The progression of beta-amyloid deposition in the frontal cortex of the aged canine

Alzheimer's Disease Neuropathological Change in Aged Non-Primate Mammals

Human brain aging is characterized by the production and deposition of β-amyloid (Aβ) in the form of senile plaques and cerebral amyloid angiopathy and the intracellular accumulation of hyper-phosphorylated tau (Hp-tau) to form neurofibrillary tangles (NFTs) and dystrophic neurites of senile plaques. The process progresses for years and eventually manifests as cognitive impairment and dementia in a subgroup of aged individuals. Aβ is produced and deposited first in the neocortex in most aged mammals, including humans; it is usually not accompanied by altered behavior and cognitive impairment. Hp-tau is less frequent than Aβ pathology, and NFTs are rare in most mammals. In contrast, NFTs are familiar from middle age onward in humans; NFTs first appear in the paleocortex and selected brain stem nuclei. NFTs precede for decades or years Aβ deposition and correlate with dementia in about 5% of individuals at the age of 65 and 25% at the age of 85. Based on these comparative data, (a) Aβ deposition is the most common Alzheimer's disease neuropathological change (ADNC) in the brain of aged mammals; (b) Hp-tau is less common, and NFTs are rare in most aged mammals; however, NFTs are the principal cytoskeletal pathology in aged humans; (c) NFT in aged humans starts in selected nuclei of the brain stem and paleocortical brain regions progressing to the most parts of the neocortex and other regions of the telencephalon; (d) human brain aging is unique among mammalian species due to the early appearance and dramatic progression of NFTs from middle age onward, matching with cognitive impairment and dementia in advanced cases; (e) neither mammalian nor human brain aging supports the concept of the amyloid cascade hypothesis.

Cellular Stress Response (Hormesis) in Response to Bioactive Nutraceuticals with Relevance to Alzheimer Disease

Significance: Alzheimer's disease (AD) is the most common form of dementia associated with aging. As the large Baby Boomer population ages, risk of developing AD increases significantly, and this portion of the population will increase significantly over the next several decades. Recent Advances: Research suggests that a delay in the age of onset by 5 years can dramatically decrease both the incidence and cost of AD. In this review, the role of nuclear factor erythroid 2-related factor 2 (Nrf2) in AD is examined in the context of heme oxygenase-1 (HO-1) and biliverdin reductase-A (BVR-A) and the beneficial potential of selected bioactive nutraceuticals. Critical Issues: Nrf2, a transcription factor that binds to enhancer sequences in antioxidant response elements (ARE) of DNA, is significantly decreased in AD brain. Downstream targets of Nrf2 include, among other proteins, HO-1. BVR-A is activated when biliverdin is produced. Both HO-1 and BVR-A also are oxidatively or nitrosatively modified in AD brain and in its earlier stage, amnestic mild cognitive impairment (MCI), contributing to the oxidative stress, altered insulin signaling, and cellular damage observed in the pathogenesis and progression of AD. Bioactive nutraceuticals exhibit anti-inflammatory, antioxidant, and neuroprotective properties and are potential topics of future clinical research. Specifically, ferulic acid ethyl ester, sulforaphane, epigallocatechin-3-gallate, and resveratrol target Nrf2 and have shown potential to delay the progression of AD in animal models and in some studies involving MCI patients. Future Directions: Understanding the regulation of Nrf2 and its downstream targets can potentially elucidate therapeutic options for delaying the progression of AD. Antioxid. Redox Signal. 38, 643-669.

Amyloidogenesis: What Do We Know So Far?

The study of protein aggregation, and amyloidosis in particular, has gained considerable interest in recent times. Several neurodegenerative diseases, such as Alzheimer's (AD) and Parkinson's (PD) show a characteristic buildup of proteinaceous aggregates in several organs, especially the brain. Despite the enormous upsurge in research articles in this arena, it would not be incorrect to say that we still lack a crystal-clear idea surrounding these notorious aggregates. In this review, we attempt to present a holistic picture on protein aggregation and amyloids in particular. Using a chronological order of discoveries, we present the case of amyloids right from the onset of their discovery, various biophysical techniques, including analysis of the structure, the mechanisms and kinetics of the formation of amyloids. We have discussed important questions on whether aggregation and amyloidosis are restricted to a subset of specific proteins or more broadly influenced by the biophysiochemical and cellular environment. The therapeutic strategies and the significant failure rate of drugs in clinical trials pertaining to these neurodegenerative diseases have been also discussed at length. At a time when the COVID-19 pandemic has hit the globe hard, the review also discusses the plausibility of the far-reaching consequences posed by the virus, such as triggering early onset of amyloidosis. Finally, the application(s) of amyloids as useful biomaterials has also been discussed briefly in this review.

Neural Derivates of Canine Induced Pluripotent Stem Cells-Like Cells From a Mild Cognitive Impairment Dog

Domestic dogs are superior models for translational medicine due to greater anatomical and physiological similarities with humans than rodents, including hereditary diseases with human equivalents. Particularly with respect to neurodegenerative medicine, dogs can serve as a natural, more relevant model of human disease compared to transgenic rodents. Herein we report attempts to develop a canine-derived in vitro model for neurodegenerative diseases through the generation of induced pluripotent stem cells from a 14-year, 9-month-old female West Highland white terrier with mild cognitive impairment (MCI). Canine induced pluripotent stem cells-like cells (ciPSCLC) were generated using human OSKM and characterized by positive expression of pluripotency markers. Due to inefficient viral vector silencing we refer to them as ciPSCLCs. Subsequently, the ciPSCLC were subjected to neural induction according to two protocols both yielding canine neural progenitor cells (cNPCs), which expressed typical NPC markers. The cNPCs were cultured in neuron differentiation media for 3 weeks, resulting in the derivation of morphologically impaired neurons as compared to iPSC-derived human counterparts generated in parallel. The apparent differences encountered in this study regarding the neural differentiation potential of ciPSCLC reveals challenges and new perspectives to consider before using the canine model in translational neurological studies.

Development of infrastructure for a systemic multidisciplinary approach to study aging in retired sled dogs

Canines represent a valuable model for mammalian aging studies as large animals with short lifespans, allowing longitudinal analyses within a reasonable time frame. Moreover, they develop a spectrum of aging-related diseases resembling that of humans, are exposed to similar environments, and have been reasonably well studied in terms of physiology and genetics. To overcome substantial variables that complicate studies of privately-owned household dogs, we have focused on a more uniform population composed of retired Alaskan sled dogs that shared similar lifestyles, including exposure to natural stresses, and are less prone to breed-specific biases than a pure breed population. To reduce variability even further, we have collected a population of 103 retired (8-11 years-old) sled dogs from multiple North American kennels in a specialized research facility named Vaika. Vaika dogs are maintained under standardized conditions with professional veterinary care and participate in a multidisciplinary program to assess the longitudinal dynamics of aging. The established Vaika infrastructure enables periodic gathering of quantitative data reflecting physical, physiological, immunological, neurological, and cognitive decline, as well as monitoring of aging-associated genetic and epigenetic alterations occurring in somatic cells. In addition, we assess the development of age-related diseases such as arthritis and cancer. In-depth data analysis, including artificial intelligence-based approaches, will build a comprehensive, integrated model of canine aging and potentially identify aging biomarkers that will allow use of this model for future testing of antiaging therapies.

