Coexpression of receptors for adrenomedullin, calcitonin gene-related peptide, and amylin in pancreatic beta-cells

Long-term effects of gestational diabetes mellitus on the pancreas of female mouse offspring

BACKGROUND

Prolonged fetal exposure to hyperglycemia may increase the risk of developing abnormal glucose metabolism and type-2 diabetes during childhood, adolescence, and adulthood; however, the mechanisms by which gestational diabetes mellitus (GDM) predisposes offspring to metabolic disorders remain unknown.

AIM

To quantify the nerve axons, macrophages, and vasculature in the pancreas from adult offspring born from mouse dams with GDM.

METHODS

GDM was induced by i.p. administration of streptozotocin (STZ) in ICR mouse dams. At 12 wk old, fasting blood glucose levels were determined in offspring. At 15 wk old, female offspring born from dams with and without GDM were sacrificed and pancreata were processed for immunohistochemistry. We quantified the density of sensory [calcitonin gene-related peptide (CGRP)] and tyrosine hydroxylase (TH) axons, blood vessels (endomucin), and macro-phages (CD68) in the splenic pancreas using confocal microscopy.

RESULTS

Offspring mice born from STZ-treated dams had similar body weight and blood glucose values compared to offspring born from vehicle-treated dams. However, the density of CGRP+ and TH+ axons, endomucin+ blood vessels, and CD68+ macrophages in the exocrine pancreas was significantly greater in offspring from mothers with GDM vs control offspring. Likewise, the microvasculature in the islets was significantly greater, but not the number of macrophages within the islets of offspring born from dams with GDM compared to control mice.

CONCLUSION

GDM induces neuronal, vascular, and inflammatory changes in the pancreas of adult progeny, which may partially explain the higher propensity for offspring of mothers with GDM to develop metabolic diseases.

Unravelling innervation of pancreatic islets

The central and peripheral nervous systems play critical roles in regulating pancreatic islet function and glucose metabolism. Over the last century, in vitro and in vivo studies along with examination of human pancreas samples have revealed the structure of islet innervation, investigated the contribution of sympathetic, parasympathetic and sensory neural pathways to glucose control, and begun to determine how the structure and function of pancreatic nerves are disrupted in metabolic disease. Now, state-of-the art techniques such as 3D imaging of pancreatic innervation and targeted in vivo neuromodulation provide further insights into the anatomy and physiological roles of islet innervation. Here, we provide a summary of the published work on the anatomy of pancreatic islet innervation, its roles, and evidence for disordered islet innervation in metabolic disease. Finally, we discuss the possibilities offered by new technologies to increase our knowledge of islet innervation and its contributions to metabolic regulation.

Classical and non-classical islet peptides in the control of β-cell function

The dual role of the pancreas as both an endocrine and exocrine gland is vital for food digestion and control of nutrient metabolism. The exocrine pancreas secretes enzymes into the small intestine aiding digestion of sugars and fats, whereas the endocrine pancreas secretes a cocktail of hormones into the blood, which is responsible for blood glucose control and regulation of carbohydrate, protein and fat metabolism. Classical islet hormones, insulin, glucagon, pancreatic polypeptide and somatostatin, interact in an autocrine and paracrine manner, to fine-tube the islet function and insulin secretion to the needs of the body. Recently pancreatic islets have been reported to express a number of non-classical peptide hormones involved in metabolic signalling, whose major production site was believed to reside outside pancreas, e.g. in the small intestine. We highlight the key non-classical islet peptides, and consider their involvement, together with established islet hormones, in regulation of stimulus-secretion coupling as well as proliferation, survival and transdifferentiation of β-cells. We furthermore focus on the paracrine interaction between classical and non-classical islet hormones in the maintenance of β-cell function. Understanding the functional relationships between these islet peptides might help to develop novel, more efficient treatments for diabetes and related metabolic disorders.

Adrenomedullin and its receptors are expressed in mouse pancreatic β-cells and suppresses insulin synthesis and secretion

Gestational diabetes mellitus (GDM) is associated with defective pancreatic β-cell adaptation in pregnancy, but the underlying mechanism remains obscure. Our previous studies demonstrated that GDM women display increased plasma adrenomedullin (ADM) levels, and non-obese GDM mice show decreased serum concentrations of insulin and the number of β-cells in pancreas islets. The aims of this study is to examine if ADM and its receptors are expressed in female mouse pancreas, and if so, whether insulin secretion is regulated by ADM in mouse β-cell line, NIT-1 cells and isolated mouse pancreatic islets. Present study shows that ADM and its receptor components CRLR, RAMPs are present in mouse pancreatic islets and co-localized with insulin. The expressions of ADM, CRLR and RAMP2 in islets from pregnant mice are reduced compared to that of non-pregnant mice. NIT-1-β cells express ADM and its receptor mRNA, and glucose dose-dependently stimulates expressions. Furthermore, ADM inhibits NIT-1-β cell growth, and this inhibition is reversed by ADM antagonist, ADM22-52. The glucose-induced insulin secretion was suppressed by ADM in NIT-1-β cells and isolated pancreatic islets from pregnant mice. These inhibitory effects are accompanied by upregulation of endoplasmic reticulum (ER) stress biomarker genes in NIT-1-β cells. This study unveils that reduced ADM and its receptors may play a role in β-cell adaptation during pregnancy, while increased plasma ADM in GDM may contribute to the β-cells dysfunction, and blockade of ADM may reverse β-cell insulin production.

α-CGRP disrupts amylin fibrillization and regulates insulin secretion: implications on diabetes and migraine

Despite being relatively benign and not an indicative signature of toxicity, fibril formation and fibrillar structures continue to be key factors in assessing the structure-function relationship in protein aggregation diseases. The inability to capture molecular cross-talk among key players at the tissue level before fibril formation greatly accounts for the missing link toward the development of an efficacious therapeutic intervention for Type II diabetes mellitus (T2DM). We show that human α-calcitonin gene-related peptide (α-CGRP) remodeled amylin fibrillization. Furthermore, while CGRP and/or amylin monomers reduce the secretion of both mouse Ins1 and Ins2 proteins, CGRP oligomers have a reverse effect on Ins1. Genetically reduced Ins2, the orthologous version of human insulin, has been shown to enhance insulin sensitivity and extend the life-span in old female mice. Beyond the mechanistic insights, our data suggest that CGRP regulates insulin secretion and lowers the risk of T2DM. Our result rationalizes how migraine might be protective against T2DM. We envision the new paradigm of CGRP : amylin interactions as a pivotal aspect for T2DM diagnostics and therapeutics. Maintaining a low level of amylin while increasing the level of CGRP could become a viable approach toward T2DM prevention and treatment.

Adiponectin paradox as a therapeutic target of the cancer evolvability in aging

Recent study suggests that protofibril-formation of amyloidogenic proteins (APs) might be involved in evolvability, an epigenetic inheritance of multiple stresses, in various biological systems. In cancer, evolvability of multiple APs, such as p53, γ-synuclein and the members of the calcitonin family of peptides, might be involved in various features, including increased cell proliferation, metastasis and medical treatment resistance. In this context, the objective of this paper is to explore the potential therapeutic benefits of reduced APs evolvability against cancer. Notably, the same APs are involved in the pathogenesis of neurodegenerative disease and cancer. Given the unsatisfactory outcomes of recent clinical trial of Aβ immunotherapy in Alzheimer's disease, it is possible that suppressing the aggregation of individual APs might also be not effective in cancer. As such, we highlight the adiponectin (APN) paradox that might be positioned upstream of AP aggregation in both neurodegenerative disease and cancer, as a common therapeutic target in both disease types. Provided that the APN paradox due to APN resistance under the diabetic conditions might promote AP aggregation, suppressing the APN paradox combined with antidiabetic treatments might be effective for the therapy of both neurodegenerative disease and cancer.

