The role of the Nrf2-mediated defense system in corneal epithelial wound healing

Research on traditional Chinese medicine as an effective drug for promoting wound healing

ETHNOPHARMACOLOGICAL RELEVANCE

The incidence of skin trauma is high and the repair process is complex, often leading to poor healing and other issues, which can result in significant economic and social burdens. Traditional Chinese medicine (TCM) is a valuable resource with proven effectiveness and safety in wound repair, widely utilized in clinical practice. A systematic analysis of wound healing with a focus on TCM research progress holds both academic and clinical importance.

AIM OF THE REVIEW

This article reviews the research progress of TCM in promoting wound healing, and provides basic data for the development of innovative drugs that promote wound healing.

MATERIALS AND METHODS

This article provides a review of the literature from the past decade and conducts a thorough analysis of various databases that contain reports on the use of TCM for wound repair. The data for this systematic research was gathered from electronic databases including CNKI, SciFinder, and PubMed. The study explores and summarizes the research findings and patterns by creating relevant charts.

RESULTS

This study reviewed the mechanism of wound healing, experimental TCM methods to promote wound healing, the theory and mode of action of TCM to promote wound healing, the active ingredients of TCM that promote wound healing, the efficacy of TCM formulae to promote wound healing, and the potential toxicity of TCM and its antidotes. This study enriched the theory of TCM in promoting wound healing.

CONCLUSION

Skin wound healing is a complex process that can be influenced by various internal and external factors. This article offers a theoretical foundation for exploring and utilizing TCM resources that enhance wound repair. By analyzing a range of TCM that promote wound healing, the article highlights the clinical importance and future potential of these medicines in promoting wound healing.

Optical microsensing reveals spatiotemporal oxygen dynamics in cornea wounds that affect healing via reactive oxygen species

Oxygen (O2) metabolism plays a critical role in cornea wound healing, regeneration, and homeostasis; however, the underlying spatiotemporal mechanisms are poorly understood. Here we used an optical sensor to profile O2 flux in intact and wounded corneas of mouse eyes. Intact corneas have unique centrifugal O2 influx profiles, smallest flux at the cornea center, and highest at the limbus. Following cornea injury, the O2 influx profile presents three distinct consecutive phases: a "decreasing" phase from 0 to 6 h, a "recovering" phase from 12 to 48 h, and a 'peak' phase from 48 to 72 h, congruent to previously described healing phases. Immediately after wounding, the O2 influx drops at wound center and wound edge but does not change significantly at the wound side or limbus. Inhibition of reactive oxygen species (ROS) in the decreasing phase significantly reduces O2 influx, decreases epithelial migration and consequently delays healing. The dynamics of O2 influx show a positive correlation with cell proliferation at the wound side, with significantly increased proliferation at the peak phase of O2 influx. This study elucidates the spatiotemporal O2 dynamics in both intact and wounded rodent cornea and shows the crucial role of O2 dynamics in regulating cell migration and proliferation through ROS metabolism, ultimately contributing to wound healing. These results demonstrate the usefulness of the micro-optrode in the characterization of spatiotemporal O2 dynamics. Injury-induced changes in O2 metabolism and ROS production modulate O2 dynamics at wound and control cell migration and proliferation, both essential for proper wound healing.

Rutin Promotes Wound Healing by Inhibiting Oxidative Stress and Inflammation in Metformin-Controlled Diabetes in Rats

Diabetes mellitus (DM) is a metabolic disorder with a notable increase in global incidence in recent years. Individuals diagnosed with diabetes are at an elevated risk of morbidity and mortality compared with the general population. For several years, the potential of phytochemicals as anti-inflammatory agents to improve the healing of diabetic wounds has been under investigation. Rutin, a flavonoid, is a particularly promising candidate for use in wound healing. Our study aims to investigate the potential impact of a topical application of rutin nanoformulation on wound healing in streptozotocin (STZ)-induced hyperglycemic rats controlled with metformin, with a focus on its anti-inflammatory and antioxidant properties. Rats are randomized into 3 groups. GI: diabetic control group; wound untreated. GII: diabetes and rutin-NP-treated wound. GIII: diabetic + β-sitosterol-treated wound. The findings suggest that topical application of rutin-NPs has the potential to enhance the wound-healing process by attenuating oxidative stress, as evidenced by restoring GSH, CAT, and SOD antioxidants, and decreasing MDA production mediated by Nrf2 activation. Also, inflammation is suppressed, as indicated by the decreased CRP, IL-1β, IL-6, and TNF-α levels. Molecular docking data confirm the biological data of rutin, where rutin is docked into the catalytic site of the X-ray crystallographic structures of CRP, Keap-1, IL-1β, IL-6, and TNF-α via grid-based ligand docking. The binding affinity and binding energy of ligand-protein interactions demonstrate the affinity and binding to the specifically selected proteins.

Oxymatrine mitigates Aspergillus fumigatus keratitis by suppressing fungal activity and restricting pyroptosis

Fungal keratitis (FK) is a refractory keratitis caused by excessive inflammation and fungal damage. Excessive inflammation can lead to tissue damage and corneal opacity, resulting in a poor prognosis for FK. Oxymatrine (OMT) is a natural alkaloid, which has rich pharmacological effects, such as antioxidant and anti-inflammation. However, its antifungal activity and the mechanism of action in FK have not been elucidated. This study confirmed that OMT suppressed Aspergillus fumigatus growth, biofilm formation, the integrity of fungal cell and conidial adherence. OMT not only effectively reduced corneal fungal load but also inflammation responses. OMT lessened the recruitment of neutrophils and macrophages in FK. In addition, OMT up-regulated the expression of Nrf2 and down-regulated the expression of IL-18, IL-1β, caspase-1, NLRP3 and GSDMD. Pre-treatment with Nrf2 inhibitor up-regulated the expression of IL-1β, IL-18, caspase-1, NLRP3 and GSDMD supressed by OMT. In conclusion, OMT has efficient anti-inflammatory and antifungal effects by suppressing fungal activity and restricting pyroptosis via Nrf2 pathway. OMT is considered as a potential option for the treatment of FK.

URP20 improves corneal injury caused by alkali burns combined with pathogenic bacterial infection in rats

Corneal alkali burns often occur in industrial production and daily life, combined with infection, and may cause severe eye disease. Oxidative stress and neovascularization (NV) are important factors leading to a poor prognosis. URP20 is an antimicrobial peptide that has been proven to treat bacterial keratitis in rats through antibacterial and anti-NV effects. Therefore, in this study, the protective effect and influence mechanism of URP20 were explored in a rat model of alkali burn together with pathogenic bacteria (Staphylococcus aureus and Escherichia coli) infection. In addition, human umbilical vein endothelial cells (HUVECs) and human corneal epithelial cells (HCECs) were selected to verify the effects of URP20 on vascularization and oxidative stress. The results showed that URP20 treatment could protect corneal tissue, reduce corneal turbidity, and reduce the NV pathological score. Furthermore, URP20 significantly inhibited the expression of the vascularization marker proteins VEGFR2 and CD31. URP20 also reduced the migration ability of HUVECs. In terms of oxidative stress, URP20 significantly upregulated SOD and GSH contents in corneal tissue and HCECs (treated with 200 μM H2O2) and promoted the expression of the antioxidant protein Nrf2/HO-1. At the same time, MDA and ROS levels were also inhibited. In conclusion, URP20 could improve corneal injury combined with bacterial infection in rats caused by alkali burns through antibacterial, anti-NV, and antioxidant activities.

