The proposed research will test the effectiveness of an eye drop formulation of a new thiol antioxidant, N- acetylcysteine amide (NACA), in preventing and treating cataracts and retinal degeneration in relevant animal models. This application's broad, long-term objectives are to develop an eye drop formulation of NACA for treatment of age-related eye diseases (AREDs) and to provide impetus for greater exploration of pharmacologic antioxidant approaches to the treatment of a variety of age-related diseases. The importance of oxidative stress damage in the pathogenesis of AREDs has been established for cataracts and the dry form of age-related macular degeneration (AMD). The lens and macula are both subjected to significant photo-oxidative stress, while the macula is the site of high rate of metabolic activity and the presence of concentrations of polyunsaturated fats. Lens and retinal cells combat oxidative stress by generating sufficient antioxidant enzymes or small molecular weight antioxidants like glutathione (GSH). Their ability to produce such antioxidants decreases with age, leading to increased oxidative damage. In the lens, the result is a progressive reduction in solubility of crystalline proteins that manifests in an opacification of te lens. In the retina, it results in mitochondrial damage and the accumulation of drusen that characterizes dry AMD. Antioxidants like N- acetyl cysteine (NAC) have shown promise in ameliorating oxidative stress damage. Our data indicates that a stable pharmaceutical analogue of NAC, NACA works much better than NAC in reducing oxidative stress. Preliminary animal studies have shown that intraperitoneal NACA reduces cataract formation while application of NACA to retinal epithelial cells prevents loss of cell viability.
The Specific Aims of the proposed research are to evaluate 1) cataract formation in male Wistar rat pups receiving selenite injections and 2) retinal degeneration in rd10+/+ and Ccl2-/- mice that spontaneously develop progressive photoreceptor cell death either early (rd10+/+) or later (Ccl2-/-). We will also use a chemically-induced model, in which sodium iodate will be injected into C57/BL6 mice to induce RPE degeneration. The protective effects of NACA will be assessed in animal models by staging cataracts and measuring opacity indices in various experimental groups, while in the rd10+/+ and Ccl2-/- mice the protective effects of NACA will be assessed by measuring the visual potential and photoreceptor function based on measurements of outer nuclear layer (ONL) density and rod and cone electroretinograms (ERGs). In all animal models, we will assess the antioxidant effects of NACA by removing the target tissue (lens or retina) and measuring a number of oxidative stress parameters, the activities of antioxidant enzymes, and the expression of pro-apoptotic and apoptotic proteins such as cytochrome c and caspases. We will also study protein oxidation of crystallins, lipid peroxidation, and protein bound GSH and cysteine.
The loss of vision from age-related eye diseases now affects over 30 million people in the United States-a number that is expected to double in the coming decades. Diseases such as cataracts and age-related macular degeneration significantly affect quality of life and represent sizable medical costs. The annual total outlay for cataract surgery each year in the U.S. is over $9 billion while the total costs of all services related to such visin problems is over $20 billion. Several experiments show that an antioxidant called N-acetylcysteine amide (NACA) may delay the onset or halt the progression of these types of diseases. This research will test whether NACA in eye drop form can prevent and treat eye diseases such as cataracts and macular degeneration in animal models. Successful results from this study will support the advance of this medication into human use. NACA eye drops would represent an alternative to costly cataract surgery, reduce health care costs related to age-related eye diseases and greatly improve the quality of life of people affected by these diseases.