Recently, it has been reported that n-alkanes are principal components of diesel exhaust nanoparticles. We investigated the effects of n-alkanes on the surface activity of a pulmonary surfactant monolayer using both fresh surfactant isolated from mouse lungs, and 1,2-dipalmitoyl-sn-glycero-3-phosphocholine (DPPC), a major component of lung surfactant. To examine the effect of n-alkanes on the surfactant, we compared surface pressure/trough area isotherm features and topographic images of DPPC in the presence and absence of a specific n-alkane (eicosane, C20H42) by Langmuir–Wilhelmy methods. The pure DPPC isotherm shows a typical plateau feature at a monolayer collapse pressure of 70 mN/m. The collapse pressure diminishes with increasing concentration of eicosane in DPPC. DPPC monolayers containing eicosane exhibit isotherms with one phase transition, but not the coexistence plateau of a liquid-expanded (LE) and liquid-condensed (LC) phase observed with a pure DPPC monolayer. Atomic force microscopy studies suggest that a DPPC monolayer containing eicosane has the phase transition from LE phase to LC phase and the protrusions are squeezed out from the monolayer, below the phase transition. On the other hand, eicosane changes the isotherm from mouse lung surfactant less dramatically than that of DPPC. The addition of increasing amounts of eicosane to mouse surfactant increases surface compressibility at 30 mN/m during the second compression, suggesting that the deposition of alkane-rich nanoparticles onto pulmonary surfactants may be related to dysfunction of surfactant activity during breathing.
