Regulation of endogenous glucose production after a mixed meal in type 2 diabetes

Complex physiology and clinical implications of time-restricted eating

Time-restricted eating (TRE) is a dietary intervention that limits food consumption to a specific time window each day. The effect of TRE on body weight and physiological functions has been extensively studied in rodent models, which have shown considerable therapeutic effects of TRE and important interactions among time of eating, circadian biology, and metabolic homeostasis. In contrast, it is difficult to make firm conclusions regarding the effect of TRE in people because of the heterogeneity in results, TRE regimens, and study populations. In this review, we 1) provide a background of the history of meal consumption in people and the normal physiology of eating and fasting; 2) discuss the interaction between circadian molecular metabolism and TRE; 3) integrate the results of preclinical and clinical studies that evaluated the effects of TRE on body weight and physiological functions; 4) summarize other time-related dietary interventions that have been studied in people; and 4) identify current gaps in knowledge and provide a framework for future research directions.

Could Dietary Modification Independent of Energy Balance Influence the Underlying Pathophysiology of Type 2 Diabetes? Implications for Type 2 Diabetes Remission

High-quality clinical trial data demonstrate that remission is possible for people living with type 2 diabetes (T2D) if they lose a large amount of weight (≥ 10 kg). Durable remission appears predicated on the long-term maintenance of weight loss. Unfortunately, long-term follow-up data from lifestyle-based weight loss programmes show that, on average, most people regain at least some of the weight lost. In addition, restoration of a diminished first-phase insulin response also appears necessary for durable remission, and this becomes less likely as T2D progresses. A pragmatic approach to enhance the effects of weight loss on durable remission is to consider whether dietary components could help control blood glucose, independent of caloric balance. This manuscript reviews current evidence on weight-neutral effects of diet on blood glucose, including high-protein, low-carbohydrate, high-fibre and plant-based diets, with a particular focus on the effect of nutrition on the underlying pathophysiology of T2D, including the first-phase insulin response. The importance of mechanistic data in enhancing our understanding of dietary strategies in T2D remission is described, and suggestions are made for future advances in remission research.

The Change in Glucagon Following Meal Ingestion Is Associated with Glycemic Control, but Not with Incretin, in People with Diabetes

BACKGROUND

We aimed to investigate the changes in glucagon levels in people with diabetes after the ingestion of a mixed meal and the correlations of variation in glucagon levels with incretin and clinico-biochemical characteristics.

METHODS

Glucose, C-peptide, glucagon, intact glucagon-like peptide 1 (iGLP-1), and intact glucose-dependent insulinotropic polypeptide (iGIP) were measured in blood samples collected from 317 people with diabetes before and 30 min after the ingestion of a standard mixed meal. The delta (Δ) is the 30-min value minus the basal value.

RESULTS

At 30 min after meal ingestion, the glucagon level showed no difference relative to the basal value, whereas glucose, C-peptide, iGLP-1, and iGIP levels showed a significant increase. In univariate analysis, Δglucagon showed not only a strong correlation with HbA1c but also a significant correlation with fasting glucose, Δglucose, and estimated glomerular filtration rate. However, Δglucagon showed no significant correlations with ΔiGLP-1 and ΔiGIP. In the hierarchical multiple regression analysis, HbA1c was the only variable that continued to show the most significant correlation with Δglucagon.

CONCLUSIONS

People with diabetes showed no suppression of glucagon secretion after meal ingestion. Patients with poorer glycemic control may show greater increase in postprandial glucagon level, and this does not appear to be mediated by incretin.

Exercise-Induced Improvements to Whole Body Glucose Metabolism in Type 2 Diabetes: The Essential Role of the Liver

Type 2 diabetes (T2D) is a metabolic disease characterized by obesity, insulin resistance, and the dysfunction of several key glucoregulatory organs. Among these organs, impaired liver function is recognized as one of the earliest contributors to impaired whole-body glucose homeostasis, with well-characterized hepatic insulin resistance resulting in elevated rates of hepatic glucose production (HGP) and fasting hyperglycemia. One portion of this review will provide an overview of how HGP is regulated during the fasted state in healthy humans and how this process becomes dysregulated in patients with T2D. Less well-appreciated is the liver's role in post-prandial glucose metabolism, where it takes up and metabolizes one-third of orally ingested glucose. An abundance of literature has shown that the process of hepatic glucose uptake is impaired in patients with T2D, thereby contributing to glucose intolerance. A second portion of this review will outline how hepatic glucose uptake is regulated during the post-prandial state, and how it becomes dysfunctional in patients with T2D. Finally, it is well-known that exercise training has an insulin-sensitizing effect on the liver, which contributes to improved whole-body glucose metabolism in patients with T2D, thereby making it a cornerstone in the management of the disease. To this end, the impact of exercise on hepatic glucose metabolism will be thoroughly discussed, referencing key findings in the literature. At the same time, sources of heterogeneity that contribute to inconsistent findings in the field will be pointed out, as will important topics for future investigation.

Determination of physiological parameters for endogenous glucose production in individuals using diurnal data

Background

Triple tracer meal experiments used to investigate organ glucose-insulin dynamics, such as endogenous glucose production (EGP) of the liver are labor intensive and expensive. A procedure was developed to obtain individual liver related parameters to describe EGP dynamics without the need for tracers.

Results

The development used an existing formula describing the EGP dynamics comprising 4 parameters defined from glucose, insulin and C-peptide dynamics arising from triple meal studies. The method employs a set of partial differential equations in order to estimate the parameters for EGP dynamics. Tracer-derived and simulated data sets were used to develop and test the procedure. The predicted EGP dynamics showed an overall mean R² of 0.91.

Conclusions

In summary, a method was developed for predicting the hepatic EGP dynamics for healthy, pre-diabetic, and type 2 diabetic individuals without applying tracer experiments.

Metabolic flexibility is impaired in response to acute exercise in the young offspring of mothers with type 2 diabetes

We assessed metabolic flexibility (MF) via a mixed meal in a group of young, healthy participants with a positive family history of maternal type 2 diabetes (T2D) (FH+) and those without a family history of T2D (FH-) under three distinct conditions; baseline (BL; no previous exercise), 1-h post high intensity interval exercise (1H), and 48-h post exercise recovery. On separate visits, participants completed a single bout of high intensity interval exercise (HIIE) and repeated the MMTT 1-h (1H) and 48 h (48H) postexercise. FH+ participants were not able to suppress fat oxidation 1-h post exercise (1H) as effectively as FH- participants were, however, this response was improved when measured at the 48H visit. Insulin AUC was significantly lowered at both 1H and 48H when compared to the BL visit. Serum NEFA AUC was elevated 1-h post exercise, when compared to BL, but was significantly reduced at the 48H visit. Young, healthy participants with a maternal history of T2D demonstrate impaired MF (related to the inability to suppress fat oxidation) in response to acute HIIE (1H) that was improved 48H. The overall effect of HIIE showed improved insulin AUC and NEFA AUC up to 48H post that did not differ by FH.

Understanding the mechanisms of reversal of type 2 diabetes

Clinical and pathophysiological studies have shown type 2 diabetes to be a condition mainly caused by excess, yet reversible, fat accumulation in the liver and pancreas. Within the liver, excess fat worsens hepatic responsiveness to insulin, leading to increased glucose production. Within the pancreas, the β cell seems to enter a survival mode and fails to function because of the fat-induced metabolic stress. Removal of excess fat from these organs via substantial weight loss can normalise hepatic insulin responsiveness and, in the early years post-diagnosis, is associated with β-cell recovery of acute insulin secretion in many individuals, possibly by redifferentiation. Collectively, these changes can normalise blood glucose levels. Importantly, the primary care-based Diabetes Remission Clinical Trial (DiRECT) showed that 46% of people with type 2 diabetes could achieve remission at 12 months, and 36% at 24 months, mediated by weight loss. This major change in our understanding of the underlying mechanisms of disease permits a reassessment of advice for people with type 2 diabetes.

