Wirkung und Wirkungsweise von Insulin-like Growth-factor-I auf das proliferative Wachstum neuroendokriner Tumorzellen am Beispiel der humanen Karzinoidzelllinie BON

Karzinoide sind neuroendokrine Tumoren des gastroenteropankreatischen Systems. Bis heute gibt es mit Ausnahme eines chirurgischen Eingriffes keine adäquate kurativeTherapiemöglichkeit. Die Expression des IGF-I-Rezeptors und von IGF-I konnte bei dieser Tumorart bereits nachgewiesen werden. Diese beiden Teile des IGF-Systems sind von besonderer Bedeutung für das Entstehen und das Erhalten verschiedener Tumorarten und gelten heute als sehr interessanter Ansatzpunkt für die Erforschung neuer Therapiestrategien. Ziel dieser Arbeit war es, am Beispiel der humanen Karzinoid-Zellinie BON, das proliferative Wachstum dieser Tumorart unter dem Einfluß von IGF-I zu untersuchen und mögliche, für die Signalvermittlung verantwortliche Transduktionswege zu entschlüsseln. In einem ersten Schritt konnte durch Rezeptor-Bindungsstudien gezeigt werden, dass BON-Zellen einen funktionstüchtigen IGF-I-Rezeptor tragen. Im Radioimmunoassay wurde zudem die IGF-I-Synthese quantitativ nachgewiesen. Die Stimulation der Zellen mit IGF-I bewirkt eine deutliche und signifikante Steigerung des proliferativen Zellwachstums. In Versuchen mit den Hemmstoffen PD 98059 als spezifischer Inhibitor der MAP-Kinasen ERK1 und 2 sowie mit LY 294002 als selektiven PI-3Kinase-Inhibitor konnte darüber hinaus gezeigt werden, dass die Signalkaskaden dieser beiden Kinasefamilien für die Signaltransduktion nach Bindung von IGF-I an seinen Rezeptor von wesentlicher Bedeutung sind. Aus diesen Hemmungsversuchen ergeben sich zudem Hinweise für eine mögliche Verknüpfung beider Transduktionswege. Im MAP-Kinase-Assay wurden die Einflüsse auf die MAP-Kinase visualisiert. Abschließend wurde durch Transfektionsstudien mit einem IGF-I-Promotor die Bedeutungen beider Signaltransduktionswege auch auf die IGF-I-Produktion der BON-Zellen nachgewiesen. Zusammen mit dem beschriebenen quantitativen Nachweis von IGF-I ergeben sich damit deutliche Hinweise für einen auto- beziehungsweise parakrinen Wirkungsmechanismus dieses Peptides bei BON-Zellen. Das IGF-I-System stellt damit einen interessanten Ansatz für die Entwicklung neuer therapeutischer Strategien zur Behandlung neuroendokriner Tumoren des gastroenteropankreatischen Systems dar. Um das IGF-I-vermittelte Wachstum also zu unterbinden erscheinen mehrere Ansatzpunkte möglich: (1.) Auf der Ebene des Rezeptors durch Antagonisierung des IGF-I-Rezeptors, (2.) auf Cytoplasmaebene durch Unterbrechung der Signaltransduktionswege beziehungsweise Antagonisierung des autokrin sezernierten IGF-I oder (3.) auf Genebene durch Störung der IGF-I-Expression selbst

Impaired Hyperglycemia-Induced Delay in Gastric Emptying in Patients With Type 1 Diabetes Deficient for Islet Amyloid Polypeptide

OBJECTIVE—Slowing of gastric emptying by hyperglycemia, a physiological response to minimize postprandial hyperglycemia, may be impaired in patients with type 1 diabetes. The causes and consequences on glucose homeostasis are unknown

Postnatal Development of Numbers and Mean Sizes of Pancreatic Islets and Beta-Cells in Healthy Mice and GIPRdn Transgenic Diabetic Mice

