A novel high-sensitivity electrochemiluminescence (ECL) sandwich immunoassay for the specific quantitative measurement of plasma glucagon

Development and validation of a fast and reliable method for the quantification of glucagon by liquid chromatography and tandem mass spectrometry

INTRODUCTION

The quantitation of glucagon remains a challenging immunoassay, mainly due to cross-reactivity. A sensitive, rapid and specific intact glucagon method is therefore necessary for quality routine analysis. A tandem mass spectrometry method to fulfill this objective is described in this work.

METHODS

Glucagon was extracted from plasma employing a mixed-mode anion exchange solid-phase extraction. Sample stability was assessed in K2-EDTA and P800 tubes at different temperatures. We compared our method to two different immunoassays. FDA and EMA guidelines were followed for validation. An external quality control program served for comparison with other laboratories.

RESULTS

Assay imprecision was below 4%. Recoveries were within 95-103%. LoQ was 8.75 pg/mL. Total analytical CV was 2.91%. Samples were found stable at 4 °C for less than 4 h. Diasource® RIA disagreed with our method. Mercodia® ELISA provided a closer agreement, also proven by external quality control samples.

CONCLUSIONS

A rapid and specific LC-MS/MS method for glucagon quantitation has been developed, validated and is suitable to routine care. The simplicity and the good performances in terms of time and specificity, could open the possibility to establish a standardized method for glucagon.

Association of Glucagon With Obesity, Glycemic Control and Renal Function in Adults With Type 2 Diabetes Mellitus

OBJECTIVES

In this study, we used a double-antibody sandwich enzyme-linked immunosorbent assay to assess the association between blood glucagon levels and indices of obesity, glycemic control and renal function in patients with type 2 diabetes mellitus (T2DM).

METHODS

This investigation was a cross-sectional study on inpatients with T2DM who had plasma glucagon levels measured during hospitalization. Associations of fasting glucagon levels (G₀), 120-minute postbreakfast plasma glucagon (G₁₂₀), fasting glucagon/C-peptide ratio (G₀/CPR₀) and postbreakfast glucagon/C-peptide ratio (G₁₂₀/CPR₁₂₀) with clinical data were evaluated using multiple regression analysis.

RESULTS

A total of 345 patients were enrolled in the study. G₀, and G₁₂₀ were significantly and positively associated with serum C-peptide levels. Moreover, G₀ and G₁₂₀ were positively associated with waist circumference, and G₀ was negatively associated with duration of diabetes mellitus. Interestingly, both G₀ and G₁₂₀ were negatively associated with the estimated glomerular filtration rate. In addition, G₁₂₀/CPR₁₂₀ was positively associated with duration of diabetes mellitus and glycoalbumin levels.

CONCLUSIONS

The balance between glucagon and insulin secretion is significantly associated with abdominal obesity and important for maintaining glucose homeostasis. Postprandial hyperglucagonemia could also be related to deterioration of renal function.

Treatment with LY2409021, a glucagon receptor antagonist, increases liver fat in patients with type 2 diabetes

AIMS

To evaluate whether treatment with LY2409021, a novel, selective glucagon receptor antagonist, is associated with changes in hepatic fat and other safety variables related to the benefit-risk profile for chronic use in patients with type 2 diabetes (T2D).

METHODS

Safety and efficacy were assessed in patients with T2D taking metformin and sulphonylurea who were randomized to LY2409021 20 mg (n = 65), placebo (n = 68), or sitagliptin 100 mg (n = 41). Key endpoints included change from baseline to month 6 in hepatic fat fraction (HFF), assessed by magnetic resonance imaging; hepatic aminotransferases; blood pressure; lipid profile; fasting plasma glucose; and glycated haemoglobin (HbA1c).

RESULTS

A significant increase in HFF was seen with LY2409021 vs sitagliptin (least squares [LS] mean difference 3.72%; P < .001) and placebo (4.44%; P < .001), accompanied by significant elevations in alanine aminotransferase levels with LY2409021 vs sitagliptin (6.8 U/L; P = .039) and vs placebo (10.7 U/L; P < .001). No patients had concomitant elevations in bilirubin levels. LY2409021 treatment showed significant HbA1c reductions vs placebo (LS mean difference -0.77%; P < .001) but not sitagliptin (-0.20%; P = .383). Similar results were observed for fasting plasma glucose. LY2409021 was also associated with significant increases in systolic blood pressure vs sitagliptin (4.9 mm Hg; P = .030) and vs placebo (4.3 mm Hg; P = .029), as well as significant increases in body weight and total cholesterol. All effects of LY2409021 were reversible.

