近年來，腸促胰島素類藥物胰高血糖素樣肽－1受體（GLP-1R）激動劑（如liraglutide，exenatide）和二肽基肽酶-4（DPP-4）抑制劑（如sitagliptin，vildagliptin）在2型糖尿病治療中得到廣泛應用。然而，2型糖尿病患者中腸促胰島素效應嚴重受損。研究表明，2型糖尿病患者的腸促胰島素激素（GLP-1和GIP）分泌並不顯著降低，因此腸促胰島素效應受損主要是由於2型糖尿病患者中β細胞對腸促胰島素激素反應性降低。GIP在2型糖尿病患者中刺激胰島素分泌的功能幾乎完全消失。相比較，GLP-1刺激胰島素分泌功能在2型糖尿病患者中部分保留。2型糖尿病中腸促胰島素效應受損的具體機制目前仍不清楚。本論文主要從2型糖尿病患者的腸促胰島素效應受損的機理及對腸促胰島素類藥物療效的影響上進行相關研究。 / 我們較早的研究發現高血糖能降低胰島β細胞GLP-1R受體的表達，從而損傷胰島β細胞GLP-1R信號通路是2型糖尿中腸促胰島素受損的部分原因。由於高血脂和高血糖都是糖尿病的主要特徵，我進一步研究了高血脂對β細胞的腸促胰島素信號通路的影響。體外實驗表明，棕櫚酸能降低胰島β細胞中GLP-1R的表達，並且抑制了GLP-1刺激的cAMP產生及CREB的磷酸化；在β細胞中外源性表達GLP-1R能部分恢復棕櫚酸損傷的GLP-1刺激cAMP產生及CREB的磷酸化。此外，在db/db小鼠和HFD誘導的肥胖及糖尿病小鼠模型中，降脂藥bezafibrate和niacin 能顯著提高腸促胰島素類藥物sitagliptin 和exendin-4的降糖效果，並且伴隨著對胰島形態結構的改善以及增加胰島β細胞質量。 / 另一方面，2型糖尿病患者胰島β細胞的功能和品質持續性的減少。其中慢性的高血糖和高血脂是兩個主要因素。臨床研究發現sitagliptin的降糖效果隨著糖尿病持續的時間增加而降低，而具體機理並不清楚。我們以前研究發現高血糖損傷胰島β細胞GLP-1R的表達及其信號通路是2型糖尿病腸促胰島素效應受損的重要原因。我進一步探討了exendin-4在STZ-HFD 誘導的較輕程度糖尿病（MH）小鼠（相對較輕的高血糖以及β細胞質量減少）和重度糖尿病(SH)小鼠（嚴重高血糖以及β細胞質量減少）的治療效果。研究發現， exendin-4只在MH小鼠中顯著降低血糖，改善糖耐量，恢復正常胰島結構及增加β細胞質量。而在兩組小鼠中exendin-4 都能降低體重，增加胰腺重量，但對食都沒影響。儘管exendin-4能顯著降低MH小鼠中胰島素耐量實驗葡萄糖水平，但HORM-IR無顯著差異。此外，exendin-4處理對胰島素刺激的肝臟及肌肉組織中磷酸化AKT和GSK水準在兩組小鼠中都無明顯改變。 / 總之，我的研究強調了血糖血脂的控制在2型糖尿病患者中的重要作用。我也發現高血糖、高血脂導致2型糖尿病患者β細胞功能持續受損的同時也損傷了GLP-1R信號通路，以至腸促胰島素類藥物療效的降低。我們的研究對腸促胰島素類藥物在2型糖尿病患者中的合理使用提供了重要資訊。 / Incretin-based drugs, such as glucagon-like peptide-1 (GLP-1) receptor agonists (e.g. liraglutide and exenatide) and dipeptidyl peptidase-4 (DPP-4) inhibitors (e.g. sitagliptin and vildagliptin), which inhibit degrading intact GLP-1, have been a novel therapeutics for the treatment of type 2 diabetes. Type 2 diabetes mellitus (T2DM) is associated with reduced incretin effects. The underlying mechanism, however, is not well understood. / Our previous studies showed that hyperglycemia downregulates glucagon-like peptide-1 (GLP-1) receptor (GLP-1R) which potentially contributes to the impaired incretin responses in cells. Whereas the effects of hyperlipidemia, another common clinical feature of T2DM, on GLP-1 response is largely unknown. In this study, I investigated the effects of free fatty acids (FFA) on incretin receptor signalings, and examined the glucose-lowering efficacy of incretin-based drugs in combination with lipid-lowering agents. I found that palmitate treatment decreased GLP-1R expression in rodent insulinoma cell lines, which was associated with impaired GLP-1 stimulated cAMP production and phosphorylation of CREB. Over-expression of GLP-1R restored the cAMP production and the phosphorylation of CREB. Treatment with bezafibrate or niacin in combination with des-fluoro-sitagliptin or exendin-4 produced more robust glycemic control associated with improved pancreatic islet morphology and islet cell function in db/db mice and HFD-fed mice. / On the other hand, chronic hyperglycemia and hyperlipidemia can cause a progressive deterioration in pancreatic beta-cell function and mass in patients with type 2 diabetes mellitus. It has been reported that the efficacy of incretin-based therapeutics is attenuated with the duration of diabetes. In our previous study, we have shown that hyperglycemia downregulates GLP-1 receptor which in turn may contribute to the impaired incretin effect in type 2 diabetes. In this study, I further investigated the efficacy of GLP-1 based drug exendin-4 in a rodent model of type 2 diabetes with different degrees of hyperglycemia and reduction of beta cell mass. I found that in moderate hyperglycemia (MH) group but not in severe hyperglycemia (SH) group, exendin-4 treatment significantly reduced fed glucose levels and plasma lipid profiles, improved glucose tolerance and glucose stimulated insulin secretion, and was associated with restored islets morphology and increased beta cell mass. Exendin-4 significantly decreased body weight gain and increased pancreatic mass both in MH and SH group. Although glucose levels were significantly reduced in MH group with exentin-4 treatment during insulin tolerance test, exendin-4 had no effects on HORM-IR, food intake, and insulin stimulated p-AKT/p-GSK in liver and muscle in both MH and SH group. / In summary, my findings highlight the importance of comprehensive lipid and glycemic control in type 2 diabetes mellitus. I found that factors including hyperglycemia and hyperlipidemia that cause progressive decline in beta cell failure impaired beta cell GLP-1R signaling as well as the efficacy of incretin-based therapies. These results add to our knowledge regarding the mechanism of incretin-based therapy in improving glycemic control in type 2 diabetic patients and provide new insights in designing treatment strategies including incretin-based therapy for type 2 diabetic patients. / Detailed summary in vernacular field only. / Detailed summary in vernacular field only. / Detailed summary in vernacular field only. / Detailed summary in vernacular field only. / Kang, Zhanfang. / Thesis (Ph.D.)