Prevention of Inherited Retinal Diseases by Therapeutic Rare Earth Nanoparticles

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There are now almost 200 genes and chromosomal loci which have been identified as causing some form of inherited retinal degeneration. Irrespective of the primary mutation or cause, all of these diseases are thought to share a major common event. This is "oxidative stress" as a result of a chronic or acute rise in Reactive Oxygen Species (ROS). Antioxidants and over-expression of antioxidant enzymes have been shown to inhibit the progression of many retinal diseases. Inorganic cerium oxide nanoparticles (nanoceria) are antioxidants which mimic the activities of catalase and super oxide dismutase by catalytically scavenging ROS and have been shown to prevent peroxide induced blindness in rats. We think of the nanoceria as being analogous to an aspirin for blindness in that they won't cure the primary defect but will decrease the severity of the disease. We have hypothesized, that because ROS represent a node common to many inherited blinding diseases, they also represent an "Achilles' heel" which can be specifically targeted using ROS-scavenging nanoceria. As a component of that strategy, nanoceria will be used in this study to inhibit the inherited programmed death of photoreceptors in a mouse strain, tubby, which is a phenotypic model for Usher's Syndrome. Specific Aim 1 will test the hypothesis that the nanoceria particles will destroy ROS and, by decreasing oxidative damage in retinal neurons, will inhibit retinal degeneration induced by the tubby mutation. The hypothesis that nanoceria will act synergistically with sulphoraphane (Specific Aim 2) or with the overexpression of the human thioredoxin transgene (Specific Aim 3) to provide enhanced and prolonged protection of the photoreceptor cells in the tubby retina will also be tested. Our preliminary and published data support the effectiveness of each of these therapies when used alone in the tubby mouse. The mechanisms by which the nanoceria function in the tubby mouse alone, and in combination with sulphoraphane, or the Trx transgene, will be identified by the following methods. Superoxide radicals in the retina will be assessed using a hydroxyethidine assay whereas H20 2 will be assayed with 2',T-dichlorodihydro- fluorescein-diacetate. ROS-induced damage will be visualized with antibodies against products of ROS activity including acrolein, nitrotyrosine and 8-hydroxy-2-deoxy-guanosine. The effects of the nanoceria on neuroprotective pathways will be analyzed by Western blots, cDNA micro arrays, and Real Time-PCR. Quantitative histology, using bright field microscopy on hematoxylin and eosin stained retinal sections, will be used to evaluate the morphological preservation of photoreceptor cells. Retinal function will be determined by electroretinography. We currently have large colonies of both the tubby and the Trx-tubby mice and will be able to complete the specific aims within two years. The successful achievement of our objectives should be directly relevant to most forms of inherited blindness in mice. The nanoceria are expected to function in humans as they do in other mammals and therefore should preserve vision and prevent blindness in humans.