Glucose-stimulated Insulin Levels Research Articles

Apigenin potentiates glucose-stimulated insulin secretion through the PKA-MEK kinase signaling pathway independent of K-ATP channels

AimApigenin, a natural bioflavonoid, is reported as an anti-diabetic agent since it possesses the ability to inhibit α-glucosidase activity, cause stimulation of insulin action and secretion, manage ROS, and prevent diabetes complications. Apigenin was identified as a new insulin secretagogue that enhances glucose-stimulated insulin secretion and seems like a better antidiabetic drug candidate. Here we explored the insulinotropic mechanism(s) of apigenin in vitro in mice islets and in vivo in diabetic rats. MethodsSize-matched pancreatic islets were divided into groups and incubated in the presence or absence of apigenin and agonists or antagonists of major insulin signaling pathways. The secreted insulin was measured by ELISA. The intracellular cAMP was estimated by cAMP acetylation assay. The acute and chronic effects of apigenin were evaluated in diabetic rats. Resultsapigenin dose-dependently enhanced insulin secretion in isolated mice islets, and its insulinotropic effect was exerted at high glucose concentrations distinctly different from glibenclamide. Furthermore, apigenin amplified glucose-induced insulin secretion in depolarized and glibenclamide-treated islets. Apigenin showed no effect on intracellular cAMP concentration; however, an additive effect was observed by apigenin in both forskolin and IBMX-induced insulin secretion. Interestingly, H89, a PKA inhibitor, and U0126, a MEK kinase inhibitor, significantly inhibited apigenin-induced insulin secretion; however, no significant effect was observed by using ESI-05, an epac2 inhibitor. Apigenin improved glucose tolerance and increased glucose-stimulated plasma insulin levels in diabetic rats. Apigenin also lowered blood glucose in diabetic rats upon chronic treatment. ConclusionApigenin exerts glucose-stimulated insulin secretion by modulating the PKA-MEK kinase signaling cascade independent of K-ATP channels.

The aryl hydrocarbon receptor in β-cells mediates the effects of TCDD on glucose homeostasis in mice

ObjectiveChronic exposure to persistent organic pollutants (POPs) is associated with increased incidence of type 2 diabetes, hyperglycemia, and poor insulin secretion in humans. Dioxins and dioxin-like compounds are a broad class of POPs that exert cellular toxicity through activation of the aryl hydrocarbon receptor (AhR). We previously showed that a single high-dose injection of 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD, aka dioxin; 20 μg/kg) in vivo reduced fasted and glucose-stimulated plasma insulin levels for up to 6 weeks in male and female mice. TCDD-exposed male mice were also modestly hypoglycemic and had increased insulin sensitivity, whereas TCDD-exposed females were transiently glucose intolerant. Whether these effects are driven by AhR activation in β-cells requires investigation. MethodsWe exposed female and male β-cell specific Ahr knockout (βAhrKO) mice and littermate Ins1-Cre genotype controls (βAhrWT) to a single high dose of 20 μg/kg TCDD and tracked the mice for 6 weeks. ResultsUnder baseline conditions, deleting AhR from β-cells caused hypoglycemia in female mice, increased insulin secretion ex vivo in female mouse islets, and promoted modest weight gain in male mice. Importantly, high-dose TCDD exposure impaired glucose homeostasis and β-cell function in βAhrWT mice, but these phenotypes were largely abolished in TCDD-exposed βAhrKO mice. ConclusionOur study demonstrates that AhR signaling in β-cells is important for regulating baseline β-cell function in female mice and energy homeostasis in male mice. We also show that β-cell AhR signaling largely mediates the effects of TCDD on glucose homeostasis in both sexes, suggesting that the effects of TCDD on β-cell function and health are driving metabolic phenotypes in peripheral tissues.

Deficiency of WTAP in islet beta cells results in beta cell failure and diabetes in mice.

