Impact of pre-analytical sample handling factors on plasma biomarkers of Alzheimer's disease.

An unmet need exists for reliable plasma biomarkers of amyloid pathology, in the clinical laboratory setting, to streamline diagnosis of Alzheimer's disease (AD). For routine clinical use, a biomarker must provide robust and reliable results under pre-analytical sample handling conditions. We investigated the impact of different pre-analytical sample handling procedures on the levels of seven plasma biomarkers in development for potential routine use in AD. Using (1) fresh (never frozen) and (2) previously frozen plasma, we evaluated the effects of (A) storage time and temperature, (B) freeze/thaw (F/T) cycles, (C) anticoagulants, (D) tube transfer, and (E) plastic tube types. Blood samples were prospectively collected from patients with cognitive impairment undergoing investigation in a memory clinic. ß-amyloid 1-40 (Aß40), ß-amyloid 1-42 (Aß42), apolipoprotein E4, glial fibrillary acidic protein, neurofilament light chain, phosphorylated-tau (phospho-tau) 181, and phospho-tau-217 were measured using Elecsys® plasma prototype immunoassays. Recovery signals for each plasma biomarker and sample handling parameter were calculated. For all plasma biomarkers measured, pre-analytical effects were comparable between fresh (never frozen) and previously frozen samples. All plasma biomarkers tested were stable for ≤24 h at 4°C when stored as whole blood and ethylenediaminetetraacetic acid (EDTA) plasma. Recovery signals were acceptable for up to five tube transfers, or two F/T cycles, and in both polypropylene and low-density polyethylene tubes. For all plasma biomarkers except Aß42 and Aß40, analyte levels were largely comparable between EDTA, lithium heparin, and sodium citrate tubes. Aß42 and Aß40 were most sensitive to pre-analytical handling, and the effects could only be partially compensated by the Aß42/Aß40 ratio. We provide recommendations for an optimal sample handling protocol for analysis of plasma biomarkers for amyloid pathology AD, to improve the reproducibility of future studies on plasma biomarkers assays and for potential use in routine clinical practice.

Age, sex and APOE-ε4 modify the balance between soluble and fibrillar ß-amyloid in non-demented individuals: topographical patterns across two independent cohorts.

Amyloid (Aß) pathology is the earliest detectable pathophysiological event along the Alzheimer's continuum, which can be measured both in the cerebrospinal fluid (CSF) and by Positron Emission Tomography (PET). Yet, these biomarkers identify two distinct Aß pools, reflecting the clearance of soluble Aß as opposed to the presence of Aß fibrils in the brain. An open question is whether risk factors known to increase Alzheimer's' disease (AD) prevalence may promote an imbalance between soluble and deposited Aß. Unveiling such interactions shall aid our understanding of the biological pathways underlying Aß deposition and foster the design of effective prevention strategies. We assessed the impact of three major AD risk factors, such as age, APOE-ε4 and female sex, on the association between CSF and PET Aß, in two independent samples of non-demented individuals (ALFA: n = 320, ADNI: n = 682). We tested our hypotheses both in candidate regions of interest and in the whole brain using voxel-wise non-parametric permutations. All of the assessed risk factors induced a higher Aß deposition for any given level of CSF Aß42/40, although in distinct cerebral topologies. While age and sex mapped onto neocortical areas, the effect of APOE-ε4 was prominent in the medial temporal lobe, which represents a target of early tau deposition. Further, we found that the effects of age and APOE-ε4 was stronger in women than in men. Our data indicate that specific AD risk factors affect the spatial patterns of cerebral Aß aggregation, with APOE-ε4 possibly facilitating a co-localization between Aß and tau along the disease continuum.

Identification of plasma metabolites associated with modifiable risk factors and endophenotypes reflecting Alzheimer's disease pathology.

