Pancreatic-polypeptide-rich regions in human pancreas

The β Cell in Diabetes: Integrating Biomarkers With Functional Measures

The pathogenesis of hyperglycemia observed in most forms of diabetes is intimately tied to the islet β cell. Impairments in propeptide processing and secretory function, along with the loss of these vital cells, is demonstrable not only in those in whom the diagnosis is established but typically also in individuals who are at increased risk of developing the disease. Biomarkers are used to inform on the state of a biological process, pathological condition, or response to an intervention and are increasingly being used for predicting, diagnosing, and prognosticating disease. They are also proving to be of use in the different forms of diabetes in both research and clinical settings. This review focuses on the β cell, addressing the potential utility of genetic markers, circulating molecules, immune cell phenotyping, and imaging approaches as biomarkers of cellular function and loss of this critical cell. Further, we consider how these biomarkers complement the more long-established, dynamic, and often complex measurements of β-cell secretory function that themselves could be considered biomarkers.

The Human Islet: Mini-Organ With Mega-Impact

This review focuses on the human pancreatic islet-including its structure, cell composition, development, function, and dysfunction. After providing a historical timeline of key discoveries about human islets over the past century, we describe new research approaches and technologies that are being used to study human islets and how these are providing insight into human islet physiology and pathophysiology. We also describe changes or adaptations in human islets in response to physiologic challenges such as pregnancy, aging, and insulin resistance and discuss islet changes in human diabetes of many forms. We outline current and future interventions being developed to protect, restore, or replace human islets. The review also highlights unresolved questions about human islets and proposes areas where additional research on human islets is needed.

Pancreatic β-cell heterogeneity in health and diabetes: classes, sources, and subtypes

Pancreatic β-cells perform glucose-stimulated insulin secretion, a process at the center of type 2 diabetes etiology. Efforts to understand how β-cells behave in healthy and stressful conditions have revealed a wide degree of morphological, functional, and transcriptional heterogeneity. Sources of heterogeneity include β-cell topography, developmental origin, maturation state, and stress response. Advances in sequencing and imaging technologies have led to the identification of β-cell subtypes, which play distinct roles in the islet niche. This review examines β-cell heterogeneity from morphological, functional, and transcriptional perspectives, and considers the relevance of topography, maturation, development, and stress response. It also discusses how these factors have been used to identify β-cell subtypes, and how heterogeneity is impacted by diabetes. We examine open questions in the field and discuss recent technological innovations that could advance understanding of β-cell heterogeneity in health and disease.

Signaling Molecules Regulating Pancreatic Endocrine Development from Pluripotent Stem Cell Differentiation

Diabetes is one of the leading causes of death globally. Currently, the donor pancreas is the only source of human islets, placing extreme constraints on supply. Hence, it is imperative to develop renewable islets for diabetes research and treatment. To date, extensive efforts have been made to derive insulin-secreting cells from human pluripotent stem cells with substantial success. However, the in vitro generation of functional islet organoids remains a challenge due in part to our poor understanding of the signaling molecules indispensable for controlling differentiation pathways towards the self-assembly of functional islets from stem cells. Since this process relies on a variety of signaling molecules to guide the differentiation pathways, as well as the culture microenvironments that mimic in vivo physiological conditions, this review highlights extracellular matrix proteins, growth factors, signaling molecules, and microenvironments facilitating the generation of biologically functional pancreatic endocrine cells from human pluripotent stem cells. Signaling pathways involved in stepwise differentiation that guide the progression of stem cells into the endocrine lineage are also discussed. The development of protocols enabling the generation of islet organoids with hormone release capacities equivalent to native adult islets for clinical applications, disease modeling, and diabetes research are anticipated.

Morphogenesis of the ventral pancreas anlagen is influenced by the SMA branching pattern

Developmentally, the uncinate process of the pancreas is derived from the ventral pancreatic anlagen, supplied by the superior mesenteric artery (SMA), and contains pancreatic polypeptide (PP)-rich islets of Langerhans. In contrast, the other parts of the pancreas originate from the dorsal anlagen supplied by the celiac system and contain PP-poor islets. This study was performed to investigate whether morphogenesis of the ventral pancreas anlagen is associated with the pattern of SMA branching. SMA branches to the pancreatic body were dissected in 44 cadavers. The cadavers were divided into two groups: the SMA group in which the SMA gave off branches to the pancreatic body and the General group in which it did not. In the SMA group, the ratio of the diameter of the SMA branch supplying the pancreatic body (SMA branch) to that of the SMA itself was calculated. After dissection was completed, tissues were collected from all pancreatic specimens for HE staining and for immunohistochemistry with PP and insulin antibodies. There were 25 cadavers in the General group and 19 in the SMA group. In 10/19 cadavers from the SMA group, PP-rich islets were confirmed in the pancreatic body. The SMA branch diameter ratio was significantly smaller in the SMA group cadavers with PP-poor islets (n = 9) than in cadavers with PP-rich islets (n = 10) (P < 0.001). These findings suggest a relation between the SMA branching pattern and the distribution of PP cells.

Modelling the endocrine pancreas in health and disease

Diabetes mellitus is a multifactorial disease affecting increasing numbers of patients worldwide. Progression to insulin-dependent diabetes mellitus is characterized by the loss or dysfunction of pancreatic β-cells, but the pathomechanisms underlying β-cell failure in type 1 diabetes mellitus and type 2 diabetes mellitus are still poorly defined. Regeneration of β-cell mass from residual islet cells or replacement by β-like cells derived from stem cells holds great promise to stop or reverse disease progression. However, the development of new treatment options is hampered by our limited understanding of human pancreas organogenesis due to the restricted access to primary tissues. Therefore, the challenge is to translate results obtained from preclinical model systems to humans, which requires comparative modelling of β-cell biology in health and disease. Here, we discuss diverse modelling systems across different species that provide spatial and temporal resolution of cellular and molecular mechanisms to understand the evolutionary conserved genotype-phenotype relationship and translate them to humans. In addition, we summarize the latest knowledge on organoids, stem cell differentiation platforms, primary micro-islets and pseudo-islets, bioengineering and microfluidic systems for studying human pancreas development and homeostasis ex vivo. These new modelling systems and platforms have opened novel avenues for exploring the developmental trajectory, physiology, biology and pathology of the human pancreas.

