Actions of redox-active compound resveratrol under hydrogen peroxide insult in C6 astroglial cells

Activation of M1 muscarinic acetylcholine receptors by proline-rich oligopeptide 7a (<EDGPIPP) from Bothrops jararaca snake venom rescues oxidative stress-induced neurotoxicity in PC12 cells

Background

The bioactive peptides derived from snake venoms of the Viperidae family species have been promising as therapeutic candidates for neuroprotection due to their ability to prevent neuronal cell loss, injury, and death. Therefore, this study aimed to evaluate the cytoprotective effects of a synthetic proline-rich oligopeptide 7a (PRO-7a;

Methods

Both cells were pre-treated for four hours with different concentrations of PRO-7a, submitted to H2O2-induced damage for 20 h, and then the oxidative stress markers were analyzed. Also, two independent neuroprotective mechanisms were investigated: a) L-arginine metabolite generation via argininosuccinate synthetase (AsS) activity regulation to produce agmatine or polyamines with neuroprotective properties; b) M1 mAChR receptor subtype activation pathway to reduce oxidative stress and neuron injury.

Results

PRO-7a was not cytoprotective in C6 cells, but potentiated the H2O2-induced damage to cell integrity at a concentration lower than 0.38 μM. However, PRO-7a at 1.56 µM, on the other hand, modified H2O2-induced toxicity in PC12 cells by restoring cell integrity, mitochondrial metabolism, ROS generation, and arginase indirect activity. The α-Methyl-DL-aspartic acid (MDLA) and L-NΩ-Nitroarginine methyl ester (L-Name), specific inhibitors of AsS and nitric oxide synthase (NOS), which catalyzes the synthesis of polyamines and NO from L-arginine, did not suppress PRO-7a-mediated cytoprotection against oxidative stress. It suggested that its mechanism is independent of the production of L-arginine metabolites with neuroprotective properties by increased AsS activity. On the other hand, the neuroprotective effect of PRO-7a was blocked in the presence of dicyclomine hydrochloride (DCH), an M1 mAChR antagonist.

Conclusions

For the first time, this work provides evidence that PRO-7a-induced neuroprotection seems to be mediated through M1 mAChR activation in PC12 cells, which reduces oxidative stress independently of AsS activity and L-arginine bioavailability.

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Key Words

• Bioactive peptide
• Bothrops jararaca
• Neuroprotection
• Proline-rich oligopeptide

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Affiliation(s)

Carlos Alberto-Silva Natural and Humanities Sciences Center (CCNH), Experimental Morphophysiology Laboratory, Federal University of ABC (UFABC), São Bernardo do Campo, SP, Brazil
Halyne Queiroz Pantaleão Natural and Humanities Sciences Center (CCNH), Experimental Morphophysiology Laboratory, Federal University of ABC (UFABC), São Bernardo do Campo, SP, Brazil
Brenda Rufino da Silva Natural and Humanities Sciences Center (CCNH), Experimental Morphophysiology Laboratory, Federal University of ABC (UFABC), São Bernardo do Campo, SP, Brazil
Julio Cezar Araujo da Silva Natural and Humanities Sciences Center (CCNH), Experimental Morphophysiology Laboratory, Federal University of ABC (UFABC), São Bernardo do Campo, SP, Brazil
Marcela Bermudez Echeverry Center for Mathematics, Computation and Cognition (CMCC), Federal University of ABC, São Bernardo do Campo, SP, Brazil

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Genotoxic and genoprotective effects of phytoestrogens: a systematic review

Phytoestrogens are xenoestrogens found in plants with a myriad of health benefits. However, various studies reported the genotoxic effects of these substances. Thus, we reviewed in vitro and in vivo studies published in PubMed, Scopus, and Web of Science to evaluate the genotoxic and the genoprotective potential of phytoestrogens. Only studies written in English and intended to study commercially available phytoestrogens were included. The screening was performed manually. Moreover, the underlying mechanism of action of phytoestrogens was described. Around half of those studies (43%) reported genoprotective results. However, several studies revealed positive results for genotoxicity with specific model organisms and with dose/concentration dependence. The assessment of the selected articles showed substantial differences in the used concentrations and a biphasic response was recorded in some phytoestrogens. As far as we know, this is the first study to assess the genotoxic and genoprotective effects of phytoestrogens systematically.

