Ceramid

Ceramide is a family of lipid molecules composed of a fatty acid amide-linked to a sphingosine backbone. As a central building block of sphingolipids, ceramides are found in cell membranes throughout animals, plants, and fungi and exist in many chain lengths and degrees of saturation, determined in part by specific ceramide synthases. In mammals, ceramides can be produced by de novo synthesis, sphingomyelin hydrolysis, or salvage pathways, and they can be further metabolized to other signaling lipids such as sphingosine and sphingosine-1-phosphate.

De novo synthesis begins with serine palmitoyltransferase, which condenses serine with a fatty acyl-CoA to form 3-ketosphinganine, then is reduced and acylated by ceramide synthases to dihydroceramide and finally desaturated to ceramide. Sphingomyelinase enzymes can generate ceramide by hydrolyzing sphingomyelin, a major membrane sphingolipid. Ceramide can be degraded by ceramidases to sphingosine, which can be phosphorylated to sphingosine-1-phosphate, a potent signaling lipid. The diversity of CerS enzymes contributes to the variety of ceramide species found in tissues.

Biologically, ceramides serve structural roles in membranes and act as bioactive signaling molecules influencing cell proliferation, differentiation, apoptosis, and inflammatory responses. They are particularly important in the skin, where ceramides help maintain the barrier and water retention. Altered ceramide metabolism is linked to skin disorders, metabolic disease, neurodegeneration, and cancer. Clinically, topical ceramides are used in skincare to support barrier repair, and ceramide pathways are studied as targets for therapeutic intervention.