Targeting the Nrf2-Keap1 antioxidant defence pathway for neurovascular protection in stroke

The Impact of Previous Physical Training on Redox Signaling after Traumatic Brain Injury in Rats: A Behavioral and Neurochemical Approach

Throughout the world, traumatic brain injury (TBI) is one of the major causes of disability, which can include deficits in motor function and memory, as well as acquired epilepsy. Although some studies have shown the beneficial effects of physical exercise after TBI, the prophylactic effects are poorly understood. In the current study, we demonstrated that TBI induced by fluid percussion injury (FPI) in adult male Wistar rats caused early motor impairment (24 h), learning deficit (15 days), spontaneous epileptiform events (SEE), and hilar cell loss in the hippocampus (35 days) after TBI. The hippocampal alterations in the redox status, which were characterized by dichlorofluorescein diacetate oxidation and superoxide dismutase (SOD) activity inhibition, led to the impairment of protein function (Na(+), K(+)-adenosine triphosphatase [ATPase] activity inhibition) and glutamate uptake inhibition 24 h after neuronal injury. The molecular adaptations elicited by previous swim training protected against the glutamate uptake inhibition, oxidative stress, and inhibition of selected targets for free radicals (e.g., Na(+), K(+)-ATPase) 24 h after neuronal injury. Our data indicate that this protocol of exercise protected against FPI-induced motor impairment, learning deficits, and SEE. In addition, the enhancement of the hippocampal phosphorylated nuclear factor erythroid 2-related factor (P-Nrf2)/Nrf2, heat shock protein 70, and brain-derived neurotrophic factor immune content in the trained injured rats suggests that protein expression modulation associated with an antioxidant defense elicited by previous physical exercise can prevent toxicity induced by TBI, which is characterized by cell loss in the dentate gyrus hilus at 35 days after TBI. Therefore, this report suggests that previous physical exercise can decrease lesion progression in this model of brain damage.

Drugs of abuse and blood-brain barrier endothelial dysfunction: A focus on the role of oxidative stress

Psychostimulants and nicotine are the most widely abused drugs with a detrimental impact on public health globally. While the long-term neurobehavioral deficits and synaptic perturbations are well documented with chronic use of methamphetamine, cocaine, and nicotine, emerging human and experimental studies also suggest an increasing incidence of neurovascular complications associated with drug abuse. Short- or long-term administration of psychostimulants or nicotine is known to disrupt blood-brain barrier (BBB) integrity/function, thus leading to an increased risk of brain edema and neuroinflammation. Various pathophysiological mechanisms have been proposed to underlie drug abuse-induced BBB dysfunction suggesting a central and unifying role for oxidative stress in BBB endothelium and perivascular cells. This review discusses drug-specific effects of methamphetamine, cocaine, and tobacco smoking on brain microvascular crisis and provides critical assessment of oxidative stress-dependent molecular pathways focal to the global compromise of BBB. Additionally, given the increased risk of human immunodeficiency virus (HIV) encephalitis in drug abusers, we have summarized the synergistic pathological impact of psychostimulants and HIV infection on BBB integrity with an emphasis on unifying role of endothelial oxidative stress. This mechanistic framework would guide further investigations on specific molecular pathways to accelerate therapeutic approaches for the prevention of neurovascular deficits by drugs of abuse.

Curcumin by down-regulating NF-kB and elevating Nrf2, reduces brain edema and neurological dysfunction after cerebral I/R

BACKGROUND

Oxidation, inflammation, and apoptosis are three critical factors for the pathogenic mechanism of cerebral ischemia/reperfusion (I/R) injury. Curcumin exhibits substantial biological properties via anti-oxidation, anti-inflammation and anti-apoptotic effects; however, the molecular mechanism underlying the effects of curcumin against cerebral I/R injury remains unclear.

OBJECTIVE

To investigate the effects of curcumin on cerebral I/R injury associated with water content, infarction volume, and the expression of nuclear factor-kappa-B (NF-κB) and nuclear factor-erythroid-related factor-2 (Nrf2).

METHODS

Middle cerebral artery occlusion (MCAO, 1-hour occlusion and 24-hour reperfusion) was performed in male Wistar rats (n=64) as a cerebral I/R injury model. In the MCAO+CUR group, the rats were administered curcumin (300mg/kg BW, i.p.) at 30min after occlusion. The same surgical procedures were performed in SHAM rats without MCAO occlusion. At 24h post-operation, the parameters, including neurological deficit scores, blood brain barrier (BBB) disruption, water content, and infarction volume, were determined. Brain tissue NF-κB and Nrf2 expression levels were assayed through immunohistochemistry.

RESULTS

Compared with the SHAM group, BBB disruption, neurological deficit, and increased brain water content and infarction volume were markedly demonstrated in the MCAO group. NF-κB expression was enhanced in the MCAO group. However, in the MCAO+CUR group, the upregulation of Nrf2, an anti-oxidation related protein, was consistent with a significant decline in the water content, infarction volume, and NF-κB expression.

CONCLUSION

The protective effects of curcumin against cerebral I/R injury reflect anti-oxidation, anti-inflammation and anti-apoptotic activities, resulting in the elevation of Nrf2 and down-regulation of NF-κB.

The NRF2 knockout rat: a new animal model to study endothelial dysfunction, oxidant stress, and microvascular rarefaction

Nuclear factor (erythroid-derived 2)-like-2 (NRF2) is a master antioxidant and cell protective transcription factor that upregulates antioxidant defenses. In this study we developed a strain of Nrf2 null mutant rats to evaluate the role of reduced NRF2-regulated antioxidant defenses in contributing to endothelial dysfunction and impaired angiogenic responses during salt-induced ANG II suppression. Nrf2(-/-) mutant rats were developed using transcription activator-like effector nuclease technology in the Sprague-Dawley genetic background, and exhibited a 41-bp deletion that included the start codon for Nrf2 and an absence of immunohistochemically detectable NRF2 protein. Expression of mRNA for the NRF2-regulated indicator enzymes heme oxygenase-1, catalase, superoxide dismutase 1, superoxide dismutase 2, and glutathione reductase was significantly lower in livers of Nrf2(-/-) mutant rats fed high salt (HS; 4% NaCl) for 2 wk compared with wild-type controls. Endothelium-dependent dilation to acetylcholine was similar in isolated middle cerebral arteries (MCA) of Nrf2(-/-) mutant rats and wild-type littermates fed low-salt (0.4% NaCl) diet, and was eliminated by short-term (3 days) HS diet in both strains. Low-dose ANG II infusion (100 ng/kg sc) reversed salt-induced endothelial dysfunction in MCA and prevented microvessel rarefaction in wild-type rats fed HS diet, but not in Nrf2(-/-) mutant rats. The results of this study indicate that suppression of NRF2 antioxidant defenses plays an essential role in the development of salt-induced oxidant stress, endothelial dysfunction, and microvessel rarefaction in normotensive rats and emphasize the potential therapeutic benefits of directly upregulating NRF2-mediated antioxidant defenses to ameliorate vascular oxidant stress in humans.

