Nrf2 activators modulate oxidative stress responses and bioenergetic profiles of human retinal epithelial cells cultured in normal or high glucose conditions

Probucol attenuates high glucose-induced Müller cell damage through enhancing the Nrf2/p62 signaling pathway

PURPOSE

This study investigated the protective effect of probucol on Müller cells exposed to high glucose conditions and examined potential mechanisms of action.

METHODS

Primary human retinal Müller cells were incubated with high glucose (HG, 35 mM) in the present or absence of different concentrations of probucol for 24 h. Cell viability was determined using the CCK-8 method. Mitochondrial membrane potential (MMP) was measured using JC-1 staining and cell cycle by flow cytometry. The expression of nuclear factor E2-related factor 2 (Nrf2), glutamate-cysteine ligase catalytic subunit, and p62 was quantified using quantitative polymerase chain reaction and western blot.

RESULTS

We found that HG inhibited cell proliferation, arrested cell cycle, and increased MMP in human Müller cells. Probucol activated the Nrf2/p62 pathway and upregulated the anti-apoptotic protein, Bcl2, and attenuated HG-mediated damage in Müller cells.

CONCLUSIONS

Our results suggest that probucol may protect Müller cells from HG-induced damage through enhancing the Nrf2/p62 signaling pathway.

New insights in the targets of action of dimethyl fumarate in endothelial cells: effects on energetic metabolism and serine synthesis in vitro and in vivo

Dimethyl fumarate is an ester from the Krebs cycle intermediate fumarate. This drug is approved and currently used for the treatment of psoriasis and multiple sclerosis, and its anti-angiogenic activity was reported some years ago. Due to the current clinical relevance of this compound and the recently manifested importance of endothelial cell metabolism on the angiogenic switch, we wanted to elucidate whether dimethyl fumarate has an effect on energetic metabolism of endothelial cells. Different experimental approximations were performed in endothelial cells, including proteomics, isotope tracing and metabolomics experimental approaches, in this work we studied the possible role of dimethyl fumarate in endothelial cell energetic metabolism. We demonstrate for the first time that dimethyl fumarate promotes glycolysis and diminishes cell respiration in endothelial cells, which could be a consequence of a down-regulation of serine and glycine synthesis through inhibition of PHGDH activity in these cells. Dimethyl fumarate alters the energetic metabolism of endothelial cells in vitro and in vivo through an unknown mechanism, which could be the cause or the consequence of its pharmacological activity. This new discovery on the targets of this compound could open a new field of study regarding the mechanism of action of dimethyl fumarate.

lncRNA HOTAIR promotes ROS generation and NLRP3 inflammasome activation by inhibiting Nrf2 in diabetic retinopathy

BACKGROUND

Diabetic retinopathy (DR) is a microvascular complication associated with damage to the retina due to inflammation induced by high glucose. Activation of the NLRP3 inflammasome plays a critical role in DR and its prevention is beneficial to patients. However, the regulation of long non-coding RNA (lncRNA) in NLRP3 inflammasome activation of DR is incompletely understood. So, this study aimed to uncover the functional and regulatory mechanism of the lncRNA HOTAIR in NLRP3 inflammasome activation in Dr.

METHODS

The vitreous humor was collected from the patients and detected the inflammatory and oxidative stress makers. Human retinal endothelial cells (HRECs) were cultured and stimulated in low D-glucose (5 mmol/L) or high D-glucose (20 mmol/L). Additionally, HRECs were knocked down HOTAIR with a si-RNA. Then, the NLRP3 inflammasome activation was analyzed by western blotting and pyroptosis cell imaging. The ROS was measured by specific probe. The activation of Nrf2 measured by Immunofluorescent staining. The interaction between HOTAIR and Nrf2 was evaluated by co-immunoprecipitation and RNA immunoprecipitation.

RESULTS

The expression of HOTAIR was significantly increased in the vitreous of patients with DR and in HRECs stimulated with high glucose. Furthermore, HOTAIR knockdown relieved NLRP3 inflammasome activation. More specifically, HOTAIR knockdown suppressed the expression of NLRP3, pro-caspase-1, and pro-IL-1β, as well as IL-1β maturation and pyroptosis. HOTAIR knockdown also interfered with the ROS generation induced by high glucose. Moreover, HOTAIR promoted the interaction between Nrf2 and Keap1 by binding and inactivating Nrf2.

CONCLUSION

The lncRNA HOTAIR promotes NLRP3 inflammasome activation and ROS generation by inhibiting Nrf2 in Dr.

Prolonged Exposure to High Glucose Induces Premature Senescence Through Oxidative Stress and Autophagy in Retinal Pigment Epithelial Cells

Chronic hyperglycemia involves persistent high-glucose exposure and correlates with retinal degeneration. It causes various diseases, including diabetic retinopathy (DR), a major cause of adult vision loss. Most in vitro studies have investigated the damaging short-term effects of high glucose exposure on retinal pigment epithelial (RPE) cells. DR is also a severe complication of diabetes. In this study, we established a model with prolonged high-glucose exposure (15 and 75 mM exogenous glucose for two months) to mimic RPE tissue pathophysiology in patients with hyperglycemia. Prolonged high-glucose exposure attenuated glucose uptake and clonogenicity in ARPE-19 cells. It also significantly increased reactive oxygen species levels and decreased antioxidant protein (superoxide dismutase 2) levels in RPE cells, possibly causing oxidative stress and DNA damage and impairing proliferation. Western blotting showed that autophagic stress, endoplasmic reticulum stress, and genotoxic stress were induced by prolonged high-glucose exposure in RPE cells. Despite a moderate apoptotic cell population detected using the Annexin V-staining assay, the increases in the senescence-associated proteins p53 and p21 and SA-β-gal-positive cells suggest that prolonged high-glucose exposure dominantly sensitized RPE cells to premature senescence. Comprehensive next-generation sequencing suggested that upregulation of oxidative stress and DNA damage-associated pathways contributed to stress-induced premature senescence of ARPE-19 cells. Our findings elucidate the pathophysiology of hyperglycemia-associated retinal diseases and should benefit the future development of preventive drugs. Prolonged high-glucose exposure downregulates glucose uptake and oxidative stress by increasing reactive oxygen species (ROS) production through regulation of superoxide dismutase 2 (SOD2) expression. Autophagic stress, ER stress, and DNA damage stress (genotoxic stress) are also induced by prolonged high-glucose exposure in RPE cells. Consequently, multiple stresses induce the upregulation of the senescence-associated proteins p53 and p21. Although both apoptosis and premature senescence contribute to high glucose exposure-induced anti-proliferation of RPE cells, the present work shows that premature senescence rather than apoptosis is the dominant cause of RPE degeneration, eventually leading to the pathogenesis of DR.

Carnosol inhibits KGN cells oxidative stress and apoptosis and attenuates polycystic ovary syndrome phenotypes in mice through Keap1-mediated Nrf2/HO-1 activation

Excessive oxidative stress and apoptosis of ovarian granulosa cells lead to abnormal follicular development and ovulation disorders in polycystic ovary syndrome (PCOS). Carnosol is a plant-derived polyphenol that has been proven to exhibit several cell protective effects. In this study, we established hyperandrogenic PCOS models both in vitro and in vivo. In the human ovarian granulosa cell line, KGN cells, decreased viability and mitochondrial membrane potential, and upregulated reactive oxygen species (ROS) level and apoptosis induced by DHT were partly reversed by carnosol. Western blotting results showed that carnosol treatment inhibited the DHT-activated mitochondrial apoptotic pathway by activating nuclear factor-erythroid 2-related factor (Nrf2)/heme oxygenase 1 (HO-1). Knockdown of Nrf2 by transfecting with siRNA or inhibiting HO-1 by zinc protoporphyrin (ZnPP) blocked the protective effects of carnosol. Computational modeling and pull-down assay results confirmed the direct binding of carnosol to kelch-like ECH-associated protein 1 (Keap1). In vivo results showed that the intraperitoneal administration of carnosol (50 and 100 mg/kg) improved estrous cycle disorders, polycystic ovary, and decreased elevated androgen in the PCOS mice. In summary, Carnosol has an effective role in inhibiting oxidative stress and apoptosis in DHT-treated KGN cells and protecting against mouse PCOS phenotypes through the Keap1-mediated activation of Nrf2/HO-1 signaling.

Dimethyl fumarate ameliorates fungal keratitis by limiting fungal growth and inhibiting pyroptosis

PURPOSE

We aimed to investigate the therapeutic role of dimethyl fumarate (DMF) in fungal keratitis.

METHODS

Human corneal epithelial cells (HCECs) and mouse models of fungal keratitis were used in this study. The antifungal effect of DMF on Aspergillus fumigatus (A. fumigatus) was confirmed by examining the minimum inhibitory concentration (MIC), biofilm formation, conidial adherence and corneal fungal loads. Slit-lamp photography, haematoxylin and eosin staining and immunostaining were used to assess the severity of corneal impairment. RT-PCR, western blot, ELISA, immunohistochemistry and immunostaining were performed to examine the effects of DMF on the expression of the inflammatory mediators during fungal infection.