--Chinese University of Hong Kong, 2012. / Includes bibliographical references (leaves 103-123). / Abstract also in Chinese. / 論文摘要 --- p.viii / Impaired Incretin Effects in Type 2 Diabetes: Mechanism and Therapeutic Implication --- p.1 / DECLARATION --- p.i / ACKNOWLEGEMENTS --- p.ii / ABBREVIATIONS --- p.iii / PUBLICATIONS AND AWARDS --- p.v / Chapter 1 --- Abstract --- p.vi / Chapter 2 --- Chapter : Introduction --- p.1 / Chapter 2.1 --- The history of incretin discovery --- p.1 / Chapter 2.2 --- The incretin hormones:GLP-1 and GIP --- p.1 / Chapter 2.3 --- Gene structure and regulation of incretin hormone gene expression --- p.2 / Chapter 2.3.1 --- Gene structure and regulation of GLP-1 gene expression --- p.2 / Chapter 2.3.2 --- Gene structure and regulation of GIP gene expression --- p.5 / Chapter 2.4 --- Secretion and metabolism of GLP-1 and GIP --- p.5 / Chapter 2.4.1 --- Regulation of GLP-1 and GIP secretion --- p.5 / Chapter 2.4.2 --- Degradation of GLP-1 and GIP by DPP-4 enzyme --- p.8 / Chapter 2.5 --- GLP-1 and GIP receptor --- p.10 / Chapter 2.6 --- biological actions of GLP-1 and GIP --- p.11 / Chapter 2.6.1 --- Actions of GLP-1 in peripheral tissues --- p.12 / Chapter 2.6.2 --- Actions of GIP in peripheral tissues --- p.17 / Chapter 2.7 --- Impaired incretin effect in type 2 diabetes patients --- p.17 / Chapter 2.7.1 --- Secretion of incretin hormones in patients with type 2 diabetes --- p.18 / Chapter 2.7.2 --- Impaired the responsiveness to GLP-1 and GIP in pancreatic beta cells --- p.19 / Chapter 2.8 --- Incretin-based drugs --- p.19 / Chapter 2.9 --- Type 2 diabetes and beta cell failure --- p.21 / Chapter 2.9.1 --- Natural history of type 2 diabetes --- p.21 / Chapter 2.9.2 --- Decline of beta cell function and mass in type 2 diabetes --- p.22 / Chapter 2.9.3 --- Factors for progressive loss of beta cell function and mass --- p.24 / Chapter 3 --- Chapter: Pharmacological reduction of free fatty acids restores the efficacy of incretin-based therapies in diabetic mouse models through beta cell GLP-1 receptor signalings --- p.30 / Chapter 3.1 --- Summary --- p.30 / Chapter 3.2 --- Introduction --- p.32 / Chapter 3.3 --- Materials and Methods --- p.35 / Chapter 3.3.1 --- Chemicals and Reagents --- p.35 / Chapter 3.3.2 --- Preparation of 8 mM sodium palmitate solution with 10.5% BSA --- p.35 / Chapter 3.3.3 --- Construct of an adenoviral vector for expressing mouse GLP-1R --- p.36 / Chapter 3.3.4 --- Cell culture and treatment --- p.37 / Chapter 3.3.5 --- RNA extraction and quantitative RT-PCR --- p.37 / Chapter 3.3.6 --- Analysis of phosphorylation of CREB --- p.38 / Chapter 3.3.7 --- Measurement of insulin secretion --- p.39 / Chapter 3.3.8 --- RT-PCR analysis of mouse GLP-1R expression --- p.39 / Chapter 3.3.9 --- Measurement of cAMP production --- p.40 / Chapter 3.3.10 --- Animals and experimental protocols --- p.40 / Chapter 3.3.11 --- Oral glucose tolerance test (OGTT) and insulin tolerance test (ITT) --- p.41 / Chapter 3.3.12 --- Acute glucose-lowering actions of Ex-4 and D-GIP in db/db Mice --- p.41 / Chapter 3.3.13 --- Lipid levels measurement --- p.42 / Chapter 3.3.14 --- Histological analysis --- p.42 / Chapter 3.3.15 --- Statistical analysis --- p.42 / Chapter 3.4 --- Results --- p.43 / Chapter 3.4.1 --- Reduced expression of GLP-1R in palmitate-treated b cells and islets of hyperlipedemic db/db mice. --- p.43 / Chapter 3.4.2 --- Palmitate impairs GLP-1 stimulated cAMP production and p-CREB in rodent insulinoma cell lines --- p.45 / Chapter 3.4.3 --- Palmitate reduced GLP-1 and GIP stimulated insulin secretion in rat INS-1E cells --- p.46 / Chapter 3.4.4 --- Mouse GLP-1R mRNA is expressed in rat INS-1E cells after infected with Ad-GLP-1R --- p.47 / Chapter 3.4.5 --- Expression of exogenous GLP-1R restores GLP-1 stimulated cAMP production and p-CREB in palmitate-treated rodent insulinoma cell lines --- p.48 / Chapter 3.4.6 --- Lipid lowering enhances the efficacy of DPP-4 inhibitor des-fluoro-sitagliptin in db/db mice --- p.50 / Chapter 3.4.7 --- Lipid-lowering enhances the efficacy of DPP-4 inhibitor des-flouro-sitagliptin in HFD-fed mice --- p.56 / Chapter 3.4.8 --- Lipid lowering enhances the efficacy of an agonist to GLP-1R (Ex-4) but not to GIPR (D-GIP) in db/db mice --- p.59 / Chapter 3.5 --- Discussion --- p.67 / Chapter 4 --- Chapter : Further study on the impairment of incretin effect by hyperglycemia in a rodent model of type 2 diabetes --- p.71 / Chapter 4.1 --- Summary --- p.71 / Chapter 4.2 --- Introduction --- p.73 / Chapter 4.3 --- Materials and Methods --- p.76 / Chapter 4.3.1 --- Animals and treatment --- p.76 / Chapter 4.3.2 --- Oral glucose tolerance test and insulin tolerance test --- p.76 / Chapter 4.3.3 --- Plasma parameters --- p.77 / Chapter 4.3.4 --- Histological staining and quantification of beta cell mass --- p.77 / Chapter 4.3.5 --- Insulin signaling analysis --- p.78 / Chapter 4.3.6 --- Western blot analysis --- p.78 / Chapter 4.3.7 --- Statistical analysis --- p.79 / Chapter 4.4 --- Results --- p.80 / Chapter 4.4.1 --- Exendin-4 reduced fed glucose levels in MH mice but not in SH mice --- p.80 / Chapter 4.4.2 --- Exendin-4 reduced body weight gain and did not affect food intake in both MH mice and SH mice --- p.81 / Chapter 4.4.3 --- Exendin-4 improved glucose tolerance and glucose stimulated insulin secretion in MH mice but not in SH mice --- p.83 / Chapter 4.4.4 --- Effects of exendin-4 on insulin sensitivity in MH and SH mice --- p.84 / Chapter 4.4.5 --- Effects of exendin-4 on lipid profiles in MH and SH mice --- p.86 / Chapter 4.4.6 --- Effects of exendin-4 on tissues weight in MH and SH mice --- p.87 / Chapter 4.4.7 --- Pancreatic islet morphology and analysis of beta cell mass --- p.88 / Chapter 4.4.8 --- Exendin-4 had no significant effects on insulin signaling pathway in liver and muscle --- p.91 / Chapter 4.5 --- Discussion --- p.94 / Chapter 5 --- Chapter : Summary --- p.100 / Chapter 6 --- References --- p.103

