Oxysterols origin

The existence of an alternate pathway for the synthesis of bile acids was suspected because it was possible for oxysterols to be converted into bile acids (N. Wachtel, 1968). It is now recognized that a variety of oxysterols produced by an assortment of cell types can be converted into bile acids. The production of these oxysterols is catalyzed by several sterol hydroxylases sterol 27-hydroxylase (CYP27A1) (J.J. Cali, 1991), cholesterol 25-hydroxylase (CH25H) (E.G. Lund, 1998), and cholesterol 24-hydroxylase (CYP46A1) (E.G. Lund, 1999). Cholesterol 25-hydroxylase is not a cytochrome P-450 monooxygenase, unlike the two other enzymes. Almost all of the 24-hydroxycholesterol that ends up in the liver originates from the brain, and it has been suggested that the production of... 

Oxysterols are a family of 27-carbon molecules that originate from the oxidation of cholesterol by both enzymatic and nonenzymatic mechanisms. Compared to cholesterol, they contain an additional hydroxyl, epoxide, or ketone group in the... 

On this basis, a versatile even if contradictory role of oxysterols may emerge, which poses the question of how they actually affect the atherosclerotic lesion development and which factors might modulate their behavior. In this connection, how much does it depend on the nature of oxysterols thanselves (e.g., chemical structure, enzymatic or nonenzymatic origin) and how much on extrinsic factors (e.g., stage of disease progression, cell phenotype, presence of other bioactive compounds) ... 

Bjorkhem I, Lutjohann D, Diczfalusy U, Stable L, Ahlborg G, Wahren J. Cholesterol homeostasis in human brain turnover of 24S-hydroxycholesterol and evidence for a cerebral origin of most of this oxysterol in the circulation. / Lipid Res. 1998 39(8) 1594-1600. 

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