How sensitive and specific is measurement of plasma chromogranin A for the diagnosis of neuroendocrine neoplasia?

The biochemical utility of chromogranin A, chromogranin B and cocaine- and amphetamine-regulated transcript for neuroendocrine neoplasia

Neuroendocrine neoplasia (NEN) is a heterogeneous group of tumours and often represents a therapeutic challenge to clinicians. The peptides chromogranin A (CgA), chromogranin B (CgB) and cocaine- and amphetamine-regulated transcript (CART) are widely distributed throughout the neuroendocrine system. CgA and CgB have been used as general NEN biomarkers for many years, while CART has only recently been identified. Of these biomarkers, CgA is the most commonly used. However, circulating CgA concentrations exhibit considerable intra-individual biological variation, are altered by proton pump inhibitors (PPIs) and somatostatin analogues and are elevated in non-NEN malignancies. Therefore, interpretation of CgA results must be in the context of these confounding factors. The effects of treatment and non-NEN conditions on circulating CgB and CART concentrations are less well understood. CgB is less affected by impaired renal function and PPIs than CgA; while, circulating CART concentrations lack a diurnal variation in humans and are more reliable markers of pancreatic NEN malignancy than CgA. The utility of circulating CgA measurements in NEN prognosis, surveillance and disease recurrence has been widely investigated. However, the utility of CgB and CART in NEN management is yet to be elucidated. Further studies are needed to establish whether CgB and CART are useful alternatives to CgA.

Plasma Chromogranin A in Patients with Prostate Cancer Improves the Diagnostic Efficacy of Free/Total Prostate-Specific Antigen Determination

INTRODUCTION

We ascertained whether plasma chromogranin A enhances the power of serology assessing prostate cancer (PC).

MATERIALS AND METHODS

We studied 56 PC and 83 benign prostatic hyperplasia (BPH) patients. In the sera we measured total prostate-specific antigen (tPSA) and free PSA (fPSA) and calculated the ratio between fPSA and tPSA (f/tPSA). In plasma samples the levels of chromogranin A (CgA) were also assayed.

RESULTS

PC patients had higher CgA (p < 0.005) and tPSA (p < 0.05) levels, and a lower f/tPSA ratio (p < 0.001), than BPH patients. When f/tPSA and CgA were combined, the diagnostic sensitivity was enhanced (57-73%), while the specificity had only an 8% reduction (from 89 to 80%). CgA was only correlated to the Gleason PC score (p < 0.05).

CONCLUSIONS

CgA determination in PC may enhance the diagnostic accuracy of the f/tPSA assay and provides useful information on the tumor grade.

Chromogranin A, a significant prognostic factor in small cell lung cancer

Chromogranin A (CgA) is a protein present in neuroendocrine vesicles. Small cell lung cancer (SCLC) is considered a neuroendocrine tumour. It is possible to demonstrate CgA expression in SCLC by immunohistochemical methods. Since CgA is released to the circulation it might also work as a clinical tumour marker. We used a newly developed two-site enzyme-linked immunosorbent assay for CgA in plasma from 150 newly diagnosed patients with SCLC. Follow-up was for a minimum of 5 years. Thirty-seven per cent of the patients had elevated pretreatment values and the values were significantly related to stage of disease. Multivariable analysis by Cox's proportional hazard model including nine known prognostic factors disclosed performance status as the most influential prognostic factor followed by stage of disease, CgA and LDH. A simple prognostic index (PI) could be established based on these four pretreatment features. In this way the patients could be separated into three groups with significant different prognosis. The median survival and 95% confidence intervals for the three groups were as follows: 424 days (311-537), 360 days (261-459) and 174 days (105-243).

Application of region-specific immunoassay for human chromogranin A: substantial clue for detection and measurement of chromogranin A in human plasma

Chromogranin A (CgA), a secretory protein, is co-released with catecholamines from storage vesicles. It is known to be elevated in the circulation of patients with neuroendocrine and endocrine tumors. For further investigation of the protein, especially in humans, it is essential to facilitate quantitative analysis of the protein in human biological materials. In order to introduce novel immunological methodology for this purpose, we purposely selected human CgA(344-374) for the synthetic immunogen to produce region-specific CgA antibodies. The anti-synthetic peptide antibody thus obtained made it possible to develop an immunological method for measurement and characterization of CgA in human plasma. The plasma CgA-immunoreactivity (LI) level measured by the method was 0.31+/-0.01 pmol/ml (mean+/-SEM) in normal subjects and 1.55+/-0.29 pmol/ml in pheochromocytoma. On gel chromatography and HPLC analysis of the plasma of patients with pheochromocytoma, the region-specific assay system enabled us to show the presence of N-terminal truncated CgA, besides CgA itself. By following up changes of plasma CgA-LI in a pheochromocytoma patient using samples that were collected consecutively over a two-year period, the present assay system using the region-specific antibody, anti-human CgA (344-374) serum, was confirmed to be extremely valuable for the measurement of CgA-LI in human plasma. The characteristic features and high sensitivity of the present assay system will give us a substantial clue to the detection and measurement of CgA to develop further investigation of the protein in humans.

