Qualification of a surrogate matrix-based absolute quantification method for amyloid-β₄₂ in human cerebrospinal fluid using 2D UPLC-tandem mass spectrometry

Continuous β-Amyloid CSF/PET Imbalance Model to Capture Alzheimer Disease Heterogeneity

BACKGROUND AND OBJECTIVES

Discordance between CSF and PET biomarkers of β-amyloid (Aβ) might reflect an imbalance between soluble and aggregated species, possibly reflecting disease heterogeneity. Previous studies generally used binary cutoffs to assess discrepancies in CSF/PET biomarkers, resulting in a loss of information on the extent of discordance. In this study, we (1) jointly modeled Aβ-CSF/PET data to derive a continuous measure of the imbalance between soluble and fibrillar pools of Aβ, (2) investigated factors contributing to this imbalance, and (3) examined associations with cognitive trajectories.

METHODS

Across 822 cognitively unimpaired (n = 261) and cognitively impaired (n = 561) Alzheimer's Disease Neuroimaging Initiative individuals (384 [46.7%] females, mean age 73.0 ± 7.4 years), we fitted baseline CSF-Aβ42 and global Aβ-PET to a hyperbolic regression model, deriving a participant-specific Aβ-aggregation score (standardized residuals); negative values represent more soluble relative to aggregated Aβ and positive values more aggregated relative to soluble Aβ. Using linear models, we investigated whether methodological factors, demographics, CSF biomarkers, and vascular burden contributed to Aβ-aggregation scores. With linear mixed models, we assessed whether Aβ-aggregation scores were predictive of cognitive functioning. Analyses were repeated in an early independent validation cohort of 383 Amyloid Imaging to Prevent Alzheimer's Disease Prognostic and Natural History Study individuals (224 [58.5%] females, mean age 65.2 ± 6.9 years).

RESULTS

The imbalance model could be fit (pseudo-R2 = 0.94) in both cohorts, across CSF kits and PET tracers. Although no associations were observed with the main methodological factors, lower Aβ-aggregation scores were associated with larger ventricular volume (β = 0.13, p < 0.001), male sex (β = -0.18, p = 0.019), and homozygous APOE-ε4 carriership (β = -0.56, p < 0.001), whereas higher scores were associated with increased uncorrected CSF p-tau (β = 0.17, p < 0.001) and t-tau (β = 0.16, p < 0.001), better baseline executive functioning (β = 0.12, p < 0.001), and slower global cognitive decline (β = 0.14, p = 0.006). In the validation cohort, we replicated the associations with APOE-ε4, CSF t-tau, and, although modestly, with cognition.

DISCUSSION

We propose a novel continuous model of Aβ CSF/PET biomarker imbalance, accurately describing heterogeneity in soluble vs aggregated Aβ pools in 2 independent cohorts across the full Aβ continuum. Aβ-aggregation scores were consistently associated with genetic and AD-associated CSF biomarkers, possibly reflecting disease heterogeneity beyond methodological influences.

Fiber-in-tube SPME-CapLC-MS/MS method to determine Aβ peptides in cerebrospinal fluid obtained from Alzheimer's patients

Mass spectrometry is characterized by its high sensitivity, ability to measure very low analyte concentrations, specificity to distinguish between closely related compounds, availability to generate high-throughput methods for screening, and high multiplexing capacity. This technique has been used as a platform to analyze fluid biomarkers for Alzheimer's disease. However, more effective sample preparation procedures, preferably antibody-independent, and more automated mass spectrometry platforms with improved sensitivity, chromatographic separation, and high throughput are needed for this purpose. This short communication discusses the development of a fiber-in-tube SPME-CapLC-MS/MS method to determine Aβ peptides in cerebrospinal fluid obtained from Alzheimer's disease patients. To obtain the fiber-in-tube SPME capillary, we longitudinally packed 22 nitinol fibers coated with a zwitterionic polymeric ionic liquid into the same length of the PEEK tube. In addition, this communication compares this fiber-in-tube SPME method with the conventional HPLC scale (HPLC-MS/MS) and when directly coupled to CapESI-MS/MS without chromatographic separation, and, as a case study, discusses the benefits and challenges inherent in miniaturizing the flow scale of the sample preparation technique (fiber-in-tube SPME) to the CapLC-MS/MS system. Fiber-in-tube SPME-CapLC-MS/MS provided LLOQ ranging from 0.09 to 0.10 ng mL-1, accuracy ranging from 91 to 117 % (recovery), and reproducibility of less than 18 % (RSD). Analysis of the cerebrospinal fluid samples obtained from Alzheimer's disease patients evidenced that the method is robust. At the capillary scale (10 µL min-1), this innovative method presented higher analytical sensitivity than the conventional HPLC-MS/MS scale. Although fiber-in-tube SPME directly coupled to CapESI-MS/MS offers advantages in terms of high throughput, the sample was dispersed and non-quantitatively desorbed from the capillary at low flow rate. These results highlighted that chromatographic separation is important to decrease the matrix effect and to achieve higher detectability, which is indispensable for bioanalysis.

Variants in the MS4A cluster interact with soluble TREM2 expression on biomarkers of neuropathology

Recent evidence suggests that Alzheimer's disease (AD) genetic risk variants (rs1582763 and rs6591561) of the MS4A locus are genome-wide significant regulators of soluble TREM2 levels such that the minor allele of the protective variant (rs1582763) is associated with higher sTREM2 and lower AD risk while the minor allele of (rs6591561) relates to lower sTREM2 and higher AD risk. Our group previously found that higher sTREM2 relates to higher Aβ40, worse blood-brain barrier (BBB) integrity (measured with the CSF/plasma albumin ratio), and higher CSF tau, suggesting strong associations with amyloid abundance and both BBB and neurodegeneration complicate interpretation. We expand on this work by leveraging these common variants as genetic tools to tune the interpretation of high CSF sTREM2, and by exploring the potential modifying role of these variants on the well-established associations between CSF sTREM2 as well as TREM2 transcript levels in the brain with AD neuropathology. Biomarker analyses leveraged data from the Vanderbilt Memory & Aging Project (n = 127, age = 72 ± 6.43) and were replicated in the Alzheimer's Disease Neuroimaging Initiative (n = 399, age = 73 ± 7.39). Autopsy analyses were performed leveraging data from the Religious Orders Study and Rush Memory and Aging Project (n = 577, age = 89 ± 6.46). We found that the protective variant rs1582763 attenuated the association between CSF sTREM2 and Aβ40 (β = -0.44, p-value = 0.017) and replicated this interaction in ADNI (β = -0.27, p = 0.017). We did not observe this same interaction effect between TREM2 mRNA levels and Aβ peptides in brain (Aβ total β = -0.14, p = 0.629; Aβ1-38, β = 0.11, p = 0.200). In contrast to the effects on Aβ, the minor allele of this same variant seemed to enhance the association with blood-brain barrier dysfunction (β = 7.0e-4, p = 0.009), suggesting that elevated sTREM2 may carry a much different interpretation in carriers vs. non-carriers of this allele. When evaluating the risk variant (rs6591561) across datasets, we did not observe a statistically significant interaction against any outcome in VMAP and observed opposing directions of associations in ADNI and ROS/MAP on Aβ levels. Together, our results suggest that the protective effect of rs1582763 may act by decoupling the associations between sTREM2 and amyloid abundance, providing important mechanistic insight into sTREM2 changes and highlighting the need to incorporate genetic context into the analysis of sTREM2 levels, particularly if leveraged as a clinical biomarker of disease in the future.

A Mass Spectrometry Strategy for Protein Quantification Based on the Differential Alkylation of Cysteines Using Iodoacetamide and Acrylamide

Mass spectrometry has become the most prominent yet evolving technology in quantitative proteomics. Today, a number of label-free and label-based approaches are available for the relative and absolute quantification of proteins and peptides. However, the label-based methods rely solely on the employment of stable isotopes, which are expensive and often limited in availability. Here we propose a label-based quantification strategy, where the mass difference is identified by the differential alkylation of cysteines using iodoacetamide and acrylamide. The alkylation reactions were performed under identical experimental conditions; therefore, the method can be easily integrated into standard proteomic workflows. Using high-resolution mass spectrometry, the feasibility of this approach was assessed with a set of tryptic peptides of human serum albumin. Several critical questions, such as the efficiency of labeling and the effect of the differential alkylation on the peptide retention and fragmentation, were addressed. The concentration of the quality control samples calculated against the calibration curves were within the ±20% acceptance range. It was also demonstrated that heavy labeled peptides exhibit a similar extraction recovery and matrix effect to light ones. Consequently, the approach presented here may be a viable and cost-effective alternative of stable isotope labeling strategies for the quantification of cysteine-containing proteins.

Alzheimer's Disease Biomarker Analysis Using Targeted Mass Spectrometry

Alzheimer's disease (AD) is characterized by several neuropathological changes, mainly extracellular amyloid aggregates (plaques), intraneuronal inclusions of phosphorylated tau (tangles), as well as neuronal and synaptic degeneration, accompanied by tissue reactions to these processes (astrocytosis and microglial activation) that precede neuronal network disturbances in the symptomatic phase of the disease. A number of biomarkers for these brain tissue changes have been developed, mainly using immunoassays. In this review, we discuss how targeted mass spectrometry (TMS) can be used to validate and further characterize classes of biomarkers reflecting different AD pathologies, such as tau- and amyloid-beta pathologies, synaptic dysfunction, lysosomal dysregulation, and axonal damage, and the prospect of using TMS to measure these proteins in clinical research and diagnosis. TMS advantages and disadvantages in relation to immunoassays are discussed, and complementary aspects of the technologies are discussed.