Endogenous glucose production after sequential meals in humans: evidence for more prolonged suppression after ingestion of a second meal

Single-meal studies have shown that carbohydrate ingestion causes rapid and persistent suppression of endogenous glucose production (EGP). However, little is known about the regulation of EGP under real-life eating patterns in which multiple carbohydrate-containing meals are consumed throughout the day. Therefore, we aimed to characterize the regulation of EGP in response to sequential meals, specifically during the breakfast-lunch transition. Nine healthy individuals (5 men, 4 women; 32 ± 2 yr; 25.0 ± 1.4 kg/m²) ingested two identical mixed meals, each containing 25 g of glucose, separated by 4 h, and EGP was determined by the variable infusion tracer-clamp approach. EGP was rapidly suppressed after both meals, with the pattern and magnitude of suppression being similar over the initial 75-min postmeal period. However, EGP suppression was more transient after breakfast compared with lunch, with EGP returning to basal rates 3 h after breakfast. In contrast, EGP remained in a suppressed state for the entire 4-h postlunch period. This occurred despite each meal eliciting similar plasma glucose and insulin responses. However, there was greater suppression of plasma glucagon levels after lunch, likely contributing to this response. These findings highlight the potential for distinct regulation of EGP with each meal of the day and suggest that EGP may be in a suppressed state for much of the day, since EGP did not return to basal rates even after a lunch meal containing a modest amount of carbohydrate.

Time course of fractional gluconeogenesis after meat ingestion in healthy adults: a D2O study

In the postprandial state, glucose homeostasis is challenged by macronutrient intake, including proteins that trigger insulin secretion and provide glucose precursors. However, little is known about the postprandial response of gluconeogenesis to a protein meal. We aimed to quantify the evolution of fractional gluconeogenesis after a meat meal. Thirteen healthy subjects received oral doses of D₂O. After fasting overnight, they ingested a steak (120 g). Glycemia, insulinemia, and ²H enrichments in glucose and plasma water were measured for 8 h after the meal. Fractional gluconeogenesis was assessed using the average method. Glucose was stable for 5 h and then decreased. There was a slight increase of insulin 1 h after the meal. ²H enrichment in the carbon 5 position of glucose (C5) increased after 2 h, whereas it decreased in plasma water. Consequently, fractional gluconeogenesis increased from 68.2 ± 7.2% before the meal to 75.5 ± 5.8% 8 h after the meal, the latter corresponding to 22 h without a glucose supply. These values are consistent with the exhaustion of glycogen stores after 24 h but represent the highest among values in the literature. The impact of methodological conditions is discussed.

A Narrative Review of Potential Future Antidiabetic Drugs: Should We Expect More?

Prevalence of diabetes mellitus, a chronic metabolic disease characterized by hyperglycemia, is growing worldwide. The majority of the cases belong to type 2 diabetes mellitus (T2DM). Globally, India ranks second in terms of diabetes prevalence among adults. Currently available classes of therapeutic agents are used alone or in combinations but seldom achieve treatment targets. Diverse pathophysiology and the need of therapeutic agents with more favourable pharmacokinetic-pharmacodynamics profile make newer drug discoveries in the field of T2DM essential. A large number of molecules, some with novel mechanisms, are in pipeline. The essence of this review is to track and discuss these potential agents, based on their developmental stages, especially those in phase 3 or phase 2. Unique molecules are being developed for existing drug classes like insulins, DPP-4 inhibitors, GLP-1 analogues; and under newer classes like dual/pan PPAR agonists, dual SGLT1/SGLT2 inhibitors, glimins, anti-inflammatory agents, glucokinase activators, G-protein coupled receptor agonists, hybrid peptide agonists, apical sodium-dependent bile acid transporter (ASBT) inhibitors, glucagon receptor antagonists etc. The heterogeneous clinical presentation and therapeutic outcomes in phenotypically similar patients is a clue to think beyond the standard treatment strategy.

Addressing Unmet Medical Needs in Type 1 Diabetes: A Review of Drugs Under Development

INTRODUCTION

The incidence of type 1 diabetes (T1D) is increasing worldwide and there is a very large need for effective therapies. Essentially no therapies other than insulin are currently approved for the treatment of T1D. Drugs already in use for type 2 diabetes and many new drugs are under clinical development for T1D, including compounds with both established and new mechanisms of action. Content of the Review: Most of the new compounds in clinical development are currently in Phase 1 and 2. Drug classes discussed in this review include new insulins, SGLT inhibitors, GLP-1 agonists, immunomodulatory drugs including autoantigens and anti-cytokines, agents that regenerate β-cells and others. Regulatory Considerations: In addition, considerations are provided with regard to the regulatory environment for the clinical development of drugs for T1D, with a focus on the United States Food and Drug Administration and the European Medicines Agency. Future opportunities, such as combination treatments of immunomodulatory and beta-cell regenerating therapies, are also discussed.

Adipose-derived mesenchymal stem cells ameliorate hyperglycemia through regulating hepatic glucose metabolism in type 2 diabetic rats

Infusion of mesenchymal stem cells (MSCs) has been identified in the rapid alleviation in hyperglycemia of diabetic individuals, but the mechanism involved has not been adequately explained by these cells' potential role in modulating system insulin sensitivity and islet regeneration. In this study, we demonstrated adipose-derived mesenchymal stem cells (ASCs) produced significantly lower blood glucose via promoting hepatic glycogen synthesis and inhibiting hepatic glucose production within 24 h after infusion in T2DM rats. In vitro, HepG2 cells treated with palmitate (PA) were used as a model of hepatic glucose metabolism disorder to confirm that ASCs stimulates the phosphorylation of hepatic AMP-activated protein kinase (AMPK) to restores hepatic glucose metabolism in type 2 diabetes. In summary, this study indicated that ASCs improve hyperglycemia via regulating hepatic glucose metabolism. Additionally, the effect of ASCs on hepatic glucose metabolism depended on the AMPK signaling pathway. Thus, this is the new research of the molecular mechanisms of MSCs administration to improve glucose metabolism, and it may indicate a new treatment target of MSCs in T2DM.

Type 2 Diabetes: The Pathologic Basis of Reversible β-Cell Dysfunction

The reversible nature of early type 2 diabetes has been demonstrated in in vivo human studies. Recent in vivo and in vitro studies of β-cell biology have established that the β-cell loses differentiated characteristics, including glucose-mediated insulin secretion, under metabolic stress. Critically, the β-cell dedifferentiation produced by long-term excess nutrient supply is reversible. Weight loss in humans permits restoration of first-phase insulin secretion associated with the return to normal of the elevated intrapancreatic triglyceride content. However, in type 2 diabetes of duration greater than 10 years, the cellular changes appear to pass a point of no return. This review summarizes the evidence that early type 2 diabetes can be regarded as a reversible β-cell response to chronic positive calorie balance.

