Microflora trigger colitis in mice deficient in selenium-dependent glutathione peroxidase and induce Gpx2 gene expression

Possible Curative Effects of Boric Acid and Bacillus clausii Treatments on TNBS-Induced Ulcerative Colitis in Rats

Crohn's disease (CD) and ulcerative colitis (UC) are two chronic relapsing inflammatory bowel diseases (IBD). Although there are several treatment options available to improve the symptoms of IBD patients, there is no effective treatment that provides a definitive solution. In the present study, we aim to investigate the antioxidative/anti-inflammatory effects of oral administration of boric acid and Bacillus clausii in a rat trinitrobenzenesulfonic acid (TNBS)-induced colitis model. The effects of boric acid and B. clausii were examined in serum and colon tissues with the help of some biochemical and histological analyses. Elevated inflammation and oxidative damage were found in the blood and colon tissue samples in the TNBS-induced group according to the complete blood count (CBC), tumor necrosis factor (TNF) alpha, interleukin-35 (IL-35), malondialdehyde (MDA), glutathione peroxidase (GPx), myeloperoxidase (MPO), nitric oxide (NO), and histological findings. Particularly, the highest IL-35 level (70.09 ± 12.62 ng/mL) in the combined treatment group, highest catalase activity (5322 ± 668.1 U/mg protein) in the TNBS-induced group, and lower relative expression of inducible nitric oxide synthase in the TNBS-induced group than the control group were striking findings. According to our results, it can be concluded that boric acid showed more curative effects, even if B. clausii probiotics was partially ameliorative.

Oral streptococci subvert the host innate immune response through hydrogen peroxide

In periodontal health, oral streptococci constitute up to 80% of the plaque biofilm. Yet, destructive inflammatory events of the periodontium are rare. This observation suggests that oral streptococci may possess mechanisms to co-exist with the host. However, the mechanisms employed by oral streptococci to modulate the innate immune response have not been well studied. One of the key virulence factors produced by oral streptococci is hydrogen peroxide (H₂O₂). In mammalian cells, H₂O₂ triggers the activation of nuclear factor erythroid 2-related factor 2 (Nrf2), a key pathway mediating antioxidant defence. This study aimed to determine (1) if H₂O₂ producing oral streptococci activated the Nrf2 pathway in macrophages, and (2) if the activation of Nrf2 influenced the innate immune response. We found that oral streptococci downregulated the innate immune response in a H₂O₂ dependent manner through the activation of the Nrf2. The activation of the Nrf2 signalling pathway led to the inhibition of nuclear factor kappa-light-chain-enhancer of activated B cells (NFĸB), the key transcription factor regulating pro-inflammatory response. This study showed for the first time that oral streptococci are unlikely passive bystanders but could play an active role in the maintenance of periodontal health by preventing overt inflammation.

Redox Pioneer: Professor Regina Brigelius-Flohé

Dr. Regina Brigelius-Flohé (PhD 1978) is recognized here as redox pioneer because she has published an article on redox biology, as first author, that has been cited >1000 times, plus four articles cited >500 times, and a total of 30 articles cited >100 times. She obtained her doctorate in biochemistry at the Institute of Biochemistry of the University of Münster, Germany. She held positions in both, academia (Münster, Munich, Düsseldorf, Hannover, and Potsdam, Germany) and industry (Aachen, Germany). Dr. Brigelius-Flohé is the pioneer who, as head of the department of biochemistry of micronutrients of the German Institute of Human Nutrition (DIfE; Potsdam-Rehbrücke, Germany), worked out the metabolism of tocopherols and tocotrienols ("Key Finding 1"). She was the first to sequence glutathione peroxidase 4 (GPx4) ("Key Finding 2"), and unraveled the role of selenium, in particular of GPxs, in inflammation and carcinogenesis ("Key Finding 3"). Her contributions, thus, focused on serious biomedical problems such as nutrition, inflammation, and carcinogenesis. She has been a member of the scientific advisory board of the German Society of Biochemistry and Molecular Biology for 6 years and was president of SFRR-Europe in 2005-2006. She edited several books and serves on the editorial board of journals in the fields of nutrition, free radicals, and redox regulation. Antioxid. Redox Signal. 35, 595-601.

Role of the microbiota in ileitis of a mouse model of inflammatory bowel disease-Glutathione peroxide isoenzymes 1 and 2-double knockout mice on a C57BL background

C57Bl6 (B6) mice devoid of glutathione peroxidases 1 and 2 (Gpx1/2-DKO) develop ileitis after weaning. We previously showed germ-free Gpx1/2-DKO mice of mixed B6.129 background did not develop ileocolitis. Here, we examine the composition of the ileitis provoking microbiota in B6 Gpx1/2-DKO mice. DNA was isolated from the ileum fecal stream and subjected to high-throughput sequencing of the V3 and V4 regions of the 16S rRNA gene to determine the abundance of operational taxonomic units (OTUs). We analyzed the role of bacteria by comparing the microbiomes of the DKO and pathology-free non-DKO mice. Mice were treated with metronidazole, streptomycin, and vancomycin to alter pathology and correlate the OTU abundances with pathology levels. Principal component analysis based on Jaccard distance of abundance showed 3 distinct outcomes relative to the source Gpx1/2-DKO microbiome. Association analyses of pathology and abundance of OTUs served to rule out 7-11 of 24 OTUs for involvement in the ileitis. Collections of OTUs were identified that appeared to be linked to ileitis in this animal model and would be classified as commensals. In Gpx1/2-DKO mice, host oxidant generation from NOX1 and DUOX2 in response to commensals may compromise the ileum epithelial barrier, a role generally ascribed to oxidants generated from mitochondria, NOX2 and endoplasmic reticulum stress in response to presumptive pathogens in IBD. Elevated oxidant levels may contribute to epithelial cell shedding, which is strongly associated with progress toward inflammation in Gpx1/2-DKO mice and predictive of relapse in IBD by allowing leakage of microbial components into the submucosa.

Dexamethasone and Tofacitinib suppress NADPH oxidase expression and alleviate very-early-onset ileocolitis in mice deficient in GSH peroxidase 1 and 2

C57BL6/J (B6) mice lacking Se-dependent GSH peroxidase 1 and 2 (GPx1/2-DKO) develop mild to moderate ileocolitis around weaning. These DKO mice have a disease resembling human very-early-onset inflammatory bowel disease (VEOIBD), which is associated with mutations in NADPH oxidase genes. Drugs including dexamethasone (Dex), Tofacitinib (Tofa; a Janus kinase/JAK inhibitor) and anti-TNF antibody are effective to treat adult, but not pediatric IBD.

AIMS

To test the efficacy of hydrophobic Dex and hydrophilic Dex phosphate (Dex phos), Tofa, anti-Tnf Ab, Noxa1ds-TAT and gp91ds-TAT peptides (inhibiting NOX1 and NOX2 assembly respectively), antioxidant MJ33 and ML090, and pifithrin-α (p53 inhibitor) on alleviation of gut inflammation in DKO weanlings.

MAIN METHODS

All treatments began on 22-day-old GPx1/2-DKO mice. The mouse intestine pathology was compared between the drug- and vehicle-treated groups after six or thirteen days of treatment.

