Beta-cell function improved by supplementing basal insulin secretion in mild diabetes

Oral antidiabetic therapy versus early insulinization on glycemic control in newly diagnosed type 2 diabetes patients: a retrospective matched cohort study

Our study aims to compare the efficacy of oral antidiabetic therapy to early insulinization on glycemic control among newly diagnosed type 2 diabetes patients in real-world clinical practice. A retrospective cohort study conducted at a medical center in Taiwan analyzed 1256 eligible patients from January 2007 to December 2017. Propensity score matching resulted in well-balanced groups of 94 patients each in the oral antidiabetic drug (OAD) and early insulinization cohorts. Glycemic outcomes were assessed in both groups. Patients exclusively using OAD showed consistently lower glycated hemoglobin (HbA1c) levels at 3, 12, 24, and 36 months compared to insulin users. At later periods, 77.7% of OAD users achieved glycemic control versus 64.9% of insulin users, with a marginally significant difference. Subgroup analyses suggested a trend favoring well-controlled diabetes in the OAD group, though not statistically significant. Our study finds oral antidiabetic therapy is not inferior to early insulinization for glycemic control in newly diagnosed type 2 diabetes patients, irrespective of initial HbA1c levels. This supports oral therapy as a rational treatment option, even in cases with elevated HbA1c at diagnosis.

Hypoxia causes pancreatic β-cell dysfunction and impairs insulin secretion by activating the transcriptional repressor BHLHE40

Hypoxia can occur in pancreatic β-cells in type 2 diabetes. Although hypoxia exerts deleterious effects on β-cell function, the associated mechanisms are largely unknown. Here, we show that the transcriptional repressor basic helix-loop-helix family member e40 (BHLHE40) is highly induced in hypoxic mouse and human β-cells and suppresses insulin secretion. Conversely, BHLHE40 deficiency in hypoxic MIN6 cells or β-cells of ob/ob mice reverses defects in insulin secretion. Mechanistically, BHLHE40 represses the expression of Mafa, encoding the transcription factor musculoaponeurotic fibrosarcoma oncogene family A (MAFA), by attenuating the binding of pancreas/duodenum homeobox protein 1 (PDX1) to its enhancer region. Impaired insulin secretion in hypoxic β-cells was recovered by MAFA re-expression. Collectively, our work identifies BHLHE40 as a key hypoxia-induced transcriptional repressor in β-cells that inhibit insulin secretion by suppressing MAFA expression.

Reduced miR-184-3p expression protects pancreatic β-cells from lipotoxic and proinflammatory apoptosis in type 2 diabetes via CRTC1 upregulation

The loss of functional β-cell mass in type 2 diabetes (T2D) is associated with molecular events that include β-cell apoptosis, dysfunction and/or dedifferentiation. MicroRNA miR-184-3p has been shown to be involved in several β-cell functions, including insulin secretion, proliferation and survival. However, the downstream targets and upstream regulators of miR-184-3p have not been fully elucidated. Here, we show reduced miR-184-3p levels in human T2D pancreatic islets, whereas its direct target CREB regulated transcription coactivator 1 (CRTC1) was increased and protects β-cells from lipotoxicity- and inflammation-induced apoptosis. Downregulation of miR-184-3p in β-cells leads to upregulation of CRTC1 at both the mRNA and protein levels. Remarkably, the protective effect of miR-184-3p is dependent on CRTC1, as its silencing in human β-cells abrogates the protective mechanism mediated by inhibition of miR-184-3p. Furthermore, in accordance with miR-184-3p downregulation, we also found that the β-cell-specific transcription factor NKX6.1, DNA-binding sites of which are predicted in the promoter sequence of human and mouse MIR184 gene, is reduced in human pancreatic T2D islets. Using chromatin immunoprecipitation analysis and mRNA silencing experiments, we demonstrated that NKX6.1 directly controls both human and murine miR-184 expression. In summary, we provide evidence that the decrease in NKX6.1 expression is accompanied by a significant reduction in miR-184-3p expression and that reduction of miR-184-3p protects β-cells from apoptosis through a CRTC1-dependent mechanism.

The β-cell glucose toxicity hypothesis: Attractive but difficult to prove

β cells in the hyperglycemic environment of diabetes have marked changes in phenotype and function that are largely reversible if glucose levels can be returned to normal. A leading hypothesis is that these changes are caused by the elevated glucose levels leading to the concept of glucose toxicity. Support for the glucose toxicity hypothesis is largely circumstantial, but little progress has been made in defining the responsible mechanisms. Then questions emerge that are difficult to answer. In the very earliest stages of diabetes development, there is a dramatic loss of glucose-induced first-phase insulin release (FPIR) with only trivial elevations of blood glucose levels. A related question is how impaired insulin action on target tissues such as liver, muscle and fat can cause increased insulin secretion. The existence of a sophisticated feedback mechanism between insulin secretion and insulin action on peripheral tissues driven by glucose has been postulated, but it has been difficult to measure increases in blood glucose levels that might have been expected. These complexities force us to challenge the simplicity of the glucose toxicity hypothesis and feedback mechanisms. It may turn out that glucose is somehow driving all of these changes, but we must develop new questions and experimental approaches to test the hypothesis.

Novel approaches to pharmacological management of type 2 diabetes in Japan

INTRODUCTION

Newly developed anti-diabetic medications have had multiple activities, beyond a blood glucose-lowering effect. Current drugs for treating type 2 diabetes mellitus (T2DM) are based on the use of gastrointestinal hormones. Representative incretin preparations, such as those with glucagon-like peptide (GLP)-1 or gastric inhibitory polypeptide (GIP) activity, aim to provide new means of controlling blood glucose levels, body weight, and lipid metabolism.

AREA COVERED

In this manuscript, the pathophysiology of T2DM and the activities and characteristics of novel diabetic drugs are reviewed in the context of the Japanese population. This review also highlights the need for novel medicines to overcome the accompanying challenges. Finally, the author provides the reader with their expert perspectives.

EXPERT OPINION

The incidence of T2DM has been increasing in the aging of Japanese society. In older people, medical development should focus on safety, easier self-administration, and the relief of caregiver burden in terms of continuous administration. In the young, the focus should be on effectiveness, with a particular emphasis on the protection of organs, increasing the ease of adherence, and safety. Novel medicines will need to push the envelope in these areas.

Age at diagnosis, glycemic trajectories, and responses to oral glucose-lowering drugs in type 2 diabetes in Hong Kong: A population-based observational study

BACKGROUND

Lifetime glycemic exposure and its relationship with age at diagnosis in type 2 diabetes (T2D) are unknown. Pharmacologic glycemic management strategies for young-onset T2D (age at diagnosis <40 years) are poorly defined. We studied how age at diagnosis affects glycemic exposure, glycemic deterioration, and responses to oral glucose-lowering drugs (OGLDs).

METHODS AND FINDINGS

In a population-based cohort (n = 328,199; 47.2% women; mean age 34.6 and 59.3 years, respectively, for young-onset and usual-onset [age at diagnosis ≥40 years] T2D; 2002-2016), we used linear mixed-effects models to estimate the association between age at diagnosis and A1C slope (glycemic deterioration) and tested for an interaction between age at diagnosis and responses to various combinations of OGLDs during the first decade after diagnosis. In a register-based cohort (n = 21,016; 47.1% women; mean age 43.8 and 58.9 years, respectively, for young- and usual-onset T2D; 2000-2015), we estimated the glycemic exposure from diagnosis until age 75 years. People with young-onset T2D had a higher mean A1C (8.0% [standard deviation 0.15%]) versus usual-onset T2D (7.6% [0.03%]) throughout the life span (p < 0.001). The cumulative glycemic exposure was >3 times higher for young-onset versus usual-onset T2D (41.0 [95% confidence interval 39.1-42.8] versus 12.1 [11.8-12.3] A1C-years [1 A1C-year = 1 year with 8% average A1C]). Younger age at diagnosis was associated with faster glycemic deterioration (A1C slope over time +0.08% [0.078-0.084%] per year for age at diagnosis 20 years versus +0.02% [0.016-0.018%] per year for age at diagnosis 50 years; p-value for interaction <0.001). Age at diagnosis ≥60 years was associated with glycemic improvement (-0.004% [-0.005 to -0.004%] and -0.02% [-0.027 to -0.0244%] per year for ages 60 and 70 years at diagnosis, respectively; p-value for interaction <0.001). Responses to OGLDs differed by age at diagnosis (p-value for interaction <0.001). Those with young-onset T2D had smaller A1C decrements for metformin-based combinations versus usual-onset T2D (metformin alone: young-onset -0.15% [-0.105 to -0.080%], usual-onset -0.17% [-0.179 to -0.169%]; metformin, sulfonylurea, and dipeptidyl peptidase-4 inhibitor: young-onset -0.44% [-0.476 to -0.405%], usual-onset -0.48% [-0.498 to -0.459%]; metformin and α-glucosidase inhibitor: young-onset -0.40% [-0.660 to -0.144%], usual-onset -0.25% [-0.420 to -0.077%]) but greater responses to other combinations containing sulfonylureas (sulfonylurea alone: young-onset -0.08% [-0.099 to -0.065%], usual-onset +0.06% [+0.059 to +0.072%]; sulfonylurea and α-glucosidase inhibitor: young-onset -0.10% [-0.266 to 0.064%], usual-onset: 0.25% [+0.196% to +0.312%]). Limitations include possible residual confounding and unknown generalizability outside Hong Kong.

