White matter damage and glymphatic dysfunction in a model of vascular dementia in rats with no prior vascular pathologies

Targeting the brain's glymphatic pathway: A novel therapeutic approach for cerebral small vessel disease

Cerebral small vessel disease encompasses a group of neurological disorders characterized by injury to small blood vessels, often leading to stroke and dementia. Due to its diverse etiologies and complex pathological mechanisms, preventing and treating cerebral small vessel vasculopathy is challenging. Recent studies have shown that the glymphatic system plays a crucial role in interstitial solute clearance and the maintenance of brain homeostasis. Increasing evidence also suggests that dysfunction in glymphatic clearance is a key factor in the progression of cerebral small vessel disease. This review begins with a comprehensive introduction to the structure, function, and driving factors of the glymphatic system, highlighting its essential role in brain waste clearance. Afterwards, cerebral small vessel disease was reviewed from the perspective of the glymphatic system, after which the mechanisms underlying their correlation were summarized. Glymphatic dysfunction may lead to the accumulation of metabolic waste in the brain, thereby exacerbating the pathological processes associated with cerebral small vessel disease. The review also discussed the direct evidence of glymphatic dysfunction in patients and animal models exhibiting two subtypes of cerebral small vessel disease: arteriolosclerosis-related cerebral small vessel disease and amyloid-related cerebral small vessel disease. Diffusion tensor image analysis along the perivascular space is an important non-invasive tool for assessing the clearance function of the glymphatic system. However, the effectiveness of its parameters needs to be enhanced. Among various nervous system diseases, including cerebral small vessel disease, glymphatic failure may be a common final pathway toward dementia. Overall, this review summarizes prevention and treatment strategies that target glymphatic drainage and will offer valuable insight for developing novel treatments for cerebral small vessel disease.

Functional abnormalities of the glymphatic system in cognitive disorders

Various pathological mechanisms represent distinct therapeutic targets for cognitive disorders, but a balance between clearance and production is essential for maintaining the stability of the brain's internal environment. Thus, the glymphatic system may represent a common pathway by which to address cognitive disorders. Using the established model of the glymphatic system as our foundation, this review disentangles and analyzes the components of its clearance mechanism, including the initial inflow of cerebrospinal fluid, the mixing of cerebrospinal fluid with interstitial fluid, and the outflow of the mixed fluid and the clearance. Each section summarizes evidence from experimental animal models and human studies, highlighting the normal physiological properties of key structures alongside their pathological manifestations in cognitive disorders. The same pathologic manifestations of different cognitive disorders appearing in the glymphatic system and the same upstream influences are main points of interest of this review. We conclude this article by discussing new findings and outlining the limitations identified in current research progress.

Serum Carotenoid Concentrations Are Associated with Enlarged Choroid Plexus, Lateral Ventricular Volume, and Perivascular Spaces on Magnetic Resonance Imaging: A Large Cohort Study

RATIONALE AND OBJECTIVES

Since carotenoids have various physiological activities, including antioxidant activity, several epidemiological studies have linked the consumption of a carotenoid-rich diet to a decreased risk of neurodegenerative diseases. Increased choroid plexus volume (CPV) and enlarged perivascular spaces (PVS) on brain magnetic resonance imaging (MRI) may be indicators of impaired glymphatic system function. The purpose of this large-scale elderly population study was to assess whether serum concentrations of major carotenoids (α-carotene, β-carotene, cis-lycopene, trans-lycopene, β-cryptoxanthin, zeaxanthin, and lutein) concentrations are associated with CPV, lateral ventricular volume (LVV), and PVS.

MATERIALS AND METHODS

This cross-sectional study included 2050 individuals (median age, 69 years; 61.02% females) who underwent 3 T MRI. The imaging characteristics included total intracranial volume (ICV), CPV, LVV, and basal ganglia-enlarged PVS on T2-weighted images.

RESULTS

Low serum β-carotene concentration was a significant independent predictor of increased CPV/ICV (p=0.046), increased LVV/ICV (p=0.035), and enlarged PVS (p=0.009) after adjusting for potential confounders (age, sex, body mass index, HbA1c level, systolic blood pressure, smoking history, drinking history, educational history, and Mini-Mental State Examination score, CRP level). Low serum α-carotene concentration was also a significant independent predictor of an enlarged PVS (p=0.014).

CONCLUSION

In this study, β-carotene concentration was associated to the CPV, LVV, and PVS, suggesting that the antioxidant activity of β-carotene may have an important role in maintaining glymphatic system function. Since β-carotene is a dietary carotenoid, our results emphasize the importance of interventions for effective β-carotene intake among elderly people.

Electroacupuncture promotes oligodendrocyte differentiation and myelin repair in a rat model of vascular dementia: Investigation of the mechanism from NF-κB-mediated inflammation

Myelin impairment is an important cause of cognitive impairment in vascular dementia (VD). Promoting myelin regeneration has become an important improvement strategy and oligodendrocytes are important targets. This study used a multiple microinfarctions (MMI)-induced VD rat model to reveal the mechanism of myelination of oligodendrocytes in the recovery of VD model, and to investigate the intervention mechanism of electroacupuncture (EA), an effective therapeutic for VD. Initially, our transcriptomic analysis identified 52 differentially expressed genes between the sham and MMI groups. These genes are primarily associated with axonal pathways, including the synaptic vesicle cycle, glutamatergic synapse, axon guidance, and sphingolipid metabolism. Compared with sham group, inflammation, impaired differentiation of oligodendrocyte precursor cells (OPCs) and myelin damage were remarkably observable in the hippocampus of MMI group, indicating the involvement of inflammation-regulated impairment of OPCs. Accordingly, pyrrolidinedithiocarbamate (PDTC), a NF-κB inhibitor could improve learning and memory impairment, reverse the hippocampal inflammation and impairment of OPCs differentiation, and decrease myelin damage in MMI rats. Importantly, EA could also improve learning and memory, attenuate the inflammatory response in the hippocampus and facilitate the differentiation of OPCs to aid in the repair of myelin damage in MMI rats. In conclusion, our data suggest that NF-κB activation is a prohibited factor for the myelin repair, while EA might reduce NF-κB activation and promote the differentiation of OPCs to repair the myelin damage in MMI rats.

Quantifying Ventricular CSF Clearance in the Human Brain Using Dynamic 18F-FDG PET: Insights into Age-Related Glymphatic Impairment

Purpose

The glymphatic system facilitates brain waste clearance via cerebrospinal fluid (CSF) flow, and its dysfunction has been linked to aging and neurodegeneration. However, clinically accessible methods to quantify glymphatic function in humans remain limited. This study aimed to examine the potential of dynamic 18F-FDG PET for measuring ventricular CSF clearance - as a surrogate marker of glymphatic function. Specifically, we evaluated its association with age, its test-retest reliability, and the feasibility of reduced scan durations for clinical applicability.

Methods

We analyzed 72 baseline 18F-FDG PET scans from participants enrolled in a prior depression trial. Time-activity curves (TACs) were extracted from the lateral ventricles and fitted with a γ-variate model to estimate influx (μ in ) and clearance (μ out ) parameters. Associations with age and clinical factors were examined using correlation and multiple linear regression. Test-retest reliability was assessed in 11 placebo-treated participants who underwent repeat scans eight weeks apart. A feasibility analysis tested whether shorter scan windows could yield comparable clearance estimates.

Results

μ out showed a strong negative correlation with age (r = -0.680, p < 0.001), whileμ in was not significantly age-related. Age remained a significant predictor ofμ out after adjusting for sex, ventricle size, and depression severity. A positive association betweenμ out and depression severity was observed after covariate adjustment. Test-retest analysis yielded an intraclass correlation coefficient of 0.702 forμ out , indicating moderate-to-good reproducibility. A shortened 30-minute scan window (starting 30 minutes post injection) preserved strong correlations with bothμ out and age, supporting the potential for abbreviated imaging protocols.

Conclusion

Dynamic 18F-FDG PET provides a reliable and noninvasive method to quantify ventricular CSF clearance, revealing age-related decline indicative of glymphatic impairment. The method demonstrates reproducibility over time and retains key clearance metrics even with shortened scan durations. These findings establish a clinically feasible 18F-FDG PET-based approach for studying brain clearance and glymphatic function in aging and disease.

Enlarging and shrinking focal perivascular spaces

Background and PurposePerivascular spaces (PVS) are interstitial fluid-filled spaces surrounding blood vessels traversing the deep gray nuclei and white matter of the brain. These are commonly encountered on CT and MR imaging and are generally asymptomatic and of no clinical significance. However, occasional changes in the size of focal PVS, for example, when enlarging, may mimic pathologies including neoplasms and infections, hence potentially confounding radiological interpretation. Given these potential diagnostic issues, we sought to better characterize common clinical and imaging features of focal PVS demonstrating size fluctuations.Materials and MethodsUpon institutional approval, we retrospectively identified 4 cases demonstrating PVS with size changes at our institution. To supplement our cases, we also performed a literature review, which identified an additional 14 cases. Their clinical and imaging data were analyzed to identify characteristic features.ResultsOf the 18 total cases (including the 4 institutional cases), 10 cases increased and 8 decreased in size. These focal PVS ranged from 0.4-4.5 cm in size. Whereas a decrease in size did not represent a diagnostic issue, focal increase in size of PVS led to concerning differential diagnoses in at least 30% of the radiology reports. These enlarging PVS were most found in the basal ganglia and temporal lobe, and in patients with previous brain radiation treatment.ConclusionFocal size change of PVS can occur, especially years after brain radiation treatment. Being cognizant of this benign finding is important to consider in the differential diagnosis to avoid undue patient anxiety or unnecessary medical intervention.

