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

INTRODUCTION: 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. MATERIALS AND METHODS: 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. RESULTS: 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. CONCLUSION: 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.