RETRACTION: Quercetin Preserves β-Cell Mass and Function in Fructose-Induced Hyperinsulinemia through Modulating Pancreatic Akt/FoxO1 Activation

Early intervention and preservation of β-cell function are essential for optimal glycemic control in the long term.Available data support the early use of the long-acting glucagon-like peptide-1 analogue liraglutide in preservation of β-cell mass and function,leading to better glycemic control.Besides glycemic control,persistent weight loss and reduced visceral adiposity are observed in type 2 diabetic patients treated with liraglutide,linking to its potential cardio-protective effects. Key words: Liraglutide ; Glucagon-like peptide-1 ; Diabetes mellitus, type 2 ; β cell function

Fructose-induced hyperinsulinemia is associated with insulin compensative secretion and predicts the onset of type 2 diabetes. In this study, we investigated the preservation of dietary flavonoid quercetin on pancreatic β-cell mass and function in fructose-treated rats and INS-1 β-cells. Quercetin was confirmed to reduce serum insulin and leptin levels and blockade islet hyperplasia in fructose-fed rats. It also prevented fructose-induced β-cell proliferation and insulin hypersecretion in INS-1 β-cells. High fructose increased forkhead box protein O1 (FoxO1) expressions in vivo and in vitro, which were reversed by quercetin. Quercetin downregulated Akt and FoxO1 phosphorylation in fructose-fed rat islets and increased the nuclear FoxO1 levels in fructose-treated INS-1 β-cells. The elevated Akt phosphorylation in fructose-treated INS-1 β-cells was also restored by quercetin. Additionally, quercetin suppressed the expression of pancreatic and duodenal homeobox 1 (Pdx1) and insulin gene (Ins1 and Ins2) in vivo and in vitro. In fructose-treated INS-1 β-cells, quercetin elevated the reduced janus kinase 2/signal transducers and activators of transcription 3 (Jak2/Stat3) phosphorylation and suppressed the increased suppressor of cytokine signaling 3 (Socs3) expression. These results demonstrate that quercetin protects β-cell mass and function under high-fructose induction through improving leptin signaling and preserving pancreatic Akt/FoxO1 activation.

This article reviews data collected from clinical studies regarding the place of early insulin treatment in preservation of β-cell function in type 2 diabetic patients. It emphasizes the stepwise progression of the data, starting with small uncontrolled studies and progressing to larger-scale controlled studies. It summarizes current knowledge in the field, emphasizing the additional information gained from the Outcome Reduction with Initial Glargine Intervention (ORIGIN) trial (1). ### Effect of glucotoxicity and lipotoxicity on β-cells Glucotoxicity and lipotoxicity have long been recognized as having a deleterious effect on both β-cell function and insulin action (2–4). Glucolipotoxicity refers to the combined deleterious effects of elevated glucose and free fatty acids on β-cell mass and function (5). Significant progress has been made in recent years toward a better understanding of the cellular and molecular basis of glucolipotoxicity (5–7). Insulin protects the β-cell by inducing rapid reversal of glucolipotoxicity and β-cell rest (8,9). The rapid reversal of glucolipotoxicity by insulin therapy is one of the justifications for early insulin treatment (2–10). ### Treat to target or treat to failure? The importance of avoiding prolonged hyperglycemia in patients with short diabetes duration in order to minimize its negative effect on late microvascular and macrovascular complications has been established (11). Hence, present guidelines (12–16) recommend early initiation of life style changes with or without metformin and subsequent addition of 2nd- and 3rd-line therapy when previous treatments fail to achieve or maintain the goal. The goals in the treatment of hyperglycemia in newly diagnosed type 2 diabetes are to achieve near-normal glucose control as early as possible in order to preserve β-cell function and maintain long-term normoglycemia. The capacity of antidiabetes medication to maintain prolonged glycemic control (glucose durability) is of great importance. In the ADOPT study, rosiglitazone (17) demonstrated the best “glucose durability” compared with sulfonylurea (SU) and metformin. …

