Lipids, human skin

We have already stressed the potential importance of lipid-rich membranes in the skin as potential targets for ROS-induced damage and ageing of human skin is morphologically identical to changes found by peroxidative processes (Serri et al., 1977). The involvement of AA metabolites in skin disease, and in particular psoriasis, has been the subject of much recent interest. Studies have included topical and intradermal administrations of AA metabolites, and assay of such products in clinical specimens. Results show that concentration of AA, 12-hydroxy-eicosatetraenoic acid (12-HETE), PG and leu-kotrienes are increased in psoriatic lesions (Hammarstrom etal., 1975 Camp etal., 1983 Brain etal., 1984 Duell et al., 1988) and also that full-thickness epidermis from normal and diseased skin has the enzymatic capacity to convert AA to some of the same metabolites (Hammarstrom etal., 1975, 1979 Camp etal., 1983 Brain etal., 1984 Ziboh et al., 1984 DueU et al., 1988). The biological effect of both 12-HETE and leukotrienes was confirmed by both topical application and intradermal injection, which caused epidermal inflammation and... 

In contrast to transition metals iron and copper, which are well-known initiators of in vitro and in vivo lipid peroxidation (numerous examples of their prooxidant activities are cited throughout this book), the ability of nontransition metals to catalyze free radical-mediated processes seems to be impossible. Nonetheless, such a possibility is suggested by some authors. For example, it has been suggested that aluminum toxicity in human skin fibroblasts is a consequence of the enhancement of lipid peroxidation [74], In that work MDA formation was inhibited by SOD, catalase, and vitamins E and C. It is possible that in this case aluminum is an indirect prooxidant affecting some stages of free radical formation. 

Most of the research on human exocrine secretions and excretions has probably been devoted to the chemistry of human skin lipids. To a certain extent, this could be due to the interest of the cosmetic industry in the chemical compounds found on the human skin and the chemical processes they are subjected to by the environment. It is possible that some of the proprietary in-... 

Particles from cationic lipids may also be useful for antisense therapy of skin disease — a nontoxic increase in the oligonucleotide uptake by cultivated keratinocytes and a sebocyte cell line has been reported [66]. Moreover, cationic dendri-mers also efficiently transfer reporter gene DNA to human keratinocytes cultivated in vitro. In the skin of hairless mice, in vivo transfection was possible with complexes, yet reporter gene expression was localized to perifollicular areas. Transfection, however, failed with the naked plasmid. For prolonged contact, biodegradable membranes coated with dendrimer/DNA complexes were used [67]. This hints at a follicular uptake of these complexes and indicates that gene transfection also may be possible with human skin, which has a thicker stratum comeum compared with mouse skin (eight to ten vs. two to three layers [58]). 

Lupulescu AP, Birmingham DJ. 1975. Effect of lipid solvents on protein, DNA, and collagen synthesis in human skin An electron microscopic autoradiographic study. J Invest Dermatol 65(5) 419-422. 

Vile, G. R, and Tyrrell, R. M. 1995. UVA radiation-induced oxidative damage to lipids and proteins in vitro and in human skin fibroblasts is dependent on iron and singlet oxygen. Free Rad. Biol. Med. 18 721-22. 

One of the main causes of cell damage, especially on skin is oxidation. In case of human skin, exposure to sunlight induces a lipid peroxidation process in human skin layer which leads to deterioration. In this matter, squalene has been reported to protect human skin from lipid peroxidation caused by either UV exposure or any other oxidative stress. 

Among the compounds present in the lipids of human skin are a variety of branched fatty acids, both free and combined. They may play a role in maintaining the ecological balance among microorganisms of the skin, and they also impart to each individual a... 

Most animal steroids arise from cholesterol, which in turn is derived from squalene. This C30 triterpene, whose biosynthesis is described in Section B, is named after the dogfish Squalus in whose liver it accumulates as a result of blockage in oxidation to cholesterol. Squalene is also a prominent constituent of human skin lipids. Its conversion to cholesterol, which takes place in most animal tissues,117/154-156 is initiated by a microsomal enzyme system that utilized 02 and NAD-PH to form squalene 2,3-oxide (Fig. 22-6, step a). 

Another striking difference between normal and cultured skin is shown in Fig. 15.6. As discussed above (see Fig. 15.3c, factor 2), cholesterol-rich pockets containing highly ordered lipid chains are occasionally detected in human skin and are characterized by a Raman-active mode of cholesterol near 700 cm-1 and an intense lipid C-C stretch near 1130 cm-1 in Fig. 15.4a and b, respectively. The intensity of the cholesterol mode is normalized to a Phe vibration near 620 cm-1 and imaged in Fig. 15.6b. As is evident there are many such pockets in the cultured skin model, in contrast to human skin where they are only rarely observed (Fig. 15.3c, factor 2), and usually in the viable epidermis rather than in the SC (as in the cultured skin). These measurements illustrate the power of confocal Raman microscopy for combining spatial measurements with molecular structure characterization. 

Stewart, M.E., and D.T. Downing. 1999. A new 6-hydroxy-4-sphingenine-containing ceramide in human skin. J Lipid Res 4 1434. 

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