N6-methyladenosine (m6A) mRNA methylation and m6A-related proteins (methyltransferase-like 3 [METTL3], methyltransferase-like 14 [METTL14] and YTH domain containing 1 [YTHDC1]) have been shown to regulate islet beta cell function and the pathogenesis of diabetes. However, whether Wilms' tumour 1-associating protein (WTAP), a key regulator of the m6A RNA methyltransferase complex, regulates islet beta cell failure during pathogenesis of diabetes is largely unknown. The present study aimed to investigate the role of WTAP in the regulation of islet beta cell failure and diabetes. Islet beta cell-specific Wtap-knockout and beta cell-specific Mettl3-overexpressing mice were generated for this study. Blood glucose, glucose tolerance, serum insulin, glucose-stimulated insulin secretion (both in vivo and in vitro), insulin levels, glucagon levels and beta cell apoptosis were examined. RNA-seq and MeRIP-seq were performed, and the data were well analysed. WTAP was downregulated in islet beta cells in type 2 diabetes, due to lipotoxicity and chronic inflammation, and islet beta cell-specific deletion of Wtap (Wtap-betaKO) induced beta cell failure and diabetes. Wtap-betaKO mice showed severe hyperglycaemia (above 20 mmol/l [360 mg/dl]) from 8 weeks of age onwards. Mechanistically, WTAP deficiency decreased m6A mRNA modification and reduced the expression of islet beta cell-specific transcription factors and insulin secretion-related genes by reducing METTL3 protein levels. Islet beta cell-specific overexpression of Mettl3 partially reversed the abnormalities observed in Wtap-betaKO mice. WTAP plays a key role in maintaining beta cell function by regulating m6A mRNA modification depending on METTL3, and the downregulation of WTAP leads to beta cell failure and diabetes. The RNA-seq and MeRIP-seq datasets generated during the current study are available in the Gene Expression Omnibus database repository ( https://www.ncbi.nlm.nih.gov/geo/query/acc.cgi?acc=GSE215156 ; https://www.ncbi.nlm.nih.gov/geo/query/acc.cgi?acc=GSE215360 ).

Intranasal Co-Administration of Insulin and C-Peptide Restores Metabolic and Hormonal Indices in Rats with Normoinsulinemic, but not with Hyperinsulinemic, Type 2 Diabetes

In type 2 diabetes mellitus (T2DM), the functions of the brain insulin system are impaired, which is associated with a decrease in insulin transport across the blood-brain barrier due to insulin resistance. To restore insulin deficiency in the brain, intranasally administered insulin (II) can be used, and its effect can be enhanced by intranasal administration of C-peptide (ICP). The aim of this work is to study the effect of ten-day treatment of male Wistar rats with hyperinsulinemic and normoinsulinemic T2DM with II (20 µg/rat/day), ICP (36 µg/rat/day) or II+ICP on metabolic and hormonal indices. Hyperinsulinemic T2DM was induced by a 3-month high-fat diet and low-dose streptozotocin treatment of adult rats, while normoinsulinemic T2DM was induced by high-dose streptozotocin treatment of 5-day-old pups. In hyperinsulinemic diabetic rats, II-monotherapy attenuated hyperglycemia, hyperinsulinemia, and hyperleptinemia, and partially restored the blood levels of fT4, tT4, and tT3 reduced in DM2 (p<0.05 as compared to untreated diabetes). ICP was not effective and, in the II+ICP group, it significantly reduced the restorative effects of II. In normoinsulinemic rats with T2DM, II monotherapy increased fT4 and tT3 levels by 31% and 26%, while ICP decreased glucose-stimulated leptin levels by 31% (p<0.05 as compared to untreated diabetes). The use of II+ICP attenuated hyperglycemia, reduced glucose-stimulated insulin levels, and restored the thyroid hormones levels to their control values. Thus, ICP and its combination with II are effective in restoring metabolic and hormonal indices in rats with normoinsulinemic T2DM, but do not improve them in rats with hyperinsulinemic T2DM.

Clinical outcome and gut development after insulin-like growth factor-1 supplementation to preterm pigs.

BackgroundElevation of circulating insulin-like growth factor-1 (IGF-1) within normal physiological levels may alleviate several morbidities in preterm infants but safety and efficacy remain unclear. We hypothesized that IGF-1 supplementation during the first 1–2 weeks after preterm birth improves clinical outcomes and gut development, using preterm pigs as a model for infants.MethodsPreterm pigs were given vehicle or recombinant human IGF-1/binding protein-3 (rhIGF-1, 2.25 mg/kg/d) by subcutaneous injections for 8 days (Experiment 1, n = 34), or by systemic infusion for 4 days (Experiment 2, n = 19), before collection of blood and organs for analyses.ResultsIn both experiments, rhIGF-1 treatment increased plasma IGF-1 levels 3-4 fold, reaching the values reported for term suckling piglets. In Experiment 1, rhIGF-1 treatment increased spleen and intestinal weights without affecting clinical outcomes like growth, blood biochemistry (except increased sodium and gamma-glutamyltransferase levels), hematology (e.g., red and white blood cell populations), glucose homeostasis (e.g., basal and glucose-stimulated insulin and glucose levels) or systemic immunity variables (e.g., T cell subsets, neutrophil phagocytosis, LPS stimulation, bacterial translocation to bone marrow). The rhIGF-1 treatment increased gut protein synthesis (+11%, p < 0.05) and reduced the combined incidence of all-cause mortality and severe necrotizing enterocolitis (NEC, p < 0.05), but had limited effects on intestinal morphology, cell proliferation, cell apoptosis, brush-border enzyme activities, permeability and levels of cytokines (IL-1β, IL-6, IL-8). In Experiment 2, rhIGF-1 treated pigs had reduced blood creatine kinase, creatinine, potassium and aspartate aminotransferase levels, with no effects on organ weights (except increased spleen weight), blood chemistry values, clinical variables or NEC.ConclusionPhysiological elevation of systemic IGF-1 levels for 8 days after preterm birth increased intestinal weight and protein synthesis, spleen weight and potential overall viability of pigs, without any apparent negative effects on recorded clinical parameters. The results add further preclinical support for safety and efficacy of supplemental IGF-1 to hospitalized very preterm infants.

