Human Insulinomas: Clinical, Cellular, and Molecular Aspects

Hypoglycemia secondary to insulinoma masking the onset of type 1 diabetes in an adolescent

Type 1 diabetes and insulinoma can co-occur in pediatric patients and may present with episodes of hypo- and hyperglycemia, significant glycemic variability, and weight gain. Surgical resection leads to development of fulminant diabetes.

Amyloid-Rich Pancreatic Neuroendocrine Tumors: a Potential Diagnostic Pitfall in Endoscopic Ultrasound-Guided Fine Needle Aspiration Cytology (EUS-FNAC)

Pancreatic neuroendocrine tumors (PanNETs) are rare neoplasms that include even rarer variants that may pose different diagnostic problems, especially in fine needle aspiration cytology (FNAC). We describe the diagnostic clues of the amyloid-rich variant of PanNETs in endoscopic ultrasound (EUS)-guided fine needle aspiration cytology (EUS-FNAC). Three cases of PanNETs with an amyloid-rich stromal component were retrieved and retrospectively reviewed. For every case, the pancreatic lesion was investigated by a EUS-FNAC procedure. The final diagnosis was supported by immunocytochemistry and Congo red staining. All cases had similar EUS-FNAC features: neoplastic cells were entrapped in an eosinophilic, homogeneous dense and amorphous matrix. The neuroendocrine nature was confirmed by immunoexpression of synaptophysin and chromogranin A, while the amorphous stroma was characterized as amyloid based on positive Congo red staining. Regarding the hormonal profile, no insulin or proinsulin reactivity was observed, but all cases were diffusely positive for amylin. The diagnosis of uncommon variants of PanNETs, such as the amyloid-rich, is challenging especially in EUS-FNAC procedures because of a unique and misleading morphology, potentially mimicking fibrotic conditions and amyloid deposition within systemic amyloidosis. In cytology specimens, the presence of amorphous material requires amyloid deposition to be considered in the differential diagnosis of pancreatic neoplasms with neuroendocrine phenotype.

Pitfalls in the Detection of Insulinomas With Glucagon-Like Peptide-1 Receptor Imaging

PURPOSE

Physiological pancreaticoduodenal uptake of radiolabeled exendin-4 in Brunner glands of the proximal duodenum is the most common pitfall for false interpretation of glucagon-like peptide-1 receptor (GLP-1R) imaging. The aim of this study was to analyze the pancreaticoduodenal uptake in GLP-1R PET/CT and SPECT/CT images and to identify additional potential reading pitfalls in patients with suspected insulinoma.

METHODS

A post hoc analysis of a prospective study, including 52 consecutive patients, was performed. All patients underwent 1 Ga-exendin-4 PET/CT and 2 In-exendin-4 SPECT/CT scans (4 and 72 hours postinjection) in a randomized crossover order. Three board-certified nuclear medicine physicians read all scans independently. They were unaware of other results. Reference standard was surgery with histopathological confirmation of an insulinoma/nesidioblastosis and normalization of blood glucose levels after surgery.

RESULTS

There were no false-positive readings. However, there were a number of false-negative PET/CT and SPECT/CT readings, respectively: (1) due to false interpretation of uptake in the pancreaticoduodenal region (falsely interpreted as physiological uptake in Brunner glands instead of an insulinoma in 0.6% vs 9.0%), (2) due to ectopic insulinoma (0% vs 2.6%), (3) due to small insulinoma (1.9% vs 5.1%), (4) due to insulinoma overlap with kidneys (1.9% vs 4.5%), and (5) due to nesidioblastosis (0.6% and 1.9%). Pitfalls were identified in all GLP-1R PET/CT and SPECT/CT scans.

CONCLUSIONS

Peripancreatic uptake, small size of an insulinoma, insulinoma overlap with kidneys, and presence of nesidioblastosis are potential pitfalls in GLP-1R imaging, which can lead to false reading results.

