Pathophysiology of insulin secretion in non-insulin-dependent diabetes mellitus

Induction of remission in diabetes by lowering blood glucose

As diabetes continues to grow as major health problem, there has been great progress in understanding the important role of pancreatic beta-cells in its pathogenesis. Diabetes develops when the normal interplay between insulin secretion and the insulin sensitivity of target tissues is disrupted. With type 2 diabetes (T2D), glucose levels start to rise when beta-cells are unable to meet the demands of insulin resistance. For type 1 diabetes (T1D) glucose levels rise as beta-cells are killed off by autoimmunity. In both cases the increased glucose levels have a toxic effect on beta-cells. This process, called glucose toxicity, has a major inhibitory effect on insulin secretion. This beta-cell dysfunction can be reversed by therapies that reduce glucose levels. Thus, it is becoming increasingly apparent that an opportunity exists to produce a complete or partial remission for T2D, both of which will provide health benefit.

Time Course of Normalization of Functional β-Cell Capacity in the Diabetes Remission Clinical Trial After Weight Loss in Type 2 Diabetes

OBJECTIVE

To assess functional β-cell capacity in type 2 diabetes during 2 years of remission induced by dietary weight loss.

RESEARCH DESIGN AND METHODS

A Stepped Insulin Secretion Test with Arginine was used to quantify functional β-cell capacity by hyperglycemia and arginine stimulation. Thirty-nine of 57 participants initially achieved remission (HbA_1c <6.5% [<48 mmol/mol] and fasting plasma glucose <7 mmol/L on no antidiabetic drug therapy) with a 16.4 ± 7.7 kg weight loss and were followed up with supportive advice on avoidance of weight regain. At 2 years, 20 participants remained in remission in the study. A nondiabetic control (NDC) group, matched for age, sex, and weight after weight loss with the intervention group, was studied once.

RESULTS

During remission, median (interquartile range) maximal rate of insulin secretion increased from 581 (480-811) pmol/min/m² at baseline to 736 (542-998) pmol/min/m² at 5 months, 942 (565-1,240) pmol/min/m² at 12 months (P = 0.028 from baseline), and 936 (635-1,435) pmol/min/m² at 24 months (P = 0.023 from baseline; n = 20 of 39 of those initially in remission). This was comparable to the NDC group (1,016 [857-1,507] pmol/min/m²) by 12 (P = 0.064) and 24 (P = 0.244) months. Median first-phase insulin response increased from baseline to 5 months (42 [4-67] to 107 [59-163] pmol/min/m²; P < 0.0001) and then remained stable at 12 and 24 months (110 [59-201] and 125 [65-166] pmol/min/m², respectively; P < 0.0001 vs. baseline) but lower than that of the NDC group (250 [226-429] pmol/min/m²; P < 0.0001).

CONCLUSIONS

A gradual increase in assessed functional β-cell capacity occurred after weight loss, becoming similar to that of NDC group participants by 12 months. This result was unchanged at 2 years with continuing remission of type 2 diabetes.

Anti-diabetic activities of agaropectin-derived oligosaccharides from Gloiopeltis furcata via regulation of mitochondrial function

The aim of the present study was to investigate whether agaropectin-derived oligosaccharides from Gloiopeltis furcata (SAOs) exert an anti-diabetic effect in sodium palmitate (PA)-induced insulin resistant HepG2 cells. We found that SAOs were co-localized with mitochondria and regulated mitochondrial function. SAOs reduced respiratory chain activities, which led to reduced respiratory oxygen consumption and increased the cellular ADP/ATP ratio in a certain degree of dose-dependent manner. Thus, SAOs alleviated the oxidative stress state in PA-treated cells and, moreover, concurrently regulated the ROS-JNK-IRS-1 pathway. As a result, SAOs enhanced insulin sensitivity and glucose metabolism by activating the IRS-1-AKT-GSK-3β-GS pathway. Additionally, SAOs activated AMPK through both PKA-LKB1 and mitochondrial-regulated energy metabolism pathways. Therefore, SAOs decreased accumulation of lipids and improved lipid metabolism via regulating HMGCR, ACC and SREBP-1 proteins in HepG2 cells. Taken together, we conclude that SAOs could significantly ameliorate diabetic states in vitro via regulating mitochondria and their downstream signaling pathways.

Development of therapeutic options on type 2 diabetes in years: Glucagon-like peptide-1 receptor agonist’s role intreatment; from the past to future

Diabetes mellitus (DM) is a chronic metabolic disease characterized by hypergly-cemia. Type 2 diabetes (T2DM) accounting for 90% of cases globally. The worldwide prevalence of DM is rising dramatically over the last decades, from 30 million cases in 1985 to 382 million cases in 2013. It’s estimated that 451 million people had diabetes in 2017. As the pathophysiology was understood over the years, treatment options for diabetes increased. Incretin-based therapy is one of them. Glucagon-like peptide-1 receptor agonist (GLP-1 RA) not only significantly lower glucose level with minimal risk of hypoglycemia but also, they have an important advantage in themanagement of cardiovascular risk and obesity. Thus, we will review here GLP-1 RAsrole in the treatment of diabetes.

Higher C-Peptide Level During Glucose Clamp Is Associated With Muscle Insulin Resistance in Nonobese Japanese Men

Context

Circulating C-peptide is generally suppressed by exogenous insulin infusion. However, steady-state serum C-peptide (SS_SC) levels during hyperinsulinemic-euglycemic clamp in obese subjects are higher than in healthy subjects, which may contribute to hyperinsulinemia to compensate for insulin resistance. Even in healthy subjects, interindividual variations in SS_SC levels are present; however, the characteristics of subjects with high SS_SC levels in those populations have not been fully elucidated.

Objective

To investigate the clinical parameters associated with interindividual variations in SS_SC levels in apparently healthy, nonobese Japanese men.

Design and Participants

We studied 49 nonobese (BMI < 25 kg/m²), healthy Japanese men. We evaluated SS_SC and insulin sensitivity using hyperinsulinemic-euglycemic clamp with tracer. Intrahepatic lipid (IHL) was measured using proton magnetic resonance spectroscopy.

Results

We divided subjects into high and low SS_SC groups based on the median SS_SC value and compared their clinical parameters. Compared with the low SS_SC group, the high SS_SC group had IHL accumulation, impaired muscle insulin sensitivity, reduced insulin clearance, and hyperinsulinemia during a 75-g oral glucose tolerance test (OGTT). All of these factors were significantly correlated with SS_SC.

Conclusions

In healthy, nonobese men, higher SS_SC was associated with impaired muscle insulin sensitivity, IHL accumulation, and hyperinsulinemia during OGTT. These findings suggest that higher endogenous insulin secretion during hyperinsulinemia, along with reduced insulin clearance, may be an early change to maintain metabolic status in the face of moderate muscle insulin resistance, even in healthy, nonobese men.

