Aims

Cerebrospinal fluid (CSF) and plasma p-tau217 and p-tau231 are considered excellent Alzheimer’s disease (AD) biomarkers. Here, we employed the ultrasensitive immunoassay detecting CSF and plasma tau simultaneously phosphorylated at both these sites - T217 and T231 (C231D217) to determine its diagnostic potential.

Methods

Technical validation of C231D217 Simoa® assay included standard curve development with use of a custom synthetic peptide phosphorylated exclusively at T217 and T231 sites, followed by assessment of antibodies cross-reactivity, dilutional linearity, sensitivity, as well as intra- and inter-assay precision. Subsequently, we measured CSF and plasma C231D217 and related reference assays - singleplex p-tau217 and singleplex p-tau231 - in two well-characterized cohorts: discovery (MCI-AD n=21, AD dementia n=19, CTRL n=15) and validation (preclinical AD n=19, MCI-AD n=20, AD dementia n=16, frontotemporal dementia n=39, CTRL n=24).

Results

In both cohorts, CSF and plasma C231D217, p-tau217, and p-tau231 levels were significantly elevated in all AD continuum groups vs. CTRL. No significant difference was observed for FTD vs. CTRL for any of the analyzed biomarkers. In plasma, ROC analysis as well as analysis of the median concentration fold change for clinical groups comparison consistently showed a superior diagnostic performance of C231D217 when compared with plasma p-tau217 and p-tau231 (Fig.1.)

Conclusions

We propose that CSF and plasma tau simultaneously phosphorylated at T217 and T231 allows for highly sensitive and specific detection of AD continuum, including its early, asymptomatic stage. Our findings support the hypothesis that qualitative and quantitative change of tau phosphorylation, e.g. increased degree and modified pattern of phosphorylation, correlate with disease severity and progression. Further studies will need to include screening larger cohorts and assessment of tau simultaneously phosphorylated at sites different than those already analyzed.

Aims

Cerebrospinal fluid and imaging Alzheimer’s disease biomarkers have excellent diagnostic properties, but they are invasive, expensive, and not widely available. In this scenario, blood-based biomarkers offer a major benefit, but they have been mainly studied in individuals from specialised memory clinics. Therefore, to transfer these results to the general population, it is necessary to validate plasma biomarkers in large oldest-old heterogeneous primary care-based studies.

Methods

We measured the plasma levels of Aβ40, Aβ42, P-tau181, NfL, and GFAP in 1007 non-demented participants, aged 79-94 years and enrolled in the German longitudinal primary care-based AgeCoDe study. We sought to determine the association between plasma biomarker levels and cognitive decline and disease progression, and their capacity to improve the prediction of future dementia of the Alzheimer’s type (DAT) that can be obtained with easily accessible and cost-effective measures. Furthermore, to investigate age-related changes, we evaluated plasma biomarker dynamics in 305 participants with a follow-up (~8 years later) plasma sample available.

Results

We confirmed that plasma biomarkers are associated with an increased risk of progressing to DAT in persons regularly visiting the primary care system. Interestingly, while P-tau181, NfL, and GFAP were associated with faster cognitive decline, Aβ42/Aβ40 ratio was not. We also observed that a predictive model including all plasma biomarkers improved discrimination capacity within a 4-year period beyond age, sex, and APOE genotype. All plasma biomarkers showed age-dependent changes that should be considered when assessing risk of progression. Importantly, we observed that plasma biomarkers seem to be stable despite lacking optimal preanalytical conditions at general practitioners’ practices.

Conclusions

Plasma biomarkers are associated with progression to DAT in non-demented participants. Assessing multiple plasma biomarkers will considerably improve risk assessment for progressing to DAT in primary care.

Aims

Plasma amyloid beta 42/40 (Aβ42/40), phosphorylated tau-181 (p-tau-181), neurofilament light (NfL), and glial fibrillary acidic protein (GFAP) have been thoroughly investigated in Alzheimer’s disease (AD) and other dementias. However, few studies have examined these biomarkers in healthy seniors, which may allow for identification of novel associations that might otherwise be masked by co-morbidities. This study investigated the effect of APOE genotype on plasma biomarkers of AD to determine whether carrying the APOE4 allele, which increases AD risk, modifies concentrations in healthy seniors.

Methods

N=370 plasma specimens from the Super Seniors study were analyzed; participants were ≥85 years old and had never been diagnosed with dementia, cancer, diabetes, cardiovascular or major pulmonary disease. Biomarkers were analysed on the Quanterix Simoa HD-X analyzer using Neurology 4-plex E and p-tau-181 assays. Group comparisons were performed using a Mann-Whitney or Fisher's exact test, and associations between genotype and biomarkers were analyzed using multivariable linear regression.

