Crosswalk study on blood collection-tube types for Alzheimer's disease biomarkers

INTRODUCTION

Blood-based Alzheimer's disease (AD) biomarkers show promise, but pre-analytical protocol differences may pose problems. We examined seven AD blood biomarkers (amyloid beta [A β ] 42 ,A β 40 ,phosphorylated tau [ p - ta u 181 , total tau [t-tau], neurofilament light chain [NfL],A β 42 40 , andp - ta u 181 A β 42 ) in three collection tube types (ethylenediaminetetraacetic acid [EDTA] plasma, heparin plasma, serum).

METHODS

Plasma and serum were obtained from cerebrospinal fluid or amyloid positron emission tomography-positive and -negative participants (N = 38) in the Wisconsin Registry for Alzheimer's Prevention. We modeled AD biomarker values observed in EDTA plasma versus heparin plasma and serum, and assessed correspondence with brain amyloidosis.

RESULTS

Results suggested bias due to tube type, but crosswalks are possible for some analytes, with excellent model fit for NfL (R 2 = 0.94), adequate for amyloid (R 2 = 0.40-0.69), and weaker for t-tau (R 2 = 0.04-0.42) andp - ta u 181 (R 2 = 0.22-0.29). Brain amyloidosis differentiated several measures, especially EDTA plasmapTa u 181 A β 42 (d = 1.29).

DISCUSSION

AD biomarker concentrations vary by tube type. However, correlations for some biomarkers support harmonization across types, suggesting cautious optimism for use in banked blood.

Five-year changes in objectively measured cardiorespiratory fitness, physical activity, and sedentary time in mid-to-late adulthood

This study examined 5-year changes in cardiorespiratory fitness, physical activity, and sedentary time in mid-to-late aged adults. Fifty-seven participants completed baseline and follow-up treadmill exercise tests and physical activity monitoring. We observed a 14% decline in fitness (p < 0.001), 12% decrease in physical activity (p = 0.010), and non-significant increase in sedentary time (p = 0.196). Age was negatively associated with 5-year change in physical activity (r = -0.31; p = 0.02) and this decline was strongest among APOE ε4 carriers (g = -0.75). Novelty: Cardiorespiratory fitness and physical activity significantly declined from mid-to-late adulthood, these findings were most pronounced among older adults and those with genetic risk for Alzheimer's disease.

Age-related differences in white matter microstructure measured by advanced diffusion MRI in healthy older adults at risk for Alzheimer's disease

Neurite orientation dispersion and density imaging (NODDI) is an advanced diffusion imaging technique, which can detect more distinct microstructural features compared to conventional Diffusion Tensor Imaging (DTI). NODDI allows the signal to be divided into multiple water compartments and derive measures for orientation dispersion index (ODI), neurite density index (NDI) and volume fraction of isotropic diffusion compartment (FISO). This study aimed to investigate which diffusion metric-fractional anisotropy (FA), mean diffusivity (MD), NDI, ODI, or FISO-is most influenced by aging and reflects cognitive function in a population of healthy older adults at risk for Alzheimer's disease (AD). Age was significantly associated with all but one diffusion parameters and regions of interest. NDI and MD in the cingulate region adjacent to the cingulate cortex showed a significant association with a composite measure of Executive Function and was proven to partially mediate the relationship between aging and Executive Function decline. These results suggest that both DTI and NODDI parameters are sensitive to age-related differences in white matter regions vulnerable to aging, particularly among older adults at risk for AD.

Circulating klotho is elevated in cerebrospinal fluid, but not serum, among KLOTHO KL-VS allele carriers at risk for Alzheimer's disease

BACKGROUND

The klotho protein supports brain health and is encoded by the KLOTHO gene. The KL-VS allele modulates klotho protein secretion and function, but it is unknown how KL-VS genotype affects circulating klotho levels in blood and cerebrospinal fluid (CSF) among people at risk for AD.

METHODS

1112 cognitively intact participants from the Wisconsin Registry for Alzheimer's Prevention and Wisconsin Alzheimer's Disease Research Center underwent genotyping for KLOTHO KL-VS (non-carrier: KL-VS_NC ; heterozygote: KL-VS_HET ; homozygote: KL-VS_HOM ) and APOE4 alleles. 1098 participants underwent venipuncture and 183 underwent lumbar puncture. Circulating klotho was measured by ELISA in serum and/or CSF. Linear regression adjusted for age and sex tested the effect of KL-VS genotype on klotho in serum or CSF. In a subset of 169 participants with both serum and CSF data, linear regression adjusted for time between specimen collections tested the effect of specimen source on klotho level.

