Sulforaphane protects astrocytes against oxidative stress and delayed death caused by oxygen and glucose deprivation

Cognition Enhancing Activity of Sulforaphane Against Scopolamine Induced Cognitive Impairment in Zebra Fish (Danio rerio)

Several epidemiological studies have shown that consumption of large quantities of vegetables especially cruciferous vegetables (Broccoli and Brussels sprouts) can protect against chronic diseases. Sulforaphane, an isothiocynate found in cruciferous vegetables has been demonstrated to have neuroprotective effects in several experimental paradigms. This study was undertaken to examine the effect of sulforaphane on cognitive impairment in zebra fish model using a novel method of fear conditioning. Initially, the normal behaviour of zebra fishes was studied in light-dark tank for 10 min daily for 10 days. Fishes were then divided into seven groups of twelve in each. Group I served as normal, group II served as fear conditioned control, group III and group IV were sulforaphane (25 µM/L) and piracetam (200 mg/L) treated respectively. Group V served as scopolamine (400 µM/L) induced memory impairment fishes. Group VI and VII were sulforaphane (25 µM/L) and piracetam (200 mg/L) treated scopolamine induced memory impairment groups respectively. In normal behavioural analysis, fishes preferred to stay in dark compartment. The average number of entries into the dark and time spent in dark were significantly more. Fishes in group II to VII were individually subjected to fear conditioning passive avoidance task and evaluated for learned task memory. It was observed that the average number of entries into dark and time spent in dark were significantly decreased. After exposure to respective treatment fishes in group III to VII were subjected to cognitive evaluation. There was no significant difference in cognition of group III and IV fishes exposed to sulforaphane and piracetam alone respectively. Fishes exposed to scopolamine showed a significant cognitive impairment. Sulforaphane exposure prior to scopolamine significantly retained the memory of learned task. These findings suggest that sulforaphane might be a promising therapeutic agent for cognitive enhancement in Alzheimer's disease.

A possible role of microglia-derived nitric oxide by lipopolysaccharide in activation of astroglial pentose-phosphate pathway via the Keap1/Nrf2 system

BACKGROUND

Toll-like receptor 4 (TLR4) plays a pivotal role in the pathophysiology of stroke-induced inflammation. Both astroglia and microglia express TLR4, and endogenous ligands produced in the ischemic brain induce inflammatory responses. Reactive oxygen species (ROS), nitric oxide (NO), and inflammatory cytokines produced by TLR4 activation play harmful roles in neuronal damage after stroke. Although astroglia exhibit pro-inflammatory responses upon TLR4 stimulation by lipopolysaccharide (LPS), they may also play cytoprotective roles via the activation of the pentose phosphate pathway (PPP), reducing oxidative stress by glutathione peroxidase. We investigated the mechanisms by which astroglia reduce oxidative stress via the activation of PPP, using TLR4 stimulation and hypoxia in concert with microglia.

METHODS

In vitro experiments were performed using cells prepared from Sprague-Dawley rats. Coexisting microglia in the astroglial culture were chemically eliminated using L-leucine methyl ester (LME). Cells were exposed to LPS (0.01 μg/mL) or hypoxia (1 % O2) for 12-15 h. PPP activity was measured using [1-(14)C]glucose and [6-(14)C]glucose. ROS and NO production were measured using 2',7'-dichlorodihydrofluorescein diacetate and diaminofluorescein-FM diacetate, respectively. The involvement of nuclear factor-erythroid-2-related factor 2 (Nrf2), a cardinal transcriptional factor under stress conditions that regulates glucose 6-phosphate dehydrogenase, the rate-limiting enzyme of PPP, was evaluated using immunohistochemistry.

RESULTS

Cultured astroglia exposed to LPS elicited 20 % increases in PPP flux, and these actions of astroglia appeared to involve Nrf2. However, the chemical depletion of coexisting microglia eliminated both increases in PPP and astroglial nuclear translocation of Nrf2. LPS induced ROS and NO production in the astroglial culture containing microglia but not in the microglia-depleted astroglial culture. LPS enhanced astroglial ROS production after glutathione depletion. U0126, an upstream inhibitor of mitogen-activated protein kinase, eliminated LPS-induced NO production, whereas ROS production was unaffected. U0126 also eliminated LPS-induced PPP activation in astroglial-microglial culture, indicating that microglia-derived NO mediated astroglial PPP activation. Hypoxia induced astroglial PPP activation independent of the microglia-NO pathway. Elimination of ROS and NO production by sulforaphane, a natural Nrf2 activator, confirmed the astroglial protective mechanism.

CONCLUSIONS

Astroglia in concert with microglia may play a cytoprotective role for countering oxidative stress in stroke.

Sulforaphane prevents rat cardiomyocytes from hypoxia/reoxygenation injury in vitro via activating SIRT1 and subsequently inhibiting ER stress

AIM

Sulforaphane (SFN), a natural dietary isothiocyanate, is found to exert beneficial effects for cardiovascular diseases. This study aimed to investigate the mechanisms underlying the protective effects of SFN in a model of myocardial hypoxia/reoxygenation (H/R) injury in vitro.

METHODS

Cultured neonatal rat cardiomyocytes pretreated with SFN were subjected to 3-h hypoxia followed by 3-h reoxygenation. Cell viability and apoptosis were detected. Caspase-3 activity and mitochondrial membrane potential (ΔΨm) was measured. The expression of ER stress-related apoptotic proteins were analyzed with Western blot analyses. Silent information regulator 1 (SIRT1) activity was determined with SIRT1 deacetylase fluorometric assay kit.

RESULTS

SFN (0.1-5 μmol/L) dose-dependently improved the viability of cardiomyocytes, diminished apoptotic cells and suppressed caspase-3 activity. Meanwhile, SFN significantly alleviated the damage of ΔΨm and decreased the expression of ER stress-related apoptosis proteins (GRP78, CHOP and caspase-12), elevating the expression of SIRT1 and Bcl-2/Bax ratio in the cardiomyocytes. Co-treatment of the cardiomyocytes with the SIRT1-specific inhibitor Ex-527 (1 μmol/L) blocked the SFN-induced cardioprotective effects.

CONCLUSION

SFN prevents cardiomyocytes from H/R injury in vitro most likely via activating SIRT1 pathway and subsequently inhibiting the ER stress-dependent apoptosis.

GSK-3β downregulates Nrf2 in cultured cortical neurons and in a rat model of cerebral ischemia-reperfusion

The NF-E2-related factor 2 (Nrf2)/antioxidant response element (ARE) pathway plays a critical role in protecting against oxidative stress in brain ischemia and reperfusion injury. Glycogen synthase kinase 3β (GSK-3β) may play a critical role in regulating Nrf2 in a Kelch-like ECH-associated protein 1 (Keap1)-independent manner. However, the relationship between GSK-3β and Nrf2 in brain ischemia and reperfusion injury is not clear. In this study, we explored the mechanisms through which GSK-3β regulates Nrf2 and Nrf-2/ARE pathways in vitro and in vivo. We used oxygen and glucose deprivation/reoxygenation (OGD/R) in primary cultured cortical neurons and a middle cerebral artery occlusion-reperfusion (MCAO/R) rat model to mimic ischemic insult. In this study, GSK-3β siRNA and inhibitors (SB216763 and LiCl) were used to inhibit GSK-3β in vitro and in vivo. After inhibiting GSK-3β, expression of total and nuclear Nrf2, Nrf2-ARE binding activity, and expression of Nrf2/ARE pathway-driven genes HO-1 and NQO-1 increased. Overexpression of GSK-3β yielded opposite results. These results suggest that GSK-3β downregulates Nrf2 and the Nrf2/ARE pathway in brain ischemia and reperfusion injury. GSK-3β may be an endogenous antioxidant relevant protein, and may represent a new therapeutic target in treatment of ischemia and reperfusion injury.

