RFX6 haploinsufficiency predisposes to diabetes through impaired beta cell function.

AIMS/HYPOTHESIS: Regulatory factor X 6 (RFX6) is crucial for pancreatic endocrine development and differentiation. The RFX6 variant p.His293LeufsTer7 is significantly enriched in the Finnish population, with almost 1:250 individuals as a carrier. Importantly, the FinnGen study indicates a high predisposition for heterozygous carriers to develop type 2 and gestational diabetes. However, the precise mechanism of this predisposition remains unknown. METHODS: To understand the role of this variant in beta cell development and function, we used CRISPR technology to generate allelic series of pluripotent stem cells. We created two isogenic stem cell models: a human embryonic stem cell model; and a patient-derived stem cell model. Both were differentiated into pancreatic islet lineages (stem-cell-derived islets, SC-islets), followed by implantation in immunocompromised NOD-SCID-Gamma mice. RESULTS: Stem cell models of the homozygous variant RFX6-/- predictably failed to generate insulin-secreting pancreatic beta cells, mirroring the phenotype observed in Mitchell-Riley syndrome. Notably, at the pancreatic endocrine stage, there was an upregulation of precursor markers NEUROG3 and SOX9, accompanied by increased apoptosis. Intriguingly, heterozygous RFX6+/- SC-islets exhibited RFX6 haploinsufficiency (54.2% reduction in protein expression), associated with reduced beta cell maturation markers, altered calcium signalling and impaired insulin secretion (62% and 54% reduction in basal and high glucose conditions, respectively). However, RFX6 haploinsufficiency did not have an impact on beta cell number or insulin content. The reduced insulin secretion persisted after in vivo implantation in mice, aligning with the increased risk of variant carriers to develop diabetes. CONCLUSIONS/INTERPRETATION: Our allelic series isogenic SC-islet models represent a powerful tool to elucidate specific aetiologies of diabetes in humans, enabling the sensitive detection of aberrations in both beta cell development and function. We highlight the critical role of RFX6 in augmenting and maintaining the pancreatic progenitor pool, with an endocrine roadblock and increased cell death upon its loss. We demonstrate that RFX6 haploinsufficiency does not affect beta cell number or insulin content but does impair function, predisposing heterozygous carriers of loss-of-function variants to diabetes. DATA AVAILABILITY: Ultra-deep bulk RNA-seq data for pancreatic differentiation stages 3, 5 and 7 of H1 RFX6 genotypes are deposited in the Gene Expression Omnibus database with accession code GSE234289. Original western blot images are deposited at Mendeley ( https://data.mendeley.com/datasets/g75drr3mgw/2 ).

Inhibition of mTOR prevents glucotoxicity-mediated increase of SA-beta-gal, p16INK4a, and insulin hypersecretion, without restoring electrical features of mouse pancreatic islets.

An over-activation of the mechanistic target of rapamycin (mTOR) pathway promotes senescence and age-related diseases like type 2 diabetes. Besides, the regenerative potential of pancreatic islets deteriorates with aging. Nevertheless, the role of mTOR on senescence promoted by metabolic stress in islet cells as well as its relevance for electrophysiological aspects is not yet known. Here, we investigated whether parameters suggested to be indicative for senescence are induced in vitro in mouse islet cells by glucotoxicity and if mTOR inhibition plays a protective role against this. Islet cells exhibit a significant increase (~ 76%) in senescence-associated beta-galactosidase (SA-beta-gal) activity after exposure to glucotoxicity for 72 h. Glucotoxicity does not markedly influence p16INK4a protein within 72 h, but p16INK4a levels increase significantly after a 7-days incubation period. mTOR inhibition with a low rapamycin concentration (1 nM) entirely prevents the glucotoxicity-mediated increase of SA-beta-gal and p16INK4a. At the functional level, reactive oxygen species, calcium homeostasis, and electrical activity are disturbed by glucotoxicity, and rapamycin fails to prevent this. In contrast, rapamycin significantly attenuates the insulin hypersecretion promoted by glucotoxicity by modifying the mRNA levels of Vamp2 and Snap25 genes, related to insulin exocytosis. Our data indicate an influence of glucotoxicity on pancreatic islet-cell senescence and a reduction of the senescence markers by mTOR inhibition, which is relevant to preserve the regenerative potential of the islets. Decreasing the influence of mTOR on islet cells exposed to glucotoxicity attenuates insulin hypersecretion, but is not sufficient to prevent electrophysiological disturbances, indicating the involvement of mTOR-independent mechanisms.