CONCLUSIONS

In this study, we observed excess glycemic exposure and rapid glycemic deterioration in young-onset T2D, indicating that improved treatment strategies are needed in this setting. The differential responses to OGLDs between young- and usual-onset T2D suggest that better disease classification could guide personalized therapy.

Should the last be first? Questions and dilemmas regarding early short-term insulin treatment in Type 2 Diabetes Mellitus

INTRODUCTION

Early short-term insulin treatment (STIT), defined as insulin administration shortly after diabetes diagnosis for only a brief period of time, is an alternative concept, aiming to entirely revise the perspective of type 2 diabetes (T2DM) management.

AREAS COVERED

The present review intends to summarize what is already known regarding early STIT in T2DM and highlight questions and dilemmas from the clinician's point of view, with a discourse on future research agenda.

EXPERT OPINION

STIT has the potential to modify the natural history of T2DM, resulting in improved drug-free remission rates by favorably affecting the underlying pathophysiology of the disease. Existing data in the field manifest significant weaknesses, mainly being the small number of trials and patients included, the lack of control groups in most studies and the wide heterogeneity between study designs and explored outcomes, which limit definitive conclusions. Therefore, before such a therapeutic strategy is incorporated into daily practice, important issues require further clarification by future trials. These issues include the optimal time point for the intervention, the ideal insulin type, the identification of patients being most likely to benefit, the STIT effects on cardiovascular and other clinical outcomes and the cost-effectiveness evaluation of this therapeutic strategy.

ABBREVIATIONS

T2DM: Type 2 Diabetes Mellitus; HbA_1C: Hemoglobin A_1c; OHA: Oral Hypoglycemic Agents; STIT: Short-term Insulin Treatment; CSII: Continuous Subcutaneous Insulin Infusion; MDI: Multiple Daily Injections; PPG: Postprandial Plasma Glucose; FPG: Fasting Plasma Glucose; HOMA-b: Homeostasis Model Assessment of beta-cell function; TDD: Total Daily Insulin Dose; DI: Disposition Index; HOMA-IR: Homeostasis Model Assessment of Insulin Resistance; ROS: Reactive Oxygen Species; TNF: Tumor Necrosis Factor; GLP-1: Glucagon-like peptide-1; GIP: Glucose-dependent Insulinotropic Polypeptide; BMI: Body Mass Index; CV: Cardiovascular; DR: Diabetic Retinopathy; SU: Sulfonylurea; IGI: Insulinogenic Index.

Prospective evaluation of insulin and incretin dynamics in obese adults with and without diabetes for 2 years after Roux-en-Y gastric bypass

AIMS/HYPOTHESIS

In this prospective case-control study we tested the hypothesis that, while long-term improvements in insulin sensitivity (S_I) accompanying weight loss after Roux-en-Y gastric bypass (RYGB) would be similar in obese individuals with and without type 2 diabetes mellitus, stimulated-islet-cell insulin responses would differ, increasing (recovering) in those with diabetes but decreasing in those without. We investigated whether these changes would occur in conjunction with favourable alterations in meal-related gut hormone secretion and insulin processing.

METHODS

Forty participants with type 2 diabetes and 22 participants without diabetes from the Longitudinal Assessment of Bariatric Surgery (LABS-2) study were enrolled in a separate, longitudinal cohort (LABS-3 Diabetes) to examine the mechanisms of postsurgical diabetes improvement. Study procedures included measures of S_I, islet secretory response and gastrointestinal hormone secretion after both intravenous glucose (frequently-sampled IVGTT [FSIVGTT]) and a mixed meal (MM) prior to and up to 24 months after RYGB.

RESULTS

Postoperatively, weight loss and S_I-_FSIVGTT improvement was similar in both groups, whereas the acute insulin response to glucose (AIRglu) decreased in the non-diabetic participants and increased in the participants with type 2 diabetes. The resulting disposition indices (DI_FSIVGTT) increased by three- to ninefold in both groups. In contrast, during the MM, total insulin responsiveness did not significantly change in either group despite durable increases of up to eightfold in postprandial glucagon-like peptide 1 levels, and S_I-MM and DI_MM increased only in the diabetes group. Peak postprandial glucagon levels increased in both groups.

CONCLUSIONS/INTERPRETATION

For up to 2 years following RYGB, obese participants without diabetes showed improvements in DI that approach population norms. Those with type 2 diabetes recovered islet-cell insulin secretion response yet continued to manifest abnormal insulin processing, with DI values that remained well below population norms. These data suggest that, rather than waiting for lifestyle or medical failure, RYGB is ideally considered before, or as soon as possible after, onset of type 2 diabetes.

TRIAL REGISTRATION

ClinicalTrials.gov NCT00433810.

Metabolic Stress and Compromised Identity of Pancreatic Beta Cells

Beta cell failure is a central feature of type 2 diabetes (T2D), but the molecular underpinnings of the process remain only partly understood. It has been suggested that beta cell failure in T2D involves massive cell death. Other studies ascribe beta cell failure to cell exhaustion, due to chronic oxidative or endoplasmic reticulum stress leading to cellular dysfunction. More recently it was proposed that beta cells in T2D may lose their differentiated identity, possibly even gaining features of other islet cell types. The loss of beta cell identity appears to be driven by glucotoxicity inhibiting the activity of key beta cell transcription factors including Pdx1, Nkx6.1, MafA and Pax6, thereby silencing beta cell genes and derepressing alternative islet cell genes. The loss of beta cell identity is at least partly reversible upon normalization of glycemia, with implications for the reversibility of T2D, although it is not known if beta cell failure reaches eventually a point of no return. In this review we discuss current evidence for metabolism-driven compromised beta cell identity, key knowledge gaps and opportunities for utility in the treatment of T2D.

Calorie restriction and reversal of type 2 diabetes

Type 2 diabetes causes major global health problems and has been believed to be a lifelong condition with inevitable worsening. Steadily increasing numbers of drugs appeared to be required to achieve even modest control. Early type 2 diabetes has now been shown to be reversed by substantial weight loss and this has allowed temporal tracking of the underlying pathophysiological changes. Areas covered: In early type 2 diabetes, negative calorie balance decreases liver fat within days, and allows return of normal control of hepatic glucose production. Over 8 weeks, the negative calorie balance allows the raised levels of intra-pancreatic fat and simultaneously first phase insulin secretion to normalise. These findings are consistent with the 2008 Twin Cycle Hypothesis of the etiology and pathogenesis of type 2 diabetes. Individuals develop type 2 diabetes when they exceed their personal fat threshold for safe storage of fat and there is no difference in pathophysiology between those with BMI above or below 30 kg/m². Expert commentary: Type 2 diabetes can now be understood as a state of excess fat in liver and pancreas, and remains reversible for at least 10 years in most individuals.

Normal weight individuals who develop Type 2 diabetes: the personal fat threshold

Type 2 diabetes (T2DM) is frequently regarded as a disease of obesity and its occurrence in individuals of normal body mass index (BMI) is often regarded as indicating a non-obesity-related subtype. However, the evidence for such a distinct, common subtype is lacking. The United Kingdom Prospective Diabetes Study (UKPDS) cohort of people diagnosed with T2DM in the 1970s and 1980s had a median BMI of only 28 kg/m2. UKPDS data form the basis of current understanding of the condition even though one in three of those studied had a BMI of less than 25 kg/m2. BMI, though, is a population measure and not a rigid personal guide. Weight loss is considered de rigueur for treating obese diabetic individuals, but it is not usually considered for those deemed to have a normal BMI. Given the new evidence that early T2DM can be reversed to normal glucose tolerance by substantial weight loss, it is important to explain why non-overweight people respond to this intervention as well as obese individuals. We hypothesize that each individual has a personal fat threshold (PFT) which, if exceeded, makes likely the development of T2DM. Subsequent weight loss to take the individual below their level of susceptibility should allow return to normal glucose control. Crucially, the hypothesized PFT is independent of BMI. It allows both understanding of development of T2DM in the non-obese and remission of diabetes after substantial weight loss in people who remain obese by definition. To illustrate this concept, we present the distribution curve of BMI at diagnosis for the UKPDS cohort, together with a diagram explaining individual behaviour within the population. The concept of PFT is of practical benefit in explaining the onset of diabetes and its logical management to the non-obese majority of people with T2DM.

