Search

Within the islets of Langerhans, beta cells orchestrate synchronized insulin secretion, a pivotal aspect of metabolic homeostasis. Despite the inherent heterogeneity and multimodal activity of individual cells, intercellular coupling acts as a homogenizing force, enabling coordinated responses through the propagation of intercellular waves. Disruptions in this coordination are implicated in irregular insulin secretion, a hallmark of diabetes. Recently, innovative approaches, such as integrating multicellular calcium imaging with network analysis, have emerged for a quantitative assessment of the cellular activity in islets. However, different groups use distinct experimental preparations, microscopic techniques, apply different methods to process the measured signals and use various methods to derive functional connectivity patterns. This makes comparisons between findings and their integration into a bigger picture difficult and has led to disputes in functional connectivity interpretations. To address these issues, we present here a systematic analysis of how different approaches influence the network representation of islet activity. Our findings show that the choice of methods used to construct networks is not crucial, although care is needed when combining data from different islets. Conversely, the conclusions drawn from network analysis can be heavily affected by the pre-processing of the time series, the type of the oscillatory component in the signals, and by the experimental preparation. Our tutorial-like investigation aims to resolve interpretational issues, reconcile conflicting views, advance functional implications, and encourage researchers to adopt connectivity analysis. As we conclude, we outline challenges for future research, emphasizing the broader applicability of our conclusions to other tissues exhibiting complex multicellular dynamics.

Actin mediates insulin secretion in pancreatic β-cells through remodeling. Hampered by limited resolution, previous studies have offered an ambiguous depiction as depolymerization and repolymerization. We report the in situ structure of actin remodeling in INS-1E β-cells during glucose-stimulated insulin secretion at nanoscale resolution. After remodeling, the actin filament network at the cell periphery exhibits three marked differences: 12% of actin filaments reorient quasi-orthogonally to the ventral membrane; the filament network mainly remains as cell-stabilizing bundles but partially reconfigures into a less compact arrangement; actin filaments anchored to the ventral membrane reorganize from a netlike to a blooming architecture. Furthermore, the density of actin filaments and microtubules around insulin secretory granules decreases, while actin filaments and microtubules become more densely packed. The actin filament network after remodeling potentially precedes the transport and release of insulin secretory granules. These findings advance our understanding of actin remodeling and its role in glucose-stimulated insulin secretion.

ABSTRACT We report case details of a morbidly obese patient with type 2 diabetes mellitus (T2DM) who became a failure of diabetes remission after laparoscopic sleeve gastrectomy (LSG). He had a marked improvement of hyperglycemia after the revision surgery using Roux‐en‐Y gastric bypass (RYGB), where passage failure of a solid food intake at the gastric angle portion disappeared after the revision surgery. Interestingly, he showed improvements of insulin and a marked glicentin secretions with minor changes in glucagon related peptide 1 (GLP‐1) and glucose‐dependent insulinotropic polypeptide (GIP) secretions in the oral glucose tolerance test OGTT after the RYGB surgery compared with post‐LSG. Although a marked increase in glucose‐induced glicentin secretion after RYGB surgery with increased insulin secretion, further studies are needed to confirm if the increased glicentin secretion after RYGB surgery is linked to stimulation of insulin secretion. [ABSTRACT FROM AUTHOR]

CD59 is a cell‐surface inhibitor of the terminal step in the complement cascade. However, in addition to its complement inhibitory function, a non‐canonical role of CD59 in pancreatic beta cells has been identified. Two recently discovered intracellular alternative splice forms of CD59, IRIS‐1 and IRIS‐2, are involved in insulin exocytosis through interactions with SNARE‐complex components. In mice, the CD59 gene has undergone duplication and to further explore the role of CD59 in insulin secretion, blood glucose homeostasis was studied in a CD59 double knockout (CD59abKO) mouse model. However, no phenotypic deviation related to insulin secretion or blood glucose homeostasis was observed for the CD59abKO mice. Instead, a CD59ba hybrid transcript formed as a consequence of the mutation induced to generate the model was identified. This hybrid transcript is expressed in pancreatic islets of the CD59abKO mice and is comprised of the remaining exons of the two CD59 genes spliced together. Similar to canonical CD59, the CD59ba hybrid was found to be glycosylated and present on the cell surface when exogenously expressed in INS‐1 832/13 cells. Furthermore, INS‐1 832/13 cells over‐expressing the mouse CD59ba hybrid retained normal insulin secretion following siRNA‐mediated knockdown of canonical CD59. Hence, although the CD59ba hybrid has lost the complement inhibitory function, the intracellular insulin secretory function remains. These results provide further information concerning the structural requirements of CD59 in its intracellular role relative to its role as a complement inhibitor. It also highlights the importance of carefully assessing plausible consequences of induced mutations in research models. [ABSTRACT FROM AUTHOR]

To be clinically efficient, beta cell replacement therapies such as pig islet xenotransplantation must ensure sufficient insulin secretion from grafted islets. While protection from host immune reaction is essential for islet engraftment and their subsequent functioning, intrinsic physiological properties of used cells are also a key factor. We have previously shown that islets with adenoviral-mediated expression of a dipeptidyl peptidase-resistant form of glucagon-like- peptide- 1 (GLP-1) and a constitutively activated form of type 3 muscarinic receptor (M3R) in their beta cells have greatly improved insulin secretory response to glucose stimulation that is otherwise 4 to 10 times lower than human islets. Here, we describe in vitro characterization of the secretory function of pancreatic islets, derived from transgenic pigs expressing the GLP-1M3R cassette under the porcine insulin promoter (InsGLP-1M3R), and their usage to treat insulin-dependent diabetes in an immunodeficient mouse model. Our results show that InsGLP-1M3R islets isolated from neonatal and adult pigs secrete up to 15-fold more insulin in response to glucose stimulation compared to wild-type (WT) islets. They also proved to be more efficient in treating diabetes in a preclinical model as shown by a significantly higher percentage of normoglycemic recipients and higher porcine C-peptide levels up to 9 mo post implantation. [ABSTRACT FROM AUTHOR]

Glucose-stimulated insulin secretion (GSIS) from pancreatic beta cells is a principal mechanism for systemic glucose homeostasis, of which regulatory mechanisms are still unclear. Here we show that kinesin molecular motor KIF5B is essential for GSIS through maintaining the voltage-gated calcium channel CaV1.2 levels, by facilitating an Hsp70-to-Hsp90 chaperone exchange to pass through the quality control in the endoplasmic reticulum (ER). Phenotypic analyses of KIF5B conditional knockout (cKO) mouse beta cells revealed significant abolishment of glucose-stimulated calcium transients, which altered the behaviors of insulin granules via abnormally stabilized cortical F-actin. KIF5B and Hsp90 colocalize to microdroplets on ER sheets, where CaV1.2 but not Kir6.2 is accumulated. In the absence of KIF5B, CaV1.2 fails to be transferred from Hsp70 to Hsp90 via STIP1, and is likely degraded via the proteasomal pathway. KIF5B and Hsc70 overexpression increased CaV1.2 expression via enhancing its chaperone binding. Thus, ER sheets may serve as the place of KIF5B- and Hsp90-dependent chaperone exchange, which predominantly facilitates CaV1.2 production in beta cells and properly enterprises GSIS against diabetes. Synopsis: The kinesin-1 molecular motor KIF5B maintains the levels of CaV1.2, a channel that is essential for insulin secretion in pancreatic beta cells. KIF5B drives chaperone exchange of de novo synthesized proteins on ER sheets, which may contribute to the effective folding of CaV1.2 protein. KIF5B prevents diabetes via maintaining glucose-stimulated insulin secretion. KIF5B regulates Ca2+-dependent actin remodeling and insulin granule dynamics. KIF5B enhances glucose-stimulated Ca2+ transients generated by CaV1.2 channel. KIF5B drives Hsp70/90 chaperone exchange required for proper folding of CaV1.2 in the ER. The kinesin-1 molecular motor KIF5B maintains the levels of CaV1.2, a channel that is essential for insulin secretion in pancreatic beta cells. KIF5B drives chaperone exchange of de novo synthesized proteins on ER sheets, which may contribute to the effective folding of CaV1.2 protein. [ABSTRACT FROM AUTHOR]