Results

80 (22%) participants were APOE4 carriers (E3E4 N=71, E4E4 N=3, E2E4 N=6) and 290 (73%) were non-carriers (E2E2 N=3, E2E3 N=58, E3E3 N=229). No significant differences were found between APOE4 carriers and non-carriers for age (p=0.3215), sex (p>0.9999), or mini mental state exam scores (p=0.1327). In APOE4 carriers, Aβ42/40 was lower (0.0596 vs 0.0618 pg/ml, p=0.0462), and p-tau-181 (3.24 vs 2.78 pg/ml, p=0.0069) and GFAP (196 vs 172 pg/ml, p=0.0474) were higher compared to non-APOE4 carriers. NfL was not associated with carrier status (p=0.1188). After adjusting for significantly associated demographic variables (sex and BMI), only p-tau-181 remained significantly associated with APOE4 carrier status (β=0.06218, p=0.0169).

Conclusions

Plasma p-tau-181 is associated with APOE4 genotype in healthy seniors, making it an important variable to account for in future analysis.

Aims

We explored the association of chronic diseases and systemic inflammation with the concentration of blood biomarkers of Alzheimer’s disease (AD) in a dementia-free community-dwelling cohort.

Methods

In this cross-sectional study, we measured five biomarkers of AD (amyloid beta[Aβ]-42/40 ratio, phosphorylated tau-181 [p-tau181], total-tau [t-tau], neurofilament light chain [NfL] and glial fibrillary acidic protein [GFAP]) on serum samples of 2370 dementia-free participants of the Swedish National Study on Aging and Care in Kungsholmen (SNAC-K). Using multi-adjusted linear regression models, we explored the association of chronic diseases and systemic inflammation with z-scored serum levels of blood biomarkers of AD.

Results

Participants had a mean (SD) age of 72.5 (10.5) years and 61.8% of them were females. The concentration of all biomarkers, except for the Aβ-42/40 ratio, increased as the number of chronic diseases increased (p for trend <0.05). The levels of AD blood biomarkers varied in relation to several individual conditions. Among the others, chronic kidney disease, heart diseases and anemia were associated with higher concentrations of all biomarkers, except for the Aβ-42/40 ratio. Obesity was associated with lower levels of NfL, and hypertension was associated with lower levels of p-tau181, t-tau and NfL. Higher levels of NfL and GFAP were also found in participants with high compared to low IL-6 concentration (β 0.21, 95%CI 0.12, 0.29 and β 0.12, 95%CI 0.02, 0.22 for highest vs. lowest IL-6 tertile).

Conclusions

In the general population, the concentrations of blood biomarkers of AD vary in relation to chronic diseases and systemic inflammation. Considering the whole clinical complexity of the individual together with blood biomarkers of AD is essential for their clinical interpretation.

Aims

Studies have found that plasma biomarkers can differentiate dementia disorders. However, they are still not used clinically. The development of disease-modifying treatments calls for the use of plasma biomarkers. This study aimed to investigate associations between plasma, routine cerebrospinal fluid (CSF) and blood biomarkers, and comorbidities in a mixed memory clinic cohort.

Methods

We included 222 paired plasma and CSF samples from healthy controls (n=44), mild cognitive impairment (n=48), Alzheimer’s disease (AD) (n=68) and non-AD (n=62). Plasma phosphorylated tau (p-tau) 181, p-tau231, beta-amyloid 1-42 (Ab42), Ab40, glial fibrillary acidic protein (GFAP), neurofilament light chain (NfL) and N-terminal (NTA)-tau were measured by Single molecule array (Simoa) technology. CSF and routine blood biomarkers were measured as part of the diagnostic work-up.

Results

P-tau181 correlated positively with age and inversely with estimated glomerular filtration rate (eGFR). P-tau231 correlated positively with haemoglobin A1c (HbA1C), CSF p-tau181, CSF total tau and inversely with mini mental state examination score (MMSE), eGFR, total cholesterol, low density lipoprotein (LDL) and CSF Ab42. Plasma Ab42 and Ab40 correlated positively with age, HbA1C and inversely with MMSE, eGFR, total cholesterol, and LDL. Ab40 also correlated inversely with MMSE, high density lipoprotein (HDL), and positively with Fazekas (FAZ). Ab42/ab40 correlated positively with CSF Ab42 and inversely with HDL. GFAP correlated inversely with alanine aminotransferase (ALT). NfL was associated with higher age, HbA1c, and FAZ and with lower MMSE, body mass index (BMI), and eGFR. NTA-tau correlated inversely with MMSE and positively with CSF p-tau181 and CSF total tau.