Early Life Thymectomy Induces Glucose Intolerance in Middle-Aged Mice

Aging is associated with accumulation of various tryptophan degradation products that may having either bone anabolic or catabolic effects. In epidemiologic studies, elevated levels of 3-hydroxyanthranilic acid (3-HAA) are associated with a higher bone mineral density (BMD). We have previously shown that the C57BL/6 mouse loses bone mass with age. Thus, we hypothesized that administering 3-HAA via a daily intraperitoneal (IP) injection would result in preserved or increased BMD. In an IACUC-approved protocol, we injected 26-month-old C57BL/6 mice with either a low dose (0.5 mg) or high dose (5 mg) of 3-HAA IP five days a week for eight weeks. At the end of this time mice were sacrificed and body composition and bone mineral density measured by DigiMus. BMD was significantly lower in the high dose 3-HAA group: 0.0570 + 0.004 vs 0.0473 + 0.006 vs 0.0432 + 0.0075 gm/cm2, (means+SD, Control vs 0.5 mg 3HAA vs 5 mg 3HAA, p=0.004, 0 vs 5.0 mg, n=6-9/group). 3-HAA had no significant impact on body composition (lean body mass: 86.7 + 1.7% vs 86.2 + 2.7% vs 86.1 + 2.0%, Control vs 0.5 mg vs 5.0 mg 3-HAA, p=ns; and fat mass 12.6 + 2.0% vs 13.8 + 2.7% vs 13.9 + 2.0% vs 0.2%, Control vs 0.5 vs 5 mg 3-HAA, p=ns). Thus, 3-HAA did not prevent bone loss in older mice but instead significantly worsened bone loss. 3-HAA is known to have both pro- and anti- oxidant effects depending on the environment. These data would suggest that at the higher concentrations 3-HAA is acting predominantly as a pro-oxidant molecule accelerating age-related bone loss.

Peripancreatic adipose tissue protects against high-fat-diet-induced hepatic steatosis and insulin resistance in mice

Background/objectivesVisceral adiposity is associated with increased diabetes risk, while expansion of subcutaneous adipose tissue may be protective. However, the visceral compartment contains different fat depots. Peripancreatic adipose tissue (PAT) is an understudied visceral fat depot. Here, we aimed to define PAT functionality in lean and high-fat-diet (HFD)-induced obese mice.Subjects/methodsFour adipose tissue depots (inguinal, mesenteric, gonadal, and peripancreatic adipose tissue) from chow- and HFD-fed male mice were compared with respect to adipocyte size (n = 4–5/group), cellular composition (FACS analysis, n = 5–6/group), lipogenesis and lipolysis (n = 3/group), and gene expression (n = 6–10/group). Radioactive tracers were used to compare lipid and glucose metabolism between these four fat depots in vivo (n = 5–11/group). To determine the role of PAT in obesity-associated metabolic disturbances, PAT was surgically removed prior to challenging the mice with HFD. PAT-ectomized mice were compared to sham controls with respect to glucose tolerance, basal and glucose-stimulated insulin levels, hepatic and pancreatic steatosis, and gene expression (n = 8–10/group).ResultsWe found that PAT is a tiny fat depot (~0.2% of the total fat mass) containing relatively small adipocytes and many “non-adipocytes” such as leukocytes and fibroblasts. PAT was distinguished from the other fat depots by increased glucose uptake and increased fatty acid oxidation in both lean and obese mice. Moreover, PAT was the only fat depot where the tissue weight correlated positively with liver weight in obese mice (R = 0.65; p = 0.009). Surgical removal of PAT followed by 16-week HFD feeding was associated with aggravated hepatic steatosis (p = 0.008) and higher basal (p < 0.05) and glucose-stimulated insulin levels (p < 0.01). PAT removal also led to enlarged pancreatic islets and increased pancreatic expression of markers of glucose-stimulated insulin secretion and islet development (p < 0.05).ConclusionsPAT is a small metabolically highly active fat depot that plays a previously unrecognized role in the pathogenesis of hepatic steatosis and insulin resistance in advanced obesity.

Insulin clearance as the major player in the hyperinsulinaemia of black African men without diabetes.