KEY FINDINGS

Among all drugs tested, Dex, Dex phos and Tofa were the strongest to suppress ileocolitis in the DKO weanlings. Dex, Dex phos and Tofa inhibited crypt apoptosis and increased crypt density. Dex or Dex phos alone also inhibited cell proliferation, exfoliation and crypt abscess in the ileum. Dex, but not Tofa, retarded mouse growth. Both Dex and Tofa inhibited ileum Nox1, Nox4 and Duox2, but not Nox2 gene expression. Noxa1ds-TAT and gp91ds-TAT peptides as well as MJ33 had subtle effect on suppressing pathology, while others had negligible effect.

SIGNIFICANCE

These findings suggest that NADPH oxidases can be novel drug targets for pediatric IBD therapy, and Tofa may be considered for treating VEOIBD.

Distinct and overlapping functions of glutathione peroxidases 1 and 2 in limiting NF-κB-driven inflammation through redox-active mechanisms

Glutathione peroxidase 2 (GPx2) is one of the five selenoprotein GPxs having a selenocysteine in the active center. GPx2 is strongly expressed in the gastrointestinal epithelium, as is another isoform, GPx1, though with a different localization pattern. Both GPxs are redox-active enzymes that are important for the reduction of hydroperoxides.

Studies on GPx2-deficient mice and human HT-29 cells with a stable knockdown (kd) of GPx2 revealed higher basal and IL-1β-induced expression of NF-κB target genes in vivo and in vitro. The activation of the IKK–IκBα–NF-κB pathway was increased in cultured GPx2 kd cells. Basal signaling was only restored by re-expressing active GPx2 in GPx2 kd cells but not by redox-inactive GPx2. As it is still not clear if the two isoforms GPx1 and GPx2 have different functions, kd cell lines for either GPx1 or GPx2 were studied in parallel. The inhibitory effect of GPx2 on NF-κB signaling and its target gene expression was stronger than that of GPx1, whereas cyclooxygenase (COX)- and lipoxygenase (LOX)-derived lipid mediator levels increased more strongly in GPx1 kd than in GPx2 kd cells. Under unstimulated conditions, the levels of the COX-derived prostaglandins PGE₂ and PGD₂ were enhanced in GPx2 as well as in GPx1 kd compared to control cells. Specifically, in GPx1 kd cells IL-1β stimulation led to a dramatic shift of the PGE₂/PGD₂ ratio towards pro-inflammatory PGE₂.

Taken together, GPx2 and GPx1 have overlapping functions in controlling inflammatory lipid mediator synthesis and, most probably, exert their anti-inflammatory effects by preventing excessive PGE₂ production. In view of the high activity of COX and LOX pathways during inflammatory bowel disease our data therefore provide new insights into the mechanisms of the protective function of GPx1 and GPx2 during colitis as well as inflammation-driven carcinogenesis.

•

Loss of GPx2 results in higher basal and IL-1β-induced NF-κB activation.

•

Suppressive effects of GPx2 on NF-κB are mediated in a redox-dependent manner.

•

Both GPx isoforms modulate the lipid mediator profile in response to IL-1β.

•

COX-derived prostaglandins increase more strongly in GPx1 than in GPx2 kd cells.

Insights into microbiome research 5: Mapping is first but function must come next

Several efforts identifying differential bacterial prevalence in the gut of multiple sclerosis (MS) patients have been reported and many more are underway. While these are critical first steps in determining the involvement of gut microbes in MS pathogenesis, functional assays (both in vitro and in vivo) are needed to explore the mechanisms underlying the observed changes and ultimately implementing interventional strategies to counter severity, progression or even reduce the chance that it develops in the first place.

NOX1 loss-of-function genetic variants in patients with inflammatory bowel disease

Genetic defects that affect intestinal epithelial barrier function can present with very early-onset inflammatory bowel disease (VEOIBD). Using whole-genome sequencing, a novel hemizygous defect in NOX1 encoding NAPDH oxidase 1 was identified in a patient with ulcerative colitis-like VEOIBD. Exome screening of 1,878 pediatric patients identified further seven male inflammatory bowel disease (IBD) patients with rare NOX1 mutations. Loss-of-function was validated in p.N122H and p.T497A, and to a lesser degree in p.Y470H, p.R287Q, p.I67M, p.Q293R as well as the previously described p.P330S, and the common NOX1 SNP p.D360N (rs34688635) variant. The missense mutation p.N122H abrogated reactive oxygen species (ROS) production in cell lines, ex vivo colonic explants, and patient-derived colonic organoid cultures. Within colonic crypts, NOX1 constitutively generates a high level of ROS in the crypt lumen. Analysis of 9,513 controls and 11,140 IBD patients of non-Jewish European ancestry did not reveal an association between p.D360N and IBD. Our data suggest that loss-of-function variants in NOX1 do not cause a Mendelian disorder of high penetrance but are a context-specific modifier. Our results implicate that variants in NOX1 change brush border ROS within colonic crypts at the interface between the epithelium and luminal microbes.

Prognostic significance of glutathione peroxidase 2 in gastric carcinoma

Increasing evidence suggests that the glutathione peroxidase 2 may actually play important roles in tumorigenesis and progression in various human cancers such as colorectal carcinomas and lung adenocarcinomas. However, the role of glutathione peroxidase 2 in gastric carcinoma remains to be determined. In this study, the expression and prognostic significance of glutathione peroxidase 2 in gastric carcinoma were investigated and the well-known prognostic factor Ki-67 labeling index was also assessed as positive control. Glutathione peroxidase 2 expression levels in the tumor tissue specimens, the matched adjacent normal tissue specimens, and the lymph node metastases of 176 patients with gastric carcinoma were evaluated by quantitative polymerase chain reaction, western blotting, and immunohistochemical staining. The associations between glutathione peroxidase 2 expression levels, as determined by immunohistochemical staining, and multiple clinicopathological characteristics were determined by Pearson's chi-square test and Spearman's correlation analysis. The relationships between glutathione peroxidase 2 expression and other clinicopathological variables and patient prognoses were analyzed further by the Kaplan-Meier method, the log-rank test, and Cox multivariate regression. The quantitative polymerase chain reaction, western blotting, and immunohistochemical staining results showed that glutathione peroxidase 2 expression levels were upregulated in both the primary tumor foci and the lymph node metastases of patients with gastric carcinoma (all p values < 0.05). Furthermore, Pearson's chi-square tests, as well as Spearman's correlation analysis, revealed that glutathione peroxidase 2 expression levels were strongly correlated with the Ki-67 labeling index, differentiation, histological patterns, Lauren classifications, lymph node metastasis, vascular invasion, tumor-node-metastasis stages, Helicobacter pylori infection, and overall survival (all p values < 0.05). Kaplan-Meier analysis, as well as the log-rank test and multivariate Cox regression analysis, showed that multiple clinicopathological risk factors and glutathione peroxidase 2 expression were novel independent prognostic factors for gastric carcinoma (all p values < 0.05). Glutathione peroxidase 2 expression is a novel independent prognostic biomarker for gastric carcinoma that may be used to devise personalized therapeutic regimens and precision treatments for this disease.

