The Identification and Quantification of Diverse Ceramides in the Stratum Corneum

As is known to all, ceramides, a kind of lipids found in skin cells, are an important part of the stratum corneum (SC). As the outermost layer of the skin, the stratum corneum (SC) is the bond to connect our body to the outside. Acting as a barrier, the SC prevent the unnecessary materials from entering our bodies and avoid too much water leaving from our bodies. Recently, the quantitative analysis to distinguish ceramides with different long-chain base lengths has been reported.

Many skin diseases, such as atopic dermatitis and psoriasis, result from the changes in the levels and components of ceramides. Therefore, it is important to recognize and quantify ceramides in skin. Ceramides are compose of a long-chain base connected to a fatty acid through an amide link. The ceramides of mammals contain any of the five types of long-chain bases – dihydrosphingosine, sphingosine, phytosphingosine, 6-hydroxysphingosine and 4,14-sphingadiene, with each of them differing from quantities and locations. As a result, twenty kinds of different human ceramides may occur if we combine each long-chain base with any one of the fatty acids. Human ceramides might be more complicated due to the existence of different chain lengths in fatty acids. The ceramides components in human skins are quite complicated. As a result, it is not easy to recognize and quantify each of these ceramides.

Researchers decided to address the complex lipidome. They successfully identify and quantify more than 300 unbound ceramides and 63 protein-bound ceramides with two and three hydroxyl groups and 18 long-chain carbon bases combining multiple reaction monitoring (MRM) mode of LC-MS/MS and various ceramides. Then, they expanded this study and include ceramides with two and three hydroxyl groups and 16 to 26 long-chain carbon bases to capture the full view of ceramide composition in human SC.

They use the MRM mode in LC/MS/MS rather than the ion scanning mode with less sensitivity to identify and quantify 1,327 unbound ceramides and 254 protein-bound ceramides. These ceramides are with two and three hydroxyl groups and 16 to 26 long-chain carbon bases. It is the first step to completely understand the skin ceramide composition of the patients with skin diseases, such as atopic dermatitis, psoriasis, and ichthyosis. It has been reported that ceramide composition has been changed under such condition. However, the certain composition has never been identified or quantified before. If we could characterize the ceramide composition in the skin diseases completely, the relationship between changes of ceramide composition and disease pathology can be explained to further help developing the methods of diagnosing and treating each diseases.

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