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Free access

Hongbin Liu, Yunshan Hu, Richard W Simpson, and Anthony E Dear

Glucagon-like peptide-1 (GLP-1) has been proposed as a target for treatment of type 2 diabetes. GLP-1 has also been demonstrated to improve endothelial cell dysfunction in diabetic patients. Elevated plasmogen activator inhibitor-1 (PAI-1) levels have been implicated in endothelial cell dysfunction. The effect of GLP-1 on PAI-1 expression in vascular endothelial cells has not been explored. In a spontaneously transformed human umbilical vein endothelial cell (HUVEC) line, C11-spontaneously transformed HUVEC (STH) and primary HUVEC cells, GLP-1 treatment, in the presence of a dipeptidyl peptidase IV inhibitor, attenuated induction of PAI-1 protein and mRNA expression by tumour necrosis factor-α (TNF-α). GLP-1 also inhibited the effect of TNF-α on a reporter gene construct harbouring the proximal PAI-1 promoter. In addition, GLP-1 attenuated TNF-α-mediated induction of Nur77 mRNA and TNF-α-mediated binding of nuclear proteins (NPs) to the PAI-1, Nur77, cis-acting response element nerve growth factor induced clone B response element (NBRE). GLP-1 treatment also inhibited TNF-α-mediated induction of Akt phosphorylation. Taken together, these observations suggest that GLP-1 inhibits TNF-α-mediated PAI-1 induction in vascular endothelial cells, and this effect may involve Akt-mediated signalling events and the modulation of Nur77 expression and NP binding to the PAI-1 NBRE.

Free access

L Monetini, F Barone, L Stefanini, A Petrone, T Walk, G Jung, R Thorpe, P Pozzilli, and MG Cavallo

Enhanced cellular immune response to bovine beta-casein has been reported in patients with type 1 diabetes. In this study we aimed to establish beta-casein-specific T cell lines from newly diagnosed type 1 diabetic patients and to characterise these cell lines in terms of phenotype and epitope specificity. Furthermore, since sequence homologies exist between beta-casein and putative beta-cell autoantigens, reactivity to the latter was also investigated. T cell lines were generated from the peripheral blood of nine recent onset type 1 diabetic patients with different HLA-DQ and -DR genotypes, after stimulation with antigen pulsed autologous irradiated antigen presenting cells (APCs) and recombinant human interleukin-2 (rhIL-2). T cell line reactivity was evaluated in response to bovine beta-casein, to 18 overlapping peptides encompassing the whole sequence of beta-casein and to beta-cell antigens, including the human insulinoma cell line, CM, and a peptide from the beta-cell glucose transporter, GLUT-2. T cell lines specific to beta-casein could not be isolated from HLA-matched and -unmatched control subjects. beta-Casein T cell lines reacted to different sequences of the protein, however a higher frequency of T cell reactivity was observed towards the C-terminal portion (peptides B05-14, and B05-17 in 5/9 and 4/9 T cell lines respectively). Furthermore, we found that 1 out of 9 beta-casein-specific T cell lines reacted also to the homologous peptide from GLUT-2, and that 3 out of 4 of tested cell lines reacted also to extracts of the human insulinoma cell line, CM. We conclude that T cell lines specific to bovine beta-casein can be isolated from the peripheral blood of patients with type 1 diabetes; these cell lines react with multiple and different sequences of the protein particularly towards the C-terminal portion. In addition, reactivity of beta-casein T cell lines to human insulinoma extracts and GLUT-2 peptide was detected, suggesting that the potential cross-reactivity with beta-cell antigens deserves further investigation.

