Dietary L-lysine supplementation altered the content of pancreatic polypeptide, enzymes involved in glutamine metabolism, and ß-actin in rats.

This study investigated the effects of Lys supplementation on serum pancreatic polypeptide (PP), glutamine (Gln) levels and the expression of PP, Gln synthetase (GlnS), glutaminase (Gls) and ß-actin in different tissues such as pancreas, skeletal muscle, liver and kidney in rats. Male Sprague-Dawley rats were fed diets containing 7% casein supplemented with either 0% (Control), 1%, 1.5%, 3% Lys or 3% Lys with 1.5% Arg for a week. All rats were necropsied for collection of blood and tissues. Expression of PP, GlnS, Gls, and ß-actin in tissues were determined using Western blotting. The results showed that the rats fed 3% supplemental Lys had significantly lower body weight gain (BWG) and food intake than the ≤ 1.5% Lys groups (P < 0.05). Supplementation with ≥ 1% Lys increased serum PP level (P < 0.05), but had no significant effect on pancreatic PP abundance (P > 0.05). GlnS expression was significantly lowered in skeletal muscle by ≥ 1.5% supplemental Lys compared to the Control (P < 0.05). The expression of Gls in the kidney was increased by the addition of 1.5% Arg to 3% Lys diet (P < 0.05). Liver ß-actin significantly increased with both Lys and Arg supplementation and muscle ß-actin significantly decreased (P < 0.05) with ≥ 1.5% supplemental Lys. Kidney ß-actin significantly increased with Arg supplementation vs 3% Lys alone (P < 0.05). These results showed that dietary supplementation with ≥ 1.5% Lys significantly suppressed GlnS expression in the skeletal muscle, which may contribute to the decreased serum Gln levels, and that increased serum PP by Lys may be due to suppressed catabolism rather than increased synthesis of PP. Lys-induced PP may play a role in reducing food intake and BWG.

Unimpaired postprandial pancreatic polypeptide secretion in Parkinson's disease and REM sleep behavior disorder.

BACKGROUND: Pancreatic polypeptide is released immediately after food ingestion. The release is operated by vagal-abdominal projections and has therefore been suggested as a test for vagal nerve integrity. Pathoanatomical and clinical studies indicate vagal dysfunction in early Parkinson's disease (PD). METHODS: We assessed the postprandial secretion of pancreatic polypeptide and motilin in healthy controls (n = 18) and patients with idiopathic rapid-eye-movement sleep behavior disorder (iRBD, n = 10), a potential premotor stage of PD, as well as in drug-naive (n = 19) and treated (n = 19) PD patients. RESULTS: The postprandial pancreatic polypeptide secretion showed a physiological pattern in all groups and even an enhanced response in drug-naive PD and iRBD. Motilin concentrations correlated with pancreatic polypeptide concentrations. CONCLUSIONS: Postprandial pancreatic polypeptide secretion is not a suitable test for vagal nerve integrity in PD. The unimpaired pancreatic polypeptide response in iRBD and PD might be explained by partially intact vagal-abdominal projections or compensatory mechanisms substituting a defective neuronal brain-gut axis.

Distribution of pancreatic endocrine cells including IAPP-expressing cells in non-diabetic and type 2 diabetic cases.

There is a lack of agreement on the distribution of islet amyloid polypeptide (IAPP) in the pancreases of healthy and diabetic subjects. Therefore, a detailed morphometrical and immunohistochemical study was performed to obtain information on the distribution of cells expressing insulin, glucagon, somatostatin, pancreatic polypeptide (PP), and IAPP in the pancreases of non-diabetic (n=4) and diabetic individuals (n=6). In the non-diabetic cases, beta-cells contributed to approximately 64%, alpha-cells to 26%, delta-cells to 8%, PP cells to 0.3%, and IAPP cells to 34% of the islet cell population. The ratio of IAPP/insulin was approximately 1:2. In diabetic cases, beta-cells were decreased by 24%, and IAPP was decreased by 57%. The alpha- and delta-cells were increased by 40% and 58%, respectively. IAPP/insulin ratio was decreased by 41%. Thus, only 50% of the beta-cells in non-diabetics and only 30% in diabetics coexpressed IAPP. In diabetics, more delta-cells coexpressed IAPP than in non-diabetics. The results seem to argue against the notion that the secretion of IAPP is increased in diabetics. It is possible that an increase in somatostatin and glucagon plays a greater role in diabetes than IAPP.

