Cinnamoyl-based Nrf2-activators targeting human skin cell photo-oxidative stress

Glutathione-sensitive mesoporous nanoparticles loaded with cinnamaldehyde for chemodynamic and immunological therapy of cancer

Chemodynamic therapy as a novel type of chemotherapy can damage the DNA structures and induce cell apoptosis and immunogenic cell death (ICD) through generating reactive oxygen species (ROS) to aggravate oxidative stress. Nonetheless, as an intrinsic antioxidative response of tumor cells, the expression of glutathione (GSH) can be upregulated to maintain the cellular redox balance and protect the tumor cells from ROS-mediated damage. In this context, it is feasible to simultaneously boost ROS generation and GSH depletion in tumor cells; however, the precise delivery and release of GSH scavengers at specific subcellular sites is of great importance. Herein, we propose a GSH-responsive mesoporous organosilica nanoparticle (MON)-based nanomedicine MON-CA-TPP@HA through sequentially covalently attaching triphenylphosphine (TPP) and electrostatically coating hyaluronic acid (HA) onto the surface of cinnamaldehyde (CA)-loaded MONs, known as MON-CA-TPP@HA, which has been demonstrated to be an extremely effective therapeutic strategy for cancer treatment through inducing ICD and apoptosis of breast cancer cells. Systematic in vitro experimental results clearly revealed that the nanomedicine can actively target the tumor cells with the help of HA, subsequently enter the tumor cells, and precisely bind with the mitochondria through TPP residues. Upon cleavaging the disulfide bond in the MONs triggered by over-expressed GSH within tumors, the CA molecules can be released inducing the excessive ROS in situ surrounding the mitochondria to activate oxidative stress to induce apoptosis and ICD of breast cancer cells. The results of the in vivo experiments confirm that the MON-CA-TPP@HA nanomedicine can effectively promote dendritic cell (DC) maturation and CD 8+ T cell activation and regulate the ratio of M1/M2 macrophages, which improve tumor immunosuppressive microenvironment. It is thus believed that the current nanomedicine has paved a new way for future cancer therapy.

Phytochemical Screening and Antioxidant Potential of Selected Extracts from Betula alba var. pendula Roth., Glycyrrhiza glabra L., and Avena sativa L

The aim of the present study was to obtain, characterize, and evaluate the antioxidant potential of some extracts obtained from the bark of Betula alba var. pendula Roth., the root of Glycyrrhiza glabra L., and the green herb of the Avena sativa. The results revealed that the lowest IC50 value, determined by all three methods, was obtained for Betulae extractum (BE) (73.6 µg/mL-DPPH method, 11.2 µg/mL-ABTS method, and 58.7 µg/mL-FRAP method), followed by Liquiritiae extractum (LE) (805.6 µg/mL, 92.1 µg/mL, and 722 µg/mL) and Avenae extractum (1.13 mg/mL-DPPH method, 99.7 µg/mL-ABTS method, and 135.1 µg/mL-FRAP method). These results correlate with total polyphenols content (expressed in g tannic acid/100 g dry extract), with BE having more polyphenols than LE and AE (47.96 ± 9.7083 for BE, compared with 9.31 ± 0.9913 for LE and 40.55 ± 6.3715 for AE). The total flavonoid content (expressed as g rutoside/100 g dry extract) is similar for BE and LE (3.75 ± 0.3140 and 3.44 ± 0.3037) and smaller for AE (1.95 ± 0.0526). Therefore, Betulae extractum has the strongest antioxidant action, with an IC50 value very close to the standard used as a reference (ascorbic acid-16.5 μg/mL solution). The FT-ICR-MS analysis confirmed the presence of the major compounds in all three extracts. The antioxidant properties of the studied extracts were further supported by molecular docking experiments that revealed the potential of the analyzed phytochemicals to act as both noncovalent and covalent activators of the Nrf2 signaling pathway, with promising benefits in treating various skin disorders.

Cinnamaldehyde Supplementation Reverts Endothelial Dysfunction in Rat Models of Diet-Induced Obesity: Role of NF-E2-Related Factor-2

Cinnamaldehyde (CN) is an activator of NF-E2-related factor 2 (Nrf2), which has the potential to reduce endothelial dysfunction, oxidative stress and inflammation in metabolic disorders. Our main purpose was to evaluate the effects of CN on vascular dysfunction in metabolic syndrome rats. Normal Wistar (W) rats were divided into eight groups: (1) Wistar (W) rats; (2) W rats fed with a high-fat diet (WHFD); (3) W rats fed with a sucrose diet (WS); (4) WHFD fed with a sucrose diet (WHFDS); (5) W treated with CN (WCn); (6) WS treated with CN (WSCn); (7) WHFD treated with CN (WHFDCn); (8) WHFDS treated with CN (WHFDSCn). CN treatment with 20 mg/kg/day was administered for 8 weeks. Evaluation of metabolic profile, inflammation, endothelial function, oxidative stress, eNOS expression levels and Nrf2 activation was performed. The metabolic dysfunction was greatly exacerbated in the WHFDS rats, accompanied by significantly higher levels of vascular oxidative stress, inflammation, and endothelial dysfunction. In addition, the WHFDS rats displayed significantly reduced activity of Nrf2 at the vascular level. CN significantly reverted endothelial dysfunction in the aortas and the mesenteric arteries. In addition, CN significantly decreased vascular oxidative damage, inflammation at vascular and perivascular level and up-regulated Nrf2 activity in the arteries of WHFDS rats. Cinnamaldehyde, an activator of Nrf2, can be used to improve metabolic profile, and to revert endothelial dysfunction in obesity and metabolic syndrome.

NRF2 in dermatological disorders: Pharmacological activation for protection against cutaneous photodamage and photodermatosis

The skin barrier and its endogenous protective mechanisms cope daily with exogenous stressors, of which ultraviolet radiation (UVR) poses an imminent danger. Although the skin is able to reduce the potential damage, there is a need for comprehensive strategies for protection. This is particularly important when developing pharmacological approaches to protect against photocarcinogenesis. Activation of NRF2 has the potential to provide comprehensive and long-lasting protection due to the upregulation of numerous cytoprotective downstream effector proteins that can counteract the damaging effects of UVR. This is also applicable to photodermatosis conditions that exacerbate the damage caused by UVR. This review describes the alterations caused by UVR in normal skin and photosensitive disorders, and provides evidence to support the development of NRF2 activators as pharmacological treatments. Key natural and synthetic activators with photoprotective properties are summarized. Lastly, the gap in knowledge in research associated with photodermatosis conditions is highlighted.

Protective actions of nuclear factor erythroid 2-related factor 2 (NRF2) and downstream pathways against environmental stressors

Environmental risk factors, including noise, air pollution, chemical agents, ultraviolet radiation (UVR) and mental stress have a considerable impact on human health. Oxidative stress and inflammation are key players in molecular pathomechanisms of environmental pollution and risk factors. In this review, we delineate the impact of environmental risk factors and the protective actions of the nuclear factor erythroid 2-related factor 2 (NRF2) in connection to oxidative stress and inflammation. We focus on well-established studies that demonstrate the protective actions of NRF2 and its downstream pathways against different environmental stressors. State-of-the-art mechanistic considerations on NRF2 signaling are discussed in detail, e.g. classical concepts like KEAP1 oxidation/electrophilic modification, NRF2 ubiquitination and degradation. Specific focus is also laid on NRF2-dependent heme oxygenase-1 induction with detailed presentation of the protective down-stream pathways of heme oxygenase-1, including interaction with BACH1 system. The significant impact of all environmental stressors on the circadian rhythm and the interactions of NRF2 with the circadian clock will also be considered here. A broad range of NRF2 activators is discussed in relation to environmental stressor-induced health side effects, thereby suggesting promising new mitigation strategies (e.g. by nutraceuticals) to fight the negative effects of the environment on our health.