Modifiable factors can influence the risk for Alzheimer's disease (AD) and serve as targets for intervention; however, the biological mechanisms linking these factors to AD are unknown. This study aims to identify plasma metabolites associated with modifiable factors for AD, including MIND diet, physical activity, smoking, and caffeine intake, and test their association with AD endophenotypes to identify their potential roles in pathophysiological mechanisms. The association between each of the 757 plasma metabolites and four modifiable factors was tested in the wisconsin registry for Alzheimer's prevention cohort of initially cognitively unimpaired, asymptomatic middle-aged adults. After Bonferroni correction, the significant plasma metabolites were tested for association with each of the AD endophenotypes, including twelve cerebrospinal fluid (CSF) biomarkers, reflecting key pathophysiologies for AD, and four cognitive composite scores. Finally, causal mediation analyses were conducted to evaluate possible mediation effects. Analyses were performed using linear mixed-effects regression. A total of 27, 3, 23, and 24 metabolites were associated with MIND diet, physical activity, smoking, and caffeine intake, respectively. Potential mediation effects include beta-cryptoxanthin in the association between MIND diet and preclinical Alzheimer cognitive composite score, hippurate between MIND diet and immediate learning, glutamate between physical activity and CSF neurofilament light, and beta-cryptoxanthin between smoking and immediate learning. Our study identified several plasma metabolites that are associated with modifiable factors. These metabolites can be employed as biomarkers for tracking these factors, and they provide a potential biological pathway of how modifiable factors influence the human body and AD risk.

Clinical performance and robustness evaluation of plasma amyloid-ß42/40 prescreening.

INTRODUCTION: Further evidence is needed to support the use of plasma amyloid ß (Aß) biomarkers as Alzheimer's disease prescreening tools. This study evaluated the clinical performance and robustness of plasma Aß42 /Aß40 for amyloid positivity prescreening. METHODS: Data were collected from 333 BioFINDER and 121 Alzheimer's Disease Neuroimaging Initiative study participants. Risk and predictive values versus percentile of plasma Aß42 /Aß40 evaluated the actionability of plasma Aß42 /Aß40 , and simulations modeled the impact of potential uncertainties and biases. Amyloid PET was the brain amyloidosis reference standard. RESULTS: Elecsys plasma Aß42 /Aß40 could potentially rule out amyloid pathology in populations with low-to-moderate amyloid positivity prevalence. However, simulations showed small measurement or pre-analytical errors in Aß42 and/or Aß40 cause misclassifications, impacting sensitivity or specificity. The minor fold change between amyloid PET positive and negative cases explains the biomarkers low robustness. DISCUSSION: Implementing plasma Aß42 /Aß40 for routine clinical use may pose significant challenges, with misclassification risks. HIGHLIGHTS: Plasma Aß42 /Aß40 ruled out amyloid PET positivity in a setting of low amyloid-positive prevalence. Including (pre-) analytical errors or measurement biases caused misclassifications. Plasma Aß42 /Aß40 had a low inherent dynamic range, independent of analytical method. Other blood biomarkers may be easier to implement as robust prescreening tools.

The potential clinical value of plasma biomarkers in Alzheimer's disease.

INTRODUCTION: Many people with cognitive complaints or impairment never receive an accurate diagnosis of the underlying condition, potentially impacting their access to appropriate treatment. To address this unmet need, plasma biomarker tests are being developed for use in Alzheimer's disease (AD). Plasma biomarker tests span various stages of development, including in vitro diagnostic devices (or tests) (IVDs), laboratory-developed tests (LDTs) and research use only devices (or tests) (RUOs). Understanding the differences between each test type is important for appropriate implementation into the AD diagnostic pathway and care continuum. METHODS: Authors reviewed scientific literature (PubMed, meeting abstracts and presentations, company press releases and websites) on AD plasma biomarkers. RESULTS: This article defines IVDs, LDTs, and RUOs, discusses potential clinical applications and highlights the steps necessary for their clinical implementation. DISCUSSION: Plasma biomarkers could revolutionize many areas of the AD diagnostic pathway and care continuum, but further research is needed. HIGHLIGHTS: There is a need for a minimally invasive Alzheimer's disease (AD) diagnostic tool. AD plasma biomarker tests exist at various stages of commercial development. Understanding the development stage of a test is important for its appropriate use. Plasma biomarker tests could function as a triage tool to streamline AD diagnosis. Further steps remain before AD plasma biomarkers can be used routinely.