Background: For ages, botanical medicine has been used in the treatment of diabetes mellitus (DM). Notoginsenoside R1 (NGR1), a Panax notoginseng (Burkill) F.H.Chen metabolite, has been documented to possess antidiabetic action in vivo. However, its precise molecular mechanism of action is not clear. Objectives: We evaluated NGR1's effects on blood glucose in vivo and then evaluated in vitro whether NGR1 has effects on insulin secretion and the probable molecular pathways involved in NGR1-induced insulin secretion. Methods: Diabetes was induced in mice by streptozotocin. Glucose tolerance test was performed before and after NGR1 was administered intraperitoneally to diabetic animals for 4 weeks. Static and perifusion experiments were performed using isolated female BALB/c mouse islets. Preproinsulin (Ins) mRNA expression was measured using q-PCR. Protein expression of PI3K/Akt pathway was assessed using the fully automated Wes™ capillary-based protein electrophoresis. Results: Treatment of diabetic mice with NGR1 improved their glucose intolerance. In vitro , NGR1 increased insulin secretion in a concentration-dependent manner. NGR1 initiated the secretion of insulin at 2 mM glucose and augmented glucose-stimulated insulin secretion which was sustained throughout NGR1 perifusion. NGR1-induced insulin secretion was not altered by a voltage gated calcium channel blocker or protein kinase A inhibitor. NGR1 did not significantly modulate Ins mRNA expression. However, NGR1 significantly increased the levels of phospho-Akt and phopho-p-85. Conclusion: In conclusion, this study has shown that NGR1 ameliorates hyperglycemia in diabetic mice. NGR1 has a direct insulin secretagogue activity on mouse islets, stimulates insulin secretion at both basal and postprandial glucose concentrations, and activates PI3K/Akt pathway to induce insulin secretion. These results suggest that NGR1 may provide an alternative therapy to manage DM. [ABSTRACT FROM AUTHOR]

Exosomes are extracellular vesicles that play a role in intercellular communication through the transportation of their cargo including mRNAs, microRNAs, proteins, and nucleic acids. Exosomes can also regulate glucose homeostasis and insulin secretion under diabetic conditions. However, the role of exosomes in insulin secretion in islet β-cells under physiological conditions remains to be clarified. The aim of this study was to investigate whether exosomes derived from pancreatic islet β-cells could affect insulin secretion in naïve β-cells. We first confirmed that exosomes derived from the RIN-m5f β-cell line interfered with the glucose-stimulated insulin secretion (GSIS) of recipient β-cells without affecting cell viability. The exosomes significantly reduced the protein expression levels of phosphorylated Akt, phosphorylated GSK3α/β, CaMKII, and GLUT2 (insulin-related signaling molecules), and they increased the protein expression levels of phosphorylated NFκB-p65 and Cox-2 (inflammation-related signaling molecules), as determined by a Western blot analysis. A bioinformatics analysis of Next-Generation Sequencing data suggested that exosome-carried microRNAs, such as miR-1224, -122-5p, -133a-3p, -10b-5p, and -423-5p, may affect GSIS in recipient β-cells. Taken together, these findings suggest that β-cell-derived exosomes may upregulate exosomal microRNA-associated signals to dysregulate glucose-stimulated insulin secretion in naïve β-cells. [ABSTRACT FROM AUTHOR]

Abnormal glucose metabolism is a common disease of the endocrine system. The effects of drugs on glucose metabolism have been reported frequently in recent years, and since abnormal glucose metabolism increases the risk of microvascular and macrovascular complications, metabolic disorders, and infection, clinicians need to pay close attention to these effects. A variety of common drugs can affect glucose metabolism and have different mechanisms of action. Hypertension is a common chronic cardiovascular disease that requires long‐term medication. Studies have shown that various antihypertensive drugs also have an impact on glucose metabolism. Among them, α‐receptor blockers, angiotensin‐converting enzyme inhibitors, angiotensin receptor blockers, and calcium channel blockers can improve insulin resistance, while β‐receptor blockers, thiazides and loop diuretics can impair glucose metabolism. The aim of this review was to discuss the mechanisms underlying the effects of various antihypertensive drugs on glucose metabolism in order to provide reference information for rational clinical drug use. [ABSTRACT FROM AUTHOR]

SNAP25 plays an essential role in the glucose‐stimulated insulin secretion (GSIS) of pancreatic β‐cells. Carbohydrate response element‐binding protein (ChREBP) is an important transcription factor in β‐cells and, in this study, we aimed to explore whether ChREBP regulates SNAP25 expression in β‐cells. We show that diabetic Goto‐Kakizaki (GK) rats exhibited impaired insulin secretion and hyperglycemia, along with decreased SNAP25 expression and ChREBP phosphorylation in islets. SNAP25 knockdown decreased GSIS in β‐cells, while SNAP25 overexpression increased GSIS in β‐cells. Activation or overexpression of ChREBP led to reduced SNAP25 expression and subsequent suppression of GSIS. Conversely, ChREBP knockdown mitigated the reduction in SNAP25 expression caused by high glucose. Mechanistically, the activation of ChREBP by high glucose increased its occupancy and decreased the level of H3K4me3 at the Snap25 promoter. Our findings reveal the novel regulatory mechanisms of SNAP25 expression in β‐cells and suggest that SNAP25 may be involved in the regulation of β‐cell secretory function controlled by ChREBP. [ABSTRACT FROM AUTHOR]

A central aspect of type 2 diabetes is decreased functional β-cell mass. The orphan nuclear receptor Nr4α1 is critical for fuel utilization, but little is known regarding its regulation and function in the β-cell. Nr4α1 expression is decreased in type 2 diabetes rodent β-cells and type 2 diabetes patient islets. We have shown that Nr4α1-deficient mice have reduced β-cell mass and that Nr4α1 knockdown impairs glucose-stimulated insulin secretion (GSIS) in INS-1 832/13 β-cells. Here, we demonstrate that glucose concentration directly regulates b-cell Nr4α1 expression. We show that 11 mM glucose increases Nr4a1 expression in INS-1 832/13 β-cells and primary mouse islets. We show that glucose functions through the cAMP/PKA/CREB pathway to regulate Nr4α1 mRNA and protein expression. Using Nr4α1-/- animals, we show that Nr4α1 is necessary for GSIS and systemic glucose handling. Using RNA-seq, we define Nr4α1-regulated pathways in response to glucose in the mouse islet, including Glut2 expression. Our data suggest that Nr4α1 plays a critical role in the β-cells response to the fed state. [ABSTRACT FROM AUTHOR]

G6PC2 encodes a glucose-6-phosphatase catalytic subunit that opposes the action of glucokinase in pancreatic islets, thereby modulating the sensitivity of insulin and glucagon secretion to glucose. In mice, G6pc2 is expressed at ~20-fold higher levels in ß-cells than in a-cells, whereas in humans G6PC2 is expressed at only ~5-fold higher levels in ß-cells. We therefore hypothesize that G6PC2 likely influences glucagon secretion to a greater degree in humans. With a view to generating a humanized mouse that recapitulates augmented G6PC2 expression levels in a-cells, we sought to identify the genomic regions that confer differential mouse G6pc2 expression in a-cells versus ß-cells as well as the evolutionary changes that have altered this ratio in humans. Studies in islet-derived cell lines suggest that the elevated G6pc2 expression in mouse ß-cells versus a-cells is mainly due to a difference in the relative activity of the proximal G6pc2 promoter in these cell types. Similarly, the smaller difference in G6PC2 expression between a-cells and ß-cells in humans is potentially explained by a change in relative proximal G6PC2 promoter activity. However, we show that both glucocorticoid levels and multiple differences in the relative activity of eight transcriptional enhancers between mice and humans likely contribute to differential G6PC2 expression. Finally, we show that a mouse-specific non-coding RNA, Gm13613, whose expression is controlled by G6pc2 enhancer I, does not regulate G6pc2 expression, indicating that altered expression of Gm13613 in a humanized mouse that contains both the human promoter and enhancers should not affect G6PC2 function. [ABSTRACT FROM AUTHOR]

• Chronic pancreatitis is the most frequent cause of diabetes secondary to pancreatic disease. • Alterations in insulin secretion can only be detected by comparisons within the same glucose tolerance range. • Chronic pancreatitis does not induce specific alterations of insulin secretion. • Diabetes with chronic pancreatitis presents a reduced functional beta-cell mass. Chronic pancreatitis (CP) is – along with acute pancreatitis - the most frequent cause of diabetes of the exocrine pancreas (DEP). Although insulin deficiency is widely accepted as the major feature of DEP, it is still unclear whether diabetes associated with CP is characterized by additional or different functional defects of the insulin secretory machinery. To identify possible functional defects specifically induced by CP, we performed a cross-sectional study in individuals with normal glucose tolerance (NGT), impaired glucose tolerance (IGT) and diabetes mellitus (DM) comparing patients with and without CP (CP vs. NCP). We administered an oral glucose tolerance test (OGTT) to all participants and, according to their glucose tolerance, classified them as NGT, IGT and DM. Insulin sensitivity and beta-cell functional parameters were derived from OGTT, hyperglycemic clamp and hyperinsulinemic euglycemic clamp. Studying 146 subjects, we found that beta-cell function and insulin secretion were significantly lower in CP compared to NCP patients. However, when we classified the subjects according to OGTT-derived glucose tolerance, we found no differences in beta-cell function or in insulin sensitivity between CP and NCP with the same glucose tolerance status. Of note, we found that arginine-stimulated insulin secretion is reduced only in subjects with CP and DM compared to NCP subjects with DM. Patients with CP had no specific alterations in insulin secretion and beta-cell function. However, in patients diagnosed with diabetes, we found a lower arginine-stimulated insulin secretion, a marker of reduced functional mass. [Display omitted] [ABSTRACT FROM AUTHOR]