Successful and Unsuccessful Brain Aging in Pets: Pathophysiological Mechanisms behind Clinical Signs and Potential Benefits from Palmitoylethanolamide Nutritional Intervention

Simple Summary

Cognitive dysfunction syndrome is a common yet underreported neurodegenerative disorder of elderly dogs and cats and a natural model of human Alzheimer’s disease. The increasingly expanding life expectancy means a larger proportion of affected animals in the coming decades. Although far from being curative, available treatments are more effective the sooner they are started. Educating veterinary practitioners and owners in the early recognition of age-related cognitive dysfunction is thus mandatory. By shedding light on the mechanism underlying the disease, novel and more effective approaches might be developed. Emerging evidence shows that successful and unsuccessful brain aging share a common underlying mechanism that is neuroinflammation. This process involves astrocytes, microglia, and mast cells and has a restorative homeostatic intent. However, for reasons not fully elucidated yet, neuroinflammation can also exert detrimental consequences substantially contributing to neurodegeneration. Here we summarize the evidence accumulated so far on the pathogenic role of neuroinflammation in the onset and progression of age-related neurodegenerative disorders, such as Alzheimer’s disease. The potential benefit of palmitoylethanolamide dietary intervention in rebalancing neuroinflammation and exerting neuroprotection is also discussed.

Abstract

Canine and feline cognitive dysfunction syndrome is a common neurodegenerative disorder of old age and a natural model of human Alzheimer’s disease. With the unavoidable expanding life expectancy, an increasing number of small animals will be affected. Although there is no cure, early detection and intervention are vitally important to delay cognitive decline. Knowledge of cellular and molecular mechanisms underlying disease onset and progression is an equally decisive factor for developing effective approaches. Uncontrolled neuroinflammation, orchestrated in the central nervous system mainly by astrocytes, microglia, and resident mast cells, is currently acknowledged as a hallmark of neurodegeneration. This has prompted scientists to find a way to rebalance the altered crosstalk between these cells. In this context, great emphasis has been given to the role played by the expanded endocannabinoid system, i.e., endocannabinoidome, because of its prominent role in physiological and pathological neuroinflammation. Within the endocannabinoidome, great attention has been paid to palmitoylethanolamide due to its safe and pro-homeostatic effects. The availability of new ultramicronized formulations highly improved the oral bioavailability of palmitoylethanolamide, paving the way to its dietary use. Ultramicronized palmitoylethanolamide has been repeatedly tested in animal models of age-related neurodegeneration with promising results. Data accumulated so far suggest that supplementation with ultramicronized palmitoylethanolamide helps to accomplish successful brain aging.

Canine Cognitive Dysfunction (CCD) scores correlate with amyloid beta 42 levels in dog brain tissue

Alzheimer's disease (AD) is a significant burden for human health that is increasing in prevalence as the global population ages. There is growing recognition that current preclinical models of AD are insufficient to recapitulate key aspects of the disease. Laboratory models for AD include mice, which do not naturally develop AD-like pathology during aging, and laboratory Beagle dogs, which do not share the human environment. In contrast, the companion dog shares the human environment and presents a genetically heterogeneous population of animals that might spontaneously develop age-associated AD-like pathology and cognitive dysfunction. Here, we quantitatively measured amyloid beta (Aβ42 or Abeta-42) levels in three areas of the companion dog brain (prefrontal cortex, temporal cortex, hippocampus/entorhinal cortex) and cerebrospinal fluid (CSF) using a newly developed Luminex assay. We found significant positive correlations between Aβ42 and age in all three brain regions. Brain Aβ42 abundance in all three brain regions was also correlated with Canine Cognitive Dysfunction Scale score in a multivariate analysis. This latter effect remained significant when correcting for age, except in the temporal cortex. There was no correlation between Aβ42 in CSF and cognitive scores; however, we found a significant positive correlation between Aβ42 in CSF and body weight, as well as a significant negative correlation between Aβ42 in CSF and age. Our results support the suitability of the companion dog as a model for AD and illustrate the utility of veterinary biobanking to make biospecimens available to researchers for analysis.

Mild Microglial Responses in the Cortex and Perivascular Macrophage Infiltration in Subcortical White Matter in Dogs with Age-Related Dementia Modelling Prodromal Alzheimer's Disease

Background:

Microglia contribute to Alzheimer’s disease (AD) pathogenesis by clearing amyloid-β (Aβ) and driving neuroinflammation. Domestic dogs with age-related dementia (canine cognitive dysfunction (CCD)) develop cerebral amyloidosis like humans developing AD, and studying such dogs can provide novel information about microglial response in prodromal AD.

Objective:

The aim was to investigate the microglial response in the cortical grey and the subcortical white matter in dogs with CCD versus age-matched cognitively normal dogs.

Methods:

Brains from aged dogs with CCD and age-matched controls without dementia were studied. Cases were defined by dementia rating score. Brain sections were stained for Aβ, thioflavin S, hyperphosphorylated tau, and the microglial-macrophage ionized calcium binding adaptor molecule 1 (Iba1). Results were correlated to dementia rating score and tissue levels of Aβ.

Results:

Microglial numbers were higher in the Aβ plaque-loaded deep cortical layers in CCD versus control dogs, while the coverage by microglial processes were comparable. Aβ plaques were of the diffuse type and without microglial aggregation. However, a correlation was found between the %Iba1 area and insoluble Aβ ₄₂ and N-terminal pyroglutamate modified Aβ(N3pE)-42. The %Iba1 area was higher in white matter, showing phosphorylation of S396 tau, versus grey matter. Perivascular macrophage infiltrates were abundant in the white matter particularly in CDD dogs.

Conclusion:

The results from this study of the microglial-macrophage response in dogs with CCD are suggestive of relatively mild microglial responses in the Aβ plaque-loaded deep cortical layers and perivascular macrophage infiltrates in the subcortical white matter, in prodromal AD.

Essential Oils as a Potential Neuroprotective Remedy for Age-Related Neurodegenerative Diseases: A Review

Despite the improvements in life expectancy, neurodegenerative conditions have arguably become the most dreaded maladies of older people. The neuroprotective and anti-ageing potentials of essential oils (EOs) are widely evaluated around the globe. The objective of this review is to analyse the effectiveness of EOs as neuroprotective remedies among the four common age-related neurodegenerative diseases. The literature was extracted from three databases (PubMed, Web of Science and Google Scholar) between the years of 2010 to 2020 using the medical subject heading (MeSH) terms "essential oil", crossed with "Alzheimer's disease (AD)", "Huntington's disease (HD)", "Parkinson's disease (PD)" or "amyotrophic lateral sclerosis (ALS)". Eighty three percent (83%) of the studies were focused on AD, while another 12% focused on PD. No classifiable study was recorded on HD or ALS. EO from Salvia officinalis has been recorded as one of the most effective acetylcholinesterase and butyrylcholinesterase inhibitors. However, only Cinnamomum sp. has been assessed for its effectiveness in both AD and PD. Our review provided useful evidence on EOs as potential neuroprotective remedies for age-related neurodegenerative diseases.