An accurate fully automated panel of plasma biomarkers for Alzheimer's disease.

INTRODUCTION: There is a great need for fully automated plasma assays that can measure amyloid beta (Aß) pathology and predict future Alzheimer's disease (AD) dementia. METHODS: Two cohorts (n = 920) were examined: Panel A+ (n = 32 cognitively unimpaired [CU], n = 106 mild cognitive impairment [MCI], and n = 89 AD) and BioFINDER-1 (n = 461 CU, n = 232 MCI). Plasma Aß42/Aß40, phosphorylated tau (p-tau)181, two p-tau217 variants, ApoE4 protein, neurofilament light, and GFAP were measured using Elecsys prototype immunoassays. RESULTS: The best biomarker for discriminating Aß-positive versus Aß-negative participants was Aß42/Aß40 (are under the curve [AUC] 0.83-0.87). Combining Aß42/Aß40, p-tau181, and ApoE4 improved the AUCs significantly (0.90 to 0.93; P< 0.01). Adding additional biomarkers had marginal effects (ΔAUC ≤0.01). In BioFINDER, p-tau181, p-tau217, and ApoE4 predicted AD dementia within 6 years in CU (AUC 0.88) and p-tau181, p-tau217, and Aß42/Aß40 in MCI (AUC 0.87). DISCUSSION: The high accuracies for Aß pathology and future AD dementia using fully automated instruments are promising for implementing plasma biomarkers in clinical trials and clinical routine.

Neuropathology-based APOE genetic risk score better quantifies Alzheimer's risk.

INTRODUCTION: Apolipoprotein E (APOE) ε4-carrier status or ε4 allele count are included in analyses to account for the APOE genetic effect on Alzheimer's disease (AD); however, this does not account for protective effects of APOE ε2 or heterogeneous effect of ε2, ε3, and ε4 haplotypes. METHODS: We leveraged results from an autopsy-confirmed AD study to generate a weighted risk score for APOE (APOE-npscore). We regressed cerebrospinal fluid (CSF) amyloid and tau biomarkers on APOE variables from the Wisconsin Registry for Alzheimer's Prevention (WRAP), Wisconsin Alzheimer's Disease Research Center (WADRC), and Alzheimer's Disease Neuroimaging Initiative (ADNI). RESULTS: The APOE-npscore explained more variance and provided a better model fit for all three CSF measures than APOE ε4-carrier status and ε4 allele count. These findings were replicated in ADNI and observed in subsets of cognitively unimpaired (CU) participants. DISCUSSION: The APOE-npscore reflects the genetic effect on neuropathology and provides an improved method to account for APOE in AD-related analyses.

Large-scale proteome and metabolome analysis of CSF implicates altered glucose and carbon metabolism and succinylcarnitine in Alzheimer's disease.

INTRODUCTION: A hallmark of Alzheimer's disease (AD) is the aggregation of proteins (amyloid beta [A] and hyperphosphorylated tau [T]) in the brain, making cerebrospinal fluid (CSF) proteins of particular interest. METHODS: We conducted a CSF proteome-wide analysis among participants of varying AT pathology (n = 137 participants; 915 proteins) with nine CSF biomarkers of neurodegeneration and neuroinflammation. RESULTS: We identified 61 proteins significantly associated with the AT category (P < 5.46 × 10-5 ) and 636 significant protein-biomarker associations (P < 6.07 × 10-6 ). Proteins from glucose and carbon metabolism pathways were enriched among amyloid- and tau-associated proteins, including malate dehydrogenase and aldolase A, whose associations with tau were replicated in an independent cohort (n = 717). CSF metabolomics identified and replicated an association of succinylcarnitine with phosphorylated tau and other biomarkers. DISCUSSION: These results implicate glucose and carbon metabolic dysregulation and increased CSF succinylcarnitine levels with amyloid and tau pathology in AD. HIGHLIGHTS: Cerebrospinal fluid (CSF) proteome enriched for extracellular, neuronal, immune, and protein processing. Glucose/carbon metabolic pathways enriched among amyloid/tau-associated proteins. Key glucose/carbon metabolism protein associations independently replicated. CSF proteome outperformed other omics data in predicting amyloid/tau positivity. CSF metabolomics identified and replicated a succinylcarnitine-phosphorylated tau association.

