Mass spectrometric determination of insulins and their degradation products in sports drug testing

Review of the lethal mechanism of insulin poisoning and the characteristic of forensic identification

Insulin, as the only hypoglycemic hormone in the body, plays a key role in blood sugar control. However, excessive insulin intake can lead to insulin poisoning and even death, which often occurs in clinical and forensic work. At present, some researches on insulin poisoning have been carried out at home and abroad, however, it seems that the mechanism and forensic characteristics of insulin poisoning are not clear and complete. Therefore, in this paper, we reviewed the potential mechanism of insulin poisoning, the methods of insulin detection and the forensic identification of poisoning cases, aiming at providing services for the forensic identification of insulin poisoning.

Is it really possible to kill with insulin without leaving traces? From lifesaver to killer, the issues surrounding the analytical characterization of postmortem insulin illustrated by an exemplary case

Evidence of an insulin overdose is very complicated in the medico-legal field. The analysis and subsequent interpretation of results is complex, especially when treating postmortem blood samples. The instability of insulin, the special pre-analytical conditions and the absence of specific analytical methods has led most laboratories not to analyze insulin in their routine with a consequent underestimation of cases. This paper aims to assess the difficulties associated with the analytical characterization of insulin by describing a case that typically represents most of the inconveniences encountered following a suspected insulin overdose. The case concerns a man found dead at home by his brother. After an external examination, which did not reveal a specific cause of death, toxicological analysis was requested which did not reveal any substance of toxicological interest. Only 9 months later, it was reported to the toxicologist that the subject was diabetic, on insulin lispro treatment and that three empty syringes were found next to his body. Following analysis by LC-high-resolution mass spectrometry, the presence of insulin lispro at a concentration of 1.1 ng/mL, a therapeutic concentration, was evidenced. Despite the low concentration found, overdose cannot be excluded and this paper will describe the criteria evaluated to reach this conclusion. This case highlights that the interpretation of a postmortem insulin concentration is very complex and requires the evaluation of various elements including the circumstances of death, the subject's medical history, the interval between death and sampling and the sample storage.

Psychosocial aspects of sports medicine in pediatric athletes: Current concepts in the 21st century

Behavioral aspects of organized sports activity for pediatric athletes are considered in a world consumed with winning at all costs. In the first part of this treatise, we deal with a number of themes faced by our children in their sports play. These concepts include the lure of sports, sports attrition, the mental health of pediatric athletes (i.e., effects of stress, anxiety, depression, suicide in athletes, ADHD and stimulants, coping with injuries, drug use, and eating disorders), violence in sports (i.e., concepts of the abused athlete including sexual abuse), dealing with supervisors (i.e., coaches, parents), peers, the talented athlete, early sports specialization and sports clubs. In the second part of this discussion, we cover ergolytic agents consumed by young athletes in attempts to win at all costs. Sports doping agents covered include anabolic steroids (anabolic-androgenic steroids or AAS), androstenedione, dehydroepiandrostenedione (DHEA), human growth hormone (hGH; also its human recombinant homologue: rhGH), clenbuterol, creatine, gamma hydroxybutyrate (GHB), amphetamines, caffeine and ephedrine. Also considered are blood doping that includes erythropoietin (EPO) and concepts of gene doping. In the last section of this discussion, we look at disabled pediatric athletes that include such concepts as athletes with spinal cord injuries (SCIs), myelomeningocele, cerebral palsy, wheelchair athletes, and amputee athletes; also covered are pediatric athletes with visual impairment, deafness, and those with intellectual disability including Down syndrome. In addition, concepts of autonomic dysreflexia, boosting and atlantoaxial instability are emphasized. We conclude that clinicians and society should protect our precious pediatric athletes who face many challenges in their involvement with organized sports in a world obsessed with winning. There is much we can do to help our young athletes find benefit from sports play while avoiding or blunting negative consequences of organized sport activities.

Behavior of Regular Insulin in a Parenteral Nutrition Admixture: Validation of an LC/MS-MS Assay and the In Vitro Evaluation of Insulin Glycation

Parenteral-nutrition (PN)-induced hyperglycemia increases morbidity and mortality and must be treated with insulin. Unfortunately, the addition of insulin to a ternary PN admixture leads to a rapid decrease in insulin content. Our study’s objective was to determine the mechanistic basis of insulin’s disappearance. The literature data suggested the presence of a glycation reaction; we therefore validated an LC-MS/MS assay for insulin and glycated insulin. In a 24-h stability study, 20 IU/L of insulin was added to a binary PN admixture at pH 3.6 or 6.3. When the samples were diluted before analysis with a near-neutral diluent, insulin was fully stable at pH 3.6, while a loss of around 50% was observed at pH 6.3. Its disappearance was shown to be inversely correlated with the appearance of monoglycated insulin (probably a Schiff base adduct). Monoglycated insulin might also undergo a back-reaction to form insulin after acidic dilution. Furthermore, a second monoglycated insulin species appeared in the PN admixture after more than 24 h at high temperature (40 °C) and a high insulin concentration (1000 IU/L). It was stable at acidic pH and might be an Amadori product. The impact of insulin glycation under non-forced conditions on insulin’s bioactivity requires further investigation.

