Determination of nanogram levels of peptide drug in rabbit and human plasma using high-performance liquid chromatography coupled with electrospray ionization mass spectrometry

Review of approaches and examples for monitoring biotransformation in protein and peptide therapeutics by MS

Biotherapeutic drugs have emerged in quantity in pharmaceutical pipelines, and increasingly diverse biomolecules are progressed through preclinical and clinical development. As purification, separation, mass spectrometer detection and data processing capabilities improve, there is opportunity to monitor drug concentration by traditional ligand-binding assay or MS measurement and to monitor metabolism, catabolism or other biomolecular mass variants present in circulation. This review highlights approaches and examples of monitoring biotransformation of biotherapeutics by MS as these techniques are poised to add value to drug development in years to come. The increased use of such approaches, and the successful quantitation of biotherapeutic structural modifications, will provide insightful data for the benefit of both researchers and patients.

Brain quantitative proteomics combining GeLC-MS and isotope-coded protein labeling (ICPL)

Proteomics has been revolutionized by the rapid advance of mass spectrometric instrumentations and techniques. Parallel methodologies for the quantification of proteomes also evolved, including in vitro stable isotope labeling. Here, we present a protocol for employing isotope-coded protein labeling (ICPL) as part of a shotgun proteomics workflow denoting its advantages and disadvantages. This protocol is suitable to studying any proteome of interest, only requiring a specific sample preparation and protein identification. Given our expertise, descriptions here are centered on the study of brain disorders.

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.

Simple and sensitive quantification of bioactive peptides in biological matrices using liquid chromatography/selected reaction monitoring mass spectrometry coupled with trichloroacetic acid clean-up

A simple and sensitive liquid chromatography/electrospray ionization tandem mass spectrometric (LC/ESI-MS/MS) method has been developed for the quantification of bioactive peptides in biological fluids. The method employs protein precipitation with 4% trichloroacetic acid (TCA) and selected reaction monitoring (SRM) using an immonium ion as the product ion. This method was applied to determine the synthetic parathyroid hormone (PTH) analog (MW 1721) in rat plasma and human hepcidin-25 (MW 2789) in human serum. TCA clean-up showed a sufficient recovery for peptides with a MW of less than 3000, and would be useful as a simple and rapid method because of direct injection of the supernatant without evaporation or dilution. In addition, TCA clean-up allowed us not only to reduce sample preparation time, but also to select an immonium ion as a product ion of SRM, which led to detection more sensitive than SRM using other types of product ions. The lower limits of quantitation (LLOQs) of the PTH analog and the human hepcidin-25 were 0.2 ng/mL and 5 ng/mL, respectively. This method was fully validated with acceptable linearity, intra- and inter-assay precisions, and accuracy. Furthermore, this simple and rapid method is applicable to pharmacokinetic studies.

Biomedical and biological mass spectrometry

This review focuses on biological and biomedical mass spectrometry, and covers a selection of publications in this area included in the MEDLINE database for the period 1987-2001. Over the last 15 years, biological and biomedical mass spectrometry has progressed out of all recognition. The development of soft ionization methods, such as electrospray ionization and matrix-assisted laser desorption ionization, has mainly contributed to the remarkable progress, because they can easily produce gas-phase ions of large, polar, and thermally labile biomolecules, such as proteins, peptides, nucleic acids and others. The innovations of ionization methods have led to remarkable progress in mass spectrometric technology and in biochemistry, biotechnology and molecular biology research. In addition, mass spectrometry is one of the powerful and effective technologies for drug discovery and development. It is applicable to studies on structural determination, drug metabolism, including pharmacokinetics and toxicokinetics, and de novo drug discovery by applying post-genomic approarches. In the present review, the innovative soft ionization methods are first discussed along with their features. Also, the characteristics of the mass spectrometers which are active in the biological and biomedical research fields are also described. In addition, examples of the applications of biological and biomedical mass spectrometry are provided.

