memory deficits, affecting spatial and nonspatial, short- and long-term memories in juvenile male and female offspring rats. Activation of the sigma(1) neuromodulatory receptor allows a significant recovery of the memory functions in PS rats.

Beta-amyloid (1-42)-induced learning and memory deficits in mice: involvement of oxidative burdens in the hippocampus and cerebral cortex

We have demonstrated that oxidative stress is involved, at least in part, in beta-amyloid protein (Abeta)-induced neurotoxicity in vivo [Eur. J. Neurosci. 1999;11:83-90; Neuroscience 2003;119:399-419]. However, mechanistic links between oxidative stress and memory loss in response to Abeta remain elusive. In the present study, we examined whether oxidative stress contributes to the memory deficits induced by intracerebroventricular injection of Abeta (1-42) in mice. Abeta (1-42)-induced memory impairments were observed, as measured by the water maze and passive avoidance tests, although these impairments were not found in Abeta (40-1)-treated mice. Treatment with antioxidant alpha-tocopherol significantly prevented memory impairment induced by Abeta (1-42). Increased activities of the cytosolic Cu,Zn-superoxide dismutase (Cu,Zn-SOD) and mitochondrial Mn-superoxide dismutase (Mn-SOD) were observed in the hippocampus and cerebral cortex of Abeta (1-42)-treated animals, as compared with Abeta (40-1)-treated mice. The induction of Cu,Zn-SOD was more pronounced than that of Mn-SOD after Abeta (1-42) insult. However, the concomitant induction of glutathione peroxidase (GPX) in response to significant increases in SOD activity was not seen in animals treated with Abeta (1-42). Furthermore, glutathione reductase (GRX) activity was only increased at 2h after Abeta (1-42) injection. Production of malondialdehyde (lipid peroxidation) and protein carbonyl (protein oxidation) remained elevated at 10 days post-Abeta (1-42), but the antioxidant alpha-tocopherol significantly prevented these oxidative stresses. Therefore, our results suggest that the oxidative stress contributes to the Abeta (1-42)-induced learning and memory deficits in mice.

A humanin derivative, S14G-HN, prevents amyloid-?-induced memory impairment in mice

Humanin (HN) is a 24-amino acid peptide that protects neuronal cells from death caused by Alzheimer's disease (AD)-related genes and amyloid-beta (Abeta). Multiple studies have revealed its biochemical and neuroprotective characteristics in vitro; however, little has been known regarding whether HN is effective in vivo in AD model systems. We examined the effect of S14G-HN, a 1,000-fold more potent derivative of HN in vitro, on amnesia induced by Abeta25-35 in mice. The Y-maze test revealed that at least 50 pmol of S14G-HN by intracerebroventricular injection prevented Abeta-induced impairment of short-term/spatial working memory; however, 5 nmol of S14A-HN, a neuroprotection-defective mutant in vitro, did not prevent Abeta-induced amnesia. These results are in agreement with the structure-function correlation shown previously in vitro. In the water-finding task, S14G-HN prevented prolongation of finding latency (the time to find water) observed in Abeta-amnesic mice, indicating that S14G-HN also blocked Abeta-induced impairment of latent learning. In accordance with these observations, immunohistochemical analysis showed that S14G-HN sustained the number of cholinergic neurons in the basal forebrain and the striata nearly to the normal level. Furthermore, genistein, a specific inhibitor of tyrosine kinases, blocked recovery from scopolamine-induced amnesia by S14G-HN, suggesting that certain tyrosine kinase(s) are involved in the inhibitory function of S14G-HN in vivo. Taking these findings together, we conclude that S14G-HN has rescue activity against memory impairment caused by AD-related insults in vivo by activating the same intracellular neuroprotective machinery as elucidated previously in vitro.

The protective role of vitamin E in vascular amyloid beta-mediated damage

Amyloid beta peptide (Abeta) accumulation produces the senile plaques in the brain parenchyma characteristic of Alzheimer's Disease (AD) and the vascular deposits of Cerebral Amyloid Angiopathy (CAA). Oxidative stress is directly involved in Abeta-mediated cytotoxicity and antioxidants have been reported as cytoprotective in AD and CAA. Vitamin E has antioxidant and hydrophobic properties that render this molecule as the main antioxidant present in biological membranes, preventing lipid peroxidation, carbonyl formation and inducing intracellular modulation of cell signalling pathways. Accordingly, vascular damage produced by Abeta and prooxidant agents can be decreased or prevented by vitamin E. The protective effect of vitamin E against Abeta cytotoxicity in vascular cells in comparison to the neuronal system is reviewed in this chapter.

