big-gastrin and Gastrinoma

The value of chromogranin A (CgA) versus gastrin and progastrin in diagnosis and control of gastrinoma patients is not settled because the peptides circulate as variable mixtures. We have addressed this complexity using defined sequence-specific assays.. Six assays were applied to plasma from 40 gastrinoma patients to measure α-amidated gastrins, glycine-extended gastrins, the total progastrin product, and assays for CgA sequence (340-348) and the 'total' CgA product.. The gastrin/progastrin parameters did not add to the diagnosis beyond that of α-amidated gastrins, except in one patient. All gastrin parameters correlated otherwise closely. The CgA results differed. Thus, 11 patients had normal CgA concentrations. By contrast, all total CgA concentrations were elevated but correlated only moderately to gastrin.. Assays measuring α-amidated gastrins have high diagnostic value except for singular patients in whom only progastrin was elevated. By contrast, CgA measurements are not valid in diagnosis or control of gastrinomas.

Topics: Adult; Aged; Biomarkers, Tumor; Chromogranin A; Female; Gastrinoma; Gastrins; Humans; Linear Models; Male; Middle Aged; Peptides; Protein Precursors; Radioimmunoassay

This study evaluates whether a new analytic principle, processing-independent analysis (PIA), offers better specificity and sensitivity than the conventional gastrin radioimmunoassay in the diagnosis of gastrinomas.. Plasma concentrations of alpha-amidated gastrins and the total progastrin product were measured with radioimmunoassay and with PIA, respectively, in 512 samples taken for gastrin measurement and in a selected group of gastrinoma patients (n=10).. Among the 512 patients were 9 with gastrinomas. In plasma from these patients the median degree of amidation (ratio of alpha-amidated gastrins to total progastrin product) was 75% (range, 25-98%), whereas in the other groups the medians varied from 41% to 86%. In the second group of gastrinoma patients all had a degree of amidation of less than 50%.. In screening for gastrinomas PIA offered no diagnostic advantages in comparison with conventional gastrin radioimmunoassay. However, in selected patients who in spite of normal or slightly increased concentrations of amidated gastrins were still suspected of having gastrinoma, additional measurement of the total progastrin product showed incomplete processing of progastrin and thus proved helpful in establishing the diagnosis.

Topics: Anti-Ulcer Agents; Case-Control Studies; Female; Gastrinoma; Gastrins; Humans; Male; Middle Aged; Pancreatic Neoplasms; Peptic Ulcer; Protein Precursors; Radioimmunoassay; Sensitivity and Specificity; Zollinger-Ellison Syndrome

Topics: Diarrhea; Duodenal Neoplasms; Gastrinoma; Gastrins; Humans; Male; Middle Aged; Protein Precursors; Secretin

Posttranslational processing is an important phase of the expression of most eucaryotic genes in terms of functional proteins. Among these, secretory proteins and peptides are of particular interest for clinical chemists, since diagnostic measurements of circulating proteins and peptides constitute a major discipline in clinical chemistry. The posttranslational covalent maturation of secretory proteins and peptides involves multiple enzymatic modifications of the corresponding proproteins along the intracellular secretory pathway. During the eighties, an increasing amount of evidence has indicated that sick secretory cells fail to process their secretory products normally. The diseased cells therefore fail to process their secretory products normally. The diseased cells therefore release also incompletely processed precursors and processing-intermediates. In order to measure the degree of disease, assays that measure proteins and peptides independent of the degree of processing are therefore desirable. We have now designed a new analytical principle, according to which secretory proteins, peptides and their precursors can be accurately quantitated irrespective of the degree of processing. This principle, named processing-independent analysis (PIA), is generally applicable to all cellular synthesized substances. The principle has been applied to and developed first for a well-defined secretory peptide system, progastrin and its products. Using this model, the results obtained so far confirm the diagnostic superiority of processing-independent analysis in comparison with conventional assays for bioactive peptides.

