Assessment of brain-derived extracellular vesicle enrichment for blood biomarker analysis in age-related neurodegenerative diseases: An international overview

INTRODUCTION

Brain-derived extracellular vesicles (BEVs) in blood allows for minimally- invasive investigations of CNS-specific markers of age-related neurodegenerative diseases (NDDs). Polymer-based EV- and immunoprecipitation (IP)-based BEV-enrichment protocols from blood have gained popularity. We systematically investigated protocol consistency across studies, and determined CNS-specificity of proteins associated with these protocols.

METHODS

NDD articles investigating BEVs in blood using polymer-based and/or IP-based BEV enrichment protocols were systematically identified, and protocols compared. Proteins used for BEV-enrichment and/or post-enrichment were assessed for CNS- and brain-cell-type- specificity; extracellular domains (ECD+); and presence in EV-databases.

RESULTS

82.1% of studies used polymer-based (ExoQuick) EV-enrichment, and 92.3% used L1CAM for IP-based BEV-enrichment. Centrifugation times differed across studies. 26.8% of 82 proteins systematically identified were CNS-specific: 50% ECD+, 77.3% were listed in EV- databases.

DISCUSSION

We identified protocol steps requiring standardization, and recommend additional CNS-specific proteins that can be used for BEV-enrichment or as BEV-biomarkers.

Recipient Reaction and Composition of Autologous Sural Nerve Tissue Grafts into the Human Brain

Parkinson's disease (PD) is a severe neurological disease for which there is no effective treatment or cure, and therefore it remains an unmet need in medicine. We present data from four participants who received autologous transplantation of small pieces of sural nerve tissue into either the basal forebrain containing the nucleus basalis of Meynert (NBM) or the midbrain substantia nigra (SN). The grafts did not exhibit significant cell death or severe host-tissue reaction up to 55 months post-grafting and contained peripheral cells. Dopaminergic neurites showed active growth in the graft area and into the graft in the SN graft, and cholinergic neurites were abundant near the graft in the NBM. These results provide a histological basis for changes in clinical features after autologous peripheral nerve tissue grafting into the NBM or SN in PD.

Rapid Activation of Neuroinflammation in Stroke: Plasma and Extracellular Vesicles Obtained on a Mobile Stroke Unit

BACKGROUND

Neuroinflammation is ubiquitous in acute stroke and worsens outcome. However, the precise timing of the inflammatory response is unknown, hindering the design of acute anti-inflammatory therapeutic interventions. We sought to identify the onset of the neuroinflammatory cascade using a mobile stroke unit.

METHODS

The study is a proof-of-concept, cohort investigation of ultra-early blood- and extracellular vesicle-derived markers of neuroinflammation and outcome in acute stroke. Blood was obtained, prehospital, on an mobile stroke unit. Outcomes were biomarker concentrations, modified Rankin Scale score, and National Institutes of Health Stroke Scale score.

RESULTS

Forty-one adults were analyzed, including 15 patients treated on the mobile stroke unit between August 2021 and April 2022, and 26 healthy controls to establish biomarker reference levels. Median patient age was 74 (range, 36-97) years, 60% were female, and 80% White. Ten (67%) were diagnosed as stroke, with 8 (53%) confirmed and 2 likely transient ischemic attack or stroke averted by thrombolysis; 5 were stroke mimics. For strokes, median initial National Institutes of Health Stroke Scale score was 11 (range, 4-19) and 6 (75%) received tPA (tissue-type plasminogen activator). Blood was obtained a median of 58 (range, 36-133) minutes after symptom onset. Within 36 minutes after stroke, plasma IL-6 (interleukin-6), neurofilament light chain, UCH-L1 (ubiquitin C-terminal hydrolase L1), and GFAP (glial fibrillary acidic protein) were elevated by as much as 10 times normal. In EVs, MMP-9 (matrix metalloproteinase-9), CXCL4 (chemokine (C-X-C motif) ligand 4), CRP (C-reactive protein), IL-6, OPN (osteopontin), and PECAM1 (platelet and endothelial cell adhesion molecule 1) were elevated. Inflammatory markers increased rapidly in the first 2 hours and continued rising for 24 hours.

CONCLUSIONS

The neuroinflammatory cascade was found to be activated within 36 to 133 minutes after stroke and progresses rapidly. This is earlier than observed previously in humans and suggests injury from neuroinflammation occurs faster than had been surmised. These findings could inform development of acute immunomodulatory stroke therapies and lead to new diagnostic tools and improved outcomes.

Extracellular vesicles from the CNS play pivotal roles in neuroprotection and neurodegeneration: lessons from in vitro experiments

Intercellular communication between diverse cell types is crucial for the maintenance of the central nervous system, and exosomes have been shown to play an important role in this process. Exosomes are small extracellular vesicles (EVs) that are released by all cell types and carry cargoes that can elicit downstream effects in recipient cells. Exosomal communication in the central nervous system has been implicated in many neurodegenerative diseases, ranging from Alzheimer's disease to major depressive disorder. Though there remain many unknowns in the field of EV biology, in vitro experiments can provide many insights into their potential roles in health and disease. In this review, we discuss the findings of many in vitro EV experiments, with a focus on the potential roles in regulating cell viability, inflammation, oxidative stress, and neurite integrity in the central nervous system.

Examining the Differences in Biomarkers of Neuronal and Glial Injury Between Autoimmune Neurologic Disease Patients and Healthy Controls

Objective

To evaluate differences in concentrations of serum-based biomarkers obtained from a screened healthy control (HC) population compared to age and sex matched autoimmune and inflammatory neurologic disease (AIND) patients.