Melatonin prevents pancreatic β-cell loss due to glucotoxicity: the relationship between oxidative stress and endoplasmic reticulum stress

Prolonged hyperglycemia results in pancreatic β-cell dysfunction and apoptosis, referred to as glucotoxicity. Although both oxidative and endoplasmic reticulum (ER) stresses have been implicated as major causative mechanisms of β-cell glucotoxicity, the reciprocal importance between the two remains to be elucidated. The aim of this study was to evaluate the differential effect of oxidative stress and ER stress on β-cell glucotoxicity, by employing melatonin which has free radical-scavenging and antioxidant properties. As expected, in β-cells exposed to prolonged high glucose levels, cell viability and glucose-stimulated insulin secretion (GSIS) were significantly impaired. Melatonin treatment markedly attenuated cellular apoptosis by scavenging reactive oxygen species via its plasmalemmal receptor-independent increase in antioxidant enzyme activity. However, treatments with antioxidants alone were insufficient to recover the impaired GSIS. Interestingly, 4-phenylbutyric acid (4-PBA), a chemical chaperone that attenuate ER stress by stabilizing protein structure, alleviated the impaired GSIS, but not apoptosis, suggesting that glucotoxicity induces oxidative and ER stress independently. We found that cotreatment of glucotoxic β-cells with melatonin and 4-PBA dramatically improved both their survival and insulin secretion. Taken together, these results suggest that ER stress may be the more critical mechanism for prolonged high-glucose-induced GSIS impairment, whereas oxidative stress appears to be more critical for the impaired β-cell viability. Therefore, combinatorial therapy of melatonin with an ER stress modifier may help recover pancreatic β-cells under glucotoxic conditions in type 2 diabetes.

Clinical evidence for the earlier initiation of insulin therapy in type 2 diabetes

The natural history of type 2 diabetes mellitus (T2DM) is a relentless progression of β-cell failure and dysregulation of β-cell function with increasing metabolic derangement. Insulin remains the only glucose-lowering therapy that is efficacious throughout this continuum. However, the timing of introduction and the choice of insulin therapy remain contentious because of the heterogeneity of T2DM and the well-recognized behavioral and therapeutic challenges associated with this mode of therapy. Nevertheless, the early initiation of basal insulin has been shown to improve glycemic control and affect long-term outcomes in people with T2DM and is a treatment strategy supported by international guidelines as part of an individualized approach to chronic disease management. The rationale for early initiation of insulin is based on evidence demonstrating multifaceted benefits, including overcoming the glucotoxic effects of hyperglycemia, thereby facilitating "β-cell rest," and preserving β-cell mass and function, while also improving insulin sensitivity. Independent of its effects on glycemic control, insulin possesses anti-inflammatory and antioxidant properties that may help protect against endothelial dysfunction and damage resulting in vascular disease. Insulin therapy and the achievement of good glycemic control earlier in T2DM provide long-term protection to end organs via "metabolic memory" regardless of subsequent treatments and degree of glycemic control. This is evidenced from long-term observations continuing from trials such as the United Kingdom Prospective Diabetes Study. As such, early initiation of insulin therapy may not only help to avoid the effects of prolonged glycemic burden, but may also positively alter the course of disease progression.

Hyperglycaemia is associated with impaired pulsatile insulin secretion: effect of basal insulin therapy

AIM

Postprandial insulin pulsatility is impaired in patients with type 2 diabetes, but the effects of exogenous insulin therapy on pulsatile insulin secretion are not known. We addressed, whether pulsatile insulin secretion is related to glycaemic control, whether basal insulin supplementation increases postprandial insulin secretion, and if so, is this accomplished by a specific improvement in pulsatile insulin secretion?

METHODS

Fourteen patients with type 2 diabetes underwent a mixed meal test before and after an 8-week treatment period with insulin glargine. Glucose, insulin and C-peptide levels were measured, and insulin pulsatility was determined by deconvolution analysis.

RESULTS

Insulin treatment lowered fasting glycaemia from 179.6 ± 7.5 mg/dl to 117.6 ± 6.5 mg/dl (p < 0.001). Postprandial insulin and C-peptide levels increased significantly after the treatment period (p < 0.0001). The total calculated insulin secretion rate increased with insulin treatment (p = 0.0039), with non-significant increases in both pulsatile and non-pulsatile insulin secretion. Insulin pulse frequency was unchanged by the intervention. There was an inverse relationship between fasting and postprandial glycaemia and insulin pulse mass (r(2) = 0.51 and 0.56, respectively), whereas non-pulsatile insulin secretion was unrelated to either fasting or postprandial glucose concentrations (r(2) = 0.0073 and 0.031).

CONCLUSIONS

Hyperglycaemia in type 2 diabetes is associated with a reduction in postprandial insulin secretion, specifically through a reduction in insulin pulsatility. Reducing chronic hyperglycaemia by basal insulin therapy enhances endogenous β-cell function in the postprandial state. These data support the use of basal insulin regimens in the pharmacotherapy of overtly hyperglycaemic patients with type 2 diabetes.

The molecular mechanisms of pancreatic β-cell glucotoxicity: recent findings and future research directions

It is well established that regular physiological stimulation by glucose plays a crucial role in the maintenance of the β-cell differentiated phenotype. In contrast, prolonged or repeated exposure to elevated glucose concentrations both in vitro and in vivo exerts deleterious or toxic effects on the β-cell phenotype, a concept termed as glucotoxicity. Evidence indicates that the latter may greatly contribute to the pathogenesis of type 2 diabetes. Through the activation of several mechanisms and signaling pathways, high glucose levels exert deleterious effects on β-cell function and survival and thereby, lead to the worsening of the disease over time. While the role of high glucose-induced β-cell overstimulation, oxidative stress, excessive Unfolded Protein Response (UPR) activation, and loss of differentiation in the alteration of the β-cell phenotype is well ascertained, at least in vitro and in animal models of type 2 diabetes, the role of other mechanisms such as inflammation, O-GlcNacylation, PKC activation, and amyloidogenesis requires further confirmation. On the other hand, protein glycation is an emerging mechanism that may play an important role in the glucotoxic deterioration of the β-cell phenotype. Finally, our recent evidence suggests that hypoxia may also be a new mechanism of β-cell glucotoxicity. Deciphering these molecular mechanisms of β-cell glucotoxicity is a mandatory first step toward the development of therapeutic strategies to protect β-cells and improve the functional β-cell mass in type 2 diabetes.

β-cell dysfunction in adolescents and adults with newly diagnosed type 2 diabetes mellitus

OBJECTIVE

To compare β-cell function in adolescents and adults with newly diagnosed type 2 diabetes (T2DM).

STUDY DESIGN

Thirty-nine adolescents with T2DM, 38 age- and weight-matched control subjects, and 19 adults with T2DM were studied. The adolescent subjects with diabetes were divided on the basis of whether they needed insulin to control their initial hyperglycemia. The primary outcome variable was the disposition index, computed from the acute insulin response to glucose corrected for insulin sensitivity (1/Homeostatic model assessment of insulin resistance).

RESULTS

The disposition index was significantly reduced in all 3 diabetic groups (control n=3360, adolescents with T2DM without insulin n=630, adolescents with T2DM with insulin n=120, adults with T2DM n=200; P<.001), and the adolescents with more severe hyperglycemia at diagnosis had lower disposition index than those with a more modest presentation (P<.05).

CONCLUSION

At the time of diagnosis, adolescents with T2DM have significant β-cell dysfunction, comparable with adults newly diagnosed with T2DM. Thus, severe β-cell impairment can develop within the first two decades of life and is likely to play a central role in the pathogenesis of T2DM in adolescents.

Insulin therapy in type 2 diabetes mellitus

Health care providers and patients have lots of choice to treat type 2 diabetes, but the blood glucose improvement is limited. The one therapy with unlimited potential (at least theoretically) is insulin. Many studies show that glucose control is achievable with insulin safely in most patients with type 2 diabetes. Effective diabetes management at the primary care or specialty level requires a belief in the importance of insulin therapy in uncontrolled patients with type 2 diabetes. This review details the theories, observed outcomes, and how-tos regarding insulin use in type 2 diabetes.

