Type 2 diabetes-a matter of beta-cell life and death?

Saponins of Momordica charantia increase insulin secretion in INS-1 pancreatic β-cells via the PI3K/Akt/FoxO1 signaling pathway

Saponins are the main bioactive substances with anti-hyperglycemic activities of Momordica charantia. This study aimed to verify the effects of M. charantia saponins on insulin secretion and explore the potential underlying mechanisms in INS-1 pancreatic β-cells. We injured INS-1 cells with 33.3mM glucose and then treated them with saponins. Saponins improved cell morphology and viability as demonstrated by inverted microscopy and CCK8 detection and significantly increased insulin secretion in a concentration-dependent manner as shown by ELISA. Thus, we obtained the optimal concentration for the subsequent experiments. Potential mechanisms were explored by immunofluorescence, western blotting, and RT-qPCR techniques. First, saponins increased the mRNA and protein levels of IRS-2 but decreased the serine 731 phosphorylation level of IRS-2. Moreover, saponins increased the phosphorylation of Akt protein and decreased the protein level of FoxO1, which were both reversed by the PI3K inhibitor ly294002. Furthermore, saponins increased the protein level of the downstream molecule and insulin initiating factor PDX-1, which was also reversed by ly294002. Saponins also increased Akt and PDX-1 mRNA and decreased FoxO1 mRNA, which were both reversed by ly294002. Saponins increased glucose-stimulated insulin secretion (GSIS) and intracellular insulin content, which were reversed by ly294002, as determined by ELISA. The immunofluorescence results also confirmed this tendency. In conclusion, our findings improve our understanding of the function of saponins in INS-1 pancreatic β-cells and suggest that saponins may increase insulin secretion via the PI3K/Akt/FoxO1 signaling pathway.

EGCG Upregulates UCP3 Levels to Protect MIN6 Pancreatic Islet Cells from Interleukin-1β-Induced Apoptosis

Objective

The protective effects of epigallocatechin gallate (EGCG) on interleukin-1β (IL-1β)-induced apoptosis were investigated in murine MIN₆ pancreatic β-cells. The role of uncoupling protein-3 (UCP₃) signaling in this process was also explored.

Methods

After treatment with IL-1β and EGCG, cells were collected and analyzed. Cell viability was measured using the CCK₈ assay and the function of β-cells was evaluated by analyzing insulin secretion. Detection of mitochondrial function in cells was performed by measuring mitochondrial membrane potential, the concentration of ATP and activity of ROS. Apoptosis was analyzed by Hochest33258 staining and flow cytometry. Expression levels of UCP₃ were interrogated using immunohistochemistry, RT-PCR and Western blotting.

Results

Compared with the control group, IL-1β treatment (20nM) for 24 h significantly decreased cell viability and insulin secretion, damaged mitochondrial function and increased ROS activity. Results also showed increased apoptosis and a decrease in UCP₃ expression levels (p<0.01). However, treatment with low (1mM) or high (5mM) concentrations of EGCG significantly decreased IL-1β-induced apoptosis (p<0.01), restored mitochondrial function and subsequently increased UCP₃ levels in IL-1β-induced β-cells (p<0.01).

Conclusion

These results suggest that EGCG protects against IL-1β-induced mitochondrial injury and apoptosis in β-cells through the up-regulation of UCP₃.

Gingival Crevicular Blood as a Potential Screening Tool: A Cross Sectional Comparative Study

Background: Diabetes is known to be one of the major global epidemic diseases, significantly associated with mortality and morbidity worldwide, conferring a substantial burden to the health care system. The epidemiological transition of this chronic disease tends to worsen unless preventive health strategies are implemented. Appropriate screening devices and standardized methods are crucial to prevent this potentially inauspicious life condition. Currently, the glucometer is the conventional device employed for blood glucose level determination that outputs the blood glucose reading. Glucometer performed in the dental office may be an important device in screening diabetes, so it can be addressed during a periodontal examination. Because gingival blood is a useful source to detect the glucose level, the focus is placed on the opportunity that might provide valuable diagnostic information. This study aimed to compare gingival crevicular blood with finger-stick blood glucose measurements using a self-monitoring glucometer, to evaluate whether gingival crevicular blood could be an alternative to allow accurate chairside glucose testing. Methods: A cross-sectional comparative study was performed among a 31–67-year-old population. Seventy participants with diagnosed type 2 diabetes and seventy healthy subjects, all with positive bleeding on probing, were enrolled. The gingival crevicular blood was collected using a glucometer to estimate the blood glucose level and compared with finger-stick blood glucose level. Results: The mean capillary blood glucose and gingival crevicular blood levels from all samples were, respectively, 160.42 ± 31.31 mg/dL and 161.64 ± 31.56 mg/dL for diabetic participants and 93.51 ± 10.35 mg/dL and 94.47 ± 9.91 mg/dL for healthy patients. In both groups, the difference between gingival crevicular blood and capillary blood glucose levels was non-significant (P < 0.05). The highly significant correlation between capillary blood glucose and gingival crevicular blood (r = 0.9834 for diabetic patients and r = 0.8153 for healthy participants) in both the groups was found. Conclusions: Gingival crevicular blood test was demonstrated as a feasible and useful primary screening tool test for detecting diabetes and for glucose estimation in non-diabetic patients. Use of gingival crevicular blood for screening is an attractive way of identifying a reasonable option of finger-stick blood glucose measurement under the appropriate circumstances. Rapid assessment may precede diagnostic evaluation in diabetic as well as healthy patients with acute severe bleeding. In addition, gingival crevicular blood levels may be needed to monitor the diabetic output.

Increased Plasma Levels of Adenylate Cyclase 8 and cAMP Are Associated with Obesity and Type 2 Diabetes: Results from a Cross-Sectional Study

Adenylate cyclases (ADCYs) catalyze the conversion of ATP to cAMP, an important co-factor in energy homeostasis. Giving ADCYs role in obesity, diabetes and inflammation, we questioned whether calcium-stimulated ADCY isoforms may be variably detectable in human plasma. We report the results of a cross-sectional study assessing circulating levels of functional ADCY1, -3 and -8 in patients with T2D vs. non-diabetic (ND) controls in association with obesity. ADCY1 levels exhibited no significant change between ND and T2D groups. ADCY3 levels were lower in obese individuals, albeit not statistically significantly. In contrast, ADCY8 plasma levels were significantly higher in obese and T2D patients compared to controls (p = 0.001) and patients with T2D only (p = 0.039). ADCY8 levels correlated positively with body mass index and Hb1Ac levels. Parallel to the increased ADCY8 levels, significantly higher cAMP levels were observed in patients with T2D compared with ND controls, and further elevated in obese individuals, irrespective of T2D status. Additionally, cAMP levels positively correlated with fasting plasma glucose levels. In conclusion, the current cross-sectional study demonstrated elevated levels of circulating plasma ADCY8 and cAMP in obesity and T2D.

Peroxiredoxin I deficiency increases pancreatic β‑cell apoptosis after streptozotocin stimulation via the AKT/GSK3β signaling pathway

Apoptosis of pancreatic β-cells is involved in the pathogenesis of type I and II diabetes. Peroxiredoxin I (Prx I) serves an important role in regulating cellular apoptosis; however, the role of Prx I in pancreatic β-cell apoptosis is not completely understood. In the present study, the role of peroxiredoxin 1 (Prx I) during streptozotocin (STZ)-induced apoptosis of pancreatic β-cells was investigated. The expression level of Prx I was decreased by STZ treatment in a time-dependent manner, and apoptosis of Prx I knockdown MIN6 cells was increased by STZ stimulation, compared with untransduced MIN6 cells. Furthermore, an intraperitoneal injection of STZ increased pancreatic islet damage in Prx I knockout mice, compared with wild-type and Prx II knockout mice. AKT and glycogen synthase kinase (GSK)-3β phosphorylation significantly decreased following Prx I knockdown in MIN6 cells. However, phosphorylated β-catenin and p65 levels significantly increased after STZ stimulation, compared with untransduced cells. The results of the present study indicate that deletion of Prx I mediated STZ-induced pancreatic β-cell death in vivo and in vitro by regulating the AKT/GSK-3β/β-catenin signaling pathway, as well as NF-κB signaling. These findings provide a theoretical basis for treatment of pancreatic damage.

Characterization of Signaling Pathways Associated with Pancreatic β-cell Adaptive Flexibility in Compensation of Obesity-linked Diabetes in db/db Mice

The onset of obesity-linked type 2 diabetes (T2D) is marked by an eventual failure in pancreatic β-cell function and mass that is no longer able to compensate for the inherent insulin resistance and increased metabolic load intrinsic to obesity. However, in a commonly used model of T2D, the db/db mouse, β-cells have an inbuilt adaptive flexibility enabling them to effectively adjust insulin production rates relative to the metabolic demand. Pancreatic β-cells from these animals have markedly reduced intracellular insulin stores, yet high rates of (pro)insulin secretion, together with a substantial increase in proinsulin biosynthesis highlighted by expanded rough endoplasmic reticulum and Golgi apparatus. However, when the metabolic overload and/or hyperglycemia is normalized, β-cells from db/db mice quickly restore their insulin stores and normalize secretory function. This demonstrates the β-cell's adaptive flexibility and indicates that therapeutic approaches applied to encourage β-cell rest are capable of restoring endogenous β-cell function. However, mechanisms that regulate β-cell adaptive flexibility are essentially unknown. To gain deeper mechanistic insight into the molecular events underlying β-cell adaptive flexibility in db/db β-cells, we conducted a combined proteomic and post-translational modification specific proteomic (PTMomics) approach on islets from db/db mice and wild-type controls (WT) with or without prior exposure to normal glucose levels. We identified differential modifications of proteins involved in redox homeostasis, protein refolding, K48-linked deubiquitination, mRNA/protein export, focal adhesion, ERK1/2 signaling, and renin-angiotensin-aldosterone signaling, as well as sialyltransferase activity, associated with β-cell adaptive flexibility. These proteins are all related to proinsulin biosynthesis and processing, maturation of insulin secretory granules, and vesicular trafficking-core pathways involved in the adaptation of insulin production to meet metabolic demand. Collectively, this study outlines a novel and comprehensive global PTMome signaling map that highlights important molecular mechanisms related to the adaptive flexibility of β-cell function, providing improved insight into disease pathogenesis of T2D.

