Connecting cellular mechanisms and extracellular vesicle cargo in traumatic brain injury.

Traumatic brain injury is followed by a cascade of dynamic and complex events occurring at the cellular level. These events include: diffuse axonal injury, neuronal cell death, blood-brain barrier break down, glial activation and neuroinflammation, edema, ischemia, vascular injury, energy failure, and peripheral immune cell infiltration. The timing of these events post injury has been linked to injury severity and functional outcome. Extracellular vesicles are membrane bound secretory vesicles that contain markers and cargo pertaining to their cell of origin and can cross the blood-brain barrier. These qualities make extracellular vesicles intriguing candidates for a liquid biopsy into the pathophysiologic changes occurring at the cellular level post traumatic brain injury. Herein, we review the most commonly reported cargo changes in extracellular vesicles from clinical traumatic brain injury samples. We then use knowledge from animal and in vitro models to help infer what these changes may indicate regrading cellular responses post traumatic brain injury. Future research should prioritize labeling extracellular vesicles with markers for distinct cell types across a range of timepoints post traumatic brain injury.

Co-registration of MALDI-MSI and histology demonstrates gangliosides co-localize with amyloid beta plaques in Alzheimer's disease.

Alzheimer's disease (AD) is a progressive neurological condition characterized by impaired cognitive function and behavioural alterations. While AD research historically centered around mis-folded proteins, advances in mass spectrometry techniques have triggered increased exploration of the AD lipidome with lipid dysregulation emerging as a critical player in AD pathogenesis. Gangliosides are a class of glycosphingolipids enriched within the central nervous system. Previous work has suggested a shift in a-series gangliosides from complex (GM1) to simple (GM2 and GM3) species may be related to the development of neurodegenerative disease. Additionally, complex gangliosides with 20 carbon sphingosine chains have been shown to increase in the aging brain. In this study, we utilized matrix assisted laser desorption ionization mass spectrometry imaging (MALDI-MSI) to interrogate the in situ relationship of a-series gangliosides with either 18 or 20 carbon sphingosine chains (d18:1 or d20:1 respectively) in the post-mortem human AD brain. Here, we expanded upon previous literature and demonstrated a significant decrease in the GM1 d20:1:GM1 d18:1 ratio in regions of the dentate gyrus and entorhinal cortex in AD relative to control brain tissue. Then we demonstrated that the MALDI-MSI profile of GM3 co-localizes with histologically confirmed amyloid beta (Aß) plaques and found a significant increase in both GM1 and GM3 in proximity to Aß plaques. Collectively these results support past literature and demonstrate a perturbation of the ganglioside profile in AD. Moreover, this work validates a pipeline for MALDI-MSI and classic histological staining in the same tissue sections. This demonstrates feasibility for integrating untargeted mass spectrometry imaging approaches into a digital pathology framework.

Thromboxane-induced cerebral microvascular rarefaction predicts depressive symptom emergence in metabolic disease.

Previous studies have suggested that the loss of microvessel density in the peripheral circulation with evolving metabolic disease severity represents a significant contributor to impaired skeletal muscle oxygenation and fatigue-resistance. Based on this and our recent work, we hypothesized that cerebral microvascular rarefaction was initiated from the increased prooxidant and proinflammatory environment with metabolic disease and is predictive of the severity of the emergence of depressive symptoms in obese Zucker rats (OZRs). In male OZR, cerebrovascular rarefaction followed the emergence of elevated oxidant and inflammatory environments characterized by increased vascular production of thromboxane A2 (TxA2). The subsequent emergence of depressive symptoms in OZR was associated with the timing and severity of the rarefaction. Chronic intervention with antioxidant (TEMPOL) or anti-inflammation (pentoxifylline) therapy blunted the severity of rarefaction and depressive symptoms, although the effectiveness was limited. Blockade of TxA2 production (dazmegrel) or action (SQ-29548) resulted in a stronger therapeutic effect, suggesting that vascular production and action represent a significant contributor to rarefaction and the emergence of depressive symptoms with chronic metabolic disease (although other pathways clearly contribute as well). A de novo biosimulation of cerebrovascular oxygenation in the face of progressive rarefaction demonstrates the increased probability of generating hypoxic regions within the microvascular networks, which could contribute to impaired neuronal metabolism and the emergence of depressive symptoms. The results of the present study also implicate the potential importance of aggressive prodromic intervention in reducing the severity of chronic complications arising from metabolic disease.NEW & NOTEWORTHY With clinical studies linking vascular disease risk to depressive symptom emergence, we used obese Zucker rats, a model of chronic metabolic disease, to identify potential mechanistic links between these two negative outcomes. Depressive symptom severity correlated with the extent of cerebrovascular rarefaction, after increased vascular oxidant stress/inflammation and TxA2 production. Anti-TxA2 interventions prevasculopathy blunted rarefaction and depressive symptoms, while biosimulation indicated that cerebrovascular rarefaction increased hypoxia within capillary networks as a potential contributing mechanism.

