Novel insights into the regulation of insulin secretion by GLP-1, GIP and glucagon

There are many contributing factors to the development of type 2 diabetes, however, failure of beta-cells to sufficiently secrete insulin is the key component. The underlying mechanism of beta-cell failure is not fully established. In this thesis, we examined the role of high glucagon levels, i.e. hyperglucagonemia, for the development of beta-cell dysfunction in pre-diabetic mice. We found that induction of 2 week hyperglucagonemia leads to defective insulin secretion. To enhance beta-cell function, there are several therapeutic strategies. One important strategy is based on the gut incretin hormone glucagon-like peptide 1 (GLP-1), which potently stimulates insulin secretion. In the clinic, GLP-1 receptor agonists and inhibitors of dipeptidyl peptidase 4 (DPP-4), the enzyme responsible for degradation of GLP-1, are currently used. A new concept of GLP-1 based therapies is to increase also endogenous GLP-1 secretion. In this thesis, we explored the importance of meal macronutrient composition for GLP-1 and insulin responses in healthy mice. We found that intake of mixed macronutrients compared to isocaloric glucose leads to a synergistic increase in GLP-1 and insulin levels. We also explored the effects of a novel GPR119 receptor agonist on GLP-1 and insulin levels after meal intake in healthy and glucose intolerant mice. GPR119 activation markedly increased GLP-1 and insulin responses to meal intake, however, only in glucose intolerant mice. Furthermore, we examined the mechanisms behind the effects of DPP-4 inhibition and found that vagal nerve signaling is important for the insulinotropic effects of DPP-4 inhibition. To conclude, the work in this thesis shed new light on possible ways to increase GLP-1 and insulin secretion, on the mechanism behind the effects of DPP-inhibition and on glucagon as a possible factor that may contribute to beta-cell failure

Perceptions of usability - a comparisonof the expert's perception with the end user's perception for improving navigations guidelines

Användbarhet är ett centralt begrepp i webbutveckling vid utvecklandet av tillgängliga och användbara webbsidor. Användbarhet strävar efter effektivitet och tillfredställelse. Webbsidans användare ska kunna utföra ärende utan ansträngning eller större tidsåtgång för att slutligen känna en tillfredställelse med sig själv och det framgångsrikt utförda ärendet. I detta examensarbete kommer användbarhet på world wide web behandlas ur två infallsvinklar, experters uppfattning respektive vardaglig användares uppfattning på begreppet. Arbetet ämnar lyfta fram tolkningar för begreppet användbarhet och hur stort värde det har vid webbutveckling, i synnerhet en global navigations värde som verktyg för orientering på en webbsida. Frågeställningen besvaras genom en analys och likhetsgranskning först mellan målgrupperna, sedan mot tidigare studier i sektion 5. Examensarbetet kommer främst baseras på en tidigare studie som även den ifrågasätter riktlinjer för användbarhet i en intervjustudie med utvecklare inom webbutveckling. Genom intervjuer kommer vardagliga användare och experters tolkningar jämföras mot tidigare studier och forskning för att betona det värde som användbarhet har för en välutvecklad och funktionellt framgångsrik webbsida med fokus på global navigation. Resultatet av undersökningen ämnar styrka eller sänka hypotesen om att satta riktlinjer för användbarhet behöver uppdateras och korrigeras efter aktuella uppfattningar hos så väl experter så väl som vardagliga användare idag. Det finns idag ingen känd forskning inom ämnet där användarens tolkning av användbarhet involveras vilket öppnar nya möjligheter till att förbättra existerande riktlinjer ytterligare. Resultatet av studien visar att målgruppernas uppfattningar kompletterar varandra men tolkas på olika sätt. Medan experter, målgrupp 1, definierar användbarhet som effektivt, tillförståeligt och tillgängligt beskriver användarna, målgrupp 2, begreppet som något enkelt och något som finns lättillgängligt och brett. Studiens främsta och mest användbara resultat är att målgrupp 1 utvecklar efter normer framför riktlinjer, och målgrupp 2 vill ha produkter byggda på standarder och normer.Usability is a central and common concept in the process of developing a usable and easily understood website for world wide web’s users. Usability strives för efficiency and satisfaction, the website’s users should be able to perform their tasks with minimum effort and within a reasonable time limit. This bachelor thesis will review the need of usability and how experts and users interprete the concept. How can the different interpretations of usability affect the need of usability online on the world wide web, and how important is a navigation designed with usability in mind? This thesis will be based on a former study within the subject usability, an interview study that is questioning the guidelines of usability today. The understandings on usability will be determined through interviews with eight interviewees, four experts and four users. The examination aims to strength or lower the hypotes “Existing guidelines for usability needs an update and reformulation to fit the understandings from experts and users of world wide web today.” There is no earlier studies on the matter where users are asked to define usability, it is more common to ask users what they think of the usability on a specific product. The results of this study shows that the two audiences understandings completes each other but are interpreted differently. Audience 1, the experts, defines usability as something efficient and easily learnable, while audience 2, the end-users, defines the concept as something simple that is easily accessible and widely spread throughout the world wide web. The most interesting result of the study is the results that shows how the experts develop with norms and standards in mind instead of guidelines and the end-users wants products built on standards that they recognize

