OBJECTIVE: To investigate the effect of ferulic acid, a natural compound, on pancreatic beta cell viability, Ca²⁺ channels, and insulin secretion. METHODS: We studied the effects of ferulic acid on rat insulinoma cell line viability using the 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide viability assay. The whole-cell patch-clamp technique and enzyme-linked immunosorbent assay were also used to examine the action of ferulic acid on Ca²⁺ channels and insulin secretion, respectively. RESULTS: Ferulic acid did not affect cell viability during exposures up to 72 h. The electrophysiological study demonstrated that ferulic acid rapidly and concentration-dependently increased L-type Ca²⁺ channel current, shifting its activation curve in the hyperpolarizing direction with a decreased slope factor, while the voltage dependence of inactivation was not affected. On the other hand, ferulic acid have no effect on T-type Ca²⁺ channels. Furthermore, ferulic acid significantly increased insulin secretion, an effect inhibited by nifedipine and Ca²⁺-free extracellular fluid, confirming that ferulic acid-induced insulin secretion in these cells was mediated by augmenting Ca²⁺ influx through L-type Ca²⁺ channel. Our data also suggest that this may be a direct, nongenomic action. CONCLUSION This is the first electrophysiological demonstration that acute ferulic acid treatment could increase L-type Ca²⁺ channel current in pancreatic β cells by enhancing its voltage dependence of activation, leading to insulin secretion.
Rats ; Animals ; Insulin Secretion ; Insulin/pharmacology* ; Insulin-Secreting Cells/metabolism* ; Coumaric Acids/metabolism* ; Calcium/metabolism*

In order to clarify the cause of intracellular ATP dependency on Zn2+ blockade of KATP channels in pancreatic beta cells, we investigated the KATP channel activity during external Zn2+ application using voltage clamp technique. Cultured beta cells were used for patch-clamp experiment. When 3 mM glucose was applied in bath, KATP channel activity was increased transiently by externally applied Zn2+ in the cell-attached mode and was recoverable. The KATP channel activity was, however, consistently increased by Zn2+ application during the 0 mM glucose in bath. Inside-out mode, internally applied Zn2+ elicited no response on the KATP channels. Another divalent cation, Mn2+, didn't have any effect on the KATP channels. Therefore, This effect, so-called external glucose-dependency on Zn2+ blockade of the KATP channels, might be due to intracellular Zn2+ metabolism which induces ATP consumption. This appears to be a mechanism that the Zn2+ blockade of the KATP channels in the pancreatic beta cells depends on the intracellular ATP concentration.
Adenosine Triphosphate* ; Baths ; Glucose ; Insulin-Secreting Cells* ; KATP Channels* ; Metabolism

OBJECTIVETo observe the structural and functional changes in islet beta cells in severely scalded rats, and to explore its relationship with dysfunction of glycometabolism.

METHODSSeventy-two Wistar rats were divided into scald (S) group and sham injury (SI) group according to the random number table, with 36 rats in each group. Rats in group S were inflicted with 50%TBSA full-thickness scald by a 12-s immersion of back and a 6-s immersion of abdomen in 94 °C hot water. Rats in group SI were sham injured through immersion of back and abdomen in 37 °C warm water. At post injury hour (PIH) 6 and on post injury day (PID) 3 and 7, plasma glucose level was measured for intraperitoneal glucose tolerance test (IPGTT) in 12 rats of each group, and the area under the curve (AUC) of plasma glucose level was calculated. After the IPGTT, pancreatic tissue was harvested and subjected to a double immunostaining for insulin and cell nuclei to determine the pancreatic insulin-positive area ratio, and the area and number of beta cells in the islets (referred to as "the three indicators in the islets"). Data were processed with the analysis of repeated measures and factorial designed analysis of variance, and LSD test was applied for paired comparison.