CONCLUSION

In this cohort of patients with T2D, chronic glucagon receptor antagonism with LY2409021 was associated with glucose-lowering but also demonstrated increases in hepatic fat, hepatic aminotransferases, and other adverse effects.

Treatment with the glucagon receptor antagonist LY2409021 increases ambulatory blood pressure in patients with type 2 diabetes

AIMS

To assess the effect of LY2409021 on systolic blood pressure (SBP) in patients with type 2 diabetes.

MATERIALS AND METHODS

This 6-week, randomized, crossover study evaluated the effects of once-daily administration of LY2409021 20 mg vs those of placebo on SBP, diastolic BP (DBP), and mean arterial pressure (MAP) using 24-hour ambulatory BP monitoring (ABPM) in 270 subjects treated with diet/exercise ± metformin. Other measures included changes in glycemic control, serum lipids, and hepatic safety markers.

RESULTS

At 6 weeks of LY2409021 treatment, 24-hour mean SBP was increased, with a least squares mean (LSM) difference of 2.26 mm Hg vs placebo (95% CI: 1.11, 3.40; P  < .001). The 24-hour mean DBP and MAP also increased, with LSM differences of 1.37 mm Hg (95% CI: 0.66, 2.08; P  < .001) and 1.67 mm Hg (95% CI: 0.86, 2.47; P  < .001) vs placebo, respectively. At week 6, LY2409021 treatment reduced glycated hemoglobin (HbA1c) levels, with an LSM difference of -0.49% (-5.4 mmol/mol) (95% CI: -0.56%, -0.42% [-6.1, -4.6 mmol/mol]; P  < .001) vs placebo. Mean HbA1c at baseline was 7.3% (56 mmol/mol). Small but significant changes in serum lipid and aminotransferase levels were observed with LY2409021 treatment (all P  < .05 vs placebo).

CONCLUSIONS

Statistically significant increases in BP, MAP and serum lipid levels were observed with LY2409021 treatment at a dose that lowered HbA1c and glucose levels. These effects may limit the clinical utility of LY2409021 as a chronic treatment for type 2 diabetes.

Characterization and quantification of oxyntomodulin in human and rat plasma using high-resolution accurate mass LC–MS

Background: A thorough understanding of the biological role of oxyntomodulin (OXM) has been limited by the availability of sensitive and specific analytical tools for reliable in vivo characterization. Here, we utilized immunoaffinity capture coupled with high-resolution accurate mass LC–MS detection to quantify OXM and its primary catabolites. Results: Quantification of intact OXM 1–37 in human and rat plasma occurred in pre- and post-prandial samples. Profiles for the major catabolites were observed allowing kinetic differences to be assessed between species. Conclusion: A validated assay in human and rat plasma was obtained for OXM 1–37 and its catabolites, 3–37 and 4–37. The value of full scan high-resolution accurate mass detection without selected reaction monitoring for low-abundance peptide quantification was also demonstrated.

Evaluation of Efficacy and Safety of the Glucagon Receptor Antagonist LY2409021 in Patients With Type 2 Diabetes: 12- and 24-Week Phase 2 Studies

OBJECTIVE

Type 2 diabetes pathophysiology is characterized by dysregulated glucagon secretion. LY2409021, a potent, selective small-molecule glucagon receptor antagonist that lowers glucose was evaluated for efficacy and safety in patients with type 2 diabetes.

RESEARCH DESIGN AND METHODS

The efficacy (HbA1c and glucose) and safety (serum aminotransferase) of once-daily oral administration of LY2409021 was assessed in two double-blind studies. Phase 2a study patients were randomized to 10, 30, or 60 mg of LY2409021 or placebo for 12 weeks. Phase 2b study patients were randomized to 2.5, 10, or 20 mg LY2409021 or placebo for 24 weeks.

