Inhibition Of Insulin Secretion Research Articles

233-OR: The Beta-Cell Specific Deletion of Complement 1q-Like-3 Secreted Protein Improves Beta-Cell Function and Glucose Homeostasis

Using bioinformatics network analysis, we identified complement-1q like-3 (C1ql3) as a secreted protein that affects pancreatic islet function in obese mice. Previously, we showed that the recombinant C1ql3 protein inhibits insulin secretion stimulated by exendin-4 (an agonist for GLP-1 receptor) from human and mouse islets. Currently, we are elucidating the role of C1ql3 in pancreatic β-cell function by using mice with β-cell-specific deletion of the C1ql3 (βKO) gene on a standard chow diet. C1ql3βKO mice showed significantly improved glucose clearance after oral glucose challenge than the control mice, whereas no difference in insulin sensitivity was observed. Moreover, the plasma insulin levels were significantly increased at 15 min after the glucose challenge in the C1ql3 βKO vs. control mice. However, islets isolated from C1ql3βKO significantly increased insulin secretion stimulated by cAMP and Exendin-4 than control islets. These results suggest that the loss of C1ql3 in β-cells increases insulin secretion to improve glucose tolerance. Adenovirus-mediated overexpression of C1ql3 in islets showed increased ER stress and decreased expression of genes involving β-cell function and maintenance. In pathophysiological conditions, increased C1ql3 expression coupled to secretion was observed from both T2D donor islets and obese mouse islets. Interestingly, reduction in C1ql3 secretion is inversely correlated with increased glucose-stimulated insulin secretion from islets of C1ql3βKOLeptinob/ob compared to Leptinob/ob control mice. These findings suggest that the loss of β-cell C1ql3 maintains ER stress and increases insulin secretion to maintain glucose homeostasis. Our work shows that an autocrine regulation of the C1ql3-signaling pathway contributes to β-cell dysfunction in obesity and type 2 diabetes. Disclosure M.Rahman: None. H.Alsharif: None. A.Michl: None. S.Bhatnagar: None. Funding National Institute of Diabetes and Digestive and Kidney Diseases (1R01DK120684-01)

1782-P: Perinatal Hypoxia Lowers the Glucose Threshold for Insulin Secretion Causing Hypoglycemia and Hyperinsulinism

Perinatal stress-induced hyperinsulinism is a common cause of persistent hypoglycemia in at-risk neonates. The hypoxia-inducible factor-1 (HIF-1) pathway regulates cellular adaptation in hypoxic conditions through hypoxia response elements. We hypothesize that perinatal hypoxia leads to activation of the HIF1 pathway causing increased insulin secretion from neonatal β-cells. We examined glucose homeostasis and insulin secretion in NeuroD1-Cre;VhlLoxp/Loxp(VhlbetaKO) and in hypoxic wild type (WT) mouse pups in the first week of life. In VhlbetaKO pups postnatal day 8 (P8), plasma glucose was significantly lower compared to littermate controls (76 vs 129 mg/dL). Plasma insulin (0.54 vs 0.27 ng/mL) and the insulin to glucose ratio were significantly greater in VhlbetaKO pups indicating a failure to suppress insulin secretion. VhlbetaKO islet perifusion showed the lower plasma glucose level was due to a lower threshold (5 mM) for glucose stimulated insulin secretion (GSIS) compared to controls (10 mM). To assess the consequences of perinatal hypoxia, we exposed WT mouse pups to hypoxia (10% O2) between embryonic day 18 and P6. Islets from the hypoxia exposed pups had a lower GSIS threshold (3 mM) compared to islets from normoxic pups (5 mM) at P6. Hypoxic islets also had a lower insulin secretion threshold when stimulated with BCH, a glutamate dehydrogenase activator, or tolbutamide, a KATP channel inhibitor, suggesting that HIF1 pathway activation leads to a decreased stimulus threshold for secretion at or distal to the KATP channel. Patch clamps revealed that β-cells from hypoxic pups were more depolarized than normoxic controls. Our results show that the HIF1 pathway is critical for setting the GSIS threshold and a potential mediator of PSHI. We posit perinatal hypoxia and the HIF1 pathway at the core of β-cell maturational defects leading to increased risk of diabetes in adult life and the long-sought answer to the cause of perinatal stress-induced hyperinsulinism. Disclosure C.Juliana: Research Support; Crinetics Pharmaceuticals, Inc., Twist Bioscience, AmideBio. D.De leon: Consultant; Zealand Pharma A/S, Crinetics Pharmaceuticals, Inc., Eiger BioPharmaceuticals, Hanmi Pharm. Co., Ltd., Research Support; Ultragenix, Crinetics Pharmaceuticals, Inc., Hanmi Pharm. Co., Ltd., Rezolute, Inc.