Association of glucagon-like peptide-1 receptor-targeted imaging probe with in vivo glucagon-like peptide-1 receptor agonist glucose-lowering effects

Aims/Introduction

Glucagon‐like peptide‐1 receptor agonists (GLP‐1RA) are used for treatment of type 2 diabetes mellitus worldwide. However, some patients do not respond well to the therapy, and caution must be taken for certain patients, including those with reduced insulin secretory capacity. Thus, it is clinically important to predict the efficacy of GLP‐1RA therapy. GLP‐1R‐targeted imaging has recently emerged to visualize and quantify β‐cells. We investigated whether GLP‐1R‐targeted imaging can predict the efficacy of GLP‐1RA treatment.

Materials and Methods

We developed ¹¹¹Indium‐labeled exendin‐4 derivative (¹¹¹In‐Ex4) as a GLP‐1R‐targeting probe. Diabetic mice were selected from NONcNZO10/LtJ male mice that were fed for different durations with 11% fat chow. After 3‐week administration of dulaglutide as GLP‐1RA therapy, mice with non‐fasting blood glucose levels <300 mg/dL and >300 mg/dL were defined as responders and non‐responders, respectively. In addition, ex vivo¹¹¹In‐Ex4 pancreatic accumulations (¹¹¹In‐Ex4 pancreatic values) were examined.

Results

The non‐fasting blood glucose levels after treatment were 172.5 ± 42.4 mg/dL in responders (n = 4) and 330.8 ± 20.7 mg/dL in non‐responders (n = 5), respectively. Ex vivo¹¹¹In‐Ex4 pancreatic values showed significant correlations with post‐treatment glycohemoglobin and glucose area under curve during an oral glucose tolerance test (R² = 0.76 and 0.80; P < 0.01 and <0.01, respectively). The receiver operating characteristic area under curve for identifying responders by ex vivo¹¹¹In‐Ex4 pancreatic values was 1.00 (P < 0.01).

Conclusion

Ex vivo¹¹¹In‐Ex4 pancreatic values reflected dulaglutide efficacy, suggesting clinical possibilities for expanding GLP‐1R‐targeted imaging applications.

Administration of mulberry leaves maintains pancreatic β-cell mass in obese/type 2 diabetes mellitus mouse model

BACKGROUND

Type 2 diabetes mellitus is characterized by insulin resistance and pancreatic β-cell dysfunction. A decrease in β-cell mass, which occurs during the progression of Type 2 diabetes mellitus, contributes to impaired insulin secretion. Mulberry leaves contain various nutritional components that exert anti-diabetic and anti-atherogenic effects. The present study analyzed the effects of mulberry leaf intake on pancreatic β-cells to clarify the mechanisms underlying its anti-diabetic function.

METHODS

Mulberry leaves (Morus alba L.) were dried at 180 °C for 8 s in a hot-air mill and fed to obesity/Type 2 diabetes mellitus db/db mouse models at 5% (w/w) as part of a normal diet from 7 to 10, 15, or 20 weeks of age. An intraperitoneal glucose tolerance test was then performed on the mice. To evaluate the β-cell mass, the pancreas was subjected to immunohistological analysis with an anti-insulin antibody. A TUNEL assay and immunohistological analysis with a proliferation marker was also performed. Expression levels of endoplasmic reticulum stress-responsible genes and proliferation markers were assessed by quantitative RT-PCR.

RESULTS

Intake of mulberry leaves maintained the β-cell function of db/db mice. Moreover, oral administration of mulberry leaves significantly decreased cell death by reducing endoplasmic reticulum stress in the pancreas. Mulberry leaves significantly increased proliferation of β-cells and the expression of pancreatic duodenal homeobox1 mRNA in the pancreas.

CONCLUSION

Considered together, these results indicate that dietary mulberry leaf administration can maintain insulin levels and pancreatic β-cell mass, at least in part, by suppressing endoplasmic reticulum stress in Type 2 diabetes mellitus mouse models.

Ultraconserved element uc.333 increases insulin sensitivity by binding to miR-223

Insulin resistance (IR) contributes to diabetes and aging. Ultraconserved elements (UCEs) are a class of long noncoding RNAs (lncRNAs) that are 100% conserved in humans, mice, and rats. We identified the lncRNA uc.333 using an lncRNA microarray and then used quantitative real-time polymerase chain reaction to analyze its expression in the livers of nonalcoholic fatty liver disease (NAFLD) patients, db/db mice, high-fat diet–fed mice, IL-6-treated mice, and TNF-α-treated mice. The underlying mechanisms of uc.333 in IR were investigated using fluorescence in situ hybridization, Western blot, and miRNA microarray analyses. The results revealed that uc.333 expression was decreased in liver tissues from NAFLD patients and treated mice. Furthermore, overexpression of uc.333 decreased IR, whereas knocking down uc.333 increased IR. We also confirmed that uc.333 binds to miR-223 and that the levels of miR-223 were increased in the livers of patients and treated mice. These findings showed that uc.333 improves IR by binding to miR-223; thus, uc.333 may be a useful target for the treatment and prevention of IR.

Inhibition of thioredoxin 2 by intracellular methylglyoxal accumulation leads to mitochondrial dysfunction and apoptosis in INS-1 cells

PURPOSE

To investigate the role of thioredoxin 2 (Trx2) inhibition induced by intracellular methylglyoxal (MGO) in pancreatic beta-cell mitochondrial dysfunction and apoptosis.

METHODS

Rat pancreatic beta-cell line INS-1 cells were treated with Glo1 siRNAs or exogenous MGO to increase intracellular MGO. AGEs formation was detected by ELISA and mitochondrial ROS was detected by probe MitoSOX. Transmission electron microscopy (TEM) analysis and ATP content were measured to evaluate mitochondrial function. Trx2 expression was manipulated by overexpression with recombinant Trx2 lentivirus or knockdown with Trx2 siRNAs, and effects on apoptosis and insulin secretion were measured by flow cytometry and ELISA, respectively.

RESULTS

The increase of intracellular MGO by Glo1 blockage or MGO treatment led to advanced glycation end products (AGEs) overproduction, mitochondrial ROS increase, and insulin secretion paralysis. These were probably due to MGO-induced inhibition of mitochondrial Trx2. Trx2 inhibition by blockage of either Glo1 or Trx2 impaired mitochondrial integrity, inhibited cytochrome C oxidases subunit 1 and 4 (Cox1 and Cox4) expression and further reduced ATP generation, and all of these might lead to insulin paralysis; whereas Trx2 overexpression partially reversed MGO-induced oxidative stress, attenuated insulin secretion by preventing mitochondrial damage. Trx2 overexpression also retarded MGO-induced apoptosis of INS-1 cell through inhibiting ASK1 activation and downregulation of the ASK1-p38 MAPK pathway.

CONCLUSIONS

Our results reveal a possible mechanism for beta-cell oxidative damage upon intracellular MGO-induced Trx2 inactivation and mitochondrial dysfunction and apoptosis.

Curcumin inhibits alloxan-induced pancreatic islet cell damage via antioxidation and antiapoptosis

The present study elucidates the possible protective effects of curcumin on β-cells damaged by oxidative stress and its significance in controlling diabetes mellitus in in vitro experiments. Pancreatic islet (RIN-m5F) cells were treated with 25 mmol/L alloxan (AXN) to induce cell damage and the protective effects of curcumin were observed. The results showed that curcumin significantly promoted the cellular activity of AXN-treated RIN-m5F cells, decreased the ratio of apoptosis, downregulated the level of malondialdehyde, upregulated the levels of superoxide dismutase and reactive oxygen species, increased the expression of Bcl-2, cleaved caspase-3, and cleaved PARP1, and decreased the expression of Bax in AXN-treated cells. These results suggest that curcumin inhibits AXN-induced damage in RIN-m5F cells via antioxidative and antiapoptotic mechanisms.

Autophagic dysfunction of β cell dysfunction in type 2 diabetes, a double-edged sword

Diabetes is an age-related disease, most of which is type 2 diabetes, and islet β cell dysfunction and insulin resistance are the main mechanisms of type 2 diabetes. Recent studies have revealed that autophagy plays an important role in maintaining the structure and function of islet beta cells and inhibiting insulin resistance and apoptosis induced by oxidative stress. In this review, we discussed the positive and negative effects of autophagy and its dysfunction on type 2 diabetes mellitus, which is the so-called double-edged sword, analysed its possible mechanism, and identified possible research hot spots.

