Studies in kernicterus. I. The protein binding of bilirubin.

The yellow staining of basal ganglia (kernicterus) in some jaundiced newborn infants has been recognized for many years (1). The association between serum bilirubin concentration and kernicterus (2, 3), the isolation of bilirubin from kernicteric brains (4, 5), and the toxic effect of bilirubin in vitro upon oxygen uptake (6) and oxidative phosphorylation (7) are further evidence of a relationship between bilirubinemia and kernicterus. Plasma concentrations of bilirubin exceeding 20 mg. per cent are considered levels above which kernicterus occurs, although many exceptions exist (8, 9), particularly in the premature infant (10). Of particular importance was the observation (11) that kernicterus occurred more frequently in premature infants given sulfisoxazole than in control infants despite lower plasma bilirubin concentrations (12). Animal studies have confirmed these findings (13). Because kernicterus can occur at bilirubin concentrations considerably below 20 mg. per cent and fail to occur at higher concentrations, a study of factors controlling distribution of bilirubin seemed indicated.' The binding of bilirubin to serum proteins has been demonstrated by many techniques (14-20). In vitro separation of bilirubin by ultrafiltration from serum protein in detectable amounts has been singularly unsuccessful (20-25). Bilirubin did not appear in ultrafiltrates of plasma unless the concentrations were greater than 80 mg. per cent (22, 25). However, bilirubin gains access to cell cytoplasm at considerably lower concentrations in vivo, and probably has to dissociate from