Overview of Radiolabeled Somatostatin Analogs for Cancer Imaging and Therapy.

Identified in 1973, somatostatin (SST) is a cyclic hormone peptide with a short biological half-life. Somatostatin receptors (SSTRs) are widely expressed in the whole body, with five subtypes described. The interaction between SST and its receptors leads to the internalization of the ligand-receptor complex and triggers different cellular signaling pathways. Interestingly, the expression of SSTRs is significantly enhanced in many solid tumors, especially gastro-entero-pancreatic neuroendocrine tumors (GEP-NET). Thus, somatostatin analogs (SSAs) have been developed to improve the stability of the endogenous ligand and so extend its half-life. Radiolabeled analogs have been developed with several radioelements such as indium-111, technetium-99 m, and recently gallium-68, fluorine-18, and copper-64, to visualize the distribution of receptor overexpression in tumors. Internal metabolic radiotherapy is also used as a therapeutic strategy (e.g., using yttrium-90, lutetium-177, and actinium-225). With some radiopharmaceuticals now used in clinical practice, somatostatin analogs developed for imaging and therapy are an example of the concept of personalized medicine with a theranostic approach. Here, we review the development of these analogs, from the well-established and authorized ones to the most recently developed radiotracers, which have better pharmacokinetic properties and demonstrate increased efficacy and safety, as well as the search for new clinical indications.

SST gene hypermethylation acts as a pan-cancer marker for pancreatic ductal adenocarcinoma and multiple other tumors: toward its use for blood-based diagnosis.

Aberrant DNA methylation is often involved in carcinogenesis. Our initial goal was to identify DNA methylation biomarkers associated with pancreatic cancer. A genomewide methylation study was performed on DNA from pancreatic ductal adenocarcinoma (PDAC) and endocrine pancreas tumors. Validation of DNA methylation patterns and concomitant alterations in expression of gene candidates was performed on patient samples and pancreatic cancer cell lines. Furthermore, validation was done on independent data from The Cancer Genome Atlas (TCGA) and Gene Expression Omnibus (GEO). Finally, droplet digital PCR was employed to detect DNA methylation marks in cell-free (cf) DNA isolated from plasma samples of PDAC patients and cancer-free blood donors. Hypermethylation of the SST gene (encoding somatostatin) and concomitant downregulation of its expression were discovered in PDAC and endocrine tumor tissues while not being present in chronic pancreatitis (inflamed) tissues and normal pancreas. Fittingly, treatment with a somatostatin agonist (octreotide) reduced cell proliferation and migration of pancreatic cancer cells. Diagnostic performance of SST methylation in a receiver operating characteristic curve analysis was 100% and 89% for tissue and plasma samples, respectively. A large body of TCGA and GEO data confirmed SST hypermethylation and downregulation in PDAC and showed a similar effect in a broad spectrum of other tumor entities. SST promoter methylation represents a sensitive and promising molecular, pan-cancer biomarker detectable in tumor tissue, and liquid biopsy samples.

Somatostatin depresses the excitability of subicular bursting cells: Roles of inward rectifier K+ channels, KCNQ channels and Epac.

The hippocampus is a crucial component for cognitive and emotional processing. The subiculum provides much of the output for this structure but the modulation and function of this region is surprisingly under-studied. The neuromodulator somatostatin (SST) interacts with five subtypes of SST receptors (sst1 to sst5 ) and each of these SST receptor subtypes is coupled to Gi proteins resulting in inhibition of adenylyl cyclase (AC) and decreased level of intracellular cAMP. SST modulates many physiological functions including cognition, emotion, autonomic responses and locomotion. Whereas SST has been shown to depress neuronal excitability in the subiculum, the underlying cellular and molecular mechanisms have not yet been determined. Here, we show that SST hyperpolarized two classes of subicular neurons with a calculated EC50 of 0.1 µM. Application of SST (1 µM) induced outward holding currents by primarily activating K+ channels including the G-protein-activated inwardly-rectifying potassium channels (GIRK) and KCNQ (M) channels, although inhibition of cation channels in some cells may also be implicated. SST-elicited hyperpolarization was mediated by activation of sst2 receptors and required the function of G proteins. The SST-induced hyperpolarization resulted from decreased activity of AC and reduced levels of cAMP but did not require the activity of either PKA or PKC. Inhibition of Epac2, a guanine nucleotide exchange factor, partially blocked SST-mediated hyperpolarization of subicular neurons. Furthermore, application of SST resulted in a robust depression of subicular action potential firing and the SST-induced hyperpolarization was responsible for its inhibitory action on LTP at the CA1-subicilum synapses. Our results provide a novel cellular and molecular mechanism that may explain the roles of SST in modulation of subicular function and be relevant to SST-related physiological functions.

