Update on hypertension and Alzheimer's disease

Revised Framingham Stroke Risk Profile: Association with Cognitive Status and MRI-Derived Volumetric Measures

BACKGROUND

The Framingham Stroke Risk Profile (FSRP) was created in 1991 to estimate 10-year risk of stroke. It was revised in 2017 (rFSRP) to reflect the modern data on vascular risk factors and stroke risk.

OBJECTIVE

This study examined the association between the rFSRP and cognitive and brain aging outcomes among participants from the National Alzheimer's Coordinating Center (NACC) Uniform Data Set (UDS).

METHODS

Cross-sectional rFSRP was computed at baseline for 19,309 participants (mean age = 72.84, SD = 8.48) from the NACC-UDS [9,697 (50.2%) normal cognition, 4,705 (24.4%) MCI, 4,907 (25.4%) dementia]. Multivariable linear, logistic, or ordinal regressions examined the association between the rFSRP and diagnostic status, neuropsychological test performance, CDR® Sum of Boxes, as well as total brain volume (TBV), hippocampal volume (HCV), and log-transformed white matter hyperintensities (WMH) for an MRI subset (n = 1,196). Models controlled for age, sex, education, racial identity, APOEɛ4 status, and estimated intracranial volume for MRI models.

RESULTS

The mean rFSRP probability was 10.42% (min = 0.50%, max = 95.71%). Higher rFSRP scores corresponded to greater CDR Sum of Boxes (β= 0.02, p = 0.028) and worse performance on: Trail Making Test A (β= 0.05, p < 0.001) and B (β= 0.057, p < 0.001), and Digit Symbol (β= -0.058, p < 0.001). Higher rFSRP scores were associated with increased odds for a greater volume of log-transformed WMH (OR = 1.02 per quartile, p = 0.015). No associations were observed for diagnosis, episodic memory or language test scores, HCV, or TBV.

CONCLUSION

These results support the rFSRP as a useful metric to facilitate clinical research on the associations between cerebrovascular disease and cognitive and brain aging.

Comorbidity of age-related macular degeneration with Alzheimer's disease: A histopathologic case-control study

Introduction

Previous studies evaluating the association between clinically diagnosed Alzheimer’s disease (AD) and age-related macular degeneration (AMD) have generated conflicting results. This study is the first to assess whether AMD prevalence is higher in AD patients than non-AD controls by using histopathology to definitively diagnose AD.

Methods

This was a retrospective case-control study utilizing diagnostic information extracted from autopsy reports of patients age 75 and above, including 115 with a neuropathological diagnosis of AD and 57 age-matched normal controls.

Results

The rate of AMD was not significantly higher in AD cases (53.0%) than in controls (59.6%) (z = 0.820, p = 0.794). AMD severity as determined by Sarks score was similar between AD patients and controls (χ² = 2.96, p = 0.706). There was also no significant association between Braak stage of AD severity and AMD (χ² = 4.55, p = 0.602).

Discussion

No significant effect of AD diagnosis or pathologic severity on AMD comorbidity was found, suggesting that any shared mechanisms between AMD and AD may be nondeterministic.

Alzheimer's disease and symbiotic microbiota: an evolutionary medicine perspective

Microorganisms resident in our bodies participate in a variety of regulatory and pathogenic processes. Here, we describe how etiological pathways implicated in Alzheimer's disease (AD) may be regulated or disturbed by symbiotic microbial activity. Furthermore, the composition of symbiotic microbes has changed dramatically across human history alongside the rise of agriculturalism, industrialization, and globalization. We postulate that each of these lifestyle transitions engendered progressive depletion of microbial diversity and enhancement of virulence, thereby enhancing AD risk pathways. It is likely that the human life span extended into the eighth decade tens of thousands of years ago, yet little is known about premodern geriatric epidemiology. We propose that microbiota of the gut, oral cavity, nasal cavity, and brain may modulate AD pathogenesis, and that changes in the microbial composition of these body regions across history suggest escalation of AD risk. Dysbiosis may promote immunoregulatory dysfunction due to inadequate education of the immune system, chronic inflammation, and epithelial barrier permeability. Subsequently, proinflammatory agents-and occasionally microbes-may infiltrate the brain and promote AD pathogenic processes. APOE genotypes appear to moderate the effect of dysbiosis on AD risk. Elucidating the effect of symbiotic microbiota on AD pathogenesis could contribute to basic and translational research.

ASSOCIATION OF DEPRESSIVE SYMPTOMS AND SUBJECTIVE MEMORY COMPLAINTS WITH THE INCIDENCE OF COGNITIVE IMPAIRMENT IN OLDER ADULTS WITH HIGH BLOOD PRESSURE

PURPOSE

High blood pressure is a relevant risk factor for vascular damage, leading to development of depressive symptoms and dementia in older adults. Moreover, subjective memory complaints are recognized as an early marker of cognitive impairment. However, it has been established that subjective memory complaints could also be a reflection of depressive symptoms. The objective of this paper is to assess the impact of depressive symptoms and subjective memory complaints on the incidence of cognitive impairment in older adults with high blood pressure.

METHODS

This is a secondary analysis of the Mexican Health and Aging Study, a representative cohort composed by individuals aged ≥ 50 years. Participants with cognitive impairment in 2012 were excluded since the outcome was incident cognitive impairment in 2015. Four groups were created according to depressive symptomatology and subjective memory complaints status, analyses were stratified according to blood pressure status. The odds incident cognitive impairment was estimated through logistic regression models.

RESULTS

A total of 6,327 participants were included, from which 6.44% developed cognitive impairment. No differences were seen regarding the development of cognitive impairment in participants without high blood pressure. However, increased risk was evident in those with both high blood pressure and depressive symptoms (OR=2.1, 95% CI 1.09 - 4.09, p =0.026) as with high blood pressure, depressive symptoms and subjective memory complaints (OR=1.91, 9% CI 1.4 - 3.2, p= 0.001).

CONCLUSION

Individuals with high blood pressure have a higher risk of developing incident cognitive impairment when depressive symptoms and/or subjective memory complaints are present. Our results suggest that a sequence of events related to altered cerebral vascular dynamics is possible.

The Coming of Age of the Angiotensin Hypothesis in Alzheimer's Disease: Progress Toward Disease Prevention and Treatment?

There is wide recognition of a complex association between midlife hypertension and cardiovascular disease and later development of Alzheimer’s disease (AD) and cognitive impairment. While significant progress has been made in reducing rates of mortality and morbidity due to cardiovascular disease over the last thirty years, progress towards effective treatments for AD has been slower. Despite the known association between hypertension and dementia, research into each disease has largely been undertaken in parallel and independently. Yet over the last decade and a half, the emergence of converging findings from pre-clinical and clinical research has shown how the renin angiotensin system (RAS), which is very important in blood pressure regulation and cardiovascular disease, warrants careful consideration in the pathogenesis of AD. Numerous components of the RAS have now been found to be altered in AD such that the multifunctional and potent vasoconstrictor angiotensin II, and similarly acting angiotensin III, are greatly altered at the expense of other RAS signaling peptides considered to contribute to neuronal and cognitive function. Collectively these changes may contribute to many of the neuropathological hallmarks of AD, as well as observed progressive deficiencies in cognitive function, while also linking elements of a number of the proposed hypotheses for the cause of AD. This review discusses the emergence of the RAS and its likely importance in AD, not only because of the multiple facets of its involvement, but also perhaps fortuitously because of the ready availability of numerous RAS-acting drugs, that could be repurposed as interventions in AD.

Alzheimer's disease: risk factors and potentially protective measures

Alzheimer's disease (AD) is the most common type of dementia and typically manifests through a progressive loss of episodic memory and cognitive function, subsequently causing language and visuospatial skills deficiencies, which are often accompanied by behavioral disorders such as apathy, aggressiveness and depression. The presence of extracellular plaques of insoluble β-amyloid peptide (Aβ) and neurofibrillary tangles (NFT) containing hyperphosphorylated tau protein (P-tau) in the neuronal cytoplasm is a remarkable pathophysiological cause in patients' brains. Approximately 70% of the risk of developing AD can be attributed to genetics. However, acquired factors such as cerebrovascular diseases, diabetes, hypertension, obesity and dyslipidemia increase the risk of AD development. The aim of the present minireview was to summarize the pathophysiological mechanism and the main risk factors for AD. As a complement, some protective factors associated with a lower risk of disease incidence, such as cognitive reserve, physical activity and diet will also be addressed.

