Reduced hepatic insulin extraction in response to gastric inhibitory polypeptide compensates for reduced insulin secretion in normal-weight and normal glucose tolerant first-degree relatives of type 2 diabetic patients

Safety of native glucose-dependent insulinotropic polypeptide in humans

In this systematic review, we assessed the safety and possible safety events of native glucose-dependent insulinotropic polypeptide (GIP)(1-42) in human studies with administration of synthetic human GIP. We searched the PubMed database for all trials investigating synthetic human GIP(1-42) administration. A total of 67 studies were included. Study duration ranged from 30 min to 6 days. In addition to healthy individuals, the studies included individuals with impaired glucose tolerance, type 2 diabetes, type 1 diabetes, chronic pancreatitis and secondary diabetes, latent autoimmune diabetes in adults, diabetes caused by a mutation in the hepatocyte nuclear factor 1-alpha gene, end-stage renal disease, chronic renal insufficiency, critical illness, hypoparathyroidism, or cystic fibrosis-related diabetes. Of the included studies, 78% did not mention safety events, 10% of the studies reported that no safety events were observed in relation to GIP administration, and 15% of the studies reported safety events in relation to GIP administration with most frequently reported event being a moderate and transient increased heart rate. Gastrointestinal safety events, and changes in blood pressure were also reported. Plasma concentration of active GIP(1-42) increased linearly with dose independent of participant phenotype. There was no significant correlation between achieved maximal concentration of GIP(1-42) and reported safety events. Clearance rates of GIP(1-42) were similar between participant groups. In conclusion, the available data indicate that GIP(1-42) in short-term (up to 6 days) infusion studies is generally well-tolerated. The long-term safety of continuous GIP(1-42) administration is unknown.

Acute Hyperglycemia Induced by Hyperglycemic Clamp Affects Plasma Amyloid-β in Type 2 Diabetes

Background

Individuals with type 2 diabetes (T2D) have an increased risk of cognitive symptoms and Alzheimer's disease (AD). Mis-metabolism with aggregation of amyloid-β peptides (Aβ) play a key role in AD pathophysiology. Therefore, human studies on Aβ metabolism and T2D are warranted.

Objective

The objective of this study was to examine whether acute hyperglycemia affects plasma Aβ1-40 and Aβ1-42 concentrations in individuals with T2D and matched controls.

Methods

Ten participants with T2D and 11 controls (median age, 69 years; range, 66-72 years) underwent hyperglycemic clamp and placebo clamp (saline infusion) in a randomized order, each lasting 4 hours. Aβ1-40, Aβ1-42, and insulin-degrading enzyme (IDE) plasma concentrations were measured in blood samples taken at 0 and 4 hours of each clamp. Linear mixed-effect regression models were used to evaluate the 4-hour changes in Aβ1-40 and Aβ1-42 concentrations, adjusting for body mass index, estimated glomerular filtration rate, and 4-hour change in insulin concentration.

Results

At baseline, Aβ1-40 and Aβ1-42 concentrations did not differ between the two groups. During the hyperglycemic clamp, Aβ decreased in the control group, compared to the placebo clamp (Aβ1-40: p = 0.034, Aβ1-42: p = 0.020), IDE increased (p = 0.016) during the hyperglycemic clamp, whereas no significant changes in either Aβ or IDE was noted in the T2D group.

Conclusions

Clamp-induced hyperglycemia was associated with increased IDE levels and enhanced Aβ40 and Aβ42 clearance in controls, but not in individuals with T2D. We hypothesize that insulin-degrading enzyme was inhibited during hyperglycemic conditions in people with T2D.

Fasting hepatic insulin clearance reflects postprandial hepatic insulin clearance: a brief report

BACKGROUND

Hepatic insulin clearance (HIC) is an important pathophysiology of type 2 diabetes mellitus (T2DM). HIC was reported to decrease in patients with type 2 diabetes and metabolic syndrome. HIC is originally calculated by post-load insulin and C-peptide from the oral glucose tolerance test (OGTT). However, OGTT or meal tolerance tests are a burden for patients, and OGTT is not suitable for overt diabetes due to the risk of hyperglycemia. If we can calculate the HIC from the fasting state, it is preferable. We hypothesized that fasting HIC correlates with postprandial HIC in both participants with T2DM and without diabetes. We investigated whether fasting HIC correlates with postprandial HIC in overt T2DM and nondiabetes subjects (non-DM) evaluated by using glucose clamp and meal load.

METHODS

We performed a meal tolerance test and hyperinsulinemic-euglycemic clamp in 70 subjects, 31 patients with T2DM and 39 non-DM subjects. We calculated the postprandial C-peptide AUC-to-insulin AUC ratio as the postprandial HIC and the fasting C-peptide-to-insulin ratio as the fasting HIC. We also calculated whole-body insulin clearance from the glucose clamp test.

RESULTS

The fasting HIC significantly correlated with postprandial HIC in T2DM (r_S = 0.82, P < 0.001). Nondiabetes subjects also showed a significant correlation between fasting and postprandial HIC (r_S = 0.71, P < 0.001). Fasting HIC in T2DM was correlated with BMI, HbA1c, gamma-glutamyl transpeptidase, HOMA-IR, HOMA-beta, M/I, and whole-body insulin clearance. Fasting HIC in nondiabetes subjects was correlated with HOMA-IR and HOMA-beta.

CONCLUSIONS

These results suggest that fasting HIC is strongly correlated with postprandial HIC in both overt T2DM and non-DM patients, as evaluated by the meal test and glucose clamp method. Fasting HIC could be a convenient marker of HIC.

Prevalence of metabolic syndrome and components in rural, semi-urban and urban areas in the littoral region in Cameroon: impact of physical activity

BACKGROUND

Living areas in developing countries impact seriously lifestyle by modifying energy consumption and energy expenditure. Thus, urbanization is associated with less practice of physical activity (PA), a leading cause of metabolic syndrome (MetS) which prevalence vary in African countries. The present study aimed to assess the effect of PA on MetS according to urbanization level in the littoral region, Cameroon.

METHODS

A cross-sectional study was conducted in three geographical settings (urban, semi-urban, and rural) in the littoral region in Cameroon. A total of 879 participants were included (urban: 372, semi-urban: 195 and rural: 312). MetS was defined according to the International Federation of Diabetes 2009. The level of PA was assessed using the Global Physical Activity questionnaire.

RESULTS

Low level of PA was (P < 0.0001) reported in urban (54.5%), semi-urban (28.7%) and rural (16.9%) and high level in rural area (77.9%). The prevalence of MetS was higher in urban areas (37.2%), then rural (36.8%) and finally semi-urban (25.9%). Hyperglycemia (p = 0.0110), low HDL-c (p < 0.0001) and high triglyceridemia (p = 0.0068) were most prevalent in urban residents. Participants with low level of PA were at risk of MetS (OR: 1.751, 95% CI 1.335-2.731, p = 0.001), hyperglycemia (OR: 1.909, 95% CI 1.335-2.731, p = 0.0004) abdominal obesity(OR: 2.007, 95% CI 1.389-2.900, p = 0.0002), low HDL-c (OR: 1.539, 95% CI 1.088-2.179, p = 0.014) and those with moderate level of PA were protected against high blood pressure(OR: 0.452, 95% CI 0.298-0.686, p = 0.0002) and compared to those with high level of PA. Urban dwellers were at the risk of MetS compared to rural residents (OR: 1.708, 95% CI. 1.277-2.285, p = 0.003) and protected against high blood pressure (OR:0.314, 95% CI 0.212-0.466, p < 0.0001), abdominal obesity (OR: 0.570, 95% CI 0.409-0.794, p = 0.0009), and low HDL-c (OR: 0.725, 95% CI 0.534-0.983, p = 0.038) compared to rural residents.

CONCLUSIONS

MetS was more prevalent in urban dwellers and was associated with a low level of PA.

Insulin clearance and incretin hormones following oral and "isoglycemic" intravenous glucose in type 2 diabetes patients under different antidiabetic treatments

It has not been elucidated whether incretins affect insulin clearance in type 2 diabetes (T2D). We aimed exploring possible associations between insulin clearance and endogenously secreted or exogenously administered incretins in T2D patients. Twenty T2D patients were studied (16 males/4 females, 59 ± 2 years (mean ± standard error), BMI = 31 ± 1 kg/m2, HbA1c = 7.0 ± 0.1%). Patients were treated with metformin, sitagliptin, metformin/sitagliptin combination, and placebo (randomized order). On each treatment period, oral and isoglycemic intravenous glucose infusion tests were performed (OGTT, IIGI, respectively). We also studied twelve T2D patients (9 males/3 females, 61 ± 3 years, BMI = 30 ± 1 kg/m2, HbA1c = 7.3 ± 0.4%) that underwent infusion of GLP-1(7-36)-amide, GIP, GLP-1/GIP combination, and placebo. Plasma glucose, insulin, C-peptide, and incretins were measured. Insulin clearance was assessed as insulin secretion to insulin concentration ratio. In the first study, we found OGTT/IIGI insulin clearance ratio weakly inversely related to OGTT/IIGI total GIP and intact GLP-1 (R2 = 0.13, p < 0.02). However, insulin clearance showed some differences between sitagliptin and metformin treatment (p < 0.02). In the second study we found no difference in insulin clearance following GLP-1 and/or GIP infusion (p > 0.5). Thus, our data suggest that in T2D there are no relevant incretin effects on insulin clearance. Conversely, different antidiabetic treatments may determine insulin clearance variations.

Dipeptidyl peptidase-4 inhibitor, anagliptin, alters hepatic insulin clearance in relation to the glycemic status in Japanese individuals with type 2 diabetes

AIMS/INTRODUCTION

This study investigated the impact of the dipeptidyl peptidase-4 inhibitor, anagliptin, on hepatic insulin clearance (HIC) in Japanese type 2 diabetes patients and explored its relationship to glycemic status.