Detection of insulin analogues and large peptides > 2 kDa in urine

Insulin analogues and large bioactive peptides may be used by athletes to enhance performance and are banned by the World Anti-Doping Agency (WADA). In addition to insulin analogues, the large peptides include a structurally diverse set of peptides including analogues of growth hormone releasing hormone (GHRH), insulin-like growth factor-1 (IGF-1), and mechano-growth factor (MGF). Detection of this class of peptides is difficult due to their absorptive losses and presence at very low concentrations in urine. In this report, a high throughput method is described that allows sensitive detection of 4 classes of large peptides in one assay. Sample extraction is performed by ultrafiltration to concentrate the urine followed by solid phase extraction in a 96-well micro-elution plate. Peptides in the urine samples are detected on a triple quadrupole mass spectrometer coupled to standard flow liquid chromatography. The method was validated and evaluated for limit of detection, limit of identification, specificity, precision, carry-over, recovery, matrix interference, and post-extraction stability. The limit of detection for insulin analogues is between 5 - 25 pg/ml and between 5 - 50 pg/ml for the other peptide classes. Specificity was good with no detection of interfering peaks in blank urine samples. Carry-over from a high concentration sample was not observed and the post-extraction stability was between 77 - 107%. The method was able to detect insulin analogues in three diabetic urine samples. Increased screening for this class of peptides will improve detection and deterrence.

Development and validation of a method for quantification of human insulin and its synthetic analogues in plasma and post-mortem sera by LC-MS/HRMS

Analysis of human insulin and its synthetic analogues is increasingly requested for clinical monitoring, for anti-doping purposes, but also for forensic cases. Indeed, insulin analogues may be abused for suicide or homicide - whence their forensic interest. Collection and storage conditions, as well as the phenomenon of degradation make post-mortem serum samples analytically challenging and consequently, the rate of exogenous insulin administration as cause of death is undoubtedly underestimated. However, with recent technological advances and the development of new extraction techniques particularly for anti-doping analyses, detection of insulins in post-mortem samples seems to be achievable. This study describes the first validated quantitative method for analysis human insulin and its six analogues (lispro, aspart, glulisine, glargine, detemir and degludec) in plasma and post-mortem sera. Various extraction processes, namely precipitation + solid phase extraction (SPE), filtration + SPE, precipitation + SPE + immunopurification, and filtration + immunopurification, were assessed to evaluate the lowest limit of detection for all target analogues. The selected sample preparation consists of filtration step followed by immunopurification extraction with an anti-body precoated ELISA plate for plasma. For post-mortem sera, the first step of precipitation was added to remove matrix interferences. The extracts were analyzed by ultra-high-performance liquid chromatography-high resolution mass spectrometry (LC-HRMS), interfaced by electrospray (ESI). The method was validated with respect linearity, precision, accuracy, recovery, matrix effect, dilution and carryover. The limit of quantification (LOQ) in plasma was 0.5 ng/mL for human insulin and rapid-acting insulins, 1.0 ng/mL for glargine, 2.5 ng/mL for degludec and 10 ng/mL for detemir. Two types of post-mortem sera were studied based on the post-mortem interval (PMI): inferior or superior to 48 h. The obtained LOQ were the same for each analogue, independent from the PMI: 1.0 ng/mL for human insulin and rapid-acting insulins, 1.0 ng/mL for glargine, 2.5 ng/mL for degludec and 10 ng/mL for detemir. At the LOQ level, for all insulins and all samples, accuracy was between 70 and 130% and precision inferior to 30%. The validated method was applied to five subjects participating in therapeutic monitoring of insulin and to seven post-mortem cases.

Detection of intact insulin analogues in post-mortem vitreous humour-Application to forensic toxicology casework

The application of proteomic techniques to forensic science widens the range of analytical capabilities available to forensic laboratories when answering complex toxicology problems. Currently, these techniques are underutilised in post-mortem toxicology because of the historic focus on smaller (<1,000 amu) drug molecules. Definitive confirmation of an insulin overdose by analysis of post-mortem biological matrices is rare and challenging, however can assist coronial investigations pertaining to accidental or intentional overdoses in both diabetic and nondiabetic populations. A semiautomated micro-solid phase extraction paired with mass spectrometry-based insulin methodology was developed and validated for routine use in a Forensic Coronial Toxicology Laboratory. This resulting work reports the first Australian cases where synthetic insulins were confirmed by mass spectrometry in the vitreous humour of Type 1 diabetics who intentionally or accidentally overdosed on their prescription medication glargine and aspart. The detection of glargine M1 in Case 1, aspart in Case 2 and glargine M1 was indicated in Case 3. This paper highlights advancements in forensic coronial toxicology and the promising potential of proteomic analysis in a forensic context.