Dysregulation of Transcription Factors: A Key Culprit Behind Neurodegenerative Disorders

Neurodegenerative diseases (NDs) are considered heterogeneous disorders characterized by progressive pathological changes in neuronal systems. Transcription factors are protein molecules that are important in regulating the expression of genes. Although the clinical manifestations of NDs vary, the pathological processes appear similar with regard to neuroinflammation, oxidative stress, and proteostasis, to which, as numerous studies have discovered, transcription factors are closely linked. In this review, we summarized and reviewed the roles of transcription factors in NDs, and then we elucidated their functions during pathological processes, and finally we discussed their therapeutic values in NDs.

Oxidative Stress: A Major Player in Cerebrovascular Alterations Associated to Neurodegenerative Events

The brain is one of the most exquisite organs in the body with high metabolic demands, and requires a tight regulation of the surrounding environment. This tight control is exerted by the neurovascular unit (NVU) comprising different cell types, where endothelial cells play the commander-in-chief role. Thus, it is assumable that even slight perturbations in NVU might affect, in some cases irreversibly, brain homeostasis and health. In this line, recent findings support the two-hit vascular hypothesis for neurodegenerative conditions, where vascular dysfunction underlies the development of neurodegenerative diseases, such as Alzheimer’s disease (AD). Knowing that endothelial cells are rich in mitochondria and nicotinamide adenine dinucleotide phosphate (NADPH) oxidases, two major reactive oxygen species (ROS) sources, this review aims to gather information on how oxidative stress is in the front line of vascular alterations observed in brain aging and neurodegenerative conditions, particularly AD. Also, a brief discussion about the therapeutic strategies aimed to protect against cerebrovascular diseases is included.

Maternal high-salt diet alters redox state and mitochondrial function in newborn rat offspring's brain

Excessive salt intake is a common feature of Western dietary patterns, and has been associated with important metabolic changes including cerebral redox state imbalance. Considering that little is known about the effect on progeny of excessive salt intake during pregnancy, the present study investigated the effect of a high-salt diet during pregnancy and lactation on mitochondrial parameters and the redox state of the brains of resulting offspring. Adult female Wistar rats were divided into two dietary groups (n 20 rats/group): control standard chow (0·675 % NaCl) or high-salt chow (7·2 % NaCl), received throughout pregnancy and for 7 d after delivery. On postnatal day 7, the pups were euthanised and their cerebellum, hypothalamus, hippocampus, prefrontal and parietal cortices were dissected. Maternal high-salt diet reduced cerebellar mitochondrial mass and membrane potential, promoted an increase in reactive oxygen species allied to superoxide dismutase activation and decreased offspring cerebellar nitric oxide levels. A significant increase in hypothalamic nitric oxide levels and mitochondrial superoxide in the hippocampus and prefrontal cortex was observed in the maternal high-salt group. Antioxidant enzymes were differentially modulated by oxidant increases in each brain area studied. Taken together, our results suggest that a maternal high-salt diet during pregnancy and lactation programmes the brain metabolism of offspring, favouring impaired mitochondrial function and promoting an oxidative environment; this highlights the adverse effect of high-salt intake in the health state of the offspring.

High-Sodium Diet Has Opposing Effects on Mean Arterial Blood Pressure and Cerebral Perfusion in a Transgenic Mouse Model of Alzheimer's Disease

BACKGROUND

Cerebral ionic homeostasis impairment, especially Ca2+, has been observed in Alzheimer's disease (AD) and also with hypertension. Hypertension and AD both have been implicated in impaired cerebral autoregulation. However, the relationship between the ionic homeostasis impairment in AD and hypertension and cerebral blood flow (CBF) autoregulation is not clear.

OBJECTIVE

To test the hypothesis that a high-salt diet regimen influences the accumulation of amyloid-β (Aβand CBF) and CBF, exacerbates cognitive decline, and increases the propensity to AD.

METHODS

Double transgenic mice harboring the amyloid-β protein precursor (APPswe), and presenilin-1 (PSEN1) along with control littermates, 2 months of age at initiation of special diet, were divided into 4 groups: Group A, APP/PS1 and Group B, controls fed a high-sodium (4.00%) chow diet for 3 months; Group C, APP/PS1 and Group D, controls fed a low-sodium (0.08%) regular chow diet for 3 months. Mean arterial blood pressure (MAP) and CBF were measured noninvasively using the tail MAP measurement device and magnetic resonance imaging, respectively. Aβ plaques numbers in the cortex and hippocampus of APP/PS1 were quantified.

RESULTS

In contrary to controls, APP/PS1 mice fed a high-salt diet did not show markedly elevated mean systolic and diastolic blood pressure (134±4.8 compared with 162±2.8 mmHg, and 114±5.0 compared with 137±20 mmHg, p< 0.0001). However, a high-salt diet increased CBF in both APP/PS1 and controls and did not alter the cerebral tissue integrity. Aβ plaques were significantly reduced in the cortex and hippocampus of mice fed a high-salt diet.

CONCLUSION

These data suggest that a high-salt diet differently affects MAP and CBF in APP/PS1 mice and controls.

Prevalence of Mild Cognitive Impairment and Its Subtypes among Chinese Older Adults: Role of Vascular Risk Factors

BACKGROUND/AIMS

The prevalence of mild cognitive impairment (MCI) and its subtypes among Chinese older adults, and the contribution of vascular risk factors (VRF) and vascular disorders to MCI remain unclear. This study aims to investigate the prevalence of MCI and its different subtypes, and clarify the role of VRF and vascular diseases in the occurrence of MCI.

METHODS

A random sample of 5,214 nondementia (DSM-IV) individuals aged ≥65 years underwent neuropsychological assessments and clinical examinations. MCI, including amnestic MCI-single domain (aMCI-SD), amnestic MCI-multiple domains (aMCI-MD), nonamnestic MCI-single domain (naMCI-SD), and nonamnestic MCI-multiple domains (naMCI-MD), was defined according to modifications of the Petersen criteria. VRF (smoking, obesity, and diabetes) and vascular disorders (myocardial infarction, atrial xFB01;brillation, stroke, and hypertension) were assessed based on information through self-report and medical records. Data were analyzed using multivariate logistic regression.

RESULTS

The prevalence of MCI was 11.33% (95% CI: 8.21-14.43), and that of aMCI-SD, aMCI-MD, naMCI-SD, and naMCI-MD was 4.48% (95% CI: 2.24-6.74), 2.09% (95% CI: 0.80-3.38), 4.22% (95% CI: 1.38-7.08), and 0.53% (95% CI: 0.32-0.75), respectively. The prevalence of MCI is higher in women than in men. Multivariate logistic regression analysis shows that VRF and vascular diseases were significantly related to increase the odds of MCI and its specific subtype.

CONCLUSIONS

The prevalence of MCI is almost 11% among Chinese older adults. VRF and vascular disorders are associated with MCI, especially naMCI.

Assessment of Basilar Artery Reactivity in Stroke and Subarachnoid Hemorrhage Using Wire Myograph

Blood flow regulation of normal cerebral arteries is a critical and important factor to supply the brain tissue with nutrients and oxygen. Stroke insult results in a disruption or reduction in cerebral arteries' blood flow with subsequent brain tissue damage. Hemorrhagic stroke is one type of stroke and accounts for about 13 % of all of stroke insults. In this type of stroke, the cerebral artery breaks open and causes bleeding in or surrounding the brain. Subsequently, this bleeding causes blood vessels to constrict in a process called vasospasm, in which the vessels narrow and impede the blood flow to brain tissue. Hemorrhagic stroke is the major cause of prolonged constriction of cerebral arteries. This leads to partial brain damage and sometimes death in patients with aneurysmal subarachnoid hemorrhage. Among the key delicate techniques to assess small blood vessel functionality is the wire myograph, which can be utilized in several cerebral injury models including stroke. The wire myograph is a device that provides information about the reactivity, stiffness, and elasticity of small blood vessels under isometric conditions. In this book chapter, we describe the techniques involved in wire myography assessment and the different measures and parameters recorded; we describe the utility of this technique in evaluating the effects of subarachnoid hemorrhage on basilar artery sensitivity to different agonists.

