<p>During development of type 1 and type 2 diabetes plasma insulin patterns are altered. Since the islet insulin release pattern has been implicated in this development, insulin secretion from single islets was studied and linked to the islet protein levels of uncoupling protein-2 (UCP2). Islets were isolated from NOD- and KKA^y- mice, GK- and GK-derived congenic rats, which are animal models of diabetes, and three human subjects with type 2 diabetes. At basal glucose (3 mM), insulin release from such islets was pulsatile and the amount released was comparable to that of control islets. When the glucose concentration was raised to 11 mM insulin release was essentially unchanged in islets isolated from older NOD- and KKA^y- mice, GK- and Niddm1i congenic rats, and NIDDM persons. In islets from Niddm1f congenic rats, younger NOD- and KKA^y-mice, control animals and normal human donors the secretion rate increased 2-9 fold when the glucose concentration was raised. This rise in secretion was manifested as increase of the amplitude of the insulin oscillations without affecting their frequency. Impaired glucose-induced insulin release was associated with reduction in glucose oxidation measured in NOD-islets, unaffected respiration measured in GK-islets and higher protein level of UCP2 measured in KKA^y-islets. When the UCP2 amounts in KKA^y-islets were reduced by culture to those of control islets, glucose-induced insulin secretion was essentially normalized. Our studies suggest that the deranged plasma insulin patterns observed in diabetes are related to decrease in the amplitude of insulin oscillations from the islets rather than loss of the oscillatory activity. This reduction of pulse amplitude may be related to impaired glucose metabolism and/or increased mitochondrial uncoupling. </p>

<p>Population pharmacokinetic-pharmacodynamic (PK-PD) models can be fitted using nonlinear mixed effects modelling (NONMEM). This is an efficient way of learning about drugs and diseases from data collected in clinical trials. Identifying covariates which explain differences between patients is important to discover patient subpopulations at risk of sub-therapeutic or toxic effects and for treatment individualization. Stepwise covariate modelling (SCM) is commonly used to this end. The aim of the current thesis work was to evaluate SCM and to develop alternative approaches. A further aim was to develop a mechanistic PK-PD model describing fasting plasma glucose, fasting insulin, insulin sensitivity and beta-cell mass.</p><p>The lasso is a penalized estimation method performing covariate selection simultaneously to shrinkage estimation. The lasso was implemented within NONMEM as an alternative to SCM and is discussed in comparison with that method. Further, various ways of incorporating information and propagating knowledge from previous studies into an analysis were investigated. In order to compare the different approaches, investigations were made under varying, replicated conditions. In the course of the investigations, more than one million NONMEM analyses were performed on simulated data. Due to selection bias the use of SCM performed poorly when analysing small datasets or rare subgroups. In these situations, the lasso method in NONMEM performed better, was faster, and additionally validated the covariate model. Alternatively, the performance of SCM can be improved by propagating knowledge or incorporating information from previously analysed studies and by population optimal design.</p><p>A model was also developed on a physiological/mechanistic basis to fit data from three phase II/III studies on the investigational drug, tesaglitazar. This model described fasting glucose and insulin levels well, despite heterogeneous patient groups ranging from non-diabetic insulin resistant subjects to patients with advanced diabetes. The model predictions of beta-cell mass and insulin sensitivity were well in agreement with values in the literature.</p>

