Liuweidihuang Pill Attenuates Early Bleomycin-Induced Pulmonary Fibrosis in Mice and Is Associated with Gut Microbiome

Background: Pulmonary fibrosis (PF) is a chronic, progressive lung disease with limited treatment options. Liuweidihuang pill (LDP), a classical formula for kidney-yin deficiency, has been reported to have anti-inflammatory and anti-oxidative activities, suggesting potential relevance to PF. Purpose: This study evaluated whether LDP attenuates bleomycin-induced PF in mice and whether gut microbiota remodeling may contribute to its protective effects. Methods: Mice received intratracheal bleomycin followed by LDP gavage. Lung pathology was assessed by hematoxylin–eosin (HE) and Masson staining. Inflammatory cytokines, hydroxyproline (HYP), and α-SMA were measured. LDP and LDP-containing serum were profiled by UPLC-MS. The gut microbiota was analyzed using 16S rDNA sequencing. To further explore whether microbiota-related changes were associated with the protective phenotype, fecal microbiota transplantation (FMT) and probiotic VSL#3 intervention were performed. In addition, LDP-containing serum was tested in a TGF-β1-induced EMT model in A549 cells. Results: LDP reduced lung index, inflammatory infiltration, interstitial fibrosis, α-SMA expression, HYP content, and pro-inflammatory cytokine levels in bleomycin-treated mice. These effects were accompanied by gut microbiota remodeling and transcriptomic changes related to inflammation, metabolism, and fibrosis. VSL#3 partially reproduced the protective phenotype, whereas FMT showed limited efficacy. LDP-containing serum had a limited inhibitory effect on EMT inhibited EMT in vitro, suggesting that systemic host responses may contribute to the in vivo effect. Conclusions: LDP attenuated early bleomycin-induced PF and was associated with reduced inflammation and gut microbiota remodeling. These findings suggest a possible role for microbiota–host interactions in LDP-associated protection; however, causal directionality, key active effectors, and protein-level pathway validation remain unresolved.