Immunostaining for vasostatin I distinguishes between ileal and lung carcinoids

Vasostatin-1: A novel circulating biomarker for ileal and pancreatic neuroendocrine neoplasms

Background

Chromogranin A (CgA) is a plasma biomarker widely used in the follow-up of patients with neuroendocrine neoplasms (NENs). However, its accuracy as a tumor biomarker is relatively low because plasma CgA can increase also in patients with other diseases or in subjects treated with proton-pump inhibitors (PPIs), a class of widely-used drugs.

Methods

In the attempt to identify a more reliable biomarker for NENs, we investigated, by ELISA, the circulating levels of full-length CgA (CgA_1-439) and of various CgA-derived fragments in 17 patients with ileal or pancreatic NENs, 10 healthy controls, and 21 healthy volunteers before and after treatment with PPIs.

Results

Patients with ileal or pancreatic NENs showed increased plasma levels of total-CgA and CgA_1-76 fragment (vasostatin-1, VS-1) compared to controls [median (25^th-75^th-percentiles); total-CgA: 1.85 nM (1.01–4.28) vs 0.75 nM (0.52–0.89), p = 0.004; VS-1: 2.76 nM (1.09–7.10) vs 0.29 nM (0.26–0.32), p<0.001, respectively], but not of CgA_1-439 or CgA_1-373 fragment. VS-1 positively correlated with total-CgA (r = 0.65, p<0.001). The Receiver Operating Characteristic area under the curve was 0.9935 for VS-1 and 0.8824 for total-CgA (p = 0.067). Treatment of patients with somatostatin analogues decreased both total-CgA and VS-1. In contrast, administration of PPIs increased the plasma levels of total-CgA, but not of VS-1.

Conclusion

These findings suggest that plasma VS-1 is a novel biomarker for ileal and pancreatic NENs. Considering that VS-1 is a well-defined fragment not induced by proton-pump inhibitors, this polypeptide might represent a biomarker for NENs diagnosis and follow-up more accurate and easier to standardize than CgA.

Characterization and plasma measurement of the WE-14 peptide in patients with pheochromocytoma

Granins and their derived peptides are valuable circulating biological markers of neuroendocrine tumors. The aim of the present study was to investigate the tumoral chromogranin A (CgA)-derived peptide WE-14 and the potential advantage to combine plasma WE-14 detection with the EM66 assay and the existing current CgA assay for the diagnosis of pheochromocytoma. Compared to healthy volunteers, plasma WE-14 levels were 5.4-fold higher in patients with pheochromocytoma, but returned to normal values after surgical resection of the tumor. Determination of plasma CgA and EM66 concentrations in the same group of patients revealed that the test assays for these markers had an overall 84% diagnostic sensitivity, which is identical to that determined for WE-14. However, we found that WE-14 measurement improved the diagnostic sensitivity when combined with the results of CgA or EM66 assays. By combining the results of the three assays, the sensitivity for the diagnosis of pheochromocytoma was increased to 95%. In fact, the combination of WE-14 with either CgA or EM66 test assays achieved 100% sensitivity for the diagnosis of paragangliomas and sporadic or malignant pheochromocytomas if taken separately to account for the heterogeneity of the tumor. These data indicate that WE-14 is produced in pheochromocytoma and secreted into the general circulation, and that elevated plasma WE-14 levels are correlated with the occurrence of this chromaffin cell tumor. In addition, in association with other biological markers, such as CgA and/or EM66, WE-14 measurement systematically improves the diagnostic sensitivity for pheochromocytoma. These findings support the notion that granin-processing products may represent complementary tools for the diagnosis of neuroendocrine tumors.

Succinate dehydrogenase B subunit immunohistochemical expression predicts aggressiveness in well differentiated neuroendocrine tumors of the ileum

Immunohistochemical loss of the succinate dehydrogenase subunit B (SDHB) has recently been reported as a surrogate biomarker of malignancy in sporadic and familial pheocromocytomas and paragangliomas through the activation of hypoxia pathways. However, data on the prevalence and the clinical implications of SDHB immunoreactivity in ileal neuroendocrine tumors are still lacking. Thirty-one consecutive, advanced primary midgut neuroendocrine tumors and related lymph node or liver metastases from 24 males and seven females were immunohistochemically assessed for SDHB. All patients were G1 tumors (Ki-67 labeling index ≤2%). SDHB immunohistochemistry results were expressed as immunostaining intensity and scored as low or strong according to the internal control represented by normal intestinal cells. Strong positivity for SDHB, with granular cytoplasmatic reactivity, was found in 77% of primary tumors (T), whilst low SDHB expression was detected in 90% of metastases (M). The combined analysis (T+M) confirmed the loss of SDHB expression in 82% of metastases compared to 18% of primary tumors. SDHB expression was inversely correlated with Ki-67 labeling index, which accounted for 1.54% in metastastic sites and 0.7% in primary tumors. A correlation between SDHB expression loss, increased Ki-67 labeling index and biological aggressiveness was shown in advanced midgut neuroendocrine tumors, suggesting a role of tumor suppressor gene.

