Role In Age-related Macular Degeneration Research Articles

Identification of the CDH18 gene associated with age-related macular degeneration using weighted gene co-expression network analysis.

Purpose: Age-related macular degeneration (AMD) is a chronic and progressive macular degenerative disease that culminates in a gradual deterioration of central vision. Despite its prevalence, the key biomarkers for AMD have not yet been fully elucidated. In this study, we aimed to efficiently identify biomarkers crucial for diagnosing AMD. Methods: Three datasets pertaining to retinal pigment epithelium (RPE)/choroid tissues associated with AMD were selected from the GEO database. The GSE50195 dataset was utilized to conduct weighted gene co-expression network analysis (WGCNA) for identifying module genes linked to AMD. KEGG and GO enrichment analyses were subsequently conducted on these module genes. GSE29801 and GSE135092 datasets were subjected to differential expression analysis to pinpoint the DEGs intersecting with the module genes. Subsequently, wet AMD (wAMD) and dry AMD (dAMD) mouse models were developed, from which RPE/choroid tissues were harvested to validate the hub genes via RT-qPCR and Western blot. Results: Using the WGCNA, we selected the "antiquewhite4" module (r = 0.91 and p = 7e-07), which contains a total of 325 genes. Through the intersection of module genes with DEGs, nine hub genes were identified. Pathways involved in complement and coagulation cascades, ECM-receptor interactions, unsaturated fatty acid biosynthesis, and fatty acid elongation play important roles in AMD. Notably, CDH18 demonstrated notable variance across all three datasets. Post validation using RT-qPCR experiments revealed a significant downregulation of CDH18 in both dAMD and wAMD. EGLN3 was expressed at low levels in wAMD. In dAMD, EYA2, LTB, and PODXL were significantly downregulated, whereas APOC1 was notably upregulated. Western blot confirmed that CDH18 was lowly expressed in dAMD and wAMD mouse models. Conclusion: CDH18 was identified as the key gene involved in the pathogenesis of AMD. An imbalance of the complement and coagulation cascades is a potential mechanism of AMD. This study provides a novel idea for diagnosing and treating AMD in the future.

SPI1-mediated macrophage polarization aggravates age-related macular degeneration.

This study revealed a core regulator and common upstream mechanisms for the multifaceted pathological processes of age-related macular degeneration (AMD) and provided proof-of-concept for this new therapeutic target. Comprehensive gene expression analysis was performed using RNA sequencing of eye cup from old mice as well as laser-induced choroidal neovascularization (CNV) mouse model. Through integrative analysis and protein-protein interaction (PPI) analysis, common pathways and key transcription factor was identified simultaneously engaged in age-related retinal degeneration and CNV, the two typical pathological process of AMD. Subsequently, the expression changes of Spi1, the key regulator, as well as the alternation of the downstream mechanisms were validated in both models through qRT-PCR, Elisa, flow cytometry and immunofluorescence. Further, we assessed the impact of Spi1 knockdown in vitro and in vivo using gene intervention vectors carried by adeno-associated virus or lentivirus to test its potential as a therapeutic target. Compared to corresponding controls, we found 1,939 and 1,319 genes differentially expressed in eye cups of old and CNV mice respectively. The integrative analysis identified a total of 275 overlapping DEGs, of which 150 genes were co-upregulated. PPI analysis verified a central transcription factor, SPI1. The significant upregulation of Spi1 expression was then validated in both models, accompanied by macrophage polarization towards the M1 phenotype. Finally, SPI1 suppression significantly inhibited M1 polarization of BMDMs and attenuated neovascularization in CNV mice. This study demonstrates that SPI1 exerts a pivotal role in AMD by regulation of macrophage polarization and innate immune response, offering promise as an innovative target for treating AMD.

Fructosyl Amino Oxidase as a Therapeutic Enzyme in Age-Related Macular Degeneration.

