A new methodology for simultaneous quantification of total-Aβ, Aβx-38, Aβx-40, and Aβx-42 by column-switching LC/MS/MS

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.

Quantitative bioanalysis of proteins by digestion and LC-MS/MS: the use of multiple signature peptides

The use of multiple signature peptides for the quantification of proteins by digestion and LC-MS/MS is reviewed and evaluated here. A distinction is made based on the purpose of the use of multiple peptides: confirmation of the protein concentration, discrimination between different protein forms or species and in vivo biotransformation. Most reports that describe methods with at least two peptides use these for confirmation, but it is not always mentioned how the peptides are used and how possible differences in concentration between the peptides are handled. Differences in concentration are often reported in the case of monitoring different protein forms or in vivo biotransformation, and this offers insight into the biological fate of the protein.

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.

A β-Amyloid(1-42) Biosensor Based on Molecularly Imprinted Poly-Pyrrole for Early Diagnosis of Alzheimer's Disease

Background:

Alzheimer’s disease (AD) is a common form of dementia, characterized by production and deposition of β-amyloid peptide in the brain. Thus, β-amyloid peptide is a potentially promising biomarker used to diagnose and monitor the progression of AD.

Objective:

The study aims to develop a biosensor based on a molecularly imprinted poly-pyrrole for detection of β-amyloid.

Material and Methods:

In this experimental study, an imprinted poly-pyrrole was employed as an artificial receptor synthesized by electro-polymerization of pyrrole on screen-printed carbon electrodes in the presence of β-amyloid. β-amyloid acts as a molecular template within the polymer. The biosensor was evaluated by cyclic voltammetry using ferro/ferricyanide marker. The parameters influencing the biosensor performance, including electro-polymerization cycle umbers and β-amyloid binding time were optimized to achieve the best biosensor sensitivity.

Results:

The β-amyloid binding affinity with the biosensor surface was evaluated by the Freundlich isotherm, and Freundlich constant and exponent were obtained as 0.22 ng mL^-1 and 10.60, respectively. The biosensor demonstrated a detection limit of 1.2 pg mL^-1. The biosensor was applied for β-amyloid determination in artificial cerebrospinal fluid.

Conclusion:

The biosensor is applicable for early Alzheimer’s disease detection.

Interface engineering of microelectrodes toward ultrasensitive monitoring of β-amyloid peptides in cerebrospinal fluid in Alzheimer's disease

Aβ monomers directed the assembly of Cu²⁺-PEI/AuNPs-hemin nanoprobes into network aggregates on a microelectrode interface for enhanced electrochemical analysis.

An UHPLC-MS/MS method for simultaneous quantification of human amyloid beta peptides Aβ1-38, Aβ1-40 and Aβ1-42 in cerebrospinal fluid using micro-elution solid phase extraction

Amyloid beta (Aβ) peptides in cerebrospinal fluid are extensively estimated for identification of Alzheimer's disease (AD) as diagnostic biomarkers. Unfortunately, their pervasive application is hampered by interference from Aβ propensity of self-aggregation, nonspecifically bind to surfaces and matrix proteins, and by lack of quantitive standardization. Here we report on an alternative Ultra-high performance liquid chromatography-tandem mass spectrometry (UHPLC-MS/MS) method for simultaneous measurement of human amyloid beta peptides Aβ1-38, Aβ1-40 and Aβ1-42 in cerebrospinal fluid (CSF) using micro-elution solid phase extraction (SPE). Samples were pre-processing by the mixed-mode micro-elution solid phase extraction and quantification was performed in the positive ion multiple reaction monitoring (MRM) mode using electrospray ionization. The stable-isotope labeled Aβ peptides ¹⁵N₅₁- Aβ1-38, ¹⁵N₅₃- Aβ1-40 and ¹⁵N₅₅- Aβ1-42 peptides were used as internal standards. And the artificial cerebrospinal fluid (ACSF) containing 5% rat plasma was used as a surrogate matrix for calibration curves. The quality control (QC) samples at 0.25, 2 and 15ng/mL were prepared. A "linear" regression (1/x² weighting): y=ax+b was used to fit the calibration curves over the concentration range of 0.1-20ng/mL for all three peptides. Coefficient of variation (CV) of intra-batch and inter-batch assays were all less than 6.44% for Aβ1-38, 6.75% for Aβ1-40 and 10.74% for Aβ1-42. The precision values for all QC samples of three analytes met the acceptance criteria. Extract recoveries of Aβ1-38, Aβ1-40 and Aβ1-42 were all greater than 70.78%, both in low and high QC samples. The stability assessments showed that QC samples at both low and high levels could be stable for at least 24h at 4°C, 4h at room temperature and through three freeze-thaw cycles without sacrificing accuracy or precision. And no significant carryover effect was observed. This validated UHPLC/MS/MS method was successfully applied to the quantitation of Aβ peptides in real human CSF samples. Our work may provide a reference method for simultaneous quantitation of human Aβ1-38, Aβ1-40 and Aβ1-42 from CSF.

