Impaired redox signaling and antioxidant gene expression in endothelial cells in diabetes: a role for mitochondria and the nuclear factor-E2-related factor 2-Kelch-like ECH-associated protein 1 defense pathway

Vanillic acid alleviates palmitic acid-induced oxidative stress in human umbilical vein endothelial cells via Adenosine Monophosphate-Activated Protein Kinase signaling pathway

Vanillic acid (VA), one of the phenolic acids metabolized by anthocyanidins, can modulate vascular reactivity by reducing the superoxide. We investigated that VA alleviated fatty acid-induced oxidative stress and clarified its potential mechanisms in human umbilical vein endothelial cells (HUVECs). Our results showed that VA reduced the production of reactive oxygen species and malondialdehyde levels. It also restored mitochondrial membrane potential and enhanced the activities of antioxidant enzymes. In addition, VA promoted the expression of p-Nrf2 and HO-1 through LKB1/AMPK signaling pathway, as well as the level of SIRT1 and PGC-1α. Moreover, compound C reduced the effect of VA on the enhancement of p-Nrf2 and HO-1. These results indicated that AMPK was an important target molecule of VA in the process of alleviating oxidative stress in HUVECs, providing a new potential evidence for vascular protection of anthocyanin in vitro. PRACTICAL APPLICATIONS: As a phenolic derivative and phase II metabolite of anthocyanins in vivo, VA can be found in various edible plants and fruits. This study revealed that VA improved oxidative stress in endothelial cells stimulated by palmitic acid by activating AMPK and its downstream proteins. VA could be a potential functional material for the protection of diabetic vascular complications.

Biomarkers of Oxidative Stress in Metabolic Syndrome and Associated Diseases

Metabolic syndrome (MS) represents worldwide public health issue characterized by a set of cardiovascular risk factors including obesity, diabetes, dyslipidemia, hypertension, and impaired glucose tolerance. The link between the MS and the associated diseases is represented by oxidative stress (OS) and by the intracellular redox imbalance, both caused by the persistence of chronic inflammatory conditions that characterize MS. The increase in oxidizing species formation in MS has been accepted as a major underlying mechanism for mitochondrial dysfunction, accumulation of protein and lipid oxidation products, and impairment of the antioxidant systems. These oxidative modifications are recognized as relevant OS biomarkers potentially able to (i) clarify the role of reactive oxygen and nitrogen species in the etiology of the MS, (ii) contribute to the diagnosis/evaluation of the disease's severity, and (iii) evaluate the utility of possible therapeutic strategies based on natural antioxidants. The antioxidant therapies indeed could be able to (i) counteract systemic as well as mitochondrial-derived OS, (ii) enhance the endogenous antioxidant defenses, (iii) alleviate MS symptoms, and (iv) prevent the complications linked to MS-derived cardiovascular diseases. The focus of this review is to summarize the current knowledge about the role of OS in the development of metabolic alterations characterizing MS, with particular regard to the occurrence of OS-correlated biomarkers, as well as to the use of therapeutic strategies based on natural antioxidants.

Hyperandrogenism and insulin resistance induce gravid uterine defects in association with mitochondrial dysfunction and aberrant reactive oxygen species production

Women with polycystic ovary syndrome (PCOS) are at increased risk of miscarriage, which often accompanies the hyperandrogenism and insulin resistance seen in these patients. However, neither the combinatorial interaction between these two PCOS-related etiological factors nor the mechanisms of their actions in the uterus during pregnancy are well understood. We hypothesized that hyperandrogensim and insulin resistance exert a causative role in miscarriage by inducing defects in uterine function that are accompanied by mitochondrial-mediated oxidative stress, inflammation, and perturbed gene expression. Here, we tested this hypothesis by studying the metabolic, endocrine, and uterine abnormalities in pregnant rats after exposure to daily injection of 5α-dihydrotestosterone (DHT; 1.66 mg·kg body wt^-1·day^-1) and/or insulin (6.0 IU/day) from gestational day 7.5 to 13.5. We showed that whereas DHT-exposed and insulin-exposed pregnant rats presented impaired insulin sensitivity, DHT + insulin-exposed pregnant rats exhibited hyperandrogenism and peripheral insulin resistance, which mirrors pregnant PCOS patients. Compared with controls, hyperandrogenism and insulin resistance in the dam were associated with alterations in uterine morphology and aberrant expression of genes responsible for decidualization (Prl8a2, Fxyd2, and Mt1g), placentation (Fcgr3 and Tpbpa), angiogenesis (Flt1, Angpt1, Angpt2, Ho1, Ccl2, Ccl5, Cxcl9, and Cxcl10) and insulin signaling (Akt, Gsk3, and Gluts). Moreover, we observed changes in uterine mitochondrial function and homeostasis (i.e., mitochondrial DNA copy number and the expression of genes responsible for mitochondrial fusion, fission, biogenesis, and mitophagy) and suppression of both oxidative and antioxidative defenses (i.e., reactive oxygen species, Nrf2 signaling, and interactive networks of antioxidative stress responses) in response to the hyperandrogenism and insulin resistance. These findings demonstrate that hyperandrogenism and insulin resistance induce mitochondria-mediated damage and a resulting imbalance between oxidative and antioxidative stress responses in the gravid uterus.

Recombinant FGF21 Protects Against Blood-Brain Barrier Leakage Through Nrf2 Upregulation in Type 2 Diabetes Mice

Blood-brain barrier (BBB) damage is a characteristic feature of diabetes mellitus pathology and plays significant roles in diabetes-associated neurological disorders. However, effective treatments for diabetes targeting BBB damage are yet to be developed. Fibroblast growth factor 21 (FGF21) is a potent regulator of lipid and glucose metabolism. In this study, we tested the hypothesis that recombinant FGF21 (rFGF21) administration may reduce type 2 diabetes (T2D)-induced BBB disruption via NF-E2-related factor-2 (Nrf2) upregulation. Our experimental results show that rFGF21 treatment significantly ameliorated BBB permeability and preserved junction protein expression in db/db mice in vivo. This protective effect was further confirmed by ameliorated transendothelial permeability and junction protein loss by rFGF21 under hyperglycemia and IL1β (HG-IL1β) condition in cultured human brain microvascular endothelial cells (HBMEC) in vitro. We further reveal that rFGF21 can activate FGF receptor 1 (FGFR1) that increases its binding with Kelch ECH-associating protein 1 (Keap1), a repressor of Nrf2, thereby reducing Keap1-Nrf2 interaction leading to Nrf2 release. These data suggest that rFGF21 administration may decrease T2D-induced BBB permeability, at least in part via FGFR1-Keap1-Nrf2 activation pathway. This study may provide an impetus for development of therapeutics targeting BBB damage in diabetes.

PM2.5 exposure induces systemic inflammation and oxidative stress in an intracranial atherosclerosis rat model

OBJECTIVES

Exposure to airborne particle (PM_2.5 ) is a risk factor for intracranial atherosclerosis (ICA). Because of the established role of systemic inflammation and oxidative stress by PM_2.5 , we determined whether these processes account for PM_2.5 -mediated ICA, and also whether omega-3 fatty acid (O3FA) dietary supplementation could attenuate them.

METHODS

Adult Sprague-Dawley rats were exposed to filtered air (FA) or PM_2.5 and fed either a normal chow diet (NCD) or a high-cholesterol diet (HCD), administered with or without O3FA (5 mg/kg/day by gavage) for 12 weeks. The lumen and thickness of the middle cerebral artery (MCA) were assessed. Serum tumor necrosis factor alpha (TNF-α), interleukin 6 (IL-6), interleukin-1β (IL-1β), and interferon gamma (IFN-γ) were detected by ELISA. Reactive oxygen species (ROS), malondialdehyde (MDA), superoxide dismutase (SOD) activity, nicotinamide adenine dinucleotide phosphate (NADPH) oxidase (NOX) activity, mRNA levels of Nrf2, HO-1, NQO-1, and protein level of NOX subunit gp91 were quantified to determine the oxidative profile of brain vessels.