Age-related macular degeneration (AMD) is an age-related disorder that is a global public health problem. The non-enzymatic Maillard reaction results in the formation of advanced glycation end products (AGEs). Accumulation of AGEs in drusen plays a key role in AMD. AGE-reducing drugs may contribute to the prevention and treatment of AGE-related disease. Fructosamine oxidase (FAOD) acts on fructosyl lysine and fructosyl valine. Based upon the published results of fructosamine 3-kinase (FN3K) and FAOD obtained in cataract and presbyopia, we studied ex vivo FAOD treatment as a non-invasive AMD therapy. On glycolaldehyde-treated porcine retinas, FAOD significantly reduced AGE autofluorescence (p = 0.001). FAOD treatment results in a breakdown of AGEs, as evidenced using UV fluorescence, near-infrared microspectroscopy on stained tissue sections of human retina, and gel permeation chromatography. Drusen are accumulations of AGEs that build up between Bruch's membrane and the retinal pigment epithelium. On microscopy slides of human retina affected by AMD, a significant reduction in drusen surface to 45 ± 21% was observed following FAOD treatment. Enzymatic digestion followed by mass spectrometry of fructose- and glucose-based AGEs (produced in vitro) revealed a broader spectrum of substrates for FAOD, as compared to FN3K, including the following: fructosyllysine, carboxymethyllysine, carboxyethyllysine, and imidazolone. In contrast to FN3K digestion, agmatine (4-aminobutyl-guanidine) was formed following FAOD treatment in vitro. The present study highlights the therapeutic potential of FAOD in AMD by repairing glycation-induced damage.

Decreased Circulating Very Small Low-Density Lipoprotein is Likely Causal for Age-Related Macular Degeneration

Abnormal changes in metabolite levels in serum or plasma have been highlighted in several studies in age-related macular degeneration (AMD), the leading cause of irreversible vision loss. Specific changes in lipid profiles are associated with an increased risk of AMD. Metabolites could thus be used to investigate AMD disease mechanisms or incorporated into AMD risk prediction models. However, whether particular metabolites causally affect the disease has yet to be established. A 3-tiered analysis of blood metabolites in the United Kingdom (UK) Biobank cohort to identify metabolites that differ in AMD patients with evidence for a putatively causal role in AMD. A total of 72376 donors from the UK Biobank cohort including participants with AMD (N=1353) and non-AMD controls (N=71023). We analyzed 325 directly measured or derived blood metabolites from the UK Biobank for 72376 donors to identify AMD-associated metabolites. Genome-wide association studies for 325 metabolites in 98316 European participants from the UK Biobank were performed. The causal effects of these metabolites in AMD were tested using a 2-sample Mendelian randomization approach. The predictive value of these measurements together with sex and age was assessed by developing a machine learning classifier. Evaluating metabolic biomarkers associated with AMD susceptibility and investigating their potential causal contribution to the development of the disease. This study noted age to be the prominent risk factor associated with AMD development. While accounting for age and sex, we identified 84 metabolic markers as significantly (false discovery rate-adjusted P value < 0.05) associated with AMD. Lipoprotein subclasses comprised the majority of the AMD-associated metabolites (39%) followed by several lipoprotein to lipid ratios. Nineteen metabolites showed a likely causative role in AMD etiology. Of these, 6 lipoproteins contain very small, very low-density lipoprotein (VLDL), and phospholipids to total lipid ratio in medium VLDL. Based on this we postulate that depletion of circulating very small VLDLs is likely causal for AMD. The risk prediction model constructed from the metabolites, age and sex, identified age as the primary predictive factor with a much smaller contribution by metabolites to AMD risk prediction. This study underscores the pronounced role of lipids in AMD susceptibility and the likely causal contribution of particular subclasses of lipoproteins to AMD. Our study provides valuable insights into the metabopathological mechanisms of AMD disease development and progression.

A narrative review on dietary components and patterns and age-related macular degeneration.