Biological effects of stored platelet-rich plasma eye-drops in corneal wound healing

BACKGROUND/AIMS

This study aimed to assess the efficacy and sterility of stored platelet-rich plasma (PRP) eye-drops for corneal epithelial wound healing compared with those of autologous serum (AS) eye-drops.

METHODS

At our single institution, PRP and AS eye-drops were prepared using peripheral blood obtained from six healthy volunteers and stored at 4°C. Platelet and leucocyte counts and transforming growth factor (TGF)-β1, epidermal growth factor (EGF), and fibronectin levels were assessed during storage for up to 4 weeks. Sterility was assessed by culturing 4-week poststorage samples. PRP, AS, and phosphate-buffered saline (PBS) eye-drop efficacies were compared using corneal epithelial wound healing assays in vitro and in vivo and monitoring wound areas under a microscope every 3 hours.

RESULTS

Higher platelet and lower leucocyte counts were seen in PRP than in whole blood on the day of preparation. After storage, TGF-β1, EGF, and fibronectin levels were significantly higher in PRP than in AS eye-drops. In vitro and in vivo, PRP eye-drops used on the day of preparation significantly promoted corneal epithelial wound healing compared with PBS. Moreover, PRP eye-drops stored for 4 weeks significantly promoted corneal wound healing compared with PBS and AS eye-drops.

CONCLUSION

PRP eye-drops stored at 4°C for 4 weeks promoted corneal epithelial wound healing with higher levels of growth factors than those observed in AS eye-drops, while maintaining sterility, suggesting that this preparation satisfies the unmet medical needs in the treatment of refractory keratoconjunctival epithelial disorders.

Salidroside alleviates oxidative stress in dry eye disease by activating autophagy through AMPK-Sirt1 pathway

Dry eye disease (DED) is a multifactorial disease, and oxidative stress plays a crucial role in its pathogenesis. Recently, multiple studies have shown that upregulation of autophagy can protect the cornea from oxidative stress damage. The present study investigated the therapeutic effects of salidroside, the main component of Rhodiola crenulata, in both in vivo and in vitro dry eye models. The results showed that topical eye drop treatment with salidroside restored corneal epithelium damage, increased tear secretion, and reduced cornea inflammation in the DED mice. Salidroside activated autophagy through AMP-activated protein kinase (AMPK)-sirtuin-1 (Sirt1) signaling pathway, which promoted the nuclear translocation of nuclear factor erythroid-2-related factor 2 (Nrf2) and increased the expression of downstream antioxidant factors heme oxygenase-1 (HO-1) and NAD(P)H quinone dehydrogenase 1 (NQO1). This process restored antioxidant enzyme activity, reduced reactive oxygen species (ROS) accumulation, and alleviated oxidative stress. The application of autophagy inhibitor chloroquine and AMPK inhibitor Compound C reversed the therapeutic efficacy of salidroside, validating the above findings. In conclusion, our data suggest that salidroside is a promising candidate for DED treatment.

Targeting NRF2 to promote epithelial repair

The transcription factor NRF2 is well known as a master regulator of the cellular stress response. As such, activation of NRF2 has gained widespread attention for its potential to prevent tissue injury, but also as a possible therapeutic approach to promote repair processes. While NRF2 activation affects most or even all cell types, its effect on epithelial cells during repair processes has been particularly well studied. In response to tissue injury, these cells proliferate, migrate and/or spread to effectively repair the damage. In this review, we discuss how NRF2 governs repair of epithelial tissues, and we highlight the increasing number of NRF2 targets with diverse roles in regulating epithelial repair.

Pluronic F127-liposome-encapsulated curcumin activates Nrf2/Keap1 signaling pathway to promote cell migration of HaCaT cells

Curcumin (CUR) is an extract of Curcuma longa Linn., which has various pharmacological activities. The instability, low water solubility and bioavailability of CUR greatly limit its clinical application. This work prepared Pluronic F127-liposome-encapsulated curcumin (CUR-LIP-F127) and explored its functional role in wound healing. Liposome-encapsulated curcumin (CUR-LIP) and CUR-LIP-F127 were prepared. Human keratinocyte cell line (HaCaT) was treated with CUR, Pluronic F127-liposome (LIP-F127) and CUR-LIP-F127, or combined with ML385 (Nrf2 inhibitor). The expression of mRNAs and proteins was detected by quantitative real-time PCR and western blotting. MTT and wound healing assays were performed to detect cell viability and migration. CUR, LIP-F127 and CUR-LIP-F127 all had no influence on cell viability of HaCaT cells. CUR-LIP-F127 treatment significantly accelerated cell migration and enhanced the expression of nuclear factor erythroid-related factor 2 (Nrf2) and kelch-like erythroid cell-derived protein 1 (Keap1) in HaCaT cells with respect to CUR or LIP-F127 treatment. ML385 treatment impaired CUR-LIP-F127-mediated promotion of migration and up-regulation of Nrf2 and Keap1 in HaCaT cells. This work demonstrated that CUR-LIP-F127 activated Nrf2/Keap1 signaling pathway to promote migration of HaCaT cells, suggesting that CUR-LIP-F127 may contribute to wound healing.

Gallic Acid Ameliorates Aspergillus Fumigatus Keratitis Through Reducing Fungal Load and Suppressing the Inflammatory Response

Purpose

The purpose of this study was to explore the antifungal and anti-inflammatory effects of gallic acid (GA) on Aspergillus fumigatus (A. fumigatus) keratitis.

Methods

CCK-8 assay and Draize eye test were used to determine the non-cytotoxic concentration of GA in RAW264.7 cells and an A. fumigatus keratitis mouse model. The antifungal effects of GA were analyzed using minimal inhibitory concentration (MIC), biofilm formation test, fungal adherence assay, calcofluor white staining, and propidium iodide staining. The therapeutic effects of GA were estimated by slit lamp photographs, clinical score, hematoxylin and eosin (H&E) staining, and Periodic acid-Schiff staining in vivo. Immunofluorescence staining and myeloperoxidase assay were conducted to identify neutrophil infiltration and activity. RT-PCR, ELISA, and Western blot were performed to detect the expression of pro-inflammatory cytokines and Nrf2/HO-1.

Results

In HCECs and A. fumigatus keratitis mouse model, GA at 100 µg/mL did not affect cell viability, thus this concentration was applied to subsequent experiments. In vitro, GA significantly inhibited A. fumigatus growth, biofilm formation, and adhesion. In vivo, 100 µg/mL GA alleviated the severity of fungal keratitis (FK) by repressing fungal load, reducing neutrophil infiltration, and lowering MPO activity. Besides, the expression of IL-1β, TNF-α, LOX-1, and COX-2 was inhibited, whereas Nrf2 and HO-1 expression was enhanced at both mRNA and protein levels in the 100 µg/mL GA treated group in comparison to PBS control.

Conclusions

GA ameliorates FK severity through inhibiting A. fumigatus load, reducing neutrophils infiltration, downregulating the expression of pro-inflammatory cytokines, and enhancing the Nrf2/HO-1 pathway, which provides new insight into A. fumigatus keratitis treatment.