RESULTS

PM_2.5 increased (P < .05) ICA, especially in the HCD group; elevated serum TNF-α, IL-6, IL-1β, and IFN-γ; increased cerebrovascular ROS, MDA, NOX activity, and gp91 protein levels; and decreased cerebrovascular SOD activity. Nrf2, HO-1, and NQO-1 mRNA levels were upregulated (P < .05) by PM_2.5 exposure, especially in the HCD group. O3FA attenuated (P < .05) PM_2.5 -induced systemic inflammation, vascular oxidative injury, and ICA.

CONCLUSIONS

PM_2.5 exposure induced systemic inflammation, cerebrovascular oxidative injury, and ICA in rats with HCD. O3FA prevented ICA development, and may therefore exert a protective effect against the atherogenic potential of PM_2.5 .

Paradoxical Roles of Oxidative Stress Response in the Digestive System before and after Carcinogenesis

Oxidative stress is recognized as a cancer-initiating stress response in the digestive system. It is produced through mitochondrial respiration and induces DNA damage, resulting in cancer cell transformation. However, recent findings indicate that oxidative stress is also a necessary anticancer response for destroying cancer cells. The oxidative stress response has also been reported to be an important step in increasing the anticancer response of newly developed molecular targeted agents. Oxidative stress might therefore be a cancer-initiating response that should be downregulated in the precancerous stage in patients at risk of cancer but an anticancer cell response that should not be downregulated in the postcancerous stage when cancer cells are still present. Many commercial antioxidant agents are marketed as “cancer-eliminating agents” or as products to improve one’s health, so cancer patients often take these antioxidant agents. However, care should be taken to avoid harming the anticancerous oxidative stress response. In this review, we will highlight the paradoxical effects of oxidative stress and antioxidant agents in the digestive system before and after carcinogenesis.

Drug screening assay based on the interaction of intact Keap1 and Nrf2 proteins in cancer cells

BACKGROUND

The Nrf2-Keap1 interaction is the major regulatory pathway for cytoprotective responses against oxidative and electrophilic stresses. Keap1, a substrate protein of a Cul3-dependent E3 ubiquitin ligase complex, is a negative regulator of Nrf2. The use of chemicals to regulate the interaction between Keap1 and Nrf2 has been proposed as a strategy for the chemoprevention of degenerative diseases and cancers.

RESULTS

The interactions between Keap1 and Nrf2 in vitro and in vivo were investigated using fluorescence resonance energy transfer (FRET) and bimolecular fluorescence complementation (BiFC) strategies in our study. Nrf2 with its N-terminal fused to eGFP and Keap1 with its C-terminal fused to mCherry were expressed and purified in vitro. When purified eGFP-Nrf2 and Keap1-mChrry proteins were mixed together, a strong FRET signal could be detected, indicating an efficient energy transfer from eGFP to mCherry. Moreover, the FRET was detected in vivo using confocal microscopy in colon cancer HCT-116 cells that were co-transfected with eGFP-Nrf2 and Keap1-mCherry. Finally, using an eGFP BiFC approach, the Keap1-Nrf2 interaction was also detected in MCF7 cells by transfecting eGFP N-terminal fused to Nrf2 (eN158-Nrf2) and eGFP C-terminal fused to Keap1 (eC159-Keap1). Using the BiFC and FRET systems, we demonstrated that the prototypical Nrf2-activiting compound tBHQ and the antitumor drug F-dUrd might interfere with the intracellular interaction between Keap1 and Nrf2 whereas the 5-Fu have little role in activating the protective response of Nrf2 pathway in cancer cells.

CONCLUSIONS

By analyzing the perturbation of the energy transfer between the donor and acceptor fluorophores and the bimolecular fluorescence complementation of eGFP, we can screen potential inhibitors for the interaction between Keap1 and Nrf2.

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

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

Inhibition of NRF2 signaling and increased reactive oxygen species during embryogenesis in a rat model of retinoic acid-induced neural tube defects

Exposure to retinoic acid (RA) during pregnancy increases the risk of serious neural tube defects (NTDs) in the developing fetus. The precise molecular mechanism for this process is unclear; however, RA is associated with oxidative stress mediated by reactive oxygen species. Nuclear factor erythroid 2-related factor 2 (NRF2) is a master regulator of oxidative stress that directs the expression of antioxidant genes and detoxifying proteins to maintain redox homeostasis. We established a rat model of NTDs in which pregnant dams were administered all-trans (at)RA on gestational day 10, and oxidative stress levels and the spatiotemporal expression of NRF2 and its downstream targets were examined in the resulting embryos and in maternal blood. In the NTD group, total antioxidative capacity decreased and 8-hydroxy-2'-deoxyguanosine increased in maternal serum and fetal spinal cord tissues. Plasma GSH content, the GSH/GSSG ratio, and glutathione peroxidase activity in fetal spinal cords were lower in the NTD group relative to controls. We detected NRF2 protein reduction and concomitant upregulation of Kelch-like ECH-associated protein 1 (KEAP1) - a cytoplasmic inhibitor of NRF2 - in the NTD group. The mRNA and protein levels of downstream targets of NRF2 were downregulated in the spinal cords of NTD embryos. These data demonstrate substantial oxidative stress and NRF2 signaling pathway disruption in a model of NTDs induced by atRA. The inhibitory effects of atRA on NRF2 signaling may lower cellular defenses against RA-induced oxidative stress and could play important roles in NTD occurrence during embryonic development.

Pulmonary vascular dysfunction in metabolic syndrome

Metabolic syndrome is a critically important precursor to the onset of many diseases, such as cardiovascular disease, and cardiovascular disease is the leading cause of death worldwide. The primary risk factors of metabolic syndrome include hyperglycaemia, abdominal obesity, dyslipidaemia, and high blood pressure. It has been well documented that metabolic syndrome alters vascular endothelial and smooth muscle cell functions in the heart, brain, kidney and peripheral vessels. However, there is less information available regarding how metabolic syndrome can affect pulmonary vascular function and ultimately increase an individual's risk of developing various pulmonary vascular diseases, such as pulmonary hypertension. Here, we review in detail how metabolic syndrome affects pulmonary vascular function.

Sulforaphane protects rabbit corneas against oxidative stress injury in keratoconus through activation of the Nrf-2/HO-1 antioxidant pathway

The aim of the present study was to examine whether activation of the nuclear factor E2-related factor 2 (Nrf-2)/heme oxygenase-1 (HO-1) antioxidant pathway in the cornea was involved in the protective effect of sulforaphane (SF) following keratoconus (KC) injury. Following epithelial debridement, collagenase type II was applied in KC groups at room temperature for 30 min. Following this, rabbits were administered with a subconjunctival (s.c.) injection of SF or placebo (maize oil) daily for a total of 2 weeks. To investigate whether HO-1 was involved in the Nrf-2-related antioxidant pathway, rabbits were injected with zinc (II) protoporphyrin IX (ZnPP IX, s.c.) treatment in combination with SF 24 h following the application of collagenase type II. The protective effects of SF were evaluated by examining the mean keratometry (Km) and central cornea thickness (CCT), measuring reactive oxygen species (ROS) production using immunofluorescent staining, and analyzing the protein expression of NADPH oxidase (Nox) family members Nox-2 and Nox-4, and Nrf-2 and HO-1 using immunohistochemistry and western blot analysis. The mRNA levels of Nox-2, Nox-4, Nrf-2 and HO-1 were quantitatively detected by reverse transcription-quantitative polymerase chain reaction (RT-qPCR) analysis. No significant difference in Km or CCT was observed among groups prior to surgery (P=0.700 and P=0.982, respectively). KC induced an apparent increase of ROS generation, and caused a significant increase in Km and a significant decrease in CCT. These changes were neutralized or reversed by SF treatment. Simultaneously, SF treatment decreased the expression of Nox-2 and Nox-4, and enhanced the expression of Nrf-2 and HO-1 in the KC corneas. The RT-qPCR results indicated that SF induced downregulation of the mRNA expression of Nox-2 and Nox-4, and upregulation of the mRNA expression of Nrf-2 and HO-1 following KC injury. The HO-1 inhibitor, ZnPP IX, counteracted the protective effects of SF on KC corneas. Therefore, the present study provided evidence that activation of the Nrf-2/HO-1 signal transduction pathway may partially promote the protective effect of the antioxidant SF in the KC cornea.