Age-related macular degeneration (AMD) is one of the most prevalent eye diseases among the ageing population worldwide. It is a leading cause of blindness in individuals over 55, particularly in industrialised Western countries. The prevalence of AMD increases with age, and genetic factors and environmental influences are believed to contribute to its development. Among the environmental factors, diet plays a significant role in AMD. This review explores the association between dietary components, dietary patterns and AMD. Various nutrients, non-nutrient substances and dietary models that have the potential to counteract oxidative stress and inflammation, which are underlying mechanisms of AMD, are discussed. Consuming fruits, vegetables, fish and seafood, whole grains, olive oil, nuts and low-glycaemic-index foods has been highlighted as beneficial for reducing the risk of AMD. Adhering to the Mediterranean diet, which encompasses these elements, can be recommended as a dietary pattern for AMD. Furthermore, the modulation of the gut microbiota through dietary interventions and probiotics has shown promise in managing AMD.

Targeting cell-type-specific, choroid-peripheral immune signaling to treat age-related macular degeneration

Age-related macular degeneration (AMD) is a leading cause of blindness featuring pathogenic neovascularization of the choroidal vasculature (CNV). Although systemic immunity plays a role in AMD, the ocular signals that recruit and activate immune cells remain poorly defined. Using single-cell RNA sequencing, we prospectively profile peripheral blood mononuclear cells from 65 individuals including AMD and controls, which we integrate with existing choroid data. We generate a network of choroid-peripheral immune interactions dysregulated in AMD, including known AMD-relevant gene vascular endothelial growth factor (VEGF) receptor 2. Additionally, we find CYR61 is upregulated in choroidal veins and may signal to circulating monocytes. In mice, we validate that CYR61 is abundant in endothelial cells within CNV lesions neighboring monocyte-derived macrophages. Mechanistically, CYR61 activates macrophage anti-angiogenic gene expression, and ocular Cyr61 knockdown increases murine CNV size, indicating CYR61 inhibits CNV. This study highlights the potential of multi-tissue human datasets to identify disease-relevant and potentially therapeutically modifiable targets.

Effects of Humanin G (HNG) on angiogenesis and neurodegeneration markers in Age-related Macular Degeneration (AMD)

Advanced stages of Age-related Macular Degeneration (AMD) are characterized by retinal neurodegeneration and aberrant angiogenesis, and mitochondrial dysfunction contributes to the pathogenesis of AMD. In this study, we tested the hypothesis that Humanin G (HNG), a cytoprotective mitochondrial-derived peptide, positively regulates cell proliferation, cell death, and the protein levels of angiogenesis and neurodegeneration markers, in normal (control) and AMD RPE transmitochondrial cybrid cell lines. These normal and AMD RPE transmitochondrial cybrid cell lines had identical nuclei derived from mitochondria-deficient ARPE-19 cell line, but differed in mitochondrial DNA (mtDNA) content that was derived from clinically characterized AMD patients and normal (control) subjects. Cell lysates were extracted from untreated and HNG-treated AMD and normal (control) cybrid cell lines, and the Luminex XMAP multiplex assay was used to examine the protein levels of angiogenesis and neurodegeneration markers. Humanin G reduced Caspase-3/7-mediated apoptosis, improved cell proliferation, and normalized the protein levels of angiogenesis and neurodegeneration markers in AMD RPE cybrid cell lines, thereby suggesting Humanin G's positive regulatory role in AMD.

The role of blood neutrophil lymphocyte ratio in predicting the initial response to anti-VEGF treatment in neovascular AMD patients.

