Stratum corneum electron microscopy

In addition, data obtained from infrared, thermal, and fluorescence spectroscopic studies of the outermost layer of skin, stratum corneum (SC), and its components imply enhancer-improved permeation of solutes through the SC is associated with alterations involving the hydrocarbon chains of the SC lipid components. Data obtained from electron microscopy and x-ray diffraction reveals that the disordering of the lamellar packing is also an important mechanism for increased permeation of drugs induced by penetration enhancers (for a recent review, see Ref. 206). 

There are several genetic skin diseases with known defects in the lipid metabolism. Atopic dermatitis, lamellar ichthyosis, and psoriasis have been the most widely studied with respect to epidermal barrier function and alterations in the lipid profile. Deviations in the lipid profile have been linked with an impaired stratum corneum barrier function. Atopic dermatitis is characterized by inflammatory, dry and easily irritable skin, and overall reduced ceramide levels in the stratum corneum [58-60]. In particular a significant decrease in the ceramide 1 level is observed, whereas the levels of oleate that is esterified to ceramide 1 are elevated [59]. Both aberrations may be responsible for the reduced order of the lamellar phases as observed with freeze fracture electron microscopy [61]. It has further been established that, in comparison to healthy stratum corneum, the fraction of lipids forming a hexagonal packing is increased [61]. A recent study reveals that the level of free fatty acids... 

Psoriasis is a chronic skin disorder, in which an abnormally fast transition of basal cells into corneocytes results in a thickening of the stratum corneum. Transmission electron microscopy studies show an aberrant stratum corneum lipid ultrastructure in psoriatic skin [66], which is expected to be related to abnormalities in the lipid profile. Particularly, a significant reduction in ceramide 1 and a predominance of sphingosine ceramides at the expense of phytosphingosine ceramides are reported in psoriatic stratum corneum [67,68],... 

A number of works investigated the interaction between niosomes and human skin. With niosomes prepared from Ci2 alcohol polyoxyethylene ether and cholesterol, vesicular structures of about 100 nm size have been observed between the first and second layers of human corneocytes 48 h after incubation as well as in the deeper strata of the skin [37], The authors concluded that the structures visualized in the deeper regions could be vesicles reorganized from individual molecules that penetrated the skin. In another study, electron micrographs illustrated that niosomes containing surfactants and cholesterol affected only the most superficial corneocytes. Moreover, two-photon fluorescence microscopy confirmed that fluorescent probe encapsulated in niosomes was confined to the intercellular spaces within the apical stratum corneum layers [56]. 

Figure 9 Freeze-fracture electron microscopy of control (a) or after treatment of alkyl-azones (b-f). (b) Hexyl-azone (c) octyl-azone (d) dodecyl-azone (e) myristyl-azone and (f) oleyl-azone. Bar represents 100 nm. represents rough structures indicating either separate domains of enhancer or more perturbation of lipid lamellae. Arrows indicate a clear presentation of the intact smooth regions of intact lamellae with steps (fracture across the lamellae). C, Corneocyte scl, stratum corneum lipid lamellae. 

B. A. I. van den Bergh, M. A. Salomons-de Vries and J. A. Bouwstra, Interactions between liposomes and stratum corneum studied by freeze substitution electron microscopy, Int. J. Pharm. 167 51-61 (1998). 

D. A. van Hal, E. E. Jeremiasse, H. E. Junginger, F. Spies, and J. A. Bouwstra, Structure of fully hydrated human stratum corneum a freeze fracture electron microscopy study, J. Invest. Dermatol. 706 89-95 (1996). 

To better understand the structure, function, and dynamics of the endogenous lipid matrix of the stratum corneum intercellular space some general principles of lipid phase behavior, dynamics, and structural organization may represent a useful starting point. Further follows a short overview of some basic physico-chemical principles that may be of relevance for stratum corneum lipid research, followed by a presentation of the new technique cryo-transmission electron microscopy of fully hydrated vitreous skin sections and how this technique recently has been applied to the study of the structural organization and formation of the lipid matrix of the stratum corneum intercellular space. 

Lanolin appears to penetrate into the stratum corneum, but remains in the more superficial layers.38 39 Using the tape stripping technique, Clark demonstrated the penetration of anhydrous lanolin (2 mg/cm2) applied to the flexor aspect of the inner forearm.40 Almost all of the applied lanolin was recovered and most was removed in the first 15 strippings. Although the bulk of lanolin may remain in the superficial layers, electron-dense lead linoleate and lead oleate topically applied in lanolin were observed by transmission electron microscopy to be localized in intracellular spaces as far down as the stratum granulosum 40... 

Electron microscopy and X-ray microanalytical methods showed that uranium as uranyl nitrate hexahydrate penetrated the stratum corneum within 15 minutes and accumulated in the intracellular space between the viable epidermis and the stratum corneum (De Rey et al. 1983). As is the case with inhalation and oral absorption, water solubility is an important determinant of absorption, and no penetration was observed with the insoluble compounds uranium dioxide, uranyl acetate, or ammonium diuranate. After 48 hours, uranium applied as uranyl nitrate was no longer found in the skin and toxicity developed, indicating that the uranium had been absorbed into the blood. 

Stratum corneum breaking strength decreases fourfold over the 0-100% RH range reaching a minimum at approximately 90% RH which is not lowered further by immersion in water. Of fundamental importance is the morphological location within the stratum corneum where failure occurs under a uniaxial load. Scanning electron microscopy (SEM) and conventional analysis of fractured samples indicate that the samples predominately fracture within the intercellular junctions rather than intracellularly (9). 

B38. Brody, I., The ultrastructure of the epidermis in psoriasis vulgaris as revealed by electron microscopy. 4. Stratum corneum in parakeratosis without keratohyalin. J. Ultrastruct. Res. 6, 354-367 (1962). 

The moisture content can be measured in vitro by means of gravimetry or electron microscopy, or by magnetic resonance techniques in vivo. The resolution of the latter technique is, however, currently not sufficiently high to enable isolated measurements on the stratum corneum. Compared with these techniques, assessment of stratum corneum hydration by means of electrical measurements (susceptance) represents an important reduction in instrumental cost and complexity. 

The ultrastructure of the stratum corneum was examined by scanning electron microscopy (SEM). The findings on SEM of skin surface replicas are... 

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