Distribution of tau hyperphosphorylation in canine dementia resembles early Alzheimer's disease and other tauopathies

Associations of tau, Aβ, and brain volume of the Papez circuit with cognition in Alzheimer's disease

This study aimed to investigate the cross-sectional associations between regional Alzheimer's disease (AD) biomarkers, including tau, β-amyloid (Aβ), and brain volume, within the Papez circuit, and neuropsychological functioning across the preclinical and clinical spectrum of AD. We utilized data from the Alzheimer's Disease Neuroimaging Initiative (ADNI) database, including 251 Aβ-positive participants. Participants were categorized into three groups based on the Clinical Dementia Rating (CDR): 73 individuals with preclinical AD (CDR = 0), 114 with prodromal AD (CDR = 0.5), and 64 with clinical AD dementia (CDR ≥ 1). Linear regression analyses, adjusted for age, gender, and education years, were employed to evaluate the associations between five regions of interest (the hippocampus, para-hippocampus, entorhinal cortex, posterior cingulate cortex, and thalamus) and five neuropsychological tests across the three imaging modalities. In the preclinical stage of AD, flortaucipir PET was associated with impaired global cognition and episodic memory (range standardized β = 0.255-0.498, p < 0.05 corrected for multiple comparisons), while florbetapir PET and brain volume were marginally related to global cognition (range standardized β = 0.221-0.231, p < 0.05). In the clinical stages of AD (prodromal and dementia), both increased flortaucipir uptake and decreased brain volume were significantly associated with poorer global neuropsychological and episodic memory performance (range standardized β = 0.222-0.621, p < 0.05, most regions of interest survived correction for multiple comparisions). However, a slight relationship was observed between florbetapir uptake and poorer global cognitive function. The regions most affected by flortaucipir PET were the hippocampus, para-hippocampus, and posterior cingulate cortex. During the clinical stages, the hippocampus and entorhinal cortex exhibited the most significant volumetric changes. Tau PET and brain volume measurements within the Papez circuit are more sensitive indicators of early cognitive deficits in AD than Aβ PET. Furthermore, during the clinical stages of AD, both flortaucipir PET and brain volume of the Papez circuit are closely correlated with cognitive decline. These findings underscore the importance of integrating multiple biomarkers for the comprehensive evaluation of AD pathology and its impact on cognition.

Protecting Human and Animal Health: The Road from Animal Models to New Approach Methods

Animals and animal models have been invaluable for our current understanding of human and animal biology, including physiology, pharmacology, biochemistry, and disease pathology. However, there are increasing concerns with continued use of animals in basic biomedical, pharmacological, and regulatory research to provide safety assessments for drugs and chemicals. There are concerns that animals do not provide sufficient information on toxicity and/or efficacy to protect the target population, so scientists are utilizing the principles of replacement, reduction, and refinement (the 3Rs) and increasing the development and application of new approach methods (NAMs). NAMs are any technology, methodology, approach, or assay used to understand the effects and mechanisms of drugs or chemicals, with specific focus on applying the 3Rs. Although progress has been made in several areas with NAMs, complete replacement of animal models with NAMs is not yet attainable. The road to NAMs requires additional development, increased use, and, for regulatory decision making, usually formal validation. Moreover, it is likely that replacement of animal models with NAMs will require multiple assays to ensure sufficient biologic coverage. The purpose of this manuscript is to provide a balanced view of the current state of the use of animal models and NAMs as approaches to development, safety, efficacy, and toxicity testing of drugs and chemicals. Animals do not provide all needed information nor do NAMs, but each can elucidate key pieces of the puzzle of human and animal biology and contribute to the goal of protecting human and animal health. SIGNIFICANCE STATEMENT: Data from traditional animal studies have predominantly been used to inform human health safety and efficacy. Although it is unlikely that all animal studies will be able to be replaced, with the continued advancement in new approach methods (NAMs), it is possible that sometime in the future, NAMs will likely be an important component by which the discovery, efficacy, and toxicity testing of drugs and chemicals is conducted and regulatory decisions are made.