Heterogenous deposition of β-amyloid in the brain of aged dogs

Dogs have been used as animal models for human diseases in which there is beta-amyloid (Aβ) deposition in the central nervous system (CNS), such as Alzheimer's and cerebral amyloid angiopathy (CAA). However, many aspects of Aβ deposition in the CNS of dogs still remain unknown. This study aimed to evaluate the deposition of Aβ in different areas of the CNS of aged dogs from different breeds. Aβ was detected in the brains of aged dogs, forming either senile plaques in the neuropil of cortical gray matter or within the walls of parenchymal or leptomeningeal blood vessels. There was a positive correlation between aging and senile plaques or CAA. In dogs older than 8 years, there was no correlation between the area of Aβ plaques and age, with frontal, temporal, and occipital cortices being affected with approximately equal frequency. There was a positive correlation between Aβ deposition in vessel walls and age. Importantly, CAA was associated with the occurrence of microperivascular hemorrhages in the brains of aged dogs. In conclusion, this study demonstrated that Aβ deposition as plaques or within vessel walls are extremely heterogenous in dogs from different breeds and sizes. Although many features of this disease in dogs are similar to those observed in humans, the choice of dog breed and size as a model for human disease will substantially affect the pattern of Aβ deposition.

Nitrosative Stress in the Frontal Cortex From Dogs With Canine Cognitive Dysfunction

Canine cognitive dysfunction (CCD) is an age-related disorder similar to human Alzheimer's disease (AD) that occurs in elderly dogs. Nitrosative stress has been implicated as one of the causes leading to neurodegenerative diseases, particularly AD. Its involvement in the development of CCD has not been studied so far. In the present study, immunohistochemical staining detected all three isoforms of nitric oxide synthases (nNOS, eNOS, and iNOS) and 3-nitrotyrosine (3-NT) in brains from CCD-affected dogs and non-demented control dogs in all layers of the canine frontal cortex. In CCD-affected and non-demented brains, nNOS was highly expressed in pyramidal-like neurons in the upper cortical layers. nNOS has also been observed in astrocytes in the CCD frontal cortex. The nNOS immunohistochemical staining was statistically significantly elevated in dogs with CCD in comparison to non-demented dogs. Blood vessel wall cells were positive for eNOS, which was also expressed in astrocytes and neurons. Intense 3-NT immunoreactivity was observed in the upper cortical layers, where amyloid-beta deposits spread in the last stage of CCD. Brain cells in the same area were highly immunoreactive for iNOS. This infers that neuroinflammation and nitrosative stress might exacerbate the neurodegenerative process in CCD-affected brains, ultimately leading to cognitive impairment.

Dogs with Cognitive Dysfunction as a Spontaneous Model for Early Alzheimer's Disease: A Translational Study of Neuropathological and Inflammatory Markers

Aged companion dogs with canine cognitive dysfunction (CCD) spontaneously develop varying degrees of progressive cognitive decline and particular neuropathological features correspondent to the changes associated with Alzheimer's disease (AD) in humans. The aim of the present study was to characterize certain aspects of neuropathology and inflammatory markers related to aging and CCD in dogs in comparison with human AD. Fifteen brains from aged dogs with normal cognitive function, mild cognitive impairment, or CCD were investigated and compared with two control brains from young dogs and brain sections from human AD subjects. The neuropathological investigations included evaluation of amyloid-β (Aβ) plaque deposition (N-terminally truncated and pyroglutamyl-modified Aβ included), tau pathology, and inflammatory markers in prefrontal cortex. Cortical Aβ deposition was found to be only of the diffuse subtype as no dense-core or neuritic plaques were found. The Aβ deposition followed a progressive pattern in four maturation stages. Accumulation of the Aβ peptide was also observed in the vessel walls. Both immunohistochemically and biochemically measured levels of Aβ pathology in prefrontal cortex showed a consistent positive correlation to age but not to cognitive deficit severity. No evidence of neurofibrillary tau pathology was found. The level of pro-inflammatory cytokines was generally low and showed no significant association to cognitive status. The findings of the present study support the senescent dog with spontaneous cognitive dysfunction as a valuable non-transgenic model for further investigations of the molecular events involved in the neurodegenerative processes associated with aging and early stage AD, especially the Aβ-related pathology.

A Review of Cognitive Abilities in Dogs, 1911 Through 2016

In this review, we pose and respond to three questions concerning canine cognition: How has the history of this field influenced what we currently know about dog cognition? How confident should we be about what we know? Finally, what should we find out next? We begin by presenting two perspectives on canine cognition. We then survey the existing literature by conducting a quantitative summary of over 100 years of empirical work, focusing on power and replicability. Last, we lament the dearth of individual-differences studies in dog cognition (only three since 1911). We claim that a test of dog IQ with good psychometric properties will benefit basic science on dog and human health (including aging and dementia research). As a complement to an existing rich program of ethological investigation, we argue that individual-differences work on dogs should be a research priority.

Promoter Variants of the ADAM10 Gene and Their Roles in Temporal Lobe Epilepsy

Previous evidence has indicated that downregulated ADAM10 gives rise to epileptic seizures in Alzheimer's disease, and this study investigated the association of ADAM10 with temporal lobe epilepsy (TLE) from a genetic perspective. A total of 496 TLE patients and 528 healthy individuals were enrolled and genotyped for ADAM10 promoter variants (rs653765 G > A and rs514049 A > C). The alleles, genotypes, and haplotypes were then compared with clarify the association of these variants with TLE and their impacts upon age at onset, initial seizure types before treatments, and responses to drug treatments. In cohorts I, II, and I + II, the frequencies of the A allele and AA genotype at rs514049 were consistently increased in the cases compared with the controls (p = 0.020 and p = 0.009; p = 0.008 and p = 0.009; p = 0.000 and p = 0.000; q = 0.003 and q = 0.002, respectively). In contrast, the frequency of the AC haplotype (rs653765-rs514049) decreased in cohorts I + II (p = 0.013). Further analyses of the TLE patients indicated that the AA genotype functioned as a predisposing factor to drug-resistant TLE and the AC haplotype as a protective factor against generalized tonic-clonic seizures (GTCS) and drug-resistant TLE. This study is the first to demonstrate an association of the ADAM10 promoter variants with TLE. In particular, the AA genotype and AC haplotype showed their effects upon GTCS and drug-resistant TLE.

The Relation between canine cognitive dysfunction and age-related brain lesions

Canine cognitive dysfunction (CCD) is a syndrome that manifests itself in abnormal behaviors, such as disorientation and wandering. β-amyloid deposition in the brain, including the senile plaque (SP) and cerebral amyloid angiopathy (CAA), has been suggested as a major cause of the syndrome. However, the pathological significance of β-amyloid deposition in CCD dogs remains unclear. The present study was conducted using 16 dogs aged 10 years or older to clarify the relationship between the age-related histopathological lesions, such as β-amyloid deposition, in the brain and the clinical symptoms of CCD as evaluated in a questionnaire previously established in a large survey. In addition, age-related brain lesions were assessed in 37 dogs. The pathological lesions were evaluated by the severity of β-amyloid deposition (SP and CAA), the amount of ubiquitin-positive granules (UBQ), GFAP-positive astrocytes, Iba-1-positive microglia and Nissle stain-positive nerve cells. The results revealed that there was no significant correlation between the severities of canine SP and CCD. The SP increased until 14 years old, but decreased thereafter, although the incidence of CCD is high at these ages. The CAA consistently increased with age, but did not correlate greatly with the CCD score. In contrast, the increases of UBQ, astrocytes and microglia were significantly correlated with CCD. Thus, the impairment in the synapse and/or myelin suggested by increased UBQ and glial activation might be involved in CCD pathogenesis, but β-amyloid deposition, especially SP, is not a direct pathogenic factor of CCD.

