sappihappojen

Sappihappojen, or bile acids, are steroid acids derived from cholesterol that circulate in bile and play a central role in the digestion and absorption of fats. They exist both as free acids and as conjugated bile salts, formed when amino acids such as glycine or taurine attach to the bile acid molecule, increasing their solubility in water.

In humans, the primary bile acids are cholic acid and chenodeoxycholic acid. These can be conjugated with glycine or taurine to form bile salts such as glycocholic and taurocholic acids. Secondary bile acids, produced by intestinal bacteria, include deoxycholic and lithocholic acids. Ursodeoxycholic acid (UDCA) is a 7β-epimer of chenodeoxycholic acid formed by gut microbes and is also used therapeutically.

The liver synthesizes primary bile acids from cholesterol via the enzyme cholesterol 7α-hydroxylase (CYP7A1). Conjugation with glycine or taurine occurs in the liver, after which bile acids are secreted into bile and stored in the gallbladder. After meals, they are released into the small intestine and undergo enterohepatic circulation, with most being reabsorbed in the ileum and recycled to the liver.

Functionally, bile acids emulsify fats by forming micelles, increasing the surface area available for pancreatic lipase. They aid in the absorption of fat-soluble vitamins and cholesterol. Disruptions in bile acid homeostasis can lead to cholestasis, pruritus, or gallstone formation. Therapeutically, UDCA is used for certain cholestatic liver diseases, and bile acid sequestrants are employed to reduce circulating bile acids in conditions such as hypercholesterolemia. Bile acid composition varies across species and dietary contexts, reflecting differences in gut microbiota and hepatic metabolism.