Validating MALDI-IMS Feasibility in Ex Vivo Brain Slices.

Matrix-assisted laser desorption ionization imaging mass spectrometry (MALDI-IMS) generates unique mass spectra in X/Y coordinates across a tissue sample, thus allowing for the spatial detection and relative quantification of biologic compounds in situ. The soft ionization of MALDI-IMS makes it an ideal technique for high-resolution imaging of complex lipid species. Lipid-based spatial chemical maps derived from MALDI-IMS provide critical insight into the unique molecular profiles of a variety of neurologic diseases. Ex vivo brain slice preparations are a prominent alternative to in vivo animal models for studying many different neurologic conditions. For the first time, we present a feasible protocol for achieving reproducible lipidomic MALDI-IMS data from ex vivo rat brain slices and provide evidence that ex vivo brain slices maintain spatiochemical lipidomic profiles representative of an intact whole brain. We conducted a methods comparison assessing the lipid profiles within the neocortex, striatum, and corpus callosum between coronal sections taken from ex vivo brain slices and the current gold standard tissue preparation method, fresh frozen whole brains. For the first time we demonstrate a technique by which 400 µm ex vivo brain slices can be extracted from an imaging chamber and prepared for MALDI-IMS in a way that preserves their lipidomic integrity. We demonstrate the feasibility of MALDI-IMS in ex vivo brain slices and provide a roadmap for MALDI-IMS utilization in uncharted neuroscience fields.

White matter hyperintensities and longitudinal cognitive decline in cognitively normal populations and across diagnostic categories: A meta-analysis, systematic review, and recommendations for future study harmonization.

INTRODUCTION: The primary aim of this paper is to improve the clinical interpretation of white matter hyperintensities (WMHs) and provide an overarching summary of methodological approaches, allowing researchers to design future studies targeting current knowledge gaps. METHODS: A meta-analysis and systematic review was performed investigating associations between baseline WMHs and longitudinal cognitive outcomes in cognitively normal populations, and populations with mild cognitive impairment (MCI), Alzheimer's disease (AD), and stroke. RESULTS: Baseline WMHs increase the risk of cognitive impairment and dementia across diagnostic categories and most consistently in MCI and post-stroke populations. Apolipoprotein E (APOE) genotype and domain-specific cognitive changes relating to strategic anatomical locations, such as frontal WMH and executive decline, represent important considerations. Meta-analysis reliability was assessed using multiple methods of estimation, and results suggest that heterogeneity in study design and reporting remains a significant barrier. DISCUSSION: Recommendations and future directions for study of WMHs are provided to improve cross-study comparison and translation of research into consistent clinical interpretation.

Assessment of executive function in a rodent model of Type 1 diabetes.