Preliminary studies of an imidazole-based alcohol derivative for imaging of Heme oxygenase 1

Heme oxygenase-1 (HO-1) has been involved in the pathogenesis of Alzheimer's disease (AD), thus constituting a promising target for AD drug development. Positron emission tomography (PET) is a fully translational imaging technology, which will help us understand the role of HO-1 in the progression of AD, facilitating to validate promising HO-1 inhibitors in clinical trials. To our knowledge, there is no report on PET imaging probe targeting HO-1 in animals and humans. We report herein the synthesis and characterization of a ¹¹C-labeled imidazole-based alcohol derivative ([¹¹C]QC-33) for imaging of HO-1 in the brain. The desired product [¹¹C]QC-33 was afforded with a radiochemical yield of 16 ± 9% (n = 3, decay corrected). The radiochemical purity was greater than 99%, and the molar radioactivity was greater than 185 GBq/μmol. In vitro autoradiography studies indicated specific binding of [¹¹C]QC-33 in the HO-1 rich regions, showing 75%, 75%, and 69% radioactivity binding reductions in cerebellum, brain stem, and midbrain, respectively. PET/CT scanning in C57BL/6 mice showed low brain uptake and poor blood-brain barrier (BBB) penetration of [¹¹C]QC-33. These results suggested that [¹¹C]QC-33 can serve as a lead compound to advance the development of next generation PET tracer with the potential to monitor HO-1 in AD progression.

A Role for NRF2-Signaling in the Treatment and Prevention of Solar Lentigines

BACKGROUND

Photoaging is premature skin aging resulting from oxidative stress generated by exposure to solar radiation. A key clinical feature is solar lentigines, areas of hyperpigmentation on sun-exposed skin. Skin pigmentation is determined by cross-talk between keratinocytes and melanocytes, which is exquisitely sensitive to oxidative stress. Toll-like receptor (TLR) signaling and NF-E2-related factor 2 (NRF2) signaling, an endogenous antioxidant system, serve as a bridge between the oxidative stress response and immune regulation. Moreover, TLR-mediated induction of IL-6 production has been shown to prevent ultraviolet (UV)-induced hyperpigmentation.

METHODS

Shave biopsies of solar lentigines were obtained from 14 individuals. An additional 7 subjects applied broccoli sprout extract (BSE) containing sulforaphane daily or vehicle on photodamaged skin. Immunofluorescence staining was used to determine total and phosphorylated NRF2 in the lentiginous skin. Dermoscopy and Fontana & Masson staining were used to assess the effect of topical BSE on UV-induced pigmentation. Similar topical treatments were performed in a mouse model of UVB-induced hyperpigmentation utilizing WT, Nrf2-/-, or K14-Cre-ERT2IL-6Rαfl/fl C57BL/6 mice.

RESULTS

NRF2 expression is altered in solar lentigines, and UV-induced skin pigmentation in humans could be ameliorated with topical BSE. Corresponding mouse models replicated the authors' clinical findings and identified a potential mechanistic link to IL-6Rα signaling in keratinocytes.

CONCLUSION

The authors' findings suggest that dysregulation of NRF2 signaling is involved in the pathogenesis of UV-induced skin pigmentation and pharmacological activation of NRF2 may represent a potential therapeutic target in photoaging.

N-Phenyl Cinnamamide Derivatives Protect Hepatocytes against Oxidative Stress by Inducing Cellular Glutathione Synthesis via Nuclear Factor (Erythroid-Derived 2)-Like 2 Activation

Substituted N-phenyl cinnamamide derivatives were designed and synthesized to confirm activation of nuclear factor (erythroid-derived 2)-like 2 (Nrf2) pathway by the electronic effect on beta-position of Michael acceptor according to introducing the R¹ and R² group. Compounds were screened using the Nrf2/antioxidant response element (ARE)-driven luciferase reporter assay. Compound 1g showed desirable luciferase activity in HepG2 cells without cell toxicity. mRNA and protein expression of Nrf2/ARE target genes such as NAD(P)H quinone oxidoreductase 1, hemeoxygenase-1, and glutamate-cysteine ligase catalytic subunit (GCLC) were upregulated by compound 1g in a concentration-dependent manner. Treatment with 1g resulted in increased endogenous antioxidant glutathione, showing strong correlation with enhanced GCLC expression for synthesis of glutathione. In addition, tert-butyl hydroperoxide (t-BHP)-generated reactive oxygen species were significantly removed by 1g, and the results of a cell survival assay in a t-BHP-induced oxidative cell injury model showed a cytoprotective effect of 1g in a concentration dependent manner. In conclusion, the novel compound 1g can be utilized as an Nrf2/ARE activator in antioxidative therapy.

Protective Effect of Lemon Peel Polyphenols on Oxidative Stress-Induced Damage to Human Keratinocyte HaCaT Cells Through Activation of the Nrf2/HO-1 Signaling Pathway

Lemon peel can be used as traditional Chinese medicine. Flavonoids are the most important components in lemon peel, which can be developed as natural medicine without side effects. This study investigated the protective effect of lemon peel polyphenols (LPP) on human keratinocyte HaCaT cells under oxidative stress. The active components of LPP were determined by high performance liquid chromatography. The abilities of LPP to scavenge DPPH and ABTS+ free radicals were studied for detection of antioxidation in vitro. Cell survival rates were determined by MTT assay. The antioxidant enzyme activity and antioxidant index of cells were determined using kit. The mRNA and protein expression of cells were determined by qPCR and western blot. The ability of LPP to scavenge DPPH and ABTS+ free radicals were stronger than those of vitamin C (Vc) at the same concentration. As expected, compared with the normal group of cells, the model group had decreased cell survival, increased lactate dehydrogenase (LDH), decreased levels of superoxide dismutase (SOD), catalase (CAT) and glutathione (GSH), and increased malondialdehyde (MDA) content. qPCR and western blot results indicated that the expression of Bcl-2-related X protein (Bax), caspases-3, erythroid-derived nuclear factor 2-related factor 2 (Nrf2), and heme oxygenase-1 (HO-1) were decreased and the expression of B-cell lymphoma-2 (Bcl-2) was increased in the model group, compared with the normal group. LPP treatment improved cell survival rate, reduced intracellular LDH and MDA levels, increased intracellular SOD, CAT, GSH levels, down-regulated Bax, caspases-3, Nrf2, HO-1 expression, and up-regulated Bcl-2 expression. Component analyses found that LPP contains gallic acid, neochlorogenic acid, (+)-catechin, caffeic acid, (-)-Catechin gallate, isochlorogenic acid A, rosmarinic acid, and protocatechuic acid. LPP was found to regulate the Nrf2/HO-1 signaling pathway through 8 active substances to protect HaCaT cells against oxidative stress in vitro.

Pathogenic and therapeutic role for NRF2 signaling in ultraviolet light-induced skin pigmentation

Mottled skin pigmentation and solar lentigines from chronic photodamage with aging involve complex interactions between keratinocytes and melanocytes. However, the precise signaling mechanisms that could serve as therapeutic targets are unclear. Herein, we report that expression of nuclear factor erythroid 2-related factor 2 (NRF2), which regulates reduction-oxidation reactions, is altered in solar lentigines and photodamaged skin. Moreover, mottled skin pigmentation in humans could be treated with topical application of the NRF2 inducer sulforaphane (SF). Similarly, UV light-induced pigmentation of WT mouse ear skin could be treated or prevented with SF treatment. Conversely, SF treatment was unable to reduce UV-induced ear skin pigmentation in mice deficient in NRF2 or in mice with keratinocyte-specific conditional deletion of IL-6Rα. Taken together, NRF2 and IL-6Rα signaling are involved in the pathogenesis of UV-induced skin pigmentation, and specific enhancement of NRF2 signaling could represent a potential therapeutic target.

