Stratum composition

Sodium dodecyl sulfate has been used to induce a dry, scaly skin condition in human subjects by daily treatment with a 4% aqueous solution on one leg over a period of 2 weeks. Measurements were made of stratum comeum hydration, scaliness, and lipid composition which were used to assess in vivo surfactant perturbations on desquamation [381]. 

Y. A. Balakirov, A. I. Chemorubashkin, G. A. Makeev, I. P. Korolev, and V. N. Glushchenko. Composition for treatment of stratum head zone—contains oxyethylated isononyl phenol, aqueous solution of hydrofluoric acid and aqueous solution of hydrochloric acid. Patent SU 1770555-A, 1992. 

B. E. Dobroskok, Z. G. Gulyaeva, N. N. Kubareva, R. Kh. Muslimov, S. A. Nizova, V. V. Terekhova, E. E. Yanchenko, A. B. Zezin, V. A. Kabanov, R. Kh. Musabirov, and S. P. Valueva. Plugging composition for hydro-insulation of oil stratum—contains polydimethyl-diallyl ammonium chloride, sodium salt of carboxy methyl cellulose, sodium chloride and water. Patent SU 1758209-A, 1992. 

R. A. Mamleev, E. M. Yulbarisov, R. N. Fakhretdinov, L. N. Zagidul-lina, A. N. Kulikov, and Z. R. Kutushev. Composition for pumping into oil stratum—contains specified biopolymer, polydimethyldiallyl ammonium chloride, water and formaldehyde. Patent SU 1828161-A, 1997. 

Other than possibly for the insensible perspiration they absorb, transdermal patches tend to operate as thermodynamically static systems, meaning as com-positionally fixed systems, from the moment they are applied until their removal. Marketed ethanol-driven estradiol and fentanyl patches are exceptions because they meter out ethanol and drive it into the stratum corneum to propel the absorption process. Compositional steadfastness is still the rule, however, and it is this feature that bestows the zero-order delivery attribute on the ordinary transdermal patch. Drug is present within the patches in reservoir amounts whether or not the reservoir compartment is easily distinguished, for there must be enough drug to sustain delivery over the full course of patch wear. 

FIGURE 13.3. Sorption isotherms of water vapor as a function of the relative humidity, composition of constituents, and water content in the stratum comeum. 

Of particular interest are membranes prepared of an inert porous support carrying natural or artificial lipids. These coatings may comprise a single component, such as isopropylmyristate or dodecanol [99, 106], or mixtures of comparable composition as the stratum corneum intercellular bilayer [107, 108], Usually, synthetic lipids are used, due to an elaborate isolation procedure for stratum corneum lipids, with limited yield and the necessity of separation of triglycerides, originating from subcutaneous fatty tissue or skin care products [109],... 

P. M. Elias, E. R. Cooper, A. Korc, and B. E. Brown. Percutaneous transport in relation to stratum corneum structure and lipid composition. J. Invest. Dermatol. 76 297-301 (1981). 

M. W. De Jager, G. S. Gooris, I. P. Dolbnya, M. Ponec, and J. A. Bouwstra. Modelling the stratum corneum lipid organisation with synthetic lipid mixtures The importance of synthetic ceramide composition. Biochim. Biophys. Acta Bio-membr. 1664 132-140 (2004). 

K. Miyajima, S. Tanikawa, M. Asano, and K. Matsuzaki. Effects of absorption enhancers and lipid composition on drug permeability through the model membrane using stratum corneum lipids. Chem. Pharm. Bull. 42 1345-1347 (1994). 

The most superficial layer of skin is the stratum comeum (SC), which consists of terminally differentiated keratinocytes (comeocytes) that originate from actively proliferating keratinocytes in lower epidermis (basale, spinosum, and granulosum cells), and contain a lamellar lipid layer secreted from lamellar bodies (Fig. 7a). Flydration of the SC is an important determinant of skin appearance and physical properties, and depends on a number of factors including the external humidity, and its structure, lipid/protein composition, barrier properties, and concentration of water-retaining osmolytes (natural moisturizing factors, NMFs) including free amino acids, ions, and other small solutes. 