Sulforaphane Ameliorates Okadaic Acid-Induced Memory Impairment in Rats by Activating the Nrf2/HO-1 Antioxidant Pathway

Okadaic acid (OKA) causes memory impairment and attenuates nuclear factor erythroid 2-related factor 2 (Nrf2) along with oxidative stress and neuroinflammation in rats. Sulforaphane (dietary isothiocyanate compound), an activator of Nrf2 signaling, exhibits neuroprotective effects. However, the protective effect of sulforaphane in OKA-induced neurotoxicity remains uninvestigated. Therefore, in the present study, the role of sulforaphane in OKA-induced memory impairment in rats was explored. A significant increased Nrf2 expression in the hippocampus and cerebral cortex was observed in trained (Morris water maze) rats, and a significant decreased Nrf2 expression in memory-impaired (OKA, 200 ng icv) rats indicated its involvement in memory function. Sulforaphane administration (5 and 10 mg/kg, ip, days 1 and 2) ameliorates OKA-induced memory impairment in rats. The treatment also restored Nrf2 and its downstream antioxidant protein expression (GCLC, HO-1) and attenuated oxidative stress (ROS, nitrite, GSH), neuroinflammation (NF-κB, TNF-α, IL-10), and neuronal apoptosis in the cerebral cortex and hippocampus of OKA-treated rats. Further, to determine whether modulation of Nrf2 signaling is responsible for the protective effect of sulforaphane, in vitro, Nrf2 siRNA and its downstream HO-1 inhibition studies were carried out in a rat astrocytoma cell line (C6). The protective effects of sulforaphane were abolished with Nrf2 siRNA and HO-1 inhibition in astrocytes. The results suggest that Nrf2-dependent activation of cellular antioxidant machinery results in sulforaphane-mediated protection against OKA-induced memory impairment in rats. Graphical Abstract ᅟ.

An overview on neuroprotective effects of isothiocyanates for the treatment of neurodegenerative diseases

The discovery of new natural compounds with pharmacological properties is a field of interest widely growing, especially for the management of neurodegenerative diseases. As no pharmacological treatment is available to prevent the development of these disorders, dietary intake of foods or plant-based extracts with antioxidant properties might have beneficial effects on human health and improve brain functions. Isothiocyanates (ITCs), derived from the hydrolysis of the corresponding glucosinolates (GLs), mainly found in Brassica vegetables (Brassicaceae) and, to a lesser extent, in Moringaceae plants, have demonstrated to exert neuroprotective properties. Specifically, strong evidences suggest that antioxidant effects may be ascribed mainly to their peculiar ability to activate the Nrf2/ARE pathway, but alternative mechanisms of action have also been suggested. This review summarizes the current knowledge about the neuroprotective effects of ITCs in counteracting oxidative stress as well as inflammatory and apoptotic mechanisms, using in vitro and in vivo models of acute and chronic neurodegenerative disease. Therefore, ITCs could be regarded as a promising source of alternative medicine for the prevention and/or treatment of neurodegenerative diseases.

Dissecting molecular cross-talk between Nrf2 and NF-κB response pathways

In most tissues, cells are exposed to frequent changes in levels of oxidative stress and inflammation. Nuclear factor (erythroid-derived 2)-like 2 (Nrf2) and nuclear factor-κB (NF-κB) are the two key transcription factors that regulate cellular responses to oxidative stress and inflammation respectively. Pharmacological and genetic studies suggest that there is functional cross-talk between these two important pathways. The absence of Nrf2 can exacerbate NF-κB activity leading to increased cytokine production, whereas NF-κB can modulate Nrf2 transcription and activity, having both positive and negative effects on the target gene expression. This review focuses on the potentially complex molecular mechanisms that link the Nrf2 and NF-κB pathways and the importance of designing more effective therapeutic strategies to prevent or treat a broad range of neurological disorders.

Antioxidant responses and cellular adjustments to oxidative stress

Redox biological reactions are now accepted to bear the Janus faceted feature of promoting both physiological signaling responses and pathophysiological cues. Endogenous antioxidant molecules participate in both scenarios. This review focuses on the role of crucial cellular nucleophiles, such as glutathione, and their capacity to interact with oxidants and to establish networks with other critical enzymes such as peroxiredoxins. We discuss the importance of the Nrf2-Keap1 pathway as an example of a transcriptional antioxidant response and we summarize transcriptional routes related to redox activation. As examples of pathophysiological cellular and tissular settings where antioxidant responses are major players we highlight endoplasmic reticulum stress and ischemia reperfusion. Topologically confined redox-mediated post-translational modifications of thiols are considered important molecular mechanisms mediating many antioxidant responses, whereas redox-sensitive microRNAs have emerged as key players in the posttranscriptional regulation of redox-mediated gene expression. Understanding such mechanisms may provide the basis for antioxidant-based therapeutic interventions in redox-related diseases.

•

Antioxidant responses are crucial for both redox signaling and redox damage.

•

Glutathione-mediated reactions and Nrf2-Keap1 pathway are key antioxidant responses.

•

Redox-related post-translational modifications activate specific signaling pathways.

•

Redox-sensitive microRNAs contribute to redox-mediated gene expression regulation.

•

ER stress and ischemia-reperfusion are antioxidant-related pathophysiological events.

Melatonin-sulforaphane hybrid ITH12674 induces neuroprotection in oxidative stress conditions by a 'drug-prodrug' mechanism of action

BACKGROUND AND PURPOSE

Neurodegenerative diseases are a major problem afflicting ageing populations; however, there are no effective treatments to stop their progression. Oxidative stress and neuroinflammation are common factors in their pathogenesis. Nuclear factor (erythroid-derived 2)-like 2 (Nrf2) is the master regulator of oxidative stress, and melatonin is an endogenous hormone with antioxidative properties that reduces its levels with ageing. We have designed a new compound that combines the effects of melatonin with Nrf2 induction properties, with the idea of achieving improved neuroprotective properties.

EXPERIMENTAL APPROACH

Compound ITH12674 is a hybrid of melatonin and sulforaphane designed to exert a dual drug-prodrug mechanism of action. We obtained the proposed hybrid in a single step. To test its neuroprotective properties, we used different in vitro models of oxidative stress related to neurodegenerative diseases and brain ischaemia.

KEY RESULTS

ITH12674 showed an improved neuroprotective profile compared to that of melatonin and sulforaphane. ITH12674 (i) mediated a concentration-dependent protective effect in cortical neurons subjected to oxidative stress; (ii) decreased reactive oxygen species production; (iii) augmented GSH concentrations in cortical neurons; (iv) enhanced the Nrf2-antioxidant response element transcriptional response in transfected HEK293T cells; and (v) protected organotypic cultures of hippocampal slices subjected to oxygen and glucose deprivation and re-oxygenation from stress by increasing the expression of haem oxygenase-1 and reducing free radical production.

CONCLUSION AND IMPLICATIONS

ITH12674 combines the signalling pathways of the parent compounds to improve its neuroprotective properties. This opens a new line of research for such hybrid compounds to treat neurodegenerative diseases.

NQO1-induced activation of AMPK contributes to cancer cell death by oxygen-glucose deprivation

Oxygen and glucose deprivation (OGD) due to insufficient blood circulation can decrease cancer cell survival and proliferation in solid tumors. OGD increases the intracellular [AMP]/[ATP] ratio, thereby activating the AMPK. In this study, we have investigated the involvement of NQO1 in OGD-mediated AMPK activation and cancer cell death. We found that OGD activates AMPK in an NQO1-dependent manner, suppressing the mTOR/S6K/4E-BP1 pathway, which is known to control cell survival. Thus, the depletion of NQO1 prevents AMPK-induced cancer cell death in OGD. When we blocked OGD-induced Ca²⁺/CaMKII signaling, the NQO1-induced activation of AMPK was attenuated. In addition, when we blocked the RyR signaling, the accumulation of intracellular Ca²⁺ and subsequent activation of CaMKII/AMPK signaling was decreased in NQO1-expressing cells under OGD. Finally, siRNA-mediated knockdown of CD38 abrogated the OGD-induced activation of Ca²⁺/CaMKII/AMPK signaling. Taken together, we conclude that NQO1 plays a key role in the AMPK-induced cancer cell death in OGD through the CD38/cADPR/RyR/Ca²⁺/CaMKII signaling pathway.

Dietary broccoli mildly improves neuroinflammation in aged mice but does not reduce lipopolysaccharide-induced sickness behavior

Aging is associated with oxidative stress and heightened inflammatory response to infection. Dietary interventions to reduce these changes are therefore desirable. Broccoli contains glucoraphanin, which is converted to sulforaphane (SFN) by plant myrosinase during cooking preparation or digestion. Sulforaphane increases antioxidant enzymes including NAD(P)H quinone oxidoreductase and heme oxygenase I and inhibits inflammatory cytokines. We hypothesized that dietary broccoli would support an antioxidant response in brain and periphery of aged mice and inhibit lipopolysaccharide (LPS)-induced inflammation and sickness. Young adult and aged mice were fed control or 10% broccoli diet for 28 days before an intraperitoneal LPS injection. Social interactions were assessed 2, 4, 8, and 24 hours after LPS, and mRNA was quantified in liver and brain at 24 hours. Dietary broccoli did not ameliorate LPS-induced decrease in social interactions in young or aged mice. Interleukin-1β (IL-1β) expression was unaffected by broccoli consumption but was induced by LPS in brain and liver of adult and aged mice. In addition, IL-1β was elevated in brain of aged mice without LPS. Broccoli consumption decreased age-elevated cytochrome b-245 β, an oxidative stress marker, and reduced glial activation markers in aged mice. Collectively, these data suggest that 10% broccoli diet provides a modest reduction in age-related oxidative stress and glial reactivity, but is insufficient to inhibit LPS-induced inflammation. Thus, it is likely that SFN would need to be provided in supplement form to control the inflammatory response to LPS.

