Loss of incretin effect is a specific, important, and early characteristic of type 2 diabetes

Gut-Based Strategies to Reduce Postprandial Glycaemia in Type 2 Diabetes

Postprandial glycemic control is an important target for optimal type 2 diabetes management, but is often difficult to achieve. The gastrointestinal tract plays a major role in modulating postprandial glycaemia in both health and diabetes. The various strategies that have been proposed to modulate gastrointestinal function, particularly by slowing gastric emptying and/or stimulating incretin hormone GLP-1, are summarized in this review.

The methionine aminopeptidase 2 inhibitor, TNP-470, enhances the antidiabetic properties of sitagliptin in mice by upregulating xenin

The therapeutic mechanism of action of methionine aminopeptidase 2 (MetAP2) inhibitors for obesity-diabetes has not yet been fully defined. Xenin, a K-cell derived peptide hormone, possesses an N-terminal Met amino acid residue. Thus, elevated xenin levels could represent a potential pharmacological mechanism of MetAP2 inhibitors, since long-acting xenin analogues have been shown to improve obesity-diabetes. The present study has assessed the ability of the MetAP2 inhibitor, TNP-470, to augment the antidiabetic utility of the incretin-enhancer drug, sitagliptin, in high fat fed (HFF) mice. TNP-470 (1 mg/kg) and sitagliptin (25 mg/kg) were administered once-daily alone, or in combination, to diabetic HFF mice (n = 10) for 18 days. Individual therapy with TNP-470 or sitagliptin resulted in numerous metabolic benefits including reduced blood glucose, increased circulating and pancreatic insulin and improved glucose tolerance, insulin sensitivity, pyruvate tolerance and overall pancreatic islet architecture. Further assessment of metabolic rate revealed that all treatments reduced respiratory exchange ratio and increased locomotor activity. All sitagliptin treated mice also exhibited increased energy expenditure. In addition, treatment with TNP-470 alone, or in combination with sitagliptin, reduced food intake and body weight, as well as elevating plasma and intestinal xenin. Importantly, combined sitagliptin and TNP-470 therapy was associated with further significant benefits beyond that observed by either treatment alone. This included more rapid restoration of normoglycaemia, superior glucose tolerance, increased circulating GIP concentrations and an enhanced pancreatic beta:alpha cell ratio. In conclusion, these data demonstrate that TNP-470 increases plasma and intestinal xenin levels, and augments the antidiabetic advantages of sitagliptin.

Effects of the linagliptin, dipeptidyl peptidase-4 inhibitor, on bone fragility induced by type 2 diabetes mellitus in obese mice

Recently, it has been suggested that glucose-dependent insulinotropic polypeptide (GIP) and glucagon-like peptide 1 (GLP-1), which play important roles in the homeostasis of glucose metabolism, could be involved in the regulation of bone metabolism. Inhibitors of dipeptidyl peptidase 4 (DPP-4), an enzyme that degrades GIP and GLP-1, are widely used clinically as a therapeutic agent for diabetes. However, the effects of DPP-4 inhibitors on bone metabolism remain unclear. In this study, we investigated the effects of linagliptin, a DPP-4 inhibitor, on bone fragility induced by type 2 diabetes mellitus (T2DM). Non-diabetic mice were used as controls, and T2DM mice were administered linagliptin orally on a daily basis for 12 weeks. In T2DM mice, decreased bone mineral density was observed in the lower limb bones along with low serum osteocalcin levels and high serum tartrate-resistant acid phosphatase-5b (TRAP) levels. In contrast, the decreased serum osteocalcin levels and increased serum TRAP levels observed in T2DM mice were significantly suppressed after the administration of linagliptin 30 mg/kg. Bone histomorphometric analysis revealed a reduced osteoid volume and osteoblast surface with an increase in the eroded surface and number of osteoclasts in T2DM mice. This decreased bone formation and increased bone resorption observed in the T2DM mice were suppressed and trabecular bone volume increased following the administration of 30 mg/kg linagliptin. Collectively, these findings suggest that linagliptin may improve the microstructure of trabecular bone by inhibiting both a decrease in bone formation and an increase in bone resorption induced by T2DM.

HIF-1α as a Mediator of Insulin Resistance, T2DM, and Its Complications: Potential Links With Obstructive Sleep Apnea

Obstructive sleep apnea syndrome (OSA) is described as an independent risk factor for the onset and progression of type 2 diabetes (T2DM), as well as for insulin resistance (IR). The mechanisms underlying these processes remain unclear. One of the proposed molecular mechanism is based on the oxygen-sensitive α-subunit of hypoxia-inducible factor 1 (HIF-1α)-a key regulator of oxygen metabolism. The concept that stabilization of HIF-1α may influence T2DM and IR is supported by cell and animal models. Cell culture studies revealed that both glucose uptake and glycolysis are regulated by HIF-1α. Furthermore, animal models indicated that increased fasting glucose may be caused by a single night with intermittent hypoxia. Moreover, in these models, hypoxia time was correlated with IR. Mice models revealed that inhibition of HIF-1α protein may downregulate fasting blood glucose and plasma insulin level. Administration of superoxide dismutase mimetic resulted in inhibition of HIF-1α protein, catecholamines, and chronic intermittent hypoxia-induced hypertension in a mice model. The hypothesis that hypoxia is an independent risk factor for IR is strengthened by experimentally confirmed improvement of insulin sensitivity among OSA patients treated with the continuous positive airway pressure. Furthermore, recent studies suggest that HIF-1α protein concentration is increased in individuals with OSA. In this literature review, we summarize the current knowledge about HIF-1α in OSA in relation to the possible pathways in which they contribute to metabolic disorders.

A Review on Semaglutide: An Oral Glucagon-Like Peptide 1 Receptor Agonist in Management of Type 2 Diabetes Mellitus

Glucagon-like peptide 1 receptor agonists (GLP-1 RAs) are a well-established class of glucose-lowering drugs. GLP-1 RAs can be classified according to their structure, duration of action and mode of administration. This review describes the basic and clinical pharmacology of orally administered semaglutide. It highlights the PIONEER clinical trial programme results, and reviews the efficacy, safety and tolerability.

Intestinal glucagon-like peptide-1 effects on food intake: Physiological relevance and emerging mechanisms

The gut-brain hormone glucagon-like peptide-1 (GLP-1) has received immense attention over the last couple of decades for its widespread metabolic effects. Notably, intestinal GLP-1 has been recognized as an endogenous satiation signal. Yet, the underlying mechanisms and the pathophysiological relevance of intestinal GLP-1 in obesity remain unclear. This review first recapitulates early findings indicating that intestinal GLP-1 is an endogenous satiation signal, whose eating effects are primarily mediated by vagal afferents. Second, on the basis of recent findings challenging a paracrine action of intestinal GLP-1, a new model for the mediation of GLP-1 effects on eating by two discrete vagal afferent subsets will be proposed. The central mechanisms processing the vagal anorexigenic signals need however to be further delineated. Finally, the idea that intestinal GLP-1 secretion and/or effects on eating are altered in obesity and play a pathophysiological role in the development of obesity will be discussed. In summary, despite the successful therapeutic use of GLP-1 receptor agonists as anti-obesity drugs, the eating effects of intestinal GLP-1 still remain to be elucidated. Specifically, the findings presented here call for a further evaluation of the vago-central neuronal substrates activated by intestinal GLP-1 and for further investigation of its pathophysiological role in obesity.

The Effect of Cell Surface Expression and Linker Sequence on the Recruitment of Arrestin to the GIP Receptor

The glucose-dependent insulinotropic polypeptide (GIP) and the glucagon-like peptide-1 (GLP-1) receptor are important targets in the treatment of both type 2 diabetes mellitus (T2DM) and obesity. Originally identified for their role in desensitization, internalization and recycling of G protein-coupled receptors (GPCRs), arrestins have since been shown to act as scaffolding proteins that allow GPCRs to signal in a G protein-independent manner. While GLP-1R has been reported to interact with arrestins, this aspect of cell signaling remains controversial for GIPR. Using a (FRET)-based assay we have previously shown that yellow fluorescent protein (YFP)-labeled GIPR does not recruit arrestin. This GIPR-YFP construct contained a 10 amino acid linker between the receptor and a XbaI restriction site upstream of the YFP. This linker was not present in the modified GIPR-SYFP2 used in subsequent FRET and bioluminescence resonance energy transfer (BRET) assays. However, its removal results in the introduction of a serine residue adjacent to the end of GIPR’s C-terminal tail which could potentially be a phosphorylation site. The resulting receptor was indeed able to recruit arrestin. To find out whether the serine/arginine (SR) coded by the XbaI site was indeed the source of the problem, it was substituted with glycine/glycine (GG) by site-directed mutagenesis. This substitution abolished arrestin recruitment in the BRET assay but only significantly reduced it in the FRET assay. In addition, we show that the presence of a N-terminal FLAG epitope and influenza hemagglutinin signal peptide were also required to detect arrestin recruitment to the GIPR, most likely by increasing receptor cell surface expression. These results demonstrate how arrestin recruitment assay configuration can dramatically alter the result. This becomes relevant when drug discovery programs aim to identify ligands with “biased agonist” properties.

