Functional pancreatic beta-cell mass: Involvement in type 2 diabetes and therapeutic intervention

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.

Acute and Chronic Exposure to Linagliptin, a Selective Inhibitor of Dipeptidyl Peptidase-4 (DPP-4), Has an Effect on Dopamine, Serotonin and Noradrenaline Level in the Striatum and Hippocampus of Rats

Linagliptin is a selective dipeptidyl peptidase-4 (DPP-4) inhibitor that indirectly elevates the glucagon-like peptide-1 (GLP-1) level. The aim of the present study was to check whether linagliptin has an influence on neurotransmission in rat brain. Rats were acutely and chronically exposed to linagliptin (10 and 20 mg/kg, intraperitoneally (i.p.)). Twenty-four hours later, the striatum and hippocampus were selected for further studies. In neurochemical experiments, using high-performance liquid chromatography with electrochemical detection (HPLC-ED), the concentrations of three major neurotransmitters-dopamine, serotonin and noradrenaline-and their metabolites were measured. The analysis of mRNA expression of dopamine (D1 and D2), serotonin (5-HT-1 and 5-HT-2) and noradrenaline (α1 and α2a) receptors was also investigated using real-time quantitative reverse transcription polymerase chain reaction (RQ-PCR) in the same brain areas. Linagliptin has the ability to influence the dopaminergic system. In the striatum, the elevation of dopamine and its metabolites was observed after repeated administration of that linagliptin, and in the hippocampus, a reduction in dopamine metabolism was demonstrated. Acute linagliptin exposure increases the serotonin level in both areas, while after chronic linagliptin administration a tendency for the mRNA expression of serotoninergic receptors (5-HT1A and 5-HT2A) to increase was observed. A single instance of exposure to linagliptin significantly modified the noradrenaline level in the striatum and intensified noradrenaline turnover in the hippocampus. The recognition of the interactions in the brain between DPP-4 inhibitors and neurotransmitters and/or receptors is a crucial step for finding novel discoveries in the pharmacology of DPP-4 inhibitors and raises hope for further applications of DPP-4 inhibitors in clinical practices.

Linagliptin and secoisolariciresinol diglucoside attenuate hyperlipidemia and cardiac hypertrophy induced by a high-methionine diet in rats via suppression of hyperhomocysteinemia-induced endoplasmic reticulum stress

Background: Cardiac hypertrophy (CH) is one of the contributing causes of morbidity and mortality. Hyperhomocysteinemia (HHcy) is one of the diseases which may predispose hyperlipidemia and CH. Linagliptin (Lina) and secoisolariciresinol diglucoside (SDG) are known to alleviate a variety of illnesses by reducing oxidative stress and inflammation. Aim: This study aimed to study the effect of HHcy on cardiac tissues, with a special focus on endoplasmic reticulum (ER) stress as a mainstay pathophysiological pathway. In addition, our study examined the protective effect of Lina, SDG, and their combination against HHcy-induced hyperlipidemia and CH in rats. Methods: Seventy-five male Sprague-Dawley rats were randomly divided into five groups, and for 60 days, the following regimen was administered: Group I: rats received distilled water; Group II: rats received methionine (MET) (2 g/kg/day, p.o.); groups III and IV: rats received Lina (3 mg/kg/day, p.o.) and SDG (20 mg/kg/day, p.o.), respectively, followed by MET (2 g/kg/day, p.o.); Group V: rats received Lina and SDG, followed by MET (2 g/kg/day, p.o.). Results: Pretreatment with Lina, SDG, and their combination showed a significant decrease in serum levels of HHcy and an improved lipid profile compared to the MET group. Moreover, both drugs improved cardiac injury, as evidenced by the substantial improvement in ECG parameters, morphological features of the cardiac muscle, and reduced serum levels of cardiac markers. Additionally, Lina and SDG significantly attenuated cardiac oxidative stress, inflammation, and apoptosis. Furthermore, Lina, SDG, and their combination remarkably downregulated the enhanced expression of endoplasmic reticulum (ER) stress markers, GRP78, PERK, ATF-4, CHOP, NF-κB, and SREBP1c compared to the MET-group. Conclusion: Lina and SDG showed cardioprotective effects against HHcy-induced heart hypertrophy and hyperlipidemia in rats.

Lower skeletal muscle mass is associated with diabetes and insulin resistance: A cross-sectional study

AIMS

The association between skeletal muscle mass and diabetes incidence/insulin resistance/glycated hemoglobin (HbA1C) is unknown. The aim of this study was to investigate such association in clinically apparently healthy males and females.

METHODS

A cross-sectional study of 372,399 Korean males and females who completed bioelectrical impedance analysis (BIA) in a health-screening programme was performed. Skeletal muscle index was used as an indicator of skeletal muscle mass. Skeletal muscle index (%) [appendicular skeletal muscle mass (kg)/body weight (kg)X100] was estimated using BIA. The study outcomes were diabetes incidence, homoeostasis model assessment of insulin resistance (HOMA-IR), and HbA1C.

RESULTS

The mean age of study participants was 38.92 ± 8.54 years. Multiple logistic regression analysis revealed a significant negative association between Skeletal muscle index and diabetes incidence/HOMA-IR/HbA1C after adjusting for various confounding factors. Odds ratios (95% confidence interval (CI)) of diabetes incidence in Q2, Q3, and Q4 compared to the lowest quantile (Q1) were 0.95 (0.85-1.05), 0.88 (0.78-0.99), and 0.79 (0.69-0.9), respectively. Beta coefficients (95% CI) of HOMA-IR in Q2, Q3, and Q3 with Q1 were 0.05 (0.03-0.07), -0.06 (-0.09∼-0.04), and -0.19 (-0.22∼-0.16), respectively. Beta coefficients (95% CI) of HbA1C in Q2, Q3, and Q4 with Q1 were 0.02 (0.01-0.03), -0.001 (-0.01∼0.01), and -0.02 (-0.03∼-0.01), respectively.

CONCLUSIONS

This study demonstrated negative associations of skeletal muscle mass with diabetes incidence, insulin resistance, and HbA1C levels in healthy adults.

Context-dependent effects of CCN2 on β-cell mass expansion and indicators of cell stress in the setting of acute and chronic stress

Stimulation of functional β-cell mass expansion can be beneficial for the treatment of type 2 diabetes. Our group has previously demonstrated that the matricellular protein CCN2 can induce β-cell mass expansion during embryogenesis, and postnatally during pregnancy and after 50% β-cell injury. The mechanism by which CCN2 stimulates β-cell mass expansion is unknown. However, CCN2 does not induce β-cell proliferation in the setting of euglycemic and optimal functional β-cell mass. We thus hypothesized that β-cell stress is required for responsiveness to CCN2 treatment. In this study, a doxycycline-inducible β-cell-specific CCN2 transgenic mouse model was utilized to evaluate the effects of CCN2 on β-cell stress in the setting of acute (thapsigargin treatment ex vivo) or chronic [high-fat diet or leptin receptor haploinsufficiency (db/+) in vivo] cellular stress. CCN2 induction during 1 wk or 10 wk of high-fat diet or in db/+ mice had no effect on markers of β-cell stress. However, CCN2 induction did result in a significant increase in β-cell mass over high-fat diet alone when animals were fed high-fat diet for 10 wk, a duration known to induce insulin resistance. CCN2 induction in isolated islets treated with thapsigargin ex vivo resulted in upregulation of the gene encoding the Nrf2 transcription factor, a master regulator of antioxidant genes, suggesting that CCN2 further activates this pathway in the presence of cell stress. These studies indicate that the potential of CCN2 to induce β-cell mass expansion is context-dependent and that the presence of β-cell stress does not ensure β-cell proliferation in response to CCN2.NEW & NOTEWORTHY CCN2 promotes β-cell mass expansion in settings of suboptimal β-cell mass. Here, we demonstrate that the ability of CCN2 to induce β-cell mass expansion in the setting of β-cell stress is context-dependent. Our results suggest that β-cell stress is necessary but insufficient for CCN2 to increase β-cell proliferation and mass. Furthermore, we found that CCN2 promotes upregulation of a key antioxidant transcription factor, suggesting that modulation of β-cell oxidative stress contributes to the actions of CCN2.

