Ghrelin in neuroendocrine tumors

Ghrelin is a 28 amino acid peptide, primarily produced by the oxyntic mucosa X/A like neuroendocrine cells in the stomach. It is also found in the small intestine, hypothalamus, pituitary gland, pancreas, heart, adipose tissue, and immune system. In gastrointestinal neuroendocrine tumors (NETs) ghrelin release has been well documented. Ghrelin is a brain-gut circuit peptide with an important role in the physiological regulation of appetite, response to hunger and starvation, metabolic and endocrine functions as energy expenditure, gastric motility and acid secretion, insulin secretion and glucose homeostasis, as well as in the potential connection to the central nervous system. Recently, there has been a significant interest in the biological effects of ghrelin in NETs. In this article, we present a comprehensive review of ghrelin's expression and a brief summary of ghrelin's physiological role in NETs patients with carcinoids, type A chronic atrophic gastritis (CAG), with or without MEN-1, and with and without liver metastases. We hope, with the research reviewed here, to offer compelling evidence of the potential significance of ghrelin in NETs, as well as to provide a useful guide to the future work in this area.     

Tumor immune escape mechanisms: impact of the neuroendocrine system

Tumor cells act upon, and react to both their proximate and more distant environment, the mechanisms by which this is achieved being both autocrine and paracrine in nature. This interaction, however, takes place not only between adjacent malignant cells, but also non-malignant cells such as those of the immune system, the latter also partaking in the modeling of the tumor environment. Although tumor cells descend from normal tissue cells and thus bear in classical immunological terms ‘self signals’, it is evident that the immune system is able to recognize tumor cells as a harassment for the body and in consequence tries to eliminate these cells. On the counterpart, tumor cells acquire various characteristics which allow them to evade this immunological surveillance, and have been collectively coined with the term “tumor escape mechanisms”. This review will describe and summarize current understanding of tumor escape strategies, and also more closely elaborate on the modulatory role of the neuroendocrine system in the immune system–tumor cell interaction.     

The ventricular system in neuroendocrine mechanisms

Summary This investigation has utilized a correlative scanning-transmission electron microscopic technique in the analysis of the primate cerebral ventricular system. This approach has demonstrated a complex network of supraependymal cellular elements upon the walls of the third cerebral ventricle in direct contact with the ventricular lumen. Type I neuronal-like cells and type II histiocytic-like cells with potential phagocytic capabilities have been observed in large numbers throughout the third ventricle. Type I neuron-like cells are discussed in the context that they may represent a population of receptor-cells which serve to assess ambient changes in the composition of bioactive peptides in the cerebrospinal fluid and may serve as a supraependymal network that integrates the endocrine hypothalamus with other circumventricular organs which may also be sites of neuroendocrine transduction.Supported by USPHS Program Project Grant NS-11642Career Development Awardee GM K04 70001     

The biological relevance of gastric neuroendocrine tumors.

Gastric neuroendocrine tumors were originally thought to have a low incidence (three percent). Since endoscopic diagnostic procedures have become clinical routine, they are now found more frequently (relative incidence up to 41 percent). In recent years, classifications have been developed that attempt to consider the biological relevance of these tumors. Four types of gastric neuroendocrine tumor may be distinguished: Type 1 gastric neuroendocrine tumor is most common. It is associated with chronic atrophic fundus gastritis, hypergastrinemia and often with pernicious anemia. Usually it is multicentric and smaller than one cm, does not produce any symptoms and has an excellent prognosis. Type 2 gastric neuroendocrine tumor is second in frequency. It has no association with other diseases, is solitary and has no predilection for a particular localization. It may be larger than 1 cm, produce a carcinoid syndrome or Zollinger-Ellison syndrome and have a metastasis rate of up to 30 percent. Type 3 gastric neuroendocrine tumor is rare and always associated with Zollinger-Ellison syndrome and multiple endocrine neoplasia type I. It occurs as multiple lesions in the gastric body fundus and has a lower metastatic rate than type 2 gastric neuroendocrine tumor. Type 4 gastric neuroendocrine tumor corresponds to a small-cell carcinoma.     

