The Protective Effect of Hispidin against Hydrogen Peroxide-Induced Oxidative Stress in ARPE-19 Cells via Nrf2 Signaling Pathway

A review on the cultivation, bioactive compounds, health-promoting factors and clinical trials of medicinal mushrooms Taiwanofungus camphoratus, Inonotus obliquus and Tropicoporus linteus

Medicinal mushrooms, such as Taiwanofungus camphoratus, Inonotus obliquus, and Tropicoporus linteus, have been used in traditional medicine for therapeutic purposes and promotion of overall health in China and many East Asian countries for centuries. Modern pharmacological studies have demonstrated the large amounts of bioactive constituents (such as polysaccharides, triterpenoids, and phenolic compounds) available in these medicinal mushrooms and their potential therapeutic properties. Due to the rising demand for the health-promoting medicinal mushrooms, various cultivation methods have been explored to combat over-harvesting of the fungi. Evidence of the robust pharmacological properties, including their anticancer, hypoglycemic, hypolipidemic, antioxidant, and antiviral activities, have been provided in various studies, where the health-benefiting properties of the medicinal fungi have been further proven through numerous clinical trials. In this review, the cultivation methods, available bioactive constituents, therapeutic properties, and potential uses of T. camphoratus, I. obliquus and T. linteus are explored.

Oxya chinensis sinuosa (OC) Extracts Protects ARPE-19 Cells against Oxidative Stress via Activation of the Mitogen-Activated Protein Kinases (MAPKs)/ Nuclear Factor-κB (NF-κB) Pathway

Oxya chinensis sinuosa (OC) is a well-known edible insect. Several researches on the health benefits of OC consumption have been performed to date; however, their effect on eye health remains largely unknown. This study aimed to assess the protective effects of OC extracts on the oxidative stress on the retinal pigment epithelium (RPE) cells. Oxidative damage has been identified as one of the key regulatory factors in age-related macular degeneration. H2O2-induced reactive oxygen species (ROS) production, a well-known oxidative stress factor, can cause cell death in retinal pigment epithelia cells. In this study, we found that three OC extracts effectively prevented H2O2-induced ROS production and subsequent death of ARPE-19 cells in a dose-dependent manner. In addition, the OC extracts inhibited the phosphorylation of mitogen-activated protein kinases including p38, JNK, and ERK. The OC extracts restored IκBα degradation induced by H2O2, indicating that OC extracts suppressed the activation of nuclear factor-κB. Furthermore, the three OC extracts were shown to have antioxidant effects by up-regulating the intracellular expression of key antioxidant proteins such as SOD, NQO, and HO-1. Here we demonstrated the antioxidant and anti-apoptotic effects of the OC extracts on ARPE-19, indicating their potential role in improving eye health. These results suggest that three OC extracts plays a critical role in oxidative stress-induced cell death protects in ARPE-19 cells.

Protective role of IL-17-producing γδ T cells in a laser-induced choroidal neovascularization mouse model

BACKGROUND

Vision loss in patients with wet/exudative age-related macular degeneration (AMD) is associated with choroidal neovascularization (CNV), and AMD is the leading cause of irreversible vision impairment in older adults. Interleukin-17A (IL-17A) is a component of the microenvironment associated with some autoimmune diseases. Previous studies have indicated that wet AMD patients have elevated serum IL-17A levels. However, the effect of IL-17A on AMD progression needs to be better understood. We aimed to investigate the role of IL-17A in a laser-induced CNV mouse model.

METHODS

We established a laser-induced CNV mouse model in wild-type (WT) and IL-17A-deficient mice and then evaluated the disease severity of these mice by using fluorescence angiography. We performed enzyme-linked immunosorbent assay (ELISA) and fluorescence-activated cell sorting (FACS) to analyze the levels of IL-17A and to investigate the immune cell populations in the eyes of WT and IL-17A-deficient mice. We used ARPE-19 cells to clarify the effect of IL-17A under oxidative stress.