A defining characteristic of type 1 diabetes mellitus (T1DM) pathophysiology is pancreatic β-cell death and dysfunction, resulting in insufficient insulin secretion to properly control blood glucose levels. Treatments that promote β-cell replication and survival, thus reversing the loss of β-cell mass, while also preserving β-cell function, could lead to a real cure for T1DM. The α-subunit of the heterotrimeric Gz protein, Gαz, is a tonic negative regulator of adenylate cyclase and downstream cAMP production. cAMP is one of a few identified signaling molecules that can simultaneously have a positive impact on pancreatic islet β-cell proliferation, survival, and function. The purpose of our study was to determine whether mice lacking Gαz might be protected, at least partially, from β-cell loss and dysfunction after streptozotocin treatment. We also aimed to determine whether Gαz might act in concert with an activator of the cAMP-stimulatory glucagon-like peptide 1 receptor, exendin-4 (Ex4). Without Ex4 treatment, Gαz-null mice still developed hyperglycemia, albeit delayed. The same finding held true for wild-type mice treated with Ex4. With Ex4 treatment, Gαz-null mice were protected from developing severe hyperglycemia. Immunohistological studies performed on pancreas sections and in vitro apoptosis, cytotoxicity, and survival assays demonstrated a clear effect of Gαz signaling on pancreatic β-cell replication and death; β-cell function was also improved in Gαz-null islets. These data support our hypothesis that a combination of therapies targeting both stimulatory and inhibitory pathways will be more effective than either alone at protecting, preserving, and possibly regenerating β-cell mass and function in T1DM.

OBJECTIVETo determine the extent of β-cell function in youth with diabetes and GAD65 and/or IA2 autoantibodies.RESEARCH DESIGN AND METHODSFasting C-peptide levels from 2,789 GAD65- and/or IA2 autoantibody-positive youth aged 1–23 years from the SEARCH for Diabetes in Youth study were used. Preserved β-cell function was defined on the basis of cut points derived from the Diabetes Control and Complications Trial (DCCT) (fasting C-peptide ≥0.23 ng/ml) and from the U.S. adolescent population of the National Health and Nutrition Examination Survey (NHANES) 5th percentile for fasting C-peptide (≥1.0 ng/ml). We compared the clinical characteristics between those with and without preserved β-cell function.RESULTSWithin the first year of diagnosis, 82.9% of youth had a fasting C-peptide ≥0.23 ng/ml and 31.2% had values ≥1.0 ng/ml. Among those with ≥5 years of diabetes duration, 10.7% had preserved β-cell function based on the DCCT cutoff and 1.0% were above the 5th percentile of the NHANES population.CONCLUSIONSWithin the 1st year of diagnosis, four of five youth with autoantibody-positive diabetes have clinically significant amounts of residual β-cell function and about one-third have fasting C-peptide levels above the 5th percentile of a healthy adolescent population. Even 5 years after diagnosis, 1 of 10 has fasting C-peptide above a clinically significant threshold. These findings have implications for clinical classification of youth with diabetes as well as clinical trials aimed to preserve β-cell function after diabetes onset.

