Finding Eden - alternative transplantation sites for pancreatic islets

Pancreatic islets transplantation is an established treatment method for type 1 diabetic patients with the hypoglycemia unawareness syndrome in whom a therapy with modern technologies fails. Islet transplantation is most commonly done using an interventional radiology method: a tissue suspension of pancreatic islets is applied into a branch of the portal vein through a percutaneously installed catheter. Although being minimally invasive unlike pancreas organ transplant, this method is associated with many technical difficulties. Possible complications of the procedure include hemorrhage and portal vein thrombosis. Unlike their natural dispersed localization in exocrine pancreas, isolated pancreatic islets are exposed to hypoxia, toxins and immunosuppressive drugs in the liver parenchyma. Direct contact with the recipients blood causes an instant blood mediated inflammatory reaction (IBMIR) resulting in the death of more than half of the pancreatic islets shortly after their application. Therefore the size of the islet graft is often insufficient and a number of transplanted patients require administration of exogenous insulin. All of these are reasons for seeking an alternative transplantation site with more hospitable conditions for long-term islet survival. Various transplantation sites have been tested in experimental and clinical research. The advantages and disadvantages of some of them are summarized in this paper. Currently, transplantation into the greater omentum seems most promising, which has already been used in clinical practice at several institutions.

Bioluminescence Imaging In Vivo Confirms the Viability of Pancreatic Islets Transplanted into the Greater Omentum

PURPOSE

The liver is the most widely used site for pancreatic islet transplantation. However, several site-specific limitations impair functional success, with instant blood-mediated inflammatory reaction being the most important. The aim of this study was to develop a preclinical model for placement of the islet graft into a highly vascularized omental flap using a fibrin gel. For this purpose, we tested islet viability by bioluminescence imaging (BLI).

PROCEDURES

Pancreatic islets were isolated from luciferase-positive and luciferase-negative rats, mixed at a 1:1 ratio, placed into a plasma-thrombin bioscaffold, and transplanted in standard (10 pancreatic islets/g wt; n = 10) and marginal (4 pancreatic islets/g wt; n = 7) numbers into the omentums of syngeneic diabetic animals. For the control, 4 pancreatic islets/g were transplanted into the liver using the standard procedure (n = 7). Graft viability was tested by bioluminescence at days 14, 30, 60, and 90 post transplant. Glucose levels, intravenous glucose tolerance, and serum C-peptide were assessed regularly.

RESULTS

Nonfasting glucose levels < 10 mmol/l were restored in all animals. While islet viability in the omentum was clearly detected by stable luminescence signals throughout the whole study period, no signals were detected from islets transplanted into the liver. The bioluminescence signals were highly correlated with stimulated C-peptide levels detected at 80 days post transplant. Glucose tolerance did not differ among the 3 groups.

CONCLUSIONS

We successfully tested a preclinical model of islet transplantation into the greater omentum using a biocompatible scaffold made from autologous plasma and human thrombin. Both standard and marginal pancreatic islet numbers in a gel-form bioscaffold placed in the omentum restored glucose homeostasis in recipients with diabetes. Bioluminescence was shown promising as a direct proof of islet viability.

Unstable Expression of Commonly Used Reference Genes in Rat Pancreatic Islets Early after Isolation Affects Results of Gene Expression Studies

