Gut microbiota-derived lactate alleviates intestinal ischemia-reperfusion injury by suppressing macrophage M1 polarization via the NF-κB pathway.

BACKGROUND: Intestinal ischemia-reperfusion (I/R) injury is a critical clinical condition whose pathogenesis is closely associated with immune-inflammatory responses. In this process, macrophage polarization plays a pivotal role in the initiation and progression of inflammation. While lactate, a microbial metabolite, has been shown to exert significant immunomodulatory effects and can influence macrophage polarization. Therefore, this study aimed to investigate the function of lactate and macrophage polarization in I/R injury. OBJECTIVE: This study aimed to investigate whether gut microbiota-derived lactate regulates macrophage M1 polarization via the NF-κB signaling pathway, thereby mitigating intestinal I/R injury. METHODS: A rat model of intestinal I/R injury was established. A time gradient of reperfusion was set to determine the optimal time point for observation. Interventions including macrophage depletion, antibiotic treatment, lactate administration, and NF-κB inhibition were employed. Intestinal injury severity, macrophage polarization status, and NF-κB pathway activity were analyzed using histopathology, immunofluorescence, Western blot, and qPCR. For in vitro experiments, macrophages were treated with LPS and/or lactate, with polarization phenotypes assessed by flow cytometry and immunofluorescence. RESULTS: Comparative analysis of Sham, I/R, and macrophage-depleted (I/R+MPD) groups revealed an increased proportion of M1 macrophages following I/R, while macrophage depletion attenuated intestinal injury, demonstrating the involvement of M1 polarization in I/R pathology. Time-course analysis demonstrated that the proportion of M1 macrophages peaked at 2-6 h of reperfusion, whereas intestinal lactate content reached its minimum at 2 h after reperfusion. Comparison among Sham, I/R, and antibiotic-treated (I/R+ABX) groups showed that gut microbiota depletion exacerbated intestinal injury and increased M1 macrophage proportion, indicating a protective role of gut microbiota against I/R injury. Furthermore, in vitro lactate treatment reduced M1 polarization in RAW264.7 cells. In vivo lactate administration alleviated intestinal tissue damage and decreased serum levels of pro-inflammatory cytokines secreted by M1 macrophages. Finally, Western blot analysis confirmed that lactate treatment suppressed phosphorylation of NF-κB pathway proteins p65 and IκBα. CONCLUSION: The gut microbiota metabolite lactate may alleviate intestinal I/R injury by inhibiting the NF-κB pathway and reducing macrophage M1 polarization.