Y1 receptor deficiency in β-cells leads to increased adiposity and impaired glucose metabolism

Insulin secretion from pancreatic β-cells is critical for maintaining glucose homeostasis and deregulation of circulating insulin levels is associated with the development of metabolic diseases. While many factors have been implicated in the stimulation of insulin secretion, the mechanisms that subsequently reduce insulin secretion remain largely unexplored. Here we demonstrate that mice with β-cell specific ablation of the Y1 receptor exhibit significantly upregulated serum insulin levels associated with increased body weight and adiposity. Interestingly, when challenged with a high fat diet these β-cell specific Y1-deficient mice also develop hyperglycaemia and impaired glucose tolerance. This is most likely due to enhanced hepatic lipid synthesis, resulting in an increase of lipid accumulation in the liver. Together, our study demonstrates that Y1 receptor signaling negatively regulates insulin release, and pharmacological inhibition of Y1 receptor signalling for the treatment of non-insulin dependent diabetes should be taken into careful consideration.

Impact of islet architecture on β-cell heterogeneity, plasticity and function

Although β-cell heterogeneity was discovered more than 50 years ago, the underlying principles have been explored only during the past decade. Islet-cell heterogeneity arises during pancreatic development and might reflect the existence of distinct populations of progenitor cells and the developmental pathways of endocrine cells. Heterogeneity can also be acquired in the postnatal period owing to β-cell plasticity or changes in islet architecture. Furthermore, β-cell neogenesis, replication and dedifferentiation represent alternative sources of β-cell heterogeneity. In addition to a physiological role, β-cell heterogeneity influences the development of diabetes mellitus and its response to treatment. Identifying phenotypic and functional markers to discriminate distinct β-cell subpopulations and the mechanisms underpinning their regulation is warranted to advance current knowledge of β-cell function and to design novel regenerative strategies that target subpopulations of β cells. In this context, the Wnt/planar cell polarity (PCP) effector molecule Flattop can distinguish two unique β-cell subpopulations with specific transcriptional signatures, functional properties and differential responses to environmental stimuli. In vivo targeting of these β-cell subpopulations might, therefore, represent an alternative strategy for the future treatment of diabetes mellitus.

Immunohistochemical analysis of pancreatic islets of platypus (Ornithorhynchus anatinus) and echidna (Tachyglossus aculeatus ssp.)

Monotremes have undergone remarkable changes to their digestive and metabolic control system; however, the monotreme pancreas remains poorly characterized. Previous work in echidna demonstrated the presence of pancreatic islets, but no information is available for platypus and the fine structure has not been described for either monotreme. Based on our recent finding that monotremes lack the ghrelin gene, which is expressed in mouse and human pancreatic islets, we investigated the structure of monotreme islets in more detail. Generally, as in birds, the islets of monotremes were smaller but greater in number compared with mouse. β-cells were the most abundant endocrine cell population in platypus islets and were located peripherally, while α-cells were observed both in the interior and periphery of the islets. δ-cells and pancreatic polypeptide (PP)-cells were mainly found in the islet periphery. Distinct PP-rich (PP-lobe) and PP-poor areas (non-PP-lobe) are present in therian mammals, and we identified these areas in echidna but not platypus pancreas. Interestingly, in some of the echidna islets, α- and β-cells tended to form two poles within the islets, which to our knowledge is the first time this has been observed in any species. Overall, monotreme pancreata share the feature of consisting of distinct PP-poor and PP-rich islets with other mammals. A higher number of islets and α- or β-cell only islets are shared between monotremes and birds. The islets of monotremes were larger than those of birds but smaller compared with therian mammals. This may indicate a trend of having fewer larger islets comprising several endocrine cell types during mammalian evolution.

Glycaemic regulation and insulin secretion are abnormal in cystic fibrosis pigs despite sparing of islet cell mass

Diabetes is a common and significant co-morbidity in cystic fibrosis (CF). The pathogenesis of cystic fibrosis related diabetes (CFRD) is incompletely understood. Because exocrine pancreatic disease is similar between humans and pigs with CF, the CF pig model has the potential to contribute significantly to the understanding of CFRD pathogenesis. We determined the structure of the endocrine pancreas in fetal, newborn and older CF and non-CF pigs and assessed endocrine pancreas function by intravenous glucose tolerance test (IV-GTT). In fetal pigs, pancreatic insulin and glucagon density was similar between CF and non-CF. In newborn and older pigs, the insulin and glucagon density was unchanged between CF and non-CF per total pancreatic area, but increased per remnant lobular tissue in CF reflecting exocrine pancreatic loss. Although fasting glucose levels were not different between CF and non-CF newborns, CF newborns demonstrated impaired glucose tolerance and increased glucose area under the curve during IV-GTT. Second phase insulin secretion responsiveness was impaired in CF newborn pigs and significantly lower than that observed in non-CF newborns. Older CF pigs had elevated random blood glucose levels compared with non-CF. In summary, glycaemic abnormalities and insulin secretion defects were present in newborn CF pigs and spontaneous hyperglycaemia developed over time. Functional changes in CF pig pancreas were not associated with a decline in islet cell mass. Our results suggest that functional islet abnormalities, independent of structural islet loss, contribute to the early pathogenesis of CFRD.

Pancreatic polypeptide regulates glucagon release through PPYR1 receptors expressed in mouse and human alpha-cells

BACKGROUND

Plasma levels of pancreatic polypeptide (PP) rise upon food intake. Although other pancreatic islet hormones, such as insulin and glucagon, have been extensively investigated, PP secretion and actions are still poorly understood.

METHODS

The release of PP upon glucose stimulation and the effects of PP on glucagon and insulin secretion were analyzed in isolated pancreatic islets. Expression of PP receptor (PPYR1) was investigated by immunoblotting, quantitative RT-PCR on sorted pancreatic islet cells, and immunohistochemistry.