Chitosan hydrogel nanoparticle enhance therapeutic effect of bovine umbilical mesenchymal stem cell conditioned medium on canine cognitive dysfunction or canine Alzheimer's like mediated by inhibition of neuronal apoptotic

In treating brain diseases, such as canine cognitive dysfunction (CCD), most currently available potent drugs have weak therapeutic efficacy. One of the causes is the inability of the substance to reach the brain in therapeutic quantities. These pharmaceuticals lacked targeted mechanisms for drug delivery, coming about in an elevated drug concentration in imperative organs, which drove to drug harmfulness. In recent years, cell-free treatment (conditioned medium) determined from animal and human stem cells has provided new promise for treating brain diseases, as CM can stimulate the regeneration of neurons and prevent the inflammation and apoptotic of neurons caused by pathology or aging. On the other hand, it is well known that chitosan-hydrogel (CH) is a polymer derived from natural sources. It has been authorized for use in biomedical use because of its uncommon biodegradability, biocompatibility, and mucoadhesive properties. CH modification has been utilized to generate nanoparticles (NPs) for intranasal and intravenous brain targeting. NPs shown upgraded drug take-up to the brain with decreased side impacts due to their drawn out contact time with the nasal mucosa, surface charge, nanosize, and capacity to extend the tight intersections inside the mucosa. Due to the aforementioned distinctive characteristics, developing Chitosan Hydrogel Nanoparticles load with bovine umbilical mesenchymal stem cell conditioned medium is crucial as a new therapeutic strategy for CCD.

Comparative neurogenetics of dog behavior complements efforts towards human neuropsychiatric genetics

Domestic dogs display a wide array of heritable behaviors that have intermediate genetic complexity thanks to a long history of human-influenced selection. Comparative genetics in dogs could address the scarcity of non-human neurogenetic systems relevant to human neuropsychiatric disorders, which are characterized by mental, emotional, and behavioral symptoms and involve vastly complex genetic and non-genetic risk factors. Our review describes the diverse behavioral "phenome" of domestic dogs, past and ongoing sources of behavioral selection, and the state of canine behavioral genetics. We highlight two naturally disordered behavioral domains that illustrate how dogs may prove useful as a comparative, forward neurogenetic system: canine age-related cognitive dysfunction, which can be examined more rapidly given the attenuated lifespan of dogs, and compulsive disorders, which may have genetic roots in purpose-bred behaviors. Growing community science initiatives aimed at the companion dog population will be well suited to investigating such complex behavioral phenotypes and offer a comparative resource that parallels human genomic initiatives in scale and dimensionality.

Going beyond established model systems of Alzheimer's disease: companion animals provide novel insights into the neurobiology of aging

Alzheimer's disease (AD) is characterized by brain plaques, tangles, and cognitive impairment. AD is one of the most common age-related dementias in humans. Progress in characterizing AD and other age-related disorders is hindered by a perceived dearth of animal models that naturally reproduce diseases observed in humans. Mice and nonhuman primates are model systems used to understand human diseases. Still, these model systems lack many of the biological characteristics of Alzheimer-like diseases (e.g., plaques, tangles) as they grow older. In contrast, companion animal models (cats and dogs) age in ways that resemble humans. Both companion animal models and humans show evidence of brain atrophy, plaques, and tangles, as well as cognitive decline with age. We embrace a One Health perspective, which recognizes that the health of humans is connected to those of animals, and we illustrate how such a perspective can work synergistically to enhance human and animal health. A comparative biology perspective is ideally suited to integrate insights across veterinary and human medical disciplines and solve long-standing problems in aging.

Activated gliosis, accumulation of amyloid β, and hyperphosphorylation of tau in aging canines with and without cognitive decline

Canine cognitive dysfunction (CCD) syndrome is a well-recognized naturally occurring disease in aged dogs, with a remarkably similar disease course, both in its clinical presentation and neuropathological changes, as humans with Alzheimer's disease (AD). Similar to human AD patients this naturally occurring disease is found in the aging canine population however, there is little understanding of how the canine brain ages pathologically. It is well known that in neurodegenerative diseases, there is an increase in inflamed glial cells as well as an accumulation of hyperphosphorylation of tau (P-tau) and amyloid beta (Aβ_1-42). These pathologies increase neurotoxic signaling and eventual neuronal loss. We assessed these brain pathologies in aged canines and found an increase in the number of glial cells, both astrocytes and microglia, and the activation of astrocytes indicative of neuroinflammation. A rise in the aggregated protein Aβ_1-42 and hyperphosphorylated tau, at Threonine 181 and 217, in the cortical brain regions of aging canines. We then asked if any of these aged canines had CCD utilizing the only current diagnostic, owner questionnaires, verifying positive or severe CCD had pathologies of gliosis and accumulation of Aβ_1-42 like their aged, matched controls. However uniquely the CCD dogs had P-tau at T217. Therefore, this phosphorylation site of tau at threonine 217 may be a predictor for CCD.