RESULTS

In the laser-induced CNV model, the CNV lesions were larger in IL-17A-deficient mice than in WT mice. The numbers of γδ T cells, CD3+CD4+RORγt+ T cells, Treg cells, and neutrophils were decreased and the number of macrophages was increased in the eyes of IL-17A-deficient mice compared with WT mice. In WT mice, IL-17A-producing γδ T-cell numbers increased in a time-dependent manner from day 7 to 28 after laser injury. IL-6 levels increased and IL-10, IL-24, IL-17F, and GM-CSF levels decreased in the eyes of IL-17A-deficient mice after laser injury. In vitro, IL-17A inhibited apoptosis and induced the expression of the antioxidant protein HO-1 in ARPE-19 cells under oxidative stress conditions. IL-17A facilitated the repair of oxidative stress-induced barrier dysfunction in ARPE-19 cells.

CONCLUSIONS

Our findings provide new insight into the protective effect of IL-17A in a laser-induced CNV model and reveal a novel regulatory role of IL-17A-producing γδ T cells in the ocular microenvironment in wet AMD.

Salicylic acid promotes terpenoid synthesis in the fungi Sanghuangporus baumii

Sanghuangporus baumii is a medicinal fungi with anti-inflammatory, liver protection and antitumour effects. Terpenoids are one of the main medicinal ingredients of S. baumii. However, terpenoid production by wild-type S. baumii cannot meet the market demand, which affects its application in medical care. Therefore, exploring how to increase terpenoid content in S. baumii is a promising path in this research field. Salicylic acid (SA) is a secondary metabolite. In this study, a concentration of 350 μmol/L SA was added into fungal cultivations for 2 and 4 days, and then the transcriptome and metabolome of untreated mycelia and treated with SA were analysed. The expression of some genes in the terpenoids biosynthesis pathway increased in SA-induced cultivations, and the content of isopentenyl pyrophosphate (IPP) and geranylgeranyl-PP (GGPP) increased significantly as well as the contents of triterpenoids, diterpenoids, sesquiterpenoids and carotenoids. The gene FPS was considered to be a key gene regulating terpenoid biosynthesis. Therefore, FPS was overexpressed in S. baumii by Agrobacterium tumefaciens-mediated genetic transformation. The gene FPS and its downstream gene (LS) expression levels were confirmed to be increased in the FPS overexpressing transformant, and terpenoid content was 36.98% higher than that of the wild-type strain in the evaluated cultivation conditions.

Polysaccharides from Phellinus linteus: A systematic review of their extractions, purifications, structures and functions

Phellinus linteus (P. linteus) is a famous Chinese medicine and has a long history in China. In recent years, P. linteus polysaccharides (PLPs) have attracted extensive attention because of their biological activities such as anti-bacteria, anti-aging, anti-oxidation, anti-inflammation, anti-tumor, hepatoprotective effect and hypoglycemic effect. In this review, we systemically summarized the advances in extractions, purifications and structural characterizations of PLPs, and also analyzed their biological functions and molecular mechanisms. Meanwhile, the structure-activity relationships of PLPs are closely related to their anti-oxidation and anti-tumor activities. So far, the applications of PLPs are still very limited, further exploring structure-activity relationships, biological functions and their mechanisms of PLPs will promote to develop functional foods.

Hispidin Inhibits Ferroptosis Induced by High Glucose via the miR-15b-5p/GLS2 Axis in Pancreatic Beta Cells

Type 2 diabetes mellitus (T2DM) is a global health issue that lacks effective treatments. Dysfunction and/or death of pancreatic β-cells (PBCs) are considered a major cause of T2DM. Therefore, elucidating the mechanisms underlying the death of PBCs might be helpful to develop novel strategies to treat T2DM. Ferroptosis is a newly identified form of cell death that has distinct features. However, knowledge regarding the role of ferroptosis in the death of PBCs remains limited. In the current study, we used high glucose (10 mM) (HG) levels to induce ferroptosis in PBC. We also observed that hispidin, a polyphenol compound that can be isolated from Phellinus linteus, could attenuate ferroptosis induced by HG in PBCs. Mechanistic investigations showed that hispidin led to the upregulation of miR-15b-5p, which directly inhibits the expression of glutaminase (GLS2) which plays an essential role in the glutamine metabolism. In addition, we found that overexpression of GLS2 could abrogate the protective effect of hispidin against ferroptosis caused by HG in PBCs. Therefore, our study provides novel insights into the mechanisms that regulate the death of PBCs.

