The biology of bilirubin production: detection and inhibition

Newborn jaundice is a benign condition commonly seen in the first postnatal week of life (or the transitional period). It is primarily due to an imbalance between the rate of production of the yellow-orange pigment bilirubin and its elimination by the liver. Infants with high bilirubin production rates (such as those who are undergoing hemolysis) or with insufficient hepatic bilirubin conjugating ability [such as those with uridine 5'-diphosho-glucuronosyltransferase (UGT1A1) deficiencies] can subsequently develop excessive circulating total serum/plasma bilirubin (TB) levels or hyperbilirubinemia. Bilirubin is formed during the degradation of heme, derived from the turnover of red blood cells (RBCs). In this reaction, which is catalyzed by the rate-limiting enzyme heme oxygenase (HO), carbon monoxide (CO), iron (Fe), and bilirubin are produced in equimolar quantities. As a result, measurements of total body CO production rates can be used as indices of bilirubin production. Standard treatment strategies for hyperbilirubinemia involves the use of phototherapy (specifically narrow-band blue wavelength light) and/or exchange transfusion. However, if infants with excessive hyperbilirubinemia are not identified or treated in a timely manner, they are at risk for developing bilirubin neurotoxicity, which can manifest as bilirubin-induced neurologic dysfunction (BIND) and result in neurologic sequelae (such as acute or chronic bilirubin encephalopathy. Here, we review the biology of bilirubin production and current technologies and approaches to identify and treat these high-risk