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Notch signaling pathway plays an important role in regulating pancreatic endocrine and exocrine cell fate during pancreas development. Notch signaling is also expressed in adult pancreas. There are few studies on the effect of Notch on adult pancreas. Here, we investigated the role of Notch in islet mass and glucose homeostasis in adult pancreas using Notch1 antisense transgenic (NAS).
Western blot analysis was performed for the liver of 8-week-old male NAS mice. We also conducted an intraperitoneal glucose tolerance test (IPGTT) and intraperitoneal insulin tolerance test in 8-week-old male NAS mice and male C57BL/6 mice (control). Morphologic observation of pancreatic islet and β-cell was conducted in two groups. Insulin secretion capacity in islets was measured by glucose-stimulated insulin secretion (GSIS) and perifusion.
NAS mice showed higher glucose levels and lower insulin secretion in IPGTT than the control mice. There was no significant difference in insulin resistance. Total islet and β-cell masses were decreased in NAS mice. The number of large islets (≥250 µm) decreased while that of small islets (<250 µm) increased. Reduced insulin secretion was observed in GSIS and perifusion. Neurogenin3, neurogenic differentiation, and MAF bZIP transcription factor A levels increased in NAS mice.
Our study provides that Notch1 inhibition decreased insulin secretion and decreased islet and β-cell masses. It is thought that Notch1 inhibition suppresses islet proliferation and induces differentiation of small islets. In conclusion, Notch signaling pathway may play an important role in β-cell mass determination and diabetes.
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An early identification of the risk groups might be beneficial in reducing morbidities in patients with gestational diabetes mellitus (GDM). Therefore, this study aimed to assess the biochemical predictors of glycemic conditions, in addition to fasting indices of glucose disposal, to predict the development of GDM in later stage and the need of glucose-lowering medication.
A total of 574 pregnant females (103 with GDM and 471 with normal glucose tolerance [NGT]) were included. A metabolic characterization was performed before 15+6 weeks of gestation by assessing fasting plasma glucose (FPG), fasting insulin (FI), fasting C-peptide (FCP), and glycosylated hemoglobin (HbA1c). Thereafter, the patients were followed-up until the delivery.
Females with NGT had lower levels of FPG, FI, FCP, or HbA1c at the early stage of pregnancy, and therefore, showed an improved insulin action as compared to that in females who developed GDM. Higher fasting levels of FPG and FCP were associated with a higher risk of developing GDM. Moreover, the predictive accuracy of this metabolic profiling was also good to distinguish the patients who required glucose-lowering medications. Indices of glucose disposal based on C-peptide improved the predictive accuracy compared to that based on insulin. A modified quantitative insulin sensitivity check index (QUICKIc) showed the best differentiation in terms of predicting GDM (area under the receiver operating characteristics curve [ROC-AUC], 72.1%) or need for pharmacotherapy (ROC-AUC, 83.7%).
Fasting measurements of glucose and C-peptide as well as the surrogate indices of glycemic condition could be used for stratifying pregnant females with higher risk of GDM at the beginning of pregnancy.
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We evaluated the clinical characteristics of insulin resistance and β-cell dysfunction in newly diagnosed, drug-naive people with type 2 diabetes by analyzing nationwide cross-sectional data.
We collected the clinical data of 912 participants with newly diagnosed diabetes from 83 primary care clinics and hospitals nationwide from 2015 to 2016. The presence of insulin resistance and β-cell dysfunction was defined as a homeostatic model assessment of insulin resistance (HOMA-IR) value ≥2.5 and fasting C-peptide levels <1.70 ng/mL, respectively.
A total of 75.1% and 22.6% of participants had insulin resistance and β-cell dysfunction, respectively. The proportion of participants with insulin resistance but no β-cell dysfunction increased, and the proportion of participants with β-cell dysfunction but no insulin resistance decreased as body mass index (BMI) increased. People diagnosed with diabetes before 40 years of age had significantly higher HOMA-IR and BMI than those diagnosed over 65 years of age (HOMA-IR, 5.0 vs. 3.0; BMI, 28.7 kg/m2 vs. 25.1 kg/m2). However, the β-cell function indices were lower in people diagnosed before 40 years of age than in those diagnosed after 65 years of age (homeostatic model assessment of β-cell function, 39.3 vs. 64.9; insulinogenic index, 10.3 vs. 18.7; disposition index, 0.15 vs. 0.25).