MATERIALS AND METHODS

Data on 765 participants in anagliptin phase 2 and 3 studies were analyzed. Adjusted changes in variables during 12 weeks of anagliptin therapy were compared with a placebo. HIC was calculated as the ratio, C-peptide area under the curve 0-120 min to insulin area under the curve 0-120 min, after a meal tolerance test. To explore the effects of baseline HIC levels on variables, participants receiving anagliptin were divided according to quartiles of baseline HIC. Furthermore, multivariate analysis investigated the association between baseline HIC levels and glycemic status.

RESULTS

Anagliptin significantly reduced glycosylated hemoglobin levels (P < 0.001 vs placebo) and HIC levels (P < 0.01). Longer duration of diabetes, lower body mass index, higher glycosylated hemoglobin and lower insulin secretion capacity were observed with increases in baseline HIC levels. Improvements in glycosylated hemoglobin, glycoalbumin and 1,5-anhydroglucitol levels were greater in the relatively higher HIC group (baseline HIC levels ≥median) than in the lower HIC group (

CONCLUSIONS

Anagliptin affected HIC levels according to HIC baseline levels. Higher baseline HIC values might result in improved hyperglycemia through reduced HIC.

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Key Words

• Dipeptidyl peptidase-4 inhibitor
• Hepatic insulin clearance
• Meal tolerance test

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MESH Headings

• Aged
• Asian People
• Diabetes Mellitus, Type 2/drug therapy
• Diabetes Mellitus, Type 2/metabolism
• Dipeptidyl-Peptidase IV Inhibitors/pharmacology
• Dipeptidyl-Peptidase IV Inhibitors/therapeutic use
• Double-Blind Method
• Female
• Humans
• Insulin/metabolism
• Liver/metabolism
• Male
• Middle Aged
• Pyrimidines/pharmacology
• Pyrimidines/therapeutic use

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Grants

• Sanwa Kagaku Kenkyusho Co., Ltd.
• Kowa Co., Ltd

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Affiliation(s)

Takahiro Abe Department of Hematology, Endocrinology and MetabolismNiigata University Faculty of MedicineNiigataJapan
Yasuhiro Matsubayashi Department of Hematology, Endocrinology and MetabolismNiigata University Faculty of MedicineNiigataJapan
Sayaka Muragishi Kowa Co., Ltd.TokyoJapan
Akihiro Yoshida Department of Hematology, Endocrinology and MetabolismNiigata University Faculty of MedicineNiigataJapan Kowa Co., Ltd.TokyoJapan
Hideki Suganami Kowa Co., Ltd.TokyoJapan
Kenichi Furusawa Sanwa Kagaku Kenkyusho Co., Ltd.NagoyaJapan
Kazuya Fujihara Department of Hematology, Endocrinology and MetabolismNiigata University Faculty of MedicineNiigataJapan
Shiro Tanaka Department of Clinical BiostatisticsGraduate School of Medicine Kyoto UniversityKyotoJapan
Kohei Kaku Kawasaki Medical SchoolOkayamaJapan
Hirohito Sone Department of Hematology, Endocrinology and MetabolismNiigata University Faculty of MedicineNiigataJapan

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Hepatic and Extrahepatic Insulin Clearance in Mice with Double Deletion of Glucagon-Like Peptide-1 and Glucose-Dependent Insulinotropic Polypeptide Receptors

The aim of this study was to investigate whether incretins, at physiological levels, affect hepatic and/or extrahepatic insulin clearance. Hepatic and extrahepatic insulin clearance was studied in 31 double incretin receptor knockout (DIRKO) and 45 wild-type (WT) mice, which underwent an Intravenous Glucose Tolerance Test (IVGTT). A novel methodology based on mathematical modeling was designed to provide two sets of values (FE_L-P1, CL_P-P1; FE_L-P2, CL_P-P2) accounting for hepatic and extrahepatic clearance in the IVGTT first and second phases, respectively, plus the respective total clearances, CL_T-P1 and CL_T-P2. A statistically significant difference between DIRKO and WT was found in CL_T-P1 (0.61 [0.48–0.82] vs. 0.51 [0.46–0.65] (median [interquartile range]); p = 0.02), which was reflected in the peripheral component, CL_P-P1 (0.18 [0.13–0.27] vs. 0.15 [0.11–0.22]; p = 0.04), but not in the hepatic component, FE_L-P1 (29.7 [26.7–34.9] vs. 28.9 [25.7–32.0]; p = 0.18). No difference was detected between DIRKO and WT in CL_T-P2 (1.38 [1.13–1.75] vs. 1.69 [1.48–1.87]; p = 0.10), neither in CL_P-P2 (0.72 [0.64–0.81] vs. 0.79 [0.69–0.87]; p = 0.27) nor in FE_L-P2 (37.8 [35.1–43.1] vs. 39.8 [35.8–44.2]; p = 0.46). In conclusion, our findings suggest that the higher insulin clearance observed in DIRKO compared with WT during the IVGTT first phase may be due to its extrahepatic component.

Influence of Liver Cirrhosis on Blood Glucose, Insulin Sensitivity and Islet Function in Mice

BACKGROUND

The relationship between cirrhosis and diabetes is controversial. We studied the influence of cirrhosis on glucose levels and islet function and explored its possible mechanisms.

MATERIALS AND METHODS

Cirrhosis was induced in male C57BL/6 mice by bile duct ligation (BDL). Serum biochemical parameters were determined, and oral glucose tolerance tests (OGTT) were performed at 4 and 8 weeks after BDL. Histopathology and phospho-NF-κB-p65/I-kappa B α immunohistochemical staining of the liver and islet were observed. The protein levels of the insulin signaling system and the gene expression of insulin-degrading enzyme (IDE) in the liver and muscle were determined. The activity of glucokinase (GCK) and glucose 6-phosphatase (G6P) and glycogen levels in liver homogenates were measured.

RESULTS

After BDL, the mice developed cirrhosis, and fasting glucose decreased significantly, but 2 h postprandial glucose increased, and the insulin areas under the curves increased. At 4 weeks of BDL, the ratios of phospho-NF-κB-p65/I-kappa B α accumulation in the liver and islet increased, the activity of G6P and the glycogen content in liver homogenates decreased, the insulin signaling system and the gene expression of IDE in the liver was downregulated, and the islet areas were decreased. After 8 weeks, these changes were more severe.

CONCLUSIONS

In different periods of cirrhosis, the levels of fasting glucose and 2 h postprandial glucose changed in different amplitudes. Glycogen concentrations and the activity of G6P in the liver were decreased. The mice developed insulin resistance and the islet areas were decreased. The NF-κB pathway may play a role in the process.

Targeting Insulin-Degrading Enzyme in Insulin Clearance

Hepatic insulin clearance, a physiological process that in response to nutritional cues clears ~50–80% of circulating insulin, is emerging as an important factor in our understanding of the pathogenesis of type 2 diabetes mellitus (T2DM). Insulin-degrading enzyme (IDE) is a highly conserved Zn²⁺-metalloprotease that degrades insulin and several other intermediate-size peptides. Both, insulin clearance and IDE activity are reduced in diabetic patients, albeit the cause-effect relationship in humans remains unproven. Because historically IDE has been proposed as the main enzyme involved in insulin degradation, efforts in the development of IDE inhibitors as therapeutics in diabetic patients has attracted attention during the last decades. In this review, we retrace the path from Mirsky’s seminal discovery of IDE to the present, highlighting the pros and cons of the development of IDE inhibitors as a pharmacological approach to treating diabetic patients.

Insulin clearance as the major player in the hyperinsulinaemia of black African men without diabetes

AIM

To investigate relationships between insulin clearance, insulin secretion, hepatic fat accumulation and insulin sensitivity in black African (BA) and white European (WE) men.

METHODS

Twenty-three BA and twenty-three WE men with normal glucose tolerance, matched for age and body mass index, underwent a hyperglycaemic clamp to measure insulin secretion and clearance, hyperinsulinaemic-euglycaemic clamp with stable glucose isotope infusion to measure whole-body and hepatic-specific insulin sensitivity, and magnetic resonance imaging to quantify intrahepatic lipid (IHL).

RESULTS

BA men had higher glucose-stimulated peripheral insulin levels (48.1 [35.5, 65.2] × 10³ vs. 29.9 [23.3, 38.4] × 10³ pmol L^-1  × min, P = .017) and lower endogeneous insulin clearance (771.6 [227.8] vs. 1381 [534.3] mL m^-2 body surface area min ^-1 , P < .001) compared with WE men. There were no ethnic differences in beta-cell insulin secretion or beta-cell responsivity to glucose, even after adjustment for prevailing insulin sensitivity. In WE men, endogenous insulin clearance was correlated with whole-body insulin sensitivity (r = 0.691, P = .001) and inversely correlated with IHL (r = -0.674, P = .001). These associations were not found in BA men.

CONCLUSIONS

While normally glucose-tolerant BA men have similar insulin secretory responses to their WE counterparts, they have markedly lower insulin clearance, which does not appear to be explained by either insulin resistance or hepatic fat accumulation. Low insulin clearance may be the primary mechanism of hyperinsulinaemia in populations of African origin.

Different physiological mechanisms underlie an adverse cardiovascular disease risk profile in men and women

CVD affect about one-third of the population and are the leading cause of mortality. The prevalence of CVD is closely linked to the prevalence of obesity because obesity is commonly associated with metabolic abnormalities that are important risk factors for CVD, including insulin resistance, pre-diabetes, and type-2 diabetes, atherosclerotic dyslipidaemia, endothelial dysfunction and hypertension. Women have a more beneficial traditional CVD risk profile (lower fasting plasma glucose, less atherogenic lipid profile) and a lower absolute risk for CVD than men. However, the relative risk for CVD associated with hyperglycaemia and dyslipidaemia is several-fold higher in women than in men. The reasons for the sex differences in CVD risk associated with metabolic abnormalities are unclear but could be related to differences in the mechanisms that cause hyperglycaemia and dyslipidaemia in men and women, which could influence the pathogenic processes involved in CVD. In the present paper, we review the influence of a person's sex on key aspects of metabolism involved in the cardiometabolic disease process, including insulin action on endogenous glucose production, tissue glucose disposal, and adipose tissue lipolysis, insulin secretion and insulin plasma clearance, postprandial glucose, fatty acid, and triglyceride kinetics, hepatic lipid metabolism and myocardial substrate use. We conclude that there are marked differences in many aspects of metabolism in men and women that are not all attributable to differences in the sex hormone milieu. The mechanisms responsible for these differences and the clinical implications of these observations are unclear and require further investigation.