Skeletal Muscle Vascular Function: A Counterbalance of Insulin Action

Insulin is a vasoactive hormone that regulates vascular homeostasis by maintaining balance of endothelial-derived NO and ET-1. Although there is general agreement that insulin resistance and the associated hyperinsulinemia disturb this balance, the vascular consequences for hyperinsulinemia in isolation from insulin resistance are still unclear. Presently, there is no simple answer for this question, especially in a background of mixed reports examining the effects of experimental hyperinsulinemia on endothelial-mediated vasodilation. Understanding the mechanisms by which hyperinsulinemia induces vascular dysfunction is essential in advancing treatment and prevention of insulin resistance-related vascular complications. Thus, we review literature addressing the effects of hyperinsulinemia on vascular function. Furthermore, we give special attention to the vasoregulatory effects of hyperinsulinemia on skeletal muscle, the largest insulin-dependent organ in the body. This review also characterizes the differential vascular effects of hyperinsulinemia on large conduit vessels versus small resistance microvessels and the effects of metabolic variables in an effort to unravel potential sources of discrepancies in the literature. At the cellular level, we provide an overview of insulin signaling events governing vascular tone. Finally, we hypothesize a role for hyperinsulinemia and insulin resistance in the development of CVD.

Addressing unmet medical needs in type 2 diabetes: a narrative review of drugs under development

The global burden of type 2 diabetes is increasing worldwide, and successful treatment of this disease needs constant provision of new drugs. Twelve classes of antidiabetic drugs are currently available, and many new drugs are under clinical development. These include compounds with known mechanisms of action but unique properties, such as once-weekly DPP4 inhibitors or oral insulin. They also include drugs with new mechanisms of action, the focus of this review. Most of these compounds are in Phase 1 and 2, with only a small number having made it to Phase 3 at this time. The new drug classes described include PPAR agonists/modulators, glucokinase activators, glucagon receptor antagonists, anti-inflammatory compounds, G-protein coupled receptor agonists, gastrointestinal peptide agonists other than GLP-1, apical sodium-dependent bile acid transporter (ASBT) inhibitors, SGLT1 and dual SGLT1/SGLT2 inhibitors, and 11beta- HSD1 inhibitors.

The regulation of glucose metabolism: implications and considerations for the assessment of glucose homeostasis in rodents

The incidence of insulin resistance and type 2 diabetes (T2D) is increasing at alarming rates. In the quest to understand the underlying causes of and to identify novel therapeutic targets to treat T2D, scientists have become increasingly reliant on the use of rodent models. Here, we provide a discussion on the regulation of rodent glucose metabolism, highlighting key differences and similarities that exist between rodents and humans. In addition, some of the issues and considerations associated with assessing glucose homeostasis and insulin action are outlined. We also discuss the role of the liver vs. skeletal muscle in regulating whole body glucose metabolism in rodents, emphasizing the importance of defective hepatic glucose metabolism in the development of impaired glucose tolerance, insulin resistance, and T2D.

Comparison of the effects of slowly and rapidly absorbed carbohydrates on postprandial glucose metabolism in type 2 diabetes mellitus patients: a randomized trial

BACKGROUND

Isomaltulose attenuates postprandial glucose and insulin concentrations compared with sucrose in patients with type 2 diabetes mellitus (T2DM). However, the mechanism by which isomaltulose limits postprandial hyperglycemia has not been clarified.

OBJECTIVE

The objective was therefore to assess the effects of bolus administration of isomaltulose on glucose metabolism compared with sucrose in T2DM.

DESIGN

In a randomized, double-blind, crossover design, 11 participants with T2DM initially underwent a 3-h euglycemic-hyperinsulinemic (0.8 mU · kg(-1) · min(-1)) clamp that was subsequently combined with 1 g/kg body wt of an oral (13)C-enriched isomaltulose or sucrose load. Hormonal responses and glucose kinetics were analyzed during a 4-h postprandial period.

RESULTS

Compared with sucrose, absorption of isomaltulose was prolonged by ∼50 min (P = 0.004). Mean plasma concentrations of insulin, C-peptide, glucagon, and glucose-dependent insulinotropic peptide were ∼10-23% lower (P < 0.05). In contrast, glucagon-like peptide 1 (GLP-1) was ∼64% higher (P < 0.001) after isomaltulose ingestion, which results in an increased insulin-to-glucagon ratio (P < 0.001) compared with sucrose. The cumulative amount of systemic glucose appearance was ∼35% lower after isomaltulose than after sucrose (P = 0.003) because of the reduction in orally derived and endogenously produced glucose and a higher first-pass splanchnic glucose uptake (SGU). Insulin action was enhanced after isomaltulose compared with sucrose (P = 0.013).

CONCLUSIONS

Ingestion of slowly absorbed isomaltulose attenuates postprandial hyperglycemia by reducing oral glucose appearance, inhibiting endogenous glucose production (EGP), and increasing SGU compared with ingestion of rapidly absorbed sucrose in patients with T2DM. In addition, GLP-1 secretion contributes to a beneficial shift in the insulin-to-glucagon ratio, suppression of EGP, and enhancement of SGU after isomaltulose consumption. This trial was registered at clinicaltrials.gov as NCT01070238.

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.

Glucose-reducing effect of the ORMD-0801 oral insulin preparation in patients with uncontrolled type 1 diabetes: a pilot study

The unpredictable behavior of uncontrolled type 1 diabetes often involves frequent swings in blood glucose levels that impact maintenance of a daily routine. An intensified insulin regimen is often unsuccessful, while other therapeutic options, such as amylin analog injections, use of continuous glucose sensors, and islet or pancreas transplantation are of limited clinical use. In efforts to provide patients with a more compliable treatment method, Oramed Pharmaceuticals tested the capacity of its oral insulin capsule (ORMD-0801, 8 mg insulin) in addressing this resistant clinical state. Eight Type I diabetes patients with uncontrolled diabetes (HbA1c: 7.5–10%) were monitored throughout the 15-day study period by means of a blind continuous glucose monitoring device. Baseline patient blood glucose behavior was monitored and recorded over a five-day pretreatment screening period. During the ensuing ten-day treatment phase, patients were asked to conduct themselves as usual and to self-administer an oral insulin capsule three times daily, just prior to meal intake. CGM data sufficient for pharmacodynamics analyses were obtained from 6 of the 8 subjects. Treatment with ORMD-0801 was associated with a significant 24.4% reduction in the frequencies of glucose readings >200 mg/dL (60.1±7.9% pretreatment vs. 45.4±4.9% during ORMD-0801 treatment; p = 0.023) and a significant mean 16.6% decrease in glucose area under the curve (AUC) (66055±5547 mg/dL/24 hours vs. 55060±3068 mg/dL/24 hours, p = 0.023), with a greater decrease during the early evening hours. In conclusion, ORMD-0801 oral insulin capsules in conjunction with subcutaneous insulin injections, well tolerated and effectively reduced glycemia throughout the day.

Banting Memorial lecture 2012: reversing the twin cycles of type 2 diabetes

It has become widely accepted that Type 2 diabetes is inevitably life-long, with irreversible and progressive beta cell damage. However, the restoration of normal glucose metabolism within days after bariatric surgery in the majority of people with Type 2 diabetes disproves this concept. There is now no doubt that this reversal of diabetes depends upon the sudden and profound decrease in food intake, and does not relate to any direct surgical effect. The Counterpoint study demonstrated that normal glucose levels and normal beta cell function could be restored by a very low calorie diet alone. Novel magnetic resonance methods were applied to measure intra-organ fat. The results showed two different time courses: a) resolution of hepatic insulin sensitivity within days along with a rapid fall in liver fat and normalisation of fasting glucose levels; and b) return of normal beta cell insulin secretion over weeks in step with a fall in pancreas fat. Now that it has been possible to observe the pathophysiological events during reversal of Type 2 diabetes, the reverse time course of events which determine the onset of the condition can be identified. The twin cycle hypothesis postulates that chronic calorie excess leads to accumulation of liver fat with eventual spill over into the pancreas. These self-reinforcing cycles between liver and pancreas eventually cause metabolic inhibition of insulin secretion after meals and onset of hyperglycaemia. It is now clear that Type 2 diabetes is a reversible condition of intra-organ fat excess to which some people are more susceptible than others.