Higher Cerebrospinal Fluid Levels of Amyloid-β40 Following Traumatic Brain Injury Relate to Confrontation Naming Performance

Background

Traumatic brain injury (TBI) may confer risk for Alzheimer's disease (AD) through amyloid-β (Aβ) overproduction. However, the relationship between TBI and Aβ levels in cerebrospinal fluid (CSF) remains unclear.

Objective

To explore whether Aβ overproduction is implicated in the relationship between TBI and AD, we compared CSF levels of Aβ in individuals with a TBI history versus controls (CTRLs) and related CSF Aβ levels to cognitive markers associated with preclinical AD.

Methods

Participants were 112 non-impaired Veterans (TBI = 56, CTRL = 56) from the Alzheimer's Disease Neuroimaging Initiative-Department of Defense database with available cognitive data (Boston Naming Test [BNT], Rey Auditory Verbal Learning Test [AVLT]) and CSF measures of Aβ42, Aβ40, and Aβ38. Mediation models explored relationships between TBI history and BNT scores with Aβ peptides as mediators.

Results

The TBI group had higher CSF Aβ40 (t = -2.43, p = 0.017) and Aβ38 (t = -2.10, p = 0.038) levels than the CTRL group, but groups did not differ in CSF Aβ42 levels or Aβ42/Aβ40 ratios (p > 0.05). Both Aβ peptides negatively correlated with BNT (Aβ40: rho = -0.20, p = 0.032; Aβ38: rho = -0.19, p = 0.048) but not AVLT (p > 0.05). Aβ40 had a significant indirect effect on the relationship between TBI and BNT performance (β= -0.16, 95% CI [-0.393, -0.004], PM = 0.54).

Conclusions

TBI may increase AD risk and cognitive vulnerability through Aβ overproduction. Biomarker models incorporating multiple Aβ peptides may help identify AD risk among those with TBI.

An LC-MS/MS-based platform for the quantification of multiple amyloid beta peptides in surrogate cerebrospinal fluid

Introduction

The accurate quantification of amyloid beta (Aβ) peptides in cerebrospinal fluid (CSF) is crucial for Alzheimer's disease (AD) research, particularly in terms of preclinical and biomarker studies. Traditional methods, such as the enzyme-linked immunosorbent assay (ELISA), have limitations. These include high costs, labor intensity, lengthy processes, and the possibility of cross-reactivity.

Objectives

The primary objectives of this research were twofold: to comprehensively characterize Aβ peptides and to develop a reliable and accurate method for the simultaneous quantification of Aβ 1-40 and Aβ 1-42 peptides in surrogate CSF that is traceable to the International System of Units (SI).

Methods

We developed a novel method that combined solid phase extraction (SPE) with isotope dilution liquid chromatography/tandem mass spectrometry (ID-LC/MSMS). SPE was employed to efficiently eliminate matrix interferences, while [15N] Aβ1-40 and [15N] Aβ1-42 served as internal standards to improve accuracy. In addition, we introduced Peptide Impurity Corrected Amino Acid Analysis (PICAA) to ensure traceability to the SI and reliable quantification of Aβ peptides.

Results

The developed platform demonstrated a linear calibration range of 300-20000 pg/ml for both Aβ1-42 and Aβ1-40 peptides, accompanied by strong correlation coefficients greater than 0.995. Quality Control (QC) samples demonstrated an accuracy of at least 90.0 %.

Conclusion

The enhanced specificity and flexibility of the developed platform potentially have implications for Alzheimer's disease diagnosis and future investigations of novel Aβ peptide biomarkers.

Comparing Symmetric Dimethylarginine and Amyloid-β42 as Predictors of Alzheimer's Disease Development

Background

Physicians may soon be able to diagnose Alzheimer's disease (AD) in its early stages using fluid biomarkers like amyloid. However, it is acknowledged that additional biomarkers need to be characterized which would facilitate earlier monitoring of AD pathogenesis.

Objective

To determine if a potential novel inflammation biomarker for AD, symmetric dimethylarginine, has utility as a baseline serum biomarker for discriminating prodromal AD from cognitively unimpaired controls in comparison to cerebrospinal fluid amyloid-β42 (Aβ42).

Methods

Data including demographics, magnetic resonance imaging and fluorodeoxyglucose-positron emission tomography scans, Mini-Mental State Examination and Functional Activities Questionnaire scores, and biomarker concentrations were obtained from the Alzheimer's Disease Neuroimaging Initiative for a total of 146 prodromal AD participants and 108 cognitively unimpaired controls.

Results

Aβ42 (p = 0.65) and symmetric dimethylarginine (p = 0.45) were unable to predict age-matched cognitively unimpaired controls and prodromal AD participants. Aβ42 was negatively associated with regional brain atrophy and hypometabolism as well as cognitive and functional decline in cognitively unimpaired control participants (p < 0.05) that generally decreased in time. There were no significant associations between Aβ42 and symmetric dimethylarginine with imaging or neurocognitive biomarkers in prodromal AD patients.

Conclusions

Correlations were smaller between Aβ42 and neuropathological biomarkers over time and were absent in prodromal AD participants, suggesting a plateau effect dependent on age and disease stage. Evidence supporting symmetric dimethylarginine as a novel biomarker for AD as a single measurement was not found.

Neurofilament-Light, a Promising Biomarker: Analytical, Metrological and Clinical Challenges

Neurofilament-light chain (Nf-L) is a non-specific early-stage biomarker widely studied in the context of neurodegenerative diseases (NDD) and traumatic brain injuries (TBI), which can be measured in biofluids after axonal damage. Originally measured by enzyme-linked immunosorbent assay (ELISA) in cerebrospinal fluid (CSF), Nf-L can now be quantified in blood with the emergence of ultrasensitive assays. However, to ensure successful clinical implementation, reliable clinical thresholds and reference measurement procedures (RMP) should be developed. This includes establishing and distributing certified reference materials (CRM). As a result of the complexity of Nf-L and the number of circulating forms, a clear definition of what is measured when immunoassays are used is also critical to achieving standardization to ensure the long-term success of those assays. The use of powerful tools such as mass spectrometry for developing RMP and defining the measurand is ongoing. Here, we summarize the current methods in use for quantification of Nf-L in biofluid showing potential for clinical implementation. The progress and challenges in developing RMP and defining the measurand for Nf-L standardization of diagnostic tests are addressed. Finally, we discuss the impact of pathophysiological factors on Nf-L levels and the establishment of a clinical cut-off.

Advances in sample preparation and HPLC-MS/MS methods for determining amyloid-β peptide in biological samples: a review

Alzheimer's disease (AD), a neurological disorder, is a major public health concern and the most common form of dementia. Its typical symptoms include memory loss, confusion, changes in personality, and cognitive impairment, which result in patients gradually losing independence. Over the last decades, some studies have focused on searching for effective biomarkers as early diagnostic indicators of AD. Amyloid-β (Aβ) peptides have been consolidated as reliable AD biomarkers and have been incorporated into modern diagnostic research criteria. However, quantitative analysis of Aβ peptides in biological samples remains a challenge because both the sample and the physical-chemical properties of these peptides are complex. During clinical routine, Aβ peptides are measured in the cerebrospinal fluid by immunoassays, but the availability of a specific antibody is critical-in some cases, an antibody may not exist, or its specificity may be inadequate, leading to low sensitivity and false results. HPLC-MS/MS has been reported as a sensitive and selective method for determining different fragments of Aβ peptides in biological samples simultaneously. Developments in sample preparation techniques (preconcentration platforms) such as immunoprecipitation, 96-well plate SPME, online SPME, and fiber-in-tube SPME have enabled not only effective enrichment of Aβ peptides present at trace levels in biological samples, but also efficient exclusion of interferents from the sample matrix (sample cleanup). This high extraction efficiency has provided MS platforms with higher sensitivity. Recently, methods affording LLOQ values as low as 5 pg mL^-1 have been reported. Such low LLOQ values are adequate for quantifying Aβ peptides in complex matrixes including cerebrospinal fluid (CSF) and plasma samples. This review summarizes the advances in mass spectrometry (MS)-based methods for quantifying Aβ peptides and covers the period 1992-2022. Important considerations regarding the development of the HPLC-MS/MS method such as the sample preparation step, optimization of the HPLC-MS/MS parameters, and matrix effects are described. Clinical applications, difficulties related to analysis of plasma samples, and future trends of these MS/MS-based methods are also discussed.

Direct coupling of fiber-in-tube solid-phase microextraction with tandem mass spectrometry to determine amyloid beta peptides as biomarkers for Alzheimer's disease in cerebrospinal fluid samples

Current research efforts at neurological diseases have focused on identifying novel biomarkers to aid in diagnosis, to provide accurate prognostic information, and to monitor disease progression. This study presents the direct coupling of fiber-in-tube solid-phase microextraction to tandem mass spectrometry as a reliable method to determine amyloid beta peptides (Aβ38, Aβ40, and Aβ42) as biomarkers for Alzheimer's disease in cerebrospinal fluid (CSF) samples. To obtain the biocompatible fiber-in-tube SPME capillary, a PEEK tube segment was longitudinally packed with fine fibers [nitinol wires coated with a zwitterionic polymeric ionic liquid], to act as selective extraction medium. The fiber-in-tube SPME-MS/MS method integrated analyte extraction/enrichment and sample cleanup (exclusion of interferents) into one step. The method provided lower limits of quantification (LLOQ: 0.2 ng mL^-1 for Aβ38 and 0.1 ng mL^-1 for Aβ40 and Aβ42), high precision (CV lower than 11.6%), and high accuracy (relative standard deviation lower than 15.1%). This method was successfully applied to determine Aβ peptides in CSF samples obtained from AD patients (n = 8) and controls (healthy volunteers, n = 10). Results showed that Aβ42 levels in the CSF samples obtained from AD patients were significantly lower compared to healthy controls (p < 0.05). On the basis of the ROC analysis results, the Aβ42/Aβ40 ratio (AUC = 0.950, p < 0.01; 95%) performed significantly better than Aβ42 alone (AUC = 0.913, p < 0.01; 95%) in discriminating between AD patients and healthy controls and presented better diagnostic ability for AD. The novelties of this study are not only related to evaluating Aβ peptides as AD biomarkers, but also to demonstrating direct online coupling of fiber-in-tube SPME with MS/MS as a quantitative high-throughput method for bioanalysis.