Circulating Adrenomedullin Is Elevated in Gestational Diabetes and Its Role in Impaired Insulin Production by β-Cells

CONTEXT

Defective pancreatic β-cell adaptation in pregnancy plays an important role in the pathophysiology of gestational diabetes mellitus (GDM), but the molecular basis remains unclear. Objectives of this study were to determine if circulating levels of adrenomedullin (ADM) in women with GDM are elevated and to assess the effects of ADM on insulin synthesis and secretion by human pancreatic β-cells.

DESIGN

A stable gene product of ADM precursor, midregional pro-adrenomedullin (MR-proADM), was measured in plasma of pregnant women with normal glucose tolerance (NGT, n = 10) or GDM (n = 11). The β-Lox5 cell line, derived from human pancreatic β-cells, was transduced with homeodomain transcription factor pancreatic-duodenal homeobox (PDX) factor 1 (PDX1) encoding lentiviral vector and treated with different doses of ADM. mRNA for insulin, ADM, and its receptor components in β-Lox5 cells and insulin in media were measured.

RESULTS

Plasma MR-proADM levels were significantly higher in GDM compared with patients with NGT. Pancreatic β-Lox5 cells express mRNA for insulin, ADM, and its receptor components. PDX1 transduction and cell-cell contact synergistically promote β-Lox5 cells insulin mRNA and secretion. Furthermore, ADM dose-dependently inhibited mRNA and secretion of insulin in β-Lox5 cell aggregates. These inhibitory effects were blocked by ADM antagonist ADM22-52, cAMP-dependent protein kinase A inhibitor KT5720, and Erk inhibitor PD98059, but not by PI-3K the inhibitor wortmannin.

CONCLUSIONS

Circulating ADM concentrations were elevated in pregnant women with GDM. ADM suppresses insulin synthesis and secretion by pancreatic β-cells in vitro. Thus, increased circulating ADM may contribute to the defective adaptation of β-cells in diabetic pregnancies, and blockade of ADM actions with its antagonists may improve β-cell functions.

Prognostic significance of CXCR7 in cancer patients: a meta-analysis

Background

CXC chemokine receptor 7 (CXCR7) is frequently overexpressed in a variety of tumors. Nevertheless, whether CXCR7 can be used as a tumor prognosis marker has not been systematically assessed. The current meta-analysis was performed to obtain an accurate evaluation of the relationship between CXCR7 level and the prognosis of cancer patients.

Methods

Embase, Web of Science, and PubMed were systematically searched according to a defined search strategy up to June 11, 2018. Then, the required data were extracted from all qualified studies which were screened out based on the defined inclusion and exclusion criteria. Finally, the hazard ratios (HR) with 95% confidence intervals (CI) were used to evaluate the prognostic significance of CXCR7 in tumor patients.

Results

A total of 28 original research studies comprising 33 cohorts and 5685 patients were included in this meta-analysis. The results showed that CXCR7 overexpression was significantly related to worse overall survival (OS) (HR 1.72; 95% CI 1.49–1.99), disease-free survival (DFS) (HR 5.58; 95% CI 3.16–9.85), progression-free survival (PFS) (HR 2.83; 95% CI 1.66–4.85) and recurrence-free survival (RFS) (HR 1.58; 95% CI 1.34–1.88) in cancer patients. Furthermore, for certain types of cancer, significant associations between higher CXCR7 expression and worse OS of glioma (HR 1.77; 95% CI 1.43–2.19), breast cancer (HR 1.45; 95% CI 1.28–1.63), esophageal cancer (HR 2.72; 95% CI 1.11–6.66) and pancreatic cancer (HR 1.46; 95% CI 1.12–1.90) were found. However, for lung cancer and hepatocellular cancer, there was no significant relationship between CXCR7 expression level and OS, (HR 2.40; 95% CI 0.34–17.07) and (HR 1.37; 95% CI 0.84–2.24) respectively.

Conclusions

Increased CXCR7 level could predict poor prognosis of tumor patients and might be regarded as a novel prognostic biomarker for tumor patients.

LYG-202 inhibits activation of endothelial cells and angiogenesis through CXCL12/CXCR7 pathway in breast cancer

Angiogenesis is critical for the growth and metastasis of triple-negative breast cancer (TNBC) and its inhibition reduces the risk of progression of metastatic TNBC. In this study, we investigated that LYG-202, a flavonoid with a piperazine substitution, inhibited angiogenesis induced by conditioned media (CM) from MDA-MB-231 cells under hypoxia and revealed its underlying mechanism. The results showed that LYG-202 decreased CXCL12 secretion and CXCR7 expression, leading to suppression of its downstream ERK/AKT/nuclear factor kappa B (NF-κB) signaling, which eventually decreased the expression of MMP-2, MMP-9, RhoA and increased VE-cadherin expression in EA.hy 926 cells treated with CM from MDA-MB-231 cells under hypoxia. The decreased migration ability, increased cell adhesion and inhibited CXCR7 pathway by LYG-202 could also be reproduced in human umbilical vein endothelial cells. More importantly, LYG-202 also inhibited tumor angiogenesis and tumor growth of human breast cancer MDA-MB-231 cells in nude mice through CXCL12/CXCR7 pathway. In summary, LYG-202 is a potential agent to prohibit tumor angiogenesis through inhibiting the activation of endothelial cells.

Biological/pathological functions of the CXCL12/CXCR4/CXCR7 axes in the pathogenesis of bladder cancer

CXC chemokine ligand 12 (CXCL12) is an important member of the CXC subfamily of chemokines, and has been extensively studied in various human body organs and systems, both in physiological and clinical states. Ligation of CXCL12 to CXCR4 and CXCR7 as its receptors on peripheral immune cells gives rise to pleiotropic activities. CXCL12 itself is a highly effective chemoattractant which conservatively attracts lymphocytes and monocytes, whereas there exists no evidence to show attraction for neutrophils. CXCL12 regulates inflammation, neo-vascularization, metastasis, and tumor growth, phenomena which are all pivotally involved in cancer development and further metastasis. Generation and secretion of CXCL12 by stromal cells facilitate attraction of cancer cells, acting through its cognate receptor, CXCR4, which is expressed by both hematopoietic and non-hematopoietic tumor cells. CXCR4 stimulates tumor progression by different mechanisms and is required for metastatic spread to organs where CXCL12 is expressed, thereby allowing tumor cells to access cellular niches, such as the marrow, which favor tumor cell survival and proliferation. It has also been demonstrated that CXCL12 binds to another seven-transmembrane G-protein receptor or G-protein-coupled receptor, namely CXCR7. These studies indicated critical roles for CXCR4 and CXCR7 mediation of tumor metastasis in several types of cancers, suggesting their contributions as biomarkers of tumor behavior as well as potential therapeutic targets. Furthermore, CXCL12 itself has the capability to stimulate survival and growth of neoplastic cells in a paracrine fashion. CXCL12 is a supportive chemokine for tumor neovascularization via attracting endothelial cells to the tumor microenvironment. It has been suggested that elevated protein and mRNA levels of CXCL12/CXCR4/CXCR7 are associated with human bladder cancer (BC). Taken together, mounting evidence suggests a role for CXCR4, CXCR7, and their ligand CXCL12 during the genesis of BC and its further development. However, a better understanding is still required before exploring CXCL12/CXCR4/CXCR7 targeting in the clinic.

