Stiffening Effect of Ceramide on Lipid Membranes Provides Non-Sacrificial Protection against Potent Chemical Damage.

Ceramide is a sphingolipid that constitutes only a small fraction of membrane biomolecules but plays a central role in regulating many biological processes. The ceramide level in cell membranes can drastically increase in response to external damage, which has been hypothesized to involve ceramide's biophysical role that increases the membrane packing density and lowers the membrane permeability. However, direct observation of the consequent influence on membrane chemistry resulting from these ceramide-induced physical properties has been absent. Using our unique field-induced droplet ionization mass spectrometry technique combined with molecular dynamics simulations, here we report that the addition of ceramide to POPC monolayer membranes at the air-water interface greatly reduces the chemical damage from potent chemicals, • OH radicals, and HCl vapor, by stiffening the membrane packing and lowering the permeability. These results shed new light on the underlying chemoprotective role of ceramide in lipid membranes, which might serve as a previously unknown protection mechanism in response to external stimuli that cause cell stress or death.