Postprandial increase in glucagon-like peptide-1 is blunted in severe heart failure

The relationship between disturbances in glucose homeostasis and heart failure (HF) progression is bidirectional. However, the mechanisms by which HF intrinsically impairs glucose homeostasis remain unknown. The present study tested the hypothesis that the bioavailability of intact glucagon-like peptide-1 (GLP-1) is affected in HF, possibly contributing to disturbed glucose homeostasis. Serum concentrations of total and intact GLP-1 and insulin were measured after an overnight fast and 15 min after the ingestion of a mixed breakfast meal in 49 non-diabetic patients with severe HF and 40 healthy control subjects. Similarly, fasting and postprandial serum concentrations of these hormones were determined in sham-operated rats, and rats with HF treated with an inhibitor of the GLP-1-degrading enzyme dipeptidyl peptidase-4 (DPP4), vildagliptin, or vehicle for 4 weeks. We found that HF patients displayed a much lower increase in postprandial intact and total GLP-1 levels than controls. The increase in postprandial intact GLP-1 in HF patients correlated negatively with serum brain natriuretic peptide levels and DPP4 activity and positively with the glomerular filtration rate. Likewise, the postprandial increases in both intact and total GLP-1 were blunted in HF rats and were restored by DPP4 inhibition. Additionally, vehicle-treated HF rats displayed glucose intolerance and hyperinsulinemia, whereas normal glucose homeostasis was observed in vildagliptin-treated HF rats. We conclude that the postprandial increase in GLP-1 is blunted in non-diabetic HF. Impaired GLP-1 bioavailability after meal intake correlates with poor prognostic factors and may contribute to the establishment of a vicious cycle between glucose disturbance and HF development and progression.

Role of fasting duration and weekday in incretin and glucose regulation

Fasting duration has been associated with lower fasting blood glucose levels, but higher 2-h post-load levels, and research has indicated an adverse effect of 'weekend behavior' on human metabolism. We investigated associations of fasting duration and weekday of examination with glucose, insulin, glucagon and incretin responses to an oral glucose tolerance test (OGTT). This cross-sectional study is based on data from the ADDITION-PRO study, where 2082 individuals attended a health examination including an OGTT. Linear regression analysis was applied to study the associations of overnight fasting duration and day of the week with glucose, insulin, glucagon, glucose-dependent insulinotropic polypeptide (GIP) and glucagon-like peptide 1 (GLP-1) responses to an OGTT. We found that a 1 h longer fasting duration was associated with 1.7% (95% CI: 0.8,2.5) higher 2-h glucose levels, as well as a 3.0% (95% CI: 1.3,4.7) higher GIP and 2.3% (95% CI: 0.3,4.4) higher GLP-1 response. Fasting insulin levels were 20.6% (95% CI: 11.2,30.7) higher on Mondays compared to the other weekdays, with similar fasting glucose levels (1.7%, 95% CI: 0.0,3.4). In this study, longer overnight fasting duration was associated with a worsening of glucose tolerance and increased incretin response to oral glucose. We found higher fasting insulin levels on Mondays compared to the other days of the week, potentially indicating a worsened glucose regulation after the weekend.

Efficacy and Safety of Dulaglutide Compared to Liraglutide: A Systematic Review and Meta-analysis in Patients with Type 2 Diabetes Mellitus

Diabetes mellitus has been always one of the most prevalent chronic diseases in the last decades. There exist a wide range of pharmacological agents for controlling this disease. However, these agents fare differently in terms of efficacy and safety. Hence, the aim of this study was to compare dulaglutide and liraglutide, two glucagon-like peptide-1 receptor agonists, in terms of efficacy and safety, drawing on a systematic review and meta-analysis. A systematic review and meta-analysis were carried out in January 2018. The articles were evaluated by two independent investigators and their quality was evaluated using Jadad scale and the Cochrane Collaboration’s tools. Finally, the eligible articles entered the study. HbA1c and FBS were considered as efficacy outcomes. Safety profile was evaluated based on several outcomes such as serious side effects and vital signs. Three articles met the inclusion and exclusion criteria. The results indicated that the mean difference (MD) of HbA1c reduction was -0.10% (95% CI, -0.20% to -0.01%, P=0.03) in the patients who received dulaglutide in comparison with the patients who received liraglutide. In addition, dulaglutide was safer than liraglutide in terms of gastrointestinal problems (RR=0.85, 95% CI, 0.73 to 0.99, P=0.04, I²=55%) and heart rate (RR=-1.14, 95% CI, -1.90 to -0.38, P=0.003, I²=0%). Once-weekly dulaglutide showed a further reduction in HbA1c compared to once-daily liraglutide. However, comparisons between these regimens indicated no significant difference between groups in either FBS reduction or safety profile. Similarly, no statistically significant difference was observed in treatment discontinuation, hypoglycemia events, and vital signs.

The role of GIP in α-cells and glucagon secretion

Glucose-dependent insulinotropic polypeptide (GIP) is an intestinally derived peptide that is secreted in response to feeding. The GIP receptor (GIPR) is expressed in many cell types involved in the regulation of metabolism, including α- and β-cells. Glucagon and insulin exert tremendous control over glucose metabolism. Thus, GIP action in islets strongly dictates metabolic control in the postprandial state. Loss of GIPR activity in β-cells is a characteristic of type 2 diabetes (T2D) which associates with reduced postprandial insulin secretion and hyperglycemia. Less is known about GIPR activity in α-cells or the control of glucagon secretion. GIP stimulates glucagon secretion in a glucose-dependent manner in healthy people, with enhanced activity at lower glycemia. However, GIP stimulates glucagon secretion even at hyperglycemia in people with T2D, suggesting that inappropriate GIPR activity in α-cells contributes to the pathogenesis of T2D. Here, we review the literature describing GIP action and GIPR activity in the α-cell, detailing the basic science that has shaped the view of how GIP regulates glucagon secretion. We also contrast the effects of GIP on glucagon secretion in healthy and T2D people. Finally, we contextualize these observations in light of recent work that redefines the role of glucagon in glucose homeostasis, suggesting that hyperglucagonemia per se does not drive hyperglycemia. As new medications for T2D that incorporate GIPR activity are being developed, it is clear that a better understanding of GIPR activity beyond the β-cell is necessary. This work highlights the importance of focusing on the GIPR in α-cells.

Evaluation of the incretin effect in humans using GIP and GLP-1 receptor antagonists

Glucose-dependent insulinotropic polypeptide (GIP) and glucagon-like peptide-1 (GLP-1) potentiate glucose-induced insulin secretion and are therefore thought to be responsible for the incretin effect. The magnitude of the incretin effect, defined as the fraction of postprandial insulin secretion stimulated by intestinal factors, has been reported to be up to ∼60% in healthy individuals. In several pathological conditions but especially in patients with type 2 diabetes, the incretin effect is severely reduced or even absent. In line with this, the insulinotropic effects of GIP and GLP-1 are impaired in patients with type 2 diabetes, even when administered in supraphysiological doses. In healthy individuals, GIP has been proposed to be the most important incretin hormone of the two, but the individual contribution of the two is difficult to determine. However, using incretin hormone receptor antagonists: the novel GIP receptor antagonist GIP(3-30)NH₂ and the widely used GLP-1 receptor antagonist exendin(9-39)NH₂, we can now distinguish between the effects of the two hormones. In this review, we present and discuss studies in which the individual contribution of GIP and GLP-1 to the incretin effect in healthy individuals have been estimated and discuss the limitations of using incretin hormone receptor antagonists.