Noncanonical Regulation of cAMP-Dependent Insulin Secretion and Its Implications in Type 2 Diabetes

Impaired glucose tolerance (IGT) and β-cell dysfunction in insulin resistance associated with obesity lead to type 2 diabetes (T2D). Glucose-stimulated insulin secretion (GSIS) from β-cells occurs via a canonical pathway that involves glucose metabolism, ATP generation, inactivation of K ATP channels, plasma membrane depolarization, and increases in cytosolic concentrations of [Ca 2+ ] c . However, optimal insulin secretion requires amplification of GSIS by increases in cyclic adenosine monophosphate (cAMP) signaling. The cAMP effectors protein kinase A (PKA) and exchange factor activated by cyclic-AMP (Epac) regulate membrane depolarization, gene expression, and trafficking and fusion of insulin granules to the plasma membrane for amplifying GSIS. The widely recognized lipid signaling generated within β-cells by the β-isoform of Ca 2+ -independent phospholipase A 2 enzyme (iPLA 2 β) participates in cAMP-stimulated insulin secretion (cSIS). Recent work has identified the role of a G-protein coupled receptor (GPCR) activated signaling by the complement 1q like-3 (C1ql3) secreted protein in inhibiting cSIS. In the IGT state, cSIS is attenuated, and the β-cell function is reduced. Interestingly, while β-cell-specific deletion of iPLA 2 β reduces cAMP-mediated amplification of GSIS, the loss of iPLA 2 β in macrophages (MØ) confers protection against the development of glucose intolerance associated with diet-induced obesity (DIO). In this article, we discuss canonical (glucose and cAMP) and novel noncanonical (iPLA 2 β and C1ql3) pathways and how they may affect β-cell (dys)function in the context of impaired glucose intolerance associated with obesity and T2D. In conclusion, we provide a perspective that in IGT states, targeting noncanonical pathways along with canonical pathways could be a more comprehensive approach for restoring β-cell function in T2D. © 2023 American Physiological Society. Compr Physiol 13:5023-5049, 2023.

The Adaptor Protein NumbL Is Involved in the Control of Glucolipotoxicity-Induced Pancreatic Beta Cell Apoptosis

Avoiding the loss of functional beta cell mass is critical for preventing or treating diabetes. Currently, the molecular mechanisms underlying beta cell death are partially understood, and there is a need to identify new targets for developing novel therapeutics to treat diabetes. Previously, our group established that Mig6, an inhibitor of EGF signaling, mediates beta cell death under diabetogenic conditions. The objective here was to clarify the mechanisms linking diabetogenic stimuli to beta cell death by investigating Mig6-interacting proteins. Using co-immunoprecipitation and mass spectrometry, we evaluated the binding partners of Mig6 under both normal glucose (NG) and glucolipotoxic (GLT) conditions in beta cells. We identified that Mig6 interacted dynamically with NumbL, whereas Mig6 associated with NumbL under NG, and this interaction was disrupted under GLT conditions. Further, we demonstrated that the siRNA-mediated suppression of NumbL expression in beta cells prevented apoptosis under GLT conditions by blocking the activation of NF-κB signaling. Using co-immunoprecipitation experiments, we observed that NumbL's interactions with TRAF6, a key component of NFκB signaling, were increased under GLT conditions. The interactions among Mig6, NumbL, and TRAF6 were dynamic and context-dependent. We proposed a model wherein these interactions activated pro-apoptotic NF-κB signaling while blocking pro-survival EGF signaling under diabetogenic conditions, leading to beta cell apoptosis. These findings indicated that NumbL should be further investigated as a candidate anti-diabetic therapeutic target.

Divergent metabolic phenotypes in two genetic syndromes of low insulin secretion

AIMS

We examined the effect of growth hormone (GH) counter-regulation on carbohydrate metabolism in individuals with life-long diminished insulin secretion (DIS).

METHODS

Adults homozygous for the E180 splice site mutation of GHR [Laron syndrome (LS)], adults with a gain-of-function mutation in CDKN1c [Guevara-Rosenbloom syndrome (GRS)], and controls were evaluated for body composition, leptin, total and high molecular weight (HMW) adiponectin, insulin-like growth factor (IGF) axis molecules, and a 5-hour oral glucose tolerance test (OGTT), with measurements of glucose, insulin, glucagon, ghrelin, pancreatic polypeptide, gastric inhibitory peptide, glucagon-like peptide-1, peptide YY, and islet amyloid polypeptide (IAPP).

RESULTS

Both syndromic cohorts displayed DIS during OGTT. LS subjects had higher serum concentrations of total and HMW adiponectin, and lower levels of IGF-I, IGF-II, and IGF-Binding Protein-3 than individuals in other study groups. Furthermore, they displayed normal glycemic responses during OGTT with the lowest IAPP secretion. In contrast, individuals with GRS had higher levels of protein glycation, deficient glucose control during OGTT, and increased secretion of IAPP.

CONCLUSIONS

A distinct metabolic phenotype depending on GH counter-regulatory status, associates with diabetes development and excess glucose-induced IAPP secretion.

Betatrophin and Insulin Resistance

Betatrophin (angiopoietin-like protein 8 (ANGPTL8)) is a hormone that was recently discovered in the human liver. Multiple homologous sequences have been detected in mammalian liver, white adipose, and brown adipose tissues. Betatrophin is crucial for the development of type 2 diabetes (T2D), insulin resistance, and lipid metabolism. Similar to the intake of insulin, thyroid hormones, irisin, and calories, betatrophin expression in the organism is usually attributed to energy consumption or heat generation. It can mediate the activity of lipoprotein lipase (LPL), which is the key enzyme of lipoprotein lipolysis. Due to its association with metabolic markers and the roles of glucose and lipid, the physiological function of betatrophin in glucose homeostasis and lipid metabolism can be more comprehensively understood. Betatrophin was also shown to facilitate pancreatic β-cell proliferation in a mouse model of insulin resistance. There are also reports that demonstrate that betatrophin regulates triglycerides (TGs) in the liver. Therefore, the process of regulating the physiological function by betatrophin is complicated, and its exact biological significance remains elusive. This study provides a comprehensive review of the current research, and it discusses the possible physiological functions of betatrophin, and specifically the mechanism of betatrophin in regulating blood glucose and blood lipids.

Adiponectin Intervention to Regulate Betatrophin Expression, Attenuate Insulin Resistance and Enhance Glucose Metabolism in Mice and Its Response to Exercise

Aims: Adiponectin stimulates mitochondrial biogenesis through peroxisome proliferator-activated receptor-coactivator1α (PGC-1α), a major regulator of mitochondrial biogenesis, and its effect on the genesis of insulin resistance is organ-specific. Expressed predominantly in fat and liver tissues, betatrophin is primarily involved in lipid metabolism, and could be a putative therapeutic target in metabolic syndrome and T2D. We hypothesized that the adiponectin pathway may regulate the production and/or secretion of betatrophin in liver. We aimed to determine whether exercise and adiponectin affect betatrophin to improve insulin resistance in mice. Methods: To investigate this hypothesis, we used wild-type C57BL/6 mice subjected to a high-fat diet, an exercise regimen, and i.p. injection of recombinant mouse adiponectin (Acrp30), and adiponectin knockout (Adipoq−/−) mice (C57BL/6 background) subjected to i.p. injection of Acrp30. Results: In Adipoq–/– mice, betatrophin levels in the plasma and liver were upregulated. In mice, plasma and liver betatrophin levels were significantly upregulated following a high-fat diet. Exercise and i.p. Acrp30 downregulated betatrophin levels and increased adiponectin mRNA and protein expression in the plasma and liver. The trend of change in PGC-1α and betatrophin levels in the liver was consistent. Conclusions/interpretation: Exercise reverses pathogenic changes in adiponectin and betatrophin levels in insulin-resistant mice. Exercise increased adiponectin levels and reduced betatrophin levels. Furthermore, exercise reduced betatrophin levels via adiponectin, which modulated the LKB1/AMPK/PGC-1α signaling axis but was not solely dependent on it for exerting its effects.