Paradoxical Roles of Antioxidant Enzymes: Basic Mechanisms and Health Implications

Reactive oxygen species (ROS) and reactive nitrogen species (RNS) are generated from aerobic metabolism, as a result of accidental electron leakage as well as regulated enzymatic processes. Because ROS/RNS can induce oxidative injury and act in redox signaling, enzymes metabolizing them will inherently promote either health or disease, depending on the physiological context. It is thus misleading to consider conventionally called antioxidant enzymes to be largely, if not exclusively, health protective. Because such a notion is nonetheless common, we herein attempt to rationalize why this simplistic view should be avoided. First we give an updated summary of physiological phenotypes triggered in mouse models of overexpression or knockout of major antioxidant enzymes. Subsequently, we focus on a series of striking cases that demonstrate "paradoxical" outcomes, i.e., increased fitness upon deletion of antioxidant enzymes or disease triggered by their overexpression. We elaborate mechanisms by which these phenotypes are mediated via chemical, biological, and metabolic interactions of the antioxidant enzymes with their substrates, downstream events, and cellular context. Furthermore, we propose that novel treatments of antioxidant enzyme-related human diseases may be enabled by deliberate targeting of dual roles of the pertaining enzymes. We also discuss the potential of "antioxidant" nutrients and phytochemicals, via regulating the expression or function of antioxidant enzymes, in preventing, treating, or aggravating chronic diseases. We conclude that "paradoxical" roles of antioxidant enzymes in physiology, health, and disease derive from sophisticated molecular mechanisms of redox biology and metabolic homeostasis. Simply viewing antioxidant enzymes as always being beneficial is not only conceptually misleading but also clinically hazardous if such notions underpin medical treatment protocols based on modulation of redox pathways.

Unraveling the Rat Intestine, Spleen and Liver Genome-Wide Transcriptome after the Oral Administration of Lavender Oil by a Two-Color Dye-Swap DNA Microarray Approach

The use of lavender oil (LO)--a commonly, used oil in aromatherapy, with well-defined volatile components linalool and linalyl acetate--in non-traditional medicine is increasing globally. To understand and demonstrate the potential positive effects of LO on the body, we have established an animal model in this current study, investigating the orally administered LO effects genome wide in the rat small intestine, spleen, and liver. The rats were administered LO at 5 mg/kg (usual therapeutic dose in humans) followed by the screening of differentially expressed genes in the tissues, using a 4×44-K whole-genome rat chip (Agilent microarray platform; Agilent Technologies, Palo Alto, CA, USA) in conjunction with a dye-swap approach, a novelty of this study. Fourteen days after LO treatment and compared with a control group (sham), a total of 156 and 154 up (≧ 1.5-fold)- and down (≦ 0.75-fold)-regulated genes, 174 and 66 up- (≧ 1.5-fold)- and down (≦ 0.75-fold)-regulated genes, and 222 and 322 up- (≧ 1.5-fold)- and down (≦ 0.75-fold)-regulated genes showed differential expression at the mRNA level in the small intestine, spleen and liver, respectively. The reverse transcription-polymerase chain reaction (RT-PCR) validation of highly up- and down-regulated genes confirmed the regulation of the Papd4, Lrp1b, Alb, Cyr61, Cyp2c, and Cxcl1 genes by LO as examples in these tissues. Using bioinformatics, including Ingenuity Pathway Analysis (IPA), differentially expressed genes were functionally categorized by their Gene Ontology (GO) and biological function and network analysis, revealing their diverse functions and potential roles in LO-mediated effects in rat. Further IPA analysis in particular unraveled the presence of novel genes, such as Papd4, Or8k5, Gprc5b, Taar5, Trpc6, Pld2 and Onecut3 (up-regulated top molecules) and Tnf, Slc45a4, Slc25a23 and Samt4 (down-regulated top molecules), to be influenced by LO treatment in the small intestine, spleen and liver, respectively. These results are the first such inventory of genes that are affected by lavender essential oil (LO) in an animal model, forming the basis for further in-depth bioinformatics and functional analyses and investigation.

The oxido-reductase enzyme glutathione peroxidase 4 (GPX4) governs Salmonella Typhimurium-induced neutrophil transepithelial migration

Neutrophil (polymorphonuclear leucocytes; PMN) transmigration across mucosal surfaces contributes to dysfunction of epithelial barrier properties, a characteristic underlying many mucosal inflammatory diseases. Using Salmonella enterica serovar Typhimurium (S. Typhimurium) as a prototypic proinflammatory insult, we have previously reported that the eicosanoid hepoxilin A₃ (HXA₃), an endogenous product of 12-lipoxygenase (12-LOX) activity, is secreted from the apical surface of the intestinal epithelium to establish a chemotactic gradient that guides PMN across the epithelial surface. Since little is known regarding the molecular mechanisms that regulate 12-LOX during S. Typhimurium infection, we investigated this pathway. We found that expression of phospholipid glutathione peroxidase (GPX4), which is known to have an inhibitory effect on 12-LOX activity, is significantly decreased at both the mRNA and protein level during infection with S. Typhimurium. Moreover, employing intestinal epithelial cell monolayers expressing siRNA against GPX4 mRNA, S. Typhimurium-induced PMN migration was significantly increased compared with the non-specific siRNA control cells. Conversely, in cells engineered to overexpress GPX4, S. Typhimurium-induced PMN migration was significantly decreased, which is consistent with the finding that partial depletion of GPX4 by RNAi resulted in a significant increase in HXA₃ secretion during S. Typhimurium infection. Mechanistically, although we found Salmonella entry not to be required for the induced decrease in GPX4, the secreted effector, SipA, which is known to induce epithelial responses leading to stimulation of HXA₃, governed the decrease in GPX4 in a process that does not lead to an overall increase in the levels of ROS. Taken together, these results suggest that S. Typhimurium induces apical secretion of HXA₃ by decreasing the expression of phospholipid GPX, which in turn leads to an increase in 12-LOX activity, and hence HXA₃ synthesis.

Does active Crohn's disease have decreased intestinal antioxidant capacity?

BACKGROUND AND AIMS

Oxidative stress is presumed to play an important role in Crohn's disease (CD) pathogenesis. Nevertheless, the evaluation of the intestinal antioxidant capacity through the analysis of glutathione peroxidase activity in CD remains to be determined.

METHODS

20 CD outpatients and 16 volunteers going through colonic cancer screening were enrolled. Colonoscopy with biopsies was performed in all individuals. Samples from inflamed and non-inflamed mucosa were taken when there was CD endoscopic activity. Spectrophotometric assays were performed to measure tissue glutathione peroxidase (GPx) activity, and total (GSHT) and oxidized (GSSG) glutathione in all samples. Demographics and clinical characteristics were collected from clinical charts.

RESULTS

Inflamed CD mucosa presented reduced GPx activity compared to non-inflamed CD mucosa (42.94mU/mg protein vs 79.62mU/mg protein, P<0.05) and control mucosa (42.94mU/mg protein vs 95.08mU/mg protein, P<0.001). GSHT concentration was reduced in inflamed mucosa when compared to non-inflamed CD mucosa (0.78μmol/g vs 1.98μmol/g, P<0.01) and the control group (0.78μmol/g vs 2.11μmol/g, P<0.001). A significant correlation was detected between GPx activity and GSSG (r=-0.599), disease duration (r=0.546), and thiopurine treatment (r=-0.480) in non-inflamed CD mucosa.

CONCLUSION

Our findings suggest that reduced GPx activity is present in inflamed CD mucosa. In addition, endoscopic activity, disease duration and thiopurine therapy could be associated with mucosal decreased antioxidant activity.

