# Multi-omics reveals an association of the gut butyrate-IDO1-tryptophan axis with Yinchenhaotang plus Zexietang-ameliorated NASH in a microbiota-dependent manner

## TL;DR

This study shows that a traditional Chinese medicine improves NASH by altering gut bacteria and boosting butyrate and tryptophan metabolism.

## Contribution

The study identifies a microbiota-dependent mechanism involving the gut butyrate-IDO1-tryptophan axis in the therapeutic effects of YCHZX on NASH.

## Key findings

- YCHZX improved liver health and cholesterol levels more effectively than its individual components.
- YCHZX enriched butyrate-producing gut bacteria and suppressed IDO1, increasing ILA levels.
- Increased ILA strengthened gut barrier function and reduced liver inflammation via AhR activation.

## Abstract

Nonalcoholic steatohepatitis (NASH) is a complex metabolic disorder with limited effective treatments, and its pathogenesis involves intricate crosstalk between gut microbiota, metabolism, and host signaling. Yinchenhaotang plus Zexietang (YCHZX), a traditional Chinese medicine (TCM) formulation, exhibits therapeutic potential in NASH, but its underlying mechanism—especially its interactions with the gut microbiota and metabolic networks—remains unclear.

A NASH mouse model was established via a high-fat/high-fructose/high-cholesterol diet. Mice were treated with YCHZX or its individual components (YCH, ZX). Serum biochemistry and liver histopathology were used to evaluate systemic therapeutic effects. Integrated multi-omics analyses (16S rRNA microbiome, serum metabolomics, colon transcriptomics) combined with immunofluorescence, immunohistochemistry, RT‒qPCR and ELISA were employed to explore regulatory networks. Complementarily, the effects of sodium butyrate and indolelactic acid (ILA) were investigated using an LPS-stimulated Caco-2 cell model. Antibiotic-mediated gut microbiota ablation was performed to verify microbiota dependency.

YCHZX outperformed YCH and ZX in improving TC, LDL-C and hepatic pathology. Integrated multi-omics analysis demonstrated that the efficacy of YCHZX was associated with a distinct restructuring of the gut microbiota, specifically enriching butyrate-producing genera such as Lachnospiraceae_NK4A136_group. Concomitantly, YCHZX intervention suppressed colonic indoleamine 2,3-dioxygenase 1 (IDO1) and significantly elevated serum levels of ILA, a shift validated in vitro by the direct inhibitory effect of sodium butyrate on IDO1. The elevated ILA was shown to strengthen the gut barrier by upregulating occludin expression in LPS-stimulated Caco-2 cells via an aryl hydrocarbon receptor (AhR)-dependent mechanism. Further, YCHZX activated the AhR, upregulating tight-junction proteins (occludin) to reduce lipopolysaccharide (LPS) translocation, and inhibiting hepatic LPS/TLR4 signaling, TG accumulation, and IL-1β inflammation. All these effects of YCHZX were diminished by antibiotic-induced gut microbiota depletion.

Our findings demonstrate that YCHZX alleviates NASH in a gut microbiota-dependent manner. We propose a mechanism whereby YCHZX enriches butyrate-producing bacteria, which is associated with the suppression of colonic IDO1 and a shift in tryptophan metabolism toward ILA production. The increased ILA, in turn, contributes to the activation of the AhR, thereby restoring gut barrier integrity and mitigating liver inflammation.

The online version contains supplementary material available at 10.1186/s13020-025-01304-w.