Punicalagin Protects Human Retinal Pigment Epithelium Cells from Ultraviolet Radiation-Induced Oxidative Damage by Activating Nrf2/HO-1 Signaling Pathway and Reducing Apoptosis

The oxidative damage of the retinal pigment epithelium (RPE) is the early event that underlies the pathogenesis of maculopathies. Numerous studies have shown that punicalagin (PUN), a polyphenol present in pomegranate, can protect several cell types from oxidative stress. Our study aims to establish if PUN protects RPE from UV radiation-induced oxidative damage. We used an experimental model which involves the use of a human-RPE cell line (ARPE-19) exposed to UV-A radiation for 1, 3, and 5 h. ARPE-19 cells were pre-treated with PUN (24 h) followed by UV-A irradiation; controls were treated identically, except for UV-A. Effects of pre-treatment with PUN on cell viability, intracellular reactive oxygen species ROS levels, modulation of Nrf2 and its antioxidant target genes, and finally apoptosis were examined. We found that pre-treatment with PUN: (1) antagonized the decrease in cell viability and reduced high levels of ROS associated with UV-A-induced oxidative stress; (2) activated Nrf2 signaling pathway by promoting Nrf2 nuclear translocation and upregulating its downstream antioxidant target genes (HO-1 and NQO1); (3) induced an anti-apoptotic effect by decreasing Bax/Bcl-2 ratio. These findings provide the first evidence that PUN can prevent UV-A-induced oxidative damage in RPE, offering itself as a possible antioxidant agent capable of contrasting degenerative eye diseases.

Download Full-text

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.

Download Full-text

Differential Mechanisms of Action and Efficacy of Vitamin E Components in Antioxidant Cytoprotection of Human Retinal Pigment Epithelium

Frontiers in Pharmacology ◽

10.3389/fphar.2021.798938 ◽

2022 ◽

Vol 12 ◽

Author(s):

R. Scott Duncan ◽

Daniel T. Hurtado ◽

Conner W. Hall ◽

Peter Koulen

Keyword(s):

Oxidative Stress ◽

Vitamin E ◽

Retinal Pigment Epithelium ◽

Oxidative Damage ◽

Mechanism Of Action ◽

Pigment Epithelium ◽

Retinal Pigment ◽

Similar Efficacy ◽

Rpe Cells ◽

Junction Protein

The purpose of this study was to determine if different vitamin E components exhibit similar efficacy and mechanism of action in protecting Retinal pigment epithelium (RPE) cells from oxidative damage. We hypothesized that α-tocopherol (αT) is unique among vitamin E components in its cytoprotective mechanism of action against oxidative stress in RPE cells and that it requires protein synthesis for optimal antioxidant effect. We used cell viability assays, fluorescent chemical labeling of DNA and actin and immuno-labeling of the antioxidant proteins Nrf2 and Sod2 and of the tight junction protein, ZO-1, and confocal microscopy to determine the effects of αT and γT against oxidative stress in immortalized human RPE cells (hTERT-RPE). Using the four main vitamin E components, αT, γT, δ-tocopherol (δT) and α-tocotrienol (αTr), we ascertained that they exhibit similar, but not identical, antioxidant activity as αT when used at equimolar concentrations. In addition, we determined that the exposure time of RPE cells to α-tocopherol is critical for its ability to protect against oxidative damage. Lastly, we determined that αT, but not γT, partially requires the synthesis of new proteins within a 24-h period and prior to exposure to tBHP for optimal cytoprotection. We conclude that, unlike γT and δT, αT appears to be unique in its requirement for transport and/or signaling for it to be an effective antioxidant. As a result, more focus should be paid to which vitamin E components are used for antioxidant interventions.

Download Full-text

Cytoprotective Effects of Punicalagin on Hydrogen–Peroxide–Mediated Oxidative Stress and Mitochondrial Dysfunction in Retinal Pigment Epithelium Cells

Antioxidants ◽

10.3390/antiox10020192 ◽

2021 ◽

Vol 10 (2) ◽

pp. 192

Author(s):

Maria Elisabetta Clementi ◽

Giuseppe Maulucci ◽

Giada Bianchetti ◽

Michela Pizzoferrato ◽

Beatrice Sampaolese ◽

...

Keyword(s):

Oxidative Stress ◽

Hydrogen Peroxide ◽

Membrane Potential ◽

Retinal Pigment Epithelium ◽

Cell Viability ◽

Mitochondrial Dysfunction ◽

Mitochondrial Membrane ◽

Caspase 3 ◽

Pigment Epithelium ◽

Retinal Pigment

The retinal pigment epithelium (RPE) is a densely pigmented, monostratified epithelium that provides metabolic and functional support to the outer segments of photoreceptors. Endogenous or exogenous oxidative stimuli determine a switch from physiological to pathological conditions, characterized by an increase of intracellular levels of reactive oxygen species (ROS). Accumulating evidence has elucidated that punicalagin (PUN), the major ellagitannin in pomegranate, is a potent antioxidant in several cell types. The present study aimed to investigate the protective effect of PUN on mitochondrial dysfunction associated with hydrogen peroxide (H2O2)–induced oxidative stress. For this purpose, we used a human RPE cell line (ARPE–19) exposed to H2O2 for 24 h. The effects of PUN pre–treatment (24 h) were examined on cell viability, mitochondrial ROS levels, mitochondrial membrane potential, and respiratory chain complexes, then finally on caspase–3 enzymatic activity. The results showed that supplementation with PUN: (a) significantly increased cell viability; (b) kept the mitochondrial membrane potential (ΔΨm) at healthy levels and limited ROS production; (c) preserved the activity of respiratory complexes; (d) reduced caspase–3 activity. In conclusion, due to its activity in helping mitochondrial functions, reducing oxidative stress, and subsequent induction of cellular apoptosis, PUN might be considered a useful nutraceutical agent in the treatment of oxidation–associated disorders of RPE.

Download Full-text