Impaired hyperglycemia-induced delay in gastric emptying in patients with type 1 diabetes deficient for islet amyloid polypeptide

A model of subcutaneous pramlintide pharmacokinetics and its effect on gastric emptying: Proof-of-concept based on populational data

Pramlintide, an amylin analog, has been coming up as an agent in type 1 diabetes dual-hormone therapies (insulin/pramlintide). Since pramlintide slows down gastric emptying, it allows for easing glucose control and reducing the burden of meal announcements. Pre-clinical in silico evaluations are a key step in the development of any closed-loop strategy. However, mathematical models are needed, and pramlintide models in the literature are scarce. This work proposes a proof-of-concept pramlintide model, describing its subcutaneous pharmacokinetics (PK) and its effect on gastric emptying (PD). The model is validated with published populational (clinical) data. The model development is divided into three stages: intravenous PK, subcutaneous PK, and PD modeling. In each stage, a set of model structures are proposed, and their performance is assessed using the Akaike Information Criterion (AIC) and the Bayesian Information Criterion (BIC). In order to evaluate the modulation of the rate of gastric emptying, a literature meal model was used. The final pramlintide model comprises four compartments and a function that modulates gastric emptying depending on plasma pramlintide. Results show an appropriate fit for the data. Some aspects are left as open questions due to the lack of specific data (e.g., the influence of meal composition on the pramlintide effect). Moreover, further validation with individual data is necessary to propose a virtual cohort of patients.

Unveiling the Effects of Copper Ions in the Aggregation of Amyloidogenic Proteins

Amyloid diseases have become a global concern due to their increasing prevalence. Transition metals, including copper, can affect the aggregation of the pathological proteins involved in these diseases. Copper ions play vital roles in organisms, but the disruption of their homeostasis can negatively impact neuronal function and contribute to amyloid diseases with toxic protein aggregates, oxidative stress, mitochondrial dysfunction, impaired cellular signaling, inflammation, and cell death. Gaining insight into the imbalance of copper ions and its impact on protein folding and aggregation is crucial for developing focused therapies. This review examines the influence of copper ions on significant amyloid proteins/peptides, offering a comprehensive overview of the current understanding in this field.

Effect of anthocyanin-rich blackberry juice on endoplasmic reticulum stress in streptozotocin-induced diabetic rats

This study investigates blackberry juice's effects on glucose metabolism, oxidative stress, inflammation, and endoplasmic reticulum stress (ER) in streptozotocin (STZ)-induced diabetic rats. Fifty Wistar rats were distributed to five groups randomly of ten rats each: Normal control, diabetic control, 9 mL/kg body weight (b.wt) blackberry juice only, blackberry juice plus diabetes, and 500 mg/kg b.wt metformin plus diabetes. A single intraperitoneal injection of 50 mg/kg b.wt STZ induced diabetes in the rats. This animal study continued for 56 days after the confirmation of diabetes. The levels of liver function and renal function, as well as insulin, glucose-6-phosphatase, glucokinase, and malondialdehyde (MDA) levels, and the activities of catalase (CAT) and superoxide dismutase (SOD), were determined. Additionally, interleukin-6 (IL-6) levels, tumor necrosis factor-alpha (TNF-α), and activated transcription factor 4 (ATF4) expressions were examined in the liver homogenate of rats. Furthermore, the liver tissues were utilized for histopathological examination. The results showed that blackberry juice prevented drastic loss of body weight and reduced food consumption in diabetic rats. Additionally, the levels of blood glucose, total protein, aspartate aminotransferase (AST), albumin, alanine aminotransferase (ALT), uric acid, creatinine, and urea improved after the administration of blackberry juice in diabetic rats. Blackberry juice significantly increased glucose metabolism and antioxidant status while reducing ER stress and inflammation in diabetic rats. Moreover, blackberry juice improved glucose metabolism by increasing insulin levels and improving the dysregulated activities of glucose-metabolizing enzymes. The microstructure of liver tissues in diabetic rats was also improved with blackberry juice treatment. Therefore, blackberry juice has the potential to alleviate diabetes in rats and could be considered as a functional food for people with diabetes.

Novel insights into the pathogenic impact of diabetes on the gastrointestinal tract

Type 2 and type 1 diabetes are common endocrine disorders with a progressively increasing incidence worldwide. These chronic, systemic diseases have multiorgan implications, and the whole gastrointestinal (GI) tract represents a frequent target in terms of symptom appearance and interdependent pathophysiological mechanisms. Metabolic alterations linked with diabetic complications, neuropathy and disrupted hormone homeostasis can lead to upper and/or lower GI symptoms in up to 75% of diabetic patients, with multifactorial involvement of the oesophagus, stomach, upper and lower intestine, and of the gallbladder. On the other hand, altered gastrointestinal motility and/or secretions are able to affect glucose and lipid homeostasis in the short and long term. Finally, diabetes has been linked with increased cancer risk at different levels of the GI tract. The presence of GI symptoms and a comprehensive assessment of GI function should be carefully considered in the management of diabetic patients to avoid further complications and to ameliorate the quality of life. Additionally, the presence of gastrointestinal dysfunction should be adequately managed to improve metabolic homeostasis, the efficacy of antidiabetic treatments and secondary prevention strategies.

Nrf2 attenuates hyperglycemia-induced nNOS impairment in adult mouse primary enteric neuronal crest cells and normalizes stomach function

Enteric neuronal cells play a vital role in gut motility in humans and experimental rodent models. Patients with diabetes are more vulnerable to gastrointestinal dysfunction due to enteric neuronal degeneration. In this study, we examined the mechanistic role and regulation of nuclear factor-erythroid 2-related factor 2 (Nrf2) in hyperglycemia-induced enteric neuronal cell apoptosis in vitro by using adult mouse primary enteric neuronal crest cells (pENCs). Our data show that hyperglycemia (HG) or inhibition of Nrf2 induces apoptosis by elevating proinflammatory cytokines, reactive oxygen species (ROS) and suppresses neuronal nitric oxide synthase (nNOS-α) via PI3K/Nrf2-mediated signaling. Conversely, treating pENCs with cinnamaldehyde (CNM), a naturally occurring Nrf2 activator, prevented HG-induced apoptosis. These novel data reveal a negative feedback mechanism for GSK-3 activation. To further demonstrate that loss of Nrf2 leads to inflammation, oxidative stress, and reduces nNOS-mediated gastric function, we have used streptozotocin (STZ)-induced diabetic and Nrf2 null female mice. In vivo activation of Nrf2 with CNM (50 mg/kg, 3 days a week, ip) attenuated impaired nitrergic relaxation and delayed gastric emptying (GE) in conventional type 1 diabetic but not in Nrf2 null female mice. Supplementation of CNM normalized diabetes-induced altered gastric antrum protein expression of 1) p-AKT/p-p38MAPK/p-GSK-3β, 2) BH4 (cofactor of nNOS) biosynthesis enzyme GCH-1, 3) nNOSα, 4) TLR4, NF-κB, and 5) inflammatory cytokines (TNF-α, IL-1β, IL-6). We conclude that activation of Nrf2 prevents hyperglycemia-induced apoptosis in pENCs and restores nitrergic-mediated gastric motility and GE in STZ-induced diabetes female mice.NEW & NOTEWORTHY Primary neuronal cell crust (pENCs) in the intestine habitats nNOS and Nrf2, which was suppressed in diabetic gastroparesis. Activation of Nrf2 restored nNOS by suppressing inflammatory markers in pENCs cells. Inhibition of Nrf2 reveals a negative feedback mechanism for the activation of GSK-3. Activation of Nrf2 alleviates STZ-induced delayed gastric emptying and nitrergic relaxation in female mice. Activation of Nrf2 restored impaired gastric BH₄ biosynthesis enzyme GCH-1, nNOSα expression thus regulating nitric oxide levels.

