NF-kappaB inhibition enhances peroxynitrite-induced enterocyte apoptosis

Bacterial Endotoxins and Their Role in Periparturient Diseases of Dairy Cows: Mucosal Vaccine Perspectives

During the periparturient period there is a significant increase in the incidence of multiple metabolic and infectious diseases in dairy cows. Dairy cows are fed high-grain diets immediately after calving to support production of large amounts of milk. Mounting evidence indicates these types of diets are associated with the release of high amounts of endotoxins in the rumen fluid. If infected, the udder and uterus additionally become important sources of endotoxins during the postpartum period. There is increasing evidence that endotoxins translocate from rumen, uterus, or udder into the systemic circulation and trigger chronic low-grade inflammatory conditions associated with multiple diseases including fatty liver, mastitis, retained placenta, metritis, laminitis, displaced abomasum, milk fever, and downer cow syndrome. Interestingly, endotoxin-related diseases are triggered by a bacterial component and not by a specific bacterium. This makes prevention of these type of diseases different from classical infectious diseases. Prevention of translocation of endotoxins into the host systemic circulation needs to take priority and this could be achieved with a new approach: mucosal vaccination. In this review article, we discuss all the aforementioned issues in detail and also report some of our trials with regards to mucosal vaccination of periparturient dairy cows.

Immunologic and Hematological Abnormalities in Necrotizing Enterocolitis

Necrotizing enterocolitis (NEC) is a leading cause of mortality in preterm infants. This article reviews the immunologic and hematological abnormalities typically seen in infants with NEC, such as elevated plasma cytokine levels, thrombocytopenia, increased or decreased neutrophil counts, low monocyte counts, and anemia. Some of these findings may provide important diagnostic and prognostic information.

Influence of electroacupuncture at Jiaji acupoints on liver NF-κB expression and liver function in nonalcoholic fatty liver rats

AIM: To investigate the role of nuclear factor-kappa B (NF-κB) in the pathogenesis of nonalcoholic fatty liver disease (NAFLD) and to observe the effect of electroacupuncture (EA) at the Jiaji acupoints on liver NF-κB expression and liver function in NAFLD rats.

METHODS: Wistar rats were randomly divided into either a normal group (11 rats) or a model group (32 rats). Rats were fed a high fat diet (composed of 20 g/L cholesterol, 100 g/L lard and 880 g/L normal feed) to induce NAFLD. After 8 wk, one rat in each of the two groups was randomly selected and killed to verify the success of modelling. The rest rats were randomly divided into two groups: an NAFLD model group (n = 15) and an EA group (n = 15). The EA group underwent acupuncture at the bilateral Jiaji acupoints (strength 1-2 mA, frequency 1.6-2.0 Hz density wave, 30 min each time) once daily. All the animals were killed after 4 wk of treatment to observe pathological changes of the liver, measure serum levels of aspartate aminotransferase (AST) and glutamic alanine aminotransferase (ALT), and detect the expression of NF-κB in the liver tissue by immunohistochemistry.

RESULTS: Compared with the normal group, rats in the model group showed moderate to severe fatty degeneration of liver cells, up-regulated expression of hepatic NF-κB, and increased serum ALT and AST levels (P < 0.05). Compared with the model group, the EA group showed reduced liver tissue changes, down-regulated liver NF-κB expression, and decreased serum ALT and AST levels (P < 0.05).

CONCLUSION: EA at the Jiaji acupoints exerts a therapeutic effect against NAFLD possibly by inhibiting the up-regulation of NF-κB expression and improving the liver function in NAFLD rats.

Inflammatory signaling in necrotizing enterocolitis

The pathogenesis of necrotizing enterocolitis (NEC) is complex and its speed of progression is variable. To gain understanding of the disease, researchers have examined tissues resected from patients with NEC; however, as these are obtained at late stages of the disease, they do not yield clues about the early pathogenic events leading to NEC. Therefore, animal models are used and have helped identify a role for several mediators of the inflammatory network in NEC. In this article, we discuss the evidence for the role of these inflammatory mediators and conclude with a current unifying hypothesis regarding NEC pathogenesis.

Enteral intestinal alkaline phosphatase administration in newborns decreases iNOS expression in a neonatal necrotizing enterocolitis rat model

PURPOSE

To determine if intestinal alkaline phosphatase (IAP) decreases intestinal injury resulting from experimentally induced necrotizing enterocolitis (NEC). We hypothesized that IAP administration prevents the initial development of NEC related intestinal inflammation.

METHODS

Pre- and full-term newborn Sprague-Dawley rat pups were sacrificed on day 1 of life. Pre-term pups were exposed to intermittent hypoxia and formula containing LPS to induce NEC. Select NEC pups were given 40, 4 or 0.4 units/kg of bovine IAP (NEC+IAP40u, IAP4u or IAP0.4u) enterally, once daily. Ileal sections were evaluated by real-time PCR (qRT-PCR) for IAP, iNOS, IL-1β, IL-6, and TNF-α mRNA and immunofluorescence for 3-nitrotyrosine (3-NT).

