Inhibition Of Insulin Secretion Research Articles

Correlation of Leptin in Patients With Type 2 Diabetes Mellitus.

The exponential increase in diabetes mellitus (DM) poses serious public health concerns. In this review, we focus on the role of leptin in type 2 DM. The peripheral actions of leptin consist of upregulating proinflammatory cytokines which play an important role in the pathogenesis of type 2 DM and insulin resistance. Moreover, leptin is known to inhibit insulin secretion and plays a significant role in insulin resistance in obesity and type 2 DM. A literature search was conducted on Medline, Cochrane, Embase, and Google Scholar for relevant articles published until December 2023. The following search strings and Medical Subject Headings (MeSH terms) were used: "Diabetes Mellitus," "Leptin," "NPY," and "Biomarker." This article aims to discuss the physiology of leptin in type 2 DM, its glucoregulatory actions, its relationship with appetite, the impact that various lifestyle modifications can have on leptin levels, and, finally, explore leptin as a potential target for various treatment strategies.

Diazoxide and moderate-intensity exercise improve skeletal muscle function by decreasing oxidants and enhancing antioxidant defenses in hypertensive male rats.

High sodium intake is decisive in the incidence increase and prevalence of hypertension, which has an impact on skeletal muscle functionality. Diazoxide is an antihypertensive agent that inhibits insulin secretion and is an opener of KATP channels (adosine triphosphate sensitive potasium channels). For this reason, it is hypothesized that moderate-intensity exercise and diazoxide improve skeletal muscle function by reducing the oxidants in hypertensive rats. Male Wistar rats were assigned into eight groups: control (CTRL), diazoxide (DZX), exercise (EX), exercise + diazoxide (EX + DZX), hypertension (HTN), hypertension + diazoxide (HTN + DZX), hypertension + exercise (HTN + EX), and hypertension + exercise + diazoxide (HTN + EX + DZX). To induce hypertension, the rats received 8% NaCl dissolved in water orally for 30 days; in the following 8 weeks, 4% NaCl was supplied to maintain the pathology. The treatment with physical exercise of moderate intensity lasted 8 weeks. The administration dose of diazoxide was 35 mg/kg intraperitoneally for 14 days. Tension recording was performed on the extensor digitorum longus and the soleus muscle. Muscle homogenates were used to measure oxidants using fluorescent probe and the activity of antioxidant systems. Diazoxide and moderate-intensity exercise reduced oxidants and increased antioxidant defenses.

Insufficient TRPM5 Mediates Lipotoxicity-induced Pancreatic β-cell Dysfunction.

While the reduction of transient receptor potential channel subfamily M member 5 (TRPM5) has been reported in islet cells from type 2 diabetic (T2D) mouse models, its role in lipotoxicity-induced pancreatic β-cell dysfunction remains unclear. This study aims to study its role. Pancreas slices were prepared from mice subjected to a high-fat-diet (HFD) at different time points, and TRPM5 expression in the pancreatic β cells was examined using immunofluorescence staining. Glucose-stimulated insulin secretion (GSIS) defects caused by lipotoxicity were mimicked by saturated fatty acid palmitate (Palm). Primary mouse islets and mouse insulinoma MIN6 cells were treated with Palm, and the TRPM5 expression was detected using qRT-PCR and Western blotting. Palm-induced GSIS defects were measured following siRNA-based Trpm5 knockdown. The detrimental effects of Palm on primary mouse islets were also assessed after overexpressing Trpm5 via an adenovirus-derived Trpm5 (Ad-Trpm5). HFD feeding decreased the mRNA levels and protein expression of TRPM5 in mouse pancreatic islets. Palm reduced TRPM5 protein expression in a time- and dose-dependent manner in MIN6 cells. Palm also inhibited TRPM5 expression in primary mouse islets. Knockdown of Trpm5 inhibited insulin secretion upon high glucose stimulation but had little effect on insulin biosynthesis. Overexpression of Trpm5 reversed Palm-induced GSIS defects and the production of functional maturation molecules unique to β cells. Our findings suggest that lipotoxicity inhibits TRPM5 expression in pancreatic β cells both in vivo and in vitro and, in turn, drives β-cell dysfunction.

