Potential of [11C]UCB-J as a PET tracer for islets of Langerhans

Biomarkers for the measurement of islets of Langerhans could help elucidate the etiology of diabetes. Synaptic vesicle glycoprotein 2 A (SV2A) is a potential marker reported to be localized in the endocrine pancreas. [11C]UCB-J is a novel positron emission tomography (PET) radiotracer that binds to SV2A and was previously evaluated as a synaptic marker in the central nervous system. Here, we evaluated whether [11C]UCB-J could be utilized as a PET tracer for the islets of Langerhans in the pancreas by targeting SV2A. The mRNA transcription of SV2A was evaluated in human isolated islets of Langerhans and exocrine tissue. In vitro autoradiography was performed on pancreas and brain sections from rats and pigs, and consecutive sections were immunostained for insulin. Sprague–Dawley rats were examined with PET-MRI and ex vivo autoradiography at baseline and with administration of levetiracetam (LEV). Similarly, pigs were examined with dynamic PET-CT over the pancreas and brain after administration of [11C]UCB-J at baseline and after pretreatment with LEV. In vivo radioligand binding was assessed using a one-compartment tissue model. The mRNA expression of SV2A was nearly 7 times higher in endocrine tissue than in exocrine tissue (p < 0.01). In vitro autoradiography displayed focal binding of [11C]UCB-J in the pancreas of rats and pigs, but the binding pattern did not overlap with the insulin-positive areas or with ex vivo autoradiography. In rats, pancreas binding was higher than that in negative control tissues but could not be blocked by LEV. In pigs, the pancreas and brain exhibited accumulation of [11C]UCB-J above the negative control tissue spleen. While brain binding could be blocked by pretreatment with LEV, a similar effect was not observed in the pancreas. Transcription data indicate SV2A to be a valid target for imaging islets of Langerhans, but [11C]UCB-J does not appear to have sufficient sensitivity for this application.

Editorial on the Special Issue: “Pancreatic Islets of Langerhans: Not Only Beta-Cells”

This year marks the centenary of the discovery of insulin [...]

Case Report: A Difficult-to-Diagnose Case of Hyperinsulinemic Hypoglycemia Surgically Treated After Developing Acute Pancreatitis

The patient is a 28-year-old Japanese man diagnosed with severe congenital hyperinsulinemic-hypoglycemia six months after birth. Clinical records revealed no imaging evidence of pancreatic tumor at the time of diagnosis. Subsequently, he had developmental disorders and epilepsy caused by recurrent hypoglycemic attacks. The patient’s hypoglycemia improved with oral diazoxide. However, he developed necrotizing acute pancreatitis at 28 years of age, thought to be due to diazoxide. Discontinuation of diazoxide caused persistent hypoglycemia, requiring continuous glucose supplementation by tube feeding and total parenteral nutrition. A selective arterial secretagogue injection test revealed diffuse pancreatic hypersecretion of insulin. He underwent subtotal distal (72%) pancreatectomy and splenectomy. There was no intraoperative visible pancreatic tumor. His hypoglycemia improved after the surgical procedure. The histopathological study revealed a high density of islets of Langerhans in the pancreatic body and tail. There were large islets of Langerhans and multiple neuroendocrine cell nests in the whole pancreas. Nests of neuroendocrine cells were also detected in lymph nodes. The pathological diagnosis was grade 1 neuroendocrine tumor (microinsulinomas) with lymph node metastases. This patient is a difficult-to-diagnose case of hyperinsulinemic hypoglycemia surgically treated after developing acute pancreatitis. We believe this is a unique case of microinsulinomas with lymph metastases diagnosed and treated as congenital hyperinsulinemic hypoglycemia for almost 28 years.

Novel Human Insulin Isoforms and Cα-peptide Product in Islets of Langerhans and Choroid Plexus

<a>Human insulin (<i>INS</i>) gene diverged from the ancestral genes of invertebrate and mammalian species millions of years ago. We previously found that mouse insulin gene (<i>Ins2</i>) isoforms are expressed in brain choroid plexus (ChP) epithelium cells where insulin secretion is regulated by serotonin and not by glucose. We further compared human <i>INS</i> isoform expression in postmortem <u>ChP</u> and islets of Langerhans. We uncovered novel <i>INS</i> upstream open reading frame (uORF) isoforms and their protein products. In addition, we found a novel alternatively spliced isoform that translates to a 74-amino acid (AA) proinsulin containing a shorter 19-AA C-peptide sequence, herein designated C</a>a-peptide. The middle portion of the conventional C-peptide contains b-sheet (GQVEL) and hairpin (GGGPG) motifs that are not present in Ca-peptide. Islet amyloid polypeptide (<i>IAPP</i>) is not expressed in ChP and its amyloid formation was inhibited <i>in vitro</i> by Ca-peptide more efficiently than by C-peptide. Of clinical relevance, the ratio of the 74-AA proinsulin to proconvertase processed Ca-peptide was significantly increased in islets from type 2 diabetes mellitus (T2DM) autopsy donors. Intriguingly, 100 years after the discovery of insulin we found that <i>INS</i> isoforms are present in ChP <a>from insulin-deficient autopsy donors.</a> <p> </p>

Novel Human Insulin Isoforms and Cα-peptide Product in Islets of Langerhans and Choroid Plexus

