Accurate analytical method for human plasma glucagon levels using liquid chromatography-high resolution mass spectrometry: comparison with commercially available immunoassays

Advances in clinical research on glucagon

We are now celebrating the 100th anniversary of the discovery of an important pancreatic hormone, glucagon. Glucagon is historically described as a diabetogenic hormone elevating glucose levels via increases in insulin resistance and hepatic gluconeogenesis. The more recently identified actions of glucagon include not only its pathophysiologic effects on glucose metabolism but also its significant roles in amino-acid metabolism in the liver. The possibility that abnormalities in α-cells' secretion of glucagon in metabolic disorders are a compensatory adaptation for the maintenance of metabolic homeostasis is another current issue. However, the clinical research concerning glucagon has been considerably behind the advances in basic research due to the lack of suitable methodology for obtaining precise measurements of plasma glucagon levels in humans. The precise physiology of glucagon secretory dynamics in individuals with metabolic dysfunction (including diabetes) has been clarified since the development in 2014 of a quantitative measurement technique for glucagon. In this review, we summarize the advances in the clinical research concerning glucagon, including those of our studies and the relevant literature.

Advances in the clinical measurement of glucagon: from diagnosis to therapy

Glucagon has many functions: it promotes glucose production, fatty acid oxidation, thermogenesis, energy consumption, lipolysis, and myocardial contraction, and suppresses lipogenesis, appetite, and gastrointestinal motility. Which of these functions are physiological and which are pharmacological is not fully understood. Although the Mercodia sandwich ELISA provides significantly higher specificity of glucagon measurement than does conventional competitive RIA, it cannot provide accurate plasma glucagon values in the presence of elevated cross-reacting plasma glicentin. This occurs in patients post-pancreatectomy or bariatric surgery and in around 30% of outpatients suspected for glucose intolerance who have not had surgery. Thus, our newly developed sandwich ELISA with higher specificity and higher sensitivity than the Mercodia sandwich ELISA is needed for accurate measurements of plasma glucagon in diabetic patients. It is expected that the new sandwich ELISA will contribute to personalized medicine for diabetes by its use in clinical tests to accurately diagnose the conditions of diabetic patients in order to design better individual treatment strategies. Meanwhile, clinical trials are being conducted worldwide to apply glucagon/GLP-1 receptor dual agonists and glucagon/GLP-1/GIP receptor triagonists to the treatment of obesity, fatty liver, and diabetes. Most clinical trials have shown that both types of drugs have stronger effects on weight reduction, improving fatty liver, and glucose tolerance than do the single GLP-1 receptor agonists. Glucagon is expected to be used as a new diagnostic marker and in a new therapeutic strategy based on a true understanding of its physiological and pharmacological functions.

Hepatic glucagon action: beyond glucose mobilization

Glucagon's ability to promote hepatic glucose production has been known for over a century, with initial observations touting this hormone as a diabetogenic agent. However, glucagon receptor agonism [when balanced with an incretin, including glucagon-like peptide 1 (GLP-1) to dampen glucose excursions] is now being developed as a promising therapeutic target in the treatment of metabolic diseases, like metabolic dysfunction-associated steatotic disease/metabolic dysfunction-associated steatohepatitis (MASLD/MASH), and may also have benefit for obesity and chronic kidney disease. Conventionally regarded as the opposing tag-team partner of the anabolic mediator insulin, glucagon is gradually emerging as more than just a "catabolic hormone." Glucagon action on glucose homeostasis within the liver has been well characterized. However, growing evidence, in part thanks to new and sensitive "omics" technologies, has implicated glucagon as more than just a "glucose liberator." Elucidation of glucagon's capacity to increase fatty acid oxidation while attenuating endogenous lipid synthesis speaks to the dichotomous nature of the hormone. Furthermore, glucagon action is not limited to just glucose homeostasis and lipid metabolism, as traditionally reported. Glucagon plays key regulatory roles in hepatic amino acid and ketone body metabolism, as well as mitochondrial turnover and function, indicating broader glucagon signaling consequences for metabolic homeostasis mediated by the liver. Here we examine the broadening role of glucagon signaling within the hepatocyte and question the current dogma, to appreciate glucagon as more than just that "catabolic hormone."

Imeglimin enhances glucagon secretion through an indirect mechanism and improves fatty liver in high-fat, high-sucrose diet-fed mice

AIMS/INTRODUCTION

Imeglimin is a recently approved oral antidiabetic agent that improves insulin resistance, and promotes insulin secretion from pancreatic β-cells. Here, we investigated the effects of imeglimin on glucagon secretion from pancreatic α-cells.

MATERIALS AND METHODS

Experiments were carried out in high-fat, high-sucrose diet-fed mice. The effects of imeglimin were examined using insulin and glucose tolerance tests, glucose clamp studies, and measurements of glucagon secretion from isolated islets. Glucagon was measured using both the standard and the sequential protocol of Mercodia sandwich enzyme-linked immunosorbent assay; the latter eliminates cross-reactivities with other proglucagon-derived peptides.

RESULTS

Plasma glucagon, insulin and glucagon-like peptide-1 levels were increased by imeglimin administration in high-fat, high-sucrose diet-fed mice. Glucose clamp experiments showed that the glucagon increase was not caused by reduced blood glucose levels. After both single and long-term administration of imeglimin, glucagon secretions were significantly enhanced during glucose tolerance tests. Milder enhancement was observed when using the sequential protocol. Long-term administration of imeglimin did not alter α-cell mass. Intraperitoneal imeglimin administration did not affect glucagon secretion, despite significantly decreased blood glucose levels. Imeglimin did not enhance glucagon secretion from isolated islets. Imeglimin administration improved fatty liver by suppressing de novo lipogenesis through decreasing sterol regulatory element binding protein-1c and carbohydrate response element binding protein and their target genes, while enhancing fatty acid oxidation through increasing carnitine palmitoyltransferase I.

CONCLUSIONS

Overall, the present results showed that imeglimin enhances glucagon secretion through an indirect mechanism. Our findings also showed that glucagon secretion promoted by imeglimin could contribute to improvement of fatty liver through suppressing de novo lipogenesis and enhancing fatty acid oxidation.

High Doses of Exogenous Glucagon Stimulate Insulin Secretion and Reduce Insulin Clearance in Healthy Humans

Glucagon is generally defined as a counterregulatory hormone with a primary role to raise blood glucose concentrations by increasing endogenous glucose production (EGP) in response to hypoglycemia. However, glucagon has long been known to stimulate insulin release, and recent preclinical findings have supported a paracrine action of glucagon directly on islet β-cells that augments their secretion. In mice, the insulinotropic effect of glucagon is glucose dependent and not present during basal euglycemia. To test the hypothesis that the relative effects of glucagon on hepatic and islet function also vary with blood glucose, a group of healthy subjects received glucagon (100 ng/kg) during fasting glycemia or experimental hyperglycemia (∼150 mg/dL) on 2 separate days. During fasting euglycemia, administration of glucagon caused blood glucose to rise due to increased EGP, with a delayed increase of insulin secretion. When given during experimental hyperglycemia, glucagon caused a rapid, threefold increase in insulin secretion, as well as a more gradual increase in EGP. Under both conditions, insulin clearance was decreased in response to glucagon infusion. The insulinotropic action of glucagon, which is proportional to the degree of blood glucose elevation, suggests distinct physiologic roles in the fasting and prandial states.

ARTICLE HIGHLIGHTS

Glucagon: Physiological and Pharmacological Functions and Pathophysiological Significance in Type 2 Diabetes

Glucagon has many functions, including the promotion of hepatic glucose production, fatty acid oxidation, thermogenesis, energy consumption, lipolysis, and myocardial contraction, as well as the suppression of lipogenesis, appetite, and gastrointestinal motility. However, it remains unclear which of these functions are physiological and which are pharmacological. Research on glucagon has lagged behind research on insulin because cross-reactivity with glucagon-related peptides in plasma has hindered the development of an accurate measurement system for glucagon. We recently developed a new glucagon sandwich enzyme-linked immunosorbent assay (ELISA) that is more specific and more sensitive to glucagon than the currently used measurement systems. The new sandwich ELISA is expected to contribute to personalized medicine for diabetes through its use in clinical examinations, the diagnosis of the pathophysiological condition of individual diabetes patients, and the choice of a treatment strategy. Efforts are continuing to develop glucagon/glucagon-like peptide-1 receptor dual agonists to improve obesity and fatty liver by enhancing glucagon's appetite-suppressing and lipolysis- and thermogenesis-promoting effects. Thus, glucagon is expected to be applied to new diagnostic and therapeutic strategies based on a more accurate understanding of its functions.

