Hypoglycemia is one of the most serious acute complications in intensively treated diabetes. Recurrent hypoglycemia predisposes individuals to subsequent hypoglycemia, and diminished counterregulatory hormone responses increase this threat. Elevated pancreatic and/or circulating somatostatin has been reported in diabetic humans and animals, and we postulated that excessive somatostatin contributes to the attenuation of counterregulatory hormone release during hypoglycemia in diabetes. It is known that somatostatin suppresses stimulated secretion of glucagon, epinephrine, and corticosterone. We hypothesized that selective somatostatin receptor type 2 (SSTR2) antagonism would: (Study 1) improve hormone counterregulation to hypoglycemia, and (Study 2) ameliorate hypoglycemia in recurrently hypoglycemic rats. Using both high (10 U/kg) and low (5 U/kg) dose insulin to induce hypoglycemia, we demonstrate that inhibiting the action of somatostatin on SSTR2 normalizes the severely attenuated glucagon and corticosterone responses to acute hypoglycemia in diabetic rats. These improvements were specific to diabetes since SSTR2 antagonism did not increase these hormones in non-diabetic rats in response to hypoglycemia. In the absence of hypoglycemia, SSTR2 antagonist neither markedly alters glycemia nor causes sustained elevations in counterregulatory hormones in diabetic animals. Diabetic rats exhibit up to 65% and 75% more pancreatic and plasma somatostatin than non-diabetic rats following hypoglycemia, respectively. Despite improvements of glucagon and corticosterone, expression of gluconeogenic enzymes PEPCK1 and G6Pase was unaltered. SSTR2 antagonism reduced the glucose requirement during a hypoglycemic clamp induced with a lower dose of insulin. In recurrently hypoglycemic diabetic rats, we demonstrate that SSTR2 antagonist treatment reduces the depth and duration of hypoglycemia and promotes the recovery to euglycemia, without affecting the glycemia-lowering effect of insulin. This amelioration of hypoglycemia by SSTR2 antagonism may be attributable in part to the observed modest improvements of glucagon, epinephrine, and corticosterone counterregulation following recurrent hypoglycemia. These results implicate an important role for increased pancreatic, and possibly circulating, somatostatin in defective hypoglycemic counterregulation in diabetes.

Impaired counterregulation during hypoglycemia in type 1 diabetes (T1D) is partly due to inadequate pancreatic islet alpha-cell glucagon secretion. We hypothesized that hypoglycemia can be prevented in autoimmune T1D by selective somatostatin receptor type 2 (SSTR2) antagonism of alpha cells to relieve SSTR2 inhibition, thereby increasing glucagon secretion. Diabetic biobreeding diabetes prone (BBDP) rats (D) vs non-diabetic BBDP (N) rats, underwent infusion of vehicle or SSTR2 antagonist (SSTR2a) during insulin-induced hypoglycaemia. D rats, treated with SSTR2a, needed little or no glucose to maintain hypoglycemia. To monitor real-time glucagon secretory response directly, we developed the technique of thin slices of the pancreas from D and N rats as well as normal human pancreas, subjected to perifusion with vehicle vs SSTR2a. SSTR2a treatment enhanced glucagon secretion in N and D rats and human pancreas. We conclude that SSTR2 antagonism can enhance hypoglycemia-stimulated glucagon release sufficient to achieve normoglycemic control.

Hypoglycemia is one of the most serious acute complications in intensively treated diabetes. Recurrent hypoglycemia predisposes individuals to subsequent hypoglycemia, and diminished counterregulatory hormone responses increase this threat. Elevated pancreatic and/or circulating somatostatin has been reported in diabetic humans and animals, and we postulated that excessive somatostatin contributes to the attenuation of counterregulatory hormone release during hypoglycemia in diabetes. It is known that somatostatin suppresses stimulated secretion of glucagon, epinephrine, and corticosterone. We hypothesized that selective somatostatin receptor type 2 (SSTR2) antagonism would: (Study 1) improve hormone counterregulation to hypoglycemia, and (Study 2) ameliorate hypoglycemia in recurrently hypoglycemic rats. Using both high (10 U/kg) and low (5 U/kg) dose insulin to induce hypoglycemia, we demonstrate that inhibiting the action of somatostatin on SSTR2 normalizes the severely attenuated glucagon and corticosterone responses to acute hypoglycemia in diabetic rats. These improvements were specific to diabetes since SSTR2 antagonism did not increase these hormones in non-diabetic rats in response to hypoglycemia. In the absence of hypoglycemia, SSTR2 antagonist neither markedly alters glycemia nor causes sustained elevations in counterregulatory hormones in diabetic animals. Diabetic rats exhibit up to 65% and 75% more pancreatic and plasma somatostatin than non-diabetic rats following hypoglycemia, respectively. Despite improvements of glucagon and corticosterone, expression of gluconeogenic enzymes PEPCK1 and G6Pase was unaltered. SSTR2 antagonism reduced the glucose requirement during a hypoglycemic clamp induced with a lower dose of insulin. In recurrently hypoglycemic diabetic rats, we demonstrate that SSTR2 antagonist treatment reduces the depth and duration of hypoglycemia and promotes the recovery to euglycemia, without affecting the glycemia-lowering effect of insulin. This amelioration of hypoglycemia by SSTR2 antagonism may be attributable in part to the observed modest improvements of glucagon, epinephrine, and corticosterone counterregulation following recurrent hypoglycemia. These results implicate an important role for increased pancreatic, and possibly circulating, somatostatin in defective hypoglycemic counterregulation in diabetes.

