Transdermal and lateral effective diffusivities for drug transport in stratum corneum from a microscopic anisotropic diffusion model

This paper presents a computational model of molecular diffusion through the interfollicular stratum corneum. Specifically, it extends an earlier two-dimensional microscopic model for the permeability in two ways: (1) a microporous leakage pathway through the intercellular lipid lamellae allows slow permeation of highly hydrophilic permeants through the tissue; and (2) the model yields explicit predictions of both lateral (D‾_‖^sc) and transdermal (D‾_⊥^sc) effective (average, homogenized) diffusivities of solutes within the tissue. We present here the mathematical framework for the analysis and a comparison of the predictions with experimental data on desorption of both hydrophilic and lipophilic solutes from human stratum corneum in vitro. Diffusion in the lipid lamellae is found to make the effective diffusivity highly anisotropic, with the predicted ratio D‾_‖^sc/D‾_⊥^sc ranging from 34-39 for fully hydrated skin and 150 to more than 1000 for partially hydrated skin. The diffusivities and their ratio are in accord with both experimental data and the results of mathematical analyses performed by others.

Low-flux electron diffraction study on body site dependence of stratum corneum structures in human skin

For analysis of the structure of human skin stratum corneum (SC), we introduced low-flux electron diffraction (ED) and developed a new statistical analysis method for obtained ED intensity profiles. By use of this method we compared the differences in the intercellular lipid organization on the SC corneocytes collected at human forehead, cheek, and forearm by the grid-stripping method. As a result, we found a significant regional difference in the distribution of lipid hydrocarbon chain packing domains in the SC; the ring-type ED pattern with orthorhombic symmetry was more often observed in the forearm SC than in the forehead and cheek SCs. We also found that the dependence of the background electron diffraction intensity on the modulus of the scattering vector differed significantly among them. The present method for the analysis of a large number of ED patterns of noninvasively obtained SC samples could be a powerful tool to scrutinize the structural difference between the SCs under various experimental conditions.

High concentration of the ester-linked ω-hydroxy ceramide increases the permeability in skin lipid model membranes

The ester-linked ω-hydroxy acyl chain linked to a sphingosine base referred to as CER EOS is essential for the skin barrier lipid organization. While the majority of the skin lipids form a dense, crystalline structure, associated with low permeability, the unsaturated moiety of CER EOS, (either the linoleate or the oleate chain) exists in a liquid phase at the skin's physiological temperature. Thus, the relationship between CER EOS and barrier function is not entirely comprehended. We studied the permeability and lipid organization in skin lipid models, gradually increasing in CER EOS concentration, mixed with non-hydroxy sphingosine-based ceramide (CER NS) in an equimolar ratio of CERs, cholesterol, and free fatty acids (FFAs) mimicking the ratio in the native skin. A significant increase in the orthorhombic-hexagonal phase transition temperature was recorded when CER EOS concentration was raised to 70 mol% of the total CER content and higher, rendering a higher fraction of lipids in the orthorhombic phase at the expense of the hexagonal phase at physiological temperature. The model's permeability did not differ when CER EOS concentration ranged between 10 and 30% but increased significantly at 70% and higher. Using CER EOS with a perdeuterated oleate chain, it was shown that the fraction of lipids in a liquid phase increased with CER EOS concentration, while the neighboring CERs and FFAs remained in a crystalline state. The increased fraction of the liquid phase therefore, had a stronger effect on permeability than the increased fraction of lipids forming an orthorhombic phase.

Mitochondrial content and gene expression profiles in oocyte-derived embryos of cattle selected on the basis of brilliant cresyl blue staining

The aim of this study was to investigate the developmental rate, lipid and mitochondrial distribution and gene expression in oocyte-derived embryos selected on the basis of brilliant cresyl blue (BCB) staining. Lipid content and mitochondrial distribution in Day 8 blastocysts were evaluated by fluorescence intensity, while gene expression was analyzed by real-time PCR. The proportion of blastocysts (30.9%) was greater (P<0.05) in BCB+ than in BCB- oocytes (13%) but not different (P>0.05) from the control group (28.2%). Total cell number was also greater in BCB+ (155.1 ± 36.2) than in BCB- (116.6 ± 40.5) and control (127.5 ± 35.7) blastocysts. Furthermore, the apoptotic cell number was less in BCB+ (3.7 ± 4.4) than in BCB- blastocysts (8.7 ± 8.7) but not different from the control group (5.9 ± 3.9). BCB+ embryos contained more mitochondria compared to BCB- embryos (P<0.05). There was no significant difference in intercellular lipid accumulation in embryos from all groups. Interferon-τ (IFNτ), transforming growth factor β1 (TGFB1) and secreted seminal-vesicle Ly-6 protein 1 (SSLP1) gene expression was greater in BCB+ than in BCB- blastocysts. By contrast, Bcl2-associated X protein (BAX) and heterogeneous nuclear ribonucleoprotein A2/B1 (HNRNPA2B1) gene expression was greater in BCB- than in BCB+ and control embryos. In conclusion, oocyte-derived embryos selected on the basis of BCB staining showed differences in developmental rate, quality, mitochondrial content and target gene expression compared to control embryos.

Thermal phase transition behavior of lipid layers on a single human corneocyte cell

We have improved the selected area electron diffraction method to analyze the dynamic structural change in a single corneocyte cell non-invasively stripped off from human skin surface. The improved method made it possible to obtain reliable diffraction images to trace the structural change in the intercellular lipid layers on a single corneocyte cell during heating from 24°C to 100°C. Comparison of the results with those of synchrotron X-ray diffraction experiments on human stratum corneum sheets revealed that the intercellular lipid layers on a corneocyte cell exhibit essentially the same thermal phase transitions as those in a stratum corneum sheet. These results suggest that the structural features of the lipid layers are well preserved after the mechanical stripping of the corneocyte cell. Moreover, electron diffraction analyses of the thermal phase transition behaviors of the corneocyte cells that had the lipid layers with different distributions of orthorhombic and hexagonal domains at 24°C suggested that small orthorhombic domains interconnected with surrounding hexagonal domains transforms in a continuous manner into new hexagonal domains.