Abstract

Inflammatory Bowel Disease (IBD) is a chronic inflammatory disorder characterized by progressive inflammation and the erosion of the gut mucosa. Although the exact cause of IBD is unknown, multiple factors contribute to its complex pathogenesis. Diet is one such factor and a strong correlation exists between the western-style, high fat diets (HFDs) and IBD incidence rates. In this study, we propose that the peroxidized fatty acid components of HFDs could contribute to inflammation of the gut. The inflammatory nature of peroxidized linoleic acid (13-HPODE), was confirmed in vitro by analyzing pro-inflammatory gene expression in Caco-2 cells via RT-PCR and ELISA. Additionally, peroxide induced apoptosis was tested by Annexin-V fluorescent staining, while permeability was tested by FITC-dextran flux and TEER. The 13-HPODE-induced inflammation of intestinal epithelium was evaluated in vivo by analyzing pro-inflammatory cytokines under acute and chronic conditions after feeding 13-HPODE to C57BL/6J mice. Our data show that 13-HPODE significantly induced pro-inflammatory gene expression of TNF-α and MCP-1 in vitro, most notably in differentiated Caco-2 cells. Further, acute and chronic 13-HPODE treatments of mice similarly induced pro-inflammatory cytokine expression in the epithelium of both the proximal and distal small intestines, resident immune cells in Peyer’s patches and peritoneal macrophages. The results of this study not only confirm the pro-inflammatory properties of peroxidized fats on the gut mucosa, but for the first time demonstrate their ability to differentially induce pro-inflammatory gene expression and influence permeability in the intestinal epithelium and mucosal cells. Collectively, our results suggest that the immunogenic properties of HFD’s in the gut may be partly caused by peroxide derivatives, providing potential insight into how these diets contribute to exacerbations of IBD.

Highlights

  • Inflammatory bowel disease (IBD) is a chronic inflammatory disorder of the gastrointestinal tract [1,2] and is categorized as either Crohn’s disease (CD) or Ulcerative Colitis (UC) depending on lesion types, pattern of progression, location and potential complications

  • As the small intestines serve as a first-line barrier to dietary products and toxins, the gut mucosa experiences the largest concentrations of peroxidized lipids (POLs) which we hypothesize may underly the intestinal inflammation observed with the high fat diets (HFDs)

  • We found that 13-HPODE directly induced TNF-α, Monocyte chemoattractant protein-1 (MCP-1), and IL-4 expression in both 13-HPODE

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Summary

Introduction

Inflammatory bowel disease (IBD) is a chronic inflammatory disorder of the gastrointestinal tract [1,2] and is categorized as either Crohn’s disease (CD) or Ulcerative Colitis (UC) depending on lesion types, pattern of progression, location and potential complications. It is believed that the high fat component is a major immunogenic factor, as patients with IBD are more likely to experience flare-ups when consuming fatty foods and is a major reason for why IBD-specific diets either significantly reduce or eliminate fats [13]. POLs are by-products of exogenous or endogenous oxidation of polyunsaturated fatty acids (PUFAs) double bonds, which are abundant in western-style diets. Both natural processes like autoxidation and artificial processes, such as deep-frying and long-term exposure to air result in the oxidation of PUFAs to POLs. As the small intestines serve as a first-line barrier to dietary products and toxins, the gut mucosa experiences the largest concentrations of POLs which we hypothesize may underly the intestinal inflammation observed with the high fat diets (HFDs). In this study, we tested the immunogenic properties of the most common dietary POL, 13-HPODE, on intestinal epithelium both in vitro and in vivo

Materials
Cell Culture
Preparation of HPODE
Treatment of Cells with 13-HPODE
Chemotaxis of THP-1 Cells and Conditioned Media
Animals
2.11. Chronic Inflammation
2.13. Isolation of Mouse Peritoneal Macrophages
2.14. Collection of Plasma and Organs
2.15. Plasma Lipid Analysis
Results
Metabolic Characteristics of Mice
Gene Analysis of Mice Proximal and Distal IEs and PPs
Gene Expression in Mouse Peritoneal Macrophages
A Member and scavenger receptor
Cytokine Array
Findings
Discussion
Conclusions
Full Text
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