Bisphenol A Is More Potent than Phthalate Metabolites in Reducing Pancreatic β-Cell Function

Bisphenol A (BPA) and phthalates are common environmental contaminants that have been proposed to influence incidence and development of types 1 and 2 diabetes. Thus, effects of BPA and three phthalate metabolites (monoisobutyl phthalate (MiBP), mono-n-butyl phthalate (MnBP), and mono-(2-ethylhexyl) phthalate (MEHP)) were studied in the pancreatic β-cell line INS-1E, after 2–72 h of exposure to 5–500 μM. Three endpoints relevant to accelerated development of types 1 or 2 diabetes were investigated: β-cell viability, glucose-induced insulin secretion, and β-cell susceptibility to cytokine-induced cell death. BPA and the phthalate metabolites reduced cellular viability after 72 h of exposure, with BPA as the most potent chemical. Moreover, BPA, MEHP, and MnBP increased insulin secretion after 2 h of simultaneous exposure to chemicals and glucose, with potency BPA > MEHP > MnBP. Longer chemical exposures (24–72 h) showed no consistent effects on glucose-induced insulin secretion, and none of the environmental chemicals affected susceptibility to cytokine-induced cell death. Overall, BPA was more potent than the investigated phthalate metabolites in affecting insulin secretion and viability in the INS-1E pancreatic β-cells. In contrast to recent literature, concentrations with relevance to human exposures (1–500 nM) did not affect the investigated endpoints, suggesting that this experimental model displayed relatively low sensitivity to environmental chemical exposure.

Download Full-text

Exendin-4 Improves β-Cell Function in Autophagy-Deficient β-Cells

Endocrinology ◽

10.1210/en.2013-1578 ◽

2013 ◽

Vol 154 (12) ◽

pp. 4512-4524 ◽

Cited By ~ 35

Author(s):

Hiroko Abe ◽

Toyoyoshi Uchida ◽

Akemi Hara ◽

Hiroki Mizukami ◽

Koji Komiya ◽

...

Keyword(s):

Type 2 Diabetes ◽

Cell Death ◽

Insulin Secretion ◽

Glucose Tolerance ◽

Cell Function ◽

Apoptotic Cell ◽

Β Cells ◽

Β Cell ◽

Β Cell Function

Autophagy is cellular machinery for maintenance of β-cell function and mass. The implication of autophagy failure in β-cells on the pathophysiology of type 2 diabetes and its relation to the effect of treatment of diabetes remains elusive. Here, we found increased expression of p62 in islets of db/db mice and patients with type 2 diabetes mellitus. Treatment with exendin-4, a glucagon like peptide-1 receptor agonist, improved glucose tolerance in db/db mice without significant changes in p62 expression in β-cells. Also in β-cell-specific Atg7-deficient mice, exendin-4 efficiently improved blood glucose level and glucose tolerance mainly by enhanced insulin secretion. In addition, we found that exendin-4 reduced apoptotic cell death and increased proliferating cells in the Atg7-deficient islets, and that exendin-4 counteracted thapsigargin-induced cell death of isolated islets augmented by autophagy deficiency. Our results suggest the potential involvement of reduced autophagy in β-cell dysfunction in type 2 diabetes. Without altering the autophagic state in β-cells, exendin-4 improves glucose tolerance associated with autophagy deficiency in β-cells. This is mainly achieved through augmentation of insulin secretion. In addition, exendin-4 prevents apoptosis and increases the proliferation of β-cells associated with autophagy deficiency, also without altering the autophagic machinery in β-cells.