Insulin therapy in acute decompensation of holocarboxylase synthetase deficiency with hyperglycemia and ketoacidosis.

An 11-month-old girl with severe acidosis, lethargy and vomiting, was diagnosed with holocarboxylase synthetase deficiency. She received biotin and was stable until age 8 years when vomiting, severe acidosis, hypoglycemia, and hyperammonemia developed. Management with intravenous glucose aiming to stimulate anabolism led to hyperglycemic ketoacidosis. Insulin therapy rapidly corrected biochemical parameters, and clinical status improved. We propose that secondary Krebs cycle disturbances affecting pancreatic beta cells impaired glucose-stimulated insulin secretion, resulting in insulinopenia.

Tyrosine nitration of glucagon impairs its function: Extending the role of heme in T2D pathogenesis.

New studies raise the possibility that the higher glucagon (GCG) level present in type 2 diabetes (T2D) is a compensatory mechanism to enhance ß-cell function, rather than induce dysregulated glucose homeostasis, due to an important role for GCG that acts directly within the pancreas on insulin secretion by intra-islet GCG signaling. However, in states of poorly controlled T2D, pancreatic α cell mass increases (overproduced GCG) in response to insufficient insulin secretion, indicating decreased local GCG activity. The reason for this decrease is not clear. Recent evidence has uncovered a new role of heme in cellular signal transduction, and its mechanism involves reversible binding of heme to proteins. Considering that protein tyrosine nitration in diabetic islets increases and glucose-stimulated insulin secretion (GSIS) decreases, we speculated that heme modulates GSIS by transient interaction with GCG and catalyzing its tyrosine nitration, and the tyrosine nitration may impair GCG activity, leading to loss of intra-islet GCG signaling and markedly impaired insulin secretion. Data presented here elucidate a novel role for heme in disrupting local GCG signaling in diabetes. Heme bound to GCG and induced GCG tyrosine nitration. Two tyrosine residues in GCG were both sensitive to the nitrating species. Further, GCG was also demonstrated to be a preferred target peptide for tyrosine nitration by co-incubation with BSA. Tyrosine nitration impaired GCG stimulated cAMP-dependent signaling in islet ß cells and decreased insulin release. Our results provided a new role of heme for impaired GSIS in the pathological process of diabetes.

Biospeciation of Oxidovanadium(IV) Imidazolyl-Carboxylate Complexes and Their Action on Glucose-Stimulated Insulin Secretion in Pancreatic Cells.

The reaction of the vanadyl ion (VO2+) with imidazole-4-carboxylic acid (Im4COOH), imidazole-2-carboxylic acid (Im2COOH) and methylimidazole-2-carboxylic acid (MeIm2COOH), respectively, in the presence of small bioligands (bL) [oxalate (Ox), lactate (Lact), citrate (Cit) and phosphate (Phos)] and high-molecular-weight (HMW) human serum proteins [albumin (HSA) and transferrin (hTf)] were studied in aqueous solution using potentiometric acid-base titrations. The species distribution diagrams for the high-molecular-mass (HMM) proteins with oxidovanadium(IV) under physiological pH were dominated by VO(HMM)2, VOL(HMM) for unsubstituted ligands (L- = Im4COO- and Im2COO-). However, for the N-substituted MeIm2COOH, the species distribution diagrams under physiological pH were dominated by VOL2, VO(HMM)2 and VO2L2(HMM). These species were further confirmed by LC-MS, MALDI-TOF-MS and EPR studies. The glucose-stimulated insulin secretion (GSIS) action of the complexes was investigated using INS-1E cells at a 1 µM concentration, which was established through cytotoxicity studies via the MTT assay. The neutral complexes, especially VO(MeIm2COO)2, showed promising results in the stimulation of insulin secretion than the cationic [VO(MeIm2CH2OH)2]2+ complex and the vanadium salt. Oxidovanadium(IV) complexes reduced insulin stimulation significantly under normoglycaemic levels but showed positive effects on insulin secretion under hyperglycaemic conditions (33.3 mM glucose media). The islets exposed to oxidovanadium(IV) complexes under hyperglycaemic conditions displayed a significant increase in the stimulatory index with 1.19, 1.75, 1.53, 1.85, 2.20 and 1.29 observed for the positive control (sulfonylurea:gliclazide), VOSO4, VO(Im4COO)2, VO(Im2COO)2, VO(MeIm2COO)2 and VO(MeIm2CH2OH)22+, respectively. This observation showed a potential further effect of vanadium complexes towards type 2 diabetes and has been demonstrated for the first time in this study.