Is insulin intoxication still the perfect crime? Analysis and interpretation of postmortem insulin: review and perspectives in forensic toxicology

Insulin is an anabolic hormone essential to glucose homeostasis. Insulin therapy, comprising human insulin (HI) or biosynthetic analogs, is critical for the management of type-1 diabetes and many of type-2 diabetes. However, medication error including non-adapted dose and confusion of insulin type, and misuse, such as massive self-administration or with criminal intent, can have lethal consequences. The aim of this paper is to review the state of knowledge of insulin analysis in biological samples and of the interpretation of insulin concentrations in the situation of insulin-related death investigations. Analytic aspects are considered, as quantification can be strongly impacted by methodology. Immunoanalysis, the historical technique, has a prominent role due to its sensitivity and ease of implementation. Recently, liquid chromatography coupled to mass spectrometry has provided indispensable selectivity in forensic contexts, distinguishing HI, analogs, and degradation products. We review the numerous antemortem (dose, associated pathology, injection-to-death interval, etc.) and postmortem parameters (in corpore degradation, in vitro degradation related to hemolysis, etc.) involved in the interpretation of insulin concentration. The interest and limitations of various alternative matrices providing a valuable complement to blood analysis are discussed. Vitreous humor is one of the most interesting, but the low diffusion of insulin in this matrix entails very low concentrations. Injection site analysis is relevant for identifying which type of insulin was administered. Muscle and renal cortex are matrices of particular interest, although additional studies are required. A table containing most case reports of fatal insulin poisoning published, with analytical data, completes this review. A logic diagram is proposed to highlight analytical issues and the main parameters to be considered for the interpretation of blood concentrations. Finally, it remains a challenge to provide reliable biological data and solid interpretation in the context of death related to insulin overdose. However, the progress of analytical tools is making the "perfect crime" ever more difficult to commit.

Recent advances in the determination of insulins from biological fluids

The qualitative and quantitative determination of insulin and its related substances (e. g., C-peptide) is of great importance in many different areas of analytical chemistry. In particular, due to the steadily increasing prevalence of metabolic disorders such as diabetes mellitus, an adequate control of the circulating amount of insulin is desirable. In addition, also in forensics and doping control analysis, the determination of insulin in blood, urine or other biological matrices plays a major role. However, in order to establish general reference values for insulin and C-peptide for diabetology, the comparability of measured concentrations is indispensable. This has not yet been fully implemented, although enormous progress has been made in recent years, and the search for a "gold standard" method is still ongoing. In addition to established ligand-binding assays, an increasing number of mass-spectrometric methods have been developed and employed as the to-date available systems (for example, high-resolution/high accuracy mass spectrometers) provide the sensitivity required to determine analyte concentrations in the sub-ng/mL (sub-100pmol/L) level. Meanwhile, also high-throughput measurements have been realized to meet the requirement of testing a high number of samples in a short period of time. Further developments aim at enabling the online measurement of insulin in the blood with the help of an insulin sensor and, in the following, in addition to a brief review, today's state of the art testing developments are summarized.

Identification of recombinant human insulin and biosynthetic insulin analogues by multiplexed targeted unlabeled mass spectrometry of proteotypic tryptic peptides

Direct qualitative methods that allow the rapid screening and identification of insulin products during early stages of the drug development process and those already in the market can be of great utility for manufacturers and regulatory agencies and the recent scientific literature describes several methods. Herein, a qualitative proteomic method is presented for the identification of recombinant human insulin and all marketed biosynthetic analogues -insulin lispro, aspart, glulisine, glargine, detemir and degludec- via tryptic digestion and identification of proteotypic peptides for each insulin. Individual insulins were first denatured under reducing conditions and the cysteine residues blocked by iodoacetamide. The proteins were then digested with trypsin and the peptide products separated by reversed phase liquid chromatography on an Ascentis® Express ES-C18 column and detected by positive polarity ESI-MS/MS. The digestion peptides were characterized using a multiplexed MRM approach that monitors the fragmentation of the doubly charged unlabeled precursor ion of each peptide into a collection of signature y and b ions. The MRM transitions for the individual peptides were optimized to allow maximal ionization on a standard triple quadrupole mass spectrometer. All products of the digestion procedure for all insulins were detected with adequate signal intensity except for the C-terminal B30Thr whenever it was present and cleaved and the tryptic B1-3 tripeptide of insulin glulisine. The unique proteotypic peptides identified for each of the insulin analogues coupled with their signature y and b ions permitted the unambiguous verification of all sequence variations and chemical modifications. The elution of the A polypeptide chain for all insulins and the tryptic peptides of the B chain, with the exception of a very few, occurred around the same time point. This underscores the close similarity in the physicochemical properties between the digestion peptides and is consistent with the subtle variations in amino acid sequence among the various insulins. Therefore, the identification and distinction of the different types of insulin based solely on the chromatographic retention time of their respective proteolytic products can be deceptive without proper mass spectrometric analysis and may result in false positives.