Vascular endothelial growth factor (VEGF) has a critical role in age-related macular degeneration (AMD), and intravitreal injection of anti-VEGF drugs is the mainstay of neovascular AMD treatment. Blood neutrophil-to-lymphocyte ratio (NLR) is shown to be a biomarker of inflammation in AMD. We aimed to investigate the role of NLR in predicting favorable short-term anti-VEGF treatment results in neovascular AMD patients. A total of 112 patients diagnosed with exudative AMD and had taken 3 monthly intravitreal bevacizumab injections were analyzed retrospectively. Medical records were reached to obtain neutrophil and lymphocyte values to calculate NLR. Best-corrected visual acuity and central macular thickness (CMT) measurements were recorded at each visit. T test or Mann-Whitney U test was used to compare continuous variables, and chi-square test was used to compare categorical variables. Receiver operating characteristics curve (ROC) analysis was performed to determine cut-off, sensitivity, and specificity values. P value of ≤ 0.05 was considered statistically significant. The mean age was 68.1 ± 7.2years, and the mean NLR was 2.11 ± 0.81. The ROC analysis revealed a cut off value of 2.0 for NLR to predict at least 100μm CMT change (sensitivity 87.1%; specificity 87.8%) and a cut off value of 2.4 for NLR to predict at least 0.1 logMAR visual improvement (sensitivity 77.2%; specificity 64.8%) after 3 monthly IVT bevacizumab injections. NLR can provide additional prognostic information for the identification of patients with a good initial response to anti-VEGF therapy.

Transcriptomic Changes Predict Metabolic Alterations in LC3 Associated Phagocytosis in Aged Mice.

LC3b (Map1lc3b) plays an essential role in canonical autophagy and is one of several components of the autophagy machinery that mediates non-canonical autophagic functions. Phagosomes are often associated with lipidated LC3b to promote phagosome maturation in a process called LC3-associated phagocytosis (LAP). Specialized phagocytes, such as mammary epithelial cells, retinal pigment epithelial (RPE) cells, and sertoli cells, utilize LAP for optimal degradation of phagocytosed material, including debris. In the visual system, LAP is critical to maintain retinal function, lipid homeostasis, and neuroprotection. In a mouse model of retinal lipid steatosis-mice lacking LC3b (LC3b-/-), we observed increased lipid deposition, metabolic dysregulation, and enhanced inflammation. Herein, we present a non-biased approach to determine if loss of LAP mediated processes modulate the expression of various genes related to metabolic homeostasis, lipid handling, and inflammation. A comparison of the RPE transcriptome of WT and LC3b-/- mice revealed 1533 DEGs, with ~73% upregulated and 27% downregulated. Enriched gene ontology (GO) terms included inflammatory response (upregulated DEGs), fatty acid metabolism, and vascular transport (downregulated DEGs). Gene set enrichment analysis (GSEA) identified 34 pathways; 28 were upregulated (dominated by inflammation/related pathways) and 6 were downregulated (dominated by metabolic pathways). Analysis of additional gene families identified significant differences for genes in the solute carrier family, RPE signature genes, and genes with a potential role in age-related macular degeneration. These data indicate that loss of LC3b induces robust changes in the RPE transcriptome contributing to lipid dysregulation and metabolic imbalance, RPE atrophy, inflammation, and disease pathophysiology.

CHAC1 as a Novel Contributor of Ferroptosis in Retinal Pigment Epithelial Cells with Oxidative Damage.

Age-related macular degeneration (AMD) is the leading cause of irreversible visual loss in the elderly population. With aging and the accumulated effects of environmental stress, retinal pigment epithelial (RPE) cells are particularly susceptible to oxidative damage, which can lead to retinal degeneration. However, the underlying molecular mechanisms of how RPE responds and progresses under oxidative damage are still largely unknown. Here, we reveal that exogenous oxidative stress led to ferroptosis characterized by Fe2+ accumulation and lipid peroxidation in RPE cells. Glutathione specific gamma-glutamylcyclotransferase 1 (Chac1), as a component of the unfolded protein response (UPR) pathway, plays a pivotal role in oxidative-stress-induced cell ferroptosis via the regulation of glutathione depletion. These results indicate the biological significance of Chac1 as a novel contributor of oxidative-stress-induced ferroptosis in RPE, suggesting its potential role in AMD.

Does senescence play a role in age-related macular degeneration?