Hispidin in the Medicinal Fungus Protects Dopaminergic Neurons from JNK Activation-Regulated Mitochondrial-Dependent Apoptosis in an MPP+-Induced In Vitro Model of Parkinson's Disease

Degenerative diseases of the brain include Parkinson's disease (PD), which is associated with moveable signs and is still incurable. Hispidin belongs to polyphenol and originates primarily from the medicinal fungi Inonotus and Phellinus, with distinct biological effects. In the study, MES23.5 cells were induced by 1-methyl-4-phenylpyridinium (MPP⁺) to build a cell model of PD in order to detect the protective effect of hispdin and to specify the underlying mechanism. Pretreatment of MES23.5 cells with 1 h of hispdin at appropriate concentrations, followed by incubation of 24 h with 2 μmol/L MPP⁺ to induce cell damage. MPP⁺ resulted in reactive oxygen species production that diminished cell viability and dopamine content. Mitochondrial dysfunction in MS23.5 cells exposed to MPP⁺ was observed, indicated by inhibition of activity in the mitochondrial respiratory chain complex I, the collapse of potential in mitochondrial transmembrane, and the liberation of mitochondrial cytochrome c. Enabling C-Jun N-terminal kinase (JNK), reducing Bcl-2/Bax, and enhancing caspase-9/caspase-3/PARP cleavage were also seen by MPP⁺ induction associated with increased DNA fragmentation. All of the events mentioned above associated with MPP⁺-mediated mitochondrial-dependent caspases cascades were attenuated under cells pretreatment with hispidin (20 µmol/L); similar results were obtained during cell pretreatment with pan-JNK inhibitor JNK-IN-8 (1 µmol/L) or JNK3 inhibitor SR3576 (25 µmol/L). The findings show that hispidin has neuroprotection against MPP⁺-induced mitochondrial dysfunction and cellular apoptosis and suggest that hispidin can be seen as an assist in preventing PD.

Cultivation of Inonotus hispidus in Stirred Tank and Wave Bag Bioreactors to Produce the Natural Colorant Hispidin

Hispidin (6-(3,4-dihydroxystyrl)-4-hydroxy-2-pyrone) production in submerged cultured mycelia of the basidiomycete Inonotus hispidus was doubled in shake flasks through irradiation with white light. The daily addition of 1 mM hydrogen peroxide as a chemical stressor and a repeated supplementation of the shake flask cultures with 2 mM caffeic acid, a biogenetic precursor, further increased the hispidin synthesis. These cultivation conditions were combined and applied to parallel fermentation trials on the 4 L scale using a classical stirred tank bioreactor and a wave bag bioreactor. No significant differences in biomass yield and colorant production were observed. The hispidin concentration in both bioreactors reached 5.5 g·L−1, the highest ever published. Textile dyeing with hispidin was successful, but impeded by its limited light stability in comparison to industrial dyes. However, following the idea of sustainability and the flawless toxicity profile, applications in natural cosmetics, other daily implements, or even therapeutics appear promising.

Hispolon alleviates oxidative damage by stimulating the Nrf2 signaling pathway in PC12 cells

Natural products derived from the daily diet are garnering increasing attention for neurodegenerative disease (ND) treatment. Hispolon (His), a small molecule from Phellinus linteus, has been reported to have various pharmacological activities. Here, we evaluated its protective effect on a neuron-like rat pheochromocytoma cell line (PC12). Results showed that His could restore cell death induced by oxidative damage. Nuclear factor-erythroid 2 (NF-E2)-related factor 2 (Nrf2) plays a significant role in maintaining cellular redox homeostasis. After treatment with His, some Nrf2-governed antioxidant genes were upregulated in a dose-dependent manner. However, the protective effect of His on PC12 cells was easily terminated by Nrf2 knockdown, demonstrating that Nrf2 is a critical component in this cytoprotective process. Taken together, our study showed that His was not only an effective activator of Nrf2 but also a promising candidate for ND treatment.

