Effect of sphingomyelin versus dipalmitoylphosphatidylcholine on the extent of lipid oxidation.

Phospholipids with sites of unsaturation are targets of peroxidation. We investigated the effect of two types of lipids with identical headgroups, sphingomyelins (SMs) and dipalmitoylphosphatidylcholine (DPPC), on the extent of oxidation of stearoyl-arachidonoyl phosphatidylcholine (SAPC) with four double bonds. Peroxidation was induced with tert-butylhydroperoxide and FeCl(2) at 35 degrees C. The decrease of SAPC versus DPPC, or N-palmitoyl SM, or N-stearoyl SM, was monitored by matrix-assisted laser desorption ionization time-of-flight mass spectrometry (MALDI-TOF MS) at various reaction times. For corresponding molar ratios of DPPC:SAPC and SM:SAPC, SAPC oxidized faster and to a greater extent when DPPC, rather than N-palmitoyl SM or bovine brain SMs, was present. However, at 35 degrees C the hydrophobic tails in SM mixtures were more disordered than in those of DPPC. The slower oxidation of SAPC in SM-rich vesicles may result from the presence of a tight network of H-bonds that bridge neighboring SM molecules and poses a stronger interfacial barrier to the passage of oxidants.