Titanium dioxide nanoparticles exacerbate DSS-induced colitis: role of the NLRP3 inflammasome.

OBJECTIVE: Western lifestyle and diet are major environmental factors playing a role in the development of IBD. Titanium dioxide (TiO2) nanoparticles are widely used as food additives or in pharmaceutical formulations and are consumed by millions of people on a daily basis. We investigated the effects of TiO2 in the development of colitis and the role of the nucleotide-binding oligomerisation domain receptor, pyrin domain containing (NLRP)3 inflammasome. DESIGN: Wild-type and NLRP3-deficient mice with dextran sodium sulfate-induced colitis were orally administered with TiO2 nanoparticles. The proinflammatory effects of TiO2 particles in cultured human intestinal epithelial cells (IECs) and macrophages were also studied, as well as the ability of TiO2 crystals to traverse IEC monolayers and accumulate in the blood of patients with IBD using inductively coupled plasma mass spectrometry. RESULTS: Oral administration of TiO2 nanoparticles worsened acute colitis through a mechanism involving the NLRP3 inflammasome. Importantly, crystals were found to accumulate in spleen of TiO2-administered mice. In vitro, TiO2 particles were taken up by IECs and macrophages and triggered NLRP3-ASC-caspase-1 assembly, caspase-1 cleavage and the release of NLRP3-associated interleukin (IL)-1ß and IL-18. TiO2 also induced reactive oxygen species generation and increased epithelial permeability in IEC monolayers. Increased levels of titanium were found in blood of patients with UC having active disease. CONCLUSION: These findings indicate that individuals with a defective intestinal barrier function and pre-existing inflammatory condition, such as IBD, might be negatively impacted by the use of TiO2 nanoparticles.

Exaggerated IL-15 and Altered Expression of foxp3+ Cell-Derived Cytokines Contribute to Enhanced Colitis in Nlrp3-/- Mice.

The pathogenesis of Crohn's disease (CD) involves defects in the innate immune system, impairing responses to microbes. Studies have revealed that mutations NLRP3 are associated with CD. We reported previously that Nlrp3-/- mice were more susceptible to colitis and exhibited reduced colonic IL-10 expression. In the current study, we sought to determine how the loss of NLRP3 might be altering the function of regulatory T cells, a major source of IL-10. Colitis was induced in wild-type (WT) and Nlrp3-/- mice by treatment with dextran sulphate sodium (DSS). Lamina propria (LP) cells were assessed by flow cytometry and cytokine expression was assessed. DSS-treated Nlrp3-/- mice exhibited increased numbers of colonic foxp3+ T cells that expressed significantly lower levels of IL-10 but increased IL-17. This was associated with increased expression of colonic IL-15 and increased surface expression of IL-15 on LP dendritic cells. Neutralizing IL-15 in Nlrp3-/- mice attenuated the severity of colitis, decreased the number of colonic foxp3+ cells, and reduced the colonic expression of IL-12p40 and IL-17. These data suggest that the NLRP3 inflammasome can regulate intestinal inflammation through noncanonical mechanisms, providing additional insight as to how NLRP3 variants may contribute to the pathogenesis of CD.

Living with inflammatory bowel disease: A Crohn's and Colitis Canada survey.

BACKGROUND: Despite improvements in therapies for inflammatory bowel diseases (IBDs), patient quality of life continues to be significantly impacted. OBJECTIVE: To assess the impact of IBD on patients and families with regard to leisure, relationships, mental well-being and financial security, and to evaluate the quality and availability of IBD information. METHODS: An online survey was advertised on the Crohn's and Colitis Canada website, and at gastroenterology clinics at the University of Alberta Hospital (Edmonton, Alberta) and University of Calgary Hospital (Calgary, Alberta). RESULTS: The survey was completed by 281 IBD patients and 32 family members. Among respondents with IBD, 64% reported a significant or major impact on leisure activities, 52% a significant or major impact on interpersonal relationships, 40% a significant or major impact on financial security, and 28% a significant or major impact on planning to start a family. Patient information needs emphasized understanding disease progression (84%) and extraintestinal symptoms (82%). There was a strong interest in support systems such as health care insurance (70%) and alternative therapies (66%). The most common source of information for patients was their gastroenterologist (70%); however, most (70%) patients preferred to obtain their information from the Crohn's and Colitis Canada website. CONCLUSIONS: The impact of IBD on interpersonal relationships and leisure activities was significant among IBD patients and their families. Understanding the disease, but also alternative treatment options, was of high interest. Currently, there is a discrepancy between interest in information topics and their availability. Respondents reported a strong desire to obtain information regarding disease progression, especially extraintestinal symptoms.

