Revisiting the role of glucagon in health, diabetes mellitus and other metabolic diseases

Multifunctional nanomaterials for smart wearable diabetic healthcare devices

Wearable diabetic healthcare devices have attracted great attention for real-time continuous glucose monitoring (CGM) using biofluids such as tears, sweat, saliva, and interstitial fluid via noninvasive ways. In response to the escalating global demand for CGM, these devices enable proactive management and intervention of diabetic patients with incorporated drug delivery systems (DDSs). In this context, multifunctional nanomaterials can trigger the development of innovative sensing and management platforms to facilitate real-time selective glucose monitoring with remarkable sensitivity, on-demand drug delivery, and wireless power and data transmission. The seamless integration into wearable devices ensures patient's compliance. This comprehensive review evaluates the multifaceted roles of these materials in wearable diabetic healthcare devices, comparing their glucose sensing capabilities with conventionally available glucometers and CGM devices, and finally outlines the merits, limitations, and prospects of these devices. This review would serve as a valuable resource, elucidating the intricate functions of nanomaterials for the successful development of advanced wearable devices in diabetes management.

(-)-Epicatechin ameliorates type 2 diabetes mellitus by reshaping the gut microbiota and Gut-Liver axis in GK rats

As one of the most abundant plant polyphenols in the human diet, (-)-epicatechin (EC) can improve insulin sensitivity and regulate glucose homeostasis. However, the primary mechanisms involved in EC anti-T2DM benefits remain unclear. The present study explored the effects of EC on the gut microbiota and liver transcriptome in type 2 diabetes mellitus (T2DM) Goto-Kakizaki rats for the first time. The findings showed that EC protected glucose homeostasis, alleviated systemic oxidative stress, relieved liver damage, and increased serum insulin. Further investigation showed that EC reshaped gut microbiota structure, including inhibiting the proliferation of lipopolysaccharide (LPS)-producing bacteria and reducing serum LPS. In addition, transcriptome analysis revealed that the insulin signaling pathway may be the core pathway of the EC anti-T2DM effect. Therefore, EC may modulate the gut microbiota and liver insulin signaling pathways by the gut-liver axis to alleviate T2DM. As a diet supplement, EC has promising potential in T2DM prevention and treatment.

Hepatic fatty acid and glucose handling in metabolic disease: Potential impact on cardiovascular disease risk

The prevalence of metabolic diseases, including type 2 diabetes mellitus (T2DM) and metabolic dysfunction-associated steatotic liver disease (MASLD) is increasing. Although invariably associated with obesity, the importance of fat deposition in non-adipose tissue organs has yet to be fully explored. Pathological ectopic fat deposition within the liver (known as (MASLD)) has been suggested to underlie the development of T2DM and is now emerging as an independent risk factor for cardiovascular disease (CVD). The process of hepatic de novo lipogenesis (DNL), that is the synthesis of fatty acids from non-lipid precursors (e.g. glucose), has received much attention as it sits at the intersect of hepatic glucose and fatty acid handling. An upregulation of the DNL pathway has been suggested to be central in the development of metabolic diseases (including MASLD, insulin resistance, and T2DM). Here we review the evidence to determine if hepatic DNL may play a role in the development of MASLD and T2DM and therefore underlie an increased risk of CVD.

Gut hormone analogues and skeletal health in diabetes and obesity: Evidence from preclinical models

Diabetes mellitus and obesity are rapidly growing worldwide. Aside from metabolic disturbances, these two disorders also affect bone with a higher prevalence of bone fractures. In the last decade, a growing body of evidence suggested that several gut hormones, including ghrelin, gastrin, glucose-dependent insulinotropic polypeptide (GIP), glucagon, and glucagon-like peptide-1 and 2 (GLP-1 and GLP-2, respectively) may affect bone physiology. Several gut hormone analogues have been developed for the treatment of type 2 diabetes and obesity, and could represent a new alternative in the therapeutic arsenal against bone fragility. In the present review, a summary of the physiological roles of these gut hormones and their analogues is presented at the cellular level but also in several preclinical models of bone fragility disorders including type 2 diabetes mellitus, especially on bone mineral density, microarchitecture and bone material properties. The present review also summarizes the impact of GLP-1 receptor agonists approved for the treatment of type 2 diabetes mellitus and the more recent dual or triple analogue on bone physiology and strength.

Intra-islet α-cell Gs signaling promotes glucagon release

Glucagon, a hormone released from pancreatic α-cells, is critical for maintaining euglycemia and plays a key role in the pathophysiology of diabetes. To stimulate the development of new classes of therapeutic agents targeting glucagon release, key α-cell signaling pathways that regulate glucagon secretion need to be identified. Here, we focused on the potential importance of α-cell Gs signaling on modulating α-cell function. Studies with α-cell-specific mouse models showed that activation of α-cell Gs signaling causes a marked increase in glucagon secretion. We also found that intra-islet adenosine plays an unexpected autocrine/paracrine role in promoting glucagon release via activation of α-cell Gs-coupled A2A adenosine receptors. Studies with α-cell-specific Gαs knockout mice showed that α-cell Gs also plays an essential role in stimulating the activity of the Gcg gene, thus ensuring proper islet glucagon content. Our data suggest that α-cell enriched Gs-coupled receptors represent potential targets for modulating α-cell function for therapeutic purposes.

