Protective Effect of Melatonin against Oxidative Stress-Induced Apoptosis and Enhanced Autophagy in Human Retinal Pigment Epithelium Cells

Age-related macular degeneration (AMD) affects the retinal macula and results in loss of vision, and AMD is the primary cause of blindness and severe visual impairment among elderly people worldwide. AMD is characterized by the accumulation of drusen in the Bruch’s membrane and dysfunction of retinal pigment epithelial (RPE) cells and photoreceptors. The pathogenesis of AMD remains unclear, and no effective treatment exists. Accumulating evidence indicates that oxidative stress plays a critical role in RPE cell degeneration and AMD. Melatonin is an antioxidant that scavenges free radicals, and it has anti-inflammatory, antitumor, and antiangiogenic effects. This study investigated the antioxidative, antiapoptotic, and autophagic effects of melatonin on oxidative damage to RPE cells. We used hydrogen peroxide (H2O2) to stimulate reactive oxygen species production to cause cell apoptosis in ARPE-19 cell lines. Our findings revealed that treatment with melatonin significantly inhibited H2O2-induced RPE cell damage, decreased the apoptotic rate, increased the mitochondrial membrane potential, and increased the autophagy effect. Furthermore, melatonin reduced the Bax/Bcl-2 ratio and the expression levels of the apoptosis-associated proteins cytochrome c and caspase 7. Additionally, melatonin upregulated the expression of the autophagy-related proteins LC3-II and Beclin-1 and downregulated the expression of p62. Thus, melatonin’s effects on autophagy and apoptosis can protect against H2O2-induced oxidative damage in human RPE cells. Melatonin may have multiple protective effects on human RPE cells against H2O2-induced oxidative damage.

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Autophagy in Age-Related Macular Degeneration: A Regulatory Mechanism of Oxidative Stress

Oxidative Medicine and Cellular Longevity ◽

10.1155/2020/2896036 ◽

2020 ◽

Vol 2020 ◽

pp. 1-13

Author(s):

Zi-Yuan Zhang ◽

Xiao-Li Bao ◽

Yun-Yi Cong ◽

Bin Fan ◽

Guang-Yu Li

Keyword(s):

Oxidative Stress ◽

Oxidative Damage ◽

Macular Degeneration ◽

Retinal Pigment ◽

The Elderly ◽

Age Related Macular Degeneration ◽

Therapeutic Interventions ◽

Cell Degeneration ◽

Rpe Cells ◽

Age Related

Age-related macular degeneration (AMD) is a leading cause of severe visual loss and irreversible blindness in the elderly population worldwide. Retinal pigment epithelial (RPE) cells are the major site of pathological alterations in AMD. They are responsible for the phagocytosis of shed photoreceptor outer segments (POSs) and clearance of cellular waste under physiological conditions. Age-related, cumulative oxidative stimuli contribute to the pathogenesis of AMD. Excessive oxidative stress induces RPE cell degeneration and incomplete digestion of POSs, leading to the continuous accumulation of cellular waste (such as lipofuscin). Autophagy is a major system of degradation of damaged or unnecessary proteins. However, degenerative RPE cells in AMD patients cannot perform autophagy sufficiently to resist oxidative damage. Increasing evidence supports the idea that enhancing the autophagic process can properly alleviate oxidative injury in AMD and protect RPE and photoreceptor cells from degeneration and death, although overactivated autophagy may lead to cell death at early stages of retinal degenerative diseases. The crosstalk among the NFE2L2, PGC-1, p62, AMPK, and PI3K/Akt/mTOR pathways may play a crucial role in improving disturbed autophagy and mitigating the progression of AMD. In this review, we discuss how autophagy prevents oxidative damage in AMD, summarize potential neuroprotective strategies for therapeutic interventions, and provide an overview of these neuroprotective mechanisms.

