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

The amyloid cascade hypothesis: an updated critical review

Results from recent clinical trials of antibodies that target amyloid-β (Aβ) for Alzheimer's disease have created excitement and have been heralded as corroboration of the amyloid cascade hypothesis. However, while Aβ may contribute to disease, genetic, clinical, imaging and biochemical data suggest a more complex aetiology. Here we review the history and weaknesses of the amyloid cascade hypothesis in view of the new evidence obtained from clinical trials of anti-amyloid antibodies. These trials indicate that the treatments have either no or uncertain clinical effect on cognition. Despite the importance of amyloid in the definition of Alzheimer's disease, we argue that the data point to Aβ playing a minor aetiological role. We also discuss data suggesting that the concerted activity of many pathogenic factors contribute to Alzheimer's disease and propose that evolving multi-factor disease models will better underpin the search for more effective strategies to treat the disease.

Aberrant Dopamine System Function in the Ferrous Amyloid Buthionine (FAB) Rat Model of Alzheimer's Disease

Antipsychotics increase the risk of death in elderly patients with Alzheimer's disease (AD). Thus, there is an immediate need for novel therapies to treat comorbid psychosis in AD. Psychosis has been attributed to a dysregulation of the dopamine system and is associated with aberrant regulation by the hippocampus. Given that the hippocampus is a key site of pathology in AD, we posit that aberrant regulation of the dopamine system may contribute to comorbid psychosis in AD. A ferrous amyloid buthionine (FAB) rodent model was used to model a sporadic form of AD. FAB rats displayed functional hippocampal alterations, which were accompanied by decreases in spontaneous, low-frequency oscillations and increases in the firing rates of putative pyramidal neurons. Additionally, FAB rats exhibited increases in dopamine neuron population activity and augmented responses to the locomotor-inducing effects of MK-801, as is consistent with rodent models of psychosis-like symptomatology. Further, working memory deficits in the Y-maze, consistent with an AD-like phenotype, were observed in FAB rats. These data suggest that the aberrant hippocampal activity observed in AD may contribute to dopamine-dependent psychosis, and that the FAB model may be useful for the investigation of comorbid psychosis related to AD. Understanding the pathophysiology that leads to comorbid psychosis in AD will ultimately lead to the discovery of novel targets for the treatment of this disease.

Oxidative Stress and Aging as Risk Factors for Alzheimer's Disease and Parkinson's Disease: The Role of the Antioxidant Melatonin

Aging and neurodegenerative diseases share common hallmarks, including mitochondrial dysfunction and protein aggregation. Moreover, one of the major issues of the demographic crisis today is related to the progressive rise in costs for care and maintenance of the standard living condition of aged patients with neurodegenerative diseases. There is a divergence in the etiology of neurodegenerative diseases. Still, a disturbed endogenous pro-oxidants/antioxidants balance is considered the crucial detrimental factor that makes the brain vulnerable to aging and progressive neurodegeneration. The present review focuses on the complex relationships between oxidative stress, autophagy, and the two of the most frequent neurodegenerative diseases associated with aging, Alzheimer's disease (AD) and Parkinson's disease (PD). Most of the available data support the hypothesis that a disturbed antioxidant defense system is a prerequisite for developing pathogenesis and clinical symptoms of ADs and PD. Furthermore, the release of the endogenous hormone melatonin from the pineal gland progressively diminishes with aging, and people's susceptibility to these diseases increases with age. Elucidation of the underlying mechanisms involved in deleterious conditions predisposing to neurodegeneration in aging, including the diminished role of melatonin, is important for elaborating precise treatment strategies for the pathogenesis of AD and PD.

The synergy of β amyloid 1-42 and oxidative stress in the development of Alzheimer's disease-like neurodegeneration of hippocampal cells

Alzheimer's disease (AD) is a type of dementia that affects memory, thinking and behavior. Symptoms eventually become severe enough to interfere with daily tasks. Understanding the etiology and pathogenesis of AD is necessary for the development of strategies for AD prevention and/or treatment, and modeling of this pathology is an important step in achieving this goal. β-amyloid peptide (Aβ) injection is a widely used approach for modeling AD. Nevertheless, it has been reported that the model constructed by injection of Aβ in combination with a prooxidant cocktail (ferrous sulfate, Aβ, and buthionine sulfoximine (BSO) (FAB)) best reflects the natural development of this disease. The relationship between oxidative stress and Aβ deposition and their respective roles in Aβ-induced pathology in different animal models of AD have been thoroughly investigated. In the current paper, we compared the effects of Aβ 1-42 alone with that of Aβ-associated oxidative stress induced by the FAB cocktail on the neurodegeneration of hippocampal cells in vitro. We constructed a FAB-induced AD model using rat primary hippocampal cells and analyzed the contribution of each compound. The study mainly focused on the prooxidant aspects of AD pathogenesis. Moreover, cellular bioenergetics was assessed and routine metabolic tests were performed to determine the usefulness of this model. The data clearly show that aggregated Aβ1-42 alone is significantly less toxic to hippocampal cells. Aggregated Aβ damages neurons, and glial cells proliferate to remove Aβ from the hippocampus. External prooxidant agents (Fe²⁺) or inhibition of internal antioxidant defense by BSO has more toxic effects on hippocampal cells than aggregated Aβ alone. Moreover, hippocampal cells fight against Aβ-induced damage more effectively than against oxidative damage. However, the combination of Aβ with external oxidative damage and inhibition of internal antioxidant defense is even more toxic, impairs cellular defense systems, and may mimic the late phase of AD-associated cell damage. Our findings strongly indicate a critical role for the combination of Aβ and oxidative stress in the development of neurodegeneration in vitro.

