The Composition of Bile Acids under Fatty Liver Model in Chicken

Bile acids is synthesized by cholesterol in the liver and exert by two different pathways, classical and alternative pathway. Two major enzymes, CYP7A1 and CYP27A1 play regulatory roles in two pathways. CA (cholic acid) and CDCA (chenodeoxycholic acid) as known as the primary bile acids which means they are major products in these two pathways and then they can be modified by gut microbiome. After modifying, the metabolites are called secondary bile acids such as lithocholic acid (LCA)、deoxycholic acid (DCA). Some researchers found that total bile acids including primary and secondary bile acids elevate in serum from non-alcoholic fatty liver (NAFL). However, the composition of bile acids in chickens upon fatty liver model is unclear. In current study, seven-week-old ISA chicken were assigned to two group, there are control group (C) (n=10) and cholesterol with low choline (CLC) group (n=10). The control group was fed with extra 0.05% choline and without cholesterol, the other group was fed with extra 2% cholesterol and without choline for six weeks to simulate as NAFL. After sacrificing, we collected serum and cecum contents to quantitation of bile acids by mass spectrometer and analyze gut microbiome by 16S amplicon sequencing. The gene expression pattern of bile acid synthetic enzymes and related transcription factors was also determined by real-time PCR. The bile acids in serum, such as TCDCA (C:CLC=6080.15nM:14555.75nM)、TLCA (C:CLC=122.31nM:2122.62nM)、5β-Cholenic Acid-7α-ol-3-one (C:CLC=1.04nM:3.87nM)、CDCA (C:CLC=3.93nM:38.13nM) are significantly elevated in CLC group and the bile acids in cecum contents such as, TLCA (C:CLC=109.8nM:8897.27nM)、TUDCA (C:CLC=15.82nM:985.0nM)、THDCA(C:CLC=718.72nM:3084.36nM)、LCA(C:CLC=4.32nM:22.88nM)、TDCA(C:CLC=10.12nM:172.28nM) are significantly increased in CLC group. The results of gene expression showed that CYP7A1 and CYP8B1 were increased in CLC group compared than control. For gut microbiome, the proportion of bile acid tolerance bacteria Alistipes in the CLC group is 9.13% which is 1.69% higher than the control group. The pleiotropic roles of bile acid have gradually been valued. In this study, we analyzed the composition of bile acids under the fatty liver of chickens. We also found that the concentration of taurine conjugated bile acid in chickens is much higher than that of glycine.