Selective quantitative bioanalysis of proteins in biological fluids by on-line immunoaffinity chromatography–protein digestion–liquid chromatography–mass spectrometry

Quantitation of endogenous GnRH by validated nano-HPLC-HRMS method: a pilot study on ewe plasma

Gonadotropin-releasing hormone isoform I (GnRH), a neuro-deca-peptide, plays a fundamental role in development and maintenance of the reproductive system in vertebrates. The anomalous release of GnRH is observed in reproductive disorder such as hypogonadotropic hypogonadism, polycystic ovary syndrome (PCOS), or following prenatal exposure to elevated androgen levels. Quantitation of GnRH plasma levels could help to diagnose and better understand these pathologies. Here, a validated nano-high-performance liquid chromatography–high-resolution mass spectrometry (HPLC-HRMS) method to quantify GnRH in ewe plasma samples is presented. Protein precipitation and solid-phase extraction (SPE) pre-treatment steps were required to purify and enrich GnRH and internal standard (lamprey-luteinizing hormone-releasing hormone-III, l-LHRH-III). For the validation process, a surrogate matrix approach was chosen following the International Council for Harmonisation (ICH) and FDA guidelines. Before the validation study, the validation model using the surrogate matrix was compared with those using a real matrix such as human plasma. All the tested parameters were analogous confirming the use of the surrogate matrix as a standard calibration medium. From the validation study, limit of detection (LOD) and limit of quantitation (LOQ) values of 0.008 and 0.024 ng/mL were obtained, respectively. Selectivity, accuracy, precision, recovery, and matrix effect were assessed with quality control samples in human plasma and all values were acceptable. Sixteen samples belonging to healthy and prenatal androgen (PNA) exposed ewes were collected and analyzed, and the GnRH levels ranged between 0.05 and 3.26 ng/mL. The nano-HPLC-HRMS developed here was successful in measuring GnRH, representing therefore a suitable technique to quantify GnRH in ewe plasma and to detect it in other matrices and species.

The potential for isotope dilution-LC-MS/MS to improve laboratory measurement of C-peptide: Reasons and critical determinants

Human C-peptide is secreted in equimolar amounts with insulin by pancreatic beta-cells. Measurement of C-peptide plays an important role in the diagnosis and treatment of diabetes where it is used to evaluate the function of islet cells. However, C-peptide measurement results across different laboratories vary considerably and there is an urgent need to improve comparability between laboratories. As it is sensitive and specific, isotope dilution-liquid chromatography-tandem mass spectrometry (ID-LC-MS/MS) has made a major contribution and will continue to play a significant role in the standardization of C-peptide measurement. Here, we reviewed the application of ID-LC-MS/MS in C-peptide measurement by discussing the biochemical properties of C-peptide, common sample preparation procedures, and the sensitivity problems often encountered with ID-LC-MS/MS C-peptide measurement. Collectively, these factors are crucial for the development of ID-LC-MS/MS methods for C-peptide measurement. We also discussed the advantages, disadvantages, and progress of implementing ID-LC-MS/MS as a routine measurement tool for C-peptide in clinical laboratories. Finally, we summarized the existing reference system and the status of C-peptide measurement in clinical laboratories to convey the necessity of improving the comparability of C-peptide measurement in clinical laboratories using ID-LC-MS/MS.

Performance comparison of three trypsin columns used in liquid chromatography

Trypsin is the most widely used enzyme in proteomic research due to its high specificity. Although the in-solution digestion is predominantly used, it has several drawbacks, such as long digestion times, autolysis, and intolerance to high temperatures or organic solvents. To overcome these shortcomings trypsin was covalently immobilized on solid support and tested for its proteolytic activity. Trypsin was immobilized on bridge-ethyl hybrid silica sorbent with 300Å pores, packed in 2.1×30mm column and compared with Perfinity and Poroszyme trypsin columns. Catalytic efficiency of enzymatic reactors was tested using N_α-Benzoyl-l-arginine 4-nitroanilide hydrochloride as a substrate. The impact of buffer pH, mobile phase flow rate, and temperature on enzymatic activity was investigated. Digestion speed generally increased with the temperature from 20 to 37°C. Digestion speed also increased with pH from 7.0 to 9.0; the activity of prototype enzyme reactor was highest at pH 9.0, when it activity exceeded both commercial reactors. Preliminary data for fast protein digestion are presented.

Immunoaffinity Chromatography: Concepts and Applications

Antibody-based separation methods, such as immunoaffinity chromatography (IAC), are powerful purification and isolation techniques. Antibodies isolated using these techniques have proven highly efficient in applications ranging from clinical diagnostics to environmental monitoring. Immunoaffinity chromatography is an efficient antibody separation method which exploits the binding efficiency of a ligand to an antibody. Essential to the successful design of any IAC platform is the optimization of critical experimental parameters such as (a) the biological affinity pair, (b) the matrix support, (c) the immobilization coupling chemistry, and (d) the effective elution conditions. These elements and the practicalities of their use are discussed in detail in this review. At the core of all IAC platforms is the high affinity interactions between antibodies and their related ligands; hence, this review entails a brief introduction to the generation of antibodies for use in immunoaffinity chromatography and also provides specific examples of their potential applications.