Residual β-cell function is present at the time of diagnosis with Type 1 diabetes. Preserving this β-cell function reduces complications. We hypothesized that exercise preserves β-cell function in Type 1 diabetes and undertook a pilot trial to address the key uncertainties in designing a definitive trial to test this hypothesis. A randomized controlled pilot trial in adults aged 16-60 years diagnosed with Type 1 diabetes within the previous 3 months was undertaken. Participants were assigned to control (usual care) or intervention (exercise consultation every month), in a 1 : 1 ratio for 12 months. The primary outcomes were recruitment rate, drop out, exercise adherence [weeks with ≥ 150 min of self-reported moderate to vigorous physical activity (MVPA)], and exercise uptake in the control group. The secondary outcomes were differences in insulin sensitivity and rate of loss of β-cell function between intervention and control at 6 and 12 months. Of 507 individuals who were approached, 58 (28 control, 30 intervention) entered the study and 41 completed it. Participants were largely white European males, BMI 24.8 ± 3.8 kg/m2 , HbA1c 75 ± 25 mmol/mol (9 ± 2%). Mean level of objectively measured MVPA increased in the intervention group (mean 243 to 273 min/week) and 61% of intervention participants reached the target of ≥ 150 min/week of self-reported MVPA on at least 42 weeks of the year. Physical activity levels fell slightly in the control group (mean 277 to 235 min of MVPA/week). There was exploratory evidence that intervention group became more insulin sensitive and required less insulin. However, the rate of loss of β-cell function appeared similar between the groups, although the change in insulin sensitivity may have affected this. We show that it is possible to recruit and randomize people with newly diagnosed Type 1 diabetes to a trial of an exercise intervention, and increase and maintain their exercise levels for 12 months. Future trials need to incorporate measures of greater adherence to exercise training targets, and include more appropriate measures of β-cell function. (Clinical Trials Registry No; ISRCTN91388505).

A decrease in β-cell mass is a well-known key pathogenic event in diabetes, not only in human subjects with type 1 patients, where β-cells are destroyed by the immune system, but also in type 2 diabetes where reduced β-cell function results in hyperglycemia and associated metabolic abnormalities (1,2). These concepts have made the search for the set of rules that control pancreatic β-cell mass an important area of islet research. An interesting emerging topic with clinical relevance is the notion that the actions of glucagon-like peptide-1 (GLP-1) on islet β-cells could be harnessed to improve and preserve β-cell function and potentially reverse defects in β-cell mass (3). GLP-1 is a proglucagon-derived peptide secreted from gut endocrine cells that acts on β-cells at multiple levels, acutely stimulating insulin secretion while chronically promoting proinsulin biosynthesis and growth and survival of β-cells. During meals, GLP-1 is secreted and acts immediately as an incretin, acutely potentiating glucose-dependent insulin release. However, GLP-1 also enhances glucose competence of β-cells and restores glucose sensitivity to diabetic β-cells in vivo. These findings, taken together with the clinical development of GLP-1 receptor (GLP-1R) agonists and dipeptidyl peptidase-4 inhibitors, have focused on attention to the extent to which incretin-based agents may exert long-term beneficial effects on preservation of β-cell function in subjects with type 2 diabetes (4). In an exciting study published in this issue of Diabetes (5), two mechanisms by which GLP-1 causes β-cell replication have been explored. As the authors state, “the overall effect of GLP-1 on increasing β-cell mass in both in vivo and in vitro conditions is relatively small, and augmenting this effect would be beneficial for the treatment or prevention of both type 1 and type 2 diabetes.” The goal of the study by Klinger et al. was to elucidate molecular mechanisms …

Ketosis-prone diabetes (KPD) is an emerging, heterogeneous syndrome. A sound classification scheme for KPD is essential to guide clinical practice and pathophysiologic studies. Four schemes have been used and are based on immunologic criteria, immunologic criteria and insulin requirement, BMI, and immunologic criteria and beta-cell function (Abeta classification). The aim of the present study is to compare the four schemes for accuracy and predictive value in determining whether KPD patients have absent or preserved beta-cell function, which is a strong determinant of long-term insulin dependence and clinical phenotype. Consecutive patients (n = 294) presenting with diabetic ketoacidosis and followed for 12-60 months were classified according to all four schemes. They were evaluated longitudinally for beta-cell autoimmunity, clinical and biochemical features, beta-cell function, and insulin dependence. beta-Cell function was defined by peak plasma C-peptide response to glucagon >or=1.5 ng/ml. The accuracy of each scheme to predict absent or preserved beta-cell function after 12 months of follow-up was tested using multiple statistical analyses. The "Abeta" classification scheme was the most accurate overall, with a sensitivity and specificity of 99.4 and 95.9%, respectively, positive and negative likelihood ratios of 24.55 and 0.01, respectively, and an area under the receiver operator characteristic curve of 0.972. The Abeta scheme has the highest accuracy and predictive value in classifying KPD patients with regard to clinical outcomes and pathophysiologic subtypes.