The β Cell in Diabetes: Integrating Biomarkers With Functional Measures

The pathogenesis of hyperglycemia observed in most forms of diabetes is intimately tied to the islet β cell. Impairments in propeptide processing and secretory function, along with the loss of these vital cells, is demonstrable not only in those in whom the diagnosis is established but typically also in individuals who are at increased risk of developing the disease. Biomarkers are used to inform on the state of a biological process, pathological condition, or response to an intervention and are increasingly being used for predicting, diagnosing, and prognosticating disease. They are also proving to be of use in the different forms of diabetes in both research and clinical settings. This review focuses on the β cell, addressing the potential utility of genetic markers, circulating molecules, immune cell phenotyping, and imaging approaches as biomarkers of cellular function and loss of this critical cell. Further, we consider how these biomarkers complement the more long-established, dynamic, and often complex measurements of β-cell secretory function that themselves could be considered biomarkers.

Inhibition of GSK-3β restores delayed gastric emptying in obesity-induced diabetic female mice

Diabetic gastroparesis (DG) is a clinical syndrome characterized by delayed gastric emptying (DGE). Loss of nuclear factor erythroid 2-related factor 2 (Nrf2) is associated with reduced neuronal nitric oxide synthase-α (nNOSα)-mediated gastric motility and DGE. Previous studies have shown that nuclear exclusion and inactivation of Nrf2 is partly regulated by glycogen synthase kinase 3β (GSK-3β). In the current study, the molecular signaling of GSK-3β-mediated Nrf2 activation and its mechanistic role on DG were investigated in high-fat diet (HFD)-induced obese/Type 2 diabetes (T2D) female mice. Adult female C57BL/6J mice were fed with HFD or normal diet (ND) with or without GSK-3β inhibitor (SB 216763, 10 mg/kg body wt ip) start from the 14th wk and continued feeding mice for an additional 3-wk time period. Our results show that treatment with GSK-3β inhibitor SB attenuated DGE in obese/T2D mice. Treatment with SB restored impaired gastric 1) Nrf2 and phase II antioxidant enzymes through PI3K/ERK/AKT-mediated pathway, 2) tetrahydrobiopterin (BH₄, cofactor of nNOS) biosynthesis enzyme dihydrofolate reductase, and 3) nNOSα dimerization in obese/T2 diabetic female mice. SB treatment normalized caspase 3 activity and downstream GSK-3β signaling in the gastric tissues of the obese/T2 diabetic female mice. In addition, GSK-3β inhibitor restored impaired nitrergic relaxation in hyperglycemic conditions. Finally, SB treatment reduced GSK3 marker, pTau in adult primary enteric neuronal cells. These findings emphasize the importance of GSK-3β on regulating gastric Nrf2 and nitrergic mediated gastric emptying in obese/diabetic rodents.NEW & NOTEWORTHY Inhibition of glycogen synthase kinase 3β (GSK-3β) with SB 216763 attenuates delayed gastric emptying through gastric nuclear factor erythroid 2-related factor 2 (Nrf2)-phase II enzymes in high-fat diet-fed female mice. SB 216763 restored impaired gastric PI3K/AKT/ β-catenin/caspase 3 expression. Inhibition of GSK-3β normalized gastric dihydrofolate reductase, neuronal nitric oxide synthase-α expression, dimerization and nitrergic relaxation. SB 216763 normalized both serum estrogen and nitrate levels in female obese/Type 2 diabetes mice. SB 216763 reduced downstream signaling of GSK-3β in enteric neuronal cells in vitro.

A Novel Dual-Hormone Insulin-and-Pramlintide Artificial Pancreas for Type 1 Diabetes: A Randomized Controlled Crossover Trial

OBJECTIVE

The rapid insulin-alone artificial pancreas improves glycemia in type 1 diabetes but daytime control remains suboptimal. We propose two novel dual-hormone artificial pancreas systems.

RESEARCH DESIGN AND METHODS

We conducted a randomized crossover trial comparing a rapid insulin-alone artificial pancreas with rapid insulin-and-pramlintide and with regular insulin-and-pramlintide artificial pancreas systems in adults with type 1 diabetes. Participants were assigned to the interventions in random order during three 24-h inpatient visits. Each visit was preceded by an outpatient hormonal open-loop run-in period of 10-14 days. The dual-hormone artificial pancreas delivered pramlintide in a basal-bolus manner, using a novel dosing algorithm, with a fixed ratio relative to insulin. The primary outcome was time in the range 3.9-10.0 mmol/L.

RESULTS

Compared with the rapid insulin-alone artificial pancreas system, the rapid insulin-and-pramlintide system increased the time in range from 74% (SD 18%) to 84% (13%) (P = 0.0014), whereas the regular insulin-and-pramlintide system did not change the time in range (69% [19%]; P = 0.22). The increased time in range with the rapid insulin-and-pramlintide system was due to improved daytime control (daytime time in range increased from 63% [23%] to 78% [16%], P = 0.0004). There were 11 (1 per 2.5 days) hypoglycemic events (<3.3 mmol/L with symptoms or <3.0 mmol/L irrespective of symptoms) with the rapid insulin-alone system, compared with 12 (1 per 2.3 days) and 18 (1 per 1.4 days) with the rapid and regular insulin-and-pramlintide systems, respectively. Gastrointestinal symptoms were reported after 0% (0 of 112) of meals with the rapid insulin-alone system, compared with 6% (6 of 108) and 11% (11 of 104) with the rapid and regular insulin-and-pramlintide systems, respectively; none of the symptoms were severe.

CONCLUSIONS

A novel rapid insulin-and-pramlintide artificial pancreas improves glucose control compared with a rapid insulin-alone artificial pancreas (ClinicalTrials.gov number NCT02814123).

Evaluation of Gastric Emptying in Cystic Fibrosis Using Bedside Ultrasonography

OBJECTIVES

Although gastric emptying rate (GER) influences incretin response and nutrient absorption, both defective in people with cystic fibrosis (CF), there are few studies in this group, and the circadian rhythm is unknown. We employed an ultrasonographic technique to assess GER in people with CF following liquid and mixed meals and also evaluated the circadian rhythm, compared to normal controls.

METHODS

Thirteen pancreatic-insufficient adults with CF and 10 healthy controls underwent a fasting oral glucose tolerance test (OGTT; liquid meal) and on a second visit underwent a fasting mixed meal test (MMT) thrice on the same day. GER was measured during the OGTT and each MMT using a 3.5-MHz abdominal transducer probe at baseline and 30, 60, 90, and 120 minutes.

RESULTS

Controls had normal GER for both OGTT and MMT. Compared to controls, people with CF had delayed GER₆₀ for OGTT (mean 46%), which increased with time (P = .001), and also delayed GER₉₀ for MMT in the morning (mean 56%), afternoon (58%), and evening (59%). The GER in the control group was better at all time points throughout the day compared to patients with CF.

CONCLUSIONS

This is the first study to use ultrasonography, an inexpensive bedside technique, to assess GER in adults with CF. For the first time, we have shown that adults with CF have delayed GER for both liquid and mixed meals, and this delay continues throughout the day.