Tocopherol (vitamin E) in Alzheimer's disease and other neurodegenerative disorders

In this article, we review the evidence that tocopherol (vitamin E) may have a role to play in the prevention and treatment of Alzheimer's disease and other neurological diseases. The theoretical rationale for the effectiveness of tocopherol as treatment and/or prevention of Alzheimer's disease is based on its antioxidant properties. Results from animal and in vitro studies provide evidence to support use of tocopherol for prevention and treatment of degenerative neurological diseases. Furthermore, several, but not all, epidemiological, cross-sectional, prospective studies indicate that tocopherol may have protective effects in Alzheimer's disease, although dietary and supplemental forms of the vitamin may differ in their efficacy. Mixed results have been obtained from clinical trials. Evidence of the use of tocopherol as a protective measure or as therapy in neurological diseases other than Alzheimer's disease is less compelling. To date, there are no clear-cut answers as to whether tocopherol is worth prescribing, but current clinical practice favours its use in the treatment of Alzheimer's disease.

Beneficial effects of the sigma1 receptor agonists igmesine and dehydroepiandrosterone against learning impairments in rats prenatally exposed to cocaine

In utero cocaine (IUC) exposure results in offspring rats in complex neurochemical and behavioral alterations, particularly affecting learning and memory processes. We examined here the impact of IUC exposure on memory functions in male and female offspring rats and report that selective sigma(1) (sigma(1)) receptor agonists are effective in reversing the deficits. Dams received a daily cocaine, 20 mg/kg ip, injection between gestational days E17 to E20. Learning was examined in offspring between day P30 and P41 using delayed alternation in the T-maze, water-maze learning and passive avoidance. Both male and female rats prenatally exposed to cocaine showed delayed alternation deficits and impairments of acquisition of a fixed platform position in the water maze, as shown by higher acquisition latencies and diminutions of time spent in the training quadrant during the probe test. The acquisition of a daily changing platform position also demonstrated impaired working memory. Finally, passive avoidance deficits were observed. Pretreatment with the synthetic sigma(1) agonist igmesine (0.1-1 mg/kg ip) or the neuroactive steroid dehydroepiandrosterone (DHEA 10-40 mg/kg ip) reversed the prenatal cocaine-induced learning deficits in offspring rats for each test. The sigma(1) antagonist BD1063 (1 mg/kg ip) failed to affect performances alone but blocked the igmesine and DHEA effects, confirming the involvement of the sigma(1) receptor. IUC exposure thus results in marked memory deficits, affecting spatial and nonspatial short- and long-term memories in juvenile male and female offspring rats. The activation of the sigma(1) neuromodulatory receptor allows a complete behavioral recovery of the memory functions in prenatally cocaine-exposed rats.

Effects of alpha-tocopherol on an animal model of tauopathies

We have reported that transgenic (Tg) mice overexpressing human tau protein develop filamentous tau aggregates in the CNS. We overexpressed the smallest human tau isoform (T44) in the mouse CNS to model tauopathies. These tau Tg mice acquire age-dependent CNS pathologies, including insoluble, hyperphosphorylated tau and argyrophilic intraneuronal inclusions formed by tau-immunoreactive filaments. Therefore, these Tg mice are a model that can be exploited for drug discovery in studies that target amelioration of tau-induced neurodegeneration as well as for elucidating mechanisms of tau pathology in various neurodegenerative tauopathies. Oxidative stress has been implicated in the pathogenesis of various neurodegenerative diseases, including tauopathies, and many epidemiological, clinical, and basic studies have suggested the neuroprotective effects of vitamin E in neurodegenerative diseases. To elucidate the role of oxidative damage in the pathological mechanisms of these Tg mice, we fed them alpha-tocopherol, the major component of antioxidant vitamin E. Supplementation of alpha-tocopherol suppressed and/or delayed the development of tau pathology, which correlated with improvement in the health and attenuation of motor weakness in the Tg mice. These results suggest that oxidative damage is involved in the pathological mechanisms of the tau Tg mice and that treatment with antioxidative agents like alpha-tocopherol may prevent neurodegenerative tauopathies.

