Regulation of insulin and glucagon secretion from rat pancreatic islets in vitro by somatostatin analogues

doi:10.1016/j.regpep.2006.07.006

Regulatory Peptides

Volume 138, Issue 1, 10 January 2007, Pages 1-9

https://doi.org/10.1016/j.regpep.2006.07.006 Get rights and content

Abstract

Somatostatin is an inhibitor of hormone secretion through specific receptors (sst_1–5). The aim of this study was to investigate the putative regulatory role of somatostatin analogues on the secretion of insulin and glucagon by rat pancreatic islets.

After 48 h exposure only the non-selective agonists (somatostatin, octreotide and SOM-230) inhibited insulin accumulation. The inhibition of insulin secretion was accompanied by increased islet insulin contents. None of the analogues showed a consistent effect on the glucagon accumulation in the medium after 48 h.

Since we observed a difference in the regulatory effect between the non-selective and selective analogues, combinations of selective analogues were studied. Combination of sst₂ + sst₅ agonists inhibited the medium insulin accumulation, while combination of sst₁ + sst₂ analogues caused a decrease in glucagon accumulation.

After removal of somatostatin a rebound effect with increased insulin secretion were observed. This effect was reversed after 6 h. For SOM-230 insulin secretion continued to be suppressed even after the analogue was removed and returned to control values after 3 h. As for glucagon secretion there was an initial decline after culture with octreotide, while the other substances failed to induce any changes.

In summary, non-selective somatostatin analogues or combinations of receptor selective analogues may cause inhibition of hormone secretion from rat pancreatic islets. For insulin and glucagon, combinations of sst₂ + sst₅ and sst₁ + sst₂, respectively may exert this effects. Thus, our data suggest that more than one sst must be involved to down-regulate islet glucagon and insulin secretion.

Introduction

Brazeau and colleagues discovered the natural cyclic peptide somatostatin in 1973 [1]. Somatostatin's first known function was to inhibit growth hormone secretion, but today somatostatin is known to be a multifunctional peptide. One such function is to play an important inhibitory role on the secretion of a number of gastroeintestinal and pancreatic peptides. Its function is mediated by five different somatostatin receptors (sst), classified as sst₁–sst₅, respectively. They all belong to the superfamily of G-protein coupled receptors with seven α-helical transmembrane spanning domains, and they are widely distributed throughout the body [2], [3].

Extensive focus has been directed towards identification of different physiological roles for the different sst subtypes. Sst_1–5 have high affinity for the naturally occurring peptides, somatostatin-14 (SST-14) and somatostatin-28. Since the half life of somatostatin in vivo is short (∼ 90 s) a more metabolically stable analogue was developed, i.e. octreotide [4]. This long-acting analogue has been used in the clinic for more than two decades to inhibit hormone secretion and thereby reduce the symptoms from endocrine tumours [5]. Octreotide binds to sst₂ and sst₅ with high affinity and with moderate affinity to sst₃ [4]. A more recently developed cyclohexapeptide analogue is SOM-230, which exhibits high affinity for all sst except sst₄ and is considered to be even more stable than octreotide [6]. Also subtype selective somatostatin receptor analogues have been developed during the years and studied in different cell lines [7], [8], [9], [10]. Immunohistochemical studies on pancreas has revealed that the majority of islet alpha-cells and beta-cells express both sst₂ and sst₅ [11], [12], [13], suggesting a possible interaction in the signalling process between the receptors and a possible need for co-stimulation to obtain a maximal effect. Functional studies on rodents have, however, shown that sst₂ mediates the inhibitory effect on glucagon secretion, while sst₅ inhibits insulin release [14], [15], [16], [17].

The aim of the present study was to investigate the regulatory effect of a panel of different somatostatin analogues on cultured isolated pancreatic rat islets. The analogues were tested in order to distinguish receptors, single or in combination, influencing the insulin or glucagon secretion.

Section snippets

Animals

Adult male Sprague–Dawley rats (Biomedical Center, Uppsala, Sweden) were used in this study. The animals had free access to water and pelleted food and were housed in a room with a 12-h light/dark cycle. The animals were anesthetized (Mebumal 60 mg/kg) and killed by cervical dislocation. The abdomen was immediately opened by a transverse incision, followed by resection of the pancreas. All experiments were approved by the local ethics committee at Uppsala University (Uppsala, Sweden).

