Oxidized low density lipoprotein induces mitochondrially associated reactive oxygen/nitrogen species formation in endothelial cells

Exposure of cells to complex mixtures of oxidized lipids such as those found in oxidized low density lipoprotein (oxLDL) induce reactive oxygen and nitrogen species (ROS/RNS) formation. The source of the ROS/RNS within the cell is unknown and this is important since it is thought they may be involved in redox cell signaling. Although initially overlooked it is becoming clear that the mitochondrion, a source of superoxide/hydrogen peroxide, may play a critical role in the response of the cell on exposure to oxidized lipids. In this study we tested the possibility that mitochondria are a potential source of oxLDL-dependent formation of ROS/RNS in endothelial cells. Using confocal microscopy we demonstrated that a significant proportion of oxLDL-dependent DCF fluorescence is colocalized to the mitochondrion. In support of this concept rho zero endothelial cells showed a substantial decrease in the ROS/RNS formation stimulated by oxLDL. In contrast, mostly non-mitochondrial DCF fluorescence was detected in cells exposed to an extracellular source of hydrogen peroxide. The exposure of cells to a nitric oxide synthase inhibitor and urate resulted in decrease in oxLDL induced DCF fluorescence that was restored by addition of nitric oxide donors to the medium. Taken together, these results suggest that oxLDL-dependent DCF-fluorescence is mitochondrially associated and may be due to the formation of peroxynitrite.