Peptide fraction from B. jararaca snake venom protects against oxidative stress-induced changes in neuronal PC12 cell but not in astrocyte-like C6 cell

Venom-derived proteins and peptides have prevented neuronal cell loss, damage, and death in the study of neurodegenerative disorders. The cytoprotective effects of the peptide fraction (PF) from Bothrops jararaca snake venom were evaluated against oxidative stress changes in neuronal PC12 cells and astrocyte-like C6 cells. PC12 and C6 cells were pre-treated for 4 h with different concentrations of PF, and then H2O2 was added (0.5 mM in PC12 cells; 0.4 mM in C6 cells) and incubated for 20 h more. In PC12 cells, PF at 0.78 μg mL-1 increased viability (113.6 ± 6.3%) and metabolism (96.3 ± 10.3%) cell against H2O2-induced neurotoxicity (75.6 ± 5.8%; 66.5 ± 3.3%, respectively), reducing oxidative stress markers such as ROS generation, NO production, and arginase indirect activity through urea synthesis. Despite that, PF showed no cytoprotective effects in C6 cells, but potentiated the H2O2-induced damage at a concentration lower than 0.07 μg mL-1. Furthermore, the role of metabolites derived from L-arginine metabolism was verified in PF-mediated neuroprotection in PC12 cells, using specific inhibitors of two of the key enzymes in the L-arginine metabolic pathway: the α-Methyl-DL-aspartic acid (MDLA) to argininosuccinate synthetase (AsS), responsible for the recycling of L-citrulline to L-arginine; and, L-NΩ-Nitroarginine methyl ester (L-Name) to nitric oxide synthase (NOS), which catalyzes the synthesis of NO from L-arginine. The inhibition of AsS and NOS suppressed PF-mediated cytoprotection against oxidative stress, indicating that its mechanism is dependent on the production pathway of L-arginine metabolites such as NO and, more importantly, polyamines from ornithine metabolism, which are involved in the neuroprotection mechanism described in the literature. Overall, this work provides novel opportunities for evaluating whether the neuroprotective properties of PF shown in particular neuronal cells are sustained and for exploring potential drug development pathways for the treatment of neurodegenerative diseases.

Captopril exhibits protective effects through anti-inflammatory and anti-apoptotic pathways against hydrogen peroxide-induced oxidative stress in C6 glioma cells

Recent studies have shown that angiotensin-converting enzyme (ACE) inhibitors have reduced oxidative damage in the central nervous system (CNS). Accumulating evidence have also demonstrated that captopril, an ACE inhibitor, has protective effects on the CNS. However, its effects on hydrogen peroxide (H2O2)-induced oxidative damage in glial cells and interaction with the inflammatory system are still uncertain. Therefore, this study was aimed to investigate the protective effect of captopril on glial cell damage after H2O2-induced oxidative stress involved in the inflammatory and apoptotic pathways. The control group was without any treatment, and the H2O2 group was treated with 0.5 mM H2O2 for 24 h. The captopril group was treated with various concentrations of captopril for 24 h. The captopril + H2O2 group was pre-treated with captopril for 1 h and then exposed to 0.5 mM H2O2 for 24 h. In the captopril + H2O2 group, captopril at all concentrations significantly increased the cell viability in C6 cells. It also significantly increased the TAS and decreased the TOS levels which are an indicator of oxidative stress. Moreover, captopril significantly reduced the inflammation markers including NF-kB, IL-1 β, COX-1, and COX-2 levels. Flow cytometry results also exhibited that captopril pretreatment significantly decreased the apoptosis rate. Besides, captopril significantly reduced apoptotic Bax and raised anti-apoptotic Bcl-2 protein levels. In conclusion, captopril has protective effects on C6 cells after H2O2-induced oxidative damage by inhibiting oxidative stress, inflammation, and apoptosis. However, further studies need to be conducted to evaluate the potential of captopril as a neuroprotective agent.