Aim: The relative contributions of insulin secretory defects and possible additional contribution of insulin resistance for the development of cystic fibrosis (CF)‐related diabetes (CFRD) are poorly understood. We aimed to (a) determine which indices of insulin resistance predict progression to CFRD, and (b) to model the relative contributions of insulin secretory function and insulin resistance to predict the risk of CFRD. Materials and Methods: Three hundred and three individuals living with CF underwent a 2‐h oral glucose tolerance test with blood sampling every 30 min at 12–24‐month intervals until they developed CFRD or until the end of follow‐up (up to 15 years). Indices of insulin resistance (e.g. Stumvoll) and insulin secretion were calculated from oral glucose tolerance test glucose and insulin measurements. CFRD‐free survival was assessed by survival analysis. Results: Estimated insulin resistance showed associations with glucose homeostasis and risk of progression to CFRD. The CFRD‐free survival was significantly different between quartiles of insulin resistance (p < 0.0001). When patients were subdivided according to both insulin resistance and insulin secretion (insulinogenic index), CFRD‐free survival was significantly lower in those with combined lowest insulin secretion and highest insulin resistance (Stumvoll) indices (hazard ratio: 11.2; p < 0.0001). There was no significant difference when the same analysis was performed for the nine other indices. Conclusions: Insulin resistance is correlated with glucose homeostasis and the risk of progression to CFRD. Patients combining low insulin secretion and high insulin resistance had the greatest odds of developing CFRD over a 15‐year period. [ABSTRACT FROM AUTHOR]

Aim: To assess the direct effect of intensive glycaemic control on periodontal tissues in patients with diabetes mellitus. Materials and Methods: Twenty‐nine patients with type 2 diabetes were enrolled and hospitalized to receive a 2‐week intensive glycaemic control regimen. We observed and analysed the systemic and oral disease indicators before and after treatment and clarified the indicators related to periodontal inflammation. Results: A significant reduction in glycaemic and periodontal parameters, including glycated albumin levels and periodontal inflamed surface area (PISA), was observed after treatment. The changes in PISA per tooth, indicative of periodontal healing, exhibited a bimodal distribution; the patients were divided into two groups on this basis. Correlations were observed between the changes in PISA per tooth and fasting plasma glucose, acetoacetic acid, and beta‐hydroxybutyrate levels in the PISA‐improved group. Significantly lower levels of C‐peptide, coefficient of variation of R‐R interval, and ankle‐brachial pressure index were observed before treatment in the PISA non‐improved group. Conclusions: Glycaemic control treatment can effectively improve periodontitis in patients with type 2 diabetes, even in the absence of specific periodontal treatments. However, the periodontal responsiveness to glycaemic control treatment depends on the systemic condition of the patient. [ABSTRACT FROM AUTHOR]

Aim: To investigate the effect of G protein‐coupled receptor 55 (GPR55) deletion on glucose homeostasis and islet function following diet‐induced obesity. Methods: GPR55−/− and wild‐type (WT) mice were fed ad libitum either standard chow (SC) or a high‐fat diet (HFD) for 20 weeks. Glucose and insulin tolerance tests were performed at 9/10 and 19/20 weeks of dietary intervention. Insulin secretion in vivo and dynamic insulin secretion following perifusion of isolated islets were also determined, as were islet caspase‐3/7 activities and β‐cell 5‐bromo‐20‐deoxyuridine (BrdU) incorporation. Results: GPR55−/− mice fed a HFD were more susceptible to diet‐induced obesity and were more glucose intolerant and insulin resistant than WT mice maintained on a HFD. Islets isolated from HFD‐fed GPR55−/− mice showed impaired glucose‐ and pcacahorbol 12‐myristate 13‐acetate‐stimulated insulin secretion, and they also displayed increased cytokine‐induced apoptosis. While there was a 5.6 ± 1.6‐fold increase in β‐cell BrdU incorporation in the pancreases of WT mice fed a HFD, this compensatory increase in β‐cell proliferation in response to the HFD was attenuated in GPR55−/− mice. Conclusions: Under conditions of diet‐induced obesity, GPR55−/− mice show impaired glucose handling, which is associated with reduced insulin secretory capacity, increased islet cell apoptosis and insufficient compensatory increases in β‐cell proliferation. These observations support that GPR55 plays an important role in positively regulating islet function. [ABSTRACT FROM AUTHOR]

Diseases in which genetic factors contribute to nearly 100% of the causation by single-gene mutations are referred to as monogenic disorders or Mendelian genetic diseases. These include neonatal diabetes mellitus (NDM), presenting within the first six months of life, maturity-onset diabetes of the young (MODY), developing later in childhood or adolescence, mitochondrial diabetes (MIDD), and insulin-resistant disorders, etc. On the other hand, common lifestyle-related diseases such as type 2 diabetes (T2DM), hypertension and dyslipidemia are multifactorial, emerging through complex interplay of genetic and environmental factors. The identification of causative genes for diabetes resulting from single-gene abnormalities not only unveils previously unknown mechanisms of insulin secretion and sensitivity at the molecular level but also reveals novel targets for drug development. Moreover, monogenic diabetes in which insulin secretion is impaired serve to clarify the pathophysiology and suggest therapeutic targets for the common multifactorial type 2 diabetes mellitus prevalent in the Japanese population, which is characterized by impaired insulin secretion. In this study, we characterize the various monogenic subtypes of diabetes so far identified. [ABSTRACT FROM AUTHOR]

Aims/hypothesis: The aim of this study was to investigate insulin secretion, insulin sensitivity, disposition index and insulin clearance by glucose tolerance status in individuals with cystic fibrosis (CF) and exocrine pancreatic insufficiency. Methods: In a cross-sectional study, we conducted an extended (ten samples) OGTT in individuals with pancreatic-insufficient CF (PI-CF). Participants were divided into normal glucose tolerance (NGT), early glucose intolerance (EGI), impaired glucose tolerance (IGT) and CF-related diabetes (CFRD) groups. We used three different oral minimal models to assess insulin secretion, insulin sensitivity and insulin clearance during the OGTT. We evaluated insulin secretion using total secretion (Φ total), first-phase secretion (Φ dynamic) and second-phase secretion (Φ static) from the model, and we estimated the disposition index by multiplying Φ total and insulin sensitivity. Results: Among 61 participants (NGT 21%, EGI 33%, IGT 16%, CFRD 30%), insulin secretion indices (Φ total, dynamic and static) were significantly lower in the CFRD group compared with the other groups. Insulin sensitivity declined with worsening in glucose tolerance (p value for trend <0.001) and the disposition index declined between NGT and EGI and between IGT and CFRD. Those with CFRD had elevated insulin clearance compared with NGT (p=0.019) and low insulin secretion (Φ total) was also associated with high insulin clearance (p<0.001). Conclusions/interpretation: In individuals with PI-CF, disposition index declined with incremental impairment in glucose tolerance due to a reduction in both insulin secretion and insulin sensitivity. Moreover in CF, reduced insulin secretion was associated with higher insulin clearance. [ABSTRACT FROM AUTHOR]

Background and Purpose Experimental Approach Key Results Conclusion and Implications The pharmacology of flavonoids on β‐cell function is largely undefined especially in the context of defective secretion of insulin. We sought to identify flavonoids that increased the insulin‐secreting function of β‐cells and to explore the underlying mechanisms.INS‐1 β‐cells in culture and islets of Langerhans isolated from control and diabetic male rats were used for insulin secretion experiments. Pharmacological and electrophysiological approaches were used for mechanistic studies.Among a set of flavonoids, exposure of INS‐1 β‐cells to resokaempferol (ResoK) enhanced glucose‐stimulated insulin secretion and therefore we further characterised its activity and its pharmacological mechanism. ResoK glucose‐dependently enhanced insulin secretion in INS‐1 β‐cells and pancreatic islets isolated from rats. Mechanistically, whole cell patch clamp recordings in INS‐1 cells showed that ResoK rapidly and dose‐dependently enhanced the L‐type Ca2+ current whereas it was inactive towards T‐type Ca2+ current. Accordingly, pharmacological inhibition of L‐type Ca2+ current but not T‐type Ca2+ current blocked the effects of ResoK on glucose‐stimulated insulin secretion. ResoK was still active on dysfunctional β‐cells as it ameliorated glucose‐stimulated insulin secretion in glucotoxicity‐induced dysfunctional INS‐1 cells and in pancreatic islets isolated from diabetic rats.ResoK is a glucose‐dependent activator of insulin secretion. Our results indicated that the effects of ResoK on insulin secretion involved its capacity to stimulate L‐type Ca2+ currents in cultured β‐cells. As ResoK was also effective on dysfunctional β‐cells, our work provides a new approach to stimulating insulin secretion, using compounds based on the structure of ResoK. [ABSTRACT FROM AUTHOR]

