Allelic deletions on chromosome 11q13 in multiple endocrine neoplasia type 1-associated and sporadic gastrinomas and pancreatic endocrine tumors

Endocrine tumors (ETs) of pancreas and duodenum occur sporadically and as a part of multiple endocrine neoplasia type 1 (MEN1). The MEN1 tumor suppressor gene has been localized to chromosome 11q13 by linkage analysis but has not yet isolated. Previous allelic deletion studies in enteropancreatic ETs suggested MEN1 gene involvement in tumorigenesis of familial pancreatic ETs (nongastrinomas) and sporadic gastrinomas. However, only a few MEN1-associated duodenal gastrinomas and sporadic pancreatic nongastrinomas have been investigated. We used tissue microdissection to analyze 95 archival pancreatic and duodenal ETs and metastases from 50 patients for loss of heterozygosity (LOH) on 11q13 with 10 polymorphic markers spanning the area of the putative MEN1 gene. Chromosome 11q13 LOH was detected in 23 of 27 (85%) MEN1-associated pancreatic ETs (nongastrinomas), 14 of 34 (41%) MEN1-associated gastrinomas, 3 of 16 (19%) sporadic insulinomas, and 8 of 18 (44%) sporadic gastrinomas. Analysis of LOH on 11q13 showed different deletion patterns in ETs from different MEN1 patients and in multiple tumors from individual MEN1 patients. The present results suggest that the MEN1 gene plays a role in all four tumor types. The lower rate of 11q13 LOH in MEN1-associated and sporadic gastrinomas and sporadic insulinomas as compared to MEN1 nongastrinomas may reflect alternative genetic pathways for the development of these tumors or mechanisms of the MEN1 gene inactivation that do not involve large deletions. The isolation of the MEN1 gene is necessary to further define its role in pathogenesis of pancreatic and duodenal ETs.

The gastrin-releasing peptide receptor is differentially coupled to adenylate cyclase and phospholipase C in different tissues

Recent studies suggest that in some tissues GRP receptor activation can both stimulate phospholipase C and the adenylate cyclase pathway and that activation of the latter pathway may be important in mediating some of its well-described growth effects. However, other studies suggest GRP-R may not be coupled to adenylate cyclase. To investigate this possibility, in the present study we determined the coupling of the GRP receptors to each pathway in mouse, rat, and guinea pig pancreatic acini and compared it to that in mouse Swiss 3T3 cells and human SCLC cells, all of which possess well-characterized GRP receptors. Moreover, we tested the effect of PKC activation on the ability of GRP-related peptides to increase cAMP accumulation in these tissues. Changes in cAMP levels were determined with or without IBMX present, with or without forskolin, or both to amplify small increases in cAMP. In mouse, rat and guinea pig pancreatic acini, murine Swiss 3T3 cells and human SCLC cells, GRP-related peptides caused a 600%, 500%, 250%, 300% and 60% increase, respectively, in [3H]IP with 1-3 nM causing a half-maximal effect. In murine Swiss 3T3 cells, IBMX, forskolin, and IBMX plus forskolin caused a 300%, 3500% and 10500% increase in cAMP, respectively. GRP-related peptides and VIP caused an additional 70% increase in cAMP with GRP causing a half-maximal (EC50) increase in cAMP at 2.1 +/- 0.5 nM, which was not significantly different from the EC50 of 3.1 +/- 0.9 nM for increasing [3H]IP in these cells. GRP-related peptides did not stimulate increases in cAMP in mouse, rat or guinea pig pancreatic acini or in SCLC cells either alone, with IBMX or forskolin or both. However, in pancreatic acini IBMX, forskolin or both increased cAMP 3 to 8-, 10 to 500-, and 100 to 1000-fold increase and the addition of VIP caused an additional 20-, 2-, and 3-fold increase in cAMP in the different species. In mouse pancreatic acini with TPA alone or IBMX plus TPA, neither bombesin nor GRP increased cAMP. Furthermore, in mouse pancreatic acini, neither TPA nor TPA plus IBMX altered basal or VIP-stimulated increases in cAMP. In mouse Swiss 3T3 cells TPA significantly increased cAMP stimulated by Bn, GRP or VIP. These results demonstrated that GRP receptor activation in normal tissues from three different species and a human tumoral cell line do not result in adenylate cyclase activation, whereas in Swiss 3T3 cells it causes such activation. The results suggest that the difference in coupling to adenylate cyclase is likely at least partially due to a difference in coupling to an adenylate cyclase subtype whose activation is regulated by PKC. Therefore, the possible growth effects mediated by this receptor in different embryonic or tumoral cells through activation of adenylate cyclase are not likely to be an important intracellular pathway for these effects in normal tissues.