This study examined the impact of Type 1 Diabetes Mellitus (T1DM) on executive function using a series of operant conditioning-based tasks in rats. Sprague Dawley rats were randomized to either non-diabetic (n = 12; 6 male) or diabetic (n = 14; 6 male) groups. Diabetes was induced using multiple low-dose streptozotocin injections. All diabetic rodents were insulin-treated using subcutaneous insulin pellet implants (9-15 mM). At week 14 of the study, rats were placed on a food restricted diet to induce 5-10 % weight loss. Rodents were familiarized and their set-shifting ability was tested on a series of tasks that required continuous adjustments to novel stimulus-reward paradigms in order to receive food rewards. Results showed no differences in the number of trials, nor number and type of errors made to successfully complete each task between groups. Therefore, we report no differences in executive function, or more specifically set-shifting abilities between non-diabetic and diabetic rodents that receive insulin.

Adolescent Δ-9-tetrahydrocannabinol exposure induces differential acute and long-term neuronal and molecular disturbances in dorsal vs. ventral hippocampal subregions.

Chronic exposure to Δ-9-tetrahydrocannabinol (THC) during adolescence is associated with long-lasting cognitive impairments and enhanced susceptibility to anxiety and mood disorders. Previous evidence has revealed functional and anatomical dissociations between the posterior vs. anterior portions of the hippocampal formation, which are classified as the dorsal and ventral regions in rodents, respectively. Notably, the dorsal hippocampus is critical for cognitive and contextual processing, whereas the ventral region is critical for affective and emotional processing. While adolescent THC exposure can induce significant morphological disturbances and glutamatergic signaling abnormalities in the hippocampus, it is not currently understood how the dorsal vs. ventral hippocampal regions are affected by THC during neurodevelopment. In the present study, we used an integrative combination of behavioral, molecular, and neural assays in a neurodevelopmental rodent model of adolescent THC exposure. We report that adolescent THC exposure induces long-lasting memory deficits and anxiety like-behaviors concomitant with a wide range of differential molecular and neuronal abnormalities in dorsal vs. ventral hippocampal regions. In addition, using matrix-assisted laser desorption/ionization imaging mass spectrometry (MALDI-IMS), we show for the first time that adolescent THC exposure induces significant and enduring dysregulation of GABA and glutamate levels in dorsal vs. ventral hippocampus. Finally, adolescent THC exposure induced dissociable dysregulations of hippocampal glutamatergic signaling, characterized by differential glutamatergic receptor expression markers, profound alterations in pyramidal neuronal activity and associated oscillatory patterns in dorsal vs. ventral hippocampal subregions.

Noise exposure in early adulthood causes age-dependent and brain region-specific impairments in cognitive function.

Hearing loss is a chronic health condition that affects millions of people worldwide. In addition to age-related hearing impairment, excessive noise exposure is a leading cause of hearing loss. Beyond the devastating effects of hearing impairment itself, epidemiological studies have identified hearing loss as a major risk factor for age-related cognitive decline, including dementia. At present, we currently lack a full understanding of the brain regions and underlying molecular changes that are responsible for mediating the link between hearing loss and cognitive impairment across aging. In the present study, we exposed 6-month-old rats to an occupational-like noise (100 dB SPL, 4 h/day × 30 days) or sham exposure and investigated both hippocampal-dependent (i.e., spatial learning and memory, assessed using the Morris water maze) and striatal-dependent (i.e., visuomotor associative learning, assessed using an operant-conditioning task) cognitive function across aging at 7, 10, and 13 months of age. We also investigated brain region-specific changes in microglial expression following noise/sham exposure in order to assess the potential contribution of this cell type to noise-induced cognitive impairments. Consistent with human studies, the occupational-like noise exposure resulted in high-frequency hearing loss, evidenced by a significant increase in hearing thresholds at 20 kHz. Ultimately, our results suggest that not all higher-level cognitive tasks or their associated brain regions appear to be equally susceptible to noise-induced deficits during aging, as the occupational-like noise exposure caused an age-dependent deficit in spatial but not visuomotor associative learning, as well as altered microglial expression in the hippocampus but not the striatum. Interestingly, we found no significant relationships between spatial learning ability and the level of hearing loss or altered microglial density in the hippocampus following noise exposure, suggesting that other changes in the brain likely contribute to hippocampal-dependent cognitive dysfunction following noise exposure. Lastly, we found that a subset of younger animals also showed noise-induced deficits in spatial learning; findings which suggest that noise exposure may represent an increased risk for cognitive impairment in vulnerable subjects. Overall, our findings highlight that even a mild occupational-like noise exposure earlier in adulthood can have long lasting implications for cognitive function later in life.