Advanced age is the most established risk factor for developing age-related macular degeneration (AMD), one of the leading causes of visual impairment in the elderly, in Western and developed countries. Similarly, after middle age, there is an exponential increase in pathologic molecular and cellular events that can induce senescence, traditionally defined as an irreversible loss of the cells' ability to divide and most recently reported to also occur in select post-mitotic and terminally differentiated cells, such as neurons. Together these facts raise the question as to whether or not cellular senescence, may play a role in the development of AMD. A number of studies have reported the effect of ocular-relevant inducers of senescence using primarily in vitro models of poorly polarized, actively dividing retinal pigment epithelial (RPE) cell lines. However, in interpretating the data, the fidelity of these culture models to the RPE in vivo, must be considered. Fewer studies have explored the presence and/or impact of senescent cells in in vivo models that present with phenotypic features of AMD, leaving this an open field for further investigation. The goal of this review is to discuss current thoughts on the potential role of senescence in AMD development and progression, with consideration of the model systems used and their relevance to human disease.

Relative Leukocyte Telomere Length and Genetic Variants in Telomere-Related Genes and Serum Levels Role in Age-Related Macular Degeneration

Our study enrolled 342 patients with AMD and 177 healthy controls. Samples of DNA from peripheral blood leukocytes were extracted by DNA salting-out method. The genotyping of TERT rs2736098, rs401681 in TERT-CLPTM1 locus, TRF1 rs1545827, rs10107605, TNKS2 rs10509637, rs10509639, and TRF2 rs251796 and relative leukocyte telomere length (T/S) measurement were carried out using the real-time polymerase chain reaction method. Serum TERF-1 and TERF2 levels were measured by enzymatic immunoassay (ELISA). We found longer telomeres in early AMD patients compared to the control group. Additionally, we revealed that minor allele C at TRF1 rs10107605 was associated with decreases the odds of both early and exudative AMD. Each minor allele G at TRF2 rs251796 and TRF1 rs1545827 C/T genotype and C/T+T/T genotypes, compared to the C/C genotype, increases the odds of having shorter telomeres. Furthermore, we found elevated TERF1 serum levels in the early AMD group compared to the control group. In conclusion, these results suggest that relative leukocyte telomere length and genetic variants of TRF1 and TRF2 play a role in AMD development. Additionally, TERF1 is likely to be associated with early AMD.

Potential role of extracellular granzyme B in wet age-related macular degeneration and fuchs endothelial corneal dystrophy.

Age-related ocular diseases are the leading cause of blindness in developed countries and constitute a sizable socioeconomic burden worldwide. Age-related macular degeneration (AMD) and Fuchs endothelial corneal dystrophy (FECD) are some of the most common age-related diseases of the retina and cornea, respectively. AMD is characterized by a breakdown of the retinal pigment epithelial monolayer, which maintains retinal homeostasis, leading to retinal degeneration, while FECD is characterized by degeneration of the corneal endothelial monolayer, which maintains corneal hydration status, leading to corneal edema. Both AMD and FECD pathogenesis are characterized by disorganized local extracellular matrix (ECM) and toxic protein deposits, with both processes linked to aberrant protease activity. Granzyme B (GrB) is a serine protease traditionally known for immune-mediated initiation of apoptosis; however, it is now recognized that GrB is expressed by a variety of immune and non-immune cells and aberrant extracellular localization of GrB substantially contributes to various age-related pathologies through dysregulated cleavage of ECM, tight junction, and adherens junction proteins. Despite growing recognition of GrB involvement in multiple age-related pathologies, its role in AMD and FECD remains poorly understood. This review summarizes the pathophysiology of, and similarities between AMD and FECD, outlines the current knowledge of the role of GrB in AMD and FECD, as well as hypothesizes putative contributions of GrB to AMD and FECD pathogenesis and highlights the therapeutic potential of pharmacologically inhibiting GrB as an adjunctive treatment for AMD and FECD.