<p><b>Background and aims:</b> Type 2 diabetes mellitus is connected with elevated glucose levels, which cause impaired glucose-stimulated insulin secretion (GSIS) and degeneration of β-cells. Mechanisms for such glucotoxic effects were explored in the present study.</p><p><b>Materials and methods:</b> INS-1E cells were cultured for 5 days in 5.5, 11, 20 or 27 mM glucose in the presence or absence of AMPK-agonist AICAR. GSIS was determined from INS-1E cells and islets obtained from type 2 diabetes and control donors. Human islets and INS-1E cells were functionally characterized (GSIS) and protein profiled (SELDI-TOF MS). Glucose-induced <i>de novo</i> synthesis of fatty acyls (HR-MAS NMR spectroscopy), fatty acid composition (GC-MS), triglyceride content and specific proteins (Western blotting) were determined in INS-1E cells.</p><p><b>Results:</b> Impaired GSIS was observed from INS-1E cells exposed to chronic hyperglycaemia and islets isolated from type 2 diabetics compared to INS-1E cells cultured at normal glucose levels and control islets, respectively. Several glucose-regulated proteins were found when type 2 diabetes and control islets or mitochondria from INS-1E cells cultured at different glucose concentrations were protein profiled. Glucose induced lipid <i>de novo</i> synthesis of both saturated and unsaturated fatty acids in specific proportions. Glucose-induced impairment of function and mass was reverted by inclusion of AICAR, which lowered levels of pro-apoptotic protein CHOP but left triglyceride content unaffected.</p><p><b>Conclusions:</b> Impaired GSIS and increased apoptosis observed in β-cells after prolonged exposure to elevated glucose concentrations involved accumulation of lipid species in specific proportions, AMPK-inactivation, ER-stress activation and complex, coordinated changes in expression patterns of mitochondrial and human islet proteins.</p>

During development of type 1 and type 2 diabetes plasma insulin patterns are altered. Since the islet insulin release pattern has been implicated in this development, insulin secretion from single islets was studied and linked to the islet protein levels of uncoupling protein-2 (UCP2). Islets were isolated from NOD- and KKAy- mice, GK- and GK-derived congenic rats, which are animal models of diabetes, and three human subjects with type 2 diabetes. At basal glucose (3 mM), insulin release from such islets was pulsatile and the amount released was comparable to that of control islets. When the glucose concentration was raised to 11 mM insulin release was essentially unchanged in islets isolated from older NOD- and KKAy- mice, GK- and Niddm1i congenic rats, and NIDDM persons. In islets from Niddm1f congenic rats, younger NOD- and KKAy-mice, control animals and normal human donors the secretion rate increased 2-9 fold when the glucose concentration was raised. This rise in secretion was manifested as increase of the amplitude of the insulin oscillations without affecting their frequency. Impaired glucose-induced insulin release was associated with reduction in glucose oxidation measured in NOD-islets, unaffected respiration measured in GK-islets and higher protein level of UCP2 measured in KKAy-islets. When the UCP2 amounts in KKAy-islets were reduced by culture to those of control islets, glucose-induced insulin secretion was essentially normalized. Our studies suggest that the deranged plasma insulin patterns observed in diabetes are related to decrease in the amplitude of insulin oscillations from the islets rather than loss of the oscillatory activity. This reduction of pulse amplitude may be related to impaired glucose metabolism and/or increased mitochondrial uncoupling.

<b>Background and aims:</b> Type 2 diabetes mellitus is connected with elevated glucose levels, which cause impaired glucose-stimulated insulin secretion (GSIS) and degeneration of β-cells. Mechanisms for such glucotoxic effects were explored in the present study. <b>Materials and methods:</b> INS-1E cells were cultured for 5 days in 5.5, 11, 20 or 27 mM glucose in the presence or absence of AMPK-agonist AICAR. GSIS was determined from INS-1E cells and islets obtained from type 2 diabetes and control donors. Human islets and INS-1E cells were functionally characterized (GSIS) and protein profiled (SELDI-TOF MS). Glucose-induced de novo synthesis of fatty acyls (HR-MAS NMR spectroscopy), fatty acid composition (GC-MS), triglyceride content and specific proteins (Western blotting) were determined in INS-1E cells. <b>Results:</b> Impaired GSIS was observed from INS-1E cells exposed to chronic hyperglycaemia and islets isolated from type 2 diabetics compared to INS-1E cells cultured at normal glucose levels and control islets, respectively. Several glucose-regulated proteins were found when type 2 diabetes and control islets or mitochondria from INS-1E cells cultured at different glucose concentrations were protein profiled. Glucose induced lipid de novo synthesis of both saturated and unsaturated fatty acids in specific proportions. Glucose-induced impairment of function and mass was reverted by inclusion of AICAR, which lowered levels of pro-apoptotic protein CHOP but left triglyceride content unaffected. <b>Conclusions:</b> Impaired GSIS and increased apoptosis observed in β-cells after prolonged exposure to elevated glucose concentrations involved accumulation of lipid species in specific proportions, AMPK-inactivation, ER-stress activation and complex, coordinated changes in expression patterns of mitochondrial and human islet proteins.

