Oxysterols are oxidized derivatives of cholesterol, which may be important in many biological processes, including cholesterol homeostasis, atherosclerosis, sphingolipid metabolism, platelet aggregation, apoptosis, and protein prenylation, though their roles are poorly understood. 
Frying foods in overused oil or smoking cigarettes can oxidize cholesterol, creating oxysterols. It is currently thought that oxysterols may play an important role in atherosclerosis progression: they are likely to promote the synthesis of an extracellular matrix scaffold - via pericyte-like cells in blood vessels - which would be needed for the calcification process (deposition of Ca-phosphate crystals).
- Schroepfer, Gj, Jr (Jan 2000). "Oxysterols: modulators of cholesterol metabolism and other processes" (FREE FULL TEXT). Physiological reviews 80 (1): 361–554. ISSN 0031-9333. PMID 10617772.
- Björkhem, I (Sep 2002). "Do oxysterols control cholesterol homeostasis?". The Journal of Clinical Investigation 110 (6): 725–30. doi:10.1172/JCI16388. PMC 151135. PMID 12235099.
- Ingemar Björkhem; Ulf Diczfalusy (2002). "Oxysterols: Friends, Foes, or Just Fellow Passengers?". Arteriosclerosis, Thrombosis, and Vascular Biology 22 (5): 734–42. doi:10.1161/01.ATV.0000013312.32196.49. PMID 12006384.
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