Surfactant protein A inhibits the non-enzymatic lipid peroxidation of porcine lung surfactant.

The ability of surfactant protein A (SP-A) to inhibit the ascorbate-Fe(2+) induced lipid peroxidation of polyunsaturated fatty acids found in porcine lung surfactant (surfacen) was assessed by measuring the light emission - chemiluminescence during a 180-min incubation period at 37 degrees C. The light emission (chemiluminescence) was concentration dependent. Changes in the fatty acid composition of surfacen were observed when the lung surfactant was incubated in an ascorbate-Fe(2+) system. The main polyunsaturated fatty acids C18:2 n6 and C20:4 n6 found in the lung surfactant decreased considerably after a 180-min lipid peroxidation process. Native SP-A isolated from pig lungs inhibited oxidation of surfactant long chain polyunsaturated fatty acids, mainly arachidonic acid, in a dose-dependent fashion that was half-maximal (60% inhibition) at a concentration of 2.0 microg/ml and almost complete (73.6% inhibition) at 4.0 microg/ml, as indicated by inhibition of light emission and fatty acid composition analysis. At the highest concentration of lung SP-A used a very good correlation between the protection of the most polyunsaturated fatty acids and inhibition of light emission was observed.