On cognitive ecology and the environmental factors that promote Alzheimer disease: lessons from Octodon degus (Rodentia: Octodontidae)

Cognitive ecologist posits that the more efficiently an animal uses information from the biotic and abiotic environment, the more adaptive are its cognitive abilities. Nevertheless, this approach does not test for natural neurodegenerative processes under field or experimental conditions, which may recover animals information processing and decision making and may explain, mechanistically, maladaptive behaviors. Here, we call for integrative approaches to explain the relationship between ultimate and proximate mechanisms behind social behavior. We highlight the importance of using the endemic caviomorph rodent Octodon degus as a valuable natural model for mechanistic studies of social behavior and to explain how physical environments can shape social experiences that might influence impaired cognitive abilities and the onset and progression of neurodegenerative disorders such as Alzheimer disease. We consequently suggest neuroecological approaches to examine how key elements of the environment may affect neural and cognitive mechanisms associated with learning, memory processes and brain structures involved in social behavior. We propose the following three core objectives of a program comprising interdisciplinary research in O. degus, namely: (1) to determine whether diet types provided after weaning can lead to cognitive impairment associated with spatial memory, learning and predisposing to develop Alzheimer disease in younger ages; (2) to examine if early life social experience has long term effects on behavior and cognitive responses and risk for development Alzheimer disease in later life and (3) To determine if an increase of social interactions in adult degu reared in different degree of social stressful conditions alter their behavior and cognitive responses.

Experimental models of Alzheimer's disease for deciphering the pathogenesis and therapeutic screening (Review)

Despite decades of laboratory and clinical research, Alzheimer's disease (AD) is still the leading cause of dementia in adults and there are no curative therapies currently available for this disease. This may be due to the pathological features of AD, which include extensive extracellular amyloid plaques and intracellular neurofibrillary tangles, as well as subsequent neuronal and synaptic loss, which begin to appear several years prior to memory loss and the damge is already irreversible and extensive at the time of clinical diagnosis. The poor therapeutic effects of current treatments necessitate the introduction of experimental models able to replicate AD pathology, particularly in the pre-symptomatic stage, and then to explore preventive and therapeutic strategies. In response to this necessity, various experimental models reproducing human AD pathology have been developed, which are also useful tools for therapeutic screening. Although none of these models fully reproduce the key features of human AD, the experimental models do provide important insight into the pathological changes which occur in AD. This review summarizes the commonly used experimental models of AD and also discusses how the models may be used to decipher the pathogenesis underlying AD and to screen novel therapies for this disease.

Detection and Quantification of β-Amyloid, Pyroglutamyl Aβ, and Tau in Aged Canines

Canine cognitive dysfunction syndrome is an age-associated disorder that resembles many aspects of human Alzheimer disease. The characterization of canine cognitive dysfunction syndrome has been restricted to selected laboratory dogs and mongrels, thereby limiting our knowledge of potential breed-related and age-related differences. We examined the brains of 24 dogs from various breeds. The frontal cortex, hippocampus, and entorhinal cortex were investigated. Deposits of β-amyloid (Aβ) and tau were analyzed phenotypically and quantified stereologically. In all dogs aged 10 years or older, plaques containing pyroglutamyl Aβ and Aβ8-17 were detected. Within the ventral hippocampus, significantly more pyroglutamyl Aβ plaques were deposited in small and medium dogs than in large dogs. Hyperphosphorylated tau with formation of neurofibrillary tangles was observed in 3 animals aged 13 to 15 years. This study provides the first investigation of pyroglutamyl Aβ in comparison with total Aβ (as shown by Aβ8-17 immunoreactivity) in dogs of different breeds, sizes, and ages. Our results indicate that canine cognitive dysfunction syndrome is relatively common among aged canines, thereby emphasizing the relevance of such populations to translational Alzheimer disease research.

Oxidative Stress and Protein Quality Control Systems in the Aged Canine Brain as a Model for Human Neurodegenerative Disorders

Aged dogs are considered the most suitable spontaneous animal model for studying normal aging and neurodegenerative diseases. Elderly canines naturally develop cognitive dysfunction and neuropathological hallmarks similar to those seen in humans, especially Alzheimer's disease-like pathology. Pet dogs also share similar living conditions and diets to humans. Oxidative damage accumulates in the canine brain during aging, making dogs a valid model for translational antioxidant treatment/prevention studies. Evidence suggests the presence of detective protein quality control systems, involving ubiquitin-proteasome system (UPS) and Heat Shock Proteins (HSPs), in the aged canine brain. Further studies on the canine model are needed to clarify the role of age-related changes in UPS activity and HSP expression in neurodegeneration in order to design novel treatment strategies, such as HSP-based therapies, aimed at improving chaperone defences against proteotoxic stress affecting brain during aging.

A method for evaluating the level of soluble β-amyloid(1-40/1-42) in Alzheimer's disease based on the binding of gelsolin to β-amyloid peptides

In the present work, a new electrochemical strategy for the sensitive and specific detection of soluble β-amyloid Aβ(1-40/1-42) peptides in a rat model of Alzheimer's disease (AD) is described. In contrast to previous antibody-based methods, β-amyloid(1-40/1-42) was quantified based on its binding to gelsolin, a secretory protein present in the cerebrospinal fluid (CSF) and plasma. The level of soluble β-amyloid peptides in the CSF and various brain regions were found with this method to be lower in rats with AD than in normal rats.

Prevention approaches in a preclinical canine model of Alzheimer's disease: benefits and challenges

Aged dogs spontaneously develop many features of human aging and Alzheimer's disease (AD) including cognitive decline and neuropathology. In this review, we discuss age-dependent learning tasks, memory tasks, and functional measures that can be used in aged dogs for sensitive treatment outcome measures. Neuropathology that is linked to cognitive decline is described along with examples of treatment studies that show reduced neuropathology in aging dogs (dietary manipulations, behavioral enrichment, immunotherapy, and statins). Studies in canine show that multi-targeted approaches may be more beneficial than single pathway manipulations (e.g., antioxidants combined with behavioral enrichment). Aging canine studies show good predictive validity for human clinical trials outcomes (e.g., immunotherapy) and several interventions tested in dogs strongly support a prevention approach (e.g., immunotherapy and statins). Further, dogs are ideally suited for prevention studies as they the age because onset of cognitive decline and neuropathology strongly support longitudinal interventions that can be completed within a 3-5 year period. Disadvantages to using the canine model are that they lengthy, use labor-intensive comprehensive cognitive testing, and involve costly housing (almost as high as that of non-human primates). However, overall, using the dog as a preclinical model for testing preventive approaches for AD may complement work in rodents and non-human primates.

PiB Fails to Map Amyloid Deposits in Cerebral Cortex of Aged Dogs with Canine Cognitive Dysfunction

Dogs with Canine Cognitive Dysfunction (CCD) accumulate amyloid beta (Aβ) in the brain. As the cognitive decline and neuropathology of these old dogs share features with Alzheimer’s disease (AD), the relation between Aβ and cognitive decline in animal models of cognitive decline is of interest to the understanding of AD. However, the sensitivity of the biomarker Pittsburgh Compound B (PiB) to the presence of Aβ in humans and in other mammalian species is in doubt. To test the sensitivity and assess the distribution of Aβ in dog brain, we mapped the brains of dogs with signs of CCD (n = 16) and a control group (n = 4) of healthy dogs with radioactively labeled PiB ([¹¹C]PiB). Structural magnetic resonance imaging brain scans were obtained from each dog. Tracer washout analysis yielded parametric maps of PiB retention in brain. In the CCD group, dogs had significant retention of [¹¹C]PiB in the cerebellum, compared to the cerebral cortex. Retention in the cerebellum is at variance with evidence from brains of humans with AD. To confirm the lack of sensitivity, we stained two dog brains with the immunohistochemical marker 6E10, which is sensitive to the presence of both Aβ and Aβ precursor protein (AβPP). The 6E10 stain revealed intracellular material positive for Aβ or AβPP, or both, in Purkinje cells. The brains of the two groups of dogs did not have significantly different patterns of [¹¹C]PiB binding, suggesting that the material detected with 6E10 is AβPP rather than Aβ. As the comparison with the histological images revealed no correlation between the [¹¹C]PiB and Aβ and AβPP deposits in post-mortem brain, the marked intracellular staining implies intracellular involvement of amyloid processing in the dog brain. We conclude that PET maps of [¹¹C]PiB retention in brain of dogs with CCD fundamentally differ from the images obtained in most humans with AD.