Gut hormones and bone homeostasis: potential therapeutic implications

Bone resorption follows a circadian rhythm, with a marked reduction in circulating markers of resorption (such as carboxy-terminal telopeptide region of collagen type I in serum) in the postprandial period. Several gut hormones, including glucose-dependent insulinotropic polypeptide (GIP), glucagon-like peptide 1 (GLP1) and GLP2, have been linked to this effect in humans and rodent models. These hormones are secreted from enteroendocrine cells in the gastrointestinal tract in response to a variety of stimuli and effect a wide range of physiological processes within and outside the gut. Single GLP1, dual GLP1-GIP or GLP1-glucagon and triple GLP1-GIP-glucagon receptor agonists have been developed for the treatment of type 2 diabetes mellitus and obesity. In addition, single GIP, GLP1 and GLP2 analogues have been investigated in preclinical studies as novel therapeutics to improve bone strength in bone fragility disorders. Dual GIP-GLP2 analogues have been developed that show therapeutic promise for bone fragility in preclinical studies and seem to exert considerable activity at the bone material level. This Review summarizes the evidence of the action of gut hormones on bone homeostasis and physiology.

Incretin and glucagon receptor polypharmacology in chronic kidney disease

Chronic kidney disease is a debilitating condition associated with significant morbidity and mortality. In recent years, the kidney effects of incretin-based therapies, particularly glucagon-like peptide-1 receptor agonists (GLP-1RAs), have garnered substantial interest in the management of type 2 diabetes and obesity. This review delves into the intricate interactions between the kidney, GLP-1RAs, and glucagon, shedding light on their mechanisms of action and potential kidney benefits. Both GLP-1 and glucagon, known for their opposing roles in regulating glucose homeostasis, improve systemic risk factors affecting the kidney, including adiposity, inflammation, oxidative stress, and endothelial function. Additionally, these hormones and their pharmaceutical mimetics may have a direct impact on the kidney. Clinical studies have provided evidence that incretins, including those incorporating glucagon receptor agonism, are likely to exhibit improved kidney outcomes. Although further research is necessary, receptor polypharmacology holds promise for preserving kidney function through eliciting vasodilatory effects, influencing volume and electrolyte handling, and improving systemic risk factors.

The role of mu-opioid receptors in pancreatic islet alpha cells

30% of people in the United States have diabetes or pre-diabetes. Many of these individuals will develop diabetic neuropathy as a comorbidity, which is often treated with exogenous opioids like morphine, oxycodone, or tramadol. Although these opioids are effective analgesics, growing evidence indicates that they may directly impact the endocrine pancreas function in human and preclinical models. One common feature of these exogenous opioid ligands is their preference for the mu opioid receptor (MOPR), so we aimed to determine if endogenous MOPRs directly regulate pancreatic islet metabolism and hormone secretion. We show that pharmacological antagonism of MOPRs enhances glucagon secretion, but not insulin secretion, from human islets under high glucose conditions. This increased secretion is accompanied by increased cAMP signaling. mRNA expression of MOPRs is enriched in human islet α-cells, but downregulated in T2D islet donors, suggesting a link between metabolism and MOPR expression. Conditional genetic knockout of MOPRs in murine α-cells increases glucagon secretion in high glucose conditions without increasing glucagon content. Consistent with downregulation of MOPRs during metabolic disease, conditional MOPR knockout mice treated with a high fat diet show impaired glucose tolerance, increased glucagon secretion, increased insulin content, and increased islet size. Finally, we show that MOPR-mediated changes in glucagon secretion are driven, in part, by KATP channel activity. Together, these results demonstrate a direct mechanism of action for endogenous opioid regulation of endocrine pancreas.

Acute pharmacodynamic responses to sitagliptin: Drug-induced increase in early insulin secretion in oral glucose tolerance test