A contemporary biological pathway of islet amyloid polypeptide for the management of diabetic dementia

Major challenges of dealing elder patients with diabetes mellitus (DM) are the individualization of consideration in persons with various comorbid types of conditions. In spite of the fact that microvascular and macrovascular problems associated with DM are well documented, there is only a few numbers of reports viewing different conditions, for example, cognitive dysfunction. Cognitive dysfunction is of specific significance due to its effect on self-care and quality of life. All in all, the etiology of cognitive dysfunction in the maturing populace is probably going to be the grouping of ischemic and degenerative pathology. It is likewise trusted that Hyperglycemia is engaged with the system of DM-related cognitive dysfunction. At present, it isn't certain in the case of enhancing glycemic control or utilizing therapeutic agents can enhance the risk of cognitive decay. Amylin was later characterized as an amyloidogenic peptide, confined from a beta cell tumor and called islet amyloid polypeptide (IAPP), and after that, amylin. Conversely, we investigate the beneficial role and hypothesizing the mechanism of amylin related expanding the level and activation of CGRP receptor to enhance the cognition declination amid diabetic dementia.

Human amylin induces CD4+Foxp3+ regulatory T cells in the protection from autoimmune diabetes

Autoimmune diabetes is a disorder of immune homeostasis that leads to targeted insulin-secreting islet β cell destruction characterized by insulitis. Human amylin (hA) is an important neuroendocrine hormone co-secreted with insulin by pancreatic β cells. Here, we report hA immune-modulatory action through inducing regulatory T cells. We ex vivo-treated human peripheral blood mononuclear cells (hPBMCs) with hA for 24 h and counted CD4+Foxp3+ regulatory T cells (Treg) using flow cytometry. Diabetic status was monitored and splenic Treg were measured in non-obese diabetic (NOD) male mice. NOD mice were intraperitoneally injected once daily with hA (n = 25) or solvent for control (n = 25) for 7 months continuously. Spleen tissues were collected at the end of intervention and processed for flow cytometry and Western blot. We found a 2.9-fold (p < 0.05) increase of CD4+Foxp3+ Treg in hPBMCs treated with 10 nmol/L hA compared with negative control. Incidence of diabetes in hA-treated NOD mice decreased 44% (p = 0.045) in the 6th month and 57% (p = 0.0002) in the 7th month. Meanwhile, the hA treatment induced a 1.5-fold increase of CD4+Foxp3+ Treg from mouse splenocytes (p = 0.0013). Expression of transforming growth factor-β (TGF-β) and toll-like receptor-4 (TLR-4) were upregulated in hA-treated mice. Human amylin might protect against autoimmune diabetes via the induction of CD4+Foxp3+ Treg, which suggests a novel approach to improve autoimmune conditions.

A Novel Pentapeptide Inhibitor Reduces Amyloid Deposit Formation by Direct Interaction with hIAPP

BACKGROUNDS

The presence of amyloid deposits of human islet amyloid polypeptide (hIAPP) in islet β-cells has been associated with type 2 diabetes occurrence and islet graft failure. Self-assembly into oligomers and fibrils during the process of aggregation by hIAPP can lead to failure and depletion of β-cells. Studies have shown that some critical regions of hIAPP might contribute to the aggregation. Thus, many studies focused on finding the effective molecules, especially the short-peptide inhibitors, that bind to these regions and disrupt the aggregation of hIAPP. In the present study, a novel pentapeptide inhibitor Phe-Leu-Pro-Asn-Phe (FLPNF) was designed and its effectiveness on the inhibition of the formation of amyloid deposits was examined.

METHODS

The binding mode between FLPNF and hIAPP was performed using molecular docking. The effectiveness of FLPNF on inhibiting hIAPP amyloid aggregation was tested by Thioflavin T (ThT) staining. Furthermore, negative stain electron microscopy was used to observe hIAPP fibrils. A biolayer interferometry analysis was used to identify the interaction between FLPNF and hIAPP. In addition, the cytotoxicity toward INS-1 cells was tested by a cell proliferation assay.

RESULTS

FLPNF was predicted to have a compact conformation to bind at the site of hIAPP. FLPNF strongly inhibited the amyloid aggregation of hIAPP at a 10 : 1 molar ratio in vitro. Coincubation of FLPNF with hIAPP decreased the amount of hIAPP fibrils. Furthermore, a direct interaction between FLPNF and hIAPP was confirmed. FLPNF could also decrease the cytotoxic effect of hIAPP.

CONCLUSIONS

The novel pentapeptide inhibitor FLPNF was constructed and inhibited the aggregation through direct binding to hIAPP. It is considered a suitable inhibitor for hIAPP amyloid deposit formation.

Non-insulin pharmacological therapies for treating type 1 diabetes

INTRODUCTION

Despite intensified insulin treatment, many persons with type 1 diabetes (T1D) do not achieve glycemic and metabolic targets. Consequently, non-insulin chemical therapies that improve glycemic control and metabolic parameters without increasing the risk of adverse events (including hypoglycemia) are of interest as adjunct therapies to insulin.

AREAS COVERED

In this review, the authors discuss the efficacy and safety of non-insulin therapies, including pramlintide, glucagon-like peptide-1 (GLP-1) receptor agonists, dipeptidyl peptidase-4 inhibitors (DPP-4), sodium-glucose cotransporter (SGLT1 and SGLT2) inhibitors, metformin, sulfonylureas, and thiazolidinediones as add-on therapies to insulin in T1D.

EXPERT OPINION

The current evidence shows that the efficacy of non-insulin therapies as add-on therapies to insulin is minimal or modest with an average HbA1c reduction of 0.2-0.5% (2-6 mmol/mol). Indeed, the current focus is on the development of SGLT inhibitors as adjuncts to insulin in type 1 diabetes. Studies of subgroups with obesity, residual beta-cell function (including newly diagnosed patients) and patients prone to hypoglycemia could be areas of future research.

Role and Cytotoxicity of Amylin and Protection of Pancreatic Islet β-Cells from Amylin Cytotoxicity

Amylin, (or islet amyloid polypeptide; IAPP), a 37-amino acid peptide hormone, is released in response to nutrients, including glucose, lipids or amino acids. Amylin is co-stored and co-secreted with insulin by pancreatic islet β-cells. Amylin inhibits food intake, delays gastric emptying, and decreases blood glucose levels, leading to the reduction of body weight. Therefore, amylin as well as insulin play important roles in controlling the level of blood glucose. However, human amylin aggregates and human amylin oligomers cause membrane disruption, endoplasmic reticulum (ER) stress and mitochondrial damage. Since cytotoxicity of human amylin oligomers to pancreatic islet β-cells can lead to diabetes, the protection of pancreatic islet β cells from cytotoxic amylin is crucial. Human amylin oligomers also inhibit autophagy, although autophagy can function to remove amylin aggregates and damaged organelles. Small molecules, including β-sheet breaker peptides, chemical chaperones, and foldamers, inhibit and disaggregate amyloid formed by human amylin, suggesting the possible use of these small molecules in the treatment of diabetes. In this review, we summarize recent findings regarding the role and cytotoxicity of amylin and the protection of pancreatic islet β-cells from cytotoxicity of amylin.

Gastric Emptying Impacts the Timing of Meal Glucose Peak in Subjects With Uncomplicated Type 1 Diabetes

CONTEXT

Diabetes mellitus is associated with gastrointestinal (GI) motility dysfunction, ranging from delayed to accelerated gastric emptying (GE).

OBJECTIVE

To evaluate GE in patients with type 1 diabetes mellitus (T1DM) without chronic complications and to investigate its relation with postprandial glucose and GI hormone responses.

DESIGN

Cross-sectional study.

SETTING/PARTICIPANTS

Forty-two patients with T1DM free of chronic complications referred to Federico II University and 31 healthy controls similar for age, sex, and body mass index.

INTERVENTIONS/MAIN OUTCOME MEASURES

GE was assessed by using the 13C-octanoate breath test with a standardized solid meal. During the meal, plasma glucose, ghrelin, and glucagon-like peptide 1 (GLP-1) responses were assessed, and GI symptoms were evaluated by a specific questionnaire.