Left ventricular diastolic dysfunction in Nrf2 knock out mice is associated with cardiac hypertrophy, decreased expression of SERCA2a, and preserved endothelial function

Increased production of reactive oxygen species and failure of the antioxidant defense system are considered to play a central role in the pathogenesis of cardiovascular disease. The transcription factor nuclear factor (erythroid-derived 2)-like 2 (Nrf2) is a key master switch controlling the expression of antioxidant and protective enzymes, and was proposed to participate in protection of vascular and cardiac function. This study was undertaken to analyze cardiac and vascular phenotype of mice lacking Nrf2. We found that Nrf2 knock out (Nrf2 KO) mice have a left ventricular (LV) diastolic dysfunction, characterized by prolonged E wave deceleration time, relaxation time and total diastolic time, increased E/A ratio and myocardial performance index, as assessed by echocardiography. LV dysfunction in Nrf2 KO mice was associated with cardiac hypertrophy, and a downregulation of the sarcoplasmic reticulum Ca(2+)-ATPase (SERCA2a) in the myocardium. Accordingly, cardiac relaxation was impaired, as demonstrated by decreased responses to β-adrenergic stimulation by isoproterenol ex vivo, and to the cardiac glycoside ouabain in vivo. Surprisingly, we found that vascular endothelial function and endothelial nitric oxide synthase (eNOS)-mediated vascular responses were fully preserved, blood pressure was decreased, and eNOS was upregulated in the aorta and the heart of Nrf2 KO mice. Taken together, these results show that LV dysfunction in Nrf2 KO mice is mainly associated with cardiac hypertrophy and downregulation of SERCA2a, and is independent from changes in coronary vascular function or systemic hemodynamics, which are preserved by a compensatory upregulation of eNOS. These data provide new insights into how Nrf2 expression/function impacts the cardiovascular system.

The role of rhynchophylline in alleviating early brain injury following subarachnoid hemorrhage in rats

Rhynchophylline (Rhy) has been demonstrated protective effects on some neurological diseases. However, the roles of Rhy in the subarachnoid hemorrhage (SAH) are still to be cleared. In the present study, the effects of Rhy on attenuation of early brain injury (EBI) after SAH have been evaluated. The adult male Sprague-Dawley rats (280-300g) were used to establish the SAH models using endovascular perforation method. Rhy was administered by intraperitoneal injection immediately following SAH. Brain edema was assessed by magnetic resonance imaging (MRI) at 24h after SAH. Neurological deficits, brain water content, malondialdehyde (MDA) concentration, myeloperoxidase (MPO) activity and reactive oxygen species (ROS) content in hippocampus were also evaluated. Immunofluorescence and western blot were used to explore the underlying protective mechanism of Rhy. The results showed that, following 10mg/kg Rhy treatment, the brain edema and neurological deficits, and blood-brain barrier (BBB) disruption were significantly attenuated at 24h after SAH. Additionally, in hippocampus, MDA concentration, MPO activity and ROS content were markedly decreased. Meanwhile, the levels of nuclear factor erythroid 2-related factor 2 (Nrf2), heme oxygenase-1 (HO-1) and NAD(P)H quinone oxidoreductase (NQO-1) were increased, while the expressions of p-p53, cleaved-caspase-3 and tumor necrosis factor-α (TNF-α) were significantly decreased. Our results indicated that Rhy could attenuate early brain injury by reducing inflammation and apoptosis in hippocampus after SAH.

Pathobiology of tobacco smoking and neurovascular disorders: untied strings and alternative products

Tobacco smoke (TS) is the leading cause of preventable deaths worldwide. In addition to a host of well characterized diseases including chronic obstructive pulmonary disease, oral and peripheral cancers and cardiovascular complications, epidemiological evidence suggests that chronic smokers are at equal risk to develop neurological and neurovascular complications such as multiple sclerosis, Alzheimer's disease, stroke, vascular dementia and small vessel ischemic disease (SVID). Unfortunately, few direct neurotoxicology studies of tobacco smoking and its pathogenic pathways have been produced so far. A major link between TS and CNS disorders is the blood-brain barrier (BBB). In this review article, we summarize the current understanding of the toxicological impact of TS on BBB physiology and function and major compensatory mechanisms such as nrf2- ARE signaling and anti-inflammatory pathways activated by TS. In the same context, we discuss the controversial role of antioxidant supplementation as a prophylactic and/or therapeutic approach in delaying or decreasing the disease complications in smokers. Further, we cover a number of toxicological studies associated with "reduced exposure" cigarette products including electronic cigarettes. Finally, we provide insights on possible avenues for future research including mechanistic studies using direct inhalation rodent models.

Modulation of oxidized-LDL receptor-1 (LOX1) contributes to the antiatherosclerosis effect of oleanolic acid

Oleanolic acid (OA) is a bioactive pentacyclic triterpenoid. The current work studied the effects and possible mechanisms of OA in atherosclerosis. Quails (Coturnix coturnix) were treated with high fat diet with or without OA. Atherosclerosis was assessed by examining lipid profile, antioxidant status and histology in serum and aorta. Human umbilical vein endothelial cells (HUVECs) were exposed to 200μg/mL ox-LDL for 24h, then cell viability was assessed with MTT assay; reactive oxygen species (ROS) was assessed with DCFDA staining. Expression levels of LOX-1, NADPH oxidase subunits, nrf2 and ho-1 were measured with real time PCR and western blotting. Furthermore, LOX-1 was silenced with lentivirus and the expression levels assessment was repeated. OA treatment improved the lipid profile and antioxidant status in quails fed with high fat diet. Histology showed decreased atherosclerosis in OA treated animals. Ox-LDL exposure decreased viability and induced ROS generation in HUVECs, and this progression was alleviated by OA pretreatment. Moreover, elevated expression of LOX-1, NADPH oxidase subunits, nrf2 and ho-1 were observed in ox-LDL exposed HUVECs. OA pretreatment prevented ox-LDL induced increase of LOX-1 and NADPH oxidase subunits expression, while further increased nrf2 and ho-1 expression. Silencing of LOX-1 abolished ox-LDL induced effects in cell viability, ROS generation and gene expression. OA could alleviate high fat diet induced atherosclerosis in quail and ox-LDL induced cytotoxicity in HUVECs; the potential mechanism involves modulation of LOX-1 activity, including inhibition of expression of NADPH oxidase subunits and increase of the expression of nrf2 and ho-1.

Procyanidin B2 attenuates neurological deficits and blood-brain barrier disruption in a rat model of cerebral ischemia

SCOPE

Disruption of the blood-brain barrier (BBB) is a major pathogenic mechanism of neurological dysfunction and death after ischemic stroke. The aim of our study was to investigate the effect of procyanidin B2 (PB), a bioactive food compound, on BBB disruption induced by ischemic stroke and explore the underlying mechanism.

METHODS AND RESULTS

PB was administrated intragastrically once a day starting at 3 h after transient middle cerebral artery occlusion (MCAO). PB treatment significantly decreased the infarction volume, brain edema, and neurological deficits after MCAO. PB prevented BBB disruption against ischemic stroke, as indicated by the reduction of Evans blue leakage and IgG levels. These results were also corroborated by immunofluorescence staining and Western blot analysis of ZO-1. Additionally, levels of reactive oxygen species and malondialdehyde were lessened in the ipsilateral ischemic area of brain by PB. The activities of antioxidant enzymes were elevated. Meanwhile, PB reversed the suppression of NF-E2-related factor nuclear translocation, and increased the protein expression of HO-1, GSTα, and NQO1 in the ipsilateral ischemic area of brain.

CONCLUSION

PB attenuates neurological deficits and BBB disruption in a rat model of cerebral ischemia, and the neuroprotection of PB is associated with activation of NF-E2-related factor pathway.

Pathophysiology and Treatments of Oxidative Injury in Ischemic Stroke: Focus on the Phagocytic NADPH Oxidase 2

SIGNIFICANCE

Phagocytes play a key role in promoting the oxidative stress after ischemic stroke occurrence. The phagocytic NADPH oxidase (NOX) 2 is a membrane-bound enzyme complex involved in the antimicrobial respiratory burst and free radical production in these cells.