Background

Protein markers of neuronal and glial injury have become important, minimally invasive biomarkers for understanding the impact of disease in various neurological disorders, including ongoing research into AINDs. Levels of these proteins in healthy individuals remain unclear.

Design/Methods

Neurofilament light (NfL), glial fibrillary acidic protein (GFAP), ubiquitin carboxyl-terminal hydrolase L1 (UCH-L1), and total tau (Tau) levels in AIND and HC participants will be compared. Multiple Sclerosis (MS) patients, as inflammatory controls, will be analyzed as well. AIND and HC participant serum samples have been collected to obtain NfL, GFAP, UCH-L1, and Tau protein levels using Quanterix SR-XTM SIMOA. We plan to analyze and compare age and sex matched HC samples to AIND patients for each biomarker, ages ranging from 20-80 years old. Concentrations will be log transformed and analyzed with mixed model regression.

Results

Healthy Controls (130), AIND (255), and newly diagnosed/treatment naïve MS samples (681) have already been collected. Nineteen HC and AIND (includes NMDA, LGI1, TRIM46, CRMP5, MOG, DPPX, GABA-A, GAD-65) participants were analyzed. Preliminary results for HC show mean Nfl (10.3 pg/mL), GFAP (78.9 pg/mL), UCH-L1 (5.65 pg/mL), and Tau (0.53 pg/mL) levels, and for AIND patients mean Nfl (186.48 pg/mL), GFAP (434.92 pg/mL), UCH-L1 (71.38 pg/mL), and Tau (51.85 pg/mL) levels. While ongoing biomarker analysis will be completed with HC that are age and sex matched, the significantly higher levels in AIND patients highlights the importance of creating baseline values in HC to understand these same biomarkers in AIND patients.

Conclusions

Preliminary results show NfL and GFAP levels are significantly higher in AIND patients versus HC. Baseline biomarker values are essential for understanding further research in biomarkers related to AIND.

Foldamers reveal and validate therapeutic targets associated with toxic α-synuclein self-assembly

Parkinson's disease (PD) is a progressive neurodegenerative disorder for which there is no successful prevention or intervention. The pathological hallmark for PD involves the self-assembly of functional Alpha-Synuclein (αS) into non-functional amyloid structures. One of the potential therapeutic interventions against PD is the effective inhibition of αS aggregation. However, the bottleneck towards achieving this goal is the identification of αS domains/sequences that are essential for aggregation. Using a protein mimetic approach, we have identified αS sequences-based targets that are essential for aggregation and will have significant therapeutic implications. An extensive array of in vitro, ex vivo, and in vivo assays is utilized to validate αS sequences and their structural characteristics that are essential for aggregation and propagation of PD phenotypes. The study aids in developing significant mechanistic and therapeutic insights into various facets of αS aggregation, which will pave the way for effective treatments for PD.

BDNF mediates improvement in cognitive performance after computerized cognitive training in healthy older adults

Introduction

The often‐cited mechanism linking brain‐derived neurotrophic factor (BDNF) to cognitive health has received limited experimental study. There is evidence that cognitive training, physical exercise, and mindfulness meditation may improve cognition. Here, we investigated whether improvements in cognition after these three types of structured interventions are facilitated by increases in BDNF.

Methods

A total of 144 heathy older adults completed a 5‐week intervention involving working memory/cognitive training, physical exercise, mindfulness meditation, or an active control condition. Serum BDNF levels and Digit Symbol Test (DST) performance were measured pre‐ and post‐intervention.

Results

Linear mixed models suggested that only the cognitive training group demonstrated augmentation of BDNF and DST performance relative to the control condition. Path analysis revealed that changes in BDNF mediate intervention‐related improvement in task performance. Regression analyses showed that, across all intervention conditions, increased BDNF levels were associated with increased DST scores.

Discussion

This study appears to be the first to suggest that BDNF helps mediate improvements in cognition after working memory training in healthy older adults.

Highlights

Older adults were randomized to physical activity, mindfulness, cognitive training (computerized cognitive training (CCT), or control.

CCT, but no other condition, led to increased serum brain‐derived neurotrophic factor (BDNF) levels.

CCT led to improvement on the untrained Digit Symbol Test (DST) of speed/working memory.

Path analysis: increases in BDNF mediate intervention‐related improvement on DST.

Increases in BDNF associated with improved DST across all experimental groups.

Curiosity-Based Interventions Increase Everyday Functioning Score But Not Serum BDNF Levels in a Cohort of Healthy Older Adults

An enriched environment is effective in stimulating learning and memory in animal models as well as in humans. Environmental enrichment increases brain-derived neurotrophic factor (BDNF) in aged rats and reduces levels of Alzheimer-related proteins in the blood, including amyloid-β (Aβ) peptides and misfolded toxic forms of tau. To address whether stimulation of curiosity, which is a form of enrichment, may provide a buffer against Alzheimer's disease (AD), we measured levels of biomarkers associated with AD at baseline and after a 6-week intervention in older adults (>65 years of age) randomized to one of three different intervention conditions. Specifically, in this pilot study, we tested the effectiveness of a traditional, structured learning environment compared to a self-motivated learning environment designed to stimulate curiosity. There were no significant differences from baseline to post-intervention in any of the groups for Aβ42/Aβ40 ratio or t-tau (total-tau) plasma levels. Serum BDNF levels decreased significantly in the control group. Interestingly, individuals who had the lowest serum BDNF levels at baseline experienced significantly higher increases in BDNF over the course of the 6-week intervention compared to individuals with higher serum BDNF levels at baseline. As expected, older individuals had lower MoCA scores. Years of education correlated negatively with Aβ levels, suggesting a protective effect of education on levels of this toxic protein. ECog scores were negatively correlated with BDNF levels, suggesting that better performance on the ECog questionnaire was associated with higher BDNF levels. Collectively, these findings did not suggest that a 6-week cognitive training intervention focused on curiosity resulted in significant alterations in blood biomarkers but showed interesting correlations between cognitive scores and BDNF levels, further supporting the role of this trophic factor in brain health in older adults.