The role of insulin and incretin-based drugs in biliary tract cancer: epidemiological and experimental evidence

Insulin and incretin-based drugs are important antidiabetic agents with complex effects on cell growth and metabolism. Emerging evidence shows that insulin and incretin-based drugs are associated with altered risk of biliary tract cancer (BTC). Observational study reveals that insulin is associated with an increased risk of extrahepatic cholangiocarcinoma (ECC), but not intrahepatic cholangiocarcinoma (ICC) or gallbladder cancer (GBC). This type-specific effect can be partly explained by the cell of origin and heterogeneous genome landscape of the three subtypes of BTC. Similar to insulin, incretin-based drugs also exhibit very interesting contradictions and inconsistencies in response to different cancer phenotypes, including BTC. Both epidemiological and experimental evidence suggests that incretin-based drugs can be a promoter of some cancers and an inhibitor of others. It is now more apparent that this type of drugs has a broader range of physiological effects on the body, including regulation of endoplasmic reticulum stress, autophagy, metabolic reprogramming, and gene expression. In particular, dipeptidyl peptidase-4 inhibitors (DPP-4i) have a more complex effect on cancer due to the multi-functional nature of DPP-4. DPP-4 exerts both catalytic and non-enzymatic functions to regulate metabolic homeostasis, immune reaction, cell migration, and proliferation. In this review, we collate the epidemiological and experimental evidence regarding the effect of these two classes of drugs on BTC to provide valuable information.

Dysregulation of β-Cell Proliferation in Diabetes: Possibilities of Combination Therapy in the Development of a Comprehensive Treatment

Diabetes mellitus (DM) is a metabolic disorder characterized by chronic hyperglycemia as a result of insufficient insulin levels and/or impaired function as a result of autoimmune destruction or insulin resistance. While Type 1 DM (T1DM) and Type 2 DM (T2DM) occur through different pathological processes, both result in β-cell destruction and/or dysfunction, which ultimately lead to insufficient β-cell mass to maintain normoglycemia. Therefore, therapeutic agents capable of inducing β-cell proliferation is crucial in treating and reversing diabetes; unfortunately, adult human β-cell proliferation has been shown to be very limited (~0.2% of β-cells/24 h) and poorly responsive to many mitogens. Furthermore, diabetogenic insults result in damage to β cells, making it ever more difficult to induce proliferation. In this review, we discuss β-cell mass/proliferation pathways dysregulated in diabetes and current therapeutic agents studied to induce β-cell proliferation. Furthermore, we discuss possible combination therapies of proliferation agents with immunosuppressants and antioxidative therapy to improve overall long-term outcomes of diabetes.

The Role of cAMP in Beta Cell Stimulus-Secretion and Intercellular Coupling

Pancreatic beta cells secrete insulin in response to stimulation with glucose and other nutrients, and impaired insulin secretion plays a central role in development of diabetes mellitus. Pharmacological management of diabetes includes various antidiabetic drugs, including incretins. The incretin hormones, glucagon-like peptide-1 and gastric inhibitory polypeptide, potentiate glucose-stimulated insulin secretion by binding to G protein-coupled receptors, resulting in stimulation of adenylate cyclase and production of the secondary messenger cAMP, which exerts its intracellular effects through activation of protein kinase A or the guanine nucleotide exchange protein 2A. The molecular mechanisms behind these two downstream signaling arms are still not fully elucidated and involve many steps in the stimulus-secretion coupling cascade, ranging from the proximal regulation of ion channel activity to the central Ca2+ signal and the most distal exocytosis. In addition to modifying intracellular coupling, the effect of cAMP on insulin secretion could also be at least partly explained by the impact on intercellular coupling. In this review, we systematically describe the possible roles of cAMP at these intra- and inter-cellular signaling nodes, keeping in mind the relevance for the whole organism and translation to humans.

Ferroptosis in Different Pathological Contexts Seen through the Eyes of Mitochondria

Ferroptosis is a recently described form of regulated cell death characterized by intracellular iron accumulation and severe lipid peroxidation due to an impaired cysteine-glutathione-glutathione peroxidase 4 antioxidant defence axis. One of the hallmarks of ferroptosis is a specific morphological phenotype characterized by extensive ultrastructural changes of mitochondria. Increasing evidence suggests that mitochondria play a significant role in the induction and execution of ferroptosis. The present review summarizes existing knowledge about the mitochondrial impact on ferroptosis in different pathological states, primarily cancer, cardiovascular diseases, and neurodegenerative diseases. Additionally, we highlight pathologies in which the ferroptosis/mitochondria relation remains to be investigated, where the process of ferroptosis has been confirmed (such as liver- and kidney-related pathologies) and those in which ferroptosis has not been studied yet, such as diabetes. We will bring attention to avenues that could be followed in future research, based on the use of mitochondria-targeted approaches as anti- and proferroptotic strategies and directed to the improvement of existing and the development of novel therapeutic strategies.

Deciphering the Neuroprotective Role of Glucagon-like Peptide-1 Agonists in Diabetic Neuropathy: Current Perspective and Future Directions

Diabetic neuropathy is referred to as a subsequential and debilitating complication belonging to type 1 and type 2 diabetes mellitus. It is a heterogeneous group of disorders with a particularly complex pathophysiology and also includes multiple forms, ranging from normal discomfort to death. The evaluation of diabetic neuropathy is associated with hyperglycemic responses, resulting in an alteration in various metabolic pathways, including protein kinase C pathway, polyol pathway and hexosamine pathway in Schwann and glial cells of neurons. The essential source of neuronal destruction is analogous to these respective metabolic pathways, thus identified as potential therapeutic targets. These pathways regulating therapeutic medications may be used for diabetic neuropathy, however, only target specific drugs could have partial therapeutic activity. Various antidiabetic medications have been approved and marketed, which possess the therapeutic ability to control hyperglycemia and ameliorate the prevalence of diabetic neuropathy. Among all antidiabetic medications, incretin therapy, including Glucagon-like peptide-1 receptor agonists and dipeptidyl peptidase-4 inhibitors, are the most favorable medications for the management of diabetes mellitus and associated peripheral neuropathic complications. Besides enhancing glucose-evoked insulin release from pancreatic β-cells, these therapeutic agents also play a vital role to facilitate neurite outgrowth and nerve conduction velocity in dorsal root ganglion. Furthermore, incretin therapy also activates cAMP and ERK signalling pathways, resulting in nerve regeneration and repairing. These effects are evidently supported by a series of preclinical data and investigations associated with these medications. However, the literature lacks adequate clinical trial outcomes related to these novel antidiabetic medications. The manuscript emphasizes the pathogenesis, current pharmacological approaches and vivid description of preclinical and clinical data for the effective management of diabetic neuropathy.

ANGPTL8 in cardio-metabolic diseases

Dyslipidemia has been identified as an important factor in obesity, diabetes mellitus, and cardiovascular diseases (CVD), grouped as cardio-metabolic disorder diseases. Accordingly, dyslipidemia has become a major determinant in health worldwide. Both genome-wide association studies (GWAS) and research studies have focused on the elucidation of potential genetic mechanisms of dyslipidemia and the identification of new gene loci which contribute to the development of cardio-metabolic disorder diseases. Recent results indicate that both the ANGPTL8 gene and ANGPTL8 protein perform vital roles in modulating serum glucose and lipid metabolism. In this review, we examine the modulatory effects of ANGPTL8 and explore the potential mechanisms whereby ANGPTL8 affects serum glucose and lipid metabolism in cardio-metabolic disorder diseases.

