Cytotoxic effects of various stressors on PC12 cells: involvement of oxidative stress and effect of antioxidants

Iron accentuated reactive oxygen species release by NADPH oxidase in activated microglia contributes to oxidative stress in vitro

BACKGROUND

Excessive iron contributes to oxidative stress after central nervous system injury. NADPH oxidase (NOX) enzymes are upregulated in microglia after pro-inflammatory activation and contribute to oxidative stress. The relationship between iron, microglia, NOX, and oxidative stress is currently unclear.

METHODS

We evaluated the effects of iron on lipopolysaccharide (LPS)-activated microglia and its secondary effect within neuronal co-cultures. Further, NOX2 and four specific inhibitors were tested to evaluate the relationship with the reactive oxygen species (ROS)-producing enzymes.

RESULTS

An iron dose-dependent increase in ROS production among microglia treated with LPS was identified. Interestingly, despite this increase in ROS, inflammatory polarization alterations were not detected among the microglia after exposure to iron and LPS. Co-culture experimentation between primary neurons and exposed microglia (iron and LPS) significantly reduced neuronal cell number at 24 h, suggesting a profound neurotoxic effect despite the lack of a change in polarization phenotype. NOX2 and NOX4 inhibition significantly reduced ROS production among microglia exposed to iron and LPS and reduced neuronal damage and death in response to microglial co-culture.

CONCLUSIONS

In conclusion, iron significantly increased ROS production and neurotoxicity without exacerbating LP-activated microglia phenotype in vitro, suggesting that iron contributes to microglia-related oxidative stress, and this may be a viable therapeutic target for injury or neurodegeneration. Further, this study highlights both NOX2 and NOX4 as potential therapeutic targets in the treatment of iron-induced microglia-related inflammation and neurotoxicity.

Evaluation of the Cellular and Animal Models for the Study of Antioxidant Activity: A Review

The mechanisms of antioxidant activities of phytochemicals are highly complex, so various methods to study them have been developed. However, the diverse available methods show inconsistent results. Different stressors, cell models, and animal models have been used to evaluate the antioxidant properties of phytochemicals. However, the literature still lacks a summary of the effects of different stressors, cell models, and animal models on the evaluation of antioxidant activities. Therefore, the mechanisms of action of different oxidative stimuli and the characteristics of the available cell models and animal models are summarized in this review.

Protective Effects of Selol Against Sodium Nitroprusside-Induced Cell Death and Oxidative Stress in PC12 Cells

Selol is an organic selenitetriglyceride formulation containing selenium at +4 oxidation level that can be effectively incorporated into catalytic sites of of Se-dependent antioxidants. In the present study, the potential antioxidative and cytoprotective effects of Selol against sodium nitroprusside (SNP)-evoked oxidative/nitrosative stress were investigated in PC12 cells and the underlying mechanisms analyzed. Spectrophoto- and spectrofluorimetic methods as well as fluorescence microscopy were used in this study; mRNA expression was quantified by real-time PCR. Selol dose-dependently improved the survival and decreased the percentage of apoptosis in PC12 cells exposed to SNP. To determine the mechanism of this protective action, the effect of Selol on free radical generation and on antioxidative potential was evaluated. Selol offered significant protection against the elevation of reactive oxidative species (ROS) evoked by SNP. Moreover, this compound restored glutathione homeostasis by ameliorating the SNP-evoked disturbance of GSH/GSSG ratio. The protective effect exerted by Selol was associated with the prevention of SNP-mediated down-regulation of antioxidative enzymes: glutathione peroxidase (Se-GPx), glutathione reductase (GR), and thioredoxin reductase (TrxR). Finally, GPx inhibition significantly abolished the cytoprotective effect of Selol. In conclusion, these results suggest that Selol effectively protected PC12 cells against SNP-induced oxidative damage and death by adjusting free radical levels and antioxidant system, and suppressing apoptosis. Selol could be successfully used in the treatments of diseases that involve oxidative stress and resulting apoptosis.

