Insulin Secretion In Pancreatic Islets Research Articles

Type 2 diabetes candidate genes, including PAX5, cause impaired insulin secretion in human pancreatic islets.

Type 2 diabetes (T2D) is caused by insufficient insulin secretion from pancreatic β cells. To identify candidate genes contributing to T2D pathophysiology, we studied human pancreatic islets from approximately 300 individuals. We found 395 differentially expressed genes (DEGs) in islets from individuals with T2D, including, to our knowledge, novel (OPRD1, PAX5, TET1) and previously identified (CHL1, GLRA1, IAPP) candidates. A third of the identified expression changes in islets may predispose to diabetes, as expression of these genes associated with HbA1c in individuals not previously diagnosed with T2D. Most DEGs were expressed in human β cells, based on single-cell RNA-Seq data. Additionally, DEGs displayed alterations in open chromatin and associated with T2D SNPs. Mouse KO strains demonstrated that the identified T2D-associated candidate genes regulate glucose homeostasis and body composition in vivo. Functional validation showed that mimicking T2D-associated changes for OPRD1, PAX5, and SLC2A2 impaired insulin secretion. Impairments in Pax5-overexpressing β cells were due to severe mitochondrial dysfunction. Finally, we discovered PAX5 as a potential transcriptional regulator of many T2D-associated DEGs in human islets. Overall, we have identified molecular alterations in human pancreatic islets that contribute to β cell dysfunction in T2D pathophysiology.

GDF15 plays a critical role in insulin secretion in INS-1 cells and human pancreatic islets.

Mounting evidence points to a link between growth differentiation factor-15 (GDF15) expression and the onset and progression of diabetes mellitus. However, the exact role of GDF15 in pancreatic β-cell function is unclear. To examine the role of GDF15 in β-cell function, bioinformatics analysis and functional experiments involving GDF15 silencing and overexpression were performed in INS-1 cells and human islets. Public microarray and RNA-seq expression data showed that islets obtained from diabetic donors express high levels of GDF15 compared to islets obtained from normal donors. Moreover, analysis of RNA-seq expression data revealed that GDF15 expression correlates positively with that of insulin (INS), KCNJ11, GLUT1, MAFA, INSR and negatively with that of Glucokinase (GCK) and Alpha-Ketoglutarate Dependent Dioxygenase (FTO). No T2D-associated genetic variants in the GDF15 were found to pass genome-wide significance in the TIGER portal. Expression silencing of Gdf15 in INS-1 cells reduced insulin release, glucose uptake levels, increased reactive oxygen species (ROS) production and apoptosis levels. While Gdf15-silenced cells downregulated mRNA expression of Ins, Pdx1, Mafa, and Glut2 genes, its overexpression human islets was associated with increased insulin secretion and upregulated expression of MAFA and GLUT1 but not INS or GCK. Silencing of Pdx1 or Mafa in INS-1 cells did not affect the expression of GDF15. These findings suggest that GDF15 plays a significant role in pancreatic β-cell function.

Steviol, the aglycon of steviol glycosides, does not reduce hyperglycemia in mice with type 2 diabetes

BackgroundSteviol glycosides, constituents of Stevia rebaudiana Bertoni, are high-intensity sweeteners that enhance glucose-induced insulin secretion and decrease hyperglycemia in mice and rats. Given the extreme sweetness and bitter aftertaste of these compounds, the non-tasting aglycon steviol might be a promising alternative food additive that also harbors anti-hyperglycemic effects. Furthermore, it has been suggested that steviol glucuronide is the main bioactive metabolite of steviol and steviol glycosides that appears in blood. AimTo investigate whether steviol and/or steviol glucuronide reduce hyperglycemia in a high-fat diet (HFD)-induced diabetic mouse model. MethodsSteviol was administered acute per os (p.o.), chronic via drinking water and intravenous (i.v.) to HFD-induced diabetic mice. The effect on glucose homeostasis was assessed using glucose tolerance tests (GTTs). Following chronic and i.v. steviol administration, steviol and steviol glucuronide plasma levels were determined. Steviol glucuronide was administered i.v. and the effect on glycemia was assessed with GTTs. ResultsAcute and chronic oral steviol administration did not lower glycemia. This is due to the very limited and short-lived bioavailability of steviol in plasma. Only after high dosage i.v. steviol, glycemia was transiently reduced shortly after administration (Δ 15 min: 76.4 ± 30.9 mg dL−1, p = 0.035). In contrast, i.v. steviol glucuronide resulted in a 16.4 ± 5.9% lower AUCGlucose(0–120 min) compared to mice that received vehicle (p = 0.040). Moreover, steviol glucuronide enhanced the glucose-induced calcium oscillation frequency in insulin-secreting pancreatic islets. ConclusionOur findings demonstrate that steviol is not a useful derivative of steviol glycosides to improve hyperglycemia in type 2 diabetes. On the other hand, steviol glucuronide has significant anti-hyperglycemic effects in living mice with type 2 diabetes.

