Bilirubin interactions with phospholipid components of lung surfactant

This work examines the dynamic surface pressure-area behavior of films of unconjugated bilirubin spread from chloroform solution at 22 degrees C on 0.15 M NaCl and buffered phosphate subphases. Film behavior is examined at pH 5.5, 7.4 and 8.0. The interactions of bilirubin in mixed films with dipalmitoyl phosphatidylcholine and with 9:1 dipalmitoyl phosphatidylcholine:dioleolyl phosphatidylcholine are examined at similar temperature and pH values. It is found that unconjugated bilirubin modifies the dynamic surface pressure-area behavior of phospholipid films in both the high and low surface pressure regimes, with bilirubin exerting its greatest effect at low pH where its subphase solubility is low. Because many premature infants suffering from the Respiratory Distress Syndrome (RDS) have accompanying hyperbilirubinemia, with possible bilirubin transport to the alveolar space, the interactions of bilirubin with phospholipid films are discussed in terms of potential effects on pulmonary surfactant in vivo.