Effects of Gender-Affirming Hormone Therapy on Insulin Sensitivity and Incretin Responses in Transgender People

OBJECTIVE

The long-term influences of sex hormone administration on insulin sensitivity and incretin hormones are controversial. We investigated these effects in 35 transgender men (TM) and 55 transgender women (TW) from the European Network for the Investigation of Gender Incongruence (ENIGI) study.

RESEARCH DESIGN AND METHODS

Before and after 1 year of gender-affirming hormone therapy, body composition and oral glucose tolerance tests (OGTTs) were evaluated.

RESULTS

In TM, body weight (2.8 ± 1.0 kg; P < 0.01), fat-free mass (FFM) (3.1 ± 0.9 kg; P < 0.01), and waist-to-hip ratio (-0.03 ± 0.01; P < 0.01) increased. Fasting insulin (-1.4 ± 0.8 mU/L; P = 0.08) and HOMA of insulin resistance (HOMA-IR) (2.2 ± 0.3 vs. 1.8 ± 0.2; P = 0.06) tended to decrease, whereas fasting glucose (-1.6 ± 1.6 mg/dL), glucose-dependent insulinotropic polypeptide (GIP) (-1.8 ± 1.0 pmol/L), and glucagon-like peptide 1 (GLP-1) (-0.2 ± 1.1 pmol/L) were statistically unchanged. Post-OGTT areas under the curve (AUCs) for GIP (2,068 ± 1,134 vs. 2,645 ± 1,248 [pmol/L] × min; P < 0.01) and GLP-1 (2,352 ± 796 vs. 2,712 ± 1,015 [pmol/L] × min; P < 0.01) increased. In TW, body weight tended to increase (1.4 ± 0.8 kg; P = 0.07) with decreasing FFM (-2.3 ± 0.4 kg; P < 0.01) and waist-to-hip ratio (-0.03 ± 0.01; P < 0.01). Insulin (3.4 ± 0.8 mU/L; P < 0.01) and HOMA-IR (1.7 ± 0.1 vs. 2.4 ± 0.2; P < 0.01) rose, fasting GIP (-1.4 ± 0.8 pmol/L; P < 0.01) and AUC GIP dropped (2,524 ± 178 vs. 1,911 ± 162 [pmol/L] × min; P < 0.01), but fasting glucose (-0.3 ± 1.4 mg/dL), GLP-1 (1.3 ± 0.8 pmol/L), and AUC GLP-1 (2,956 ± 180 vs. 2,864 ± 93 [pmol/L] × min) remained unchanged.

CONCLUSIONS

In this cohort of transgender persons, insulin sensitivity but also post-OGTT incretin responses tend to increase with masculinization and to decrease with feminization.

What Is GLP-1 Really Doing in Obesity?

Glucagon-like peptide-1 (GLP-1) is a gastrointestinal hormone released in response to meal ingestion and enhances insulin secretion from pancreatic β cells. In several human studies, GLP-1 secretory responses to oral glucose load or a meal were decreased in subjects with obesity, glucose intolerance, or diabetes compared with those in healthy subjects. However, the results of meta-analysis and cohort studies do not necessarily support this concept. Results from animal studies are also inconsistent; in multiple studies, GLP-1 secretory responses to a meal were repeatedly higher in diet-induced obese rats than in control rats. Thus, the postprandial GLP-1 response is not necessarily decreased but rather enhanced during obesity development, which is likely to play a protective role against glucose intolerance.

The Association Between Femoral Artery Intima-Media Thickness and Serum Glucagon-Like Peptide-1 Levels Among Newly Diagnosed Patients with Type 2 Diabetes Mellitus

INTRODUCTION

Endothelium dysfunction and decrease of incretin effects occur early in type 2 diabetes mellitus and these changes contribute to diabetic cardiovascular complications such as atherosclerosis, thick intima-media, coronary, and peripheral arterial diseases. In patients with diabetes, the femoral artery is a site of a high incidence of injury in peripheral vascular diseases, and atherosclerotic changes may appear earlier in the femoral artery compared to the carotid artery. This study was conducted to determine the prevalence of increased femoral artery intima-media thickness (IMT) and atherosclerotic plaque and their correlation with serum glucagon-like peptide-1 (GLP-1) levels in newly-diagnosed patients with type 2 diabetes mellitus.

MATERIALS AND METHODS

A cross-sectional study was conducted on 332 patients with nT2D in the National Endocrinology Hospital, Vietnam from January 2015 to May 2018. IMT was measured by Doppler ultrasound and GLP-1 by enzyme-linked immunosorbent assay (ELISA). All data were analyzed with SPSS version 26 for Windows (SPSS Inc, Chicago, IL).

RESULTS

Prevalence of thick femoral artery IMT and atherosclerotic plaque was 38.2 and 22.3%, respectively. There was a relationship between IMT and age, waist to hip ratio (WHR), systolic blood pressure (SBP), diastolic blood pressure (DBP), fasting GLP-1, high sensitive CRP (hsCRP) and 24-hour microalbuminuria secretion (24-h MAUS). The fasting serum GLP-1 (fGLP-1) levels were reduced significantly in patients with thickness and atherosclerosis femoral artery (p = 0.001). After adjusting with other related factors, namely, DBP and estimated glomerular filtration rate (eGFR), whilst hsCRP and 24-h MAUS showed a significantly positive correlation to IMT (Standardized B and p of 0.242, 0.004 and 0.178, 0.043, respectively), fGLP-1 showed a significantly negative correlation to IMT (Standardized B = -0.288, p = 0.001).

CONCLUSION

Among n2TD, the percentage for femoral artery thick IMT and atherosclerosis was 38.2% and 22.3% respectively, and serum GLP-1 was negatively correlated with thick IMT and atherosclerosis.

Glucagon-Like Peptide 1 and Atrial Natriuretic Peptide in a Female Mouse Model of Obstructive Pulmonary Disease

Glucagon-like peptide-1 (GLP-1) is protective in lung disease models but the underlying mechanisms remain elusive. Because the hormone atrial natriuretic peptide (ANP) also has beneficial effects in lung disease, we hypothesized that GLP-1 effects may be mediated by ANP expression. To study this putative link, we used a mouse model of chronic obstructive pulmonary disease (COPD) and assessed lung function by unrestrained whole-body plethysmography. In 1 study, we investigated the role of endogenous GLP-1 by genetic GLP-1 receptor (GLP-1R) knockout (KO) and pharmaceutical blockade of the GLP-1R with the antagonist exendin-9 to -39 (EX-9). In another study the effects of exogenous GLP-1 were assessed. Lastly, we investigated the bronchodilatory properties of ANP and a GLP-1R agonist on isolated bronchial sections from healthy and COPD mice.

Lung function did not differ between mice receiving phosphate-buffered saline (PBS) and EX-9 or between GLP-1R KO mice and their wild-type littermates. The COPD mice receiving GLP-1R agonist improved pulmonary function (P < .01) with less inflammation, but no less emphysema compared to PBS-treated mice. Compared with the PBS-treated mice, treatment with GLP-1 agonist increased ANP (nppa) gene expression by 10-fold (P < .01) and decreased endothelin-1 (P < .01), a peptide associated with bronchoconstriction. ANP had moderate bronchodilatory effects in isolated bronchial sections and GLP-1R agonist also showed bronchodilatory properties but less than ANP. Responses to both peptides were significantly increased in COPD mice (P < .05, P < .01).

Taken together, our study suggests a link between GLP-1 and ANP in COPD.

The relationship between elevated serum xenin and insulin resistance in women with polycystic ovary syndrome: a case-control study

This study aims to determine whether serum xenin-25 levels are altered in women with polycystic ovary syndrome (PCOS). The study included 31 women diagnosed with PCOS according to the 2003 Rotterdam criteria and 30 healthy controls. The primary outcome was serum xenin-25 levels. Other variables evaluated were menstrual history, physical findings, Ferriman-Gallwey hirsutism score, blood pressure, transvaginal ultrasonography, fasting blood glucose, insulin, total cholesterol, LDL-cholesterol, HDL-cholesterol, triglycerides, C-reactive protein, follicle stimulating hormone, luteinizing hormone, estradiol, total testosterone, dehydroepiandrosterone sulfate, and day-21 progesterone. Median (min-max) values of xenin-25 were 45.50 pg/mL (7.10-656.40) and 9.85 pg/mL (7.00-564.40) for cases and controls, respectively, demonstrating a significant difference (Z = 2.803, p = .007). The ROC curve for xenin-25 predicting the PCOS risk had an area under the curve of 0.747. The optimal cutoff value of xenin-25 for detecting PCOS was calculated as ≥32.60 pg/mL with sensitivity, specificity values of 61.3% and 86.7%, respectively. A logistic regression model including xenin-25, FSH, Ferriman-Gallwey score, and Menstrual cycle frequency demonstrated the independent relationship of xenin-25 on PCOS (p < .05). This study demonstrated that xenin-25 may contribute to the diagnosis of PCOS. Further studies are needed to fully elucidate the effects of xenin-25 in the pathogenesis of PCOS.