Accurate mass measurement using multiple sprayer nano-electrospray mass spectrometry combined with nano-scale high-performance liquid chromatography on a magnetic sector instrument

A new technique for accurate mass measurement utilizing multiple sprayer nano-electrospray ionization mass spectrometry (nano-ESI-MS) combined with nano-scale high-performance liquid chromatography (nano-HPLC) on a magnetic sector instrument is described. Both metal-coated glass capillaries and fused-silica capillaries were used as nano-ESI sprayers. A metal-coated glass capillary was used for the introduction of the Ref. compound solution, and a metal-coated fused-silica capillary was used for connection to the nano-HPLC column. By shifting each sprayer's position relative to the sampling orifice, spectra were obtained of both the sample components as eluted from the column and reference compounds. Several standard compounds were examined and satisfactory accurate masses were obtained. Problems arising from differences in ionization efficiency between the sample and reference compounds were not observed.

Differential stable isotope labeling of peptides for quantitation and de novo sequence derivation

We have demonstrated the use of per-methyl esterification of peptides for relative quantification of proteins between two mixtures of proteins and automated de novo sequence derivation on the same dataset. Protein mixtures for comparison were digested to peptides and resultant peptides methylated using either d0- or d3-methanol. Methyl esterification of peptides converted carboxylic acids, such as are present on the side chains of aspartic and glutamic acid as well as the carboxyl terminus, to their corresponding methyl esters. The separate d0- and d3-methylated peptide mixtures were combined and the mixture subjected to microcapillary high performance liquid chromatography/tandem mass spectrometry (HPLC/MS/MS). Parent proteins of methylated peptides were identified by correlative database searching of peptide tandem mass spectra. Ratios of proteins in the two original mixtures could be calculated by normalization of the area under the curve for identical charge states of d0- to d3-methylated peptides. An algorithm was developed that derived, without intervention, peptide sequence de novo by comparison of tandem mass spectra of d0- and d3-peptide methyl esters.

Hyphenated chromatographic methods for biomaterials

The improvement in hyphenated analytical techniques has significantly widened their applications to the analysis of biomaterials. In this article, we discuss recent advances in applications of hyphenated chromatographic techniques including capillary electrophoresis to the analyses of biological samples. As tools of separation, gas chromatography, high-performance liquid chromatography and capillary electrophoresis are considered with special emphasis on applications utilizing the hyphenation of these methods to mass spectrometry. Moreover, applications using other detection methods such as Fourier transform infrared spectroscopy hyphenated to gas chromatography and photodiode array detector combined with high-performance liquid chromatography or capillary electrophoresis are also discussed. Owing to their high sensitivity, luminescence-based detection systems such as laser-induced fluorescence and chemiluminescence are also included in this review.

Development of a sensitive liquid chromatography-electrospray ionization mass spectrometry method for the measurement of KW-5139 in rat plasma

A sensitive method for the determination of a prokinetic peptide, KW-5139 (Leu(13)-motilin), in rat plasma has been developed utilizing liquid chromatography-electrospray ionization mass spectrometry (LC-ESI-MS). KW-5139 was separated by reversed-phase HPLC, with a mixture of 75 mM ammonium formate (pH 3.0) and acetonitrile (4:1, v/v), and monitored by single ion recording (SIR)-ESI-MS at m/z 894 ([M+3H](3+)). Simple protein precipitation and the LC-ESI-MS analysis allowed the determination of KW-5139 in rat plasma with the mean precision and accuracy at the lower limit of quantitation (LLOQ, 0.5 ng/mL) of 5.7 and 11.2%, respectively. The method was applied to the monitoring of the plasma time-concentration profile of KW-5139, intravenously administered to rats at a dose of 1 microg/kg.

Accurate mass determination by multiple sprayers nano-electrospray mass spectrometry on a magnetic sector instrument

A new technique for accurate mass determination by using multiple sprayers nano-electrospray ionization mass spectrometry (nano-ESI-MS) on a magnetic sector instrument is described. Metal coated glass capillaries were used as nano-ESI sprayers. One of the sprayers was used for the reference compound solution, and others were used for the introduction of sample solutions. The spectra of the different compounds were obtained by shifting each sprayer's position relative to the sampling orifice. The accurate masses of several standard compounds were obtained with good accuracy, without problems arising from differences in ionization efficiency between the sample compounds and reference compound.