Hepatic insulin clearance is increased in patients with high HbA1c type 2 diabetes: a preliminary report

INTRODUCTION

Hepatic insulin clearance (HIC) is an important pathophysiology of type 2 diabetes. HIC was reported to decrease in patients with type 2 diabetes and metabolic syndrome. However, hyperglycemia was suggested to enhance HIC, and it is not known whether poorly controlled diabetes increases HIC in patients with type 2 diabetes. We investigated whether HIC was increased in patients with poorly controlled diabetes, and whether HIC was associated with insulin resistance and incretins.

RESEARCH DESIGN AND METHODS

We performed a meal tolerance test and the hyperinsulinemic-euglycemic clamp in 21 patients with type 2 diabetes. We calculated the postprandial C-peptide area under the curve (AUC)-to-insulin AUC ratio as the HIC; measured fasting and postprandial glucagon-like peptide-1 (GLP-1), glucose-dependent insulinotropic polypeptide (GIP) and glucagon levels and analyzed serum adiponectin and zinc transporter-8 (ZnT8) gene polymorphism.

RESULTS

The HIC significantly correlated with glycated hemoglobin (HbA1c) (r_S=0.58, p<0.01). In patients with high HIC above the median of 6.5, the mean HbA1c was significantly higher compared with low HIC below the median. Homeostatic model assessment (HOMA)-beta (r_S=-0.77, p<0.01) and HOMA-IR (r_S=-0.66, p<0.005) were correlated with HIC. The M/I value in the clamp study was correlated with HIC. GLP-1-AUC and GIP-AUC were not correlated with HIC. Glucagon-AUC was negatively correlated with HIC, but there were no significant differences between the high and low HIC groups. Adiponectin was positively correlated with HIC. The ZnT8 gene polymorphism did not affect HIC.

CONCLUSIONS

These results suggest that HIC was increased in patients with high HbA1c type 2 diabetes, low insulin secretion, low insulin resistance and high adiponectin conditions.

Reduced Insulin Clearance and Insulin-Degrading Enzyme Activity Contribute to Hyperinsulinemia in African Americans

BACKGROUND

African Americans (AAs) are at a higher risk for developing type 2 diabetes compared with non-Hispanic whites (NHWs). The causal role of β-cell glucose sensitivity (β-GS) and insulin clearance in hyperinsulinemia in AA adults is unclear.

OBJECTIVE

Using a cross-sectional study design, we compared β-cell function and insulin clearance in nondiabetic AAs (n = 36) and NHWs (n = 47) after a mixed meal test (MMT).

METHODS

Insulin secretion rate, glucose sensitivity, rate sensitivity, and insulin sensitivity during MMT were derived from a mathematical model. Levels of insulin-degrading enzyme (IDE) and carcinoembryonic antigen-related cell adhesion molecule-1 (CEACAM1), key players in insulin clearance, were measured (by enzyme-linked immunosorbent assay) in hepatic cytosolic fractions from age-, sex-, and body mass index-matched AA and NHW cadaveric donors (n = 10).

RESULTS

Fasting and mean postprandial plasma glucose levels were similar in both ethnic groups. AAs had significantly higher fasting and mean postprandial plasma insulin levels. However, fasting ISR, total insulin output, and insulin sensitivity during MMT were not different between the groups. β-GS and rate sensitivity were higher in AAs. Fasting and meal plasma insulin clearance were lower in AAs. Hepatic levels of IDE and CEACAM-1 were similar in AAs and NHWs. Hepatic IDE activity was significantly lower in AAs.

CONCLUSIONS

In this study, lower insulin clearance contributes to higher plasma insulin levels in AAs. Reduced insulin clearance may be explained by lower IDE activity levels in AAs. Further confirmatory studies are needed to investigate diminished insulin clearance in AAs as a result of lower IDE activity levels.

Endogenously released GIP reduces and GLP-1 increases hepatic insulin extraction

GIP was proposed to play a key role in the development of non- alcoholic fatty liver disease (NAFLD) in response to sugar intake. Isomaltulose, is a 1,6-linked glucose-fructose dimer which improves glucose homeostasis and prevents NAFLD compared to 1,2-linked sucrose by reducing glucose-dependent insulinotropic peptide (GIP) in mice. We compared effects of sucrose vs. isomaltulose on GIP and glucagon-like peptide-1 (GLP-1) secretion, hepatic insulin clearance (HIC) and insulin sensitivity in normal (NGT), impaired glucose tolerant (IGT) and Type 2 diabetes mellitus (T2DM) participants. A randomized crossover study was performed in 15 NGT, 10 IGT and 10 T2DM subjects. In comparison to sucrose, peak glucose concentrations were reduced by 2.3, 2.1 and 2.5 mmol/l (all p < 0.05) and insulin levels were 88% (p < 0.01, NGT), 32% (p < 0.05, IGT) and 55% (T2DM) lower after the isomaltulose load. Postprandial GIP_iAUC concentrations were decreased (56%, p < 0.01 in NGT; 42%, p < 0.05 in IGT and 40%,p < 0.001 in T2DM) whereas GLP-1_iAUC was 77%, 85% and 85% higher compared to sucrose (p < 0.01), respectively. This resulted in ∼35 - 50% improved insulin sensitivity and reduced insulinogenic index after isomaltulose, which correlated closely with improved HIC, respectively (r = 0.62, r=-0.70; p < 0.001). HIC was inversely related to GIP (r=-0.44, p < 0.001) and positively related to GLP-1 levels (r = 0.40, p = 0.001). CONCLUSION: Endogenously released GIP correlated with reduced, and GLP-1 with increased hepatic insulin extraction. Increased peripheral insulin levels may contribute to insulin resistance and obesity. We propose that the unfavorable effects of high glycemic index Western diets are related to increased GIP-release and reduced HIC.

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

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

Insulin Clearance After Oral and Intravenous Glucose Following Gastric Bypass and Gastric Banding Weight Loss

OBJECTIVE

Hepatic insulin clearance is a significant regulator of glucose homestasis. We hypothesized that the improvement in insulin clearance rates (ICRs) under fasting conditions and in response to oral and intravenous (IV) glucose would improve similarly after Roux-en-Y gastric bypass (RYGB) and adjustable gastric banding (AGB) as a function of weight loss; the difference in ICR after oral and IV glucose stimulation will be enhanced after RYGB compared with AGB, an effect mediated by glucagon-like peptide 1 (GLP-1).

RESEARCH DESIGN AND METHODS

In study 1, the ICR was calculated under fasting condition (F-ICR), after oral glucose (O-ICR), and after an isoglycemic IV glucose clamp (IV-ICR) in individuals from an established cohort with type 2 diabetes mellitus (T2DM) before, after 10% matched weight loss, and 1 year after either RYGB (n = 22) or AGB (n = 12). In study 2, O-ICR was studied in a separate cohort of individuals with T2DM (n = 22), before and 3 months after RYGB, with and without exendin(9-39) infusion.

RESULTS

In study 1, age, BMI, T2DM duration and control, and ICR did not differ between RYGB and AGB preintervention. Weight loss at 1 year was two times greater after RYGB than after AGB (31.6 ± 5.9% vs. 16.6 ± 9.8%; P < 0.05). RYGB and AGB both significantly increased F-ICR, O-ICR, and IV-ICR at 1 year. ICR was inversely associated with insulinemia. The difference between IV-ICR and O-ICR was significantly greater after RYGB versus AGB. GLP-1 antagonism with exendin(9-39) led to an increase in O-ICR in subjects post-RYGB.

CONCLUSIONS

Weight loss increased ICR, an effect more pronounced after RYGB compared with AGB. Our data support a potential role for endogenous GLP-1 in the control of postprandial ICR after RYGB.

Glucagon and insulin secretion, insulin clearance, and fasting glucose in GIP receptor and GLP-1 receptor knockout mice

It is not known whether GIP receptor and GLP-1 receptor knockout (KO) mice have perturbations in glucagon secretion or insulin clearance, and studies on impact on fasting glycemia have previously been inconsistent in these mice. We therefore studied glucagon secretion after oral whey protein (60 mg) and intravenous arginine (6.25 mg), insulin clearance after intravenous glucose (0.35 g/kg) and fasting glucose, insulin, and glucagon levels after standardized 5-h fasting in female GIP receptor and GLP-1 receptor KO mice and their wild-type (WT) littermates. Compared with WT controls, GIP receptor KO mice had normal glucagon responses to oral protein and intravenous arginine, except for an enhanced 1-min response to arginine, whereas glucagon levels after oral protein and intravenous arginine were enhanced in GLP-1 receptor KO mice. Furthermore, the intravenous glucose test revealed normal insulin clearance in both GIP receptor and GLP-1 receptor KO mice, whereas β-cell glucose sensitivity was enhanced in GIP receptor KO mice and reduced in GLP-1 receptor KO mice. Finally, GIP receptor KO mice had reduced fasting glucose (6.7 ± 0.1, n = 56, vs. 7.4 ± 0.1 mmol/l, n = 59, P = 0.001), whereas GLP-1 receptor KO mice had increased fasting glucose (9.1 ± 0.2, n = 44, vs. 7.7 ± 0.1 mmol/l, n = 41, P < 0.001). We therefore suggest that GIP has a limited role for glucagon secretion in mice, whereas GLP-1 is of importance for glucagon regulation, that GIP and GLP-1 are of importance for the regulation of β-cell function beyond their role as incretin hormones, and that they are both of importance for fasting glucose.