Rab26 restricts insulin secretion via sequestering Synaptotagmin-1.

Rab26 is known to regulate multiple membrane trafficking events, but its role in insulin secretion in pancreatic β cells remains unclear despite it was first identified in the pancreas. In this study, we generated Rab26-/- mice through CRISPR/Cas9 technique. Surprisingly, insulin levels in the blood of the Rab26-/- mice do not decrease upon glucose stimulation but conversely increase. Deficiency of Rab26 promotes insulin secretion, which was independently verified by Rab26 knockdown in pancreatic insulinoma cells. Conversely, overexpression of Rab26 suppresses insulin secretion in both insulinoma cell lines and isolated mouse islets. Islets overexpressing Rab26, upon transplantation, also failed to restore glucose homeostasis in type 1 diabetic mice. Immunofluorescence microscopy revealed that overexpression of Rab26 results in clustering of insulin granules. GST-pulldown experiments reveal that Rab26 interacts with synaptotagmin-1 (Syt1) through directly binding to its C2A domain, which interfering with the interaction between Syt1 and SNAP25, and consequently inhibiting the exocytosis of newcomer insulin granules revealed by TIRF microscopy. Our results suggest that Rab26 serves as a negative regulator of insulin secretion, via suppressing insulin granule fusion with plasma membrane through sequestering Syt1.

Excessive iron inhibits insulin secretion via perturbing transcriptional regulation of SYT7 by OGG1.

Although iron overload is closely related to the occurrence of type2diabetesmellitus (T2DM), the specific mechanism is unclear. Here, we found that excessive iron inhibited the secretion of insulin (INS) and impaired islet β cell function through downregulating Synaptotagmin 7 (SYT7) in iron overload model in vivo and in vitro. Our results further demonstrated that 8-oxoguanine DNA glycosylase (OGG1), a key protein in the DNA base excision repair, was an upstream regulator of SYT7. Interestingly, such regulation could be suppressed by excessive iron. Ogg1-null mice, iron overload mice and db/db mice exhibit reduced INS secretion, weakened β cell function and subsequently impaired glucose tolerance. Notably, SYT7 overexpression could rescue these phenotypes. Our data revealed an intrinsic mechanism by which excessive iron inhibits INS secretion through perturbing the transcriptional regulation of SYT7 by OGG1, which suggested that SYT7 was a potential target in clinical therapy for T2DM.

A selective nonpeptide somatostatin receptor 5 agonist effectively decreases insulin secretion in hyperinsulinism

Congenital hyperinsulinism (HI), a beta cell disorder most commonly caused by inactivating mutations of beta cell KATP channels, results in dysregulated insulin secretion and persistent hypoglycemia. Children with KATP-HI are unresponsive to diazoxide, the only FDA-approved drug for HI, and utility of octreotide, the second line therapy, is limited because of poor efficacy, desensitization, and somatostatin receptor type 2 (SST2)-mediated side effects. Selective targeting of SST5, an SST receptor associated with potent insulin secretion suppression, presents a new avenue for HI therapy. Here, we determined that CRN02481, a highly selective nonpeptide SST5 agonist, significantly decreased basal and amino acid-stimulated insulin secretion in both Sur1-/- (a model for KATP-HI) and wild type mouse islets. Oral administration of CRN02481 significantly increased fasting glucose and prevented fasting hypoglycemia compared to vehicle in Sur1-/- mice. During a glucose tolerance test, CRN02481 significantly increased glucose excursion in both WT and Sur1-/- mice compared to control. CRN02481 also reduced glucose- and tolbutamide-stimulated insulin secretion from healthy, control human islets similar to the effects observed with SS14 and peptide somatostatin analogs. Moreover, CRN02481 significantly decreased glucose- and amino acid-stimulated insulin secretion in islets from two infants with KATP-HI and one with Beckwith-Weideman Syndrome-HI. Taken together, these data demonstrate that a potent and selective SST5 agonist effectively prevents fasting hypoglycemia and suppresses insulin secretion not only in a KATP-HI mouse model, but also in healthy human islets and islets from HI patients.