Background: This case report explores the long-term dynamics of insulin secretion and glycemic control in two patients with diabetes mellitus type 2 over 20 years. The observations underscore the impact of lifestyle interventions, including weight loss and calorie restriction, on insulin secretion patterns and glucose levels during 75 g oral glucose tolerance tests. Additionally, the role of hemoglobin A1c fluctuations, influenced by various factors such as body weight, exercise, and pharmacological interventions, is investigated. Case presentation: Case 1 involves a Japanese woman now in her late 70s who successfully maintained her hemoglobin A1c below 7% for over two decades through sustained weight loss and lifestyle changes. Despite a gradual decline in the homeostasis model assessment of β cell function, the patient exhibited remarkable preservation of insulin secretion patterns over the 20-year follow-up. In case 2, a Japanese woman, now in her early 70s, experienced an improvement in hemoglobin A1c to 6.3% after a period of calorie limitation due to a wrist fracture in 2018. This incident seemed to trigger a temporary rescue of pancreatic β cell function, emphasizing the dynamic nature of insulin secretion. Both cases highlight the potential for pancreatic β cell rescue and underscore the persistence of insulin secretion over the 20-year follow-up. Additionally, we have briefly discussed three additional cases with follow-ups ranging from 10 to 17 years, demonstrating similar trends in glucose and insulin ratios. Conclusions: Long-term lifestyle interventions, such as weight loss and calorie restriction, can preserve pancreatic β cell function and maintain glycemic control in type 2 diabetes patients over 20 years. Two patients showed stable or improved insulin secretion and favorable hemoglobin A1c levels, challenging the traditional view of irreversible β cell decline. The findings highlight the importance of personalized, nonpharmacological approaches, suggesting that sustained lifestyle changes can significantly impact diabetes management and potentially rescue β cell function. [ABSTRACT FROM AUTHOR]

Type 1 diabetes recipients of intrahepatic islet transplantation exhibit glucose-dependent suppression of insulin and activation of glucagon secretion in response to insulin-induced hypoglycemia associated with clinical protection from hypoglycemia. Whether sympathetic activation of adrenergic receptors on transplanted islets is required for these responses in defense against hypoglycemia is not known. To evaluate the adrenergic contribution to posttransplant glucose counterregulation, we performed a randomized, double-blind crossover study of responses during a hyperinsulinemic euglycemic-hypoglycemic clamp under phentolamine (α-adrenergic blockage), propranolol (β-adrenergic blockage), or placebo infusion. Characteristics of participants (5 females/4 males) were as follows: median (range) age 53 (34–63) yr, diabetes duration 29 (18–56) yr, posttransplant 7.0 (1.9–8.4) yr, HbA1c 5.8 (4.5–6.8)%, insulin in-/dependent 5/4, all on tacrolimus-based immunosuppression. During the clamp, blood pressure was lower with phentolamine and heart rate was lower with propranolol versus placebo (P < 0.05). There was no difference in the suppression of endogenous insulin secretion (derived from C-peptide measurements) during the euglycemic or hypoglycemic phases, and although levels of glucagon were similar with phentolamine or propranolol vs. placebo, the increase in glucagon from eu- to hypoglycemia was greater with propranolol vs. placebo (P < 0.05). Pancreatic polypeptide was greater with phentolamine versus placebo during the euglycemic phase (P < 0.05), and free fatty acids were lower and the glucose infusion rate was higher with propranolol versus placebo during the hypoglycemic phase (P < 0.05 for both). These results indicate that neither physiological α- nor β-adrenergic blockade attenuates transplanted islet responses to hypoglycemia, suggesting sympathetic reinnervation of the islet graft is not necessary for posttransplant glucose counterregulation. NEW & NOTEWORTHY: Whether adrenergic input to islets is necessary for glucose homeostasis in humans is debated. Here, the adrenergic contribution to intrahepatically transplanted islet cell responses to hypoglycemia in individuals with type 1 diabetes was investigated through α- or β-adrenergic receptor blockade during hyperinsulinemic euglycemic-hypoglycemic clamps. Neither α- nor β-adrenergic blockage affected the suppression of endogenous insulin or activation of glucagon secretion, suggesting that sympathetic reinnervation of islet grafts is not required for posttransplant defense against hypoglycemia. [ABSTRACT FROM AUTHOR]

Aims: To investigate the effects of the selective serotonin reuptake inhibitors (SSRIs) sertraline and paroxetine at therapeutically relevant concentrations on beta‐cell mass and function. Methods: Viability was quantified in mouse insulinoma (MIN6) beta cells and mouse islets after 48‐h exposure to sertraline (1–10 μM) or paroxetine (0.01–1 μM) using the Trypan blue exclusion test. The effects of therapeutic concentrations of these SSRIs on insulin secretion were determined by static incubation and perifusion experiments, while islet apoptosis was investigated by Caspase‐Glo 3/7 assay, TUNEL staining and quantitative PCR analysis. Finally, proliferation of MIN6 and mouse islet beta cells was assessed by bromodeoxyuridine (BrdU) enzyme‐linked immunosorbent assay and immunofluorescence. Results: Sertraline (0.1–1 μM) and paroxetine (0.01–0.1 μM) were well tolerated by MIN6 beta cells and islets, whereas 10 μM sertraline and 1 μM paroxetine were cytotoxic. Exposure to 1 μM sertraline and 0.1 μM paroxetine significantly potentiated glucose‐stimulated insulin secretion from mouse and human islets. Moreover, they showed protective effects against cytokine‐ and palmitate‐induced apoptosis of islets, they downregulated cytokine‐induced Stat1 and Traf1 mRNA expression, and they significantly increased proliferation of mouse beta cells. Conclusions: Our data demonstrate that sertraline and paroxetine act directly on beta cells to enhance glucose‐stimulated insulin secretion and stimulate beta‐cell mass expansion by increasing proliferation and decreasing apoptosis. These drugs are therefore likely to be appropriate for treating depression in people with type 2 diabetes. [ABSTRACT FROM AUTHOR]

Dysfunction or loss of pancreatic β cells can cause insulin deficiency and impaired glucose regulation, resulting in conditions like type 2 diabetes. The ATP-binding cassette transporter A1 (ABCA1) plays a key role in the reverse cholesterol transport system, and its decreased expression is associated with pancreatic β cell lipotoxicity, resulting in abnormal insulin synthesis and secretion. Increased glutamate release can cause glucotoxicity in β cells, though the detailed mechanisms remain unclear. This study investigated the effect of N-methyl-D-aspartic acid (NMDA) on ABCA1 expression in INS-1 cells and primary pancreatic islets to elucidate the signaling mechanisms that suppress insulin secretion. Using Western blotting, microscopy, and biochemical analyses, we found that NMDA activated the mitogen-activated protein kinase (MEK)-dependent pathway, suppressing ABCA1 protein and mRNA expression. The MEK-specific inhibitor PD98059 restored ABCA1 promoter activity, indicating the involvement of the extracellular signal-regulated kinase (MEK/ERK) pathway. Furthermore, we identified the liver X receptor (LXR) as an effector transcription factor in NMDA regulation of ABCA1 transcription. NMDA treatment increased cholesterol and triglyceride levels while decreasing insulin secretion, even under high-glucose conditions. These effects were abrogated by treatment with PD98059. This study reveals that NMDA suppresses ABCA1 expression via the MEK/ERK/LXR pathway, providing new insights into the pathological suppression of insulin secretion in pancreatic β cells and emphasizing the importance of investigating the role of NMDA in β cell dysfunction. [ABSTRACT FROM AUTHOR]

Shortcomings in cell-based therapies for patients with diabetes have been revealed to be, in part, a result of an improper extracellular matrix (ECM) environment. In vivo, pancreatic islets are emersed in a diverse ECM that provides physical support and is crucial for healthy function. β1-Integrin receptors have been determined to be responsible for modulation of beneficial interactions with ECM proteins influencing beta-cell development, proliferation, maturation, and function. β1-Integrin signaling has been demonstrated to augment insulin secretion by impacting the actin cytoskeleton via activation of focal adhesion kinase and downstream signaling pathways. In other secretory cells, evidence of a bidirectional relationship between integrins and exocytotic machinery has been demonstrated, and, thus, this relationship could be present in pancreatic beta cells. In this review, we will discuss the role of ECM–β1-integrin interplay with exocytotic proteins in controlling pancreatic beta-cell insulin secretion through their dynamic and unique signaling pathway. [ABSTRACT FROM AUTHOR]

SNAP25 plays an essential role in the glucose‐stimulated insulin secretion (GSIS) of pancreatic β‐cells. Carbohydrate response element‐binding protein (ChREBP) is an important transcription factor in β‐cells and, in this study, we aimed to explore whether ChREBP regulates SNAP25 expression in β‐cells. We show that diabetic Goto‐Kakizaki (GK) rats exhibited impaired insulin secretion and hyperglycemia, along with decreased SNAP25 expression and ChREBP phosphorylation in islets. SNAP25 knockdown decreased GSIS in β‐cells, while SNAP25 overexpression increased GSIS in β‐cells. Activation or overexpression of ChREBP led to reduced SNAP25 expression and subsequent suppression of GSIS. Conversely, ChREBP knockdown mitigated the reduction in SNAP25 expression caused by high glucose. Mechanistically, the activation of ChREBP by high glucose increased its occupancy and decreased the level of H3K4me3 at the Snap25 promoter. Our findings reveal the novel regulatory mechanisms of SNAP25 expression in β‐cells and suggest that SNAP25 may be involved in the regulation of β‐cell secretory function controlled by ChREBP.