No signs of progressive beta cell damage during 20 years of prospective follow-up of autoantibody-negative diabetes

Both type 1 and type 2 diabetes are considered to be associated with different degrees of progressive beta cell damage. However, few long-term studies have been made. Our aim was to study the clinical course of 20 years of diabetes disease, including diabetes progression, comorbidity, and mortality in a prospectively studied cohort of consecutively diagnosed diabetic patients. Among all 233 patients diagnosed with diabetes during 1985-1987 in Malmö, Sweden, 50 of 118 surviving patients were followed-up after 20 years. The age at diagnose was 42.3 ± 23.1 and 57.5 ± 13.6 years for antibody-positive and antibody-negative patients, respectively. HbA1c and plasma lipids were analyzed with regard to metabolic control. Islet antibody-negative patients at diagnosis had highly preserved C-peptide levels after 20 years in contrast to antibody-positive patients (antibody negative: C-peptide 0 years 0.78 ± 0.47 and 20 years 0.70 ± 0.46 (nmol/l), P = 0.51 and antibody positive: C-peptide 0 years 0.33 ± 0.35 and 20 years 0.10 ± 0.18; P < 0.001. Islet antibodies but not age, BMI, or C-peptide at diagnosis were predictors of C-peptide levels at 20 years when analyzed by logistic regression (P < 0.05). HbA1c did not differ between the groups after 20 years. The 20-year mortality was higher among antibody-negative patients, dependent on the higher age at diagnosis in this group (number of deaths: antibody positive: 18 of 56 vs. antibody negative: 109 of 188, P < 0.001). Of the deceased, 79% had died from diseases or complications that may be associated with diabetes. We found no progressive beta cell damage in autoantibody-negative diabetes at a 20-year follow-up of the clinical course of diabetes.

Chronic reduction of fasting glycemia with insulin glargine improves first- and second-phase insulin secretion in patients with type 2 diabetes

OBJECTIVE

Insulin secretion is often diminished in hyperglycemic patients with type 2 diabetes. We examined whether chronic basal insulin treatment with insulin glargine improves glucose-induced insulin secretion.

RESEARCH DESIGN AND METHODS

Fourteen patients with type 2 diabetes on metformin monotherapy received an add-on therapy with insulin glargine over 8 weeks. Intravenous glucose tolerance tests (IVGTTs) were performed before and after the intervention, with and without previous adjustment of fasting glucose levels using a 3-h intravenous insulin infusion.

RESULTS

Fasting glycemia was lowered from 179.6 ± 7.5 to 117.6 ± 6.5 mg/dL (P < 0.001), and HbA(1c) levels declined from 8.4 ± 0.5 to 7.1 ± 0.2% (P = 0.0046). The final insulin dose was 59.3 ± 10.2 IU. Acute normalization of fasting glycemia by intravenous insulin reduced C-peptide levels during the IVGTT (P < 0.0001). In contrast, insulin and C-peptide responses to intravenous glucose administration were significantly greater after the glargine treatment period (P < 0.0001, respectively). Both first- and second-phase insulin secretion increased significantly after the glargine treatment period (P < 0.05, respectively). These improvements in insulin secretion were observed during both the experiments with and without acute adjustment of fasting glycemia.

CONCLUSIONS

Chronic supplementation of long-acting basal insulin improves glucose-induced insulin secretion in hyperglycemic patients with type 2 diabetes, whereas acute exogenous insulin administration reduces the β-cell response to glucose administration. These data provide a rationale for basal insulin treatment regiments to improve postprandial endogenous insulin secretion in hyperglycemic patients with type 2 diabetes.

Effects of long-term cranberry supplementation on endocrine pancreas in aging rats

The effects of long-term cranberry consumption on age-related changes in endocrine pancreas are not fully understood. Here we treated male Fischer 344 rats with either 2% whole cranberry powder supplemented or normal rodent chow from 6 to 22 month old. Both groups displayed an age-related decline in basal plasma insulin concentrations, but this age-related decline was delayed by cranberry. Cranberry supplementation led to increased β-cell glucose responsiveness during the oral glucose tolerance test. Portal insulin concentration was 7.6-fold higher in rats fed cranberry, coupled with improved β-cell function. However, insulin resistance values were similar in both groups. Total β-cell mass and expression of pancreatic and duodenal homeobox 1 and insulin within islets were significantly enhanced in rats fed cranberry relative to controls. Furthermore, cranberry increased insulin release of an insulin-producing β-cell line, revealing its insulinotropic effect. These findings suggest that cranberry is of particular benefit to β-cell function in normal aging rats.

Pancreatic beta-cell responses to GLP-1 after near-normalization of blood glucose in patients with type 2 diabetes

This study investigated the effects of strict glycaemic control on beta-cell function in nine obese subjects with type 2 diabetes (T2DM), using graded glucose infusions together with infusions of saline or GLP-1 before (HbA(1)c: 8.0+/-0.4%) and after four weeks of near-normalization of blood glucose (BG) using insulin (mean diurnal BG: 6.4+/-0.3 mmol/l; HbA(1)c: 6.6+/-0.3%). Nine matched healthy subjects acted as controls. In controls, area-under-curve (AUC) for amylin, C-peptide and proinsulin were higher with GLP-1 than saline (P<0.001). The AUC amylin/C-peptide ratio was similar on both days, while AUC proinsulin/C-peptide ratio was higher with GLP-1 (P=0.02). In the patients, amylin, C-peptide and proinsulin AUCs were unaltered by near-normoglycaemia per se. Proinsulin responses to GLP-1 were unchanged, but amylin and C-peptide AUCs increased (P<0.05) after insulin treatment, and AUC amylin/C-peptide ratios rose to control levels. Near-normoglycaemia tended to reduce AUC proinsulin/C-peptide ratio, which was significant (P=0.04) with GLP-1, but still higher than with saline (P=0.004). In conclusion, amylin, C-peptide and proinsulin responses to glucose were unaffected by four weeks of near-normoglycaemia, whereas GLP-1 increased amylin and C-peptide secretion and amylin/C-peptide ratio. Near-normoglycaemia reduced proinsulin/C-peptide ratio during stimulation with GLP-1, suggesting that strict glycaemic control might ameliorate some of the disturbances in beta-cell function characterizing T2DM.

The contribution of incretin hormones to the pathogenesis of type 2 diabetes

The incretin effect, that is, the postprandial augmentation of insulin secretion by gastrointestinal hormones, mediates approximately 50-70% of the overall insulin responses after a mixed meal or glucose ingestion in healthy subjects. In patients with type 2 diabetes, the incretin effect is markedly reduced, and this has been attributed to defects in the secretion and insulinotropic action of the two main incretin hormones, namely gastric inhibitory polypeptide (GIP) and glucagon-like peptide 1 (GLP-1). It has been speculated that a reduced incretin effect might precede the onset of hyperglycaemia in patients with type 2 diabetes. However, the secretion and action of GIP and GLP-1 is relatively unaltered in normal glucose-tolerant individuals at high risk for type 2 diabetes (e.g., first-degree relatives) and a diminished incretin effect is also detectable in other types of diabetes, thereby arguing against such reasoning. This article will describe the defects in the incretin system in patients with type 2 diabetes, summarise their relevance in the development of hyperglycaemia and discuss the potential individual roles of GIP and GLP-1 in the pathogenesis of type 2 diabetes.

Thiazolidinediones in prediabetes and early type 2 diabetes: what can be learned about that disease's pathogenesis

Several clinical trials have shown a high success rate of thiazolidinediones (TZDs) in prediabetes and early type 2 diabetes. The presumed mechanism of this effect has shifted from the best known effect of these agents to improve insulin sensitivity, to preservation of beta-cell function. The common explanation for this effect is unloading of the islet beta cell from the insulin resistance-induced hyperstimulation that eventually leads to beta-cell failure, so-called beta-cell rest. However, a recent finding is powerful biological effects of peroxisome proliferator-activated receptor (PPAR)gamma signaling in islet beta cells. This article reviews this topic by first describing the TZD intervention studies. Then it provides an overview of the current concepts regarding the beta-cell overwork and rest hypotheses, and the recent information about PPARgamma signaling effects in beta cells.

Four weeks of near-normalisation of blood glucose improves the insulin response to glucagon-like peptide-1 and glucose-dependent insulinotropic polypeptide in patients with type 2 diabetes

OBJECTIVE

The incretin effect is attenuated in patients with type 2 diabetes mellitus, partly as a result of impaired beta cell responsiveness to glucose-dependent insulinotropic polypeptide (GIP) and glucagon-like peptide-1 (GLP-1). The aim of the present study was to investigate whether 4 weeks of near-normalisation of the blood glucose level could improve insulin responses to GIP and GLP-1 in patients with type 2 diabetes.