Analysis of candidate colitis genes in the Gdac1 locus of mice deficient in glutathione peroxidase-1 and -2

Background

Mice that are deficient for glutathione peroxidases 1 and 2 (GPX) show large variations in the penetrance and severity of colitis in C57BL/6J and 129S1/SvImJ backgrounds. We mapped a locus contributing to this difference to distal chromosome 2 (∼119–133 mbp) and named it glutathione peroxidase-deficiency-associated colitis 1 (Gdac1). The aim of this study was to identify the best gene candidates within the Gdac1 locus contributing to the murine colitis phenotype.

Method/Principal Findings

We refined the boundaries of Gdac1 to 118–125 mbp (95% confidence interval) by increasing sample size and marker density across the interval. The narrowed region contains 128 well-annotated protein coding genes but it excludes Fermt1, a human inflammatory bowel disease candidate that was within the original boundaries of Gdac1. The locus we identified may be the Cdcs3 locus mapped by others studying IL10-knockout mice. Using in silico analysis of the 128 genes, based on published colon expression data, the relevance of pathways to colitis, gene mutations, presence of non-synonymous-single-nucleotide polymorphisms (nsSNPs) and whether the nsSNPs are predicted to have an impact on protein function or expression, we excluded 42 genes. Based on a similar analysis, twenty-five genes from the remaining 86 genes were analyzed for expression-quantitative-trait loci, and another 15 genes were excluded.

Conclusion/Significance

Among the remaining 10 genes, we identified Pla2g4f and Duox2 as the most likely colitis gene candidates, because GPX metabolizes PLA2G4F and DUOX2 products. Pla2g4f is a phospholipase A2 that has three potentially significant nsSNP variants and showed expression differences across mouse strains. PLA2G4F produces arachidonic acid, which is a substrate for lipoxygenases and, in turn, for GPXs. DUOX2 produces H₂O₂ and may control microbial populations. DUOX-1 and -2 control microbial populations in mammalian lung and in the gut of several insects and zebrafish. Dysbiosis is a phenotype that differentiates 129S1/SvImJ from C57BL/6J and may be due to strain differences in DUOX2 activity.

Evaluation of dextrose water, black tea and orange juice on histopathologic recovery of surgery-induced intestinal damage in rabbits

BACKGROUND

The increase in intestinal permeability following damage to the intestinal mucosa in any surgical procedure, trauma or fasting is well- known.

OBJECTIVES

Our objective was to experimentally evaluate whether antioxidant consumption is associated with decreased intestinal damage in intestinal surgical procedures.

MATERIALS AND METHODS

Forty rabbits were used to compare the pathological changes in the intestine after consumption of dextrose water 5% (D5W), black tea and orange juice in fasting and in cases with intestine resection and anastomosis. They were divided in to five groups as shams (GI), NPO (G II), D5W (GIII), black tea (GIV) and orange juice groups (GV). In GII to GV group with median laparotomy, a 2 cm segment of jejunum was resected and ends of the bowel were anastomosed. Postoperatively, animals fasted for five days. Animals in GII were killed after five days of fasting. On day five case groups were given free access to drinking D5w (GIII), black tea solution (G IV) and orange juice (GV) for a further 7 days. On day 8, animals were reoperated and the repaired segment of intestine was removed. Morphologic data were compared in groups.

RESULTS

There were 8 rabbits in each group. There was a significant difference in villi lengths in the groups (P = 0.003). GV rabbits had obvious recovery of the villous architecture.

CONCLUSIONS

Orange juice as a source of vitamin C may be an appropriate liquid for postoperative recovery following intestinal surgery.

Bacterial composition and activity determines host gene-expression responses in gnotobiotic Atlantic cod (Gadus morhua) larvae

In this study the effects of different live versus dead bacteria on the survival and gene-expression patterns in Atlantic cod (Gadus morhua) larvae were examined. Seventeen different gnotobiotic conditions were tested in a 5-day experiment, and the effects of these conditions on the expression of selected genes involved in immune response, xenobiotic breakdown and nutrition (C3, Gpx, Cyp1a1 and Fdps) were investigated. For some of the conditions where dead bacteria were added, we observed significantly higher survival compared to the axenic control. Microbial specificity of host-responses was observed for all four genes, for both live and dead bacteria, although expression of Gpx and Fdps was more influenced by active bacteria. Live bacteria generally resulted in higher transcript levels of all the genes investigated, indicating that these host-responses are partly dependent on microbial activity, and not just due to interactions with bacteria as particles. The observed microbial specificity toward dead bacteria highlights the need to take into account the role of bacterial components when investigating host-microbe relationships.

Long-term selenium deficiency increases the pathogenicity of a Citrobacter rodentium infection in mice

Citrobacter rodentium is a mouse pathogen that causes infectious colitis and shares characteristics with human enteropathogenic (EPEC) and enterohemorrhagic (EHEC) Escherichia coli, including the ability to cause attaching and effacing lesions in the colon and serves as a useful model to study the pathogenicity of these bacteria. In this study, mice were fed a selenium-deficient diet for 5 or 20 weeks and then infected with C. rodentium. Colonization of the colon by C. rodentium was similar in mice fed adequate or selenium-deficient diets, but total bacterial colonization of the spleen was elevated in mice fed selenium-deficient diet for 20 weeks. Infection-induced changes to the colon included inflammatory cell infiltration, gross changes in crypt architecture, and ulceration and denuding of the epithelial layer that were greatest in mice fed a selenium-deficient diet for 20 weeks. Expression of pro-inflammatory genes was significantly higher 12-days post-infection in mice fed the selenium-deficient diet for 20 weeks compared to mice fed a selenium-adequate diet or selenium-deficient diet for 5 weeks. Diarrhea was prevalent in mice fed the selenium-deficient diet for 20 weeks but not 5 weeks, and this was associated with decreased expression of solute carrier family 26a3 and carbonic anhydrase IV, genes involved in ion transport. These results indicated that selenium played an important role in resistance to the pathological effects of a C. rodentium infection, and therefore, selenium status may be important in the expression of human disease caused by common food-borne bacteria.

Basic principles and emerging concepts in the redox control of transcription factors

Convincing concepts of redox control of gene transcription have been worked out for prokaryotes and lower eukaryotes, whereas the knowledge on complex mammalian systems still resembles a patchwork of poorly connected findings. The article, therefore, reviews principles of redox regulation with special emphasis on chemical feasibility, kinetic requirements, specificity, and physiological context, taking well investigated mammalian transcription factor systems, nuclear transcription factor of bone marrow-derived lymphocytes (NF-κB), and kelch-like ECH-associated protein-1 (Keap1)/Nrf2, as paradigms. Major conclusions are that (i) direct signaling by free radicals is restricted to O(2)•- and •NO and can be excluded for fast reacting radicals such as •OH, •OR, or Cl•; (ii) oxidant signals are H(2)O(2), enzymatically generated lipid hydroperoxides, and peroxynitrite; (iii) free radical damage is sensed via generation of Michael acceptors; (iv) protein thiol oxidation/alkylation is the prominent mechanism to modulate function; (v) redox sensors must be thiol peroxidases by themselves or proteins with similarly reactive cysteine or selenocysteine (Sec) residues to kinetically compete with glutathione peroxidase (GPx)- and peroxiredoxin (Prx)-type peroxidases or glutathione-S-transferases, respectively, a postulate that still has to be verified for putative mammalian sensors. S-transferases and Prxs are considered for system complementation. The impact of NF-κB and Nrf2 on hormesis, management of inflammatory diseases, and cancer prevention is critically discussed.

