Lipid peroxidation is well established to contribute to the etiology of many deteriorative conditions including neurodegeneration, cardiovascular disease, cancer, aging, and recently in ferroptosis—a regulated, necrotic modality of cell death that results from the accumulation of lipid hydroperoxides. Recent high-throughput screening efforts have uncovered ferrostatin-1 (Fer-1) and liproxstatin-1 (Lip-1) as two premiere inhibitors of ferroptosis. We propose that these compounds function as radical trapping antioxidants. We employ a systematic methodology of evaluating inherent radical trapping antioxidant (RTA) activity of Lip-1, Fer-1, and various aryl amine and aryl nitroxide analogues to put forward a biologically relevant mechanism of action based on our previous work in the field. Joining these observations with the efficacy of tetrahydronaphthyridinols (THNs), the results support a clear role of autoxidation in the execution of ferroptosis. Next, we expand the THN repertoire by targeting the payload towards the engine of our cells, the mitochondria. Decades of research have implicated mitochondrial dysfunction brought about by the peroxidation of mitochondrial membranes and the leaking of downstream oxidants, in the death of their symbiotic host cells. Isolated successes in the field have been demonstrated academically, though viable drugs remain to be developed, partially due to the lack of effective diagnostic tools. We endeavor to address some of these issues by investigating mitochondrially-targeted THNs (MitoTHNs) as a targeted chain-breaking antioxidant of unparalleled potency. Furthermore, we advance development of the THNs towards therapeutic applications by demonstrating their biodistribution in mice.

Lipid peroxidation has been implicated in the onset and progression of many degenerative diseases, including cardiovascular disease, Alzheimer’s disease and cancer. Accordingly, for more than 50 years, considerable effort has been devoted to the design of synthetic compounds or the discovery of natural products that can slow lipid peroxidation. Despite the enormous investments made to date, no clear antioxidant strategies have emerged for the treatment and/or prevention of degenerative disease. We argue that this is because of a lack of fundamental understanding of the chemical reactivity of these compounds in relevant contexts. Herein, we describe studies of our optimized synthetic radical-trapping antioxidant (RTA) – the tetrahydronaphthyridinols (THNs). We first present the synthesis of a series of THN analogs of α-tocopherol (Nature’s premier lipid-soluble radical-trapping antioxidant) with varying sidechain substitution and then demonstrate how systematic changes in the lipophilicity of these potent antioxidants impact their peroxyl radical-trapping activities in lipid bilayers and mammalian cell culture. Their regenerability by water-soluble reductants in lipid bilayers, binding to human tocopherol transport protein (hTTP), and cytotoxicity were also evaluated to provide insight on whether this type of antioxidant can be potentially pushed toward animal studies. We also describe analogous studies of natural products such as the garlic-derived thiosulfinate allicin and the grape-derived polyphenol resveratrol. These compounds have attracted significant attention in the past 20 years due to their purported health benefits, which are often ascribed to their purported radical-trapping activities. To date, systematic studies on their radical-trapping activities in solution, lipid bilayers and mammalian cells have been lacking. We have determined that allicin and petivericin, while effective RTAs in solution, are not so in lipid bilayers. Moreover, the compounds are not antioxidants in cell culture, but instead kill the cells. Similarly, resveratrol and its dimers pallidol and quadrangularin A, are found to be inefficient RTAs in lipid bilayers. Our studies to date rather suggest that they autoxidize readily to produce hydrogen peroxide, which may induce expression of phase 2 antioxidant enzymes, affording cytoprotection. Our insights underscore the need for systematic studies of antioxidant activity in multiple contexts.