Topics: Amino Acid Sequence; Animals; Chemistry, Clinical; Clinical Laboratory Techniques; Duodenal Ulcer; Gastrinoma; Gastrins; Humans; Molecular Sequence Data; Peptides; Protein Precursors; Protein Processing, Post-Translational; Proteins; Radioimmunoassay; Zollinger-Ellison Syndrome

Several peptides derived from the gastrin-predicted preprohormone sequence were isolated from a human gastrinoma by gel permeation, anion exchange, and reverse phase chromatography. The peptides were identified and characterized structurally by a combination of radioimmunoassays, mass spectral analysis, and microsequence analysis. The largest peptide, progastrin-(1-35) (cryptagastrin), extends from the putative processing site for the signal peptidase to the double basic residues adjacent to the amino terminus of gastrin 34. A shorter form of this peptide, progastrin-(6-35) (cryptagastrin-(6-35), was also isolated in smaller amounts. In addition, sulfated and nonsulfated gastrin 17 amides (progastrin-(55-71)) and the glycine-extended nonsulfated gastrin 17 (progastrin-(55-72)) were identified by radioimmunoassay, and their structures were confirmed by mass spectral analysis. Isolation of cryptagastrin indicates that the signal peptide of human preprogastrin contains 21 amino acid residues, and progastrin, therefore, contains 80 amino acids. There is minimal processing of the cryptic peptide preceding the sequence of gastrin 34. An amidated gastrin form larger than gastrin 34 could contain 71 amino acids. No evidence was obtained for processing that would produce gastrins containing more than 34 but less than 71 amino acid residues.

Topics: Amino Acid Sequence; Amino Acids; Chromatography, Gel; Chromatography, Ion Exchange; Endopeptidases; Gastrinoma; Gastrins; Humans; Membrane Proteins; Molecular Sequence Data; Peptides; Protein Precursors; Protein Processing, Post-Translational; Radioimmunoassay; Serine Endopeptidases; Spectrometry, Mass, Fast Atom Bombardment

Functional gastrin-containing tumor cells were maintained for up to 8 wk without fibroblastoid cell overgrowth. Short-term cultures consisted mainly of colonies composed of small polygonal cells, 70%-90% of which stained positive for immunoreactive gastrin. Cultures exhibited limited growth but viability remained high for 2-3 wk. Culture medium contained component I, and gastrin 34, 17, and 14. With time the major C-terminal gastrin species in medium changed from gastrin 17 at 3 days to gastrin 34 at 5 wk. Extracts of cultured cells contained gastrin 34, 17, and 14; gastrin 17 was the major form detected at all times. Ultrastructurally, cultured tumor cells retained morphological integrity for several weeks; however, with time changes in the appearance of the secretory granules accompanied by evidence of cellular retrodifferentiation were gradually observed. Secretin, gastrin-releasing peptide, 8-bromoadenosine 3':5'-cyclic monophosphate, and phorbol, 12-myristate, 13-acetate stimulated the release of gastrin from cultured cells in a time-dependent fashion. Secretin, bombesin, gastrin-releasing peptide, L-tryptophan, and ethylamine stimulated gastrin release in a dose-dependent fashion. Somatostatin 14 inhibited secretin, bombesin, and gastrin-releasing peptide stimulated gastrin release but did not alter basal release. Cultured cells demonstrated de novo gastrin synthesis, evidenced by their ability to incorporate radiolabeled amino acids into immunoadsorbable gastrinlike material. Primary cultures of gastrin-containing tumor cells free from stromal contamination offer unique advantages for studies of factors that regulate the synthesis and secretion of gastrin and may prove of potential value for studies on cell differentiation and growth.

Topics: Culture Media; Gastrinoma; Gastrins; Humans; Immunoenzyme Techniques; Pancreatic Neoplasms; Protein Precursors; Time Factors; Tumor Cells, Cultured

Processing-independent radioimmunoanalysis for progastrin showed that extracts of normal pancreatic tissue from normal subjects (n = 5) and from patients with adenocarcinoma of the papilla of Vater (n = 4) contain progastrin and its products. The concentrations varied from 0.1 to 5.8 pmol/g tissue, of which carboxyamidated bioactive gastrins constituted 0.03-1.9 pmol/g. In histologically normal and nonneoplastic pancreatic tissue from patients with duodenal (n = 3) and pancreatic (n = 2) gastrinomas the expression of gastrin was significantly higher-14.5 pmol/g (median), of which 28% was bioactive amidated gastrins. Gastrin-17 was the main bioactive product, but its immediate precursor, glycine-extended gastrin-17, constituted the predominant part of the preprogastrin product in pancreatic tissue. Proper gastrinoma tissue contained several precursor forms, including intact unprocessed progastrin. Progastrins were also found in high concentrations in plasma from the gastrinoma patients. The results raise the possibility that increased expression of progastrin and its products in non-neoplastic pancreatic tissue is a primary defect predisposing to neoplasia.