Review of methods for measuring β-cell function: Design considerations from the Restoring Insulin Secretion (RISE) Consortium

The Restoring Insulin Secretion (RISE) study was initiated to evaluate interventions to slow or reverse the progression of β-cell failure in type 2 diabetes (T2D). To design the RISE study, we undertook an evaluation of methods for measurement of β-cell function and changes in β-cell function in response to interventions. In the present paper, we review approaches for measurement of β-cell function, focusing on methodologic and feasibility considerations. Methodologic considerations included: (1) the utility of each technique for evaluating key aspects of β-cell function (first- and second-phase insulin secretion, maximum insulin secretion, glucose sensitivity, incretin effects) and (2) tactics for incorporating a measurement of insulin sensitivity in order to adjust insulin secretion measures for insulin sensitivity appropriately. Of particular concern were the capacity to measure β-cell function accurately in those with poor function, as is seen in established T2D, and the capacity of each method for demonstrating treatment-induced changes in β-cell function. Feasibility considerations included: staff burden, including time and required methodological expertise; participant burden, including time and number of study visits; and ease of standardizing methods across a multicentre consortium. After this evaluation, we selected a 2-day measurement procedure, combining a 3-hour 75-g oral glucose tolerance test and a 2-stage hyperglycaemic clamp procedure, augmented with arginine.

Baicalin and its metabolites suppresses gluconeogenesis through activation of AMPK or AKT in insulin resistant HepG-2 cells

Scutellaria baicalensis Georgi (S. baicalensis), as a traditional Chinese herbal medicine, is an important component of several famous Chinese medicinal formulas for treating patients with diabetes mellitus. Baicalin (BG), a main bioactive component of S. baicalensis, has been reported to have antidiabetic effects. However, pharmacokinetic studies have indicated that BG has poor oral bioavailability. Therefore, it is hard to explain the pharmacological effects of BG in vivo. Interestingly, several reports show that BG is extensively metabolized in rats and humans. Therefore, we speculate that the BG metabolites might be responsible for the pharmacological effects. In this study, BG and its three metabolites (M1-M3) were examined their effects on glucose consumption in insulin resistant HepG-2 cells with a commercial glucose assay kit. Real-time PCR and western blot assay were used to confirm genes and proteins of interest, respectively. The results demonstrate that BG and its metabolites (except for M3) enhanced the glucose consumption which might be associated with inhibiting the expression of the key gluconeogenic genes, including glucose-6-phosphatase (G6Pase), phosphoenolypyruvate carboxykinase (PEPCK) and glucose transporter 2 (GLUT2). Further study found that BG and M1 could suppress hepatic gluconeogenesis via activation of the AMPK pathway, while M2 could suppress hepatic gluconeogenesis via activation of the PI3K/AKT signaling pathway. Taken together, our findings suggest that both BG and its metabolites have antihyperglycemic activities, and might be the active forms of oral doses of BG in vivo.

Effects of Allium hookeri root water extracts on inhibition of adipogenesis and GLUT-4 expression in 3T3-L1 adipocytes

Anti-adipogenic and antidiabetic activities of Allium hookeri root water extracts (ARW) were assessed. Oil Red O staining showed that treatment with ARW caused a dose-dependent reduction in lipid accumulation. ARW was also involved in adipocyte lipolysis via LPL activity, and in the concentration of glycerol in a culture medium. On the basis of the concentration of adipokines following ARW treatment, ARW appeared to inhibit expression of PPAR-γ, to reduce concentrations of leptin and resistin, to increase the concentration of adiponectin, and to inhibit lipid accumulation. ARW modulated adipokine expression associated with insulin resistance and sensitivity. 3T3-L1 adipocytes treated with ARW showed increased GLUT-4 expression with increased glucose uptake into adipocytes. ARW showed effectiveness for improvement of diabetic conditions.

Pathophysiology and treatment of type 2 diabetes: perspectives on the past, present, and future

Glucose metabolism is normally regulated by a feedback loop including islet β cells and insulin-sensitive tissues, in which tissue sensitivity to insulin affects magnitude of β-cell response. If insulin resistance is present, β cells maintain normal glucose tolerance by increasing insulin output. Only when β cells cannot release sufficient insulin in the presence of insulin resistance do glucose concentrations rise. Although β-cell dysfunction has a clear genetic component, environmental changes play an essential part. Modern research approaches have helped to establish the important role that hexoses, aminoacids, and fatty acids have in insulin resistance and β-cell dysfunction, and the potential role of changes in the microbiome. Several new approaches for treatment have been developed, but more effective therapies to slow progressive loss of β-cell function are needed. Recent findings from clinical trials provide important information about methods to prevent and treat type 2 diabetes and some of the adverse effects of these interventions. However, additional long-term studies of drugs and bariatric surgery are needed to identify new ways to prevent and treat type 2 diabetes and thereby reduce the harmful effects of this disease.

Profile of vildagliptin in type 2 diabetes: efficacy, safety, and patient acceptability

Vildagliptin is a selective and potent dipeptidyl peptidase-4 inhibitor that improves glycemic control by inhibiting the degradation of both endogenous glucagon-like peptide-1 and glucose-dependent insulinotropic peptide. This article is a comprehensive review of the safety and efficacy of vildagliptin in patients with type 2 diabetes. Clinical evidence has proven that it effectively decreases hemoglobin A_1c with a low risk of hypoglycemia and is weight neutral. The addition of vildagliptin to metformin improves glucose control and significantly reduces gastrointestinal adverse events, particularly in patients inadequately controlled with metformin monotherapy. Its long-term advantages include preservation of β-cell function, reduction in total cholesterol, decrease in fasting lipolysis in adipose tissue, and triglyceride storage in non-fat tissues. Vildagliptin is well tolerated with a low incidence of AEs, and it does not increase the risk of cardiovascular/cerebrovascular (CCV) events. It can be taken before or after meals, and has little drug interaction, thus it will be well accepted.

The protective effect of berberine on β-cell lipoapoptosis

AIMS

To evaluate the protective effect of berberine on β-cell lipoapoptosis induced by palmitate and to explore the possible underlying mechanisms.

MATERIALS AND METHODS

HIT-T15 pancreatic β-cells were divided into the following treatment groups: untreated controls; 100 μM berberine; 0.5 mM palmitate; 0.5 mM palmitate + 0.1 μM berberine; 0.5 mM palmitate + 1 μM berberine; 0.5 mM palmitate + 10 μM berberine; and 0.5 mM palmitate + 100 μM berberine. After 48 h, cell apoptosis was assessed by flow cytometry and the Hoechst 33258 fluorescent assay. Basal and glucose-stimulated insulin levels in culture medium were measured by radioimmunoassay. Peroxisome proliferator- activated receptor-γ (PPAR-γ) mRNA and protein levels were determined by real-time PCR and immunocytochemistry, respectively.

RESULTS

Apoptosis was significantly increased upon treatment with palmitate as compared to the untreated controls (p<0.0001). In addition, glucose-stimulated insulin secretion (GSIS), PPAR-γ mRNA and protein expression were significantly reduced in response to palmitate (p<0.0001); however, palmitate-induced apoptosis and reduction in PPAR-γ expression were reversed in response to berberine in a dose-dependent manner (p<0.05). Furthermore, there was a non-significant increase in GSIS with increasing berberine dose.

CONCLUSION

Palmitate exerted lipotoxic effects on HIT-T15 cells, inducing apoptosis and reducing GSIS. Berberine reduced palmitate-induced lipoapoptosis and tended to increase GSIS in HIT-T15 cells, possibly through increased PPAR-γ expression.

