Muricholic

Muricholic acids are a group of bile acids synthesized in the liver that are especially prominent in rodents, such as mice and rats. The two principal members are alpha-muricholic acid (α-MCA) and beta-muricholic acid (β-MCA). Both are 3α,7-hydroxylated, 5β-cholanoic acids, differing in the configuration at the 7 position. In typical rodent physiology, these acids are often found in taurine-conjugated forms, known as tauro-muricholate derivatives, with taurine conjugation being more common in rodents than glycine conjugation.

Chemical and physical properties: Muricholic acids are 5β-cholanoic acids, a configuration that influences their three-dimensional shape, hydrophilicity, and detergent-like properties. These characteristics affect their behavior in the enterohepatic circulation, their interaction with gut microbiota, and their capacity to activate or modulate bile acid receptors.

Biosynthesis and metabolism: Muricholic acids arise from cholesterol through the liver’s primary bile acid synthesis pathways in rodents. After secretion into bile and release into the intestine, gut bacteria can deconjugate and modify these acids, generating additional metabolites. Reabsorption in the enterohepatic cycle recycles them back to the liver.

Physiological role and signaling: Muricholic acids contribute to fat digestion and cholesterol homeostasis. In mice, certain muricholic acids, particularly some tauro-conjugates, can act as antagonists of the farnesoid X receptor (FXR) in the intestine. This antagonism influences feedback regulation of bile acid synthesis and can affect lipid metabolism and gut microbial composition. The exact balance of α- and β- muricholic acids and their conjugates shapes overall bile acid signaling in rodents.

Human relevance: Muricholic acids are not produced in significant amounts in humans; the human bile acid pool is dominated by cholic, chenodeoxycholic, deoxycholic, lithocholic, and ursodeoxycholic acids. Species differences mean rodent models may not fully reflect human bile acid physiology.