Somatostatin inhibition of insulin and gastrin hypersecretion in pancreatic islet-cell carcinoma

Somatostatin analogues for the treatment of hyperinsulinaemic hypoglycaemia

Hyperinsulinaemic hypoglycaemia (HH) is a biochemical finding of low blood glucose levels due to the dysregulation of insulin secretion from pancreatic β-cells. Under normal physiological conditions, glucose metabolism is coupled to β-cell insulin secretion so that blood glucose levels are maintained within the physiological range of 3.5-5.5 mmol/L. However, in HH this coupling of glucose metabolism to insulin secretion is perturbed so that insulin secretion becomes unregulated. HH typically occurs in the neonatal, infancy and childhood periods and can be due to many different causes. Adults can also present with HH but the causes in adults tend to be different. Somatostatin (SST) is a peptide hormone that is released by the delta cells (δ-cells) in the pancreas. It binds to G protein-coupled SST receptors to regulate a variety of location-specific and selective functions such as hormone inhibition, neurotransmission and cell proliferation. SST plays a potent role in the regulation of both insulin and glucagon secretion in response to changes in glucose levels by negative feedback mechanism. The half-life of SST is only 1-3 min due to quick degradation by peptidases in plasma and tissues. Thus, a direct continuous intravenous or subcutaneous infusion is required to achieve the therapeutic effect. These limitations prompted the discovery of SST analogues such as octreotide and lanreotide, which have longer half-lives and therefore can be administered as injections. SST analogues are used to treat different forms of HH in children and adults and therapeutic effect is achieved by suppressing insulin secretion from pancreatic β-cells by complex mechanisms. These treatments are associated with several side effects, especially in the newborn period, with necrotizing enterocolitis being the most serious side effect and hence SS analogues should be used with extreme caution in this age group.

Serum gastrin in Zollinger-Ellison syndrome: I. Prospective study of fasting serum gastrin in 309 patients from the National Institutes of Health and comparison with 2229 cases from the literature

The assessment of fasting serum gastrin (FSG) is essential for the diagnosis and management of patients with the Zollinger-Ellison syndrome (ZES). Although many studies have analyzed FSG levels in patients with gastrinoma, limited information has resulted from these studies because of their small size, different methodologies, and lack of correlations of FSG levels with clinical, laboratory, or tumor features in ZES patients. To address this issue, we report the results of a prospective National Institutes of Health (NIH) study of 309 patients with ZES and compare our results with those of 2229 ZES patients in 513 small series and case reports in the literature. In the NIH and literature ZES patients, normal FSG values were uncommon (0.3%-3%), as were very high FSG levels >100-fold normal (4.9%-9%). Two-thirds of gastrinoma patients had FSG values <10-fold normal that overlap with gastrin levels seen in more common conditions, like Helicobacter pylori infection or antral G-cell hyperplasia/hyperfunction. In these patients, FSG levels are not diagnostic of ZES, and gastrin provocative tests are needed to establish the diagnosis. Most clinical variables (multiple endocrine neoplasia type 1 status, presence or absence of the most common symptoms, prior medical treatment) are not correlated with FSG levels, while a good correlation of FSG values was found with other clinical features (prior gastric surgery, diarrhea, duration from onset to diagnosis). Increasing basal acid output, but not maximal acid output correlated closely with increasing FSG. Numerous tumoral features correlated with the magnitude of FSG in our study, including tumor location (pancreatic > duodenal), primary size (larger > smaller) and extent (liver metastases > local disease). In conclusion, this detailed analysis of FSG in a large number of patients with ZES allowed us to identify important clinical guidelines that should contribute to improved diagnosis and management of patients with ZES.

Clinical uses of gut peptides

OBJECTIVE

The authors review clinical applications of gut-derived peptides as diagnostic and therapeutic agents.

SUMMARY BACKGROUND DATA

An increasing number of gut peptides have been evaluated for clinical use. Earlier uses as diagnostic agents have been complemented more recently by increasing application of gut peptides as therapeutic agents.

METHOD

The authors conducted a literature review.