Islet isolation and culture

Pancreatic

Effects of long-term exposure to SST-14, octreotide or SOM-230

After 48 h culture with the somatostatin analogues SST-14, octreotide or SOM-230 the culture medium was removed and the insulin accumulation measured (Fig. 1A). SST-14, octreotide inhibited the insulin medium accumulation in a dose-dependent manner. SOM-230 had a stronger inhibitory effect of about 60% and this was observed already at the lowest concentration (10^− 9 M). The islet insulin content was elevated after culture with the somatostatin analogues as compared to control islets (Fig. 1B).

Discussion

Somatostatin is a peptide known to inhibit secretion of several hormones and these actions are mediated via sst_1–5 expressed in many tissues and organs in the body. In the endocrine cells of the rat pancreatic islets a recent study showed that all five sst subtypes are expressed although the expression varies in intensity and distribution pattern [12]. Beta-cells express sst₁, sst₂ and sst₅, while a majority (80%) of the alpha-cells co-express the sst₂ and sst₅ and 40% also express sst₁. In the

Acknowledgements

The technical expertise of Ing-Britt Hallgren, Ulla-Britta Jansson and Inger Olsson is gratefully acknowledged. This work was supported by grants from the Swedish Research Council (72X-8273), the Swedish Diabetes Association, the Swedish Cancer Foundation, the Novo Nordisk Foundation, the Family Ernfors Fund, the European Foundation for the Study of Diabetes and the Lions Foundations for Cancer Research at the University Hospital, Uppsala, Sweden.

References (24)

L.N. Moller et al.
Somatostatin receptors
Biochim Biophys Acta
(2003)
Y.C. Patel
Somatostatin and its receptor family
Front Neuroendocrinol
(1999)
W. Bauer et al.
SMS 201–995: a very potent and selective octapeptide analogue of somatostatin with prolonged action
Life Sci
(1982)
M.G. Cattaneo et al.
Selective stimulation of somatostatin receptor subtypes: differential effects on Ras/MAP kinase pathway and cell proliferation in human neuroblastoma cells
FEBS Lett
(2000)
P. Brazeau et al.
Hypothalamic polypeptide that inhibits the secretion of immunoreactive pituitary growth hormone
Science
(1973)
E.T. Janson et al.
Somatostatin receptor ligands and their use in the treatment of endocrine disorders
Curr Pharm Des
(1999)
C. Bruns et al.
SOM230: a novel somatostatin peptidomimetic with broad somatotropin release inhibiting factor (SRIF) receptor binding and a unique antisecretory profile
Eur J Endocrinol
(2002)
E. Ludvigsen et al.
Subtype selective interactions of somatostatin and somatostatin analogs with sst(1), sst(2), and sst(5) in BON-1 cells
Med Oncol
(2004)
M.C. Zatelli et al.
Somatostatin receptor subtypes 2 and 5 differentially affect proliferation in vitro of the human medullary thyroid carcinoma cell line tt
J Clin Endocrinol Metab
(2001)
M.C. Zatelli et al.
Somatostatin, but not somatostatin receptor subtypes 2 and 5 selective agonists, inhibits calcitonin secretion and gene expression in the human medullary thyroid carcinoma cell line, TT
Horm Metab Res
(2002)

U. Kumar et al.

Subtype-selective expression of the five somatostatin receptors (hSSTR1–5) in human pancreatic islet cells: a quantitative double-label immunohistochemical analysis

Diabetes

(1999)

E. Ludvigsen et al.

Expression and distribution of somatostatin receptor subtypes in the pancreatic islets of mice and rats

J Histochem Cytochem

(2004)