Evidence That Endogenous Somatostatin Inhibits Episodic, but Not Surge, Secretion of LH in Female Sheep.

Two modes of gonadotropin-releasing hormone (GnRH) and luteinizing hormone (LH) secretion are necessary for female fertility: surge and episodic secretion. However, the neural systems that regulate these GnRH secretion patterns are still under investigation. The neuropeptide somatostatin (SST) inhibits episodic LH secretion in humans and sheep, and several lines of evidence suggest SST may regulate secretion during the LH surge. In this study, we examined whether SST alters the LH surge in ewes by administering a SST receptor (SSTR) 2 agonist (octreotide) or antagonist [CYN154806 (CYN)] into the third ventricle during an estrogen-induced LH surge and whether endogenous SST alters episodic LH secretion. Neither octreotide nor CYN altered the amplitude or timing of the LH surge. Administration of CYN to intact ewes during the breeding season or anestrus increased LH secretion and increased c-Fos in a subset GnRH and kisspeptin cells during anestrus. To determine if these stimulatory effects are steroid dependent or independent, we administered CYN to ovariectomized ewes. This SSTR2 antagonist increased LH pulse frequency in ovariectomized ewes during anestrus but not during the breeding season. This study provides evidence that endogenous SST contributes to the control of LH secretion. The results demonstrate that SST, acting through SSTR2, inhibits episodic LH secretion, likely acting in the mediobasal hypothalamus, but action at this receptor does not alter surge secretion. Additionally, these data provide evidence that SST contributes to the steroid-independent suppression of LH pulse frequency during anestrus.

Somatostatin Agonist Pasireotide Inhibits Exercise-Stimulated Growth in the Male Siberian Hamster (Phodopus sungorus).

The Siberian hamster (Phodopus sungorus) is a seasonal mammal, exhibiting a suite of physiologically and behaviourally distinct traits dependent on the time of year and governed by changes in perceived day length (photoperiod). These attributes include significant weight loss, reduced food intake, gonadal atrophy and pelage change with short-day photoperiod as in winter. The central mechanisms driving seasonal phenotype change during winter are mediated by a reduced availability of hypothalamic triiodothyronine (T3), although the downstream mechanisms responsible for physiological and behavioural changes are yet to be fully clarified. With access to a running wheel (RW) in short photoperiod, Siberian hamsters that have undergone photoperiod-mediated weight loss over-ride photoperiod-drive for reduced body weight and regain weight similar to a hamster held in long days. These changes occur despite retaining the majority of hypothalamic gene expression profiles appropriate for short-day hamsters. Utilising the somatostatin agonist pasireotide, we recently provided evidence for an involvement of the growth hormone (GH) axis in the seasonal regulation of bodyweight. In the present study, we employed pasireotide to test for the possible involvement of the GH axis in RW-induced body weight regulation. Pasireotide successfully inhibited exercise-stimulated growth in short-day hamsters and this was accompanied by altered hypothalamic gene expression of key GH axis components. Our data provide support for an involvement of the GH axis in the RW response in Siberian hamsters.

Changes of growth hormone-releasing hormone and somatostatin neurons in the rat hypothalamus induced by genistein: a stereological study.

OBJECTIVES: Genistein is a plant-derived estrogenic isoflavone commonly found in dietary and therapeutic supplements, due to its potential health benefits. Growth hormone-releasing hormone (GHRH) and somatostatin (SS) are neurosecretory peptides synthesized in neurons of the hypothalamus and regulate the growth hormone secretion. Early reports indicate that estrogens have highly involved in the regulation of GHRH and SS secretions. Since little is known about the potential effects of genistein on GHRH and SS neurons, we exposed rats to genistein. METHODS: Genistein were administered to adult rats in dose of 30 mg/kg, for 3 weeks. The estradiol-dipropionate treatment was used as the adequate controls to genistein. Using applied stereology on histological sections of hypothalamus, we obtained the quantitative information on arcuate (Arc) and periventricular (Pe) nucleus volume and volume density of GHRH neurons and SS neurons. Image analyses were used to obtain GHRH and SS contents in the median eminence (ME). RESULTS: Administration of estradiol-dipropionate caused the increase of Arc and Pe nucleus volume, SS neuron volume density, GHRH and SS staining intensity in the ME, when compared with control. Genistein treatment increased: Arc nucleus volume and the volume density of GHRH neurons (by 26%) and SS neurons (1.5 fold), accompanied by higher GHRH and SS staining intensity in the ME, when compared to the orhidectomized group. DISCUSSION: These results suggest that genistein has a significant effect on hypothalamic region, involved in the regulation of somatotropic system function, and could contribute to the understanding of genistein as substance that alter the hormonal balance.