How far is the goal of applying β-amyloid in cerebrospinal fluid for clinical diagnosis of Alzheimer's disease with standardization of measurements?

Cerebrospinal fluid (CSF) β-amyloid (Aβ) is important for early diagnosis of Alzheimer's disease (AD). However, the cohort distributions and cut-off values have large variation across different analytical assays, kits, and laboratories. In this review, we summarize the cut-off values and diagnostic performance for CSF Aβ1-42 and Aβ1-42/Aβ1-40, and explore the important effect factors. Based on the Alzheimer's Association external quality control program (AAQC program), the peer group coefficient of variation of manual ELISA assays for CSF Aβ1-42 was unsatisfied (>20%). Fully automated platforms with better performance have recently been developed, but still not widely applied. In 2020, the certified reference material (CRM) for CSF Aβ1-42 was launched; however, the AAQC 2021-round results did not show effective improvements. Thus, further development and popularization of CRM for CSF Aβ1-42 and Aβ1-40 are urgently required. Standardizing the diagnostic procedures of AD and related status and the pre-analytical protocols of CSF samples, improving detection performance of analytical assays, and popularizing the application of fully automated platforms are also important for the establishment of uniform cut-off values. Moreover, each laboratory should verify the applicability of uniform cut-off values, and evaluate whether it is necessary to establish its own population- and assay-specific cut-off values.

Robustness of CSF Aβ42/40 and Aβ42/P-tau181 measured using fully automated immunoassays to detect AD-related outcomes

INTRODUCTION

This study investigated the comparability of cerebrospinal fluid (CSF) cutoffs for Elecsys immunoassays for amyloid beta (Aβ)42/Aβ40 or Aβ42/phosphorylated tau (p-tau)181 and the effects of measurement variability when predicting Alzheimer's disease (AD)-related outcomes (i.e., Aβ-positron emission tomography [PET] visual read and AD neuropathology).

METHODS

We studied 750 participants (BioFINDER study, Alzheimer's Disease Neuroimaging Initiative [ADNI], and University of California San Francisco [UCSF]). Youden's index was used to identify cutoffs and to calculate accuracy (Aβ-PET visual read as outcome). Using longitudinal variability in Aβ-negative controls, we identified a gray zone around cut-points where the risk of an inconsistent predicted outcome was >5%.

RESULTS

For Aβ42/Aβ40, cutoffs across cohorts were <0.059 (BioFINDER), <0.057 (ADNI), and <0.058 (UCSF). For Aβ42/p-tau181, cutoffs were <41.90 (BioFINDER), <39.20 (ADNI), and <46.02 (UCSF). Accuracy was ≈90% for both Aβ42/Aβ40 and Aβ42/p-tau181 using these cutoffs. Using Aβ-PET as an outcome, 8.7% of participants fell within a gray zone interval for Aβ42/Aβ40, compared to 4.5% for Aβ42/p-tau181. Similar findings were observed using a measure of overall AD neuropathologic change (7.7% vs. 3.3%). In a subset with CSF and plasma Aβ42/40, the number of individuals within the gray zone was ≈1.5 to 3 times greater when using plasma Aβ42/40.

DISCUSSION

CSF Aβ42/p-tau181 was more robust to the effects of measurement variability, suggesting that it may be the preferred Elecsys-based measure in clinical practice and trials.

Fluid biomarkers in Alzheimer's disease

Alzheimer's disease (AD) characterization has progressed from being indexed using clinical symptomatology followed by neuropathological examination at autopsy to in vivo signatures using cerebrospinal fluid (CSF) biomarkers and positron emission tomography. The core AD biomarkers reflect amyloid-β plaques (A), tau pathology (T) and neurodegeneration (N), following the ATN schedule, and are now being introduced into clinical routine practice. This is an important development, as disease-modifying treatments are now emerging. Further, there are now reproducible data on CSF biomarkers which reflect synaptic pathology, neuroinflammation and common co-pathologies. In addition, the development of ultrasensitive techniques has enabled the core CSF biomarkers of AD pathophysiology to be translated to blood (e.g., phosphorylated tau, amyloid-β and neurofilament light). In this chapter, we review where we stand with both core and novel CSF biomarkers, as well as the explosion of data on blood biomarkers. Also, we discuss potential applications in research aiming to better understand the disease, as well as possible use in routine clinical practice and therapeutic trials.

Biological correlates of elevated soluble TREM2 in cerebrospinal fluid

Cerebrospinal fluid (CSF) soluble triggering receptor expressed on myeloid cells-2 (sTREM2) is an emerging biomarker of neuroinflammation in Alzheimer's disease (AD). Yet, sTREM2 expression has not been systematically evaluated in relation to concomitant drivers of neuroinflammation. While associations between sTREM2 and tau in CSF are established, we sought to determine additional biological correlates of CSF sTREM2 during the prodromal stages of AD by evaluating CSF Aβ species (Aβ_x-40), a fluid biomarker of blood-brain barrier integrity (CSF/plasma albumin ratio), and CSF biomarkers of neurodegeneration measured in 155 participants from the Vanderbilt Memory and Aging Project. A novel association between high CSF levels of both sTREM2 and Aβ_x-40 was observed and replicated in an independent dataset. Aβ_x-40 levels, as well as the CSF/plasma albumin ratio, explained additional and unique variance in sTREM2 levels above and beyond that of CSF biomarkers of neurodegeneration. The component of sTREM2 levels correlated with Aβ_x-40 levels best predicted future cognitive performance. We highlight potential contributions of Aβ homeostasis and blood-brain barrier integrity to elevated CSF sTREM2, underscoring novel biomarker associations relevant to disease progression and clinical outcome measures.

Residual reserve index modifies the effect of amyloid pathology on fluorodeoxyglucose metabolism: Implications for efficiency and capacity in cognitive reserve

Background

The residual approach to measuring cognitive reserve (using the residual reserve index) aims to capture cognitive resilience conferred by cognitive reserve, but may be confounded by factors representing brain resilience. We sought to distinguish between brain and cognitive resilience by comparing interactions between the residual reserve index and amyloid, tau, and neurodegeneration ["AT(N)"] biomarkers when predicting executive function. We hypothesized that the residual reserve index would moderate at least one path from an AT(N) biomarker to executive function (consistent with cognitive resilience), as opposed to moderating a path between two AT(N) biomarkers (suggestive of brain resilience).

Methods

Participants (N = 332) were from the Alzheimer's Disease Neuroimaging Initiative. The residual reserve index represented the difference between observed and predicted memory performance (a positive residual reserve index suggests higher cognitive reserve). AT(N) biomarkers were: CSF β-amyloid1-42/β-amyloid1-40 (A), plasma phosphorylated tau-181 (T), and FDG metabolism in AD-specific regions ([N]). AT(N) biomarkers (measured at consecutive time points) were entered in a sequential mediation model testing the indirect effects from baseline amyloid to executive function intercept (third annual follow-up) and slope (baseline to seventh follow-up), via tau and/or FDG metabolism. The baseline residual reserve index was entered as a moderator of paths between AT(N) biomarkers (e.g., amyloid-tau), and paths between AT(N) biomarkers and executive function.

Results

The residual reserve index interacted with amyloid pathology when predicting FDG metabolism: the indirect effect of amyloid → FDG metabolism → executive function intercept and slope varied as a function of the residual reserve index. With lower amyloid pathology, executive function performance was comparable at different levels of the residual reserve index, but a higher residual reserve index was associated with lower FDG metabolism. With higher amyloid pathology, a higher residual reserve index predicted better executive function via higher FDG metabolism.

Conclusion

The effect of the residual reserve index on executive function performance via FDG metabolism was consistent with cognitive resilience. This suggests the residual reserve index captures variation in cognitive reserve; specifically, neural efficiency, and neural capacity to upregulate metabolism to enhance cognitive resilience in the face of greater amyloid pathology. Implications for future research include the potential bidirectionality between neural efficiency and amyloid accumulation.

CSF biomarkers for dementia

Although cerebrospinal fluid (CSF) biomarker testing is incorporated into some current guidelines for the diagnosis of dementia (such as England's National Institute for Health and Care Excellence (NICE)), it is not widely accessible for most patients for whom biomarkers could potentially change management. Here we share our experience of running a clinical cognitive CSF service and discuss recent developments in laboratory testing including the use of the CSF amyloid-β 42/40 ratio and automated assay platforms. We highlight the importance of collaborative working between clinicians and laboratory staff, of preanalytical sample handling, and discuss the various factors influencing interpretation of the results in appropriate clinical contexts. We advocate for broadening access to CSF biomarkers by sharing clinical expertise, protocols and interpretation with colleagues working in psychiatry and elderly care, especially when access to CSF may be part of a pathway to disease-modifying treatments for Alzheimer's disease and other forms of dementia.

