Disturbances in beta-cell function in impaired fasting glycemia

A Narrative Review of Human Clinical Trials on the Impact of Phenolic-Rich Plant Extracts on Prediabetes and Its Subgroups

Phenolic-rich plant extracts have been demonstrated to improve glycemic control in individuals with prediabetes. However, there is increasing evidence that people with prediabetes are not a homogeneous group but exhibit different glycemic profiles leading to the existence of prediabetes subgroups. Prediabetes subgroups have been identified as: isolated impaired fasting glucose (IFG), isolated impaired glucose tolerance (IGT), and combined impaired fasting glucose and glucose intolerance (IFG/IGT). The present review investigates human clinical trials examining the hypoglycemic potential of phenolic-rich plant extracts in prediabetes and prediabetes subgroups. Artemisia princeps Pampanini, soy (Glycine max (L.) Merrill) leaf and Citrus junos Tanaka peel have been demonstrated to improve fasting glycemia and thus may be more useful for individuals with IFG with increasing hepatic insulin resistance. In contrast, white mulberry (Morus alba Linn.) leaf, persimmon (Diospyros kaki) leaf and Acacia. Mearnsii bark were shown to improve postprandial glycemia and hence may be preferably beneficial for individuals with IGT with increasing muscle insulin resistance. Elaeis guineensis leaf was observed to improve both fasting and postprandial glycemic measures depending on the dose. Current evidence remains scarce regarding the impact of the plant extracts on glycemic control in prediabetes subgroups and therefore warrants further study.

Glycemic variability indices determined by self-monitoring of blood glucose are associated with β-cell function in Chinese patients with type 2 diabetes

INTRODUCTION

Glycemic control plays an important role in diabetes management, and self-monitoring of blood glucose (SMBG) is critical to achieving good glycemic control. However, there are few studies about the relationship between SMBG-estimated glycemic indices and β-cell function. Here we investigated the association between glucose variation indices estimated by SMBG and β-cell function among Chinese patients with type 2 diabetes mellitus (T2DM).

METHODS

In this cross‑sectional study, 397 patients with T2DM were recruited from February 2015 to October 2016. β-cell function was monitored using the Homeostasis Model Assessment 2 (HOMA2)-%β index. The parameters evaluated by SMBG were the mean blood glucose (MBG), standard deviation of MBG (SDBG), largest amplitude of glycemic excursions (LAGE), and postprandial glucose excursion (PPGE).

RESULTS

HOMA2-%β was negatively correlated with SDBG, LAGE, PPGE, and MBG (r = -0.350, -0.346, -0.178, and -0.631, respectively; all p < 0.01). After adjusting for confounding characteristics (diabetic duration, triglyceride, total cholesterol, fasting C-peptide, HOMA2-insulin resistance index, hypoglycemia, and diabetic treatments) and glycated hemoglobin A1c on a continuous scale, odds ratios of SDBG, LAGE, PPGE, and MBG between the patients in the lowest and highest HOMA2-%β quartiles were 2.02 (1.14-3.57), 1.24 (1.04-1.49), 1.13 (0.86-1.51), and 2.26 (1.70-3.00). HOMA2-%β was independently associated with SDBG, LAGE, and MBG.

CONCLUSIONS

Increased SDBG and LAGE assessed by SMBG are associated with β-cell dysfunction in Chinese patients with T2DM.

Comparing the effects of 6 months aerobic exercise and resistance training on metabolic control and β-cell function in Chinese patients with prediabetes: A multicenter randomized controlled trial

BACKGROUND

It is clear that aerobic training (AT) can delay pancreatic exhaustion and slow the progression from prediabetes to type 2 diabetes (T2D), but there is little information regarding the effects of resistance training (RT) in people with prediabetes. This study compared the effectiveness of RT and AT in improving metabolic control and protecting β-cell function in people with prediabetes.

METHODS

Chinese subjects (n = 248) with prediabetes were randomized to three groups: AT (n = 83), RT (n = 82) and control (n = 83). Subjects in the RT group performed 13 different resistance exercises per session using an elastic string. Those in the AT group performed aerobic exercises at 60%-70% of maximum heart rate. In both cases, exercises were performed three times per week for a period of 6 months. The primary outcome was improvement in metabolic control. Longitudinal changes between groups were tested using repeated-measures analysis of variance.

RESULTS

Of the initial 248 participants, 217 finished the study, but all participants were included in the intention-to-treat analyses. There were no significant differences in demographic characteristics among the RT, AT, and control groups (P > 0.05). Changes in HbA1c were not significantly greater in RT than AT cohort (P = 0.059), but the decrease in HbA1c in both exercise groups was higher than in the control group (P < 0.05).

CONCLUSIONS

In subjects with prediabetes, RT appears to improve metabolic control and preserve β-cell function comparable to AT.

Effect of the Incretin Hormones on the Endocrine Pancreas in End-Stage Renal Disease

CONTEXT

The insulin-stimulating and glucagon-regulating effects of the 2 incretin hormones, glucagon-like peptide 1 (GLP-1) and glucose-dependent insulinotropic polypeptide (GIP), contribute to maintain normal glucose homeostasis. Impaired glucose tolerance occurs with high prevalence among patients with end-stage renal disease (ESRD).

OBJECTIVE

To evaluate the effect of the incretin hormones on endocrine pancreatic function in patients with ESRD.

DESIGN AND SETTING

Twelve ESRD patients on chronic hemodialysis and 12 matched healthy controls, all with normal oral glucose tolerance test, were included. On 3 separate days, a 2-hour euglycemic clamp followed by a 2-hour hyperglycemic clamp (3 mM above fasting level) was performed with concomitant infusion of GLP-1 (1 pmol/kg/min), GIP (2 pmol/kg/min), or saline administered in a randomized, double-blinded fashion. A 30% lower infusion rate was used in the ESRD group to obtain comparable incretin hormone plasma levels.

RESULTS

During clamps, comparable plasma glucose and intact incretin hormone concentrations were achieved. The effect of GLP-1 to increase insulin concentrations relative to placebo levels tended to be lower during euglycemia in ESRD and was significantly reduced during hyperglycemia (50 [8-72]%, P = 0.03). Similarly, the effect of GIP relative to placebo levels tended to be lower during euglycemia in ESRD and was significantly reduced during hyperglycemia (34 [13-50]%, P = 0.005). Glucagon was suppressed in both groups, with controls reaching lower concentrations than ESRD patients.

CONCLUSIONS

The effect of incretin hormones to increase insulin release is reduced in ESRD, which, together with elevated glucagon levels, could contribute to the high prevalence of impaired glucose tolerance among ESRD patients.

Influence of Diabetogenic Factors on Fasting and Postprandial Glucose Levels in Patients with Type 2 Diabetes Mellitus

Background: This study evaluated the relative influence of insulin resistance (IR), first-phase insulin secretion (FPIS), second-phase insulin secretion (SPIS), and glucose effectiveness (GE) in determining the difference between fasting plasma glucose (FPG) and postprandial plasma glucose (PPG) (ΔPG), in a Chinese population with type 2 diabetes (T2D) mellitus. Methods: In total, we enrolled 1213 participants with T2D (479 women). IR, FPIS, SPIS, and GE were estimated by using equations we built previously. ΔPG was defined as FPG - PPG. Results: The relative contribution of the four diabetogenic factors (DFs) was analyzed by multiple linear regression, and GE was the greatest contributor in the ΔPG value (β = 0.171, P < 0.001), whereas IR had the least influence on ΔPG (β = -0.040, P = 0.439). DFs were analyzed by using binary logistic regression to ascertain if ΔPG ≥0 (high fasting plasma glucose, HFG). Three models were built: Model 0: SPIS, Model 1: SPIS + FPIS, and Model 2: Model 1 + GE. Model 2 had the most accurate predictive power; the equation for Model 2 is P = 1/(1 - e^-x), where x = -11.88 + 312.89 × (GE) -1.22 × log(SPIS) +1.63 × log(FPIS). In this equation, P refers to the risk of HFG. Conclusions: For Chinese patients, GE had the most profound effect in determining ΔPG, followed by FPIS, SPIS, and IR. The model suggested that participants with high FPIS, SPIS, and GE would have a high incidence of HFG.