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PGC-1α Protects RPE Cells of the Aging Retina against Oxidative Stress-Induced Degeneration through the Regulation of Senescence and Mitochondrial Quality Control. The Significance for AMD Pathogenesis

International Journal of Molecular Sciences ◽

10.3390/ijms19082317 ◽

2018 ◽

Vol 19 (8) ◽

pp. 2317 ◽

Cited By ~ 32

Author(s):

Kai Kaarniranta ◽

Jakub Kajdanek ◽

Jan Morawiec ◽

Elzbieta Pawlowska ◽

Janusz Blasiak

Keyword(s):

Oxidative Stress ◽

Cellular Senescence ◽

Mitochondrial Biogenesis ◽

Vision Loss ◽

Pigment Epithelium ◽

Retinal Pigment ◽

Sirtuin 1 ◽

Age Related Macular Degeneration ◽

Rpe Cells ◽

Age Related

PGC-1α (peroxisome proliferator-activated receptor gamma coactivator 1-alpha) is a transcriptional coactivator of many genes involved in energy management and mitochondrial biogenesis. PGC-1α expression is associated with cellular senescence, organismal aging, and many age-related diseases, including AMD (age-related macular degeneration), an important global issue concerning vision loss. We and others have developed a model of AMD pathogenesis, in which stress-induced senescence of retinal pigment epithelium (RPE) cells leads to AMD-related pathological changes. PGC-1α can decrease oxidative stress, a key factor of AMD pathogenesis related to senescence, through upregulation of antioxidant enzymes and DNA damage response. PGC-1α is an important regulator of VEGF (vascular endothelial growth factor), which is targeted in the therapy of wet AMD, the most devastating form of AMD. Dysfunction of mitochondria induces cellular senescence associated with AMD pathogenesis. PGC-1α can improve mitochondrial biogenesis and negatively regulate senescence, although this function of PGC-1α in AMD needs further studies. Post-translational modifications of PGC-1α by AMPK (AMP kinase) and SIRT1 (sirtuin 1) are crucial for its activation and important in AMD pathogenesis.

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Oxidative stress-mediated TXNIP loss causes RPE dysfunction

Experimental & Molecular Medicine ◽

10.1038/s12276-019-0327-y ◽

2019 ◽

Vol 51 (10) ◽

pp. 1-13 ◽

Cited By ~ 7

Author(s):

Min Ji Cho ◽

Sung-Jin Yoon ◽

Wooil Kim ◽

Jongjin Park ◽

Jangwook Lee ◽

...

Keyword(s):

Oxidative Stress ◽

Cell Function ◽

Pigment Epithelium ◽

Retinal Pigment ◽

Common Factor ◽

Age Related Macular Degeneration ◽

Autophagic Flux ◽

Blood Retinal Barrier ◽

Rpe Cells ◽

Age Related

Abstract The disruption of the retinal pigment epithelium (RPE), for example, through oxidative damage, is a common factor underlying age-related macular degeneration (AMD). Aberrant autophagy also contributes to AMD pathology, as autophagy maintains RPE homeostasis to ensure blood–retinal barrier (BRB) integrity and protect photoreceptors. Thioredoxin-interacting protein (TXNIP) promotes cellular oxidative stress by inhibiting thioredoxin reducing capacity and is in turn inversely regulated by reactive oxygen species levels; however, its role in oxidative stress-induced RPE cell dysfunction and the mechanistic link between TXNIP and autophagy are largely unknown. Here, we observed that TXNIP expression was rapidly downregulated in RPE cells under oxidative stress and that RPE cell proliferation was decreased. TXNIP knockdown demonstrated that the suppression of proliferation resulted from TXNIP depletion-induced autophagic flux, causing increased p53 activation via nuclear localization, which in turn enhanced AMPK phosphorylation and activation. Moreover, TXNIP downregulation further negatively impacted BRB integrity by disrupting RPE cell tight junctions and enhancing cell motility by phosphorylating, and thereby activating, Src kinase. Finally, we also revealed that TXNIP knockdown upregulated HIF-1α, leading to the enhanced secretion of VEGF from RPE cells and the stimulation of angiogenesis in cocultured human retinal microvascular endothelial cells. This suggests that the exposure of RPE cells to sustained oxidative stress may promote choroidal neovascularization, another AMD pathology. Together, these findings reveal three distinct mechanisms by which TXNIP downregulation disrupts RPE cell function and thereby exacerbates AMD pathogenesis. Accordingly, reinforcing or restoring BRB integrity by targeting TXNIP may serve as an effective therapeutic strategy for preventing or attenuating photoreceptor damage in AMD.

