Ginsenoside Rg1 Alleviates Acute Ulcerative Colitis by Modulating Gut Microbiota and Microbial Tryptophan Metabolism

Abstract

Ulcerative colitis (UC) is a chronic and recurrent inflammatory disorder in the gastrointestinal tract. Here, we examined the pharmacological effects of ginsenoside Rg1, a natural compound with low bioavailability, on the acute experimental colitis mice induced by dextran sulfate sodium (DSS) and explored underlying mechanisms. Acute UC was induced in C57BL/6 mice by 2.5% DSS for 7 days, meanwhile, 2 mg/10 g b.w. ginsenoside Rg1 was administrated to treat the mice. Body weight, colon length, colon tissue pathology, and colon tissue inflammatory cytokines were assessed. The composition structure of gut microbiota was profiled using 16s rRNA sequencing. Global metabolomic profiling of the feces was performed, and tryptophan and its metabolites in the serum were detected. The results showed that Rg1 significantly ameliorated DSS-induced colonic injury and colonic inflammation. In addition, Rg1 also partly reversed the imbalance of gut microbiota composition caused by DSS. Rg1 intervention can regulate various metabolic pathways of gut microbiota such as valine, leucine, and isoleucine biosynthesis and vitamin B6 metabolism and the most prominent metabolic alteration was tryptophan metabolism. DSS decreased the levels of tryptophan metabolites in the serum, including indole-3-carboxaldehyde, indole-3-lactic acid, 3-indolepropionic acid, and niacinamide and Rg1 can increase the levels of these metabolites. In conclusion, the study discovered that Rg1 can protect the intestinal barrier and alleviate colon inflammation in UC mice, and the underlying mechanism is closely related to the regulation of gut microbiota composition and microbial tryptophan metabolism.

Keywords: ginsenoside Rg1; gut microbiota; metabolomics; tryptophan; ulcerative colitis.

Figure 1

The effect of Rg1 on the DSS-induced UC mice. (A) Chemical structure of ginsenoside Rg1. (B) Inducement of UC mice model and the treatment of Rg1. (C) Daily changes in body weight of each group during UC mice model induction. (D) Changes in fecal bleeding of each group during UC mice model induction. (E) Changes in fecal viscosity of each group during UC mice model induction. (F) Colon length was measured for each group on the 7^th day. Significance levels are indicated as *P < 0.05, ***P < 0.001 and ns stands for not statistically significant.

Figure 2

The changes of colonic histopathology and inflammatory factors. (A-1) HE staining results in colon tissue. (A-2) AB-APS staining results of colon tissue. (B, C) The levels change of inflammatory factors including in colon tissues of each group, including IL-2 and TNF-α. (D) Histopathological score of three groups. P < 0.05 was considered to be statistically significant. Significance levels are indicated as ***P < 0.001 and ns stands for not statistically significant.

Figure 3

The change of the gut microbiota after DSS and Rg1 intervention. (A) The Venn diagram shows the overlap of OTUs in each group. Alpha diversity indicators: Ace (B-1) and Chao (B-2) show the change in community richness. The bars represent the maximum, upper quartile, median, lower quartile, and minimum from top to bottom. (C) PCoA analysis reflects the similarities and differences among the three groups. (D) Histogram shows the percent of community abundance on the phylum level. (E) The differential bacteria among three groups at the phylum level. (F) The differential bacteria among three groups at the genus level. P < 0.05 was considered to be statistically significant. Significance levels are indicated as *P < 0.05, **P < 0.01, and ***P < 0.001.

Figure 4

Rg1 modulated the fecal metabolism in ESI positive ion mode. (A) QA analysis result shows the reliability of the data. (B) PCA score plots show that reflect the distribution of all samples. (C) OPLS-DA sore plot reflects the difference between the Control group and the DSS group. (D) OPLS-DA sore plot reflects the difference between the DSS group and the Rg1 group. (E) The volcano map reflects the different specific metabolites between the Control group and the DSS group. (F) The volcano map reflects the different specific metabolites between the DSS group and the Rg1 group.

Figure 5

KEGG pathway enrichment analysis of differential metabolites.

Figure 6

The change of serum tryptophan and its metabolites in all groups. Data are shown as mean ± SD (n=6). P < 0.05 was considered to be statistically significant. Significance levels are indicated as *P < 0.05, **P < 0.01, ***P < 0.001, and ns stands for not statistically significant.