The microbiome and butyrate regulate energy metabolism and autophagy in the mammalian colon

The microbiome is being characterized by large-scale sequencing efforts, yet it is not known whether it regulates host metabolism in a general versus tissue-specific manner or which bacterial metabolites are important. Here, we demonstrate that microbiota have a strong effect on energy homeostasis in the colon compared to other tissues. This tissue specificity is due to colonocytes utilizing bacterially produced butyrate as their primary energy source. Colonocytes from germfree mice are in an energy-deprived state and exhibit decreased expression of enzymes that catalyze key steps in intermediary metabolism including the TCA cycle. Consequently, there is a marked decrease in NADH/NAD(+), oxidative phosphorylation, and ATP levels, which results in AMPK activation, p27(kip1) phosphorylation, and autophagy. When butyrate is added to germfree colonocytes, it rescues their deficit in mitochondrial respiration and prevents them from undergoing autophagy. The mechanism is due to butyrate acting as an energy source rather than as an HDAC inhibitor.

The pathogenicity of an enteric Citrobacter rodentium Infection is enhanced by deficiencies in the antioxidants selenium and vitamin E

The pathogenesis of a Citrobacter rodentium infection was evaluated in mice fed diets with a single deficiency in either selenium or vitamin E or with a double deficiency in both selenium and vitamin E compared to mice on nutritionally adequate diets. Mice fed the selenium- and vitamin E-deficient diet for 6 weeks had increased loads of C. rodentium in the colon and spleen, which were not observed in mice fed either of the singly deficient diets or the adequate diet. Infected mice fed the doubly deficient diet had increased colon crypt hyperplasia and an influx of infiltrating cells along with gross changes to crypt architecture, including ulceration and denuding of the epithelial layer. Cytokine and chemokine mRNA levels in the colon were measured by real-time PCR. Expression of proinflammatory cytokines and chemokines was upregulated on day 12 after infection with C. rodentium in mice fed the doubly deficient diet compared to mice fed the control diet. Heme oxygenase 1, an enzyme upregulated by oxidative stress, also was more highly induced in infected mice fed the doubly deficient diet. Production of C. rodentium antigen-specific IgM and IgG antibodies was not affected by feeding the doubly deficient diet. The results indicated that selenium and vitamin E play an important role in host resistance and in the pathology induced by C. rodentium, an infection that mimics disease caused by common food-borne bacterial pathogens in humans.

Marked changes in endogenous antioxidant expression precede vitamin A-, C-, and E-protectable, radiation-induced reductions in small intestinal nutrient transport

Rapidly proliferating epithelial crypt cells of the small intestine are susceptible to radiation-induced oxidative stress, yet there is a dearth of data linking this stress to expression of antioxidant enzymes and to alterations in intestinal nutrient absorption. We previously showed that 5-14 days after acute γ-irradiation, intestinal sugar absorption decreased without change in antioxidant enzyme expression. In the present study, we measured antioxidant mRNA and protein expression in mouse intestines taken at early times postirradiation. Observed changes in antioxidant expression are characterized by a rapid decrease within 1h postirradiation, followed by dramatic upregulation within 4h and then downregulation a few days later. The cell type and location expressing the greatest changes in levels of the oxidative stress marker 4HNE and of antioxidant enzymes are, respectively, epithelial cells responsible for nutrient absorption and the crypt region comprising mainly undifferentiated cells. Consumption of a cocktail of antioxidant vitamins A, C, and E, before irradiation, prevents reductions in transport of intestinal sugars, amino acids, bile acids, and peptides. Ingestion of antioxidants may blunt radiation-induced decreases in nutrient transport, perhaps by reducing acute oxidative stress in crypt cells, thereby allowing the small intestine to retain its absorptive function when those cells migrate to the villus days after the insult.

Atherogenic diets exacerbate colitis in mice deficient in glutathione peroxidase

BACKGROUND

The proinflammatory effect of high-fat diet has been observed beyond the cardiovascular system, but there is little evidence to support its role in triggering inflammatory bowel disease. GPx1/2-double-knockout (DKO) mice deficient in 2 intracellular glutathione peroxidases, GPx1 and GPx2, on a C57BL/6 (B6) background, have mild ileocolitis on a conventional chow.

METHODS

We fed B6 DKO mice 2 atherogenic diets to test the dietary effect on atherosclerosis and ileocolitis. Both atherogenic diets have high cholesterol-the Chol+/CA diet has cholic acid (CA), and the Chol+ diet has no CA.

RESULTS

The Chol+/CA diet induced severe colitis, but not ileitis, in the DKO mice compared with the Chol+ and the Chol- control diet. On the Chol+/CA diet, the wild-type (WT) mice had levels of aortic lesions and hypercholesterolemia similar to those of DKO mice but had no intestinal pathology. The diet-associated inflammatory responses in the DKO mice included increased colonic proinflammatory serum amyloid A3 expression, plasma lipopolysaccharide, and TNF-α levels. The Chol+/CA diet lowered the expression of the unfolded protein response genes ATF6, CHOP, unspliced Xbp(U) , and Grp78/Bip, in WT and DKO mice compared with mice on the Chol- diet.

CONCLUSIONS

We concluded that a cholesterol diet weakens the colon unfolded protein response, which can aggravate spontaneous colitis, leading to gut barrier breakdown. GPx has no impact on atherosclerosis without ultrahypercholesterolemia.

Part of the Series: From dietary antioxidants to regulators in cellular signaling and gene regulation

The association of decreased cancer risk with intake of cruciferous vegetables and selenium is stronger than that reported for fruits and vegetables in general. An active constituent in cruciferae is sulforaphane. Chemopreventive effects of both, sulforaphane and selenium have been attributed to an antioxidant action which certainly is too simplicistic. Sulforaphane induces via activation of the Nrf2/Keap1 system phase 2 enzymes that protect against carcinogens and oxidants. Induced enzymes comprise the selenoproteins thioredoxin reductase-1 (TrxR1) and gastrointestinal glutathione peroxidase (GI-GPx, GPx2), which contain antioxidant response elements (ARE) in their promoter regions. Translational realisation of the enhanced transcripts depends on adequate selenium supply, which explains the synergism of Nrf2 activators and selenium. Regarding tumorigenesis the role of TrxR1 is ambiguous: it is essential for fast tumor cell growth but also diminishes vascularisation of tumors. The anticarcinogenic role of GI-GPx is evident from enhanced gastrointestinal tumor formation in gpx2/gpx1 double KO mice.

Fasting-induced intestinal damage is mediated by oxidative and inflammatory responses

Background

Green tea has been shown to repair fasting-induced mucosal damage in rat intestine. The aim of this study was to elucidate the underlying mechanism.

Methods

Five groups of rats were used. Group 1 had free access to chow diet and water, and those in group 2 were fasted for 3 days. Animals in group 3 were fasted for 3 days, then were allowed drinking water for a further 7 days. Groups 4 and 5 were fasted for 3 days, then given drinking water containing green tea or vitamin E respectively for 7 days. Blood was collected for estimation of total plasma antioxidants, and jejunal samples were used for immunohistochemical analysis of superoxide dismutase (SOD), catalase and glutathione peroxidase (GPx), and for estimation of myeloperoxidase (MPO) activity.

