Glyoxalase-I Is Upregulated in Acute Cerulein-Induced Pancreatitis: A New Mechanism in Pancreatic Inflammation?

Inflammation caused by oxidative stress (ROS) demonstrates an essential mechanism in the pathogenesis of acute pancreatitis (AP). Important sources for ROS comprise the reactive compound methylglyoxal (MGO) itself and the MGO-derived formation of advanced glycation end-products (AGEs). AGEs bind to the transmembrane receptor RAGE and activate NF-κB, and lead to the production of pro-inflammatory cytokines. MGO is detoxified by glyoxalase-I (Glo-I). The importance of Glo-I was shown in different models of inflammation and carcinogenesis. Nevertheless, the role of Glo-I and MGO in AP has not been evaluated so far. This study analyzed Glo-I in cerulein-(CN)-induced AP and determined the effects of Glo-I knockdown, overexpression and pharmacological modulation. METHODS: AP was induced in C57BL6/J mice by i.p. injection of CN. Glo-I was analyzed in explanted pancreata by Western Blot, qRT-PCR and immunohistochemistry. AR42J cells were differentiated by dexamethasone and stimulated with 100 nM of CN. Cells were simultaneously treated with ethyl pyruvate (EP) or S-p-bromobenzylglutathione-cyclopentyl-diester (BrBz), two Glo-I modulators. Knockdown and overexpression of Glo-I was achieved by transient transfection with Glo-I siRNA and pEGFP-N1-Glo-I-Vector. Amylase secretion, TNF-α production (ELISA) and expression of Glo-I, RAGE and NF-κB were measured. RESULTS: Glo-I was significantly upregulated on protein and mRNA levels in CN-treated mice and AR42J cells. Dexamethasone-induced differentiation of AR42J cells increased the expression of Glo-I and RAGE. Treatment of AR42J cells with CN and EP or BrBz resulted in a significant reduction of CN-induced amylase secretion, NF-κB, RAGE and TNF-α. Overexpression of Glo-I led to a significant reduction of CN-induced amylase levels, NF-κB expression and TNF-α, whereas Glo-I knockdown revealed only slight alterations. Measurements of specific Glo-I activity and MGO levels indicated a complex regulation in the model of CN-induced AP. CONCLUSION: Glo-I is overexpressed in a model of CN-induced AP. Pharmacological modulation and overexpression of Glo-I reduced amylase secretion and the release of pro-inflammatory cytokines in AP in vitro. Targeting Glo-I in AP seems to be an interesting approach for future in vivo studies of AP.

Pitfalls in AR42J-model of cerulein-induced acute pancreatitis.

BACKGROUND: AR42J are immortalized pancreatic adenocarcinoma cells that share similarities with pancreatic acinar cells. AR42J are often used as a cell-culture model of cerulein (CN)-induced acute pancreatitis (AP). Nevertheless, it is controversial how to treat AR42J for reliable induction of AP-like processes. Gene knockout and/or overexpression often remain challenging, as well. In this study, we demonstrate conditions for a reliable induction of proinflammatory markers upon CN treatment in AR42J and high transfection efficacy using Glyoxalase-I (Glo-I) as a target of interest. METHODS: Effects of dexamethasone (dexa) and CN on cell morphology and amylase secretion were analyzed via ELISA of supernatant. IL-6, TNF-α and NF-κB-p65 were measured via qRT-PCR, ELISA and Western Blot (WB). Transfection efficacy was determined by WB, qRT-PCR and immune fluorescence of pEGFP-N1-Glo-I-Vector and Glo-I-siRNA. RESULTS: Treatment of AR42J with 100 nm dexa is mandatory for differentiation to an acinar-cell-like phenotype and amylase production. CN resulted in secretion of amylase but did not influence amylase production. High levels of CN-induced amylase secretion were detected between 3 and 24 hours of incubation. Treatment with LPS alone or in combination with CN did not influence amylase release compared to control or CN. CN treatment resulted in increased TNF-α production but not secretion and did not influence IL-6 mRNA. CN-induced stimulation of NF-κB was found to be highest on protein levels after 6h of incubation. Transient transfection was able to induce overexpression on protein and mRNA levels, with highest effect after 12 to 24 hours. Gene-knockdown was achieved by using 30 pmol of siRNA leading to effective reduction of protein levels after 72 hours. CN did not induce amylase secretion in AR42J cell passages beyond 35. CONCLUSION: AR42J cells demonstrate a reliable in-vitro model of CN-induced AP but specific conditions are mandatory to obtain reproducible data.