Postprandial Reactive Hypoglycemia

Reactive hypoglycemia (RH) is the condition of postprandially hypoglycemia occurring 2-5 hours after food intake. RH is clinically seen in three different forms as follows: idiopathic RH (at 180 min), alimentary (within 120 min), and late RH (at 240–300 min). When the first-phase insulin response decreases, firstly, blood glucose starts to rise after the meal. This leads to late but excessive secretion of the second-phase insulin secretion. Thus, late reactive hypoglycemia occurs. Elevated insulin levels also cause down-regulation of the insulin post-receptor on the muscle and fat cells, thus decreasing insulin sensitivity. The cause of the increase in insulin sensitivity in IRH at 3 h is not completely clear. However, there is a decrease in insulin sensitivity in late reactive hypoglycaemia at 4 or 5 hours. Thus, patients with hypoglycemia at 4 or 5 h who have a family history of diabetes and obesity may be more susceptible to diabetes than patients with hypoglycemia at 3 h. We believe that some cases with normal glucose tolerance in OGTT should be considered as prediabetes at <55 or 60 mg/dl after 4-5 hours after OGTT. Metformin and AGI therapy may be recommended if there is late RH with IFG. Also Metformin, AGİ, TZD, DPP-IVInhibitors, GLP1RA therapy may be recommended if there is late RH with IGT. As a result, postprandial RH (<55 or 60 mg/dl), especially after 4 hours may predict diabetes. Therefore, people with RH along with weight gain and with diabetes history in the family will benefit from a lifestyle modification as well as the appropriate antidiabetic approach in the prevention of diabetes.

Effect of body mass index on diabetogenesis factors at a fixed fasting plasma glucose level

Aim

The present study evaluated the relative influence of body mass index (BMI) on insulin resistance (IR), first-phase insulin secretion (FPIS), second-phase insulin secretion (SPIS), and glucose effectiveness (GE) at a fixed fasting plasma glucose level in an older ethnic Chinese population.

Methods

In total, 265 individuals aged 60 years with a fasting plasma glucose level of 5.56 mmol/L were enrolled. Participants had BMIs of 20.0–34.2 kg/m². IR, FPIS, SPIS, and GE were estimated using our previously developed equations. Pearson correlation analysis was conducted to assess the correlations between the four diabetogenesis factors and BMI. A general linear model was used to determine the differences in the percentage of change among the four factor slopes against BMI.

Results

Significant correlations were observed between BMI and FPIS, SPIS, IR, and GE in both women and men, which were higher than those reported previously. In men, BMI had the most profound effect on SPIS, followed by IR, FPIS, and GE, whereas in women, the order was slightly different: IR, followed by FPIS, SPIS, and GE. Significant differences were observed among all these slopes, except for the slopes between FPIS and SPIS in women (p = 0.856) and IR and FPIS in men (p = 0.258).

Conclusions

The contribution of obesity to all diabetes factors, except GE, was higher than that reported previously. BMI had the most profound effect on insulin secretion in men and on IR in women in this 60-year-old cohort, suggesting that lifestyle modifications for obesity reduction in women remain the most important method for improving glucose metabolism and preventing future type 2 diabetes mellitus.

Serum undercarboxylated osteocalcin correlates with hemoglobin A1c in children with recently diagnosed pediatric diabetes

BACKGROUND

Osteocalcin (OC), a hormone secreted by osteoblasts, improves beta-cell function in vitro and in vivo. We aimed to understand the relationship between OC and hemoglobin A1c (HbA1c) in pediatric diabetes.

METHODS

Children (n = 70; mean [SD] age = 11.8 years [3.1]; 34.3% non-Hispanic white, 46.3% Hispanic, 14.9% African-American, 4.5% other) newly diagnosed with diabetes (69.1% type 1 diabetes [T1D], 30.9% type 2 diabetes [T2D]) were studied. We collected clinical data at diagnosis and first clinical visit (V1) 9 weeks later (interquartile range [IQR] = 7.9-12.0). Serum undercarboxylated OC (uOC) and carboxylated OC (cOC) were measured 7.0 weeks (IQR 4.3-8.9) after diagnosis.

RESULTS

Mean [SD] uOC was 20.3 (19.6) ng/mL, cOC 29.7 [13.7] ng/mL and u/cOC 0.68 [0.81]. uOC, cOC, or u/cOC were not different by gender, race/ethnicity, age, diabetes type, BMI percentile, or random C-peptide, glucose or HbA1c at diagnosis. However, among 61 children with V1 within 4 months of diagnosis, uOC was higher in those with V1 HbA1c < 7.5% (HbA1c < 58 mmol/mol) (uOC=33.1 [22.0]) compared with children with HbA1c ≥ 7.5% (uOC=17.4 [2.3], P = .0004). The difference was larger among patients with T2D (34.6 and 4.7 ng/mL, respectively, P = .0001) than T1D (32.2 and 19.3, P = .0169), and in males (36.1 and 17.4, P = .018) than females (27.6 and 17.3, P = .072). Analysis for u/cOC were similar while there were no differences in cOC. uOC was inversely correlated with HbA1c at V1 (Spearman's rho = -0.29, P = .02).

CONCLUSION

Our findings suggest that serum uOC is inversely related to HbA1c shortly after diagnosis of pediatric diabetes. This potentially modifiable factor of glucose metabolism warrants further studies.

Predicting Glucose Effectiveness in Chinese Participants Using Routine Measurements

BACKGROUND

Glucose effectiveness (GE) is the capacity of glucose to increase its own uptake and to maintain endogenous hepatic glucose output under basal insulin levels. In addition to decreased insulin sensitivity (IS) and impaired insulin secretion, GE plays a critical role in glucose balance in patients with type 2 diabetes (T2DM). In the study, we developed an equation for predicting GE.

METHODS

We enrolled 227 participants with glucose tolerances ranging from normal glucose tolerance to diabetes. Of the participants, 75% (171) participants were randomly assigned to the study group, whose data were used to construct the equation for estimating GE. The remaining 56 participants comprised the validation group. All participants underwent a frequently sampled intravenous glucose tolerance test; IS, GE, and the acute insulin response after the glucose load were determined.

RESULTS

Age, triglyceride (TG), and fasting plasma glucose (FPG) were independently correlated with GE and selected for inclusion in multiple linear regression analysis. We constructed the following equation: GE = (29.196 - 0.103 × age - 2.722 × TG - 0.592 × FPG) × 10^-3. Using this same equation, we also calculated the GE of the validation group. The calculated GE was significantly correlated with the measured GE (r = 0.430, P = 0.001).

CONCLUSIONS

Using the equation based on routine measurements enabled the GE to be predicted with acceptable accuracy (r = 0.430). This method of predicting GE may aid clinicians in further understanding the underlying pathological mechanisms of T2DM.

Comparison of Second-Phase Insulin Secretion Derived from Standard and Modified Low-Dose Graded Glucose Infusion Tests

OBJECTIVES

Insulin secretion has 2 phases, first-phase and second-phase insulin secretion (SPIS). The purpose of our study was to validate the SPIS derived from the modified low-dose graded glucose infusion test (MLDGGI) by using the standard SPIS derived from the low-dose graded glucose infusion test (LDGGI).

METHODS

Fourteen participants were enrolled. The participants underwent the LDGGI for 200 minutes and MLDGGI for 60 minutes. The LDGGI was administered using the standard Polonsky method, which entails 5 40-minute stages of glucose infusion (1, 4, 8, 6 and 24 mg/kg/min). The slopes of the insulin levels vs. the glucose levels obtained during the test were regarded as SPIS (SPIS-I). Furthermore, deconvolution was performed, and slopes of the insulin secretion rate (ISR) against glucose levels during the test (SPIS-D) were obtained and regarded as the gold standard SPIS. The MLDGGI was administered with 3 20-minute stages of glucose infusion (2, 8 and 24 mg/kg/min) for 20 minutes each. The slopes of the insulin levels vs. the glucose levels obtained during the test were regarded as SPIS (MSPIS-I). In addition, deconvolution was performed, and the slopes of the ISR against glucose levels during the test (MSPIS-D) were obtained.

RESULTS

Significant correlations were observed between SPIS-I and SPIS-D (r=0.843; p<0.001) and between MSPIS and SPIS-D (r=0.786; p<0.001).

CONCLUSIONS

SPIS could be determined simply by using the LDGGI without deconvolution. Moreover, MLDGGI was proved to be useful in estimating SPIS easily on the basis of insulin levels.

Assessment of Insulin Resistance in Subjects with Normal Glucose Tolerance, Hyperinsulinemia with Normal Blood Glucose Tolerance, Impaired Glucose Tolerance, and Newly Diagnosed Type 2 Diabetes (Prediabetes Insulin Resistance Research)

AIM

To evaluate the differences in insulin resistance (IR) among subjects with normal glucose tolerance (NGT), hyperinsulinemia with NGT (HINS), impaired glucose tolerance (IGT), and newly diagnosed type 2 diabetes mellitus (T2DM).

METHODS

5 NGT, 25 HINS, 25 IGT, and 25 T2DM subjects participated in this research. The hyperinsulinemic-euglycemic clamp technique (HECT) was performed in all of them to evaluate IR levels. The relative factors influencing IR were evaluated. The simple insulin sensitivity indices were calculated, and the correlation between each index and the M value was analyzed.