Determination of a cyclic hexapeptide, a novel antifungal agent, in human plasma by high-performance liquid chromatography with ion spray and turbo ion spray tandem mass spectrometric detection

Methods for the determination of a semi-synthetic cyclic hexapeptide (I, MK-0991) in human plasma based on high-performance liquid chromatography (HPLC) with tandem mass spectrometric (MS-MS) detection using pneumatically assisted electrospray (ion spray, ISP) and turbo ion spray (TISP) interfaces were developed. Drug and internal standard (II, an isostere of I) were isolated from plasma by solid-phase extraction (SPE). The eluent from SPE was evaporated to dryness, the residue was reconstituted in mobile phase and injected into the HPLC system. The use of ISP, TISP and heated nebulizer (HN) interfaces as sample introduction systems were evaluated and showed that the heated nebulizer was not adequate for analysis due to thermal instability and/or adsorption of I and II to glass surfaces of the interface. Compounds I and II were chromatographed on a wide pore (300 A), 150x4.6 mm C8 analytical column, and the HPLC flow-rate of 1.2 ml/min was split 1:20 prior to introduction to the ISP or TISP interface of the mass spectrometric system. The MS-MS detection was performed on a PE Sciex API III Plus tandem mass spectrometer operated in selected reaction monitoring mode (SRM). The precursor-->product ion combinations of m/z 1093.7-->1033.6 and 1094.7-->1033.6 were used to quantify I and II, respectively, after chromatographic separation of the analytes. The assay was validated in the concentration range of 10-1000 ng/ml using ISP, and 2.5-500 ng/ml of plasma using TISP with good precision and adequate accuracy. The effects of HPLC mobile-phase components on the ionization efficiency and sensitivity of detection in the positive ionization mode, the evaluation of the matrix effect, and limitations in sensitivity of detection of I due to the formation of multiply charged species are presented.

Quantitative electrospray LC-MS and LC-MS/MS in biomedicine

The use of electrospray LC-MS and LC-MS/MS for the quantitative determination of two low molecular weight (< 500 Da) organic compounds in human plasma (Lovastatin) and cell supernatants (Arachidonic acid) and medium molecular weight (> 2000 Da) endogenous peptides (Endothelins) in supernatants of human umbilical vein endothelial cell cultures is reported. These methods make use either of deuterium labelled or structurally similar molecules as internal standards for quantitation and one or more pre-purification steps previous the LC-MS analysis. Linear calibration curves and detection limits around 50 pg ml(-1) were obtained in all three cases.

What is hemoglobin A1c? An analysis of glycated hemoglobins by electrospray ionization mass spectrometry

Hemoglobin A1c (HbA1c) is a stable minor Hb variant formed in vivo by posttranslational modification by glucose, originally identified by using cation exchange chromatography, and containing primarily glycated N-terminal β-chains. However, the structure(s) of the quantified species has not been elucidated, and the available methods lack a reference standard. We used electrospray ionization mass spectrometry to determine the extent of glycation of samples separated by boronate affinity and/or cation exchange chromatography. Analyses of clinical samples were consistent with the curvilinear relationship of patient glucose and HbA1c. As glycation increased, the ratio of β-chain to α-chain glycation increased, and the number of glycation sites on the β-chain increased, although these were relatively minor components. We found several glycated species that cochromatographed with HbA1c on cation exchange, including species with both glycated α- and β-chains, nonglycated α- and glycated β-chains, and multiply glycated β-chains. The combined use of affinity and cation exchange chromatography with structural confirmation by electrospray ionization mass spectrometry was found to be useful in producing samples of sufficient purity for the standardization of glycohemoglobin clinical assays.

Liquid chromatography-mass spectrometry in forensic and clinical toxicology

This paper reviews liquid chromatographic-mass spectrometric (LC-MS) procedures for the identification and/or quantification of drugs of abuse, therapeutic drugs, poisons and/or their metabolites in biosamples (whole blood, plasma, serum, urine, cerebrospinal fluid, vitreous humor, liver or hair) of humans or animals (cattle, dog, horse, mouse, pig or rat). Papers published from 1995 to early 1997, which are relevant to clinical toxicology, forensic toxicology, doping control or drug metabolism and pharmacokinetics, were taken into consideration. They cover the following analytes: amphetamines, cocaine, lysergide (LSD), opiates, anabolics, antihypertensives, benzodiazepines, cardiac glycosides, corticosteroids, immunosuppressants, neuroleptics, non-steroidal anti-inflammatory drugs (NSAID), opioids, quaternary amines, xanthins, biogenic poisons such as aconitines, aflatoxins, amanitins and nicotine, and pesticides. LC-MS interface types, mass spectral detection modes, sample preparation procedures and chromatographic systems applied in the reviewed papers are discussed. Basic information about the biosample assayed, work-up, LC column, mobile phase, interface type, mass spectral detection mode, and validation data of each procedure is summarized in tables. Examples of typical LC-MS applications are presented.