Vildagliptin inhibits high fat and fetuin-A mediated DPP-4 expression, intracellular lipid accumulation and improves insulin secretory defects in pancreatic beta cells

Dipeptidyl peptidase-4 (DPP-4), a ubiquitous proteolytic enzyme, inhibits insulin secretion from pancreatic beta cells by inactivating circulating incretin hormones GLP-1 and GIP. High circulating levels of DPP-4 is presumed to compromise insulin secretion in people with type 2 diabetes (T2D). Our group recently reported lipid induced DPP-4 expression in pancreatic beta cells, mediated by the TLR4-NFkB pathway. In the present study, we looked at the role of Vildagliptin on pancreatic DPP-4 inhibition, preservation of islet mass and restoration of insulin secretion. MIN6 mouse insulinoma cells incubated with palmitate and fetuin-A, a proinflammatory organokine associated with insulin resistance, showed activation of TLR4-NFkB pathway, which was rescued on Vildagliptin treatment. In addition, Vildagliptin, by suppressing palmitate-fetuin-A mediated DPP-4 expression in MIN6, prevented the secretion of IL-1beta and fetuin-A in the culture media. DPP-4 siRNA abrogated TLR4-NFkB pathway mediated islet cell inflammation. Vildagliptin also reduced palmitate-fetuin-A mediated intracellular lipid accumulation in MIN6 and isolated islets from high fat fed (HFD) mice as observed by Oil O Red staining with downregulation of CD36 and PPARgamma. Vildagliptin also preserved islet mass and rescued insulin secretory defect in HFD mice. Our results suggest that inhibition of DPP-4 by Vildagliptin protects pancreatic beta cells from the deleterious effects of lipid and fetuin-A, preserves insulin secretory functions and improves hyperglycemia.

Mediation effect of serum zinc on insulin secretion inhibited by methyl tert-butyl ether in gas station workers.

Methyl tert-butyl ether (MTBE), a type of gasoline additive, has been found to affect insulin function and glucose homeostasis in animal experiments, but there is still no epidemiological evidence. Zinc (Zn) is a key regulatory element of insulin secretion and function, and Zn homeostasis can be disrupted by MTBE exposure through inducing oxidative stress. Therefore, we suspected that Zn might be involved and play an important role in the process of insulin secretion inhibited by MTBE exposure. In this study, we recruited 201 male subjects including occupational and non-occupational MTBE exposure from Anhui Province, China in 2019. Serum insulin and functional analog fibroblast growth factor 1 (FGF1) and blood MTBE were detected by Elisa and headspace solid-phase microextraction and gas chromatography-high-resolution mass spectrometry. According to MTBE internal exposure level, the workers were divided into low- and high-exposed groups and found that the serum insulin level in the high-exposed group was significantly lower than that in the low-exposed group (p = 0.003) while fasting plasma glucose (FPG) level increased obviously in the high-exposed group compared to the low-exposed group (p = 0.001). Further analysis showed that MTBE exposure level was positively correlated with FPG level, but negatively correlated with serum insulin level, which suggested that the FPG level increase might be related to the decrease of serum insulin level induced by MTBE exposure. The results of further mediation effect analysis showed that changes in serum zinc levels played a major intermediary role in the process of insulin secretion inhibition and blood glucose elevation caused by MTBE exposure. In addition, a significant negative correlation was found between MTBE exposure and serum Zn level, which might play a strong mediating effect on the inhibition of insulin secretion induced by MTBE exposure. In conclusion, our study provided evidence that MTBE could inhibit insulin secretion and interfere with Zn metabolism in gas station workers for the first time, and found that Zn might play an important mediation effect during the process of inhibiting insulin secretion and interfering with glucose metabolism induced by MTBE exposure.

LncRNA HCP5 is Highly Expressed in Gestational Diabetes Mellitus to Suppress Insulin Secretion.