Alzheimer's disease: a scoping review of biomarker research and development for effective disease diagnosis

INTRODUCTION

Alzheimer's disease (AD) is regarded as the foremost reason for neurodegeneration that prominently affects the geriatric population. Characterized by extracellular accumulation of amyloid-beta (Aβ), intracellular aggregation of hyperphosphorylated tau (p-tau), and neuronal degeneration that causes impairment of memory and cognition. Amyloid/tau/neurodegeneration (ATN) classification is utilized for research purposes and involves amyloid, tau, and neuronal injury staging through MRI, PET scanning, and CSF protein concentration estimations. CSF sampling is invasive, and MRI and PET scanning requires sophisticated radiological facilities which limit its widespread diagnostic use. ATN classification lacks effectiveness in preclinical AD.

AREAS COVERED

This publication intends to collate and review the existing biomarker profile and the current research and development of a new arsenal of biomarkers for AD pathology from different biological samples, microRNA (miRNA), proteomics, metabolomics, artificial intelligence, and machine learning for AD screening, diagnosis, prognosis, and monitoring of AD treatments.

EXPERT OPINION

It is an accepted observation that AD-related pathological changes occur over a long period of time before the first symptoms are observed providing ample opportunity for detection of biological alterations in various biological samples that can aid in early diagnosis and modify treatment outcomes.

Microglial Activation, Tau Pathology, and Neurodegeneration Biomarkers Predict Longitudinal Cognitive Decline in Alzheimer's Disease Continuum

Purpose

Biomarkers used for predicting longitudinal cognitive change in Alzheimer's disease (AD) continuum are still elusive. Tau pathology, neuroinflammation, and neurodegeneration are the leading candidate predictors. We aimed to determine these three aspects of biomarkers in cerebrospinal fluid (CSF) and plasma to predict longitudinal cognition status using Alzheimer's Disease Neuroimaging Initiative (ADNI) cohort.

Patients and Methods

A total of 430 subjects including, 96 cognitive normal (CN) with amyloid β (Aβ)-negative, 54 CN with Aβ-positive, 195 mild cognitive impairment (MCI) with Aβ-positive, and 85 AD with amyloid-positive (Aβ-positive are identified by CSF Aβ42/Aβ40 < 0.138). Aβ burden was evaluated by CSF and plasma Aβ42/Aβ40 ratio; tau pathology was evaluated by CSF and plasma phosphorylated-tau (p-tau181); microglial activation was measured by CSF soluble TREM2 (sTREM2) and progranulin (PGRN); neurodegeneration was measured by CSF and plasma t-tau and structural magnetic resonance imaging (MRI); cognition was examined annually over the subsequent 8 years using the Alzheimer's Disease Assessment Scale Cognition 13-item scale (ADAS13) and Mini-Mental State Exam (MMSE). Linear mixed-effects models (LME) were applied to assess the correlation between biomarkers and longitudinal cognition decline, as well as their effect size on the prediction of longitudinal cognitive decline.

Results

Baseline CSF Aβ42/Aβ40 ratio was decreased in MCI and AD compared to CN, while CSF p-tau181 and t-tau increased. Baseline CSF sTREM2 and PGRN did not show any differences in MCI and AD compared to CN. Baseline brain volumes (including the hippocampal, entorhinal, middle temporal lobe, and whole-brain) decreased in MCI and AD groups. For the longitudinal study, there were significant interaction effects of CSF p-tau181 × time, plasma p-tau181 × time, CSF sTREM2 × time, and brain volumes × time, indicating CSF, and plasma p-tau181, CSF sTREM2, and brain volumes could predict longitudinal cognition deterioration rate. CSF sTREM2, CSF, and plasma p-tau181 had similar medium prediction effects, while brain volumes showed stronger effects in predicting cognition decline.

Conclusion

Our study reported that baseline CSF sTREM2, CSF, and plasma p-tau181, as well as structural MRI, could predict longitudinal cognitive decline in subjects with positive AD pathology. Plasma p-tau181 can be used as a relatively noninvasive reliable biomarker for AD longitudinal cognition decline prediction.

Validation and application of hybridization liquid chromatography-tandem mass spectrometry methods for quantitative bioanalysis of antisense oligonucleotides

Background: Antisense oligonucleotide (ASO), an emerging modality in drug research and development, demands accurate and sensitive bioanalysis to understand its pharmacokinetic and pharmacodynamic properties. Results: By combining the advantages of both ligand binding and liquid chromatography-mass spectrometry/tandem mass (LC-MS/MS), hybridization LC-MS/MS methods were successfully developed and validated/qualified in a good lab practice (GLP) environment for the quantitation of an ASO drug candidate in monkey serum, cerebrospinal fluid (CSF) and tissues in the range of 0.5-500 ng/ml. Special treatment of CSF samples was employed to mitigate nonspecific binding, improve long-term storage stability and enable the usage of artificial CSF as a more accessible surrogate matrix. The method was also qualified and applied to ASO quantitation in various monkey tissue samples using a cocktail tissue homogenate as a surrogate matrix. Conclusion: This work was the first reported GLP validation and application of ASO bioanalysis using the hybridization LC-MS/MS platform.

Biomarker A+T-: is this Alzheimer's disease or not? A combined CSF and pathology study

The biological definition of Alzheimer's disease using CSF biomarkers requires abnormal levels of both amyloid (A) and tau (T). However, biomarkers and corresponding cutoffs may not always reflect the presence or absence of pathology. Previous studies suggest that up to 32% of individuals with autopsy-confirmed Alzheimer's disease show normal CSF p-tau levels in vivo, but these studies are sparse and had small sample sizes. Therefore, in three independent autopsy cohorts, we studied whether or not CSF A+T- excluded Alzheimer's disease based on autopsy. We included 215 individuals, for whom ante-mortem CSF collection and autopsy had been performed, from three cohorts: (i) the Amsterdam Dementia Cohort (ADC) [n = 80, 37 (46%) Alzheimer's disease at autopsy, time between CSF collection and death 4.5 ± 2.9 years]; (ii) the Antwerp Dementia Cohort (DEM) [n = 92, 84 (91%) Alzheimer's disease at autopsy, time CSF collection to death 1.7 ± 2.3 years]; and (iii) the Alzheimer's Disease Neuroimaging Initiative (ADNI) [n = 43, 31 (72%) Alzheimer's disease at autopsy, time CSF collection to death 5.1 ± 2.5 years]. Biomarker profiles were based on dichotomized CSF Aβ1-42 and p-tau levels. The accuracy of CSF AT profiles to detect autopsy-confirmed Alzheimer's disease was assessed. Lastly, we investigated whether the concordance of AT profiles with autopsy diagnosis improved when CSF was collected closer to death in 9 (10%) DEM and 30 (70%) ADNI individuals with repeated CSF measurements available. In total, 50-73% of A+T- individuals and 100% of A+T+ individuals had Alzheimer's disease at autopsy. Amyloid status showed the highest accuracy to detect autopsy-confirmed Alzheimer's disease (accuracy, sensitivity and specificity in the ADC: 88%, 92% and 84%; in the DEM: 87%, 94% and 12%; and in the ADNI cohort: 86%, 90% and 75%, respectively). The addition of CSF p-tau did not further improve these estimates. We observed no differences in demographics or degree of Alzheimer's disease neuropathology between A+T- and A+T+ individuals with autopsy-confirmed Alzheimer's disease. All individuals with repeated CSF measurements remained stable in Aβ1-42 status during follow-up. None of the Alzheimer's disease individuals with a normal p-tau status changed to abnormal; however, four (44%) DEM individuals and two (7%) ADNI individuals changed from abnormal to normal p-tau status over time, and all had Alzheimer's disease at autopsy. In summary, we found that up to 73% of A+T- individuals had Alzheimer's disease at autopsy. This should be taken into account in both research and clinical settings.

Soluble amyloid-beta isoforms predict downstream Alzheimer's disease pathology

Background

Changes in soluble amyloid-beta (Aβ) levels in cerebrospinal fluid (CSF) are detectable at early preclinical stages of Alzheimer’s disease (AD). However, whether Aβ levels can predict downstream AD pathological features in cognitively unimpaired (CU) individuals remains unclear. With this in mind, we aimed at investigating whether a combination of soluble Aβ isoforms can predict tau pathology (T+) and neurodegeneration (N+) positivity.

Methods

We used CSF measurements of three soluble Aβ peptides (Aβ_1–38, Aβ_1–40 and Aβ_1–42) in CU individuals (n = 318) as input features in machine learning (ML) models aiming at predicting T+ and N+. Input data was used for building 2046 tuned predictive ML models with a nested cross-validation technique. Additionally, proteomics data was employed to investigate the functional enrichment of biological processes altered in T+ and N+ individuals.

Results

Our findings indicate that Aβ isoforms can predict T+ and N+ with an area under the curve (AUC) of 0.929 and 0.936, respectively. Additionally, proteomics analysis identified 17 differentially expressed proteins (DEPs) in individuals wrongly classified by our ML model. More specifically, enrichment analysis of gene ontology biological processes revealed an upregulation in myelinization and glucose metabolism-related processes in CU individuals wrongly predicted as T+. A significant enrichment of DEPs in pathways including biosynthesis of amino acids, glycolysis/gluconeogenesis, carbon metabolism, cell adhesion molecules and prion disease was also observed.

Conclusions

Our results demonstrate that, by applying a refined ML analysis, a combination of Aβ isoforms can predict T+ and N+ with a high AUC. CSF proteomics analysis highlighted a promising group of proteins that can be further explored for improving T+ and N+ prediction.

Supplementary Information

The online version contains supplementary material available at 10.1186/s13578-021-00712-3.

