Effects of in vitro testing of glycyrrhetinic acid (GA) on the lipid metabolism of channel catfish (Ictalurus punctatus) fed a high-fat diet

Fatty liver always strongly correlates with low growth and reduced harvest yield. However, some herbs in China can reduce the storage of hepatic fat. This study aimed to examine the lipid-lowering effect of glycyrrhetinic acid (GA) in channel catfish (Ictalurus punctatus) in vitro. Two different methods were performed to measure the effect of GA on the metabolism of fats in the fingerling of catfish. First method: GA was injected directly into the abdominal cavity, where fish were fed on a high-fat diet with different time points (0H, 3H, 6H, 12H, 18H, 24H & 36H), and the highest TG level was found at 18 hours so this time was chosen to treat with GA. The fish were then injected with five levels of GA (0, 0.15, 0.3, 0.6, 1.2 mg/kg) in two diet groups of fish; normal-fat diet (ND) and high-fat diet (HFD). Injections of GA in channel catfish enhanced plasma and liver TC, TG, HDL & LDL, and lipid metabolism gene expression compared to HFD and ND. Nevertheless, treatment with GA significantly decreased gene expression of inositol requiring enzyme 1 (IRE1), spliced X box-binding protein 1 (xbp1s), DnaJ heat shock protein family (Hsp40) member B9 (DNAJB9), and glucose-regulated protein 78 (GRP78), an increased level of gene expression of MTTP and Apolipoprotein B(ApoB) in both ND groups and HFD groups. The best results of lipid profile parameters and gene expression of lipid metabolism genes have been observed at the injection level of 0.3 mg/kg GA both in ND and HFD. Second method: cell culture of catfish hepatopancreas, five different levels of GA (0 - 0.15 - 0.3 - 0.6 - 1.2) μMwere tested with oleic acid (OA) as a fat source with a concentration of 0.4 mM. The use of GA with OA in cell culture led to reduced IRE1, xbp1s, DNAJB9, and GRP78 and increased MTTP & ApoB expression levels, while the opposite was observed when treated with OA alone. The best expression level was at a concentration of 0.3 μM GA. In conclusion, a high-fat diet could lead to aberrant lipid secretion by activating the IRE1/XBP1 pathway. However, adding GA restored this parameter to the normal level.