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.

Evaluation of water-soluble DBS for small proteins: a conceptual study using insulin as a model analyte

Aim: Water-soluble sampling materials for DBS have been introduced to solve some of the common challenges of DBS. Methodology: Carboxymethyl cellulose (CMC) as water-soluble material was evaluated for small proteins using insulin as model analyte. 15 µl of whole blood was deposited and dried on a sheet of CMC prior to dissolvation of the whole spot, matrix precipitation with acetonitrile and LC–MS/MS analysis. Results: CMC was shown to promote matrix precipitation resulting in cleaner extracts than precipitation without CMC present. The recovery of insulin from the spot was 68 ± 4%, and the spotted samples were stable for at least 1 week in room temperature. Conclusion: Water-soluble DBS showed promising performance also in analysis of small proteins.

A simple dilute and shoot methodology for the identification and quantification of illegal insulin

The occurrence of illegal medicines is a well-established global problem and concerns mostly small molecules. However, due to the advances in genomics and recombinant expression technologies there is an increased development of polypeptide therapeutics. Insulin is one of the best known polypeptide drug, and illegal versions of this medicine led to lethal incidents in the past. Therefore, it is crucial for the public health sector to develop reliable, efficient, cheap, unbiased and easily applicable active pharmaceutical ingredient (API) identification and quantification strategies for routine analysis of suspected illegal insulins. Here we demonstrate that our combined label-free full scan approach is not only able to distinguish between all those different versions of insulin and the insulins originating from different species, but also able to chromatographically separate human insulin and insulin lispro in conditions that are compatible with mass spectrometry (MS). Additionally, we were also able to selectively quantify the different insulins, including human insulin and insulin lispro according to the validation criteria, put forward by the United Nations (UN), for the analysis of seized illicit drugs. The proposed identification and quantification method is currently being used in our official medicines control laboratory to analyze insulins retrieved from the illegal market.

Quantitation of Insulin Analogues in Serum Using Immunoaffinity Extraction, Liquid Chromatography, and Tandem Mass Spectrometry

Insulin analysis is used in combination with glucose, C-peptide, beta-hydroxybutyrate, and proinsulin determination for the investigation of adult hypoglycemia. The most common cause is the administration of too much insulin or insulin secretagogue to a diabetic patient or inadequate caloric intake after administration of either. Occasionally there is a question as to whether hypoglycemia has been caused by an exogenous insulin-whether by accident, intent, or even malicious intent. While traditionally this was confirmed by a low or undetectable C-peptide in a hypoglycemic specimen, this finding is not entirely specific and would also be expected in the context of impaired counter-regulatory response, fatty acid oxidation defects, and liver failure-though beta-hydroxybutyrate levels can lend diagnostic clarity. For this reason, insulin is often requested. However, popular automated chemiluminescent immunoassays for insulin have distinctly heterogeneous performance in detecting analogue synthetic insulins with cross-reactivities ranging from near 0 % to greater than 100 %. The ability to detect synthetic insulins is vendor-specific and varies between insulin products. Liquid Chromatography and Tandem Mass Spectrometry (LC-MS/MS) offers a means to circumvent these analytical issues and both quantify synthetic insulins and identify the specific type. We present an immunoaffinity extraction and LC-MS/MS method capable of independent identification and quantitation of native sequence insulins (endogenous, Insulin Regular, Insulin NPH), and analogues Glargine, Lispro, Detemir, and Aspart with an analytical sensitivity for endogenous insulin of between 1 and 2 μU/mL in patient serum samples.