Reactive astrogliosis is associated with higher cerebral glucose consumption in the early Alzheimer's continuum.

PURPOSE: Glial activation is one of the earliest mechanisms to be altered in Alzheimer's disease (AD). Glial fibrillary acidic protein (GFAP) relates to reactive astrogliosis and can be measured in both cerebrospinal fluid (CSF) and blood. Plasma GFAP has been suggested to become altered earlier in AD than its CSF counterpart. Although astrocytes consume approximately half of the glucose-derived energy in the brain, the relationship between reactive astrogliosis and cerebral glucose metabolism is poorly understood. Here, we aimed to investigate the association between fluorodeoxyglucose ([18F]FDG) uptake and reactive astrogliosis, by means of GFAP quantified in both plasma and CSF for the same participants. METHODS: We included 314 cognitively unimpaired participants from the ALFA + cohort, 112 of whom were amyloid-ß (Aß) positive. Associations between GFAP markers and [18F]FDG uptake were studied. We also investigated whether these associations were modified by Aß and tau status (AT stages). RESULTS: Plasma GFAP was positively associated with glucose consumption in the whole brain, while CSF GFAP associations with [18F]FDG uptake were only observed in specific smaller areas like temporal pole and superior temporal lobe. These associations persisted when accounting for biomarkers of Aß pathology but became negative in Aß-positive and tau-positive participants (A + T +) in similar areas of AD-related hypometabolism. CONCLUSIONS: Higher astrocytic reactivity, probably in response to early AD pathological changes, is related to higher glucose consumption. With the onset of tau pathology, the observed uncoupling between astrocytic biomarkers and glucose consumption might be indicative of a failure to sustain the higher energetic demands required by reactive astrocytes.

Test-retest variability of plasma biomarkers in Alzheimer's disease and its effects on clinical prediction models.

INTRODUCTION: The effect of random error on the performance of blood-based biomarkers for Alzheimer's disease (AD) must be determined before clinical implementation. METHODS: We measured test-retest variability of plasma amyloid beta (Aß)42/Aß40, neurofilament light (NfL), glial fibrillary acidic protein (GFAP), and phosphorylated tau (p-tau)217 and simulated effects of this variability on biomarker performance when predicting either cerebrospinal fluid (CSF) Aß status or conversion to AD dementia in 399 non-demented participants with cognitive symptoms. RESULTS: Clinical performance was highest when combining all biomarkers. Among single-biomarkers, p-tau217 performed best. Test-retest variability ranged from 4.1% (Aß42/Aß40) to 25% (GFAP). This variability reduced the performance of the biomarkers (≈ΔAUC [area under the curve] -1% to -4%) with the least effects on models with p-tau217. The percent of individuals with unstable predicted outcomes was lowest for the multi-biomarker combination (14%). DISCUSSION: Clinical prediction models combining plasma biomarkers-particularly p-tau217-exhibit high performance and are less effected by random error. Individuals with unstable predicted outcomes ("gray zone") should be recommended for further tests.

Synaptic Changes in Parkinson Disease Assessed with in vivo Imaging.