The efficiency of insulin production and its content in insulin-expressing model β-cells correlate with their Zn2+ levels

Insulin is produced and stored inside the pancreatic β-cell secretory granules, where it is assumed to form Zn2+-stabilized oligomers. However, the actual storage forms of this hormone and the impact of zinc ions on insulin production in vivo are not known. Our initial X-ray fluorescence experiment on granules from native Langerhans islets and insulinoma-derived INS-1E cells revealed a considerable difference in the zinc content. This led our further investigation to evaluate the impact of the intra-granular Zn2+ levels on the production and storage of insulin in different model β-cells. Here, we systematically compared zinc and insulin contents in the permanent INS-1E and BRIN-BD11 β-cells and in the native rat pancreatic islets by flow cytometry, confocal microscopy, immunoblotting, specific messenger RNA (mRNA) and total insulin analysis. These studies revealed an impaired insulin production in the permanent β-cell lines with the diminished intracellular zinc content. The drop in insulin and Zn2+ levels was paralleled by a lower expression of ZnT8 zinc transporter mRNA and hampered proinsulin processing/folding in both permanent cell lines. To summarize, we showed that the disruption of zinc homeostasis in the model β-cells correlated with their impaired insulin and ZnT8 production. This indicates a need for in-depth fundamental research about the role of zinc in insulin production and storage.

Histologic and Molecular Profile of Pediatric Insulinomas: Evidence of a Paternal Parent-of-Origin Effect

CONTEXT

Acquired insulinomas are rare causes of hyperinsulinemic hypoglycemia in children and are much less common than focal lesions of congenital hyperinsulinism. The latter are known to be associated with isodisomy for paternally transmitted ATP-sensitive potassium channel mutations on 11p15; however, the molecular basis for pediatric insulinomas is not well characterized.

OBJECTIVE

The purpose of this study was to characterize the histopathological and molecular defects in a large group of 12 pediatric insulinomas seen at The Children's Hospital of Philadelphia.

RESULTS

Twelve children with insulinomas were seen between 1971 and 2013, compared to 201 cases with focal congenital hyperinsulinism seen between 1997 and 2014. The age of insulinoma patients ranged from 4-16 years at the time of surgery. Features of MEN1 syndrome were present in five of the 12, including four cases with heterozygous mutations of MEN1 on 11q. Immunohistochemical analysis revealed nuclear loss of p57 staining consistent with loss of the maternal 11p15 allele in 11 of the 12 insulinomas, including all five MEN1-associated tumors. Imbalance of the paternal 11p allele was confirmed by single nucleotide polymorphism genotyping and methylation assays of the 11p imprinting control loci in four of five MEN1-associated tumors and six of seven sporadic insulinomas. In addition, single nucleotide polymorphism genotyping revealed extensive tumor aneuploidy beyond chromosome 11.

CONCLUSIONS

These data indicate that MEN1 mutations are more common in insulinomas in children than in adults. Aneuploidy of chromosome 11 and other chromosomes is common in both MEN1 and non-MEN1 insulinomas. The novel observation of a paternal parent-of-origin effect in all MEN1 and most non-MEN1 tumors suggests a critical role for imprinted growth-regulatory genes in the 11p region in the genesis of β-cell endocrine tumors in children.

Co-existence of glucagonoma with recurrent insulinoma in a patient with multiple endocrine neoplasia-type 1 (MEN-1)

Multiple endocrine neoplasia type 1 (MEN1) is an autosomal dominant disorder characterized by tumors of the parathyroid glands, the anterior pituitary, and the endocrine pancreas. Our patient was a 58-year-old man who manifested typical features of MEN-1 including primary hyperparathyroidism, lung carcinoid, and lipomas and insulinoma. He was admitted to our hospital because of recurrent hypoglycemia and a growth of pancreatic tumors. The first operation for insulinoma was performed when he was 20 years old. We found a germline mutation of the MEN1 gene (E45G, exon 2) in this patient. According to these examinations and his clinical course, the patient was diagnosed as having a recurrence of insulinoma. He subsequently underwent surgery for the pancreatic tumors. The majority of these tumor cells were immunohistochemically positive for insulin and negative for glucagon. A few nodules showed immunohistochemical staining positivity for glucagon but they were negative for insulin. Although it is uncommon for patients with MEN1 to exhibit insulinoma and glucagonoma, this case suggests the need for careful analysis of pancreatic tumors in patients with MEN1.

Abnormalities of proinsulin processing in functioning insulinomas: clinical implications

OBJECTIVE

Abnormal proinsulin processing in insulinomas may result in secretory granules containing both insulin and proinsulin, a finding not encountered in healthy beta-cells. The aim of this study was to test whether such abnormalities in the proinsulin to insulin conversion have clinical implications in patients with hypoglycaemic disorders.

DESIGN

Case-series.