METHODS

Eight obese patients with type 2 diabetes with poor glycaemic control (HbA(1c) 8.6 +/- 1.3%), were investigated before and after 4 weeks of near-normalisation of blood glucose (mean blood glucose 7.4 +/- 1.2 mmol/l) using insulin treatment. Before and after insulin treatment the participants underwent three hyperglycaemic clamps (15 mmol/l) with infusion of GLP-1, GIP or saline. Insulin responses were evaluated as the incremental area under the plasma C-peptide curve.

RESULTS

Before and after near-normalisation of blood glucose, the C-peptide responses did not differ during the early phase of insulin secretion (0-10 min). The late phase C-peptide response (10-120 min) increased during GIP infusion from 33.0 +/- 8.5 to 103.9 +/- 24.2 (nmol/l) x (110 min)(-1) (p < 0.05) and during GLP-1 infusion from 48.7 +/- 11.8 to 126.6 +/- 32.5 (nmol/l) x (110 min)(-1) (p < 0.05), whereas during saline infusion the late-phase response did not differ before vs after near-normalisation of blood glucose (40.2 +/- 11.2 vs 46.5 +/- 12.7 [nmol/l] x [110 min](-1)).

CONCLUSIONS

Near-normalisation of blood glucose for 4 weeks improves beta cell responsiveness to both GLP-1 and GIP by a factor of three to four. No effect was found on beta cell responsiveness to glucose alone. CLINICALTRIALS.GOV ID NO.: NCT 00612950.

FUNDING

This study was supported by The Novo Nordisk Foundation, The Medical Science Research Foundation for Copenhagen.

Near normalisation of blood glucose improves the potentiating effect of GLP-1 on glucose-induced insulin secretion in patients with type 2 diabetes

AIMS/HYPOTHESIS

The ability of glucagon-like peptide-1 (GLP-1) to enhance beta cell responsiveness to i.v. glucose is impaired in patients with type 2 diabetes mellitus compared with healthy individuals. We investigated whether 4 weeks of near normalisation of blood glucose (BG) improves the potentiation of glucose-stimulated insulin secretion by GLP-1.

METHODS

Nine obese patients with type 2 diabetes and inadequate glycaemic control (HbA(1c) 8.0+/-0.4%) were investigated before and after 4 weeks of near normalisation of BG using insulin treatment (mean diurnal blood glucose 6.4+/-0.3 mmol/l, HbA(1c) 6.6+/-0.3%). Nine matched healthy participants were also studied. Beta cell function was investigated before and after insulin treatment using stepwise glucose infusions and infusion of saline or GLP-1 (1.0 pmol kg(-1) min(-1)), resulting in supraphysiological total GLP-1 concentrations of approximately 200 pmol/l. The responsiveness to glucose or glucose+GLP-1 was expressed as the slope of the linear regression line relating insulin secretion rate (ISR) and plasma glucose concentration (pmol kg(-1) min(-1) [mmol/l](-1)).

RESULTS

In the diabetic participants, the slopes during glucose+saline infusion did not differ before and after insulin treatment (0.33+/-0.07 and 0.39+/-0.04, respectively; p=NS). In contrast, near normalisation of blood glucose improved beta cell sensitivity to glucose during glucose+GLP-1 infusion (1.27+/-0.2 before vs 1.73+/-0.31 after; p<0.01). In the healthy participants, the slopes during the glucose+saline and glucose+GLP-1 infusions were 1.01+/-0.14 and 4.79+/-0.53, respectively.

CONCLUSIONS/INTERPRETATION

A supraphysiological dose of GLP-1 enhances beta cell responses to glucose in patients with type 2 diabetes, and 4 weeks of near normalisation of blood glucose further improves this effect.

beta-cell function and anti-diabetic pharmacotherapy

Type 2 diabetes is a chronic disease characterized by progressive worsening of glycaemic control as indicated by the United Kingdom Prospective Diabetes Study (UKPDS). The progressive nature of the disease is mainly due to continuous loss of beta-cell mass and function. Though much of this loss is due to intrinsic defects of the beta-cell several factors may accelerate such process. These include the metabolic environment where hyperglycaemia and increased circulating free-fatty acid exert a toxic effect on the beta-cell. Therefore, tight metabolic control may prevent not only the risk of long-term diabetic complication but also preserve beta-cell function. Several therapeutic agents are currently used for treatment of type 2 diabetic patients. However, their effect on maintenance of beta-cell function has not been yet systematically reviewed. By literature searching we have then analysed in detail the effect of sulfonylureas and non-sulfonylureic secretagogues, incretin-mimetics, insulin sensitizers, alpha-glucosidase inhibitors, and insulin on beta-cell function. Moreover, promising future approaches aiming at preserving beta-cell function and mass are discussed.

Islet beta cell failure in type 2 diabetes

The major focus of this Review is on the mechanisms of islet beta cell failure in the pathogenesis of obesity-associated type 2 diabetes (T2D). As this demise occurs within the context of beta cell compensation for insulin resistance, consideration is also given to the mechanisms involved in the compensation process, including mechanisms for expansion of beta cell mass and for enhanced beta cell performance. The importance of genetic, intrauterine, and environmental factors in the determination of "susceptible" islets and overall risk for T2D is reviewed. The likely mechanisms of beta cell failure are discussed within the two broad categories: those with initiation and those with progression roles.

Long-range negative correlation of glucose dynamics in humans and its breakdown in diabetes mellitus

Diurnal fluctuations in glucose levels continuously monitored during normal daily life are investigated using an extended random walk analysis, referred to as detrended fluctuation analysis (DFA), in 12 nondiabetic subjects and 15 diabetic patients. The DFA exponent alpha = 1.25 +/- 0.29 for healthy individuals in the "long-range" (>2 h) regime is shown to be significantly (P < 0.01) smaller than the reference "uncorrelated" value of alpha = 1.5, suggesting that the instantaneous net effects of the dynamical balance of glucose flux and reflux, causing temporal changes in glucose concentration, are long-range negatively correlated. By contrast, in diabetic patients, the DFA exponent alpha = 1.65 +/- 0.30 is significantly (P < 0.05) higher than that in nondiabetic subjects, evidencing a breakdown of the long-range negative correlation. It is suggested that the emergence of such positive long-range glucose correlations in diabetic patients-indicating that the net effects of the flux and reflux persist for many hours-likely reflects pathogenic mechanisms of diabetes, i.e., the lack of long-term stability of blood glucose and that the long-range negatively correlated glucose dynamics are functional in maintaining normal glucose homeostasis.

Pathogenesis of type 2 diabetes mellitus

The pathological sequence for type 2 diabetes is complex and entails many different elements that act in concert to cause that disease. This review proposes a sequence of events and how they interact by a careful analysis of the human and animal model literature. A genetic predisposition must exist, although to date very little is known about specific genetic defects in this disease. Whether the diabetes phenotype will occur depends on many environmental factors that share an ability to stress the glucose homeostasis system, with the current explosion of obesity and sedentary lifestyle being a major cause of the worldwide diabetes epidemic. We also propose that a lowered beta-cell mass either through genetic and/or beta-cell cytotoxic factors predisposes for glucose intolerance. As the blood glucose level rises even a small amount above normal, then acquired defects in the glucose homeostasis system occur--initially to impair the beta cell's glucose responsiveness to meals by impairing the first phase insulin response--and cause the blood glucose level to rise into the range of impaired glucose tolerance (IGT). This rise in blood glucose, now perhaps in concert with the excess fatty acids that are a typical feature of obesity and insulin resistance, cause additional deterioration in beta-cell function along with further insulin resistance, and the blood glucose levels rise to full-blown diabetes. This sequence also provides insight into how to better prevent or treat type 2 diabetes, by studying the molecular basis for the early defects, and developing targeted therapies against them.

Differential effects of acute and extended infusions of glucagon-like peptide-1 on first- and second-phase insulin secretion in diabetic and nondiabetic humans

OBJECTIVE

The purpose of this study was to determine whether an extended infusion of the incretin hormone glucagon-like peptide 1 (GLP-1) has a greater effect to promote insulin secretion in type 2 diabetic subjects than acute administration of the peptide.

RESEARCH DESIGN AND METHODS

Nine diabetic subjects and nine nondiabetic volunteers of similar age and weight were studied in identical protocols. First-phase insulin release (FPIR; the incremental insulin response in the first 10 min after the intravenous glucose bolus) and second-phase insulin release (SPIR; the incremental insulin response from 10-60 min after intravenous glucose) were measured during three separate intravenous glucose tolerance tests (IVGTTs): 1). without GLP-1 (control); 2). with acute administration of GLP-1 as a square wave starting just before glucose administration; and 3). with an extended infusion of GLP-1 for 3 h before and during the IVGTT.