Potential of circulatory procalcitonin as a biomarker reflecting inflammation among South Indian diabetic foot ulcers

OBJECTIVE

Diabetic foot ulcer (DFU), the major complication associated with diabetes mellitus, has been shown to precede amputation in up to 90% of cases. Recent data reveal that procalcitonin (PCT) is a valid marker for the diagnosis of bacterial infections compared with traditional markers like white blood cell count, C-reactive protein levels, and erythrocyte sedimentation rate in DFU patients. Furthermore, cytokines are proposed to act as modulators and mediators for the expression and release of PCT into the circulation. Hence, this preliminary study was conducted to evaluate the diagnostic accuracy of PCT compared with other traditional markers and to predict the association of PCT plasma levels with inflammatory cytokines and clinical parameters of incident diabetes among South Indian DFU subjects.

METHODS

There were 185 subjects with type 2 diabetes mellitus (T2DM) selected in this cross-sectional study, subdivided into three groups: group I, control/T2DM subjects free from DFU (n = 75; male, 43; female, 32); group II, T2DM subjects with noninfected DFU (n = 34; male, 19; female, 15); and group III, T2DM subjects with infected DFU (IDFU; n = 76; male, 46; female, 30). Patients with IDFU were further divided into three subgroups as per the Infectious Diseases Society of America-International Working Group on the Diabetic Foot classification criteria: grade 2 (n = 27), grade 3 (n = 38), and grade 4 (n = 11). Subjects with type 1 diabetes, gestational diabetes, pneumonia, sepsis, inflammatory bowel disease, meningitis, or hematologic diseases and those who underwent surgery in the past 2 to 3 weeks were excluded from this study. For investigation of clinical parameters, blood samples were drawn from all the study subjects; plasma samples were used for estimating PCT by the enzyme-linked immunosorbent assay method. The profiling of plasma cytokines was carried out using a multiplex bead-based assay. Data are presented as mean ± standard deviation for clinical and biochemical variables and as geometric mean with 95% confidence interval (CI) for cytokines. All analysis was done using the Statistical Package for the Social Sciences (version 20.0; IBM Corp, Armonk, NY); P < .05 was considered to be statistically significant.

RESULTS

We found PCT to be a valid diagnostic marker for IDFU with higher sensitivity and specificity than other traditional markers. For PCT, the area under the receiver operating characteristic curve was found to be high (0.99; 95% CI, 0.96-1.0), followed by C-reactive protein levels (0.78; 95% CI, 0.65-0.81), white blood cell count (0.76; 95% CI, 0.67-0.86), and erythrocyte sedimentation rate (0.74; 95% CI, 0.68-0.80) in IDFU subjects. We found the cutoff value of ≥0.5 ng/mL to have 54% sensitivity and 100% specificity for PCT with a positive predictive value of 100% and a negative predictive value of 12% for IDFU diagnosis. Moreover, PCT circulatory levels showed a positive correlation with helper T-cell subtype 1 cytokines, such as interferon γ (r = 0.21; P = .03) and interleukin 28A (r = 0.31; P = .003), and subtype 17 cytokines, such as interleukin 29/interferon λ1 (r = 0.20; P = .037).

CONCLUSIONS

PCT could be a valuable marker for diagnosis of T2DM patients with IDFU.

The Molecular Physiopathogenesis of Islet Amyloidosis

Human islet amyloid polypeptide or amylin (hA) is a 37-amino acid peptide hormone produced and co-secreted with insulin by pancreatic β-cells. Under physiological conditions, hA regulates a broad range of biological processes including insulin release and slowing of gastric emptying, thereby maintaining glucose homeostasis. However, under the pathological conditions associated with type 2 diabetes mellitus (T2DM), hA undergoes a conformational transition from soluble random coil monomers to alpha-helical oligomers and insoluble β-sheet amyloid fibrils or amyloid plaques. There is a positive correlation between hA oligomerization/aggregation, hA toxicity, and diabetes progression. Because the homeostatic balance between hA synthesis, release, and uptake is lost in diabetics and hA aggregation is a hallmark of T2DM, this chapter focuses on the biophysical and cell biology studies investigating molecular mechanisms of hA uptake, trafficking, and degradation in pancreatic cells and its relevance to h's toxicity. We will also discuss the regulatory role of endocytosis and proteolytic pathways in clearance of toxic hA species. Finally, we will discuss potential pharmacological approaches for specific targeting of hA trafficking pathways and toxicity in islet β-cells as potential new avenues toward treatments of T2DM patients.

Adrenomedullin regulates intestinal physiology and pathophysiology

Adrenomedullin (AM) and proadrenomedullin N-terminal 20 peptide (PAMP) are 2 biologically active peptides produced by the same gene, ADM, with ubiquitous distribution and many physiological functions. Adrenomedullin is composed of 52 amino acids, has an internal molecular ring composed by 6 amino acids and a disulfide bond, and shares structural similarities with calcitonin gene-related peptide, amylin, and intermedin. The AM receptor consists of a 7-transmembrane domain protein called calcitonin receptor-like receptor in combination with a single transmembrane domain protein known as receptor activity-modifying protein. Using morphologic techniques, it has been shown that AM and PAMP are expressed throughout the gastrointestinal tract, being specially abundant in the neuroendocrine cells of the gastrointestinal mucosa; in the enterochromaffin-like and chief cells of the gastric fundus; and in the submucosa of the duodenum, ileum, and colon. This wide distribution in the gastrointestinal tract suggests that AM and PAMP may act as gut hormones regulating many physiological and pathologic conditions. To date, it has been proven that AM and PAMP act as autocrine/paracrine growth factors in the gastrointestinal epithelium, play key roles in the protection of gastric mucosa from various kinds of injury, and accelerate healing in diseases such as gastric ulcer and inflammatory bowel diseases. In addition, both peptides are potent inhibitors of gastric acid secretion and gastric emptying; they regulate the active transport of sugars in the intestine, regulate water and ion transport in the colon, modulate colonic bowel movements and small-intestine motility, improve endothelial barrier function, and stabilize circulatory function during gastrointestinal inflammation. Furthermore, AM and PAMP are antimicrobial peptides, and they contribute to the mucosal host defense system by regulating gut microbiota. To get a formal demonstration of the effects that endogenous AM and PAMP may have in gut microbiota, we developed an inducible knockout of the ADM gene. Using this model, we have shown, for the first time, that lack of AM/PAMP leads to changes in gut microbiota composition in mice. Further studies are needed to investigate whether this lack of AM/PAMP may have an impact in the development and/or progression of intestinal diseases through their effect on microbiota composition.