NUPR1 preserves insulin secretion of pancreatic ß-cells during inflammatory stress by multiple low-dose streptozotocin and high-fat diet.

Obesity is associated with dyslipidemia and subclinical inflammation that promotes metabolic disturbances including insulin resistance and pancreatic ß-cell dysfunction. The nuclear protein, transcriptional regulator 1 (NUPR1) responds to cellular stresses and features tissue protective properties. To characterize the role of NUPR1 in endocrine pancreatic islets during inflammatory stress, we generated transgenic mice with ß-cell-specific Nupr1 overexpression (ßNUPR1). Under normal conditions, ßNUPR1 mice did not differ from wild type (WT) littermates and display normal glucose homeostasis and ß-cell mass. For induction of inflammatory conditions, mice were treated with multiple low-dose streptozotocin (mld-STZ) and/or fed a high-fat diet (HFD). All treatments significantly worsened glycaemia in WT mice, while ßNUPR1 mice substantially preserved insulin secretion and glucose tolerance. HFD increased ß-cell mass in all animals, with ßNUPR1 mice tending to show higher values. The improved outcome of ßNUPR1 mice was accompanied by decreased NF-κB activation and lymphocyte infiltration in response to mld-STZ. In vitro, isolated ßNUPR1 islets preserved insulin secretion and content with insignificantly low apoptosis during culture stress and IL-1ß exposure. These findings suggest that NUPR1 plays a vital role in the protection of ß-cells from apoptosis, related degradation of insulin storages and subsequent secretion during inflammatory and obesity-related tissue stress.

Azithromycin does not improve disease severity in acute experimental pancreatitis.

Acute pancreatitis is a severe systemic disease triggered by a sterile inflammation and initial local tissue damage of the pancreas. Immune cells infiltrating into the pancreas are main mediators of acute pancreatitis pathogenesis. In addition to their antimicrobial potency, macrolides possess anti-inflammatory and immunomodulatory properties which are routinely used in patients with chronic airway infections and might also beneficial in the treatment of acute lung injury. We here tested the hypothesis that the macrolide antibiotic azithromycin can improve the course of acute experimental pancreatitis via ameliorating the damage imposed by sterile inflammation, and could be used as a disease specific therapy. However, our data show that azithromycin does not have influence on caerulein induced acute pancreatitis in terms of reduction of organ damage, and disease severity. Furthermore Infiltration of immune cells into the pancreas or the lungs was not attenuated by azithromycin as compared to controls or ampicillin treated animals with acute experimental pancreatitis. We conclude that in the chosen model, azithromycin does not have any beneficial effects and that its immunomodulatory properties cannot be used to decrease disease severity in the model of caerulein-induced pancreatitis in mice.

p8 deficiency leads to elevated pancreatic beta cell mass but does not contribute to insulin resistance in mice fed with high-fat diet.

BACKGROUND: p8 was initially described as being overexpressed in acute pancreatitis and encoding a ubiquitous stress protein. Analysis of insulin sensitivity and glucose tolerance in p8-knockout and haplodeficient mice revealed counterintuitive results. Thus, we determined glycemic control of p8 in mice fed with standard (SD) and high-fat diet (HFD). METHODS: p8-/- and wild type (p8+/+) mice were used for analysis of glucagon (immunohistochemistry), insulin levels (ELISA) and beta cell mass. Hyperinsulinemic- euglycemic glucose clamp technique, i.p. glucose tolerance test (ipGTT), i.p. insulin tolerance test (ipITT) and metabolic chamber analysis were performed in SD (4% fat) and HFD (55% fat) groups. RESULTS: p8-/- mice showed no differences in glucagon or insulin content but higher insulin secretion from pancreatic islets upon glucose stimulation. p8 deficiency resulted in elevated beta cell mass but was not associated with increased insulin resistance in ipGTT or ipITT. Glucose clamp tests also revealed no evidence of association of p8 deficiency with insulin resistance. Metabolic chamber analysis showed equal energy expenditure in p8-/- mice and wild type animals. CONCLUSION: p8 depletion may contribute to glucose metabolism via stress-induced insulin production and elevated beta cell mass. Nevertheless, p8 knockout showed no impact on insulin resistance in SD and HFD-fed mice.

Loss of Bace1 in mice does not alter the severity of caerulein induced pancreatitis.