The population of northern Sweden has previously been shown to be well suited for the mapping of monogenic diseases. In this thesis we have tested the hypothesis that this population could also be used for efficient identification of risk genes for common diseases. In Paper I we have hypothesised that despite the admixture of Swedish, Finnish and Sami, the northern Swedish population consists of sub-populations geographically restricted by the main river valleys running through the region. This geographic isolation, in combination with founder effects and genetic drift, could represent a unique resource for genetic studies. On the other hand, it also underlines the importance of accounting for this e.g. in genetic association studies. To test this hypothesis, we studied the patterns of marriage within and between river valley regions and compared allelic frequencies of genetic markers between these regions. The tendency to find a spouse and live in the river valley where one was born is strong, and allelic frequencies of genetic markers vary significantly between adjacent regions. These data support our hypothesis that the river valleys are home to distinct sub-populations and that this is likely to affect mapping of genetic diseases in these populations. In Paper II, we tested the applicability of the population in mapping HSAN V, a monogenic disease. This disease was identified in only three consanguineous individuals suffering from a severe loss of deep pain perception and an impaired perception of heat. A genome-wide scan combined with sequencing of candidate genes resulted in the identification of a causative point mutation in the nerve growth factor beta (NGFB) gene. In Paper III, a large family with multiple members affected by familial forms of type 1 diabetes mellitus (T1DM) and autoimmune thyroiditis (AITD) was studied. This syndrome was mapped to the IDDM12 region on 2q33, giving positive lodscores when conditioning on HLA haplotype. The linkage to HLA and to the IDDM12 region thus confirmed previous reports of linkage and/or association of T1DM and AITD to these loci and provided evidence that the same genetic factors may be mediating these diseases. This also supported the feasibility of mapping complex diseases in northern Sweden by the use of familial forms of these diseases. In Paper IV, we applied the same approach to study type 2 diabetes mellitus (T2DM). A non-parametric genome-wide scan was carried out on a family material from northern Sweden, and linkage was found to the calpain-10 locus, a previously described T2DM-susceptibility gene on 2q37. Together, these findings demonstrate that selecting for familial forms of even complex diseases, and choosing families from the same geographical region can efficiently reduce the genetic heterogeneity of the disease and facilitate the identification of risk genes for the disease.