Role of Phytochemicals in Skin Photoprotection via Regulation of Nrf2

Ethnopharmacological studies have become increasingly valuable in the development of botanical products and their bioactive phytochemicals as novel and effective preventive and therapeutic strategies for various diseases including skin photoaging and photodamage-related skin problems including abnormal pigmentation and inflammation. Exploring the roles of phytochemicals in mitigating ultraviolet radiation (UVR)-induced skin damage is thus of importance to offer insights into medicinal and ethnopharmacological potential for development of novel and effective photoprotective agents. UVR plays a role in the skin premature aging (or photoaging) or impaired skin integrity and function through triggering various biological responses of skin cells including apoptosis, oxidative stress, DNA damage and inflammation. In addition, melanin produced by epidermal melanocytes play a protective role against UVR-induced skin damage and therefore hyperpigmentation mediated by UV irradiation could reflect a sign of defensive response of the skin to stress. However, alteration in melanin synthesis may be implicated in skin damage, particularly in individuals with fair skin. Oxidative stress induced by UVR contributes to the process of skin aging and inflammation through the activation of related signaling pathways such as the mitogen-activated protein kinase (MAPK)/activator protein-1 (AP-1), the phosphatidylinositol 3-kinase (PI3K)/protein kinase B (Akt), the nuclear factor kappa B (NF-κB) and the signal transducer and activator of transcription (STAT) in epidermal keratinocytes and dermal fibroblasts. ROS formation induced by UVR also plays a role in regulation of melanogenesis in melanocytes via modulating MAPK, PI3K/Akt and the melanocortin 1 receptor (MC1R)-microphthalmia-associated transcription factor (MITF) signaling cascades. Additionally, nuclear factor erythroid 2-related factor 2 (Nrf2)-regulated antioxidant defenses can affect the major signaling pathways involved in regulation of photoaging, inflammation associated with skin barrier dysfunction and melanogenesis. This review thus highlights the roles of phytochemicals potentially acting as Nrf2 inducers in improving photoaging, inflammation and hyperpigmentation via regulation of cellular homeostasis involved in skin integrity and function. Taken together, understanding the role of phytochemicals targeting Nrf2 in photoprotection could provide an insight into potential development of natural products as a promising strategy to delay skin photoaging and improve skin conditions.

Bioactive Compounds in Oxidative Stress-Mediated Diseases: Targeting the NRF2/ARE Signaling Pathway and Epigenetic Regulation

Oxidative stress is a pathological condition occurring due to an imbalance between the oxidants and antioxidant defense systems in the body. Nuclear factor E2-related factor 2 (NRF2), encoded by the gene NFE2L2, is the master regulator of phase II antioxidant enzymes that protect against oxidative stress and inflammation. NRF2/ARE signaling has been considered as a promising target against oxidative stress-mediated diseases like diabetes, fibrosis, neurotoxicity, and cancer. The consumption of dietary phytochemicals acts as an effective modulator of NRF2/ARE in various acute and chronic diseases. In the present review, we discussed the role of NRF2 in diabetes, Alzheimer's disease (AD), Parkinson's disease (PD), cancer, and atherosclerosis. Additionally, we discussed the phytochemicals like curcumin, quercetin, resveratrol, epigallocatechin gallate, apigenin, sulforaphane, and ursolic acid that have effectively modified NRF2 signaling and prevented various diseases in both in vitro and in vivo models. Based on the literature, it is clear that dietary phytochemicals can prevent diseases by (1) blocking oxidative stress-inhibiting inflammatory mediators through inhibiting Keap1 or activating Nrf2 expression and its downstream targets in the nucleus, including HO-1, SOD, and CAT; (2) regulating NRF2 signaling by various kinases like GSK3beta, PI3/AKT, and MAPK; and (3) modifying epigenetic modulation, such as methylation, at the NRF2 promoter region; however, further investigation into other upstream signaling molecules like NRF2 and the effect of phytochemicals on them still need to be investigated in the near future.

Combinations of peptides synergistically activate the regenerative capacity of skin cells in vitro

Objective

To explore synergistic effects related to skin regeneration, peptides with distinct biological mechanisms of action were evaluated in combination with different skin cell lines in the presence or absence of niacinamide (Nam). Furthermore, the synergistic responses of peptide combinations on global gene expression were compared with the changes that occur with fractional laser resurfacing treatment, a gold standard approach for skin rejuvenation, to further define optimal peptide combinations.

Methods

Microarray profiling was used to characterize the biological responses of peptide combinations (+/− Nam) relative to the individual components in epidermal keratinocyte and dermal fibroblast cell lines. Cellular functional assays were utilized to confirm the synergistic effects of peptide combinations. Bioinformatics approaches were used to link the synergistic effects of peptide combinations on gene expression to the transcriptomics of the skin rejuvenation response from fractional laser treatment.

Results

Microarray analysis of skin cells treated with peptide combinations revealed synergistic changes in gene expression compared with individual peptide controls. Bioinformatic analysis of synergy genes in keratinocytes revealed the activation of NRF2‐mediated oxidative stress responses by a combination of Ac‐PPYL, Pal‐KTTKS and Nam. Additional analysis revealed direct downstream transcriptional targets of NRF2/ARE exhibiting synergistic regulation by this combination of materials, which was corroborated by a cellular reporter assay. NRF2‐mediated oxidative stress response pathways were also found to be activated in the transcriptomics of the early skin rejuvenation response to fractional laser treatment, suggesting the importance of this biology in the early stages of tissue repair. Additionally, the second combination of peptides (pal‐KT and Ac‐PPYL) was found to synergistically restore cellular ATP levels that had been depleted due to the presence of ROS, indicating an additional mechanism, whereby peptide synergies may accelerate skin repair.

Conclusion

Through combinatorial synergy studies, we have identified additional in vitro skin repair mechanisms beyond the previously described functions of individual peptides and correlated these to the transcriptomics of the skin rejuvenation response of fractional laser treatment. These findings suggest that specific peptides can act together, via complementary and synergistic mechanisms, to holistically enhance the regenerative capacity of in vitro skin cells.

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.

PLGA nanoparticles containing Lingzhi extracts rescue corneal epithelial cells from oxidative damage

Oxidative stress-related ocular surface epithelial damage can be initiated by ambient oxygen, UV radiation, and chemical burns. The oxidative damage to cornea can lead to inflammation and even vision loss. Lingzhi (Ganoderma lucidum) is a Chinese herbal drug and has been shown to prevent chronic diseases in clinical practices and has been proven to possess anti-oxidative and anti-inflammatory properties. In the study, we prepared poly (lactic-co-glycolic acid) (PLGA) nanoparticles (NPs) as a sustained drug release system of Lingzhi (LZH) to improve bioavailability. The particle size of developed NPs containing LZH (LZH-NPs) was ~184 nm with narrow size distribution. The results of cellular uptake revealed that using NPs as a drug delivery system could significantly increases the intracellular retention time. The results of the cell viability and chemiluminescence assay revealed that 5 μg/ml of LZH-NPs might be the threshold concentration for cultivation of corneal epithelial cells. After treating LZH-NPs in oxidative damaged cells, the results showed that the inflammation-related gene expression and DNA fragmentation level were both significantly decreased. Post-treatment of LZH-NPs in damaged corneal epithelial cells could increase the cell survival rate. In the rabbit corneal alkali burn model, topical instillation of LZH-NPs could promote corneal wound healing and decrease the inflammation. These results suggest that LZH-NPs may have the potential to treat ocular surface diseases caused by oxidative stress.

