Properties of Ceramides and Their Impact on the Stratum Corneum Structure: A Review

Abstract

The lipid matrix of the stratum corneum (SC) is the major diffusion-rate-limiting pathway by which most drugs intracellularly pass the SC. The major lipid classes extracted from the SC are ceramides, cholesterol and free fatty acids. Ceramides that comprise nine subclasses play a crucial role in maintaining the barrier function of the skin. A profound knowledge of the physical properties of ceramides is essential for a deeper understanding of the impact of each ceramide species on the barrier function. The review summarizes the thermotropic and/or lyotropic behaviour of sphingosine-type ceramides (CER AS, CER NS) and phytosphingosine-type ceramides (CER AP, CER NP) revealed by differential scanning calorimetry, X-ray diffraction, Fourier transform infrared spectroscopy and Fourier transform Raman spectroscopy in past decades. Polymorphism is a characteristic feature of ceramides. At physiological temperatures, all crystalline phases of ceramides exhibit lamellar structures with highly ordered hydrocarbon chains. The differential behaviour of the head groups of ceramides may be an important determinant for the skin barrier function.

Potential Applications of Phyto-Derived Ceramides in Improving Epidermal Barrier Function

“…The acyl chain of CERs also exhibits heterogeneity in terms of chain length (C16-C30), the degree of unsaturation (predominantly saturated), and hydroxylation pattern [23]. The FAs in the epidermal CERs can be non-hydroxy acids, α-hydroxy acids, ω-hydroxy acids, or ester-linked ω-hydroxy acids [27]. While acyl chain lengths C24-C26 are the predominant FAs, chain lengths of C16-C18 are found in small amounts [19].…”

“…The deficiency of β-glucocerebrosidase in the epidermis alters the distribution of CERs and GlcCERs and the epidermal permeability barrier [36,43]. The impact of epidermal sphingolipids on the SC structure as well as their role in skin disorders have been reviewed by different authors [27,44]. …”

“…Low amounts of ω-9-monounsaturated very long-chain FAs (C22-C26), mostly α-hydroxynervonic acid (C24:1) in the leaf GlcCERs, are also found in plants [86,87,88]. On the other hand, skin CERs contain non-hydroxy, α-hydroxy or ω-hydroxy FAs, the latter having a chain length up to C32 and mostly ester-linked with unsaturated FA [5]. In plants ω-hydroxy FAs containing GlcCERs have not been yet found.…”

“…Ceramides (CERs) are essential components of the intercellular lipids of the SC. They play an important role in establishing and maintaining the water-retaining properties of the skin [5]. Studies have shown that the level of epidermal CERs is reduced in skin diseases such as atopic dermatitis (AD) [6,7] and psoriasis [8,9] and with increasing age [6,10], resulting in defective skin barrier and skin dryness.…”

Comparative atomic-scale hydration of the ceramide and phosphocholine headgroup in solution and bilayer environments

“…[22][23][24] The sphingolipid ceramide is a major component of the skin 25 and is involved in many cellular processes, such as signalling, 26 and is implicated in membrane regulation through lipid flip flop. 27 Additionally, both of these lipids have been shown to act as biomarkers for Alzheimer's disease.…”