Usefulness of chromogranin A as a marker for detection of relapses of carcinoid tumours

It is well known that peptide-producing endocrine tumours cosecrete immunoreactive chromogranin A with their characteristic hormones. Into this study 187 patients with the diagnosis malignant carcinoids or other malignancies were entered. Using chromogranin A at a cut-off level of 30.3 U/ml it was possible to discriminate between patients in remission and patients suffering a relapse with a sensitivity of 91.7% and a specificity of 96.4%, which may be of important diagnostic value. In our study that lasted over one year we could clearly show that the measurement of chromogranin A is impressively superior to 5-hydroxyindoleacetic-acid for detecting a relapse of carcinoids.

Plasma chromogranin A in prostatic carcinoma and neuroendocrine tumors

PURPOSE

Chromogranin A is a good tumor marker for neuroendocrine cells. Whether plasma chromogranin A could be a useful marker for neuroendocrine differentiation of prostatic carcinoma and neuroendocrine tumors was investigated using an enzyme-linked immunosorbent assay.

MATERIALS AND METHODS

Plasma levels of chromogranin A were measured by enzyme-linked immunosorbent assay in 33 patients with prostatic carcinoma, 10 with benign prostatic hyperplasia (BPH) and 13 with neuroendocrine tumors (2 medullary thyroid carcinomas, 1 thymic carcinoid, 1 gastrin producing duodenal carcinoid, 3 nonfunctioning pancreatic endocrine tumors, 2 neuroblastomas, 3 pheochromocytomas and 1 carotid body tumor).

RESULTS

The normal level of chromogranin A from 40 healthy volunteers was 30 +/- 11 units per 1. (mean plus or minus standard deviation). Mean plasma chromogranin A in patients with BPH and prostatic carcinoma was 52.4 +/- 12.9 and 67.5 +/- 22.9 units per 1., respectively. All patients with neuroendocrine tumors, except 1 with a nonfunctioning pancreatic endocrine tumor, had elevated chromogranin A (mean 401 +/- 409 units per 1.). There were significant differences in plasma chromogranin A level between patients with BPH and neuroendocrine tumors (p < 0.01), prostatic carcinoma and neuroendocrine tumors (p < 0.01), and BPH and prostatic carcinoma (p < 0.05). Of the 33 patients with prostatic carcinoma 5 had elevated chromogranin A, only 1 of whom had elevated prostate specific antigen.

CONCLUSIONS

Chromogranin A is an excellent marker for neuroendocrine tumors, particularly nonfunctioning tumors, and measurement of chromogranin A is also useful to detect prostatic carcinoma in patients whose prostate specific antigen is not elevated.

Characterisation of circulating chromogranin A in human cancer patients

The structure of circulating chromogranin A (CgA) of phaeochromocytoma patients was characterised and compared with that of CgA extracted from tumours. Size exclusion chromatography experiments provided evidence that CgA is present in the blood of different patients, as well as in tumour extracts, as multiple forms having different hydrodynamic sizes of 600 kDa (CgA-I), 100 kDa (CgA-II) and 55 kDA (CgA-III). The amount of each CgA form as a proportion of the total antigenic material was different in different patients. Western blot analysis of chromatographic fractions indicated that these forms are made up by polypeptides of similar molecular weight (about 60-70 kDa). All CgA forms express the epitopes recognised by two monoclonal antibodies (A11 and B4E11), directed against residues 68-70 and 81-90 of human CgA. However, their relative immunoreactivity was markedly different. No evidence for the presence of multimeric complexes in the CgA-I fraction was obtained by various immunological and biochemical methods. These results suggest that circulating CgA in phaeochromocytoma patients consists of at least three forms that appear to be made up by polypeptides with similar molecular weight and different hydrodynamic properties and immunoreactivity. We hypothesise that different conformations and shapes contribute to the heterogeneity of circulating CgA.