Nicotinamide riboside kinase 1 protects against diet and age-induced pancreatic β-cell failure

ObjectiveDisturbances in NAD+ metabolism have been described as a hallmark for multiple metabolic and age-related diseases, including type 2 diabetes. While alterations in pancreatic β-cell function are critical determinants of whole-body glucose homeostasis, the role of NAD+ metabolism in the endocrine pancreas remains poorly explored. Here, we aimed to evaluate the role of nicotinamide riboside (NR) metabolism in maintaining NAD+ levels and pancreatic β-cell function in pathophysiological conditions. MethodsWhole body and pancreatic β-cell-specific NRK1 knockout (KO) mice were metabolically phenotyped in situations of high-fat feeding and aging. We also analyzed pancreatic β-cell function, β-cell mass and gene expression. ResultsWe first demonstrate that NRK1, the essential enzyme for the utilization of NR, is abundantly expressed in pancreatic β-cells. While NR treatment did not alter glucose-stimulated insulin secretion in pancreatic islets from young healthy mice, NRK1 knockout mice displayed glucose intolerance and compromised β-cells response to a glucose challenge upon high-fat feeding or aging. Interestingly, β cell dysfunction stemmed from the functional failure of other organs, such as liver and kidney, and the associated changes in circulating peptides and hormones, as mice lacking NRK1 exclusively in β-cells did not show altered glucose homeostasis. ConclusionsThis work unveils a new physiological role for NR metabolism in the maintenance of glucose tolerance and pancreatic β-cell function in high-fat feeding or aging conditions.

Investigating the Expression and Function of the Glucose Transporter GLUT6 in Obesity.

Obesity-related insulin resistance is a highly prevalent and growing health concern, which places stress on the pancreatic islets of Langerhans by increasing insulin secretion to lower blood glucose levels. The glucose transporters GLUT1 and GLUT3 play a key role in glucose-stimulated insulin secretion in human islets, while GLUT2 is the key isoform in rodent islets. However, it is unclear whether other glucose transporters also contribute to insulin secretion by pancreatic islets. Herein, we show that SLC2A6 (GLUT6) is markedly upregulated in pancreatic islets from genetically obese leptin-mutant (ob/ob) and leptin receptor-mutant (db/db) mice, compared to lean controls. Furthermore, we observe that islet SLC2A6 expression positively correlates with body mass index in human patients with type 2 diabetes. To investigate whether GLUT6 plays a functional role in islets, we crossed GLUT6 knockout mice with C57BL/6 ob/ob mice. Pancreatic islets isolated from ob/ob mice lacking GLUT6 secreted more insulin in response to high-dose glucose, compared to ob/ob mice that were wild type for GLUT6. The loss of GLUT6 in ob/ob mice had no adverse impact on body mass, body composition, or glucose tolerance at a whole-body level. This study demonstrates that GLUT6 plays a role in pancreatic islet insulin secretion in vitro but is not a dominant glucose transporter that alters whole-body metabolic physiology in ob/ob mice.

Intermittent Hypoxia Interferes with Autocrine Effects of GABA on Insulin Secretion in Postnatal Rodents-Implications for Pediatric Obstructive Sleep Apnea.

Gamma-amino butyric acid (GABA) is well known to help elevate pancreatic β cell vitality and insulin levels in blood. GABA works via a coupling with GABA receptors; thus, the concentration of GABAA receptors on the plasma membrane of β cells appears to be critical for insulin regulation. Various medical conditions, such as pediatric and adult obstructive sleep apnea (OSA), show high levels of Type 2 diabetes; such patients also are exposed to intermittent hypoxia (IH), which modifies the GABA levels. To evaluate the potential therapeutic roles of GABA for diabetic patients with OSA, we studied the interactions of IH with GABA and GABAA receptors in young rats. Using rat pups and primary pancreatic islets, we evaluated the roles of GABA in insulin secretion. We show that GABA effectively increased the insulin secretion of pancreatic islets under normal ambient oxygen levels, as well as in culture medium with a glucose level of 2 mM. GABA also increased islet insulin secretion conditioned under IH in a 16 mM glucose medium. When islets were IH-treated, insulin secretion decreased due to lower intracellular chloride levels in accordance with the increased KCC2 levels. The results show that IH challenges down-regulate the GABAA receptor levels in pancreatic islets, which decreases GABA–GABAA receptor coupling action, as well as membrane depolarization for insulin secretion. The findings have the potential to suggest novel interventions for insulin regulation during IH of disordered breathing, including OSA.