Download Full-text

In Vitro Studies to Assess the α-Glucosidase Inhibitory Activity and Insulin Secretion Effect of Isorhamnetin 3-O-Glucoside and Quercetin 3-O-Glucoside Isolated from Salicornia herbacea

Processes ◽

10.3390/pr9030483 ◽

2021 ◽

Vol 9 (3) ◽

pp. 483

Author(s):

Dahae Lee ◽

Jun Yeon Park ◽

Sanghyun Lee ◽

Ki Sung Kang

Keyword(s):

Insulin Secretion ◽

Cell Function ◽

Ethanolic Extract ◽

Ethyl Acetate Fraction ◽

Gradient Elution ◽

Glucosidase Activity ◽

Β Cell Function ◽

Glucose Stimulated Insulin Secretion ◽

Salicornia Herbacea

In this study, we examined the effect of ethanolic extract of Salicornia herbacea (ESH), isorhamnetin 3-O-glucoside (I3G), quercetin 3-O-glucoside (Q3G), quercetin, and isorhamnetin on α-glucosidase activity and glucose-stimulated insulin secretion (GSIS) in insulin-secreting rat insulinoma (INS-1) cells. A portion of the ethyl acetate fraction of ESH was chromatographed on a silica gel by a gradient elution with chloroform and methanol to provide Q3G and I3G. ESH, Q3G, and quercetin inhibited α-glucosidase activity, and quercetin (IC50 value was 29.47 ± 3.36 μM) inhibited the activity more effectively than Q3G. We further demonstrated that ESH, Q3G, quercetin, I3G, and isorhamnetin promote GSIS in INS-1 pancreatic β-cells without inducing cytotoxicity. Among them, I3G was the most effective in enhancing GSIS. I3G enhanced the phosphorylation of total extracellular signal-regulated kinase (ERK), insulin receptor substrate-2 (IRS-2), phosphatidylinositol 3-kinase (PI3K), Akt, and activated pancreatic and duodenal homeobox-1 (PDX-1), which are associated with insulin secretion and β-cell function. As components of ESH, Q3G has the potential to regulate blood glucose by inhibiting α-glucosidase activity, and I3G enhances the insulin secretion, but its bioavailability should be considered in determining biological importance.

Download Full-text

mTORC1 and mTORC2 regulate insulin secretion through Akt in INS-1 cells

Journal of Endocrinology ◽

10.1530/joe-12-0351 ◽

2012 ◽

Vol 216 (1) ◽

pp. 21-29 ◽

Cited By ~ 21

Author(s):

Olivier Le Bacquer ◽

Gurvan Queniat ◽

Valery Gmyr ◽

Julie Kerr-Conte ◽

Bruno Lefebvre ◽

...

Keyword(s):

Insulin Secretion ◽

Cell Function ◽

Antagonistic Effect ◽

Dominant Negative ◽

Insulin Content ◽

Insulin Biosynthesis ◽

Direct Role ◽

Β Cell Function ◽

Glucose Stimulated Insulin Secretion

Regulated associated protein of mTOR (Raptor) and rapamycin-insensitive companion of mTOR (rictor) are two proteins that delineate two different mTOR complexes, mTORC1 and mTORC2 respectively. Recent studies demonstrated the role of rictor in the development and function of β-cells. mTORC1 has long been known to impact β-cell function and development. However, most of the studies evaluating its role used either drug treatment (i.e. rapamycin) or modification of expression of proteins known to modulate its activity, and the direct role of raptor in insulin secretion is unclear. In this study, using siRNA, we investigated the role of raptor and rictor in insulin secretion and production in INS-1 cells and the possible cross talk between their respective complexes, mTORC1 and mTORC2. Reduced expression of raptor is associated with increased glucose-stimulated insulin secretion and intracellular insulin content. Downregulation of rictor expression leads to impaired insulin secretion without affecting insulin content and is able to correct the increased insulin secretion mediated by raptor siRNA. Using dominant-negative or constitutively active forms of Akt, we demonstrate that the effect of both raptor and rictor is mediated through alteration of Akt signaling. Our finding shed new light on the mechanism of control of insulin secretion and production by the mTOR, and they provide evidence for antagonistic effect of raptor and rictor on insulin secretion in response to glucose by modulating the activity of Akt, whereas only raptor is able to control insulin biosynthesis.