Protection from β-cell apoptosis by inhibition of TGF-β/Smad3 signaling

Prevailing insulin resistance and the resultant hyperglycemia elicits a compensatory response from pancreatic islet beta cells (β-cells) that involves increases in β-cell function and β-cell mass. However, the sustained metabolic stress eventually leads to β-cell failure characterized by severe β-cell dysfunction and progressive loss of β-cell mass. Whereas, β-cell dysfunction is relatively well understood at the mechanistic level, the avenues leading to loss of β-cell mass are less clear with reduced proliferation, dedifferentiation, and apoptosis all potential mechanisms. Butler and colleagues documented increased β-cell apoptosis in pancreas from lean and obese human Type 2 diabetes (T2D) subjects, with no changes in rates of β-cell replication or neogenesis, strongly suggesting a role for apoptosis in β-cell failure. Here, we describe a permissive role for TGF-β/Smad3 in β-cell apoptosis. Human islets undergoing β-cell apoptosis release increased levels of TGF-β1 ligand and phosphorylation levels of TGF-β's chief transcription factor, Smad3, are increased in human T2D islets suggestive of an autocrine role for TGF-β/Smad3 signaling in β-cell apoptosis. Smad3 phosphorylation is similarly increased in diabetic mouse islets undergoing β-cell apoptosis. In mice, β-cell-specific activation of Smad3 promotes apoptosis and loss of β-cell mass in association with β-cell dysfunction, glucose intolerance, and diabetes. In contrast, inactive Smad3 protects from apoptosis and preserves β-cell mass while improving β-cell function and glucose tolerance. At the molecular level, Smad3 associates with Foxo1 to propagate TGF-β-dependent β-cell apoptosis. Indeed, genetic or pharmacologic inhibition of TGF-β/Smad3 signals or knocking down Foxo1 protects from β-cell apoptosis. These findings reveal the importance of TGF-β/Smad3 in promoting β-cell apoptosis and demonstrate the therapeutic potential of TGF-β/Smad3 antagonism to restore β-cell mass lost in diabetes.

Glucolipotoxicity, β-Cells, and Diabetes: The Emperor Has No Clothes

Reduction of β-cell mass and function is central to the pathogenesis of type 2 diabetes. The terms glucotoxicity, lipotoxicity, and glucolipotoxicity are used to describe potentially responsible processes. The premise is that chronically elevated glucose levels are toxic to β-cells, that elevated lipid levels in the form of circulating free fatty acids (FFA) also have toxic effects, and that the combination of the two, glucolipotoxicity, is particularly harmful. Much work has shown that high concentrations of FFA can be very damaging to β-cells when used for in vitro experiments, and when infused in large amounts in humans and rodents they produce suppression of insulin secretion. The purpose of this Perspective is to raise doubts about whether the FFA levels found in real-life situations are ever high enough to cause problems. Evidence supporting the importance of glucotoxicity is strong because there is such a tight correlation between defective insulin secretion and rising glucose levels. However, there is virtually no convincing evidence that the alterations in FFA levels occurring during progression to diabetes are pathogenic. Thus, the terms lipotoxicity and glucolipotoxicity should be used with great caution, if at all, because evidence supporting their importance has not yet emerged.

Total White Blood Cell Count Mediated the Association Between Increased Arterial Stiffness and Risk of Type 2 Diabetes Mellitus in Chinese Adults

OBJECTIVE

Type 2 diabetes mellitus (T2DM) is known to be related to increased arterial stiffness. However, little is known about the risk of T2DM due to accelerated arterial stiffness and the underlying mechanism involved. We aimed to examine arterial stiffness, as determined by brachial-ankle pulse wave velocity (baPWV), in relation to T2DM among a community-based population and whether the association was mediated by white blood cell (WBC) counts. Approach and results: A total of 1036 Chinese adults aged 64.3 years with complete data were qualified in the present study. The dose-response association between baPWV levels, WBC counts, and risk of T2DM were explored using generalized linear models or multivariate logistic regression models. A mediation analysis was conducted to investigate the role of WBC counts on the association between baPWV and T2DM. After multivariate adjustments, we observed a dose-responsive relationship between increased baPWV and elevated risk of T2DM: comparing extreme tertiles of baPWV, the adjusted odds ratio for T2DM risk was 2.29 (95% CI, 1.32-3.98; P for trend =0.005). In addition, significant dose-dependent relationships were found across baPWV tertiles with increasing total or differential WBC counts, which in turn, were positively related to higher risk of T2DM (all P for trend <0.05). Mediation analyses indicated that total WBC count mediated 4.5% of the association between increased baPWV and elevated T2DM risk.

CONCLUSIONS

Increased arterial stiffness might increase T2DM risk among middle-aged and older Chinese adults, which was partially mediated by total WBC count.

Exposure to Aroclor 1254 differentially affects the survival of pancreatic β-cells and α-cells in the male mice and the potential reason

Previous works showed that chronic exposure to Aroclor 1254 disrupted glucose homeostasis and induced insulin resistance in male mice. To further observe the different effects of Aroclor 1254 exposure on the pancreatic α-cells and β-cells, male mice were exposed to Aroclor 1254 (0, 0.5, 5, 50, 500 μg/kg) for 60 days, the pancreas was performed a histological examination. The results showed that the percentage of apoptosis cell (indicated by TUNEL assay) was increased in both α-cells and β-cells, as the Aroclor 1254 dose was increased; the proliferation (indicated by PCNA expression) rate of β-cells was elevated while that of α-cells was not affected, resulting in an increased β-cell mass and a decreased α-cell mass in a dose-depend manner. The number of Pdx-1 positive β-cells was significantly increased whereas that of Arx positive α-cells was markedly decreased, indicating an enhanced β-cell neogenesis and a weakened α-cell neogenesis. The drastically reduction of serum testosterone levels in all the treatments suggested an anti-androgenic potency of Aroclor 1254. The up-regulation of estrogen receptors (ERα and ERβ) and androgen receptor in β-cells might be responsible for the increased β-cell mass and neogenesis.

Chikusetsu saponin IVa protects pancreatic β cell against intermittent high glucose-induced injury by activating Wnt/β-catenin/TCF7L2 pathway

Islet β cell mass reduction induced by glucose fluctuation is crucial for the development and progression of T2DM. Chikusetsu saponin IVa (CHS) had protective effects against DM and related injuries. Here we aimed to investigate the role of CHS in β cell injuries and its possible mechanism involved. Isolated rat islets, βTC3 cells and T2DM mice were used in this study. The results showed that CHS restored the secretion activity, promoted β cell survival by increasing β cell proliferation and decreasing apoptosis which induced by intermittent high glucose (IHG). In vivo, CHS protected β cell apoptosis to normalize blood glucose and improve insulin sensitivity in DM mice. Further studies showed that CHS activated Wnt3a signaling, inhibited HBP1, promoted β-catenin nuclear translocation, enhanced expressions of TCF7L2, GIPR and GLP-1R, inhibited p53, p27 and p21. The protective effect of CHS was remarkably suppressed by siRNAs against TCF7L2 or XAV-939 (a Wnt/β-catenin antagonist) in vitro and in β-catenin^-/- mice. In conclusion, we identified a novel role of CHS in protecting β cell survival and regeneration by mechanisms involving the activation of Wnt3a/β-catenin/TCF7L2 signaling. Our results indicated the potential value of CHS as a possible intervention drug for T2DM.

Disruption of Beta-Cell Mitochondrial Networks by the Orphan Nuclear Receptor Nor1/Nr4a3

Nor1, the third member of the Nr4a subfamily of nuclear receptor, is garnering increased interest in view of its role in the regulation of glucose homeostasis. Our previous study highlighted a proapoptotic role of Nor1 in pancreatic beta cells and showed that Nor1 expression was increased in islets isolated from type 2 diabetic individuals, suggesting that Nor1 could mediate the deterioration of islet function in type 2 diabetes. However, the mechanism remains incompletely understood. We herein investigated the subcellular localization of Nor1 in INS832/13 cells and dispersed human beta cells. We also examined the consequences of Nor1 overexpression on mitochondrial function and morphology. Our results show that, surprisingly, Nor1 is mostly cytoplasmic in beta cells and undergoes mitochondrial translocation upon activation by proinflammatory cytokines. Mitochondrial localization of Nor1 reduced glucose oxidation, lowered ATP production rates, and inhibited glucose-stimulated insulin secretion. Western blot and microscopy images revealed that Nor1 could provoke mitochondrial fragmentation via mitophagy. Our study unveils a new mode of action for Nor1, which affects beta-cell viability and function by disrupting mitochondrial networks.

Bombesin Receptor Subtype-3 in Human Diseases

This review summarizes the recent findings of the roles of bombesin receptor subtype-3 (BRS-3) in various patho-physiological conditions. Studies have demonstrated that two mammalians bombesin-like peptides, GRP and NMB, exhibit a large range of functions by binding to three receptors. Knockout studies showed that the mice BRS-3 has important effects on tumor growth, energy homeostasis, glucose regulation, satiety, and lung development (1,7). BRS-3 is an orphan receptor whose natural ligand is unknown. However, several agonists and antagonists have been synthesized which facilitate its characterization, (D-Tyr6, β-Ala11, Phe13, Nle14) Bn-(6-14) and MK-5046 are agonists, whereas ML-18 and Bantag-1 are antagonists. With the development of several selective, high-affinity BRS-3 agonists and antagonists, recent studies provided some insights into the biological effects of BRS-3 in several disease states including lung cancer, obesity, diabetes mellitus, asthma, and kidney diseases.