RESULTS

Experimentally induced NEC decreased IAP mRNA expression by 66% (p ≤ 0.001). IAP supplementation increased IAP mRNA expression to control. Supplemental enteral IAP decreased nitrosative stress as measured by iNOS mRNA expression and 3-NT staining in the NEC stressed pups (p ≤ 0.01), as well as decreased intestinal TNF-α mRNA expression. In addition, IAP decreased LSP translocation into the serum in the treated pups.

CONCLUSIONS

We conclude that enterally administered IAP prevents NEC-related intestinal injury and inflammation. Enteral IAP may prove a useful strategy in the prevention of NEC in preterm neonates.

Simultaneous inhibition of COX-2 and activation of PPAR-γ resulted in the same level and pattern of neuroprotection as they were targeted separately

The inflammatory response is an immune response of the body when exposed to internal and external stimuli. Cyclooxygenases (COX) are major inflammatory mediators implicated in inflammation. COX-2 is reported to be involved in neuroinflammation. Moreover, 15-Deoxy-D (12,14)-prostaglandin J2 (15d-PGJ2), an endogenous ligand of peroxisome proliferator-activated receptor gamma (PPAR-γ), has been demonstrated to have anti-inflammatory actions. In this study, we investigated whether co-therapy of a selective COX-2 inhibitor NS-398 and 15d-PGJ2 as a PPAR-γ ligand could exert additional neuroprotective effects in rat pheochromocytoma (PC12) cells. Our findings showed that 15d-PGJ2 and NS-398 suppress the apoptotic pathway in PC12 cells exposed to H(2)O(2) by attenuation of the Bax/Bcl-2 ratio. This effect was mediated through PPAR-γ, as it was reversed by GW9662 (a PPAR-γ inhibitor). Also, 15d-PGJ2 and NS-398 induced the Nrf2 signaling pathway and decreased NF-κB level in a PPAR-γ-dependent manner. We found that coadministration of a selective COX-2 inhibitor and a PPAR-γ ligand in PC12 cells has equal neuroprotective effect compared to their effects when used separately. Considering the higher affinity of 15d-PGJ2 for PPAR-γ than NS-398, it seems that the observed neuroprotection of this combination therapy was from 15d-PGJ2.

Role of the host defense system and intestinal microbial flora in the pathogenesis of necrotizing enterocolitis

BACKGROUND

Necrotizing enterocolitis (NEC) is a devastating disease that affects primarily the intestine of premature infants. Despite recent advances in neonatology, NEC remains a major cause of morbidity and mortality in neonates. Neonatal mucosal defenses and adherence of bacterial pathogens may play an important role in the pathogenesis of NEC.

METHODS

Review and synthesis of pertinent literature.

RESULTS

Putative factors that have been implicated in the pathogenesis of NEC include abnormal patterns of gut colonization by bacteria, immaturity of the host immune system and mucosal defense mechanisms, intestinal ischemia, formula feeding, and loss of intestinal epithelial barrier integrity.

CONCLUSION

Host defenses and intestinal microbial ecology are believed to play important roles in the pathogenesis of NEC. Commensal bacteria and probiotic therapy may be of therapeutic utility in the maintenance of the gut epithelial barrier.

Peroxynitrite-induced p38 MAPK pro-apoptotic signaling in enterocytes

Enterocyte apoptosis in necrotizing enterocolitis is partly due to the elaboration of toxic intermediates of nitric oxide (NO), such as peroxynitrite (PN). Because p38 mitogen-activated protein kinase (MAPK) and serine-threonine kinase (AKT) are well-characterized pro- and anti-apoptotic mediators, respectively, we hypothesized that PN could induce enterocyte apoptosis via activation of p38 and deactivation of AKT. To test this hypothesis, the rat intestinal cell line, IEC-6, was treated with PN. PN caused phosphorylation of p38, its upstream activator, MKK3/6, and downstream effector, transcription factor ATF-2. PN-induced apoptosis was inhibited by the p38 inhibitor, SB202190, and by p38 siRNA. PN decreased AKT phosphorylation; this effect was abrogated by pre-treatment with SB202190 or p38 siRNA. PN exposure also increased the activity of the protein phosphatase 2A (PP2A). These data demonstrate that PN-mediated apoptosis depends on the p38 pathway and that p38 mediates deactivation of AKT survival pathways possibly by the involvement of PP2A.