Enhanced Nrf2 up-regulation by extracellular basic pH in a human skin equivalent system

Extracellular basic pH regulates cellular processes in wounds, and consequently influenced wound healing. Oxidative defence system modulation in the skin helps heal wounds, inhibits skin ageing and improves the skin condition. Moreover, the role of keratinocyte growth factor (KGF) and nuclear factor erythroid 2‐related factor 2 (Nrf2) in antioxidant systems has been reported in various skin models. However, the effects of extracellular basic pH on wound‐ or skin ageing‐related skin damage have not been examined. Thus, we investigated the antioxidant systems affected by extracellular basic pH in a 3D human skin equivalent system (3HSE). Extracellular basic pH decreased KGF expression and enhanced the oxidative defence system, and thus activated Nrf2 in the 3HSE. Additionally, extracellular basic pH and KGF treatment up‐regulated Nrf2 activation and its regulation of the oxidative defence system in the 3HSE. This indicates that Nrf2 up‐regulation is enhanced by reactive oxygen species production, rather than KGF, and by extracellular basic pH of the skin. The inhibition of skin damage through pH imbalance and KGF regulation suggests that the development of pH‐regulating or pH‐maintaining materials may provide effective therapeutic strategies for maintaining a healthy skin.

Perillaldehyde Ameliorates Aspergillus fumigatus Keratitis by Activating the Nrf2/HO-1 Signaling Pathway and Inhibiting Dectin-1-Mediated Inflammation

Purpose

The purpose of this study was to investigate the therapeutic effect of perillaldehyde (PAE) on Aspergillus fumigatus (A. fumigatus) keratitis.

Methods

Human corneal epithelial cells (HCECs) were pretreated with PAE and stimulated with A. fumigatus mycelium. C57BL/6 mice were infected with A. fumigatus and treated with or without PAE 1 day after infection. Clinical scores, PCR, ELISA, and Western blotting were used to detect the expression of pro-inflammatory mediators, dendritic cell-associated c-type lectin-1 (Dectin-1), nuclear factor (erythroid-derived 2) like 2 (Nrf2), and heme oxygenase (HO-1). Nrf2 expression in HCECs pretreated with PAE was observed by immunofluorescence. NIMP-R14 protein expression and localization in mouse corneas were observed by immunofluorescence staining after treatment with PAE. Corneal colony counting, time-kill tests, and mycelial transformation inhibition tests were used to evaluate the antifungal effect of PAE.

Results

C57BL/6 mice treated with PAE at 1 day after infection had a lower clinical score and decreased IL-1β, TNF-α, IL-6, Dectin-1, and MPO levels. PAE treatment significantly reduced neutrophil recruitments to the corneal stroma. Compared with the DMSO-treated group, PAE treatment significantly decreased mRNA and protein levels of pro-inflammatory cytokines and Dectin-1 in HCECs. PAE pretreatment before A. fumigatus stimulation obviously elevated the mRNA and protein levels of components of the Nrf2/HO-1 axis. HCECs pretreated with PAE before infection showed a weakened ability to inhibit inflammation in the presence of brusatol (BT; an Nrf2 inhibitor) or ZnPP (an HO-1 inhibitor). PAE treatment significantly reduced the fungal load of C57BL/6 mouse corneas and inhibited fungal growth in vitro.

Conclusions

These data proved that PAE may ameliorate A. fumigatus keratitis by activating the Nrf2/HO-1 signaling pathway and inhibiting the Dectin-1 mediated inflammatory response and neutrophil recruitment. Furthermore, PAE exerts direct fungicidal activity on A. fumigatus.

Paeoniflorin accelerates foot wound healing in diabetic rats though activating the Nrf2 pathway

As one of the most frequent diabetic complications, diabetic foot ulcer (DFU) can cause limb ischemia or even amputation. Paeoniflorin (PF) has been reported to possess many kinds of biological functions, such as antioxidant and anti-inflammatory effects. However, the role of PF in DFU remains unknown. In this study, streptozotocin (STZ)-induced diabetic rat models and high glucose (HG)-treated Human immortalized keratinocytes (HaCaT) cells were established. Histological analysis, immunohistochemistry, Electrophoretic mobility shift assay, MTT assay, TUNEL assay, oxidative stress analysis, ELISA assay and western blot were used to investigate the role and underlying mechanisms of PF on healing in DFU. Our results showed that the STZ-induced diabetic rats had delayed wound healing compared with the normal rats, exhibited by intense oxidative DNA damage, low vascular endothelial growth factor (VEGF) and transforming growth factor β1 (TGF-β1) expression, as well as increased apoptosis. PF treatment activated the expression of nuclear factor-E2-related factor 2 (Nrf2) and improved wound healing in DFU rats. Our in vitro experiments confirmed that PF accelerated wound healing through the Nrf2 pathway under hyperglycemic conditions, with alleviated oxidative stress, increased cell proliferation and migration, decreased apoptosis, and increased the expression of VEGF and TGF-β1. Our study demonstrates the therapeutic benefits of PF in diabetic wound healing, which provides a reference for future clinical trials using PF in DFU treatment.

Antifibrotic effects of sulforaphane treatment on gingival elasticity reduces orthodontic relapse after rotational tooth movement in beagle dogs

Objective

Increased gingival elasticity has been implicated as the cause of relapse following orthodontic rotational tooth movement and approaches to reduce relapse are limited. This study aimed to investigate the effects of sulforaphane (SFN), an inhibitor of osteoclastogenesis, on gene expression in gingival fibroblasts and relapse after rotational tooth movement in beagle dogs.

Methods

The lower lateral incisors of five beagle dogs were rotated. SFN or dimethylsulfoxide (DMSO) were injected into the supra-alveolar gingiva of the experimental and control group, respectively, and the effect of SFN on relapse tendency was evaluated. Changes in mRNA expression of extracellular matrix components associated with gingival elasticity in beagles were investigated by real-time polymerase chain reaction. Morphology and arrangement of collagen fibers were observed on Masson's trichrome staining of buccal gingival tissues of experimental and control teeth.

Results

SFN reduced the amount and percentage of relapse of orthodontic rotation. It also decreased the gene expression of lysyl oxidase and increased the gene expression of matrix metalloproteinase (MMP) 1 and MMP 12, compared with DMSO control subjects. Histologically, collagen fiber bundles were arranged irregularly and were not well connected in the SFN-treated group, whereas the fibers extended in parallel and perpendicular directions toward the gingiva and alveolar bone in a more regular and well-ordered arrangement in the DMSO-treated group.

Conclusions

Our findings demonstrated that SFN treatment may be a promising pharmacologic approach to prevent orthodontic rotational relapse caused by increased gingival elasticity of rotated teeth in beagle dogs.