RESULTS

In isolated mouse pancreatic islets, glucose stimulation increased PP release, while insulin secretion was up and glucagon release was down. Direct exposure of islets to PP inhibited glucagon release. In mouse islets, PPYR1 protein was observed by immunoblotting and quantitative RT-PCR revealed PPYR1 expression in the FACS-enriched glucagon alpha-cell fraction. Immunohistochemistry on pancreatic sections showed the presence of PPYR1 in alpha-cells of both mouse and human islets, while the receptor was absent in other islet cell types and exocrine pancreas.

CONCLUSIONS

Glucose stimulates PP secretion and PP inhibits glucagon release in mouse pancreatic islets. PP receptors are present in alpha-cells of mouse and human pancreatic islets.

GENERAL SIGNIFICANCE

These data demonstrate glucose-regulated secretion of PP and its effects on glucagon release through PPYR1 receptors expressed by alpha-cells.

Distinct function of the head region of human pancreas in the pathogenesis of diabetes

The large size of the human pancreas challenges unbiased quantitative analyses that require a practical stereological approach. While many histological studies of the pancreas in the past lacked regional information, we have shown marked heterogeneity within an individual, where islet distribution/density is relatively low in the head and gradually increases through the body toward the tail region by>2-fold. Studies focusing on the tail region may be prone to overestimation of β-cell/islet mass when normalizing measured values per person by using pancreas weight or volume. In this article, beyond technical issues, we discuss the pathophysiological importance of studying the head region of the human pancreas regarding its unique characteristics in early development, and the anatomical disposition that may lead to a preferential loss of β-cells in patients with type 2 diabetes and the development of pancreatic cancer.

Regional differences in islet distribution in the human pancreas--preferential beta-cell loss in the head region in patients with type 2 diabetes

While regional heterogeneity in islet distribution has been well studied in rodents, less is known about human pancreatic histology. To fill gaps in our understanding, regional differences in the adult human pancreas were quantitatively analyzed including the pathogenesis of type 2 diabetes (T2D). Cadaveric pancreas specimens were collected from the head, body and tail regions of each donor, including subjects with no history of diabetes or pancreatic diseases (n = 23) as well as patients with T2D (n = 12). The study further included individuals from whom islets were isolated (n = 7) to study islet yield and function in a clinical setting of islet transplantation. The whole pancreatic sections were examined using an innovative large-scale image capture and unbiased detailed quantitative analyses of the characteristics of islets from each individual (architecture, size, shape and distribution). Islet distribution/density is similar between the head and body regions, but is >2-fold higher in the tail region. In contrast to rodents, islet cellular composition and architecture were similar throughout the pancreas and there was no difference in glucose-stimulated insulin secretion in islets isolated from different regions of the pancreas. Further studies revealed preferential loss of large islets in the head region in patients with T2D. The present study has demonstrated distinct characteristics of the human pancreas, which should provide a baseline for the future studies integrating existing research in the field and helping to advance bi-directional research between humans and preclinical models.

Novel approaches to studying the role of innervation in the biology of pancreatic islets

The autonomic nervous system helps regulate glucose homeostasis by acting on pancreatic islets of Langerhans. Despite decades of research on the innervation of the pancreatic islet, the mechanisms used by the autonomic nervous input to influence islet cell biology have not been elucidated. This article discusses how these barriers can be overcome to study the role of the autonomic innervation of the pancreatic islet in glucose metabolism. It describes recent advances in microscopy and novel approaches to studying the effects of nervous input that may help clarify how autonomic axons regulate islet biology.

Quantitative analysis of pancreatic polypeptide cell distribution in the human pancreas

The pancreatic islet is mainly composed of beta-, alpha- and delta-cells with small numbers of pancreatic polypeptide (PP) and epsilon cells. It is known that there is a region in the head of the pancreas that is rich in PP-cells. In the present study, we examined the distribution of PP-cells, and assessed the influence of the PP-cell rich region to quantify the total islet mass. Pancreatic tissues were collected from donors with no history of diabetes or pancreatic diseases (n = 12). A stereological approach with a computer-assisted large-scale analysis of whole pancreatic sections was applied to quantify the entire distribution of endocrine cells within a given section. The initial whole pancreas analysis showed that a PP-cell rich region was largely restricted to the uncinate process with a clear boundary. The distinct distribution of PP-cells includes irregularly shaped clusters composed solely of PP-cells. Furthermore, in the PP-cell rich region, beta- and alpha-cell mass is significantly reduced compared to surrounding PP-cell poor regions. The results suggest that the analysis of the head region should distinguish the PP-cell rich region, which is best examined separately. This study presents an important implication for the regional selection and interpretation of the results.

Pancreatic polypeptide administration enhances insulin sensitivity and reduces the insulin requirement of patients on insulin pump therapy

INTRODUCTION

The effects of pancreatic polypeptide (PP) infusion were examined in patients on insulin pump therapy to determine whether PP administration can reduce insulin requirements in patients with type 1 diabetes mellitus (T1DM) or type 3c diabetes mellitus (T3cDM; pancreatogenic).

METHODS

Ten subjects with long-standing T1DM (n = 7) or T3cDM (n = 3) on insulin pump treatment received a 72 h subcutaneous infusion of 2 pmol/kg/min bovine PP or saline by portable infusion pump in a single-blinded, randomized, crossover design.

RESULTS

Pancreatic polypeptide infusion raised plasma PP levels to 450-700 pmol/liter. Daily insulin infusion requirements (I) fell from 48 ± 6.9 to 40 ± 7.5 U on day 2 (p < .05) and from 46 ± 7.7 to 37 ± 6.6 U on day 3 (p < .05) of PP infusion compared with saline. Corrected for average blood glucose concentration (G), I/G fell in 10/10 subjects during the second 24 h period and in 7/10 subjects during the third 24 h period; sensitivity to insulin, calculated as 1/(I/G), increased 45% ± 12% on day 2 (p < .01) and 34% ± 14% on day 3 (p < .05) of PP infusion. Pancreatic polypeptide responses to a test meal were compared with the change in insulin infusion requirements in 5 subjects; the reduction in insulin requirements seen during PP infusion correlated with the degree of baseline PP deficiency (p < .002).

