Evidence for the presence of 7-hydroperoxycholest-5-en-3β-ol in oxidized human LDL

Low density lipoprotein (LDL) cholesterol is known to be oxidized both in vitro and in vivo giving rise to oxygenated sterols. Conflicting results, however, have been reported concerning both the nature and the relative concentrations of these compounds in oxidized human LDL. We examined the extracts obtained from Cu²⁺-oxidized LDL. Thin layer chromatography analysis showed that the sterol mixture became more complex with reaction time. Analysis of the components by thin layer chromatography and mass spectrometry allowed to establish that 7α- and 7β-hydroperoxycholest-5-en-3β-ol (7αOOH and βOOH) are largely prevalent among the oxysterols at early times of oxidation. These hydroperoxy derivatives have not been previously identified in oxidized LDL. The concentration of 7-hydroperoxycholest-5-en-3β-ol decreased with oxidation time with a concomitant increase of cholest-5-en-3β,7α-diol (7αOH), cholest-5-en-3β,7β-diol (7βOH), cholesta-3,5-dien-7-one (CD) and cholest-5-en-3β-ol-7-one (7CO). After 24 h of oxidation a minor component of the LDL sterols was cholestan-3β-ol-5,6-oxide (EP).