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Pechtold
X-ray microanalysis of cryopreserved human skin to study the effect of iontophoresis on percutaneous ion transport.Pechtold LA, Bodde HE, Junginger HE, Koerten HK, Bouwstra JA. Pharm Res. 2001 Jul;18(7):1012-7.
"PURPOSE: To study at the ultrastructural level which part of the skin is associated with percutaneous iodide transport by passive diffusion and iontophoresis.
METHODS: Following passive diffusion or iontophoresis of iodide, the morphology and the ion distribution of the skin was preserved by rapid freezing. The skin was kept frozen until and during examination by transmission electron microscopy (TEM) and X-ray microanalysis (XRMA). The intrinsic electron absorbing characteristics of cryopreserved skin allow direct TEM examination without additional staining. XRMA can be used to obtain in a relatively nondestructive way in situ information on ion distributions across the skin.
RESULTS: After passive diffusion, iodide was mainly found in the stratum corneum (SC), whereas there was little iodide in the viable epidermis. Iontophoresis up to 300 microA/cm2 did not significantly affect this distribution. With iontophoresis at 1,000 microA/cm2, the amount of iodide increased dramatically and was equally distributed over the SC and viable epidermis. The presence of iodide in the SC suggests that iodide is present inside corneocytes.
CONCLUSIONS: Iontophoresis up to 300 microA/cm2 does not significantly perturb skin structures in contrast to iontophoresis at 1,000 microA/cm2. The presence of iodide inside corneocytes suggests the possibility of transcellular percutaneous iodide transport."
Characterization of the stratum corneum lipid matrix using fluorescence spectroscopy.Pechtold LA, Abraham W, Potts RO. J Investig Dermatol Symp Proc. 1998 Aug;3(2):105-9. [abstract only]
"Using fluorescence techniques, we studied the dynamics of the lipid bilayer matrix of human stratum corneum (SC) and compared the results with that of distearoyl-phosphatidylcholine (DSPC). We employed a series of 9-anthroyloxy fatty acids (AF) that partitioned into the bilayer, enabling us to evaluate this structure as a function of depth within the lamellae. With AF probes, the re-orientation of the fluorophore is known to be affected by the polarity, hydrogen bonding, and rigidity of the surrounding medium, altering the emission maximum and lifetime in the excited state. In addition, we evaluated quenching, in which iodide collides with the fluorophore, revealing information on the accessibility of the fluorophore located in the bilayer. The emission and lifetime data showed that the reorientation of the fluorophore in SC was more hindered than in DSPC, indicating that SC bilayers were more rigid than DSPC bilayers. Quenching data of both SC and DSPC indicated that the deeper the fluorophore was positioned in the bilayer, the less accessible it was to iodide, pointing to a gradient in accessibility. In addition, the quenching results also showed that the SC is less accessible to iodide than in DSPC. The observed differences in bilayer rigidity and quencher accessibility between the two systems can be explained by differences in lipid composition and hydration. Whereas the DSPC bilayer consists of phospholipids, SC bilayers are composed of more anhydrous lipids like cholesterol and ceramides, which form a tight bilayer packing. In this way SC lipids exist in a relatively anhydrous and rigid environment, forming an effective diffusion barrier to water and ions."
The influence of an electric field on ion and water accessibility to stratum corneum lipid lamellae.Pechtold LA, Abraham W, Potts RO. Pharm Res. 1996 Aug;13(8):1168-73. [abstract only]
"PURPOSE: To study ion transport through stratum corneum (SC) lipid lamellae under passive and iontophoretic conditions.
METHODS: Iodide ion transport was measured by fluorescence quenching. Since the process involves diffusion of an iodide ion to the fluorophore located within the SC lamellae, the accessibility of iodide ions was measured. Moreover, the use of anthroyloxy fatty acid probes, provided information as a function of depth within the lamellae.
RESULTS: Fluorescence quenching by iodide ions increased with iontophoretic current density, suggesting increased ion accessibility within the SC lamellae. In addition, at constant current, quenching decreased as the fluorophore was located deeper within the lamellae. This gradient in ion accessibility suggests that more iodide is found near the head-group than near the core of the SC lipid lamellae. Results obtained in the absence of iodide also show increased water accessibility during iontophoresis.
CONCLUSIONS: These results show that in the presence of an applied electric field the SC lipid lamellae interior becomes more accessible to water and ions. These results imply that during iontophoresis, ion and water transport through human skin is associated, at least in part, with the SC lipid lamellae."
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