Activation of the Nrf2/HO-1 antioxidant pathway contributes to the protective effects of Lycium barbarum polysaccharides in the rodent retina after ischemia-reperfusion-induced damage

Lycium barbarum polysaccharides (LBP), extracts from the wolfberries, are protective to retina after ischemia-reperfusion (I/R). The antioxidant response element (ARE)–mediated antioxidant pathway plays an important role in maintaining the redox status of the retina. Heme oxygenase-1 (HO-1), combined with potent AREs in its promoter, is a highly effective therapeutic target for the protection against neurodegenerative diseases, including I/R-induced retinal damage. The aim of our present study was to investigate whether the protective effect of LBP after I/R damage was mediated via activation of the Nrf2/HO-1-antioxidant pathway in the retina. Retinal I/R was induced by an increase in intraocular pressure to 130 mm Hg for 60 minutes. Prior to the induction of ischemia, rats were orally treated with either vehicle (PBS) or LBP (1 mg/kg) once a day for 1 week. For specific experiments, zinc protoporphyrin (ZnPP, 20 mg/kg), an HO-1 inhibitor, was intraperitoneally administered at 24 h prior to ischemia. The protective effects of LBP were evaluated by quantifying ganglion cell and amacrine cell survival, and by measuring cell apoptosis in the retinal layers. In addition, HO-1 expression was examined using Western blotting and immunofluorescence analyses. Cytosolic and nuclear Nrf2 was measured using immunofluorescent staining. LBP treatment significantly increased Nrf2 nuclear accumulation and HO-1 expression in the retina after I/R injury. Increased apoptosis and a decrease in the number of viable cells were observed in the ganglion cell layer (GCL) and inner nuclear layer (INL) in the I/R retina, which were reversed by LBP treatment. The HO-1 inhibitor, ZnPP, diminished the LBP treatment-induced protective effects in the retina after I/R. Taken together, these results suggested that LBP partially exerted its beneficial neuroprotective effects via the activation of Nrf2 and an increase in HO-1 protein expression.

Over-expression of Nrf2 diminishes ethanol-induced oxidative stress and apoptosis in neural crest cells by inducing an antioxidant response

Nuclear factor erythroid 2-related factor (Nrf2) is a key transcription factor that regulates antioxidant defense in cells. In this study, we investigated whether over-expression of Nrf2 can prevent ethanol-induced oxidative stress and apoptosis in neural crest cells (NCCs). We found that transfection of NCCs with pcDNA3.1-Nrf2 resulted in statistically significant increases in the Nrf2 protein levels in control and ethanol-exposed NCCs as compared to the cells transfected with control vector. Luciferase reporter gene assay revealed that over-expression of Nrf2 significantly increased the antioxidant response element (ARE) promoter activity in NCCs. Nrf2 over-expression also increased the protein expression and activities of Nrf2 target antioxidants in NCCs. In addition, over-expression of Nrf2 significantly decreased ROS generation and diminished apoptosis in ethanol-exposed NCCs. These results demonstrate that over-expression of Nrf2 can confer protection against ethanol-induced oxidative stress and apoptosis in NCCs by the induction of an antioxidant response.

Sulforaphane as a potential protective phytochemical against neurodegenerative diseases

A wide variety of acute and chronic neurodegenerative diseases, including ischemic/traumatic brain injury, Alzheimer's disease, and Parkinson's disease, share common characteristics such as oxidative stress, misfolded proteins, excitotoxicity, inflammation, and neuronal loss. As no drugs are available to prevent the progression of these neurological disorders, intervention strategies using phytochemicals have been proposed as an alternative form of treatment. Among phytochemicals, isothiocyanate sulforaphane, derived from the hydrolysis of the glucosinolate glucoraphanin mainly present in Brassica vegetables, has demonstrated neuroprotective effects in several in vitro and in vivo studies. In particular, evidence suggests that sulforaphane beneficial effects could be mainly ascribed to its peculiar ability to activate the Nrf2/ARE pathway. Therefore, sulforaphane appears to be a promising compound with neuroprotective properties that may play an important role in preventing neurodegeneration.

Attenuation of β-amyloid-induced oxidative cell death by sulforaphane via activation of NF-E2-related factor 2

β-amyloid peptide (Aβ), a major component of senile plaques, plays important roles in neuropathology of Alzheimer's disease (AD). An array of in vitro and in vivo data indicates that Aβ-induced neuronal death is mediated by oxidative stress. In this study, we aimed to investigate effects of sulforaphane (SUL), an isothiocyanate in cruciferous vegetables, on Aβ-induced oxidative cell death in SH-SY5Y cells. Cells treated with Aβ_25–35 exhibited decreased cell viability and underwent apoptosis as determined by MTT assay and TUNEL, respectively. Aβ_25–35-induced cytotoxicity and apoptotic characteristics such as activation of c-JNK, dissipation of mitochondrial membrane potential, altered expression of Bcl-2 family proteins, and DNA fragmentation were effectively attenuated by SUL pretreatment. The antiapoptotic activity of SUL seemed to be mediated by inhibition of intracellular accumulation of reactive oxygen species and oxidative damages. SUL exerted antioxidant potential by upregulating expression of antioxidant enzymes including γ-glutamylcysteine ligase, NAD(P)H:quinone oxidoreductase-1, and heme oxygenase-1 via activation of NF-E2-related factor 2(Nrf2). The protective effect of SUL against Aβ_25–35-induced apoptotic cell death was abolished by siRNA of Nrf2. Taken together, the results suggest that pharmacologic activation of Nrf2 signaling pathway by SUL might be a practical prevention and/or protective treatment for the management of AD.

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.

Sulforaphane protects against ethanol-induced oxidative stress and apoptosis in neural crest cells by the induction of Nrf2-mediated antioxidant response

BACKGROUND AND PURPOSE

Nuclear factor erythroid 2-related factor (Nrf2) is a transcription factor that up-regulates a diverse array of antioxidant genes and protects cells from oxidative damage. This study is designed to determine whether D-L-sulforaphane (SFN) can protect neural crest cells (NCCs), an ethanol-sensitive cell population implicated in fetal alcohol spectrum disorders, against ethanol-induced apoptosis and whether protective effects of SFN are mediated by the induction of Nrf2-mediated antioxidant response.

EXPERIMENTAL APPROACH

Control, SFN-treated or Nrf2-siRNA transfected NCCs were exposed to ethanol. Nrf2 activation, the expression and activities of Nrf2 downstream antioxidant proteins, reactive oxygen species generation and apoptosis were determined in control and ethanol-exposed NCCs.

KEY RESULTS

Exposure of NCCs to SFN alone significantly increased Nrf2 activation and the expression of Nrf2 downstream antioxidants as well as the activities of the antioxidant enzymes. Treatment of NCCs with SFN along with ethanol significantly decreased ethanol-induced oxidative stress and apoptosis. In contrast, knockdown of Nrf2 by siRNA significantly increased the sensitivity of NCCs to ethanol-induced oxidative stress and apoptosis. Suppression of Nrf2 signalling in NCCs also significantly diminished SFN-mediated antioxidant response and abolished the protective effects of SFN on ethanol-induced oxidative stress and apoptosis.

CONCLUSIONS AND IMPLICATIONS

These results demonstrated that Nrf2-mediated antioxidant response plays an important role in the susceptibility of NCCs to ethanol-induced oxidative stress and apoptosis and that the protection of SFN against ethanol-induced oxidative stress and apoptosis in NCCs is mediated by the induction of Nrf2 signalling.

Nutritional strategies to modulate inflammation and oxidative stress pathways via activation of the master antioxidant switch Nrf2

The nuclear factor E2-related factor 2 (Nrf2) plays an important role in cellular protection against cancer, renal, pulmonary, cardiovascular and neurodegenerative diseases where oxidative stress and inflammation are common conditions. The Nrf2 regulates the expression of detoxifying enzymes by recognizing the human Antioxidant Response Element (ARE) binding site and it can regulate antioxidant and anti-inflammatory cellular responses, playing an important protective role on the development of the diseases. Studies designed to investigate how effective Nrf2 activators or modulators are need to be initiated. Several recent studies have shown that nutritional compounds can modulate the activation of Nrf2-Keap1 system. This review aims to discuss some of the key nutritional compounds that promote the activation of Nrf2, which may have impact on the human health.

