Microbial metabolism 4-hydroxybenzoic acid protects against airway mucus secretion in ovalbumin-allergic mice

<bold>Background and Aims:</bold> Previous studies have found that the occurrence of asthma was related to the dysregulation of intestinal microbiota. This study aimed to investigate the effect of mucus secretion of probiotic Lactobacillus Rhamnosus 76 (LR76) on ovalbumin (OVA)-allergic mice and the mechanism of LR76 affecting mucus secretion in asthma. <bold>Methods:</bold> OVA-allergic mice were supplemented with LR76 and microbial metabolism to observe the effect of LR76. The mucous secretion of mouse lung tissue was exhibited by periodic acid-Schiff (PAS) staining and immunohistochemical (IHC) staining. Serum metabolites of mice were detected by high-performance liquid chromatography. Expression of AHR/NRF2 pathway was examined by western blot (WB). Reactive oxygen species (ROS) of lung tissue was detected by enzyme-linked immunosorbent assay (ELISA). <bold>Results:</bold> 1. LR76 alleviated mucus secretion (p<0.0001) and decreased the expression of MUC5AC in OVA sensitized mice (P<0.001). 2. Microbial metabolism 4-hydroxybenzoic acid (4-HB) was significantly increased after supplementing LR76 in OVA-allergic mice (p<0.05). 3. Metabolism 4-HB decreased mucus secretion (p<0.001) and decreased the expression of MUC5AC in OVA sensitized mice (P<0.01). 4. After supplementing 4-HB, expressions of AHR (p<0.01), NRF2 (P<0.01), and SOD1 (P<0.05) were increased, and expressions of ROS (P<0.01) and p-STAT6 (P<0.01) were decreased in OVA-allergic mice. <bold>Conclusions:</bold> LR76 improved mucus secretion in OVA-allergic mice may result from the activation of the AHR/NRF2 pathway by microbial metabolism 4-HB.