To investigate relationships between insulin clearance, insulin secretion, hepatic fat accumulation and insulin sensitivity in black African (BA) and white European (WE) men. Twenty-three BA and twenty-three WE men with normal glucose tolerance, matched for age and body mass index, underwent a hyperglycaemic clamp to measure insulin secretion and clearance, hyperinsulinaemic-euglycaemic clamp with stable glucose isotope infusion to measure whole-body and hepatic-specific insulin sensitivity, and magnetic resonance imaging to quantify intrahepatic lipid (IHL). BA men had higher glucose-stimulated peripheral insulin levels (48.1 [35.5, 65.2] × 103 vs. 29.9 [23.3, 38.4] × 103 pmol L-1 × min, P = .017) and lower endogeneous insulin clearance (771.6 [227.8] vs. 1381 [534.3] mL m-2 body surface area min -1 , P < .001) compared with WE men. There were no ethnic differences in beta-cell insulin secretion or beta-cell responsivity to glucose, even after adjustment for prevailing insulin sensitivity. In WE men, endogenous insulin clearance was correlated with whole-body insulin sensitivity (r = 0.691, P = .001) and inversely correlated with IHL (r = -0.674, P = .001). These associations were not found in BA men. While normally glucose-tolerant BA men have similar insulin secretory responses to their WE counterparts, they have markedly lower insulin clearance, which does not appear to be explained by either insulin resistance or hepatic fat accumulation. Low insulin clearance may be the primary mechanism of hyperinsulinaemia in populations of African origin.

SLC6A4 5HTTLPR Polymorphism Affects Insulin Secretion in Patients with Polycystic Ovary Syndrome.

Purpose To investigate in a pilot study of genetic polymorphisms in serotonin system influencing basal- and glucose-stimulated insulin secretion in women with polycystic ovary syndrome (PCOS). Methods A cross-sectional study included 65 female patients with PCOS followed up at the endocrine outpatient clinic of the University Medical Center Ljubljana and a control group of 94 young healthy female blood donors. Oral glucose tolerance test was performed only in PCOS patients and basal- and glucose-stimulated blood glucose and insulin levels were measured. All the subjects were genotyped for 5HTR1A rs6295, 5HTR1B rs13212041, and SLC6A4 5HTTLPR polymorphisms in the serotonin system. Results Genotype distributions were in accordance with the Hardy-Weinberg equilibrium (HWE), except for 5HTR1A rs6295 in healthy controls and 5HTR1B rs13212041 in PCOS patients that were not consistent with HWE. SLC6A4 5HTTLPR polymorphism was significantly associated with insulin secretion (p = 0.030) and with the area under the curve of insulin blood levels during OGTT (p = 0.021). None of the investigated polymorphisms was significantly associated with basal- or glucose-stimulated blood glucose levels at any point in time during OGTT or with the basal insulin concentration. Conclusions Serotonin system may play a role in glucose-stimulated insulin secretion in patients with insulin resistance (IR) and decreased insulin sensitivity. Further studies are needed to conclude whether the observed effect is characteristic for PCOS-related metabolic disturbances or for the identified mutation in different high metabolic risk populations.

GLP-2 receptor signaling controls circulating bile acid levels but not glucose homeostasis in Gcgr−/− mice and is dispensable for the metabolic benefits ensuing after vertical sleeve gastrectomy

ObjectiveTherapeutic interventions that improve glucose homeostasis such as attenuation of glucagon receptor (Gcgr) signaling and bariatric surgery share common metabolic features conserved in mice and humans. These include increased circulating levels of bile acids (BA) and the proglucagon-derived peptides (PGDPs), GLP-1 and GLP-2. Whether BA acting through TGR5 (Gpbar1) increases PGDP levels in these scenarios has not been examined. Furthermore, although the importance of GLP-1 action has been interrogated in Gcgr−/− mice and after bariatric surgery, whether GLP-2 contributes to the metabolic benefits of these interventions is not known. MethodsTo assess whether BA acting through Gpbar1 mediates improved glucose homeostasis in Gcgr−/− mice we generated and characterized Gcgr−/−:Gpbar1−/− mice. The contribution of GLP-2 receptor (GLP-2R) signaling to intestinal and metabolic adaptation arising following loss of the Gcgr was studied in Gcgr−/−:Glp2r−/− mice. The role of the GLP-2R in the metabolic improvements evident after bariatric surgery was studied in high fat-fed Glp2r−/− mice subjected to vertical sleeve gastrectomy (VSG). ResultsCirculating levels of BA were markedly elevated yet similar in Gcgr−/−:Gpbar1+/+ vs. Gcgr−/−:Gpbar1−/− mice. Loss of GLP-2R lowered levels of BA in Gcgr−/− mice. Gcgr−/−:Glp2r−/− mice also exhibited shifts in the proportion of circulating BA species. Loss of Gpbar1 did not impact body weight, intestinal mass, or glucose homeostasis in Gcgr−/− mice. In contrast, small bowel growth was attenuated in Gcgr−/−:Glp2r−/− mice. The improvement in glucose tolerance, elevated circulating levels of GLP-1, and glucose-stimulated insulin levels were not different in Gcgr−/−:Glp2r+/+ vs. Gcgr−/−:Glp2r−/− mice. Similarly, loss of the GLP-2R did not attenuate the extent of weight loss and improvement in glucose control after VSG. ConclusionsThese findings reveal that GLP-2R controls BA levels and relative proportions of BA species in Gcgr−/− mice. Nevertheless, the GLP-2R is not essential for i) control of body weight or glucose homeostasis in Gcgr−/− mice or ii) metabolic improvements arising after VSG in high fat-fed mice. Furthermore, despite elevations of circulating levels of BA, Gpbar1 does not mediate elevated levels of PGDPs or major metabolic phenotypes in Gcgr−/− mice. Collectively these findings refine our understanding of the relationship between Gpbar1, elevated levels of BA, PGDPs, and the GLP-2R in amelioration of metabolic derangements arising following loss of Gcgr signaling or after vertical sleeve gastrectomy.