Beneficial and Paradoxical Roles of Anti-Oxidative Nutritional Support for Non-Alcoholic Fatty Liver Disease

Oxidative stress is being recognized as a key factor in the progression of chronic liver disease (CLD), especially non-alcoholic fatty liver disease (NAFLD). Many NAFLD treatment guidelines recommend the use of antioxidants, especially vitamin E. Many prospective studies have described the beneficial effects of such agents for the clinical course of NAFLD. However, as these studies are usually short-term evaluations, lasting only a few years, whether or not antioxidants continue to exert favorable long-term effects, including in cases of concomitant hepatocellular carcinoma, remains unclear. Antioxidants are generally believed to be beneficial for human health and are often commercially available as health-food products. Patients with lifestyle-related diseases often use such products to try to be healthier without practicing lifestyle intervention. However, under some experimental NAFLD conditions, antioxidants have been shown to encourage the progression of hepatocellular carcinoma, as oxidative stress is toxic for cancer cells, just as for normal cells. In this review, we will highlight the paradoxical effects of antioxidants against NAFLD and related hepatocellular carcinoma.

CFTR Deletion Confers Mitochondrial Dysfunction and Disrupts Lipid Homeostasis in Intestinal Epithelial Cells

Background: Cystic Fibrosis (CF) is a genetic disease in which the intestine exhibits oxidative and inflammatory markers. As mitochondria are the central source and the main target of reactive oxygen species, we hypothesized that cystic fibrosis transmembrane conductance regulator (CFTR) defect leads to the disruption of cellular lipid homeostasis, which contributes to mitochondrial dysfunction. Methods. Mitochondrial functions and lipid metabolism were investigated in Caco-2/15 cells with CFTR knockout (CFTR^-/-) engineered by the zinc finger nuclease technique. Experiments were performed under basal conditions and after the addition of the pro-oxidant iron-ascorbate (Fe/Asc) complex. Results. Mitochondria of intestinal cells with CFTR^-/-, spontaneously showed an altered redox homeostasis characterised by a significant decrease in the expression of PPARα and nuclear factor like 2. Consistent with these observations, 8-oxoguanine-DNA glycosylase, responsible for repair of ROS-induced DNA lesion, was weakly expressed in CFTR^-/- cells. Moreover, disturbed fatty acid β-oxidation process was evidenced by the reduced expression of CPT1 and acyl-CoA dehydrogenase long-chain in CFTR^-/- cells. The decline of mitochondrial cytochrome c and B-cell lymphoma 2 expression pointing to magnified apoptosis. Mitochondrial respiration was also affected as demonstrated by the low expression of respiratory oxidative phosphorylation (OXPHOS) complexes and a high adenosine diphosphate/adenosine triphosphate ratio. In contrast, the FAS and ACC enzymes were markedly increased, thereby indicating lipogenesis stimulation. This was associated with an augmented secretion of lipids, lipoproteins and apolipoproteins in CFTR^-/- cells. The addition of Fe/Asc worsened while butylated hydroxy toluene partially improved these processes. Conclusions: CFTR silencing results in lipid homeostasis disruption and mitochondrial dysfunction in intestinal epithelial cells. Further investigation is needed to elucidate the mechanisms underlying the marked abnormalities in response to CFTR deletion.

Transcriptomics provides mechanistic indicators of mixture toxicology for IMX-101 and IMX-104 formulations in fathead minnows (Pimephales promelas)

Within the US military, new insensitive munitions (IMs) are rapidly replacing conventional munitions improving safety from unintended detonation. Toxicity data for IM chemicals are expanding rapidly, however IM constituents are typically deployed in mixture formulations, and very little is known about their mixture toxicology. In the present study we sought to characterize the mixture effects and toxicology of the two predominant IM formulations IMX-101 and IMX-104 in acute (48 h) larval fathead minnow (Pimephales promelas) exposures. IMX-101 consists of a mixture of 2,4-dinitroanisole (DNAN), 3-nitro-1,2,4-triazol-5-one (NTO), and nitroguanidine (NQ) while IMX-104 is composed of DNAN, NTO, and hexahydro-1,3,5-trinitro-1,3,5-triazine (RDX). DNAN was the most potent constituent in IMX-101 eliciting an LC50 of 36.1 mg/L, whereas NTO and NQ did not elicit significant mortality in exposures up to 1040 and 2640 mg/L, respectively. Toxic unit calculations indicated that IMX-101 elicited toxicity representative of the component concentration of DNAN within the mixture. Toxicogenomic responses for the individual constituents of IMX-101 indicated unique transcriptional expression and functional responses characteristic of: oxidative stress, impaired energy metabolism, tissue damage and inflammatory responses in DNAN exposures; impaired steroid biosynthesis and developmental cell-signaling in NQ exposures; and altered mitogen-activated protein kinase signaling in NTO exposures. Transcriptional responses to the IMX-101 mixture were driven by the effects of DNAN where expression and functional responses were nearly identical comparing DNAN alone versus the fractional equivalent of DNAN within IMX-101. Given that each individual constituent of the IMX-101 mixture elicited unique functional responses, and NTO and NQ did not interact with DNAN within the IMX-101 mixture exposure, the overall toxicity and toxicogenomic responses within acute exposures to the IMX-101 formulation are indicative of "independent" mixture toxicology. Alternatively, in the IMX-104 exposure both DNAN and RDX were each present at concentrations sufficient to elicit lethality (RDX LC50 = 28.9 mg/L). Toxic-unit calculations for IMX-104 mixture formulation exposures indicated slight synergistic toxicity (ΣTU LC50 = 0.82, 95% confidence interval = 0.73-0.90). Unique functional responses relative to DNAN were observed in the IMX-104 exposure including responses characteristic of RDX exposure. Based on previous transcriptomics responses to acute RDX exposures in fathead minnow larvae, we hypothesize that the potentially synergistic responses within the IMX-104 mixture are related to interactive effects of each DNAN and RDX on oxidative stress mitigation pathways.

Impact of carbonylation on glutathione peroxidase-1 activity in human hyperglycemic endothelial cells

AIMS

High levels of glucose and reactive carbonyl intermediates of its degradation pathway such as methylglyoxal (MG) may contribute to diabetic complications partly via increased generation of reactive oxygen species (ROS). This study focused on glutathione peroxidase-1 (GPx1) expression and the impact of carbonylation as an oxidative protein modification on GPx1 abundance and activity in human umbilical vein endothelial cells (HUVEC) under conditions of mild to moderate oxidative stress.

RESULTS

High extracellular glucose and MG enhanced intracellular ROS formation in HUVECs. Protein carbonylation was only transiently augmented pointing to an effective antioxidant defense in these cells. Nitric oxide synthase expression was decreased under hyperglycemic conditions but increased upon exposure to MG, whereas superoxide dismutase expression was not significantly affected. Increased glutathione peroxidase (GPx) activity seemed to compensate for a decrease in GPx1 protein due to enhanced degradation via the proteasome. Mass spectrometry analysis identified Lys-114 as a possible carbonylation target which provides a vestibule for the substrate H2O2 and thus enhances the enzymatic reaction.

INNOVATION

Oxidative protein carbonylation has so far been associated with functional inactivation of modified target proteins mainly contributing to aging and age-related diseases. Here, we demonstrate that mild oxidative stress and subsequent carbonylation seem to activate protective cellular redox signaling pathways whereas severe oxidative stress overwhelms the cellular antioxidant defense leading to cell damage.

CONCLUSIONS

This study may contribute to a better understanding of redox homeostasis and its role in the development of diabetes and related vascular complications.