Apoptosis regulating genes in neuroendocrine tumors

Neuroendocrine tumors (NETs) are a heterogeneous group of neoplasms. They are relatively uncommon and characterised by a relatively indolent clinical course. The indolent nature of NETs has long been enigmatic and recent advances in apoptosis research have led to speculation regarding the role of programmed cell death in NET tumorigenesis. It is hoped that a fundamental molecular understanding will help explain these variant behaviors that are so evident to the clinician, and ultimately yield novel and more effective therapies. Recent studies have demonstrated that deregulation of programmed cell death may be a critical component in the multistep tumorigenesis of NETs and that the frequent expression of the BCL-2 oncoprotein in these tumors may contribute to their pathogenesis. The genetic complementation of simultaneously deregulated BCL-2 and c-MYC may be implicated in the multistep tumorigenesis of human NETs. It is also clear that numerous cellular gene products can and will be shown to impact upon apoptosis in NETs; some of these may even be molecules identified as oncoproteins or tumor suppressors. The major challenge will be to ascribe primary pathogenetic significance to tumor-associated derangements in expression of these molecules, and hopefully to then exploit our knowledge toward therapeutic benefit.     

Pancreatic neuroendocrine tumors in glucagon receptor-deficient mice

Inhibition of glucagon signaling causes hyperglucagonemia and pancreatic α cell hyperplasia in mice. We have recently demonstrated that a patient with an inactivating glucagon receptor mutation (P86S) also exhibits hyperglucagonemia and pancreatic α cell hyperplasia but further develops pancreatic neuroendocrine tumors (PNETs). To test the hypothesis that defective glucagon signaling causes PNETs, we studied the pancreata of mice deficient in glucagon receptor (Gcgr^−/−) from 2 to 12 months, using WT and heterozygous mice as controls. At 2–3 months, Gcgr^−/− mice exhibited normal islet morphology but the islets were mostly composed of α cells. At 5–7 months, dysplastic islets were evident in Gcgr^−/− mice but absent in WT or heterozygous controls. At 10–12 months, gross PNETs (≥1 mm) were detected in most Gcgr^−/− pancreata and micro-PNETs (<1 mm) were found in all (n = 14), whereas the islet morphology remained normal and no PNETs were found in any WT (n = 10) or heterozygous (n = 25) pancreata. Most PNETs in Gcgr^−/− mice were glucagonomas, but some were non-functioning. No tumors predominantly expressed insulin, pancreatic polypeptide, or somatostatin, although some harbored focal aggregates of tumor cells expressing one of those hormones. The PNETs in Gcgr^−/− mice were well differentiated and occasionally metastasized to the liver. Menin expression was aberrant in most dysplatic islets and PNETs. Vascular endothelial growth factor (VEGF) was overexpressed in PNET cells and its receptor Flk-1 was found in the abundant blood vessels or blood islands inside the tumors. We conclude that defective glucagon signaling causes PNETs in the Gcgr^−/− mice, which may be used as a model of human PNETs. Our results further suggest that completely inhibiting glucagon signaling may not be a safe approach to treat diabetes.     

Cross-regulation in development of neuroendocrine and immune systems

Cross-regulatory effects of immune and neuroendocrine systems on their appearance and functioning occur during a whole life period. At different stages of ontogenesis, the functions of these systems are diverse. In perinatal ontogenesis hormones, neuropeptides and neurotransmitters control the processes of growth and differentiation of various embryo tissues, particularly lymphoid. In the postnatal period, their functions are mostly in homeostasis maintaining of the immune system in response to changes of the environment. Conversely, transmitters of the immune system, such as cytokines, whose synthesis is increased in inflammation, and thymic peptides, program the development of the neuroendocrine system of the embryo. The perinatal period is crucial for final appearance of these systems. Changes in one of the interacting systems, caused by negative environmental factors at this stage, usually provoke changes in other developing systems for a long period. Plasticity of physiological systems in perinatal development allows the organism to adapt to changed conditions. However, these changes can limit physiological functions in interacting systems and induce the appearance of various pathologies in postnatal life.     

Biomarkers and molecular imaging in gastroenteropancreatic neuroendocrine tumors

Neuroendocrine gastrointestinal and pancreatic tumors (GEP-NETs) are a heterogenous group of cancers with various clinical expressions. All tumors produce and secret various amines and peptides, which can be used as tissue and circulating markers. Chromogranin A (CgA) is a general tumor marker stored in secretory granules within the tumor cell and released upon stimulation. CgA is the best general tumor marker at the moment, expressed in 80-90% in all patients with GEP-NETs. CgA and NSE are used as tissue markers for the delineation of the neuroendocrine features of the tumors, but recently also the proliferation marker Ki-67 has been included in the standard procedure for evaluation of the proliferation. GEP-NETs are classified into well differentiated neuroendocrine tumors (Ki-67<2%), well-differentiated neuroendocrine carcinoma (Ki-67 2-20%), poorly differentiated neuroendocrine carcinoma (Ki-67>20%). The molecular imaging of NETs is based on the ability of these tumor cells to express somatostatin receptors as well as the APUD features. Octreoscan has been applied for imaging and staging of the disease for more than 2 decades and will nowadays be replaced by 68Ga-DOTA-Octreotate, with higher specificity and sensitivity. 18Fluoro-DOPA and 11C-5HTP are specific tracers for NETs with high specificity and selectivity. A new potential biomarker is auto-antibodies to paraneoplastic antigen MA2, which might indicate early recurrence of carcinoids after surgery with a curative intent. Circulating tumor cells (CTC) have been applied in GEP-NETs quite recently. There is still an unmet need for new markers.     