Centre of pressure velocity shows impairments in NCAA Division I athletes six months post-concussion during standing balance

Sport-related concussion return to play (RTP) decisions are largely based on the resolution of self-reported symptoms and neurocognitive function. Some evaluators also incorporate balance; however, an objective approach to balance that can detect effects beyond the acute condition is warranted. The purpose of this study is to examine linear measures of biomechanical balance up to 6 months post-concussion, and to present preliminary diagnostic thresholds useful for RTP. Each concussed athlete participated in instrumented standing balance tasks at 4 timepoints post-concussion. The measures from concussed athletes were compared to the sport-matched non-concussed athlete group at each timepoint. Centre of pressure (COP) mediolateral (ML) velocity in double-leg stance on a hard surface discriminated well between non-concussed and concussed athletes. COP anterior-posterior (AP) velocity in tandem stance on foam showed sensitivity to concussion. Sixty per cent of athletes at 6 months post-concussion did not recover to within the proposed COP ML velocity threshold in double-leg stance on a hard surface. Seventy-one per cent of athletes at 6 months post-concussion did not recover to within the COP AP velocity threshold in tandem stance on foam. This lack of recovery potentially indicates vestibular and motor control impairments long past the typical period of RTP.

Regional binding of tau and amyloid PET tracers in Down syndrome autopsy brain tissue

INTRODUCTION

Tau pathology is a major age-related event in Down syndrome with Alzheimer's disease (DS-AD). Although recently, several different Tau PET tracers have been developed as biomarkers for AD, these tracers showed different binding properties in Alzheimer disease and other non-AD tauopathies. They have not been yet investigated in tissue obtained postmortem for DS-AD cases. Here, we evaluated the binding characteristics of two Tau PET tracers (³H-MK6240 and ³H-THK5117) and one amyloid (³H-PIB) ligand in the medial frontal gyrus (MFG) and hippocampus (HIPP) in tissue from adults with DS-AD and DS cases with mild cognitive impairment (MCI) compared to sporadic AD.

METHODS

Tau and amyloid autoradiography were performed on paraffin-embedded sections. To confirm respective ligand targets, adjacent sections were immunoreacted for phospho-Tau (AT8) and stained for amyloid staining using Amylo-Glo.

RESULTS

The two Tau tracers showed a significant correlation with each other and with AT8, suggesting that both tracers were binding to Tau deposits. ³H-MK6240 Tau binding correlated with AT8 immunostaining but to a lesser degree than the ³H-THK5117 tracer, suggesting differences in binding sites between the two Tau tracers. ³H-THK5117, ³H-MK6240 and ³H-PIB displayed dense laminar binding in the HIPP and MFG in adult DS brains. A regional difference in Tau binding between adult DS and AD was observed suggesting differential regional Tau deposition in adult DS compared to AD, with higher THK binding density in the MFG in adult with DS compared to AD. No significant correlation was found between ³H-PIB and Amylo-Glo staining in adult DS brains suggesting that the amyloid PIB tracer binds to additional sites.

CONCLUSIONS

This study provides new insights into the regional binding distribution of a first-generation and a second-generation Tau tracer in limbic and neocortical regions in adults with DS, as well as regional differences in Tau binding in adult with DS vs. those with AD. These findings provide new information about the binding properties of two Tau radiotracers for the detection of Tau pathology in adults with DS in vivo and provide valuable data regarding Tau vs. amyloid binding in adult DS compared to AD.

A Cohort Study of the Temporal Stability of ImPACT Scores Among NCAA Division I Collegiate Athletes: Clinical Implications of Test-Retest Reliability for Enhancing Student Athlete Safety

OBJECTIVE

In this study we examined the temporal stability of the Immediate Post-Concussion Assessment and Cognitive Test (ImPACT) within NCAA Division I athletes across various timepoints using an exhaustive series of statistical models.

METHODS

Within a cohort design, 48 athletes completed repeated baseline ImPACT assessments at various timepoints. Intraclass correlation coefficients (ICC) were calculated using a two-way mixed effects model with absolute agreement.

RESULTS

Four ImPACT composite scores (Verbal Memory, Visual Memory, Visual Motor Speed, and Reaction Time) demonstrated moderate reliability (ICC = 0.51-0.66) across the span of a typical Division I athlete's career, which is below previous reliability recommendations (0.90) for measures used in individual decision-making. No evidence of fixed bias was detected within Verbal Memory, Visual Motor Speed, or Reaction Time composite scores, and minimal detectable change values exceeded the limits of agreement.

CONCLUSIONS

The demonstrated temporal stability of the ImPACT falls below the published recommendations, and as such, fails to provide robust support for the NCAA's recommendation to obtain a single preparticipation cognitive baseline for use in sports-related concussion management throughout an athlete's career. Clinical interpretation guidelines are provided for clinicians who utilize baseline ImPACT scores for later performance comparisons.