Ca2+ signaling in mouse pancreatic polypeptide cells.

Ca2+ signaling was studied in pancreatic polypeptide (PP)-secreting cells isolated from mouse islets of Langerhans. After measuring the cytoplasmic Ca2+ concentration ([Ca2+]i), the cells were identified by immunocytochemistry. Most PP-cells reacted to carbachol and epinephrine with prompt and reversible elevation of [Ca2+]i, often manifested as slow oscillations. The carbachol effect was muscarinic, because it was inhibited by atropine. Beta-adrenergic elevation of cAMP explains the epinephrine stimulation, which was mimicked by an activator of adenylate cyclase and blocked by an inhibitor of protein kinase A. The responses to carbachol and epinephrine apparently involve depolarization with opening of voltage-dependent Ca2+ channels, because the effects were prevented by the Ca2+ channel antagonist methoxyverapamil and by diazoxide, which activates ATP-dependent K+ (K(ATP)) channels. Being equipped with K(ATP) channels, the PP-cells often responded to tolbutamide or high concentrations of glucose with elevation of [Ca2+]i. Somatostatin reversed the [Ca2+]i elevation obtained by carbachol, epinephrine, tolbutamide, and glucose. These preliminary studies support the idea that glucose has a direct stimulatory effect on the PP-cells, which can be masked by locally released somatostatin. Expressing both K(ATP) channels and voltage-dependent Ca2+ channels, the PP-cells share fundamental regulatory mechanisms with other types of islet cells.

PYY in developing murine islet cells: comparisons to development of islet hormones, NPY, and BrdU incorporation.

Exhaustive characterizations of antisera to the structurally related peptides pancreatic polypeptide (PP), neuropeptide Y (NPY), and peptide YY (PYY) enabled us to establish the developmental pattern of these peptides in rat and mouse pancreas. PYY was the earliest detectable peptide and was present in all early appearing endocrine cell types. NPY appeared later and occurred exclusively in a subpopulation of insulin cells, whereas PP cells arose latest. At the earliest stage studied, all endocrine cells stored PYY. Most of these cells also contained glucagon. Subsequently, the endocrine cells comprised glucagon+PYY cells and glucagon+PYY+insulin cells. Later, cells storing either only insulin or insulin+PYY appeared. Quantitations of the relative numbers of these cell populations during development were consistent with a precursor role of triple-positive (insulin+glucagon+PYY) cells. Moreover, bromodeoxyuridine (BrdU) injections at E15.5 showed that a large percentage of triple-positive cells were in S-phase and therefore were actively dividing, whereas almost no pure insulin cells or insulin+PYY cells synthesized DNA at this time. These results suggest that PYY-positive endocrine cells may represent precursors for mature islet cells.

Transcription factor expression and hormone production in pancreatic AR42J cells.

AR42J is an exocrine pancreatic cell line that has been reported to differentiate towards an endocrine phenotype when stimulated with various growth factors, such as activin A, hepatocyte growth factor (HGF), betacellulin or glucagon-like peptide 1. In our experiments, AR42J-B13 cells differentiated morphologically in response to the growth factor treatment as reported previously. However, they failed to express the insulin gene. We found that the cells did not express several transcription factors known to be found in the beta-cell, including Nkx6.1, isl-1, Pax4 and Pax6. In addition, the mRNA level for pdx-1 and Nkx2.2 were very low in comparison to the insulinoma cell lines INS-1 and RINm5F. However, some transcription factors typically found in beta-cells and neuroendocrine cells were expressed also in the AR42J-B13 cells. These included BETA2/NeuroD, HNF1alpha, C/EBPbeta and IA-1. Unlike the insulinoma cells, AR42J cells expressed the exocrine transcription factor p48. In order to induce endocrine differentiation, we transfected the AR42J-B13 cells with the full length cDNAs of isl-1, Nkx6.1, Nkx2.2 and pdx-1 under the control of the CMV promoter, both separately and in combinations. The expression of Nkx2.2 led consistently to the appearance of pancreatic polypeptide but not insulin, glucagon or somatostatin mRNA. The PP mRNA expression in Nkx2.2 cDNA transfected cells was independent of the growth factor treatment used for differentiating AR42J cells. In conclusion, the AR42J-B13 line possesses some features of a pancreatic neuroendocrine cell. However, we were unable to confirm the capacity of these cells to differentiate into insulin-producing cells. Our results indicate that Nkx2.2 plays a role in the transcriptional regulation of PP expression.