LncRNA HCP5 has been reported to participate in high glucose-induced pathological processes, whereas its role in gestational diabetes mellitus (GDM) is unclear. This study aimed to explore the role of HCP5 in GDM. This study enrolled a total of 220 pregnant women (gestational age = 1 month). A follow-up study was performed until delivery. The occurrence of GDM was checked every month during follow-up. Plasma samples were collected from all participants and expression of HCP5 was determined with RT-qPCR. The 220 patients were divided into high and low GDM groups, and GDM-free curves were plotted for both groups and compared. The ROC curve was plotted to explore the predictive value of plasma HCP5 on the day of admission for GDM. INS-1 cells were transfected with HCP5 expression vector or siRNA, and cell viability under high glucose was determined by the MTT assay. An ELISA was applied to determine insulin levels in the cell culture medium. During follow-up, the level of HCP5 was increased during pregnancy and the high HCP5 level group showed a significantly higher incidence of GDM. Plasma levels of HCP5 on the day of admission effectively separated GDM patients from healthy controls. HCP5 negatively regulated cell viability and insulin secretion under high glucose treatment. HCP5 may act as a predictor for GDM, and it negatively regulated INS-1 cell viability and insulin secretion under high glucose conditions.

Diabetes mellitus in acromegaly: prevalence, pathophysiological particulars and treatment strategies

The prevalence of diabetes mellitus in acromegaly is significantly higher than that in the general population. Carbohydrate metabolism abnormalities often precede other phenotypic manifestations of acromegaly. The review presents data on the prevalence of carbohydrate metabolism disorders in acromegaly and describes their pathophysiological characteristics and approaches to treatment.
 Growth hormone (GH) excess is recognized as a key factor of glucose homeostasis abnormalities due to decreased insulin sensitivity (resulting from active lipolysis) and direct stimulation of insulin secretion. Insulin-like growth factor 1 (IGF1) improves insulin sensitivity; however, the GH diabetogenic effects prevail over the insulin-sensitizing impact of IGF1. Surgical and radiation treatment for somatotropinoma may indirectly improve carbohydrate metabolism, because they decrease the GH levels. Treatment with first generation somatostatin analogues can both improve glycemic control due to decreased GH levels and worsen it due to deterioration of postprandial insulin release, especially in patients with already manifest carbohydrate metabolism disorders. The GH receptor antagonist pegvisomant blocks the effects of excess GH on the target tissues without suppressing insulin secretion, which results in better glucose control; treatment with this agent can be preferred in patients with acromegaly and diabetes mellitus. Management of carbohydrate metabolism disorders in acromegaly is done in accordance with general treatment principles for type 2 diabetes mellitus.

Glucocorticoid receptor-NECAB1 axis can negatively regulate insulin secretion in pancreatic β-cells

The mechanisms of impaired glucose-induced insulin secretion from the pancreatic β-cells in obesity have not yet been completely elucidated. Here, we aimed to assess the effects of adipocyte-derived factors on the functioning of pancreatic β-cells. We prepared a conditioned medium using 3T3-L1 cell culture supernatant collected at day eight (D8CM) and then exposed the rat pancreatic β-cell line, INS-1D. We found that D8CM suppressed insulin secretion in INS-1D cells due to reduced intracellular calcium levels. This was mediated by the induction of a negative regulator of insulin secretion—NECAB1. LC–MS/MS analysis results revealed that D8CM possessed steroid hormones (cortisol, corticosterone, and cortisone). INS-1D cell exposure to cortisol or corticosterone increased Necab1 mRNA expression and significantly reduced insulin secretion. The increased expression of Necab1 and reduced insulin secretion effects from exposure to these hormones were completely abolished by inhibition of the glucocorticoid receptor (GR). NECAB1 expression was also increased in the pancreatic islets of db/db mice. We demonstrated that the upregulation of NECAB1 was dependent on GR activation, and that binding of the GR to the upstream regions of Necab1 was essential for this effect. NECAB1 may play a novel role in the adipoinsular axis and could be potentially involved in the pathophysiology of obesity-related diabetes mellitus.

Protective effects of curcumin on desipramine-induced islet β-cell damage via AKAP150/PKA/PP2B complex.

