The Protective Effects of <scp> <i>Lactobacillus reuteri</i> </scp> Combined With <scp> <i>Clostridium butyricum</i> </scp> Miyairi 588 on Intestinal Barrier Function, Water Transport, and Oxidative Stress in a Rat Model of <scp>5FU</scp> ‐Induced Di

5-Fluorouracil (5FU) is a commonly employed and highly effective chemotherapeutic agent in clinical oncology. Nevertheless, one of the most frequent and debilitating adverse effects associated with 5FU treatment is diarrhea. These gastrointestinal complications can affect patients' quality of life and adherence to treatment regimens. Consequently, addressing and mitigating diarrhea during 5FU therapy presents a critical and urgent challenge in oncological care. This study investigated whether probiotic <i>Lactobacillus reuteri</i> combined with <i>Clostridium butyricum</i> Miyairi 588 (LCs) can alleviate 5FU-induced diarrhea and the potential mechanism. Wistar rats received 5FU (50 mg/kg, intraperitoneal injection) for 5 consecutive days to establish a 5FU-induced colitis diarrhea model. LCs were administered 15 days before the 5FU injection and continued until the day of sacrifice. Tissue morphology, inflammatory and oxidative stress markers, as well as the expression of mRNA related to intestinal barrier integrity, apoptosis, and aquaporins (AQPs) were evaluated in the colon tissue samples. These analyses used hematoxylin and eosin staining, enzyme-linked immunosorbent assay (ELISA), and quantitative real-time reverse transcription-polymerase chain reaction (qRT-PCR) techniques. Additionally, the concentrations of short-chain fatty acids (SCFAs) were measured using gas chromatography-flame ionization detection (GC-FID) analysis. In this colitis model, LCs mitigated 5FU-induced weight loss, diarrhea, bloody stool, shortened colon length, and colonic histopathology. Treatment with LCs resulted in reduced levels of MDA, TNF-α, IL-1β, and MPO activity, as well as decreased mRNA expression of IFN-γ, AKT, NF-κB, TNF-α, and iNOS. Additionally, LCs significantly downregulated the expression of VCAM-1, CXCL4, MAPK, and caspase-3, while upregulating the tight junction protein occludin expression. LCs also notably diminished the mRNA expression levels of AQP7, VIP, and PKA. This study demonstrates that LCs have therapeutic effects on colitis, primarily through their antioxidant properties, anti-apoptotic effects, mucosal barrier integrity maintenance, neutrophil infiltration reduction, and inflammatory cytokines and aquaporin expression modulation.