Effects of Nicotinamide Riboside on Endocrine Pancreatic Function and Incretin Hormones in Nondiabetic Men With Obesity

OBJECTIVE

Augmenting nicotinamide adenine dinucleotide (NAD+) metabolism through dietary provision of NAD+ precursor vitamins translates to improved glucose handling in rodent models of obesity and diabetes. Preclinical evidence suggests that the NAD+/SIRT1 axis may be implicated in modulating important gut-related aspects of glucose regulation. We sought to test whether NAD+ precursor supplementation with nicotinamide riboside (NR) affects β-cell function, α-cell function, and incretin hormone secretion as well as circulating bile acid levels in humans.

DESIGN

A 12-week randomized, double-blind, placebo-controlled, parallel-group trial in 40 males with obesity and insulin resistance allocated to NR at 1000 mg twice daily (n = 20) or placebo (n = 20). Two-hour 75-g oral glucose tolerance tests were performed before and after the intervention, and plasma concentrations of glucose, insulin, C-peptide, glucagon, glucagon-like peptide 1 (GLP-1), and glucose-dependent insulinotropic polypeptide (GIP) were determined. β-Cell function indices were calculated based on glucose, insulin, and C-peptide measurements. Fasting plasma concentrations of bile acids were determined.

RESULTS

NR supplementation during 12 weeks did not affect fasting or postglucose challenge concentrations of glucose, insulin, C-peptide, glucagon, GLP-1, or GIP, and β-cell function did not respond to the intervention. Additionally, no changes in circulating adipsin or bile acids were observed following NR supplementation.

CONCLUSION

The current study does not provide evidence to support that dietary supplementation with the NAD+ precursor NR serves to impact glucose tolerance, β-cell secretory capacity, α-cell function, and incretin hormone secretion in nondiabetic males with obesity. Moreover, bile acid levels in plasma did not change in response to NR supplementation.

Acute administration of interleukin-6 does not increase secretion of glucagon-like peptide-1 in mice

Interleukin 6 (IL‐6) is a cytokine secreted from skeletal muscle in response to exercise which, based on animal and cell studies, has been suggested to contribute to glucose metabolism by increasing secretion of the incretin hormone glucagon‐like peptide‐1 (GLP‐1) and affecting secretion of insulin and glucagon from the pancreatic islets. We investigated the effect of IL‐6 on GLP‐1 secretion in GLP‐1 producing cells (GLUTag) and using the perfused mouse small intestine (harboring GLP‐1 producing cells). Furthermore, the direct effect of IL‐6 on insulin and glucagon secretion was studied using isolated perfused mouse pancreas. Incubating GLUTag cells with 1000 ng/mL of IL‐6 for 2 h did not significantly increase secretion of GLP‐1 whereas 10 mmol/L glucose (positive control) did. Similarly, IL‐6 (100 ng/mL) had no effect on GLP‐1 secretion from perfused mouse small intestine whereas bombesin (positive control) increased secretion. Finally, administering IL‐6 (100 ng/mL) to perfused mouse pancreases did not significantly increase insulin or glucagon secretion regardless of perfusate glucose levels (3.5 vs. 12 mmol/L glucose). Acute effects of IL‐6 therefore do not seem to include a stimulatory effect on GLP‐1 secretion in mice.

A Dual GLP-1/GIP Receptor Agonist Does Not Antagonize Glucagon at Its Receptor but May Act as a Biased Agonist at the GLP-1 Receptor

Glucagon-like peptide-1 (GLP-1) and glucose-dependent insulinotropic polypeptide (GIP) are important regulators of metabolism, making their receptors (GLP-1R and GIPR) attractive targets in the treatment of type 2 diabetes mellitus (T2DM). GLP-1R agonists are used clinically to treat T2DM but the use of GIPR agonists remains controversial. Recent studies suggest that simultaneous activation of GLP-1R and GIPR with a single peptide provides superior glycemic control with fewer adverse effects than activation of GLP-1R alone. We investigated the signaling properties of a recently reported dual-incretin receptor agonist (P18). GLP-1R, GIPR, and the closely related glucagon receptor (GCGR) were expressed in HEK-293 cells. Activation of adenylate cyclase via Gα_s was monitored using a luciferase-linked reporter gene (CRE-Luc) assay. Arrestin recruitment was monitored using a bioluminescence resonance energy transfer (BRET) assay. GLP-1, GIP, and glucagon displayed exquisite selectivity for their receptors in the CRE-Luc assay. P18 activated GLP-1R with similar potency to GLP-1 and GIPR with higher potency than GIP. Interestingly, P18 was less effective than GLP-1 at recruiting arrestin to GLP-1R and was inactive at GCGR. These data suggest that P18 can act as both a dual-incretin receptor agonist, and as a G protein-biased agonist at GLP-1R.

The incretin system in healthy humans: The role of GIP and GLP-1

The incretin effect, the amplification of insulin secretion occurring when glucose is taken in orally as compared to infused intravenously, is one of the factors that help the body to tolerate carbohydrate/glucose ingestion. These include 1) amount and type of carbohydrates; 2) gastric emptying rate; 3) digestion and absorption of the carbohydrates; 4) secretion and effect of the incretin hormones; 5) disposition of absorbed nutrients/glucose. The incretin effect can also be viewed as the fraction of the ingested glucose load handled via gastrointestinal mechanisms (including the incretin effect); it is calculated by comparison of the amount of glucose required to copy, by intravenous infusion, the oral load. Typically, for 75 g of oral glucose, about 25 g are required. This means that the GastroIntestinal Glucose Disposal (GIGD) is 66%. Both the GIGD and the incretin effect depend on the amount of glucose ingested: for higher doses the GIGD may amount to 80%, which shows that this effect is a major contributor to glucose tolerance. The main mechanism behind it is stimulation of insulin secretion by a proportional secretion of the insulinotropic hormones GIP and GLP-1. Recently it has become possible to estimate their contributions in healthy humans using specific and potent receptor antagonists. Both hormones act to improve glucose tolerance (i.e. the antagonists impair tolerance) and their effects are additive. GIP seems to be quantitatively the most important, particularly regarding insulin secretion, whereas the action of GLP-1 is mainly displayed via inhibition of glucagon secretion.

Hepatocyte-specific HIF-1α ablation improves obesity-induced glucose intolerance by reducing first-pass GLP-1 degradation

The decrease in incretin effects is an important etiologic component of type 2 diabetes with unknown mechanisms. In an attempt to understand obesity-induced changes in liver oxygen homeostasis, we found that liver HIF-1α expression was increased mainly by soluble factors released from obese adipocytes, leading to decreased incretin effects. Deletion of hepatocyte HIF-1α protected obesity-induced glucose intolerance without changes in body weight, liver steatosis, or insulin resistance. In-depth mouse metabolic phenotyping revealed that obesity increased first-pass degradation of an incretin hormone GLP-1 with increased liver DPP4 expression and decreased sinusoidal blood flow rate, reducing active GLP-1 levels in peripheral circulation. Hepatocyte HIF-1α KO blocked these changes induced by obesity. Deletion of hepatocyte HIF-2α did not change liver DPP4 expression but improved hepatic steatosis. Our results identify a previously unknown pathway for obesity-induced impaired beta cell glucose response (incretin effects) and the development of glucose intolerance through inter-organ communications.

Neuropeptide 26RFa (QRFP) is a key regulator of glucose homeostasis and its activity is markedly altered in obese/hyperglycemic mice

Recent studies have shown that the hypothalamic neuropeptide 26RFa regulates glucose homeostasis by acting as an incretin and increasing insulin sensitivity. In this study, we further characterized the role of the 26RFa/GPR103 peptidergic system in the global regulation of glucose homeostasis using a 26RFa receptor antagonist and also assessed whether a dysfunction of the 26RFa/GPR103 system occurs in obese hyperglycemic mice. First, we demonstrate that administration of the GPR103 antagonist reduces the global glucose-induced incretin effect and insulin sensitivity whereas, conversely, administration of exogenous 26RFa attenuates glucose-induced hyperglycemia. Using a mouse model of high-fat diet-induced obesity and hyperglycemia, we found a loss of the antihyperglcemic effect and insulinotropic activity of 26RFa, accompanied with a marked reduction of its insulin-sensitive effect. Interestingly, this resistance to 26RFa is associated with a downregulation of the 26RFa receptor in the pancreatic islets, and insulin target tissues. Finally, we observed that the production and release kinetics of 26RFa after an oral glucose challenge is profoundly altered in the high-fat mice. Altogether, the present findings support the view that 26RFa is a key regulator of glucose homeostasis whose activity is markedly altered under obese/hyperglycemic conditions.