PATIENTS AND METHODS

Fifteen patients with histologically confirmed insulinoma and two patients with islet cell hyperplasia were included. The immunohistochemical distribution pattern of proinsulin within the tumour cells was classified as Golgi pattern (predominantly perinuclear immunolabelling) or diffuse pattern (immunolabelling in the periphery of the cells, indicating the presence of proinsulin in secretory granules). Data obtained from the 72-h fast and arterial calcium stimulation and hepatic venous sampling (ASVS) test were related to the morphological classification.

RESULTS

Six insulinomas exhibited a diffuse proinsulin distribution pattern, while nine insulinomas and two islet cell hyperplasias disclosed a Golgi pattern. Median proinsulin concentrations at the termination of the fast tended to be higher in patients with the diffuse proinsulin distribution pattern than in patients with the Golgi pattern (86.9 vs. 18.8 pmol/l, P = 0.07). Higher insulin (P < 0.005) and proinsulin (P < 0.05) concentrations were significantly correlated with earlier occurrence of hypoglycaemia during the prolonged fast. During the ASVS test, tumours with the diffuse proinsulin distribution pattern exhibited a higher increase in both insulin (median, 37.3- vs. 10.5-fold, P < 0.05) and proinsulin (6.3- vs. 1.6 fold, P < 0.005) concentrations following calcium stimulation than the tumours with the Golgi pattern.

CONCLUSIONS

Abnormalities in the proinsulin to insulin conversion in patients with insulinomas and islet cell hyperplasia correlate with impaired regulation of both insulin and proinsulin secretion during the prolonged fast as well as the ASVS test.

Expression of the two isoforms of the vesicular monoamine transporter (VMAT1 and VMAT2) in the endocrine pancreas and pancreatic endocrine tumors

The uptake of monoamines into the secretory granules of monoamine-storing neuroendocrine cells is mediated by vesicular monoamine transporter protein 1 or 2 (VMAT1 or VMAT2). This study analyzed the expression of VMAT1 and VMAT2 in endocrine cells of normal human and monkey pancreas. The expression of VMAT1 and VMAT2 was also examined in infants with hyperinsulinemic hypoglycemia and in adults with pancreatic endocrine tumors (PETs). Using immunohistochemistry (IHC) and in situ hybridization (ISH), we demonstrated the mutually exclusive expression of VMAT1 in endocrine cells of the duct system and of VMAT2 in many cells of the islets of Langerhans. By confocal laser scanning microscopy, VMAT1-positive cells were identified as enterochromaffin (EC) cells and VMAT2-positive cells as beta-cells. In PETs, VMAT1 was found exclusively in all serotonin-containing tumors. In contrast, VMAT2 expression was lost in many insulinomas, independent of their biological behavior. VMAT2 was expressed by some non-insulin-producing tumors. The mutually exclusive expression of VMAT1 in EC cells and of VMAT2 in beta-cells suggests that both cell types store monoamines. Monoamine storage mediated by VMAT1 in EC cells is apparently maintained in EC cell tumors. In contrast, many insulinomas appear to lose their ability to accumulate monoamines via VMAT2.

Putative tumor suppressor loci at 6q22 and 6q23-q24 are involved in the malignant progression of sporadic endocrine pancreatic tumors

Our previous comparative genomic hybridization study on sporadic endocrine pancreatic tumors (EPTs) revealed frequent losses on chromosomes 11q, 3p, and 6q. The aim of this study was to evaluate the importance of 6q losses in the oncogenesis of sporadic EPTs and to narrow down the smallest regions of allelic deletion. A multimodal approach combining polymerase chain reaction-based allelotyping, double-target fluorescence in situ hybridization, and comparative genomic hybridization was used in a collection of 109 sporadic EPTs from 93 patients. Nine polymorphic microsatellite markers (6q13 to 6q25-q27) were investigated, demonstrating a loss of heterozygosity (LOH) in 62.2% of the patients. A LOH was significantly more common in tumors >2 cm in diameter than below this threshold as well as in malignant than in benign tumors. We were able to narrow down the smallest regions of allelic deletion at 6q22.1 (D6S262) and 6q23-q24 (D6S310-UTRN) with LOH-frequencies of 50.0% and 41.2 to 56.3%, respectively. Several promising tumor suppressor candidates are located in these regions. Additional fluorescence in situ hybridization analysis on 46 EPTs using three locus-specific probes (6q21, 6q22, and 6q27) as well as a centromere 6-specific probe revealed complete loss of chromosome 6 especially in metastatic disease. We conclude that the two hot spots found on 6q may harbor putative tumor suppressor genes involved not only in the oncogenesis but maybe also in the malignant and metastatic progression of sporadic EPTs.