Activation of NRF2 by topical apocarotenoid treatment mitigates radiation-induced dermatitis

Radiation therapy is a frontline treatment option for cancer patients; however, the effects of radiotherapy on non-tumor tissue (e.g. radiation-induced dermatitis) often worsen patient quality of life. Previous studies have implicated the importance of redox balance in preventing dermatitis, specifically in reference to modulation of the nuclear factor (erythroid-derived 2)-like 2 (NRF2) signaling pathway. Due to the cytoprotective functions of transcriptional target genes of NRF2, we investigated how modulation of NRF2 expression could affect DNA damage, oxidative stress, and cell viability in response to radiotherapy. Specifically, it was noted that NRF2 knockdown sensitized human skin keratinocytes to ionizing radiation; likewise, genetic ablation of NRF2 in vivo increased radiosensitivity of murine epidermis. Oppositely, pharmacological induction of NRF2 via the apocarotenoid bixin lowered markers of DNA damage and oxidative stress, while preserving viability in irradiated keratinocytes. Mechanistic studies indicated that topical pretreatment using bixin as an NRF2 activator antagonized initial DNA damage by raising cellular glutathione levels. Additionally, topical application of bixin prevented radiation-induced dermatitis, epidermal thickening, and oxidative stress in the skin of SKH1 mice. Overall, these data indicate that NRF2 is critical for mitigating the harmful skin toxicities associated with ionizing radiation, and that topical upregulation of NRF2 via bixin could prevent radiation-induced dermatitis.

The role of natural products in revealing NRF2 function

Covering: up to 2020The transcription factor NRF2 is one of the body's major defense mechanisms, driving transcription of >300 antioxidant response element (ARE)-regulated genes that are involved in many critical cellular processes including redox regulation, proteostasis, xenobiotic detoxification, and primary metabolism. The transcription factor NRF2 and natural products have an intimately entwined history, as the discovery of NRF2 and much of its rich biology were revealed using natural products both intentionally and unintentionally. In addition, in the last decade a more sinister aspect of NRF2 biology has been revealed. NRF2 is normally present at very low cellular levels and only activated when needed, however, it has been recently revealed that chronic, high levels of NRF2 can lead to diseases such as diabetes and cancer, and may play a role in other diseases. Again, this "dark side" of NRF2 was revealed and studied largely using a natural product, the quassinoid, brusatol. In the present review, we provide an overview of NRF2 structure and function to orient the general reader, we will discuss the history of NRF2 and NRF2-activating compounds and the biology these have revealed, and we will delve into the dark side of NRF2 and contemporary issues related to the dark side biology and the role of natural products in dissecting this biology.

A cell-based assay system for activators of the environmental cell stress response

Improved health span and lifespan extension in a wide phylogenetic range of species is associated with the induction of the environmental cell stress response through a signalling pathway regulated by the transcription factor Nrf2. Phytochemicals which stimulate this response may form part of therapeutic interventions which stimulate endogenous cytoprotective mechanisms, thereby delaying the onset of age-related diseases and promoting healthy ageing in humans. In order to identify compounds that activate the Nrf2 pathway, a cell-based reporter system was established in HepG2 cells using a luciferase reporter gene under the control of the Nqo1 promoter. Sulforaphane, an isothiocyanate derived from cruciferous vegetables and a known activator of the Nrf2 pathway, was used to validate the reporter system. The transfected cell line HepG2 C1 was subsequently used to screen natural product libraries. Five compounds were identified as activating the bioluminescent reporter by greater than 5-fold. The two most potent compounds, MBC20 and MBC37, were further characterised and shown to stimulate endogenous cytoprotective gene and protein expression. The bioluminescent reporter system will allow rapid, in vitro identification of novel compounds that have the potential to improve health span through activation of the environmental stress response.

Non-covalent NRF2 Activation Confers Greater Cellular Protection than Covalent Activation

The transcription factor NRF2 confers cellular protection by maintaining cellular redox homeostasis and proteostasis. Basal NRF2 levels are normally low due to KEAP1-mediated ubiquitylation and subsequent proteasomal degradation. KEAP1, a substrate adaptor protein of a KEAP1-CUL3-RBX1 E3 ubiquitin ligase complex, contains a critical cysteine (C151) that is modified by electrophiles or oxidants, resulting in inactivation of the E3 ligase and inhibition of NRF2 degradation. Currently, nearly all NRF2 inducers are electrophilic molecules that possess unwanted off-target effects due to their reactive nature. Here, we report a group of NRF2 inducers, ent-kaurane diterpenoid geopyxins, with and without C151 reactive electrophilic moieties. Among 16 geopyxins, geopyxin F, a non-electrophilic NRF2 activator, showed enhanced cellular protection relative to an electrophilic NRF2 activator, geopyxin C. To our knowledge, this is the first detailed structure-activity relationship study of covalent versus non-covalent NRF2 activators, showing the promise of non-covalent NRF2 activators as potential therapeutic compounds.

TLR4-directed Molecular Strategies Targeting Skin Photodamage and Carcinogenesis

Background:

Exposure to solar ultraviolet (UV) radiation is a causative factor in skin photodamage and carcinogenesis, and inflammatory dysregulation is a key mechanism underlying detrimental effects of acute and chronic UV exposure. The health and economic burden of skin cancer treatment is substantial, creating an increasingly urgent need for the development of improved molecular strategies for photoprotection and photochemoprevention.

Methods:

A structured search of bibliographic databases for peer-reviewed research literature revealed 139 articles including our own that are presented and critically evaluated in this TLR4-directed review.

Objective:

To understand the molecular role of Toll-like receptor 4 (TLR4) as a key regulator of skin anti-microbial defense, wound healing, and cutaneous tumorigenic inflammation. The specific focus of this review is on recent published evidence suggesting that TLR4 represents a novel molecular target for skin photoprotection and cancer photochemoprevention.

Results:

Cumulative experimental evidence indicates that pharmacological and genetic antagonism of TLR4 suppresses UV-induced inflammatory signaling involving the attenuation of cutaneous NF-κB and AP-1 stress signaling observable in vitro and in vivo. TLR4-directed small molecule pharmacological antagonists [including eritoran, (+)-naloxone, ST2825, and resatorvid] have now been identified as a novel class of molecular therapeutics. TLR4 antagonists are in various stages of preclinical and clinical development for the modulation of dysregulated TLR4-dependent inflammatory signaling that may also contribute to skin photodamage and photocarcinogenesis in human populations.

Conclusion:

Future research should explore the skin photoprotective and photochemopreventive efficacy of topical TLR4 antagonism if employed in conjunction with other molecular strategies including sunscreens.

