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

An electrostatic cluster guides Aβ40 fibril formation in sporadic and Dutch-type cerebral amyloid angiopathy

Cerebral amyloid angiopathy (CAA) is associated with the accumulation of fibrillar Aβ peptides upon and within the cerebral vasculature, which leads to loss of vascular integrity and contributes to disease progression in Alzheimer's disease (AD). We investigate the structure of human-derived Aβ40 fibrils obtained from patients diagnosed with sporadic or familial Dutch-type (E22Q) CAA. Using cryo-EM, two primary structures are identified containing elements that have not been observed in in vitro Aβ40 fibril structures. One population has an ordered N-terminal fold comprised of two β-strands stabilized by electrostatic interactions involving D1, E22, D23 and K28. This charged cluster is disrupted in the second population, which exhibits a disordered N-terminus and is favored in fibrils derived from the familial Dutch-type CAA patient. These results illustrate differences between human-derived CAA and AD fibrils, and how familial CAA mutations can guide fibril formation.

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.

The ZmbHLH47-ZmSnRK2.9 Module Promotes Drought Tolerance in Maize

Drought stress globally poses a significant threat to maize (Zea mays L.) productivity and the underlying molecular mechanisms of drought tolerance remain elusive. In this study, we characterized ZmbHLH47, a basic helix-loop-helix (bHLH) transcription factor, as a positive regulator of drought tolerance in maize. ZmbHLH47 expression was notably induced by both drought stress and abscisic acid (ABA). Transgenic plants overexpressing ZmbHLH47 displayed elevated drought tolerance and ABA responsiveness, while the zmbhlh47 mutant exhibited increased drought sensitivity and reduced ABA sensitivity. Mechanistically, it was revealed that ZmbHLH47 could directly bind to the promoter of ZmSnRK2.9 gene, a member of the subgroup III SnRK2 kinases, activating its expression. Furthermore, ZmSnRK2.9-overexpressing plants exhibited enhanced ABA sensitivity and drought tolerance, whereas the zmsnrk2.9 mutant displayed a decreased sensitivity to both. Notably, overexpressing ZmbHLH47 in the zmsnrk2.9 mutant closely resembled the zmsnrk2.9 mutant, indicating the importance of the ZmbHLH47-ZmSnRK2.9 module in ABA response and drought tolerance. These findings provided valuable insights and a potential genetic resource for enhancing the environmental adaptability of maize.

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.

The basic helix-loop-helix transcription factor gene, OsbHLH38, plays a key role in controlling rice salt tolerance

The plant hormone abscisic acid (ABA) is crucial for plant seed germination and abiotic stress tolerance. However, the association between ABA sensitivity and plant abiotic stress tolerance remains largely unknown. In this study, 436 rice accessions were assessed for their sensitivity to ABA during seed germination. The considerable diversity in ABA sensitivity among rice germplasm accessions was primarily reflected by the differentiation between the Xian (indica) and Geng (japonica) subspecies and between the upland-Geng and lowland-Geng ecotypes. The upland-Geng accessions were most sensitive to ABA. Genome-wide association analyses identified four major quantitative trait loci containing 21 candidate genes associated with ABA sensitivity of which a basic helix-loop-helix transcription factor gene, OsbHLH38, was the most important for ABA sensitivity. Comprehensive functional analyses using knockout and overexpression transgenic lines revealed that OsbHLH38 expression was responsive to multiple abiotic stresses. Overexpression of OsbHLH38 increased seedling salt tolerance, while knockout of OsbHLH38 increased sensitivity to salt stress. A salt-responsive transcription factor, OsDREB2A, interacted with OsbHLH38 and was directly regulated by OsbHLH38. Moreover, OsbHLH38 affected rice abiotic stress tolerance by mediating the expression of a large set of transporter genes of phytohormones, transcription factor genes, and many downstream genes with diverse functions, including photosynthesis, redox homeostasis, and abiotic stress responsiveness. These results demonstrated that OsbHLH38 is a key regulator in plant abiotic stress tolerance.

Annual stability of the plasma Aß40/42 ratio and associated factors

OBJECTIVE

The plasma Aß40/42 ratio is a biomarker of brain amyloidosis. However, the threshold difference between amyloid positivity and negativity is only 10-20% and fluctuates with circadian rhythms, aging, and APOE-ε4 during the decades of evolution of Alzheimer's disease.