Download Full-text

Differential Loss of β-cell Function in Youth vs. Adults Following Treatment Withdrawal in the Restoring Insulin Secretion (RISE) Study

Diabetes Research and Clinical Practice ◽

10.1016/j.diabres.2021.108948 ◽

2021 ◽

pp. 108948

Author(s):

Kristina M. Utzschneider ◽

Mark T. Tripputi ◽

Alexandra Kozedub ◽

Elena Barengolts ◽

Sonia Caprio ◽

...

Keyword(s):

Insulin Secretion ◽

Cell Function ◽

Treatment Withdrawal ◽

Β Cell ◽

Β Cell Function

Download Full-text

Functional Role of Serotonin in Insulin Secretion in a Diet-Induced Insulin-Resistant State

Endocrinology ◽

10.1210/en.2014-1687 ◽

2014 ◽

Vol 156 (2) ◽

pp. 444-452 ◽

Cited By ~ 55

Author(s):

Kyuho Kim ◽

Chang-Myung Oh ◽

Mica Ohara-Imaizumi ◽

Sangkyu Park ◽

Jun Namkung ◽

...

Keyword(s):

Insulin Secretion ◽

Pancreatic Islets ◽

Cell Function ◽

Β Cell ◽

Pancreas Perfusion ◽

Insulin Resistant ◽

Β Cell Function ◽

Resistant State ◽

Insulin Resistant State

The physiological role of serotonin, or 5-hydroxytryptamine (5-HT), in pancreatic β-cell function was previously elucidated using a pregnant mouse model. During pregnancy, 5-HT increases β-cell proliferation and glucose-stimulated insulin secretion (GSIS) through the Gαq-coupled 5-HT2b receptor (Htr2b) and the 5-HT3 receptor (Htr3), a ligand-gated cation channel, respectively. However, the role of 5-HT in β-cell function in an insulin-resistant state has yet to be elucidated. Here, we characterized the metabolic phenotypes of β-cell-specific Htr2b−/− (Htr2b βKO), Htr3a−/− (Htr3a knock-out [KO]), and β-cell-specific tryptophan hydroxylase 1 (Tph1)−/− (Tph1 βKO) mice on a high-fat diet (HFD). Htr2b βKO, Htr3a KO, and Tph1 βKO mice exhibited normal glucose tolerance on a standard chow diet. After 6 weeks on an HFD, beginning at 4 weeks of age, both Htr3a KO and Tph1 βKO mice developed glucose intolerance, but Htr2b βKO mice remained normoglycemic. Pancreas perfusion assays revealed defective first-phase insulin secretion in Htr3a KO mice. GSIS was impaired in islets isolated from HFD-fed Htr3a KO and Tph1 βKO mice, and 5-HT treatment improved insulin secretion from Tph1 βKO islets but not from Htr3a KO islets. Tph1 and Htr3a gene expression in pancreatic islets was not affected by an HFD, and immunostaining could not detect 5-HT in pancreatic islets from mice fed an HFD. Taken together, these results demonstrate that basal 5-HT levels in β-cells play a role in GSIS through Htr3, which becomes more evident in a diet-induced insulin-resistant state.

Download Full-text

Let7b-5p is Upregulated in the Serum of Emirati Patients with Type 2 Diabetes and Regulates Insulin Secretion in INS-1 Cells

Experimental and Clinical Endocrinology & Diabetes ◽

10.1055/a-1261-5282 ◽

2020 ◽

Author(s):

Hayat Aljaibeji ◽

Noha Mousaad Elemam ◽

Abdul Khader Mohammed ◽

Hind Hasswan ◽

Mahammad Al Thahyabat ◽

...