Parallel Inhibition of Dopamine Amacrine Cells and Intrinsically Photosensitive Retinal Ganglion Cells in a Non-Image-Forming Visual Circuit of the Mouse Retina.

An inner retinal microcircuit composed of dopamine (DA)-containing amacrine cells and melanopsin-containing, intrinsically photosensitive retinal ganglion cells (M1 ipRGCs) process information about the duration and intensity of light exposures, mediating light adaptation, circadian entrainment, pupillary reflexes, and other aspects of non-image-forming vision. The neural interaction is reciprocal: M1 ipRGCs excite DA amacrine cells, and these, in turn, feed inhibition back onto M1 ipRGCs. We found that the neuropeptide somatostatin [somatotropin release inhibiting factor (SRIF)] also inhibits the intrinsic light response of M1 ipRGCs and postulated that, to tune the bidirectional interaction of M1 ipRGCs and DA amacrine cells, SRIF amacrine cells would provide inhibitory modulation to both cell types. SRIF amacrine cells, DA amacrine cells, and M1 ipRGCs form numerous contacts. DA amacrine cells and M1 ipRGCs express the SRIF receptor subtypes sst(2A) and sst4 respectively. SRIF modulation of the microcircuit was investigated with targeted patch-clamp recordings of DA amacrine cells in TH-RFP mice and M1 ipRGCs in OPN4-EGFP mice. SRIF increases K(+) currents, decreases Ca(2+) currents, and inhibits spike activity in both cell types, actions reproduced by the selective sst(2A) agonist L-054,264 (N-[(1R)-2-[[[(1S*,3R*)-3-(aminomethyl)cyclohexyl]methyl]amino]-1-(1H-indol-3-ylmethyl)-2-oxoethyl]spiro[1H-indene-1,4'-piperidine]-1'-carboxamide) in DA amacrine cells and the selective sst4 agonist L-803,087 (N(2)-[4-(5,7-difluoro-2-phenyl-1H-indol-3-yl)-1-oxobutyl]-L-arginine methyl ester trifluoroacetate) in M1 ipRGCs. These parallel actions of SRIF may serve to counteract the disinhibition of M1 ipRGCs caused by SRIF inhibition of DA amacrine cells. This allows the actions of SRIF on DA amacrine cells to proceed with adjusting retinal DA levels without destabilizing light responses by M1 ipRGCs, which project to non-image-forming targets in the brain.

Recent developments on thiourea based anticancer chemotherapeutics.

The recent emergence of anticancer activity of thiourea derivatives have inspired the medicinal chemist to design and synthesize new thiourea derivatives. These thiourea based anticancer chemotherapeutics inhibit cancer propagation by acting as inhibitors of topoisomerase, protein tyrosine kinase, somatostatin agonists, sirtuins, and carbonic anhydrase (CA). This review summarizes the recent developments on the thiourea based anticancer chemotherapeutics.