Abstract Background This case report explores the long-term dynamics of insulin secretion and glycemic control in two patients with diabetes mellitus type 2 over 20 years. The observations underscore the impact of lifestyle interventions, including weight loss and calorie restriction, on insulin secretion patterns and glucose levels during 75 g oral glucose tolerance tests. Additionally, the role of hemoglobin A1c fluctuations, influenced by various factors such as body weight, exercise, and pharmacological interventions, is investigated. Case presentation Case 1 involves a Japanese woman now in her late 70s who successfully maintained her hemoglobin A1c below 7% for over two decades through sustained weight loss and lifestyle changes. Despite a gradual decline in the homeostasis model assessment of β cell function, the patient exhibited remarkable preservation of insulin secretion patterns over the 20-year follow-up. In case 2, a Japanese woman, now in her early 70s, experienced an improvement in hemoglobin A1c to 6.3% after a period of calorie limitation due to a wrist fracture in 2018. This incident seemed to trigger a temporary rescue of pancreatic β cell function, emphasizing the dynamic nature of insulin secretion. Both cases highlight the potential for pancreatic β cell rescue and underscore the persistence of insulin secretion over the 20-year follow-up. Additionally, we have briefly discussed three additional cases with follow-ups ranging from 10 to 17 years, demonstrating similar trends in glucose and insulin ratios. Conclusions Long-term lifestyle interventions, such as weight loss and calorie restriction, can preserve pancreatic β cell function and maintain glycemic control in type 2 diabetes patients over 20 years. Two patients showed stable or improved insulin secretion and favorable hemoglobin A1c levels, challenging the traditional view of irreversible β cell decline. The findings highlight the importance of personalized, nonpharmacological approaches, suggesting that sustained lifestyle changes can significantly impact diabetes management and potentially rescue β cell function.

Diabetes is an epidemic caused by a multitude of factors. Despite the studies attempting to unravel its mechanism, there is still more to discover about glucose–insulin dynamics. In a recent issue of the Journal of Clinical Investigation, Cheruiyot et al. uncovered a translational regulatory circuit during β‐cell glucose toxicity that inherently affects the translational makeup and protein expression in functioning β‐cells.Journal of Clinical Investigation, Cheruiyot et al. uncovered a translational regulatory circuit during β‐cell glucose toxicity that inherently affects the translational makeup and protein expression in functioning β‐cells. Their multiomics approach might provide a deeper understanding of high glucose and translational regulation of genes involved in β‐cell insulin impairment caused by prolonged high‐glucose exposure.

Introduction: Imeglimin is a first-in-class, novel, oral glucose-lowering agent for the treatment of type 2 diabetes mellitus. The efficacy and safety of imeglimin as an antidiabetic agent have been investigated in clinical trials. However, its metabolic effects in humans have not yet been fully elucidated. Methods: The Study to InveStIgate the Metabolic Action of Imeglimin on patients with type 2 diabetes mellitus (SISIMAI) is a single-arm intervention study. In this study, we have recruited 25 patients with type 2 diabetes to receive 2000 mg/day imeglimin for 20 weeks. We perform a 75-g oral glucose tolerance test (OGTT) with double-glucose tracers, a two-step hyperinsulinemic-euglycemic clamp with glucose tracer, ectopic fat measurement by proton magnetic resonance spectroscopy, visceral/subcutaneous fat area measurement by magnetic resonance imaging, muscle biopsy, and evaluation of fitness level by cycle ergometer before and after imeglimin administration. Planned Outcomes: The primary outcome is the change in area under the curve of glucose levels during the OGTT after 20 weeks of imeglimin treatment. We also calculate the endogenous glucose production, rate of oral glucose appearance, and rate of glucose disappearance from the data during the 75-g OGTT and compare them between pre- and post-treatment. Additionally, we will compare other parameters, such as the changes in tissue-specific insulin sensitivity, ectopic fat accumulation, visceral/subcutaneous fat area accumulation, and fitness level between each point. This is the first study to investigate the organ-specific metabolic action of imeglimin in patients with type 2 diabetes mellitus using the 75-g OGTT with the double tracer method. The results of this study are expected to provide useful information for drug selection based on the pathophysiology of individual patients with type 2 diabetes mellitus. Trial Registration: jRCTs031210600. [ABSTRACT FROM AUTHOR]

Background We evaluated changes in glycemic status, over 1 year, of coronavirus disease 2019 (COVID-19) survivors with dysglycemia in acute COVID-19. Methods COVID-19 survivors who had dysglycemia (defined by glycosylated hemoglobin [HbA1c] 5.7% to 6.4% or random glucose ≥10.0 mmol/L) in acute COVID-19 were recruited from a major COVID-19 treatment center from September to October 2020. Matched non-COVID controls were recruited from community. The 75-g oral glucose tolerance test (OGTT) were performed at baseline (6 weeks after acute COVID-19) and 1 year after acute COVID-19, with HbA1c, insulin and C-peptide measurements. Progression in glycemic status was defined by progression from normoglycemia to prediabetes/diabetes, or prediabetes to diabetes. Results Fifty-two COVID-19 survivors were recruited. Compared with non-COVID controls, they had higher C-peptide (P< 0.001) and trend towards higher homeostasis model assessment of insulin resistance (P=0.065). Forty-three COVID-19 survivors attended 1-year reassessment. HbA1c increased from 5.5%±0.3% to 5.7%±0.2% (P

Abstract Nowadays, the focus of diabetes treatment has switched from lowering the glucose level to preserving glycemic homeostasis and slowing the disease progression. The main pathophysiology of both type 1 diabetes and long‐standing type 2 diabetes is pancreatic β‐cell mass loss and dysfunction. According to recent research, human pancreatic β‐cells possess the ability to proliferate in response to elevated insulin demands. It has been demonstrated that in insulin‐resistant conditions in humans, such as obesity or pregnancy, the β‐cell mass increases. This ability could be helpful in developing novel treatment approaches to restore a functional β‐cell mass. Treatment strategies aimed at boosting β‐cell function and mass may be a useful tool for managing diabetes mellitus and stopping its progression. This review outlines the processes of β‐cell failure and detail the many β‐cell abnormalities that manifest in people with diabetes mellitus. We also go over standard techniques for determining the mass and function of β‐cells. Lastly, we provide the therapeutic implications of utilizing antidiabetic drugs in controlling the mass and function of pancreatic β‐cells.

Introduction: Type 2 diabetes (T2D) is the predominant form of diabetes mellitus and is among the leading causes of death with an increasing prevalence worldwide. However, the pathological mechanism underlying T2D remains complex and unclear. An increasing number of studies have suggested an association between circadian clock disruption and high T2D prevalence. Method: This review explores the physiological and genetic evidence underlying T2D symptoms associated with circadian clock disturbances, including insulin secretion and glucose metabolism. Results and Discussion: Notably, circadian clock disruption reduces insulin secretion and insulin sensitivity and negatively affects glucose homeostasis. The circadian clock regulates the hypothalamic-pituitary-adrenal axis, an important factor that regulates glucose metabolism and influences T2D progression. Therefore, circadian clock regulation is an attractive, novel therapeutic approach for T2D, and various circadian clock stabilizers play therapeutic roles in T2D. Lastly, this review suggests novel therapeutic and preventive approaches using circadian clock regulators for T2D. [ABSTRACT FROM AUTHOR]

Aim: MicroRNAs (miRNAs) regulate β‐cell function, and β‐cell mitochondria and insulin secretion are perturbed in diabetes. We aimed to identify key miRNAs regulating β‐cell mitochondrial metabolism and novel β‐cell miRNA‐mitochondrial pathways. Methods: TargetScan (http://www.targetscan.org/) was used to predict if 16 miRNAs implicated in β‐cell function target 27 cis‐eGenes implicated in mitochondrial activity. The expression of candidate miRNAs and insulin secretion after 24 and 1 h pre‐incubation in 2.8, 11.1‐ and 16.7‐mM glucose was measured in clonal INS‐1 832/13 β‐cells. MiR‐29 silenced INS‐1 832/13 cells were assessed for insulin secretion (glucose, pyruvate, and K+), target cis‐eGene expression (Ndufv3 and Ndufa10 components of mitochondrial complex I (CI)), OXPHOS (CI‐V) protein expression, and mitochondrial OXPHOS respiration/activity. The expression of differentially expressed miR‐29 miRNAs was evaluated in Goto‐Kakizaki (GK) rat, db/db mouse and type 2 diabetic (T2D) human islets, as well as NMRI mouse islets cultured under glucolipotoxic conditions. Results: MiR‐29, miR‐15 and miR‐124 were predicted to regulate ~20 cis‐eGenes, while miR‐29 alone was predicted to regulate ≥12 of these in rat and human species. MiR‐29 expression and insulin secretion were reduced in INS‐1 832/13 cells after 24 h in elevated glucose. MiR‐29 knockdown increased all tested insulin secretory responses, Nudfv3, Ndufa10, complex I and II expression, and cellular mitochondrial OXPHOS. MiR‐29 expression was reduced in db/db islets but increased in GK rat and T2D human islets. Conclusion: We conclude miR‐29 is a key miRNA in regulating β‐cell mitochondrial metabolism and insulin secretion via underlying miR‐29‐OXPHOS complex pathways. Furthermore, we infer reduced miR‐29 expression compensatorily enhances insulin secretion under glucotoxicity. [ABSTRACT FROM AUTHOR]

