Exercise-induced Metabolite N-lactoyl-phenylalanine Ameliorates Colitis by Inhibiting M1 Macrophage Polarization via the Suppression of the NF-κB Signaling Pathway

Although the anti-inflammatory benefits of exercise are well-documented, the specific mechanisms responsible for these advantages remain uncertain. N-lactoyl-phenylalanine (Lac-Phe), a major metabolite produced during exercise, is synthesized through the condensation of lactic acid and phenylalanine, catalyzed by the CNDP2. However, the potential anti-inflammatory properties of Lac-Phe remain poorly understood. This study aimed to investigate the anti-inflammatory effects of Lac-Phe in the context of inflammatory bowel disease (IBD) and to examine the underlying mechanisms. The levels of Lac-Phe were measured in both patients and mice with IBD utilizing enzyme-linked immunosorbent assay kits. The anti-inflammatory effects of Lac-Phe were demonstrated through colitis models. The impacts of Lac-Phe on macrophage polarization and the associated mechanisms were determined by flow cytometry, quantitative polymerase chain reaction, RNA sequencing, Western blotting, and immunofluorescence. Our study revealed a reduction in plasma Lac-Phe content in patients with IBD, in conjunction with a decrease in the expression of CNDP2 in the colon, which exhibited a negative correlation with disease activity scores. Exercise mitigated dextran sulfate sodium-induced colitis in mice by elevating plasma Lac-Phe levels and inhibiting the polarization of M1 macrophages. Mechanistically, Lac-Phe impedes the movement of p65 protein from the cytoplasm into the nucleus, consequently suppressing the activation of the NF-κB signaling pathway and macrophage M1 polarization. Furthermore, the supplementation of phenylalanine, a substrate of Lac-Phe, was observed to enhance the generation of Lac-Phe and to exert a protective effect in the murine colitis model. Our results suggest that exercise can induce the production of Lac-Phe, which plays a preventive role against dextran sulfate sodium-induced colitis in mice. Lac-Phe mitigates colitis through inhibition of the polarization of M1 macrophage. Adjusting macrophage polarization with Lac-Phe and phenylalanine supplementation may offer a potential therapeutic strategy for managing IBD.