The Role of Statins (HMG-CoA Reductase Inhibitors) on Insulin Secretion from the Islets of Langerhans: A Systematic Review

Context: Statins are administered to decrease atherosclerosis in patients with coronary heart disease. These drugs enhance the risk of diabetes by affecting islets insulin secretion. Objectives: Therefore, this systematic review investigates the effect of statins on insulin secretion of islets of Langerhans in the related original studies. Methods: A preliminary search was performed in the PubMed, Scopus, Web of Science, and ProQuest databases. The search strategy terms were statin (hydroxymethylglutaryl-CoA reductase inhibitors), insulin secretion, and islets of Langerhans. The search elements were evaluated using the Mesh term system. Limits were used to include only review articles and no limits were set on language. The quality of the method and risk of bias was assessed by its tool. Results: After removing irrelevant articles to the subject, 20 articles fulfilled the inclusion criteria. In vivo studies revealed that pravastatin and rosuvastatin increase and decrease islets insulin secretion, while atorvastatin and fluvastatin reduced this variable, and pitavastatin had no effect. The results of in vitro studies showed that pravastatin and induced both increasing and decreasing effects on insulin secretion from the pancreatic islet cells. Also, administration of atorvastatin, rosuvastatin, fluvastatin, pitavastatin, simvastatin, and lovastatin decreased islet insulin secretion in the medium. Conclusions: Pravastatin could enhance pancreatic islet insulin secretion while other statins reduced this variable. Finally, the contradictory effect of statins on islets’ insulin secretion can indicate the existence of laboratory and clinical research in this regard.

Deletion of serine racemase reverses neuronal insulin signaling inhibition by amyloid-β oligomers.

Dysregulation of insulin signaling in the Alzheimer's disease (AD) brain has been extensively reported. Serine racemase (SR) modulates insulin secretion in pancreatic islets. This study aimed to examine whether SR regulates insulin synthesis and secretion in neurons, thereby modulating insulin signaling in the AD brain. Srr-knockout (Srr-/- ) mice generated with the CRISPR/Cas9 technique were used. Using immunofluorescence and fluorescence in situ hybridization, levels of insulin protein and insulin(ins2) mRNA were significantly increased in the hippocampal but not in hypothalamic sections of Srr-/- mice compared with WT mice. Real-time quantitative PCR revealed that ins2 mRNA from primary hippocampal neuronal cultures of Srr-/- mice was significantly increased compared with that from cultured neurons of WT mice. Notably, the secretion of proinsulin C-peptide was increased in Srr-/- neurons relative to WT neurons. By examining membrane fractional proteins with immunoblotting, Srr-/- neurons retained ATP-dependent potassium channels on plasmalemma and correspondingly contained higher levels of p-AMPK. After treatment with Aβ42, the phosphorylation levels of insulin receptor substrate at serine 616 636 (p-IRS1ser616,636 ) were significantly lower, whereas p-AKT308 and p-AKT473 were higher in Srr-/- neurons than in WT neurons, respectively. The phosphorylated form of c-Jun N-terminal kinase decreased in the cultured Srr-/- neurons relative to the WT neurons upon Aβ42 treatment. In contrast, phosphorylated protein kinase R remained at the same levels. Further, reactive oxygen species were reduced in cultured Srr-/- neurons under Aβ42 treatment relative to the WT neurons. Collectively, our study indicated that Srr deletion promoted insulin synthesis and secretion of proinsulin C-peptide, thereby reversing insulin resistance by Aβ42. This study suggests that targeting the neuronal SR may be utilized to enhance insulin signaling which is inhibited at the early stage of the AD brain.

Lipid-induced glucose intolerance is driven by impaired glucose kinetics and insulin metabolism in healthy individuals