Insulin Sensitivity, Islet Cell Function, and Incretin Axis in Pregnant Women With and Without Gestational Diabetes Mellitus

Introduction

The aim of this study was to compare insulin sensitivity, islet cell function, and incretin axes in pregnant subjects with GDM and normal healthy controls.

Methods

Pregnant women at 24 to 28 weeks of gestation were subjected to a 75 g oral glucose tolerance test (OGTT). Samples for glucose, insulin, glucagon, glucagon-like peptide-1 (GLP-1) and glucose-dependent insulinotropic polypeptide (GIP) were collected at 0, 30, 60, and 120 min during the OGTT. The Matsuda index (MI) and insulin secretion and sensitivity index-2 (ISSI-2) were assessed. The glucagon suppression index (GSI) was calculated along with the area under the curve (AUC) for glucose, insulin, glucagon, GLP-1, and GIP.

Results

A total of 48 pregnant women (25 GDM and 23 controls) were finally analysed. The MI and ISSI-2 were low in the GDM group [4.31 vs. 5.42; P = 0.04], [1.99 vs. 3.18, P ≤ 0.01] respectively). Total AUCglucagon was higher in the GDM group (7411.7 vs. 6320.1, P = 0.02). GSI30 was significantly lower in the GDM group (-62.6 vs. -24.7, P = 0.03). Fasting GLP-1 levels were low in GDM women (17.3 vs. 22.2, P = 0.04). The total AUCGLP-1 positively correlated with total GSI in the GDM group.

Conclusion

Asian-Indian GDM women have high insulin insensitivity, islet cell dysfunction, and low fasting GLP-1. Incretin axis dysfunction plays a potential role in their islet cell dysfunction.

Quantitative analysis of therapeutic proteins in biological fluids: recent advancement in analytical techniques

Pharmaceutical application of therapeutic proteins has been continuously expanded for the treatment of various diseases. Efficient and reliable bioanalytical methods are essential to expedite the identification and successful clinical development of therapeutic proteins. In particular, selective quantitative assays in a high-throughput format are critical for the pharmacokinetic and pharmacodynamic evaluation of protein drugs and to meet the regulatory requirements for new drug approval. However, the inherent complexity of proteins and many interfering substances presented in biological matrices have a great impact on the specificity, sensitivity, accuracy, and robustness of analytical assays, thereby hindering the quantification of proteins. To overcome these issues, various protein assays and sample preparation methods are currently available in a medium- or high-throughput format. While there is no standard or universal approach suitable for all circumstances, a liquid chromatography-tandem mass spectrometry (LC-MS/MS) assay often becomes a method of choice for the identification and quantitative analysis of therapeutic proteins in complex biological samples, owing to its high sensitivity, specificity, and throughput. Accordingly, its application as an essential analytical tool is continuously expanded in pharmaceutical R&D processes. Proper sample preparation is also important since clean samples can minimize the interference from co-existing substances and improve the specificity and sensitivity of LC-MS/MS assays. A combination of different methods can be utilized to improve bioanalytical performance and ensure more accurate quantification. This review provides an overview of various protein assays and sample preparation methods, with particular emphasis on quantitative protein analysis by LC-MS/MS.

Tutorial review for peptide assays: An ounce of pre-analytics is worth a pound of cure

The recent increase in peptidomimetic-based medications and the growing interest in peptide hormones has brought new attention to the quantification of peptides for diagnostic purposes. Indeed, the circulating concentrations of peptide hormones in the blood provide a snapshot of the state of the body and could eventually lead to detecting a particular health condition. Although extremely useful, the quantification of such molecules, preferably by liquid chromatography coupled to mass spectrometry, might be quite tricky. First, peptides are subjected to hydrolysis, oxidation, and other post-translational modifications, and, most importantly, they are substrates of specific and nonspecific proteases in biological matrixes. All these events might continue after sampling, changing the peptide hormone concentrations. Second, because they include positively and negatively charged groups and hydrophilic and hydrophobic residues, they interact with their environment; these interactions might lead to a local change in the measured concentrations. A phenomenon such as nonspecific adsorption to lab glassware or materials has often a tremendous effect on the concentration and needs to be controlled with particular care. Finally, the circulating levels of peptides might be low (pico- or femtomolar range), increasing the impact of the aforementioned effects and inducing the need for highly sensitive instruments and well-optimized methods. Thus, despite the extreme diversity of these peptides and their matrixes, there is a common challenge for all the assays: the need to keep concentrations unchanged from sampling to analysis. While significant efforts are often placed on optimizing the analysis, few studies consider in depth the impact of pre-analytical steps on the results. By working through practical examples, this solution-oriented tutorial review addresses typical pre-analytical challenges encountered during the development of a peptide assay from the standpoint of a clinical laboratory. We provide tips and tricks to avoid pitfalls as well as strategies to guide all new developments. Our ultimate goal is to increase pre-analytical awareness to ensure that newly developed peptide assays produce robust and accurate results.

Simultaneous monitoring of multiple hormones from human islets of Langerhans using solid-phase extraction-mass spectrometry

Islets of Langerhans release peptide hormones in controlled amounts and patterns to ensure proper maintenance of blood glucose levels. The overall release of the hormones is shaped by external factors and by autocrine and paracrine interactions occurring within the islets. To better understand what controls the secretion of islet-secreted peptides, and how these processes go awry in diabetes, methods to monitor the release of multiple hormones simultaneously are needed. While antibody-based assays are typically used, they are most often applied to quantification of a single hormone. Mass spectrometry (MS), on the other hand, is well suited for quantifying multiple hormones simultaneously but typically requires time-consuming separation steps with biological samples. In this report, response surface methodology was used to identify a set of optimal solid-phase extraction (SPE) conditions for the islet-secreted peptides, insulin, C-peptide, glucagon, and somatostatin. The optimized SPE method was used with multiple reaction monitoring and isotopically labeled standards to quantify secretion levels. Calibrations were linear from 0.5 to 50 nM with < 15% RSD peak area ratios. A microfluidic system was used to perfuse 30 human islets with different glucose conditions, and fractions were collected every 2 min for SPE-MS analysis. Results showed the release dynamics of the individual peptides, as well as patterns, such as positively and negatively correlated release and oscillations. This rapid SPE-MS method is expected to be useful for examining other peptide and small-molecule secretions from islets and could be applied to a number of other biological systems for investigating cellular communication.

A liquid chromatography tandem mass spectrometry method for plasma glucagon

Glucagon is a peptide involved in controlling the body's blood glucose levels. The majority of analytical methods used for its quantitation are based on immunoassays that suffer from cross-reactivity with other peptides. For accurate routine analysis a liquid chromatography tandem mass spectrometry (LC-MSMS) was developed. Glucagon was extracted from plasma samples by a combination of protein precipitation using ethanol and mixed anion exchange solid phase extraction. Linearity for glucagon was above 0.99 (r²) up to a concentration range of 771 ng/L with a lower limit of quantification established at 19 ng/L. Precision of the method was below 9% (coefficient of variation). Recovery was 93%. Correlations with the existing immunoassay displayed a significant negative bias.

Newly discovered knowledge pertaining to glucagon and its clinical applications

Glucagon has been defined as an 'insulin counteracting hormone', which raises blood glucose levels. Recent progress in basic research has shown that glucagon is closely involved in glucose and amino acid metabolism. Additionally, its secretion is intricately, but precisely, regulated by various mechanisms involving molecules in addition to glucose, thus showing its critical role in systemic nutrient metabolism. An innovative dual-antibody-linked immunosorbent assay for glucagon that improves measurement accuracy has been developed, and substantial clinical findings have been obtained using this new system. This discovery expanded the pathophysiological significance of glucagon and accelerated the development of its clinical applications in diabetes.