Decreased development of necrotizing enterocolitis in IL-18-deficient mice

Necrotizing enterocolitis (NEC) is a devastating gastrointestinal disease predominantly of prematurely born infants, characterized in its severest from by extensive hemorrhagic inflammatory necrosis of the distal ileum and proximal colon. Proinflammatory cytokines have been implicated in the development of NEC, and we have previously shown that IL-18 is significantly elevated in the well-established neonatal rat model of NEC. To determine whether IL-18 contributes to intestinal pathology in NEC, we subjected IL-18 knockout mice to the protocol used to develop experimental NEC in newborn rats. Newborn B6.129P2-Il18(tm1Aki)/J (NEC IL-18(-/-)) and wild-type (NEC WT) mice were hand fed every 3 h with cow's milk-based formula and exposed to asphyxia and cold stress twice daily. After 72 h, animals were killed and distal ileum and liver were removed. Disease development was determined via histological changes in the ileum as scored by a blinded evaluator. The number of TNF-alpha-, IL-12-, and IL-1beta-positive cells and macrophages were determined in both ileum and liver via immunohistology. IkappaB-alpha and IkappaB-beta were determined from protein extracts from both ileum and liver using Western blot analysis. The incidence and severity of NEC was significantly reduced in NEC IL-18(-/-) mice compared with NEC WT. Furthermore, mean ileal macrophages and hepatic IL-1beta were significantly reduced in IL-18(-/-) mice subjected to the NEC protocol. There were no statistically significant changes in Kupffer cells, hepatic TNF-alpha, ileal IL-1beta, or IL-12. IkappaB-alpha and IkappaB-beta were significantly increased in NEC IL-18(-/-) mice ileum and liver, respectively. These results confirm that IL-18 plays a crucial role in experimental NEC pathogenesis.

Glutamine Regulates the Human Epithelial Intestinal HCT-8 Cell Proteome under Apoptotic Conditions

Glutamine plays a key role in the metabolism of rapidly dividing cells, including enterocytes and lymphocytes, which may contribute to its beneficial clinical effects. Gut mucosal homeostasis is achieved through a balance between cell proliferation and apoptosis. In T cells, glutamine up-regulates antiapoptotic proteins and down-regulates proapoptotic proteins. In gut mucosa, glutamine prevents apoptosis in rat epithelial cell lines, whereas glutamine starvation induces apoptosis through caspase activation. Finally glutamine specifically prevents tumor necrosis factor-alpha-related apoptosis in the human intestinal cell line HT-29. Comparative functional proteomics enables the characterization of each differentially expressed protein in intestinal cells in response to modifications of nutritional environment. The influence of glutamine on intestinal proteome expression in apoptotic conditions has not been studied and evaluated. This comparative proteomics study was performed in the human epithelial intestinal cell line HCT-8 under experimental apoptotic conditions to investigate the influence of glutamine on protein expression during apoptosis. The pharmaconutritional effects of glutamine were determined under 2 mm (physiological concentration) and 10 mm (pharmaconutritional concentration) conditions. About 1,800 protein spots were revealed in both conditions. Comparative assessments indicated that 28 proteins were differentially expressed significantly (i.e. at least 2-fold modulated and Student's t test with p </= 0.05) in response to an increase of glutamine concentration in the culture medium. Twenty-four proteins were identified by mass spectrometry and associated databases. From these proteins, 34% are involved in cell cycle and apoptosis mechanisms, 17% are involved in signal transduction, and 13% are involved in cytoskeleton organization. These data were integrated in a proposed schema of the interactome under apoptotic conditions. In conclusion, this study provides the first holistic picture of proteome modulation by glutamine in a human enterocytic cell line under apoptotic conditions and supports further evaluation of nutritional modulation of human intestinal proteome in various pathological conditions where apoptosis may be involved.

Cytokines, NF-kappaB, microenvironment, intestinal inflammation and cancer

Inflammation and cancer have been viewed as closely linked for many years. This link is not merely a loose association but causative. In colorectal cancer (CRC), chronic inflammation as observed in inflammatory bowel (IBD) disease is a key predisposing factor and IBD-associated CRC comprises five percent of all CRCs. Although the molecular mechanisms linking IBD with CRC are not well understood, recent results obtained in preclinical models point to the transcription factor NF-kappaB as a central player. On the one hand, NF-kappaB regulates the expression of various cytokines and modulates the inflammatory processes in IBD. On the other, NF-kappaB stimulates the proliferation of tumor cells and enhances their survival through the regulation of anti-apoptotic genes. Furthermore, it has been clearly established that most carcinogens and tumor promoters activate NF-kappaB, while chemopreventive agents generally suppress this transcription factor. Actually, several lines of evidence suggest that activation of NF-kappaB may cause cancer. These include the finding that NF-kappaB genes can be oncogenes, and that this transcription factor controls apoptosis, cell-cycle progression and proliferation, and possibly also cell differentiation.

Heparin-binding epidermal growth factor-like growth factor reduces intestinal apoptosis in neonatal rats with necrotizing enterocolitis

PURPOSE

We have previously demonstrated that enterally administered heparin-binding epidermal growth factor-like growth factor (HB-EGF) decreases the incidence and severity of necrotizing enterocolitis (NEC) in a neonatal rat model. Because apoptosis contributes to gut barrier failure in this model, the aim of this study was to investigate the effect of HB-EGF on apoptosis during the development of NEC.

METHODS

NEC was induced in neonatal rats by exposure to hypoxia, hypothermia, hypertonic formula feeding (HHHTF) plus enteral administration of lipopolysaccharide (LPS). Fifty-one neonatal rats were randomly divided into the following groups: (1) breast-fed (BF), (2) HHHTF + LPS, and (3) HHHTF + LPS with HB-EGF (600 microg/kg) added to the formula. NEC was evaluated using a standard histological scoring system. Apoptotic cells in intestinal tissues were detected by terminal deoxynucleotidyltransferase-mediated dUTP nick end labeling (TUNEL) and by active caspase 3 immunohistochemical staining.