Hypoglycemic and insulin-sensitizing effects of berberine in high-fat diet- and streptozotocin-induced diabetic rats

Hypoglycemic effects of berberine (BBR) have been reported in several studies in cell and animal models. However, the mechanisms of action are not fully understood. The present study was therefore aimed at determining the effect and underlying mechanisms of action of BBR on diabetes in a high-fat diet- and streptozotocin-induced diabetic rat model. Ninety male Sprague-Dawley rats, 150 to 170 g, were housed individually in cages. Two groups (n = 12 each) were fed the AIN-93G diet (normal control) and the same diet modified to contain 33% fat and 2% cholesterol (high-fat control), respectively. The third group (n = 66) was fed the high-fat diet and injected intraperitoneally 2 weeks later with 35 mg/kg body weight of streptozotocin in citrate buffer (pH 4.5). The rats in both control groups were injected with the vehicle. After 12 days, rats with semifasting (5 hours) blood glucose levels between 14 and 25 mmol/L were divided into 4 groups (n = 12 each) and treated with 0 (diabetic control), 50, 100, and 150 mg/kg/d of BBR for 6 weeks while continuing on the high-fat diet. Hypoglycemic effects of BBR were consistently demonstrated by semifasting and fasting blood glucose levels, and insulin-sensitizing effects were seen during oral glucose tolerance testing. Berberine also reduced food intake while having no effect on body weight in diabetic rats. No effect of BBR was observed on plasma levels of insulin, adipokines (leptin and adiponectin), or inflammatory cytokines (tumor necrosis factor-α and C-reactive protein). Berberine did not affect the state of oxidative stress as assessed by the activity of superoxide dismutase and the concentrations of malondialdehyde and reduced and oxidized glutathione in the liver. These findings demonstrated the hypoglycemic and insulin-sensitizing capabilities of BBR, with the underlying mechanisms awaiting further investigation.

Determinants of glucose control in patients with chronic pancreatitis

AIMS/HYPOTHESIS

Diabetes frequently develops in patients with chronic pancreatitis (CP). Partial pancreatectomy has emerged as a treatment option for such patients. We addressed whether the development of diabetes in CP patients is related to pancreatic beta cell area or clinical variables, and which factors predict the diabetes risk after partial pancreatectomy.

METHODS

Fractional beta cell area was determined in pancreatic tissue samples obtained from 114 CP patients undergoing pancreatic surgery and related to measures of glucose control, as well as clinical and anthropometric data. Seventy-four patients without diabetes at the time of surgery were contacted again 2.5 +/- 1.0 years after partial pancreatectomy in order to obtain information about the post-operative development of diabetes.

RESULTS

In the surgical samples in the whole cohort, pancreatic beta cell area was 0.40 +/- 0.06% in patients with and 0.64 +/- 0.06% in those without previously known diabetes (p = 0.039). There was an inverse non-linear relationship between pancreatic beta cell area and fasting glucose concentrations (r = 0.29) as well as HbA(1c) levels (r = 0.36). Nineteen out of 74 previously normoglycaemic patients (26%) developed diabetes over an average period of 2.5 years of follow-up. Pre-operative fasting glucose levels, HbA(1c) and BMI were identified as predictors of diabetes after partial pancreatectomy. However, pancreatic beta cell area did not differ in those who subsequently developed diabetes (0.66 +/- 0.15%) and those who did not (0.62 +/- 0.08%, p = 0.45).

CONCLUSIONS/INTERPRETATION

Hyperglycaemia in CP patients is associated with reduced beta cell area. However, reduced beta cell area does not predict the development of diabetes, suggesting that other factors are more important determinants of alterations in glucose metabolism in patients with CP.

CS-917, a fructose 1,6-bisphosphatase inhibitor, improves postprandial hyperglycemia after meal loading in non-obese type 2 diabetic Goto-Kakizaki rats

Postprandial hyperglycemia is one of the features of type 2 diabetes. Increased hepatic gluconeogenesis is a predominant cause of postprandial hyperglycemia in type 2 diabetes. In this study, we evaluated the effect of gluconeogenesis inhibition on postprandial hyperglycemia using CS-917, a novel inhibitor of fructose 1,6-bisphphosphatase (FBPase) which is one of the rate-limiting enzymes of gluconeogenesis. The suppressive effect of CS-917 on postprandial hyperglycemia was evaluated in a meal loading test in Goto-Kakizaki (GK) rats, non-obese type 2 diabetic animal model characterized by impaired insulin secretion. In addition, we describe acute effect of CS-917 on fasting hyperglycemia in overnight-fasted GK rats and chronic effect of CS-917 in multiple dosing GK rats.CS-917 suppressed plasma glucose elevation after meal loading in a dose-dependent manner at doses ranging from 10 to 40 mg/kg. In an overnight-fasted state, CS-917 decreased the plasma glucose levels dose-dependently at doses ranging from 2.5 to 40 mg/kg. Consistent with the inhibition of FBPase, glucose-lowering was associated with an accumulation of hepatic d-fructose 1,6-bisphosphate and a reduction in hepatic d-fructose 6-phosphate. Chronic treatment of CS-917 decreased plasma glucose significantly, and no significant increase in plasma lactate and no profound elevation in plasma triglycerides were observed by both acute and chronic treatment of CS-917 in GK rats.These findings suggest that enhanced gluconeogenesis contributes to hyperglycemia in postprandial conditions as well as in fasting conditions, and that CS-917 as an FBPase inhibitor corrects postprandial hyperglycemia as well as fasting hyperglycemia.

An examination of beta-cell function measures and their potential use for estimating beta-cell mass

A characteristic and dominant feature of type 2 diabetes is a reduction in beta-cell function that is associated with a decrease in beta-cell volume. A decline in the first-phase insulin response following intravenous glucose administration can be demonstrated as the fasting glucose concentration increases. This response is completely absent before the glucose threshold that defines diabetes has been reached and at a time when beta-cells are clearly still present, implying that a functional beta-cell lesion has to exist independent of beta-cell loss. Surgical or chemical reductions of up to 65% of beta-cell volume demonstrate that functional adaptation of the normal beta-cell prevents a rise in fasting glucose or reduction in first-phase insulin response. However, the ability of glucose to potentiate the beta-cell's response to non-glucose secretagogues is reduced and is more closely associated with the reduction in beta-cell volume. The future, in terms of prevention and treatment of type 2 diabetes, lies in the ability to prevent and revert both beta-cell loss and dysfunction. However, until beta-cell volume can be quantified reliably and non-invasively, we will need to rely on the ability of glucose to potentiate insulin release as the best surrogate estimate of the number of beta-cells.