NRF2 Activation Inhibits Both TGF-β1- and IL-13-Mediated Periostin Expression in Fibroblasts: Benefit of Cinnamaldehyde for Antifibrotic Treatment

Systemic fibrosing or sclerotic disorders are life-threatening, but only very limited treatment modalities are available for them. In recent years, periostin (POSTN), a major extracellular matrix component, was established by several studies as a novel key player in the progression of systemic fibrotic disease. In this research, we revealed the involvement of oxidative stress in the expression of POSTN induced by TGF-β1 and IL-13 in dermal fibroblasts. We found that the antioxidant cinnamaldehyde activated the NRF2/HMOX1 pathway. Cinnamaldehyde also alleviated TGF-β1- and IL-13-mediated production of reactive oxygen species and subsequent POSTN upregulation in dermal fibroblasts. In contrast, NRF2 silencing abolished the cinnamaldehyde-mediated downregulation of POSTN. These results suggest that cinnamaldehyde is a broad inhibitor of POSTN expression covering both TGF-β1 and IL-13 signaling. Cinnamaldehyde may thus be beneficial for the treatment of systemic fibrotic diseases.

Topical Bixin Confers NRF2-Dependent Protection Against Photodamage and Hair Graying in Mouse Skin

Environmental exposure to solar ultraviolet (UV) radiation causes acute photodamage, premature aging, and skin cancer, attributable to UV-induced genotoxic, oxidative, and inflammatory stress. The transcription factor NRF2 [nuclear factor erythroid 2 (E2)-related factor 2] is the master regulator of the cellular antioxidant response protecting skin against various environmental stressors including UV radiation and electrophilic pollutants. NRF2 in epidermal keratinocytes can be activated using natural chemopreventive compounds such as the apocarotenoid bixin, an FDA-approved food additive and cosmetic ingredient from the seeds of the achiote tree (Bixa orellana). Here, we tested the feasibility of topical use of bixin for NRF2-dependent skin photoprotection in two genetically modified mouse models [SKH1 and C57BL/6J (Nrf2^+/+ versus Nrf2^-/- )]. First, we observed that a bixin formulation optimized for topical NRF2 activation suppresses acute UV-induced photodamage in Nrf2^+/+ but not Nrf2^-/- SKH1 mice, a photoprotective effect indicated by reduced epidermal hyperproliferation and oxidative DNA damage. Secondly, it was demonstrated that topical bixin suppresses PUVA (psoralen + UVA)-induced hair graying in Nrf2^+/+ but not Nrf2^-/- C57BL/6J mice. Collectively, this research provides the first in vivo evidence that topical application of bixin can protect against UV-induced photodamage and PUVA-induced loss of hair pigmentation through NRF2 activation. Topical NRF2 activation using bixin may represent a novel strategy for human skin photoprotection, potentially complementing conventional sunscreen-based approaches.

Trans-cinnamic acid attenuates UVA-induced photoaging through inhibition of AP-1 activation and induction of Nrf2-mediated antioxidant genes in human skin fibroblasts

BACKGROUND

UVA irradiation-induced skin damage/photoaging is associated with redox imbalance and collagen degradation.

OBJECTIVE

Dermato-protective efficacies of trans-cinnamic acid (t-CA), a naturally occurring aromatic compound have been investigated against UVA irradiation, and elucidated underlying molecular mechanism.

METHODS

Human foreskin fibroblast-derived (Hs68) cells and nude mice were treated with t-CA prior to UVA exposure, and assayed the anti-photoaging effects of t-CA.

RESULTS

We found t-CA (20-100 μM) pretreatment substantially ameliorated UVA (3 J/cm²)-induced cytotoxicity, and inhibited intracellular ROS production in Hs68 cells. UVA-induced profound upregulation of metalloproteinase (MMP)-1/-3 and degradation of type I procollagen in dermal fibroblasts were remarkably reversed by t-CA, possibly through inhibition of AP-1 (c-Fos, but not c-Jun) translocation. The t-CA-mediated anti-photoaging properties are associated with increased nuclear translocation of Nrf2. Activation of Nrf2 signaling is accompanied with induction of HO-1 and γ-GCLC expressions in t-CA-treated fibroblasts. Furthermore t-CA-induced Nrf2 translocation is mediated through PKC, AMPK, CKII or ROS signaling cascades. This phenomenon was confirmed with respective pharmacological inhibitors, GF109203X, Compound C, CKII inhibitor or NAC, which blockade t-CA-induced Nrf2 activation. Silencing of Nrf2 signaling with siRNA showed no anti-photoaging effects of t-CA against UVA-induced ROS production, loss of HO-1 and type I collagen degradation in fibroblasts. In vivo evidence on nude mice revealed that t-CA pretreatment (20 or 100 mM/day) significantly suppressed MMP-1/-3 activation and maintained sufficient type I procollagen levels in biopsied skin tissue against UVA irradiation (3 J/cm²/day for 10-day).

CONCLUSION

t-CA treatment diminished UVA-induced photoaging/collagen degradation, and protected structural integrity of the skin.

Targeting NRF2 for Improved Skin Barrier Function and Photoprotection: Focus on the Achiote-Derived Apocarotenoid Bixin

The transcription factor NRF2 (nuclear factor-E2-related factor 2) orchestrates major cellular defense mechanisms including phase-II detoxification, inflammatory signaling, DNA repair, and antioxidant response. Recent studies strongly suggest a protective role of NRF2-mediated gene expression in the suppression of cutaneous photodamage induced by solar UV (ultraviolet) radiation. The apocarotenoid bixin, a Food and Drug Administration (FDA)-approved natural food colorant (referred to as ‘annatto’) originates from the seeds of the achiote tree native to tropical America, consumed by humans since ancient times. Use of achiote preparations for skin protection against environmental insult and for enhanced wound healing has long been documented. We have recently reported that (i) bixin is a potent canonical activator of the NRF2-dependent cytoprotective response in human skin keratinocytes; that (ii) systemic administration of bixin activates NRF2 with protective effects against solar UV-induced skin damage; and that (iii) bixin-induced suppression of photodamage is observable in Nrf2^+/+ but not in Nrf2^−/− SKH-1 mice confirming the NRF2-dependence of bixin-induced antioxidant and anti-inflammatory effects. In addition, bixin displays molecular activities as sacrificial antioxidant, excited state quencher, PPAR (peroxisome proliferator-activated receptor) α/γ agonist, and TLR (Toll-like receptor) 4/NFκB (nuclear factor kappa-light-chain-enhancer of activated B cells) antagonist, all of which might be relevant to the enhancement of skin barrier function and environmental stress protection. Potential skin photoprotection and photochemoprevention benefits provided by topical application or dietary consumption of this ethno-pharmacologically validated phytochemical originating from the Americas deserves further preclinical and clinical examination.

Nrf2: a potential therapeutic target for diabetic neuropathy

Different aspects involved in pathophysiology of diabetic neuropathy are related to inflammatory and apoptotic pathways. This article summarizes evidence that Nrf2 acts as a bridging link in various inflammatory and apoptotic pathways impacting progression of diabetic neuropathy. Nrf2 is involved in expression of various antioxidant proteins (such as detoxifying enzymes) via antioxidant response element (ARE) binding site. Under normal conditions, Nrf2 is inactive and remains in the cytosol. Hyperglycemia is a strong stimulus for oxidative stress and inflammation that downregulates the activity of Nrf2 through various neuroinflammatory pathways. Acute hyperglycemia increases the expression of Nrf2, but persistent hyperglycemia decreases its expression. This downregulation of Nrf2 causes various microvascular changes, which result in diabetic neuropathy. The key contribution of Nrf2 in progression of diabetic neuropathy has been summarized in the article. Despite involvement of Nrf2 in progression of diabetic neuropathy, targeting Nrf2 activators as a therapeutic potential will provide important new insights into the ways that influence treatment of diabetic neuropathy.