Establishing pre-analytical requirements and maximizing peptide recovery in the analytical phase for mass spectrometric quantification of amyloid-β peptides 1-42 and 1-40 in CSF

OBJECTIVES

Amyloid-β (Aβ) peptides in cerebrospinal fluid (CSF), including Aβ42 (residues 1-42) and Aβ40 (residues 1-40), are utilized as biomarkers in the diagnostic workup of Alzheimer's disease. Careful consideration has been given to the pre-analytical and analytical factors associated with measurement of these peptides via immunoassays; however, far less information is available for mass spectrometric methods. As such, we performed a comprehensive evaluation of pre-analytical and analytical factors specific to Aβ quantification using mass spectrometry.

METHODS

Using our quantitative mass spectrometry assay for Aβ42 and Aβ40 in CSF, we investigated the potential for interference from hemolysate, bilirubin, lipids, and anti-Aβ-antibodies. We also optimized the composition of the calibrator surrogate matrix and Aβ recovery during and after solid phase extraction (SPE).

RESULTS

There was no interreference observed with total protein up to 12 g/L, hemolysate up to 10% (v/v), bilirubin up to 0.5% (v/v), intralipid up to 1% (v/v), or anti-Aβ-antibodies at expected therapeutic concentrations. For hemolysate, bilirubin and lipids, visual CSF contamination thresholds were established. In the analytical phase, Aβ recovery was increased by ∼50% via SPE solvent modifications and by over 150% via modification of the SPE collection plate, which also extended analyte stability in the autosampler.

CONCLUSIONS

Attention to mass spectrometric-specific pre-analytical and analytical considerations improved analytical sensitivity and reproducibility, as well as, established CSF specimen acceptance and rejection criteria for use by the clinical laboratory.

Biological and methodological complexities of beta-amyloid peptide: Implications for Alzheimer's disease research

Although controversial, the amyloid cascade hypothesis remains central to the Alzheimer's disease (AD) field and posits amyloid-beta (Aβ) as the central factor initiating disease onset. In recent years, there has been an increase in emphasis on studying the role of low molecular weight aggregates, such as oligomers, which are suggested to be more neurotoxic than fibrillary Aβ. Other Aβ isoforms, such as truncated Aβ, have also been implicated in disease. However, developing a clear understanding of AD pathogenesis has been hampered by the complexity of Aβ biochemistry in vitro and in vivo. This review explores factors contributing to the lack of consistency in experimental approaches taken to model Aβ aggregation and toxicity and provides an overview of the different techniques available to analyse Aβ, such as electron and atomic force microscopy, nuclear magnetic resonance spectroscopy, dye-based assays, size exclusion chromatography, mass spectrometry and SDS-PAGE. The review also explores how different types of Aβ can influence Aβ aggregation and toxicity, leading to variation in experimental outcomes, further highlighting the need for standardisation in Aβ preparations and methods used in current research.

Mass spectrometry-based methods for robust measurement of Alzheimer's disease biomarkers in biological fluids

Alzheimer's disease (AD) is the most common form of dementia affecting 60%-70% of people afflicted with this disease. Accurate antemortem diagnosis is urgently needed for early detection of AD to enable reliable estimation of prognosis, intervention, and monitoring of the disease. The National Institute on Aging/Alzheimer's Association sponsored the 'Research Framework: towards a biological definition of AD', which recommends using different biomarkers in living persons for a biomarker-based definition of AD regardless of clinical status. Fluid biomarkers represent one of key groups of them. Since cerebrospinal fluid (CSF) is in direct contact with brain and many proteins present in the brain can be detected in CSF, this fluid has been regarded as the best biofluid in which to measure AD biomarkers. Recently, technological advancements in protein detection made possible the effective study of plasma AD biomarkers despite their significantly lower concentrations versus to that in CSF. This and other challenges that face plasma-based biomarker measurements can be overcome by using mass spectrometry. In this review, we discuss AD biomarkers which can be reliably measured in CSF and plasma using targeted mass spectrometry coupled to liquid chromatography (LC/MS/MS). We describe progress in LC/MS/MS methods' development, emphasize the challenges, and summarize major findings. We also highlight the role of mass spectrometry and progress made in the process of global standardization of the measurement of Aβ42/Aβ40. Finally, we briefly describe exploratory proteomics which seek to identify new biomarkers that can contribute to detection of co-pathological processes that are common in sporadic AD.

N-Terminally Truncated and Pyroglutamate-Modified Aβ Forms Are Measurable in Human Cerebrospinal Fluid and Are Potential Markers of Disease Progression in Alzheimer's Disease

Alzheimer's disease (AD) is a pathology characterized by the accumulation in the brain of intracellular and extracellular amyloid-β (Aβ) aggregates, especially of Aβ1-40 and Aβ1-42 peptides. It is known that N-terminally truncated or modified Aβ forms also exist in AD brains and cerebrospinal fluid (CSF), and they play a key role in the pathogenesis of the disease. Herein, we developed an antibody-free method based on Solid-Phase Extraction and Electrospray Ionization Liquid Chromatography Mass Spectrometry for the identification and quantitation in human CSF of Aβ isoforms. In human CSF, we could detect and quantify a panel of 19 Aβ isoforms, including N-terminally truncated and pyroglutamate-modified forms, never quantified before in CSF. Among these, we identified novel N-terminally truncated Aβ species: four bound to copper and two phosphorylated forms, which were found to be the most common proteoforms in human CSF along with Aβ1-40, Aβ3-40, and AβpE11-42. We tested the newly developed and validated method in a pilot study on CSF from elderly individuals with subjective memory complaints (SMCs, n = 9), mild cognitive impairment (MCI, n = 18), and AD (n = 15); along with Aβ1-42, five N-terminally truncated forms (Aβ11-40, Aβ3-42, AβpE11-42, AβpE3-40, and Aβ4-40 Cu²⁺) are altered in AD/MCI. Thus, we demonstrated that N-terminally truncated and pyroglutamate-modified Aβ can be quantified in human CSF, and five of them, along with Aβ1-42, are potential markers of AD progression. The described method could represent a useful tool for patients' stratification and monitoring. Moreover, the newly identified Aβ CSF species might represent new potential therapeutic targets.

Refining the amyloid β peptide and oligomer fingerprint ambiguities in Alzheimer's disease: Mass spectrometric molecular characterization in brain, cerebrospinal fluid, blood, and plasma

Since its discovery, amyloid-β (Aβ) has been the principal target of investigation of in Alzheimer's disease (AD). Over the years however, no clear correlation was found between the Aβ plaque burden and location, and AD-associated neurodegeneration and cognitive decline. Instead, diagnostic potential of specific Aβ peptides and/or their ratio, was established. For instance, a selective reduction in the concentration of the aggregation-prone 42 amino acid-long Aβ peptide (Aβ42) in cerebrospinal fluid (CSF) was put forward as reflective of Aβ peptide aggregation in the brain. With time, Aβ oligomers-the proposed toxic Aβ intermediates-have emerged as potential drivers of synaptic dysfunction and neurodegeneration in the disease process. Oligomers are commonly agreed upon to come in different shapes and sizes, and are very poorly characterized when it comes to their composition and their "toxic" properties. The concept of structural polymorphism-a diversity in conformational organization of amyloid aggregates-that depends on the Aβ peptide backbone, makes the characterization of Aβ aggregates and their role in AD progression challenging. In this review, we revisit the history of Aβ discovery and initial characterization and highlight the crucial role mass spectrometry (MS) has played in this process. We critically review the common knowledge gaps in the molecular identity of the Aβ peptide, and how MS is aiding the characterization of higher order Aβ assemblies. Finally, we go on to present recent advances in MS approaches for characterization of Aβ as single peptides and oligomers, and convey our optimism, as to how MS holds a promise for paving the way for progress toward a more comprehensive understanding of Aβ in AD research.

Exploring the Potential of Neuroproteomics in Alzheimer's Disease

Alzheimer's disease (AD) is progressive brain amyloidosis that damages brain regions associated with memory, thinking, behavioral and social skills. Neuropathologically, AD is characterized by intraneuronal hyperphosphorylated tau inclusions as neurofibrillary tangles (NFTs), and buildup of extracellular amyloid-beta (Aβ) peptide as senile plaques. Several biomarker tests capturing these pathologies have been developed. However, for the full clinical expression of the neurodegenerative events of AD, there exist other central molecular pathways. In terms of understanding the unidentified underlying processes for the progression and development of AD, a complete comprehension of the structure and composition of atypical aggregation of proteins is essential. Presently, to aid the prognosis, diagnosis, detection, and development of drug targets in AD, neuroproteomics is elected as one of the leading essential tools for the efficient exploratory discovery of prospective biomarker candidates estimated to play a crucial role. Therefore, the aim of this review is to present the role of neuroproteomics to analyze the complexity of AD.

Biomarkers of Alzheimer Disease

BACKGROUND

Alzheimer disease (AD) was once a clinical diagnosis confirmed by postmortem autopsy. Today, with the development of AD biomarkers, laboratory assays to detect AD pathology are able to complement clinical diagnosis in symptomatic individuals with uncertain diagnosis. A variety of commercially available assays are performed as laboratory-developed tests, and many more are in development for both clinical and research purposes.

CONTENT

The role of laboratory medicine in diagnosing and managing AD is expanding; thus, it is important for laboratory professionals and ordering physicians to understand the strengths and limitations of both existing and emerging AD biomarker assays. In this review, we will provide an overview of the diagnosis of AD, discuss existing laboratory assays for AD and their recommended use, and examine the clinical performance of emerging AD biomarkers.

SUMMARY

The field of AD biomarker discovery and assay development is rapidly evolving, with recent studies promising to improve both the diagnosis of symptomatic individuals and enrollment and monitoring of asymptomatic individuals in research studies. However, care must be taken to ensure proper use and interpretation of these assays. For clinical purposes, these assays are meant to aid in diagnosis but are not themselves diagnostic. For individuals without symptoms, AD biomarker tests are still only appropriate for research purposes. Additionally, there are analytical challenges that require careful attention, especially for longitudinal use of AD tests.