CONCLUSIONS

A concurrent subcutaneous infusion of PP enhances insulin sensitivity and reduces insulin requirements in patients with long-standing T1DM and T3cDM on insulin pump therapy. The benefit of PP infusion correlated with the degree of PP deficiency.

Microscopic anatomy of the human islet of Langerhans

Human islets of Langerhans are complex micro-organs responsible for maintaining glucose homeostasis. Islets contain five different endocrine cell types, which react to changes in plasma nutrient levels with the release of a carefully balanced mixture of islet hormones into the portal vein. Each endocrine cell type is characterized by its own typical secretory granule morphology, different peptide hormone content, and specific endocrine, paracrine, and neuronal interactions. During development, a cascade of transcription factors determines the formation of the endocrine pancreas and its constituting islet cell types. Differences in ontogeny between the ventrally derived head section and the dorsally derived head, body, and tail section are responsible for differences in innervation, blood supply, and endocrine composition. Islet cells show a close topographical relationship to the islet vasculature, and are supplied with a five to tenfold higher blood flow than the exocrine compartment. Islet microanatomy is disturbed in patients with type 1 diabetes, with a marked reduction in beta-cell content and the presence of inflammatory infiltrates. Histopathological lesions in type 2 diabetes are less pathognomonic with a more limited reduction in beta-cell content and occasional deposition of amyloid in the islet interstitial space.

Immunohistochemical and electron microscopic studies of a case of duodenal gangliocytic paraganglioma

Gangliocytic paraganglioma (GPG) is a rare tumor, occurring almost exclusively in the duodenum. In the present case, a submucosal tumor 2.5 x 2 x 1.5 cm in size was located on the anal side of the papilla of Vater, with clear margins and without capsule on cut-surface examination. Tumor cells included three types of cells: ganglion-like cells (GCs), endocrine cells (ECs), and Schwann cells (SCs). The GCs were large with eccentric nuclei with large nucleoli and clear abundant cytoplasm. ECs were detected in small nests, surrounded by bundles of SCs. Immunohistochemically, GCs were positive for synaptophysin, neuron-specific enolase (NSE), and CD56. ECs were positive for chromogranin A, NSE, somatostatin, pancreatic polypeptide, and CD56, and were associated with S100 protein-positive SCs. On fine structural examination, ECs contained numerous membrane-bounded secretory granules, 250-450 nm in diameter, in their cytoplasm, surrounded by a branched, complex basal lamina. SCs possessed basal lamina along their long interlacing cytoplasmic processes. The histogenesis of GPG most likely involves proliferation and differentiation of pluripotent stem cells in the duodenal crypts in the duodenum as a true tumor, although it is also possible that the retroperitoneal components of both GCs and SCs proliferate, together with ECs, from ventral primordial tissue of the pancreas in the duodenum. The immunohistochemical and ultrastructural findings of a case of GPG are reported, focusing on three major cellular components: GCs, ECs, and SCs.

Update on pancreatic polypeptide as a specific marker for endocrine tumours of the pancreas and gut

Serum levels of pancreatic polypeptide (PP) were determined in 31 patients with endocrine tumours, localized in the pancreas (n = 16), small intestine (n = 13) and respiratory tract (n = 2). Two further patients with laxative abuse were investigated. Elevated serum levels in the peripheral circulation were noted in 56% of the patients with pancreatic tumours, in 60% of those with gut or bronchial tumours and in both patients with laxative abuse. Our study suggests that the elevated PP concentrations found in connection with endocrine gastrointestinal tumours originate from non-tumour pancreatic PP cells and only occasionally from the tumour. PP is a valuable tumour marker for endocrine gastrointestinal tumours, although it is not specific for pancreatic tumours. Certain inflammatory diseases, renal function and consumption of laxatives must be considered when evaluating elevated PP levels. Serum PP seems to be of limited value for evaluating the response to cytotoxic therapy.

Unusual fusion between ventral and dorsal primordia causes anomalous pancreaticobiliary junction

Anomalous pancreaticobiliary junction (APBJ) is a congenital anomaly in which the pancreatic duct joins the common bile duct proximal to the sphincter of Oddi. Anatomical and immunohistochemical examination of the pancreas with APBJ has rarely been performed. A 72-year-old woman with gallbladder cancer and APBJ died of respiratory failure. Macroscopic features of the pancreas were examined in detail. Immunohistochemistry using anti-pancreatic polypeptide (anti-PP) antibody was done to discriminate ventral and dorsal pancreas. Macroscopically the inferior part of the head of the pancreas was smaller than normal. The posterior surface of the head was obliquely grooved. Part of the pancreatic head protruded into the posterior side of the pancreatic head. A PP-rich region was located in the superioposterior position of the pancreas head. Considering the relationship between the ventral and dorsal pancreas, it was inferred that the ventral primordium could obliquely fuse with the dorsal primordium during embryological development. As a result, APBJ occurs through an abnormal fusion between ventral and dorsal primordia.

A Pancreatic Polypeptide-Producing Pancreatic Tumor Causing WDHA Syndrome

We report the case of a 46-year-old female patient with WDHA (watery diarrhea/hypokalemia/achlorhydria) syndrome caused by a pancreatic polypeptide-producing tumor in the head of the pancreas. Whereas VIP and other pancreatic endocrine hormones were in the normal range, only serum levels of pancreatic polypeptide were elevated. Imaging studies identified a pancreatic tumor in the head of the gland. After laparotomy, the tumor of 3 cm in size was enucleated. Final pathology documented a pancreatic endocrine tumor with immunohistochemical staining demonstrating the presence of pancreatic polypeptide. The patient remained cured after a follow-up of more than three years. The present case illustrates that, although rare, WDHA syndrome may be associated with a pancreatic polypeptide-secreting endocrine tumor of the pancreas.