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Protective Effect of Metformin against Hydrogen Peroxide-Induced Oxidative Damage in Human Retinal Pigment Epithelial (RPE) Cells by Enhancing Autophagy through Activation of AMPK Pathway

Oxidative Medicine and Cellular Longevity ◽

10.1155/2020/2524174 ◽

2020 ◽

Vol 2020 ◽

pp. 1-14

Author(s):

Xia Zhao ◽

Linlin Liu ◽

Yizhou Jiang ◽

Marta Silva ◽

Xuechu Zhen ◽

...

Keyword(s):

Oxidative Damage ◽

Pigment Epithelium ◽

Retinal Pigment ◽

Age Related Macular Degeneration ◽

Protective Effects ◽

Rpe Cells ◽

Mitochondria Membrane Potential ◽

Ampk Pathway ◽

Age Related ◽

Diabetes Drug

Age-related macular degeneration (AMD) is a leading cause of blindness with limited effective treatment. Although the pathogenesis of this disease is complex and not fully understood, the oxidative damage caused by excessive reactive oxygen species (ROS) in retinal pigment epithelium (RPE) has been considered as a major cause. Autophagy is essential for the degradation of cellular components damaged by ROS, and its dysregulation has been implicated in AMD pathogenesis. Therefore, strategies aiming to boost autophagy could be effective in protecting RPE cells from oxidative damage. Metformin is the first-line anti-type 2 diabetes drug and has been reported to stimulate autophagy in many tissues. We therefore hypothesized that metformin may be able to protect RPE cells against H2O2-induced oxidative damage by autophagy activation. In the present study, we found that metformin attenuated H2O2-induced cell viability loss, apoptosis, elevated ROS levels, and the collapse of the mitochondria membrane potential in D407 cells. Autophagy was stimulated by metformin, and inhibition of autophagy by 3-methyladenine (3-MA) and chloroquine (CQ) or knockdown of Beclin1 and LC3B blocked the protective effects of metformin. In addition, we showed that metformin could activate the AMPK pathway, whereas both pharmacological and genetic inhibitions of AMPK blocked the autophagy-stimulating and protective effects of metformin. Metformin conferred a similar protection against H2O2-induced oxidative damage in primary cultured human RPE cells. Taken together, these results demonstrate that metformin could protect RPE cells from H2O2-induced oxidative damage by stimulating autophagy via the activation of the AMPK pathway, supporting its potential use in the prevention and treatment of AMD.

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Autophagy Upregulation by the TFEB Inducer Trehalose Protects against Oxidative Damage and Cell Death Associated with NRF2 Inhibition in Human RPE Cells

Oxidative Medicine and Cellular Longevity ◽

10.1155/2020/5296341 ◽

2020 ◽

Vol 2020 ◽

pp. 1-18

Author(s):

Samuel Abokyi ◽

Sze wan Shan ◽

Chi-ho To ◽

Henry Ho-lung Chan ◽

Dennis Yan-yin Tse

Keyword(s):

