Vasopressinergic,Oxytocinergic, and Somatostatinergic Neuronal Activity after Adrenalectomy and Immobilization Stress

Twenty days after bilateral adrenalectomy (ADX) or immediately after the last of three 6-h long immobilization periods, the levels of hypothalamic and neurohypophyseal L-[³⁵S]Cys-labeled arginine vasopressin (AVP), oxytocin (OT), and somatostatin-14 (SRIF) (only stressed animals) were measured simultaneously in male Wistar rats, after third ventricular administration of the labeled precursor, via guide-cannulae. The acetic acid-extracted labeled peptide fractions were purified by two sequential HPLC steps. After a 4 h period of labeling, only L-[³⁵S]Cys-AVP was selectively increased in the hypothalami of ADX-ized rats, compared to the sham-operated animals, possibly reflecting a significant activation of the paraventricular parvocellular (PVC) AVP/corticotropin-releasing factor (CRF) neurons. The increased accumulation of neurohypophyseal L-[³⁵S]Cys-labeled AVP and OT in these animals, without changes in the endogenous levels of these peptides, as measured by UV absorbance, also suggests a moderate activation of the magnocellular (MGC) AVP and OT neurons, as a consequence of adrenal insufficiency. In response to immobilization stress, levels of L-[³⁵S]Cys-OT were selectively increased in the hypothalami and corresponding neurohypophyses, 2 h and 4 h after receiving the label, concomitantly with a statistically significant reduction in the stores of OT in the neural lobes. AVP and SRJF biosynthesis remained unaffected by immobilization; the neurohypophyseal AVP stores likewise remained unchanged. These observations suggest the selective activation of MGC-OT neurons in response to chronic immobilization stress. Selective increases in hypothalamic L-[³⁵S]Cys-AVP in ADX-ized rats, and in hypothalamic L-[³⁵S]Cys-OT in chronically stress-immobilized rats, are presented as a measure of PVC-AVP/CRF and MGC-OT neuronal activation, respectively.     

SOMATOSTATIN-LIKE IMMUNOREACTIVE CELLS IN THE GROUND SQUIRREL RETINA

Immunocytochemical techniques were employed to locate somatostatin (SS)-containing cells in the retina of the 13-lined ground squirrel (Spermophilus tridecemlineatus). In normal retinas immunostain was limited to neuronal processes, yet distinctly labeled somata were detected in retinas of animals pretreated with colchicine. Labeled cell bodies were located in the outermost and innermost portions of the inner nuclear layer (INL) and in the ganglion cell layer (GCL). The largest population of SS-like immunoreactive neurons was found in the innermost INL. These cells were identified as small and medium sized amacrine cells whose soma diameters ranged from 4 to 14μm. A smaller population of immunoreactive cells was observed in the outermost region of the INL. These cells, presumptive horizontal cells, were found mainly in peripheral regions of the retina. Immunoreactive cells in the GCL were of two types: displaced amacrines, and retinal ganglion cells. SS-positive axons in the optic fiber layer suggest that some of the immunoreactive GCL neurons were ganglion cells, and it is our opinion that these cells belong to a class of associational ganglion cells previously identified in other species.     