Activation of ACE2/angiotensin (1–7) attenuates pancreatic β cell dedifferentiation in a high-fat-diet mouse model

ObjectiveAngiotensin-converting enzyme 2 (ACE2) has been identified in pancreatic islets and can preserve β cells. In this study, we aimed to examine the possible role of ACE2 and its end product, angiotensin 1–7 (A1–7), in reducing β cell dedifferentiation during metabolic stress. MethodsFirst, a lineage-tracing experiment was performed to track β cells in mice fed a high-fat diet (HFD). Second, the ACE2/A1–7 axis was evaluated in the HFD mouse model. Intraperitoneal glucose tolerance tests (IPGTTs) and intraperitoneal insulin tolerance tests (IPITTs) were conducted. Phenotypic changes in β cells were detected by immunohistochemistry and quantitative real-time PCR. Pancreatic sections were immunostained for vascular endothelial growth factor (VEGF) and inducible nitric oxide synthase (iNOS). Finally, the effects of the ACE2/A1–7 axis were explored in isolated mouse islets exposed to different concentrations of glucose. Glucose-stimulated insulin release and levels of insulin mRNA and OCT4 mRNA were measured. ResultsPancreatic β cell dedifferentiation occurred both in vitro and in vivo in response to metabolic stress and was accompanied by ACE2 reduction. HFD-induced insulin resistance and glucose intolerance were exacerbated in ACE2-knockout (ACE2KO) mice but were alleviated by exogenous A1–7 in C57BL/6J mice. Approximately 20% of β cells were dedifferentiated in ACE2KO mice fed a standard rodent chow diet (SD). A higher percentage of dedifferentiated β cells was detected in ACE2KO mice than in wild-type (WT) mice under HFD conditions. In contrast, the administration of A1–7 alleviated HFD-induced β cell dedifferentiation in C57BL/6J mice. Moreover, the exogenous injection of A1–7 improved microcirculation in islets and decreased the production of iNOS in islets of C57BL/6J mice fed an HFD. Additionally, ACE2 was found to be mainly expressed in α cells of mice, while Mas, the receptor of A1–7, was distributed in β cells. ConclusionsOverall, this study is the first to demonstrate that the ACE2/A1–7/Mas axis may be one of the intra-islet paracrine mechanisms of communication between α and β cells. Enhancing the ACE2/A1–7 axis exerts a protective effect by ameliorating β cell dedifferentiation, and this effect might be partially mediated through improvements in islet microcirculation and suppression of islet iNOS.

Involvement of receptor-interacting protein 140 in palmitate-stimulated macrophage infiltration of pancreatic beta cells.

