Effects of ozone on stratum corneum lipid integrity and assembly.

The stratum corneum (SC) acts as the main barrier of the skin against exogenous substances (e.g. air pollutants) and against the loss of endogenous substances such as water. The SC consists of keratin-rich dead cells surrounded by crystalline lamellar lipid regions. The main lipid classes are ceramides (CERs), free fatty acids (FFAs), and cholesterol (CHOL). Tropospheric ozone (O) is a potent oxidant compound that reacts instantly with biological molecules such as lipids and proteins. Although it has been reported that O induces biological responses at the cellular level, to the best of our knowledge, there is no information related to the damages O can cause at the level of the SC extracellular lipid matrix. The aim of our work was to investigate which SC lipid subclasses are prone to oxidation when exposed to O and how the changes in chemical structures affect the lipid organization in a stratum corneum substitute (SCS) membrane. Ultimately, the barrier properties of the SCS were examined. Our studies revealed that O induces chemical modifications of the unsaturated bonds in CERs and CHOL. The appearance of carbonyl groups at the headgroup level and the removal of the linoleate moiety of omega‑O‑acylceramides (CER EOS) impact the lamellar organization of the lipid assembly and to a lesser extent the lateral packing of the lipids. Unexpectedly, these changes improved the barrier function of the SCS.