Bilirubin metabolism

Bilirubin metabolism refers to the sequential degradation of heme (primarily from erythrocyte breakdown), producing biliverdin (via heme oxygenase), then bilirubin (via biliverdin reductase). Unconjugated bilirubin is insoluble and circulates bound to albumin. It is taken up by hepatocytes, conjugated with glucuronic acid (via UDP-glucuronosyltransferase, a family of enzymes), making it water-soluble. Conjugated bilirubin is excreted in bile and further metabolized by gut bacteria into colorless urobilinogen and then stercobilin, which are excreted in feces or reabsorbed and excreted in urine. Key steps are tightly regulated, as accumulation of bilirubin or its intermediates is toxic. Bilirubin metabolism is crucial for detoxification, prevention of oxidative damage (antioxidant effects), and diagnostic assessment of liver and hemolytic diseases[1][3][4][7]. In summary, "Bilirubin metabolism" is a metabolic pathway, not a discrete molecule or direct drug target. The pathway involves several enzymes (notably: heme oxygenase, biliverdin reductase, UDP-glucuronosyltransferase), transporters, and binding proteins.

Increase or decrease of conjugation (e.g., UDP-glucuronosyltransferase induction); Enhancement of excretion (e.g., bile acids); Structural modification for increased solubility (e.g., phototherapy alters unconjugated bilirubin)