Analysis of Patents Issued in China for Antihyperglycemic Therapies for Type 2 Diabetes Mellitus

Type 2 diabetes mellitus (T2DM) is prevalent, with a dramatic increase in recent years. Moreover, its microvascular and macrovascular complications cause significant societal issues. The demand for new and effective antidiabetic therapies grows with each passing day and motivates organizations and individuals to pay more attention to such products. In this article, we focused on oral antihyperglycemic drugs patented in China and introduced them according to their antihyperglycemic mechanisms. By searching the website of State Intellectual Property Office of the People's Republic of China (http://www.sipo.gov.cn), 2,500 antihyperglycemic patents for T2DM were identified and analyzed. These consisted of 4 patents for derivatives of herbal extracts (0.2%), 162 patents for herbal extracts (6.5%), 61 compositions for traditional Chinese medicine (TCM) (2.4%), 2,263 patents for synthetic compounds (90.5%), and 10 (0.4%) patents of the combination of synthetic compounds and TCM. As the most common drugs for diabetes mellitus, synthetic compounds can also be classified into several categories according to their working mechanisms, such as insulin secretion promotor agents, insulin sensitizer agents, α-glucosidase inhibitors, and so forth. This article discussed the chemical structure, potential antihyperglycemic mechanism of these antihyperglycemic drugs in patents in China. Expert opinion: Insulin sensitivity and β-cell function could be improved by weight loss to prevent prediabetes into T2DM. However, 40-50% patients with impaired glucose tolerance (IGT) still progress to T2DM, even after successful long-term weight loss. Antihyperglycemic remedies provide a treatment option to improve insulin sensitivity and maintain β-cell function. Combination therapy is the best treatment for diabetes. Combination therapy can reduce the dosage of each single drug option, and avoid the side effects. Drugs with different mechanisms are complementary, and are better adapted to patients with changing conditions. Classical combination therapies include combinations such as sulfonylureas plus biguanides or glucosidase inhibitors, biguanide plus glucosidase inhibitors or insulin sensitizers, insulin treatment plus biguanides or glucosidase inhibitors. The general principle of combination therapy is that two drugs with different mechanisms are selected jointly, and the combination of three types of hypoglycemic drugs is not recommended. After reading a large amount of literature, we have rarely found a case of three oral hypoglycemic agents, which may mean that the combination of three oral hypoglycemic agents is unnecessary and has unpredictable risks. There is no objection to the idea of multi-drug therapy. But multiple drugs can only be used when it shows a significant benefit to the patients. Combined use of multiple antidiabetic drugs poses a risk to patients due to drug interactions and overtreatment.

From the Incretin Concept and the Discovery of GLP-1 to Today's Diabetes Therapy

Researchers have been looking for insulin-stimulating factors for more than 100 years, and in the 1960ties it was definitively proven that the gastrointestinal tract releases important insulinotropic factors upon oral glucose intake, so-called incretin hormones. The first significant factor identified was the duodenal glucose-dependent insulinotropic polypeptide, GIP, which however, turned out not to stimulate insulin secretion in patients with type 2 diabetes. But resection experiments clearly indicated the presence of an additional incretin, and in 1986, an unexpected processing fragment of the recently identified glucagon precursor, proglucagon, namely truncated glucagon-like peptide 1 (GLP-1 7-36 amide), was isolated from the gut and found to both stimulate insulin secretion and inhibit glucagon secretion. The peptide also inhibited appetite and food intake. Unlike GIP, this peptide had preserved effects in patients with type 2 diabetes and it was soon documented to have powerful antidiabetic effects in clinical studies. Its utility was limited, however, because of an extremely short half-life in humans, but this problem had two solutions, both of which gave rise to important antidiabetic drugs: (1) orally active inhibitors of the enzyme dipeptidylpeptidase 4 (DPP-4 inhibitors), which was responsible for the rapid degradation; the inhibitors protect endogenous GLP-1 from degradation and thereby unfold its antidiabetic activity, and (2) long-acting injectable analogs of GLP-1 protected against DPP-4 degradation. Particularly, the latter, the GLP-1 receptor agonists, either alone or in various combinations, are so powerful that treatment allows more than 2/3 of type 2 diabetes patients to reach glycemic targets. In addition, these agents cause a weight loss which, with the most successful compounds, may exceed 10% of body weight. Most recently they have also been shown to be renoprotective and reduce cardiovascular risk and mortality.

Menaquinone-4 Amplified Glucose-Stimulated Insulin Secretion in Isolated Mouse Pancreatic Islets and INS-1 Rat Insulinoma Cells

Vitamin K2 is indispensable for blood coagulation and bone metabolism. Menaquinone-4 (MK-4) is the predominant homolog of vitamin K2, which is present in large amounts in the pancreas, although its function is unclear. Meanwhile, β-cell dysfunction following insulin secretion has been found to decrease in patients with type 2 diabetes mellitus. To elucidate the physiological function of MK-4 in pancreatic β-cells, we studied the effects of MK-4 treatment on isolated mouse pancreatic islets and rat INS-1 cells. Glucose-stimulated insulin secretion significantly increased in isolated islets and INS-1 cells treated with MK-4. It was further clarified that MK-4 enhanced cAMP levels, accompanied by the regulation of the exchange protein directly activated by the cAMP 2 (Epac2)-dependent pathway but not the protein kinase A (PKA)-dependent pathway. A novel function of MK-4 on glucose-stimulated insulin secretion was found, suggesting that MK-4 might act as a potent amplifier of the incretin effect. This study therefore presents a novel potential therapeutic approach for impaired insulinotropic effects.

Comparative Effects of Proximal and Distal Small Intestinal Glucose Exposure on Glycemia, Incretin Hormone Secretion, and the Incretin Effect in Health and Type 2 Diabetes

OBJECTIVE

Cells releasing glucose-dependent insulinotropic polypeptide (GIP) and glucagon-like peptide 1 (GLP-1) are distributed predominately in the proximal and distal gut, respectively. Hence, the region of gut exposed to nutrients may influence GIP and GLP-1 secretion and impact on the incretin effect and gastrointestinal-mediated glucose disposal (GIGD). We evaluated glycemic and incretin responses to glucose administered into the proximal or distal small intestine and quantified the corresponding incretin effect and GIGD in health and type 2 diabetes mellitus (T2DM).

RESEARCH DESIGN AND METHODS

Ten healthy subjects and 10 patients with T2DM were each studied on four occasions. On two days, a transnasal catheter was positioned with infusion ports opening 13 cm and 190 cm beyond the pylorus, and 30 g glucose with 3 g 3-O-methylglucose (a marker of glucose absorption) was infused into either site and 0.9% saline into the alternate site over 60 min. Matching intravenous isoglycemic clamp studies were performed on the other two days. Blood glucose, serum 3-O-methylglucose, and plasma hormones were evaluated over 180 min.

RESULTS

In both groups, blood glucose and serum 3-O-methylglucose concentrations were higher after proximal than distal glucose infusion (all P < 0.001). Plasma GLP-1 increased minimally after proximal, but substantially after distal, glucose infusion, whereas GIP increased promptly after both infusions, with concentrations initially greater, but less sustained, with proximal versus distal infusion (all P < 0.001). Both the incretin effect and GIGD were less with proximal than distal glucose infusion (both P ≤ 0.009).

CONCLUSIONS

The distal, as opposed to proximal, small intestine is superior in modulating postprandial glucose metabolism in both health and T2DM.