Conclusions

Our data confirms the importance of taking comorbidities and biological confounders into account when using blood-based biomarkers for diagnosing dementia disorders in a mixed memory clinic population.

Aims

While plasma biomarkers hold great promise for early Alzheimer’s disease (AD) diagnosis, they do not consistently align with clinical symptomology. Substantial biomarker evidence may exhibit mild clinical symptoms, whereas individuals with fewer biomarker abnormalities may experience more severe cognitive deficits.

In this study, we present the the differences in biological and clinical staging using plasma p-tau markers. Moreover, we investigated the predictive power of p-tau markers to assess progression from preclinical to MCI.

Methods

We included cases and controls (n=439) according to the following criteria:

1) Cognitively normal (controls or SCD) with normal CSF Aβ42/40 ratio and normal p-tau181 biomarkers (CN A-/T-, n=168).

2) CN or MCI participants with pathological Aβ42/40 ratio, but normal p-tau181 (All A+/T-, n=53; CN=27; MCI=26).

3) pathological Aβ42/40 ratio and p-tau181 (All A+/T+, n=149; CN=39; MCI=110)

CSF and plasma biomarkers (p-tau 181, 217, 231, brain-derived tau, GFAP and NfL) were measured on the Simoa HD-X platform.

Results

The mean fold change as compared to CN A-/T- was greater for plasma p-tau217 in both A+/T- 0.57) and A+/T+ (1.02) groups as compared to ptau-181 (0.32 & 0.57 respectively) and p-tau231 (0.15 & 0.46 respectively). Mean fold changes for all plasma ptau-epitopes were similar for the A-/T+ groups (between 0.20 and 0.21).

Plasma p-tau217 was the only marker associated with performance in the Consortium to Establish a Registry for Alzheimer’s Disease (CERAD) test overtime in CN individuals (b=-0.09, p<0.05). In participants with MCI, plasma p-tau217 was associated with performance in CERAD at baseline and overtime (b=-0.57, p<0.001 and b=-0.13, p<0.001, respectively).

Conclusions

Plasma p-tau217 has a superior performance detecting the presence of early amyloid pathology and follow clinical progression, suggesting higher concordance between biological and clinical staging.

Aims

Renal function may affect blood and plasma constituents, including ATN biomarkers. However, relationships between renal function and plasma biomarkers are less known among populations with excess renal dysfunction and cardiometabolic risk. We test a cardiometabolic–renal-brain hypothesis among diverse middle-aged and older community dwelling US Hispanics/Latinos.

Methods

Data from the Study of Latinos-Investigation of Neurocognitive Aging (SOL-INCA; unweighted n=5,858), a multisite, prospective cohort of middle-aged and older diverse Hispanics/Latinos were used. Outcomes included 5 plasma ATN biomarkers (AB40, AB42, [AB42/AB40], p-tau181, NfL, GFAP; [Simoa, Quanterix, Billerica, MA]). Exposures included two measures of renal function: 1) estimated glomerular function ratio (eGFR; Chronic Kidney Disease [CKD] stages: eGFR>=90 [normal], 60-89 [mild], 30-59 [moderate], <30 [severe/end stage]; 2) urinary albumin-creatinine ratio (uACR [A1:<30 mg/g, A2:30-300 mg/g, A3: >300 mg/g]). Analyses: Generalized linear models adjusted for complex sampling design, independently and covarying for age, sex, Hispanic/Latino heritage, APOE genotype, and baseline BMI, diabetes and hypertension.

Results

54% were female; mean age was 63.4+/-8.2 years; 41.3% had a BMI of 30+, 28.5% met ADA criteria for diabetes, nearly 50% had baseline hypertension; 8.4% had moderate/severe/end stage CKD. We found strong positive dose effects for associations between CKD stages (lower eGFR and uACR) and all plasma ATN measures, except for AB42/40. The associations were only minimally attenuated and still significant by covariable adjustments, including cardiovascular risk factors.

Conclusions

In this large and representative cohort of middle-aged and older diverse Hispanics/Latinos, plasma ATN biomarkers were associated with increasing CKD stage severities, except AB42/40. CKD in the presence of diabetes was associated with marked increases of neurodegeneration biomarkers among diverse Hispanics/Latinos.