Protective effects of CRTH2 suppression in dry age-related macular degeneration

Age-related macular degeneration (AMD) is the leading cause of central vision loss in the elderly. Oxidative stress-induced retinal pigment epithelium (RPE) cell apoptosis is a crucial pathogenic hallmark in AMD. Chemoattractant receptor-homologous molecule expressed on T helper type 2 cells (CRTH2), a prostaglandin (PG) D2 receptor, has been implicated in various pathophysiological events, especially inflammation and stress-induced cell apoptosis. However, its specific role in AMD is not fully understood. Here we studied the effect of CRTH2 on AMD. Our results showed that when stimulated by H2O2, CRTH2 mRNA expression in cells tended to increase. Flow cytometry revealed that the CRTH2 inhibitor could protect the RPE from apoptosis. After NaIO3 injection, a larger area of retinal degeneration was observed in wild-type mice than in CRTH2−/− mice. Optical coherence tomography (OCT) and Hematoxylin and Eosin (H&E) staining of retinal sections showed that sodium iodate-induced loss of photoreceptor cells was reduced in CRTH2−/− mice after treatment; TUNEL-positive cells were mostly found in the outer nuclear layer. In the control group, NaIO3 stimulation increased the number of TUNEL-positive cells, whereas the percentage of TUNEL-positive cells was significantly lower in CRTH2−/− mice. Similarly, the CRTH2 receptor inhibitor CAY10471 similarly inhibited sodium iodate-induced retinal damage. Our results suggest that targeting CRTH2 is a promising therapeutic strategy for the treatment of progressive retinal degeneration in AMD.

(-)-Epicatechin Provides Neuroprotection in Sodium Iodate-Induced Retinal Degeneration.

Oxidative stress, mitochondrial impairment, and pathological amyloid beta (Aβ) deposition are involved in the pathogenesis of dry age-related macular degeneration (AMD). The natural flavonoid (–)-epicatechin (EC) is known to be an antioxidant and neuroprotective compound. Whether EC plays a therapeutic role in AMD is unknown. In this work, we aimed to assess the efficacy and molecular mechanisms of EC against sodium iodate (NaIO3)-induced retinal degeneration in C57BL/6 mice via bioinformatic, morphological, and functional methods. We demonstrated that EC had no toxic effects on the retina and could ameliorate retinal deformation and thinning. EC treatment prevented outer retinal degeneration, reduced drusen-like deposits, increased b-wave amplitude in electroretinography, blocked retinal gliosis, and increased the number and quality of mitochondria. Importantly, EC increased the protein expression of OPA1 and decreased the expression of PINK1, indicating the role of EC in mitochondrial fusion that impaired by NaIO3. Moreover, EC downregulated APP and TMEM97 levels, upregulated PGRMC1 levels, and reduced subretinal Aβ accumulation. This study illustrated that EC, which may become a promising therapeutic strategy for AMD, prevented NaIO3-induced retinal degeneration, and this improvement may be associated with the mitochondrial quality control and the TMEM97/PGRMC1/Aβ signaling pathway.

Activation of LXRs Reduces Oxysterol Lipotoxicity in RPE Cells by Promoting Mitochondrial Function.

Effective treatments for age-related macular degeneration (AMD), the most prevalent neurodegenerative form of blindness in older adults, are lacking. Genome-wide association studies have identified lipid metabolism and inflammation as AMD-associated pathogenic changes. Liver X receptors (LXRs) play a critical role in intracellular homeostases, such as lipid metabolism, glucose homeostasis, inflammation, and mitochondrial function. However, its specific role in AMD and its underlying molecular mechanisms remain unknown. In this study, we investigated the effects of lipotoxicity in human retinal pigmental epithelial (ARPE-19) cells and evaluated how LXRs reduce 7-ketocholesterol (7KCh) lipotoxicity in RPE cells using models, both in vivo and in vitro. A decrease in oxidative lipid accumulation was observed in mouse retinas following the activation of the LXRs; this result was also confirmed in cell experiments. At the same time, LXRs activation reduced RPE cell apoptosis induced by oxysterols. We found that oxysterols decreased the mitochondrial membrane potential in ARPE-19 cells, while LXR agonists counteracted these effects. In cultured ARPE-19 cells, activating LXRs reduced p62, mTOR, and LC3I/II levels, and the knockdown of LXRs elevated the expression of these proteins, indicating that activating LXRs could boost mitophagy. The findings of this study suggest LXR-active pharmaceuticals as a potential therapeutic target for dry AMD.