Recent rodent models for Alzheimer's disease: clinical implications and basic research

Alzheimer's disease (AD) is the most common origin of dementia in the elderly. Although the cause of AD remains unknown, several factors have been identified that appear to play a critical role in the development of this debilitating disorder. In particular, amyloid precursor protein (APP), tau hyperphosphorylation, and the secretase enzymes, have become the focal point of recent research. Over the last two decades, several transgenic and non-transgenic animal models have been developed to elucidate the mechanistic aspects of AD and to validate potential therapeutic targets. Transgenic rodent models over-expressing human β-amyloid precursor protein (β-APP) and mutant forms of tau have become precious tools to study and understand the pathogenesis of AD at the molecular, cellular and behavioural levels, and to test new therapeutic agents. Nevertheless, none of the transgenic models of AD recapitulate fully all of the pathological features of the disease. Octodon degu, a South American rodent has been recently found to spontaneously develop neuropathological signs of AD in old age. This review aims to address the limitations and clinical relevance of transgenic rodent models in AD, and to highlight the potential for O. degu as a natural model for the study of AD neuropathology.

Neurobiology of the aging dog

Aged canines naturally accumulate several types of neuropathology that may have links to cognitive decline. On a gross level, significant cortical atrophy occurs with age along with an increase in ventricular volume based on magnetic resonance imaging studies. Microscopically, there is evidence of select neuron loss and reduced neurogenesis in the hippocampus of aged dogs, an area critical for intact learning and memory. The cause of neuronal loss and dysfunction may be related to the progressive accumulation of toxic proteins, oxidative damage, cerebrovascular pathology, and changes in gene expression. For example, aged dogs naturally accumulate human-type beta-amyloid peptide, a protein critically involved with the development of Alzheimer's disease in humans. Further, oxidative damage to proteins, DNA/RNA and lipids occurs with age in dogs. Although less well explored in the aged canine brain, neuron loss, and cerebrovascular pathology observed with age are similar to human brain aging and may also be linked to cognitive decline. Interestingly, the prefrontal cortex appears to be particularly vulnerable early in the aging process in dogs and this may be reflected in dysfunction in specific cognitive domains with age.

Amyloid-beta peptide and oligomers in the brain and cerebrospinal fluid of aged canines

The study of Alzheimer's disease (AD) pathogenesis requires the use of animal models that develop some amount of amyloid pathology in the brain. Aged canines (beagles) naturally accumulate human-type amyloid-beta peptide (Abeta) and develop parallel declines in cognitive function. However, the type and quantity of biochemically extracted Abeta in brain and cerebrospinal fluid (CSF), its link to aging, and similarity to human aging has not been examined systematically. Thirty beagles, aged 4.5-15.7 years, were studied. Abeta40 and Abeta42 were measured in CSF by ELISA, and from SDS and formic acid extracted prefrontal cortex. A sample of the contralateral hemisphere, used to assess immunohistochemical amyloid load, was used for comparison. In the brain, increases in Abeta42 were detected at a younger age, prior to increases in Abeta40, and were correlated with an increased amyloid load. In the CSF, Abeta42 decreased with age while Abeta40 levels remained constant. The CSF Abeta42/40 ratio was also a good predictor of the amount of Abeta in the brain. The amount of soluble oligomers in CSF was inversely related to brain extractable Abeta, whereas oligomers in the brain were correlated with SDS soluble Abeta42. These findings indicate that the Abeta in the brain of the aged canine exhibits patterns that mirror Abeta deposited in the human brain. These parallels support the idea that the aged canine is a useful intermediate between transgenic mice and humans for studying the development of amyloid pathology and is a potentially useful model for the refinement of therapeutic interventions.

Synergistic effects of long-term antioxidant diet and behavioral enrichment on beta-amyloid load and non-amyloidogenic processing in aged canines

A long-term intervention (2.69 years) with an antioxidant diet, behavioral enrichment, or the combined treatment preserved and improved cognitive function in aged canines. Although each intervention alone provided cognitive benefits, the combination treatment was additive. We evaluate the hypothesis that antioxidants, enrichment, or the combination intervention reduces age-related beta-amyloid (Abeta) neuropathology, as one mechanism mediating observed functional improvements. Measures assessed were Abeta neuropathology in plaques, biochemically extractable Abeta(40) and Abeta(42) species, soluble oligomeric forms of Abeta, and various proteins in the beta-amyloid precursor protein (APP) processing pathway. The strongest and most consistent effects on Abeta pathology were observed in animals receiving the combined antioxidant and enrichment treatment. Specifically, Abeta plaque load was significantly decreased in several brain regions, soluble Abeta(42) was decreased selectively in the frontal cortex, and a trend for lower Abeta oligomer levels was found in the parietal cortex. Reductions in Abeta may be related to shifted APP processing toward the non-amyloidogenic pathway, because alpha-secretase enzymatic activity was increased in the absence of changes in beta-secretase activity. Although enrichment alone had no significant effects on Abeta, reduced Abeta load and plaque maturation occurred in animals receiving antioxidants as a component of treatment. Abeta measures did not correlate with cognitive performance on any of the six tasks assessed, suggesting that modulation of Abeta alone may be a relatively minor mechanism mediating cognitive benefits of the interventions. Overall, the data indicate that multidomain treatments may be a valuable intervention strategy to reduce neuropathology and improve cognitive function in humans.

Alzheimer's disease and the amyloid-beta peptide

Alzheimer's disease (AD) pathogenesis is widely believed to be driven by the production and deposition of the amyloid-beta peptide (Abeta). For many years, investigators have been puzzled by the weak to nonexistent correlation between the amount of neuritic plaque pathology in the human brain and the degree of clinical dementia. Recent advances in our understanding of the development of amyloid pathology have helped solve this mystery. Substantial evidence now indicates that the solubility of Abeta, and the quantity of Abeta in different pools, may be more closely related to disease state. The composition of these pools of Abeta reflects different populations of amyloid deposits and has definite correlates with the clinical status of the patient. Imaging technologies, including new amyloid imaging agents based on the chemical structure of histologic dyes, are now making it possible to track amyloid pathology along with disease progression in the living patient. Interestingly, these approaches indicate that the Abeta deposited in AD is different from that found in animal models. In general, deposited Abeta is more easily cleared from the brain in animal models and does not show the same physical and biochemical characteristics as the amyloid found in AD. This raises important issues regarding the development and testing of future therapeutic agents.