Role of Cholesterol and Phospholipids in Amylin Misfolding, Aggregation and Etiology of Islet Amyloidosis

Amyloidosis is a biological event in which proteins undergo structural transitions from soluble monomers and oligomers to insoluble fibrillar aggregates that are often toxic to cells. Exactly how amyloid proteins, such as the pancreatic hormone amylin, aggregate and kill cells is still unclear. Islet amyloid polypeptide, or amylin, is a recently discovered hormone that is stored and co-released with insulin from pancreatic islet β-cells. The pathology of type 2 diabetes mellitus (T2DM) is characterized by an excessive extracellular and intracellular accumulation of toxic amylin species, soluble oligomers and insoluble fibrils, in islets, eventually leading to β-cell loss. Obesity and elevated serum cholesterol levels are additional risk factors implicated in the development of T2DM. Because the homeostatic balance between cholesterol synthesis and uptake is lost in diabetics, and amylin aggregation is a hallmark of T2DM, this chapter focuses on the biophysical and cell biology studies exploring molecular mechanisms by which cholesterol and phospholipids modulate secondary structure, folding and aggregation of human amylin and other amyloid proteins on membranes and in cells. Amylin turnover and toxicity in pancreatic cells and the regulatory role of cholesterol in these processes are also discussed.

High plasma levels of islet amyloid polypeptide in young with new-onset of type 1 diabetes mellitus

Aims/Hypothesis

Islet amyloid polypeptide (IAPP) is a beta cell hormone secreted together with insulin upon glucose stimulation. IAPP participates in normal glucose regulation, but IAPP is also known for its ability to misfold and form islet amyloid. Amyloid fibrils form through smaller cell toxic intermediates and deposited amyloid disrupts normal islet architecture. Even though IAPP and amyloid formation are much discussed in type 2 diabetes, our aim was to study the significance of IAPP in type 1 diabetes.

Results

Plasma IAPP levels in children and adolescents with newly diagnosed type 1 diabetes (n = 224) were analysed and concentrations exceeding 100 pmol/L (127.2 – 888.7 pmol/L) were found in 11% (25/224). The IAPP increase did not correlate with C-peptide levels.

Conclusions/Interpretation

Plasma levels of IAPP and insulin deviate in a subpopulation of young with newly-diagnosed type 1 diabetes. The determined elevated levels of IAPP might increase the risk for IAPP misfolding and formation of cell toxic amyloid in beta cells. This finding add IAPP-aggregation to the list over putative pathological factors causing type 1 diabetes.

Analysis of Foxo1-regulated genes using Foxo1-deficient pancreatic β cells

Several reports have suggested that Foxo1, a key regulator in differentiation, growth and metabolism, is involved in pancreatic β-cell function. However, detailed analyses have been hampered by a lack of Foxo1-deficient β cells. To elucidate Foxo1's function in β cells, we produced a β-cell line with inducible Foxo1 deletion. We generated a conditional knockout mouse line, in which Cre recombinase deletes the Foxo1 gene. We then established a β-cell line from an insulinoma induced in this knockout mouse by the β-cell-specific expression of simian virus 40 T antigen. In this cell line, designated MIN6-Foxo1flox/flox, adenovirus-mediated Cre expression ablates the Foxo1 gene, generating MIN6-Foxo1-KO cells. Using these knockout and floxed cell lines, we found that Foxo1 ablation enhanced the glucose-stimulated insulin secretion (GSIS) at high glucose concentrations and enhanced β-cell proliferation. We also conducted DNA microarray analyses of MIN6-Foxo1-KO cells infected with either an adenovirus vector expressing a constitutively active FOXO1 or a control vector and identified several Foxo1-regulated genes, including some known to be related to β-cell function. These cells should be useful for further studies on Foxo1's roles in β-cells and may lead to novel strategies for treating the impaired insulin secretion in type 2 diabetes mellitus.

Role of chemokine receptor CXCR7 in bladder cancer progression

Bladder cancer is one of the most common tumors of the genitourinary tract; however, the molecular events underlying growth and invasion of the tumor remain unclear. Here, role of the CXCR7 receptor in bladder cancer was further explored. CXCR7 protein expression was examined using high-density tissue microarrays. Expression of CXCR7 showed strong epithelial staining that correlated with bladder cancer progression. In vitro and in vivo studies in bladder cancer cell lines suggested that alterations in CXCR7 expression were associated with the activities of proliferation, apoptosis, migration, invasion, angiogenesis and tumor growth. Moreover, CXCR7 expression was able to regulate expression of the proangiogenic factors IL-8 or VEGF, which may involve in the regulation of tumor angiogenesis. Finally, we found that signaling by the CXCR7 in bladder cancer cells activates AKT, ERK and STAT3 pathways. The AKT and ERK pathways may reciprocally regulate, which are responsible for in vitro and in vivo epithelial to mesenchymal transition (EMT) process of bladder cancer. Simultaneously targeting the two pathways by using U0126 and LY294002 inhibitors or using CCX733, a selective CXCR7 antagonist drastically reduced CXCR7-induced EMT process. Taken together, our data show for the first time that CXCR7 plays a role in the development of bladder cancer. Targeting CXCR7 or its downstream-activated AKT and ERK pathways may prove beneficial to prevent metastasis and provide a more effective therapeutic strategy for bladder cancer.

The enteroendocrine "letter cells" - time for a new nomenclature?

Abstract The endocrine cells of the gastrointestinal (GI) tract and the pancreas, referred to as the enteroendocrine cells, secrete a large variety of peptides and amines that regulate functions of the digestive tract itself and of distant organs. Taken together, the enteroendocrine cells form the largest system of endocrine cells in the body, presently comprising 16 cell types. Many of them have been named after letters of the alphabet, but the names are only occasionally related to morphological or functional characteristics of the cell. In this review of the normal, adult, mammalian enteroendocrine cells, we summarize synonyms, functions, locations, structure, stored hormones/amines, receptors, and other cellular expressions. We propose that the enteroendocrine cells should be renamed after their most well-known hormone/amine and, when applicable, their anatomical location, with opportunities for future revisions.

CXCL12 / CXCR4 / CXCR7 chemokine axis and cancer progression

Chemokines, small pro-inflammatory chemoattractant cytokines that bind to specific G-protein-coupled seven-span transmembrane receptors, are major regulators of cell trafficking and adhesion. The chemokine CXCL12 (also called stromal-derived factor-1) is an important α-chemokine that binds primarily to its cognate receptor CXCR4 and thus regulates the trafficking of normal and malignant cells. For many years, it was believed that CXCR4 was the only receptor for CXCL12. Yet, recent work has demonstrated that CXCL12 also binds to another seven-transmembrane span receptor called CXCR7. Our group and others have established critical roles for CXCR4 and CXCR7 on mediating tumor metastasis in several types of cancers, in addition to their contributions as biomarkers of tumor behavior as well as potential therapeutic targets. Here, we review the current concepts regarding the role of CXCL12 / CXCR4 / CXCR7 axis activation, which regulates the pattern of tumor growth and metastatic spread to organs expressing high levels of CXCL12 to develop secondary tumors. We also summarize recent therapeutic approaches to target these receptors and/or their ligands.

Gut microbiota in health and disease

Gut microbiota is an assortment of microorganisms inhabiting the length and width of the mammalian gastrointestinal tract. The composition of this microbial community is host specific, evolving throughout an individual's lifetime and susceptible to both exogenous and endogenous modifications. Recent renewed interest in the structure and function of this "organ" has illuminated its central position in health and disease. The microbiota is intimately involved in numerous aspects of normal host physiology, from nutritional status to behavior and stress response. Additionally, they can be a central or a contributing cause of many diseases, affecting both near and far organ systems. The overall balance in the composition of the gut microbial community, as well as the presence or absence of key species capable of effecting specific responses, is important in ensuring homeostasis or lack thereof at the intestinal mucosa and beyond. The mechanisms through which microbiota exerts its beneficial or detrimental influences remain largely undefined, but include elaboration of signaling molecules and recognition of bacterial epitopes by both intestinal epithelial and mucosal immune cells. The advances in modeling and analysis of gut microbiota will further our knowledge of their role in health and disease, allowing customization of existing and future therapeutic and prophylactic modalities.