RECENT ADVANCES

Different oxidants have been shown to induce opposite effects on neuronal homeostasis after a stroke. However, several experimental models support the detrimental effects of NOX activity (especially the phagocytic isoform) on brain recovery after stroke. Therapeutic strategies selectively targeting the neurotoxic ROS and increasing neuroprotective oxidants have recently produced promising results.

CRITICAL ISSUES

NOX2 might promote carotid plaque rupture and stroke occurrence. In addition, NOX2-derived reactive oxygen species (ROS) released by resident and recruited phagocytes enhance cerebral ischemic injury, activating the inflammatory apoptotic pathways. The aim of this review is to update evidence on phagocyte-related oxidative stress, focusing on the role of NOX2 as a potential therapeutic target to reduce ROS-related cerebral injury after stroke.

FUTURE DIRECTIONS

Radical scavenger compounds (such as Ebselen and Edaravone) are under clinical investigation as a therapeutic approach against stroke. On the other hand, NOX inhibition might represent a promising strategy to prevent the stroke-related injury. Although selective NOX inhibitors are not yet available, nonselective compounds (such as apocynin and fasudil) provided encouraging results in preclinical studies. Whereas additional studies are needed to better evaluate this therapeutic potential in human beings, the development of specific NOX inhibitors (such as monoclonal antibodies, small-molecule inhibitors, or aptamers) might further improve brain recovery after stroke.

Sappanone A exhibits anti-inflammatory effects via modulation of Nrf2 and NF-κB

Homoisoflavonoids constitute a small class of natural products. In the present study, we investigated the anti-inflammatory effect of sappanone A (SPNA), a homoisoflavanone that is isolated from the heartwood of Caesalpinia sappan (Leguminosae), in murine macrophages. SPNA inhibited the production of nitric oxide (NO), prostaglandin E2 (PGE2) and interleukin-6 (IL-6) as well as the expression of inducible nitric oxide synthase (iNOS), cyclooxygenase-2 (COX-2) and IL-6 in lipopolysaccharide (LPS)-stimulated RAW264.7 cells. Moreover, SPNA protected C57BL/6 mice from LPS-induced mortality. Treatment of RAW264.7 cells with SPNA induced heme oxygenase (HO)-1 protein and mRNA expression and increased nuclear translocation of the nuclear factor-E2-related factor 2 (Nrf2) as well as the expression of Nrf2 target genes such as

NAD(P)H

quinone oxidoreductase 1 (NQO1). Knockdown of Nrf2 by siRNA blocked SPNA-mediated HO-1 induction. SB203580, p38 mitogen-activated protein kinase (MAPK) inhibitor, blocked SPNA-induced HO-1 expression and nuclear translocation of Nrf2, suggesting that SPNA induces HO-1 expression by activating Nrf2 through the p38 MAPK pathway. Consistent with the notion that the Nrf2/HO-1 pathway has anti-inflammatory properties, inhibiting HO-1 significantly abrogated the anti-inflammatory effects of SPNA in LPS-stimulated RAW264.7 cells. Moreover, SPNA suppressed LPS-induced nuclear factor κB (NF-κB) activation via inhibiting Ser 536 phosphorylation and transcriptional activity of RelA/p65 subunit of NF-κB. Taken together, these findings suggest that SPNA exerts its anti-inflammatory effect by modulating the Nrf2 and NF-κB pathways, and may be a valuable compound to prevent or treat inflammatory diseases.

Comprehensive assessment of genetic sequence variants in the antioxidant 'master regulator' NRF2 in idiopathic Parkinson's disease

Parkinson’s disease (PD) is a complex neurodegenerative disorder influenced by a combination of genetic and environmental factors. The molecular mechanisms that underlie PD are unknown; however, oxidative stress and impairment of antioxidant defence mechanisms have been implicated as major contributors to disease pathogenesis. Previously, we have reported a PD patient-derived cellular model generated from biopsies of the olfactory mucosa, termed hONS cells, in which the NRF2-mediated antioxidant response pathway genes were among the most differentially-expressed. To date, few studies have examined the role of the NRF2 encoding gene, NFE2L2, and PD. In this study, we comprehensibly assessed whether rare and common NFE2L2 genetic variations modify susceptibility to PD using a large Australian case-control sample (PD=1338, controls=1379). We employed a haplotype-tagging approach that identified an association with the tagging SNP rs2364725 and PD (OR = 0.849 (0.760-0.948), P = 0.004). Further genetic screening in hONS cell lines produced no obvious pathogenic variants in the coding regions of NFE2L2. Finally, we investigated the relationship between xenobiotic exposures and NRF2 function, through gene-environment interactions, between NFE2L2 SNPs and smoking or pesticide exposure. Our results demonstrated a significant interaction between rs2706110 and pesticide exposure (OR = 0.597 (0.393-0.900), P = 0.014). In addition, we were able to identify some age-at-onset modifying SNPs and replicate an ‘early-onset’ haplotype that contains a previously identified ‘functional promoter’ SNP (rs6721961). Our results suggest a role of NFE2L2 genetic variants in modifying PD susceptibility and onset. Our findings also support the utility of testing gene-environment interactions in genetic studies of PD.

Sulfiredoxin-1 attenuates oxidative stress via Nrf2/ARE pathway and 2-Cys Prdxs after oxygen-glucose deprivation in astrocytes

Sulfiredoxin-1 (Srxn1), an endogenous antioxidant protein, is involved in keeping the balance of the cell's oxidation/reduction and can resist oxidative stress. However, the exact antioxidant effects of Srxn1 remain fully unclear. The study aims to examine the effects of Srxn1 on oxidative stress and explore the potential mechanisms in astrocytes with 6 h/oxygen-glucose deprivation (OGD), 24 h/respiration. In the study, silencing Srxn1 was performed before exposure to 6 h/OGD, 24 h/respiration in primary astrocytes. Decreased cell viability and increased cellular damage measured by CellTiter 96H AQueous Non-Radioactive Cell Proliferation Assay (MTS) and lactate dehydrogenase (LDH) were observed in Srxn1 silencing astrocytes. In addition, Srxn1 silencing resulted in a decrease in both intracellular superoxide dismutase (SOD) and glutathione (GSH). NF-E2-related factor 2 (Nrf2), a transcription factor known to influence susceptibility to oxidative stress, upregulated Srxn1 expression during oxidative stress caused by OGD in the astrocytes. Electromobility shift assay (EMSA) demonstrated a decreased binding of Nrf2 to oligomers containing Srxn1 ter-specific antioxidant response element (ARE)-binding site in Nrf2 silencing astrocytes. We also found that a reduction of peroxiredoxin (Prdx)-SO3 was closely dependent on Srxn1. In addition, 2-Cys Prdxs protein levels were increased in the astrocytes exposed to OGD, as evaluated by immunoblot analysis. All taken together, the study suggested that silencing Srxn1 would result into increasing sensitivity to OGD-induced oxidative stress injury in astrocytes. Furthermore, Nrf2/ARE pathway was involved into Srxn1, playing its antioxidant protection against oxidative stress, all of which would provide a novel therapeutic theory for treating acute ischemic brain injury.