Ampelopsin Improves Cognitive Impairment in Alzheimer's Disease and Effects of Inflammatory Cytokines and Oxidative Stress in the Hippocampus

BACKGROUND

Neuroinflammation and oxidative stress have significant effects on cognitive deficiency in the pathophysiological development of Alzheimer's disease (AD). In the present study, we studied the influences of Ampelopsin (AMP) on proinflammatory cytokines (PICs, IL-1β, IL-6 and TNF-α), and products of oxidative stress 8-isoprostaglandin F2α (8-iso PGF2α, a product of oxidative stress); and 8-hydroxy-2'-deoxyguanosine (8-OHdG, a key biomarker of protein oxidation) in the hippocampus using a rat model of AD.

METHODS

ELISA was used to examine PICs and oxidative stress production; and western blotting to examine NADPH oxidase (NOXs). The Spatial working memory tests and Morris water maze were utilized to assess cognitive functions.

RESULTS

We observed amplification of IL-1β, IL-6 and TNF-α as well as 8-iso PGF2α and 8-OHdG in the hippocampus of AD rats. AMP attenuated upregulation of PICs and oxidative stress production. AMP also inhibited NOX4 in the AD rat hippocampus. Notably, AMP mostly improved learning performance in AD rat and this was linked to signal pathways of PIC and oxidative stress.

CONCLUSION

AMP plays a significant role in improving the memory deficiency in AD rats via inhibition of signal pathways of neuroinflammation and oxidative stress, suggesting that AMP is likely to prospect in preventing and relieving development of the cognitive dysfunctions in AD as a complementary alternative intervention.

The effects of astaxanthin treatment on a rat model of Alzheimer's disease

Alzheimer's disease (AD), a progressive neurodegenerative disorder characterized by memory loss and dementia, could be a consequence of the abnormalities of cortical milieu, such as oxidative stress, inflammation, and/or accompanied with the aggregation of β-amyloid. The majority of AD patients are sporadic, late-onset AD, which predominantly occurs over 65 years of age. Our results revealed that the ferrous amyloid buthionine (FAB)-infused sporadic AD-like model showed deficits in spatial learning and memory and with apparent loss of choline acetyltransferase (ChAT) expression in medial septal (MS) nucleus. In hippocampal CA1 region, the loss of pyramidal neurons was accompanied with cholinergic fiber loss and neuroinflammatory responses including glial reaction and enhanced expression of inducible nitric oxide synthase (iNOS). Surviving hippocampal CA1 pyramidal neurons showed the reduction of dendritic spines as well. Astaxanthin (ATX), a potent antioxidant, reported to improve the outcome of oxidative-stress-related diseases. The ATX treatment in FAB-infused rats decreased neuroinflammation and restored the ChAT + fibers in hippocampal CA1 region and the ChAT expression in MS nucleus. It also partly recovered the spine loss on hippocampal CA1 pyramidal neurons and ameliorated the behavioral deficits in AD-like rats. From these data, we believed that the ATX can be a potential option for slowing the progression of Alzheimer's disease.

Impact of Cerebral Radiofrequency Exposures on Oxidative Stress and Corticosterone in a Rat Model of Alzheimer's Disease

BACKGROUND

Alzheimer's disease (AD) is the most common type of neurodegenerative disease leading to dementia. Several studies suggested that mobile phone radiofrequency electromagnetic field (RF-EMF) exposures modified AD memory deficits in rodent models.

OBJECTIVE

Here we aimed to test the hypothesis that RF-EMF exposure may modify memory through corticosterone and oxidative stress in the Samaritan rat model of AD.

METHODS

Long-Evans male rats received intracerebroventricular infusion with ferrous sulphate, amyloid-beta 1-42 peptide, and buthionine-sufloximine (AD rats) or with vehicle (control rats). To mimic cell phone use, RF-EMF were exposed to the head for 1 month (5 days/week, in restraint). To look for hazard thresholds, high brain averaged specific absorption rates (BASAR) were tested: 1.5 W/Kg (15 min), 6 W/Kg (15 min), and 6 W/Kg (45 min). The sham group was in restraint for 45 min. Endpoints were spatial memory in the radial maze, plasmatic corticosterone, heme oxygenase-1 (HO1), and amyloid plaques.

RESULTS

Results indicated similar corticosterone levels but impaired memory performances and increased cerebral staining of thioflavine and of HO1 in the sham AD rats compared to the controls. A correlative increase of cortical HO1 staining was the only effect of RF-EMF in control rats. In AD rats, RF-EMF exposures induced a correlative increase of hippocampal HO1 staining and reduced corticosterone.