The Alzheimer's Association international guidelines for handling of cerebrospinal fluid for routine clinical measurements of amyloid β and tau

The core cerebrospinal fluid (CSF) Alzheimer's disease (AD) biomarkers amyloid beta (Aβ42 and Aβ40), total tau, and phosphorylated tau, have been extensively clinically validated, with very high diagnostic performance for AD, including the early phases of the disease. However, between-center differences in pre-analytical procedures may contribute to variability in measurements across laboratories. To resolve this issue, a workgroup was led by the Alzheimer's Association with experts from both academia and industry. The aim of the group was to develop a simplified and standardized pre-analytical protocol for CSF collection and handling before analysis for routine clinical use, and ultimately to ensure high diagnostic performance and minimize patient misclassification rates. Widespread application of the protocol would help minimize variability in measurements, which would facilitate the implementation of unified cut-off levels across laboratories, and foster the use of CSF biomarkers in AD diagnostics for the benefit of the patients.

Quantitative Measurement of Cerebrospinal Fluid Amyloid-β Species by Mass Spectrometry

Background:

High sensitivity liquid chromatography mass spectrometry (LC-MS/MS) was recently introduced to measure amyloid-β (Aβ) species, allowing for a simultaneous assay that is superior to ELISA, which requires more assay steps with multiple antibodies.

Objective:

We validated the Aβ_1-38, Aβ_1-40, Aβ_1-42, and Aβ_1-43 assay by LC-MS/MS and compared it with ELISA using cerebrospinal fluid (CSF) samples to investigate its feasibility for clinical application.

Methods:

CSF samples from 120 subjects [8 Alzheimer’s disease (AD) with dementia (ADD), 2 mild cognitive dementia due to Alzheimer’s disease (ADMCI), 14 cognitively unimpaired (CU), and 96 neurological disease subjects] were analyzed. Aβ species were separated using the Shimadzu Nexera X2 system and quantitated using a Qtrap 5500 LC-MS/MS system. Aβ_1-40 and Aβ_1-42 levels were validated using ELISA.

Results:

CSF levels in CU were 666±249 pmol/L in Aβ_1-38, 2199±725 pmol/L in Aβ_1-40, 153.7±79.7 pmol/L in Aβ_1-42, and 9.78±4.58 pmol/L in Aβ_1-43. The ratio of the amounts of Aβ_1-38, Aβ_1-40, Aβ_1-42, and Aβ_1-43 was approximately 68:225:16:1. Linear regression analyses showed correlations among the respective Aβ species. Both Aβ_1-40 and Aβ_1-42 values were strongly correlated with ELISA measurements. No significant differences were observed in Aβ_1-38 or Aβ_1-40 levels between AD and CU. Aβ_1-42 and Aβ_1-43 levels were significantly lower, whereas the Aβ_1-38/1-42, Aβ_1-38/1-43, and Aβ_1-40/Aβ_1-43 ratios were significantly higher in AD than in CU. The basic assay profiles of the respective Aβ species were adequate for clinical usage.

Conclusion:

A quantitative LC-MS/MS assay of CSF Aβ species is as reliable as specific ELISA for clinical evaluation of CSF biomarkers for AD.

Volumetric distribution of perivascular space in relation to mild cognitive impairment

Vascular contributions to early cognitive decline are increasingly recognized, prompting further investigation into the nature of related changes in perivascular spaces (PVS). Using magnetic resonance imaging, we show that, compared to a cognitively normal sample, individuals with early cognitive dysfunction have altered PVS presence and distribution, irrespective of Amyloid-β. Surprisingly, we noted lower PVS presence in the anterosuperior medial temporal lobe (asMTL) (1.29 times lower PVS volume fraction in cognitively impaired individuals, p < 0.0001), which was associated with entorhinal neurofibrillary tau tangle deposition (beta (standard error) = -0.98 (0.4); p = 0.014), one of the hallmarks of early Alzheimer's disease pathology. We also observed higher PVS volume fraction in centrum semi-ovale of the white matter, but only in female participants (1.47 times higher PVS volume fraction in cognitively impaired individuals, p = 0.0011). We also observed PVS changes in participants with history of hypertension (higher in the white matter and lower in the asMTL). Our results suggest that anatomically specific alteration of the PVS is an early neuroimaging feature of cognitive impairment in aging adults, which is differentially manifested in female.

Cerebrospinal fluid total tau levels indicate aberrant neuronal plasticity in Alzheimer's disease

Alzheimer's disease (AD) is characterised by abnormal amyloid beta and tau processing. Previous studies reported that cerebrospinal fluid (CSF) total tau (t-tau) levels vary between patients. Here we show that CSF t-tau variability is associated with distinct impairments in neuronal plasticity mediated by gene repression factors SUZ12 and REST. AD individuals with abnormal t-tau levels have increased CSF concentrations of plasticity proteins regulated by SUZ12 and REST. AD individuals with normal t-tau, on the contrary, have decreased concentrations of these plasticity proteins and increased concentrations in proteins associated with blood-brain and blood CSF-barrier dysfunction. Genomic analyses suggested that t-tau levels in part depend on genes involved in gene expression. The distinct plasticity abnormalities in AD as signaled by t-tau urge the need for personalised treatment.

Derivation and utility of an Aβ-PET pathology accumulation index to estimate Aβ load

OBJECTIVE

To evaluate a novel β-amyloid (Aβ)-PET-based quantitative measure (Aβ accumulation index [Aβ index]), including the assessment of its ability to discriminate between participants based on Aβ status using visual read, CSF Aβ₄₂/Aβ₄₀, and post-mortem neuritic plaque burden as standards of truth.

METHODS

One thousand one hundred twenty-one participants (with and without cognitive impairment) were scanned with Aβ-PET: Swedish BioFINDER, n = 392, [¹⁸F]flutemetamol; Alzheimer's Disease Neuroimaging Initiative (ADNI), n = 692, [¹⁸F]florbetapir; and a phase 3 end-of-life study, n = 100, [¹⁸F]flutemetamol. The relationships between Aβ index and standardized uptake values ratios (SUVR) from Aβ-PET were assessed. The diagnostic performances of Aβ index and SUVR were compared with visual reads, CSF Aβ₄₂/Aβ₄₀, and Aβ histopathology used as reference standards.

RESULTS

Strong associations were observed between Aβ index and SUVR (R ²: BioFINDER 0.951, ADNI 0.943, end-of-life, 0.916). Both measures performed equally well in differentiating Aβ-positive from Aβ-negative participants, with areas under the curve (AUCs) of 0.979 to 0.991 to detect abnormal visual reads, AUCs of 0.961 to 0.966 to detect abnormal CSF Aβ₄₂/Aβ₄₀, and AUCs of 0.820 to 0.823 to detect abnormal Aβ histopathology. Both measures also showed a similar distribution across postmortem-based Aβ phases (based on anti-Aβ 4G8 antibodies). Compared to models using visual read alone, the addition of the Aβ index resulted in a significant increase in AUC and a decrease in Akaike information criterion to detect abnormal Aβ histopathology.

CONCLUSION

The proposed Aβ index showed a tight association to SUVR and carries an advantage over the latter in that it does not require the definition of regions of interest or the use of MRI. Aβ index may thus prove simpler to implement in clinical settings and may also facilitate the comparison of findings using different Aβ-PET tracers.

CLASSIFICATION OF EVIDENCE

This study provides Class III evidence that the Aβ accumulation index accurately differentiates Aβ-positive from Aβ-negative participants compared to Aβ-PET visual reads, CSF Aβ₄₂/Aβ₄₀, and Aβ histopathology.

Certification of Amyloid-Beta (Aβ) Certified Reference Materials by Amino Acid-Based Isotope Dilution High-Performance Liquid Chromatography Mass Spectrometry and Sulfur-Based High-Performance Liquid Chromatography Isotope Dilution Inductively Coupled Plasma Mass Spectrometry

The use of amyloid-beta (Aβ) biomarkers could contribute to an early diagnosis of Alzheimer's disease (AD); however, there are still large variations among results from different assays. This variability can be overcome by standardization of those assays through the use of certified reference materials (CRMs) and the establishment of a traceability chain. In this study, Aβ₄₀ (GBW09874) and Aβ₄₂ (GBW09875) solution CRMs with the certified values and uncertainties of 7.58 ± 0.30 and 7.62 ± 0.30 μg g^-1 were developed with high-purity Aβ as raw materials. For the first time, isotope dilution high-performance liquid chromatography mass spectrometry (ID-LC-MS) and high-performance liquid chromatography isotope dilution inductively coupled plasma mass spectrometry (HPLC-ID-ICP-MS) strategies were employed to certify the candidate Aβ solution CRMs. The two candidate CRMs showed good homogeneity, and good stability was also demonstrated for at least 5 days at -20 °C and 14 months at -70 °C. These CRMs are primarily intended to be used for value assignment to secondary calibrators or CRMs with a clinical matrix, which will help in early diagnosis of AD.

Effect of escitalopram dose and treatment duration on CSF Aβ levels in healthy older adults: A controlled clinical trial

OBJECTIVE

To determine whether treatment with escitalopram compared with placebo would lower CSF β-amyloid 42 (Aβ₄₂) levels.

RATIONALE

Serotonin signaling suppresses Aβ₄₂ in animal models of Alzheimer disease (AD) and young healthy humans. In a prospective study in older adults, we examined dose and treatment duration effects of escitalopram.

