Epidermal surface lipids

Abstract

A layer of lipids, which are of both sebaceous and keratinocyte origin, covers the surface of the skin. The apparent composition of surface lipids varies depending on the selected method of sampling. Lipids produced by the epidermal cells are an insignificant fraction of the total extractable surface lipid on areas rich in sebaceous glands. Due to the holocrine activity of the sebaceous gland, its product of secretion (sebum) is eventually released to the surface of the skin and coats the fur as well. Lipids of epidermal origin fill the spaces between the cells, like mortar or cement. The sebaceous lipids are primarily non polar lipids as triglycerides, wax esters and squalene, while epidermal lipids are a mixture of ceramides, free fatty acids and cholesterol. The composition of the sebaceous lipids is unique and intriguing and elevated sebum excretion is a major factor involved in the pathophysiology of acne. Recent studies have elucidated the roles that epidermal surface lipids have on normal skin functions and acne. IntroductionThe sebaceous gland is now considered to be an important endocrine organ. The holocrine eruption of the sebaceous cells results in the secretion and release of sebum, which eventually coats the surface of the skin and the fur. The majority of the epidermal surface lipids are in fact of sebaceous origin while the lipids produced by the epidermis are an insignificant fraction of the total extractable surface lipid. 1 That is more apparent on areas rich in sebaceous glands, where the epidermal origin lipids average between 5 to 10 μg per sq cm, compared with average recoveries of 150 to 300 μg of sebum per sq cm from the forehead. Since this chapter is part of a sebaceous forum, the focus will include both classes of lipids on the surface of the skin. In addition, areas rich in sebaceous glands are the areas that acne lesions are manifested.Human sebum is a mixture of non-polar lipids, mainly triglycerides, wax esters, squalene, fatty acids and smaller amounts of cholesterol, cholesterol esters and diglycerides. [2][3][4][5] On the other hand, lipids produced by keratinocytes are a mixture of almost equal proportions of free fatty acids, cholesterol and ceramides. 6 Figure 1 shows the representative structures of the various lipid classes of epidermal surface lipids. Sebaceous LipidsThe sebaceous lipids are unique and intriguing. According to Nicolaides: 7 "two key words characterize the uniqueness of skin lipids: complexity and perversity". The relative composition of sebum depends on the sampling method used. In particular, if the major components of sebum, triglycerides, are sampled before or after their modification by bacteria, which hydrolyze them to free fatty acids and glycerol. [7][8][9][10][11] The mean weight % that is often cited in the literature is given in Table 1.Interestingly, human sebaceous lipids are significantly different in quantity and quality from sebaceous lipids of other species. [12][13][14] The reason for such a unique sebum composition is not understood; how...

An Absence of Nuclear Lamins in Keratinocytes Leads to Ichthyosis, Defective Epidermal Barrier Function, and Intrusion of Nuclear Membranes and Endoplasmic Reticulum into the Nuclear Chromatin

“…Recently, Adeyo et al (46) found lipid droplet accumulation with a deficiency of SLURP1, a secreted peptide of keratinocytes. Triglyceride hydrolysis in the epidermal keratinocytes is known to be important for producing the lipids for lamellar bodies, which play key roles in skin barrier function (47)(48)(49)(50). We were able to identify lamellar bodies in the keratinocytes of Lmna Ϫ/Ϫ Lmnb1 ⌬/⌬ Lmnb2 ⌬/⌬ mice, but we suspect that they were ineffective in establishing a normal skin barrier, given the disorganization in the upper layers of the epidermis.…”

Raman active components of skin cancer

“…We observed that the amount of collagen was substantially lower in nonmelanoma skin cancer lesions as compared to normal skin. This could be explained by the breakdown of collagen in dermis due to the role metalloproteinases (MMP) play in degrading collagen and prohibiting procollagen biosynthesis [35]. The thickening of the epidermis also leads to reduced collagen signal collected by the probe.…”

“…Epidermal lipids act like a cement to fill the spaces between the cells. The major constituents of sebaceous lipids are triglycerides (triolein), wax esters and squalene, while the epidermal lipids are a mixture of ceramides, free fatty acids and cholesterol [35,36]. Ceramide is an important epidermal surface lipid as it composes almost half of the SC lipids [32].…”

Beyond acne: Current aspects of sebaceous gland biology and function

“…Sebum is a group of complex lipids including triglycerides and fatty acid breakdown products, wax esters, squalene, cholesterol esters and cholesterol [9][10][11][12][13] (Fig. 1).…”