Differential oxidative stress thresholds distinguishes cellular response to vascular occlusion and chemotoxicity in vivo.

BACKGROUND: A major effect of cyanide toxicity (CN) and vascular occlusion (VO) is the production of reactive oxygen species (ROS) linked with a defective energy coupling process in the mitochondria. In CN, oxygen is present but its conversion is blocked in the mitochondria (Complex V). By contrast, in VO, oxidative stress is induced via reduction of oxygen (blood) circulation to the occluded brain region. We hypothesize that differential oxygen concentration in both forms of ischemia affect ROS production rate in the mitochondria; thus distinguishing the cytotoxicity pattern for CN and VO.

METHOD: Male, adult Wistar rats (N = 30) were separated into three groups. A set of n = 12 animals were treated with orally administered potassium ferricyanide. Global vascular occlusion (GVO) was induced in a second set of animals (n = 12) using neck cuffs to occlude the common carotid arteries and brachiocephalic vein. The control group (n = 6) received normal saline for the total duration of the treatment (10 days). Glutathione (GSH), superoxide dismutase (SOD), glutathione peroxidase (GPx), malondialdehyde (MDA) and acid phosphatase (ACP) levels were assayed in tissue homogenate using colorimetric assay techniques while Cathepsin D (CAD+) was demonstrated through antigen retrieval immunohistochemistry. Data were analyzed in One Way ANOVA with Tukey's post-hoc test. Significance was set p < 0.05.

RESULTS/DISCUSSION: Cyanide treatment and VO caused a significant rise in SOD; attributed to ROS formation in both forms of ischemia. However, an increase in GSH levels demonstrates mitochondria-ROS production in cyanide treatment while no significant change in GSH was observed in VO versus the control (reduced mitochondria-ROS production). In addition, CN recorded a significant increase in GSH when compared with the control and VO (p < 0.001). The level of ROS was also proportional to the degree of lipid peroxidation (GPx) and autophagic cell response (ACP/CAD+). Ultimately, the lipid peroxidation/ROS effect was more significant in CN than VO.

CONCLUSION: Although CN and VO induced oxidative stress through ROS production, our findings suggest a difference in the threshold of ROS production and cytotoxicity for both forms of ischemia. However, this threshold is dependent on the availability of oxygen to fuel mitochondria-ROS production in oxidative stress. Ultimately, the difference in oxygen availability in vivo determined the significance of lipid peroxidation, calcium-shift and autophagic cell response associated with the ischemia. CN treatment generated more ROS and was associated with prominent cellular changes when compared with VO.