Assessment of Long-Term Effects of Sports-Related Concussions: Biological Mechanisms and Exosomal Biomarkers

Concussion or mild traumatic brain injury (mTBI) in athletes can cause persistent symptoms, known as post-concussion syndrome (PCS), and repeated injuries may increase the long-term risk for an athlete to develop neurodegenerative diseases such as chronic traumatic encephalopathy (CTE), and Alzheimer's disease (AD). The Center for Disease Control estimates that up to 3.8 million sport-related mTBI are reported each year in the United States. Despite the magnitude of the phenomenon, there is a current lack of comprehensive prognostic indicators and research has shown that available monitoring tools are moderately sensitive to short-term concussion effects but less sensitive to long-term consequences. The overall aim of this review is to discuss novel, quantitative, and objective measurements that can predict long-term outcomes following repeated sports-related mTBIs. The specific objectives were (1) to provide an overview of the current clinical and biomechanical tools available to health practitioners to ensure recovery after mTBIs, (2) to synthesize potential biological mechanisms in animal models underlying the long-term adverse consequences of mTBIs, (3) to discuss the possible link between repeated mTBI and neurodegenerative diseases, and (4) to discuss the current knowledge about fluid biomarkers for mTBIs with a focus on novel exosomal biomarkers. The conclusions from this review are that current post-concussion clinical tests are not sufficiently sensitive to injury and do not accurately quantify post-concussion alterations associated with repeated mTBIs. In the current review, it is proposed that current practices should be amended to include a repeated symptom inventory, a cognitive assessment of executive function and impulse control, an instrumented assessment of balance, vestibulo-ocular assessments, and an improved panel of blood or exosome biomarkers.

RvE1 treatment prevents memory loss and neuroinflammation in the Ts65Dn mouse model of Down syndrome

Inflammation can be resolved by pro-homeostatic lipids called specialized pro-resolving mediators (SPMs) upon activation of their receptors. Dysfunctional inflammatory resolution is now considered as a driver of chronic neuroinflammation and Alzheimer's disease (AD) pathogenesis. We have previously shown that SPM levels were reduced and also that SPM-binding receptors were increased in patients with AD compared to age-matched controls. Individuals with Down syndrome (DS) exhibit accelerated acquisition of AD neuropathology, dementia, and neuroinflammation at an earlier age than the general population. Beneficial effects of inducing resolution in DS have not been investigated previously. The effects of the SPM resolvin E1 (RvE1) in a DS mouse model (Ts65Dn) were investigated with regard to inflammation, neurodegeneration, and memory deficits. A moderate dose of RvE1 for 4 weeks in middle-aged Ts65Dn mice elicited a significant reduction in memory loss, along with reduced levels of serum pro-inflammatory cytokines, and reduced microglial activation in the hippocampus of Ts65Dn mice but had no effects in age-matched normosomic mice. There were no observable adverse side effects in Ts65Dn or in normosomic mice. These findings suggest that SPMs may represent a novel drug target for individuals with DS and others at risk of developing AD.

Traumatic brain injury increases plasma astrocyte-derived exosome levels of neurotoxic complement proteins

Possible involvement of complement (C) systems in the pathogenesis of traumatic brain injury (TBI) was investigated by quantifying Cproteins in plasma astrocyte-derived exosomes (ADEs) of subjects with sports-related TBI (sTBI) and TBI in military veterans (mtTBI) without cognitive impairment. All sTBI subjects (n = 24) had mild injuries, whereas eight of the mtTBI subjects had moderate, and 17 had mild injuries. Plasma levels of ADEs were decreased after acute sTBI and returned to normal within months. Cprotein levels in ADEs were from 12- to 35-fold higher than the corresponding levels in neuron-derived exosomes. CD81 exosome marker-normalized ADE levels of classical pathway C4b, alternative pathway factor D and Bb, lectin pathway mannose-binding lectin (MBL), and shared neurotoxic effectors C3b and C5b-9 terminal C complex were significantly higher and those of C regulatory proteins CR1 and CD59 were lower in the first week of acute sTBI (n = 12) than in controls (n = 12). Most C abnormalities were no longer detected in chronic sTBI at 3-12 months after acute sTBI, except for elevated levels of factor D, Bb, and MBL. In contrast, significant elevations of ADE levels of C4b, factor D, Bb, MBL, C3b and C5b-9 terminal C complex, and depressions of CR1 and CD59 relative to those of controls were observed after 1-4 years in early chronic mtTBI (n = 10) and persisted for decades except for normalization of Bb, MBL, and CD59 in late chronic mtTBI (n = 15). Complement inhibitors may be useful therapeutically in acute TBI and post-concussion syndrome.

Serum pro-BDNF levels correlate with phospho-tau staining in Alzheimer's disease

Disruption of brain-derived neurotrophic factor (BDNF) biosynthesis and/or signaling has been implicated in the pathogenesis of Alzheimer's disease (AD). We used postmortem brain and fluid samples from 20 patients with variable severity of AD and 11 controls to investigate whether BDNF levels in serum and brain tissue correlated with hippocampal pathology. Total BDNF, precursor BDNF (pro-BDNF), and mature BDNF were measured in cerebrospinal fluid, serum, and 3 postmortem brain regions. Histological markers for AD pathology, the BDNF cognate receptor (TrkB), and glia were measured in the hippocampus (HIP). Lower pro-BDNF levels were observed in the entorhinal and frontal cortices in AD cases compared with controls. AD cases also exhibited significantly lower staining densities of the cognate BDNF receptor TrkB in the HIP compared with controls, and TrkB staining was inversely correlated with both Amylo-Glo and pTau staining in the same region, suggesting a relationship between the density of the cognate BDNF receptor and accumulation of AD pathology. In addition, higher serum pro-BDNF levels correlated with lower HIP pro-BDNF levels and higher pTau staining in the HIP. Total BDNF levels in cortical regions were also negatively correlated with Amylo-Glo staining in the HIP suggesting that reduced BDNF cortical levels might influence hippocampal amyloid accumulation. These results strongly suggest that altered BDNF and TrkB receptors are involved in AD pathology and therefore warrant investigations into therapies involving the BDNF pathway.