Pancreatic-polypeptide cell hyperplasia associated with pancreatic or duodenal gastrinomas.

An immunohistochemical investigation of pancreatic-polypeptide (PP) cells in the PP-rich region of the pancreas, of ventral embryological origin, was performed in three female patients affected by or previously operated on for functioning duodenal or pancreatic gastrinomas not associated with multiple endocrine neoplasia syndrome. A pronounced PP-cell hyperplasia showing histological patterns of endocrine cell dysplasia and focal adenomatosis as defined by Jaffe et al was found in all cases. Morphometric analysis showed that in these patients the fraction of ventral-type pancreatic lobules occupied by PP-immunoreactive cells was 14.77 +/- 5.73%, 8.94 +/- 2.92%, and 10.83 +/- 5.64%, respectively. These values were three to five times higher than the upper values found in controls (mean, 2.20%; range, 1.54 to 2.93%; P < .0001). PP-cell hyperplasia may contribute for the increased circulating levels of PP found in gastrinoma patients. In this regard, elevation of fasting blood PP was found in one of four determinations done in one patient, indicating that PP-cell hyperplasia may be responsible for, at least, transient PP hypersecretion. In one of our patients, PP-cell hyperplasia was found 15 years after normalization of gastrin levels by removal of a single pancreatic gastrinoma. This finding is against a trophic role for hypergastrinemia in the development of PP-cell hyperplasia. In one of two patients in whom the pancreatic regions of dorsal embryological origin (ie, body and tail of the gland) were examined, ventral-type, PP-rich islets were frequently encountered, a finding at variance with their exceptional detection in control cases. This finding suggests that PP cell hyperplasia of the PP-rich pancreatic region may be a feature of a more diffuse disorder of PP cell development in the pancreas of gastrinoma patients.

Expression of non-classical islet hormone-like peptides during the embryonic development of the pancreas.

Understanding of islet embryogenesis may prove to be key in the design of future therapies for diabetes directed at re-initiating islet growth, with the goal to replace and/or replenish the impaired beta-cell mass in the disease. In this context, studies of islet neurohormonal peptides, known to play a role in the local regulation of islet function, and their expression during islet embryogenesis are important. Here we review our studies on the embryonic islet expression of islet amyloid polypeptide (IAPP) and the PP-fold peptides pancreatic polypeptide (PP), peptide YY (PYY) and neuropeptide Y (NPY). IAPP, which is constitutively expressed in beta- and delta-cells in the adult rat, was found to occur in the assumed pluripotent islet progenitor cell, together with PYY, glucagon, and to a lesser extent with insulin. As development proceeds, the insulin/IAPP phenotype is segregated from that of PYY/glucagon; with the formation of islet-like structures, insulin/IAPP-expressing cells primarily occupy their central portions, while PYY/glucagon-expressing cells are found in their periphery. At the time of formation of islet-like structures, expression of NPY is induced in the insulin/IAPP-containing cells. Whereas NPY-expression ceases at birth, PYY is constitutively expressed in non-beta-cells in the mature rat. Expression of PP is induced just prior to birth in a separate population of islet cells, occasionally co-expressed with PYY. Although a clear role for these peptides during embryogenesis has not been identified, they conceivably could play a role in the control of insulin secretion, islet growth and islet blood flow.

Pancreatic polypeptide-producing tumors. Silent lesions of the pancreas?