Naringenin from Citrus junos has an inhibitory effect on acetylcholinesterase and a mitigating effect on amnesia

This study was performed to identify safe and more effective acetylcholinesterase (AChE) inhibitors in the treatment of Alzheimer's disease. The total methanol extract of Citrus junos had a significant inhibitory effect on AChE in vitro. By sequential fractionation of C.junos, the active component was finally identified as naringenin. Naringenin inhibited AChE activity in a dose-dependent manner. In this study, we also evaluated the anti-amnesic activity of naringenin, a major flavanone constituent isolated from C. junos, in vivo using ICR mice with amnesia induced by scopolamine (1 mg/kg body weight). Naringenin, when administered to mice at 4.5 mg/kg body weight, significantly ameliorated scopolamine-induced amnesia as measured in both the passive avoidance and the Y-maze test. These results suggest that naringenin may be a useful chemopreventive agent against Alzheimer's disease.

Protection against beta-amyloid peptide-induced memory impairment with long-term administration of extract of Angelica gigas or decursinol in mice

We investigated the effect of long-term oral administration of ethanolic extract of Angelica gigas Nakai (Umbelliferae) (EAG) or decursinol, a coumarin isolated from A. gigas, on beta-amyloid peptide 1-42 (Abeta(1-42))-induced memory impairment in mice. Mice were allowed free access to drinking water (control) or water containing different concentrations of EAG. After 4 weeks, Abeta(1-42) (410 pmol) was administered via intracerebroventricular injection. Pretreatment of mice with EAG (0.1%) for 4 weeks significantly blocked the Abeta(1-42)-induced impairment in passive avoidance performance. Next, mice were fed with chow mixed with various doses of decursinol for 4 weeks before intracerebroventricular injection of Abeta(1-42) (410 pmol). Pretreatment of mice with decursinol (0.001%, 0.002%, and 0.004%) for 4 weeks significantly attenuated the Abeta(1-42)-induced impairment in passive avoidance performance. Decursinol (0.004%) also significantly blunted the Abeta(1-42)-induced decrease in alternation behavior (spatial working memory) in the Y-maze test without change in general locomotor activity. These findings suggest that EAG or decursinol may have preventive effect against memory impairment related with Abeta of Alzheimer's disease.

Association between antioxidant nutritional indicators and the incidence of dementia: results from the PAQUID prospective cohort study

OBJECTIVE

To analyse the relation between antioxidant vitamins A, E, and malondialdehyde (MDA) lipoperoxidation product plasma concentrations with incident dementia.

DESIGN

: A nested case-control within the PAQUID (Personnes Agées QUID) cohort.

SETTING

The PAQUID population-based prospective cohort in southwestern France.

SUBJECTS

Among 626 subjects with blood collection at baseline, 46 developed a dementia during the follow-up and were considered to be cases. Each case was matched (on age and sex) to three controls.

RESULTS

Plasma vitamin E concentrations were lower among cases (mean value at 22.62 micromol/l (s.d.: 7.38) vs 24.99 (s.d.: 6.73 among controls). The same trend was observed for vitamin A concentrations, but the difference was not significant. On the contrary, MDA concentrations tended to be higher (mean value 1.35 micromol/l (s.d.: 0.53) vs 1.23 (s.d.: 0.44)) among cases. In logistic regression models, plasma values were split into tertiles. Adjusted for confounders, the risk of dementia was significantly increased in the lowest vitamin E tertile (< or =21.0 micromol/l) (OR=3.12, P=0.033) compared to the highest one (> or =25.5 micromol/l). The risk of Alzheimer's disease was also increased, with borderline significance (OR=3.06, P=0.053). Risks associated with vitamin A were nonsignificant. Similarly, there was a trend to an increased risk of dementia in the highest tertile of MDA (OR=1.67, P=0.31).

CONCLUSIONS

These results suggest that subjects with low plasma vitamin E concentrations are at a higher risk of developing a dementia in subsequent years.

Prevention of age-related spatial memory deficits in a transgenic mouse model of Alzheimer's disease by chronic Ginkgo biloba treatment

