Oligemic hypoperfusion differentially affects tau and amyloid-{beta}

Influence of Tau on Neurotoxicity and Cerebral Vasculature Impairment Associated with Alzheimer's Disease

Alzheimer's disease is a fatal chronic neurodegenerative condition marked by a gradual decline in cognitive abilities and impaired vascular function within the central nervous system. This affliction initiates its insidious progression with the accumulation of two aberrant protein entities including Aβ plaques and neurofibrillary tangles. These chronic elements target distinct brain regions, steadily erasing the functionality of the hippocampus and triggering the erosion of memory and neuronal integrity. Several assumptions are anticipated for AD as genetic alterations, the occurrence of Aβ plaques, altered processing of amyloid precursor protein, mitochondrial damage, and discrepancy of neurotropic factors. In addition to Aβ oligomers, the deposition of tau hyper-phosphorylates also plays an indispensable part in AD etiology. The brain comprises a complex network of capillaries that is crucial for maintaining proper function. Tau is expressed in cerebral blood vessels, where it helps to regulate blood flow and sustain the blood-brain barrier's integrity. In AD, tau pathology can disrupt cerebral blood supply and deteriorate the BBB, leading to neuronal neurodegeneration. Neuroinflammation, deficits in the microvasculature and endothelial functions, and Aβ deposition are characteristically detected in the initial phases of AD. These variations trigger neuronal malfunction and cognitive impairment. Intracellular tau accumulation in microglia and astrocytes triggers deleterious effects on the integrity of endothelium and cerebral blood supply resulting in further advancement of the ailment and cerebral instability. In this review, we will discuss the impact of tau on neurovascular impairment, mitochondrial dysfunction, oxidative stress, and the role of hyperphosphorylated tau in neuron excitotoxicity and inflammation.

Longitudinal trajectories of Alzheimer's disease CSF biomarkers and blood pressure in cognitively healthy subjects

INTRODUCTION

We examined whether hypertension (HTN) was associated with Alzheimer's disease-related biomarkers in cerebrospinal fluid (CSF) and how changes in blood pressure (BP) related to changes in CSF biomarkers over time.

METHODS

A longitudinal observation of cognitively healthy normotensive subjects (n = 134, BP < 140/90, with no antihypertensive medication), controlled HTN (n = 36, BP < 140/90, taking antihypertensive medication), and 35 subjects with uncontrolled HTN (BP ≥ 140/90). The follow-up range was 0.5to15.6 years.

RESULTS

Total tau (T-tau) and phospho-tau181 (P-tau 181) increased in all but controlled HTN subjects (group×time interaction: p < 0.05 for both), but no significant Aβ42 changes were seen. Significant BP reduction was observed in uncontrolled HTN, and it was related to increase in T-tau (p = 0.001) and P-tau 181 (p < 0.001).

DISCUSSION

Longitudinal increases in T-tau and P-tau 181 were observed in most subjects; however, only uncontrolled HTN had both markers increase alongside BP reductions. We speculate cumulative vascular injury renders the brain susceptible to relative hypoperfusion with BP reduction.

HIGHLIGHTS

Over the course of the study, participants with uncontrolled HTN at baseline showed greater accumulation of CSF total tau and phospho-tau181 (P-tau 181) than subjects with normal BP or with controlled HTN. In the group with uncontrolled HTN, increases in total tau and P-tau 181 coincided with reduction in BP. We believe this highlights the role of HTN in vascular injury and suggests decline in cerebral perfusion resulting in increased biomarker concentrations in CSF. Medication use was the main factor differentiating controlled from uncontrolled HTN, indicating that earlier treatment was beneficial for preventing accumulations of pathology.

Orthostatic Hypotension Promotes the Progression From Mild Cognitive Impairment to Dementia in Type 2 Diabetes Mellitus

CONTEXT

In type 2 diabetes mellitus (T2DM), orthostatic hypotension (OH) is associated with cognition, but the mechanisms governing the link between OH and cognition are still unclear.

OBJECTIVE

We sought to analyze Alzheimer's disease (AD) biomarkers and the part of complement proteins in modulating the association of OH with cognitive impairment and examine whether OH could accelerate the clinical progression of mild cognitive impairment (MCI) to dementia in T2DM.

METHODS

We recruited patients with T2DM with MCI and collected general healthy information and blood samples. Complement proteins of astrocyte-derived exosomes were isolated and AD biomarkers of neuronal cell-derived exosomes isolated were quantified by enzyme-linked immunosorbent assay. Cognitive assessments were performed at patient enrollment and follow-up.

RESULTS

Mediation analysis showed that the influence of OH on cognition in T2DM was partly mediated by baseline AD biomarkers and complement proteins. Cox proportional-hazards regression proved the OH group had a higher risk of developing dementia compared to the T2DM without OH group.

CONCLUSION

In T2DM with MCI patients, AD biomarkers and complement proteins mediate the effects of OH on cognitive impairment and OH may be a risk factor of progression from MCI to dementia in T2DM.

Associations of Orthostatic Hypotension and Orthostatic Intolerance with Domain-Specific Cognitive Decline in Patients with Early Parkinson Disease: An 8-Year Follow-up

OBJECTIVE

Although orthostatic hypotension (OH) and orthostatic intolerance (OI) are prevalent in patients with Parkinson disease (PD), it remains unclear how these conditions primarily affect the trajectory of decline in specific cognitive domains. This study aimed to explore the effects of OH and OI on longitudinal domain-specific cognitive changes in patients with PD.

DESIGN

An 8-year follow-up of the Parkinson Progression Markers Initiative cohort study.

SETTING AND PARTICIPANTS

A total of 403 patients with early, untreated PD and 195 matched healthy controls were included. They were classified into OH, OI, and normal groups. OH was defined according to the international consensus, and OI was defined as the presence of orthostatic symptoms without meeting the criteria for OH.

METHODS

The patients underwent detailed neuropsychological testing annually for up to 8 years of follow-up. Linear mixed effects models were used to investigate the associations between OH, OI, and longitudinal cognitive changes.

RESULTS

The prevalence of both OH and OI in patients with PD was significantly higher than that in controls (13.4% vs 7.2%, P = .002, for OH, and 29.3% vs 14.4%, P < .001, for OI). The OH group in patients with PD showed a faster decline in Letter-Number Sequencing (LNS) (β = -0.11, 95% CI -0.20 to -0.02, t = -2.44, P = .015) and Semantic Fluency Test (SFT) (β = -0.44, 95% CI -0.81 to -0.08, t = -2.42, P = .016) scores than the normal group. Similarly, the OI group showed a steeper decline in LNS (β = -0.08, 95% CI -0.14 to -0.01, t = -2.20, P = .028) and SFT (β = -0.36, 95% CI -0.63 to -0.08, t = -2.55, P = .011) scores compared to the normal group. There were no significant longitudinal changes in the other neuropsychological test scores between the groups.

CONCLUSIONS AND IMPLICATIONS

Both OH and OI may be associated with a faster decline in executive function among cognitive domains of patients with PD. These findings may highlight the potential importance of orthostatic blood pressure control in PD patients with OH and even those with orthostatic symptoms without OH.

Simulating Cerebral Edema and Ischemia After Traumatic Acute Subdural Hematoma Using Triphasic Swelling Biomechanics

Poor outcome following traumatic acute subdural hematoma (ASDH) is associated with the severity of the primary injury and secondary injury including cerebral edema and ischemia. However, the underlying secondary injury mechanism contributing to elevated intracranial pressure (ICP) and high mortality rate remains unclear. Cerebral edema occurs in response to the exposure of the intracellular fixed charge density (FCD) after cell death, causing ICP to increase. The increased ICP from swollen tissue compresses blood vessels in adjacent tissue, restricting blood flow and leading to ischemic damage. We hypothesize that the mass occupying effect of ASDH exacerbates the ischemic injury, leading to ICP elevation, which is an indicator of high mortality rate in the clinic. Using FEBio (febio.org) and triphasic swelling biomechanics, this study modeled clinically relevant ASDHs and simulated post-traumatic brain swelling and ischemia to predict ICP. Results showed that common convexity ASDH significantly increased ICP by exacerbating ischemic injury, and surgical removal of the convexity ASDH may control ICP by preventing ischemia progression. However, in cases where the primary injury is very severe, surgical intervention alone may not effectively decrease ICP, as the contribution of the hematoma to the elevated ICP is insignificant. In addition, interhemispheric ASDH, located between the cerebral hemispheres, does not significantly exacerbate ischemia, supporting the conservative surgical management generally recommended for interhemispheric ASDH. The joint effect of the mass occupying effect of the blood clot and resulting ischemia contributes to elevated ICP which may increase mortality. Our novel approach may improve the fidelity of predicting patient outcome after motor vehicle crashes and traumatic brain injuries due to other causes.

