Side-Chain Oxidized Oxysterols in Health and Disease

Among the many oxidized derivatives of cholesterol present in biological systems, those carrying the oxygen function in the steroid side-chain are of particular importance. These steroids are used as transport forms of cholesterol in elimination pathways and as regulators of a great number of biochemical processes. They are also used as signaling molecules. They are important players in the development of atherosclerosis and in neurodegenerative diseases as well as in inflammation and immunologic defense reactions. They may also be of importance in cell differentiation during development. A characteristic feature of these steroids is that they have a unique capacity to pass biomembranes. The most obvious example is that side-chain oxidized oxysterols are able to pass the blood–brain barrier which is impermeable for cholesterol itself. Another feature is a rapid metabolism and a short half-life. Given their potent effects, the metabolism of these oxysterols may in part be regarded as a detoxification.