Somatostatin half-life: a case report in one healthy volunteer and a three month follow-up

Somatostatin: One of the Rare Multifunctional Inhibitors of Mammalian Species

This review article has for major main objectives to give an overlook of the major physiological effects of somatostatin on different organs. It will cover first the general aspect of the hormone, its cDNA and its protein maturation process, as well as its characterization in various organs. This aspect will be followed by the factors involved in the control of its secretion, its intracellular mode of action, and its general action on physiological processes. Secondly, the review will focus on the pancreas, looking at its in vivo and in vitro actions with special attention on its effects on normal pancreas growth and pancreatic tumors.

Somatostatin modulates insulin-degrading-enzyme metabolism: implications for the regulation of microglia activity in AD

The deposition of β-amyloid (Aβ) into senile plaques and the impairment of somatostatin-mediated neurotransmission are key pathological events in the onset of Alzheimer's disease (AD). Insulin-degrading-enzyme (IDE) is one of the main extracellular protease targeting Aβ, and thus it represents an interesting pharmacological target for AD therapy. We show that the active form of somatostatin-14 regulates IDE activity by affecting its expression and secretion in microglia cells. A similar effect can also be observed when adding octreotide. Following a previous observation where somatostatin directly interacts with IDE, here we demonstrate that somatostatin regulates Aβ catabolism by modulating IDE proteolytic activity in IDE gene-silencing experiments. As a whole, these data indicate the relevant role played by somatostatin and, potentially, by analogue octreotide, in preventing Aβ accumulation by partially restoring IDE activity.

ADME Investigations of Unnatural Peptides: Distribution of a14C-Labeledβ3-Octaarginine in Rats

The highly positively charged, cell-penetrating beta3-octaarginine has been prepared with a radioactive label by acetylation at the N-terminus with a doubly (14)C-labeled acetyl group ((14)CH3-(14)CO). With the radioactive compound, an ADME study (Absorption, Distribution, Metabolism, Excretion) was performed in male rats following an intravenous or oral dose of 1 mg/kg. Sampling was carried out after periods ranging from 5 min to 4 d or 7 d for blood/excretia and quantitative whole-body autoradioluminography (QWBA), respectively. After p.o. dosing, no systemic exposure to peptide-related radioactivity was observed, and the dose was completely excreted in the feces within 24 h suggesting the absence of relevant absorption; less than 3% of the i.v. dose was excreted from the animals within 4 d. Blood levels, after i.v. dosing, dropped within 4 d to less than 2% of Cmax and decreased afterwards only very slowly. No metabolites were observed in the systemic circulation. QWBA Data indicated that the distribution of the acetyl-beta-octaarginine-related radioactivity in the organs and tissues shifted over time. Notably, after 7 d, the highest concentration was measured in the lymph nodes, and the largest amount was found in the liver. A comparison with the results of two previous ADME investigations of beta-peptides (cf. Table 1) reveals that the distribution of the compounds within the animals is structure-dependent, and that there is a full range from oral availability with rather rapid excretion (of a tetrapeptide) to essentially complete lack of both oral absorption and excretion after i.v. administration (of a highly charged octapeptide). A discussion is presented about the in vivo stability and 'drug-ability' of peptides. In general, beta-peptides bearing proteinogenic side chains are compared with peptides consisting entirely of D-alpha-amino acid residues (the enantiomers of the 'natural' building blocks), and suggestions are made regarding a possible focus of future biomedical investigations with beta-peptides.

Treatment of Metastatic Disease in Patients with Neuroendocrine Tumors

Gastroenteropancreatic neuroendocrine tumors (GENTs) compromise a heterogeneous group of relatively uncommon neoplasms with a yearly incidence rate of 1.2 to 3.0 per 100,000 population. These tumors share numerous histologic and biologic features, allowing their consideration as a common entity. They are postulated to arise from neuroendocrine cells, but most are not from neural crest origin. Their predominant site of origin is the gastrointestinal tract, where most involve the small intestine and appendix, but are also found in the adrenal medulla, bronchopulmonary system, pancreas, thyroid, parathyroid, and paraganglia cells. A common feature is their often indolent course, but some tumors are poorly differentiated and behave aggressively. This article addresses the surgical management of endocrine malignancies and the treatment of metastatic disease in patients with neuroendocrine tumors.

A novel somatostatin conjugate with a high affinity to all five somatostatin receptor subtypes

BACKGROUND

Somatostatin receptors (SRS, five subtypes) are expressed in a variety of human tumors, including most tumors of neuroendocrine origin, breast tumors, certain brain tumors, renal cell tumors, lymphomas, and prostate cancer. Somatostatin (SMS) triggers cytostatic and cytotoxic effects and has a general inhibitory effect on secretion mediated through its interaction with SRS. That is the basis for its use in the treatment of SRS-positive tumors. Radiolabeled SMS analogs can also be used for systemic radiotherapy and for diagnostic investigations.