Alzheimer's disease (AD) is characterized by cognitive decline and deposition of beta-amyloid (Abeta) plaques in cortex and hippocampus. A transgenic mouse AD model (Tg2576) that overexpresses a mutant form of human Abeta precursor protein exhibits age-related cognitive deficits, Abeta plaque deposition, and oxidative damage in the brain. We tested the ability of Ginkgo biloba, a flavonoid-rich antioxidant, to antagonize the age-related behavioral impairment and neuropathology exhibited by Tg2576 mice. At 8 months of age, 16 female Tg2576 and 15 female wild-type (wt) littermate mice were given ad lib access to tap water or Ginkgo biloba (70 mg/kg/day in water). After 6 months of treatment, all mice received Morris water maze training (4 trials/day for 10 days) to assess hippocampal dependent spatial learning. All mice received a 60-s probe test of spatial memory retention 24 h after the 40th trial. Untreated Tg2576 mice exhibited a spatial learning impairment, relative to wt mice, while Ginkgo biloba-treated Tg2576 mice exhibited spatial memory retention comparable to wt during the probe test. Spatial learning was not different between Ginkgo biloba-treated and untreated wt mice. There were no group differences in learning to swim to a visible platform. Soluble Abeta and hippocampal Abeta plaque burden did not differ between the Tg2576 groups. Brain levels of protein carbonyls were paradoxically elevated in Ginkgo biloba-treated mice. These data indicate that chronic Ginkgo biloba treatment can block an age-dependent decline in spatial cognition without altering Abeta levels and without suppressing protein oxidation in a transgenic mouse model of AD.

Amnesia induced by β-amyloid fragments is counteracted by cannabinoid CB1 receptor blockade

Administration of drugs activating cannabinoid CB(1) receptors in the brain induces memory deficit in rodents, and blockade of these receptors may restore memory capacity in these animals. Central administration of beta-amyloid or beta-amyloid fragments may also lead to memory disturbances. This study was undertaken to study the involvement of cannabinoid CB(1) receptors in amnesia induced by beta-amyloid fragments in mice tested in a step-through passive avoidance paradigm. Pre-training intracerebroventricular (i.c.v.) injection of beta-amyloid fragments, beta-amyloid peptide-(25-35) (4, 8 or 16 nmol/mouse) or beta-amyloid peptide-(1-42) (200, 400, 800 pmol/mouse) 7 days prior to the learning trial reduced in a dose-dependent manner the retention of passive avoidance response. This effect was observed in two retention tests, 1 and 7 days after the learning trial. The two beta-amyloid fragments showed similar potency in reducing retention of passive avoidance behavior. This effect was counteracted by a single intraperitoneal (i.p.) injection of the cannabinoid CB(1) receptor antagonist, N-(piperidin-l-yl)-5-(4-chlorophenyl)-1-(2,4-dichlorophenyl)-4-methyl-1H-pyrazole-3-carboxamide hydrochloride (SR141716A, 1 mg/kg), made 30 min prior to the second retention test. The injection of SR141716A per se did not affect memory capacity of mice. The i.c.v. administration of beta-amyloid peptide-(25-35) (8 nmol/mouse) or of beta-amyloid peptide-(1-42) (400 pmol/mouse) made 30 min prior to the learning trial failed to affect the retention capacity of mice as measured 1 and 7 days later. Also, the i.p. injection of SR 141716A (1 mg/kg) made 30 min prior to the learning trial did not influence the behavioral response of mice injected with beta-amyloid peptide-(25-35) (8 nmol/mouse) or of beta-amyloid peptide-(1-42) (400 pmol/mouse) 7 days prior to the learning trial. These results show that beta-amyloid fragments induce a dose-dependent memory deficit. Their effect on memory retention depends upon the time of administration and seems to involve cannabinoid CB(1) receptors in the brain.

Immunocytochemical evidence that amyloid beta (1-42) impairs endogenous antioxidant systems in vivo

Amyloid beta, the major constituent of the senile plaques in the brains of patients with Alzheimer's disease, is cytotoxic to neurons and has a central role in the pathogenesis of the disease. We have previously demonstrated that potent antioxidants idebenone and alpha-tocopherol prevent learning and memory impairment in rats which received a continuous intracerebroventricular infusion of amyloid beta, suggesting a role for oxidative stress in amyloid beta-induced learning and memory impairment. To test the hypothesis, in the present study, we investigated alterations in the immunoreactivity of endogenous antioxidant systems such as mitochondrial Mn-superoxide dismutase, glutathione, glutathione peroxidase and glutathione-S-transferase following the continuous intracerebroventricular infusion of amyloid beta for 2 weeks. The infusion of amyloid beta (1-42) resulted in a significant reduction of the immunoreactivity of these antioxidant substances in such brain areas as the hippocampus, parietal cortex, piriform cortex, substantia nigra and thalamus although the same treatment with amyloid beta (40-1) had little effect. The alterations induced by amyloid beta (1-42) were not uniform, but rather specific for each immunoreactive substance in a brain region-dependent manner. These results demonstrate a cytological effect of oxidative stress induced by amyloid beta (1-42) infusion. Furthermore, our findings may indicate a heterogeneous susceptibility to the oxidative stress produced by amyloid beta.

