Ketoconazole inhibits oxidative modification of low density lipoprotein

Known cytochrome P450-dependent oxygenase inhibitor ketoconazole (5-50 microM) blocked the murine macrophage-mediated modification of human low density lipoprotein (LDL) as measured by production of thiobarbituric acid-reactive substance, stimulation of [125I]LDL degradation in a fresh set of macrophages and LDL electrophoretic mobility, in a dose-dependent manner with complete inhibition at 30-40 microM. When resident macrophages were incubated with LDL in the presence of metyrapone, methoxsalen and alpha-naphthaflavone at concentrations that have been shown to inhibit the cytochrome P450-dependent oxygenases, there was no change in LDL modification. Induction of benzo[alpha]pyrene hydroxylase activity in macrophages by 24 h incubation with benzo[alpha]pyrene was accompanied by a 1.5-fold increase of LDL modification which has been leveled down by ketoconazole as well as methoxsalen and alpha-naphthaflavone. Furthermore, ketoconazole effectively diminished cell-free LDL oxidation induced by iron, but not copper ions, and reduced the spontaneous and zymosan-stimulated lucigenin-amplified chemiluminescence of macrophages. The data allow us to suggest that ketoconazole inhibits LDL oxidation by acting as an iron chelator and/or inhibitor of prooxidant forms of iron-containing enzymes.