Selenium-Containing Amino Acids Protect Dextran Sulfate Sodium-Induced Colitis via Ameliorating Oxidative Stress and Intestinal Inflammation

Abstract

Background: Inflammatory bowel disease (IBD) is characterized by chronic relapsing inflammation of the gastrointestinal tract. Oxidative stress plays a pivotal role in the pathogenesis of IBD. Selenium-containing amino acids reportedly have anti-oxidative and anti-inflammatory properties, but it remains unknown if selenium-containing amino acids can be used to treat IBD. This study aimed to investigate the effects of two selenium-containing amino acids - selenocysteine and selenocystine - on oxidative stress and chronic inflammation in a mouse model of dextran sulfate sodium (DSS)-induced IBD.

Methodology: C57BL/6 mice were randomly assigned to the following six groups: control, DSS, DSS+selenocysteine, DSS+selenocystine, DSS+sodium selenite, and DSS+N-acetylcysteine (NAC). IBD was induced by 3% DSS. Pro-inflammatory cytokines [interleukin-1β (IL-1β), monocyte chemotactic protein 1 (MCP-1), IL-6, and tumor necrosis factor-α (TNF-α)] and markers for oxidative and anti-oxidative stress [malondialdehyde (MDA), reactive oxygen species (ROS), superoxide dismutase (SOD), and glutathione peroxidase (GPx)] were measured using immunohistochemical analysis.

Results: Selenocysteine and selenocystine significantly attenuated IBD-related symptoms, including preventing weight loss, decreasing disease activity index (DAI) scores, and increasing colon length. Selenocysteine and selenocystine significantly ameliorated the DSS-induced oxidative stress, as demonstrated by a reduction in ROS and MDA activity and an increase in SOD and GPx activity. IL-1, MCP-1, IL-6, and TNF-α levels were significantly increased in the IBD mice, while treatment with the selenium-containing amino acids significantly reduced the levels of these pro-inflammatory cytokines. In vivo safety analysis showed minimal side effects of the selenium-containing amino acids.

Conclusion: We found that selenocysteine and selenocystine ameliorated DSS-induced IBD via reducing oxidative stress and intestinal inflammation, indicating that selenium-containing amino acids could be a novel therapeutic option for patients with IBD.

Keywords: Inflammatory bowel diseases; colitis; inflammation; oxidative stress; selenium-containing amino acids; selenocysteine; selenocystine.

Figure 1

Chemical structure of selenium-containing amino acids used in this study. Chemical structure of (A) selenocystine and (B) selenocysteine.

Figure 2

Effects of selenium-containing amino acids on the main symptoms of IBD in mice. Weight loss, DAI scores, and colon length were compared between groups. (A) Weight loss; (B) DAI scores; (C) colon length; and (D) colon images in different groups. Eight mice per group; ^#P < 0.05, compared with DSS group. ^$P < 0.05, compared with selenocysteine group. ^&P < 0.05, compared with selenocystine group. Data are expressed as mean ± SEM.

Figure 3

Histological examinations of effects of selenium-containing amino acids on DSS-induced IBD in mice. (A) Representative H&E-stained colon sections of each group (scale bar, 200 μm); (B) Histological scoring of mice treated with selenium-containing amino acids in DSS-induced IBD. Eight mice per group; ^#P < 0.05, compared with DSS group. ^$P < 0.05, compared with selenocysteine group. ^&P < 0.05, compared with selenocystine group. Data are expressed as mean ± SEM.

Figure 4

Effects of selenium-containing amino acids on oxidative stress markers in DSS-induced IBD in mice. Levels of oxidative stress markers including (A) ROS, (B) SOD, (C) MDA, and (D) GPx in colon tissues from different groups. Eight mice per group; ^#P < 0.05, compared with DSS group. ^$P < 0.05, compared with selenocysteine group. ^&P < 0.05, compared with selenocystine group. Data are expressed as mean ± SEM.

Figure 5

Effects of selenium-containing amino acids on levels of pro-inflammatory cytokines in DSS-induced IBD in mice. Levels of (A) IL-1β, (B) IL-6, (C) MCP-1, and (D)TNF-α in colon tissues of mice from different groups. Eight mice per group; ^#P < 0.05, compared with DSS group. ^$P < 0.05, compared with selenocysteine group. ^&P < 0.05, compared with selenocystine group. Data are expressed as mean ± SEM.

Figure 6

Effects of selenium-containing amino acids on biochemical test parameters in DSS-induced IBD in mice. Serum levels of (A) ALT, (B) AST, (C) BUN, and (D) CRE in different groups. Differences were assessed via one-way analysis of variance (ANOVA) with Tukey’s multiple comparison tests. Six mice per group; Data are expressed as mean ± SEM.

Figure 7

Histological examination of the safety of selenium-containing amino acids. Lung, kidney, heart, liver, and spleen tissues were collected, H&E stained, and analyzed for the safety profile of selenium-containing amino acids. Scale bar is 100 μm.