Ricerc@Sapienza

It is now widely accepted that oxysterols are more than metabolic intermediates but are actually bona fide lipid mediators. To qualify as a bona fide lipid mediator, a lipid compound should meet three conditions. First to be endogenous, second to have its levels altered depending on the physiological or pathological situation, and third to induce a signaling response when its levels are altered. As is evident from the papers published in this Special issue, oxysterols largely qualify as bona fide lipid mediators. First, they are endogenously produced, for the most part from cholesterol, via enzymatic reactions or following oxidation by reactive oxygen species. Second, the number of situations where altered oxysterol levels have been reported is continuing to increase. Such alterations have been described in situations as diverse as diseases of the cardiovascular system, central nervous system, eyes, the metabolic syndrome or cancer. Third, oxysterols can induce signaling responses either by altering cell membrane properties or by binding and activating several receptors.