Enhanced permeation and stratum corneum structural alterations in the presence of dithiothreitol

Stratum corneum protein biochemical and biophysical structural contributions 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 diffusion cells (32 degrees C). DTT enhancement ratios, KP(DTT)/KP(PBS), ranging from 1.6 to 32, were dependent on skin donor and DTT concentrations. DTT did not alter stratum corneum uptake of mannitol or sucrose nor mannitol solubility in DTT/PBS solutions. Stratum corneum biophysical structure was ascertained by FTIR in solvent replacement experiments. DTT-induced protein conformational alterations were apparent in the emergence of an Amide I band near 1615 cm-1, which is generally associated with beta-sheet-like conformers. Therefore, DTT alters stratum corneum biophysical structure through interactions with proteins. After exposure of stratum corneum protein sheets to DTT/PBS solutions, the free thiol concentration increased from < 1 nmol SH/mg protein sheet to approx. 130 nmol/mg. The enhanced permeation which increased with increasing concentrations of DTT, was associated with diffusion mechanisms involving the cornified cells of the stratum corneum. These results indicate that corneocyte protein integrity does contribute to barrier function of the skin and influences the transport of polar solutes.