Pathophysiology of acute experimental pancreatitis: Lessons from genetically engineered animal models and new molecular approaches

The incidence of acute pancreatitis is growing and worldwide population-based studies report a doubling or tripling since the 1970s. 25% of acute pancreatitis are severe and associated with histological changes of necrotizing pancreatitis. There is still no specific medical treatment for acute pancreatitis. The average mortality resides around 10%. In order to develop new specific medical treatment strategies for acute pancreatitis, a better understanding of the pathophysiology during the onset of acute pancreatitis is necessary. Since it is difficult to study the early acinar events in human pancreatitis, several animal models of acute pancreatitis have been developed. By this, it is hoped that clues into human pathophysiology become possible. In the last decade, while employing molecular biology techniques, a major progress has been made. The genome of the mouse was recently sequenced. Various strategies are possible to prove a causal effect of a single gene or protein, using either gain-of-function (i.e., overexpression of the protein of interest) or loss-of-function studies (i.e., genetic deletion of the gene of interest). The availability of transgenic mouse models and gene deletion studies has clearly increased our knowledge about the pathophysiology of acute pancreatitis and enables us to study and confirm in vitro findings in animal models. In addition, transgenic models with specific genetic deletion or overexpression of genes help in understanding the role of one specific protein in a cascade of inflammatory processes such as pancreatitis where different proteins interact and co-react. This review summarizes the recent progress in this field. Copyright (c) 2005 S. Karger AG, Basel

Interleukin-1 Stimulates β-Cell Necrosis and Release of the Immunological Adjuvant HMGB1

BACKGROUND: There are at least two phases of β-cell death during the development of autoimmune diabetes: an initiation event that results in the release of β-cell-specific antigens, and a second, antigen-driven event in which β-cell death is mediated by the actions of T lymphocytes. In this report, the mechanisms by which the macrophage-derived cytokine interleukin (IL)-1 induces β-cell death are examined. IL-1, known to inhibit glucose-induced insulin secretion by stimulating inducible nitric oxide synthase expression and increased production of nitric oxide by β-cells, also induces β-cell death. METHODS AND FINDINGS: To ascertain the mechanisms of cell death, the effects of IL-1 and known activators of apoptosis on β-cell viability were examined. While IL-1 stimulates β-cell DNA damage, this cytokine fails to activate caspase-3 or to induce phosphatidylserine (PS) externalization; however, apoptosis inducers activate caspase-3 and the externalization of PS on β-cells. In contrast, IL-1 stimulates the release of the immunological adjuvant high mobility group box 1 protein (HMGB1; a biochemical maker of necrosis) in a nitric oxide-dependent manner, while apoptosis inducers fail to stimulate HMGB1 release. The release of HMGB1 by β-cells treated with IL-1 is not sensitive to caspase-3 inhibition, while inhibition of this caspase attenuates β-cell death in response to known inducers of apoptosis. CONCLUSIONS: These findings indicate that IL-1 induces β-cell necrosis and support the hypothesis that macrophage-derived cytokines may participate in the initial stages of diabetes development by inducing β-cell death by a mechanism that promotes antigen release (necrosis) and islet inflammation (HMGB1 release)

Overexpression of SIRT1 Protects Pancreatic β-Cells Against Cytokine Toxicity by Suppressing the Nuclear Factor-κB Signaling Pathway

OBJECTIVE—SIRT1, a class III histone/protein deacetylase, is known to interfere with the nuclear factor-κB (NF-κB) signaling pathway and thereby has an anti-inflammatory function. Because of the central role of NF-κB in cytokine-mediated pancreatic β-cell damage, we postulated that SIRT1 might work in pancreatic β-cell damage models

Isotope separation in plasmas by use of ion cyclotron resonance

Selective ion-cyclotron-resonance acceleration of individual K, Ne, Cl, A, and Xe isotopes has been observed in plasmas of density 109 to 1011 cm^-3. Energy discriminating probes show good resolution of accelerated species in all cases. Mass spectrometer analyses of potassium samples, collected on cooled tungsten ribbons, showed 41K to 39K abundance ratios of 4 rather than the normal value of 0.07

Islet expression of the DNA repair enzyme 8-oxoguanosine DNA glycosylase (Ogg1) in human type 2 diabetes