Blood Pressure Variability and Plasma Biomarkers of Neuronal Injury and Alzheimer's Disease: A Clinic-Based Study of Patients with Diseases Along the Heart-Brain Axis

 Higher blood pressure variability (BPV) predisposes to cognitive decline. To investigate underlying mechanisms, we measured 24-h ambulatory BPV, nocturnal dipping and orthostatic hypotension in 518 participants with vascular cognitive impairment, carotid occlusive disease, heart failure, or reference participants. We determined cross-sectional associations between BPV indices and plasma biomarkers of neuronal injury (neurofilament light chain) and Alzheimer's disease (phosphorylated-tau-181 and Aβ42/Aβ40). None of the BPV indices were significantly associated with any of the biomarkers. Hence, in patients with diseases along the heart-brain axis, we found no evidence for an association between BPV and selected markers of neuronal injury or Alzheimer's disease.

Amyloid Beta-Mediated Neurovascular Toxicity in Alzheimer's Disease

The brain vascular system receives one-fifth of the total oxygen from the cardiac output, and this transport system is highly dependent on blood-brain barrier (BBB) integrity. The cerebral blood flow is controlled by neurovascular coupling through neurovascular units (NVUs). The NVU includes different types of cells, such as mural cells, astrocytes, pericytes, endothelial cells (ECs), and vascular smooth muscle cells (VSMCs). The cellular composition of NVU varies throughout the vascular tree. Amyloid β (Aβ) is abundantly present in the central nervous system, but the pathological accumulation of misfolded Aβ protein causes vascular damage, resulting in neurovascular dysfunction. Aβ aggregation can activate the astrocytes and endothelial cells. It is followed by pericyte degeneration which results in dysregulation of cerebral blood flow (CBF), neurovascular uncoupling, and BBB breakdown. Thus, understanding the cellular and molecular mechanisms of Aβ-induced neurovascular toxicity is crucial for determining normal and diseased brain function. This chapter discusses the components of NVU, neurovascular uncoupling, Aβ-induced cerebrovascular reactivity, and cerebral blood flow reduction in neurodegenerative disorders, with special emphasis on Alzheimer's disease.

The risk factors of postoperative cognitive dysfunction in patients undergoing carotid endarterectomy: an updated meta-analysis

OBJECTIVE

The purpose of the current meta-analysis was to determine the incidence and risk factors to provide a scientific basis for prevention and treatment of postoperative cognitive dysfunction (POCD) after carotid endarterectomy (CEA).

METHODS

Relevant articles published before October 2022 were searched from Pubmed/MEDLINE, Cochrane and Embase databases. The outcomes were the incidence and risk factors for POCD. A random-effects model was applied to estimate the overall odds ratios (ORs) and mean differences (MDs) for all risk factors through STATA 14.0 and RevMan 5.4. The quality of eligible studies was evaluated by Newcastle-Ottawa Scale (NOS) as previously described.

RESULTS

A total of 22 articles involving 3459 CEA patients were finally identified. The weighted mean incidence of POCD was 19% (95% confidence intervals (95% CI) 0.16-0.24, P < 0.001). Of the 16 identified risk factors, hyperperfusion (OR: 0.54, 95% CI 0.41-0.71) and degree of internal carotid artery (ICA) stenosis (OR: 5.06, 95% CI 0.86-9.27) were the potential risk factors of POCD, whereas patients taking statins preoperative had a lower risk of POCD (OR: 0.54, 95% CI 0.41-0.71). Subgroup analysis revealed that the risk of POCD at 1 month after CEA was higher in patients with diabetes (OR: 1.70, 95% CI 1.07-2.71).

CONCLUSION

The risk factors of POCD were hyperperfusion and degree of ICA stenosis, while diabetes could significantly increase the incidence of POCD at 1 month after surgery. Additionally, preoperative statin use could be a protective factor for POCD following CEA.

Independent effect of Aβ burden on cognitive impairment in patients with small subcortical infarction

BACKGROUND

The effect of amyloid-β (Aβ) on cognitive impairment in patients with small subcortical infarction remains controversial, although a growing body of evidence shows a substantial overlap between Alzheimer's disease (AD) and subcortical ischemic vascular dementia, another form of cerebral small vessel disease (cSVD). Therefore, we investigated the relationships between Aβ positivity and the development of post-stroke cognitive impairment (PSCI) in patients with small subcortical infarction.

METHODS

We prospectively recruited 37 patients aged ≥ 50 years, with first-ever small subcortical infarction, who underwent amyloid positron emission tomography, 3 months after stroke at Korea University Guro Hospital. We also enrolled CU participants matched for age and sex with stroke patients for comparison of Aβ positivity. Patients were followed up at 3 and 12 months after the stroke to assess cognitive decline. Logistic and linear mixed-effect regression analyses were performed to identify the effect of Aβ positivity on PSCI development and long-term cognitive trajectories.

RESULTS

At 3 months after stroke, 12/37 (32.4%) patients developed PSCI, and 11/37 (29.7%) patients had Aβ deposition. Aβ positivity (odds ratio [OR] = 72.2, p = 0.024) was predictive of PSCI development regardless of cSVD burden. Aβ positivity (β = 0.846, p = 0.014) was also associated with poor cognitive trajectory, assessed by the Clinical Dementia Rating-Sum of Box, for 1 year after stroke.

CONCLUSIONS

Our findings highlight that Aβ positivity is an important predictor for PSCI development and cognitive decline over 1 year. Furthermore, our results provide evidence that anti-AD medications may be a strategy for preventing cognitive decline in patients with small subcortical infarctions.

Cooperation between neurovascular dysfunction and Aβ in Alzheimer's disease

The amyloid-β (Aβ) hypothesis was once believed to represent the pathogenic process of Alzheimer's disease (AD). However, with the failure of clinical drug development and the increasing understanding of the disease, the Aβ hypothesis has been challenged. Numerous recent investigations have demonstrated that the vascular system plays a significant role in the course of AD, with vascular damage occurring prior to the deposition of Aβ and neurofibrillary tangles (NFTs). The question of how Aβ relates to neurovascular function and which is the trigger for AD has recently come into sharp focus. In this review, we outline the various vascular dysfunctions associated with AD, including changes in vascular hemodynamics, vascular cell function, vascular coverage, and blood-brain barrier (BBB) permeability. We reviewed the most recent findings about the complicated Aβ-neurovascular unit (NVU) interaction and highlighted its vital importance to understanding disease pathophysiology. Vascular defects may lead to Aβ deposition, neurotoxicity, glial cell activation, and metabolic dysfunction; In contrast, Aβ and oxidative stress can aggravate vascular damage, forming a vicious cycle loop.

Hypertension, antihypertensive drugs, and age at onset of Huntington's disease

BACKGROUND

Associations between blood pressure (BP) with age at onset of Huntington's disease (HD) have reported inconsistent findings. We used Mendelian randomization (MR) to assess effects of BP and lowering systolic BP (SBP) via the genes encoding targets of antihypertensive drugs on age at onset of HD.

METHODS

Genetic variants from genome-wide association studies(GWAS) of BP traits and BP-lowering variants in genes encoding antihypertensive drugs targets were extracted. Summary statistics for age at onset of HD were retrieved from the GWAS meta-analysis of HD residual age at onset from the GEM-HD Consortium included 9064 HD patients of European ancestry (4417 males and 4,647 females). MR estimates were calculated using the inverse variance weighted method, supplemented by MR-Egger, weighted median, and MR-PRESSO methods.

RESULTS

Genetically predicted SBP or diastolic BP increase was associated with a later age at onset of HD. However, after SBP/DBP was present as a covariate using multivariable MR method, no significant causal association was suggested. A 10-mm Hg reduction in SBP through variants in genes encoding targets of calcium channel blockers (CCB) was associated with an earlier age at onset of HD (β=-0.220 years, 95% CI =-0.337 to -0.102, P = 2.42 × 10^- 4). We did not find a causal association between angiotensin converting enzyme inhibitors and β-blockers with the earlier HD onset. No heterogeneity and horizontal pleiotropy were identified.

CONCLUSIONS

This MR analysis provided evidence that genetically determined SBP lowering through antihypertensive drugs might be associated with an earlier age at onset of HD. The results may have a potential impact on management of hypertension in the pre-motor-manifest HD population.