Keratinocyte-Macrophage Crosstalk by the Nrf2/Ccl2/EGF Signaling Axis Orchestrates Tissue Repair

Unveiling the molecular mechanisms underlying tissue regeneration provides new opportunities to develop treatments for diabetic ulcers and other chronic skin lesions. Here, we show that Ccl2 secretion by epidermal keratinocytes is directly orchestrated by Nrf2, a prominent transcriptional regulator of tissue regeneration that is activated early after cutaneous injury. Through a unique feedback mechanism, we find that Ccl2 from epidermal keratinocytes not only drives chemotaxis of macrophages into the wound but also triggers macrophage expression of EGF, which in turn activates basal epidermal keratinocyte proliferation. Notably, we find dysfunctional activation of Nrf2 in epidermal keratinocytes of diabetic mice after wounding, which partly explains regenerative impairments associated with diabetes. These findings provide mechanistic insight into the critical relationship between keratinocyte and macrophage signaling during tissue repair, providing the basis for continued investigation of the therapeutic value of Nrf2.

Corneal Opacity Induced by Light in a Mouse Model of Gelatinous Drop-Like Corneal Dystrophy

Gelatinous drop-like corneal dystrophy (GDLD) is a severe inherited corneal dystrophy characterized by subepithelial corneal amyloid deposition. We had previously succeeded in identifying the responsible gene, TACSTD2, and subsequently found that the epithelial barrier function is significantly decreased. As with GDLD patients, the knockout mice showed severe loss of tight junction, progressive opacity, and neovascularization in the cornea. We devised an easy method to confirm the loss of the corneal barrier function even before corneal opacity is observed. Furthermore, by using knockout mice, we were able to verify clinical findings, such as the wound healing delay and light-induced acceleration of the disease. This mouse model should prove to be a highly useful tool for investigating the pathology of GDLD and for developing new therapies.

Pharmaceutic application of vitamin D3 on particle-induced fibrotic effects through induction of Nrf2 signals

Fine particulate matter, a major air pollutant across the world, causes a series of pulmonary diseases. Vitamin D is a typical vitamin with emerging roles in inflammation and fibrosis. Different situations and diseases need different doses and modes of vitamin D administration, which challenges the existing vitamin D supplementary rules. Thus, studies of vitamin D applications and their mechanisms in various diseases are important for its future therapeutic applications. In this study, the therapeutic application of vitamin D₃ in chronic particle-exposure-associated lung fibrosis and tissue remodeling was investigated. In vivo studies showed that vitamin D₃ significantly attenuated fibrosis effects by decreasing α-smooth muscle actin-regulated extracellular matrix deposition and restoring expressions of E-cadherin and N-cadherin. With the importance of activated macrophage in the regulation of local epithelium and fibroblast in the process of tissue fibrosis, two separate in vitro systems of co-culture of macrophages with lung epithelium or fibroblast were built. The results confirmed that vitamin D₃ promoted the proliferation of lung epithelium and depressed the fibrosis effects of fibroblasts as well. In addition, our results indicated that the therapeutic effects of vitamin D₃ were through Nrf2 signals. Our work provides convincing experimental evidence for vitamin D therapeutic application to promote tissue repair and improve particle-associated lung fibrosis.

Potential Protective and Therapeutic Roles of the Nrf2 Pathway in Ocular Diseases: An Update

Nuclear factor- (erythroid-derived 2-) like 2 (Nrf2) is a regulator of many processes of life, and it plays an important role in antioxidant, anti-inflammatory, and antifibrotic responses and in cancer. This review is focused on the potential mechanism of Nrf2 in the occurrence and development of ocular diseases. Also, several Nrf2 inducers, including noncoding RNAs and exogenous compounds, which control the expression of Nrf2 through different pathways, are discussed in ocular disease models and ocular cells, protecting them from dysfunctional changes. Therefore, Nrf2 might be a potential target of protecting ocular cells from various stresses and preventing ocular diseases.

Dimethyl itaconate protects against fungal keratitis by activating the Nrf2/HO-1 signaling pathway

Dimethyl itaconate (DI) is a membrane‐permeable itaconate derivative with anti‐inflammatory functions. However, the anti‐inflammatory effect of DI has never been studied in fungal keratitis. In this study, we tested the protective effect of DI against fungal keratitis and assessed the role of NF‐E2‐related factor‐2 (Nrf2)/heme oxygenase‐1 (HO‐1) signaling in this process. Eyes of C57BL/6 (B6) mice were treated with 2 mm DI after infection with Aspergillus fumigatus. Human corneal epithelial cells (HCECs) were pretreated with 0.25 mm DI and then incubated with A. fumigatus. Clinical scoring, slit‐lamp photography, myeloperoxidase determination, flow cytometry and immunostaining were used to assess the disease response and treatment efficacy. PCR, Western blot and ELISA were used to assess the expression of interleukin‐1β (IL‐1β), chemokine (C–X–C motif) ligand 1, IL‐6, IL‐8, Nrf2 and HO‐1. In addition, quantification of viable fungi, absorbance assays and fluorimetry were used to measure DI fungistatic activity. We observed that DI‐treated eyes showed decreased clinical scores, fungal loads, polymorphonuclear neutrophil (PMN) infiltration and cytokine expression, compared with phosphate‐buffered saline‐treated infected eyes. DI treatment decreased the cytokine levels in infected corneas and in HCECs stimulated with A. fumigatus. Moreover, DI treatment increased Nrf2 and HO‐1 expression in corneas and nuclear Nrf2 accumulation in HCECs. DI‐induced cytokine downregulation was inhibited by pretreatment with an Nrf2 or HO‐1 inhibitor. Finally, DI treatment reduced the A. fumigatus absorbance and fungal mass. These data indicate that DI protects against fungal keratitis by limiting inflammation via the Nrf2/HO‐1 signaling pathway and that DI inhibits the growth of A. fumigatus.

MicroRNA expression profile of Lacrimal Glands in rabbit autoimmune dacryoadenitis model

Purpose: To identify the differential expression of microRNAs (miRs) and the related gene networks and signal pathways in lacrimal glands (LGs) of rabbit autoimmune dacryoadenitis. Methods: Autoimmune dacryoadenitis in rabbits was induced by transferring activated peripheral blood lymphocytes (PBLs). The LGs of normal and model group rabbits were collected for small RNA sequencing. The most differentially expressed miRs were validated by quantitative real time-polymerase chain reaction (qRT-PCR). Further, bioinformatics analysis including target gene prediction, Gene Ontology (GO) terms and Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway enrichment analyses were performed. Results: A total of 15 miRs were differentially expressed in the LGs of rabbit autoimmune dacryoadenitis relative to normal controls. GO and KEGG analysis revealed that most target genes of these dysregulated miRs were implicated in MAPK signaling pathway. Conclusion: Our results showed for the first time the differentially expressed miRs and the related pathways involved in the pathogenesis of rabbit autoimmune dacryoadenitis. These results may contribute to elucidating molecular pathogenesis of Sjögren's syndrome (SS) dry eye.

Remodeling of Substance P Sensory Nerves and Transient Receptor Potential Melastatin 8 (TRPM8) Cold Receptors After Corneal Experimental Surgery

Purpose

To investigate changes in corneal nerves positive to substance P (SP) and transient receptor potential melastatin 8 (TRPM8) and gene expression in the trigeminal ganglia (TG) following corneal surgery to unveil peripheral nerve mechanism of induced dry eye-like pain (DELP).