Skeuomorphic vs flat design : A comparison of preferences of design techniques between two generations

Purpose: The purpose of the study was to compare two visually opposite design techniques: skeuomorphic design, recognizable for its realistic presentation, and flat design, an abstract design option that has gained popularity in the last years. The two designs were compared using two generations of Internet users to find out what the preferences were for each generation. A knowledge gap was found in which design that would be the most beneficial to use for each generation. Methodology: To fulfill the purpose of the study, two methods were used; a literature study and an empirical study. The empirical study included experiments, interviews and questionnaires. The participants were contacted personally or via social media. All participants were in the age of 20-30 or 65+. Findings: Based on the collected literature and empirical evidence, it was concluded that the older generation of users might tend to prefer the skeuomorphic, realistic design online. Bright colors and a pedagogical style creates a good visual for elderly eyes and inexpert of using internet. The younger generation might tend to prefer the flat and abstract way of design online. A modern appeal with less clutter compared to the skeuomorphic style is considered beneficial. This opens up for further investigation. Implications: The empirical study included 20 people, who all participated in the experiment, interviews and answered questionnaires. The study groups consisted of 10 persons at the age span 20-30 years and 10 persons at the age span of 65+ years. Limitations: The study was only focused on two specific age groups with a small population found through convenient sampling. This means that in the future, the research could be conducted in a broader matter including more age groups and a larger population with a more specific sampling. The study's extent was affected by the time period in which it was executed. A longer period of time could have contributed to a more extensive study, perhaps with additional age groups and more participants in each group

Upregulated insulin secretion in insulin-resistant mice: evidence of increased islet GLP1 receptor levels and GPR119-activated GLP1 secretion.

We previously demonstrated that the overall incretin effect and the β-cell responsiveness to glucagon-like peptide-1 (GLP1) are increased in insulin-resistant mice and may contribute to the upregulated β-cell function. Now we examined whether this could, first, be explained by increased islet GLP1 receptor (GLP1R) protein levels and, secondly, be leveraged by G-protein-coupled receptor 119 (GPR119) activation, which stimulates GLP1 secretion. Female C57BL/6J mice, fed a control (CD, 10% fat) or high-fat (HFD, 60% fat) diet for 8 weeks, were anesthetized and orally given a GPR119 receptor agonist (GSK706A; 10 mg/kg) or vehicle, followed after 10 min with gavage with a liquid mixed meal (0.285 kcal). Blood was sampled for determination of glucose, insulin, intact GLP1, and glucagon, and islets were isolated for studies on insulin and glucagon secretion and GLP1R protein levels. In HFD vs CD mice, GPR119 activation augmented the meal-induced increase in the release of both GLP1 (AUCGLP1 81±9.6 vs 37±6.9 pM×min, P=0.002) and insulin (AUCINS 253±29 vs 112±19 nM×min, P<0.001). GPR119 activation also significantly increased glucagon levels in both groups (P<0.01) with, however, no difference between the groups. By contrast, GPR119 activation did not affect islet hormone secretion from isolated islets. Glucose elimination after meal ingestion was significantly increased by GPR119 activation in HFD mice (0.57±0.04 vs 0.43±0.03% per min, P=0.014) but not in control mice. Islet GLP1R protein levels was higher in HFD vs CD mice (0.8±0.1 vs 0.5±0.1, P=0.035). In conclusion, insulin-resistant mice display increased islet GLP1R protein levels and augmented meal-induced GLP1 and insulin responses to GPR119 activation, which results in increased glucose elimination. We suggest that the increased islet GLP1R protein levels together with the increased GLP1 release may contribute to the upregulated β-cell function in insulin resistance

Synergism by individual macronutrients explains the marked early GLP-1 and islet hormone responses to mixed meal challenge in mice.