Altered Nrf2 signaling mediates hypoglycemia-induced blood-brain barrier endothelial dysfunction in vitro

Hypoglycemia impairs blood-brain barrier (BBB) endothelial function; a major hallmark in the pathogenesis of various CNS disorders. Previously, we have demonstrated that prolonged hypoglycemic exposure down-regulated BBB endothelial NF-E2 related factor-2 (Nrf2) expression; a redox-sensitive transcriptional factor that regulates endothelial function. Here, we sought to determine the functional role of Nrf2 in preserving BBB integrity and molecular mechanisms underlying hypoglycemia-induced Nrf2 down-regulation in vitro using human cerebral microvascular endothelial cell line (hCMEC/D3). Cell monolayers were exposed to normal or hypoglycemic (5.5 or 2.2mM D-glucose) media for 3-24h. Pharmacological or gene manipulation (by silencing RNA) approaches were used to investigate specific molecular pathways implicated in hypoglycemia-induced Nrf2 degradation. BBB integrity was assessed by paracellular permeability to labeled dextrans of increasing molecular sizes (4-70kDa). Silencing Nrf2 expression in hCMEC/D3 cells abrogated the expression of claudin-5 and VE-cadherin, while ZO-1 was up-regulated. These effects were paralleled by a decrease in electrical resistance of hCMEC/D3 monolayers and potential increase in permeability to all labeled dextrans. Hypoglycemic exposure (3-24h) led to progressive and sustained down-regulation of Nrf2 (without affecting mRNA) and its target, NQO-1, with a concomitant increase in the cytosolic pool of E3 ubiquitin ligase, Siah2 (but not Keap1). Pretreatment with protease inhibitor MG132, or selective knock-down of Siah2 (but not Keap1) significantly attenuated hypoglycemia-induced Nrf2 destabilization. While hypoglycemic exposure triggered a significant increase in BBB permeability to dextrans, silencing Siah2 gene abrogated the effects of hypoglycemia and restored BBB integrity. In summary, our data indicate a potential role for Nrf2 signaling in regulating tight junction integrity and maintaining BBB function. Nrf2 suppression by increased Siah2-driven proteasomal degradation mediates hypoglycemia-evoked endothelial dysfunction and loss of BBB integrity. Overall, this study suggests that sustained activation of endothelial Nrf2 signaling could have therapeutic potential to prevent hypoglycemia-induced cerebrovascular dysfunction.

Targeting transporters: promoting blood-brain barrier repair in response to oxidative stress injury

The blood-brain barrier (BBB) is a physical and biochemical barrier that precisely regulates the ability of endogenous and exogenous substances to accumulate within brain tissue. It possesses structural and biochemical features (i.e., tight junction and adherens junction protein complexes, influx and efflux transporters) that work in concert to control solute permeation. Oxidative stress, a critical component of several diseases including cerebral hypoxia/ischemia and peripheral inflammatory pain, can cause considerable injury to the BBB and lead to significant CNS pathology. This suggests a critical need for novel therapeutic approaches that can protect the BBB in diseases with an oxidative stress component. Recent studies have identified molecular targets (i.e., putative membrane transporters, intracellular signaling systems) that can be exploited for optimization of endothelial drug delivery or for control of transport of endogenous substrates such as the antioxidant glutathione (GSH). In particular, targeting transporters offers a unique approach to protect BBB integrity by promoting repair of cell-cell interactions at the level of the brain microvascular endothelium. This review summarizes current knowledge in this area and emphasizes those targets that present considerable opportunity for providing BBB protection and/or promoting BBB repair in the setting of oxidative stress. This article is part of a Special Issue entitled SI: Cell Interactions In Stroke.

The influences of hyperbaric oxygen therapy with a lower pressure and oxygen concentration than previous methods on physiological mechanisms in dogs

Recently, hyperbaric oxygen therapy with a lower pressure and oxygen concentration (L-HBOT) than previous methods has been used for dogs in Japan; however, the influences of L-HBOT on dogs have not been clarified. To verify the influences of L-HBOT on physiological mechanism in dogs, we investigated blood gas parameters, glutathione peroxidase (GPx) activity, heart rate variability, stress-related hormones and skin conductance (SC) in 4 clinically normal beagle dogs with catheters in their carotid arteries and jugular veins when they were quiet, after running, after receiving L-HBOT (30% oxygen concentration, 1.3 atmospheres absolute, 30 min) or after not receiving L-HBOT. The results showed there were no changes in blood gas parameters, heart rate variability and catecholamine levels after L-HBOT. GPx activity was significantly higher, and the SC and cortisol level were lower in dogs that received L-HBOT than those when they were quiet. These results suggested that L-HBOT may have a small influence on oxygenation dynamics, activate antioxidant enzymes such as GPx, restrain autonomic nervous activity and control the balance between oxidation and antioxidation inside the body.

Caffeoylglycolic acid methyl ester, a major constituent of sorghum, exhibits anti-inflammatory activity via the Nrf2/heme oxygenase-1 pathway

Caffeoylglycolic acid methyl ester, a major constituent of sorghum, exhibits anti-inflammatory activityviaactivating the Nrf2/HO-1 pathway.

MicroRNA-424 protects against focal cerebral ischemia and reperfusion injury in mice by suppressing oxidative stress

BACKGROUND AND PURPOSE

We previously showed that the microRNA miR-424 protects against permanent cerebral ischemic injury in mice by suppressing microglia activation. This study investigated the role of miR-424 in transient cerebral ischemia in mice with a focus on oxidative stress-induced neuronal injury.

METHODS

Transient cerebral ischemia was induced in C57/BL6 mice by middle cerebral artery occlusion for 1 hour followed by reperfusion (ischemia/reperfusion). The miR-424 level in the peri-infarct cortex was quantified. Mice were also administered miR-424 angomir by intracerebroventricular injection. Cerebral infarct volume, neuronal apoptosis, and levels of oxidative stress markers and antioxidants were evaluated. In an in vitro experiment, primary cortical neurons were exposed to H2O2 and treated with miR-424 angomir, nuclear factor erythroid 2-related factor 2 siRNA, and superoxide dismutase (SOD) inhibitor; cell activity, lactate dehydrogenase release, malondialdehyde level, and manganese (Mn)SOD activity were then evaluated.

RESULTS

MiR-424 levels in the peri-infarct cortex increased at 1 and 4 hours then decreased 24 hours after reperfusion. Treatment with miR-424 decreased infarct volume and inhibited neuronal apoptosis after ischemia/reperfusion, reduced reactive oxygen species and malondialdehyde levels in the cortex, and increased the expression and activation of MnSOD as well as the expression of extracellular SOD and the redox-sensitive transcription factor nuclear factor erythroid 2-related factor. In neuronal cultures, miR-424 treatment abrogated H2O2-induced injury, as evidenced by decreased lactate dehydrogenase leakage and malondialdehyde level and increased cell viability and MnSOD activity; the protective effects of miR-424 against oxidative stress were reversed by nuclear factor erythroid 2-related factor knockdown and SOD inhibitor treatment.

CONCLUSIONS

MiR-424 protects against transient cerebral ischemia/reperfusion injury by inhibiting oxidative stress.

Protective effect of nuclear factor E2-related factor 2 on inflammatory cytokine response to brominated diphenyl ether-47 in the HTR-8/SVneo human first trimester extravillous trophoblast cell line

Polybrominated diphenyl ethers (PBDEs) are widely used flame retardants, and BDE-47 is a prevalent PBDE congener detected in human tissues. Exposure to PBDEs has been linked to adverse pregnancy outcomes in humans. Although the underlying mechanisms of adverse birth outcomes are poorly understood, critical roles for oxidative stress and inflammation are implicated. The present study investigated antioxidant responses in a human extravillous trophoblast cell line, HTR-8/SVneo, and examined the role of nuclear factor E2-related factor 2 (Nrf2), an antioxidative transcription factor, in BDE-47-induced inflammatory responses in the cells. Treatment of HTR-8/SVneo cells with 5, 10, 15, and 20μM BDE-47 for 24h increased intracellular glutathione (GSH) levels compared to solvent control. Treatment of HTR-8/SVneo cells with 20μM BDE-47 for 24h induced the antioxidant response element (ARE) activity, indicating Nrf2 transactivation by BDE-47 treatment, and resulted in differential expression of redox-sensitive genes compared to solvent control. Pretreatment with tert-butyl hydroquinone (tBHQ) or sulforaphane, known Nrf2 inducers, reduced BDE-47-stimulated IL-6 release with increased ARE reporter activity, reduced nuclear factor kappa B (NF-κB) reporter activity, increased GSH production, and stimulated expression of antioxidant genes compared to non-Nrf2 inducer pretreated groups, suggesting that Nrf2 may play a protective role against BDE-47-mediated inflammatory responses in HTR-8/SVneo cells. These results suggest that Nrf2 activation significantly attenuated BDE-47-induced IL-6 release by augmentation of cellular antioxidative system via upregulation of Nrf2 signaling pathways, and that Nrf2 induction may be a potential therapeutic target to reduce adverse pregnancy outcomes associated with toxicant-induced oxidative stress and inflammation.

