Therapeutic Options Under Development for Nonneovascular Age-Related Macular Degeneration and Geographic Atrophy

Melatonin protects retinal pigment epithelium cells against ferroptosis in AMD via the PI3K/AKT/MDM2/P53 pathway

Introduction

Oxidative stress-prompted degeneration of the retinal pigment epithelium (RPE) notably contributes to the onset of age-related macular degeneration (AMD). However, the pathways leading to RPE deterioration and possible preventative strategies are not yet completely comprehended.

Methods

Ferroptosis was assayed through the evaluation of lipid peroxidation (C11-BODIPY and MDA), reactive oxygen species (ROS), transmission electron microscopy (TEM), iron content measurement, q-PCR, western blotting, and immunofluorescence. To assess the structure and retinal function of RPE in mice, ERG (electroretinography), OCT (optical coherence tomography), and H&E (hematoxylin and eosin) staining were employed. Network pharmacology methods were utilized to elucidate the potential mechanisms underlying melatonin's protective effects against ferroptosis in RPE cells in AMD. Genetic engineering techniques were applied to investigate the regulatory relationships among phosphatidylinositol 3-kinase (PI3K), protein kinase-B (AKT), murine double minute-2 (MDM2), protein 53 (P53), and solute carrier family 7 member 11 (SLC7A11). In vitro knockdown experiments of MDM2 were conducted to explore its regulatory role in ferroptosis within RPE cells.

Results

Aβ1-40 can trigger ferroptosis in RPE cells. Melatonin can inhibit the oxidative stress and ferroptosis induced by Aβ1-40 in RPE cells. Melatonin exhibits a protective effect on Aβ1-40-induced AMD, significantly improving the structure of the mouse retina and RPE layer, and facilitating the restoration of visual function. Network pharmacology methods revealed that the potential targets of melatonin in AMD are closely related to ferroptosis, and indicated that the predominant pathways are significantly associated with the PI3K/AKT/MDM2/P53 signaling pathway. Knocking down the specific expression of MDM2 can significantly weaken the inhibitory effect of melatonin on oxidative stress and ferroptosis.

Discussion

Melatonin can suppress cell death by ferroptosis in RPE via the PI3K/AKT/MDM2/P53 pathway, thereby preventing and decelerating the progression of AMD.

Repurposing Drugs for Treatment of Age-Related Macular Degeneration

The need for new drugs to treat dry forms of age-related macular degeneration remains high. A promising approach is repurposing of FDA-approved medications to treat AMD. Databases containing medical and drug records allow for retroactive identification of drugs whose use correlates with reduced AMD diagnosis. This short review summarizes progress in several classes of drugs considered for repurposing: GPR-143 agonists (L-DOPA), anti-diabetic drugs (metformin, acarbose, empagliflozin, fenofibrate), mitochondrial activators (PU-91), and serotonin pathway drugs (fluoxetine, flibanserin, xaliproden, buspirone). The promises and caveats of repurposing are discussed herein.

Bone marrow-derived mononuclear stem cells in the treatment of retinal degenerations

Retinal degenerative diseases affecting the outer retina in its many forms (inherited, acquired or induced) are characterized by photoreceptor loss, and represent currently a leading cause of irreversible vision loss in the world. At present, there are very few treatments capable of preventing, recovering or reversing photoreceptor degeneration or the secondary retinal remodeling, which follows photoreceptor loss and can also cause the death of other retinal cells. Thus, these diseases are nowadays one of the greatest challenges in the field of ophthalmological research. Bone marrow derived-mononuclear stem cell transplantation has shown promising results for the treatment of photoreceptor degenerations. These cells may have the potential to slow down photoreceptor loss, and therefore should be applied in the early stages of photoreceptor degenerations. Furthermore, because of their possible paracrine effects, they may have a wide range of clinical applications, since they can potentially impact on several retinal cell types at once and photoreceptor degenerations can involve different cells and/or begin in one cell type and then affect adjacent cells. The intraocular injection of bone marrow derived-mononuclear stem cells also enhances the outcomes of other treatments aimed to protect photoreceptors. Therefore, it is likely that future investigations may combine bone marrow derived-mononuclear stem cell therapy with other systemic or intraocular treatments to obtain greater therapeutic effects in degenerative retinal diseases.

Complement Mediators in Development to Treat Age-Related Macular Degeneration

Over recent years, great attention has been paid to the role of the complement system in the pathogenesis of age-related macular degeneration (AMD). In particular, several studies have highlighted a link between AMD development and complement dysregulation, which can probably be explained as a complement cascade hyperactivation resulting from the presence of a series of risk factors such as aging; smoking; obesity; alcohol consumption; exposure to pesticides, industrial chemicals, or pollution; and other causes of oxidative stress. This hypothesis has been mainly supported by the presence of complement mediators as constituents of drusen, representing one of the earliest and most characteristic signs of retinal damage in AMD. Additionally, activated complement mediators and some complement regulators, such as vitronectin, have been found not only in the drusen and adjacent retinal areas but also in the peripheral blood of patients with AMD. Therefore, we aim to provide a review of recently studied complement factors to highlight their role in the pathogenesis of AMD and to evaluate new potential therapeutic strategies.

Biomarkers for Nonexudative Age-Related Macular Degeneration and Relevance for Clinical Trials: A Systematic Review

TOPIC

The purpose of the review was to identify structural, functional, blood-based, and other types of biomarkers for early, intermediate, and late nonexudative stages of age-related macular degeneration (AMD) and summarize the relevant data for proof-of-concept clinical trials.

CLINICAL RELEVANCE

AMD is a leading cause of blindness in the aging population, yet no treatments exist for its most common nonexudative form. There are limited data on the diagnosis and progression of nonexudative AMD compared to neovascular AMD. Our objective was to provide a comprehensive, systematic review of recently published biomarkers (molecular, structural, and functional) for early AMD, intermediate AMD, and geographic atrophy and to evaluate the relevance of these biomarkers for use in future clinical trials.

METHODS

A literature search of PubMed, ScienceDirect, EMBASE, and Web of Science from January 1, 1996 to November 30, 2020 and a patent search were conducted. Search terms included "early AMD," "dry AMD," "intermediate AMD," "biomarkers for nonexudative AMD," "fundus autofluorescence patterns," "color fundus photography," "dark adaptation," and "microperimetry." Articles were assessed for bias and quality with the Mixed-Methods Appraisal Tool. A total of 94 articles were included (61,842 individuals).

RESULTS

Spectral-domain optical coherence tomography was superior at highlighting detailed structural changes in earlier stages of AMD. Fundus autofluorescence patterns were found to be most important in estimating progression of geographic atrophy. Delayed rod intercept time on dark adaptation was the most widely recommended surrogate functional endpoint for early AMD, while retinal sensitivity on microperimetry was most relevant for intermediate AMD. Combinational studies accounting for various patient characteristics and machine/deep-learning approaches were best suited for assessing individualized risk of AMD onset and progression.

CONCLUSION

This systematic review supports the use of structural and functional biomarkers in early AMD and intermediate AMD, which are more reproducible and less invasive than the other classes of biomarkers described. The use of deep learning and combinational algorithms will gain increasing importance in future clinical trials of nonexudative AMD.