Lipid mixture for improved skin protection

Differentiating cells stop to divide but start a programme of selected genes to be highly expressed. Genes encoding proteins being used for creation of the fully keratinised epidermis – such as involucrin, loricrin, filaggrin and transglutaminase-1 – start to be expressed in the spinous layer during this differentiation process. The nuclei of keratinocytes degenerate and large keratin macromolecules align in parallel to the keratinocyte membrane and cross-linking enzymes interconnect the various proteins to the cell membranes creating the cornified envelope.

The formation of the cornified cell envelope (CE) during the late stages of epidermal differentiation is essential for a fully-functional epidermal barrier function. It is a complex protein-lipid composite that replaces the plasma membrane of terminally differentiated keratinocytes and originates from the cross-linkage of precursor proteins including involucrin, small proline rich proteins and loricrin. The protein-enriched keratinocytes will become anuclear and flattened cells, which are now called corneocytes. These are embedded in a continuous lipid enriched, intercellular matrix comprising of ceramides, free fatty acids and cholesterol. Ceramides and fatty acids are produced during the differentiation from the phospholipids and glycolipids and are packaged in so-called “lamellar bodies”, membrane coated granules which fuse with the plasma membrane and secrete their content into the intercellular space. The lipids of the intercorneocytic cement of the skin are arranged in lamellar double layers, or lamellae and build up stacks of several membrane layers between the corneocytes. (Fig. 1).

Ceramides are the major lipid components of the epidermal lipid fraction and are credited with playing an important role in the physical organisation of the extracellular matrix, which consists of multiple lipid bilayers with crystalline gel structures. Ceramides are members of the large family of sphingolipids and can achieve a variety of molecular structural variations. These are dependent on the type of sphingoid base, and the chain length and functionality of the attached fatty acid.