Timing of Antioxidant Gene Therapy: Implications for Treating Dry AMD

Abstract

PurposeTo investigate whether antioxidant gene therapy protects the structure and function of retina in a murine model of RPE atrophy, and to determine whether antioxidant gene therapy can prevent degeneration once it has begun.MethodsWe induced mitochondrial oxidative stress in RPE by conditional deletion of Sod2, the gene for manganese superoxide dismutase (MnSOD). These mice exhibited localized atrophy of the RPE and overlying photoreceptors. We restored Sod2 to the RPE of one eye using adeno-associated virus (AAV) by subretinal injection at an early (6 weeks) and a late stage (6 months), injecting the other eye with an AAV vector expressing green fluorescent protein (GFP). Retinal degeneration was monitored over a period of 9 months by electroretinography (ERG) and spectral-domain optical coherence tomography (SD-OCT). Immunohistochemical and histologic analyses were conducted to measure oxidative stress markers and to visualize retinal structure.ResultsOne month after delivery, the AAV-Sod2 injection resulted in production of MnSod in the RPE and negligible expression in the neural retina. Electroretinography and OCT suggested no adverse effects due to increased expression of MnSOD or subretinal injection. Decrease in the ERG response and thinning retinal thickness was significantly delayed in eyes with early treatment with the Sod2 vector, but treatment at 6 months of age did not affect the ERG decline seen in these mice.ConclusionsWe conclude that antioxidant gene therapy may be effective in preventing the detrimental effects of oxidative stress, but may not be beneficial once substantial tissue damage has occurred.

Endonuclease G promotes mitochondrial genome cleavage and replication

“…Immunodetection was performed using mouse-anti-human DNA POLγ (Santa Cruz, sc-390634 [ 95 ]) and EndoG (Santa Cruz, sc-365359 [ 20 ]) primary antibodies. Mouse-anti-human α-tubulin (Abcam, ab7291 [ 96 ]) and Glyceraldehyde-3-phosphate-dehydrogenase (GAPDH, Abcam, ab9484 [ 97 ]) served as loading controls. Horseradish peroxidase (HRP)-conjugated goat-anti-mouse (Rockland) was utilised as secondary antibody.…”

Stimulation of AMPK prevents degeneration of photoreceptors and the retinal pigment epithelium

“…In addition to increased metabolism, we found increased expression of SOD2 and reduced oxidative damage. While gene delivery of SOD2 has been shown to protect photoreceptors and the RPE, it is unlikely that the protective mechanism of metformin is simply due to increased oxidative defense, since antioxidant therapies are not effective at delaying degeneration from inherited mutations (38). Since we observed increases in both oxidant defense and markers of metabolism with metformin treatment, we hypothesize that both factors are contributing to metformin-induced protection.…”

Intravitreal Delivery of Melatonin Is Protective Against the Photoreceptor Loss in Mice: A Potential Therapeutic Strategy for Degenerative Retinopathy

“…As a well known anti-oxidant, melatonin is not only able to scavenge directly the free radical, but also to enhance the production of endogenous anti-oxidative enzymes (Rodriguez et al, 2004). We show that the melatonin therapy enhances the expression levels of Cu-Zn-SOD and MnSOD, both of which are ubiquitous oxidation protectors in retina (Akpinar et al, 2007;Biswal et al, 2017). On the other hand, melatonin could reduce the level of MDA and 8-OHdG, which are classic markers of lipid and DNA peroxidation (Celebi et al, 2002;Deliyanti et al, 2018).…”