N-domain of angiotensin-converting enzyme hydrolyzes human and rat amyloid-β(1-16) peptides as arginine specific endopeptidase potentially enhancing risk of Alzheimer's disease

Alzheimer’s disease (AD) is a multifactorial neurodegenerative disorder. Amyloid-β (Aβ) aggregation is likely to be the major cause of AD. In contrast to humans and other mammals, that share the same Aβ sequence, rats and mice are invulnerable to AD-like neurodegenerative pathologies, and Aβ of these rodents (ratAβ) has three amino acid substitutions in the metal-binding domain 1-16 (MBD). Angiotensin-converting enzyme (ACE) cleaves Aβ-derived peptide substrates, however, there are contradictions concerning the localization of the cleavage sites within Aβ and the roles of each of the two ACE catalytically active domains in the hydrolysis. In the current study by using mass spectrometry and molecular modelling we have tested a set of peptides corresponding to MBDs of Aβ and ratAβ to get insights on the interactions between ACE and these Aβ species. It has been shown that the N-domain of ACE (N-ACE) acts as an arginine specific endopeptidase on the Aβ and ratAβ MBDs with C-amidated termini, thus assuming that full-length Aβ and ratAβ can be hydrolyzed by N-ACE in the same endopeptidase mode. Taken together with the recent data on the molecular mechanism of zinc-dependent oligomerization of Aβ, our results suggest a modulating role of N-ACE in AD pathogenesis.

The Rationale and Design of the Reducing Pathology in Alzheimer's Disease through Angiotensin TaRgeting (RADAR) Trial

BACKGROUND

Anti-hypertensives that modify the renin angiotensin system may reduce Alzheimer's disease (AD) pathology and reduce the rate of disease progression.

OBJECTIVE

To conduct a phase II, two arm, double-blind, placebo-controlled, randomized trial of losartan to test the efficacy of Reducing pathology in Alzheimer's Disease through Angiotensin TaRgeting (RADAR).

METHODS

Men and women aged at least 55 years with mild-to-moderate AD will be randomly allocated 100 mg encapsulated generic losartan or placebo once daily for 12 months after successful completion of a 2-week open-label phase and 2-week placebo washout to establish drug tolerability. 228 participants will provide at least 182 subjects with final assessments to provide 84% power to detect a 25% difference in atrophy rate (therapeutic benefit) change over 12 months at an alpha level of 0.05. We will use intention-to-treat analysis, estimating between-group differences in outcomes derived from appropriate (linear or logistic) multivariable regression models adjusting for minimization variables.

RESULTS

The primary outcome will be rate of whole brain atrophy as a surrogate measure of disease progression. Secondary outcomes will include changes to 1) white matter hyperintensity volume and cerebral blood flow; 2) performance on a standard series of assessments of memory, cognitive function, activities of daily living, and quality of life. Major assessments (for all outcomes) and relevant safety monitoring of blood pressure and bloods will be at baseline and 12 months. Additional cognitive assessment will also be conducted at 6 months along with safety blood pressure and blood monitoring. Monitoring of blood pressure, bloods, and self-reported side effects will occur during the open-label phase and during the majority of the post-randomization dispensing visits.

CONCLUSION

This study will identify whether losartan is efficacious in the treatment of AD and whether definitive Phase III trials are warranted.

Increased pulmonary arteriolar tone associated with lung oxidative stress and nitric oxide in a mouse model of Alzheimer's disease

Vascular dysfunction and decreased cerebral blood flow are linked to Alzheimer's disease (AD). Loss of endothelial nitric oxide (NO) and oxidative stress in human cerebrovascular endothelium increase expression of amyloid precursor protein (APP) and enhance production of the Aβ peptide, suggesting that loss of endothelial NO contributes to AD pathology. We hypothesize that decreased systemic NO bioavailability in AD may also impact lung microcirculation and induce pulmonary endothelial dysfunction. The acute effect of NO synthase (NOS) inhibition on pulmonary arteriolar tone was assessed in a transgenic mouse model (TgAD) of AD (C57BL/6‐Tg(Thy1‐APPSwDutIowa)BWevn/Mmjax) and age‐matched wild‐type controls (C57BL/6J). Arteriolar diameters were measured before and after the administration of the NOS inhibitor, L‐NAME. Lung superoxide formation (DHE) and formation of nitrotyrosine (3‐NT) were assessed as indicators of oxidative stress, inducible NOS (iNOS) and tumor necrosis factor alpha (TNF‐α) expression as indicators of inflammation. Administration of L‐NAME caused either significant pulmonary arteriolar constriction or no change from baseline tone in wild‐type (WT) mice, and significant arteriolar dilation in TgAD mice. DHE, 3‐NT, TNF‐α, and iNOS expression were higher in TgAD lung tissue, compared to WT mice. These data suggest L‐NAME could induce increased pulmonary arteriolar tone in WT mice from loss of bioavailable NO. In contrast, NOS inhibition with L‐NAME had a vasodilator effect in TgAD mice, potentially caused by decreased reactive nitrogen species formation, while significant oxidative stress and inflammation were present. We conclude that AD may increase pulmonary microvascular tone as a result of loss of bioavailable NO and increased oxidative stress. Our findings suggest that AD may have systemic microvascular implications beyond central neural control mechanisms.

Hypertension impairs neurovascular coupling and promotes microvascular injury: role in exacerbation of Alzheimer's disease

Hypertension in the elderly substantially increases both the risk of vascular cognitive impairment (VCI) and Alzheimer's disease (AD); however, the underlying mechanisms are not completely understood. This review discusses the effects of hypertension on structural and functional integrity of cerebral microcirculation, including hypertension-induced alterations in neurovascular coupling responses, cellular and molecular mechanisms involved in microvascular damage (capillary rarefaction, blood-brain barrier disruption), and the genesis of cerebral microhemorrhages and their potential role in exacerbation of cognitive decline associated with AD. Understanding and targeting the hypertension-induced cerebromicrovascular alterations that are involved in the onset and progression of AD and contribute to cognitive impairment are expected to have a major role in preserving brain health in high-risk older individuals.

Towards the virtual human patient. Quantitative Systems Pharmacology in Alzheimer's disease

Development of successful therapeutic interventions in Central Nervous Systems (CNS) disorders is a daunting challenge with a low success rate. Probable reasons include the lack of translation from preclinical animal models, the individual variability of many pathological processes converging upon the same clinical phenotype, the pharmacodynamical interaction of various comedications and last but not least the complexity of the human brain. This paper argues for a re-engineering of the pharmaceutical CNS Research & Development strategy using ideas focused on advanced computer modeling and simulation from adjacent engineering-based industries. We provide examples that such a Quantitative Systems Pharmacology approach based on computer simulation of biological processes and that combines the best of preclinical research with actual clinical outcomes can enhance translation to the clinical situation. We will expand upon (1) the need to go from Big Data to Smart Data and develop predictive and quantitative algorithms that are actionable for the pharma industry, (2) using this platform as a "knowledge machine" that captures community-wide expertise in an active hypothesis-testing approach, (3) learning from failed clinical trials and (4) the need to go beyond simple linear hypotheses and embrace complex non-linear hypotheses. We will propose a strategy for applying these concepts to the substantial individual variability of AD patient subgroups and the treatment of neuropsychiatric problems in AD. Quantitative Systems Pharmacology is a new 'humanized' tool for supporting drug discovery and development in general and CNS disorders in particular.