Effect of gastrin-releasing peptide receptor number on receptor affinity, coupling, degradation, and modulation

The relationship between receptor number and agonist-induced intracellular responses has been well studied in receptors coupled to adenylate cyclase; however, for receptors coupled to phospholipase C (PLC), very little is known about the effect of receptor number on receptor-mediated processes. To explore this issue, we investigated the effect of the number of receptors for gastrin-releasing peptide (GRP) on ligand affinity and on the ability to activate intracellular messengers [PLC, tyrosine phosphorylation of p125 focal adhesion kinase (p125FAK)] and cause receptor modulation (internalization, desensitization, down-regulation) and ligand degradation. Three BALB 3T3 cell lines were made that stably expressed the gastrin-releasing peptide receptor (GRP-R) with receptor numbers varying by 280-fold (GRP-R-Low, GRP-R-Med, and GRP-R-Hi). Each cell line had the same affinity for agonist. The efficacy for bombesin to increase [3H]inositol phosphates but not tyrosine phosphorylation of p125FAK correlated well with receptor number. In contrast, the EC50 value for [3H]inositol phosphate generation for bombesin was the same in each cell line. Receptor number did not alter internalization. In the absence of protease inhibitors, there was an inverse correlation between receptor number and receptor down-regulation and desensitization. However, with protease inhibitors present, GRP-R-Med and GRP-R-Hi down-regulated significantly less than the GRP-R-Low. Similarly, GRP-R-Low desensitized significantly more than GRP-R-Med or GRP-R-Hi. GRP-R-Hi caused significantly greater ligand degradation than GRP-R-Low, and protease inhibitors completely inhibited degradation by GRP-R-Low and inhibited degradation by 70% for GRP-R-Hi. In conclusion, we show that for the PLC-coupled GRP-R, receptor number had little or no effect on binding affinity, potency for activating PLC, tyrosine phosphorylation of p125FAK, or extent of receptor internalization. In contrast, receptor number had an effect on ligand degradation, down-regulation, desensitization, and efficacy of PLC activation without altering the efficacy of tyrosine phosphorylation of p125FAK. These results demonstrate that the effect of receptor number differs for the different functions mediated by the GRP receptor and differs from that reported for adenylate cyclase-coupled receptors such as receptors mediating the action of adrenergic agents, secretin, and opioids.

Colonic smooth muscle cells possess a different subtype of somatostatin receptor from gastric smooth muscle cells

Somatostatin (SS) alters colonic motility. To investigate whether SS has a direct effect on colonic smooth muscle cells, we prepared isolated muscle cells from the descending guinea pig colon and compared the effects of SS with those on isolated gastric smooth muscle cells. In gastric cells, SS had no effect on carbachol-induced contraction, whereas in colonic cells it caused inhibition. In colonic muscle cells, SS-28 caused >85% inhibition of contraction by cholecystokinin octapeptide (CCK-8), bombesin, 12-O-tetradecanoylphorbol-13-acetate, and ionomycin, whereas it had no effect on contraction by these agents in gastric cells. In gastric cells, SS inhibited relaxation. Three synthetic SS analogs had different relative affinities for causing effects in gastric and colonic cells. Pertussis toxin inhibited the action of SS-28 in each muscle cell type by 50-75%. SS-28 alone had a small contractile effect on cells from the circular layer of the colon. SS-28 inhibited carbachol-induced contraction in colonic cells from both the longitudinal and circular layers. These results demonstrate that the action of SS differs in colonic and gastric smooth muscle cells. SS inhibits contractants in colonic cells and relaxants in gastric cells. In colonic cells, SS has a weak contractile effect due to an effect on circular muscle cells and an inhibitory effect on cells from both longitudinal and circular layers. A different SS receptor subtype mediates the actions of SS in colonic and gastric muscle cells. In both cell types, the actions of SS are mediated by pertussis toxin-sensitive and -insensitive G proteins.

Primary cardiac gastrinoma causing Zollinger-Ellison syndrome

Primary cardiac tumors are rare, and there are no reports of patients with a functional gastroenteropancreatic tumor syndrome caused by such a tumor. This case report describes a patient with a cardiac gastrinoma causing Zollinger-Ellison syndrome. Evidence is presented that this tumor represents a primary cardiac tumor. The exact identification of this gastrinoma in an extra-abdominal site was facilitated by the use of [111In-DTPA-DPhe1]octreotide scanning for somatostatin receptors, which these tumors characteristically possess in high numbers. The recent availability of this novel localization method may facilitate identification of extra-abdominal sites in an increasing proportion of patients with gastrinomas and related neuroendocrine functional tumors in which no intra-abdominal primary tumor is currently found.

Value of somatostatin receptor scintigraphy: a prospective study in gastrinoma of its effect on clinical management

BACKGROUND & AIMS

Recently [111In-DTPA-D-Phe1]-octreotide was approved for somatostatin receptor scintigraphy (SRS) of gastroenteropancreatic tumors. SRS and other tumor localization methods can be time consuming, expensive, and involve patient inconvenience. The role of SRS in comparison to other tumor localization modalities remains undefined because the relative effects of these methods on management have not been studied. The aim of this study was to determine whether SRS alters clinical management in Zollinger-Ellison syndrome.