Xueshuantong injection (lyophilized) combined with salvianolate lyophilized injection protects against focal cerebral ischemia/reperfusion injury in rats through attenuation of oxidative stress

Salvianolate lyophilized injection (SLI) and Xueshuantong injection (lyophilized) (XST) are two herbal standardized preparations that have been widely used in China for the treatment of acute cerebral infarction. In this study, we investigated the neuroprotective effects of SLI combined with XST in a rat model of middle cerebral artery occlusion-reperfusion (MCAO/R). Wistar rats were subjected to 1.5 h of MCAO followed by reperfusion for 3 h, then were treated with SLI or XST alone, or with their combinations via tail vein injection daily for 3 d. Edaravone (EDI, 6 mg·kg^-1·d^-1) was used as a positive control drug, We showed that administration of a combination of 1X1S (XST 100 mg·kg^-1·d^-1 plus SLI 21 mg·kg^-1·d^-1) more effectively protected the ischemic brains than SLI or XST used alone. Administration of 1X1S not only significantly decreased neurological deficit scores and infarct volumes and increased regional cerebral blood flow, but also inhibited the activation of both microglia and astrocytes in the hippocampus. Furthermore, administration of 1X1S significantly decreased the levels of MDA and ROS with concomitant increases in the levels of antioxidant activity (SOD, CAT and GSH) in the brain tissues as compared with SLI and XST used alone. Moreover, administration of 1X1S remarkably upregulated the expression of Nrf-2, HO-1 and NQO-1, and downregulated the expression of Keap1 and facilitated the nuclear translocation of Nrf-2 in the brain tissues as compared with XST used alone. Our study demonstrates that a combination of 1X1S effectively protects MCAO/R injury via suppressing oxidative stress and the Nrf-2/Keap1 pathway.

Fibroblast growth factor 19 protects the heart from oxidative stress-induced diabetic cardiomyopathy via activation of AMPK/Nrf2/HO-1 pathway

Diabetes affects cardiac structure and function, where it leads to diabetic cardiomyopathy. Reactive oxygen species (ROS) produced by oxidative stress play an important role in the development of diabetic cardiomyopathy. Fibroblast growth factor (FGF) 19, an enterokine, is synthesized and released into the ileum. In the present study, we revealed that FGF19 induced an antioxidant response through stimulating the expression of nuclear erythroid factor 2 (NE-F2)-related factor 2 (Nrf2) and as well as reducing ROS production through the AMPK signaling pathway. Additionally, AMPK inhibition by the AMPK-specific inhibitor compound C decreased Nrf2 and heme oxygenase-1 (HO-1) protein expression. Taken together, these results suggested that FGF19, through the anti-oxidative defense system, attenuated the development of diabetic cardiomyopathy and restored cardiac function.

Oxidative stress biomarkers in type 2 diabetes mellitus for assessment of cardiovascular disease risk

AIMS

Type-2 Diabetes Mellitus (T2DM) is one of the most prevalent and progressive metabolic conditions affecting approximately 8.5% of the global population. Individuals with T2DM have a significantly increased risk of developing chronic conditions such as cardiovascular disease (CVD) and its associated complications, therefore, it is of great importance to establish strategies for combatting T2DM and its associated chronic conditions. Current literature has identified several biomarkers that are known to play a key role in the pathogenesis of CVD. Many of these biomarkers affecting CVD are influenced by an increase in oxidative stress as seen in T2DM. The purpose of this review is to analyse and correlate the oxidative stress-related biomarkers that have been identified in the literature to provide an updated summary of their significance in CVD risk factors.

DATA SYNTHESIS

This review has analysed current research on T2DM, CVD, and oxidative stress. Four key cardiovascular risk factors: thrombosis, inflammation, vascular homeostasis and cellular proliferation were searched to identify potential biomarkers for this review. These biomarkers stem from seven major cellular pathways; NF-κB, Keap1-Nrf2, protein kinase-C, macrophage activation, arachidonic acid mobilisation, endothelial dysfunction and advanced glycation end products.

CONCLUSIONS

The pathways and biomarkers were analysed to show their role as contributing factors to CVD development and a summary is made regarding the assessment of cardiovascular risk in T2DM individuals.

Long noncoding RNA MALAT1 regulates generation of reactive oxygen species and the insulin responses in male mice

The metastasis-associated lung adenocarcinoma transcript 1 (MALAT1) is a long noncoding RNA and its overexpression is associated with the development of many types of malignancy. MALAT1 null mice show no overt phenotype. However, in transcriptome analysis of MALAT1 null mice we found significant upregulation of nuclear factor-erythroid 2 p45-related factor 2 (Nrf2) regulated antioxidant genes including Nqo1 and Cat with significant reduction in reactive oxygen species (ROS) and greatly reduced ROS-generated protein carbonylation in hepatocyte and islets. We performed lncRNA pulldown assay using biotinylated antisense oligonucleotides against MALAT1 and found MALAT1 interacted with Nrf2, suggesting Nrf2 is transcriptionally regulated by MALAT1. Exposure to excessive ROS has been shown to cause insulin resistance through activation of c-Jun N-terminal kinase (JNK) which leads to inhibition of insulin receptor substrate 1 (IRS-1) and insulin-induced phosphorylation of serine/threonine kinase Akt. We found MALAT1 ablation suppressed JNK activity with concomitant insulin-induced activation of IRS-1 and phosphorylation of Akt suggesting MALAT1 regulated insulin responses. MALAT1 null mice exhibited sensitized insulin-signaling response to fast-refeeding and glucose/insulin challenges and significantly increased insulin secretion in response to glucose challenge in isolated MALAT1 null islets, suggesting an increased insulin sensitivity. In summary, we demonstrate that MALAT1 plays an important role in regulating insulin sensitivity and has the potential as a therapeutic target for the treatment of diabetes as well as other diseases caused by excessive exposure to ROS.

Role of MicroRNA in Endothelial Dysfunction and Hypertension

Purpose of Review

Hypertension is either a cause or a consequence of the endothelial dysfunction and a major risk factor for cardiovascular disease (CVD). In vitro and in vivo studies established that microRNAs (miRNAs) are decisive for endothelial cell gene expression and function in various pathological conditions associated with CVD.

This review provides an overview of the miRNA role in controlling the key connections between endothelial dysfunction and hypertension.

Recent Findings

Herein we summarize the present understanding of mechanisms underlying hypertension and its associated endothelial dysfunction as well as the miRNA role in endothelial cells with accent on the modulation of renin-angiotensin-aldosterone-system, nitric oxide, oxidative stress and on the control of vascular inflammation and angiogenesis in relation to endothelial dysfunction in hypertension. In particular, latest insights in the identification of endothelial-specific microRNAs and their targets are added to the understanding of miRNA significance in hypertension.

Summary

This comprehensive knowledge of the role of miRNAs in endothelial dysfunction and hypertension and of molecular mechanisms proposed for miRNA actions may offer novel diagnostic biomarkers and therapeutic targets for controlling hypertension-associated endothelial dysfunction and other cardiovascular complications.

Inhibition of miR-92a Suppresses Oxidative Stress and Improves Endothelial Function by Upregulating Heme Oxygenase-1 in db/db Mice

AIMS

Inhibition of microRNA-92a (miR-92a) is reported to suppress endothelial inflammation and delay atherogenesis. We hypothesize that miR-92a inhibition protects endothelial function through suppressing oxidative stress in diabetic db/db mice.

RESULTS

In this study, we found elevated expression of miR-92a in aortic endothelium from db/db mice and in renal arteries from diabetic subjects. Endothelial cells (ECs) exposed to advanced glycation end products (AGEs) and oxidized low-density lipoprotein express higher level of miR-92a. Overexpression of miR-92a impairs endothelium-dependent relaxations (EDRs) in C57BL/6 mouse aortas. Overexpression of miR-92a suppresses expression of heme oxygenase-1 (HO-1), a critical cytoprotective enzyme, whereas inhibition of miR-92a increases HO-1 expression in human umbilical vein ECs (HUVECs) and db/db mouse aortas. Importantly, miR-92a inhibition by Ad-anti-miR-92a improved EDRs and reduced reactive oxygen species (ROS) production in db/db mouse aortas. HO-1 inhibition by SnMP or HO-1 knockdown by shHO-1 reversed the suppressive effect of miR-92a inhibition on ROS production induced by AGE treatment in C57BL/6 mouse aortas. In addition, SnMP reversed miR-92a inhibition-induced improvement of EDRs in AGE-treated C57BL/6 mouse aortas and in db/db mouse aortas.

INNOVATION

Expression of miR-92a is increased in diabetic aortic endothelium and inhibition of miR-92a exerts vasoprotective effect in diabetic mice through HO-1 upregulation in ECs.