Hyperinsulinemia and elevated systolic blood pressure independently predict white matter hyperintensities with associated cognitive decrement in the middle-aged offspring of dementia patients

Cerebrovascular disease is an independent risk factor for dementia that may also be synergistic with Alzheimer's disease. In recent years attention has switched from cerebral infarcts to microvascular disease as the primary cause of cerebrovascular cognitive decline, with damage to the white matter the primary mechanism. Uncertainties remain regarding the risks posed by different types vascular threat, the extent to which cerebrovascular damage occurs in middle age, and whether relatively "normal" amounts of white matter damage are accompanied by meaningful degrees of cognitive decline. We explored these issues via laboratory, cardiovascular, cognitive, and magnetic resonance imaging (MRI) data in 67 middle-aged cognitively normal offspring of dementia patients. The sample was enriched for vascular risk. Plasma insulin, 24-h systolic blood pressure, body mass index, age, and % small dense LDL cholesterol were the strongest correlates of MRI white matter hyperintensity (WMH) volume. With shared variance controlled for, 24 h systolic BP, plasma insulin, and age remained as significant predictors of WMH volume. An interaction variable (24 h BP * insulin) did not improve the prediction of WMH. WMH volume correlated negatively with cognition. No evidence for an ApoE ε4 effect emerged for either WMH or cognition. Hypertension and hyperinsulinemia appear to pose independent, consequential threats to the cerebral small vessel vasculature in middle age, reflected in the presence of areas of WMH on MRI scans. Our data show that even modest WMH volumes in middle age are associated with cognitive decrement, underscoring the importance of aggressive treatment and lifestyle modifications to address vascular risk throughout adulthood.

Memory is preserved in older adults taking AT1 receptor blockers

Background

Prior work suggests that some but not all antihypertensive treatments may benefit cognition and risk for Alzheimer’s disease, independent of stroke. Angiotensin II receptor blockers (ARBs) have been highlighted as one antihypertensive drug class that may confer greatest benefit.

Methods

The participants comprised 1626 nondemented adults, aged 55–91 years, recruited from Alzheimer’s Disease Neuroimaging Initiative sites. Three groups were compared: ARB users (HTN-ARBs), other antihypertensive drug users (HTN-Other), and normotensives. In post hoc analyses, we also examined (1) users of ARBs and angiotensin-converting enzyme inhibitors (ACEIs), (2) users of blood-brain barrier (BBB)-crossing ARBs and users of non-BBB-crossing ARBs, and (3) users of BBB-crossing ARBs and ACEIs (BBB crossers) and users of non-BBB-crossing ARBs and ACEIs (BBB noncrossers). Groups were compared regarding cognition and magnetic resonance imaging measures of brain volume and white matter hyperintensities (WMH), using analysis of covariance and multilevel models.

Results

At baseline, the HTN-Other group performed worse than normotensives on Rey Auditory Verbal Learning Test (RAVLT) Immediate Recall (p = 0.002), Delayed Recall (p < 0.001), Recognition Memory (p = 0.001), and Trails A (p < 0.001) and B (p = 0.01). ARB users performed better than the HTN-Other group on Recognition Memory (p = 0.04) and worse than normotensives on Trails A (p = 0.04). The HTN-Other group performed worse than normotensives on Logical Memory Immediate (p = 0.02) and Delayed Recall over the 3-year follow-up (p = 0.007). Over the follow-up period, those taking BBB-crossing ARBs performed better than the HTN-Other group on AVLT Delayed Recall (p = 0.04), Logical Memory Immediate (p = 0.02), and Delayed Recall (p = 0.05). They also had fewer WMH than the HTN-Other group (p = 0.008) and those taking non-BBB-crossing ARBs (p = 0.05). There were no group differences in brain volume. Users of BBB-crossing medications (ARBs or ACEIs) showed better performance on AVLT Delayed Recall over time than all other groups, including normotensives (all p < 0.01), and had less WMH volume over time than the BBB noncrossers group (p = 0.03), although they had more WMH volume than normotensives (p = 0.01). The BBB noncrossers group performed worse than normotensives on Logical Memory Delayed Recall over time (p = 0.01), but the BBB crossers group was not significantly different (p = 0.13).

Conclusions

Hypertensive participants demonstrated worse baseline memory and executive function, as well as greater memory decline, over the 3-year follow-up than normotensives, unless they were ARB users, who showed preserved memory compared with those taking other antihypertensive drugs. Users of BBB-crossing ARBs showed superior memory performance over time compared with other antihypertensive drug users and had less WMH volume. Users of BBB-crossing medications (ARBs or ACEIs) showed better list-learning memory performance over time than all other groups, including normotensives, and had less WMH volume over time than users of non-BBB-crossing medications. These findings demonstrate that ARBs, especially those of the BBB-crossing variety, are associated with greater memory preservation and less WMH volume than other antihypertensive medications.

Electronic supplementary material

The online version of this article (doi:10.1186/s13195-017-0255-9) contains supplementary material, which is available to authorized users.

Elevated Soluble Vascular Cell Adhesion Molecule-1 Is Associated With Cerebrovascular Resistance and Cognitive Function

BACKGROUND

Elevated plasma soluble vascular cell adhesion molecule-1 (sVCAM-1) is a presumed marker of endothelial dysfunction, both in the brain and systemic circulation. Impairments in memory and cognition have been associated with cardiovascular diseases, but little is known about their relationships to abnormal cerebral endothelial function.

METHODS

We studied the cross-sectional association between sVCAM-1 and markers of cerebrovascular hemodynamics and cognitive function in 680 community-dwelling participants in the MOBILIZE Boston Study, aged 65 years and older. Cognitive function was assessed using the Hopkins Verbal Learning Memory Test and Trail Making Tests (TMTs) A and B. Global cognitive impairment was defined as Mini-Mental State Examination (MMSE) score less than 24. sVCAM-1 was measured by ELISA assay. Beat-to-beat blood flow velocity (BFV) and cerebrovascular resistance (CVR = mean arterial pressure / BFV) in the middle cerebral artery were assessed at rest by transcranial Doppler ultrasound.

RESULTS

sVCAM-1 concentrations were higher among participants with an MMSE score <24 versus ≥24 (1,201±417 vs 1,122±494ng/mL). In regression models adjusted for sociodemographic characteristics and health conditions, increasing levels of sVCAM-1 were linearly associated with higher resting CVR (p = .006) and lower performance on the Hopkins Verbal Learning Memory (immediate recall and delayed recall) and adjusted TMT B tests (p < .05). Higher levels of sVCAM-1 were also associated with global cognitive impairment on the MMSE (odds ratio = 3.9; 95% confidence interval: 1.4-10.9; p = .011).

CONCLUSIONS

In this cohort of elderly participants, we observed a cross-sectional association between elevated sVCAM-1 levels and both cognitive impairment and increased cerebrovascular resistance. Longitudinal studies are needed to determine whether elevated sVCAM-1 is a cause or consequence of cerebrovascular damage.

Chemically treated plasma Aβ is a potential blood-based biomarker for screening cerebral amyloid deposition

BACKGROUND

Plasma β-amyloid (Aβ) is a potential candidate for an Alzheimer's disease (AD) biomarker because blood is an easily accessible bio-fluid, which can be collected routinely, and Aβ is one of the major hallmarks of AD pathogenesis in the brain. However, the association between plasma Aβ levels and AD diagnosis is still unclear due to the instability and inaccurate measurements of plasma Aβ levels in the blood of patients with AD. If a consistent value of plasma Aβ from the blood can be obtained, this might help determine whether plasma Aβ is a potential biomarker for AD diagnosis.

METHODS

We predicted the brain amyloid deposit by measuring the plasma Aβ levels. This cross-sectional study included 353 participants (215 cognitively normal, 79 with mild cognitive impairment, and 59 with AD dementia) who underwent Pittsburgh-compound B positron emission tomography (PiB-PET) scans. We treated a mixture of protease inhibitors and phosphatase inhibitors (MPP) and detected plasma Aβ42 and Aβ40 (MPP-Aβ42 and MPP-Aβ40) in a stable manner using xMAP technology.

RESULTS

MPP-Aβ40 and MPP-Aβ42/40 (MPP-Aβs) were significantly different between subjects with positive amyloid deposition (PiB+) and those with negative amyloid deposition (PiB-) (P < 0.0001). Furthermore, MPP-Aβ40 (P < 0.0001, r = 0.23) and MPP-Aβ42/40 ratio (P < 0.0001, r = -0.23) showed significant correlation with global PiB deposition (standardized uptake value ratio). In addition, our integrated multivariable (MPP-Aβ42/40, gender, age, and apolipoprotein E genotypes) logistic regression model proposes a new standard for the prediction of cerebral amyloid deposition.