Covert cerebrospinal fluid dynamics dysfunction: evolution from conventional to innovative therapies

Cerebrospinal fluid (CSF) dynamics disorders are intricately linked to diverse neurological pathologies, though they usually are mild and covert. Contemporary insights into glymphatic system function, particularly the CSF transport, drainage, and its role in clearing metabolic waste and toxic substances in both normal and pathological states, and the pivotal role of aquaporin-4 (AQP4) in CSF-interstitial fluid (ISF) exchange, have established novel theoretical frameworks of subclinical CSF dynamics dysfunction, and have promoted the development of non-surgical therapeutic approaches for them simultaneously. This review comprehensively analyzes the advancement of non-surgical interventions for CSF dynamics disorders, emphasizing the transition from established methodologies to innovative approaches. Current non-surgical treatment strategies primarily encompass three directions: pharmacological therapy, physical therapy, and biological regulation therapy. In terms of pharmacological interventions, developments from traditional diuretics to novel small-molecule drugs show promising therapeutic potential. In physical therapy, innovative techniques such as lower body negative pressure, transcranial magnetic stimulation, and vagus nerve stimulation have provided new options for clinical practice. Meanwhile, biological regulation therapy, exemplified by recombinant VEGF-C administration, has established novel therapeutic paradigms. These therapeutic strategies have demonstrated potential in improving CSF dynamics and enhancing CSF waste elimination. Future research should focus on developing individualized treatment protocols, elucidating of therapeutic mechanisms, and assessing longitudinal outcomes. This will facilitate the development of more precise therapeutic strategies and exploration of optimized multimodal treatment combinations in handling the so-called convert CSF dynamics dysfunction.

Glymphatic system: a self-purification circulation in brain

The glymphatic system theory introduces a new perspective on fluid flow and homeostasis in the brain. Here, cerebrospinal fluid and interstitial fluid (CSF-ISF) moves from the perivascular spaces (PVS) of arteries to those of veins for drainage. Aquaporin-4 (AQP4) plays a crucial role in driving fluid within the PVS. The impairment to AQP4 is closely linked to the dysfunction of the glymphatic system. The function of the glymphatic system is less active during waking but enhanced during sleep. The efficiency of the glymphatic system decreases with aging. Damage to the glymphatic system will give rise to the development and progression of many brain diseases, such as Alzheimer's disease (AD), Parkinson's disease (PD), chronic traumatic encephalopathy (CTE), and vascular dementia (VaD). Here, we reviewed previous research associated with the glymphatic system, including its concepts, principles, and influencing factors. We hypothesize that AQP4 could be a target for the prevention and treatment of certain brain diseases through the regulation on the glymphatic system.

The enlarged perivascular spaces in the hippocampus is associated with memory function in patients with type 2 diabetes mellitus

Early detection of cognitive dysfunction in patients with type 2 diabetes mellitus (T2DM) is important for preventive measures due to the lack of effective treatments. The purpose of this study is to investigate the relationship between enlarged perivascular space in the hippocampus (H-EPVS) and cognitive performance in patients with T2DM, and to determine whether it can serve as an imaging marker for cognitive dysfunction. 66 T2DM patients with cognitive impairment (T2DM-CI) and 71 T2DM patients with normal cognitive function (T2DM-NC) underwent cranial MRI scans and comprehensive neuropsychological assessments. H-EPVS counts were visually calculated on T2WI imaging according to a previous scale. The differences in the counts of H-EPVS, demographic data, laboratory test results, and cognitive assessment scores between the two groups were compared. The partial correlation analysis was used to explore the relationship between H-EPVS and glymphatic system function (indicated by the DTI-ALPS index), as well as markers of CSVD. Multiple linear regression models were conducted to explore the association between H-EPVS and cognitive functions. Compared with the T2DM-NC group, T2DM-CI exhibited significantly higher counts of H-EPVS in both the total (sum of the left and right side) and left side (P < 0.001). The T2DM-CI group had lower DTI-ALPS index and RAVLT total score. The total H-EPVS counts were significantly correlated with the DTI-ALPS index (r = - 0.240, P = 0.005), BG-EPVS (r = 0.325, P < 0.001), and CSO-EPVS (r = 0.183, P = 0.033). Multiple linear regression showed the total H-EPVS counts exhibited a negative correlation with MMSE (β = - 0.324, 95% CI: - 0.091, - 0.320), immediate memory (β = - 0.380, 95% CI: - 0.673, - 1.766) and delayed recall (β = - 0.252, 95% CI: - 0.052, - 0.463). H-EPVS may serve as a potential neuroimaging biomarker for cognitive impairment in patients with T2DM, warranting further investigation and validation in future studies.

Association of Glymphatic Function With Clinical Characteristics in Patients With Clinical and Asymptomatic Creutzfeldt-Jakob Disease

BACKGROUND AND OBJECTIVES

Abnormal glymphatic system-related proteins have been identified in a small-scale pathologic study of patients with Creutzfeldt-Jakob disease (CJD). However, it remains unclear whether glymphatic dysfunction occurs in vivo in patients with CJD and whether this decline begins during the preclinical stage. This study aimed to investigate the relationship between glymphatic dysfunction and clinical characteristics in patients with CJD, as well as potential glymphatic impairment in preclinical CJD.

METHODS

This prospective cohort study recruited patients with CJD and healthy controls (HCs) from the Department of Neurology at Xuanwu Hospital, Capital Medical University, Beijing, China, from 2018 to 2022. In addition, a family with preclinical genetic CJD carrying the G114V pathogenic variant was followed over 6 years with 3 evaluations. All participants underwent diffusion tensor imaging along the perivascular space (DTI-ALPS) to measure glymphatic function in vivo and 18F-fludeoxyglucose-PET to identify CJD-related metabolic patterns. Associations between the DTI-ALPS index and Medical Research Council Prion Disease Rating Scale (MRC-PDRS) score were evaluated using multiple linear regression.

RESULTS

We enrolled 35 patients with CJD (mean age 59.6 ± 10.7 years, 40% female, with the time from onset to glymphatic dysfunction assessment averaging 39% of the total disease course), 28 age-matched and sex-matched HCs, and a family with preclinical genetic CJD consisting of 7 carriers and 7 noncarriers. Patients with CJD exhibited lower DTI-ALPS values compared with HCs (p < 0.001). Partial correlation analyses revealed significant correlations between the DTI-ALPS index and MRC-PDRS score (r = 0.346, p = 0.049) and disease progression (r = -0.468, p = 0.006), but not with disease duration or cognitive severity after adjusting for age and sex. Multivariate linear analysis demonstrated that poorer MRC-PDRS scores (β = 0.702, p = 0.014) were associated with a lower DTI-ALPS index. The DTI-ALPS index of asymptomatic G114V carriers showed no significant difference compared with noncarriers. However, a preclinical CJD case exhibited an 8.2% decrease in the DTI-ALPS index 3.3 years before onset. No significant correlation was found between regional metabolic standardized uptake value ratios and DTI-ALPS index.

DISCUSSION

Our study indicates that glymphatic dysfunction is associated with CJD severity and disease progression. Glymphatic dysfunction may occur in the preclinical stage, but these findings should be interpreted with caution because they are based on individual findings.

Glymphatic system: a gateway for neuroinflammation

The glymphatic system is a relatively recently identified fluid exchange and transport system in the brain. Accumulating evidence indicates that glymphatic function is impaired not only in central nervous system disorders but also in systemic diseases. Systemic diseases can trigger the inflammatory responses in the central nervous system, occasionally leading to sustained inflammation and functional disturbance of the central nervous system. This review summarizes the current knowledge on the association between glymphatic dysfunction and central nervous system inflammation. In addition, we discuss the hypothesis that disease conditions initially associated with peripheral inflammation overwhelm the performance of the glymphatic system, thereby triggering central nervous system dysfunction, chronic neuroinflammation, and neurodegeneration. Future research investigating the role of the glymphatic system in neuroinflammation may offer innovative therapeutic approaches for central nervous system disorders.

Exploring the effects of moxibustion on cognitive function in rats with multiple cerebral infarctions from the perspective of glial vascular unit repairing

Objective

This study aimed to explore the effect of moxibustion at Governor Vessel (GV) acupoints, including Baihui (GV 20), Shenting (GV 24) and Dazhui (GV 14) for 14 days on glial vascular unit (GVU) in rats with multiple microinfarctions (MMI), and to explore its action mechanism.

Methods

The effect and mechanism of moxibustion on vascular dementia (VD) were studied in MMI rats by means of behavioral and molecular biology experiments.

Results

Rats receiving MMI showed impairment of memory function, reduction of cerebral blood flow, damage of blood-brain barrier (BBB) integrity and increased brain mass. MMI also increased neuronal degeneration in the hippocampus. Notably, levels of glial fibrillary acidic protein (GFAP) and complement component 3 significantly increased, but those of Connexin43 (CX43) and platelet derived growth factor receptor β (PDGFRβ) significantly decreased in the hippocampus of the rats receiving MMI. Moxibustion, as well as oxiracetam (ORC) treatment improved memory function and neuronal degeneration, ameliorated BBB integrity, increased cerebral blood flow and decreased brain mass. In addition, moxibustion as well as oxiracetam (ORC) treatment reduced the decrease of CX43 protein and increased PDGFRβ protein level in the hippocampus of MMI rats. Moreover, moxibustion treatment reversed MMI-induced increase of the GFAP/CX43 ratio in vascular structural units. Importantly, after PDGFRβ inhibition, VD rats treated with moxibustion had impaired learning and memory, decreased cerebral blood flow, and BBB disruption.

Conclusion

Moxibustion treatment at various GV acupoints improved cerebral blood flow and repaired BBB function in rats with MMI, likely through protecting GVU.

