The Alleviating Effects And Mechanism Of Eicosapentaenoic Acid-Enriched Phosphatidylcholine From Sea Cucumber On Non-Alcoholic Fatty Liver Disease

Non-alcoholic fatty liver disease (NAFLD) is chronic hepatic disease induced bylipid metabolism disorders, characterized with lipid accumulation in liver. Themorbidity of NAFLD increased continusly with the the improvement of people’sliving standards and the changes of the diet. Owing to the high morbidity of nearly15percents in developed area in our country, NAFLD has become a serious public hleathproblem. In addition, as an important element of metabolic syndrome, NAFLD has adeep relationship with obesity, hypertension, diabetes and other cardiovascular andcerebrovascular diseases. In consideration of NAFLD’s severe threat to human health,the precautions and therapies of NAFLD has attracted researchers’ attention.Eicosapentaenoic acid (EPA) and phosphatidylcholine (PC) are two bioactiveagents exhibiting alleviating effects on NAFLD. Both of them have mature functionalfood products in the market. However, the EPA enriched PC owning dual activities ofthe two substances are still rare currently. Sea cucumber is a traditional tonic andmarine medicine in China, whose body wall contains various kinds of activecomponents. Analysis showed that the lipid concentrations and compositions in seacucumber of different origins varied a lot. Previous study certified that the seacucumber from Frigid Zone contained more PC in total lipid of the body wall.Moreover, the fatty acid and structure analysis indicated that the EPA contents in thePC of Frigid Zone sea cucumber ranged from17.7to32.4percents. The EPA wasenriched in Sn-2position of the sea cucumber PC, constituted the specific bioactiveagent of sea cucumber: eicosapentaenoic acid-enriched phosphatidylcholine(EPA-PC). In present study, we isolated the EPA-PC from Cusumaria frondosa, andinvestigated its regulating effects on lipid metabolism in NAFLD rats induced by1%orotic acid diet. Further more, we studied the mechanism of EPA-PC on aspects of hepatic fatty acid, triglyceride and cholesterol metabolism. The results were asfollows.After administrated with EPA-PC for3weeks, the TC and TG levels of serumand liver were both markedly lowered in the NAFLD rats. The fatty acidcompositions of lipid in serum and liver were also optimized. In addition, theexcrement lipid concentrations were elevated significantly. These results indicatedthat EPA-PC could remarkably impair the hepatic lipid accumulation in NAFLD ratsand promote the lipid excretion.To detect the mechanism of EPA-PC, we used the RT-PCR to determine thetranscriptions of the crucial genes in fatty acid, triglyceride, and cholesterolmetabolism in the rats’ liver. For fatty acid metabolism, enzymes activity test showedthat EPA-PC notably inhibited the enzymes activity of FAS, ME and G6PDH, andimoproved the enzymes activity of CPT-1and ACOX. Additionally, RT-PCR analysisshowed that the transcriptions of hepatic SREBP-1c, ACC1, FAS, SCD1, ME,G6PDH decreased significantly in EPA-PC group. However, the mRNA expressionsof PPAR-α, CPT-1and ACOX were stimulated. These results suggested that EPA-PCcould promote the fatty acid metabolism in NAFLD rats through suppressing the fattyacid synthesis and activating the β-oxidation. On aspect of triglyceride metabolism,the RT-PCR results showed that EPA-PC could lower the mRNA expression levels ofkey enzymes in triglyceride biosynthesis such as GPAT and DGAT. At the same time,the transcriptions of genes relevant to triglyceride decomposition like ATGL and HSLwere also regulated.As to cholesterol metabolism, the EPA-PC inhibited the mRNA expression ofHMGR and CYP7A, which were rate-limiting enzymes in cholesterol synthesis andconversion to bile acid respectively. Nevertheless, the expression levels of SCP2weremarkedly increased in EPA-PC group. These results indicated that EPA-PC couldpromote hepatic cholesterol metabolism mainly through suppressing the endogenouscholesterol synthesis and stimulating cholesterol secretion to bile. Finally, theEPA-PC could also up-regulate the transcription of AMPK via stimulating theexpression of LKB1and CAMKK, which are two upstream kinases of AMPK. Further more, all the changes in the expression of genes analyzed above conformed tothe regulating mechanism of AMPK. These results illustrated that the underlyingmechanism of EPA-PC’s promoting effects on NAFLD involved in the activation ofAMPK. In conclusion, we discovered that EPA-PC exhibited excellent regulatingeffects on lipid metabolism in NAFLD. The present research provided theory basis forthe utilization of EPA-PC as a new functional food and medicine.