Diabetes in Zucker diabetic fatty rat

Male Zucker diabetic fatty fa/fa (ZDF) rats develop obesity and insulin resistance at a young age, and then with aging, progressively develop hyperglycemia. This hyperglycemia is associated with impaired pancreatic β-cell function, loss of pancreatic β-cell mass, and decreased responsiveness of liver and extrahepatic tissues to the actions of insulin and glucose. Of particular interest are the insights provided by studies of these animals into the mechanism behind the progressive impairment of carbohydrate metabolism. This feature among others, including the development of obesity- and hyperglycemia-related complications, is common between male ZDF rats and humans with type 2 diabetes associated with obesity. We discuss the diabetic features and complications found in ZDF rats and why these animals are widely used as a genetic model for obese type 2 diabetes.

The association of insulin resistance with subclinical thyrotoxicosis

BACKGROUND

Although overt thyrotoxicosis is associated with reduced insulin sensitivity (IS), the effects of subclinical thyrotoxicosis (SCTox) (i.e., suppressed serum thyroid-stimulating hormone with free thyroxine and tri-iodothyronine within the reference range) on glucose metabolism are not clear. SCTox may be of endogenous origin or due to ingestion of supraphysiological amounts of thyroid hormone. Our hypotheses were that reduced IS is present in SCTox and that the degree of reduction differs between SCTox of endogenous and exogenous origin.

METHODS

The study population consisted of 125 premenopausal, normal-weight women, divided into four groups: exogenous SCTox due to L-T4 treatment for benign goiter or hypothyroidism (SCTox-ExogG) (n = 53), endogenous SCTox (SCTox-Endog) (n = 12), exogenous SCTox due to L-T4 treatment for differentiated thyroid cancer (SCTox-ExogDTC) (n = 20), and finally euthyroid women (C) (n = 40) as a control group. After a mixed meal challenge, glucose and insulin were determined at baseline and 120 minutes later. IS was assessed by homeostasis model assessment of insulin resistance (HOMA-IR) index, quantitative IS check index (QUICKI), and 2 hours IS Avignon's index amended by Aloulou for mixed food. Secretion by pancreatic B-cells was calculated by HOMA-B index. Comparison among groups was done by analysis of variance followed by Tukey test. Linear regression analysis of T3 versus HOMA-IR was calculated.

RESULTS

IS was reduced in all types of SCTox when compared with C. All SCTox groups had significantly higher levels of insulin (baseline and postmeal) and HOMA-IR and lower values of QUICKI and Aloulou when compared with controls. SCTox-Endog, however, had higher baseline insulin levels and HOMA-IR and a lower QUICKI index than the rest of the SCTox groups. Although within the normal range, total T4, free T4, and T3 levels were also significantly higher in the SCTox groups than in euthyroids. In SCTox-Endog, T3/T4 ratio was increased above the rest of SCTox groups. A moderate linear relationship between T3 and HOMA-IR was found in the whole population.

CONCLUSIONS

IR is associated with SCTox of either endogenous or exogenous origin. However, based on our findings of lower IS compared with the rest of the SCTox groups, the endogenous subclinical form might have an even larger metabolic impact.

JTT-130, a novel intestine-specific inhibitor of microsomal triglyceride transfer protein, ameliorates impaired glucose and lipid metabolism in Zucker diabetic fatty rats

AIM

Microsomal triglyceride transfer protein (MTP) takes part in the mobilization of triglyceride-rich lipoproteins from enterocytes and hepatocytes. We investigated the effects of JTT-130, a novel intestine-specific MTP inhibitor, on impaired glucose and lipid metabolism in Zucker diabetic fatty (ZDF) rats.

METHODS

Male ZDF rats were fed a regular powdered diet with or without JTT-130 as a food admixture (0.01-0.02%) for 6 weeks. Food intake, body weight, blood biochemical parameters, fecal lipid contents, hepatic lipid contents, tissue mRNA levels and glucose utilization in adipose tissues were assessed. An intraperitoneal glucose tolerance test (IPGTT) and histological analysis of the pancreas were performed.

RESULTS

JTT-130 treatment decreased food intake, glycated hemoglobin, plasma levels of glucose, triglycerides and total cholesterol, hepatic levels of triglycerides and cholesterol and hepatic mRNA levels of glucose-6-phosphatase, phosphoenolpyruvate carboxykinase and fructose-1,6-bisphosphatase. JTT-130 treatment increased fecal levels of free fatty acids and cholesterol, plasma levels of glucagon-like peptide-1 and peptide YY, mRNA levels of glucose transporter 4 (GLUT4) and lipoprotein lipase in adipose tissues and GLUT4 in muscle and glucose utilization in adipose tissues. Plasma insulin decreased after 2 weeks and increased after 4 weeks of JTT-130 treatment. Plasma glucose in the JTT-130-treated rats was lower with higher plasma insulin than in the control rats during the IPGTT. The islets of the JTT-130-treated rats were larger and contained more insulin than those of the control rats.

CONCLUSIONS

JTT-130 ameliorates impaired glucose and lipid metabolism in the ZDF rats thereby suggesting that JTT-130 could be useful for prevention and treatment of type 2 diabetes.

Effects of type 2 diabetes on insulin secretion, insulin action, glucose effectiveness, and postprandial glucose metabolism

OBJECTIVE

In this study, we sought to determine whether postprandial insulin secretion, insulin action, glucose effectiveness, and glucose turnover were abnormal in type 2 diabetes.

RESEARCH DESIGN AND METHODS

Fourteen subjects with type 2 diabetes and 11 nondiabetic subjects matched for age, weight, and BMI underwent a mixed-meal test using the triple-tracer technique. Indexes of insulin secretion, insulin action, and glucose effectiveness were assessed using the oral "minimal" and C-peptide models.

RESULTS

Fasting and postprandial glucose concentrations were higher in the diabetic than nondiabetic subjects. Although peak insulin secretion was delayed (P < 0.001) and lower (P < 0.05) in type 2 diabetes, the integrated total postprandial insulin response did not differ between groups. Insulin action, insulin secretion, disposition indexes, and glucose effectiveness all were lower (P < 0.05) in diabetic than in nondiabetic subjects. Whereas the rate of meal glucose appearance did not differ between groups, the percent suppression of endogenous glucose production (EGP) was slightly delayed and the increment in glucose disappearance was substantially lower (P < 0.01) in diabetic subjects during the first 3 h after meal ingestion. Together, these defects resulted in an excessive rise in postprandial glucose concentrations in the diabetic subjects.

CONCLUSIONS

When measured using methods that avoid non-steady-state error, the rate of appearance of ingested glucose was normal and suppression of EGP was only minimally impaired. However, when considered in light of the prevailing glucose concentration, both were abnormal. In contrast, rates of postprandial glucose disappearance were substantially decreased due to defects in insulin secretion, insulin action, and glucose effectiveness.