Proinsulin is sensitive to reflect glucose intolerance

AIMS/INTRODUCTION

We investigated associations between glucose tolerance and β-cell function using a series of estimation methods in a population-based study.

MATERIALS AND METHODS

Data from the Dynamics of Lifestyle and Neighborhood Community on Health Study were analyzed. A total of 489 participants (263 women) were divided into three groups: normal glucose tolerance (NGT), prediabetes (PDM) and diabetes group. We estimated β-cell function by the homeostasis model assessment of β-cell function, proinsulin level (PI), C-peptide index, proinsulin-to-C-peptide ratio (PI/CPR) and proinsulin-to-insulin ratio. Because data on all five parameters of β-cell function showed skewed distributions, the values of these parameters were normalized by natural logarithmic (ln) transformation. Next, the association between glucose tolerance and β-cell function among participants without diabetes was examined. In this analysis, glucose tolerance was assessed based on glycated hemoglobin levels.

RESULTS

In the crude analysis, ln(PI) and ln(PI/CPR) were significantly higher in the diabetes group than those in the PDM and NGT groups, and these parameters were significantly higher in the PDM group than in the NGT group. Only ln(PI) in the PDM group was significantly higher compared with that in the NGT group after adjustment for age, sex and body mass index (ln[PI]: PDM group 2.38 pmol/L, 95% confidence interval 2.29-2.47 pmol/L; NGT group 2.17 pmol/L, 95% confidence interval 2.12-2.22 pmol/L; P < 0.05). In addition, ln(PI) levels were significantly and positively correlated with glycated hemoglobin quartile in participants without diabetes.

CONCLUSIONS

Our results showed that PI was the most sensitive to reflect glucose intolerance.

Noninvasive Evaluation of GPR119 Agonist Effects on β-Cell Mass in Diabetic Male Mice Using 111In-Exendin-4 SPECT/CT

Longitudinal observation of pancreatic β-cell mass (BCM) remains challenging because noninvasive techniques for determining BCM in vivo have not been established. Such observations would be useful for the monitoring of type 2 diabetes mellitus, a progressive disease involving loss of pancreatic BCM and function. An indium 111 (111In)-labeled exendin-4 derivative ([Lys12(111In-BnDTPA-Ahx)]exendin-4) targeting the glucagon-like peptide-1 receptor has been developed recently as a promising probe for quantifying the BCM noninvasively. In the present study, we used the 111In-exendin-4 single-photon emission CT/CT (SPECT/CT) technique to investigate the efficacy of DS-8500a, a novel G protein-coupled receptor-119 agonist currently under investigation for type 2 diabetes mellitus treatment in prediabetic db/db mice under dietary restriction. During the 8-week study, the treatment of mice with DS-8500a delayed and attenuated the progression of glucose intolerance compared with mice under dietary restriction alone. 111In-exendin-4 SPECT/CT of db/db mice revealed continuously decreasing radioactive isotope (RI) intensity in the pancreas during the 8-week intervention. DS-8500a attenuated this decrease and preserved pancreatic RI accumulation compared with dietary restriction alone at the end of the observation period. This result was corroborated not only by ex vivo pancreatic analysis using the [Lys12(111In-BnDTPA-Ahx)]exendin-4 probe but also by conventional histological BCM analysis. These results indicate that DS-8500a attenuates the progression of BCM loss beyond that of dietary restriction alone in prediabetic db/db mice. These results have shown that 111In-exendin-4 SPECT/CT will be useful for noninvasive longitudinal investigation of BCM in vivo.

Roux-en-Y-Bariatric Surgery Reduces Markers of Metabolic Syndrome in Morbidly Obese Patients

Background

Obesity is closely linked to increased markers of metabolic syndrome and development of diabetes. Roux-en-Y bariatric surgery reduces hyperinsulinemia and improves insulin sensitivity and hence benefits morbidly obese patients.

Aim

To determine changes in markers of metabolic syndrome, pancreatic function, and hepatic insulin sensitivity in patients before and 1 year after undergoing Roux-en-Y gastric bypass surgery.

Methods

We enrolled 43 consecutive patients in a single center. Markers for metabolic syndrome included proinsulin, insulin, C-peptide, liver enzymes, and serum levels of selected microRNAs hsa-miR-122, hsa-miR-130, hsa-miR-132, and hsa-miR-375.

Results

After surgery, all patients showed a significant 37% drop of body mass index (p < 0.001). Furthermore, proinsulin (59% reduction, p < 0.001), insulin (76% reduction, p < 0.001), and C-peptide (56% reduction, p < 0.001) were all reduced 1 year after surgery. Using the hepatic insulin clearance score, we determined a significant increase in hepatic insulin clearance after surgery (76% increase, p < 0.001). Especially diabetic patients showed a marked 2.1-fold increase after surgery. Hepatic enzymes ALT (35% reduction, p = 0.002) and γGT (48% reduction, p < 0.001) were significantly reduced in all patients with similar improvement in diabetic and non-diabetic patients. miRNAs hsa-miR-122, hsa-miR-130, and hsa-miR-132 were all significantly reduced whereas hsa-miR-375 was increased after gastric bypass surgery (p < 0.001 for all miRNAs).

Conclusion

Both liver and pancreatic stress parameters were reduced significantly 1 year after Roux-en-Y gastric bypass surgery suggesting an overall amelioration of the metabolic syndrome in all patients regardless of previous health status.

Neratinib protects pancreatic beta cells in diabetes

The loss of functional insulin-producing β-cells is a hallmark of diabetes. Mammalian sterile 20-like kinase 1 (MST1) is a key regulator of pancreatic β-cell death and dysfunction; its deficiency restores functional β-cells and normoglycemia. The identification of MST1 inhibitors represents a promising approach for a β-cell-protective diabetes therapy. Here, we identify neratinib, an FDA-approved drug targeting HER2/EGFR dual kinases, as a potent MST1 inhibitor, which improves β-cell survival under multiple diabetogenic conditions in human islets and INS-1E cells. In a pre-clinical study, neratinib attenuates hyperglycemia and improves β-cell function, survival and β-cell mass in type 1 (streptozotocin) and type 2 (obese Lepr^db/db) diabetic mouse models. In summary, neratinib is a previously unrecognized inhibitor of MST1 and represents a potential β-cell-protective drug with proof-of-concept in vitro in human islets and in vivo in rodent models of both type 1 and type 2 diabetes.

Type 1 as well as type 2 diabetes are characterized by a loss of insulin-producing β-cells. Here the authors show that the FDA-approved drug neratinib has beneficial effects on β-cell survival, insulin secretion, and glycemic control in mouse models of diabetes.

Noninvasive longitudinal quantification of β-cell mass with [111In]-labeled exendin-4

Currently, quantifying β-cell mass (BCM) requires harvesting the pancreas. In this study, we investigated a potential noninvasive method to quantify BCM changes longitudinally using [Lys12(111In-BnDTPA-Ahx)]exendin-4 ([111In]-Ex4) and single-photon emission computed tomography (SPECT). We used autoradiography and transgenic mice expressing green fluorescent protein under the control of mouse insulin 1 gene promotor to evaluate the specificity of [111In]-Ex4 toward β cells. Using nonobese diabetic (NOD) mice, we injected [111In]-Ex4 (3.0 MBq) intravenously and performed SPECT 30 min later, repeating this at a 2-wk interval. After the second scan, we harvested the pancreas and calculated BCM from immunohistochemically stained pancreatic sections. Specific accumulation of [111In]-Ex4 in β cells was confirmed by autoradiography, with a significant correlation (r = 0.94) between the fluorescent and radioactive signal intensities. The radioactive signal from the pancreas in the second SPECT scan significantly correlated (r = 0.89) with BCM calculated from the immunostained pancreatic sections. We developed a regression formula to estimate BCM from the radioactive signals from the pancreas in SPECT scans. BCM can be quantified longitudinally and noninvasively by SPECT imaging with [111In]-Ex4. This technique successfully demonstrated longitudinal changes in BCM in NOD mice before and after onset of hyperglycemia.-Fujita, N., Fujimoto, H., Hamamatsu, K., Murakami, T., Kimura, H., Toyoda, K., Saji, H., Inagaki, N. Noninvasive longitudinal quantification of β-cell mass with [111In]-labeled exendin-4.

Time-dependent alteration to the tight junction structure of distal intestinal epithelia in type 2 prediabetic mice

AIM

High-fat diet (HFD) intake has been associated with changes in intestinal microbiota composition, increased intestinal permeability, and onset of type 2 diabetes mellitus (T2DM). The aim of this work was twofold: 1) to investigate the structural and functional alterations of the tight junction (TJ)-mediated intestinal epithelial barrier of ileum and colon, that concentrate most of the microbiota, after exposure to a HFD for 15, 30 and 60 days, and 2) to assess the effect of in vitro exposure to free fatty acids (FFAs), one of the components of HFD, on paracellular barrier of colon-derived Caco-2 cells.

METHODS/KEY FINDINGS

HFD exposure induced progressive metabolic changes in male mice that culminated in prediabetes after 60d. Morphological analysis of ileum and colon mucosa showed no signs of epithelial rupture or local inflammation but changes in the junctional content/distribution and/or cellular content of TJ-associated proteins (claudins-1, -2, -3, and occludin) in intestinal epithelia were seen mainly after a prediabetes state has been established. This impairment in TJ structure was not associated with significant changes in intestinal permeability to FITC-dextran. Exposure of Caco-2 monolayers to palmitic or linoleic acids seems to induce a reinforcement of TJ structure while treatment with oleic acid had a more diverse effect on TJ protein distribution.