Free access

J Han and Y Q Liu

Pyruvate carboxylase (PC) activity is enhanced in the islets of obese rats, but it is reduced in the islets of type 2 diabetic rats, suggesting the importance of PC in β-cell adaptation to insulin resistance as well as the possibility that PC reduction might lead to hyperglycemia. However, the causality is currently unknown. We used obese Agouti mice (AyL) as a model to show enhanced β-cell adaptation, and type 2 diabetic db/db mice as a model to show severe β-cell failure. After comparison of the two models, a less severe type 2 diabetic Agouti-K (AyK) mouse model was used to show the changes in islet PC activity during the development of type 2 diabetes mellitus (T2DM). AyK mice were separated into two groups: mildly (AyK-M, blood glucose <250 mg/dl) and severely (AyK-S, blood glucose >250 mg/dl) hyperglycemic. Islet PC activity, but not protein level, was increased 1.7-fold in AyK-M mice; in AyK-S mice, islet PC activity and protein level were reduced. All other changes including insulin secretion and islet morphology in AyK-M mice were similar to those observed in AyL mice, but they were worse in AyK-S mice where these parameters closely matched those in db/db mice. In 2-day treated islets, PC activity was inhibited by high glucose but not by palmitate. Our findings suggest that islet PC might play a role in the development of T2DM where reduction of PC activity might be a consequence of mild hyperglycemia and a cause for severe hyperglycemia.

Free access

VA Gault, PR Flatt, P Harriott, MH Mooney, CJ Bailey, and FP O'Harte

The therapeutic potential of glucagon-like peptide-1 (GLP-1) in improving glycaemic control in diabetes has been widely studied, but the potential beneficial effects of glucose-dependent insulinotropic polypeptide (GIP) have until recently been almost overlooked. One of the major problems, however, in exploiting either GIP or GLP-1 as potential therapeutic agents is their short duration of action, due to enzymatic degradation in vivo by dipeptidylpeptidase IV (DPP IV). Therefore, this study examined the plasma stability, biological activity and antidiabetic potential of two novel NH2-terminal Ala2-substituted analogues of GIP, containing glycine (Gly) or serine (Ser). Following incubation in plasma, (Ser2)GIP had a reduced hydrolysis rate compared with native GIP, while (Gly2)GIP was completely stable. In Chinese hamster lung fibroblasts stably transfected with the human GIP receptor, GIP, (Gly2)GIP and (Ser2)GIP stimulated cAMP production with EC(50) values of 18.2, 14.9 and 15.0 nM respectively. In the pancreatic BRIN-BD11 beta-cell line, (Gly2)GIP and (Ser2)GIP (10(-8) M) evoked significant increases (1.2- and 1.5-fold respectively; P<0.01 to P<0.001) in insulinotropic activity compared with GIP. In obese diabetic ob/ob mice, both analogues significantly lowered (P<0.001) the glycaemic excursion in response to i.p. glucose. This enhanced glucose-lowering ability was coupled to a significantly raised (P<0.01) and more protracted insulin response compared with GIP. These data indicate that substitution of the penultimate Ala2 in GIP by Gly or Ser confers resistance to plasma DPP IV degradation, resulting in enhanced biological activity, therefore raising the possibility of their use in the treatment of type 2 diabetes.

Free access

Isabel Göhring and Hindrik Mulder

In this issue of Journal of Endocrinology, Dr Han and colleagues report a protective effect of the glutamate dehydrogenase activator 2-aminobicyclo-(2,2,1)-heptane-2-carboxylic acid (BCH) under diabetes-like conditions that impair β-cell function in both a pancreatic β-cell line and db/db mice. Based on these observations, the authors suggest that BCH could serve as a novel treatment modality in type 2 diabetes. The present commentary discusses the importance of the findings. Some additional questions are raised, which may be addressed in future investigations, as there is some concern regarding the BCH treatment of β-cell failure.