The ADMR receptor mediates the effects of adrenomedullin on pancreatic cancer cells and on cells of the tumor microenvironment

Background

Adrenomedullin (AM) is highly expressed in pancreatic cancer and stimulates pancreatic cancer cells leading to increased tumor growth and metastasis. The current study examines the role of specific AM receptors on tumor and cells resembling the tumor microenvironment (human pancreatic stellate - HPSC, human umbilical vein – HUVEC and mouse lung endothelial cells - MLEC).

Methods and Findings

AM receptors ADMR and CRLR were present in HPSC, HUVEC and MLECs while PDAC cells possessed only ADMR receptors as assessed by RT-PCR and western blotting. All cell lines expressed and secreted AM as indicated by ELISA. The growth of each of the cell lines was stimulated by exogenous AM and inhibited by the antagonist AMA. AM also stimulated in vitro angiogenesis assessed by polygon formation of endothelial cell lines. SiRNA-mediated silencing of ADMR, but not CRLR, reduced basal growth of all cells examined and reduced polygon formation of endothelial cells in vitro. Orthotopic tumors developed with shADMR bearing cancer cells had dramatically reduced primary tumor volume (>90%) and lung and liver metastasis compared to shControl bearing cells. To validate ADMR as a potential therapeutic target, in vivo studies were conducted using neutral nanoliposomes to systemically deliver human siRNA to ADMR to silence human cancer cells and mouse siRNA to ADMR to silence mouse tumor stromal cells. Systemic silencing of both human and mouse ADMR had no obvious adverse effects but strongly reduced tumor development.

Conclusion

ADMR mediates the stimulatory effects of AM on cancer cells and on endothelial and stellate cells within the tumor microenvironment. These data support the further development of ADMR as a useful target treatment of pancreatic cancer.

The role of stromal-derived factor-1--CXCR7 axis in development and cancer

Cancer metastasis is a major clinical problem that contributes to unsuccessful therapy. Augmenting evidence indicates that metastasizing cancer cells employ several mechanisms that are involved in developmental trafficking of normal stem cells. Stromal-derived factor-1 (SDF-1) is an important alpha-chemokine that binds to the G-protein-coupled seven-transmembrane span CXCR4. The SDF-1-CXCR4 axis regulates trafficking of normal and malignant cells. SDF-1 is an important chemoattractant for a variety of cells including hematopoietic stem/progenitor cells. For many years, it was believed that CXCR4 was the only receptor for SDF-1. However, several reports recently provided evidence that SDF-1 also binds to another seven-transmembrane span receptor called CXCR7, sharing this receptor with another chemokine family member called Interferon-inducible T-cell chemoattractant (I-TAC). Thus, with CXCR7 identified as a new receptor for SDF-1, the role of the SDF-1-CXCR4 axis in regulating several biological processes becomes more complex. Based on the available literature, this review addresses the biological significance of SDF-1's interaction with CXCR7, which may act as a kind of decoy or signaling receptor depending on cell type. Augmenting evidence suggests that CXCR7 is involved in several aspects of tumorogenesis and could become an important target for new anti-metastatic and anti-cancer drugs.

Review of pramlintide as adjunctive therapy in treatment of type 1 and type 2 diabetes

Pramlintide (Symlin^®), a synthetic analog of a neurohormone amylin, was approved by the US Food and Drug Administration for use along with premeal insulin in patients with type 1. In patients with type 2 diabetes, pramlintide is approved for addition to premeal insulin in those patients who are either only on premeal insulin or those receiving the combination of insulin and metformin and/or a sulfonylurea. This article reviews the pharmacology, pharmacokinetics, dosing, clinical trials, safety, contraindications, and drug interactions of pramlintide therapy. A search for published clinical trials and therapeutic reviews in the English language was done in the following databases: Iowa Drug Information Service (1966 to July 2008), MEDLINE (1966 to July 2008), and International Pharmaceutical Abstracts (1970 to July 2008). Pramlintide and amylin were used as keywords and title words. References of key articles were also reviewed to identify additional publications. Amylin is a 37 amino acid peptide neurohormone cosecreted from the beta cells of the pancreas, along with insulin, in response to meals. Amylin lowers serum glucose by decreasing glucagon release, slowing gastric emptying and decreasing food intake. Pramlintide, a synthetic analog of amylin, reduces 2-hour postprandial blood glucose between 3.4 and 5 mmol/L, reduces A1C by 0.2% to 0.7% and has no effect on fasting glucose levels. The use of pramlintide was associated with up to a 1.6 kg weight loss. Nausea was the most commonly reported adverse event. Pramlintide is an amylin analog that was FDA approved for the treatment of type 1 and type 2 diabetes. Its use results in modest reduction of A1C and the most frequent side effects are hypoglycemia and nausea.

Central control of body weight and appetite

CONTEXT

Energy balance is critical for survival and health, and control of food intake is an integral part of this process. This report reviews hormonal signals that influence food intake and their clinical applications.

EVIDENCE ACQUISITION

A relatively novel insight is that satiation signals that control meal size and adiposity signals that signify the amount of body fat are distinct and interact in the hypothalamus and elsewhere to control energy homeostasis. This review focuses upon recent literature addressing the integration of satiation and adiposity signals and therapeutic implications for treatment of obesity.

EVIDENCE SYNTHESIS

During meals, signals such as cholecystokinin arise primarily from the GI tract to cause satiation and meal termination; signals secreted in proportion to body fat such as insulin and leptin interact with satiation signals and provide effective regulation by dictating meal size to amounts that are appropriate for body fatness, or stored energy. Although satiation and adiposity signals are myriad and redundant and reduce food intake, there are few known orexigenic signals; thus, initiation of meals is not subject to the degree of homeostatic regulation that cessation of eating is. There are now drugs available that act through receptors for satiation factors and which cause weight loss, demonstrating that this system is amenable to manipulation for therapeutic goals.

CONCLUSIONS

Although progress on effective medical therapies for obesity has been relatively slow in coming, advances in understanding the central regulation of food intake may ultimately be turned into useful treatment options.

Adrenomedullin is expressed in pancreatic cancer and stimulates cell proliferation and invasion in an autocrine manner via the adrenomedullin receptor, ADMR

The current study investigated adrenomedullin as a potential autocrine regulator of pancreatic cancer cell function. Adrenomedullin was localized in the neoplastic epithelium of 90% (43 of 48) of human pancreatic adenocarcinomas analyzed by immunohistochemistry and was expressed by 100% (8 of 8) of pancreatic cancer cell lines analyzed by reverse transcription-PCR. Pancreatic cancer cell lines also secreted adrenomedullin into the culture medium as determined by ELISA (5 of 5). Exogenous adrenomedullin treatment of Panc-1, BxPC3, and MPanc96 cells in vitro stimulated cell proliferation, invasion, and nuclear factor kappaB activity, indicating the ability of the cells to respond to adrenomedullin. Treatment of the cell cultures with an adrenomedullin antagonist inhibited basal levels of proliferation and nuclear factor kappaB activity, supporting the autocrine function of this molecule. Furthermore, increasing adrenomedullin levels by gene transfer to Panc-1 cells increased, whereas adrenomedullin small hairpin RNA silencing in MPanc96 cells inhibited tumor growth and metastasis in vivo. Adrenomedullin is able to act through at least two different receptors, adrenomedullin receptor (ADMR) and calcitonin receptor-like receptor (CRLR). Reverse transcription-PCR and Western blotting indicated that pancreatic cancer cells expressed only ADMR but not CRLR. In contrast, cells found in the tumor microenvironment, primary human pancreatic stellate and endothelial (HUVEC) cells, expressed both ADMR and CRLR. Small hairpin RNA silencing of ADMR in pancreatic cancer cells blocked adrenomedullin-induced growth and invasion, indicating that this receptor is involved in the autocrine actions of adrenomedullin. These data indicate that adrenomedullin acting via ADMR increases the aggressiveness of pancreatic cancer cells and suggests that these molecules may be useful therapeutic targets.