RESULTS

Patients with T1DM showed a significantly slower GE half-emptying time (GE t1/2) (113 ± 34 minutes) than did controls (89 ± 17 minutes; P < 0.001). Thirty-six percent of T1DM showed a delayed GE (t1/2 > 120 minutes), whereas all controls showed a normal GE. When patients with T1DM were stratified according to GE t1/2, postmeal glucose response was significantly different between those with delayed and those with normal GE (P = 0.013). In particular, patients with T1DM and delayed GE showed a significantly longer mean time to peak glucose than did patients with normal GE (P = 0.004). In addition, GE t1/2 was an independent predictor of the time to peak glucose (β = 0.329; P = 0.025). GLP-1 and ghrelin responses to the test meal, as well as the prevalence of GI symptoms, were similar between patients with T1DM and controls and between patients with T1DM with normal GE and those with delayed GE.

CONCLUSIONS

Delayed GE time is associated with a longer time to peak glucose. GE evaluation could be useful for individualizing the timing of preprandial insulin bolus in patients with T1DM.

13C-Acetic Acid Breath Test Monitoring of Gastric Emptying during Disease Progression in Diabetic Rats

Gastric motility disturbance is commonly found in long-standing hyperglycemia. Both delayed and rapid gastric emptying has been reported in diabetes. However, very few studies have followed the changes in gastric emptying during disease progression in diabetes because of technical limitations. ¹³C-Acetic acid breath test is a validated method which is non-invasive and can be used repeatedly or serially to evaluate gastric emptying changes in animal. We investigated the gastric emptying changes in different stages of diabetes using ¹³C-acetic acid breath test, as well as its related mechanisms involving interstitial cells of Cajal (ICCs), and stem cell factor (SCF) in streptozotocin-induced diabetic rats. The results showed that gastric emptying was accelerated at the early stage (12 weeks of diabetes) whereas intramuscular ICCs (ICC-IM) networks were not different from normal group. At long-term stage (28 weeks of diabetes), gastric emptying had returned to normal pattern with no delayed. ICC-IM networks were decreased in the diabetic group compared to 12th weeks, and were lower than in the normal group at the same time point. SCF levels were constantly high in the diabetic group than in the normal group. This result indicated that ¹³C-acetic acid breath test is useful to track the alteration in gastric emptying during disease progression. The change of gastric emptying was not found to be significantly associated with ICC-IM. Elevated SCF may help to preserve ICC-IM, especially in the early phase of diabetes.

IAPP and type 1 diabetes: implications for immunity, metabolism and islet transplants

Islet amyloid polypeptide (IAPP), the main component of islet amyloid in type 2 diabetes and islet transplants, is now recognized as a contributor to beta cell dysfunction. Increasingly, evidence warrants its investigation in type 1 diabetes owing to both its immunomodulatory and metabolic actions. Autoreactive T cells to IAPP-derived epitopes have been described in humans, suggesting that IAPP is an islet autoantigen in type 1 diabetes. In addition, although aggregates of IAPP have not been implicated in type 1 diabetes, they are potent pro-inflammatory stimuli to innate immune cells, and thus, could influence autoimmunity. IAPP aggregates also occur rapidly in transplanted islets and likely contribute to islet transplant failure in type 1 diabetes through sterile inflammation. In addition, since type 1 diabetes is a disease of both insulin and IAPP deficiency, clinical trials have examined the potential benefits of IAPP replacement in type 1 diabetes with the injectable IAPP analogue, pramlintide. Pramlintide limits postprandial hyperglycemia by delaying gastric emptying and suppressing hyperglucagonemia, underlining the possible role of IAPP in postprandial glucose metabolism. Here, we review IAPP in the context of type 1 diabetes: from its potential involvement in type 1 diabetes pathogenesis, through its role in glucose metabolism and use of IAPP analogues as therapeutics, to its potential role in clinical islet transplant failure and considerations in this regard for future beta cell replacement strategies.

Islet amyloid polypeptide: Another key molecule in Alzheimer's pathogenesis?

Recent epidemiological evidence reveals that patients suffering from type 2 diabetes mellitus (T2DM) often experience a significant decline in cognitive function, and approximately 70% of those cases eventually develop Alzheimer's disease (AD). Although several pathological processes are shared by AD and T2DM, the exact molecular mechanisms connecting these two diseases are poorly understood. Aggregation of human islet amyloid polypeptide (hIAPP), the pathological hallmark of T2DM, has also been detected in brain tissue and is associated with cognitive decline and AD development. In addition, hIAPP and amyloid β protein (Aβ) share many biophysical and physiological properties as well as exert similar cytotoxic mechanisms. Therefore, it is important to examine the possible role of hIAPP in the pathogenesis of AD. In this article, we introduce the basics on this amyloidogenic protein. More importantly, we discuss the potential mechanisms of hIAPP-induced AD development, which will be beneficial for proposing novel and feasible strategies to optimize AD prevention and/or treatment in diabetics.

Relationship Between Gastric Emptying and Diurnal Glycemic Control in Type 1 Diabetes Mellitus: A Randomized Trial

CONTEXT

In type 1 diabetes (T1D), delayed gastric emptying (GE) may predispose to a mismatch between insulin delivery and glucose absorption. Previous studies evaluated, only partly, the relationship between delayed GE and postprandial, but not diurnal, glycemia.

OBJECTIVE

To assess the relationship between GE disturbances and glycemic control in T1D and the effects of accelerating GE on glycemic control.

DESIGN, SETTING, AND PARTICIPANTS

This was a randomized placebo-controlled trial in 30 patients with T1D on an insulin pump at an academic medical center.

INTERVENTION(S)

GE was evaluated with a [13C]-Spirulina breath test at baseline (GEbaseline), during intravenous saline or erythromycin (2 or 3 mg/kg; GEiv), and after 7 days of oral erythromycin or placebo (GEoral). Weighed meals were provided throughout the study.

MAIN OUTCOME MEASURE(S)

These were GE and continuous glucose monitoring (CGM).

RESULTS

The baseline glycosylated hemoglobin was 7.6% ± 0.8% (60 ± 8.7 mmol/mol); 12 patients (40%) had delayed GE; faster GE was associated with a greater postprandial CGM-based glucose, but slower GE was not associated with postprandial hypoglycemia (<70 mg/dL). Intravenous (3 mg/kg) but not oral erythromycin accelerated GE. The relationship between GE and glycemia differed between the postprandial periods and the entire day. After adjusting for carbohydrate intake and insulin consumption, faster GE was associated with more hyperglycemia during the postprandial period but lower glucose values across the entire study.

CONCLUSIONS

In T1D, pharmacologically mediated acceleration of GE increases postprandial CGM-based glucose. In contrast, delayed GE is associated with greater CGM-based glucose values over the entire day.

Non-insulin drugs to treat hyperglycaemia in type 1 diabetes mellitus

Insulin treatment of individuals with type 1 diabetes has shortcomings and many patients do not achieve glycaemic and metabolic targets. Consequently, the focus is on novel non-insulin therapeutic approaches that reduce hyperglycaemia and improve metabolic variables without increasing the risk of hypoglycaemia or other adverse events. Several therapies given in conjunction with insulin have been investigated in clinical trials, including pramlintide, glucagon-like peptide-1 receptor agonists, dipeptidyl peptidase-4 inhibitors, sodium-glucose co-transporter inhibitors, metformin, sulfonylureas, and thiazolidinediones. These drugs have pleiotropic effects on glucose metabolism and different actions complementary to those of insulin-this Review reports the effects of these drugs on glycaemic control, glucose variability, hypoglycaemia, insulin requirements, and bodyweight. Existing studies are of short duration with few participants; evidence for the efficacy of concomitant treatments is scarce and largely clinically insignificant. A subgroup of patients with type 1 diabetes for whom non-insulin antidiabetic drugs could significantly benefit glycaemic control cannot yet be defined, but we suggest that obese patients prone to hypoglycaemia and patients with residual β-cell function are populations of interest for future trials.