Natural non-trasgenic animal models for research in Alzheimer's disease

The most common animal models currently used for Alzheimer disease (AD) research are transgenic mice that express a mutant form of human Aβ precursor protein (APP) and/or some of the enzymes implicated in their metabolic processing. However, these transgenic mice carry their own APP and APP-processing enzymes, which may interfere in the production of different amyloid-beta (Aβ) peptides encoded by the human transgenes. Additionally, the genetic backgrounds of the different transgenic mice are a possible confounding factor with regard to crucial aspects of AD that they may (or may not) reproduce. Thus, although the usefulness of transgenic mice is undisputed, we hypothesized that additional relevant information on the physiopathology of AD could be obtained from other natural non-transgenic models. We have analyzed the chick embryo and the dog, which may be better experimental models because their enzymatic machinery for processing APP is almost identical to that of humans. The chick embryo is extremely easy to access and manipulate. It could be an advantageous natural model in which to study the cell biology and developmental function of APP and a potential assay system for drugs that regulate APP processing. The dog suffers from an age-related syndrome of cognitive dysfunction that naturally reproduces key aspects of AD including Aβ cortical pathology, neuronal degeneration and learning and memory disabilities. However, dense core neuritic plaques and neurofibrillary tangles have not been consistently demonstrated in the dog. Thus, these species may be natural models with which to study the biology of AD, and could also serve as assay systems for Aβ-targeted drugs or new therapeutic strategies against this devastating disease.

Prevalence and risk factors of behavioural changes associated with age-related cognitive impairment in geriatric dogs

OBJECTIVES

The aim of this study was to describe the prevalence and severity of behavioural changes associated with age and their relationship to risk factors such as sex, reproductive status, bodyweight and age.

METHODS

A cross-sectional study design was chosen. A total of 325 geriatric dogs were included. Owners of dogs older than nine years were interviewed by a veterinary behaviourist. Structured phone interviews were used to gather information about four behavioural categories related to cognitive impairment: sleep/wake cycles, social interaction, learning and house training and signs of disorientation.

RESULTS

Signs of cognitive impairment showed a prevalence of 22.5 per cent in geriatric dogs. Sex and age emerged as significant predictor variables. Females and neutered dogs were significantly more affected than males and entire dogs, respectively. Prevalence and severity increased with age. Although weight was not a statistically significant predictor variable, smaller animals had greater odds of showing age-related cognitive impairment. The most impaired behavioural categories were social interaction and house training.

CLINICAL SIGNIFICANCE

Age-related behavioural changes should be considered by practicing veterinarians because of their relative high prevalence among geriatric dogs, especially in females.

MRI and histological analysis of beta-amyloid plaques in both human Alzheimer's disease and APP/PS1 transgenic mice

PURPOSE

To investigate the relationship between MR image contrast associated with beta-amyloid (Abeta) plaques and their histology and compare the histopathological basis of image contrast and the relaxation mechanism associated with Abeta plaques in human Alzheimer's disease (AD) and transgenic APP/PS1 mouse tissues.

MATERIALS AND METHODS

With the aid of the previously developed histological coil, T(2) (*)-weighted images and R(2) (*) parametric maps were directly compared with histology stains acquired from the same set of Alzheimer's and APP/PS1 tissue slices.

RESULTS

The electron microscopy and histology images revealed significant differences in plaque morphology and associated iron concentration between AD and transgenic APP/PS1 mice tissue samples. For AD tissues, T(2) (*) contrast of Abeta-plaques was directly associated with the gradation of iron concentration. Plaques with significantly less iron load in the APP/PS1 animal tissues are equally conspicuous as the human plaques in the MR images.

CONCLUSION

These data suggest a duality in the relaxation mechanism where both high focal iron concentration and highly compact fibrillar beta-amyloid masses cause rapid proton transverse magnetization decay. For human tissues, the former mechanism is likely the dominant source of R(2) (*) relaxation; for APP/PS1 animals, the latter is likely the major cause of increased transverse proton relaxation rate in Abeta plaques. The data presented are essential for understanding the histopathological underpinning of MRI measurement associated with Abeta plaques in humans and animals.

Beta-amyloid cortical deposits are accompanied by the loss of serotonergic neurons in the dog

Dogs may naturally suffer an age-related cognitive impairment that has aroused a great deal of interest, even beyond the field of the veterinary clinic. This canine senile dementia reproduces several key aspects of Alzheimer's disease (AD), including the presence of beta-amyloid (A beta) deposits in the cerebral cortex, neurodegeneration, and learning and memory impairments. In the present study, we have used unbiased stereological procedures to estimate the number of the dorsal and median raphe nuclei (DRN and MRN, respectively) serotonergic neurons immunolabeled with an anti-tryptophan hydroxylase (TrH) monoclonal antibody in young and aged dogs without A beta cortical deposits and in aged dogs with A beta cortical deposits. The estimated total number of TrH-labeled neurons (mean +/- SD) was 94,790 +/- 26,341 for the DRN and 40,404 +/- 8,692 for the MRN. The statistical analyses revealed that aged dogs with A beta cortical pathology had 33% fewer serotonergic neurons in the DRN and MRN than aged dogs without A beta cortical deposits (108,043 +/- 18,800 vs. 162,242 +/- 39,942, respectively; P = 0.01). In contrast, no significant variations were found between young and aged dogs without A beta cortical deposits. These results suggest that degeneration of the serotonergic neurons could be involved in the cognitive damage that accompanies A beta cortical pathology in the dog and reinforce the use of the canine model for exploring the potential mechanisms linking the cortical A beta pathology and serotonergic neurodegeneration that occurs during the course of AD.

Rhinal and dorsolateral prefrontal cortex lesions produce selective impairments in object and spatial learning and memory in canines

To examine the effects of rhinal and dorsolateral prefrontal cortex lesions on object and spatial recognition memory in canines, we used a protocol in which both an object (delayed nonmatching to sample, or DNMS) and a spatial (delayed nonmatching to position or DNMP) recognition task were administered daily. The tasks used similar procedures such that only the type of stimulus information to be remembered differed. Rhinal cortex (RC) lesions produced a selective deficit on the DNMS task, both in retention of the task rules at short delays and in object recognition memory. By contrast, performance on the DNMP task remained intact at both short and long delay intervals in RC animals. Subjects who received dorsolateral prefrontal cortex (dlPFC) lesions were impaired on a spatial task at a short, 5-second delay, suggesting disrupted retention of the general task rules; however, this impairment was transient, and long-term spatial memory performance was unaffected in dlPFC subjects. The present results provide support for the involvement of the RC in object, but not visuospatial, processing and recognition memory, whereas the dlPFC appears to mediate retention of a nonmatching rule. These findings support theories of functional specialization within the medial temporal lobe and frontal cortex and suggest that rhinal and dorsolateral prefrontal cortices in canines are functionally similar to analogous regions in other mammals.

Dogs with canine counterpart of Alzheimer's disease lose noradrenergic neurons

Degeneration of noradrenergic neurons in the locus ceruleus is a well-described feature of Alzheimer's disease (AD). In spite of extensive utilization of the dog as a model for human degenerative diseases, there is no data on the response to aging of the noradrenergic system in dogs. We have used modern unbiased stereology to estimate the total number of A6-A7 noradrenergic neurons in normal, aged dogs and dogs with the canine counterpart of AD. In small-breed dogs with no cognitive impairments, the total mean number of tyrosine hydroxylase immunolabeled A6-A7 neurons was 17,228+/-1655, with no differences between young and aged dogs. In contrast, aged dogs with cognitive impairments exhibited a significant reduction in the total number of A6-A7 neurons (13,487+/-1374; P=0.001). Additionally, we found a negative correlation between the number of A6-A7 neurons and the extent of beta-amyloid deposits in the prefrontal cortex. These results suggest that the canine model could be useful in exploring the potential benefits of noradrenergic drugs for the treatment of AD.