BACKGROUND: It has become increasingly clear that β-cell failure plays a critical role in the pathogenesis of type 2 diabetes. Free-radical mediated β-cell damage has been intensively studied in type 1 diabetes, but not in human type 2 diabetes. Therefore, we studied the protein expression of the DNA repair enzyme Ogg1 in pancreases from type 2 diabetics. Ogg1 was studied because it is the major enzyme involved in repairing 7,8-dihydro-8-oxoguanosine DNA adducts, a lesion previously observed in a rat model of type 2 diabetes. Moreover, in a gene expression screen, Ogg1 was over-expressed in islets from a human type 2 diabetic. METHODS: Immunofluorescent staining of Ogg1 was performed on pancreatic specimens from healthy controls and patients with diabetes for 2–23 years. The intensity and islet area stained for Ogg1 was evaluated by semi-quantitative scoring. RESULTS: Both the intensity and the area of islet Ogg1 staining were significantly increased in islets from the type 2 diabetic subjects compared to the healthy controls. A correlation between increased Ogg1 fluorescent staining intensity and duration of diabetes was also found. Most of the staining observed was cytoplasmic, suggesting that mitochondrial Ogg1 accounts primarily for the increased Ogg1 expression. CONCLUSION: We conclude that oxidative stress related DNA damage may be a novel important factor in the pathogenesis of human type 2 diabetes. An increase of Ogg1 in islet cell mitochondria is consistent with a model in which hyperglycemia and consequent increased β-cell oxidative metabolism lead to DNA damage and the induction of Ogg1 expression

The Toll-Like Receptor Signaling Molecule Myd88 Contributes to Pancreatic Beta-Cell Homeostasis in Response to Injury

Commensal flora and pathogenic microbes influence the incidence of diabetes in animal models yet little is known about the mechanistic basis of these interactions. We hypothesized that Myd88, an adaptor molecule in the Toll-like-receptor (TLR) pathway, regulates pancreatic β-cell function and homeostasis. We first examined β-cells histologically and found that Myd88−/− mice have smaller islets in comparison to C57Bl/6 controls. Myd88−/− mice were nonetheless normoglycemic both at rest and after an intra-peritoneal glucose tolerance test (IPGTT). In contrast, after low-dose streptozotocin (STZ) challenge, Myd88−/−mice had an abnormal IPGTT relative to WT controls. Furthermore, Myd88−/− mice suffer enhanced β-cell apoptosis and have enhanced hepatic damage with delayed recovery upon low-dose STZ treatment. Finally, we treated WT mice with broad-spectrum oral antibiotics to deplete their commensal flora. In WT mice, low dose oral lipopolysaccharide, but not lipotichoic acid or antibiotics alone, strongly promoted enhanced glycemic control. These data suggest that Myd88 signaling and certain TLR ligands mediate a homeostatic effect on β-cells primarily in the setting of injury

Pancreatic β-Cell Death in Response to Pro-Inflammatory Cytokines Is Distinct from Genuine Apoptosis

A reduction in functional β-cell mass leads to both major forms of diabetes; pro-inflammatory cytokines, such as interleukin-1beta (IL-1β) and gamma-interferon (γ-IFN), activate signaling pathways that direct pancreatic β-cell death and dysfunction. However, the molecular mechanism of β-cell death in this context is not well understood. In this report, we tested the hypothesis that individual cellular death pathways display characteristic phenotypes that allow them to be distinguished by the precise biochemical and metabolic responses that occur during stimulus-specific initiation. Using 832/13 and INS-1E rat insulinoma cells and isolated rat islets, we provide evidence that apoptosis is unlikely to be the primary pathway underlying β-cell death in response to IL-1β+γ-IFN. This conclusion was reached via the experimental results of several different interdisciplinary strategies, which included: 1) tandem mass spectrometry to delineate the metabolic differences between IL-1β+γ-IFN exposure versus apoptotic induction by camptothecin and 2) pharmacological and molecular interference with either NF-κB activity or apoptosome formation. These approaches provided clear distinctions in cell death pathways initiated by pro-inflammatory cytokines and bona fide inducers of apoptosis. Collectively, the results reported herein demonstrate that pancreatic β-cells undergo apoptosis in response to camptothecin or staurosporine, but not pro-inflammatory cytokines