CONCLUSIONS

MPP-Aβ might be one of the potential blood biomarkers for the prediction of PiB-PET positivity in the brain.

Hypertension, cerebrovascular impairment, and cognitive decline in aged AβPP/PS1 mice

Cardiovascular risk factors, especially hypertension, are also major risk factors for Alzheimer's disease (AD). To elucidate the underlying vascular origin of neurodegenerative processes in AD, we investigated the relation between systolic blood pressure (SBP) cerebral blood flow (CBF) and vasoreactivity with brain structure and function in a 16-18 months old double transgenic AβPP_swe/PS1_dE9 (AβPP/PS1) mouse model for AD. These aging AβPP/PS1 mice showed an increased SBP linked to a declined regional CBF. Furthermore, using advanced MRI techniques, decline of functional and structural connectivity was revealed in the AD-like mice coupled to impaired cognition, increased locomotor activity, and anxiety-related behavior. Post mortem analyses demonstrated also increased neuroinflammation, and both decreased synaptogenesis and neurogenesis in the AβPP/PS1 mice. Additionally, deviant levels of fatty acids and sterols were present in the brain tissue of the AβPP/PS1 mice indicating maladapted brain fatty acid metabolism. Our findings suggest a link between increased SBP, decreased cerebral hemodynamics and connectivity in an AD mouse model during aging, leading to behavioral and cognitive impairments. As these results mirror the complex clinical symptomatology in the prodromal phase of AD, we suggest that this AD-like murine model could be used to investigate prevention and treatment strategies for early AD patients. Moreover, this study helps to develop more efficient therapies and diagnostics for this very early stage of AD.

Pathophysiologic relationship between Alzheimer's disease, cerebrovascular disease, and cardiovascular risk: A review and synthesis

As the population ages due to demographic trends and gains in life expectancy, the incidence and prevalence of dementia increases, and the need to understand the etiology and pathogenesis of dementia becomes ever more urgent. Alzheimer's disease (AD), the most common form of dementia, is a complex disease, the mechanisms of which are poorly understood. The more we learn about AD, the more questions are raised about our current conceptual models of disease. In the absence of a cure or the means by which to slow disease progress, it may be prudent to apply our current knowledge of the intersection between AD, cardiovascular disease, and cerebrovascular disease to foster efforts to delay or slow the onset of AD. This review discusses our current understanding of the epidemiology, genetics, and pathophysiology of AD, the intersection between AD and vascular causes of dementia, and proposes future directions for research and prevention.

Functional vascular contributions to cognitive impairment and dementia: mechanisms and consequences of cerebral autoregulatory dysfunction, endothelial impairment, and neurovascular uncoupling in aging

Increasing evidence from epidemiological, clinical and experimental studies indicate that age-related cerebromicrovascular dysfunction and microcirculatory damage play critical roles in the pathogenesis of many types of dementia in the elderly, including Alzheimer's disease. Understanding and targeting the age-related pathophysiological mechanisms that underlie vascular contributions to cognitive impairment and dementia (VCID) are expected to have a major role in preserving brain health in older individuals. Maintenance of cerebral perfusion, protecting the microcirculation from high pressure-induced damage and moment-to-moment adjustment of regional oxygen and nutrient supply to changes in demand are prerequisites for the prevention of cerebral ischemia and neuronal dysfunction. This overview discusses age-related alterations in three main regulatory paradigms involved in the regulation of cerebral blood flow (CBF): cerebral autoregulation/myogenic constriction, endothelium-dependent vasomotor function, and neurovascular coupling responses responsible for functional hyperemia. The pathophysiological consequences of cerebral microvascular dysregulation in aging are explored, including blood-brain barrier disruption, neuroinflammation, exacerbation of neurodegeneration, development of cerebral microhemorrhages, microvascular rarefaction, and ischemic neuronal dysfunction and damage. Due to the widespread attention that VCID has captured in recent years, the evidence for the causal role of cerebral microvascular dysregulation in cognitive decline is critically examined.

Biomarkers for Alzheimer's Disease Diagnosis

OBJECTIVE

The dramatic increase in the population with dementia expected in the next decades is accompanied by the establishment of novel and innovated methods that will offer accurate and efficient detection of the disease in its early stages. While Alzheimer's disease is the most common cause of dementia, by the time it is typically diagnosed, substantial neuronal loss and neuropathological lesions can damage many brain regions. The aim of this study is to investigate the main risk factors that affect and increase Alzheimer's disease progression over time even in cases with no significant memory impairment present. Several potential markers are discussed such as oxidative stress, metal ions, vascular disorders, protein dysfunctions and alterations in the mitochondrial populations.

CONCLUSION

A multiparametric model of Alzheimer's biomarkers is presented according to the latest classification of the disease.

New horizons: the management of hypertension in people with dementia

The optimal management of hypertension in people with dementia is uncertain. This review explores if people with dementia experience greater adverse effects from antihypertensive medications, if cognitive function is protected or worsened by controlling blood pressure (BP) and if there are subgroups of people with dementia for whom antihypertensive therapy is more likely to be harmful. Robust evidence is scant, trials of antihypertensive medications have generally excluded those with dementia. Observational data show changes in risk association over the life course, with high BP being a risk factor for cognitive decline in mid-life, while low BP is predictive in later life. It is therefore possible that excessive BP lowering in older people with dementia might harm cognition. From the existing literature, there is no direct evidence of benefit or harm from treating hypertension in people with dementia. So what practical steps can the clinician take? Assess capacity, establish patient preferences when making treatment decisions, use ambulatory monitoring to thoroughly assess BP, individualise and consider deprescribing where side effects (e.g. hypotension) outweigh the benefits. Future research might include pragmatic randomised trials of targeted deprescribing, which include patient-centred outcome measures to help support decision-making and studies to address mechanistic uncertainties.

Effects of a multicomponent exercise program in institutionalized elders with Alzheimer's disease

This study examined the effect of a Multicomponent Training (MT) intervention on cognitive function, functional fitness and anthropometric variables in institutionalized patients with Alzheimer's disease (AD). Thirty-seven institutionalized elders (84.05 ± 5.58 years) clinically diagnosed with AD (mild and moderate stages) were divided into two groups: Experimental Group (EG, n = 19) and Control Group (CG, n = 18). The EG participated in a six-month supervised MT program (aerobic, muscular resistance, flexibility and postural exercises) of 45-55 minutes/session, twice/week. Cognitive function (MMSE), physical fitness (Senior Fitness Test) and anthropometric variables (Body Mass Index and Waist Circumference), were assessed before (M1), after three months (M2) and after six months (M3) of the experimental protocol. A two-way ANOVA, with repeated measures, revealed significant group and time interactions on cognitive function, chair stand, arm curl, 2-min step, 8-foot up-and-go (UG), chair sit-and-reach (CSR) and back scratch tests as well as waist circumference. Accordingly, for those variables a different response in each group was evident over the time, supported by a significantly better EG performance in chair stand, arm curl, 2-min step, UG, CSR and back scratch tests from M1 to M3, and a significant increase in MMSE from M1 to M2. The CG's performance decreased over time (M1 to M3) in chair stand, arm curl, 2-min step, UG, CSR, back scratch and MMSE. Results suggest that MT programs may be an important non-pharmacological strategy to improve physical and cognitive functions in institutionalized AD patients.