SIGNIFICANCE

TJ structure in distal intestinal epithelia can be specifically impaired by HFD intake at early stage of T2DM, but not by FFAs in vitro. Since the TJ change in ileum/colon was marginal, probably it does not contribute to the disease onset.

Urinary bisphenol A concentration and glucose homeostasis in non-diabetic adults: a repeated-measures, longitudinal study

AIMS/HYPOTHESIS

Bisphenol A (BPA) has been shown to be potentially associated with type 2 diabetes; however, there is little evidence associating BPA exposure with glucose metabolic outcomes prior to diabetes onset. We aimed to examine BPA exposure in relation to glucose homeostasis among non-diabetic individuals.

METHODS

This longitudinal cohort study comprised 2336 Chinese adults aged 40 years or above (62.8% women) and free of diabetes at baseline in 2009, followed for 4 years. Urinary BPA and glucose metabolic traits including fasting plasma glucose (FPG), 2 h post-load plasma glucose, fasting serum insulin, HOMA-IR and HOMA-B were measured at baseline and follow-up. Repeated-measures analysis was performed to evaluate associations of urinary BPA concentration with markers of glucose homeostasis.

RESULTS

After full adjustment for confounders including BMI, each tenfold increase in urinary BPA concentrations was associated with a 3.39% increase in FPG (95% CI 2.24%, 4.55%) and an 11.6% decrease in HOMA-B (95% CI -15.8%, -7.18%) in women. The inverse association between urinary BPA and HOMA-B was more prominent among overweight or obese individuals (change -13.7%; 95% CI -19.3%, -7.61%) compared with those who were of normal weight (change -6.74%; 95% CI -13.2%, 0.20%) (p_interaction = 0.07). Moreover, the ORs of fasting hyperglycaemia and beta cell dysfunction corresponding to a tenfold increase in urinary BPA concentrations were 1.37 (95% CI 1.10, 1.72) and 1.30 (95% CI 1.02, 1.65) in women, respectively. No significant associations existed between urinary BPA and glucose metabolic markers in men.

CONCLUSIONS/INTERPRETATION

Our findings suggest that exposure to BPA was independently associated with impaired glucose homeostasis before the development of diabetes in middle-aged and elderly women.

Effects of dapagliflozin and/or insulin glargine on beta cell mass and hepatic steatosis in db/db mice

OBJECTIVE

To explore the beneficial effects of dapagliflozin and/or insulin glargine on the pancreatic beta cell mass and hepatic steatosis in db/db mice.

METHODS

Six-week-old db/db mice were assigned to one of four groups: untreated (Placebo), treated with dapagliflozin (Dapa), treated with insulin glargine (Gla), or treated with dapagliflozin and insulin glargine (Dapa+Gla). After 8 weeks of treatment, we determined glucose tolerance, beta cell mass, hepatic lipid content and gene expression.

RESULTS

Glucose tolerance was significantly ameliorated in the three treated groups to the same degree compared with the Placebo group. Immunohistochemical analysis revealed that the pancreatic beta cell mass was significantly maintained in the Dapa and Dapa+Gla groups, but not in the Gla group, compared with the Placebo group (Placebo 2.25 ± 1.44 mg, Dapa 5.01 ± 1.63 mg, Gla 3.79 ± 0.96 mg, Dapa+Gla 5.19 ± 1.78 mg). However, the triglyceride content of the liver was markedly elevated in the Gla group compared with that in the other three groups (Placebo 24.1 ± 11.5 mg, Dapa 30.6 ± 12.9 mg, Gla 128 ± 49.7 mg, Dapa+Gla 54.4 ± 14.1 mg per gram liver). The expression levels of genes related to fatty acid synthesis and lipid storage were significantly upregulated in the Gla group.

CONCLUSIONS

Our results showed that beta cell mass was sustained and hepatic steatosis was prevented, after 8 weeks of treatment with either dapagliflozin or dapagliflozin plus insulin glargine, but not with insulin glargine alone, in db/db mice.

Gadofullerene Nanoparticles Reverse Dysfunctions of Pancreas and Improve Hepatic Insulin Resistance for Type 2 Diabetes Mellitus Treatment

Type 2 diabetes mellitus (T2DM) has been one of the most prevalent metabolic disorders. Nonetheless, the commonly used anti-T2DM drugs failed to substant to treat T2DM when anti-T2DM was withdrawn. Here we put forward a superior and sustainable anti-diabetic strategy using intraperitoneal administration of amino-acid-functionalized gadofullerene nanoparticles (GFNPs) in db/db diabetic mice. Highly accumulated in the pancreas and liver, GFNPs could prominently decrease hyperglycemia, along with permanently maintaining normal blood sugar levels in T2DM mice and even stopping administration. Importantly, GFNPs reversed the pancreas islets dysfunctions by reducing oxidative stress and inflammation responses and fundamentally normalized the insulin secretory function of the pancreas islets. Mechanistically, GFNPs improved hepatic insulin resistance by regulating glucose and lipid metabolism through the activation of IRS2/PI3K/AKT signal pathways, resulting in inhibiting gluconeogenesis and increasing glycogenesis in the liver. Additionally, GFNPs relieved hepatic steatosis in the liver, ultimately maintaining systemic glucose and lipid metabolic homeostasis without obvious toxicity. Together, GFNPs reverse the dysfunctions of the pancreas and improve hepatic insulin resistance, providing a promising approach for T2DM treatment.

Hypoxylonol F Isolated from Annulohypoxylon annulatum Improves Insulin Secretion by Regulating Pancreatic β-cell Metabolism

Insulin plays a key role in glucose homeostasis and is hence used to treat hyperglycemia, the main characteristic of diabetes mellitus. Annulohypoxylon annulatum is an inedible ball-shaped wood-rotting fungus, and hypoxylon F is one of the major compounds of A. annulatum. The aim of this study is to evaluate the effects of hypoxylonol F isolated from A. annulatum on insulin secretion in INS-1 pancreatic β-cells and demonstrate the molecular mechanisms involved. Glucose-stimulated insulin secretion (GSIS) values were evaluated using a rat insulin ELISA kit. Moreover, the expression of proteins related to pancreatic β-cell metabolism and insulin secretion was evaluated using Western blotting. Hypoxylonol F isolated from A. annulatum was found to significantly enhance glucose-stimulated insulin secretion without inducing cytotoxicity. Additionally, hypoxylonol F enhanced insulin receptor substrate-2 (IRS-2) levels and activated the phosphatidylinositol 3-kinase/protein kinase B (PI3K/Akt) pathway. Interestingly, it also modulated the expression of peroxisome proliferator-activated receptor γ (PPARγ) and pancreatic and duodenal homeobox 1 (PDX-1). Our findings showed that A. annulatum and its bioactive compounds are capable of improving insulin secretion by pancreatic β-cells. This suggests that A. annulatum can be used as a therapeutic agent to treat diabetes.

Vascular endothelial PDPK1 plays a pivotal role in the maintenance of pancreatic beta cell mass and function in adult male mice

AIMS/HYPOTHESIS

The aim of this study was to elucidate the impact of 3'-phosphoinositide-dependent protein kinase-1 (PDPK1) in vascular endothelial cells on the maintenance of pancreatic beta cell mass and function.

METHODS

Male vascular endothelial cell-specific Pdpk1-knockout mice (Tie2^+/-/Pdpk1^flox/flox mice) and their wild-type littermates (Tie2^-/-/Pdpk1^flox/flox mice; control) were used for this study. At 12 weeks of age, an IPGTT and OGTT were conducted. Pancreatic blood flow was measured under anaesthesia. Thereafter, islet blood flow was measured by the microsphere method. Mice were killed for islet isolation and further functional study and mRNA was extracted from islets. Pancreases were sampled for immunohistochemical analyses.

RESULTS

During the IPGTT, the blood glucose level was comparable between knockout mice and control flox mice, although serum insulin level was significantly lower in knockout mice. During the OGTT, glucose tolerance deteriorated slightly in knockout mice, accompanied by a decreased serum insulin level. During an IPGTT after pre-treatment with exendin-4 (Ex-4), glucose tolerance was significantly impaired in knockout mice. In fact, glucose-stimulated insulin secretion of isolated islets from knockout mice was significantly reduced compared with control flox mice, and addition of Ex-4 revealed impaired sensitivity to incretin hormones in islets of knockout mice. In immunohistochemical analyses, both alpha and beta cell masses were significantly reduced in knockout mice. In addition, the CD31-positive area was significantly decreased in islets of knockout mice. The proportion of pimonidazole-positive islets was significantly increased in knockout mice. mRNA expression levels related to insulin biosynthesis (Ins1, Ins2, Mafa, Pdx1 and Neurod [also known as Neurod1]) and beta cell function (such as Gck and Slc2a2) were significantly decreased in islets of knockout mice. Microsphere experiments revealed remarkably reduced islet blood flow. In addition, mRNA expression levels of Hif1α (also known as Hif1a) and its downstream factors such as Adm, Eno1, Tpi1 (also known as Ets1), Hmox1 and Vegfa, were significantly increased in islets of knockout mice, indicating that islets of knockout mice were in a more hypoxic state than those of control flox mice. As a result, mRNA expression levels related to adaptive unfolded protein response and endoplasmic reticulum stress-related apoptotic genes were significantly elevated in islets of knockout mice. In addition, inflammatory cytokine levels were increased in islets of knockout mice. Electron microscopy revealed reduced endothelial fenestration and thickening of basal membrane of vascular endothelium in islets of knockout mice.