The Association Between 24-Hour Blood Pressure Profiles and Dementia

Midlife hypertension increases risk for dementia. Around one third of adults have diagnosed hypertension; however, many adults are undiagnosed, or remain hypertensive despite diagnosis or treatment. Since blood pressure (BP) follows a circadian rhythm, ambulatory BP monitoring allows for the assessment of BP over a 24-hour period and provides an important tool for improving the diagnosis and management of hypertension. The measurement of 24-hour BP profiles, especially nocturnal BP, demonstrate better predictive ability for cardiovascular disease and mortality than office measurement. However, few studies have examined 24-hour BP profiles with respect to dementia risk. This is an important topic since improvements in BP management could facilitate the primary prevention of vascular cognitive impairment and dementia. Therefore, this review discusses the evidence linking BP to dementia, with a focus on whether the implementation of 24-hour BP measurements can improve risk prediction and prevention strategies. Pathways linking nocturnal BP to dementia are also discussed as are risk reduction strategies. Overall, limited research suggests an association between 24-hour BP elevation and poorer cognition, cerebral small vessel disease, and dementia. However, most studies were cross-sectional. Further evidence is needed to substantiate 24-hour BP profiles, over and above office BP, as predictors of vascular cognitive impairment and incident dementia.

Chronic Cerebral Hypoperfusion Aggravates Parkinson’s Disease Dementia-Like Symptoms and Pathology in 6-OHDA-Lesioned Rat through Interfering with Sphingolipid Metabolism

Chronic cerebral hypoperfusion (CCH) is a cardinal risk factor for Parkinson's disease dementia (PDD), but this potential causality lacks mechanistic evidence. We selected bilateral common carotid artery occlusion (BCCAO) to simulate chronic cerebral hypoperfusion in the rat model of PD induced by typical neurotoxin 6-hydroxy dopamine (6-OHDA). Four weeks after unilateral injection of 6-OHDA into the medial forebrain bundle, rats underwent BCCAO. Male Sprague-Dawley rats were divided into five groups of ten, including sham, PD+BCCAO 2 weeks, PD+BCCAO 1 week, PD, and BCCAO 2 weeks. Then, open field test (OFT) and Morris water maze test (MWM) were used to assess the PDD-like symptoms in rats. Also, the pathological manifestations and mechanisms of BCCAO impairing cognitive functions have been explored via hematoxylin-eosin staining, Nissl staining, immunohistochemistry, immunofluorescence, RNA sequencing analysis, lipidomics, and quantitative real-time polymerase chain reaction. In this study, we found that CCH could aggravate PDD-like cognitive symptoms (i.e., learning memory and spatial cognition) and PDD-like pathology (higher expression of α-Syn and Aβ in prefrontal cortex and striatum). Moreover, a potential relationship between differentially expressed mRNAs and lipid metabolism was revealed by RNA sequencing analysis. Lipidomics showed that CCH could affect the intensity of 5 lipids, including sphingomyelin (SM 9:0;2O/26:2; SM 8:1;2O/25:0; and SM 8:0;2O/28:4), cardiolipin, lysophosphatidylcholine, cholesteryl ester, and triacylglycerol. Interestingly, the KEGG pathway analysis of both RNA sequencing analysis and lipidomics suggested that CCH leaded to learning impairment by affecting sphingolipid metabolism. Finally, we found that CCH disrupts the sphingolipid metabolism by affecting the mRNA expression of SMPD1 and SMS2, leading to the accumulation of sphingomyelin in the prefrontal cortex. In summary, CCH, an independent exacerbating reason for impairment in learning and memory within the pathopoiesis of PD, aggravates Parkinson's disease dementia-like symptoms and pathology in 6-OHDA-lesioned rat through interfering with sphingolipid metabolism.

Neuroinflammation in Vascular Cognitive Impairment and Dementia: Current Evidence, Advances, and Prospects

Vascular cognitive impairment and dementia (VCID) is a major heterogeneous brain disease caused by multiple factors, and it is the second most common type of dementia in the world. It is caused by long-term chronic low perfusion in the whole brain or local brain area, and it eventually develops into severe cognitive dysfunction syndrome. Because of the disease’s ambiguous classification and diagnostic criteria, there is no clear treatment strategy for VCID, and the association between cerebrovascular pathology and cognitive impairment is controversial. Neuroinflammation is an immunological cascade reaction mediated by glial cells in the central nervous system where innate immunity resides. Inflammatory reactions could be triggered by various damaging events, including hypoxia, ischemia, and infection. Long-term chronic hypoperfusion-induced ischemia and hypoxia can overactivate neuroinflammation, causing apoptosis, blood–brain barrier damage and other pathological changes, triggering or aggravating the occurrence and development of VCID. In this review, we will explore the mechanisms of neuroinflammation induced by ischemia and hypoxia caused by chronic hypoperfusion and emphasize the important role of neuroinflammation in the development of VCID from the perspective of immune cells, immune mediators and immune signaling pathways, so as to provide valuable ideas for the prevention and treatment of the disease.

The Systemic Effects of Exercise on the Systemic Effects of Alzheimer's Disease

Alzheimer’s disease (AD) is a progressive degenerative disorder and a leading cause of dementia in the elderly. The etiology of AD is multifactorial, including an increased oxidative state, deposition of amyloid plaques, and neurofibrillary tangles of the tau protein. The formation of amyloid plaques is considered one of the first signs of the illness, but only in the central nervous system (CNS). Interestingly, results indicate that AD is not just localized in the brain but is also found in organs distant from the brain, such as the cardiovascular system, gut microbiome, liver, testes, and kidney. These observations make AD a complex systemic disorder. Still, no effective medications have been found, but regular physical activity has been considered to have a positive impact on this challenging disease. While several articles have been published on the benefits of physical activity on AD development in the CNS, its peripheral effects have not been discussed in detail. The provocative question arising is the following: is it possible that the beneficial effects of regular exercise on AD are due to the systemic impact of training, rather than just the effects of exercise on the brain? If so, does this mean that the level of fitness of these peripheral organs can directly or indirectly influence the incidence or progress of AD? Therefore, the present paper aims to summarize the systemic effects of both regular exercise and AD and point out how common exercise-induced adaptation via peripheral organs can decrease the incidence of AD or attenuate the progress of AD.

Medial Temporal Atrophy Contributes to Cognitive Impairment in Cerebral Small Vessel Disease

Background

The role of brain atrophy in cognitive decline related to cerebral small vessel disease (CSVD) remains unclear. This study used AccuBrain™ to identify major CSVD-related brain changes and verified the relationship between brain atrophy and different cognition domains in CSVD patients.

Methods

All enrolled 242 CSVD patients and 76 healthy participants underwent magnetic resonance imaging examinations and detailed neuropsychological scale assessments were collected at the same time. The AccuBrain™ technology was applied to fully automated image segmentation, measurement, and calculation of the acquired imaging results to obtain the volumes of different brain partitions and the volume of WMH for quantitative analysis. Correlation analyses were used to estimate the relationship between MRI features and different cognitive domains. Multifactor linear regression models were performed to analyze independent predictors of MTA and cognitive decline.

Results

CSVD patients exhibited multiple gray matter nucleus volume decreases in the basal ganglia regions and brain lobes, including the temporal lobe (P = 0.019), especially in the medial temporal lobe (p < 0.001), parietal lobe (p = 0.013), and cingulate lobe (p = 0.036) compare to HC. The volume of PWMH was an independent predictor of MTA for CSVD patients. Both medial temporal atrophy (MTA) and PWMH were associated with cognition impairment in CSVD-CI patients. MTA mediated the effect of PWMH on executive function in CSVD-CI patients.

Conclusions

Our results showed that MTA was related to cognition impairment in CSVD patients, which might become a potential imaging marker for CSVD-CI.

Selective neurodegeneration of the hippocampus caused by chronic cerebral hypoperfusion: F-18 FDG PET study in rats

Background

Chronic cerebral hypoperfusion (CCH) is known to induce Alzheimer’s disease (AD) pathology, but its mechanism remains unclear. The purpose of this study was to identify the cerebral regions that are affected by CCH, and to evaluate the development of AD pathology in a rat model of CCH.

Methods

A rat model of CCH was established by bilaterally ligating the common carotid arteries in adult male rats (CCH group). The identical operations were performed on sham rats without arteries ligation (control group). Regional cerebral glucose metabolism was evaluated at 1 and 3 months after bilateral CCA ligation using positron emission tomography with F-18 fluorodeoxyglucose. The expression levels of amyloid β40 (Aβ40), amyloid β42 (Aβ42), and hyperphosphorylated tau were evaluated using western blots at 3 months after the ligation. Cognitive function was evaluated using the Y-maze test at 3 months after the ligation.

Results

At 1 month after the ligation, cerebral glucose metabolism in the entorhinal, frontal association, motor, and somatosensory cortices were significantly decreased in the CCH group compared with those in the control group. At 3 months after the ligation, cerebral glucose metabolism was normalized in all regions except for the anterodorsal hippocampus, which was significantly decreased compared with that of the control group. The expression of Aβ42 and the Aβ42/40 ratio were significantly higher in the CCH group than those in the control group. The phosphorylated-tau levels of the hippocampus in the CCH group were significantly lower than those in the control group. Cognitive function was more impaired in the CCH group than that in the control group.