DPP4 inhibitors are widely prescribed as treatments for type 2 diabetes. Because drug responses vary among individuals, we initiated investigations to identify genetic variants associated with the magnitude of drug responses. Sitagliptin (100 mg) was administered to 47 healthy volunteers. Several endpoints were measured to assess clinically relevant responses - including the effect of sitagliptin on glucose and insulin levels during an oral glucose tolerance test (OGTT). This pilot study confirmed that sitagliptin (100 mg) decreased the area under the curve for glucose during an OGTT (p = 0.0003). Furthermore, sitagliptin promoted insulin secretion during the early portion of the OGTT as reflected by an increase in the ratio of plasma insulin at 30 min divided by plasma insulin at 60 min (T30:T60) from mean ± SEM 0.87 ± 0.05 to 1.62 ± 0.36 mU/L (p = 0.04). The magnitude of sitagliptin's effect on insulin secretion (as judged by the increase in the T30:T60 ratio for insulin) was correlated with the magnitude of sitagliptin-induced increase in the area under the curve for intact plasma GLP1 levels during the first hour of the OGTT. This study confirmed previously reported sex differences in glucose and insulin levels during an OGTT. Specifically, females exhibited higher levels of glucose and insulin at the 90-180 min time points. However, we did not detect significant sex-associated differences in the magnitude of sitagliptin-induced changes in T30:T60 ratios for either glucose or insulin. In conclusion, T30:T60 ratios for insulin and glucose during an OGTT provide useful indices to assess pharmacodynamic responses to DPP4 inhibitors.

NKX2-2 based nuclei sorting on frozen human archival pancreas enables the enrichment of islet endocrine populations for single-nucleus RNA sequencing

BACKGROUND

Current approaches to profile the single-cell transcriptomics of human pancreatic endocrine cells almost exclusively rely on freshly isolated islets. However, human islets are limited in availability. Furthermore, the extensive processing steps during islet isolation and subsequent single cell dissolution might alter gene expressions. In this work, we report the development of a single-nucleus RNA sequencing (snRNA-seq) approach with targeted islet cell enrichment for endocrine-population focused transcriptomic profiling using frozen archival pancreatic tissues without islet isolation.

RESULTS

We cross-compared five nuclei isolation protocols and selected the citric acid method as the best strategy to isolate nuclei with high RNA integrity and low cytoplasmic contamination from frozen archival human pancreata. We innovated fluorescence-activated nuclei sorting based on the positive signal of NKX2-2 antibody to enrich nuclei of the endocrine population from the entire nuclei pool of the pancreas. Our sample preparation procedure generated high-quality single-nucleus gene-expression libraries while preserving the endocrine population diversity. In comparison with single-cell RNA sequencing (scRNA-seq) library generated with live cells from freshly isolated human islets, the snRNA-seq library displayed comparable endocrine cellular composition and cell type signature gene expression. However, between these two types of libraries, differential enrichments of transcripts belonging to different functional classes could be observed.

CONCLUSIONS

Our work fills a technological gap and helps to unleash frozen archival pancreatic tissues for molecular profiling targeting the endocrine population. This study opens doors to retrospective mappings of endocrine cell dynamics in pancreatic tissues of complex histopathology. We expect that our protocol is applicable to enrich nuclei for transcriptomics studies from various populations in different types of frozen archival tissues.

Association Between Triglyceride-Glucose Index and Hearing Threshold Shifts of Adults in the United States: National Health and Nutrition Examination Survey, 2015-2016

Objective

Sensorineural Hearing Loss (SNHL) is a representative human sensory impairment, few studies have paid attention to the correlation between the Triglyceride-Glucose (TyG) index and SNHL to date. We conducted this analysis to elucidate the correlation between the TyG index and pure tone hearing thresholds among US adults.

Methods

Our analysis included 1226 adults (age range: 20 to 69 years old) from the 2015-2016 National Health and Nutrition Examination Survey (NHANES) data. TyG index was scored into three quartiles. Weighted univariate analysis, weighted multivariate linear regression analyses as well as smooth curve fittings evaluated the associations between TyG index and pure tone hearing thresholds.

Results

In the multiple regression analysis, the second tertile of TyG index was negatively associated with high-frequency hearing thresholds shifts. Furthermore, the non-linear relationships between TyG index and speech-frequency and high-frequency hearing thresholds were identified by smooth curve fittings. After adjusting for potential confounders, the fitted smooth curves were approximately U-shaped, and the two-segment linear regression models were constructed to calculate their inflection points.

Conclusion

Our findings suggested that the TyG index was nearly U-shaped association with speech-frequency and high-frequency hearing thresholds. These results may imply the importance of maintaining a balanced TyG index in health management.

Lowest Glucagon/Highest C-Peptide in Oral Glucose Tolerance Test: Clinical Utility in Monitoring Glucose Control in Type 2 Diabetes Mellitus

Purpose

Understanding factors that influence blood glucose levels in patients with type 2 diabetes mellitus (T2DM) is crucial for managing hyperglycemia. Currently, there is no standardized interpretation method for glucagon levels in oral glucose tolerance test (OGTT). This study aims to assess the relationship between the lowest glucagon/highest C-peptide ratio (Lglc/Hcp) in OGTT and glucose control levels in T2DM.

Patients and Methods

Clinical data from 120 patients with T2DM were examined to compare the correlations of Lglc/Hcp and other pancreatic islet function-associated indices with fasting blood glucose (G0), glucose at 120 minutes in OGTT (G120), hemoglobin A1c (HbA1c), and the area under the glucose curve in OGTT (AUCglu). Additionally, the study investigated difference in Lglc/Hcp between patient groups based on the highest blood glucose levels (Hglu) in OGTT (Hglu ≥ 16.7 mmol/L vs Hglu < 16.7 mmol/L).