AimsHypertriglyceridemia is associated with an increased risk of type 2 diabetes. We aimed to comprehensively examine the effects of hypertriglyceridemia on major glucose homeostatic mechanisms involved in diabetes progression. MethodsIn this randomized, cross-over, single-blinded study, two dual-labeled, 3-hour oral glucose tolerance tests were performed during 5-hour intravenous infusions of either 20 % Intralipid or saline in 12 healthy subjects (age 27.9 ± 2.6 years, 11 men, BMI 22.6 ± 1.4 kg/m2) to evaluate lipid-induced changes in insulin metabolism and glucose kinetics. Insulin sensitivity, β cell secretory function, and insulin clearance were assessed by modeling glucose, insulin and C-peptide data. Intestinal glucose absorption, endogenous glucose production, and glucose clearance were assessed from glucose tracers. The effect of triglycerides on β-cell secretory function was examined in perifusion experiments in murine pseudoislets and human pancreatic islets. ResultsMild acute hypertriglyceridemia impaired oral glucose tolerance (mean glucose: +0.9 [0.3, 1.5] mmol/L, p = 0.008) and whole-body insulin sensitivity (Matsuda index: −1.67 [−0.50, −2.84], p = 0.009). Post-glucose hyperinsulinemia (mean insulin: +99 [17, 182] pmol/L, p = 0.009) resulted from reduced insulin clearance (−0.16 [−0.32, −0.01] L min−1 m−2, p = 0.04) and enhanced hyperglycemia-induced total insulin secretion (+11.9 [1.1, 22.8] nmol/m2, p = 0.02), which occurred despite a decline in model-derived β cell glucose sensitivity (−41[−74, −7] pmol min−1 m−2 mmol−1 L, p = 0.04). The analysis of tracer-derived glucose metabolic fluxes during lipid infusion revealed lower glucose clearance (−96 [−152, −41] mL/kgFFM, p = 0.005), increased 2-hour oral glucose absorption (+380 [42, 718] μmol/kgFFM, p = 0.04) and suppressed endogenous glucose production (−448 [−573, −123] μmol/kgFFM, p = 0.005). High-physiologic triglyceride levels increased acute basal insulin secretion in murine pseudoislets (+11 [3, 19] pg/aliquot, p = 0.02) and human pancreatic islets (+286 [59, 512] pg/islet, p = 0.02). ConclusionOur findings support a critical role for hypertriglyceridemia in the pathogenesis of type 2 diabetes in otherwise healthy individuals and dissect the glucose homeostatic mechanisms involved, encompassing insulin sensitivity, β cell function and oral glucose absorption.

Design, Synthesis, and Characterization of a Novel Fluoroprobe for Live Human Islet Cell Imaging of Serotonin 5-HT1A Receptor.

Mounting evidence suggests that the serotonin system serves in signal transmission to regulate insulin secretion in pancreatic islets of Langerhans. Among the 5-HT receptor subtype found in pancreatic islets, serotonin receptor 1A (5-HT1A ) demonstrates a unique ability to inhibit β-cell insulin secretion. We report the design, synthesis, and characterization of two novel fluorescent probes for the 5-HT1A receptor. The compounds were prepared by conjugating the scaffold of the 5-HT1A receptor agonist 8-OH-DPAT with two fluorophores suitable for live-cell imaging. Compound 5a {5-(dimethylamino)-N-[5-[(8-hydroxy-1,2,3,4-tetrahydronaphthalen-2-yl)(propyl)amino]pentyl]naphtalen-1-sulfonammide} showed high affinity for the 5-HT1A receptor (Ki =1.8 nM). Fluoroprobe 5a was able to label the 5-HT1A receptor in pancreatic islet cell cultures in a selective manner, as the fluorescence emission was significantly attenuated by co-administration of the 5-HT1A receptor antagonist WAY-100635. Thus, fluoroprobe 5a showed useful properties to further characterize this unique receptor's role.

Mechanistic Investigation of GHS-R Mediated Glucose-Stimulated Insulin Secretion in Pancreatic Islets.

Ghrelin receptor, a growth hormone secretagogue receptor (GHS-R), is expressed in the pancreas. Emerging evidence indicates that GHS-R is involved in the regulation of glucose-stimulated insulin secretion (GSIS), but the mechanism by which GHS-R regulates GSIS in the pancreas is unclear. In this study, we investigated the role of GHS-R on GSIS in detail using global Ghsr−/− mice (in vivo) and Ghsr-ablated pancreatic islets (ex vivo). GSIS was attenuated in both Ghsr−/− mice and Ghsr-ablated islets, while the islet morphology was similar between WT and Ghsr−/− mice. To elucidate the mechanism underpinning Ghsr-mediated GSIS, we investigated the key steps of the GSIS signaling cascade. The gene expression of glucose transporter 2 (Glut2) and the glucose-metabolic intermediate—glucose-6-phosphate (G6P) were reduced in Ghsr-ablated islets, supporting decreased glucose uptake. There was no difference in mitochondrial DNA content in the islets of WT and Ghsr−/− mice, but the ATP/ADP ratio in Ghsr−/− islets was significantly lower than that of WT islets. Moreover, the expression of pancreatic and duodenal homeobox 1 (Pdx1), as well as insulin signaling genes of insulin receptor (IR) and insulin receptor substrates 1 and 2 (IRS1/IRS2), was downregulated in Ghsr−/− islets. Akt is the key mediator of the insulin signaling cascade. Concurrently, Akt phosphorylation was reduced in the pancreas of Ghsr−/− mice under both insulin-stimulated and homeostatic conditions. These findings demonstrate that GHS-R ablation affects key components of the insulin signaling pathway in the pancreas, suggesting the existence of a cross-talk between GHS-R and the insulin signaling pathway in pancreatic islets, and GHS-R likely regulates GSIS via the Akt-Pdx1-GLUT2 pathway.

