The pancreatic beta cell is a key site for mediating the effects of leptin on glucose homeostasis

The hormone leptin plays a crucial role in maintenance of body weight and glucose homeostasis. This occurs through central and peripheral pathways, including regulation of insulin secretion by pancreatic beta cells. To study this further in mice, we disrupted the signaling domain of the leptin receptor gene in beta cells and hypothalamus. These mice develop obesity, fasting hyperinsulinemia, impaired glucose-stimulated insulin release, and glucose intolerance, similar to leptin receptor null mice. However, whereas complete loss of leptin function causes increased food intake, this tissue-specific attenuation of leptin signaling does not alter food intake or satiety responses to leptin. Moreover, unlike other obese models, these mice have reduced fasting blood glucose. These results indicate that leptin regulation of glucose homeostasis extends beyond insulin sensitivity to influence beta cell function, independent of pathways controlling food intake. These data suggest that defects in this adipoinsular axis could contribute to diabetes associated with obesity.     

Dynamin-related protein 1 mediates high glucose induced pancreatic beta cell apoptosis

The pancreatic beta cell dysfunction is critical cycle in the pathogenesis of diabetes. Hyperglycemia is one of factors that induce pancreatic beta cell dysfunction, but the underlying mechanisms have not been well elucidated. In this study, we reported that a mitochondrial fission modulator, Dynamin-related protein 1 (Drp-1), plays an important role in high glucose induced beta cell apoptosis. Drp-1 expressed in islet beta cells was increased drastically under hyperglycemia conditions. Induction of Drp-1 expression significantly promoted high glucose induced apoptosis in Drp-1WT (Drp-1 wild type) inducible beta cell line, but not in Drp-1K38A (a dominant negative mutant of Drp1) inducible beta cell line. We further demonstrated that mitochondrial fission, cytochrome C release, mitochondrial membrane potential decreased, caspase-3 activation and generation of reactive oxygen species were enhanced by induction of Drp-1WT, but prevented by Drp-1K38A in pancreatic beta cells under high glucose condition. These results indicated that Drp-1 mediates high glucose induced pancreatic beta cell apoptosis.     

A SIRTain role in pancreatic beta cell function

Genes formerly thought to be involved solely in the regulation of life span have increasingly become implicated in the regulation of metabolic processes. Moynihan et al.(2005[this issue of Cell Metabolism]) now demonstrate that increasing levels of Sirt1 in the pancreatic beta cells of mice result in a more efficient glucose handling due to enhanced glucose-stimulated insulin secretion.     

Tumor necrosis factor-alpha enhances inhibitory effects of interleukin-1 beta on Leydig cell steroidogenesis

Human recombinant tumor necrosis factor-alpha (rTNF alpha) alone (up to 1000 units/ml) did not alter either basal or human chorionic gonadotropin (hCG)-induced testosterone formation in primary culture of rat Leydig cells. However, concomitant addition of rTNF alpha with human recombinant interleukin-1 beta (rIL-1 beta) enhanced the inhibitory effects of rIL-1 beta. The rIL-1 beta dose response curve was shifted to the left (IC50 changed from 1 ng/ml to 0.3 ng/ml). Even though rTNF alpha had no effect on testosterone formation, hCG-stimulated cyclic AMP formation was inhibited by rTNF alpha in a dose dependent manner. In the presence of both rTNF alpha and rIL-1 beta, hCG-induced cyclic AMP formation and binding of [125I]-hCG to Leydig cells were further inhibited. Testicular macrophages represent about 20% of the interstitial cells. TNF alpha and IL-1 may be produced locally by interstitial macrophages and have paracrine effects on Leydig cell function.     

Adrenalectomy enhances the susceptibility of pancreatic islets to interleukin-1 beta: immunohistochemical study.

To determine the importance of adrenal steroid in the effects of interleukin-1, we investigated changes in the number of islet cells reactive toward antiserum to insulin (anti-Ins) by intraperitoneal administration of recombinant human interleukin-1 beta (IL-1) in intact and adrenalectomized (ADX) rats. IL-1 significantly reduced serum insulin levels in ADX rats only, while it similarly decreased plasma glucose levels. In intact rats, IL-1 did not affect the number of islet cells reactive to anti-Ins, although cytoplasmic immunostaining tended to be reduced by IL-1 treatment. Only adrenalectomy decreased the number of islet cells immunostained by anti-Ins. Furthermore, IL-1 treatment significantly reduced the number of islet cells reactive to anti-Ins in ADX rats. The present study immunohistochemically supported our working hypothesis that the withdrawal of adrenal steroids by adrenalectomy enhances the islet cell sensitivity to exogenous administration of IL-1.     