Associations between physical activity and cognitive dysfunction in older companion dogs: results from the Dog Aging Project

Canine cognitive dysfunction (CCD) is a form of dementia that shares many similarities with Alzheimer's disease. Given that physical activity is believed to reduce risk of Alzheimer's disease in humans, we explored the association between physical activity and cognitive health in a cohort of companion dogs, aged 6-18 years. We hypothesized that higher levels of physical activity would be associated with lower (i.e., better) scores on a cognitive dysfunction rating instrument and lower prevalence of dementia, and that this association would be robust when controlling for age, comorbidities, and other potential confounders. Our sample included 11,574 companion dogs enrolled through the Dog Aging Project, of whom 287 had scores over the clinical threshold for CCD. In this observational, cross-sectional study, we used owner-reported questionnaire data to quantify dog cognitive health (via a validated scale), physical activity levels, health conditions, training history, and dietary supplements. We fit regression models with measures of cognitive health as the outcome, and physical activity-with several important covariates-as predictors. We found a significant negative relationship between physical activity and current severity of cognitive dysfunction symptoms (estimate =  - 0.10, 95% CI: - 0.11 to - 0.08, p < 0.001), extent of symptom worsening over a 6-month interval (estimate =  - 0.07, 95% CI: - 0.09 to - 0.05, p < 0.001), and whether a dog reached a clinical level of CCD (odds ratio = 0.53, 95% CI: 0.45 to 0.63, p < 0.001). Physical activity was robustly associated with better cognitive outcomes in dogs. Our findings illustrate the value of companion dogs as a model for investigating relationships between physical activity and cognitive aging, including aspects of dementia that may have translational potential for Alzheimer's disease. While the current study represents an important first step in identifying a relationship between physical activity and cognitive function, it cannot determine causality. Future studies are needed to rule out reverse causation by following the same dogs prospectively over time, and to evaluate causality by administering physical activity interventions.

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.

Characterization of microtubule-associated protein tau isoforms and Alzheimer's disease-like pathology in normal sheep (Ovis aries): relevance to their potential as a model of Alzheimer's disease

Alzheimer's disease is a chronic neurodegenerative disease that accounts for up to 80% of all dementias. Characterised by deteriorations of memory and cognitive function, the key neuropathological features are accumulations of β-amyloid and hyperphosphorylated tau, as 'plaques' and 'tangles', respectively. Despite extensive study, however, the exact mechanism underlying aggregate formation in Alzheimer's disease remains elusive, as does the contribution of these aggregates to disease progression. Importantly, a recent evaluation of current Alzheimer's disease animal models suggested that rodent models are not able to fully recapitulate the pathological intricacies of the disease as it occurs in humans. Therefore, increasing attention is being paid to species that might make good alternatives to rodents for studying the molecular pathology of Alzheimer's disease. The sheep (Ovis aries) is one such species, although to date, there have been few molecular studies relating to Alzheimer's disease in sheep. Here, we investigated the Alzheimer's disease relevant histopathological characteristics of 22 sheep, using anti-β-amyloid (Abcam 12267 and mOC64) and phosphorylation specific anti-tau (AT8 and S396) antibodies. We identified numerous intraneuronal aggregates of both β-amyloid and tau that are consistent with early Alzheimer's disease-like pathology. We confirmed the expression of two 3-repeat (1N3R, 2N3R) and two 4-repeat (1N4R, 2N4R) tau isoforms in the ovine brain, which result from the alternative splicing of two tau exons. Finally, we investigated the phosphorylation status of the serine396 residue in 30 sheep, and report that the phosphorylation of this residue begins in sheep aged as young as 2 years. Together, these data show that sheep exhibit naturally occurring β-amyloid and tau pathologies, that reflect those that occur in the early stages of Alzheimer's disease. This is an important step towards the validation of the sheep as a feasible large animal species in which to model Alzheimer's disease.

Assessment of risk factors in dogs with presumptive advanced canine cognitive dysfunction

OBJECTIVES

The aim of this study was to investigate the potential risk factors involved in the development of presumptive advanced canine cognitive dysfunction (pACCD).

