18β-Glycyrrhetinic acid mitigates adverse effects of high-fat diets on liver fibrosis in largemouth bass (Micropterus salmoides) by reducing mitochondrial Ca2+ level

Appropriately increasing the level of fat in feed exhibits potential protein-saving effects, but high levels of fat in the feed can cause liver injury in fish of largemouth bass. 18β-Glycyrrhetinic acid (GA), a natural extract from <i>G</i> <i>lycyrrhiza</i>, has been shown to enhance growth performance and improve intestinal health in animals. Thus, the present study was to investigate the effects of dietary GA on high-fat-induced liver fibrosis and the potential mechanisms in juvenile largemouth bass. The experiment comprised five different diets, including normal control (NC) diet (NC group), high-fat (HF) diet (HF group), HF diet supplemented with 0.5 mg/kg GA (HFL group), HF diet supplemented with 1.0 mg/kg GA (HFM group), and HF diet supplemented with 1.5 mg/kg GA (HFH group). A total of 750 healthy largemouth bass with an initial average weight of 17.39 ± 0.09 g were selected and randomly divided into five treatment groups, with three replicates per group and 50 fish per replicate. The feeding experiment was conducted for 11 weeks. In the liver, compared to NC, HF diet led to a marked reduction of the mitochondria-associated membranes (MAMs) gap, resulting in mitochondrial Ca²⁺ overload, augmented liver Ca²⁺ transport proteins expressions and reactive oxygen species (ROS) content (<i>P</i> < 0.05), decreased mitochondrial membrane potential (MMP) and adenosine 5'-triphosphate (ATP) content in the liver (<i>P</i> < 0.05). Thus, the activation of transforming growth factorβ1 (TGFβ1)-SMAD family member 2 (Smad2/3) signaling pathway resulted in the upregulation of pro-fibrogenic markers (<i>α-Sma</i>, collagen I, fibrontein, and <i>Mmp9</i>) mRNA expressions (<i>P</i> < 0.05). However, GA could alleviate this phenomenon. Through virtual docking analysis showed that the docking energy between GA and Sirtuin 3 (SIRT3) was -9.0 kcal/mol, and the binding effect between the two was stable. Such proposed mechanism was further corroborated by the SIRT3 siRNA transfection cell experiment, indicating that GA may potentially influence the mitochondrial calcium uniporter (MCU) expression by targeting SIRT3, thereby reducing mitochondrial Ca²⁺ content. Together, this study elucidates the essential role of GA in ameliorating liver lipid accumulation and improving liver health, highlighting that GA improves liver fibrosis and mitigates mitochondrial Ca²⁺ overload-mediated liver injury. Consequently, GA holds promise as a potential health-functional additive or therapeutic agent for liver fibrosis.