Renal tubule-specific Atgl deletion links kidney lipid metabolism to glucagon-like peptide 1 and insulin secretion independent of renal inflammation or lipotoxicity.

OBJECTIVE: Lipotoxic injury from renal lipid accumulation in obesity and type 2 diabetes (T2D) is implicated in associated kidney damage. However, models examining effects of renal ectopic lipid accumulation independent of obesity or T2D are lacking. We generated renal tubule-specific adipose triglyceride lipase knockout (RT-SAKO) mice to determine if this targeted triacylglycerol (TAG) over-storage affects glycemic control and kidney health. METHODS: Male and female RT-SAKO mice and their control littermates were tested for changes in glycemic control at 10-12 and 16-18 weeks of age. Markers of kidney health and blood lipid and hormone concentrations were analyzed. Kidney and blood lysophosphatidic acid (LPA) levels were measured, and a role for LPA in mediating impaired glycemic control was evaluated using the LPA receptor 1/3 inhibitor Ki-16425. RESULTS: All groups remained insulin sensitive, but 16- to 18-week-old male RT-SAKO mice became glucose intolerant, without developing kidney inflammation or fibrosis. Rather, these mice displayed lower circulating insulin and glucagon-like peptide 1 (GLP-1) levels. Impaired first-phase glucose-stimulated insulin secretion was detected and restored by Exendin-4. Kidney and blood LPA levels were elevated in older male but not female RT-SAKO mice, associated with increased kidney diacylglycerol kinase epsilon. Inhibition of LPA-mediated signaling restored serum GLP-1 levels, first-phase insulin secretion, and glucose tolerance. CONCLUSIONS: TAG over-storage alone is insufficient to cause renal tubule lipotoxicity. This work is the first to show that endogenously derived LPA modulates GLP-1 levels in vivo, demonstrating a new mechanism of kidney-gut-pancreas crosstalk to regulate insulin secretion and glucose homeostasis.

Overexpression of lysophospholipid acyltransferase, LPLAT10/LPCAT4/LPEAT2, in the mouse liver increases glucose-stimulated insulin secretion.

Postprandial hyperglycemia is an early indicator of impaired glucose tolerance that leads to type 2 diabetes mellitus (T2DM). Alterations in the fatty acid composition of phospholipids have been implicated in diseases such as T2DM and nonalcoholic fatty liver disease. Lysophospholipid acyltransferase 10 (LPLAT10, also called LPCAT4 and LPEAT2) plays a role in remodeling fatty acyl chains of phospholipids; however, its relationship with metabolic diseases has not been fully elucidated. LPLAT10 expression is low in the liver, the main organ that regulates metabolism, under normal conditions. Here, we investigated whether overexpression of LPLAT10 in the liver leads to improved glucose metabolism. For overexpression, we generated an LPLAT10-expressing adenovirus (Ad) vector (Ad-LPLAT10) using an improved Ad vector. Postprandial hyperglycemia was suppressed by the induction of glucose-stimulated insulin secretion in Ad-LPLAT10-treated mice compared with that in control Ad vector-treated mice. Hepatic and serum levels of phosphatidylcholine 40:7, containing C18:1 and C22:6, were increased in Ad-LPLAT10-treated mice. Serum from Ad-LPLAT10-treated mice showed increased glucose-stimulated insulin secretion in mouse insulinoma MIN6 cells. These results indicate that changes in hepatic phosphatidylcholine species due to liver-specific LPLAT10 overexpression affect the pancreas and increase glucose-stimulated insulin secretion. Our findings highlight LPLAT10 as a potential novel therapeutic target for T2DM.

A vascularized 3D model of the human pancreatic islet forex vivostudy of immune cell-islet interaction.