Nrf2 upregulates ATP binding cassette transporter expression and activity at the blood-brain and blood-spinal cord barriers

Activation of nuclear factor E2-related factor-2 (Nrf2), a sensor of oxidative stress, is neuroprotective in animal models of cerebral ischemia, traumatic brain injury, subarachnoid hemorrhage, and spinal cord injury. We show here that Nrf2 activation with sulforaphane (SFN) in vivo or in vitro increases expression and transport activity of three ATP-driven drug efflux pumps at the blood-brain barrier [P-glycoprotein, ATP binding cassette b1 (Abcb1); multidrug resistance-associated protein-2 (Mrp2), Abcc2; and breast cancer resistance protein (Bcrp), Abcg2]. Dosing rats with SFN increased protein expression of all three transporters in brain capillaries and decreased by 50% brain accumulation of the P-glycoprotein substrate verapamil. Exposing rat or mouse brain capillaries to SFN increased P-glycoprotein, Bcrp, and Mrp2 transport activity and protein expression; SFN increased P-glycoprotein activity in mouse spinal cord capillaries. Inhibiting transcription or translation abolished upregulation of P-glycoprotein activity. No such effects were seen in brain capillaries from Nrf2-null mice, indicating Nrf2 dependence. Nrf2 signaled indirectly to increase transporter activity/expression. The p53 inhibitor pifithrin abolished the SFN-induced increase in transporter activity/expression, and the p53-activator nutlin-3 increased P-glycoprotein activity. SFN did not alter P-glycoprotein transport activity in brain and spinal cord capillaries from p53-null mice. Inhibitors of p38 MAPK and nuclear factor κB (NF-κB) blocked the effects of SFN and nutlin-3 on P-glycoprotein activity. These results implicate Nrf2, p53, and NF-κB in the upregulation of P-glycoprotein, Bcrp, and Mrp2 at blood-CNS barriers. They imply that the barriers are tightened selectively (efflux transporter upregulation) by oxidative stress, providing increased neuroprotection, but also reduced penetration of many therapeutic drugs.

Temporal activation of Nrf2 in the penumbra and Nrf2 activator-mediated neuroprotection in ischemia-reperfusion injury

Oxidative stress plays a critical role in mediating tissue injury and neuron death during ischemia-reperfusion injury (IRI). The Keap1-Nrf2 defense pathway serves as a master regulator of endogenous antioxidant defense, and Nrf2 has been attracting attention as a target for the treatment of IRI. In this study, we evaluated Nrf2 expression in IRI using OKD (Keap1-dependent oxidative stress detector) mice and investigated the neuroprotective ability of an Nrf2 activator. We demonstrated temporal changes in Nrf2 expression in the same mice with luciferase assays and an Nrf2 activity time course using Western blotting. We also visualized Nrf2 expression in the ischemic penumbra and investigated Nrf2 expression in mice and humans using immunohistochemistry. Endogenous Nrf2 upregulation was not detected early in IRI, but expression peaked 24h after ischemia. Nrf2 expression was mainly detected in the penumbra, and it was found in neurons and astrocytes in both mice and humans. Intravenous administration of the Nrf2 activator bardoxolone methyl (BARD) resulted in earlier upregulation of Nrf2 and heme oxygenase-1. Furthermore, BARD decreased infarction volume and improved neurological symptoms after IRI. These findings indicate that earlier Nrf2 activation protects neurons, possibly via effects on astrocytes.

Morroniside improves microvascular functional integrity of the neurovascular unit after cerebral ischemia

Treating the vascular elements within the neurovascular unit is essential for protecting and repairing the brain after stroke. Acute injury on endothelial systems results in the disruption of blood-brain barrier (BBB), while post-ischemic angiogenesis plays an important role in delayed functional recovery. Here, we considered alterations in microvessel integrity to be targets for brain recovery, and tested the natural compound morroniside as a therapeutic approach to restore the vascular elements of injured tissue in a rat model of focal cerebral ischemia. Sprague-Dawley rats were subjected to middle cerebral artery occlusion (MCAO) model, and morroniside was then administered intragastrically once a day at doses of 30, 90, and 270 mg/kg. BBB integrity and associated factors were analyzed to identify cerebrovascular permeability 3 days after MCAO. The recruitment of endothelial progenitor cells (EPCs), the expression of angiogenic factors and the new vessel formation in the peri-infarct cortex of rats were examined 7 days after MCAO to identify the angiogenesis. We demonstrated that at 3 days post-ischemia, morroniside preserved neurovascular unit function by ameliorating BBB injury. By 7 days post-ischemia, morroniside amplified angiogenesis, in part by enhancing endothelial progenitor cell proliferation and expression of angiogenic factors. Morever, the increase in the amount of vWF⁺ vessels induced by ischemia could be extended to 28 days after administration of morroniside, indicating the crucial role of morroniside in angiogenesis during the chronic phase. Taken together, our findings suggested that morroniside might offer a novel therapeutic approach for promoting microvascular integrity recovery and provide a thoroughly new direction for stroke therapy.

Activation of the phase II enzymes for neuroprotection by ginger active constituent 6-dehydrogingerdione in PC12 cells

The cellular endogenous antioxidant system plays pivotal roles in counteracting or retarding the pathogenesis of many neurodegenerative diseases. Molecules with the ability to enhance the antioxidant defense thus are promising candidates for neuroprotective drugs. 6-Dehydrogingerdione (6-DG), one of the major components of dietary ginger, has received increasing attention due to its multiple pharmacological activities. However, how this pleiotropic molecule works on the neuronal system has not been studied. This paper reports that 6-DG efficiently scavenges various free radicals in vitro and displays remarkable cytoprotection against oxidative stress-induced neuronal cell damage in the neuron-like rat pheochromocytoma cell line, PC12 cells. Pretreatment of PC12 cells with 6-DG significantly up-regulates a panel of phase II genes as well as the corresponding gene products, such as glutathione, heme oxygenase,

NAD(P)H

quinone oxidoreductase, and thioredoxin reductase. Mechanistic study indicates that activation of the Keap1-Nrf2-ARE pathway is the molecular basis for the cytoprotection of 6-DG. This is the first revelation of this novel mechanism of 6-DG as an Nrf2 activator against oxidative injury, providing the potential therapeutic use of 6-DG as neuroprotective agent.