Neuroprotective effect of sulforaphane in 6-hydroxydopamine-lesioned mouse model of Parkinson's disease

Parkinson's disease (PD) is characterized by the selective loss of dopaminergic nigrostriatal neurons, which leads to disabling motor disturbances. Sulforaphane (SFN), found in cruciferous vegetables, is a potent indirect antioxidant and recent advances have shown its neuroprotective activity in various experimental models of neurodegeneration. This study was undertaken to examine the effects of SFN on behavioral changes and dopaminergic neurotoxicity in mice exposed to 6-hydroxydopamine (6-OHDA). For this purpose, mice were treated with SFN (5mg/kg twice a week) for four weeks after the unilateral intrastriatal injection of 6-OHDA. The increase in 6-OHDA-induced rotations and deficits in motor coordination were ameliorated significantly by SFN treatment. In addition, SFN protected 6-OHDA-induced apoptosis via blocking DNA fragmentation and caspase-3 activation. These results were further supported by immunohistochemical findings in the substantia nigra that showed that SFN protected neurons from neurotoxic effects of 6-OHDA. The neuroprotective effect of SFN may be attributed to its ability to enhance glutathione levels and its dependent enzymes (glutathione-S-transferase and glutathione reductase) and to modulate neuronal survival pathways, such as ERK1/2, in the brain of mice. These results suggest that SFN may potentially be effective in slowing down the progression of idiopathic PD by the modulation of oxidative stress and apoptotic machinery.

Pesticides, microglial NOX2, and Parkinson's disease

Accumulating evidence indicates that pesticide exposure is associated with an increased risk for developing Parkinson's disease (PD). Several pesticides known to damage dopaminergic (DA) neurons, such as paraquat, rotenone, lindane, and dieldrin also demonstrate the ability to activate microglia, the resident innate immune cell in the brain. While each of these environmental toxicants may impact microglia through unique mechanisms, they all appear to converge on a common final pathway of microglial activation: NADPH oxidase 2 (NOX2) activation. This review will detail the role of microglia in selective DA neurotoxicity, highlight what is currently known about the mechanism of microglial NOX2 activation in these key pesticides, and describe the importance for DA neuron survival and PD etiology.

Metabolic effects of sulforaphane oral treatment in streptozotocin-diabetic rats

Diabetes has reached epidemic levels in the whole world, and the use of bioactive compounds that may have the capacity to prevent and treat diabetes is of great interest. Sulforaphane (SFN) is a compound which is found in cruciferous vegetables and that acts as both a potent antioxidant and regulator of gene expression. The aim of this study was to evaluate the effect of SFN in diabetes induced by streptozotocin (STZ). Male Wistar rats were gavaged with water or 0.1, 0.25, or 0.5 mg/kg of SFN before an injection of STZ (80 mg/kg). Animals treated with SFN showed fasting glycemia, insulin sensitivity, and hepatic glycogen concentrations, similar to the control group (nondiabetic), and different from the diabetic group. Diabetic animals also presented elevated levels of serum triacylglycerols (TAG), urea, and creatinine, and all SFN doses were able to reverse these alterations. However, the same doses of SFN accentuated alterations in total cholesterol, alanine, and aspartate aminotransferase levels, and had no effect on hepatic TAG, HDL cholesterol, and uptake of 2-deoxy glucose in adipose tissue and soleum muscle. Based on the effects inferred by the present data, SFN presented some positive effects against diabetes induction, although the impairment of hepatic function and cholesterol levels were aggravated after treatment with the compound.

Sulforaphane protects primary cultures of cortical neurons against injury induced by oxygen-glucose deprivation/reoxygenation via antiapoptosis

OBJECTIVE

To determine whether sulforaphane (SFN) protects neurons against injury caused by oxygen-glucose deprivation/reoxygenation (OGD/R) and, if so, to investigate the possible mechanisms.

METHODS

Primary cultures of neurons were prepared from the cerebral cortex of 1-day-old Sprague-Dawley rats. On days 5-6 in vitro, the neurons were exposed to OGD for 1 h, followed by reoxygenation for 24 h. Cells were treated with 0, 0.1, 0.2, 0.5, 1, 2.5, or 5 μmol/L SFN, with or without 10 μmol/L LY294002, a PI3K-specific inhibitor, during OGD/R (a total of 25 h). After 24-h reoxygenation, MTT was used to assess viability and injury was assessed by Hoechst 33258/propidium iodide (PI) staining; immunofluorescence staining and Western blot were performed to detect molecular events associated with apoptosis.

RESULTS

The MTT assay showed that 1 μmol/L SFN significantly increased viability, and Hoechst 33258/PI staining showed that the numbers of injured neurons were reduced significantly in the SFN group. Furthermore, immunofluorescence staining and Western blot showed that SFN increased Bcl-2 and decreased cleaved caspase-3 levels. Moreover, LY294002 inhibited the phosphorylated-Akt expression evoked by SFN, decreased Bcl-2 expression and increased cleaved caspase-3 expression.

CONCLUSION

SFN protects neurons against injury from OGD/R and this effect may be partly associated with an antiapoptosis pathway.

Pharmacokinetics and pharmacodynamics of phase II drug metabolizing/antioxidant enzymes gene response by anticancer agent sulforaphane in rat lymphocytes

This study assesses the pharmacokinetics (PK) and pharmacodynamics (PD) of Nrf2-mediated increased expression of phase II drug metabolizing enzymes (DME) and antioxidant enzymes which represents an important component of cancer chemoprevention in rat lymphocytes following intravenous (iv) administration of an anticancer phytochemical sulforaphane (SFN). SFN was administered intravenously to four groups of male Sprague-Dawley JVC rats each group comprising four animals. Blood samples were drawn at selected time points. Plasma were obtained from half of each of the blood samples and analyzed using a validated LC-MS/MS method. Lymphocytes were collected from the remaining blood samples using Ficoll-Paque Plus centrifuge medium. Lymphocyte RNAs were extracted and converted to cDNA, quantitative real-time PCR analyses were performed, and fold changes were calculated against those at time zero for the relative expression of Nrf2-target genes of phase II DME/antioxidant enzymes. PK-PD modeling was conducted based on Jusko's indirect response model (IDR) using GastroPlus and bootstrap method. SFN plasma concentration declined biexponentially and the pharmacokinetic parameters were generated. Rat lymphocyte mRNA expression levels showed no change for GSTM1, SOD, NF-κB, UGT1A1, or UGT1A6. Moderate increases (2-5-fold) over the time zero were seen for HO-1, Nrf2, and NQO1, and significant increases (>5-fold) for GSTT1, GPx1, and Maf. PK-PD analyses using GastroPlus and the bootstrap method provided reasonable fitting for the PK and PD profiles and parameter estimates. Our present study shows that SFN could induce Nrf2-mediated phase II DME/antioxidant mRNA expression for NQO1, GSTT1, Nrf2, GPx, Maf, and HO-1 in rat lymphocytes after iv administration, suggesting that Nrf2-mediated mRNA expression in lymphocytes may serve as surrogate biomarkers. The PK-PD IDR model simultaneously linking the plasma concentrations of SFN and the PD response of lymphocyte mRNA expression is valuable for quantitating Nrf2-mediated effects of SFN. This study may provide a conceptual framework for future clinical PK-PD studies of dietary cancer chemopreventive agents in human.

[Astrogliopathy as a loss of astroglial protective function against glycoxidative stress under hyperglycemia]

Reactive oxygen species (ROS) derived from mitochondria play an essential role in stroke as well as in neurodegenerative disorders. Although hyperglycemia associated with diabetes mellitus is well known to enhance ROS production in vascular endothelial cells, the effects of either acute or chronic high glucose environments on neurons and glial cells remain unclear. Astroglia play a pivotal role in glucose metabolism. Thus, the astroglial metabolic response to high glucose environments is an interesting subject. In particular, the glutathione/pentose phosphate pathway (PPP) system, which is a major defense mechanism against ROS in the brain, contributes to glucose metabolism and is more active in astroglia. We propose that high glucose environments activate PPP through an increased flux to the hexosamine biosynthetic pathway (HBP). HBP is known to induce endoplasmic reticulum (ER) stress under hyperglycemia, resulting in the nuclear translocation of nuclear factor-erythroid-2-related factor 2 (Nrf2), a master regulator of phase 2 detoxifying enzymes including glucose-6-phosphate dehydrogenase that regulates PPP activity, as Nrf2 is reported to be a direct substrate of protein kinase RNA (PKR)-like ER kinase (PERK), a transducer of ER stress. Therefore, the phosphorylation of Nrf2 by hyperglycemia-induced ER stress facilitates Nrf2 translocation through PERK, thus activating the PPP. If acute or chronic hyperglycemia induces PPP activation in astroglia to reduce ROS, reducing the glucose concentration may be accompanied by a risk, which may explain the lack of evidence that strict glycemic control during the acute phase of stroke conveys no beneficial effect.