Insulin is an essential regulator of blood glucose homeostasis that is produced exclusively byßcells within the pancreatic islets of healthy individuals. In those affected by diabetes, immune inflammation, damage, and destruction of isletßcells leads to insulin deficiency and hyperglycemia. Current efforts to understand the mechanisms underlyingßcell damage in diabetes rely onin vitro-cultured cadaveric islets. However, isolation of these islets involves removal of crucial matrix and vasculature that supports islets in the intact pancreas. Unsurprisingly, these islets demonstrate reduced functionality over time in standard culture conditions, thereby limiting their value for understanding native islet biology. Leveraging a novel, vascularized micro-organ (VMO) approach, we have recapitulated elements of the native pancreas by incorporating isolated human islets within a three-dimensional matrix nourished by living, perfusable blood vessels. Importantly, these islets show long-term viability and maintain robust glucose-stimulated insulin responses. Furthermore, vessel-mediated delivery of immune cells to these tissues provides a model to assess islet-immune cell interactions and subsequent islet killing-key steps in type 1 diabetes pathogenesis. Together, these results establish the islet-VMO as a novel,ex vivoplatform for studying human islet biology in both health and disease.

Dectin-2 Deficiency Promotes Proinflammatory Cytokine Release From Macrophages and Impairs Insulin Secretion.

Pancreatic islet inflammation plays a crucial role in the etiology of type 2 diabetes (T2D). Macrophages residing in pancreatic islets have emerged as key players in islet inflammation. Macrophages express a plethora of innate immune receptors that bind to environmental and metabolic cues and integrate these signals to trigger an inflammatory response that contributes to the development of islet inflammation. One such receptor, Dectin-2, has been identified within pancreatic islets; however, its role in glucose metabolism remains largely unknown. Here we have demonstrated that mice lacking Dectin-2 exhibit local inflammation within islets, along with impaired insulin secretion and ß-cell dysfunction. Our findings indicate that these effects are mediated by proinflammatory cytokines, such as interleukin (IL)-1α and IL-6, which are secreted by macrophages that have acquired an inflammatory phenotype because of the loss of Dectin-2. This study provides novel insights into the mechanisms underlying the role of Dectin-2 in the development of islet inflammation.

An updated patent review of GPR40/ FFAR1 modulators (2020 - present).

INTRODUCTION: Free fatty acid receptor 1 (FFAR1) is a potential therapeutic target for type 2 diabetes mellitus (T2DM) because it could clinically stimulate insulin release in a glucose-dependent manner without inducing hypoglycemia. In both the pharmaceutical industry and academic community, FFAR1 agonists have attracted considerable attention. AREAS COVERED: The review presents a patent overview of FFAR1 modulators in 2020-2023, along with chemical structures, the biological activities and therapeutic applications of the representative compounds. Our patent survey used the major electronic databases, namely SciFinder, and Web of Science and Innojoy. EXPERT OPINION: Although FFAR1 agonists exhibit outstanding advantages, they are also associated with significant challenges. At present, reducing the molecular weight and overall lipophilicity and developing tissue-specific FFAR1 agonists may be the strategies for alleviating hepatotoxicity.

Identification of Crocetin as a Dual Agonist of GPR40 and GPR120 Responsible for the Antidiabetic Effect of Saffron.

Crocin, a glycoside of crocetin, has been known as the principal component responsible for saffron's antidiabetic, anticancer, and anti-inflammatory effects. Crocetin, originating from the hydrolytic cleavage of crocin in biological systems, was subjected to ligand-based virtual screening in this investigation. Subsequent biochemical analysis unveiled crocetin, not crocin, as a novel dual GPR40 and GPR120 agonist, demonstrating a marked preference for GPR40 and GPR120 over peroxisome proliferator-activated receptors (PPAR)γ. This compound notably enhanced insulin and GLP-1 secretion from pancreatic ß-cells and intestinal neuroendocrine cells, respectively, presenting a dual mechanism of action in glucose-lowering effects. Docking simulations showed that crocetin emulates the binding characteristics of natural ligands through hydrogen bonds and hydrophobic interactions, whereas crocin's hindered fit within the binding pocket is attributed to steric constraints. Collectively, for the first time, this study unveils crocetin as the true active component of saffron, functioning as a GPR40/120 agonist with potential implications in antidiabetic interventions.

Mitochondrial Dynamics and Insulin Secretion.