CONCLUSIONS/INTERPRETATION

Vascular endothelial PDPK1 plays an important role in the maintenance of pancreatic beta cell mass and function by maintaining vascularity of pancreas and islets and protecting them from hypoxia, hypoxia-related endoplasmic reticulum stress, inflammation and distortion of capillary structure.

Arachidonic acid-rich ARASCO oil has anti-inflammatory and antidiabetic actions against streptozotocin + high fat diet induced diabetes mellitus in Wistar rats

OBJECTIVES

The aim of this study was to investigate the effects of arachidonic acid (AA)-rich ARASCO oil on high-fat diet (HFD) + streptozotocin (STZ)-induced diabetes mellitus in male Wistar rats and its possible mechanisms of action.

METHODS

Male Wistar rats with HFD + STZ-induced diabetes were employed in the present study. ARASCO oil was administered orally for the first 7 d consecutively, followed by once weekly throughout the study (14 wk). At various time points, blood glucose and body weight and oral glucose tolerance tests were measured. At the end of the study, animals were sacrificed to collect plasma and various organs and stored at -80°C. Plasma insulin, tumor necrosis factor-α, interleukin-6, and lipoxin A4 were measured. Expression of the following genes was determined: nuclear factor-κΒ (NF-κB), cyclooxygenase-2 (COX-2), 12-lipoxygenase (12-LOX) in pancreas and lipocalin 2 (LPCLN2) in adipose tissue. Various antioxidants were measured in the plasma and other tissues. Area under the curve and insulin sensitivity index were assessed by computing homeostatic model of assessment for insulin resistance, quantitative insulin check index, Matsuda, and Belfiore indices.

RESULTS

ARASCO oil treatment decreased hyperglycemia, restored insulin sensitivity, suppressed inflammation, enhanced plasma lipoxin A4 levels, and reversed altered antioxidant status to near normal in animals with HFD + STZ-induced diabetes.

CONCLUSION

These results suggest that ARASCO, a rich source of AA, can prevent HFD + STZ-induced diabetes in Wistar rats owing to its anti-inflammatory action. It remains to be seen whether ARASCO oil is useful in preventing or postponing the development of type 2 diabetes mellitus in humans.

Amorphous solid dispersion of Berberine mitigates apoptosis via iPLA2β/Cardiolipin/Opa1 pathway in db/db mice and in Palmitate-treated MIN6 β-cells

Aims: Berberine (BBR) improves beta-cell function in Type 2 diabetes (T2D) because of its anti-apoptotic activity, and our laboratory developed a new preparation named Huang-Gui Solid Dispersion (HGSD) to improve the oral bioavailability of BBR. However, the mechanism by which BBR inhibits beta-cell apoptosis is unclear. We hypothesized that the Group VIA Ca²⁺-Independent Phospholipase A₂ (iPLA₂β)/Cardiolipin(CL)/Opa1 signaling pathway could exert a protective role in T2D by regulating beta-cell apoptosis and that HGSD could inhibit β-cell apoptosis through iPLA₂β/CL/Opa1 upregulation.

Methods: We examined how iPLA₂β and BBR regulated apoptosis and insulin secretion through CL/Opa1 in vivo and in vitro. In in vitro studies, we developed Palmitate(PA)-induced apoptotic cell death model in mouse insulinoma cells (MIN6). iPLA₂β overexpression and silencing technology were used to examine how the iPLA₂β/CL/Opa1 interaction may play an important role in BBR treatment. In in vivo studies, db/db mice were used as a diabetic animal model. The pancreatic islet function and morphology, beta-cell apoptosis and mitochondrial injury were examined to explore the effects of HGSD. The expression of iPLA₂β/CL/Opa1 was measured to explore whether the signaling pathway was damaged in T2D and was involved in HGSD treatment.

Results: The overexpression of iPLA₂β and BBR treatment significantly attenuated Palmitate- induced mitochondrial injury and apoptotic death compared with Palmitate-treated MIN6 cell. In addition, iPLA₂β silencing could simultaneously partly abolish the anti-apoptotic effect of BBR and decrease CL/Opa1 signaling in MIN6 cells. Moreover, HGSD treatment significantly decreased beta-cell apoptosis and resulted in the upregulation of iPLA₂β/CL/Opa1 compared to those of the db/db mice.

Conclusion: The results indicated that the regulation of iPLA₂β/CL/Opa1 by HGSD may prevent beta-cell apoptosis and may improve islet beta-cell function in Type 2 diabetic mice and in palmitate-treated MIN6 cells.

Exposure to Aroclor 1254 persistently suppresses the functions of pancreatic β-cells and deteriorates glucose homeostasis in male mice

Polychlorinated biphenyls (PCBs) are a class of persistent organic pollutants that have been shown to be related to the occurrence of type 2 diabetes mellitus (T2DM). Nevertheless, it is necessary to further explore the development of T2DM caused by PCBs and its underlying mechanisms. In the present study, 21-day-old C57BL/6 male mice were orally treated with Aroclor 1254 (0.5, 5, 50 or 500 μg kg^-1) once every three days. After exposure for 66 d, the mice showed impaired glucose tolerance, 13% and 14% increased fasting serum insulin levels (FSIL), and 63% and 69% increases of the pancreatic β-cell mass in the 50 and 500 μg kg^-1 groups, respectively. After stopping exposure for 90 d, treated mice returned to normoglycemia and normal FSIL. After re-exposure of these recovered mice to Aroclor 1254 for 30 d, fasting plasma glucose showed 15%, 28% and 16% increase in the 5, 50 and 500 μg kg^-1 treatments, FSIL exhibited 35%, 27%, 30% and 32% decrease in the 0.5, 5, 50 or 500 μg kg^-1 groups respectively, and there was no change in pancreatic β-cell mass. Transcription of the pancreatic insulin gene (Ins2) was significantly down-regulated in the 50 and 500 μg kg^-1 groups, while DNA-methylation levels were simultaneously increased in the Ins2 promoter during the course of exposure, recovery and re-exposure. Reduced insulin levels were initially rescued by a compensative increase in β-cell mass. However, β-cell mass eventually failed to make sufficient levels of insulin, resulting in significant increases in fasting blood glucose, and indicating the development of T2DM.

Integrated multiscale mathematical modeling of insulin secretion reveals the role of islet network integrity for proper oscillatory glucose-dose response

The integrated multiscale mathematical model we present in this paper is built on two of our previous ones: a model of electrical oscillation in β-cells connected to neighboring cells within a three-dimensional (3D) network, and a model of glucose-induced β-cell intracellular insulin granule trafficking and insulin secretion. In order to couple these two models, we assume that the rate at which primed and release-ready insulin granules fuse at the cell membrane increases with the intracellular calcium concentration. Moreover, by assuming that the fraction of free K_ATP-channels decreases with increasing glucose concentration, we take into account the effect of glucose dose on membrane potential and, indirectly via the effect on the potential, on intracellular calcium. Numerical analysis of our new model shows that a single step increase in glucose concentration yields the experimentally observed characteristic biphasic insulin release. We find that the biphasic response is typically oscillatory in nature for low and moderate glucose concentrations. The plateau fraction (the time that the β-cells spend in their active firing phase) increases with increasing glucose dose, as does the total insulin secretion. At high glucose concentrations, the oscillations tend to vanish due to a constantly elevated membrane potential of the β-cells. Our results also demonstrate how insulin secretion characteristics in various glucose protocols depend on the degree of β-cell loss, highlighting the potential impact from disease. In particular, both the secretory capacity (average insulin secretion rate per β-cell) and the oscillatory response diminish as the islet cell network becomes compromised.

Analysis of Association between Vitamin D Deficiency and Insulin Resistance

Recent evidence revealed extra skeleton activity of vitamin D, including prevention from cardiometabolic diseases and cancer development as well as anti-inflammatory properties. It is worth noting that vitamin D deficiency is very common and may be associated with the pathogenesis of insulin-resistance-related diseases, including obesity and diabetes. This review aims to provide molecular mechanisms showing how vitamin D deficiency may be involved in the insulin resistance formation. The PUBMED database and published reference lists were searched to find studies published between 1980 and 2019. It was identified that molecular action of vitamin D is involved in maintaining the normal resting levels of ROS and Ca2+, not only in pancreatic β-cells, but also in insulin responsive tissues. Both genomic and non-genomic action of vitamin D is directed towards insulin signaling. Thereby, vitamin D reduces the extent of pathologies associated with insulin resistance such as oxidative stress and inflammation. More recently, it was also shown that vitamin D prevents epigenetic alterations associated with insulin resistance and diabetes. In conclusion, vitamin D deficiency is one of the factors accelerating insulin resistance formation. The results of basic and clinical research support beneficial action of vitamin D in the reduction of insulin resistance and related pathologies.