Protein redox modification as a cellular defense mechanism against tissue ischemic injury

Protein oxidative or redox modifications induced by reactive oxygen species (ROS) or reactive nitrogen species (RNS) not only can impair protein function, but also can regulate and expand protein function under a variety of stressful conditions. Protein oxidative modifications can generally be classified into two categories: irreversible oxidation and reversible oxidation. While irreversible oxidation usually leads to protein aggregation and degradation, reversible oxidation that usually occurs on protein cysteine residues can often serve as an “on and off” switch that regulates protein function and redox signaling pathways upon stress challenges. In the context of ischemic tolerance, including preconditioning and postconditioning, increasing evidence has indicated that reversible cysteine redox modifications such as S-sulfonation, S-nitrosylation, S-glutathionylation, and disulfide bond formation can serve as a cellular defense mechanism against tissue ischemic injury. In this review, I highlight evidence of cysteine redox modifications as protective measures in ischemic injury, demonstrating that protein redox modifications can serve as a therapeutic target for attenuating tissue ischemic injury. Prospectively, more oxidatively modified proteins will need to be identified that can play protective roles in tissue ischemic injury, in particular, when the oxidative modifications of such identified proteins can be enhanced by pharmacological agents or drugs that are available or to be developed.

(-)-Epigallocatechin gallate protects against cerebral ischemia-induced oxidative stress via Nrf2/ARE signaling

(-)-Epigallocatechin gallate (EGCG) has recently been shown to exert neuroprotection in a variety of neurological diseases; however, its role and the underlying mechanisms in cerebral ischemic injury are not fully understood. This study was conducted to investigate the potential neuroprotective effects of EGCG and the possible role of the nuclear factor erythroid 2-related factor 2 (Nrf2)/antioxidant response element (ARE) pathway in the putative neuroprotection against experimental stroke in rats. The results revealed that EGCG exhibit significant neuroprotection, as evidenced by reduced infarction size and the decrease in transferase dUTP nick end labeling-positive neurons. Furthermore, EGCG also enhanced levels of Nrf2 and its downstream ARE pathway genes such as heme oxygenase-1, glutamate-cysteine ligase modulatory subunit and glutamate-cysteine ligase regulatory subunit, as compared to control groups. In accordance with its induction of Nrf2 activation, EGCG exerted a robust attenuation of reactive oxygen species generation and an increase in glutathione content in ischemic cortex. Taken together, these results demonstrated that EGCG exerted significant antioxidant and neuroprotective effects following focal cerebral ischemia, possibly through the activation of the Nrf2/ARE signaling pathway.

Effects of vitamin E on peroxisome proliferator-activated receptor γ and nuclear factor-erythroid 2-related factor 2 in hypercholesterolemia-induced atherosclerosis

Atherosclerosis and associated cardiovascular complications such as stroke and myocardial infarction are major causes of morbidity and mortality. We have previously reported a significant increase in mRNA levels of the scavenger receptor CD36 in aortae of cholesterol-fed rabbits and shown that vitamin E treatment attenuated increased CD36 mRNA expression. In the present study, we further investigated the redox signaling pathways associated with protection against atherogenesis induced by high dietary cholesterol and correlated these with CD36 expression and the effects of vitamin E supplementation in a rabbit model. Male albino rabbits were assigned to either a control group fed with a low vitamin E diet alone or a test group fed with a low vitamin E diet containing 2% cholesterol in the absence or presence of daily intramuscular injections of vitamin E (50mg/kg). To elucidate the mechanisms by which vitamin E supplementation alters the effects of hypercholesterolemia in rabbit aortae, we measured peroxisome proliferator-activated receptor γ (PPARγ), ATP-binding cassette transporter A1 (ABCA1), and matrix metalloproteinase-1 (MMP-1) mRNA levels by quantitative RT-PCR and the expression of MMP-1, nuclear factor-erythroid 2-related factor 2 (Nrf2), and glutathione S-transferase α (GSTα) protein by immunoblotting. The increased MMP-1 and decreased GSTα expression observed suggests that a cholesterol-rich diet contributes to the development of atherosclerosis, whereas vitamin E supplementation affords protection by decreasing MMP-1 and increasing PPARγ, GSTα, and ABCA1 levels in aortae of rabbits fed a cholesterol-rich diet. Notably, protein expression of Nrf2, the antioxidant transcription factor, was increased in both the cholesterol-fed and the vitamin E-supplemented groups. Although Nrf2 activation can promote CD36-mediated cholesterol uptake by macrophages, the increased induction of Nrf2-mediated antioxidant genes is likely to contribute to decreased lesion progression. Thus, our study demonstrates that Nrf2 can mediate both pro- and antiatherosclerotic effects.

Impact of altered glycaemia on blood-brain barrier endothelium: an in vitro study using the hCMEC/D3 cell line

BACKGROUND

Cerebrovascular complications involving endothelial dysfunction at the blood-brain barrier (BBB) are central to the pathogenesis of diabetes-related CNS disorders. However, clinical and experimental studies have reported contrasting evidence in relation to the effects of hyperglycemia on BBB permeability and function. Similarly the effect of hypoglycemia on BBB integrity is not well understood. Therefore, we assessed the differential impact of hypo and hyperglycemic conditions on BBB integrity and endothelial function in vitro using hCMEC/D3, a well characterized human brain microvascular endothelial cell line.

METHODS

Parallel monolayers of hCMEC/D3 were exposed to normal, hypo- or hyperglycemic media, containing 5.5, 2.2 or 35 mM D-glucose, respectively. Following 3-24h exposure, the expression and distribution of BBB tight junction (ZO-1 and claudin-5) adherence junction (VE-cadherin) proteins, and glucose transporters as well as inflammatory (VCAM-1) and oxidative stress (Nrf-2) markers were analyzed by immunofluorescence and western blotting. Endothelial release of growth factors and pro-inflammatory cytokines were determined by ELISA. Further, the impact of altered glycemia on BBB permeability was assessed in hCMEC/D3 - astrocyte co-cultures on Transwell supports using fluorescent dextrans (4-70 kDa).

RESULTS

Compared to controls, exposure to hypoglycemia (3 and 24h) down-regulated the expression of claudin-5 and disrupted the ZO-1 localization at cell-cell contacts, while hyperglycemia marginally reduced claudin-5 expression without affecting ZO-1 distribution. Permeability to dextrans (4-10 kDa) and VEGF release at 24h were significantly increased by hypo- and hyperglycemia, although 70 kDa dextran permeability was increased only under hypoglycemic conditions. The expression of SGLT-1 was up-regulated at 24h hypoglycemic exposure while only a modest increase of GLUT-1 expression was observed. In addition, the expression of Nrf-2 and release of interleukin-6 and PDGF-BB, were down-regulated by hypoglycemia (but not hyperglycemia), while both conditions induced a marginal and transient increase in VCAM-1 expression from 3 to 24h, including a significant increase in VE-cadherin expression at 3 h following hyperglycemia.

CONCLUSIONS

In summary, our findings demonstrate a potential impairment of BBB integrity and function by hypo or hyperglycemia, through altered expression/distribution of TJ proteins and nutrient transporters. In addition, hypoglycemic exposure severely affects the expression of oxidative and inflammatory stress markers of BBB endothelium.