Attenuated glucose-stimulated insulin secretion during an acute IGF-1 LR3 infusion into fetal sheep does not persist in isolated islets.

Insulin-like growth factor-1 (IGF-1) is a critical fetal growth hormone that has been proposed as a therapy for intrauterine growth restriction. We previously demonstrated that a 1-week IGF-1 LR3 infusion into fetal sheep reduces in vivo and in vitro insulin secretion suggesting an intrinsic islet defect. Our objective herein was to determine whether this intrinsic islet defect was related to chronicity of exposure. We therefore tested the effects of a 90-min IGF-1 LR3 infusion on fetal glucose-stimulated insulin secretion (GSIS) and insulin secretion from isolated fetal islets. We first infused late gestation fetal sheep (n = 10) with either IGF-1 LR3 (IGF-1) or vehicle control (CON) and measured basal insulin secretion and in vivo GSIS utilizing a hyperglycemic clamp. We then isolated fetal islets immediately following a 90-min IGF-1 or CON in vivo infusion and exposed them to glucose or potassium chloride to measure in vitro insulin secretion (IGF-1, n = 6; CON, n = 6). Fetal plasma insulin concentrations decreased with IGF-1 LR3 infusion (P < 0.05), and insulin concentrations during the hyperglycemic clamp were 66% lower with IGF-1 LR3 infusion compared to CON (P < 0.0001). Insulin secretion in isolated fetal islets was not different based on infusion at the time of islet collection. Therefore, we speculate that while acute IGF-1 LR3 infusion may directly suppress insulin secretion, the fetal β-cell in vitro retains the ability to recover GSIS. This may have important implications when considering the long-term effects of treatment modalities for fetal growth restriction.

Dopamine receptor agonists mechanism of actions on glucose lowering and their connections with prolactin actions.

Robust experiment evidence suggests that prolactin can enhance beta-cell proliferation and increase insulin secretion and sensitivity. Apart from acting as an endocrine hormone, it also function as an adipokine and act on adipocytes to modulate adipogenesis, lipid metabolism and inflammation. Several cross-sectional epidemiologic studies consistently showed that circulating prolactin levels positive correlated with increased insulin sensitivity, lower glucose and lipid levels, and lower prevalence of T2D and metabolic syndrome. Bromocriptine, a dopamine receptor agonist used to treat prolactinoma, is approved by Food and Drug Administration for treatment in type 2 diabetes mellitus since 2009. Prolactin lowering suppress insulin secretion and decrease insulin sensitivity, therefore dopamine receptor agonists which act at the pituitary to lower serum prolactin levels are expected to impair glucose tolerance. Making it more complicating, studies exploring the glucose-lowering mechanism of bromocriptine and cabergoline have resulted in contradictory results; while some demonstrated actions independently on prolactin status, others showed glucose lowering partly explained by prolactin level. Previous studies showed that a moderate increase in central intraventricular prolactin levels stimulates hypothalamic dopamine with a decreased serum prolactin level and improved glucose metabolism. Additionally, sharp wave-ripples from the hippocampus modulates peripheral glucose level within 10 minutes, providing evidence for a mechanistic link between hypothalamus and blood glucose control. Central insulin in the mesolimbic system have been shown to suppress dopamine levels thus comprising a feedback control loop. Central dopamine and prolactin levels plays a key role in the glucose homeostasis control, and their dysregulation could lead to the pathognomonic central insulin resistance depicted in the "ominous octet". This review aims to provide an in-depth discussion on the glucose-lowering mechanism of dopamine receptor agonists and on the diverse prolactin and dopamine actions on metabolism targets.

Outbred Mice with Streptozotocin-Induced Diabetes Show Sex Differences in Glucose Metabolism.

Outbred mice (ICR) with different genotypes and phenotypes have been reported to be more suitable for scientific testing than inbred mice because they are more similar to humans. To investigate whether the sex and genetic background of the mice are important factors in the development of hyperglycemia, we used ICR mice and divided them into male, female, and ovariectomized female (FOVX) groups and treated them with streptozotocin (STZ) for five consecutive days to induce diabetes. Our results show that fasting blood glucose and hemoglobin A1c (HbA1c) levels were significantly higher in diabetes-induced males (M-DM) and ovariectomized diabetes-induced females (FOVX-DM) than in diabetes-induced females (F-DM) at 3 and 6 weeks after STZ treatment. Furthermore, the M-DM group showed the most severe glucose tolerance, followed by the FOVX-DM and F-DM groups, suggesting that ovariectomy affects glucose tolerance in female mice. The size of pancreatic islets in the M-DM and FOVX-DM groups was significantly different from that of the F-DM group. The M-DM and FOVX-DM groups had pancreatic beta-cell dysfunction 6 weeks after STZ treatment. Urocortin 3 and somatostatin inhibited insulin secretion in the M-DM and FOVX-DM groups. Overall, our results suggest that glucose metabolism in mice is dependent on sex and/or genetic background.