Deuterated docosahexaenoic acid protects against oxidative stress and geographic atrophy-like retinal degeneration in a mouse model with iron overload.

Oxidative stress plays a central role in age‐related macular degeneration (AMD). Iron, a potent generator of hydroxyl radicals through the Fenton reaction, has been implicated in AMD. One easily oxidized molecule is docosahexaenoic acid (DHA), the most abundant polyunsaturated fatty acid in photoreceptor membranes. Oxidation of DHA produces toxic oxidation products including carboxyethylpyrrole (CEP) adducts, which are increased in the retinas of AMD patients. In this study, we hypothesized that deuterium substitution on the bis‐allylic sites of DHA in photoreceptor membranes could prevent iron‐induced retinal degeneration by inhibiting oxidative stress and lipid peroxidation. Mice were fed with either DHA deuterated at the oxidation‐prone positions (D‐DHA) or control natural DHA and then given an intravitreal injection of iron or control saline. Orally administered D‐DHA caused a dose‐dependent increase in D‐DHA levels in the neural retina and retinal pigment epithelium (RPE) as measured by mass spectrometry. At 1 week after iron injection, D‐DHA provided nearly complete protection against iron‐induced retinal autofluorescence and retinal degeneration, as determined by in vivo imaging, electroretinography, and histology. Iron injection resulted in carboxyethylpyrrole conjugate immunoreactivity in photoreceptors and RPE in mice fed with natural DHA but not D‐DHA. Quantitative PCR results were consistent with iron‐induced oxidative stress, inflammation, and retinal cell death in mice fed with natural DHA but not D‐DHA. Taken together, our findings suggest that DHA oxidation is central to the pathogenesis of iron‐induced retinal degeneration. They also provide preclinical evidence that dosing with D‐DHA could be a viable therapeutic strategy for retinal diseases involving oxidative stress.

Dark Adaptation and Its Role in Age-Related Macular Degeneration.

Dark adaptation (DA) refers to the slow recovery of visual sensitivity in darkness following exposure to intense or prolonged illumination, which bleaches a significant amount of the rhodopsin. This natural process also offers an opportunity to understand cellular function in the outer retina and evaluate for presence of disease. How our eyes adapt to darkness can be a key indicator of retinal health, which can be altered in the presence of certain diseases, such as age-related macular degeneration (AMD). A specific focus on clinical aspects of DA measurement and its significance to furthering our understanding of AMD has revealed essential findings underlying the pathobiology of the disease. The process of dark adaptation involves phototransduction taking place mainly between the photoreceptor outer segments and the retinal pigment epithelial (RPE) layer. DA occurs over a large range of luminance and is modulated by both cone and rod photoreceptors. In the photopic ranges, rods are saturated and cone cells adapt to the high luminance levels. However, under scotopic ranges, cones are unable to respond to the dim luminance and rods modulate the responses to lower levels of light as they can respond to even a single photon. Since the cone visual cycle is also based on the Muller cells, measuring the impairment in rod-based dark adaptation is thought to be particularly relevant to diseases such as AMD, which involves both photoreceptors and RPE. Dark adaptation parameters are metrics derived from curve-fitting dark adaptation sensitivities over time and can represent specific cellular function. Parameters such as the cone-rod break (CRB) and rod intercept time (RIT) are particularly sensitive to changes in the outer retina. There is some structural and functional continuum between normal aging and the AMD pathology. Many studies have shown an increase of the rod intercept time (RIT), i.e., delays in rod-mediated DA in AMD patients with increasing disease severity determined by increased drusen grade, pigment changes and the presence of subretinal drusenoid deposits (SDD) and association with certain morphological features in the peripheral retina. Specifications of spatial testing location, repeatability of the testing, ease and availability of the testing device in clinical settings, and test duration in elderly population are also important. We provide a detailed overview in light of all these factors.

