Dietary Phytochemicals as Potential Interventions for Inflammatory Bowel Disease

Open Access
Author:
Bitzer, Zachary T
Graduate Program:
Food Science
Degree:
Doctor of Philosophy
Document Type:
Dissertation
Date of Defense:
December 17, 2014
Committee Members:
  • Joshua D Lambert, Dissertation Advisor
  • Ryan John Elias, Dissertation Advisor
  • Andrew David Patterson, Committee Member
  • Robert F Roberts, Committee Member
Keywords:
  • Inflammatory Bowel Disease
  • IBD
  • Soy
  • EGCG
  • DSS
  • Permeability
  • Inflammasome
  • Colorectal Cancer
  • Ulcerative Colitis
  • ROS
Abstract:
Inflammatory bowel disease (IBD) afflicts nearly 2.2 million people worldwide. IBD is composed of two main groups, ulcerative colitis (UC) and Crohn’s disease. Nearly 20% of those who suffer from IBD will develop colorectal cancer and 50% will die as a result. In addition to the decrease in quality of life and increases in colorectal cancer risk, IBD also presents a significant economic burden. The total economic burden of ulcerative colitis (UC) and Crohn’s disease in the United States is estimated to be US$19 – 30 billion annually. IBD patients suffer from increased inflammatory gene expression, cytokine production, oxidative stress, and decreased gut barrier function. This decrease in gut barrier function is a result of modulation of tight junction proteins responsible for modulating paracellular transport in the epithelium. Decreased gut barrier function allows for intestinal endotoxins, such as lipopolysaccharide (LPS), to pass from the lumina into the systemic circulation causing further inflammation. Dietary intervention is of particular interest when studying IBD as many phytochemicals have biological activity and some have been shown to decrease inflammation. Though some may are not very bioavailable, they may have activity through direct interaction with epithelial cells. The overall goal of this project was to investigate the beneficial effects of dietary supplementation with dietary phytochemicals on dextran sulfate sodium (DSS)-induced colonic inflammation and gastrointestinal permeability. The specific objectives were: a) to evaluate the effect of epigallocatechin-3-gallate (EGCG) on markers of inflammation, oxidative stress, gut barrier function, and nutrition in mice with DSS-induced ulcerative colitis and in DSS-treated Caco-2 cell monolayers in culture, b) evaluate the effect of an isoflavone-free soy protein concentrate on markers of inflammation, oxidative stress, gut barrier function, and inflammasome formation in mice with DSS-induced ulcerative colitis and in DSS-treated Caco-2 cell monolayers in culture. EGCG, the most abundant green tea polyphenol, has been shown to inhibit oxidative stress in animal and cell studies. We examined the effect of EGCG on DSS-induced permeability in Caco-2 cell monolayers and found that EGCG treatment significantly reduced permeability. We examined the anti-inflammatory, anti-nutritional, and intestinal permeability effects of EGCG in the DSS-induced mouse model of ulcerative colitis. Mice received DSS (1.5% w/v) for 7 days to induce ulcerative colitis and then received 0.32% EGCG as their sole source of drinking water for an additional 3 days. Colonic levels of the inflammatory markers, interleukin (IL)-1β, IL-6, and tumor necrosis factor alpha (TNF-α), were increased in DSS-treated mice, but the effect was mitigated as a result of EGCG administration. Gut barrier improvements were seen in the mice that received EGCG intervention as measured by a multi-sugar permeability assay. These results indicate that EGCG decreases the inflammatory response of the intestine and modulates intestinal permeability. In spite of these anti-inflammatory effects, we observed that EGCG decreased feeding efficiency and enhanced body weight loss compared to DSS-treated control mice. These changes were related to increases in fecal proteins and lipids and were observed in EGCG-treated mice suggesting that EGCG exerted anti-nutritional effects and indicating a potential dose-limiting toxicity. Soy (Glycine max), a widely consumed dietary component, has been reported to have beneficial effects against a number of chronic diseases. We examined the ability of soy protein concentrate (SPC) to suppress inflammation and oxidative stress, and improve gut barrier function both in vivo and in a cell culture model. In vitro, SPC exhibited radical scavenging activity. This activity was further supported by an in vivo experiment where SPC protected Caco-2 human colon cells from H2O2-induced cytotoxicity. DSS-induced increases in Caco-2 monolayer permeability were also decreased as a result of SPC treatment. In a DSS-induced ulcerative colitis CF-1 mouse model, mice received 1.5% DSS for 7 days and consumed dietary SPC (6% or 12%) throughout the course of the study. Dietary SPC reduced colonic cytokine levels of IL-1β, IL-6, and monocyte chemotactic protein-1 (MCP-1). Gene expression of IL-1β, EGF-like Module-containing Mucin-like Hormone Receptor-Like 1 (EMR-1), nucleotide-binding oligomerization domain receptor-3 (NLRP3), and toll-like receptor 4 (TLR-4) were also observed. SPC decreased Caspase-1 activity, suggesting inhibition of inflammasome formation. In the mice, protein levels of glucagon-like peptide 2 (GLP-2) increased and mRNA expression of tight junction proteins, claudin-1 and occludin, tended to normalize as compared to the negative control. Our results suggest that SPC attenuates colonic inflammation in part by suppressing oxidative stress and intestinal permeability. Collectively, we have demonstrated that dietary treatment with EGCG and SPC can reduce inflammation and improve gut barrier function in DSS-induced ulcerative colitis in mice. These results are supported by studies of antioxidant and epithelial protective effects in cell culture. While the exact mechanism of each of the treatments remains to be investigated further, it suggests that dietary intervention with plant based phytochemicals may be a viable route to reducing inflammation and improving intestinal barrier function in the context of IBD.