Insulin resistance and beta-cell dysfunction, two factors central to the pathogenesis of type 2 diabetes, were studied in relation to the development of diabetes in a group of participants with impaired glucose tolerance in the Diabetes Prevention Program (DPP) at baseline and after specific interventions designed to prevent diabetes. Participants were randomly assigned to placebo (n = 1,082), metformin (850 mg twice a day) (n = 1,073), or intensive lifestyle intervention (n = 1,079). The diabetes hazard rate was negatively associated with baseline insulin sensitivity (hazard rate ratio = 0.62-0.94 per SD difference, depending on treatment group and measure of sensitivity) and with baseline insulin secretion (hazard rate ratio = 0.57-0.76 per SD). Improvements in insulin secretion and insulin sensitivity were associated with lower hazard rates in all treatment arms (hazard rate ratio = 0.46-0.95 per SD increase and 0.29-0.79 per SD increase, respectively). In multivariate models that included the three metabolic variables (changes in body weight, insulin sensitivity, and insulin secretion) each significantly and independently predicted progression to diabetes when adjusted for the other two variables. The intensive lifestyle intervention, which elicited the greatest reduction in diabetes incidence, produced the greatest improvement in insulin sensitivity and the best preservation of beta-cell function after 1 year, whereas the placebo group, which had the highest diabetes incidence, had no significant change in insulin sensitivity and beta-cell function after 1 year. In the metformin group, diabetes risk, insulin sensitivity, and beta-cell function at 1 year were intermediate between those in the intensive lifestyle and placebo groups. In conclusion, higher insulin secretion and sensitivity at baseline and improvements in response to treatment were associated with lower diabetes risk in the DPP. The better preventive effectiveness of intensive lifestyle may be due to improved insulin sensitivity concomitant with preservation of beta-cell function.

Low insulin resistance and preserved β-cell function contribute to human longevity but are not associated with TH–INS genes

β-Cell dysfunction is central to the pathogenesis of impaired glucose tolerance (IGT) and type 2 diabetes. Compared with adults, youth have hyperresponsive β-cells and their decline in β-cell function appears to be more rapid. However, there are no direct comparisons of β-cell responses to pharmacological intervention between the two age-groups. The Restoring Insulin Secretion (RISE) Adult Medication Study and the RISE Pediatric Medication Study compared interventions to improve or preserve β-cell function. Obese youth (n = 91) and adults (n = 132) with IGT or recently diagnosed type 2 diabetes were randomized to 3 months of insulin glargine followed by 9 months of metformin, or 12 months of metformin. Hyperglycemic clamps conducted at baseline, after 12 months of medication, and 3 months after medication withdrawal assessed β-cell function as steady-state and maximal C-peptide responses adjusted for insulin sensitivity. Temporal changes in β-cell function were distinctly different. In youth, β-cell function deteriorated during treatment and after treatment withdrawal, with no differences between treatment groups. In adults, β-cell function improved during treatment, but this was not sustained after treatment withdrawal. The difference in β-cell function outcomes in response to medications in youth versus adults supports a more adverse trajectory of β-cell deterioration in youth.