Inhibitory designer receptors aggravate memory loss in a mouse model of down syndrome

The pontine nucleus locus coeruleus (LC) is the primary source of noradrenergic (NE) projections to the brain and is important for working memory, attention, and cognitive flexibility. Individuals with Down syndrome (DS) develop Alzheimer's disease (AD) with high penetrance and often exhibit working memory deficits coupled with degeneration of LC-NE neurons early in the progression of AD pathology. Designer receptors exclusively activated by designer drugs (DREADDs) are chemogenetic tools that allow targeted manipulation of discrete neuronal populations in the brain without the confounds of off-target effects. We utilized male Ts65Dn mice (a mouse model for DS), and male normosomic (NS) controls to examine the effects of inhibitory DREADDs delivered via an AAV vector under translational control of the synthetic PRSx8, dopamine β hydroxylase (DβH) promoter. This chemogenetic tool allowed LC inhibition upon administration of the inert DREADD ligand, clozapine-N-oxide (CNO). DREADD-mediated LC inhibition impaired performance in a novel object recognition task and reversal learning in a spatial task. DREADD-mediated LC inhibition gave rise to an elevation of α-adrenoreceptors both in NS and in Ts65Dn mice. Further, microglial markers showed that the inhibitory DREADD stimulation led to increased microglial activation in the hippocampus in Ts65Dn but not in NS mice. These findings strongly suggest that LC signaling is important for intact memory and learning in Ts65Dn mice and disruption of these neurons leads to increased inflammation and dysregulation of adrenergic receptors.

Exosome release and cargo in Down syndrome

Down syndrome (DS) is a multisystem disorder affecting 1 in 800 births worldwide. Advancing technology, medical treatment, and social intervention have dramatically increased life expectancy, yet there are many etiologies of this disorder that are in need of further research. The advent of the ability to capture extracellular vesicles (EVs) in blood from specific cell types allows for the investigation of novel intracellular processes. Exosomes are one type of EVs that have demonstrated great potential in uncovering new biomarkers of neurodegeneration and disease, and also that appear to be intricately involved in the transsynaptic spread of pathogenic factors underlying Alzheimer's disease and other neurological diseases. Exosomes are nanosized vesicles, generated in endosomal multivesicular bodies (MVBs) and secreted by most cells in the body. Since exosomes are important mediators of intercellular communication and genetic exchange, they have emerged as a major research focus and have revealed novel biological sequelae involved in conditions afflicting the DS population. This review summarizes current knowledge on exosome biology in individuals with DS, both early in life and in aging individuals. Collectively these studies have demonstrated that complex multicellular processes underlying DS etiologies may include abnormal formation and secretion of extracellular vesicles such as exosomes.

Neuron-Derived Exosome Proteins May Contribute to Progression From Repetitive Mild Traumatic Brain Injuries to Chronic Traumatic Encephalopathy

The recent recognition that Alzheimer disease-like pathology may be found in chronic traumatic encephalopathy (CTE) even after acute mild traumatic brain injury (mTBI) has increased the urgency of elucidating mechanisms, identifying biomarkers predictive of high risk of development of CTE, and establishing biomarker profiles indicative of impactful effects of treatments. Of the many proteins that are loaded into neuron-derived exosomes (NDEs) from damaged neurons after acute TBI, the levels of prion cellular protein (PRPc), coagulation factor XIII (XIIIa), synaptogyrin-3, IL-6, and aquaporins remain elevated for months. Prolonged heightened expression of aquaporins and IL-6 may account for the persistent central nervous system edema and inflammation of CTE. PRPc, XIIIa and synaptogyrin-3 bind and concentrate neurotoxic forms of oligomeric amyloid β peptides or P-tau for delivery into neurons at or distant from the site of trauma. Our progression factor hypothesis of CTE asserts that physiological neuronal proteins, such as PRPc, XIIIa, synaptogyrin-3, IL-6 and aquaporins, that increase in concentration in neurons and NDEs for months after acute TBI, are etiological contributors to CTE by either direct actions or by recruiting neurotoxic forms of Aβ peptides or P-tau. Such progression factors also may be useful new targets for development of drugs to prevent CTE.

Altered levels of plasma neuron-derived exosomes and their cargo proteins characterize acute and chronic mild traumatic brain injury