The protective effect of fermented Curcuma longa L. on memory dysfunction in oxidative stress-induced C6 gliomal cells, proinflammatory-activated BV2 microglial cells, and scopolamine-induced amnesia model in mice

BACKGROUND

Curcuma longa L. is a well-known medicinal plant that has been used for its anti-cancer, neuroprotective, and hepatoprotective effects. However, the neuroprotective effect of fermented C. longa (FCL) has not been reported. Therefore, in this study, the effectiveness of FCL for the regulation of memory dysfunction was investigated in two brain cell lines (rat glioma C6 and murine microglia BV2) and scopolamine-treated mice.

METHODS

C. longa powder was fermented by 5% Lactobacillus plantarum K154 containing 2% (w/v) yeast extract at 30 °C for 72 h followed by sterilization at 121 °C for 15 min. The protective effects of fermented C. longa (FCL) on oxidative stress induced cell death were analyzed by MTT assay in C6 cells. The anti-inflammatory effects of FCL were investigated by measuring the production of nitric oxide (NO) and prostaglandin E₂ (PGE₂) as well as the expression levels of inducible NO synthase (iNOS) and cyclooxygenase-2 (COX-2) in LPS-stimulated BV2 cells. The step-through passive avoidance test, Morris water maze test, acetylcholinesterase (AChE) activity, and expression of cAMP response element-binding protein (CREB) and brain-derived neurotropic factor (BDNF) were employed to determine the effects of FCL on scopolamine-induced memory deficit in mice. The contents of curcuminoids were analyzed through LC/MS.

RESULTS

Pretreatment with FCL effectively prevented the cell death induced by oxidative stress in C6 cells. Moreover, FCL inhibited the production NO and PGE₂ via the inhibition of iNOS and COX-2 expression in BV2 cells. FCL significantly attenuated scopolamine-induced memory impairment in mice and prevented scopolamine-induced AChE activity in the hippocampus. Additionally, FCL reversed the reduction of CREB and BDNF expression. The curcuminoids content in FCL was 1.44%.

CONCLUSION

FCL pretreatment could alleviate scopolamine-induced memory impairment in mice, as well as oxidative stress and inflammation in C6 and BV2 cells, respectively. Thus, FCL might be a useful material for preventing impairment of learning and memory.

The Neuro-Protective Effect of the Methanolic Extract of Perilla frutescens var. japonicaand Rosmarinic Acid against H₂O₂-Induced Oxidative Stress in C6 Glial Cells

Neurodegenerative diseases are often associated with oxidative damage in neuronal cells. This study was conducted to investigate the neuro-protective effect of methanolic (MeOH) extract of Perilla frutescens var. japonica and its one of the major compounds, rosmarinic acid, under oxidative stress induced by hydrogen peroxide (H₂O₂) in C6 glial cells. Exposure of C6 glial cells to H₂O₂ enhanced oxidative damage as measured by 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide and thiobarbituric acid-reactive substance assays. The MeOH extract and rosmarinic acid prevented oxidative stress by increasing cell viability and inhibiting cellular lipid peroxidation. In addition, the MeOH extract and rosmarinic acid reduced H₂O₂-induced expression of inducible nitric oxide synthase (iNOS) and cyclooxygenase-2 (COX-2) at the transcriptional level. Moreover, iNOS and COX-2 protein expression was down-regulated in H₂O₂-indcued C6 glial cells treated with the MeOH extract and rosmarinic acid. These findings suggest that P. frutescens var. japonica and rosmarinic acid could prevent the progression of neurodegenerative diseases through attenuation of neuronal oxidative stress.

Estrogen regulates excitatory amino acid carrier 1 (EAAC1) expression through sphingosine kinase 1 (SphK1) transacting FGFR-mediated ERK signaling in rat C6 astroglial cells