DISCUSSION

According to our data, neither AD nor control rats showed modified memory after RF-EMF exposures. Unlike control rats, AD rats showed higher hippocampal oxidative stress and reduced corticosterone with the higher BASAR. This data suggests more fragility related to neurodegenerative disease toward RF-EMF exposures.

Inhibition of microRNA-155 Alleviates Cognitive Impairment in Alzheimer's Disease and Involvement of Neuroinflammation

BACKGROUND

Neuroinflammation has important effects on cognitive functions in the pathophysiological process of Alzheimer's Disease (AD). In the current report, we determined the effects of microRNA-155 (miR-155) on the levels of IL-1β, IL-6 and TNF-α, and their respective receptors in the hippocampus using a rat model of AD.

METHODS

Real-time RT-PCR, ELISA and western blot analysis were used to examine the miR-155, PICs and PIC receptors. The Morris water maze and spatial working memory tests were used to assess cognitive functions.

RESULTS

miR-155 was increased in the hippocampus of AD rats, accompanied by amplification of IL-1β, IL-6 and TNF-α. Intracerebroventricular infusion of miR-155 inhibitor, but not its scramble attenuated the increases of IL-1β, IL-6 and TNF-α and upregulation of their receptors. MiR-155 inhibitor also attenuated upregulation of apoptotic Caspase-3 in the hippocampus of AD rats. Notably, inhibition of miR- 155 or PIC receptors largely recovered the impaired learning performance in AD rat.

CONCLUSION

We showed the critical role of miR-155 in regulating the memory impairment in AD rats likely via engagement of neuroinflammatory mechanisms, suggesting that miR-155 and its signaling molecules may present prospects in preventing and/or improving the development of the impaired cognitive functions in AD.

β-amyloid and Oxidative Stress: Perspectives in Drug Development

Alzheimer's Disease (AD) is a slow-developing neurodegenerative disorder in which the main pathogenic role has been assigned to β-amyloid protein (Aβ) that accumulates in extracellular plaques. The mechanism of action of Aβ has been deeply analyzed and several membrane structures have been identified as potential mediators of its effect. The ability of Aβ to modify neuronal activity, receptor expression, signaling pathways, mitochondrial function, and involvement of glial cells have been analyzed. In addition, extensive literature deals with the involvement of oxidative stress in Aβ effects. Herein we focus more specifically on the reciprocal regulation of Aβ, that causes oxidative stress, that favors Aβ aggregation and toxicity and negatively affects the peptide clearance. Analysis of this strict interaction may offer novel opportunities for therapeutic intervention. Both common and new molecules endowed with antioxidant properties deserve attention in this regard.

Utility of Animal Models to Understand Human Alzheimer's Disease, Using the Mastermind Research Approach to Avoid Unnecessary Further Sacrifices of Animals

To diagnose and treat early-stage (preclinical) Alzheimer’s disease (AD) patients, we need body-fluid-based biomarkers that reflect the processes that occur in this stage, but current knowledge on associated processes is lacking. As human studies on (possible) onset and early-stage AD would be extremely expensive and time-consuming, we investigate the potential value of animal AD models to help to fill this knowledge gap. We provide a comprehensive overview of processes associated with AD pathogenesis and biomarkers, current knowledge on AD-related biomarkers derived from on human and animal brains and body fluids, comparisons of biomarkers obtained in human AD and frequently used animal AD models, and emerging body-fluid-based biomarkers. In human studies, amyloid beta (Aβ), hyperphosphorylated tau (P-tau), total tau (T-tau), neurogranin, SNAP-25, glial fibrillary acidic protein (GFAP), YKL-40, and especially neurofilament light (NfL) are frequently measured. In animal studies, the emphasis has been mostly on Aβ. Although a direct comparison between human (familial and sporadic) AD and (mostly genetic) animal AD models cannot be made, still, in brain, cerebrospinal fluid (CSF), and blood, a majority of similar trends are observed for human AD stage and animal AD model life stage. This indicates the potential value of animal AD models in understanding of the onset and early stage of AD. Moreover, animal studies can be smartly designed to provide mechanistic information on the interrelationships between the different AD processes in a longitudinal fashion and may also include the combinations of different conditions that may reflect comorbidities in human AD, according to the Mastermind Research approach.

The New Application of UHPLC-DAD-TOF/MS in Identification of Inhibitors on β-Amyloid Fibrillation From Scutellaria baicalensis

Literary evidence depicts that aggregated β-amyloid (Aβ) leads to the pathogenesis of Alzheimer's disease (AD). Although many traditional Chinese medicines (TCMs) are effective in treating neurodegenerative diseases, there is no effective way for identifying active compounds from their complicated chemical compositions. Instead of using a traditional herbal separation method with low efficiency, we herein apply UHPLC-DAD-TOF/MS for the accurate identification of the active compounds that inhibit the fibrillation of Aβ (1-42), via an evaluation of the peak area of individual chemical components in chromatogram, after incubation with an Aβ peptide. Using the neuroprotective herbal plant Scutellaria baicalensis (SB) as a study model, the inhibitory effect on Aβ by its individual compounds, were validated using the thioflavin-T (ThT) fluorescence assay, biolayer interferometry analysis, dot immunoblotting and native gel electrophoresis after UHPLC-DAD-TOF/MS analysis. The viability of cells after Aβ (1-42) incubation was further evaluated using both the tetrazolium dye (MTT) assay and flow cytometry analysis. Thirteen major chemical components in SB were identified by UHPLC-DAD-TOF/MS after incubation with Aβ (1-42). The peak areas of two components from SB, baicalein and baicalin, were significantly reduced after incubation with Aβ (1-42), compared to compounds alone, without incubation with Aβ (1-42). Consistently, both compounds inhibited the formation of Aβ (1-42) fibrils and increased the viability of cells after Aβ (1-42) incubation. Based on the hypothesis that active chemical components have to possess binding affinity to Aβ (1-42) to inhibit its fibrillation, a new application using UHPLC-DAD-TOF/MS for accurate identification of inhibitors from herbal plants on Aβ (1-42) fibrillation was developed.