The effect of N-terminal extension on the structure and function of human interleukin-1 beta

Interleukin-1 beta (IL-1 beta) and N-terminally extended Met-Glu-Ala-Glu-IL-1 beta (MEAE-IL-1 beta) were cloned and expressed in E. coli. Extension of the chain results in a limited conformational change reflected by the CD spectrum in the far ultraviolet, while the aromatic side chains responsible for the CD in the near ultraviolet are not affected. No difference in immunoreactivity between IL-1 beta and MEAE-IL-1 beta is observed in the IL-1 beta ELISA. Like IL-1 beta, MEAE-IL-1 beta exhibits biological activity tested in the costimulatory mouse thymocyte (LAF) assay. The specific biological activity of IL-1 beta is 3 x 10(8) U/mg and that of MEAE-IL-1 beta 3 x 10(6) U/mg. Like IL-1 beta, MEAE-IL-1 beta displaces [125I]IL-1 beta from mouse thymocytes and the binding affinities of the two forms differ by a factor of 10(2). Finally the inhibitory effect of the two IL-1 beta forms on in vitro insulin secretion from isolated rat islets of Langerhans was measured. Again MEAE-IL-1 beta is 10(2) times less potent than IL-1 beta. The structure-activity relationship for IL-1 beta and MEAE-IL-1 beta is discussed.     

Investigation of the effects of sulfonylurea exposure on pancreatic beta cell metabolism

Prolonged exposure of pancreatic beta cells to the sulfonylureas glibencamide and tolbutamide induces subsequent desensitization to the actions of these drugs. The precise mechanisms underlying this desensitization remain unknown, prompting the present study, which investigated the impact of prolonged sulfonylurea exposure on glucose and energy metabolism using clonal pancreatic BRIN-BD11 beta cells. Following prolonged exposure to tolbutamide, BRIN-BD11 beta cells were incubated in the presence of [U-(13)C]glucose, and isotopomer analysis revealed that there was a change in the ratio of flux through pyruvate carboxylase (EC 6.4.1.1) and pyruvate dehydrogenase (EC 1.2.4.1, EC 2.3.1.12, EC 1.8.1.4). Energy status in intact BRIN-BD11 cells was determined using (31)P-NMR spectroscopy. Exposure to tolbutamide did not alter the nucleotide triphosphate levels. Collectively, data from the present study demonstrate that prolonged exposure of beta cells to tolbutamide results in changes in flux through key enzymes involved in glucose metabolism that, in turn, may impact on glucose-induced insulin secretion.     

Purification of interleukin-1 beta converting enzyme, the protease that cleaves the interleukin-1 beta precursor.

We have purified the IL-1 beta converting enzyme from the THP-1 cell line using standard chromatographic techniques and obtained the N-terminal amino acid sequence of this novel protein. After stimulation of THP-1 cells with lipopolysaccharide, hydroxyurea, and silica, the protease was solubilized by multiple freeze/thawing. The protein was purified by ion-exchange chromatography, affinity chromatography on blue agarose, gel filtration, and chromatofocusing. The molecular weight of the protein is approximately 22,000 Da and the pI is between 7.1 and 6.8. The overall yield for this procedure was 16% of the activity found in the initial cell lysates. An antiserum raised against a peptide based on the N-terminus was used to precipitate the protease, confirming our identification of the 22,000-Da protein as the IL-1 beta converting enzyme.     

The effects of interleukin-1 therapy on peripheral blood granulocyte function in humans

During a phase I trial of interleukin-1 (IL-1) in patients with ovarian carcinomas, the effects of this treatment on blood granulocyte respiratory burst and locomotive responses were examined. Differences in baseline granulocyte function in patients as well as dose-related effects of IL-1 treatment were observed. Patients enrolled early in the trial (low-dose patients) had significantly lower locomotive responses before treatment than their paired controls; these low responses normalized after 5 days of continuous-infusion IL-1 treatment. Patients enrolled later (high-dose patients) had normal locomotive responses before treatment and IL-1 treatment was associated with suppression of responses to selected stimuli at the end of treatment. Pretreatment respiratory burst responses in both low-and high-dose patient groups were essentially normal, but the rates of granulocyte H₂O₂ production following phorbol myristate acetate stimulation became significantly less than control values at the end of treatment. In vitro exposure of either patient or control cells to 150 U/ml IL-1 did not alter their locomotive or respiratory burst responses, suggesting the observed in vivo effects were not mediated directly by IL-1. Treatment with IL-1 is associated with changes in ex vivo granulocyte function that are related to the IL-1 dose. Treatment with low doses of IL-1 may provide a means of normalizing abnormal polymorphonuclear leukocyte function in some patients with ovarian malignancies.     