Anti-diabetic properties of chrysophanol and its glucoside from rhubarb rhizome

An ethanol extract of rhubarb rhizome exhibited marked glucose transport activity in differentiated L6 rat myotubes. Activity-guided fractionation resulted in the isolation of two anthraquinones, chrysophanol-8-O-beta-D-glucopyranoside (1) and chrysophanol (2). The anti-diabetic effect was examined by glucose transport activity, glucose transporter 4 (Glut4) expression in myotubes, and the level of insulin receptor (IR) tyrosine phosphorylation as influenced by tyrosine phosphatase 1B, each of which is a major target of diabetes treatment. Chrysophanol-8-O-beta-D-glucopyranoside up to 25 microM dose-dependently activated glucose transport in insulin-stimulated myotubes. Increased tyrosine phosphorylation of IR due to tyrosine phosphatase 1B inhibitory activity with an IC50 value of 18.34+/-0.29 microM and unchanged Glut4 mRNA levels was observed following chrysophanol-8-O-beta-D-glucopyranoside treatment. Chrysophanol up to 100 microM exerted mild glucose transport activity and elevated the tyrosine phosphorylation of IR via tyrosine phosphatase 1B inhibition (IC50=79.86+/-0.12 microM); Glut4 mRNA expression was also significantly increased by 100 microM. The ED50 values of the two compounds were 59.38+/-0.66 and 79.69+/-0.03 microM, respectively. Therefore, these two anthraquinones from rhubarb rhizome, chrysophanol-8-O-beta-D-glucopyranoside and chrysophanol, have mild cytotoxicity and anti-diabetic properties and could play metabolic roles in the insulin-stimulated glucose transport pathway.

Antidiabetic medications in overweight/obese patients with type 2 diabetes: drawbacks of current drugs and potential advantages of incretin-based treatment on body weight

The vast majority of patients with type 2 diabetes are overweight or obese. Lifestyle intervention to lose weight is recommended in most diabetic patients to improve glycaemic control and reduce associated risk factors for microvascular and macrovascular complications. Even modest weight loss can significantly improve glucose homeostasis and lessen cardiometabolic risk factors, although achieving this level of weight reduction remains difficult for many patients. Complicating the matter, many agents used to target hyperglycaemia are associated with weight gain, making management of overweight or obese patients with type 2 diabetes quite challenging. Incretin-based therapies with the new classes of glucagon-like peptide-1 mimetics (e.g. exenatide, liraglutide) and dipeptidyl peptidase 4 (DPP-4) inhibitors (e.g. sitagliptin, vildagliptin) may be of particular value in the treatment of overweight/obese type 2 diabetic patients because of their efficacy in improving glycaemic control and their favourable or neutral effects on body weight. In addition, DPP-4 inhibitors have a low risk for causing hypoglycaemia, undesirable gastrointestinal effects, or other prominent adverse effects that might limit their use. These classes of drugs hold promise for the treatment of type 2 diabetes, alone or in combination with other classes of antidiabetic agents.

Berberine stimulates glucose transport through a mechanism distinct from insulin

Berberine exerts a hypoglycemic effect, but the mechanism remains unknown. In the present study, the effect of berberine on glucose uptake was characterized in 3T3-L1 adipocytes. It was revealed that berberine stimulated glucose uptake in 3T3-L1 adipocytes in a dose- and time-dependent manner with the maximal effect at 12 hours. Glucose uptake was increased by berberine in 3T3-L1 preadipocytes as well. Berberine-stimulated glucose uptake was additive to that of insulin in 3T3-L1 adipocytes, even at the maximal effective concentrations of both components. Unlike insulin, the effect of berberine on glucose uptake was insensitive to wortmannin, an inhibitor of phosphatidylinositol 3-kinase, and SB203580, an inhibitor of p38 mitogen-activated protein kinase. Berberine activated extracellular signal-regulated kinase (ERK) 1/2, but PD98059, an ERK kinase inhibitor, only decreased berberine-stimulated glucose uptake by 32%. Berberine did not induce Ser473 phosphorylation of Akt nor enhance insulin-induced phosphorylation of Akt. Meanwhile, the expression and cellular localization of glucose transporter 4 (GLUT4) were not altered by berberine. Berberine did not increase GLUT1 gene expression. However, genistein, a tyrosine kinase inhibitor, completely blocked berberine-stimulated glucose uptake in 3T3-L1 adipocytes and preadipocytes, suggesting that berberine may induce glucose transport via increasing GLUT1 activity. In addition, berberine increased adenosine monophosphate-activated protein kinase and acetyl-coenzyme A carboxylase phosphorylation. These findings suggest that berberine increases glucose uptake through a mechanism distinct from insulin, and activated adenosine monophosphate-activated protein kinase seems to be involved in the metabolic effect of berberine.

Synthesis and antihyperglycemic evaluation of various protoberberine derivatives

Various berberine derivatives (2-17) were synthesized and their antihyperglycemic activities were evaluated in a model of beta-cell-membrane chromatography and a model of alloxan-induced diabetes mice. The results indicated that compounds 5 and 14 exhibited antihyperglycemic activity. Their structure-activity relationships were discussed.

Insulin sensitizing and insulinotropic action of berberine from Cortidis rhizoma

Our preliminary study demonstrated that 70% ethanol Cortidis Rhizoma extracts (CR) had a hypoglycemic action in diabetic animal models. We determined whether CR fractions acted as anti-diabetic agent, and a subsequent investigation of the action mechanism of the major compound, berberine ([C(20)H(18)NO(4)](+)), was carried out in vitro. The 20, 40 and 60% methanol fractions from the XAD-4 column contained the most insulin sensitizing activities in 3T3-L1 adipocytes. The common major peak in these fractions was berberine. Treatment with 50 microM berberine plus differentiation inducers significantly reduced triglyceride accumulation by decreased differentiation of 3T3-L1 fibroblasts to adipocytes and triglyceride synthesis. Significant insulin sensitizing activity was observed in 3T3-L1 adipocytes which were given 50 microM berberine plus 0.2 nM insulin to reach a glucose uptake level increased by 10 nM of insulin alone. This was associated with increased glucose transporter-4 translocation into the plasma membrane via enhancing insulin signaling pathways and the insulin receptor substrate-1-phosphoinositide 3 Kinase-Akt. Berberine also increased glucose-stimulated insulin secretion and proliferation in Min6 cells via an enhanced insulin/insulin-like growth factor-1 signaling cascade. Data suggested that berberine can act as an effective insulin sensitizing and insulinotropic agent. Therefore, berberine can be used as anti-diabetic agent for obese diabetic patients.

Metabolic response to oral lipid overload in diabetes and impaired glucose tolerance

Post-prandial hyperglycemia and hypertriglyceridemia have been related to atherogenesis. The aim of this study was to evaluate the response of plasma lipoproteins to a lipid overload in subjects with diabetes (DM), impaired glucose tolerance (IGT) and normals (N). Seventy-seven subjects were selected, 36-85 years, plasma glucose (G)<140 mg/dl and triglycerides (TG)<150 mg/dl; those without diabetes underwent a glucose tolerance test (GTT), which classified them into three groups: N, 2h G<140 mg/dl, n=37; IGT, 2h G 140-200mg/dl, n=20; and DM, previous diabetes or 2h G>200mg/dl, n=20. They were submitted to a clinical evaluation and an oral lipid overload (1000 kcal, 58% fat). Fasting, 4 and 6-h blood samples after the meal were collected for G, insulinaemia (I), TG, cholesterol and their fractions, and HOMA-IR. Fasting and post-lipid overload lipoproteins were similar between groups, but 6h TG was still high in DM versus IGT and N as compared to their 4h values. There was a positive correlation between fasting TG versus 6h TG (r=0.78, p<0.001). We conclude that individuals with impaired glucose tolerance and with diabetes mellitus have a slower plasma reduction of triglycerides after lipid overload, as well as an altered glucose and post-prandial insulin response.