New insights into ANGPTL8 in modulating the development of cardio-metabolic disorder diseases

Dyslipidemia is being identified as the most important factors of several health problems, such as obesity, diabetes mellitus, and cardiovascular diseases (CVD), which are always grouped together as cardio-metabolic disorder diseases. Consistently, dyslipidemia has become one of the most rising crisis of general health. Recently, it is worth noting that both genome-wide association studies (GWAS) and experimental research are being taken advantage to elucidate the potential genetic mechanisms of dyslipidemia and to identify new gene loci which contribute to the development of cardio-metabolic disorder diseases. According to the results, both ANGPTL8 gene and ANGPTL8 protein has been shown to embrace vital functions in modulating serum glucose and lipid metabolism. In the current review, the modulatory effects of ANGPTL8 in cardio-metabolic disorder diseases were summarized. In addition, novel insights which elucidate the potential mechanisms whereby ANGPTL8 affects glucose and lipid metabolism were also provided.

The Benefits of Including Hummus and Hummus Ingredients into the American Diet to Promote Diet Quality and Health: A Comprehensive Review

Over the last decade, hummus has become an increasingly popular food. Given the ingredients (i.e., primarily chickpeas and tahini), nutrient composition, versatility, and acceptability, hummus can play a unique role when included in the American diet, to promote diet quality and improve health. The purpose of this paper is to provide a comprehensive review of the scientific evidence examining the effects of acute and long-term consumption of hummus and hummus ingredients on diet quality and risk factors related to type 2 diabetes, cardiovascular disease, and obesity. In addition, food pattern/menu modeling is included to illustrate the potential nutritional impact of consuming hummus to meet dietary guidelines. In general, the consumption of hummus and/or its respective ingredients has been shown to improve postprandial glycemic control, fasting lipids, appetite control, and daily food intake compared to other commonly consumed foods. The incorporation of hummus into the American diet can also improve diet quality by replacing foods higher in saturated fats, sodium, or added sugars. Collectively, these findings support the addition of hummus and/or hummus ingredients as an important component of a healthy dietary pattern.

Single-Cell Transcriptome Analysis Dissects the Replicating Process of Pancreatic Beta Cells in Partial Pancreatectomy Model

Heterogeneity of gene expression and rarity of replication hamper molecular analysis of β-cell mass restoration in adult pancreas. Here, we show transcriptional dynamics in β-cell replication process by single-cell RNA sequencing of murine pancreas with or without partial pancreatectomy. We observed heterogeneity of Ins1-expressing β-cells and identified the one cluster as replicating β-cells with high expression of cell proliferation markers Pcna and Mki67. We also recapitulated cell cycle transition accompanied with switching expression of cyclins and E2F transcription factors. Both transient activation of endoplasmic reticulum stress responders like Atf6 and Hspa5 and elevated expression of tumor suppressors like Trp53, Rb1, and Brca1 and DNA damage responders like Atm, Atr, Rad51, Chek1, and Chek2 during the transition to replication associated fine balance of cell cycle progression and protection from DNA damage. Taken together, these results provide a high-resolution map depicting a sophisticated genetic circuit for replication of the β-cells.

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Single cell RNA sequencing dissects a sequence of replication process of beta cells

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ER stress responders are transiently activated in initiation of the proliferation

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Physiological replication accompanied with induced expression of tumor suppressors

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Fine balance of proliferation genes and tumor suppressors is a key of the replication

Intermittent Fasting for Twelve Weeks Leads to Increases in Fat Mass and Hyperinsulinemia in Young Female Wistar Rats

Fasting is known to cause physiological changes in the endocrine pancreas, including decreased insulin secretion and increased reactive oxygen species (ROS) production. However, there is no consensus about the long-term effects of intermittent fasting (IF), which can involve up to 24 hours of fasting interspersed with normal feeding days. In the present study, we analyzed the effects of alternate-day IF for 12 weeks in a developing and healthy organism. Female 30-day-old Wistar rats were randomly divided into two groups: control, with free access to standard rodent chow; and IF, subjected to 24-hour fasts intercalated with 24-hours of free access to the same chow. Alternate-day IF decreased weight gain and food intake. Surprisingly, IF also elevated plasma insulin concentrations, both at baseline and after glucose administration collected during oGTT. After 12 weeks of dietary intervention, pancreatic islets displayed increased ROS production and apoptosis. Despite their lower body weight, IF animals had increased fat reserves and decreased muscle mass. Taken together, these findings suggest that alternate-day IF promote β -cell dysfunction, especially in developing animals. More long-term research is necessary to define the best IF protocol to reduce side effects.

Flavone Hispidulin Stimulates Glucagon-Like Peptide-1 Secretion and Ameliorates Hyperglycemia in Streptozotocin-Induced Diabetic Mice

SCOPE

Loss of functional β-cell mass is central for the deterioration of glycemic control in diabetes. The incretin hormone glucagon-like peptide-1 (GLP-1) plays a critical role in maintaining glycemic homeostasis via potentiating glucose-stimulated insulin secretion and promoting β-cell mass. Agents that can directly promote GLP-1 secretion, thereby increasing insulin secretion and preserving β-cell mass, hold great potential for the treatment of T2D.

METHODS AND RESULTS

GluTag L-cells, INS832/13 cells, and mouse ileum crypts and islets are cultured for examining the effects of flavone hispidulin on GLP-1 and insulin secretion. Mouse livers and isolated hepatocytes are used for gluconeogenesis. Streptozotocin-induced diabetic mice are treated with hispidulin (20 mg kg^-1 day^-1 , oral gavage) for 6 weeks to evaluate its anti-diabetic potential. Hispidulin stimulates GLP-1 secretion from the L-cell line, ileum crypts, and in vivo. This hispidulin action is mediated via activation of cyclic adenosine monophosphate/protein kinase A signaling. Hispidulin significantly improves glycemic control in diabetic mice, concomitant with improved insulin release, and β-cell survival. Additionally, hispidulin decreases hepatic pyruvate carboxylase expression in diabetic mice and suppresses gluconeogenesis in hepatocytes. Furthermore, hispidulin stimulates insulin secretion from β-cells.

CONCLUSION

These findings suggest that Hispidulin may be a novel dual-action anti-diabetic compound via stimulating GLP-1 secretion and suppressing hepatic glucose production.

Long Non-Coding RNAs as Key Modulators of Pancreatic β-Cell Mass and Function

Numerous studies have sought to decipher the genetic and other mechanisms contributing to β-cell loss and dysfunction in diabetes mellitus. However, we have yet to fully understand the etiology of the disease or to develop satisfactory treatments. Since the majority of diabetes susceptibility loci are mapped to non-coding regions within the genome, understanding the functions of non-coding RNAs in β-cell biology might provide crucial insights into the pathogenesis of type 1 (T1D) and type 2 (T2D) diabetes. During the past decade, numerous studies have indicated that long non-coding RNAs play important roles in the maintenance of β-cell mass and function. Indeed, lncRNAs have been shown to be involved in controlling β-cell proliferation during development and/or β-cell compensation in response to hyperglycaemia. LncRNAs such as TUG-1 and MEG3 play a role in both β-cell apoptosis and function, while others sensitize β-cells to apoptosis in response to stress signals. In addition, several long non-coding RNAs have been shown to regulate the expression of β-cell-enriched transcription factors in cis or in trans. In this review, we provide an overview of the roles of lncRNAs in maintaining β-function and mass, and discuss their relevance in the development of diabetes.