Current trends in mass spectrometry of peptides and proteins: Application to veterinary and sports-doping control

Detection of misuse of peptides and proteins as growth promoters is a major issue for sport and food regulatory agencies. The limitations of current analytical detection strategies for this class of compounds, in combination with their efficacy in growth-promoting effects, make peptide and protein drugs highly susceptible to abuse by either athletes or farmers who seek for products to illicitly enhance muscle growth. Mass spectrometry (MS) for qualitative analysis of peptides and proteins is well-established, particularly due to tremendous efforts in the proteomics community. Similarly, due to advancements in targeted proteomic strategies and the rapid growth of protein-based biopharmaceuticals, MS for quantitative analysis of peptides and proteins is becoming more widely accepted. These continuous advances in MS instrumentation and MS-based methodologies offer enormous opportunities for detection and confirmation of peptides and proteins. Therefore, MS seems to be the method of choice to improve the qualitative and quantitative analysis of peptide and proteins with growth-promoting properties. This review aims to address the opportunities of MS for peptide and protein analysis in veterinary control and sports-doping control with a particular focus on detection of illicit growth promotion. An overview of potential peptide and protein targets, including their amino acid sequence characteristics and current MS-based detection strategies is, therefore, provided. Furthermore, improvements of current and new detection strategies with state-of-the-art MS instrumentation are discussed for qualitative and quantitative approaches.

Is isolation of comprehensive human plasma peptidomes an achievable quest?

The low molecular weight (LMW; <10kDa)* plasma peptidome has been considered a source of useful diagnostic biomarkers and potentially therapeutic molecules, as it contains many cytokines, peptide hormones, endogenous peptide products and potentially bioactive fragments derived from the parent proteome. The small size of the peptides allows them almost unrestricted vascular and interstitial access, and hence distribution across blood-brain barriers, tumour and other vascular permeability barriers. Therefore, the peptidome may carry specific signatures or fingerprints of an individual's health, wellbeing or disease status. This occurs primarily because of the advantage the peptidome has in being readily accessible in human blood and/or other biofluids. However, the co-expression of highly abundant proteins (>10kDa) and other factors present inherently in human plasma make direct analysis of the blood peptidome one of the most challenging tasks faced in contemporary analytical biochemistry. A comprehensive compendium of extraction and fractionation tools has been collected concerning the isolation and micromanipulation of peptides. However, the search for a reliable, accurate and reproducible single or combinatorial separation process for capturing and analysing the plasma peptidome remains a challenge. This review outlines current techniques used for the separation and detection of plasma peptides and suggests potential avenues for future investigation. This article is part of a Special Issue entitled: HUPO 2014.

Advances in the quantitation of therapeutic insulin analogues by LC-MS/MS

Insulin analogues represent a major and growing class of biotherapeutics, and their quantitation is an important focus of commercial and public effort across a number of different fields. As LC-MS has developed, it has become an increasingly practicable and desirable alternative to ligand-binding-based approaches for quantitation of this class of compounds. The sensitivity challenge of measuring trace levels of this large peptide molecule in a protein-containing matrix is considerable; however, different approaches to detection, extraction and separation are described to overcome this challenge, including immunoaffinity capture, SPE and low-flow HPLC. Considerations such as bioanalytical assay acceptance criteria and antidrug antibody effects during drug development are included, alongside descriptions of recent sports doping and clinical applications. Factors affecting the correlation and agreement of MS with biological ligand-binding methods are discussed, with ways to anticipate and appreciate differences between the values derived from each technique. The 'future perspective' section discusses the likely trend towards MS-based analysis for these compounds and the impact of HRMS. A high degree of scientific creativity, combined with science-defined regulatory approaches that define suitable validation criteria, will be needed to meet the demanding requirements for high-throughput analysis of insulin by LC-MS.

Sensitive detection of human insulin using a designed combined pore approach

A unique combined pore approach to the sensitive detection of human insulin is developed. Through a systematic study to understand the impact of pore size and surface chemistry of nanoporous materials on their enrichment and purification performance, the advantages of selected porous materials are integrated to enhance detection sensitivity in a unified two-step process. In the first purification step, a rationally designed large pore material (ca. 100 nm in diameter) is chosen to repel the interferences from nontarget molecules. In the second enrichment step, a hydrophobically modified mesoporous material with a pore size of 5 nm is selected to enrich insulin molecules. A low detection limit of 0.05 ng mL(-1) in artificial urine is achieved by this advanced approach, similar to most antibody-based analysis protocols. This designer approach is efficient and low cost, and thus has great potential in the sensitive detection of biomolecules in complex biological systems.

Assessment of the metabolism of therapeutic proteins and antibodies

INTRODUCTION

In the last decade, our increased knowledge of factors governing the pharmacokinetics and metabolism of biologics (recombinant therapeutic proteins) has driven, and will continue to support, biological engineering and the design of delivery systems for more efficient biologics. Further research in analytical methods for assessing their in vitro and/or in vivo metabolism will also support these developments.

AREAS COVERED

In this review we will discuss the main components affecting the metabolism of biologics, and try to demonstrate how novel analytical evaluations will facilitate their future development. We will focus on the use of radiolabeled drugs, ligand-binding assays and mass spectrometry.