Open access

Tingting Yang, Min He, Hailiang Zhang, Paula Q Barrett, and Changlong Hu

Aldosterone, which plays a key role in the regulation of blood pressure, is produced by zona glomerulosa (ZG) cells of the adrenal cortex. Exaggerated overproduction of aldosterone from ZG cells causes primary hyperaldosteronism. In ZG cells, calcium entry through voltage-gated calcium channels plays a central role in the regulation of aldosterone secretion. Previous studies in animal adrenals and human adrenal adrenocortical cell lines suggest that the T-type but not the L-type calcium channel activity drives aldosterone production. However, recent clinical studies show that somatic mutations in L-type calcium channels are the second most prevalent cause of aldosterone-producing adenoma. Our objective was to define the roles of T and L-type calcium channels in regulating aldosterone secretion from human adrenals. We find that human adrenal ZG cells mainly express T-type CaV3.2/3.3 and L-type CaV1.2/1.3 calcium channels. TTA-P2, a specific inhibitor of T-type calcium channel subtypes, reduced basal aldosterone secretion from acutely prepared slices of human adrenals. Surprisingly, nifedipine, the prototypic inhibitor of L-type calcium channels, also decreased basal aldosterone secretion, suggesting that L-type calcium channels are active under basal conditions. In addition, TTA-P2 or nifedipine also inhibited aldosterone secretion stimulated by angiotensin II- or elevations in extracellular K+. Remarkably, blockade of either L- or T-type calcium channels inhibits basal and stimulated aldosterone production to a similar extent. Low concentrations of TTA-P2 and nifedipine showed additive inhibitory effect on aldosterone secretion. We conclude that T- and L-type calcium channels play equally important roles in controlling aldosterone production from human adrenals.

Free access

M Nasu, T Sugimoto, H Kaji, and K Chihara

Although there is clinical evidence showing that combined therapy with parathyroid hormone (PTH) and estrogen is additively effective in increasing the bone mass of patients with osteoporosis, the mechanism of the interaction between these hormones remains unclear. The present study was performed to determine whether estrogen would affect osteoblast proliferation and function modulated by PTH in human osteoblastic SaOS-2 cells. Human PTH-(1-34) significantly inhibited [(3)H]thymidine (TdR) incorporation, which was attenuated by 24 h pretreatment with 10(-10) to 10(-7) M 17 beta-estradiol (17 beta-E(2)) in a concentration-dependent manner. PTH significantly stimulated alkaline phosphatase (ALP) activity, collagen synthesis and type-1 procollagen mRNA expression after pretreatment with 17 beta-E(2 )in these cells. Tamoxifen, an anti-estrogen, antagonized these 17 beta-E(2)-induced effects. Pretreatment with insulin-like growth factor-I (IGF-I) mimicked estrogen action, and coincubation of 3 microg/ml anti-IGF-I antibody antagonized the effects of 17 beta-E(2 )as well as those of IGF-I. In the presence of 17 beta-E(2 )pretreatment, PTH strongly stimulated IGF-binding protein (IGFBP)-5 mRNA expression in these cells, and recombinant IGFBP-5 increased type-1 procollagen mRNA expression and ALP activity. In conclusion, estrogen attenuates PTH-induced inhibition of osteoblast proliferation and PTH stimulates osteoblast function in the presence of estrogen pretreatment. IGF-I and/or IGFBP-5 seemed to be involved in the estrogen-induced modulation of PTH action on osteoblast proliferation and function.

Free access

GW Aberdeen, GJ Pepe, and ED Albrecht

In the present study, we determined whether expression of the messenger ribonucleic acids (mRNAs) for insulin-like growth factor-II (IGF-II), and its principal IGF type-1 receptor and IGF-binding protein-2 (IGFBP-2), as well as basic fibroblast growth factor (bFGF), was developmentally regulated in the baboon fetal adrenal gland. In the second phase of this study, fetal pituitary ACTH was suppressed by the administration of betamethasone to determine the possible effect on the mRNA levels for those factors, i.e. IGF-II and IGFBP-2, shown to be expressed at high levels in the adrenal late in fetal development. Adrenals were obtained from fetuses delivered via Cesarean section on days 60 (early), 100 (mid), and 165 (late) of gestation (term=184 days) from untreated baboons and on day 165 from baboons in which betamethasone was administered to the fetus, or to fetus and mother, every other day between days 150 and 164 of gestation. Although the mRNA levels of IGF-II in the fetal adrenal were similar at early, mid and late gestation, IGF type-1 receptor mRNA levels were approximately 2- to 3-fold greater (P<0.01) at mid than at early or late gestation. In contrast, there was an increase (P<0.001) in fetal adrenal IGFBP-2 and bFGF mRNA levels in late gestation. Although fetal adrenal weights and width of the zone of definitive/transitional cells exhibiting immunocytochemical staining for Delta(5)-3beta-hydroxysteroid dehydrogenase (3beta-HSD) were markedly suppressed (P<0.01) by the administration of betamethasone, IGF-II and IGFBP-2 mRNA expression was not decreased. In summary, very different patterns of mRNA levels for IGF-II, IGF type-1 receptor, IGFBP-2 and bFGF were exhibited in the developing baboon fetal adrenal gland, which may reflect functionally important differences in their respective cellular localization within the cortex, as well as a divergence in the functional development of the fetal, transitional and definitive zones of the baboon fetal adrenal cortex.