The role of linagliptin, a selective dipeptidyl peptidase-4 inhibitor, in the morphine rewarding effects in rats

Linagliptin is a selective dipeptidyl peptidase-4 (DPP-4) inhibitor which suppresses the rapid degradation of endogenous glucagon-like peptide-1 (GLP-1). In clinical practice, it is used as an antidiabetic drug, but recent studies have confirmed its role in the activity of the central nervous system (CNS). The reported study focused on the role of linagliptin (10 and 20 mg/kg, ip) in the morphine rewarding effect, analyzing how the agent had influenced the conditioned place preference (CPP) in rats via the expression, acquisition, extinction and reinstatement of the morphine rewarding effect. The obtained results clearly demonstrated linagliptin to inhibit the expression and acquisition, to accelerate the extinction and, eventually, to reduce the reinstatement of morphine-induced CPP. The undertaken experiments significantly extended our knowledge on the mechanisms behind the morphine rewarding effect.

Oxaliplatin reverses the GLP-1R-mediated promotion of intrahepatic cholangiocarcinoma by altering FoxO1 signaling

Intrahepatic cholangiocarcinoma (ICC) is the second most common primary liver cancer, with a 5-year survival rate of <10%; effective drug treatment for ICC is currently lacking. Glucagon-like peptide-1 receptor (GLP-1R) is upregulated in ICC; however, the functions of GLP-1R in ICC remain unknown. In this study, the upregulation of GLP-1R was confirmed in ICC cells using reverse transcription-quantitative polymerase chain reaction and western blot analysis, and GLP-1R was determined to promote the migration and invasion of ICC cells using Transwell assays. This tumor-promoting effect depended on the upregulation of epithelial-mesenchymal transformation-associated proteins, which was mediated by the FoxO1 signaling pathway. It was also indicated that following oxaliplatin treatment, the effects of GLP-1R on EMT and invasion were reversed. This functional reversion was associated with the reduced phosphorylation of S256 in forkhead box O1 (FoxO1) and an increase in the levels of unphosphorylated FoxO1. These findings suggest that incretin-based therapies may increase the risk of ICC metastasis and should not be used solely for the treatment of patients with ICC.

Secretagogin is increased in plasma from type 2 diabetes patients and potentially reflects stress and islet dysfunction

Beta cell dysfunction accompanies and drives the progression of type 2 diabetes mellitus (T2D), but there are few clinical biomarkers available to assess islet cell stress in humans. Secretagogin, a protein enriched in pancreatic islets, demonstrates protective effects on beta cell function in animals. However, its potential as a circulating biomarker released from human beta cells and islets has not been studied. In this study primary human islets, beta cells and plasma samples were used to explore secretion and expression of secretagogin in relation to the T2D pathology. Secretagogin was abundantly and specifically expressed and secreted from human islets. Furthermore, T2D patients had an elevated plasma level of secretagogin compared with matched healthy controls, which was confirmed in plasma of diabetic mice transplanted with human islets. Additionally, the plasma secretagogin level of the human cohort had an inverse correlation to clinical assessments of beta cell function. To explore the mechanism of secretagogin release in vitro, human beta cells (EndoC-βH1) were exposed to elevated glucose or cellular stress-inducing agents. Secretagogin was not released in parallel with glucose stimulated insulin release, but was markedly elevated in response to endoplasmic reticulum stressors and cytokines. These findings indicate that secretagogin is a potential novel biomarker, reflecting stress and islet cell dysfunction in T2D patients.

Effects of Glucagon-Like Peptide-1 on Oxidative Stress and Nrf2 Signaling

Oxidative cellular damage caused by free radicals is known to contribute to the pathogenesis of various diseases such as cancer, diabetes, and neurodegenerative diseases, as well as to aging. The transcription factor nuclear factor erythroid 2-related factor 2 (Nrf2) and Kelch-like ECH-associated protein1 (Keap1) signaling pathways play an important role in preventing stresses including oxidative and inflammatory stresses. Nrf2 is a master regulator of cellular stress responses, induces the expression of antioxidant and detoxification enzymes, and protects against oxidative stress-induced cell damage. Glucagon-like peptide-1 (GLP-1) is an incretin hormone, which was originally found to increase insulin synthesis and secretion. It is now widely accepted that GLP-1 has multiple functions beyond glucose control in various tissues and organs including brain, kidney, and heart. GLP-1 and GLP-1 receptor agonists are known to be effective in many chronic diseases, including diabetes, via antioxidative mechanisms. In this review, we summarize the current knowledge regarding the role of GLP-1 in the protection against oxidative damage and the activation of the Nrf2 signaling pathway.

ANGPTL8 (betatrophin) role in diabetes and metabolic diseases

Diabetes is a major disease worldwide that is reaching epidemic levels. Its increased prevalence as well as its association with a high number of complications such as cardiovascular diseases, nephropathy, and retinopathy makes it an important disease for investigation. ANGPTL8 is a recently identified hormone that has been associated with two functionally important processes in the development of type 2 diabetes, insulin resistance as well as lipid metabolism. Initial work has shown that ANGPTL8 was expressed in liver, white adipose, and brown adipose tissues. ANGPTL8 regulates the activity of lipoprotein lipase, which is a key enzyme in lipoprotein lipolysis pathway through its direct interaction with ANGPTL3. It has been also reported that it regulates the replication of β-cells in response to insulin resistance. As a result, many recent studies have focused on the association of ANGPTL8 with diabetes and obesity as well as its association with various metabolic markers in order to better understand its physiological role in glucose homeostasis and lipid metabolism. In this review, we will highlight some of the key clinical findings, mainly from human studies, that investigated the role of ANGPTL8 in metabolic diseases such as diabetes, obesity, and the metabolic syndrome.

Circulating microRNA-375 as biomarker of pancreatic beta cell death and protection of beta cell mass by cytoprotective compounds

Objective

Previous studies demonstrated that circulating microRNA-375 (miR-375) is a suitable plasma biomarker for real-time detection of beta cell death. The present study evaluated the use of this biomarker to assess the beta cytoprotective effect of phenylpropenoic acid glucoside (PPAG), which was previously demonstrated to protect beta cells against various types of injury, and of exendin-4, which is an established antidiabetic drug.

Methods

PPAG or exendin-4 were administered in mice treated with streptozotocin (STZ) to acutely induce beta cell death. Beta cell mass and apoptotic death were measured in pancreatic tissue sections. Circulating miR-375 was measured in blood plasma by RT-qPCR. The release of miR-375 was also measured in vitro by MIN-6 beta cells.

Results

Administration of STZ resulted in measurable circulating levels of miR-375, a decrease in beta cell mass and increase in frequency of apoptotic beta cells. In vitro, there was a good correlation between miR-375 release and the extent of beta cell death. Treatment of mice with PPAG or exendin-4 significantly attenuated STZ-induced loss of beta cell mass and beta cell apoptosis, and normalized the blood level of miR-375.

Conclusions

These findings show the potential use of serological miR-375 measurements to evaluate the beta cytoprotective effect of (potential) antidiabetic drugs in vivo.

The regulatory role of DPP4 in atherosclerotic disease

The increasing prevalence of atherosclerosis has become a worldwide health concern. Although significant progress has been made in the understanding of atherosclerosis pathogenesis, the underlying mechanisms are not fully understood. Recent studies suggest dipeptidyl peptidase-4 (DPP4), a regulator of inflammation and metabolism, may be involved in the development of atherosclerotic diseases. There has been increasing clinical and pre-clinical evidence showing DPP4-incretin axis is involved in cardiovascular disease. Although the cardiovascular outcome of DPP4 inhibition or incretin analogues has been or being evaluated by several large scale clinical trials, the exact role of DPP4 in atherosclerotic diseases is not completely understood. In the current review, we will summarize the recent advances in direct and indirect regulatory role of DPP4 in atherosclerosis.