Cognitive dysfunction and the neurobiology of ageing in cats

With improvements in nutrition and veterinary medicine the life expectancy of pet cats is increasing. Accompanying this growing geriatric population there are increasing numbers of cats with signs of apparent senility. A recent study suggests that 28 per cent of pet cats aged 11 to 14 years develop at least one geriatric onset behavioural problem, and this increases to over 50 per cent for cats of 15 years of age or older. While behavioural changes may result from systemic illness, organic brain disease or true behavioural problems, the possibility of age-related cognitive dysfunction is often overlooked. Studies have revealed a number of changes in the brains of geriatric cats that showed signs of cognitive dysfunction, and potential causes include vascular insufficiency leading to hypoxia, increased free radical damage and the deposition of beta-amyloid plaques and/or the modification of other proteins. By recognising the importance of behavioural changes in old cats, investigating them fully for potentially treatable medical conditions, and instigating dietary and environmental modifications to meet their changing needs, we can make the lives of our geriatric cats much more comfortable and rewarding.

Diffuse beta-amyloid plaques and hyperphosphorylated tau are unrelated processes in aged dogs with behavioral deficits

Single and double-labeling immunocytochemistry has been used to learn about the localization, distribution, and possible relationship between beta-amyloid protein (Abeta) deposition and tau hyperphosphorylation in the canine cerebral cortex with age. Behavioral impairment, as reported by the owners and tested in all dogs, correlated with increased Abeta burden in old dogs. Abeta plaques were diffuse and they were not accompanied by modifications in synaptic protein expression. Plaques were not associated with increased active mitogen activated protein kinase (MAPK/ERK-P) and p38 kinase (p38-P) expression, and tau hyperphosphorylation in neighboring cell processes. Yet tau hyperphosphorylation, as revealed with phospho-specific antibodies to tauThr181 and tauSer396, increased with age in individual neurons. Moreover, the subcellular pattern shifted from perinuclear localization to granular cytoplasmic and nuclear distribution with age. Our results in dog suggest that Abeta diffuse plaque formation and tau hyperphosphorylation are independent events, both occurring during the process of aging. Although increased cognitive dysfunction is associated with increased tau hyperphosphorylation, further investigation is needed to understand whether tau hyperphosphorylation is causative of cognitive impairment or an independent process related to aging.

Ageing changes in cat brains demonstrated by beta-amyloid and AT8-immunoreactive phosphorylated tau deposits

The life expectancy of domestic pet cats is increasing, along with the occurrence of geriatric-onset behavioural problems, such as cognitive dysfunction syndrome (CDS). While the cause of CDS is unclear, it has been suggested that it may result from age-related neurodegeneration. In aged and in particular senile human beings, histopathological changes may include the extracellular accumulation of plaque-like deposits of beta-amyloid (Abeta) protein and the intracellular accumulation of an abnormally hyperphosphorylated form of the microtubule-associated protein, tau. In severe cases, the latter may form into neurofibrillary tangles. Brain material was assessed from 19 cats, aged from 16 weeks to 14 years; 17 of which had clinical signs of neurological dysfunction. Immunohistochemical methods were used to detect Abeta and its intracellular precursor protein (amyloid precursor protein (APP)) and hyperphosphorylated-tau. APP was constitutively expressed, with diffuse staining of neurons and blood vessels being detected in all cats. More intense staining and diffuse extracellular Abeta staining deposits were found within the deep cortical areas of the anterior- and occasionally mid-cerebrum of seven cats, all of which were over 10 years of age. Neurons staining intensely positive for AT8-immunoreactivity were seen in two cats, aged 11 and 13 years. However, no mature neurofibrillary tangles were detected. This study demonstrated that extracellular Abeta accumulation and AT8-immunoreactivity within neurons are age-related phenomena in cats, and that they can occur concurrently. There are similarities between these changes and those observed in the brains of aged people and other old mammals.

Cytoarchitectonic organization of the entorhinal cortex of the canine brain

The present study describes the cytoarchitectonic and chemoarchitectonic organization of the canine entorhinal cortex (EC). We distinguished medial, laterodorsal, and latero-intermediate subdivisions based on the organization of cortical layers using Nissl and Timm staining and AChE histochemistry. The medial subdivision is located at the border of the parasubiculum and is characterized by a narrow cortex, wide layer II, and densely packed cells in layer V. At its caudal extent, distinct spherical groups of small cells are situated at the border of layer I/II. The laterodorsal subdivision is located along the rhinal sulcus and borders area 35 of the perirhinal cortex. Its cortex is wide and layers tend to merge. Layer II of the laterodorsal subdivision contains scattered "stellate" cells, which are not organized into islands. The latero-intermediate subdivision displays a complex layer organization. The most easily distinguished is layer II, which is comprised of two main cell populations; "stellate" neurons arranged into "islands" and small, round cells distributed within and below the stellate cells. Layer III contains sparse cells that are arranged into vertical clusters, whereas layer IV (lamina dissecans) is especially wide. Nine fields, named according to their rostral to caudal position, were distinguished based on further analyses of layer differentiation. The main features of the rostrocaudal differentiation are a gradual disappearance of "island" organization in layer II, increasing cortical thickness, and wider layers containing small and more densely packed cells. Cytoarchitectonic differentiation was determined by observation of specific histochemical patterns of AChE- and Timm-stained sections.

Canine cognitive deficit correlates with diffuse plaque maturation and S100beta (-) astrocytosis but not with insulin cerebrospinal fluid level

Like humans, canines develop with aging beta-amyloid (Abeta) plaques and a progressive cognitive deficit on tasks similar to those used in diagnosis and follow-up of Alzheimer's disease. Owing to that, dogs are quite unique to investigate the early events taking place in the diffuse Abeta plaque maturation and its relationship with cognitive deficit. The aim of the present investigation was to study the link between the diffuse Abeta plaque maturation and the astro- and microglial reactivity. The involvement of insulin and beta-subunit of S100 protein (S100beta) overexpression in the process was also investigated. Abeta plaques were measured and counted in prefrontal cortex of 16 pet dogs of different breeds, weight and sex, classified as control and with a light or severe cognitive deficit. A correlation between canine graded cognitive deficit, diffuse plaque maturation, and S100beta (-) astrocytosis, but not with cerebrospinal fluid insulin level, was found that may reflect the very early events of Abeta deposition in Alzheimer's disease.

Metabolism of amyloid beta peptide and pathogenesis of Alzheimer's disease. Towards presymptomatic diagnosis, prevention and therapy

The conversion of what has been interpreted as "normal brain aging" to Alzheimer's disease (AD) via a transition state, i.e. mild cognitive impairment, appears to be a continuous process caused primarily by aging-dependent accumulation of amyloid beta peptide (Abeta) in the brain. This notion give us a hope that, by manipulating the Abeta levels in the brain, we may be able not only to prevent and cure the disease but also to partially control some very significant aspects of brain aging. Abeta is constantly produced from its precursor and immediately catabolized under normal conditions, whereas dysmetabolism of Abeta seems to lead to pathological deposition upon aging. We have focused our attention on elucidation of the unresolved mechanism of Abeta catabolism in the brain. In this review, we describe a new approach to prevent AD development by reducing Abeta burdens in aging brains through up-regulation the catabolic mechanism involving neprilysin that can degrade both monomeric and oligomeric forms of Abeta. The strategy of combining presymptomatic diagnosis with preventive medicine seems to be the most pragmatic in both medical and socio-economical terms. We also introduce a novel non-invasive amyloid imaging approach using a high-power magnetic resonance imaging (MRI) for the presymptomatic diagnosis of AD.

