Venant Tchokonte-Nana

Mesenchymal cells are required for epithelial duct cell-to-beta cell maturation and function in an injured adult pancreas in the rat

The islet, the endocrine portion of the pancreas - develops from an invagination of the pancreatic duct epithelial cells (PDECs) into the surrounding tissue. The contact of the PDECs with mesenchymal cells (MSCs) may be an essential drive for endocrine cell fate. During pancreatic development, cells that express Neurogenin-3 (Ngn3) biomarker are precursors of insulin- producing beta cells. These precursors have been reported in the neogenesis of islets from adult tissues following the surgical ligation of the main pancreatic duct (PDL). But the capacity of these precursors to induce the appropriate signals to complete the entire neogenesis program has been questioned. We studied the fate of co-culture of PDECs and MSCs from the ligated adult pancreas and established the exact location of adult stem- or progenitor-like cells that give rise to beta cells. PDECs were cultured in direct contact with or without MSCs in serum-containing culture media. The cytomorphology of the cells in co-cultures was determined and the immunocytochemical study of the cells was carried out using anti-Ngn3, anti-insulin and anti-cytokeratin-7 (CK7) antibodies. Both the PDEC/MSC- and PDEC/MSC+ cultures showed out- pocketing from duct epithelium by the end of the second week, which are distinct as cell clusters only in PDEC/MSC+ cells later in week four, exhibiting numerous branching ducts. Co-expression of Ngn3 with insulin was observed in both cultures from the second week. However, characterizations of these Ngn3+ cells in the PDEC/MSC+ culture revealed that these cells also co-expressed a CK7 biomarker. This study provides new evidence of the ductal epithelial nature of beta cells in injured adult pancreata; and that the mesenchymal stromal cells are required to sustain Ngn3 expression for beta cell maturation and function.

Early islets and mesenchyme from an injured adult pancreas improve syngeneic engraftments and islet graft function in diabetic rats

A decrease in mass of isografts and a decline in islet function are major challenges in islet transplantations. Despite this, transplantation of 84 h harvested pancreatic duct ligation (PDL) tissues have been shown to have the same functional ability to foetal pancreata, but there was only 40% success in reverting hyperglycaemia. We tested the potential of early islets with mesenchymal stromal cells (MSCs) to promote isogeneic grafts survival and to restore normoglycemia in diabetic rats, in comparison with late islets. Islets were isolated from injured adult pancreata of donor rats at 24 h post ligation either with MSCs (24 h islet/MSC+) or without MSCs (24 h islet/MSC-), and at 84 h without MSCs (84 h islet/MSC-). These cells were transplanted under the renal capsule of syngeneic STZ-diabetic recipient rats. The islet grafts were monitored using the BGLs of recipients and the immunohistomorphology of the grafts were analysed using anti-insulin and anti-Ki67 antibodies. The mean BGL in 24 h islet/MSC+ recipients was reduced over time toward the control value. The curves of the mean BGLs in the control islet/MSC- and the 24 h islet/MSC- recipients dropped significantly below the control normal glucose groups levels to reach their nadirs on weeks 4 and 6, respectively. Both curves had a peak overshoot on week 9, with no statistical significant difference between them. Engrafted islets were evident in these recipients, lasted for 5 and 6 weeks and correspondingly survived failure. However, insulin+ cells were present in the isografts of all recipients; but, only isografts in the 24 h islet/MSC+ presented with a homogenous subcapsular beta cell mass. In addition, the tendency of 24 h islet/MSC- to restore normoglycaemia with its survival capacity was statistically highly significant compared to the 84 islet/MSC- recipients (80%; 20%; p = 0.001). Transplantation of early islets with MSCs from injured adult pancreata prolongs islet graft survival and improves isograft function in diabetic rats. This novel observation requires much further exploration for its clinical application, but this model already provides hope for new sources of donor islets for transplantation.

Hyperbolic relation between beta-cell function and insulin sensitivity for type 2 diabetes mellitus, malaria, influenza, Helicobacter pylori, Chlamydia pneumoniae, and hepatitis C virus infection-induced inflammation/oxidative stress and temporary insulin resistance in Central Africans

Background/aim: We calculated the homeostatic model assessment (HOMA) for estimating insulin sensitivity and beta-cell function in normal, healthy nondiabetics with infections (malaria, influenza, HIV, Helicobacter pylori, Chlamydia pneumoniae, and hepatitis C virus), type 2 diabetic black patients, and healthy controls from Kinshasa, DR Congo. Materials and methods: A case-control study was carried out between 2006 and 2007 for black Central African participants managed for HOMA.Results: In total, 219 patients and 110 healthy controls were matched for sex and age. The hyperbolic product for 85 infected patients occupied an intermediate position between the hyperbolic product for 110 controls and that of 134 type 2 diabetics. Inflammation/oxidative stress was present in all infected patients, as well as in the type 2 diabetics. Of the patients, 39.3% and 49.8% had insulin resistance and metabolic syndrome, respectively. Insulin resistance was more prevalent in nondiabetics with inflammation/oxidative stress (47.1%; P = 0.041) than in type 2 diabetics (34.3%). Type 2 diabetics had higher insulin sensitivity and lower beta-cell function but a similar HOMA-IR score. Conclusion: We recommend the assessment of insulin resistance in Central African patients with severe infections and type 2 diabetes.

Efficiency of Co-Expression of Transcription Factors Pdx1, Ngn3, NeuroD and Pax6 with Insulin: A Statistical Approach

Aim: The objective of this study was to investigate the time related profile and efficiency of co-expression of the homeodomain proteins Pdx1, NeuroD, Ngn3, Pax6 and caspase3 with insulin, and to establish the time periods post PDL optimum for islets transplantation. Study Design/Methods: In this experimental study, immunofluorescent staining procedure was performed on deparaffinized pancreatic duct ligated (PDL) tissues of 78 Sprague-Dawley rats. Quantification of protein coexpression was made using a computerized morphometry. The efficiency of co-expression was arbitrary defined by the value of mean ratio (score without unit) of insulin expression divided by each expression index of the other proteins, occurring within the time interval of 12-24 h post PDL. Statistical tool was used to analyze the efficiency of co-expression of proteins; analysis of variances (one way ANOVA) was used to compare the means of co-expression indexes across the time periods pre- and post PDL. P-values less than 0.05 were considered statistically significant; no post hoc test was done. Results: The curve of insulin expression showed a crossover with that of the co-expression at different time periods pre- and post PDL. The optimal or higher efficiency of co-expression was observed for insulin and Ngn3 co-expression, while a good or medium efficiency was noted for the co-expression of insulin with Pdx1, insulin with NeuroD and insulin with Pax6. Low or weak efficiency was observed for the co-expression of insulin with caspase3. Conclusion: We therefore propose an early islets transplantation using 12-24 h post PDL harvested pancreatic tissues.