Protective effects of the antioxidant sulforaphane on behavioral changes and neurotoxicity in mice after the administration of methamphetamine

RATIONALE

Methamphetamine (METH) is a powerfully addictive stimulant associated with serious health conditions. Accumulating evidence suggests a role of oxidative stress in METH-induced behavioral abnormalities. Sulforaphane (SFN), found in cruciferous vegetables, is a potent antioxidant. It is of interest to determine whether SFN can attenuate behavioral and neuropathological changes associated with METH exposure.

OBJECTIVES

This study was undertaken to examine the effects of SFN on behavioral changes and dopaminergic neurotoxicity in mice exposed to METH.

METHODS

The effects of SFN on acute hyperlocomotion and the development of behavioral sensitization induced by the administration of METH were examined. Levels of dopamine (DA) and its major metabolite 3,4-dihydroxyphenyl acetic acid (DOPAC) in the striatum were measured. In addition, DA transporter (DAT) immunoreactivity was also performed.

RESULTS

Pretreatment with SFN at 1, 3, and 10 mg/kg elicited a dose-dependent attenuation of acute hyperlocomotion in mice, after a single administration of METH (3 mg/kg). The development of behavioral sensitization after repeated administrations of METH (3 mg/kg/day, once daily for 5 days) was significantly reduced by pretreatment with SFN (10 mg/kg). In addition, the lowering of DA levels and DOPAC as well as DAT immunoreactivity in the striatum, usually seen after repeated administration of METH, was significantly attenuated by both pretreatment and the subsequent administration of SFN. Furthermore, SFN significantly reduced microglial activation in the striatum after repeated exposure to METH.

CONCLUSION

It is therefore likely that SFN can be a useful drug for the treatment of signs associated with METH abuse in humans.

Eriodictyol protects against H(2)O(2)-induced neuron-like PC12 cell death through activation of Nrf2/ARE signaling pathway

Eriodictyol, a flavonoid isolated from the Chinese herb Dracocephalum rupestre has long been established as an antioxidant. The present study was designed to explore the protective effects of eriodictyol against hydrogen peroxide (H(2)O(2))-induced neurotoxicity with cultured rat pheochromocytoma cells (PC12 cells) and the possible mechanisms involved. For this purpose, differentiated PC12 cells were cultured and exposed to 200 μM H(2)O(2) in the absence or presence of eriodictyol (20, 40 and 80 μM). In addition, the potential contribution of the Nrf2/ARE neuroprotective pathway in eriodictyol-mediated protection against H(2)O(2)-induced neurotoxicity was also investigated. The results showed that H(2)O(2)-induced cell death can be inhibited in the presence of eriodictyol as measured by assays for MTT and apoptosis. Further study revealed that eriodictyol induced the nuclear translocation of Nrf2, enhanced the expression of heme oxygenase (HO-1) and γ-glutamylcysteine synthetase (γ-GCS), and increased the levels of intracellular glutathione. Treatment of PC12 cells with Nrf2 small interference RNA abolished eriodictyol-induced HO-1 and γ-GCS expression and its protective effects. In conclusion, these results suggest that eriodictyol upregulates HO-1 and γ-GCS expression through the activation of Nrf2/ARE pathway and protects PC12 cells against H(2)O(2)-induced oxidative stress.

Decreased oxidative stress during glycolytic inhibition enables maintenance of ATP production and astrocytic survival

Depressed energy metabolism and oxidative stress are common features in many pathological situations in the brain, including stroke. In order to investigate astrocytic responses to such stress, we induced metabolic depression in cultured rat astrocytes. Iodoacetate (IA), an inhibitor of the glycolytic enzyme glyceraldehyde-3-phosphate dehydrogenase (GAPDH) was used and resulted in a rapid inhibition of GAPDH activity. After 1h of GAPDH inhibition the ATP levels started to decrease and were completely abolished at 4h. In parallel, the activity of reactive oxygen species (ROS) was significantly increased, followed by extensive cell death involving flipping of phosphatidylserine and translocation of apoptosis-inducing factor, but not caspase-3 activation. When IA was combined with azide, a respiratory chain complex IV inhibitor, the ATP levels decreased immediately. Interestingly, with azide present, the ROS activity remained low and the astrocytes remained viable even at very low ATP levels. Addition of exogenous ROS-scavengers prevented the IA-induced ROS activity, the ATP levels were maintained and cell death was prevented. Similar protection could be obtained when astrocytes, prior to addition of IA, were incubated with substances known to activate the nuclear factor erythroid 2-related factor 2 (Nrf2)-regulated endogenous antioxidant system. When IA was washed out, after a relatively moderate ATP depression, massive cell death occurred. This was efficiently prevented by addition of azide or ROS scavengers during the IA treatment or by pre-activation of the Nrf2 system. Our results demonstrate that astrocytes in culture can endure and recover from glycolytic inhibition if the ROS activity remained at a low level and suggest that oxidative stress can be an important component for astrocytic cell death following metabolic stress.

Targeting microglia-mediated neurotoxicity: the potential of NOX2 inhibitors

Microglia are key sentinels of central nervous system health, and their dysfunction has been widely implicated in the progressive nature of neurodegenerative diseases. While microglia can produce a host of factors that are toxic to neighboring neurons, NOX2 has been implicated as a common and essential mechanism of microglia-mediated neurotoxicity. Accumulating evidence indicates that activation of the NOX2 enzyme complex in microglia is neurotoxic, both through the production of extracellular reactive oxygen species that damage neighboring neurons as well as the initiation of redox signaling in microglia that amplifies the pro-inflammatory response. More specifically, evidence supports that NOX2 redox signaling enhances microglial sensitivity to pro-inflammatory stimuli, and amplifies the production of neurotoxic cytokines, to promote chronic and neurotoxic microglial activation. Here, we describe the evidence denoting the role of NOX2 in microglia-mediated neurotoxicity with an emphasis on Alzheimer's and Parkinson's disease, describe available inhibitors that have been tested, and detail evidence of the neuroprotective and therapeutic potential of targeting this enzyme complex to regulate microglia.

Protective effects of isothiocyanates on blood-CSF barrier disruption induced by oxidative stress

The choroid plexuses (CPs) form the blood-cerebrospinal fluid (CSF) barrier (BCSFB) and play an important role in maintaining brain normal function and the brain response to injury. Many neurological disorders are associated with oxidative stress that can impact CP function. This study examined the effects of isothiocyanates, an abundant component in cruciferous vegetables, on H(2)O(2)-induced BCSFB disruption and CP cell death in vitro. It further examined the potential role of a transcription factor, nuclear factor erythroid 2-related factor 2 (Nrf2), in isothiocyanate-induced protection. Sulforaphane (SF) significantly reduced H(2)O(2)-induced BCSFB disruption as assessed by transepithelial electrical resistance (29 ± 7% reduction vs. 92 ± 2% decrease in controls) and [(3)H]mannitol permeability. Allyl-isothiocyanate (AITC) had a similar protective effect. H(2)O(2)-induced epithelial cell death was also reduced by these isothiocyanates. In primary CP cells, SF and AITC reduced cell death by 42 ± 3% and 53 ± 10%, respectively. Similar protection was found in a CP cell line Z310. Protection was only found with pretreatment for 12-48 h and not with acute exposure (1 h). The protective effects of SF and AITC were associated with Nrf2 nuclear translocation and upregulated expression of antioxidative systems regulated by Nrf2, including heme oxygenase-1, NAD(P)H quinine oxidoreductase, and cysteine/glutamate exchange transporter. Thus isothiocyanates, as diet or medicine, may be a method for protecting BCSFB in neurological disorders.

