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Activities:
Barrier integrity, cell signaling, anti-inflammatory, cellular differentiation and apoptosis,1 intermediate in sphingomyelin synthesis (effects on cell membranes)2,3
Important Chemical Components:
Sphingolipids (sphingosine, phytosphingosine, or 6-hydroxysphingosine)
Linoleic acid
Origin Classification:
Ceramides are naturally occurring but synthetic forms and pseudoceramides are also available.
Personal Care Category:
Barrier repair moisturizer
Recommended for the following Baumann Skin Types:
DRNT, DRNW, DRPT, DRPW, DSNT, DSNW, DSPT, and DSPW. Important to use in all S4 (allergic) sensitive skin types.
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Ceramides are derived from the precursor glucosylceramides (GC), which is formed in large quantities by the epidermis and stored in lamellar granules. The enzyme responsible for GC synthesis has been localized to the golgi apparatus and is called ceramide glucosyltransferase.4 Structured in lamellar sheets, the primary lipids of the epidermis – ceramides, cholesterol, and free fatty acids – play a crucial role in the barrier function of the skin (see Chapter 19, Barrier Repair Ingredients). The intercellular lipids of the SC are composed of approximately equal proportions of ceramides (which may constitute up to 40 percent),5 cholesterol, and fatty acids.6 Ceramides are found in the upper levels of the stratum corneum (SC) but are not found in significant supply in the lower levels of the epidermis such as the stratum granulosum or basal layer. This is simply because ceramides are produced in the lamellar bodies in the granular layer of the SC.
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There are several ways to generate ceramides in mammalian cells7–9:
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Catabolism of sphingomyelin by the enzyme sphingomyelinase, which is coded by the gene SMPD1. (This is the most important pathway because sphingomyelin is abundant in most cell membranes.)
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De novo synthesis from palmitate and serine by the enzyme serine palmitoyltransferase (SPT), which is coded in part by the gene SPTLC1.10
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Hydrolysis of glucosylceramides by β-glucocerebrosidase.
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Hydrolysis of galactosylceramides by galactoceramidase.
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Synthesis from sphinogosine and fatty acid.
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Dephosphorylation of ceramide 1-phosphate.
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Production of ceramides is affected by many processes. Exposure to ultraviolet B (UVB) radiation and cytokines has been associated with an increase in the regulatory enzyme for ceramide synthesis, SPT and increased sphingolipid synthesis at the mRNA and protein levels.11 Stress and other causes of increased cortisol and exposure to glucocorticoids affect barrier function, but the mechanism has not yet been delineated.12 Dexamethasone stimulates ceramide biosynthesis by upregulating gene expression of SPT.13 Ceramide production has been shown to be increased by 1,25-dihydroxyvitamin D3, retinoic acid, ursolic acid, and lactic acid.14–17 An alkaline pH suppresses β-glucocerebrosidase and acid sphingomyelinase activity (these enzymes need an acidic pH).18 This is one of the reasons that alkaline soaps can result in poor barrier formation. In addition, a low or neutral pH is associated with poor barrier recovery.19
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Cytokines may also play a role ...