Receptor-interacting protein 140 (RIP140) in macrophages stimulates the nuclear factor-κB subunit RelA to activate tumor necrosis factor (TNF)-α and interleukin (IL)-6 transcription. However, under lipotoxic conditions, the involvement of RIP140 in the infiltration of beta cells by macrophages remains unknown. In the present study, murine RAW264.7 macrophages were transfected with a RIP140 overexpression plasmid or siRNA prior to macrophage activation with 500 µM palmitate. Palmitate-free conditioned media was then collected and added to murine insulinoma MIN6 cells. Significant decreases were observed in cell viability (P<0.01), glucose-stimulated insulin secretion (P<0.01) and levels of peroxisome proliferator-activated receptor-γ coactivator-1α (P<0.05), phosphoenolpyruvate carboxykinase and proliferating cell nuclear antigen mRNA (P<0.01) in MIN6 cells. In addition, conditioned media from palmitate-treated and RIP140-upregulated macrophages significantly increased the levels of uncoupling protein-2 (P<0.01), inducible nitric oxide synthase 1 (P<0.01) and pancreatic and duodenal homeobox 1 (P<0.05) mRNA and levels of activated Jun N-terminal kinase (JNK) (P<0.01) and extracellular signal-regulated kinase (ERK) 1/2 (P<0.01). In turn, the conditioned media was found to be significantly enriched in TNF-α and IL-6 (both P<0.05). These results were the opposite of those obtained from MIN6 cells treated with conditioned media from palmitate-treated and RIP140-knockdown macrophages. MIN6 cells were transfected with RIP140 overexpression plasmid or siRNA prior to treatment with 500 µM palmitate and supernatant was collected for use in macrophage chemotaxis assays. In the palmitate-activated and RIP140-overexpressing MIN6 cells, TNF-α and IL-6 secretion increased significantly (both P<0.05) and macrophage chemotaxis towards MIN6 cells was enhanced. By contrast, downregulating RIP140 in MIN6 cells had the opposite effect. These data suggest that RIP140 in macrophages mediates the transcription of inflammatory cytokines when concentration of palmitate is high. Macrophage RIP140 may also impair beta cell function by activating the JNK and ERK1/2 signaling pathways and promoting specific gene transcription. Furthermore, expression of RIP140 in pancreatic beta cells may stimulate macrophage chemotaxis, thus triggering local low-grade inflammation.

Gpr1 is an active chemerin receptor influencing glucose homeostasis in obese mice.

Chemerin is an adipose-derived signaling protein (adipokine) that regulates adipocyte differentiation and function, immune function, metabolism, and glucose homeostasis through activation of chemokine-like receptor 1 (CMKLR1). A second chemerin receptor, G protein-coupled receptor 1 (GPR1) in mammals, binds chemerin with an affinity similar to CMKLR1; however, the function of GPR1 in mammals is essentially unknown. Herein, we report that expression of murine Gpr1 mRNA is high in brown adipose tissue and white adipose tissue (WAT) and skeletal muscle. In contrast to chemerin (Rarres2) and Cmklr1, Gpr1 expression predominates in the non-adipocyte stromal vascular fraction of WAT. Heterozygous and homozygous Gpr1-knockout mice fed on a high-fat diet developed more severe glucose intolerance than WT mice despite having no difference in body weight, adiposity, or energy expenditure. Moreover, mice lacking Gpr1 exhibited reduced glucose-stimulated insulin levels and elevated glucose levels in a pyruvate tolerance test. This study is the first, to our knowledge, to report the effects of Gpr1 deficiency on adiposity, energy balance, and glucose homeostasis in vivo. Moreover, these novel results demonstrate that GPR1 is an active chemerin receptor that contributes to the regulation of glucose homeostasis during obesity.

Incretin levels 1 month after laparoscopic single anastomosis gastric bypass surgery in non-morbid obese type 2 diabetes patients

Bariatric surgery is an efficient procedure for the remission of type 2 diabetes (T2DM) from morbid obesity. However, in Asian countries, the mean body mass index (BMI) of T2DM patients is about 25kg/m(2). Various data on patients undergoing gastric bypass surgery suggest that the control of T2DM after surgery occurs rapidly. We hypothesized that even in nonobese patients with T2DM, the levels of incretin and insulin changed along with the improvement of T2DM as a consequence of the gastric bypass. From March to December 2011, 12 nonobese patients (mean BMI; 26.2kg/m(2)) with poorly-controlled [mean glycated hemoglobin (HbA1C); 9.5%] diabetes underwent gastric bypass surgery. Values related to diabetes, including incretin [gastric inhibitory peptide (GIP) and glucagon-like peptide-1 (GLP-1)] levels were measured before and 1 month after surgery. All values were measured in response to a 75g oral glucose tolerance test (OGTT). On average, the BMI decreased by 2.1±0.7kg/m(2). Mean HbA1C level decreased by 1.6±2%. Oral glucose-stimulated insulin levels increased and GLP-1 levels also increased significantly. Oral glucose-stimulated GIP levels decreased sharply. Soon after gastric bypass in nonobese T2DM patients, control of T2DM is achieved. The incretin release after oral glucose is improved. This could be a consequence of changes of the enteroinsular axis, particularly in the incretins.