OBJECTIVE: Parkinson disease is characterized by motor and nonmotor symptoms, reduced striatal dopamine signaling, and loss of dopamine neurons in the substantia nigra. It is now known that the pathological process in Parkinson disease may begin decades before the clinical diagnosis and include a variety of neuronal alterations in addition to the dopamine system. METHODS: This study examined the density of all synapses with synaptic vesicle glycoprotein 2A (SV2A) in Parkinson disease subjects with mild bilateral disease (n = 12) and matched normal controls (n = 12) using in vivo high-resolution positron emission tomographic imaging as well as postmortem autoradiography in an independent sample with Parkinson disease (n = 15) and normal controls (n = 13) in the substantia nigra and putamen. RESULTS: A group-by-brain region interaction effect (F10, 22 = 3.52, p = 0.007) was observed in the primary brain areas with in vivo SV2A binding. Post hoc analyses revealed that the Parkinson disease group exhibited lower SV2A in the substantia nigra (-45%; p < 0.001), red nucleus (-31%; p = 0.03), and locus coeruleus (-17%; p = 0.03). Exploratory analyses also revealed lower SV2A binding in clinically relevant cortical areas. Using autoradiography, we confirmed lower SV2A in the substantia nigra (-17%; p < 0.005) and nonsignificant findings in the putamen (-4%; p = 0.06). INTERPRETATION: This work provides the first evidence of synaptic loss in brainstem nuclei involved in the pathogenesis of Parkinson disease in living patients. SV2A imaging holds promise for understanding synaptic changes central to the disease. Ann Neurol 2020;87:329-338.

Peripheral cytokine and fatty acid associations with neuroinflammation in AD and aMCI patients: An exploratory study.

Neuroinflammation is thought to be important in the progression of Alzheimer's disease (AD). To evaluate cerebral inflammation radioligands that target TSPO, a translocator protein strongly expressed in microglia and macrophages during inflammation, can be used in conjunction with positron emission tomography (PET) imaging. In AD patients, neuroinflammation is up-regulated compared to both healthy volunteers as well as to subjects with amnestic Mild Cognitive Impairment. Peripheral biomarkers, such as serum cytokines and total fatty acids (FAs), can also be indicative of the inflammatory state of subjects with neurodegenerative disorders. To understand whether peripheral biomarkers are predictive of neuroinflammation we conducted a secondary exploratory analysis of two TSPO imaging studies conducted in subjects with AD, aMCI and aged matched healthy volunteers. We examined the association between candidate peripheral biomarkers (including amyloid beta, cytokines and serum total fatty acids) with brain TSPO levels. Our results showed that serum IL-6 and IL-10 are higher in AD compared to the aMCI and healthy volunteers while levels of some fatty acids are modulated during the disease. A limited number of associations were observed between region-specific inflammation and fatty acids in aMCI patients, and between amyloid beta 42 and brain inflammation in AD, however no associations were present with systemic cytokines. Our study suggests that while TSPO binding and systemic IL-6 and IL-10 were elevated in AD, serum amyloid beta, cytokines and fatty acids were generally not predictive of the disease nor correlated with neuroinflammation.

Quantitative imaging of neuroinflammation in human white matter: a positron emission tomography study with translocator protein 18 kDa radioligand, [18F]-FEPPA.

The ability to quantify translocator protein 18 kDa (TSPO) in white matter (WM) is important to understand the role of neuroinflammation in neurological disorders with WM involvement. This article aims to extend the utility of TSPO imaging in WM using a second-generation radioligand, [18F]-FEPPA, and high-resolution research tomograph (HRRT) positron emission tomography (PET) camera system. Four WM regions of interests (WM-ROI), relevant to the study of aging and neuroinflammatory diseases, were examined. The corpus callosum, cingulum bundle, superior longitudinal fasciculus, and posterior limb of internal capsule were delineated automatically onto subject's T1 -weighted magnetic resonance image using a diffusion tensor imaging-based WM template. The TSPO polymorphism (rs6971) stratified individuals to three genetic groups: high-affinity binders (HAB), mixed-affinity binders (MAB), and low-affinity binders. [18F]-FEPPA PET scans were acquired on 32 healthy subjects and analyzed using a full kinetic compartment analysis. The two-tissue compartment model showed moderate identifiability (coefficient of variation 15-19%) for [18F]-FEPPA total volume distribution (VT ) in WM-ROIs. Noise affects VT variability, although its effect on bias was small (6%). In a worst-case scenario, ≤6% of simulated data did not fit reliably. A simulation of increased TSPO density exposed minimal effect on variability and identifiability of [18F]-FEPPA VT in WM-ROIs. We found no association between age and [18F]-FEPPA VT in WM-ROIs. The VT values were 15% higher in HAB than in MAB, although the difference was not statistically significant. This study provides evidence for the utility and limitations of [18F]-FEPPA PET to measure TSPO expression in WM.

