Ceramides

are a family of lipid molecules. A ceramide is composed of sphingosine and a fatty acid. Ceramides are found in high concentrations within the cell membrane of cells. They are one of the component lipids that make up sphingomyelin, one of the major lipids in the lipid bilayer. For years, it was assumed that ceramides and other sphingolipids found in the cell membrane were purely structural elements. This is now known to be not completely true. Perhaps one of the most fascinating aspects of ceramide is the fact that it can be released from the cell membrane by enzymes and then act as a signaling molecule. The most well-known functions of ceramides as cellular signals include regulating the differentiation, proliferation, programmed cell death (PCD), and apoptosis (Type I PCD) of cells. Due to this function, ceramides are sometimes called "messengers of cell death"