RESULTS

In vitro, DMF limited A. fumigatus growth, biofilm formation, and conidial adherence and reduced the mRNA levels of AldA, GlkA, GAPDH, HxkA, PgkA, Sdh2, GelA and ChsF in A. fumigatus. In vivo, DMF effectively decreased corneal fungal loads. DMF attenuated corneal inflammatory impairment by suppressing inflammatory cell accumulation and downregulating cytokine expression. DMF notably downregulated the high expression of NLRP3, cleaved GSDMD, cleaved caspase-1, mature IL-1β and mature IL-18 induced by fungi. The production of Nrf2 and HO-1 could be further increased by DMF in infected HCECs. Nrf2 siRNA pretreatment counteracted DMF-mediated downregulation of the expression of the active forms of IL-18, IL-1β, caspase-1 and GSDMD.

CONCLUSION

DMF limits fungal growth by suppressing biofilm formation, conidial adherence and respiratory metabolism. It also exerts an anti-inflammatory effect on fungal keratitis by inhibiting pyroptosis, which could be regulated by Nrf2. Our results suggest that DMF plays a therapeutic role in fungal keratitis.

Dimethyl Fumarate Protects Retinal Pigment Epithelium from Blue Light-Induced Oxidative Damage via the Nrf2 Pathway

The purpose of this study is to investigate the protective effect of dimethyl fumarate (DMF), the methyl-ester of fumaric acid, against blue-light (BL) exposure in retinal pigment epithelial (RPE) cells. ARPE-19 cells, a human RPE cell line, were cultured with DMF followed by exposure to BL. Reactive oxygen species (ROS) generation, cell viability, and cell death rate were determined. Real-time polymerase chain reaction and Western blotting were performed to determine the change in nuclear factor (erythroid-derived)-like 2 (NRF2) expression. Twenty-seven inflammatory cytokines in the supernatant of culture medium were measured. BL exposure induced ROS generation in ARPE-19 cells, which DMF alleviated in a concentration-dependent manner. BL exposure increased the ARPE-19 cell death rate, which DMF alleviated. BL exposure induced ARPE-19 cell apoptosis, again alleviated by DMF. Under BL exposure, DMF increased the NRF2 mRNA level and promoted NRF2 expression in the nucleus. BL also strongly increased interleukin (IL)-1β and fibroblast growth factor (FGF) expression. BL strongly induced RPE cell damage with apoptotic change while DMF mainly reduced inflammation in BL-induced RPE damage, resulting in blockade of cell death. DMF has a protective effect in RPE cells against BL exposure via activation of the NRF2 pathway.

Carnosol attenuates high glucose damage in human retinal endothelial cells through regulation of ERK/Nrf2/HO-1 pathway

Carnosol is a natural compound with antioxidant properties. Based on this evidence, in the present study we investigated whether this compound can protect retinal vascular endothelium from hyperglycemic insult responsible for diabetic retinopathy development. We performed in vitro study on human retinal endothelial cells (HREC) cultured both in normal and high glucose conditions to assess the effects of carnosol on cell viability, Nrf2 expression, HO-1 activity, and ERK1/2 expression. HREC exposed to high glucose insult were treated with carnosol. Data indicated that carnosol treatment is able to induce HO-1 expression via Nrf2 activation and counteracts the damage elicited by high glucose. Further, carnosol activation of Nrf2/HO-1 signaling axis involves ERK1/2 pathway. These data confirm the therapeutic value of carnosol by suggesting its use to treat diabetic retinopathy.

Bioengineering approaches for modelling retinal pathologies of the outer blood-retinal barrier

Alterations of the junctional complex of the outer blood-retinal barrier (oBRB), which is integrated by the close interaction of the retinal pigment epithelium, the Bruch's membrane, and the choriocapillaris, contribute to the loss of neuronal signalling and subsequent vision impairment in several retinal inflammatory disorders such as age-related macular degeneration and diabetic retinopathy. Reductionist approaches into the mechanisms that underlie such diseases have been hindered by the absence of adequate in vitro models using human cells to provide the 3D dynamic architecture that enables expression of the in vivo phenotype of the oBRB. Conventional in vitro cell models are based on 2D monolayer cellular cultures, unable to properly recapitulate the complexity of living systems. The main drawbacks of conventional oBRB models also emerge from the cell sourcing, the lack of an appropriate Bruch's membrane analogue, and the lack of choroidal microvasculature with flow. In the last years, the advent of organ-on-a-chip, bioengineering, and stem cell technologies is providing more advanced 3D models with flow, multicellularity, and external control over microenvironmental properties. By incorporating additional biological complexity, organ-on-a-chip devices can mirror physiologically relevant properties of the native tissue while offering additional set ups to model and study disease. In this review we first examine the current understanding of oBRB biology as a functional unit, highlighting the coordinated contribution of the different components to barrier function in health and disease. Then we describe recent advances in the use of pluripotent stem cells-derived retinal cells, Bruch's membrane analogues, and co-culture techniques to recapitulate the oBRB. We finally discuss current advances and challenges of oBRB-on-a-chip technologies for disease modelling.

Nrf2 Activation in Chronic Kidney Disease: Promises and Pitfalls

The nuclear factor erythroid 2-related factor 2 (Nrf2) protects the cell against oxidative damage. The Nrf2 system comprises a complex network that functions to ensure adequate responses to redox perturbations, but also metabolic demands and cellular stresses. It must be kept within a physiologic activity range. Oxidative stress and alterations in Nrf2-system activity are central for chronic-kidney-disease (CKD) progression and CKD-related morbidity. Activation of the Nrf2 system in CKD is in multiple ways related to inflammation, kidney fibrosis, and mitochondrial and metabolic effects. In human CKD, both endogenous Nrf2 activation and repression exist. The state of the Nrf2 system varies with the cause of kidney disease, comorbidities, stage of CKD, and severity of uremic toxin accumulation and inflammation. An earlier CKD stage, rapid progression of kidney disease, and inflammatory processes are associated with more robust Nrf2-system activation. Advanced CKD is associated with stronger Nrf2-system repression. Nrf2 activation is related to oxidative stress and moderate uremic toxin and nuclear factor kappa B (NF-κB) elevations. Nrf2 repression relates to high uremic toxin and NF-κB concentrations, and may be related to Kelch-like ECH-associated protein 1 (Keap1)-independent Nrf2 degradation. Furthermore, we review the effects of pharmacological Nrf2 activation by bardoxolone methyl, curcumin, and resveratrol in human CKD and outline strategies for how to adapt future Nrf2-targeted therapies to the requirements of patients with CKD.

Evaluation of the Effects of Fucoidans from Fucus Species and Laminaria hyperborea against Oxidative Stress and Iron-Dependent Cell Death

Fucoidans are algal polysaccharides that exhibit protective properties against oxidative stress. The aim of this study was to investigate different fucoidans from brown seaweeds for their ability to protect against iron-dependent oxidative stress (ferroptosis), a main hallmark of retinal and brain diseases, including hemorrhage. We investigated five new high-molecular weight fucoidan extracts from Fucus vesiculosus, F. serratus, and F. distichus subsp. evanescens, a previously published Laminaria hyperborean extract, and commercially available extracts from F. vesiculosus and Undaria pinnatifida. We induced oxidative stress by glutathione depletion (erastin) and H2O2 in four retinal and neuronal cell lines as well as primary cortical neurons. Only extracts from F. serratus, F. distichus subsp. evanescens, and Laminaria hyperborea were partially protective against erastin-induced cell death in ARPE-19 and OMM-1 cells, while none of the extracts showed beneficial effects in neuronal cells. Protective fucoidans also attenuated the decrease in protein levels of the antioxidant enzyme GPX4, a key regulator of ferroptosis. This comprehensive analysis demonstrates that the antioxidant abilities of fucoidans may be cell type-specific, besides depending on the algal species and extraction method. Future studies are needed to further characterize the health-benefiting effects of fucoidans and to determine the exact mechanism underlying their antioxidative abilities.

Adipose tissue senescence is mediated by increased ATP content after a short-term high-fat diet exposure

In the context of obesity, senescent cells accumulate in white adipose tissue (WAT). The cellular underpinnings of WAT senescence leading to insulin resistance are not fully elucidated. The objective of the current study was to evaluate the presence of WAT senescence early after initiation of high‐fat diet (HFD, 1–10 weeks) in 5‐month‐old male C57BL/6J mice and the potential role of energy metabolism. We first showed that WAT senescence occurred 2 weeks after HFD as evidenced in whole WAT by increased senescence‐associated ß‐galactosidase activity and cyclin‐dependent kinase inhibitor 1A and 2A expression. WAT senescence affected various WAT cell populations, including preadipocytes, adipose tissue progenitors, and immune cells, together with adipocytes. WAT senescence was associated with higher glycolytic and mitochondrial activity leading to enhanced ATP content in HFD‐derived preadipocytes, as compared with chow diet‐derived preadipocytes. One‐month daily exercise, introduced 5 weeks after HFD, was an effective senostatic strategy, since it reversed WAT cellular senescence, while reducing glycolysis and production of ATP. Interestingly, the beneficial effect of exercise was independent of body weight and fat mass loss. We demonstrated that WAT cellular senescence is one of the earliest events occurring after HFD initiation and is intimately linked to the metabolic state of the cells. Our data uncover a critical role for HFD‐induced elevated ATP as a local danger signal inducing WAT senescence. Exercise exerts beneficial effects on adipose tissue bioenergetics in obesity, reversing cellular senescence, and metabolic abnormalities.

