Oxidative damage is considered to be a significant, if not major, factor responsible for the development of many of the age related diseases and the aging process in humans and all animals. Oxygen is essential for life since respiration is the major process that creates energy for all cells, but respiration also produces a small amount of highly reactive oxygen species (ROS) that can cause oxidative damage to macromolecules in the cells. Nucleic acids, proteins and membranes are known to be susceptible to oxidative damage by ROS. Animal cells have developed mechanisms to protect against oxidative damage that include 1) destroying the ROS before they can do damage and 2) repairing the oxidative damage that has already occurred to the macromolecules in cells. Thus, it is important that cells maintain a balance between the production of ROS and their ability to protect against oxidative damage. Aging is believed to be due, in part, to the increased production of ROS as an animal ages and the inability of the cellular protective mechanisms to prevent the increase in oxidative damage. This theory is supported by previous genetic studies that increasing the level of a cellular protective mechanism can increase the life span of animals. Our laboratory discovered a mechanism that protects cells against oxidative damage to proteins. The amino acid methionine in proteins is readily oxidized to methionine sulfoxide by ROS, which can alter the function of the protein. The methionine sulfoxide reductase (Msr) system can reduce the methionine sulfoxide back to methionine, which repairs the damage, but this system also functions as part of a mechanism to scavenge ROS. The two major Msr proteins are MsrA and MsrB. Previously it was shown that transgenic flies that over- express MsrA have an extended life span, and other studies have shown that the Msr system can protect retinal pigmented epithelial (RPE) cells in culture against oxidative damage. The retina is also known to contain high levels of MsrA, and diseases of the retina often involve oxidative damage. In the present proposal we provide evidence that both MsrA and MsrB can be markedly activated in vitro by compounds whose structures are related to fusaricidin A, a known bacterial metabolite, containing a cyclic hexapeptide with a lipid tail. A lead compound, analogue 2, has been identified. Our goals are to 1) understand the mechanism of Msr activation by analogue 2, 2) to study the in vitro effect of analogue 2 on oxidative damage to RPE cells in culture and 3) to test analogue 2 in an in vivo animal model of light damage to the retina. There is no effective treatment for the dry form of AMD and other retinal diseases and positive results in this study have the potential for developing therapies for a large number of age related diseases.