Bisphenol-A alters microbiota metabolites derived from aromatic amino acids and worsens disease activity during colitis

Abstract

Inflammatory bowel disease is a complex collection of disorders. Microbial dysbiosis as well as exposure to toxins including xenoestrogens are thought to be risk factors for inflammatory bowel disease development and relapse. Bisphenol-A has been shown to exert estrogenic activity in the colon and alter intestinal function, but the role that xenoestrogens, such as bisphenol-A , play in colonic inflammation has been previously described but with conflicting results. We investigated the ability of bisphenol-A to exacerbate colonic inflammation and alter microbiota metabolites derived from aromatic amino acids in an acute dextran sulfate sodium-induced colitis model. Female C57BL/6 mice were ovariectomized and exposed to bisphenol-A daily for 15 days. Disease activity measures include body weight, fecal consistency, and rectal bleeding. Colons were scored for inflammation, injury, and nodularity. Alterations in the levels of microbiota metabolites derived from aromatic amino acids known to reflect phenotypic changes in the gut microbiome were analyzed. Bisphenol-A exposure increased mortality and worsened disease activity as well as inflammation and nodularity scores in the middle colon region following dextran sulfate sodium exposure. Unique patterns of metabolites were associated with bisphenol-A consumption. Regardless of dextran sulfate sodium treatment, bisphenol-A reduced levels of tryptophan and several metabolites associated with decreased inflammation in the colon. This is the first study to show that bisphenol-A treatment alone can reduce microbiota metabolites derived from aromatic amino acids in the colon which may be associated with increased colonic inflammation and inflammatory bowel disease. Impact statement As rates of inflammatory bowel disease rise, discovery of the mechanisms related to the development of these conditions is important. Environmental exposure is hypothesized to play a role in etiology of the disease, as are alterations in the gut microbiome and the metabolites they produce. This study is the first to show that bisphenol-A alone alters tryptophan and microbiota metabolites derived from aromatic amino acids in a manner consistent with autoimmune diseases, specifically inflammatory bowel diseases, regardless of dextran sulfate sodium treatment. These findings indicate a potential mechanism by which bisphenol-A negatively affects gut physiology to exacerbate inflammation.

Keywords: Bisphenol-A; colitis; inflammatory bowel disease; microbiota metabolites; tryptophan; xenoestrogen.

Figure 1.

Experimental design.

Figure 2.

Survival curve. Animals alive at start of day, expressed as percent of total group size at start of experiment. n = 10 to 12 per group at the start of the study and declined over time as shown. Log-rank P < 0.0001. *indicates significant difference; P < 0.05.

Figure 3.

Measures of disease activity. Scoring system adapted from Murthy et al. Dig Dis Sci 1993 and Singh et al. Immunity 2014. n = 10 to 12 per group at the start of the study; n declined over time as shown in the survival curve. Mean ± SEM. Points without a common letter differ on the given day; P < 0.05. (a) Average body weight. (b) Average fecal score. Scoring system: 0 = Normal stool, 1 = Soft but formed pellet, 2 = Very soft pellet, 3 = Diarrhea (no pellet), 4 = Dysenteric diarrhea (blood in diarrhea). (c) Average rectal bleeding score. Scoring system: 0 = No visible blood, 2: presence of visible blood in stool (red/dark pellet), 4: gross macroscopic bleeding (blood around anus). (d) Disease activity index. Average of body weight loss, fecal consistency, and rectal bleeding scores.

Figure 4.

(a) BPA and colonic inflammation in the absence of DSS. (b) BPA and colonic inflammation in the presence of DSS. (c) Nodularity in the presence of DSS. Mean ± SEM. *indicates significant difference compared to control; P < 0.05. (d) Representative image of increased inflammation in middle portion of colon. Inflamed portion of the middle colon is indicated by black arrows. (e) Representative image of ulceration in the colon. Ulcer is indicated by the black arrow. (f) Representative image of erosion of the colon. Erosion is indicated by the black arrow. (g) Representative image of nodular inflammation. Nodular inflammation is indicated by the black arrow. (h) Representative image of diffuse inflammation. Diffuse inflammation is indicated by the black arrow. (A color version of this figure is available in the online journal.)

Figure 5.

Concentration of cytokines in the middle portion of colon. (a) IL-1α. (b) IL-12p(70). (c) IL-13. (d) IL-31. (e) VEGF. Mean ± SEM. Bars without a common letter differ; P < 0.05.

Figure 6.

Concentration of specific metabolites in feces on day 8 in control compared to BPA-treated animals in the absence of DSS treatment. (a) 3-indole acetic acid. (b) 5-hydroxy indole 3-acetic acid. (c) Anthranilic acid. (d) Indole 3-acetamide. (e) Indole 3-carboxaldehyde. (f) Serotonin. (g) Shikimic Acid. (h) Tryptamine. (i) Tryptophan. Mean ± SEM. *indicates significant difference compared to control; P < 0.05.

Figure 7.

Concentration of specific metabolites in feces on day 8 in control compared to BPA treated co-treated with DSS. (a) 3-indole acetic acid. (b) 5-hydroxy indole 3-acetic acid. (c) Anthranilic acid. (d) Indole 3-acetamide. (e) Indole 3-carboxaldehyde. (f) Serotonin. (g) Shikimic acid. (h) Tryptamine. (i) Tryptophan. Mean ±SEM. *indicates significant difference compared to DSS alone; P < 0.05.