Dopamine D2 and D3 binding in people at clinical high risk for schizophrenia, antipsychotic-naive patients and healthy controls while performing a cognitive task.

BACKGROUND: The dopamine (DA) D2 receptors exist in 2 states: a high-affinity state (D2 high) that is linked to second messenger systems, responsible for functional effects, exhibits high affinity for agonists (e.g., DA), and a low-affinity state that is functionally inert exhibits lower affinity for agonists. The DA D3 receptor subtype exhibits high agonist affinity, whereas the existence of the multiple affinity states is controversial. Preclinical studies in animal models of psychosis have shown a selective increase of D2 high as the common factor in psychosis, and the D3 receptor has been suggested to be involved in the pathophysiology of schizophrenia. METHODS: We studied D2 high and D3 in people at clinical high risk (CHR) for schizophrenia and in antipsychotic-naive patients with schizophrenia using the novel positron emission tomography radiotracer, [11C]-(+)-PHNO. The binding potential nondisplaceable (BP(ND)) was examined in the regions of interest (ROI; caudate, putamen, ventral striatum, globus pallidus, substantia nigra and thalamus) using an ROI and a voxel-wise approach while participants performed a cognitive task. RESULTS: We recruited 12 CHR individuals and 13 antipsychotic-naive patients with schizophrenia-spectrum disorder, whom we compared with 12 age- and sex-matched healthy controls. The BP(ND) between patients and controls did not differ in any of the ROIs, consistent with the voxel-wise analysis. Correlations between the BP(ND) in D3-rich regions and psychopathology warrant further investigation. LIMITATIONS: In the absence of resting-state (baseline) BP(ND) data, or following a depletion paradigm (i.e., α-methyl partyrosine), it is not possible to ascertain whether the lack of difference among the groups is owing to different levels of baseline DA or to release during the cognitive task. CONCLUSION: To our knowledge, the present study represents the first effort to measure the D2 and D3 receptors under a cognitive challenge in individuals putative/prodromal for schizophrenia using [11C]-(+)-PHNO.

Current Diagnostic Pathways for Alzheimer's Disease: A Cross-Sectional Real-World Study Across Six Countries.

Background: Diagnostic pathways for patients presenting with cognitive complaints may vary across geographies. Objective: To describe diagnostic pathways of patients presenting with cognitive complaints across 6 countries. Methods: This real-world, cross-sectional study analyzed chart-extracted data from healthcare providers (HCPs) for 6,744 patients across China, France, Germany, Spain, UK, and the US. Results: Most common symptoms at presentation were cognitive (memory/amnestic; 89.86%), followed by physical/behavioral (87.13%). Clinical/cognitive tests were used in > 95%, with Mini-Mental State Examination being the most common cognitive test (79.0%). Blood tests for APOE ɛ4/other mutations, or to rule out treatable causes, were used in half of the patients. Clinical and cognitive tests were used at higher frequency at earlier visits, and amyloid PET/CSF biomarker testing at higher frequency at later visits. The latter were ordered at low rates even by specialists (across countries, 5.7% to 28.7% for amyloid PET and 5.0% to 27.3% for CSF testing). Approximately half the patients received a diagnosis (52.1% of which were Alzheimer's disease [AD]). Factors that influenced risk of not receiving a diagnosis were HCP type (higher for primary care physicians versus specialists) and region (highest in China and Germany). Conclusion: These data highlight variability in AD diagnostic pathways across countries and provider types. About 45% of patients are referred/told to 'watch and wait'. Improvements can be made in the use of amyloid PET and CSF testing. Efforts should focus on further defining biomarkers for those at risk for AD, and on dismantling barriers such low testing capacity and reimbursement challenges.

The recency ratio assessed by story recall is associated with cerebrospinal fluid levels of neurodegeneration biomarkers.