Impact of Nutrient Type and Sequence on Glucose Tolerance: Physiological Insights and Therapeutic Implications

Pharmacological and dietary interventions targeting postprandial glycemia have proved effective in reducing the risk for type 2 diabetes and its cardiovascular complications. Besides meal composition and size, the timing of macronutrient consumption during a meal has been recently recognized as a key regulator of postprandial glycemia. Emerging evidence suggests that premeal consumption of non-carbohydrate macronutrients (i.e., protein and fat "preloads") can markedly reduce postprandial glycemia by delaying gastric emptying, enhancing glucose-stimulated insulin release, and decreasing insulin clearance. The same improvement in glucose tolerance is achievable by optimal timing of carbohydrate ingestion during a meal (i.e., carbohydrate-last meal patterns), which minimizes the risk of body weight gain when compared with nutrient preloads. The magnitude of the glucose-lowering effect of preload-based nutritional strategies is greater in type 2 diabetes than healthy subjects, being comparable and additive to current glucose-lowering drugs, and appears sustained over time. This dietary approach has also shown promising results in pathological conditions characterized by postprandial hyperglycemia in which available pharmacological options are limited or not cost-effective, such as type 1 diabetes, gestational diabetes, and impaired glucose tolerance. Therefore, preload-based nutritional strategies, either alone or in combination with pharmacological treatments, may offer a simple, effective, safe, and inexpensive tool for the prevention and management of postprandial hyperglycemia. Here, we survey these novel physiological insights and their therapeutic implications for patients with diabetes mellitus and altered glucose tolerance.

Ethnic differences in insulin secretory function between black African and white European men with early type 2 diabetes

AIM

To test the hypothesis that men of black (West) African ethnicity (black African men [BAM]) with early type 2 diabetes (T2D) would have greater insulin secretory deficits compared with white European men (WEM), following prediabetic hypersecretion.

METHODS

In 19 BAM and 15 WEM, matched for age, body mass index and duration of diabetes, we assessed and modelled insulin secretory responses to hyperglycaemia stimulated intravenously (hyperglycaemic clamp) and orally (meal tolerance test).

RESULTS

With similar post-challenge glucose responses, BAM had lower second-phase C-peptide responses to intravenous glucose (BAM 70.6 vs WEM 115.1 nmol/L/min [ratio of geometric mean 0.55, 95% confidence interval {CI} 0.37, 0.83]; P = .006) and to oral glucose (BAM 65.4 vs WEM 88.5 nmol/L/min [mean difference -23.2, 95% CI -40.0, -6.3]; P = .009). Peripheral insulin response in BAM to oral glucose was preserved (BAM 47.4 vs WEM 59.4 nmol/L/min [ratio of geometric mean 0.89, 95% CI 0.59, 1.35]; P = .566), with relative reductions in insulin clearance (BAM 506.2 vs WEM 630.1 mL/m² BSA/min [mean difference -123.9, 95% CI -270.5, 22.6]; P = .095), associated with enhanced incretin responses (gastric inhibitory polypeptide incremental area under the curve: BAM 46.8 vs WEM 33.9 μg/L/min [mean difference 12.9, 95% CI 2.1, 23.7]; P = .021).

CONCLUSIONS

In early T2D, BAM had significantly lower insulin secretory responses to intravenous and oral stimulation than WEM. Lower insulin clearance, potentially driven by increased incretin responses, may act to preserve peripheral insulin concentrations. Tailoring early management strategies to reflect distinct ethnic-specific pathophysiology may improve outcomes in this high-risk population.

Increased insulin clearance in mice with double deletion of glucagon-like peptide-1 and glucose-dependent insulinotropic polypeptide receptors

To establish whether incretin hormones affect insulin clearance, the aim of this study was to assess insulin clearance in mice with genetic deletion of receptors for both glucagon-like peptide-1 (GLP-1) and glucose-dependent insulinotropic polypeptide (GIP), so called double incretin receptor knockout mice (DIRKO). DIRKO ( n = 31) and wild-type (WT) C57BL6J mice ( n = 45) were intravenously injected with d-glucose (0.35 g/kg). Blood was sampled for 50 min and assayed for glucose, insulin, and C-peptide. Data were modeled to calculate insulin clearance; C-peptide kinetics was established after human C-peptide injection. Assessment of C-peptide kinetics revealed that C-peptide clearance was 1.66 ± 0.10 10−3 1/min. After intravenous glucose administration, insulin clearance during first phase insulin secretion was markedly higher in DIRKO than in WT mice (0.68 ± 0.06 10−3 l/min in DIRKO mice vs. 0.54 ± 0.03 10−3 1/min in WT mice, P = 0.02). In contrast, there was no difference between the two groups in insulin clearance during second phase insulin secretion ( P = 0.18). In conclusion, this study evaluated C-peptide kinetics in the mouse and exploited a mathematical model to estimate insulin clearance. Results showed that DIRKO mice have higher insulin clearance than WT mice, following intravenous injection of glucose. This suggests that incretin hormones reduce insulin clearance at physiological, nonstimulated levels.

Increase in hepatic and decrease in peripheral insulin clearance characterize abnormal temporal patterns of serum insulin in diabetic subjects

Insulin plays a central role in glucose homeostasis, and impairment of insulin action causes glucose intolerance and leads to type 2 diabetes mellitus (T2DM). A decrease in the transient peak and sustained increase of circulating insulin following an infusion of glucose accompany T2DM pathogenesis. However, the mechanism underlying this abnormal temporal pattern of circulating insulin concentration remains unknown. Here we show that changes in opposite direction of hepatic and peripheral insulin clearance characterize this abnormal temporal pattern of circulating insulin concentration observed in T2DM. We developed a mathematical model using a hyperglycemic and hyperinsulinemic-euglycemic clamp in 111 subjects, including healthy normoglycemic and diabetic subjects. The hepatic and peripheral insulin clearance significantly increase and decrease, respectively, from healthy to borderline type and T2DM. The increased hepatic insulin clearance reduces the amplitude of circulating insulin concentration, whereas the decreased peripheral insulin clearance changes the temporal patterns of circulating insulin concentration from transient to sustained. These results provide further insight into the pathogenesis of T2DM, and thus may contribute to develop better treatment of this condition.

Type 2 diabetes mellitus (T2DM) is one of the fastest growing public health problems, characterized by chronic hyperglycemia with the failure of glucose homeostasis. Evaluating alteration in biological functions regulating circulating glucose concentration is complicated due to the mutual relation between circulating glucose and insulin. A team led by Wataru Ogawa at Kobe University designed clinical experiments for breaking such feedback relations, and a team led by Shinya Kuroda at University of Tokyo developed mathematical models for specifically quantifying the functions from the clinical data. The estimated model parameters revealed the significant increase in hepatic and decrease in peripheral insulin clearance, which occur before and after insulin delivery into systemic circulation, respectively, from healthy to T2DM subjects. Model analysis suggested these insulin clearances centrally regulate the dynamics of circulating insulin concentration in the glucose-insulin regulatory system.

Synthetic and phytocompounds based dipeptidyl peptidase-IV (DPP-IV) inhibitors for therapeutics of diabetes

Currently antidiabetic therapeutic strategies are mainly based on synthetic hypoglycemic agent. Antidiabetic drugs are associated with significant adverse effects of hypoglycemia, dysfunction of insulin and weight gain. Nowadays, the novel Dipeptidyl peptidase-IV (DPP-IV) inhibitors unique approach for the management of diabetes has been considered to be safe, as DPP-IV inhibitors reduce blood glucose level by monitoring hyperglycemia including positive effects on body weight as it remains neutral, improves glycated hemoglobin levels and do not induce hypoglycemia. Inhibitors help to protect degradation of Glucagon-like peptide-1 (GLP-1) and gastric inhibitory peptide (GIP), gut hormones which helps to suppresses postprandial glucagon release, delay gastric emptying and regulate satiety. Therefore, the innovation of DPP-IV inhibitor based drugs regulates activity of incretin hormones such as GLP-1 and GIP. Commercially available DPP-IV inhibitors are chemically synthesized with good therapeutic value. However, the durability and long-term safety of DPP-IV inhibitors remains to be established. On the other hand, phytocompounds-based DPP-IV inhibitors are alternative and safe to use as compared to synthetic. Numerous novel antidiabetic compounds and group of compounds emerging in clinical development are through DPP-IV inhibition. This review summarized recent progress made on DPP-IV inhibitors from both synthetic as well as from natural sources.

Relationships of the early insulin secretory response and oral disposition index with gastric emptying in subjects with normal glucose tolerance

The oral disposition index, the product of the early insulin secretory response during an oral glucose tolerance test and insulin sensitivity, is used widely for both the prediction of, and evaluation of the response to interventions, in type 2 diabetes. Gastric emptying, which determines small intestinal exposure of nutrients, modulates postprandial glycemia. The aim of this study was to determine whether the insulin secretory response and the disposition index (DI) related to gastric emptying in subjects with normal glucose tolerance. Thirty-nine subjects consumed a 350 mL drink containing 75 g glucose labeled with ^99mTc-sulfur colloid. Gastric emptying (by scintigraphy), blood glucose (G) and plasma insulin (I) were measured between t = 0-120 min. The rate of gastric emptying was derived from the time taken for 50% emptying (T₅₀) and expressed as kcal/min. The early insulin secretory response was estimated by the ratio of the change in insulin (∆I_0-30) to that of glucose at 30 min (∆G_0-30) represented as ∆I_0-30/∆G_0-30 Insulin sensitivity was estimated as 1/fasting insulin and the DI was then calculated as ∆I_0-30/∆G_0-30 × 1/fasting insulin. There was a direct relationship between ∆G_0-30 and gastric emptying (r = 0.47, P = 0.003). While there was no association of either ∆I_0-30 (r = -0.16, P = 0.34) or fasting insulin (r = 0.21, P = 0.20), there were inverse relationships between the early insulin secretory response (r = -0.45, P = 0.004) and the DI (r = -0.33, P = 0.041), with gastric emptying. We conclude that gastric emptying is associated with both insulin secretion and the disposition index in subjects with normal glucose tolerance, such that when gastric emptying is relatively more rapid, both the early insulin secretory response and the disposition index are less. These findings should be interpreted as "hypothesis generating" and provide the rationale for longitudinal studies to examine the impact of baseline rate of gastric emptying on the prospective risk of type 2 diabetes.

Insulin-degrading enzyme: new therapeutic target for diabetes and Alzheimer's disease?