Surgical treatment of non-functioning pancreatic islet cell tumors

Pancreatic endocrine tumors (PETs) are rare neoplasms originating from the amine precursor uptake and decarboxylation (APUD) stem cells. Although the majority of PETs are sporadic, they frequently occur in familial syndromes. PETs may cause a variety of functional syndromes or symptoms of local progression if they are non-functional. General neuroendocrine tumor markers are highly sensitive in the diagnostic assessment of a PET. Imaging studies for tumor localization and staging include computer tomography (CT) scan, magnetic resonance imaging (MRI), In(111)-octreotide scan, MIBG, and endoscopic ultrasonography (EUS). Treatment of PETs often requires a multi-modality approach; however, surgical resection remains the only curative therapy for localized (non-metastatic) disease. Treatment of metastatic disease includes biologic agents, cytotoxic chemotherapy, and liver-directed therapies.

Cellular localization of endocrine cells in the adult pancreas of the house musk shrew, Suncus murinus: a comparative immunocytochemical study

The right and left lobes of the pancreas in the house musk shrew, Suncus murinus, were found to be completely separated. A morphologic study of the pancreas in S. murinus in terms of the blood supplies and innervation of the right and left lobes was performed in our previous study. It revealed clearly different blood supply and innervation patterns in the right and left lobes, suggesting that the right lobe of the pancreas corresponded to the ventral pancreas, and the left lobe related to the dorsal pancreas. To test this perspective from the histology, in this study, we investigated the immunolocalization of the cells of Langerhans islets in the pancreas of the animal. The distribution of insulin-, glucagon-, somatostatin-, and pancreatic polypeptide (PP)-secreting cells of the right and left lobes of the pancreas was examined in 10 animals. The glucagon-immunoreactive cells were distributed in both the right and left lobes. The PP-immunoreactive cells were extremely abundant in the right lobe and distributed throughout almost all the islets of Langerhans in the right lobe. By contrast, in the left lobe, immunoreactive PP cells were absent in the islets of Langerhans, and only very few immunoreactive PP cells were scattered in the exocrine parenchyma in part of the specimens. Therefore, these findings support our previous studies, and showed that the right and left lobes of the S. murinus pancreas could be related to an embryological origin from the ventral and dorsal pancreatic primordium, respectively, and that the S. murinus pancreas is suitable as a new experimental model to study the development of the human pancreas.

Persistence of the left part of the ventral pancreas may cause congenital biliary dilatation

INTRODUCTION

Congenital biliary dilatation (CBD) is a congenital anomaly by which pancreaticobiliary maljunction (PBMJ) is accompanied in most patients. The etiology of these conditions is unknown. AIMS To clarify the pattern of fusion between the ventral and dorsal parts of the pancreas.

METHODOLOGY

We examined the pancreases from five patients who had PBMJ with or without CBD and five control subjects, and we detected pancreatic polypeptide (PP) immunohistochemically.

RESULTS

In cases of CBD, the pancreatic head was huge, while the uncinate process was undetectable. The dorsal portion of the head was formed by the ventral pancreas macroscopically. It was divided into PP-rich and PP-poor portions immunohistochemically. In cases of PBMJ without CBD, the uncinate process was relatively small. The PP-rich portion (ventral pancreas) was situated obliquely dorsal to the PP-poor portion (dorsal pancreas).

CONCLUSIONS

In case of CBD, the PP-rich and PP-poor portions of the ventral pancreas may be derived from the right and left parts of the ventral primordia, respectively. CBD may occur when the remnant of the left part of the ventral primordium prevents normal recanalization of the common bile duct, resulting in dilatation of the duct. In cases of PBMJ without CBD, PBMJ without CBD may be caused by abnormal fusion between the ventral and dorsal primordia.

An immunohistochemical and morphometric analysis of insulin, insulin-like growth factor I, glucagon, somatostatin, and PP in the development of the gastro-entero-pancreatic system of Xenopus laevis

The ontogeny of the classical islet hormones insulin (INS), glucagon (GLUC), somatostatin (SOM), and pancreatic polypeptide (PP) as well as insulin-like growth factor I (IGF-I) in the gastro-entero-pancreatic (GEP) system of Xenopus laevis (stages 41-66) was studied using double immunofluorescence and morphometric analysis. As early as stage 41, clustered INS-immunoreactive (-IR) and isolated GLUC-IR cells occurred in the pancreas. The first SOM-IR cells appeared at stage 43, followed by PP-IR cells at stage 46. About 79% of the PP immunoreactivity was confined to a subpopulation of the GLUC-IR cells. Both the GLUC/PP-IR cells and the PP-IR cells were located in a distinct area of the pancreas. The first islets occurred in premetamorphosis (around stage 50) and comprised mainly INS-IR and GLUC-IR cells. The majority of SOM-IR, PP-IR, and GLUC/PP-IR cells was dispersed. The numbers of hormone cells remained quite constant until the end of prometamorphosis (stage 58). Around stages 60-62, the islets were partly disintegrated and the numbers of islet cells slightly decreased. At stage 63, the cell number began to increase and reached the levels typical for the adult around stage 66. After metamorphic climax, the islets were reformed. In the gastrointestinal tract, transient INS-IR cells occurred prior to the adaptation of the gastrointestinal tract to feeding (stages 41-44) and during metamorphosis when there is remodeling of the gastrointestinal tract (stages 60-63). Therefore, INS released from the transient mucosal INS-IR cells may be involved in the temporary proliferation of mucosal epithelial cells. The first GLUC-IR and SOM-IR cells were seen at stage 41. PP-IR cells followed at stage 46. In contrast to the islets, GLUC-IR and PP-IR cells constituted different cell populations. Around stage 46, the first IGF-I immunoreactions appeared in the GEP-system. In pancreas, IGF-I immunoreactivity was found in the GLUC/PP-IR, cells (85-99%) but was absent from INS-IR, GLUC-IR, and SOM-IR cells. The IGF-I-IR gastro-entero-endocrine cells, however, seemed to contain none of the classical islet hormones.