Neuron-derived exosomes (NDEs) were enriched by anti-L1CAM antibody immunoabsorption from plasmas of subjects ages 18-26 yr within 1 wk after a sports-related mild traumatic brain injury (acute mTBI) ( n = 18), 3 mo or longer after the last of 2-4 mTBIs (chronic mTBI) ( n = 14) and with no recent history of TBI (controls) ( n = 21). Plasma concentrations of NDEs, assessed by counts and levels of extracted exosome marker CD81, were significantly depressed by a mean of 45% in acute mTBI ( P < 0.0001), but not chronic mTBI, compared with controls. Mean CD81-normalized NDE levels of a range of functional brain proteins were significantly abnormal relative to those of controls in acute but not chronic mTBI, including ras-related small GTPase 10, 73% decrease; annexin VII, 8.8-fold increase; ubiquitin C-terminal hydrolase L1, 2.5-fold increase; AII spectrin fragments, 1.9-fold increase; claudin-5, 2.7-fold increase; sodium-potassium-chloride cotransporter-1, 2.8-fold increase; aquaporin 4, 8.9-fold increase (3.6-fold increase in chronic mTBI); and synaptogyrin-3, 3.1-fold increase (1.3-fold increase in chronic mTBI) (all acute mTBI proteins P < 0.0001). In chronic mTBI, there were elevated CD81-normalized NDE levels of usually pathologic β-amyloid peptide 1-42 (1.6-fold, P < 0.0001), P-T181-tau (2.2-fold, P < 0.0001), P-S396-tau (1.6-fold, P < 0.01), IL-6 (16-fold, P < 0.0001), and prion cellular protein (PRPc) (5.1-fold, P < 0.0001) with lesser or greater (IL-6, PRPc) increases in acute mTBI. Increases in NDE levels of most neurofunctional proteins in acute, but not chronic, mTBI, and elevations of most NDE neuropathological proteins in chronic and acute mTBI delineated phase-specificity. Longitudinal studies of more mTBI subjects may identify biomarkers predictive of and etiologically involved in mTBI-induced neurodegeneration.-Goetzl, E. J., Elahi, F. M., Mustapic, M., Kapogiannis, D., Pryhoda, M., Gilmore, A., Gorgens, K. A., Davidson, B., Granholm, A.-C., Ledreux, A. Altered levels of plasma neuron-derived exosomes and their cargo proteins characterize acute and chronic mild traumatic brain injury.

Differential Effects of Physical Exercise, Cognitive Training, and Mindfulness Practice on Serum BDNF Levels in Healthy Older Adults: A Randomized Controlled Intervention Study

Previous studies have indicated that an active lifestyle is associated with better brain health and a longer life, compared to a more sedentary lifestyle. These studies, both on human and animal subjects, have typically focused on a single activity, usually physical exercise, but other activities have received an increasing interest. One proposed mechanism is that physical exercise increases levels of brain-derived neurotrophic factor (BDNF) in the brain. For the first time, the long-term effects on serum BDNF levels were compared in persons who engaged in either physical exercise training, cognitive training, or mindfulness practice during 5 weeks, and compared with an active control group. Two cohorts of healthy older individuals, one from the Boston area in the US and one from the Växjö area in Sweden, participated. A total of 146 participants were randomly assigned to one of the four groups. All interventions were structurally similar, using interactive, computer-based software that directed participants to carry out specified activities for 35 minutes/day, 5 days per week for 5 weeks. Blood samples were obtained at baseline and soon after the completion of the 5-week long intervention program, and serum BDNF levels were measured using a commercially available ELISA. Only the group that underwent cognitive training increased their serum BDNF levels after 5 weeks of training (F1,74 = 4.22, p = 0.044, partial η2 = 0.054), corresponding to an average 10% increase. These results strongly suggest that cognitive training can exert beneficial effects on brain health in an older adult population.

Exosomal biomarkers in Down syndrome and Alzheimer's disease

Every person with Down syndrome (DS) has the characteristic features of Alzheimer's disease (AD) neuropathology in their brain by the age of forty, and most go on to develop AD dementia. Since people with DS show highly variable levels of baseline function, it is often difficult to identify early signs of dementia in this population. The discovery of blood biomarkers predictive of dementia onset and/or progression in DS is critical for developing effective clinical diagnostics. Our recent studies show that neuron-derived exosomes, which are small extracellular vesicles secreted by most cells in the body, contain elevated levels of amyloid-beta peptides and phosphorylated-Tau that could indicate a preclinical AD phase in people with DS starting in childhood. We also found that the relative levels of these biomarkers were altered following dementia onset. Exosome release and signaling are dependent on cellular redox homeostasis as well as on inflammatory processes, and exosomes may be involved in the immune response, suggesting a dual role as both triggers of inflammation in the brain and propagators of inflammatory signals between brain regions. Based on recently reported connections between inflammatory processes and exosome release, the elevated neuroinflammatory state observed in people with DS may affect exosomal AD biomarkers. Herein, we discuss findings from studies of people with DS, people with DS and AD (DS-AD), and mouse models of DS showing new connections between neuroinflammatory pathways, oxidative stress, exosomes, and exosome-mediated signaling, which may inform future AD diagnostics, preventions, and treatments in the DS population as well as in the general population.

A noradrenergic lesion aggravates the effects of systemic inflammation on the hippocampus of aged rats

Neuroinflammation is potentiated by early degeneration of the locus coeruleus noradrenergic pathway (LC-NE) commonly seen in aging-related neurodegenerative diseases such as Alzheimer’s disease and Parkinson’s disease. In animal models, lipopolysaccharide (LPS) induces strong peripheral immune responses that can cause cognitive changes secondary to neuroinflammation. The influence of the peripheral immune response on cognition might be exacerbated by LC-NE degeneration, but this has not been well characterized previously. In this study, we investigated how systemic inflammation affects neuroinflammation and cognition in aged rats that have had either normal or damaged LC-NE transmitter systems. Rats were first exposed to the selective noradrenergic (NE) neurotoxin N-(2-chloroethyl)-N-ethyl-2-bromobenzylamine (DSP4) to induce degeneration of central NE pathways. Two weeks later, the rats received a low dose of LPS. This resulted in 3 treatment groups (Control, LPS-, and DSP4+LPS-treated rats) studied at 4 hours (short-term subgroup) and 7 days (long-term subgroup) following the LPS injection. DSP4+LPS-treated rats exhibited increased serum levels of several pro-inflammatory cytokines, increased astroglial and microglial activation in the hippocampus, and poorer performance in the novel object recognition task (NORT) compared to controls and LPS-treated rats. Additionally, serum and brain tissue levels of brain-derived neurotrophic factor (BDNF) were modulated over time in the DSP4+LPS group compared to the other two groups. Specifically, DSP4+LPS-treated rats in the short-term subgroup had lower hippocampal BDNF levels (~25%) than controls and LPS-treated rats, which negatively correlated with hippocampal astrogliosis and positively correlated with hippocampal IL-1β levels. Serum and hippocampal BDNF levels in the DSP4+LPS-treated rats in the long-term subgroup returned to levels similar to the control group. These results show that systemic inflammation in LC-NE-lesioned aged rats promotes an exacerbated systemic and central inflammatory response compared to LC-NE-intact rats and alters BDNF levels, indicating the important role of this neurotransmitter system in response to neuroinflammation.