Tricyclic antidepressants (TCAs) are widely used to treat depression and anxiety-related mood disorders. But evidence shows that TCAs elevate blood glucose levels and inhibit insulin secretion, suggesting that TCAs are a risk factor, particularly for individuals with diabetes. Curcumin is a bioactive molecule from the rhizome of the Curcuma longa plant, which has shown both antidepressant and anti-diabetic activities. In the present study, we investigated the protective effect of curcumin against desipramine-induced apoptosis in β cells and the underlying molecular mechanisms. In the mouse forced swimming test (FST), we found that lower doses of desipramine (5 and 10 mg/kg) or curcumin (2.5 mg/kg) alone did not affect the immobility time, whereas combined treatment with curcumin (2.5 mg/kg) and desipramine (5, 10 mg/kg) significantly decreased the immobility time. Furthermore, desipramine dose-dependently inhibited insulin secretion and elevated blood glucose levels, whereas the combined treatment normalized insulin secretion and blood glucose levels. In RIN-m5F pancreatic β-cells, desipramine (10 μM) significantly reduced the cell viability, whereas desipramine combined with curcumin dose-dependently prevented the desipramine-induced impairment in glucose-induced insulin release, most effectively with curcumin (1 and 10 μM). We demonstrated that desipramine treatment promoted the cleavage and activation of Caspase 3 in RIN-m5F cells. Curcumin treatment inhibited desipramine-induced apoptosis, increased mitochondrial membrane potential and Bcl-2/Bax ratio. Desipramine increased the generation of reactive oxygen species, which was reversed by curcumin treatment. Curcumin also inhibited the translocation of forkhead box protein O1 (FOXO1) from the cytoplasm to the nucleus and suppressed the binding of A-kinase anchor protein 150 (AKAP150) to protein phosphatase 2B (PP2B, known as calcineurin) that was induced by desipramine. These results suggest that curcumin protects RIN-m5F pancreatic β-cells against desipramine-induced apoptosis by inhibiting the phosphoinositide 3-kinase/AKT/FOXO1 pathway and the AKAP150/PKA/PP2B interaction. This study suggests that curcumin may have therapeutic potential as an adjunct to antidepressant treatment.

THU309 Ghrelin Deficiency Does Not Improve Glucose Tolerance And Insulin Secretion In Female Mice

Abstract Disclosure: D. Gupta: None. K. Shankar: None. S. Varshney: None. O. Singh: None. S. Paul: None. S.B. Ogden: None. S. Osborne-Lawrence: None. A.W. Burstein: None. N.P. Metzger: None. C.P. Richard: None. J.M. Zigman: None. Background: Ghrelin is a peptide hormone secreted primarily from specialized enteroendocrine cells of the stomach. Ghrelin’s ability to regulate blood glucose has emerged as one of its well-recognized actions. For instance, administered ghrelin increases blood glucose in rodents and humans, while ghrelin-knockout (GKO) mice and ghrelin receptor-knockout (GHSR-KO) mice exhibit reduced blood glucose upon fasting, improved glucose tolerance when on regular chow or when on obesogenic diets, and frank hypoglycemia when chronically food restricted. Upon obesogenic diet or glucose challenge, plasma insulin is higher in GKO and GHSR-KO mice, suggesting that ghrelin affects blood glucose at least in part by inhibiting insulin secretion. Notably, ghrelin’s glucoregulatory actions, including its effects to alter insulin secretion, have almost exclusively been studied in males. Because sex significantly impacts the pathogenesis of metabolic disorders and type 2 diabetes, here we studied ghrelin’s effects on glucose tolerance and insulin secretion in female mice and in the setting of pregnancy. Methods: Separate cohorts of 12-13 week-old female GKO and wildtype (WT) littermates with 11.5 gestational days induced by timed pregnancy, and aged matched GKO and WT non-pregnant female mice were fasted for 6 h after which oral glucose tolerance test (OGTT) was performed. Briefly, mice were administered D-glucose (2 g/kg BW) by oral gavage at t = 0 min. Blood glucose was measured from nicked tails at t = 0, 15, 30, 60, 90 and 120 min and insulin was assayed in blood samples collected at t = 0, 15 and 30 min of glucose administration. Results: In OGTT, blood glucose increased significantly and similarly 15 min after oral glucose gavage in GKO and WT mice with or without pregnancy. Blood glucose AUC was 74.2% and 72.8% decreased with pregnancy in WT and GKO mice, respectively. No difference in plasma insulin was observed 15 min after glucose gavage in GKO mice vs WT mice with or without pregnancy. AUC of plasma insulin was significantly increased with pregnancy by 112.6% and by 123.8% in WT mice and GKO mice, respectively. Conclusions: With pregnancy, plasma insulin elevates (presumably as a means to maintain or improve glucose tolerance). Ghrelin deficiency during pregnancy is dispensable for this elevation in insulin and improvement in glucose tolerance. Ghrelin’s response to glucose tolerance and insulin secretion was blunted in female mice suggesting ghrelin’s actions on glucose tolerance and insulin secretion exhibit sexual diversity. Disclosure: The authors have no competing interest. Funding. This work was supported through research grants from the NIH (R01 DK103884 and R01 DK119341 to J.M.Z) Presentation: Thursday, June 15, 2023

