ENHANCED PERMEATION AND STRATUM-CORNEUM STRUCTURAL ALTERATIONS IN THEPRESENCE OF DITHIOTHREITOL

Stratum corneum protein biochemical and biophysical structural contrib utions to the barrier properties of human epidermis were determined in the presence of the reducing agent dithiothreitol (DTT). Mannitol and sucrose permeation through human epidermis in the presence of 0 to 50 mM DTT in PBS (pH 7.4) was measured in symmetric, side-by-side diffus ion cells (32 degrees C). DTT enhancement ratios, K-P(DTT)/K-P(PBS), r anging from 1.6 to 32, were dependent on skin donor and DTT concentrat ions. DTT did not alter stratum corneum uptake of mannitol or sucrose nor mannitol solubility in DTT/PBS solutions. Stratum corneum biophysi cal structure was ascertained by FTIR in solvent replacement experimen ts. DTT-induced protein conformational alterations were apparent in th e emergence of an Amide I band near 1615 cm(-1), which is generally as sociated with beta-sheet-like conformers. Therefore, DTT alters stratu m corneum biophysical structure through interactions with proteins. Af ter exposure of stratum corneum protein sheets to DTT/PBS solutions, t he free thiol concentration increased from < 1 nmol SH/mg protein shee t to approx. 130 nmol/mg. The enhanced permeation which increased with increasing concentrations of DTT, was associated with diffusion mecha nisms involving the cornified cells of the stratum corneum. These resu lts indicate that corneocyte protein integrity does contribute to barr ier function of the skin and influences the transport of polar solutes .