METHODS

One hundred twenty-two consecutive patients were studied prospectively. Each patient was assigned to one of five different clinical categories. Conventional imaging studies (ultrasonography, computerized tomography, magnetic resonance image, angiography, and bone scan) were performed, and the management was proposed. SRS was then performed. Clinical management was reassessed, and whether SRS altered management was determined based on six criteria.

RESULTS

SRS was superior to any single imaging study. SRS altered management in 47% overall and in 22%-60% of patients in the five different clinical categories. Primary tumor localization and clarification of equivocal localization results from conventional studies were the principal reasons for altering management. SRS was equally useful in patients with or without metastatic liver disease.

CONCLUSIONS

Because of the ability of SRS to alter clinical management combined with its superior sensitivity, high specificity, simplicity, and cost-effectiveness, SRS should be the initial imaging modality for patients with gastrinomas.

Characterization of bombesin binding sites in the rat stomach

We characterized the bombesin receptor population in the rat stomach and determined the receptor subtype mediating the contractile effect of bombesin in the gastric fundus. Using in vitro receptor autoradiography, we evaluated the ability of the specific gastrin-releasing peptide-preferring receptor antagonist [D-F5,Phe6,D-Ala11]bombesin-(6-13) methyl ester to inhibit binding of 125I-[Tyr4]bombesin to the gastric fundus, corpus and antrum. Binding to these regions was completely inhibited by [D-F5,Phe6,D-Ala11]bombesin-(6-13) methyl ester suggesting that these receptors are the gastrin-releasing peptide-preferring subtype. We found that the rank order of potency for the contractile effect of bombesin, and the related mammalian peptides neuromedin C and neuromedin B, was bombesin > neuromedin C > neuromedin B. [D-F5,Phe6,D-Ala11]bombesin-(6-13) methyl ester was equipotent in antagonizing contractions produced by all three peptides. Furthermore, receptor tachyphylaxis to either neuromedin C or neuromedin B abolished the subsequent contractile response elicited by neuromedin C and neuromedin B, suggesting that one bombesin receptor subtype mediates rat gastric fundal contractions. Together, these results demonstrate that the bombesin receptor subtype in the rat stomach is gastrin-releasing peptide-preferring subtype and that this subtype is responsible for the effects of bombesin-like peptides on fundal smooth muscle contraction.

Inhibition of protein synthesis in small cell lung cancer cells induced by the diphtheria toxin-related fusion protein DAB389 GRP

DAB389 GRP is composed of the catalytic and transmembrane domains of diphtheria toxin fused to gastrin-releasing peptide (GRP). DAB389 GRP is selectively targeted to, and inhibits protein synthesis in, cell lines expressing GRP receptors. Protein synthesis in 5'ET4 cells (BALB/3T3 fibroblasts transfected with the gene encoding the GRP receptor) was inhibited by 50% in the presence of 20 pM DAB389 GRP (IC50, 20 pM). DAB389 GRP did not inhibit protein synthesis in untransfected BALB/3T3 cells. A second neuropeptide-conjugated toxin, DAB389 SP, directed to cells expressing substance P receptors, was not cytotoxic to 5'ET4 cells, nor was DAB389 GRP cytotoxic to substance P receptor-bearing cells. DAB389 GRP cytotoxic effects were receptor specific and were inhibited either by excess GRP or anti-GRP antibody. Cytotoxicity was mediated by passage through an acidic vesicle, because addition of 10 microM chloroquine to the reaction inhibited cytotoxicity. DAB389 GRP and DAB389 SP were tested on a number of tumor cell lines. DAB389 GRP inhibited protein synthesis in AR42J rat pancreatic acinar cells and HuTu 80 human duodenal adenocarcinoma cells with IC50s of 65 and 200 pM, respectively. DAB389 SP had an IC50 of 9.5 pM for the AR42J cells and 12 nM for the HuTu 80 cell line. A number of small cell lung cancer cell (SCLC) lines were tested, and the IC50 for DAB389 GRP ranged from 1.1 to 85 nM. Sensitivity to DAB389 GRP appeared to be based on receptor number and receptor type (i.e., GRP or neuromedin B preferring). SCLC cells were also sensitive to DAB389 SP, with IC50s ranging from 2.4 to 11.5 nM. These results suggest that a potential use exists for diphtheria-based fusion toxins as therapeutic agents for treatment of SCLC and other neuropeptide receptor-bearing cancers.

Management of the Zollinger-Ellison syndrome in pregnancy

OBJECTIVE

There is almost no information on the management of patients with functional pancreatic endocrine tumors such as Zollinger-Ellison syndrome during pregnancy. The purpose of this study was to develop an approach for the management of such cases during pregnancy on the basis of experience with five recent cases.