Impaired counterregulation during hypoglycemia in type 1 diabetes (T1D) is partly due to inadequate pancreatic islet alpha-cell glucagon secretion. We hypothesized that hypoglycemia can be prevented in autoimmune T1D by selective somatostatin receptor type 2 (SSTR2) antagonism of alpha cells to relieve SSTR2 inhibition, thereby increasing glucagon secretion. Diabetic biobreeding diabetes prone (BBDP) rats (D) vs non-diabetic BBDP (N) rats, underwent infusion of vehicle or SSTR2 antagonist (SSTR2a) during insulin-induced hypoglycaemia. D rats, treated with SSTR2a, needed little or no glucose to maintain hypoglycemia. To monitor real-time glucagon secretory response directly, we developed the technique of thin slices of the pancreas from D and N rats as well as normal human pancreas, subjected to perifusion with vehicle vs SSTR2a. SSTR2a treatment enhanced glucagon secretion in N and D rats and human pancreas. We conclude that SSTR2 antagonism can enhance hypoglycemia-stimulated glucagon release sufficient to achieve normoglycemic control.

Systemic inflammatory networks and local signaling cascades trigger culprit pathogenic mechanisms relating clinical cardiovascular disease (CVD) risk factors to atherosclerotic plaque progression and rupture. Imaging vascular inflammation affords a valuable marker of atherosclerotic disease activity to reveal important mechanistic insights for CVD research, to quantify early anti-inflammatory effects of new atherosclerosis drugs, and, ultimately, to help improve CVD risk prediction. While carotid, aortic, and peripheral arterial inflammation can be measured by 18F-fluorodeoxyglucose (FDG) PET-computed tomography (CT), as a glucose analog, high 18F-FDG signal spillover owing to physiological myocardial muscle metabolism prevents reliable coronary interpretation. Lack of cell specificity, and the influence of hypoxia on 18F-FDG uptake within macrophages and other plaque cells, are further limitations that drive the search for an alternative PET tracer for imaging inflammation in atherosclerosis. Up-regulation of the G-protein coupled receptor somatostatin receptor subtype-2 (SST2) occurs on the cell surface of activated macrophages. The central hypothesis tested in this thesis is that vascular SST2 PET imaging using 68Ga-DOTATATE might offer a more accurate marker of macrophage inflammation than 18F-FDG, with superior coronary imaging and therefore better power to discriminate high-risk vs. low-risk atherosclerotic lesions. Comprehensive molecular, histological and clinical evaluation of this experimental CVD imaging biomarker was undertaken, including a prospective clinical study with head-to-head comparison to 18F-FDG in coronary, carotid, and aortic vasculature. In vitro data showed that (i) target SSTR2 gene expression occurred in “pro-inflammatory” M1 macrophages, (ii) specific 68Ga-DOTATATE ligand binding to SST2 receptors occurred in CD68-positive macrophage-rich carotid plaque regions, and (iii) and carotid SSTR2 mRNA was highly correlated with both the pan-macrophage marker CD68 and in vivo 68Ga-DOTATATE PET signals. In clinical imaging, increased 68Ga-DOTATATE inflammatory signals correctly identified culprit vs. non-culprit arteries in patients with acute coronary syndrome and transient ischemic attack/stroke. 68Ga-DOTATATE also demonstrated good diagnostic accuracy for high-risk coronary CT features, and strong correlations with clinical CVD risk factors and 18F-FDG-defined vascular inflammation. While 18F-FDG also differentiated culprit vs. non-culprit carotid and high-risk coronary arteries, myocardial 18F-FDG overspill rendered coronary scans uninterpretable in most patients. In contrast, 68Ga-DOTATATE allowed unimpeded coronary interpretation in all patients. Findings of this thesis provide compelling evidence, from gene, to cell, to plaque, to patient, that SST2 PET imaging using 68Ga-DOTATATE provides a quantifiable marker of macrophage-related atherosclerotic inflammation and disease activity. Further studies are needed to establish whether 68Ga-DOTATATE PET can improve CVD risk prediction when added to current clinical methods, or offer a novel imaging platform to rapidly test the anti-inflammatory capacity of emerging atherosclerosis drugs. Broader translational applications of 68Ga-DOTATATE PET include possible use in diagnosis and therapeutic monitoring of vasculitis, endocarditis, myocarditis, and other manifestations of cardiovascular inflammation.

