Bilirubin, an end product of heme catabolism, forms from the breakdown of erythrocyte hemoglobin in the reticuloendothelial system. Heme oxygenase converts the heme of hemoglobin to biliverdin, and subsequently an NADPH-dependent biliverdin reductase converts biliverdin to bilirubin.

Bilirubin is commonly found bound to serum albumin, when circulating in blood, in its dianion form. Bilirubin is also associated with bile salts, in its monoanion form.

Disorders of hyperbilirubinemia may occur due to increased bilirubin synthesis or decreased bilirubin clearance.

Bilirubin has been used:

• in phantom preparation
• in in vitro experiments
• in the preparation of bilirubin solutions for infusion

Bilirubin has been studied for its properties as an endogenous antioxidant, such as for its capabilities to scavenge reactive oxygen species (ROS) and to inhibit NADPH-oxidase activity. It appears to function as an efficient peroxyl radical scavenger, protecting membrane lipids from oxidation by these radicals. At nanomolar concentrations it has been shown to protect neurons from oxidative damage.

Well over 99% of total bilirubin is transported as a conjugate with albumin. Abnormally high levels of bilirubin can cause severe neurological damage, but mildly elevated levels are linked to protection from oxidative stress.

A major component of hemoglobin decomposition. The principal pigment of bile, and the yellow color in jaundice.

Protect from light.