A carbohydrate-reduced high-protein diet acutely decreases postprandial and diurnal glucose excursions in type 2 diabetes patients

The aim of the study was to assess whether a simple substitution of carbohydrate in the conventionally recommended diet with protein and fat would result in a clinically meaningful reduction in postprandial hyperglycaemia in subjects with type 2 diabetes mellitus (T2DM). In all, sixteen subjects with T2DM treated with metformin only, fourteen male, with a median age of 65 (43-70) years, HbA1c of 6·5 % (47 mmol/l) (5·5-8·3 % (37-67 mmol/l)) and a BMI of 30 (sd 4·4) kg/m2 participated in the randomised, cross-over study. A carbohydrate-reduced high-protein (CRHP) diet was compared with an iso-energetic conventional diabetes (CD) diet. Macronutrient contents of the CRHP/CD diets consisted of 31/54 % energy from carbohydrate, 29/16 % energy from protein and 40/30 % energy from fat, respectively. Each diet was consumed on 2 consecutive days in a randomised order. Postprandial glycaemia, pancreatic and gut hormones, as well as satiety, were evaluated at breakfast and lunch. Compared with the CD diet, the CRHP diet reduced postprandial AUC of glucose by 14 %, insulin by 22 % and glucose-dependent insulinotropic polypeptide by 17 % (all P<0·001), respectively. Correspondingly, glucagon AUC increased by 33 % (P<0·001), cholecystokinin by 24 % (P=0·004) and satiety scores by 7 % (P=0·035), respectively. A moderate reduction in carbohydrate with an increase in fat and protein in the diet, compared with an energy-matched CD diet, greatly reduced postprandial glucose excursions and resulted in increased satiety in patients with well-controlled T2DM.

Amino acid transporters in the regulation of insulin secretion and signalling

Amino acids are increasingly recognised as modulators of nutrient disposal, including their role in regulating blood glucose through interactions with insulin signalling. More recently, cellular membrane transporters of amino acids have been shown to form a pivotal part of this regulation as they are primarily responsible for controlling cellular and circulating amino acid concentrations. The availability of amino acids regulated by transporters can amplify insulin secretion and modulate insulin signalling in various tissues. In addition, insulin itself can regulate the expression of numerous amino acid transporters. This review focuses on amino acid transporters linked to the regulation of insulin secretion and signalling with a focus on those of the small intestine, pancreatic β-islet cells and insulin-responsive tissues, liver and skeletal muscle. We summarise the role of the amino acid transporter B⁰AT1 (SLC6A19) and peptide transporter PEPT1 (SLC15A1) in the modulation of global insulin signalling via the liver-secreted hormone fibroblast growth factor 21 (FGF21). The role of vesicular vGLUT (SLC17) and mitochondrial SLC25 transporters in providing glutamate for the potentiation of insulin secretion is covered. We also survey the roles SNAT (SLC38) family and LAT1 (SLC7A5) amino acid transporters play in the regulation of and by insulin in numerous affective tissues. We hypothesise the small intestine amino acid transporter B⁰AT1 represents a crucial nexus between insulin, FGF21 and incretin hormone signalling pathways. The aim is to give an integrated overview of the important role amino acid transporters have been found to play in insulin-regulated nutrient signalling.

Post-transplant diabetes mellitus in patients with solid organ transplants

Solid organ transplantation (SOT) is a life-saving procedure and an established treatment for patients with end-stage organ failure. However, transplantation is also accompanied by associated cardiovascular risk factors, of which post-transplant diabetes mellitus (PTDM) is one of the most important. PTDM develops in 10-20% of patients with kidney transplants and in 20-40% of patients who have undergone other SOT. PTDM increases mortality, which is best documented in patients who have received kidney and heart transplants. PTDM results from predisposing factors (similar to type 2 diabetes mellitus) but also as a result of specific post-transplant risk factors. Although PTDM has many characteristics in common with type 2 diabetes mellitus, the prevention and treatment of the two disorders are often different. Over the past 20 years, the lifespan of patients who have undergone SOT has increased, and PTDM becomes more common over the lifespan of these patients. Accordingly, PTDM becomes an important condition not only to be aware of but also to treat. This Review presents the current knowledge on PTDM in patients receiving kidney, heart, liver and lung transplants. This information is not only for transplant health providers but also for endocrinologists and others who will meet these patients in their clinics.

Stem-cell based organ-on-a-chip models for diabetes research

Diabetes mellitus (DM) ranks among the severest global health concerns of the 21st century. It encompasses a group of chronic disorders characterized by a dysregulated glucose metabolism, which arises as a consequence of progressive autoimmune destruction of pancreatic beta-cells (type 1 DM), or as a result of beta-cell dysfunction combined with systemic insulin resistance (type 2 DM). Human cohort studies have provided evidence of genetic and environmental contributions to DM; yet, these studies are mostly restricted to investigating statistical correlations between DM and certain risk factors. Mechanistic studies, on the other hand, aimed at re-creating the clinical picture of human DM in animal models. A translation to human biology is, however, often inadequate owing to significant differences between animal and human physiology, including the species-specific glucose regulation. Thus, there is an urgent need for the development of advanced human in vitro models with the potential to identify novel treatment options for DM. This review provides an overview of the technological advances in research on DM-relevant stem cells and their integration into microphysiological environments as provided by the organ-on-a-chip technology.

Does obesity cause type 2 diabetes mellitus (T2DM)? Or is it the opposite?

Obesity is believed to be a promoter of type 2 diabetes mellitus (T2DM). Reports indicate that severe obesity in childhood and adolescence increases the risk of T2DM in youth and young adults. T2DM, which is commonly asymptomatic, frequently is not recognized until random blood glucose is measured. Screening blood glucose levels measured in obese individuals are more effective for identifying undiagnosed persons, than screening the general population and therefore introduces a selection bias for discovery. The following commentary will indicate why these observations do not indicate that obesity is the cause of T2DM. Also, it will be shown that the insulin resistance of T2DM occurs primarily in the muscles of lean individuals predisposed to diabetes before they become obese. This insulin resistance is not secondary to, but instead, is the cause of the excessive fat accumulation associated with T2DM. Moreover, this early muscle insulin resistance is the etiology of the hyperlipidemia and excess fat accumulation characteristic of T2DM.

Endogenous glucagon-like peptide-1 system response is impaired during ST-elevation myocardial infarction in type 2 diabetes patients

We previously demonstrated increased glucagon-like peptide-1 (GLP-1) secretion during acute ST elevation myocardial infarction (STEMI) in non-diabetic (ND) patients. Whether the endogenous GLP-1 system response is different in patients with type 2 diabetes (T2D) during STEMI is unknown. Patients with STEMI (20 ND, 13 T2D) and 3 control groups (non-STEMI [14 ND, 13 T2D], stable angina pectoris [SAP] [8 ND, 10 T2D] patients and healthy subjects) (n = 25) were studied. Plasma levels of total and active GLP-1 and soluble dipeptidyl peptidase-4 (sDPP4) were estimated by enzyme-linked immunosorbent assay on admission and at 24 and 48 hours after percutaneous coronary intervention in all patients. Sharply elevated levels of total and active GLP-1 were found in ND STEMI patients at 24 h (P < 0.05 and P < 0.005, respectively), but not in T2D STEMI patients. All patients demonstrated decreased sDPP4 levels compared with healthy controls (P < 0.0005) accompanied by increased active/total GLP-1 ratio regardless of their ischemic state. These data demonstrate that T2D patients fail to further upregulate their endogenous GLP-1 system during STEMI. This may underlie their worse cardiovascular outcome.

Glutamate as intracellular and extracellular signals in pancreatic islet functions

l-Glutamate is one of the most abundant amino acids in the body and is a constituent of proteins and a substrate in metabolism. It is well known that glutamate serves as a primary excitatory neurotransmitter and a critical neuromodulator in the brain. Recent studies have shown that in addition to its pivotal role in neural functions, glutamate plays many important roles in a variety of cellular functions, including those as intracellular and extracellular signals. In pancreatic islets, glutamate is now known to be required for the normal regulation of insulin secretion, such as incretin-induced insulin secretion. In this review, we primarily discuss the physiological and pathophysiological roles of glutamate as intracellular and extracellular signals in the functions of pancreatic islets.

Glucose metabolism in patients with psoriasis

BACKGROUND

Epidemiological studies strongly suggest that psoriasis predisposes to type 2 diabetes. Several theories have been proposed to explain how these disease entities might be pathophysiologically connected.

OBJECTIVES

Our primary objective was to elucidate whether clinical data support the notion of common pathophysiological denominators in patients with psoriasis and type 2 diabetes, and thus to delineate the association between the two conditions that has arisen on the basis of epidemiological studies.