Mitochondria are involved in the regulation of cellular energy metabolism, calcium homeostasis, and apoptosis. For mitochondrial quality control, dynamic processes, such as mitochondrial fission and fusion, are necessary to maintain shape and function. Disturbances of mitochondrial dynamics lead to dysfunctional mitochondria, which contribute to the development and progression of numerous diseases, including Type 2 Diabetes (T2D). Compelling evidence has been put forward that mitochondrial dynamics play a significant role in the metabolism-secretion coupling of pancreatic ß cells. The disruption of mitochondrial dynamics is linked to defects in energy production and increased apoptosis, ultimately impairing insulin secretion and ß cell death. This review provides an overview of molecular mechanisms controlling mitochondrial dynamics, their dysfunction in pancreatic ß cells, and pharmaceutical agents targeting mitochondrial dynamic proteins, such as mitochondrial division inhibitor-1 (mdivi-1), dynasore, P110, and 15-oxospiramilactone (S3).

Metformin Can Attenuate Beta-Cell Hypersecretion-Implications for Treatment of Children with Obesity.

In children with obesity, insulin hypersecretion is proposed to precede insulin resistance. We investigated if metformin could be used to attenuate insulin secretion from palmitate-treated isolated islets and its implication for children with obesity. Human islets were exposed to palmitate for 0.5 or 1 day, when metformin was introduced. After culture, glucose-stimulated insulin secretion (GSIS) was measured. Children with obesity, who had received metformin for over six months (n = 21, age 13.9 ± 1.8), were retrospectively evaluated. Children were classified as either "reducing" or "increasing" based on the difference between AUC0-120 of insulin during OGTT before and after metformin treatment. In human islets, GSIS increased after culture in palmitate for up to 1 day but declined with continued palmitate exposure. Whereas adding metformin after 1 day of palmitate exposure increased GSIS, adding metformin after 0.5 days reduced GSIS. In children with "reducing" insulin AUC0-120 (n = 9), 2 h glucose and triglycerides decreased after metformin treatment, which was not observed in patients with "increasing" insulin AUC0-120 (n = 12). In isolated islets, metformin attenuated insulin hypersecretion if introduced when islet secretory capacity was maintained. In children with obesity, improved glycemic and lipid levels were accompanied by reduced insulin levels during OGTT after metformin treatment.

A pathway model of glucose-stimulated insulin secretion in the pancreatic ß-cell.

The pancreas plays a critical role in maintaining glucose homeostasis through the secretion of hormones from the islets of Langerhans. Glucose-stimulated insulin secretion (GSIS) by the pancreatic ß-cell is the main mechanism for reducing elevated plasma glucose. Here we present a systematic modeling workflow for the development of kinetic pathway models using the Systems Biology Markup Language (SBML). Steps include retrieval of information from databases, curation of experimental and clinical data for model calibration and validation, integration of heterogeneous data including absolute and relative measurements, unit normalization, data normalization, and model annotation. An important factor was the reproducibility and exchangeability of the model, which allowed the use of various existing tools. The workflow was applied to construct a novel data-driven kinetic model of GSIS in the pancreatic ß-cell based on experimental and clinical data from 39 studies spanning 50 years of pancreatic, islet, and ß-cell research in humans, rats, mice, and cell lines. The model consists of detailed glycolysis and phenomenological equations for insulin secretion coupled to cellular energy state, ATP dynamics and (ATP/ADP ratio). Key findings of our work are that in GSIS there is a glucose-dependent increase in almost all intermediates of glycolysis. This increase in glycolytic metabolites is accompanied by an increase in energy metabolites, especially ATP and NADH. One of the few decreasing metabolites is ADP, which, in combination with the increase in ATP, results in a large increase in ATP/ADP ratios in the ß-cell with increasing glucose. Insulin secretion is dependent on ATP/ADP, resulting in glucose-stimulated insulin secretion. The observed glucose-dependent increase in glycolytic intermediates and the resulting change in ATP/ADP ratios and insulin secretion is a robust phenomenon observed across data sets, experimental systems and species. Model predictions of the glucose-dependent response of glycolytic intermediates and biphasic insulin secretion are in good agreement with experimental measurements. Our model predicts that factors affecting ATP consumption, ATP formation, hexokinase, phosphofructokinase, and ATP/ADP-dependent insulin secretion have a major effect on GSIS. In conclusion, we have developed and applied a systematic modeling workflow for pathway models that allowed us to gain insight into key mechanisms in GSIS in the pancreatic ß-cell.

Insulin secretion hot spots in pancreatic ß cells as secreting adhesions.