STUDY DESIGN

Five women with Zollinger-Ellison syndrome who had seven pregnancies were the subject of this study. Each patient had an initial evaluation to confirm the diagnosis and to establish gastrinoma location and for the presence or absence of multiple endocrine neoplasia type I. In patients with Zollinger-Ellison syndrome diagnosed before conception, various medical or surgical treatments were established before conception and were used to control acid secretion throughout the pregnancy. The presence of upper gastrointestinal symptoms during pregnancy, maternal and fetal complications, gender, and weight of the infant were determined in all cases. Acid control was determined in four of the five patients during six pregnancies.

RESULTS

The interval between the onset of Zollinger-Ellison syndrome and the subsequent pregnancy varied from 0.6 to 9.9 years (mean 6.9 +/- 1.7 years). Zollinger-Ellison syndrome was unrecognized before pregnancy in two patients (40%); it was diagnosed between 0.2 and 2.4 years after the pregnancy. In three patients the time of diagnosis varied from 2.6 to 9 years before pregnancy. All patients had symptoms from gastric hypersecretion and elevated fasting serum gastrin levels that varied from 20% above normal to 37-fold above normal with mean of 2536 pg/ml (range 124 to 6970 pg/ml). Four of the five patients (80%) had positive secretin and calcium provocative tests. Two patients had multiple endocrine neoplasia type I. The five patients had seven pregnancies. Acid secretion was treated during pregnancy with antacids only (one patient), ranitidine alone (one patient), prior curative gastrinoma resection (one patient, two pregnancies), prior parietal cell vagotomy with incomplete tumor resection (one patient, two pregnancies), and prior parathyroidectomy and use of ranitidine in a patient with multiple endocrine neoplasia type I. In five pregnancies in three of the cases, no gastric antisecretory medications were needed during pregnancy. The mean acid secretion during pregnancy was 11.9 mEq/hr (range 0 to 42 mEq/hr). In the two cases with poor acid control and unrecognized Zollinger-Ellison syndrome mild fetal complications occurred.

CONCLUSIONS

It is possible for patients with Zollinger-Ellison syndrome to have pregnancies that are not complicated by gastric acid hypersecretion. If the Zollinger-Ellison syndrome is diagnosed before pregnancy, curative resection with parietal cell vagotomy may obviate the need for gastric antisecretory drugs. If metastases are present or the diagnosis of Zollinger-Ellison syndrome is made after conception, ranitidine in the lowest possible dose should be used to control acid secretion. If acid secretion in uncontrolled, the dose may be increased or omeprazole may be used.

Definition of the role of somatostatin receptor scintigraphy in gastrointestinal neuroendocrine tumor localization

There are six major steps in the management of patients with neuroendocrine tumors (NETs) (carcinoids and pancreatic endocrine tumors). One of the steps that is increasing in its importance is the need to assess primary tumor location and tumor extent in these patients. Without such information, it is not possible to adequately manage these patients. Conventional imaging studies (CT scan, MRI, ultrasound, angiography), functional localization studies measuring hormonal gradients, endoscopic ultrasound, and most recently, somatostatin receptor scintigraphy (SRS) with [125I-DTPA-DPhe1]-octreotide have all been advocated to localize NETs in different studies. Whereas it is now established that for all NETs, except insulinomas, SRS has the greatest sensitivity, it remains unclear whether this increased sensitivity translates into increased clinical usefulness. It, therefore, remains unclear based on fiscal and clinical considerations what should be the recommended algorithm for the use of the different localization methods. To address this issue, we have recently performed two prospective studies on patients with gastrinomas. In this paper, the methods and results of each are summarized and based on these results, an algorithm for localization studies in NETs is proposed. One study assessed the role of SRS in management in 122 patients and shows that the use of SRS changed management in 47 percent of patients according to six different criteria when the patients were stratified according to their principal management problem. Determining whether liver metastases were present is one of the major goals of tumor localization studies and is frequently a source of confusion because of the difficulty in distinguishing small NETs liver metastases from hemangiomas. In the second study, the ability of SRS and other tumor localization methods to distinguish these two possibilities was assessed in 15 patients with small hemangiomas and 15 patients with small hepatic metastases (mean size 1.3 cm). SRS correctly identified 93 percent of the patients with liver metastases and was not positive in any patient with a hemangioma, suggesting it was not a liver metastases. SRS had greater negative and positive predictive value than conventional studies. Based on these two studies, and SRS's greater sensitivity and fiscal considerations, it is proposed that SRS should be the initial tumor imaging study in all NETs except insulinomas, and algorithms for the use of other localization studies in both NETs and insulinomas are proposed.