Doctor of Philosophy / Department of Animal Sciences and Industry / Bradley J. Johnson / Research regarding rumen epithelial adaptation and potential mechanisms during the transition period of the dairy cow is lacking. The rumen epithelium has a tremendous capacity for the absorption of volatile fatty acids (VFA) produced from microbial fermentation in the rumen. Absorption of VFA from the rumen pool delivers energy substrates to the animal and provides stability to the rumen environment. Increased epithelial surface area from the development and adaptation of rumen papillae facilitates VFA absorption. Manipulation of the diet to alter rumen fermentation can have positive effects upon the rumen papillae development supporting VFA absorption. We hypothesized that enhancing rumen epithelial surface area through dietary alterations could lead to greater VFA absorption and improve rumen stability. Experiments were conducted to determine the effects of diets formulated with cane molasses to stimulate the production of ruminal butyrate and thereby increase rumen epithelial surface area and to investigate a potential mechanism for glucagon-like peptide-2 (GLP-2) to impact epithelial development. Feeding cane molasses in the dry period improved dry matter intake during the close-up period and during lactation. Milk production was increased for cows that were fed cane molasses during the dry period. Ruminal absorption of valerate was greater during the close-up period than the far-off period but was not influenced by the addition of cane molasses. Total VFA concentration measured during the dry period was not affected by the addition of cane molasses to the diet. The presence of glucagon-like peptide receptor (GLP-2R) mRNA was confirmed in bovine tissue obtained from rumen epithelium, omasum, abomasum, duodenum, jejunum, ileum, large intestine, and pancreas. The greatest level of expression of mRNA for GLP-2R was in the small intestine and large intestine. Expression of GLP-2R mRNA during the prepartum period tended to be increased with the addition of cane molasses. Postpartum expression of GLP-2R was not increased by supplementing cane molasses in the dry cow diet. Results from these experiments indicate that dry cow diets formulated to contain cane molasses can positively influence transition cow performance and that the presence of glucagonlike peptide-2 receptor could play a pivotal role in rumen epithelial development.