Okadaic Acid and Hypoxia Induced Dementia Model of Alzheimer's Type in Rats

Alzheimer's disease (AD) is the most common cause of progressive decline of memory function in aged humans. To study about a disease mechanism and progression, animal models for the specific disease are needed. For AD, although highly valid animal models exist, none of the existing models recapitulates all aspects of human AD. The pathogenic mechanisms involved in AD are diverse and thus it is difficult to recapitulate human AD in model organisms. Intracerebroventricular (ICV) injection of okadaic acid (OKA), a protein phosphatase 2A (PP2A) inhibitor, in rats causes neurotoxicity associated with neurofibrillary degeneration. However, this model lacks amyloid pathology as observed in AD. We aimed at combining two different treatments and hence producing a better animal model of AD which may mimic most of the neuropathological, neurobehavioral, and neurochemical changes observed in AD. For this, OKA (200 ng) was microinjected bilaterally into the hippocampus of male Wistar rats followed by exposure of same rats to hypoxic conditions (10%) for 3 days. The result of which, the combination model exhibited tau hyperphosphorylation along with Aβ upregulation as evident by western blotting and immunohistochemistry. The observed changes were accompanied with dysfunction of neurotransmitter system, i.e., decreased acetylcholine activity and expression. This combinatorial model also exhibited cognitive deficiency which was assessed by Morris water maze and avoidance tests along with enhanced oxidative stress which is thought to be a major player in AD pathogenesis. Taken together, we established an easily reproducible and reliable rat model for sporadic dementia of Alzheimer's type in rats which allows effective testing of new therapeutic strategies.

APP21 transgenic rats develop age-dependent cognitive impairment and microglia accumulation within white matter tracts

BACKGROUND

Most of the animal models commonly used for preclinical research into Alzheimer's disease (AD) largely fail to address the pathophysiology, including the impact of known risk factors, of the widely diagnosed sporadic form of the disease. Here, we use a transgenic rat (APP21) that does not develop AD-like pathology spontaneously with age, but does develop pathology following vascular stress. To further the potential of this novel rat model as a much-needed pre-clinical animal model of sporadic AD, we characterize APP21 transgenic rats behaviorally and histologically up to 19 months of age.

METHODS

The open field test was used as a measure of activity; and the Morris water maze was used to assess learning, memory, and strategy shift. Neuronal loss and microglia activation were also assessed throughout the brain.

RESULTS

APP21 transgenic rats showed deficits in working memory from an early age, yet memory recall performance after 24 and 72 h was equal to that of wildtype rats and did not deteriorate with age. A deficit in strategy shift was observed at 19 months of age in APP21 transgenic rats compared to Fischer wildtype rats. Histologically, APP21 transgenic rats demonstrated accelerated white matter inflammation compared to wildtype rats, but interestingly no differences in neuron loss were observed.

CONCLUSIONS

The combined presence of white matter pathology and executive function deficits mirrored what is often found in patients with mild cognitive impairment or early dementia, and suggests that this rat model will be useful for translationally meaningful studies into the development and prevention of sporadic AD. The presence of widespread white matter inflammation as the only observed pathological correlate for cognitive deficits raises new questions as to the role of neuroinflammation in cognitive decline.

Cerebral mTOR signal and pro-inflammatory cytokines in Alzheimer's disease rats

As a part of Alzheimer’s disease (AD) development the mammalian target of rapamycin (mTOR) has been reported to play a crucial role in regulating cognition and can be used as a neuronal marker. Neuro-inflammation is also a cause of the pathophysiological process in AD. Thus, we examined the protein expression levels of mTOR and its downstream pathways as well as pro-inflammatory cytokines (PICs) in the brain of AD rats. We further examined the effects of blocking mTOR on PICs, namely IL-1β, IL-6 and TNF-α. Our results showed that the protein expression of p-mTOR, mTOR-mediated phosphorylation of 4E-binding protein 4 (4E-BP1) and p70 ribosomal S6 protein kinase 1 (S6K1) pathways were amplified in the hippocampus of AD rats compared with controls. Blocking mTOR by using rapamycin selectively enhanced activities of IL-6 and TNF-α signaling pathways, which was accompanied with an increase of Caspase-3, indicating cellular apoptosis and worsened learning performance. In conclusion, our data for the first time revealed specific signaling pathways engaged in the development of AD, including a regulatory role by the activation of mTOR in PIC mechanisms. Stimulation of mTOR is likely to play a beneficial role in modulating neurological deficits in AD.Targeting one or more of these signaling molecules may present with new opportunities for treatment and clinical management of AD