Reduced production of isoprostanes by peri-pancreatic adipose tissue from Zucker fa/fa rats as a new mechanism for β-cell compensation in insulin resistance and obesity

During early stages of type 2 diabetes, named prediabetes, pancreatic β-cells compensate for insulin resistance through increased insulin secretion in order to maintain normoglycemia. Obesity leads to the development of ectopic fat deposits, among which peri-pancreatic white adipose tissue (pWAT) can communicate with β-cells through soluble mediators. Thus we investigated whether pWAT produced oxygenated lipids, namely isoprostanes and neuroprostanes and whether they can influence β-cell function in obesity. In the Zucker fa/fa rat model, pWAT and epididymal white adipose tissue (eWAT) displayed different inflammatory profiles. In obese rats, pWAT, but not eWAT, released less amounts of 5-F2t-isoprostanes, 15-F2t-isoprostanes, 4-F4t-neuroprostanes and 10-F4t-neuroprostane compared to lean animals. These differences could be explained by a greater induction of antioxidant defenses enzymes such as SOD-1, SOD-2, and catalase in pWAT of obese animals compared to eWAT. In addition, sPLA2 IIA, involved in the release of isoprostanoids from cellular membranes, was decreased in pWAT of obese animals, but not in eWAT, and may also account for the reduced release of oxidized lipids by this tissue. At a functional level, 15-F2t-isoprostane epimers, but not 5-F2t-isoprostanes, were able to decrease glucose-induced insulin secretion in pancreatic islets from Wistar rats. This effect appeared to be mediated through activation of the thromboxane A2 receptor and reduction of cAMP signaling in pancreatic islets. In conclusion, through the removal of an inhibitory tone exerted by isoprostanes, we have shown, for the first time, a new mechanism allowing β-cells to compensate for insulin resistance in obesity that is linked to a biocommunication between adipose tissue and β-cells.

Microtubules regulate pancreatic β-cell heterogeneity via spatiotemporal control of insulin secretion hot spots.

Heterogeneity of glucose-stimulated insulin secretion (GSIS) in pancreatic islets is physiologically important but poorly understood. Here, we utilize mouse islets to determine how microtubules (MTs) affect secretion toward the vascular extracellular matrix at single cell and subcellular levels. Our data indicate that MT stability in the β-cell population is heterogenous, and that GSIS is suppressed in cells with highly stable MTs. Consistently, MT hyper-stabilization prevents, and MT depolymerization promotes the capacity of single β-cell for GSIS. Analysis of spatiotemporal patterns of secretion events shows that MT depolymerization activates otherwise dormant β-cells via initiation of secretion clusters (hot spots). MT depolymerization also enhances secretion from individual cells, introducing both additional clusters and scattered events. Interestingly, without MTs, the timing of clustered secretion is dysregulated, extending the first phase of GSIS and causing oversecretion. In contrast, glucose-induced Ca2+ influx was not affected by MT depolymerization yet required for secretion under these conditions, indicating that MT-dependent regulation of secretion hot spots acts in parallel with Ca2+ signaling. Our findings uncover a novel MT function in tuning insulin secretion hot spots, which leads to accurately measured and timed response to glucose stimuli and promotes functional β-cell heterogeneity.

Low-grade elevation of palmitate and lipopolysaccharide synergistically induced β-cell damage via inhibition of neutral ceramidase