2-Fluorofucose Attenuates Hydrogen Peroxide-Induced Oxidative Stress in HepG2 Cells via Nrf2/keap1 and NF-κB Signaling Pathways

Fucosylation is one of the most important glycan terminal modifications that affects multiple biological activities of proteins. 2-Fluorofucose (2FF), its specific inhibitor, has recently been reported to reveal numerous biological effects by blocking fucosylation both in vitro and in vivo. The current study aimed to evaluate the effect of 2FF on hydrogen peroxide (H₂O₂)-induced oxidative damage in vitro. In our study, treatment with H₂O₂ increased the level of fucosylation, and 2FF improved the cell viability in H₂O₂-treated HepG2 cells. Our study also showed that 2FF significantly decreased the overproduction of reactive oxygen species (ROS) induced by H₂O₂ and the activities of catalase, glutathione and Mn-superoxide dismutase were remarkably increased by 2FF pretreatment. Furthermore, 2FF attenuated H₂O₂-induced early mitochondria dysfunction. The second part of the study revealed that 2FF enhanced antioxidant capacity by affecting Nrf2/keap1 and NF-κB signaling pathways in HepG2 cells. Being pretreated with 2FF significantly increased the nuclear translocation of Nrf2 and simultaneously promoted the expression of downstream proteins, such as HO-1 and NQO1. Moreover, 2FF remarkably suppressed the expression of inflammation-associated proteins. Taken together, these data suggest that 2FF might have a potential therapeutic effect for oxidative stress.

Pilot Study: Nutritional and Preclinical Safety Investigation of Fermented Hispidin-Enriched Sanghuangporus sanghuang Mycelia: A Promising Functional Food Material to Improve Sleep

Sleep disturbances have been the hallmark of the recent coronavirus disease 2019 pandemic. Studies have shown that once sleep is disrupted, it can lead to psychological and physical health issues which can, in turn, disrupt circadian rhythm and induce further sleep disruption. As consumers are trying to establish healthy routines, nutritional and preclinical safety investigation of fermented hispidin-enriched Sanghuangporus sanghuang mycelia (GKSS) as a novel food material for spontaneous sleep in Sprague-Dawley rats is conducted for the first time. Results showed that the nutritional analysis of GKSS including moisture, ash, crude lipid, crude protein, carbohydrate, and energy were found to be 2.4 ± 0.3%, 8.0 ± 2.5%, 1.7 ± 0.3%, 22.9 ± 1.2%, 65.1 ± 3.1%, and 367.1 ± 10.2 kcal/100 g respectively. In the 28-day repeated-dose oral toxicity study, only Sprague-Dawley male rats receiving 5 g/kg showed a slight decrease in feed consumption at week 3, but no associated clinical signs of toxicity or significant weight loss were observed. Although a significant reduction of the platelet count was found in mid- and high-dose GKSS treated male groups, such changes were noted to be within the normal range and were not correlated with relative spleen weight changes. Hence, the no observed adverse effect level (NOAEL) of GKSS was identified to be higher than 5 g/kg in rats. After the safety of GKSS is confirmed, the sleep-promoting effect of GKSS ethanolic extract enriched with hispidin was further assessed. Despite 75 mg/kg of GKSS ethanolic extract does not affect wakefulness, rapid eye movement (REM) sleep and non-REM (NREM) sleep, GKSS ethanolic extract at 150 mg/kg significantly decreased wakefulness and enhanced NREM and REM sleep. Interestingly, such effects seem to be mediated through anti-inflammatory activities via NF-E2-related factor-2 (Nrf2) signaling pathway. Taken together, these findings provide the preliminary evidence to studies support the claims suggesting that GKSS contained useful phytochemical hispidin could be considered as and is safe to use as a functional food agent or nutraceutical for relieving sleep problems mediated by Nrf2 pathway, which the results are useful for future clinical pilot study.