Water-soluble fractions from defatted sesame seeds protect human neuroblast cells against peroxyl radicals and hydrogen peroxide-induced oxidative stress

Oxidative stress is involved in the development of aging-related diseases, such as neurodegenerative diseases. Dietary antioxidants that can protect neuronal cells from oxidative damage play an important role in preventing such diseases. Previously, we reported that water-soluble fractions purified from defatted sesame seed flour exhibit good antioxidant activity in vitro. In the present study, we investigated the protective effects of white and gold sesame seed water-soluble fractions (WS-wsf and GS-wsf, respectively) against 2,2'-azobis(2-amidinopropane) dihydrochloride (AAPH) and hydrogen peroxide (H2O2) induced oxidative stress in human neuroblast SH-SY5Y cells. Pretreatment with WS-wsf and GS-wsf did not protect cells against AAPH-induced cytotoxicity, while simultaneous co-treatment with AAPH significantly improved cell viability and inhibited membrane lipid peroxidation. These results suggest that WS-wsf and GS-wsf protect cells from AAPH-induced extracellular oxidative damage via direct scavenging of peroxyl radicals. When oxidative stress was induced by H2O2, pretreatment WS-wsf and GS-wsf significantly enhanced cell viability. These results suggest that in addition to radical scavenging, WS-wsf and GS-wsf enhance cellular resistance to intracellular oxidative stress by activation of the Nrf-2/ARE pathway as confirmed by the increased Nrf2 protein level in the nucleus and increased heme oxygenase 1 (HO-1) mRNA expression. The roles of ferulic and vanillic acids as bioactive antioxidants in these fractions were also confirmed. In conclusion, our results indicated that WS-wsf and GS-wsf, which showed antioxidant activity in vitro, are also efficient antioxidants in a cell system protecting SH-SY5Y cells against both extracellular and intracellular oxidative stress.

Oxidative stress-mediated intrinsic apoptosis in human promyelocytic leukemia HL-60 cells induced by organic arsenicals

Arsenic trioxide has shown the excellent therapeutic efficiency for acute promyelocytic leukemia. Nowadays, more and more research focuses on the design of the arsenic drugs, especially organic arsenicals, and on the mechanism of the inducing cell death. Here we have synthesized some organic arsenicals with Schiff base structure, which showed a better antitumor activity for three different kinds of cancer cell lines, namely HL-60, SGC 7901 and MCF-7. Compound 2a (2-(((4-(oxoarsanyl)phenyl)imino)methyl)phenol) and 2b (2-methoxy-4-(((4-(oxoarsanyl)phenyl)imino)methyl)phenol) were chosen for further mechanism study due to their best inhibitory activities for HL-60 cells, of which the half inhibitory concentration (IC₅₀) were 0.77 μM and 0.51 μM, respectively. It was illustrated that 2a or 2b primarily induced the elevation of reactive oxygen species, decrease of glutathione level, collapse of mitochondrial membrane potential, release of cytochrome c, activation of Caspase-3 and apoptosis, whereas all of the phenomena can be eliminated by the addition of antioxidants. Therefore, we concluded that compound 2a and 2b can induce the oxidative stress-mediated intrinsic apoptosis in HL-60 cells. Both the simplicity of structure with Schiff base group and the better anticancer efficiency demonstrate that organic arsenicals are worthy of further exploration as a class of potent antitumor drugs.

A SIRT3/AMPK/autophagy network orchestrates the protective effects of trans-resveratrol in stressed peritoneal macrophages and RAW 264.7 macrophages

Resveratrol gains a great interest for its strong antioxidant properties, while the molecular mechanisms underlie the beneficial effects on psychosocial stress remain controversial. In this study, we demonstrated that resveratrol protected peritoneal macrophages and RAW 264.7 cells from stress-induced decrease in the total cell count, phagocytic capability, reactive oxygen species generation, monodansylcadaverine and mitochondrial membrane potential in stressed mice. Resveratrol promoted stress-induced autophagy in both models. Modulation of autophagy by rapamycin or 3-methyladenine regulated the protective effect of resveratrol, suggesting a role of autophagy in the protective mechanisms of resveratrol. The comparison studies revealed that distinct mechanisms were implicated in the protective effect of resveratrol and other antioxidants (vitamin C and edaravone). Resveratrol promoted autophagy via upregulating SIRT3 expression and phosphorylation of AMP-activated protein kinase (AMPK). Knockdown of SIRT3 resulted in decreased autophagy and abolished protective effect of resveratrol. SIRT1 was also involved in the protective mechanism of resveratrol, although its effect on autophagy was unnoticeable. Pharmacological manipulation of autophagy modulated the effects of resveratrol on SIRT3 and AMPK, revealing the engagement of a positive feedback loop. In sharp contrast, vitamin C and edaravone effectively protected macrophages from stress-induced cytotoxicity, accompanied by downregulated SIRT3 expression and AMPK phosphorylation, and decreased level of autophagy response. Taken together, we conclude that a SIRT3/AMPK/autophagy network orchestrates in the protective effect of resveratrol in macrophages.

Implications for blood-brain-barrier permeability, in vitro oxidative stress and neurotoxicity potential induced by mesoporous silica nanoparticles: effects of surface modification

MSNs are shown to have the potential to overcome the BBB and cause neuronal damage. However, the neurotoxicity potential could be mediated with surface modification.