Results

Use of green tea was associated with a significant increase in total plasma antioxidants (P &lt; 0·001), and mucosal SOD (P &lt; 0·001), catalase (P = 0·006) and GPx (P = 0·017), but a significant decrease in MPO activity (P &lt; 0·001). Vitamin E produced similar changes, but the effects were smaller.

Conclusion

Green tea reverses the fasting-induced damage to the intestinal mucosa by its antioxidant and anti-inflammatory effect.

Impact of gut microbiota on intestinal and hepatic levels of phase 2 xenobiotic-metabolizing enzymes in the rat

Using immunoblotting, we compared levels of phase 2 enzymes in liver, small intestine, cecum, and colon of germ-free and control rats (reassociated with rat intestinal microbiota). In addition, colonic levels were studied after association with human intestinal microbiota. The glutathione transferases (GSTs) studied, gastrointestinal glutathione peroxidase (GPX2), both epoxide hydrolases (EPHXs), and N-acetyltransferase (NAT) 1, were detected in all tissues. GPX2 and GSTP1 were highest in large bowel; the other enzymes of this group were highest in liver. NAT2 was found in the large bowel but not in the liver or small bowel. Sulfotransferases (SULTs) were detected in liver but were absent in small intestine; two forms were present at moderate levels in the large intestine. Strong gender-dependent differences were observed for several enzymes in liver but not in gut. Colonic levels in germ-free animals differed from those in control animals (* indicates statistical significance) for GSTA1/2 (4.0*- and 5.0*-fold in males and females, respectively), GSTA4 (1.5*/1.9*-fold), GSTM1 (1.1/1.5*-fold), EPHX1 (3.5*/2.4*-fold), EPHX2 (1.4/2.1*-fold), SULT1B1 (0.4*/0.6*-fold), SULT1C2 (1.3/1.6*-fold), and NAT2 (1.4/1.5*-fold). Smaller effects were observed when rats were colonized with human, compared with rat, intestinal bacteria. Cecal enzyme levels in germ-free rats were changed similarly to those in colon. No effects were seen in small intestine. In liver, SULT1A1, SULT1C1, and SULT1C2 were elevated in germ-free animals of both genders (1.5- to 2.6-fold); hepatic EPHX2 was elevated 1.6-fold in females. In conclusion, intestinal microbiota can affect levels of xenobiotic-metabolizing enzymes in large intestine and liver, but the effects observed were moderate compared with tissue-dependent expression differences.

GPx2 counteracts PGE2 production by dampening COX-2 and mPGES-1 expression in human colon cancer cells

GPx2, the gastrointestinal glutathione peroxidase, is a selenoprotein predominantly expressed in the intestine. An anti-inflammatory and anticarcinogenic potential has been inferred from the development of colitis and intestinal cancer in GPx1 and GPx2 double knockout mice. Further, induction by Nrf2 activators classifies GPx2 as a protective enzyme. In contrast, enhanced COX-2 expression is consistently associated with inflammation. The antagonistic roles and an intriguing co-localization of GPx2 and COX-2 prompted us to investigate their possible mutual regulation. Both enzymes were upregulated in tissues of patients with colorectal cancer and colitis, and co-localized in the endoplasmic reticulum. A stable knockdown of GPx2 in HT-29 cells by siRNA resulted in a high basal and IL-1-induced expression of COX-2 and mPGES-1, enzymes required for the production of the pro-inflammatory PGE(2). Accordingly, si-GPx2 cells released high concentrations of PGE(2). Observed effects were specific for GPx2, since COX-2 and mPGES-1 expression was not affected by selenium-deprivation which resulted in the disappearance of GPx1. It is concluded that GPx2 by compartmentalized removal of hydroperoxides silences COX-2 activity and suppresses PGE(2)-dependent COX-2 expression. Thus, GPx2 may prevent undue responses to inflammatory stimuli and, in consequence, inflammation-driven initiation of carcinogenesis.

Glutathione peroxidase 2 and aquaporin 8 as new markers for colonic inflammation in experimental colitis and inflammatory bowel diseases: an important role for H2O2?

OBJECTIVE

Different mouse models of inflammatory bowel diseases (IBD) demonstrate various aspects of the pathophysiology of IBD. We looked for overlapping gene expression profiles in three different mouse models of experimental colitis and analysed whether these overlapping genes are of help to find new genes that could be used as general markers in human IBD.

METHODS

Using Agilent mouse TOX oligonucleotide microarrays, we analysed the gene expression profiles in three widely used models of experimental colitis: 2,4,6-trinitrobenzene sulphonic acid, dextran sodium sulfate and CD4CD45RB transfer and looked for overlapping gene expression in these models. Overlapping genes were analysed using Lightcycler (Roche Diagnostics, Mannheim, Germany) in biopsy materials from human IBD and control tissue.

RESULTS

Compared with control mice in dextran sodium sulfate, 2,4,6-trinitrobenzene sulphonic acid and the CD45RB transfer colitis mice five known genes, extracellular proteinase inhibitor (Expi), glutathione peroxidase 2 (Gpx2), mast cell protease 1 (Mcpt1), resistin-like beta (Retnlb) and sulphatase 2 (Sulf2), and two unknown genes were upregulated and the two genes aquaporin 8 (Aqp8) and kallikrein 5 (Klk5) were downregulated in all three models. In human Crohn's disease and ulcerative colitis biopsies, one of the upregulated glutathione peroxidase (Gpx2) and one of the downregulated Aqp8 genes in the mouse models were also differentially expressed in affected colonic tissue of patients with IBD.

CONCLUSION

Experimental mouse models are suitable models for the search of new markers for human IBD. As both Gpx2 and Aqp8 are involved in H2O2 metabolism (Gpx2 as a radical scavenger whereas Aqp8 facilitates its diffusion), upregulation of Gpx2 and downregulation of Aqp8 could be a mechanism to defend against severe oxidative stress and indicate that H2O2 is a universal mediator in the inflammatory process in the colon. This provides a focus on homeostasis of the antioxidant pathway and its importance in IBD.

Mutation Accumulation in the Intestine and Colon of Mice Deficient in Two Intracellular Glutathione Peroxidases

Mice deficient in two glutathione peroxidases (GPX), Gpx1 and Gpx2, [Gpx1/2-double knockout (DKO) mice] are prone to ileocolitis on a mixed C57BL/6 and 129S1/SvJ (B6.129) genetic background. We reported previously that approximately 25% of B6.129 Gpx1/2-DKO mice develop ileocolonic tumors by 6 to 9 months of age, when their non-DKO littermates [having at least one wild-type (WT) Gpx1 or Gpx2 allele] rarely have inflammation and none have tumors. Because genetic background affects tumor susceptibility, we have generated a B6 Gpx1/2-DKO colony and discovered that these mice have fewer inflammatory cells, milder ileocolitis, and low mortality, and only 2.5% of B6 mice developed tumors. The mutant frequency of a cII reporter gene was about 2- to 3-fold higher in 28-day-old Gpx1/2-DKO and 4-fold higher in 8-month-old Gpx1/2-DKO ileal mucosa than in controls in both genetic backgrounds. In contrast, mutant frequencies in the unaffected B6 liver were not significantly different between WT and Gpx1/2-DKO mice. The mutant frequency of 8-month-old B6.129 Gpx1/2-DKO ileum was 38.94 +/- 15.5(-5), which was not significantly higher than the age-matched B6 ileum, 25.54 +/- 10.33(-5). The mutation spectra analysis has shown that B6 Gpx1/2-DKO ileum had a 3-fold increase in small nucleotide deletions at mononucleotide repeats over control B6, which are a signature mutation associated with oxidative stress. Unexpectedly, B6 Gpx1/2-DKO mice had fewer C to T transitions at CpG dinucleotides than the WT B6 (18.0% versus 40.1%; P < 0.001). Our results suggest that inflammation drives gene mutations, which leads to neoplastic transformation of intestinal epithelium in the B6.129 Gpx1/2-DKO mice but rarely in the B6 Gpx1/2-DKO mice.