METHODS

Using lumbar punctures to sample CSF levels before and after a course of escitalopram treatment, cognitively normal older adults (n = 114) were assigned to placebo, 20 mg escitalopram × 2 weeks, 20 mg escitalopram × 8 weeks, or 30 mg escitalopram × 8 weeks; CSF sampled pretreatment and posttreatment and within-subject percent change in Aβ₄₂ was used as the primary outcome in subsequent analyses.

RESULTS

An overall 9.4% greater reduction in CSF Aβ₄₂ was found in escitalopram-treated compared with placebo-treated groups (p < 0.001, 95% confidence interval [CI] 4.9%-14.2%, d = 0.81). Positive baseline Aβ status (CSF Aβ₄₂ levels <250 pg/mL) was associated with smaller Aβ₄₂ reduction (p = 0.006, 95% CI -16.7% to 0.5%, d = -0.52) compared with negative baseline amyloid status (CSF Aβ₄₂ levels >250 pg/mL).

CONCLUSIONS

Short-term longitudinal doses of escitalopram decreased CSF Aβ₄₂ in cognitively normal older adults, the target group for AD prevention.

CLINICALTRIALSGOV IDENTIFIER

NCT02161458.

CLASSIFICATION OF EVIDENCE

This study provides Class II evidence that for cognitively normal older adults, escitalopram decreases CSF Aβ₄₂.

Association of CSF Aβ, amyloid PET, and cognition in cognitively unimpaired elderly adults

OBJECTIVE

To compare CSF β-amyloid (Aβ) and florbetapir PET measurements in cognitively unimpaired (CU) elderly adults in order to detect the earliest abnormalities and compare their predictive effect for cognitive decline.

METHODS

A total of 259 CU individuals were categorized as abnormal (+) or normal (-) on CSF Aβ_1-42/Aβ_1-40 analyzed with mass spectrometry and Aβ PET measured with ¹⁸F-florbetapir. Simultaneous longitudinal measurements of CSF and PET were compared for 39 individuals who were unambiguously Aβ-negative at baseline (CSF-/PET-). We also examined the relationship between baseline CSF/PET group membership and longitudinal changes in CSF Aβ, Aβ PET, and cognition.

RESULTS

The proportions of individuals in each discordant group were similar (8.1% CSF+/PET- and 7.7% CSF-/PET+). Among baseline Aβ-negative (CSF-/PET-) individuals with longitudinal CSF and PET measurements, a larger proportion subsequently worsened on CSF Aβ (odds ratio 4 [95% confidence interval (CI) 1.1, 22.1], p = 0.035) than Aβ PET over 3.5 ± 1.0 years. Compared to CSF-/PET- individuals, CSF+/PET- individuals had faster (estimate 0.009 [95% CI 0.005, 0.013], p < 0.001) rates of Aβ PET accumulation over 4.4 ± 1.7 years, while CSF-/PET+ individuals had faster (estimate -0.492 [95% CI -0.861, -0.123], p = 0.01) rates of cognitive decline over 4.5 ± 1.9 years.

CONCLUSIONS

The proportions of discordant PET and CSF Aβ-positive individuals were similar cross-sectionally. However, unambiguously Aβ-negative (CSF-/PET-) individuals are more likely to show subsequent worsening on CSF than PET, supporting the idea that CSF detects the earliest Aβ changes. In discordant cases, only PET abnormality predicted cognitive decline, suggesting that abnormal Aβ PET changes are a later phenomenon in cognitively normal individuals.

First amyloid β1-42 certified reference material for re-calibrating commercial immunoassays

INTRODUCTION

Reference materials based on human cerebrospinal fluid were certified for the mass concentration of amyloid beta (Aβ)1-42 (Aβ₄₂ ). They are intended to be used to calibrate diagnostic assays for Aβ₄₂ .

METHODS

The three certified reference materials (CRMs), ERM-DA480/IFCC, ERM-DA481/IFCC and ERM-DA482/IFCC, were prepared at three concentration levels and characterized using isotope dilution mass spectrometry methods. Roche, EUROIMMUN, and Fujirebio used the three CRMs to re-calibrate their immunoassays.

RESULTS

The certified Aβ₄₂ mass concentrations in ERM-DA480/IFCC, ERM-DA481/IFCC, and ERM-DA482/IFCC are 0.45, 0.72, and 1.22 μg/L, respectively, with expanded uncertainties (k = 2) of 0.07, 0.11, and 0.18 μg/L, respectively. Before re-calibration, a good correlation (Pearson's r > 0.97), yet large biases, were observed between results from different commercial assays. After re-calibration the between-assay bias was reduced to < 5%.

DISCUSSION

The Aβ₄₂ CRMs can ensure the equivalence of results between methods and across platforms for the measurement of Aβ₄₂ .

An automated clinical mass spectrometric method for identification and quantification of variant and wild-type amyloid-β 1-40 and 1-42 peptides in CSF

INTRODUCTION

We developed an automated liquid chromatography-tandem mass spectrometry high performance liquid chromatography tandem mass spectrometry (HPLC-MS/MS) method for multiplex quantification of wild-type (wt) amyloid β (Aβ) peptides 1-40 (Aβ40) and 1-42 (Aβ42) and detection of variant Aβ peptides in cerebrospinal fluid.

METHODS

The multiplex Aβ HPLC-MS/MS assay was validated in a clinically accredited laboratory following regulatory guidelines, with Aβ42 calibration assigned to the ERM/IFCC certified reference material; sequence variants were additionally multiplexed into the method.

RESULTS

Sample preparation was fully automated on a liquid handler. The assay quantified wt-Aβ42 and wt-Aβ40 and detected sequence variants, when present, within the Aβ42 sequence.

DISCUSSION

Extension of the HPLC-MS/MS approach for quantification of wt-Aβ42 and wt-Aβ40 to include known sequence variants increases analytical accuracy of the mass spectrometric approach and enables identification of cases of autosomal dominant Alzheimer's disease. Development of an automated workflow and selection of appropriate instrumentation enabled deployment of this method in routine clinical testing.

Proteomic applications in pathology and laboratory medicine: Present state and future prospects

Clinical mass spectrometry applications have traditionally focused on small molecules, particularly in the areas of therapeutic drug monitoring, toxicology, and measurement of endogenous and exogenous steroids. More recently, the use of matrix assisted laser desorption/ionization time of flight mass spectrometry for the identification of microbial pathogens has been widely implemented. Following this evolution, there has been an expanding role for the measurement of peptides and proteins in pathology and laboratory medicine. This review explores the current state of protein measurement by clinical mass spectrometry and the analytical strategies employed, as well as emerging applications in clinical chemistry, clinical microbiology and anatomical pathology.

LC-MS/MS analysis of twelve neurotransmitters and amino acids in mouse cerebrospinal fluid

BACKGROUND

So far, analytical investigation of neuroactive molecules in cerebrospinal fluid (CSF) of rodent models has been limited to rats, given the intrinsic anatomic difficulties related to mice sampling and the corresponding tiny amounts of CSF obtained. This poses a challenge for the research in neuroscience, where many, if not most, animal models for neuronal disorders rely on mice.

NEW METHOD

We introduce a new, sensitive and robust LC-MS/MS method to analyze a panel of twelve neuroactive molecules (NM) from mouse CSF (aspartic acid, serine, glycine, glutamate, γ-aminobutyric acid, norepinephrine, epinephrine, acetylcholine, dopamine, serotonin, histamine and its metabolite 1-metylhistamine). The paper describes the sampling procedure that allows the collection of 1-2 microliters of pure CSF from individual mouse specimens.

RESULTS

To test its applicability, we challenged our method on the field, by sampling 37 individual animals, thus demonstrating its strength and reliability.

COMPARISON WITH EXISTING METHOD(S)

Compared to other methods, our procedure does not involve any extraction nor derivatization steps: samples are simply diluted and analyzed as such by LC-MS/MS, using a dedicated ion pairing agent in the chromatographic setup. The panel of neuroactive molecules that is analyzed in a single run is also significantly higher compared to other methods.

CONCLUSIONS

Given the number of mouse models used in the neuroscience research, we believe that our work will pave new ways to more advanced research in this field.

Analytical and Clinical Performance of Amyloid-Beta Peptides Measurements in CSF of ADNIGO/2 Participants by an LC-MS/MS Reference Method

BACKGROUND

Cerebrospinal fluid (CSF) amyloid-β1-42 (Aβ42) reliably detects brain amyloidosis based on its high concordance with plaque burden at autopsy and with amyloid positron emission tomography (PET) ligand retention observed in several studies. Low CSF Aβ42 concentrations in normal aging and dementia are associated with the presence of fibrillary Aβ across brain regions detected by amyloid PET imaging.

METHODS

An LC-MS/MS reference method for Aβ42, modified by adding Aβ40 and Aβ38 peptides to calibrators, was used to analyze 1445 CSF samples from ADNIGO/2 participants. Seventy runs were completed using 2 different lots of calibrators. For preparation of Aβ42 calibrators and controls spiking solution, reference Aβ42 standard with certified concentration was obtained from EC-JRC-IRMM (Belgium). Aβ40 and Aβ38 standards were purchased from rPeptide. Aβ42 calibrators' accuracy was established using CSF-based Aβ42 Certified Reference Materials (CRM).

RESULTS

CRM-adjusted Aβ42 calibrator concentrations were calculated using the regression equation Y (CRM-adjusted) = 0.89X (calibrators) + 32.6. Control samples and CSF pools yielded imprecision ranging from 6.5 to 10.2% (Aβ42) and 2.2 to 7.0% (Aβ40). None of the CSF pools showed statistically significant differences in Aβ42 concentrations across 2 different calibrator lots. Comparison of Aβ42 with Aβ42/Aβ40 showed that the ratio improved concordance with concurrent [18F]-florbetapir PET as a measure of fibrillar Aβ (n = 766) from 81 to 88%.