Lutein and Zeaxanthin and Their Roles in Age-Related Macular Degeneration-Neurodegenerative Disease.

Lutein and zeaxanthin belong to the xanthophyll family of carotenoids, which are pigments produced by plants. Structurally, they are very similar, differing only slightly in the arrangement of atoms. Key sources of these carotenoids include kale, savoy cabbage, spinach, broccoli, peas, parsley, corn, and egg yolks. The recommended daily intake of lutein is approximately 10.0 mg and that of zeaxanthin is 2 mg. Lutein intake in adults varies, with average intakes being 1–2 mg/day. Due to the lack of synthesis of consumption of these compounds in humans, these substances are extremely important for the proper functioning of certain organs of the body (eye, skin, heart, intestines). Eating a lot of dark leafy vegetables and some fruits can help to prevent our bodies from developing diseases. The protective effects of carotenoids are mainly related to their defense against oxidative stress and their ability to scavenge free radicals. Lutein and zeaxanthin are the only dietary carotenoids that accumulate in the retina, specifically the macula, and are called macular pigments. These carotenoids are concentrated by the action of specific binding proteins such as StARD3, which binds lutein, and GSTP1, which binds zeaxanthin and its dietary metabolite, mesozeaxanthin. It has been shown that supportive therapy with lutein and zeaxanthin can have a beneficial effect in delaying the progression of eye diseases such as age-related macular degeneration (AMD) and cataracts. This article presents the current state of knowledge on the role of lutein and zeaxanthin, especially from human studies targeting their metabolism and bioavailability, with recommendations to consume xanthophyll-rich foods.

Luteolin Alleviates Epithelial-Mesenchymal Transformation Induced by Oxidative Injury in ARPE-19 Cell via Nrf2 and AKT/GSK-3β Pathway.

Oxidative stress plays a critical role in age-related macular degeneration (AMD), and epithelial-mesenchymal transition (EMT) is involved in this process. The aim of this study was to investigate the protective effects of luteolin, a natural flavonoid with strong antioxidant activity, on H2O2-induced EMT in ARPE-19 cells. ARPE-19 cells were incubated with H2O2 at 200 μΜ to induce oxidative stress-associated injury. Cell viability assay showed that luteolin at 20 and 40 μM significantly promoted cell survival in H2O2-treated ARPE-19 cells. Luteolin also markedly protected ARPE-19 cells from H2O2-induced apoptosis. Cell migration assay presented that luteolin significantly reduced H2O2-induced migration in APRE-19 cells. EMT in ARPE-19 cells was detected by western blotting and immunofluorescence. The results showed that H2O2 significantly upregulated the expression of α-SMA and vimentin and downregulated the expression of ZO-1 and E-cadherin, while cells pretreated with luteolin showed a reversal. Meanwhile, the assessment of effects of luteolin on the Nrf2 pathway indicated that luteolin promoted Nrf2 nuclear translocation and upregulated the expressions of HO-1 and NQO-1. In addition, luteolin significantly increased the activities of SOD and GSH-PX and decreased intracellular levels of ROS and MDA in H2O2-treated ARPE-19 cells. Meanwhile, we observed that the expression of TGF-β2, p-AKT, and p-GSK-3β was upregulated in H2O2-treated ARPE-19 cells and downregulated in luteolin-treated cells, revealing that luteolin inhibited the activation of the AKT/GSK-3β pathway. However, these effects of luteolin were all annulled by transfecting ARPE-19 cells with Nrf2 siRNA. Our current data collectively indicated that inhibition of luteolin on EMT was induced by oxidative injury in ARPE-19 cell through the Nrf2 and AKT/GSK-3β pathway, suggesting that luteolin could be a potential drug for the treatment of dry AMD.