밀순으로부터 추출한 비 전분 다당류가 제1형 당뇨병 모델에서 췌장 베타세포의 인슐린 분비 촉진 : 이선희

다국어 초록 (Multilingual Abstract)

Diabetes mellitus is a metabolic disease associated with abnormally high levels of glucose in the blood, which is caused by insufficient production of insulin or the inability of cells to use insulin. The lack of insulin generally is in contact with a destructive process affecting the insulin producing pancreatic b cells in type 1 diabetes and a steady decline of beta cells in type 2 diabetes. The previous study demonstrated that the aqueous extracts of Triticum aestivum attenuated blood glucose level in the streptozotocin (STZ)-induced diabetic mice, which is an animal model of human insulin-dependent type 1 diabetes.
This study demonstrates the regulating effects of non-starch polysaccharide isolated from T. aestivum (TAP) on insulin secretion in pancreatic b cells and on glucose homeostasis in STZ-induced diabetic mice. RINm5F pancreatic b cell line and isolated rat islets were used for insulin secretion activity. Level of Insulin was measured by enzyme-linked immunosorbent assay (ELISA), real-time RT-PCR, and 45Ca2+ uptake assay. For in vivo oral glucose tolerance test (OGTT) and anti-hyperglycemic activity, TAP was administrated orally to STZ-induced diabetic mice.
In this study, TAP (0.1 to 2 mg/ml) augmented glucose-stimulated insulin secretion in the presence of stimulatory glucose concentration (16.7 mM), but not basal concentration (1.1 mM) in a dose-dependent manner. Although TAP failed to enhance the high K+-induced insulin secretion, the insulinotropic effect of TAP was significantly inhibited by diazoxide, an opener of ATP-sensitive K+ channel blocking insulin release. TAP potentiated the insulin secretion induced by other secretagogues, such as IBMX and tolbutamide. Moreover, TAP significantly increased glucose-induced 45Ca2+ uptake and subsequently enhanced phosphorylation of extra cellular signal-regulated protein kinases (ERK1/2) and protein kinase C (PKC). In addition, specific inhibitors of ERK and PKC attenuated the increase in insulin secretion induced by TAP in RINm5F cells. On the other hand, when TAP was administrated to the fasted mice, it decreased the rise in blood glucose level after starch loading in OGTT, and increased the serum insulin level in mice. Furthermore, oral treatment of TAP markedly improved the blood glucose level through increase of serum insulin level in STZ-induced diabetic mice. Immunohistochemical staining of islet showed that TAP induced the increase in insulin-producing b cells compared to the vehicle control.
Overall, the results indicate that TAP has the stimulating effect on insulin secretion and production in the pancreatic b cells via K+channel closure, calcium influx, and activation of PKC and ERK1/2 signaling pathway. These findings suggest that TAP might be useful in the control of hyperglycemia in insulin-dependent diabetes mellitus through the action as insulin secretagogues.

목차 (Table of Contents)

• List of tables Ⅰ
• List of figures Ⅱ
• Abbreviations Ⅳ
• Abstract 1
• Introduction
• 1. Introduction to the present study 4
• 1.1 Diabetes 8
• 1.2 Triticum aestivum 9
• 2. Literature review
• 2.1 Pancreas 11
• 2.2 b cells 12
• 2.3 Insulin 14
• 2.4 Insulin transcription 14
• 2.5 Insulin biosynthesis 16
• 2.6 Insulin release 17
• 2.7 Regulation of insulin secretion by glucose 19
• 2.8 The effects of glucose on insulin transcription and translation 20
• 2.9 Insulin transcription by glucose control 21
• Materials and methods
• In vitro
• 1. Cells and materials 24
• 2. Extraction and purification of TAP 25
• 3. Cytotoxicity assay 26
• 4. Insulin assay 27
• 5. Western blot analysis 27
• 6. 45Ca2+ uptake assay 28
• 7. RNA isolation and real-time RT-PCR 29
• In vivo
• 1. Animals 29
• 2. Oral glucose tolerance in fasted normal mice 30
• 3. Type 1 diabetes induction 30
• 4. Immunohistochemistry 31
• Results
• 1. The effects of TAP on insulin secretion in RINm5F cells and isolated rat islets 33
• 2. The effects of TAP on cell viability in RINm5F cell 34
• 3. The effects of TAP on insulin secretion in the presence of K+ 35
• 4. The effects of TAP in the presence of insulin secretagogues 36
• 5. Involvement of PKC and ERK1/2 in TAP-triggered responses in RINm5F cells 37
• 6. The effects of TAP on Ca2+ uptake and preproinsulin mRNA expression 38
• 7. Effects of TAP on levels of blood glucose regulation and serum insulin in vivo 39
• 8. The effects of TAP on the insulin production of pancreatic b cells in type 1 diabetes 40
• Discussion 42
• References 48
• Abstract (in Korean) 79