Frequency of abnormal carbohydrate metabolism and diabetes in a population-based screening of adolescents

OBJECTIVE

To document the frequency of glucose intolerance in adolescents in a population-based study of primarily African-American/Non-Hispanic whites in an urban-suburban school district.

STUDY DESIGN

Measurement of fasting and 2-hour post-glucose load plasma glucose concentrations.

RESULTS

Carbohydrate intolerance (either impaired fasting glucose, impaired glucose tolerance, or both) was identified in 8.0%, near-diabetes (1 fasting glucose > or = 126 mg/dL [7.0 mmol/L] and/or 2-hour glucose > or = 200 mg/dL [11.1 mmol/L]) in 0.3%, and diabetes in 0.36% (type 1A = 0.24%; type 2 = 0.08%; undiagnosed type 2 = 0.04%). A model for abnormal carbohydrate metabolism was constructed with regression analysis in the Carbohydrate Intolerance (CI)/near-diabetes group and with logistic regression in the entire study population. Risk factors for the development of CI/near-diabetes included having a 1 unit increase in body mass index (BMI) z-score and either being non-Hispanic white or in the pubertal group. Increased fasting glucose correlated with having puberty and decreased BMI z-score, whereas 2-hour glucose correlated with increased BMI z-score. By using National Health and Nutrition Survey (NHANES) III (1988-1994) definitions, impaired fasting glucose was present in 2.0% in this study versus 1.7% (NHANES III).

CONCLUSION

The prevalence of CI/near-diabetes was 8.3%. Undiagnosed diabetes mellitus was rare. One third of adolescents with diabetes mellitus could be classified as having type 2 diabetes mellitus. The adult model of the progression of insulin resistance to type 2 diabetes mellitus in adolescents may be valid. Despite the increase in the overweight population since NHANES III, abnormalities in glucose metabolism have not changed significantly.

Long-term treatment with the Na+-glucose cotransporter inhibitor T-1095 causes sustained improvement in hyperglycemia and prevents diabetic neuropathy in Goto-Kakizaki Rats

We examined the effects of T-1095, an orally active inhibitor of Na(+)-glucose cotransporter (SGLT), on the development and severity of diabetes in Goto-Kakizaki (GK) rat, a spontaneous, non-obese model of type 2 diabetes. T-1095 was administered as dietary admixture (0.1% w/w) beginning at 7 weeks of age for 32 weeks. Untreated male GK rats were hyperglycemic compared with Wistar rats. Throughout the study, T-1095 treatment significantly decreased both blood glucose and hemoglobin A(1C) levels in the GK rats. The concomitant increase of urinary glucose excretion indicated that the hypoglycemic action of T-1095 is derived from the enhancement of urinary glucose disposal. Although food intake was not changed in the T-1095-treated rats, the body weight gain was retarded. T-1095 treatment partially ameliorated oral glucose tolerance but not the impaired glucose-induced insulin secretion. Homeostasis model assessment (HOMA) indicated the existence of insulin resistance in GK rats and a significant restoration by T-1095-treatment. There was a reduction of the thermal response in tail-flick testing following long-term hyperglycemia (diabetic neuropathy). Treatment of T-1095 significantly prevented the development of diabetic neuropathy in male GK rats. Sustained improvement of hyperglycemia and prevention of diabetic neuropathy by the T-1095-treatment provide further support the use of SGLT inhibitors for the treatment of diabetes.

Postprandial hyperglycaemia in type 2 diabetes: pathophysiological aspects, teleological notions and flags for clinical practice

Type 2 diabetes subjects carry an excess risk for micro- and macrovascular disease and a higher cardiovascular morbidity and mortality rate. The beneficial impact of tight glycaemic control-evidenced by the integrated marker of fasting glucose and postprandial glucose values, the HbA1c-for the prevention of microvascular complications is definitely confirmed. Over the past few years, several studies have identified postprandial hyperglycaemia as a better predictor of cardiovascular or even of all-cause mortality, as well as an independent risk factor for atherosclerosis. The continuous glucose monitoring could offer a rationale means for the detection of postprandial hyperglycaemia and ultimately for its effective management. Advances in technology keep a promise for a reliable, convenient and closer to the idea of the artificial endocrine pancreas glucose sensor. Subcutaneous glucose levels charted by one of the new sensors were found to be well correlated with venous glucose measurements. Intervention for a healthy lifestyle is frequently hampered by patients' poor compliance. The availability of diverse antidiabetic agents provides options for targeting the glycaemic goal and a choice more fitted to the particularized pathophysiology of each individual subject. Drugs targeting postprandial glycaemia may prove to represent the 'sine qua non' for the 'return' of postprandial glucose values at a 'non-deleterious' threshold, either as monotherapy for the early stages of the disease or as combination therapy later in the progression of diabetes.

Nateglinide alone or with metformin safely improves glycaemia to target in patients up to an age of 84

AIM

To assess the effect of nateglinide on efficacy [fasting plasma glucose (FPG), postprandial plasma glucose (PPG) plasma glucose and HbA1c], tolerability and safety in patients with type 2 diabetes mellitus (T2Dm) on diet alone or on metformin in subjects up to an age of 84.

METHODS

In an open-labelled 12-week, parallel study of 358 patients, aged 35-84 years with T2Dm, nateglinide was given as either monotherapy in patients previously on diet alone or low-dose sulfonylureas, which required washout before the study (group 1), or as an addition therapy in patients on steady dose of metformin (group 2). Nateglinide 120 mg was given before main meals. HbA1c, FPG and PPG values were taken at the time of breakfast at the beginning and the end of the study.

RESULTS

HbA1c fell by a mean of 0.83%, 95% confidence interval (CI) (-0.97, -0.69) (p < 0.001) in group 1, and 0.67%, 95% CI (-0.77, -0.58) (p < 0.001) in group 2. There was a significant improvement in PPG in group 1 by a mean reduction of -3.47 mmol/l, 95% CI (-4.08, -2.87) (p < 0.0001) and in group 2 of -2.41 mmol/l, 95% CI (-2.84, -1.99) (p < 0.0001). There was an improvement in FPG of -1.2 mmol/l, 95% CI (-1.49, -0.81) (p < 0.0001) and -0.8 mmol/l, 95% CI -(1.07, -0.53) (p < 0.0001) in group 1 and 2 respectively. 44% of patients in group 1 and 34% in group 2 achieved target of HbA1c < 7.0 and 66% in group 1 and 59% in group 2 achieved of HbA1c < 7.5%. Only one subject on nateglinide and metformin was withdrawn due to the side effect of hypoglycaemia. No patient required third-party assistance nor was admitted to hospital due to hypoglycaemia.

CONCLUSION

These data demonstrate that nateglinide is a safe and effective agent in treatment to target in patients with T2Dm up to an age of 84 years.

