Tea polyphenols improve lipid metabolism in hybrid grouper (♀ Epinephelus fuscoguttatus × ♂ E. lanceolatu) fed high-lipid diets

Long-term ingestion of high-lipid diets causes lipid metabolism disorder and excess lipid deposition. This investigation aimed to determine whether dietary tea polyphenols (TP) would alleviate the adverse effect of high-lipid diets in hybrid grouper (♀ Epinephelus fuscoguttatus × ♂ E. lanceolatu). Six isonitrogenous (51 %) and isolipidic (16.7 %) diets were formulated: 0 %, 0.01 %, 0.02 %, 0.04 %, 0.08 % and 0.16 % dietary TP, and named TP1 (control), TP2, TP3, TP4, TP5, and TP6. After an 8-week feeding high-lipid diets trial, the results showed that weight gain rate significantly increased in TP-treated groups which had no difference in themselves. Protein efficiency ratio of TP4 group was significantly higher than that of the control group, while the other TP-treated groups had no significant difference from the control group. Hepatosomatic index dramatically decreased in TP-treated groups. TP markedly reduced lipid content and increased protein content of muscle and whole body. TP supplement significantly reduced contents of total cholesterol, low-density lipoprotein cholesterol and very low-density lipoprotein cholesterol, but increased content of high-density lipoprotein cholesterol in the serum. Hepatic lipase, lipoprotein lipase, and fatty acid synthetase activities in the liver significantly increased in TP-treated groups. The histology of hepatic tissue indicated that lipid droplet reduced with the increase of dietary TP, and there was no obvious difference in lipid-lowering effect observed in TP4 and TP5. Hepatic expression of peroxisome proliferator-activated receptors (α, β and γ), hormone-sensitive lipase, adipose triglyceride lipase, carnitine palmitoyl transferase1, sterol regulatory element-binding protein-1, acetyl-CoA carboxylase and fatty acid synthetase were distinctly up-regulated by dietary TP (P < 0.05). These results imply that dietary TP primarily mediated the activation of lipolysis to improve lipid metabolism in grouper fed high-lipid diets. Based on the broken-line regressions analysis of the serous LDL and hepatic VLDL contents, 0.045–0.067 % was recommended in juvenile grouper high-lipid diets for improving lipid metabolism.