Glymphatic influx and clearance are perturbed in Huntington's disease

The accumulation of mutant huntingtin protein aggregates in neurons is a pathological hallmark of Huntington's disease (HD). The glymphatic system, a brain-wide perivascular network, facilitates the exchange of interstitial fluid and cerebrospinal fluid (CSF), supporting interstitial solute clearance of brain wastes. In this study, we employed dynamic glucose-enhanced (DGE) MRI to measure d-glucose clearance from CSF as a tool to predict glymphatic function in a mouse model of HD. We found significantly diminished CSF clearance efficiency in HD mice before phenotypic onset. The impairment of CSF clearance efficiency worsened with disease progression. These DGE MRI findings in compromised glymphatic function were further verified with fluorescence-based imaging of CSF tracer influx, suggesting an impaired glymphatic function in premanifest HD. Moreover, expression of the astroglial water channel aquaporin-4 in the perivascular compartment, a key mediator of glymphatic function, was significantly diminished in both HD mouse brain and human HD brain. Our data, acquired using a clinically translatable MRI, indicate a perturbed glymphatic network in the HD brain. Further validation of these findings in clinical studies will provide insights into the potential of glymphatic clearance as a therapeutic target as well as an early biomarker in HD.

Unstable Plaque is a Treatable Cause of Cognitive Decline

While many risk factors are modifiable, there remains a compelling need for novel approaches to prevent cognitive impairment. We propose that unstable carotid plaque causes microemboli that, in turn, cause microinfarcts and other adverse pathophysiological cerebral processes, which individually do not manifest clinically but cumulatively manifest as cognitive decline and ultimately cognitive impairment. Animal models support multiple cerebral microemboli having adverse effects on cognition. By addressing the source for microembolization by endarterectomy or stenting, patients with high-grade atherosclerotic stenosis may have better cognitive outcomes. If our hypothesis is verified, then treatment of carotid plaque at elevated risk of generating cerebral microemboli would be effective in preserving cognition, regardless of whether the stenosis is high-grade or causing cerebral hemispheric hypoperfusion.

Pathogenesis of Cerebral Small Vessel Disease: Role of the Glymphatic System Dysfunction

Cerebral small vessel disease (CSVD) is a group of pathologies that affect the cerebral blood vessels. CSVD accounts for 25% of strokes and contributes to 45% of dementia. However, the pathogenesis of CSVD remains unclear, involving a variety of complex mechanisms. CSVD may result from dysfunction in the glymphatic system (GS). The GS contains aquaporin-4 (AQP-4), which is in the perivascular space, at the endfeet of the astrocyte. The GS contributes to the removal of waste products from the central nervous system, occupying perivascular spaces and regulating the exchange and movement of cerebrospinal fluid and interstitial fluid. The GS involves astrocytes and aquaporin channels, which are components of the blood-brain barrier, and problems with them may constitute the pathogenesis of CSVD. Vascular risk factors, including diabetes, dilate the perivascular space, disrupting the glymphatic system and the active regulation of AQP-4. CSVD exacerbation due to disorders of the GS is associated with multiple vasculopathies. Dysfunction of the glymphatic system and AQP-4 interferes with the functioning of the blood-brain barrier, which exacerbates CSVD. In a long-term follow-up of CSVD patients with microbleeds, lacunar infarcts, and white matter hyperintensity, several vascular risk factors, including hypertension, increased the risk of ischemic stroke. Dysfunction of the GS may be the cause of CSVD; however, the underlying treatment needs to be studied further.

Treatment of vascular dementia in female rats with AV-001, an Angiopoietin-1 mimetic peptide, improves cognitive function

Background

Vascular dementia (VaD) is a complex neurodegenerative disorder. We previously found that treatment of VaD in middle-aged male rats subjected to multiple microinfarction (MMI) with AV-001, a Tie2 receptor agonist, significantly improves cognitive function. Age and sex affect the development and response of VaD to therapeutic intervention. Thus, the present study investigated the therapeutic effect of AV-001 on VaD in aged female rats subjected to MMI.

Methods

Female 18-month-old Wistar rats were subjected to MMI by injecting either 1,000 (low dose, LD-MMI) or 6,000 (high dose, HD-MMI) cholesterol crystals of size 70-100 μm into the right internal carotid artery. AV-001 (1 μg/Kg, i.p.) was administered once daily after MMI for 1 month, with treatment initiated 1 day after MMI. A battery of behavioral tests to examine sensorimotor and cognitive functions was performed at 21-28 days after MMI. All rats were sacrificed at 1 month after MMI.

Results

Aged female rats subjected to LD-MMI exhibit severe neurological deficits, memory impairment, and significant white matter (WM) and oligodendrogenesis injury in the corpus callosum compared with control rats. HD-MMI in aged female rats induces significant anxiety- and depression-like behaviors, which were not detected in LD-MMI aged female rats. Also, HD-MMI induces significantly increased WM injury compared to LD-MMI. AV-001 treatment of LD-MMI and HD-MMI increases oligodendrogenesis, myelin and axon density in the corpus callosum and striatal WM bundles, promotes WM integrity and attenuates neurological and cognitive deficits. Additionally, both LD-MMI and HD-MMI rats exhibit a significant increase, while AV-001 significantly decreases the levels of inflammatory factors in the cerebrospinal fluid (CSF).

Conclusion

MMI reduces oligodendrogenesis, and induces demyelination, axonal injury and WM injury, and causes memory impairment, while HD-MMI induces increased WM injury and further depression-like behaviors compared to LD-MMI rats. AV-001 has a therapeutic effect on aged female rats with MMI by reducing WM damage and improving neuro-cognitive outcomes.

Imaging Interstitial Fluid With MRI: A Narrative Review on the Associations of Altered Interstitial Fluid With Vascular and Neurodegenerative Abnormalities

Interstitial fluid (ISF) refers to the fluid between the parenchymal cells and along the perivascular spaces (PVS). ISF plays a crucial role in delivering nutrients and clearing waste products from the brain. This narrative review focuses on the use of MRI techniques to measure various ISF characteristics in humans. The complementary value of contrast-enhanced and noncontrast-enhanced techniques is highlighted. While contrast-enhanced MRI methods allow measurement of ISF transport and flow, they lack quantitative assessment of ISF properties. Noninvasive MRI techniques, including multi-b-value diffusion imaging, free-water-imaging, T2-decay imaging, and DTI along the PVS, offer promising alternatives to derive ISF measures, such as ISF volume and diffusivity. The emerging role of these MRI techniques in investigating ISF alterations in neurodegenerative diseases (eg, Alzheimer's disease and Parkinson's disease) and cerebrovascular diseases (eg, cerebral small vessel disease and stroke) is discussed. This review also emphasizes current challenges of ISF imaging, such as the microscopic scale at which ISF has to be measured, and discusses potential focus points for future research to overcome these challenges, for example, the use of high-resolution imaging techniques. Noninvasive MRI methods for measuring ISF characteristics hold significant potential and may have a high clinical impact in understanding the pathophysiology of neurodegenerative and cerebrovascular disorders, as well as in evaluating the efficacy of ISF-targeted therapies in clinical trials. LEVEL OF EVIDENCE: 3 TECHNICAL EFFICACY: Stage 2.

The Association between Glymphatic System and Perivascular Macrophages in Brain Waste Clearance

The glymphatic system suggests the convective bulk flow of cerebrospinal fluid (CSF) through perivascular spaces and the interstitial spaces of the brain parenchyma for the rapid removal of toxic waste solutes from the brain. However, the presence of convective bulk flow within the brain interstitial spaces is still under debate. We first addressed this argument to determine the involvement of the glymphatic system in brain waste clearance utilizing contrast-enhanced 3D T1-weighted imaging (T1WI), diffusion tensor imaging (DTI), and confocal microscopy imaging. Furthermore, perivascular macrophages (PVMs), which are immune cells located within perivascular spaces, have not been thoroughly explored for their association with the glymphatic system. Therefore, we investigated tracer uptake by PVMs in the perivascular spaces of both the arteries/arterioles and veins/venules and the potential association of PVMs in assisting the glymphatic system for interstitial waste clearance. Our findings demonstrated that both convective bulk flow and diffusion are responsible for the clearance of interstitial waste solutes from the brain parenchyma. Furthermore, our results suggested that PVMs may play an important function in glymphatic system-mediated interstitial waste clearance. The glymphatic system and PVMs could be targeted to enhance interstitial waste clearance in patients with waste-associated neurological conditions and aging.

Glymphatic and lymphatic communication with systemic responses during physiological and pathological conditions in the central nervous system

Crosstalk between central nervous system (CNS) and systemic responses is important in many pathological conditions, including stroke, neurodegeneration, schizophrenia, epilepsy, etc. Accumulating evidence suggest that signals for central-systemic crosstalk may utilize glymphatic and lymphatic pathways. The glymphatic system is functionally connected to the meningeal lymphatic system, and together these pathways may be involved in the distribution of soluble proteins and clearance of metabolites and waste products from the CNS. Lymphatic vessels in the dura and meninges transport cerebrospinal fluid, in part collected from the glymphatic system, to the cervical lymph nodes, where solutes coming from the brain (i.e., VEGFC, oligomeric α-syn, β-amyloid) might activate a systemic inflammatory response. There is also an element of time since the immune system is strongly regulated by circadian rhythms, and both glymphatic and lymphatic dynamics have been shown to change during the day and night. Understanding the mechanisms regulating the brain-cervical lymph node (CLN) signaling and how it might be affected by diurnal or circadian rhythms is fundamental to find specific targets and timing for therapeutic interventions.

The relationship between amyloid pathology, cerebral small vessel disease, glymphatic dysfunction, and cognition: a study based on Alzheimer's disease continuum participants

BACKGROUND

Glymphatic dysfunction is a crucial pathway for dementia. Alzheimer's disease (AD) pathologies co-existing with cerebral small vessel disease (CSVD) is the most common pathogenesis for dementia. We hypothesize that AD pathologies and CSVD could be associated with glymphatic dysfunction, contributing to cognitive impairment.