RESULTS

Visual inspection for outliers excluded four high serum klotho values (range 2461.5-4171.3 pg/mL; two KL-VS_NC , one KL-VS_HET , one KL-VS_HOM ); no CSF values were excluded. The mean participant age was 62.4 ± 6.6 and education was 15.8 ± 2.7 years. The majority were female (69.4%), White (92.6%), and had family history of dementia (72.6%), and 38.1% were APOE4 carriers. KL-VS genotype distribution was 73.1% KL-VS_NC , 25.2% KL-VS_HET , and 1.7% KL-VS_HOM . Mean serum klotho in KL-VS_NC was 800.8 ± 252.8 pg/mL and was not different in KL-VS_HET (b=17.7, SE=17.5, p=.31) or KL-VS_HOM (b=84.0, SE=58.1, p=.15). Mean CSF klotho in KL-VS_NC was 932.2 ± 153.2 pg/mL and was significantly higher in KL-VS_HET (b = 225.8, SE = 25.1, p< .001) and KL-VS_HOM (b=327.8, SE=75.5, p< .001). Mean CSF klotho was significantly higher than serum klotho in the entire subset (b=162.8, SE=25.9), p< .001) and within each KL-VS genotype (p's< .05).

CONCLUSIONS

In adults at risk for AD, CSF klotho is elevated in heterozygotic and homozygotic carriers of the KLOTHO KL-VS allele. Serum levels are lower than CSF and did not differ by genotype. Klotho specimen source should be considered in analyses of circulating klotho on brain health.

Effect of insulin resistance on the association between cardiorespiratory fitness and cognition in adults at risk for Alzheimer's disease

BACKGROUND

Cardiorespiratory fitness (CRF) and cognition have been found to be correlated, though it is unclear what mechanisms are responsible for this correlation. CRF and cognition are also closely related to insulin resistance. We investigated whether insulin resistance explains the relationship between CRF and cognition.

METHOD

This study included 1157 participants, all cognitively unimpaired and without history of diabetes. CRF was estimated using a validated equation that takes age, sex, BMI, resting heart rate, and self-reported physical activity habits as inputs. Insulin resistance was quantified by the Homeostatic Model Assessment for Insulin Resistance (HOMA-IR). Composite scores for executive function, immediate learning, delayed recall, and the Preclinical Alzheimer's Cognitive Composite (PACC3) were calculated from neuropsychological tests administered by trained technicians. For each cognitive score, linear regression models were utilized to test the influence of CRF on cognition. Mediation analyses were performed to determine whether HOMA-IR contributed to significant associations between CRF and cognition. All analyses controlled for age, sex, years of education, familial history of Alzheimer's disease, and Apolipoprotein E4 (APOE4) carriage. Bootstrapped confidence intervals were used to estimate the effect of HOMA-IR on the CRF/cognition relationship.

RESULT

The sample was comprised of 69.8% females and 38.7% APOE4 carriers with a mean age of 64.5 ± 7.2 years and a mean 16.3 ± 2.8 years of education. CRF was positively associated with executive function (total effect: B=.015, SE=.005, p=.003), but was not associated with immediate learning (p=.920), delayed recall (p=.970), or PACC3 (p=.258). HOMA-IR was further investigated as a mediator between CRF and executive function. CRF was negatively associated with HOMA-IR (B=-.241, SE=.013, p<.001) and HOMA-IR had a non-significant negative association with executive function (B=-.013, SE=.012, p=.264). While adjusting for HOMA-IR as a mediator, the association of CRF with executive function was positive and significant (direct effect: B=.012, SE=.006 p=.040). The bootstrapped estimate of the effect of HOMA-IR on the CRF/executive function relationship was insignificant (B=.0031, CI = [-.0020, .0087]).

CONCLUSION

HOMA-IR did not significantly mediate the relationship between CRF and executive function among individuals at heightened risk for Alzheimer's disease.

The Interaction between Ventricle to Brain Ratio and Serum Klotho on Cognition in Older Adults at Risk for Alzheimer's Disease

BACKGROUND

Ventricle to brain volume ratio (VBR) may be associated with Alzheimer's disease (AD) progression and is a robust correlate of cognition in AD. Klotho is a circulating protein positively associated with cognition. The purpose of this study was to evaluate whether serum klotho attenuates the adverse effect of higher VBR on cognition in older adults at risk for AD.