The pivotal role of CXCL12 (SDF-1)/CXCR4 axis in bone metastasis

Tumor cells are known to adapt to and utilize existing physiological mechanisms to promote survival and metastasis. The role of the microenvironment in the establishment of a metastatic lesion has become increasingly important as several factors secreted by stromal cells regulate metastatic pattern in a variety of tumor types. Tumor cells interact with osteoblasts, osteoclasts and bone matrix to form a vicious cycle that is essential for successful metastases. Here we review the current concepts regarding the role of an important chemokine/chemokine receptor (SDF-1 or CXCL12/CXCR4) pathway in tumor development and metastasis. CXCL12 secretion by stromal cells is known to attract cancer cells via stimulation of the CXCR4 receptor that is up regulated by tumor cells. CXCL12/CXCR4 activation regulates the pattern of metastatic spread with organs expressing high levels of CXCL12 developing secondary tumors (i.e., the bone marrow compartment). CXCL12 has a wide range of effects in regards to tumor development but the primary role of CXCL12 appears to be the mobilization of hematopoietic stem cells and the establishment of the cancer stem-like cell niche where high levels of CXCL12 recruit a highly tumorigenic population of tumor cells and promotes cell survival, proliferation, angiogenesis, and metastasis.

Adrenomedullin inhibits insulin exocytosis via pertussis toxin-sensitive G protein-coupled mechanism

Direct effects of adrenomedullin on insulin secretion from pancreatic beta-cells were investigated using a differentiated insulin-secreting cell line INS-1. Adrenomedullin (1-100 pM) inhibited insulin secretion at both basal (3 mM) and high (15 mM) glucose concentrations, although this inhibitory effect was not observed at higher concentrations of adrenomedullin. The inhibition of glucose-induced insulin secretion by adrenomedullin was restored with 12-h pretreatment with 1 microg/ml pertussis toxin (PTX), suggesting that this effect could be mediated by PTX-sensitive G proteins. Cellular glucose metabolism evaluated by 3-(4,5-dimethyl-2-thiazolyl)-2,5-diphenyl-2H-tetrazolium bromide colorimetric assay was not affected by adrenomedullin at concentrations that inhibited insulin secretion. Moreover, electrophysiological studies revealed that 10 pM adrenomedullin had no effect on membrane potential, voltage-gated calcium currents, or cytosolic calcium concentration induced by 15 mM glucose. Finally, insulin release induced by cAMP-raising agents, such as forskolin plus 3-isobutyl-1-methylxanthine or the calcium ionophore ionomycin, was significantly inhibited by 10 and 100 pM adrenomedullin. In conclusion, adrenomedullin at picomolar concentrations directly inhibited insulin secretion from beta-cells. This effect is likely due to the inhibition of insulin exocytosis through the activation of PTX-sensitive G proteins.

The orphan G-protein coupled receptor RDC1: evidence for a role in chondrocyte hypertrophy and articular cartilage matrix turnover

OBJECTIVE

RDC1 is a class A orphan G-protein coupled receptor of unknown function. The purpose of this study was to identify compound RDC1 agonists and use these as tools to determine the effect of RDC1 activation in human chondrocytes and cartilage explant tissue.

METHODS

Computational chemistry was employed to build a homology model of the RDC1 receptor. A virtual screen of in-house compounds was then performed and positive hits screened for their ability to invoke a Ca2+ response in a recombinant RDC1 HEK293 cell line, as measured by FLIPR. The effect of RDC1 activation on human chondrocytes and cartilage explant gene expression was determined by quantitative real-time polymerase chain reaction (PCR), and these effects validated as being mediated by RDC1 using siRNA antisense.

RESULTS

Tissue expression profiling demonstrated that RDC1 expression was predominant in cartilage tissue. Treatment of human primary chondrocytes with RDC1 agonist induced a Ca2+ response, suggesting the receptor is active in this tissue type. Treatment for 24h with RDC1 agonist led to altered expression of a number of genes associated with chondrocyte hypertrophy and increased matrix degradation in human primary chondrocytes, and elevated total matrix metalloproteinase (MMP) activity in cartilage explant. Transfection with RDC1 siRNA caused a >90% reduction in human primary chondrocyte RDC1 expression and significantly reduced the impact of RDC1 agonist on the previously identified RDC1-regulated genes.

CONCLUSIONS

RDC1 activation in human chondrocytes and cartilage explant leads to changes in gene expression and activity associated with chondrocyte hypertrophy, angiogenesis and increased matrix degradation, suggesting signalling via the RDC1 receptor may play an important role in the early development of osteoarthritis (OA).

Association between endocrine pancreas and ductal system. More than an epiphenomenon of endocrine differentiation and development?

Traditional histological descriptions of the pancreas distinguish between the exocrine and the endocrine pancreas, as if they were two functionally distinct glands. This view has been proven incorrect and can be considered obsolete. Interactions between acinar and islet tissues have been well established through numerous studies that reveal the existence of anatomical and functional relationships between these compartments of the gland. Less attention, however, has traditionally been paid to the relationships occurring between the endocrine pancreas and the ductal system. Associations between islet tissue and ducts are considered by most researchers as only a transient epiphenomenon of endocrine development. This article reviews the evidence that has emerged in the last 10 years demonstrating the existence of stable, close, and systematic relationships between these two pancreatic compartments. Functional and pathophysiological implications are considered, and the existence of an "acinar-duct-islet" axis is put forward. The pancreas appears at present to be an integrated organ composed of three functionally related components of well-orchestrated endocrine and exocrine physiological responses.

Development of angiotensin II-induced hypertension: role of CGRP and its receptor

OBJECTIVE

To determine the role of endogenous calcitonin gene-related peptide (CGRP) and its receptor in development of angiotensin II (Ang II)-induced hypertension.

DESIGN AND METHODS

Seven-week-old male Wistar rats were given either Ang II (100 ng/kg per min) or saline via mini osmotic pumps with or without minoxidil (9 mg/kg per day) in their drinking water for 10 days. Mean arterial pressure (MAP) and its response to alpha-CGRP (1 microg/kg, iv) and its receptor antagonist, CGRP(8-37) (1 mg/kg, iv), were determined in conscious and unrestrained rats. Radioimmunoassay and Western blotting were employed, respectively, to determine CGRP levels in plasma and dorsal root ganglia (DRG) and CGRP receptor protein content in mesenteric arteries.

