Oxysteroids: a new class of steroids with autocrine and paracrine functions.

Oxysteroids are a new classification for sterol intermediates in cholesterol synthesis that undergo enzyme-catalyzed stereo-specific 25R,26-hydroxylation and thus bypass cholesterol as the expected end-product. Recently, they were identified in micromolar amounts in the plasma of patients with Smith-Lemli-Opitz syndrome (SLOS). An additional three oxysteroids, the 25,26-hydroxy derivatives of lanosterol, zymosterol, and desmosterol, respectively, were generated in vitro by CYP27A1-transfected bacteria. As there are 19 steps between cholesterol and lanosterol, the first post-squalene sterol, a potentially large class of oxysteroids exists. Limited studies of 25r,26-7-dehydrocholesterol indicate a traditional role as a ligand for nuclear receptors, but complete evaluation of oxysteroids for novel biologic activities is lacking. Currently, the lack of authentic oxysteroid standards limits both their detection in biologic fluids and evaluation of their biologic effects.