Pancreatic ß cell secretion of insulin is crucial to the maintenance of glucose homeostasis and prevention of diseases related to glucose regulation, including diabetes. Pancreatic ß cells accomplish efficient insulin secretion by clustering secretion events at the cell membrane facing the vasculature. Regions at the cell periphery characterized by clustered secretion are currently termed insulin secretion hot spots. Several proteins, many associated with the microtubule and actin cytoskeletons, are known to localize to and serve specific functions at hot spots. Among these proteins are the scaffolding protein ELKS, the membrane-associated proteins LL5ß and liprins, the focal adhesion-associated protein KANK1, and other factors typically associated with the presynaptic active zone in neurons. These hot spot proteins have been shown to contribute to insulin secretion, but many questions remain regarding their organization and dynamics at hot spots. Current studies suggest microtubule- and F-actin are involved in regulation of hot spot proteins and their function in secretion. The hot spot protein association with the cytoskeleton networks also suggests a potential role for mechanical regulation of these proteins and hot spots in general. This perspective summarizes the existing knowledge of known hot spot proteins, their cytoskeletal-mediated regulation, and discuss questions remaining regarding mechanical regulation of pancreatic beta cell hot spots.

Asiatic acid improves insulin secretion of ß cells in type 2 diabetes through TNF-α/Mfn2 pathway. / ç§¯é›ªè‰é ¸é€šè¿‡è°ƒæŽ§TNF-α/Mfn2通路改善2åž‹ç³–å°¿ç— ßç»†èƒžèƒ°å²›ç´ åˆ†æ³ŒåŠŸèƒ½.

OBJECTIVES: To investigate the effects and molecular mechanisms of asiatic acid on ß-cell function in type 2 diabetes mellitus (T2DM). METHODS: The T2DM model was established by high fat diet and streptozotocin injection in ICR mice, and the effects of asiatic acid on glucose regulation were investigated in model mice. The islets were isolated from palmitic acid-treated diabetic mice. ELISA was used to detect the glucose-stimulated insulin secretion, tumor necrosis factor (TNF)-α and interleukin (IL)-6. ATP assay was applied to measure ATP production, and Western blotting was used to detect protein expression of mature ß cell marker urocortin (Ucn) 3 and mitofusin (Mfn) 2. The regulatory effects of asiatic acid on glucose-stimulated insulin secretion (GSIS) and Ucn3 expression were also investigated after siRNA interference with Mfn2 or treatment with TNF-α. RESULTS: Asiatic acid with the dose of 25 mg·kg－1·d－1 had the best glycemic control in T2DM mice and improved the homeostasis model assessment ß index. Asiatic acid increased the expression of Mfn2 and Ucn3 protein and improved the GSIS function of diabetic ß cells in vitro and in vivo (both P<0.05). Moreover, it improved the ATP production of islets of T2DM mice in vitro (P<0.05). Interfering Mfn2 with siRNA blocked the up-regulation of Ucn3 and GSIS induced by asiatic acid. Asiatic acid inhibited islet TNF-α content and increased Mfn2 and Ucn3 protein expression inhibited by TNF-α. CONCLUSIONS: Asiatic acid improves ß cell insulin secretion function in T2DM mice by maintaining the ß cell maturity, which may be related to the TNF-α/Mfn2 pathway.

Development of electrochemical Zn2+ sensors for rapid voltammetric detection of glucose-stimulated insulin release from pancreatic ß-cells.

Diabetes is a chronic disease characterized by elevated blood glucose levels resulting from absent or ineffective insulin release from pancreatic ß-cells. ß-cell function is routinely assessed in vitro using static or dynamic glucose-stimulated insulin secretion (GSIS) assays followed by insulin quantification via time-consuming, costly enzyme-linked immunosorbent assays (ELISA). In this study, we developed a highly sensitive electrochemical sensor for zinc (Zn2+), an ion co-released with insulin, as a rapid and low-cost method for measuring dynamic insulin release. Different modifications to glassy carbon electrodes (GCE) were evaluated to develop a sensor that detects physiological Zn2+ concentrations while operating within a biological Krebs Ringer Buffer (KRB) medium (pH 7.2). Electrodeposition of bismuth and indium improved Zn2+ sensitivity and limit of detection (LOD), and a Nafion coating improved selectivity. Using anodic stripping voltammetry (ASV) with a pre-concentration time of 6 min, we achieved a LOD of 2.3 µg/L over the wide linear range of 2.5-500 µg/L Zn2+. Sensor performance improved with 10-min pre-concentration, resulting in increased sensitivity, lower LOD (0.18 µg/L), and a bilinear response over the range of 0.25-10 µg/L Zn2+. We further characterized the physicochemical properties of the Zn2+ sensor using scanning electron microscopy (SEM), cyclic voltammetry (CV), and electrochemical impedance spectroscopy (EIS). Finally, we demonstrated the sensor's capability to measure Zn2+ release from glucose-stimulated INS-1 ß-cells and primary mouse islets. Our results exhibited a high correlation with secreted insulin and validated the sensor's potential as a rapid alternative to conventional two-step GSIS plus ELISA methods.

