The islet-acinar axis of the pancreas

Incidence and Clinical Implications of Anatomical Variations in the Pancreas and Its Ductal System: A Systematic Review and Meta-Analysis

OBJECTIVE

This systematic review analyzes the anatomical variants in the pancreas and its ductal system to report on their association with pancreatic pathologies.

METHODS

We conducted a search of the MEDLINE, Scopus, Web of Science, Google Scholar, CINAHL, and LILACS databases from their inception to July 2023. The methodological quality was assessed with the Anatomical Quality Assessment (AQUA) tool. Finally, the pooled prevalence was estimated using a random effects model.

RESULTS

55 studies were found that met the eligibility criteria. The overall prevalence of pancreas divisum (PD) was 18% (95% CI = 15-21%). The prevalence of PD associated with pancreatitis was 30% (95% CI = 1-61%).

CONCLUSIONS

An anatomical variant of the pancreas such as PD may be the cause of bile duct obstruction, resulting in various clinical complications, such as pancreatitis. Hence, knowing this variant is extremely important for surgeons, especially for those who treat the gastroduodenal region.

Relationship between circulating levels of pancreatic proteolytic enzymes and pancreatic hormones

BACKGROUND

While the close morphological relationship between the exocrine and endocrine pancreas is well established, their functional interaction remains poorly understood. The aim of this study was to investigate the associations between circulating levels of pancreatic proteolytic enzymes and insulin, as well as other pancreatic hormones.

METHODS

Fasting venous blood samples were collected and analyzed for trypsin, chymotrypsin, insulin, glucagon, somatostatin, and pancreatic polypeptide. Linear regression analysis was used in unadjusted and two adjusted (accounting for prediabetes/diabetes, body mass index, smoking, and other covariates) statistical models.

RESULTS

A total of 93 individuals with a history of acute pancreatitis were included in this cross-sectional study. Chymotrypsin was significantly associated with insulin in the two adjusted models (p = 0.005; p = 0.003) and just missed statistical significance in the unadjusted model (p = 0.066). Chymotrypsin was significantly associated with glucagon in both unadjusted (p = 0.025) and adjusted models (p = 0.014; p = 0.015); as well as with somatostatin - in both unadjusted (p = 0.001) and adjusted models (p = 0.001; p = 0.002). Trypsin was not significantly associated with insulin in any of the models but was significantly associated with glucagon in both unadjusted (p < 0.001) and adjusted models (p < 0.001), and pancreatic polypeptide in both unadjusted (p < 0.001) and adjusted (p < 0.001) models.

CONCLUSION

The state of hyperinsulinemia is characterized by a dysfunction of the exocrine pancreas. In particular, chymotrypsin is increased in the state of hyperinsulinemia and trypsin is significantly associated with glucagon and pancreatic polypeptide.

Formation of Cholangiogenic Cysts Following Intrahepatic Islet Transplantation in Streptozotocin Diabetic Rats

Permanent hyperinsulinemia and the resulting overstimulation of the insulin receptor signaling pathway is suspected as a trigger of cancer genesis in the livers of type 2 diabetic patients. Liver tissue (LT) surrounding transplanted pancreatic islets (PI) can be permanently exposed to insulin in even higher concentrations than in type 2 diabetic patients. Therefore, this study examines the effect of PI transplantation (Tx) on LT in animals with streptozotocin (STZ)-induced diabetes mellitus. The suboptimal mass (400 or 1000) of isogeneic PI was transplanted into either the portal vein or under the kidney capsule of diabetic Brown Norway (BN) rats. Healthy BN rats treated with 400 isogeneic PI transplanted in the portal vein served as a control group. During the first 6 months after PI Tx, small and infrequent cystic lesions developed in animals with STZ diabetes, irrespective of the Tx site. In 10 months, frequent and complex cystic lesions appeared in these animals. In the control group, several small lesions were detected but not until 10 months after the PI Tx. In summary, STZ is the likely main inductor of hepatic cystic lesions, but the contribution of PI was not confirmed.

Decreased insulin secretion and glucose clearance in exocrine pancreas-insufficient pigs

The effect of exocrine pancreatic function on the glucose-mediated insulin response and glucose utilization were studied in an exocrine pancreas-insufficient (EPI) pig model. Five 10-week-old EPI pigs after pancreatic duct ligation and 6 age-matched, non-operated control pigs were used in the study. Blood glucose, plasma insulin and C-peptide concentrations were monitored during meal (MGTT), oral (OGTT) and intravenous (IVGTT) glucose tolerance tests. Upon post-mortem examination, the pancreatic remnants of the EPI pigs showed acinar fibrotic atrophy but normal islets and β-cell morphology. The EPI pigs displayed increased fasting glucose concentrations compared with control animals (6.4 ± 0.4 versus 4.8 ± 0.1 mmol l(-1) , P < 0.0001) but unchanged insulin concentrations (2.4 ± 0.6 versus 2.1 ± 0.2 pmol l(-1) ). During the OGTT and IVGTT, the EPI pigs showed slower, impaired glucose utilization, with the disruption of a well-timed insulin response. Plasma C-peptide concentrations confirmed the delayed insulin response during the IVGTT in EPI pigs. Oral pancreatic enzyme supplementation (PES) of EPI pigs improved glucose clearance during IVGTT [AUC(glucose) 1295 ± 70 mmol l(-1) × (120 min) in EPI versus 1044 ± 32 mmol l(-1) × (120 min) in EPI + PES, P < 0.0001] without reinforcing the release of insulin [AUC(C-peptide) 14.4 ± 3.8 nmol l(-1) × (120 min) in EPI versus 6.4 ± 1.3 nmol l(-1) × (120 min) in EPI + PES, P < 0.002]. The results suggest the existence of an acino-insular axis regulatory communication. The presence of pancreatic enzymes in the gut facilitates glucose utilization in an insulin-independent manner, indicating the existence of a gut-derived pancreatic enzyme-dependent mechanism involved in peripheral glucose utilization.

