Tracing of benzidine-reactive substances in ROS, RPE and choroid after light-induced peroxidation

Abstract 

· Background: A new method for the ultrastructural localization of lipid peroxides as benzidine-reactive substances (BRS) was recently developed in our laboratory. The aim of the present study was to localize BRS in the eye after intense light exposure. The light protocol was chosen to either hamper disc shedding or to induce a shedding peak. · Methods: Long-Evans rats were either kept under constant irradiation to enhance lipid peroxidation or under physiological light conditions. The light-induced peroxidation was carried out either by constant irradiation for 24 h or by constant irradiation for 20 h followed by a dark period of 4 h. The eye cups were fixed by glutaraldehyde, incubated with or without tetramethylbenzidine and embedded for electron microscopy. · Results: After constant irradiation for 24 h smooth nonlamellar BRS appear exclusively intracellularly over the complete rod outer segments (ROS). After the initiation of disc shedding smooth BRS are localized in the extracellular space of the ROS and extracellularly in the basal labyrinth of the retinal pigment epithelium (RPE). Fine-lamellar BRS emerge in vacuoles of the RPE, in the basal labyrinth and in the lumen of choroidal capillaries. · Conclusion: Light conditions that trigger the disc shedding possibly activate a mechanism to extrude peroxidative damaged material over the complete ROS into the extracellular space to diminish peroxidative damage inside the ROS. Indigestible residual material from the ROS degradation in the phagosomes consists of membranous lipids associated with peroxidative damaged proteins. The residual material seems to be transported through Bruch’s membrane into the choriocapillaris.