Blockade of cannabinoid 1 receptor improves glucose responsiveness in pancreatic beta cells

Cannabinoid 1 receptors (CB1Rs) are expressed in peripheral tissues, including islets of Langerhans, where their function(s) is under scrutiny. Using mouse β‐cell lines, human islets and CB1R‐null (CB1R^?/?) mice, we have now investigated the role of CB1Rs in modulating β‐cell function and glucose responsiveness. Synthetic CB1R agonists diminished GLP‐1‐mediated cAMP accumulation and insulin secretion as well as glucose‐stimulated insulin secretion in mouse β‐cell lines and human islets. In addition, silencing CB1R in mouse β cells resulted in an increased expression of pro‐insulin, glucokinase (GCK) and glucose transporter 2 (GLUT2), but this increase was lost in β cells lacking insulin receptor. Furthermore, CB1R^?/? mice had increased pro‐insulin, GCK and GLUT2 expression in β cells. Our results suggest that CB1R signalling in pancreatic islets may be harnessed to improve β‐cell glucose responsiveness and preserve their function. Thus, our findings further support that blocking peripheral CB1Rs would be beneficial to β‐cell function in type 2 diabetes.     

The effects of the microwaves on E. coli cells depend on oxygen concentration and static magnetic field

The effects of non-thermal microwaves (MW), 10(-4) and 10(-10) W/cm(2), on conformation of nucleoids in E. coli cells were analyzed by the method of anomalous viscosity time dependence (AVTD). MW exposure was performed at different values of static magnetic field and concentration of oxygen, 8-90 microT, and 2.3-7.8 mg/l, respectively. It was shown, that slight changes in both static magnetic field and oxygen concentration result in significant changes of MW effects up to their disappearance. It was established, that changes in static magnetic field affected significantly the time kinetics of the MW effects. The obtained data provide further evidence for strong dependence of the effects of non-thermal microwaves on physical parameters of exposure and physiological factors. These dependences should be taken into account in replication studies. The obtained results encourage further investigation of possible modulation of non-thermal MW effects by additional electromagnetic fields.     

The three-dimensional structure of interleukin-1 beta

The three-dimensional structure of human recombinant interleukin-1 beta has been determined at 0.24 nm resolution by X-ray crystallographic techniques. The partially refined model has a crystallographic R-factor of just under 19%. The structure is composed of 12 beta-strands forming a complex network of hydrogen bonds. The core of the structure can best be described as a tetrahedron whose edges are each formed by two antiparallel beta-strands. The interior of this structure is filled with hydrophobic side-chains. There is a 3-fold repeat in the folding of the polypeptide chain. Although this folding pattern suggests gene triplication, no significant internal sequence homology between topologically corresponding residues exists. The folding topology of interleukin-1 beta is very similar to that described by A. D. McLachlan [(1979) J. Mol. Biol. 133, 557-563] for soybean trypsin inhibitor.     

Crystal structure of the cytokine interleukin-1 beta.

The crystal structure of human recombinant interleukin-1 beta has been determined at 3.0 A resolution by the isomorphous replacement method in conjunction with solvent flattening techniques. The model prior to refinement has a crystallographic R-factor of 42.3%. The structure is composed of 12 beta-strands forming a complex network of hydrogen bonds. The core of the structure can best be described as a tetrahedron whose edges are each formed by two antiparallel beta-strands. The interior of this structure is filled with hydrophobic side chains. There is a 3-fold repeat in the folding of the polypeptide chain. Although this folding pattern suggests gene triplication, no strong internal sequence homology between topologically corresponding residues exists. The folding topology of interleukin-1 beta is very similar to that described by McLachlan (1979) J. Mol. Biol., 133, 557-563, for soybean trypsin inhibitor.