WHAT YOU WILL LEARN IN THIS ARTICLE:
- Ceramides: What Are They?
- What Types of Ceramides Can We Find?
- What Is Their Role in the Skin?
- How to Study Ceramides
- How to Evaluate the Effect of a Formulation on Ceramides
Ceramides can be found in countless cosmetic formulations, as you may have probably noticed when walking down the personal care products aisle in the supermarket or strolling through any cosmetic store. Even more, cosmetology experts and skincare influencers everywhere sing the praises of these ceramide-containing formulations.
Some people refer to them as “a must-have skincare ingredient” or even as “miraculous”. But… What is their role in the skin’s health and beauty? And most importantly, are their benefits real?
Let’s take a look first at what they are and the different types of ceramides we can find. Next, we’ll discuss their role in the skin and precise their importance in the skin’s health and beauty.
Ceramides: What Are They?
Ceramides are – chemically speaking – a type of lipid. More specifically, they result from the combination of a sphingoid base with a fatty acid. Both moieties are bonded through an amide linkage.
Figure 1. Basic chemical structure of ceramides. In this example, ceramide N24S18 is illustrated.
The epidermis is the most superficial layer of the skin, and its main cellular components are keratinocytes. We can distinguish four epidermal sublayers according to the differentiation state of the epidermal keratinocytes. Terminally differentiated keratinocytes (therefore localized in the outermost sublayer, the stratum corneum) are known as corneocytes, which are the cells responsible for synthesizing and secreting ceramides.
The stratum corneum is frequently compared to a brick-and-mortar type of arrangement since it is essentially made of corneocytes (the “bricks”) embedded in a lipidic matrix of not only ceramides but also cholesterol and free fatty acids (the “mortar”). This matrix is also known as “intercorneocyte cement” precisely because it helps fill the spaces between the cells, creating a compact barrier that protects the body from the external environment. Just as important, the skin’s barrier function prevents dehydration and moisture loss.
Furthermore, ceramides play a role in epidermal self-renewal, and immune responses. Indeed, disease states, including several inflammatory dermatoses, are caused by an altered metabolism of ceramides.
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What Types of Ceramides Can We Find?
In terms of chemical structure, we can find a wide diversity of ceramides species, and their distribution varies according to the body site evaluated (e.g., skin, hair, nails, etc.).
They are classified into different types based on both the molecular type of sphingoid base and the molecular type of fatty acid. Sphingoid bases can be of four types: dihydro-sphingosine (DS), sphingosine (S), phytosphingosine (P), and hydroxy-sphingosine (H); whereas fatty acids (FA) can be of roughly three types: non-hydroxy FA (N), α-hydroxy FA (A), and esterified ω-hydroxy FA (EO).
The different combinations of sphingoid bases and fatty acids result in 12 types of ceramides, as shown in the table below:
| Sphingoid base (right) // Fatty acid (down) | Dihydro-sphingosine (DS) | Sphingosine (S) | Phytosphingosine (P) | Hydroxy-sphingosine (H) |
| Non-hydroxy (N) | NDS | NS (Cer2) | NP (Cer3) | NH (Cer8) |
| α-Hydroxy (A) | ADS | AS (Cer5) | AP (Cer6) | AH (Cer7) |
| Esterified ω-hydroxy (EO) | EODS | EOS (Cer1) | EOP (Cer9) | EOH (Cer4) |
Table 1. Classification of ceramides based on the types of sphingoid base and fatty acid.
What Is Their Role in the Skin?
As mentioned before, ceramides contribute to the integrity of the epithelial barrier that protects the body from external stresses, such as factors causing TEWL (Transepidermal Water Loss). Since ceramides are the main lipid species found in the epidermal barrier, preventing dehydration and moisture loss relies on an appropriate balance of ceramide species. Unfortunately, it has been observed that levels of ceramides naturally decline with age, which contributes to skin dehydration and irritation.
Apart from the natural aging process, several skin diseases and conditions have been correlated to a modification of the ceramide species profile. Examples of this are atopic dermatitis, acne, and psoriasis.
So, ceramides are not only crucial for maintaining a youthful-looking skin but also determinant for skin homeostasis and health, which explains the great interest they attract in the dermatology and cosmetic fields.
How to Study Ceramides
In the past, the study of ceramides relied greatly on the use of Thin Layer Chromatography (TLC). This technique enabled the detection of ceramides in a sample, but it only provided general information regarding the species present, namely the ceramide class (Cer1-9, as seen in Table 1).
Today, the study of ceramides relies mainly on the use of LC-MS (Liquid Chromatography coupled to Mass Spectrometry). Chromatography and Mass Spectrometry are analytical techniques that enable the separation and precise identification of the different ceramides present in a given sample. The combination of LC and MS is the most useful when analyzing epidermal ceramides. Briefly, ceramides are fragmented into product ions and then separated according to their mass-to-charge ratio (m/z) values. What allows the identification of the different ceramides is the characteristic and distinct fragmentation patterns generated.
The scanning mode is usually used for qualitative analysis (identification of the species present in the sample), whereas other methods –which rely on the use of internal standards– allow a quantitative analysis (both detection and quantification).
The results of an LC-MS analysis can be visualized as a chromatogram. In these graphs, the x-axis represents the retention time, and the y-axis the signal intensity (directly proportional to the abundance of the species). In this way, each peak can be univocally associated with a unique molecular species.
Figure 2. Example of a chromatogram. Sebaceous lipids were recovered by clinical swab, and further LC-MS analysis confirmed the presence of ceramides.
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How to Evaluate the Effect of a Formulation on Ceramides
QIMA Life Sciences provides you with qualitative and semi-quantitative assays to evaluate the ability of your compound to modulate ceramides synthesis and elongation.
This is of particular interest to derma and cosmetics manufacturers since it provides a means to study how short- and long-chain ceramides abundance is affected by their products or ingredients. Assays can be performed either in vitro (2D or 3D models) or in vivo (clinical studies) followed by LC/MS ceramides analysis.
In Fig. 3 (left), we can observe the opposite effects of two compounds on the abundance of ceramides present in a Normal Human Epidermal Keratinocytes (NHEK) 2D in vitro model. The first compound (CTRL+) increased the amount of ceramides, while the second one (CTRL-) inhibited their synthesis.
In Fig. 3 (right), we can observe how increasing concentrations of the same compound (CTRL+) resulted in increasing amounts of long-chain ceramides in a Reconstructed Human Epidermis (RHE) 3D in vitro model.
Figure 3. Evaluation of the in vitro effect of two compounds (CTRL+ and CTRL-) on ceramides synthesis and elongation. To see other examples and learn more about our in vitro assays to evaluate the ability of your compound to modulate ceramide synthesis and elongation, download our flyer.
Long-chain ceramides are particularly important since they have a more predominant role in the barrier function. Unlike short-chain ceramides, long-chain ceramides favor lateral order in lipid packing due to greater polar interaction between the aliphatic tails.
In this sense, 3D in vitro models are particularly useful since they help us evaluate the chain elongation process: the more superficial the location in a multilayer arrangement, the higher the proportion of long-chain ceramides. Indeed, this phenomenon is associated with keratinocyte differentiation: the prolonged incubation of the 3D model provides additional time for the enzymes responsible for chain elongation to act on ceramides.
As mentioned before, samples can also be collected directly from patients or subjects during a clinical study. An excellent way of achieving this is by using collection kits based on swabbing. This universal method is non-invasive and incredibly versatile, i.e., it can be used to collect samples from different parts of the body (including lipids on the skin surface).
References
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