Comparative analysis of diagnostic techniques for localization of gastrointestinal neuroendocrine tumors

In vitro studies have shown that gastroenteropancreatic tumors, with the exception of insulinomas, have a high density of somatostatin receptors and can be imaged in vivo using somatostatin receptor scintigraphy (SRS) with either [123I-Tyr3]octreotide or [111In DTPA,DPhe1]octreotide. However, the sensitivity in relation to conventional imaging studies (ultrasound, CT, MRI, angiography) remains unclear. To address this question, we performed a prospective study of 80 patients with gastrinomas where SRS was compared with other conventional imaging techniques for detecting extrahepatic gastrinomas or liver metastases. Extrahepatic gastrinomas were identified by SRS in 58 percent of patients, whereas conventional imaging studies detected gastrinomas in 9 percent to 48 percent of patients. In detecting hepatic metastases in 24 patients with histologically-proven metastases, SRS was positive in 92 percent; ultrasound, CT or angiography in 42 percent to 62 percent; and MRI in 71 percent of patients. These results are compared with other studies in detecting gastrinomas as well as series including other PETs, excluding insulinomas, with insulinomas alone, and with carcinoid tumors. An analysis of the ability of SRS to identify gastrinomas found in different sites at surgery was performed. The role of endoscopic ultrasound (EUS) in detecting various PETs, in comparison to that of SRS, is yet to be established, particularly for extrapancreatic PETs. Therefore, the results of EUS in various studies containing patients with PETs are compared to those with SRS and conventional imaging studies. These data suggest that EUS is the first choice of localization methods for detecting insulinoma, which is an intrapancreatic tumor in almost all cases. In other PETs there still is not sufficient data to establish the relative roles of EUS and SRS.

Distinguishing small hepatic hemangiomas from vascular liver metastases in gastrinoma: use of a somatostatin-receptor scintigraphic agent

PURPOSE

To compare somatostatin-receptor scintigraphy and conventional imaging modalities in the differentiation of small hepatic hemangiomas from small liver metastases in Zollinger-Ellison syndrome.

MATERIALS AND METHODS

Twenty-nine patients had hypervascular liver lesions smaller than 2 cm that could have been either metastases or hemangiomas. Fourteen patients had metastases, 14 had hemangiomas, and one had both. Scintigraphy was compared with computed tomography (CT), magnetic resonance (MR) imaging, and angiography for the correct identification of the lesions.

RESULTS

The hemangiomas and liver metastases both had a mean size of 1.3 cm. In the patients with hepatic hemangiomas, scintigraphy showed no lesions. CT, angiography, or MR imaging showed a lesion in 40%-93%. With metastases present, any liver lesion was detected in 93% with scintigraphy versus 20%-60% with another modality. Scintigraphy depicted liver metastases in 93% of patients, which was higher than the sensitivities of other modalities. The accuracy (96%) and positive (100%) and negative (93%) predictive values of scintigraphy for detecting liver metastases were superior to those of other modalities. There were 45 liver metastases and 31 hemangiomas; a per lesion analysis gave results similar to the per patient analysis results.

CONCLUSION

In Zollinger-Ellison syndrome, somatostatin-receptor scintigraphy provides an excellent diagnostic tool to differentiate small hepatic hemangiomas from small liver metastases.

Studies on the interrelation between Zollinger-Ellison syndrome, Helicobacter pylori, and proton pump inhibitor therapy

BACKGROUND & AIMS

The interrelation between Helicobacter pylori infection and proton pump inhibitor therapy in patients with Zollinger-Ellison syndrome is unknown. The aim of this study was to evaluate the influence of these factors on parameters of Zollinger-Ellison syndrome.

METHODS

Prevalence of H. pylori was determined by biopsy and antibody testing in 84 patients. The influence of H. pylori status on clinical and laboratory parameters of Zollinger-Ellison syndrome was evaluated. Seroconversion after surgery was assessed retrospectively in infected patients.

RESULTS

The prevalence of H. pylori exposure was 23% (10% with active infection). Acid output was higher in H. pylori-negative patients, but other clinical and biochemical parameters did not differ. Parameters were also similar for patients determined to be H. pylori positive by histology or antibody testing alone. Seroconversion rates did not differ between those rendered or not rendered disease free despite a significant reduction in acid output.

CONCLUSIONS

H. pylori infection is not a risk factor for peptic ulceration in patients with Zollinger-Ellison syndrome. The prevalence is lower than in the general population and much lower than for patients with idiopathic peptic ulcer disease. Long-term omeprazole therapy in H. pylori-positive patients with Zollinger-Ellison syndrome may-lead to a reduction in parietal cell mass.

Gastrointestinal endocrine tumours. Gastrinoma

Since the description of the Zollinger-Ellison syndrome in two patients in 1955, there have been significant advances in the understanding of its pathogenesis, natural history, relationship to multiple endocrine neoplasia type 1, diagnosis, methods of tumour localization and management. The main focus in treatment is now shifting from management of the gastric acid hypersecretory state which can now be controlled medically in almost every patient, to the management of the gastrinoma. Recent studies are beginning to provide insights into the natural history of gastrinomas, factors that are associated with invasiveness in some gastrinomas, defining the role of surgery in managing patients with different disease extents, or with MEN 1 and being able to provide insights into molecular abnormalities that may be important in their pathogenesis. In this article each of these advances is briefly reviewed with emphasis primarily on recent advances.