Excitatory amino acid carrier 1 (EAAC1) is one important subtype of the excitatory amino acid transporters (EAATs), and its absence can increase the vulnerability to oxidative stress in neural tissue. Enhanced expression of EAAC1 can provide neuroprotection in multiple disorders, including ischemia and multiple sclerosis. However, the mechanism regulating EAAC1 expression is not fully understood. Using rat C6 astroglial cells, which specifically express EAAC1, we found that 17β-estradiol (E2) and (±)-1-[(3aR(∗),4S(∗),9bS(∗))-4-(6-bromo-1,3-benzodioxol-5-yl)-3a,4,5,9b-tetrahydro-3H-cyclopenta[c]quinolin-8-yl]-ethanone (G1), an agonist of the G-protein-coupled estrogen receptor (GPR30), strongly increased EAAC1 protein levels and protected cells from hydrogen peroxide (H2O2) toxicity. We further found that E2/G1 activated sphingosine kinase 1 (SphK1) via GPR30, resulting in the transcription of fibroblast growth factor 2 (FGF2), which stimulated its receptor (FGFR) and led to the phosphorylation of FGFR substrate 2α (FRS2α). This triggered downstream ERK1/2 signaling for the expression of EAAC1. Both the knockdown of FGF2 by siRNA and the pharmacological suppression of the FGFR-ERK cascade abolished the E2/G1 effect on EAAC1 expression. Overall, our work characterizes a signaling pathway by which E2 transactivates FGFR-ERK to induce EAAC1 expression in an FGF2-dependent manner. This occurs through SphK1 activation via GPR30 and leads to a resistance to H2O2 toxicity. This signal transduction pathway may provide novel insights into our understanding of the neuroprotective effects of E2 and may reveal new therapeutic targets or drugs for regulating the oxidative toxicity effects of various neurological diseases.

Octadecaneuropeptide ODN prevents hydrogen peroxide-induced oxidative damage of biomolecules in cultured rat astrocytes

Oxidative stress, associated with a variety of disorders including neurodegenerative diseases, is a major cause of cellular dysfunction and biomolecule damages which play a crucial role in neuronal apoptosis. Astrocytes specifically synthesize and release endozepines, a family of regulatory peptides, including the octadecaneuropeptide ODN. We have recently shown that ODN is a potent glioprotective agent that prevents hydrogen peroxide (H2O2)-induced oxidative stress and apoptosis. The purpose of the present study was to investigate the potential protective effect of ODN on oxidative-generated damage of biomolecules in cultured rat astrocytes. Incubation of cells with subnanomolar concentrations of ODN (0.1fM-0.1nM) inhibited H2O2-evoked reactive oxygen species accumulation and cell death in a concentration-dependent manner. Exposure of H2O2-treated cells to 0.1nM ODN inhibited superoxide anion generation and blocked oxidative damage of cell molecules caused by H2O2i.e. formation and accumulation of lipid oxidation products, malondialdehydes and conjugated dienes, and protein carbonyl compounds. Taken together, these data demonstrate for the first time that ODN prevents oxidative stress-induced alteration of cellular constituents. ODN is thus a potential candidate to reduce neuronal damage in various pathological conditions involving oxidative neurodegeneration.

Resveratrol increases antioxidant defenses and decreases proinflammatory cytokines in hippocampal astrocyte cultures from newborn, adult and aged Wistar rats

Astrocytes are responsible for modulating neurotransmitter systems and synaptic information processing, ionic homeostasis, energy metabolism, maintenance of the blood-brain barrier, and antioxidant and inflammatory responses. Our group recently published a culture model of cortical astrocytes obtained from adult Wistar rats. In this study, we established an in vitro model for hippocampal astrocyte cultures from adult (90 days old) and aged (180 days old) Wistar rats. Resveratrol, a polyphenol found in grapes and red wine, exhibits antioxidant, anti-inflammatory, anti-aging and neuroprotective effects that modulate glial functions. Here, we evaluated the effects of resveratrol on GSH content, GS activity, TNF-α and IL-1β levels in hippocampal astrocytes from newborn, adult and aged Wistar rats. We observed a decrease in antioxidant defenses and an increase in the inflammatory response in hippocampal astrocytes from adult and aged rats compared to classical astrocyte cultures from newborn rats. Resveratrol prevented these effects. These findings reinforce the neuroprotective effects of resveratrol, which are mainly associated with antioxidant and anti-inflammatory activities.

