Generic approach for the sensitive absolute quantification of large undigested peptides in plasma using a particular liquid chromatography–mass spectrometry setup

Advances and perspectives in the analytical technology for small peptide hormones analysis: A glimpse to gonadorelin

In the last twenty years, we have witnessed an important evolution of bioanalytical approaches moving from conventional lab bench instrumentation to simpler, easy-to-use techniques to deliver analytical responses on-site, with reduced analysis times and costs. In this frame, affinity reagents production has also jointly advanced from natural receptors to biomimetic, abiotic receptors, animal-free produced. Among biomimetic ones, aptamers, and molecular imprinted polymers (MIPs) play a leading role. Herein, our motivation is to provide insights into the evolution of conventional and innovative analytical approaches based on chromatography, immunochemistry, and affinity sensing referred to as peptide hormones. Indeed, the analysis of peptide hormones represents a current challenge for biomedical, pharmaceutical, and anti-doping analysis. Specifically, as a paradigmatic example, we report the case of gonadorelin, a neuropeptide that in recent years has drawn a lot of attention as a therapeutic drug misused in doping practices during sports competitions.

Application of a modified MWCNT-based d-µSPE procedure for determination of bisphenols in soft drinks

Herein, a facile dispersive micro-solid phase extraction (d-µSPE) procedure using carboxylated multi-walled carbon nanotubes modified with silver nanoparticles (Ag/MWCNTs-COOH) was successfully developed for the adsorption and subsequent determination of low levels of two well-known contaminants, namely bisphenol A and S (BPA and BPS) in water and soft drink samples. The detection and measurement of the above-mentioned compounds were performed by HPLC-UV instrument. The applied d-µSPE procedure has several advantages such as rapidity, high degree of sensitivity, precision and efficiency. A combination of polar/non-polar interactions seems to play a key role in the adsorption process. Under the optimized conditions, the calibration curves were linear over the concentration range of 1-500 µg/L for the both targets. The practical limit of quantifications (LOQ) for the both analytes were determined to be 1.0 µg/L. The average relative recoveries obtained from the fortified samples varied between 92 and 110% with the relative standard deviations (RSD%) of 2.9-9.5%.

Robust and sensitive peptidomics workflow for plasma based on specific extraction, lipid removal, capillary LC setup and multinozzle ESI emitter

We present a new workflow for the LC-MS determination of native peptides in plasma at picomolar levels. Collected whole blood was quickly diluted with an ice-cold solution in order to stop protease activity. Diluted plasma samples were extracted by protein denaturation followed by solid-phase-extraction with a polymeric stationary phase that removed most proteins and lipids. Using a specific LC-MS setup with 3 pumps, 240 μL of extracts were injected without drying-reconstitution, a step known to cause peptide losses. After an 18-fold dilution on-line, peptides were trapped on a 1 × 10 mm C8 column, back-flushed and resolved on a 0.3 × 100 mm C18 column. Extract reproducibility, robustness (column clogging), extraction yields, matrix effects, calibration curves and limits of detection were evaluated with plasma extracts and spiked-in standards. The sensitivity and applicability of 3 electrospray sources were evaluated at capillary flow rates (10 μL/min). We show that ionization sources must have a spray angle with the MS orifice when "real" extracts are injected and that a multinozzle emitter can improve very significantly peptide detection. Finally, using our workflow, we have performed a peptidomics study on dried-blood-spots collected over 65 h in a healthy volunteer and discovered 5 fragments (2.9-3.8 KDa) of the protein statherin showing circadian oscillations. This is the first time that statherin is observed in blood where its role clearly deserves further investigations. Our peptidomic protocol shows low picomolar limits of detection and can be readily applied with or without minor modifications for most peptide determinations in various biomatrices.

Validated mass spectrometric assay for the quantification of substance P and human hemokinin-1 in plasma samples: A design of experiments concept for comprehensive method development

INTRODUCTION

Elevated plasma concentrations of the inflammatory neurokinins Substance P (SP) and human Hemokinin-1 (hHK-1) were found in infectious diseases. SP and hHK-1 plasma levels in diseased subjects are determined by immunoassays although not recommended by most immunoassay suppliers owing to their limitations to differentiate accurately between both peptides. A selective and reliable alternative (e.g. mass spectrometric (MS) assay) was missing because of a lack of sensitivity for the determination of endogenous plasma levels.

METHOD

Using a Design of Experiments (DoE) concept, a highly sensitive MS assay was developed for the quantification of SP, its inactive analog as the free acid, and hHK-1 in human plasma. Critical method aspects as the plasma extraction, peptide separation, and the method sensitivity were comprehensively optimized. The method was validated according to international bioanalytical guidelines and its applicability was evaluated in plasma of volunteers.