Astroglial pentose phosphate pathway rates in response to high-glucose environments

ROS (reactive oxygen species) play an essential role in the pathophysiology of diabetes, stroke and neurodegenerative disorders. Hyperglycaemia associated with diabetes enhances ROS production and causes oxidative stress in vascular endothelial cells, but adverse effects of either acute or chronic high-glucose environments on brain parenchymal cells remain unclear. The PPP (pentose phosphate pathway) and GSH participate in a major defence mechanism against ROS in brain, and we explored the role and regulation of the astroglial PPP in response to acute and chronic high-glucose environments. PPP activity was measured in cultured neurons and astroglia by determining the difference in rate of ¹⁴CO₂ production from [1-¹⁴C]glucose and [6-¹⁴C]glucose. ROS production, mainly H₂O₂, and GSH were also assessed. Acutely elevated glucose concentrations in the culture media increased PPP activity and GSH level in astroglia, decreasing ROS production. Chronically elevated glucose environments also induced PPP activation. Immunohistochemical analyses revealed that chronic high-glucose environments induced ER (endoplasmic reticulum) stress (presumably through increased hexosamine biosynthetic pathway flux). Nuclear translocation of Nrf2 (nuclear factor-erythroid 2 p45 subunit-related factor 2), which regulates G6PDH (glyceraldehyde-6-phosphate dehydrogenase) by enhancing transcription, was also observed in association with BiP (immunoglobulin heavy-chain-binding protein) expression. Acute and chronic high-glucose environments activated the PPP in astroglia, preventing ROS elevation. Therefore a rapid decrease in glucose level seems to enhance ROS toxicity, perhaps contributing to neural damage when insulin levels given to diabetic patients are not properly calibrated and plasma glucose levels are not adequately maintained. These findings may also explain the lack of evidence for clinical benefits from strict glycaemic control during the acute phase of stroke.

Analysis of Nrf2-mediated transcriptional induction of antioxidant response in early embryos

Nrf2 is a transcription factor that regulates the induction of an expansive set of antioxidant proteins that act in synergy to remove reactive oxygen species (ROS). We have recently discovered that Nrf2 signaling is involved in the induction of antioxidant response in ethanol-exposed embryos. We have also demonstrated that chemically induced transcriptional activation of Nrf2 and subsequent induction of a broad spectrum of antioxidant proteins can act as an endogenous protective system against ethanol-induced oxidative stress and apoptosis in early mouse embryos. This chapter describes the methods used to analyze Nrf2-mediated transcriptional induction of antioxidant response in mouse embryos. Data which have been generated by using these methods have also been included to provide examples of their usefulness in evaluating Nrf2-mediated antioxidant response in early embryos.

Natural isothiocyanates: genotoxic potential versus chemoprevention

Isothiocyanates, occurring in many dietary cruciferous vegetables, show interesting chemopreventive activities against several chronic-degenerative diseases, including cancer, cardiovascular diseases, neurodegeneration, diabetes. The electrophilic carbon residue in the isothiocyanate moiety reacts with biological nucleophiles and modification of proteins is recognized as a key mechanism underlying the biological activity of isothiocyanates. The nuclear factor-erythroid-2-related factor 2 system, which orchestrates the expression of a wide array of antioxidant genes, plays a role in the protective effect of isothiocyanates against almost all the pathological conditions reported above. Recent emerging findings suggest a further common mechanism. Chronic inflammation plays a central role in many human diseases and isothiocyanates inhibit the activity of many inflammation components, suppress cyclooxygenase 2, and irreversibly inactivate the macrophage migration inhibitory factor. Due to their electrophilic reactivity, some isothiocyanates are able to form adducts with DNA and induce gene mutations and chromosomal aberrations. DNA damage has been demonstrated to be involved in the pathogenesis of various chronic-degenerative diseases of epidemiological relevance. Thus, the genotoxicity of the isothiocyanates should be carefully considered. In addition, the dose-response relationship for genotoxic compounds does not suggest evidence of a threshold. Thus, chemicals that are genotoxic pose a greater potential risk to humans than non-genotoxic compounds. Dietary consumption levels of isothiocyanates appear to be several orders of magnitude lower than the doses used in the genotoxicity studies and thus it is highly unlikely that such toxicities would occur in humans. However, the beneficial properties of isothiocyanates stimulated an increase of dietary supplements and functional foods with highly enriched isothiocyanate concentrations on the market. Whether such concentrations may exert a potential health risk cannot be excluded with certainty and an accurate evaluation of the toxicological profile of isothiocyanates should be prompted before any major increase in their consumption be recommended or their clinical use suggested.

A defect in Nrf2 signaling constitutes a mechanism for cellular stress hypersensitivity in a genetic rat model of type 2 diabetes

Nrf2 regulates the expression and coordinated induction of a battery of antioxidant phase 2 genes that protect cells against the cumulative damaging effects of oxidative stress (OS), a major contributor in the development of chronic diabetic complications. Using cultured dermal fibroblasts from rats with type 2 diabetes (DFs), we investigated the intracellular redox status and the adaptive response to OS, in which Nrf2 plays a central role. Our data confirmed that the generation of superoxide by NADPH oxidase and the mitochondria was enhanced in DFs compared with corresponding controls. This was associated with a decrease in the antioxidant capacity and an increase in the sensitivity of these DFs to hydrogen peroxide-induced necrotic cell death. Nrf2 levels in total cell extracts were diminished, and this abnormality appears to stem from a diabetes-related decrease in Nrf2 protein stability. Endogenous (oligomycin) and exogenous (tert-butylhydroquinone) induction of OS enhanced the nuclear translocation of Nrf2 and increased the mRNA expression of Nrf2-sensitive genes in control but not DFs. The activity of the GSK-3β/Fyn axis was increased markedly in DFs when compared with the corresponding controls. Chemical inhibition of GSK-3β mitigated the diabetes-related suppression of the OS-induced nuclear accumulation of Nrf2 and the transcriptional activation of the genes downstream of Nrf2. Overall, these findings suggest that an augmentation in GSK-3β/Fyn signaling during diabetes contributes to a deficit in both the cellular redox state and the Nrf2-based adaptive response to OS. Moreover, they may also offer a new perspective in the understanding and treatment of nonhealing diabetic wounds.

Cellular stress responses, hormetic phytochemicals and vitagenes in aging and longevity

Modulation of endogenous cellular defense mechanisms represents an innovative approach to therapeutic intervention in diseases causing chronic tissue damage, such as in neurodegeneration. This paper introduces the emerging role of exogenous molecules in hormetic-based neuroprotection and the mitochondrial redox signaling concept of hormesis and its applications to the field of neuroprotection and longevity. Maintenance of optimal long-term health conditions is accomplished by a complex network of longevity assurance processes that are controlled by vitagenes, a group of genes involved in preserving cellular homeostasis during stressful conditions. Vitagenes encode for heat shock proteins (Hsp) Hsp32, Hsp70, the thioredoxin and the sirtuin protein systems. Dietary antioxidants, such as polyphenols and L-carnitine/acetyl-L-carnitine, have recently been demonstrated to be neuroprotective through the activation of hormetic pathways, including vitagenes. Hormesis provides the central underpinning of neuroprotective responses, providing a framework for explaining the common quantitative features of their dose response relationships, their mechanistic foundations, their relationship to the concept of biological plasticity as well as providing a key insight for improving the accuracy of the therapeutic dose of pharmaceutical agents within the highly heterogeneous human population. This paper describes in mechanistic detail how hormetic dose responses are mediated for endogenous cellular defense pathways including sirtuin, Nrfs and related pathways that integrate adaptive stress responses in the prevention of neurodegenerative diseases. This article is part of a Special Issue entitled: Antioxidants and Antioxidant Treatment in Disease.

Protective effect of combination of sulforaphane and riluzole on glutamate-mediated excitotoxicity

Threohydroxyaspartate (THA) causes glutamate excitotoxicity in motor neurons in organotypic culture of rat spinal cord. Some drugs, including sulforaphane (SF) and riluzole, can protect motor neuron against excitotoxicity. It has been demonstrated that SF is a potent inducer of Phase II enzymes, while riluzole is a classic anti-glutamate agent. The objective of the current study is to investigate whether the combination of SF and riluzole is superior to either one used alone. In our study, the combination of SF with riluzole not only stimulates the expression of nuclear factor erythroid 2-related factor 2 (Nrf2), reduced nicotinamide adenine dinucleotide phosphate (NADPH): quinone oxidoreductase 1 (NQO1) and heme oxygenase 1 (HO-1), but also reduces the extracellular accumulation of glutamate. When used at optimal doses, SF (10 microM) and riluzole (5 microM), either alone or in combination, all exert significant and similar neuroprotection, as measured by the number of motor neuron, medium malondialdehyde (MDA) level and lactate dehydrogenase (LDH) level. When used at low doses, the combination is better than each agent used alone. In conclusion, these results suggest the potential utility of combination use of SF and riluzole for protection of motor neuron against excitotoxicity.

