Bacteroides fragilis-derived nicotinamide riboside attenuates radiation-induced intestinal injury by suppressing Gasdermin E-mediated pyroptosis in intestinal epithelial cells

Introduction : IR (IR) is a common complication in patients with colorectal cancer (CRC) after radiotherapy. Currently, the search for effective treatments has become an urgent priority. Nicotinamide riboside (NR), the precursor of vitamin B3 derivative and NAD (+), was enriched in IR after treatment with commensal Bacteroides fragilis , suggesting that NR may perform a protective role. However, the specific role of NR in IR remains unclear. In this study, we investigated the therapeutic effects of NR on IR. Methods : C57BL/6J, Gsdme ^ΔIEC (lacking GSDME in intestinal epithelial cells, IECs), and wild-type littermates were treated with NR after abdominal radiation exposure at 10Gy. The intestinal crypt-derived organoids and cell lines FHC, NCM460, and IEC-6 were irradiated with or without administration of the SIRT1 inhibitor EX527 under NR stimulation. A series of assays were subsequently carried out to explore the therapeutic effects, the degree of IECs repair, and the underlying mechanism. Results : NR significantly ameliorated IR in mice, as evidenced by reduced weight loss, shortened intestinal and colonic length, improved histological associated index, and restored the intestinal flora, which increased the relative abundance of the commensal Muribaculaceae , and decreased the relative abundance of Escherichia_coli . Additionally, NR increased goblet cell density, increased crypt length, promoted Ki-67 and ZO-1 expression, reduced reactive oxygen species (ROS) levels, and maintained mitochondrial morphology in IECs. Mechanistically, NR activated SIRT1 and inhibited gasdermin E (GSDME)-induced pyroptosis. Further investigations using an experimental Gsdme ^ΔIEC mouse model (lacking GSDME in IECs) and a SIRT1 inhibitor revealed that NR promoted intestinal barrier repair through GSDME inhibition in a SIRT1-dependent manner. Compared with those in healthy controls, the GSDME level in radiation-injured intestinal mucosa from CRC patients after radiotherapy increased with the downregulation of SIRT1, Ki-67, and ZO-1. Conclusion : Our study demonstrated that NR mitigates IR by inhibiting GSDME-mediated pyroptosis and restoring IECs homeostasis. These findings suggest that NR could serve as a promising therapeutic strategy for IR following radiotherapy.