Preserving the function and survival of pancreatic beta-cells, in order to achieve long-term glycemic control and prevent complications, is an essential feature for an innovative drug to have clinical value in the treatment of diabetes. Innovative research is developing therapeutic strategies to prevent pathogenic mechanisms and protect beta-cells from the deleterious effects of inflammation and/or chronic hyperglycemia over time. A better understanding of receptors and signaling pathways, and of how they interact with each other in beta-cells, remains crucial and is a prerequisite for any strategy to develop therapeutic tools aimed at modulating beta-cell function and/or mass. Here, we present a comprehensive review of our knowledge on membrane and intracellular receptors and signaling pathways as targets of interest to protect beta-cells from dysfunction and apoptotic death, which opens or could open the way to the development of innovative therapies for diabetes. [ABSTRACT FROM AUTHOR]

Uncarboxylated osteocalcin (ucOC) is a hormone secreted by osteoblasts that strengthens bone during mineralization and is a biomarker for ongoing bone formation. It also regulates glucose homeostasis by stimulating insulin secretion from pancreatic β-cells. However, its effect on β-cells under hyperglycemic diabetic conditions is unclear. The objective of this study was to investigate ucOC's effect on insulin secretion in β-cells maintained under high glucose conditions. We hypothesized that hyperglycemia potentiates insulin secretion in response to ucOC stimulation. Using INS-1 cells, we performed insulin secretion experiments, intracellular calcium recordings, and RT-qPCR to determine ucOC's effect on glucose-stimulated insulin secretion (GSIS)-related genes. The results reveal that ucOC significantly increased insulin secretion under hyperglycemic conditions compared to lower glucose levels. High glucose conditions also potentiated the effect of ucOC on calcium signals, which enhanced insulin secretion. The increase in intracellular calcium was due to an influx from the extracellular space via voltage-dependent calcium channels (VDCCs). Interestingly, the treatment of cells with NPS-2143, a GPRC6A blocker, failed to abolish the calcium signals. Uncarboxylated osteocalcin upregulated the expression of GSIS-related genes under high glucose conditions (450 mg/dL) compared to cells under standard culture conditions (200 mg/dL). In conclusion, hyperglycemia potentiates ucOC-induced insulin secretion in β-cells by opening VDCCs and upregulating GSIS genes. These findings provide a better understanding of ucOC's mechanism in the diabetic state and could lead to alternative treatments to stimulate insulin secretion. [ABSTRACT FROM AUTHOR]

The association between chronic HCV infection and type 2 diabetes mellitus (T2DM) has been established; however, there is limited research on β-cell function particularly in the pre-diabetic population. Here, we evaluated indices of β-cell function and insulin sensitivity across the spectrum from normal glucose tolerance to T2DM in individuals with and without chronic hepatitis C (CHC), and the effects of antiviral treatments on these variables. A total of 153 non-cirrhotic, non-fibrotic CHC patients with a BMI <25 were enrolled in the study. Among them, 119 were successfully treated with either direct acting antiviral (DAA) drugs or pegylated interferon/ribavirin (IFN/RBV) anti-HCV therapy. Fasting state- and oral glucose tolerance test (OGTT)-derived indexes were used to evaluate β-cell function and insulin sensitivity. Among all subjects, 19 (13%) had T2DM and 21% exhibited pre-diabetes including 8% isolated impaired fasting glucose (IFG) and 13% combined IFG and impaired glucose tolerance (IGT). Early and total insulin secretion adjusted for the degree of insulin resistance were decreased in pre-diabetic CHC patients compared to HCV-uninfected individuals. Viral eradication through DAA or IFN/RBV therapy demonstrated positive impacts on insulin sensitivity and β-cell function in CHC patients who achieved sustained virologic response (SVR), regardless of fasting or OGTT state. These findings emphasize the role of HCV in the development of β-cell dysfunction, while also suggesting that viral eradication can improve insulin secretion, reverse insulin resistance, and ameliorate glycemic control. These results have important implications for managing pre-diabetic CHC patients and could prevent diabetes-related clinical manifestations and complications. [ABSTRACT FROM AUTHOR]

In a number of investigations on the mechanism of the metabolic amplification of insulin secretion, differences between the response of freshly isolated islets and of islets cultured for one day have been observed. Since no trivial explanation like insufficient numbers of viable cells after cell culture could be found, a more thorough investigation into the mechanisms responsible for the difference was made, concentrating on the function of the mitochondria as the site where the metabolism of nutrient stimulators of secretion forms the signals impacting on the transport and fusion of insulin granules. Using combinations of inhibitors of oxidative phosphorylation, we come to the conclusion that the mitochondrial membrane potential is lower and the exchange of mitochondrial reducing equivalents is faster in freshly isolated islets than in cultured islets. The significantly higher rate of oxygen consumption in fresh islets than in cultured islets (13 vs. 8 pmol/min/islet) was not caused by a different activity of the F1F0-ATPase, but by a larger proton leak. These observations raise the questions as to whether the proton leak is a physiologically regulated pathway and whether its larger size in fresh islets reflects the working condition of the islets within the pancreas. [ABSTRACT FROM AUTHOR]

Neprilysin is a ubiquitous peptidase that can modulate glucose homeostasis by cleaving insulinotropic peptides. While global deletion of neprilysin protects mice against high-fat diet (HFD)-induced insulin secretory dysfunction, strategies to ablate neprilysin in a tissue-specific manner are favored to limit off-target effects. Since insulinotropic peptides are produced in the gut, we sought to determine whether gut-specific neprilysin deletion confers beneficial effects on insulin secretion similar to that of global neprilysin deletion in mice fed a HFD. Mice with conditional deletion of neprilysin in enterocytes (NEPGut−/−) were generated by crossing Vil-Cre and floxed neprilysin mice. Neprilysin activity was almost abolished throughout the gut in NEPGut−/− mice, and was similar in plasma, pancreas, and kidney in NEPGut−/− vs control mice. An oral glucose tolerance test was performed at baseline and following 14 weeks of HFD feeding, during which glucose tolerance and glucose-stimulated insulin secretion (GSIS) were assessed. Despite similar body weight gain at 14 weeks, NEPGut−/− displayed lower fasting plasma glucose levels, improved glucose tolerance, and increased GSIS compared to control mice. In conclusion, gut-specific neprilysin deletion recapitulates the enhanced GSIS seen with global neprilysin deletion in HFD-fed mice. Thus, strategies to inhibit neprilysin specifically in the gut may protect against fat-induced glucose intolerance and beta-cell dysfunction. [ABSTRACT FROM AUTHOR]

Aims/hypothesis: Mutations in Isl1, encoding the insulin enhancer-binding protein islet-1 (ISL1), may contribute to attenuated insulin secretion in type 2 diabetes mellitus. We made an Isl1E283D mouse model to investigate the disease-causing mechanism of diabetes mellitus. Methods: The ISL1E283D mutation (c. 849A>T) was identified by whole exome sequencing on an early-onset type 2 diabetes family and then the Isl1E283D knockin (KI) mouse model was created and an IPGTT and IPITT were conducted. Glucose-stimulated insulin secretion (GSIS), expression of Ins2 and other ISL1 target genes and interacting proteins were evaluated in isolated pancreas islets. Transcriptional activity of Isl1E283D was evaluated by cell-based luciferase reporter assay and electrophoretic mobility shift assay, and the expression levels of Ins2 driven by Isl1 wild-type (Isl1WT) and Isl1E283D mutation in rat INS-1 cells were determined by RT-PCR and western blotting. Results: Impaired GSIS and elevated glucose level were observed in Isl1E283D KI mice while expression of Ins2 and other ISL1 target genes Mafa, Pdx1, Slc2a2 and the interacting protein NeuroD1 were downregulated in isolated islets. Transcriptional activity of the Isl1E283D mutation for Ins2 was reduced by 59.3%, and resulted in a marked downregulation of Ins2 expression when it was overexpressed in INS-1 cells, while overexpression of Isl1WT led to an upregulation of Ins2 expression. Conclusions/interpretation: Isl1E283D mutation reduces insulin expression and secretion by regulating insulin and other target genes, as well as its interacting proteins such as NeuroD1, leading to the development of glucose intolerance in the KI mice, which recapitulated the human diabetic phenotype. This study identified and highlighted the Isl1E283D mutation as a novel causative factor for type 2 diabetes, and suggested that targeting transcription factor ISL1 could offer an innovative avenue for the precise treatment of human type 2 diabetes. [ABSTRACT FROM AUTHOR]