Is reoperation for gastrinoma excision indicated in Zollinger-Ellison syndrome?

BACKGROUND

Surgical excision of gastrinomas in patients with Zollinger-Ellison syndrome (ZES) decreases the incidence of hepatic metastases, but long-term biochemical cures are achieved in fewer than 30% of cases. A growing number of patients have persistent or recurrent disease after initial operation. The effect of reoperation in these patients has not been previously reported.

METHODS

From December 1982 to August 1995, 120 patients with ZES underwent operation for gastrinoma resection. Seventy-eight patients had recurrent or persistent ZES after operation; 17 patients underwent 18 reoperations. After initial operation all patients underwent yearly functional and imaging studies. If a tumor was unequivocally imaged, reexploration was done.

RESULTS

Five patients, all with sporadic disease, were disease free after operation, with a median follow-up of 28 months. Tumor was found in all 18 reoperations and resected in 17. In patients with continuing disease-free intervals, locations of gastrinomas included pancreatic head lymph nodes (three), liver metastasis (one), and pancreatic tail lymph node (one). There were no deaths in the cured group; two patients in the group with persistent disease have died (median follow-up, 34 months).

CONCLUSIONS

Reoperation for gastrinoma excision resulted in elimination of disease in 30% of patients and should be considered for patients with imageable disease.

Somatostatin receptor scintigraphy: its sensitivity compared with that of other imaging methods in detecting primary and metastatic gastrinomas. A prospective study

OBJECTIVE

To compare the sensitivity of somatostatin receptor scintigraphy done using [111In-DTPA-DPhe1]octreotide with that of other imaging methods in the localization of gastrinomas in patients with the Zollinger-Ellison syndrome.

DESIGN

Prospective study.

SETTING

Referral-based clinical research center.

PATIENTS

80 consecutive patients with the Zollinger-Ellison syndrome.

INTERVENTIONS

Conventional tumor localization studies (ultrasonography, computed tomography [CT], magnetic resonance imaging [MRI], selective angiography, and bone scanning) and somatostatin receptor scintigraphy done using [111In-DTPA-DPhe1]octreotide with single-photon emission CT imaging at 4 and 24 hours. Patients with possible liver metastases had biopsies done for confirmation, and 15 patients had exploratory laparotomies done to assess primary tumor localization.

RESULTS

Extrahepatic gastrinomas or liver metastases were identified by ultrasonography in 19% of patients, by CT in 38% of patients, by MRI in 45% of patients, by angiography in 40% of patients, and by somatostatin receptor scintigraphy in 70% of patients. Somatostatin receptor scintigraphy was as sensitive as the other tests combined (59%), and when the results of all other tests were added to the somatostatin receptor scintigraphy results, tumors were localized in 75% of patients. Among patients with a possible primary tumor, the results of ultrasonography were positive in 9%, the results of CT were positive in 31%, the results of MRI were positive in 30%, the results of angiography were positive in 28%, and the results of somatostatin receptor scintigraphy were positive in 58%. Somatostatin receptor scintigraphy was as sensitive as all of the other imaging studies combined; when the results of scintigraphy were added to the results of the other studies, possible primary tumors were identified in 68% of patients. In 24 patients who had histologically proven metastatic liver disease, sensitivities for the detection of any metastatic liver lesions were 46% for ultrasonography, 42% for CT, 71% for MRI, 62% for angiography, and 92% for somatostatin receptor scintigraphy. Somatostatin receptor scintigraphy was significantly better than all of the conventional imaging methods in the identification of gastrinomas later found at surgery (P = 0.004), but it still missed 20% of gastrinomas.

CONCLUSIONS

Somatostatin receptor scintigraphy is the single most sensitive method for imaging either primary or metastatic liver lesions in patients with the Zollinger-Ellison syndrome. Because of its sensitivity, simplicity, and cost-effectiveness, it should be the first imaging method used in these patients. For patients with negative results on somatostatin receptor scintigraphy, guidelines about the use of other imaging studies are proposed.

Gastric chief cells possess NK1 receptors which mediate pepsinogen secretion and are regulated by agents that increase cAMP and phospholipase C