RESULTS(1) At PIH 6 and on PID 3, the overall plasma glucose levels of rats in group S before and after injection of glucose and at each time point were obviously higher than those of rats in group SI (with F values of main effects respectively 79.372 and 32.962, P values all below 0.001; with P values of paired comparison below 0.05 or 0.01). On PID 7, the overall plasma glucose levels in the two groups before and after injection of glucose and at each time point were close (with P values all above 0.05). (2) The overall AUC of plasma glucose levels of rats in group S was higher than that of rats in group SI (main effects: F = 337.87, P < 0.01). Compared with those of rats in group SI [(1019 ± 32), (1003 ± 72) mmol·min·L(-1)], the AUCs of plasma glucose levels of rats in group S were higher at PIH 6 and on PID 3 [(1501 ± 163), (1132 ± 67) mmol·min·L(-1), P values all below 0.001]. The AUCs of plasma glucose levels were close between two groups on PID 7 (P > 0.05). The AUCs of plasma glucose levels on PID 3 and 7 were both lower than that at PIH 6 in rats of group S (with P values all below 0.001). (3) The three indicators in the islets in rats of group S were all lower than those of rats in group SI (with F values of main effects respectively 135.17, 24.75 and 39.35, P values all below 0.01). There were no significant differences in the three indicators in the islets at PIH 6 between two groups (with P values all above 0.05). The three indicators in the islets of rats in group S on PID 3 and 7 [0.47 ± 0.05, 0.51 ± 0.07; (0.032 ± 0.008), (0.037 ± 0.008) mm(2); (303 ± 64), (341 ± 58) cells] were significantly lower than those of rats in group SI [0.63 ± 0.05, 0.64 ± 0.06; (0.043 ± 0.011), (0.044 ± 0.012) mm(2); (398 ± 112), (387 ± 90) cells; P < 0.05 or P < 0.01] and that at PIH 6 within group S (P < 0.05 or P < 0.01).

CONCLUSIONSThe number of beta cells is reduced, and the insulin secretion function of beta cells is decreased in the scalded rats, and they may constitute the cause of dysfunction of glycometabolism, mainly manifested as hyperglycemia.

Animals ; Blood Glucose ; metabolism ; Burns ; metabolism ; Insulin ; metabolism ; Insulin-Secreting Cells ; metabolism ; Male ; Rats ; Rats, Wistar

BACKGROUNDThere are studies suggesting smoking may increase the risk of type 2 diabetes. Effects of smoking on insulin secretion and insulin resistance (IR) are, however, controversial.

METHODSThis is a cross-sectional study. Since there were very few smokers among Hong Kong Chinese women, only men (n = 1068) were analyzed in this report. Fasting and 2-hour plasma glucose and insulin were measured. Insulinogenic index as well as beta-cell function and IR based on homeostatic model assessment (HOMA) by computer model (HOMA Calculator v2.2) were calculated.

RESULTSOf the 1068 men, 147 had newly diagnosed diabetes, 131 newly diagnosed impaired glucose tolerance (IGT) and 790 were non-diabetic normal controls. Smokers had similar fasting and 2-hour insulin levels, insulinogenic index and HOMA derived beta-cell function as compared to non-smokers in the groups with diabetes, IGT or normal oral glucose tolerance test (OGTT). IR was also similar between smokers, ex-smokers and non-smokers in those with normal OGTT. In men with IGT or diabetes, after adjustment for age and body mass index, smokers were more insulin resistant as compared to non-smokers (IR, IGT: 1.59 +/- 1.07 vs 1.03 +/- 0.54, P < 0.05; diabetes: 1.96 +/- 1.36 vs 1.06 +/- 0.45, P < 0.01). With Logistic regression analysis, comparing smokers and non-smokers, IR was independently associated with smoking (odds ratio (95% CI), IGT: 2.23 (1.05, 4.71); diabetes: 3.92 (1.22, 12.58)). None of the other insulin parameters enter into the model among those with normal OGTT or comparing ex-smokers and non-smoker or smokers and ex-smokers.

CONCLUSIONSIn Chinese men, smoking did not show any direct association with insulin levels and pancreatic insulin secretion. Smoking men with IGT or diabetes appeared more insulin resistant than their non-smoking counterparts.

Adult ; Female ; Glucose Intolerance ; metabolism ; Humans ; Insulin ; secretion ; Insulin Resistance ; Insulin-Secreting Cells ; secretion ; Male ; Middle Aged ; Smoking ; metabolism