Bioanalytical strategies for developing highly sensitive liquid chromatography/tandem mass spectrometry based methods for the peptide GLP-1 agonists in support of discovery PK/PD studies

Highly sensitive liquid chromatography/tandem mass spectrometry (LC/MS/MS)-based methods have been developed and implemented for the quantitative determination of a number of peptides under evaluation in our Glucagon-Like Peptide-1 (GLP-1) discovery program for the treatment of diabetes. These peptides are GLP-1 receptor agonists. Due to the high potency, low dose, and low exposure of these peptides, LC/MS/MS-based methods with Lower Limits of Quantitation (LLOQs) (low picomolar range) were required to support discovery pharmacokinetic/ pharmacodynamic (PK/PD) studies. Compared with small molecules, many of these peptides posed significant bioanalytical challenges in the development of highly sensitive methods because of their parent signal splitting as a result of the formation of multiply charged states, the unfavorable fragmentation patterns for Selected Reaction Monitoring (SRM) transitions due to the generation of a large number of small mass product ions with relative low intensities, and adsorption issues observed during sample preparation. This paper details the strategies developed to maximize the sensitivity and improve LLOQs from aspects of mass spectrometry, chromatography, and sample preparation. A LLOQ of 10 picomolar was achieved for all of the investigated peptides using 100 μL of mouse plasma. This is a 100-fold improvement on LLOQs over generic LC/MS/MS-based methods when the same sample volume and the same mass spectrometer platform were used. The methods have been implemented in the support of discovery PK/PD studies.

Immunoaffinity chromatography: an introduction to applications and recent developments

Immunoaffinity chromatography (IAC) combines the use of LC with the specific binding of antibodies or related agents. The resulting method can be used in assays for a particular target or for purification and concentration of analytes prior to further examination by another technique. This review discusses the history and principles of IAC and the various formats that can be used with this method. An overview is given of the general properties of antibodies and of antibody-production methods. The supports and immobilization methods used with antibodies in IAC and the selection of application and elution conditions for IAC are also discussed. Several applications of IAC are considered, including its use in purification, immunodepletion, direct sample analysis, chromatographic immunoassays and combined analysis methods. Recent developments include the use of IAC with CE or MS, ultrafast immunoextraction methods and the use of immunoaffinity columns in microanalytical systems.

Immunoaffinity chromatography

Antibody-based separation methods, such as immunoaffinity chromatography (IAC), are powerful purification and isolation techniques. Antibodies isolated using these techniques have proven highly efficient in applications ranging from clinical diagnostics to environmental monitoring. IAC is an efficient antibody separation method which exploits the binding efficiency of a ligand to an antibody. Essential to the successful design of any IAC platform is the optimisation of critical experimental parameters such as: (a) the biological affinity pair, (b) the matrix support, (c) the immobilisation coupling chemistry, and (d) the effective elution conditions. These elements and the practicalities of their use are discussed in detail in this review. At the core of all IAC platforms is the high-affinity interactions between antibodies and their related ligands; hence, this review entails a brief introduction to the generation of antibodies for use in IAC and also provides specific examples of their potential applications.

Quantitative liquid chromatography tandem mass spectrometry analysis of macromolecules using signature peptides in biological fluids

Targeted protein quantification using peptide surrogates has increasingly become important to the validation of biomarker candidates and development of protein therapeutics. These approaches have been proposed and employed as alternatives to immunoassays in biological fluids. Technological advances over the last 20 years in biochemistry and mass spectrometry have prompted the use of peptides as surrogates to quantify enzyme digested proteins using triple quadrupole mass spectrometers. Multiple sample preparation processes are often incorporated to achieve quantification of target proteins using these signature peptides. This review article focuses on these processes or hyphenated techniques for quantification of proteins with peptide surrogates. The most recent advances and strategies involved with hyphenated techniques are discussed.

Bioanalysis of recombinant proteins and antibodies by mass spectrometry

In recent years, biotechnologically-derived drugs have been a major focus of research and development in the pharmaceutical industry. Their pharmacokinetics and pharmacokinetic/pharmacodynamic relationships impact every stage of the development process and require their assessment in the circulation in preclinical species and in humans. To this end, immunoassays are a reference, but standardisation remains an issue owing to the restricted pattern of antibody specificity and interference with endogenous components. As an alternative, we report here analytical strategies involving liquid chromatography coupled to mass spectrometry (LC-MS) for the accurate quantification of therapeutic proteins and antibodies in biological fluids.