Engineering a new β-cell: a critical venture requiring special attention to constantly changing physiological needs

As both type 1 and type 2 diabetes are characterized by reduced islet beta-cell mass and impaired insulin secretion, engineering new beta-cells for replacement therapy is appealing. For this to be successful, the intricate peptide processing and secretory machinery of the beta-cell must be duplicated. Further, the engineered beta-cell must be capable of modulating its function in response to physiological changes such as puberty, pregnancy and aging, and to more short-term challenges such as infection, exercise and weight fluctuation. The new cell should have a low risk for recurrence of the primary disease and ensuring its survival should not be worse than diabetes itself.

Clinical pharmacokinetics of nateglinide: a rapidly-absorbed, short-acting insulinotropic agent

The prevalence and medical and economic impact of type 2 diabetes mellitus is increasing in Western societies. New agents have been developed that act primarily to reduce postprandial glucose excursions, which may be of particular significance now that postprandial glucose excursions are known to be correlated with cardiovascular morbidity and mortality. Nateglinide is a phenylalanine derivative that blocks K+ channels in pancreatic beta-cells, facilitating insulin secretion. Nateglinide sensitises beta-cells to ambient glucose, reducing the glucose concentration needed to stimulate insulin secretion. The pharmacokinetics of nateglinide are characterised by rapid absorption and elimination, with good (73%) bioavailability. Nateglinide is more rapidly absorbed when given 0-30 minutes prior to meal ingestion than if given during the meal. Nateglinide is extensively metabolised, primarily by cytochrome P450 2C9, and eliminated primarily by the kidney. Nateglinide pharmacokinetics are linear over the dose range 60-240 mg. No significant pharmacokinetic alterations occur in renally impaired patients, in the elderly, or in mildly hepatically impaired patients. Nateglinide administered prior to meals stimulates rapid, short-lived insulin secretion in a dose-dependent manner, thus decreasing mealtime plasma glucose excursions. Its effects on insulin secretion are synergistic with those of a meal. With increasing nateglinide doses, the risk of hypoglycaemia also increases, but its incidence is low. Even if a meal is missed, and the patient skips the dose of nateglinide (as recommended in the event of a missed meal), the incidence of subsequent hypoglycaemia remains low compared with long-acting agents. The postprandial insulinotropic effects of nateglinide are more rapid than those of repaglinide and more rapid and greater than those of glibenclamide (glyburide), while producing less prolonged insulin exposure and less risk of delayed hypoglycaemia. Further investigation is required to determine if nateglinide inhibition of postprandial glucose excursions will help to prevent diabetic complications or preserve pancreatic beta-cell function.

Gliclazide at a lower concentration than therapeutic dose increases the sensitivity of insulin secretion to glucose in perfused rat pancreas

OBJECTIVES

We studied the difference between effects of therapeutic dose and sub-therapeutic dose of gliclazide on the glucose-induced insulin secretion.

METHODS

The normal rat pancreas was isolated and perfused with Krebs-Ringer buffer containing 1-14 mmol/l glucose. Influcences of 0.25 and 2.5 microg/ml gliclazide on the glucose concentration-insulin secretion curve was examined.

RESULTS

Gliclazide at 0.25 microg/ml significantly potentiated 5-8 mmol/l glucose-induced insulin secretion (2.5 +/- 0.5 vs 1.0 +/- 0.3 mU for 15 min at 6.5 mmol/l glucose, P<0.01), but did not give influence on either 1-3 or 10-14 mmol/l glucose-induced insulin secretion. The glucose concentration, at which half-maximal insulin secretion was observed, was lower with gliclazide (5.9 mmol/l) than in the control (7.5 mmol/l). Gliclazide at 2.5 microg/ml markedly increased the maximally glucose-stimulated insulin secretion from 3.9 +/- 0.5 mU for 15 min in the control to 6.6 +/- 0.7 mU for 15 min (P<0.01). The half-maximal insulin secretion was observed at a lower glucose concentration (5.0 mmol/l) than in the absence of gliclazide.

CONCLUSION

Gliclazide in sub-therapeutically low dose has different effects on insulin secretion from in therapeutic dose, namely sharpens the insulin secretion sensitivity to glucose with no influence on the maximal insulin secretion. It is possible that low doses of gliclazide might be of interest in some type 2 diabetics whose main pathophysiology is the blunting of insulin secretion response to hyperglycemia.

Decreased beta-cell mass in diabetes: significance, mechanisms and therapeutic implications

Increasing evidence indicates that decreased functional beta-cell mass is the hallmark of both Type 1 and Type 2 diabetes. This underlies the absolute or relative insulin insufficiency in both conditions. In this For Debate, we consider the possible mechanisms responsible for beta-cell death and impaired function and their relative contribution to insulin insufficiency in diabetes. Beta-cell apoptosis and impaired proliferation consequent to hyperglycaemia is one pathway that could be operating in all forms of diabetes. Autoimmunity and other routes to beta-cell death are also considered. Recognition of decreased functional beta-cell mass and its overlapping multifactorial aetiology in diabetic states, leads us to propose a unifying classification of diabetes.

Effects of stevioside on glucose transport activity in insulin-sensitive and insulin-resistant rat skeletal muscle

Stevioside (SVS), a natural sweetener extracted from Stevia rebaudiana, has been used as an antihyperglycemic agent. However, little is known regarding its potential action on skeletal muscle, the major site of glucose disposal. Therefore, the purpose of the present study was to determine the effect of SVS treatment on skeletal muscle glucose transport activity in both insulin-sensitive lean (Fa/-) and insulin-resistant obese (fa/fa) Zucker rats. SVS was administered (500 mg/kg body weight by gavage) 2 hours before an oral glucose tolerance test (OGTT). Whereas the glucose incremental area under the curve (IAUC(glucose)) was not affected by SVS in lean Zucker rats, the insulin incremental area under the curve (IAUC(insulin)) and the glucose-insulin index (product of glucose and insulin IAUCs and inversely related to whole-body insulin sensitivity) were decreased (P<.05) by 42% and 45%, respectively. Interestingly, in the obese Zucker rat, SVS also reduced the IAUC(insulin) by 44%, and significantly decreased the IAUC(glucose) (30%) and the glucose-insulin index (57%). Muscle glucose transport was assessed following in vitro SVS treatment. In lean Zucker rats, basal glucose transport in type I soleus and type IIb epitrochlearis muscles was not altered by 0.01 to 0.1 mmol/L SVS. In contrast, 0.1 mmol/L SVS enhanced insulin-stimulated (2 mU/mL) glucose transport in both epitrochlearis (15%) and soleus (48%). At 0.5 mmol/L or higher, the SVS effect was reversed. Similarly, basal glucose transport in soleus and epitrochlearis muscles in obese Zucker rats was not changed by lower doses of SVS (0.01 to 0.1 mmol/L). However, these lower doses of SVS significantly increased insulin-stimulated glucose transport in both obese epitrochlearis and soleus (15% to 20%). In conclusion, acute oral SVS increased whole-body insulin sensitivity, and low concentrations of SVS (0.01 to 0.1 mmol/L) modestly improved in vitro insulin action on skeletal muscle glucose transport in both lean and obese Zucker rats. These results indicate that one potential site of action of SVS is the skeletal muscle glucose transport system.

