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

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.

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.

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.

The role of glucagon after bariatric/metabolic surgery: much more than an "anti-insulin" hormone

The biological activity of glucagon has recently been proposed to both stimulate hepatic glucose production and also include a paradoxical insulinotropic effect, which could suggest a new role of glucagon in the pathophysiology type 2 diabetes mellitus (T2DM). An insulinotropic role of glucagon has been observed after bariatric/metabolic surgery that is mediated through the GLP-1 receptor on pancreatic beta cells. This effect appears to be modulated by other members of the proglucagon family, playing a key role in the beneficial effects and complications of bariatric/metabolic surgery. Glucagon serves a dual role after sleeve gastrectomy (SG) and Roux-en-Y gastric bypass (RYGB). In addition to maintaining blood glucose levels, glucagon exhibits an insulinotropic effect, suggesting that glucagon has a more complex function than simply an "anti-insulin hormone".

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.

Glucagon responses to glucose challenge in patients with idiopathic postprandial syndrome

BACKGROUND

Postprandial syndrome is characterized by hunger, weakness and anxiety neurosis occurring after meals. Although abnormal glucagon response has been suggested, inaccuracies of the conventional glucagon measurement method have prevented from precise analysis. Recently, a more reliable dual-antibody sandwich enzyme-linked immunosorbent assay for glucagon has been developed.

METHODS

We conducted a 75 g oral glucose tolerance test (OGTT) extending to 4 hours in 14 patients with idiopathic postprandial syndrome. In addition to blood glucose and insulin, we have measured glucagon concentrations using the novel method and analyzed retrospectively.

RESULTS

Median (lower quartile, upper quartile) of age and BMI were 40 years old (30, 49) and 24.9 (23.1, 26.2), respectively. The OGTT revealed that one patient had a diabetic pattern, and two were glucose intolerant. Fasting insulin was 7.6 μU/mL (6.8, 8.8) and reached 73.7 (54.3, 82.6) at 30 min. Insulin remained elevated until 180 min. The fasting glucagon was 21.1 pg/mL (16.1, 33.8), falling at 60 min to a nadir of 6.9 (3.5, 10.3), one-third of the baseline, then remaining suppressed until 180 min. Furthermore, we have found that two types of glucagon dynamics: one is lower fasting glucagon with further suppression and the other is normal or higher fasting glucagon with subsequent big drop.

CONCLUSIONS

These data suggest that glucagon suppression is stronger in patients with idiopathic postprandial syndrome than in normal subjects previously reported. The present data will contribute to further understanding and future research of this syndrome.