Eight patients with pancreatic polypeptide (PP)-producing islet cell tumors and one patient with pseudo-PP-producing tumors were examined. Their age range was 20 to 74 years. Clinical features included abdominal pain in four patients, weight loss in four patients, diarrhea in two patients, gastrointestinal bleeding in two patients, and jaundice in one patient. The range of the basal serum level of PP was 394 to 35,100 pg/mL. In two patients the PP-producing tumors were associated with multiple endocrine neoplasia. Two patients had diffuse hepatic metastases at the time of diagnosis and four patients had disease limited to the pancreas. Pancreaticoduodenectomy and 80% pancreatectomy were performed in four and two patients, respectively. Immunohistochemical staining was positive for PP and neuron-specific enolase in all cases and was negative for other peptides except in one specimen with microadenomatosis. Patients who underwent curative resection are asymptomatic with normal serum levels of PP.

Distribution of pancreatic polypeptide and peptide YY.

The cellular distribution of PP and PYY in mammals is reviewed. Expression of PP is restricted to endocrine cells mainly present in the pancreas predominantly in the duodenal portion (head) but also found in small numbers in the gastro-intestinal tract. PYY has a dual expression in both endocrine cells and neurons. PYY expressing endocrine cells occur all along the gastrointestinal tract and are frequent in the distal portion. Islet cells expressing PYY are found in many species. In rodents they predominate in the splenic portion (tail) of the pancreas. A limited expression of PYY is found also in endocrine cells in the adrenal gland, respiratory tract and pituitary. Peripheral, particularly enteric, neurons also express PYY as does a restricted set of central neurons.

Pancreatic polypeptide in pancreatitis.

Pancreatitis is a disease with increasing incidence which can be divided into an acute and a chronic form. In both acute and chronic pancreatitis, changes in plasma concentration of pancreatic polypeptide (PP) and its regulation have been reported. In daily clinical work a serologic test for the precise diagnosis and staging of acute and chronic pancreatitis is still desirable. Therefore, many studies have investigated plasma concentrations of PP in acute and chronic pancreatitis as a diagnostic marker and as a therapeutic option to treat pancreatogenic diabetes mellitus. Although the study results are presently inconclusive and potentially contradictory, the findings are nevertheless encouraging, and indicate that PP might have a role in diagnosis, grading and estimation of the prognosis of pancreatitis. Further data and prospective controlled studies are needed to judge whether PP is of clinical value for diagnosing, staging and predicting long-term outcome in acute and chronic pancreatitis.

Developmental expression of NPY, PYY and PP in the rat pancreas and their coexistence with islet hormones.

It has been suggested that members of the neuropeptide Y (NPY) family of regulatory peptides [NPY, peptide YY (PYY) and pancreatic polypeptide (PP)] play an important role in the development of the endocrine pancreas. The development of rat endocrine pancreas from embryonic (E) day 12 until 30 days postpartum (P) was studied with emphasis on NPY, PYY and PP and their co-existence with insulin, glucagon and somatostatin using single and double immunostaining and in situ hybridization. Already at E12, PYY was detectable in small endocrine cell clusters and found to be co-localised with both insulin and glucagon, which at this stage occurred in the same cells. At E16 most of the insulin-immunoreactive (IR) cells were distinct from the glucagon/PYY-IR cells. Interestingly, at E16 NPY mRNA, and at E17 NPY immunoreactivity appeared in a few, scattered endocrine cells. Virtually all NPY-IR endocrine cells were insulin-producing beta cells. At E18 the endocrine cells started to form typical islets with centrally located insulin/NPY-IR cells surrounded by glucagon/PYY-IR cells. AT E20-E21, the vast majority of insulin-producing cells also expressed NPY. However, at birth (day 0) islet cell NPY mRNA was lacking. Postnatally the number and immunostaining intensity of NPY-IR islet cells rapidly declined, being non-detectable at P5. Cells containing PP immunoreactivity and PP mRNA were first detected at E21. The adult pattern of islet peptide distribution, with NPY confined to neuronal elements. PYY and PP exclusively in endocrine cells, was established at P5. The beta cell expression of NPY during the latter part of embryogenesis coincides with the prepartal glucocorticoid surge and with rapid islet cell replication and differentiation. This is compatible with steroid induction of NPY expression and with a role for NPY in the maturation of beta cells and their hormone release, which occurs in the immediate neonatal period.

Gallbladder emptying and cholecystokinin and pancreatic polypeptide responses to a liquid meal in patients with diabetes mellitus.

