Multiple hormone secretion by a human pancreatic glucagonoma in culture

Gastrointestinal endocrine tumours. Glucagonomas

Glucagonoma is an uncommon, challenging but treatable disease with varied manifestations. Despite its predominantly malignant nature, prolonged symptom-free survival can be achieved using a targeted combination of surgery, hepatic artery embolization and somatostatin analogues. Given the difficult management issues, an initial assessment in an experienced tertiary referral centre may also be of benefit. This chapter has looked at the long-term follow-up of 18 such patients over a 25-year period. Given the rarity of the tumour, the numbers are small, but valuable lessons can be learnt from the study in the clinical management of these patients.

Molecular and cellular analysis of a neoplastic pancreatic A cell tumor

Endocrine tumors of the pancreas may produce characteristic syndromes attributable to the increased secretion of one or more hormones. These tumors provide valuable opportunities for the analysis of hormone biosynthesis and secretion in the neoplastic human endocrine cell. The authors studied a pancreatic endocrine tumor obtained from a patient with classical glucagonoma syndrome. Characterization of plasma and tumor glucagon-like immunoreactivity (GLI) by high-performance liquid chromatography and radioimmunoassay for GLI showed different chromatographic profiles, with glucagon the major molecular form in the tumor, and glicentin and oxyntomodulin predominating in plasma. Although immunocytochemical staining of the tumor showed only focal weak positivity for glucagon, tumor extracts contained large amounts of immunoreactive GLI peptide. Northern blot analysis of tumor RNA demonstrated that abundant glucagon mRNA transcripts were present, just slightly larger in size than those detected in normal pancreas and intestine. Electron microscopic analysis of the tumor cellular ultrastructure revealed only occasional small electron dense secretory granules. A large number of complex lysosome-like structures of variable size and electron density were detected throughout the cytoplasm and ringing the nucleus of most cells, a feature atypical of endocrine tumors of the pancreas. Primary cultures of dispersed tumor cells were established and, in contrast to previous results, were obtained using normal or neoplastic islet cell models, GLI secretion was found to be stimulated eightfold by incubation with 5 mM dibutyryl cyclic adenosine monophosphate. Phorbol myristate acetate, the calcium ionophore A23187, and sodium butyrate had no effect on GLI secretion in vitro. These observations indicate that neoplastic human A cells may have abnormalities at different points in the biosynthesis and secretion of glucagon.

Gastrinoma in vitro: morphological and physiological studies of primary cell cultures

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.

Glucagon-like immunoreactive peptides in a rat ileal epithelial cell line (IEC-18)

The presence of cells containing glucagon-like immunoreactive (GLI) peptides was demonstrated in a rat ileal epithelial cell line (IEC-18) by both immunofluorescence and radioimmunoassay. When cell extracts were subjected to gel filtration chromatography, the cells were found to contain 3.5 Kd glucagon in addition to significant quantities of large molecular weight GLI peptides (apparent molecular weights of 4, 6, 8 and 10 Kd) and a 9 Kd peptide with apparent glucagon immunoreactivity. This was in contrast to extracts of adult rat ileum, which contained only large molecular weight GLI peptides (apparent molecular weights of 6 and 12 Kd). Production of GLI peptides by the IEC-18 cells was stimulated by glucose (p less than 0.02) and inhibited by insulin (p less than 0.01). In conclusion, these results demonstrate that the IEC-18 cells produce both GLI peptides and glucagon, and thus support the notion that proglucagon processing is cell-specific. IEC-18 cells may therefore provide a tool for investigations of some aspects of GLI peptide and glucagon synthesis.