Oxidative Stress ◽

Oxidative Damage ◽

Retinal Pigment ◽

Age Related Macular Degeneration ◽

Mrna Levels ◽

Neuroprotective Effects ◽

Rpe Cells ◽

Age Related ◽

Protein Expressions

Trehalose is a natural dietary molecule that has shown antiaging and neuroprotective effects in several animal models of neurodegenerative diseases. The role of trehalose in the management of age-related macular degeneration (AMD) is yet to be investigated and whether trehalose could be a remedy for the treatment of diseases linked to oxidative stress and NRF2 dysregulation. Here, we showed that incubation of human retinal pigment epithelial (RPE) cells with trehalose enhanced the mRNA and protein expressions of TFEB, autophagy genes ATG5 and ATG7, as well as protein expressions of macroautophagy markers, LC3B and p62/SQTM1, and the chaperone-mediated autophagy (CMA) receptor LAMP2. Cathepsin D, a hydrolytic lysosomal enzyme, was also increased by trehalose, indicating higher proteolytic activity. Moreover, trehalose upregulated autophagy flux evident by an increase in the endogenous LC3B level, and accumulation of GFP-LC3B puncta and free GFP fragments in GFP-LC3 ̶ expressing cells in the presence of chloroquine. In addition, the mRNA levels of key molecular targets implicated in RPE damage and AMD, such as vascular endothelial growth factor- (VEGF-) A and heat shock protein 27 (HSP27), were downregulated, whereas NRF2 was upregulated by trehalose. Subsequently, we mimicked in vitro AMD conditions using hydroquinone (HQ) as the oxidative insult on RPE cells and evaluated the cytoprotective effect of trehalose compared to vehicle treatment. HQ depleted NRF2, increased oxidative stress, and reduced the viability of cells, while trehalose pretreatment protected against HQ-induced toxicity. The cytoprotection by trehalose was dependent on autophagy but not NRF2 activation, since autophagy inhibition by shRNA knockdown of ATG5 led to a loss of the protective effect. The results support the transcriptional upregulation of TFEB and autophagy by trehalose and its protection against HQ-induced oxidative damage in RPE cells. Further investigation is, therefore, warranted into the therapeutic value of trehalose in alleviating AMD and retinal diseases associated with impaired NRF2 antioxidant defense.

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Genetic LAMP2 deficiency accelerates the age-associated formation of basal laminar deposits in the retina

Proceedings of the National Academy of Sciences ◽

10.1073/pnas.1906643116 ◽

2019 ◽

Vol 116 (47) ◽

pp. 23724-23734 ◽

Cited By ~ 11

Author(s):

Shoji Notomi ◽

Kenji Ishihara ◽

Nikolaos E. Efstathiou ◽

Jong-Jer Lee ◽

Toshio Hisatomi ◽

...

Keyword(s):

Basal Lamina ◽

Pigment Epithelium ◽

Retinal Pigment ◽

Critical Role ◽

Age Related Macular Degeneration ◽

Bruch's Membrane ◽

Bruch’S Membrane ◽

Rpe Cells ◽

Age Related ◽

Deficient Mice

The early stages of age-related macular degeneration (AMD) are characterized by the accumulation of basal laminar deposits (BLamDs). The mechanism for BLamDs accumulating between the retinal pigment epithelium (RPE) and its basal lamina remains elusive. Here we examined the role in AMD of lysosome-associated membrane protein-2 (LAMP2), a glycoprotein that plays a critical role in lysosomal biogenesis and maturation of autophagosomes/phagosomes. LAMP2 was preferentially expressed by RPE cells, and its expression declined with age. Deletion of the Lamp2 gene in mice resulted in age-dependent autofluorescence abnormalities of the fundus, thickening of Bruch’s membrane, and the formation of BLamDs, resembling histopathological changes occurring in AMD. Moreover, LAMP2-deficient mice developed molecular signatures similar to those found in human AMD—namely, the accumulation of APOE, APOA1, clusterin, and vitronectin—adjacent to BLamDs. In contrast, collagen 4, laminin, and fibronectin, which are extracellular matrix proteins constituting RPE basal lamina and Bruch’s membrane were reduced in Lamp2 knockout (KO) mice. Mechanistically, retarded phagocytic degradation of photoreceptor outer segments compromised lysosomal degradation and increased exocytosis in LAMP2-deficient RPE cells. The accumulation of BLamDs observed in LAMP2-deficient mice was eventually followed by loss of the RPE and photoreceptors. Finally, we observed loss of LAMP2 expression along with ultramicroscopic features of abnormal phagocytosis and exocytosis in eyes from AMD patients but not from control individuals. Taken together, these results indicate an important role for LAMP2 in RPE function in health and disease, suggesting that LAMP2 reduction may contribute to the formation of BLamDs in AMD.