The B6 -vitamer Pyridoxal is a Sensitizer of UVA-induced Genotoxic Stress in Human Primary Keratinocytes and Reconstructed Epidermis

UVA-driven photooxidative stress in human skin may originate from excitation of specific endogenous chromophores acting as photosensitizers. Previously, we have demonstrated that 3-hydroxypyridine-derived chromophores including B₆ -vitamers (pyridoxine, pyridoxamine and pyridoxal) are endogenous photosensitizers that enhance UVA-induced photooxidative stress in human skin cells. Here, we report that the B₆ -vitamer pyridoxal is a sensitizer of genotoxic stress in human adult primary keratinocytes (HEKa) and reconstructed epidermis. Comparative array analysis indicated that exposure to the combined action of pyridoxal and UVA caused upregulation of heat shock (HSPA6, HSPA1A, HSPA1L, HSPA2), redox (GSTM3, EGR1, MT2A, HMOX1, SOD1) and genotoxic (GADD45A, DDIT3, CDKN1A) stress response gene expression. Together with potentiation of UVA-induced photooxidative stress and glutathione depletion, induction of HEKa cell death occurred only in response to the combined action of pyridoxal and UVA. In addition to activational phosphorylation indicative of genotoxic stress [p53 (Ser15) and γ-H2AX (Ser139)], comet analysis indicated the formation of Fpg-sensitive oxidative DNA lesions, observable only after combined exposure to pyridoxal and UVA. In human reconstructed epidermis, pyridoxal preincubation followed by UVA exposure caused genomic oxidative base damage, procaspase 3 cleavage and TUNEL positivity, consistent with UVA-driven photooxidative damage that may be relevant to human skin exposed to high concentrations of B₆ -vitamers.

New hits as phase II enzymes inducers from a focused library with heteroatom-heteroatom and Michael-acceptor motives

The increased activity of phase-II-detoxification enzymes, such as quinone reductase (QR) and glutation S-transferase (GST), correlates with protection against chemically induced carcinogenesis. Herein we studied 11 different chemotypes, pyrazole, 1,2,4-oxadiazole, 1,2,5-oxadiazole, 1,2,3-thiadiazole, 1,2,4-thiazole, 1,3,4-oxathiazole, thienyl hydrazone, α,β-unsaturated-oxime, α,β-unsaturated-N-oxide, coumarin and α,β-unsaturated-carbonyl, as phase-II enzymes inducers in order to identify new pharmacophores with chemopreventive activity. Fifty-four compounds were analyzed on wild-type mouse-hepatoma Hepa-1c1c7 and on the aryl-hydrocarbon-nuclear-translocator (Arnt)-defective mutant BpRc1 cells. New monofunctional inducers of QR and GST were identified, the 1,2,5-oxadiazol-2-oxide (3), the 1,2,4-triazine-4-oxides (23) and (32) and the tetrahydropyrimidinones (28) and (49). It was confirmed that Nrf2 nuclear translocation is the operative molecular mechanism that allows compound (3) to exert protective effects via expression of downstream phase-II enzymes.

Cancer chemoprevention is the prevention, delay or reversal of the carcinogenesis by administration of drugs. A group of chemopreventative agents includes quinone reductase and glutation S-transferase. Herein we have studied 11 chemotypes, trying to identify new pharmacophores for chemopreventives. We found new inducers of quinone reductase and glutation S-transferase, with excellent in vitro chemopreventive indexes, the 1,2,5-oxadiazol-2-oxide (3), the 1,2,4-triazine-4-oxides (23) and (32) and the tetrahydropyrimidinones (28) and (49), confirming that Nrf2 nuclear translocation is the operative molecular mechanism that allows compound (3) to exert protection. We have therefore highlighted good candidates for further in vivo studies of cancer chemopreventive activity.

Activation of Nrf2 Reduces UVA-Mediated MMP-1 Upregulation via MAPK/AP-1 Signaling Cascades: The Photoprotective Effects of Sulforaphane and Hispidulin

UVA irradiation plays a role in premature aging of the skin through triggering oxidative stress-associated stimulation of matrix metalloproteinase-1 (MMP-1) responsible for collagen degradation, a hallmark of photoaged skin. Compounds that can activate nuclear factor E2-related factor 2 (Nrf2), a transcription factor regulating antioxidant gene expression, should therefore serve as effective antiphotoaging agents. We investigated whether genetic silencing of Nrf2 could relieve UVA-mediated MMP-1 upregulation via activation of mitogen-activated protein kinase (MAPK)/activator protein 1 (AP-1) signaling using human keratinocyte cell line (HaCaT). Antiphotoaging effects of hispidulin (HPD) and sulforaphane (SFN) were assessed on their abilities to activate Nrf2 in controlling MMP-1 and collagen expressions in association with phosphorylation of MAPKs (extracellular signal-regulated kinase, c-Jun N-terminal kinase, and p38), c-Jun, and c-Fos, using the skin of BALB/c mice subjected to repetitive UVA irradiation. Our findings suggested that depletion of Nrf2 promoted both mRNA expression and activity of MMP-1 in the UVA-irradiated HaCaT cells. Treatment of Nrf2 knocked-down HaCaT cells with MAPK inhibitors significantly suppressed UVA-induced MMP-1 and AP-1 activities. Moreover, pretreatment of the mouse skin with HPD and SFN, which could activate Nrf2, provided protective effects against UVA-mediated MMP-1 induction and collagen depletion in correlation with the decreased levels of phosphorylated MAPKs, c-Jun, and c-Fos in the mouse skin. In conclusion, Nrf2 could influence UVA-mediated MMP-1 upregulation through the MAPK/AP-1 signaling cascades. HPD and SFN may therefore represent promising antiphotoaging candidates.

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.

Paeoniflorin attenuates ultraviolet B-induced apoptosis in human keratinocytes by inhibiting the ROS-p38-p53 pathway

Ultraviolet (UV) light is one of the most harmful environmental factors that contribute to skin damage. Exposure to UV induces extensive generation of reactive oxygen species (ROS), and results in photoaging and skin cancer development. One approach to protecting human skin against UV radiation is the use of antioxidants. In recent years, naturally occurring herbal compounds have gained considerable attention as protective agents for UV exposure. Paeoniflorin (PF) is a novel natural antioxidant, which is isolated from peony root (Radix Paeoniae Alba). The present study evaluated the protective effects of PF on UV‑induced skin damage in vitro, and demonstrated that the effects were mediated via the ROS‑p38‑p53 pathway. The results of the present study demonstrated that treatment with PF (25, 50, and 100 µM) significantly increased the percentage of viable keratinocytes after UV‑B exposure. In addition, cell death analysis indicated that PF treatment markedly reduced UV‑B‑radiation‑induced apoptosis in keratinocytes, which was accompanied by increased procaspase 3 expression and decreased cleaved caspase 3 expression. Treatment with PF markedly reduced the production of ROS, and inhibited the activation of p38 and p53 in human keratinocytes, thus suggesting that the ROS‑p38‑p53 pathway has a role in UV‑B‑induced skin damage. In conclusion, the present study reported that PF was able to attenuate UV‑B‑induced cell damage in human keratinocytes. Notably, these effects were shown to be mediated, at least in part, via inhibition of the ROS-p38-p53 pathway.

Diabetic Wound Healing and Activation of Nrf2 by Herbal Medicine

Nrf2 defense is a very important cellular mechanism to control oxidative stress, which is implicated in wound healing. Nrf2 can induce many cytoprotective genes, including HO-1, NQO1 and G6PD. Among many natural products that have been reported as Nrf2 activators, sulforaphane and curcumin have been studied more widely than any others, and both are in clinical trials for non-cancerous disorders. Recently, we reported 4-ethyl catechol and 4-vinyl catechol as Nrf2 co-factors that can induce Nrf2 as potently as sulforaphane and curcumin. These new Nrf2 co-factors were identified in hot aqueous extract of an herbal medicine Barleria lupulina, and fermented Noni (Morinda citrifolia) juice, which are used traditionally for diabetic wound healing.

