| EPA and DHA fatty acids in fish oil have many biological activities, such as adjusting blood fat, improving memory, regulating lipid metabolism, enhancing the immunity, etc. As most studies have only studied EPA and DHA mixtures such as fish oil capsules or oily fish diet or supplements rather than the individual fatty acids, it is still unclear if EPA and DHA have independent physiological effects for NAFLD. And the two major dietary n-3 PUFA, eicosapentaenoic acid(EPA; C20:5n-3) and docosahexaenoic acid(DHA; C22:6n-3) produce distinctly different responses both in vitro and vivo. In addition, most studies were conducted by using unpurified fish oil containing EPA, DHA and some other fatty acids in the form of ethyl ester or FFA; Studies showed that fatty acids of different forms have different bioavailability in vivo, for instance, ethyl ester for only 21%, FFA for 95%, triglyceride for 60%. but unstable, readily oxidizable, irritating the digestive tract, but relatively chemically stable. In this paper, we evaluated tri EPA and tri DHA both with purity of 80% that prepared from our lab through enzymatic methods, using mice as animal model to explore their effect on the regulation of nonalcoholic fatty liver disease, and the mechanism is discussed in this paper.Nonalcoholic fatty liver disease in mice model was established through adding 1% cholesterol and 20% long chain fatty acids in the diet to study the effect of tri EPA and tri DHA on mice nonalcoholic fatty liver disease. According to the results, high fat diet induced liver macrovesicular steatosis in mice, while the liver index, ALT and AST activities, TG and TC contents in liver, serum FFA, HOMA-IR and hepatic macrovesicular steatosis in tri EPA and tri DHA groups were significantly decreased. In conclusion, tri EPA and tri DHA could effectively prevent and improve non-alcoholic fatty liver disease in mice, but there were no significant differences between tri EPA and tri DHA in those aspects above.The accelerated oxidation of lipids in the liver caused by supplementation of n-3 PUFA may lead to the accumulation of ROS. In order to reduce the excessive ROS, Vitamin E as a phenolic compound which majorly distributes in lipid bilayer and could eliminate free radicals and inhibit lipids oxidation, is included in the research. The results showed that, after 8 w, compared to the tri EPA, tri DHA raised the hepatic GSH-Px, GSH greater, suggesting a better oxidation resistance. Compared to the n-3 PUFA groups, hepatic GSH content and GSH-Px activity and SOD activity from n-3 PUFA+vitamin E groups were significantly increased and ALT and AST from those groups were significantly decreased. There were no significant differences existing among the groups supplemented with n-3 PUFAs in other indexes. Vitamin E supplementation alone does not improve indicators compared to model group, but vitamin E has synergistic effect with n-3 PUFA on NAFLD.To further understand the mechanism of n-3 PUFA on nonalcoholic fatty liver disease in mice, we also studied the influences produced by tri DHA and tri EPA on lipids profile and gene expression in the liver. RT-PCR results showed that SREBP-1 expression but not PPARα in the liver from tri EPA and tri DHA supplemented mice was significantly decreased. Hepatic lipids profile showed that, after 8-w supplementation of tri EPA and tri DHA, the amount of polyunsaturated fatty acids fatty acids was increased significantly, and arachidonic acid content was declined significantly. DHA content was significantly higher than EPA content in the liver from both tri EPA and tri DHA supplemented mice. In this regards, we can concluded that tri EPA and tri DHA could adjust the liver fatty acid composition and the expression of lipid metabolism related genes to improve NAFLD in mice, and EPA mainly serves as a precursor for synthesis of DHA. |
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