THU530 What Works For Ferret, Works For Man

Abstract Disclosure: P.J. Bhatt: None. S. Bendaram: None. V. Kantorovich: None. Insulinomas are rare pancreatic neuroendocrine tumors with an incidence of 4 cases per million per year and present with hypoglycemic symptoms due to uncontrolled and excessive insulin secretion by the tumor. Although most commonly benign and treated with surgery, 5-10% are malignant, inoperable and are managed medically with somatostatin analogs, chemotherapy, mTOR inhibitors and diazoxide. A 28 year old male with a history of metastatic insulinoma with progressive disease and refractory hypoglycemia presented with lethargy, diaphoresis, and blood glucose (BG) level of 32mg/dL [65-99]. He was previously admitted for severe hypoglycemia and was treated with FOLFOX, LUTATHERA, Octreotide, TPN, steroids and diazoxide suspension. Sugars were monitored via continuous glucose monitor (CGM) and insulin and C-peptide levels were closely monitored outpatient. Treatment was effective and medications were tapered off so that he no longer needed a CGM and was only on FOLFOX and octreotide prior to presentation. On admission, insulin level was 172 uIU/mL [<17], peaking at 312 uIU/mL and BG dropping to 22mg/dL. He was placed on a dextrose 10% infusion, TPN, diazoxide suspension, and CGM. This admission, however, his insulin levels were much higher requiring higher doses of diazoxide, but he was unable to tolerate the diazoxide solution due to extreme nausea and projectile vomiting, resigning him to a long-term stay in the ICU. Due to a lack of availability of other oral formulations in the US, compounding pharmacies were contacted and pharmaceutical grade diazoxide powder was compounded into 100mg capsules by an outside pharmacy. Dose was adjusted while monitoring BG and insulin levels. Prior to discharge, insulin level was 77.7 uIU/mL and BG levels had normalized. He was sent home on diazoxide 200mg twice a day, TPN, and CGM. FOLFOX was resumed. Outpatient follow up revealed euglycemia and suppressed insulin level of 12.3 uIU/mL [<17], allowing for further tapering of diazoxide dose and discontinuation of TPN. Diazoxide is known to be a safe and effective treatment for hypoglycemia in humans and ferrets alike. It inhibits insulin secretion in pancreatic B cells and increases hepatic glucose production. Side effects of nausea and vomiting can be a barrier to compliance, as seen in our patient. Currently, only oral solutions of diazoxide have been approved for human consumption whereas ferrets, commonly afflicted with insulinomas, are treated with oral pills. Changing the oral formulation to pill form allowed for better compliance, easy dose adjustments using insulin as a marker for response, and symptom resolution due to adequate suppression of insulin levels. Most importantly, it allowed for our patient to transfer out of the ICU and be discharged home with improved quality of life, a feat that was impossible without this change in formulation. Presentation: Thursday, June 15, 2023