RESULTS

The incidence of NEC in the HHHTF + LPS group was higher than that in the BF group (65% vs 0%, P < .05). With administration of HB-EGF, the incidence of NEC significantly decreased to 23.8% (P < .05). The median TUNEL and active caspase 3 scores in the HHHTF + LPS group were higher than those in the BF group (1.9 vs 0.9 and 1.75 vs 0.6, respectively, P < .05). The median TUNEL and active caspase 3 scores were significantly decreased in the HHHTF + LPS + HB-EGF group compared with the HHHTF + LPS group (1.24 vs 1.9 and 1.0 vs 1.75, respectively, P < .05).

CONCLUSION

HB-EGF reduces the incidence of NEC in a neonatal rat model in part by decreasing apoptosis. These results support the use of HB-EGF-based clinical regimens for the treatment of NEC.

Cytokines, NF-kappaB, microenvironment, intestinal inflammation and cancer

Inflammation and cancer have been viewed as closely linked for many years. This link is not merely a loose association but causative. In colorectal cancer (CRC), chronic inflammation as observed in inflammatory bowel (IBD) disease is a key predisposing factor and IBD-associated CRC comprises five percent of all CRCs. Although the molecular mechanisms linking IBD with CRC are not well understood, recent results obtained in preclinical models point to the transcription factor NF-kappaB as a central player. On the one hand, NF-kappaB regulates the expression of various cytokines and modulates the inflammatory processes in IBD. On the other, NF-kappaB stimulates the proliferation of tumor cells and enhances their survival through the regulation of anti-apoptotic genes. Furthermore, it has been clearly established that most carcinogens and tumor promoters activate NF-kappaB, while chemopreventive agents generally suppress this transcription factor. Actually, several lines of evidence suggest that activation of NF-kappaB may cause cancer. These include the finding that NF-kappaB genes can be oncogenes, and that this transcription factor controls apoptosis, cell-cycle progression and proliferation, and possibly also cell differentiation.

Epidermal growth factor reduces hepatic sequelae in experimental necrotizing enterocolitis

BACKGROUND AND AIM

Neonatal necrotizing enterocolitis (NEC) is the most common gastrointestinal disease of premature infants. We recently demonstrated that the gut/liver axis plays an important role in the pathophysiology of NEC through the release of inflammatory mediators into the intestinal lumen. We have also shown that supplementation of formula with epidermal growth factor (EGF) dramatically decreases ileal pathology associated with experimental NEC. In this study, we examined the effects of EGF on the liver portion of the gut/liver axis in the neonatal rat model of NEC.

METHODS

Newborn rats were divided into three experimental groups, NEC, hand-fed with growth-factor free formula; NEC + EGF, hand-fed with formula supplemented with 500 ng/ml rat EGF; or DF, dam fed. All animals were exposed to asphyxia and cold stress twice daily for 4 days to develop NEC.

RESULTS

EGF receptor expression was significantly (p <or= 0.01) decreased in the NEC+EGF group compared to the NEC group. EGF supplementation significantly decreased Kupffer cell numbers (p <or= 0.01) as well as hepatic tumor necrosis factor (TNF)-alpha and interleukin-18 production (p <or= 0.05). Further, TNF-alpha in the intestinal luminal contents of the NEC+EGF group were normalized to levels observed in DF controls compared to the NEC group (p <or= 0.05). Activated nuclear factor-kappaB was also substantially decreased in the NEC+EGF group versus the NEC group.

CONCLUSION

The results of this study indicate that EGF normalizes cytokine overproduction in the liver of neonatal rats with NEC, which contributes to diminished intestinal damage during the development of experimental NEC. These data suggest that supplementation of formula with EGF can have beneficial effects on the gut/liver axis during NEC pathogenesis.

Attenuation of apoptosis in enterocytes by blockade of potassium channels

Apoptosis plays an important role in maintaining the balance between proliferation and cell loss in the intestinal epithelium. Apoptosis rates may increase in intestinal pathologies such as inflammatory bowel disease and necrotizing enterocolitis, suggesting pharmacological prevention of apoptosis as a therapy for these conditions. Here, we explore the feasibility of this approach using the rat epithelial cell line IEC-6 as a model. On the basis of the known role of K+ efflux in apoptosis in various cell types, we hypothesized that K+ efflux is essential for apoptosis in enterocytes and that pharmacological blockade of this efflux would inhibit apoptosis. By probing intracellular [K+] with the K+-sensitive fluorescent dye and measuring the efflux of 86Rb+, we found that apoptosis-inducing treatment with the proteasome inhibitor MG-132 leads to a twofold increase in K+ efflux from IEC-6 cells. Blockade of K+ efflux with tetraethylammonium, 4-aminopyridine, stromatoxin, chromanol 293B, and the recently described K+ channel inhibitor 48F10 prevents DNA fragmentation, caspase activation, release of cytochrome c from mitochondria, and loss of mitochondrial membrane potential. Thus K+ efflux occurs early in the apoptotic program and is required for the execution of later events. Apoptotic K+ efflux critically depends on activation of p38 MAPK. These results demonstrate for the first time the requirement of K+ channel-mediated K+ efflux for progression of apoptosis in enterocytes and suggest the use of K+ channel blockers to prevent apoptotic cell loss occurring in intestinal pathologies.