The role of calpain in an in vivo model of oxidative stress-induced retinal ganglion cell damage

PURPOSE

In this study, we set out to establish an in vivo animal model of oxidative stress in the retinal ganglion cells (RGCs) and determine whether there is a link between oxidative stress in the RGCs and the activation of calpain, a major part of the apoptotic pathway.

MATERIALS AND METHODS

Oxidative stress was induced in the RGCs of C57BL/6 mice by the intravitreal administration of 2,2'-azobis (2-amidinopropane) dihydrochloride (AAPH, 30mM, 2μl). Control eyes were injected with 2μl of vehicle. Surviving Fluorogold (FG)-labeled RGCs were then counted in retinal flat mounts. Double staining with CellROX and Annexin V was performed to investigate the co-localization of free radical generation and apoptosis. An immunoblot assay was used both to indirectly evaluate calpain activation in the AAPH-treated eyes by confirming α-fodrin cleavage, and also to evaluate the effect of SNJ-1945 (a specific calpain inhibitor: 4% w/v, 100mg/kg, intraperitoneal administration) in these eyes.

RESULTS

Intravitreal administration of AAPH led to a significant decrease in FG-labeled RGCs 7days after treatment (control: 3806.7±575.2RGCs/mm(2), AAPH: 3156.1±371.2RGCs/mm(2), P<0.01). CellROX and Annexin V signals were co-localized in the FG-labeled RGCs 24h after AAPH injection. An immunoblot assay revealed a cleaved α-fodrin band that increased significantly 24h after AAPH administration. Intraperitoneally administered SNJ-1945 prevented the cleavage of α-fodrin and had a neuroprotective effect against AAPH-induced RGC death (AAPH: 3354.0±226.9RGCs/mm(2), AAPH+SNJ-1945: 3717.1±614.6RGCs/mm(2), P<0.01).

CONCLUSION

AAPH administration was an effective model of oxidative stress in the RGCs, showing that oxidative stress directly activated the calpain pathway and induced RGC death. Furthermore, inhibition of the calpain pathway protected the RGCs after AAPH administration.

Tocotrienol prevents AAPH-induced neurite degeneration in neuro2a cells

OBJECTIVES

Reactive oxygen species induce neurite degeneration before inducing cell death. However, the degenerative mechanisms have not yet been elucidated. While tocotrienols have a known neuroprotective function, the underlying mechanism remains unclear and may or may not involve antioxidant action. In this study, we hypothesize that free radical-derived membrane injury is one possible mechanism for inducing neurite degeneration. Therefore, we examined the potential neuroprotective effect of tocotrienols mediated through its antioxidant activity.

METHODS

Mouse neuroblastoma neuro2a cells were used to examine the effect of the water-soluble free radical generator 2,2'-azobis(2-methylpropionamide) dihydrochloride (AAPH) on neurite dynamics. After 24 hours of AAPH treatment, cell viability, neurite number, and the number of altered neurites were measured in the presence or absence of α-tocotrienol.

RESULTS

Treatment of neuro2a cells with a low concentration of AAPH induces neurite degeneration, but not cell death. Treatment with 5 µM α-tocotrienol significantly inhibited neurite degeneration in AAPH-treated neuro2a cells. Furthermore, morphological changes in AAPH-treated neuro2a cells were similar to those observed with colchicine treatment.

CONCLUSIONS

α-Tocotrienol may scavenge AAPH-derived free radicals and alkoxyl radicals that are generated from AAPH-derived peroxyl radicals on cell membranes. Therefore, α-tocotrienol may have a neuroprotective effect mediated by its antioxidant activity.

P2X7 Cell Death Receptor Activation and Mitochondrial Impairment in Oxaliplatin-Induced Apoptosis and Neuronal Injury: Cellular Mechanisms and In Vivo Approach

