Blunted cerebrovascular response is associated with elevated beta-amyloid

Kappa opioid receptor availability predicts severity of anhedonia in schizophrenia

The kappa opioid receptor (KOR) and its endogenous agonist dynorphin have been implicated in multiple psychiatric conditions including psychotic disorders. We tested the hypotheses that kappa expression is elevated and associated with psychotic symptoms in schizophrenia. We measured kappa expression in unmedicated patients with schizophrenia (7 female, 6 male) and matched controls (7 female, 6 male) with positron emission tomography (PET). We also acquired a measurement of cumulative dopamine activity over the life span in the same subjects using neuromelanin sensitive MRI. We hypothesized that neuromelanin accumulation would be higher in patients than controls and that in patients there would be a positive association between KOR availability and neuromelanin accumulation. Fourteen patients and thirteen controls were enrolled. Whole brain dynamic PET imaging data using the KOR selective tracer [18F]LY245998 were acquired. Distribution volume (VT) was measured with region of interest analysis in 14 brain regions. Neuromelanin accumulation in midbrain dopaminergic nuclei was assessed in the same subjects. Positive and negative symptoms were measured by a clinical psychologist. We did not observe group level differences in KOR expression, neuromelanin accumulation or relationships of these to positive symptoms. Unexpectedly, we did observe strong positive associations between KOR expression and symptoms of anhedonia in the patients (Pearson r > 0.7, uncorrected p < 0.01 in 8 cortical brain regions). We also observed moderate associations between KOR expression and neuromelanin levels in patients. In conclusion, we did not observe a relationship between kappa and symptoms of psychosis but the observed relationship to the negative symptom of anhedonia is in line with recent work testing kappa antagonism as a therapy for anhedonia in depression.

Associations Between Korean Coronary Heart Disease Risk Score and Cognitive Function in Dementia-Free Korean Older Adults

BACKGROUND

Cardiovascular risk is a modifiable factor that can help prevent dementia. Given the dearth of optimal treatment options, managing dementia risk factors is crucial. We examined the association between cardiovascular risk, as measured by the Korean coronary heart disease risk score (KRS), and cognitive function in dementia-free elderly individuals.

METHODS

We enrolled 8,600 individuals (average age: 69.74 years; 5,206 women) who underwent a medical evaluation from the National Health Insurance Service. KRS was calculated using age, sex, blood pressure, lipid profile, diabetes, and smoking status. Cognitive function was evaluated using Korean Dementia Screening Questionnaire-Cognition (KDSQ-C). Scores of ≥ 6 indicated a cognitive decline. Logistic regression analysis was used to estimate the odds ratio (OR) and 95% confidence interval (CI). Weight, height, stroke history, coronary heart disease history, alcohol consumption, and physical activity engagement were adjusted.

RESULTS

The lowest, middle, and highest groups, according to the KRS, were 5,923 (68.9%), 2,343 (27.2%), and 334 (3.9%), respectively. The highest KRS group in all participants exhibited a greater risk of cognitive decline than the lowest KRS group (OR, 1.339; 95% CI, 1.034-1.734; P = 0.027). The highest KRS female group aged 71-75 years old exhibited greater cognitive decline than the corresponding lowest KRS group (OR, 1.595; 95% CI, 1.045-2.434; P = 0.031).

CONCLUSION

Individuals with high cardiovascular risk were associated with poorer cognitive function than those with low risk, especially older women. Cardiovascular risk factors should be carefully managed to promote healthy mental aging in dementia-free elderly individuals.

Sex Differences in Resilience and Resistance to Brain Pathology and Dysfunction Moderated by Cerebrovascular Response to Exercise and Genetic Risk for Alzheimer's Disease

Sex as a biological variable appears to contribute to the multifactorial etiology of Alzheimer's disease. We tested sex-based interactions between cerebrovascular function and APOE4 genotype on resistance and resilience to brain pathology and cognitive executive dysfunction in cognitively-normal older adults. Female APOE4 carriers had higher amyloid-β deposition yet achieved similar cognitive performance to males and female noncarriers. Further, female APOE4 carriers with robust cerebrovascular responses to exercise possessed lower amyloid-β. These results suggest a unique cognitive resilience and identify cerebrovascular function as a key mechanism for resistance to age-related brain pathology in females with high genetic vulnerability to Alzheimer's disease.

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.