Acute effects of drinks containing blackcurrant and citrus (poly)phenols and dietary fibre on postprandial glycaemia, gut hormones, cognitive function and appetite in healthy adults: two randomised controlled trials.

(Poly)phenol (PP)-rich blackcurrant (BC) extracts reduce postprandial glucose concentrations. Combinations with other fruit (poly)phenols and fruit fibre may enhance the effect. This study investigated the acute effects of combinations of BC extracts, high (H-BC) and low (L-BC) (poly)phenol concentrations, sweet orange extracts (SO) and fibre-rich orange pulp (F) in reducing postprandial glycaemia. In two randomised, double-blind, crossover design studies, healthy participants consumed seven types of 200 mL beverages: in the GLU-FX trial, H-BC (1600 mg PP); L-BC (800 mg PP); SO (800 mg PP); BC + SO (1600 mg PP) or CON (placebo); in the GLU-MIX trial, BC + F (800 mg PP), F (1.5 g fibre), or CON2 (placebo), immediately followed by consumption of 75 g available carbohydrate (starch and sugars). Blood was sampled at baseline and postprandially to measure changes in glucose, insulin, and gut hormones; appetite changes were assessed by visual analogue scales and, in GLU-MIX, ad libitum food intake and cognitive function were assessed. Twenty-nine and thirty-seven adults completed GLU-FX and GLU-MIX, respectively. L-BC reduced early postprandial glycaemia (0-30 min) with no differences in glucose incremental Cmax or total glycaemic response. No significant effect was observed following other drinks relative to CON. L-BC and H-BC drinks inhibited insulin secretion up to 30 min and GIP up to 120 min. In GLU-MIX, BC + F improved some indicators of cognitive function but not all. Measures of appetite were unaffected. The impact of (poly)phenol-rich BC extracts on total postprandial glycaemia in healthy participants was minimal and not enhanced when administered in combination with an orange (poly)phenol extract or orange pulp. Clinical Trials registered at https://www.clinicaltrials.gov: NCT03184064 (GLU-FX) and NCT03572296 (GLU-MIX).

PS-R03-5: HYPOTENSIVE AND HYPERGLYCEMIC EFFECTS OF DIAZOXIDE IN A CASE OF INSULINOMA

Case report: We report the case of sporadic insulinoma in a 70-year-old female with breast cancer and hypertension treated by irbesartan 100 mg and benidipine 8 mg, who presented with a 1-month history of episodic tremulousness, diaphoresis, increased hunger, confusion and fainting. Initial laboratory investigations showed low blood glucose (21 mg/dL) and high blood insulin (107 μU/mL) levels. The hypoglycemic symptoms were relieved greatly by glucose administration and Whipple's triad for insulinoma was met. An abdominal contrast-enhanced computed tomography scan showed a 12 mm, small, well demarcated, heterogeneously enhancing lesion within the tail of pancreas without dilatation of pancreatic duct. The site also showed a well-defined accumulation of boundaries on PET-CT. Patient was diagnosed with insulinoma. Since Patient did not initially wish to undergo surgery, blood glucose control was performed by taking diazoxide 225 mg, gradually reduced to 50 mg. Before and after taking diazoxide, blood glucose increased from 75 ± 40 mg/dL to 124 ± 35 mg/dL significantly (p &lt; 0.05). On the other hand, blood pressure was significantly reduced from 141 ± 3/78 ± 3 mmHg to 126 ± 3/75 ± 3 mmHg. Benidipine was withdrawn to about 130/80 mmHg. Then, Patient changed her mind and underwent laparoscopic caudal pancreatic resection. Histopathological examination of the pancreatic mass confirmed neuroendocrine tumor (insulinoma). Patient had an uneventful recovery. Blood pressure re-increased above 140/90 mmHg and benidipine was resumed. Although diazoxide suppresses insulin secretion in the pancreas due to its KATP channel opening action and improves hypoglycemic attacks with insulinoma, it also acts on the KATP channel of vascular smooth muscle and show a hypotensive effect. It is important to pay close attention not only to blood glucose but also to blood pressure fluctuations when using diazoxide.