To investigate gallbladder motility and its regulation in patients with diabetes mellitus (DM), we examined the gallbladder response to an intraduodenal test meal by measuring the temporal course of plasma cholecystokinin (CCK) and pancreatic polypeptide (PP) levels. Eighteen patients with type 2 DM and 7 healthy subjects (controls) were enrolled. The gallbladder volume was calculated by the sum-of-cylinders method from ultrasonographic images, and plasma CCK and PP were measured by radioimmunoassays. No significant difference was found in either the gallbladder response or in the CCK response between patients with DM and controls. However, the fasting plasma PP level of patients with DM was more than tenfold higher than that of controls. The integrated PP response (IPPR) of patients with DM to the test meal was 8.3-fold higher than that of controls. When patients with DM were grouped according to whether they had been treated with insulin or not, the fasting plasma PP of patients with DM without insulin treatment was significantly higher than the level in those treated with insulin. These results suggest that overproduction of PP-like immunoreactive substance(s) may occur in patients with DM, but the high plasma PP immunoreactivity does not appear to be related to the fasting gallbladder volume or to gallbladder emptying and filling.

Endocrine pancreatic carcinoma.

Endocrine carcinomas of the pancreas are rare, but they should be treated aggressively because they threaten the patient's life by both malignant growth and hormone excess. Resection for cure should be attempted, but is hardly ever possible. Debulking should be performed primarily in hormone-active tumours so that symptoms can be controlled by subsequent medical treatment; this can be directed against tumour growth and/or hormone production, and it can reduce stomach acid secretion in the gastrinoma syndrome. Surgery should be undertaken whenever possible since the patient's life can be considerably prolonged in most cases. Palliative surgery can reduce the patient's symptoms that may be caused by excessive hormone production and/or obstruction of the bile duct or the duodenum.

Carcinoid tumor of the cystic duct.

A 69-year-old male was admitted to an outside institution for severe right abdominal pain radiating to the flank. An extensive work-up, including lower GI series, IVP, and ultrasound of the kidneys were normal. Ultrasound of the liver demonstrated a thickened gallbladder as well as cholelithiasis. Despite some improvement, his symptoms returned intermittently and cholecystectomy was performed. Pathologic examination of the gallbladder showed a carcinoid tumor, 5.4 mm in maximum diameter, in the cystic duct. A small metastatic focus was also found in the cystic duct lymph node. In this paper we compare the clinical presentation, pathological findings and outcome of this case to the previously reported six cases of cystic duct carcinoid. A comparison is also made between the general features of carcinoid at this rare location and the more common gastrointestinal carcinoid.

Disseminated pancreatic polypeptidioma.

Pancreatic polypeptidioma, a pancreatic endocrine tumor, is an extremely uncommon disease and its clinical features and responses to therapy are not well known. We present a 33-year-old woman with disseminated pancreatic polypeptidioma, who subsequently showed various signs and symptoms of metastases, including bone pain, cranial nerve palsy, spinal block, and hematuria, and died 22 months after the presentation. Responses to various therapeutic regimens including hepatic arterial embolization, radiation therapy, systemic chemotherapy, and administration of interferon-alpha or somatostatin analogue, are discussed. Particular note in this case is a prompt response of bone metastases to the radiotherapy.

Vesicular monoamine transporter, type 2 (VMAT2) expression as it compares to insulin and pancreatic polypeptide in the head, body and tail of the human pancreas.

The vesicular monoamine transporter, type 2 (VMAT2) is responsible for sequestering monoamine neurotransmitters into exocytic vesicles in neurons, enterochromaffin-like cells of the stomach and cells arising from the common myeloid progenitor. VMAT2 is also present in the pancreas and is expressed by insulin producing ß cells, but not by glucagon or somatostatin expressing islet cells. Positron emission tomography (PET) targeting of VMAT2 is currently being evaluated as a non-invasive tool to measure ß cell mass (BCM) in living humans. In recent trials, PET measurements of VMAT2 in the pancreas overestimated BCM in type 1 diabetes (T1D) patients predicted to have little to no BCM by metabolic measures. Recently, tissue immunohistochemistry studies suggested that VMAT2 staining may also co-localize with pancreatic polypeptide (PP) staining cells in pancreas tissue, but these studies were not quantitative. In this report, we evaluated VMAT2 specificity for ß cells in sub-regions of the human pancreas using antibodies targeting VMAT2, insulin and PP by double-label immunofluorescence. Immunostaining for VMAT2 and insulin demonstrated 89 ± 8% overlap in the body and tail of the pancreas. However, 44 ± 12% and 53 ± 15% of VMAT2 cells co-stained with PP- and insulin-staining cells, respectively in the pancreatic head. Significant co-staining for VMAT2 and PP cells in the head of the pancreas may partly explain the apparent overestimation of BCM in T1D by PET. Specific targeting of the pancreatic body and tail using VMAT2 PET scanning may reflect BCM more accurately.

