Multimodal Fundus Imaging of Sodium Iodate-Treated Mice Informs RPE Susceptibility and Origins of Increased Fundus Autofluorescence

Abstract

PurposeBy multimodal imaging, and the use of mouse and in vitro models, we have addressed changes in fundus autofluorescence (488 and 790 nm) and observed interactions between the photooxidative stress imposed by RPE bisretinoid lipofuscin and the oxidative impact of systemic sodium iodate (NaIO3).MethodsAbca4−/−, wild-type, and Rpe65rd12 mice were given systemic injections of NaIO3 (30 mg/kg). Analysis included noninvasive imaging of fundus autofluorescence (short-wavelength [SW-AF]; near-infrared excitation [NIR-AF]), quantitative fundus AF (qAF; 488 nm); light microscopy, RPE flat-mounts and measurements of outer nuclear layer (ONL) thickness. NaIO3 also was studied by using in vitro assays.ResultsIn SW-AF and NIR-AF images, fundus mottling was visible 3 and 7 days after NaIO3 injection with changes being more pronounced in Abca4−/− mice that are characterized by an abundance of RPE bisretinoid lipofuscin. In Abca4−/− mice, qAF was elevated 3 and 7 days after NaIO3 administration. In light micrographs and RPE flat-mounts stained to reveal tight junctions (ZO-1) and nuclei, the RPE monolayer was disorganized, and clumping and loss of RPE was visible. ONL thinning was most pronounced in Abca4−/− mice. Treatment of ARPE-19 cells with NaIO3 together with the photooxidation of the bisretinoid A2E by exposure to 430-nm light produced an additive effect whereby loss of cell viability was greater than with either perturbation alone.ConclusionsElevations in SW-AF intensity can occur due to photoreceptor cell dysfunction as induced secondarily by NaIO3. Photooxidative stress associated with RPE cell bisretinoid lipofuscin may confer increased susceptibility to the oxidant NaIO3.

Geographic Atrophy: Confocal Scanning Laser Ophthalmoscopy, Histology, and Inflammation in the Region of Expanding Lesions

“…Additional reports imaging Stargardt disease 1 (STGD1) patients carrying mutations in the ABCA4 gene and Abca4 − / − mice challenged the assumption that near-infrared AF originates only from melanin. 47,48 STGD1 patients, with central RPE atrophy, displayed gray level nearinfrared AF intensity values consistently elevated. Similarly, Abca4 − / − agouti mice, a model of accelerated formation of bisretinoid lipofuscin, also displayed increased near-infrared AF signal.…”

Iron promotes oxidative cell death caused by bisretinoids of retina

“…A2E was then extracted and quantified by HPLC ( 17 ). Cytotoxicity was measured by the MTT (4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide) colorimetric assay (Roche Diagnostics Corporation) ( 72 ). Synthesized A2E ( 9 ) (50 µM in distilled water with 0.5% DMSO) was incubated with FeSO 4 (200 µM), H 2 O 2 (500 µM), and DFP (600 µM) for 3 h at 37 °C and peak areas were quantified by UPLC ( 73 ).…”

Transplanted Erythropoietin-Expressing Mesenchymal Stem Cells Promote Pro-survival Gene Expression and Protect Photoreceptors From Sodium Iodate-Induced Cytotoxicity in a Retinal Degeneration Model

“…By observing the results in Figure 7 , the phototransduction pathway was inhibited in the sham group but activated in the MSC and MSC EPO groups. The sham group also exhibited an activation of the necroptosis pathway, which is the main cell death pathway that is triggered by NaIO 3 in the retina ( Hanus et al, 2016 ; Zhao et al, 2017 ). This finding complemented the work of other studies in necroptotic retinal cell death.…”