Free access

Lucy M Hinder, Anuradha Vivekanandan-Giri, Lisa L McLean, Subramaniam Pennathur, and Eva L Feldman

Diabetic neuropathy (DN) is the most common complication of diabetes and is characterized by distal-to-proximal loss of peripheral nerve axons. The idea of tissue-specific pathological alterations in energy metabolism in diabetic complications-prone tissues is emerging. Altered nerve metabolism in type 1 diabetes models is observed; however, therapeutic strategies based on these models offer limited efficacy to type 2 diabetic patients with DN. Therefore, understanding how peripheral nerves metabolically adapt to the unique type 2 diabetic environment is critical to develop disease-modifying treatments. In the current study, we utilized targeted liquid chromatography–tandem mass spectrometry (LC/MS/MS) to characterize the glycolytic and tricarboxylic acid (TCA) cycle metabolomes in sural nerve, sciatic nerve, and dorsal root ganglia (DRG) from male type 2 diabetic mice (BKS.Cg-m+/+Leprdb; db/db) and controls (db/+). We report depletion of glycolytic intermediates in diabetic sural nerve and sciatic nerve (glucose-6-phosphate, fructose-6-phosphate, fructose-1,6-bisphosphate (sural nerve only), 3-phosphoglycerate, 2-phosphoglycerate, phosphoenolpyruvate, and lactate), with no significant changes in DRG. Citrate and isocitrate TCA cycle intermediates were decreased in sural nerve, sciatic nerve, and DRG from diabetic mice. Utilizing LC/electrospray ionization/MS/MS and HPLC methods, we also observed increased protein and lipid oxidation (nitrotyrosine; hydroxyoctadecadienoic acids) in db/db tissue, with a proximal-to-distal increase in oxidative stress, with associated decreased aconitase enzyme activity. We propose a preliminary model, whereby the greater change in metabolomic profile, increase in oxidative stress, and decrease in TCA cycle enzyme activity may cause distal peripheral nerves to rely on truncated TCA cycle metabolism in the type 2 diabetes environment.

Free access

Jennifer S ten Kulve, Dick J Veltman, Liselotte van Bloemendaal, Paul F C Groot, Henricus G Ruhé, Frederik Barkhof, Michaela Diamant, and Richard G Ijzerman

Glucagon-like peptide-1 (GLP1) affects appetite, supposedly mediated via the central nervous system (CNS). In this study, we investigate whether modulation of CNS responses to palatable food consumption may be a mechanism by which GLP1 contributes to the central regulation of feeding. Using functional MRI, we determined the effects of endogenous GLP1 and treatment with the GLP1 analogue liraglutide on CNS activation to chocolate milk receipt. Study 1 included 20 healthy lean individuals and 20 obese patients with type 2 diabetes (T2DM). Scans were performed on two occasions: during infusion of the GLP1 receptor antagonist exendin 9–39 (blocking actions of endogenous GLP1) and during placebo infusion. Study 2 was a randomised, cross-over intervention study carried out in 20 T2DM patients, comparing treatment with liraglutide to insulin, after 10 days and 12 weeks. Compared with lean individuals, T2DM patients showed reduced activation to chocolate milk in right insula (P = 0.04). In lean individuals, blockade of endogenous GLP1 effects inhibited activation in bilateral insula (P ≤ 0.03). Treatment in T2DM with liraglutide, vs insulin, increased activation to chocolate milk in right insula and caudate nucleus after 10 days (P ≤ 0.03); however, these effects ceased to be significant after 12 weeks. Our findings in healthy lean individuals indicate that endogenous GLP1 is involved in the central regulation of feeding by affecting central responsiveness to palatable food consumption. In obese T2DM, treatment with liraglutide may improve the observed deficit in responsiveness to palatable food, which may contribute to the induction of weight loss observed during treatment. However, no long-term effects of liraglutide were observed.