RESULTS

LY2409021 produced reductions in HbA1c that were significantly different from placebo over both 12 and 24 weeks. After 12 weeks, least squares (LS) mean change from baseline in HbA1c was -0.83% (10 mg), -0.65% (30 mg), and -0.66% (60 mg) (all P < 0.05) vs. placebo, 0.11%. After 24 weeks, LS mean change from baseline in HbA1c was -0.45% (2.5 mg), -0.78% (10 mg, P < 0.05), -0.92% (20 mg, P < 0.05), and -0.15% with placebo. Increases in serum aminotransferase, fasting glucagon, and total fasting glucagon-like peptide-1 (GLP-1) were observed; levels returned to baseline after drug washout. Fasting glucose was also lowered with LY2409021 at doses associated with only modest increases in aminotransferases (mean increase in alanine aminotransferase [ALT] ≤10 units/L). The incidence of hypoglycemia in the LY2409021 groups was not statistically different from placebo.

CONCLUSIONS

In patients with type 2 diabetes, glucagon receptor antagonist treatment significantly lowered HbA1c and glucose levels with good overall tolerability and a low risk for hypoglycemia. Modest, reversible increases in serum aminotransferases were observed.

Endogenous GLP1 and GLP1 analogue alter CNS responses to palatable food consumption

Glucagon-like peptide-1 (GLP1) affects appetite, supposedly mediated via the central nervous system (CNS). In this study, we investigate whether modulation of CNS responses to palatable food consumption may be a mechanism by which GLP1 contributes to the central regulation of feeding. Using functional MRI, we determined the effects of endogenous GLP1 and treatment with the GLP1 analogue liraglutide on CNS activation to chocolate milk receipt. Study 1 included 20 healthy lean individuals and 20 obese patients with type 2 diabetes (T2DM). Scans were performed on two occasions: during infusion of the GLP1 receptor antagonist exendin 9-39 (blocking actions of endogenous GLP1) and during placebo infusion. Study 2 was a randomised, cross-over intervention study carried out in 20 T2DM patients, comparing treatment with liraglutide to insulin, after 10 days and 12 weeks. Compared with lean individuals, T2DM patients showed reduced activation to chocolate milk in right insula (P = 0.04). In lean individuals, blockade of endogenous GLP1 effects inhibited activation in bilateral insula (P ≤ 0.03). Treatment in T2DM with liraglutide, vs insulin, increased activation to chocolate milk in right insula and caudate nucleus after 10 days (P ≤ 0.03); however, these effects ceased to be significant after 12 weeks. Our findings in healthy lean individuals indicate that endogenous GLP1 is involved in the central regulation of feeding by affecting central responsiveness to palatable food consumption. In obese T2DM, treatment with liraglutide may improve the observed deficit in responsiveness to palatable food, which may contribute to the induction of weight loss observed during treatment. However, no long-term effects of liraglutide were observed.

2015 White Paper on recent issues in bioanalysis: focus on new technologies and biomarkers (Part 2 – hybrid LBA/LCMS and input from regulatory agencies)

The 2015 9th Workshop on Recent Issues in Bioanalysis (9th WRIB) took place in Miami, Florida with participation of over 600 professionals from pharmaceutical and biopharmaceutical companies, biotechnology companies, contract research organizations and regulatory agencies worldwide. It is once again a 5-day week long event – a full immersion bioanalytical week – specifically designed to facilitate sharing, reviewing, discussing and agreeing on approaches to address the most current issues of interest in bioanalysis. The topics covered included both small and large molecules, and involved LCMS, hybrid LBA/LCMS, LBA approaches including the focus on biomarkers and immunogenicity. This 2015 White Paper encompasses recommendations that emerged from the extensive discussions held during the workshop, and is aimed at providing the bioanalytical community with key information and practical solutions on topics and issues addressed, in an effort to advance scientific excellence, improve quality and deliver better regulatory compliance. Due to its length, the 2015 edition of this comprehensive White Paper has been divided into three parts. Part 2 covers the recommendations for hybrid LBA/LCMS and regulatory agencies’ inputs. Part 1 (small molecule bioanalysis using LCMS) and Part 3 (large molecule bioanalysis using LBA, biomarkers and immunogenicity) will be published in volume 7 of Bioanalysis, issues 22 and 24, respectively.

Endogenous GLP-1 mediates postprandial reductions in activation in central reward and satiety areas in patients with type 2 diabetes

AIMS/HYPOTHESIS

The central nervous system (CNS) is a major player in the regulation of food intake. The gut hormone glucagon-like peptide-1 (GLP-1) has been proposed to have an important role in this regulation by relaying information about nutritional status to the CNS. We hypothesised that endogenous GLP-1 has effects on CNS reward and satiety circuits.