Fully human monoclonal antibodies antagonizing the glucagon receptor improve glucose homeostasis in mice and monkeys

Antagonizing the glucagon signaling pathway represents an attractive therapeutic approach for reducing excess hepatic glucose production in patients with type 2 diabetes. Despite extensive efforts, there is currently no human therapeutic that directly inhibits the glucagon/glucagon receptor pathway. We undertook a novel approach by generating high-affinity human monoclonal antibodies (mAbs) to the human glucagon receptor (GCGR) that display potent antagonistic activity in vitro and in vivo. A single injection of a lead antibody, mAb B, at 3 mg/kg, normalized blood glucose levels in ob/ob mice for 8 days. In addition, a single injection of mAb B dose-dependently lowered fasting blood glucose levels without inducing hypoglycemia and improved glucose tolerance in normal C57BL/6 mice. In normal cynomolgus monkeys, a single injection improved glucose tolerance while increasing glucagon and active glucagon-like peptide-1 levels. Thus, the anti-GCGR mAb could represent an effective new therapeutic for the treatment of type 2 diabetes.

Increased glucose production in mice overexpressing human fructose-1,6-bisphosphatase in the liver

Increased endogenous glucose production (EGP) predominantly from the liver is a characteristic feature of type 2 diabetes, which positively correlates with fasting hyperglycemia. Gluconeogenesis is the biochemical pathway shown to significantly contribute to increased EGP in diabetes. Fructose-1,6-bisphosphatase (FBPase) is a regulated enzyme in gluconeogenesis that is increased in animal models of obesity and insulin resistance. However, whether a specific increase in liver FBPase can result in increased EGP has not been shown. The objective of this study was to determine the role of upregulated liver FBPase in glucose homeostasis. To achieve this goal, we generated human liver FBPase transgenic mice under the control of the transthyretin promoter, using insulator sequences to flank the transgene and protect it from site-of-integration effects. This resulted in a liver-specific model, as transgene expression was not detected in other tissues. Mice were studied under the following conditions: 1) at two ages (24 wk and 1 yr old), 2) after a 60% high-fat diet, and 3) when bred to homozygosity. Hemizygous transgenic mice had an approximately threefold increase in total liver FBPase mRNA with concomitant increases in FBPase protein and enzyme activity levels. After high-fat feeding, hemizygous transgenics were glucose intolerant compared with negative littermates (P < 0.02). Furthermore, when bred to homozygosity, chow-fed transgenic mice showed a 5.5-fold increase in liver FBPase levels and were glucose intolerant compared with negative littermates, with a significantly higher rate of EGP (P < 0.006). This is the first study to show that FBPase regulates EGP and whole body glucose homeostasis in a liver-specific transgenic model. Our homozygous transgenic model may be useful for testing human FBPase inhibitor compounds with the potential to treat patients with type 2 diabetes.

Insulin administration and rate of glucose appearance in people with type 1 diabetes

OBJECTIVE

To assess whether prandial insulin, in addition to basal insulin, has an effect on the rate of glucose appearance from a meal in people with type 1 diabetes.

RESEARCH DESIGN AND METHODS

The rate of glucose appearance from a mixed meal (Ra(meal)) was investigated in six adult (aged 24 +/- 2 years), lean (BMI 23.6 +/- 1.5 kg/m(2)) subjects with well-controlled type 1 diabetes (duration 7.9 +/- 6.9 years, A1C 7.6 +/- 0.9%) with/without prandial insulin. Actrapid was infused to maintain euglycemia before meals were consumed. Subjects consumed two identical meals on separate occasions, and Ra(meal) was measured using a dual isotope method. [6,6-(2)H(2)]glucose was incorporated into the meal (0.081 g/kg body wt), and a primed constant/variable rate infusion of [1,2,3,4,5,6,6-(2)H(2)]glucose was administered. In the tests with prandial insulin, an additional bolus dose of Actrapid was given 20 min before the meal at 0.1 units/kg body wt.

RESULTS

Insulin concentration with prandial insulin was significantly higher than during basal insulin studies (119 +/- 16 vs. 66 +/- 15 pmol/l, P = 0.03 by paired t test). Despite differences in insulin concentration, there were no differences in total glucose appearance (3,398 +/- 197 vs. 3,307 +/- 343 micromol/kg) or time taken for 25% (33.1 +/- 3.3 vs. 31.7 +/- 3.5 min), 50% (54.6 +/- 3.5 vs. 54.1 +/- 4.7 min), and 75% (82.9 +/- 7.1 vs. 82.8 +/- 5.8 min) of total glucose appearance. The fraction of the glucose dose appearing in the circulation was the same for basal (73 +/- 8%) and prandial (75 +/- 4%) study days.

CONCLUSIONS

These results suggest that meal glucose appearance is independent of prandial insulin concentration in people with type 1 diabetes.

Pathogenesis of type 2 diabetes: tracing the reverse route from cure to cause

The metabolic abnormalities of type 2 diabetes can be reversed reproducibly by bariatric surgery. By quantifying the major pathophysiological abnormalities in insulin secretion and insulin action after surgery, the sequence of events leading to restoration of normal metabolism can be defined. Liver fat levels fall within days and normal hepatic insulin sensitivity is restored. Simultaneously, plasma glucose levels return towards normal. Insulin sensitivity of muscle remains abnormal, at least over the weeks and months after bariatric surgery. The effect of the surgery is explicable solely in terms of energy restriction. By combining this information with prospective observation of the changes immediately preceding the onset of type 2 diabetes, a clear picture emerges. Insulin resistance in muscle, caused by inherited and environmental factors, facilitates the development of fatty liver during positive energy balance. Once established, the increased insulin secretion required to maintain plasma glucose levels will further increase liver fat deposition. Fatty liver causes resistance to insulin suppression of hepatic glucose output as well as raised plasma triacylglycerol. Exposure of beta cells to increased levels of fatty acids, derived from circulating and locally deposited triacylglycerol, suppresses glucose-mediated insulin secretion. This is reversible initially, but eventually becomes permanent. The essential time sequence of the pathogenesis of type 2 diabetes is now evident. Muscle insulin resistance determines the rate at which fatty liver progresses, and ectopic fat deposition in liver and islet underlies the related dynamic defects of hepatic insulin resistance and beta cell dysfunction. These defects are capable of dramatic reversal under hypoenergetic feeding conditions, completely in early diabetes and to a worthwhile extent in more established disease.

Pioglitazone decreases fasting and postprandial endogenous glucose production in proportion to decrease in hepatic triglyceride content

OBJECTIVE

Hepatic triglyceride is closely associated with hepatic insulin resistance and is known to be decreased by thiazolididinediones. We studied the effect of pioglitazone on hepatic triglyceride content and the consequent effect on postprandial endogenous glucose production (EGP) in type 2 diabetes.

RESEARCH DESIGN AND METHODS

Ten subjects with type 2 diabetes on sulfonylurea therapy were treated with pioglitazone (30 mg daily) for 16 weeks. EGP was measured using a dynamic isotopic methodology after a standard liquid test meal both before and after pioglitazone treatment. Liver and muscle triglyceride levels were measured by (1)H magnetic resonance spectroscopy, and intra-abdominal fat content was measured by magnetic resonance imaging.

RESULTS

Pioglitazone treatment reduced mean plasma fasting glucose and mean peak postprandial glucose levels. Fasting EGP decreased after pioglitazone treatment (16.6 +/- 1.0 vs. 12.2 +/- 0.7 micromol . kg(-1) . min(-1), P = 0.005). Between 80 and 260 min postprandially, EGP was twofold lower on pioglitazone (2.58 +/- 0.25 vs. 1.26 +/- 0.30 micromol . kg(-1) . min(-1), P < 0.001). Hepatic triglyceride content decreased by approximately 50% (P = 0.03), and muscle (anterior tibialis) triglyceride content decreased by approximately 55% (P = 0.02). Hepatic triglyceride content was directly correlated with fasting EGP (r = 0.64, P = 0.01) and inversely correlated to percentage suppression of EGP (time 150 min, r = -0.63, P = 0.02). Muscle triglyceride, subcutaneous fat, and visceral fat content were not related to EGP. CONCLUSIONS Reduction in hepatic triglyceride by pioglitazone is very closely related to improvement in fasting and postprandial EGP in type 2 diabetes.