Embryonic exposures to perfluorooctanesulfonic acid (PFOS) disrupt pancreatic organogenesis in the zebrafish, Danio rerio

Perfluorooctanesulfonic acid (PFOS) is a ubiquitous environmental contaminant, previously utilized as a non-stick application for consumer products and firefighting foam. It can cross the placenta, and has been repeatedly associated with increased risk for diabetes in epidemiological studies. Here, we sought to establish the hazard posed by embryonic PFOS exposures on the developing pancreas in a model vertebrate embryo, and develop criteria for an adverse outcome pathway (AOP) framework to study the developmental origins of metabolic dysfunction. Zebrafish (Danio rerio) embryos were exposed to 16, 32, or 64 μM PFOS beginning at the mid-blastula transition. We assessed embryo health, size, and islet morphology in Tg(insulin-GFP) embryos at 48, 96 and 168 hpf, and pancreas length in Tg(ptf1a-GFP) embryos at 96 and 168 hpf. QPCR was used to measure gene expression of endocrine and exocrine hormones, digestive peptides, and transcription factors to determine whether these could be used as a predictive measure in an AOP. Embryos exposed to PFOS showed anomalous islet morphology and decreased islet size and pancreas length in a U-shaped dose-response curve, which resemble congenital defects associated with increased risk for diabetes in humans. Expression of genes encoding islet hormones and exocrine digestive peptides followed a similar pattern, as did total larval growth. Our results demonstrate that embryonic PFOS exposures can disrupt pancreatic organogenesis in ways that mimic human congenital defects known to predispose individuals to diabetes; however, future study of the association between these defects and metabolic dysfunction are needed to establish an improved AOP framework.

Gluten-free diet increases beta-cell volume and improves glucose tolerance in an animal model of type 2 diabetes

BACKGROUND

Gluten-free (GF) diet alleviates type 1 diabetes in animal models and possibly in humans. We recently showed that fatty acid-induced insulin secretion is enhanced by enzymatically digested gluten (gliadin) stimulation in INS-1E insulinoma cells. We therefore hypothesized that GF diet would induce beta-cell rest and ameliorate type 2 diabetes.

METHODS

C57BL/6JBomTac (B6) mice were fed a high-fat (HF), gluten-free high-fat (GF-HF), standard (STD) or gluten-free (GF) diet for 42 weeks.

RESULTS

Short-term (6-24 weeks) GF-HF versus HF feeding impaired glucose tolerance and increased fasting glucose. Long-term (36-42 weeks) GF-HF versus HF feeding improved glucose tolerance and decreased fasting leptin. Mice fed a GF-HF versus HF diet for 42 weeks showed higher volumes of beta cells, islets and pancreas. The beta-cell volume correlated with the islet- and pancreas volume as well as body weight. GF-HF versus HF diet did not influence toll-like receptor 4 (Tlr4), interleukin 1 (IL-1), interleukin 6 (IL-6) or tumour necrosis factor-alpha (TNF-alpha) mRNA expression in intestine. STD versus GF feeding did not affect any parameter studied.

CONCLUSIONS

Long-term feeding with GF-HF versus HF increases beta-cell volume and improves glucose tolerance in B6 mice. The mechanism may include beta-cell rest, but is unlikely to include TLR4 and proinflammatory cytokines in the intestine. Beta-cell volume correlates with pancreas volume and body weight, indicating that insulin secretion capacity controls pancreas volume. Thus, long-term GF diets may be beneficial for obese type 2 diabetes patients and trials should be performed. Copyright © 2016 John Wiley & Sons, Ltd.

mTORC1 pathway mediates beta cell compensatory proliferation in 60 % partial-pancreatectomy mice

Beta cell replication is the major component for maintenance of beta cell mass in adult rodents; however, little is known about what is the earliest signals that initiate rodent beta cell proliferation. The mTORC1 pathway integrates signals from growth factors and nutrients and regulates cell growth and survival. Here, we used normoglycemic 60 % partial-pancreatectomy (60 % Px) mouse model to determine whether mTORC1 pathway was required for compensatory beta cell proliferation. C57BL/6 J male mice were subjected to 60 % Px or sham operation, and subsequently treated with either rapamycin or vehicle for 7 days. Metabolic profile, pancreatic beta cell mass, and proliferation were examined, and expression levels of cell cycle regulators were determined. Beta cell proliferation was increased by 2.5-fold, and mTORC1 signaling was activated in islets post-Px. Rapamycin treatment impaired glucose tolerance and glucose stimulating insulin secretion in 60 % Px mice, but did not affect their insulin sensitivity in peripheral tissue. Rapamycin inhibited mTORC1 activity in beta cells, suppressed compensatory beta cell proliferation and growth, and reduced beta cell mass and insulin content in 60 % Px mice. Px caused an increase of the cyclin D2 at protein level and promoted cyclin D2 nuclear localization in an mTOR-dependent manner. Disrupting mTORC1 signaling suppressed cell proliferation and simultaneously diminished cyclin D2 protein abundance in RINm5F cells. Our data demonstrated that mTORC1 plays an essential role in beta cell adaption to significant beta cell mass loss in 60 % Px model and in early compensatory beta cell proliferation via cyclin D2 pathway.

Anti-Inflammatory Effects of GLP-1-Based Therapies beyond Glucose Control

Glucagon-like peptide-1 (GLP-1) is an incretin hormone mainly secreted from intestinal L cells in response to nutrient ingestion. GLP-1 has beneficial effects for glucose homeostasis by stimulating insulin secretion from pancreatic beta-cells, delaying gastric emptying, decreasing plasma glucagon, reducing food intake, and stimulating glucose disposal. Therefore, GLP-1-based therapies such as GLP-1 receptor agonists and inhibitors of dipeptidyl peptidase-4, which is a GLP-1 inactivating enzyme, have been developed for treatment of type 2 diabetes. In addition to glucose-lowering effects, emerging data suggests that GLP-1-based therapies also show anti-inflammatory effects in chronic inflammatory diseases including type 1 and 2 diabetes, atherosclerosis, neurodegenerative disorders, nonalcoholic steatohepatitis, diabetic nephropathy, asthma, and psoriasis. This review outlines the anti-inflammatory actions of GLP-1-based therapies on diseases associated with chronic inflammation in vivo and in vitro, and their molecular mechanisms of anti-inflammatory action.

[Potential of pharmacological modulation of level and activity incretins on diabetes mellitus type 2]

This review summarizes data on the main approaches used for the search of biologically active compounds modulating the level and physiological activity of incretins. Currently two groups of drugs are used in clinical practice: they either replenish the deficit of incretins (glucagon-like peptide-1 receptor agonists) or inhibit the degradation processes (dipeptidyl peptidase 4 inhibitors). In addition, new groups of substances are actively searched. These include non-peptide agonists of glucagon-like peptide-1 receptors, agonists/antagonists of glucose-dependent insulinotropic peptide, the hybrid polypeptides based on glucagon-like peptide-1 and glucagon.

Short-term intensive insulin therapy at diagnosis in type 2 diabetes: plan for filling the gaps

Short-term intensive insulin therapy is unique amongst therapies for type 2 diabetes because it offers the potential to preserve and improve beta-cell function without additional pharmacological treatment. On the basis of clinical experience and the promising results of a series of studies in newly diagnosed patients, mostly in Asian populations, an expert workshop was convened to assess the available evidence and the potential application of short-term intensive insulin therapy should it be advocated for inclusion in clinical practice. Participants included primary care physicians and endocrinologists. We endorse the concept of short-term intensive insulin therapy as an option for some patients with type 2 diabetes at the time of diagnosis and have identified the following six areas where additional knowledge could help clarify optimal use in clinical practice: (1) generalizability to primary care, (2) target population and biomarkers, (3) follow-up treatment, (4) education of patients and providers, (5) relevance of ethnicity, and (6) health economics.

