Ethnopharmacological relevance

Citrus depressa, traditionally used in Chenpi preparations for respiratory ailments, was previously shown in our studies to exhibit anti-SARS-CoV-2 activity.

Aim of the study

This study aims to investigate the therapeutic potential of C. depressa and to clarify its underlying mechanism in pulmonary fibrosis.

Materials and methods

We prepared an ethanolic extract of Citrus depressa (Cd) and assessed its activity following oral administration in a bleomycin-induced BEAS-2B cell and murine model by measuring TGF-β1, epithelial-mesenchymal transition (EMT), and extracellular matrix (ECM) level. Metabolomics was performed on mouse blood, urine, feces, and lung tissue, with pathway enrichment analysis using Ingenuity Pathway Analysis (IPA) highlighting aromatic amino acids (AAA). Serum pharmacology identified potential flavonoids, which, along with the AAA, were then validated in our established animal model. Finally, targeted metabolomics mapped in-vivo metabolic pathway, and enzyme expression in related pathways was measured.

Results

In this study, we demonstrated that C. depressa extract (Cd) alleviates bleomycin (BLM)-induced pulmonary fibrosis in both cell and murine models by reducing TGF-β1 levels, suppressing EMT, and limiting EC accumulation. Metabolomic profiling revealed increased levels of endogenous aromatic amino acids and significant activation of the tryptophan catabolism pathway, suggesting its involvement in the anti-fibrotic effect. Notably, administration of AAA in fibrotic mice produced comparable therapeutic effects to Cd and restored kynurenine pathway in lung tissue, supporting the mechanistic link.

Conclusion

These results suggest that Cd may mitigate lung fibrosis, possibly by raising endogenous aromatic amino acid levels and modulating the kynurenine pathway. Collectively, these results suggest that both Cd and AAA hold therapeutic potential for pulmonary fibrosis and warrant further investigation in clinical settings.