Er-Chen Decoction ameliorates metabolic dysfunction–associated steatotic liver disease via gut microbiota-barrier axis-driven hepatic metabolic reprogramming

Background: Metabolic dysfunction-associated steatotic liver disease (MASLD) constitutes a critical global health challenge, with gut-liver axis dysfunction and metabolic endotoxemia serving as key drivers. The traditional Chinese medicinal formula Er-Chen Decoction (ECD) has proven effective in treating metabolic disorders, yet the specific mechanisms by which it modulates gut-liver crosstalk have not been fully elucidated. Methods: A mouse model of MASLD was established via a high-fat diet (HFD). The therapeutic effects of ECD were evaluated using the glucagon-like peptide-1 (GLP-1) receptor agonist semaglutide (SE) as a positive control. A comprehensive analysis of the underlying mechanisms of ECD treatment was conducted by integrating fecal metagenomic sequencing, untargeted serum metabolomic profiling, hepatic transcriptomic analysis, and molecular biology assays. Results: was markedly and specifically elevated following ECD treatment. Serum metabolomic profiling revealed that ECD specifically activated the tryptophan-indole metabolic pathway, as evidenced by elevated concentrations of indoleacrylic acid and indole-3-acetic acid. Correlation analyses established a strong positive correlation between these indole derivatives and the bacterial genera enriched by ECD. Mechanistically, our findings suggest that elevated indoles activate the aryl hydrocarbon receptor (AHR) in the colon, upregulating tight junction proteins ZO-1 and Occludin and restoring intestinal barrier integrity, thereby significantly reducing serum lipopolysaccharide (LPS) levels. In hepatic tissue, the diminished LPS influx alleviated the suppression of DNA methyltransferase 3B (DNMT3B), thereby promoting the epigenetic silencing of the lipid droplet fusion protein CIDEA and inhibiting pathological hepatic lipogenesis. Conclusion: Our findings elucidate a novel mechanism through which ECD may ameliorate MASLD via the distinctive "gut microbiota-indole-barrier" axis. In contrast to SE, ECD modulates gut microbiota composition to boost indole production and subsequently activate AHR signaling. This activation inhibits endotoxin translocation and induces hepatic DNMT3B-mediated epigenetic reprogramming to reverse hepatic steatosis. These results offer scientific evidence supporting the potential of ECD as an effective therapeutic strategy for MASLD.