Conclusion

Our findings suggest that CCH causes selective neurodegeneration of the anterodorsal hippocampus, which may be a trigger point for the development of AD pathology.

Remote Ischemic Conditioning: A Potential Treatment for Chronic Cerebral Hypoperfusion

BACKGROUND

Chronic cerebral hypoperfusion (CCH) is a clinical syndrome, which is characterized by significantly decreased cerebral blood flow (CBF). CCH is a common consequence of cerebrovascular and cardiovascular diseases and the elderly. CCH results in a series of pathological damages, increasing cell death, autophagy dysfunction, amyloid β (Aβ) peptide accumulation, blood-brain barrier (BBB) disruption, and endothelial damage, which are found in CCH models. In addition, CCH is a prominent risk factor of cognitive impairment, such as vascular dementia, and CCH contributes to the occurrence and development of Alzheimer's disease. Therefore, the treatment of patients with CCH is of great value. It has been confirmed that remote ischemic conditioning (RIC) is a safe, promising treatment for acute and chronic cerebrovascular diseases. RIC significantly increases CBF in both CCH models and patients, inhibits neuronal apoptosis, reduces Aβ deposition, protects BBB integrity and endothelial function, alleviates neuroinflammation, improves cognitive impairment, and exerts neuroprotection.

SUMMARY

With the development of animal models, the pathophysiological mechanisms of CCH and RIC are increasingly revealed. Key Messages: We discuss the mechanisms related to hypoperfusion in the brain and explore the potential treatment of RIC for CCH to promote its transformation and application in humans.

Late-life longitudinal blood pressure trajectories as predictor of dementia

While hypertension is widely recognized as a risk factor for dementia, few observational studies and clinical trials fully accounted for the effect of age on blood pressure (BP) changes prior to dementia onset. In this territory-wide population-based longitudinal study of 16,591 community-living dementia-free older adults, we followed their BP and cognitive status and tested if loss of longitudinal increase in BP in late life was associated with higher dementia risk in 6 years, with consideration of the confounding effects of hypertension, hypotension, BP variability, and other health problems and behaviours and, in the data analysis, exclusion of individuals who developed dementia within 3 years after baseline to minimize risk of reverse causality. Over 72,997 person-years of follow-up, 1429 participants developed dementia. We found that loss of longitudinal increase in systolic BP (defined as SBP increased by either < 10 mmHg or 10%) from baseline to Year 3 was independently associated with higher risk of incident dementia at Years 4 to 6 (adjusted OR 1.22, 95% CI 1.02-1.45, p = 0.03; adjusted OR 1.24, 95% CI 1.03-1.50, p = 0.02; respectively). Our findings suggest that late-life SBP trajectory changes might independently predict dementia onset and highlight the importance of including longitudinal BP monitoring in dementia risk assessment.

Endothelial Progenitor Cells and Vascular Alterations in Alzheimer’s Disease

Alzheimer’s disease (AD) is a neurodegenerative disease representing the most common type of dementia worldwide. The early diagnosis of AD is very difficult to achieve due to its complexity and the practically unknown etiology. Therefore, this is one of the greatest challenges in the field in order to develop an accurate therapy. Within the different etiological hypotheses proposed for AD, we will focus on the two-hit vascular hypothesis and vascular alterations occurring in the disease. According to this hypothesis, the accumulation of β-amyloid protein in the brain starts as a consequence of damage in the cerebral vasculature. Given that there are several vascular and angiogenic alterations in AD, and that endothelial progenitor cells (EPCs) play a key role in endothelial repair processes, the study of EPCs in AD may be relevant to the disease etiology and perhaps a biomarker and/or therapeutic target. This review focuses on the involvement of endothelial dysfunction in the onset and progression of AD with special emphasis on EPCs as a biomarker and potential therapeutic target.

Asymptomatic Carotid Disease and Cognitive Impairment: What Is the Evidence?

The development of cognitive dysfunction and dementia is a complex, multifactorial process. One of the contributors to various types of cognitive dysfunction is carotid atherosclerosis which can frequently be seen in asymptomatic individuals. There are a number of different manifestations of asymptomatic carotid atherosclerosis including arterial stiffness, carotid intima-media thickening, flow-limiting stenosis, and complex, atherosclerotic plaque. Each of these forms of atherosclerosis may contribute to cerebral parenchymal damage, contributing to cognitive dysfunction. In this review article, we will discuss each of these forms of carotid atherosclerosis, present the potential mechanistic underpinnings behind an association, and then review the scientific evidence supporting potential associations to cognitive dysfunction and dementia.

Nitric Oxide Pathways in Neurovascular Coupling Under Normal and Stress Conditions in the Brain: Strategies to Rescue Aberrant Coupling and Improve Cerebral Blood Flow

The brain has impressive energy requirements and paradoxically, very limited energy reserves, implying its huge dependency on continuous blood supply. Aditionally, cerebral blood flow must be dynamically regulated to the areas of increased neuronal activity and thus, of increased metabolic demands. The coupling between neuronal activity and cerebral blood flow (CBF) is supported by a mechanism called neurovascular coupling (NVC). Among the several vasoactive molecules released by glutamatergic activation, nitric oxide (^•NO) is recognized to be a key player in the process and essential for the development of the neurovascular response. Classically, ^•NO is produced in neurons upon the activation of the glutamatergic N-methyl-D-aspartate (NMDA) receptor by the neuronal isoform of nitric oxide synthase and promotes vasodilation by activating soluble guanylate cyclase in the smooth muscle cells of the adjacent arterioles. This pathway is part of a more complex network in which other molecular and cellular intervenients, as well as other sources of ^•NO, are involved. The elucidation of these interacting mechanisms is fundamental in understanding how the brain manages its energy requirements and how the failure of this process translates into neuronal dysfunction. Here, we aimed to provide an integrated and updated perspective of the role of ^•NO in the NVC, incorporating the most recent evidence that reinforces its central role in the process from both viewpoints, as a physiological mediator and a pathological stressor. First, we described the glutamate-NMDA receptor-nNOS axis as a central pathway in NVC, then we reviewed the link between the derailment of the NVC and neuronal dysfunction associated with neurodegeneration (with a focus on Alzheimer's disease). We further discussed the role of oxidative stress in the NVC dysfunction, specifically by decreasing the ^•NO bioavailability and diverting its bioactivity toward cytotoxicity. Finally, we highlighted some strategies targeting the rescue or maintenance of ^•NO bioavailability that could be explored to mitigate the NVC dysfunction associated with neurodegenerative conditions. In line with this, the potential modulatory effects of dietary nitrate and polyphenols on ^•NO-dependent NVC, in association with physical exercise, may be used as effective non-pharmacological strategies to promote the ^•NO bioavailability and to manage NVC dysfunction in neuropathological conditions.

Cerebrovascular alterations in NAFLD: Is it increasing our risk of Alzheimer's disease?

Non-alcoholic fatty liver disease (NAFLD) is a multisystem disease, which has been classified as an emerging epidemic not only confined to liver-related morbidity and mortality. It is also becoming apparent that NAFLD is associated with moderate cerebral dysfunction and cognitive decline. A possible link between NAFLD and Alzheimer's disease (AD) has only recently been proposed due to the multiple shared genes and pathological mechanisms contributing to the development of these conditions. Although AD is a progressive neurodegenerative disease, the exact pathophysiological mechanism remains ambiguous and similarly to NAFLD, currently available pharmacological therapies have mostly failed in clinical trials. In addition to the usual suspects (inflammation, oxidative stress, blood-brain barrier alterations and ageing) that could contribute to the NAFLD-induced development and progression of AD, changes in the vasculature, cerebral perfusion and waste clearance could be the missing link between these two diseases. Here, we review the most recent literature linking NAFLD and AD, focusing on cerebrovascular alterations and the brain's clearance system as risk factors involved in the development and progression of AD, with the aim of promoting further research using neuroimaging techniques and new mechanism-based therapeutic interventions.