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Somatostatin analogue pasireotide (SOM230) inhibits catecholamine secretion in human pheochromocytoma cells
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Accordingly, inhibitory effects with similar concentrations have been previously observed in cells cultured from human cancer such as growth hormone-secreting pituitary adenoma and growth hormone-releasing hormone-producing bronchial carcinoid [59,60]. However, this concentration is relatively high compared to the IC50 (ranging from 0.2 to 1 nM) reported after long lasting treatment of SOM230 on the secretory activity of rat pituitary cells, rat pancreatic islets, mouse corticotroph adenoma cells and human pituitary adenoma cells [56,57,61,62], raising the question of the mechanisms by which SOM230 inhibits catecholamine secretion in human Pheo cells. As frequency and amplitude of exocytic events depend on the level of secretagogue-evoked intracellular calcium elevation [63,64], it was tempting to imagine that SOM230 might affect secretory granule exocytosis upstream of calcium entry.
Increasingly common, neuroendocrine tumors (NETs) are regarded nowadays as neoplasms potentially causing debilitating symptoms and life-threatening medical conditions. Pheochromocytoma is a NET that develops from chromaffin cells of the adrenal medulla, and is responsible for an excessive secretion of catecholamines. Consequently, patients have an increased risk for clinical symptoms such as hypertension, elevated stroke risk and various cardiovascular complications. Somatostatin analogues are among the main anti-secretory medical drugs used in current clinical practice in patients with NETs. However, their impact on pheochromocytoma-associated catecholamine hypersecretion remains incompletely explored. This study investigated the potential efficacy of octreotide and pasireotide (SOM230) on human tumor cells directly cultured from freshly resected pheochromocytomas using an implemented catecholamine secretion measurement by carbon fiber amperometry. SOM230 treatment efficiently inhibited nicotine-induced catecholamine secretion both in bovine chromaffin cells and in human tumor cells whereas octreotide had no effect. Moreover, SOM230 specifically decreased the number of exocytic events by impairing the stimulation-evoked calcium influx as well as the nicotinic receptor-activated inward current in human pheochromocytoma cells. Altogether, our findings indicate that SOM230 acts as an inhibitor of catecholamine secretion through a mechanism involving the nicotinic receptor and might be considered as a potential anti-secretory treatment for patients with pheochromocytoma.
Gastrointestinal Peptides: Gastrin, Cholecystokinin, Somatostatin, and Ghrelin. Gastrin, Cholecystokinin, Somatostatin, and Ghrelin
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Gastrointestinal Peptides: Gastrin, Cholecystokinin, Somatostatin, and Ghrelin
2012, Physiology of the Gastrointestinal Tract
Cell-to-cell communication and cellular environment alter the somatostatin status of delta cells
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Somatostatin acts through five receptor subtypes (SSTR1–SSTR5) [2] observed in various body tissues. The concurrent activation of both SSTR2 and SSTR5 in the pancreatic beta-cell inhibits insulin secretion in rodents [3]. Somatostatin receptors have also been credited with suppressing beta-cell proliferation [4] and blockade of GLP-1 stimulated insulin secretion in vitro[5].
Somatostatin, released from pancreatic delta cells, is a potent paracrine inhibitor of insulin and glucagon secretion. Islet cellular interactions and glucose homeostasis are essential to maintain normal patterns of insulin secretion. However, the importance of cell-to-cell communication and cellular environment in the regulation of somatostatin release remains unclear.
This study employed the somatostatin-secreting TGP52 cell line maintained in DMEM:F12 (17.5 mM glucose) or DMEM (25 mM glucose) culture media. The effect of pseudoislet formation and culture medium on somatostatin content and release in response to a variety of stimuli was measured by somatostatin EIA. In addition, the effect of pseudoislet formation on cellular viability (MTT and LDH assays) and proliferation (BrdU ELISA) was determined.
TGP52 cells readily formed pseudoislets and showed enhanced functionality in three-dimensional form with increased E-cadherin expression irrespective of the culture environment used. However, culture in DMEM decreased cellular somatostatin content (P < 0.01) and increased somatostatin secretion in response to a variety of stimuli including arginine, calcium and PMA (P < 0.001) when compared with cells grown in DMEM:F12. Configuration of TGP52 cells as pseudoislets reduced the proliferative rate and increased cellular cytotoxicity irrespective of culture medium used.
Somatostatin secretion is greatly facilitated by cell-to-cell interactions and E-cadherin expression. Cellular environment and extracellular glucose also significantly influence the function of delta cells.
Growth hormone excess and the effect of octreotide in cats with diabetes mellitus
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In this prospective study 16 cats with diabetes mellitus were examined for concurrent acromegaly by measuring plasma growth hormone (GH) and insulin-like growth factor-I concentrations, and magnetic resonance imaging (MRI) of the pituitary fossa. Additionally, the effects of octreotide administration on the plasma concentrations of glucose, GH, α-melanocyte-stimulating hormone (α-MSH), adrenocorticotrophic hormone (ACTH), and cortisol were measured.
Five cats were diagnosed with hypersomatotropism. The pituitary was enlarged in these 5 cats and in 2 other cats. Six cats that required a maximum lente insulin dosage ≥1.5 IU/kg body weight per injection had pituitary enlargement and 5 of these cats had acromegaly. Plasma concentrations of GH, ACTH, and cortisol decreased significantly after single intravenous administration of the somatostatin analogue octreotide in the acromegalic cats. The effect on GH concentrations was more pronounced in some of the acromegalic cats than in others. In the non-acromegalic cats only ACTH concentrations decreased significantly. In both groups plasma glucose concentrations increased slightly but significantly, whereas α-MSH concentrations were not significantly affected.
In conclusion, the incidence of hypersomatotropism with concomitant pituitary enlargement appears to be high among diabetic cats with severe insulin resistance. Some of these cats responded to octreotide administration with a pronounced decrease in the plasma GH concentration, which suggests that octreotide administration could be used as a pre-entry test for treatment with somatostatin analogues.
Function and expression of somatostatin receptors of the endocrine pancreas
2008, Molecular and Cellular Endocrinology
Somatostatin (SST) regulates multiple biological processes via five genetically distinct, G-protein coupled receptors. Clinical interest in therapy for neuroendocrine and metabolic disorders has resulted in the development of new tools for exploring the function of somatostatin receptors (SSTRs). The development of highly SSTR-selective agonists and antagonists, animal models with the deletion of individual SSTRs, as well as SSTR-specific antibodies have all been utilized in delineating SSTR functions. In the pancreas, SST is a potent regulator of insulin and glucagon secretion. Indeed, the inappropriate regulation of pancreatic A- and B-cell function in metabolic diseases provides an impetus to evaluate the SSTRs as therapeutic targets. By combining the results obtained from molecular biology, pharmacology and immunochemical studies the current review provides a summary of important recent developments which have extended our knowledge of SST actions in the endocrine pancreas.