CONTEXT: Beta-site alpha-amyloid protein cleaving enzyme1 (BACE1) plays a key role in the pathogenesis of Alzheimer's disease. Additional to its moderate expression in the brain, high levels of BACE1 mRNA were found in the pancreas. Murine Bace1 has been immunohistochemicaly detected at the apical pole of acinar cells within the exocrine pancreas of mice and Bace1 activity was observed in pancreatic juice. In vitro experiments revealed enteropeptidase as a putative substrate for Bace1 suggesting a role in acute pancreatitis. OBJECTIVE: The aim of this study was to address a protective mechanism of Bace1 in acute experimental pancreatitis in mice. METHODS: Acute experimental pancreatitis was induced by intraperitoneal injection of caerulein in homozygote Bace1-/- mice and wild type mice. Serum and tissue analyses were carried out after 4 h, 8 h and 24 h. Measurement of plasma amylase and lipase was performed to confirm pancreatitis induction. In order to assess the severity of pancreatitis H&E stained pancreatic sections were examined regarding edema, inflammation and apoptosis. Immunohistochemical detection of myeloperoxidase (MPO) positive cells was carried out to further quantify the extent of inflammation. Expression of Bace2 within the pancreas was analyzed by immunohistochemistry and RT-qPCR. RESULTS: We demonstrate that total loss of Bace1 in mice leads to no alterations in the course of acute experimental caerulein-pancreatitis. Bace1-/- mice develop a moderate pancreatitis that is comparable in histomorphological and serological features with those seen in wild type mice. DISCUSSION: We discuss the results in the context of the applied caerulein induced edematous pancreatitis model and possible compensatory mechanisms via Bace2 that might be responsible for the observed results.

Circulating adipocyte fatty acid-binding protein induces insulin resistance in mice in vivo.

OBJECTIVE: Circulating levels of the adipokine adipocyte fatty acid-binding protein (AFABP) are increased in obesity. However, the influence of circulating AFABP on insulin sensitivity in vivo remains unclear. METHODS: C57BL/6NTac mice (10 weeks) were treated over 8 weeks i.p. with saline (control) or recombinant AFABP (0.5 mg/kg/d). A comprehensive characterization of metabolic parameters, body composition, and energy expenditure was performed. Furthermore, the effect of AFABP on pancreatic ß-cell responsiveness, hepatic glycogen content, and peroxisome proliferator-activated receptor (PPAR) γ protein expression was elucidated. RESULTS: In male mice, AFABP treatment induced insulin resistance with significantly increased fasting insulin, C-peptide, and homeostasis model assessment of insulin resistance. In female animals, a similar trend was observed. In both genders, no difference in body weight, lipid parameters, body composition, or energy expenditure could be detected between AFABP-treated and control mice. Insulin resistance in male AFABP-treated mice was accompanied by decreased PPARγ protein content in perigonadal adipose tissue and diminished circulating adiponectin. AFABP treatment did not affect pancreatic ß-cell responsiveness and hepatic glycogen content. CONCLUSIONS: Circulating AFABP induces insulin resistance in male mice. AFABP-mediated degradation of PPARγ in adipose tissue and subsequently decreased expression of insulin-sensitizing adiponectin are potential mechanisms for this effect.

P8 deficiency increases cellular ROS and induces HO-1.

The gene p8 encodes for a small cytoprotective protein with no apparent enzymatic activity being proposed to act as co-transcription factor whose expression is increased during inflammation. Recent data from astrocytes demonstrates that p8 suppression leads to induction of heme oxygenase 1 (HO-1). Here, we assessed the cross-talk between p8 and HO-1 in mouse embryonic fibroblasts (MEF) observing an increased expression of HO-1 in p8-deficient (p8(-/-)) MEFs in non-treated and treated conditions. This effect was independent of the cell cycle. Our findings revealed that generation of reactive oxygen species (ROS) was higher in p8(-/-) MEFs. Mitochondria and NADPH oxidases were not the origin of ROS. This observation was not restricted to MEF as suppression of p8 gene transcription in MiaPaCa-2 cells also led to increased intracellular ROS. Additionally, p8 deficiency did not affect the Rac1 dependant NADPH oxidase complex. Our data shows that p8 deficiency increases ROS and subsequently the expression of anti-oxidative enzymes, such as HO-1, suggesting an involvement in the anti-oxidative defense. Moreover, we suggest that the severity of AP observed in p8(-/-) mice is induced by an impaired anti oxidative capacity of the pancreas, which is caused by increased generation of ROS.

p8 Deficiency causes siderosis in spleens and lymphocyte apoptosis in acute pancreatitis.