Apart from glucose, proteins and lipids also stimulate incretin and islet hormone secretion. However, the glucoregulatory effect of macronutrients in combination is poorly understood. We therefore developed an oral mixed meal model in mice to 1) explore the glucagon-like peptide-1 (GLP-1) and islet hormone responses to mixed meal versus isocaloric glucose, and 2) characterize the relative contribution of individual macronutrients to these responses. Anesthetized C57BL/6J female mice were orally gavaged with 1) a mixed meal (0.285kcal; glucose, whey protein and peanut oil; 60/20/20% kcal) versus an isocaloric glucose load (0.285kcal), and 2) a mixed meal (0.285kcal) versus glucose, whey protein or peanut oil administered individually in their mixed meal caloric quantity, i.e., 0.171, 0.055 and 0.055kcal, respectively. Plasma was analyzed for glucose, insulin and intact GLP-1 before and during oral challenges. Plasma glucose was lower after mixed meal versus after isocaloric glucose ingestion. In spite of this, the peak insulin response (P=0.02), the peak intact GLP-1 levels (P=0.006) and the estimated β-cell function (P=0.005) were higher. Furthermore, the peak insulin (P=0.004) and intact GLP-1 (P=0.006) levels were higher after mixed meal ingestion than the sum of responses to individual macronutrients. Compared to glucose alone, we conclude that there is a marked early insulin response to mixed meal ingestion, which emanates from a synergistic, rather than an additive, effect of the individual macronutrients in the mixed meal and is in part likely caused by increased levels of GLP-1

Evidence for neural contribution to islet effects of DPP-4 inhibition in mice

It has been suggested that neural mechanisms may contribute to effects of the incretin hormones, and, therefore, also to the effects of dipeptidyl peptidase (DPP-4) inhibition. We therefore examined whether muscarinic mechanisms are involved in the stimulation of insulin secretion by DPP-4 inhibition. Fasted, anesthetized mice were given intraperitoneal saline or the muscarinic antagonist atropine (5mg/kg) before duodenal glucose (75mg/mouse), with or without the DPP-4 inhibitor NVPDPP728 (0.095mg/mouse), or before intravenous glucose (0.35g/kg) with or without co-administration with GLP-1 or glucose-dependent insulinotropic polypeptide (GIP) (both 3nmol/kg). Furthermore, isolated islets were incubated (1h) in 2.8 and 11.1mM glucose, with or without GIP or GLP-1 (both 100nM), in the presence or absence of atropine (100µM). Duodenal glucose increased circulating insulin and this effect was potentiated by DPP-4 inhibition. The increase in insulin achieved by DPP-4 inhibition was reduced by atropine by approximately 35%. Duodenal glucose also elicited an increase in circulating intact GLP-1 and GIP and this was augmented by DPP-4 inhibition, but these effects were not affected by atropine. Atropine did also not affect the augmentation by GLP-1 and GIP on glucose-stimulated insulin secretion from isolated islets. Based on these findings, we suggest that muscarinic mechanisms contribute to the stimulation of insulin secretion by DPP-4 inhibition through neural effects induced by GLP-1 and GIP whereas neural effects do not affect the levels of GLP-1 or GIP or the islet effects of the two incretin hormones

Incretin hormone receptors are required for normal beta cell development and function in female mice