In vitro biochemical assessment of mixture effects of two endocrine disruptors on INS-1 cells

4-tert-Octylphenol (4-tOP) is a component of non-ionic surfactants alkylphenol polyethoxylates while triclosan (TCS) is an antibacterial present in personal care products. Both compounds can co-exist in environmental matrices such as soil and water. The mixture effects of these micropollutants in vitro remains unknown. INS-1 cells were exposed to 20 µM or 30 µM 4-tOP and 8 µM or 12.5 µM TCS as well as equimolar mixture of the chemicals (Mix) in total concentration of 12.5 µM or 25 µM for 48 h. Mitochondrial related parameters were investigated using high content analytical techniques. The cytotoxicity of the chemicals (IC50) varied according to TCS > Mix > 4-tOP. Increased glucose uptake and loss of mitochondrial membrane potential were recorded in TCS and Mix treated cells. Fold values of glucose-galactose assay varied according to dinitrophenol > TCS > 4-tOP > Mix in decreasing order of mitochondrial toxicity. The loss of the intracellular Ca2+ influx by all the test substances and Mix was not substantial whereas glibenclamide and diazoxide increased the intracellular Ca2+ influx when compared with the Blank. The recorded increase in Ca2+ influx by diazoxide which contrasted with its primary role of inhibiting insulin secretion need be re-investigated. It is concluded that the toxic effects of TCS and Mix but not 4-tOP on INS-1 cells was mitochondria-mediated.

PSUN304 CRN04777 an Oral, Nonpeptide SST5-selective Somatostatin Agonist Dose Dependently Suppresses Basal and Stimulated Insulin Secretion

Abstract Congenital hyperinsulinism (HI) is the most common cause of persistent hypoglycemia in neonates, infants, and children, and is caused by genetic mutations in the insulin secretion pathway in pancreatic beta-cells. Current medical and surgical treatments are often highly burdensome, only partially effective, and associated with significant morbidity. CRN04777 is a potent orally bioavailable SST5 agonist (EC50=0.41 nM) that is &amp;gt;1300 fold selective over other SST receptor subtypes. CRN04777 has been shown to suppress both glucose- and sulfonylurea (SU)-induced insulin secretion in rats. The latter is a model for the most common known monogenic form of human congenital HI. We report initial results from a randomized, double-blinded, placebo-controlled single ascending dose study evaluating the safety, pharmacokinetics and pharmacodynamics of CRN04777 in 74 healthy volunteers. Endogenous insulin secretion was stimulated using intravenous glucose tolerance tests (IVGTT) or SU challenges in separate cohorts of volunteers. In the IVGTT cohorts, single doses of CRN04777 (0.5-120 mg) were administered after an overnight fast and 1 hour prior to an IV bolus of 300 mg/kg glucose, followed by serial measurements of blood glucose and insulin over 180 minutes. The SU-challenge cohorts received single doses of CRN04777 (30 and 60 mg) one hour after SU administration (5 mg of glibenclamide/glyburide), followed by measurement of the IV glucose infusion rate (GIR) over 8 hours under automated euglycemic clamp conditions (ClampArt®). CRN04777 was orally absorbed (Tmax 1-3 hours) and demonstrated a dose dependent increase in systemic exposures with an apparent terminal elimination t1/2 of approximately 40 hours. Basal insulin secretion was reduced dose-dependently, with a 73% reduction following 120 mg of CRN04777. Likewise, glucose stimulated insulin secretion during the IVGTT (plasma insulin AUC) was reduced dose-dependently by approximately 50% with a parallel doubling of plasma glucose AUC following 120 mg of CRN04777. CRN04777 resulted in dose-dependent reversal of SU-induced insulin secretion, with 79% and 90% reductions in insulin AUC5-180min, respectively, at 30 and 60 mg doses. At the 60 mg dose of CRN04777, no exogenous glucose infusion was needed to prevent SU-induced hypoglycemia. CRN04777 was well tolerated across the dose range evaluated. All adverse events (AEs) were considered mild or moderate and there were no serious AEs. The data from this single-dose, proof-of-concept study show that the selective SST5 agonist CRN04777 is well tolerated after oral administration in healthy volunteers, is suitable for once daily dosing and suppresses insulin secretion under basal and stimulated conditions, including in a pharmacologic model of congenital HI. Multiple ascending dose evaluations in healthy volunteers are underway to support future studies in congenital HI patients. Presentation: Sunday, June 12, 2022 12:30 p.m. - 2:30 p.m.