Splanchnic regulation of glucose production

The liver plays a key role for the maintenance of blood glucose homeostasis under widely changing physiological conditions. In the overnight fasted state, breakdown of hepatic glycogen and synthesis of glucose from lactate, amino acids, glycerol, and pyruvate contribute about equally to hepatic glucose production. Postprandial glucose uptake by the liver is determined by the size of the glucose load reaching the liver, the rise in insulin concentration, and the route of glucose delivery. Hepatic glycogen stores are depleted within 36 to 48 hours of fasting, but gluconeogenesis continues to provide glucose for tissues with an obligatory glucose requirement. Glucose output from the liver increases during exercise; during short-term intensive exertion, hepatic glycogenolysis is the primary source of extra glucose for skeletal muscle, and during prolonged exercise, hepatic gluconeogenesis becomes gradually more important in keeping with falling insulin and rising glucagon levels. Type 1 diabetes is accompanied by diminished hepatic glycogen stores, augmented gluconeogenesis, and increased basal hepatic glucose production in proportion to the severity of the diabetic state. The hyperglycemia of type 2 diabetes is in part caused by an overproduction of glucose from the liver that is secondary to accelerated gluconeogenesis.

Pathogenesis of pre-diabetes: mechanisms of fasting and postprandial hyperglycemia in people with impaired fasting glucose and/or impaired glucose tolerance

Thirty-two subjects with impaired fasting glucose (IFG) and 28 subjects with normal fasting glucose (NFG) ingested a labeled meal and 75 g glucose (oral glucose tolerance test) on separate occasions. Fasting glucose, insulin, and C-peptide were higher (P < 0.05) in subjects with IFG than in those with NFG, whereas endogenous glucose production (EGP) did not differ, indicating hepatic insulin resistance. EGP was promptly suppressed, and meal glucose appearance comparably increased following meal ingestion in both groups. In contrast, glucose disappearance (R(d)) immediately after meal ingestion was lower (P < 0.001) in subjects with IFG/impaired glucose tolerance (IGT) and IFG/diabetes but did not differ in subjects with IFG/normal glucose tolerance (NGT) or NFG/NGT. Net insulin action (S(i)) and insulin-stimulated glucose disposal (S(i)*) were reduced (P < 0.001, ANOVA) in subjects with NFG/IGT, IFG/IGT, and IFG/diabetes but did not differ in subjects with NFG/NGT or IFG/NGT. Defective insulin secretion also contributed to lower postprandial R(d) since disposition indexes were lower (P < 0.001, ANOVA) in subjects with NFG/IGT, IFG/IGT, and IFG/diabetes but did not differ in subjects with NFG/NGT and IFG/NGT. We conclude that postprandial hyperglycemia in individuals with early diabetes is due to lower rates of glucose disappearance rather than increased meal appearance or impaired suppression of EGP, regardless of their fasting glucose. In contrast, insulin secretion, action, and the pattern of postprandial turnover are essentially normal in individuals with isolated IFG.

Inhibition of fructose 1,6-bisphosphatase reduces excessive endogenous glucose production and attenuates hyperglycemia in Zucker diabetic fatty rats

Gluconeogenesis is increased in type 2 diabetes and contributes significantly to fasting and postprandial hyperglycemia. We recently reported the discovery of the first potent and selective inhibitors of fructose 1,6-bisphosphatase (FBPase), a rate-controlling enzyme of gluconeogenesis. Herein we describe acute and chronic effects of the lead inhibitor, MB06322 (CS-917), in rodent models of type 2 diabetes. In fasting male ZDF rats with overt diabetes, a single dose of MB06322 inhibited gluconeogenesis by 70% and overall endogenous glucose production by 46%, leading to a reduction in blood glucose of >200 mg/dl. Chronic treatment of freely feeding 6-week-old male Zucker diabetic fatty (ZDF) rats delayed the development of hyperglycemia and preserved pancreatic function. Elevation of lactate ( approximately 1.5-fold) occurred after 4 weeks of treatment, as did the apparent shunting of precursors into triglycerides. Profound glucose lowering ( approximately 44%) and similar metabolic ramifications were associated with 2-week intervention therapy of 10-week-old male ZDF rats. In high-fat diet-fed female ZDF rats, MB06322 treatment for 2 weeks fully attenuated hyperglycemia without evidence of metabolic perturbation other than a modest reduction in glycogen stores ( approximately 20%). The studies confirm that excessive gluconeogenesis plays an integral role in the pathophysiology of type 2 diabetes and suggest that FBPase inhibitors may provide a future treatment option.

Group 1B phospholipase A2-mediated lysophospholipid absorption directly contributes to postprandial hyperglycemia

Postprandial hyperglycemia is an early indicator of abnormality in glucose metabolism leading to type 2 diabetes. However, mechanisms that contribute to postprandial hyperglycemia have not been identified. This study showed that mice with targeted inactivation of the group 1B phospholipase A2 (Pla2g1b) gene displayed lower postprandial glycemia than that observed in wild-type mice after being fed a glucose-rich meal. The difference was caused by enhanced postprandial glucose uptake by the liver, heart, and muscle tissues as well as altered postprandial hepatic glucose metabolism in the Pla2g1b-/- mice. These differences were attributed to a fivefold decrease in the amount of dietary phospholipids absorbed as lysophospholipids in Pla2g1b-/- mice compared with that observed in Pla2g1b+/+ mice. Elevating plasma lysophospholipid levels in Pla2g1b-/- mice via intraperitoneal injection resulted in glucose intolerance similar to that exhibited by Pla2g1b+/+ mice. Studies with cultured hepatoma cells revealed that lysophospholipids dose-dependently suppressed insulin-stimulated glycogen synthesis. These results demonstrated that reduction of lysophospholipid absorption enhances insulin-mediated glucose metabolism and is protective against postprandial hyperglycemia.

Mechanisms for abnormal postprandial glucose metabolism in type 2 diabetes

To assess mechanisms for postprandial hyperglycemia, we used a triple-isotope technique ([\3-(3)H]glucose and [(14)C]bicarbonate and oral [6,6-dideutero]glucose iv) and indirect calorimetry to compare components of glucose release and pathways for glucose disposal in 26 subjects with type 2 diabetes and 15 age-, weight-, and sex-matched normal volunteers after a standard meal. The results were as follows: 1) diabetic subjects had greater postprandial glucose release (P<0.001) because of both increased endogenous and meal-glucose release; 2) the greater endogenous glucose release (P<0.001) was due to increased gluconeogenesis (P<0.001) and glycogenolysis (P=0.01); 3) overall tissue glucose uptake, glycolysis, and storage were comparable in both groups (P>0.3); 4) glucose clearance (P<0.001) and oxidation (P=0.004) were reduced, whereas nonoxidative glycolysis was increased (P=0.04); and 5) net splanchnic glucose storage was reduced by approximately 45% (P=0.008) because of increased glycogen cycling (P=0.03). Thus in type 2 diabetes, postprandial hyperglycemia is primarily due to increased glucose release; hyperglycemia overcomes the effects of impaired insulin secretion and sensitivity on glucose transport, but intracellular defects persist so that pathways of glucose metabolism are abnormal and glucose is shunted away from normal sites of storage (e.g., liver and muscle) into other tissues.