A Positive Causal Influence of IL-18 Levels on the Risk of T2DM: A Mendelian Randomization Study

A large number of clinical studies have shown that interleukin-18 (IL-18) plasma levels are positively correlated with the pathogenesis and development of type 2 diabetes mellitus (T2DM), but it remains unclear whether IL-18 causes T2DM, primarily due to the influence of reverse causality and residual confounding factors. Genome-wide association studies have led to the discovery of numerous common variants associated with IL-18 and T2DM and opened unprecedented opportunities for investigating possible associations between genetic traits and diseases. In this study, we employed a two-sample Mendelian randomization (MR) method to analyze the causal relationships between IL-18 plasma levels and T2DM using IL18-related SNPs as genetic instrumental variables (IVs). We first selected eight SNPs that were significantly associated with IL-18 but independent of T2DM. We then used these SNPs as IVs to evaluate their effects on T2DM using the inverse-variance weighted (IVW) method. Finally, we conducted sensitivity analysis and MR-Egger regression analysis to evaluate the heterogeneity and pleiotropic effects of each variant. The results based on the IVW method demonstrate that high IL-18 plasma levels significantly increase the risk of T2DM, and no heterogeneity or pleiotropic effects appeared after the sensitivity and MR-Egger analyses.

Levels of circulating insulin cell-free DNA in women with polycystic ovary syndrome - a longitudinal cohort study

BACKGROUND

Women with Polycystic Ovary Syndrome (PCOS) present a heterogeneous reproductive and metabolic profile with an increased lifetime risk of Type 2 Diabetes (T2D). Early biomarkers of these metabolic disturbances in PCOS women have not been identified. The abundance of circulating insulin gene promotor cell-free DNA (INS cfDNA) was shown to be valuable as a predictive biomarker of β-cell death in individuals with Type 1 diabetes (T1D) as well as with gestational diabetes. Since β-cell death is common to the development of T1D as well as in T2D, we aimed to investigate if insulin-coding DNA is more abundant in circulation of PCOS women (vs Controls) and if their levels change after 6 yr. follow-up as a potential measure to predict future T2D.

METHODS

A cohort of 40 women diagnosed with PCOS according to Rotterdam 2003 criteria and eight healthy controls were examined at baseline and 6 years follow-up. Clinical measurements for evaluation of glucose homeostasis as well as blood/serum samples were obtained at each visit. Methylated and unmethylated INS cfDNA were quantified using droplet digital PCR. Differences between groups were assessed using Kruskall-Wallis test and Wilcoxon Signed rank test.

RESULTS

At baseline, there was no detectable difference in copy number (copies/μL) of methylated (p = 0.74) or unmethylated INS cfDNA (p = 0.34) between PCOS and Control groups. At follow up, neither methylated (p = 0.50) nor unmethylated INScfDNA levels (p = 0.48) differed significantly between these groups. Likewise, when pooling the groups, there was no difference between baseline and follow up, in terms of copies of methylated or unmethylated INS cfDNA (p = 0.38 and p = 0.52, respectively). There were no significant correlations between counts of unmethylated or methylated cfDNA and the clinical measurements of β-cell function and pre-diabetes.

CONCLUSION

The circulating level of unmethylated and methylated INScfDNA is similar between PCOS and Controls and cannot be used to predict islet β-cell loss and progression to Type 2 diabetes in a 6-year follow-up.

TRIAL REGISTRATION

The Danish Data Protection Agency (REG-31-2016. Approval: 01-12-2015) and by the Danish Scientific Ethical committee of Region Zealand (Journal no. SJ-525. Approval: 13-06-2016), Clinicaltrials.gov, ( NCT03142633 , registered 1. March, 2017, Retrospectively registered).

Gut microbiota disorders cause type 2 diabetes mellitus and homeostatic disturbances in gut-related metabolism in Japanese subjects

Few studies have investigated the host-microbe metabolic axis in people with type 2 diabetes mellitus (T2DM). This study aimed to determine and compare the nutrient intakes and metabolic markers and to elucidate the relationships among these factors in Japanese T2DM patients and control individuals. Fifty-nine Japanese T2DM patients and 59 matched healthy control individuals participated in this study. We examined the differences regarding the participants’ dietary habits, microbiota, and fecal short-chain fatty acids, and analyzed the relationships between the gut microbiota and blood metabolic markers in the T2DM patients and the control subjects. The T2DM patients consumed more carbohydrates, and had lower fecal propionate and butyrate concentrations, larger fecal populations of Bifidobacterium spp. and bacteria of the order Lactobacillales, and smaller fecal Bacteroides spp. populations than the control individuals. In the T2DM patients, the level of Bifidobacterium spp. correlated negatively with the carbohydrate intake and the level of bacteria of the order Lactobacillales correlated negatively with the protein intake. T2DM patients have gut dysbiosis that may contribute to disease onset and influence its prognosis. Furthermore, homeostatic disturbances in the gut-related metabolism may underlie the pathogenesis of T2DM.

Pancreatic 18F-FDG uptake is increased in type 2 diabetes patients compared to non-diabetic controls

INTRODUCTION

Increasing evidence indicates that the development of type 2 diabetes is driven by chronic low grade beta-cell inflammation. However, it is unclear whether pancreatic inflammation can be noninvasively visualized in type 2 diabetes patients. We aimed to assess pancreatic 18F-FDG uptake in type 2 diabetes patients and controls using 18F-fluorodeoxylglucose positron emission tomography/computed tomography (18F-FDG PET/CT).

MATERIAL AND METHODS

In this retrospective cross-sectional study, we enrolled 20 type 2 diabetes patients and 65 controls who had undergone a diagnostic 18F-FDG PET/CT scan and obtained standardized uptake values (SUVs) of pancreas and muscle. Pancreatic SUV was adjusted for background uptake in muscle and for fasting blood glucose concentrations.

RESULTS

The maximum pancreatic SUVs adjusted for background muscle uptake (SUVmax.m) and fasting blood glucose concentration (SUVglucose) were significantly higher in diabetes patients compared to controls (median 2.86 [IQR 2.24-4.36] compared to 2.15 [IQR 1.51-2.83], p = 0.006 and median 2.76 [IQR 1.18-4.34] compared to 1.91 [IQR 1.27-2.55], p<0.001, respectively). In linear regression adjusting for age and body mass index, diabetes remained the main predictor of SUVmax.m and SUVglucose.

CONCLUSION

Pancreatic 18F-FDG uptake adjusted for background muscle uptake and fasting blood glucose concentration was significantly increased in type 2 diabetes patients.

Effects of chronic exercise on gut microbiota and intestinal barrier in human with type 2 diabetes

BACKGROUND

Intestinal dysbiosis has been proposed as a possible contributor of the development of type 2 diabetes (T2D). Indeed, commensal fungi and opportunistic bacteria stimulate the local immune system, altering intestinal permeability with consequent leaky gut, which in turn activates systemic inflammation responsible for insulin resistance. It is also well known that chronic exercise improves glucose control and diabetes-induced damage. The aim of this study was to evaluate the role of chronic exercise on gut flora composition and leaky gut in T2D stable patients.

METHODS

Thirty clinically stable patients with T2D were studied before and after a six months program of endurance, resistance and flexibility training. Metabolic and anthropometric evaluations were carried out. Gut flora and intestinal permeability were measured in stools by selective agar culture medium and molecular biology measurements of zonulin, which is the protein that modulates enterocyte tight junctions.

RESULTS

Diabetes causes significant intestinal mycetes overgrowth, increased intestinal permeability and systemic low-grade inflammation. However, exercise improved glycemia, functional and anthropometric variables. Moreover, chronic exercise reduced intestinal mycetes overgrowth, leaky gut, and systemic inflammation. Interestingly, these variables are closely correlated.

CONCLUSIONS

Exercise controls diabetes by also modifying intestinal microbiota composition and gut barrier function. This data shows an additional mechanism of chronic exercise and suggests that improving gut flora could be an important step in tailored therapies of T2D.

The orphan nuclear receptor Nor1/Nr4a3 is a negative regulator of β-cell mass

The Nr4a subfamily of nuclear receptor comprises three members in mammalian cells: Nur77/Nr4a1, Nurr1/Nr4a2, and Nor1/Nr4a3. Nr4a proteins play key roles in the regulation of glucose homeostasis in peripheral metabolic tissues. However, their biological functions in β-cells remain relatively uncharacterized. Here we sought to investigate the potential role of Nor1 in the regulation of β-cell mass and, in particular, β-cell survival/apoptosis. We used histological analysis to examine the consequences of genetic deletion of either Nur77 and Nor1 on β-cell mass, investigated the expression patterns of Nr4as in human islets and INS cells and performed gain- and loss-of-function experiments to further characterize the role of Nor1 in β-cell apoptosis. Surprisingly, Nor1 knockout mice displayed increased β-cell mass, whereas mice with genetic deletion of Nur77 did not exhibit any significant differences compared with their WT littermates. The increase in β-cell mass in Nor1 knockout mice was accompanied by improved glucose tolerance. A gene expression study performed in both human islets and INS cells revealed that Nor1 expression is significantly increased by pro-inflammatory cytokines and, to a lesser extent, by elevated concentrations of glucose. Nor1 overexpression in both INS and human islet cells caused apoptosis, whereas siRNA-mediated Nor1 knockdown prevented cytokine-induced β-cell death. Finally, Nor1 expression was up-regulated in islets of individuals with type 2 diabetes. Altogether, our results uncover that Nor1 negatively regulates β-cell mass. Nor1 represents a promising molecular target in diabetes treatment to prevent β-cell destruction.