Atrial cardiopathy and cognitive impairment.

Cognitive impairment involves complex interactions between multiple pathways and mechanisms, one of which being cardiac disorders. Atrial cardiopathy (AC) is a structural and functional disorder of the left atrium that may be a substrate for other cardiac disorders such as atrial fibrillation (AF) and heart failure (HF). The association between AF and HF and cognitive decline is clear; however, the relationship between AC and cognition requires further investigation. Studies have shown that several markers of AC, such as increased brain natriuretic peptide and left atrial enlargement, are associated with an increased risk for cognitive impairment. The pathophysiology of cognitive decline in patients with AC is not yet well understood. Advancing our understanding of the relationship between AC and cognition may point to important treatable targets and inform future therapeutic advancements. This review presents our current understanding of the diagnosis of AC, as well as clinical characteristics and potential pathways involved in the association between AC and cognitive impairment.

Mechanisms and Biomarker Potential of Extracellular Vesicles in Stroke.

Stoke is a prevalent and devastating neurologic condition with limited options for therapeutic management. Since brain tissue is rarely accessible clinically, peripheral biomarkers for the central nervous system's (CNS's) cellular response to stroke may prove critical for increasing our understanding of stroke pathology and elucidating novel therapeutic targets. Extracellular vesicles (EVs) are cell-derived, membrane-enclosed vesicles secreted by all cell types within the CNS that can freely pass the blood-brain barrier (BBB) and contain unique markers and content linked to their cell of origin. These unique qualities make brain-derived EVs novel candidates for non-invasive blood-based biomarkers of both cell specificity and cell physiological state during the progression of stroke and recovery. While studies are continuously emerging that are assessing the therapeutic potential of EVs and profiling EV cargo, a vast minority of these studies link EV content to specific cell types. A better understanding of cell-specific EV release during the acute, subacute, and chronic stages of stroke is needed to further elucidate the cellular processes responsible for stroke pathophysiology. Herein, we outline what is known about EV release from distinct cell types of the CNS during stroke and the potential of these EVs as peripheral biomarkers for cellular function in the CNS during stroke.

Spectroscopy detects skeletal muscle microvascular dysfunction during onset of sepsis in a rat fecal peritonitis model.

Sepsis is a dysregulated host inflammatory response to infection potentially leading to life-threatening organ dysfunction. The objectives of this study were to determine whether early microvascular dysfunction (MVD) in skeletal muscle can be detected as dynamic changes in microvascular hemoglobin (MVHb) levels using spectroscopy and whether MVD precedes organ histopathology in septic peritonitis. Skeletal muscle of male Sprague-Dawley rats was prepared for intravital microscopy. After intraperitoneal injection of fecal slurry or saline, microscopy and spectroscopy recordings were taken for 6 h. Capillary red blood cell (RBC) dynamics and SO2 were quantified from digitized microscopy frames and MVHb levels were derived from spectroscopy data. Capillary RBC dynamics were significantly decreased by 4 h after peritoneal infection and preceded macrohemodynamic changes. At the same time, low-frequency oscillations in MVHb levels exhibited a significant increase in Power in parts of the muscle and resembled oscillations in RBC dynamics and SO2. After completion of microscopy, tissues were collected. Histopathological alterations were not observed in livers, kidneys, brains, or muscles 6 h after induction of peritonitis. The findings of this study show that, in our rat model of sepsis, MVD occurs before detectable organ histopathology and includes ~ 30-s oscillations in MVHb. Our work highlights MVHb oscillations as one of the indicators of MVD onset and provides a foundation for the use of non-invasive spectroscopy to continuously monitor MVD in septic patients.

