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Free access

Xiaofeng Wang and Catherine B Chan

n-3 polyunsaturated fatty acids (PUFAs) are a subgroup of fatty acids with broad health benefits, such as lowering blood triglycerides and decreasing the risk of some types of cancer. A beneficial effect of n-3 PUFAs in diabetes is indicated by results from some studies. Defective insulin secretion is a fundamental pathophysiological change in both types 1 and 2 diabetes. Emerging studies have provided evidence of a connection between n-3 PUFAs and improved insulin secretion from pancreatic β-cells. This review summarizes the recent findings in this regard and discusses the potential mechanisms by which n-3 PUFAs influence insulin secretion from pancreatic β-cells.

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

Guillaume Mabilleau, Marie Pereira and Chantal Chenu

Type 2 diabetes mellitus (T2DM) leads to bone fragility and predisposes to increased risk of fracture, poor bone healing and other skeletal complications. In addition, some anti-diabetic therapies for T2DM can have notable detrimental skeletal effects. Thus, an appropriate therapeutic strategy for T2DM should not only be effective in re-establishing good glycaemic control but also in minimising skeletal complications. There is increasing evidence that glucagon-like peptide-1 receptor agonists (GLP-1RAs), now greatly prescribed for the treatment of T2DM, have beneficial skeletal effects although the underlying mechanisms are not completely understood. This review provides an overview of the direct and indirect effects of GLP-1RAs on bone physiology, focusing on bone quality and novel mechanisms of action on the vasculature and hormonal regulation. The overall experimental studies indicate significant positive skeletal effects of GLP-1RAs on bone quality and strength although their mechanisms of actions may differ according to various GLP-1RAs and clinical studies supporting their bone protective effects are still lacking. The possibility that GLP-1RAs could improve blood supply to bone, which is essential for skeletal health, is of major interest and suggests that GLP-1 anti-diabetic therapy could benefit the rising number of elderly T2DM patients with osteoporosis and high fracture risk.

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P S Leung, H C Chan, L X M Fu and P Y D Wong

Abstract

Previous studies have demonstrated the existence of several key components of the renin–angiotensin system in the pancreas. In the present study, the localization of angiotensin II receptor subtypes, type I (AT1) and type II (AT2), in the mouse and the rat pancreas was studied by immunocytochemistry using specific antipeptide antibodies against the second extracellular loops of AT1 and AT2 receptors in conjunction with confocal laser scanning microscopy. In the mouse, immunoreactivity for AT1 and AT2 was observed predominantly in the endothelia of the blood vessels and the epithelia of the pancreatic ductal system. Similar distribution of immunoreactivity for AT1 and AT2 was also observed. However, the intensity of immunoreactivity for AT1 and AT2 was stronger in the rat than that found in the mouse pancreas. Much weaker immunostaining for both AT1 and AT2, as compared with that found in ductal regions, was also found in the acini of the rodent pancreas. Together with the previous findings, the present results suggest that AT1 and/or AT2 receptors may play a role in regulating pancreatic functions in the rodent.

Journal of Endocrinology (1997) 153, 269–274

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

Haijiang Wu, Xinna Deng, Yonghong Shi, Ye Su, Jinying Wei and Huijun Duan

Type 2 diabetes mellitus (T2DM) is a chronic disease characterized by glucose metabolic disturbance. A number of transcription factors and coactivators are involved in this process. Peroxisome proliferator-activated receptor gamma coactivator 1 alpha (PGC-1α) is an important transcription coactivator regulating cellular energy metabolism. Accumulating evidence has indicated that PGC-1α is involved in the regulation of T2DM. Therefore, a better understanding of the roles of PGC-1α may shed light on more efficient therapeutic strategies. Here, we review the most recent progress on PGC-1α and discuss its regulatory network in major glucose metabolic tissues such as the liver, skeletal muscle, pancreas and kidney. The significant associations between PGC-1α polymorphisms and T2DM are also discussed in this review.

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.

Restricted access

S. J. Winder, S. D. Wheatley and I. A. Forsyth

ABSTRACT

Sucrose density centrifugation was used to prepare a partially purified membrane fraction from the mammary glands of non-pregnant, pregnant and lactating sheep. The binding of125 I-labelled insulin-like growth factor-I (IGF-I) was dependent on membrane protein concentration, pH, time and temperature. The binding showed the characteristics of a type-1 IGF receptor, being displaced by IGF-I (median effective dose (ED50) 0·55 nmol/l), less effectively by IGF-II (ED50 8·8 nmol/l) and least effectively by insulin. Glucagon, ovine prolactin and ovine placental lactogen could not displace binding. A molecular weight of 135 000 was determined by affinity cross-linking using disuccinimidyl suberate; this was consistent with the reported size of the type-1 receptor α-subunit. Scatchard analysis was used to determine binding affinity and numbers of IGF-I-binding sites. A single class of high-affinity binding sites was found in all physiological states. In non-pregnant sheep and sheep at days 40, 75 and 110–120 of pregnancy and at term, the binding affinity was similar (apparent dissociation constant (K d) 2·73 ±0·31 nmol/l, n = 22). In lactating sheep (weeks 1, 4 and 10), the binding affinity was significantly (P = 0·02) higher (K d 0·77± 0·06 nmol/l n = 9). Binding capacity was similar in non-pregnant and pregnant sheep (1005 ± 113 fmol/mg, n = 19), but fell by parturition and remained low in lactation (570±52 fmol/mg membrane protein, n = 12). The results suggest that the mammary growth of pregnancy is not regulated at the level of the type-1 IGF receptor.

Journal of Endocrinology (1993) 136, 297–304

Free access

Yuichiro Takeuchi, Keishi Yamauchi, Junko Nakamura, Satoshi Shigematsu and Kiyoshi Hashizume

The biological effects of angiotensin II (AngII) are mediated by two major subtypes of AngII receptors, type 1 (AT1R) and type 2 (AT2R). In this study, we attempted to elucidate the role of AngII subtype receptor-specific regulation in migration and proliferation of mouse cultured mesangial (MSG) cells. We found that 100 nM AngII stimulated weak migration of MSG cells. Cell motility increased more in the presence of AT2R than in the presence of AT1R, and it was suppressed by guanylate cyclase inhibitors. On the other hand, the activation of AT1R resulted in increased cell numbers, while AT2R activation inhibited cell proliferation. Moreover, high concentrations of glucose (25 mM) stimulated the expression of AT2R but not AT1R. These results indicate that there are receptor subtype-specific roles in MSG cells, and it is therefore possible that the activation of AT2R stimulates repair of glomerular tissue defect, by regulation of migration and proliferation of MSG cells. Taken together, these results suggest that the relative concentrations of AT1R and AT2R are important factors in the regulation of AngII function in glomerular tissue, and alterations in the concentrations of these receptors may contribute to progression of or protection from diabetic nephropathy.