Insulin resistance in young adults born small for gestational age (SGA)

This work aimed to assess glucose metabolism and insulin sensitivity in young adults born small for gestational age (SGA) as well as to measure the body composition and adipocytokines of these subjects. A total of 108 out of 342 SGA-born participants were invited for reexamination from the former Bavarian Longitudinal Study (BLS), in which 7505 risk-newborns of the years 1985 to 1986 were prospectively followed. Of these, 76 (34 female/42 male) participants at the age of 19.7±0.5 years were enrolled. Clinical examination and oral glucose tolerance testing (oGTT) was performed with assessment of insulin resistance indices, HbA1c, body mass index (BMI), adipocytokines, and body composition by bioimpedance analysis (BIA). A total of 25 out of 76 (32.9%) patients had abnormal fasting and/or glucose-stimulated insulin levels. Glucose values measured during oGTT showed no abnormalities, except one participant who had impaired glucose tolerance. Homeostasis model assessment insulin resistance index (HOMA-IR) was 1.92±4.2, and insulin sensitivity index by Matsuda (ISI(Matsuda)) showed mean values of 7.85±4.49. HOMA-IR>2.5 was found in 8 patients (10.5%), and 20 patients (26.3%) had an ISI(Matsuda)<5, both interpreted as insulin resistant. No alterations of adipocytokines were found. Fat mass (FM) measured by BIA was within the normal range for both genders and correlated significantly with BMI (r=0.465, p<0.001) and leptin (r=0.668, p>0.001), but not with adiponectin. Insulin resistance correlated with change in weight-for-height Z-score during the first 3 months of age, indicating that weight gain during that early phase might be a risk factor for the development of insulin resistance in children born SGA. A high percentage of insulin-resistant subjects were reconfirmed in a large German cohort of young adults born SGA. Therefore, regular screening for disturbances in glucose metabolism is recommended in these subjects.

Effects of biotin supplementation in the diet on insulin secretion, islet gene expression, glucose homeostasis and beta-cell proportion

Besides its role as a carboxylase cofactor, biotin has a wide repertoire of effects on gene expression, development and metabolism. Pharmacological concentrations of biotin enhance insulin secretion and the expression of genes and signaling pathways that favor islet function in vitro. However, the in vivo effects of biotin supplementation on pancreatic islet function are largely unknown. In the present study, we investigated whether in vivo biotin supplementation in the diet has positive effects in rodent pancreatic islets. Male BALB/cAnN Hsd mice were fed a control or a biotin-supplemented diet over 8 weeks postweaning and tested for glucose homeostasis, insulin secretion, islet gene expression and pancreatic morphometry. Insulin secretion increased from the islets of biotin-supplemented mice, together with the messenger RNA (mRNA) expression of several transcription factors regulating insulin expression and secretion, including forkhead box A2, pancreatic and duodenal homeobox 1 and hepatocyte nuclear factor 4α. The mRNA abundance of glucokinase, Cacna1d, acetyl-CoA carboxylase, and insulin also increased. Consistent with these effects, glucose tolerance improved, and glucose-stimulated serum insulin levels increased in biotin-supplemented mice, without changes in fasting glucose levels or insulin tolerance. Biotin supplementation augmented the proportion of beta cells by enlarging islet size and, unexpectedly, also increased the percentage of islets with alpha cells at the islet core. mRNA expression of neural cell adhesion molecule 1, an adhesion protein participating in the maintenance of islet architecture, decreased in biotin-supplemented islets. These findings provide, for the first time, insight into how biotin supplementation exerts its effects on function and proportion of beta cells, suggesting a role for biotin in the prevention and treatment of diabetes.

Characterizing the induction of diabetes in juvenile cynomolgus monkeys with different doses of streptozotocin

Juvenile (2-23 years old) cynomolgus monkeys are frequently used as recipients in non-human primate islet transplantation studies. The aim of this study was to examine the effects of different doses of streptozotocin (STZ), and find the optimal dose for inducing diabetes in these monkeys. Fifteen juvenile (2-3 years old) cynomolgus monkeys were separated into three groups and administered with different doses of STZ (100, 68 or 60 mg kg(-1)). Basal and glucose-stimulated blood glucose, insulin, and C-peptide levels, as well as body weights were monitored. Hepatic and renal function tests and pancreatic immunohistochemistry were performed before and after STZ treatment. Monkeys treated with both 100 and 68 mg kg(-1) of STZ exhibited continuous hyperglycemia, which coincided with a nearly complete loss of islet β-cells. Two monkeys received 60 mg kg(-1) of STZ, but only one became completely diabetic. During the first week following STZ treatment, hepatic and renal function slightly increased in these three groups. However, 24 hours post-STZ, serum total bile acid levels were significantly increased in monkeys treated with 100 mg kg(-1) than those treated with 68 mg kg(-1) of STZ (P<0.05). These data suggest that 100 mg kg(-1) and 68 mg kg(-1) of STZ can safely induce diabetes in cynomolgus monkeys aged 2-3 years, but 68 mg kg(-1) of STZ, rather than 100 mg kg(-1) of STZ, may be more appropriate for inducing diabetes in these monkeys. Furthermore, body surface area, rather than body weight, was a more reliable determinant of dosage, where 700 mg m(-2) of STZ should be the lower limit for inducing diabetes in juvenile monkeys.