Microglial Inflammation and Cognitive Dysfunction in Comorbid Rat Models of Striatal Ischemic Stroke and Alzheimer's Disease: Effects of Antioxidant Catalase-SKL on Behavioral and Cellular Pathology.

Ischemic stroke often co-occurs with Alzheimer's disease (AD) leading to a worsened clinical outcome. Neuroinflammation is a critical process implicated in AD and ischemic pathology, associated with cognitive decline. We sought to investigate the combined effects of ischemic stroke induced by endothelin-1 injection in two AD rat models, using motor function, memory and microglial inflammation in the basal forebrain and striatum as readouts. In addition, we sought to determine the effectiveness of the antioxidant biologic CAT-SKL in one of the models. The early AD model employed the bilateral intracerebroventricular injections of the toxic ß-amyloid peptide Aß25-35, the prodromal AD model used the transgenic Fischer 344 rat overexpressing a pathological mutant human amyloid precursor protein. Motor function was assessed using a cylinder, modified sticky tape and beam-walk tasks; learning and memory were tested in the Morris water maze. Microglial activation was examined using immunohistochemistry. Aß25-35 toxicity and stroke combination greatly increased microglial inflammation in the basal forebrain. Prodromal AD-pathology coupled with ischemia in the transgenic rat resulted in a greater microgliosis in the striatum. Combined transgenic rats showed balance alterations, comorbid Aß25-35 rats showed a transient sensorimotor deficit, and both demonstrated spatial reference memory deficit. CAT-SKL treatment ameliorated memory impairment and basal forebrain microgliosis in Aß25-35 rats with stroke. Our results suggest that neuroinflammation could be one of the early processes underlying the interaction of AD with stroke and contributing to the cognitive impairment, and that therapies such as antioxidant CAT-SKL could be a potential therapeutic strategy.

Proceedings from the Albert Charitable Trust Inaugural Workshop on 'Understanding the Acute Effects of Exercise on the Brain'.

An inaugural workshop supported by "The Leo and Anne Albert Charitable Trust," was held October 4-7, 2019 in Scottsdale, Arizona, to focus on the effects of exercise on the brain and to discuss how physical activity may prevent or delay the onset of aging-related neurodegenerative conditions. The Scientific Program Committee (led by Dr. Jeff Burns) assembled translational, clinical, and basic scientists who research various aspects of the effects of exercise on the body and brain, with the overall goal of gaining a better understanding as to how to delay or prevent neurodegenerative diseases. In particular, research topics included the links between cardiorespiratory fitness, the cerebrovasculature, energy metabolism, peripheral organs, and cognitive function, which are all highly relevant to understanding the effects of acute and chronic exercise on the brain. The Albert Trust workshop participants addressed these and related topics, as well as how other lifestyle interventions, such as diet, affect age-related cognitive decline associated with Alzheimer's and other neurodegenerative diseases. This report provides a synopsis of the presentations and discussions by the participants, and a delineation of the next steps towards advancing our understanding of the effects of exercise on the aging brain.

Expanding the horizon of research into the pathogenesis of the white matter diseases: Proceedings of the 2021 Annual Workshop of the Albert Research Institute for White Matter and Cognition.

White matter pathologies are critically involved in the etiology of vascular cognitive impairment-dementia (VCID), Alzheimer's disease (AD), and Alzheimer's disease and related diseases (ADRD), and therefore need to be considered a treatable target ( Roseborough A, Hachinski V, Whitehead S. White matter degeneration - a treatable target? Roseborough et al. JAMA Neurol [Internet]. 2020 Apr 27;77(7):793-4, [1] . To help address this often-missed area of research, several workshops have been sponsored by the Leo and Anne Albert Charitable Trust since 2015, resulting in the incorporation of "The Albert Research Institute for White Matter and Cognition" in 2020. The first annual "Institute" meeting was held virtually on March 3-4, 2021. The Institute provides a forum and workspace for communication and support of the advancement of white matter science and research to better understand the evolution and prevention of dementia. It serves as a platform for young investigator development, to introduce new data and debate biology mechanisms and new ideas, and to encourage and support new research collaborations and directions to clarify how white matter changes, with other genetic and health risk factors, contribute to cognitive impairment. Similar to previous Albert Trust-sponsored workshops (Barone et al. in J Transl Med 14:1-14, [2]; Sorond et al. in GeroScience 42:81-96, [3]), established expert investigators were identified and invited to present. Opportunities to attend and present were also extended by invitation to talented research fellows and younger scientists. Also, updates on institute-funded research collaborations were provided and discussed. The summary that follows is a synopsis of topics and discussion covered in the workshop.

