Sterols, epidermal

A totally different rationale has to be applied to the transport of hydrocarbons. These extremely hydrophobic compounds seem to reside in the interior of the lipophorin particles. A mechanism involving uptake and degradation of the lipoprotein might be possible for the transport of hydrocarbons to the epidermal cells. This type of mechanism might be important in certain stages of insect development, when the lipoprotein could deliver amino acids and other lipid components necessary for the construction of the cuticle. A similar process may also exist for the delivery of carotenoids and sterols. 

Another abnormality noted in Table 9 is the decreased amount of esterified cholesterol present. This probably represents a greater contribution of epidermal lipid to the total in relation to lipid coming from the sebaceous gland since Nicolaides and Rothman (Nl) showed that the epidermis is primarily responsible for the formation of free sterols. 

Modulation of epidermal lipid biosynthesis has been reported to boost drag delivery. It has also been suggested that it is both the hydrophobic nature of the lipids as well as their tortuous, extracellular localization that are responsible for the restriction in the transport of most molecules across the stratum comeum. The function of this barrier depends on three key lipids cholesterol, fatty acid, or ceramides. Delays of synthesis ceramides in the epidermis have been reported as means of barrier perturbation. Inhibitors of lipid synthesis were used to enhance the trans-A cmaV dehvery of hdocaine or caffeine. Alteration of barrier function was produced by the fatty acid synthesis inhibitor S-(tetradecyloxy)-2-furancarboxylic acid, the cholesterol synthesis inhibitor fluvastatin, or the cholesterol sulfate, which resulted in a further increase in lidocaine absorption (38). The major components of sebaceous lipids in the skin are 45-60% TAGs, 25% wax and sterol esters, 12-15% squalene and 10% free fatty acids (39). Some fatty acids, especially unsaturated fatty acids, are well-known skin penetration enhancers. The addition of PC to dermal dosage forms has been reported to increase percutaneous absorption. Lipid disperse systems (LDSs) containing polar lipids, such as PC and glycosylceramide, are also useful for... 

Several lines of evidence point to a connection between lipid metabolism and scaly skin. Inhibitors of cholesterol biosynthesis such as triparanol and nicotinic acid can produce scaly lesions superficially resembling ichthyosis. A disturbance of cutaneous sterol ester biosynthesis accompanies the hyperkeratosis of essential fatty acid deficiency, and increased ratios of free sterol to sterol esters have been reported in psoriasis and atopic eczema . We have recently shown that epidermal lipid biosynthesis is increased in lesions of psoriasis and lichen simplex, with the free sterol fraction affected more than other lipid classes. 

Epidermal sterol biosynthesis in ichthyosis vulgaris was studied by Summerly and Yardley , who found that acetate incorporation into sterols was increased (but not significantly so). These results were weight-corrected, and so may have been distorted by the presence of inert scale in the ichthyotic samples. We therefore decided to reinvestigate sterol biosynthesis in ichthyosis, within the context of total epidermal lipogenesis. 

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