The hydrogen sulfide releasing compounds ATB-346 and diallyl trisulfide attenuate streptozotocin-induced cognitive impairment, neuroinflammation, and oxidative stress in rats: involvement of asymmetric dimethylarginine

Hydrogen sulfide (H2S) has attracted interest as a gaseous mediator involved in diverse processes in the nervous system, particularly with respect to learning and memory. However, its therapeutic potential in Alzheimer disease (AD) is not fully explored. Therefore, the effects of H2S-releasing compounds against AD-like behavioural and biochemical abnormalities were investigated. Memory deficit was induced by intracerberoventicular injection of streptozotocin (STZ, 3 mg·kg−1). Animals were randomly assigned into 5 groups (12 rats each): normal control, STZ treated, and 3 drug-treated groups receiving naproxen, H2S-releasing naproxen (ATB-346), and diallyl trisulfide in 20, 32, 40 mg·kg−1·day−1, respectively. Memory function was assessed by passive avoidance and T-maze tasks. After 21 days, hippocampal IL-6, malondialdehyde, reduced glutathione (GSH), asymmetric dimethylarginine (ADMA), and acetylcholinestrase activity were determined. ATB-346 and diallyl trisulfide ameliorated behavioural performance and reduced malondialdehyde, ADMA, and acetylcholinestrase activity while increasing GSH. This study demonstrates the beneficial effects of H2S release in STZ-induced memory impairment by modulation of neuroinflammation, oxidative stress, and cholinergic function. It also delineates the implication of ADMA to the cognitive impairment induced by STZ. These findings draw the attention to H2S-releasing compounds as new candidates for treating neurodegenerative disorders that have prominent oxidative and inflammatory components such as AD.

Alzheimer's disease due to loss of function: A new synthesis of the available data

Alzheimer's Disease (AD) is a highly complex disease involving a broad range of clinical, cellular, and biochemical manifestations that are currently not understood in combination. This has led to many views of AD, e.g. the amyloid, tau, presenilin, oxidative stress, and metal hypotheses. The amyloid hypothesis has dominated the field with its assumption that buildup of pathogenic β-amyloid (Aβ) peptide causes disease. This paradigm has been criticized, yet most data suggest that Aβ plays a key role in the disease. Here, a new loss-of-function hypothesis is synthesized that accounts for the anomalies of the amyloid hypothesis, e.g. the curious pathogenicity of the Aβ42/Aβ40 ratio, the loss of Aβ caused by presenilin mutation, the mixed phenotypes of APP mutations, the poor clinical-biochemical correlations for genetic variant carriers, and the failure of Aβ reducing drugs. The amyloid-loss view accounts for recent findings on the structure and chemical features of Aβ variants and their coupling to human patient data. The lost normal function of APP/Aβ is argued to be metal transport across neuronal membranes, a view with no apparent anomalies and substantially more explanatory power than the gain-of-function amyloid hypothesis. In the loss-of-function scenario, the central event of Aβ aggregation is interpreted as a loss of soluble, functional monomer Aβ rather than toxic overload of oligomers. Accordingly, new research models and treatment strategies should focus on remediation of the functional amyloid balance, rather than strict containment of Aβ, which, for reasons rationalized in this review, has failed clinically.

A Rat Model of Alzheimer's Disease Based on Abeta42 and Pro-oxidative Substances Exhibits Cognitive Deficit and Alterations in Glutamatergic and Cholinergic Neurotransmitter Systems

Alzheimer's disease (AD) is one of the most serious human, medical, and socioeconomic burdens. Here we tested the hypothesis that a rat model of AD (Samaritan; Taconic Pharmaceuticals, USA) based on the application of amyloid beta42 (Abeta42) and the pro-oxidative substances ferrous sulfate heptahydrate and L-buthionine-(S, R)-sulfoximine, will exhibit cognitive deficits and disruption of the glutamatergic and cholinergic systems in the brain. Behavioral methods included the Morris water maze (MWM; long-term memory version) and the active allothetic place avoidance (AAPA) task (acquisition and reversal), testing spatial memory and different aspects of hippocampal function. Neurochemical methods included testing of the NR1/NR2A/NR2B subunits of NMDA receptors in the frontal cortex and CHT1 transporters in the hippocampus, in both cases in the right and left hemisphere separately. Our results show that Samaritan rats(™) exhibit marked impairment in both the MWM and active place avoidance tasks, suggesting a deficit of spatial learning and memory. Moreover, Samaritan rats exhibited significant changes in NR2A expression and CHT1 activity compared to controls rats, mimicking the situation in patients with early stage AD. Taken together, our results corroborate the hypothesis that Samaritan rats are a promising model of AD in its early stages.