Multidimensional liquid phase separations for mass spectrometry

Large part of the current research in biology, medicine, and biotechnology depends on the analysis of DNA (genomics), proteins (proteomics), or metabolites (metabolomics). The advances in biotechnology also command development of adequate analytical instrumentation capable to analyze minute amounts of samples. The analysis of the content of single cells may serve as an example of ultimate analytical applications. Most of the separation techniques have been developed in the last three decades and alternative approaches are being investigated. At present, the main protocols for analyses of complex mixtures include 2-DE (IEF) followed by electrophoresis in SDS polyacrylamide gel (SDS-PAGE) and chromatographic techniques. Information-rich techniques such as MS and NMR are essential for the identification and structure analysis of the analyzed compounds. High resolution separation of the individual sample components is often a prerequisite for success. High resolution proteomic analysis in the majority of laboratories still relies on the time consuming and laborious offline methods. This review highlights some of the important aspects of 2-D separations including microfluidics.

Automated detection of covalent adducts to human serum albumin by immunoaffinity chromatography, on-line solution phase digestion and liquid chromatography–mass spectrometry

A generic method for the detection of covalent adducts to the cysteine-34 residue of human serum albumin (HSA) has been developed, based on an on-line combination of immunoaffinity chromatography for selective sample pre-treatment, solution phase digestion, liquid chromatography and tandem mass spectrometry. Selective anti-HSA antibodies immobilized on agarose were used for sample pre-concentration and purification of albumin from the chemically produced alkylated HSA. After elution, HSA and HSA adducts are mixed with pronase and directed to a reaction capillary kept at a digestion temperature of 70 degrees C. The digestion products were trapped on-line on a C18 SPE cartridge. The peptides were separated on a reversed-phase column using a gradient of organic modifier and subsequently detected using tandem mass spectrometry. Modified albumin samples consisted of synthetically alkylated HSA by the reactive metabolite of acetaminophen, N-acetyl-p-benzoquinoneimine (NAPQI), and using the alkylating agent 1-chloro-2,4-dinitrobenzene (CDNB) as reference. The resulting mixture of alkylated versus non-modified albumin has been applied to the on-line system, and alkylation of HSA is revealed by the detection of the modified marker tetra-peptide glutamine-cysteine-proline-phenylalanine (QCPF) adducts NAPQI-QCPF and CDNB-QCPF. Detection of alkylated species was enabled by the use of data comparison algorithms to distinguish between unmodified and modified HSA samples. The in-solution digestion proved to be a useful tool for enabling fast (less than 2 min) and reproducible on-line digestion of HSA. A detection limit of 1.5 micromol/L of modified HSA could be obtained by applying 10 microL of NAPQI-HSA sample.

An integrated high-performance liquid chromatography-mass spectrometry system for the activity-dependent analysis of matrix metalloproteases

Matrix metalloproteases (MMPs) comprise a family of enzymes that play important roles in mediating angiogenesis, the remodelling of tissues and in cancer metastasis. Consequently, they are attractive targets for therapeutic intervention in chronic inflammation, cancer and neurological disorders. In order to study MMPs in body fluids in an activity-dependent manner, we have developed an automated, integrated system comprising an immobilized inhibitor cartridge for activity-dependent enrichment, an immobilized trypsin reactor for rapid on-line proteolysis and a capillary or nanoLC-MS system for separation and identification of the obtained peptide fragments. This targeted proteomics system was optimized with respect to recovery and evaluated through the analysis of urine samples that were spiked with recombinant MMP-12. MMP-12 specific peptide fragments were easily detected in a nanoLC-MS analysis of 500 microL crude urine spiked at a level of 8 nM. These results show the feasibility of selective, activity-dependent enrichment of MMPs from a non-treated biofluid at low nM concentrations.

A rapid surface plasmon resonance (SPR) biosensor immunoassay for screening of somatotropins in injection preparations

The use of growth hormones (recombinant somatotropins (rSTs)) is approved in several countries, e.g. the USA, Brazil and Australia to enhance growth or lactating performances of livestock. Their use in the EU is banned, however, due to the widespread application, the illegal use within the EU cannot be excluded. To screen for rSTs in injection preparations, a biosensor immunoassay (BIA) using surface plasmon resonance (SPR) technology was developed. Compared to existing analysis methods for rSTs, like radio immunoassay (RIA) and enzyme-linked immunosorbent assay (ELISA), this technique provides a rapid (7 min) alternative. A direct BIA was compared to an indirect (inhibition) BIA and the performances of several antibodies against (r)STs were compared in the indirect BIA. In the final inhibition assay, using rabbit anti-bovine rST, extracts from several injection preparations were shown to contain bovine rST (rbST). The limit of detection for rbST in the assay is 0.008 microg mL(-1) which is far below the expected concentrations in injection preparations. Although the cross-reactivities for STs of other species were low, screening of injection preparations for porcine, equine and human ST was feasible through the analysis of less diluted extracts. Tryptic digestion followed by nano-electrospray liquid chromatography-ion trap tandem mass spectrometry (nano-LC-MS/MS) was used to identify STs.