Pegvisomanto para acromegalia / Pegvisomanto for acromegaly

CONTEXTO: A acromegalia é uma doença sistêmica crônica caracterizada pela produção excessiva de hormônio do crescimento (GH) após o fechamento das epífises e que pode ser causada por diferentes condições clínicas. O Ministério da Saúde elaborou e disponibilizou, por meio da Portaria nº 199, de 25 de fevereiro de 2013, Protocolo Clínico e Diretrizes Terapêuticas para o tratamento da doença e o SUS faz a oferta de toda a linha de cuidado prevista no referido protocolo, que inclui além de procedimento cirúrgico e radiológico, o tratamento por meio de medicamentos como os análogos da somatostatina (octreotida e lanreotida) e agonistas da dopamina. Atualmente, o medicamento pegvisomanto é indicado em bula para acromegálicos que apresentaram resposta inadequada à cirurgia e/ou à radioterapia e para aqueles pacientes cujo tratamento médico com análogos da somatostatina não normalizou as concentrações séricas de IGF-I ou não foi tolerado. A TECNOLOGIA: O pegvisomanto é produzido em E. Coli por tecnologia de DNA recombinante. É uma proteína contendo 191 resíduos de aminoácidos para os quais vários polímeros de polietilenoglicol (PEG) estão covalentemente ligados (predominantemente 4 a 6 PEG/molécula de proteína). O pegvisomanto é um análogo do hormônio de crescimento humano (GH) geneticamente modificado para agir como antagonista do receptor do hormônio de crescimento. O pegvisomanto liga-se seletivamente aos receptores do hormônio de crescimento na superfície das células, bloqueando a ligação do hormônio de crescimento endógeno, interferindo, dessa forma, na transdução do sinal intracelular do hormônio de crescimento. EVIDÊNCIAS CIENTÍFICAS: Foram analisados quatro estudos intervencionais e três observacionais por meio dos quais se avaliaram a intervenção de pegvisomanto em parâmetros bioquímicos de população heterogênea de pacientes acromegálicos com diferentes histórias e respostas a tratamentos prévios. Além disso, avaliaram-se também a influência do tratamento com pegvisomanto em sinais e sintomas clínicos da acromegalia como artralgia, pressão sanguínea e alguns parâmetros cardiovasculares. Observou-se, pela análise dos estudos intervencionais, que pegvisomanto normalizou os níveis sanguíneos de IGF-1 para a idade em 56 a 80% dos pacientes tratados com diferentes esquemas posológicos do medicamento em monoterapia e em associação. A influência do tratamento em sinais e sintomas da doença foi pouco expressiva e bastante heterogênea entre os pacientes recrutados para participar dos estudos. Da mesma forma observou-se pequena alteração na qualidade de vida de pacientes tratados no período de 7 a 27 meses. Em estudo observacional utilizado para acompanhar a evolução clínica de 1.288 pacientes com acromegalia e em tratamento com pegvisomanto por cinco anos observou-se taxa de normalização dos níveis sanguíneos de IGF-1 em pouco mais de 63% do grupo de pacientes acompanhados. CONSIDERAÇÕES FINAIS: A possibilidade de incorporação de pegvisomanto para o tratamento de acromegalia ao SUS foi avaliada em pelo menos dois momentos. Em uma primeira avaliação conduzida pela própria CONITEC, constatou-se não haver estudos com tempo de seguimento suficiente para que se determinasse a eficácia e segurança do medicamento em longo prazo, considerando a necessidade de uso crônico de pegvisomanto. Depois, em 2013, o Ministério da Saúde publicou protocolo clínico baseado em ampla revisão da literatura por meio do qual decidiu não incluir o medicamento ao arsenal ofertado para o tratamento medicamentoso da doença no SUS. Uma nova análise provocada pelo demandante nessa segunda submissão identificou que o medicamento é eficaz em estudos controlados quando se avaliam como desfechos a redução dos níveis sanguíneos de IGF-1 e o controle de alguns dos sinais e sintomas característicos da doença. DELIBERAÇÃO FINAL: Os membros da CONITEC presentes na reunião do plenário do dia 06/05/2015 deliberaram, por unanimidade, recomendar a não incorporação de pegvisomanto em monoterapia para o tratamento de acromegalia. DECISÃO: PORTARIA Nº 24, de 8 de junho de 2015 - Torna pública a decisão de não incorporar o pegvisomanto para tratamento da acromegalia no âmbito do Sistema Único de Saúde - SUS.

Positron emission tomographic imaging of copper 64- and gallium 68-labeled chelator conjugates of the somatostatin agonist tyr3-octreotate.

The bifunctional chelator and radiometal have been shown to have a direct effect on the pharmacokinetics of somatostatin receptor (SSTR)-targeted imaging agents. We evaluated three Y3-TATE analogues conjugated to NOTA-based chelators for radiolabeling with 64Cu and 68Ga for small-animal positron emission tomographic/computed tomographic (PET/CT) imaging. Two commercially available NOTA analogues, p-SCN-Bn-NOTA and NODAGA, were evaluated. The p-SCN-Bn-NOTA analogues were conjugated to Y3-TATE through ß-Ala and PEG8 linkages. The NODAGA chelator was directly conjugated to Y3-TATE. The analogues labeled with 64Cu or 68Ga were analyzed in vitro for binding affinity and internalization and in vivo by PET/CT imaging, biodistribution, and Cerenkov imaging (68Ga analogues). We evaluated the effects of the radiometals, chelators, and linkers on the performance of the SSTR subtype 2--targeted imaging agents and also compared them to a previously reported agent, 64Cu-CB-TE2A-Y3-TATE. We found that the method of conjugation, particularly the length of the linkage between the chelator and the peptide, significantly impacted tumor and nontarget tissue uptake and clearance. Among the 64Cu- and 68Ga-labeled NOTA analogues, NODAGA-Y3-TATE had the most optimal in vivo behavior and was comparable to 64Cu-CB-TE2A-Y3-TATE. An advantage of NODAGA-Y3-TATE is that it allows labeling with 64Cu and 68Ga, providing a versatile PET probe for imaging SSTr subtype 2-positive tumors.