METHODS

This was a randomised, crossover, placebo-controlled intervention study, performed in a university medical centre in the Netherlands. We included patients with type 2 diabetes and healthy lean control subjects. Individuals were eligible if they were 40-65 years. Inclusion criteria for the healthy lean individuals included a BMI <25 kg/m(2) and normoglycaemia. Inclusion criteria for the patients with type 2 diabetes included BMI >26 kg/m(2), HbA1c levels between 42 and 69 mmol/mol (6.0-8.5%) and treatment for diabetes with only oral glucose-lowering agents. We assessed CNS activation, defined as blood oxygen level dependent (BOLD) signal, in response to food pictures in obese patients with type 2 diabetes (n = 20) and healthy lean individuals (n = 20) using functional magnetic resonance imaging (fMRI). fMRI was performed in the fasted state and after meal intake on two occasions, once during infusion of the GLP-1 receptor antagonist exendin 9-39, which was administered to block actions of endogenous GLP-1, and on the other occasion during saline (placebo) infusion. Participants were blinded for the type of infusion. The order of infusion was determined by block randomisation. The primary outcome was the difference in BOLD signal, i.e. in CNS activation, in predefined regions in the CNS in response to viewing food pictures.

RESULTS

All patients were included in the analyses. Patients with type 2 diabetes showed increased CNS activation in CNS areas involved in the regulation of feeding (insula, amygdala and orbitofrontal cortex) in response to food pictures compared with lean individuals (p ≤ 0.04). Meal intake reduced activation in the insula in response to food pictures in both groups (p ≤ 0.05), but this was more pronounced in patients with type 2 diabetes. Blocking actions of endogenous GLP-1 significantly prevented meal-induced reductions in bilateral insula activation in response to food pictures in patients with type 2 diabetes (p ≤ 0.03).

CONCLUSIONS/INTERPRETATION

Our findings support the hypothesis that endogenous GLP-1 is involved in postprandial satiating effects in the CNS of obese patients with type 2 diabetes.

TRIAL REGISTRATION

ClinicalTrials.gov NCT 01363609. Funding The study was funded in part by a grant from Novo Nordisk.

Development of a high-throughput UHPLC-MS/MS (SRM) method for the quantitation of endogenous glucagon from human plasma

BACKGROUND

Published LC-MS/MS methods are not sensitive enough to quantify endogenous levels of glucagon.

RESULTS

An ultra high performance liquid chromatography-MS/MS (SRM) method for the quantitation of endogenous levels glucagon was successfully developed and qualified. A novel 2D extraction procedure was used to reduce matrix suppression, background noise and interferences. Glucagon levels in samples from healthy volunteers were found to agree with radioimmunoassay (RIA) derived literature values. Bland-Altman analysis showed a concentration-dependent positive bias of the LC/MS-MS assay versus an RIA. Both assays produced similar pharmacokinetic profiles, both of which were feasible considering the nature of the study.

CONCLUSION

Our method is the first peer reviewed LC-MS/MS method for the quantitation of endogenous levels of glucagon, and offers a viable alternative to RIA-based approaches.

Calculations for Adjusting Endogenous Biomarker Levels During Analytical Recovery Assessments for Ligand-Binding Assay Bioanalytical Method Validation

It is often necessary to adjust for detectable endogenous biomarker levels in spiked validation samples (VS) and in selectivity determinations during bioanalytical method validation for ligand-binding assays (LBA) with a matrix like normal human serum (NHS). Described herein are case studies of biomarker analyses using multiplex LBA which highlight the challenges associated with such adjustments when calculating percent analytical recovery (%AR). The LBA test methods were the Meso Scale Discovery V-PLEX® proinflammatory and cytokine panels with NHS as test matrix. The NHS matrix blank exhibited varied endogenous content of the 20 individual cytokines before spiking, ranging from undetectable to readily quantifiable. Addition and subtraction methods for adjusting endogenous cytokine levels in %AR calculations are both used in the bioanalytical field. The two methods were compared in %AR calculations following spiking and analysis of VS for cytokines having detectable endogenous levels in NHS. Calculations for %AR obtained by subtracting quantifiable endogenous biomarker concentrations from the respective total analytical VS values yielded reproducible and credible conclusions. The addition method, in contrast, yielded %AR conclusions that were frequently unreliable and discordant with values obtained with the subtraction adjustment method. It is shown that subtraction of assay signal attributable to matrix is a feasible alternative when endogenous biomarkers levels are below the limit of quantitation, but above the limit of detection. These analyses confirm that the subtraction method is preferable over that using addition to adjust for detectable endogenous biomarker levels when calculating %AR for biomarker LBA.

