Applied Cosmetic Science and Technology Applied Cosmetic Science and Technology

This study was conducted to clarify the role of disulfide bonds (SS) in corneocytes on the barrier function and the regulatory mechanism of the formation of SS in the stratum corneum (SC). Trans-epidermal water loss (TEWL) was measured in reconstituted human epidermal models (RHEMs) in which SS levels were modulated by the cleavage of SS with dithiothreitol (DTT). In corneocytes, thiol groups (SH) derived from SS treated with DTT and free SH were separately visualized by labeling with maleimide conjugated to different fluorophores. The oxidation of SH to SS in corneocytes was measured by the decrease in SH or the binding of dansyl glutathione (D-GSH) to corneocytes. Hydrophobicity was estimated by measuring the fluorescence intensity of 1-anilinonaphthalene-8-sulfonic acid (ANS). Quiescin sulfhydryl oxidases (QSOXs) in corneocytes were detected immunochemically. The reduction of SS in corneocytes of RHEMs increased TEWL and concomitantly decreased hydrophobicity. The decreased ratio of SH to SS in corneocytes toward the surface of the skin indicated that the oxidation of SH to SS progresses during cornification. In addition, we consider that QSOX1 could play a role in the oxidation of SH since it was present in corneocytes and the SC. Although SH in corneocytes decreased when incubated in a humidified atmosphere, SH did not decrease when incubated at a relative humidity of 4%. The binding of D-GSH to SH in corneocytes was faster at an acidic pH than at a neutral pH. These results indicated that SS in corneocytes play a crucial role in maintaining the SC barrier, and that SH might be oxidized enzymatically by QSOX1. Furthermore, they showed that a sufficient water content and a pH gradient toward an acidic pH at the surface are required to regulate the oxidation of SH to SS.