High concentrations of free fatty acids (FFAs) or lipopolysaccharide (LPS) could lead to β-cell apoptosis and dysfunction, while low-grade elevation of FFAs or LPS, which are more common in people with type 2 diabetes mellitus (T2DM) or obesity, have no obvious toxic effect on β-cells. Palmitate is a component closely related to metabolic disorders in FFAs. Recent studies have found that low-grade elevation of palmitate and LPS synergistically affects the sphingolipid signaling pathway by activating Toll-like receptor 4 (TLR4) and further enhances the expression of inflammatory cytokines in immune cells. Previous studies demonstrated that sphingolipids also played an important role in the occurrence and development of T2DM. This study aimed to investigate the synergistic effects of low-grade elevation of palmitate and LPS on viability, apoptosis and insulin secretion in the rat pancreatic β-cell line INS-1 or islets and the role of sphingolipids in this process. We showed that low-grade elevation of palmitate or LPS alone did not affect the viability, apoptosis, glucose-stimulated insulin secretion (GSIS) or intracellular insulin content of INS-1 cells or islets, while the combination of the two synergistically inhibited cell viability, induced apoptosis and decreased basal insulin secretion in INS-1 cells or islets. Treatment with palmitate and LPS markedly upregulated TLR4 protein expression and downregulated neutral ceramidase (NCDase) activity and protein expression. Additionally, low-grade elevation of palmitate and LPS synergistically induced a significant increase in ceramide and a decrease in sphingosine-1-phosphate. Blocking TLR4 signaling or overexpressing NCDase remarkably attenuated INS-1 cell injury induced by the combination of palmitate and LPS. However, inhibition of ceramide synthase did not ameliorate injury induced by palmitate and LPS. Overall, we show for the first time that low-grade elevation of palmitate and LPS synergistically induced β-cell damage by activating TLR4 signaling, inhibiting NCDase activity, and further modulating sphingolipid metabolism, which was different from a high concentration of palmitate-induced β-cell injury by promoting ceramide synthesis.

The risk variant of CDKAL1 (rs7756992) impairs fasting glucose levels and insulin resistance improvements after a partial meal-replacement hypocaloric diet

BackgroundThe CDKAL1 (CDK5 Regulatory Subunit Associated Protein 1 Like 1) gene encodes cyclin-dependent kinase 5 (CDK5) regulatory subunit-associated proten1 like 1. This protein has been shown to contribute to the glucose-dependent regulation of insulin secretion in pancreatic islets. AimsThe aim of our study was to analyze the effects of the rs7756992 genetic variant of CDKAL1 gene on fasting glucose and insulin resistance after weight loss secondary to partial meal replacement hypocaloric diet (pMRHD). MethodsThis was a non-randomized, single-treatment study with a formula-diet in 44 obese subjects. The patients received nutritional education and a modified diet with two intakes of a normocaloric hyperproteic formula for 3-months. Anthropometric parameter and biochemical profile were measured at basal time and after 3 months. The variant of CDKAL1 gene rs7756992 was assessed. ResultsThe following genetic distribution was observed; [27AA (61.3%), 12 AG (27.3%) and 5 GG (11.4%)]. After the pMRHD, body weight, the body mass index (BMI), fat mass, waist circumference and blood pressure decreased in both genotypes. Non-G allele carriers showed a significant improvement in fasting glucose levels (AA vs. AG + GG) (−6.1 ± 1.4 md/dl vs. −1.2 ± 0.7 mg/dl; p = 0.01), fasting insulin levels (−3.6 ± 0.2 mU/l vs. −1.3 ± 0.6 mU/l; p = 0.02) and HOMA-IR (−1.2 ± 0.2 units vs. −0.3 ± 0.2 units; p = 0.01). Fasting plasma glucose levels were higher in G allele carriers than non G allele carriers. ConclusionsOur data suggest that the genetic variant (rs7756992) of CDKAL1 gene is associated with glycaemic status after a pMRHD, with greater improvements in fasting glucose, insulin and HOMA-IR in subjects without the G allele.

Soy isoflavones recover pancreatic islet function and prevent metabolic dysfunction in male rats.

We tested whether chronic supplementation with soy isoflavones could modulate insulin secretion levels and subsequent recovery of pancreatic islet function as well as prevent metabolic dysfunction induced by early overfeeding in adult male rats. Wistar rats raised in small litters (SL, three pups/dam) and normal litters (NL, nine pups/dam) were used as models of early overfeeding and normal feeding, respectively. At 30 to 90 days old, animals in the SL and NL groups received either soy isoflavones extract (ISO) or water (W) gavage serving as controls. At 90 days old, body weight, visceral fat deposits, glycemia, insulinemia were evaluated. Glucose-insulin homeostasis and pancreatic-islet insulinotropic response were also determined. The early life overnutrition induced by small litter displayed metabolic dysfunction, glucose, and insulin homeostasis disruption in adult rats. However, adult SL rats treated with soy isoflavones showed improvement in glucose tolerance, insulin sensitivity, insulinemia, fat tissue accretion, and body weight gain, compared with the SL-W group. Pancreatic-islet response to cholinergic, adrenergic, and glucose stimuli was improved in both isoflavone-treated groups. In addition, different isoflavone concentrations increased glucose-stimulated insulin secretion in islets of all groups with higher magnitude in both NL and SL isoflavone-treated groups. These results indicate that long-term treatment with soy isoflavones inhibits early overfeeding-induced metabolic dysfunction in adult rats and modulated the process of insulin secretion in pancreatic islets.

