Intraocular iron injection induces oxidative stress followed by elements of geographic atrophy and sympathetic ophthalmia

Abstract

Iron has been implicated in the pathogenesis of age-related retinal diseases, including age-related macular degeneration (AMD). Previous work showed that intravitreal (IVT) injection of iron induces acute photoreceptor death, lipid peroxidation, and autofluorescence (AF). Herein, we extend this work, finding surprising chronic features of the model: geographic atrophy and sympathetic ophthalmia. We provide new mechanistic insights derived from focal AF in the photoreceptors, quantification of bisretinoids, and localization of carboxyethyl pyrrole, an oxidized adduct of docosahexaenoic acid associated with AMD. In mice given IVT ferric ammonium citrate (FAC), RPE died in patches that slowly expanded at their borders, like human geographic atrophy. There was green AF in the photoreceptor ellipsoid, a mitochondria-rich region, 4 h after injection, followed later by gold AF in rod outer segments, RPE and subretinal myeloid cells. The green AF signature is consistent with flavin adenine dinucleotide, while measured increases in the bisretinoid all-trans-retinal dimer are consistent with the gold AF. FAC induced formation carboxyethyl pyrrole accumulation first in photoreceptors, then in RPE and myeloid cells. Quantitative PCR on neural retina and RPE indicated antioxidant upregulation and inflammation. Unexpectedly, reminiscent of sympathetic ophthalmia, autofluorescent myeloid cells containing abundant iron infiltrated the saline-injected fellow eyes only if the contralateral eye had received IVT FAC. These findings provide mechanistic insights into the potential toxicity caused by AMD-associated retinal iron accumulation. The mouse model will be useful for testing antioxidants, iron chelators, ferroptosis inhibitors, anti-inflammatory medications, and choroidal neovascularization inhibitors.

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

“…Moreover, we found that IVT iron-induced damage appears to be less severe with the DHA diet than our previous study in mice fed with "regular chow" (LabDiet 5001) (Liu et al, 2021). We previously observed ironinduced retinal AF throughout the retina in mice fed with LabDiet 5001 at 1 week after iron injection, and "kidney bean" shaped geographic atrophy always occurred at 4 weeks after iron injection (Liu et al, 2021). In the current study, we observed that iron-induced AF was more limited to the superior retina in mice fed with DHA for 4 weeks at 1 week after iron injection (Figure S2), and the "kidney (Angelova et al, 2015;Shchepinov et al, 2011), Alzheimer's disease (Elharram et al, 2017;Raefsky et al, 2018), Huntington's disease (Hatami et al, 2018), and infantile neuroaxonal dystrophy (Kinghorn et al, 2015).…”

“…To evaluate whether D-DHA could protect against geographic atrophy in this model, mice were continued on their respective diets for 4 weeks after iron or saline injection. IVT iron-induced retinal AF, oxidative stress, accumulation of carboxyethylpyrrole (CEP), a DHA-specific oxidation product, and photoreceptor degeneration followed by progressive geographic atrophy, replicating features of human AMD (Liu et al, 2021). In this study, we have found that dosing of D-DHA completely protected against all these iron-induced retinal changes.…”

“…We previously reported IVT iron-induced retinal AF and degeneration (Liu et al, 2021). To evaluate the protective effect of 0.25% D-DHA diet, confocal scanning laser ophthalmoscopy (cSLO) and optical coherence tomography (OCT) were employed for in vivo imaging at 1 week after injections.…”

“…Mice given D-DHA for 4 weeks showed complete retinal protection 1 week after iron injection (Figure 2). Our previous study showed geographic atrophy in the superior retina within a month of IVT iron injection (Liu et al, 2021). To evaluate whether D-DHA could protect against geographic atrophy in this model, mice were continued on their respective diets for 4 weeks after iron or saline injection.…”

Effects of Excess Iron on the Retina: Insights From Clinical Cases and Animal Models of Iron Disorders

“…The amount of retinal injury and rate of progression associated with systemic iron loading appears to be varied depending on the specific regulatory protein involved, in addition to the age and sex of the mice (Hahn et al, 2009). While there is an increasing interest in incorporating electroretinography and in vivo imaging, as well as gene expression changes in retinal studies in animal models of iron loading (Liu et al, 2021), the number of such studies are still limited. More comprehensive time course studies, particularly using complementary tools such as electroretinography and in vivo imaging to define the earliest retinal deficits would help to define the role of iron regulation on retinal degeneration.…”