RESULTS

The M values of NGT, HINS, IGT, and T2DM groups were 11.88 ± 2.93 mg · kg(-1) · min(-1), 6.23 ± 1.73 mg · kg(-1) · min(-1), 6.37 ± 2.12 mg · kg(-1) · min(-1), and 6.19 ± 1.89 mg · kg(-1) · min(-1), respectively. M values in HINS, IGT, and T2DM groups were lower than those in the NGT group (P = 0.005); however, the differences among the HINS, IGT, and T2DM groups were not statistically significant (P = 0.835). The independent factors influencing the M value were waistline and fasting insulin level (FINS). The simple insulin sensitivity indices, especially Matsuda and Gutt index, were significantly associated with the M value (P < 0.01).

CONCLUSION

IR existed in the HINS, IGT, and T2DM groups, and IR levels were consistent in the three groups. The independent factors influencing IR were waistline and FINS.

Pharmacokinetic Model of the Transport of Fast-Acting Insulin From the Subcutaneous and Intradermal Spaces to Blood

Pharmacokinetic (PK) models describing the transport of insulin from the injection site to blood assist clinical decision making and are part of in silico platforms for developing and testing of insulin delivery strategies for treatment of patients with diabetes. The ability of these models to accurately describe all facets of the in vivo insulin transport is therefore critical for their application. Here, we propose a new model of fast-acting insulin analogs transport from the subcutaneous and intradermal spaces to blood that can accommodate clinically observed biphasic appearance and delayed clearance of injected insulin, 2 phenomena that are not captured by existing PK models. To develop the model we compare 9 insulin transport PK models which describe hypothetical insulin delivery pathways potentially capable of approximating biphasic appearance of exogenous insulin. The models are tested with respect to their ability to describe clinical data from 10 healthy volunteers which received 1 subcutaneous and 2 intradermal insulin injections on 3 different occasions. The optimal model, selected based on information and posterior identifiability criteria, assumes that insulin is delivered at the administrative site and is then transported to the bloodstream via 2 independent routes (1) diffusion-like process to the blood and (2) combination of diffusion-like processes followed by an additional compartment before entering the blood. This optimal model accounts for biphasic appearance and delayed clearance of exogenous insulin. It agrees better with the clinical data as compared to commonly used models and is expected to improve the in silico development and testing of insulin treatment strategies, including artificial pancreas systems.

Levels of the first-phase insulin secretion deficiency as a predictor for type 2 diabetes onset by using clinical-metabolic models

AIMS

Type 2 diabetes mellitus (T2DM) is characterized by both decreased insulin sensitivity and impaired insulin secretion. The 2 phases of insulin secretion are the first-phase insulin secretion (1st ISEC) and the second-phase insulin secretion. In this study, we tried to build clinical-metabolic models to predict the 1st ISEC deficiency (ISEC-D) in non-diabetic subjects so that early intervention could be started.

DESIGN AND SETTINGS

A cross-sectional study was conducted in the clinical research department of a hospital in Taiwan from 2010 to 2011.

METHODS

A total of 89 subjects without diabetes were enrolled in the study, including 49 with normal glucose tolerance and 40 pre-diabetes. A frequently sampled intravenous glucose tolerance test was done to determine insulin sensitivity and acute insulin response after the glucose load, which is regarded as the 1st ISEC. Subjects with the lowest tertile of the 1st ISEC were defined as ISEC-D. From the simplest to the most complex, 3 models were build: Model 0: fasting plasma glucose (FPG); Model 1: FPG + body mass index (BMI) + High-density lipoprotein cholesterol (HDL-C); Model 2: Model 1+ fasting plasma insulin (FPI). The area under the receiver-operating characteristic curve (aROC curve) was used to determine the predictive power among these models. An optimal cut-off value was also determined.

RESULTS

Among metabolic syndrome (MetS) components (FPG, BMI, and HDL-C), FPG had the greatest aROC curve (70.9%). Moreover, the aROC curves of Models 1 and 2 were all significantly greater than that of FPG (80.4% and 82.3%, respectively). Their aROC curves were also greater than that of the homeostasis model assessment b-cell (HOMA-b) function, which is the most commonly used method to evaluate b-cell function.

CONCLUSION

By using only MetS components, ISEC-D could be predicted with an acceptable sensitivity of 84.0% and a specificity of 74.0%. However, after adding FPI into the Model, the predictive power of Model 2 did not increase. These model-derived MetS components could be widely used in clinical settings and early detection of non-diabetic subjects with high risk for T2DM.

Type 2 diabetes, PUFAs, and vitamin D: their relation to inflammation

Chronic diseases have become one of the most important public health problems, due to their high costs for treatment and prevention. Until now, researchers have considered that the etiology of Type 2 diabetes mellitus (T2DM) is multifactorial. Recently, the study of the innate immune system has offered an explanation model of the pathogenesis of T2DM. On the other hand, there is evidence about the beneficial effect of polyunsaturated fatty acids (PUFA) n-3 and n-6 in patients with chronic inflammatory diseases including diabetes. Furthermore, high vitamin D plasmatic concentrations have been associated with the best performance of pancreatic β cells and the improving of this disease. In conclusion, certain fatty acids in the adequate proportion as well as 25-hydroxivitamin D can modulate the inflammatory response in diabetic people, modifying the evolution of this disease.

Trajectories of cardiometabolic risk factors before diagnosis of three subtypes of type 2 diabetes: a post-hoc analysis of the longitudinal Whitehall II cohort study

BACKGROUND

Most clinicians acknowledge that type 2 diabetes is multifactorial and has heterogeneous characteristics, but neither prevention nor treatment is systematically stratified. To address the heterogeneity of the disease, we examined whether patients diagnosed on the basis of fasting glucose concentrations, those diagnosed on the basis of 2 h concentrations, and those diagnosed on the basis of both criteria differed in terms of pathogenesis or cardiovascular risks.

METHODS

Retrospectively, we analysed trajectories of cardiometabolic risk factors and 10 year cardiovascular risks in the prospective Whitehall II study cohort by use of multilevel longitudinal modelling. Participants were diagnosed by 75 g oral glucose-tolerance tests. We classified those diagnosed with type 2 diabetes into three subgroups: diagnosed on the basis of fasting glucose concentrations, diagnosed on the basis of 2 h glucose concentrations, and diagnosed on the basis of both concentrations. We also developed a classification tree for identification of individuals who are likely to have high fasting and 2 h glucose concentrations, but for whom only fasting concentrations are available.

RESULTS

Median follow-up was 14·2 years with 15,826 person-examinations (1991-2009). Of 10,308 individuals, 6843 were included and 6569 remained diabetes free. 274 cases of type 2 diabetes were identified: 55 had high fasting glucose concentrations only, 148 had high 2 h concentrations only, and 71 had high fasting and 2 h concentrations. At diagnosis, participants with high fasting and 2 h glucose concentrations had higher mean body-mass indices (30·9 kg/m(2) [SD 5·7]) than did those with high fasting concentrations (28·4 kg/m(2) [4·4]; p=0·0009) or 2 h concentrations (27·9 kg/m(2) [4·9]; <0·0001). Mean glycated haemoglobin A1c concentrations were also higher in the fasting and 2 h subgroup (7·4% [1·6]) than in the fasting (5·9% [0·5]; <0·0001) or 2 h (5·9% [0·6]; <0·0001) sugroups. Additionally, the fasting and 2 h subgroup had a higher proportion of individuals with moderate or high risk of cardiovascular disease than did the fasting subgroup (p=0·02). A classic pattern of β-cell decompensation before diagnosis was noted only in the fasting and 2 h subgroup. Additionally, glucose concentrations and insulin resistance accelerated more substantially before diagnosis in the fasting and 2 h subgroup than in the fasting subgroup or the 2 h subgroup.

INTERPRETATION

Patients with type 2 diabetes diagnosed on the basis of increased fasting glucose concentrations or 2 h glucose concentrations, or both, have distinct cardiometabolic risk development before diagnosis.

FUNDING

UK Medical Research Council, UK Economic and Social Research Council, British Heart Foundation, UK Health and Safety Executive, UK Department of Health, US National Heart Lung and Blood Institute, US National Institute on Aging, US Agency for Health Care Policy Research, and John D and Catherine T MacArthur Foundation.

Beta-cell function and insulin sensitivity at various degrees of glucose tolerance in Chinese subjects

AIMS

The aim of this study was to evaluate the relative importance of insulin sensitivity (SI), and the first (1st ISEC) and second phase insulin secretion (2nd ISEC) in the development of type 2 diabetes (T2D) in Chinese subjects.

METHODS

A total of 96 subjects, including 19 with normal fasting glucose, 21 with pre-diabetes, and 56 with T2D were enrolled. Subjects underwent a modified low dose graded glucose infusion (M-LDGGI; a simplified version of Polonsky's method) and frequently sampled intravenous glucose tolerance test. The results were interpreted as the slope of the changes of plasma insulin against the glucose levels. By observing the respective percentage reduction, the deterioration rate of each parameter was compared.

RESULTS

As fasting plasma glucose (FPG) levels increased, SI decreased mildly and non-significantly, while the 1st and 2nd ISECs decreased more dramatically and significantly. More importantly, the decrease of the 1st ISEC from baseline was greater than that of the 2nd ISEC.