Discovery of ciliary G protein-coupled receptors regulating pancreatic islet insulin and glucagon secretion.

Multiple G protein-coupled receptors (GPCRs) are expressed in pancreatic islet cells, but the majority have unknown functions. We observed specific GPCRs localized to primary cilia, a prominent signaling organelle, in pancreatic α and β cells. Loss of cilia disrupts β-cell endocrine function, but the molecular drivers are unknown. Using functional expression, we identified multiple GPCRs localized to cilia in mouse and human islet α and β cells, including FFAR4, PTGER4, ADRB2, KISS1R, and P2RY14. Free fatty acid receptor 4 (FFAR4) and prostaglandin E receptor 4 (PTGER4) agonists stimulate ciliary cAMP signaling and promote glucagon and insulin secretion by α- and β-cell lines and by mouse and human islets. Transport of GPCRs to primary cilia requires TULP3, whose knockdown in primary human and mouse islets relocalized ciliary FFAR4 and PTGER4 and impaired regulated glucagon or insulin secretion, without affecting ciliary structure. Our findings provide index evidence that regulated hormone secretion by islet α and β cells is controlled by ciliary GPCRs providing new targets for diabetes.

Alkaloidal extract from Zanthoxylum zanthoxyloides stimulates insulin secretion in normoglycemic and nicotinamide/streptozotocin-induced diabetic rats

IntroductionIncrease in the prevalence of type-2 diabetes in Sub-Sahara Africa has created the need for robust treatment and management programs. However, an effective diabetes management program requires a high annual budget that most countries in this region cannot afford. That said, various plants and plant products in this region have either been confirmed and/or ethnopharmacologically used for the management of type-2 diabetes. AimTo investigate the antidiabetic and insulin secretory effects of an alkaloidal extract derived from Zanthoxylum zanthoxyloides in normoglycemic and experimental diabetic rats. Materials and methodsAlkaloidal extract was prepared from leaves of Zanthoxylum zanthoxyloides (ZZAE). Nicotinamide/streptozotocin-induced type-2 diabetes was modeled in male Sprague Dawley rats weighing between 130 to 150 g. The experimental diabetic rats were grouped into six treatment groups [Model, 20% Tween20, chlorpropamide, and ZZAE (50, 100, and 150 mg/kg)], and one control group. Fasting blood glucose (FBG), and body weight were measured weekly. Rats were sacrificed 2 days after treatment under chloroform anesthesia to collect blood samples and to isolate major organs for biochemical, and histological analyses respectively. Islets of Langerhans were isolated from normoglycemic rats and co-cultured with ZZAE and chlorpropamide (10 μg/mL) to assess the insulin secretory effect of ZZAE. ResultsZZAE improved glucose kinetics curve in normoglycemic (p < 0.001) and experimental diabetic rats (p < 0.05) compared to the model. ZZAE (100 and 150 mg/kg) restored islets population, and improved kidney, and liver, histoarchitecture. ZZAE (150 mg/kg) improved post-treatment serum insulin levels compared to the model group (p < 0.001) and the Chlorpropamide group (p < 0.05). ZZAE also restored glycogen synthesis in skeletal muscles of experimental diabetic rats and stimulated insulin secretion in pancreatic islets of Langerhans isolated from normoglycemic rats. ConclusionThese results showed that ZZAE has active alkaloids that can be explored for diabetes management.

682-P: Novel Dual Glucagon and Glucagon-Like Peptide-1 Receptor Agonist LY3305677 Improves Glucose Control, Reduces Body Weight, and Increases Energy Expenditure in Mice