METHOD

Participants completed with amyloid PET, diffusion tensor imaging (DTI), and T2 fluid-attenuated inversion-recovery (FLAIR) sequences were included from the Alzheimer's Disease Neuroimaging Initiative (ADNI). White matter hyperintensities (WMH), the most common CSVD marker, was evaluated from T2FLAIR images and represented the burden of CSVD. Amyloid PET was used to assess Aβ aggregation in the brain. We used diffusion tensor image analysis along the perivascular space (DTI-ALPS) index, the burden of enlarged perivascular spaces (PVS), and choroid plexus volume to reflect glymphatic function. The relationships between WMH burden/Aβ aggregation and these glymphatic markers as well as the correlations between glymphatic markers and cognitive function were investigated. Furthermore, we conducted mediation analyses to explore the potential mediating effects of glymphatic markers in the relationship between WMH burden/Aβ aggregation and cognition.

RESULTS

One hundred and thirty-three participants along the AD continuum were included, consisting of 40 CN - , 48 CN + , 26 MCI + , and 19 AD + participants. Our findings revealed that there were negative associations between whole-brain Aβ aggregation (r =  - 0.249, p = 0.022) and WMH burden (r =  - 0.458, p < 0.001) with DTI-ALPS. Additionally, Aβ aggregation (r = 0.223, p = 0.041) and WMH burden (r = 0.294, p = 0.006) were both positively associated with choroid plexus volume. However, we did not observe significant correlations with PVS enlargement severity. DTI-ALPS was positively associated with memory (r = 0.470, FDR-p < 0.001), executive function (r = 0.358, FDR-p = 0.001), visual-spatial (r = 0.223, FDR-p < 0.040), and language (r = 0.419, FDR-p < 0.001). Conversely, choroid plexus volume showed negative correlations with memory (r =  - 0.315, FDR-p = 0.007), executive function (r =  - 0.321, FDR-p = 0.007), visual-spatial (r =  - 0.233, FDR-p = 0.031), and language (r =  - 0.261, FDR-p = 0.021). There were no significant correlations between PVS enlargement severity and cognitive performance. In the mediation analysis, we found that DTI-ALPS acted as a mediator in the relationship between WMH burden/Aβ accumulation and memory and language performances.

CONCLUSION

Our study provided evidence that both AD pathology (Aβ) and CSVD were associated with glymphatic dysfunction, which is further related to cognitive impairment. These results may provide a theoretical basis for new targets for treating AD.

Role of the glymphatic system and perivascular spaces as a potential biomarker for post-stroke epilepsy

Stroke is one of the most common causes of acquired epilepsy, which can also result in disability and increased mortality rates particularly in elderly patients. No preventive treatment for post-stroke epilepsy is currently available. Development of such treatments has been greatly limited by the lack of biomarkers to reliably identify high-risk patients. The glymphatic system, including perivascular spaces (PVS), is the brain's waste clearance system, and enlargement or asymmetry of PVS (ePVS) is hypothesized to play a significant role in the pathogenesis of several neurological conditions. In this article, we discuss potential mechanisms for the role of perivascular spaces in the development of post-stroke epilepsy. Using advanced MR-imaging techniques, it has been shown that there is asymmetry and impairment of glymphatic function in the setting of ischemic stroke. Furthermore, studies have described a dysfunction of PVS in patients with different focal and generalized epilepsy syndromes. It is thought that inflammatory processes involving PVS and the blood-brain barrier, impairment of waste clearance, and sustained hypertension affecting the glymphatic system during a seizure may play a crucial role in epileptogenesis post-stroke. We hypothesize that impairment of the glymphatic system and asymmetry and dynamics of ePVS in the course of a stroke contribute to the development of PSE. Automated ePVS detection in stroke patients might thus assist in the identification of high-risk patients for post-stroke epilepsy trials. PLAIN LANGUAGE SUMMARY: Stroke often leads to epilepsy and is one of the main causes of epilepsy in elderly patients, with no preventative treatment available. The brain's waste removal system, called the glymphatic system which consists of perivascular spaces, may be involved. Enlargement or asymmetry of perivascular spaces could play a role in this and can be visualised with advanced brain imaging after a stroke. Detecting enlarged perivascular spaces in stroke patients could help identify those at risk for post-stroke epilepsy.

Deregulation of the Glymphatic System in Alzheimer's Disease: Genetic and Non-Genetic Factors

Alzheimer's disease (AD) is the most prevalent form of dementia and is characterized by progressive degeneration of brain function. AD gradually affects the parts of the brain that control thoughts, language, behavior and mental function, severely impacting a person's ability to carry out daily activities and ultimately leading to death. The accumulation of extracellular amyloid-β peptide (Aβ) and the aggregation of intracellular hyperphosphorylated tau are the two key pathological hallmarks of AD. AD is a complex condition that involves both non-genetic risk factors (35%) and genetic risk factors (58-79%). The glymphatic system plays an essential role in clearing metabolic waste, transporting tissue fluid, and participating in the immune response. Both non-genetic and genetic risk factors affect the glymphatic system to varying degrees. The main purpose of this review is to summarize the underlying mechanisms involved in the deregulation of the glymphatic system during the progression of AD, especially concerning the diverse contributions of non-genetic and genetic risk factors. In the future, new targets and interventions that modulate these interrelated mechanisms will be beneficial for the prevention and treatment of AD.

Clearance dysfunction of trans-barrier transport and lymphatic drainage in cerebral small vessel disease: Review and prospect

Cerebral small vessel disease (CSVD) causes 20%-25% of stroke and contributes to 45% of dementia cases worldwide. However, since its early symptoms are inconclusive in addition to the complexity of the pathological basis, there is a rather limited effective therapies and interventions. Recently, accumulating evidence suggested that various brain-waste-clearance dysfunctions are closely related to the pathogenesis and prognosis of CSVD, and after a comprehensive and systematic review we classified them into two broad categories: trans-barrier transport and lymphatic drainage. The former includes blood brain barrier and blood-cerebrospinal fluid barrier, and the latter, glymphatic-meningeal lymphatic system and intramural periarterial drainage pathway. We summarized the concepts and potential mechanisms of these clearance systems, proposing a relatively complete framework for elucidating their interactions with CSVD. In addition, we also discussed recent advances in therapeutic strategies targeting clearance dysfunction, which may be an important area for future CSVD research.

Imaging glymphatic response to glioblastoma

BACKGROUND

The glymphatic system actively exchanges cerebrospinal fluid (CSF) and interstitial fluid (ISF) to eliminate toxic interstitial waste solutes from the brain parenchyma. Impairment of the glymphatic system has been linked to several neurological conditions. Glioblastoma, also known as Glioblastoma multiforme (GBM) is a highly aggressive form of malignant brain cancer within the glioma category. However, the impact of GBM on the functioning of the glymphatic system has not been investigated. Using dynamic contrast-enhanced magnetic resonance imaging (CE-MRI) and advanced kinetic modeling, we examined the changes in the glymphatic system in rats with GBM.

METHODS

Dynamic 3D contrast-enhanced T1-weighted imaging (T1WI) with intra-cisterna magna (ICM) infusion of paramagnetic Gd-DTPA contrast agent was used for MRI glymphatic measurements in both GBM-induced and control rats. Glymphatic flow in the whole brain and the olfactory bulb was analyzed using model-derived parameters of arrival time, infusion rate, clearance rate, and residual that describe the dynamics of CSF tracer over time.

RESULTS

3D dynamic T1WI data identified reduced glymphatic influx and clearance, indicating an impaired glymphatic system due to GBM. Kinetic modeling and quantitative analyses consistently indicated significantly reduced infusion rate, clearance rate, and increased residual of CSF tracer in GBM rats compared to control rats, suggesting restricted glymphatic flow in the brain with GBM. In addition, our results identified compromised perineural pathway along the optic nerves in GBM rats.

CONCLUSIONS

Our study demonstrates the presence of GBM-impaired glymphatic response in the rat brain and impaired perineural pathway along the optic nerves. Reduced glymphatic waste clearance may lead to the accumulation of toxic waste solutes and pro-inflammatory signaling molecules which may affect the progression of the GBM.

The effect of AQP4 on tau protein aggregation in neurodegeneration and persistent neuroinflammation after cerebral microinfarcts

This study aimed to investigate the effect of aquaporin-4 (AQP4) on tau protein aggregation in neurodegeneration and persistent neuroinflammation after cerebral microinfarcts. A model of diffuse ischemic brain injury was established, and adenovirus was injected stereotactically through the lateral ventricle of mice. The water content of the brain tissue was measured. The co-expression of glial fibrillary acidic protein (GFAP) and AQP4 and the aggregation of p-tau and neuronal marker were detected through immunofluorescence double staining. The expression of phosphorylated microtubule-associated protein tau (p-tau, Ser202/Thr205, Thr205, Ser396, Ser404), interleukin(IL)-6, IL-1β, tumor necrosis factor (TNF)-a, growth associated protein43 (GAP43), GFAP, and ionized calcium-binding adapter molecule 1 (Iba1) was detected through Western blot. It was found that the brain water content in the model group was increased and decreased after the AQP4 interference. Compared with the sham group, the expression of GFAP, p-tau, IL-1β, TNF-a, Iba1, and p-tau was increased in the model group (p < 0.05). Compared with the model group, the expression of p-tau, IL-6, IL-1β, TNF-a, GFAP, and Iba1 was decreased after AQP4 interference (p < 0.05). It is indicated that AQP4 positively regulates neurodegeneration and persistent neuroinflammation caused by tau protein aggregation after cerebral microinfarcts.

The Association between Glymphatic System and Perivascular Macrophages in Brain Waste Clearance

The glymphatic system suggests the convective bulk flow of cerebrospinal fluid (CSF) through perivascular spaces and the interstitial spaces of the brain parenchyma for the rapid removal of toxic waste solutes from the brain. However, the presence of convective bulk flow within the brain interstitial spaces is still under debate. We first addressed this argument to determine the involvement of the glymphatic system in brain waste clearance utilizing contrast-enhanced 3D T1-weighted imaging (T1WI), diffusion tensor imaging (DTI), and confocal microscopy imaging. Furthermore, perivascular macrophages (PVMs), which are immune cells located within perivascular spaces, have not been thoroughly explored for their association with the glymphatic system. Therefore, we investigated tracer uptake by PVMs in the perivascular spaces of both the arteries/arterioles and veins/venules and the potential association of PVMs in assisting the glymphatic system for interstitial waste clearance. Our findings demonstrated that both convective bulk flow and diffusion are responsible for the clearance of interstitial waste solutes from the brain parenchyma. Furthermore, our results suggested that PVMs play an important function in glymphatic system-mediated interstitial waste clearance. The glymphatic system and PVMs could be targeted to enhance interstitial waste clearance in patients with waste-associated neurological conditions and aging.