Glucose-impaired Corneal Re-epithelialization Is Promoted by a Novel Derivate of Dimethyl Fumarate

Glucose induces corneal epithelial dysfunctions characterized by delayed wound repair. Nuclear erythroid 2-related factor 2 (Nrf2) mediates cell protection mechanisms even through the Heme oxygenase-1 (HO-1) up-regulation. Here, we synthesized new HO-1 inducers by modifying dimethyl fumarate (DMF) and used docking studies to select VP13/126 as a promising compound with the best binding energy to Kelch-like ECH-associated protein 1 (keap1), which is the the regulator of Nrf2 nuclear translocation. We verified if VP13/126 protects SIRC cells from hyperglycemia compared to DMF. SIRC were cultured in normal (5 mM) or high glucose (25 mM, HG) in presence of DMF (1–25 μM) or VP13/126 (0.1–5 μM) with or without ERK1/2 inhibitor PD98059 (15 μM). VP13/126 was more effective than DMF in the prevention of HG-induced reduction of cell viability and proliferation. Reduction of wound closure induced by HG was similarly counteracted by 1 μM VP13/126 and 10 μM DMF. VP13/126 strongly increased phospho/total ERK1/2 and restored HO-1 protein in HG-treated SIRC; these effects are completely counteracted by PD98059. Moreover, high-content screening analysis showed a higher rate of Nrf2 nuclear translocation induced by VP13/126 than DMF in HG-stimulated SIRC. These data indicate that VP13/126 exerts remarkable pro-survival properties in HG-stimulated SIRC, promoting the Nrf2/HO-1 axis.

Attenuation of High Glucose-Induced Damage in RPE Cells through p38 MAPK Signaling Pathway Inhibition

This study aimed to investigate the high glucose damage on human retinal pigment epithelial (RPE) cells, the role of p38 MAPK signaling pathway and how dimethyl fumarate can regulate that. We carried out in vitro studies on ARPE-19 cells exposed to physiological and high glucose (HG) conditions, to evaluate the effects of DMF on cell viability, apoptosis, and expression of inflammatory and angiogenic biomarkers such as COX-2, iNOS, IL-1β, and VEGF. Our data have demonstrated that DMF treatment attenuated HG-induced apoptosis, as confirmed by reduction of BAX/Bcl-2 ratio. Furthermore, in RPE cells exposed to HG we observed a significant increase of iNOS, COX-2, and IL-1β expression, that was reverted by DMF treatment. Moreover, DMF reduced the VEGF levels elicited by HG, inhibiting p38 MAPK signaling pathway. The present study demonstrated that DMF provides a remarkable protection against high glucose-induced damage in RPE cells through p38 MAPK inhibition and the subsequent down-regulation of VEGF levels, suggesting that DMF is a small molecule that represents a good candidate for diabetic retinopathy treatment and warrants further in vivo and clinical evaluation.

Regulatory Role of Nrf2 Signaling Pathway in Wound Healing Process

Wound healing involves a series of cellular events in damaged cells and tissues initiated with hemostasis and finally culminating with the formation of a fibrin clot. However, delay in the normal wound healing process during pathological conditions due to reactive oxygen species, inflammation and immune suppression at the wound site represents a medical challenge. So far, many therapeutic strategies have been developed to improve cellular homeostasis and chronic wounds in order to accelerate wound repair. In this context, the role of Nuclear factor erythroid 2-related factor 2 (Nrf2) during the wound healing process has been a stimulating research topic for therapeutic perspectives. Nrf2 is the main regulator of intracellular redox homeostasis. It increases cytoprotective gene expression and the antioxidant capacity of mammalian cells. It has been reported that some bioactive compounds attenuate cellular stress and thus accelerate cell proliferation, neovascularization and repair of damaged tissues by promoting Nrf2 activation. This review highlights the importance of the Nrf2 signaling pathway in wound healing strategies and the role of bioactive compounds that support wound repair through the modulation of this crucial transcription factor.

Bardoxolone Methyl Displays Detrimental Effects on Endothelial Bioenergetics, Suppresses Endothelial ET-1 Release, and Increases Endothelial Permeability in Human Microvascular Endothelium

Nrf2 is a master regulator of antioxidant cellular defence, and agents activating the Nrf2 pathway have been tested in various diseases. However, unexpected side effects of cardiovascular nature reported for bardoxolone methyl in patients with type 2 diabetes mellitus and stage 4 chronic kidney disease (the BEACON trial) still have not been fully explained. Here, we aimed to characterize the effects of bardoxolone methyl compared with other Nrf2 activators—dimethyl fumarate and L-sulforaphane—on human microvascular endothelium. Endothelial toxicity, bioenergetics, mitochondrial membrane potential, endothelin-1 (ET-1) release, endothelial permeability, Nrf2 expression, and ROS production were assessed in human microvascular endothelial cells (HMEC-1) incubated for 3 and 24 hours with 100 nM–5 μM of either bardoxolone methyl, dimethyl fumarate, or L-sulforaphane. Three-hour incubation with bardoxolone methyl (100 nM–5 μM), although not toxic to endothelial cells, significantly affected endothelial bioenergetics by decreasing mitochondrial membrane potential (concentrations ≥ 3 μM), decreasing spare respiratory capacity (concentrations ≥ 1 μM), and increasing proton leak (concentrations ≥ 500 nM), while dimethyl fumarate and L-sulforaphane did not exert such actions. Bardoxolone methyl at concentrations ≥ 3 μM also decreased cellular viability and induced necrosis and apoptosis in the endothelium upon 24-hour incubation. In turn, endothelin-1 decreased permeability in endothelial cells in picomolar range, while bardoxolone methyl decreased ET-1 release and increased endothelial permeability even after short-term (3 hours) incubation. In conclusion, despite that all three Nrf2 activators exerted some beneficial effects on the endothelium, as evidenced by a decrease in ROS production, bardoxolone methyl, the most potent Nrf2 activator among the tested compounds, displayed a distinct endothelial profile of activity comprising detrimental effects on mitochondria and cellular viability and suppression of endothelial ET-1 release possibly interfering with ET-1–dependent local regulation of endothelial permeability.

The protective effects of resveratrol on ulcerative colitis via changing the profile of Nrf2 and IL-1β protein

Ulcerative colitis (UC) is an inflammatory bowel disease (IBD) with increasing incidence and prevalence in developed countries. The presence of inflammatory cytokines is considered the main detrimental factor in severe types of IBD. The Nrf2 transcription factor plays an important role in reducing the expression of inflammatory agents such as interleukin (IL)-1β and increasing reparative factors such as IL-11. Resveratrol, a plant-derived phenolic compound, reduces the damage in chronic experimentally induced colitis. Twenty patients with UC and also 20 healthy controls were recruited in this study. The proteins expression of Nrf2 and IL-1β was assessed in colonic biopsies by Western blotting. Caco-2 cells were challenged with TNF-α (in vitro simulation of UC), in the presence or not of 190 nM (24 h) and 75 nM (48 h) Resveratrol. Then, Nrf2 and IL-1β in gene and protein expression were measured by real time-PCR and Western blotting in different treatments. Finally, IL-11 proteins expression was measured in culture supernatant by ELISA. A significant increase of IL-1β protein was detected in inflamed colonic tissues from UC patients compared with the control individuals. In Caco-2 cells challenged with TNF-α, protein expression of IL-1β and p-Nrf2 showed an increase, while gene expression of Nrf2 did not show a significant difference. After treatment with Resveratrol, both IL-1β mRNA and protein levels were reduced, while IL-11 protein levels showed any increase. The p-Nrf2 is a dominant form which is prevalent in inflamed tissues from UC patients. Resveratrol can reverse the inflammatory effects of TNF-α by reducing IL-1β and increasing IL-11 production.