Pancreatic polypeptide is a useful plasma marker for radiographically evident pancreatic islet cell tumors in patients with multiple endocrine neoplasia type 1

BACKGROUND

The usefulness of human pancreatic polypeptide (hPP) as a plasma marker for islet cell neoplasms is controversial. We sought to determine the relation between fasting plasma hPP levels and radiographically detectable pancreatic islet cell tumors in patients with multiple endocrine neoplasia type 1 (MEN 1).

METHODS

Fasting plasma hPP levels were measured prospectively in 202 individuals from 31 independent kindreds with MEN 1. Plasma levels greater than 3.0 times the normal age-specific values were defined as elevated. Patients with elevated plasma hPP levels were evaluated with computed tomographic scanning and magnetic resonance imaging, octreotide scanning, or selective angiography.

RESULTS

Twenty-two patients had elevated fasting plasma hPP levels, and 20 of these patients were evaluated radiographically. Pancreatic lesions were detected in 19 patients. A group of eight patients with normal basal fasting plasma hPP levels were evaluated with computed tomography, magnetic resonance imaging, octreotide scanning, or selective angiography based on clinical presentation. One patient in this group had an imaging study that was positive for a pancreatic lesion.

CONCLUSIONS

The presence of a markedly elevated fasting plasma hPP level in patients with MEN 1 is 95% sensitive and 88% specific for the presence of radiographically detectable pancreatic islet cell tumors.

Relationships among residual beta cells, exocrine pancreas, and islet cell antibodies in insulin-dependent diabetes mellitus

Quantitative analysis was performed using computerized morphometry on the relationships between residual beta cells, pancreatic exocrine glands, and islet cell antibodies (ICA) in 14 pancreata of insulin-dependent diabetic (IDDM) patients. Both pancreatic exocrine glands and beta cells were markedly reduced in weight in IDDM patients compared with non-insulin-dependent diabetic (NIDDM) patients or nondiabetic controls. beta cells were preserved in six cases and were completely abolished in eight cases. In nine IDDM pancreata weighed at autopsy, the weights of pancreatic exocrine glands in six patients with either no or virtually no residual beta cells (32.3 +/- 1.6 g) were greater than those in three patients with residual beta cells (23.1 +/- 2.5 g, P < .05). Infiltration of lymphocytes positive for leukocyte common antigen (LCA) around the islet was observed in only one case with ICA and residual beta cells. Infiltration of LCA-positive lymphocytes around pancreatic acinar cells was observed in 50% (six of 12) of patients examined. The weight of pancreatic exocrine glands in patients with LCA-positive lymphocyte infiltration (26.2 +/- 2.3 g) was lower than that in patients without this condition (33.2 +/- 2.4 g, P < .05). Pancreatic cytokeratin autoantibodies (PKA) were detected in four of 10 patients examined. In addition, all four ICA-positive patients had residual beta cells, while only one of seven ICA-negative patients had residual beta cells (P = .03).(ABSTRACT TRUNCATED AT 250 WORDS)

Onset of cell-specific gene expression in the developing mouse pancreas

A central question in developmental biology has been the initiation of cell-specific gene expression and its temporal relationship to morphogenesis. We have coupled embryo microdissection with the exquisite sensitivity of the polymerase chain reaction to define the onset of cell-specific gene expression during pancreatic organogenesis. Using the precise assignment of gestational age by the number of somites in each embryo, we determined the onset of transcription of major genes of the endocrine and exocrine pancreas during mouse development to within 2-3 hr. Somatostatin mRNA was detected at the 10-somite stage throughout the foregut, consistent with the presence of somatostatin-producing cells throughout the adult gut. Mature mRNA for insulin and glucagon first appears surprisingly early, at the 20-somite stage in the wall of the embryonic foregut and is restricted to only the area of the duodenum from which the pancreas will arise 10-12 hr later. In contrast, exocrine gene transcription begins 24 hr after formation of the pancreatic diverticulum. Thus cell-specific gene expression in the endocrine pancreas begins in a "pre-morphogenetic phase." This early expression of insulin and glucagon could reflect the initiation of an endocrine cell lineage.

Metastatic pancreatic polypeptide producing tumour presenting with diabetes mellitus

A metastatic pancreatic polypeptide tumour is described which presented clinically with diabetes mellitus. This is the first case to present this way.

Do the pancreatic primordial buds in embryogenesis have the potential to produce all pancreatic endocrine cells?

A heterogeneity in the cellular composition of the endocrine pancreas, with a preponderance of pancreatic polypeptide cells in the lower head region, has been linked to the dual origin of the organ. The pancreas develops from a ventral bud thought to contain potential pancreatic polypeptide cells and a dorsal bud contributing the non pancreatic polypeptide cells. This does not explain, however, several anomalies including the results reported here of a homogenous distribution of non insulin cells in the foetal baboon whilst the adult pancreas exhibits a heterogenous distribution with the pancreatic polypeptide-rich area in the lower head of the pancreas. If this heterogeneity is associated with the dual origin of the pancreas, it would be expected to be more pronounced in the foetus. The anomalies could be explained if both primordial buds contained progenitor cells of all endocrine cell types which could be expressed to meet the requirements of the body at any particular time.

Ontogenic development of peptide hormones in the mammalian fetal pancreas

The ontogeny of insulin, glucagon, PP and somatostatin in the mammalian fetal pancreas has been examined in recent years largely by immunocytochemistry and in some instances by radioimmunoassay. Complete ontogenic data are available only for the rat, human, pig and sheep. Figure 3 compares the time of appearance of the endocrine cell-types within the fetal pancreas when the periods of gestation of the four species are converted to a uniform scale. The striking ontogenic difference in the rat probably reflects the immaturity of the rodent fetus at birth compared with the human, pig and sheep. In the fetal pancreas, differences in cell number of glucagon and PP cells in the dorsal and ventral lobes become apparent from an early gestational period. Factors responsible for the functional and structural maturation of the fetal pancreatic endocrine cells and the processes involved in pancreatic organogenesis are poorly understood. Studies in these areas would have clinical implications since it may be possible in the future to employ agents for selective replication of fetal beta-cells for transplantation in patients with Type I diabetes, bearing in mind that such cells must have the capacity to respond to normal stimuli and repressors when transplanted. The presence of the other islet cell-types may be obligatory for these appropriate responses. This would require a more complete knowledge of those factors which produce the normal selectivity of the four hormonal cell-types.

