Alteration of fatty acid profiles in different pulmonary surfactant phospholipids in acute respiratory distress syndrome and severe pneumonia

Impairment of alveolar surfactant function has been documented in the acute respiratory distress syndrome (ARDS) and in severe pneumonia (PNEU); howev er, the underlying mechanisms are not completely understood. In the current report we present a detailed analysis of fatty acid (FA) profiles of diffe rent surfactant phospholipid (PL) classes isolated from bronchoalveolar lav age fluids (BALF) and large surfactant aggregates (LSA) from mechanically v entilated patients with ARDS (n = 8), ARDS associated with lung infection ( ARDS + PNEU, n = 9), and PNEU (n = 22). Healthy volunteers served as contro l subjects (n = 8). PLs were isolated by thin-layer chromatography, and the FA profile of each PL class was assessed by gas chromatography. In additio n, the minimal surface tension (gamma min) of untreated LSA and of LSA afte r supplementation with additional dipalmitoylated phosphatidylcholine (DPPC ) was analyzed (pulsating bubble surfactometer). As compared with control L SA, the percentage of palmitic acid in phosphatidylcholine (PC) was signifi cantly decreased in all patient groups (ARDS 63.0 +/- 2.0%, ARDS + PNEU 64. 6 +/- 4.9%, PNEU 65.6 +/- 1.5%, control subjects 80.1 +/- 1.7%), whereas th e relative amount of unsaturated species in PC increased significantly in a ll groups. Phosphatidylglycerol (PC) and phosphatidylinositol (PI) presente d similar FA profiles in control subjects, but differed in the patients. Th e FA pattern of sphingomyelin (SPH) and phosphatidylethanolamine (PE) displ ayed only minor changes under conditions of respiratory failure. As compare d with control subjects a highly significant increase of gamma min from nea r zero to approximately 16 mN/m was observed in all patients and was found to be inversely correlated to the percentage of palmitic acid in PC of LSA or BALF. Accordingly, values for gamma min were significantly improved upon secondary supplementation of LSA with DPPC up to control values. We conclu de that marked changes in the FA composition of the predominant surfactant PL classes occur, both in ARDS triggered by nonpulmonary events and PNEU. T he marked reduction of palmitic acid in the PC fraction may be related to c hanges in surfactant function under these conditions.