Somatostatin receptor-2 negatively regulates ß-adrenergic receptor mediated Ca(2+) dependent signaling pathways in H9c2 cells.

In the present study, we report that somatostatin receptor 2 (SSTR2) plays a crucial role in modulation of ß1AR and ß2AR mediated signaling pathways that are associated with increased intracellular Ca(2+) and cardiac complications. In H9c2 cells, SSTR2 colocalizes with ß1AR or ß2AR in receptor specific manner. SSTR2 selective agonist inhibits isoproterenol and formoterol stimulated cAMP formation and PKA phosphorylation in concentration dependent manner. In the presence of SSTR2 agonist, the expression of PKCα and PKCß was comparable to the basal condition, however SSTR2 agonist inhibits isoproterenol or formoterol induced PKCα and PKCß expression, respectively. Furthermore, the activation of SSTR2 not only inhibits calcineurin expression and its activity, but also blocks NFAT dephosphorylation and its nuclear translocation. SSTR2 selective agonist abrogates isoproterenol mediated increase in cell size and protein content (an index of hypertrophy). Taken together, the results described here provide direct evidence in support of cardiac protective role of SSTR2 via modulation of Ca(2+) associated signaling pathways attributed to cardiac hypertrophy.

Epidemiología de la acromegalia en España / Epidemiology of acromegaly in Spain

La epidemiología de la acromegalia en España no difiere de la de otras series publicadas. La prevalencia es de alrededor de 60 casos por millón, el máximo de diagnósticos ocurre en la edad media de la vida, hay predominio de mujeres (61%) y se objetiva un gran retraso entre la aparición de los primeros síntomas y el diagnóstico. Los estudios del registro español de acromegalia (REA) y OASIS han analizado la epidemiología, las características clínicas y el tratamiento de la acromegalia en España. El tratamiento principal ha sido y sigue siendo la cirugía (en más del 80% de los pacientes), aunque en la última década más pacientes han recibido terapia médica como primera línea de tratamiento. En las últimas décadas se ha observado una disminución significativa en las tasas de radioterapia. Los análogos de la somatostatina (SSA) son los fármacos más utilizados. Alrededor del 85% de los pacientes reciben terapia con SSA, aunque solo un 12-15% persisten con tratamiento médico como terapia exclusiva. La curación quirúrgica es pobre, alcanzando el 38,4% en la última década según el REA sin influencia del tratamiento con SSA previo. En la última década la segunda línea de tratamiento tras el fracaso quirúrgico fue los SSA en un 49%, la reintervención en un 27%, la radioterapia en un 11%, Pegvisomant en el 15% y agonistas dopaminérgicos en el 5%. El coste medio del tratamiento de la acromegalia es de 9.668 (Euro) (datos estimados en 2009 y ajustados en 2010) y un 71% corresponde al coste de los SSA. Los pacientes que reciben Pegvisomant presentan una acromegalia más agresiva con mayor tasa de comorbilidades

Epidemiology of acromegaly in Spain does not differ from that reported in other published series. Prevalence rate is approximately 60 cases per million, peak incidence occurs in middle age, more women are affected (61%), and there is a substantial delay between occurrence of the first symptoms and diagnosis. Studies REA (Spanish Acromegaly Registry) and OASIS analyzed the epidemiology, clinical characteristics, and management of the disease in Spain. Surgery, performed in more than 80% of patients, has been (and continues to be) the main treatment for the past four decades. In the past decade, however, more patients have received somatostatin analogs (SSAs) as first-line treatment. Use of radiation therapy has significantly decreased in recent decades. Somatostatin analogs (SSAs) are the most commonly used drugs, administered to 85% of patients; however, only 12%-15% continue on drug treatment alone. The surgical remission rate was 38.4% in the last decade, with a significant improvement over decades. Preoperative treatment with SSAs has no influence on surgical cure rates. Second-line therapies used after surgical failure in the past decade included SSAs in 49% of patients, repeat surgery in 27%, radiotherapy in 11%, pegvisomant in 15%, and dopamine agonists in 5%. Mean cost of acromegaly treatment was 9.668€ (data estimated in 2009 and adjusted in 2010), of which 71% was due to the cost of SSAs. Patients treated with pegvisomant have a more aggressive form of the disease and higher comorbidity rates

Laparoscopic resection of primary midgut carcinoid tumors.