Made available in DSpace on 2016-08-19T18:16:06Z (GMT). No. of bitstreams: 1 Dissertacao Bruno.pdf: 2654529 bytes, checksum: 8a96ae87802691862664f63085d257f5 (MD5) Previous issue date: 2012-03-12 / FUNDAÇÃO DE AMPARO À PESQUISA E AO DESENVOLVIMENTO CIENTIFICO E TECNOLÓGICO DO MARANHÃO / Pituitary tumors represent 15% of intracranial neoplasms and are usually benign. The treatment primary is surgical resection with exception for prolactinomas because dopamine agonists are very effective in the treatment these tumors. If surgery does not lead to healing, it is necessary other therapeutic strategy in a attempt to control hormone levels and tumor size reduction. The radiotherapy and medical treatment with somatostatin analogs and agonist dopamine are often used. The study aimed to analyze the presence, distribution and frequency of somatostatin receptor and dopamine receptor (DR2) in pituitary adenomas, and compared their mRNA expression and protein expression. We studied 38 patients with pituitary adenomas. The GH-secreting adenomas showed immunoreactivity more frequent SST2 and SST3 present in 100% of the tumors followed SST5, SST4 and SST1 respectively. Clinically nonfunctioning adenomas SST3 receptor was most widely distributed, present in 13 of 14 tumors followed SST2, SST4, SST1 and SST5 respectively. The mRNA expression of SST2 and SST5 receptor was present in all pituitary adenomas with higher expression of SST2. The DR2 receptor was present and 85% of samples analyzed. In conclusion, the high expression of SST2 in somatotropinomas support the possibility of the use of octreotide as an adjunct therapy in the treatment of acromegalic patients. Patients with clinically nonfunctioning adenomas showed expression of somatostatin receptor and dopamine which indicates the possibility of treating these patients with the somatostatin analogues and / or dopamine agonists. / Os tumores hipofisários correspondem por cerca de 15% das neoplasias intracranianas e são geralmente benignos. O tratamento primário mais comumente utilizado é a cirurgia com exceção para os prolactinomas, devido a eficácia do tratamento com a utilização de agonistas dopaminérgicos. Caso o resultado cirúrgico não leve a ressecção da doença, faz-se necessário o uso de outras modalidades terapêuticas, na tentativa de controlar os níveis hormonais e crescimento tumoral. A radioterapia e o tratamento medicamentoso com os análogos da somatostatina e/ou os agonistas dopaminérgicos são frequentemente utilizados como tratamento adjuvante. O presente estudo teve por objetivo analisar a presença, distribuição e frequência dos receptores da somatostatina e da dopamina (DR2) em adenomas hipofisários e comparar as suas expressões do mRNA e proteicas, através de testes por qPCR em tempo real e por imunohistoquímicos. Foram analisados 38 pacientes diagnosticados com adenomas hipofisários. Os adenomas secretores de GH apresentaram imunoreatividade mais frequente dos receptores SST2 e SST3, presentes em 100% dos tumores, seguidos pelos receptores SST5, SST4 e SST1, respectivamente. Nos adenomas clinicamente não funcionantes o receptor mais amplamente distribuído foi o SST3, presente em 13 dos 14 tumores seguidos pelo SST2, SST4, SST1 e SST5 respectivamente. A expressão do mRNA dos receptores SST2 e SST5 estava presente em todos os adenomas hipofisários estudados, com maior expressão do subtipo SST2. A expressão do mRNA do receptor DR2 foi encontrada em aproximadamente 85% das amostras analisadas. Em conclusão, a elevada expressão do SST2 nos somatotropinomas reforça a possibilidade do uso do octreotide como terapia complementar no tratamento dos pacientes acromegálicos. Os pacientes com adenomas clinicamente não funcionantes apresentaram expressão dos receptores da somatostatina e da dopamina o que indica a possibilidade de tratamento destes pacientes com os análogos da somatostatina e/ou agonistas dopaminérgicos.