As an emollient, squalene is expected to increase skin hydration due to skin surface occlusions. In addition, squalene is a substance believed to maintain moisture in the stratum corneum. Novel substitutes were researched for vernix caseosa which is a reported highly efficient barrier cream for facilitating stratum corneum hydration for barrier-deficient skins. For this purpose, various lipid fractions were mixed with squalene, triglycerides, cholesterol, ceramides, and fatty acids to produce a mixture that can generate similar compositions of vernix caseosa (Rissmann et ah,... 

Microscopically, the skin is a multilayered organ composed of many histological layers. It is generally subdivided into three layers the epidermis, the dermis, and the hypodermis [1]. The uppermost nonviable layer of the epidermis, the stratum corneum, has been demonstrated to constitute the principal barrier to percutaneous penetration [2,3]. The excellent barrier properties of the stratum corneum can be ascribed to its unique structure and composition. The viable epidermis is situated beneath the stratum corneum and responsible for the generation of the stratum corneum. The dermis is directly adjacent to the epidermis and composed of a matrix of connective tissue, which renders the skin its elasticity and resistance to deformation. The blood vessels that are present in the dermis provide the skin with nutrients and oxygen [1]. The hypodermis or subcutaneous fat tissue is the lowermost layer of the skin. It supports the dermis and epidermis and provides thermal isolation and mechanical protection of the body. 

In the first part of this chapter, the formation and structure of the stratum corneum will be discussed. The second part describes the composition and organization of the intercellular stratum corneum lipids in vivo and in vitro. 

The lipid composition changes dramatically during terminal differentiation. After extrusion from the lamellar bodies, the polar lipid precursors are enzymatically converted into more hydrophobic lipids. As a result, phospholipids are almost absent in the stratum corneum. The lipid lamellae surrounding the corneocytes are predominantly composed of ceramides, cholesterol, and free fatty acids. It is generally assumed that these lipids are present in nearly equimolar ratios. However, inspection of literature data shows that there is a high interindividual variability in the lipid composition [37],... 

The composition of the free fatty acids is also unique. In both human and pig stratum cornea, the free fatty acid fraction consists mainly of long and saturated hydrocarbon chains [44,45], Oleic and linoleic acid are the only unsaturated free fatty acids detected in the stratum corneum. There are various sterols present in human stratum corneum, of which cholesterol predominates. Cholesterol is the only major lipid class that is present in both plasma membranes and the intercellular lipid lamellae. Cholesterol is synthesized in the epidermis and this synthesis is independent of the hepatic one. A minor fraction is sulfated to... 

Altered Lipid Composition and Organization in Stratum Corneum of Diseased and Dry Skin... 

All the above-mentioned changes in lipid composition and organization in diseased and dry skin likely contribute to an impaired stratum corneum barrier function and increased susceptibility to dry skin. However, as previously indicated, abnormalities in the process of envelope formation may also strongly influence the stratum corneum barrier integrity. Therefore, more information is required to elucidate the precise mechanisms by which stratum corneum structure and function are altered. 

The above results demonstrate that the unique stratum corneum lipid organization can be reproduced in vitro with mixtures based on cholesterol, free fatty acids, and a limited number of synthetic ceramides. The results further reveal that the formation of the LPP is rather insensitive toward changes in the total composition of cholesterol, CER, and free fatty acids over a wide range of molar ratios. This is in excellent agreement with the in vivo situation, in which a high interindividual variability in stratum corneum lipid composition usually does not lead to substantial changes in the lipid organization. 

Wertz, P.W., et al. 1985. The composition of the ceramides from human stratum corneum and from comedones. J Invest Dermatol 84 410. 

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