RESULTS

In the subjects with diabetes, FPIR was severely impaired-a defect that was only modestly improved by acute administration of GLP-1 (197 +/- 97 vs. 539 +/- 218 pmol/l. min, P < 0.05), while SPIR was substantially increased (1952 +/- 512 vs. 8072 +/- 1664 pmol/l. min, P < 0.05). In contrast, the 3-h preinfusion of GLP-1 normalized fasting hyperglycemia (7.9 +/- 0.5 vs. 5.2 +/- 0.6, P < 0.05), increased FPIR by 5- to 6-fold (197 +/- 97 vs. 1141 +/- 409 pmol/l. min, P < 0.05), and augmented SPIR significantly (1952 +/- 512 vs. 4026 +/- 851 pmol/l. min, P < 0.05), but to a lesser degree than the acute administration of GLP-1. In addition, only the 3-h GLP-1 preinfusion significantly improved intravenous glucose tolerance (K(g) control 0.61 +/- 0.04, acute infusion 0.71 +/- 0.04, P = NS; 3-h infusion 0.92 +/- 0.08%/min, P < 0.05). These findings were also noted in the nondiabetic subjects in whom acute administration of GLP-1 significantly increased SPIR relative to the control IVGTT (9439 +/- 2885 vs. 31553 +/- 11660 pmol/l. min, P < 0.001) with less effect on FPIR (3221 +/- 918 vs. 4917 +/- 1614 pmol/l. min, P = 0.075), while the 3-h preinfusion of GLP-1 significantly increased both FPIR (3221 +/- 918 vs. 7948 +/- 2647 pmol/l. min, P < 0.01) and SPIR (9439 +/- 2885 vs. 21997 +/- 9849 pmol/l. min, P < 0.03).

CONCLUSIONS

Extended administration of GLP-1 not only augments glucose-stimulated insulin secretion, but also shifts the dynamics of the insulin response to earlier release in both diabetic and nondiabetic humans. The restitution of some FPIR in subjects with type 2 diabetes is associated with significantly improved glucose tolerance. These findings demonstrate the benefits of a 3-h infusion of GLP-1 on beta-cell function beyond those of an acute insulin secretagogue, and support the development of strategies using continuous or prolonged GLP-1 receptor agonism for treating diabetic patients.

Overnight inhibition of insulin secretion restores pulsatility and proinsulin/insulin ratio in type 2 diabetes

Impaired insulin secretion in type 2 diabetes is characterized by decreased first-phase insulin secretion, an increased proinsulin-to-insulin molar ratio in plasma, abnormal pulsatile insulin release, and heightened disorderliness of insulin concentration profiles. In the present study, we tested the hypothesis that these abnormalities are at least partly reversed by a period of overnight suspension of beta-cell secretory activity achieved by somatostatin infusion. Eleven patients with type 2 diabetes were studied twice after a randomly ordered overnight infusion of either somatostatin or saline with the plasma glucose concentration clamped at approximately 8 mmol/l. Controls were studied twice after overnight saline infusions and then at a plasma glucose concentration of either 4 or 8 mmol/l. We report that in patients with type 2 diabetes, 1) as in nondiabetic humans, insulin is secreted in discrete insulin secretory bursts; 2) the frequency of pulsatile insulin secretion is normal; 3) the insulin pulse mass is diminished, leading to decreased insulin secretion, but this defect can be overcome acutely by beta-cell rest with somatostatin; 4) the reported loss of orderliness of insulin secretion, attenuated first-phase insulin secretion, and elevated proinsulin-to-insulin molar ratio also respond favorably to overnight inhibition by somatostatin. The results of these clinical experiments suggest the conclusion that multiple parameters of abnormal insulin secretion in patients with type 2 diabetes mechanistically reflect cellular depletion of immediately secretable insulin that can be overcome by beta-cell rest.

Long-term exposure of isolated rat islets of Langerhans to supraphysiologic glucose concentrations decreases insulin mRNA levels

Chronic hyperglycemia has been postulated to contribute to beta-cell dysfunction in type 2 diabetic patients. A deleterious effect of prolonged exposure to high glucose concentrations on insulin gene expression has been demonstrated in insulin-secreting cell lines. This study was designed to investigate in isolated rat islets the effects of long-term exposure to supraphysiologic glucose concentrations on insulin, GLUT2, and glucokinase gene expression. The acute effects of glucose on gene expression were investigated by culturing rat islets in 2.8 or 16.7 mmol/L glucose for 24 hours. Insulin, GLUT2, and glucokinase mRNA levels were assessed by semiquantitative reverse transcriptase-polymerase chain reaction (RT-PCR). As expected, glucose acutely increased relative insulin and GLUT2 mRNA levels by 2.8- +/- 0.5-fold (n = 5, P < .005) and 1.8- +/- 0.3-fold (n = 5, P < .05), respectively, but had no effect on glucokinase gene expression (1.1- +/- 0.1-fold increase, n = 4, NS). These results validate the use of semiquantitative RT-PCR to detect changes in gene expression in rat islets. Islets were then cultured in 5.6 or 16.7 mmol/L glucose for 2, 4, or 6 weeks. Relative insulin mRNA levels were higher in islets cultured in high glucose after 2 weeks (1.8+/-0.1 v 1.0+/-0.1, n = 4, P < .05), identical after 4 weeks (0.9+/-0.1 v 1.00+/-0.2, n = 4, NS), and significantly lower after 6 weeks (0.6+/-0.1 v 1.0+/-0.2, n = 6, P < .05). Relative GLUT2 mRNA levels were higher in islets cultured in high glucose after 2 weeks (1.7+/-0.2 v 1.0+/-0.2, n = 3, P < .05) and then identical in both groups after 4 weeks (1.0+/-0.1 v 1.0+/-0.1, n = 3, NS) and 6 weeks (1.0+/-0.2 v 1.0+/-0.1, n = 6, NS). Relative glucokinase mRNA levels were identical under both culture conditions at 2 (1.4+/-0.4 v 1.0+/-0.2, n = 3, NS), 4 (0.8+/-0.5 v 1.0+/-0.3, n = 3, NS), and 6 (0.9+/-0.2 v 1.0+/-0.1, n = 6, NS) weeks. These results indicate that a 6-week exposure of rat islets to supraphysiologic glucose concentrations decreases insulin mRNA levels without affecting GLUT2 and glucokinase gene expression. We conclude that the phenomenon of glucose toxicity decreasing insulin gene expression is not restricted to transformed cells, and might provide insight into the mechanisms by which chronic hyperglycemia adversely affects beta-cell function.

Defects in insulin secretion and insulin action in non-insulin-dependent diabetes mellitus are inherited. Metabolic studies on offspring of diabetic probands

No studies are available that have compared early defects in glucose metabolism in the offspring of insulin-deficient and insulin-resistant probands with non-insulin-dependent diabetes mellitus (NIDDM). To investigate this issue, we evaluated insulin secretion capacity with oral and intravenous glucose tolerance tests and with the hyperglycemic clamp, and insulin action with the euglycemic insulin clamp in 20 offspring of NIDDM patients with low fasting C-peptide (+/-450 pmol/liter), reflecting deficient insulin secretion (IS-group), 18 offspring of NIDDM patients with high fasting C-peptide (>/= 880 pmol/liter), reflecting insulin resistance (IR-group), and 14 healthy control subjects without a family history of NIDDM. The frequency of impaired glucose tolerance was 45.0% in the IS-group and 50% in the IR-group. The IS-group had lower insulin-glucose response at 30 min in the oral glucose tolerance test (85.2+/-10.0 pmol insulin per mmol glucose) than the control group (136.4+/-23.1 pmol insulin per mmol glucose; P < 0.05) and the IR-group (115.6+/-11.8 pmol insulin per mmol glucose; P = 0.05). Furthermore, the acute insulin response during the first 10 min of an intravenous glucose tolerance test was lower in the IS-group than in the IR-group. Maximal insulin secretion capacity evaluated by C-peptide levels during the hyperglycemic clamp did not differ between the groups. The IR-group had lower rates of whole body glucose uptake (60.1+/-4.6 micromol per lean body mass per minute) than did the control group (84.2+/-5.0 micromol per lean body mass per minute; P < 0.001) or the IS-group (82.6+/-5.9 micromol per lean body mass per minute; P < 0.01) and this was due to reduced glucose nonoxidation. To conclude, both impaired insulin secretion and insulin action seem to be inherited and could represent the primary defects in glucose metabolism in the offspring of NIDDM probands.