Les GEPNETs (tumeurs neuroendocrines gastroentéropancréatiques), représentent le deuxième cancer digestif. L’octréotide (agoniste Sst2) contrôle efficacement leurs sécrétions et plus modérément la croissance cellulaire. Au cours de ma première partie de thèse, j’ai développé la culture primaire de GEPNETs humaines. Ceci m’a permis d’étudier l’effet antiprolifératif et antisécretoire du pasireotide (pan agoniste Sst) et de l’évérolimus (inhibiteur de la voie pi3 kinase Akt) en comparaison avec l’octréotide. J’ai mis en évidence un effet inhibiteur significatif et similaire de l’octréotide et du pasiréotide sur la viabilité cellulaire et la sécrétion de chromogranine A. Cependant, le trafic intracellulaire du Sst2 est diffèrent en présence de pasireotide. L’évérolimus inhibe la viabilité et la secretion cellulaire des GEPNETs de manière similaire aux SSA. Nous n’avons pas retrouvé d’additivité entre l’évérolimus et les SSA. Dans la deuxième partie de mon travail j'ai étudié l’effet de la surexpression du Sst2 dans les cellules de prolactinomes et NFPA humains. Apres surexpression de Sst2, l’octréotide est capable d’inhiber la sécrétion de PRL et la prolifération cellulaire des NFPAs. Cette surexpression n’améliore pas la sensibilité aux dopastatines (agonistes chimériques Sst2-D2DR) des prolactinomes alors qu’une amélioration est bien observée dans les NFPAs. En conclusion, la culture primaire des GEPNETs représente un bon modèle d’étude pharmacologique. La coopération Sst2–D2DR dans les NFPA est effective dans ce modèle et permettra l’étude des mécanismes mises en jeu par les dopastatines. / GEPNETs represent, in terms of prevalence, the second digestive cancer. Octreotide (Sst2 agonists) effectively control their secretion and partially cell growth. we developed a primary cell culture of human GEPNETs. Cell culture allowed the study of antisecretory and antiproliferative effect of pasireotide and everolimus, alone or in combination, as compared to octreotide, in 20 tumors. We highlighted a significant and similar maximal inhibitory effect of octreotide and Pasireotide either on cell viability or on chromogranin A secretion in all analyzed tumors. However, the intracellular trafficking of Sst2 was strikely different in the presence of pasireotide and octreotide. In all analyzed tumors, everolimus inhibits cell viability and secretion of GEPNETs similarly to SSA. We couldn’t reveal any additivity between everolimus and SSA in cell viability suppression.My second goal was to study the effect of overexpression of Sst2 by adenoviral transfer in cells of human prolactinomas and NFPA. In both cell types. Nevertheless, octreotide efficiently suppressed PRL secretion and cell proliferation (NFPA). Overexpression of Sst2 did not improve the efficcacy of dopastatines (chimeric Sst2 - D2DR agonists) on prolactin secretion in prolactinomas, but clealy improved suppression of cell proliferation in NFPA. These results suggest that dopostatin promotes a Sst2 D2DR cooperation in NFPA, but not in prolactinomas, where DRDR activation remains dominant. In conclusion, GEPNETs primary cell culture represents a good model for pharmacological In pituitary adenomas, Sst2 overexpression opens an interesting perspective for gene therapy in recurrent NFPA after surgery.

