Hydrogen inhalation ameliorates hepatic inflammation and modulates gut microbiota in rats with high-fat diet-induced non-alcoholic fatty liver disease

Nonalcoholic fatty liver disease (NAFLD) is a multisystem metabolic disease associated with gut microflora dysbiosis and inflammation. Hydrogen (H-2) is a novel and effective antiinflammatory agent. The present study was aimed to clarify the effects of 4% H-2 inhalation on NAFLD and its mechanism of action. Sprague-Dawley rats were fed a high-fat diet for 10 weeks to induce NAFLD. Rats in treatment group inhaled 4% H-2 each day for 2 h. The protective effects on hepatic histopathology, glucose tolerance, inflammatory markers, and intestinal epithelial tight junctions were assessed. Transcriptome sequencing of liver and 16 S-seq of cecal contents were also performed to explore the related mechanisms of H-2 inhalation. H-2 improved the hepatic histological changes and glucose tolerance, decreased the liver function parameters of plasma alanine aminotransferase and aspartate aminotransferase, and relieved liver inflammation. Liver transcriptomic data suggested that H-2 treatment significantly downregulated inflammatory response genes, and the lipopolysaccharide (LPS)/Toll-like receptor (TLR) 4/nuclear transcription factor kappa B (NF-kappa B) signaling pathway might be involved, and the expressions of critical proteins were further validated. Meanwhile, the plasma LPS level was significantly decreased by the H-2 intervention. H-2 also improved the intestinal tight junction barrier by enhancing the expressions of zonula occludens-1 and occluding. Based on 16S rRNA sequencing, H-2 altered the composition of gut microbiota, improving the relative abundance of Bacteroidetes-to-Firmicutes. Collectively, our data show that H-2 could prevent NAFLD induced by high-fat diet, and the anti-NAFLD effect is associated with the modulation of gut microbiota and inhibition of LPS/TLR4/NF-kappa B inflammatory pathway.