METHODS

We reviewed clinical studies investigating parameters of glucose metabolism in patients with psoriasis. The PubMed and Embase databases were searched for studies investigating glucose metabolism in adult patients with psoriasis as a primary or secondary end point. Studies had to include a relevant control group.

RESULTS

Twenty-six clinical studies reporting on insulin resistance, glucose tolerance or insulin secretion were eligible for review. The results were widely conflicting, with less than half of the studies showing results suggestive of defective glucose metabolism in patients with psoriasis. In general, the studies suffered from a lack of information regarding possible confounders and patient characteristics. Furthermore, the research methods varied, and in all but one study they might not have been appropriate to detect early and subtle defects in glucose metabolism.

CONCLUSIONS

The available literature does not unequivocally support common pathophysiological denominators in psoriasis and type 2 diabetes. Well-designed clinical studies are needed to expose potential diabetogenic defects in the glucose metabolism in patients with psoriasis.

Intestinal CART is a regulator of GIP and GLP-1 secretion and expression

Impaired incretin effect is a culprit in Type 2 Diabetes. Cocaine- and amphetamine-regulated transcript (CART) is a regulatory peptide controlling pancreatic islet hormone secretion and beta-cell survival. Here we studied the potential expression of CART in enteroendocrine cells and examined the role of CART as a regulator of incretin secretion and expression. CART expression was found in glucose-dependent insulinotropic polypeptide (GIP)-producing K-cells and glucagon-like peptide-1 (GLP-1)-producing L-cells in human duodenum and jejunum and circulating CART levels were increased 60 min after a meal in humans. CART expression was increased by fatty acids and GIP, but unaffected by glucose in GLUTag and STC-1 cells. Exogenous CART had no effect on GIP and GLP-1 expression and secretion in GLUTag or STC-1 cells, but siRNA-mediated silencing of CART reduced GLP-1 expression and secretion. Furthermore, acute intravenous administration of CART increased GIP and GLP-1 secretion during an oral glucose-tolerance test in mice. We conclude that CART is a novel constituent of human K- and L-cells with stimulatory actions on incretin secretion and that interfering with the CART system may be a therapeutic avenue for T2D.

Acute Effects of Dietary Carbohydrate Restriction on Glycemia, Lipemia and Appetite Regulating Hormones in Normal-Weight to Obese Subjects

Postprandial responses to food are highly dependent on the macronutrient composition of the diet. We investigated the acute effects of transition from the recommended moderately high carbohydrate (HC) diet towards a carbohydrate-reduced high-protein (CRHP) diet on postprandial glycemia, insulinemia, lipemia, and appetite-regulating hormones in non-diabetic adults. Fourteen subjects, including five males (Mean ± SD: age 62 ± 6.5; BMI 32 ± 7.6 kg/m²; hemoglobin A_1c (HbA_1c) 40 ± 3.0 mmol/mol; HOMA2-IR 2.1 ± 0.9) were included in this randomized, cross-over study. Iso-caloric diets were consumed for two consecutive days with a median wash-out period of 21 days (range 2–8 weeks) between diets (macronutrient energy composition: CRHP/HC; 31%/54% carbohydrate, 29%/16% protein, 40%/30% fat). Postprandial glucose, insulin secretion rate (ISR), triglycerides (TGs), non-esterified fatty acids (NEFAs), and satiety ratings were assessed after ingestion of breakfast (Br) and lunch (Lu), and gut hormones and glucagon were assessed after ingestion of Br. Compared with the HC diet, the CRHP diet reduced peak glucose concentrations (Br 11%, p = 0.024; Lu 11%, p < 0.001), glucose excursions (Br 80%, p = 0.20; Lu 85%, p < 0.001), and ISR (Br 31%; Lu 64%, both p < 0.001) whereas CRHP, as compared with HC, increased glucagon-like peptide-1 (Br 27%, p = 0.015) and glucagon values (Br 249%, p < 0.001). NEFA and TG levels increased in the CRHP diet as compared with the HC diet after Br, but no difference was found after Lu (NEFA Br 22%, p < 0.01; TG Br 42%, p = 0.012). Beta-cell glucose sensitivity, insulin clearance, cholecystokinin values, and subjective satiety ratings were unaffected. It is possible to achieve a reduction in postprandial glycemia and insulin without a deleterious effect on beta-cell glucose sensitivity by substituting part of dietary carbohydrate with iso-caloric protein and fat in subjects without type 2 diabetes mellitus (T2DM). The metabolic effects are more pronounced after the second meal.

The effect of meals on bone turnover - a systematic review with focus on diabetic bone disease

INTRODUCTION

Type 2 diabetes is associated with an increased risk of bone fractures. Bone mineral density (BMD) is increased and bone turnover is low in type 2 diabetes and the increased BMD does not explain the increased fracture risk. However, the low bone turnover may lead to insufficient bone renewal with unrepaired micro-cracks and thus increase fracture risk. Ingestion of food acutely decreases bone resorption markers and the macronutrient composition of meals and meal frequency may influence bone metabolism adversely in subjects with unhealthy eating patterns, e.g., patients with type 2 diabetes.

AREAS COVERED

The treatment strategy of bone disease in type 2 diabetics is covered in this review. The current management of diabetic bone disease consists of anti-osteoporotic treatment. However, anti-resorptives may further reduce an already low bone turnover with uncertain effects. Furthermore, the acute and long-term effects of meal ingestion, weight loss alone and in combination with exercise as well as the possible underlying mechanisms are covered in this systematic review.

EXPERT COMMENTARY

Current management of diabetic bone disease is based on principles of anti-osteoporotic treatment in non-diabetic subjects. However, studies are urged to investigate whether anti-resorptives are equally beneficial in type 2 diabetes as in non-diabetic individuals.

Clinical pharmacology of glucagon-like peptide-1 receptor agonists

Glucagon-like peptide-1 receptor agonists (GLP-1 RAs) are an important asset in the armamentarium for the treatment of type 2 diabetes mellitus (type 2 DM). Incretin failure is a critical etiopathogenetic feature of type 2 DM, which, if reversed, results in improved glycaemic control. GLP-1 RAs are injectable peptides that resemble the structure and function of endogenous incretin GLP-1, but as they are not deactivated by the dipeptidyl peptidase-4 (DPP-4), their half-life is prolonged compared with native GLP-1. Based on their ability to activate GLP-1 receptor, GLP-1 RAs are classified as short-acting (exenatide twice-daily and lixisenatide once-daily), and long-acting (liraglutide once-daily and the once-weekly formulations of exenatide extended-release, dulaglutide, and albiglutide). Semaglutide, another long-acting, once-weekly GLP-1 RA, was recently approved by the FDA and EMA. Although all of these agents potently reduce haemoglobin A1C (HbA1c), there are unique features and fundamental differences among them related to fasting and postprandial hyperglycaemia reduction, weight loss potency, cardiovascular protection efficacy, and adverse events profile. It is imperative that current evidence be integrated and applied in the context of an individualised patient-centred approach. This should include not only glucose management but also targeting as many as possible of the pathophysiologic mechanisms responsible for type 2 DM development and progression.

Long-term treatment with acylated analogues of apelin-13 amide ameliorates diabetes and improves lipid profile of high-fat fed mice

Previous studies have shown that modified apelin analogues exhibited enzyme resistance in plasma and improved circulating half-life compared to apelin-13. This study investigated the antidiabetic effects of chronic administration of stable long acting fatty acid modified apelin analogues, namely, (Lys8GluPAL)apelin-13 amide and pGlu(Lys8GluPAL)apelin-13 amide, in high-fat fed obese-diabetic mice. Male NIH Swiss mice (groups n = 8) were maintained either on a high-fat diet (45% fat) from 8 to 28 weeks old, or control mice were fed a normal diet (10% fat). When diet induced obesity-diabetes was established after high-fat feeding, mice were injected i.p. once daily with apelin analogues, liraglutide (25 nmol/kg) or saline (controls). Administration of (Lys8GluPAL)apelin-13 amide and pGlu(Lys8GluPAL)apelin-13 amide for 28 days significantly reduced food intake and decreased body weight. Non-fasting glucose was reduced (p<0.01 to p<0.001) and plasma insulin concentrations increased (p<0.01 to p<0.001). This was accompanied by enhanced insulin responses (p<0.01 to p<0.001) and significant reductions in glucose excursion after oral (p<0.01) or i.p. (p<0.01) glucose challenges and feeding. Apelin analogues also significantly improved HbA1c (p<0.01), enhanced insulin sensitivity (p<0.01), reduced triglycerides (p<0.001), increased HDL-cholesterol (p<0.01) and decreased LDL-cholesterol (p<0.01), compared to high-fat fed saline treated control mice. Cholesterol levels were decreased (p<0.01) by pGlu(Lys8GluPAL)apelin-13 amide and both apelin treated groups showed improved bone mineral content, reduced fat deposits and increased plasma GLP-1. Daily treatment with liraglutide mirrored many of these changes (not on bone or adipose tissue), but unlike apelin analogues increased plasma amylase. Consumption of O2, production of CO2, respiratory exchange ratio and energy expenditure were improved by apelin analogues. These results indicate that long-term treatment with acylated analogues (Lys8GluPAL)apelin-13 amide and particularly pGlu(Lys8GluPAL)apelin-13 amide resulted in similar or enhanced therapeutic responses to liraglutide in high-fat fed mice. Fatty acid derived apelin analogues represent a new and exciting development in the treatment of obesity-diabetes.