METHODS

Sms-14 was conjugated to a periodate-activated dextran70 (mean molecular weight, 70 kD) by reductive amination. The human tumor cell line LCC-18, from a neuroendocrine colonic tumor, was used for stable transfection with each SRS gene separately; transfection was achieved with the expression system TETon (Clontech, Palo Alto, CA). Clones were selected by culturing with G418 and hygromycin B, and positive clones were identified by reverse transcriptase-polymerase chain reaction and binding of iodine-125-labeled SMS-14. The binding affinity for each SRS subtype was then determined for the SMS-dextran conjugate (with SMS-14 used as a positive control).

RESULTS

Sms-dextran70 showed high affinity binding to all five receptor subtypes. The IC50 values were between 3 and 80 nM.

CONCLUSIONS

This conjugate has a long circulation half-life (i.e., approximately 27 hours after subcutaneous administration in mice) and, with high SRS pan-affinity demonstrated in this study, it has potential in the therapy of SRS-positive tumors. Currently, the clinical significance of SMS-dextran70 is being explored in a clinical Phase I-II study of patients with hormone-refractory prostate cancer. The outcome of this study will be reported when it is available.

Somatostatin receptor imaging of olfactory neuroblastoma

Neural-crest tumours, including neuroblastomas, express somatostatin receptors. This can be shown by radionuclide labelling of octreotide, a somatostatin analogue. Studies on imaging with this substance have dealt with childhood neuroblastomas. Olfactory neuroblastoma (aesthesioneuroblastoma) is a rare tumour in which somatostatin receptor content has not been analysed, nor have radionuclide methods for diagnostic purposes been described. We report a case of olfactory neuroblastoma, in which scanning with 111In-labelled octreotide was performed. A strong uptake was seen at the base of the skull. This was confirmed as a recurrent tumour by magnetic resonance (MR) imaging. Uptake was also observed in the neck and chest, indicating extensive spread of the disease. Somatostatin receptor expression has been shown to correlate with prognosis in childhood neuroblastoma. The accuracy of labelled octreotide in the diagnosis of olfactory neuroblastoma indicates that it might be useful in radionuclide therapy of patients with advanced disease, when no other treatment modalities are available.

Somatostatin-induced modulation of inflammation in experimental arthritis

OBJECTIVE

To study the antiinflammatory effect of different doses of intraarticular somatostatin in experimental arthritis in rabbits.

METHODS

Chronic arthritis was induced by a single injection of fibrin into the knee joint of rabbits previously sensitized to this antigen. The effects of sequential intraarticular injections of somatostatin into the rabbit knee, at doses of 500, 750, and 1,000 micrograms, were monitored by measuring knee joint circumferences and hematologic parameters. The measurements were compared with those obtained following use of triamcinolone acetonide and placebo. At the end of the experiments, the knee joints were examined histologically.

RESULTS

Somatostatin treatment induced a statistically significant and dose-related reduction of knee joint swelling. This effect was shorter than that produced by triamcinolone acetonide; however, the antiinflammatory activity elicited by successive doses of triamcinolone acetonide declined both in extent and duration, while the effects of somatostatin remained unchanged at each successive treatment. Histopathologic observations showed that both somatostatin and triamcinolone acetonide reduced the inflammatory signs in the joint structures, although triamcinolone acetonide appeared to be more effective.

CONCLUSION

These findings suggest that somatostatin exerts an antiinflammatory effect in this model of experimental arthritis and may represent a valid and safer alternative to corticosteroids for intraarticular therapy of arthritis.

Efficacy, pharmacokinetics and tolerability of a somatostatin analogue (L-363,586) in insulin-dependent diabetes mellitus

To assess the pharmacologic properties and possible use in the treatment of diabetes mellitus of a recently developed analogue somatostatin (L-363,586), the analogue (2, 5, 10 or 40 micrograms/hr), somatostatin (200 micrograms/hr), or placebo were infused intravenously for 5 hours in 6 insulin-dependent diabetic subjects who were given a standard meal containing xylose. The metabolic clearance rate of the analogue (approximately 300 ml/min) was 1/6 that previously reported for somatostatin (approximately 2000 ml/min) and its half-life was approximately 20 times as great as that reported for somatostatin (45 vs 2 min). At a dose of 10 micrograms/hr, the analogue produced suppression of plasma glucagon, growth hormone, glucose, xylose and triglyceride responses to meal ingestion which were comparable to those observed when somatostatin was infused at a rate of 200 micrograms/hr. We conclude that L-363,586 is a long-acting and potent analogue of somatostatin, which has the potential for use as an adjunct to insulin in the treatment of diabetes mellitus.