Results

The generalized linear model suggested that Lglc/Hcp significantly correlated with G0 (B = 0.85, P < 0.001), G120(B = 1.46, P < 0.001), HbA1c (B = 0.67, P < 0.001), and AUCglu (B = 3.46, P < 0.001). This correlation surpassed C-peptide and glucagon-related parameters, even after adjusting for confounding factors. Furthermore, Lglc/Hcp was notably higher in patients with Hglu ≥ 16.7 mmol/L compared to those with Hglu < 16.7 mmol/L (Z = -3.71, p < 0.001).

Conclusion

Lglc/Hcp in OGTT closely relates to blood glucose control in patients with T2DM, potentially reflecting the overall pancreatic islet function in regulating glucose levels. Moreover, inhibiting glucagon secretion may be a crucial consideration for patients requiring insulin treatment.

Glucagon kinetics assessed by mathematical modelling during oral glucose administration in people spanning from normal glucose tolerance to type 2 diabetes

Background/Objectives

Glucagon is important in the maintenance of glucose homeostasis, with also effects on lipids. In this study, we aimed to apply a recently developed model of glucagon kinetics to determine the sensitivity of glucagon variations (especially, glucagon inhibition) to insulin levels ("alpha-cell insulin sensitivity"), during oral glucose administration.

Subjects/Methods

We studied 50 participants (spanning from normal glucose tolerance to type 2 diabetes) undergoing frequently sampled 5-hr oral glucose tolerance test (OGTT). The alpha-cell insulin sensitivity and the glucagon kinetics were assessed by a mathematical model that we developed previously.

Results

The alpha-cell insulin sensitivity parameter (named SGLUCA; "GLUCA": "glucagon") was remarkably variable among participants (CV=221%). SGLUCA was found inversely correlated with the mean glycemic values, as well as with 2-hr glycemia of the OGTT. When stratifying participants into two groups (normal glucose tolerance, NGT, N=28, and impaired glucose regulation/type 2 diabetes, IGR_T2D, N=22), we found that SGLUCA was lower in the latter (1.50 ± 0.50·10-2 vs. 0.26 ± 0.14·10-2 ng·L-1 GLUCA/pmol·L-1 INS, in NGT and IGR_T2D, respectively, p=0.009; "INS": "insulin").

Conclusions

The alpha-cell insulin sensitivity is highly variable among subjects, and it is different in groups at different glucose tolerance. This may be relevant for defining personalized treatment schemes, in terms of dietary prescriptions but also for treatments with glucagon-related agents.

Glucose turnover at whole-body and skeletal muscle level in response to parenteral nutrition in male patients with alcoholic liver cirrhosis

BACKGROUND & AIMS

Cirrhosis is associated with insulin resistance and impaired glucose tolerance, which may be caused by impairments at different tissue levels (liver, skeletal muscle, and/or beta cell).

METHODS

Here, glucose kinetics at whole-body and skeletal muscle level in patients with cirrhosis (Child-Pugh A and B) were studied during parenteral nutrition using the isotope dilution technique and arteriovenous balance approach across the leg. As opposed to the euglycemic hyperinsulinemic clamp or glucose tolerance tests applied in previous studies, this approach provides a nutrient composition more similar to a normal meal while circumventing any possible portal-systemic shunting, impaired hepatic uptake and incretin effect.

RESULTS

We confirmed the presence of hepatic and peripheral insulin resistance in our patient population. Endogenous glucose production was less suppressed in response to parenteral nutrition. However, glucose uptake in skeletal muscle was increased.

CONCLUSION

Our results suggests that in our study participants with cirrhosis, the hepatic and peripheral insulin resistance is compensated for by increased insulin secretion and thus, increased glucose uptake in muscle. Hereby, glucose homeostasis is maintained.

Glucagon-Like Peptide-1 Based Therapies: A New Horizon in Obesity Management

Obesity is a significant risk factor for health issues like type 2 diabetes and cardiovascular disease. It often proves resistant to traditional lifestyle interventions, prompting a need for more precise therapeutic strategies. This has led to a focus on signaling pathways and neuroendocrine mechanisms to develop targeted obesity treatments. Recent developments in obesity management have been revolutionized by introducing novel glucagon-like peptide-1 (GLP-1) based drugs, such as semaglutide and tirzepatide. These drugs are part of an emerging class of nutrient-stimulated hormone-based therapeutics, acting as incretin mimetics to target G-protein-coupled receptors like GLP-1, glucose-dependent insulinotropic polypeptide (GIP), and glucagon. These receptors are vital in regulating body fat and energy balance. The development of multiagonists, including GLP-1-glucagon and GIP-GLP-1-glucagon receptor agonists, especially with the potential for glucagon receptor activation, marks a significant advancement in the field. This review covers the development and clinical efficacy of various GLP-1-based therapeutics, exploring the challenges and future directions in obesity management.

