Surface properties after a simulated PLA2 hydrolysis of pulmonary surfactant's main component, DPPC

The inflammation, so conspicuous in cases of respiratory distress, pneumonia, and asthma, is associated with an airway invasion of plasma proteins and a release into the airway lumen of phospholipase A2 (PLA2). This enzyme catalyzes hydrolysis of surfactant phospholipids, the most abundant and important of which is dipalmitoylphosphatidylcholine (DPPC). Its hydrolysis yields equimolar proportions of lysophosphatidylcholine and palmitic acid (LPC/PA). Exact quantification of DPPC hydrolysis is complicated. Consequently, it was decided to simulate hydrolysis whereby DPPC (3 mg/ml) was gradually replaced with LPC/PA (3 mg/ml), yielding seven different grades of simulated hydrolysis: 0, 17, 33, 50, 67, 83, and 100%. Surface properties of the seven mixtures were examined with various concentrations of albumin added. The Bubble Surfactometer was used to study the surfactant film that is given time to develop at a spherical air-liquid interface. A Capillary Surfactometer was used to evaluate surface properties required for airway patency. It was found, using both of these instruments that the surface activity improved as the simulated hydrolysis of DPPC to LPC/PA increased toward 100%, where the activity was maximal. With the Bubble Surfactometer, surface activity of LPC/PA, 3 mg/ml, improved as albumin concentration increased, and when it reached 15 mg/ml, surface tension became 0 mN/m after only 2 min. With the Capillary Surfactometer, requiring a much faster film adsorption, albumin had an opposite effect. LPC/PA alone maintained patency 100% of the time studied, while even a minimal addition of albumin inhibited surfactant function.