Insulin-degrading enzyme (IDE) is a major enzyme responsible for insulin degradation. In addition to insulin, IDE degrades many targets including glucagon, atrial natriuretic peptide, and beta-amyloid peptide, regulates proteasomal degradation and other cell functions. IDE represents a pathophysiological link between type 2 diabetes (T2DM) and late onset Alzheimer's disease (AD). Potent and selective modulators of IDE activity are potential drugs for therapies of both diseases. Acute treatment with a novel IDE inhibitor was recently tested in a mouse study as a therapeutic approach for the treatment of T2DM. In contrast, effective IDE activators can be used for the AD treatment. However, because of the pleiotropic IDE action, the sustained treatment with systemic IDE modulators should be carefully tested in animal studies. Development of substrate-selective IDE modulators could overcome possible adverse effects of IDE modulators associated with multiplicity of IDE targets. KEY MESSAGES Insulin-degrading enzyme (IDE) represents a pathophysiological link between type 2 diabetes (T2DM) and Alzheimer's disease (AD). Selective modulators of IDE activity are potential drugs for both T2DM and AD treatment. Development of substrate-selective IDE modulators could overcome possible adverse effects of IDE modulators associated with multiplicity of IDE targets.

Fenofibrate Decreases Insulin Clearance and Insulin Secretion to Maintain Insulin Sensitivity

High fat diet reduces the expression of CEACAM1 (carcinoembryonic antigen-related cell adhesion molecule 1), a transmembrane glycoprotein that promotes insulin clearance and down-regulates fatty acid synthase activity in the liver upon its phosphorylation by the insulin receptor. Because peroxisome proliferator-activated receptor α (PPARα) transcriptionally suppresses CEACAM1 expression, we herein examined whether high fat down-regulates CEACAM1 expression in a PPARα-dependent mechanism. By activating PPARα, the lipid-lowering drug fenofibrate reverses dyslipidemia and improves insulin sensitivity in type 2 diabetes in part by promoting fatty acid oxidation. Despite reducing glucose-stimulated insulin secretion, fenofibrate treatment does not result in insulin insufficiency. To examine whether this is mediated by a parallel decrease in CEACAM1-dependent hepatic insulin clearance pathways, we fed wild-type and Pparα^-/- null mice a high fat diet supplemented with either fenofibrate or Wy14643, a selective PPARα agonist, and examined their effect on insulin metabolism and action. We demonstrated that the decrease in insulin secretion by fenofibrate and Wy14643 is accompanied by reduction in insulin clearance in wild-type but not Pparα^-/- mice, thereby maintaining normoinsulinemia and insulin sensitivity despite continuous high fat intake. Intact insulin secretion in L-CC1 mice with protected hepatic insulin clearance and CEACAM1 levels provides in vivo evidence that insulin secretion responds to changes in insulin clearance to maintain physiologic insulin and glucose homeostasis. These results also emphasize the relevant role of hepatic insulin extraction in regulating insulin sensitivity.

Review: Development and therapeutic potential of incretin hormone analogues for type 2 diabetes

The rising prevalence of type 2 diabetes and increasing burden of diabetic complications requires new approaches to diabetes therapy. An encouraging new approach for development of future anti-diabetic drugs is based on analogues of incretin hormones, glucagon-like peptide-1 (GLP-1) and glucose-dependent insulinotropic polypeptide (GIP). Both peptides reduce postprandial glucose by stimulating glucose-dependent insulin release and exert a number of other beneficial actions including trophic effects on the beta-cell. Efforts are currently focused on developing stable analogues of GLP-1 and GIP which are resistant to dipeptidylpeptidase IV mediated degradation and renal filtration. Thus, by increasing the half-life and potency of these incretins, they should become a new class of agents for the treatment of type 2 diabetes.

Sustained effects of a protein and lipid preload on glucose tolerance in type 2 diabetes patients

BACKGROUND

Small amounts of nutrients given as a 'preload' can reduce post-meal hyperglycaemic peaks in type 2 diabetes (T2D) patients by activating a number of mechanisms involved in glucose homoeostasis. This study was undertaken to ascertain whether this positive effect extends to the late absorptive phase and to identify the main mechanisms involved.

MATERIAL AND METHODS

Eight well-controlled T2D patients, aged 40-70 years, were randomized to consume a 'preload' of either water or non-glucidic nutrients (50g of Parmesan cheese, one boiled egg) 30min before a 300-min oral glucose tolerance test.

RESULTS

After the nutrient preload, significant reductions were observed in peak glucose (-49%; P<0.02), total plasma glucose (iAUC: -28%; P<0.03), exogenous glucose (iAUC: -30%; P<0.03) and insulin clearance (-28%; P<0.04), with enhancement of insulin secretion (iAUC: +22%; P<0.003). These effects were associated with higher plasma levels of GLP-1 (iAUC: +463%; P<0.002), GIP (iAUC: +152%; P<0.0003) and glucagon (iAUC: +144%; P<0.0002).

CONCLUSION

In T2D patients, a protein and lipid preload improves glucose tolerance throughout the whole post-absorptive phase mainly by reducing the appearance of oral glucose, and improving both beta-cell function and insulin bioavailability.

Mixed meal ingestion diminishes glucose excursion in comparison with glucose ingestion via several adaptive mechanisms in people with and without type 2 diabetes

AIMS

To study the integrative impact of macronutrients on postprandial glycaemia, β-cell function, glucagon and incretin hormones in humans.

METHODS

Macronutrients were ingested alone (glucose 330 kcal, protein 110 kcal or fat 110 kcal) or together (550 kcal) by healthy subjects (n = 18) and by subjects with drug-naïve type 2 diabetes (T2D; n = 18). β-cell function and insulin clearance were estimated by modelling glucose, insulin and C-peptide data. Secretion of glucose-dependent insulinotropic polypeptide (GIP) and glucagon-like peptide-1 (GLP-1) were measured, and paracetamol was administered to estimate gastric emptying.

RESULTS

In both groups, the mixed-meal challenge diminished glucose excursion compared with glucose challenge alone, and insulin levels, but not C-peptide levels, rose more than after the mixed meal than after glucose alone. β-cell function was augmented, insulin clearance was reduced and glucagon levels were higher after the mixed meal compared with glucose alone. GLP-1 and GIP levels increased after all challenges and GIP secretion was markedly higher after the mixed meal than after glucose alone. The appearance of paracetamol was delayed after the mixed-meal challenge compared with glucose alone.

CONCLUSIONS

Adding protein and fat macronutrients to glucose in a mixed meal diminished glucose excursion. This occurred in association with increased β-cell function, reduced insulin clearance, delayed gastric emptying and augmented glucagon and GIP secretion. This suggests that the macronutrient composition regulates glycaemia through both islet and extra-islet mechanisms in both healthy subjects and in subjects with T2D.

Significance of Hepatic Insulin Clearance in Patients with Chronic Hepatitis C and Non-alcoholic Fatty Liver Disease

Objective Hyperinsulinemia plays an important role in the pathophysiological processes of chronic hepatitis C (CHC) and non-alcoholic fatty liver disease (NAFLD). However, there are few reports on hepatic insulin clearance in patients with these diseases. Methods A total of 74 CHC patients and 37 NAFLD patients were enrolled in this study. We evaluated their hepatic insulin clearance, insulin sensitivity and β-cell function with an oral glucose tolerance test. Results Hepatic insulin clearance in the patients with CHC was significantly correlated with platelets (r=0.271, p=0.020) and liver fibrosis (r=-0.234, p=0.045) and was significantly affected by both steatosis (mild: 0.157±0.078, severe: 0.114±0.053, p=0.024) and fibrosis (mild: 0.167±0.0857, severe: 0.125±0.052, p=0.010). There were no significant differences in (homeostasis model assessment) HOMA-β among steatosis and fibrosis stages. In the NAFLD patients, those with severe fibrosis had significantly reduced hepatic insulin clearance (mild: 0.135±0.045, severe: 0.098±0.031, p=0.013) and significantly increased HOMA-β (mild: 115.6±67.1, severe: 172.8±65.7, p=0.018) compared with the patients with mild fibrosis. Conclusion Liver fibrosis development is associated with hepatic insulin clearance in both the CHC and NAFLD patients.

Glucose Homeostatic Law: Insulin Clearance Predicts the Progression of Glucose Intolerance in Humans

Homeostatic control of blood glucose is regulated by a complex feedback loop between glucose and insulin, of which failure leads to diabetes mellitus. However, physiological and pathological nature of the feedback loop is not fully understood. We made a mathematical model of the feedback loop between glucose and insulin using time course of blood glucose and insulin during consecutive hyperglycemic and hyperinsulinemic-euglycemic clamps in 113 subjects with variety of glucose tolerance including normal glucose tolerance (NGT), impaired glucose tolerance (IGT) and type 2 diabetes mellitus (T2DM). We analyzed the correlation of the parameters in the model with the progression of glucose intolerance and the conserved relationship between parameters. The model parameters of insulin sensitivity and insulin secretion significantly declined from NGT to IGT, and from IGT to T2DM, respectively, consistent with previous clinical observations. Importantly, insulin clearance, an insulin degradation rate, significantly declined from NGT, IGT to T2DM along the progression of glucose intolerance in the mathematical model. Insulin clearance was positively correlated with a product of insulin sensitivity and secretion assessed by the clamp analysis or determined with the mathematical model. Insulin clearance was correlated negatively with postprandial glucose at 2h after oral glucose tolerance test. We also inferred a square-law between the rate constant of insulin clearance and a product of rate constants of insulin sensitivity and secretion in the model, which is also conserved among NGT, IGT and T2DM subjects. Insulin clearance shows a conserved relationship with the capacity of glucose disposal among the NGT, IGT and T2DM subjects. The decrease of insulin clearance predicts the progression of glucose intolerance.

