Loss of glucose-stimulated insulin secretion (GSIS) from the pancreatic beta-cells is one of the earliest detectable defects in the pathogenesis of type 2 diabetes. However, despite its relevance, the mechanisms that govern GSIS are still not completely understood. ARNT/HIF-1β is a member of the bHLH-PAS family of transcription factors, with a prominent role in the transcriptional regulation of enzymes required for the metabolism of xenobiotics as well as regulation of genes that are critical for cellular responses to hypoxia. Recent research has uncovered a previously unknown function for ARNT/HIF-1β in the pancreatic beta-cells, where the gene was found to be 90% down-regulated in human type 2 diabetic islets and loss of ARNT/HIF-1β protein leads to defective GSIS in pancreatic beta-cells of mice. The main focus of this thesis was to understand the mechanisms by which ARNT/HIF-1β maintains normal GSIS from pancreatic beta-cells and understand how loss of ARNT/HIF-1β leads to beta-cell dysfunction and type 2 diabetes in mice. ARNT/HIF-1β was found to positively regulate GSIS in both INS-1 derived 832/13 cell line and mice islets. In the 832/13 cells, loss of ARNT/HIF-1β leads to a reduction in glycolysis without affecting the glucose oxidation and the ATP/ADP ratio suggesting that the regulation of GSIS takes place in a manner that is independent of the KATP channels. In order to further assess the mechanism of lowered GSIS in the absence of ARNT/HIF-1β in the 832/13 cells, a metabolite profiling was performed which revealed a significant reduction in the metabolite levels of glycolysis and the TCA cycle intermediates and glucose-induced fatty acid production, suggesting the involvement of ARNT/HIF-1β in regulating glucose-stimulated anaplerosis, which is believed to play a key role in the regulation of GSIS from the pancreatic beta-cells. The changes in metabolite levels in the absence of ARNT/HIF-1β were associated with corresponding changes in the gene expression pattern of key enzymes regulating glycolysis, the TCA cycle and fatty acid synthesis in beta-cells. In an attempt to understand how loss of ARNT/HIF-1β leads to beta-cell dysfunction and type 2 diabetes in mice, a pancreatic beta-cell specific ARNT/HIF-1β knock out mouse (β-ARNT KO) was generated using the Cre-loxP technology. Functional characterization of islets from both male and female β-ARNT KO mice revealed a significant impairment in GSIS, which was attributed due to a small, but significant reduction in rise in intracellular calcium upon glucose stimulation. Further analysis revealed reduced secretory response to glucose in the presence of KCl and diazoxide indicating a defect in the amplifying pathway of GSIS in β-ARNT KO islets. Expression of pyruvate carboxylase (PC) was significantly reduced in β-ARNT KO islets suggesting possible impairments in anaplerosis and consistent with this, defect in GSIS in β-ARNT KO islets could be almost completely rescued by treatment with membrane permeable TCA intermediates. Surprisingly, both male and female β-ARNT KO mice have normal glucose homeostasis. In an attempt to assess how β-ARNT KO mice maintained normal blood glucose levels, indirect calorimetry was used to understand changes in whole-body energy expenditure. This investigation revealed that β-ARNT KO mice exhibited a small but significant increase in respiratory exchange ratio (RER), suggesting a preference in utilizing carbohydrates as a fuel source, possibly leading to improved glucose uptake from the blood stream. Response to exogenous insulin was completely normal in β-ARNT KO mice suggesting intact functioning of the skeletal muscles. To conclude, based on our in vitro data, we believe that ARNT/HIF-1β plays an indispensable role in maintaining normal beta-cell secretory function, however, results from β-ARNT KO mice indicates that these mice are protected from the adverse effects of hyperglycemia. Although loss of ARNT/HIF-1β alone is not sufficient for the genesis of type 2 diabetes, it creates a perfect storm in the pancreatic beta-cells that may eventually lead to an imbalance in the whole body glucose homeostasis. Our study provides significant information to the scientific community that engages in assessing the pharmacological potential of gene targets for the treatment of type 2 diabetes.

Thesis (M.S.)--University of Michigan, 1997. / Includes bibliographical references.

Thesis (Ph. D.)--Duke University, 2008. / Includes bibliographical references.

Thesis (doctoral)--Karolinska Institutet. / Text in English with summaries in English and Swedish. Added title page. Dissertation is a summary of several publications by the author appearing in various dental journals.

Thesis (doctoral)--Karolinska Institutet. / Text in English with summaries in English and Swedish. Added title page. Dissertation is a summary of several publications by the author appearing in various dental journals.

Thesis (M.S.)--University of Michigan, 1997. / Includes bibliographical references.