Frontal lobe volume, function, and beta-amyloid pathology in a canine model of aging

Application of magnetic resonance imaging (MRI) techniques reveals that human brain aging varies across cortical regions. One area particularly sensitive to normal aging is the frontal lobes. In vitro neuropathological studies and behavioral measures in a canine model of aging previously suggested that the frontal lobes of the dog might be sensitive to aging. In the present study, MRI scans were acquired to compare age-related changes in frontal lobe volume with changes in executive functions and beta-amyloid pathology in the frontal cortex of beagle dogs aged 3 months to 15 years. Decreases in total brain volume appeared only in senior dogs (aged 12 years and older), whereas frontal lobe atrophy developed earlier, appearing in the old dogs (aged 8-11 years). Hippocampal volume also declined with age, but not occipital lobe volume past maturity. Reduced frontal lobe volume correlated with impaired performance on measures of executive function, including inhibitory control and complex working memory, and with increased beta-amyloid accumulation in the frontal cortex. Age-related hippocampal atrophy also correlated with complex working memory but not inhibitory control, whereas occipital lobe volume did not correlate with any cognitive measure. These findings are consistent with the frontal lobe theory of aging in humans, which suggests that the frontal lobes and functions subserved by this region are compromised early in aging.

Beta-amyloid deposition and tau phosphorylation in clinically characterized aged cats

The current study describes both Abeta and tau abnormalities that accumulate in the brains of aged (16-21 years), but not young (<4 years) clinically characterized cats. Diffuse plaques that were morphologically different from what is typically observed in the human brain could be detected with 4G8 (Abeta17-24) or an Abeta1-42-specific antibody but not with N-terminal Abeta or an Abeta1-40-specific antibody. SELDI-TOF mass spectrometry experiments indicated that cat brain Abeta consisted almost entirely of Abeta1-42. Markers of tau hyperphosphorylation (AT8 and PHF-1) labeled a subset of neurons in two aged animals. In the hilus of the hippocampus, a subset of AT8 positive neurons showed a sprouting morphology similar to that observed in human brain. Western blot analysis with antibodies against hyperphosphorylated tau indicated that tau is hyperphosphorylated in the aged cat and contains many of the same epitopes found in Alzheimer's disease (AD) brain. Thus, the aged cat brain develops AD-related lesions with important morphological and biochemical differences compared to human brain.

Severe cognitive impairment correlates with higher cerebrospinal fluid levels of lactate and pyruvate in a canine model of senile dementia

Diagnosis of dementia of the Alzheimer's type depends on clinical criteria and exclusion of other disorders because, at this time, a validated biological marker, aside from histological brain examination, remains to be established. The canine counterpart of senile dementia of the Alzheimer type (ccSDAT) is considered a promising model for examining behavioral, cellular and molecular processes involved in early phases of human brain aging and Alzheimer disease (AD). In order to investigate the first events taking place in canine cognitive dysfunction, in this paper we established a new and rapid behavioral test that finely discriminates the degrees of cognitive impairment. Cerebrospinal fluid (CSF) analysis was performed to determine the relationship between each disease stage and modification of cerebral energy metabolism. Our results demonstrate a parallel increase of lactate, pyruvate and potassium concentrations in the severe cognitive deficit. These differences are discussed in view of the neuroprotective role presently given to lactate.

Effects of scopolamine challenge on regional cerebral blood volume. A pharmacological model to validate the use of contrast enhanced magnetic resonance imaging to assess cerebral blood volume in a canine model of aging

Cognitive impairment resulting from disruption of cholinergic function may occur through modulation of cerebrovascular volume (CBV). In the present study, dynamic susceptibility contrast magnetic resonance imaging (DSC-MRI) was used to examine cerebrovascular volume in young and old dogs during baseline and after administration of a cholinergic antagonist (scopolamine). In the first study, 24 animals (2-15 years of age) were given a baseline scan followed by a second scan after scopolamine administration (30 microg/kg). Gray matter rCBV was significantly higher than white matter rCBV during baseline and scopolamine administration. In the second study a subset of 7 dogs (4 young and 3 old) received scopolamine before anesthesia was induced for a second DSC-MRI scan. Consistent with the first study, gray matter rCBV was significantly higher than white matter rCBV. Scopolamine administered before anesthesia however, resulted in higher rCBV values compared to baseline in cerebral gray matter. Additionally, rCBVs were higher in young dogs at baseline in gray and white matter and marginally higher in gray matter when scopolamine was administered before anesthesia. These results indicate that in the dog, rCBV varies with brain compartment, decreases with age, and that DSC-MRI provides a measure of cerebrovascular function which may be related to age-dependent changes in cognition, brain structure, and neuropathology.

The canine model of human cognitive aging and dementia: pharmacological validity of the model for assessment of human cognitive-enhancing drugs

For the past 15 years we have investigated the aged beagle dog as a model for human aging and dementia. We have shown that dogs develop cognitive deficits and neuropathology seen in human aging and dementia. These similarities increase the likelihood that the model will be able to accurately predict the efficacy of Alzheimer's disease (AD) treatments as well as detect therapeutics with limited or no efficacy. Better predictive validity of cognitive-enhancing therapeutics (CETs) could lead to enormous cost savings by reducing the number of failed human clinical trials and also may reduce the likelihood of negative outcomes such as those recently observed in the AN-1792 clinical trials. The current review assesses the pharmacological validity of the canine model of human aging and dementia. We tested the efficacy of (1) CP-118,954 and phenserine, two acetylcholinesterase inhibitors, (2) an ampakine, (3) selegiline hydrochloride, two drugs that have failed human AD trials, and (4) adrafinil, a putative CET. Our research demonstrates that dogs not only develop isomorphic changes in human cognition and brain pathology, but also accurately predict the efficacy of known AD treatments and the absence or limited efficacy of treatments that failed clinical trials. These findings collectively support the utilization of the dog model as a preclinical screen for identifying novel CETs for both age-associated memory disorder and dementia.

Assessment of nutritional interventions for modification of age-associated cognitive decline using a canine model of human aging

The present review focuses on the utility of a canine model in evaluating nutritional interventions for age-related cognitive dysfunction. Aged dogs demonstrate progressive cognitive decline with concurrent amyloid-beta pathology that parallels the pathology observed in aging humans. Dogs, therefore, provide a natural model of human pathological aging. We have and are in the process of evaluating several nutritional-based interventions aimed at preventing cognitive decline and brain aging. In a three-year longitudinal study, we examined the effects of a diet enriched with antioxidants and mitochondrial cofactors on several measures of cognition and brain aging. Compared to controls, aged dogs on the enriched diet demonstrated both short- and long-term cognitive benefits, as well decreased deposition of amyloid-beta protein. The diet also reduced behavioral signs associated with canine Cognitive Dysfunction Syndrome when assessed in veterinary clinical trials. We also have preliminary evidence suggesting a beneficial effect of a proprietary blend of docosahexaenoic acid and phospholipids on both cognitive and physiological measures. Collectively, our data indicate (1) that the dog, either in the laboratory or in the clinic, provides an important tool for assessing nutritional interventions and (2) that combination interventions aimed at several mechanisms of pathological aging may prove more effective than single nutritive components in human trials.