Cerebral hypoperfusion and glucose hypometabolism: Key pathophysiological modulators promote neurodegeneration, cognitive impairment, and Alzheimer's disease

Aging, hypertension, diabetes, hypoxia/obstructive sleep apnea (OSA), obesity, vitamin B12/folate deficiency, depression, and traumatic brain injury synergistically promote diverse pathological mechanisms including cerebral hypoperfusion and glucose hypometabolism. These risk factors trigger neuroinflammation and oxidative-nitrosative stress that in turn decrease nitric oxide and enhance endothelin, Amyloid-β deposition, cerebral amyloid angiopathy, and blood-brain barrier disruption. Proinflammatory cytokines, endothelin-1, and oxidative-nitrosative stress trigger several pathological feedforward and feedback loops. These upstream factors persist in the brain for decades, upregulating amyloid and tau, before the cognitive decline. These cascades lead to neuronal Ca²⁺ increase, neurodegeneration, cognitive/memory decline, and Alzheimer's disease (AD). However, strategies are available to attenuate cerebral hypoperfusion and glucose hypometabolism and ameliorate cognitive decline. AD is the leading cause of dementia among the elderly. There is significant evidence that pathways involving inflammation and oxidative-nitrosative stress (ONS) play a key pathophysiological role in promoting cognitive dysfunction. Aging and several comorbid conditions mentioned above promote diverse pathologies. These include inflammation, ONS, hypoperfusion, and hypometabolism in the brain. In AD, chronic cerebral hypoperfusion and glucose hypometabolism precede decades before the cognitive decline. These comorbid disease conditions may share and synergistically activate these pathophysiological pathways. Inflammation upregulates cerebrovascular pathology through proinflammatory cytokines, endothelin-1, and nitric oxide (NO). Inflammation-triggered ONS promotes long-term damage involving fatty acids, proteins, DNA, and mitochondria; these amplify and perpetuate several feedforward and feedback pathological loops. The latter includes dysfunctional energy metabolism (compromised mitochondrial ATP production), amyloid-β generation, endothelial dysfunction, and blood-brain-barrier disruption. These lead to decreased cerebral blood flow and chronic cerebral hypoperfusion- that would modulate metabolic dysfunction and neurodegeneration. In essence, hypoperfusion deprives the brain from its two paramount trophic substances, viz., oxygen and nutrients. Consequently, the brain suffers from synaptic dysfunction and neuronal degeneration/loss, leading to both gray and white matter atrophy, cognitive dysfunction, and AD. This Review underscores the importance of treating the above-mentioned comorbid disease conditions to attenuate inflammation and ONS and ameliorate decreased cerebral blood flow and hypometabolism. Additionally, several strategies are described here to control chronic hypoperfusion of the brain and enhance cognition. © 2016 Wiley Periodicals, Inc.

The Effect of a High-Fat Diet on Brain Plasticity, Inflammation and Cognition in Female ApoE4-Knockin and ApoE-Knockout Mice

Apolipoprotein E4 (ApoE4), one of three common isoforms of ApoE, is a major risk factor for late-onset Alzheimer disease (AD). ApoE-deficient mice, as well as mice expressing human ApoE4, display impaired learning and memory functions and signs of neurodegeneration. Moreover, ApoE protects against high-fat (HF) diet induced neurodegeneration by its role in the maintenance of the integrity of the blood-brain barrier. The influence of a HF diet on the progression of AD-like cognitive and neuropathological changes was assessed in wild-type (WT), human ApoE4 and ApoE-knockout (ApoE^-/-) mice to evaluate the modulatory role of ApoE in this process. From 12 months of age, female WT, ApoE4, and ApoE^-/- mice were fed either a standard or a HF diet (19% butter, 0.5% cholate, 1.25% cholesterol) throughout life. At 15 months of age mice performed the Morris water maze, evaluating spatial learning and memory. ApoE^-/- showed increased spatial learning compared to WT mice (p = 0.009). HF diet improved spatial learning in WT mice (p = 0.045), but did not affect ApoE4 and ApoE^-/- mice. Immunohistochemical analyses of the hippocampus demonstrated increased neuroinflammation (CD68) in the cornu ammonis 1 (CA1) region in ApoE4 (p = 0.001) and in ApoE^-/- (p = 0.032) mice on standard diet. HF diet tended to increase CD68 in the CA1 in WT mice (p = 0.052), while it decreased in ApoE4 (p = 0.009), but ApoE^-/- remained unaffected. A trend towards increased neurogenesis (DCX) was found in both ApoE4 (p = 0.052) and ApoE^-/- mice (p = 0.068). In conclusion, these data suggest that HF intake induces different effects in WT mice compared to ApoE4 and ApoE^-/- with respect to markers for cognition and neurodegeneration. We propose that HF intake inhibits the compensatory mechanisms of neuroinflammation and neurogenesis in aged female ApoE4 and ApoE^-/- mice.

Relations of blood pressure and head injury to regional cerebral blood flow

Hypertension confers increased risk for cognitive decline, dementia, and cerebrovascular disease. These associations have been attributed, in part, to cerebral hypoperfusion. Here we posit that relations of higher blood pressure to lower levels of cerebral perfusion may be potentiated by a prior head injury. Participants were 87 community-dwelling older adults - 69% men, 90% white, mean age=66.9years, 27.6% with a history of mild traumatic brain injury (mTBI) defined as a loss of consciousness ≤30min resulting from an injury to the head, and free of major medical (other than hypertension), neurological or psychiatric comorbidities. All engaged in clinical assessment of systolic and diastolic blood pressure (SBP, DBP) and single photon emission computed tomography (SPECT). Computerized coding of the SPECT images yielded relative ratios of blood flow in left and right cortical and select subcortical regions. Cerebellum served as the denominator. Sex-stratified multiple regression analyses, adjusted for age, education, race, alcohol consumption, smoking status, and depressive symptomatology, revealed significant interactions of blood pressure and head injury to cerebral blood flow in men only. Specifically, among men with a history of head injury, higher systolic blood pressure was associated with lower levels of perfusion in the left orbital (β=-3.21, p=0.024) and left dorsolateral (β=-2.61, p=0.042) prefrontal cortex, and left temporal cortex (β=-3.36, p=0.014); higher diastolic blood pressure was marginally associated with lower levels of perfusion in the left dorsolateral prefrontal cortex (β=-2.79, p=0.051). Results indicate that men with a history of head injury may be particularly vulnerable to the impact of higher blood pressure on cerebral perfusion in left anterior cortical regions, thus potentially enhancing risk for adverse brain and neurocognitive outcomes.

Dual-specificity phosphatase 26 (DUSP26) stimulates Aβ42 generation by promoting amyloid precursor protein axonal transport during hypoxia

Amyloid beta peptide (Aβ) is a pathological hallmark of Alzheimer's disease (AD) and is generated through the sequential cleavage of amyloid precursor protein (APP) by β- and γ-secretases. Hypoxia is a known risk factor for AD and stimulates Aβ generation by γ-secretase; however, the underlying mechanisms remain unclear. In this study, we showed that dual-specificity phosphatase 26 (DUSP26) regulates Aβ generation through changes in subcellular localization of the γ-secretase complex and its substrate C99 under hypoxic conditions. DUSP26 was identified as a novel γ-secretase regulator from a genome-wide functional screen using a cDNA expression library. The phosphatase activity of DUSP26 was required for the increase in Aβ42 generation through γ-secretase, but this regulation did not affect the amount of the γ-secretase complex. Interestingly, DUSP26 induced the accumulation of C99 in the axons by stimulating anterograde transport of C99-positive vesicles. Additionally, DUSP26 induced c-Jun N-terminal kinase (JNK) activation for APP processing and axonal transport of C99. Under hypoxic conditions, DUSP26 expression levels were elevated together with JNK activation, and treatment with JNK inhibitor SP600125, or the DUSP26 inhibitor NSC-87877, reduced hypoxia-induced Aβ generation by diminishing vesicle trafficking of C99 to the axons. Finally, we observed enhanced DUSP26 expression and JNK activation in the hippocampus of AD patients. Our results suggest that DUSP26 mediates hypoxia-induced Aβ generation through JNK activation, revealing a new regulator of γ-secretase-mediated APP processing under hypoxic conditions. We propose the role of phosphatase dual-specificity phosphatase 26 (DUSP26) in the selective regulation of Aβ42 production in neuronal cells under hypoxic stress. Induction of DUSP26 causes JNK-dependent shift in the subcellular localization of γ-secretase and C99 from the cell body to axons for Aβ42 generation. These findings provide a new strategy for developing new therapeutic targets to arrest AD progression.

Hypertension and Dementia: Epidemiological and Experimental Evidence Revealing a Detrimental Relationship

Hypertension and dementia represent two major public health challenges worldwide, notably in the elderly population. Although these two conditions have classically been recognized as two distinct diseases, mounting epidemiological, clinical and experimental evidence suggest that hypertension and dementia are strictly intertwined. Here, we briefly report how hypertension profoundly affects brain homeostasis, both at the structural and functional level. Chronic high blood pressure modifies the cerebral vasculature, increasing the risk of Aβ clearance impairment. The latter, excluding genetic etiologies, is considered one of the main causes of Aβ deposition in the brain. Studies have shown that hypertension induces cerebral arterial stiffening and microvascular dysfunction, thus contributing to dementia pathophysiology. This review examines the existing and the updated literature which has attempted to explain and clarify the relationship between hypertension and dementia at the pathophysiological level.