Type 1 diabetes (T1D) is characterised by an absolute insulin deficiency resulting from the chronic and progressive destruction of pancreatic β-cells by the immune system cells. Continuous subcutaneous insulin infusion (CSII) is becoming a popular technique for insulin delivery among T1D patients. Exercise is known to exert anti-inflammatory effects and metabolic control. Therefore it was of interest to study this in T1D using CSII. The objectives of this thesis were to further understanding of the effect of exercise on blood glucose, hemoglobin A1c, lipids, insulin and inflammatory markers in healthy and T1D volunteers. Three studies have been investigated where the diabetic volunteers used multi daily injections (MDI) or CSII. Firstly a survey was conducted aimed to investigate the effect of exercise on T1D patients using CSII therapy. The second study examined the acute and chronic effects of resistance and cardio exercise at moderate intensity on inflammatory markers such as IL-6, IL-1β, TNF-α and IFN-γ in healthy and T1D using MDI or CSII. Finally, a study was undertaken to find out the effects of chronic moderate intensity exercise on lipids profile and glycaemic control in healthy and T1D using MDI or CSII. The statistical analysis of the survey showed that CSII therapy for T1D had a significant reduction on A1c, insulin requirement and improvement of lipids profile compared to MDI. Moreover, majority of CSII users (63%) rarely suffered from hypoglycemia during exercise. The second study demonstrated that acute and chronic exercises have a positive impact on the inflammatory markers among CSII users e.g. in CSII users statistically significant increase in IL-6 and TNF-α levels were observed (P=0.014 and P=0.001 respectively). The last study showed that lipids profile, total daily insulin units were improved and A1c levels were significantly reduced in CSII as well as MDI groups after 6 weeks of exercise. T1D affects major organs e.g. heart, kidneys, blood vessels etc. However, good glycaemic control can reduce the risk of diabetes complications. This study suggested that CSII therapy along with exercise can maintain the BG level close to normal, as all 5 participants of the study showed an improvement in their BG levels after exercise.

Introduction: The management of type 1 diabetes through the use of Continuous Subcutaneous Insulin Infusion (CSII); also known as insulin pump therapy, has become an increasingly popular option for children and adolescents. A systematic review of studies that measured Quality of Life (QoL) in children associated with CSII was conducted. Eighteen studies were reviewed, and the results showed insufficient evidence to conclude that CSII improves QoL in children and adolescents with type 1 diabetes. The current study aimed to address the gap in the literature by exploring children and parents’ perspectives on the use of CSII for managing diabetes. Method: Data were gathered from five children aged 8 – 14 years (and five parents), using one to one semi-structured interviews. Interviews were recorded, transcribed and analysed using Interpretative Phenomenological Analysis (IPA). Results: Five super-ordinate themes were identified for parents: ‘Parenting a Child with Diabetes’; ‘Worth the Hard Work’; ‘Strive for Normality’; The Pump as an Enabler’; and ‘An eye on the Future’. Three Super-ordinate themes were identified for children ‘Feeling Different’; Grappling for Control’; and ‘Better…’ which were associated with a central theme of ‘Developing a Relationship with the Pump’. Children’s data is presented separately within a journal article format. Discussion: Findings suggest that parents value the insulin pump, despite acknowledging the challenges, particularly the hard work required to manage it. Children seemed to have an ambivalent but developing relationship with the insulin pump. They experience a number of benefits and drawbacks associated with the use of CSII and it seems to affect their identity and their locus of control. Conclusion: This research provides a greater insight into the lived experience of CSII for children and their parents. The benefits of CSII seemed to outweigh the challenges involved particularly for parents; and children seemed to be developing a relationship with the pump within the realms of their relationship with diabetes.

Achieving tight glucose control safely in type 1 diabetes with currently available methods of insulin delivery is challenging. Aggressive regimens carry an increased risk of hypoglycaemia, particularly overnight. Both alcohol consumption and exercise predispose further to low glucose levels. The demands are even greater in pregnancy where, in addition to limiting hypoglycaemia, avoidance of postprandial hyperglycaemia is critical to minimising adverse obstetric outcomes. The aim of my studies was to evaluate feasibility and safety of a closed-loop or ’artificial pancreas’ system linking insulin delivery with continuous glucose monitoring (CGM), in adults with type 1 diabetes in a controlled setting. Three randomised crossover studies compared closed-loop insulin delivery with conventional insulin pump therapy on two separate occasions, matched in meals and activities. During closed-loop visits, CGM values were entered into a computer containing a model predictive control algorithm which advised on basal insulin infusion for subcutaneous delivery, every 15 minutes. During control visits, usual insulin pump regimen was continued. The feasibility study evaluated overnight closed-loop in 12 adults (seven females, mean age 37.7 years, HbA1c 7.8%) following 60g- carbohydrate evening meal. A follow-up study assessed overnight closed-loop in 12 further adults (seven females, mean age 37.2 years, HbA1c 7.8%) following 100g-carbohydrate meal and (mean 564 ml) white wine. The third study evaluated 24 hours of closed-loop in 12 pregnant women (mean age 32.9 years, 19 to 23 weeks gestation, HbA1c 6.4%) during normal daily activities, including low and moderate intensity exercise. Activity and glucose levels were also measured during free-living. CGM performance during exercise was evaluated. Overnight closed-loop insulin delivery in adults, compared with conventional pump therapy, increased time spent with plasma glucose in target range (3.9−8.0 mmol/l) following both standard meal (81% versus 57%; p = 0.012) and large meal accompanied by alcohol (70% versus 46%; p = 0.012). Glycaemic variability, and time spent in hypo- and hyper- glycaemia were lowered. In pregnant women, day and night closed-loop insulin delivery was as effective as usual pump regimen (81% versus 81% time spent with plasma glucose 3.5−7.8 mmol/l; p = 0.754). Hypoglycaemia occurred following exercise, although closed-loop prevented nocturnal episodes. Glycaemic control during free-living was suboptimal, compared with controlled diet and exercise conditions. Accuracy of CGM was lower during exercise. In conclusion, these studies confirm the feasibility and efficacy of overnight closed-loop insulin delivery in adults with type 1 diabetes. Closed-loop is safe during pregnancy and may be beneficial in women with suboptimal glycaemic control. Meals and physical activity currently limit optimal daytime use of closed-loop.

No description available.