Immunohistochemical and biochemical studies with region-specific antibodies to chromogranins A and B and secretogranins II and III in neuroendocrine tumors

This short review deals with our investigations in neuroendocrine tumors (NETs) with antibodies against defined epitopes of chromogranins (Cgs) A and B and secretogranins (Sgs) II and III. The immunohistochemical expression of different epitopes of the granin family of proteins varies in NE cells in normal human endocrine and non-endocrine organs and in NETs, suggesting post-translational processing. In most NETs one or more epitopes of the granins were lacking, but variations in the expression pattern occurred both in benign and malignant NETs. A few epitopes displayed patterns that may be valuable in differentiating between benign and malignant NET types, e.g., well-differentiated NET types expressed more CgA epitopes than the poorly differentiated ones and C-terminal secretoneurin visualized a cell type related to malignancy in pheochromocytomas. Plasma concentrations of different epitopes of CgA and CgB varied. In patients suffering from carcinoid tumors or endocrine pancreatic tumors the highest concentrations were found with epitopes from the mid-portion of CgA. For CgB the highest plasma concentrations were recorded for the epitope 439-451. Measurements of SgII showed that patients with endocrine pancreatic tumors had higher concentrations than patients with carcinoid tumors or pheochromocytomas. SgIII was not detectable in patients with NETs.

Granins and granin-related peptides in neuroendocrine tumours

This review focus on neuroendocrine tumours (NETs), with special reference to the immunohistochemical analysis of granins and granin-related peptides and their usefulness in identifying and characterizing the great diversity of NET types. Granins, their derived peptides, and complex protein-processing enzyme systems that cleave granins and prohormones, have to some extent cell-specific expression patterns in normal and neoplastic NE cells. The marker most commonly used in routine histopathology to differentiate between non-NETs and NETs is chromogranin (Cg) A, to some extent CgB. Other members of the granin family may also be of diagnostic value by identifying special NET types, e.g. secretogranin (Sg) VI was only found in pancreatic NETs and phaeochromocytomas. SgIII has recently arisen as an important NET marker; it was strongly expressed in NETs, with some exceptions--phaeochromocytomas expressed few cells and parathyroid adenomas none. Some expression patterns of granin-related peptides seem valuable in differentiating between some benign and malignant NETs, some may also provide prognostic information, among which: well-differentiated NET types expressed more CgA epitopes than the poorly differentiated ones, except insulinomas, where the opposite was noted; medullary thyroid carcinomas containing few cells immunoreactive to a CgB antibody were related to a bad prognosis; C-terminal secretoneurin visualized a cell type related to malignancy in phaeochromocytomas. Further research will probably establish new staining patterns with marker functions for granins in NETs which may be of histopathological diagnostic value.

Granin-derived peptides as diagnostic and prognostic markers for endocrine tumors

Chromogranin A-like immunoreactivity (CgA-LI) has been, and remains, the most widely used diagnostic and prognostic marker for endocrine tumors. The availability of assay kits combined with moderately high sensitivity and specificity has meant that there has been no great incentive to develop alternative markers. However, circulating concentrations of CgA-LI are elevated in several non-neoplastic diseases and in patients receiving acid-suppression therapy which may lead to false positive diagnosis. Additionally, certain endocrine tumors, such as rectal carcinoids, do not express the CgA gene so that there is a need for additional markers to complement CgA measurements. Plasma concentrations of the CgA-derived peptide, pancreastatin, measured with antisera of defined regional specificity, have a prognostic value in patients with metastatic midgut carcinoid tumors receiving somatostatin analog therapy or hepatic artery chemoembolization. Other CgA-derived peptides with potential as tumor markers are vasostatin-1, WE-14, catestatin, GE-25, and EL-35 but their value has yet to be fully assessed. Circulating concentrations of chromogranin B-like immunoreactivity (CgB-LI) are not elevated in non-neoplastic diseases and measurements of CCB, the COOH-terminal fragment of CgB, may be useful as a biochemical marker for neuroendocrine differentiation in lung tumors. Antisera to the secretogranin II-derived peptide, secretoneurin detects carcinoid tumors of the appendix with greater frequency than antisera to CgA and are of value in identifying therapy-resistant carcinoma of the prostate (clinical stage D3). Measurement of concentrations of a second secretogranin II-derived peptide, EM-66 in tumor tissue has been used to differentiate between benign and malignant pheochromocytoma. These examples point to a limited although potentially valuable role for granin-derived peptides as tumor markers.

