Phyllanthin Targets GBP5 to Suppress Macrophage M1 Polarization and Alleviate DSS-Induced Colitis in a Murine Model

In traditional practice, Phyllanthus species are utilized to address gastrointestinal ailments, including dysentery and diarrhea. A major bioactive lignan, Phyllanthin (PHY), which is a substance of this genus, has been reported to exhibit anti-inflammatory activity. This evidence provides a strong rationale for investigating its role in inflammatory bowel disease (IBD).

This study aimed to investigate the therapeutic potential of PHY, a lignan of Phyllanthus species, in the dextran sulfate sodium (DSS)-induced murine colitis model with the aim of elucidating its dual role in decreasing intestinal inflammation and repairing the intestinal barrier.

C57BL/6 mice were utilized to establish a DSS-induced experimental colitis model, with treatment of PHY at 10, 20, 40 mg/kg. Disease severity was evaluated based on changes in body weight, DAI scores, colon length, histological examination, and endoscopic findings. Intestinal barrier function was evaluated via FITC-dextran permeability, transmission electron microscopy, immunofluorescence of tight junction proteins, and AB-PAS staining. The macrophage polarization in colonic tissues and LPS + IFN-γ/IL-4 + IL-13 stimulated RAW264.7 cells were assessed using flow cytometry, ELISA, RT-qPCR, and immunofluorescence. The mechanism was investigated through transcriptomic sequencing, molecular docking, GTPase activity assays, and in vitro/vivo GBP5 gain-and loss-of-function studies.

PHY administration significantly ameliorated DSS-induced colitis, as manifested by mitigated body weight loss, improved DAI scores, restored colon length, and diminished pathological damage, all in a dose-dependent manner. PHY also markedly restored intestinal barrier integrity, as demonstrated by decreased permeability, ultrastructural repair of tight junctions, and upregulation of ZO-1, Claudin-1, and MUC2. Most importantly, PHY could selectively inhibit pro-inflammatory M1 macrophage polarization in colonic mucosa and in vitro, and did not markedly promote M2 macrophage polarization-associated markers or phenotype under our experimental conditions. Further investigation revealed that PHY likely directly binds to the GBP5 GTPase domain, thereby impeding its GTPase activity and counteracting its upregulation induced by LPS/IFN-γ. Furthermore, GBP5 knockdown reproduced the inhibitory effect of PHY on M1 polarization, whereas GBP5 overexpression exacerbated colitis.

Collectively, our gain-of-function and loss-of-function experiments have confirmed that PHY is a promising therapeutic agent. It alleviates experimental colitis by targeting GBP5 to regulate M1 macrophage polarization and restore intestinal barrier function. Mechanistically, PHY may inhibit the enzymatic activity of GBP5 by engaging its GTP-binding pocket. This study not only identifies PHY as an attractive lead compound for the treatment of IBD but also provides robust experimental evidence that GBP5 is a promising therapeutic target for inflammatory diseases.