Targeting postprandial hyperglycemia: a comparative study of insulinotropic agents in type 2 diabetes

This study was designed to compare the efficacy of three insulinotropic agents in the control of postprandial hyperglycemia in type 2 diabetes. Fifteen subjects with noninsulin-requiring type 2 diabetes were admitted to the General Clinical Research Center on four separate occasions. During the control study and following 7-10 d on each study medication, daylong glucose profiles were performed to investigate the effects of the assigned medication on postprandial hyperglycemia. During each admission, placebo or study medications were administered before three isocaloric meals as follows: immediate-release glipizide 30 min before breakfast and 30 min before supper, glipizide gastrointestinal therapeutic system (GITS) 30 min before breakfast, or nateglinide 120 mg 10 min before breakfast, before lunch, and before supper. Blood was drawn for analysis of glucose, insulin, and C-peptide at -0.05, 0, 0.25, 0.5, 1, 2, 3, and 4 h relative to each test meal. Immediate-release glipizide, nateglinide, or glipizide GITS administration resulted in significantly lower integrated daylong (glucose area under the curve) and peak glucose levels, compared with placebo. There were no significant differences in the daylong integrated glucose levels among the three study medications. The peak postbreakfast glucose level (but not glucose area under the curve) was lower with nateglinide, compared with either immediate-release glipizide or glipizide GITS. Postlunch and postdinner integrated glucose levels were significantly lower with immediate-release glipizide or glipizide GITS, compared with nateglinide. C-peptide levels were significantly higher with immediate-release glipizide, compared with glipizide GITS. Insulin levels did not differ among the three study medications. Once-daily glipizide GITS, twice-daily immediate-release glipizide, or three-times-a-day administration of nateglinide results in equivalent control of postmeal hyperglycemia in type 2 diabetes. The decision to prescribe one of these three insulinotropic agents should be based on factors such as the patient's ability to comply with complex dosing regimens, the need to control fasting hyperglycemia, the risk of interprandial hypoglycemia, and pharmacoeconomic considerations, rather than postprandial glucose-lowering efficacy.

The major diabetes prevention trials

Type 2 diabetes (T2D) is a devastating disease with multiple complications affecting many tissues, most notably the cardiovascular system. To be able to prevent a chronic disease such as T2D, certain requirements have to be met. Knowledge about its natural history with a preclinical phase, modifiable risk factors, effective and simple screening tools to identify high-risk subjects, and effective intervention that is affordable and acceptable are necessary. In addition, the efficacy of the intervention has to be proven under a clinical trial setting. Several major lifestyle intervention trials have been successfully carried out, with consistent results: the risk of T2D in high-risk subjects can be halved, the effect of lifestyle changes is rapid, and benefits are similar in different ethnic groups. Thus, the prevention of T2D is possible in most high-risk subjects, but how to achieve this at the population level remains a major challenge.

Insulin resistance is a poor predictor of type 2 diabetes in individuals with no family history of disease

In normoglycemic offspring of two type 2 diabetic parents, low insulin sensitivity (S(I)) and low insulin-independent glucose effectiveness (S(G)) predict the development of diabetes one to two decades later. To determine whether low S(I), low S(G,) or low acute insulin response to glucose are predictive of diabetes in a population at low genetic risk for disease, 181 normoglycemic individuals with no family history of diabetes (FH-) and 150 normoglycemic offspring of two type 2 diabetic parents (FH+) underwent i.v. glucose tolerance testing (IVGTT) between the years 1964-82. During 25 +/- 6 years follow-up, comprising 2,758 person years, the FH- cohort (54 +/- 9 years) had an age-adjusted incidence rate of type 2 diabetes of 1.8 per 1,000 person years, similar to that in other population-based studies, but significantly lower than 16.7 for the FH+ cohort. Even when the two study populations were subdivided by initial values of S(I) and S(G) derived from IVGTT's performed at study entry, there was a 10- to 20-fold difference in age-adjusted incidence rates for diabetes in the FH- vs. FH+ individuals with low S(I) and low S(G). The acute insulin response to glucose was not predictive of the development of diabetes when considered independently or when assessed as a function of S(I), i.e., the glucose disposition index. These data demonstrate that low glucose disposal rates are robustly associated with the development of diabetes in the FH+ individuals, but insulin resistance per se is not sufficient for the development of diabetes in individuals without family history of disease and strongly suggest a familial factor, not detectable in our current measures of the dynamic responses of glucose or insulin to an IVGTT is an important risk factor for type 2 diabetes. Low S(I) and low S(G), both measures of glucose disposal, interact with this putative familial factor to result in a high risk of type 2 diabetes in the FH+ individuals, but not in the FH- individuals.

Adaptation of ovine fetal pancreatic insulin secretion to chronic hypoglycaemia and euglycaemic correction

Fetal pancreatic adaptations to relative hypoglycaemia, a characteristic of intra-uterine growth restriction, may limit pancreatic beta-cell capacity to produce and/or secrete insulin. The objective of this study was to measure beta-cell responsiveness in hypoglycaemic (H) fetal sheep and ascertain whether a 5 day euglycaemic recovery period would restore insulin secretion capacity. Glucose-stimulated insulin secretion (GSIS) was measured in euglycaemic (E) control fetuses, fetuses made hypoglycaemic for 14 days, and in a subset of 14-day hypoglycaemic fetuses returned to euglycaemia for 5 days (R fetuses). Hypoglycaemia significantly decreased plasma insulin concentrations in H (0.13 +/- 0.01 ng ml(-1)) and R fetuses (0.11 +/- 0.01 ng ml(-1)); insulin concentrations returned to euglycaemic control values (0.30 +/- 0.01 ng ml(-1)) in R fetuses (0.29 +/- 0.04 ng ml(-1)) during their euglycaemic recovery period. Mean steady-state plasma insulin concentration during the GSIS study was reduced in H fetuses (0.40 +/- 0.07 vs. 0.92 +/- 0.10 ng ml(-1) in E), but increased (P < 0.05) in R fetuses (0.73 +/- 0.10 ng ml(-1)) to concentrations not different from those in the E group. Nonlinear modelling of GSIS showed that response time was greater (P < 0.01) in both H (15.6 +/- 2.8 min) and R (15.4 +/- 1.5 min) than in E fetuses (6.3 +/- 1.1 min). In addition, insulin secretion responsiveness to arginine was reduced by hypoglycaemia (0.98 +/- 0.11 ng ml(-1) in H vs. 1.82 +/- 0.17 ng ml(-1) in E, P < 0.05) and did not recover (1.21 +/- 0.15 ng ml(-1) in R, P < 0.05 vs. E). Thus, a 5 day euglycaemic recovery period from chronic hypoglycaemia reestablished GSIS to normal levels, but there was a persistent reduction of beta-cell responsiveness to glucose and arginine. We conclude that programming of pancreatic insulin secretion responsiveness can occur in response to fetal glucose deprivation, indicating a possible mechanism for establishing, in fetal life, a predisposition to type 2 diabetes.