Topics: Adenocarcinoma; Ampulla of Vater; Common Bile Duct Neoplasms; Gastrinoma; Gastrins; Gene Expression; Humans; Pancreas; Pancreatic Neoplasms; Protein Precursors; Protein Processing, Post-Translational; Zollinger-Ellison Syndrome

The characterization of the tumors and their metastasis in patients with the Zollinger-Ellison syndrome is currently based on the immunohistochemical identification of gastrin cells. However, sometimes tumoral cells fail to react with common C-terminal gastrin antibodies. In order to clarify this failure, we carried out morphologic, morphometric and immunocytochemical analyses performed on light and electron microscope levels of 6 pancreatic and 1 metastatic gastrinomas, using antibodies raised against various sequences of human progastrin. On the basis, in light microscopy, of qualitative analysis of immunostaining within cells and of immunostained cell numbers, gastrin 34 residue seemed to be the prominent form in 2 of the tumor tissues, G-17 in 1 tumor which was not responsive with C terminus progastrin and N terminus G-34 antisera, and progastrin in the metastatic tissue that did not contain typical gastrin (G-like) cells. Two tumors failed to react with all antisera used. At the electron microscope level, immunogold staining revealed that progastrin was present only in the progranules and gastrin 34 in both progranules and intermediate granules. Quantitative studies performed on 3 tumors showed that, within a given tumoral cell, about 25 percent of progranules contained progastrin while 75 percent contained gastrin 34. We concluded that different forms of gastrin can be immunodetected in a gastrinoma tissue, depending on the regions, and that the distribution of progastrin fragments is variable from tumor to tumor. So, specific antibodies to different fragments of progastrin may help to the characterization of gastrinomas.

Topics: Antibodies; Epitopes; Gastrinoma; Gastrins; Humans; Immune Sera; Immunohistochemistry; Microscopy, Electron; Pancreatic Neoplasms; Protein Precursors

There is a general agreement on the cell specificity of gastrin processing. In order to investigate this processing in Zollinger-Ellison (ZE) patients, we have studied in two primary gastrinoma cultures (one from a pancreatic tumor, the other from a liver metastasis) the proportion of progastrin fragments using immunochemical and immunohistological methods. In tumor extracts as well as in sera, the predominant gastrin form differed between the two patients (i.e. being G17 and G34, respectively). In the two gastrinoma cultures, RIA determinations and electron microscopic observations indicated that the proportion of progastrin increased with time while that of G17 and G34 decreased. On the other hand, as the culture time extended, an increasing proportion of nonimmunostained secretory granules was observed suggesting the presence of other gastrin precursors (e.g. Gly-extended progastrin). From these findings, we suggest that gastrinoma culture cells could be a valuable tool in the biochemical approach to gastrin processing in ZE tumors.

Topics: Cells, Cultured; Gastrinoma; Gastrins; Humans; Pancreatic Neoplasms; Protein Precursors; Staining and Labeling

Topics: Amino Acid Sequence; Animals; Base Sequence; DNA; Exons; Gastrinoma; Gastrins; Gene Expression Regulation; Humans; Introns; Pancreatic Neoplasms; Protein Precursors; Species Specificity

Tissue pieces of a metastatic human gastrinoma (ultrastructural Type II) were successfully transplanted to the anterior eye-chamber of rats immunosuppressed with Cyclosporin A. Immunocytochemical investigation of the transplants showed evidence for preserved endocrine activity of tumour cells with immunoreactivity towards the C-terminal of the gastrin/cholecystokinin molecule. Studies of gastric acid secretion in tumour-bearing rats and sham-operated controls with chronic gastric fistulas showed that the basal acid output did not differ between the groups during 3 weeks of study. However, the stimulated gastric acid secretion decreased after 5 days in both groups to remain significantly depressed throughout the study, an effect probably due to Cyclosporin A treatment of the groups. The concentration of immunoreactive gastrin in plasma from rats with tumours in oculo was 5 times higher than in sham-operated rats. Gastrin-34 was the major immunoreactive component in both patient serum and rat plasma. An immunoreactive fraction corresponding to component I was found in the patient serum, but not in the rat plasma, although present in the chamber fluid. Components corresponding to gastrin-17 were found both in the patient serum and in the rat plasma. The chromatographic pattern of the tumour was similar to that in rat chamber fluid. The dominating component corresponded to gastrin-17, while gastrin-34 represented the quantitatively smaller component. Gastrin-34 was, however, relatively more abundant in the tumour extract than in the chamber fluid. The study also indicates that a gastrin-producing tumour transplanted in oculo in immunosuppressed rats may increase the rat plasma concentration of the same molecular forms of gastrin as seen in the clinical situation.

