Omics Analysis Of Metabolites In The Intestinal Tracts During The Development Of Fatty Liver In Goose

Goose fatty liver(or foie gras)is a delicious and nutritious high-end food.Different from pathological non-alcoholic fatty liver diseases(NAFLD)in human and other mammals,it results from a short-term overfeeding on the liver-purposed breed of goose,Landes goose.In recent years,studies on NAFLD in human and rodent model animals have shown that gut microbes and metabolites play an important role in the formation of NAFLD.Bacterial metabolites participate in the formation of NAFLD by affecting intestinal peristalsis,permeability,nutrient absorption.and inflammatory response as well as gene expression in other tissues indirectly through blood circulation.Compared with these findings from mammalian NAFLD studies,the relationship between intestinal metabolites and the formation of goose fatty liver,a unique physiological fatty liver,and the underlying mechanism are rarely investigated.In this study,80 70-day-old male Landes geese were randomly divided into overfeeding group and control group.The liver and intestinal content(jejunum,ileum and cecum)sainples were collected from 16 geese each group that were slaughtered on day 0,12 and day 24 of overfeeding.Non-targeting GC-TOF-MS method was used to analyze the metabolites in the liver and from different intestinal tracts.The differential metabolites between control group and overfeeding group were screened,and metabolic pathways were also analyzed.Secondly,the effects of arachidonic acid and tetrahydrocorticosterone on the expression of key genes were analyzed in the treated cells.Finally,Landes geese were fed with lactic acid supplemented diet to validate the inhibitory effect of lactic acid on complement gene expression in the liver.The main results are as follows:1.Compared with the control group,24 days of overfeeding resulted in significant changes in the contents of metabolites in the liver(187 metabolites in total,3 increased and 184 decreased),jejunum(10 metabolites in total,4 increased and 6 decreased),ileum(33 metabolites in total,5 increased and 28 decreased)and cecum(124 in total,42 increased and 82 decreased)(VIP>1,P<0.05).These differential metabolites belong to the categories of fatty acid,amino acid,organic acid,amine and other compounds.Different intestinal segments have different metabolite profiles,which may be resulted from different compositions of gut microbes over different intestinal segments.Liver and intestine share some different metabolites,suggesting that gut nicrobes can affect the formation of goose fatty liver through metabolites.KEGG pathway and metabolic pathway analyses showed that differential metabolites were mainly involved in fatty acid biosynthesis pathway,citric acid cycle pathway,mitochondrial fatty acid chain extension pathway,pantothenate and coenzyme A biosynthesis pathway,glycolysis or gluconeogenesis pathway,primary bile acid biosynthesis pathway as well as glycine,serine and threonine metabolism pathway.Among them,some pathways may be involved in fatty acid synthesis,change in mitochondrial function and oxidative stress in the liver,which are known to be closely related to the formation of fatty liver.2.The contents of arachidonic acid(AA)and tetrahydrocorticosterone in the intestine and liver was correlated with the formation of goose fatty liver,timely,the content of arachidonic acid in goose fatty liver was decreased significantly 24 days after feeding,while the contents of tetrahydrocorticosterone in ileum and cecum were also decreased significantly in the late period of overfeeding.Experiments with cultured cells showed that the expression of ALOX5 in goose primary intestinal cells treated with medium and high concentration of AA(0.5 mmol/L,1 mmol/L)could be significantly induced,suggesting that the decrease of AA content in goose fatty liver at the late stage of overfeeding might be related to oxidative stress and inflammation.The expression of CYP27A1 gene was inhibited by the treatment of geese primary hepatocytes with 1 micromol/L tetrahydrocorticosterone,suggesting that the decrease of tetrahydrocorticosterone content in ileum and cecum at the late stage of goose fatty liver could affect the balance of cholesterol,sterol and other lipids through CYP27A1,thus promoting the formation of goose fatty liver.3.The content of lactic acid in different intestinal segments of goose was higher than that of control group,and the addition of lactic acid to diet could inhibit the expression of C5 gene in liver.These findings confirm that lactic acid in the intestine is involved in the regulation of complement gene expression in the liver and intestine,thereby affecting the level of inflammation in the liver.In conclusion,intestinal metabolites are important participants in the formation of goose fatty liver.They play their biological roles through various metabolic pathways.Arachidonic acid,tetrahydrocorticosterone and lactic acid may play a part in the formation of goose fatty liver by influencing oxidative stress,lipid balance and inflammatory level,respectively.These results laid a foundation for further study on the relationship between intestinal metabolites and the formation of goose fatty liver as well as the underlying mechanism.