METHOD

This study included 359 cognitively unimpaired participants from the Wisconsin Alzheimer's Disease Research Center and Wisconsin Registry for Alzheimer's Prevention (mean age = 61.8 ± 6.5, 67% female). VBR was calculated from structural T1 MRI scans as the ratio of total ventricle volume to the sum of grey and white matter. Fasting venipuncture was conducted and analyzed for serum klotho. Neuropsychological examination was conducted for global cognition (PACC3) and composite scores were calculated for executive function, immediate learning, and delayed recall. Linear regression models were performed to assess the effect of VBR on cognition, accounting for APOE, gender, age, and time difference between MRI and serum klotho measurements. Next, models were fitted with an interaction for VBR x klotho. Follow-up analyses, stratified by median age (63.2 years), assessed age-specific effects.

RESULT

Higher VBR predicted poorer delayed recall (β(SE)=-6.3(3.1); p=.043), but not global cognition (β(SE)=-4.9(3.0); p=.101), executive function (β(SE)=-4.4(3.3); p=.178), or immediate learning (β(SE)=-4.4(3.3); p=.185). Significant VBR x klotho interactions existed for global cognition (p=.024) and executive function (p=.009) whereby higher serum klotho attenuated the adverse effect of VBR. This effect was absent for immediate learning (p=.162) and delayed recall (p=.267). Among older participants, VBR predicted worse global cognition (β=-7.4; p=.055), executive function (B=-8.8; p=.048), and nearly delayed recall (β=-8.1; p=.061), but not for immediate learning (p=.521). There were no effects among younger individuals (all p's ≥ .203). Lastly, the VBR x klotho interaction on executive function was significant among older participants (p=.037).

CONCLUSION

Serum klotho may protect against the adverse effect of high VBR on cognition, particularly among older individuals.

Circulating Klotho Is Higher in Cerebrospinal Fluid than Serum and Elevated Among KLOTHO Heterozygotes in a Cohort with Risk for Alzheimer's Disease

BACKGROUND

Klotho is a longevity and neuroprotective hormone encoded by the KLOTHO gene, and heterozygosity for the KL-VS variant confers a protective effect against neurodegenerative disease.

OBJECTIVE

Test whether klotho concentrations in serum or cerebrospinal fluid (CSF) vary as a function of KLOTHO KL-VS genotype, determine whether circulating klotho concentrations from serum and CSF differ from one another, and evaluate whether klotho levels are associated with Alzheimer's disease risk factors.

METHODS

Circulating klotho was measured in serum (n = 1,116) and CSF (n = 183) of cognitively intact participants (aged 62.4 ± 6.5 years; 69.5% female). KLOTHO KL-VS zygosity (non-carrier; heterozygote; homozygote) was also determined. Linear regression was used to test whether klotho hormone concentration varied as a function of KL-VS genotype, specimen source, and demographic and clinical characteristics.

RESULTS

Serum and CSF klotho were higher in KL-VS carriers than non-carriers. Klotho concentration was higher in CSF than in serum. Females had higher serum and CSF klotho, while younger age was associated with higher klotho in CSF.

CONCLUSION

In a cohort enriched for risk for Alzheimer's disease, heterozygotic and homozygotic carriers of the KL-VS allele, females, and younger individuals have higher circulating klotho. Fluid source, KL-VS genotype, age, and sex should be considered in analyses of circulating klotho on brain health.

Effect of Aerobic Exercise Training on Mood and Cognition in Adults at Risk for Alzheimer's Disease

BACKGROUND

Aerobic exercise is positively associated with mood and cognition, but its effect on protection against decline in mood and cognition in late-middle aged adults at risk for Alzheimers disease (AD) is unknown.

METHOD

23 late-middle aged adults from a cohort enriched with family history of AD and the APOE4 allele were randomized into Usual or Enhanced Physical Activity (PA) groups. Enhanced PA completed a progressive 26-week supervised aerobic exercise program at 70-80% heart rate reserve for 50 minutes, 3 times per week to achieve or exceed public health guidelines. Usual PA only received materials regarding active lifestyle. The Profile of Mood States (POMS) assessed total mood disturbance (TMD), characterized by fatigue, depression, tension, confusion, anger, and vigor. The California Verbal Learning Test II (CVLT-II) measured verbal learning and memory via the total, short, and long delayed recall, and learning slope. The Delis-Kaplan Executive Function System (DKEFS) assessed executive function via the trail-making, color-word interference (CWI), verbal fluency, and tower subtests. Graded treadmill exercise testing assessed cardiorespiratory fitness (CRF), and triaxial accelerometry measured moderate-to-vigorous physical activity (MVPA). Independent samples t-tests between groups and Pearson's correlations were conducted on baseline to post-intervention change scores.