Carotid Stiffness is Associated with Brain Amyloid-β Burden in Amnestic Mild Cognitive Impairment

BACKGROUND

Vascular dysfunction has been implicated in the onset and progression of Alzheimer's disease (AD), yet the relationship of arterial stiffening with brain amyloid-β (Aβ) burden in at risk patients is unclear.

OBJECTIVE

We aimed to determine the relationship of aortic and carotid arterial stiffening with Aβ burden in patients with amnestic mild cognitive impairment (aMCI), a proposed transitional stage between normal aging and AD.

METHODS

Thirty-two older adults with aMCI underwent 18Florbetapir PET amyloid imaging to ascertain Aβ burden via standardized uptake value ratio (SUVR). Carotid-femoral pulse wave velocity (cfPWV), which reflects aortic stiffness, and carotid β stiffness index and distensibility, which reflect local cerebral arterial stiffness, thus having direct impact on the cerebral circulation, were measured using applanation tonometry and ultrasonography.

RESULTS

Region-of-interest based analysis showed that precuneus and mean cortex Aβ SUVR were correlated positively with carotid β stiffness index and negatively with carotid distensibility after adjusting for age, sex, mean arterial pressure (MAP), pulse pressure (PP), and APOE4 status. Whole-brain voxel-wise analysis showed that Aβ SUVR was positively correlated with carotid β stiffness index, and negatively with carotid distensibility at the precuneus/cingulate gyrus after multiple comparison correction. cfPWV was not correlated with Aβ SUVR.

CONCLUSIONS

Carotid rather than aortic stiffening was independently associated with brain Aβ burden in patients with aMCI after adjusting for age, sex, MAP, PP, and APOE4 status. These findings provide evidence that arterial stiffening, particularly carotid artery stiffening, may contribute to AD pathology in patients with aMCI.

Personalized treatment interventions: nonpharmacological and natural treatment strategies in Alzheimer's disease

Introduction: Alzheimer's disease (AD) is a slow, irreversible, progressive, complex, and fatal neurodegenerative disorder. Available pharmacological treatment, known for almost two decades, does not cure the disease, but only alleviates the symptoms, with various efficacy and different side effects. Therefore, there is an unmet need to find other person-centered or personalized approaches to treat AD.Areas covered: This article describes the application of precision medicine-like approaches utilizing nonpharmacological treatment strategies and the use of natural products in personalized care for patients with AD.Expert opinion: Due to the heterogeneity of disease symptoms, somatic conditions, and patient preferences, there is definitely no "one size fits all" intervention. Therefore, individualized treatment choice is based on dementia stage, medical and psychiatric comorbidity, leading symptoms, patient preferences, and remaining capacity of the patient. In the absence of disease-modifying agents, a patient-centered, multidisciplinary team approach appears to be the best option to alleviate the heavy symptomatic burden in this unfortunate population. Hence, appropriate interventions can be offered along the AD continuum, while a better understanding of personal characteristics might help in establishing optimal individualized treatment, as well as its duration and intensity, to deliver interventions in the most effective ways.

Effects of age and sex on middle cerebral artery blood velocity and flow pulsatility index across the adult lifespan

Reduced middle cerebral artery blood velocity (MCAv) and flow pulsatility are contributors to age-related cerebrovascular disease pathogenesis. It is unknown whether the rate of changes in MCAv and flow pulsatility support the hypothesis of sex-specific trajectories with aging. Therefore, we sought to characterize the rate of changes in MCAv and flow pulsatility across the adult lifespan in females and males as well as within specified age ranges. Participant characteristics, mean arterial pressure, end-tidal carbon dioxide, unilateral MCAv, and flow pulsatility index (PI) were determined from study records compiled from three institutional sites. A total of 524 participants [18-90 yr; females 57 (17) yr, n = 319; males 50 (21) yr, n = 205] were included in the analysis. MCAv was significantly higher in females within the second (P < 0.001), fifth (P = 0.01), and sixth (P < 0.01) decades of life. Flow PI was significantly lower in females within the second decade of life (P < 0.01). Rate of MCAv decline was significantly greater in females than males (-0.39 vs. -0.26 cm s^-1·yr, P = 0.04). Rate of flow PI rise was significantly greater in females than males (0.006 vs. 0.003 flow PI, P = 0.01). Rate of MCAv change was significantly greater in females than males in the sixth decade of life (-1.44 vs. 0.13 cm s^-1·yr, P = 0.04). These findings indicate that sex significantly contributes to age-related differences in both MCAv and flow PI. Therefore, further investigation into cerebrovascular function within and between sexes is warranted to improve our understanding of the reported sex differences in cerebrovascular disease prevalence.NEW & NOTEWORTHY We present the largest dataset (n = 524) pooled from three institutions to study how age and sex affect middle cerebral artery blood velocity (MCAv) and flow pulsatility index (PI) across the adult lifespan. We report the rate of MCAv decline and flow PI rise is significantly greater in females compared with in males. These data suggest that sex-specific trajectories with aging and therapeutic interventions to promote healthy brain aging should consider these findings.