EXPERT OPINION

Future marketed biologics will be complex structures, such as glycoengineered, fused, or chemically modified proteins. Their in vivo efficiencies will be strongly dependent on their metabolic stabilities. Similarly to small molecular drugs, for which in vitro and in vivo biochemical platforms and analytical techniques have helped to rationalize preclinical and clinical developments, we would expect this also to translate to effective approaches to study the metabolism of biologics in the near future. Mass spectrometry should emerge as a standard technique for in vivo characterization of the biotransformation products of biologics.

Parallel workflow for high-throughput (>1,000 samples/day) quantitative analysis of human insulin-like growth factor 1 using mass spectrometric immunoassay

Insulin-like growth factor 1 (IGF1) is an important biomarker for the management of growth hormone disorders. Recently there has been rising interest in deploying mass spectrometric (MS) methods of detection for measuring IGF1. However, widespread clinical adoption of any MS-based IGF1 assay will require increased throughput and speed to justify the costs of analyses, and robust industrial platforms that are reproducible across laboratories. Presented here is an MS-based quantitative IGF1 assay with performance rating of >1,000 samples/day, and a capability of quantifying IGF1 point mutations and posttranslational modifications. The throughput of the IGF1 mass spectrometric immunoassay (MSIA) benefited from a simplified sample preparation step, IGF1 immunocapture in a tip format, and high-throughput MALDI-TOF MS analysis. The Limit of Detection and Limit of Quantification of the resulting assay were 1.5 μg/L and 5 μg/L, respectively, with intra- and inter-assay precision CVs of less than 10%, and good linearity and recovery characteristics. The IGF1 MSIA was benchmarked against commercially available IGF1 ELISA via Bland-Altman method comparison test, resulting in a slight positive bias of 16%. The IGF1 MSIA was employed in an optimized parallel workflow utilizing two pipetting robots and MALDI-TOF-MS instruments synced into one-hour phases of sample preparation, extraction and MSIA pipette tip elution, MS data collection, and data processing. Using this workflow, high-throughput IGF1 quantification of 1,054 human samples was achieved in approximately 9 hours. This rate of assaying is a significant improvement over existing MS-based IGF1 assays, and is on par with that of the enzyme-based immunoassays. Furthermore, a mutation was detected in ∼1% of the samples (SNP: rs17884626, creating an A→T substitution at position 67 of the IGF1), demonstrating the capability of IGF1 MSIA to detect point mutations and posttranslational modifications.

Quantitative Insulin Analysis Using Liquid Chromatography–Tandem Mass Spectrometry in a High-Throughput Clinical Laboratory

BACKGROUND

Circulating insulin concentrations reflect the amount of endogenous insulin produced by the pancreas and can be monitored to check for insulin resistance. Insulin is commonly measured using immunochemiluminometric assays (ICMA). Unfortunately, differing crossreactivities of the various ICMA antibodies have led to variability in assay results. In contrast, liquid chromatography–tandem mass spectrometry (LC-MS/MS)-based approaches can provide a highly specific alternative to immunoassays.

METHODS

Insulin was extracted from patient serum and reduced to liberate the insulin B chain. Subsequent resolution of the peptide was achieved by LC coupled to triple-quadrupole MS. Selected-reaction monitoring of B-chain transitions was used for quantification. Recombinant human insulin was used as a calibrator and was compared against the National Institute for Biological Standards and Control (NIBSC) reference standard. Bovine insulin and a stable isotopic-labeled (13C/15N) human insulin B chain were used and compared as internal standards.

RESULTS

The LC-MS/MS assay described herein has been validated according to CLIA guidelines with a limit of detection of 1.8 μIU/mL (10.8 pmol/L) and a limit of quantitation of 3 μIU/mL (18.0 pmol/L). A correlation between the LC-MS/MS assay and a US Food and Drug Administration-approved ICMA was completed for patient samples and the resulting Deming regression revealed good agreement. A reference interval for the assay was established.

CONCLUSIONS

A simple, high-throughput, quantitative LC-MS/MS insulin assay traceable to the NIBSC standard has been successfully developed and validated.

Development of a fast method for direct analysis of intact synthetic insulins in human plasma: the large peptide challenge

Background: Intact insulins are difficult to analyze by LC–MS/MS due to nonspecific binding and poor sensitivity, solubility and fragmentation. This work aims to provide a simpler, faster LC–MS method and focuses on solving the above issues. Results: A novel charged-surface chromatographic column produced peak widths for insulin that were significantly narrower than traditional C18 columns when using formic acid as mobile phase. Mass spectral fragments m/z >700 provided greater specificity, significantly reducing endogenous background. Detection limits in human plasma were 0.2 ng/ml for insulin glargine, glulisine and detemir, and 0.5 ng/ml for insulin aspart. Average accuracy for standard curve and QC samples was 93.4%. Conclusion: A simple SPE LC–MS analysis was developed for direct, simultaneous quantification of insulin glargine, detemir, aspart and glulisine.