Insulin secretory defect plays a major role in the development of diabetes in patients with distal pancreatectomy

To investigate the pathogenesis of distal pancreatectomy (d-Px)-induced diabetes in Korean patients, we investigated insulin secretory and sensitivity indexes obtained by oral glucose tolerance testing in 20 patients that had received d-Px (10 with d-Px-induced diabetes and 10 with normal glucose tolerance with d-Px [NGT d-Px]) and in 164 control subjects (77 with type 2 diabetes mellitus and 87 with NGT) that did not receive d-Px. The pancreatectomized subjects had lower fasting serum insulin, homeostasis model assessment of pancreatic beta-cell function (HOMA-beta) levels, and insulinogenic indices than the NGT controls. The HOMA-beta values of nonobese NGT d-Px- and d-Px-induced diabetic subjects were 73.7% and 38.7% of those for nonobese NGT controls, respectively, and HOMA-beta was significantly lower only for d-Px-induced diabetic subjects (P < .01). In obese subjects, the HOMA-beta values of obese d-Px-induced diabetic subjects were significantly lower than those of obese NGT controls (P < .05). The insulin sensitivity was significantly lower in nonobese type 2 diabetes mellitus controls than in nonobese NGT d-Px or in nonobese d-Px-induced diabetic subjects (P < .001 and .05, respectively). These results show that a reduced insulin secretory function is a typical feature of glucose homeostasis in distal pancreatectomized patients and that insulin secretory defect plays a major role in the development of diabetes in these patients. In addition, the study suggests that pancreatic resections of 60% or less and body mass index are not the main causes of diabetes onset after d-Px in this study.

Is non-insulin dependent glucose uptake a therapeutic alternative? Part 1: physiology, mechanisms and role of non insulin-dependent glucose uptake in type 2 diabetes

Several decades of research for treating type 2 diabetes have yielded new drugs but the actual experience with the available oral antidiabetic compounds clearly shows that therapeutic needs are not matched. This highlights the urgent need for exploring other pathways. All cell types have the capacity to take up glucose independently of insulin, whereby basal but also hyperglycaemia-promoted glucose supply is ensured. Although poorly explored, insulin-independent glucose uptake might nevertheless represent a therapeutic target, as an alternative to the clear limits of actual drug treatments. This review not only critically examines some major pathways not requiring insulin (although they may be influenced by the hormone) but importantly, this analysis extends to the clinical applicability of these potential therapeutic principles by also considering their predictable tolerability for long-term therapy. In particular vascular safety (the ultimate problem linked with diabetes) will be envisaged because of the ubiquitous distribution of glucose transporters and some linked mechanisms. Several mechanisms can be identified which do not require insulin for their functioning. The first part of this review deals with the description, the regulation and the limits of some mechanisms representing potential pharmacological targets capable of having a highly significant impact on glucose uptake. These selected topics are: a) unmasking and/or activation of glucose transporters in cell plasma membranes, b) insulin mimetics acting at postreceptor level, c) activation of AMPK, d) increasing nitric oxide and e) increasing glucose-6P and glycogen stores.

Real-time assessment of postprandial fat storage in liver and skeletal muscle in health and type 2 diabetes

Liver and skeletal muscle triglyceride stores are elevated in type 2 diabetes and correlate with insulin resistance. As postprandial handling of dietary fat may be a critical determinant of tissue triglyceride levels, we quantified postprandial fat storage in normal and type 2 diabetes subjects. Healthy volunteers (n = 8) and diet-controlled type 2 diabetes subjects (n = 12) were studied using a novel 13C magnetic resonance spectroscopy protocol to measure the postprandial increment in liver and skeletal muscle triglyceride following ingestion of 13C-labeled fatty acids given with a standard mixed meal. The postprandial increment in hepatic triglyceride was rapid in both groups (peak increment controls: +7.3 +/- 1.5 mmol/l at 6 h, P = 0.002; peak increment diabetics: +10.8 +/- 3.4 mmol/l at 4 h, P = 0.009). The mean postprandial incremental AUC of hepatic 13C enrichment between the first and second meals (0 and 4 h) was significantly higher in the diabetes group (6.1 +/- 1.4 vs. 1.7 +/- 0.6 mmol x l(-1) x h(-1), P = 0.019). Postprandial increment in skeletal muscle triglyceride in the control group was small compared with the diabetic group, the mean 24-h postprandial incremental AUC being 0.2 +/- 0.3 vs. 1.7 +/- 0.4 mmol x l(-1) x h(-1) (P = 0.009). We conclude that the postprandial uptake of fatty acids by liver and skeletal muscle is increased in type 2 diabetes and may underlie the elevated tissue triglyceride stores and consequent insulin resistance.

Alterations in postprandial hepatic glycogen metabolism in type 2 diabetes

Decreased skeletal muscle glucose disposal and increased endogenous glucose production (EGP) contribute to postprandial hyperglycemia in type 2 diabetes, but the contribution of hepatic glycogen metabolism remains uncertain. Hepatic glycogen metabolism and EGP were monitored in type 2 diabetic patients and nondiabetic volunteer control subjects (CON) after mixed meal ingestion and during hyperglycemic-hyperinsulinemic-somatostatin clamps applying 13C nuclear magnetic resonance spectroscopy (NMRS) and variable infusion dual-tracer technique. Hepatocellular lipid (HCL) content was quantified by 1H NMRS. Before dinner, hepatic glycogen was lower in type 2 diabetic patients (227 +/- 6 vs. CON: 275 +/- 10 mmol/l liver, P < 0.001). After meal ingestion, net synthetic rates were 0.76 +/- 0.16 (type 2 diabetic patients) and 1.36 +/- 0.15 mg x kg(-1) x min(-1) (CON, P < 0.02), resulting in peak concentrations of 283 +/- 15 and 360 +/- 11 mmol/l liver. Postprandial rates of EGP were approximately 0.3 mg x kg(-1) x min(-1) (30-170 min; P < 0.05 vs. CON) higher in type 2 diabetic patients. Under clamp conditions, type 2 diabetic patients featured approximately 54% lower (P < 0.03) net hepatic glycogen synthesis and approximately 0.5 mg x kg(-1) x min(-1) higher (P < 0.02) EGP. Hepatic glucose storage negatively correlated with HCL content (R = -0.602, P < 0.05). Type 2 diabetic patients exhibit 1) reduction of postprandial hepatic glycogen synthesis, 2) temporarily impaired suppression of EGP, and 3) no normalization of these defects by controlled hyperglycemic hyperinsulinemia. Thus, impaired insulin sensitivity and/or chronic glucolipotoxicity in addition to the effects of an altered insulin-to-glucagon ratio or increased free fatty acids accounts for defective hepatic glycogen metabolism in type 2 diabetic patients.

Endogenous Glucose Production in Type 2 Diabetes: Basal and Postprandial. Role of Diurnal Rhythms

Glycemia in type 2 diabetes is characterized by a nonsteady but stable diurnal cycle. This leads to morning fasting hyperglycemia. It arises from an underlying circadian pattern in endogenous glucose production because the metabolic clearance rate of glucose is decreased but constant. Therefore, it is important to use appropriate nonsteady tracer methods to measure this rate even under basal conditions. Postprandially, in diabetes, the endogenous glucose production continues to decrease, with only minor deviations from the slope of the basal curve. This suggests a decoupling of endogenous glucose production from the regulatory factors (insulin, glucose) that prevail under normal circumstances. As the duration of diabetes increases, metabolic clearance of glucose continues to deteriorate. This may be partially compensated by a decrease in glucose production. This rate remains, however, inappropriate because its impact on glycemia does not decline.