The Many Faces of Post-Ischemic Tau Protein in Brain Neurodegeneration of the Alzheimer's Disease Type

Recent data suggest that post-ischemic brain neurodegeneration in humans and animals is associated with the modified tau protein in a manner typical of Alzheimer’s disease neuropathology. Pathological changes in the tau protein, at the gene and protein level due to cerebral ischemia, can lead to the development of Alzheimer’s disease-type neuropathology and dementia. Some studies have shown increased tau protein staining and gene expression in neurons following ischemia-reperfusion brain injury. Recent studies have found the tau protein to be associated with oxidative stress, apoptosis, autophagy, excitotoxicity, neuroinflammation, blood-brain barrier permeability, mitochondrial dysfunction, and impaired neuronal function. In this review, we discuss the interrelationship of these phenomena with post-ischemic changes in the tau protein in the brain. The tau protein may be at the intersection of many pathological mechanisms due to severe neuropathological changes in the brain following ischemia. The data indicate that an episode of cerebral ischemia activates the damage and death of neurons in the hippocampus in a tau protein-dependent manner, thus determining a novel and important mechanism for the survival and/or death of neuronal cells following ischemia. In this review, we update our understanding of proteomic and genomic changes in the tau protein in post-ischemic brain injury and present the relationship between the modified tau protein and post-ischemic neuropathology and present a positive correlation between the modified tau protein and a post-ischemic neuropathology that has characteristics of Alzheimer’s disease-type neurodegeneration.

Trajectory patterns of blood pressure change up to six years and the risk of dementia: a nationwide cohort study

The present study aimed to investigate the associations between the trajectory of blood pressure (BP) change and the risk of subsequent dementia and to explore the differences in age, gender, and hypertension subgroups. We included 10,660 participants aged ≥ 60 years from 1998 to 2018 waves of the Chinese Longitudinal Healthy Longevity Survey. Latent growth mixture models were used to estimate BP trajectories. Cox-proportional hazard models were used to analyze the effects of BP trajectories on the risk of dementia. According to the results, stabilized systolic BP (SBP) was found to be associated with a higher risk of dementia compared with normal SBP [adjusted hazard ratio (aHR): 1.62; 95% confidence interval (CI): 1.27-2.07] and elevated SBP (aHR: 2.22; 95% CI: 1.51-3.28) in and only in the subgroups of the oldest-old, women, and subjects without hypertension at baseline. Similarly, stabilized pulse pressure (PP) was associated with a higher risk of dementia compared with normal PP (aHR: 1.52; 95% CI: 1.24-1.88) and elevated PP (aHR: 2.12; 95% CI: 1.48-3.04) in and only in the subgroups of the oldest-old, women, and subjects with hypertension at baseline. These findings suggest that stabilized SBP and PP have predictive significance for the occurrence of dementia in late life, and the factors of age, gender, and late-life hypertension should be considered when estimating the risk of BP decline on dementia.

Apolipoprotein E4 Moderates the Association Between Vascular Risk Factors and Brain Pathology

BACKGROUND

The strongest genetic risk factor for late-onset Alzheimer disease (AD), Apolipoprotein E4 (APOE4), increases cardiovascular disease risk and may also act synergistically with vascular risk factors to contribute to AD pathogenesis. Here, we assess the interaction between APOE4 and vascular risk on cerebrovascular dysfunction and brain pathology.

METHODS

This is an observational study of cognitively normal older adults, which included positron emission tomography imaging and vascular risk factors. We measured beat-to-beat blood pressure and middle cerebral artery velocity at rest and during moderate-intensity exercise. Cerebrovascular measures included cerebrovascular conductance index and the cerebrovascular response to exercise.

RESULTS

There was a significant interaction between resting cerebrovascular conductance index and APOE4 carrier status on β-amyloid deposition (P=0.026), with poor conductance in the cerebrovasculature associated with elevated β-amyloid for the APOE4 carriers only. There was a significant interaction between non-high-density lipoprotein cholesterol and APOE4 carrier status (P=0.014), with elevated non-high-density lipoprotein cholesterol predicting a blunted cerebrovascular response to exercise in APOE4 carriers and the opposite relationship in noncarriers.

CONCLUSIONS

Both cerebral and peripheral vascular risk factors are preferentially associated with brain pathology in APOE4 carriers. These findings provide insight into pathogenic vascular risk mechanisms and target strategies to potentially delay AD onset.

Altered Amyloid-β and Tau Proteins in Neural-Derived Plasma Exosomes of Type 2 Diabetes Patients with Orthostatic Hypotension

BACKGROUND

Emerging evidence suggests a role for orthostatic hypotension (OH) in contributing to the progression of Alzheimer's disease (AD). The exosomes in the blood can reflect the pathological changes in the brain.

OBJECTIVE

To investigate whether neural-derived plasma exosomes pathogenic proteins of AD levels are associated with OH in diabetes mellitus (DM) patients.

METHODS

There were 274 subjects without dementia included in the study: 81 control participants (controls), 101 normotensive patients with DM without OH, and 92 patients with DM and neurogenic OH (DMOH). Neural-derived exosomal proteins were measured by ELISA kits for amyloid-β (Aβ) and tau.

RESULTS

The neural-derived exosome levels of Aβ42, total tau (T-tau), and tau phosphorylated at threonine 181 (P-T181-tau) in the DM with OH group were higher than those in the DM and control groups. Multivariable linear regression analysis showed that the presence of OH in patients with DM was associated with elevated exosomal Aβ42 (β= 0.172, p = 0.018), T-tau (β= 0.159, p = 0.030), and P-T181-tau (β= 0.220, p = 0.003) levels after adjustment for age, sex, APOE ɛ4, duration of type 2 diabetes, HbA1c, and cardiovascular risk factors. Furthermore, the levels of Aβ42, T-tau, and P-T181-tau in neural-derived exosomes were correlated with HIF-1α levels and the drop in mean cerebral blood flow velocity from the supine to upright position.

CONCLUSION

The presence of OH in DM patients was independently associated with elevated the Aβ42, T-tau, and P-T181-tau levels in neural-derived plasma exosomes. Cerebral hypoperfusion from DM with OH are likely candidate mechanisms.

Vascular Hypothesis of Alzheimer Disease: Topical Review of Mouse Models

[Figure: see text].

Cholinergic White Matter Lesions, AD-Signature Cortical Thickness, and Change in Cognition: The Northern Manhattan Study

BACKGROUND

How cerebrovascular disease and neurodegeneration affect each other to impact cognition is not yet known. We aimed to test whether Alzheimer's disease-signature (AD) cortical thickness mediates the association between cholinergic white matter lesion load and change in domain-specific cognition.

METHODS

Clinically stroke-free participants from the Northern Manhattan Study with both regional white matter hyperintensity volume (WMHV) and gray matter measurements were included (N = 894). Tract-specific WMHVs were quantified through FSL using the Johns Hopkins University white matter tract atlas. We used Freesurfer 5.1 to estimate regional cortical thickness. We fit structural equation models, including multiple indicator latent change score models, to examine associations between white matter hyperintensity volume (WMHV) in cholinergic tracts, AD-signature region cortical thickness (CT), and domain-specific cognition.

RESULTS

Our sample (N = 894) had a mean (SD) age = 70 (9) years, years of education = 10 (5), 63% women, and 67% Hispanics/Latinos. Greater cholinergic WMHV was significantly related to worse processing speed at baseline (standardized β = -0.17, SE = 0.05, p = .001) and over time (standardized β = -0.28, SE = 0.09, p = .003), with a significant indirect effect of AD-signature region CT (baseline: standardized β = -0.02, SE = 0.01, p = .023; change: standardized β = -0.03, SE = 0.02, p = .040).

CONCLUSIONS

Cholinergic tract WMHV is associated with worse processing speed, both directly and indirectly through its effect on AD-signature region CT.

Microvascular Alterations in Alzheimer's Disease

Alzheimer's disease (AD) is a neurodegenerative disorder associated with continual decline in cognition and ability to perform routine functions such as remembering familiar places or understanding speech. For decades, amyloid beta (Aβ) was viewed as the driver of AD, triggering neurodegenerative processes such as inflammation and formation of neurofibrillary tangles (NFTs). This approach has not yielded therapeutics that cure the disease or significant improvements in long-term cognition through removal of plaques and Aβ oligomers. Some researchers propose alternate mechanisms that drive AD or act in conjunction with amyloid to promote neurodegeneration. This review summarizes the status of AD research and examines research directions including and beyond Aβ, such as tau, inflammation, and protein clearance mechanisms. The effect of aging on microvasculature is highlighted, including its contribution to reduced blood flow that impairs cognition. Microvascular alterations observed in AD are outlined, emphasizing imaging studies of capillary malfunction. The review concludes with a discussion of two therapies to protect tissue without directly targeting Aβ for removal: (1) administration of growth factors to promote vascular recovery in AD; (2) inhibiting activity of a calcium-permeable ion channels to reduce microglial activation and restore cerebral vascular function.

A preliminary study of cerebral blood flow, aging and dementia in people with Down syndrome

BACKGROUND

People with Down syndrome (DS) develop Alzheimer's disease (AD) at an earlier age of onset than those with sporadic AD. AD neuropathology is typically present in DS by 40 years of age with an onset of dementia approximately 10 years later. This early onset is due to the overexpression of amyloid precursor protein from the third copy of chromosome 21. Cerebrovascular neuropathology is thought to contribute in 40-60% of cases sporadic AD. However, the vascular contribution to dementia in people with DS has been relatively unexplored. We hypothesised that vascular perfusion is compromised in older adults with DS relative to younger individuals and is further exacerbated in those with dementia.