Antioxidant protection: A promising therapeutic intervention in neurodegenerative disease

Oxidative stress has been consistently linked to ageing-related neurodegenerative diseases. Neurodegenerative diseases are characterized by progressive dysfunction and death of neurons. Oxidative stress is associated with dysfunction of the mitochondria and endoplasmic reticulum, inducing apoptosis and protein misfolding in neurons. Decreased activities of antioxidant enzymes like SOD, catalase, glutathione, glutathione peroxidase in neurodegenerative states signifies role of reduced antioxidant potential in neurodegeneration. Among the cellular pathways conferring protection against oxidative stress, a key role is played by vitagenes, which include Hsp70, heme oxygenase-1, thioredoxin and sirtuins. Cellular signalling pathways and molecular mechanisms that mediate hormetic responses typically involve antioxidant enzymes and transcription factors such as Nrf-2 and NFκB. Vitagenes, either individually or by acting in concert, contribute to counteract the ROS mediated damage. In this review the importance of oxidative stress and the potential use of antioxidants in the prevention and treatment of neurodegenerative disorders are discussed.

Primary culture of cellular subtypes from postnatal mouse for in vitro studies of oxygen glucose deprivation

One of the most widely utilized in vitro models of ischemia or oxygen glucose deprivation (OGD) is the hippocampal organotypical culture (HOTC). The HOTC is used not only for the study of the mechanisms of cell death, but also has been the cornerstone of synaptic physiology. Although the intact nature of the HOTC is one of its primary advantages, some studies require a dissociated preparation in order to distinguish cell type specific responses. Typically, primary dissociated neuronal cultures are prepared from embryonic tissue. Since the HOTC is prepared from postnatal pups, we wanted to establish a primary culture of hippocampus from postnatal pups to parallel our studies in the HOTC preparation. Mixed cultures were prepared by enzymatic dissociation of hippocampus from 7-day-old mouse pups. These cultures responded to OGD with a time course of delayed cell death that was similar to that reported in HOTC. Dual label immunocytochemical staining revealed that neurons, but not astrocytes, were dying from apoptosis following OGD. To examine this vulnerability further, we also prepared neuronal enriched cultures by treating mixed cultures with cytosine-β-d-arabinofuranoside (CBA). These neuronal cultures appear to be even more sensitive to OGD. In addition, we have established primary astrocyte-enriched cultures from the same age pups to examine the vulnerability of astrocytes to OGD. These three culture preparations are useful for comparison of the responses of the two major cell types in the same culture, and the enriched cultures will allow biochemical, electrophysiological and molecular studies of homogenous cell populations.

Fumaric acid esters exert neuroprotective effects in neuroinflammation via activation of the Nrf2 antioxidant pathway

Inflammation and oxidative stress are thought to promote tissue damage in multiple sclerosis. Thus, novel therapeutics enhancing cellular resistance to free radicals could prove useful for multiple sclerosis treatment. BG00012 is an oral formulation of dimethylfumarate. In a phase II multiple sclerosis trial, BG00012 demonstrated beneficial effects on relapse rate and magnetic resonance imaging markers indicative of inflammation as well as axonal destruction. First we have studied effects of dimethylfumarate on the disease course, central nervous system, tissue integrity and the molecular mechanism of action in an animal model of chronic multiple sclerosis: myelin oligodendrocyte glycoprotein induced experimental autoimmune encephalomyelitis in C57BL/6 mice. In the chronic phase of experimental autoimmune encephalomyelitis, preventive or therapeutic application of dimethylfumarate ameliorated the disease course and improved preservation of myelin, axons and neurons. In vitro, the application of fumarates increased murine neuronal survival and protected human or rodent astrocytes against oxidative stress. Application of dimethylfumarate led to stabilization of the transcription factor nuclear factor (erythroid-derived 2)-related factor 2, activation of nuclear factor (erythroid-derived 2)-related factor 2-dependent transcriptional activity and accumulation of NADP(H) quinoline oxidoreductase-1 as a prototypical target gene. Furthermore, the immediate metabolite of dimethylfumarate, monomethylfumarate, leads to direct modification of the inhibitor of nuclear factor (erythroid-derived 2)-related factor 2, Kelch-like ECH-associated protein 1, at cysteine residue 151. In turn, increased levels of nuclear factor (erythroid-derived 2)-related factor 2 and reduced protein nitrosylation were detected in the central nervous sytem of dimethylfumarate-treated mice. Nuclear factor (erythroid-derived 2)-related factor 2 was also upregulated in the spinal cord of autopsy specimens from untreated patients with multiple sclerosis. In dimethylfumarate-treated mice suffering from experimental autoimmune encephalomyelitis, increased immunoreactivity for nuclear factor (erythroid-derived 2)-related factor 2 was detected by confocal microscopy in neurons of the motor cortex and the brainstem as well as in oligodendrocytes and astrocytes. In mice deficient for nuclear factor (erythroid-derived 2)-related factor 2 on the same genetic background, the dimethylfumarate mediated beneficial effects on clinical course, axon preservation and astrocyte activation were almost completely abolished thus proving the functional relevance of this transcription factor for the neuroprotective mechanism of action. We conclude that the ability of dimethylfumarate to activate nuclear factor (erythroid-derived 2)-related factor 2 may offer a novel cytoprotective modality that further augments the natural antioxidant responses in multiple sclerosis tissue and is not yet targeted by other multiple sclerosis therapies.

Brain mitochondria from rats treated with sulforaphane are resistant to redox-regulated permeability transition

Oxidative stress promotes Ca2+-dependent opening of the mitochondrial inner membrane permeability transition pore (PTP), causing bioenergetic failure and subsequent cell death in many paradigms, including those related to acute brain injury. One approach to pre-conditioning against oxidative stress is pharmacologic activation of the Nrf2/ARE pathway of antioxidant gene expression by agents such as sulforaphane (SFP). This study tested the hypothesis that administration of SFP to normal rats increases resistance of isolated brain mitochondria to redox-sensitive PTP opening. SFP or DMSO vehicle was administered intraperitoneally to adult male rats at 10 mg/kg 40 h prior to isolation of non-synaptic brain mitochondria. Mitochondria were suspended in medium containing a respiratory substrate and were exposed to an addition of Ca2+ below the threshold for PTP opening. Subsequent addition of tert-butyl hydroperoxide (tBOOH) resulted in a cyclosporin A-inhibitable release of accumulated Ca2+ into the medium, as monitored by an increase in fluorescence of Calcium Green 5N within the medium, and was preceded by a decrease in the autofluorescence of mitochondrial NAD(P)H. SFP treatment significantly reduced the rate of tBOOH-induced Ca2+ release but did not affect NAD(P)H oxidation or inhibit PTP opening induced by the addition of phenylarsine oxide, a direct sulfhydryl oxidizing agent. SFP treatment had no effect on respiration by brain mitochondria and had no effect on PTP opening or respiration when added directly to isolated mitochondria. We conclude that SFP confers resistance of brain mitochondria to redox-regulated PTP opening, which could contribute to neuroprotection observed with SFP.

Stabilization of Nrf2 protein by D3T provides protection against ethanol-induced apoptosis in PC12 cells

Previous studies have demonstrated that maternal ethanol exposure induces a moderate increase in Nrf2 protein expression in mouse embryos. Pretreatment with the Nrf2 inducer, 3H-1, 2-dithiole-3-thione (D3T), significantly increases the Nrf2 protein levels and prevents apoptosis in ethanol-exposed embryos. The present study, using PC12 cells, was designed to determine whether increased Nrf2 stability is a mechanism by which D3T enhances Nrf2 activation and subsequent antioxidant protection. Ethanol and D3T treatment resulted in a significant accumulation of Nrf2 protein in PC 12 cells. CHX chase analysis has shown that ethanol treatment delayed the degradation of Nrf2 protein in PC12 cells. A significantly greater decrease in Nrf2 protein degradation was observed in the cells treated with D3T alone or with both ethanol and D3T. In addition, D3T treatment significantly reduced ethanol-induced apoptosis. These results demonstrate that the stabilization of Nrf2 protein by D3T confers protection against ethanol-induced apoptosis.

