Sebaceous lipids

The earliest morphological change in the sebaceous follicle is an abnormal follicular epithelial differentiation, which results in ductal hypercornification. Cornified cells in the upper section of the follicular canal become abnormally adherent. Comedones represent the retention of hyperproliferating ductal keratinoc-ytes in the duct. Several factors have been implicated in the induction of hyperproliferation sebaceous lipid composition, androgens, local cytokine production (IL-i, EGF) and bacteria (P. acnes). 

A linearization of the steady-state concentration gradient could be demonstrated by relating the depth to the weight of the tissue, removed per piece of adhesive tape. However, large errors, especially, within the first tapes, cast doubt over these findings [127, 128], The procedure is time-consuming and artifacts, due to absorption and desorption of moisture, formulation excipients, or sebaceous lipids, are likely. 

Pilgram, G.S.K., et al. 2001. The influence of two azones and sebaceous lipids on the lateral organization of lipids isolated from human stratum corneum. Biochim Biophys Acta Biomembr 1511 244. 

Thermal lipid transitions in the physiologic temperature range have also been reported for porcine [32] and neonatal murine [43] SC. Based on arguments similar to those presented above, the transition near 20°C in porcine SC detected by IR has been attributed, not to sebaceous lipids, but to a solid-to-fluid phase change for a small fraction of SC lipids. 

The major components of sebaceous lipids in the skin are 45-60% triacylgly-cerols, 25% wax and sterol esters, 12-15% squalene and 10% free fatty acids (34). 

The general rational to use certain oils in cosmetics is usually based on the belief that TAG oils with fatty acids similar in composition to the human skin will have beneficial properties. This belief is not entirely true the major components of sebaceous lipids are 45-60% TAG, 25% wax and sterol esters, 12-15% squalene, and 10% free fatty acids (34). 

The greatest amounts and variety of waxes in terrestrial mammals are associated with the skin. The epidermal cells play a role in synthesizing surface lipid but the major input is provided by the sebaceous glands. These are connected via a duct into a hair canal from which sebaceous lipid travels to the surface over a period of about a week. 

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... 

Other anal sac constituents which are commonly encountered products of microbial activity include trimethylamine, noted in the anal sac secretions of the red fox (42), coyote and domestic dog [36), and the aromatic acids phenylacetic acid and 3-phenyl-propionic acid (and related phenolic acids), together with the diamines putrescine and cadaverine as well as ammonia in the anal sac secretions of the red fox and the lion (25,29,35). Indole has also been noted. The lower molecular weight lipids of lion anal sac secretion include many substances expected as hydrolysis products of sebaceous lipids (2. Red fox anal sac secretion also exhibits an anomalous free amino-acid composition with 5-aminovaleric acid predominating ( ). The possibility that the sulfur-containing volatiles present in mustelid anal sac secretions are of microbial origin is at present under investigation in our laboratories. 

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