Modulation of insulin degrading enzyme activity and liver cell proliferation

Diabetes mellitus type 2 (T2DM), insulin therapy, and hyperinsulinemia are independent risk factors of liver cancer. Recently, the use of a novel inhibitor of insulin degrading enzyme (IDE) was proposed as a new therapeutic strategy in T2DM. However, IDE inhibition might stimulate liver cell proliferation via increased intracellular insulin concentration. The aim of this study was to characterize effects of inhibition of IDE activity in HepG2 hepatoma cells and to analyze liver specific expression of IDE in subjects with T2DM. HepG2 cells were treated with 10 nM insulin for 24 h with or without inhibition of IDE activity using IDE RNAi, and cell transcriptome and proliferation rate were analyzed. Human liver samples (n = 22) were used for the gene expression profiling by microarrays. In HepG2 cells, IDE knockdown changed expression of genes involved in cell cycle and apoptosis pathways. Proliferation rate was lower in IDE knockdown cells than in controls. Microarray analysis revealed the decrease of hepatic IDE expression in subjects with T2DM accompanied by the downregulation of the p53-dependent genes FAS and CCNG2, but not by the upregulation of proliferation markers MKI67, MCM2 and PCNA. Similar results were found in the liver microarray dataset from GEO Profiles database. In conclusion, IDE expression is decreased in liver of subjects with T2DM which is accompanied by the dysregulation of p53 pathway. Prolonged use of IDE inhibitors for T2DM treatment should be carefully tested in animal studies regarding its potential effect on hepatic tumorigenesis.

A high-protein breakfast induces greater insulin and glucose-dependent insulinotropic peptide responses to a subsequent lunch meal in individuals with type 2 diabetes

BACKGROUND

The previous meal modulates the postprandial glycemic responses to a subsequent meal; this is termed the second-meal phenomenon.

OBJECTIVE

This study examined the effects of high-protein vs. high-carbohydrate breakfast meals on the metabolic and incretin responses after the breakfast and lunch meals.

METHODS

Twelve type 2 diabetic men and women [age: 21-55 y; body mass index (BMI): 30-40 kg/m(2)] completed two 7-d breakfast conditions consisting of 500-kcal breakfast meals as protein (35% protein/45% carbohydrate) or carbohydrate (15% protein/65% carbohydrate). On day 7, subjects completed an 8-h testing day. After an overnight fast, the subjects consumed their respective breakfast followed by a standard 500-kcal high-carbohydrate lunch meal 4 h later. Blood samples were taken throughout the day for assessment of 4-h postbreakfast and 4-h postlunch total area under the curve (AUC) for glucose, insulin, C-peptide, glucagon, glucose-dependent insulinotropic peptide (GIP), and glucagon-like peptide 1 (GLP-1).

RESULTS

Postbreakfast glucose and GIP AUCs were lower after the protein (17%) vs. after the carbohydrate (23%) condition (P < 0.05), whereas postbreakfast insulin, C-peptide, glucagon, and GLP-1 AUCs were not different between conditions. A protein-rich breakfast may reduce the consequences of hyperglycemia in this population. Postlunch insulin, C-peptide, and GIP AUCs were greater after the protein condition vs. after the carbohydrate condition (second-meal phenomenon; all, P < 0.05), but postlunch AUCs were not different between conditions. The overall glucose, glucagon, and GLP-1 responses (e.g., 8 h) were greater after the protein condition vs. after the carbohydrate condition (all, P < 0.05).

CONCLUSIONS

In type 2 diabetic individuals, compared with a high-carbohydrate breakfast, the consumption of a high-protein breakfast meal attenuates the postprandial glucose response and does not magnify the response to the second meal. Insulin, C-peptide, and GIP concentrations demonstrate the second-meal phenomenon and most likely aid in keeping the glucose concentrations controlled in response to the subsequent meal. The trial was registered at www.clinicaltrials.gov/ct2/show/NCT02180646 as NCT02180646.

Relationship between disease severity, hyperinsulinemia, and impaired insulin clearance in patients with nonalcoholic steatohepatitis

Hyperinsulinemia is believed to play a key role in the pathogenesis of nonalcoholic steatohepatitis (NASH) and associated cardiovascular risk. However, the relative contribution of insulin clearance to hyperinsulinemia and its relationship to liver histology have not been carefully evaluated before. To examine this, we enrolled 190 patients (32 without nonalcoholic fatty liver disease [NAFLD], 36 with simple steatosis [SS], and 122 with biopsy-proven NASH). Insulin secretion and hepatic insulin clearance were estimated by means of an oral glucose tolerance test, whereas peripheral insulin sensitivity and whole-body insulin clearance were measured during a euglycemic insulin clamp. A liver biopsy was performed to assess histology (grade/stage). Patients with NASH had similar hepatic insulin sensitivity, compared to patients with SS, but more severe adipose tissue insulin resistance and worse hyperinsulinemia. Patients with SS and NASH had a similar ∼30% reduction (P<0.01) in hepatic insulin clearance, when compared to patients without NAFLD. Reduced hepatic insulin clearance was not associated with severity of inflammation, ballooning, and fibrosis. In contrast, worse histological inflammation and ballooning (but not steatosis or fibrosis) were associated with a progressive reduction in whole-body insulin clearance (P<0.001 for trend). There was no significant difference in insulin secretion between patients with SS versus NASH.

CONCLUSION

Decreased hepatic insulin clearance develops with a mild increase in liver fat (LFAT) accumulation. It appears to be largely driven by hepatic steatosis, whereas steatohepatitis is more closely associated with reduced whole-body insulin clearance. Hyperinsulinemia in NAFLD correlated strongly with impaired insulin clearance, but not with insulin secretion. Strategies that reduce LFAT and improve insulin clearance hold the potential to revert the unfavorable effects of hyperinsulinemia in these patients.

Insulin sensitivity and insulin clearance are heritable and have strong genetic correlation in Mexican Americans

OBJECTIVE

The GUARDIAN (Genetics UndeRlying DIAbetes in HispaNics) consortium is described, along with heritability estimates and genetic and environmental correlations of insulin sensitivity and metabolic clearance rate of insulin (MCRI).

METHODS

GUARDIAN is comprised of seven cohorts, consisting of 4,336 Mexican-American individuals in 1,346 pedigrees. Insulin sensitivity (SI ), MCRI, and acute insulin response (AIRg) were measured by frequently sampled intravenous glucose tolerance test in four cohorts. Insulin sensitivity (M, M/I) and MCRI were measured by hyperinsulinemic-euglycemic clamp in three cohorts. Heritability and genetic and environmental correlations were estimated within the family cohorts (totaling 3,925 individuals) using variance components.

RESULTS

Across studies, age, and gender-adjusted heritability of insulin sensitivity (SI , M, M/I) ranged from 0.23 to 0.48 and of MCRI from 0.35 to 0.73. The ranges for the genetic correlations were 0.91 to 0.93 between SI and MCRI; and -0.57 to -0.59 for AIRg and MCRI (all P < 0.0001). The ranges for the environmental correlations were 0.54 to 0.74 for SI and MCRI (all P < 0.0001); and -0.16 to -0.36 for AIRg and MCRI (P < 0.0001-0.06).

CONCLUSIONS

These data support a strong familial basis for insulin sensitivity and MCRI in Mexican Americans. The strong genetic correlations between MCRI and SI suggest common genetic determinants.

Hepatic insulin clearance is closely related to metabolic syndrome components

OBJECTIVE

Insulin clearance is decreased in type 2 diabetes mellitus (T2DM) for unknown reasons. Subjects with metabolic syndrome are hyperinsulinemic and have an increased risk of T2DM. We aimed to investigate the relationship between hepatic insulin clearance (HIC) and different components of metabolic syndrome and tested the hypothesis that HIC may predict the risk of metabolic syndrome.

RESEARCH DESIGN AND METHODS

Individuals without diabetes from the Metabolic Syndrome Berlin Brandenburg (MeSyBePo) study (800 subjects with the baseline examination and 189 subjects from the MeSyBePo recall study) underwent an oral glucose tolerance test (OGTT) with assessment of insulin secretion (insulin secretion rate [ISR]) and insulin sensitivity. Two indices of HIC were calculated.

RESULTS

Both HIC indices showed lower values in subjects with metabolic syndrome (P < 0.001) at baseline. HIC indices correlate inversely with waist circumference, diastolic blood pressure, fasting glucose, triglycerides, and OGTT-derived insulin secretion index. During a mean follow-up of 5.1 ± 0.9 years, 47 individuals developed metabolic syndrome and 33 subjects progressed to impaired glucose metabolism. Both indices of HIC showed a trend of an association with increased risk of metabolic syndrome (HICC-peptide odds ratio 1.13 [95% CI 0.97-1.31], P = 0.12, and HICISR 1.38 [0.88-2.17], P = 0.16) and impaired glucose metabolism (HICC-peptide 1.12 [0.92-1.36], P = 0.26, and HICISR 1.31 [0.74-2.33] P = 0.36), although point estimates reached no statistical significance.

CONCLUSIONS

HIC was associated with different components of metabolic syndrome and markers of insulin secretion and insulin sensitivity. Decreased HIC may represent a novel pathophysiological mechanism of the metabolic syndrome, which may be used additionally for early identification of high-risk subjects.

The diabetes-susceptible gene SLC30A8/ZnT8 regulates hepatic insulin clearance

Recent genome-wide association studies demonstrated that common variants of solute carrier family 30 member 8 gene (SLC30A8) increase susceptibility to type 2 diabetes. SLC30A8 encodes zinc transporter-8 (ZnT8), which delivers zinc ion from the cytoplasm into insulin granules. Although it is well known that insulin granules contain high amounts of zinc, the physiological role of secreted zinc remains elusive. In this study, we generated mice with β cell-specific Slc30a8 deficiency (ZnT8KO mice) and demonstrated an unexpected functional linkage between Slc30a8 deletion and hepatic insulin clearance. The ZnT8KO mice had low peripheral blood insulin levels, despite insulin hypersecretion from pancreatic β cells. We also demonstrated that a substantial amount of the hypersecreted insulin was degraded during its first passage through the liver. Consistent with these findings, ZnT8KO mice and human individuals carrying rs13266634, a major risk allele of SLC30A8, exhibited increased insulin clearance, as assessed by c-peptide/insulin ratio. Furthermore, we demonstrated that zinc secreted in concert with insulin suppressed hepatic insulin clearance by inhibiting clathrin-dependent insulin endocytosis. Our results indicate that SLC30A8 regulates hepatic insulin clearance and that genetic dysregulation of this system may play a role in the pathogenesis of type 2 diabetes.