Photoprotection by dietary phenolics against melanogenesis induced by UVA through Nrf2-dependent antioxidant responses

Dietary phenolics may play a protective role in UV-mediated skin pigmentation through their antioxidant and UV-absorbing actions. In this study, we investigated whether genetic silencing of Nrf2, regulating the transcription of antioxidant genes, affected melanogenesis in primary human epidermal melanocytes (HEMn) and B16F10 melanoma cells subjected to UVA (8 J/cm²) exposure. Then, we explored the antimelanogenic actions of phenolics; caffeic acid (CA) and ferulic acid (FA) providing partial UVA protection; quercetin (QU) and rutin (RU) providing strong UVA protection and; avobenzone (AV), an efficient UVA filter, in association with modulation of Nrf2-mediated antioxidant defenses in response to UVA insults in B16F10 cells. Upon oxidative insults, Nrf2 silencing promoted melanogenesis in both HEMn and B16F10 cells irradiated with UVA. Stimulation of melanogenesis by UVA correlated with increased ROS and oxidative DNA damage (8-OHdG), GSH depletion as well as a transient downregulation of Nrf2 nuclear translocation and of Nrf2-ARE signaling in B16F10 cells. All test compounds exerted antimelanogenic effects with respect to their abilities to reverse UVA-mediated oxidative damage as well as downregulation of Nrf2 activity and its target antioxidants (GCLC, GST and NQO1) in B16F10 cells. In conclusion, defective Nrf2 may promote melanogenesis under UVA irradiation through oxidative stress mechanisms. Compounds with antioxidant and/or UVA absorption properties could protect against UVA-induced melanogenesis through indirect regulatory effect on Nrf2-ARE pathway.

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Depletion of Nrf2 could stimulate melanogenesis under UVA-mediated oxidative stress.

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UVA caused time-course changes of Nrf2 activity and its target antioxidants.

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Phenolics could inhibit UVA-induced melanogenesis through modulation of Nrf2 pathway.

Systemic administration of the apocarotenoid bixin protects skin against solar UV-induced damage through activation of NRF2

Exposure to solar ultraviolet (UV) radiation is a causative factor in skin photodamage and carcinogenesis, and an urgent need exists for improved molecular photoprotective strategies different from (or synergistic with) photon absorption. Recent studies suggest a photoprotective role of cutaneous gene expression orchestrated by the transcription factor NRF2 (nuclear factor-E2-related factor 2). Here we have explored the molecular mechanism underlying carotenoid-based systemic skin photoprotection in SKH-1 mice and provide genetic evidence that photoprotection achieved by the FDA-approved apocarotenoid and food additive bixin depends on NRF2 activation. Bixin activates NRF2 through the critical Cys-151 sensor residue in KEAP1, orchestrating a broad cytoprotective response in cultured human keratinocytes as revealed by antioxidant gene expression array analysis. Following dose optimization studies for cutaneous NRF2 activation by systemic administration of bixin, feasibility of bixin-based suppression of acute cutaneous photodamage from solar UV exposure was investigated in Nrf2(+/+) versus Nrf2(-/-) SKH-1 mice. Systemic administration of bixin suppressed skin photodamage, attenuating epidermal oxidative DNA damage and inflammatory responses in Nrf2(+/+) but not in Nrf2(-/-) mice, confirming the NRF2-dependence of bixin-based cytoprotection. Taken together, these data demonstrate feasibility of achieving NRF2-dependent cutaneous photoprotection by systemic administration of the apocarotenoid bixin, a natural food additive consumed worldwide.

Nrf2--A regulator of keratinocyte redox signaling

The skin is frequently exposed to environmental challenges, such as UV irradiation, toxic chemicals, and mechanical wounding. These insults cause an increase in the levels of reactive oxygen species, resulting in oxidative stress and concomitant inflammation, skin aging, and even cancer development. Therefore, an efficient antioxidant defense strategy is of major importance in this tissue. Since the Nrf2 transcription factor regulates a battery of genes involved in the defense against reactive oxygen species and in compound metabolism, it plays a key role in skin homeostasis, repair, and disease. In this review we summarize current knowledge on the expression and function of Nrf2 in normal skin and its role in the acute and chronic UV response as well as in the pathogenesis of epithelial skin cancer and of different inflammatory skin diseases. Finally, we discuss the potential of Nrf2-activating compounds for skin protection under stress conditions and for the treatment of major human skin disorders.

TrxR1 as a potent regulator of the Nrf2-Keap1 response system

SIGNIFICANCE

All cells must maintain a balance between oxidants and reductants, while allowing for fluctuations in redox states triggered by signaling, altered metabolic flow, or extracellular stimuli. Furthermore, they must be able to rapidly sense and react to various challenges that would disrupt the redox homeostasis.

RECENT ADVANCES

Many studies have identified Keap1 as a key sensor for oxidative or electrophilic stress, with modification of Keap1 by oxidation or electrophiles triggering Nrf2-mediated transcriptional induction of enzymes supporting reductive and detoxification pathways. However, additional mechanisms for Nrf2 regulation are likely to exist upstream of, or in parallel with, Keap1.

CRITICAL ISSUES

Here, we propose that the mammalian selenoprotein thioredoxin reductase 1 (TrxR1) is a potent regulator of Nrf2. A high chemical reactivity of TrxR1 and its vital role for the thioredoxin (Trx) system distinguishes TrxR1 as a prime target for electrophilic challenges. Chemical modification of the selenocysteine (Sec) in TrxR1 by electrophiles leads to rapid inhibition of thioredoxin disulfide reductase activity, often combined with induction of NADPH oxidase activity of the derivatized enzyme, thereby affecting many downstream redox pathways. The notion of TrxR1 as a regulator of Nrf2 is supported by many publications on effects in human cells of selenium deficiency, oxidative stress or electrophile exposure, as well as the phenotypes of genetic mouse models.

FUTURE DIRECTIONS

Investigation of the role of TrxR1 as a regulator of Nrf2 activation will facilitate further studies of redox control in diverse cells and tissues of mammals, and possibly also in animals of other classes.

Searching phase II enzymes inducers, from Michael acceptor-[1,2]dithiolethione hybrids, as cancer chemopreventive agents

Background: Cancer chemoprevention involves the carcinogenic process prevention, delay or reverse by the administration of chemopreventive agents, which are able to suppress or block the carcinogen metabolic activation/formation. The increased activity of phase II detoxification enzymes such as quinone-reductase (QR) and glutation-S-transferase (GST) correlates with the protection against chemically-induced carcinogenesis. It has been shown that synthetic chalcones and 3H-[1,2]-dithiole-3-thiones promote expression of genes involved in chemoprevention. Materials & Methods: Herein, the induction of phase II enzymes by designed Michael acceptor-dithiolethione hybrids was studied. Results & Discussion: Hybrids 5 and 7 displayed the induction of quinone-reductase and glutation-S-transferase in vitro in the same order on the wild-type mouse-hepatoma Hepa 1c1c7 and on the aryl-hydrocarbon-nuclear-translocator (Arnt)-defective mutant BPrc1 cells indicating that 7 displays the best chemopreventive potential.

