Do I Have IBS?
Melissa G. Hunt, Aaron T. Beck in Reclaim Your Life From IBS, 2022
One frequently overlooked cause of chronic diarrhea is bile acid. Bile acid is produced by the liver, stored in the gall bladder, and then secreted into the intestines where it plays a very important role in the digestion of fats and the regulation of cholesterol. In a healthy GI system, the liver produces the right amount, the gall bladder squirts the right amount into the upper part of the small intestine, where it does its thing, and then most of the excess bile acid is reabsorbed in the ileum, which is the last part of the small intestine, and thriftily returned to the liver for recirculation. A little escapes into the large intestine, where it is further transformed into secondary bile acid, and very small quantities are excreted in the stool every day. That’s if everything is working correctly. Unfortunately, there are several ways for this process to go wrong, and when it does, you end up with too much bile acid in the large intestine, which can cause chronic diarrhea, urgency, and even fecal incontinence.
Gastrointestinal Tract as a Major Route of Pharmaceutical Administration
Shayne C. Gad in Toxicology of the Gastrointestinal Tract, 2018
Bile acids are synthesized from cholesterol in the liver and secreted into the small intestine where they facilitate the absorption of lipids and some fat-soluble vitamins. The vast majority of bile acids are reabsorbed from the intestine, returned to the liver via the portal venous circulation, and re-secreted into bile in a cycle termed the “enterohepatic cycle.” Over 90% of the intestinal bile acids are reabsorbed so less than 10% are excreted in the feces. Substances and their metabolites that are excreted in bile are actively transported across the biliary membrane. In the intestine, bile is reclaimed through a combination of passive absorption in the jejunum, by active transport in the distal ileum, and by passive absorption in the colon. Bile acids are actively transported in the terminal ileum by the well-characterized ileal apical sodium bile acid cotransporter (ASBT—apical sodium-dependent bile acid transporter). This sodium transporter moves bile acids from the lumen of the small intestine across the membrane and into the portal circulation (Sharifi and Ghafourian, 2014; Stringer, 2015).
Gut Microbiota—Specific Food Design
Megh R. Goyal, Preeti Birwal, Santosh K. Mishra in Phytochemicals and Medicinal Plants in Food Design, 2022
Bile acids in the small intestine largely influence the digestion and absorption of dietary lipids. Chemically, the synthesis of primary bile acids takes place in the liver and secondary bile acids take place in the large intestine. Majority of primary bile acids (cholic acid and chenodeoxychlic acid) will be absorbed from Ileum for recycling in the liver. The remaining bile acids (1%–5%) reaching the colon will be modulated by the gut microbiota. The gut microflora regulates the bile acid synthesis as well as the conjugation of secondary bile acids (biotransformation). The secondary bile acids like deoxycholic acid have greater detergent properties thereby controlling the bacterial populations. The gut microbes have bile salt hydrolase (BSH) enzymes, which mediates the biotransformation of bile by hydrolyzing the glycol and tauro conjugates. Some of the genera reported to produce BSH are the Bacteroides, Bifidobacterium, Clostridium, Lactobacillus, and Listeria.
The role of gut microbiome in prevention, diagnosis and treatment of gestational diabetes mellitus
Published in Journal of Obstetrics and Gynaecology, 2022
Ermioni Tsarna, Panagiotis Christopoulos
Lastly, the role of bile acids homeostasis has been suggested as a potential mechanism to link the gut microbiome with glucose metabolism (Di Ciaula et al. 2017; Gérard and Vidal 2019). Bile acids are synthesised in the liver, stored in the gallbladder and released to the intestines postprandially (Di Ciaula et al. 2017). Via the portal circulation, the majority of bile acids return to the liver, a process termed as enterohepatic recycling (Di Ciaula et al. 2017). The primary role of bile acids is to facilitate the absorption of lipids and fat-soluble nutrients in the intestines, where bile acids act as surfactants (Di Ciaula et al. 2017). However, it becomes increasingly evident that they also affect glucose metabolism (Di Ciaula et al. 2017). It has been shown that in animal models differential expression of enzymes involved in bile acids biosynthesis directly affects glucose metabolism and adiposity (Li et al. 2010). In addition, bile acids are involved in fat browning and can, thus, improve glucose metabolism (Watanabe et al. 2006). Notably, the gut microbiome can affect bile acids homeostasis both by inhibiting bile acids biosynthesis in the liver and by transforming them to secondary bile acids, which cannot be reabsorbed by the gut and therefore recycled (Ridlon et al. 2006; Sayin et al. 2013).
Studies of xenobiotic-induced gut microbiota dysbiosis: from correlation to mechanisms
Published in Gut Microbes, 2021
Liang Chi, Pengcheng Tu, Hongyu Ru, Kun Lu
Bile acids are originally synthesized from cholesterol in livers known as primary bile acids, stored in gall bladders and then secreted to small intestines to solubilize lipid and fat-soluble vitamins as potent detergents after a meal. Most of the bile acids can be reabsorbed and backed to our bodies, which is called bile acid enterohepatic circulation. Gut bacteria can hydrolyze the amino acid residues (taurine or glycine) in conjugated bile acids to generate free bile acids. Moreover, some gut bacteria also can synthesize secondary bile acids utilizing primary bile acids.117 Gut bacteria-performed bile acid biotransformation is a critical interaction between the gut microbiota and host, which is not only required to maintain the bile acid homeostasis but also provides key metabolic signaling to multiple tissues in host bodies.118
Diversification of host bile acids by members of the gut microbiota
Published in Gut Microbes, 2020
Jenessa A. Winston, Casey M. Theriot
High concentrations of conjugated primary bile acids are noted within the duodenum, jejunum, and proximal ileum.13 The primary role of bile acids in the small intestine is to aid in fat emulsification and absorption. Bile acids undergo enterohepatic recirculation, a process which involves: (1). Passive absorption of conjugated and unconjugated bile acids in the small intestine and colon; (2) High-affinity active transport in the distal ileum.1,17,23 Absorbed bile acids enter into the portal bloodstream and are rapidly taken up by hepatocytes and resecreted into bile (Figure 1). A small fraction of bile acids escape enterohepatic recirculation and spill into systemic circulation, which allows bile signaling to occur in other organs and tissues.24,25 Enterohepatic recirculation is extremely efficient, with 95% of bile acids reabsorbed and only 5% lost into the feces.1 Hepatocytes maintain the bile acid pool by synthesizing bile acids to make up for fecal loss. In healthy humans, the total bile acid pool cycles about 10 times each day, which requires enterocytes and hepatocytes to transport about 20 g of bile acids every hour.5,26