Suppression of free fatty acid receptor 1 expression in pancreatic β-cells in obese type 2 diabetic db/db mice: a potential role of pancreatic and duodenal homeobox factor 1

It is known that long-chain fatty acids bind to free fatty acid receptor 1 (Ffar1), also known as G protein-coupled receptor 40 (GPR40), and amplify glucose-stimulated insulin secretion (GSIS) from pancreatic β-cells and that Ffar1 agonists facilitates insulin secretion and ameliorates glycemic control. On the other hands, pancreatic and duodenal homeobox factor 1 (Pdx1) is an important transcription factor for various β-cell-related genes including insulin gene and thereby contributes to the maintenance of mature β-cell function. The aim of this study was to evaluate how Ffar1 expression in β-cells is altered under diabetic conditions. In this study, we used male obese type 2 diabetic mice and control mice. We evaluated Ffar1 and Pdx1 mRNA and protein expression levels in both mice. In addition, we examined whether Pdx1 is a possible regulator of Ffar1 expression using small interfering RNA for Pdx1 (siPdx1) in β-cell-derived cell line. As the results, Ffar1 mRNA and protein expression in β-cells were significantly lower in obese type 2 diabetic db/db mice compared to control mice which was accompanied by the decreased expression of Pdx1. In addition, down-regulation of Pdx1 expression using siPdx1 suppressed Ffar1 expression. Furthermore, adenoviral Pdx1 overexpression significantly increased Ffar1 expression. In conclusion, Ffar1 expression is markedly down-regulated under diabetic conditions which is accompanied by decreased expression of Pdx1. Furthermore, it is likely that Pdx1 is a regulator of Ffar1 expression in β-cells.

The eye as a novel imaging site in diabetes research

Diabetes develops due to deficient functional β cell mass, insulin resistance, or both. Yet, various challenges in understanding the mechanisms underlying diabetes development in vivo remain to be overcome owing to the lack of appropriate intravital imaging technologies. To meet these challenges, we have exploited the anterior chamber of the eye (ACE) as a novel imaging site to understand diabetes basics and clinics in vivo. We have developed a technology platform transplanting pancreatic islets into the ACE where they later on can be imaged non-invasively for long time. It turns out that the ACE serves as an optimal imaging site and provides implanted islets with an oxygen-rich milieu and an immune-privileged niche where they undergo optimal engraftment, rich vascularization and dense innervation, preserve organotypic features and live with satisfactory viability and functionality. The ACE technology has led to a series of significant observations. It enables in vivo microscopy of islet cytoarchitecture, function and viability in the physiological context and intravital imaging of a variety of pathological events such as autoimmune insulitis, defects in β cell function and mass and insulin resistance during diabetes development in a real-time manner. Furthermore, application of the ACE technology in humanized mice and non-human primates verifies translational and clinical values of the technology. In this article, we describe the ACE technology in detail, review accumulated knowledge gained by means of the ACE technology and delineate prospective avenues for the ACE technology.

Association of the Glycemic Fluctuation as well as Glycemic Control with the Pancreatic β-cell Function in Japanese Subjects with Type 2 Diabetes Mellitus

Objective It is important to preserve the pancreatic β-cell function in order to maintain good glycemic control for a long period. The aim of this study was to examine which factors are associated with the β-cell function in subjects with type 2 diabetes mellitus. Methods A total of 372 subjects with type 2 diabetes who had been hospitalized for the amelioration of their glycemic control and/or education about diabetes in Kawasaki Medical School Hospital were included in this study. We evaluated the remnant β-cell function as the HOMA-%β using the computer software program HOMA2 and estimated the glycemic fluctuation with the glycoalbumin (GA)/hemoglobin A1c (HbA1c) ratio. In addition, we divided the subjects into a relatively young group (<65 years old) (n=210) and an elderly group (≥65 years old) (n=162) and performed several analyses in each group. Results The GA/HbA1c ratio, GA and HbA1c were independent determinant factors for the HOMA-%β regardless of age. We obtained almost the same results even after excluding those subjects using insulin secretagogues. These data suggest that the glycemic fluctuation and glycemic control are associated with the remnant β-cell function in Japanese subjects with type 2 diabetes. Conclusion It is very important to reduce glycemic fluctuation as well as to maintain good glycemic control in order to preserve β-cell function in subjects with type 2 diabetes.

The role of Cox-2 and prostaglandin E2 receptor EP3 in pancreatic β-cell death

Elevated levels of lipids, in particular saturated fatty acids, are known to be associated with type 2 diabetes (T2D) and to have a negative effect on β-cell function and survival. We bring new evidence indicating that palmitate up-regulates cyclooxygenase-2 (COX-2) expression levels in human islets and in MIN6 β cells, and that it is elevated in islets isolated from T2D donors. Both small interfering specific cyclooxygenase-2 small interfering RNA (siRNA) or the COX-2 inhibitor celecoxib significantly inhibited apoptosis induced by palmitate. Prostaglandin E₂ (PGE₂), the predominant product of COX-2 enzymatic activity, activates membrane receptors, which are members of the GPCR-family (EP1-EP4). In the present study, elevated expression of the PGE₂ receptor subtype 3 (EP3) receptor was observed in β cells exposed to palmitate and in islets from individuals with T2D. Down-regulation of the pathway using EP3 siRNA or the specific L-798,106 antagonist markedly decreased the levels of palmitate-induced apoptosis. Altogether, our data put forward the COX-2-PGE₂-EP3 pathway as one of the mediators of palmitate-induced apoptosis in β-cells.-Amior, L., Srivastava, R., Nano, R., Bertuzzi, F., Melloul, D. The role of Cox-2 and prostaglandin E₂ receptor EP3 in pancreatic β-cell death.

Insight into miRNAs related with glucometabolic disorder

A microRNA (miRNA) is a single-stranded, small and non-coding RNA molecule that contains 20-25 nucleotides. More than 2000 miRNAs have been identified in human genes since the first miRNA was discovered in Caenorhabditis elegans in the early 1990s. miRNAs play a crucial role in various biological processes by regulating gene expression through post-transcriptional mechanisms. The alterations of their levels are associated with various diseases, such as glucometabolic disorder and lipid metabolism disorder. In recent years, miRNAs have been proved to be involved in regulating the functions of pancreatic β-cells, insulin resistance and other biological behaviors related to glucometabolic disorder and the pathogenesis of diabetes mellitus (DM). This review summarized specific miRNAs, including miRNA-375 (miR-375), miRNA-155 (miR-155), miRNA-21 (miR-21), miRNA-33 (miR-33), the let-7 family and some other miRNAs related to glucometabolic regulation, introduced the obstacles and challenges in miRNA therapy, and discussed the prospect of new treatment methods for glucometabolic disorder.

Pancreatic β-Cell Rest Replenishes Insulin Secretory Capacity and Attenuates Diabetes in an Extreme Model of Obese Type 2 Diabetes

The onset of common obesity-linked type 2 diabetes (T2D) is marked by exhaustive failure of pancreatic β-cell functional mass to compensate for insulin resistance and increased metabolic demand, leading to uncontrolled hyperglycemia. Here, the β-cell-deficient obese hyperglycemic/hyperinsulinemic KS db/db mouse model was used to assess consequential effects on β-cell functional recovery by lowering glucose homeostasis and/or improving insulin sensitivity after treatment with thiazolidinedione therapy or glucagon-like peptide 1 receptor agonism alone or in combination with sodium/glucose cotransporter 2 inhibition (SGLT-2i). SGLT-2i combination therapies improved glucose homeostasis, independent of changes in body weight, resulting in a synergistic increase in pancreatic insulin content marked by significant recovery of the β-cell mature insulin secretory population but with limited changes in β-cell mass and no indication of β-cell dedifferentiation. Restoration of β-cell insulin secretory capacity also restored biphasic insulin secretion. These data emphasize that by therapeutically alleviating the demand for insulin in vivo, irrespective of weight loss, endogenous β-cells recover significant function that can contribute to attenuating diabetes. Thus, this study provides evidence that alleviation of metabolic demand on the β-cell, rather than targeting the β-cell itself, could be effective in delaying the progression of T2D.

Single-cell gene expression analysis reveals β-cell dysfunction and deficit mechanisms in type 2 diabetes

BACKGROUND

Type 2 diabetes (T2D) is one of the most common chronic diseases. Studies on T2D are mainly built upon bulk-cell data analysis, which measures the average gene expression levels for a population of cells and cannot capture the inter-cell heterogeneity. The single-cell RNA-sequencing technology can provide additional information about the molecular mechanisms of T2D at single-cell level.

RESULTS

In this work, we analyze three datasets of single-cell transcriptomes to reveal β-cell dysfunction and deficit mechanisms in T2D. Focused on the expression levels of key genes, we conduct discrimination of healthy and T2D β-cells using five machine learning classifiers, and extracted major influential factors by calculating correlation coefficients and mutual information. Our analysis shows that T2D β-cells are normal in insulin gene expression in the scenario of low cellular stress (especially oxidative stress), but appear dysfunctional under the circumstances of high cellular stress. Remarkably, oxidative stress plays an important role in affecting the expression of insulin gene. In addition, by analyzing the genes related to apoptosis, we found that the TNFR1-, BAX-, CAPN1- and CAPN2-dependent pathways may be crucial for β-cell apoptosis in T2D. Finally, personalized analysis indicates cell heterogeneity and individual-specific insulin gene expression.

CONCLUSIONS

Oxidative stress is an important influential factor on insulin gene expression in T2D. Based on the uncovered mechanism of β-cell dysfunction and deficit, targeting key genes in the apoptosis pathway along with alleviating oxidative stress could be a potential treatment strategy for T2D.