RESULTS

After the 10-day treatment, MAP was higher in the Ang II group compared to control (Con), control plus minoxidil (Con-Min), and Ang II plus minoxidil (Ang II-Min) (P < 0.01). CGRP decreased MAP in the Ang II group compared to Con, Con-Min and Ang II-Min rats (P < 0.01). In contrast, CGRP8-37 increased MAP in Con-Min and Ang II-Min groups compared with Con and Ang II groups (P < 0.01). Radioimmunoassay showed that CGRP levels in plasma and DRG were not different among the four groups. Western blots showed that calcitonin receptor-like receptor (CRLR) and receptor activity-modifying protein 1 (RAMP1), which constitute a CGRP receptor, were significantly upregulated in mesenteric arteries in the Ang II group compared to the other three groups (P < 0.05).

CONCLUSION

These data indicate that long-term Ang II infusion is accompanied by an increase in CGRP receptor expression in mesenteric arteries but not in CGRP levels in plasma and DRG. The increase in mesenteric CGRP receptor expression appears to be pressure dependent and to enhance the blood pressure response to CGRP. Minoxidil enhances the hypertensive effect of CGRP8-37 to the same degree in control and Ang II-treated rats, indicating that this KATP channel activator sensitizes the blood pressure response regardless of the baseline pressure while CGRP receptors are blocked.

Amylin agonists: a novel approach in the treatment of diabetes

Amylin is a peptide hormone that is cosecreted with insulin from the pancreatic beta-cell and is thus deficient in diabetic people. It inhibits glucagon secretion, delays gastric emptying, and acts as a satiety agent. Amylin replacement could therefore possibly improve glycemic control in some people with diabetes. However, human amylin exhibits physicochemical properties predisposing the peptide hormone to aggregate and form amyloid fibers, which may play a part in beta-cell destruction in type 2 diabetes. This obviously makes it unsuitable for pharmacological use. A stable analog, pramlintide, which has actions and pharmacokinetic and pharmacodynamic properties similar to the native peptide, has been developed. The efficacy and safety of pramlintide administration has been tested in a vast number of clinical trials. Approximately 5,000 insulin-treated patients have received pramlintide and approximately 250 for > or =2 years. The aims of this review are to 1) briefly describe actions of amylin as demonstrated in animal and human models and 2) primarily review results from clinical trials with the amylin analog pramlintide.

Human osteoblast-like cell proliferation induced by calcitonin-related peptides involves PKC activity

The calcitonin peptides [calcitonin (CT), calcitonin gene-related peptide (CGRP), amylin] share many biological actions, including activity on bone cells. In the present study, CT (10(-11) to 10(-9) M) stimulated [(3)H]thymidine incorporation in primary cultures of human osteoblasts (hOB), as already demonstrated for CGRP and amylin. RT-PCR analysis showed that the calcitonin receptor and the calcitonin receptor-like receptor are both expressed in hOB. In these cells, CT (10(-10) M) and amylin (10(-9) M), in contrast to CGRP (10(-8) M), did not increase cAMP production. All three peptides stimulated protein kinase C (PKC) activity. To evaluate PKC involvement in hOB proliferation, cells were incubated with phorbol 12,13-dibutyrate, a stimulator of PKC activity; cell proliferation was increased in a dose-dependent manner (EC(50) = 3.4 x 10(-8) M). Staurosporine (10(-9) M), a PKC inhibitor, blocked phorbol 12,13-dibutyrate-induced PKC activity and cell proliferation. Inhibition of PKC by staurosporine also counteracted the stimulatory effect of CT, CGRP, and amylin on hOB proliferation. From these data, it is deduced that the activation of PKC is important for hOB proliferation and that it is involved in the anabolic effect of CT peptides on bone.

Adrenomedullin: expression and possible role in human skin and hair growth

BACKGROUND

Adrenomedullin (AM) is a regulatory peptide that is synthesized and secreted by a wide number of cells and tissues. AM is a potent vasodilator, but also exerts other functions, such as regulating cell growth and antimicrobial defence. Two receptors, L1 and calcitonin receptor-like receptor (CRLR), which are able to bind AM, have been cloned and characterized.

OBJECTIVES

To investigate expression of AM protein and its receptors in human skin and during different stages of the human hair cycle and, moreover, because of the suggested antimicrobial function of AM in skin, to investigate AM immunoreactivity (IR) in inflammatory acne lesions compared with healthy pilosebaceous follicles.

METHODS

We used immunohistochemistry to determine the distribution of AM and its receptors in human skin and during different stages of the human hair cycle. AM IR in inflammatory acne lesions was investigated to evaluate the antimicrobial function of the protein, and hair follicle cultures were performed to examine the role of AM in differentiation and proliferation of hair follicle keratinocytes.

RESULTS

Strong IR for AM and its receptors was present in the suprabasal epidermis, in the melanocytes of the epidermis, and in sweat and sebaceous glands. In the hair follicle, AM protein was strongly expressed in the basal and suprabasal layers of the hair bulb and the proximal outer root sheath (ORS). In the distal ORS, AM expression was increasingly suprabasal, especially in proximity to the bulge region where the basal cell layer was free of IR. IR for the CRLR revealed a similar expression pattern to that seen for AM. In contrast, L1 IR showed a suprabasal pattern of IR throughout the ORS. Similar expression of AM and its receptors was observed in catagen and early anagen follicles. AM expression was not markedly upregulated in acne lesions, suggesting a minor role for this antimicrobial peptide in acne. Despite its well-documented mitogenic effects, particularly in oral and skin keratinocytes, AM had no significant effect on hair follicle growth in vitro.

CONCLUSIONS

AM and its receptors are expressed in human hair follicles, and both AM and its receptors are colocalized in the same compartments and cell types of the skin. This finding is consistent with the proposed autocrine/paracrine mechanism in the physiology of AM.

Amylin, released from the gastric fundus, stimulates somatostatin and thus inhibits histamine and acid secretion in mice

BACKGROUND & AIMS

Amylin, a peptide that displays 50% homology with calcitonin gene-related peptide (CGRP), is colocalized with somatostatin in endocrine cells of the gastric fundus. The present study was designed to determine the mechanism of action of amylin on gastric exocrine and endocrine secretion.

METHODS

Acid secretion was measured in the isolated mouse stomach by titration. Somatostatin and histamine secretion were measured in rat fundic segments by radioimmunoassay.

RESULTS

In isolated mouse stomach, amylin caused a concentration-dependent decrease in acid secretion. In rat fundic segments, amylin and CGRP each caused a concentration-dependent increase in somatostatin and a decrease in histamine secretion. Changes in histamine secretion induced by amylin reflected changes in somatostatin secretion and could be abolished by addition of somatostatin antibody. Both the somatostatin and the histamine responses to amylin were abolished by the selective amylin antagonist AC187 but were unaffected by the CGRP antagonist CGRP8-37. In contrast, the responses to CGRP were abolished by CGRP8-37 but were unaffected by AC187. AC187 alone decreased somatostatin and increased histamine in fundic segments and increased acid secretion in isolated stomach, indicating that endogenous amylin participates in the regulation of gastric endocrine (somatostatin and histamine) and exocrine (acid) secretion.

CONCLUSIONS

In gastric fundus, release of amylin from somatostatin cells interacts with distinct amylin receptors to enhance somatostatin secretion via an autocrine pathway that leads to inhibition of histamine and acid secretion.