Recency refers to the information learned at the end of a study list or task. Recency forgetting, as tracked by the ratio between recency recall in immediate and delayed conditions, i.e., the recency ratio (Rr), has been applied to list-learning tasks, demonstrating its efficacy in predicting cognitive decline, conversion to mild cognitive impairment (MCI), and cerebrospinal fluid (CSF) biomarkers of neurodegeneration. However, little is known as to whether Rr can be effectively applied to story recall tasks. To address this question, data were extracted from the database of the Alzheimer's Disease Research Center at the University of Wisconsin - Madison. A total of 212 participants were included in the study. CSF biomarkers were amyloid-beta (Aß) 40 and 42, phosphorylated (p) and total (t) tau, neurofilament light (NFL), neurogranin (Ng), and α-synuclein (a-syn). Story Recall was measured with the Logical Memory Test (LMT). We carried out Bayesian regression analyses with Rr, and other LMT scores as predictors; and CSF biomarkers (including the Aß42/40 and p-tau/Aß42 ratios) as outcomes. Results showed that models including Rr consistently provided best fits with the data, with few exceptions. These findings demonstrate the applicability of Rr to story recall and its sensitivity to CSF biomarkers of neurodegeneration, and encourage its inclusion when evaluating risk of neurodegeneration with story recall.

Identifying clinically useful biomarkers in neurodegenerative disease through a collaborative approach: the NeuroToolKit.

BACKGROUND: Alzheimer's disease (AD) is a complex and heterogeneous disease, which requires reliable biomarkers for diagnosis and monitoring disease activity. Preanalytical protocol and technical variability associated with biomarker immunoassays makes comparability of biomarker data across multiple cohorts difficult. This study aimed to compare cerebrospinal fluid (CSF) biomarker results across independent cohorts, including participants spanning the AD continuum. METHODS: Measured on the NeuroToolKit (NTK) prototype panel of immunoassays, 12 CSF biomarkers were evaluated from three cohorts (ALFA+, Wisconsin, and Abby/Blaze). A correction factor was applied to biomarkers found to be affected by preanalytical procedures (amyloid-ß1-42, amyloid-ß1-40, and alpha-synuclein), and results between cohorts for each disease stage were compared. The relationship between CSF biomarker concentration and cognitive scores was evaluated. RESULTS: Biomarker distributions were comparable across cohorts following correction. Correlations of biomarker values were consistent across cohorts, regardless of disease stage. Disease stage differentiation was highest for neurofilament light (NfL), phosphorylated tau, and total tau, regardless of the cohort. Correlation between biomarker concentration and cognitive scores was comparable across cohorts, and strongest for NfL, chitinase-3-like protein-1 (YKL40), and glial fibrillary acidic protein. DISCUSSION: The precision of the NTK enables merging of biomarker datasets, after correction for preanalytical confounders. Assessment of multiple cohorts is crucial to increase power in future studies into AD pathogenesis.

Liver-Specific Polygenic Risk Score Is Associated with Alzheimer's Disease Diagnosis.

BACKGROUND: Our understanding of the pathophysiology underlying Alzheimer's disease (AD) has benefited from genomic analyses, including those that leverage polygenic risk score (PRS) models of disease. The use of functional annotation has been able to improve the power of genomic models. OBJECTIVE: We sought to leverage genomic functional annotations to build tissue-specific AD PRS models and study their relationship with AD and its biomarkers. METHODS: We built 13 tissue-specific AD PRS and studied the scores' relationships with AD diagnosis, cerebrospinal fluid (CSF) amyloid, CSF tau, and other CSF biomarkers in two longitudinal cohort studies of AD. RESULTS: The AD PRS model that was most predictive of AD diagnosis (even without APOE) was the liver AD PRS: n = 1,115; odds ratio = 2.15 (1.67-2.78), p = 3.62×10-9. The liver AD PRS was also statistically significantly associated with cerebrospinal fluid biomarker evidence of amyloid-ß (Aß42:Aß40 ratio, p = 3.53×10-6) and the phosphorylated tau:amyloid-ß ratio (p = 1.45×10-5). CONCLUSION: These findings provide further evidence of the role of the liver-functional genome in AD and the benefits of incorporating functional annotation into genomic research.

Impact of asthma on the brain: evidence from diffusion MRI, CSF biomarkers and cognitive decline.