Lack of associations between betatrophin/ANGPTL8 level and C-peptide in type 2 diabetic subjects

Background

Betatrophin has been suggested as an inducer of β-cell proliferation in mice in addition to its function in regulating triglyceride. Recent data showed that betatrophin was increased in Type 2 Diabetes (T2D), however, its ability to induce insulin production has been questioned. We hypothesized that the increased betatrophin in T2D is not affecting insulin production from β-cells. To test this hypothesis, we investigated the association between betatrophin and C-peptide level in humans, which acts as a measure of endogenous insulin production from β-cells.

Methods

This study was designed to examine the association between plasma betatrophin level and C-peptide in 749 T2D and non-diabetics.

Results

Betatrophin and C-peptide levels were higher in T2D subjects compared with non-diabetics subjects. Betatrophin showed strong correlation with C-peptide in non-diabetics subjects (r = 0.28, p = < 0.0001). No association between betatrophin and C-peptide were observed in T2D subjects (r = 0.07, p = 0.3366). Dividing obese and non-obese subjects into tertiles according to betatrophin level showed significantly higher C-peptide levels at higher tertiles of betatrophin in obese non-diabetics subjects P-trend = 0.0046. On the other hand, C-peptide level was significantly higher in subject with higher betatrophin level in non-diabetics subjects across all age groups but not in T2D subjects. Multiple logistic regression models adjusted for age, BMI, gender, ethnicity as well as C-peptide level showed that subjects in the highest tertiles of betatrophin had higher odds of having T2D [odd ratio (OR) = 7.3, 95 % confidence interval (CI) 4.0–13.3].

Conclusion

Increased betatrophin level in obese subjects is correlated with an increase in C-peptide level; which is possibly caused by the increased insulin resistance. On the other hand, no correlation is observed between increased betatrophin level and C-peptide in T2D subjects. In conclusion, the increased betatrophin in T2D subject does not cause any increase in insulin production as indicated by C-peptide level.

PED/PEA-15 inhibits hydrogen peroxide-induced apoptosis in Ins-1E pancreatic beta-cells via PLD-1

The small scaffold protein PED/PEA-15 is involved in several different physiologic and pathologic processes, such as cell proliferation and survival, diabetes and cancer. PED/PEA-15 exerts an anti-apoptotic function due to its ability to interfere with both extrinsic and intrinsic apoptotic pathways in different cell types. Recent evidence shows that mice overexpressing PED/PEA-15 present larger pancreatic islets and increased beta-cells mass. In the present work we investigated PED/PEA-15 role in hydrogen peroxide-induced apoptosis in Ins-1E beta-cells. In pancreatic islets isolated from Tg_PED/PEA-15 mice hydrogen peroxide-induced DNA fragmentation was lower compared to WT islets. TUNEL analysis showed that PED/PEA-15 overexpression increases the viability of Ins-1E beta-cells and enhances their resistance to apoptosis induced by hydrogen peroxide exposure. The activity of caspase-3 and the cleavage of PARP-1 were markedly reduced in Ins-1E cells overexpressing PED/PEA-15 (Ins-1E_PED/PEA-15). In parallel, we observed a decrease of the mRNA levels of pro-apoptotic genes Bcl-xS and Bad. In contrast, the expression of the anti-apoptotic gene Bcl-xL was enhanced. Accordingly, DNA fragmentation was higher in control cells compared to Ins-1E_PED/PEA-15 cells. Interestingly, the preincubation with propranolol, an inhibitor of the pathway of PLD-1, a known interactor of PED/PEA-15, responsible for its deleterious effects on glucose tolerance, abolishes the antiapoptotic effects of PED/PEA-15 overexpression in Ins-1E beta-cells. The same results have been obtained by inhibiting PED/PEA-15 interaction with PLD-1 in Ins-1E_PED/PEA-15. These results show that PED/PEA-15 overexpression is sufficient to block hydrogen peroxide-induced apoptosis in Ins-1E cells through a PLD-1 mediated mechanism.

The effect of glucagon-like peptide-1 in the management of diabetes mellitus: cellular and molecular mechanisms

Incretins, such as glucagon-like peptide-1 (GLP)-1, have been shown to elevate plasma insulin concentration. The purpose of this study is to investigate the cellular and molecular basis of the beneficial effects of GLP-1. Normal and diabetic male Wistar rats were treated with GLP-1 (50 ng/kg body weight) for 10 weeks. At the end of the experiment, pancreatic tissues were taken for immunohistochemistry, immunoelectron microscopy and real-time polymerase chain reaction studies. Samples of blood were retrieved from the animals for the measurement of enzymes and insulin. The results show that treatment of diabetic rats with GLP-1 caused significant (P < 0.05) reduction in body weight gain and blood glucose level. GLP-1 (10(-12)-10(-6) M) induced significant (P < 0.01) dose-dependent increases in insulin release from the pancreas of normal and diabetic rats compared to basal. Diabetes-induced abnormal liver (aspartate aminotransferase and alanine aminotransferase) and kidney (blood urea nitrogen and uric acid) parameters were corrected in GLP-1-treated rats compared to controls. GLP-1 treatment induced significant (P < 0.05) elevation in the expression of pancreatic duodenal homeobox-1, heat shock protein-70, glutathione peroxidase, insulin receptor and GLP-1-receptor genes in diabetic animals compared to controls. GLP-1 is present in pancreatic beta cells and significantly (P < 0.05) increased the number of insulin-, glutathione reductase- and catalase-immunoreactive islet cells. The results of this study show that GLP-1 is co-localized with insulin and seems to exert its beneficial effects by increasing cellular concentrations of endogenous antioxidant genes and other genes involved in the maintenance of pancreatic beta cell structure and function.

Role of bioactive food components in diabetes prevention: effects on Beta-cell function and preservation

Bioactive compounds found in fruits and vegetables can have anti-oxidant, anti-inflammatory, and anti-carcinogenic effects and can be protective against various diseases and metabolic disorders. These beneficial effects make them good candidates for the development of new functional foods with potential protective and preventive properties for type 1 and type 2 diabetes. This review summarizes the most relevant results concerning the effects of various bioactive compounds such as flavonoids, vitamins, and carotenoids on several aspects of beta-cell functionality. Studies using animal models with induced diabetes and diabetic patients support the hypothesis that bioactive compounds could ameliorate diabetic phenotypes. Published data suggest that there might be direct effects of bioactive compounds on enhancing insulin secretion and preventing beta-cell apoptosis, and some compounds might modulate beta-cell proliferation. Further research is needed to establish any clinical effects of these compounds.

Activation of glucagon-like peptide-1 receptor inhibits growth and promotes apoptosis of human pancreatic cancer cells in a cAMP-dependent manner

Glucagon-like peptide-1 (GLP-1) promotes pancreatic β-cell regeneration through GLP-1 receptor (GLP-1R) activation. However, whether it promotes exocrine pancreas growth and thereby increases the risk of pancreatic cancer has been a topic of debate in recent years. Clinical data and animal studies published so far have been controversial. In the present study, we report that GLP-1R activation with liraglutide inhibited growth and promoted apoptosis in human pancreatic cancer cell lines in vitro and attenuated pancreatic tumor growth in a mouse xenograft model in vivo. These effects of liraglutide were mediated through activation of cAMP production and consequent inhibition of Akt and ERK1/2 signaling pathways in a GLP-1R-dependent manner. Moreover, we examined GLP-1R expression in human pancreatic cancer tissues and found that 43.3% of tumor tissues were GLP-1R-null. In the GLP-1R-positive tumor tissues (56.7%), the level of GLP-1R was lower compared with that in tumor-adjacent normal pancreatic tissues. Furthermore, the GLP-1R-positive tumors were significantly smaller than the GLP-1R-null tumors. Our study shows for the first time that GLP-1R activation has a cytoreductive effect on human pancreatic cancer cells in vitro and in vivo, which may help address safety concerns of GLP-1-based therapies in the context of human pancreatic cancer.