Mechanisms of nitric oxide-mediated intestinal barrier failure in necrotizing enterocolitis

Necrotizing enterocolitis (NEC) is the leading intestinal emergency in premature infants. The underlying etiology of NEC remains elusive, but hypoxic conditions and early enteral feeding are consistently implicated as the main risk factors in the pathogenesis of NEC. We postulate that nitric oxide (NO) plays a key role as a molecular signaling "hub" in the generation of gut barrier failure in NEC. Clinical studies suggest that inflammatory cytokines and excessive NO production may contribute to the pathogenesis of NEC. One of the major challenges in defining the critical signaling pathways that lead to the development of NEC is the lack of specific biochemical markers that consistently delineate the early stages of NEC. Intestinal pathology and molecular markers derived from late-stage NEC represent end-stage findings and thus provide little insight into the early events that led to intestinal inflammation. Such markers may not represent viable therapeutic targets for the treatment or prevention of NEC. Therefore, novel strategies are needed to identify the patients at risk for NEC and define the clinically relevant molecules that characterize the early stages of NEC. This review will examine the mechanisms of NO-mediated gut barrier failure and propose novel genetic-based approaches for elucidating the critical molecular pathways in NEC.

Poly (ADP-ribose) polymerase-1 haplotypes are associated with coeliac disease

In coeliac disease (CD) there is an inflammatory status of the intestinal mucosa because of a high expression of proinflammatory mediators. The nuclear protein poly (ADP-ribose) polymerase-1 (PARP-1) has been implicated in the initial inflammatory response by modulating transcription of inflammation-related genes. The aim of this work was to investigate the role of PARP-1 gene promoter region haplotypes in relation to coeliac disease susceptibility. We analysed a coeliac population consisting of a case-control panel with 120 CD patients and 311 healthy blood donors. A CA microsatellite, as haplotype-defining variant of the whole PARP-1 promoter, was typed using a polymerase chain reaction (PCR) method combined with fluorescence technology. We considered two promoter haplotypes: A defined by short CA alleles (83-87 bp) and B defined by long CA alleles (89-101 bp). Haplotype A was significantly increased within the coeliac patients group (P = 0.007 OR 1.6 95%CI 1.12-2.35). Additionally, we observed a significant dose effect, showing homozygous individuals for haplotype A higher risk for CD susceptibility (P = 0.007, OR 1.79 95%CI 1.14-2.82). Our results provide the first evidence that PARP-1 haplotypes are related with coeliac disease susceptibility.

Total glutathione is not decreased in infants with necrotizing enterocolitis

BACKGROUND

Glutathione (GSH) is the major intracellular antioxidant protecting against free radical-mediated damage. Oxidative stress is implicated in the pathogenesis of necrotizing enterocolitis (NEC), and damage could be enhanced by a relative deficiency of GSH. We hypothesized that infants with NEC would have lower levels of erythrocyte GSH when compared with controls.

METHODS

Total erythrocyte GSH concentration (per gram of hemoglobin [g Hb]) was determined in blood samples from infants with NEC (n = 16) referred for surgical intervention. Nonseptic infants referred for other conditions (eg, patent ductus arteriosus ligation) served as controls (n = 10).

RESULTS

Controls and infants with NEC were demographically similar. Mean erythrocyte GSH concentration in infants with NEC was 0.076 +/- 0.004 micromol/g Hb and in controls it was 0.078 +/- 0.005 micromol/g Hb (P = .73). There was no significant correlation between GSH concentration and weight, gestational age, or C-reactive protein levels. In infants with NEC, there was no difference in GSH levels between infants with stage 2 and stage 3 diseases nor between those who died and survived, but a trend toward lower GSH levels in infants with more extensive diseases exists.

CONCLUSIONS

Total GSH levels are similar in infants with NEC and controls. It is possible that a relative rather than absolute deficiency of antioxidant compounds exists and may contribute to the development of NEC.

Increased expression and function of integrins in enterocytes by endotoxin impairs epithelial restitution

BACKGROUND & AIMS

Experimental necrotizing enterocolitis (NEC) is characterized by circulating endotoxin (lipopolysaccharide [LPS]) and impaired enterocyte migration. We hypothesized that LPS increases integrin function and cell-matrix adhesion, leading to impaired enterocyte migration in the pathogenesis of NEC.

METHODS

NEC-like intestinal injury was induced in newborn rats by hypoxia/gavage feedings, and restitution was determined by assessing bromodeoxyuridine-labeled enterocytes along the crypt-villus axis. Newborn mice were injected with 5 mg/kg LPS. IEC-6 cells were treated with LPS +/- LY294002 or wortmannin, and beta 1- and alpha 3-integrins were assessed by sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) and immunofluorescence. Beta 1-integrin function was determined by adherence of fibronectin beads to IEC-6 monolayers. Migration of IEC-6 cells into a scraped wound was measured by time-lapse microscopy.