LY3305677 (LY) is a synthetic peptide analog of mammalian oxyntomodulin with a fatty acyl side chain to extend time action. LY functions are mediated by binding and activation of both glucagon (GcgR) and glucagon-like peptide-1 (GLP-1R) receptors. LY is bound with potent binding affinity (Ki) to human and mouse GcgR (Ki: 17.7 nM and 15.9 nM, respectively) and GLP-1R (Ki: 28.6 nM and 25.1 nM, respectively). LY dose-dependently stimulated insulin secretion in mouse pancreatic islets (EC50: 5.2 nM) and in mice. In oral glucose tolerance tests of diet-induced obese (DIO) and streptozotocin-induced diabetic mice, a single subcutaneous (SC) dose of LY significantly reduced glucose area under the curve by up to 65%. SC injections of LY to DIO mice dose-dependently reduced serum triglycerides and PCSK9 (proprotein convertase subtilisin/kexin type 9) levels and dose-dependently increased FGF21 (fibroblast growth factor 21) levels. In DIO mice treated over 18 days, LY 30 nmol/kg reduced body weight to a greater extent (33%) than semaglutide 60 nmol/kg (12%), and decreased food intake by 50% compared to vehicle. At Day 18, LY 30 nmol/kg group lost 33% of initial bodyweight, which was primarily due to 70% reduced fat mass. LY reduced liver triglycerides by greater than 70% and increased serum ketones by more than 3-fold compared to vehicle, suggestive of increased fatty acid oxidation. LY decreased body weight in both GcgR knock-out (KO) and GLP-1R KO mice, indicating that activation of both receptors contributed to greater weight loss. To assess potential changes in energy expenditure, DIO mice were treated chronically with SC LY (15 nmol/kg), semaglutide (60 nmol/kg), or vehicle. LY, but not semaglutide, increased energy expenditure as compared with vehicle. These preclinical studies indicate that novel dual GcgR and GLP-1R agonist LY may have potential to enhance metabolic health by improving dyslipidemia, hyperglycemia, or obesity. Disclosure Y. Chen: None. H. Qu: Employee; Self; Eli Lilly and Company, Stock/Shareholder; Self; Eli Lilly and Company. A. Mezo: None. T. Coskun: Employee; Self; Eli Lilly and Company, Stock/Shareholder; Self; Eli Lilly and Company. M. Song: None. W. C. Roell: Employee; Self; Eli Lilly and Company, Stock/Shareholder; Self; Eli Lilly and Company. K. B. Bokvist: Employee; Self; Eli Lilly and Company, Sanofi-Aventis Deutschland GmbH, Stock/Shareholder; Self; Johnson &amp; Johnson, Sanofi-Aventis Deutschland GmbH, Stock/Shareholder; Spouse/Partner; Novo Nordisk A/S. J. S. Moyers: Employee; Self; Eli Lilly and Company, Stock/Shareholder; Self; Eli Lilly and Company. M. K. Thomas: Employee; Self; Eli Lilly and Company, Stock/Shareholder; Self; Eli Lilly and Company. F. Valenzuela: None. Funding Eli Lilly and Company

99-OR: Effects of Early Time-Restricted Feeding during Gestation on Offspring Glucose Homeostasis in Mice

Time-Restricted Feeding (TRF) is an increasingly common diet that may improve insulin sensitivity. This practice merits study in the setting of pregnancy, as the diet is common, pregnancy represents a critical period for the health of both mother and offspring, and the effects of TRF during pregnancy on maternal gestational health and long-term offspring consequences remain unexamined. To test these effects, female mice were randomized to 6 hours of food availability in the dark cycle (early-time restricted feeding, eTRF), or given 24-hour ad libitum (AL) food access. After one week of acclimatization, females were mated. Food intake and body composition were measured weekly throughout gestation; insulin sensitivity was assessed at day 16 of pregnancy. Offspring birth rate, survival, birthweight, and gestational age were assessed. Body composition and food intake were assessed weekly. After 70 days on a normal diet, all offspring were switched to a 45% high-fat diet (HFD) with continued weekly monitoring. Glucose tolerance and insulin tolerance tests were conducted before and after 10 weeks of HFD feeding. Our data suggests that maternal eTRF does not affect birth weight or gestational age, but does reduce litter size (7.7 pups vs. 6.0 pups) and 3-day pup survival (95% vs. 58%) compared to AL. eTRF offspring had similar insulin and glucose tolerance compared to AL counterparts until adulthood (70 days of age). After 12 weeks of high-fat diet feeding, eTRF males develop concomitant glucose intolerance (auc, p&amp;lt;0.0001) and insulin sensitivity (auc, p=0.006), which was absent in females. These metabolic changes were present despite eTRF males having similar fat mass, body weight, and food intake when compared to AL males. Taken together, these data suggest that eTRF during pregnancy followed by offspring HFD feeding results in male-specific impaired glucose metabolism. Further work planned will evaluate the role of pancreatic islet insulin secretion in vivo and in vitro in future cohorts. Disclosure M. E. Carter: None. N. El habbal: None. D. S. Snyder: None. J. R. Redd: None. B. Gregg: None. D. Bridges: None. Funding National Institute of Diabetes and Digestive and Kidney Diseases (R01DK107535); University of Michigan