Effects of oleamide on choline acetyltransferase and cognitive activities

We screened 50 Korean traditional natural plants to measure the activation effect on choline acetyltransferase and attenuation of scopolamine-induced amnesia. The methanolic extracts from Zizyphus jujuba among the tested 50 plants, showed the highest activatory effect (34.1%) on choline acetyltransferase in vitro. By sequential fractionation of Zizyphus jujuba, the active component was finally identified as cis-9-octadecenoamide (oleamide). After isolation, oleamide showed a 65% activation effect. Administration of oleamide (0.32%) to mice significantly reversed the scopolamine-induced memory and/or cognitive impairment in the passive avoidance test and Y-maze test. Injection of scopolamine to mice impaired performance on the passive avoidance test (31% decrease in step-through latency), and on the Y-maze test (16% decrease in alternation behavior). In contrast, mice treated with oleamide before scopolamine injection were protected from these changes (12-25% decrease in step-through latency; 1-10% decrease in alternation behavior). These results suggest that oleamide should be a useful chemo-preventive agent against Alzheimer's disease.

Tyrosine nitration of a synaptic protein synaptophysin contributes to amyloid beta-peptide-induced cholinergic dysfunction

Amyloid beta (Abeta) is a critical factor involved in the pathogenesis of Alzheimer's disease (AD). We have previously demonstrated that continuous intracerebroventricular infusion of Abeta1-40 induced a time-dependent expression of the inducible nitric oxide (NO) synthase (iNOS) and an overproduction of NO in the rat hippocampus. The pathophysiological significance of the overproduction of NO on brain function was manifested by an impairment of nicotine-evoked acetylcholine(ACh) release and memory deficits.(4) Molecular mechanisms by which NO participates in the Abeta-induced brain dysfunction, however, remain to be determined. Here we show that chronic Abeta1-40 infusion caused a robust peroxynitrite formation and subsequent tyrosine nitration of proteins in the hippocampus. Immunoprecipitation and Western blot analyses further revealed that synaptophysin, a synaptic protein, was a main target of tyrosine nitration. Chronic infusion of Abeta1-40 resulted in an impairment of nicotine-evoked ACh release as analyzed by microdialysis. Daily treatment with the iNOS inhibitor aminoguanidine (AG) or the peroxynitrite scavenger uric acid (UA) prevented the tyrosine nitration of synaptophysin as well as the impairment of nicotine-evoked ACh release induced by Abeta. Our findings suggest that the tyrosine nitration of synaptophysin is related to Abeta-induced impairment of ACh release.

Activation of Wnt signaling rescues neurodegeneration and behavioral impairments induced by beta-amyloid fibrils

Alzheimer's disease (AD) is a progressive neurodegenerative disorder, which is probably caused by the cytotoxic effect of the amyloid beta-peptide (Abeta). We report here molecular changes induced by Abeta, both in neuronal cells in culture and in rats injected in the dorsal hippocampus with preformed Abeta fibrils, as an in vivo model of the disease. Results indicate that in both systems, Abeta neurotoxicity resulted in the destabilization of endogenous levels of beta-catenin, a key transducer of the Wnt signaling pathway. Lithium chloride, which mimics Wnt signaling by inhibiting glycogen synthase kinase-3beta promoted the survival of post-mitotic neurons against Abeta neurotoxicity and recovered cytosolic beta-catenin to control levels. Moreover, the neurotoxic effect of Abeta fibrils was also modulated with protein kinase C agonists/inhibitors and reversed with conditioned medium containing the Wnt-3a ligand. We also examined the spatial memory performance of rats injected with preformed Abeta fibrils in the Morris water maze paradigm, and found that chronic lithium treatment protected neurodegeneration by rescuing beta-catenin levels and improved the deficit in spatial learning induced by Abeta. Our results are consistent with the idea that Abeta-dependent neurotoxicity induces a loss of function of Wnt signaling components and indicate that lithium or compounds that mimic this signaling cascade may be putative candidates for therapeutic intervention in Alzheimer's patients.