RESULTS

Newborn intestinal injury was associated with decreased intestinal restitution and increased alpha 3- and beta 1-integrin expression in the ileal mucosa, which also was observed after LPS injection. In IEC-6 cells, LPS caused an increase in the expression of alpha 3- and beta 1-integrins, a shift of beta 1-integrins from the cytoplasm to the plasma membrane and an increase in fibronectin bead adhesion during which beta 1-integrins accumulated underneath attached beads. These effects could be reversed with LY294002 or wortmannin, suggesting phosphatidylinositol-3-phosphate kinase (PI3K) dependence. The increased integrin-matrix adhesion by LPS led to an inhibition of enterocyte migration, which could be reversed by anti-beta 1-antibodies.

CONCLUSIONS

Enterocyte migration is inhibited by LPS through increased expression and function of alpha 3- and beta 1-integrins. Modulation of enterocyte migration via integrins may provide novel insights into the pathogenesis of NEC, in which intestinal restitution is impaired.

Disordered enterocyte signaling and intestinal barrier dysfunction in the pathogenesis of necrotizing enterocolitis

Necrotizing enterocolitis (NEC) is the leading cause of death from gastrointestinal disease in neonates, and is characterized by the development of diffuse intestinal necrosis in the stressed, pre-term infant. Systemic stress causes a breakdown in the intestinal mucosal barrier, which leads to translocation of bacteria and endotoxin and the initiation of a signaling response within the enterocyte. This review summarizes recent evidence defining a clear role that defective enterocyte signaling plays in the pathogenesis of NEC through the following mechanisms: 1) The localized production of nitric oxide by villus enterocytes results in an increase in enterocyte apoptosis and impaired proliferation; 2) The translocation of endotoxin results in a PI3K-dependent activation of RhoA-GTPase within the enterocyte leading to decreased enterocyte migration and impaired restitution; 3) Dysregulated sodium-proton exchange within the enterocyte by endotoxin renders the enterocyte monolayer more susceptible to damage in the face of the acidic microenvironment characteristic of systemic sepsis; and 4) Endotoxin causes a p38-dependent release of the pro-inflammatory molecule COX-2 by the enterocyte, which potentiates the systemic inflammatory response. An understanding of the mechanisms by which disordered enterocyte signaling contributes to the pathogenesis of barrier failure and NEC--through these and other mechanisms--may lead to the identification of novel therapeutic approaches for this devastating disease.

Role of nitric oxide in apoptosis of human peritoneal and adhesion fibroblasts after hypoxia

OBJECTIVE

To study the modulation of the inducible nitric oxide synthase/nitric oxide (iNOS/NO) expression system in fibroblasts isolated from human peritoneum and adhesion tissues by hypoxia.

DESIGN

Prospective experimental study.

SETTING

University medical center.

PATIENT(S)

Cultures of fibroblasts from both peritoneum and adhesion tissues of five patients.

INTERVENTION(S)

Hypoxia treatment of the primary cultured fibroblasts.

MAIN OUTCOME MEASURE(S)

We used Western and Northern blots to determine whether iNOS mRNA and its protein were present in peritoneal and adhesion fibroblasts and whether this expression is modulated by hypoxia. Multiplex reverse transcription polymerase chain reaction (RT-PCR) technique was used to quantify type I collagen mRNA in response to NG-nitro-L-arginine methyl ester (L-NAME). A terminal deoxynucleotidyl transferase mediated dUTP nick-end-labeling (TUNEL) assay was used to quantify apoptosis in response to NO donor S-nitro-N-acetyl-penicillamine (SNAP) treatment. A Griess assay was used to measure NO levels.

RESULT(S)

Peritoneal fibroblasts have significantly higher NO levels than adhesion fibroblasts. Hypoxia decreased NO in peritoneal fibroblasts to levels observed for adhesion fibroblasts. In addition, hypoxia increased both mRNA and protein levels of the iNOS gene in peritoneal and adhesion fibroblasts. Augmentation of NO by SNAP treatment increased apoptosis in adhesion fibroblasts. In contrast, SNAP had no effect on apoptosis of peritoneal fibroblasts. Inhibition of NO by L-NAME treatment increased type I collagen mRNA levels in peritoneal fibroblasts.

CONCLUSION(S)

Our findings confirm that adhesion fibroblasts produce less NO than normal peritoneal fibroblasts; NO may be the mechanism responsible for the creation and persistence of the adhesion phenotype.

Protective effects of sodium ferulate on injury in acetic acid-induced rat colitis

AIM: To study the effects of sodium ferulate on acetic acid-induced rat colitis and its mechanism.

METHODS: The colitis model of rats was produced by intracolon enema with acetic acid. The experiment animals were divided into 5 groups: normal group, model group, SF groups (200 mg/kg, 400 mg/kg, 800 mg/kg), and treated intracolonically with saline and SF respectively once per day for 7 d. At the end of the experiment, the colon mucosa damage index (CMDI) and the occult blood test (OBT) were evaluated.The contents of MDA, NO, PGE₂, and TXB₂ , the activities of myelopexoxidase (MPO) and SOD, the expression of COX-2 and NF-Bp65 in the rat colon were detected. Platelet agglutinability was also measured.

