C20D3-Vitamin A Prevents Retinal Pigment Epithelium Atrophic Changes in a Mouse Model

Lipofuscin, Its Origin, Properties, and Contribution to Retinal Fluorescence as a Potential Biomarker of Oxidative Damage to the Retina

Lipofuscin accumulates with age as intracellular fluorescent granules originating from incomplete lysosomal digestion of phagocytosed and autophagocytosed material. The purpose of this review is to provide an update on the current understanding of the role of oxidative stress and/or lysosomal dysfunction in lipofuscin accumulation and its consequences, particularly for retinal pigment epithelium (RPE). Next, the fluorescence of lipofuscin, spectral changes induced by oxidation, and its contribution to retinal fluorescence are discussed. This is followed by reviewing recent developments in fluorescence imaging of the retina and the current evidence on the prognostic value of retinal fluorescence for the progression of age-related macular degeneration (AMD), the major blinding disease affecting elderly people in developed countries. The evidence of lipofuscin oxidation in vivo and the evidence of increased oxidative damage in AMD retina ex vivo lead to the conclusion that imaging of spectral characteristics of lipofuscin fluorescence may serve as a useful biomarker of oxidative damage, which can be helpful in assessing the efficacy of potential antioxidant therapies in retinal degenerations associated with accumulation of lipofuscin and increased oxidative stress. Finally, amendments to currently used fluorescence imaging instruments are suggested to be more sensitive and specific for imaging spectral characteristics of lipofuscin fluorescence.

Geographic atrophy: pathophysiology and current therapeutic strategies

Geographic atrophy (GA) is an advanced stage of age-related macular degeneration (AMD) that leads to gradual and permanent vision loss. GA is characterized by the loss of photoreceptor cells and retinal pigment epithelium (RPE), leading to distinct atrophic patches in the macula, which tends to increase with time. Patients with geographic atrophy often experience a gradual and painless loss of central vision, resulting in difficulty reading, recognizing faces, or performing activities that require detailed vision. The primary risk factor for the development of geographic atrophy is advanced age; however, other risk factors, such as family history, smoking, and certain genetic variations, are also associated with AMD. Diagnosis is usually based on a comprehensive eye examination, including imaging tests such as fundus photography, optical coherence tomography (OCT), and fluorescein angiography. Numerous clinical trials are underway, targeting identified molecular pathways associated with GA that are promising. Recent approvals of Syfovre and Izervay by the FDA for the treatment of GA provide hope to affected patients. Administration of these drugs resulted in slowing the rate of progression of the disease. Though these products provide treatment benefits to the patients, they do not offer a cure for geographic atrophy and are limited in efficacy. Considering these safety concerns and limited treatment benefits, there is still a significant need for therapeutics with improved efficacy, safety profiles, and better patient compliance. This comprehensive review discusses pathophysiology, currently approved products, their limitations, and potential future treatment strategies for GA.

Discovery of Nonretinoid Inhibitors of CRBP1: Structural and Dynamic Insights for Ligand-Binding Mechanisms

The dysregulation of retinoid metabolism has been linked to prevalent ocular diseases including age-related macular degeneration and Stargardt disease. Modulating retinoid metabolism through pharmacological approaches holds promise for the treatment of these eye diseases. Cellular retinol-binding protein 1 (CRBP1) is the primary transporter of all-trans-retinol (atROL) in the eye, and its inhibition has recently been shown to protect mouse retinas from light-induced retinal damage. In this report, we employed high-throughput screening to identify new chemical scaffolds for competitive, nonretinoid inhibitors of CRBP1. To understand the mechanisms of interaction between CRBP1 and these inhibitors, we solved high-resolution X-ray crystal structures of the protein in complex with six selected compounds. By combining protein crystallography with hydrogen/deuterium exchange mass spectrometry, we quantified the conformational changes in CRBP1 caused by different inhibitors and correlated their magnitude with apparent binding affinities. Furthermore, using molecular dynamic simulations, we provided evidence for the functional significance of the "closed" conformation of CRBP1 in retaining ligands within the binding pocket. Collectively, our study outlines the molecular foundations for understanding the mechanism of high-affinity interactions between small molecules and CRBPs, offering a framework for the rational design of improved inhibitors for this class of lipid-binding proteins.

Posterior placoid-like maculopathy and macular hole associated with vitamin A deficiency

Purpose

To report a case of bilateral posterior placoid-like maculopathy and a macular hole associated with vitamin A deficiency.

Observations

A 72-year-old male presented with nyctalopia and progressive vision loss in both eyes. Examination and multimodal imaging were consistent with posterior placoid-like maculopathy bilaterally and a macular hole in the right eye. A workup for infectious, inflammatory, and paraneoplastic etiologies revealed a severely low serum vitamin A level. Two months after initiation of vitamin A repletion, there was improvement in best-corrected Snellen visual acuity as well as macular hole closure. A diagnosis of posterior placoid-like maculopathy in the setting of vitamin A deficiency (VAD) was made.

Conclusions and importance

VAD should be considered when symmetric posterior pole placoid-like lesions are observed and other, more common etiologies have been ruled out.

Vitamin A, systemic T-cells, and the eye: Focus on degenerative retinal disease

The first discovered vitamin, vitamin A, exists in a range of forms, primarily retinoids and provitamin carotenoids. The bioactive forms of vitamin A, retinol and retinoic acid, have many critical functions in body systems including the eye and immune system. Vitamin A deficiency is associated with dysfunctional immunity, and presents clinically as a characteristic ocular syndrome, xerophthalmia. The immune functions of vitamin A extend to the gut, where microbiome interactions and nutritional retinoids and carotenoids contribute to the balance of T cell differentiation, thereby determining immune status and contributing to inflammatory disease around the whole body. In the eye, degenerative conditions affecting the retina and uvea are influenced by vitamin A. Stargardt's disease (STGD1; MIM 248200) is characterised by bisretinoid deposits such as lipofuscin, produced by retinal photoreceptors as they use and recycle a vitamin A-derived chromophore. Age-related macular degeneration features comparable retinal deposits, such as drusen featuring lipofuscin accumulation; and is characterised by parainflammatory processes. We hypothesise that local parainflammatory processes secondary to lipofuscin deposition in the retina are mediated by T cells interacting with dietary vitamin A derivatives and the gut microbiome, and outline the current evidence for this. No cures exist for Stargardt's or age-related macular degeneration, but many vitamin A-based therapeutic approaches have been or are being trialled. The relationship between vitamin A's functions in systemic immunology and the eye could be further exploited, and further research may seek to leverage the interactions of the gut-eye immunological axis.