Chronic hyperglycemia before acute ischemic stroke impairs the bilateral cerebrovascular response to exercise during the subacute recovery period

BACKGROUND AND PURPOSE

Chronic hyperglycemia contributes to cerebrovascular dysfunction by damaging blood vessels. Poor glucose control has been tied to impairments in cerebral blood flow, which may be particularly detrimental for people recovering from major cerebrovascular events such as acute ischemic stroke. In this secondary analysis, we explore for the first time the connection between chronic hyperglycemia before acute stroke and the cerebrovascular response (CVR) to exercise 3 and 6 month into the subacute recovery period.

METHODS

We recorded middle cerebral artery velocity (MCAv) using transcranial Doppler ultrasound bilaterally at rest and during moderate-intensity exercise in stroke patients at 3 (n = 19) and 6 (n = 12) months post-stroke. We calculated CVR as the difference between MCAv during steady-state exercise and resting MCAv. We obtained hemoglobin A1c levels (HbA1c; a measure of blood glucose over the prior 3 months) from the electronic medical record (EMR) and divided participants by HbA1c greater or less than 7%.

RESULTS

Participants with high HbA1c (>7%) at the time of acute stroke had significantly lower CVR to exercise for both the stroke-affected (p = .009) and non-affected (p = .007) hemispheres at 3 months post-stroke. These differences remained significant at 6 months post-stroke (stroke-affected, p = .008; non-affected, p = .016).

CONCLUSIONS

Patients with chronic hyperglycemia before acute ischemic stroke demonstrated impaired cerebrovascular function during exercise months into the subacute recovery period. These findings highlight the importance of maintaining tight glucose control to reduce morbidity and improve recovery post-stroke and could have implications for understanding cerebrovascular pathophysiology.

Optimizing Recruitment Strategies and Physician Engagement for Stroke Recovery Research

BACKGROUND AND PURPOSE

A major challenge for stroke rehabilitation and recovery research is the recruitment and retention of participants. Our prior challenges and successes have influenced our team to rethink our approach and the potential for large-scale stroke recruitment.

SUMMARY OF KEY POINTS

In this special interest article, we highlight how the adoption and implementation of recruitment strategies such as physician engagement and a streamlined "customer service" approach helped us improve our enrollment and maximize efficiency. Another positive outcome of enrollment was increased representation of those who identify as underrepresented minority or live in rural areas.

RECOMMENDATIONS FOR CLINICAL PRACTICE

Rethinking our recruitment processes and infrastructure allowed for greater interprofessional interactions, minimal burden for our stroke physician team members, and maximized enrollment into our stroke studies.Video Abstract available for more insights from the authors (see the Video, Supplemental Digital Content 1, available at: http://links.lww.com/JNPT/A324).

Targeting Transcription Factor Nrf2 (Nuclear Factor Erythroid 2-Related Factor 2) for the Intervention of Vascular Cognitive Impairment and Dementia

Vascular cognitive impairment and dementia (VCID) is an age-related, mild to severe mental disability due to a broad panel of cerebrovascular disorders. Its pathobiology involves neurovascular dysfunction, blood-brain barrier disruption, white matter damage, microRNAs, oxidative stress, neuroinflammation, and gut microbiota alterations, etc. Nrf2 (Nuclear factor erythroid 2-related factor 2) is the master regulator of redox status and controls the transcription of a panel of antioxidative and anti-inflammatory genes. By interacting with NF-κB (nuclear factor-κB), Nrf2 also fine-tunes the cellular oxidative and inflammatory balance. Aging is associated with Nrf2 dysfunction, and increasing evidence has proved the role of Nrf2 in mitigating the VCID process. Based on VCID pathobiologies and Nrf2 studies from VCID and other brain diseases, we point out several hypothetical Nrf2 targets for VCID management, including restoration of endothelial function and neurovascular coupling, preservation of blood-brain barrier integrity, reduction of amyloidopathy, promoting white matter integrity, and mitigating oxidative stress and neuroinflammation. Collectively, the Nrf2 pathway could be a promising direction for future VCID research. Targeting Nrf2 would shed light on VCID managing strategies.