CONCLUSIONS

Since the 1st ISEC decreased the most with increasing FPG levels, it is concluded that the 1st ISEC is the key trigger of T2D development. On the contrary, the 2nd ISEC remained more stable across increasing FPG levels. This latter finding may explain the effectiveness of insulin secretagogues during the early stage of T2D. The results of this study can be helpful in the development of interventions aimed at stopping the progression and/or treating T2D in Chinese populations.

Glucocorticoid receptor gene polymorphisms are associated with reduced first-phase glucose-stimulated insulin secretion and disposition index in women, but not in men

AIM

Glucocorticoids are efficacious anti-inflammatory agents, but, in susceptible individuals, these drugs may induce glucose intolerance and diabetes by affecting β-cell function and insulin sensitivity. We assessed whether polymorphisms in the glucocorticoid receptor gene NR3C1 associate with measures of β-cell function and insulin sensitivity derived from hyperglycaemic clamps in subjects with normal or impaired glucose tolerance.

METHODS

A cross-sectional cohort study was conducted in four academic medical centres in the Netherlands and Germany. Four hundred and forty-nine volunteers (188 men; 261 women) were recruited with normal glucose tolerance (n=261) and impaired glucose tolerance (n=188). From 2-h hyperglycaemic clamps, first- and second-phase glucose-stimulated insulin secretion, as well as insulin sensitivity index and disposition index, were calculated. All participants were genotyped for the functional NR3C1 polymorphisms N363S (rs6195), BclI (rs41423247), ER22/23EK (rs6189/6190), 9β A/G (rs6198) and ThtIIII (rs10052957). Associations between these polymorphisms and β-cell function parameters were assessed.

RESULTS

In women, but not in men, the N363S polymorphism was associated with reduced disposition index (P=1.06 10(-4) ). Also only in women, the ER22/23EK polymorphism was associated with reduced first-phase glucose-stimulated insulin secretion (P=0.011) and disposition index (P=0.003). The other single-nucleotide polymorphisms were not associated with β-cell function. Finally, none of the polymorphisms was related to insulin sensitivity.

CONCLUSION

The N363S and ER22/23EK polymorphisms of the NR3C1 gene are negatively associated with parameters of β-cell function in women, but not in men.

Distinct β-cell defects in impaired fasting glucose and impaired glucose tolerance

To characterize the defects in β-cell function in subjects with impaired fasting glucose (IFG) and compare the results to impaired glucose tolerance (IGT) and normal glucose tolerance (NGT) subjects, β-cell glucose sensitivity and rate sensitivity during the oral glucose tolerance test were measured with the model by Mari in 172 Mexican Americans. A subgroup (n=70) received a 2-h hyperglycemic clamp (+125 mg/dL), and first- and second-phase insulin secretion were quantitated. Compared with NGT, subjects with IFG and IGT manifested a decrease in β-cell glucose sensitivity; IFG subjects, but not IGT subjects, had decreased β-cell rate sensitivity. In IFG subjects, the defect in β-cell glucose sensitivity was time dependent, began to improve after 60 min, and was comparable to NGT after 90 min. The incremental area under the plasma C-peptide concentration curve during the first 12 min of the hyperglycemic clamp (ΔC-pep[AUC]0-12) was inversely related with the increase in FPG concentration (r=-36, r=0.001), whereas ΔC-pep[AUC]15-120 positively correlated with FPG concentration (r=0.29, r<0.05). When adjusted for the prevailing level of insulin resistance, first-phase insulin secretion was markedly decreased in both IFG and IGT, whereas second-phase insulin secretion was decreased only in IGT. These results demonstrate distinct defects in β-cell function in IFG and IGT.

Impaired early- but not late-phase insulin secretion in subjects with impaired fasting glucose

Subjects with impaired fasting glucose (IFG) are at increased risk for type 2 diabetes. We recently demonstrated that IFG subjects have increased hepatic insulin resistance with normal insulin sensitivity in skeletal muscle. In this study, we quantitated the insulin secretion rate from deconvolution analysis of the plasma C-peptide concentration during an oral glucose tolerance test (OGTT) and compared the results in IFG subjects with those in subjects with impaired glucose tolerance (IGT) and normal glucose tolerance (NGT). One hundred and one NGT subjects, 64 subjects with isolated IGT, 24 subjects with isolated IFG, and 48 subjects with combined (IFG + IGT) glucose intolerance (CGI) received an OGTT. Plasma glucose, insulin, and C-peptide concentrations were measured before and every 15 min after glucose ingestion. Insulin secretion rate (ISR) was determined by deconvolution of plasma C-peptide concentration. Inverse of the Matsuda index of whole body insulin sensitivity was used as a measure of insulin resistance; 56 subjects also received a euglycemic hyperinsulinemic clamp. The insulin secretion/insulin resistance (disposition) index was calculated as the ratio between incremental area under the ISR curve (∆ISR[AUC]) to incremental area under the glucose curve (∆G[AUC]) factored by the severity of insulin resistance (measured by Matsuda index during OGTT or glucose disposal during insulin clamp). Compared to NGT, the insulin secretion/insulin resistance index during first 30 min of OGTT was reduced by 47, 49, and 74% in IFG, IGT, and CGI, respectively (all < 0.0001). The insulin secretion/insulin resistance index during the second hour (60-120 min) of the OGTT in subjects with IFG was similar to that in NGT (0.79 ± 0.6 vs. 0.72 ± 0.5, respectively, P = NS), but was profoundly reduced in subjects with IGT and CGI (0.31 ± 0.2 and 0.19 ± 0.11, respectively; P < 0.0001 vs. both NGT and IFG). Early-phase insulin secretion is impaired in both IFG and IGT, while the late-phase insulin secretion is impaired only in subjects with IGT.

From pre-diabetes to type 2 diabetes in obese youth: pathophysiological characteristics along the spectrum of glucose dysregulation

OBJECTIVE

Impaired fasting glucose (IFG) and impaired glucose tolerance (IGT) are considered pre-diabetes states. There are limited data in pediatrics in regard to their pathophysiology. We investigated differences in insulin sensitivity and secretion among youth with IFG, IGT, and coexistent IFG/IGT compared with those with normal glucose tolerance (NGT) and type 2 diabetes.

RESEARCH DESIGN AND METHODS

A total of 24 obese adolescents with NGT, 13 with IFG, 29 with IGT, 11 with combined IFG/IGT, and 30 with type 2 diabetes underwent evaluation of hepatic glucose production ([6,6-(2)H(2)]glucose), insulin-stimulated glucose disposal (R(d), euglycemic clamp), first- and second-phase insulin secretion (hyperglycemic clamp), body composition (dual-energy X-ray absorptiometry), abdominal adiposity (computed tomography), and substrate oxidation (indirect calorimetry).

RESULTS

Adolescents with NGT, pre-diabetes, and type 2 diabetes had similar body composition and abdominal fat distribution. R(d) was lower (P = 0.009) in adolescents with type 2 diabetes than in those with NGT. Compared with adolescents with NGT, first-phase insulin was lower in those with IFG, IGT, and IFG/IGT with further deterioration in those with type 2 diabetes (P < 0.001), and β-cell function relative to insulin sensitivity (glucose disposition index [GDI]) was also lower in those with IFG, IGT, and IFG/IGT (40, 47, and 47%, respectively), with a further decrease (80%) in those with type 2 diabetes (P < 0.001). GDI was the major determinant of fasting and 2-h glucose levels.

CONCLUSIONS

Obese adolescents who show signs of glucose dysregulation, including abnormal fasting glucose, glucose intolerance or both, are more likely to have impaired insulin secretion rather than reduced insulin sensitivity. Given the impairment in insulin secretion, they are at high risk for progression to type 2 diabetes. Further deterioration in insulin sensitivity or secretion may enhance the risk for this progression.

Effect of Rosiglitazone and Ramipril on {beta}-cell function in people with impaired glucose tolerance or impaired fasting glucose: the DREAM trial

OBJECTIVE The objective of this study was to determine the degree to which ramipril and/or rosiglitazone changed beta-cell function over time among individuals with impaired fasting glucose (IFG) and/or impaired glucose tolerance (IGT) who participated in the Diabetes Reduction Assessment With Ramipril and Rosiglitazone Medication (DREAM) Trial, which evaluated whether ramipril and/or rosiglitazone could prevent or delay type 2 diabetes in high-risk individuals. RESEARCH DESIGN AND METHODS The present analysis included subjects (n = 982) from DREAM trial centers in Canada who had oral glucose tolerance tests at baseline, after 2 years, and at the end of the study. beta-Cell function was assessed using the fasting proinsulin-to-C-peptide ratio (PI/C) and the insulinogenic index (defined as 30-0 min insulin/30-0 min glucose) divided by homeostasis model assessment of insulin resistance (insulinogenic index [IGI]/insulin resistance [IR]). RESULTS Subjects receiving rosiglitazone had a significant increase in IGI/IR between baseline and end of study compared with the placebo group (25.59 vs. 1.94, P < 0.0001) and a significant decrease in PI/C (-0.010 vs. -0.006, P < 0.0001). In contrast, there were no significant changes in IGI/IR or PI/C in subjects receiving ramipril compared with placebo (11.71 vs. 18.15, P = 0.89, and -0.007 vs. -0.008, P = 0.64, respectively). The impact of rosiglitazone on IGI/IR and PI/C was similar within subgroups of isolated IGT and IFG + IGT (all P < 0.001). Effects were more modest in those with isolated IFG (IGI/IR: 8.95 vs. 2.13, P = 0.03; PI/C: -0.003 vs. -0.001, P = 0.07). CONCLUSIONS Treatment with rosiglitazone, but not ramipril, resulted in significant improvements in measures of beta-cell function over time in pre-diabetic subjects. Although the long-term sustainability of these improvements cannot be determined from the present study, these findings demonstrate that the diabetes preventive effect of rosiglitazone was in part a consequence of improved beta-cell function.

