Cer(d16:1/20:4(6Z,8E,10E,14Z)-2OH(5S,12R)) is an oxidized ceramide (Cer). As all ceramides, oxidized ceramides are members of the class of compounds known as sphingolipids (SPs), or glycosylceramides. SPs are lipids containing a backbone of sphingoid bases (e.g. sphingosine or sphinganine) that are often covalently bound to a fatty acid derivative through N-acylation. SPs are found in cell membranes, particularly in peripheral nerve cells and the cells found in the central nervous system (including the brain and spinal cord). Sphingolipids are extremely versatile molecules that have functions controlling fundamental cellular processes such as cell division, differentiation, and cell death. Impairments associated with sphingolipid metabolism are associated with many common human diseases such as diabetes, various cancers, microbial infections, diseases of the cardiovascular and respiratory systems, Alzheimer’s disease and other neurological syndromes. The biosynthesis and catabolism of sphingolipids involves a large number of intermediate metabolites where many different enzymes are involved. Simple sphingolipids, which include the sphingoid bases and ceramides, make up the early products of the sphingolipid synthetic pathways, while complex sphingolipids may be formed by the addition of head groups to the ceramide template (Wikipedia). In humans, ceramides are phosphorylated to ceramide phosphates (CerPs) through the action of a specific ceramide kinase (CerK). Ceramide phosphates are important metabolites of ceramides as they act as a mediators of the inflammatory response. Ceramides are also one of the hydrolysis byproducts of sphingomyelins (SMs) through the action of the enzyme sphingomyelin phosphodiesterase, which has been identified in the subcellular fractions of human epidermis (PMID: 25935) and many other tissues. Ceramides can also be synthesized from serine and palmitate in a de novo pathway and are regarded as important cellular signals for inducing apoptosis (PMID: 14998372). Ceramides are key in the biosynthesis of glycosphingolipids and gangliosides. In terms of its appearance and structure, Cer(d18:1/22:1(13Z)) is a colorless solid that consists of an unsaturated 18-carbon sphingoid base with an attached unsaturated 13Z-docosenoyl fatty acid side chain. In most mammalian SPs, the 18-carbon sphingoid bases are predominant (PMID: 9759481).