FRI668 Insulinoma As A Cause Of New Onset Hypoglycemic Episodes

Abstract Disclosure: S. Zahra: None. M.A. Abbas: None. R. Subramani: None. F. Manas: None. S. Yavuz: None. 37 years old female with a past medical history of hypothyroidism presented with complaints of shakiness, lightheadedness, and palpitations, relieved by eating. The physical examination was unremarkable. Fasting blood work showed low glucose of 41 mg/dl (70-99 mg/dl), normal insulin levels of 8.4 UIU/ ml (normal:1.9-23 UIU/ml), elevated proinsulin 21.1 pmol/ L (normal:<8.0 pmol/L), normal C Peptide 2.5 ng/ ml (normal:1.1-4.4 ng/ml), and negative for insulin antibody. Serum ACTH and cortisol levels were normal. Blood testing for hypoglycemia-inducing medications was negative. CT and MRI abdomen pelvis contrast was normal. She was prescribed to wear Dexcom to monitor her blood glucose round the clock. She continued to have low blood glucose, sometimes without symptoms and was rescued by the alarm. She underwent endoscopic ultrasound and was found to have a 10mm x 9mm ill-defined rounded pancreatic head mass with diffuse echogenicity of the pancreas. Biopsy of the mass revealed clusters of epithelial cells with neuroendocrine differentiation, compatible with insulinoma. She underwent surgical resection of the mass. She was also referred to genetic testing due to the association of pancreatic tumors with MEN syndrome. The diagnosis of Insulinomas is clinical as well as biochemical with presenting symptoms of Whipple’s Triad along with the presence of the following lab findings: hypoglycemia with plasma glucose of less than 50mg /dl, insulin greater than 5 UIU/L, C-Peptide greater than 0.2 nmol/L (0.6 ng/mL), Insulin/C-Peptide ratio of greater than 1.0, Proinsulin greater than 20pmol/L, and the absence of sulfonylurea metabolites in plasma or urine. Insulinoma is the most common pancreatic neuroendocrine and functional endocrine tumor of the beta cells of the pancreas with a prevalence of 1-4 people per million with equal gender distribution. They are mainly seen in the fifth decade of life but can occur at any age. They can occur sporadically or can be associated with MEN 1. Insulinomas are mostly benign, about 5-10% can be malignant. When to do medical vs surgical management? For benign insulinomas, surgical resection is preferred. For locally invasive and malignant tumors, aggressive surgical resection is performed, unless surgery is contraindicated for any other reason or patient refuses it. Medical treatment is reserved for the patients with diffuse Beta cell disease, multiple insulinoma and unresected malignant insulinoma. In the presence of unresectable metastatic disease; radiofrequency ablation, selective embolization, intraarterial chemotherapy, alone or in combination has been shown to be effective in controlling hypoglycemic episodes and improving quality of life. Octreotide, via inhibiting insulin secretion, normalizes the blood glucose levels. For better detection of hypoglycemia and adequate response to medical therapy, continuous glucose monitoring is helpful. Presentation: Friday, June 16, 2023

The leptin receptor has no role in delta-cell control of beta-cell function in the mouse.

Leptin inhibits insulin secretion from isolated islets from multiple species, but the cell type that mediates this process remains elusive. Several mouse models have been used to explore this question. Ablation of the leptin receptor (Lepr) throughout the pancreatic epithelium results in altered glucose homeostasis and ex vivo insulin secretion and Ca2+ dynamics. However, Lepr removal from neither alpha nor beta cells mimics this result. Moreover, scRNAseq data has revealed an enrichment of LEPR in human islet delta cells. We confirmed LEPR upregulation in human delta cells by performing RNAseq on fixed, sorted beta and delta cells. We then used a mouse model to test whether delta cells mediate the diminished glucose-stimulated insulin secretion in response to leptin. Ablation of Lepr within mouse delta cells did not change glucose homeostasis or insulin secretion, whether mice were fed a chow or high-fat diet. We further show, using a publicly available scRNAseq dataset, that islet cells expressing Lepr lie within endothelial cell clusters. In mice, leptin does not influence beta-cell function through delta cells.