Systematic evaluation of validated type 2 diabetes and glycaemic trait loci for association with insulin clearance

AIMS/HYPOTHESIS

Insulin clearance is a highly heritable trait, for which few quantitative trait loci have been discovered. We sought to determine whether validated type 2 diabetes and/or glycaemic trait loci are associated with insulin clearance.

METHODS

Hyperinsulinaemic-euglycaemic clamps were performed in two Hispanic-American family cohorts totalling 1329 participants in 329 families. The Metabochip was used to fine-map about 50 previously identified loci for type 2 diabetes, fasting glucose, fasting insulin, 2 h glucose or HbA1c. This resulted in 17,930 variants, which were tested for association with clamp-derived insulin clearance via meta-analysis of the two cohorts.

RESULTS

In the meta-analysis, 38 variants located within seven loci demonstrated association with insulin clearance (p < 0.001). The top signals for each locus were rs10241087 (DGKB/TMEM195 [TMEM195 also known as AGMO]) (p = 4.4 × 10(-5)); chr1:217605433 (LYPLAL1) (p = 3.25 × 10(-4)); rs2380949 (GLIS3) (p = 3.4 × 10(-4)); rs55903902 (FADS1) (p = 5.6 × 10(-4)); rs849334 (JAZF1) (p = 6.4 × 10(-4)); rs35749 (IGF1) (p = 6.7 × 10(-4)); and rs9460557 (CDKAL1) (p = 6.8 × 10(-4)).

CONCLUSIONS/INTERPRETATION

While the majority of validated loci for type 2 diabetes and related traits do not appear to influence insulin clearance in Hispanics, several of these loci do show evidence of association with this trait. It is therefore possible that these loci could have pleiotropic effects on insulin secretion, insulin sensitivity and insulin clearance.

Meta-analysis of the effect of HHEX gene polymorphism on the risk of type 2 diabetes

In the past decade, a number of case-control studies have been carried out to investigate the relationship between the HHEX polymorphism and type 2 diabetes (T2D). However, the results have been inconclusive. To investigate this inconsistency, we performed a meta-analysis of all available studies dealing with the relationship between the HHEX polymorphism and T2D. In total, 22 association studies on two HHEX polymorphisms (rs1111875 and rs7923837) and risk of T2D published before April 2010, including a total of 36 695 T2D cases and 51 800 controls were included. We also explored potential sources of heterogeneity. In a combined analysis, the summary per-allele odds ratio (OR) for T2D of the rs1111875 and rs7923837 polymorphism was 1.17 [95% confidence interval (CI): 1.13-1.21] and 1.23 (95% CI: 1.18-1.28), respectively. The haplotype analysis also showed significant association in the pooled international populations with an OR of 1.19 (95% CI: 1.15-1.22). In the subgroup analysis by ethnicity, significantly increased risks were found in Asians and Caucasians for these polymorphisms in almost all genetic models. Subgroup analysis also showed that ethnicity is the main source of heterogeneity between pooled studies. This meta-analysis demonstrated that the risk allele of HHEX polymorphisms (rs1111875 and rs7923837) is a risk factor for developing T2D. However, additional very large-scale studies are warranted to provide conclusive evidence on the effects of the HHEX gene on risk of T2D.

Targeted disruption of pancreatic-derived factor (PANDER, FAM3B) impairs pancreatic beta-cell function

OBJECTIVE

Pancreatic-derived factor (PANDER, FAM3B) is a pancreatic islet-specific cytokine-like protein that is secreted from beta-cells upon glucose stimulation. The biological function of PANDER is unknown, and to address this we generated and characterized a PANDER knockout mouse.

RESEARCH DESIGN AND METHODS

To generate the PANDER knockout mouse, the PANDER gene was disrupted and its expression was inhibited by homologous recombination via replacement of the first two exons, secretion signal peptide and transcriptional start site, with the neomycin gene. PANDER(-/-) mice were then phenotyped by a number of in vitro and in vivo tests to evaluate potential effects on glucose regulation, insulin sensitivity, and beta-cell morphology and function.

RESULTS

Glucose tolerance tests demonstrated significantly higher blood glucose levels in PANDER(-/-) versus wild-type male mice. To identify the mechanism of the glucose intolerance, insulin sensitivity and pancreatic beta-cell function were examined. Hyperinsulinemic-euglycemic clamps and insulin tolerance testing showed similar insulin sensitivity for both the PANDER(-/-) and wild-type mice. The in vivo insulin response following intraperitoneal glucose injection surprisingly produced significantly higher insulin levels in the PANDER(-/-) mice, whereas insulin release was blunted with arginine administration. Islet perifusion and calcium imaging studies showed abnormal responses of the PANDER(-/-) islets to glucose stimulation. In contrast, neither islet architecture nor insulin content was impacted by the loss of PANDER. Interestingly, the elevated insulin levels identified in vivo were attributed to decreased hepatic insulin clearance in the PANDER(-/-) islets. Taken together, these results demonstrated decreased pancreatic beta-cell function in the PANDER(-/-) mouse.

CONCLUSIONS

These results support a potential role of PANDER in the pancreatic beta-cell for regulation or facilitation of insulin secretion.

Polymorphisms within insulin-degrading enzyme (IDE) gene determine insulin metabolism and risk of type 2 diabetes

Insulin-degrading enzyme (IDE) is the ubiquitously expressed major enzyme responsible for insulin degradation. Insulin-degrading enzyme gene is located on chromosome region 10q23-q25 and exhibits a well-replicated peak of linkage with type 2 diabetes (T2DM). Several genetic association studies examined IDE gene as a susceptibility gene for T2DM with controversial results. However, pathophysiological mechanisms involved have remained elusive. We verified associations of two IDE polymorphisms (rs1887922 and rs2149632) with T2DM risk in two independent German cohorts and evaluated in detail the association of common variants with insulin metabolism and glycemic traits. We confirmed previously published findings for diabetes-associated rs1887922 and rs2149632 in the European Prospective Investigation into Cancer and Nutrition-Potsdam cohort (n = 3049; RR 1.26, p = 0.003 and RR 1.33, p < 0.0001 for additive model). Haplotypes which carried one risk allele of rs2149632 or two risk alleles of both studied IDE SNPs also demonstrated a strong association with increased T2DM risk in this cohort (p = 0.001 and p < 0.0001, respectively). However, we found no significant T2DM association in the cross-sectional metabolic syndrome Berlin-Potsdam cohort (n = 1026). In nondiabetic subjects (NGT+IFG/IGT; n = 739), we found an association of rs2149632 with impaired glucose-derived insulin secretion and a trend to decreased insulin sensitivity for rs1887922. In the NGT subjects (n = 440), the association with decreased insulin secretion for rs2149632 remain significant, and the association with decreased hepatic insulin degradation for rs1887922 were observed additionally. This study validates and confirms the association of IDE polymorphisms with T2DM risk in the prospective German cohort and provides novel evidence of influences of IDE genetic variants on insulin metabolism.

Glucose inhibits the insulin-induced activation of the insulin-degrading enzyme in HepG2 cells

AIMS/HYPOTHESIS

Hepatic insulin degradation decreases in type 2 diabetes. Insulin-degrading enzyme (IDE) plays a key role in insulin degradation and its gene is located in a diabetes-associated chromosomal region. We hypothesised that IDE may be regulated by insulin and/or glucose in a liver cell model. To validate the observed regulation of IDE in vivo, we analysed biopsies of human adipose tissue during different clamp experiments in men.

METHODS

Human hepatoma HepG2 cells were incubated in normal (1 g/l) or high (4.5 g/l) glucose medium and treated with insulin for 24 h. Catalytic activity, mRNA and protein levels of IDE were assessed. IDE mRNA levels were measured in biopsies of human subcutaneous adipose tissue before and at 240 min of hyperinsulinaemic, euglycaemic and hyperglycaemic clamps.

RESULTS

In HepG2 cells, insulin increased IDE activity under normal glucose conditions with no change in IDE mRNA or protein levels. Under conditions of high glucose, insulin increased mRNA levels of IDE without changes in IDE activity. Both in normal and high glucose medium, insulin increased levels of the catalytically more active 15a IDE isoform compared with the 15b isoform. In subcutaneous adipose tissue, IDE mRNA levels were not significantly upregulated after euglycaemic or hyperglycaemic clamps.

CONCLUSIONS/INTERPRETATION

Insulin increases IDE activity in HepG2 cells in normal but not in high glucose conditions. This disturbance cannot be explained by corresponding alterations in IDE protein levels or IDE splicing. The loss of insulin-induced regulation of IDE activity under hyperglycaemia may contribute to the reduced insulin extraction and peripheral hyperinsulinaemia in type 2 diabetes.

Therapeutic potential for GIP receptor agonists and antagonists

Glucose-dependent insulinotropic polypeptide (GIP or gastric inhibitory polypeptide) is a 42-amino-acid hormone, secreted from the enteroendocrine K cells, which has insulin-releasing and extrapancreatic glucoregulatory actions. However, the unfavourable pharmacokinetic profile and the weak biological effects of native GIP limit its effectiveness for the treatment of type 2 diabetes. To overcome this, longer-acting GIP agonists exhibiting enzymatic stability and enhanced bioactivity have been generated and successfully tested in animal models of diabetes. Thus, GIP receptor agonists offer one of the newest classes of potential antidiabetic drug. GIP is also known to play a role in lipid metabolism and fat deposition. Accordingly, both genetic and chemical ablation of GIP signalling in mice with obesity-diabetes can protect against, or even reverse many of the obesity-associated metabolic disturbances. Strong parallels exist with the beneficial metabolic effects of Roux-en-Y gastric bypass in obese, insulin-resistant humans that surgically ablates GIP-secreting K cells. The purpose of this article is to highlight the therapeutic potential of GIP-based therapeutics in the treatment of type 2 diabetes and obesity.

