Metformin and butyrate attenuate chronic radiation proctitis by alleviating inflammation and macrophage senescence

Chronic radiation proctitis (RP) is characterized by persistent inflammation and impaired tissue repair. This study investigates the potential of a metformin-butyrate (MeBu) combination to modulate radiation-induced senescence-associated changes in macrophages to mitigate chronic injury.

BALB/c mice received a 15 Gy fraction of rectal brachytherapy. From weeks 4 to 8 post-irradiation, mice were treated with rectal enemas of metformin, butyrate, or the MeBu combination. Tissue histology (H&E and Masson's Trichrome staining), macrophage polarization (iNOS/CD163) were evaluated. Effects on senescence markers were analyzed in irradiated bone marrow-derived macrophages (BMDMs) using SA-β-gal staining and qPCR for p16 and p21. A composite Senescence Burden Index (SBI) was developed to integrate transcriptional senescence signals.

MeBu treatment was associated with a reduction in mucosal fibrosis and a phenotypic shift in macrophages toward a more reparative M2-like profile (increased CD163/iNOS ratio). In BMDMs, MeBu significantly reduced SA-β-Gal positivity and suppressed p21 expression (p = 0.0074), with a downward trend in p16 (p = 0.0568). The integrated SBI demonstrated that MeBu significantly attenuated the overall senescence burden compared to the irradiated group (p < 0.01). This combined effect was more robust than that of either metformin or butyrate alone.

Our findings suggest that the MeBu combination may attenuate chronic RP by modulating macrophage-associated senescence and inflammation. These results indicate that metabolic-based senomorphic strategies hold potential to mitigate chronic inflammatory sequelae following pelvic radiotherapy.