RESULTS

Current experience with clinical use of gut peptides is described. Initial clinical applications focused on using secretomotor effects of gut peptides in diagnostic tests, many of which have now fallen into disuse. More recently, attention has been directed toward harnessing these secretomotor effects for therapeutic use in a variety of disorders, and also using the trophic effects of gut peptides to modulate gut mucosal growth in benign and malignant disease. Gut peptides have been evaluated in a variety of other clinical situations including use as adjuncts to imaging techniques, and modification of behaviors such as feeding and panic disorder.

CONCLUSIONS

Gut peptides have been used successfully in an increasing variety of clinical conditions. Further refinements in analogue and antagonist design are likely to lead to even more selective agents that may have important clinical applications. Further studies are needed to identity and evaluate these new agents.

Metastatic pancreatic neuroendocrine carcinoma causing Cushing's syndrome. ACTH secretion by metastases 3 years after resection of nonfunctioning primary cancer

CONCLUSION

Following resection of a nonfunctioning neuroendocrine carcinoma of the pancreas, subsequent metastases, in the absence of a primary cancer (resected), developed the capacity to secrete ACTH and create the Cushing syndrome.

BACKGROUND

Although neuroendocrine carcinomas of the pancreas may produce one or more hormones and may switch secretion to a different hormone, no report is identified of a metastasis, in the absence of the primary tumor, developing de novo the capacity to secrete ACTH.

METHODS

A nonfunctioning islet cell carcinoma was resected and immunochemically stained for multiple hormones. Three years later hepatic metastases were partially resected and stained as before.

RESULTS

The primary cancer stained negative for ACTH and cortisol, positive for serotonin, and focally positive for gastrin. Three years later, after the development of a florid Cushing syndrome, the metastasis stained strongly for ACTH and negative for serotonin.

Use of octreotide acetate for control of symptoms in patients with islet cell tumors

Gut tumor syndromes are rare, occurring in less than two cases per million population per year: Insulinomas are most common and gastrinomas are less common; all the others are extremely rare. Conventional treatment of the symptoms caused by these tumors has included surgery, hepatic arterial embolization, and chemotherapy; some patients with Zollinger-Ellison syndrome (ZES) have been treated with specific agents such as gastric antisecretory drugs. The development of octreotide, a synthetic, long-acting analogue of the natural peptide somatostatin, has offered an alternative to such therapies. Octreotide has a half life of > 100 minutes and inhibits both physiological- and tumor release of many peptides. It also has direct effects on the gut that modify secretion and motility. Octreotide has been shown to be particularly useful for the symptoms of tumors producing vasoactive intestinal peptide (VIP), and of the carcinoid syndrome. It is also useful in patients with glucagonomas, with growth hormone-releasing hormone producing tumors, and in some patients with Cushing's syndrome and unresectable insulinomas. Octreotide is effective in patients with ZES, but alternative therapies such as omeprazole are more effective, safer, and more convenient for those patients. Side effects of octreotide have not been troublesome in these patients, but the incidence of long term effects is still not entirely clear. Octreotide has proved to be a significant advance in the treatment of patients with islet cell tumors.

Mechanism for increase of gastrin release by secretin in Zollinger-Ellison syndrome

In patients with Zollinger-Ellison syndrome, serum gastrin level is increased by secretin and is decreased by somatostatin. To elucidate the cellular mechanism for these actions, we investigated the direct effects of secretin and somatostatin on dispersed gastrinoma cells from a patient with Zollinger-Ellison syndrome. In the presence of 3-isobutyl-1-methylxanthine, secretin significantly stimulated gastrin release from dispersed gastrinoma cells, which was inhibited by somatostatin. In the presence of guanosine 5'-triphosphate, furthermore, secretin enhanced adenylate cyclase activation in the membranes from these cells, and this activation was reduced by somatostatin, whereas neither secretin nor somatostatin affected inositol phospholipid turnover. On the other hand, removal of guanosine 5'-triphosphate from incubation medium abolished both the stimulatory effect of secretin and the inhibitory effect of somatostatin on adenylate cyclase activation. Furthermore, pertussis toxin pretreatment reversed the ability of somatostatin to inhibit secretin-induced increase in gastrin release and activation of adenylate cyclase. Thus, in this gastrinoma patient, secretin and somatostatin appeared to act directly on gastrinoma cells to stimulate and inhibit gastrin secretion, respectively, by modulating adenylate cyclase activation, probably via guanine nucleotide-binding proteins.