The influence of genetic variations in HHEX gene on insulin metabolism in the German MESYBEPO cohort

BACKGROUND

In the present study, we aimed to validate the type 2 diabetes (T2DM) susceptibility alleles identified in the first genome-wide association study in the hematopoietically expressed homeobox protein (HHEX) gene region (rs1111875 and rs7923837). Furthermore, we investigated quantitative metabolic risk phenotypes of these two variants for association with three key components of the insulin metabolism: insulin secretion, insulin sensitivity and insulin degradation.

METHODS

Two HHEX polymorphisms were genotyped in 1026 subjects from the German MESYBEPO cohort. Complete OGTT data were available for a subset of 420 with normal glucose tolerance (NGT), 282 with impaired glucose tolerance/impaired fasting glucose (IGT/IFG) and 146 diabetic subjects.

RESULTS

We validated association of both HHEX polymorphisms with T2DM. In the non-diabetic subcohort including NGT and IFG/IGT subjects, the risk alleles of rs7923837 and rs1111875 were significantly associated with decreased first and second phases of insulin secretion and lower insulinogenic index after oral glucose loading. In healthy, normal glucose-tolerant subjects, the same association of HHEX SNP rs1111875 with OGTT-derived phases of insulin secretion were detectable, however, rs7923837 was only weakly associated with reduced insulinogenic index. For both polymorphisms, no significant correlations with insulin sensitivity were obtained. Reduced insulin clearance was also observed in heterozygous carriers of rs1111875.

CONCLUSIONS

We validated the association of polymorphisms of the HHEX gene with T2DM in the MESYBEPO cohort. Importantly, variations within the HHEX gene conferred the impaired insulin secretion and changes of insulin degradation but no alteration in insulin sensitivity in carriers of risk alleles.

Oral disposition index predicts the development of future diabetes above and beyond fasting and 2-h glucose levels

OBJECTIVE

We sought to determine whether an oral disposition index (DI(O)) predicts the development of diabetes over a 10-year period. First, we assessed the validity of the DI(O) by demonstrating that a hyperbolic relationship exists between oral indexes of insulin sensitivity and beta-cell function.

RESEARCH DESIGN AND METHODS

A total of 613 Japanese-American subjects (322 men and 291 women) underwent a 75-g oral glucose tolerance test (OGTT) at baseline, 5 years, and 10 years. Insulin sensitivity was estimated as 1/fasting insulin or homeostasis model assessment of insulin sensitivity (HOMA-S). Insulin response was estimated as the change in insulin divided by change in glucose from 0 to 30 min (DeltaI(0-30)/DeltaG(0-30)).

RESULTS

DeltaI(0-30)/DeltaG(0-30) demonstrated a curvilinear relationship with 1/fasting insulin and HOMA-S with a left and downward shift as glucose tolerance deteriorated. The confidence limits for the slope of the log(e)-transformed estimates included -1 for DeltaI(0-30)/DeltaG(0-30) versus 1/fasting insulin for all glucose tolerance groups, consistent with a hyperbolic relationship. When HOMA-S was used as the insulin sensitivity measure, the confidence limits for the slope included -1 only for subjects with normal glucose tolerance (NGT) or impaired fasting glucose (IFG)/impaired glucose tolerance (IGT) but not diabetes. On the basis of this hyperbolic relationship, the product of DeltaI(0-30)/DeltaG(0-30) and 1/fasting insulin was calculated (DI(O)) and decreased from NGT to IFG/IGT to diabetes (P < 0.001). Among nondiabetic subjects at baseline, baseline DI(O) predicted cumulative diabetes at 10 years (P < 0.001) independent of age, sex, BMI, family history of diabetes, and baseline fasting and 2-h glucose concentrations.

CONCLUSIONS

The DI(O) provides a measure of beta-cell function adjusted for insulin sensitivity and is predictive of development of diabetes over 10 years.

Inhibition of dipeptidyl peptidase-4 by vildagliptin during glucagon-like Peptide 1 infusion increases liver glucose uptake in the conscious dog

OBJECTIVE

This study investigated the acute effects of treatment with vildagliptin on dipeptidyl peptidase-4 (DPP-4) activity, glucagon-like peptide 1 (GLP-1) concentration, pancreatic hormone levels, and glucose metabolism. The primary aims were to determine the effects of DPP-4 inhibition on GLP-1 clearance and on hepatic glucose uptake.

RESEARCH DESIGN AND METHODS

Fasted conscious dogs were studied in the presence (n = 6) or absence (control, n = 6) of oral vildagliptin (1 mg/kg). In both groups, GLP-1 was infused into the portal vein (1 pmol . kg(-1) . min(-1)) for 240 min. During the same time, glucose was delivered into the portal vein at 4 mg . kg(-1) . min(-1) and into a peripheral vein at a variable rate to maintain the arterial plasma glucose level at 160 mg/dl.

RESULTS

Vildagliptin fully inhibited DPP-4 over the 4-h experimental period. GLP-1 concentrations were increased in the vildagliptin-treated group (50 +/- 3 vs. 85 +/- 7 pmol/l in the portal vein in control and vildagliptin-treated dogs, respectively; P < 0.05) as a result of a 40% decrease in GLP-1 clearance (38 +/- 5 and 22 +/- 2 ml . kg(-1) . min(-1), respectively; P < 0.05). Although hepatic insulin and glucagon levels were not significantly altered, there was a tendency for plasma insulin to be greater (hepatic levels were 73 +/- 10 vs. 88 +/- 15 microU/ml, respectively). During vildagliptin treatment, net hepatic glucose uptake was threefold greater than in the control group. This effect was greater than that predicted by the change in insulin.

CONCLUSIONS

Vildagliptin fully inhibited DPP-4 activity, reduced GLP-1 clearance by 40%, and increased hepatic glucose disposal by means beyond the effects of GLP-1 on insulin and glucagon secretion.

Daily administration of the GIP-R antagonist (Pro3)GIP in streptozotocin-induced diabetes suggests that insulin-dependent mechanisms are critical to anti-obesity-diabetes actions of (Pro3)GIP

AIM

Glucose-dependent insulinotropic polypeptide-receptor (GIP-R) antagonism using (Pro3)GIP improves glucose tolerance and ameliorates insulin resistance and abnormalities of islet structure and function in a commonly used model of obesity-diabetes, namely ob/ob mice. The effect of GIP-R antagonism in a streptozotocin (STZ)-induced model of insulin deficiency has not been evaluated. The present study has investigated the effects of daily administration of (Pro(3))GIP to STZ-treated mice.

METHODS

Swiss TO mice received once-daily injection of (Pro3)GIP (25 nmol/kg body weight) or saline 4 days prior to and 16 days after injection of STZ, and effects on metabolic parameters and islet architecture were assessed.

RESULTS

(Pro3)GIP treatment had no significant effect on hyperphagia or body weight loss. However, hyperglycaemia and glycated haemoglobin were worsened, glucose tolerance further decreased and insulin sensitivity was impaired by (Pro3)GIP. These effects were observed on an STZ-induced background characterized by severe reductions of circulating insulin, beta-cell mass and pancreatic insulin stores.

CONCLUSIONS

These data indicate that the beneficial actions of the GIP-R antagonist, (Pro3)GIP, in obesity-diabetes appear to be largely mediated through insulin-dependent mechanisms that merit further investigation.

C-terminal mini-PEGylation of glucose-dependent insulinotropic polypeptide exhibits metabolic stability and improved glucose homeostasis in dietary-induced diabetes

Glucose-dependent insulinotropic polypeptide has been proposed as a potential therapeutic for type 2 diabetes, however, efforts to bring forward this drug have been hindered due to its short circulating half-life. We have adopted a novel strategy to increase potency and prolong GIP action through C-terminal mini-PEGylation (GIP[mPEG]). In contrast to GIP, GIP[mPEG] was resistant to dipeptidylpeptidase-IV (DPP-IV) up to and including 24h. Both GIP[mPEG] and GIP concentration-dependently stimulated cAMP production (EC50 6.6 and 0.7 nM, respectively) and insulin secretion (p < 0.01 to p < 0.001) in pancreatic BRIN-BD11 cells. Acute injection of GIP[mPEG] together with glucose to high fat fed mice significantly lowered plasma glucose (p < 0.05) and increased plasma insulin responses (p < 0.05). Furthermore, GIP[mPEG] markedly lowered plasma glucose when administered 4-24h prior to a glucose load (p < 0.05). Daily administration of GIP[mPEG] for 20 days in high fat mice did not alter body weight, food intake or non-fasting plasma insulin, however, non-fasting plasma glucose concentrations were significantly lowered (p < 0.05). Moreover, glucose tolerance was significantly improved (p < 0.05) together with glucose-mediated plasma insulin responses (p < 0.05). Insulin sensitivity, pancreatic insulin content, triglyceride and adiponectin levels were not changed. In summary, these data demonstrate that C-terminal mini-PEGylation of GIP is a useful strategy to prolong metabolic stability and improve biological action thus representing a novel therapeutic option for type 2 diabetes.

Incretin hormone mimetics and analogues in diabetes therapeutics

The incretin hormones glucagon-like peptide-1 (GLP-1) and glucose-dependent insulinotropic polypeptide (GIP) are physiological gut peptides with insulin-releasing and extrapancreatic glucoregulatory actions. Incretin analogues/mimetics activate GLP-1 or GIP receptors whilst avoiding physiological inactivation by dipeptidyl peptidase 4 (DPP-4), and they represent one of the newest classes of antidiabetic drug. The first clinically approved GLP-1 mimetic for the treatment of type-2 diabetes is exenatide (Byetta/exendin) which is administered subcutaneously twice daily. Clinical trials of liraglutide, a GLP-1 analogue suitable for once-daily administration, are ongoing. A number of other incretin molecules are at earlier stages of development. This review discusses the various attributes of GLP-1 and GIP for diabetes treatment and summarises current clinical data. Additionally, it explores the therapeutic possibilities offered by preclinical agents, such as non-peptide GLP-1 mimetics, GLP-1/glucagon hybrid peptides, and specific GIP receptor antagonists.