BACKGROUND: Laparoscopic intestinal surgery is the preferable technique for the majority of intestinal surgical disorders. However, no series on laparoscopic resection of intestinal midgut carcinoid tumors (MCTs) has been reported to date. This is related to the rarity of these tumors as well as the technical difficulties resecting the large mesenteric root lymph node mass commonly found with these tumors and the occasional difficulty identifying the primary MCT, which may be small and undetected on preoperative imaging studies. This is the first series to report the results for laparoscopic resection of MCT. METHODS: All consecutive patients with MCT (excluding appendiceal carcinoid tumor) between 2002 and 2012 underwent laparoscopic resection. The patient's clinical data, preoperative endocrine workup, imaging studies, operative data, final histology, and outcome were recorded and analyzed. RESULTS: During the study period, 35 patients underwent surgery for primary intestinal carcinoid tumor. Of the 35 patients, 20 (12 women and 8 men ages 26-86 years) had surgery for primary MCT, and the remainder had a colorectal carcinoid tumor. In the MCT group, ten patients had liver metastases at the time of surgery. In three patients, multiple synchronous MCTs were detected intraoperatively. All the patients underwent a laparoscopic resection with en bloc resection of the corresponding mesenteric root mass. No conversion to open surgery was needed, and no major morbidity occurred. Two patients (10 %) each experienced minor morbidity with wound infection and prolonged ileus. The median hospital length of stay was 6 days (range 4-9 days). During a follow-up period of 3-96 months, no patients experienced local or regional recurrence. No distant metastases were detected during the follow-up period in any patients who had surgery with intent to cure. CONCLUSION: Although technically difficult, laparoscopic resection of primary MCTs is feasible and safe, with the additional known significant advantages of laparoscopic surgery in general. Similar to the large-scale prospective studies that proved the oncologic safety of laparoscopic surgery for colorectal cancer, this small series showed that the laparoscopic technique also may be oncologically safe for these rare tumors.

Central actions of somatostatin-28 and oligosomatostatin agonists to prevent components of the endocrine, autonomic and visceral responses to stress through interaction with different somatostatin receptor subtypes.

Somatostatin was discovered four decades ago and since then its physiological role has been extensively investigated, first in relation with its inhibitory effect on growth hormone secretion but soon it expanded to extrapituitary actions influencing various stressresponsive systems. Somatostatin is expressed in distinct brain nuclei and binds to five somatostatin receptor subtypes which are also widely expressed in the brain with a distinct distribution pattern. The last few years witnessed the discovery of highly selective peptide somatostatin receptor agonists and antagonists representing valuable tools to delineate the respective pathways of somatostatin signaling. Here we review the centrally mediated actions of somatostatin and related selective somatostatin receptor subtype agonists to influence the endocrine, autonomic, and visceral components of the stress response and basal behavior as well as thermogenesis.

Inhibitory effect of somatostatin receptor subtype-4 agonist NNC 26-9100 on micturition reflex in rats.

OBJECTIVE: To investigate the effects of activation of somatostatin subtype 4 (SST4) on the micturition reflex in rats. METHODS: Continuous cystometrograms (0.04 mL/min infusion rate) were performed in female Sprague-Dawley rats (242-265 g) under urethane anesthesia. After stable micturition cycles were established, a selective SST4 receptor agonist, NNC 26-9100, was administered intravenously in normal rats or rats pretreated with capsaicin 4 days before the experiments. The micturition parameters were recorded and compared before and after drug administration. RESULTS: Intravenous administration of NNC 26-9100 (10-300 µg/kg) significantly increased the intercontraction interval in a dose-dependent fashion. Intravenous administration of NNC 26-9100 (10-300 µg/kg) also significantly increased the pressure threshold in a dose-dependent fashion. No significant changes were seen in the baseline pressure, maximum voiding pressure, or postvoid residual urine volume. However, NNC 26-9100-induced increases in the intercontraction intervals and pressure threshold were not seen in rats with C-fiber desensitization induced by capsaicin pretreatment. CONCLUSION: These results indicate that in urethane-anesthetized rats, activation of the SST4 receptor can inhibit the micturition reflex by suppression of capsaicin-sensitive C-fiber afferent pathways. Thus, the SST4 receptor could be a potential target for the treatment of C-fiber afferent-mediated bladder dysfunction.