Disorderly and nonstationary insulin secretion in relatives of patients with NIDDM

To further explore the role of the beta-cell as a pathogenic factor behind non-insulin-dependent diabetes mellitus (NIDDM), insulin secretion at modest hyperglycemia was examined in 15 healthy first-degree relatives of NIDDM patients and 13 anthropometrically and age-matched controls. The oral glucose tolerance test was normal in all, but the relatives had impaired insulin-stimulated glucose uptake (P < 0.05). During a constant intravenous glucose infusion we performed a time-series analysis of serum insulin in samples obtained at 1-min intervals for 75 min (60-135 min). The recently introduced scale- and model-independent statistic approximate entropy (ApEn) and the coefficient of variation for a 6- (9 and 15) point moving average (MA) were applied to test regularity and stationarity, respectively, of insulin secretion. Both ApEn and 6-point MA were able to significantly discern the insulin time series of the two groups (P < 0.05), demonstrating a higher degree of irregularity and nonstationarity among the offspring. Moreover, when the two complementary sets of statistics were combined into a single "index of nonpulsatility," an even more notable distinction was available (P < 0.01). No relationship was found between altered insulin secretion and insulin resistance. In conclusion, this experimental and statistical model demonstrates that the stimulated insulin secretion of glucose-tolerant relatives of NIDDM patients is characterized by disorderliness. Whether the model can predict the risk for developing a clinically important beta-cell dysfunction remains to be clarified.

Chronic exposure of betaTC-6 cells to supraphysiologic concentrations of glucose decreases binding of the RIPE3b1 insulin gene transcription activator

We have shown previously that chronic exposure of HIT-T15 cells to supraphysiologic glucose concentrations causes decreased insulin gene transcription and decreased binding activities of two beta-cell specific transcription factors, STF-1 and the RIPE3b1 activator, and have suggested that these events may provide a mechanism for glucose toxicity on beta-cell function. However, this contention can be criticized because it is not clear whether these observations are unique to the HIT-T15 cell or generalizable to other beta-cell lines and the islet. Therefore, we cultured betaTC-6 cells for up to 41 wk in either 11.1 or 0.8 mM glucose. We observed a passage-dependent decrease in insulin content and insulin mRNA levels in betaTC-6 cells chronically cultured in 11.1 mM glucose. Cells chronically cultured in 0.8 mM glucose had higher insulin mRNA levels than cells chronically cultured in 11.1 mM glucose. The relative activity of a chloramphenicol acetyl transferase (CAT) reporter gene controlled by the 5' regulatory region of the human insulin gene was decreased in late passage betaTC-6 cells chronically cultured in 11.1 mM glucose, but was preserved in late passages of cells chronically cultured in 0.8 mM glucose. Electromobility shift assays demonstrated that binding of a specific nuclear protein that recognizes the RIPE3b1 binding site of the insulin gene was markedly diminished in late passage cells chronically exposed to 11.1 mM glucose, whereas binding activities of STF-1 and ICE activators were unchanged. RIPE3b1 binding activity was preserved in late passage cells chronically exposed to 0.8 mM glucose. Mutation of the RIPE3b1 binding site almost completely abolished insulin gene transcription as well as binding activity. We conclude that chronic exposure of betaTC-6 cells to high glucose concentrations paradoxically decreases insulin gene transcription, in part, by decreasing activity of the trans-activating factor which binds to the RIPE3b1 sequence. This study uniquely demonstrates that altered binding to the RIPE3b1 sequence mediates glucose toxicity in betaTC-6 cells, thus reinforcing the importance of this cis-acting element in the regulation of insulin gene transcription. We conclude that the phenomenon of glucose toxicity decreasing binding of transcription factors and thereby reducing insulin gene expression is not a feature solely of HIT-T15 cells and may be demonstrable generally in beta-cell lines.

An integrated view of beta-cell dysfunction in type-II diabetes

Type-II (non-insulin-dependent) diabetes mellitus (NIDDM) is a heterogeneous disease resulting from insulin resistance and beta-cell dysfunction. beta-Cell dysfunction in Type-II diabetes is characterized by a specific lack of first-phase glucose-induced insulin secretion. This defect is readily reversible upon normalization of blood glucose levels. Chronic hyperglycemia itself is harmful to the beta-cell and affects both insulin biosynthesis and exocytosis. No unique intracellular defect has been demonstrated to be responsible for all common forms of the disease. However, mutations of the glucokinase gene have been identified in maturity onset diabetes in the young, a particular form of NIDDM.

The genetics and pathophysiology of type II and gestational diabetes

The development of both type II diabetes and gestational diabetes is probably governed by a complex and variable interaction of genes and environment. Molecular genetics has so far failed to identify discrete gene mutations accounting for metabolic changes in NIDDM. Both beta cell dysfunction and insulin resistance are operative in the manifestation of these disorders. Specific and sensitive immunoradiometric assays found fasting hyperproinsulinemia and first-phase hypoinsulinemia early in the natural history of the disorder. A lack of specificity of early radioimmunoassays for insulin resulted in measuring not only insulin but also proinsulins, leading to overestimation of insulin and misleading conclusions about its role in diabetes. The major causes of insulin resistance are the genetic deficiency of glycogen synthase activation, compounded by additional defects due to metabolic disorders, receptor downregulation, and glucose transporter abnormalities, all contributing to the impairment in muscle glucose uptake. The liver is also resistant to insulin in NIDDM, reflected in persistent hepatic glucose production despite hyperglycemia. Insulin resistance is present in many nondiabetics, but in itself is insufficient to cause type II diabetes. Gestational diabetes is closely related to NIDDM, and the combination of insulin resistance and impaired insulin secretion is of importance in its pathogenesis.

Insulin treatment improves relative hypersecretion of amylin to insulin in rats with non-insulin-dependent diabetes mellitus induced by neonatal streptozocin injection

The dissociated release of insulin and amylin in the hyperglycemic state has been reported. This relative hypersecretion of amylin is thought to provide an important insight into how amylin aggregates to form islet amyloid deposits in non-insulin-dependent diabetes mellitus (NIDDM). The aim of the present study was to characterize the alterations of amylin hypersecretion in NIDDM with exacerbation or amelioration of diabetic control. For this purpose, neonatally streptozocin (nSTZ) diabetic rats were treated with dexamethasone (0.25 mg/kg) or Lente insulin (3 to 5 U/kg) daily for 14 days, and responses of amylin and insulin to 16.7 mmol/L glucose or 10 mmol/L arginine were evaluated in vitro using an isolated perfused pancreas system. nSTZ rats exhibited moderate elevations of plasma glucose compared with normal rats. In the isolated perfused pancreas, the molar ratio of secreted amylin to insulin in response to 16.7 mmol/L glucose by nSTZ pancreas (1.8% +/- 0.2%) was significantly greater than that of normal rat pancreas (1.2% +/- 0.1%). Plasma glucose levels in nSTZ rats (7.3 +/- 0.4 mmol/L) increased with dexamethasone treatment (17.8 +/- 1.1 mmol/L, P < .005) and decreased with insulin treatment (5.8 +/- 0.4 mmol/L, P < .05). The secreted amylin to insulin ratio in dexamethasone-treated nSTZ rats was significantly greater than that of the controls (P < .05). Moreover, insulin-treated nSTZ rats exhibited decreased amylin to insulin molar ratios compared with saline-treated nSTZ rats (P < .05), which had the same levels as normal rats.(ABSTRACT TRUNCATED AT 250 WORDS)

Diet treatment of newly presenting type 2 diabetes improves insulin secretory capacity, but has no effect on insulin sensitivity

Fifteen newly diagnosed obese Type 2 diabetic subjects were treated with diet alone for 3 months with a median 1.5 kg weight loss. Each had a Continuous Infusion of Glucose with Model Assessment (CIGMA) test, at diagnosis and at 3 months, measuring insulin and C-peptide responses, and deriving mathematically modelled measures of beta-cell function and insulin sensitivity. Median fasting glucoses were 9.6 mmol l-1 at diagnosis and 8.5 mmol l-1 at 3 months (NS). Median fasting insulin was 9.3 mU l-1 at diagnosis and 11.7 mU l-1 at 3 months (NS). Median fasting C-peptide was 0.58 nmol l-1 at diagnosis and 0.64 nmol l-1 at 3 months (p < 0.05). Median achieved plasma insulin increased from 13.8 mU l-1 at diagnosis to 17 mU l-1 at 3 months (p < 0.02); median achieved plasma C-peptide increased from 0.72 nmol l-1 at diagnosis to 0.81 nmol l-1 at 3 months (p < 0.002). Modelled beta-cell function rose from median 26% at diagnosis to 37% at 3 months (p < 0.02). Modelled insulin sensitivity showed no significant change (median 0.31 at diagnosis, 0.27 at 3 months, NS). Elevation of achieved C-peptide was positively correlated with weight loss (Rs = 0.53, p < 0.05), but not with change in fasting glucose. Diet treatment of newly diagnosed Type 2 diabetes, with modest weight loss, results primarily in improvement of insulin secretory capacity, rather than insulin sensitivity.