Glutathione peroxidases and redox-regulated transcription factors

Analysis of the selenoproteome identified five glutathione peroxidases (GPxs) in mammals: cytosolic GPx (cGPx, GPx1), phospholipid hydroperoxide GPx (PHGPX, GPx4), plasma GPx (pGPX, GPx3), gastrointestinal GPx (GI-GPx, GPx2) and, in humans, GPx6, which is restricted to the olfactory system. GPxs reduce hydroperoxides to the corresponding alcohols by means of glutathione (GSH). They have long been considered to only act as antioxidant enzymes. Increasing evidence, however, suggests that nature has not created redundant GPxs just to detoxify hydroperoxides. cGPx clearly acts as an antioxidant, as convincingly demonstrated in GPx1-knockout mice. PHGPx specifically interferes with NF-kappaB activation by interleukin-1, reduces leukotriene and prostanoid biosynthesis, prevents COX-2 expression, and is indispensable for sperm maturation and embryogenesis. GI-GPx, which is not exclusively expressed in the gastrointestinal system, is upregulated in colon and skin cancers and in certain cultured cancer cells. GI-GPx is a target for Nrf2, and thus is part of the adaptive response by itself, while PHGPx might prevent cancer by interfering with inflammatory pathways. In conclusion, cGPx, PHGPx and GI-GPx have distinct roles, particularly in cellular defence mechanisms. Redox sensing and redox regulation of metabolic events have become attractive paradigms to unravel the specific and in part still enigmatic roles of GPxs.

Estrogen selectively up-regulates the phospholipid hydroperoxide glutathione peroxidase in the oviducts

The oviduct plays a crucial role in mammalian reproduction by providing an optimal environment for the final maturation and transport of gametes, fertilization, and early embryonic development. It is now recognized that these reproductive events in vitro can be either negatively or positively affected by reactive oxygen species such as hydrogen peroxide and lipid hydroperoxides. In the current study, we analyzed the expression of the phospholipid hydroperoxide glutathione peroxidase (PHGPx or GPx-4), a selenoenzyme that directly reduces membrane-bound lipid hydroperoxides in the bovine oviduct. Using in situ hybridization, we demonstrated that GPx-4 expression is almost restricted to the oviductal luminal epithelium in contrast to GPx-1, which is widely distributed, and GPx-2 and -3, which are mainly detected in the epithelial cells and lamina propria. Interestingly, real-time quantitative RT-PCR analysis showed that GPx-4 expression was highest during the follicular and postovulatory phases. In addition, GPx-4 expression was highest in the isthmus proximal to the dominant follicle during the follicular stage and remained high during the postovulatory period. This increased in expression of GPx-4 corresponded to increased GPx-4 enzymatic activity. Based on intrauterine infusion of estradiol, we determined that the increase in expression and activity of GPx-4 is estrogen mediated. This work clearly demonstrates that GPx-4 gene expression is influenced by the proximity of the dominant follicle in the oviduct in vivo. We propose that GPx-4 has an important role in the physiological control of peroxide tone in the bordering cells of the oviductal lumen.

Epithelium-specific glutathione peroxidase, Gpx2, is involved in the prevention of intestinal inflammation in selenium-deficient mice

Mice deficient in 2 intracellular selenium (Se)-dependent glutathione peroxidases (Gpx1 and Gpx2), by genetically disrupting both alleles of the Gpx1 and Gpx2 genes (Gpx1(-/-)Gpx2(-/-)), develop ileocolitis around weaning. However, decreased Gpx activity in Se-depleted wild-type animals does not produce pathology in the gastrointestinal tract. Because a small percentage of Se-sufficient Gpx1(+/-)Gpx2(-/-) mice have mild ileocolitis, we hypothesized that Se-deficient Gpx1(+/-)Gpx2(-/-) mice will develop severe ileocolitis similarly to the Gpx1(-/-)Gpx2(-/-) mice, and even a trace amount of Gpx2 can protect intestinal mucosa against inflammation. To test our hypothesis, we fed mice at various stages of development with either Gpx1(+/)(-)Gpx2(-/-) or Gpx1(-/-)Gpx2(+/)(-) genotypes an Se-deficient diet for 4-5 wk and assessed the symptoms and pathology. Gpx1(+/)(-)Gpx2(-/-) mice that were deprived of Se in utero or at weaning (18-22 d of age), but not as young adults (31-51 d of age), manifested significantly worse pathology than their Se-sufficient counterparts. Both Gpx1 and Gpx2 activities and mRNA levels were significantly depressed in the ileum of Se-deprived mice. In mice deprived in utero, the pathology included acute inflammation with neutrophil and monocyte infiltration particularly in the colon and was externally manifested by perianal alopecia and ulceration. On the other hand, Gpx1(-/-)Gpx2(+/)(-) mice were unaffected by Se deprivation, regardless of the age of onset. The results show that a trace amount of Gpx2 is protective against ileocolitis, and Se-deficient young Gpx1(+/-)Gpx2(-/-) mice will develop pathology and symptoms similar to Se-adequate Gpx1(-/-)Gpx2(-/-) mice.

Gene expression profile analysis of mouse colon embryonic development

During late embryogenesis, the mouse colon develops from a pseudostratified, undifferentiated endoderm to a single-layered columnar epithelium with accompanying mesenchymal maturation. To identify regulatory genetic programs underlying these morphological changes, we profiled gene expression of the developing mouse colon by microarray from embryonic day (E)13.5 to E18.5. Unbiased cluster analysis of 13,484 cDNA elements revealed two distinct groups of genes whose expression changes reflect the dynamic morphological events of the epithelium and mesenchyme during this period. Additional analyses revealed two subsets of genes whose expression is either upregulated or downregulated over the same developmental period. Of those genes whose expression increases from E13.5 to E18.5 (n = 158), known functions include acquisition and/or maintenance of colonic differentiation. Genes whose transcription is downregulated over this period (n = 49) have demonstrated roles in nuclear organization, transcriptional regulation, and cell proliferation. These results provide the basis for a molecular portrait of colonic development during late embryogenesis and should be a valuable resource for investigators interested in colonic development and neoplasia, as well as comparative organogenesis.