SSTR2 is the functionally dominant somatostatin receptor in human pancreatic ß- and α-cells.

Somatostatin-14 (SST) inhibits insulin and glucagon secretion by activating G protein-coupled somatostatin receptors (SSTRs), of which five isoforms exist (SSTR1-5). In mice, the effects on pancreatic ß-cells are mediated by SSTR5, whereas α-cells express SSTR2. In both cell types, SSTR activation results in membrane hyperpolarization and suppression of exocytosis. Here, we examined the mechanisms by which SST inhibits secretion from human ß- and α-cells and the SSTR isoforms mediating these effects. Quantitative PCR revealed high expression of SSTR2, with lower levels of SSTR1, SSTR3, and SSTR5, in human islets. Immunohistochemistry showed expression of SSTR2 in both ß- and α-cells. SST application hyperpolarized human ß-cells and inhibited action potential firing. The membrane hyperpolarization was unaffected by tolbutamide but antagonized by tertiapin-Q, a blocker of G protein-gated inwardly rectifying K⁺ channels (GIRK). The effect of SST was mimicked by an SSTR2-selective agonist, whereas a SSTR5 agonist was marginally effective. SST strongly (>70%) reduced depolarization-evoked exocytosis in both ß- and α-cells. A slightly weaker inhibition was observed in both cell types after SSTR2 activation. SSTR3- and SSTR1-selective agonists moderately reduced the exocytotic responses in ß- and α-cells, respectively, whereas SSTR4- and SSTR5-specific agonists were ineffective. SST also reduced voltage-gated P/Q-type Ca²âº currents in ß-cells, but normalization of Ca²âº influx to control levels by prolonged depolarizations only partially restored exocytosis. We conclude that SST inhibits secretion from both human ß- and α-cells by activating GIRK and suppressing electrical activity, reducing P/Q-type Ca²âº currents, and directly inhibiting exocytosis. These effects are mediated predominantly by SSTR2 in both cell types.

The Liege Acromegaly Survey (LAS): a new software tool for the study of acromegaly.

Acromegaly is a chronic rare disease associated with negative pathological effects on multiple systems and organs. We designed a new informatics tool to study data from patients with acromegaly, the Liege Acromegaly Survey (LAS). This relational database permits the inclusion of anonymous historical and prospective data on patients and includes pathophysiology, clinical features, responses to therapy and long term outcomes of acromegaly. We deployed the LAS in a validation study at a single center in order to study the characteristics of patients with acromegaly diagnosed at our center from 1970-2011. A total of 290 patients with acromegaly were included (147 males and 143 females). There was a linear relationship between age at diagnosis and the date of diagnosis, indicating that older patients are being diagnosed with acromegaly more frequently. A majority presented with macroadenomas (77.5%) and the median diameter was 14 mm. Patients with macroadenomas were significantly younger than patients with microadenomas (P=0.01). GH values at diagnosis decreased with the age of the patients (P=0.01) and there was a correlation between GH values and tumor size at diagnosis (P=0.02). No correlation existed between insulin-like growth factor 1 (IGF-1) levels and tumor characteristics. The prevalence of diabetes was 21.4% in this population and 41.0% had hypertension. The presence of hypertension and diabetes were significantly associated with one another (P<0.001). There was a linear relation between initial GH and IGF-1 levels at diagnosis and those obtained during SSA analog treatment and the lowest GH and IGF-1 values following SSA therapy were obtained in older patients (GH: P<0.001; IGF-1: P<0.001). The LAS is a new relational database that is feasible to use in the clinical research setting and permits ready pooling of anonymous patient data from multiple study sites to undertake robust statistical analyses of clinical and therapeutic characteristics.

Stimulatory effect of SOM230 on human and rat adrenal corticosteroid secretion in vitro.