Abelmoschus manihot (L.) Medic flower (AMf) exhibits both nutritional value and bioactivities such as antioxidative, anti-inflammatory, neuroprotective, cardioprotective, and hepatoprotective effects. The aim of this investigation was to examine the potential impact of three different solvent extracts of AMf: supercritical CO2 extraction extract, water extract, and ethanol extract (AME), on management of diabetes. All three extracts demonstrated significant inhibitory effects on α-glucosidase (IC50 = 157–261 μg/mL) and lipase (IC50 = 401–577 μg/mL) activities while enhancing the α-amylase activity (32.4–41.8 folds at 200 μg/mL). Moreover, all three extracts exhibited notable inhibition of the formation of advanced glycation end-products, including the Amadori products (inhibition rates = 15.7–36.6%) and the dicarbonyl compounds (inhibition rates = 18.6–28.3%). Among the three extracts, AME exhibited the most pronounced inhibitory effect. AME displayed substantial in vitro and intracellular antioxidative activity, and effectively reduced ROS production (135% at 500 μg/mL) in β-cells under hyperglycemic (HG) conditions. AME also enhanced the activity and gene expression of antioxidant enzymes, which were markedly decreased in the HG-induced β-cells. Furthermore, AME protected β-cell viability and maintained normal insulin secretion under HG conditions, likely due to its ability to reduce oxidative stress within β-cells. This study demonstrated the potential of AME in preventing and managing diabetes and its associated complications. Further in vivo research is necessary to thoroughly elucidate the preventive effects and their underlying mechanisms. [ABSTRACT FROM AUTHOR]

Context Multiple common genetic variants have been associated with type 2 diabetes, but the mechanism by which they predispose to diabetes is incompletely understood. One such example is variation in MTNR1B, which implicates melatonin and its receptor in the pathogenesis of type 2 diabetes. Objective To characterize the effect of diabetes-associated genetic variation at rs10830963 in the MTNR1B locus on islet function in people without type 2 diabetes. Design The association of genetic variation at rs10830963 with glucose, insulin, C-peptide, glucagon, and indices of insulin secretion and action were tested in a cohort of 294 individuals who had previously undergone an oral glucose tolerance test (OGTT). Insulin sensitivity, β-cell responsivity to glucose, and Disposition Indices were measured using the oral minimal model. Setting The Clinical Research and Translation Unit at Mayo Clinic, Rochester, MN. Participants Two cohorts were utilized for this analysis: 1 cohort was recruited on the basis of prior participation in a population-based study in Olmsted County. The other cohort was recruited on the basis of TCF7L2 genotype at rs7903146 from the Mayo Biobank. Intervention Two-hour, 7-sample OGTT. Main Outcome Measures Fasting, nadir, and integrated glucagon concentrations. Results One or 2 copies of the G-allele at rs10830963 were associated with increased postchallenge glucose and glucagon concentrations compared to subjects with the CC genotype. Conclusion The effects of rs10830963 on glucose homeostasis and predisposition to type 2 diabetes are likely to be partially mediated through changes in α-cell function. [ABSTRACT FROM AUTHOR]

Context Metabolic measures are frequently used to predict type 1 diabetes (T1D) and to understand effects of disease-modifying therapies. Objective Compare metabolic endpoints for their ability to detect preventive treatment effects and predict T1D. Methods Six-month changes in metabolic endpoints were assessed for (1) detecting treatment effects by comparing placebo and treatment arms from the randomized controlled teplizumab prevention trial, a multicenter clinical trial investigating 14-day intravenous teplizumab infusion and (2) predicting T1D in the TrialNet Pathway to Prevention natural history study. For each metabolic measure, t-Values from t tests for detecting a treatment effect were compared with chi-square values from proportional hazards regression for predicting T1D. Participants in the teplizumab prevention trial and participants in the Pathway to Prevention study selected with the same inclusion criteria used for the teplizumab trial were studied. Results Six-month changes in glucose-based endpoints predicted diabetes better than C-peptide–based endpoints, yet the latter were better at detecting a teplizumab effect. Combined measures of glucose and C-peptide were more balanced than measures of glucose alone or C-peptide alone for predicting diabetes and detecting a teplizumab effect. Conclusion The capacity of a metabolic endpoint to detect a treatment effect does not necessarily correspond to its accuracy for predicting T1D. However, combined glucose and C-peptide endpoints appear to be effective for both predicting diabetes and detecting a response to immunotherapy. These findings suggest that combined glucose and C-peptide endpoints should be incorporated into the design of future T1D prevention trials. [ABSTRACT FROM AUTHOR]

Introduction: Biphasic insulin secretion is an intrinsic characteristic of the pancreatic islet and has clinical relevance due to the loss of first-phase in patients with Type 2 diabetes. As it has long been shown that first-phase insulin secretion only occurs in response to rapid changes in glucose, we tested the hypothesis that islet response to an increase in glucose is a combination of metabolism plus an osmotic effect where hypertonicity is driving first-phase insulin secretion. Methods: Experiments were performed using perifusion analysis of rat, mouse, and human islets. Insulin secretion rate (ISR) and other parameters associated with its regulation were measured in response to combinations of D-glucose and membrane-impermeable carbohydrates (L-glucose or mannitol) designed to dissect the effect of hypertonicity from that of glucose metabolism. Results: Remarkably, the appearance of first-phase responses was wholly dependent on changes in tonicity: no first-phase in NAD(P)H, cytosolic calcium, cAMP secretion rate (cAMP SR), or ISR was observed when increased D-glucose concentration was counterbalanced by decreases in membraneimpermeable carbohydrates. When D-glucose was greater than 8 mM, rapid increases in L-glucose without any change in D-glucose resulted in first-phase responses in all measured parameters that were kinetically similar to D-glucose. First-phase ISR was completely abolished by H89 (a non-specific inhibitor of protein kinases) without affecting first-phase calcium response. Defining firstphase ISR as the difference between glucose-stimulated ISR with and without a change in hypertonicity, the peak of first-phase ISR occurred after second-phase ISR had reached steady state, consistent with the well-established glucosedependency of mechanisms that potentiate glucose-stimulated ISR. Discussion: The data collected in this study suggests a new model of glucosestimulated biphasic ISR where first-phase ISR derives from (and after) a transitory amplification of second-phase ISR and driven by hypertonicity-induced rise in H89- inhibitable kinases likely driven by first-phase responses in cAMP, calcium, or a combination of both. [ABSTRACT FROM AUTHOR]

We aimed to determine if cheese could reduce glucose intolerance in aged rats with overt type 2 diabetes (T2D). Male Sprague-Dawley rats treated with high-fat diet (HFD) and streptozotocin (STZ) to elicit T2D were hyperglycemic. One week after STZ injection, low-fat (LOW) or regular-fat (REG) cheese was provided for 5 weeks and compared with T2D and low-fat diet reference (REF) groups. Food intake and weight gain were similar in all groups. Oral glucose tolerance tests revealed glucose intolerance in T2D rats that was partially ameliorated by LOW but not REG. Insulin secretion during the oral glucose tolerance test was impaired in T2D and REG at 10 min (p < 0.05) but the iAUC was highly variable in all groups and statistical differences were not detected (p > 0.05). β-cell mass and pancreatic insulin content in T2D and REG were 50% lower than REF (p < 0.05), whereas LOW was not significantly different. Although isolated islets from all groups responded to glucose, the absolute amount of insulin secreted by T2D and REG was markedly reduced compared with REF, while LOW islets had relatively normal secretion. In conclusion, LOW but not REG cheese enhanced β-cell recovery from HFD/STZ treatment that led to amelioration of glucose tolerance within 5 weeks. [ABSTRACT FROM AUTHOR]