METHOD

Cerebral blood flow (CBF) was measured using pulsed arterial spin labelling in 35 cognitively characterised adults with DS (26-65 years). DS participants were also compared with 15 control subjects without DS or dementia (26-65 years). Linear regression evaluated the difference in CBF across groups and diagnosis along with assessing the association between CBF and cognitive measures within the DS cohort.

RESULTS

Cerebral blood flow was significantly lower among DS participants with probable AD compared with controls (P = 0.02) and DS participants with no dementia (P = 0.01). Within the DS cohort, CBF was significantly associated with the Severe Impairment Battery (SIB) measure and the Dementia Questionnaire for People with Learning Disabilities (DLD) rating (F_3,25  = 5.13; P = 0.007). Both the SIB (β = 0.74; t = 2.71; P = 0.01) and DLD (β = -0.96; t = -3.87; P < 0.001) indicated greater impairment as global CBF decreased. Age was significantly associated with CBF among participants with DS. There was a non-linear effect of age, whereby CBF declined more rapidly after 45 years of age.

CONCLUSIONS

This preliminary study of CBF in DS indicates that cerebrovascular pathology may be a significant contributor to dementia in DS. CBF was associated with diagnosis, cognition and age. Notably, CBF decreases at a greater rate after age 45 and may represent a significant prodromal event in AD progression.

Amyloid-beta peptide and phosphorylated tau in the frontopolar cerebral cortex and in the cerebellum of toothed whales: aging versus hypoxia

Hypoxia could be a possible risk factor for neurodegenerative alterations in cetaceans' brain. Among toothed whales, the beaked whales are particularly cryptic and routinely dive deeper than 1000 m for about 1 h in order to hunt squids and fishes. Samples of frontal cerebral and cerebellar cortex were collected from nine animals, representing six different species of the suborder Odontoceti. Immunohistochemical analysis employed anti-β-amyloid (Aβ) and anti-neurofibrillary tangle (NFT) antibodies. Six of nine (67%) animals showed positive immunolabeling for Aβ and/or NFT. The most striking findings were intranuclear Aβ immunopositivity in cerebral cortical neurons and NFT immunopositivity in cerebellar Purkinje neurons with granulovacuolar degeneration. Aβ plaques were also observed in one elderly animal. Herein, we present immunohistopathological findings classic of Alzheimer's and other neurodegenerative diseases in humans. Our findings could be linked to hypoxic phenomena, as they were more extensive in beaked whales. Despite their adaptations, cetaceans could be vulnerable to sustained and repetitive brain hypoxia.

Toward refining Alzheimer's disease into overlapping subgroups

Alzheimer's disease (AD) is an age-related neurodegenerative disorder characterized by progressive anterograde amnesia, cerebral atrophy, and eventual death. Current treatment has limited efficacy and cannot decelerate the disease progression. Clinical trials targeting the removal of the neuropathological hallmarks of AD, including accumulation of amyloid plaques or neurofibrillary tangles, have failed to modify disease progression. Without new or innovative hypotheses, AD is poised to become a public health crisis within this decade. We present an alternative hypothesis-that AD is the result of multiple interrelated causalities. The intention of this manuscript is to initiate a discussion regarding these multiple causalities and their overlapping similarities. The idea of creating subgroups allows for better identification of biomarkers across a narrower patient population for improved pharmacotherapeutic opportunities. The interrelatedness of many of these proposed subgroups indicates the complexity of this disorder. However, it also supports that no one single factor may initiate the cascade of events.

Glucose transporters in brain in health and disease

Energy demand of neurons in brain that is covered by glucose supply from the blood is ensured by glucose transporters in capillaries and brain cells. In brain, the facilitative diffusion glucose transporters GLUT1-6 and GLUT8, and the Na⁺-d-glucose cotransporters SGLT1 are expressed. The glucose transporters mediate uptake of d-glucose across the blood-brain barrier and delivery of d-glucose to astrocytes and neurons. They are critically involved in regulatory adaptations to varying energy demands in response to differing neuronal activities and glucose supply. In this review, a comprehensive overview about verified and proposed roles of cerebral glucose transporters during health and diseases is presented. Our current knowledge is mainly based on experiments performed in rodents. First, the functional properties of human glucose transporters expressed in brain and their cerebral locations are described. Thereafter, proposed physiological functions of GLUT1, GLUT2, GLUT3, GLUT4, and SGLT1 for energy supply to neurons, glucose sensing, central regulation of glucohomeostasis, and feeding behavior are compiled, and their roles in learning and memory formation are discussed. In addition, diseases are described in which functional changes of cerebral glucose transporters are relevant. These are GLUT1 deficiency syndrome (GLUT1-SD), diabetes mellitus, Alzheimer’s disease (AD), stroke, and traumatic brain injury (TBI). GLUT1-SD is caused by defect mutations in GLUT1. Diabetes and AD are associated with changed expression of glucose transporters in brain, and transporter-related energy deficiency of neurons may contribute to pathogenesis of AD. Stroke and TBI are associated with changes of glucose transporter expression that influence clinical outcome.

Hypertension and Alzheimer's disease: indirect effects through circle of Willis atherosclerosis

Hypertension is common among older adults and is believed to increase susceptibility to Alzheimer's disease, but mechanisms underlying this relationship are unclear. Hypertension also promotes circle of Willis atherosclerosis, which contributes to cerebral hypoperfusion and arterial wall stiffening, two potential mechanisms linking hypertension to Alzheimer's disease. To examine the role of circle of Willis atherosclerosis in the association between hypertension and Alzheimer's disease neuropathology, we analysed post-mortem neuropathological data on 2198 decedents from the National Alzheimer's Coordinating Center database [mean (standard deviation) age at last visit 80.51 (1.95) and 47.1% female] using joint simultaneous (i.e. mediation) modelling. Within the overall sample and among Alzheimer's dementia decedents, hypertension was indirectly associated with increased neuritic plaques and neurofibrillary tangles through its association with circle of Willis atherosclerosis. Similar indirect effects were observed for continuous measures of systolic and diastolic blood pressure. These results suggest that hypertension may promote Alzheimer's disease pathology indirectly through intracranial atherosclerosis by limiting cerebral blood flow and/or dampening perivascular clearance. Circle of Willis atherosclerosis may be an important point of convergence between vascular risk factors, cerebrovascular changes and Alzheimer's disease neuropathology.

Association between atherosclerosis and Alzheimer's disease: A systematic review and meta-analysis

BACKGROUND

To evaluate the relationship between atherosclerosis and Alzheimer's disease (AD), we conducted a systematic review and meta-analysis to study the difference of carotid intima-media thickness (CIMT) and the prevalence of atherosclerosis between AD patients and non-AD controls.

METHODS

The studies on the association between atherosclerosis and AD were manually searched in PubMed, Embase, Cochrane Library, and CNKI (China National Knowledge Infrastructure) spanned to September 2018 according to PRISMA (the Preferred Reporting Items for Systematic Reviews and Meta-Analyses) guidelines.

RESULTS

Thirteen studies were included in the final analysis, seven studies with data on the mean CIMT (610 cases and 417 controls) and ten studies reporting on the prevalence of atherosclerosis (1,698 cases and 6,452 controls). Compared with controls, AD group showed a significantly higher CIMT (overall standard mean difference = 0.94; 95% CI, 0.48-1.40; p < .0001) and an increased prevalence of atherosclerosis (OR = 1.46; 95% CI, 1.26-1.68; p < .0001).

CONCLUSIONS

Atherosclerosis is significantly associated with AD. CIMT might be a useful marker to predict the risk of AD and assess the vascular burden. The finding is also important for possible prevention and treatment of AD in the future.

An Integrated View on Vascular Dysfunction in Alzheimer's Disease

BACKGROUND

Cerebrovascular disease is a common comorbidity in patients with Alzheimer's disease (AD). It is believed to contribute additively to the cognitive impairment and to lower the threshold for the development of dementia. However, accumulating evidence suggests that dysfunction of the cerebral vasculature and AD neuropathology interact in multiple ways. Vascular processes even proceed AD neuropathology, implicating a causal role in the etiology of AD. Thus, the review aims to provide an integrated view on vascular dysfunction in AD.

