The purpose of this study was to clarify the effects of fish oil on the gut microbiota of rats with alcoholic liver damage. Thirty-six male Wistar rats (8 weeks old) were divided into six groups: C (control), CF25 (control diet with 25% fish oil substitution), CF57 (control diet with 57% fish oil substitution), E (ethanol-containing diet), EF25 (ethanol-containing diet with 25% fish oil substitution), and EF57 (ethanol-containing diet with 57% fish oil substitution) groups. All groups were pair-fed an isoenergetic diet based on the E group. Rats were sacrificed after 8 weeks. Rats in the E group showed significant hepatic injuries including high plasma aspartate transaminase and alanine transaminase activities, hepatic cytokine levels, plasma endotoxin level, and protein expression of the toll-like receptor-4 signaling pathway; moreover, lipid accumulation and inflammation based on histological examinations were also observed. In contrast, these phenomena was ameliorated in rats of the EF25 and EF57 groups. Although the intestinal structure did not change among the groups, alterations in the gut microbiotic composition were observed due to chronic ethanol intake and fish oil replacement such as the Firmicutes-to-Bacteroidetes ratio, Chao-1 index, ACE index, a principal component analysis and linear discriminant analysis of effect size. In terms of the gut-liver axis, this study confirmed that fish oil replacement exerted ameliorative effects on ethanol-induced liver injuries in rats by acting through alterations in the microbiotic composition.
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