Coexistence of pancreatic polypeptide (PP)-and glucagon-immunoreactivity in pancreatic endocrine cells of mouse

Immunocytochemical double staining techniques were used to study PP- and glucagon-like-immunoreactivity in pancreatic endocrine cells of mouse. An antiserum against FMRFamide appeared to react with all PP-immunoreactive endocrine cells. With fluorescence microscopy most PP/FMRFamide-immunoreactive cells also showed glucagon-immunoreactivity, but cells containing only PP- or glucagon-like substances were found as well. The proportion of cells containing PP-, glucagon, and both immunoreactivities varied strongly from islet to islet in all parts of the pancreas. Using an electron microscopical immunogold double staining procedure on Lowicryl-embedded pancreas, PP/FMRFamide- and glucagon-immunoreactivity appeared to be present in the majority of endocrine A cells; both immunoreactivities were randomly distributed within the granules of these cells. Cells containing only PP/FMRFamide- or glucagon-immunoreactivity were also found. Glucagon- and a faint FMRFamide-immunoreactivity was also observed in osmicated epon-embedded tissue. Independent of their immunoreactivity all positive cells showed the same round electron dense secretory granules.

Secretion of pancreatic polypeptide in patients with pancreatic endocrine tumors

Pancreatic polypeptide is often secreted by pancreatic endocrine tumors and is considered a marker for such tumors. To investigate the diagnostic value of this marker, we studied 323 patients with proved pancreatic endocrine tumors. We found plasma concentrations of pancreatic polypeptide to be elevated (more than 300 pmol per liter) in 144 patients (diagnostic sensitivity, 45 percent). However, plasma levels of pancreatic polypeptide can also be elevated in the absence of a pancreatic tumor. To ascertain whether the administration of atropine could distinguish between normal and tumor-associated polypeptide secretion, we studied 30 patients with pancreatic tumors and high plasma levels of pancreatic polypeptide, 18 patients without tumors who had elevated levels of pancreatic polypeptide, and eight normal controls. Polypeptide levels in the 18 patients without tumors were substantially lower than in the 30 patients with tumors. Atropine (1 mg intramuscularly) did not suppress polypeptide levels in patients with tumors, but did suppress plasma levels by more than 50 percent in all subjects without tumors. Thus, although its diagnostic sensitivity is low, pancreatic polypeptide appears to be a useful adjunctive marker of many pancreatic endocrine tumors, and the atropine suppression test can be used to distinguish normal from tumor-related secretion of the polypeptide. Identification of the type of pancreatic endocrine tumor still requires measurement of the hormone that is specific for the tumor.

Immunocytochemical identification and localization of peptide hormones in the gastro-entero-pancreatic (GEP) endocrine system of the mouse and a stomachless fish, Barbus conchonius

A large number of antisera mainly raised against mammalian hormones are tested immunocytochemically on the GEP-endocrine system of mouse and fish (Barbus conchonius). The endocrine pancreas of mouse and fish appeared to contain the same four endocrine cell types; insulin-, glucagon-, PP- and somatostatin-immunoreactive cells. In mouse about 13 GEP endocrine cell types are distinguished: 1. insulin-, 2. somatostatin-, 3. glucagon-, 4. PP-, 5. (entero)glucagon-/PP-like, 6. CCK-like, 7. substance P-, 8. neurotensin-, 9. VIP-, 10. gastrin-, 11. secretin-, 12. beta-endorphin-, 13. serotonin-immunoreactive cells. Based on this and a previous study at least 13 GEP endocrine cell types seems to be present in stomachless fish: 1-9 as described for mouse, 10. (entero)glucagon-like, 11. met-enkephalin, 12. VIP-like, 13. unspecific immunoreactive endocrine cells. Coexistence of glucagon and PP-like peptides is found in the gut and pancreas of mice and in the gut of B. conchonius. In mouse pancreas and fish gut, endocrine cells showing only PP- or glucagon-like immunoreactivity are found too. In mouse stomach some endocrine cells showing only PP-immunoreactivity are demonstrated. In the same region coexistence of C-t-gastrin- and FMRF-amide-immunoreactivity is found in endocrine cells. The importance of these phenomena are discussed. Enteric nerves immunoreactive with antisera raised against substance P and GRP are found in mouse, against somatostatin and met-enkephalin in both mouse and fish and against VIP in fish.

Immunohistochemical morphometry of pancreatic endocrine cells in diabetic, normoglycaemic glucose-intolerant and normal cats

The anatomical distribution and volume fractions of pancreatic A cells (glucagon), B cells (insulin) and D cells (somatostatin) were evaluated by an immunoperoxidase technique in 6 diabetic cats, 6 normoglycaemic glucose-intolerant cats and 6 normal control cats. Islets lacking A cells were observed in some sections from the right lobe of the pancreas which correlated with a significantly lower A cell volume fraction in the right pancreatic lobe. Endocrine cell volume fractions in normoglycaemic glucose-intolerant cats were not significantly different from controls. Thus, a reduction in B cell volume fraction was not necessary for the occurrence of impaired glucose tolerance in these cats. However, the reduction of B cell volume fraction in the 2 normoglycaemic glucose-intolerant cats with insular amyloidosis may in part explain the more severely impaired glucose tolerance previously observed in these cats. Insular amyloidosis in our feline diabetics, as in human type II diabetics, was associated with a significant decrease in A and B cell volume fractions. In both human type II and feline diabetes mellitus, however, the reduction in B cell mass does not appear sufficient alone to lead to diabetes mellitus. Therefore, amyloid replacement of functional endocrine cells does not appear to be the primary diabetogenic event in feline diabetes mellitus, but may contribute to progression of the condition due to loss of functional B cell reserves. We thus postulate that a B cell defect precedes deposition of islet amyloid and that these amyloid deposits may thus provide an important biochemical clue to specific B cell derangements occurring in adult-onset diabetics.