Type 2 diabetes mellitus( T2 DM) is a common chronic metabolic disease characterized by persistent hyperglycemia and insulin resistance. In pancreatic β-cells,glucose-stimulated insulin secretion( GSIS) plays a pivotal role in maintaining the balance of blood glucose level. Previous studies have shown that geniposide,one of the active components of Gardenia jasminoides,could quickly regulate the absorption and metabolism of glucose,and affect glucose-stimulated insulin secretion in pancreatic β cells,but the specific mechanism needs to be further explored. Emerging evidence indicated that glycosylation of glucose transporter( GLUT) has played a key role in sensing cell microenvironmental changes and regulating glucose homeostasis in eucaryotic cells. In this study,we studied the effects of geniposide on the key molecules of GLUT2 glycosylation in pancreatic β cells. The results showed that geniposide could significantly up-regulate the mRNA and protein levels of Glc NAc T-Ⅳa glycosyltransferase( Gn T-Ⅳa) and galectin-9 but had no signi-ficant effect on the expression of clathrin,and geniposide could distinctively regulate the protein level of Gn T-Ⅳa in a short time( 1 h) under the conditions of low and medium glucose concentrations,but had no significant effect on the protein level of galectin-9. In addition,geniposide could also remarkably affect the protein level of glycosylated GLUT2 in a short-time treatment. The above results suggested that geniposide could quickly regulate the protein level of Gn T-Ⅳa,a key molecule of protein glycosylation in INS-1 rat pancreatic βcells and affect the glycosylation of GLUT2. These findings suggested that the regulation of geniposide on glucose absorption,metabolism and glucose-stimulated insulin secretion might be associated with its efficacy in regulating GLUT2 glycosylation and affecting its distribution on the cell membrane and cytoplasm in pancreatic β cells.
Animals ; Diabetes Mellitus, Type 2/metabolism* ; Glucose/metabolism* ; Glycosylation ; Insulin/metabolism* ; Insulin-Secreting Cells/metabolism* ; Iridoids ; Rats

Insulin is produced and secreted by pancreatic β cells in the pancreas, which plays a key role in maintaining euglycemia. Insufficient secretion or deficient usage of insulin is the main cause of diabetes mellitus (DM). Drug therapy and islets transplantation are classical treatments for DM. Pancreatic β cell replacement therapy could help patients to get rid of drugs and alleviate the problem of lacking in transplantable donors. Pancreatic β-like cells can be acquired by cell reprogramming techniques or directed induction of stem cell differentiation. These cells are proved to be functional both in vitro and in vivo. Some hospitals have already performed clinical trials for pancreatic β cell replacement therapy. Functional pancreatic β-like cells, which obtained from in vitro pathway, could be a reliable source of cell therapy for treating DM. In this review, the approaches of obtaining pancreatic β cells are summarized and the remaining problems are discussed. Some thoughts are provided for further acquisition and application of pancreatic β cells.
Cell Differentiation ; Diabetes Mellitus/therapy* ; Humans ; Insulin/metabolism* ; Insulin-Secreting Cells/metabolism* ; Islets of Langerhans Transplantation ; Pancreas/metabolism*

Diabetes mellitus is a complex metabolic disorder characterized by chronic hyperglycemia due to absolute or relative lack of insulin. Though great efforts have been made to investigate the pathogenesis of diabetes, the underlying mechanism behind the development of diabetes and its complications remains unexplored. Cumulative evidence has linked mitochondrial modification to the pathogenesis of diabetes and its complications and they are also observed in various tissues affected by diabetes. Proteomics is an attractive tool for the study of diabetes since it allows researchers to compare normal and diabetic samples by identifying and quantifying the differentially expressed proteins in tissues, cells or organelles. Great progress has already been made in mitochondrial proteomics to elucidate the role of mitochondria in the pathogenesis of diabetes and its complications. Further studies on the changes of mitochondrial protein specifically post-translational modifications during the diabetic state using proteomic tools, would provide more information to better understand diabetes.
Adipose Tissue ; metabolism ; Diabetes Complications ; Diabetes Mellitus ; metabolism ; pathology ; Humans ; Insulin ; metabolism ; Insulin-Secreting Cells ; cytology ; metabolism ; Liver ; metabolism ; Mitochondria ; metabolism ; Muscle, Skeletal ; metabolism ; Proteome ; metabolism ; Proteomics

Mitochondrial dynamics and distribution is critical for their role in bioenergetics and cell survival. We investigated the consequence of altered fission/fusion on mitochondrial function and motility in INS-1E rat clonal beta-cells. Adenoviruses were used to induce doxycycline-dependent expression of wild type (WT-Mfn1) or a dominant negative mitofusin 1 mutant (DN-Mfn1). Mitochondrial morphology and motility were analyzed by monitoring mitochondrially-targeted red fluorescent protein. Adenovirus-driven overexpression of WT-Mfn1 elicited severe aggregation of mitochondria, preventing them from reaching peripheral near plasma membrane areas of the cell. Overexpression of DN-Mfn1 resulted in fragmented mitochondria with widespread cytosolic distribution. WT-Mfn1 overexpression impaired mitochondrial function as glucose- and oligomycin-induced mitochondrial hyperpolarization were markedly reduced. Viability of the INS-1E cells, however, was not affected. Mitochondrial motility was significantly reduced in WT-Mfn1 overexpressing cells. Conversely, fragmented mitochondria in DN-Mfn1 overexpressing cells showed more vigorous movement than mitochondria in control cells. Movement of these mitochondria was also less microtubule-dependent. These results suggest that Mfn1-induced hyperfusion leads to mitochondrial dysfunction and hypomotility, which may explain impaired metabolism-secretion coupling in insulin-releasing cells overexpressing Mfn1.
Adenoviridae ; Animals ; Cell Membrane ; Cell Survival ; Cytosol ; Energy Metabolism ; Insulin ; Insulin-Secreting Cells ; Luminescent Proteins ; Mitochondria ; Mitochondrial Dynamics ; Rats

