The regulation of somatostatin production in human medullary thyroid carcinoma cells by dexamethasone

The Never-Ending History of Octreotide in Thymic Tumors: A Vintage or A Contemporary Drug?

Simple Summary

Thymic epithelial tumors are rare tumors frequently associated with paraneoplastic syndromes, the most common being myasthenia gravis and pure red cell aplasia. While patients with limited-stage cancer can often undergo resolutive surgery, advanced surgically unresectable and metastatic tumors can be refractory to first-line platinum-based treatment and represent a medical challenge. Somatostatin receptor expression was documented in thymic tumors both in vivo and in vitro and represents the rationale for therapeutic use. Despite single-case reports and three single-arm phase II studies, as well as the inclusion of somatostatin analogs in National Comprehensive Cancer Network guidelines, the role of these drugs in thymic epithelial tumors is still rather undefined.

Abstract

Thymic epithelial tumors are rare tumors usually presenting as a mass located in the anterior mediastinum and/or with symptoms deriving from associated paraneoplastic syndromes. Unresectable platinum-refractory tumors are often treated with alternative regimens, including chemotherapeutic agents as well as chemo-free regimens. The most popular unconventional therapy is represented by the somatostatin analog octreotide, which can be used alone or with prednisone. The in vivo expression of somatostatin receptors documented by imaging with indium-labeled octreotide or gallium-68 Dotapeptides, the successful use of octreotide and prednisone in a chemo-refractory patient, and, thereafter, the experiences from a case series have enforced the idea that this treatment merits consideration—as proved by its inclusion in the National Comprehensive Cancer Network guidelines. In the present review, we analyze the preclinical basis for the therapeutic use of somatostatin and prednisone in refractory thymic tumors and discuss the available studies looking at future perspectives.

Modulation of synovial cell function by somatostatin in patients with rheumatoid arthritis

OBJECTIVE

To elucidate the role of neurologic, endocrine, and immune system interactions in the development of pathologic responses in patients with rheumatoid arthritis (RA), we studied somatostatin (SOM) production and somatostatin receptor (SOMR) expression in RA synovium and its function in patients with RA.

METHODS

The effects of SOM on proinflammatory cytokine (interleukin-6 [IL-6] and IL-8) and collagenase production by RA synovial cells were estimated by enzyme-linked immunosorbent assay, and their messenger RNA expression was assessed by reverse transcription-polymerase chain reaction (RT-PCR) using limiting dilutions of the complementary DNA. The expression of SOMR by RA synovial cells was also studied by RT-PCR. Local production of SOM was estimated by RT-PCR and immunohistochemical staining.

RESULTS

Physiologic concentrations (approximately 10(-10)M) of SOM inhibited proliferation of RA synovial cells. The production of proinflammatory cytokines and matrix metalloproteinases by RA synovial cells was also modulated by SOM. SOMR subtypes 1 and 2 were expressed on fibroblast-like synovial cells, and the expression of SOMR-2 was up-regulated by proinflammatory cytokine treatment of the synovial cells from patients with RA. RA fibroblast-like cells synthesized SOM by themselves, suggesting that SOM acts as an autocrine regulator of synovial cell function in patients with RA.

CONCLUSION

SOM inhibited aberrant synovial cell function in patients with RA, suggesting possible clinical applications of this neuropeptide.

Characterization of Substance P-Like Immunoreactivity and Tachykinin-Encoding mRNAs in Rat Medullary Thyroid Carcinoma Cell Lines

Rat thyroid tissue and three rat medullary thyroid carcinoma cell lines, 6-23, WE4/2, and CA77, have been examined for substance P (SP) and SP-like peptide expression. Analysis by combined HPLC and radioimmunoassay revealed the presence of SP in thyroid and 6-23 cell extracts. The presence of SP-encoding mRNAs was also detected in 6-23 cells by solution hybridization-nuclease protection analysis. SP-encoding mRNA expression was increased (fourfold) by maintaining the 6-23 cells in low serum (2%) for 4 or 10 days. The 6-23 cells also expressed other SP-like immunoreactive species, which were chromatographically and immunologically distinct from established tachykinin peptides. WE4/2 cells did not contain SP but did display SP-like immunoreactivity (SPLI), which migrated like the unidentified SPLI in 6-23 cells. CA77 cells did not contain SP or SP-encoding mRNA but did contain SPLI that migrated identically to the unidentified SPLI in the other cell lines. This novel SPLI was detected with an antiserum directed against the SP carboxyl terminus and to a lesser extent with an antiserum directed against the neurokinin A carboxyl terminus, but it showed minimal cross-reactivity using an antiserum directed against the midportion of SP. Treatment with 50 mM KCl resulted in secretion of this SPLI from CA77 cells. Gel filtration analysis demonstrated that this novel SPLI had an apparent molecular weight of approximately 1,000. These results are discussed in terms of cell lines that express tachykinin peptides and in terms of the molecular nature of the new SPLI detected in CA77 cells.