OBJECTIVES: The gene p8 was initially described in pancreatic tissue during acute experimental pancreatitis, a disease that is characterized by a systemic immune response. Although early reports suggested that p8 affects leukocyte migration during acute pancreatitis (AP), no studies revealing its immune-modulatory effects have been performed. METHODS: We investigated the composition of the cellular immune system in naive p8 knockout (p8(−/−)) mice and compared with matched wild-type mice during pancreatitis. RESULTS: In young mice, there were no relevant differences in the composition of peripheral and splenic CD3(+), CD3(+)CD4(+), CD3(+)CD8(+), CD11b(+)Gr-1(-), and Gr-1 cells. In mature p8(−/−) mice, increased splenic CD4CD25FoxP3 cells, spleen siderosis, and increased marginal zones in the splenic white pulp were found. During AP, peripheral and splenic CD3(+) and CD3CD4 declined stronger in the p8(−/−) mice. The spleen of the p8(−/−) mice showed severe hypoplasia of the white pulp and mild hyperplasia of the red pulp. This was associated with a significantly increased rate of apoptosis. CONCLUSIONS: We conclude that p8 has no impact on the cellular composition of the adaptive and innate immune systems in noninflammatory conditions. However, it may limit apoptosis and maintain homeostasis of the immune reaction during AP.

Genetic and biochemical evidence for a functional role of BACE1 in the regulation of insulin mRNA expression.

OBJECTIVE: Beta-site amyloid precursor protein cleaving enzyme (BACE1) is highly expressed in pancreatic ß-cells. The BACE1 gene is located in a region associated with a high diabetes risk in PIMA Indians. DESIGN AND METHODS: INS-1E cells were used to study the impact of siRNA-mediated BACE1 knockdown and glucose metabolism was characterized in Bace1(-/-) mice. BACE1 gene was sequenced in DNA samples from 48 subjects and 13 representative single nucleotide polymorphisms (SNPs) were then genotyped for association studies in 1,527 Caucasians. RESULTS: Reduction of Bace1 expression results in a significant decrease in insulin mRNA expression in INS-1E cells. Bace1(-/-) mice display significantly lower body weight, lower plasma insulin concentrations, but normal glucose tolerance and insulin sensitivity. In a case-control study including 538 healthy controls and 989 patients with type 2 diabetes (T2D), one SNP (rs535860) was significantly associated with T2D (P < 3.5 × 10(-5) , adjusted for age, sex, and BMI). CONCLUSIONS: Reduced Bace1 expression causes impaired insulin expression in pancreatic ß-cells of Bace1(-/-) mice, suggesting that BACE1 plays a role in the regulation of insulin biogenesis. The functionally relevant rs535860 SNP may decrease BACE1 expression by creating a new miR-661 binding site and could therefore contribute to T2D development.

Diverse functional properties of Wilson disease ATP7B variants.

BACKGROUND & AIMS: Wilson disease is a severe disorder of copper metabolism caused by mutations in ATP7B, which encodes a copper-transporting adenosine triphosphatase. The disease presents with a variable phenotype that complicates the diagnostic process and treatment. Little is known about the mechanisms that contribute to the different phenotypes of the disease. METHODS: We analyzed 28 variants of ATP7B from patients with Wilson disease that affected different functional domains; the gene products were expressed using the baculovirus expression system in Sf9 cells. Protein function was analyzed by measuring catalytic activity and copper ((64)Cu) transport into vesicles. We studied intracellular localization of variants of ATP7B that had measurable transport activities and were tagged with green fluorescent protein in mammalian cells using confocal laser scanning microscopy. RESULTS: Properties of ATP7B variants with pathogenic amino-acid substitution varied greatly even if substitutions were in the same functional domain. Some variants had complete loss of catalytic and transport activity, whereas others lost transport activity but retained phosphor-intermediate formation or had partial losses of activity. In mammalian cells, transport-competent variants differed in stability and subcellular localization. CONCLUSIONS: Variants in ATP7B associated with Wilson disease disrupt the protein's transport activity, result in its mislocalization, and reduce its stability. Single assays are insufficient to accurately predict the effects of ATP7B variants the function of its product and development of Wilson disease. These findings will contribute to our understanding of genotype-phenotype correlation and mechanisms of disease pathogenesis.