A newly developed glucagon sandwich ELISA is useful for more accurate glucagon evaluation than the currently used sandwich ELISA in subjects with elevated plasma proglucagon-derived peptide levels

AIMS/INTRODUCTION

Glucagon, a peptide hormone produced from proglucagon, is involved in the pathophysiology of diabetes. Plasma glucagon levels are currently measured by sandwich enzyme-linked immunosorbent assay (ELISA), but the currently used sandwich ELISA cross-reacts with proglucagon-derived peptides, thereby providing incorrect results in subjects with elevated plasma proglucagon-derived peptide levels. We aimed to develop a more broadly reliable ELISA for measuring plasma glucagon levels.

MATERIALS AND METHODS

A new sandwich ELISA was developed using newly generated monoclonal antibodies against glucagon. After its validation, plasma glucagon levels were measured with the new ELISA and the currently used ELISA in subjects who underwent laparoscopic sleeve gastrectomy (LSG) and in outpatients with suspected glucose intolerance. The ELISA results were compared with those from liquid chromatography-high resolution mass (LC-HRMS) analysis, which we previously established as the most accurate measuring system.

RESULTS

The new ELISA has high specificity (<1% cross-reactivities) and high sensitivity (a lower range of 0.31 pmol/L). Plasma glucagon values in the subjects who underwent laparoscopic sleeve gastrectomy and some outpatients with suspected glucose intolerance differed between the new ELISA and the currently used ELISA. These subjects also showed markedly high plasma glicentin levels. Despite the elevated plasma glicentin levels, the new ELISA showed better positive correlation with LC-HRMS than did the currently used ELISA.

CONCLUSIONS

The new ELISA enables more accurate measurement of plasma glucagon than the currently used ELISA, even in subjects with elevated proglucagon-derived peptide levels. It should be clinically useful in elucidating the pathophysiology of individual diabetic patients.

A reappraisal of the role of cyclic AMP in the physiological action of glucagon

Effects of the metabolic hormone glucagon can be physiological or supraphysiological, based on agonist concentration and the mediating cellular signal. The threshold concentration (TC) for activating the AC/cAMP signal pathway in liver is ≥ 100 pM. By contrast, mean plasma concentrations are around 20-45 pM, depending on the vascular bed. Accordingly, effects produced at TCs below 100 pM are physiological and mediated by cellular signal pathways other than AC/cAMP. Effects generated at concentrations above 100 pM are supraphysiological, often mediated by simultaneous activation of cAMP-independent and -dependent pathways. Physiological responses, and their established or implicated signal pathways, include stimulation of: glucose mobilization, fatty acid oxidation, and urea synthesis in liver (PLC/IP3/Ca²⁺/CaM); lipolysis in white and brown adipose tissue and oxygen consumption in brown adipose of the rat but not in humans (PLC/IP3/Ca²⁺/CaM); renal potassium and phosphate excretion in rodents and GFR in humans (signal undetermined); and glucose utilization in rat heart (PI3K/akt). Supraphysiological responses involve the AC/cAMP pathway and include: enhanced stimulation of glucose mobilization and stimulation of urea synthesis in liver; further stimulation of white and brown adipose lipolysis and thermogenesis in brown adipose tissue; stimulation of renal Cl^- transport; and increased rat heart contractility. The AC/cAMP pathway is likely recruited when plasma glucagon rises above 100 pM during periods of elevated metabolic stress and systemic glucose demand, such as in the early neonate or strenuously exercising adult. The current cAMP-centered model should therefore be reconsidered and replaced with one that places more emphasis on cAMP-independent pathways.

Characteristic changes in plasma glutamate levels and free amino acid profiles in Japanese patients with type 1 diabetes mellitus

AIMS/INTRODUCTION

In addition to absolute insulin deficiency, dysregulated glucagon in type 1 diabetes is considered pathophysiologically important. Previously, we confirmed the presence of dysregulated glucagon in Japanese patients with type 1 diabetes, and found a significant correlation between plasma glucagon and blood urea nitrogen levels, suggesting an association between glucagon and amino acid metabolism. In this study, we evaluated plasma amino acid levels in Japanese patients with type 1 diabetes in the context of their functional relationship with glucagon.

MATERIALS AND METHODS

We assessed plasma free amino acid levels using liquid chromatography-mass spectrometry in 77 Japanese patients with type 1 diabetes, and statistically analyzed their characteristics and relationships with clinical parameters, including glucagon.

RESULTS

Participants with type 1 diabetes showed a large decrease in glutamate levels together with a characteristic change in plasma free amino acid profiles. The network structural prediction analyses showed correlations between each amino acid and glucagon in type 1 diabetes.

CONCLUSIONS

Participants with type 1 diabetes showed characteristic changes in plasma glutamate levels and free amino acid profiles compared with controls and type 2 diabetes patients. Glucagon showed a closer correlation with amino acids than with parameters of glucose metabolism, suggesting that type 1 diabetes includes dysregulation in amino acids through dysregulated glucagon from remaining pancreatic α-cells, together with that in glucose by insulin deficiency.

Effects of luseogliflozin on the secretion of islet hormones and incretins in patients with type 2 diabetes

The insufficient activity of insulin and the hyperactivity of glucagon are responsible for glucose intolerance in patients with type 2 diabetes. Whereas sodium-glucose cotransporter-2 (SGLT2) inhibitors improve blood glucose levels in patients with type 2 diabetes, their effects on the secretion profiles of glucagon and incretins remain unclear. Therefore, to investigate the effects of the SGLT2 inhibitor luseogliflozin on metabolic and endocrine profiles, 19 outpatients with type 2 diabetes were administered luseogliflozin for 12 weeks. It is of note that all subjects were treated only with diet and exercise therapy, and we were able to investigate the effects of luseogliflozin separately from the effects of other antidiabetic agents. Body weight, body fat mass, fat-free mass, and muscle mass were significantly reduced after 12 weeks of luseogliflozin administration. Glycosylated hemoglobin significantly decreased from the baseline of 8.2% ± 0.8% to 7.3% ± 0.7% (p < 0.0001). The meal tolerance test demonstrated that luseogliflozin significantly recovered glucose tolerance, accompanied by improved insulin resistance and β-cell function, whereas glucagon secretion was unaffected. Furthermore, GLP-1 secretion was significantly increased after luseogliflozin administration. Thus, luseogliflozin improved metabolic and endocrine profiles accompanied by increased GLP-1 secretion in type 2 diabetic patients without any antidiabetic medication, but did not affect glucagon secretion.

13C15N: glucagon-based novel isotope dilution mass spectrometry method for measurement of glucagon metabolism in humans

Background

Glucagon serves as an important regulatory hormone for regulating blood glucose concentration with tight feedback control exerted by insulin and glucose. There are critical gaps in our understanding of glucagon kinetics, pancreatic α cell function and intra-islet feedback network that are disrupted in type 1 diabetes. This is important for translational research applications of evolving dual-hormone (insulin + glucagon) closed-loop artificial pancreas algorithms and their usage in type 1 diabetes. Thus, it is important to accurately measure glucagon kinetics in vivo and to develop robust models of glucose-insulin-glucagon interplay that could inform next generation of artificial pancreas algorithms.

Methods

Here, we describe the administration of novel ¹³C¹⁵N heavy isotope-containing glucagon tracers—FF glucagon [(Phe 6 ¹³C₉,¹⁵N; Phe 22 ¹³C₉,¹⁵N)] and FFLA glucagon [(Phe 6 ¹³C₉,¹⁵N; Phe 22 ¹³C₉,¹⁵N; Leu 14 ¹³C₆,¹⁵N; Ala 19 ¹³C₃)] followed by anti-glucagon antibody-based enrichment and LC–MS/MS based-targeted assays using high-resolution mass spectrometry to determine levels of infused glucagon in plasma samples. The optimized assay results were applied for measurement of glucagon turnover in subjects with and without type 1 diabetes infused with isotopically labeled glucagon tracers.

Results

The limit of quantitation was found to be 1.56 pg/ml using stable isotope-labeled glucagon as an internal standard. Intra and inter-assay variability was < 6% and < 16%, respectively, for FF glucagon while it was < 5% and < 23%, respectively, for FFLA glucagon. Further, we carried out a novel isotope dilution technique using glucagon tracers for studying glucagon kinetics in type 1 diabetes.

Conclusions

The methods described in this study for simultaneous detection and quantitation of glucagon tracers have clinical utility for investigating glucagon kinetics in vivo in humans.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12014-022-09344-2.