Use of long-acting somatostatin analog SMS 201-995 in patients with pancreatic islet cell tumors

Natural somatostatin reduces plasma concentrations of many peptides, and is of short term benefit in patients with islet cell tumors, but has to be given as a continuous intravenous infusion. We review the published experience with the long acting synthetic somatostatin analogue SMS 201-995 in patients with islet cell tumors. Fifteen of 18 patients with vasoactive intestinal peptide-producing tumors, 8 of 8 patients with glucagonomas, 7 of 7 patients with unresectable insulinomas, and 3 of 3 patients with growth hormone releasing factor-producing tumors had a good sustained symptomatic response to SMS 201-995. Patients with benign insulinomas responded variably and are best treated by surgery. Patients with gastrinomas are best treated by oral gastric antisecretory agents. In all these syndromes, the clinical response to SMS 201-995 did not necessarily parallel the change in plasma concentration of marker peptide, suggesting that SMS 201-995 may have actions at various sites. The effect of SMS 201-995 on tumor size has been assessed in 46 patients, less than 20% of whom showed a reduction in tumor size. Side effects have been mild, but include steatorrhea and gastrointestinal disturbances. More studies will be required to fully assess the effects of long-term administration of SMS 201-995.

Effect of the long-acting somatostatin analogue SMS 201-995 on small-intestinal interdigestive motility in the dog

The long-acting somatostatin analogue SMS 201-995, also called Sandostatin, is used in the treatment of acromegaly and peptide-secreting tumors. Little is known about its effect on gut motility, although such an effect might be expected considering the spectrum of activities of its parent molecule, somatostatin. We have studied the effect on the interdigestive motility of intravenous boluses of 0, 0.1, 0.5, 1.5, and 5.0 micrograms/kg of this analogue in 10 dogs with bipolar electrodes implanted along the entire small bowel. All doses induced, within 5 min of administration, premature phase-3 activity that was isolated to one segment, normally progressive, or simultaneous (stationary) in all channels. Only low doses induced isolated phase 3, whereas the frequency of the induction of stationary phase 3 increased with higher doses. In the next cycle of the migrating motor complex the duration of phase 1 was increased, although the duration of the whole cycle was not changed. This cycle ended with mostly ectopic phase-3 activity. During phase 2 of the following cycle ultra-rapid rushes of spiking activity progressing at a speed of 25 +/- 3 cm/sec in the upper jejunum were regularly observed. Although this pattern occurs very rarely under control conditions, it was present in 20%, 80%, and 100% of the experiments after doses of 0.5, 1.5, and 5.0 micrograms/kg, respectively. We conclude that gastrointestinal side effects observed during administration of SMS 201-995 might be related to these motility effects, which warrant further investigation. SMS 201-995 may be a tool to study the mechanism of the induction of ultra-rapid rushes and of stationary phase 3.

Clinical and hormonal effects of a long-acting somatostatin analogue in pancreatic endocrine tumors and in carcinoid syndrome

Nine patients with pancreatic apudomas (seven gastrinomas, one glucagonoma, one tumor secreting a substance P-like component) and nine with metastasized carcinoid tumors were treated with a somatostatin analogue (SMS 201-995), administered subcutaneously twice daily for 3 days. Treatment was pursued for 2 to 12 months in nine patients in whom SMS was clinically and/or biologically beneficial. In gastrinomas, SMS decreased plasma gastrin in all but one patient, inhibited the residual gastric acid secretion under H2-blockers and improved diarrhea; in the glucagonoma patient, glucagonemia decreased and skin lesions disappeared. In carcinoid syndrome, clinical efficacy was partial and inconstant; daily 5-hydroxyindole acetic acid (5-HIAA) output was slightly decreased. Plasma substance P levels decreased in six patients with initially high concentrations. No antitumoral activity or side effects have been so far evidenced. SMS 201-995 is a useful, well-tolerated agent in secreting pancreatic apudomas and to a lesser extent in carcinoid syndrome, where high-dosage regimens may be required.