Epidermal growth factor receptor (EGFR) cell signaling plays a central role in beta-cell mass/function regulation, and provides a new strategy for the treatment of diabetes, but its mechanisms of action remain poorly understood. In developmental biology, pancreatic islet development is impaired in lacking EGFR of mice. The attenuation of EGFR signaling in the islets leads to markedly reduced beta-cell proliferation. EGFR ligands BTC can increase proliferation and neogenesis. In this article EGFR and their ligands in the pancreas, EGFR cell signaling, and EGFR effects in pancreatic beta-cell mass/function regulation were reviewed.
Betacellulin ; Humans ; Insulin-Secreting Cells ; metabolism ; Intercellular Signaling Peptides and Proteins ; metabolism ; Ligands ; Receptor, Epidermal Growth Factor ; metabolism ; Signal Transduction ; physiology

BACKGROUND: Glucocorticoid plays an important role in the control of carbohydrate metabolism. Patients with Cushing's syndrome have been reported to have an increased incidence of carbohydrate intolerance due to peripheral insulin resistance and hyperinsulinemia, although the exact incidence and nature of this disorder have remained unclear. Few results have been published about insulin resistance and insulin secretion according to the level of glucose concentration, or about the reversibility of such defects in patients with Cushing's syndrome. METHODS: To assess the effect of glucocorticoid on the insulin sensitivity and insulin secretion in Cushing's syndrome, 15 patients with Cushing's syndrome were classified into 3 groups (normal glucose tolerance: NGT, impaired glucose tolerance: IGT, diabetes: DM) according to the degree of glucose tolerance based on the oral glucose tolerance test (OGTT). Insulin modified, frequentlysampled, intravenous glucose tolerance test (FSIGT) was performed before and after curative surgery on these patients and on 15 healthy control subjects. Data were evaluated by non-parametric statistical analysis. RESULTS: 1) Among the 15 patients with Cushing's syndrome, 3 (20%) were NGT, 4 (27%) IGT, and 8 (53%) DM, based on OGTT. Twenty-four hour urinary free cortisol (UFC) was significantly higher in the DM group. 2) Insulin sensitivity index (SI) of Cushing's syndrome was significantly lower than that of the control group (P=0.0024), but was not significantly different among the three Cushing's syndrome groups of NGT, IGT and DM. 3) Glucose mediated glucose disposal (SG) (Ed- confirm this abbreviation; it does not seem to match the definition) of Cushing's syndrome was not significantly different from that of the control group. 4) Insulin secretion (AIRg) of Cushing's syndrome tended to be high, but it was not significantly different from that of control. However, according to the level of glucose concentration there was significant difference in AlRg among the three Cushing's syndrome groups (P=0.0031); AIRg of DM was significantly lower than that of NGT. 5) After surgical treatment, parameters of insulin sensitivity and insulin secretion were normalized in 6 cured patients; 1 with NGT, 1 with IGT, and 4 with DM, preoperatively. Median SI of all 6 patients was significantly improved up to the normal range postoperatively (P=0.0022). Median AIRg of these 6 patients was balanced around that of normal control postoperatively (P=0.0286). CONCLUSION: Eighty percent of patients with Cushing's syndrome had abnormality of carbohydrate metabolism. Insulin sensitivity was significantly decreased in Cushing's syndrome. Insulin secretion was significantly higher only in the NGT and IGT groups of Cushing's syndrome. As the hypercortisolemia is exacerbated, insulin secretion is significantly decreased and causes DM, suggesting that glucocorticoid has a direct or indirect toxic effect on the pancreatic beta cell.
Carbohydrate Metabolism ; Cushing Syndrome* ; Glucose Tolerance Test ; Glucose* ; Humans ; Hydrocortisone ; Hyperinsulinism ; Incidence ; Insulin Resistance* ; Insulin* ; Insulin-Secreting Cells ; Metabolism* ; Reference Values