Protective Effects of a Lutein Ester Prodrug, Lutein Diglutaric Acid, against H2O2-Induced Oxidative Stress in Human Retinal Pigment Epithelial Cells

Oxidative stress-induced cell damage and death of the retinal pigmented epithelium (RPE), a polarized monolayer that maintains retinal health and homeostasis, lead to the development of age-related macular degeneration (AMD). Several studies show that the naturally occurring antioxidant Lutein (Lut) can protect RPE cells from oxidative stress. However, the poor solubility and low oral bioavailability limit the potential of Lut as a therapeutic agent. In this study, lutein diglutaric acid (Lut-DG), a prodrug of Lut, was synthesized and its ability to protect human ARPE-19 cells from oxidative stress was tested compared to Lut. Both Lut and Lut-DG significantly decreased H₂O₂-induced reactive oxygen species (ROS) production and protected RPE cells from oxidative stress-induced death. Moreover, the immunoblotting analysis indicated that both drugs exerted their protective effects by modulating phosphorylated MAPKs (p38, ERK1/2 and SAPK/JNK) and downstream molecules Bax, Bcl-2 and Cytochrome c. In addition, the enzymatic antioxidants glutathione peroxidase (GPx) and catalase (CAT) and non-enzymatic antioxidant glutathione (GSH) were enhanced in cells treated with Lut and Lut-DG. In all cases, Lut-DG was more effective than its parent drug against oxidative stress-induced damage to RPE cells. These findings highlight Lut-DG as a more potent compound than Lut with the protective effects against oxidative stress in RPE cells through the modulation of key MAPKs, apoptotic and antioxidant molecular pathways.

Therapeutic Potential of Hispidin-Fungal and Plant Polyketide

There is a large number of bioactive polyketides well-known for their anticancer, antibiotic, cholesterol-lowering, and other therapeutic functions, and hispidin is among them. It is a highly abundant secondary plant and fungal metabolite, which is investigated in research devoted to cancer, metabolic syndrome, cardiovascular, neurodegenerative, and viral diseases. This review summarizes over 20 years of hispidin studies of its antioxidant, anti-inflammatory, anti-apoptotic, antiviral, and anti-cancer cell activity.

Farrerol Enhances Nrf2-Mediated Defense Mechanisms against Hydrogen Peroxide-Induced Oxidative Damage in Human Retinal Pigment Epithelial Cells by Activating Akt and MAPK

Oxidative stress of the retinal pigment epithelium (RPE) is an essential element contributing to the progression of age-related macular degeneration (AMD). Notably, the activation of Nrf2 is regarded as an effective strategy for controlling oxidation. The novel 2,3-dihydroflavonoid compound farrerol, which is extracted from Rhododendron, possesses antioxidant properties. In this study, we investigated the mechanism by which farrerol protects against oxidative damage mediated by hydrogen peroxide (H₂O₂) in adult retinal pigment epithelial cell line 19 (ARPE-19) cells. Farrerol supplementation conspicuously reversed H₂O₂-related cell damage through declining the generation of intracellular reactive oxygen species (ROS) and MDA and increasing the concentrations of GSH and SOD. According to the results of the apoptosis assay, a farrerol pretreatment decreased the protein expression of the Bax/Bcl-2, cleaved caspase-3, PARP, caspase-8, and caspase-9 proteins. Furthermore, farrerol markedly activated Nrf2, thereby increasing the levels of antioxidant enzymes downstream of Nrf2, such as HO-1, NQO1, and GCLM. Knockdown of Nrf2 with a specific siRNA successfully suppressed farrerol-mediated HO-1 transcription and partially abolished the cytoprotective effect on ARPE-19 cells. Meanwhile, farrerol induced Akt and MAPK phosphorylation in a dose-related way. However, inhibiting Akt and MAPK substantially blocked the cytoprotective functions of farrerol. Therefore, farrerol enhanced Nrf2-mediated cytoprotection of oxidative damage caused by H₂O₂, which may be inseparable from the activation of Akt and MAPK.