Relationship Between Control of Glycemia and Gastric Emptying Disturbances in Diabetes Mellitus

BACKGROUND & AIMS

Hyperglycemia is implicated as a major risk factor for delayed gastric emptying in diabetes mellitus and vice versa. However, the extent to which hyperglycemia can affect gastric emptying and vice versa and the implications for clinical practice are unclear. We systematically reviewed the evidence for this bidirectional relationship and the effects of pharmacotherapy for diabetes on gastric emptying.

METHODS

Full-length articles investigating the relationship between diabetes mellitus and gastroparesis were reviewed primarily to quantify the relationship between blood glucose concentrations and gastrointestinal sensorimotor functions, particularly gastric emptying, and gastrointestinal symptoms. The effects of drugs and hormones that affect glycemia on gastrointestinal sensorimotor functions were also evaluated.

RESULTS

Acute severe hyperglycemia delayed gastric emptying relative to euglycemia in type 1 diabetes; the corresponding effects in type 2 diabetes are unknown. Limited evidence suggests that even mild hyperglycemia (8 mmol/L) can delay gastric emptying in type 1 diabetes. Long-term hyperglycemia is an independent risk factor for delayed gastric emptying in type 1 diabetes. There is little evidence that delayed gastric emptying causes hypoglycemia in diabetes and no evidence that improved control of glycemia improves gastric emptying or vice versa. Glucagon-like peptide-1 agonists but not dipeptidylpeptidase-4 inhibitors given acutely delay gastric emptying, but tachyphylaxis may occur.

CONCLUSIONS

Although acute severe and chronic hyperglycemia can delay gastric emptying, there is limited evidence that delayed gastric emptying is an independent risk factor for impaired glycemic control or hypoglycemia in diabetes. The impact of improved glycemic control on gastric emptying and vice versa in diabetes is unknown.

Increased Expression of Pyloric ERβ Is Associated With Diabetic Gastroparesis in Streptozotocin-Induced Male Diabetic Rats

BACKGROUND

Gastroparesis is a significant co-morbidity affecting up to 50% of patients with diabetes and is disproportionately found in women. Prior studies have suggested that loss of interstitial cells of Cajal, hyperglycemia, and nitric oxide dysfunction are potential causes of gastroparesis. Since diabetic gastroparesis affects more women than men, we performed an exploratory study with a diabetic rat model to determine if sex hormone signaling is altered in those where gastroparesis develops.

METHODS

We injected male rats with streptozotocin (STZ) to model type I diabetes, as confirmed by blood glucose levels. Gastroparesis was determined by acetaminophen gavage and serum acetaminophen levels. Rats were grouped based on acetaminophen and blood glucose data: diabetic (DM), diabetic and gastroparetic (DM + GP), and control (CM). Serum levels of testosterone, estrogen, and insulin were determined as well as aromatase expression in pyloric tissue and serum. Androgen receptor and estrogen receptor α (ERα) and β (ERβ) were also measured in the pylorus.

RESULTS

Compared to CM, estrogen increased and testosterone decreased in both DM and DM + GP rats. Sex hormone levels were not different between DM and DM + GP. Serum aromatase was increased in DM and DM + GP rats; however, pyloric tissue levels were not significantly different from controls. ERα was unchanged and androgen receptor decreased in DM and DM + GP. ERβ was increased only in DM + GP animals.

CONCLUSION

Our study implicates increased pyloric ERβ in the development of gastroparesis in STZ-induced male diabetic rats. Increased serum aromatase is likely responsible for altered sex hormone levels. Our study supports the implication of sex hormone signaling in diabetic development and demonstrates a potential unique role for pyloric ERβ in male diabetic gastroparesis.

Neuroendocrine hormone amylin in diabetes

The neuroendocrine hormone amylin, also known as islet amyloid polypeptide, is co-localized, co-packaged and co-secreted with insulin from adult pancreatic islet β cells to maintain glucose homeostasis. Specifically, amylin reduces secretion of nutrient-stimulated glucagon, regulates blood pressure with an effect on renin-angiotensin system, and delays gastric emptying. The physiological actions of human amylin attribute to the conformational α-helix monomers whereas the misfolding instable oligomers may be detrimental to the islet β cells and further transform to β-sheet fibrils as amyloid deposits. No direct evidence proves that the amylin fibrils in amyloid deposits cause diabetes. Here we also have performed a systematic review of human amylin gene changes and reported the S20G mutation is minor in the development of diabetes. In addition to the metabolic effects, human amylin may modulate autoimmunity and innate inflammation through regulatory T cells to impact on both human type 1 and type 2 diabetes.

Effect of Pramlintide on Postprandial Glucose Fluxes in Type 1 Diabetes

CONTEXT

Early postprandial hyperglycemia and delayed hypoglycemia remain major problems in current management of type 1 diabetes (T1D).

OBJECTIVE

Our objective was to investigate the effects of pramlintide, known to suppress glucagon and delay gastric emptying, on postprandial glucose fluxes in T1D.

DESIGN

This was a single-center, inpatient, randomized, crossover study.

PATIENTS

Twelve patients with T1D who completed the study were analyzed.

INTERVENTIONS

Subjects were studied on two occasions with or without pramlintide. Triple tracer mixed-meal method and oral minimal model were used to estimate postprandial glucose turnover and insulin sensitivity (SI). Integrated liver insulin sensitivity was calculated based on glucose turnover. Plasma glucagon and insulin were measured.

MAIN OUTCOME MEASURE

Glucose turnover and SI were the main outcome measures.

RESULTS

With pramlintide, 2-hour postprandial glucose, insulin, glucagon, glucose turnover, and SI indices showed: plasma glucose excursions were reduced (difference in incremental area under the curve [iAUC], 444.0 mMmin, P = .0003); plasma insulin concentrations were lower (difference in iAUC, 7642.0 pMmin; P = .0099); plasma glucagon excursions were lower (difference in iAUC, 1730.6 pg/mlmin; P = .0147); meal rate of glucose appearance was lower (difference in iAUC: 1196.2 μM/kg fat free mass [FFM]; P = .0316), endogenous glucose production was not different (difference in iAUC: -105.5 μM/kg FFM; P = .5842), rate of glucose disappearance was lower (difference in iAUC: 1494.2 μM/kg FFM; P = .0083). SI and liver insulin sensitivity were not different between study visits (P > .05).

CONCLUSIONS

Inhibition of glucagon and gastric emptying delaying reduced 2-hour prandial glucose excursions in T1D by delaying meal rate of glucose appearance.

Gastroretentive systems - a proposed strategy to modulate anthocyanin release and absorption for the management of diabetes

Several reports have indicated a positive correlation between the consumption of anthocyanins (ACN) and biomarkers relating to the improvement of type 2 diabetes (T2D). However, the results from in vitro studies often do not translate into clinical evidence. Potential causes of these discrepancies are experimental conditions that lack physiological relevancy; extensive degradation of these compounds in vivo due to changes in pH and metabolism; and a short residence time in the absorption window in relation to the absorption rate. Here, gastroretentive systems (GRS) are proposed as a strategy to overcome the limitations in ACN delivery and to reduce the existing bench-to-subject gap. This review summarizes recent literature on the use of ACN for the management and control of T2D, followed by GRS platforms to promote a sustained release of ACN for increased health benefits.