Eye-Light on Age-Related Macular Degeneration: Targeting Nrf2-Pathway as a Novel Therapeutic Strategy for Retinal Pigment Epithelium

Age-related macular degeneration (AMD) is a common disease with a multifactorial aetiology, still lacking effective and curative therapies. Among the early events triggering AMD is the deterioration of the retinal pigment epithelium (RPE), whose fundamental functions assure good health of the retina. RPE is physiologically exposed to high levels of oxidative stress during its lifespan; thus, the integrity and well-functioning of its antioxidant systems are crucial to maintain RPE homeostasis. Among these defensive systems, the Nrf2-pathway plays a primary role. Literature evidence suggests that, in aged and especially in AMD RPE, there is an imbalance between the increased pro-oxidant stress, and the impaired endogenous detoxifying systems, finally reverberating on RPE functions and survival. In this in vitro study on wild type (WT) and Nrf2-silenced (siNrf2) ARPE-19 cells exposed to various AMD-related noxae (H2O2, 4-HNE, MG132 + Bafilomycin), we show that the Nrf2-pathway activation is a physiological protective stress response, leading downstream to an up-regulation of the Nrf2-targets HO1 and p62, and that a Nrf2 impairment predisposes the cells to a higher vulnerability to stress. In search of new pharmacologically active compounds potentially useful for AMD, four nature-inspired hybrids (NIH) were individually characterized as Nrf2 activators, and their pharmacological activity was investigated in ARPE-19 cells. The Nrf2 activator dimethyl-fumarate (DMF; 10 μM) was used as a positive control. Three out of the four tested NIH (5 μM) display both direct and indirect antioxidant properties, in addition to cytoprotective effects in ARPE-19 cells under pro-oxidant stimuli. The observed pro-survival effects require the presence of Nrf2, with the exception of the lead compound NIH1, able to exert a still significant, albeit lower, protection even in siNrf2 cells, supporting the concept of the existence of both Nrf2-dependent and independent pathways mediating pro-survival effects. In conclusion, by using some pharmacological tools as well as a reference compound, we dissected the role of the Nrf2-pathway in ARPE-19 stress response, suggesting that the Nrf2 induction represents an efficient defensive strategy to prevent the stress-induced damage.

Bicalutamide Elicits Renal Damage by Causing Mitochondrial Dysfunction via ROS Damage and Upregulation of HIF-1

Combined androgen blockade using bicalutamide (Bic) is a therapeutic choice for treating prostate cancer (PCa). However, even at regular clinical dosages, Bic frequently shows adverse effects associated with cardiovascular and renal damage. Previously, we found that Bic selectively damaged mesangial cells compared to tubular cells and in an in vivo rat model, we also found renal damage caused by Bic. In the present study, a rat mesangial cell model was used to further the investigation. Results indicated that Bic enhanced lactate dehydrogenase release, reactive oxygen species (ROS) production, lysosome population and kidney injury molecule-1 and decreased N-cadherin. Bic elicited mitochondrial swelling and reduced the mitochondrial potential, resulting in severe suppression of the oxygen consumption rate (OCR), maximum respiration and ATP production. The hypoxia-inducible factor (HIF)-1α transcriptional activity and messenger RNA were significantly upregulated in dose-dependent manners. The HIF-1α protein reached a peak value at 24 h then rapidly decayed. BCL2/adenovirus E1B 19-kDa protein-interacting protein 3 and cleaved caspase-3 were dose-dependently upregulated by Bic (60 μM) and that eventually led to cell apoptosis. It is suggested that Bic induces renal damage via ROS and modulates HIF-1α pathway and clinically, some protective agents like antioxidants are recommended for co-treatment.

Nrf2 deficiency aggravates PM2.5-induced cardiomyopathy by enhancing oxidative stress, fibrosis and inflammation via RIPK3-regulated mitochondrial disorder

PM_2.5 is a well-known air pollutant threatening public health, and long-term exposure to PM_2.5 increases the risk of cardiovascular diseases. Nrf2 plays a pivotal role in the amelioration of PM_2.5-induced lung injury. However, if Nrf2 is involved in PM_2.5-induced heart injury, and the underlying molecular mechanisms have not been explored. In this study, wild type (Nrf2^+/+) and Nrf2 knockout (Nrf2^-/-) mice were exposed to PM_2.5 for 6 months. After PM_2.5 exposure, Nrf2^-/- mice developed severe physiological changes, lung injury and cardiac dysfunction. In the PM_2.5-exposed hearts, Nrf2 deficiency caused significant collagen accumulation through promoting the expression of fibrosis-associated signals. Additionally, Nrf2^-/- mice exhibited greater oxidative stress in cardiac tissues after PM_2.5 exposure. Furthermore, PM_2.5-induced inflammation in heart samples were accelerated in Nrf2^-/- mice through promoting inhibitor of α/nuclear factor κB (IκBα/NF-κB) signaling pathways. We also found that Nrf2^-/- aggravated autophagy initiation and glucose metabolism disorder in hearts of mice with PM_2.5 challenge. Cardiac receptor-interacting protein kinase 3 (RIPK3) expression triggered by PM_2.5 was further enhanced in mice with the loss of Nrf2. Collectively, these results suggested that strategies for enhancing Nrf2 could be used to treat PM_2.5-induced cardiovascular diseases.

A novel compound AB38b attenuates oxidative stress and ECM protein accumulation in kidneys of diabetic mice through modulation of Keap1/Nrf2 signaling

Extracellular matrix (ECM) deposition following reactive oxygen species (ROS) overproduction has a key role in diabetic nephropathy (DN), thus, antioxidant therapy is considered as a promising strategy for treating DN. Here, we investigated the therapeutic effects of AB38b, a novel synthetic α, β-unsaturated ketone compound, on the oxidative stress (OS) and ECM accumulation in type 2 diabetes mice, and tried to clarify the mechanisms underlying the effects in high glucose (HG, 30 mM)-treated mouse glomerular mesangial cells (GMCs). Type 2 diabetes model was established in mice with high-fat diet feeding combined with streptozocin intraperitoneal administration. The diabetic mice were then treated with AB38b (10, 20, 40 mg· kg^-1· d^-1, ig) or a positive control drug resveratrol (40 mg· kg^-1· d^-1, ig) for 8 weeks. We showed that administration of AB38b or resveratrol prevented the increases in malondialdehyde level, lactate dehydrogenase release, and laminin and type IV collagen deposition in the diabetic kidney. Simultaneously, AB38b or resveratrol markedly lowered the level of Keap1, accompanied by evident activation of Nrf2 signaling in the diabetic kidney. The underlying mechanisms of antioxidant effect of AB38b were explored in HG-treated mouse GMCs. AB38b (2.5-10 μM) or resveratrol (10 μM) significantly alleviated OS and ECM accumulation in HG-treated GMCs. Furthermore, AB38b or resveratrol treatment effectively activated Nrf2 signaling by inhibiting Keap1 expression without affecting the interaction between Keap1 and Nrf2. Besides, AB38b treatment effectively suppressed the ubiquitination of Nrf2. Taken together, this study demonstrates that AB38b ameliorates experimental DN through antioxidation and modulation of Keap1/Nrf2 signaling pathway.

African and Asian Mitochondrial DNA Haplogroups Confer Resistance Against Diabetic Stresses on Retinal Pigment Epithelial Cybrid Cells In Vitro

Diabetic retinopathy (DR) is the most common cause of blindness for individuals under the age of 65. This loss of vision can be due to ischemia, neovascularization, and/or diabetic macular edema, which are caused by breakdown of the blood-retina barrier at the level of the retinal pigment epithelium (RPE) and inner retinal vasculature. The prevalence of diabetes and its complications differ between Caucasian-Americans and certain minority populations, such as African-Americans and Asian-Americans. Individuals can be classified by their mitochondrial haplogroups, which are collections of single nucleotide polymorphisms (SNPs) in mitochondrial DNA (mtDNA) representing ancient geographic origins of populations. In this study, we compared the responses of diabetic human RPE cybrids, cell lines containing identical nuclei but mitochondria from either European (maternal European) or maternal African or Asian individuals, to hypoxia and high glucose levels. The African and Asian diabetic ([Afr+Asi]/DM) cybrids showed (1) resistance to both hyperglycemic and hypoxic stresses; (2) downregulation of pro-apoptotic indicator BAX; (3) upregulation of DNA methylation genes, such as DNMT3A and DNMT3B; and (4) resistance to DNA demethylation by the methylation inhibitor 5-Aza-2'-deoxycytidine (5-Aza-dC) compared to European diabetic (Euro/DM) cybrids. Our findings suggest that mitochondria from African and Asian diabetic subjects possess a "metabolic memory" that confers resistance against hyperglycemia, hypoxia, and demethylation, and that this "metabolic memory" can be transferred into the RPE cybrid cell lines in vitro.

A New Human Blood-Retinal Barrier Model Based on Endothelial Cells, Pericytes, and Astrocytes

Blood-retinal barrier (BRB) dysfunction represents one of the most significant changes occurring during diabetic retinopathy. We set up a high-reproducible human-based in vitro BRB model using retinal pericytes, retinal astrocytes, and retinal endothelial cells in order to replicate the human in vivo environment with the same numerical ratio and layer order. Our findings showed that high glucose exposure elicited BRB breakdown, enhanced permeability, and reduced the levels of junction proteins such as ZO-1 and VE-cadherin. Furthermore, an increased expression of pro-inflammatory mediators (IL-1β, IL-6) and oxidative stress-related enzymes (iNOS, Nox2) along with an increased production of reactive oxygen species were observed in our triple co-culture paradigm. Finally, we found an activation of immune response-regulating signaling pathways (Nrf2 and HO-1). In conclusion, the present model mimics the closest human in vivo milieu, providing a valuable tool to study the impact of high glucose in the retina and to develop novel molecules with potential effect on diabetic retinopathy.