Protective effect of sulforaphane against oxidative stress: recent advances

Sulforaphane [1-isothiocyanate-(4R)-(methylsulfinyl)butane] is a natural dietary isothiocyanate produced by the enzymatic action of the myrosinase on glucopharanin, a 4-methylsulfinylbutyl glucosinolate contained in cruciferous vegetables of the genus Brassica such as broccoli, brussel sprouts, and cabbage. Studies on this compound is increasing because its anticarcinogenic and cytoprotective properties in several in vivo experimental paradigms associated with oxidative stress such as focal cerebral ischemia, brain inflammation, intracerebral hemorrhage, ischemia and reperfusion induced acute renal failure, cisplatin induced-nephrotoxicity, streptozotocin-induced diabetes, carbon tetrachloride-induced hepatotoxicity and cardiac ischemia and reperfusion. This protective effect also has been observed in in vitro studies in different cell lines such as human neuroblastoma SH-SY5Y, renal epithelial proximal tubule LLC-PK1 cells and aortic smooth muscle A10 cells. Sulforaphane is considered an indirect antioxidant; this compound is able to induce many cytoprotective proteins, including antioxidant enzymes, through the Nrf2-antioxidant response element pathway. Heme oxygenase-1, NAD(P)H: quinone oxidoreductase, glutathione-S-transferase, gamma-glutamyl cysteine ligase, and glutathione reductase are among the cytoprotective proteins induced by sulforaphane. In conclusion, sulforaphane is a promising antioxidant agent that is effective to attenuate oxidative stress and tissue/cell damage in different in vivo and in vitro experimental paradigms.

4-hydroxybenzyl alcohol ameliorates cerebral injury in rats by antioxidant action

4-hydroxybenzyl alcohol (4-HBA), one of the phenolic constituents found in many herbal medicinal plants, exhibits beneficial effects in neurological disorders. In the present study, we evaluated 4-HBA's role in transient cerebral ischemia and its potential mechanism. Pre-treatment with 4-HBA (50,100 mg/kg) significantly reduced the cerebral infarct size and improved the neurological symptoms. Morphological examinations showed 4-HBA reduced the number of degenerated neurons. Oxidative stress was evaluated superoxide dismutase (SOD) activity and malondialdehyde (MDA) level. Anti-oxidative mechanisms were studied by Immunofluorescence staining and western immunoblot analysis. 4-HBA increased the expression of NAD(P)H: quinone oxidoreductase1 (NQO1) and ultimately inhibited oxidative stress. In addition, we evaluated the time course expression of NQO1, which was upregulated in the ischemic brain beginning at 1 h. Taken together, these results suggested that 4-HBA ameliorated cerebral injury in rats, This neuroprotective effect is likely related to its antioxidant activities.

Repeated transient sulforaphane stimulation in astrocytes leads to prolonged Nrf2-mediated gene expression and protection from superoxide-induced damage

Oxidative stress is a major contributor to slowly developing diseases like Parkinson's disease, Alzheimer's disease and cancer and one of the main causes of tissue damage following ischemic insults in the brain. Nrf2 is a transcription factor responsible for much of the inducible cellular defense against oxidative stress. Nrf2 can also be activated by xenobiotics like sulforaphane, a component highly enriched in cruciferous vegetables such as broccoli. Ingestion of broccoli or sulforaphane results in long-term protection against radical damage, although absorbed sulforaphane is cleared from the body within a few hours. Here we have examined whether the prolonged protection induced by sulforaphane is explained by a slow down regulation of the Nrf2 response. Furthermore, to simulate daily ingestion of sulforaphane, we examined the hypothesis that repeated transient sulforaphane stimulation results in an accumulation of Nrf2-mediated gene expression and an increased protection against oxidative damage. The kinetics of sulforaphane-induced Nrf2 response was studied in astrocytes, a cell type known to be highly involved in the defense against oxidative stress in the brain. Sulforaphane stimulation for 4 h induced an Nrf2-dependent increase of Nqo1 and Hmox1 mRNA that remained elevated for 24 h, and the corresponding proteins remained elevated for over 48 h. In addition, peroxide-clearing activity and the levels of glutathione were elevated for more than 20 h after stimulation for 4 h with sulforaphane, resulting in an increased resistance to superoxide-induced cell damage. Repeated sulforaphane stimulation resulted in an accumulation of mRNA and protein levels of Nqo1 and a persistent cell protection against oxidative damage. These findings indicate that brief stimulation of the Nrf2 pathway by sulforaphane results in long-lasting elevation of endogenous antioxidants in astrocytes. The findings also demonstrate that part of this response can be built up by repeated transient stimulation, possibly explaining how intermittent intake of sulforaphane can result in long-term protection from radical-induced disease.

Triterpenoids CDDO-ethyl amide and CDDO-trifluoroethyl amide improve the behavioral phenotype and brain pathology in a transgenic mouse model of Huntington's disease

Oxidative stress is a prominent feature of Huntington's disease (HD) due to mitochondrial dysfunction and the ensuing overproduction of reactive oxygen species (ROS). This phenomenon ultimately contributes to cognitive and motor impairment, as well as brain pathology, especially in the striatum. Targeting the transcription of the endogenous antioxidant machinery could be a promising therapeutic approach. The NF-E2-related factor-2 (Nrf2)/antioxidant response element (ARE) signaling pathway is an important pathway involved in antioxidant and anti-inflammatory responses. Synthetic triterpenoids, which are derived from 2-Cyano-3,12-Dioxooleana-1,9-Dien-28-Oic acid (CDDO) activate the Nrf2/ARE pathway and reduce oxidative stress in animal models of neurodegenerative diseases. We investigated the effects of CDDO-ethyl amide (CDDO-EA) and CDDO-trifluoroethyl amide (CDDO-TFEA) in N171-82Q mice, a transgenic mouse model of HD. CDDO-EA or CDDO-TFEA were administered in the diet at various concentrations, starting at 30days of age. CDDO-EA and CDDO-TFEA upregulated Nrf2/ARE induced genes in the brain and peripheral tissues, reduced oxidative stress, improved motor impairment and increased longevity. They also rescued striatal atrophy in the brain and vacuolation in the brown adipose tissue. Therefore compounds targeting the Nrf2/ARE pathway show great promise for the treatment of HD.

Induction of the Nrf2-driven antioxidant response by tert-butylhydroquinone prevents ethanol-induced apoptosis in cranial neural crest cells

Previous studies have shown that ethanol exposure causes apoptosis in cranial neural crest cells (NCCs), an ethanol-sensitive cell population implicated in Fetal Alcohol Spectrum Disorders (FASD). Additionally, induction of endogenous antioxidants through activation of nuclear factor-erythroid 2-related factor 2 (Nrf2) has been shown to prevent oxidative stress and apoptosis in ethanol-exposed mouse embryos. The objective of this study was to test whether tert-butylhydroquinone (tBHQ), an Nrf2 inducer, can protect NCCs against ethanol-induced apoptosis. Ethanol exposure was shown to cause a moderate increase in the protein expression of Nrf2 and its downstream antioxidants in the NCCs. Treatment of NCCs with tBHQ alone significantly increased the protein expression of Nrf2 and its downstream antioxidants and also significantly increased the activities of the antioxidant enzymes. In NCCs exposed to ethanol, the tBHQ-mediated antioxidant response prevented oxidative stress and apoptosis. These results clearly demonstrate that the activation of Nrf2 signaling confers protection against ethanol-induced apoptosis in NCCs.

Sulforaphane protects immature hippocampal neurons against death caused by exposure to hemin or to oxygen and glucose deprivation

Oxidative stress is a mediator of cell death following cerebral ischemia/reperfusion and heme toxicity, which can be an important pathogenic factor in acute brain injury. Induced expression of phase II detoxification enzymes through activation of the antioxidant response element (ARE)/Nrf2 pathway has emerged as a promising approach for neuroprotection. Little is known, however, about the neuroprotective potential of this strategy against injury in immature brain cells. In this study, we tested the hypothesis that sulforaphane (SFP), a naturally occurring isothiocyanate that is also a known activator of the ARE/Nrf2 antioxidant pathway, can protect immature neurons from oxidative stress-induced death. The hypothesis was tested with primary mouse hippocampal neurons exposed to either O(2) and glucose deprivation (OGD) or hemin. Treatment of immature neurons with SFP immediately after the OGD during reoxygenation was effective in protecting immature neurons from delayed cell death. Exposure of immature hippocampal neurons to hemin induced significant cell death, and both pre- and cotreatment with SFP were remarkably effective in blocking cytotoxicity. RT-PCR analysis indicated that several Nrf2-dependent cytoprotective genes, including NAD(P)H quinone oxidoreductase 1 (NQO1), heme oxygenase 1 (HO1), and glutamate-cysteine ligase modifier subunit (GCLM), which is involved in glutathione biosynthesis, were up-regulated following SFP treatment both in control neurons and following exposure to OGD and hemin. These results indicate that SFP activates the ARE/Nrf2 pathway of antioxidant defense and protects immature neurons from death caused by stress paradigms relevant to those associated with ischemic and traumatic injury to the immature brain.