Background: Type 2 diabetes is thought to result from interactions between genetic and lifestyle factors, but few robust examples exist. The overarching aim of this thesis was to discover such interactions by studying cohorts of white youth and adults from northern Europe in which physical activity, genotypes, and diabetes-related traits or diabetes incidence had been ascertained.   Methods: The thesis includes four papers. In Paper I, we investigated associations and interactions between 35 common PPARGC1A polymorphisms and cardiovascular and metabolic disease traits in 2,101 Danish and Estonian children from the European Youth Heart Study (EYHS). Paper II used the same cohort to test associations and interactions on cardiometabolic traits for the diabetes-predisposing TCF7L2 polymorphism. In Paper III, we assessed associations for 17 type 2 diabetes gene polymorphisms on impaired glucose regulation (IGR) or incident type 2 diabetes, and tested whether these effects are modified by physical activity in a prospective cohort study of ~16,000 initially non-diabetic Swedish adults – the Malmö Preventive Project (MPP). Paper IV aimed to replicate main genetic effects and gene x physical activity interactions for an FTO polymorphism on obesity in 18,435 primarily non-diabetic Swedish (MPP) and Finnish (Prevalence, Prediction and Prevention of Diabetes in Botnia) adults. Results: In Paper I, nominally significant associations were observed for BMI (rs10018239, P=0.039), waist circumference (rs7656250, P=0.012; rs8192678 [Gly482Ser], P=0.015; rs3755863, P=0.02; rs10018239, P=0.043), systolic blood pressure (rs2970869, P=0.018) and fasting glucose concentrations (rs11724368, P=0.045). Stronger associations were observed for aerobic fitness (rs7656250, P=0.005; rs13117172, P=0.008) and fasting glucose concentrations (rs7657071, P=0.002). None remained significant after correcting for multiple statistical comparisons. We proceeded by testing for gene × physical activity interactions for the polymorphisms that showed statistical evidence of association (P&lt;0.05) in the main effect models, but none was statistically significant. In Paper II, the minor T allele at the rs7903146 variant was associated with higher glucose levels in older (beta=–0.098 mmol/l per minor allele copy, P=0.029) but not in younger children (beta=–0.001 mmol/l per minor allele copy, P=0.972). A significant inverse association between the minor allele at rs7903146 and height was evident in boys (beta=–1.073 cm per minor allele copy, P=0.001), but not in girls. The test of interaction between the TCF7L2 rs7903146 variant and physical activity on HOMA-B was nominally statistically significant (beta=0.022, Pinteraction=0.015), whereby physical activity reduced the effect of the risk allele on estimated beta-cell function. In Paper III, tests of gene x physical activity interactions on IGR-risk for three polymorphisms were nominally statistically significant: CDKN2A/B rs10811661 (Pinteraction=0.015); HNF1B rs4430796 (Pinteraction=0.026); PPARG rs1801282 (Pinteraction=0.04). Consistent interactions were observed for the CDKN2A/B (Pinteraction=0.013) and HNF1B (Pinteraction=0.0009) variants on 2 hr glucose concentrations. Where type 2 diabetes was the outcome, only one statistically significant interaction effect was observed and this was for the HNF1B rs4430796 variant (Pinteraction=0.0004). The interaction effects for HNF1B on 2 hr glucose and incident diabetes remained significant after correction for multiple testing (Pinteraction=0.015 and 0.0068, respectively). In Paper IV, the minor A allele at rs9939609 was associated with higher BMI (P&lt;0.0001). The tests of gene x physical activity interaction on BMI were not statistically significant in either cohort (Sweden: P=0.71, Finland: P=0.18). Conclusions: Variation at PPARGC1A is unlikely to have a major impact on cardiometabolic health in European children, but physical activity may modify the effect of the TFC7L2 variants on beta-cell function in this cohort. In Swedish adults, physical activity modifies the effects of common HNF1B and CDKN2A/B variants on risk of IGR and also modifies the effect of the HNF1B on type 2 diabetes risk. In Swedish and Finnish adults, we were unable to confirm previous reports of an interaction between FTO gene variation and physical activity on obesity predisposition.

Type 2 diabetes is usually caused by a combination of pancreatic β-cell failure and insulin resistance in target tissues like liver, muscle and fat. Insulin resistance is characterised by an impaired effect of insulin to reduce hepatic glucose production and to promote glucose uptake in peripheral tissues. The focus of this study was to further elucidate cellular mechanisms for insulin resistance that may be of relevance for type 2 diabetes in humans. We used rat and human adipocytes as an established model of insulin’s target cells. Glucocorticoids, e.g. cortisol, can induce insulin resistance in vivo. In the present study, pretreatment of rat adipocytes in vitro for 24 h with the cortisol analogue dexamethasone produced a downregulation of glucose uptake capacity as well as a marked depletion of cellular insulin receptor substrate 1 (IRS-1) and protein kinase B (PKB), two proteins suggested to play a critical role in the intracellular signal transduction pathway of insulin. The amount of phosphorylated PKB in response to acute insulin treatment was decreased in parallel to total PKB content. The basal rate of lipolysis was enhanced, but insulin’s antilipolytic effect was not consistently altered following dexamethasone pretreatment. Alterations in blood glucose as well as insulin levels may be of great importance for cellular as well as whole-body insulin resistance. High glucose (≥15 mM) for 24 h induced a decrease in glucose uptake capacity in rat adipocytes and IRS-1 content was reduced whereas IRS-2 was increased. Long-term pretreatment with a high insulin concentration downregulated insulin binding capacity and when combined with high glucose, it produced a pronounced reduction of cellular IRS-1 and 2 content together with insensitivity to insulin’s effect to activate PKB and a decrease in glucose uptake capacity. A common denominator for a decrease in glucose uptake capacity in our rat adipocyte studies seems to be a decrease in IRS-1 content. Adipocytes from type 2 diabetes patients are insulin-resistant, but in our work the insulin resistance could be reversed by incubation of the cells at a physiological glucose level for 24 h. Insulin resistance in fresh adipocytes from type 2 diabetes patients was associated with in vivo insulin resistance and glycemic level and with adipocyte cell size and waist-hip ratio (WHR). As a potential mechanism for postprandial dyslipidemia in type 2 diabetes, we examined the nutritional regulation of subcutaneous adipose tissue lipoprotein lipase (LPL) activity. It was upregulated by ~40-50 % after a standardised lipid-enriched meal and this was very similar in type 2 diabetes patients and control subjects, suggesting that the postprandial hypertriglyceridemia found in type 2 diabetes is not explained by an altered nutritional regulation of LPL in subcutaneous fat. In conclusion, the present work provides evidence for novel interactions between glucocorticoids and insulin in the regulation of glucose metabolism that may potentially contribute to the development of insulin resistance. High levels of glucose and insulin produce perturbations in the insulin signalling pathway that may be of relevance for human type 2 diabetes. Cellular insulin resistance may be secondary to the diabetic state in vivo, e.g. via glucotoxicity. This is supported by our finding that insulin resistance in adipocytes from type 2 diabetes patients can be reversed after incubation at a physiological glucose level. Key words: adipocyte, insulin resistance, type 2 diabetes, insulin signalling, glucose uptake, insulin, glucose, dexamethasone, insulin receptor substrate, protein kinase B, GLUT4, lipoprotein lipase.