Chronic exposure of HIT cells to high glucose concentrations paradoxically decreases insulin gene transcription and alters binding of insulin gene regulatory protein

Chronically culturing HIT-T15 cells in media containing high glucose concentrations leads to decreased insulin mRNA levels, insulin content, and insulin secretion. These changes can be prevented by culturing the cells in media containing lower glucose levels (Robertson, R. P., H.-J. Zhang, K. L. Pyzdrowski, and T. F. Walseth. 1992. J. Clin. Invest. 90:320-325). The mechanism of this seemingly paradoxical phenomenon was examined by transiently transfecting HIT cells with a chloramphenicol acetyl transferase (CAT) reporter gene controlled by the 5'-regulatory domain of the human insulin gene (INSCAT). Early passages of HIT cells readily expressed INSCAT, whereas late passages of cells chronically cultured in 11.1 mM glucose expressed only 28.7 +/- 2.3% (mean +/- SEM) of the CAT activity expressed in early passages. In contrast, late passages of HIT cells chronically cultured in 0.8 mM glucose retained the ability to express the INSCAT reporter gene to 69.6 +/- 10.0% of the CAT activity observed in early passages. The decrease in INSCAT expression in late passages of cells serially cultured in 11.1 mM glucose was associated with the inability to form a specific nuclear protein-DNA complex with the CT motifs of the human insulin promoter. Formation of this specific protein-DNA complex was preserved in late passages of HIT cells when serially cultured in 0.8 mM glucose. Mutations of the CT motifs caused markedly diminished CAT activity in all passages examined. These data indicate that chronic exposure of the beta cell to high glucose concentrations can paradoxically decrease insulin gene transcription, in part, by altering the ability of a regulatory protein (GSTF) to interact with the insulin gene promoter. This provides a potential mechanism for glucotoxic effects on the beta cell at the level of the insulin gene.

Preservation of insulin mRNA levels and insulin secretion in HIT cells by avoidance of chronic exposure to high glucose concentrations

Glucose toxicity of the pancreatic beta cell is considered to play a secondary role in the pathogenesis of type II diabetes mellitus. To gain insights into possible mechanisms of action of glucose toxicity, we designed studies to assess whether the loss of insulin secretion associated with serial passages of HIT-T15 cells might be caused by chronic exposure to high glucose levels since these cells are routinely cultured in media containing supramaximal stimulatory concentrations of glucose. We found that late passages of HIT cells serially cultured in media containing 11.1 mM glucose lost insulin responsivity and had greatly diminished levels of insulin content and insulin mRNA. In marked contrast, late passages of HIT cells cultured serially in media containing 0.8 mM glucose retained insulin mRNA, insulin content, and insulin responsivity to glucose in static incubations and during perifusion with glucose. No insulin gene mutation or alteration of levels of GLUT-2 were found in late passages of HIT cells cultured with media containing 11.1 mM glucose. These data uniquely indicate that loss of beta cell function in HIT cells passed serially under high glucose conditions is caused by loss of insulin mRNA, insulin content, and insulin secretion and is preventable by culturing HIT cells under low glucose conditions. This strongly suggests potential genetic mechanisms of action for glucose toxicity of beta cells.

Effects of a combination of bedtime intermediate-acting insulin and glibenclamide in type 2 (non-insulin-dependent) diabetic patients with secondary failure to respond to oral hypoglycaemic agents

The effect of a subcutaneous injection of an intermediate-acting insulin at bedtime combined with glibenclamide has been evaluated in 16 non-insulin-diabetic patients with secondary failure to respond to oral agents. The patients showed poor metabolic control (HbA1 greater than 11%) after two months on diet and glibenclamide treatment (15 mg.day-1). For 3 months the glibenclamide was continued together with an injection of an intermediate-acting insulin at bedtime in order to maintain fasting blood glucose under 120 mg.dl-1. A significant reduction in fasting blood glucose and HbA1 (15.50 vs 10.35%) and fructosamine (2.03 vs 1.69 mmol.l-1) was observed (230 to 141 mg.dl-1) at a mean insulin dose of 0.28 U.kg-1. The peak blood glucose after a standard test meal was also significantly improved (290 vs 203 mg.dl-1). Two months after the bedtime insulin injection had been withdrawn, only one patient was still being treated with oral agents alone. Except for another patient who dropped out, all the others had to be treated again with insulin because their fasting blood glucose exceeded 180 mg.dl-1. It is concluded that a single subcutaneous injection of an intermediate-acting insulin at bedtime combined with glibenclamide improved fasting and post-meal blood glucose concentrations in non-insulin-dependent patients resistant to diet and oral hypoglycaemic treatment. Almost all of the patients relapsed after insulin was withdrawn.

Defective insulin secretion in NIDDM: integral part of a multiplier hypothesis

Non-insulin dependent diabetes mellitus (NIDDM) is characterized by a specific defect in glucose recognition by the pancreatic islet beta cell. This is in clear distinction to patients with insulin dependent diabetes mellitus (IDDM) who undergo pancreatic islet beta cell death and no longer have the ability to synthesize, store, and release insulin. Defective glucose-induced first phase insulin responses in patients with NIDDM can be partially restored by exogenous insulin treatment and by other pharmacologic therapy. These observations provide strength for the theory of glucose desensitization of the pancreatic beta cell as an important secondary defect in the pathogenesis of abnormal insulin secretion in NIDDM. However, even though defective insulin secretion is an essential part of the pathogenesis of NIDDM, in itself it is not sufficient. A multiplicative effect is required involving interaction between tissue resistance to insulin action and defective insulin secretion whose product is the syndrome of NIDDM.

Masking of diabetic phenotype on a low-energy diet despite persistence of impaired insulin response

Type 2 diabetes has been postulated to be a "thrifty genotype" that aids fuel conservation; to investigate this hypothesis, type 2 diabetic and nondiabetic subjects, normal weight and obese, were studied after both 6 days on a 700-calorie diet and 6 days on a 2,800-calorie diet. On 2,800 calories per day, the median basal plasma glucose was raised in diabetics compared with nondiabetic subjects (median, 5.5 and 4.5 mmol/L, respectively; P = .003), but on the low-energy diet there was no difference (4.1 and 3.7 mmol/L, respectively; P greater than .05). Basal plasma insulin levels were similar in the diabetic and nondiabetic subjects and were twofold to threefold higher on the high- than low-energy diet in both diabetic (median, 7.8 and 3.1 mU/L on high- and low-energy diets, respectively; P = .007) and nondiabetic subjects (6.8 and 2.6 mU/L, respectively; P = .005). Similarly, the postprandial insulin concentrations increased to the same degree on the high- compared with the low-energy diet in diabetic (median postprandial increment, 14.9 and 3.4 mU/L; P = .005) and nondiabetic patients (9.5 and 3.0 mU/L; P = .005) and the beta cells in type 2 diabetes appeared to modulate normally to different calorie intakes. On both diets, the diabetic subjects had an impaired first-phase insulin response to an intravenous glucose load compared with nondiabetic subjects (high-energy diet median first-phase increment, 4.3 and 21.2 mU/L in diabetic and nondiabetic subjects, P = .0007; low-energy diet, 4.0 and 20.4 mU/L, respectively, P = .003).(ABSTRACT TRUNCATED AT 250 WORDS)

No glucotoxicity after 53 hours of 6.0 mmol/l hyperglycaemia in normal man

In vitro and in vivo studies have suggested that metabolic deterioration can be induced by hyperglycaemia per se. The effect of 53 h of 2.2 mg glucose.kg ideal body weight-1.min-1 was examined in four normal male subjects. This produced overnight hyperglycaemia of 6.0 mmol/l on the two nights of the study compared with 4.7 mmol/l on the control night (p less than 0.05). In response there was a sustained, two-fold increase in basal plasma insulin (p less than 0.005) and C-peptide (p less than 0.05) levels. After two days of hyperglycaemia an increased Beta-cell response was demonstrated in response to an additional glucose infusion stimulus (estimated Beta-cell function median of 84% on the control day to 100% after two days glucose infusion). Plasma insulin and C-peptide responses to a 10.0 mmol/l hyperglycaemic clamp increased over the two days of the study (insulin from median 48 mU/l to 73 mU/l and C-peptide from median 2.0 pmol/ml to 2.6 pmol/l). Glucose tolerance to the additional glucose infusion stimulus improved, suggesting that the increased insulin response during hyperglycaemia was enhancing peripheral glucose uptake. The calculated peripheral insulin sensitivity was unchanged during the hyperglycaemic clamp. Thus, in response to the two days of basal hyperglycaemia, both the basal and stimulated Beta-cell responses were enhanced and there was no evidence for 'glucose toxicity' to the Beta-cells.