Quantitative analysis of exogenous peptides in plasma using immobilized enzyme cleavage and gas chromatography-mass spectrometry with negative ion chemical ionization

A method is presented for the analysis of peptides in plasma at picomole to femtomole levels. Peptides are isolated from plasma by solid-phase extraction, the peptide of interest is purified by reversed-phase high-performance liquid chromatography (HPLC) and selectively digested using immobilized trypsin or chymotrypsin to yield specific di- or tripeptides. These di- and tripeptides are esterified using heptafluorobutyric anhydride, alkylated with pentafluorobenzyl bromide, then quantified by gas chromatography-mass spectrometry with negative ion chemical ionization. This method has been evaluated for a model synthetic heptapeptide, using a deuterium labeled analog as an internal standard. The half-life of the heptapeptide in human plasma was found to be 2 min. Extraction efficiencies of a tritiated peptide of similar size to the heptapeptide, [3H]DSLET, from plasma using either C18 or strong cation-exchange columns were 85+/-3 and 70+/-2%, respectively. Quantitation of fragments from the heptapeptide indicated that the analysis was linear from 1-50 ng of the heptapeptide per ml of plasma. This method was subsequently employed for pharmacokinetic studies of the biologically active peptide Met-enkephalin-Arg-Gly-Leu, where linearity was obtained from 50 to 1000 ng/ml in rat plasma. This method demonstrated negligible side reaction by-products due to autolysis, and has potential for extensive use given the wide availability of gas chromatography-mass spectrometry.

An automated MALDI mass spectrometry approach for optimizing cyclosporin extraction and quantitation

A combinatorial extraction method and an automated matrix-assisted laser desorption/ionization (MALDI) mass spectrometry procedure were used to improve the clinical analysis of the immunosuppressant drug cyclosporin A. Cyclosporin extracts from whole blood were analyzed by MALDI and electrospray ionization (ESI) mass spectrometry, allowing for their identification and quantification. Due to limitations associated with the current multistep cyclosporin extraction procedure from whole blood, a combinatorial approach was devised to optimize this extraction. Optimization was performed by generating an array of solvent systems to be used for extraction from blood, and an automated analysis was carried out on a MALDI mass spectrometer to identify successful extractions. The first generation of experiments revealed four binary solvent systems to be effective for cyclosporin extraction (hexane/EtOH, ACN/H2O, ACN/MeOH, and hexane/CHCl3). A new array based on these solvent systems was generated, and a second iteration of these experiments was then performed. In the second generation of experiments, hexane/CHCl3 (70:30) was found to provide the most effective single-step extraction of these solvent systems for cyclosporin and its metabolites. The limits of detection were determined to be 15 ng/mL in whole blood for ESI/MS and MALDI-MS and could also be used for identifying major drug metabolites. In addition to applying this combinatorial approach to extraction procedures, this experimental design could easily be extended to examine other approaches, such as optimizing chemical reactions and screening inhibitors in enzymatic reactions.

Quantitative analysis of two opioid peptides in plasma by liquid chromatography-electrospray ionization tandem mass spectrometry

Quantitative analysis of two opioid peptides, DSLET [(D-Ser2)Leu-enkephalin-Thr6] and Met-enkephalin-Arg-Gly-Leu, was performed using microbore liquid chromatography interfaced to electrospray ionization tandem mass spectrometry. Validation of the methodology was demonstrated for each peptide in plasma. Quantitative analyses were performed through the use of a deuterium labelled peptide analog as an internal standard. Linearity was observed for the analysis of DSLET (5-1000 ng/ml) and Met-enkephalin-Arg-Gly-Leu (1-1000 ng/ml) in plasma with a limit of detection of 0.25 ng/ml for Met-enkephalin-Arg-Gly-Leu and 1.0 ng/ml for DSLET. In general, the observed concentrations showed good reproducibility with coefficients of variation of within 15%. In the concentration range studied, only 0.5 ml of plasma was required for optimal detection of Met-enkephalin-Arg-Gly-Leu and 0.25 ml for DSLET. Application of this method was demonstrated by studying the disposition of DSLET in a rat. DSLET administered to a rat exhibited a short half-life and a high clearance value.