Gene variants in the novel type 2 diabetes loci CDC123/CAMK1D, THADA, ADAMTS9, BCL11A, and MTNR1B affect different aspects of pancreatic beta-cell function

OBJECTIVE

Recently, results from a meta-analysis of genome-wide association studies have yielded a number of novel type 2 diabetes loci. However, conflicting results have been published regarding their effects on insulin secretion and insulin sensitivity. In this study we used hyperglycemic clamps with three different stimuli to test associations between these novel loci and various measures of beta-cell function.

RESEARCH DESIGN AND METHODS

For this study, 336 participants, 180 normal glucose tolerant and 156 impaired glucose tolerant, underwent a 2-h hyperglycemic clamp. In a subset we also assessed the response to glucagon-like peptide (GLP)-1 and arginine during an extended clamp (n = 123). All subjects were genotyped for gene variants in JAZF1, CDC123/CAMK1D, TSPAN8/LGR5, THADA, ADAMTS9, NOTCH2/ADAMS30, DCD, VEGFA, BCL11A, HNF1B, WFS1, and MTNR1B.

RESULTS

Gene variants in CDC123/CAMK1D, ADAMTS9, BCL11A, and MTNR1B affected various aspects of the insulin response to glucose (all P < 6.9 x 10(-3)). The THADA gene variant was associated with lower beta-cell response to GLP-1 and arginine (both P < 1.6 x 10(-3)), suggesting lower beta-cell mass as a possible pathogenic mechanism. Remarkably, we also noted a trend toward an increased insulin response to GLP-1 in carriers of MTNR1B (P = 0.03), which may offer new therapeutic possibilities. The other seven loci were not detectably associated with beta-cell function.

CONCLUSIONS

Diabetes risk alleles in CDC123/CAMK1D, THADA, ADAMTS9, BCL11A, and MTNR1B are associated with various specific aspects of beta-cell function. These findings point to a clear diversity in the impact that these various gene variants may have on (dys)function of pancreatic beta-cells.

Pathophysiology of prediabetes

The term prediabetes refers to subjects with impaired fasting glucose and/or impaired glucose tolerance who are at increased risk for type 2 diabetes mellitus. Although both types of patients are at increased risk for developing type 2 diabetes mellitus and cardiovascular disease, they manifest distinct metabolic abnormalities. In this article, we summarize the metabolic abnormalities that characterize each state and the contribution of these metabolic abnormalities to the increased risk of diabetes and cardiovascular disease.

Changes in insulin sensitivity and insulin release in relation to glycemia and glucose tolerance in 6,414 Finnish men

OBJECTIVE

We evaluated insulin sensitivity and insulin secretion across the entire range of fasting (FPG) and 2-h plasma glucose (PG), and we investigated the differences in insulin sensitivity and insulin release in different glucose tolerance categories.

RESEARCH DESIGN AND METHODS

A total of 6,414 Finnish men (aged 57 +/- 7 years, BMI 27.0 +/- 3.9 kg/m2) from our ongoing population-based METSIM (Metabolic Syndrome in Men) study were included. Of these subjects, 2,168 had normal glucose tolerance, 2,859 isolated impaired fasting glucose (IFG), 217 isolated impaired glucose tolerance (IGT), 701 a combination of IFG and IGT, and 469 newly diagnosed type 2 diabetes.

RESULTS

The Matsuda index of insulin sensitivity decreased substantially within the normal range of FPG (-17%) and 2-h PG (-37%) and was approximately -65 and -53% in the diabetic range of FPG and 2-h PG, respectively, compared with the reference range (FPG and 2-h PG <5.0 mmol/l). Early-phase insulin release declined by only approximately -5% within the normal range of FPG and 2-h PG but decreased significantly in the diabetic range of FPG (by 32-70%) and 2-h PG (by 33-51%). Changes in insulin sensitivity and insulin secretion in relation to hyperglycemia were independent of obesity. The predominant feature of isolated IGT was impaired peripheral insulin sensitivity. Isolated IFG was characterized by impaired early and total insulin release.

CONCLUSIONS

Peripheral insulin sensitivity was already decreased substantially at low PG levels within the normoglycemic range, whereas impairment in insulin secretion was observed mainly in the diabetic range of FPG and 2-h PG. Obesity did not affect changes in insulin sensitivity or insulin secretion in relation to hyperglycemia.

Classical and model-based estimates of beta-cell function during a mixed meal vs. an OGTT in a population-based cohort

This study compared classical and model-based beta-cell responses during an oral glucose tolerance test (OGTT) and a meal tolerance test (MTT) in a population-based cohort. Individuals with normal glucose metabolism (NGM, n=161), impaired glucose metabolism (IGM, n=19) and type 2 diabetes mellitus (DM, n=20) underwent a 75 g-OGTT and an MTT (75 g carbohydrates, 50 g fat, 24 g proteins). Classical estimates of beta-cell function (insulinogenic index and the ratio of areas under insulin and glucose curves) were calculated. Mathematical modelling was used to determine beta-cell glucose sensitivity, rate sensitivity and potentiation. Insulin sensitivity was characterized by three surrogate estimates. Both classical and model-based estimates of beta-cell function were higher during MTT than during OGTT (P<0.05). Regarding the model-based parameters, especially beta-cell sensitivity was increased following MTT as compared with OGTT (P<0.05). Both during OGTT and MTT, across most parameters describing beta-cell function, the largest reduction in beta-cell response occurred between IGM and DM, while the largest reduction in insulin sensitivity occurred between NGM and IGM. We conclude that beta-cell response is stronger after a mixed meal than after an OGTT with equal carbohydrate quantity, both for classical and model-based parameters. The higher response was mostly explained by higher beta-cell sensitivity during the meal.

Diabetes and cardiovascular autonomic dysfunction: application of animal models

When diabetes is associated with cardiovascular autonomic dysfunction, there is a poor prognosis and increased morbidity and mortality. Information on the mechanisms of diabetes-associated autonomic dysfunction has been provided by advanced studies using physiological, pharmacological, anatomical and molecular methods in experimental animal models of insulin deficiency and resistance. This has been augmented by new approaches which combine diabetes induction with genetically modified animal models. The aim of this review is to outline and discuss the animal models used for the study of insulin deficiency and insulin resistance with a focus on autonomic neural interactions. The goal is to better understand the clinical relevance of cardiovascular autonomic dysfunction associated with diabetes.

Differences in insulin action and secretion, plasma lipids and blood pressure levels between impaired fasting glucose and impaired glucose tolerance in Japanese subjects

We examined insulin action/secretion and cardiovascular disease risk factors in Japanese subjects with impaired fasting glucose (IFG) and/or impaired glucose tolerance (IGT) who were not taking any medications known to affect glucose tolerance, blood pressure (BP) or plasma lipids (PLs). A total of 1,399 subjects received measurements of anthropometry, BP, PLs, and plasma glucose/insulin concentrations during 75 g-oral glucose tolerance test (OGTT). According to 2003 American Diabetes Association criteria, subjects were classified as having normal fasting glucose (NFG)/normal glucose tolerance (NGT) (n = 1,173), IFG (n = 128), IGT (n = 55), and IFG/IGT (n = 43). Insulin action was calculated using the HOMA-R (index of hepatic insulin resistance) and Matsuda index (reflects whole body insulin sensitivity). The ratio of the incremental area under the curve of insulin to that of glucose during OGTT (delta AUC(PI)/delta AUC(PG)) was used as an index of beta-cell function. HOMA-R was higher in IFG (2.3 +/- 0.1) and IFG/IGT (2.5 +/- 0.2) than in NFG/NGT (1.8 +/- 0.03). The Matsuda index was lower in IFG (6.5 +/- 0.3), IGT (5.4 +/- 0.4) and IFG/IGT (5.1 +/- 0.5) than in NFG/NGT (9.6 +/- 0.2). Delta AUC(PI)/delta AUC(PG) was lower in IGT (0.6 +/- 0.05) and IFG/IGT (0.5 +/- 0.05) than in IFG (1.4 +/- 0.12) or NFG/NGT (1.2 +/- 0.03). Mean BP was higher in IGT (100 +/- 1.7 mmHg) than in NFG/NGT (91 +/- 0.3) or IFG (95 +/- 1.1). The plasma triglyceride level was higher in IGT (155 +/- 14 mg/dL) and IGT/IFG (173 +/- 12) than in IFG (132 +/- 7) or NFG/NGT (122 +/- 2). In conclusion, 1) whole body insulin sensitivity is decreased in IFG and IGT, with a greater reduction in IGT, 2) hepatic insulin resistance and preserved beta-cell function are characteristics of IFG, and 3) higher BP and triglyceride levels are observed in IGT. IGT is more closely associated with risk factors for cardiovascular disease than is IFG.