Hormonally defined pancreatic and duodenal neuroendocrine tumors differ in their transcription factor signatures: expression of ISL1, PDX1, NGN3, and CDX2.

We recently identified the transcription factor (TF) islet 1 gene product (ISL1) as a marker for well-differentiated pancreatic neuroendocrine tumors (P-NETs). In order to better understand the expression of the four TFs, ISL1, pancreatico-duodenal homeobox 1 gene product (PDX1), neurogenin 3 gene product (NGN3), and CDX-2 homeobox gene product (CDX2), that mainly govern the development and differentiation of the pancreas and duodenum, we studied their expression in hormonally defined P-NETs and duodenal (D-) NETs. Thirty-six P-NETs and 14 D-NETs were immunostained with antibodies against the four pancreatic hormones, gastrin, serotonin, calcitonin, ISL1, PDX1, NGN3, and CDX2. The TF expression pattern of each case was correlated with the tumor's hormonal profile. Insulin-positive NETs expressed only ISL1 (10/10) and PDX1 (9/10). Glucagon-positive tumors expressed ISL1 (7/7) and were almost negative for the other TFs. Gastrin-positive NETs, whether of duodenal or pancreatic origin, frequently expressed PDX1 (17/18), ISL1 (14/18), and NGN3 (14/18). CDX2 was mainly found in the gastrin-positive P-NETs (5/8) and rarely in the D-NETs (1/10). Somatostatin-positive NETs, whether duodenal or pancreatic in origin, expressed ISL1 (9/9), PDX1 (3/9), and NGN3 (3/9). The remaining tumors showed labeling for ISL1 in addition to NGN3. There was no association between a particular TF pattern and NET features such as grade, size, location, presence of metastases, and functional activity. We conclude from our data that there is a correlation between TF expression patterns and certain hormonally defined P-NET and D-NET types, suggesting that most of the tumor types originate from embryologically determined precursor cells. The observed TF signatures do not allow us to distinguish P-NETs from D-NETs.

Biosynthesis of pancreatic polypeptide. Identification of a precursor and a co-synthesized product.

Pseudoislets obtained by gyrotational incubation of purified endocrine cells from canine duodenal pancreas were incubated with [3H]leucine and [35S]methionine to study the biosynthesis of pancreatic polypeptide. Gel filtration of islet extracts demonstrated two major radiolabeled peptides which were immunoprecipitable with antisera against pancreatic polypeptide. One had a molecular weight similar to that of pancreatic polypeptide (4300), whereas the other had an apparent molecular weight of about 9000. On polyacrylamide gel electrophoresis, the larger labeled peptide co-migrated with a large immunoreactive form of pancreatic polypeptide which reacts in immunoassays directed towards the NH2-terminal region of pancreatic polypeptide, but not in an assay depending on the COOH-terminal tyrosine amide. Sequential Edman degradation of both immunoprecipitable labeled peptides identified [3H]leucine at position 3 and [35S]methionine at position 17, positions which align with the leucine and methionine residues in the NH2-terminal sequence of pancreatic polypeptide. In pulse-chase labeling experiments, the larger peptide appeared early and disappeared rapidly, whereas pancreatic polypeptide and an additional smaller peptide appeared later and reached a plateau as th precursor was processed. That both pancreatic polypeptide and the smaller peptide arise from the same precursor was further supported by electrophoretic mapping of the tryptic fragments from the three peptides. We conclude that pancreatic polypeptide and a peptide with a molecular weight of 2500 to 3000 are co-synthesized from a larger precursor and that the pancreatic polypeptide sequence is located at the far NH2-terminal end of the precursor form.