Acute ammonia exposure induces hepatic lipid metabolism disorders in wild burbot (lota lota) via the gut-liver axis: New insight into conservation of threatened species.

Accumulating evidence indicates that exogenous toxins can induce lipid metabolic disorders by influencing the gut microbiome. However, the effects of ammonia nitrogen on the gut microbiota and hepatic lipid metabolism of the burbot (lota lota) remain unknown. Therefore, we integrated biochemical measurements, 16S rDNA sequencing, and transcriptomic analysis to evaluate the impact of 96 h of ammonia nitrogen exposure on oxidative stress, the immune response, lipid metabolism, and gut microbiota in the liver and intestine of lota lota. In this study, lota lota exhibited oxidative damage and immunosuppression following ammonia nitrogen exposure, as evidenced by decreased antioxidant and immune enzyme activities and a concomitant increase in malondialdehyde (MDA) content. Furthermore, ammonia nitrogen exposure altered gut microbial diversity: the abundance of Proteobacteria decreased, whereas that of Bacteroidota and Firmicutes increased. In addition, transcriptomic analysis revealed that the expression of genes related to fatty acid metabolism (fabp, elovl6, pltp) and gut barrier dysfunction (collagen, ecm) was altered. Notably, lipopolysaccharide (LPS) was identified as a key microbial-derived signal triggered by ammonia nitrogen, as demonstrated by ELISA. The translocation of LPS from gut to liver, resulting from compromised intestinal barrier integrity, activated the gut-liver axis and contributed to hepatic lipid metabolic disorders. Overall, the current study elucidates the gut-liver axis-mediated mechanism of ammonia nitrogen toxicity and provides valuable information for understanding the toxic effects of ammonia nitrogen on lota lota and conserving this threatened cold-water species.