Protein oxidation in human stratum corneum: Susceptibility of keratins to oxidation in vitro and presence of a keratin oxidation gradient in vivo

The stratum corneum is located at the interface between body and environmen t and thus is constantly exposed to a pro-oxidative environment. Previously , we have demonstrated that stratum corneum lipids are targets of oxidative stress induced by ozone and by ultraviolet A and B exposure, Here, we empl oyed an immunoblotting technique to detect protein oxidation in human strat um corneum obtained by tape stripping, After lysis, protein carbonyl groups were measured by derivatization with dinitrophenylhydrazine, separation by sodium dodecylsulfate-polyacrylamide gel electrophoresis, and immunoblotti ng using antibodies against dinitrophenyl groups. Keratin 10, identified by use of specific antibodies and by microsequencing, was demonstrated in vit ro to be oxidizable by ultraviolet A irradiation, hypochlorite, and benzoyl peroxide. In vivo, a keratin 10 oxidation gradient with low levels in the lower stratum corneum layers, and about 3-fold higher contents of carbonyl groups towards the outer layers was demonstrated in forehead stratum corneu m of healthy volunteers (n = 6). As protein oxidation can be associated wit h an increased susceptibility to proteases, this finding may be important f or better understanding the process of desquamation.