α- and β-Carotenes in low density lipoprotein are the preferred target for nitric oxide-induced oxidation

Whereas low plasma levels of carotenes are strongly associated with the elevated risk of atherosclerosis, the reason for this is still unknown. We hypothesized that lipoprotein oxidation in the arterial wall might selectively deplete carotenes, thus explaining the observed effects. In order to assess this hypothesis, we incubated plasma low density lipoprotein (LDL) with different oxidants and measured the consumption of carotenes and tocopherols. We found that when LDL oxidation was induced by nitric oxide, both α- and β-carotene were consumed at a significantly higher relative rate than α- or γ-tocopherol. In contrast, superoxide, peroxynitrite, hypochlorite or transition metal ions were unable to induce selective consumption of carotenes in LDL. These data suggest that the decreased plasma levels of α- and β-carotene frequently measured in atherosclerosis may be related to their preferred consumption by reactive nitrogen species in the arterial wall.