No description available.

Glucagon-like peptide-2 (GLP-2) augments intestinal adaptation in animal models of short bowel syndrome (SBS) and in adult patients with SBS. However, GLP-2 has not been used as a therapy for pediatric SBS. In this thesis, it is hypothesized that exogenous GLP-2 therapy will improve outcomes of intestinal adaptation in proximal intestinal resection (JI) and distal intestinal resection (JC) neonatal piglet models of SBS. Improvements in morphological parameters (increased small intestinal length) and histological parameters (increased jejunal villus length or jejunal crypt depth) of intestinal adaptation in JI and JC neonatal piglets treated with GLP-2 were observed. However, improved clinical outcomes (fewer days of diarrhea, fewer days on parenteral nutrition, more days on enteral nutrition alone) were only observed in GLP-2 treated JC animals. Since the JC anatomical subtype (no remnant ileum) represents the majority of clinical cases of neonatal SBS, these results support a potential role for GLP-2 therapy in pediatric SBS.

Glucagon-like peptide-2 (GLP-2) augments intestinal adaptation in animal models of short bowel syndrome (SBS) and in adult patients with SBS. However, GLP-2 has not been used as a therapy for pediatric SBS. In this thesis, it is hypothesized that exogenous GLP-2 therapy will improve outcomes of intestinal adaptation in proximal intestinal resection (JI) and distal intestinal resection (JC) neonatal piglet models of SBS. Improvements in morphological parameters (increased small intestinal length) and histological parameters (increased jejunal villus length or jejunal crypt depth) of intestinal adaptation in JI and JC neonatal piglets treated with GLP-2 were observed. However, improved clinical outcomes (fewer days of diarrhea, fewer days on parenteral nutrition, more days on enteral nutrition alone) were only observed in GLP-2 treated JC animals. Since the JC anatomical subtype (no remnant ileum) represents the majority of clinical cases of neonatal SBS, these results support a potential role for GLP-2 therapy in pediatric SBS.

