Bilirubin influence on oxidative lung damage and surfactant surface tension properties

To study the hypothesis that hyperbilirubinemia might reduce in vivo oxidative lung damage while also diminishing lung surfactant surface tension properties during acute lung injury, we performed a randomized study in a rabbit model of acute lung injury. Twenty rabbits were randomized to receive bilirubin or saline intravenously. Acute lung injury was induced by lung lavages with saline. Lung tissue oxidation was evaluated by measuring total hydroperoxide (TH), advanced oxidation protein products (AOPP), and protein carbonyls (PC) in bronchial aspirate (BA) samples. Surface surfactant activity was studied in BA samples using a capillary surfactometer. Bilirubin BA concentration increased in bilirubin-treated rabbits, while it remained undetectable in controls. A similar increase in TH, AOPP, and PC bronchial aspirate concentrations was found in both the study and control groups, while surfactant surface activity was lower in the bilirubin than in the control group. We conclude that during hyperbilirubinemia, bilirubin enters the lung tissue, where it can be detected in BA fluid. Bilirubin is not effective as an antioxidant agent and exerts a detrimental effect on lung surfactant surface tension properties. These findings may have relevance to the management of premature neonates suffering from respiratory distress syndrome and hyperbilirubinemia.