Specific binding and characteristics of 18β-glycyrrhetinic acid in rat brain

18β-Glycyrrhetinic acid (GA) is the aglycone of glycyrrhizin that is a component of Glycyrrhiza, and has several pharmacological actions in the central nervous system. Recently, GA has been demonstrated to reach the brain by crossing the blood-brain barrier in rats after oral administration of a Glycyrrhiza-containing traditional Japanese medicine, yokukansan. These findings suggest that there are specific binding sites for GA in the brain. Here we show evidence that [³H]GA binds specifically to several brain areas by quantitative autoradiography; the density was higher in the hippocampus, moderate in the caudate putamen, nucleus accumbens, amygdala, olfactory bulb, cerebral cortex, thalamus, and mid brain, and lower in the brain stem and cerebellum. Several kinds of steroids, gap junction-blocking reagents, glutamate transporter-recognized compounds, and glutamate receptor agonists did not inhibit the [³H]GA binding. Microautoradiography showed that the [³H]GA signals in the hippocampus were distributed in small non-neuronal cells similar to astrocytes. Immunohistochemical analysis revealed that immunoreactivity of 11β-hydroxysteroid dehydrogenase type-1 (11β-HSD1), a defined molecule recognized by GA, was detected mainly in neurons, moderately in astrocytes, and very slightly in microglial cells, of the hippocampus. These results demonstrate that specific binding sites for GA exist in rat brain tissue, and suggest that the pharmacological actions of GA may be related to 11β-HSD1 in astrocytes. This finding provides important information to understand the pharmacology of GA in the brain.

Mitochondrial ferritin in neurodegenerative diseases

Mitochondrial ferritin (FtMt) is a novel protein encoded by an intronless gene mapped to chromosome 5q23.1. Ferritin is ubiquitously expressed; however, FtMt expression is restricted to specific tissues such as the testis and the brain. The distribution pattern of FtMt suggests a functional role for this protein in the brain; however, data concerning the roles of FtMt in neurodegenerative diseases remain scarce. In the human cerebral cortex, FtMt expression was increased in Alzheimer's disease patients compared to control cases. Cultured neuroblastoma cells showed low-level expression of FtMt, which was increased by H2O2 treatment. FtMt overexpression showed a neuroprotective effect against H2O2-induced oxidative stress and Aβ-induced neurotoxicity in neuroblastoma cells. FtMt expression was also detected in dopaminergic neurons in the substantia nigra and was increased in patients with restless legs syndrome, while FtMt had a protective effect against cell death in a neuroblastoma cell line model of Parkinson's disease. FtMt is involved in other neurodegenerative diseases such as age-related macular degeneration (AMD), with an FtMt gene mutation identified in AMD patients, and Friedreich's ataxia, which is caused by a deficiency in frataxin. FtMt overexpression in frataxin-deficient cells increased cell resistance to H2O2 damage. These results implicate a neuroprotective role of FtMt in neurodegenerative diseases.

Functional MRI and neural responses in a rat model of Alzheimer's disease

Based on the hypothesis that brain plaques and tangles can affect cortical function in Alzheimer's disease (AD), we investigated functional responses in an AD rat model (called the Samaritan Alzheimer's rat achieved by ventricular infusion of amyloid peptide) and age-matched healthy control. High-field functional magnetic resonance imaging (fMRI) and extracellular neural activity measurements were applied to characterize sensory-evoked responses. Electrical stimulation of the forepaw led to BOLD and neural responses in the contralateral somatosensory cortex and thalamus. In AD brain we noted much smaller BOLD activation patterns in the somatosensory cortex (i.e., about 50% less activated voxels compared to normal brain). While magnitudes of BOLD and neural responses in the cerebral cortex were markedly attenuated in AD rats compared to normal rats (by about 50%), the dynamic coupling between the BOLD and neural responses in the cerebral cortex, as assessed by transfer function analysis, remained unaltered between the groups. However thalamic BOLD and neural responses were unaltered in AD brain compared to controls. Thus cortical responses in the AD model were indeed diminished compared to controls, but the thalamic responses in the AD and control rats were quite similar. Therefore these results suggest that Alzheimer's disease may affect cortical function more than subcortical function, which may have implications for interpreting altered human brain functional responses in fMRI studies of Alzheimer's disease.

Modeling Alzheimer's disease with non-transgenic rat models

Alzheimer's disease (AD), for which there is no cure, is the most common form of dementia in the elderly. Despite tremendous efforts by the scientific community, the AD drug development pipeline remains extremely limited. Animal models of disease are a cornerstone of any drug development program and should be as relevant as possible to the disease, recapitulating the disease phenotype with high fidelity, to meaningfully contribute to the development of a successful therapeutic agent. Over the past two decades, transgenic models of AD based on the known genetic origins of familial AD have significantly contributed to our understanding of the molecular mechanisms involved in the onset and progression of the disease. These models were extensively used in AD drug development. The numerous reported failures of new treatments for AD in clinical trials indicate that the use of genetic models of AD may not represent the complete picture of AD in humans and that other types of animal models relevant to the sporadic form of the disease, which represents 95% of AD cases, should be developed. In this review, we will discuss the evolution of non-transgenic rat models of AD and how these models may open new avenues for drug development.