Effect of Somatostatin Analog on Postprandial Satiation in Obesity

Objective: Altered satiation may impact postprandial symptoms and potentially change food intake in obesity. Our aim was to compare effects of octreotide and placebo on postprandial symptoms, satiation, and gastric volumes in obesity. Research Methods and Procedures: In a randomized, parallel‐group, double‐blind, placebo‐controlled study, 26 obese but otherwise healthy participants received 100 μg of octreotide or placebo subcutaneously 30 minutes before each study. Studies were performed on 2 separate days and included validated non‐invasive techniques: ^99mTc‐single photon emission computed tomography imaging to measure fasting stomach volume and gastric volume changes after 90 mL of water and 240 mL of Ensure and a standardized nutrient drink test to measure the maximum tolerated volume and postprandial symptoms. Results: Relative to placebo, octreotide increased gastric volume after 90 mL of water; however, fasting and gastric volume change post‐Ensure and maximum tolerated volume of Ensure were not different. Octreotide decreased sensations of fullness (p = 0.035) and bloating (p = 0.05) and tended to reduce aggregate symptoms (p = 0.07) after the fully satiating meal. Discussion: In obese individuals, somatostatin analog significantly reduced postprandial sensations after a satiating meal without altering maximum tolerated meal volume or postnutrient gastric volume, suggesting an effect on upper gut sensation. The role of somatostatin as a permissive factor in the development of obesity by reducing postprandial sensations deserves further study.     

Inhibition of human non-small cell lung cancers with a targeted cytotoxic somatostatin analog, AN-162

Human non-small cell lung cancers (NSCLCs) express receptors for somatostatin. The cytotoxic analog of somatostatin AN-162 (AEZS-124), consisting of doxorubicin linked to a somatostatin analog RC-121 binds to receptors for somatostatin and is targeted to tumors expressing these receptors. The aim of this study was to investigate the effect of targeted cytotoxic somatostatin analog AN-162 on a panel of human NSCLC cell lines (A549, H460, H838, H1299) in vitro (at 0.5–100 μM concentrations) and in vivo on H460 and H1299 NSCLCs xenografted into nude mice (at the dose of 2.5 μmol/kg, i.v., once a week). The expression of mRNA for somatostatin receptor subtypes was investigated by RT-PCR in cell lines and tumor tissues. Somatostatin receptor proteins were also characterized by ligand competition assay and Western blotting. AN-162 significantly decreased cell proliferation in vitro and tumor growth (p < 0.05 vs. all groups) of H460 and H1299 NSCLCs in vivo. Based on real-time PCR array data, AN-162 induced several apoptosis-related genes in vivo in both models. Our results suggest that cytotoxic somatostatin analog AN-162 (AEZS-124) should be considered for the further development of a therapy of patients with NSCLC.     

Role of somatostatin receptor 1 and 5 on epidermal growth factor receptor mediated signaling

Epidermal growth factor (EGF) regulates normal and tumor cell proliferation via epidermal growth factor receptor (EGFR) phosphorylation, homo- or heterodimerization and activation of mitogen-activated protein kinases (MAPKs) and PI3K/AKT cell survival pathways. In contrast, SST via activation of five different receptor subtypes inhibits cell proliferation and has been potential target in tumor treatment. To gain further insight for the effect of SSTRs on EGFR activated signaling, we determine the role of SSTR1 and SSTR1/5 in human embryonic kidney (HEK) 293 cells. We here demonstrate that cells transfected with SSTR1 or SSTR1/5 negatively regulates EGF mediated effects attributed to the inhibition of EGFR phosphorylation, MAPKs as well as the cell survival signaling. Furthermore, SSTR effects were significantly enhanced in cells when EGFR was knock down using siRNA or treated with selective antagonist (AG1478). Most importantly, the presence of SSTR in addition to modulating signaling pathways leads to the dissociation of the constitutive and EGF induced heteromeric complex of EGFR/ErbB2. Furthermore, cells cotransfected with SSTR1/5 display pronounced effect of SST on the signaling and dissociation of the EGFR/ErbB2 heteromeric complex than the cells expressing SSTR1 alone. Taken together this study provides the first evidence that the presence of SSTR controls EGF mediated cell survival pathway via dissociation of ErbB heteromeric complex. We propose that the activation of SSTR and blockade of EGFR might serve novel therapeutic approach in inhibition of tumor proliferation.     