Illicit organogenesis: Methods and substances of doping and manipulation

Doping and manipulation are undesirable companions of professional and amateur sport. Numerous adverse analytical findings as well as confessions of athletes have demonstrated the variety of doping agents and methods as well as the inventiveness of cheating sportsmen. Besides 'conventional' misuse of drugs such as erythropoietin and insulins, experts fear that therapeutics that are currently undergoing clinical trials might be part of current or future doping regimens, which aim for an increased functionality and performance or organs and tissues. Emerging drugs such as selective androgen receptor modulators (SARMs), hypoxia-inducible factor (HIF) complex stabilizers or modulators of muscle fiber calcium channels are considered relevant for current and future doping controls due to their high potential for misuse in sports.

Analytical challenges in the detection of peptide hormones for anti-doping purposes

Although significant progress has been achieved during the past few years with the introduction of new assays and analytical methodologies, the detection and quantification of protein analytes, in particular of peptide hormones, continues to pose analytical challenges for the World Anti-Doping Agency-accredited anti-doping laboratories. In this article, the latest achievements in the application of MS-based methodologies and specific biochemical and immunological assays to detect some of the prohibited substances listed in section S2 of the World Anti-Doping Agency List of Prohibited Substances and Methods are reviewed. In addition, we look towards the future by focusing on some of the most promising analytical approaches under development for the detection of so-called ‘biomarkers of doping’.

RNA interference for performance enhancement and detection in doping control

RNA interference represents a comparably new route of regulating and manipulating specific gene expression. Promising results were obtained in experimental therapies aim at the treatment of different kinds of diseases including cancer, diabetes mellitus or Dychenne muscular dystrophy. While studies on down-regulation efficiency are often performed by analyzing the regulated protein, the direct detection of small, interfering RNA molecules and antisense oligonucleotides is of great interest for the investigation of the metabolism and degradation and also for the detection of a putative misuse of these molecules in sports. Myostatin down-regulation was shown to result in increased performance and muscle growth and the regulation of several other proteins could be relevant for performance enhancement. This mini-review summarizes current approaches for the mass spectrometric analysis of siRNA and antisense oligonucleotides from biological matrices and the available data on biodistribution, metabolism, and half-life of relevant substances are discussed.

Metabolism of biologics: biotherapeutic proteins

Recombinant therapeutic protein drugs have now been in clinical use for nearly three decades and have advanced considerably in complexity over this time period. Regulatory approvals of some early pioneering protein drugs did not require characterization of metabolism, but more recently regulatory expectations and guidance have appropriately evolved. Sponsors may now be expected to investigate metabolism of newer biologics as the structural complexity of proteins has increased markedly, particularly with the introduction of conjugated and modified proteins. This review discusses the value and need for metabolite characterization of some therapeutic proteins by presenting select examples. Regulatory expectations will undoubtedly evolve further with the development of other novel macromolecular biologic therapeutics based on modified nucleic acids, novel conjugated lipids and polysaccharides.

Peptide and protein drugs: the study of their metabolism and catabolism by mass spectrometry

Peptide and protein drugs have evolved in recent years into mainstream therapeutics, representing a significant portion of the pharmaceutical market. Peptides and proteins exhibit highly diverse structures, broad biological activities as hormones, neurotransmitters, structural proteins, metabolic modulators and therefore have a significant role as both therapeutics and biomarkers. Understanding the metabolism of synthetic or biotechnologically derived peptide and protein drugs is critical for pharmaceutical development as metabolism has a significant impact on drug efficacy and safety. Although the same principles of pharmacokinetics and metabolism of small molecule drugs apply to peptide and protein drugs, there are few notable differences. Moreover, the study of peptide and protein drug metabolism is a rather complicated process which requires sophisticated analytical techniques, and mass spectrometry based approaches have provided the capabilities for efficient and reliable quantification, characterization, and metabolite identification. This review article will focus on the current use of mass spectrometry for the study of the metabolism of peptide and protein drugs.