Vascular Health is Associated with Amyloid-β in Cognitively Normal Older Adults

Background:

Vascular health is closely related to Alzheimer’s disease (AD). Vascular function measured by flow mediated dilation (FMD) or pulsatility index (PI) can be used as marker of peripheral and central vascular health but is poorly characterized in those at risk for AD.

Objective:

To assess the relationship of peripheral and central vascular function with amyloid-β (Aβ) and white matter lesion burden among cognitively normal older adults.

Methods:

We enrolled participants 65 years of age and older. Using Doppler ultrasound, we assessed brachial artery FMD, and middle cerebral artery (PI). Global Aβ burden, quantified using [18F] Florbetapir PET imaging, and white matter lesion volume (WML) were used as measures of AD pathology and vascular brain injury.

Results:

After adjusting for age and cardiovascular risk factors, the data (n = 83) showed a negative association between FMD and Aβ burden (β= –0.03, p < 0.001). FMD at a cut-off of 4.45% had 88% specificity and 75% sensitivity to elevated Aβ (AUC = 0.86, 95% CI: 0.77–0.95). FMD was not related to WML volume (p = 0.8), and PI was unrelated to Aβ burden or WML volume (0 > 0.4).

Conclusions:

Among cognitively normal older adults, blunted peripheral vascular function, as measured by brachial artery FMD, is associated with Aβ burden. These findings provide support for further exploration into the pathophysiological relationship of vascular health and AD risk as measured by Aβ.

Heat therapy: possible benefits for cognitive function and the aging brain

Alzheimer's disease (AD) is the most common neurodegenerative disease, yet there are no disease-modifying treatments available and there is no cure. It is becoming apparent that metabolic and vascular conditions such as type 2 diabetes (T2D) and hypertension promote the development and accumulation of Alzheimer's disease-related dementia pathologies. To this end, aerobic exercise, which is a common lifestyle intervention for both metabolic disease and hypertension, is shown to improve brain health during both healthy aging and dementia. However, noncompliance or other barriers to exercise response are common in exercise treatment paradigms. In addition, reduced intracellular proteostasis and mitochondrial function could contribute to the etiology of AD. Specifically, compromised chaperone systems [i.e., heat shock protein (HSP) systems] can contribute to protein aggregates (i.e., β-amyloid plaques and neurofibrillary tangles) and reduced mitochondrial quality control (i.e., mitophagy). Therefore, novel therapies that target whole body metabolism, the vasculature, and chaperone systems (like HSPs) are needed to effectively treat AD. This review focuses on the role of heat therapy in the treatment and prevention of AD. Heat therapy has been independently shown to reduce whole body insulin resistance, improve vascular function, activate interorgan cross talk via endocytic vesicles, and activate HSPs to improve mitochondrial function and proteostasis in a variety of tissues. Thus, heat therapy could offer immense clinical benefit to patients suffering from AD. Importantly, future studies in patients are needed to determine the safety and efficacy of heat therapy in preventing AD.

The Effect of Stroke on Middle Cerebral Artery Blood Flow Velocity Dynamics During Exercise

BACKGROUND AND PURPOSE

Previous work demonstrates that older adults have a lower response in the middle cerebral artery velocity (MCAv) to an acute bout of moderate-intensity exercise when compared with young adults. However, no information exists regarding MCAv response to exercise after stroke. We tested whether MCAv response to an acute bout of moderate-intensity exercise differed between participants 3 months after stroke and an age- and sex-matched control group of older adults (CON). A secondary objective was to compare MCAv response between the stroke- and non-stroke-affected MCAv.

METHODS

Using transcranial Doppler ultrasound, we recorded MCAv during a 90-second baseline (BL) followed by a 6-minute moderate-intensity exercise bout using a recumbent stepper. Heart rate (HR), end-tidal CO2 (PETCO2), and beat-to-beat mean arterial blood pressure (MAP) were additional variables of interest. The MCAv response measures included BL, peak response amplitude (Amp), time delay (TD), and time constant (τ).