The relationship between fasting hyperglycemia and insulin secretion in subjects with normal or impaired glucose tolerance

To assess the relationship between the fasting plasma glucose (FPG) concentration and insulin secretion in normal glucose tolerance (NGT) and impaired glucose tolerance (IGT) subjects, 531 nondiabetic subjects with NGT (n = 293) and IGT (n = 238; 310 Japanese and 232 Mexican Americans) received an oral glucose tolerance test (OGTT) with measurement of plasma glucose, insulin, and C-peptide every 30 min. The insulin secretion rate was determined by plasma C-peptide deconvolution. Insulin sensitivity (Matsuda index) was measured from plasma insulin and glucose concentrations. The insulin secretion/insulin resistance (IS/IR) or disposition index was calculated as DeltaISR/DeltaG / IR. As FPG increased in NGT subjects, the IS/IR index declined exponentially over the range of FPG from 70 to 125 mg/dl. The relationship between the IS/IR index and FPG was best fit with the equation: 28.8 exp(-0.036 FPG). For every 28 mg/dl increase in FPG, the IS/IR index declined by 63%. A similar relationship between IS/IR index and FPG was observed in IGT. However, the decay constant was lower than in NGT. The IS/IR index for early-phase insulin secretion (0-30 min) was correlated with the increase in FPG in both NGT and IGT (r = -0.43, P < 0.0001 and r = -0.20, P = 0.001, respectively). However, the correlation between late-phase insulin secretion (60-120 min) and FPG was not significant. In conclusion, small increments in FPG, within the "normal" range, are associated with a marked decline in glucose-stimulated insulin secretion and the decrease in insulin secretion with increasing FPG is greater in subjects with NGT than IGT and primarily is due to a decline in early-phase insulin secretion.

Insulin sensitivity, insulin release and glucagon-like peptide-1 levels in persons with impaired fasting glucose and/or impaired glucose tolerance in the EUGENE2 study

AIMS/HYPOTHESIS

We examined the phenotype of individuals with impaired fasting glucose (IFG) and/or impaired glucose tolerance (IGT) with regard to insulin release and insulin resistance.

METHODS

Non-diabetic offspring (n=874; mean age 40+/-10.4 years; BMI 26.6+/-4.9 kg/m(2)) of type 2 diabetic patients from five different European Centres (Denmark, Finland, Germany, Italy and Sweden) were examined with regard to insulin sensitivity (euglycaemic clamps), insulin release (IVGTT) and glucose tolerance (OGTT). The levels of glucagon-like peptide-1 (GLP-1) and gastric inhibitory polypeptide (GIP) were measured during the OGTT in 278 individuals.

RESULTS

Normal glucose tolerance was found in 634 participants, while 110 had isolated IFG, 86 had isolated IGT and 44 had both IFG and IGT, i.e. about 28% had a form of reduced glucose tolerance. Participants with isolated IFG had lower glucose-corrected first-phase (0-10 min) and higher second-phase insulin release (10-60 min) during the IVGTT, while insulin sensitivity was reduced in all groups with abnormal glucose tolerance. Similarly, GLP-1 but not GIP levels were reduced in individuals with abnormal glucose tolerance.

CONCLUSIONS/INTERPRETATION

The primary mechanism leading to hyperglycaemia in participants with isolated IFG is likely to be impaired basal and first-phase insulin secretion, whereas in isolated IGT the primary mechanism leading to postglucose load hyperglycaemia is insulin resistance. Reduced GLP-1 levels were seen in all groups with abnormal glucose tolerance and were unrelated to the insulin release pattern during an IVGTT.

The dipeptidyl peptidase-4 inhibitor vildagliptin improves beta-cell function and insulin sensitivity in subjects with impaired fasting glucose

OBJECTIVE

To evaluate the effect of treatment with the dipeptidyl peptidase (DPP)-4 inhibitor vildagliptin on insulin sensitivity and beta-cell function in subjects with impaired fasting glucose (IFG).

RESEARCH DESIGN AND METHODS

A total of 22 subjects with IFG (11 female and 11 male, mean +/- SD age 59.6 +/- 11.5 years) were treated orally with 100 mg vildagliptin once daily in a single-blind study. Subjects received placebo for 2 weeks (run-in) followed by vildagliptin for 6 weeks (treatment) and then placebo for 2 weeks (washout). A frequently sampled intravenous glucose tolerance test (FSIGT), followed by a 2-h meal tolerance test (MTT), was performed at 2, 8, and 10 weeks. From the FSIGT, the acute insulin response to glucose (AIR(g)) and insulin sensitivity index (S(I)) were determined and used to compute the disposition index (AIR(g) x S(I)) as a measure of beta-cell function.

RESULTS

Fasting plasma glucose did not change after 6 weeks of vildagliptin treatment. With treatment, mean +/- SEM AIR(g) increased from 224 +/- 44 to 286 +/- 52 pmol/l (P < 0.05), and S(I) improved from 2.8 +/- 0.5 to 3.5 +/- 0.5 x 10(-5) x min(-1) x pmol(-1) x l (P < 0.01), resulting in an increase in the disposition index from 688 +/- 180 to 1,164 +/- 318 x 10(-5)/min (P < 0.05). These effects were not sustained after washout. During the MTT, the incremental area under the glucose curve was significantly decreased after treatment (240 +/- 15 vs. 191 +/- 14 mmol x l(-1) x min(-1); P = 0.002), but this effect was not sustained after washout.

CONCLUSIONS

The DPP-4 inhibitor vildagliptin improves insulin sensitivity and beta-cell function, leading to improved postprandial glycemia in subjects with IFG, who are known to have beta-cell dysfunction. Thus, vildagliptin may prevent progression to diabetes in high-risk subjects.

The role of beta-cell dysfunction in the cardiometabolic syndrome

The regulation of blood glucose levels involves a finely tuned relationship between insulin sensitivity, hepatic glucose output, and production of insulin. The cardiometabolic syndrome includes in its definition criteria a disturbance of normal glucose tolerance and implies development of both insulin resistance and beta-cell dysfunction. There is now abundant evidence pointing toward a central role of dysregulation of the beta-cell function and mass in the development of impaired glucose tolerance. Mechanisms implicated in beta-cell dysfunction include genetic abnormalities, prenatal and early postnatal insults, and environmental events along with obesity, dyslipidemia-lipotoxicity, glucotoxicity, oxidative stress, chronic low-grade inflammation, amyloid deposition, and activation of the local renin-angiotensin system. Novel therapeutic characteristics of known medications such as metformin, thiazolidinediones, angiotensin-converting enzyme inhibitors/angiotensin receptor blockers, and novel medications such as exendin-4 promise encouraging possibilities to battle against the cardiometabolic syndrome and the future development of cardiovascular disease.

Awareness of pathophysiological concepts of type 2 diabetes: a survey in 847 physicians

AIMS

The aim of the study was to determine physicians' knowledge of specific concepts generally implicated in the pathophysiology of type 2 diabetes (T2D).

METHODS

A multiple choice online survey was completed by 847 physicians, of which 516 were engaged in primary care (PCP) and 331 in specialized care (SCP) in the US, the UK, Germany and France (3-30 years in practice, at least 40 patients with T2D). A continuous rating system was used to measure familiarity ("totally familiar" to "never heard of") or agreement with a statement (from "totally agree" to "totally disagree").

RESULTS

The term "insulin resistance" was recognized by 74% of PCPs and 90% of SCPs (p<0.05) and 76% felt that it was "a key but not the sole determinant of T2D". Only 47% agreed that "beta cell dysfunction is a key determinant of T2D onset" and 57% agreed with "beta cell dysfunction being a key determinant of T2D progression". Even among SCPs, 6% were not familiar with the term "beta cell dysfunction" (16% among PCPs, p<0.05). The overall familiarity with the following terms was: 55% with "beta cell dysfunction", 56% with "beta cells", 38% with "glucagon", 32% with "alpha cells", 55% with "hepatic glucose output", 15% with "incretins" and 18% with "GLP-1". SCPs were significantly more familiar with all terms than PCPs (all p-values <0.05).