We observed that the main pathogenic mechanism of type 2 diabetes is insulin resistance in participants with newly diagnosed type 2 diabetes. In addition, young adults with diabetes are more likely to have higher insulin resistance with obesity and have higher insulin secretory defect with severe hyperglycemia in the early period of diabetes than older populations.
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The original homeostasis model assessment (HOMA1) and the updated HOMA model (HOMA2) have been used to evaluate insulin resistance (IR) and β-cell function, but little is known about the usefulness of HOMA2 for the prediction of diabetes in Koreans. The aim of this study was to demonstrate the usefulness of HOMA2 as a predictor of type 2 diabetes mellitus in Koreans without diabetes.
The study population consisted of 104,694 Koreans enrolled at a health checkup program and followed up from 2001 to 2012. Participants were divided into a normal glucose tolerance (NGT) group and a pre-diabetes group according to fasting glucose and glycosylated hemoglobin levels. Anthropometric and laboratory data were measured at the baseline checkup, and HOMA values were calculated at the baseline and follow-up checkups. The hazard ratios (HRs) of the HOMA1 and HOMA2 values and the prevalence of diabetes at follow-up were evaluated using a multivariable Cox proportional hazards model and Kaplan-Meier analysis.
After adjusting for several diabetes risk factors, all of the HOMA values except 1/HOMA1-β and 1/HOMA2-β in the NGT group were significant predictors of the progression to diabetes. In the NGT group, there was no significant difference in HOMA1-IR (HR, 1.09; 95% confidence interval [CI], 1.04 to 1.14) and HOMA2-IR (HR, 1.11; 95% CI, 1.04 to 1.19). However, in the pre-diabetes group, 1/HOMA2-β was a more powerful marker (HR, 1.29; 95% CI, 1.26 to 1.31) than HOMA1-IR (HR, 1.23; 95% CI, 1.19 to 1.28) or 1/HOMA1-β (HR, 1.14; 95% CI, 1.12 to 1.16). In the non-diabetic group (NGT+pre-diabetes), 1/HOMA2-β was also a stronger predictor of diabetes (HR, 1.27; 95% CI, 1.25 to 1.29) than HOMA1-IR (HR, 1.14; 95% CI, 1.12 to 1.15) or 1/HOMA1-β (HR, 1.13; 95% CI, 1.11 to 1.14).
HOMA2 is more predictive than HOMA1 for the progression to diabetes in pre-diabetes or non-diabetic Koreans.
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This study aimed to compare the patterns of insulin secretion and resistance between Korean subjects in the 1990s and 2000s.
Insulin secretion and resistance indices were calculated from subjects who underwent 75-g oral glucose tolerance tests in the year 1997 to 1999 and 2007 to 2011 at the Seoul St. Mary's Hospital, Korea.
A total of 578 subjects from the 1990s (mean age, 48.5 years) and 504 subjects from the 2000s (mean age, 50.2 years) were enrolled. Compared with the subjects from the 1990s, those from the 2000s exhibited increased insulin resistance (increased homeostatic model assessment for insulin resistance), and reduced insulin sensitivity (reduced Matsuda index and quantitative insulin sensitivity check index), regardless of their glucose tolerance status. However, insulinogenic index did not reveal significant differences between the 2 decades in subjects with or without diabetes. A distinct relationship was confirmed between Matsuda index and total area under the curve (insulin/glucose) in each glucose tolerance group. The mean product of the Matsuda index and the total area under the curve (insulin/glucose) as well as the oral disposition index, was lower in subjects with normal glucose tolerance from the 2000s than in those from the 1990s.
After rapid economic growth and changes in lifestyle patterns, insulin resistance has worsened across the glucose tolerance status; however, the insulin secretory function remained unchanged, which resulted in an increase in the susceptibility to the development of type 2 diabetes mellitus among Korean subjects without diabetes. We could not rule out the potential selection bias and therefore, further studies in general Korean population are needed.
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Hyperglycemia, a characteristic feature of diabetes, induces glucotoxicity in pancreatic β-cells, resulting in further impairment of insulin secretion and worsening glycemic control. Thus, preservation of insulin secretory capacity is essential for the management of type 2 diabetes. In this study, we evaluated the ability of an
We measured insulin mRNA expression and glucose-stimulated insulin secretion (GSIS) in OS-treated INS-1 cells after exposure to a high glucose (HG; 30 mM) concentration.