Gliopreventive effects of guanosine against glucose deprivation in vitro

Guanosine, a guanine-based purine, is recognized as an extracellular signaling molecule that is released from astrocytes and confers neuroprotective effects in several in vivo and in vitro studies. Astrocytes regulate glucose metabolism, glutamate transport, and defense mechanism against oxidative stress. C6 astroglial cells are widely used as an astrocyte-like cell line to study the astrocytic function and signaling pathways. Our previous studies showed that guanosine modulates the glutamate uptake activity, thus avoiding glutamatergic excitotoxicity and protecting neural cells. The goal of this study was to determine the gliopreventive effects of guanosine against glucose deprivation in vitro in cultured C6 cells. Glucose deprivation induced cytotoxicity, an increase in reactive oxygen and nitrogen species (ROS/RNS) levels and lipid peroxidation as well as affected the metabolism of glutamate, which may impair important astrocytic functions. Guanosine prevented glucose deprivation-induced toxicity in C6 cells by modulating oxidative and nitrosative stress and glial responses, such as the glutamate uptake, the glutamine synthetase activity, and the glutathione levels. Glucose deprivation decreased the level of EAAC1, the main glutamate transporter present in C6 cells. Guanosine also prevented this effect, most likely through PKC, PI3K, p38 MAPK, and ERK signaling pathways. Taken together, these results show that guanosine may represent an important mechanism for protection of glial cells against glucose deprivation. Additionally, this study contributes to a more thorough understanding of the glial- and redox-related protective properties of guanosine in astroglial cells.

Resveratrol protects C6 astrocyte cell line against hydrogen peroxide-induced oxidative stress through heme oxygenase 1

Resveratrol, a polyphenol presents in grapes and wine, displays antioxidant and anti-inflammatory properties and cytoprotective effect in brain pathologies associated to oxidative stress and neurodegeneration. In previous work, we demonstrated that resveratrol exerts neuroglial modulation, improving glial functions, mainly related to glutamate metabolism. Astrocytes are a major class of glial cells and regulate neurotransmitter systems, synaptic processing, energy metabolism and defense against oxidative stress. This study sought to determine the protective effect of resveratrol against hydrogen peroxide (H₂O₂)-induced cytotoxicity in C6 astrocyte cell line, an astrocytic lineage, on neurochemical parameters and their cellular and biochemical mechanisms. H₂O₂ exposure increased oxidative-nitrosative stress, iNOS expression, cytokine proinflammatory release (TNFα levels) and mitochondrial membrane potential dysfunction and decreased antioxidant defenses, such as SOD, CAT and creatine kinase activity. Resveratrol strongly prevented C6 cells from H₂O₂-induced toxicity by modulating glial, oxidative and inflammatory responses. Resveratrol per se increased heme oxygenase 1 (HO1) expression and extracellular GSH content. In addition, HO1 signaling pathway is involved in the protective effect of resveratrol against H₂O₂-induced oxidative damage in astroglial cells. Taken together, these results show that resveratrol represents an important mechanism for protection of glial cells against oxidative stress.

Resveratrol prevents ammonia toxicity in astroglial cells

Ammonia is implicated as a neurotoxin in brain metabolic disorders associated with hyperammonemia. Acute ammonia toxicity can be mediated by an excitotoxic mechanism, oxidative stress and nitric oxide (NO) production. Astrocytes interact with neurons, providing metabolic support and protecting against oxidative stress and excitotoxicity. Astrocytes also convert excess ammonia and glutamate into glutamine via glutamine synthetase (GS). Resveratrol, a polyphenol found in grapes and red wines, exhibits antioxidant and anti-inflammatory properties and modulates glial functions, such as glutamate metabolism. We investigated the effect of resveratrol on the production of reactive oxygen species (ROS), GS activity, S100B secretion, TNF-α, IL-1β and IL-6 levels in astroglial cells exposed to ammonia. Ammonia induced oxidative stress, decreased GS activity and increased cytokines release, probably by a mechanism dependent on protein kinase A (PKA) and extracellular signal-regulated kinase (ERK) pathways. Resveratrol prevented ammonia toxicity by modulating oxidative stress, glial and inflammatory responses. The ERK and nuclear factor-κB (NF-κB) are involved in the protective effect of resveratrol on cytokines proinflammatory release. In contrast, other antioxidants (e.g., ascorbic acid and trolox) were not effective against hyperammonemia. Thus, resveratrol could be used to protect against ammonia-induced neurotoxicity.