Modeling transient ischemic attack via photothrombosis

The health significance of transient ischemic attacks (TIAs) is largely underestimated. Often, TIAs are not given significant importance, and in vain, because TIAs are a predictor of the development of serious cardiovascular diseases and even death. Because of this, and because of the difficulty in diagnosing the disease, TIAs and related microinfarcts are poorly investigated. Photothrombotic models of stroke and TIA allow reproducing the occlusion of small brain vessels, even single ones. When dosing the concentration of photosensitizer, intensity and irradiation time, it is possible to achieve occlusion of well-defined small vessels with high reproducibility, and with the help of modern methods of blood flow assessment it is possible to achieve spontaneous restoration of blood flow without vessel rupture. In this review, we discuss the features of microinfarcts and the contemporary experimental approaches used to model TIA and microinfarcts, with an emphasis on models using the principle of photothrombosis of brain vessels. We review modern techniques for in vivo detection of blood flow in small brain vessels, as well as biomarkers of microinfarcts.

Assessment of factors influencing glymphatic activity and implications for clinical medicine

The glymphatic system is a highly specialized fluid transport system in the central nervous system. It enables the exchange of the intercellular fluid of the brain, regulation of the movement of this fluid, clearance of unnecessary metabolic products, and, potentially, brain immunity. In this review, based on the latest scientific reports, we present the mechanism of action and function of the glymphatic system and look at the role of factors influencing its activity. Sleep habits, eating patterns, coexisting stress or hypertension, and physical activity can significantly affect glymphatic activity. Modifying them can help to change lives for the better. In the next section of the review, we discuss the connection between the glymphatic system and neurological disorders. Its association with many disease entities suggests that it plays a major role in the physiology of the whole brain, linking many pathophysiological pathways of individual diseases.

Early therapeutic effects of an Angiopoietin-1 mimetic peptide in middle-aged rats with vascular dementia

Background

Vascular Dementia (VaD) refers to dementia caused by cerebrovascular disease and/or reduced blood flow to the brain and is the second most common form of dementia after Alzheimer's disease. We previously found that in middle-aged rats subjected to a multiple microinfarction (MMI) model of VaD, treatment with AV-001, a Tie2 receptor agonist, significantly improves short-term memory, long-term memory, as well as improves preference for social novelty compared to control MMI rats. In this study, we tested the early therapeutic effects of AV-001 on inflammation and glymphatic function in rats subjected to VaD.

Methods

Male, middle-aged Wistar rats (10-12 m), subjected to MMI, were randomly assigned to MMI and MMI + AV-001 treatment groups. A sham group was included as reference group. MMI was induced by injecting 800 ± 200, 70-100 μm sized, cholesterol crystals into the internal carotid artery. Animals were treated with AV-001 (1 μg/Kg, i.p.) once daily starting at 24 h after MMI. At 14 days after MMI, inflammatory factor expression was evaluated in cerebrospinal fluid (CSF) and brain. Immunostaining was used to evaluate white matter integrity, perivascular space (PVS) and perivascular Aquaporin-4 (AQP4) expression in the brain. An additional set of rats were prepared to test glymphatic function. At 14 days after MMI, 50 μL of 1% Tetramethylrhodamine (3 kD) and FITC conjugated dextran (500 kD) at 1:1 ratio were injected into the CSF. Rats (4-6/group/time point) were sacrificed at 30 min, 3 h, and 6 h from the start of tracer infusion, and brain coronal sections were imaged using a Laser scanning confocal microscope to evaluate tracer intensities in the brain.

Result

Treatment of MMI with AV-001 significantly improves white matter integrity in the corpus callosum at 14 days after MMI. MMI induces significant dilation of the PVS, reduces AQP4 expression and impairs glymphatic function compared to Sham rats. AV-001 treatment significantly reduces PVS, increases perivascular AQP4 expression and improves glymphatic function compared to MMI rats. MMI significantly increases, while AV-001 significantly decreases the expression of inflammatory factors (tumor necrosis factor-α (TNF-α), chemokine ligand 9) and anti-angiogenic factors (endostatin, plasminogen activator inhibitor-1, P-selectin) in CSF. MMI significantly increases, while AV-001 significantly reduces brain tissue expression of endostatin, thrombin, TNF-α, PAI-1, CXCL9, and interleukin-6 (IL-6).

Conclusion

AV-001 treatment of MMI significantly reduces PVS dilation and increases perivascular AQP4 expression which may contribute to improved glymphatic function compared to MMI rats. AV-001 treatment significantly reduces inflammatory factor expression in the CSF and brain which may contribute to AV-001 treatment induced improvement in white matter integrity and cognitive function.

Interrogation of dynamic glucose-enhanced MRI and fluorescence-based imaging reveals a perturbed glymphatic network in Huntington's disease

Huntington's disease (HD) is a neurodegenerative disorder that presents with progressive motor, mental, and cognitive impairment leading to early disability and mortality. The accumulation of mutant huntingtin protein aggregates in neurons is a pathological hallmark of HD. The glymphatic system, a brain-wide perivascular network, facilitates the exchange of interstitial fluid (ISF) and cerebrospinal fluid (CSF), supporting interstitial solute clearance including abnormal proteins from mammalian brains. In this study, we employed dynamic glucose-enhanced (DGE) MRI to measure D-glucose clearance from CSF as a tool to assess CSF clearance capacity to predict glymphatic function in a mouse model of HD. Our results demonstrate significantly diminished CSF clearance efficiency in premanifest zQ175 HD mice. The impairment of CSF clearance of D-glucose, measured by DGE MRI, worsened with disease progression. These DGE MRI findings in compromised glymphatic function in HD mice were further confirmed with fluorescence-based imaging of glymphatic CSF tracer influx, suggesting an impaired glymphatic function in premanifest stage of HD. Moreover, expression of the astroglial water channel aquaporin-4 (AQP4) in the perivascular compartment, a key mediator of glymphatic function, was significantly diminished in both HD mouse brain as well as postmortem human HD brain. Our data, acquired using a clinically translatable MRI approach, indicate a perturbed glymphatic network in the HD brain as early as in the premanifest stage. Further validation of these findings in clinical studies should provide insights into potential of glymphatic clearance as a HD biomarker and for glymphatic functioning as a disease-modifying therapeutic target for HD.

Deep cortical microinfarction induced by femtosecond laser in mice: Long-term secondary pathological changes in corresponding superficial cortex

BACKGROUND AND PURPOSE

Previous studies have explored the clinical consequences of cortical microinfarction, mainly age-related cognitive decline. However, functional impairment of deep cortical microinfarction remains poorly understood. Based on anatomical knowledge and previous research, we infer that damage to the deep cortex may lead to cognitive deficits and communication impairment between the superficial cortex and thalamus. This study aimed to develop a new model of deep cortical microinfarction based on femtosecond laser ablation of a perforating artery.

METHODS

Twenty-eight mice were anesthetized with isoflurane, and a cranial window was thinned using a microdrill. Intensively focused femtosecond laser pulses were used to produce perforating arteriolar occlusions and ischemic brain damage was examined using histological analysis.

RESULTS

Occlusion of different perforating arteries induced different types of cortical microinfarctions. Blocking the perforating artery, which enters the cerebral cortex vertically and has no branches within 300 μm below, can result in deep cortical microinfarction. Moreover, this model showed neuronal loss and microglial activation in the lesions as well as dysplasia of nerve fibers and β-amyloid deposition in the corresponding superficial cortex.

CONCLUSIONS

We present here a new model of deep cortical microinfarction in mice, in which specific perforating arteries are selectively occluded by a femtosecond laser, and we preliminarily observe several long-term effects related to cognition. This animal model is helpful in investigating the pathophysiology of deep cerebral microinfarction. However, further clinical and experimental studies are required to explore deep cortical microinfarctions in greater molecular and physiological detail.

The effect of a novel AQP4 facilitator, TGN-073, on glymphatic transport captured by diffusion MRI and DCE-MRI

The glymphatic system is a low resistance pathway, by which cerebrospinal fluid enters the brain parenchyma along perivascular spaces via AQP4 channels. It is hypothesised that the resulting convective flow of the interstitial fluid provides an efficient mechanism for the removal of waste toxins from the brain. Therefore, enhancing AQP4 function might protect against neurodegenerative diseases such as Alzheimer's disease (AD), in which the accumulation of harmful proteins and solutes is a hallmark feature. Here, we test the effect of a putative AQP4 facilitator, TGN-073, on glymphatic transport in a normal rat brain by employing different MRI techniques. Surgical procedures were undertaken to catheterise the cisterna magna, thereby enabling infusion of the MRI tracer. Followed by the intraperitoneal injection of either TGN-073, or the vehicle. Using a paramagnetic contrast agent (Gd-DTPA) as the MRI tracer, dynamic 3D T1 weighted imaging of the glymphatic system was undertaken over two hours. Further, the apparent diffusion coefficient was measured in different brain regions using diffusion-weighted imaging (DWI). While physiological parameters and arterial blood gas analysis were monitored continuously. We found that rats treated with TGN-073 showed the distribution of Gd-DTPA was more extensive and parenchymal uptake was higher compared with the vehicle group. Water diffusivity was increased in the brain of TGN-073 treated group, which indicates greater water flux. Also, MRI showed the glymphatic transport and distribution in the brain is naturally heterogeneous, which is consistent with previous studies. Our results indicate that compounds such as TGN-073 can improve glymphatic function in the brain. Since glymphatic impairment due to AQP4 dysfunction is potentially associated with several neurological disorders such as AD, dementia and traumatic brain injury, enhancing AQP4 functionality might be a promising therapeutic target.