Neurons commonly have a primary cilium, which is a non-motile organelle extending from the centrosome into the extracellular space. In most brain regions, neuronal cilia are enriched in either somatostatin receptor type 3 (SstR3) or melanin concentrating hormone receptor type 1 (MCHR1), or both. The present immunohistochemical study provides novel evidence that primary cilia regulate neuronal excitability via G-protein coupled receptors (GPCRs), and that their identity is governed by brain region and by competition, both in adulthood and in postnatal development. The hippocampus, which is particularly vulnerable to seizures, has opposing gradients of SstR3(+) and MCHR1(+) ciliary GPCRs. We hypothesized that there is a competition between these two ciliary GPCRs, which might take place on any level from gene expression to presence in the cilium. We examined whether receptor colocalization occurs transiently in development before ciliary GPCR dominance is established in neurons in the CNS. In postnatal CA1 and CA3, the first GPCR to appear in cilia was the one that will dominate in adults: MCHR1 in CA1 and SstR3 in CA3. Some days later, the second GPCR was expressed along with the first; dual-receptor cilia were the exclusive type until single-receptor cilia emerged again around P14. Single-receptor cilia then increased in numbers through adulthood. By identifying ciliary receptors that modulate seizure activity in mice, the present study lays a foundation for therapeutic approaches to reduce neuronal excitotoxicity underlying cell death in epilepsy, CNS injury, and neurodegenerative diseases.

Neuroendocrine tumours generally show an overexpression of somatostatin receptors on their cell membranes, mainly subtype 2. This is taken advantage of in diagnosis and therapy by using synthetic somatostatin analogues that can be labelled with radionuclides to visualize and treat tumours with an overexpression of somatostatin receptors. The method traditionally used for visualization is somatostatin receptor scintigraphy (SRS) with 111In-DTPA-octreotide but this method is gradually being substituted by 68Ga-DOTATOC PET/CT. To evaluate patients for peptide receptor radionuclide therapy, it is mandatory for the patient to be examined by both methods. In the evaluation, the tumours are graded according to the Krenning scale on the images from the SRS. Patients with sufficient tumour uptake of somatostatin analogues are eligible for peptide receptor radionuclide therapy (PRRT). The aim of this study was to compare the tumour’s Krenning scores from SRS to the Krenning scores, quantitative indices and TNR-values from the 68Ga-DOTATOC PET/CT images. This was done to investigate if the Krenning scale could be applied to PET/CT enabling the patient to undergo only PET/CT for diagnosis and evaluation prior to PRRT. This study, including 28 patients, found no strong correlation between the Krenning scores from the SRS and the scores from 68Ga-DOTATOC PET/CT. However, a better correlation was shown between the Krenning scores from SRS and TNR-values where the quantitative indices SUVmax and SUVmean were divided with the SUVmean of the spleen. These findings could be worth exploring further in future studies, incorporating larger number of patients.

Coordination of transition metals to peptides, either through the incorporation of unnatural chelating groups or amino acid ligating side-chains, expands the utility of peptides for biological studies. The first part of this project describes induction of α-helical secondary structure in pentapeptides upon side-chain coordination of inert transition metal ions. The second part of this project describes the syntheses of biologically active peptide species that contain a macrobicyclic hexaamine ligand that can complex radioactive metal ions for diagnostic imaging purposes. / Short peptide sequences do not form thermodynamically stable α-helices in water. The capacity of two metal clips, cis-[Ru(NH3)4(solvent)2]2+ and cis [Pd(en)(solvent)2]2+ to induce α-helicity in peptides that are five amino acids long, Ac HARAH NH2 and Ac MARAM-NH2 has been explored. In all cases at pH < 5, the metal ions bind to the side-chains of amino acid residues at positions i, i+4 of the pentapeptides resulting in formation of bidentate macrocyclic species. Circular dichroism and 1H nuclear magnetic resonance data indicate that the metal complexes of Ac-MARAM-NH2 are highly α helical in water, and in the most spectacular case, coordination of Ac-MARAM-NH2 to cis-[Ru(NH3)4(solvent)2]2+ results in up to 80% α-helicity. In contrast, metal complexes of Ac-HARAH-NH2 exhibit significantly less α-helicity in water. / 64Cu-radiolabelled peptides have been investigated for their ability to target specific tissue or cell types. These peptides require a chelating group that binds copper ions strongly. Macrobicyclic hexaamine ligands, based on the compound commonly referred to as “sarcophagine”, have demonstrated extremely high stability under biological conditions. Here we describe the synthesis of diaminosarcophagine chelators with carboxylate groups for conjugation to peptides. These new chelators have been attached to the N-terminus or lysine side-chain of biologically-active peptides, including Tyr3 octreotate, Lys3-bombesin and an integrin targeting peptide. Spectroscopic and voltammetric studies of these species suggest that the conjugated sarcophagine group retains the high metal binding affinity and structural properties of the parent species, diaminosarcophagine. These are among the first sarcophagine-peptide compounds that have been properly characterised. The new sarcophagine-peptide conjugates can be easily radiolabelled with 64Cu2+ over a wide pH range at ambient temperature.