In order to determine whether tachykinins alter the function of chief cells and to characterize the receptors mediating the effect, we investigated the abilities of various substance P (SP)-related peptides to inhibit the binding of 125I-Bolton-Hunter labeled substance P (125I-BH-SP) and their abilities to alter cell function in dispersed chief cells from guinea pig stomach. Binding of 125I-BH-SP was saturable, reversible, time- and temperature-dependent and was inhibited by several SP-related peptides with relative potencies of SP = physalaemin (IC50:0.19 nM) > SP methyl ester (SP-ME) (IC50:3.3 nM) > eledoisin (IC50:6.1 nM) > neurokinin A (NKA) (IC50: 65 nM) > neurokinin B (NKB) (IC50:80 nM). Analyses of these binding data demonstrated that chief cells possess a high and low affinity class of binding sites. Neither 125I-NKA nor [phenylalanyl-3,4,5-3H]senktide demonstrated saturable binding to chief cells. Acid stripping experiments demonstrated rapid ligand internalization with 55% of the bound radioligand internalized by 10 min. Phospholipase C activating agents (carbachol, CCK-8), adenylate cyclase activating agents (secretin, VIP), TPA and the calcium ionophore, A23187, all inhibited the binding of 125I-BH-SP and it was due to inhibition of ligand internalization with no change in surface bound parameters. SP (0.1 microM) stimulated pepsinogen secretion but was 4-times less efficacious than CCK-8 (10 nM) or carbachol (1 mM). 10 nM SP stimulated a rapid increase in cytoplasmic free calcium concentration ([Ca2+]i) followed by a sustained elevation lasting 2 min. Single cell spectroscopy demonstrated SP (10 pM to 1 microM) did not cause calcium oscillations. The NK1 receptor antagonist, CP96,345 specifically inhibited the SP-stimulated changes in [Ca2+]i and pepsinogen secretion. The relative potencies of SP-related peptides to stimulate pepsinogen secretion and [Ca2+]i demonstrated a close agreement with their abilities to inhibit the binding of 125I-BH-SP, and comparison of the dose-response curves suggests occupation of the low affinity sites mediate changes in biologic activity. In conclusion, the present study demonstrates that chief cells possess a NK1 subtype of tachykinin receptor, occupation of the low affinity sites of this receptor cause calcium mobilization and pepsinogen secretion, and that binding to this receptor is regulated by agents that activate phospholipase C, adenylate cyclase, protein kinase C and calcium mobilization.

Prolonged hypergastrinemia does not increase the frequency of colonic neoplasia in patients with Zollinger-Ellison syndrome

Whereas considerable experimental evidence suggests chronic hypergastrinemia can increase the occurrence of colonic neoplasia, the risks in man remain unclear. Zollinger-Ellison syndrome (ZES) is associated with marked plasma elevation of all forms of gastrin and, because of its prolonged course, has been shown to be an excellent model disease to study the effects of chronic hypergastrinemia in man. To determine whether profound chronic hypergastrinemia affects the occurrence of colonic dysplasia and neoplasia, 97 consecutive patients with ZES were studied. All patients underwent colonoscopic examination to the cecum, and the location, size, and type of polyps/tumors were determined. The patients had a mean fasting gastrin level 31 times above normal and a mean disease duration of 10 years; 17/97 (18%) had adenomatous polyps, 67/97 (69%) no adenomatous polyps, and 2/97 (2%) had colonoscopy and/or autopsy studies fo asymptomatic controls. Stratification by age or gender, presence of MEN-I, tumor extent, and duration of degree of hypergastrinemia did not increase prevalence. This study shows that despite prolonged, profound hypergastrinemia, no increased rate of colonic neoplasia (polyps or cancer) was noted. These data suggest that the development of hypergastrinemia secondary to continuous use of H+,K+-ATPase inhibitors for as long as 10 years is unlikely to cause an increased risk of developing colonic neoplasia in man.

A prospective study of the effectiveness of low dose omeprazole as initial therapy in Zollinger-Ellison syndrome

BACKGROUND

The proton pump inhibitors (omeprazole and lansoprazole) are the drugs of choice for the medical management of gastric acid hypersecretion in Zollinger-Ellison syndrome (ZES). These drugs are safe for long-term therapy but are acid-labile and high doses are expensive. The recommended starting dose of omeprazole is 60 mg/day. However, it has been shown in recent studies that the maintenance dose of omeprazole could be safely reduced to 20 mg once or twice a day in more than two-thirds of patients with ZES. The purpose of this study is to determine if an initial starting dose of omeprazole 20 mg/day is safe and effective in patients with ZES.

METHODS

Forty-nine consecutive patients with ZES being treated with ranitidine for at least 2 weeks were admitted to the NIH. Omeprazole 20 mg was started on day 1 of the admission and ranitidine discontinued 4 h after the first dose. Gastric acid output was measured for 1 h prior to the next omeprazole dose on day 2, then on day 3 if the value was > 10 mmol/h on the previous day. If acid-peptic symptoms developed or the gastric acid output remained > 10 mmol/h on day 3, the patient was considered to have failed omeprazole 20 mg/day initial therapy and the dose titrated daily to achieve adequate control of acid-peptic symptoms and gastric secretion.

RESULTS

In 33 of the 49 patients (68%) omeprazole 20 mg/day was successful as initial therapy. Sixteen patients (32%) failed this initial omeprazole dose (eight patients owing to persistent peptic symptoms and eight patients owing to inadequate acid control). The final daily omeprazole dose required in these patients was 40 mg in eight patients (16%), 60 mg in one patient (2%) and 80 mg in seven patients (14%). Basal acid output (BAO) was the only clinical or laboratory feature that was significantly different between the two groups in which low dose initial omeprazole therapy was or was not successful; all patients with basal acid output < 20 mmol/h had a successful outcome.

