Pancreatic β-cell homeostasis is a balance between programmed cell death (apoptosis) and regeneration. Although autoimmune diabetes mellitus type 1 (DM1) is the most-studied cause of β-cell mass loss by pro-inflammatory cytokine-induced apoptosis, influences of a pro-inflammatory environment on β-cell regenerative response have been poorly studied. In this study, we assess the anti-proliferative effect of pro-inflammatory cytokines and glucose concentration on rat pancreatic β cells and the potential protective role of glucagon-like peptide (GLP-1). Apoptotic and proliferating islet cells were stained using the DeadEnd Fluorimetric TUNEL System and 5-bromo-2′-deoxyuridine label respectively, in the presence–absence of varying concentrations of glucose, pro-inflammatory cytokines, and GLP-1. The potential signaling pathways involved were evaluated by western blot. Considerable anti-proliferative effects of pro-inflammatory cytokines interleukin (IL)-1β, interferon (IFN)-γ, and tumour necrosis factor-α (TNF-α) were observed. The effects were synergistic and independent of glucose concentration, and appeared to be mediated by the inhibition of extracellular signal-regulated kinase 1/2 (ERK1/2) activation, the signaling pathway involved in β-cell replication. GLP-1 completely reversed the cytokine-induced inhibition of ERK phosphorylation and increased β-cell proliferation threefold in cytokine-treated cultures. While pro-inflammatory cytokines reduced islet cell ERK1/2 activation and β-cell proliferation in pancreatic islet culture, GLP-1 was capable of reversing this effect. These data suggest a possible pharmacological application of GLP-1 in the treatment of early stage DM1, to prevent the loss of pancreatic β cells as well as to delay the development of overt diabetes.

Nitric oxide (NO) is involved in several biological processes. In type 1 diabetes mellitus (T1DM), proinflammatory cytokines activate an inducible isoform of NOS (iNOS) inβcells, thus increasing NO levels and inducing apoptosis. The aim of the current study is to determine the role of NO (1) in the antiproliferative effect of proinflammatory cytokines IL-1β, IFN-γ, and TNF-αon cultured isletβcells and (2) during the insulitis stage prior to diabetes onset using the Biobreeding (BB) rat strain as T1DM model. Our results indicate that NO donors exert an antiproliferative effect onβcell obtained from cultured pancreatic islets, similar to that induced by proinflammatory cytokines. This cytokine-induced antiproliferative effect can be reversed by L-NMMA, a general NOS inhibitor, and is independent of guanylate cyclase pathway. Assays using NOS isoform specific inhibitors suggest that the NO implicated in the antiproliferative effect of proinflammatory cytokines is produced by inducible NOS, although not in an exclusive way. In BB rats, early treatment with L-NMMA improves the initial stage of insulitis. We conclude that NO is an important mediator of antiproliferative effect induced by proinflammatory cytokines on culturedβcell and is implicated inβ-cell proliferation impairment observed early from initial stage of insulitis.

In autoimmune type 1 diabetes mellitus, proinflammatory cytokine-mediated apoptosis of β-cells has been considered to be the first event directly responsible for β-cell mass reduction. In the Bio-Breeding (BB) rat, an in vivo model used in the study of autoimmune diabetes, β-cell apoptosis is observed from 9 wk of age and takes place after an insulitis period that begins at an earlier age. Previous studies by our group have shown an antiproliferative effect of proinflammatory cytokines on cultured β-cells in Wistar rats, an effect that was partially reversed by Exendin-4, an analogue of glucagon-like peptide-1. In the current study, the changes in β-cell apoptosis and proliferation during insulitis stage were also determined in pancreatic tissue sections in normal and thymectomized BB rats, as well as in Wistar rats of 5, 7, 9, and 11 wk of age. Although stable β-cell proliferation in Wistar and thymectomized BB rats was observed along the course of the study, a decrease in β-cell proliferation and β-cell mass from the age of 5 wk, and prior to the commencement of apoptosis, was noted in BB rats. Exendin-4, in combination with anti-interferon-γ antibody, induced a near-total recovery of β-cell proliferation during the initial stages of insulitis. This highlights the importance of early intervention and, as well, the possibilities of new therapeutic approaches in preventing autoimmune diabetes by acting, initially, in the insulitis stage and, subsequently, on β-cell regeneration and on β-cell apoptosis.

Aims: Roux-en-Y gastric bypass (RYGB) is one of the most effective surgical therapies for the rapid resolution of type 2 diabetes. However, the mechanisms underlying the entero-hormonal response after surgery and the role of peptide tyrosine tyrosine (PYY) in the restoration of normoglycemia are still not clear. Methods: We reproduced the RYGB technique in Wistar and Goto–Kakizaki rats and performed serum hormonal, histological, and hormonal-infusion test. Results: Using the diabetic Goto–Kakizaki (GK) rat model, we demonstrated that PYY plasma levels showed a remarkable peak approximately 30 min earlier than GLP-1 or GIP after mixed-meal administration in RYGB-operated rats with PYY. The GLP-1 and GIP areas under the curve (AUCs) increased after RYGB in GK rats. Additionally, the findings suggested that PYY (3-36) infusion led to increased GLP-1 and GIP plasma levels close to those obtained after a meal. Finally, the number of GLP-1-positive cells appeared to increase in the three segments of the small intestine in GK-RYGB-operated rats beyond the early presence of nutrient stimulation in the ileum. Nevertheless, PYY-positive cell numbers appeared to increase only in the ileum. Conclusion: At least in rats, these data demonstrate an earlier essential role for PYY in gut hormone regulation after RYGB. We understand that PYY contributes to GLP-1 and GIP release and there must be the existence of enteroendocrine communication routes between the distal and proximal small intestine.

Background: Ghrelin is a peptide hormone with pleiotropic effects. It stimulates cell proliferation and inhibits apoptosis‐mediated cell death. It prevents diabetes mellitus in several models of chemical, surgical and biological toxic insults to pancreas in both in vivo and in vitro models and promotes glucose‐stimulated insulin secretion under cytotoxic conditions. It has not yet been tested in vivo in an autoimmune model of diabetes with a persistent insult to the β‐cell. Given the immunomodulating effects of ghrelin and its trophic effects on β‐cells, we hypothesized that ghrelin treatment during the early stages of insulitis would delay diabetes onset.Methods: BioBreeding/Worcester male rats received ghrelin (10 ng/kg/day) before insulitis development. Glucose metabolism was characterized by glucose and insulin tolerance tests. β‐cell mass, islet area, islet number, β‐cell clusters, proliferation and apoptosis and degree of insulitis were analysed by histomorphometry. A Kaplan–Meier survival curve was plotted and analysed applying the log‐rank (Mantel–Cox) test.Results: Ghrelin treatment significantly reduced the probability of developing diabetes in our model (p < 0.0001). It decreased islet infiltration and partially prevented β‐cell mass loss, enabling the maintenance of β‐cell neogenesis and proliferation rates. Furthermore, ghrelin treatment did not induce any metabolic perturbations.Conclusions: These findings support the hypothesis that ghrelin delays the development of autoimmune diabetes by attenuating insulitis and supporting β‐cell mass.General Significance: Ghrelin promotes β‐cell viability and function through diverse mechanisms that may have significant implications for diabetes prevention, therapy and also transplant success of both islets and complete pancreas. Copyright © 2016 John Wiley & Sons, Ltd.