Population pharmacokinetic-pharmacodynamic (PK-PD) models can be fitted using nonlinear mixed effects modelling (NONMEM). This is an efficient way of learning about drugs and diseases from data collected in clinical trials. Identifying covariates which explain differences between patients is important to discover patient subpopulations at risk of sub-therapeutic or toxic effects and for treatment individualization. Stepwise covariate modelling (SCM) is commonly used to this end. The aim of the current thesis work was to evaluate SCM and to develop alternative approaches. A further aim was to develop a mechanistic PK-PD model describing fasting plasma glucose, fasting insulin, insulin sensitivity and beta-cell mass. The lasso is a penalized estimation method performing covariate selection simultaneously to shrinkage estimation. The lasso was implemented within NONMEM as an alternative to SCM and is discussed in comparison with that method. Further, various ways of incorporating information and propagating knowledge from previous studies into an analysis were investigated. In order to compare the different approaches, investigations were made under varying, replicated conditions. In the course of the investigations, more than one million NONMEM analyses were performed on simulated data. Due to selection bias the use of SCM performed poorly when analysing small datasets or rare subgroups. In these situations, the lasso method in NONMEM performed better, was faster, and additionally validated the covariate model. Alternatively, the performance of SCM can be improved by propagating knowledge or incorporating information from previously analysed studies and by population optimal design. A model was also developed on a physiological/mechanistic basis to fit data from three phase II/III studies on the investigational drug, tesaglitazar. This model described fasting glucose and insulin levels well, despite heterogeneous patient groups ranging from non-diabetic insulin resistant subjects to patients with advanced diabetes. The model predictions of beta-cell mass and insulin sensitivity were well in agreement with values in the literature.

Chronic hyperlipidemia (lipotoxicity) and hyperglycemia (glucotoxicity) have recently been shown to induce Endoplasmic Reticulum (ER) stress, which may contribute to pancreatic beta-cell dysfunction in type 2 diabetes. This thesis examined the involvement of ER stress in beta-cell lipotoxicity and glucotoxicity. Although chronic treatment with saturated free fatty acids (FFA) in vitro induced ER stress, altering ER stress by increasing or knocking-down GRP78 chaperone expression had no effect on apoptosis induction. Conversely, overexpression of ER chaperones rescued the reduction in proinsulin protein levels caused by chronic exposure to high glucose, although it had no effect on the decreased insulin mRNA levels and proinsulin translation rate. Thus, ER stress is likely not the main mechanism involved in saturated FFA-induced beta-cell apoptosis in vitro, but it may contribute to glucotoxic effects on proinsulin levels. These findings have increased our understanding of the link between ER stress and beta-cell dysfunction in type 2 diabetes.