CONCLUSIONS

Because of the need to rapidly control gastric acid hypersecretion owing to the high risk of complications from peptic ulcer disease, patients with ZES should continue to be started on omeprazole 60 mg/day and the dose adjusted by acute titration methods as is currently recommended. After a maintenance dose is established, attempts should be undertaken to reduce the dose to 20 mg/ day once or twice a day. Only the minority of patients with ZES in whom basal acid output is known to be < 20 mmol/h (20% of patients) should be started on a low initial omeprazole dose.

Metastatic gastrinomas: localization with selective arterial injection of secretin

PURPOSE

To evaluate localization of hepatic metastases with the intraarterial secretin injection test in Zollinger-Ellison syndrome (ZES).

MATERIALS AND METHODS

Results in 74 patients with ZES (aged 15-70 years) were retrospectively studied. All patients had undergone computed tomography (CT), magnetic resonance (MR) imaging, ultrasound, abdominal angiography, and an intraarterial secretin test, in which venous blood is sampled periodically after injection of secretin.

RESULTS

Twenty-two patients had liver metastases. An increase in venous gastrin concentration of at least 25% at 20 seconds or 50% at 30 seconds after injection indicated a positive result. Results were positive in 41% of patients with and 2% without liver metastases (P < .0001). Sensitivity of the intraarterial secretin test was 41%; of CT and ultrasound, 64%; and of MR imaging and angiography, 77%. Intraarterial secretin test results assisted in clinical management in 22% of patients.

CONCLUSION

With the criteria developed, the intraarterial secretin test had high specificity but low sensitivity. It should be used when imaging results are unclear.

CCKB/gastrin receptor antagonists: recent advances and potential uses in gastric secretory disorders

Cholecystokinin (CCK) and the structurally related peptide, gastrin, have numerous effects on tissues in the central nervous system and gastrointestinal tract. Recent studies show these effect are mediated by a CCKA and CCKB receptor. Knowledge of the physiological role and role of CCKB receptors in pathologic processes has been particularly limited by the availability of selective, potent receptor antagonists. Recently, new members of five different classes of non-peptide CCKB receptor antagonists are reported and are reviewed briefly. these include compounds isolated from Streptomyces (tetronothiodin, virginiamycin analogues), ureido-acetamide analogues (RP 69758, RP 72540, RP 73870), newer benzodiazepine analogues (L-368,935, L-740,093, YM022), pyrazolidimine analogues (LY 262,691) and glutamic acid analogues (CR2194). Many of these compounds have greater than 1000-fold selectivity for the CCKB over the CCKA receptor and some have greater than 10,000-fold selectivity. The pharmacology and effects of CCKB receptor antagonists on gastric acid secretion is briefly reviewed. Furthermore, the possible clinical usefulness of CCKB receptor antagonists in treating disorders of gastric acid secretion, in inhibiting the trophic effects of gastrin and in other clinical conditions is briefly discussed.

Comparison of the peptide structural requirements for high affinity interaction with bombesin receptors

Recently it has been established that both a gastrin-releasing peptide (GRP)-preferring bombesin receptor and a neuromedin B-preferring bombesin receptor mediate the mammalian actions of bombesin-related peptides. Because many tissues used for studies of the structure-activity relationship of these peptides possess both receptor subtypes and none possess only the neuromedin B-preferring subtype, there is minimal information on the peptide structural features determining receptor selectivity and it is unknown whether the determinants of agonism at both bombesin receptor subtypes are similar. In the present study we have used native cells either possessing only one bombesin receptor subtype or stably transfected with one subtype to study in detail the peptide structural requirements for interacting and activating each receptor subtype. For the naturally occurring agonists, at the GRP-preferring bombesin receptor the relative affinities were litorin = ranatensin = bombesin > GRP >> neuromedin B, phyllolitorin and at the neuromedin B-preferring bombesin receptor were litorin = neuromedin B = ranatensin > bombesin, phyllolitorin >> GRP. For the GRP-preferring bombesin receptor the heptapeptide and for the neuromedin B-preferring bombesin receptor the octapeptide was the minimal carboxyl fragment interacting with the receptor/or causing biologic activity, and the nonapeptide and full decapeptide, respectively, were the minimal required for full affinity. Making neuromedin B more bombesin- or GRP-like by replacing amino acids in position 3, 6, and 9 demonstrated that position 3 was the most important, followed by position 9 for receptor subtype selectivity. A conformationally restricted GRP analogue, [D-Cys6,D-Ala11,Cys14]bombesin-(6-14) had a significantly higher affinity for GRP-preferring bombesin receptor than NMB receptor. These results demonstrate that: (1) the structure-function relations for the two mammalian bombesin receptors have important differences; (2) suggest that the active conformation of neuromedin B must differ markedly from the beta-sheet model proposed for GRP; and (3) suggest that one important function of the NH2 terminus of GRP and neuromedin B is determining receptor subtype selectivity.