Loss of PTEN expression in neuroendocrine pancreatic tumors

PTEN (phosphatase and tensin homologue deleted from chromosome 10) is a well established tumor suppressor gene, which was cloned to chromosome 10q23. PTEN plays an important role in controlling cell growth, apoptosis, cell adhesion, and cell migration. In various studies, a genetic change as well as loss of PTEN expression by different carcinomas has been described. To date, the role of PTEN as a differentiation marker for neuroendocrine tumors (NET) and for the loss of PTEN expression is still unknown. It is assumed that loss of PTEN expression is important for tumor progression of NETs. We hypothesize that PTEN might be used as a new prognostic marker. We report 38 patients with a NET of the pancreas. Tumor tissues were surgically resected, fixed in formalin, and embedded in paraffin. PTEN expression was evaluated by immunohistochemistry and was correlated with several clinical and pathological parameters of each individual tumor. After evaluation of our immunohistochemistry data using a modified Remmele Score, a widely accepted method for categorizing staining results for reports and statistical evaluation, staining results of PTEN expression were correlated with the clinical and pathological parameters of each individual tumor. Our data demonstrates a significant difference in survival with existence of lymph node or distant metastases. Negative patients show a significant better survival compared with positive patients. Furthermore, we show a significant difference between PTEN expression and WHO or TNM classification. Taken together, our data shows a positive correlation between WHO classification and the new TNM classification of NETs, and loss of PTEN expression as well as survival. These results strongly implicate that PTEN might be helpful as a new prognostic factor.     

Plasticity of neuroendocrine and immune systems in early development

This article provides an analysis of our own and published data on the reciprocal morphogenetic influence of the neuroendocrine and immune systems on their formation and function in mammals. It is substantiated that, in early ontogeny, neurohormones regulate the growth and differentiation of various tissues in the body, including the lymphoid tissue. Thymic peptides, in turn, affect the development of the hypothalamic-pituitary-adrenal and gonadal systems. Various adverse factors and changes in the physiological concentrations of hormones in the critical periods of development of these systems change their functions, and the plasticity of physiological systems in early ontogeny allows the body to adapt to new conditions. Disturbances in the interaction of the neuroendocrine and immune systems in the perinatal period induce a predisposition to various diseases in progeny.     

促泌素在胃肠道神经内分泌肿瘤中的表达及其临床意义

目的 比较促泌素(secretagogin,SCGN)与传统的神经内分泌标记物在胃肠道神经内分泌肿瘤中的表达差异.方法 收集胃肠道手术标本共88例,其中实验组为8例类癌和20例非典型类癌,对照组为40例腺癌伴神经内分泌分化和20例腺癌.所有标本均使用SCGN、PGP9.5、CD56、NSE、Syn及CgA进行免疫组织化学SP两步法染色.结果 SCGN可在胃肠道粘膜同有层腺体的弥散性神经内分泌细胞中表达,多显示“开放型”的神经内分泌细胞.除CD56和NSE各在1例胃肠道腺癌中阳性表达外,SCGN及其它标记物在20例腺癌中均无表达,所有标记物之间均无统计学差异(P＞0.05).SCGN在40例胃肠道腺癌伴神经内分泌分化、20例非典型类癌和8例类癌巾的阳性表达率均最高,分别为62.5％ (25/40)、90％(18/20)和100％(8/8),PGP9.5阳性表达率均最低分别为32.5％(13/40)、45％ (9/20)和37.5％(3/8),两标记物在这三组肿瘤中的表达均有显著统计学差异(P＜0.01),而CD56、NSE、Syn和CgA在以上三组肿瘤中的表达率均较高,与SCGN比较均无统计学差异(P＞0.05).所有标记物在腺癌伴神经内分泌分化、非典型类癌和类癌中的阳性表达率均明显高于腺癌(P＜0.01);SCGN、Syn和CgA在非典型类癌和类癌巾的阳性表达均高于腺癌伴神经内分泌分化(P＜0.05);所有标记物在非典型类癌和类癌之间的阳性表达率均无统计学差异(P＞0.05).结论 SCGN作为一种新型的神经内分泌标记物与传统标记物Syn和CgA联合,可应用于胃肠道神经内分泌肿瘤的临床病理诊断.     