Glucagon, cyclic AMP, and hepatic glucose mobilization: A half‐century of uncertainty

For at least 50 years, the prevailing view has been that the adenylate cyclase (AC)/cyclic AMP (cAMP)/protein kinase A pathway is the predominant signal mediating the hepatic glucose‐mobilizing actions of glucagon. A wealth of evidence, however, supports the alternative, that the operative signal most of the time is the phospholipase C (PLC)/inositol‐phosphate (IP3)/calcium/calmodulin pathway. The evidence can be summarized as follows: (1) The consensus threshold glucagon concentration for activating AC ex vivo is 100 pM, but the statistical hepatic portal plasma glucagon concentration range, measured by RIA, is between 28 and 60 pM; (2) Within that physiological concentration range, glucagon stimulates the PLC/IP3 pathway and robustly increases glucose output without affecting the AC/cAMP pathway; (3) Activation of a latent, amplified AC/cAMP pathway at concentrations below 60 pM is very unlikely; and (4) Activation of the PLC/IP3 pathway at physiological concentrations produces intracellular effects that are similar to those produced by activation of the AC/cAMP pathway at concentrations above 100 pM, including elevated intracellular calcium and altered activities and expressions of key enzymes involved in glycogenolysis, gluconeogenesis, and glycogen synthesis. Under metabolically stressful conditions, as in the early neonate or exercising adult, plasma glucagon concentrations often exceed 100 pM, recruiting the AC/cAMP pathway and enhancing the activation of PLC/IP3 pathway to boost glucose output, adaptively meeting the elevated systemic glucose demand. Whether the AC/cAMP pathway is consistently activated in starvation or diabetes is not clear. Because the importance of glucagon in the pathogenesis of diabetes is becoming increasingly evident, it is even more urgent now to resolve lingering uncertainties and definitively establish glucagon’s true mechanism of glycemia regulation in health and disease.

Postprandial Dynamics of Proglucagon Cleavage Products and Their Relation to Metabolic Health

INTRODUCTION

While oral glucose ingestion typically leads to a decrease in circulating glucagon levels, a substantial number of persons display stable or rising glucagon concentrations when assessed by radioimmunoassay (RIA). However, these assays show cross-reactivity to other proglucagon cleavage products. Recently, more specific assays became available, therefore we systematically assessed glucagon and other proglucagon cleavage products and their relation to metabolic health.

RESEARCH DESIGN AND METHODS

We used samples from 52 oral glucose tolerance tests (OGTT) that were randomly selected from persons with different categories of glucose tolerance in an extensively phenotyped study cohort.

RESULTS

Glucagon concentrations quantified with RIA were non-suppressed at 2 hours of the OGTT in 36% of the samples. Non-suppressors showed lower fasting glucagon levels compared to suppressors (p=0.011). Similar to RIA measurements, ELISA-derived fasting glucagon was lower in non-suppressors (p<0.001). Glucagon 1-61 as well as glicentin and GLP-1 kinetics were significantly different between suppressors and non-suppressors (p=0.004, p=0.002, p=0.008 respectively) with higher concentrations of all three hormones in non-suppressors. Levels of insulin, C-peptide, and free fatty acids were comparable between groups. Non-suppressors were leaner and had lower plasma glucose concentrations (p=0.03 and p=0.047, respectively). Despite comparable liver fat content and insulin sensitivity (p≥0.3), they had lower 2-hour post-challenge glucose (p=0.01).

CONCLUSIONS

Glucagon 1-61, glicentin and GLP-1 partially account for RIA-derived glucagon measurements due to cross-reactivity of the assay. However, this contribution is small, since the investigated proglucagon cleavage products contribute less than 10% to the variation in RIA measured glucagon. Altered glucagon levels and higher post-challenge incretins are associated with a healthier metabolic phenotype.

Effect of dipeptidyl peptidase-4 inhibitors on postprandial glucagon level in patients with type 2 diabetes mellitus: A systemic review and meta-analysis

AIMS

Hyperglucagonemia occurs in the pathogenesis of type 2 diabetes mellitus (T2DM). In this meta-analysis, we summarized the effects of DPP4 inhibitors on glucagon levels in patients with T2DM.

MATERIALS AND METHODS

Randomized controlled trials (RCTs) comparing the influence of DPP4 inhibitors on circulating glucagon levels with placebo or other oral antidiabetic drugs (OADs) in patients with T2DM were identified by searches of Medline (PubMed), Embase (Ovid), and CENTER (Cochrane Library). Only studies reporting changes in glucagon level presented as total area under the curve (AUC_glucagon) using a meal or oral glucose tolerance test were included. Results were combined using a random-effects model that incorporated potential heterogeneity among the included studies.

RESULTS

A total of 36 RCTs with moderate to high quality were included. Overall, the numbers of T2DM patients included for the meta-analyses comparing DPP4 inhibitors with placebo and other OADs were 4266 and 1652, respectively. Compared to placebo, DPP4 inhibitors significantly reduced circulating glucagon levels (standard mean difference [SMD]: -0.32, 95% CI: -0.40 to -0.24, P<0.001; I^{2 =} 28%). Analysis of subgroups revealed that study characteristics had no significant effect on results, such as study design (parallel group or crossover), number of patients, mean patient age, proportion of men, baseline HbA1c, duration of diabetes, background therapy, treatment duration, or methods for glucagon measurement (all P for subgroup differences >0.05). Moreover, DPP4 inhibitors significantly reduced glucagon levels compared to other OADs (SMD: -0.35, 95% CI: -0.53 to -0.16, P<0.001; I² = 66%), and the reduction in glucagon was greater in comparison with insulin secretagogues than in comparison with non-insulin secretagogues (P for subgroup difference =0.03).

SYSTEMATIC REVIEW REGISTRATION

https://inplasy.com/, identifier INPLASY202280104.

CONCLUSIONS

DPP4 inhibitors are effective at reducing the circulating postprandial glucagon level in T2DM patients.

Disordered branched chain amino acid catabolism in pancreatic islets is associated with postprandial hypersecretion of glucagon in diabetic mice

Dysregulation of glucagon is associated with the pathophysiology of type 2 diabetes. We previously reported that postprandial hyperglucagonemia is more obvious than fasting hyperglucagonemia in type 2 diabetes patients. However, which nutrient stimulates glucagon secretion in the diabetic state and the underlying mechanism after nutrient intake are unclear. To answer these questions, we measured plasma glucagon levels in diabetic mice after oral administration of various nutrients. The effects of nutrients on glucagon secretion were assessed using islets isolated from diabetic mice and palmitate-treated islets. In addition, we analyzed the expression levels of branched chain amino acid (BCAA) catabolism-related enzymes and their metabolites in diabetic islets. We found that protein, but not carbohydrate or lipid, increased plasma glucagon levels in diabetic mice. Among amino acids, BCAAs, but not the other essential or nonessential amino acids, increased plasma glucagon levels. BCAAs also directly increased the intracellular calcium concentration in α cells. When BCAAs transport was suppressed by an inhibitor of system L-amino acid transporters, glucagon secretion was reduced even in the presence of BCAAs. We also found that the expression levels of BCAA catabolism-related enzymes and their metabolite contents were altered in diabetic islets and palmitate-treated islets compared to control islets, indicating disordered BCAA catabolism in diabetic islets. Furthermore, BCKDK inhibitor BT2 suppressed BCAA-induced hypersecretion of glucagon in diabetic islets and palmitate-treated islets. Taken together, postprandial hypersecretion of glucagon in the diabetic state is attributable to disordered BCAA catabolism in pancreatic islet cells.

Measurement of Plasma Glucagon Levels Using Mass Spectrometry in Patients with Type 2 Diabetes on Maintenance Hemodialysis

BACKGROUND

Recently, attention has been focused on the effect of glucagon on blood glucose variability. The dynamics of glucagon have attracted attention as a new target in the treatment of diabetes patients. However, the dynamics of glucagon in hemodialysis (HD) patients with type 2 diabetes mellitus (T2DM) remain unclear.

OBJECTIVES

The aim of this study was to assess the dynamics of glucagon in HD patients with T2DM.

MATERIALS AND METHODS

We measured plasma glucagon in HD patients with T2DM by liquid chromatography-high-resolution mass spectrometry (LC-HRMS), sandwich enzyme-linked immunosorbent assay (ELISA), and radioimmunoassay (RIA). The glucagon levels measured by each method were compared. We used the glucagon levels determined by our developed LC-HRMS method as the standard in this study.

