Gallensäurezynthese

Gallensäurezynthese, or bile acid synthesis, is a biological process occurring primarily in the liver, through which cholesterol is converted into bile acids. Bile acids are critical for the digestion and absorption of dietary fats and fat-soluble vitamins. They also play roles in regulating cholesterol levels and maintaining lipid homeostasis.

The synthesis of bile acids begins with cholesterol, which undergoes enzymatic conversion through a series of biochemical steps. The two main pathways are the classic (or neutral) pathway and the alternative (or acidic) pathway. The classic pathway involves the enzyme cholesterol 7α-hydroxylase (CYP7A1), which hydroxylates cholesterol at the 7α-position. This pathway produces primary bile acids, mainly cholic acid and chenodeoxycholic acid. The alternative pathway, initiated by sterol 27-hydroxylase (CYP27A1), contributes to the production of bile acids, especially under different physiological conditions.

Bile acids are synthesized in the hepatocytes and conjugated with amino acids such as glycine or taurine to increase their solubility before being secreted into bile. The secretion into the gastrointestinal tract facilitates lipid emulsification and absorption. After fulfilling their digestive function, most bile acids are reabsorbed in the ileum and transported back to the liver via the enterohepatic circulation for reuse, conserving resources.

Regulation of gallensäurezynthese involves feedback mechanisms primarily mediated by bile acid receptor activation, which inhibits the activity of key enzymes in the synthesis pathways when bile acid levels are sufficient. Disruptions in this process can lead to metabolic disorders, including cholestasis and hypercholesterolemia. Overall, bile acid synthesis is essential for lipid digestion and cholesterol regulation in mammals.