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Regulation of insulin and glucagon secretion from rat pancreatic islets in vitro by somatostatin analogues

Abstract

Introduction

Section snippets

Animals

Islet isolation and culture

Effects of long-term exposure to SST-14, octreotide or SOM-230

Discussion

Acknowledgements

Biochim Biophys Acta

Front Neuroendocrinol

Life Sci

FEBS Lett

Hypothalamic polypeptide that inhibits the secretion of immunoreactive pituitary growth hormone

Science

Somatostatin receptor ligands and their use in the treatment of endocrine disorders

Curr Pharm Des

SOM230: a novel somatostatin peptidomimetic with broad somatotropin release inhibiting factor (SRIF) receptor binding and a unique antisecretory profile

Eur J Endocrinol

Subtype selective interactions of somatostatin and somatostatin analogs with sst(1), sst(2), and sst(5) in BON-1 cells

Med Oncol

Somatostatin receptor subtypes 2 and 5 differentially affect proliferation in vitro of the human medullary thyroid carcinoma cell line tt

J Clin Endocrinol Metab

Somatostatin, but not somatostatin receptor subtypes 2 and 5 selective agonists, inhibits calcitonin secretion and gene expression in the human medullary thyroid carcinoma cell line, TT

Horm Metab Res

Subtype-selective expression of the five somatostatin receptors (hSSTR1–5) in human pancreatic islet cells: a quantitative double-label immunohistochemical analysis

Diabetes

Expression and distribution of somatostatin receptor subtypes in the pancreatic islets of mice and rats

J Histochem Cytochem