Mass spectrometry of peptides and proteins from human blood

It is difficult to convey the accelerating rate and growing importance of mass spectrometry applications to human blood proteins and peptides. Mass spectrometry can rapidly detect and identify the ionizable peptides from the proteins in a simple mixture and reveal many of their post-translational modifications. However, blood is a complex mixture that may contain many proteins first expressed in cells and tissues. The complete analysis of blood proteins is a daunting task that will rely on a wide range of disciplines from physics, chemistry, biochemistry, genetics, electromagnetic instrumentation, mathematics and computation. Therefore the comprehensive discovery and analysis of blood proteins will rank among the great technical challenges and require the cumulative sum of many of mankind's scientific achievements together. A variety of methods have been used to fractionate, analyze and identify proteins from blood, each yielding a small piece of the whole and throwing the great size of the task into sharp relief. The approaches attempted to date clearly indicate that enumerating the proteins and peptides of blood can be accomplished. There is no doubt that the mass spectrometry of blood will be crucial to the discovery and analysis of proteins, enzyme activities, and post-translational processes that underlay the mechanisms of disease. At present both discovery and quantification of proteins from blood are commonly reaching sensitivities of ∼1 ng/mL.

OMICS-strategies and methods in the fight against doping

During the past decade OMICS-methods not only continued to have their impact on research strategies in life sciences and in particular molecular biology, but also started to be used for anti-doping control purposes. Research activities were mainly reasoned by the fact that several substances and methods, which were prohibited by the World Anti-Doping Agency (WADA), were or still are difficult to detect by direct methods. Transcriptomics, proteomics, and metabolomics in theory offer ideal platforms for the discovery of biomarkers for the indirect detection of the abuse of these substances and methods. Traditionally, the main focus of transcriptomics and proteomics projects has been on the prolonged detection of the misuse of human growth hormone (hGH), recombinant erythropoietin (rhEpo), and autologous blood transfusion. An additional benefit of the indirect or marker approach would also be that similarly acting substances might then be detected by a single method, without being forced to develop new direct detection methods for new but comparable prohibited substances (as has been the case, e.g. for the various forms of Epo analogs and biosimilars). While several non-OMICS-derived parameters for the indirect detection of doping are currently in use, for example the blood parameters of the hematological module of the athlete's biological passport, the outcome of most non-targeted OMICS-projects led to no direct application in routine doping control so far. The main reason is the inherent complexity of human transcriptomes, proteomes, and metabolomes and their inter-individual variability. The article reviews previous and recent research projects and their results and discusses future strategies for a more efficient application of OMICS-methods in doping control.

Evaluation of commercially available assays for the measurement of equine insulin

Determining circulating equine insulin concentrations is becoming increasingly important in equine clinical practice and research. Most available assays are optimized for human medicine, but there is strong equine cross-reactivity because of the highly conserved nature of insulin. To identify an accurate and reliable assay for equine insulin, 6 commercial immunoassays were evaluated for precision, accuracy, and specificity. Only 1 assay initially reached the requisite standard: Mercodia Equine Insulin Enzyme-linked Immunosorbent assay (ELISA). Plasma matrix interferences were identified when the provided assay buffer was used with the Siemens Count-a-Coat Insulin radioimmunoassay (RIA) but not when charcoal-stripped equine plasma was used as the diluent. This modified RIA and the Mercodia Equine Insulin ELISA were evaluated further by directly examining accuracy by comparing their results for 18 equine plasma samples with values obtained using liquid chromatography and high-resolution/high-accuracy mass spectrometry (LC-MS). Compared with LC-MS measurements, the modified Siemens Insulin RIA rendered a moderate Lin's concordance coefficient (ρ(c)) of 0.41, whereas the Mercodia Equine Insulin ELISA rendered a very poor ρ(c) of 0.06. This suggests that the Siemens Insulin RIA is appropriate to use for routine evaluations when LC-MS is not available.

Mass spectrometric immunoassay of intact insulin and related variants for population proteomics studies

PURPOSE

The purpose of the work presented herein was to develop a high-throughput assay for the quantification of human insulin in plasma samples while simultaneously detecting, with high mass accuracy, any additional variant forms of insulin that might be present in each sample.

EXPERIMENTAL DESIGN

A mass spectrometric immunoassay (MSIA) was designed in which anti-human insulin antibodies were immobilized to commercially available mass spectrometric immunoassay pipette tips and used to capture insulin and related protein variants from human plasma.

RESULTS

Standard curves for insulin exhibited linearity (average R(2) for three days of analysis=0.99) and assay concentration limits of detection and limits of quantification for insulin were found to be 1 and 15 pM, respectively. Estimated coefficient of variations for inter-day experiments (n=3 days) were <8%. Simultaneously, the assay was shown to detect and identify insulin metabolites and synthetic insulin analogs (e.g. Lantus). Notably, insulin variants not known to exist in plasma were detected in diabetics.

CONCLUSIONS AND CLINICAL RELEVANCE

This introductory study sets a foundation toward the screening of large populations to investigate insulin isoforms, isoform frequencies, and their quantification.