Effects of Sulfated Fucans from Laminaria hyperborea Regarding VEGF Secretion, Cell Viability, and Oxidative Stress and Correlation with Molecular Weight

BACKGROUND

Sulfated fucans show interesting effects in the treatment of ocular diseases (e.g., age-related macular degeneration), depending on their chemical structure. Here, we compared three purified sulfated fucans from Laminaria hyperborea (LH) regarding cell viability, oxidative stress protection, and vascular endothelial growth factor (VEGF) secretion in ocular cells.

METHODS

High-molecular-weight sulfated fucan (Mw = 1548.6 kDa, Fuc1) was extracted with warm water and purified through ultrafiltration. Lower-molecular-weight samples (Mw = 499 kDa, Fuc2; 26.9 kDa, Fuc3) were obtained by mild acid hydrolysis of ultrapurified sulfated fucan and analyzed (SEC-MALS (Size-exclusion chromatography-Multi-Angle Light Scattering), ICP-MS, and GC). Concentrations between 1 and 100 µg/mL were tested. Cell viability was measured after 24 h (uveal melanoma cell line (OMM-1), retinal pigment epithelium (RPE) cell line ARPE-19, primary RPE cells) via MTT/MTS (3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide/3-(4,5-Dimethylthiazol-2-yl)-5-(3-carboxymethoxyphenyl)-2-(4-sulfophenyl)-2H-tetrazolium) assay. Oxidative stress protection was determined after 24 h (OMM-1, ARPE-19). VEGF secretion was analyzed via ELISA after three days (ARPE-19, RPE).

RESULTS

Fuc2 and Fuc3 were antiproliferative for OMM-1, but not for ARPE. Fuc1 protected OMM-1. VEGF secretion was lowered with all fucans except Fuc3 in ARPE-19 and RPE. The results suggest a correlation between molecular weight and biological activity, with efficiency increasing with size.

CONCLUSION

The LH sulfated fucan Fuc1 showed promising results regarding VEGF inhibition and protection, encouraging further medical research.

N-Acetyl-L-cysteine Protects Human Retinal Pigment Epithelial Cells from Oxidative Damage: Implications for Age-Related Macular Degeneration

Age-related macular degeneration (AMD) involves the loss of retinal pigment epithelium (RPE) and photoreceptors and is one of the leading causes of blindness in the elderly. Oxidative damage to proteins, lipids, and DNA has been associated with RPE dysfunction and AMD. In this study, we evaluated oxidative stress in AMD and the efficacy of antioxidant, N-acetyl-L-cysteine (NAC), in protecting RPE from oxidative damage. To test this idea, primary cultures of RPE from human donors with AMD (n = 32) or without AMD (No AMD, n = 21) were examined for expression of NADPH oxidase (NOX) genes, a source of reactive oxygen species (ROS). Additionally, the cells were pretreated with NAC for 2 hours and then treated with either hydrogen peroxide (H₂O₂) or tert-butyl hydroperoxide (t-BHP) to induce cellular oxidation. Twenty-four hours after treatment, ROS production, cell survival, the content of glutathione (GSH) and adenosine triphosphate (ATP), and cellular bioenergetics were measured. We found increased expression of p22phox, a NOX regulator, in AMD cells compared to No AMD cells (p = 0.02). In both AMD and No AMD cells, NAC pretreatment reduced t-BHP-induced ROS production and protected from H₂O₂-induced cell death and ATP depletion. In the absence of oxidation, NAC treatment improved mitochondrial function in both groups (p < 0.01). Conversely, the protective response exhibited by NAC was disease-dependent for some parameters. In the absence of oxidation, NAC significantly reduced ROS production (p < 0.001) and increased GSH content (p = 0.02) only in RPE from AMD donors. Additionally, NAC-mediated protection from H₂O₂-induced GSH depletion (p = 0.04) and mitochondrial dysfunction (p < 0.05) was more pronounced in AMD cells compared with No AMD cells. These results demonstrate the therapeutic benefit of NAC by mitigating oxidative damage in RPE. Additionally, the favorable outcomes observed for AMD RPE support NAC's relevance and the potential therapeutic value in treating AMD.

The impact of hyperglycemia on the corneal epithelium: Molecular mechanisms and insight

Type 2 Diabetes Mellitus (T2DM) is reaching epidemic levels worldwide and with it, there is a significant increase in complications associated with the disease. T2DM affects virtually all organ systems including the eye. While frequently overlooked, diabetic keratopathy is the most common ocular complication of diabetes and can manifest in mild to severe forms, the latter of which poses a major threat to vision. As the initial barrier between the environment and the eye, the corneal epithelium functions in innate immune defense. Compromise of this barrier may predispose the cornea to infection and can hinder the refractive capabilities of the eye. The clinical burden in patients with diabetic keratopathy lies primarily in the inability of the corneal epithelium to repair damage and maintain its tight barrier function. Current therapies for diabetic keratopathy are supportive, centering on the prevention of infection and promotion of an optimal healing environment. With no clear disease-modifying agent identified as of yet, a thorough understanding of the pathophysiology that underlies the development of diabetic keratopathy at the cellular level is critical to identify and develop potential therapeutic agents capable of promoting corneal re-epithelialization to accelerate the wound healing process. The focus of this review is to examine what is known regarding the cellular and molecular mechanisms needed to maintain epithelial homeostasis and how it goes awry in diabetes.

Puerarin prevents cataract development and progression in diabetic rats through Nrf2/HO‑1 signaling

Puerarin is the major bioactive ingredient isolated from the dry root of Pueraria lobata, a plant used in traditional Chinese medicine. Puerarin has been used to treat diabetes and cataracts in China; however, its underlying mechanism of action remains unclear. The aim of the present study was to investigate the effectiveness and mechanism of puerarin in preventing cataracts in diabetic rats. Diabetes was induced by streptozocin (STZ) administration and rats were intraperitoneally injected with puerarin (25, 50 and 100 mg/kg). Blood glucose levels and cataract development were examined in the different experimental groups. In addition, the expression levels of markers associated with oxidative stress, including nuclear factor erythroid 2 like 2 (Nrf2) and heme oxygenase‑1 (HO‑1), were analyzed. The present results suggested that treatment with puerarin at 25, 50 and 100 mg/kg significantly reduced blood glucose levels and the incidence of cataract in STZ‑induced diabetic rats. Additionally, puerarin treatment reduced oxidative stress, restoring the levels of malondialdehyde and glutathione, and the activity of glutathione peroxidase. Furthermore, puerarin administration decreased the expression levels of retinal vascular endothelial growth factor and interleukin‑1β and increased the mRNA expression levels of Nrf2 and HO‑1, thus inhibiting oxidative stress. The present findings suggested that puerarin had hypoglycemic effects and that it prevented cataract development and progression in diabetic rats by reducing oxidative stress through the Nrf2/HO‑1 signaling pathway.

Effects of Fucoidans from Five Different Brown Algae on Oxidative Stress and VEGF Interference in Ocular Cells

BACKGROUND

Fucoidans are interesting for potential usage in ophthalmology, and especially age-related macular degeneration. However, fucoidans from different species may vary in their effects. Here, we compare fucoidans from five algal species in terms of oxidative stress protection and vascular endothelial growth factor (VEGF) interference in ocular cells.

METHODS

Brown algae (Fucus vesiculosus, Fucus distichus subsp. evanescens, Fucus serratus, Laminaria digitata, Saccharina latissima) were harvested and fucoidans isolated by hot-water extraction. Fucoidans were tested in several concentrations (1, 10, 50, and 100 µg/mL). Effects were measured on a uveal melanoma cell line (OMM-1) (oxidative stress), retinal pigment epithelium (RPE) cell line ARPE19 (oxidative stress and VEGF), and primary RPE cells (VEGF). Oxidative stress was induced by H2O2 or tert-Butyl hydroperoxide (TBHP). Cell viability was investigated with methyl thiazolyl tetrazolium (MTT or MTS) assay, and VEGF secretion with ELISA. Affinity to VEGF was determined by a competitive binding assay.

RESULTS

All fucoidans protected OMM-1 from oxidative stress. However, in ARPE19, only fucoidan from Saccharina latissima was protective. The affinity to VEGF of all fucoidans was stronger than that of heparin, and all reduced VEGF secretion in ARPE19. In primary RPE, only the fucoidan from Saccharina latissima was effective.

CONCLUSION

Among the fucoidans from five different species, Saccharina latissima displayed the most promising results concerning oxidative stress protection and reduction of VEGF secretion.