Amyloid β peptides modify the expression of antioxidant repair enzymes and a potassium channel in the septohippocampal system

Alzheimer's disease (AD) is a progressive, neurodegenerative brain disorder characterized by extracellular accumulations of amyloid β (Aβ) peptides, intracellular accumulation of abnormal proteins, and early loss of basal forebrain neurons. Recent studies have indicated that the conformation of Aβ is crucial for neuronal toxicity, with intermediate misfolded forms such as oligomers being more toxic than the final fibrillar forms. Our previous work shows that Aβ blocks the potassium (K(+)) currents IM and IA in septal neurons, increasing firing rates, diminishing rhythmicity and firing coherence. Evidence also suggests that oxidative stress (OS) plays a role in AD pathogenesis. Thus we wished to determine the effect of oligomeric and fibrillar forms of Aβ₁₋₄₂ on septohippocampal damage, oxidative damage, and dysfunction in AD. Oligomeric and fibrillar forms of Aβ₁₋₄₂ were injected into the CA1 region of the hippocampus in live rats. The rats were sacrificed 24 hours and 1 month after Aβ or sham injection to additionally evaluate the temporal effects. The expression levels of the K(+) voltage-gated channel, KQT-like subfamily, member 2 (KCNQ₂) and the OS-related genes superoxide dismutase 1, 8-oxoguanine DNA glycosylase, and monamine oxidase A, were analyzed in the hippocampus, medial, and lateral septum. Our results show that both forms of Aβ exhibit time-dependent differential modulation of OS and K(+) channel genes in the analyzed regions. Importantly, we demonstrate that Aβ injected into the hippocampus triggered changes in gene expression in anatomical regions distant from the injection site. Thus the Aβ effect was transmitted to anatomically separate sites, because of the functional coupling of the brain structures.

Accumulation of exogenous amyloid-beta peptide in hippocampal mitochondria causes their dysfunction: a protective role for melatonin

Amyloid-beta (Aβ) pathology is related to mitochondrial dysfunction accompanied by energy reduction and an elevated production of reactive oxygen species (ROS). Monomers and oligomers of Aβ have been found inside mitochondria where they accumulate in a time-dependent manner as demonstrated in transgenic mice and in Alzheimer's disease (AD) brain. We hypothesize that the internalization of extracellular Aβ aggregates is the major cause of mitochondrial damage and here we report that following the injection of fibrillar Aβ into the hippocampus, there is severe axonal damage which is accompanied by the entrance of Aβ into the cell. Thereafter, Aβ appears in mitochondria where it is linked to alterations in the ionic gradient across the inner mitochondrial membrane. This effect is accompanied by disruption of subcellular structure, oxidative stress, and a significant reduction in both the respiratory control ratio and in the hydrolytic activity of ATPase. Orally administrated melatonin reduced oxidative stress, improved the mitochondrial respiratory control ratio, and ameliorated the energy imbalance.

Alzheimer's disease: pathological mechanisms and the beneficial role of melatonin

Alzheimer's disease (AD) is a highly complex neurodegenerative disorder of the aged that has multiple factors which contribute to its etiology in terms of initiation and progression. This review summarizes these diverse aspects of this form of dementia. Several hypotheses, often with overlapping features, have been formulated to explain this debilitating condition. Perhaps the best-known hypothesis to explain AD is that which involves the role of the accumulation of amyloid-β peptide in the brain. Other theories that have been invoked to explain AD and summarized in this review include the cholinergic hypothesis, the role of neuroinflammation, the calcium hypothesis, the insulin resistance hypothesis, and the association of AD with peroxidation of brain lipids. In addition to summarizing each of the theories that have been used to explain the structural neural changes and the pathophysiology of AD, the potential role of melatonin in influencing each of the theoretical processes involved is discussed. Melatonin is an endogenously produced and multifunctioning molecule that could theoretically intervene at any of a number of sites to abate the changes associated with the development of AD. Production of this indoleamine diminishes with increasing age, coincident with the onset of AD. In addition to its potent antioxidant and anti-inflammatory activities, melatonin has a multitude of other functions that could assist in explaining each of the hypotheses summarized above. The intent of this review is to stimulate interest in melatonin as a potentially useful agent in attenuating and/or delaying AD.

Caprospinol: discovery of a steroid drug candidate to treat Alzheimer's disease based on 22R-hydroxycholesterol structure and properties

The overall ability of the brain to synthesise neuroactive steroids led us to the identification of compounds that would reproduce aspects of neurosteroid pharmacology. The rate-determining step in neurosteroid biosynthesis is the import of the substrate cholesterol into the mitochondria, where it is metabolised into pregnenolone via the intermediate 22R-hydroxycholesterol. The levels of translocator protein 18-kDa, mediating the import of cholesterol into mitochondria, correlated with increased pregnenolone formation and reduced levels of 22R-hydroxycholesterol in biopsies from Alzheimer's disease (AD), but not age-matched control, brains. 22R-hydroxycholesterol was shown to protect against β-amyloid (Aβ(42) )-induced neurotoxicity. In search of 22R-hydroxycholesterol stable analogues, we identified the naturally occurring heterospirostenol, (22R,25R)-20α-spirost-5-en-3β-yl hexanoate (caprospinol) and derivatives that protect neuronal cells against Aβ(1-42) neurotoxicity. The neuroprotective effect of caprospinol is the result of a combination of overlapping properties, including: (i) the ability to bind to Aβ(42) and reduce plaque formation in the brain in vivo; (ii) interaction with components of the mitochondria respiratory chain resulting in an anti-uncoupling effect; (iii) the capacity to scavenge Aβ(42) monomers present in mitochondria; and (iv) the property of being a sigma-1 receptor ligand. In vivo, caprospinol crosses the blood-brain barrier, accumulates in the brain, and restores cognitive impairment in a pharmacological rat model of AD. Caprospinol is stable, does not bind to known steroid receptors, is devoid of mutagenic and genotoxic properties, and is devoid of acute toxicity in rodents. The pharmacokinetics and pharmacodynamics of caprospinol were studied, and long-term toxicity studies are under investigation, aiming to develop this compound as a disease-modifying drug for the treatment of AD.