BDNF Responses in Healthy Older Persons to 35 Minutes of Physical Exercise, Cognitive Training, and Mindfulness: Associations with Working Memory Function

Brain-derived neurotrophic factor (BDNF) has a central role in brain plasticity by mediating changes in cortical thickness and synaptic density in response to physical activity and environmental enrichment. Previous studies suggest that physical exercise can augment BDNF levels, both in serum and the brain, but no other study has examined how different types of activities compare with physical exercise in their ability to affect BDNF levels. By using a balanced cross over experimental design, we exposed nineteen healthy older adults to 35-minute sessions of physical exercise, cognitive training, and mindfulness practice, and compared the resulting changes in mature BDNF levels between the three activities. We show that a single bout of physical exercise has significantly larger impact on serum BDNF levels than either cognitive training or mindfulness practice in the same persons. This is the first study on immediate BDNF effects of physical activity in older healthy humans and also the first study to demonstrate an association between serum BDNF responsivity to acute physical exercise and working memory function. We conclude that the BDNF increase we found after physical exercise more probably has a peripheral than a central origin, but that the association between post-intervention BDNF levels and cognitive function could have implications for BDNF responsivity in serum as a potential marker of cognitive health.

Neuronal exosomes reveal Alzheimer's disease biomarkers in Down syndrome

INTRODUCTION

Individuals with Down syndrome (DS) exhibit Alzheimer's disease (AD) neuropathology and dementia early in life. Blood biomarkers of AD neuropathology would be valuable, as non-AD intellectual disabilities of DS and AD dementia overlap clinically. We hypothesized that elevations of amyloid β (Aβ) peptides and phosphorylated-tau in neuronal exosomes may document preclinical AD.

METHODS

AD neuropathogenic proteins Aβ_1-42, P-T181-tau, and P-S396-tau were quantified by enzyme-linked immunosorbent assays in extracts of neuronal exosomes purified from blood of individuals with DS and age-matched controls.

RESULTS

Neuronal exosome levels of Aβ_1-42, P-T181-tau, and P-S396-tau were significantly elevated in individuals with DS compared with age-matched controls at all ages beginning in childhood. No significant gender differences were observed.

DISCUSSION

These early increases in Aβ_1-42, P-T181-tau, and P-S396-tau in individuals with DS may provide a basis for early intervention as targeted treatments become available.

Memory and hippocampal architecture following short-term midazolam in western diet-treated rats

The impact of short-term benzodiazepine exposure on cognition in middle-aged or older patients is a highly debated topic among anesthesiologists, critical care physicians and public media. "Western diet" (WD) consumption is linked to impaired cognition as well. The combination of benzodiazepines with substantial exposure to WD might set the stage for increased hippocampal vulnerability for benzodiazepines leading to exaggerated cognitive impairment in the postoperative period. In this study, Fischer 344 rats were fed either WD or standard rodent diet from 5 to 10.5 months of age. Rats were exposed to midazolam or placebo two days prior to an MRI scan using Diffusional Kurtosis Imaging (DKI) to assess brain microstructural integrity, followed by behavioral testing using a water radial arm maze. Hippocampal tissue was collected to assess alterations in protein biochemistry in brain regions associated with learning and memory. Our results showed that rats exposed to the combination of midazolam and WD had significantly delayed time of learning and exhibited spatial memory impairment. Further, we observed an overall increase of kurtosis metrics in the hippocampus and increased expression of the mitochondrial protein VDAC2 in midazolam-treated rats. Our data suggest that both the short-acting benzodiazepine midazolam and WD contribute to negatively affect the brain in middle-aged rats. This study is the first application of DKI on the effects of midazolam and WD exposure, and the findings demonstrate that diffusion metrics are sensitive indicators of changes in the complexity of neurite architecture.

BDNF levels are increased by aminoindan and rasagiline in a double lesion model of Parkinson׳s disease

The anti-Parkinsonian drug rasagiline is a selective, irreversible inhibitor of monoamine oxidase and is used in the treatment of Parkinson׳s disease (PD). Its postulated neuroprotective effects may be attributed to MAO inhibition, or to its propargylamine moiety. The major metabolite of rasagiline, aminoindan, has shown promising neuroprotective properties in vitro but there is a paucity of studies investigating in vivo effects of this compound. Therefore, we examined neuroprotective effects of rasagiline and its metabolite aminoindan in a double lesion model of PD. Male Fisher 344 rats received i.p. injections of the noradrenergic neurotoxin DSP-4 and intra-striatal stereotaxic microinjections of the dopamine neurotoxin 6-OHDA. Saline, rasagiline or aminoindan (3mg/kg/day s.c.) were delivered via Alzet minipumps for 4 weeks. Rats were then tested for spontaneous locomotion and a novel object recognition task. Following behavioral testing, brain tissue was processed for ELISA measurements of growth factors and immunohistochemistry. Double-lesioned rats treated with rasagiline or aminoindan had reduced behavioral deficits, both in motor and cognitive tasks compared to saline-treated double-lesioned rats. BDNF levels were significantly increased in the hippocampus and striatum of the rasagiline- and aminoindan-lesioned groups compared to the saline-treated lesioned group. Double-lesioned rats treated with rasagiline or aminoindan exhibited a sparing in the mitochondrial marker Hsp60, suggesting mitochondrial involvement in neuroprotection. Tyrosine hydroxylase (TH) immunohistochemistry revealed a sparing of TH-immunoreactive terminals in double-lesioned rats treated with rasagiline or aminoindan in the striatum, hippocampus, and substantia nigra. These data provide evidence of neuroprotection by aminoindan and rasagiline via their ability to enhance BDNF levels.