Statically Adsorbed Coatings for High Separation Efficiency and Resolution in CE-MS Peptide Analysis: Strategies and Implementation

Coatings are necessary to prevent protein and peptide adsorption to the capillary surface and obtain high intermediate precision. In this protocol, we first present our basic strategy to address peptide separation using three different coatings: one neutral and two cationic coatings, the latter largely differing in their induced electroosmotic mobility. In detail, we will describe how we apply the statically adsorbed coatings to obtain very high plate numbers and high repeatability.With some model examples, we clearly describe the scope of the method for the analysis of peptide samples: tryptic digests are addressed as well as small glycoproteins and glycopeptides largely differing in their effective electrophoretic mobility. We also show that the method is suitable for a fast screening of peptide samples despite a high matrix load comprising of up to 500 mmol/L sodium chloride. We demonstrate that this basic CE-MS method is rather independent of the polarity of the analytes with a very fast near-baseline separation of very hydrophobic Aβ peptides related to the onset of Alzheimer's disease. These examples will give an impression, which coating is most suitable for a specific analytical application.Special attention is paid to difficult aspects of the coating procedure and the CE-MS method, e.g., the potential of cross-contamination when changing the coatings.

Gelsolin bound β-amyloid peptides(1-40/1-42): electrochemical evaluation of levels of soluble peptide associated with Alzheimer's disease

A method for the highly sensitive determination of soluable β-amyloid peptides (Aβ(1-40/1-42)) that employs a detection bioconjugate of HRP-Au-gelsolin as the electrochemical nanoprobe is presented. Contrary to previous detection notions that utilized antibodies, which could specifically recognize the N- or C-terminus of peptides, we demonstrate herein that the reported specific binding between gelsolin and Aβ might provide an alternative way to evaluate the peptides sensitively and selectively. The HRP-Au-gelsolin nanohybrid was designed by one-pot functionalization of Au nanaoparticles (NPs) with horseradish peroxidase (HRP) and gelsolin. Through a sandwich-type sensor array, soluble Aβ(1-40/1-42) were captured onto the array due to the interactions between targeted peptides and surface-confined gelsolin and electrochemical signals were amplified by abundant attachments of HRP labeled on AuNPs, which could specifically catalyse its substrate, 3,3',5,5'-tetramethylbenzidine (TMB) in the presence of H2O2 to give rise to measurable signals. The proposed gelsolin-bound Aβ methodology displayed satisfactory sensitivity and wide linear range towards Aβ(1-40/1-42) with a detection limit down to 28 pM, which are verified to be sensitive-enough for the assessment of Aβ levels both in normal and Alzheimer's disease (AD) rat brains. Experimental results indicated that compared with normal group, soluble β-amyloid peptide levels in cerebrospinal fluid (CSF) and targeted brain tissues of AD rats all declined with differentiable degrees. In short, the newly unfolding strategy presents valuable information related to pathological events in brain and will exhibit a braw perspective for the early diagnosis of AD process.

Novel methodologies in analysis of small molecule biomarkers and living cells

Enzyme-linked immuno-sorbent assay (ELISA) is widely used for biomarker detection. A good biomarker can distinguish patients from healthy or benign diseases. However, the ELISA method is not suitable for small molecule or trace substance detection. Along with the development of new technologies, an increasing level of biomaterials, especially small molecules, will be identified as novel biomarkers. Quantitative immuno-PCR, chromatography-mass spectrometry, and nucleic acid aptamer are emerging methodologies for detection of small molecule biomarkers, even in living cells. In this review, we focus on these novel technologies and their potential for small molecule biomarkers and living cell analysis.

Amyloid-beta isoform metabolism quantitation by stable isotope-labeled kinetics

Abundant evidence suggests a central role for the amyloid-beta (Aβ) peptide in Alzheimer's disease (AD) pathogenesis. Production and clearance of different Aβ isoforms have been established as targets of proposed disease-modifying therapeutic treatments of AD. However, previous studies used multiple sequential purification steps to isolate the isoforms individually and quantitate them based on a common mid-domain peptide. We created a method to simultaneously purify Aβ isoforms and quantitate them by the specific C-terminal peptides in order to investigate Aβ isoform physiology in the central nervous system. By using standards generated from in vitro metabolic labeling, the relative quantitation of four peptides representing total amount of Aβ (Aβ-Total), Aβ38, Aβ40, and Aβ42 were achieved both in cell culture and in human cerebrospinal fluid (CSF). Standard curves for each isoform demonstrated good sensitivity with very low limits of detection and high accuracy. Because the assay does not require antibody development for each Aβ isoform peptide, significant improvements in the throughput and accuracy of isoform quantitation were achieved.