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

Abstract

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.

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

“…The results of the present study on the one hand confirm and reinforce the observations of our previous study [ 33 ], while on the other hand provide important new information on the protective role of PUN against oxidative damage in RPE. We hypothesize that the protective mechanism underlying the effect of PUN in RPE has a dual pathway.…”

“…At this point of the study, and supported by the results of our previous study [ 33 ], we hypothesized that PUN’s effect on the mitochondrial membrane potential, both in terms of the basal conditions and in the presence of H 2 O 2 , is caused by the upstream activation of Keap1–Nrf2 antioxidant defence system. In fact, it is well known that Nrf2 can influence many aspects of mitochondrial physiology, including increasing the mitochondrial membrane potential [ 41 , 42 ].…”

“…We report here that the H 2 O 2 treatment markedly reduced the cellular viability and promoted mitochondrial dysfunction due to an increase of ROS mitochondrial levels and a reduction of mitochondrial membrane potential. However, these pathological changes were antagonized by pre–treatment for 24 with 10 μM PUN before the oxidative damage by H 2 O 2 , confirming the protective properties of the compound in RPE cells [ 33 ]. In particular, we found that PUN decreased H 2 O 2 –induced ROS generation and improved mitochondrial function, completely reversing mitochondrial membrane potential loss caused by the oxidative stimulus.…”

“…Punicalagin, a polyphenolic phytochemical responsible for more than the half of pomegranate juice’s antioxidant effects, possesses a wide range of biological activities in numerous different tissues and cell types [ 26 , 27 , 28 , 49 ]. Recently, our group demonstrated for the first time that PUN also has antioxidant properties in RPE, lowering exogenous oxidative–damage–induced ROS levels and improving cell viability via the Keap/Nrf2/ARE signaling pathway [ 33 ]. In the present study, we reinforce this hypothesis by extending the antioxidant action range of the PUN to the mitochondria of RPE cells.…”

“…Such properties are mainly ascribed to its antioxidant activity and its ability to promote cellular mitochondrial functions [ 30 , 31 , 32 ]. In this regard, we previously showed in vitro, and for the first time, that PUN is also able to protect RPE from oxidative damage via the Kelch–like ECH–associated protein–1/nuclear factor erythroid 2–related factor 2/antioxidant responsive elements (Keap/Nrf2/ARE) signaling pathway, confirming its antioxidant properties at the ocular level [ 33 ]. However, a better understanding of the mechanisms underlying PUN’s antioxidant activity in the RPE could provide the scientific basis for new therapeutic strategies and options for the prevention or delay of the pathological progression of retinal degenerative diseases.…”