Novel insights into the effects of diabetes on gastric motility

Recent data from the Diabetes Control and Complications Trial/Epidemiology of Diabetic Interventions and Complications cohort indicate that the disease burden of gastroparesis in diabetes remains high, consistent with the outcome of cross-sectional studies in type 1 and 2 diabetes. An improved understanding of the pathogenesis of diabetic gastroparesis at the cellular level has emerged in the last decade, particularly as a result of initiatives such as the National Institute of Health funded Gastroparesis Clinical Research Consortium in the US. Management of diabetic gastroparesis involves dietary and psychological support, attention to glycaemic control, and the use of prokinetic agents. Given that the relationship between upper gastrointestinal symptoms and the rate of gastric emptying is weak, therapies targeted specifically at symptoms, such as nausea or pain, are important. The relationship between gastric emptying and postprandial glycaemia is complex and inter-dependent. Short-acting glucagon-like peptide-1 agonists, that slow gastric emptying, can be used to reduce postprandial glycaemic excursions and, in combination with basal insulin, result in substantial reductions in glycated haemoglobin in type 2 patients.

Gastric Emptying Is More Rapid in Adolescents With Type 1 Diabetes and Impacts on Postprandial Glycemia

CONTEXT

Gastric emptying is a critical determinant of postprandial glycemic control in health and type 1 diabetes. There are few studies that assess the relationship between gastric emptying and postprandial glycaemia in adolescents with type 1 diabetes.

OBJECTIVE

The objectives of the study were to quantify gastric emptying in adolescents with type 1 diabetes and examine its relationship to postprandial glycaemia and autonomic function.

DESIGN

This was a case-control study. Gastric half-emptying time of a solid meal was measured by a (13)C-octanoate breath test. Cardio-autonomic function was measured by heart rate variability. Chronic and postprandial gastrointestinal symptoms were evaluated by questionnaire and visual analog scales. Blood glucose concentrations were monitored frequently during the study.

SETTING

The study was conducted at a tertiary pediatric hospital in South Australia.

PARTICIPANTS

Thirty adolescents (aged 15 ± 2.5 y) with type 1 diabetes and age- and sex-matched controls (gastric emptying, n = 20; heart rate variability, n = 135) participated in the study.

MAIN OUTCOME

Gastric half-emptying time was the main outcome in the study.

RESULTS

Gastric emptying was more rapid in subjects with type 1 diabetes than controls [median half emptying time 78 (interquartile range 61-99) vs 109 (interquartile range 71-124) min, P = .02]. The postprandial rise in blood glucose at 60 minutes was strongly related to gastric half-emptying time (R = -0.65, P = .0001). Gastric emptying was slower in subjects with fasting hyperglycemia but was not related to heart rate variability. Nausea, bloating, and anxiety were related to fasting glycemia (P = .03).

CONCLUSION

Rapid gastric emptying is a major determinant of postprandial glycemia in adolescents with type 1 diabetes. This observation has significant implications for therapy.

Relationship between glycemic control and gastric emptying in poorly controlled type 2 diabetes

BACKGROUND & AIMS

Acute hyperglycemia delays gastric emptying in patients with diabetes. However, it is not clear whether improved control of glycemia affects gastric emptying in these patients. We investigated whether overnight and short-term (6 mo) improvements in control of glycemia affect gastric emptying.

METHODS

We studied 30 patients with poorly controlled type 2 diabetes (level of glycosylated hemoglobin, >9%). We measured gastric emptying using the [(13)C]-Spirulina platensis breath test on the patients' first visit (visit 1), after overnight administration of insulin or saline, 1 week later (visit 2), and 6 months after intensive therapy for diabetes. We also measured fasting and postprandial plasma levels of C-peptide, glucagon-like peptide 1, and amylin, as well as autonomic functions.

RESULTS

At visit 1, gastric emptying was normal in 10 patients, delayed in 14, and accelerated in 6; 6 patients had gastrointestinal symptoms; vagal dysfunction was associated with delayed gastric emptying (P < .05). Higher fasting blood levels of glucose were associated with shorter half-times of gastric emptying (thalf) at visits 1 (r = -0.46; P = .01) and 2 (r = -0.43; P = .02). Although blood levels of glucose were lower after administration of insulin (132 ± 7 mg/dL) than saline (211 ± 15 mg/dL; P = .0002), gastric emptying thalf was not lower after administration of insulin, compared with saline. After 6 months of intensive therapy, levels of glycosylated hemoglobin decreased from 10.6% ± 0.3% to 9% ± 0.4% (P = .0003), but gastric emptying thalf did not change (92 ± 8 min before, 92 ± 7 min after). Gastric emptying did not correlate with plasma levels of glucagon-like peptide 1 and amylin.

CONCLUSIONS

Two-thirds of patients with poorly controlled type 2 diabetes have mostly asymptomatic yet abnormal gastric emptying. Higher fasting blood levels of glucose are associated with faster gastric emptying. Overnight and sustained (6 mo) improvements in glycemic control do not affect gastric emptying.

Effects of delayed gastric emptying on postprandial glucose kinetics, insulin sensitivity, and β-cell function

Controlling meal-related glucose excursions continues to be a therapeutic challenge in diabetes mellitus. Mechanistic reasons for this need to be understood better to develop appropriate therapies. To investigate delayed gastric emptying effects on postprandial glucose turnover, insulin sensitivity, and β-cell responsivity and function, as a feasibility study prior to studying patients with type 1 diabetes, we used the triple tracer technique C-peptide and oral minimal model approach in healthy subjects. A single dose of 30 μg of pramlintide administered at the start of a mixed meal was used to delay gastric emptying rates. With delayed gastric emptying rates, peak rate of meal glucose appearance was delayed, and rate of endogenous glucose production (EGP) was lower. C-peptide and oral minimal models enabled the assessments of β-cell function, insulin sensitivity, and β-cell responsivity simultaneously. Delayed gastric emptying induced by pramlintide improved total insulin sensitivity and decreased total β-cell responsivity. However, β-cell function as measured by total disposition index did not change. The improved whole body insulin sensitivity coupled with lower rate of appearance of EGP with delayed gastric emptying provides experimental proof of the importance of evaluating pramlintide in artificial endocrine pancreas approaches to reduce postprandial blood glucose variability in patients with type 1 diabetes.

A model of glucose-insulin-pramlintide pharmacokinetics and pharmacodynamics in type I diabetes

Type 1 diabetes mellitus (T1DM) complications are significantly reduced when normoglycemic levels are maintained via intensive therapy. The artificial pancreas is designed for intensive glycemic control; however, large postprandial excursions after a meal result in poor glucose regulation. Pramlintide, a synthetic analog of the hormone amylin, reduces the severity of postprandial excursions by reducing appetite, suppressing glucagon release, and slowing the rate of gastric emptying. The goal of this study is to create a glucose-insulin-pramlintide physiological model that can be employed into a controller to improve current control approaches used in the artificial pancreas. A model of subcutaneous (SC) pramlintide pharmacokinetics (PK) was developed by revising an intravenous (IV) pramlintide PK model and adapting SC insulin PK from a glucose-insulin model. Gray-box modeling and least squares optimization were used to obtain parameter estimates. Pharmacodynamics (PD) were obtained by choosing parameters most applicable to pramlintide mechanisms and then testing using a proportional PD effect using least squares optimization. The model was fit and validated using 27 data sets, which included placebo, PK, and PD data. SC pramlintide PK root mean square error values range from 1.98 to 10.66 pmol/L. Pramlintide PD RMSE values range from 10.48 to 42.76 mg/dL. A new in silico model of the glucose-insulin-pramlintide regulatory system is presented. This model can be used as a platform to optimize dosing of both pramlintide and insulin as a combined therapy for glycemic regulation, and in the development of an artificial pancreas as the kernel for a model-based controller.