RESULT

Fatigue decreased significantly in Enhanced PA compared to Usual PA (-1.18 ± 4.05 vs 2.92 ± 2.68, p= .009), and the decreases in TMD (-7.64 ± 17.78 vs 6.00 ± 16.42, p=.07) and tension (-2.00 ± 4.41 vs 0.67 ± 2.39, p= .08) among Enhanced PA were nearly significant. Changes in other mood subcategories and in cognition were not different between groups (all p's> .15), except improved executive function on the DKEFS CWI as previously published (Gaitán et al. 2019). Correlations of mood with verbal learning and memory or executive function were not significant (all r's < .17, all p's> .44). Correlations of mood or cognition with CRF or MVPA were not significant (p's> .175), except between DKEFS CWI and CRF as previously published (Gaitán et al. 2019).

CONCLUSION

Aerobic exercise training may protect against fatigue in adults at risk for AD. However, change in mood was not associated with cognitive changes in this cohort.

EXERT: Impact of COVID‐19 on retention and intervention delivery of a large multisite exercise trial in adults with MCI

Background

EXERT, a multisite 18‐month RCT, is testing the effects of aerobic exercise vs. stretching on cognition and AD biomarkers in sedentary adults with MCI. In the first 12 months, participant exercise 2x/week under the supervision of YMCA trainers, and 2x/week on their own. In months 13‐18, participants continue to exercise 4x/week but without supervision. Here we describe the impact of the COVID‐19 pandemic on delivery of this support‐intensive intervention that involved many challenges but also opportunities for innovation.

Method

In February 2020, EXERT met the recruitment goal with 296 enrolled. In March 2020 when COVID‐19 incidence rates began to climb in the US, study assessments and per‐protocol intervention delivery were paused. During the pause, all YMCAs were closed, and the majority of study‐certified YMCA trainers were furloughed.

Result

At the time of the pause (March 23), 153 participants were in the supervised phase of the study, and 65 participants were in the unsupervised phase. To keep participants engaged and encourage adherence to the intervention, sites initiated weekly calls with active participants to provide support, address barriers to exercise and collect self‐report adherence data. By September, 7 of 14 sites resumed study activities. Weekly call completion rates during the pause exceeded 85%, and participants reported completing a mean of 3.3 40‐minute exercise sessions per week. On these calls, participants frequently expressed gratitude for the regular contact. By February 2021, all sites resumed activities despite COVID infection rates that have continued to climb across the US. In response, supervised exercise for the majority of participants was transitioned from in‐person to web‐conferencing. Even with this change that can be challenging for MCI, supervised session adherence rates are 72% for the aerobic group and 79% for the stretching group. Retention has remained high at 87%.

Conclusion

The COVID‐19 pandemic presented unprecedented challenges, but it also provided unique opportunities to adapt intervention delivery so that a community‐based exercise trial could continue – even during a debilitating global health crisis. EXERT’s adaptations may ultimately impact resilience of the intervention to even the most challenging of circumstances that older adults with MCI will face now and in the future.

Impact of sex and APOE ε4 on age-related cerebral perfusion trajectories in cognitively asymptomatic middle-aged and older adults: A longitudinal study

Cerebral hypoperfusion is thought to contribute to cognitive decline in Alzheimer's disease, but the natural trajectory of cerebral perfusion in cognitively healthy adults has not been well-studied. This longitudinal study is consisted of 950 participants (40-89 years), who were cognitively unimpaired at their first visit. We investigated the age-related changes in cerebral perfusion, and their associations with APOE-genotype, biological sex, and cardiometabolic measurements. During the follow-up period (range 0.13-8.24 years), increasing age was significantly associated with decreasing cerebral perfusion, in total gray-matter (β=-1.43), hippocampus (-1.25), superior frontal gyrus (-1.70), middle frontal gyrus (-1.99), posterior cingulate (-2.46), and precuneus (-2.14), with all P-values < 0.01. Compared with male-ɛ4 carriers, female-ɛ4 carriers showed a faster decline in global and regional cerebral perfusion with increasing age, whereas the age-related decline in cerebral perfusion was similar between male- and female-ɛ4 non-carriers. Worse cardiometabolic profile (i.e., increased blood pressure, body mass index, total cholesterol, and blood glucose) was associated with lower cerebral perfusion at all the visits. When time-varying cardiometabolic measurements were adjusted in the model, the synergistic effect of sex and APOE-ɛ4 on age-related cerebral perfusion-trajectories became largely attenuated. Our findings demonstrate that APOE-genotype and sex interactively impact cerebral perfusion-trajectories in mid- to late-life. This effect may be partially explained by cardiometabolic alterations.