Pharmacological studies of somatostatin and somatostatin-analogues: therapeutic advances and perspectives

This article is aimed at reviewing and analyzing studies that are related to the possible therapeutic use of a potent and ubiquitously-distributed hormone--somato-statin (SS-14), and its analogues. Administration of these substances has provided beneficial effects in treating acromegaly, gastro-intestinal hemorrhagic and hypersecretory disorders, acute pancreatitis, diabetes mellitus, and certain types of cancer. Further studies with SS-14-analogues might provide new therapies for treating certain life-threatening disorders of man.

[Islet cell cancer with organic hyperinsulinism. Clinical aspects, diagnosis and therapy]

About 8%-15% of the patients with organic hyperinsulinism have an islet cell carcinoma (13% in our series). In addition to a history of complaints of relatively recent onset, the patients present clinically the typical intermittent neurologic-psychiatric symptoms concurrently associated with hypoglycemia. The diagnosis is established biochemically on the basis of hypoglycemia, with inadequate incrementation of the insulin concentration subsequent to suppression and provocation tests. Elevated serum proinsulin and, in most patients, an increased insulin secretion rate are usually found after administration of agents such as glucose or leucine. Localization of the tumors is achieved by selective coeliacography as well as abdominal computerized axial tomography. The islet cell carcinoma is found most frequently in the tail of the pancreas, less frequently in the body and head of the pancreas. Metastatic spread is seen early into adjacent lymph nodes and especially in the liver. The treatment of choice is surgical resection of the tumor. Even in cases with advanced metastatic involvement, surgical intervention appears indicated. Medical treatment includes the administration of diazoxide, long-acting glucagon as well as the cytostatic agent streptozotocin. The average survival time is 30-40 months after diagnosis (in our series 79 months). Thus, the prognosis of patients with islet cell carcinoma appears relatively favorable, especially when compared with adenocarcinoma of the pancreas.

Effects of somatostatin in a case of severe hypoglycemia due to nesidioblastosis

The Authors have studied the effects of somatostatin (SRIF) treatment in an infant affected by hypoglycemia due to nesidioblastosis. During iv infusion with SRIF we observed a marked increase of blood glucose levels; concomitantly insulin secretion was almost completely suppressed. In contrast, during treatment with protamine zinc-somatostatin (PZ-SRIF), a long acting SRIF preparation, the blood glucose levels did not rise and insulin concentrations were inappropriately elevated. Therefore in this case the long term treatment of hypoglycemia due to nesidioblastosis with PZ-somatostatin was unfeasible.

Effects of somatostatin on insulin and glucagon in patients with insulinoma

Effects of somatostatin on fasting and arginine-or tolbutamide-stimulated insulin release were studied in four patients with insulinoma. Somatostatin (bolus or bolus + infusion) reduced fasting insulin values in all patients; insulin response to tolbutamide was partially reduced in two patients; somatostatin bolus impaired the insulin response to arginine. Fasting glucagon levels and glucagon response to arginine were also reduced by somatostatin. These results indicate the potential usefulness of somatostatin in the diagnosis of insulinoma even if its effect on insulin is only partial.

[Somatostatin -- a review (author's transl)]

Somatostatin, a peptide isolated from ovine hypothalami, prevents growth hormone secretion in vivo and in vitro. Moreover, somatostatin interferes with the secretion of various other hormones: TSH insulin, glucagon, gastrin, VIP and GIP. Under certain conditions a blunting effect on the secretion of prolactin and ACTH can be demonstrated.

The mechanism whereby growth hormone-release inhibiting hormone (somatostatin) inhibits food stimulated gastric acid secretion in the cat

Growth hormone-release inhibiting hormone (somatostatin) inhibits the gastric acid response to food in concious cats. We have confirmed that this tetradecapeptide blocks the food stimulated gastrin release. However, the inhibition of gastrin release is delayed relative to that of acid secretion, &howing that the inhibition of food stimulated acid secretion is by primary effect on the acid secretory mechanism. No evidence was found of potentiation of either the gastric acid output or serum concentration of gastric in response to food.