SOM230 (pasireotide, Signifor), a recently developed somatostatin analog, has been tested in ACTH-secreting pituitary tumors with promising results. No study has yet evaluated whether this analog also directly affects adrenal steroid production. The aim of the current study was to evaluate whether SOM230 modulates corticosteroid secretion by normal adrenals in vitro. Primary cultures from normal human and rat adrenals were incubated with 10-100 nM SOM230 with and without 10nM ACTH. Dose-response studies with 1 nM-1 µM SOM230 were performed on rat adrenals. Cortisol/corticosterone levels in medium were measured after 4 and 24h. SOM230 (10nM) significantly increased corticosteroid levels after 24h incubation in both human (36.4 ± 0.43 ng/well vs 27.7 ± 3.17 ng/well, p<0.05) and rat (16.2 ± 1.16 ng/well vs 11.6 ± 0.92 ng/well p<0.05) adrenals; lesser effects were observed with 100 nM SOM (33.4 ± 2.59 ng/well vs 27.7 ± 3.17 ng/well p<0.05; 13.4 ± 0.82 ng/well vs 11.6 ± 0.92 ng/well, N.S. vs baseline secretion for human and rat adrenals, respectively). Dose-response curves confirmed maximal effect at 10nM SOM230. The corticosteroid secretory response to ACTH was unaffected by SOM230 co-incubation. In conclusion, SOM230 exerts a moderate stimulatory effect on adrenal corticosteroid secretion in vitro. This argues against a direct adrenal involvement in the clinical efficacy of SOM230 in patients with ACTH-secreting pituitary tumors and widens the known range of action of SOM230.

Controlled release of octreotide and assessment of peptide acylation from poly(D,L-lactide-co-hydroxymethyl glycolide) compared to PLGA microspheres.

PURPOSE: To investigate the in vitro release of octreotide acetate, a somatostatin agonist, from microspheres based on a hydrophilic polyester, poly(D,L-lactide-co-hydroxymethyl glycolide) (PLHMGA). METHODS: Spherical and non-porous octreotide-loaded PLHMGA microspheres (12 to 16 µm) and loading efficiency of 60-70% were prepared by a solvent evaporation. Octreotide release profiles were compared with commercial PLGA formulation (Sandostatin LAR(®)); possible peptide modification with lactic, glycolic and hydroxymethyl glycolic acid units was monitored. RESULTS: PLHMGA microspheres showed burst release (~20%) followed by sustained release for 20-60 days, depending on the hydrophilicity of the polymer. Percentage of released loaded peptide was high (70-90%); > 60% of released peptide was native octreotide. PLGA microspheres did not show peptide release for the first 10 days, after which it was released in a sustained manner over the next 90 days; > 75% of released peptides were acylated adducts. CONCLUSIONS: PLHMGA microspheres are promising controlled systems for peptides with excellent control over release kinetics. Moreover, substantially less peptide modification occurred in PLHMGA than in PLGA microspheres.

Central administration of pan-somatostatin agonist ODT8-SST prevents abdominal surgery-induced inhibition of circulating ghrelin, food intake and gastric emptying in rats.

BACKGROUND: Activation of brain somatostatin receptors (sst(1-5) ) with the stable pan-sst(1-5) somatostatin agonist, ODT8-SST blocks acute stress and central corticotropin-releasing factor (CRF)-mediated activation of endocrine and adrenal sympathetic responses. Brain CRF signaling is involved in delaying gastric emptying (GE) immediately post surgery. We investigated whether activation of brain sst signaling pathways modulates surgical stress-induced inhibition of gastric emptying and food intake. METHODS: Fasted rats were injected intracisternally (i.c.) with somatostatin agonists and underwent laparotomy and 1-min cecal palpation. Gastric emptying of a non-nutrient solution and circulating acyl and desacyl ghrelin levels were assessed 50min post surgery. Food intake was monitored for 24 h. KEY RESULTS: The abdominal surgery-induced inhibition of GE (65%), food intake (73% at 2h) and plasma acyl ghrelin levels (67%) was completely prevented by ODT8-SST (1µg per rat, i.c.). The selective sst(5) agonist, BIM-23052 prevented surgery-induced delayed GE, whereas selective sst(1) , sst(2) , or sst(4) agonists had no effect. However, the selective sst(2) agonist, S-346-011 (1µg per rat, i.c.) counteracted the abdominal surgery-induced inhibition of acyl ghrelin and food intake but not the delayed GE. The ghrelin receptor antagonist, [D-Lys(3) ]-GHRP-6 (0.93mg kg(-1) , intraperitoneal, i.p.) blocked i.p. ghrelin-induced increased GE, while not influencing i.c. ODT8-SST-induced prevention of delayed GE and reduced food intake after surgery. CONCLUSIONS & INFERENCES: ODT8-SST acts in the brain to prevent surgery-induced delayed GE likely via activating sst(5) . ODT8-SST and the sst(2) agonist prevent the abdominal surgery-induced decrease in food intake and plasma acyl ghrelin indicating dissociation between brain somatostatin signaling involved in preventing surgery-induced suppression of GE and feeding response.