Cognition impairment in the genetic model of aging klotho gene mutant mice: a role of oxidative stress

A new gene, termed klotho, is associated with the suppression of several aging phenotypes. Because high expression of klotho gene was detected in the brain, it would be plausible that klotho gene is involved in the regulation of brain aging. We investigated the changes in mnemonic function accompanying aging in klotho mutant mice. Cognitive function measured by novel-object recognition and conditioned-fear tests in klotho mutant mice was normal at the age of 6 wk, but markedly impaired at the age of 7 wk. Lipid (malondialdehyde) and DNA (8-hydroxy-2'-deoxyguanosine) peroxide levels in the hippocampus of klotho mutant mice increased at the age of 5 wk, 2 wk before the development of cognition deficits. Pro-death Bax increased, whereas anti-death Bcl-2 and Bcl-XL decreased, and apoptotic TUNEL-positive cells were detected in the hippocampus of klotho mutant mice at the age of 7 wk. A potent antioxidant, a-tocopherol, prevented cognition impairment and lipid peroxide accumulation and decreased the number of apoptotic cells in klotho mutant mice. These results suggest that oxidative stress has a crucial role in the aging-associated cognition impairment in klotho mutant mice. Klotho protein may be involved in the regulation of antioxidative defense.

Memory impairment induced by chronic intracerebroventricular infusion of beta-amyloid (1-40) involves downregulation of protein kinase C

Signaling pathways underlying the cognitive deficit of the Alzheimer's disease (AD) are not completely understood. Protein kinase C (PKC), a major neuronal protein plays a critical role in cellular signal transduction and it is known to be subjected to modulation in AD. We showed previously that, chronic infusion of beta-amyloid (1-40) into rat cerebroventricle leads to deficit in spatial and non-spatial memory formation. As an attempt to identify the cellular correlates of the memory deficit, in the present study we investigated the PKC activation in different brain areas. Chronic infusion of beta-amyloid (1-40) for 14 days into the rat cerebroventricle decreased the activity of soluble protein kinase C (PKC) in the hippocampus. Subcellular translocation of PKC to membrane fraction in hippocampal slices of rats treated with beta-amyloid (1-40) was completely abolished under acute stimulation with 0.5 microM phorbol-dibutyrate (PDBu). We also reported a decreased affinity (k(D)) for PDBu binding in the hippocampus, cerebral cortex and striatum. The total number of binding sites for PDBu (B(max)) was increased, in the three brain areas analyzed on the day 14, but the changes were not statistically significant. Our data indicate that chronic accumulation of beta-amyloid (1-40) into the rat brain reduced activation of PKC, effect that would substantially contribute to the memory deficit found in these animals.

Amyloid beta-peptide 25-35 reduces [3H]acetylcholine release in retinal neurons. Involvement of metabolic dysfunction

Cholinergic pathways serve important functions in learning and memory processes. The loss of basal forebrain cholinergic neurons and the presence of senile plaques composed by amyloid beta-peptide (A beta) are found in post-mortem brains of Alzheimer's disease (AD) patients. However, the role of A beta in the cholinergic dysfunction observed in AD is not yet clarified. In this study, we observed that the release of [3H]acetylcholine evoked by K(+)-depolarization was significantly lower in cells treated with A beta 25-35 peptide, than in untreated cells or in cells exposed to the reverse sequence peptide A beta 35-25. The levels of pyruvate, the substrate for pyruvate dehydrogenase, the enzyme involved in acetyl coenzyme A synthesis in the brain, which is rate-limiting for the synthesis of acetylcholine, were significantly decreased, about 40%, in A beta treated cells. A beta 25-35 did not affect choline acetyltransferase activity or [3H]choline uptake. 2-[3H]-deoxyglucose uptake was decreased when cells were exposed to A beta 25-35 or to A beta 1-40. Taken together these data suggest that an impairment of glycolysis, and the consequent decrease in pyruvate levels, may be responsible for the decrement of acetylcholine release observed in A beta treated cells, thus sustaining the hypothesis that the cholinergic dysfunction, observed in AD patients, might be associated with extracellular A beta accumulation.

Neuroplasticity in Alzheimer's disease

Ramon y Cajal proclaimed in 1928 that "once development was ended, the founts of growth and regeneration of the axons and dendrites dried up irrevocably. In the adult centers the nerve paths are something fixed, ended and immutable. Everything must die, nothing may be regenerated. It is for the science of the future to change, if possible, this harsh decree." (Ramon y Cajal, 1928). In large part, despite the extensive knowledge gained since then, the latter directive has not yet been achieved by 'modern' science. Although we know now that Ramon y Cajal's observation on CNS plasticity is largely true (for lower brain and primary cortical structures), there are mechanisms for recovery from CNS injury. These mechanisms, however, may contribute to the vulnerability to neurodegenerative disease. They may also be exploited therapeutically to help alleviate the suffering from neurodegenerative conditions.