Background: We evaluated changes in glycemic status, over 1 year, of coronavirus disease 2019 (COVID-19) survivors with dysglycemia in acute COVID-19. Methods: COVID-19 survivors who had dysglycemia (defined by glycosylated hemoglobin [HbA1c] 5.7% to 6.4% or random glucose ≥10.0 mmol/L) in acute COVID-19 were recruited from a major COVID-19 treatment center from September to October 2020. Matched non-COVID controls were recruited from community. The 75-g oral glucose tolerance test (OGTT) were performed at baseline (6 weeks after acute COVID-19) and 1 year after acute COVID-19, with HbA1c, insulin and C-peptide measurements. Progression in glycemic status was defined by progression from normoglycemia to prediabetes/diabetes, or prediabetes to diabetes. Results: Fifty-two COVID-19 survivors were recruited. Compared with non-COVID controls, they had higher C-peptide (P< 0.001) and trend towards higher homeostasis model assessment of insulin resistance (P=0.065). Forty-three COVID-19 survivors attended 1-year reassessment. HbA1c increased from 5.5%±0.3% to 5.7%±0.2% (P<0.001), with increases in glucose on OGTT at fasting (P=0.089), 30-minute (P=0.126), 1-hour (P=0.014), and 2-hour (P=0.165). At baseline, 19 subjects had normoglycemia, 23 had prediabetes, and one had diabetes. Over 1 year, 10 subjects (23.8%; of 42 non-diabetes subjects at baseline) had progression in glycemic status. C-peptide levels remained unchanged (P=0.835). Matsuda index decreased (P=0.007) and there was a trend of body mass index increase from 24.4±2.7 kg/m2 to 25.6±5.2 (P=0.083). Subjects with progression in glycemic status had more severe COVID-19 illness than non-progressors (P=0.030). Reassessment was not performed in the control group. Conclusion: Subjects who had dysglycemia in acute COVID-19 were characterized by insulin resistance. Over 1 year, a quarter had progression in glycemic status, especially those with more severe COVID-19. Importantly, there was no significant deterioration in insulin secretory capacity. [ABSTRACT FROM AUTHOR]

Objectives: Dopamine and related receptors are evidenced in pancreatic endocrine tissue, but the impact on islet β-cell stimulus-secretion as well as (patho)physiological role are unclear. Methods: The present study has evaluated islet cell signalling pathways and biological effects of dopamine, as well as alterations of islet dopamine in rodent models of diabetes of different aetiology. Key findings: The dopamine precursor l-DOPA partially impaired glucose tolerance in mice and attenuated glucose-, exendin-4, and alanine-induced insulin secretion. The latter effect was echoed by the attenuation of glucose-induced [Ca2+]i dynamics and elevation of ATP levels in individual mouse islet cells. l-DOPA significantly decreased β-cell proliferation rates, acting predominantly via the D2 receptor, which was most abundant at the mRNA level. The administration of streptozotocin (STZ) or high-fat diet (HFD) in mice significantly elevated numbers of dopamine-positive islet cells, with HFD also increasing colocalization of dopamine with insulin. At the same time, colocalization of dopamine with glucagon was increased in STZ-treated and pregnant mice, but unaffected by HFD. Conclusion: These findings highlight a role for dopamine receptor signalling in islet cell biology adaptations to various forms of metabolic stress. [ABSTRACT FROM AUTHOR]

Imidazolines, also known as dihydroimidazolines, are an important class of aromatic five-membered heterocycles that include two nitrogen atoms. Imidazolines are present in a wide range of biologically active natural and synthetic compounds. The synthesis of imidazoline-containing drugs has expanded dramatically after the findings of the imidazoline binding site (IBS) in 1984. Furthermore, many substituted imidazolines have shown potential therapeutic efficacy in the treatment of a variety of disorders, including anthelmintics, antifungal, anticancer, hypertension, and hyperglycemia, as well as Parkinson's and Alzheimer's diseases. Moreover, chiral imidazolines are extensively used as organocatalysts in the synthesis of a wide range of natural and synthetic organic molecules. This overview highlights the different pharmacological and biological activities of imidazolines derivatives. [ABSTRACT FROM AUTHOR]

Prostaglandin E2 (PGE2) is a key mediator of inflammation and is derived from the omega-6 polyunsaturated fatty acid, arachidonic acid (AA). In the β-cell, the PGE2 receptor, Prostaglandin EP3 receptor (EP3), is coupled to the unique heterotrimeric G protein alpha subunit, Gɑz to reduce the production of cyclic adenosine monophosphate (cAMP), a key signaling molecule that activates β-cell function, proliferation, and survival pathways. Nonobese diabetic (NOD) mice are a strong model of type 1 diabetes (T1D), and NOD mice lacking Gɑz are protected from hyperglycemia. Therefore, limiting systemic PGE2 production could potentially improve both the inflammatory and β-cell dysfunction phenotype of T1D. Here, we sought to evaluate the effect of eicosapentaenoic acid (EPA) feeding, which limits PGE2 production, on the early T1D phenotype of NOD mice in the presence and absence of Gαz. Wild-type and Gαz knockout NOD mice were fed a control or EPA-enriched diet for 12 weeks, beginning at age 4 to 5 weeks. Oral glucose tolerance, splenic T-cell populations, islet cytokine/chemokine gene expression, islet insulitis, measurements of β-cell mass, and measurements of β-cell function were quantified. EPA diet feeding and Gɑz loss independently improved different aspects of the early NOD T1D phenotype and coordinated to alter the expression of certain cytokine/chemokine genes and enhance incretin-potentiated insulin secretion. Our results shed critical light on the Gαz-dependent and -independent effects of dietary EPA enrichment and provide a rationale for future research into novel pharmacological and dietary adjuvant therapies for T1D. [ABSTRACT FROM AUTHOR]

The literature on green tea consumption and glucose metabolism has reported conflicting findings. This cross-sectional study examined the association of green tea consumption with abnormal glucose metabolism among 3000 rural residents aged 40–60 years in Khánh Hòa province in Vietnam. Multinomial logistic regression analysis was conducted to examine the association of green tea consumption (0, < 200, 200–< 400, 400–< 600 or ≥ 600 ml/d) with prediabetes and diabetes (based on the American Diabetes Association criteria). Linear regression analysis was performed to examine the association between green tea consumption and the log-transformed homeostatic model assessment of insulin resistance (HOMA-IR) (a marker of insulin resistance) and the log-transformed homeostatic model assessment of β -cell function (HOMA- β) (a marker of insulin secretion). The OR for prediabetes and diabetes among participants who consumed ≥ 600 ml/d v. those who did not consume green tea were 1·61 (95 % CI = 1·07, 2·42) and 2·04 (95 % CI = 1·07, 3·89), respectively. Higher green tea consumption was associated with a higher level of log-transformed HOMA-IR (P for trend = 0·04) but not with a lower level of log-transformed HOMA- β (P for trend = 0·75). Higher green tea consumption was positively associated with the prevalence of prediabetes, diabetes and insulin resistance in rural Vietnam. The findings of this study indicated prompting the need for further research considering context in understanding the link between green tea consumption and glucose metabolism, especially in rural settings in low- and middle-income countries. [ABSTRACT FROM AUTHOR]

Pancreatic β cells play an essential role in the control of systemic glucose homeostasis as they sense blood glucose levels and respond by secreting insulin. Upon stimulating glucose uptake in insulin‐sensitive tissues post‐prandially, this anabolic hormone restores blood glucose levels to pre‐prandial levels. Maintaining physiological glucose levels thus relies on proper β‐cell function. To fulfill this highly specialized nutrient sensor role, β cells have evolved a unique genetic program that shapes its distinct cellular metabolism. In this review, the unique genetic and metabolic features of β cells will be outlined, including their alterations in type 2 diabetes (T2D). β cells selectively express a set of genes in a cell type‐specific manner; for instance, the glucose activating hexokinase IV enzyme or Glucokinase (GCK), whereas other genes are selectively "disallowed", including lactate dehydrogenase A (LDHA) and monocarboxylate transporter 1 (MCT1). This selective gene program equips β cells with a unique metabolic apparatus to ensure that nutrient metabolism is coupled to appropriate insulin secretion, thereby avoiding hyperglycemia, as well as life‐threatening hypoglycemia. Unlike most cell types, β cells exhibit specialized bioenergetic features, including supply‐driven rather than demand‐driven metabolism and a high basal mitochondrial proton leak respiration. The understanding of these unique genetically programmed metabolic features and their alterations that lead to β‐cell dysfunction is crucial for a comprehensive understanding of T2D pathophysiology and the development of innovative therapeutic approaches for T2D patients. [ABSTRACT FROM AUTHOR]

Nowadays, the focus of diabetes treatment has switched from lowering the glucose level to preserving glycemic homeostasis and slowing the disease progression. The main pathophysiology of both type 1 diabetes and long‐standing type 2 diabetes is pancreatic β‐cell mass loss and dysfunction. According to recent research, human pancreatic β‐cells possess the ability to proliferate in response to elevated insulin demands. It has been demonstrated that in insulin‐resistant conditions in humans, such as obesity or pregnancy, the β‐cell mass increases. This ability could be helpful in developing novel treatment approaches to restore a functional β‐cell mass. Treatment strategies aimed at boosting β‐cell function and mass may be a useful tool for managing diabetes mellitus and stopping its progression. This review outlines the processes of β‐cell failure and detail the many β‐cell abnormalities that manifest in people with diabetes mellitus. We also go over standard techniques for determining the mass and function of β‐cells. Lastly, we provide the therapeutic implications of utilizing antidiabetic drugs in controlling the mass and function of pancreatic β‐cells. [ABSTRACT FROM AUTHOR]