Defining the role of GLP-1 in the enteroinsulinar axis in type 2 diabetes using DPP-4 inhibition and GLP-1 receptor blockade

Understanding the incretin pathway has led to significant advancements in the treatment of type 2 diabetes (T2D). Still, the exact mechanisms are not fully understood. In a randomized, placebo-controlled, four-period, crossover study in 24 patients with T2D, dipeptidyl peptidase-4 (DPP-4) inhibition and its glucose-lowering actions were tested after an oral glucose tolerance test (OGTT). The contribution of GLP-1 was examined by infusion of the GLP-1 receptor (GLP-1r) antagonist exendin-9. DPP-4 inhibition reduced glycemia and enhanced insulin levels and the incretin effect (IE). Glucagon was suppressed, and gastric emptying (GE) was decelerated. Exendin-9 increased glucose levels and glucagon secretion, attenuated insulinemia and the IE, and accelerated GE. With the GLP-1r antagonist, the glucose-lowering effects of DPP-4 inhibition were reduced by ∼ 50%. However, a significant effect on insulin secretion remained during GLP-1r blockade, whereas the inhibitory effects of DPP-4 inhibition on glucagon and GE were abolished. Thus, in this cohort of T2D patients with a substantial IE, GLP-1 contributed ∼ 50% to the insulin excursion after an OGTT with and without DPP-4 inhibition. Thus, a significant DPP-4-sensitive glucose-lowering mechanism contributes to glycemic control in T2D patients that may be not mediated by circulating GLP-1.

In silico design of optimal ratio for co-administration of pramlintide and insulin in type 1 diabetes

BACKGROUND

The ability to simulate in silico experiments is crucial for fast and cost-effective preliminary studies prior to clinical trials. We present an in silico approach to the design of optimal pramlintide-to-insulin (P/I) ratios, using our computer simulator of the human metabolic system, with a population of virtual adult type 1 diabetes mellitus patients and with individual parameters modified to account for the dynamic effects of pramlintide.

MATERIALS AND METHODS

A model of pramlintide action on gastric emptying was built using data of 15 type 1 diabetes mellitus subjects studied twice with a standardized dual-tracer meal on placebo and pramlintide, which was incorporated in our type 1 diabetes simulator. Extensive in silico experiments on 100 virtual subjects were performed to optimize the co-administration of pramlintide and insulin prior to its submission to clinical trials; several P/I ratios were tested in terms of efficacy, in attenuating postprandial hyperglycemia, and in hypoglycemia safety.

RESULTS

In silico experiments estimated the optimal P/I ratio to be 9 μg of pramlintide per unit (U) of insulin. Additional simulations narrowing the investigated range indicated that P/I ratios of 8 and 10 μg/U would achieve similar performance. Moreover, simulation results suggested that in clinical trials, insulin boluses should be reduced by approximately 21% at a P/I ratio of 9 μg/U to account for the effects of pramlintide and avoid postprandial hypoglycemia.

CONCLUSIONS

We can assert that a valid simulation model of pramlintide action was developed, leading to in silico estimation of optimal pramlintide:insulin co-administration ratio. Clinical trials will confirm (or adjust) this initial estimation.

Thermodynamic and structural determinants of differential Pdx1 binding to elements from the insulin and IAPP promoters

In adult mammals, the production of insulin and other peptide hormones, such as the islet amyloid polypeptide (IAPP), is limited to β-cells due to tissue-specific expression of a set of transcription factors, the best known of which is pancreatic duodenal homeobox protein 1 (Pdx1). Like many homeodomain transcription factors, Pdx1 binds to a core DNA recognition sequence containing the tetranucleotide 5'-TAAT-3'; its consensus recognition element is 5'-CTCTAAT(T/G)AG-3'. Currently, a complete thermodynamic profile of Pdx1 binding to near-consensus and native promoter sequences has not been established, obscuring the mechanism of target site selection by this critical transcription factor. Strikingly, while Pdx1 responsive elements in the human insulin promoter conform to the pentanucleotide 5'-CTAAT-3' sequence, the Pdx1 responsive elements in the human iapp promoter all contain a substitution to 5'-TTAAT-3'. The crystal structure of Pdx1 bound to the consensus nucleotide sequence does not explain how Pdx1 identifies this natural variation, if it does at all. Here we report a combination of isothermal calorimetric titrations, NMR spectroscopy, and extensive multi-microsecond molecular dynamics calculations of Pdx1 that define its interactions with a panel of natural promoter elements and consensus-derived sequences. Our results show a small preference of Pdx1 for a C base 5' relative to the core TAAT promoter element. Molecular mechanics calculations, corroborated by experimental NMR data, lead to a rational explanation for sequence discrimination at this position. Taken together, our results suggest a molecular mechanism for differential Pdx1 affinity to elements from the insulin and iapp promoter sequences.

Absorption patterns of meals containing complex carbohydrates in type 1 diabetes

AIMS/HYPOTHESIS

Successful postprandial glycaemia management requires understanding of absorption patterns after meals containing variable complex carbohydrates. We studied eight young participants with type 1 diabetes to investigate a large low-glycaemic-load (LG) meal and another eight participants to investigate a high-glycaemic-load (HG) meal matched for carbohydrates (121 g).

METHODS

On Visit 1, participants consumed an evening meal. On follow-up Visit 2, a variable-target glucose clamp was performed to reproduce glucose and insulin levels from Visit 1. Adopting stable-label tracer dilution methodology, we measured endogenous glucose production on Visit 2 and subtracted it from total glucose appearance measured on Visit 1 to obtain meal-attributable glucose appearance.

RESULTS

After the LG meal, 25%, 50% and 75% of cumulative glucose appearance was at 88 ± 21, 175 ± 39 and 270 ± 54 min (mean ± SD), whereas glucose from the HG meal appeared significantly faster at 56 ± 12, 100 ± 25 and 153 ± 39 min (p < 0.001 to 0.003), and resulted in a 50% higher peak appearance (p < 0.001). Higher apparent bioavailability by 15% (p = 0.037) was observed after the LG meal. We documented a 20 min deceleration of dietary mixed carbohydrates compared with dietary glucose for the HG meal and a twofold deceleration for the LG meal.

CONCLUSIONS/INTERPRETATION

Absorption patterns may be influenced by glycaemic load and/or meal composition, affecting optimum prandial insulin dosing in type 1 diabetes.

Pramlintide: profile of an amylin analog

Amylin is a naturally occurring hormone that regulates food intake and postprandial glucose excursions. Amylin is synthesized in the β cell and cosecreted with insulin. Type 1 diabetes and insulin-requiring Type 2 diabetes are amylin-deficient as well as insulin-deficient states. Pramlintide is a synthetic amylin analog that is used for replacement therapy. Pramlintide therapy slows diabetes-mediated accelerated gastric emptying and restores meal-mediated suppression of glucagon secretion in patients with diabetes. Amylin receptors are primarily located in the CNS, which mediates all of its effects including decreases in food intake. In patients with diabetes, pramlintide treatment reduces hemoglobin A1C (HbA1c) 0.3-0.7% and decreases bodyweight. Side effects include nausea and hypoglycemia. Both can be minimized by an appropriate titration program. Recent pramlintide studies address improvements in delivery systems, use in pediatric and Type 2 diabetic populations, patient treatment satisfaction and new insights into its mechanisms of action.