MATERIALS AND METHODS

A questionnaire was developed to identify dogs with presumptive canine cognitive dysfunction (CCD) based on an adapted Canine Dementia Scale and to evaluate for potential risk factors among the presumptive advanced cognitive dysfunction group. The questionnaire was distributed to 7,574 owners of dogs (≥8 years of age) who presented to the CSU VTH between 2017 and 2020. Dogs were classified into four groups based on the Canine Dementia Scale score (normal, mild, moderate, and severe cognitive impairment) and two subgroups for the cognitively impaired groups based on the presence or absence of underlying medical conditions. Comparisons between normal and presumptive advanced cognitively impaired groups, with and without underlying medical conditions, were made against various risk factors. Chi-square tests and logistic regression analysis were used to determine associations between categorical variables and a p-value of <0.05 was considered indicative of evidence of association.

RESULTS

The completed response rate for the questionnaire was 14.2% (1,079/7,574). Among those, 231 dogs were classified as having presumptive advanced cognitive dysfunction. The prevalence of presumptive advanced cognitive dysfunction in the included age groups was 8.1% in ages 8 to <11 years, 18.8% in ages 11 to <13 years, 45.3% in ages 13 to <15 years, 67.3% in ages 15 to <17 years, and 80% in ages >17 years. Dogs with a thin body condition score had the largest contribution to the chi-square statistic. Based on the logistic regression model, both age (p < 0.001) and BCS (p = 0.0057) are associated with presumptive ACCD.

CONCLUSION AND RELEVANCE

The chi-square test and logistic regression analysis both suggested an association between a thin body condition and an increased chance of cognitive decline. However, it is difficult to determine if the thin BCS in this group could be secondary to another confounding factor. The prevalence of cognitive dysfunction rapidly increased with age in this study. These findings warrant continued studies including veterinary evaluations to explore risk factors of canine dementia.

Inhibition of NLRP1-Dependent Pyroptosis Prevents Glycogen Synthase Kinase-3β Overactivation-Induced Hyperphosphorylated Tau in Rats

Our previous study indicated that inhibition of NLRP1-dependent pyroptosis could decrease intracerebroventricular (ICV) injection of a protein kinase A (PKA) agonist- or streptozotocin (STZ)-induced hyperphosphorylated tau. In this study, we used a glycogen synthase kinase-3β (GSK-3β) overactivation rat model to reconfirm our previous results. ICV injection of wortmannin (WT, a PI3K inhibitor) and GF-109203X (GFX, a PKC inhibitor) was used to induce overactivation of GSK-3β in rats. We injected NLRP1 siRNA together with WT/GFX to evaluate the effect of the inhibition of NLRP1-dependent neuronal pyroptosis on hyperphosphorylated tau. Our results indicated that ICV injection of NLRP1 siRNA prevented ICV-WT/GFX-induced neuronal death, further improving the spatial memory of the rats in the Morris water maze test. ICV injection of NLRP1 siRNA downregulated the expression of ASC, caspase-1, and GSDMD and the contents of IL-1β and IL-18 in rat brains. ICV injection of NLRP1 siRNA also decreased hyperphosphorylated tau and the activity of GSK-3β. Thus, these results support our previous study that NLRP1-dependent pyroptosis could enhance hyperphosphorylation of tau protein.

Autologous skin-derived neural precursor cell therapy reverses canine Alzheimer dementia-like syndrome in a proof of concept veterinary trial

BACKGROUND

Older companion dogs naturally develop a dementia-like syndrome with biological, clinical and therapeutic similarities to Alzheimer disease (AD). Given there has been no new safe, clinically effective and widely accessible treatment for AD for almost 20 years, an all-new cell therapeutic approach was trialled in canine veterinary patients, and further modelled in aged rats for more detailed neurobiological analysis.

METHODS

A Phase 1/2A veterinary trial was conducted in N = 6 older companion dogs with definitive diagnosis of Canine Cognitive Dysfunction (CCD). Treatment comprised direct microinjection of 250,000 autologous skin-derived neuroprecursors (SKNs) into the bilateral hippocampus using MRI-guided stereotaxis. Safety was assessed clinically and efficacy using the validated Canine Cognitive Dysfunction Rating Scale (CCDR) at baseline and 3-month post treatment. Intention to treat analysis imputed a single patient that had a surgical adverse event requiring euthanasia. Three dog brains were donated following natural death and histology carried out to quantify Alzheimer pathology as well as immature neurons and synapses; these were compared to a brain bank (N = 12) of untreated aged dogs with and without CCD. Further, an age-related memory dysfunction rat model (N = 16) was used to more closely evaluate intrahippocampal engraftment of canine SKN cells, focusing on mnemonic and synaptic effects as well as donor cell survival, neurodifferentation and electrophysiologic circuit integration in a live hippocampal slice preparation.