Notoginsenoside R1-mediated neuroprotection involves estrogen receptor-dependent crosstalk between Akt and ERK1/2 pathways: a novel mechanism of Nrf2/ARE signaling activation

Notoginsenoside R1 (NGR1), a novel phytoestrogen isolated from Panax notoginseng, has antioxidant and anti-apoptotic properties. Oxidative stress plays a pivotal role in neurodegenerative diseases. To mimic oxidative stress in neurons and explore the neuroprotection of NGR1, H₂O₂-induced neurotoxicity in NGF-induced differentiation of PC12 cells was used. In this study, NGR1 preconditioning provided neuroprotective effects via suppressing H₂O₂-induced the intracellular ROS accumulation, the increase in the product of lipid peroxidation (MDA), protein oxidation (protein carbonyl), and DNA fragmentation (8-OHdG), and mitochondrial membrane depolarization as well as caspase-3 activation. Moreover, NGR1 treatment alone potently increased the nuclear translocation of Nrf2, augmented ARE enhancer activity, and upregulated the expression and activity of phase II antioxidant enzymes including HO-1, NQO-1, and γ-GCSc. NGR1 could also increase the ERE activity and activate Akt and ERK1/2 pathways. NGR1-mediated activation of Nrf2/ARE signaling and neuroprotection were abolished by genetic silencing of Nrf2 using siRNA or the pharmacological blockade of estrogen receptors using ICI-182780, and partially inhibited by Akt siRNA or ERK siRNA transfection. In addition, the phosphorylation of ERK1/2 mediated by NGR1 was markedly inhibited in PC12 cells transfected with Akt siRNA. On the contrary, ERK1/2 siRNA transfection hardly had any effect on the phosphorylation of Akt mediated by NGR1. NGR1-mediated activation of Akt and ERK1/2 pathways was blocked by ICI-182780. In conclusion, NGR1 provided neuroprotection via inducing an estrogen receptor-dependent crosstalk between Akt and ERK1/2 pathways, subsequently activating Nrf2/ARE signaling and thereby up-regulating phase II antioxidant enzymes.

Signaling properties of 4-hydroxyalkenals formed by lipid peroxidation in diabetes

Peroxidation of polyunsaturated fatty acids is intensified in cells subjected to oxidative stress and results in the generation of various bioactive compounds, of which 4-hydroxyalkenals are prominent. During the progression of type 2 diabetes mellitus, the ensuing hyperglycemia promotes the generation of reactive oxygen species (ROS) that contribute to the development of diabetic complications. It has been suggested that ROS-induced lipid peroxidation and the resulting 4-hydroxyalkenals markedly contribute to the development and progression of these pathologies. Recent findings, however, also suggest that noncytotoxic levels of 4-hydroxyalkenals play important signaling functions in the early phase of diabetes and act as hormetic factors to induce adaptive and protective responses in cells, enabling them to function in the hyperglycemic milieu. Our studies and others' have proposed such regulatory functions for 4-hydroxynonenal and 4-hydroxydodecadienal in insulin secreting β-cells and vascular endothelial cells, respectively. This review presents and discusses the mechanisms regulating the generation of 4-hydroxyalkenals under high glucose conditions and the molecular interactions underlying the reciprocal transition from hormetic to cytotoxic agents.

Sulforaphane preconditioning of the Nrf2/HO-1 defense pathway protects the cerebral vasculature against blood-brain barrier disruption and neurological deficits in stroke

Disruption of the blood-brain barrier (BBB) and cerebral edema are the major pathogenic mechanisms leading to neurological dysfunction and death after ischemic stroke. The brain protects itself against infarction via activation of endogenous antioxidant defense mechanisms, and we here report the first evidence that sulforaphane-mediated preactivation of nuclear factor erythroid 2-related factor 2 (Nrf2) and its downstream target heme oxygenase-1 (HO-1) in the cerebral vasculature protects the brain against stroke. To induce ischemic stroke, Sprague-Dawley rats were subjected to 70 min middle cerebral artery occlusion (MCAo) followed by 4, 24, or 72 h reperfusion. Nrf2 and HO-1 protein expression was upregulated in cerebral microvessels of peri-infarct regions after 4-72 h, with HO-1 preferentially associated with perivascular astrocytes rather than the cerebrovascular endothelium. In naïve rats, treatment with sulforaphane increased Nrf2 expression in cerebral microvessels after 24h. Upregulation of Nrf2 by sulforaphane treatment prior to transient MCAo (1h) was associated with increased HO-1 expression in perivascular astrocytes in peri-infarct regions and cerebral endothelium in the infarct core. BBB disruption, lesion progression, as analyzed by MRI, and neurological deficits were reduced by sulforaphane pretreatment. As sulforaphane pretreatment led to a moderate increase in peroxynitrite generation, we suggest that hormetic preconditioning underlies sulforaphane-mediated protection against stroke. In conclusion, we propose that pharmacological or dietary interventions aimed to precondition the brain via activation of the Nrf2 defense pathway in the cerebral microvasculature provide a novel therapeutic approach for preventing BBB breakdown and neurological dysfunction in stroke.

Oral administration of the flavanol (-)-epicatechin bolsters endogenous protection against focal ischemia through the Nrf2 cytoprotective pathway

Consumption of flavan-3-ols, notably (-)-epicatechin (EC), has been highly recommended in complementary and alternative medicine (CAM) due to reports that flavan-3-ols boost antioxidant activity, support vascular function, and prevent cardiovascular disease. To date, in vivo efficacy and mechanisms of action for many CAM therapies, including EC, remain elusive in brain ischemia. In contrast to its purported direct antioxidant role, we hypothesized protection through activation of the endogenous transcriptional factor Nrf2. To screen cellular protection and investigate Nrf2 activation, we adopted a pretreatment paradigm using enriched primary neuronal cultures from mice and washed out EC prior to oxygen glucose deprivation to attenuate direct antioxidant effects. EC protected primary neurons from oxygen glucose deprivation by increasing neuronal viability (40.2 ± 14.1%) and reducing protein oxidation, effects that occurred concomitantly with increased Nrf2-responsive antioxidant protein expression. We also utilized wildtype and Nrf2 C57BL/6 knockout mice in a permanent model of focal brain ischemia to evaluate glial cell regulation and complex sensorimotor functioning. EC-treated wildtype mice displayed a reduction or absence of forelimb motor coordination impairments that were evident in vehicle-treated mice. This protection was associated with reduced anatomical injury (54.5 ± 8.3%) and microglia/macrophage activation/recruitment (56.4 ± 13.0%). The protective effects elicited by EC in both model systems were abolished in tissues and neuronal cultures from Nrf2 knockout mice. Together, these data demonstrate EC protection through Nrf2 and extend the benefits to improved performance on a complex sensorimotor task, highlighting the potential of flavan-3-ols in CAM approaches in minimizing subsequent stroke injury.

Ginkgolide B reduces LOX-1 expression by inhibiting Akt phosphorylation and increasing Sirt1 expression in oxidized LDL-stimulated human umbilical vein endothelial cells

Oxidized low-density lipoprotein (ox-LDL) is an important risk factor in the development of atherosclerosis. LOX-1, a lectin-like receptor for ox-LDL, is present primarily on endothelial cells and upregulated by ox-LDL, tumor necrosis factor a, shear stress, and cytokines in atherosclerosis. Recent studies demonstrated that ginkgolide B, a platelet-activating factor receptor antagonist, has antiinflammatory and antioxidant effects on endothelial and nerve cells. The present study investigated the effects of ginkgolide B on LOX-1 expression and the possible mechanism of action. Our results showed that ginkgolide B inhibited LOX-1 and intercellular cell adhesion molecule-1 (ICAM-1) expression in ox-LDL-stimulated endothelial cells through a mechanism associated with the attenuation of Akt activation. Similar data were obtained by silencing Akt and LY294002. We also evaluated Sirt1 and nuclear factor erythroid 2-related factor 2 (Nrf2) expression. These molecules play a protective role in endothelial cell injury. The results showed that ginkgolide B increased Sirt1 expression in ox-LDL-treated cells. The inhibitory effects of ginkgolide B on LOX-1 and ICAM-1 expression were reduced in Sirt1 siRNA-transfected cells. Nrf2 expression was increased in ox-LDL-treated cells, and ginkgolide B downregulated Nrf2 expression. These results suggest that ginkgolide B reduces Nrf2 expression by inhibiting LOX-1 expression, consequently reducing oxidative stress injury in ox-LDL-stimulated cells. Altogether, these results indicate that the protective effect of ginkgolide B on endothelial cells may be attributable to a decrease in LOX-1 expression and an increase in Sirt1 expression in ox-LDL-stimulated endothelial cells, the mechanism of which is linked to the inhibition of Akt activation. Ginkgolide B may be a multiple-target drug that exerts protective effects in ox-LDL-treated human umbilical vein endothelial cells.

