(647j) The Impact of Cannabidiol and ?-Tocopherol on the Surface Activity of DPPC Monolayers

Vaping has raised concerns due to an increase in cases of EVALI (E-cigarette or Vaping Product Use-Associated Lung Injury). Common vape additives can disrupt the functioning of lung surfactants (LS) through unclear mechanisms. The LS is a mixture of proteins and lipids, with dipalmitoylphosphatidylcholine (DPPC) being the main component, constituting over 50 wt%. In the lungs, a monolayer of LS coats the surface of the alveoli, reducing tension between air and water, thereby facilitating breathing. Consequently, damage to the LS film can lead to dysfunctional breathing. We hypothesize that vaping additives may compromise the film structure and stability by displacing LS components from the surface. Furthermore, the accumulation of contaminants in the film might alter rheological properties and affect LS’s respreading ability during consecutive inspiration and expiration cycles.

In this work, we evaluate how two common vape additives, namely Cannabidiol (CBD) and α-tocopherol (Vitamin E), impact the surface activity of DPPC films when subjected to dilatational stress. To simulate area changes that alveoli experience during breathing, we used a Langmuir trough equipped with movable ribbon barriers. In dilatation experiments, the surface pressure is monitored during multiple compression and expansion cycles, and the film compressional moduli are calculated from the isotherm slopes during compression. These measurements help to elucidate film packing alterations caused by the presence of vaping additives, including phase transitions. Additionally, dilatational rheology measurements were performed with barrier oscillation experiments at 1% area change and a frequency of 200 mHz. With rheology experiments, we measured the dilatational moduli when (dynamic) oscillations occurred at a wide range of surface pressures, from 5 to over 70 mN/m. Taken together, our measurements characterize both the quasi-static and dynamic surface behaviors of DPPC films across multiple phase changes, including near zero-tension conditions (up to ~70 mN/m surface pressures).

Overall, our results showed that CBD only marginally impacts the surface activity and rheology of DPPC films. Conversely, the addition of 2.5 wt% Vitamin E significantly impacts film surface properties during compression, altering phase transitions and collapse. The maximum surface pressure upon compression of a pure DPPC film decreased from over 70 mN/m to about 65 mN/m with Vitamin E. Further, there was a significant decrease in dilatational moduli during oscillation experiments, especially in surface pressures near normal lung operation (~ 40 – 50 mN/m). Collectively, our results attest to the health risk posed by using electronic cigarettes, as accumulated vaping additives can interact with the LS monolayer, reducing film stability and respreading capabilities.