Metabolomics of various samples advancing biomarker discovery and pathogenesis elucidation for diabetic retinopathy.

Diabetic retinopathy (DR) is a universal microvascular complication of diabetes mellitus (DM), which is the main reason for global sight damage/loss in middle-aged and/or older people. Current clinical analyses, like hemoglobin A1c, possess some importance as prognostic indicators for DR severity, but no effective circulating biomarkers are used for DR in the clinic currently, and studies on the latent pathophysiology remain lacking. Recent developments in omics, especially metabolomics, continue to disclose novel potential biomarkers in several fields, including but not limited to DR. Therefore, based on the overview of metabolomics, we reviewed progress in analytical technology of metabolomics, the prominent roles and the current status of biomarkers in DR, and the update of potential biomarkers in various DR-related samples via metabolomics, including tear as well as vitreous humor, aqueous humor, retina, plasma, serum, cerebrospinal fluid, urine, and feces. In this review, we underscored the in-depth analysis and elucidation of the common biomarkers in different biological samples based on integrated results, namely, alanine, lactate, and glutamine. Alanine may participate in and regulate glucose metabolism through stimulating N-methyl-D-aspartate receptors and subsequently suppressing insulin secretion, which is the potential pathogenesis of DR. Abnormal lactate could cause extensive oxidative stress and neuroinflammation, eventually leading to retinal hypoxia and metabolic dysfunction; on the other hand, high-level lactate may damage the structure and function of the retinal endothelial cell barrier via the G protein-coupled receptor 81. Abnormal glutamine indicates a disturbance of glutamate recycling, which may affect the activation of Müller cells and proliferation via the PPP1CA-YAP-GS-Gln-mTORC1 pathway.

Physiological levels of adrenaline fail to stop pancreatic beta cell activity at unphysiologically high glucose levels.

Adrenaline inhibits insulin secretion from pancreatic beta cells to allow an organism to cover immediate energy needs by unlocking internal nutrient reserves. The stimulation of α2-adrenergic receptors on the plasma membrane of beta cells reduces their excitability and insulin secretion mostly through diminished cAMP production and downstream desensitization of late step(s) of exocytotic machinery to cytosolic Ca2+ concentration ([Ca2+]c). In most studies unphysiologically high adrenaline concentrations have been used to evaluate the role of adrenergic stimulation in pancreatic endocrine cells. Here we report the effect of physiological adrenaline levels on [Ca2+]c dynamics in beta cell collectives in mice pancreatic tissue slice preparation. We used confocal microscopy with a high spatial and temporal resolution to evaluate glucose-stimulated [Ca2+]c events and their sensitivity to adrenaline. We investigated glucose concentrations from 8-20 mM to assess the concentration of adrenaline that completely abolishes [Ca2+]c events. We show that 8 mM glucose stimulation of beta cell collectives is readily inhibited by the concentration of adrenaline available under physiological conditions, and that sequent stimulation with 12 mM glucose or forskolin in high nM range overrides this inhibition. Accordingly, 12 mM glucose stimulation required at least an order of magnitude higher adrenaline concentration above the physiological level to inhibit the activity. To conclude, higher glucose concentrations stimulate beta cell activity in a non-linear manner and beyond levels that could be inhibited with physiologically available plasma adrenaline concentration.

Research Advancements on Fluorinated and Non-Fluorinated 4- Phenyl(thio)ureido-Substituted 2,2-Dimethylchromans Acting as Inhibitors of Insulin Release and Smooth Muscle Relaxants.

The present study aimed at characterizing the impact of the presence or absence of fluorine atoms on the phenyl and benzopyran rings of 4-phenyl(thio)ureido-substituted 2,2- dimethylchromans on their ability to inhibit insulin release from pancreatic β-cells or to relax vascular smooth muscle cells. Most compounds were found to inhibit insulin secretion and to provoke a marked myorelaxant activity. The lack of a fluorine or chlorine atom at the 6-position of the 2,2-dimethylchroman core structure reduced the inhibitory activity on the pancreatic endocrine tissue. One of the most active compounds on both tissues, compound 11h (BPDZ 678), was selected for further pharmacological investigations. The biological data suggested that 11h mainly expressed the profile of a KATP channel opener on pancreatic β-cells, although a calcium entry blockade effect was also observed. On vascular smooth muscle cells, 11h behaved as a calcium entry blocker.