The effects of white matter hyperintensities on MEG power spectra in population with mild cognitive impairment

Cerebrovascular disease is responsible for up to 20% of cases of dementia worldwide, but also it is a major comorbid contributor to the progression of other neurodegenerative diseases, like Alzheimer's disease. White matter hyperintensities (WMH) are the most prevalent imaging marker in cerebrovascular disease. The presence and progression of WMH in the brain have been associated with general cognitive impairment and the risk to develop all types of dementia. The aim of this piece of work is the assessment of brain functional differences in an MCI population based on the WMH volume. One-hundred and twenty-nine individuals with mild cognitive impairment (MCI) underwent a neuropsychological evaluation, MRI assessment (T1 and Flair), and MEG recordings (5 min of eyes closed resting state). Those participants were further classified into vascular MCI (vMCI; n = 61, mean age 75 ± 4 years, 35 females) or non-vascular MCI (nvMCI; n = 56, mean age 72 ± 5 years, 36 females) according to their WMH total volume, assessed with an automatic detection toolbox, LST (SPM12). We used a completely data-driven approach to evaluate the differences in the power spectra between the groups. Interestingly, three clusters emerged: One cluster with widespread larger theta power and two clusters located in both temporal regions with smaller beta power for vMCI compared to nvMCI. Those power signatures were also associated with cognitive performance and hippocampal volume. Early identification and classification of dementia pathogenesis is a crucially important goal for the search for more effective management approaches. These findings could help to understand and try to palliate the contribution of WMH to particular symptoms in mixed dementia progress.

Diffusion along perivascular spaces as marker for impairment of glymphatic system in Parkinson's disease

The brain glymphatic system is involved in the clearance of misfolding α-synuclein, the impaired glymphatic system may contribute to the progression of Parkinson's disease (PD). We aimed to analyze the diffusion tensor image along the perivascular space (DTI-ALPS) and perivascular space (PVS) burden to reveal the relationship between the glymphatic system and PD. A cross-sectional study using a 7 T MRI of 76 PD patients and 48 controls was performed to evaluate the brain's glymphatic system. The DTI-ALPS and PVS burden in basal ganglia were calculated. Correlation analyses were conducted between DTI-ALPS, PVS burden and clinical features. We detected lower DTI-ALPS in the PD subgroup relative to controls, and the differences were more pronounced in patients with Hoehn & Yahr stage greater than two. The decreased DTI-ALPS was only evident in the left hemisphere in patients in the early stage but involved both hemispheres in more advanced PD patients. Decreased DTI-ALPS were also correlated with longer disease duration, higher Unified Parkinson's Disease Rating Scale motor score (UPDRS III) and UPDRS total scores, as well as higher levodopa equivalent daily dose. Moreover, the decreased DTI-ALPS correlated with increased PVS burden, and both indexes correlated with PD disease severity. This study demonstrated decreased DTI-ALPS in PD, which might initiate from the left hemisphere and progressively involve right hemisphere with the disease progression. Decreased DTI-ALPS index correlated with increased PVS burden, indicating that both metrics could provide supporting evidence of an impaired glymphatic system. MRI evaluation of the PVS burden and diffusion along PVS are potential imaging biomarkers for PD for disease progression.

Associations of MRI-visible perivascular spaces with longitudinal cognitive decline across the Alzheimer's disease spectrum

OBJECTIVE

To investigate the characteristics and associations of MRI-visible perivascular spaces (PVS) with clinical progression and longitudinal cognitive decline across the Alzheimer's disease spectrum.

METHODS

We included 1429 participants (641 [44.86%] female) from the Alzheimer's Disease Neuroimaging Initiative (ADNI) database. PVS number and grade in the centrum semiovale (CSO-PVS), basal ganglia (BG-PVS), and hippocampus (HP-PVS) were compared among the control (CN), mild cognitive impairment (MCI), and Alzheimer's disease (AD) groups. PVS were tested as predictors of diagnostic progression (i.e., CN to MCI/AD or MCI to AD) and longitudinal changes in the 13-item Alzheimer's Disease Assessment Scale-cognitive subscale (ADAS-Cog 13), Mini-Mental State Examination (MMSE), memory (ADNI-MEM), and executive function (ADNI-EF) using multiple linear regression, linear mixed-effects, and Cox proportional hazards modeling.

RESULTS

Compared with CN subjects, MCI and AD subjects had more CSO-PVS, both in number (p < 0.001) and grade (p < 0.001). However, there was no significant difference in BG-PVS and HP-PVS across the AD spectrum (p > 0.05). Individuals with moderate and frequent/severe CSO-PVS had a higher diagnostic conversion risk than individuals with no/mild CSO-PVS (log-rank p < 0.001 for all) in the combined CN and MCI group. Further Cox regression analyses revealed that moderate and frequent/severe CSO-PVS were associated with a higher risk of diagnostic conversion (HR = 2.007, 95% CI = 1.382-2.914, p < 0.001; HR = 2.676, 95% CI = 1.830-3.911, p < 0.001, respectively). A higher CSO-PVS number was associated with baseline cognitive performance and longitudinal cognitive decline in all cognitive tests (p < 0.05 for all).

CONCLUSIONS

CSO-PVS were more common in MCI and AD and were associated with cognitive decline across the AD spectrum.

Wasteosomes (corpora amylacea) as a hallmark of chronic glymphatic insufficiency

In different organs and tissues, the lymphatic system serves as a drainage system for interstitial fluid and is useful for removing substances that would otherwise accumulate in the interstitium. In the brain, which lacks lymphatic circulation, the drainage and cleaning function is performed by the glymphatic system, called so for its dependence on glial cells and its similar function to that of the lymphatic system. In the present article, we define glymphatic insufficiency as the inability of the glymphatic system to properly perform the brain cleaning function. Furthermore, we propose that corpora amylacea or wasteosomes, which are protective structures that act as waste containers and accumulate waste products, are, in fact, a manifestation of chronic glymphatic insufficiency. Assuming this premise, we provide an explanation that coherently links the formation, distribution, structure, and function of these bodies in the human brain. Moreover, we open up new perspectives in the study of the glymphatic system since wasteosomes can provide information about which variables have the greatest impact on the glymphatic system and which diseases occur with chronic glymphatic insufficiency. For example, based on the presence of wasteosomes, it seems that aging, sleep disorders, and cerebrovascular pathologies have the highest impact on the glymphatic system, whereas neurodegenerative diseases have a more limited impact. Furthermore, as glymphatic insufficiency is a risk factor for neurodegenerative diseases, information provided by wasteosomes could help to define the strategies and actions that can prevent glymphatic disruptions, thus limiting the risk of developing neurodegenerative diseases.

Structural network efficiency mediates the association between glymphatic function and cognition in mild VCI: a DTI-ALPS study

Background and objective: Vascular cognitive impairment (VCI) can be caused by multiple types of cerebrovascular pathology and is considered a network disconnection disorder. The heterogeneity hinders research progress in VCI. Glymphatic failure has been considered as a key common pathway to dementia recently. The emergence of a new method, Diffusion Tensor Image Analysis Along the Perivascular Space (DTI-ALPS), makes it possible to investigate the changes of the glymphatic function in humans non-invasively. We aimed to investigate alterations of glymphatic function in VCI and its potential impact on network connectivity. Methods: We recruited 79 patients with mild VCI, including 40 with cerebral small vessel disease cognitive impairment (SVCI) and 39 with post-stroke cognitive impairment (PSCI); and, 77 normal cognitive (NC) subjects were recruited. All subjects received neuropsychological assessments and multimodal magnetic resonance imaging scans. ALPS-index was calculated and structural networks were constructed by deterministic tractography, and then, the topological metrics of these structural connectivity were evaluated. Results: The ALPS-index of VCI patients was significantly lower than that of NC subjects (P < 0.001). Multiple linear regression analysis showed that ALPS-index affects cognitive function independently (β = 0.411, P < 0.001). The results of correlation analysis showed that the ALPS-index was correlated with overall vascular risk factor burden (r = -0.263, P = 0.001) and multiple cerebrovascular pathologies (P < 0.05). In addition, global efficiency (Eg) of network was correlated with ALPS-index in both SVCI (r = 0.348, P = 0.028) and PSCI (r = 0.732, P < 0.001) patients. Finally, the results of mediation analysis showed that Eg partially mediated in the impact of glymphatic dysfunction on cognitive impairment (indirect effect = 7.46, 95% CI 4.08-11.48). Conclusion: In both major subtypes of VCI, the ALPS-index was decreased, indicating impaired glymphatic function in VCI. Glymphatic dysfunction may affect cognitive function in VCI by disrupting network connectivity, and, may be a potential common pathological mechanism of VCI. ALPS-index is expected to become an emerging imaging marker for VCI.

Magnetic resonance imaging reveals microemboli-mediated pathological changes in brain microstructure in diabetic rats: relevance to vascular cognitive impairment/dementia

Diabetes doubles the risk of vascular cognitive impairment, but the underlying reasons remain unclear. In the present study, we determined the temporal and spatial changes in the brain structure after microemboli (ME) injection using diffusion MRI (dMRI). Control and diabetic rats received cholesterol crystal ME (40-70 µm) injections. Cognitive tests were followed up to 16 weeks, while dMRI scans were performed at baseline and 12 weeks post-ME. The novel object recognition test had a lower d2 recognition index along with a decrease in spontaneous alternations in the Y maze test in diabetic rats with ME. dMRI showed that ME injection caused infarction in two diabetic animals (n=5) but none in controls (n=6). In diabetes, radial diffusivity (DR) was increased while fractional anisotropy (FA) was decreased in the cortex, indicating loss of tissue integrity and edema. In the dorsal hippocampus, mean diffusivity (MD), axial diffusivity (DA), and DR were significantly increased, indicating loss of axons and myelin damage. Histological analyses confirmed more tissue damage and microglial activation in diabetic rats with ME. These results suggest that ME injury and associated cerebrovascular dysfunction are greater in diabetes, which may cause cognitive deficits. Strategies to improve vascular function can be a preventive and therapeutic approach for vascular cognitive impairment.

