Mitochondrial quality control in non-exudative age-related macular degeneration: From molecular mechanisms to structural and functional recovery.

Non-exudative age-related macular degeneration (NE-AMD) is the leading blindness cause in the elderly. Clinical and experimental evidence supports that early alterations in macular retinal pigment epithelium (RPE) mitochondria play a key role in NE-AMD-induced damage. Mitochondrial dynamics (biogenesis, fusion, fission, and mitophagy), which is under the central control of AMP-activated kinase (AMPK), in turn, determines mitochondrial quality. We have developed a NE-AMD model in C57BL/6J mice induced by unilateral superior cervical ganglionectomy (SCGx), which progressively reproduces the disease hallmarks circumscribed to the temporal region of the RPE/outer retina that exhibits several characteristics of the human macula. In this work we have studied RPE mitochondrial structure, dynamics, function, and AMPK role on these parameters' regulation at the nasal and temporal RPE from control eyes and at an early stage of experimental NE-AMD (i.e., 4 weeks post-SCGx). Although RPE mitochondrial mass was preserved, their function, which was higher at the temporal than at the nasal RPE in control eyes, was significantly decreased at 4 weeks post-SCGx at the same region. Mitochondria were bigger, more elongated, and with denser cristae at the temporal RPE from control eyes. Exclusively at the temporal RPE, SCGx severely affected mitochondrial morphology and dynamics, together with the levels of phosphorylated AMPK (p-AMPK). AMPK activation with metformin restored RPE p-AMPK levels, and mitochondrial dynamics, structure, and function at 4 weeks post-SCGx, as well as visual function and RPE/outer retina structure at 10 weeks post-SCGx. These results demonstrate a key role of the temporal RPE mitochondrial homeostasis as an early target for NE-AMD-induced damage, and that pharmacological AMPK activation could preserve mitochondrial morphology, dynamics, and function, and, consequently, avoid the functional and structural damage induced by NE-AMD.

Anatomical and Functional Outcomes with Prompt versus Delayed Initiation of Anti-VEGF in Exudative Age-Related Macular Degeneration.

PURPOSE: To investigate the correlation between time from diagnosis of treatment-naïve exudative age-related macular degeneration (AMD) to the introduction of anti-VEGF treatment and anatomical and functional outcomes. DESIGN: Retrospective cohort study. METHODS: Included were treatment-naïve exudative AMD patients who presented to a single tertiary medical center between 2012 and 2018. All patients were treated within the first 30 days of their diagnosis with three monthly intravitreal injections of bevacizumab. Patients were divided into three groups: group 1 (prompt anti-VEGF) were injected with bevacizumab within ten days, group 2 (intermediate anti-VEGF) within 11-20 days, and group 3 (delayed anti-VEGF) within 21-30 days from diagnosis. Baseline characteristics and clinical outcomes were compared up to two years from treatment. RESULTS: 146 eyes of 146 patients were included. Sixty-eight patients were in the prompt anti-VEGF group, 31 in the intermediate anti-VEGF group, and 47 in the delayed anti-VEGF group. Following the induction phase of three intravitreal bevacizumab injections, the mean central subfield macular thickness (328.0 ± 115.4 µm vs. 364.6 ± 127.2 µm vs. 337.7 ± 150.1 µm, p = 0.432) and the best-corrected visual acuity (0.47 ± 0.38 vs. 0.59 ± 0.48 vs. 0.47 ± 0.44 logMAR units, p = 0.458) were comparable between the prompt, intermediate and delayed anti-VEGF groups. Anatomical and functional outcomes, treatment burden, number of relapses and eyes with second-line anti-VEGF therapy were comparable between the groups at both 1-year and 2-year timepoints. CONCLUSIONS: Our real-world evidence data emphasize that even if anti-VEGF induction cannot be initiated promptly within ten days from diagnosis of naïve exudative AMD, the visual and anatomical prognosis of the patients may not worsen if the treatment is started within one month of diagnosis.

Flavoprotein fluorescence elevation is a marker of mitochondrial oxidative stress in patients with retinal disease.

Purpose: Recent studies of glaucoma, age-related macular degeneration, and diabetic retinopathy have demonstrated that flavoprotein fluorescence (FPF) can be utilized non-invasively as an indicator of mitochondrial oxidative stress in the retina. However, a comprehensive assessment of the validity and reliability of FPF in differentiating between healthy and diseased eyes across multiple disease states is lacking. Here, we evaluate the sensitivity and specificity of FPF in discriminating between healthy and diseased eyes in four leading causes of visual impairment worldwide, one of which has not been previously evaluated using FPF. We also evaluate the association between FPF and visual acuity. Methods: A total of 88 eyes [21 eyes of 21 unaffected controls, 20 eyes from 20 retinal vein occlusion (RVO) patients, 20 eyes from 20 diabetic retinopathy (DR) patients, 17 eyes from 17 chronic exudative age-related macular degeneration (exudative AMD) patients, and 10 eyes from 10 central serous retinopathy (CSR) patients] were included in the present cross-sectional observational study. Eyes were imaged non-invasively using a specially configured fundus camera OcuMet Beacon® (OcuSciences, Ann Arbor, MI). The macula was illuminated using a narrow bandwidth blue light (455 - 470 nm) and fluorescence was recorded using a narrow notch filter to match the peak emission of flavoproteins from 520 to 540 nm. AUROC analysis was used to determine the sensitivity of FPF in discriminating between diseased eyes and healthy eyes. Nonparametric Kruskal-Wallis Tests with post-hoc Mann Whitney U tests with the Holm-Bonferroni correction were performed to assess differences in FPF intensity, FPF heterogeneity, and best corrected visual acuity (BCVA) between the five groups. Spearman rank correlation coefficients were calculated to assess the relationship between FPF and BCVA. Results: AUROC analysis indicated that FPF intensity is highly sensitive for detecting disease, particularly for exudative AMD subjects (0.989; 95% CI = 0.963 - 1.000, p=3.0 x 107). A significant difference was detected between the FPF intensity, FPF heterogeneity, and BCVA in all four disease states compared to unaffected controls (Kruskal-Wallis Tests, p = 1.06 x 10-8, p = 0.002, p = 5.54 x 10-8, respectively). Compared to healthy controls, FPF intensity values were significantly higher in RVO, DR, exudative AMD, and CSR (p < 0.001, p < 0.001, p < 0.001, and p = 0.001, respectively). Spearman rank correlation coefficient between FPF intensity and BCVA was ρ = 0.595 (p = 9.62 x 10-10). Conclusions: Despite variations in structural retinal findings, FPF was found to be highly sensitive for detecting retinal disease. Significant FPF elevation were seen in all four disease states, with the exudative AMD patients exhibiting the highest FPF values compared to DR, CSR, and RVO subjects. This is consistent with the hypothesis that there is elevated oxidative stress in all of these conditions as previously demonstrated by blood studies. FPF intensity is moderately correlated with the late-in disease-marker BCVA, which suggests that the degree of FPF elevation can be used as a metabolic indicator of disease severity.