CONCLUSION

MiR-92a expression is elevated in diabetic ECs. MiR-92a overexpression impairs endothelial function and suppresses HO-1 expression in ECs. Inhibition of miR-92a attenuates oxidative stress and improves endothelial function through enhancing HO-1 expression and activity in db/db mouse aortas. Antioxid. Redox Signal. 28, 358-370.

Macrophages sensing oxidized DAMPs reprogram their metabolism to support redox homeostasis and inflammation through a TLR2-Syk-ceramide dependent mechanism

OBJECTIVE

Macrophages control tissue homeostasis and inflammation by sensing and responding to environmental cues. However, the metabolic adaptation of macrophages to oxidative tissue damage and its translation into inflammatory mechanisms remains enigmatic.

METHODS

Here we identify the critical regulatory pathways that are induced by endogenous oxidation-derived DAMPs (oxidized phospholipids, OxPL) in vitro, leading to formation of a unique redox-regulatory metabolic phenotype (Mox), which is strikingly different from conventional classical or alternative macrophage activation.

RESULTS

Unexpectedly, metabolomic analyses demonstrated that Mox heavily rely on glucose metabolism and the pentose phosphate pathway (PPP) to support GSH production and Nrf2-dependent antioxidant gene expression. While the metabolic adaptation of macrophages to OxPL involved transient suppression of aerobic glycolysis, it also led to upregulation of inflammatory gene expression. In contrast to classically activated (M1) macrophages, Hif1α mediated expression of OxPL-induced Glut1 and VEGF but was dispensable for Il1β expression. Mechanistically, we show that OxPL suppress mitochondrial respiration via TLR2-dependent ceramide production, redirecting TCA metabolites to GSH synthesis. Finally, we identify spleen tyrosine kinase (Syk) as a critical downstream signaling mediator that translates OxPL-induced effects into ceramide production and inflammatory gene regulation.

CONCLUSIONS

Together, these data demonstrate the metabolic and bioenergetic requirements that enable macrophages to translate tissue oxidation status into either antioxidant or inflammatory responses via sensing OxPL. Targeting dysregulated redox homeostasis in macrophages could therefore lead to novel therapies to treat chronic inflammation.

The Role of Nrf2 in Cardiovascular Function and Disease

Free radicals, reactive oxygen/nitrogen species (ROS/RNS), hydrogen sulphide, and hydrogen peroxide play an important role in both intracellular and intercellular signaling; however, their production and quenching need to be closely regulated to prevent cellular damage. An imbalance, due to exogenous sources of free radicals and chronic upregulation of endogenous production, contributes to many pathological conditions including cardiovascular disease and also more general processes involved in aging. Nuclear factor erythroid 2-like 2 (NFE2L2; commonly known as Nrf2) is a transcription factor that plays a major role in the dynamic regulation of a network of antioxidant and cytoprotective genes, through binding to and activating expression of promoters containing the antioxidant response element (ARE). Nrf2 activity is regulated by many mechanisms, suggesting that tight control is necessary for normal cell function and both hypoactivation and hyperactivation of Nrf2 are indicated in playing a role in different aspects of cardiovascular disease. Targeted activation of Nrf2 or downstream genes may prove to be a useful avenue in developing therapeutics to reduce the impact of cardiovascular disease. We will review the current status of Nrf2 and related signaling in cardiovascular disease and its relevance to current and potential treatment strategies.

Airborne PM2.5-Induced Hepatic Insulin Resistance by Nrf2/JNK-Mediated Signaling Pathway

Animal and epidemiological studies have suggested that exposure to airborne particulate matter (PM) with an aerodynamic diameter less than 2.5 μm (PM_2.5) is associated with the risk of developing type 2 diabetes. However, the mechanism underlying this risk is poorly understood. In the present study, we investigated the effects of PM_2.5 exposure on glucose homeostasis and related signaling pathways in mice. Wild-type and nuclear factor erythroid 2-related factor 2 (Nrf2) knockout (Nrf2^−/−) C57BL/6 male mice were exposed to either ambient concentrated PM_2.5 or filtered air (FA) for 12 weeks through a whole-body PM exposure system. At the end of the exposure, we assessed liver damage, and performed metabolic studies, gene expressions, as well as molecular signal transductions to determine the signaling pathways involving oxidative responses, insulin signaling, and glucose metabolism. Our results indicated that PM_2.5 exposure for 12 weeks caused significant liver damage as evidenced by elevated levels of aminotransferase (AST) and alanine aminotransferase (ALT). Furthermore, PM_2.5 exposure induced impaired glucose tolerance and inhibited glycogen synthesis, leading to hepatic insulin resistance indicated by higher glucose levels, higher area under the curve (AUC), and homeostasis model assessment of insulin resistance (HOMA-IR) values. We further found that PM_2.5 exposure significantly increased the expressions of Nrf2 and Nrf2-regulated antioxidant genes. Moreover, PM_2.5 exposure activated the c-Jun N-terminal kinase (JNK) signaling pathway and increased insulin receptor substrate-1 (IRS-1) phosphorylation at Ser³⁰⁷, but reduced protein kinase B phosphorylation at Ser⁴⁷³. Taken together, our study demonstrated PM_2.5 exposure triggered Nrf2-mediated oxidative responses and activated the JNK-mediated inhibitory signaling pathway, resulting in hepatic insulin resistance.

Endothelial microparticles prevent lipid-induced endothelial damage via Akt/eNOS signaling and reduced oxidative stress

Endothelial microparticles (EMPs) are endothelium-derived submicron vesicles that are released in response to diverse stimuli and are elevated in cardiovascular disease, which is correlated with risk factors. This study investigates the effect of EMPs on endothelial cell function and dysfunction in a model of free fatty acid (FFA) palmitate-induced oxidative stress. EMPs were generated from TNF-α-stimulated HUVECs and quantified by using flow cytometry. HUVECs were treated with and without palmitate in the presence or absence of EMPs. EMPs were found to carry functional eNOS and to protect against oxidative stress by positively regulating eNOS/Akt signaling, which restored NO production, increased superoxide dismutase and catalase, and suppressed NADPH oxidase and reactive oxygen species (ROS) production, with the involvement of NF-erythroid 2-related factor 2 and heme oxygenase-1. Conversely, under normal conditions, EMPs reduced NO release and increased ROS and redox-sensitive marker expression. In addition, functional assays using EMP-treated mouse aortic rings that were performed under homeostatic conditions demonstrated a decline in endothelium-dependent vasodilatation, but restored the functional response under lipid-induced oxidative stress. These data indicate that EMPs harbor functional eNOS and potentially play a role in the feedback loop of damage and repair during homeostasis, but are also effective in protecting against FFA-induced oxidative stress; thus, EMP function is reflected by the microenvironment.-Mahmoud, A. M., Wilkinson, F. L., McCarthy, E. M., Moreno-Martinez, D., Langford-Smith, A., Romero, M., Duarte, J., Alexander, M. Y. Endothelial microparticles prevent lipid-induced endothelial damage via Akt/eNOS signaling and reduced oxidative stress.

The Transcription Factor Nrf2 Protects Angiogenic Capacity of Endothelial Colony-Forming Cells in High-Oxygen Radical Stress Conditions

Background

Endothelial colony forming cells (ECFCs) have shown a promise in tissue engineering of vascular constructs, where they act as endothelial progenitor cells. After implantation, ECFCs are likely to be subjected to elevated reactive oxygen species (ROS). The transcription factor Nrf2 regulates the expression of antioxidant enzymes in response to ROS.

Methods

Stable knockdown of Nrf2 and Keap1 was achieved by transduction with lentiviral shRNAs; activation of Nrf2 was induced by incubation with sulforaphane (SFN). Expression of Nrf2 target genes was assessed by qPCR, oxidative stress was assessed using CM-DCFDA, and angiogenesis was quantified by scratch-wound and tubule-formation assays Results. Nrf2 knockdown led to a reduction of antioxidant gene expression and increased ROS. Angiogenesis was disturbed after Nrf2 knockdown even in the absence of ROS. Conversely, angiogenesis was preserved in high ROS conditions after knockdown of Keap1. Preincubation of ECFCs with SFN reduced intracellular ROS in the presence of H₂O₂ and preserved scratch-wound closure and tubule-formation.