Can acetate via FFA receptors contribute to the diabetogenic effect of statins?

Despite the proven effects of statins in preventing cardiovascular disease, their diabetogenic effect has caused concern. The mechanism of this diabetogenic effect is unknown. We suggest a novel mechanism that may contribute to the diabetogenic effect of statins, through an effect of statins that has apparently escaped previous consideration. Briefly, by inhibiting HMG-CoA reductase, statins may cause accumulation of acetate, which through FFA2 and FFA3 stimulation may inhibit insulin secretion.

SAA1 exacerbates pancreatic β-cell dysfunction through activation of NF-κB signaling in high-fat diet-induced type 2 diabetes mice

Insufficient decompensated insulin secretion and insulin resistance caused by pancreatic β-cell dysfunction are the pathological bases of type 2 diabetes mellitus (T2DM). Glucolipotoxicity in pancreatic β-cells is an important factor leading to their dysfunction, closely related to inflammatory signals, oxidative stress, mitochondrial dysfunction, and endoplasmic reticulum stress (ERs). However, there may be other unproven regulatory mechanisms that govern pancreatic β-cell dysfunction. Therefore, further elucidation of the underlying mechanisms that lead to pancreatic β-cells dysfunction will provide a sufficient theoretical basis for the more effective prevention and treatment of T2DM. As a stress protein with pro-inflammatory properties, Serum Amyloid 1 (SAA1) promotes the progression of metabolic syndrome-related diseases by activating immune cells and damaging endothelial cells. In the development of T2DM, the activation of nuclear factor-kappa B (NF-κB) signaling aggravates pancreatic β-cells dysfunction under the stimulation of free fatty acids (FFAs), inflammatory factors, and chemokines. Moreover, the facilitating effect of SAA1 on the activation of the NF-κB signaling pathway has been demonstrated in other studies. In the present study, we demonstrated that SAA1 inhibits insulin secretion and promotes apoptotic molecular expression in pancreatic cells and islets and that NF-κB signaling inhibitors could reduce this effect of SAA1. SAA1 deficiency improved high-fat diet (HFD)-induced pancreatic β-cell dysfunction and decreased expression of NF-κB signaling molecules. Our findings suggested that HFD-induced SAA1 might exacerbate T2DM by enhancing pancreatic β-cell dysfunction; such a function of SAA1 might depend on NF-κB signaling activation.

SGLT2 Inhibitors and Perioperative Euglycemic Diabetic Ketoacidosis

Sodium-glucose cotransporter 2 (SGLT2) inhibitors are a new class of diabetes medications that act at the level of the kidney to increase renal glucose clearance. The resultant hypoglycemia suppresses insulin secretion and stimulates glucagon, lipolysis, and ketogenesis, which creates a state of starvation. Since SGLT2 inhibitors also decrease sodium reabsorption, patients are at risk for dehydration. An unusual side effect of this drug class is the development of euglycemic diabetic ketoacidosis (eDKA). A case report describes a patient taking Synjardy® (empagliflozin/metformin) who underwent laparoscopic cholecystectomy and developed perioperative eDKA. It is critical to maintain a high index of suspicion to recognize eDKA and institute immediate therapy tenants of intravenous fluid hydration, insulin infusion, and aggressive electrolyte repletion.

Hypoxia causes pancreatic β-cell dysfunction and impairs insulin secretion by activating the transcriptional repressor BHLHE40.

Hypoxia can occur in pancreatic β-cells in type 2 diabetes. Although hypoxia exerts deleterious effects on β-cell function, the associated mechanisms are largely unknown. Here, we show that the transcriptional repressor basic helix-loop-helix family member e40 (BHLHE40) is highly induced in hypoxic mouse and human β-cells and suppresses insulin secretion. Conversely, BHLHE40 deficiency in hypoxic MIN6 cells or β-cells of ob/ob mice reverses defects in insulin secretion. Mechanistically, BHLHE40 represses the expression of Mafa, encoding the transcription factor musculoaponeurotic fibrosarcoma oncogene family A (MAFA), by attenuating the binding of pancreas/duodenum homeobox protein 1 (PDX1) to its enhancer region. Impaired insulin secretion in hypoxic β-cells was recovered by MAFA re-expression. Collectively, our work identifies BHLHE40 as a key hypoxia-induced transcriptional repressor in β-cells that inhibit insulin secretion by suppressing MAFA expression.