Effects of Blood Pressure Lowering With Different Antihypertensive Agents on Cognitive Function and Plasma Brain-derived Neurotrophic Factor Levels: A Comparative Study

PURPOSE

Hypertension is a risk factor for cognitive impairment (CI). However, the specific effect of antihypertensive therapy on cognitive function is still controversial. We aimed to investigate the effect of antihypertensive agents targeting the renin-angiotensin system (RAS) on CI and brain-derived neurotropic factor (BDNF).

METHODS

We included 62 patients who had been using the same antihypertensive agent for at least 3 months. Patients who had relevant conditions that could contribute to CI were excluded. After subjects were divided into 3 groups according to their current antihypertensive medication, the cognitive status of each patient was assessed by the mini-mental state examination (MMSE). BDNF and plasma renin activity were evaluated.

RESULTS

There was a negative association between systolic blood pressure and MMSE independent of medication (rho = -0.251, P = 0.049). There was no significant correlation between MMSE and BDNF. The MMSE score was slightly higher in the non-RAS group, but the difference did not reach statistical significance (P = 0.09). There was also no significant difference in BDNF levels between study groups (P = 0.32). Mean plasma renin activity levels were significantly lower in the non-RAS group compared with the angiotensin converting enzyme inhibitor and angiotensin receptor blocker groups (P = 0.007).

CONCLUSIONS

We suggest that the essential intervention for CI in hypertensive patients is appropriate for blood pressure control.

Survival in Subcortical Vascular Dementia: Predictors and Comparison to Probable Alzheimer's Disease in a Tertiary Memory Clinic Population

BACKGROUND

Subcortical vascular dementia (SVaD) is one of the most common dementias, after Alzheimer's disease (AD) dementia. Few survival analyses in SVaD patients have been reported.

METHODS

The dates and causes of death of 146 SVaD and 725 AD patients were included. We used the Cox proportional hazards model to compare survival between SVaD and AD patients and to explore possible factors related to survival of SVaD patients.

RESULTS

The median survival time after the onset of SVaD (109 months) was shorter than that recorded for AD (152 months). The most common cause of death in SVaD was stroke (47.1%). Factors associated with shorter survival in SVaD were late onset, male sex, worse baseline cognition, absence of hypertension and a family history of stroke.

CONCLUSIONS

Stroke prevention may be important in SVaD treatment because 47.1% of SVaD patients died of stroke. A family history of stroke and absence of hypertension were associated with a shorter survival in SVaD, suggesting the existence of genetic or unknown risk factors.

Transient Cerebral Ischemia Promotes Brain Mitochondrial Dysfunction and Exacerbates Cognitive Impairments in Young 5xFAD Mice

Alzheimer's disease (AD) is heterogeneous and multifactorial neurological disorder; and the risk factors of AD still remain elusive. Recent studies have highlighted the role of vascular factors in promoting the progression of AD and have suggested that ischemic events increase the incidence of AD. However, the detailed mechanisms linking ischemic insult to the progression of AD is still largely undetermined. In this study, we have established a transient cerebral ischemia model on young 5xFAD mice and their non-transgenic (nonTg) littermates by the transient occlusion of bilateral common carotid arteries. We have found that transient cerebral ischemia significantly exacerbates brain mitochondrial dysfunction including mitochondrial respiration deficits, oxidative stress as well as suppressed levels of mitochondrial fusion proteins including optic atrophy 1 (OPA1) and mitofusin 2 (MFN2) in young 5xFAD mice resulting in aggravated spatial learning and memory. Intriguingly, transient cerebral ischemia did not induce elevation in the levels of cortical or mitochondrial Amyloid beta (Aβ)1-40 or 1–42 levels in 5xFAD mice. In addition, the glucose- and oxygen-deprivation-induced apoptotic neuronal death in Aβ-treated neurons was significantly mitigated by mitochondria-targeted antioxidant mitotempo which suppresses mitochondrial superoxide levels. Therefore, the simplest interpretation of our results is that young 5xFAD mice with pre-existing AD-like mitochondrial dysfunction are more susceptible to the effects of transient cerebral ischemia; and ischemic events may exacerbate dementia and worsen the outcome of AD patients by exacerbating mitochondrial dysfunction.

Disrupted white matter structure underlies cognitive deficit in hypertensive patients

OBJECTIVES

Hypertension is considered a risk factor of cognitive impairments and could result in white matter changes. Current studies on hypertension-related white matter (WM) changes focus only on regional changes, and the information about global changes in WM structure network is limited.

METHODS

We assessed the cognitive function in 39 hypertensive patients and 37 healthy controls with a battery of neuropsychological tests. The WM structural networks were constructed by utilizing diffusion tensor tractography and calculated topological properties of the networks using a graph theoretical method. The direct and indirect correlations among cognitive impairments, brain WM network disruptions and hypertension were analyzed with structural equation modelling (SEM).

RESULTS

Hypertensive patients showed deficits in executive function, memory and attention compared with controls. An aberrant connectivity of WM networks was found in the hypertensive patients (P Eglob = 0.005, P Lp = 0.005), especially in the frontal and parietal regions. Importantly, SEM analysis showed that the decline of executive function resulted from aberrant WM networks in hypertensive patients (p = 0.3788, CFI = 0.99).

CONCLUSIONS

These results suggest that the cognitive decline in hypertensive patients was due to frontal and parietal WM disconnections. Our findings highlight the importance of brain protection in hypertension patients.

KEY POINTS

• Hypertension has a negative effect on the performance of the cognitive domains • Reduced efficiencies of white matter networks were shown in hypertension • Disrupted white matter networks are responsible for poor cognitive function in hypertension.

Association between comorbidities and dementia in diabetes mellitus patients: population-based retrospective cohort study

AIMS

Most diabetes mellitus (DM) patients have several comorbidities; the correlation of these comorbidities with dementia in DM requires clarification.

METHODS

Using claims data from Taiwan National Health Insurance, we identified 33,709 DM adults before the year 2000 and randomly selected 67,066 non-DM patients matched by sex and age. Subjects were followed until diagnosis with dementia, excluded due to death/withdrawal from the insurance program, or followed until 2011. We compared the incidence and hazard ratio (HR) for dementia in both cohorts.

RESULTS

Comorbidities were more prevalent in DM patients, including hypertension, hyperlipidemia, stroke, coronary artery and/or kidney disease. The HR was higher for the DM cohort with comorbidities than those without: 1.88 vs. 1.46 with hypertension; 1.56 vs. 1.39 with hyperlipidemia; 1.73 vs. 1.37 with coronary artery disease; 2.36 vs. 2.29 with stroke and 1.88 vs. 1.50 with kidney disease. The HR for dementia in diabetics rose from 1.41 in those without comorbidities to 2.49 in those with ≥4 comorbidities. In the DM cohort, HR was 1.22 for non-insulin-users and 1.41 for insulin-users, and 1.49 for type 1 DM and 1.23 for type 2 DM.

CONCLUSION

Diabetic patients have an elevated risk of dementia, and comorbidity increases this risk.

The increased potassium intake improves cognitive performance and attenuates histopathological markers in a model of Alzheimer's disease

Alzheimer's disease (AD) is a neurodegenerative disorder characterized by hallmarks that include an accumulation of amyloid-β peptide (Aβ), inflammation, oxidative stress and synaptic dysfunction, which lead to a decrease in cognitive function. To date, the onset and progression of AD have been associated with pathologies such as hypertension and diabetes. Hypertension, a disease with a high incidence worldwide, is characterized by a chronic increase in blood pressure. Interestingly, this disease has a close relationship to the eating behavior of patients because high Na(+) intake is a significant risk factor for hypertension. In fact, a decrease in Na(+) consumption, along with an increase in K(+) intake, is a primary non-pharmacological approach to preventing hypertension. In the present work, we examined whether an increase in K(+) intake affects the expression of certain neuropathological markers or the cognitive performance of a murine model of AD. We observed that an increase in K(+) intake leads to a change in the aggregation pattern of the Aβ peptide, a partial decrease in some epitopes of tau phosphorylation and improvement in the cognitive performance. The recovery in cognitive performance was correlated with a significant improvement in the generation of long-term potentiation. We also observed a decrease in markers related to inflammation and oxidative stress such as glial fibrillary acidic protein (GFAP), interleukin 6 (IL-6) and 4-hydroxynonenal (4-HNE). Together, our data support the idea that changes in diet, such as an increase in K(+) intake, may be important in the prevention of AD onset as a non-pharmacological therapy.