Bioengineering and vascularization strategies for islet organoids: advancing toward diabetes therapy

Diabetes presents a pressing healthcare crisis, necessitating innovative solutions. Organoid technologies have rapidly advanced, leading to the emergence of bioengineering islet organoids as an unlimited source of insulin-producing cells for treating insulin-dependent diabetes. This advancement surpasses the need for cadaveric islet transplantation. However, clinical translation of this approach faces two major limitations: immature endocrine function and the absence of a perfusable vasculature compared to primary human islets. In this review, we summarize the latest developments in bioengineering functional islet organoids in vitro and promoting vascularization of organoid grafts before and after transplantation. We highlight the crucial roles of the vasculature in ensuring long-term survival, maturation, and functionality of islet organoids. Additionally, we discuss key considerations that must be addressed before clinical translation of islet organoid-based therapy, including functional immaturity, undesired heterogeneity, and potential tumorigenic risks.

Differential diagnosis of post pancreatitis diabetes mellitus based on pancreatic and gut hormone characteristics

PURPOSE

Distinguishing different types of diabetes is important in directing optimized treatment strategies and correlated epidemiological studies. Through detailed analysis of hormone responses to mixed meal tolerance test (MMTT), we aimed to find representing characteristics of post-acute pancreatitis diabetes mellitus (PPDM-A) and post-chronic pancreatitis diabetes mellitus (PPDM-C).

METHODS

Participants with PPDM-A, PPDM-C, type 1 diabetes, type 2 diabetes and normal controls underwent MMTT. Fasting and postprandial responses of serum glucose, C-peptide, insulin, glucagon, pancreatic polypeptide (PP), ghrelin, gastric inhibitory peptide (GIP), glucagon like peptide-1 (GLP-1) and peptide YY (PYY) were detected and compared among different groups. Focused analysis on calculated insulin sensitivity and secretion indices were performed to reason major causes of hyperglycemia in different conditions.

RESULTS

Participants with PPDM-A were characterized by increased C-peptide, insulin, glucagon and PP, while decreased ghrelin, GIP and PYY compared with controls. Patients with PPDM-C showed secretion insufficiency of C-peptide, insulin, ghrelin and PYY, higher postprandial responses of glucagon and PP than controls. In particular, both fasting and postprandial levels of ghrelin in PPDM-C were significantly lower than other diabetes groups. PYY responses in patients with PPDM-A and PPDM-C were markedly reduced. Besides, the insulin sensitivity of PPDM-A was decreased, and the insulin secretion for PPDM-C was decreased.

CONCLUSIONS

Along with the continuum from acute to chronic pancreatitis, the pathological mechanism of PPDM changes from insulin resistance to insulin deficiency. Insufficient PYY secretion is a promising diagnostic marker for distinguishing PPDM from type 1 and type 2 diabetes. Absent ghrelin secretion to MMTT may help identify PPDM-C.

Poly-Agonist Pharmacotherapies for Metabolic Diseases: Hopes and New Challenges

The use of glucagon-like peptide-1 (GLP-1) receptor-based multi-agonists in the treatment of type 2 diabetes and obesity holds great promise for improving glycaemic control and weight management. Unimolecular dual and triple agonists targeting multiple gut hormone-related pathways are currently in clinical trials, with recent evidence supporting their efficacy. However, significant knowledge gaps remain regarding the biological mechanisms and potential adverse effects associated with these multi-target agents. The mechanisms underlying the therapeutic efficacy of GLP-1 receptor-based multi-agonists remain somewhat mysterious, and hidden threats may be associated with the use of gut hormone-based polyagonists. In this review, we provide a critical analysis of the benefits and risks associated with the use of these new drugs in the management of obesity and diabetes, while also exploring new potential applications of GLP-1-based pharmacology beyond the field of metabolic disease.

An extended minimal model of OGTT: estimation of α- and β-cell dysfunction, insulin resistance, and the incretin effect

