A Brief Look of Bile Acids

Bile acid is an important component of bile and plays an important role in fat metabolism. Bile acids are mainly found in the enterohepatic circulatory system and play a protective role through recycling. Only a small portion of bile acids enters the peripheral circulation.

The driving force for promoting bile acid enterohepatic circulation is the liver cell transport system --- absorb bile acid and secrete it into bile, cholecystokinin-induced gallbladder contraction, small bowel advancing peristalsis, active transport of ileum mucosa, and Inflow.

At present, many experts in the animal medical field have researched this, and research has found that bile acids emulsify fat in animal bodies and expand the contact area with lipases; regulate the activity of pancreatic lipase and lipoprotein esterase to increase their hydrolytic metabolism; Transports fat in the intestine and promotes fat absorption. In addition, bile acids significantly reduce the catabolism of autologous fats by regulating the activity of hormone-sensitive lipases. To sum up, bile acid can save energy raw materials, improve energy utilization rate, improve growth performance and slaughter performance, and it is "positive energy" to save resources.

Secretory effect

Active transport of bile acids to bile promotes the excretion of water and solutes. The secretion of cholesterol and lecithin is largely dependent on the secretion of bile acids. Bile acids and lecithin have important roles in maintaining cholesterol levels in bile.

Disruption of enterohepatic circulation may cause a decrease in bile acid / cholesterol and lecithin / cholesterol ratios in bile. At this time, the bile showed a state of cholesterol supersaturation. Cholesterol solubility and the formation of cholesterol gallstones are closely related to the size of circulating bile acid pools.

Metabolic effect

Bile acid helps to emulsify fat, enhances the lipolysis of the pancreas, and improves the solubility of lipids by forming mixed colloids to promote the absorption of lipids by the intestine. The important role of bile acids in fat absorption is confirmed by fat dysentery and symptoms that cause a decrease in intestinal bile salt concentration, such as bile congestion, cirrhosis, and taking bile acid-binding drugs.

Bile acids play an important regulatory role in lipid metabolism. Bile acids not only participate in the regulation of cholesterol, but also play an important role in the metabolism of triacylglycerols. It has been reported that cholesterol receptor coactivator protein knockout mice have a defect in bile salt output pump function, which can cause triacylglycerol malabsorption. . The rate of bile acid synthesis is associated with an increase in plasma triglyceride levels in patients with hyperlipidemia. Bile acids sequestrants can increase the synthesis of bile acids and triacylglycerols. CDCA treatment can reduce triacylglycerol levels in the plasma of hyperlipidemia patients. Bile acids can regulate triacylglycerol metabolism through different mechanisms, including bile acid-mediated activation of FXRa and TGR5 regulation. Bile acid is a natural ligand of FXR, which is involved in the regulation of lipids through a variety of mechanisms, including the regulation of triacylglycerols and lipoproteins. It has been reported that high-fat fed FXR knockout mice have significantly higher triacylglycerol levels than the control group, and that triglyceride levels are significantly lower than those of the control group after administration of FXR agonists. It has been pointed out that FXR can induce the expression of peroxisome proliferator-activated receptors and pyruvate dehydrogenase kinase, inhibit pyruvate dehydrogenase and increase the oxidation of fatty acids. FXR agonists can significantly improve hypercholesterolemia in ob / ob mice and db / dh mice. These suggest that bile acids have a role in regulating lipid metabolism. Bile acid also activates TGR5. TGR5 is the first confirmed serosal-bound G protein-coupled bile acid receptor. Male and female TGR5 knockout mice on a high-fat diet for 8 weeks develop liver fat and cause elevated triglyceride levels in female mice, while TGR5 agonist 6αethyl23 (S) methylcholic acid reduces Plasma triacylglycerol levels above indicate that TGR5 has a role in regulating lipid metabolism, and also that bile acids also play an important role in lipid metabolism.

Clinical significance

1. Hepatobiliary disease


2. Gastrointestinal disorders

3． Other diseases that cause changes in bile acid metabolism

When studying the interference effects of various diseases on bile acids analysis metabolism, biological specimens are often subjected to strict fractionation, and each bile acid component is thoroughly studied using chromatography technology. However, in clinical practice, in most cases, such as screening for liver disease, only a simple enzymatic determination of total bile acid levels is required. This chapter will focus on the effects of serum total bile acids on liver diseases, and briefly discuss the clinical levels of total bile acids in stool, bile, and intestinal extracts.