Localization of damage induced by reactive oxygen species in cultured cells

N18-RE-105 neuron-derived hybridoma cells were employed to determine the location and degree of damage induced by each of three reactive oxygen species (ROS) generators: 6-hydroxydopamine (6-OHDA), H2O2, and cumene hydroperoxide. Two readily distinguishable plasma membrane markers were used to assess cell surface damage, namely the active transport of a-aminoisobutyric acid (AIB) and the facilitated diffusion of glucose. In addition, staining of mitochondria with a tetrazolium dye, 3[4,5-Dimethylthiazol-2-yl]-2,5-diphenyltetrazolium bromide (MTT), was used as an intracellular marker to measure the integrity of the metabolic function of the mitochondria. The dose-response curve of inactivation of transport or of metabolic function varied with the ROS generator used and conformed to one of two patterns of toxicity: either threshold-dependent or single-hit inactivation. We determined that 6-OHDA acts simultaneously on multiple targets and steps in the cells, resulting in a very steep dose-effect curve. Similarly, damage induced by H2O2 to the AIB transporters and to mitochondria is consistent with simultaneous inactivation of multiple steps, but damage to glucose transporters conforms to single-hit inactivation of the transporter. Conversely, treatment with cumene hydroperoxide resulted in single-hit inactivation of the AIB transporter, but inactivation of the glucose transporter conformed to threshold-dependent inactivation. Thus, to evaluate quantitatively damage produced by ROS at the subcellular level, both the type of toxic agent and the target to be evaluated must be considered. Finally, the inactivation of each of the targets observed in this study for all of the ROS generators used conform to one of two simple inactivation models. Fitting the appropriate model to the data allows precise quantitative analysis of the inactivation process and provides insight into the chemistry of the inactivation process.