Probiotic Escherichia coli Nissle 1917 and commensal E. coli K12 differentially affect the inflammasome in intestinal epithelial cells.

BACKGROUND: The probiotic bacterial strain Escherichia coli Nissle 1917 (EcN) is used for the treatment of ulcerative colitis (UC), diarrhea and constipation. Its beneficial effects in the treatment of UC have been demonstrated in several controlled clinical studies; however, the mechanism of action on the cellular level is still not completely clear. The intracellular pattern recognition receptor NLRP3 is expressed in intestinal epithelial cells (IEC), activates caspase-1 within the inflammasome complex and has been implicated to play a role in the etiology of inflammatory bowel diseases. METHODS: Probiotic EcN and commensal E. coli K12 were applied to IEC in vitro. Inflammasome activation, interleukin (IL)-18 release and caspase-1 activation were determined by coimmunoprecipitation, Western blot and ELISA. Apoptosis was investigated by Western blot. RESULTS: Incubation of Caco-2 cells with EcN resulted in lower inflammasome activation and subsequent secretion of mature IL-18 as compared to the commensal strain K12. Induction of apoptosis as determined by cleavage of caspase-3 and poly (ADP-ribose) polymerase were lower in EcN-stimulated cells. Autophagy was induced by both bacterial strains, but to a higher extent by K12. CONCLUSION: These findings indicate that genetically very similar E. coli strains differ markedly in their ability to activate the inflammasome.

Regulation of two renal chloride transporters, AE1 and pendrin, by electrolytes and aldosterone.

The renal handling of salt and protons and bicarbonate are intricately linked through shared transport mechanisms for sodium, chloride, protons, and bicarbonate. In the collecting duct, the regulated fine-tuning of salt and acid-base homeostasis is achieved by a series of transport proteins located in different cell types, intercalated and principal cells. Intercalated cells are considered to be of less importance for salt handling but recent evidence has suggested that the anion exchanger pendrin may participate in salt reabsorption and blood pressure regulation. Here, we examined the regulated expression of two functionally related but differentially expressed anion exchangers, AE1 and pendrin, by dietary electrolyte intake and aldosterone. Cortical expression of pendrin was regulated on mRNA and protein level. The combination of NaHCO3 and DOCA enhanced pendrin mRNA and protein levels, whereas DOCA or NaHCO3 alone had no effect. NaCl or KHCO3 increased pendrin mRNA, KCl decreased its mRNA abundance. On protein level, NH4Cl, NaCl, and KCl reduced pendrin expression, the other treatments were without effect. In contrast, AE1 mRNA or protein expression in kidney cortex was regulated by none of these treatments. In kidney medulla, NaHCO3/DOCA or NaHCO3 alone enhanced AE1 mRNA levels. AE1 protein abundance was increased by NH4Cl, NaHCO3/DOCA, and NaCl. Immunolocalization showed that during NH4Cl treatment the relative number of AE1 positive cells was increased and pendrin expressing cells reduced. Thus, pendrin and AE1 are differentially regulated with distinct mechanisms that separately affect mRNA and protein levels. Pendrin is regulated by acidosis and chloride intake, whereas AE1 is enhanced by acidosis, NaCl, and the combination of DOCA and NaHCO3.

Protein tyrosine phosphatase nonreceptor type 2 regulates autophagosome formation in human intestinal cells.