CONCLUSIONS

The pathogenetic role of beta cell dysfunction in the onset and progression of T2D did not seem to be well established. "Insulin resistance" was a well known concept even among PCPs, while "hepatic glucose output", "pancreatic alpha cells" and "glucagon" were not. Incretin hormones and GLP-1 were widely unknown. This may effect prescribing behaviour and how well an individual's therapy is based on pathophysiology.

Mechanisms of impaired fasting glucose and glucose intolerance induced by an approximate 50% pancreatectomy

Impaired fasting glucose (IFG) and impaired glucose tolerance (IGT) often coexist and as such represent a potent risk factor for subsequent development of type 2 diabetes. beta-Cell mass is approximately 50% deficient in IFG and approximately 65% deficient in type 2 diabetes. To establish the effect of a approximately 50% deficit in beta-cell mass on carbohydrate metabolism, we performed a approximately 50% partial pancreatectomy versus sham surgery in 14 dogs. Insulin secretion was quantified from insulin concentrations measured in the portal vein at 1-min sampling intervals under basal conditions, after a 30-g oral glucose, and during a hyperglycemic clamp. Insulin sensitivity was measured by a hyperinsulinemic-euglycemic clamp combined with isotope dilution. Partial pancreatectomy resulted in IFG and IGT. After partial pancreatectomy both basal and glucose-stimulated insulin secretion were decreased through the mechanism of a selective approximately 50 and approximately 80% deficit in insulin pulse mass, respectively (P < 0.05). These defects in insulin secretion were partially offset by decreased hepatic insulin clearance (P < 0.05). Partial pancreatectomy also caused a approximately 40% decrease in insulin-stimulated glucose disposal (P < 0.05), insulin sensitivity after partial pancreatectomy being related to insulin pulse amplitude (r = 0.9, P < 0.01). We conclude that a approximately 50% deficit in beta-cell mass can recapitulate the alterations in glucose-mediated insulin secretion and insulin action in humans with IFG and IGT. These data support a mechanistic role of a deficit in beta-cell mass in the evolution of IFG/IGT and subsequently type 2 diabetes.

Insulin secretion and action in subjects with impaired fasting glucose and impaired glucose tolerance: results from the Veterans Administration Genetic Epidemiology Study

This study was conducted to observe changes in insulin secretion and insulin action in subjects with impaired fasting glucose (IFG) and/or impaired glucose tolerance (IGT). A total of 319 subjects were studied with an oral glucose tolerance test (OGTT). Fasting plasma glucose and insulin concentrations were measured at baseline and every 30 min during the OGTT. Fifty-eight subjects also received a euglycemic-hyperinsulinemic clamp. Insulin sensitivity was calculated as the total glucose disposal (TGD) during the last 30 min of the clamp. Homeostasis model assessment of insulin resistance (HOMA-IR) was calculated from fasting plasma glucose and insulin concentrations. Subjects with IFG had TGD similar to normal glucose-tolerant subjects, while subjects with IGT and combined IFG/IGT had significantly reduced TGD. HOMA-IR in subjects with IFG was similar to that in subjects with combined IFG/IGT and significantly higher than HOMA-IR in subjects with IGT or NGT. Insulin secretion, measured by the insulinogenic index (DeltaI(0-30)/DeltaG(0-30)) and by the ratio of the incremental area under the curve (AUC) of insulin to the incremental AUC of glucose (0-120 min), was reduced to the same extent in all three glucose-intolerant groups. When both measurements of beta-cell function were adjusted for severity of insulin resistance, subjects with IGT and combined IFG/IGT had a significantly greater reduction in insulin secretion than subjects with IFG. Subjects with IGT and IFG have different metabolic characteristics. Differences in insulin sensitivity and insulin secretion may predict different rates of progression to type 2 diabetes and varying susceptibility to cardiovascular disease.

Contributions of beta-cell dysfunction and insulin resistance to the pathogenesis of impaired glucose tolerance and impaired fasting glucose

Impaired glucose tolerance (IGT) and impaired fasting glucose (IFG) are intermediate states in glucose metabolism that exist between normal glucose tolerance and overt diabetes. Epidemiological studies demonstrate that the two categories describe distinct populations with only partial overlap, suggesting that different metabolic abnormalities characterize IGT and IFG. Insulin resistance and impaired beta-cell function, the primary defects observed in type 2 diabetes, both can be detected in subjects with IGT and IFG. However, clinical studies suggest that the site of insulin resistance varies between the two disorders. While subjects with IGT have marked muscle insulin resistance with only mild hepatic insulin resistance, subjects with IFG have severe hepatic insulin resistance with normal or near-normal muscle insulin sensitivity. Both IFG and IGT are characterized by a reduction in early-phase insulin secretion, while subjects with IGT also have impaired late-phase insulin secretion. The distinct metabolic features present in subjects with IFG and IGT may require different therapeutic interventions to prevent their progression to type 2 diabetes.

Different contributions of insulin resistance and beta-cell dysfunction in overweight Israeli Arabs with IFG and IGT

BACKGROUND

Impaired glucose tolerance (IGT) and impaired fasting glucose (IFG) are both intermediate stages that exist between normal glucose tolerance and overt type 2 diabetes. Epidemiological studies demonstrated that the two categories define distinct populations. In this study, we examined the contributions of insulin resistance and beta-cell dysfunction to both states in overweight subjects of Arab origin.

METHODS

Twelve subjects with isolated IFG, 10 with isolated IGT, and 20 with IFG and IGT (combined glucose in tolerance-CGT) were compared with 30 subjects with normal glucose tolerance (NGT) subjects; all were of Arab origin and were overweight or obese. Different indices for insulin resistance and beta-cell function were calculated from oral glucose tolerance (OGTT) values.

RESULTS

Subjects with isolated IFG and CGT were more obese and had significantly higher values of insulin resistance than subjects with isolated IGT and NFG. There was no significant difference between the insulin resistance in subjects with isolated IGT and that in subjects with NGT. Indices of beta cell function were severely reduced among subjects with isolated IGT and CGT when compared with those with both isolated IFG and NGT, while subjects with isolated IFG had similar beta-cell indices to subjects with NGT.

CONCLUSION

These data demonstrate that beta-cell dysfunction and insulin resistance contribute differently to the pathogenesis of IFG and IGT among overweight Arab subjects.

Role of the renin-angiotensin system in the endocrine pancreas: implications for the development of diabetes

Activation of the renin-angiotensin system has a pivotal role in the pathogenesis of diabetic complications. However, recent evidence suggests that it may also contribute to the development of diabetes itself. In the endocrine pancreas, all the components of an active renin-angiotensin system are present, which modulate a range of activities including local blood flow, hormone release and prostaglandin synthesis. In both types 1 and 2 diabetes, there is an up-regulation of its expression and activity in the endocrine pancreas. Whether these changes have a direct pathogenetic role or reflect a response to local stress or tissue injury remains to be established. Angiotensin-mediated increases in oxidative stress, inflammation and free fatty acids levels potentially contribute to beta-cell dysfunction in diabetes. In addition, activation of the renin-angiotensin system appears to potentiate the action of other pathogenic pathways including glucotoxicity, lipotoxicity and advanced glycation. In experimental models of type 2 diabetes, blockade of the renin-angiotensin system with angiotensin converting enzyme inhibitors or angiotensin receptor antagonists results in the improvement of islet structure and function. Moreover, the incidence of de novo diabetes appears to be significantly reduced by blockade of the renin-angiotensin system in clinical studies. At least two large controlled trials are currently underway to study the role of renin-angiotensin system in the development of diabetes. It is hoped that these studies will demonstrate the true potential of the blockade of the renin-angiotensin system for the prevention of diabetes.

Type 2 diabetes: principles of pathogenesis and therapy

Type 2 diabetes mellitus has become an epidemic, and virtually no physician is without patients who have the disease. Whereas insulin insensitivity is an early phenomenon partly related to obesity, pancreas beta-cell function declines gradually over time already before the onset of clinical hyperglycaemia. Several mechanisms have been proposed, including increased non-esterified fatty acids, inflammatory cytokines, adipokines, and mitochondrial dysfunction for insulin resistance, and glucotoxicity, lipotoxicity, and amyloid formation for beta-cell dysfunction. Moreover, the disease has a strong genetic component, but only a handful of genes have been identified so far: genes for calpain 10, potassium inward-rectifier 6.2, peroxisome proliferator-activated receptor gamma, insulin receptor substrate-1, and others. Management includes not only diet and exercise, but also combinations of anti-hyperglycaemic drug treatment with lipid-lowering, antihypertensive, and anti platelet therapy.

A comparison of urinary albumin excretion rate and microalbuminuria in various glucose tolerance subjects

AIMS

To investigate the difference of urinary albumin excretion rate (UAER) and microalbuminuria (MAU) in various glucose tolerance subjects, especially between isolated-impaired glucose tolerance subjects and isolated-impaired fasting glycaemia subjects.