The adipocyte-enriched secretory protein tetranectin exacerbates type 2 diabetes by inhibiting insulin secretion from β cells.

Pancreatic β cell failure is a hallmark of diabetes. However, the causes of β cell failure remain incomplete. Here, we report the identification of tetranectin (TN), an adipose tissue–enriched secretory molecule, as a negative regulator of insulin secretion in β cells in diabetes. TN expression is stimulated by high glucose in adipocytes via the p38 MAPK/TXNIP/thioredoxin/OCT4 signaling pathway, and elevated serum TN levels are associated with diabetes. TN treatment greatly exacerbates hyperglycemia in mice and suppresses glucose-stimulated insulin secretion in islets. Conversely, knockout of TN or neutralization of TN function notably improves insulin secretion and glucose tolerance in high-fat diet–fed mice. Mechanistically, TN binds with high selectivity to β cells and inhibits insulin secretion by blocking L-type Ca2+ channels. Our study uncovers an adipocyte–β cell cross-talk that contributes to β cell dysfunction in diabetes and suggests that neutralization of TN levels may provide a new treatment strategy for type 2 diabetes.

Long Noncoding RNA-5657 Inhibits the Proliferation of Pancreatic Cells and Insulin Secretion in Gestational Diabetes by Inhibiting the NADPH Oxidase 4 (NOX4)

Multiple comorbidities are observed during pregnancy and there are many challenges for pregnant women with a previous history of diabetes. Pancreatic β-cell dysfunction is associated with gestational diabetes mellitus (GDM). This study intends to explore LncRNA-5657’s effect on proapoptotic cell proliferation and insulin secretion in gestational diabetes. Real-time quantitative fluorescence PCR measured LncRNA-5657 expression in GDM patient placental tissues along with analysis of cell activity, proliferation and insulin secretion by MTT assay, BrdU staining and ELISA. The relation between LncRNA-5657 and NOX4 was assessed by dual luciferase reporter assay. LncRNA-5657 was overexpressed in placental tissue of GDM patients compared to normal pregnant women. LncRNA-5657 overexpression promoted cell proliferation and insulin secretion, which was reversed by LncRNA-5657 downregulation. In addition, LncRNA-5657 negatively regulated NOX4 expression. Overexpression of NOX4 abolished the effect of LncRNA-5657 mimics on pancreatic β-cells, and knockdown of LncRNA-5657 promoted insulin secretion by upregulating NOX4 expression. In conclusion, LncRNA-5657 inhibits insulin secretion and β-cell proliferation by targeting NOX4, indicating that LncRNA-5657 might be a novel target for the treatment of GDM.

Syntaxin interacts with arachidonic acid to prevent diabetes mellitus

Syntaxin regulates pancreatic β cell mass and participates in insulin secretion by regulating insulin exocytosis. In addition, syntaxin 4 reduces IFNγ and TNF-α signaling via NF-ĸB in islet β-cells that facilitates plasma glucose sensing and appropriate insulin secretion. Arachidonic acid (AA) has potent anti-inflammatory actions and prevents the cytotoxic actions of alloxan and streptozotocin (STZ) against pancreatic β cells and thus, prevents the development of type 1 diabetes mellitus (induced by alloxan and STZ) and by virtue of its anti-inflammatory actions protects against the development of type 2 diabetes mellitus (DM) induced by STZ in experimental animals that are models of type 1 and type 2 DM in humans. AA has been shown to interact with syntaxin and thus, potentiate exocytosis. AA enhances cell membrane fluidity, increases the expression of GLUT and insulin receptors, and brings about its anti-inflammatory actions at least in part by enhancing the formation of its metabolite lipoxin A4 (LXA4). Prostaglandin E2 (PGE2), the pro-inflammatory metabolite of AA, activates ventromedial hypothalamus (VMH) neurons of the hypothalamus and inhibits insulin secretion leading to reduced glucose tolerance and decreases insulin sensitivity in the skeletal muscle and liver. This adverse action of PGE2 on insulin release and action can be attributed to its (PGE2) pro-inflammatory action and inhibitory action on vagal tone (vagus nerve and its principal neurotransmitter acetylcholine has potent anti-inflammatory actions). High fat diet fed animals have hypothalamic inflammation due to chronic elevation of PGE2. Patients with type 2 DM show low plasma concentrations of AA and LXA4 and elevated levels of PGE2. Administration of AA enhances LXA4 formation without altering or reducing PGE2 levels and thus, tilts the balance more towards anti-inflammatory events. These results suggest that administration of AA is useful in the prevention and management of DM by enhancing the action of syntaxin, increasing cell membrane fluidity, and reducing VMH inflammation. Docosahexaenoic acid (DHA) has actions like AA: it increases cell membrane fluidity; has anti-inflammatory actions by enhancing the formation of its anti-inflammatory metabolites resolvins, protectins and maresins; interacts with syntaxin and enhance exocytosis in general and of insulin. But the DHA content of cell membrane is lower compared to AA and its content in brain is significant. Hence, it is likely DHA is important in neurotransmitters secretion and regulating hypothalamic inflammation. It is likely that a combination of AA and DHA can prevent DM.