METHODS

Plasma Aß40 and Aß42 levels in 1472 participants aged between 19 and 93 years in the Iwaki Health Promotion Project for 4 years were statistically analyzed.

RESULTS

The means and standard deviations of annual inter-individual coefficients of variation were 5.3 ± 3.2% for Aß40, 7.8 ± 4.6% for Aß42, and 6.4 ± 4.1% for the Aß40/42 ratio. No significant age-dependent changes were observed in inter-individual coefficients of variation. Age-dependent increases in Aβ42 levels were suppressed, whereas those in the Aβ40/42 ratio were enhanced in APOE-ε4 carriers. The change points of Aß42, Aß40, and the Aß40/42 ratio were 36.4, 38.2, and 43.5 years, respectively. In the presence of APOE-ε4, the Aß40/42 ratio increased in middle-aged and elderly subjects while Aβ42 levels decreased in elderly subjects.

INTERPRETATION

Individual values for Aß40, Aß42, and the Aß40/42 ratio did not fluctuate annually or in an age-dependent manner. If the plasma Aβ40/42 ratio changes by more than 14.7% (+2 standard deviations) relative to age- and APOE-ε4-adjusted normal annual fluctuations, other biomarkers also need to be examined.

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.

Plasma ApoE4 Levels Are Lower than ApoE2 and ApoE3 Levels, and Not Associated with Plasma Aβ40/42 Ratio as a Biomarker of Amyloid-β Amyloidosis in Alzheimer's Disease

BACKGROUND

APOE4 is the strongest risk factor for Alzheimer's disease (AD). However, limited information is currently available on APOE4 and the pathological role of plasma apolipoprotein E (ApoE) 4 remains unclear.

OBJECTIVE

The aims of the present study were to measure plasma levels of total ApoE (tE), ApoE2, ApoE3, and ApoE4 using mass spectrometry and elucidate the relationships between plasma ApoE and blood test items.

METHODS

We herein examined plasma levels of tE, ApoE2, ApoE3, and ApoE4 in 498 subjects using liquid chromatograph-mass spectrometry (LC-MS/MS).

RESULTS

Among 498 subjects, mean age was 60 years and 309 were female. tE levels were distributed as ApoE2/E3 = ApoE2/E4 >ApoE3/E3 = ApoE3/E4 >ApoE4/E4. In the heterozygous group, ApoE isoform levels were distributed as ApoE2 >ApoE3 >ApoE4. ApoE levels were not associated with aging, the plasma amyloid-β (Aβ) 40/42 ratio, or the clinical diagnosis of AD. Total cholesterol levels correlated with the level of each ApoE isoform. ApoE2 levels were associated with renal function, ApoE3 levels with low-density lipoprotein cholesterol and liver function, and ApoE4 levels with triglycerides, high-density lipoprotein cholesterol, body weight, erythropoiesis, and insulin metabolism.

CONCLUSION

The present results suggest the potential of LC-MS/MS for the phenotyping and quantitation of plasma ApoE. Plasma ApoE levels are regulated in the order of ApoE2 >ApoE3 >ApoE4 and are associated with lipids and multiple metabolic pathways, but not directly with aging or AD biomarkers. The present results provide insights into the multiple pathways by which peripheral ApoE4 influences the progression of AD and atherosclerosis.

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.

Applications of Tandem Mass Spectrometry (MS/MS) in Protein Analysis for Biomedical Research

Mass Spectrometry (MS) allows the analysis of proteins and peptides through a variety of methods, such as Electrospray Ionization-Mass Spectrometry (ESI-MS) or Matrix-Assisted Laser Desorption Ionization-Mass Spectrometry (MALDI-MS). These methods allow identification of the mass of a protein or a peptide as intact molecules or the identification of a protein through peptide-mass fingerprinting generated upon enzymatic digestion. Tandem mass spectrometry (MS/MS) allows the fragmentation of proteins and peptides to determine the amino acid sequence of proteins (top-down and middle-down proteomics) and peptides (bottom-up proteomics). Furthermore, tandem mass spectrometry also allows the identification of post-translational modifications (PTMs) of proteins and peptides. Here, we discuss the application of MS/MS in biomedical research, indicating specific examples for the identification of proteins or peptides and their PTMs as relevant biomarkers for diagnostic and therapy.

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.