Expression of amino acid sequences of the chromogranin A molecule and synaptic vesicle protein 2 in neuroendocrine tumors of the lung

Chromogranin A (CgA) and its valuable complement synaptic vesicle protein 2 (SV2) are neuroendocrine (NE) markers. Post-translational processing of CgA has been reported to vary in different NE cell types and tumors, but little is known regarding the expression of various CgA epitopes and SV2 in NE pulmonary tumors. We studied the immunoreactivity to six CgA epitopes and SV2 in ten typical (TC) and ten atypical (ACT) carcinoids, five large-cell NE carcinomas (LCNEC) and five small-cell carcinomas (SCLC), also comparing the results with clinicopathological characteristics of tumors. The sequences CgA 17--38 (vasostatin), 176--195 (chromacin), 375--384 (parastatin) and 411--424 (C-terminal parastatin) and SV2 were relevant markers for the CT/ATC group, whereas the antibody to CgA 176--195 was a better marker for the LCNEC/SCLC group. An inverse correlation was found between proliferative activity and granule-related markers in the CT/ACT group, and a direct correlation in poorly differentiated tumors. The expression of granule-related markers did not correlate with hormone content or clinical characteristics of NE tumors. The expression of CgA epitopes and SV2 occurs in all NE tumors, differing between better differentiated and poorly differentiated tumors but not within the respective groups.

An investigation into the role of Bcl-2 in neuroendocrine differentiation

INTRODUCTION

In addition to its role in apoptosis suppression, Bcl-2 has been reported to be co-expressed with neuroendocrine markers in several tissues, leading to speculation that this oncoprotein may promote neuroendocrine differentiation.

AIM

This study investigated whether Bcl-2 modulated neuroendocrine biopeptide expression.

METHODS

Levels of chromogranin A, neurone specific enolase, protein gene peptide 9.5, pancreatic polypeptide, and the chromogranin-derived peptides, intervening peptide and vasostatin-1 were examined by immunocytochemistry in rat phaeochromocytoma (PC12) cell lines genetically engineered to over-express Bcl-2 and their mock-transfected controls. Intensity of fluorescence was graded using a semi-quantitative scale from (-) indicating negative expression to (+++) indicating intense positivity.

RESULTS

Mann-Whitney U analysis indicated that no significant differences in expression existed between control and Bcl2 over-expressing cell lines for any of the six peptides examined.

CONCLUSIONS

The results of this study do not support the hypothesis that Bcl-2 promotes the acquisition of a neuroendocrine phenotype.

Chromogranin a processing in human pituitary adenomas and carcinomas: analysis with region-specific antibodies

The expression of various chromogranin A (CgA) peptide fragments was examined with region-specific antisera in benign and malignant pituitary tumors. Analysis of the proconvertases responsible for proteolytic processing of CgA, prohormone convertase 1/3 (PC1/3), and PC2 was also performed. Adenomas were studied using tissue microarrays, and a larger tissue section of a subset of the prolactin (PRL) adenomas was used to compare to the tissue microarray analysis. Carcinomas were analyzed using larger tissue sections. There were differences in CgA proteolytic products detected between the functional (PRL, adrenocorticotropic hormone [ACTH], and growth hormone tumors and the nonfunctional (gonadotroph and null cell) tumors, with the former group expressing lower levels of many peptides. These differences were most notable in the PRL adenomas and carcinomas in which the region-specific antisera against vasostatin I and vasostatin II detected these fragments in the lowest percentage of tumors and/or had the weakest immunoreactivity. The CgA peptide fragment detected by CgA 176-195 (chromacin) antiserum was expressed by the highest percentage of most functional and nonfunctional benign and malignant pituitary tumors. ACTH carcinomas (n = 3) were more strongly immunoreactive compared to the ACTH adenomas. These results show that there is differential expression of CgA peptide fragments and PC1/3 among different types of pituitary tumors and that ACTH pituitary carcinomas have higher levels of immunoreactive CgA peptide fragments compared to ACTH adenomas. This study also shows the utility of tissue microarrays in the analysis of a large group of tumors with regionspecific antisera.

Chromogranin A in human neuroendocrine tumors: an immunohistochemical study with region-specific antibodies

Antibodies to six specific regions of the chromogranin A (CgA) molecule were used to study their immunoreactivity in human neuroendocrine (NE) tumors. Tissue specimens from endocrine pancreatic tumors (n = 14), duodenal carcinoids (n = 2), bronchial carcinoids (n = 5), ileal carcinoids (n = 5) appendix carcinoids (n = 2), medullary thyroid carcinomas (n = 6), parathyroid adenomas (n = 2), and pheochromocytomas (n = 8) were analyzed. The results showed that the NE tumor types expressed varying numbers of CgA fragments. A variation in frequency of the expression of immunoreactive cells was sometimes seen also within the same tumor type. The midportion fragment CgA 176-195 (chromacin) was the only fragment expressed in all tumors. Benign and malignant tumors expressed different patterns, being especially true of insulinomas and pheochromocytomas. These findings suggest that region-specific antibodies to CgA fragments can be used as a diagnostic tool for the characterization of NE tumors.