BMAL1 modulates ROS generation and insulin secretion in pancreatic β-cells: An effect possibly mediated via NOX2

The pancreatic β cells circadian clock plays a relevant role in glucose metabolism. NADPH oxidase (NOX) family is responsible for producing reactive oxygen species (ROS), such as superoxide anion and hydrogen peroxide, using NADPH as an electron donor. In pancreatic β-cells, NOX-derived ROS inhibits basal and glucose-stimulated insulin secretion. Thus, we hypothesized that the absence of BMAL1, a core circadian clock component, could trigger an increase of NOX2-derived ROS in pancreatic β cells, inhibiting insulin secretion under basal and stimulated glucose conditions. To test such hypothesis, Bmal1 knockdown (KD) was performed in cultured clonal β-cell line (INS-1E) and knocked out in isolated pancreatic islets, using a tissue-specific β-cells Bmal1 knockout (KO) mice. The insulin secretion was assessed in the presence of NOX inhibitors. The Bmal1 KD within INS-1E cells elicited a rise of intracellular ROS content under both glucose stimuli (2.8 mM and 16.7 mM), associated with an increase in Nox2 expression. Additionally, alterations of glutathione levels, CuZnSOD and catalase activities, reduction of ATP/ADP ratio, glyceraldehyde-3-phosphate dehydrogenase (GAPDH), and aconitase activities, followed by glucokinase and Slc2a2 (Glut2) expression were also observed in INS-1E β-cells, reflecting in a diminished insulin secretion pattern. The isolated islets from β-cell Bmal1−/− mice have shown a similar cellular response, where an increased NOX2-derived ROS content and a reduced basal- and glucose-stimulated insulin secretion were observed. Therefore, together with NOX inhibition (Apocynin), polyethene-glycol linked to superoxide dismutase (PEG-SOD), phorbol myristate acetate (PMA), and diethyldithiocarbamate (DDC) data, our findings suggest a possible BMAL1-mediated NOX2-derived ROS generation in pancreatic β cells, leading to the modulation of both basal- and glucose-stimulated insulin secretion.

Following Roux-en-Y gastric bypass surgery, serum ceramides demarcate patients that will fail to achieve normoglycemia and diabetes remission

Obesity is a prevalent health threat and risk factor for type 2 diabetes. In this study, we evaluate the relationship between ceramides, which inhibit insulin secretion and sensitivity, and markers of glucose homeostasis and diabetes remission or recursion in patients who have undergone a Roux-en-Y gastric bypass (RYGB). The Utah Obesity Study is a prospective cohort study, with targeted ceramide and dihydroceramide measurements performed on banked serum samples. The Utah Obesity Study consists of 1,156 participants in three groups: a RYGB surgery group, a non-surgery group denied insurance coverage, and severely obese population controls. Clinical examinations and ceramide assessments were performed at baseline and 2 and 12 years after RYGB surgery. Surgery patients (84% female, 42.2 ± 10.6 years of age at baseline) displayed lower levels of several serum dihydroceramides and ceramides at 2 and 12 years after RYGB. By contrast, neither the control group (77% female, 48.7± 6.4 years of age at baseline) nor the non-surgery group (95% female, 43.0± 11.4 years of age at baseline) experienced significant decreases in any species. Using a linear mixed effect model, we found that multiple dihydroceramides and ceramides positively associated with the glycemic control measures HOMA-IR and HbA1c. In surgery group participants with prevalent diabetes, ceramides inversely predict diabetes remission, independent of changes in weight. Ceramide decreases may explain the insulin sensitization and diabetes resolution observed in most RYGB surgery patients. Funded by the National Institutes of health (NIH), The Juvenile Diabetes Research Foundation, and the American Heart Association.