The link between selenium and chemoprevention: a case for selenoproteins

Selenium is effective in reducing cancer incidence in animal models, and epidemiologic data, as well as supplementation trials, have indicated that selenium is likely to be effective in humans. The mechanism by which selenium prevents cancer remains unknown. The mammalian genome encodes 25 selenoprotein genes, each containing one or more molecules of selenium in the form of the amino acid selenocysteine, translationally inserted into the growing peptide in response to the UGA codon. There is evidence that several of these proteins may be involved with the mechanism by which selenium provides its anticancer effects. Data are reviewed indicating that genetic variants of the cytosolic glutathione peroxidase are associated with increased cancer risk, and that loss of one of the copies of this same gene may be involved with malignant progression. Similarly, allelic differences in the gene for a second selenoprotein, Sep15, may be relevant to the protection provided by selenium, and allelic loss at this locus have been reported as well. These data, along with the differential expression patterns reported for other selenoproteins in tumor vs. normal tissues, support the role of selenoproteins in the chemoprotection by selenium.

Loss of detoxification in inflammatory bowel disease: dysregulation of pregnane X receptor target genes

BACKGROUND & AIMS

Phase 1, phase 2, and cellular efflux transporters are critical components in intestinal barrier function against xenobiotics and bacteria. We therefore performed global gene expression profiling in patients with ulcerative colitis (UC) and Crohn's disease as well as control specimens, with a special emphasis on genes involved in detoxification and epithelial membrane integrity.

METHODS

Mucosal biopsy specimens from nonaffected regions of the colon and the terminal ileum were subjected to DNA microarray analysis and pathway-related data mining. Real-time reverse-transcription polymerase chain reaction was used for verification of selected regulated candidate genes in larger inflammatory bowel disease sample numbers and intestinal cell lines.

RESULTS

Several dysregulated genes were identified in both disease groups and tissues. A set of genes coordinately down-regulated in the colon of patients with UC was composed of cellular detoxification and defense genes, which are target genes for the transcription factor pregnane X receptor (PXR). Messenger RNA expression of ABCB1 (MDR1) and PXR was significantly reduced in the colon of patients with UC but was unaffected in patients with Crohn's disease. In contrast to some of its target genes, the expression of PXR was not sensitive to tumor necrosis factor alpha stimulation of intestinal cell lines.

CONCLUSIONS

A disease- and tissue-specific decrease in the expression of detoxification enzymes and ABC transporters was observed, which may be explained by a loss of PXR expression. Thus, dysregulation of xenobiotic metabolism and PXR activity in the gut is likely to contribute to the pathophysiology of UC.

Role of Se-dependent glutathione peroxidases in gastrointestinal inflammation and cancer

Increase in reactive oxygen species plays an integral part in the inflammatory response, and chronic inflammation increases cancer risk. Selenium-dependent glutathione peroxidase (GPX) is well recognized for its antioxidant, and thus anti-inflammatory, activity. However, due to the multiple antioxidant families present in the gastrointestinal tract, it has been difficult to demonstrate the importance of individual antioxidant enzymes. Using genetically altered mice deficient in individual Gpx genes has provided insight into the physiological functions of these genes. Insufficient GPX activity in the mucosal epithelium can trigger acute and chronic inflammation. The presence of certain microflora, such as Helicobacter species, may affect cancer risk significantly. However, when damaged cells have progressed into a precancerous status, increased GPX activity may become procarcinogenic, presumably due to inhibition of hydroperoxide-mediated apoptosis. This review summarizes the current view of GPX in inflammation and cancer with emphasis on the GI tract.

Bacteria-induced intestinal cancer in mice with disrupted Gpx1 and Gpx2 genes

Two glutathione peroxidase (GPX) isozymes, GPX-1 and GPX-2 (GPX-GI), are the major enzymes that reduce hydroperoxides in intestinal epithelium. We have previously demonstrated that targeted disruption of both the Gpx1 and Gpx2 genes (GPX-DKO) results in a high incidence of ileocolitis in mice raised under conventional conditions, which include the harboring of Helicobacter species [non-specific-pathogen-free (non-SPF) conditions]. In this study, we have characterized GPX-DKO mice that have microflora-associated intestinal cancers, which are correlated with increased intestinal pathology/inflammation. We found that GPX-DKO mice raised under germ-free conditions have virtually no pathology or tumors. After colonizing germ-free mice with commensal microflora without any known pathogens (SPF), <9% of GPX-DKO mice develop tumors in the ileum or the colon. However, about one-fourth of GPX-DKO mice raised under non-SPF conditions from birth or transferred from SPF conditions at weaning have predominantly ileal tumors. Nearly 30% of tumors are cancerous; most are invasive adenocarcinomas and a few signet-ring cell carcinomas. On the basis of these results, we conclude that GPX-DKO mice are highly susceptible to bacteria-associated inflammation and cancer. The sensitivity exhibited in these mice suggests that peroxidative stress plays an important role in ileal and colonic pathology and inflammation, which can lead to tumorigenesis.

Gnotobiotic zebrafish reveal evolutionarily conserved responses to the gut microbiota

Animals have developed the means for supporting complex and dynamic consortia of microorganisms during their life cycle. A transcendent view of vertebrate biology therefore requires an understanding of the contributions of these indigenous microbial communities to host development and adult physiology. These contributions are most obvious in the gut, where studies of gnotobiotic mice have disclosed that the microbiota affects a wide range of biological processes, including nutrient processing and absorption, development of the mucosal immune system, angiogenesis, and epithelial renewal. The zebrafish (Danio rerio) provides an opportunity to investigate the molecular mechanisms underlying these interactions through genetic and chemical screens that take advantage of its transparency during larval and juvenile stages. Therefore, we developed methods for producing and rearing germ-free zebrafish through late juvenile stages. DNA microarray comparisons of gene expression in the digestive tracts of 6 days post fertilization germ-free, conventionalized, and conventionally raised zebrafish revealed 212 genes regulated by the microbiota, and 59 responses that are conserved in the mouse intestine, including those involved in stimulation of epithelial proliferation, promotion of nutrient metabolism, and innate immune responses. The microbial ecology of the digestive tracts of conventionally raised and conventionalized zebrafish was characterized by sequencing libraries of bacterial 16S rDNA amplicons. Colonization of germ-free zebrafish with individual members of its microbiota revealed the bacterial species specificity of selected host responses. Together, these studies establish gnotobiotic zebrafish as a useful model for dissecting the molecular foundations of host-microbial interactions in the vertebrate digestive tract.

Epithelial transport and gut barrier function in colitis

PURPOSE OF REVIEW

Colitis is an inflammatory bowel disease that is confined to the colon and is characterized by a watery diarrhea that can also be accompanied by blood in the stool. The inflammation associated with colitis is generally confined to the mucosal and submucosal layers, although Crohn's colitis may be transmural. The principal functions of the colonic mucosa are to act as a barrier to the luminal contents of the intestinal tract and to facilitate the bidirectional transport of water and electrolytes. It is well established that barrier and transport defects occur in colitis and may be involved in pathogenesis. Consequently, this review discusses recent evidence of potential mechanisms that may be involved in the perturbation of mucosal transport and barrier functions in colitis and therapeutic advances to counteract these defects.

RECENT FINDINGS

Mechanisms responsible for transport dysfunction and barrier defects in colitis are discussed, including decreased activity of transport proteins such as CFTR, bacterial interactions with the epithelium, including understanding of the regulation and function of NOD-2, and altered expression of components of the intestinal barrier, such as mucins and multidrug resistance proteins.

SUMMARY

Recent advances in our understanding of how changes in barrier and transport function occur in colitis may illuminate the pathophysiology of this condition. The work discussed may also identify novel targets that are functionally altered in colitis, which potentially can be modulated therapeutically either with existing medications or with newer agents that are in development.