BACKGROUND: Autophagy is a process of central importance for maintaining cell homeostasis, survival, and the regulation of inflammation. Recent studies associated variants within the gene loci, encoding protein tyrosine phosphatase nonreceptor type 2 (PTPN2), and autophagy genes, such as autophagy-related 16-like 1 (ATG16L1), with chronic inflammatory disorders, such as Crohn's disease (CD). We show that PTPN2 regulates autophagy in human intestinal epithelial cells (IEC) and primary colonic lamina propria fibroblasts (CLPF). METHODS: Protein analysis in IEC and CLPF was performed by western blotting. Autophagososme formation was assessed by LC3B immunofluorescence or immunohistochemistry. Human intestinal tissue samples were obtained from noninflammatory bowel disease (IBD) control or from CD patients and genotyped for disease-associated PTPN2 or ATG16L1 variations. RESULTS: Knockdown of PTPN2 causes impaired autophagosome formation and dysfunctional autophagy resulted in increased levels of intracellular Listeria monocytogenes (LM) and elevated IEC apoptosis in response to tumor necrosis factor (TNF) and interferon gamma (IFN-γ). Similar findings were observed in primary CLPF derived from CD patients carrying the CD-associated PTPN2 variant. Presence of the ATG16L1 variant prevented the cytokine-induced rise in PTPN2 protein, finally resulting in impaired LC3B-II levels in IEC. Actively inflamed intestinal biopsies from CD patients carrying either ATG16L1 or PTPN2 genetic variants revealed aberrant LC3B expression patterns when compared with samples from non-IBD control patients. CONCLUSIONS: Our results demonstrate that PTPN2 regulates autophagosome formation in human intestinal cells. We provide a model of how a dysfunction of the CD susceptibility genes, PTPN2 and/or ATG16L1, may contribute to the onset and perpetuation of chronic intestinal inflammation.

Microparticles and their impact on intestinal immunity.

Microparticles are small (<1 µm), nonbiological particles that are used in many areas of daily life. As food additive they are used as anticaking agents or food colorants. The most common food-derived ingested compounds are aluminium silicate and titanium dioxide (TiO(2)), the latter being a white pigment used in toothpaste or sugar toppings. The increasing abundance of microparticles in the Western diet raises the question of the potential risks associated with gastrointestinal diseases such as Crohn's disease (CD). Accumulation of particles has been shown in cells of Peyer's patches, but it is not clear whether this also has pathological effects. NLRP3 is a member of the intracellular pattern recognition receptor family and it is part of the inflammasome, a multiprotein complex containing caspase-1 which activates the proinflammatory cytokines interleukin (IL)-1ß and IL-18. With regard to recent findings identifying small particles such as asbestos and monosodium urate as NLRP3 activators, TiO(2) may be another potential target for inflammasome studies. We found that macrophage-like cells readily take up TiO(2) after 6 h. Incubation of cells with TiO(2) resulted in the assembly of NLRP3 with caspase-1. This inflammasome assembly correlated with secretion of IL-1ß. In intestinal epithelial cells, TiO(2) also was found to be ingested. The counting of particles localized intracellularly revealed a dose-dependent increase of TiO(2)-positive cells. This points to the fact that in humans with a leaky intestinal barrier (such as IBD patients), TiO(2) microparticles may be taken up by macrophages and intestinal epithelial cells, may activate the inflammasome and induce IL-1ß and IL-18 secretion. This may aggravate inflammation in susceptible individuals.

Localization of members of MCT monocarboxylate transporter family Slc16 in the kidney and regulation during metabolic acidosis.

The monocarboxylate transporter family (MCT) comprises 14 members with distinct transport properties and tissue distribution. The kidney expresses several members of the MCT family, but only little is known about their exact distribution and function. Here, we investigated selected members of the MCT family in the mouse kidney. MCT1, MCT2, MCT7, and MCT8 localized to basolateral membranes of the epithelial cells lining the nephron. MCT1 and MCT8 were detected in proximal tubule cells whereas MCT7 and MCT2 were located in the thick ascending limb and the distal tubule. CD147, a beta-subunit of MCT1 and MCT4, showed partially overlapping expression with MCT1 and MCT2. However, CD147 was also found in intercalated cells. We also detected SMCT1 and SMCT2, two Na(+)-dependent monocarboxylate cotransporters, on the luminal membrane of type A intercalated cells. Moreover, mice were given an acid load for 2 and 7 days. Acidotic animals showed a marked but transient increase in urinary lactate excretion. During acidosis, a downregulation of MCT1, MCT8, and SMCT2 was observed at the mRNA level, whereas MCT7 and SMCT1 showed increased mRNA abundance. Only MCT7 showed lower protein abundance whereas all other transporters remained unchanged. In summary, we describe for the first time the localization of various MCT transporters in mammalian kidney and demonstrate that metabolic acidosis induces a transient increase in urinary lactate excretion paralleled by lower MCT7 protein expression.