Dilated perivascular spaces can present incidental CSF-isointense foci within the ventral forebrain of dogs and cats in transverse MR images

Objective

Virchow-Robin-Spaces (VRS) are cerebrospinal fluid (CSF)-containing perivascular spaces encompassing brain vessels while coursing through the parenchyma. VRS can enlarge and become visible in magnetic resonance imaging (MRI). While dilatated VRS are mostly incidental findings, they were associated with degenerative brain disease in humans. This study aimed to evaluate their occurrence and MRI morphology within the ventral forebrain of structurally normal canine and feline brains and physiological cerebrospinal fluid analysis.

Sample

Retro- and prospective, observational study reviewing medical records of client-owned dogs and cats which underwent MRI brain scans for unrelated reasons between 2011 and 2021. We comprised studies with various magnetic field strengths (1 Tesla/3 Tesla). Out of 2500 brain scans, three hundred thirty-five patients (293 dogs, 42 cats) presented with absent intracranial pathology and physiological CSF analysis and were included.

Procedure

The ventral forebrain of the included animals was assessed for bi- or unilateral CSF-isointense foci in the transverse plane. Statistical correlations were evaluated between dilated VRS presence, field strength, age, gender, weight, and cranium conformation. Additionally, a post-mortem histopathologic analysis of one dog and one cat showing dilated VRS on MRI was performed to confirm perforating arteries in the gray matter of the ventral forebrain.

Results

57% of patients presented dilated VRS (N = 191: 170 dogs, 21 cats). 43% did not display dilated VRS (control group; N = 144: 123 dogs, 21 cats). A significant relation between increased magnetic field strength and detection of dilated VRS was observed in dogs; there was a 2.4 increase (p = 0.0001) in detection using 3 Tesla vs. 1 Tesla. There was a 2.4-fold increase in dilated VRS occurrence in male dogs compared to female dogs. Detection also increased with the rise of body weight. We detected no statistically significant difference between dilated VRS and the control group in age, species or cranium conformation.

Conclusion and Clinical Relevance

Dilated VRS can be seen within the ventral forebrain at the level of the rostral commissure on transverse MR images as symmetrical or unilateral, dot-like, CSF-isointense areas. Understanding their signal intensity features and localization prevents misinterpretation and helps differentiate them from various pathological conditions.

Liver transplantation in rare late-onset ornithine transcarbamylase deficiency with central nervous system injury: A case report and review of the literature

BACKGROUND

Ornithine transcarbamylase deficiency (OTCD) is a genetic metabolic disease. Its clinical manifestations are mainly central nervous system dysfunction caused by high blood ammonia. Late-onset OTCD combined with central nervous system injury has a poor therapeutic response, which is one of the main factors affecting the prognosis and quality of life of patients. liver transplantation (LT) has gradually become a radical treatment for OTCD, which has achieved good results. However, there is no consensus on the timing of LT and problems of nervous system damage and repair.

METHODS

We report the development of late-onset OTCD with central nervous system injury in an 11-year-old child who received liver transplantation at our transplant center. His first symptoms were nonprojectile vomiting, followed by irritability and disturbance of consciousness, after which the disease progressed rapidly and finally resulted in a coma. After liver transplantation, the child's consciousness returned to normal, muscle strength of the limbs gradually recovered from grade 0 to grade 4, and muscle tone gradually recovered from grade 4 to grade 1, suggesting that the motor nerves had gradually recovered. However, the child is currently mentally retarded, and the language center has not yet fully recovered.At the same time, we made a literature review of OTCD.

CONCLUSION

For OTCD patients with central nervous system injury, liver transplantation can fundamentally solve the problem of ammonia metabolism in the liver and avoids further damage to the central nervous system caused by hyperammonemia. At the same time, children's nervous systems are in the developmental stage when neuroplasticity is greatest. If liver transplantation is performed as soon as possible, nerve repair is still possible.

Enlarged perivascular spaces and white matter hyperintensities in patients with frontotemporal lobar degeneration syndromes

Objective

The aim of this study was to investigate the distribution characteristics of enlarged perivascular spaces (EPVS) and white matter hyperintensities (WMH) and their associations with disease severity across the frontotemporal lobar degeneration (FTLD) syndromes spectrum.

Methods

This study included 73 controls, 39 progressive supranuclear palsy Richardson’s syndrome (PSP-RS), 31 corticobasal syndrome (CBS), 47 behavioral variant frontotemporal dementia (bvFTD), 36 non-fluent variant primary progressive aphasia (nfvPPA), and 50 semantic variant primary progressive aphasia (svPPA). All subjects had brain magnetic resonance imaging (MRI) and neuropsychological tests, including progressive supranuclear palsy rating scale (PSPRS) and FTLD modified clinical dementia rating sum of boxes (FTLD-CDR). EPVS number and grade were rated on MRI in the centrum semiovale (CSO-EPVS), basal ganglia (BG-EPVS), and brain stem (BS-EPVS). Periventricular (PWMH) and deep (DWMH) were also graded on MRI. The distribution characteristics of EPVS and WMH were compared between control and disease groups. Multivariable linear regression analysis was performed to evaluate the association of EPVS and WMH with disease severity.

Results

Compared with control subjects, PSP-RS and CBS had more BS-EPVS; CBS, bvFTD, and nfvPPA had less CSO-EPVS; all disease groups except CBS had higher PWMH (p < 0.05). BS-EPVS was associated with PSPRS in PSP-RS (β = 2.395, 95% CI 0.888–3.901) and CBS (β = 3.115, 95% CI 1.584–4.647). PWMH was associated with FTLD-CDR in bvFTD (β = 1.823, 95% CI 0.752–2.895), nfvPPA (β = 0.971, 95% CI 0.030–1.912), and svPPA (OR: 1.330, 95% CI 0.457–2.204).

Conclusion

BS-EPVS could be a promising indicator of disease severity in PSP-RS and CBS, while PWMH could reflect the severity of bvFTD, nfvPPA, and svPPA.

MRI-Visible Perivascular Spaces Associated With Cognitive Impairment in Military Veterans With Traumatic Brain Injury Mediated by CSF P-Tau

Objective

To investigate the association of MRI-visible perivascular spaces (PVS) with cognitive impairment in military veterans with traumatic brain injury (TBI), and whether cerebrospinal fluid (CSF) p-tau and Aβ mediate this effect.

Materials and Methods

We included 55 Vietnam War veterans with a history of TBI and 52 non-TBI Vietnam War veterans from the Department of Defense Alzheimer's Disease Neuroimaging Initiative (ADNI) database. All the subjects had brain MRI, CSF p-tau, Aβ, and neuropsychological examinations. MRI-visible PVS number and grade were rated on MRI in the centrum semiovale (CSO-PVS) and basal ganglia (BG-PVS). Multiple linear regression was performed to assess the association between MRI-visible PVS and cognitive impairment and the interaction effect of TBI. Additionally, mediation effect of CSF biomarkers on the relationship between MRI-visible PVS and cognitive impairment was explored in TBI group.

Results

Compared with military control, TBI group had higher CSO-PVS number (p = 0.001), CSF p-tau (p = 0.022) and poorer performance in verbal memory (p = 0.022). High CSO-PVS number was associated with poor verbal memory in TBI group (β = -0.039, 95% CI -0.062, -0.016), but not in military control group (β = 0.019, 95% CI -0.004, 0.043) (p-interaction = 0.003). Further mediation analysis revealed that CSF p-tau had a significant indirect effect (β = -0.009, 95% CI: -0.022 -0.001, p = 0.001) and mediated 18.75% effect for the relationship between CSO-PVS and verbal memory in TBI group.

Conclusion

MRI-visible CSO-PVS was more common in Vietnam War veterans with a history of TBI and was associated with poor verbal memory, mediated partially by CSF p-tau.

The Attenuating Effect of Beta-Carotene on Streptozotocin Induced Diabetic Vascular Dementia Symptoms in Rats

This study investigated the ameliorative effects of beta-carotene (BC) on diabetes-associated vascular dementia and its action against biomolecule oxidation. The diabetic vascular dementia (VaD) was induced by administration of nicotinamide (NA; 50 mg/kg; i.p.) and streptozotocin (STZ; 50 mg/kg; i.p.). The test compound, BC (50 and 100 mg/kg; p.o.), and the reference compound, donepezil (DP) (1 mg/kg; p.o.), were administered for 15 consecutive days. Changes in learning and memory were assessed by escape latency time (ELT) and times spent in target quadrant (TSTQ) in the Morris water maze (MWM) test. The changes in neurotransmitter, i.e., acetylcholinesterase (AChE) and oxidative stress markers, i.e., thiobarbituric acid reactive substance (TBARS) and reduced glutathione (GSH), were estimated in hippocampal tissue of the rat brain. The administration of STZ caused significant deterioration of cognitive function (decreased ELT and raised the TSTQ) as compared to the normal group. Treatment with BC and DP diminished the increased AChE activity, TBARS level and decreased GSH level caused by STZ. Thus, BC ameliorates the diabetic vascular complications in VaD due to its potential anticholinergic, antioxidative and free radical scavenging actions.