Suitability of the Neuro-2a cell line for the detection of palytoxin and analogues (neurotoxic phycotoxins)

Palytoxin and related compounds are neurotoxic phycotoxins produced by benthic microalgae belonging to the genus Ostreopsis. For several years this family of phycotoxins has been posing a threat to human health since they can bioaccumulate in shellfish. With the aim of replacing current biological assays, such as the mouse or hemolytic assays, we investigated using the Neuro-2a neuroblastoma cell line to detect palytoxin and related compounds. Cell death induced by the effects of PlTX and analogues on Na+, K+-ATPase were measured using the 1-(4,5-dimethylthiazol-2-yl)-3,5-diphenylformazan (MTT) assay for mitochondrial reductase activity as a surrogate for cell number. The specificity of the Neuro-2a cell-based assay for palytoxin detection was confirmed by using ouabain, which also acts on Na+, K+-ATPase. Pre-treatment of the Neuro-2a cells with ouabain minimizes the effects of palytoxin. The specificity of the Neuro-2a assay was confirmed by the finding that cell death was not detected when Neuro-2a cells were exposed to other phycotoxins with unrelated cellular targets. When the Neuro-2a assay was used to detect palytoxin in mussel extracts spiked with levels of palytoxin around the proposed regulatory value of 250 microg palytoxin/kg shellfish, a good correlation was observed between the levels found and the expected values. We conclude by proposing an experimental design for functional assays using the Neuro-2a cell line for the specific detection of four neurotoxic phycotoxin families: saxitoxins, brevetoxins, ciguatoxins and palytoxins.

Application of the neuroblastoma assay for paralytic shellfish poisons to neurotoxic freshwater cyanobacteria: interlaboratory calibration and comparison with other methods of analysis

Paralytic shellfish poisons (PSPs) are produced by freshwater cyanobacteria and pose a threat to human and animal drinking-water supplies. The wide range of toxin analogues (and the likelihood that further analogues remain to be discovered) means that chromatographic methods are not always reliable indicators of toxicity. Although the mouse bioassay remains the method of choice in the seafood industry, its use is increasingly being questioned on ethical grounds. The cell-based Neuro-2A neuroblastoma toxicity assay is an alternative bioassay validated for testing shellfish extracts, so it was of interest to determine its applicability with the different suite of toxin analogues produced by cyanobacteria. Cyanobacterial bloom samples from Australia, Brazil, and France were assayed using the neuroblastoma assay, liquid chromatography-tandem mass spectrometry (LC-MS/MS), high-performance liquid chromatography with postcolumn derivatization and fluorescence detection, and the Jellett Rapid Test for PSP. To assess interlaboratory variability, the neuroblastoma assay was set up in laboratories in Paris (France) and Adelaide (Australia). Neuroblastoma and chromatographic methods gave comparable results except in the case of the neurotoxic Brazilian samples: LC-MS/MS did not detect the putative new PSPs contained in these samples. Inter- and intralaboratory variability of the neuroblastoma assay was typical of biological assays but no greater than that found for interassay variability between different chromatographic determinations. The batch of Jellett Rapid Tests for PSP used did not yield quantitative results. Overall, the neuroblastoma assay was useful as a screening assay for determination of toxicity caused by saxitoxin neurotoxins in freshwater cyanobacteria, having the advantage of being sensitive to unidentified toxins that currently cannot be quantified by chromatographic means.

First report in a river in France of the benthic cyanobacterium Phormidium favosum producing anatoxin-a associated with dog neurotoxicosis

The first identification of anatoxin-a in a French lotic system is reported. Rapid deaths of dogs occurred in 2003 after the animals drank water from the shoreline of the La Loue River in eastern France. Sediments, stones and macrophytes surfaces at the margin of the river were covered by a thick biofilm containing large quantities of several benthic species of filamentous, non-heterocystous cyanobacteria. Known cyanotoxins, such as microcystins, saxitoxins and anatoxins were screened from biofilm samples by biochemical and analytical assays. A compound with similar UV spectra to the anatoxin-a standard was detected by high-performance liquid chromatography (HPLC) coupled with photo-diode array detector. This toxin was further identified by HPLC coupled with a UV detector and by electrospray ionisation-Quadrupole-Time-Of-Flight mass spectrometer, and confirmed by tandem mass spectrometry. These two techniques were necessary to discriminate anatoxin-a in phenylalanine-containing matrices such as liver samples of poisoned dogs. The toxin and the aromatic amino acid, phenylalanine, present the same pseudomolecular ion at m/z 166, but have differing fragmentation patterns, retention times and UV spectra. Finally, several cyanobacterial strains were isolated from the green biofilm and tested for anatoxin-a production. Phormidium favosum was identified as a new anatoxin-a producing species.