Reactive oxygen species serve as signals mediating glucose-stimulated somatostatin secretion from cultured rat gastric primary D-cells

Abstract

Somatostatin plays an important role in glucose homeostasis. It is normally secreted in response to glucose and ATP generation is believed to be the key transduction signal of glucose-stimulated somatostatin secretion (GSSS). However, in the present study, in cultured rat gastric primary D-cells, GSSS was accompanied by increases in cellular reactive oxygen species (ROS). GSSS is dependent on the cellular ROS and independently of the ATP production linked to glucose metabolism. The antioxidant, α-lipoic acid or catalase inhibitor, 3-aminotriazole can influence the intracellular calcium concentration and abolish or further elevate GSSS. It is suggested that ROS production may serve as a signal modulating the necessary Ca²⁺ recruitment for GSSS. Since somatostatin is thought to exert broad regulatory functions on gastrointestinal physiology and nutrient intake, the interaction with ROS may lead to potential targets for mediating nutrition and energy homeostasis.     

Immunoreactive and bioactive somatostatin-like material is present in tobacco (Nicotiana tabacum)

Immunoreactive and biologically active somatostatin-like material is present in extracts of tobacco plants (Nicotiana tabacum). Comparative chromatographic and immunological characterization of this peptide along with synthetic (hypothalamic-like) somatostatin-14 and -28, indicates that both molecular forms are present in the plant. Tobacco-somatostatin inhibits the prostaglandin E2-induced release of growth hormone from cultured anterior pituitary cells. This finding raises questions concerning the evolutionary mechanisms responsible for the presence of this neuropeptide in plants, and the physiological significance of this phenomena.     

四种胃肠激素对链佐霉素诱发的小鼠高血糖的影响

本实验用腹腔注射链佐霉素(Streptozotocin简称STZ)方法破坏小鼠胰岛B细胞以诱发高血糖,观察生长抑素(Somatostatin,SS)、神经降压素(neurotensin,NT)、胰高血糖素(glucagon,GC)和促甲状腺素释放激素(TRH)4种胃肠激素对小鼠高血糖的影响。在每天腹腔注射STZ(60mg/kg)前10分钟分别经皮下注射上述4种胃肠激素,连续注射5天,在实验的第1,6,8,10,15天取血测血清葡萄糖浓度,对照组注射生理盐水(NS)。结果发现:(1)预先注射SS和NT可不同程度地抑制由STZ引起的实验性高血糖,并呈剂量一效应关系,(2)预先注射GC和TRH,血糖浓度仍明显升高,与NS对照组比较无显著差异,(3)取注射STZ后第15天的高血糖小鼠(血糖高于350mg％者)分为8组,分别以SS和NT作治疗性注射,每天一次共5日,并未见对小鼠高血糖有缓解效果;(4)正常小鼠单独皮下注射NS、SS、NT、GC、和TRH,每天一次连续5天,在注射后15天内未见对血糖水平有明显影响。以上结果提示:预防性注射SS和NT可显著抑制由STZ诱发的高血糖的产生。     

New somatostatin-drug conjugates for effective targeting pancreatic cancer

Pancreatic cancer poorly responds to available drugs, and finding novel approaches to target this cancer type is of high significance. Here, based on a common property of pancreatic cancer cells to express somatostatin receptors (SSTR), we designed drug conjugates with novel somatostatin-derived cyclic peptides (SSTp) with broad selectivity towards SSTR types to facilitate drug targeting of the pancreatic cancer cells specifically. Uptake of our newly designed SSTps was facilitated by SSTRs expressed in the pancreatic cancers, including SSTR2, SSTR3, SSTR4 and SSTR5. Three major drugs were conjugated to our best SSTps that served as delivery vehicles, including Camptothecin (CPT), Combretastatin-4A (COMB) and Azatoxin (AZA). All designed drug conjugates demonstrated penetration to pancreatic cancer cell lines, and significant toxicity towards them. Furthermore, the drug conjugates specifically accumulated in tumors in the animal xenograft model, though some accumulation was also seen in kidney. Overall these findings lay the basis for development of novel drug series that could target the fatal pancreatic cancer.