RESULTS

Plasma glucagon levels measured by LC-HRMS before HD were significantly higher than those measured after HD. Plasma glucagon levels measured using sandwich ELISA had a significantly higher correlation with those measured using LC-HRMS compared with RIA.

CONCLUSIONS

This was the first study to assess glucagon levels in HD patients with T2DM using LC-HRMS, which is considered a highly accurate method. Sandwich ELISA was shown to measure glucagon levels accurately as well.

Pseudo-hyperglucagonemia was observed in pancreatectomized patients when measured by glucagon sandwich enzyme-linked immunosorbent assay

Glucagon is detected in plasma even after total pancreatectomy, and it is debated whether this glucagon is derived from the gastrointestinal tract. Here, we applied sandwich enzyme-linked immunosorbent assay (ELISA) and liquid chromatography-high-resolution mass spectrometry to measure plasma glucagon levels in one patient after partial pancreatectomy (one-seventh of the pancreas remaining) and three patients after total pancreatectomy. Sandwich ELISA detected higher glucagon levels in pancreatectomy patients than in healthy individuals. In contrast, liquid chromatography-high-resolution mass spectrometry showed that plasma glucagon levels in pancreatectomy patients were below the lower limit of quantification. Plasma glucagon measured by sandwich ELISA showed a striking correlation with plasma glicentin, suggesting cross-reaction with this gastrointestinal glucagon-related peptide. These results indicated that pancreatectomized patients falsely showed pseudo-hyperglucagonemia when measured by glucagon sandwich ELISA.

Variation in plasma glucagon levels according to obesity status in Japanese Americans with normal glucose tolerance

Japanese Americans living in the United States are genetically identical to Japanese people, but have undergone a rapid and intense westernization of their lifestyle. This study investigated variability in glucagon secretion after glucose loading among Japanese Americans with normal glucose tolerance (NGT) according to obesity status. The 75-g oral glucose tolerance test (OGTT) was performed for 138 Japanese Americans (aged 40-75 years) living in Los Angeles. Plasma glucagon levels measured using the sandwich enzyme-linked immunosorbent assay were compared according to body mass index (BMI) categories among 119 individuals with NGT. The individuals were classified into three categories according to their BMI values: <22 kg/m² (n = 37), 22-24.9 kg/m² (n = 46), and ≥25 kg/m² (n = 36). Fasting plasma glucagon levels and glucagon-area under the curve levels during the OGTT were the highest in the BMI ≥25 kg/m² group. Fasting glucagon levels were correlated with BMI (r = 0.399, p < 0.001), fasting insulin levels (r = 0.275, p = 0.003) and the homeostasis model assessment-insulin resistance (r = 0.262, p = 0.004). In conclusion, our findings suggest that fasting hyperglucagonemia is associated with obesity and insulin resistance even during the NGT stage in the Japanese American population.

Impact of glucagon response on early postprandial glucose excursions irrespective of residual β-cell function in type 1 diabetes: A cross-sectional study using a mixed meal tolerance test

Aims/Introduction

Controlling postprandial glucose levels in patients with type 1 diabetes is challenging even under the adequate treatment of insulin injection. Recent studies showed that dysregulated glucagon secretion exacerbates hyperglycemia in type 2 diabetes patients, but little is known in type 1 diabetes patients. We investigated whether the glucagon response to a meal ingestion could influence the postprandial glucose excursion in patients with type 1 diabetes.

Materials and Methods

We enrolled 34 patients with type 1 diabetes and 23 patients with type 2 diabetes as controls. All patients underwent a liquid mixed meal tolerance test. We measured levels of plasma glucose, C‐peptide and glucagon at fasting (0 min), and 30, 60 and 120 min after meal ingestion. All type 1 diabetes patients received their usual basal insulin and two‐thirds of the necessary dose of the premeal bolus insulin.

Results

The levels of plasma glucagon were elevated and peaked 30 min after the mixed meal ingestion in both type 1 diabetes and type 2 diabetes patients. The glucagon increments from fasting to each time point (30, 60 and 120 min) in type 1 diabetes patients were comparable to those in type 2 diabetes patients. Among the type 1 diabetes patients, the glucagon response showed no differences between the subgroups based on diabetes duration (<5 vs ≥5 years) and fasting C‐peptide levels (<0.10 vs ≥0.10 nmol/L). The changes in plasma glucose from fasting to 30 min were positively correlated with those in glucagon, but not C‐peptide, irrespective of diabetes duration and fasting C‐peptide levels in patients with type 1 diabetes.

Conclusions

The dysregulated glucagon likely contributes to postprandial hyperglycemia independent of the residual β‐cell functions during the progression of type 1 diabetes.

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.

Plasma glucagon levels measured by sandwich ELISA are correlated with impaired glucose tolerance in type 2 diabetes

Glucagon dysfunction as well as insulin dysfunction is associated with the pathogenesis of type 2 diabetes (T2DM). However, it is still unclear whether the measurement of plasma glucagon levels is useful in understanding the pathophysiology of T2DM. We recently reported that sandwich ELISA provides more accurate plasma glucagon values than conventional RIA in healthy subjects. Here we used sandwich ELISA as well as RIA to assess plasma glucagon levels, comparing them in T2DM patients and healthy subjects during oral glucose (OGTT) or meal tolerance tests (MTT). We confirmed that sandwich ELISA was able to detect more significant difference between healthy subjects and T2DM patients in the fasting levels and the response dynamics of plasma glucagon than RIA. We also found significant differences in the following glucagon parameters: (1) fasting glucagon, (2) the area under the curve (AUC) of glucagon in OGTT, and (3) the change in glucagon between 0 and 30 min (ΔGlucagon_0-0.5h) in OGTT or MTT. Among these, the most apparent difference was ΔGlucagon_0-0.5h in MTT. When we divided T2DM patients into two groups whose ΔGlucagon_0-0.5h in MTT was either below or above the maximum value in healthy subjects, the group with higher ΔGlucagon_0-0.5h showed more significant impairment of glucose tolerance. These results suggest that the assessment of plasma glucagon levels by sandwich ELISA might enhance our understanding of the pathophysiology of T2DM.

Beginning of a new era in glucagon research: Breakthrough by the new glucagon assay

There is a new concept of diabetes as a "comprehensive nutrition disorder", caused due to both insulin and glucagon dysregulation. Dysregulated glucagon secretion in α-cells exacerbates multiple metabolic disorders: glycemic control and amino acid metabolism, together with insulin deficiency.

Parallel Reaction Monitoring Mass Spectrometry Method for Detection of Both Casein and Whey Milk Allergens from a Baked Food Matrix

Milk allergy is among the most common food allergies present in early childhood, which in some cases may persist into adulthood as well. Proteins belonging to both casein and whey fractions of milk can trigger an allergic response in susceptible individuals. Milk is present as an ingredient in many foods, and it can also be present as casein- or whey-enriched milk-derived ingredients. As whey proteins are more susceptible to thermal processing than caseins, conventional methods often posed a challenge in accurate detection of whey allergens, particularly from a processed complex food matrix. In this study, a targeted mass spectrometry method has been developed to detect the presence of both casein and whey allergens from thermally processed foods. A pool of 19 candidate peptides representing four casein proteins and two whey proteins was identified using a discovery-driven target selection approach from various milk-derived ingredients. These target peptides were evaluated by parallel reaction monitoring of baked cookie samples containing known amounts of nonfat dry milk (NFDM). The presence of milk could be detected from baked cookies incurred with NFDM at levels as low as 1 ppm using seven peptides representing α-, β-, and κ-casein proteins and three peptides representing a whey protein, β-lactoglobulin, by this consensus PRM method.

