Deuterated docosahexaenoic acid protects against oxidative stress and geographic atrophy-like retinal degeneration in a mouse model with iron overload

Abstract

Oxidative stress plays a central role in age-related macular degeneration (AMD). Iron, a potent generator of hydroxyl radicals through the Fenton reaction, has been implicated in AMD. One easily oxidized molecule is docosahexaenoic acid (DHA), the most abundant polyunsaturated fatty acid in photoreceptor membranes. Oxidation of DHA produces toxic oxidation products including carboxyethylpyrrole (CEP) adducts, which are increased in the retinas of AMD patients. In this study, we hypothesized that deuterium substitution on the bis-allylic sites of DHA in photoreceptor membranes could prevent iron-induced retinal degeneration by inhibiting oxidative stress and lipid peroxidation. Mice were fed with either DHA deuterated at the oxidation-prone positions (D-DHA) or control natural DHA and then given an intravitreal injection of iron or control saline. Orally administered D-DHA caused a dose-dependent increase in D-DHA levels in the neural retina and retinal pigment epithelium (RPE) as measured by mass spectrometry. At 1 week after iron injection, D-DHA provided nearly complete protection against iron-induced retinal autofluorescence and retinal degeneration, as determined by in vivo imaging, electroretinography, and histology. Iron injection resulted in carboxyethylpyrrole conjugate immunoreactivity in photoreceptors and RPE in mice fed with natural DHA but not D-DHA. Quantitative PCR results were consistent with iron-induced oxidative stress, inflammation, and retinal cell death in mice fed with natural DHA but not D-DHA. Taken together, our findings suggest that DHA oxidation is central to the pathogenesis of iron-induced retinal degeneration. They also provide preclinical evidence that dosing with D-DHA could be a viable therapeutic strategy for retinal diseases involving oxidative stress.

Keywords: age-related macular degeneration; deuterium; docosahexaenoic acid; iron; isotope effect; lipid peroxidation; oxidative stress; polyunsaturated fatty acid.