Results

Nrf2 knockdown led to a reduction of antioxidant gene expression and increased ROS. Angiogenesis was disturbed after Nrf2 knockdown even in the absence of ROS. Conversely, angiogenesis was preserved in high ROS conditions after knockdown of Keap1. Preincubation of ECFCs with SFN reduced intracellular ROS in the presence of H₂O₂ and preserved scratch-wound closure and tubule-formation.

Conclusion

The results of this study indicate that Nrf2 plays an important role in the angiogenic capacity of ECFCs, particularly under conditions of increased oxidative stress. Pretreatment of ECFCs with SFN prior to implantation may be a protective strategy for tissue-engineered constructs or cell therapies.

Metabolic Syndrome as a Multifaceted Risk Factor for Oxidative Stress

SIGNIFICANCE

Metabolic syndrome (MetS) is associated with a greater risk of diabetes and cardiovascular diseases. It is estimated that this multifactorial condition affects 20%-30% of the world's population. A detailed understanding of MetS mechanisms is crucial for the development of effective prevention strategies and adequate intervention tools that could curb its increasing prevalence and limit its comorbidities, particularly in younger age groups. With advances in basic redox biology, oxidative stress (OxS) involvement in the complex pathophysiology of MetS has become widely accepted. Nevertheless, its clear association with and causative effects on MetS require further elucidation. Recent Advances: Although a better understanding of the causes, risks, and effects of MetS is essential, studies suggest that oxidant/antioxidant imbalance is a key contributor to this condition. OxS is now understood to be a major underlying mechanism for mitochondrial dysfunction, ectopic lipid accumulation, and gut microbiota impairment.

CRITICAL ISSUES

Further studies, particularly in the field of translational research, are clearly required to understand and control the production of reactive oxygen species (ROS) levels, especially in the mitochondria, since the various therapeutic trials conducted to date have not targeted this major ROS-generating system, aimed to delay MetS onset, or prevent its progression.

FUTURE DIRECTIONS

Multiple relevant markers need to be identified to clarify the role of ROS in the etiology of MetS. Future clinical trials should provide important proof of concept for the effectiveness of antioxidants as useful therapeutic approaches to simultaneously counteract mitochondrial OxS, alleviate MetS symptoms, and prevent complications. Antioxid. Redox Signal. 26, 445-461.

Epigenetic regulation of redox signaling in diabetic retinopathy: Role of Nrf2

Diabetic retinopathy is a major vision threatening disease among working age adults, and increased oxidative stress is one of the prime causative factors in its pathogenesis. Increased reactive oxygen species (ROS) in the cytosol damage mitochondria, and due to compromised antioxidant signaling system and dysfunctional mitochondria with damaged mitochondrial DNA, ROS continue to pile up, accelerating capillary cell loss. In addition to other cellular and enzymatic defense systems, the retina is also equipped with the nuclear erythroid-2-p45-related factor-2 (Nrf2) antioxidant response element signaling pathway, which controls the expression of genes important in detoxification and elimination of ROS. However, in diabetes, its transcriptional activity is impaired, further exacerbating and exposing the retina to elevated stress. Diabetic milieu also alters epigenetic factors responsible for chromatin modifications and gene regulation, and kelch-like ECH-associated protein 1 (Keap1), important in regulating Nrf2-antioxidant signaling axis, is epigenetically modified, impeding nuclear translocation of Nrf2, and this inhibits the transcription of genes with Antioxidant Response Element. This review discusses antioxidant signaling, especially the role of Nrf2, in diabetic retinopathy, and possible involvement of epigenetic modifications in antioxidant signaling and Nrf2 transcriptional activity. Therapies targeting Nrf2 activation, including epigenetic modifications, have potentional to prevent mitochondrial damage and inhibit the development, and progression of this sight-threatening disease which most of the patients get after 20-25 years of diabetes.

Hyperglycemia Aggravates Hepatic Ischemia Reperfusion Injury by Inducing Chronic Oxidative Stress and Inflammation

Aim. To investigate whether hyperglycemia will aggravate hepatic ischemia reperfusion injury (HIRI) and the underlying mechanisms. Methods. Control and streptozotocin-induced diabetic Sprague-Dawley rats were subjected to partial hepatic ischemia reperfusion. Liver histology, transferase, inflammatory cytokines, and oxidative stress were assessed accordingly. Similarly, BRL-3A hepatocytes were subjected to hypoxia/reoxygenation (H/R) after high (25 mM) or low (5.5 mM) glucose culture. Cell viability, reactive oxygen species (ROS), and activation of nuclear factor-erythroid 2-related factor 2 (Nrf2) and nuclear factor of kappa light polypeptide gene enhancer in B-cells (NF-κB) were determined. Results. Compared with control, diabetic rats presented more severe hepatic injury and increased hepatic inflammatory cytokines and oxidative stress. HIRI in diabetic rats could be ameliorated by pretreatment of N-acetyl-L-cysteine (NAC) or apocynin. Excessive ROS generation and consequent Nrf2 and NF-κB translocation were determined after high glucose exposure. NF-κB translocation and its downstream cytokines were further increased in high glucose cultured group after H/R. While proper regulation of Nrf2 to its downstream antioxidases was observed in low glucose cultured group, no further induction of Nrf2 pathway by H/R after high glucose culture was identified. Conclusion. Hyperglycemia aggravates HIRI, which might be attributed to chronic oxidative stress and inflammation and potential malfunction of antioxidative system.

Recurrent Sleep Fragmentation Induces Insulin and Neuroprotective Mechanisms in Middle-Aged Flies

Lack of quality sleep increases central nervous system oxidative stress and impairs removal of neurotoxic soluble metabolites from brain parenchyma. During aging poor sleep quality, caused by sleep fragmentation, increases central nervous system cellular stress. Currently, it is not known how organisms offset age-related cytotoxic metabolite increases in order to safeguard neuronal survival. Furthermore, it is not understood how age and sleep fragmentation interact to affect oxidative stress protection pathways. We demonstrate sleep fragmentation increases systems that protect against oxidative damage and neuroprotective endoplasmic reticulum molecular chaperones, as well as neuronal insulin and dopaminergic expression in middle-aged Drosophila males. Interestingly, even after sleep recovery the expression of these genes was still upregulated in middle-aged flies. Finally, sleep fragmentation generates higher levels of reactive oxygen species (ROS) in middle-aged flies and after sleep recovery these levels remain significantly higher than in young flies. The fact that neuroprotective pathways remain upregulated in middle-aged flies beyond sleep fragmentation suggests it might represent a strong stressor for the brain during later life.

Histidine Prevents Cu-Induced Oxidative Stress and the Associated Decreases in mRNA from Encoding Tight Junction Proteins in the Intestine of Grass Carp (Ctenopharyngodon idella)

Copper (Cu) is a common heavy metal pollutant in aquatic environments that originates from natural as well as anthropogenic sources. The present study investigated whether Cu causes oxidative damage and induces changes in the expression of genes that encode tight junction (TJ) proteins, cytokines and antioxidant-related genes in the intestine of the grass carp (Ctenopharyngodon idella). We demonstrated that Cu decreases the survival rate of fish and increases oxidative damage as measured by increases in malondialdehyde and protein carbonyl contents. Cu exposure significantly decreased the expression of genes that encode the tight junction proteins, namely, claudin (CLDN)-c, -3 and -15 as well as occludin and zonula occludens-1, in the intestine of fish. In addition, Cu exposure increases the mRNA levels of the pro-inflammatory cytokines, specifically, IL-8, TNF-α and its related signalling factor (nuclear factor kappa B, NF-κB), which was partly correlated to the decreased mRNA levels of NF-κB inhibitor protein (IκB). These changes were associated with Cu-induced oxidative stress detected by corresponding decreases in glutathione (GSH) content, as well as decreases in the copper, zinc-superoxide dismutase (SOD1) and glutathione peroxidase (GPx) activities and mRNA levels, which were associated with the down-regulated antioxidant signalling factor NF-E2-related factor-2 (Nrf2) mRNA levels, and the Kelch-like-ECH-associated protein1 (Keap1) mRNA levels in the intestine of fish. Histidine supplementation in diets (3.7 up to 12.2 g/kg) blocked Cu-induced changes. These results indicated that Cu-induced decreases in intestinal TJ proteins and cytokine mRNA levels might be partially mediated by oxidative stress and are prevented by histidine supplementation in fish diet.