Favourable effect of the sodium-glucose co-transporter-2 inhibitor canagliflozin plus the dipeptidyl peptidase-4 inhibitor teneligliptin in combination on glycaemic fluctuation: An open-label, prospective, randomized, parallel-group comparison trial (the CALMER study)

This multicentre, prospective, randomized, open-label, blinded-endpoint, parallel-group, short-term (4-5 weeks) controlled trial was conducted to investigate the superiority of the effect of reducing mean amplitude of glycaemic excursions (MAGE) during meal tolerance tests (MTTs) for the combination of dipeptidyl peptidase-4 (DPP-4) inhibitor and sodium-glucose co-transporter-2 (SGLT2) inhibitor compared with SGLT2 inhibitor monotherapy. Ninety-nine patients with type 2 diabetes who were taking teneligliptin (20 mg/d) were randomized to one of the following two groups: those who switched to 100 mg/d of canagliflozin (SWITCH group) or those who added 100 mg/d of canagliflozin (COMB group). MAGE in the COMB group was significantly decreased compared with that in the SWITCH group (COMB 117.5 ± 39.8 to 92.2 ± 28.0 mg/dL vs SWITCH 110.7 ± 29.8 to 104.2 ± 27.6 mg/dL; P<0.01). Mean blood glucose decreased significantly during MTTs in both groups, although the extent of the reduction was significantly greater in the COMB group (COMB 142.3 ± 28.7 to 119.5 ± 25.1 mg/dL vs SWITCH 146.4 ± 25.5 to 135.5 ± 22.4 mg/dL; P < 0.01). SGLT2 inhibitor combined with DPP-4 inhibitor therapy strongly reduced glycaemic fluctuation compared with SGLT2 inhibitor monotherapy.

Consistency of plasma glucagon levels in patients with type 1 diabetes after a 1-year period

Recent progress in research on glucagon and α-cells highlights their pathophysiological roles in diabetes. We previously showed that plasma glucagon levels measured by newly developed enzyme-linked immunosorbent assay were dysregulated in patients with type 1 diabetes with respect to plasma glucose levels, suggesting dysregulated secretion. In the current study, the annual change in plasma glucagon levels was assessed in these same patients. We found that the plasma glucagon levels in the 66 Japanese patients involved in the study were significantly correlated between both years. In addition, they were significantly associated with serum blood urea nitrogen levels in a multivariate linear regression analysis, as reported in our previous study. The statistical correlation in glucagon levels between annual checkups and the sustained significant correlation between glucagon and blood urea nitrogen suggest a constant dysregulation of glucagon in association with altered amino acid metabolism in patients with type 1 diabetes.

Effect of Combination Therapy of Canagliflozin Added to Teneligliptin Monotherapy in Japanese Subjects with Type 2 Diabetes Mellitus: A Retrospective Study

Recently, dipeptidyl peptidase-4 (DPP-4) inhibitors and sodium-glucose cotransporter 2 (SGLT2) inhibitors have been very often used in subjects with type 2 diabetes mellitus (T2DM). In addition, combination drugs of both inhibitors have attracted much attention in aspects of its cost-effectiveness and improvement of patients' adherence. However, it is still poorly understood which factors are related to the efficacy of SGLT2 inhibitors as add-on therapy to DPP-4 inhibitors. Therefore, we aimed to elucidate in which type of individuals and/or under which conditions canagliflozin as add-on therapy to teneligliptin could exert more beneficial effects on glycemic control and/or renal protection. We retrospectively analyzed 56 Japanese subjects with T2DM in the real-world clinical practice. Three months after starting the combination therapy, the change of HbA1c (ΔHbA1c) was strongly related to HbA1c levels at baseline. As expected, serum glucagon level was increased after starting the combination therapy. Interestingly, however, the change of glucagon levels (Δglucagon) was not related to HbA1c levels at baseline, ΔHbA1c, and other parameters, which indicated that the increase of glucagon did not clinically affect the effectiveness of combination therapy. In addition, the change of urinary albumin excretion (ΔUAE) was negatively correlated with systolic blood pressure and HbA1c levels at baseline and positively correlated with the change of systolic blood pressure (ΔsBP) in univariate analysis. Furthermore, in multivariate analysis, only ΔsBP was the independent factor associated with ΔUAE. Taken together, canagliflozin as add-on therapy to teneligliptin improves glycemic control in a Δglucagon-independent manner and reduces UAE in a ΔsBP-dependent manner in Japanese subjects with T2DM.

Impaired early-phase suppression of glucagon secretion after glucose load is associated with insulin requirement during pregnancy in gestational diabetes

AIMS/INTRODUCTION

The role of glucagon abnormality has recently been reported in type 2 diabetes; however, its role in gestational diabetes mellitus (GDM) is still unknown. The glucose intolerance in GDM is heterogeneous, and not all patients require insulin treatment during pregnancy. Here, we investigated whether glucagon abnormality is associated with the requirement for insulin treatment during pregnancy.

MATERIALS AND METHODS

A total of 49 pregnant women diagnosed with GDM were enrolled. They underwent a 75-g oral glucose tolerance test during mid-gestation, and we measured their plasma glucagon levels (by a new sandwich enzyme-linked immunosorbent assay) at fasting (0 min), and at 30, 60 and 120 min after glucose load in addition to the levels of plasma glucose and serum insulin. All participants underwent another oral glucose tolerance test at postpartum.

RESULTS

Of the 49 patients, 15 required insulin treatment (Insulin group) and 34 were treated with diet therapy alone until delivery (Diet group). The early-phase glucagon secretion after glucose load, as determined by the changes in glucagon from the baseline to 30 min, was paradoxically augmented during mid-gestation in the Insulin group, but not in the Diet group. The impaired glucagon suppression during mid-gestation in the Insulin group was not associated with insulin secretory/sensitivity indexes studied, and was ameliorated postpartum, although the plasma glucose levels remained higher in the Insulin group versus the Diet group.

CONCLUSIONS

Impaired early-phase suppression of glucagon could be associated with the requirement for insulin treatment during pregnancy in patients with GDM.

Effects of anagliptin on plasma glucagon levels and gastric emptying in patients with type 2 diabetes: An exploratory randomized controlled trial versus metformin

AIMS

Glucagon has an important role in glucose homeostasis. Recently, a new plasma glucagon assay based on liquid chromatography-high resolution mass spectrometry was developed. We evaluated the influence of a dipeptidyl peptidase-4 inhibitor (anagliptin) on plasma glucagon levels in Japanese patients with type 2 diabetes by using this new assay.

METHODS

Twenty-four patients with type 2 diabetes were enrolled in a prospective, single-center, randomized, open-label study and were randomly allocated to 4 weeks of treatment with metformin (1000 mg/day) or anagliptin (200 mg/day). A liquid test meal labeled with sodium [¹³C] acetate was ingested before and after the treatment period. Samples of blood and expired air were collected over 3 h. Plasma levels of glucose, glucagon, C-peptide, glucagon-like peptide-1 (GLP-1), and glucose-dependent insulinotropic polypeptide (GIP) were measured, and gastric emptying was also evaluated.

RESULTS

Twenty-two patients completed the study (metformin group: n = 10; anagliptin group: n = 12). Glycemic control showed similar improvement in both groups. In the anagliptin group, there was a slight decrease of the incremental area under the plasma concentration versus time curve for glucagon after the test meal (P = 0.048). In addition, the plasma level of active GLP-1 and GIP was increased, and plasma C-peptide was also increased versus baseline. Neither anagliptin nor metformin delayed gastric emptying.

CONCLUSIONS

In patients with type 2 diabetes maintained endogenous insulin secretion, anagliptin increased the plasma level of active GLP-1 and GIP in association with a slight stimulation of insulin secretion and slight inhibition of glucagon secretion, but did not delay gastric emptying. Clinical Trial Registry: University hospital Medical Information Network UMIN000028293.

Quantitative Proteomic and Network Analysis of Differentially Expressed Proteins in PBMC of Friedreich's Ataxia (FRDA) Patients

Friedreich’s ataxia (FRDA) is an autosomal recessive neurodegenerative disorder caused by an expanded (GAA) trinucleotide repeat in the FXN gene. The extended repeats expansion results in reduced transcription and, thereby, decreased expression of the mitochondrial protein, frataxin. Given the ongoing drug trials, identification of reliable and easily accessible biomarkers for monitoring disease progression and therapeutic intervention is a foremost requirement. In this study, comparative proteomic profiling of PBMC proteins from FRDA patients and age- and gender-matched healthy controls was done using 2D-Differential in-Gel Electrophoresis (2D-DIGE). Protein–protein interaction (PPI) was analyzed using BioGRID and STRING pathway analysis tools. Using biological variance analysis (BVA) and LC/MS, we found eight differentially expressed proteins with fold change ≥1.5; p ≤ 0.05. Based on their cellular function, the identified proteins showed a strong pathological role in neuroinflammation, cardiomyopathy, compromised glucose metabolism, and iron transport, which are the major clinical manifestations of FRDA. Protein–protein network analysis of differentially expressed proteins with frataxin further supports their involvement in the pathophysiology of FRDA. Considering their crucial role in the cardiac and neurological complications, respectively, the two down-regulated proteins, actin α cardiac muscle 1 (ACTC1) and pyruvate dehydrogenase E1 component subunit β (PDHE1), are suggested as potential prognostic markers for FRDA.