Microvessel stenosis, enlarged perivascular spaces, and fibrinogen deposition are associated with ischemic periventricular white matter hyperintensities.

Periventricular white matter hyperintensities (pvWMH) are neuroimaging abnormalities surrounding the lateral ventricles that are apparent on magnetic resonance imaging (MRI). They are associated with age, neurodegenerative disease, and cerebrovascular risk factors. While pvWMH ultimately represent a loss of white matter structural integrity, the pathological causes are heterogeneous in nature, and currently, cannot be distinguished using neuroimaging alone. pvWMH could occur because of a combination of small vessel disease (SVD), ependymal loss, blood-brain barrier dysfunction, and microgliosis. In this study we aimed to characterize microvascular stenosis, fibrinogen extravasation, and microgliosis within pvWMH with and without imaging evidence of periventricular infarction. Using postmortem neuroimaging of human brains (n = 20), we identified pvWMH with and without periventricular infarcts (PVI). We performed histological analysis of microvessel stenosis, perivascular spaces, microgliosis, and immunohistochemistry against fibrinogen as a measure of serum protein extravasation. Herein, we report distinctions between pvWMH with and without periventricular infarcts based on associations with microvessel stenosis, enlarged perivascular spaces, and fibrinogen IHC. Microvessel stenosis was significantly associated with PVI and with cellular deposition of fibrinogen in the white matter. The presence of fibrinogen was associated with PVI and increased number of microglia. These findings suggest that neuroimaging-based detection of infarction within pvWMH may help distinguish more severe lesions, associated with underlying microvascular disease and BBB dysfunction, from milder pvWMH that are a highly frequent finding on MRI.

GABAB Receptor Agonist R-Baclofen Reverses Altered Auditory Reactivity and Filtering in the Cntnap2 Knock-Out Rat.

Altered sensory information processing, and auditory processing, in particular, is a common impairment in individuals with autism spectrum disorder (ASD). One prominent hypothesis for the etiology of ASD is an imbalance between neuronal excitation and inhibition. The selective GABAB receptor agonist R-Baclofen has been shown previously to improve social deficits and repetitive behaviors in several mouse models for neurodevelopmental disorders including ASD, and its formulation Arbaclofen has been shown to ameliorate social avoidance symptoms in some individuals with ASD. The present study investigated whether R-Baclofen can remediate ASD-related altered sensory processing reliant on excitation/inhibition imbalance in the auditory brainstem. To assess a possible excitation/inhibition imbalance in the startle-mediating brainstem underlying ASD-like auditory-evoked behaviors, we detected and quantified brain amino acid levels in the nucleus reticularis pontis caudalis (PnC) of rats with a homozygous loss-of-function mutation in the ASD-linked gene Contactin-associated protein-like 2 (Cntnap2) and their wildtype (WT) littermates using Matrix-Assisted Laser Desorption Ionization Mass Spectrometry (MALDI MS). Abnormal behavioral read-outs of brainstem auditory signaling in Cntnap2 KO rats were accompanied by increased levels of GABA, glutamate, and glutamine in the PnC. We then compared the effect of R-Baclofen on behavioral read-outs of brainstem auditory signaling in Cntnap2 KO and WT rats. Auditory reactivity, sensory filtering, and sensorimotor gating were tested in form of acoustic startle response input-output functions, short-term habituation, and prepulse inhibition before and after acute administration of R-Baclofen (0.75, 1.5, and 3 mg/kg). Systemic R-Baclofen treatment improved disruptions in sensory filtering in Cntnap2 KO rats and suppressed exaggerated auditory startle responses, in particular to moderately loud sounds. Lower ASR thresholds in Cntnap2 KO rats were increased in a dose-dependent fashion, with the two higher doses bringing thresholds close to controls, whereas shorter ASR peak latencies at the threshold were further exacerbated. Impaired prepulse inhibition increased across various acoustic prepulse conditions after administration of R-Baclofen in Cntnap2 KO rats, whereas R-Baclofen did not affect prepulse inhibition in WT rats. Our findings suggest that GABAB receptor agonists may be useful for pharmacologically targeting multiple aspects of sensory processing disruptions involving neuronal excitation/inhibition imbalances in ASD.