RESULTS

Within 106 experiments utilizing the DoE concept, the sensitivity of the assay was substantially improved to achieve limits of detection of 5.8 pg/mL for SP, 6.2 pg/mL for its free acid, and 5.3 pg/mL for hHK-1 in plasma. The lean method development was followed by the successful validation according to the regulatory guidelines resulting in a wide quantification range of 7.8-2000 pg/mL. In the volunteers' plasma, no SP and hHK-1 were detectable. Instead, the free acid of SP was quantified in individually distinct levels (202.5-1024.1 pg/mL).

CONCLUSION

An accurate and precise MS assay for the quantification of SP, its free acid, and hHK-1 in plasma was established. The mass spectrometric quantification of the free acid of SP in human plasma samples lead to the question about possible cross-reactivity of the immunoassays in former determinations.

Novel nanoporous covalent organic frameworks for the selective extraction of endogenous peptides

Endogenous peptides are important biomarkers, but their low abundance and abundant interference in biosamples impede their analysis. In this study, a novel nanoporous covalent organic framework (COF) was prepared and successfully applied for selective extraction of endogenous peptides from human serum. This novel COF exhibited strong retention and high adsorption capacity toward peptides, as well as efficient exclusion of large proteins, ascribed to its strong hydrophobicity, uniform pore size (∼2.5 nm) and large surface area (826.5 m² g⁻¹). These features facilitated the extraction of endogenous peptides from complex biosamples, resulting in 27 identified peptides from tryptic digests of bovine serum albumin (BSA) mixed with 1000 mass folds of BSA protein. Moreover, the adsorption rate of the peptides was 3.6-fold faster than that of proteins on this novel COF. After application the novel COF to 5 μL human serum, 416 unique peptides were unambiguously identified. These results demonstrated the excellent properties of the novel COF in extraction of endogenous peptides. We envisage that COFs with adjustable organic building units and unique physicochemical properties will qualify their potential applications in peptidomics research.

Endogenous peptides are important biomarkers, but their low abundance and abundant interference in biosamples impede their analysis.

A candidate liquid chromatography mass spectrometry reference method for the quantification of the cardiac marker 1-32 B-type natriuretic peptide

BACKGROUND

B-type natriuretic peptide (BNP) is a 32 amino acid cardiac hormone routinely measured by immunoassays to diagnose heart failure. While it is reported that immunoassay results can vary up to 45%, no attempt of standardization and/or harmonization through the development of certified reference materials (CRMs) or reference measurement procedures (RMPs) has yet been carried out.

METHODS

B-type natriuretic peptide primary calibrator was quantified traceably to the International System of Units (SI) by both amino acid analysis and tryptic digestion. A method for the stabilization of BNP in plasma followed by protein precipitation, solid phase extraction (SPE) and liquid chromatography (LC) mass spectrometry (MS) was then developed and validated for the quantification of BNP at clinically relevant concentrations (15-150 fmol/g).

RESULTS

The candidate reference method was applied to the quantification of BNP in a number of samples from the UK NEQAS Cardiac Markers Scheme to demonstrate its applicability to generate reference values and to preliminary evaluate the commutability of a potential CRM. The results from the reference method were consistently lower than the immunoassay results and discrepancy between the immunoassays was observed confirming previous data.

CONCLUSIONS

The application of the liquid chromatography-mass spectrometry (LC-MS) method to the UK NEQAS samples and the correlation of the results with the immunoassay results shows the potential of the method to support external quality assessment schemes, to improve understanding of the bias of the assays and to establish RMPs for BNP measurements. Furthermore, the method has the potential to be multiplexed for monitoring circulating truncated forms of BNP.

LC–MS/MS in endocrinology: what is the profit of the last 5 years?

Currently, chromatography (GC but more commonly HPLC) is the analytical method of choice for several hormones, either because the immunoassays suffer from extensive crossreactivity or because chromatography permits simultaneous measurements of hormones. However, sometimes the conventional detection systems with HPLC methods do not meet desired specificity. With the increase of robust and affordable LC–MS/MS systems, the next step forward in specificity was taken. LC–MS/MS is rapidly being incorporated in the endocrine laboratories. To be useful in the clinical diagnostic practice, it is of utmost importance that methods are both analytically and clinically vaidated, as until now, the majority of applications of LC–MS/MS in the clinical laboratories are ‘home-made’ methods, therefore special case must be taken. This review aims to focus on Clinical and Laboratory Standards Institute or comparable validated LC–MS/MS methods for targeted hormone analysis used for diagnostic purposes in human samples, published in the last 5 years.

Direct bioanalytical sample injection with 2D LC–MS

New analytical platforms have been developed in response to the need for attaining increased peak capacity for multicomponent complex analysis with higher sensitivity and characterization of the analytes, and high-throughput capabilities. This review outlines the fundamental principles of target and comprehensive 2D LC method development and encompasses applications of LC–LC and LC × LC coupled to MS in bioanalysis using a variety of online analytical procedures. It also provides a rationale for the usage of the most employed mass analyzers and ionization sources on these platforms.