RESULTS

The Amp was significantly lower in the stroke-affected MCAv compared with CON (P < 0.01) and in the nonaffected MCAv compared with CON (P = 0.03). No between-group differences were found between TD and τ. No significant differences were found during exercise for PETCO2 and MAP while HR was lower in participants with stroke (P < 0.01). Within the group of participants with stroke, no differences were found between the stroke-affected and non-stroke-affected sides for any measures.

DISCUSSION AND CONCLUSIONS

Resolution of the dynamic response profile has the potential to increase our understanding of the cerebrovascular control mechanisms and test cerebrovascular response to physical therapy-driven interventions such as exercise.Video Abstract available for more insights from the authors (see the Video, Supplemental Digital Content 1, available at: http://links.lww.com/JNPT/A284).

Cardiovascular disease risk is associated with middle cerebral artery blood flow velocity in older adults

PURPOSE

The aim of this study was to evaluate the relationship of cardiovascular disease (CVD) on middle cerebral blood flow velocity (MCAv) at rest and during exercise. A secondary aim was to explore the relationship between MCAv and 1) the presence of white matter lesions and 2) cognitive function.

METHODS

We recruited individuals who were cognitively normal older adults. CVD risk was assessed by the Pooled Cohort atherosclerotic cardiovascular disease (ASCVD) risk score. Transcranial Doppler ultrasound measured middle cerebral artery at rest and during a bout of moderate intensity exercise. We quantified white matter lesions from MRI and cognitive function outcomes included executive function, language, processing speed, and attention.

RESULTS

Seventy-two participants 70.1 ± 4.7 years of age completed the study protocol. ASCVD risk score was significantly associated with resting and exercise MCAv (p<0.01) but not associated with white matter lesions (p>0.468). We observed a significant association between resting and exercise MCAv and language processing (p=0.010) but not other cognitive domains.

CONCLUSION

In cognitively normal older adults, higher ASCVD risk score was associated with blunted resting and exercise MCAv and with lower language processing performance. These results highlight the need for CVD risk management to maintain optimal brain health.

Self-Reported Omega-3 Supplement Use Moderates the Association between Age and Exercising Cerebral Blood Flow Velocity in Older Adults

Cerebral blood flow (CBF) decreases across the lifespan, and chronic conditions such as dementia and stroke accelerate this decline. Impaired CBF results in reduced delivery of oxygen and nutrients, which can damage the brain over time. Thus, there is a need to identify lifestyle interventions, including diet and exercise, to maintain CBF with aging and in the presence of chronic disease. In the present study, we used transcranial Doppler ultrasound to record middle cerebral artery velocity (MCAv), a surrogate measure of CBF, during moderate-intensity exercise in sedentary, cognitively normal older adults (n = 90). A multiple linear regression model (F(4, 85) = 3.21, p = 0.02) showed that self-reported omega-3 supplement use significantly moderated the association between age and mean exercising MCAv in these individuals (p = 0.01). Older age was associated with lower exercising MCAv in the group not taking omega-3 supplements, while exercising MCAv showed no decline with increasing age in the group who reported omega-3 supplement use. These findings suggest omega-3 supplementation may have an important role in the preservation of CBF with aging.

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.

TCD Cerebral Hemodynamic Changes during Moderate-Intensity Exercise in Older Adults

BACKGROUND AND PURPOSE

Exercise plays an important role in supporting overall brain health. However, the mechanisms by which exercise supports brain health are imprecisely defined. Further, brain hemodynamic changes during exercise are not clearly understood, especially in older adults. The primary aim of this study was to compare cerebral blood flow velocity and pulsatility index (PI) during moderate-intensity exercise between older adults with normal pulsatile flow (normal PI) and older adults with elevated pulsatile flow (elevated PI). Secondary aims were to compare cardiovascular disease risk and cognitive function between individuals with elevated and nonelevated PI.

METHODS

Using transcranial Doppler ultrasound (TCD), middle cerebral artery blood velocity (MCAv) and PI were recorded during the rest and moderate-intensity exercise. End tidal carbon dioxide (PET CO2 ) and beat-to-beat mean arterial blood pressure were also recorded.