Circulating pancreastatin is a marker for the enterochromaffin-like cells of the rat stomach

BACKGROUND/AIMS

Peptides of the chromogranin family occur in peptide hormone-producing cells throughout the body. One source of such peptides is the enterochromaffin-like (ECL) cells, which constitute the predominant population of endocrine cells in the fundus (the acid-producing part) of the rat stomach. The purpose of this study was to examine whether ECL cells, which are controlled by gastrin, represent a major source of circulating pancreastatin, a fragment of chromogranin A.

METHODS

Rats underwent surgical procedures and treatments in which the ECL cells could be manipulated. The procedures included antrectomy, fundectomy, and gastrectomy (and adrenalectomy), and the treatments included fasting or feeding, gastrin-17 infusion, and administration of omeprazole or ranitidine. The concentrations of pancreastatin-like immunoreactivity (LI) and gastrin in the serum were determined by radioimmunoassay.

RESULTS

The serum pancreastatin-LI concentration was lowered by about 80% by fundectomy and gastrectomy; both of these procedures eliminated the ECL cell population. Adrenalectomy had no effect on the serum pancreastatin-LI concentration. Gastrin infusion, which activates the ECL cells, promptly increased serum pancreastatin-LI concentration. Refeeding after fasting and administration of omeprazole or ranitidine increased the serum pancreastatin-LI concentrations; these responses were prevented by antrectomy.

CONCLUSIONS

The concentration of circulating pancreastatin-LI reflects the activity of the ECL cells and the size of the ECL cell population in the rat stomach.

Neuroendocrine differentiation in carcinoma of the prostate. Diagnostic, prognostic, and therapeutic implications

Endocrine-paracrine cells of the prostate (also known as APUD or neuroendocrine cells) constitute, in addition to the basal and exocrine secretory cells, a third population of highly specialized epithelial cells in the prostate gland. These endocrine-paracrine cells contain, and most likely secrete, serotonin and calcitonin, as well as variety of other peptides. Little is known of the functional role of these cells, but they probably subserve a paracrine or local regulatory role. They may also regulate via endocrine, lumencrine, or neurocrine mechanisms. These endocrine-paracrine cells probably play a significant role during prostatic growth and differentiation as well as regulating the secretory process of the mature gland. Neuroendocrine differentiation in prostatic carcinoma occurs in the form of the relatively rare small cell carcinoma and carcinoid or carcinoid-like tumor, but most commonly as focal neuroendocrine differentiation in a conventional prostatic adenocarcinoma that is a very frequent, if not ubiquitous phenomenon, and reflects tumor cell heterogeneity mimicking the normal differentiation process. The world's literature on neuroendocrine differentiation in prostatic carcinoma is reviewed. Neuroendocrine differentiation in all types of prostatic carcinoma appears to correlate with a poor prognosis. This correlation is probably multifactorial and may relate to a positive correlation with grade, a direct resistance to hormonal manipulation, and/or autocrine/paracrine growth factor activity due to the secretion of neuroendocrine products. Neuron-specific enolase and chromogranin, as well as other neuroendocrine products, may be useful as serum markers in patients with prostatic carcinoma with neuroendocrine differentiation. New therapeutic strategies need to be developed to treat these tumors. This includes the use of specialized protocols that have been effective against neuroendocrine carcinomas arising in other organ systems.

Chromogranin A as tumor marker in medullary thyroid carcinoma

We measured plasma levels of chromogranin A (CgA) and calcitonin (CT) in 61 patients with surgically confirmed medullary thyroid carcinoma (MTC). CT was elevated in 46 patients, whereas CgA was elevated in 14 patients. Plasma levels of CgA and CT were moderately correlated (r = 0.87), but CgA became elevated in most patients only in advanced disease. Patients with high plasma CT values (greater than 10 micrograms/L) also had elevated CgA in 83% of cases. An elevated plasma CgA level despite normal CT levels was found in only 1 patient. In 8 MTC patients with moderately elevated basal CT levels, pentagastrin as a secretagogue usually was not able to release detectable amounts of CgA from MTC tissue. In 2 MTC patients, i.v. catheter sampling gave sharp gradients for CT concentrations (greater than 2.7-fold peak to peripheral ratios) and, therefore, precise MTC tissue localization, whereas no gradients were demonstrable for CgA (less than 1.2-fold). One patient with MTC and elevated CgA reached normal CgA plasma levels within 8 days after thyroidectomy. In metastatic tissue from 8 patients with MTC, CgA and CT were detectable immunohistologically in all cases, but plasma CgA was elevated only in 2 and CT in 7 of them. Plasma CgA levels in patients with MTC usually became elevated only in advanced disease and were not able to detect early disease stages, were correlated with CT levels, were not useful in stimulation tests or venous localization studies, and probably resulted from the release from MTC tissue as the major tissue source, as shown in the sporadic cases.