昆虫蛹滞育的神经内分泌调控

从神经内分泌的角度,分别介绍了脑、前胸腺和咽侧体在昆虫蛹滞育中所起的作用。脑主要是通过对促前胸腺激素的合成和释放的控制来参与滞育调节的;而前胸腺的活性过低,分泌的蜕皮激素远远低于启动成虫发育所需要的量,是导致蛹滞育的最根本原因;咽侧体在某些虫种中对蛹滞育可能起到间接的调控作用。     

Effect oh millimeter waves on the immune system in mice with experimental tumors

The effect of low-level millimeter fractionated radiation on the production of tumor necrosis factor, intreleukin-2, interleukine-3, and nitric oxide and on the activity of natural killer cells and proliferation of T and B lymphocytes in mice was studied. Cell activity was measured in four groups of male Balb/c mice (control, exposed, tumor-bearing unexposed, and exposed tumor-bearing animals) within 30 days of tumoral growth and microwave exposure (42.2 GHz, 10 Hz amplitude modulation, 0.5 microW/cm2, 1.5 h daily). A significant increase in the production of tumor necrosis factor and nitric oxide and in the activity of natural killer cells was observed at the early stage of tumor development; this effect was considered as adaptive response. In healthy mice, millimeter radiation produced both stimulating and immunodepressive effects. The changes were nonmonotonous; as the exposure duration was increased, the stimulating effect became weaker and on day 30 it was not observed. Irradiation of tumor-bearing mice did not induce any significant changes in the activity of cells compared to unirradiated tumor-bearing animals. Moreover, exposure to millimeter waves impaired some characteristics of cell immunity in tumor-bearing mice. It was concluded that low-intensity millimeter waves do not increase the resistance against tumor as it was shown earlier in our experiments with centimeter waves.     

The parathyroid hormone-related protein associated with malignancy is secreted by neuroendocrine tumors

We have demonstrated the production of the PTH-related protein (PTHrP) associated with hypercalcemia of malignancy by human neuroendocrine cell lines that also produce calcitonin gene products and chromogranin A. PTHrP was demonstrable in the cells by immunocytochemistry and immunoassay and Northern analysis of the cells revealed the presence of multiple mRNAs for PTHrP. The cell lines also secreted PTHrP in a regulated fashion, with the most potent secretagogue being phorbol. Thus, PTHrP is secreted by neuroendocrine cells and it may have neuroectodermal lineage. The coexpression of calcitonin gene products and chromogranin A, also neuroendocrine, with PTHRP may influence its secretion and ultimate biological effects in vivo.     

The clinicopathological significance of angiogenesis in hindgut neuroendocrine tumors obtained via an endoscopic procedure

Background

As the World Health Organization grading system for gastroenteropancreatic-neuroendocrine tumors (GEP-NETs) may not always correlate with tumor progression, it is imperative that other independent predictors of tumor progression be established. To identify such predictors, we conducted a retrospective histopathological study of hindgut NETs, obtained from endoscopic procedures, and used statistical analyses to evaluate predictive factors.

Methods

We first obtained clinicopathological data of cases of hindgut NETs. Tissue sections from tumor samples were prepared and subjected to pathological examination. In particular, we calculated the microvessel density (MVD) and lymphatic microvessel density (LMVD) values, and performed appropriate statistical analyses.

Results

A total of 42 cases of hindgut NETs were selected for the study, 41 from the rectum and 1 from the sigmoid colon. Based on the Ki-67 labeling index, 34 cases were classified as NET G1 tumors and 8 as NET G2 tumors. MVD values ranged from 1.4/mm² to 73.9/mm² and LMVD values from 0/mm² to 22.9/mm². MVD and LMVD were identified as risk factors for venous and lymphatic invasion of hindgut NETs. Moreover, MVD positively correlated with the maximum diameter of the tumor.

Conclusions

Tumor progression of NETs may cause angiogenesis and lymphangiogenesis, via an unknown mechanism, as well as lymphovascular invasion. Angiogenesis likely plays an important role in occurrence and progression in the initial phase of hindgut NETs.