Pancreatic polypeptide inhibits amylase release by rat pancreatic acini

Pancreatic polypeptide (PP), a mammalian islet cell peptide, is released after a meal. Exogenously administered PP in physiologic doses inhibits cholecystokinin and secretin-stimulated pancreatic secretion in vivo. Whether PP acts directly on exocrine pancreatic cells is unknown. We studied the effects of PP on dispersed acini prepared from rat pancreas. Amylase release was determined after 30-min incubations of pancreatic acini with octapeptide of cholecystokinin (OP-CCK), secretin, and PP. The response to OP-CCK was augmented by secretin. PP decreased optimal amylase release evoked by OP-CCK and OP-CCK plus secretin. These observations demonstrate that PP acts directly on pancreatic cells to reduce acinar cell amylase release evoked by potent secretagogues.

Islet cell hyperplasia: an unusual cause of hypoglycemia in an adult

This is a case presentation of a 32-year-old man with a one year history of symptomatic hypoglycemia and documented elevations of his fasting plasma insulin to glucose ratio, caused by islet cell hyperplasia. Islet cell hyperplasia is a common cause of hypoglycemia in the pediatric population, but is very rare in adults. As in the pediatric group, adults should be treated with subtotal (75-85%) resection of the pancreas and with diazoxide for symptomatic recurrence of hypoglycemia. We suggest that the term islet cell hyperplasia is preferred to designate a diffuse proliferation of endocrine cells that may express itself with different morphologic patterns, varying from case to case. Islet cell hyperplasia, therefore, comprises nesidioblastosis, endocrine cell budding from ductal structures, as well as islet and islet cell hypertrophy, septal islets, islet dysplasia, and adenomatosis. Immunohistochemistry is a valuable method for the demonstration of the polymorphic hormonal content of the proliferated islet cells. We propose that the term nesidioblastosis, previously used to describe some similar cases, should be avoided because of confusion about its definition.

Glucagon- and PP-related peptides of intestinal L cells and pancreatic/gastric A or PP cells. Possible interrelationships of peptides and cells during evolution, fetal development and tumor growth

The immunohistochemical detection of six distinct sequences of proglucagon and its derivatives (GRPP, glicentin, glucagon-37, glucagon-29, GLP1, GLP2 and MPGF) in both intestinal L cells and pancreatic or gastric A cells of some mammals (dog, man, guinea pig) confirms that the two cell types produce the same proglucagon molecule, although the final step of its post-translational processing differs in the two cells. Immunohistochemical and ultrastructural patterns of glucagon/glicentin cells in the pancreas of lower vertebrates and early human fetuses, as well as tumor cell studies, suggest an evolution of gastropancreatic A cells from L cells. On the contrary, the PP-related peptide PYY of intestinal L cells, and PP with its C-terminal icosapeptide extension of pancreatic PP cells, likely originate from different prohormones. Although intermediate patterns of peptide expression can be observed, including some F-type PP cells of the dog pancreas (uncinate process) and pyloric mucosa showing PYY immunoreactivity or rare PYY and/or HPP immunoreactive cells of the human rectum lacking glicentin reactivity, no obvious relationship can be established between L cells and pancreatic (F-type) PP cells. However, some evolutionary, embryogenetic and oncogenetic link may exist between L cells and human D1-type PP cells, a minor population of PP cells scattered in the pancreatic tissue of dorsal pouch origin and a major fraction of tumor PP cells.

Pancreatic endocrine tumours associated with WDHA syndrome. An immunohistochemical and electron microscopic study

Nine pancreatic endocrine tumours of patients with watery diarrhoea hypokalaemia achlorhydria (WDHA) syndrome were examined by immunohistochemistry and electron microscopy. All cases revealed neoplastic proliferation of VIP (vasoactive intestinal peptide)-immunoreactive (IR) cells. Immunoreactivity to a novel peptide hormone PHM-27, which is processed from a common big precursor peptide of VIP (prepro VIP/PHM-27), was identified in VIP-IR cells of 8 tumours. VIP-PHM-IR cells had secretory granules measuring about 130 to 220 nm in diameter. Radioimmunoassay of tumour tissue extracts showed high VIP and PHM contents in proportional amounts in most cases. According to the results of immunostaining, the 8 tumours fell into two large groups; 5 with PP (pancreatic polypeptide)-IR cells and 3 with CT (calcitonin)-IR cells. The former group demonstrated VIP cells and PP cells intermingled in various proportions, including one tumour in which coexistence of PP-IR and VIP-IR in the same cells was demonstrated. Cell heterogeneity of the tumours and possible relationships of VIP, PP and CT cells were discussed.

Development of the human pancreas: variations and pathology. A tentative classification

The pathology of the pancreas is sometimes related to the embryological development of the organ. The first part of this paper is a presentation of the embryology, morphogenesis and cytogenesis of the pancreas. A tentative classification is then proposed to group together the lesions directly related to anomalies of the position and differentiation of the pancreatic buds. Pathological processes affecting the pancreas can be divided into those related to the ducts and those related to the parenchyma of the gland. In each case anomalies arising at a given stage of development lead to different diseases of the pancreas.

Conformational studies on the pancreatic polypeptide hormone family

Pancreatic polypeptide has been extracted and sequenced from a wide range of species. The 36-residue polypeptides have some hormonal characteristics, and show a high degree of sequence homology. Two recently isolated polypeptides, from porcine gut and brain, also show a high degree of sequence homology with the pancreatic polypeptides. It was proposed that these polypeptides were members of a related family. The X-ray determined structure of one member of the family, turkey pancreatic polypeptide, is known to high resolution, but there is no structural information for the others. Studies designed to give an insight into the tertiary structure of these related molecules have been carried out, including model building using interactive computer graphics, circular dichroic spectroscopy and secondary structure prediction using a variety of algorithms. The results indicate that a compact globular conformation, similar to that observed in turkey pancreatic polypeptide may be adopted by all molecules and that this may be more highly conserved than the individual amino acid sequences.