METHODS

A total of 2934 subjects were divided into five groups with various glucose tolerances, based on a 75-g oral glucose tolerance test. Microalbuminuria was defined when urinary albumin excretion rate was between 20 and 200 microg/min.

RESULTS

(i) The UAER in the newly diagnosed Type 2 diabetes mellitus group, impaired glucose tolerance/impaired fasting glycaemia group and isolated-impaired glucose tolerance group were all higher than that in the isolated-impaired fasting glycaemia group and normal glucose tolerance group, but it was comparable between isolated-impaired fasting glycemia group and normal glucose tolerance group. The prevalence of MAU and the odds ratio for MAU with adjustment for age and sex in various glucose tolerance groups showed the same trend as the UAER. (ii) After adjusting for age and sex, there is a significant association between logUAER and independent risk factors (partial correlation coefficients: r = 0.26 for 2-h post-challenge blood glucose, r = 0.26 for systolic blood pressure, r = 0.27 for diastolic blood pressure, r = 0.27 for body mass index and r = -0.13 for high density lipoprotein-cholesterol, all P < 0.001). The risks for MAU were 2-h post-challenge blood glucose, body mass index and diastolic blood pressure, while high density lipoprotein-cholesterol was protective.

CONCLUSIONS

The urinary albumin excretion rate and prevalence of microalbuminuria were higher in isolated-impaired glucose tolerance subjects than those in isolated-impaired fasting glycaemia subjects. At early abnormal glucose tolerance stage, the increasing post-challenge glycaemia might be a more important risk factor for urinary albumin excretion rate and microalbuminuria than increasing fasting glycaemia.

Impaired fasting glucose vs. glucose intolerance in pre-menopausal women: distinct metabolic entities and cardiovascular disease risk?

BACKGROUND

Impaired glucose tolerance (IGT) is associated with an increased cardiovascular disease risk. Less is known about cardiovascular disease risk among subjects with impaired fasting glucose (IFG) or with combined IFG and IGT.

AIMS

To compare body composition, body fat distribution, plasma glucose-insulin homeostasis and plasma lipid-lipoprotein profile between pre-menopausal women having either a normal glucose tolerance (NGT), isolated IFG, isolated IGT or combined IFG and IGT.

METHODS

Three hundred and thirty-four women with NGT, 11 women with IFG, 35 women with IGT and 10 women with both IFG and IGT were studied.

RESULTS

Women with IFG were characterized by a higher visceral adipose tissue (AT) accumulation than women with NGT (P < 0.05). Also, they were characterized by a higher subcutaneous AT area and by higher body fat mass than NGT and IGT women (P < 0.05). However, their lipid-lipoprotein profile was comparable with that of NGT women, except for reduced HDL-cholesterol concentrations (P < 0.05). After adjustment for visceral AT, women with IFG had lower total cholesterol, LDL-cholesterol and apolipoprotein B (apoB) levels than the three other groups. They also had lower HDL(2)-cholesterol than NGT women and lower total cholesterol/HDL-cholesterol ratio than IGT women. Women with IGT showed higher triglyceride and apoB concentrations and a higher total cholesterol/HDL-cholesterol ratio than women with NGT (P < 0.05). Overall, women with combined IFG and IGT showed body fatness characteristics and alterations in their metabolic risk profile which were essentially similar to women with isolated IGT.

CONCLUSIONS

These results indicate that there are significant differences in anthropometric and metabolic variables between pre-menopausal women with IFG vs. IGT and that the association between body fatness-body fat distribution indices and the metabolic profile may differ between IFG and IGT women.

Insulin-like growth factors and pancreas beta cells

Abstract Insulin-like growth factors (IGFs) have been implicated in normal growth, and especially foetal pancreas beta-cell development. As low birth weight has been implicated in the development of obesity and type 2 diabetes, much research has evolved into the importance of IGF and their signalling pathways for pancreas beta-cell development, and for type 2 diabetes. Insulin-like growth factor-I signalling has a lot in common with insulin signalling, and is involved in diverse cellular effects such as antiapoptosis, protein synthesis, cell growth and mitogenesis. Insulin-like growth factor-II can be bound by the insulin receptor A subtype and the IGF-1 receptor, which may explain its antiapoptotic effect. Various knock-out model studies indicate that absence of IGF-I or the IGF-1 receptor is critical for foetal and postnatal growth. Similarly, knock-out models of post-receptor molecules (such as IRS-2) point to the physiological role of IGFs for pancreas beta-cell development. A beta-cell-specific IGF-1 receptor knock out model indicates the importance of IGF-I for beta-cell function. The Goto-Kakizaki (GK) rat, a model for diabetes, has insufficient beta-cell development, which may be related to its defective IGF-II synthesis. As normal pancreas beta cells adapt to the prevailing insulin resistance with increasing beta-cell function, it is possible that insulin resistance interacts with IGF signalling in pancreas beta cells.

Genetic factors and insulin secretion: gene variants in the IGF genes

IGFs are important regulators of pancreatic beta-cell development, growth, and maintenance. Mutations in the IGF genes have been found to be associated with type 2 diabetes, myocardial infarction, birth weight, and obesity. These associations could result from changes in insulin secretion. We have analyzed glucose-stimulated insulin secretion using hyperglycemic clamps in carriers of a CA repeat in the IGF-I promoter and an ApaI polymorphism in the IGF-II gene. Normal and impaired glucose-tolerant subjects (n = 237) were independently recruited from three different populations in the Netherlands and Germany to allow independent replication of associations. Both first- and second-phase insulin secretion were not significantly different between the various IGF-I or IGF-II genotypes. Remarkably, noncarriers of the IGF-I CA repeat allele had both a reduced insulin sensitivity index (ISI) and disposition index (DI), suggesting an altered balance between insulin secretion and insulin action. Other diabetes-related parameters were not significantly different for both the IGF-I and IGF-II gene variant. We conclude that gene variants in the IGF-I and IGF-II genes are not associated with detectable variations in glucose-stimulated insulin secretion in these three independent populations. Further studies are needed to examine the exact contributions of the IGF-I CA repeat alleles to variations in ISI and DI.

Predominant role of reduced beta-cell sensitivity to glucose over insulin resistance in impaired glucose tolerance

AIMS/HYPOTHESIS

Impaired glucose tolerance (IGT) is an insulin-resistant state and a risk factor for Type 2 diabetes. The relative roles of insulin resistance and insulin deficiency in IGT have been disputed.

METHODS

In 40 IGT subjects and 63 sex-, age-, and weight-matched controls with normal glucose tolerance (NGT), we measured (i) indices of insulin sensitivity of fasting glucose production (by tracer glucose) and glucose disposal (M value on a 240 pmol x min(-1) x m(-2) insulin clamp) and (ii) indices of beta-cell function (glucose sensitivity, rate sensitivity, and potentiation) derived from model analysis (Am J Physiol 283:E1159-E1166, 2002) of the insulin secretory response (by C-peptide deconvolution) to oral glucose.

RESULTS

In comparison with NGT, IGT were modestly insulin resistant (M=29+/-2 vs 35+/-2 micromol x min(-1) x kg(FFM)(-1), p=0.01); insulin sensitivity of glucose production also was reduced, in approximate proportion to M. Despite higher baseline insulin secretion rates, IGT was characterized by a 50% reduction in glucose sensitivity [53 (36) vs 102 (123) pmol x min(-1) x m(-2) x mM(-1), median (interquartile range), p=0.001] and impaired potentiation [1.6 (0.8) vs 2.0 (1.5) units, p<0.04] of insulin release, whereas rate sensitivity [1.15 (1.15) vs 1.38 (1.28) nmol x m(-2) x mM(-1)] was not significantly reduced. Glucose sensitivity made the single largest contribution (approximately 50%) to the observed variability of glucose tolerance.

CONCLUSION/INTERPRETATION

In IGT the defect in glucose sensitivity of insulin release quantitatively predominates over insulin resistance in the genesis of the reduced tolerance to oral glucose.

Variations in insulin secretion in carriers of the E23K variant in the KIR6.2 subunit of the ATP-sensitive K(+) channel in the beta-cell

An association between type 2 diabetes and genetic variation in the KIR6.2 gene has been reported in several populations. Based on in vitro studies with cell lines expressing the Glu(23)Lys (E23K) mutation, it was recently suggested that this mutation might result in altered insulin secretion. We have examined glucose-stimulated insulin secretion in relation to this KIR6.2 gene variant in two independent Dutch cohorts. Subjects with normal (n = 65) or impaired (n = 94) glucose tolerance underwent 3-h hyperglycemic clamps at 10 mmol/l glucose. We did not observe significant differences in first- or second-phase insulin secretion between carriers and noncarriers of the gene variant in either of the study populations (all P > 0.45). Furthermore, we found no evidence for a significant interaction with disease-associated gene variants in the sulfonylurea receptor (SUR1) gene. We conclude that the E23K mutation in the KIR6.2 gene is not associated with detectable alterations in glucose-stimulated insulin secretion in two independent populations from the Netherlands.