Topics: Adolescent; Animals; Anterior Chamber; Chromatography, Gel; Female; Gastric Acid; Gastrinoma; Gastrins; Humans; Immunosuppression Therapy; Male; Microscopy, Electron; Neoplasm Transplantation; Pancreatic Neoplasms; Protein Precursors; Radioimmunoassay; Rats; Rats, Inbred Strains

Topics: Duodenal Neoplasms; Gastric Mucosa; Gastrinoma; Gastrins; Glycine; Humans; Pancreatic Neoplasms; Protein Precursors

There is a potential phosphorylation site in the C-terminal region of the precursor for the acid-stimulating hormone gastrin, which is immediately adjacent to an important cleavage point. In the present study we have sought to identify, separate, quantify and characterize phosphorylated and unphosphorylated forms of human progastrin and its fragments. Identification was made by two radioimmunoassays: (a) a novel assay employing an antibody raised to intact human progastrin; and (b) an assay using antibody reacting with the C-terminal tryptic fragment of human progastrin, as well as progastrin itself. Two forms of human progastrin isolated from a gastrinoma were separated by ion-exchange h.p.l.c., and had similar elution positions on reverse-phase h.p.l.c. and on gel filtration. The more acidic peptide contained close to equimolar amounts of phosphate. On trypsinization, peptides were released that co-eluted on ion-exchange h.p.l.c. with, and had the immunochemical properties of, naturally occurring C-terminal fragments of progastrin. One of the latter was isolated and shown by Edman degradation after derivatization with ethanethiol to have the sequence Ser (P)-Ala-Glu-Asp-Glu-Asn. Similar peptides occur in antral mucosa resected from ulcer patients. The unphosphorylated forms of progastrin predominated, whereas the phosphorylated forms of the C-terminal fragments were predominant. This distribution could be explained by preferential cleavage of phosphorylated progastrin. We conclude that in human progastrin, Ser-96 can occur in the phosphorylated form; this residue immediately follows a pair of basic residues (Arg-Arg) that are cleaved during synthesis of the biologically active product.

Topics: Amino Acid Sequence; Chromatography, High Pressure Liquid; Gastric Mucosa; Gastrinoma; Gastrins; Humans; Liver Neoplasms; Molecular Sequence Data; Peptide Fragments; Phosphorylation; Protein Precursors; Trypsin

Most peptide hormone assays measure only fully processed bioactive peptides. Such assays are unsuited to detect hormone gene expression by alternative or attenuated prohormone processing (tissue- or cell-specific processing). The gastrin system is expressed in several different tissues and is therefore useful for studies of tissue-specific processing. Consequently we have developed a simple processing-independent radioimmunoanalysis for progastrin. Using antisera against the NH2-terminus of a sequence, devoid of processing sites (preprogastrin76-86) after trypsination of neighboring cleavage sites, the assay quantitates the mRNA product irrespective of degree of processing. Used together with a conventional assay for the mature carboxyamidated gastrins, the processing-independent analysis shows that in different tissues only 1 to 55% of the total translation product is processed to bioactive gastrins. Thus processing-independent analysis greatly improves the detection of gastrin gene expression at the peptide level. The principle of the assay should be applicable to all protein and peptide systems.

Topics: Amino Acid Sequence; Chromatography, Gel; Gastric Mucosa; Gastrinoma; Gastrins; Humans; Lung Neoplasms; Molecular Sequence Data; Peptide Fragments; Protein Precursors; Protein Processing, Post-Translational; Radioimmunoassay; Trypsin