New insights into oxidative stress and immune mechanisms involved in age-related macular degeneration tackled by novel therapies

The prevalence of age-related macular degeneration (AMD) has increased in the last years. Although anti-VEGF agents have improved the prognosis of exudative AMD, dry AMD has still devastating effects on elderly people vision. Oxidative stress and inflammation are mechanisms involved in AMD pathogenesis and its progression. Molecular pathways involving epidermal growth factor receptor (EGFR), bone morphogenetic protein (BMP4) and the nuclear erythroid related factor 2 (Nrf2) are behind oxidative stress in AMD due to their participation in antioxidant cellular pathways. As a consequence of the disbalance produced in the antioxidant mechanisms, there is an activation of innate and adaptative immune response with cell recruitment, changes in complement factors expression, and modification of cellular milieu. Different therapies are being studied to treat dry AMD based on the possible effects on antioxidant molecular pathways or their action on the immune response. There is a wide range of treatments presented in this review, from natural antioxidant compounds to cell and gene therapy, based on their mechanisms. Finally, we hypothesize that alpha-1-antitrypsin (AAT), an anti-inflammatory and immunomodulatory molecule that can also modulate antioxidant cellular defenses, could be a good candidate for testing in AMD. This article is part of the special ssue on 'The Quest for Disease-Modifying Therapies for Neurodegenerative Disorders'.

Deciphering the antitumoral potential of the bioactive metabolites from medicinal mushroom Inonotus obliquus

ETHNOPHARMACOLOGICAL RELEVANCE

The crude extracts of the medicinal mushroom Inonotus obliquus have been used as an effective traditional medicine to treat malicious tumors, gastritis, gastric ulcers, and other inflammatory conditions in Russia and most Baltic countries.

AIM OF THIS REVIEW

Deciphering the antitumoral potential of the bioactive metabolites from I. obliquus and addressing its possibility to be used as effective agents for tumor treatment, restoration of compromised immunity and protection of gastrointestinal damage caused by chemotherapy.

MATERIALS AND METHODS

We analysed the current achievements and dilemma in tumor chemo- or immunotherapy. In this context, we searched the published literatures on I. obliquus covering from 1990 to 2020, and summarized the activities of antitumor, antioxidation, and immunomodulation by the polysaccharides, triterpenoids, small phenolic compounds, and hispidin polyphenols. By comparing the merits and shortcomings of current and traditional methodology for tumor treatment, we further addressed feasibility for the use of I. obliquus as an effective natural drug for tumor treatment and prevention.

RESULTS

The diverse bioactive metabolites confer I. obliquus great potential to inhibit tumor growth and metastasis. Its antitumor activities are achieved either through suppressing multiple oncogenic signals including but not limited to the activation of NF-κB and FAK, and the expression of RhoA/MMP-9 via ERK1/2 and PI3K/Akt signaling pathway. The antitumor activities can also be achieved by inhibiting tyrosinase activity via PAK1-dependent signaling pathway or altering lysosomal membrane permeabilization through blocking tubulin polymerization and/or disturbing energy metabolism through LKB1/AMPK pathway. In addition, the metabolites from I. obliquus also harbour the potentials to reverse MDR either through selective inhibition on P-gp/ABCB1 or MRP1/ABCC1 proteins or the induction of G2/M checkpoint arrest in tumor cells of chemoresistant phenotypes mediated by Nox/ROS/NF-kB/STAT3 signaling pathway. In addition to the eminent effects in tumor inhibition, the metabolites in I. obliquus also exhibit immunomodulatory potential to restore the compromised immunity and protect against ulcerative damage of GI tract caused by chemotherapy.

CONCLUSIONS

I. obliquus possesses the potential to reduce incidence of tumorigenesis in healthy people. For those whose complete remission has been achieved by chemotherapy, administration of the fungus will inhibit the activation of upstream oncogenic signals and thereby prevent metastasis; for those who are in the process of chemotherapy administration of the fungus will not only chemosensitize the tumor cells and thereby increasing the chemotherapeutic effects, but also help to restore the compromised immunity and protect against ulcerative GI tract damage and other side-effects induced by chemotherapy.