RESULTS

We enrolled 104 older adults into the study. The change in PI was greater in normal PI group (35.5% vs. 21.3%, P = .005). The change in MCAv was similar in both groups (11.6% for normal PI vs. 10.6% for elevated PI; P = .22). There was no significant difference in cardiovascular disease risk between the two groups (P = .77). Individuals with elevated PI performed significantly worse in WAIS-R Digit Symbol and Trail Making Test A (P = .04 and = .01, respectively).

CONCLUSIONS

The percent increase in PI from rest to moderate-intensity exercise was attenuated in the older adults with elevated resting PI. Higher resting PI may negatively affect brain health as evidenced by the slower processing speed scores.

Brain perivascular macrophages: Recent advances and implications in health and diseases

Brain perivascular macrophages (PVMs) belong to a distinct population of brain‐resident myeloid cells located within the perivascular space surrounding arterioles and venules. Their characterization depends on the combination of anatomical localization, phagocytic capacity, and molecular markers. Under physiological status, they provide structural and functional support for maintaining brain homeostasis, including facilitation of blood‐brain barrier integrity and lymphatic drainage, and exertion of immune functions such as phagocytosis and antigen presentation. Increasing evidence also implicates their specific roles in diseased brain, ranging from cerebrovascular diseases, Aβ pathologies, infections, and autoimmunity. Collectively, PVMs are key components of the brain‐resident immune system, actively participate in a broad‐spectrum of processes in normal and diseased status. Details of the processes are largely underexplored. Targeting PVMs would lead to new insights and be a promising strategy for a broad array of human diseases.

Exercise intensity and middle cerebral artery dynamics in humans

Despite its necessity for understanding healthy brain aging, the influence of exercise intensity on cerebrovascular kinetics is currently unknown. We, therefore characterized middle cerebral artery blood flow velocity (MCAv) kinetics associated with two exercise intensities: low and moderate. We hypothesized that increasing exercise intensity would increase the MCAv amplitude response (Amp) and that age and estimated fitness (V̇O2max) would be related to Amp. Baseline (BL) values were collected for 90-seconds followed by a 6-minute exercise bout. Heart rate, end-tidal CO2, mean arterial pressure and MCAv were recorded throughout. MCAv kinetics were described by Amp, time delay (TD) and time constant (τ). Sixty-four adults completed the study. Amp was greater during moderate compared to low exercise intensity (p < 0.001) while no difference was observed in either TD (p = 0.65) or τ (p = 0.47). Amp was negatively associated with age (p < 0.01) and positively correlated with estimated V̇O2max (p < 0.01). Although Amp declines with age, maintaining higher V̇O2max may benefit the cerebrovascular response to exercise.

Cerebrovascular Reactivity Impairment in Preclinical Alzheimer's Disease

BACKGROUND AND PURPOSE

A substantial overlap exists between declines in cerebral vasoreactivity (CVR) and symptomatic Alzheimer's disease (AD). CVR can be quantified using transcranial Doppler (TCD) measurement of cerebral blood flow velocities (CBFV) in the middle cerebral artery (MCA) with CO₂ as a vasodilatory stimulus. The breath-hold acceleration index (BHAI) is a new, more reliable measure of CVR developed recently in our laboratory. Our primary goal is to explore the possibility of using TCD for asymptomatic AD screening.

METHODS

A pilot study population was divided into three groups: 9 healthy control subjects, 8 subjects identified as preclinical AD, and 10 patients diagnosed with prodromal or mild AD. Control subjects had a Clinical Dementia Rating (CDR) score of 0 without elevated amyloid-β (Aβ) on amyloid positron emission tomography (PET) imaging, preclinical AD subjects had CDR = 0 with elevated Aβ, and prodromal to mild AD subjects had CDR scores ≥.5 and elevated Aβ. CVR was calculated using two indices: the conventional breath-holding index (BHI) and the new BHAI. TCD parameters between the three groups were compared.

RESULTS

BHAI was able to distinguish between 9 normal control subjects and 8 preclinical-AD subjects with high statistical significance (P < .001). BHI and pulsatility index were able only to distinguish AD from healthy and preclinical subjects (P < .001).

CONCLUSIONS

In this exploratory pilot study, CVR was significantly decreased in preclinical, prodromal, and mild AD subjects as compared to the healthy group. Lower CVR in the preclinical AD group was detected using the new BHAI index but not the conventional BHI index.