Resveratrol preconditioning increases methionine sulfoxide reductases A expression and enhances resistance of human neuroblastoma cells to neurotoxins

Methionine sulfoxide reductases A (MsrA) has been postulated to act as a catalytic antioxidant system involved in the protection of oxidative stress-induced cell injury. Recently, attention has turned to MsrA in coupling with the pathology of Parkinson's disease, which is closely related to neurotoxins that cause dopaminergic neuron degeneration. Here, we firstly provided evidence that pretreatment with a natural polyphenol resveratrol (RSV) up-regulated the expression of MsrA in human neuroblastoma SH-SY5Y cells. It was also observed that the expression and nuclear translocation of forkhead box group O 3a (FOXO3a), a transcription factor that activates the human MsrA promoter, increased after RSV pretreatment. Nicotinamide , an inhibitor of silent information regulator 1 (SIRT1), prevented RSV-induced elevation of FOXO3a and MsrA expression, indicating that the effect of RSV was mediated by a SIRT1-dependent pathway. RSV preconditioning increased methionine sulfoxide(MetO)-reducing activity in SH-SY5Y cells and enhanced their resistance to neurotoxins, including chloramine-T and 1-methyl-4-phenyl-pyridinium. In addition, the enhancement of cell resistance to neurotoxins caused by RSV preconditioning can be largely prevented by MsrA inhibitor dimethyl sulfoxide. Our findings suggest that treatment with polyphenols such as RSV can be used as a potential regulatory strategy for MsrA expression and function.

The effects of resveratrol and selected metabolites on the radiation and antioxidant response

Excess reactive oxygen species (ROS) generated from ionizing radiation (IR) or endogenous sources like cellular respiration and inflammation produce cytotoxic effects that can lead to carcinogenesis. Resveratrol (RSV), a polyphenol with antioxidant and anticarcinogenic capabilities, has shown promise as a potential radiation modifier. The present study focuses on examining the effects of RSV or RSV metabolites as a radiation modifier in normal tissue. RSV or a RSV metabolite, piceatannol (PIC) did not protect human lung fibroblasts (1522) from the radiation-induced cell killing. Likewise, neither RSV nor PIC afforded protection against lethal total body IR in C3H mice. Additional research has shown protection in cells against hydrogen peroxide when treated with RSV. Therefore, clonogenic survival was measured in 1522 cells with RSV and RSV metabolites. Only the RSV derivative, piceatannol (PIC), showed protection against hydrogen peroxide mediated cytotoxicity; whereas, RSV enhanced hydrogen peroxide sensitivity at a 50 µM concentration; the remaining metabolites evaluated had little to no effect on survival. PIC also showed enhancement to peroxide exposure at a higher concentration (150 µM). A potential mechanism for RSV-induced sensitivity to peroxides could be its ability to block 1522 cells in the S-phase, which is most sensitive to hydrogen peroxide treatment. In addition, both RSV and PIC can be oxidized to phenoxyl radicals and quinones, which may exert cytotoxic effects. These cytotoxic effects were abolished when HBED, a metal chelator, was added. Taken together RSV and many of its metabolic derivatives are not effective as chemical radioprotectors and should not be considered for clinical use.

Inactivation of astrocytic glutamine synthetase by hydrogen peroxide requires iron

The specific activity of brain glutamine synthetase (GS) is lowered in several neurodegenerative diseases that involve iron-mediated oxidative stress. The present study has investigated whether H₂O₂ directly inactivates GS or whether GS is primarily inactivated by hydroxyl radicals that are produced by the Fenton reaction when H₂O₂ reacts with ferrous iron. Exposure of purified sheep brain GS to supraphysiological concentrations of H₂O₂ (1 mM for 30 min) reduced its specific activity by only 41%, indicating that the enzyme is fairly resistant to oxidation by peroxide. However, the enzyme was completely inactivated when co-incubated with H₂O₂, iron and ascorbate, indicating a vulnerability to oxidation by conditions that favour the production of hydroxyl radicals. Similarly, specific GS activity in cultured mouse astrocytes was resistant to supraphysiological concentrations of H₂O₂, with approximately 37% of activity remaining 3h after incubation with 1mM H₂O₂. This inactivation was prevented by the iron chelators 2,2'-dipyridyl or 1,10-phenanthroline, but not by their non-chelating analogues. These data suggest that inactivation of astrocytic GS is caused by H₂O₂ indirectly via the Fenton reaction as it required the presence of chelatable intracellular iron.