Infrared Spectroscopic Imaging Tracks Lateral Distribution in Human Stratum Corneum

Abstract

IR imaging provides concentration profiles, diffusion coefficients, and unique molecular level information about structural changes in the endogenous SC constituents and exogenous agents upon their mutual interaction. Transport along glyphs is the dominant mode of distribution for OA-d.

A quantitative radioluminographic imaging method for evaluating lateral diffusion rates in skin

“…The lateral diffusivities determined in this study are of the same order of magnitude as those estimated for other permeants in human SC by IR imaging [19] and FRAP [18] methods. In the former study, D || values were estimated to be in the range (3-10) × 10 − 9 cm 2 /s for perdeuterated oleic acid and 100 × 10 −9 cm 2 /s for perdeuterated dimethyl sulfoxide (DMSO).…”

“…It is shown in the Supplementary Material that the ratio D || /D ⊥ should be approximately equal to the corneocyte aspect ratio of 37.5. However, the values of D || /D ⊥ appearing in Table 3 or estimated from the results of Zhang et al [19] are much larger. Based on the deposition depth concept introduced in Ref.…”

“…The 27% reduction of D || in tapestripped SC versus undamaged SC was statistically significant (p b 0.05), yet it failed to explain the nearly 40-fold difference between the model prediction and experimental value for D || . Given that other groups are also finding high values for D || [18,19], it may be the assumption inherent in Wang et al's Model 2 that six lipid bilayers per corneocyte must be crossed during lateral transport is in error. Perhaps nature has not optimized the barrier for lateral transport in the SC, unlike that for transverse diffusion; i.e.…”

“…The permeants studied by Zhang et al [19] are known skin penetration enhancers, which may also contribute to their high lateral diffusion rates. DMSO, in particular, is thought to modify the structure of both the protein and lipid components of SC [19], thus could be a powerful enhancer even in the lipid-depleted, desquamating skin layers.…”

“…To gain experience withand confidence in -this method we included two chemically stable, well studied reference compounds, caffeine and testosterone [17], in the investigation. The phosphorimaging method is complementary to two other recently developed techniques in which either fluorescence after photo-bleaching (FRAP) [18] or high resolution infrared (IR) spectroscopy [19] was used to obtain similar information on lateral transport rates in skin. Development of these molecular imaging procedures overcomes many of limitations imposed by previous methods that rely on the analysis of dissected tissues [20][21][22][23][24][25].…”