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

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.

Supplementary Information

The online version contains supplementary material available at 10.1186/s40360-020-00471-w.

Antioxidative Effects of Chrysoeriol via Activation of the Nrf2 Signaling Pathway and Modulation of Mitochondrial Function

Retinal pigment epithelium (RPE) cell dysfunction caused by excessive oxidative damage is partly involved in age-related macular degeneration, which is among the leading causes of visual impairment in elderly people. Here, we investigated the protective role of chrysoeriol against hydrogen peroxide (H₂O₂)-induced oxidative stress in RPE cells. The cellular viability, reactive oxygen species (ROS) generation, and mitochondrial function of retinal ARPE-19 cells were monitored under oxidative stress or pre-treatment with chrysoeriol. The expression levels of mitochondrial-related genes and associated transcription factors were assessed using reverse transcription-quantitative polymerase chain reaction (RT-qPCR). Moreover, the protein expression of antioxidant signal molecules was characterized by Western blot analysis. Chrysoeriol significantly increased cell viability, reduced ROS generation, and increased the occurrence of antioxidant molecules in H₂O₂-treated ARPE-19 cells. Additionally, mitochondrial dysfunction caused by H₂O₂-induced oxidative stress was also considerably diminished by chrysoeriol treatment, which reduced the mitochondrial membrane potential (MMP) and upregulated mitochondrial-associated genes and proteins. Chrysoeriol also markedly enhanced key transcription factors (Nrf2) and antioxidant-associated genes (particularly HO-1 and NQO-1). Therefore, our study confirms the protective effect of chrysoeriol against H₂O₂-induced oxidative stress in RPE cells, thus confirming that it may prevent mitochondrial dysfunction by upregulating antioxidant-related molecules.

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.

Kaempferol Protects Against Hydrogen Peroxide-Induced Retinal Pigment Epithelium Cell Inflammation and Apoptosis by Activation of SIRT1 and Inhibition of PARP1

Purpose: This study investigated the protective effect of Kaempferol against hydrogen peroxides (H₂O₂)-induced retinal pigment epithelium (RPE) cell oxidative stress, inflammation, and apoptosis and investigated if this protection involves modulation of poly(ADP-ribose) polymerase-1 (PARP1)/silent information regulator 1 (SIRT1) signaling pathway. Methods: ARPE-19 cells were pretreated with increasing doses of Kaempferol (10, 25, 50, 100 μM) for 24 h in Dulbecco's modified Eagle's medium/F-12 medium with or without postincubation with H₂O₂. Control cells remained untreated. Results: Kaempferol, in a dose-dependent manner, significantly increased cell survival and reduced levels of reactive oxygen species, malondialdehyde, single-stranded DNA (ssDNA), and lactate dehydrogenase but increased levels of glutathione (GSH) and manganese-superoxide dismutase (MnSOD) in H₂O₂-treated ARPE-19 cells. It also increased GSH and MnSOD in a dose-dependent manner in control + Kaempferol treated cells. At a dose of 50 μM, the most effective dose, Kaempferol also inhibited protein levels of tumor necrosis factor alpha and interleukin-6, nuclear activity and protein levels of total, acetylated, and cleaved PARP1, and increased nuclear levels and activity of SIRT1 in H₂O₂-treated cells. In parallel, it increased total nuclear levels of Nrf2 but reduced the acetylation of p53, Nrf2, nuclear factor-κB (NF-κB) p65, and forkhead transcriptional factor 1 (FOXO1). Of interest, the stimulatory role of Kaempferol in the nuclear accumulation and activation of SIRT1 and the nuclear levels of Nrf2, as well as in reducing the acetylation of Nrf2, NF-κB p65, and FOXO1, was shown in nuclei of control + Kaempferol-treated cells. Conclusion: Kaempferol protective effect against H₂O₂-induced ARPE-19 damage involves antioxidant and anti-inflammatory effects mediated, at least, by stimulating the nuclear accumulation, activation, and deacetylase ability of SIRT1 and concurrent inhibition of PARP1.