Limited information is available regarding the cellular mechanisms of oxaliplatin-induced painful neuropathy during exposure of patients to this drug. We therefore determined oxidative stress in cultured cells and evaluated its occurrence in C57BL/6 mice. Using both cultured neuroblastoma (SH-SY5Y) and macrophage (RAW 264.7) cell lines and also brain tissues of oxaliplatin-treated mice, we investigated whether oxaliplatin (OXA) induces oxidative stress and apoptosis. Cultured cells were treated with 2–200 µM OXA for 24 h. The effects of pharmacological inhibitors of oxidative stress or inflammation (N-acetyl cysteine, ibuprofen, acetaminophen) were also tested. Inhibitors were added 30 min before OXA treatment and then in combination with OXA for 24 h. In SH-SY5Y cells, OXA caused a significant dose-dependent decrease in viability, a large increase in ROS and NO production, lipid peroxidation and mitochondrial impairment as assessed by a drop in mitochondrial membrane potential, which are deleterious for the cell. An increase in levels of negatively charged phospholipids such as cardiolipin but also phosphatidylserine and phosphatidylinositol, was also observed. Additionally, OXA caused concentration-dependent P2X7 receptor activation, increased chromatin condensation and caspase-3 activation associated with TNF-α and IL-6 release. The majority of these toxic effects were equally observed in Raw 264.7 which also presented high levels of PGE2. Pretreatment of SH-SY5Y cells with pharmacological inhibitors significantly reduced or blocked all the neurotoxic OXA effects. In OXA-treated mice (28 mg/kg cumulated dose) significant cold hyperalgesia and oxidative stress in the tested brain areas were shown. Our study suggests that targeting P2X7 receptor activation and mitochondrial impairment might be a potential therapeutic strategy against OXA-induced neuropathic pain.

Neuroprotective effect of a caffeic acid derivative from Abacopteris penangiana

CONTEXT

A new caffeic acid derivative, named (7'Z)-3-O-(3, 4-dihydroxyphenylethenyl)-caffeic acid (CADP), extracted from Abacopteris penangiana (Hook.) Ching.

OBJECTIVE

To elucidate the neuroprotective effect of CADP against H₂O₂-induced cytotoxicity in PC12 cells and D-galactose (D-gal)-induced neurotoxicity in mice brain.

MATERIALS AND METHODS

CADP was isolated from the methanol extract of the rhizomes of A. penangiana. In vitro, the protective effect of CADP (0.1-10 μM) against H₂O₂-induced oxidative damage on PC12 cells was investigated by a MTT assay. In vivo, behavioral tests and antioxidant enzymes measurements were performed to investigate the protective effect of intraperitoneal (i.p.) injection of CADP (5 or 10 mg/kg/day) for 2 weeks on D-gal-induced neurotoxicity in mice.

RESULTS

The results showed that CADP significantly attenuated cell toxicity in a dose-dependent manner, and the EC₅₀ value of CADP was 0.83 ± 0.02 μM. In vivo, it was found that CADP significantly improved the behavioral performance of D-gal-treated mice in both Morris water maze (MWM) test and step-down avoidance test. As compared with model group, CADP (5, 10 mg/kg/day) attenuated the decrease in superoxide dismutase (SOD) activities by 40.5 and 75.4%, respectively; attenuated the decrease in glutathione peroxidase (GPx) activities by 53.8 and 73.2%, respectively; attenuated the decrease in catalase activities by 12.0 and 53.3%, respectively; reduced the increased levels of malondialdehyde (MDA) by 38.6 and 79.9%, respectively.

DISCUSSION AND CONCLUSION

The results suggested that CADP has significant neuroprotective effects which can be attributed to inhibiting the generation of free radical and enhancing the activity of endogenous antioxidant enzymes.

Protective effect of bixin on cisplatin-induced genotoxicity in PC12 cells

Bixin is the main carotenoid found in annatto seeds (Bixa orellana L.) and is responsible for their reddish-orange color. The antioxidant properties of this compound are associated with its ability to scavenge free radicals, which may reduce damage and protect tissues against toxicity caused by anticancer drugs such as cisplatin. In this study, the genotoxicity and antigenotoxicity of bixin on cisplatin-induced toxicity in PC12 cells was assessed. Cytotoxicity was evaluated using the MTT assay, mutagenicity, genotoxicity, and protective effect of bixin were evaluated using the micronucleus test and comet assay. PC12 cells were treated with bixin (0.05, 0.08, and 0.10μg/mL), cisplatin (0.1μg/mL) or a combination of both bixin and cisplatin. Bixin was neither cytotoxic nor genotoxic compared to the controls. In the combined treatment bixin significantly reduced the percentage of DNA in tail and the frequency of micronuclei induced by cisplatin. This result suggests that bixin can function as a protective agent, reducing cisplatin-induced DNA damage in PC12 cells, and it is possible that this protection could also extend to neuronal cells. Further studies are being conducted to better understand the mechanisms involved in the activity of this protective agent prior to using it therapeutically.