The EndoBarrier: Duodenal-Jejunal Bypass Liner for Diabetes and Weight Loss

The rapid rise of obesity and type 2 diabetes poses a global threat to healthcare and is a major cause of mortality and morbidity. Bariatric surgery has revolutionised the treatment of both these conditions but is invasive and associated with an increased risk of complications. The EndoBarrier is a device placed endoscopically in the duodenum, which is designed to mimic the effects of gastric bypass surgery with the aim of inducing weight loss and improving glycaemic control. This review outlines the current clinical evidence of the device, its efficacy, potential mechanisms of action, and utility in clinical practice.

Glucotypes reveal new patterns of glucose dysregulation

Diabetes is an increasing problem worldwide; almost 30 million people, nearly 10% of the population, in the United States are diagnosed with diabetes. Another 84 million are prediabetic, and without intervention, up to 70% of these individuals may progress to type 2 diabetes. Current methods for quantifying blood glucose dysregulation in diabetes and prediabetes are limited by reliance on single-time-point measurements or on average measures of overall glycemia and neglect glucose dynamics. We have used continuous glucose monitoring (CGM) to evaluate the frequency with which individuals demonstrate elevations in postprandial glucose, the types of patterns, and how patterns vary between individuals given an identical nutrient challenge. Measurement of insulin resistance and secretion highlights the fact that the physiology underlying dysglycemia is highly variable between individuals. We developed an analytical framework that can group individuals according to specific patterns of glycemic responses called "glucotypes" that reveal heterogeneity, or subphenotypes, within traditional diagnostic categories of glucose regulation. Importantly, we found that even individuals considered normoglycemic by standard measures exhibit high glucose variability using CGM, with glucose levels reaching prediabetic and diabetic ranges 15% and 2% of the time, respectively. We thus show that glucose dysregulation, as characterized by CGM, is more prevalent and heterogeneous than previously thought and can affect individuals considered normoglycemic by standard measures, and specific patterns of glycemic responses reflect variable underlying physiology. The interindividual variability in glycemic responses to standardized meals also highlights the personal nature of glucose regulation. Through extensive phenotyping, we developed a model for identifying potential mechanisms of personal glucose dysregulation and built a webtool for visualizing a user-uploaded CGM profile and classifying individualized glucose patterns into glucotypes.

Sepsis-induced activation of endogenous GLP-1 system is enhanced in type 2 diabetes

BACKGROUND

High levels of circulating GLP-1 are associated with severity of sepsis in critically ill nondiabetic patients. Whether patients with type 2 diabetes (T2D) display different activation of the endogenous GLP-1 system during sepsis and whether it is affected by diabetes-related metabolic parameters are not known.

METHODS

Serum levels of GLP-1 (total and active forms) and its inhibitor enzyme sDPP-4 were determined by ELISA on admission and after 2 to 4 days in 37 sepsis patients with (n = 13) and without T2D (n = 24) and compared to normal healthy controls (n = 25). Correlations between GLP-1 system activation and clinical, inflammatory, and diabetes-related metabolic parameters were performed.

RESULTS

A 5-fold (P < .001) and 2-fold (P < .05) increase in active and total GLP-1 levels, respectively, were found on admission as compared to controls. At 2 to 4 days from admission, the level of active GLP-1 forms in surviving patients were decreased significantly (P < .005), and positively correlated with inflammatory marker CRP (r = 0.33, P = .05). T2D survivors displayed a similar but more enhanced pattern of GLP-1 response than nondiabetic survivors. Nonsurvivors demonstrate an early extreme increase of both total and active GLP-1 forms, 9.5-fold and 5-fold, respectively (P < .05). The initial and late levels of circulating GLP-1 inhibitory enzyme sDPP-4 were twice lower in all studied groups (P < .001), compared with healthy controls.

CONCLUSIONS

Taken together, these data indicate that endogenous GLP-1 system is activated during sepsis. Patients with T2D display an enhanced and prolonged activation as compared to nondiabetic patients. Extreme early increased GLP-1 levels during sepsis indicate poor prognosis.

Human GIP(3-30)NH2 inhibits G protein-dependent as well as G protein-independent signaling and is selective for the GIP receptor with high-affinity binding to primate but not rodent GIP receptors

GIP(3-30)NH₂ is a high affinity antagonist of the GIP receptor (GIPR) in humans inhibiting insulin secretion via G protein-dependent pathways. However, its ability to inhibit G protein-independent signaling is unknown. Here we determine its action on arrestin-recruitment and receptor internalization in recombinant cells. As GIP is adipogenic, we evaluate the inhibitory actions of GIP(3-30)NH₂ in human adipocytes. Finally, we determine the receptor selectivity of GIP(3-30)NH₂ among other human and animal GPCRs. cAMP accumulation and β-arrestin 1 and 2 recruitment were studied in transiently transfected HEK293 cells and real-time internalization in transiently transfected HEK293A and in HEK293A β-arrestin 1 and 2 knockout cells. Furthermore, human subcutaneous adipocytes were assessed for cAMP accumulation following ligand stimulation. Competition binding was examined in transiently transfected COS-7 cells using human ¹²⁵I-GIP(3-30)NH₂. The selectivity of human GIP(3-30)NH₂ was examined by testing for agonistic and antagonistic properties on 62 human GPCRs. Human GIP(3-30)NH₂ inhibited GIP(1-42)-induced cAMP and β-arrestin 1 and 2 recruitment on the human GIPR and Schild plot analysis showed competitive antagonism with a pA₂ and Hill slope of 16.8 nM and 1.11 ± 0.02 in cAMP, 10.6 nM and 1.15 ± 0.05 in β-arrestin 1 recruitment, and 10.2 nM and 1.06 ± 0.05 in β-arrestin 2 recruitment. Efficient internalization of the GIPR was dependent on the presence of either β-arrestin 1 or 2. Moreover, GIP(3-30)NH₂ inhibited GIP(1-42)-induced internalization in a concentration-dependent manner and notably also inhibited GIP-mediated signaling in human subcutaneous adipocytes. Finally, the antagonist was established as GIPR selective among 62 human GPCRs being species-specific with high affinity binding to the human and non-human primate (Macaca fascicularis) GIPRs, and low affinity binding to the rat and mouse GIPRs (K_d values of 2.0, 2.5, 31.6 and 100 nM, respectively). In conclusion, human GIP(3-30)NH₂ is a selective and species-specific GIPR antagonist with broad inhibition of signaling and internalization in transfected cells as well as in human adipocytes.

Peptides from frog skin with potential for development into agents for Type 2 diabetes therapy

Several frog skin peptides, first identified as result of their antimicrobial or immunomodulatory activities, have subsequently been shown to stimulate insulin release both in vitro and in vivo and so show potential for development into incretin-based drugs for treatment of patients with Type 2 diabetes mellitus. However, their therapeutic potential as anti-diabetic agents is not confined to this activity as certain frog skin-derived peptides, such as magainin-AM2 and CPF-SE1 and analogs of hymenochirin-1B, tigerinin-1R, and esculentin-2CHa, have been shown to increase insulin sensitivity, promote β-cell proliferation, suppress pancreatic and circulating glucagon concentrations, improve the lipid profile, and selectively alter expression of genes involved in insulin secretion and action in mice with diet-induced obesity, insulin resistance and impaired glucose tolerance. This review assesses the therapeutic possibilities of peptides from frogs belonging to the Pipidae, Dicroglossidae, and Ranidae families, focusing upon work that has been carried out since 2014.