1550-P: A Gain-of-Function Maturity-Onset Diabetes of the Young (MODY)–Associated TALK1 Mutation Impairs Glucose Metabolism in Mice

A Leu substitution with Pro at position 114 (L114P) of TALK1 K+ channels has recently been identified in a MODY (maturity-onset-diabetes-of-the-young) family. Previous in vitro studies have shown this gain-of-function TALK1-L114P mutant may attenuate Ca2+ homeostasis and inhibit insulin secretion; nevertheless, how this mutant induces diabetes in vivo remains elusive. In this study, we have generated a transgenic mouse line that carries a TALK1-L114P mutation. About three-quarters of TALK1L/P and TALK1P/- mice died within ten days after birth due to hyperglycemia. Interestingly, those survival mice till adulthood exhibited diverse levels of glucose intolerance with islet morphology that is commonly observed in patients with type 2 diabetes. Electrophysiological recording further indicated that only a portion of the beta cells is glucose responsive, and high glucose challenge often yielded in low-frequency action potential bursting. According to our results, we hypothesized that despite the augment of membrane K+ conductance by the TALK1-L114P channel, high glucose might still be enough to depolarize beta cells and generate action potential bursting. This dampened beta cell excitation may result in a weakened Ca2+ influx and insufficient insulin secretion to cause glucose intolerance. In conclusion, this study has revealed a vital role of the TALK1 channel in regulating glucose homeostasis and a plausible diabetogenic mechanism of TALK1-L114P mutation. Disclosure W.Tsai: None. S.Yang: None. Funding National Science and Technology Council, Taiwan (111-2320-B-001-008-MY3)

286-OR: Using iPSC-Derived Islets to Model the Effect of an ABCC8 Arg1420His Mutation in Fetal and Adult Islets

We previously reported an Arg1420His mutation in ABCC8 in an Indigenous community that resulted in hyperinsulinemic hypoglycemia in infancy in a homozygous carrier and a doubling in type 2 diabetes (T2D) risk in heterozygous carriers (3% of the population). Previous studies of ABCC8 mutations have suggested a loss of pancreatic beta cells as a probable cause of future T2D. To understand the pathomechanism behind the increased risk of T2D due to the Arg1420His mutation, we generated two sets of isogenic iPSCs from two different Indigenous community members. These iPSCs were used to generate pancreatic islets and assess insulin secretion using a dynamic glucose stimulated insulin secretion (D-GSIS) assay when the islets were immature (resembling fetal islets) and during multiple days after maturation (resembling adult islets). In immature islets, the D-GSIS assay confirmed the clinical phenotype of significantly higher insulin secretion in islets with the His-allele under basal conditions (2mM glucose) and a lower response to diazoxide in islets homozygous for the His-allele. Both Arg1420 and His1420 mature islets had lower insulin secretion under basal conditions, however, insulin secretory response to high glucose (20mM) and Tolbutamide (sulphonylurea) was significantly lower in islets heterozygous for the His-allele whereas no response was seen in islets homozygous for the His-allele despite having similar proportion of beta cells as assessed by flow cytometry (~50% cells positive for INS and NKX6-1). This suggests a mechanism other than beta cell loss as the cause of lower insulin secretory response in these impaired islets. Single cell RNA sequencing showed higher expression of G6PC2, which inhibits insulin secretion by opposing the action of GCK, in islets with the His-allele. Our ongoing work includes knockout of G6PC2 in the isogenic iPSCs and using a GCK activator (Dorzagliatin) to correct the insulin secretory response to high glucose in the His-allele carrying islets. Disclosure A.K.Nair: None. K.Barkho: None. M.Traurig: None. R.G.Nelson: None. C.Bogardus: None. L.Baier: None. Funding National Institute of Diabetes and Digestive and Kidney Diseases

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)