Loss of insulin sensitivity, α- and β-cell dysfunction, and impairment in incretin effect have all been implicated in the pathophysiology of type 2 diabetes (T2D). Parsimonious mathematical models are useful in quantifying parameters related to the pathophysiology of T2D. Here, we extend the minimum model developed to describe the glucose-insulin-glucagon dynamics in the isoglycemic intravenous glucose infusion (IIGI) experiment to the oral glucose tolerance test (OGTT). The extended model describes glucose and hormone dynamics in OGTT including the contribution of the incretin hormones, glucose-dependent insulinotropic polypeptide (GIP), and glucagon-like peptide-1 (GLP-1), to insulin secretion. A new function describing glucose arrival from the gut is introduced. The model is fitted to OGTT data from eight individuals with T2D and eight weight-matched controls (CS) without diabetes to obtain parameters related to insulin sensitivity, β- and α-cell function. The parameters, i.e., measures of insulin sensitivity, a1, suppression of glucagon secretion, k1, magnitude of glucagon secretion, γ2, and incretin-dependent insulin secretion, γ3, were found to be different between CS and T2D with P values < 0.002, <0.017, <0.009, <0.004, respectively. A new rubric for estimating the incretin effect directly from modeling the OGTT is presented. The average incretin effect correlated well with the experimentally determined incretin effect with a Spearman rank test correlation coefficient of 0.67 (P < 0.012). The average incretin effect was found to be different between CS and T2D (P < 0.032). The developed model is shown to be effective in quantifying the factors relevant to T2D pathophysiology.NEW & NOTEWORTHY A new extended model of oral glucose tolerance test (OGTT) has been developed that includes glucagon dynamics and incretin contribution to insulin secretion. The model allows the estimation of parameters related to α- and β-cell dysfunction, insulin sensitivity, and incretin action. A new function describing the influx of glucose from the gut has been introduced. A new rubric for estimating the incretin effect directly from the OGTT experiment has been developed. The effect of glucose dose was also investigated.

Connections between body composition and dysregulation of islet α- and β-cells in type 2 diabetes

BACKGROUND

Accompanying islet α- and β-cell dysregulation in type 2 diabetes (T2D) at the microscopic scale, alterations in body composition at the macroscopic scale may affect the pathogenesis of T2D. However, the connections between body composition and islet α-cell and β-cell functions in T2D have not been thoroughly explored.

METHODS

For this cross-sectional study, we recruited a total of 729 Chinese Han patients with T2D in a consecutive manner. Dual-energy X-ray absorptiometry (DXA) was used to measure body composition, which included total bone-free mass, total fat and lean mass, trunk fat and lean mass and limb fat and lean mass. Every patient underwent an oral glucose tolerance test to simultaneously detect glucose, C-peptide and glucagon. The indices of islet α-cell function included fasting glucagon levels and the area under the curve of glucagon after a challenge (AUCglucagon), while the indices of β-cell function included the insulin sensitivity index derived from C-peptide (ISIC-peptide) and the area under the curve of C-peptide after a challenge (AUCC-peptide).

RESULTS

Among all patients, fat mass, especially trunk fat mass, was significantly correlated with ISIC-peptide and AUCC-peptide levels (r = - 0.330 and 0.317, respectively, p < 0.001), while lean mass, especially limb lean mass, was significantly correlated with fasting glucagon and AUCglucagon levels (r = - 0.196 and - 0.214, respectively, p < 0.001). Moreover, after adjusting for other relevant variables via multivariate linear regression analysis, increased trunk fat mass was independently associated with decreased ISIC-peptide (β = - 0.247, t = - 3.628, p < 0.001, partial R2 = 10.9%) and increased AUCC-peptide (β = 0.229, t = 3.581, p < 0.001, partial R2 = 8.2%), while decreased limb lean mass was independently associated with increased fasting glucagon (β = - 0.226, t = - 2.127, p = 0.034, partial R2 = 3.8%) and increased AUCglucagon (β = - 0.218, t = - 2.050, p = 0.041, partial R2 = 2.3%). Additionally, when separate analyses were performed with the same concept for both sexes, we found that increased trunk fat mass was still independently associated with decreased ISIC-peptide and increased AUCC-peptide, while decreased limb lean mass was still independently associated with increased fasting glucagon and AUCglucagon.

CONCLUSIONS

Increased trunk fat mass may partly account for decreased insulin sensitivity and increased insulin secretion, while decreased limb lean mass may be connected to increased fasting glucagon and postprandial glucagon secretion.

Conflicting Views About Interactions Between Pancreatic α-Cells and β-Cells

In type 1 diabetes, the reduced glucagon response to insulin-induced hypoglycemia has been used to argue that β-cell secretion of insulin is required for the full glucagon counterregulatory response. For years, the concept has been that insulin from the β-cell core flows downstream to suppress glucagon secretion from the α-cells in the islet mantle. This core-mantle relationship has been supported by perfused pancreas studies that show marked increases in glucagon secretion when insulin was neutralized with antisera. Additional support comes from a growing number of studies focused on vascular anatomy and blood flow. However, in recent years this core-mantle view has generated less interest than the argument that optimal insulin secretion is due to paracrine release of glucagon from α-cells stimulating adjacent β-cells. This mechanism has been evaluated by knockout of β-cell receptors and impairment of α-cell function by inhibition of Gi designer receptors exclusively activated by designer drugs. Other studies that support this mechanism have been obtained by pharmacological blocking of glucagon-like peptide 1 receptor in humans. While glucagon has potent effects on β-cells, there are concerns with the suggested paracrine mechanism, since some of the supporting data are from isolated islets. The study of islets in static incubation or perifusion systems can be informative, but the normal paracrine relationships are disrupted by the isolation process. While this complicates interpretation of data, arguments supporting paracrine interactions between α-cells and β-cells have growing appeal. We discuss these conflicting views of the relationship between pancreatic α-cells and β-cells and seek to understand how communication depends on blood flow and/or paracrine mechanisms.