One week's treatment with the long-acting glucagon-like peptide 1 derivative liraglutide (NN2211) markedly improves 24-h glycemia and alpha- and beta-cell function and reduces endogenous glucose release in patients with type 2 diabetes

Glucagon-like peptide 1 (GLP-1) is potentially a very attractive agent for treating type 2 diabetes. We explored the effect of short-term (1 week) treatment with a GLP-1 derivative, liraglutide (NN2211), on 24-h dynamics in glycemia and circulating free fatty acids, islet cell hormone profiles, and gastric emptying during meals using acetaminophen. Furthermore, fasting endogenous glucose release and gluconeogenesis (3-(3)H-glucose infusion and (2)H(2)O ingestion, respectively) were determined, and aspects of pancreatic islet cell function were elucidated on the subsequent day using homeostasis model assessment and first- and second-phase insulin response during a hyperglycemic clamp (plasma glucose approximately 16 mmol/l), and, finally, on top of hyperglycemia, an arginine stimulation test was performed. For accomplishing this, 13 patients with type 2 diabetes were examined in a double-blind, placebo-controlled crossover design. Liraglutide (6 micro g/kg) was administered subcutaneously once daily. Liraglutide significantly reduced the 24-h area under the curve for glucose (P = 0.01) and glucagon (P = 0.04), whereas the area under the curve for circulating free fatty acids was unaltered. Twenty-four-hour insulin secretion rates as assessed by deconvolution of serum C-peptide concentrations were unchanged, indicating a relative increase. Gastric emptying was not influenced at the dose of liraglutide used. Fasting endogenous glucose release was decreased (P = 0.04) as a result of a reduced glycogenolysis (P = 0.01), whereas gluconeogenesis was unaltered. First-phase insulin response and the insulin response to an arginine stimulation test with the presence of hyperglycemia were markedly increased (P < 0.001), whereas the proinsulin/insulin ratio fell (P = 0.001). The disposition index (peak insulin concentration after intravenous bolus of glucose multiplied by insulin sensitivity as assessed by homeostasis model assessment) almost doubled during liraglutide treatment (P < 0.01). Both during hyperglycemia per se and after arginine exposure, the glucagon responses were reduced during liraglutide administration (P < 0.01 and P = 0.01). Thus, 1 week's treatment with a single daily dose of the GLP-1 derivative liraglutide, operating through several different mechanisms including an ameliorated pancreatic islet cell function in individuals with type 2 diabetes, improves glycemic control throughout 24 h of daily living, i.e., prandial and nocturnal periods. This study further emphasizes GLP-1 and its derivatives as a promising novel concept for treatment of type 2 diabetes.

Nonesterified fatty acids and hepatic glucose metabolism in the conscious dog

We used tracer and arteriovenous difference techniques in conscious dogs to determine the effect of nonesterified fatty acids (NEFAs) on net hepatic glucose uptake (NHGU). The protocol included equilibration ([3-(3)H]glucose), basal, and two experimental periods (-120 to -30, -30 to 0, 0-120 [period 1], and 120-240 min [period 2], respectively). During periods 1 and 2, somatostatin, basal intraportal insulin and glucagon, portal glucose (21.3 micromol.kg(-1).min(-1)), peripheral glucose (to double the hepatic glucose load), and peripheral nicotinic acid (1.5 mg.kg(-1).min(-1)) were infused. During period 2, saline (nicotinic acid [NA], n = 7), lipid emulsion (NA plus lipid emulsion [NAL], n = 8), or glycerol (NA plus glycerol [NAG], n = 3) was infused peripherally. During period 2, the NA and NAL groups differed (P < 0.05) in rates of NHGU (10.5 +/- 2.08 and 4.7 +/- 1.9 micromol.g(-1).min(-1)), respectively, endogenous glucose R(a) (2.3 +/- 1.4 and 10.6 +/- 1.0 micromol.kg(-1).min(-1)), net hepatic NEFA uptakes (0.1 +/- 0.1 and 1.8 +/- 0.2 micromol.kg(-1).min(-1)), net hepatic beta-hydroxybutyrate output (0.1 +/- 0.0 and 0.4 +/- 0.1 micromol.kg(-1).min(-1)), and net hepatic lactate output (6.5 +/- 1.7 vs. -2.3 +/- 1.2 micromol.kg(-1).min(-1)). Hepatic glucose uptake and release were 2.6 micro mol. kg(-1). min(-1) less and 3.5 micro mol. kg(-1). min(-1) greater, respectively, in the NAL than NA group (NS). The NAG group did not differ significantly from the NA group in any of the parameters listed above. In the presence of hyperglycemia and relative insulin deficiency, elevated NEFAs reduce NHGU by stimulating hepatic glucose release and suppressing hepatic glucose uptake.

Hepatic glucose metabolism in humans--its role in health and disease

The liver is mainly responsible for maintaining normal concentrations of blood glucose by its ability to store glucose as glycogen and to produce glucose from glycogen breakdown or gluconeogenic precursors. During the last decade, new techniques have made it possible to gain further insight into the turnover of hepatic glucose and glycogen in humans. Hepatic glycogen varies from approximately 200 to approximately 450 mM between overnight fasted and postprandial conditions. Patients with type-1 diabetes (T1DM), type 2 diabetes (T2DM) or partial agenesis of the pancreas exhibit increased endogenous glucose production and synthesize only 25-45% of hepatic glycogen compared with non-diabetic humans. This defect can be partly restored in T1DM by combined long- and short-term optimized treatment with insulin. In T2DM, increased gluconeogenesis was identified as the main cause of elevated glucose production and fasting hyperglycaemia. These patients also exhibit augmented intracellular lipid accumulation which could hint at a link between deranged glucose and lipid metabolism in insulin-resistant states.

Glucose-induced suppression of endogenous glucose production: dynamic response to differing glucose profiles

To determine whether, in the presence of constant insulin concentrations, a change in glucose concentrations results in a reciprocal change in endogenous glucose production (EGP), glucagon ( approximately 130 ng/l) and insulin ( approximately 65 pmol/l) were maintained at constant "basal" concentrations while glucose was clamped at approximately 5.3 mM (euglycemia), approximately 7.0 mM (sustained hyperglycemia; n = 10), or varied to create a "postprandial" profile (profile; n = 11). EGP fell slowly over the 6 h of the euglycemia study. In contrast, an increase in glucose to 7.13 +/- 0.3 mmol/l resulted in prompt and sustained suppression of EGP to 9.65 +/- 1.21 micromol x kg-1 x min-1. On the profile study day, glucose increased to a peak of 11.2 +/- 0.5 mmol/l, and EGP decreased to a nadir of 6.79 +/- 2.54 micromol x kg-1 x min-1 by 60 min. Thereafter, the fall in glucose was accompanied by a reciprocal rise in EGP to rates that did not differ from those observed on the euglycemic study day (11.31 +/- 2.45 vs. 12.11 +/- 3.21 micromol x kg-1 x min-1). Although the pattern of change of glucose differed markedly on the sustained hyperglycemia and profile study days, by design the area above basal did not. This resulted in equivalent suppression of EGP below basal (-1,952 +/- 204 vs. -1,922 +/- 246 mmol. kg-1. 6 h-1). These data demonstrate that, in the presence of a constant basal insulin concentration, changes in glucose within the physiological range rapidly and reciprocally regulate EGP.