Reversal of propoxur-induced impairment of step-down passive avoidance, transfer latency and oxidative stress by piracetam and ascorbic acid in rats

Propoxur, a carbamate pesticide has been shown to adversely affect memory and induce oxidative stress. The present study was designed to correlate the effect of propoxur, piracetam (a nootropic drug) and ascorbic acid (an antioxidant) on oxidative stress and cognitive function. Cognitive function was assessed using step-down latency (SDL) on a passive avoidance apparatus and transfer latency (TL) on elevated plus maze. Oxidative stress was assessed by examining brain malondialdehyde (MDA) and non-protein thiol (NP-SH) levels. A significant reduction in SDL and prolongation of TL was found for the propoxur-treated group at weeks 6 and 7 as compared with control (p<0.001). One week treatment by piracetam (400mg/kg/d, i.p.) or ascorbic acid (120mg/kg/d, i.p.) antagonized the effect of propoxur on SDL as well as TL. Both piracetam and ascorbic acid attenuated the propoxur-induced increase in brain MDA levels and decrease in brain NP-SH levels. Results of the present study show that ascorbic acid and piracetam have the potential to reverse cognitive dysfunction and oxidative stress induced by propoxur in the brain.

Identification of a benzamide derivative that inhibits stress-induced adrenal corticosteroid synthesis

Elevated serum glucocorticoid levels contribute to the progression of many diseases, including depression, Alzheimer’s disease, hypertension, and acquired immunodeficiency syndrome. Here we show that the benzamide derivative N-[2-(4-cyclopropanecarbonyl-3-methyl-piperazin-1-yl)-1-(tert-butyl-1H-indol-3-yl-methyl)-2-oxo-ethyl]-4-nitrobenzamide (SP-10) inhibits dibutyryl cyclic AMP (dbcAMP)-induced corticosteroid synthesis in a dose-dependent manner in Y-1 adrenal cortical mouse tumor cells, without affecting basal steroid synthesis and reduced stress-induced corticosterone increases in rats without affecting the physiological levels of the steroid in blood. SP-10 did not affect cholesterol transport and metabolism by the mitochondria but was unexpectedly found to increase 3-hydroxy-3-methylglutaryl-coenzyme A, low density lipoprotein receptor, and scavenger receptor class B type I (SR-BI) expression. However, it also markedly reduced dbcAMP-induced NBD-cholesterol uptake, suggesting that this is a compensatory mechanism aimed at maintaining cholesterol levels. SP-10 also induced a redistribution of filamentous (F-) and monomeric (G-) actin, leading to decreased actin levels in the submembrane cytoskeleton suggesting that SP-10-induced changes in actin distribution might prevent the formation of microvilli– cellular structures required for SR-BI-mediated cholesterol uptake in adrenal cells.

The rat as an animal model of Alzheimer's disease

As a disease model, the laboratory rat has contributed enormously to neuroscience research over the years. It has also been a popular animal model for Alzheimer's disease but its popularity has diminished during the last decade, as techniques for genetic manipulation in rats have lagged behind that of mice. In recent years, the rat has been making a comeback as an Alzheimer's disease model and the appearance of increasing numbers of transgenic rats will be a welcome and valuable complement to the existing mouse models. This review summarizes the contributions and current status of the rat as an animal model of Alzheimer's disease.

Use of liquid chromatography with electrochemical detection for the determination of antioxidants in less common fruits

Neurodegenerative disorders (NDD) have become the common global health burden over the last several decades. According to World Health Organization (WHO), a staggering 30 million people will be affected by Alzheimer's disease in Europe and the USA by 2050. Effective therapies in this complex field considering the multitude of symptoms associated with NDD indications, have not been found yet. Based on the results of NDD related studies, prevention appears to be the promise alternative. Antioxidative and anti-inflammatory properties are hypothesized for natural phenolics, a group of plant secondary products that may positively impact neurodegenerative diseases. In these studies, phenolic-rich extracts from less common fruit species: Blue honeysuckle (Lonicera edulis, Turcz. ex. Freyn), Saskatoon berry (Amelanchier alnifolia Nutt.), and Chinese hawthorn (Crateagus pinnatifida Bunge) were obtained and analyzed to detect neuroprotective substances content and establish a potential therapeutic value. High performance liquid chromatography with electrochemical detection was optimized and further applied on analysis of the extracts of less common fruit species. It was observed that Chinese hawthorn and Blue honeysuckle extracts are potent source of neuroprotective phenolic antioxidants. In accordance the results, it appears that the fruit or formulated products may have the potential for the prevention of neurodegenerative diseases.

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.