Curcumin prevents high glucose damage in retinal pigment epithelial cells through ERK1/2-mediated activation of the Nrf2/HO-1 pathway

To study the effects of curcumin on human retinal pigment epithelial (RPE) cells exposed to high glucose (HG) insult, we performed in vitro studies on RPE cells cultured both in normal and HG conditions to assess the effects of curcumin on the cell viability, nuclear factor erythroid 2-related factor 2 (Nrf2) expression, HO-1 activity, and ERK1/2 expression. RPE cells exposed to HG insult were treated with curcumin. The cell viability, apoptosis, HO-1 activity, ERK, and Nrf2 expression were evaluated. The data indicated that treatment with curcumin caused a significant decrease in terms of apoptosis. Further, curcumin was able to induce HO-1 expression via Nrf2 activation and counteracts the damage elicited by HG. The present study demonstrated that curcumin provides protection against HG-induced damage in RPE cells through the activation of Nrf2/HO-1 signaling that involves the ERK pathway, suggesting that curcumin may have therapeutic value in the treatment of diabetic retinopathy.

Activation of Nrf2 signaling by natural products-can it alleviate diabetes?

Type 2 diabetes mellitus (DM) has reached pandemic proportions and effective prevention strategies are wanted. Its onset is accompanied by cellular distress, the nuclear factor erythroid 2-related factor 2 (Nrf2) is a transcription factor boosting cytoprotective responses, and many phytochemicals activate Nrf2 signaling. Thus, Nrf2 activation by natural products could presumably alleviate DM. We summarize function, regulation and exogenous activation of Nrf2, as well as diabetes-linked and Nrf2-susceptible forms of cellular stress. The reported amelioration of insulin resistance, β-cell dysfunction and diabetic complications by activated Nrf2 as well as the status quo of Nrf2 in precision medicine for DM are reviewed.

Intermittent high glucose-induced oxidative stress modulates retinal pigmented epithelial cell autophagy and promotes cell survival via increased HMGB1

Background

In this study, we evaluated the effects of intermittent high glucose on oxidative stress production in retinal pigmented epithelial (RPE) cells and explored whether the mechanisms of autophagy and apoptosis in oxidative stress are associated with high-mobility group box 1 (HMGB1) protein.

Methods

Cultured human RPE cell line ARPE-19 cells were exposed to intermittent high glucose-induced oxidative stress. Reactive oxygen species (ROS) was determined by 2′, 7′-dichlorofluorescin diacetate (DCFH-DA); and malonyldialdehyde (MDA), superoxide dismutase (SOD) by commercial kits. Transmission electron microscopy was used to observe the generation of autophagosome. And MTT assay was used to examine the effect of autophagy on cell viability. For the inhibition experiments, cells were pre-incubated with lysosomal inhibitors NH4Cl or N-acetyl cysteine (NAC).Western blot was used to measure the expression patterns of autophagic markers, including LC3 and p62. The expression of HMGB1 was detected by immunohistochemistry.Cells were pre-incubated with HMGB1 inhibitor ethyl pyruvate (EP) ,then detected the expression pattern of autophagic markers and level of cellular ROS.

Results

We found that intermittent high glucose significantly increased oxidative stress levels (as indicated by ROS, MDA, SOD), increased in the generation of autophagosome, decreased the level of p62, induced conversion of LC3 I to LC3 II. We further demonstrated that the NH4Cl/NAC inhibited intermittent high glucose-induced autophage by altered level of LC3 and p62. Intermittent high glucose-induced autophagy is independent of HMGB1 signaling, inhibition of HMGB1 release by EP decreased expression pattern of autophagic markers and level of cellular viability.

Conclusions

Under intermittent high glucose condition, autophagy may be required for preventing oxidative stress-induced injury in RPE. HMGB1 plays important roles in signaling for both autophagy and oxidative stress.

Nrf2 protects against diabetic dysfunction of endothelial progenitor cells via regulating cell senescence

Diabetes is associated with an increased risk of cardio-vascular disease. A decrease in the number and functionality of endothelial progenitor cells (EPCs) leads to reduced endothelial repair and the development of cardiovascular disease. The aim of the present study was to explore the effect and underlying mechanisms of nuclear factor erythroid 2-related factor 2 (Nrf2) on EPC dysfunction caused by diabetic mellitus. The biological functions of EPCs in streptozotocin-induced diabetic mice were evaluated, including migration, proliferation, angiogenesis and the secretion of vascular endothelial growth factor (VEGF), stromal-derived growth factor (SDF) and nitric oxide (NO). Oxidative stress levels in diabetic EPCs were also assessed by detecting intracellular reactive oxygen species (ROS), superoxide dismutase (SOD) and malondialdehyde (MDA). EPC senescence was evaluated by measuring p16 and b-gal expression and observing the senescence-associated secretory phenotype. In addition, the function of EPCs and level of oxidative stress were assessed following Nrf2 silencing or activation. Nrf2 silencing resulted in a decrease of EPC biological functions, accelerated cell senescence and increased oxidative stress, as indicated by ROS and MDA upregulation accompanied with decreased SOD activity. Furthermore, Nrf2 silencing inhibited migration, proliferation and secretion in EPCs, while it increased oxidative stress and cell senescence. Nrf2 activation protected diabetic EPCs against the effects of oxidative stress and cell senescence, ameliorating the biological dysfunction of EPCs derived from mice with diabetes. In conclusion, Nrf2 overexpression protected against oxidative stress-induced functional damage in EPCs derived from diabetic mice by regulating cell senescence.

The intraocular staining potential of anthocyanins and their retinal biocompatibility: a preclinical study

PURPOSE

To perform preclinical studies to determine the efficacy and safety of anthocyanins as stains for the internal limiting membrane (ILM) of the eye.

MATERIALS AND METHODS

Cyanidin (Cya), delphinidin (Del), luteolinidin (Lut), peonidin (Peo) and pelargonidin (Pel) were evaluated. These natural dyes were used to stain the lens capsule and ILM of pig eyes. The effects of these dyes on retinal cell viability was determined using a water-soluble tetrazolium salt assay, and oxidative stress was measured in vitro. Histopathology, in situ TUNEL labelling, transmission electronic microscopy (TEM), and electroretinography (ERG) were performed on rats following the intravitreal and subretinal injection of the neuroprotective dyes.

RESULTS

All anthocyanins stained the lens capsule and ILM of the pigs at a concentration of 1 mg/ml. Del, Lut and Peo were non-toxic and produced survival rates in the ARPE19 and RGC5 cells that were similar to those in control cells. We treated eyes with H₂O₂ and three dyes (Del, Lut, and Peo) to explore the possible neuroprotective effects and observed significantly higher survival rates in the ARPE19 cells treated with Del, Lut or Peo and the RGC5 cells treated with Lut or Peo than those in the control cells. Three dyes were intravitreally and subretinally injected into rats in vivo, and the histology showed mildly disorganized retinal cell layers. TUNEL staining and TEM examinations did not reveal additional toxic effects. Rat ERGs were not altered after intravitreal injections.

CONCLUSIONS

This preclinical study, Del, Lut, and Peo show potential as staining agents and warrant further investigation as vital dyes.

Therapeutic targets for altering mitochondrial dysfunction associated with diabetic retinopathy

INTRODUCTION

Retinopathy remains as one of the most feared blinding complications of diabetes, and with the prevalence of this life-long disease escalating at an alarming rate, the incidence of retinopathy is also climbing. Although the cutting edge research has identified many molecular mechanisms associated with its development, the exact mechanism how diabetes damages the retina remains obscure, limiting therapeutic options for this devastating disease. Areas covered: This review focuses on the central role of mitochondrial dysfunction/damage in the pathogenesis of diabetic retinopathy, and how damaged mitochondria initiates a self-perpetuating vicious cycles of free radicals. We have also reviewed how mitochondria could serve as a therapeutic target, and the challenges associated with the complex double mitochondrial membranes and a well-defined blood-retinal barrier for optimal pharmacologic/molecular approach to improve mitochondrial function. Expert opinion: Mitochondrial dysfunction provides many therapeutic targets for ameliorating the development of diabetic retinopathy including their biogenesis, DNA damage and epigenetic modifications. New technology to enhance pharmaceuticals uptake inside the mitochondria, nanotechnology to deliver drugs to the retina, and maintenance of mitochondrial homeostasis via lifestyle changes and novel therapeutics to prevent epigenetic modifications, could serve as some of the welcoming avenues for a diabetic patient to target this sight-threatening disease.

Models of retinal diseases and their applicability in drug discovery

INTRODUCTION

The impact of vision debilitating diseases is a global public health concern, which will continue until effective preventative and management protocols are developed. Two retinal diseases responsible for the majority of vision loss in the working age adults and elderly populations are diabetic retinopathy (DR) and age-related macular degeneration (AMD), respectively. Model systems, which recapitulate aspects of human pathology, are valid experimental modalities that have contributed to the identification of signaling pathways involved in disease development and consequently potential therapies. Areas covered: The pathology of DR and AMD, which serve as the basis for designing appropriate models of disease, is discussed. The authors also review in vitro and in vivo models of DR and AMD and evaluate the utility of these models in exploratory and pre-clinical studies. Expert opinion: The complex nature of non-Mendelian diseases such as DR and AMD has made identification of effective therapeutic treatments challenging. However, the authors believe that while in vivo models are often criticized for not being a 'perfect' recapitulation of disease, they have been valuable experimentally when used with consideration of the strengths and limitations of the experimental model selected and have a place in the drug discovery process.