Quinolinic acid stimulates somatostatin gene expression in cultured rat cortical neurons

Striatal atrophy in Huntington's disease (HD) is characterized by selective preservation of a subclass of neurons colocalizing NADPH-diaphorase (NADPH-d), somatostatin (SS), and neuropeptide Y (NPY), which have been reported to show three- to fivefold increases in SS-like immunoreactivity (SSLI) and NPY content. Since HD brain is capable of producing excessive quantities of the excitotoxin quinolinic acid (Quin), an N-methyl-D-aspartate (NMDA) receptor agonist, and since experimental Quin lesions show neuronal loss with sparing of NADPH-d/SS/NPY neurons, it has been suggested that Quin may be important in the pathogenesis of HD. In the present study we determined whether Quin stimulates SS gene function in cultured cortical cells known to be rich in NADPH-d/SS/NPY neurons. Cultures of dispersed fetal rat cortical cells were exposed to Quin (1 and 10 mM) with or without (-)-2-amino-5-phosphonovaleric acid (APV; 0.5 mM), an NMDA receptor antagonist, NMDA (0.2 and 0.5 mM), and glutamate (Glu; 0.5 mM). Medium and cellular SSLI was determined by radioimmunoassay and SS mRNA by Northern analysis with a cRNA probe. Quin induced significant (p less than 0.01) 1.6- and 2.5-4 fold increases in SSLI and SS mRNA accumulation, respectively, which were abolished by APV. Release of SSLI into the culture medium was stimulated two- to fivefold by Quin over a 2- to 20-h period. The increase in SS mRNA produced by Quin was time and dose dependent. A similar dose-dependent increase in SS mRNA comparable with that observed with Quin was induced by NMDA.(ABSTRACT TRUNCATED AT 250 WORDS)

Neurotransmitter abnormalities in Borna disease

Borna disease (BD) agent is an infectious pathogen that causes progressive central nervous system (CNS) dysfunction in a wide range of vertebrate hosts. The course of BD in adult rats is biphasic. The acute phase is characterized by aggressive behavior and inflammatory cell infiltrates in brain. With chronic infection animals become listless and inflammation resolves. BD antigens are similarly distributed in neurons in hippocampus, neocortex, cerebellum and brainstem in acutely and chronically infected animals. We have recently examined brain levels of neuronal transcripts in rats with acute and chronic BD. Levels for 3 of these mRNAs, cholecystokinin, glutamic acid decarboxylase and somatostatin, were decreased in acutely infected rats and increased toward control values in chronically infected rats. A fourth transcript, MuBr8, correlated in distribution with BD antigen, was persistently decreased throughout the course of infection. These data may have implications for understanding the pathogenesis of neurologic disturbances in BD and other inflammatory CNS diseases.

Gastric, duodenal, and pancreatic somatostatin-like immunoreactivity during hypovolemic shock

Because hypovolemic shock is known to cause gastric ulcers in animals and human beings, we investigated the tissue levels of somatostatin-like immunoreactivity (SLI) in the gastric corpus and antrum, duodenum, and pancreas during hypovolemic shock in rats. We studied male Wistar rats (N = 10 each) 15 min, 2 hr, and 12 hr after hypovolemic shock and compared results to a control group (N = 15). Two rats in both 2-hr and 12-hr groups showed gastric ulcers: three corporal and one antral. One animal developed multiple ulcers. In the gastric corpus and antrum and in the duodenum, tissue SLI showed significant decrease 15 min and 2 hr after shock. Gastric SLI remained low, whereas duodenal SLI recovered and rose above control level at 12 hr. Pancreatic SLI showed no significant changes during hypovolemic shock. Gastric tissue SLI levels that were significantly lower after shock than those of normal controls may have contributed to the peptic ulcer disease induced by hypovolemic shock in this experimental model.

Somatostatin in neuropsychiatric disorders

1. Somatostatin is a peptide that is widely and discretely distributed throughout the central nervous system. 2. Its relevance to neuropsychiatric disorders is suggested both by the existence of disease-related alterations in somatostatin content in brain and cerebrospinal fluid as well as by the manifold neuroregulatory capabilities of somatostatin and related peptides. 3. This article will summarize the central nervous system effects of somatostatin, identify those neuropsychiatric disorders that are characterized by changes in somatostatin, and review the evidence for and potential significance of decreases in cerebrospinal fluid somatostatin in depression.