The use of RT-qPCR provides a powerful tool for gene expression studies; however, the proper interpretation of the obtained data is crucially dependent on accurate normalization based on stable reference genes. Recently, strong evidence has been shown indicating that the expression of many commonly used reference genes may vary significantly due to diverse experimental conditions. The isolation of pancreatic islets is a complicated procedure which creates severe mechanical and metabolic stress leading possibly to cellular damage and alteration of gene expression. Despite of this, freshly isolated islets frequently serve as a control in various gene expression and intervention studies. The aim of our study was to determine expression of 16 candidate reference genes and one gene of interest (F3) in isolated rat pancreatic islets during short-term cultivation in order to find a suitable endogenous control for gene expression studies. We compared the expression stability of the most commonly used reference genes and evaluated the reliability of relative and absolute quantification using RT-qPCR during 0–120 hrs after isolation. In freshly isolated islets, the expression of all tested genes was markedly depressed and it increased several times throughout the first 48 hrs of cultivation. We observed significant variability among samples at 0 and 24 hrs but substantial stabilization from 48 hrs onwards. During the first 48 hrs, relative quantification failed to reflect the real changes in respective mRNA concentrations while in the interval 48–120 hrs, the relative expression generally paralleled the results determined by absolute quantification. Thus, our data call into question the suitability of relative quantification for gene expression analysis in pancreatic islets during the first 48 hrs of cultivation, as the results may be significantly affected by unstable expression of reference genes. However, this method could provide reliable information from 48 hrs onwards.

Activation of the Jak/Stat signalling pathway by leukaemia inhibitory factor stimulates trans-differentiation of human non-endocrine pancreatic cells into insulin-producing cells

Differentiation of pancreatic β-cells is regulated by a wide range of signalling pathways. The aim of our current work was to evaluate the effect of the Jak/Stat signalling pathway on the differentiation of human non-endocrine pancreatic cells into insulin-producing cells. Activation of the Jak/Stat signalling pathway by leukaemia inhibitory factor (LIF) stimulated differentiation of C-peptide-negative human non-endocrine pancreatic cells into insulin-producing cells in 6.3 ± 2.0 % cells (N = 5) and induced expression of pro-endocrine transcription factor neurogenin 3, Notch signalling pathway suppressor HES6 and stimulator of β-cell neogenesis REG3A. The expression of the REG3A gene and increased rate of differentiation into insulin-producing cells (10.2 ± 2.1 %) were further stimulated by a combination of LIF with nicotinamide and dexamethasone. Glucose-stimulated (5 vs. 20 mM) C-peptide secretion confirmed proper insulin secretory function of trans-differentiated insulin-producing cells (0.51 vs. 2.03 pmol C-peptide/μg DNA, P < 0.05). Our results indicate that Jak/Stat signalling critically contributes to trans-differentiation of non-endocrine pancreatic cells into functional insulin-producing cells. The positive effect of the Jak/Stat signalling pathway on trans-differentiation is mediated by the key genes that activate differentiation of pancreatic β-cells.

The effect of epigenetic factors on differentiation of pancreatic progenitor cells into insulin-producing cells

Differentiation of pancreatic progenitors into insulin-producing β cells is regulated by various transcription factors. To be expressed the genes coding these transcription factors need to be in accessible DNA. Whether a particular gene is present in a form of active euchromatin structure with accessible DNA or in an inactive heterochromatin structure with inaccessible DNA is determined by various epigenetic modifications. We studied the effect of epigenetic modifiers on differentiation of human nonendocrine cells into insulin-producing cells with the aim to evaluate the effect of epigenetic modifications in that process. Within 3 days of cultivation nonendocrine cells form isletlike cell clusters (ILCCs) containing mainly cytokeratin-19-positive cells. After cultivation with epigenetic modifiers and further differentiation, the highest number of C-peptide-positive cells (10.3% ± 2.9%) as well as glucagon-positive cells (7.2% ± 2.8%) was observed in a sample supplemented with a combination of 5-Aza-2'-deoxycytidine modifiers, BIX01294 and MC1568. In response to glucose stimulation (5 vs 20 mmol/L) these ILCCs secreted increased amounts of C-peptide (0.45 vs 1.05 pmol C-peptide/μg DNA). Control samples treated without any epigenetic modifiers showed significantly lower numbers of C-peptide-positive cells (3.5% ± 1.6%). These results showed that a combination of epigenetic modifiers 5-Aza-2'-deoxycytidine (BIX01294 and MC1568) significantly improved reproducible differentiation of nonendocrine pancreatic cells into insulin-producing cells.