Incretin receptor null mice reveal key role of GLP-1 but not GIP in pancreatic beta cell adaptation to pregnancy

Islet adaptations to pregnancy were explored in C57BL6/J mice lacking functional receptors for glucagon-like peptide 1 (GLP-1) and gastric inhibitory polypeptide (GIP). Pregnant wild type mice and GIPRKO mice exhibited marked increases in islet and beta cell area, numbers of medium/large sized islets, with positive effects on Ki67/Tunel ratio favouring beta cell growth and enhanced pancreatic insulin content. Alpha cell area and glucagon content were unchanged but prohormone convertases PC2 and PC1/3 together with significant amounts of GLP-1 and GIP were detected in alpha cells. Knockout of GLP-1R abolished these islet adaptations and paradoxically decreased pancreatic insulin, GLP-1 and GIP. This was associated with abolition of normal pregnancy-induced increases in plasma GIP, L-cell numbers, and intestinal GIP and GLP-1 stores. These data indicate that GLP-1 but not GIP is a key mediator of beta cell mass expansion and related adaptations in pregnancy, triggered in part by generation of intra-islet GLP-1.

Early liraglutide treatment is better in glucose control, β-cell function improvement and mass preservation in db/db mice

Glucagon-like peptide-1 (GLP-1) has been proved to have effects of anti-hyperglycemia and β-cell preservation. However, it is still unclear whether there are differences between early and late GLP-1 intervention in type 2 diabetes mellitus (T2DM). We divided the mice into 5 groups: early treated group (n=7, 8-week old, fasting glucose>10mmol/l), late treated group (n=7, 10-week old, fasting glucose>20mmol/l), early control group (n=7), late control group (n=7) and wild type group (n=7). Treated group was injected with liraglutide (a GLP-1 analog) 300μg/kg bid for 4 weeks, while control group was given saline at the same time. The results showed that compared with control group, food intake and body weight gain were reduced in both early and late treated group (p<0.05), and there was no significance between the two treated groups. Early liraglutide intervention showed better improvements in glucose control, acute insulin response to glucose (AIRg) and disposition index (before vs. after treatment, AIRg 1.01±0.53 vs. 2.98±0.63, disposition index 10.81±0.89 vs. 27.4±2.15) than late intervention (AIRg 0.99±0.02 vs. 1.41±0.32, disposition index 3.47±0.38 vs. 6.43±1.62, p=0.001). The histopathology of the pancreas showed the estimated β-cell mass (BCM) was increased more in early treated group than that in late one (0.03 vs. 0.01g). Expressions of the proliferation related genes PDX-1, MafA and GLP-1 receptor (GLP-1R) in early treated group were 1.81, 2.57 and 1.59 times as much as that in late treated group. In conclusion, early liraglutide intervention was better in glucose control, β-cell function improvement and β-cell mass preservation.

Regulation of pancreatic islet beta-cell mass by growth factor and hormone signaling

Dysfunction and destruction of pancreatic islet beta cells is a hallmark of diabetes. Better understanding of cellular signals in beta cells will allow development of therapeutic strategies for diabetes, such as preservation and expansion of beta-cell mass and improvement of beta-cell function. During the past several decades, the number of studies analyzing the molecular mechanisms, including growth factor/hormone signaling pathways that impact islet beta-cell mass and function, has increased exponentially. Notably, somatolactogenic hormones including growth hormone (GH), prolactin (PRL), and insulin-like growth factor-1 (IGF-1) and their receptors (GHR, PRLR, and IGF-1R) are critically involved in beta-cell growth, survival, differentiation, and insulin secretion. In this chapter, we focus more narrowly on GH, PRL, and IGF-1 signaling, and GH-IGF-1 cross talk. We also discuss how these signaling aspects contribute to the regulation of beta-cell proliferation and apoptosis. In particular, our novel findings of GH-induced formation of GHR-JAK2-IGF-1R protein complex and synergistic effects of GH and IGF-1 on beta-cell signaling, proliferation, and antiapoptosis lead to a new concept that IGF-1R may serve as a proximal component of GH/GHR signaling.

Beta cell dynamics: beta cell replenishment, beta cell compensation and diabetes

Type 2 diabetes, characterized by persistent hyperglycemia, arises mostly from beta cell dysfunction and insulin resistance and remains a highly complex metabolic disease due to various stages in its pathogenesis. Glucose homeostasis is primarily regulated by insulin secretion from the beta cells in response to prevailing glycemia. Beta cell populations are dynamic as they respond to fluctuating insulin demand. Beta cell replenishment and death primarily regulate beta cell populations. Beta cells, pancreatic cells, and extra-pancreatic cells represent the three tiers for replenishing beta cells. In rodents, beta cell self-replenishment appears to be the dominant source for new beta cells supported by pancreatic cells (non-beta islet cells, acinar cells, and duct cells) and extra-pancreatic cells (liver, neural, and stem/progenitor cells). In humans, beta cell neogenesis from non-beta cells appears to be the dominant source of beta cell replenishment as limited beta cell self-replenishment occurs particularly in adulthood. Metabolic states of increased insulin demand trigger increased insulin synthesis and secretion from beta cells. Beta cells, therefore, adapt to support their physiology. Maintaining physiological beta cell populations is a strategy for targeting metabolic states of persistently increased insulin demand as in diabetes.

Novel genes underlying beta cell survival in metabolic stress

Relative insulin deficiency, in response to increased metabolic demand (obesity, genetic insulin resistance, pregnancy and aging) lead to Type2 diabetes. Susceptibility of the type 2 diabetes has a genetic basis, as a subset of people with risk factors (obesity, Insulin Resistance, pregnancy), develop Type2 Diabetes. We aimed to identify 'cluster' of overexpressed genes, underlying increased beta cell survival in diabetes resistant C57BL/6J ob/ob mice (compared to diabetes susceptible BTBR ob/ob mice). We used 'consensus' overexpression status to identify 'cluster' of 11 genes consisting of Aldh18a1, Rfc4, Dynlt3, Prom1, H13, Psen1, Ssr4, Dad1, Anpep, Fam111a and Plk1. Information (biological processes, molecular functions, cellular components, protein-protein interactions/associations, gene deletion/knockout/inhibition studies) of all the genes in 'cluster' were collected by text mining using different literature search tools, gene information databases and protein-protein interaction databases. Beta cell specific function of these genes were also inferred using meta analysis tool of Beta Cell Biology Consortium, by studying the expression pattern of these genes in microarray studies related to beta-cell stimulation/injury, pancreas development and growth and cell differentiation. In the 'clusters', 6 genes (Dad1, Psen1, Ssr4, Rfc4, H13, Plk1) have a role in cell survival. Only Psen1 was previously identified to have role in successful beta cell compensation. We advocate these genes to be potentially involved in successful beta cell compensation and prevent T2D in humans, by conferring protection against diabetogenic insults.

Ampicillin-improved glucose tolerance in diet-induced obese C57BL/6NTac mice is age dependent

Ampicillin has been shown to improve glucose tolerance in mice. We hypothesized that this effect is present only if treatment is initiated prior to weaning and that it disappears when treatment is terminated. High-fat fed C57BL/6NTac mice were divided into groups that received Ampicillin at different ages or not at all. We found that both diet and Ampicillin significantly changed the gut microbiota composition in the animals. Furthermore, there was a significant improvement in glucose tolerance in Ampicillin-treated, five-week-old mice compared to nontreated mice in the control group. At study termination, expressions of mRNA coding for tumor necrosis factor, serum amyloid A, and lactase were upregulated, while the expression of tumor necrosis factor (ligand) superfamily member 15 was downregulated in the ileum of Ampicillin-treated mice. Higher dendritic cell percentages were found systemically in high-fat diet mice, and a lower tolerogenic dendritic cell percentage was found both in relation to high-fat diet and late Ampicillin treatment. The results support our hypothesis that a "window" exists early in life in which an alteration of the gut microbiota affects glucose tolerance as well as development of gut immunity and that this window may disappear after weaning.