Lower Blood Pressure Is Associated With Smaller Subcortical Brain Volumes in Older Persons

BACKGROUND

Both high and low blood pressure (BP) have been positively as well as negatively associated with brain volumes in a variety of populations. The objective of this study was to investigate whether BP is associated with cortical and subcortical brain volumes in older old persons with mild cognitive deficits.

METHODS

Within the Discontinuation of Antihypertensive Treatment in the Elderly trial, the cross-sectional relation of BP parameters with both cortical and subcortical brain volumes was investigated in 220 older old persons with mild cognitive deficits (43% men, mean age = 80.7 (SD = 4.1), median Mini-Mental State Examination score = 26 (interquartile range: 25-27)), using linear regression analysis. All analyses were adjusted for age, gender, volume of white matter hyperintensities, and duration of antihypertensive treatment. Brain volumes were determined on 3DT1-weighted brain magnetic resonance imaging scans.

RESULTS

Lower systolic BP, diastolic BP, and mean arterial pressure (MAP) were significantly associated with lower volumes of thalamus and putamen (all P ≤ 0.01). In addition, lower MAP was also associated with reduced hippocampal volume (P = 0.035). There were no associations between any of the BP parameters with cortical gray matter or white matter volume.

CONCLUSION

In an older population using antihypertensive medication with mild cognitive deficits, a lower BP, rather than a high BP is associated with reduced volumes of thalamus, putamen, and hippocampus.

Pathophysiological Links Among Hypertension and Alzheimer's Disease

Genetic Alzheimer's disease (AD) accounts for only few AD cases and is almost exclusively associated to increased amyloid production in the brain. Instead, the majority of patients is affected with the AD sporadic form with typical alterations of clearance mechanisms of the brain. Most studies use engineered animal models that mimic genetic AD. Since it is emerging the existence of a pathophysiological link between cardiovascular risk factors and AD etiology, the strategy to develop animal models of vascular related AD pathology could be the key toward developing novel successful therapies. On this issue, we have demonstrated that mice that have been chronically subjected to high blood pressure show deposition of amyloid aggregates, the main histological feature of AD, and loss of memory in specific tasks. More importantly, we have identified that the hypertensive challenge increases the expression of the receptor for advanced glycated end products (RAGE), leading to beta-amyloid (Aβ) deposition and learning impairment. Here, we review different murine models of hypertension, induced either pharmacologically or mechanically, leading in the long time to plaque formation in the brain parenchyma and around blood vessels. The major findings obtained till now in this particular experimental setting allow us to suggest that this appears to be a unique possibility to study the pathogenetic mechanisms of sporadic AD triggered by vascular risk factors.

Longitudinal changes in cortical thinning associated with hypertension

BACKGROUND

Cross-sectional studies of the association between hypertension (HTN) and brain atrophy have shown reductions in prefrontal, temporal, and hippocampal volumes, and have identified thinner cortices across the cortical mantle.

METHOD

In the current study, we followed 96 participants enrolled in the Baltimore Longitudinal Study of Aging over a mean interval of 8 years (mean age at baseline = 68.7) and compared those who are hypertensive (n = 49) throughout the study with those who are normotensive (n = 47).

RESULTS

Hypertensive individuals show an increased rate of thinning compared with normotensive individuals in several regions, including the frontomarginal gyrus in the left hemisphere, and the superior temporal, fusiform, and lateral orbitofrontal cortex in the right hemisphere. We also investigated the effects of midlife blood pressure (BP), intervisit variability in BP prior to imaging, and duration of HTN on areas that show subsequent differences in the rates of cortical thinning between groups. We found that higher midlife BP and longer durations of HTN predicted a higher rate of thinning in the right superior temporal gyrus. We also found that greater variability in SBP but not DBP predicted a higher rate of thinning in the right superior temporal gyrus, frontomarginal gyrus, and occipital pole.

CONCLUSION

These findings demonstrate that hypertensive individuals show increased rates of thinning compared with normotensive individuals and suggest intervisit BP variability and midlife BP contribute to these longitudinal differences.

Impaired myogenic response and autoregulation of cerebral blood flow is rescued in CYP4A1 transgenic Dahl salt-sensitive rat

We have reported that a reduction in renal production of 20-HETE contributes to development of hypertension in Dahl salt-sensitive (SS) rats. The present study examined whether 20-HETE production is also reduced in the cerebral vasculature of SS rats and whether this impairs the myogenic response and autoregulation of cerebral blood flow (CBF). The production of 20-HETE, the myogenic response of middle cerebral arteries (MCA), and autoregulation of CBF were compared in SS, SS-5(BN) rats and a newly generated CYP4A1 transgenic rat. 20-HETE production was 6-fold higher in cerebral arteries of CYP4A1 and SS-5(BN) than in SS rats. The diameter of the MCA decreased to 70 ± 3% to 65 ± 6% in CYP4A1 and SS-5(BN) rats when pressure was increased from 40 to 140 mmHg. In contrast, the myogenic response of MCA isolated from SS rats did not constrict. Administration of a 20-HETE synthesis inhibitor, HET0016, abolished the myogenic response of MCA in CYP4A1 and SS-5(BN) rats but had no effect in SS rats. Autoregulation of CBF was impaired in SS rats compared with CYP4A1 and SS-5(BN) rats. Blood-brain barrier leakage was 5-fold higher in the brain of SS rats than in SS-5(BN) and SS.CYP4A1 rats. These findings indicate that a genetic deficiency in the formation of 20-HETE contributes to an impaired myogenic response in MCA and autoregulation of CBF in SS rats and this may contribute to vascular remodeling and cerebral injury following the onset of hypertension.

CD36 upregulation mediated by intranasal LV-NRF2 treatment mitigates hypoxia-induced progression of Alzheimer's-like pathogenesis

AIMS

There is extensive evidence that oxidative stress induces cellular dysfunction in the brain and plays a critical role in Alzheimer's disease (AD) pathogenesis. Hypoxia increases factors involved in oxidative stress injury and contributes to the onset and progression of AD. Nuclear factor erythroid 2-related factor 2 (NRF2), a major component regulating antioxidant response, is attenuated in the AD brain. Importantly, NRF2 directly regulates the alternative first exons of CD36, an important participant in oxidative and inflammatory processes. To explore the effects of hypoxia-induced deterioration of AD-like pathogenesis and investigate the correlation between hypoxia-induced NRF2 signal alterations and CD36 expression, we examined the NRF2 signaling, CD36, and oxidative stress events in hypoxia-treated APPswe/PSEN1dE9 (APP/PS1) mice brain.

RESULTS

We observed that hypoxia treatment increased oxidative stress, exacerbated inflammation, and aggravated learning defects in aged APP/PS1 mice. Microglia from hypoxia-treated mice brain exhibited marked reduction in CD36 expression and inhibition of β-amyloid (Aβ) degradation. Accordingly, hypoxia treatment caused a decrease in transactivation of NRF2 target genes in the aging mouse brain. Intranasal administration with a lentiviral vector encoding human NRF2 increased CD36 expression, ameliorated the weak antioxidant response triggered by hypoxia, diminished Aβ deposition, and improved spatial memory defects.

INNOVATION

In this study, we demonstrated for the first time that NRF2 intranasal treatment-induced increases of CD36 could enhance Aβ clearance in AD transgenic mouse.

CONCLUSION

These results suggest that targeting NRF2-mediated CD36 expression might provide a beneficial intervention for cognitive impairment and oxidative stress in AD progression.