The incretin hormones, glucose dependent insulinotropic polypeptide (GIP) and glucagon-like peptide 1 (GLP-1), potentiate insulin secretion and are responsible for the majority of insulin secretion that occurs after a meal. They may also, however, have a fundamental role in pancreatic beta cell development and function, independently of their role in potentiating insulin secretion after a meal. This has led to observations that a loss of GIP or GLP-1 action affects normal beta cell function, however each one of the incretin hormones may compensate when the action of the other is lost and therefore the overall impact of the incretin hormones on beta cell function is not known. We therefore utilized a mouse line deficient in both the GLP-1 and GIP receptor genes, the double incretin receptor knockout (DIRKO), to determine the consequences of a lifelong, complete lack of incretin hormone action on beta cell function, in vivo, in intact animals. We found that DIRKO mice displayed impaired glucose tolerance and insulin secretion in response to both oral glucose and mixed meal tolerance tests compared to wild-type mice. Assessment of beta cell function using the hyperglycemic clamp technique revealed an 80% decrease in first phase insulin response in DIRKO mice, but a normal second phase insulin secretion. A similar decline was seen when wild-type mice were given acute intravenous injection of glucose together with the GLP-1 receptor antagonist Ex9-39. Ex vivo assessments of the pancreas revealed significantly fewer islets in the pancreata of DIRKO mice despite no differences in total pancreatic mass. Insulin secretion from isolated islets of DIRKO mice was impaired to a similar extent to that seen during the hyperglycemic clamp. Insulin secretion in wild-type islets was impaired by acute treatment with Ex9-39 to a similar extent as the in vivo intravenous glucose tolerance tests. In conclusion, a loss of the action of both incretin hormones results in direct impairment of beta cell function both in vivo and in vitro in a process that appears to be independent of the intestinally secreted incretin hormones. We therefore conclude that the incretin hormones together significantly impact both beta-cell function and beta-cell development

Defective insulin secretion by chronic glucagon receptor activation in glucose intolerant mice.

Stimulation of insulin secretion by short-term glucagon receptor (GCGR) activation is well characterized, however, the effect of long-term GCGR activation on beta-cell function is not known, but of interest, since hyperglucagonemia occurs early during development of type 2 diabetes. Therefore, we examined whether chronic GCGR activation affects insulin secretion in glucose intolerant mice. To induce chronic GCGR activation, high-fat diet fed mice were continuously (2wk) infused with the stable glucagon analogue ZP-GA-1 and challenged with oral glucose and intravenous glucose +/- GLP-1. Islets were isolated to evaluate the insulin secretory response to glucose +/- GLP-1 and pancreases were collected for immunohistochemical analysis. Two-week ZP-GA-1 infusion reduced insulin secretion both after oral and intravenous glucose challenges in vivo and in isolated islets. These inhibitory effects were corrected for by GLP-1. Also, we observed increased beta-cell area and islet size. We conclude that induction of chronic ZP-GA-1 levels in glucose intolerant mice markedly reduces insulin secretion, and thus, we suggest that chronic activation of the GCGR may contribute to the failure of beta-cell function during development of type 2 diabetes

Time to Peak Glucose and Peak C-Peptide During the Progression to Type 1 Diabetes in the Diabetes Prevention Trial and TrialNet Cohorts

OBJECTIVE To assess the progression of type 1 diabetes using time to peak glucose or C-peptide during oral glucose tolerance tests (OGTTs) in autoantibody-positive relatives of people with type 1 diabetes. RESEARCH DESIGN AND METHODS We examined 2-h OGTTs of participants in the Diabetes Prevention Trial Type 1 (DPT-1) and TrialNet Pathway to Prevention (PTP) studies. We included 706 DPT-1 participants (mean ± SD age, 13.84 ± 9.53 years; BMI Z-score, 0.33 ± 1.07; 56.1% male) and 3,720 PTP participants (age, 16.01 ± 12.33 years; BMI Z-score, 0.66 ± 1.3; 49.7% male). Log-rank testing and Cox regression analyses with adjustments (age, sex, race, BMI Z-score, HOMA-insulin resistance, and peak glucose/C-peptide levels, respectively) were performed. RESULTS In each of DPT-1 and PTP, higher 5-year diabetes progression risk was seen in those with time to peak glucose >30 min and time to peak C-peptide >60 min (P < 0.001 for all groups), before and after adjustments. In models examining strength of association with diabetes development, associations were greater for time to peak C-peptide versus peak C-peptide value (DPT-1: χ2 = 25.76 vs. χ2 = 8.62; PTP: χ2 = 149.19 vs. χ2 = 79.98; all P < 0.001). Changes in the percentage of individuals with delayed glucose and/or C-peptide peaks were noted over time. CONCLUSIONS In two independent at-risk populations, we show that those with delayed OGTT peak times for glucose or C-peptide are at higher risk of diabetes development within 5 years, independent of peak levels. Moreover, time to peak C-peptide appears more predictive than the peak level, suggesting its potential use as a specific biomarker for diabetes progression