Glucose-Lowering Effects of Imeglimin and Its Possible Beneficial Effects on Diabetic Complications.

Mitochondrial dysfunction is a prominent pathological feature of type 2 diabetes, which contributes to ß-cell mass reduction and insulin resistance. Imeglimin is a novel oral hypoglycemic agent with a unique mechanism of action targeting mitochondrial bioenergetics. Imeglimin reduces reactive oxygen species production, improves mitochondrial function and integrity, and also improves the structure and function of endoplasmic reticulum (ER), changes which enhance glucose-stimulated insulin secretion and inhibit the apoptosis of ß-cells, leading to ß-cell mass preservation. Further, imeglimin inhibits hepatic glucose production and ameliorates insulin sensitivity. Clinical trials into the effects of imeglimin monotherapy and combination therapy exhibited an excellent hypoglycemic efficacy and safety profile in type 2 diabetic patients. Mitochondrial impairment is closely associated with endothelial dysfunction, which is a very early event in atherosclerosis. Imeglimin improved endothelial dysfunction in patients with type 2 diabetes via both glycemic control-dependent and -independent mechanisms. In experimental animals, imeglimin improved cardiac and kidney function via an improvement in mitochondrial and ER function or/and an improvement in endothelial function. Furthermore, imeglimin reduced ischemia-induced brain damage. In addition to glucose-lowering effects, imeglimin can be a useful therapeutic option for diabetic complications in type 2 diabetic 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 ß-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.

Chemical Constituents from the Roots of Angelica reflexa That Improve Glucose-Stimulated Insulin Secretion by Regulating Pancreatic ß-Cell Metabolism.

The aim of this study was to discover bioactive constituents of Angelica reflexa that improve glucose-stimulated insulin secretion (GSIS) in pancreatic ß-cells. Herein, three new compounds, namely, koseonolin A (1), koseonolin B (2), and isohydroxylomatin (3), along with 28 compounds (4-31) were isolated from the roots of A. reflexa by chromatographic methods. The chemical structures of new compounds (1-3) were elucidated through spectroscopic/spectrometric methods such as NMR and HRESIMS. In particular, the absolute configuration of the new compounds (1 and 3) was performed by electronic circular dichroism (ECD) studies. The effects of the root extract of A. reflexa (KH2E) and isolated compounds (1-31) on GSIS were detected by GSIS assay, ADP/ATP ratio assay, and Western blot assay. We observed that KH2E enhanced GSIS. Among the compounds 1-31, isohydroxylomatin (3), (-)-marmesin (17), and marmesinin (19) increased GSIS. In particular, marmesinin (19) was the most effective; this effect was superior to treatment with gliclazide. GSI values were: 13.21 ± 0.12 and 7.02 ± 0.32 for marmesinin (19) and gliclazide at a same concentration of 10 µM, respectively. Gliclazide is often performed in patients with type 2 diabetes (T2D). KH2E and marmesinin (19) enhanced the protein expressions associated with pancreatic ß-cell metabolism such as peroxisome proliferator-activated receptor γ, pancreatic and duodenal homeobox 1, and insulin receptor substrate-2. The effect of marmesinin (19) on GSIS was improved by an L-type Ca2+ channel agonist and K+ channel blocker and was inhibited by an L-type Ca2+ channel blocker and K+ channel activator. Marmesinin (19) may improve hyperglycemia by enhancing GSIS in pancreatic ß-cells. Thus, marmesinin (19) may have potential use in developing novel anti-T2D therapy. These findings promote the potential application of marmesinin (19) toward the management of hyperglycemia in T2D.