The Keap1-Nrf2-ARE Pathway As a Potential Preventive and Therapeutic Target: An Update

The Keap1-Nrf2-ARE ((Kelch-like ECH-Associating protein 1) nuclear factor erythroid 2 related factor 2-antioxidant response element) pathway is one of the most important defense mechanisms against oxidative and/or electrophilic stresses, and it is closely associated with inflammatory diseases, including cancer, neurodegenerative diseases, cardiovascular diseases, and aging. In recent years, progress has been made in strategies aimed at modulating the Keap1-Nrf2-ARE pathway. The Nrf2 activator DMF (Dimethylfumarates) has been approved by the FDA as a new first-line oral drug to treat patients with relapsing forms of multiple sclerosis, while a phase 3 study of another promising candidate, CDDO-Me, was terminated for safety reasons. Directly inhibiting Keap1-Nrf2 protein-protein interactions as a novel Nrf2-modulating strategy has many advantages over using electrophilic Nrf2 activators. The development of Keap1-Nrf2 protein-protein interaction inhibitors has become a topic of intense research, and potent inhibitors of this target have been identified. In addition, inhibiting Nrf2 activity has attracted an increasing amount of attention because it may provide an alternative cancer therapy. This review summarizes the molecular mechanisms and biological functions of the Keap1-Nrf2-ARE system. The main focus of this review is on recent progress in studies of agents that target the Keap1-Nrf2-ARE pathway and the therapeutic applications of such agents.

Mitochondrial Dysfunction in Alzheimer's Disease and the Rationale for Bioenergetics Based Therapies

Alzheimer’s disease (AD) is a debilitating neurodegenerative disorder characterized by the progressive loss of cholinergic neurons, leading to the onset of severe behavioral, motor and cognitive impairments. It is a pressing public health problem with no effective treatment. Existing therapies only provide symptomatic relief without being able to prevent, stop or reverse the pathologic process. While the molecular basis underlying this multifactorial neurodegenerative disorder remains a significant challenge, mitochondrial dysfunction appears to be a critical factor in the pathogenesis of this disease. It is therefore important to target mitochondrial dysfunction in the prodromal phase of AD to slow or prevent the neurodegenerative process and restore neuronal function. In this review, we discuss mechanisms of action and translational potential of current mitochondrial and bioenergetic therapeutics for AD including: mitochondrial enhancers to potentiate energy production; antioxidants to scavenge reactive oxygen species and reduce oxidative damage; glucose metabolism and substrate supply; and candidates that target apoptotic and mitophagy pathways to remove damaged mitochondria. While mitochondrial therapeutic strategies have shown promise at the preclinical stage, there has been little progress in clinical trials thus far.

Nrf2 antioxidant defense is involved in survival signaling elicited by 27-hydroxycholesterol in human promonocytic cells

Cholesterol oxidation products such as oxysterols are considered critical factors in the atherosclerotic plaque formation since they induce oxidative stress, inflammation and apoptotic cell death. 27-hydroxycholesterol (27-OH) is one of the most represented oxysterols in atherosclerotic lesions. We recently showed that relatively low concentrations of 27-OH generated a strong survival signaling through an early and transient increase of cellular ROS level, that enhanced MEK-ERK/PI3K-Akt phosphorylation, in turn responsible of a sustained quenching of ROS production. It remains to identify the link between ERK/Akt up-regulation and the consequent quenching effect on ROS intracellular level that efficiently and markedly delay the pro-apoptotic effect of the oxysterol. Here we report on the potent activation of Nrf2 redox-sensitive transcription factor by low micromolar amount of 27-OH added to U937 promonocytic cells. The 27-OH-exerted induction of Nrf2 and subsequently of the target genes, HO-1 and NQO-1, was proved to be: (i) dependent upon the activation of ERK and Akt pathways, (ii) directly responsible for the quenching of intracellular oxidative stress and by this way (iii) ultimately responsible for the observed oxysterol-induced pro-survival response.

Microparticulate/Nanoparticulate Powders of a Novel Nrf2 Activator and an Aerosol Performance Enhancer for Pulmonary Delivery Targeting the Lung Nrf2/Keap-1 Pathway

This systematic and comprehensive study reports for the first time on the successful rational design of advanced inhalable therapeutic dry powders containing dimethyl fumarate, a first-in-class Nrf2 activator drug to treat pulmonary inflammation, using particle engineering design technology for targeted delivery to the lungs as advanced spray dried (SD) one-component DPIs. In addition, two-component co-spray dried (co-SD) DMF:D-Man DPIs with high drug loading were successfully designed for targeted lung delivery as advanced DPIs using organic solution advanced spray drying in closed mode. Regional targeted deposition using design of experiments (DoE) for in vitro predictive lung modeling based on aerodynamic properties was tailored based on composition and spray drying parameters. These findings indicate the significant potential of using D-Man in spray drying to improve particle formation and aerosol performance of small molecule with a relatively low melting point. These respirable microparticles/nanoparticles in the solid-state exhibited excellent aerosol dispersion performance with an FDA-approved human DPI device. Using in vitro predictive lung deposition modeling, the aerosol deposition patterns of these particles show the capability to reach lower airways to treat inflammation in this region in pulmonary diseases such as acute lung injury (ALI), chronic obstructive pulmonary disease (COPD), pulmonary hypertension (PH), and pulmonary endothelial disease.

Mitochondrial Quality Control as a Therapeutic Target

In addition to oxidative phosphorylation (OXPHOS), mitochondria perform other functions such as heme biosynthesis and oxygen sensing and mediate calcium homeostasis, cell growth, and cell death. They participate in cell communication and regulation of inflammation and are important considerations in aging, drug toxicity, and pathogenesis. The cell's capacity to maintain its mitochondria involves intramitochondrial processes, such as heme and protein turnover, and those involving entire organelles, such as fusion, fission, selective mitochondrial macroautophagy (mitophagy), and mitochondrial biogenesis. The integration of these processes exemplifies mitochondrial quality control (QC), which is also important in cellular disorders ranging from primary mitochondrial genetic diseases to those that involve mitochondria secondarily, such as neurodegenerative, cardiovascular, inflammatory, and metabolic syndromes. Consequently, mitochondrial biology represents a potentially useful, but relatively unexploited area of therapeutic innovation. In patients with genetic OXPHOS disorders, the largest group of inborn errors of metabolism, effective therapies, apart from symptomatic and nutritional measures, are largely lacking. Moreover, the genetic and biochemical heterogeneity of these states is remarkably similar to those of certain acquired diseases characterized by metabolic and oxidative stress and displaying wide variability. This biologic variability reflects cell-specific and repair processes that complicate rational pharmacological approaches to both primary and secondary mitochondrial disorders. However, emerging concepts of mitochondrial turnover and dynamics along with new mitochondrial disease models are providing opportunities to develop and evaluate mitochondrial QC-based therapies. The goals of such therapies extend beyond amelioration of energy insufficiency and tissue loss and entail cell repair, cell replacement, and the prevention of fibrosis. This review summarizes current concepts of mitochondria as disease elements and outlines novel strategies to address mitochondrial dysfunction through the stimulation of mitochondrial biogenesis and quality control.

Heme oxygenase-1-derived bilirubin protects endothelial cells against high glucose-induced damage

Hyperglycemia and diabetes are associated with endothelial cell dysfunction arising from enhanced oxidative injury, leading to the progression of diabetic vascular pathologies. The redox-sensitive transcription factor nuclear factor-E2-related factor 2 (Nrf2) is a master regulator of antioxidant genes, such as heme oxygenase-1 (HO-1), involved in cellular defenses against oxidative stress. We have investigated the pathways involved in high glucose-induced activation of HO-1 in endothelial cells and examined the molecular mechanisms underlying cytoprotection. Elevated d-glucose increased intracellular generation of reactive oxygen species (ROS), leading to nuclear translocation of Nrf2 and HO-1 expression in bovine aortic endothelial cells, with no changes in cell viability. Superoxide scavenging and inhibition of endothelial nitric oxide synthase (eNOS) abrogated upregulation of HO-1 expression by elevated glucose. Inhibition of HO-1 increased the sensitivity of endothelial cells to high glucose-mediated damage, while addition of bilirubin restored cell viability. Our findings establish that exposure of endothelial cells to high glucose leads to activation of endogenous antioxidant defense genes via the Nrf2/ARE pathway. Upregulation of HO-1 provides cytoprotection against high glucose-induced oxidative stress through the antioxidant properties of bilirubin. Modulation of the Nrf2 pathway in the early stages of diabetes may thus protect against sustained damage by hyperglycemia during progression of the disease.