Serum IGF1 and insulin levels in girls with normal and precocious puberty

IGF1 plays an important role in growth and metabolism during puberty. IGF1 levels are increased in girls with central precocious puberty (CPP). However, the relationship with insulin before and during gonadal suppression is unknown. In addition, the influence of the exon 3-deleted GH receptor gene (GHRd3) on IGF1 levels was evaluated. Nine hundred and eleven healthy and 23 early pubertal girls (15 with CPP) participated and were evaluated by dual-energy X-ray absorptiometry (DXA) scans, fasting and oral glucose-stimulated insulin levels, IGF1 levels, and GHR genotyping. Fifteen girls with early puberty (13 with CPP) were treated with GNRH agonists and reevaluated after 3 and 12 months. IGF1 and insulin levels were higher in girls with CPP compared with healthy controls after adjustment for age, bone age, and breast development (all P≤0.02). IGF1 levels were only significantly positively correlated with insulin levels in girls with CPP at baseline (P≤0.03). During gonadal suppression, changes in IGF1 levels were inversely associated with changes in insulin levels (P=0.04). The GHRd3/d3 genotype was associated with significantly higher IGF1 levels (P=0.01) but not with earlier pubertal timing in healthy girls. The distribution of the GHRd3 genotypes among girls with CPP did not differ significantly from healthy girls (P=0.2). The increased IGF1 and insulin levels in girls with CPP may be causally interrelated. In addition, the GHRd3 allele positively influences IGF1 levels in a copy number-response relationship but not pubertal timing in healthy girls.

Acute Disruption of Leptin Signaling in Vivo Leads to Increased Insulin Levels and Insulin Resistance

Leptin, an adipocyte-derived hormone, plays an essential role in the maintenance of normal body weight and energy expenditure, as well as glucose homeostasis. Indeed, leptin-deficient ob/ob mice are obese with profound hyperinsulinemia, insulin resistance, and often hyperglycemia. Interestingly, low doses of exogenous leptin can reverse the hyperinsulinemia and hyperglycemia in these animals without altering body weight. The hyperinsulinemia in ob/ob mice may result directly from the absence of leptin signaling in pancreatic β-cells and, in turn, contribute to both obesity and insulin resistance. Here, we acutely attenuated endogenous leptin signaling in normal mice with a polyethylene glycol (PEG)ylated mouse leptin antagonist (PEG-MLA) to determine the contribution of leptin signaling in the regulation of glucose homeostasis. PEG-MLA was either injected or continuously administered via osmotic minipumps for several days, and various metabolic parameters were assessed. PEG-MLA-treated mice had increased fasting and glucose-stimulated plasma insulin levels, decreased whole-body insulin sensitivity, elevated hepatic glucose production, and impaired insulin-mediated suppression of hepatic glucose production. Moreover, PEG-MLA treatment resulted in increased food intake and increased respiratory quotient without significantly altering energy expenditure or body composition as assessed by the lean:lipid ratio. Our findings indicate that alterations in insulin sensitivity occur before changes in the lean:lipid ratio and energy expenditure during the acute disruption of endogenous leptin signaling.

The metabolic effects of Olanzapine and Topiramate in rats and humans

In humans the anti-psychotic Olanzapine (OLZ) has negative side effects on metabolism: it causes weight gain and increases the risk of developing type 2 Diabetes. The anti-convulsant Topiramate (TPM) has the opposite effects: it reduces body weight and improves insulin sensitivity. Because of this, it has been proposed to use TPM to counteract OLZs side effects. The underlying mechanisms by which OLZ and TPM influence metabolism are unknown. To study this, we performed a series of studies in both rats and humans. In rats we administered OLZ and TPM via a permanent intragastric cannula, to mimic oral drug administration, and found that chronic OLZ treatment stimulates weight gain and causes insulin resistance reflected by increased insulin responses during an intravenous-glucose tolerance test OLZ also decreased locomotor activity and core temperature, pointing to a reduction in energy expenditure. OLZ also increased weight gain in humans, accompanied with decreased daily physical activity, reduced body temperature and increased baseline and glucosestimulated insulin levels during an oral glucose tolerance test. TPM reduced the OLZ-induced overeating and weight gain in both rats and humans combined with an increased postprandial satiety rating (in humans). We conclude that, in both rats and humans, a reduction in energy expenditure may explain, at least in part, the OLZ effects on weight gain and that the OLZ-induced effects on insulin resistance has a peripheral side of action. We also conclude that TPM may prevent the negative metabolic side effects induced by OLZ. Supported by: Top Institute Pharma.