Methods

Surgery was performed on mice by removing the central epithelial and anterior stromal nerves. Mice were euthanized at different times up to 15 weeks. Immunostaining was performed with TRPM8, SP, or protein gene product 9.5 (PGP9.5) antibodies, and epithelial nerve densities were calculated. The origin of TRPM8- and SP-TG neurons were analyzed by retrograde tracing. Gene expression in TG was studied by real-time PCR analysis.

Results

SP-positive epithelial corneal nerves were more abundant than TRPM8 and were expressed in different TG neurons. After injury, epithelial nerve regeneration occurs in two distinct stages. An early regeneration of the remaining epithelial bundles reached the highest density on day 3 and then rapidly degraded. From day 5, the epithelial nerves originated from the underlying stromal nerves were still lower than normal levels by week 15. The SP- and TRPM8-positive nerve fibers followed the same pattern as the total nerves. TRPM8-positive terminals increased slowly and reached only half of normal values by 3 months. Corneal sensitivity gradually increased and reached normal values on day 12. Corneal injury also induced significant changes in TG gene expression, decreasing trpm8 and tac1 genes.

Conclusions

Abnormal SP expression, low amounts of TRPM8 terminals, and hypersensitive nerve response occur long after the injury and changes in gene expression in the TG suggest a contribution to the pathogenesis of corneal surgery-induced DELP.

Tissue-specific role of Nrf2 in the treatment of diabetic foot ulcers during hyperbaric oxygen therapy

Hyperbaric oxygen (HBO) therapy is proven to be very successful for diabetic foot ulcer (DFU) treatment due to its antimicrobial effect, increased angiogenesis and enhanced collagen synthesis. The molecular mechanism underlying HBO therapy particularly the involvement of Nrf2 in the wound healing process was investigated in the present study. In addition, we have studied the levels of angiogenic markers in ulcer tissues and their correlation with Nrf2 during HBO therapy compared with standard therapy (Non-HBO) for DFU. A total of 32 Patients were recruited and randomized to standard wound care procedure alone (n = 17) or HBO therapy in combination with standard wound care procedure (n = 15) for 20 days. Our results showed that the tissue levels of Nrf2 along with its downstream targets were significantly increased in patients who underwent HBO therapy when compared to Non-HBO therapy. Further, HBO therapy induced angiogenesis as assessed by increased levels of angiogenesis markers such as EGF, VEGF, PDGF, FGF-2 and CXCL10 in the tissue samples. The expressions of eNOS and nitrite concentrations were also significantly increased in HBO therapy when compared to Non-HBO therapy subjects. Moreover, HBO therapy sensitises the macrophages to release FGF-2 and EGF thereby promotes angiogenesis. Further, it increased the levels of neutrophil attractant CXCL-8 thereby promotes the release of chemokine CCL2, a well-known mediator of neovascularization. The Pearson correlation showed that Nrf2 has a positive correlation with EGF, VEGF and PDGF. In conclusion, the findings of the present study suggest that HBO therapy promotes wound healing by increasing oxygen supply and distribution to damaged tissues, stimulating angiogenesis, decreasing inflammation, and increasing the nitrite levels. Increased levels of Nrf2 transiently regulate the expression of angiogenic genes in wound biopsies, which may result in accelerated healing of chronic wounds.

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.

Bee venom improves diabetic wound healing by protecting functional macrophages from apoptosis and enhancing Nrf2, Ang-1 and Tie-2 signaling

Impaired wound healing is a serious complication of diabetes that negatively affects the patient's socioeconomic life. Multiple mechanisms contribute to impaired diabetic wound healing including deficient recruitment of wound macrophages/neutrophils and impaired neovascularization. Bee venom (BV) has been used as an anti-inflammatory agent for the treatment of several diseases. Nevertheless, the impacts of BV on the diabetic wound healing have been poorly studied. In the present study, we investigated the molecular mechanisms underlying BV treatment on diabetic wound healing in a type I diabetic mouse model. Three experimental groups were used: group 1, non-diabetic control mice; group 2, vehicle-diabetic mice; and group 3, BV-treated diabetic mice. We found that the diabetic mice exhibited impaired wound closure characterized by a significant decrease in collagen and β-defensin-2 (BD-2) expression compared to control non-diabetic mice. The impairment of diabetic wound healing is attributed to increased ROS levels and abolished antioxidant enzymes activity in the wounded tissues. Additionally, wounded tissue in diabetic mice revealed aberrantly decreased levels of Ang-1 and Nrf2 (the agonist ligands of Tie-2) followed by a marked reduction in the phosphorylation of Tie2 and downstream signaling eNOS, AKT and ERK. Impaired diabetic wound healing was also characterized by a significant reduction in activities of total antioxidant enzymes followed by a marked reduction in the levels of CCL2, CCL3 and CXCL2; which led to impaired recruitment and functions of wound macrophages/neutrophils; and significant reduction in the expression of CD31, a marker for neovascularization and angiogenesis of the injured tissue. Interestingly, BV treatment significantly enhanced wound closure in diabetic mice by increasing collagen and BD-2 expression and restoring the levels of Ang-1 and Nrf2 and hence enhancing the Tie-2 downstream signaling. Most importantly, treatment of diabetic mice with BV significantly restored the activities of wounded tissue antioxidant enzymes and the levels of chemokines, and subsequently rescued wound macrophages from mitochondrial membrane potential-induced apoptosis. Our findings reveal the immune-enhancing effects of BV for improving healing process of diabetic wounds and provide the first insight concerning the underlying molecular mechanisms.

Therapeutic potential of bixin in PM2.5 particles-induced lung injury in an Nrf2-dependent manner

Fine particulate matter (PM 2.5) is a well-known air pollutant threatening public health. Studies has confirmed that long-term exposure to the particles could reduce the pulmonary function, cause exacerbation of asthma and chronic obstructive pulmonary disease, and increase incidence and mortality of lung cancer. Bixin is a natural compound that is widely used as a food additive. Our previous studies demonstrated that bixin i.p. administration could protect against particles intratracheal exposure (56 days)-induced lung injury in an Nrf2-dependent manner. But the detail mechanisms are still unclarified. Our current study aimed to explore the further therapeutic potential and mechanism of bixin to slow the progression of lung injury and inflammation in vivo and in vitro. The results from the in vivo study showed that bixin treatment attenuated the accumulation of inflammatory cells, decreased the levels of tissue apoptosis, and increase the ability of cell proliferation. Besides that, bixin also could regulate the expression of MMP9, TGFβ1, and its downstream Fibronectin (FN), along with activation of Nrf2 signals. In vitro experiments in human bronchial epithelial cells demonstrated that Nrf2 activated by bixin contributes to tissue repair by alleviating oxidative stress, increasing proliferation and migration, decreasing apoptosis, which may be partially through modulating the expression of MMP9, TGFβ1, and FN. This study provides convincing experimental evidences that bixin could be used therapeutically to promote tissue repair and improve pulmonary injury induced by particles exposure.