Keyword(s):

Type 2 Diabetes ◽

Insulin Secretion ◽

Cell Viability ◽

Cell Function ◽

Serum Levels ◽

Insulin Content ◽

Β Cell ◽

Control Subjects ◽

Β Cell Function

Abstract Let7b-5p is a member of the Let-7 miRNA family and one of the top expressed miRNAs in human islets that implicated in glucose homeostasis. The levels of Let7b-5p in type 2 diabetes (T2DM) patients or its role in β-cell function is still unclear. In the current study, we measured the serum levels of let7b-5p in Emirati patients with T2DM (with/without complications) and control subjects. Overexpression or silencing of let7b-5p in INS-1 (832/13) cells was performed to investigate the impact on insulin secretion, content, cell viability, apoptosis, and key functional genes. We found that serum levels of let7b-5p are significantly (p<0.05) higher in T2DM-patients or T2DM with complications compared to control subjects. Overexpression of let7b-5p increased insulin content and decreased glucose-stimulated insulin secretion, whereas silencing of let7b-5p reduced insulin content and secretion. Modulation of the expression levels of let7b-5p did not influence cell viability nor apoptosis. Analysis of mRNA and protein expression of hallmark genes in let7b-5p transfected cells revealed a marked dysregulation of Insulin, Pancreatic And Duodenal Homeobox 1 (PDX1), glucokinase (GCK), glucose transporter 2 (GLUT2), and INSR. In conclusion, an appropriate level of let7b-5p is essential to maintain β-cell function and may be regarded as a biomarker for T2DM.

Download Full-text

Impact of lack of suppression of glucagon on glucose tolerance in humans

AJP Endocrinology and Metabolism ◽

10.1152/ajpendo.1999.277.2.e283 ◽

1999 ◽

Vol 277 (2) ◽

pp. E283-E290 ◽

Cited By ~ 23

Author(s):

Pankaj Shah ◽

Ananda Basu ◽

Rita Basu ◽

Robert Rizza

Keyword(s):

Insulin Secretion ◽

Glucose Concentration ◽

Cell Function ◽

Hormone Secretion ◽

Glucose Production ◽

Glucagon Secretion ◽

Β Cell ◽

Β Cell Function ◽

Glucagon Suppression

People with type 2 diabetes have defects in both α- and β-cell function. To determine whether lack of suppression of glucagon causes hyperglycemia when insulin secretion is impaired but not when insulin secretion is intact, twenty nondiabetic subjects were studied on two occasions. On both occasions, a “prandial” glucose infusion was given over 5 h while endogenous hormone secretion was inhibited. Insulin was infused so as to mimic either a nondiabetic ( n = 10) or diabetic ( n = 10) postprandial profile. Glucagon was infused at a rate of 1.25 ng ⋅ kg−1 ⋅ min−1, beginning either at time zero to prevent a fall in glucagon (nonsuppressed study day) or at 2 h to create a transient fall in glucagon (suppressed study day). During the “diabetic” insulin profile, lack of glucagon suppression resulted in a marked increase ( P < 0.002) in both the peak glucose concentration (11.9 ± 0.4 vs. 8.9 ± 0.4 mmol/l) and the area above basal of glucose (927 ± 77 vs. 546 ± 112 mmol ⋅ l−1 ⋅ 6 h) because of impaired ( P < 0.001) suppression of glucose production. In contrast, during the “nondiabetic” insulin profile, lack of suppression of glucagon resulted in only a slight increase ( P< 0.02) in the peak glucose concentration (9.1 ± 0.4 vs. 8.4 ± 0.3 mmol/l) and the area above basal of glucose (654 ± 146 vs. 488 ± 118 mmol ⋅ l−1 ⋅ 6 h). Of interest, when glucagon was suppressed, glucose concentrations differed only minimally during the nondiabetic and diabetic insulin profiles. These data indicate that lack of suppression of glucagon can cause substantial hyperglycemia when insulin availability is limited, therefore implying that inhibitors of glucagon secretion and/or glucagon action are likely to be useful therapeutic agents in such individuals.

Download Full-text