Concurrent Use of Teneligliptin and Canagliflozin Improves Glycemic Control with Beneficial Effects on Plasma Glucagon and Glucagon-Like Peptide-1: A Single-Arm Study

INTRODUCTION

We investigated the mechanisms of the glucose-lowering effects of teneligliptin and canagliflozin, a sodium-glucose cotransporter-2 (SGLT2) inhibitor, by monitoring several gastrointestinal peptides using the most appropriate measuring methods during multiple meal tolerance tests (MTTs) and flash glucose monitoring.

METHODS

Twelve Japanese patients with type 2 diabetes were enrolled in the 14-day study. Subjects were treated with teneligliptin 20 mg/day from day 4, followed by a combination tablet of teneligliptin 20 mg and canagliflozin 100 mg (T/C) per day from day 11. MTTs were conducted on days 3 (premedication; Pre), 10 (teneligliptin; T) and 13 (T/C) to evaluate plasma glucose, C-peptide, glucagon, active glucagon-like peptide-1 (GLP-1), active gastric inhibitory polypeptide (GIP), ghrelin and des-acyl ghrelin.

RESULTS

Plasma glucose was significantly decreased with the progress of treatment intervention, and C-peptide was significantly decreased in T/C compared to the others. Plasma postprandial glucagon was increased for 90 min from fasting in Pre, but only for 30 min in T and T/C. Plasma postprandial active GLP-1 was significantly increased in T compared to Pre, and that of T/C was significantly higher than T. Plasma postprandial active GIP was increased in T and T/C compared to Pre. Plasma ghrelin and des-acyl ghrelin levels did not change during the treatment.

CONCLUSION

Teneligliptin increased incretin hormones and suppressed postprandial glucagon secretion as expected. Concurrent use of canagliflozin and teneligliptin improved glycemic control without increasing postprandial glucagon secretion, and increased postprandial GLP-1 secretion and decreased the required amount of postprandial insulin secretion. The underlying mechanisms may involve canagliflozin's inhibitory activity against not only SGLT2 but also SGLT1.

TRIAL REGISTRATION

UMIN identifier, UMIN000030043.

FUNDING

Mitsubishi Tanabe Pharma Corporation and a Grant for Clinical Research from Miyazaki University Hospital.

Basal glucagon hypersecretion and response to oral glucose load in prediabetes and mild type 2 diabetes

Dysregulation of glucagon secretion plays an important role in the pathogenesis of type 2 diabetes (T2DM). However it hasn't been elucidated involvement of glucagon dysregulation in pathophysiology of T2DM. Recently a new glucagon sandwich enzyme-linked immunosorbent assay (ELISA) became available that can measure plasma glucagon level with higher accuracy and simpler procedure than the conventional RIA method. We performed OGTT for adult subjects aged 20-69 years to define normal glucose tolerance (NGT, n = 25), borderline glucose intolerance (defined as pre-diabetes mellitus: preDM, n = 15), or diabetes mellitus (DM, n = 13), and we measured glucagon levels with this new ELISA method at fasting and during OGTT. Plasma glucose, insulin, glucagon and active GLP-1 were also measured. This study took place in diabetes outpatient clinic in Kitasato University Hospital and an affiliated outpatient clinic. PreDM and DM exhibited higher fasting plasma glucagon levels than NGT (34.4 ± 4.6 and 44.1 ± 5.0 vs. 20.6 ± 3.6 pg/mL), and statistical significance was observed between NGT and DM (p < 0.05). There was significant correlation between fasting glucagon level and indexes of insulin sensitivity. During OGTT, glucagon levels were less suppressed in DM and preDM than in NGT, whereas no apparent relationship was observed between glucagon and GLP-1 secretion. Significant positive correlation was observed between glucagon levels during OGTT and fasting TG. In conclusion, subjects with mild T2DM exhibited fasting hyperglucagonemia and insufficient suppression to oral glucose load compared to NGT subjects.

Effects of sodium-glucose cotransporter 2 inhibitor (dapagliflozin) on food intake and plasma fibroblast growth factor 21 levels in type 2 diabetes patients

The objective of this study was to investigate whether sodium-glucose cotransporter 2 inhibitors (SGLT2i) treatment in patients with type 2 diabetes induced compensatory hyperphagia by reducing fibroblast growth factor 21 (FGF21) secretion. This prospective study was performed in 26 type 2 diabetes patients treated with dapagliflozin (5 mg/day). Hormonal factors associated with glucose metabolism, dietary intakes estimated by brief self-administered diet-history questionnaire (BDHQ), body weight (BW), and body composition were measured at baseline, and 4 and 12 weeks after dapagliflozin. At 12 weeks, HbA1c levels and BW decreased significantly (both p < 0.0001). BMI at baseline was predictive to baseline log₁₀ (FGF21) (p = 0.037). This study showed no change in FGF21, but insulin and glucagon levels decreased significantly (both p < 0.05). Although hyperphagia was found in 10 patients (38.5%), defining hyperphagia as >20% increase in carbohydrate intake, dapagliflozin treatment induced no hyperphagia, when analyzed by all subjects, and there was no significant association between changes in FGF21 levels and carbohydrate intake. On the other hand, a positive correlation between changes in FGF21 levels or carbohydrate intake and BW was observed (both p < 0.005). Taken together, this study demonstrates that the intervention to maintain the reduced levels in FGF21 is beneficial for BW reduction in type 2 diabetes patients treated with SGLT2i.

Positive correlation between fasting plasma glucagon and serum C-peptide in Japanese patients with diabetes

Aims

Glucagon plays pivotal roles in systemic glucose homeostasis mainly by promoting hepatic glucose output. Using a sandwich enzyme-linked immunosorbent assay (ELISA), we evaluated fasting plasma glucagon levels in hospitalized patients with type 1 or type 2 diabetes, and assessed the relationships between glucagon levels and various clinical parameters.

Methods

We enrolled adult Japanese diabetes patients admitted to Osaka University Medical Hospital for glycemic control between July 2017 and May 2018 in this study. After patients had fasted for 12 h, blood samples were obtained and plasma glucagon levels were measured using a sandwich ELISA.

Results

Total 107 patients participated in the study. The mean fasting plasma glucagon level of patients with acute onset type 1 diabetes was significantly lower than that of patients with type 2 diabetes (p < 0.05). Plasma glucagon levels were not significantly correlated with plasma glucose levels in patients with type 1 diabetes or in patients with type 2 diabetes. Multiple regression analysis indicated that fasting glucagon levels were independently and significantly correlated with fasting serum C-peptide levels in patients with type 2 diabetes.

Conclusions

Our results suggest that insulin and glucagon secretion are balanced in the fasting state in patients with type 2 diabetes.

Contribution of pancreatic α-cell function to insulin sensitivity and glycemic variability in patients with type 1 diabetes

AIMS/INTRODUCTION

To evaluate the contribution of pancreatic α-cell function to the dawn phenomenon, insulin sensitivity, hepatic glucose uptake and glycemic variability in patients with type 1 diabetes.

MATERIALS AND METHODS

In 40 patients with type 1 diabetes, arginine stimulation tests were carried out, and the area under the curve (AUC) of glucagon was measured using radioimmunoassays (AUCglc RIA ) and enzyme-linked immunosorbent assays (AUCglc ELISA ). The ratio of the insulin dose delivered by an artificial pancreas to maintain euglycemia between 04.00 and 08.00 hours or between 00.00 and 04.00 hours was measured as the dawn index. The glucose infusion rate and hepatic glucose uptake were measured using hyperinsulinemic euglycemic clamp and clamp oral glucose loading tests. Glycemic variability in 96 h was measured by continuous glucose monitoring.