RESULTS: The extents of CMDI and OBT, the contents of MDA, NO, PGE₂ and TXB₂, the activity of MPO, the expression of COX-2 and NF-Bp65 in the colon and the platelet agglutinability in the model group were higher than those in normal group, while the activity of SOD was lower than that in normal group. SF could alleviate the CMDI and OBT, and ameliorate the abnormity of these detected indexes in a dose-depended manner.

CONCLUSION: Treatment with SF intracolon can relieve the inflammation reaction, attenuate the colon mucosal damage in the rat colitis through resisting oxidative stress, restraining arachidonic acid metabolism, platelet activation and the expression of NF-B.

Ameliorative effects of sodium ferulate on experimental colitis and their mechanisms in rats

AIM: To investigate the ameliorative effects of sodium ferulate (SF) on acetic acid-induced colitis and their mechanisms in rats.

METHODS: The colitis model of Sprague-Dawley rats was induced by intracolon enema with 8% (V/V) of acetic acid. The experimental animals were randomly divided into model control, 5-aminosalicylic acid therapy group and three dose of SF therapy groups. The 5 groups were treated intracolonically with normal saline, 5-aminosalicylic acid (100 mg•kg^-1), and SF at the doses of 200, 400 and 800 mg·kg^-1 respectively and daily (8: 00 am) for 7 d 24 h following the induction of colitis. A normal control group of rats clystered with normal saline instead of acetic acid was also included in the study. Pathological changes of the colonic mucosa were evaluated by the colon mucosa damage index (CMDI) and the histopathological score (HS). The insulted colonic mucosa was sampled for a variety of determinations at the end of experiment when the animals were sacrificed by decapitation. Colonic activities of myeloperoxidase (MPO) and superoxide dismutase (SOD), and levels of malondialdehyde (MDA) and nitric oxide (NO) were assayed with ultraviolet spectrophotometry. Colonic contents of prostaglandin E2 (PGE2) and thromboxane B2 (TXB2) were determined by radioimmunoassay. The expressions of inducible nitric oxide synthase (iNOS), cyclo-oxygenase-2 (COX-2) and nuclear factor kappa B (NF-κB) p65 proteins in the colonic tissue were detected with immunohistochemistry.

RESULTS: Enhanced colonic mucosal injury, inflammatory response and oxidative stress were observed in the animals clystered with acetic acid, which manifested as the significant increase of CMDI, HS, MPO activities, MDA and NO levels, PGE₂ and TXB₂ contents, as well as the expressions of iNOS, COX-2 and NF-κB p65 proteins in the colonic mucosa, although the colonic SOD activity was significantly decreased compared with the normal control (CMDI: 2.9 ± 0.6 vs 0.0 ± 0.0; HS: 4.3 ± 0.9 vs 0.7 ± 1.1; MPO: 98.1 ± 26.9 vs 24.8 ± 11.5; MDA: 57.53 ± 12.36 vs 9.21 ± 3.85; NO: 0.331 ± 0.092 vs 0.176 ± 0.045; PGE₂: 186.2 ± 96.2 vs 42.8 ± 32.8; TXB₂: 34.26 ± 13.51 vs 8.83 ± 3.75; iNOS: 0.365 ± 0.026 vs 0.053 ± 0.015; COX-2: 0.296 ± 0.028 vs 0.034 ± 0.013; NF-κB p65: 0.314 ± 0.026 vs 0.039 ± 0.012; SOD: 28.33 ± 1.17 vs 36.14 ± 1.91; P < 0.01). However, these parameters were found to be significantly ameliorated in rats treated locally with SF at the given dose protocols, especially at 400 mg·kg^-1 and 800 mg·kg^-1 doses (CMDI: 1.8 ± 0.8, 1.6 ± 0.9; HS: 3.3 ± 0.9, 3.1 ± 1.0; MPO: 63.8 ± 30.5, 36.2 ± 14.2; MDA: 41.84 ± 10.62, 37.34 ± 8.58; NO: 0.247 ± 0.042; 0.216 ± 0.033; PGE₂: 77.2 ± 26.9, 58.4 ± 23.9; TXB₂: 18.07 ± 14.83; 15.52 ± 8.62; iNOS:0.175 ± 0.018, 0.106 ± 0.019; COX-2: 0.064 ± 0.018, 0.056 ± 0.014; NF-κBp65: 0.215 ± 0.019, 0.189 ± 0.016; SOD: 32.15 ± 4.26, 33.24 ± 3.69; P < 0.05-0.01). Moreover, a therapeutic dose protocol of 800 mg·kg^-1 SF was observed as effective as 100 mg·kg^-1 of 5-ASA in the amelioration of colonic mucosal injury as evaluated by CMDI and HS.

CONCLUSION: Administration of SF intracolonically may have significant therapeutic effects on the rat model of colitis induced by acetic acid enema, which was probably due to the mechanism of antioxidation, inhibition of arachidonic acid metabolism and NF-κB expression.