The Role of Microglia in Diabetic Retinopathy: Inflammation, Microvasculature Defects and Neurodegeneration

Diabetic retinopathy is a common complication of diabetes mellitus, which appears in one third of all diabetic patients and is a prominent cause of vision loss. First discovered as a microvascular disease, intensive research in the field identified inflammation and neurodegeneration to be part of diabetic retinopathy. Microglia, the resident monocytes of the retina, are activated due to a complex interplay between the different cell types of the retina and diverse pathological pathways. The trigger for developing diabetic retinopathy is diabetes-induced hyperglycemia, accompanied by leukostasis and vascular leakages. Transcriptional changes in activated microglia, mediated via the nuclear factor kappa-light-chain-enhancer of activated B cells (NFκB) and extracellular signal–regulated kinase (ERK) signaling pathways, results in release of various pro-inflammatory mediators, including cytokines, chemokines, caspases and glutamate. Activated microglia additionally increased proliferation and migration. Among other consequences, these changes in microglia severely affected retinal neurons, causing increased apoptosis and subsequent thinning of the nerve fiber layer, resulting in visual loss. New potential therapeutics need to interfere with these diabetic complications even before changes in the retina are diagnosed, to prevent neuronal apoptosis and blindness in patients.

Phloretin Prevents Diabetic Cardiomyopathy by Dissociating Keap1/Nrf2 Complex and Inhibiting Oxidative Stress

Hyperglycemia induces chronic inflammation and oxidative stress in cardiomyocyte, which are the main pathological changes of diabetic cardiomyopathy (DCM). Treatment aimed at these processes may be beneficial in DCM. Phloretin (PHL), a promising natural product, has many pharmacological activities, such as anti-inflammatory, anticancer, and anti-oxidative function. The aim of this study was to investigate whether PHL could ameliorate the high glucose-mediated oxidation, hypertrophy, and fibrosis in H9c2 cells and attenuate the inflammation- and oxidation-mediated cardiac injury. In this study, PHL induced significantly inhibitory effect on the expression of pro-inflammatory, hypertrophy, pro-oxidant, and fibrosis cytokines in high glucose-stimulated cardiac H9c2 cells. Furthermore, PHL decreased the levels of serum lactate dehydrogenase, aspartate aminotransferase, and creatine kinase-MB, and attenuated the progress in the fibrosis, oxidative stress, and pathological parameters via Kelch-like ECH-associated protein 1 (Keap1)/nuclear factor E2-related factor 2 (Nrf2) pathway in diabetic mice. In additional, molecular modeling and immunoblotting results confirmed that PHL might obstruct the interaction between Nrf2 and Keap1 through direct binding Keap1, and promoting Nrf2 expression. These results provided evidence that PHL could suppress high glucose-induced cardiomyocyte oxidation and fibrosis injury, and that targeting Keap1/Nrf2 may provide a novel therapeutic strategy for human DCM in the future.

Epigenetic Treatment of Neurodegenerative Ophthalmic Disorders: An Eye Toward the Future

Eye disease is one of the primary medical conditions that requires attention and therapeutic intervention in ageing populations worldwide. Further, the global burden of diabetes and obesity, along with heart disease, all lead to secondary manifestations of ophthalmic distress. Therefore, there is increased interest in developing innovative new approaches that target various mechanisms and sequelae driving conditions that result in adverse vision. The research challenge is even greater given that the terrain of eye diseases is difficult to landscape into a single therapeutic theme. This report addresses the burden of eye disease due to mitochondrial dysfunction, including antioxidant, autophagic, epigenetic, mitophagic, and other cellular processes that modulate the biomedical end result. In this light, we single out lipoic acid as a potent known natural activator of these pathways, along with alternative and potentially more effective conjugates, which together harness the necessary potency, specificity, and biodistribution parameters required for improved therapeutic outcomes.

Quercetin Mitigates Inflammatory Responses Induced by Vascular Endothelial Growth Factor in Mouse Retinal Photoreceptor Cells through Suppression of Nuclear Factor Kappa B

Retinal vascular endothelial growth factor (VEGF) increased by neovascularization is well known as a pathogenic factor in ocular neovascular diseases. However, it is still unclear how retinal neurons are damaged by VEGF. The aims of this study are to demonstrate the inflammatory protein expression regulated by VEGF using mouse photoreceptor-derived cells and the protective effect of quercetin against VEGF-induced inflammatory response. Expression and phosphorylation of protein and expression of mRNA were detected by immunoblot and reverse transcriptase polymerase chain reaction. VEGF-induced degradation of limiting membrane and translocation of nuclear factor kappa B (NF-κB) were analyzed by immunocytochemistry. VEGF treatment activated angiogenic signaling pathway in photoreceptor cells. In addition, adhesion molecules and matrix metalloproteinases were increased in VEGF-treated photoreceptor cells. All these events were reversed by quercetin. Zona occludins-1 and β-catenin decreased by VEGF were recovered by quercetin. NF-κB signaling pathway regulated by VEGF through phosphorylations of mitogen-activated protein kinases (MAPK) and protein kinase B (Akt) was suppressed by quercetin. These results suggest that quercetin suppressed VEGF-induced excessive inflammatory response in retinal photoreceptor cells by inactivation of NF-κB signals through inhibition of MAPKs and Akt. These data may provide a basic information for development of pharmaceuticals or nutraceuticals for treatment of retinal diseases caused by excessive VEGF.

Nrf2, a Potential Therapeutic Target against Oxidative Stress in Corneal Diseases

Corneal diseases are one of the major causes of blindness worldwide. Conservative medical agents, which may prevent sight-threatening corneal disease progression, are urgently desired. Numerous evidences have revealed the involvement of oxidative stress in various corneal diseases, such as corneal wound healing and Fuchs endothelial corneal dystrophy (FECD). Nuclear factor (erythroid-derived 2)-like 2 (Nrf2)/Kelch-like erythroid-cell-derived protein with CNC homology- (ECH-) associated protein 1 (Keap1)/antioxidant response element (ARE) signaling is well known as one of the main antioxidative defense systems. To the best of our knowledge, this is the first review to elucidate the different expression profiles of Nrf2 signaling as well as the underlying mechanisms in corneal diseases, implicating that Nrf2 may serve as a potentially promising therapeutic target for corneal diseases.

Effects of Novel Nitric Oxide-Releasing Molecules against Oxidative Stress on Retinal Pigmented Epithelial Cells

Oxidative stress is a hallmark of retinal degenerations such as age-related macular degeneration and diabetic retinopathy. Enhancement of heme oxygenase-1 (HO-1) activity in the retina would exert beneficial effects by protecting cells from oxidative stress, therefore promoting cell survival. Because a crosstalk exists between nitric oxide (NO) and HO-1 in promotion of cell survival under oxidative stress, we designed novel NO-releasing molecules also capable to induce HO-1. Starting from curcumin and caffeic acid phenethyl ester (CAPE), two known HO-1 inducers, the molecules were chemically modified by acylation with 4-bromo-butanoyl chloride and 2-chloro-propanoyl chloride, respectively, and then treated in the dark with AgNO₃ to obtain the nitrate derivatives VP10/12 and VP10/39. Human retinal pigment epithelial cells (ARPE-19) subjected to H₂O₂-mediated oxidative stress were treated with the described NO-releasing compounds. VP10/39 showed significant (p < 0.05) antioxidant and protecting activity against oxidative damage, in comparison to VP10/12, which in turn showed at 100 μM concentration a slight but significant cell toxicity. Only VP10/39 significantly (p < 0.05) induced HO-1 in ARPE-19, most likely through covalent bond formation at Cys151 of the Keap1-BTB domain, as revealed from molecular docking analysis. In conclusion, the present data indicate VP10/39 as a promising candidate to protect ARPE-19 cells against oxidative stress.

Metabolomics study of cadmium-induced diabetic nephropathy and protective effect of caffeic acid phenethyl ester using UPLC-Q-TOF-MS combined with pattern recognition

Diabetic nephropathy (DN) is the most severe complication of diabetes and multiple factors are involved in the pathogenesis of DN. Among them, cadmium (Cd) acts as a risk factor inducing the occurrence of DN. The present study focused on investigating the protective role of caffeic acid phenethyl ester (CAPE), an active component of propolis from honeybee hives, against Cd-induced DN in mice based on ultra performance liquid chromatography coupled with quadrupole time-of-flight mass spectrometry (UPLC-Q-TOF-MS)and pattern recognition. Serum and urine biochemical indexes were detected and histopathological observation has been done to evaluate the damage of Cd on animals. Moreover, the global serum profiles of different groups were distinguished by UPLC-Q-TOF-MS and principal component analysis (PCA) were applied for group differentiation and marker selection. Moreover, the influence of Cd on the oxidative status in DN mice were also evaluated by assessing the parameters of oxidative stress, proinflammatory cytokines and antioxidant competence. As shown in the scores plots, the distinct clustering among controls, DN and CAPE groups were observed, significant changes in serum levels of LysoPC(18:1(11Z)), 2,3-dinor-8-iso-PGF2a, PS(18:1(9Z)/18:1(9Z)), DG(17:0/22:4 (7Z,10Z, 13Z, 16Z)/0:0) and Arachidonic acid(AA) were noted and identified as potential biomarkers, the effect of CAPE reverted them back to near normalcy. Further, It was observed a significant improvement in lipid peroxides (LPO) and protein carbonyls (PCO) levels in Cd-induced DN kidneys along with a significant decline in superoxide dismutase (SOD), catalase (CAT), and reduced glutathione (GSH) levels, however, CAPE relieved these changes. In conclusion, the study suggested that the pathogenesis of DN caused by Cd probably owes to the perturbations of lipid metabolism and AA metabolism; CAPE seems to be effective agent and may be related to its potent antioxidant, anti-inflammatory properties and action as an Nrf2 activator.