RESULTS

The median dawn index (1.7, interquartile range 1.0-2.8) was not correlated with AUCglc RIA (R2  = 0.03, P = 0.39) or AUCglc ELISA (R2  = 0.04, P = 0.32). The median glucose infusion rate (7.3 mg/kg/min, interquartile range 6.4-9.2 mg/kg/min) was significantly correlated with AUCglc RIA (R2  = 0.20, P = 0.02) and AUCglc ELISA (R2  = 0.21, P = 0.02). The median hepatic glucose uptake (65.3%, interquartile range 40.0-87.3%) was not correlated with AUCglc RIA (R2  = 0.07, P = 0.26) or AUCglc ELISA (R2  = 0.26, P = 0.79). The standard deviation of glucose levels measured by continuous glucose monitoring was significantly correlated with AUCglc RIA (R2  = 0.11, P = 0.049), but not with AUCglc ELISA (R2  = 0.01, P = 0.75).

CONCLUSIONS

Pancreatic α-cell function contributed to insulin sensitivity in patients with type 1 diabetes.

Glucagon secretions are impaired in patients with fulminant type 1 diabetes

Arginine‐challenge test in various types of diabetes.

Mechanistic insights from sequential combination therapy with a sodium glucose co-transporter-2 inhibitor and a dipeptidyl peptidase-4 inhibitor: Results from the CANARIS Trial using canagliflozin and teneligliptin

AIM

To elucidate the mechanisms involved in the sequential use of SGLT2 and DPP4 inhibitors (SGLT2i and DPP-4i).

METHODS

Twenty-six type-2 diabetes mellitus patients were recruited into a stepped regimen of 100 mg of canagliflozin daily from day 1, supplemented with 20 mg of teneligliptin daily from day 4. Glucose (Glu), insulin and glucagon were measured at fasting and after ingesting a mixed meal on days 1, 4 and 6.

RESULTS

Canagliflozin decreased fasting plasma glucose to an extent inversely proportional to the change in the glucagon-to-insulin (G/I) ratio. This correlation at fasting was maintained when adding teneligliptin, while the change in the area under the curve of Glu (GluAUC) correlated closely with that in the G/I ratio at fasting and 60 min with canagliflozin. Moreover, these correlations persisted at 60 and 120 min postprandially, but not at fasting on day 6 when teneligliptin was added.

CONCLUSION

The result suggested that the dominant mechanism responsible for the glucose metabolism reflected in the G/I ratio was attributable to SGLT2i and that its active mechanism persisted, despite adding a DPP-4i.

Response to "Preserved" glucagon secretion in fulminant type 1 diabetes

We compared the glucagon responses to arginine stimulation in five patients with fulminant type 1 diabetes and five age- and diabetes duration-matched acute-onset type 1 diabetes, and the curves of the glucagon responses were similar. In our study, we measured the glucagon levels by not only radioimmunoassay, but also novel enzyme-linked immunosorbent assay.

Postprandial Plasma Glucagon Kinetics in Type 2 Diabetes Mellitus: Comparison of Immunoassay and Mass Spectrometry

CONTEXT

Accurate glucagon level measurements are necessary for investigation of mechanisms for postprandial hyperglycemia in type 2 diabetes.

OBJECTIVE

To evaluate the accuracy of postprandial glucagon level measurements using a sandwich ELISA vs a recently established liquid chromatography-high resolution mass spectrometry (LC-HRMS) method in type 2 diabetes mellitus.

DESIGN AND PARTICIPANTS

Twenty patients with type 2 diabetes treated with insulin underwent a meal test before and after administration of the dipeptidyl peptidase-4 inhibitor anagliptin for 4 weeks. Blood samples were taken serially after the meal, and glucagon levels were measured using both ELISA and LC-HRMS. We compared the change from baseline to 4 weeks (Δ0-4W) using the area under the curve for plasma glucagon during the meal test [area under the curve (AUC)0-3h] measured using ELISA and LC-HRMS.

RESULTS

ELISA-based glucagon AUC0-3h was higher than LC-HRMS-based AUC0-3h at baseline and 4 weeks. However, differences in Δ0-4W-AUC0-3h measured using ELISA and LC-HRMS were not statistically significant. Additionally, Δ0-4W-AUC0-3h measured using ELISA and LC-HRMS were strongly correlated (r = 0.87, P < 0.001).

CONCLUSIONS

Plasma glucagon levels during a meal test in patients with type 2 diabetes measured using ELISA were consistently higher than those measured using LC-HRMS. However, given that the changes in glucagon levels measured using ELISA before and after dipeptidyl peptidase-4 inhibitor therapy were similar to those based on LC-HRMS, this ELISA seems to be useful for evaluating the effect of the drug interventions on postprandial glucagon levels.

Dysregulated plasma glucagon levels in Japanese young adult type 1 diabetes patients

Currently, the clinical dynamics of glucagon need to be revised based on previous data obtained from conventional glucagon radioimmunoassays. In the present study, we evaluated plasma glucagon levels in type 1 diabetes patients using a newly-developed sandwich enzyme-linked immunosorbent assay, and its association with clinical parameters and markers of diabetes complications were statistically assessed. The plasma glucagon level in 77 Japanese type 1 diabetes patients was 28.1 ± 17.7 pg/mL, and comparable with that reported previously for type 2 diabetes patients. However, the values were widely spread and did not correlate with plasma glucose values. Additionally, the average glucagon levels in patients in a hypoglycemic state (glucose level <80 mg/dL) did not increase (21.7 ± 12.2 pg/mL). The average glucagon level of patients experiencing hypoglycemia unawareness was significantly lower. Plasma glucagon levels evaluated using the new enzyme-linked immunosorbent assay were dysregulated in type 1 diabetes patients in respect to plasma glucose levels, suggesting dysregulation of secretion.

Multiplex Assay for Quantification of Acute Phase Proteins and Immunoglobulin A in Dried Blood Spots

Inflammation is the first line defense mechanism against infection, tissue damage, or cancer development. However, inappropriate inflammatory response may also trigger diseases. The quantification of inflammatory proteins is essential to distinguish between harmful and beneficial immune response. Currently used immunoanalytical assays may suffer specificity issues due to antigen-antibody interaction and possible cross-reactivity of antibody with other protein species. In addition, immunoanalytical assays typically require invasive blood sampling and additional logistics; they are relatively costly and highly challenging to multiplex. We present a multiplex assay based on selected reaction monitoring (SRM) for quantification of seven acute-phase proteins (i.e., SAA1, SAA2-isoform1, SAA4, CRP, A1AT-isoform1, A1AG1, A1AG2) and the adaptive immunity effector IGHA1 in dried blood spots. This type of sample is readily available from all human subjects including newborns. The study utilizes proteotypic isotopically labeled peptides with trypsin-cleavable tag and presents optimized and reproducible workflow and several important practical remarks regarding quantitative SRM assays development. The panel of inflammatory proteins was quantified with sequence specificity capable to differentiate protein isoforms with intra- and interday precision (<16.4% coefficient of variation (CV) and <14.3% CV, respectively). Quantitative results were correlated with immuno-nephelometric assay (typically greater than 0.9 Pearson's R).

Comparative study of the effects of ipragliflozin and sitagliptin on multiple metabolic variables in Japanese patients with type 2 diabetes: A multicentre, randomized, prospective, open-label, active-controlled study

In the present randomized study, we assessed the efficacy of ipragliflozin compared with sitagliptin in 124 Japanese patients with type 2 diabetes. Sodium-glucose co-transporter-2 inhibitor-naïve and incretin-related agent-naïve patients were randomly assigned to receive additional 50 mg ipragliflozin or sitagliptin. The primary endpoint was the proportion of participants with >0.5% decrease in glycated haemoglobin (HbA1c) without body weight gain at 12 weeks. For secondary endpoints, we measured several biomarkers related to metabolic changes. After 12 weeks, 53.9% of participants in the ipragliflozin and 42.9% in the sitagliptin group reached the primary endpoint (P = 0.32). Decreases in homeostatic model assessment of insulin resistance, body fat percentage and skeletal muscle mass index, and increases in free fatty acids, ketone body concentration and HDL cholesterol levels were greater in the ipragliflozin group. Increases in homeostatic model assessment of β-cell function and decreases in proinsulin-to-insulin ratio were greater in the sitagliptin group. No serious adverse events occurred in either group. In conclusion, ipragliflozin had beneficial effects on fat reduction, insulin resistance and lipid metabolism, while sitagliptin had beneficial effects on β-cell function.