CONCLUSIONS

Long-term performance assessment substantiates our modified LC-MS/MS reference method for 3 Aβ peptides. The improved diagnostic performance of the CSF ratio Aβ42/Aβ40 suggests that Aβ42 and Aβ40 should be measured together and supports the need for an Aβ40 CRM.

Perspectives in fluid biomarkers in neurodegeneration from the 2019 biomarkers in neurodegenerative diseases course-a joint PhD student course at University College London and University of Gothenburg

Until relatively recently, a diagnosis of probable Alzheimer's disease (AD) and other neurodegenerative disorders was principally based on clinical presentation, with post-mortem examination remaining a gold standard for disease confirmation. This is in sharp contrast to other areas of medicine, where fluid biomarkers, such as troponin levels in myocardial infarction, form an integral part of the diagnostic and treatment criteria. There is a pressing need for such quantifiable and easily accessible tools in neurodegenerative diseases.In this paper, based on lectures given at the 2019 Biomarkers in Neurodegenerative Diseases Course, we provide an overview of a range of cerebrospinal fluid (CSF) and blood biomarkers in neurodegenerative disorders, including the 'core' AD biomarkers amyloid β (Aβ) and tau, as well as other disease-specific and general markers of neuroaxonal injury. We then highlight the main challenges in the field, and how those could be overcome with the aid of new methodological advances, such as assay automation, mass spectrometry and ultrasensitive immunoassays.As we hopefully move towards an era of disease-modifying treatments, reliable biomarkers will be essential to increase diagnostic accuracy, allow for earlier diagnosis, better participant selection and disease activity and treatment effect monitoring.

Detection of Alzheimer Disease Pathology in Patients Using Biochemical Biomarkers: Prospects and Challenges for Use in Clinical Practice

BACKGROUND

Thirty-four years ago, amyloid-β 1-42 peptide was identified in amyloid plaques from brain tissue obtained from patients with Alzheimer disease (AD) and Down syndrome. This finding led to development of immunoassays for this marker of amyloid plaque burden in cerebrospinal fluid (CSF) approximately 10 years later. Subsequently, research immunoassays were developed for total τ protein and τ phosphorylated at the threonine 181 position. Subsequent studies documented the clinical utility of these biomarkers of amyloid plaque burden or τ tangle pathology in cohorts of living patients.

CONTENT

We describe the following: (a) clinical utility of AD biomarkers; (b) measurement challenges, including development of mass spectrometry-based reference methods and automated immunoassays; (c) development of "appropriate use criteria" (AUC) guidelines for safe/appropriate use of CSF testing for diagnosis of AD developed by neurologists, a neuroethicist, and laboratorians; (d) a framework, sponsored by the National Institute of Aging-Alzheimer's Association (NIA-AA), that defines AD on the basis of CSF and imaging methods for detecting amyloid plaque burden, τ tangle pathology, and neurodegeneration. This framework's purpose was investigative but has important implications for future clinical practice; (e) recognition of copathologies in AD patients and challenges for developing methods to detect these in living patients.

SUMMARY

The field can expect availability of validated research tools for detection of AD pathology that support clinical treatment trials of disease-modifying agents and, ultimately, use in clinical practice. Validated methods are becoming available for CSF testing; emergence of validated methods for AD biomarkers in plasma can be expected in the next few years.

A multipredictor model to predict the conversion of mild cognitive impairment to Alzheimer's disease by using a predictive nomogram

Predicting the probability of converting from mild cognitive impairment (MCI) to Alzheimer's disease (AD) is still a challenging task. This study aims at providing a personalized MCI-to-AD conversion estimation by using a multipredictor nomogram that integrates neuroimaging features, cerebrospinal fluid (CSF) biomarker, and clinical assessments. To do so, 290 MCI patients were collected from the Alzheimer's Disease Neuroimaging Initiative (ADNI), of whom 76 has converted to AD and 214 remained with MCI. All subjects were randomly divided into a primary and validation cohort. Radiomics signature (Rad-sig) was obtained based on 17 cerebral cortex features selected by using Least Absolute Shrinkage and Selection Operator (LASSO) algorithm. Clinical factors and amyloid-beta peptide (Aβ) concentration were selected by using Spearman correlation between the converted and not-converted patients. Then, a nomogram that combines image features, clinical factor, and Aβ concentration was constructed and validated. Furthermore, we explored the associations between various predictors from the macro- to the microperspective by assessing gene expression patterns. Our results showed that the multipredictor nomogram (C-index 0.978 and 0.956 in both cohorts, respectively) outperformed the nomogram using either Rad-sig or Aβ concentration as individual predictors. Significant associations were found between neuropsychological scores, cerebral cortex features, Aβ levels, and underlying gene pathways. Our study may have a clinical impact as a powerful predictive tool for predicting the conversion probability of MCI and providing associations between cognitive impairment, structural changes, Aβ levels, and underlying biological patterns from the macro- to the microperspective.

Method comparison study of the Elecsys® β-Amyloid (1-42) CSF assay versus comparator assays and LC-MS/MS

BACKGROUND

Alzheimer's disease (AD) biomarkers, such as cerebrospinal fluid (CSF) amyloid-β (1-42; Aβ42), can provide high diagnostic accuracy. Several immunoassays are available for Aβ42 quantitation, but standardisation across assays remains an issue. We compared the Elecsys® β-Amyloid (1-42) CSF assay with three assays and two liquid chromatography tandem mass spectrometry (LC-MS/MS) methods.

METHODS

Three method comparison studies evaluated the correlation between the Elecsys® β-Amyloid (1-42) CSF assay versus: INNOTEST® β-AMYLOID(1-42) (860 samples) and the Roche Diagnostics-developed LC-MS/MS method (250 samples); INNO-BIA AlzBio3 and the University of Pennsylvania (UPenn)-developed LC-MS/MS method (250 samples); and ADx-EUROIMMUN Beta-Amyloid (1-42) enzyme-linked immunosorbent assay (ELISA) (49 samples).

RESULTS

High correlation was demonstrated between Elecsys® β-Amyloid (1-42) CSF and comparator assays: INNOTEST® β-AMYLOID(1-42) (Spearman's ρ, 0.954); INNO-BIA AlzBio3 (Spearman's ρ, 0.864); ADx-EUROIMMUN Beta-Amyloid (1-42) ELISA (Pearson's r, 0.925). Elecsys® assay and LC-MS/MS measurements were highly correlated: Pearson's r, 0.949 (Roche Diagnostics-developed method) and 0.943 (UPenn-developed method).

CONCLUSION

Findings from this multicentre evaluation further support use of the Elecsys® β-Amyloid (1-42) CSF assay to aid AD diagnosis. CSF-based certified reference materials should improve agreement across assays and mass spectrometry-based methods, which is essential to establish a global uniform CSF Aβ42 cut-off to detect amyloid pathology.

Mass spectrometry: A platform for biomarker discovery and validation for Alzheimer's and Parkinson's diseases

Accurate, reliable, and objective biomarkers for Alzheimer's disease (AD), Parkinson's disease (PD), and related age-associated neurodegenerative disorders are urgently needed to assist in both diagnosis, particularly at early stages, and monitoring of disease progression. Technological advancements in protein detection platforms over the last few decades have resulted in a plethora of reported molecular biomarker candidates for both AD and PD; however, very few of these candidates are developed beyond the discovery phase of the biomarker development pipeline, a reflection of the current bottleneck within the field. In this review, the expanded use of selected reaction monitoring (SRM) targeted mass spectrometry will be discussed in detail as a platform for systematic verification of large panels of protein biomarker candidates prior to costly validation testing. We also advocate for the coupling of discovery-based proteomics with modern targeted MS-based approaches (e.g., SRM) within a single study in future workflows to expedite biomarker development and validation for AD and PD. It is our hope that improving the efficiency within the biomarker development process by use of an SRM pipeline may ultimately hasten the development of biomarkers that both decrease misdiagnosis of AD and PD and ultimately lead to detection at early stages of disease and objective assessment of disease progression. This article is part of the special issue "Proteomics".

Prostaglandins E2 and F2α levels in human menstrual fluid by online Solid Phase Extraction coupled to Liquid Chromatography tandem Mass Spectrometry (SPE-LC-MS/MS)

This paper reports an online SPE-LC-MS/MS method for the simultaneous quantification of prostaglandins (PGE₂ and PGF_2α) in menstrual fluid samples. To meet this goal human peripheral serum was used as surrogate matrix. The analytes were trapped on an OASIS HLB cartridge for 3 min, for sample cleanup and enrichment, and then transferred during only 42 s to an HSS T3 C18 analytical column, for separation and analysis. Prostaglandins (PGs) were detected by selected reaction monitoring in negative ion mode, PGE₂ (m/z 351 → 315) and PGF_2α (m/z 353 → 193) using isotope-labeled internal standard (PGE₂-d₄, m/z 355 → 319). The concentration linear range was of 10.34-1.034 ng mL^-1 and the lower limit of quantification (LLOQ) was 10.34 ng mL^-1 for both PGs. Validation parameters were successfully assessed according to the European Medicines Agency guideline (EMA), also comprising the FDA normative. The method showed no matrix effect and process efficiency around 100%, in addition to only 15 min of analysis time with lower solvent consumption. The method application was carried out using two menstrual fluid sample groups: control (n = 15) and treatment group (n = 7; samples from women that used Tahiti lemon juice). The PGF_2α levels were found to be higher in treated group than in control group (p ≤ 0.05), denoting an effect of the intake of Tahiti lemon juice on the menstrual inflammatory process. The on-line method herein reported could be useful for the analysis of PGs from large research studies.