RESULTS

Four out-of-five dogs improved on the primary clinical CCDR endpoint, three fell below diagnostic threshold, and remarkably, two underwent full syndromal reversal lasting up to 2 years. At post mortem, synaptic density in the hippocampus specifically was nine standard deviations above non-treated dogs, and intensity of new neurons also several fold higher. There was no impact on AD pathology or long-term safety signals. Modelling in aged rats replicated the main canine trial findings: hippocampally-dependent place memory deficits were reversed and synaptic depletion rescued. In addition, this model confirmed donor cell survival and migration throughout the hippocampus, neuronal differentiation in situ, and physiologically-correct integration into pyramidal layer circuits.

CONCLUSIONS

With further development, SKN cell therapy may have potential for treating carefully chosen AD patients based on neurosynaptic restoration in the hippocampus.

PET Imaging in Animal Models of Alzheimer’s Disease

The successful development and translation of PET imaging agents targeting β-amyloid plaques and hyperphosphorylated tau tangles have allowed for in vivo detection of these hallmarks of Alzheimer’s disease (AD) antemortem. Amyloid and tau PET have been incorporated into the A/T/N scheme for AD characterization and have become an integral part of ongoing clinical trials to screen patients for enrollment, prove drug action mechanisms, and monitor therapeutic effects. Meanwhile, preclinical PET imaging in animal models of AD can provide supportive information for mechanistic studies. With the recent advancement of gene editing technologies and AD animal model development, preclinical PET imaging in AD models will further facilitate our understanding of AD pathogenesis/progression and the development of novel treatments. In this study, we review the current state-of-the-art in preclinical PET imaging using animal models of AD and suggest future research directions.

Neuronal Deposition of Amyloid-β Oligomers and Hyperphosphorylated Tau Is Closely Connected with Cognitive Dysfunction in Aged Dogs

Background

Canine cognitive dysfunction (CCD) is a progressive syndrome recognized in mature to aged dogs with a variety of neuropathological changes similar to human Alzheimer's disease (AD), for which it is thought to be a good natural model. However, the presence of hyperphosphorylated tau protein (p-Tau) in dogs with CCD has only been demonstrated infrequently.

Objective

The aim of the present study was to investigate the presence of p-Tau and amyloid-β oligomer (Aβo) in cerebral cortex and hippocampus of dogs with CCD, with focus on an epitope retrieval protocol to unmask p-Tau.

Methods

Immunohistochemical and immunofluorescence analysis of the cortical and hippocampal regions of five CCD-affected and two nondemented aged dogs using 4G8 anti-Aβp, anti-Aβ_1 - 42 nanobody (PrioAD13) and AT8 anti-p-Tau (Ser202, Thr205) antibody were used to demonstrate the presence of Aβ plaques (Aβp) and Aβ_1 - 42 oligomers and p-Tau deposits, respectively.

Results

The extracellular Aβ senile plaques were of the diffuse type which lack the dense core normally seen in human AD. While p-Tau deposits displayed a widespread pattern and closely resembled the typical human neuropathology, they did not co-localize with the Aβp. Of considerable interest, however, widespread intraneuronal deposition of Aβ_1 - 42 oligomers were exhibited in the frontal cortex and hippocampal region that co-localized with p-Tau.

Conclusion

Taken together, these findings reveal further shared neuropathologic features of AD and CCD, supporting the case that aged dogs afflicted with CCD offer a relevant model for investigating human AD.

A Review of the Current Mammalian Models of Alzheimer's Disease and Challenges That Need to Be Overcome

Alzheimer's disease (AD) is one of the looming health crises of the near future. Increasing lifespans and better medical treatment for other conditions mean that the prevalence of this disease is expected to triple by 2050. The impact of AD includes both the large toll on individuals and their families as well as a large financial cost to society. So far, we have no way to prevent, slow, or cure the disease. Current medications can only alleviate some of the symptoms temporarily. Many animal models of AD have been created, with the first transgenic mouse model in 1995. Mouse models have been beset by challenges, and no mouse model fully captures the symptomatology of AD without multiple genetic mutations and/or transgenes, some of which have never been implicated in human AD. Over 25 years later, many mouse models have been given an AD-like disease and then 'cured' in the lab, only for the treatments to fail in clinical trials. This review argues that small animal models are insufficient for modelling complex disorders such as AD. In order to find effective treatments for AD, we need to create large animal models with brains and lifespan that are closer to humans, and underlying genetics that already predispose them to AD-like phenotypes.

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.

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.