Identification of plasma protease derived metabolites of glucagon and their formation under typical laboratory sample handling conditions

RATIONALE

Glucagon modulates glucose production, and it is also a biomarker for several pathologies. It is known to be unstable in human plasma, and consequently stabilisers are often added to samples, although these are not particularly effective. Despite this, there have not been any studies to identify in vitro plasma protease derived metabolites; such a study is described here. Knowledge of metabolism should allow the development of more effective sample stabilisation strategies.

METHODS

Several novel metabolites resulting from the incubation of glucagon in human plasma were identified using high-resolution mass spectrometry with positive electrospray ionisation. Tandem mass spectrometric (MS/MS) scans were acquired for additional confirmation using a QTRAP. Separation was performed using reversed-phase ultra-high-performance liquid chromatography. The formation of these metabolites was investigated during a time-course experiment and under specific stress conditions representative of typical laboratory handling conditions. Clinical samples were also screened for metabolites.

RESULTS

Glucagon(3-29) and [pGlu](3) glucagon(3-29) were the major metabolites detected, both of which were also present in clinical samples. We also identified two oxidised forms of [pGlu](3) glucagon(3-29) as well as glucagon(19-29), or 'miniglucagon', along with the novel metabolites glucagon(20-29) and glucagon(21-29). The relative levels of these metabolites varied throughout the time-course experiment, and under the application of the different sample handling conditions. Aprotinin stabilisation of samples had negligible effect on metabolite formation.

CONCLUSIONS

Novel plasma protease metabolites of glucagon have been confirmed, and their formation characterised over a time-course experiment and under typical laboratory handling conditions. These metabolites could be monitored to assess the effectiveness of new sample stabilisation strategies, and further investigations into their formation could suggest specific enzyme inhibitors to use to increase sample stability. In addition the potential of the metabolites to affect immunochemistry-based assays as a result of cross-reactivity could be investigated.

Validation of a multiplex electrochemiluminescent immunoassay platform in human and mouse samples

BACKGROUND

Despite the widespread use of multiplex immunoassays, there are very few scientific reports that test the accuracy and reliability of a platform prior to publication of experimental data. Our laboratory has previously demonstrated the need for new assay platform validation prior to use of biologic samples from large studies in order to optimize sample handling and assay performance.

METHODS

In this study, our goal was to test the accuracy and reproducibility of an electrochemiluminescent multiplex immunoassay platform (Meso Scale Discovery, MSD®) and compare this platform to validated, singleplex immunoassays (R&D Systems®) using actual study subject (human plasma and mouse bronchoalveolar lavage fluid (BAL) and plasma) samples.

RESULTS

We found that the MSD platform performed well on intra- and inter-assay comparisons, spike and recovery and cross-platform comparisons. The mean intra-assay CV% and range for MSD were 3.49 (0.0-10.4) for IL-6 and 2.04 (0.1-7.9) for IL-8. The correlation between values for identical samples measured on both MSD and R&D was R=0.97 for both analytes. The mouse MSD assay had a broader range of CV% with means ranging from 9.5 to 28.5 depending on the analyte. The range of mean CV% was similar for single plex ELISAs at 4.3-23.7 depending on the analyte. Regardless of species or sample type, CV% was more variable at lower protein concentrations.

CONCLUSIONS

In conclusion, we validated a multiplex electrochemiluminescent assay system and found that it has superior test characteristics in human plasma compared to mouse BALF and plasma. Both human and MSD assays compared favorably to well-validated singleplex ELISAs.

Sensitive glucagon quantification by immunochemical and LC–MS/MS methods

The peptide hormone glucagon plays an important role in homeostasis of glucose concentrations in the blood. Its biological importance is evidenced through the conservation of its peptide sequence between species. Reliable assays for glucagon in biological samples are important for gaining a better understanding of the pathology and treatment of diabetes. Numerous assays are available for the analysis of glucagon in biological samples, the majority of which employ an immunochemical approach and have been available for many years. However, recent advances in MS instrumentation and the amenability of glucagon for analysis by LC–MS/MS has brought these new methods to the forefront. Concentrations of glucagon determined from different methods are not always consistent and this review provides suggestions of how to improve the reliability of methods for glucagon analysis.