Probiotic-derived extracellular vesicles attenuate cholestatic liver damage via gut-liver axis

Gut-liver axis disturbance is the unifying pathogenesis of cholestatic liver diseases. The purpose of this study was to explore the underlying mechanisms of the probiotic Lactobacillus amylovorus (LA) and its secreted extracellular vesicles (EVs) on liver damage and fibrosis in 3,5-diethoxycarbonyl-1,4-dihydrocollidine (DDC)-fed and multidrug resistance protein 2 knockout (Mdr2^-/-) mice. Direct replenishment of LA is sufficient to correct the DDC-fed and Mdr2^-/--induced liver damage and fibrosis. Mechanistic studies show that the secretion of EVs is required for the LA-induced liver protective effects. RNA sequencing results demonstrated that the enrichment of differentially expressed genes was associated with glutathione metabolism, microbial metabolism in diverse environments and inflammatory mediator regulation of TRP channels in DDC-fed mice. Our findings revealed that LAEVs reshaped the gut microbiota, which was associated with increased bile acids (BAs) deconjugation and fecal BAs excretion, repaired gut barrier function, activated intestinal Farnesoid X receptor/Fibroblast growth factor 15 (FXR/FGF-15) axis, reduced liver BAs and oxidative stress level, which ultimately mitigated liver damage and fibrosis in both DDC-fed and Mdr2^-/- mice. Notably, LAEVs did not ameliorate DDC-induced liver damage or fibrosis in antibiotic-treated mice. Furthermore, LAEVs provided protection against DDC-induced liver injury and fibrosis in fecal microbiota transplantation mice. LAEVs did not ameliorate DDC-induced liver damage or fibrosis in BSH inhibitor (CAPE)-treated mice. LAEVs also failed to improve liver damage and fibrosis in DDC-induced intestinal epithelial cell-specific FXR knockout (Fxr^△IE) mice. This study revealed that LAEVs mitigated cholestatic liver fibrosis via regulating gut microbiota-bile acid-ROS axis in mice.