Simultaneous LC-MS determination of glucose regulatory peptides secreted by stem cell-derived islet organoids

For studying stem cell-derived islet organoids (SC-islets) in an organ-on-chip (OoC) platform, we have developed a reversed-phase liquid chromatography-tandem mass spectrometry (RPLC-MS/MS) method allowing for simultaneous determination of insulin, somatostatin-14, and glucagon, with improved matrix robustness compared to earlier methodology. Combining phenyl/hexyl-C18 separations using 2.1 mm inner diameter LC columns and triple quadrupole mass spectrometry, identification and quantification were secured with negligible variance in retention time and quantifier/qualifier ratios, negligible levels of carryover (<2%), and sufficient precision (±10% RSD) and accuracy (±15% relative error) with and without use of an internal standard. The obtained lower limits of quantification were 0.2 µg/L for human insulin, 0.1 µg/L for somatostatin-14, and 0.05 µg/L for glucagon. The here-developed RPLC-MS/MS method showed that the SC-islets have an insulin response dependent on glucose concentration, and the SC-islets produce and release somatostatin-14 and glucagon. The RPLC-MS/MS method for these peptide hormones was compatible with an unfiltered offline sample collection from SC-islets cultivated on a pumpless, recirculating OoC (rOoC) platform. The SC-islets background secretion of insulin was not significantly different on the rOoC device compared to a standard cell culture well-plate. Taken together, RPLC-MS/MS method is well suited for multi-hormone measurements of SC-islets on an OoC platform.

Protein and amino acids in obesity: friends or foes?

PURPOSE OF REVIEW

Nutritional interventions using protein and amino acids in obesity are popular therapeutical strategies to limit obesity development. However, the effects of dietary protein intake and amino acid metabolic alterations involved in obesity pathophysiology have not been completely unravelled. Significant recent studies have brought to light new findings in these areas, which are the primary focus of this review.

RECENT FINDINGS

We describe the effects of protein intake on weight regain prevention, the influence on gut microbiota, the response to low-protein highly processed foods, and the contrasting impacts of a high-protein diet on adults and children. We also explore newly discovered correlations between amino acids, liver fat accumulation, and the dysregulation of the liver-pancreas axis due to alterations in amino acid levels in the context of obesity. Lastly, we consider branched-chain amino acids, along with glycine and tryptophan, as significant biomarkers during periods of positive or negative energy balance.

SUMMARY

Interventions using dietary protein in obesity may be useful, especially during energy restriction but also in sarcopenic obesity. Furthermore, metabolic profiles that encompass alterations in certain amino acids can provide valuable insights into the metabolic condition of patients with obesity, particularly in relation to insulin resistance and the risk of developing type 2 diabetes.

Acute pharmacodynamic responses to sitagliptin: Drug-induced increase in early insulin secretion in oral glucose tolerance test

Aim

DPP4 inhibitors are widely prescribed as treatments for type 2 diabetes. Because drug responses vary among individuals, we initiated investigations to identify genetic variants associated with the magnitude of drug responses.

Methods

Sitagliptin (100 mg) was administered to 47 healthy volunteers. Several endpoints were measured to assess clinically relevant responses - including the effect of sitagliptin on glucose and insulin levels during an oral glucose tolerance test (OGTT).

Results

This pilot study confirmed that sitagliptin (100 mg) decreased the area under the curve for glucose during an OGTT (p=0.0003). Furthermore, sitagliptin promoted insulin secretion during the early portion of the OGTT as reflected by an increase in the ratio of plasma insulin at 30 min divided by plasma insulin at 60 min (T30:T60) from 0.87+/-0.05 to 1.62+/-0.36 mU/L (p=0.04). The magnitude of sitagliptin's effect on insulin secretion (as judged by the increase in the T30:T60 ratio for insulin) was correlated with the magnitude of sitagliptin-induced increase in the area under the curve for intact plasma GLP1 levels during the first hour of the OGTT. This study confirmed previously reported sex differences in glucose and insulin levels during an OGTT. Specifically, females exhibited higher levels of glucose and insulin at the 90-180 min time points. However, we did not detect significant sex-associated differences in the magnitude of sitagliptin-induced changes in T30:T60 ratios for either glucose or insulin.

Conclusions

T30:T60 ratios for insulin and glucose during an OGTT provide useful indices to assess pharmacodynamic responses to DPP4 inhibitors.