SUMMARY

In AD, the cerebral vasculature undergoes pronounced cellular, morphological and structural changes, which alters regulation of blood flow, vascular fluid dynamics and vessel integrity. Stiffening of central blood vessels lead to transmission of excessive pulsatile energy to the brain microvasculature, causing end-organ damage. Moreover, a dysregulated hemostasis and chronic vascular inflammation further impede vascular function, where its mediators interact synergistically. Changes of the cerebral vasculature are triggered and driven by systemic vascular abnormalities that are part of aging, and which can be accelerated and aggravated by cardiovascular diseases. Key Messages: In AD, the cerebral vasculature is the locus where multiple pathogenic processes converge and contribute to cognitive impairment. Understanding the molecular mechanism and pathophysiology of vascular dysfunction in AD and use of vascular blood-based and imaging biomarker in clinical studies may hold promise for future prevention and therapy of the disease.

Benign Regulation of the Astrocytic Phospholipase A2-Arachidonic Acid Pathway: The Underlying Mechanism of the Beneficial Effects of Manual Acupuncture on CBF

Background

The astrocytic phospholipase A₂ (PLA₂)-arachidonic acid (AA) pathway is crucial in understanding the reduction of cerebral blood flow (CBF) prior to cognitive deterioration. In complementary and alternative medicine, manual acupuncture (MA) is used as one of the most important therapies for Alzheimer’s disease (AD). The beneficial effects of MA on CBF were reported in our previous study. However, the underlying molecular mechanism remains largely elusive.

Objective

To investigate the effect of MA on the astrocytic PLA₂-AA pathway in SAMP8 mice hippocampi.

Methods

SAMP8 mice were divided into the SAMP8 control (Pc) group, the SAMP8 MA (Pm) group and the SAMP8 donepezil (Pd) group. SAMR1 mice were used as the SAMRl control (Rc) group. Mice in the Pd group were treated with donepezil hydrochloride at 0.65 μg/g. In the Pm group, MA was applied at Baihui (GV20) and Yintang (GV29) for 20 min. The above treatments were administered once a day for 26 consecutive days. The Morris water maze was applied to assess spatial learning and memory. Immunofluorescence staining, western blot and liquid chromatography-tandem mass spectrometry were used to investigate the expression of related proteins and measure the contents of the metabolic intermediates of the PLA₂-AA pathway.

Results

Compared with that in the Rc group, the escape latency in the Pc group significantly increased (p < 0.01); whereas, the platform crossover number and percentage of time and swimming distance in the platform quadrant decreased (p < 0.01). The hippocampal expression of PLA₂, cyclooxygenase-1, cytochrome P450 proteins 2C23 and the levels of AA, prostaglandin E₂ and epoxyeicosatrienoic acids of the Pc group was drastically higher than that in the Rc group (p < 0.01). These changes were reversed by MA and donepezil (p < 0.01 or p < 0.05).

Conclusion

MA can effectively improve the learning and memory abilities of SAMP8 mice and has a negative regulatory effect on the PLA₂-AA pathway. We propose that the increase of the arterial tone, which is induced by the inhibition of vasodilatory pathway, may be a reason for the beneficial effect of MA on CBF.

Tau as a potential therapeutic target for ischemic stroke

Tau is a protein mainly expressed in adult human brain. It plays important roles both in neurodegenerative diseases and stroke. Stroke is an important cause of adult death and disability, ischemic stroke almost account for 80% in all cases. Abundant studies have proven that the increase of dysfunctional tau may act as a vital factor in pathological changes after ischemic stroke. However, the relationship between tau and ischemic stroke remains ununified. Based on present studies, we firstly introduced the structure and biological function of tau protein. Secondly, we summarized the potential regulatory mechanisms of tau protein in the process of ischemic stroke. Thirdly, we discussed about the findings in therapeutic researches of ischemic stroke. This review may be helpful in implementing new therapies for ischemic stroke and may be beneficial for the clinical and experimental studies.

Association of Midlife to Late-Life Blood Pressure Patterns With Incident Dementia

Importance

The association between late-life blood pressure (BP) and cognition may depend on the presence and chronicity of past hypertension. Late-life declines in blood pressure following prolonged hypertension may be associated with poor cognitive outcomes.

Objective

To examine the association of midlife to late-life BP patterns with subsequent dementia, mild cognitive impairment, and cognitive decline.

Design, Setting, and Participants

The Atherosclerosis Risk in Communities prospective population-based cohort study enrolled 4761 participants during midlife (visit 1, 1987-1989) and followed-up over 6 visits through 2016-2017 (visit 6). BP was examined over 24 years at 5 in-person visits between visits 1 and 5 (2011-2013). During visits 5 and 6, participants underwent detailed neurocognitive evaluation. The setting was 4 US communities: Washington County, Maryland; Forsyth County, North Carolina; Jackson, Mississippi; and Minneapolis, Minnesota. Follow-up ended on December 31, 2017.

Exposures

Five groups based on longitudinal patterns of normotension, hypertension (>140/90 mm Hg), and hypotension (<90/60 mm Hg) at visits 1 to 5.

Main Outcomes and Measures

Primary outcome was dementia onset after visit 5, based on Ascertain Dementia-8 informant questionnaires, Six-Item Screener telephone assessments, hospital discharge and death certificate codes, and the visit 6 neurocognitive evaluation. Secondary outcome was mild cognitive impairment at visit 6, based on the neurocognitive evaluation.

Results

Among 4761 participants (2821 [59%] women; 979 [21%] black race; visit 5 mean [SD] age, 75 [5] years; visit 1 mean age range, 44-66 years; visit 5 mean age range, 66-90 years), there were 516 (11%) incident dementia cases between visits 5 and 6. The dementia incidence rate for participants with normotension in midlife (n = 833) and late life was 1.31 (95% CI, 1.00-1.72 per 100 person-years); for midlife normotension and late-life hypertension (n = 1559), 1.99 (95% CI, 1.69-2.32 per 100 person-years); for midlife and late-life hypertension (n = 1030), 2.83 (95% CI, 2.40-3.35 per 100 person-years); for midlife normotension and late-life hypotension (n = 927), 2.07 (95% CI, 1.68-2.54 per 100 person-years); and for midlife hypertension and late-life hypotension (n = 389), 4.26 (95% CI, 3.40-5.32 per 100 person-years). Participants in the midlife and late-life hypertension group (hazard ratio [HR], 1.49 [95% CI, 1.06-2.08]) and in the midlife hypertension and late-life hypotension group (HR, 1.62 [95% CI, 1.11-2.37]) had significantly increased risk of subsequent dementia compared with those who remained normotensive. Irrespective of late-life BP, sustained hypertension in midlife was associated with dementia risk (HR, 1.41 [95% CI, 1.17-1.71]). Compared with those who were normotensive in midlife and late life, only participants with midlife hypertension and late-life hypotension had higher risk of mild cognitive impairment (37 affected individuals (odds ratio, 1.65 [95% CI, 1.01-2.69]). There was no significant association of BP patterns with late-life cognitive change.

Conclusions and Relevance

In this community-based cohort with long-term follow-up, sustained hypertension in midlife to late life and a pattern of midlife hypertension and late-life hypotension, compared with midlife and late-life normal BP, were associated with increased risk for subsequent dementia.

Re-thinking the Etiological Framework of Neurodegeneration

Neurodegenerative diseases are among the leading causes of disability and death worldwide. The disease-related socioeconomic burden is expected to increase with the steadily increasing life expectancy. In spite of decades of clinical and basic research, most strategies designed to manage degenerative brain diseases are palliative. This is not surprising as neurodegeneration progresses "silently" for decades before symptoms are noticed. Importantly, conceptual models with heuristic value used to study neurodegeneration have been constructed retrospectively, based on signs and symptoms already present in affected patients; a circumstance that may confound causes and consequences. Hence, innovative, paradigm-shifting views of the etiology of these diseases are necessary to enable their timely prevention and treatment. Here, we outline four alternative views, not mutually exclusive, on different etiological paths toward neurodegeneration. First, we propose neurodegeneration as being a secondary outcome of a primary cardiovascular cause with vascular pathology disrupting the vital homeostatic interactions between the vasculature and the brain, resulting in cognitive impairment, dementia, and cerebrovascular events such as stroke. Second, we suggest that the persistence of senescent cells in neuronal circuits may favor, together with systemic metabolic diseases, neurodegeneration to occur. Third, we argue that neurodegeneration may start in response to altered body and brain trophic interactions established via the hardwire that connects peripheral targets with central neuronal structures or by means of extracellular vesicle (EV)-mediated communication. Lastly, we elaborate on how lifespan body dysbiosis may be linked to the origin of neurodegeneration. We highlight the existence of bacterial products that modulate the gut-brain axis causing neuroinflammation and neuronal dysfunction. As a concluding section, we end by recommending research avenues to investigate these etiological paths in the future. We think that this requires an integrated, interdisciplinary conceptual research approach based on the investigation of the multimodal aspects of physiology and pathophysiology. It involves utilizing proper conceptual models, experimental animal units, and identifying currently unused opportunities derived from human data. Overall, the proposed etiological paths and experimental recommendations will be important guidelines for future cross-discipline research to overcome the translational roadblock and to develop causative treatments for neurodegenerative diseases.