The role of endogenous incretin secretion as amplifier of glucose-stimulated insulin secretion in healthy subjects and patients with type 2 diabetes

In order to quantify the role of incretins in first- and second-phase insulin secretion (ISR) in type 2 diabetes mellitus (T2DM), a double-blind, randomized study with 12 T2DM subjects and 12 healthy subjects (HS) was conducted using the hyperglycemic clamp technique together with duodenal nutrition perfusion and intravenous infusion of the glucagon-like peptide 1 (GLP-1) receptor antagonist exendin(9-39). Intravenous glucose alone resulted in a significantly greater first- and second-phase ISR in HS compared with T2DM subjects. Duodenal nutrition perfusion augmented both first- and second-phase ISR but first-phase ISR more in T2DM subjects (approximately eight- vs. twofold). Glucose-related stimulation of ISR contributed only 20% to overall ISR. Infusion with exendin(9-39) significantly reduced first- and second-phase ISR in both HS and T2DM subjects. Thus, both GLP-1 and non-GLP-1 incretins contribute to the incretin effect. In conclusion, both phases of ISR are impaired in T2DM. In particular, the responsiveness to glucose in first-phase ISR is blunted. GLP-1 and glucose-dependent insulinotropic polypeptide (GIP) secretions are unaltered. The absolute incretin effect is reduced in T2DM; its relative importance, however, appears to be increased, highlighting its role as an important amplifier of first-phase ISR in T2DM.

Pathophysiology of postprandial hyperglycaemia in women with type 1 diabetes during pregnancy

AIMS/HYPOTHESIS

Although maternal hyperglycaemia is associated with increased risk of adverse pregnancy outcome, the mechanisms of postprandial hyperglycaemia during pregnancy are poorly understood. We aimed to describe glucose turnover in pregnant women with type 1 diabetes, according to stage of gestation (early vs late gestation).

METHODS

The rates of systemic glucose appearance (R(a)) and glucose disposal (R(d)) were measured in ten pregnant women with type 1 diabetes during early (12-16 weeks) and late (28-32 weeks) gestation. Women ate standardised meals--a starch-rich 80 g carbohydrate dinner and a sugar-rich 60 g carbohydrate breakfast--and fasted between meals and overnight. Stable-label isotope tracers ([6,6-(2)H(2)]glucose and [U-(13)C]glucose) were used to determine R(a), R(d) and glucose bioavailability. Closed-loop insulin delivery maintained stable glycaemic conditions.

RESULTS

There were no changes in fasting R(a) (10 ± 2 vs 11 ± 2 μmol kg(-1) min(-1); p = 0.32) or fasting R(d) (11 ± 2 vs 11 ± 1 μmol kg(-1) min(-1); p = 0.77) in early vs late gestation. There was increased hepatic insulin resistance (381 ± 237 vs 540 ± 242 μmol kg(-1) min(-1) × pmol/l; p = 0.04) and decreased peripheral insulin sensitivity (0.09 ± 0.04 vs 0.05 ± 0.02 μmol kg(-1) min(-1) per pmol/l dinner, 0.11 ± 0.05 vs 0.07 ± 0.03 μmol kg(-1) min(-1) per pmol/l breakfast; p = 0.002) in late gestation. It also took longer for insulin levels to reach maximal concentrations (49 [37-55] vs 71 [52-108] min; p = 0.004) with significantly delayed glucose disposal (108 [87-125] vs 135 [110-158] min; p = 0.005) in late gestation.

CONCLUSIONS/INTERPRETATION

Postprandial glucose control is impaired by significantly slower glucose disposal in late gestation. Early prandial insulin dosing may help to accelerate glucose disposal and potentially ameliorate postprandial hyperglycaemia in late pregnancy.

TRIAL REGISTRATION

ISRCTN 62568875

FUNDING

Diabetes UK Project Grant BDA 07/003551. H.R. Murphy is funded by a National Institute for Health Research (NIHR) research fellowship (PDF/08/01/036). Supported also by the Juvenile Diabetes Research Foundation (JDRF), Abbott Diabetes Care (Freestyle Navigator CGM and sensors free of charge), Medical Research Council Centre for Obesity and Related Metabolic Diseases and NIHR Cambridge Biomedical Research Centre.

Gut microbiota in health and disease

Gut microbiota is an assortment of microorganisms inhabiting the length and width of the mammalian gastrointestinal tract. The composition of this microbial community is host specific, evolving throughout an individual's lifetime and susceptible to both exogenous and endogenous modifications. Recent renewed interest in the structure and function of this "organ" has illuminated its central position in health and disease. The microbiota is intimately involved in numerous aspects of normal host physiology, from nutritional status to behavior and stress response. Additionally, they can be a central or a contributing cause of many diseases, affecting both near and far organ systems. The overall balance in the composition of the gut microbial community, as well as the presence or absence of key species capable of effecting specific responses, is important in ensuring homeostasis or lack thereof at the intestinal mucosa and beyond. The mechanisms through which microbiota exerts its beneficial or detrimental influences remain largely undefined, but include elaboration of signaling molecules and recognition of bacterial epitopes by both intestinal epithelial and mucosal immune cells. The advances in modeling and analysis of gut microbiota will further our knowledge of their role in health and disease, allowing customization of existing and future therapeutic and prophylactic modalities.

Adjunct therapy for type 1 diabetes mellitus

Insulin replacement therapy in type 1 diabetes mellitus (T1DM) is nonphysiologic. Hyperinsulinemia is generated in the periphery to achieve normal insulin concentrations in the liver. This mismatch results in increased hypoglycemia, increased food intake with weight gain, and insufficient regulation of postprandial glucose excursions. Islet amyloid polypeptide is a hormone synthesized in pancreatic beta cells and cosecreted with insulin. Circulating islet amyloid polypeptide binds to receptors located in the hindbrain and increases satiety, delays gastric emptying and suppresses glucagon secretion. Thus, islet amyloid polypeptide complements the effects of insulin. T1DM is a state of both islet amyloid polypeptide and insulin deficiency. Pramlintide, a synthetic analog of islet amyloid polypeptide, can replace this hormone in patients with T1DM. When administered as adjunctive therapy to such patients treated with insulin, pramlintide decreases food intake and causes weight loss. Pramlintide therapy is also associated with suppression of glucagon secretion and delayed gastric emptying, both of which decrease postprandial plasma glucose excursions. Pramlintide therapy improves glycemic control and lessens weight gain. Agents that decrease intestinal carbohydrate digestion (alpha-glucosidase inhibitors) or decrease insulin resistance (metformin) might be alternative adjunctive therapies in T1DM, though its benefits are marginally supported by clinical data.

Diabetes mellitus and gastric emptying: questions and issues in clinical practice

It is long known that both type 1 and type 2 diabetes can be associated with changes in gastric emptying; a number of publications have linked diabetes to delayed gastric emptying of variable severity and often with poor relationship to gastrointestinal symptomatology. In contrast, more recent studies have reported accelerated gastric emptying when adjusted for glucose concentration in patients with diabetes, indicating a reciprocal relationship between gastric emptying and ambient glucose concentrations. This review proposes that gastroparesis or gastroparesis diabeticorum, a severe condition characterized by a significant impairment of gastric emptying accompanied by severe nausea, vomiting, and malnutrition, is often overdiagnosed and not well contrasted with delays in gastric emptying. The article offers a clinically relevant definition of gastroparesis that should help differentiate this rare condition from (often asymptomatic) delays in gastric emptying. The fact that delayed gastric emptying can also be observed in non-diabetic individuals under experimental conditions in which hyperglycaemia is artificially induced suggests that a delay in gastric emptying rate when blood glucose concentrations are high is actually an appropriate physiological response to hyperglycaemia, slowing further increases in blood glucose. The article discusses the strengths and weaknesses of various methodologies for assessing gastric emptying, especially with respect to the diabetes population, and reviews newer diabetes therapies that decelerate the rate of gastric emptying. These therapies may be a beneficial tool in managing postprandial hyperglycaemia because they attenuate rapid surges in glucose concentrations by slowing the delivery of meal-derived glucose.