The aim of this study was to examine postnatal islet and beta-cell expansion in healthy female control mice and its disturbances in diabetic GIPRdn transgenic mice, which exhibit an early reduction of beta-cell mass. Pancreata of female control and GIPRdn transgenic mice, aged 10, 45, 90 and 180 days were examined, using state-of-the-art quantitative-stereological methods. Total islet and beta-cell volumes, as well as their absolute numbers increased significantly until 90 days in control mice, and remained stable thereafter. The mean islet volumes of controls also increased slightly but significantly between 10 and 45 days of age, and then remained stable until 180 days. The total volume of isolated beta-cells, an indicator of islet neogenesis, and the number of proliferating (BrdU-positive) islet cells were highest in 10-day-old controls and declined significantly between 10 and 45 days. In GIPRdn transgenic mice, the numbers of islets and beta-cells were significantly reduced from 10 days of age onwards vs. controls, and no postnatal expansion of total islet and beta-cell volumes occurred due to a reduction in islet neogenesis whereas early islet-cell proliferation and apoptosis were unchanged as compared to control mice. Insulin secretion in response to pharmacological doses of GIP was preserved in GIPRdn transgenic mice, and serum insulin to pancreatic insulin content in response to GLP-1 and arginine was significantly higher in GIPRdn transgenic mice vs. controls. We could show that the increase in islet number is mainly responsible for expansion of islet and beta-cell mass in healthy control mice. GIPRdn transgenic mice show a disturbed expansion of the endocrine pancreas, due to perturbed islet neogenesis

Pharmacology and therapeutic implications of current drugs for type 2 diabetes mellitus

Type 2 diabetes mellitus (T2DM) is a global epidemic that poses a major challenge to health-care systems. Improving metabolic control to approach normal glycaemia (where practical) greatly benefits long-term prognoses and justifies early, effective, sustained and safety-conscious intervention. Improvements in the understanding of the complex pathogenesis of T2DM have underpinned the development of glucose-lowering therapies with complementary mechanisms of action, which have expanded treatment options and facilitated individualized management strategies. Over the past decade, several new classes of glucose-lowering agents have been licensed, including glucagon-like peptide 1 receptor (GLP-1R) agonists, dipeptidyl peptidase 4 (DPP-4) inhibitors and sodium/glucose cotransporter 2 (SGLT2) inhibitors. These agents can be used individually or in combination with well-established treatments such as biguanides, sulfonylureas and thiazolidinediones. Although novel agents have potential advantages including low risk of hypoglycaemia and help with weight control, long-term safety has yet to be established. In this Review, we assess the pharmacokinetics, pharmacodynamics and safety profiles, including cardiovascular safety, of currently available therapies for management of hyperglycaemia in patients with T2DM within the context of disease pathogenesis and natural history. In addition, we briefly describe treatment algorithms for patients with T2DM and lessons from present therapies to inform the development of future therapies

The evolving place of incretin-based therapies in type 2 diabetes

Treatment options for type 2 diabetes based on the action of the incretin hormone glucagon-like peptide-1 (GLP-1) were first introduced in 2005. These comprise the injectable GLP-1 receptor agonists solely acting on the GLP-1 receptor on the one hand and orally active dipeptidyl-peptidase inhibitors (DPP-4 inhibitors) raising endogenous GLP-1 and other hormone levels by inhibiting the degrading enzyme DPP-4. In adult medicine, both treatment options are attractive and more commonly used because of their action and safety profile. The incretin-based therapies stimulate insulin secretion and inhibit glucagon secretion in a glucose-dependent manner and carry no intrinsic risk of hypoglycaemia. GLP-1 receptor agonists allow weight loss, whereas DPP-4 inhibitors are weight neutral. This review gives an overview of the mechanism of action and the substances and clinical data available

Spontaneous Calcium Oscillations in Clonal Endocrine Pancreatic Glucagon-Secreting Cells

Measurements of the cytosolic calcium concentration in single cells of the clonal endocrine pancreatic glucagon-secreting cell line INR1 G9 revealed the existence of spontaneous calcium oscillations in 20 - 70 % of these cells. Inhibition of these spontaneous oscillations by thapsigargin as well as the phospholipase C inhibitor U 73122 demonstrated involvement of calcium release from intracellular stores, probably mediated by a high basal activity of phospholipase C. Removal of extracellular calcium but not the L-type calcium channel antagonists verapamil or nifedipine terminated the spontaneous oscillations, suggesting that calcium influx by a pathway distinct from L-type channels contributed to the oscillations. Similar spontaneous calcium oscillations could be the pacemaker of pulsatile glucagon release in endocrine pancreatic A-cells.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/31185/1/0000086.pd