Blockade of glucagon increases muscle mass and alters fiber type composition in mice deficient in proglucagon-derived peptides

AIMS/INTRODUCTION

Glucagon is secreted from pancreatic α-cells and plays an important role in amino acid metabolism in liver. Various animal models deficient in glucagon action show hyper-amino acidemia and α-cell hyperplasia, indicating that glucagon contributes to feedback regulation between the liver and the α-cells. In addition, both insulin and various amino acids, including branched-chain amino acids and alanine, participate in protein synthesis in skeletal muscle. However, the effect of hyperaminoacidemia on skeletal muscle has not been investigated. In the present study, we examined the effect of blockade of glucagon action on skeletal muscle using mice deficient in proglucagon-derived peptides (GCGKO mice).

MATERIALS AND METHODS

Muscles isolated from GCGKO and control mice were analyzed for their morphology, gene expression and metabolites.

RESULTS

GCGKO mice showed muscle fiber hypertrophy, and a decreased ratio of type IIA and an increased ratio of type IIB fibers in the tibialis anterior. The expression levels of myosin heavy chain (Myh) 7, 2, 1 and myoglobin messenger ribonucleic acid were significantly lower in GCGKO mice than those in control mice in the tibialis anterior. GCGKO mice showed a significantly higher concentration of arginine, asparagine, serine and threonine in the quadriceps femoris muscles, and also alanine, aspartic acid, cysteine, glutamine, glycine and lysine, as well as four amino acids in gastrocnemius muscles.

CONCLUSIONS

These results show that hyperaminoacidemia induced by blockade of glucagon action in mice increases skeletal muscle weight and stimulates slow-to-fast transition in type II fibers of skeletal muscle, mimicking the phenotype of a high-protein diet.

GDF15 increases insulin action in the liver and adipose tissue via a β-adrenergic receptor-mediated mechanism

Growth differentiation factor 15 (GDF15) induces weight loss and increases insulin action in obese rodents. Whether and how GDF15 improves insulin action without weight loss is unknown. Obese rats were treated with GDF15 and displayed increased insulin tolerance 5 h later. Lean and obese female and male mice were treated with GDF15 on days 1, 3, and 5 without weight loss and displayed increased insulin sensitivity during a euglycemic hyperinsulinemic clamp on day 6 due to enhanced suppression of endogenous glucose production and increased glucose uptake in WAT and BAT. GDF15 also reduced glucagon levels during clamp independently of the GFRAL receptor. The insulin-sensitizing effect of GDF15 was completely abrogated in GFRAL KO mice and also by treatment with the β-adrenergic antagonist propranolol and in β1,β2-adrenergic receptor KO mice. GDF15 activation of the GFRAL receptor increases β-adrenergic signaling, in turn, improving insulin action in the liver and white and brown adipose tissue.

Central and peripheral actions of nicotine that influence blood glucose homeostasis and the development of diabetes

Cigarette smoking has long been recognized as a risk factor for type 2 diabetes (T2D), although the precise causal mechanisms underlying this relationship remain poorly understood. Recent evidence suggests that nicotine, the primary reinforcing component in tobacco, may play a pivotal role in connecting cigarette smoking and T2D. Extensive research conducted in both humans and animals has demonstrated that nicotine can elevate blood glucose levels, disrupt glucose homeostasis, and induce insulin resistance. The review aims to elucidate the genetic variants of nicotinic acetylcholine receptors associated with diabetes risk and provide a comprehensive overview of the available data on the mechanisms through which nicotine influences blood glucose homeostasis and the development of diabetes. Here we emphasize the central and peripheral actions of nicotine on the release of glucoregulatory hormones, as well as its effects on glucose tolerance and insulin sensitivity. Notably, the central actions of nicotine within the brain, which encompass both insulin-dependent and independent mechanisms, are highlighted as potential targets for intervention strategies in diabetes management.

Effect of Isocaloric Meals on Postprandial Glycemic and Metabolic Markers in Type 1 Diabetes-A Randomized Crossover Trial

The aim of this study was to assess the effect of four isocaloric meals with different macronutrient compositions on postprandial blood glucose, lipids, and glucagon in adults with type 1 diabetes (T1D). Seventeen subjects tested four isocaloric meals in a randomized crossover design. The meal compositions were as follows: high-carbohydrate (HC); high-carbohydrate with extra fiber (HC-fiber); low-carbohydrate high-protein (HP); and low-carbohydrate high-fat (HF). Blood glucose and lipid measurements were collected up to 4 h and glucagon up to 3 h postprandially. Mean postprandial glucose excursions were lower after the HP compared to the HC (p = 0.036) and HC-fiber meals (p = 0.002). There were no differences in mean glucose excursions after the HF meal compared to the HC and HP meals. The HF meal resulted in higher triglyceride excursions compared to the HP meal (p < 0.001) but not compared to the HC or HC-fiber meals. Glucagon excursions were higher at 180 min after the HP meal compared to the HC and HF meals. In conclusion, the low-carbohydrate HP meal showed the most favorable glycemic and metabolic effects during a 4 h postprandial period in subjects with T1D.