Plasma Amyloid Beta and Tau Levels Are Predictors of Post-stroke Cognitive Impairment: A Longitudinal Study

Objectives: Post-stroke cognitive impairment (PSCI) is a common disease that may occur within 3 months after a stroke or even later. However, the mechanism of PSCI development is unclear. The present study investigated whether the levels of plasma amyloid beta-42 (Aβ42) and tau are associated with the onset of PSCI. Methods: Fifty-five patients admitted within 7 days of acute ischemic stroke were enrolled and followed up for 1 year. Montreal Cognitive Assessment (MoCA) was administered at 3 months and 1 year, and plasma Aβ42 and tau levels were determined using an ultrasensitive immunoassay (immunomagnetic reduction) within 7 days of the stroke event and 3 months later. Results: In this study, 13 of 55 patients developed PSCI (MoCA score <23) at 3 months. Seven patients with PSCI at 3 months recovered to a cognitively normal state at 1 year, whereas seven cognitively normal patients developed PSCI at 1 year. The patients with PSCI at 1 year had a higher incidence of cognitive function deterioration between 3 months and 1 year compared with those without PSCI at 1 year. Plasma Aβ42 and tau levels at 3 months were lower in the patients with PSCI at 1 year than in those without PSCI (Aβ42: 15.1 vs. 17.2 pg/mL, P = 0.013; tau: 16.7 vs. 19.9 pg/mL, P = 0.018). Low education levels and pre-existing white matter disease were the most significant predictors of PSCI at 3 months, and poor cognitive performance at 3 months and low plasma Aβ42 and tau levels at 3 months were the most significant predictors of PSCI at 1 year. Conclusion: The pathogenesis of PSCI is complex and changes with time. Ischemia-induced Aβ42/tau pathology might be involved in PSCI development.

Low Cerebrospinal Fluid Aβ42 and Aβ40 are Related to White Matter Lesions in Cognitively Normal Elderly

Background:

Low cerebrospinal fluid (CSF) levels of Aβ₄₂ may be the earliest manifestation of Alzheimer’s disease (AD). Knowledge on how CSF Aβ interacts with different brain pathologies early in the disease process is limited. We examined how CSF Aβ markers relate to brain atrophy and white matter lesions (WMLs) in octogenarians with and without dementia to explore the earliest pathogenetic pathways of AD in the oldest old.

Objective:

To study CSF amyloid biomarkers in relation to brain atrophy and WMLs in 85-year-olds with and without dementia.

Methods:

53 octogenarians took part in neuropsychiatric examinations and underwent both a lumbar puncture and a brain CT scan. CSF levels of Aβ₄₂ and Aβ₄₀ were examined in relation to cerebral atrophy and WMLs. Dementia was diagnosed.

Results:

In 85-year-olds without dementia, lower levels of both CSF Aβ₄₂ and CSF Aβ₄₀ were associated with WMLs. CSF Aβ₄₂ also correlated with measures of central atrophy, but not with cortical atrophy. In participants with dementia, lower CSF levels of Aβ₄₂ were related to frontal, temporal, and parietal cortical atrophy but not to WMLs.

Conclusions:

Our findings may suggest that there is an interrelationship between Aβ and subcortical WMLs in older persons without dementia. After onset of dementia, low CSF Aβ₄₂, probably representing amyloid deposition in plaques, is associated with cortical atrophy. WMLs may be an earlier manifestation of Aβ deposition than cortical degeneration.

Brain-derived and circulating vesicle profiles indicate neurovascular unit dysfunction in early Alzheimer's disease

Vascular factors that reduce blood flow to the brain are involved in apparition and progression of dementia. We hypothesized that cerebral hypoperfusion (CH) might alter the molecular compositions of brain intercellular communication mechanisms while affecting the neurovascular unit in preclinical and clinical human dementias. To test that hypothesis, mice were subjected to bilateral common carotid stenosis (BCAS) and the molecular compositions of brain-derived and circulating extracellular vesicles (EVs) were assessed. Murine brain vesicle profiles were then analyzed in parallel with brain EVs from post-mortem subjects affected by preclinical Alzheimer's Disease (AD) and mixed dementias. Brain EVs were identified with molecular mediators of hypoxia responses, neuroprotection and neurotoxicity in BCAS mice, patterns also partially resembled by subjects with preclinical AD and mixed dementias. Together these findings indicate that brain EVs represent a promising source of therapeutic targets and circulating markers of neurovascular insult in idiopathic dementias. Furthermore, the results obtained generate novel and compelling hypotheses about the molecular involvement of the vascular component in the etiology of human dementias.

Visualization of ischemic stroke-related changes on 18F-THK-5351 positron emission tomography

Background

The ¹⁸F-THK-5351 radiotracer has been used to detect the in vivo tau protein distribution in patients with tauopathy, such as Alzheimer’s disease and corticobasal syndrome. In addition, ¹⁸F-THK-5351 can also monitor neuroinflammatory process due to high affinity to astrogliosis. We aimed to explore ¹⁸F-THK-5351 distribution patterns and characteristics in patients with recent ischemic stroke.

Results

Fifteen patients received ¹⁸F-THK-5351 positron emission tomography (PET) and diffusion tensor imaging (DTI) approximately 3 months after ischemic stroke. A region of interest (ROI) was placed in the peri-ischemic area and was mirrored on the contralateral side as the control, and a proportional value was derived from the ratio of the peri-ischemic ROI value over the mirrored ROI value. Increased ¹⁸F-THK-5351 retention was observed in the areas around and remote from the stroke location. The proportional ¹⁸F-THK-5351 values were negatively correlated with the proportional fractional anisotropy values (r = − 0.39, P = 0.04).

Conclusion

¹⁸F-THK-5351 PET imaging provides a potential tool for in vivo visualization of the widespread ischemia-related changes associated with a microstructural disruption in recent ischemic stroke patients.

Electronic supplementary material

The online version of this article (10.1186/s13550-018-0417-1) contains supplementary material, which is available to authorized users.

The effect of white matter hyperintensities on cognition is mediated by cortical atrophy

White matter hyperintensities (WMH) have been linked to cognitive dysfunction and dementia, although the reasons are unclear. One possibility is that WMH promote neurodegeneration, which, in turn, affects cognition. We examined whether cortical thickness, a marker of neurodegeneration, mediates the relationship between WMH and cognition among 519 older adults. Using conditional process analysis modeling techniques, we examined the association between WMH volume and global cognition and tested whether cortical thickness mediates this relationship statistically. We also tested specific regional hypotheses to determine whether cortical thickness or volume in the medial temporal lobe mediates the relationship between WMH volume and memory. Increased total WMH volume was associated with poorer global cognition and memory. Global cortical thickness and medial temporal lobe thickness/volume mediated the relationship of WMH volume on global cognition and memory functioning. The mediating relationship was similar across racial and ethnic groups and across diagnostic groups (i.e., mild cognitive impairment/Alzheimer's disease). The findings suggest that WMH promote atrophy, which, in turn, drives cognitive decline and highlight a potential pathway in which small vessel cerebrovascular disease affects cognition by promoting neurodegenerative changes directly.

Cognitive impairment and intracranial atherosclerotic stenosis in general population

OBJECTIVE

To investigate the association between asymptomatic intracranial atherosclerosis and cognitive impairment in the Atherosclerosis Risk in Communities (ARIC) cohort.

METHODS

ARIC participants underwent high-resolution 3T magnetic resonance angiography and a neuropsychology battery and neurologic examination adjudicated by an expert panel to detect mild cognitive impairment (MCI) and dementia. We adjusted for demographic and vascular risk factors in weighted logistic regression analysis, accounting for stratified sampling design and attrition, to determine the association of intracranial atherosclerotic stenosis (ICAS) with cognitive impairment.

RESULTS

In 1,701 participants (mean age 76 ± 5.3, 41% men, 71% whites, 29% blacks) with adequate imaging quality and no history of stroke, MCI was identified in 578 (34%) and dementia in 79 (4.6%). In white participants, after adjustment for demographic and vascular risk factors, ICAS ≥50% (vs no ICAS) was strongly associated with dementia (odds ratio [OR] 4.1, 95% confidence interval [CI] 1.7-10.0) and with any cognitive impairment (OR 1.7, 95% CI 1.1-2.8). In contrast, no association was found between ICAS ≥50% and MCI or dementia in blacks, although the sample size was limited and estimates were imprecise.

CONCLUSION

Our results suggest that asymptomatic ICAS is independently associated with cognitive impairment and dementia in whites.