Adrenomedullin as a pancreatic hormone

Adrenomedullin (AM) is a multiregulatory peptide which is expressed in a wide range of tissues. In the pancreas, AM was first found in mammals, including man, and its colocalization with the pancreatic polypeptide (PP) was established in islet F cells. In addition, three different AM receptors have been characterized in B-cells. AM has been also located in the pancreatic cells of other vertebrate classes. The frequency and distribution of AM cells vary between different animals; they can be found scattered among the exocrine tissue, in the islets, or in ductal epithelia. The colocalization of AM with other hormones presents different patterns, although in birds, as in mammals, it seems to colocalize only with PP. The best-determined pancreatic AM function is the inhibition of insulin secretion in B-cells, which seems to be linked to a recently discovered binding protein, factor H. In relation to this physiological role, clinical data show that AM is raised in some groups of both types I and II diabetic patients and AM might have triggered the disease in a subset of them. On the other hand, AM pancreatic cells are also involved in the response to septic shock by increasing AM circulating levels. A third putative function is the inhibition of amylase secretion by the exocrine pancreatic cells. AM has been found in embryonic mammalian pancreas from the earliest stages of the development, colocalizing with all pancreatic hormones, although in adults only coexpression with PP is kept. AM may play a role in the growth and morphogenesis of the pancreas.

Neutralization of adrenomedullin inhibits the growth of human glioblastoma cell lines in vitro and suppresses tumor xenograft growth in vivo

Presently, there is no effective treatment for glioblastoma, the most malignant and common brain tumor. Growth factors are potential targets for therapeutic strategies because they are essential for tumor growth and progression. Peptidylglycine alpha-amidating monooxygenase is the enzyme producing alpha-amidated bioactive peptides from their inactive glycine-extended precursors. The high expression of peptidylglycine alpha-amidating monooxygenase mRNA in glioblastoma and glioma cell lines points to the involvement of alpha-amidated peptides in tumorigenic growth processes in the brain. After screening of amidated peptides, it was found that human glioblastoma cell lines express high levels of adrenomedullin (AM) mRNA, and that immunoreactive AM is released into the culture medium. AM is a multifunctional regulatory peptide with mitogenic and angiogenic capabilities among others. Real-time quantitative reverse transcriptase-polymerase chain reaction analysis showed that AM mRNA was correlated to the tumor type and grade, with high expression in all glioblastomas analyzed, whereas a low expression was found in anaplastic astrocytomas and barely detectable levels in low-grade astrocytomas and oligodendrogliomas. In the present study we also demonstrate the presence of mRNA encoding the putative AM receptors, calcitonin receptor-like receptor/receptor activity-modifying protein-2 and -3 (CRLR/RAMP2; CRLR/RAMP3) in both glioma tissues and glioblastoma cell lines and further show that exogenously added AM can stimulate the growth of these glioblastoma cells in vitro. These findings suggest that AM may function as an autocrine growth factor for glioblastoma cells. One way to test the autocrine hypothesis is to interrupt the function of the endogenously produced AM. Herein, we demonstrate that a polyclonal antibody specific to AM, blocks the binding of the hormone to its cellular receptors and decreases by 33% (P < 0.001) the growth of U87 glioblastoma cells in vitro. Intratumoral administration of the anti-AM antibody resulted in a 70% (P < 0.001) reduction in subcutaneous U87 xenograft weight 21 days after treatment. Furthermore, the density of vessels was decreased in the antibody-treated tumors. These findings support that AM may function as a potent autocrine/paracrine growth factor for human glioblastomas and demonstrate that inhibition of the action of AM (produced by tumor cells) may suppress tumor growth in vivo.

Neurotoxicant-induced elevation of adrenomedullin expression in hippocampus and glia cultures

Adrenomedullin (AM), a vasoactive peptide first isolated from pheochromocytoma, has been reported to be present in neurons in the central nervous system and in tumors of neural and glial origin. In this study, we investigated AM expression both in the hippocampus and in glial cell cultures using a chemical-induced model of injury. An acute intraperitoneal injection of the organometal trimethyltin (TMT) results in neurodegeneration of the hippocampal CA3-4 pyramidal cell layer. Within 4 days of injection, sparse, punctate staining for AM and lectin was evident in the CA3-4 region; by 10 days, a minimal level of CA3-4 neuronal degeneration was evident, with an increase in glial fibrillary acidic protein (GFAP)-positive astrocytes throughout the hippocampus. Degeneration progressed in severity until 30 days post-TMT, with distinct positive immunoreactivity for AM in the CA4 region. mRNA levels for tumor necrosis factor (TNF)-alpha, interleukin (IL)-1alpha, GFAP, and AM in the hippocampus were increased over control levels within 4 days following TMT. In cultured glial cells, a 6 hr exposure to TMT (10 microM) produced a morphological response of the cells and increased immunoreactivity for vimentin, GFAP, and AM. mRNA levels for TNFalpha, IL-1alpha, GFAP, vimentin, and AM were elevated within 3-6 hr of exposure. In culture, neutralizing antibodies to IL-1alpha and TNFalpha were effective in inhibiting the TMT-induced elevation of AM mRNA. These data suggest an interaction between the proinflammatory cytokines and glia response in the regulation of AM in response to injury.

Novel actions of proadrenomedullin N-terminal 20 peptide (PAMP)

Poadrenomedullin N-terminal 20 peptide (PAMP) is a hypotensive peptide derived from the precursor of adrenomedullin. We identified novel actions of proadrenomedullin N-terminal 20 peptide (PAMP) on blood glucose, food intake and gastric emptying after exogenous administration. PAMP elevated blood glucose levels after central injection in fasted mice. PAMP had affinity for bombesin (BN) receptor and the hyperglycemic effect of PAMP was blocked by a BN antagonist, indicating that the elevation of blood glucose after central administration of PAMP was mediated by BN receptor. Centrally administered PAMP inhibited food intake and gastric emptying in fasted conscious mice. However, studies using a BN antagonist and BN receptor knockout mice suggested that the inhibitory effects of PAMP on feeding and gastric emptying were mediated not via BN receptor but via another receptor specific for PAMP. In the present review, we summarize these effects of PAMP and report other novel actions of PAMP on body temperature and oxygen consumption. In addition, the mechanism underlying the cardiovascular functions of PAMP is discussed.

Amylin receptor agonists: a novel pharmacological approach in the management of insulin-treated diabetes mellitus

Amylin is a peptide hormone which is co-secreted with insulin from the pancreatic beta-cell. Type 1 diabetic individuals and some Type 2 diabetic individuals are characterised by amylin deficiency. Animal experiments have revealed several actions of amylin on intermediary metabolism, of these some have been demonstrated to be of potential physiological relevance in humans. In particular amylin appears to have important actions in controlling prandial glucose homeostasis. The peptide hormone inhibits postprandial glucagon secretion and delays gastric emptying thereby modifying postprandial hyperglycaemia in diabetic individuals which presumably adds to overall glycaemic control without a concomitant increase in the number of severe hypoglycaemic episodes. Moreover, amylin acts as a satiety agent. Amylin replacement may therefore improve glycaemic control in diabetes mellitus. However, human amylin exhibits physicochemical properties predisposing the peptide hormone to aggregate and form amyloid fibres, which makes it unsuitable for pharmacological use. A stable analogue, pramlintide, with actions and pharmacokinetic and pharmacodynamic properties similar to the native peptide has therefore been developed. The efficacy and safety of pramlintide administration to diabetic individuals have been tested in a large number of clinical trials. It is the aim of this review to describe possible (patho)physiological actions of amylin as demonstrated in animal and human models, to discuss the background for potential amylin (analogue) replacement in diabetes mellitus and to review results from clinical trials with the amylin receptor analogue pramlintide.