Regulation of the Nrf2 antioxidant pathway by microRNAs: New players in micromanaging redox homeostasis

MicroRNAs are now thought to play a central role in the regulation of many diverse aspects of cell biology; however, it remains to be fully elucidated how microRNAs can orchestrate cellular redox homeostasis, which plays a central role in a multitude of physiological and pathophysiological processes. The redox-sensitive transcription factor nuclear factor erythroid 2-related factor 2 (Nrf2) serves as a "master regulator" of cell survival through the coordinated induction of phase II and antioxidant defense enzymes to counteract oxidative stress and modulate redox signaling events. MicroRNAs are able to "fine-tune" the regulation of processes including those directly interacting with the Nrf2 pathway and the generation of reactive oxygen species (ROS). This review highlights that cellular redox homeostasis can be regulated by microRNAs through their modulation of Nrf2-driven antioxidant gene expression as well as key enzymes that generate ROS, which in turn can alter the biogenesis and processing of microRNAs. Therefore redox sensitive microRNAs or "redoximiRs" add an important regulatory mechanism for redox signaling beyond the well-characterized actions of Nrf2. The potential exists for microRNA-based therapies where diminished antioxidant defenses and dysregulated redox signaling can lead to cardiovascular diseases, cancers, neurodegeneration, and accelerated aging.

Neohesperidin attenuates cerebral ischemia-reperfusion injury via inhibiting the apoptotic pathway and activating the Akt/Nrf2/HO-1 pathway

Oxidative stress is well known to play a pivotal role in cerebral ischemia-reperfusion injury. On the basis of this fact, antioxidative agents have been demonstrated to be neuroprotective. Neohesperidin (NH) is abundant in citrus flavonoids and possesses reactive oxygen species scavenging activity and neuroprotective effects in vitro. However, little is known about its effects on cerebral ischemia-reperfusion injury and the underlying mechanisms. In this study, we use a rat model of middle cerebral artery occlusion (MCAO) to investigate the neuroprotective effects of NH. NH significantly improved neurological functions and attenuated MCAO-induced infarct volume, pathological changes, and neuronal loss. Moreover, it enhanced antioxidant capacity and suppressed oxidative stress in the brain. NH inhibited the MCAO-induced upregulation of Bax, cytochrome c, and cleaved caspase-9 and -3, as well as the downregulation of Bcl-2. Interestingly, NH treatment upregulated heme oxygenase-1 (HO-1) in a concentration-dependent manner, which was due to the NH-mediated activation of the protein kinase B (Akt)/nuclear factor erythroid 2-related factor 2 (Nrf2) pathway. NH also abolished the MCAO-induced inhibition of the Akt/Nrf2 pathway. In conclusion, NH attenuates cerebral ischemia-reperfusion injury via the inhibition of neuronal apoptosis and oxidative stress through the regulation of the apoptotic pathway and the Akt/Nrf2/HO-1 pathway. NH might be a promising preventive agent for ischemic stroke.

Temporal and spatial distribution of Nrf2 in rat brain following stroke: quantification of nuclear to cytoplasmic Nrf2 content using a novel immunohistochemical technique

Activation of the redox-sensitive transcription factor NF-E2 related factor 2 (Nrf2) affords protection against cerebral ischaemia-reperfusion injury via the upregulation of antioxidant defence genes. We have quantified for the first time Nrf2 content in brains from rats subjected to stroke and from cultured bEnd.3 brain endothelial cells using a novel immunohistochemical technique. Male Sprague-Dawley rats were subjected to middle cerebral artery occlusion for 70 min followed by reperfusion for 4, 24 or 72 h. Coronal brain sections were incubated with anti-Nrf2 primary and biotinylated-horseradish peroxidase-conjugated secondary antibody, after which sections were reacted with 3,3-diaminobenzidine (DAB) in the presence of hydrogen peroxide. The initial rates of DAB polymer formation were directly proportional to the Nrf2 protein concentration. Image processing was used to determine the temporal and spatial distribution of Nrf2 in nuclear and cytoplasmic compartments in stroke-affected and contralateral hemispheres. Nuclear to cytoplasmic Nrf2 ratios were increased in the stroke region after 24 h reperfusion and declined after 72 h reperfusion. Pretreatment with the Nrf2 inducer sulforaphane reduced total cellular Nrf2 levels in peri-infarct and core regions of the stroke hemisphere after 24 h reperfusion. Treatment of cultured murine brain endothelial cells with sulforaphane (2.5 μm) increased nuclear accumulation of Nrf2 over 1-4 h. We report the first quantitative measurements of spatial and temporal nuclear Nrf2 expression in rat brains following stroke, and show that sulforaphane pretreatment affects Nrf2 distribution in the brain of naïve rats and animals subjected to cerebral ischaemia. Our findings provide novel insights for targeting endogenous redox-sensitive antioxidant pathways to ameliorate the damaging consequences of stroke.

Allicin ameliorates cardiac hypertrophy and fibrosis through enhancing of Nrf2 antioxidant signaling pathways

AIM

To evaluate the protective effects of allicin on Ang II-induced cardiac hypertrophy.

METHODS

Sprague-Dawley male rats were randomized into 3 groups:1)sham group (saline)(n = 12), 2) Ang II group(n = 9), 3) allicin group (Ang II + allicin)(n = 9). They received infusions of either saline or Ang II (250 ng/kg body weight per min) through mini-osmotic pumps implanted subcutaneously for 2 weeks and given a diet containing 180 mg/kg/day of allicin for 8 consecutive weeks. Hemodynamic, morphological, histological, and biochemical changes were evaluated at corresponding time points.

RESULTS

Ang II infusion increased blood pressure, heart rate and heart weight to body weight ratio, and resulted in anatomical and functional changes, such as increased LV mass, posterior wall thickness and LV end-diastolic diameter, and decreased fractional shortening and EF compared with sham rats. Nrf2 and HO-1 in the hearts of rats in the Ang II group were moderately elevated at both mRNA and protein levels compared to sham group mice, but NQO1 andγ-GCS were significantly lower. GPx activities, levels of GSH and T-AOC in the hearts of the rats in the Ang II group were also significantly lower, and the levels of TBARS, reactive oxygen species and protein carbonyl were significant increased. Allicin attenuated LV mass, posterior wall thickness and LV end-diastolic diameter (1.10 ± 0.04 vs. 1.37 ± 0.05, 2.26 ± 0.08 vs. 2.96 ± 0.12, 7.27 ± 0.36 vs. 8.56 ± 0.41, respectively; all P < 0.05), and increased fractional shortening and EF (28.30 ± 3.21 vs. 25.40 ± 2.57, 60.27 ± 5.63 vs. 51.30 ± 4.78, respectively; both P < 0.05) in the Ang II-induced hypertrophic rats compared to the untreated Ang II rats. Furthermore, allicin treatment attenuated the accumulation of interstitial collagen and collagen I/III (P < 0.01 vs. the untreated Ang II group), decreased the levels of reactive oxygen species, protein carbonyl and TBARS and increased GPx activities. Moreover, allicin significantly increased mRNA expression and protein levels of Nrf2, NQO1, and γ-GCS ( P < 0.01, P < 0.05 vs. the untreated Ang II group).

CONCLUSION

Allicin could prevent the development of cardiac remodeling and the progression of cardiac hypertrophy to cardiac dysfunction caused by enhancing the Nrf2 antioxidant signaling pathways.