The hexane extract of OS elevated mRNA expression of insulin as well as pancreatic and duodenal homeobox-1 of INS-1 cells in a dose-dependent manner. The hexane OS extract also increased the levels of phosphorylated phosphatidylinositol 3-kinase (PI3K) in a concentration-dependent manner. Additionally, Akt phosphorylation was elevated by treatment with 100 and 200 µmol of the hexane OS extract. Three days of HG exposure suppressed insulin mRNA expression and GSIS; these expressions were restored by treatment with the hexane OS extract. HG elevated peroxide levels in the INS-1 cells. These levels were unaffected by OS treatment under both normal and hyperglycemic conditions.
Our results suggested that the hexane extract of OS elevates insulin mRNA expression and prevents glucotoxicity induced by a 3-day treatment with HG. This was associated with the activation of PI-3K and Akt.
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Increased triglycerides (TGs) and decreased high density lipoprotein cholesterol (HDL-C) levels are established as diabetic risks for nondiabetic subjects. The aim of this study was to investigate the relationship among TG, HDL-C, TG/HDL-C ratio, and early-phase insulin secretion in normoglycemic and prediabetic subjects.
We evaluated 663 Japanese subjects who underwent the 75-g oral glucose tolerance test. On the basis of these results, the subjects were divided into four groups: those with normal glucose tolerance (NGT;
In prediabetic subjects (i-IFG, i-IGT, and IFG+IGT), linear regression analyses revealed that IGI and DI were positively correlated with HDL-C levels. Moreover, in subjects with i-IGT and (IFG+IGT), but not with i-IFG, the indices of insulin secretion were negatively correlated with the log-transformed TG and TG/HDL-C ratio. In both the subjects with i-IGT, multivariate linear regression analyses revealed that DI was positively correlated with HDL-C and negatively with log-transformed TG and TG/HDL-C ratio. On the other hand, in subjects with NGT, there was no association between insulin secretion and lipid profiles.
These results revealed that serum TG and HDL-C levels have different impacts on early-phase insulin secretion on the basis of their glucose tolerance status.
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Adenosine triphosphate (ATP)-sensitive potassium (KATP) channels in pancreatic β-cells play a crucial role in insulin secretion and glucose homeostasis. These channels are composed of two subunits: a pore-forming subunit (Kir6.2) and a regulatory subunit (sulphonylurea receptor-1). Recent studies identified large number of gain of function mutations in the regulatory subunit of the channel which cause neonatal diabetes. Majority of mutations cause neonatal diabetes alone, however some lead to a severe form of neonatal diabetes with associated neurological complications. This review focuses on the functional effects of these mutations as well as the implications for treatment.
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A growing body of evidence suggests that hyperglycemia-induced oxidative stress plays an important role in diabetic complications, especially β-cell dysfunction and failure. Under physiological conditions, reactive oxygen species serve as second messengers that facilitate signal transduction and gene expression in pancreatic β-cells. However, under pathological conditions, an imbalance in redox homeostasis leads to aberrant tissue damage and β-cell death due to a lack of antioxidant defense systems. Taking into account the vulnerability of islets to oxidative damage, induction of endogenous antioxidant enzymes or exogenous antioxidant administration has been proposed as a way to protect β-cells against diabetic insults. Here, we consider recent insights into how the redox response becomes deregulated under diabetic conditions, as well as the therapeutic benefits of antioxidants, which may provide clues for developing strategies aimed at the treatment or prevention of diabetes associated with β-cell failure.
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The pancreatic islet β-cell is uniquely specialized to couple its metabolism and rates of insulin secretion with the levels of circulating nutrient fuels, with the mitochondrial playing a central regulatory role in this process. In the β-cell, mitochondrial activation generates an integrated signal reflecting rates of oxidativephosphorylation, Kreb's cycle flux, and anaplerosis that ultimately determines the rate of insulin exocytosis. Mitochondrial activation can be regulated by proton leak and mediated by UCP2, and by alkalinization to utilize the pH gradient to drive substrate and ion transport. Converging lines of evidence support the hypothesis that substrate cycles driven by rates of Kreb's cycle flux and by anaplerosis play an integral role in coupling responsive changes in mitochondrial metabolism with insulin secretion. The components and mechanisms that account for the integrated signal of ATP production, substrate cycling, the regulation of cellular redox state, and the production of other secondary signaling intermediates are operative in both rodent and human islet β-cells.
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