Distinct Nrf2 Signaling Mechanisms of Fumaric Acid Esters and Their Role in Neuroprotection against 1-Methyl-4-Phenyl-1,2,3,6-Tetrahydropyridine-Induced Experimental Parkinson's-Like Disease

A promising approach to neurotherapeutics involves activating the nuclear-factor-E2-related factor 2 (Nrf2)/antioxidant response element signaling, which regulates expression of antioxidant, anti-inflammatory, and cytoprotective genes. Tecfidera, a putative Nrf2 activator, is an oral formulation of dimethylfumarate (DMF) used to treat multiple sclerosis. We compared the effects of DMF and its bioactive metabolite monomethylfumarate (MMF) on Nrf2 signaling and their ability to block 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP)-induced experimental Parkinson's disease (PD). We show that in vitro DMF and MMF activate the Nrf2 pathway via S-alkylation of the Nrf2 inhibitor Keap1 and by causing nuclear exit of the Nrf2 repressor Bach1. Nrf2 activation by DMF but not MMF was associated with depletion of glutathione, decreased cell viability, and inhibition of mitochondrial oxygen consumption and glycolysis rates in a dose-dependent manner, whereas MMF increased these activities in vitro However, both DMF and MMF upregulated mitochondrial biogenesis in vitro in an Nrf2-dependent manner. Despite the in vitro differences, both DMF and MMF exerted similar neuroprotective effects and blocked MPTP neurotoxicity in wild-type but not in Nrf2 null mice. Our data suggest that DMF and MMF exhibit neuroprotective effects against MPTP neurotoxicity because of their distinct Nrf2-mediated antioxidant, anti-inflammatory, and mitochondrial functional/biogenetic effects, but MMF does so without depleting glutathione and inhibiting mitochondrial and glycolytic functions. Given that oxidative damage, neuroinflammation, and mitochondrial dysfunction are all implicated in PD pathogenesis, our results provide preclinical evidence for the development of MMF rather than DMF as a novel PD therapeutic.

SIGNIFICANCE STATEMENT

Almost two centuries since its first description by James Parkinson, Parkinson's disease (PD) remains an incurable disease with limited symptomatic treatment. The current study provides preclinical evidence that a Food and Drug Administration-approved drug, dimethylfumarate (DMF), and its metabolite monomethylfumarate (MMF) can block nigrostriatal dopaminergic neurodegeneration in a 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine mouse model of PD. We elucidated mechanisms by which DMF and its active metabolite MMF activates the redox-sensitive transcription factor nuclear-factor-E2-related factor 2 (Nrf2) to upregulate antioxidant, anti-inflammatory, mitochondrial biosynthetic and cytoprotective genes to render neuroprotection via distinct S-alkylating properties and depletion of glutathione. Our data suggest that targeting Nrf2-mediated gene transcription using MMF rather than DMF is a promising approach to block oxidative stress, neuroinflammation, and mitochondrial dysfunction for therapeutic intervention in PD while minimizing side effects.

Fumarate decreases edema volume and improves functional outcome after experimental stroke

BACKGROUND

Oxidative stress and inflammation exacerbate tissue damage in the brain after ischemic stroke. Dimethyl-fumarate (DMF) and its metabolite monomethyl-fumarate (MMF) are known to stimulate anti-oxidant pathways and modulate inflammatory responses. Considering these dual effects of fumarates, we examined the effect of MMF treatment after ischemic stroke in mice.

METHODS

Permanent middle cerebral artery occlusion (pMCAO) was performed using adult, male C57BL/6 mice. Thirty minutes after pMCAO, 20mg/kg MMF was administered intravenously. Outcomes were evaluated 6, 24 and 48h after pMCAO. First, we examined whether a bolus of MMF was capable of changing expression of kelch-like erythroid cell-derived protein with CNC homology-associated protein 1 (Keap1) and nuclear factor erythroid 2-related factor (Nrf)2 in the infarcted brain. Next, we studied the effect of MMF on functional recovery. To explore mechanisms potentially influencing functional changes, we examined infarct volumes, edema formation, the expression of heat shock protein (Hsp)72, hydroxycarboxylic acid receptor 2 (Hcar2), and inducible nitric oxide synthase (iNOS) in the infarcted brain using real-time PCR and Western blotting. Concentrations of a panel of pro- and anti-inflammatory cytokines (IFNγ, IL-1β, IL-2, IL-4, IL-5, IL-6, IL-10, IL-12p70, TNF) were examined in both the infarcted brain tissue and plasma samples 6, 24 and 48h after pMCAO using multiplex electrochemoluminiscence analysis.

RESULTS

Administration of MMF increased the protein level of Nrf2 6h after pMCAO, and improved functional outcome at 24 and 48h after pMCAO. MMF treatment did not influence infarct size, however reduced edema volume at both 24 and 48h after pMCAO. MMF treatment resulted in increased Hsp72 expression in the brain 6h after pMCAO. Hcar2 mRNA levels increased significantly 24h after pMCAO, but were not different between saline- and MMF-treated mice. MMF treatment also increased the level of the anti-inflammatory cytokine IL-10 in the brain and plasma 6h after pMCAO, and additionally reduced the level of the pro-inflammatory cytokine IL-12p70 in the brain at 24 and 48h after pMCAO.

CONCLUSIONS

A single intravenous bolus of MMF improved sensory-motor function after ischemic stroke, reduced edema formation, and increased the levels of the neuroprotective protein Hsp72 in the brain. The early increase in IL-10 and reduction in IL-12p70 in the brain combined with changes in systemic cytokine levels may also contribute to the functional recovery after pMCAO.

Palmitic acid triggers cell apoptosis in RGC-5 retinal ganglion cells through the Akt/FoxO1 signaling pathway

Hallmarks of the pathophysiology of glaucoma are oxidative stress and apoptotic death of retinal ganglion cells (RGCs). Lipotoxicity, involving a series of pathological cellular responses after exposure to elevated levels of fatty acids, leads to oxidative stress and cell death in various cell types. The phosphatidylinositol-3-kinase/protein kinase B/Forkhead box O1 (PI3K/Akt/FoxO1) pathway is crucial for cell survival and apoptosis. More importantly, FoxO1 gene has been reported to confer relatively higher risks for eye diseases including glaucoma. However, little information is available regarding the interaction between FoxO1 and RGC apoptosis, much less a precise mechanism. In the present study, immortalized rat retinal ganglion cell line 5 (RGC-5) was used as a model to study the toxicity of palmitic acid (PA), as well as underlying mechanisms. We found that PA exposure significantly decreased cell viability by enhancing apoptosis in RGC-5 cells, as measured by 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) assay and flow cytometry. PA also induced a remarkable increase in reactive oxygen species and malondialdehyde. Moreover, PA significantly decreased the level of phospho-Akt and phospho-FoxO1 in cells. Finally, shRNA knockdown and plasmid overexpression studies displayed that downregulation of Akt protein or upregulation of FoxO1 protein augmented cell death, while knockdown of FoxO1 or overexpression of Akt1 abolished PA-induced cell death. Collectively, our results indicated that PA-induced cell death is mediated through modulation of Akt/FoxO1 pathway activity.

Hypoxia-Inducible Factor-1α Target Genes Contribute to Retinal Neuroprotection

Hypoxia-inducible factor (HIF) is a transcription factor that facilitates cellular adaptation to hypoxia and ischemia. Long-standing evidence suggests that one isotype of HIF, HIF-1α, is involved in the pathogenesis of various solid tumors and cardiac diseases. However, the role of HIF-1α in retina remains poorly understood. HIF-1α has been recognized as neuroprotective in cerebral ischemia in the past two decades. Additionally, an increasing number of studies has shown that HIF-1α and its target genes contribute to retinal neuroprotection. This review will focus on recent advances in the studies of HIF-1α and its target genes that contribute to retinal neuroprotection. A thorough understanding of the function of HIF-1α and its target genes may lead to identification of novel therapeutic targets for treating degenerative retinal diseases including glaucoma, age-related macular degeneration, diabetic retinopathy, and retinal vein occlusions.