The relative contributions of insulin resistance and beta-cell dysfunction to the pathophysiology of Type 2 diabetes

The relative contributions of insulin resistance and beta-cell dysfunction to the pathophysiology of Type 2 diabetes have been debated extensively. The concept that a feedback loop governs the interaction of the insulin-sensitive tissues and the beta cell as well as the elucidation of the hyperbolic relationship between insulin sensitivity and insulin secretion explains why insulin-resistant subjects exhibit markedly increased insulin responses while those who are insulin-sensitive have low responses. Consideration of this hyperbolic relationship has helped identify the critical role of beta-cell dysfunction in the development of Type 2 diabetes and the demonstration of reduced beta-cell function in high risk subjects. Furthermore, assessments in a number of ethnic groups emphasise that beta-cell function is a major determinant of oral glucose tolerance in subjects with normal and reduced glucose tolerance and that in all populations the progression from normal to impaired glucose tolerance and subsequently to Type 2 diabetes is associated with declining insulin sensitivity and beta-cell function. The genetic and molecular basis for these reductions in insulin sensitivity and beta-cell function are not fully understood but it does seem that body-fat distribution and especially intra-abdominal fat are major determinants of insulin resistance while reductions in beta-cell mass contribute to beta-cell dysfunction. Based on our greater understanding of the relative roles of insulin resistance and beta-cell dysfunction in Type 2 diabetes, we can anticipate advances in the identification of genes contributing to the development of the disease as well as approaches to the treatment and prevention of Type 2 diabetes.

Control of postprandial hyperglycemia: optimal use of short-acting insulin secretagogues

OBJECTIVE

This study was designed to compare the efficacy of acute premeal administration of glipizide versus nateglinide in controlling postprandial hyperglycemia in subjects with non-insulin-requiring type 2 diabetes.

RESEARCH DESIGN AND METHODS

A total of 20 subjects (10 female, 10 male) with non-insulin-requiring type 2 diabetes were admitted overnight to the General Clinical Research Center on four occasions. In random order, 10 mg glipizide (30 min premeal), 120 mg nateglinide (15 min premeal), 10 mg glipizide plus nateglinide (30 and 15 min premeal, respectively), or placebo pills (30 and 15 min premeal) were administered in a double-blind fashion before a standardized breakfast. Blood was drawn for analysis of glucose, insulin, and C-peptide at -0.05, 0, 0.5, 1, 2, 3, and 4 h relative to the meal.

RESULTS

The subjects were aged 56 +/- 2 years and were moderately obese (BMI 31 +/- 1 kg/m(2)), with a mean HbA(1c) of 7.4 +/- 0.4%. The peak postprandial glucose excursion above baseline was higher with placebo (6.1 +/- 0.5 mmol/l) than glipizide (4.3 +/- 0.6 mmol/l, P = 0.002), nateglinide (4.2 +/- 0.4 mmol/l, P = 0.001), or glipizide plus nateglinide (4.1 +/- 0.5 mmol/l, P = 0.001). The area under the curve for the glucose excursion above baseline was also higher with placebo (14.1 +/- 1.8 mmol/h. l) compared with glipizide (6.9 +/- 2.4 mmol/h. l, P = 0.002), nateglinide (9.7 +/- 2 mmol/h. l, P = 0.004), or glipizide plus nateglinide (5.6 +/- 2.2 mmol/h. l, P < 0.001). Peak and integrated glucose excursions did not differ significantly between glipizide and nateglinide. However, by 4 h postmeal, plasma glucose levels were significantly higher with nateglinide (9 +/- 0.9 mmol/l) compared with the premeal baseline (7.8 +/- 0.6 mmol/l, P = 0.04) and compared with the 4-h postprandial glucose level after administration of glipizide (7.6 +/- 0.6 mmol/l, P = 0.02). Integrated postprandial insulin levels were higher with glipizide (1,556 +/- 349 pmol/h. l) than nateglinide (1,364 +/- 231 pmol/h. l; P = 0.03). Early insulin secretion, as measured by insulin levels at 30 min postmeal, did not differ between glipizide and nateglinide.

CONCLUSIONS

Acute premeal administration of nateglinide or glipizide has equal efficacy in controlling postbreakfast hyperglycemia in type 2 diabetes when each drug is administered at the optimum time before the meal. Glipizide causes a more pronounced and sustained postmeal insulin secretory response compared with nateglinide. Glipizide facilitates the return to near-fasting glucose levels at 4 h postmeal, but with the possible risk of increased frequency of postmeal hypoglycemia in drug-naive patients. The clinical decision to use glipizide versus nateglinide should be based on factors other than the control of postprandial hyperglycemia in type 2 diabetes.

Nateglinide improves glycaemic control when added to metformin monotherapy: results of a randomized trial with type 2 diabetes patients

AIMS/HYPOTHESIS

This study evaluated the addition of nateglinide, a d-phenylalanine derivative that restores early phase insulin release, to metformin in type 2 diabetes patients stabilized on high-dose metformin.

METHODS

This multicentre, double-blind, parallel group trial included 467 metformin-treated patients with glycosylated haemoglobin (HbA1c) between 6.8% and 11%. Patients were randomized to add nateglinide 60 mg, 120 mg or placebo before three meals to metformin 1000 mg b.i.d. for 24 weeks.

RESULTS

HbA1c was significantly reduced with nateglinide 60 mg and 120 mg plus metformin compared with metformin control (-0.36%, p = 0.003; -0.59%, p < 0.001 respectively). Greater benefits occurred if patients had elevated HbA1c at baseline (-1.38% with nateglinide 120 mg in patients with HbA1c > 9.5%). A modest fasting plasma glucose reduction was observed. Most symptoms suggestive of hypoglycaemia occurred in patients with low HbA1c levels (<or= 8%) at baseline, although no confirmed cases of hypoglycaemia occurred with nateglinide 60 mg in this patient group. Events suggestive of hypoglycaemia were confirmed in 1.1% of cases (plasma glucose <or= 3.3 mmol/l). Weight gain over 24 weeks was 0.9 kg with nateglinide 120 mg vs. metformin alone, and plasma lipids remained unchanged.

CONCLUSIONS/INTERPRETATION

In patients stabilized on high-dose metformin, the addition of nateglinide improved glycaemic control. The combination of these agents was well tolerated and both doses of nateglinide proved effective. The efficacy of nateglinide 60 mg and the low rate of hypoglycaemia observed at this dose make it suitable for patients close to their therapeutic target on metformin monotherapy.

Signals and pools underlying biphasic insulin secretion

Rapid and sustained stimulation of beta-cells with glucose induces biphasic insulin secretion. The two phases appear to reflect a characteristic of stimulus-secretion coupling in each beta-cell rather than heterogeneity in the time-course of the response between beta-cells or islets. There is no evidence indicating that biphasic secretion can be attributed to an intrinsically biphasic metabolic signal. In contrast, the biphasic rise in cytoplasmic Ca(2+) concentration ([Ca(2+)](i)) induced by glucose is important to shape the two phases of secretion. The first phase requires a rapid and marked elevation of [Ca(2+)](i) and corresponds to the release of insulin granules from a limited pool. The magnitude of the second phase is determined by the elevation of [Ca(2+)](i), but its development requires production of another signal. This signal corresponds to the amplifying action of glucose and may serve to replenish the pool of granules that are releasable at the prevailing [Ca(2+)](i). The species characteristics of biphasic insulin secretion and its perturbations in pathological situations are discussed.