A competitive chemiluminescent enzyme-linked immunosorbent assay for the determination of RMP-7 in human blood

RMP-7, a bradykinin agonist, is a synthetic nonapeptide designed to enhance the delivery of therapeutics to the central nervous system. A sensitive, competitive chemiluminescent enzyme-linked immunosorbent assay (ELISA) for quantifying RMP-7 in human blood samples has been developed. Rabbit antibodies against RMP-7 were produced using the conjugate of RMP-7 to keyhole limpet hemocyanin through glutaraldehyde. Biotinylated RMP-7, conjugated via N-hydroxysuccinimide ester, was used as the tracer. A premixed solution of biotinylated alkaline phosphatase and avidin was used to quantify the tracer, with a dioxetane-based compound as the chemiluminescent substrate. The method involves treating blood samples with organic solvents to precipitate proteins, evaporating the supernatants to dryness, reconstituting residues in PBS and assaying the buffer solutions with the ELISA. The assay, using 1.0 ml of whole blood, has precision and accuracy within +/- 20% over the concentration range 25-800 pg ml-1. There are no significant endogenous interferences. The assay has been successfully used to support clinical trials of RMP-7.

Determination of BMS-186318 in dog, rat and monkey plasma by liquid chromatography-ionspray mass spectrometry

BMS-186318 is a member of the recently discovered "aminodiol" class of HIV protease inhibitors. A simple but sensitive method was developed for the determination of BMS-186318 in dog plasma and then applied to monkey and rat plasma. The compound was extracted from dog plasma with methyl tert-butyl ether at basic pH. The dried extract was reconstituted in mobile phase and injected into a 150 x 2.1 mm i.d. Zorbax Rx-C18 HPLC column. A portion of the effluent was directed into the LC-ionspray MS system, where the [M+H]+ ion of the secondary amine compound was monitored. The HPLC conditions were chosen in order to achieve a short run time and large sample throughput, with both analyte and internal standard eluting within 1.5 min. The liquid-liquid extraction procedure provided very clean extracts so that sufficient signal-to-noise ratio was obtained with single-stage mass spectrometry instead of the more costly tandem mass spectrometry. The required lower limit of quantitation of 2.5 ng ml-1 was easily achieved. The method has also been validated for BMS-186318 in monkey plasma without modification. The method has been modified for rat plasma. Owing to irreproducibility observed when applying the liquid-liquid extraction method to rat plasma, a solid-phase extraction method was developed. The addition of phenylmethylsulfonyl fluoride was necessary to stabilize BMS-186318 in rat blood and plasma.

Fumonisin B1 analysis with capillary electrophoresis-electrospray ionization mass spectrometry

Fumonisin B1, a mycotoxin produced by a common fungal contaminant of corn, Fusarium moniliforme, was analyzed by capillary electrophoresis-electrospray ionization mass spectrometry. System performance was maximal with uncoated columns. System efficiencies of approximately 44,000 plates/m and reproducible analysis times of about 13 min were obtained. System efficiency with methyl-coated columns was approximately 24,000 plates/m. Reproducible analysis times of about 3.5 min were obtained with these columns. With uncoated columns, the concentration limit of detection was 156 ppb with a s/n ratio of approximately 10. The estimated injected mass at 156 ppb was 1.1 pg. Repeated injections of extracts containing constant fumonisin B1 concentrations showed that peak areas were slightly inconsistent, although generally similar to variations encountered with liquid chromatography-electrospray ionization mass spectrometry. The source of this inconsistency was traced to sample solubility, errors inherent in electrophoresis injections, and electrospray instability. Minimizing these problem areas will produce a technique with peak area reproducibilities comparable to liquid chromatography-electrospray ionization mass spectrometry, but with potentially greater resolving power.