Recruitment of a multi-site randomized controlled trial of aerobic exercise for older adults with amnestic mild cognitive impairment: The EXERT trial

INTRODUCTION

Effective strategies to recruit older adults with mild cognitive impairment (MCI) into nonpharmacological intervention trials are lacking.

METHODS

Recruitment for EXERT, a multisite randomized controlled 18-month trial examining the effects of aerobic exercise on cognitive trajectory in adults with amnestic MCI, involved a diverse portfolio of strategies to enroll 296 participants.

RESULTS

Recruitment occurred September 2016 through March 2020 and was initially slow. After mass mailings of 490,323 age- and geo-targeted infographic postcards and brochures, recruitment rates increased substantially, peaking at 16 randomizations/month in early 2020. Mass mailings accounted for 52% of randomized participants, whereas 25% were recruited from memory clinic rosters, electronic health records, and national and local registries. Other sources included news broadcasts, public service announcements (PSA), local advertising, and community presentations.

DISCUSSION

Age- and geo-targeted mass mailing of infographic materials was the most effective approach in recruiting older adults with amnestic MCI into an 18-month exercise trial.

Soft tissue radiodensity parameters mediate the relationship between self-reported physical activity and lower extremity function in AGES-Reykjavík participants

Although previous studies have highlighted the association between physical activity and lower extremity function (LEF) in elderly individuals, the mechanisms underlying this relationship remain debated. Our recent work has recognized the utility of nonlinear trimodal regression analysis (NTRA) parameters in characterizing changes in soft tissue radiodensity as a quantitative construct for sarcopenia in the longitudinal, population-based cohort of the AGES-Reykjavík study. For the present work, we assembled a series of prospective multivariate regression models to interrogate whether NTRA parameters mediate the 5-year longitudinal relationship between physical activity and LEF in AGES-Reykjavík participants. Healthy elderly volunteers from the AGES-Reykjavík cohort underwent mid-thigh X-ray CT scans along with a four-part battery of LEF tasks: normal gait speed, fastest-comfortable gait speed, isometric leg strength, and timed up-and-go. These data were recorded at two study timepoints which were separated by approximately 5 years: AGES-I (n = 3157) and AGES-II (n = 3098). Participants in AGES-I were likewise administered a survey to approximate their weekly frequency of engaging in moderate-to-vigorous physical activity (PAAGES-I). Using a multivariate mediation analysis framework, linear regression models were assembled to test whether NTRA parameters mediated the longitudinal relationship between PAAGES-I and LEFAGES-II; all models were covariate-adjusted for age, sex, BMI, and baseline LEF, and results were corrected for multiple statistical comparisons. Our first series of models confirmed that all four LEF tasks were significantly related to PAAGES-I; next, modelling the relationship between PAAGES-I and NTRAAGES-II identified muscle amplitude (Nm) and location (μm) as potential mediators of LEF to test. Finally, adding these two parameters into our PAAGES-I → LEFAGES-II models attenuated the prior effect of PAAGES-I; bootstrapping confirmed Nm and μm as significant partial mediators of the PAAGES-I → LEFAGES-II relationship, with the strongest effect found in isometric leg strength. This work describes a novel approach toward clarifying the mechanisms that underly the relationship between physical activity and LEF in aging individuals. Identifying Nm and μm as significant partial mediators of this relationship provides strong evidence that physical activity protects aging mobility through the preservation of both lean tissue quantity and quality.

Cardiorespiratory fitness mitigates brain atrophy and cognitive decline in adults at risk for Alzheimer's disease

INTRODUCTION

Cardiorespiratory fitness (CRF) may mitigate Alzheimer's disease (AD) progression. This study examined the longitudinal associations of CRF with brain atrophy and cognitive decline in a late-middle-aged cohort of adults at risk for AD.

METHODS

One hundred ten cognitively unimpaired adults (66% female, mean age at baseline 64.2 ± 5.7 years) completed a baseline graded treadmill exercise test, two brain magnetic resonance imaging scans (over 4.67 ± 1.17 years), and two to three cognitive assessments (over 3.26 ± 1.02 years). Linear mixed effects models examined the longitudinal associations adjusted for covariates.

RESULTS

Participants with higher baseline CRF had slower annual decline in total gray matter volume (P = .013) and cognitive function (P = .048), but not hippocampal volume (P = .426). Exploratory analyses suggested these effects may be stronger among apolipoprotein E ε4 carriers.

DISCUSSION

CRF is a modifiable physiological attribute that may be targeted during the preclinical phase of AD in effort to delay disease progression, perhaps most effectively among those with genetic risk.