Nrf2 at the heart of oxidative stress and cardiac protection

The NFE2L2 gene encodes the transcription factor Nrf2 best known for regulating the expression of antioxidant and detoxification genes. Gene knockout approaches have demonstrated its universal cytoprotective features. While Nrf2 has been the topic of intensive research in cancer biology since its discovery in 1994, understanding the role of Nrf2 in cardiovascular disease has just begun. The literature concerning Nrf2 in experimental models of atherosclerosis, ischemia, reperfusion, cardiac hypertrophy, heart failure, and diabetes supports its cardiac protective character. In addition to antioxidant and detoxification genes, Nrf2 has been found to regulate genes participating in cell signaling, transcription, anabolic metabolism, autophagy, cell proliferation, extracellular matrix remodeling, and organ development, suggesting that Nrf2 governs damage resistance as well as wound repair and tissue remodeling. A long list of small molecules, most derived from natural products, have been characterized as Nrf2 inducers. These compounds disrupt Keap1-mediated Nrf2 ubquitination, thereby prohibiting proteasomal degradation and allowing Nrf2 protein to accumulate and translocate to the nucleus, where Nrf2 interacts with sMaf to bind to ARE in the promoter of genes. Recently alternative mechanisms driving Nrf2 protein increase have been revealed, including removal of Keap1 by autophagy due to p62/SQSTM1 binding, inhibition of βTrCP or Synoviolin/Hrd1-mediated ubiquitination of Nrf2, and de novo Nrf2 protein translation. We review here a large volume of literature reporting historical and recent discoveries about the function and regulation of Nrf2 gene. Multiple lines of evidence presented here support the potential of dialing up the Nrf2 pathway for cardiac protection in the clinic.

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.

Non-steroidal anti-inflammatory drug delays corneal wound healing by reducing production of 12-hydroxyheptadecatrienoic acid, a ligand for leukotriene B4 receptor 2

Non-steroidal anti-inflammatory drugs (NSAIDs) are widely used to reduce inflammation by suppressing cyclooxygenases (COXs). NSAID eye drops are frequently prescribed after ocular surgery to reduce inflammation and pain, but this treatment has clinically significant side effects, including corneal ulcer and perforation. The molecular mechanisms underlying these side effects remain unknown. Recently, the COX product 12(S)-hydroxyheptadeca-5Z,8E,10E-trienoic acid (12-HHT) was identified as an endogenous ligand for leukotriene B₄ receptor 2 (BLT2), which is important in maintenance of epithelial homeostasis. We hypothesized that NSAID-dependent corneal damage is caused by reduced production of 12-HHT. Diclofenac eye drops decreased the abundance of downstream products of COX and delayed corneal wound healing in BALB/c mice. Expression of BLT2 was observed in murine ocular tissues including cornea, and in human corneal epithelial cell line and human primary corneal epithelial cells. In BLT2-knockout mice, corneal wound healing was delayed, but the diclofenac-dependent delay in corneal wound healing disappeared. 12-HHT accelerated wound closure both in BLT2-transfected corneal cell line and human primary corneal epithelial cells. Thus, our results reveal that NSAIDs delay corneal wound healing by inhibiting 12-HHT production, and suggest that stimulation of the 12-HHT/BLT2 axis represents a novel therapeutic approach to corneal wound healing.

Glutathione peroxidase 4 plays an important role in oxidative homeostasis and wound repair in corneal epithelial cells

Oxidative stress is involved in the pathologies of corneal epithelial cells. However, the importance of specific antioxidant enzymes in corneal epithelial cells is not fully understood. The purpose of this study is to elucidate the role of glutathione peroxidase 4 (GPx4) in corneal epithelial cells. For in vitro experiments, an immortalized human corneal epithelial cell line was used. Cytotoxicity measured through LDH activity, lipid peroxidation immunostained for 4‐hydroxynonenal, cell viability, and cell death were compared between cells transfected with either GPx4 siRNA or scrambled control siRNA. In addition, the rescue effects of α‐tocopherol and ferrostatin‐1, a ferroptosis inhibitor, were examined in the cells with deficient GPx4 expression. For in vivo experiments, we applied n‐heptanol on the cornea of GPx4^+/+ and GPx4^+/− mice to create corneal epithelial wound. The epithelial defect area size was measured up to 48 h after epithelial wound creation. Knockdown of GPx4 strongly induced cytotoxicity and cell death in human corneal epithelial cells. Cell death induced by GPx4 knockdown was characterized by positive staining for both annexin V and propidium iodide, nuclear translocation of AIF, and without activation of caspase 3, and was rescued by α‐tocopherol and ferrostatin‐1. The delayed wound healing of GPx4 siRNA‐transfected cells were ameliorated by α‐tocopherol in vitro. In addition, loss of one GPx4 allele was sufficient to significantly delay the healing of experimental corneal epithelial wounds in vivo. Our results suggest that the antioxidant enzyme GPx4 plays an important role in oxidative homeostasis, cell survival, and wound healing in corneal epithelial cells.

An Essential Role of NRF2 in Diabetic Wound Healing

The high mortality and disability of diabetic nonhealing skin ulcers create an urgent need for the development of more efficacious strategies targeting diabetic wound healing. In the current study, using human clinical specimens, we show that perilesional skin tissues from patients with diabetes are under more severe oxidative stress and display higher activation of the nuclear factor-E2-related factor 2 (NRF2)-mediated antioxidant response than perilesional skin tissues from normoglycemic patients. In a streptozotocin-induced diabetes mouse model, Nrf2(-/-) mice have delayed wound closure rates compared with Nrf2(+/+) mice, which is, at least partially, due to greater oxidative DNA damage, low transforming growth factor-β1 (TGF-β1) and high matrix metalloproteinase 9 (MMP9) expression, and increased apoptosis. More importantly, pharmacological activation of the NRF2 pathway significantly improves diabetic wound healing. In vitro experiments in human immortalized keratinocyte cells confirm that NRF2 contributes to wound healing by alleviating oxidative stress, increasing proliferation and migration, decreasing apoptosis, and increasing the expression of TGF-β1 and lowering MMP9 under high-glucose conditions. This study indicates an essential role for NRF2 in diabetic wound healing and the therapeutic benefits of activating NRF2 in this disease, laying the foundation for future clinical trials using NRF2 activators in treating diabetic skin ulcers.

Hydrogen-Rich Water Intake Accelerates Oral Palatal Wound Healing via Activation of the Nrf2/Antioxidant Defense Pathways in a Rat Model

The wound healing process attempts to restore the integrity and function of the injured tissue. Additionally, proinflammatory cytokines, growth factors, and oxidative stress play important roles in wound healing. The aim of this study was to determine whether hydrogen-rich water intake induces the activation of the Nrf2/antioxidant defense pathway in rat palatal tissue, thereby reducing systemic oxidative stress and proinflammatory cytokine levels and promoting healing-associated genes. A circular excisional wound was created in the oral palatal region, and the wound healing process was observed. The rats were divided into two experimental groups in which either hydrogen-rich water or distilled water was consumed. In the drinking hydrogen-rich water, the palatal wound healing process was accelerated compared to that in the control group. As molecular hydrogen upregulated the Nrf2 pathway, systemic oxidative stresses were decreased by the activation of antioxidant activity. Furthermore, hydrogen-rich water intake reduced proinflammatory cytokine levels and promoted the expression of healing-associated factors in rat palatal tissue. In conclusion, hydrogen-rich water intake exhibited multiple beneficial effects through activation of the Nrf2/antioxidant defense pathway. The results of this study support the hypothesis that oral administration of hydrogen-rich water benefits the wound healing process by decreasing oxidative stress and inflammatory responses.