Precocious White Matter Inflammation and Behavioural Inflexibility Precede Learning and Memory Impairment in the TgAPP21 Rat Model of Alzheimer Disease.

Neuroinflammation and behavioural inflexibility are both common in late adulthood but far more profound in Alzheimer disease (AD). To investigate the relationship between ageing, AD, neuroinflammation, and behavioural flexibility, male wild-type Fischer 344 (Wt) and the transgenic APP21 (TgAPP21) rats were aged to 4, 8, 13, and 22 months and evaluated for neuroinflammation and cognitive impairment. TgAPP21 rats overexpress a pathogenic variant of the human amyloid precursor protein (hAPP; Swedish and Indiana mutations) but do not spontaneously develop overt pathology related to AD. In both genotypes, learning and memory were similarly impaired in older rats. However, at 8 months of age, TgAPP21 rats demonstrated behavioural inflexibility in set shifting, reversal, and the Morris water maze, while Wt rats showed inflexibility at 13 and 22 months of age. This early inflexibility in TgAPP21 rats was accompanied by a precocious increase in microglia activation within the corpus callosum; 8- and 13-month-old TgAPP21 rats had similar levels of microglia activation as 13- and 22-month-old Wt rats, respectively. However, while neuroinflammation within the white matter continued to progress with age, behavioural inflexibility peaked in 8-month-old TgAPP21 rats; in older TgAPP21 rats, memory and learning impairments masked inflexibility. These findings suggest that the behavioural inflexibility and white matter inflammation seen in normal ageing are accelerated in AD and may precede impairments of learning and memory.

Brain Targeting and Toxicological Assessment of the Extracellular Vesicle-Packaged Antioxidant Catalase-SKL Following Intranasal Administration in Mice.

The antioxidant enzyme catalase represents an important therapeutic target due to its role in mitigating cellular reactive oxygen species that contribute to the pathogenesis of many disease states. Catalase-SKL (CAT-SKL), a genetically engineered, peroxisome-targeted, catalase derivative, was developed in order to increase the therapeutic potential of the enzyme, and has previously been shown to be effective in combating oxidative stress in a variety of in vitro and in vivo models, thereby mitigating cellular degeneration and death. In the present study we addressed important considerations for the development of an extracellular vesicle-packaged version of CAT-SKL (evCAT-SKL) as a therapeutic for neurodegenerative diseases by investigating its delivery potential to the brain when administered intranasally, and safety by assessing off-target toxicity in a mouse model. Mice received weekly intranasal administrations of evCAT-SKL or empty extracellular vesicles for 4 weeks. Fluorescent labeling for CAT-SKL was observed throughout all sections of the brain in evCAT-SKL-treated mice, but not in empty extracellular vesicle-treated mice. Furthermore, we found no evidence of gross or histological abnormalities following evCAT-SKL or empty extracellular vesicle treatment in a full-body toxicological analysis. Combined, the successful brain targeting and the lack of off-target toxicity demonstrates that intranasal delivery of extracellular vesicle-packaged CAT-SKL holds promise as a therapeutic for addressing neurological disorders.