Dynamic infrared imaging of cerebrospinal fluid tracer influx into the brain

Significance: The glymphatic system has been described recently as a series of perivascular channels that facilitate fluid exchange and solute clearance in the brain. Glymphatic dysfunction has been implicated in numerous pathological conditions, including Alzheimer's disease, traumatic brain injury, and stroke. Existing methods for assessing glymphatic function have been challenging: dynamic methods, such as two-photon microscopy and contrast-enhanced magnetic resonance imaging require expensive instrumentation and specific technical skills; slice-based fluorescent imaging is more readily implemented but lacks temporal resolution. Aim: To develop a straightforward and adaptable dynamic imaging approach for assessing glymphatic function in vivo in mice. Approach: Using a widely available small animal infrared (IR) imaging system (LICOR Pearl), visualization of IR cerebrospinal fluid tracer distribution over the cortical surface enables time-resolved measurement of the dynamics of glymphatic exchange. Using co-injection of IR and conventional fixable fluorescent tracers, dynamic imaging can be paired with whole-slice fluorescence imaging, permitting the quantification of glymphatic function throughout the brain as well as subsequent histological assessment. Results: These techniques were validated against one another, comparing differences between animals anesthetized with ketamine/xylazine and isoflurane. Conclusions: This technique permits sensitive dynamic imaging of glymphatic function, with the concurrent visualization of resolution of deeper structures.

Understanding brain function in vascular cognitive impairment and dementia with EEG and MEG: A systematic review

Vascular Cognitive Impairment (VCI) is the second most prevalent dementia after Alzheimer's Disease (AD), and cerebrovascular disease (CBVD) is a major comorbid contributor to the progression of most neurodegenerative diseases. Early differentiation of cognitive impairment is critical given both the high prevalence of CBVD, and that its risk factors are modifiable. The ability for electroencephalogram (EEG) and magnetoencephalogram (MEG) to detect changes in brain functioning for other dementias suggests that they may also be promising biomarkers for early VCI. The present systematic review aims to summarize the literature regarding electrophysiological patterns of mild and major VCI. Despite considerable heterogeneity in clinical definition and electrophysiological methodology, common patterns exist when comparing patients with VCI to healthy controls (HC) and patients with AD, though there is a low specificity when comparing between VCI subgroups. Similar to other dementias, slowed frequency patterns and disrupted inter- and intra-hemispheric connectivity are repeatedly reported for VCI patients, as well as longer latencies and smaller amplitudes in evoked responses. Further study is needed to fully establish MEG and EEG as clinically useful biomarkers, including a clear definition of VCI and standardized methodology, allowing for comparison across groups and consolidation of multicenter efforts.

Treatment With an Angiopoietin-1 Mimetic Peptide Improves Cognitive Outcome in Rats With Vascular Dementia

Background and Purpose

Vascular dementia (VaD) is a complex neurodegenerative disease affecting cognition and memory. There is a lack of approved pharmacological treatments specifically for VaD. In this study, we investigate the therapeutic effects of AV-001, a Tie2 receptor agonist, in middle-aged rats subjected to a multiple microinfarct (MMI) model of VaD.

Methods

Male, 10-12 month-old, Wistar rats were employed. The following experimental groups were used: Sham, MMI, MMI+1 μg/Kg AV-001, MMI+3 μg/Kg AV-001, MMI+6 μg/Kg AV-001. AV-001 treatment was initiated at 1 day after MMI and administered once daily via intraperitoneal injection. An investigator blinded to the experimental groups conducted a battery of neuro-cognitive tests including modified neurological severity score (mNSS) test, novel object recognition test, novel odor recognition test, three chamber social interaction test, and Morris water maze test. Rats were sacrificed at 6 weeks after MMI.

Results

There was no mortality observed after 1, 3, or 6 μg/Kg AV-001 treatment in middle-aged rats subjected to MMI. AV-001 treatment (1, 3, or 6 μg/Kg) does not significantly alter blood pressure or heart rate at 6 weeks after MMI compared to baseline values or the MMI control group. Treatment of MMI with 1 or 3 μg/Kg AV-001 treatment does not significantly alter body weight compared to Sham or MMI control group. While 6 μg/Kg AV-001 treated group exhibit significantly lower body weight compared to Sham and MMI control group, the weight loss is evident starting at 1 day after MMI when treatment was initiated and is not significantly different compared to its baseline values at day 0 or day 1 after MMI. AV-001 treatment significantly decreases serum alanine aminotransferase, serum creatinine, and serum troponin I levels compared to the MMI control group; however, all values are within normal range. MMI induces mild neurological deficits in middle-aged rats indicated by low mNSS scores (<6 on a scale of 0-18). Compared to control MMI group, 1 μg/Kg AV-001 treatment group did not exhibit significantly different mNSS scores, while 3 and 6 μg/Kg AV-001 treatment induced significantly worse mNSS scores on days 21-42 and 14-42 after MMI, respectively. MMI in middle-aged rats induces significant cognitive impairment including short-term memory loss, long-term memory loss, reduced preference for social novelty and impaired spatial learning and memory compared to sham control rats. Rats treated with 1 μg/Kg AV-001 exhibit significantly improved short-term and long-term memory, increased preference for social novelty, and improved spatial learning and memory compared to MMI rats. Treatment with 3 μg/Kg AV-001 improves short-term memory and preference for social novelty but does not improve long-term memory or spatial learning and memory compared to MMI rats. Treatment with 6 μg/Kg AV-001 improves only long-term memory compared to MMI rats. Thus, 1 μg/Kg AV-001 treatment was selected as an optimal dose. Treatment of middle-aged rats subjected to MMI with 1 μg/Kg AV-001 significantly increases axon density, myelin density and myelin thickness in the corpus callosum, as well as increases synaptic protein expression, neuronal branching and dendritic spine density in the cortex, oligodendrocytes and oligodendrocyte progenitor cell number in the cortex and striatum and promotes neurogenesis in the subventricular zone compared to control MMI rats.

Conclusions

In this study, we present AV-001 as a novel therapeutic agent to improve cognitive function and reduce white matter injury in middle aged-rats subjected to a MMI model of VaD. Treatment of MMI with 1 μg/Kg AV-001 significantly improves cognitive function, and increases axon density, remyelination and neuroplasticity in the brain of middle-aged rats.

The comprehensive mechanistic insight into the effects of vitamin D on dementia – a review

Purpose

This paper aims to depict the mechanistic role of vitamin D on dementia prevention, relief of the severity and the complication of the disease. All papers indexed in scientific databases, including Scopus, Elsevier, PubMed, Embase and Google Scholar between 2000 and 2021 were extracted and discussed. To present the mechanistic role of vitamin D in declining the severity of dementia, keywords including dementia, vitamin D, oxidative stress, inflammation, amyloid beta-Peptides were used.

Design/methodology/approach

Dementia is a prevalent cognitive disorder worldwide, especially in elderly people, which is accompanied by serious disabilities. Besides genetic, biological and lifestyle factors are involved in the incidence of dementia. An unhealthy diet along with micronutrient deficiencies are among modifiable factors. Vitamin D is one of the important micronutrients in brain health. Besides the involvement in gene expression, bone mineralization, apoptosis, inflammation, skeletal maturation, neurotropic action and hemostasis of phosphate and calcium, vitamin D also exerts neuroprotective effects via genomic and non-genomic pathways.

Findings

Vitamin D up-regulates the expression of various genes involved in dementia incidence via various mechanisms. Decreasing oxidative stress and the neuro-inflammatory cytokines levels, regulation of the expression of alternated Proteins including Tau and Amyloid-ß, calcium homeostasis in the central nervous system and also vascular are considered main mechanisms.

Originality/value

Considering the importance of diet in preventing dementia, adherence to a healthy diet that provides essential nutrients to brain function seems to be urgent. Controlling serum levels of vitamin D periodically and providing vitamin D by related sources or supplements, if there is a deficiency, is recommended. Future studies are needed to clarify other related mechanisms.

Fluid transport in the brain

The brain harbors a unique ability to, figuratively speaking, shift its gears. During wakefulness, the brain is geared fully toward processing information and behaving, while homeostatic functions predominate during sleep. The blood-brain barrier establishes a stable environment that is optimal for neuronal function, yet the barrier imposes a physiological problem; transcapillary filtration that forms extracellular fluid in other organs is reduced to a minimum in brain. Consequently, the brain depends on a special fluid [the cerebrospinal fluid (CSF)] that is flushed into brain along the unique perivascular spaces created by astrocytic vascular endfeet. We describe this pathway, coined the term glymphatic system, based on its dependency on astrocytic vascular endfeet and their adluminal expression of aquaporin-4 water channels facing toward CSF-filled perivascular spaces. Glymphatic clearance of potentially harmful metabolic or protein waste products, such as amyloid-β, is primarily active during sleep, when its physiological drivers, the cardiac cycle, respiration, and slow vasomotion, together efficiently propel CSF inflow along periarterial spaces. The brain's extracellular space contains an abundance of proteoglycans and hyaluronan, which provide a low-resistance hydraulic conduit that rapidly can expand and shrink during the sleep-wake cycle. We describe this unique fluid system of the brain, which meets the brain's requisites to maintain homeostasis similar to peripheral organs, considering the blood-brain-barrier and the paths for formation and egress of the CSF.

Exosomes as bio-inspired nanocarriers for RNA delivery: preparation and applications

Nanocarriers as drug/biomolecule delivery systems have been significantly developed during recent decades. Given the stability, reasonable delivery efficiency, and safety of nanocarriers, there are several barriers in the fulfillment of successful clinical application of these delivery systems. These challenges encouraged drug delivery researchers to establish innovative nanocarriers with longer circulation time, high stability, and high compatibility. Exosomes are extracellular nanometer-sized vesicles released through various cells. These vesicles serve as nanocarriers, possessing great potential to overcome some obstacles encountered in gene and drug delivery due to their natural affinity to recipient cells and the inherent capability to shuttle the genes, lipids, proteins, and RNAs between cells. So far, there has been a lot of valuable research on drug delivery by exosomes, but research on RNA delivery, especially mRNA, is very limited. Since mRNA-based vaccines and therapies have recently gained particular prominence in various diseases, it is essential to find a suitable delivery system due to the large size and destructive nature of these nucleic acids. That's why we're going to take a look at the unique features of exosomes and their isolation and loading methods, to embrace this idea that exosome-mediated mRNA-based therapies would be introduced as a very efficient strategy in disease treatment within the near future.