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Hydroquinone Induces NLRP3-Independent IL-18 Release from ARPE-19 Cells

Cells ◽

10.3390/cells10061405 ◽

2021 ◽

Vol 10 (6) ◽

pp. 1405

Author(s):

Niina Bhattarai ◽

Eveliina Korhonen ◽

Yashavanthi Mysore ◽

Kai Kaarniranta ◽

Anu Kauppinen

Keyword(s):

Pigment Epithelium ◽

Retinal Pigment ◽

Retinal Disease ◽

Oxidase Inhibitor ◽

Age Related Macular Degeneration ◽

Rpe Cells ◽

Pyrin Domain ◽

Age Related ◽

Domain 3 ◽

Human Rpe Cells

Age-related macular degeneration (AMD) is a retinal disease leading to impaired vision. Cigarette smoke increases the risk for developing AMD by causing increased reactive oxygen species (ROS) production and damage in the retinal pigment epithelium (RPE). We have previously shown that the cigarette tar component hydroquinone causes oxidative stress in human RPE cells. In the present study, we investigated the propensity of hydroquinone to induce the secretion of interleukin (IL)-1β and IL-18. The activation of these cytokines is usually regulated by the Nucleotide-binding domain, Leucine-rich repeat, and Pyrin domain 3 (NLRP3) inflammasome. ARPE-19 cells were exposed to hydroquinone, and cell viability was monitored using the lactate dehydrogenase (LDH) and 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide salt (MTT) assays. Enzyme-linked immunosorbent assays (ELISAs) were used to measure the levels of proinflammatory cytokines IL-1β and IL-18 as well as NLRP3, caspase-1, and poly (ADP-ribose) polymerase (PARP). Hydroquinone did not change IL-1β release but significantly increased the secretion of IL-18. Cytoplasmic NLRP3 levels increased after the hydroquinone treatment of IL-1α-primed RPE cells, but IL-18 was equally released from primed and nonprimed cells. Hydroquinone reduced the intracellular levels of PARP, which were restored by treatment with the ROS scavenger N-acetyl-cysteine (NAC). NAC concurrently reduced the NLRP3 levels but had no effect on IL-18 release. In contrast, the NADPH oxidase inhibitor ammonium pyrrolidinedithiocarbamate (APDC) reduced the release of IL-18 but had no effect on the NLRP3 levels. Collectively, hydroquinone caused DNA damage seen as reduced intracellular PARP levels and induced NLRP3-independent IL-18 secretion in human RPE cells.

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Improved effect of a mitochondria-targeted antioxidant on hydrogen peroxide-induced oxidative stress in human retinal pigment epithelium cells

BMC Pharmacology and Toxicology ◽

10.1186/s40360-020-00471-w ◽

2021 ◽

Vol 22 (1) ◽

Author(s):

Myung Hee Kim ◽

Do-Hun Kim ◽

Su Geun Yang ◽

Dae Yu Kim

Keyword(s):

Oxidative Stress ◽

Hydrogen Peroxide ◽

Transcription Factors ◽

Mitochondrial Dysfunction ◽

Pigment Epithelium ◽

Retinal Pigment ◽

Age Related Macular Degeneration ◽

Ros Generation ◽

Rpe Cells ◽

Age Related

Abstract Background Oxidative damage to retinal pigment epithelial (RPE) cells contributes to the development of age-related macular degeneration, which is among the leading causes of visual loss in elderly people. In the present study, we evaluated the protective role of triphenylphosphonium (TPP)-Niacin against hydrogen peroxide (H2O2)-induced oxidative stress in RPE cells. Methods The cellular viability, lactate dehydrogenase release, reactive oxygen species (ROS) generation, and mitochondrial function of retinal ARPE-19 cells were determined under treatment with H2O2 or pre-treatment with TPP-Niacin. The expression level of mitochondrial related genes and some transcription factors were assessed using real-time polymerase chain reaction (RT-qPCR). Results TPP-Niacin significantly improved cell viability, reduced ROS generation, and increased the antioxidant enzymes in H2O2-treated ARPE-19 cells. Mitochondrial dysfunction from the H2O2-induced oxidative stress was also considerably diminished by TPP-Niacin treatment, along with reduction of the mitochondrial membrane potential (MMP) and upregulation of the mitochondrial-associated gene. In addition, TPP-Niacin markedly enhanced the expression of transcription factors (PGC-1α and NRF2) and antioxidant-associated genes (especially HO-1 and NQO-1). Conclusion We verified the protective effect of TPP-Niacin against H2O2-induced oxidative stress in RPE cells. TPP-Niacin is believed to protect against mitochondrial dysfunction by upregulating antioxidant-related genes, such as PGC-1α, NRF2, HO-1, and NQO-1, in RPE cells.