Nrf2-dependent suppression of azoxymethane/dextran sulfate sodium-induced colon carcinogenesis by the cinnamon-derived dietary factor cinnamaldehyde

The progressive nature of colorectal cancer and poor prognosis associated with the metastatic phase of the disease create an urgent need for the development of more efficacious strategies targeting colorectal carcinogenesis. Cumulative evidence suggests that the redox-sensitive transcription factor Nrf2 (nuclear factor-E2-related factor 2), a master regulator of the cellular antioxidant defence, represents a promising molecular target for colorectal cancer chemoprevention. Recently, we have identified cinnamon, the ground bark of Cinnamomum aromaticum (cassia cinnamon) and Cinnamomum verum (Ceylon cinnamon), as a rich dietary source of the Nrf2 inducer cinnamaldehyde (CA) eliciting the Nrf2-regulated antioxidant response in human epithelial colon cells, conferring cytoprotection against electrophilic and genotoxic insult. Here, we have explored the molecular mechanism underlying CA-induced Nrf2 activation in colorectal epithelial cells and have examined the chemopreventive potential of CA in a murine colorectal cancer model comparing Nrf2(+/+) with Nrf2(-/-) mice. In HCT116 cells, CA caused a Keap1-C151-dependent increase in Nrf2 protein half-life via blockage of ubiquitination with upregulation of cytoprotective Nrf2 target genes and elevation of cellular glutathione. After optimizing colorectal Nrf2 activation and target gene expression by dietary CA-supplementation regimens, we demonstrated that CA suppresses AOM/DSS-induced inflammatory colon carcinogenesis with modulation of molecular markers of colorectal carcinogenesis. Dietary suppression of colorectal cancer using CA supplementation was achieved in Nrf2(+/+) but not in Nrf2(-/-) mice confirming the Nrf2 dependence of CA-induced chemopreventive effects. Taken together, our data suggest feasibility of colorectal cancer suppression by dietary CA, an FDA-approved food additive derived from the third most consumed spice in the world.

The Tryptophan-Derived Endogenous Aryl Hydrocarbon Receptor Ligand 6-Formylindolo[3,2-b]Carbazole Is a Nanomolar UVA Photosensitizer in Epidermal Keratinocytes

Endogenous UVA-chromophores may act as sensitizers of oxidative stress underlying cutaneous photoaging and photocarcinogenesis, but the molecular identity of non-DNA key chromophores displaying UVA-driven photodyamic activity in human skin remains largely undefined. Here we report that 6-formylindolo[3,2-b]carbazole (FICZ), a tryptophan photoproduct and endogenous high affinity aryl hydrocarbon receptor (AhR) agonist, acts as a nanomolar photosensitizer potentiating UVA-induced oxidative stress irrespective of AhR ligand activity. In human HaCaT and primary epidermal keratinocytes, photodynamic induction of apoptosis was elicited by the combined action of solar simulated UVA and FICZ, whereas exposure to the isolated action of UVA or FICZ did not impair viability. In a human epidermal tissue reconstruct, FICZ/UVA-cotreatment caused pronounced phototoxicity inducing keratinocyte cell death, and FICZ photodynamic activity was also substantiated in a murine skin exposure model. Array analysis revealed pronounced potentiation of cellular heat shock, ER stress, and oxidative stress response gene expression observed only upon FICZ/UVA-cotreatment. FICZ photosensitization caused intracellular oxidative stress, and comet analysis revealed introduction of formamidopyrimidine-DNA glycosylase (FPG)-sensitive oxidative DNA lesions suppressible by antioxidant cotreatment. Taken together, our data demonstrate that the endogenous AhR ligand FICZ displays nanomolar photodynamic activity representing a molecular mechanism of UVA-induced photooxidative stress potentially operative in human skin.

An inelastic neutron scattering study of dietary phenolic acids

The conformational preferences and hydrogen-bonding motifs of several potential chemopreventive hydroxycinnamic derivatives were determined by inelastic neutron scattering spectroscopy. The aim is to understand their recognized beneficial activity and establish reliable structure-activity relationships for these types of dietary phytochemicals. A series of phenolic acids with different hydroxyl/methoxyl ring substitution patterns were studied: trans-cinnamic, p-coumaric, m-coumaric, trans-caffeic and ferulic acids. Their INS spectra were completely assigned by theoretical calculations performed at the Density Functional Theory level, for the isolated molecule, dimeric centrosymmetric species and the solid (using plane-wave expansion approaches). Access to the low energy vibrational region of the spectra enabled the identification of particular modes associated with intermolecular hydrogen-bonding interactions, which are the determinants of the main conformational preferences and antioxidant capacity of these systems.

The emerging role of redox-sensitive Nrf2-Keap1 pathway in diabetes

The pathogenic processes involving in the development of diabetes range from autoimmune destruction of pancreatic β-cells with consequent insulin deficiency to abnormalities that result in resistance to insulin action. The major contributing factor for excessive β-cell death includes oxidative stress-mediated mitochondrial damage, which creates an imbalance in redox homeostasis. Yet, β-cells have evolved adaptive mechanisms to endure a wide range of stress conditions to safeguard its potential functions. These include 'Nrf2/Keap1' pathway, a key cellular defense mechanism, to combat oxidative stress by regulating phase II detoxifying and antioxidant genes. During diabetes, redox imbalance provokes defective Nrf2-dependent signaling and compromise antioxidant capacity of the pancreas which turnout β-cells to become highly vulnerable against various insults. Hence, identification of small molecule activators of Nrf2/Keap1 pathway remains significant to enhance cellular defense to overcome the burden of oxidative stress related disturbances. This review summarizes the molecular mechanism behind Nrf2 activation and the impact of Nrf2 activators in diabetes and its complications.

Effect of redox modulating NRF2 activators on chronic kidney disease

Chronic kidney disease (CKD) is featured by a progressive decline of kidney function and is mainly caused by chronic diseases such as diabetes mellitus and hypertension. CKD is a complex disease due to cardiovascular complications and high morbidity; however, there is no single treatment to improve kidney function in CKD patients. Since biological markers representing oxidative stress are significantly elevated in CKD patients, oxidative stress is receiving attention as a contributing factor to CKD pathology. Nuclear factor erythroid-2 related factor 2 (NRF2) is a predominant transcription factor that regulates the expression of a wide array of genes encoding antioxidant proteins, thiol molecules and their generating enzymes, detoxifying enzymes, and stress response proteins, all of which can counteract inflammatory and oxidative damages. There is considerable experimental evidence suggesting that NRF2 signaling plays a protective role in renal injuries that are caused by various pathologic conditions. In addition, impaired NRF2 activity and consequent target gene repression have been observed in CKD animals. Therefore, a pharmacological intervention activating NRF2 signaling can be beneficial in protecting against kidney dysfunction in CKD. This review article provides an overview of the role of NRF2 in experimental CKD models and describes current findings on the renoprotective effects of naturally occurring NRF2 activators, including sulforaphane, resveratrol, curcumin, and cinnamic aldehyde. These experimental results, coupled with recent clinical experiences with a synthetic triterpenoid, bardoxolone methyl, have brought a light of hope for ameliorating CKD progression by preventing oxidative stress and maintaining cellular redox homeostasis.