OBJECTIVE: To review the evidence surrounding a potential association between liraglutide and pancreatitis. DATA SOURCES: A literature search was conducted in MEDLINE (1948-July 12, 2012) and EMBASE (1974-week 27, 2012) using the search terms pancreatitis, liraglutide, and glucagon-like peptide 1/adverse effects. Reference citations from identified publications were reviewed. The manufacturer was contacted and regulatory documents from the Food and Drug Administration website were reviewed for unpublished data related to cases of pancreatitis associated with liraglutide use. STUDY SELECTION AND DATA EXTRACTION: All identified sources that were published in English were considered for inclusion. DATA SYNTHESIS: Eleven cases of pancreatitis have been reported in patients taking liraglutide. Seven were from the LEAD (Liraglutide Effect and Action in Diabetes) studies, 1 was reported in the extension of a clinical trial, and 1 was in an unpublished obesity trial. Two were published postmarketing case reports. Nine of the cases reported were diagnosed as acute pancreatitis, while 2 were classified as chronic pancreatitis. The mean age of the patients was 57.5 years and mean body mass index was 33.92 kg/m2. Six of the 11 cases occurred in male patients. Nine of the patients were white and 1 was African American. In 7 of the cases, onset occurred at liraglutide doses at or above 1.8 mg daily. Common comorbidities included history of pancreatitis, cholelithiasis, and diabetes. One case was fatal. CONCLUSIONS: Pancreatitis is a potential complication with liraglutide therapy. Liraglutide should be used cautiously in patients at risk of pancreatitis (eg, alcohol abuse, history of pancreatitis, cholelithiasis).

Fan, Rongrong. / Thesis (Ph.D.)--Chinese University of Hong Kong, 2011. / Includes bibliographical references (leaves 130-150). / Electronic reproduction. Hong Kong : Chinese University of Hong Kong, [2012] System requirements: Adobe Acrobat Reader. Available via World Wide Web. / Abstract also in Chinese.

Lu, Zengbing. / Thesis (Ph.D.)--Chinese University of Hong Kong, 2013. / Includes bibliographical references (leaves 206-217). / Electronic reproduction. Hong Kong : Chinese University of Hong Kong, [2012] System requirements: Adobe Acrobat Reader. Available via World Wide Web. / Abstract also in Chinese.

The hormone glucagon-like peptide-2 (GLP-2) is important in the regulation of intestinal growth and blood flow in nonruminant animals. However, no research reports the existence of GLP-2 in ruminants. Therefore, this dissertation examined the existence of GLP-2 and its receptor, their response to physiological stimuli, and its ability to induce gastrointestinal growth and intestinal blood flow in ruminants. Experiments 1 and 2 established the gastrointestinal distribution of mRNA for proglucagon (the GLP-2 precursor) and the GLP-2 receptor. Furthermore, these experiments determined the effects of changing dietary energy intake on plasma GLP-2 concentrations and proglucagon and GLP-2 receptor mRNA expression. Experiment 3 examined the effect of exogenous bovine GLP-2 on splanchnic blood flow, splanchnic nutrient flux, and gastrointestinal growth. This research shows that ruminants possess a functional GLP-2 signaling system that responds to nutrient ingestion. Based on observed receptor distribution and growth changes with GLP-2 treatment, GLP-2 targets the small intestine and does not affect forestomach or large intestinal growth. Increases in ileal proglucagon mRNA expression and plasma GLP-2 with increasing energy intake demonstrate that GLP-2 responds to physiologic changes in nutrient intake and can be relevant to feeding practices. Furthermore, observed increases in small intestinal growth and blood flow with GLP-2 suggest that it could substantially affect the capacity of the gastrointestinal tract for nutrient absorption. Modification of GLP-2 through diet could allow for improvements in nutrient utilization and animal productivity. This research also has important implications for use of GLP-2 for human disease therapy as the observed downregulation in the blood flow response to 10-d GLP-2 administration has never been reported in any species prior to this dissertation. This research systematically characterized and evaluated the potential role of GLP-2 in the control of gastrointestinal growth and splanchnic blood flow in ruminants. While it extends the knowledge of hormonal control of the gastrointestinal tract in ruminants, it also adds crucial information to the larger body of work investigating the actions of GLP- 2. This dissertation research has contributed to the groundwork necessary to enable the use of GLP-2 in improving the health and productivity of a diverse group of mammalian species.

Thesis (Ph. D.)--University of Alabama at Birmingham, 2006. / Title from first page of PDF file (viewed Feb. 22, 2007). Includes bibliographical references (p. 92-107).