<a>Human insulin (<i>INS</i>) gene diverged from the ancestral genes of invertebrate and mammalian species millions of years ago. We previously found that mouse insulin gene (<i>Ins2</i>) isoforms are expressed in brain choroid plexus (ChP) epithelium cells where insulin secretion is regulated by serotonin and not by glucose. We further compared human <i>INS</i> isoform expression in postmortem <u>ChP</u> and islets of Langerhans. We uncovered novel <i>INS</i> upstream open reading frame (uORF) isoforms and their protein products. In addition, we found a novel alternatively spliced isoform that translates to a 74-amino acid (AA) proinsulin containing a shorter 19-AA C-peptide sequence, herein designated C</a>a-peptide. The middle portion of the conventional C-peptide contains b-sheet (GQVEL) and hairpin (GGGPG) motifs that are not present in Ca-peptide. Islet amyloid polypeptide (<i>IAPP</i>) is not expressed in ChP and its amyloid formation was inhibited <i>in vitro</i> by Ca-peptide more efficiently than by C-peptide. Of clinical relevance, the ratio of the 74-AA proinsulin to proconvertase processed Ca-peptide was significantly increased in islets from type 2 diabetes mellitus (T2DM) autopsy donors. Intriguingly, 100 years after the discovery of insulin we found that <i>INS</i> isoforms are present in ChP <a>from insulin-deficient autopsy donors.</a> <p> </p>

The Role of Mesenchymal Stem Cells with Ascorbic Acid and N-Acetylcysteine on TNF-α, IL 1β, and NF-κβ Expressions in Acute Pancreatitis in Albino Rats

Severe acute pancreatitis (SAP) is a necrotic pancreatic inflammation associated with high mortality rate (up to 70%). Bone marrow (BM) mesenchymal stem cells (MSCs) have been investigated in pancreatic cellular regeneration, but still their effects are controversial. Therefore, the present study is aimed at examining the enrichment of the stem cells with ascorbic acid (AA) and N-acetylcysteine (NAC) and explore their combined action on the expression of the inflammatory cytokines: interleukin 1β (IL 1β), tumor necrosis factor-α (TNF-α), and nuclear factor-κβ (NF-κβ). A total of twenty adult male Sprague-Dawley albino rats were divided into four groups: the control group, cerulein group (to induce acute pancreatitis), BM-MSCs group, and combined BM-MSCs with AA and NAC group. Homing and proliferation of stem cells were revealed by the appearance of PKH26-labelled BM-MSCs in the islets of Langerhans. AA and NAC combination with BM-MSCs (group IV) was demonstrated to affect the expression of the inflammatory cytokines: IL 1β, TNF-α, and NF-κβ. In addition, improvement of the biochemical and histological parameters is represented in increasing body weight, normal blood glucose, and insulin levels and regeneration of the islet cells. Immunohistochemical studies showed an increase in proliferating cell nuclear antigen (PCNA) and decrease in caspase-3 reactions, detected markedly in group IV, after the marked distortion of the classic pancreatic lobular architecture was induced by cerulein. It could be concluded that treatment with BM-MSCs combined with antioxidants could provide a promising therapy for acute pancreatitis and improve the degeneration, apoptosis, necrosis, and inflammatory processes of the islets of Langerhans. TNF-α, IL 1β, and NF-κβ are essential biomarkers for the evaluation of MSC regenerative effectiveness.

Histological and Histochemical Description of the Pancreas in the Adult Lesser Capybara (Hydrochoerus isthmius)

The aim of this study was to describe histologically and histochemically the pancreas of three adult Hydrochoerus isthmius, attacked by feral dog in Buenavista, Córdoba, Colombia. A complete necropsy was performed and pancreatic fragments were collected and stored in 10% buffered formalin and Bouin liquid. Then, they were dehydrated, diaphanized and embedded in paraffin, stained with Hematoxylin & Eosin, P.A.S., Gomori trichrome, Grimelius and Masson Fontana modified. The H. isthmius pancreas presented a duodenal mesenteric pattern. The exocrine portion was described as a composite tubuloacinar gland. The endocrine portion of the pancreas was constituted by pancreatic islets of Langerhans and a diffuse neuroendocrine system. The histological and histochemical techniques used allowed us to identify the exocrine and endocrine portion of the organ. It is suggested to complement this study with some special techniques for the identification of specific endocrine cells, such as Beta, Alpha, Delta, Epsilon, PP or Gamma.

Whole-Slide Image Analysis of Human Pancreas Samples to Elucidate the Immunopathogenesis of Type 1 Diabetes Using the QuPath Software

Type 1 diabetes is a chronic disease of the pancreas characterized by the loss of insulin-producing beta cells. Access to human pancreas samples for research purposes has been historically limited, restricting pathological analyses to animal models. However, intrinsic differences between animals and humans have made clinical translation very challenging. Recently, human pancreas samples have become available through several biobanks worldwide, and this has opened numerous opportunities for scientific discovery. In addition, the use of new imaging technologies has unraveled many mysteries of the human pancreas not merely in the presence of disease, but also in physiological conditions. Nowadays, multiplex immunofluorescence protocols as well as sophisticated image analysis tools can be employed. Here, we described the use of QuPath—an open-source platform for image analysis—for the investigation of human pancreas samples. We demonstrate that QuPath can be adequately used to analyze whole-slide images with the aim of identifying the islets of Langerhans and define their cellular composition as well as other basic morphological characteristics. In addition, we show that QuPath can identify immune cell populations in the exocrine tissue and islets of Langerhans, accurately localizing and quantifying immune infiltrates in the pancreas. Therefore, we present a tool and analysis pipeline that allows for the accurate characterization of the human pancreas, enabling the study of the anatomical and physiological changes underlying pancreatic diseases such as type 1 diabetes. The standardization and implementation of these analysis tools is of critical importance to understand disease pathogenesis, and may be informative for the design of new therapies aimed at preserving beta cell function and halting the inflammation caused by the immune attack.