Chromogranin A in familial pheochromocytoma: diagnostic screening value, prediction of tumor mass, and post-resection kinetics indicating two-compartment distribution

PURPOSE

Chromogranin A, co-released with catecholamines from the adrenal medullary and sympathetic neuronal vesicles, is elevated in plasma from patients with pheochromocytoma. We assessed its diagnostic screening value, its plasma level in correlation with tumor mass, and its disposition kinetics in familial pheochromocytoma and sporadic pheochromocytoma.

PATIENTS AND METHODS

The sensitivity and specificity of chromogranin A's diagnostic value for pheochromocytoma were established through one kindred with familial pheochromocytoma associated with von Hippel-Lindau syndrome (13 available members) and in seven subjects with sporadic pheochromocytoma. Serial postoperative plasma samples were also obtained (5 minutes to 4 days) from eight subjects with pheochromocytoma in order to study chromogranin A post-resection kinetics. Chromogranin A was measured by radioimmunoassay based on purified pheochromocytoma chromogranin A.

RESULTS

In this kindred, elevations of chromogranin A (greater than 52 ng/mL) were sensitive (83%, five of six) and specific (100%, 10 of 10) in detecting familial pheochromocytoma; these diagnostic values comparable to those achieved by conventional evaluations for pheochromocytoma, such as urinary catecholamines, urinary catecholamine metabolites or imaging methods. Elevated levels of plasma chromogranin A specifically indicated pheochromocytoma, rather than von Hippel-Lindau syndrome gene carrier status. In 13 preoperative subjects with either familial or sporadic pheochromocytoma, plasma chromogranin A concentration predicted tumor size (r = 0.81, p less than 0.01). The change in chromogranin A plasma concentration after pheochromocytoma resection best fit a two-compartment model, with an initial rapid half-life time of 16 minutes, followed by a longer half-life time of 520 minutes. The model also predicted a 23.8:1 compartmental ratio of extravascular/intravascular chromogranin A, suggesting substantial tissue sequestration or binding of chromogranin A.

CONCLUSIONS

(1) Plasma chromogranin A is a valuable (sensitive and specific) diagnostic tool in detecting both familial and sporadic pheochromocytoma. (2) The concentration of plasma chromogranin A predicts the size of the pheochromocytoma. (3) Chromogranin A post-resection kinetics suggest extravascular sequestration of chromogranin A.

Chromogranin A. Storage and release in hypertension

The chromogranins/secretogranins are a family of acidic, soluble proteins with widespread neuroendocrine distribution in secretory vesicles. Although the precise function of the chromogranins remains elusive, knowledge of their structure, distribution, and potential intracellular and extracellular roles, especially that of chromogranin A, has greatly expanded during recent years. Chromogranin A is coreleased with catecholamines by exocytosis from vesicles in the adrenal medulla and sympathetic nerve endings. Thus, measurement of its circulating concentration by radioimmunoassay may be a useful probe of exocytotic sympathoadrenal activity in humans, under both physiological and pathological conditions. Here, we explore the storage, structure, and function of chromogranin A, and parameters that influence its circulating levels. We have also measured plasma chromogranin A concentrations in different groups of patients with hypertension, including those with pheochromocytoma.

Fragmentation of bovine chromogranin A by plasma kallikrein

Chromogranin A has been reported to be processed in vivo by an as yet undefined proteinase(s) suggesting that it is a precursor of biologically active peptides such as pancreastatin. In this study, plasma kallikrein was used as a model proteinase to identify the cleavage sites exposed in bovine parathyroid chromogranin A. Purified bovine parathyroid chromogranin A was digested with human plasma kallikrein. The proteolytic fragments produced were isolated by HPLC and chemically characterized by amino acid composition and sequence analysis. The combined results indicate that the enzyme has preference for specific single Arg residues, cutting C-terminal to this amino acid, although certain pairs of basic sites were also cleaved. The characterized fragments were released in a selective manner from the whole molecule with rapid production of the fragments covering positions 1-247 and 352-358.

Biochemistry of the chromogranin A protein family

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