Chronic systemic inflammation increases the risk of neurodegeneration, but the mechanisms remain unclear. Part of the challenge in reaching a nuanced understanding is the presence of multiple risk factors that interact to potentiate adverse consequences. To address modifiable risk factors and mitigate downstream effects, it is necessary, although difficult, to tease apart the contribution of an individual risk factor by accounting for concurrent factors such as advanced age, cardiovascular risk, and genetic predisposition. Using a case-control design, we investigated the influence of asthma, a highly prevalent chronic inflammatory disease of the airways, on brain health in participants recruited to the Wisconsin Alzheimer's Disease Research Center (31 asthma patients, 186 non-asthma controls, aged 45-90 years, 62.2% female, 92.2% cognitively unimpaired), a sample enriched for parental history of Alzheimer's disease. Asthma status was determined using detailed prescription information. We employed multi-shell diffusion weighted imaging scans and the three-compartment neurite orientation dispersion and density imaging model to assess white and gray matter microstructure. We used cerebrospinal fluid biomarkers to examine evidence of Alzheimer's disease pathology, glial activation, neuroinflammation and neurodegeneration. We evaluated cognitive changes over time using a preclinical Alzheimer cognitive composite. Using permutation analysis of linear models, we examined the moderating influence of asthma on relationships between diffusion imaging metrics, CSF biomarkers, and cognitive decline, controlling for age, sex, and cognitive status. We ran additional models controlling for cardiovascular risk and genetic risk of Alzheimer's disease, defined as a carrier of at least one apolipoprotein E (APOE) ε4 allele. Relative to controls, greater Alzheimer's disease pathology (lower amyloid-ß42/amyloid-ß40, higher phosphorylated-tau-181) and synaptic degeneration (neurogranin) biomarker concentrations were associated with more adverse white matter metrics (e.g. lower neurite density, higher mean diffusivity) in patients with asthma. Higher concentrations of the pleiotropic cytokine IL-6 and the glial marker S100B were associated with more salubrious white matter metrics in asthma, but not in controls. The adverse effects of age on white matter integrity were accelerated in asthma. Finally, we found evidence that in asthma, relative to controls, deterioration in white and gray matter microstructure was associated with accelerated cognitive decline. Taken together, our findings suggest that asthma accelerates white and gray matter microstructural changes associated with aging and increasing neuropathology, that in turn, are associated with more rapid cognitive decline. Effective asthma control, on the other hand, may be protective and slow progression of cognitive symptoms.

Blood-based biomarkers in Alzheimer's disease: Future directions for implementation.

INTRODUCTION: Disease-modifying therapies (DMTs) for Alzheimer's disease (AD) will increase diagnostic demand. A non-invasive blood-based biomarker (BBBM) test for detection of amyloid-ß pathology may reduce diagnostic barriers and facilitate DMT initiation. OBJECTIVE: To explore heterogeneity in AD care pathways and potential role of BBBM tests. METHODS: Survey of 213 healthcare professionals/payers in US/China/UK/Germany/Spain/France and two advisory boards (US/Europe). RESULTS: Current diagnostic pathways are heterogeneous, meaning many AD patients are missed while low-risk patients undergo unnecessary procedures. Confirmatory amyloid testing (cerebrospinal fluid biomarkers/positron emission tomography) is utilized in few patients, resulting in diagnostic/treatment delays. A high negative-predictive-value test could streamline the diagnostic pathway by reducing unnecessary procedures in low-risk patients; supporting confirmatory testing where needed. Imminent approval of DMTs will increase need for fast and reliable AD diagnostic tests. DISCUSSION: An easy-to-use, accurate, non-invasive BBBM test for amyloid pathology could guide diagnostic procedures or referral, streamlining early diagnosis and DMT initiation. Highlights: This study explored AD care pathways and how BBBM may meet diagnostic demandsCurrent diagnostic pathways are heterogeneous, with country and setting variationsMany AD patients are missed, while low-risk patients undergo unnecessary proceduresAn easy-to-use, accurate, non-invasive BBBM test for amyloid pathology is neededThis test could streamline early diagnosis of amyloid pathology and DMT initiation.