Peroxynitrite inhibits enterocyte proliferation and modulates Src kinase activity in vitro

Overproduction of nitric oxide (NO) or its toxic metabolite, peroxynitrite (ONOO-), after endotoxemia promotes gut barrier failure, in part, by inducing enterocyte apoptosis. We hypothesized that ONOO- may also inhibit enterocyte proliferation by disrupting the Src tyrosine kinase signaling pathway, thereby blunting repair of the damaged mucosa. We examined the effect of ONOO- on enterocyte proliferation and Src kinase activity. Sprague-Dawley rats were challenged with LPS or saline, whereas intestinal epithelial cell line cells were treated with ONOO- or decomposed ONOO- in vitro. Enterocyte proliferation in vivo and in vitro was measured by 5-bromo-2'-deoxyuridine (BrdU) or [3H]thymidine incorporation. Src kinase activity in cell lysates was determined at various times. LPS challenge in vivo and ONOO- treatment in vitro inhibited enterocyte proliferation. ONOO- treatment blunted the activity of Src and its downstream target, focal adhesion kinase, in a time-dependent manner. ONOO- blocked mitogen (FBS, EGF)-induced enterocyte proliferation and Src phosphorylation while increasing Src nitration. Thus ONOO- may promote gut barrier failure not only by inducing enterocyte apoptosis but also by disrupting signaling pathways involved in enterocyte proliferation.

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AKT inhibition is associated with chemosensitisation in the pancreatic cancer cell line MIA-PaCa-2

Activation of the serine/threonine kinase AKT is common in pancreatic cancer; inhibition of which sensitises cells to the apoptotic effect of chemotherapy. Of the various downstream targets of AKT, we examined activation of the NF-kappaB transcription factor and subsequent transcriptional regulation of BCL-2 gene family in pancreatic cancer cells. Inhibition of either phosphatidylinositol-3 kinase or AKT led to a decreased protein level of the antiapoptotic gene BCL-2 and an increased protein level of the proapoptotic gene BAX. Furthermore, inhibition of AKT decreased the function of NF-kappaB, which is capable of transcriptional regulation of the BCL-2 gene. Inhibiting this pathway had little effect on the basal level of apoptosis in pancreatic cancer cells, but increased the apoptotic effect of chemotherapy. The antiapoptotic effect of AKT activation in pancreatic cancer cells may involve transcriptional induction of a profile of BCL-2 proteins that confer resistance to apoptosis; alteration of this balance allows sensitisation to the apoptotic effect of chemotherapy.

Mechanism of intestinal-derived fungal sepsis by gliotoxin, a fungal metabolite

BACKGROUND/PURPOSE

Gut barrier dysfunction resulting from fungal overgrowth may be caused by the interaction of gliotoxin (GT), a fungal metabolite, with enterocytes. The goal of this study was to determine the mechanisms by which gliotoxin (GT), a fungal metabolite, causes enterocyte apoptosis.

METHODS

The authors measured enterocyte apoptosis, caspase-3 activity, pro-caspase-3, and poly (ADP-ribose) polymerase (PARP) cleavage in GT-exposed IEC-6 cells, a rat intestinal cell line.

RESULTS

GT induced apoptosis in IEC-6 cells. The pan-caspase inhibitor ZVAD suppressed this GT-mediated apoptosis. GT induced a 15-fold increase in caspase-3 activity over media control. The authors detected PARP cleavage by after GT exposure. DTT pretreatment decreased apoptosis compared with GT alone.

CONCLUSIONS

This study supports the concept that fungal overgrowth may lead to gut barrier dysfunction by the local release of gliotoxin and the induction enterocyte apoptosis.

Peroxynitrite-induced cytotoxicity: mechanism and opportunities for intervention

Peroxynitrite is formed in biological systems when superoxide and nitric oxide are produced at near equimolar ratio. Although not a free radical by chemical nature (as it has no unpaired electron), peroxynitrite is a powerful oxidant exhibiting a wide array of tissue damaging effects ranging from lipid peroxidation, inactivation of enzymes and ion channels via protein oxidation and nitration to inhibition of mitochondrial respiration. Low concentrations of peroxynitrite trigger apoptotic death, whereas higher concentrations induce necrosis with cellular energetics (ATP and NAD) serving as switch between the two modes of cell death. Peroxynitrite also damages DNA and thus triggers the activation of DNA repair systems. A DNA nick sensor enzyme, poly(ADP-ribose) polymerase-1 (PARP-1) also becomes activated upon sensing DNA breakage. Activated PARP-1 cleaves NAD(+) into nicotinamide and ADP-ribose and polymerizes the latter on nuclear acceptor proteins. Peroxynitrite-induced overactivation of PARP consumes NAD(+) and consequently ATP culminating in cell dysfunction, apoptosis or necrosis. This cellular suicide mechanism has been implicated among others in the pathomechanism of stroke, myocardial ischemia, diabetes and diabetes-associated cardiovascular dysfunction. Here, we review the cytotoxic effects (apoptosis and necrosis) of peroxynitrite focusing on the role of accelerated ADP-ribose turnover. Regulatory mechanisms of peroxynitrite-induced cytotoxicity such as antioxidant status, calcium signalling, NFkappaB activation, protein phosphorylation, cellular adaptation are also discussed.