Diabetes and ageing-induced vascular inflammation

Diabetes and the ageing process independently increase the risk for cardiovascular disease (CVD). Since incidence of diabetes increases as people get older, the diabetic older adults represent the largest population of diabetic subjects. This group of patients would potentially be threatened by the development of CVD related to both ageing and diabetes. The relationship between CVD, ageing and diabetes is explained by the negative impact of these conditions on vascular function. Functional and clinical evidence supports the role of vascular inflammation induced by the ageing process and by diabetes in vascular impairment and CVD. Inflammatory mechanisms in both aged and diabetic vasculature include pro-inflammatory cytokines, vascular hyperactivation of nuclear factor-кB, increased expression of cyclooxygenase and inducible nitric oxide synthase, imbalanced expression of pro/anti-inflammatory microRNAs, and dysfunctional stress-response systems (sirtuins, Nrf2). In contrast, there are scarce data regarding the interaction of these mechanisms when ageing and diabetes co-exist and its impact on vascular function. Older diabetic animals and humans display higher vascular impairment and CVD risk than those either aged or diabetic, suggesting that chronic low-grade inflammation in ageing creates a vascular environment favouring the mechanisms of vascular damage driven by diabetes. Further research is needed to determine the specific inflammatory mechanisms responsible for exacerbated vascular impairment in older diabetic subjects in order to design effective therapeutic interventions to minimize the impact of vascular inflammation. This would help to prevent or delay CVD and the specific clinical manifestations (cognitive decline, frailty and disability) promoted by diabetes-induced vascular impairment in the elderly.

Keap1-Nrf2 regulated redox signaling in utero: Priming of disease susceptibility in offspring

Intrauterine exposure to gestational diabetes, pre-eclampsia or intrauterine growth restriction alters the redox status of the developing fetus. Such pregnancy-related diseases in most cases do not have a readily identifiable genetic cause, and epigenetic 'priming' mechanisms in utero may predispose both mother and child to later-life onset of cardiovascular and metabolic diseases. The concept of 'fetal programing' or 'developmental priming' and its association with an increased risk of disease in childhood or adulthood has been reviewed extensively. This review focuses on adaptive changes in the in utero redox environment during normal pregnancy and the consequences of alterations in redox control associated with pregnancies characterized by oxidative stress. We evaluate the evidence that the Keap1-Nrf2 pathway is important for protecting the fetus against adverse conditions in utero and may itself be subject to epigenetic priming, potentially contributing to an increased risk of vascular disease and insulin resistance in later life.

Mechanisms of activation of the transcription factor Nrf2 by redox stressors, nutrient cues, and energy status and the pathways through which it attenuates degenerative disease

Nuclear factor-erythroid 2 p45-related factor 2 (Nrf2) regulates the basal and stress-inducible expression of a battery of genes encoding key components of the glutathione-based and thioredoxin-based antioxidant systems, as well as aldo-keto reductase, glutathione S-transferase, and

NAD(P)H

quinone oxidoreductase-1 drug-metabolizing isoenzymes along with multidrug-resistance-associated efflux pumps. It therefore plays a pivotal role in both intrinsic resistance and cellular adaptation to reactive oxygen species (ROS) and xenobiotics. Activation of Nrf2 can, however, serve as a double-edged sword because some of the genes it induces may contribute to chemical carcinogenesis by promoting futile redox cycling of polycyclic aromatic hydrocarbon metabolites or confer resistance to chemotherapeutic drugs by increasing the expression of efflux pumps, suggesting its cytoprotective effects will vary in a context-specific fashion. In addition to cytoprotection, Nrf2 also controls genes involved in intermediary metabolism, positively regulating those involved in NADPH generation, purine biosynthesis, and the β-oxidation of fatty acids, while suppressing those involved in lipogenesis and gluconeogenesis. Nrf2 is subject to regulation at multiple levels. Its ability to orchestrate adaptation to oxidants and electrophiles is due principally to stress-stimulated modification of thiols within one of its repressors, the Kelch-like ECH-associated protein 1 (Keap1), which is present in the cullin-3 RING ubiquitin ligase (CRL) complex CRLKeap1. Thus modification of Cys residues in Keap1 blocks CRLKeap1 activity, allowing newly translated Nrf2 to accumulate rapidly and induce its target genes. The ability of Keap1 to repress Nrf2 can be attenuated by p62/sequestosome-1 in a mechanistic target of rapamycin complex 1 (mTORC1)-dependent manner, thereby allowing refeeding after fasting to increase Nrf2-target gene expression. In parallel with repression by Keap1, Nrf2 is also repressed by β-transducin repeat-containing protein (β-TrCP), present in the Skp1-cullin-1-F-box protein (SCF) ubiquitin ligase complex SCFβ-TrCP. The ability of SCFβ-TrCP to suppress Nrf2 activity is itself enhanced by prior phosphorylation of the transcription factor by glycogen synthase kinase-3 (GSK-3) through formation of a DSGIS-containing phosphodegron. However, formation of the phosphodegron in Nrf2 by GSK-3 is inhibited by stimuli that activate protein kinase B (PKB)/Akt. In particular, PKB/Akt activity can be increased by phosphoinositide 3-kinase and mTORC2, thereby providing an explanation of why antioxidant-responsive element-driven genes are induced by growth factors and nutrients. Thus Nrf2 activity is tightly controlled via CRLKeap1 and SCFβ-TrCP by oxidative stress and energy-based signals, allowing it to mediate adaptive responses that restore redox homeostasis and modulate intermediary metabolism. Based on the fact that Nrf2 influences multiple biochemical pathways in both positive and negative ways, it is likely its dose-response curve, in terms of susceptibility to certain degenerative disease, is U-shaped. Specifically, too little Nrf2 activity will lead to loss of cytoprotection, diminished antioxidant capacity, and lowered β-oxidation of fatty acids, while conversely also exhibiting heightened sensitivity to ROS-based signaling that involves receptor tyrosine kinases and apoptosis signal-regulating kinase-1. By contrast, too much Nrf2 activity disturbs the homeostatic balance in favor of reduction, and so may have deleterious consequences including overproduction of reduced glutathione and NADPH, the blunting of ROS-based signal transduction, epithelial cell hyperplasia, and failure of certain cell types to differentiate correctly. We discuss the basis of a putative U-shaped Nrf2 dose-response curve in terms of potentially competing processes relevant to different stages of tumorigenesis.

The role of Nrf2 in protection against Pb-induced oxidative stress and apoptosis in SH-SY5Y cells

Lead exerts severe adverse effects on the nervous system in which oxidative stress might mediate impairments. In this study, we focused on Nrf2, which has been identified to significantly influence the protection of a cellular system against many xenobiotic compounds. We found that PbAc exhibited neurotoxicity mainly through oxidant-based processes and could be inhibited by NAC and DPI in SH-SY5Y cells. As a defense response, Nrf2 was activated when exposed to PbAc, thereby inducing a rapid increase in Nrf2 nuclear accumulation, as well as Nrf2-ARE binding activities in a ROS-dependent manner. Analysis of Nrf2-regulated gene expression and protein showed that PbAc could induce the mRNA transcription of HO-1, GSTα1, GCLM, GCLC, and NQO1, as well as the protein expression of HO-1 and γ-GCS. The responses of these genes to PbAc were regulated by Nrf2. Silencing Nrf2 expression in SH-SY5Y cells inhibited PbAc-induced gene transcription and protein expression. Overexpression of Nrf2 led to decreased ROS production and cell apoptosis, as well as increased cell viability under PbAc exposure. These results indicated that the Nrf2-ARE system exhibited a protective role in Pb-induced neurotoxicity, providing potential therapeutic strategies for the prevention and treatment of Pb-related diseases.