Nrf2 null enhances UVB-induced skin inflammation and extracellular matrix damages

Nrf2 plays a critical role in defending against oxidative stress and inflammation. We previously reported that Nrf2 confers protection against ultraviolet-B (UVB)-induced inflammation, sunburn reaction, and is involved in sulforaphane-mediated photo-protective effects in the skin. In this study, we aimed to demonstrate the protective role of Nrf2 against inflammation-mediated extracellular matrix (ECM) damage induced by UVB irradiation. Ear biopsy weights were significantly increased in both Nrf2 wild-type (Nrf2 WT) and knockout (Nrf2 KO) mice one week after UVB irradiation. However, these weights increased more significantly in KO mice compared to WT mice, suggesting a greater inflammatory response in KO mice. In addition, we analyzed the protein expression of numerous markers, including macrophage inflammatory protein-2 (MIP-2), pro-matrix metalloproteinase-9 (MMP-9), and p53. p53, a regulator of DNA repair, was overexpressed in Nrf2 KO mice, indicating that the absence of Nrf2 led to more sustained DNA damage. There was also more substantial ECM degradation and increased inflammation in UVB-irradiated Nrf2 KO mice compared to UVB-irradiated WT mice. Furthermore, the protective effects of Nrf2 in response to UVB irradiation were mediated by increased HO-1 protein expression. Collectively, our results show that Nrf2 plays a key role in protecting against UVB irradiation and that the photo-protective effect of Nrf2 is closely related to the inhibition of ECM degradation and inflammation.

Plant extracts of the family Lauraceae: a potential resource for chemopreventive agents that activate the nuclear factor-erythroid 2-related factor 2/antioxidant response element pathway

Cells and tissues counteract insults from exogenous or endogenous carcinogens through the expression of genes encoding antioxidants and phase II detoxifying enzymes regulated by antioxidant response element promoter regions. Nuclear factor-erythroid 2-related factor 2 plays a key role in regulating the antioxidant response elements-target gene expression. Hence, the Nrf2/ARE pathway represents a vital cellular defense mechanism against damage caused by oxidative stress and xenobiotics, and is recognized as a potential molecular target for discovering chemopreventive agents. Using a stable antioxidant response element luciferase reporter cell line derived from human breast cancer MDA-MB-231 cells combined with a 96-well high-throughput screening system, we have identified a series of plant extracts from the family Lauraceae that harbor Nrf2-inducing effects. These extracts, including Litsea garrettii (ZK-08), Cinnamomum chartophyllum (ZK-02), C. mollifolium (ZK-04), C. camphora var. linaloolifera (ZK-05), and C. burmannii (ZK-10), promoted nuclear translocation of Nrf2, enhanced protein expression of Nrf2 and its target genes, and augmented intracellular glutathione levels. Cytoprotective activity of these extracts against two electrophilic toxicants, sodium arsenite and H2O2, was investigated. Treatment of human bronchial epithelial cells with extracts of ZK-02, ZK-05, and ZK-10 significantly improved cell survival in response to sodium arsenite and H2O2, while ZK-08 showed a protective effect against only H2O2. Importantly, their protective effects against insults from both sodium arsenite and H2O2 were Nrf2-dependent. Therefore, our data provide evidence that the selected plants from the family Lauraceae are potential sources for chemopreventive agents targeting the Nrf2/ARE pathway.

Estrogen receptor and PI3K/Akt signaling pathway involvement in S-(-)equol-induced activation of Nrf2/ARE in endothelial cells

S-(-)equol, a natural product of the isoflavone daidzein, has been reported to offer cytoprotective effects with respect to the cardiovascular system, but how this occurs is unclear. Interestingly, S-(-)equol is produced by the human gut, suggesting a role in physiological processes. We report that treatment of human umbilical vein endothelial cells and EA.hy926 cells with S-(-)equol induces ARE-luciferase reporter gene activity that is dose and time dependent. S-(-)equol (10-250 nM) increases nuclear factor-erythroid 2-related factor 2 (Nrf2) as well as gene products of Nrf2 target genes heme oxygenase-1 (HO-1) and NAD(P)H (nicotinamide-adenine-dinucleotide-phosphate) quinone oxidoreductase 1 (NQO1). Endothelial cells transfected with an HA-Nrf2 expression plasmid had elevated HA-Nrf2, HO-1, and NQO1 in response to S-(-)equol exposure. S-(-)equol treatment affected Nrf2 mRNA only slightly but significantly increased HO-1 and NQO1 mRNA. The pretreatment of cells with specific ER inhibitors or PI3K/Akt (ICI182,780 and LY294002) increased Nrf2, HO-1, and NQO1 protein, impaired nuclear translocation of HA-Nrf2, and decreased ARE-luciferase activity. Identical experiments were conducted with daidzein, which had effects similar to S-(-)equol. In addition, DPN treatment (an ERβ agonist) induced the ARE-luciferase reporter gene, promoting Nrf2 nuclear translocation. Cell pretreatment with an ERβ antagonist (PHTPP) impaired S-(-)equol-induced Nrf2 activation. Pre-incubation of cells followed by co-treatment with S-(-)equol significantly improved cell survival in response to H2O2 or tBHP and reduced apoptotic and TUNEL-positively-stained cells. Notably, the ability of S-(-)equol to protect against H2O2-induced cell apoptosis was attenuated in cells transfected with an siRNA against Nrf2. Thus, beneficial effects of S-(-)equol with respect to cytoprotective antioxidant gene activation may represent a novel strategy to prevent and treat cardiovascular diseases.

The Nrf2-inducers tanshinone I and dihydrotanshinone protect human skin cells and reconstructed human skin against solar simulated UV

Exposure to solar ultraviolet (UV) radiation is a causative factor in skin photocarcinogenesis and photoaging, and an urgent need exists for improved strategies for skin photoprotection. The redox-sensitive transcription factor Nrf2 (nuclear factor-E2-related factor 2), a master regulator of the cellular antioxidant defense against environmental electrophilic insult, has recently emerged as an important determinant of cutaneous damage from solar UV, and the concept of pharmacological activation of Nrf2 has attracted considerable attention as a novel approach to skin photoprotection. In this study, we examined feasibility of using tanshinones, a novel class of phenanthrenequinone-based cytoprotective Nrf2 inducers derived from the medicinal plant Salvia miltiorrhiza, for protection of cultured human skin cells and reconstructed human skin against solar simulated UV. Using a dual luciferase reporter assay in human Hs27 dermal fibroblasts pronounced transcriptional activation of Nrf2 by four major tanshinones [tanshinone I (T-I), dihydrotanshinone (DHT), tanshinone IIA (T-II-A) and cryptotanshinone (CT)] was detected. In fibroblasts, the more potent tanshinones T-I and DHT caused a significant increase in Nrf2 protein half-life via blockage of ubiquitination, ultimately resulting in upregulated expression of cytoprotective Nrf2 target genes (GCLC, NQO1) with the elevation of cellular glutathione levels. Similar tanshinone-induced changes were also observed in HaCaT keratinocytes. T-I and DHT pretreatment caused significant suppression of skin cell death induced by solar simulated UV and riboflavin-sensitized UVA. Moreover, feasibility of tanshinone-based cutaneous photoprotection was tested employing a human skin reconstruct exposed to solar simulated UV (80 mJ/cm² UVB; 1.53 J/cm² UVA). The occurrence of markers of epidermal solar insult (cleaved procaspase 3, pycnotic nuclei, eosinophilic cytoplasm, acellular cavities) was significantly attenuated in DHT-treated reconstructs that displayed increased immunohistochemical staining for Nrf2 and γ-GCS together with the elevation of total glutathione levels. Taken together, our data suggest the feasibility of achieving tanshinone-based cutaneous Nrf2-activation and photoprotection.

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Tanshinones are phenanthrenequinone-based Nrf2 inducers active in human skin cells.

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Tanshinones upregulate Nrf2 target gene expression with the elevation of glutathione.

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Dihydrotanshinone protects cultured human skin cells against solar simulated UV.

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Dihydrotanshinone protects reconstructed human skin against acute photodamage.