Three-dimensional analysis of the islet vasculature

The pancreatic islets of Langerhans are highly vascularized structures scattered throughout the pancreas that contain a capillary network 5-10 times denser than that of the exocrine pancreas. A simple method for three-dimensional (3D) analysis of this intricate intraislet vasculature has been difficult because of the intrinsic opacity of the pancreas. We developed a whole-mount imaging technique that allows relatively easy visualization of the islet vasculature. In combination with confocal microscopy and the use of 3D imaging software, we were able to readily reconstruct the 3D architecture of an islet, allowing delineation of the islet volume, length of the intraislet vessels, and the number of vessel branch-points. This technique allows for straightforward 3D image analysis that may help toward understanding islet function.

Conversion of non-endocrine human pancreatic cells to insulin-producing cells for treatment of diabetes

Type I diabetes results from the autoimmune destruction of the insulin-secreting pancreatic β-cells, affecting many millions of people worldwide. The optimal treatment is to restore the endogenous supply of insulin either through the transplantation of pancreas or the transplantation of islets of langerhans or simply the β-cells. However, the donated pancreas organs are limited and the available organs are only able to treat a small portion of the diabetes patients. Thus, glucose-responsive, insulin-producing cells from human origin are urgently needed. The aim of this chapter is to give some insight views to how to turn the potential human pancreatic non-endocrine cells into cells that are capable of secreting insulin in response to glucose and ameliorating insulin-deficient diabetes conditions after transplantation.

γ-aminobutyric acid secreted from islet β-cells modulates exocrine secretion in rat pancreas

AIM: To investigate the role of endogenous γ-amino-butyric acid (GABA) in pancreatic exocrine secretion.

METHODS: The isolated, vascularly perfused rat pancreas was employed in this study to eliminate the possible influences of extrinsic nerves and hormones. Cholecystokinin (CCK; 10 pmol/L) was intra-arterially given to stimulate exocrine secretion of the pancreas.

RESULTS: Glutamine, a major precursor of GABA, which was given intra-arterially at concentrations of 1, 4 and 10 mmol/L, dose-dependently elevated the CCK-stimulated secretions of fluid and amylase in the normal pancreas. Bicuculline (10 μmol/L), a GABA_A receptor antagonist, blocked the enhancing effect of glutamine (4 mmol/L) on the CCK-stimulated exocrine secretions. Glutamine, at concentrations of 1, 4 and 10 mmol/L, dose-dependently increased the GABA concentration in portal effluent of the normal pancreas. The effects of glutamine on the CCK-stimulated exocrine secretion as well as the GABA secretion were markedly reduced in the streptozotocin-treated pancreas.

CONCLUSION: GABA could be secreted from β-cells into the islet-acinar portal system after administration of glutainine, and could enhance the CCK-stimulated exocrine secretion through GABA_A receptors. Thus, GABA in islet β-cells is a hormone modulating pancreatic exocrine secretion.

Dietary amino acids promote pancreatic protease synthesis at the translation stage in rats

In some tissues, amino acids (AA) stimulate translation initiation via interactions between eukaryote initiation factor (eIF) 4E-binding protein 1 (4E-BP1), eIF4E and eIF4G. Dietary AA have been shown to induce pancreatic proteases independently of cholecystokinin in rats, the mechanism of which has not yet been clarified. In the present study, we examined the mechanism in rats for protease induction by dietary AA and determined the involvement of translation initiation. Male Wistar/ST rats were fed a 20 or 60% casein or AA mixture diet for 7 d and were intravenously injected with [35S] methionine (Met) 30 min before killing on d 7 (expt. 1). In expt. 2, rats were fed a 20 or 60% AA diet for 7 d and after food deprivation and refeeding with the respective diet on d 7 were killed at 0, 1 or 3 h. We measured mRNA and [35S] Met incorporation into chymotrypsinogen, phosphorylation status of 4E-BP1 and the association of eIF4E with 4E-BP1 or eIF4G. In expt. 1, chymotrypsin activity and synthesis were higher in both of the 60% diet groups than in the 20% diet groups, but the mRNA level and 4E-BP1 status did not differ. In expt. 2, chymotrypsin activity increased in the 60% AA diet group in a time-dependent manner. The translation initiation activity via the mTOR pathway indicated an increase similar to chymotrypsin activity. There were no differences in chymotrypsin mRNA level at any point. These results indicate that dietary AA induce chymotrypsin synthesis by promoting translation, and transient activation of translation initiation via mTOR may be associated with this induction.