In the U.S., ∼21 × 106 individuals have type 2 diabetes, and twice as many have impaired glucose tolerance (IGT). Approximately 40–50% of individuals with IGT will progress to type 2 diabetes over their lifetime. Therefore, treatment of high-risk individuals with IGT to prevent type 2 diabetes has important medical, economic, social, and human implications. Weight loss, although effective in reducing the conversion of IGT to type 2 diabetes, is difficult to achieve and maintain. Moreover, 40–50% of IGT subjects progress to type 2 diabetes despite successful weight reduction. In contrast, pharmacological treatment of IGT with oral antidiabetic agents that improve insulin sensitivity and preserve β-cell function—the characteristic pathophysiological abnormalities present in IGT and type 2 diabetes—uniformly have been shown to prevent progression of IGT to type 2 diabetes. The most consistent results have been observed with the thiazolidinediones (Troglitazone in the Prevention of Diabetes [TRIPOD], Pioglitazone in the Prevention of Diabetes [PIPOD], Diabetes Reduction Assessment with Ramipril and Rosiglitazone Medication [DREAM], and Actos Now for the Prevention of Diabetes [ACT NOW]), with a 50–70% reduction in IGT conversion to diabetes. Metformin in the U.S. Diabetes Prevention Program (DPP) reduced the development of type 2 diabetes by 31% and has been recommended by the American Diabetes Association (ADA) for treating high-risk individuals with IGT. The glucagon-like peptide-1 analogs, which augment insulin secretion, preserve β-cell function, and promote weight loss, also would be expected to be efficacious in preventing the progression of IGT to type 2 diabetes. Because individuals in the upper tertile of IGT are maximally/near-maximally insulin resistant, have lost 70–80% of their β-cell function, and have an ∼10% incidence of diabetic retinopathy, pharmacological intervention, in combination with diet plus exercise, should be instituted.

Introduction: The incidence of type 2 diabetes mellitus (T2DM) has risen to epidemic proportions, and this is associated with enormous cost. T2DM is preceded by ‘prediabetes’, and the diagnosis of impaired glucose tolerance (IGT) and/or impaired fasting glucose (IFG) provides an opportunity for targeted intervention. Prediabetic subjects manifest both core defects characteristic of T2DM, that is, insulin resistance and β-cell dysfunction. Interventions which improve insulin sensitivity and/or preserve β-cell function are logical strategies to delay the conversion of IGT/IFG to T2DM or revert glucose tolerance to normal.Areas covered: The authors examine pharmacologic agents that have proven to decrease the conversion of IGT to T2DM and represent potential treatment options in prediabetes.Expert opinion: Weight loss improves whole body insulin sensitivity, preserves β-cell function and decreases progression of prediabetes to T2DM. In real life long-term weight loss is the exception and, even if successful, 40 – 50% of IGT individuals still progress to T2DM. Pharmacotherapy provides an alternative strategy to improve insulin sensitivity and preserve β-cell function. Thiazolidinediones (TZDs) are highly effective in T2DM prevention. Long-acting glucagon-like peptide-1 (GLP-1) analogs, because they augment β-cell function and promote weight loss, are effective in preventing IGT progression to T2DM. Metformin is considerably less effective than TZDs or GLP-1 analogs.

SUMMARY Impaired β-cell function in Type 2 diabetes mellitus (T2DM) is generally progressive. The commonly used sulfonylureas (SU) lose efficacy over time and are associated with impaired β-cell function, and undesirable events such as weight gain and hypoglycemia. Thus, there is a strong need to develop antidiabetic agents that control glycemia without weight gain and hypoglycemia, and preserve β-cell function. Glucagon-like-peptide-1 (GLP-1) is known to improve glycemic control by enhancement of glucose-stimulated insulin secretion, preserving β-cell function, and minimizing hypoglycemia and weight gain. Liraglutide, a human GLP-1 analog, has recently been approved for use in Japanese patients with T2DM. To assess liraglutide in management of Japanese patients with T2DM, the results of clinical studies in Japan is summarized and also compared with the data from Europe and the USA. Clinical studies have shown liraglutide to be effective in achieving and maintaining glycemic control, while restoring insul...

Insulin lispro is as effective as regular insulin in optimising metabolic control and preserving β-cell function at onset of type 1 diabetes mellitus