Frequency Modulated Translocational Oscillations of Nrf2 Mediate the Antioxidant Response Element Cytoprotective Transcriptional Response

AIMS

Stress responsive signaling coordinated by nuclear factor erythroid 2-related factor 2 (Nrf2) provides an adaptive response for protection of cells against toxic insults, oxidative stress and metabolic dysfunction. Nrf2 regulates a battery of protective genes by binding to regulatory antioxidant response elements (AREs). The aim of this study was to examine how Nrf2 signals cell stress status and regulates transcription to maintain homeostasis.

RESULTS

In live cell microscopy we observed that Nrf2 undergoes autonomous translocational frequency-modulated oscillations between cytoplasm and nucleus. Oscillations occurred in quiescence and when cells were stimulated at physiological levels of activators, they decrease in period and amplitude and then evoke a cytoprotective transcriptional response. We propose a mechanism whereby oscillations are produced by negative feedback involving successive de-phosphorylation and phosphorylation steps. Nrf2 was inactivated in the nucleus and reactivated on return to the cytoplasm. Increased frequency of Nrf2 on return to the cytoplasm with increased reactivation or refresh-rate under stress conditions activated the transcriptional response mediating cytoprotective effects. The serine/threonine-protein phosphatase PGAM5, member of the Nrf2 interactome, was a key regulatory component.

INNOVATION

We found that Nrf2 is activated in cells without change in total cellular Nrf2 protein concentration. Regulation of ARE-linked protective gene transcription occurs rather through translocational oscillations of Nrf2. We discovered cytoplasmic refresh rate of Nrf2 is important in maintaining and regulating the transcriptional response and links stress challenge to increased cytoplasmic surveillance. We found silencing and inhibition of PGAM5 provides potent activation of Nrf2.

CONCLUSION

Frequency modulated translocational oscillations of Nrf2 mediate the ARE-linked cytoprotective transcriptional response.

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

Retinal pigment epithelial cells exert an important supporting role in the eye and develop adaptive responses to oxidative stress or high glucose levels, as observed during diabetes. Endogenous antioxidant defences are mainly regulated by Nrf2, a transcription factor that is activated by naturally-derived and electrophilic compounds. Here we investigated the effect of the Nrf2 activators dimethylfumarate (DMF) and carnosol on antioxidant pathways, oxygen consumption rate and wound healing in human retinal pigment epithelial cells (ARPE-19) cultured in medium containing normal (NG, 5mM) or high (HG, 25 mM) glucose levels. We also assessed wound healing using an in vivo corneal epithelial injury model. We found that Nrf2 nuclear translocation and heme oxygenase activity increased in ARPE cells treated with 10 μM DMF or carnosol irrespective of glucose culture conditions. However, HG rendered retinal cells more sensitive to regulators of glutathione synthesis or inhibition and caused a decrease of both cellular and mitochondrial reactive oxygen species. Culture in HG also reduced ATP production and mitochondrial function as measured with the Seahorse XF analyzer and electron microscopy analysis revealed morphologically damaged mitochondria. Acute treatment with DMF or carnosol did not restore mitochondrial function in HG cells; conversely, the compounds reduced cellular maximal respiratory and reserve capacity, which were completely prevented by N-acetylcysteine thus suggesting the involvement of thiols in this effect. Interestingly, the scratch assay showed that wound closure was faster in cells cultured in HG than NG and was accelerated by carnosol. This effect was reversed by an inhibitor of heme oxygenase activity. Moreover, topical application of carnosol to the cornea of diabetic rats significantly accelerated wound healing. In summary, these data indicate that culture of retinal epithelial cells in HG does not affect the activation of the Nrf2/heme oxygenase axis but influences other crucial oxidative and mitochondrial-dependent cellular functions. The additional effect on wound closure suggests that results obtained in in vitro experimental settings need to be carefully evaluated in the context of the glucose concentrations used in cell culture.

Nrf2 activation attenuates both orthodontic tooth movement and relapse

During orthodontic tooth movement, osteoclasts resorb the alveolar bone at the compress side of periodontium. Reactive oxygen species (ROS) works as intracellular signaling molecules of RANKL during osteoclastogenesis, although ROS has cytotoxicity against cells such as lipid oxidation. To deal with oxidative stress, cells have a defense system that is scavenging ROS by augmented antioxidative stress enzymes via transcriptional regulation with nuclear factor E2-related factor 2 (Nrf2). Previously, we reported that augmented antioxidative stress enzymes by Nrf2-gene transfer inhibited bone destruction. In the present study, we examined the effects of Nrf2 activation on osteoclastogenesis and, thereby, orthodontic tooth movement and orthodontic relapse. Mouse macrophage cell line RAW264.7 cells were used as osteoclast progenitor cells and stimulated with recombinant RANKL (100 ng/mL) with or without Nrf2 activator sulforaphane (SFN) and epigallocatechin gallate (EGCG) or ROS scavenger catechin. Osteoclastogenesis, resorption activity, and osteoclast marker gene expression were examined. Intracellular ROS was analyzed by flow cytometry. Maxillary first molars of C57BL6 male mice were moved palatally with 0.012-inch NiTi wire (100-mN force); SFN or EGCG was injected into the palatal gingiva once a week; and phosphate buffered saline was injected on the contralateral side. Tooth movement was monitored using a stone model with precise impression, and the amount of the tooth movement was compared among groups. SFN and EGCG significantly, but catechin weakly, inhibited RANKL-mediated osteoclastogenesis in vitro. Western blot analysis revealed that SFN and EGCG augmented the nuclear translocation of Nrf2 and the expression of anti-oxidative stress enzymes such as HO-1, although catechin did not. SFN and EGCG significantly, but catechin weakly, attenuated the intracellular ROS. Finally, animal experiment revealed that both SFN and EGCG successfully inhibited the orthodontic tooth movement. Additionally, SFN inhibited the relapse. These results suggest that Nrf2 activation could be therapeutic target for the anchorage enforcement in orthodontic treatment and pharmacologic retention against relapse.

Activation of NRF2 Signaling in HEK293 Cells by a First-in-Class Direct KEAP1-NRF2 Inhibitor

Under basal conditions, the antioxidant transcription factor nuclear factor (erythroid-derived 2)-like 2 (NRF2) is bound to the Kelch-like ECH-associated protein 1 (KEAP1) protein and targeted for proteasomal degradation in the cytoplasm. In response to cellular injury or chemical treatment, NRF2 dissociates from KEAP1 and activates the transcription of protective genes and defends against injury. LH601A is a first-in-class direct inhibitor of the KEAP1-NRF2 protein-protein interaction. The purpose of this study was to determine whether LH601A activates NRF2 signaling in human kidney cells. Human embryonic kidney 293 (HEK293) cells were treated with LH601A or the indirect NRF2 activator, sulforaphane (SFN) for 6 or 16 h. SFN and LH601A upregulated NRF2 target genes heme oxygenase-1 (HO-1) (two- to sevenfold), thioredoxin 1 (TRX1) (twofold) and NAD(P)H quinone oxidoreductase 1 (NQO1) mRNAs (twofold). Both compounds also elevated HO-1 and TRX1 protein expression. Since NRF2 activation can protect tissues from injury, LH601A, a direct inhibitor of the KEAP1-NRF2 interaction may be used to defend against kidney injury and/or diseases.