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Heterochromatin protects retinal pigment epithelium cells from oxidative damage by silencing p53 target genes

Proceedings of the National Academy of Sciences ◽

10.1073/pnas.1715237115 ◽

2018 ◽

Vol 115 (17) ◽

pp. E3987-E3995 ◽

Cited By ~ 12

Author(s):

Lili Gong ◽

Fangyuan Liu ◽

Zhen Xiong ◽

Ruili Qi ◽

Zhongwen Luo ◽

...

Keyword(s):

Retinal Pigment Epithelium ◽

Oxidative Damage ◽

Target Genes ◽

Pigment Epithelium ◽

Retinal Pigment ◽

Critical Role ◽

Age Related Macular Degeneration ◽

Protective Function ◽

Heterochromatin Formation ◽

Age Related

Oxidative stress (OS)-induced retinal pigment epithelium (RPE) cell apoptosis is critically implicated in the pathogenesis of age-related macular degeneration (AMD), a leading cause of blindness in the elderly. Heterochromatin, a compact and transcriptional inert chromatin structure, has been recently shown to be dynamically regulated in response to stress stimuli. The functional mechanism of heterochromatin on OS exposure is unclear, however. Here we show that OS increases heterochromatin formation both in vivo and in vitro, which is essential for protecting RPE cells from oxidative damage. Mechanistically, OS-induced heterochromatin selectively accumulates at p53-regulated proapoptotic target promoters and inhibits their transcription. Furthermore, OS-induced desumoylation of p53 promotes p53–heterochromatin interaction and regulates p53 promoter selection, resulting in the locus-specific recruitment of heterochromatin and transcription repression. Together, our findings demonstrate a protective function of OS-induced heterochromatin formation in which p53 desumoylation-guided promoter selection and subsequent heterochromatin recruitment play a critical role. We propose that targeting heterochromatin provides a plausible therapeutic strategy for the treatment of AMD.

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Improved Effect of a Mitochondria-Targeted Antioxidant on Hydrogen Peroxide-Induced Oxidative Stress in Human Retinal Pigment Epithelium Cells

10.21203/rs.3.rs-37398/v3 ◽

2021 ◽

Author(s):

MYUNG HEE KIM ◽

Do Hun Kim ◽

Su Geun Yang ◽

Dae Yu Kim

Keyword(s):

Oxidative Stress ◽

Hydrogen Peroxide ◽

Transcription Factors ◽

Mitochondrial Dysfunction ◽

Pigment Epithelium ◽

Retinal Pigment ◽

Age Related Macular Degeneration ◽

Ros Generation ◽

Rpe Cells ◽

Age Related

Abstract Background: Oxidative damage to retinal pigment epithelial (RPE) cells contributes to the development of age-related macular degeneration, which is among the leading causes of visual loss in elderly people. In the present study, we evaluated the protective role of triphenylphosphonium (TPP)-Niacin against hydrogen peroxide (H2O2)-induced oxidative stress in RPE cells.Methods: The cellular viability, lactate dehydrogenase release, reactive oxygen species (ROS) generation, and mitochondrial function of retinal ARPE-19 cells were determined under treatment with H2O2 or pre-treatment with TPP-Niacin. The expression level of mitochondrial related genes and some transcription factors were assessed using real-time polymerase chain reaction (RT-qPCR). Results: TPP-Niacin significantly improved cell viability, reduced ROS generation, and increased the antioxidant enzymes in H2O2-treated ARPE-19 cells. Mitochondrial dysfunction from the H2O2-induced oxidative stress was also considerably diminished by TPP-Niacin treatment, along with reduction of the mitochondrial membrane potential (MMP) and upregulation of the mitochondrial-associated gene. In addition, TPP-Niacin markedly enhanced the expression of transcription factors (PGC-1α and NRF2) and antioxidant-associated genes (especially HO-1 and NQO-1).Conclusion: We verified the protective effect of TPP-Niacin against H2O2-induced oxidative stress in RPE cells. TPP-Niacin is believed to protect against mitochondrial dysfunction by upregulating antioxidant-related genes, such as PGC-1α, NRF2, HO-1, and NQO-1, in RPE cells.

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