Macrophage autophagy and oxidative stress: an ultrastructural and immunoelectron microscopical study

The word autophagy broadly refers to the cellular catabolic processes that lead to the removal of damaged cytosolic proteins or cell organelles through lysosomes. Although autophagy is often observed during programmed cell death, it may also serve as a cell survival mechanism. Accumulation of reactive oxygen species within tissues and cells induces various defense mechanisms or programmed cell death. It has been shown that, besides inducing apoptosis, oxidative stress can also induce autophagy. To date, however, the regulation of autophagy in response to oxidative stress remains largely elusive and poorly understood. Therefore, the present study was designed to examine the ratio between oxidative stress and autophagy in macrophages after oxidant exposure (AAPH) and to investigate the ultrastructural localization of beclin-1, a protein essential for autophagy, under basal and stressful conditions. Our data provide evidence that oxidative stress induces autophagy in macrophages. We demonstrate, for the first time by immunoelectron microscopy, the subcellular localization of beclin-1 in autophagic cells.

Oxidative mechanisms contribute to nanosize silican dioxide-induced developmental neurotoxicity in PC12 cells

Neurotoxicity was investigated in nano-SiO2-treated cultured PC12 cells, an in vitro neuronal cell model, in order to define a relatively safe dose range for its application. The following were observed in the present study: (1) A dose-dependent increase in the level of reactive oxygen species (ROS) with a corresponding decrease in the level of glutathione (R2=0.965) suggesting 20- and 50-nm SiO2-induced free radical generation and glutathione depletion. (2) A dose- and time-dependent decrease in cell viability that was associated with elevation of ROS level, especially after 24-h nano-SiO2 exposure (R2=0.965), suggesting the role of oxidative stress on nano-SiO2 induced cell death. (3) An increase in the level of thiobarbituric-acid reactive species that correlated reversely with cell viability of the PC12 cells treated with nano-SiO2 (R2=0.945) suggesting nano-SiO2-induced membrane damage caused by lipid peroxidation. (4) A dose-dependent increase in sub-G1 population in SiO2-exposed cells along with cell shrinkage and nuclear condensation from morphological examination suggesting nano-SiO2-induced cell apoptosis. Furthermore, nano-SiO2 exposure diminished the ability of neurite extension in response to nerve growth factor in treated PC12 cells. In summary, SiO2 nanoparticle exposure resulted in dose-dependent neurotoxicity in cultured PC12 cells that was probably associated with oxidative stress and induced apoptosis.

Role of glutathione in augmenting the anticancer activity of pyrroloquinoline quinone (PQQ)

Pyrroloquinoline quinone (PQQ), a bacterial redox co-factor and antioxidant, is highly reactive with nucleophilic compounds present in biological fluids. PQQ induced apoptosis in human promonocytic leukemia U937 cells and this was accompanied by depletion of the major cellular antioxidant glutathione and increase in intracellular reactive oxygen species (ROS). Treatment with glutathione (GSH) or N-acetyl-L-cysteine (NAC) did not spare PQQ toxicity but resulted in a 2-5-fold increase in PQQ-induced apoptosis in U937 cells. Cellular GSH levels increased following treatment by NAC alone but were severely depleted by co-treatment with NAC and PQQ. This was accompanied by an increase in intracellular ROS. Alternatively, depletion of glutathione also resulted in increased PQQ cytotoxicity. However, the cells underwent necrosis as evidenced by dual labeling with annexin V and propidium iodide. PQQ-induced cytotoxicity is thus critically regulated by the cellular redox status. An increase in GSH can augment apoptosis and its depletion can switch the mode of cell death to necrosis in the presence of PQQ. Our data suggest that modulation of intracellular GSH can be used as an effective strategy to potentiate cytotoxicity of quinones like PQQ.

Protective effects of polyphenolic compounds on oxidative stress-induced cytotoxicity in PC12 cells

To investigate the beneficial properties associated with polyphenols, we screened 12 polyphenols for their ability to increase the viability of PC12 cells subjected to oxidative stress via CoCl2 and H2O2. Cell viability data demonstrate that 50 micromol/L methyl gallate and 50 micromol/L fisetin significantly increase viability of H2O2-stressed cells. Further, viability data suggest that 100 micromol/L epigallocatechin gallate (EGCG) increases basal viability, but has no rescue effect on cells stressed with CoCl2 or H2O2. Analysis of intracellular reactive oxygen species (ROS) shows that EGCG, methyl gallate, and gallic acid are effective in reducing CoCl2-derived ROS, and that methyl gallate is effective in attenuating H2O2-derived ROS. Examination of nitric oxide concentrations shows that methyl gallate significantly increases nitric oxide, both in nonstressed and H2O2-stressed cells, whereas EGCG results are consistent with the scavenging of nitric oxide under nonstressed and stressed conditions. Furthermore, analysis of total glutathione levels reveals that EGCG, methyl gallate, and gallic acid pretreatments with and without H2O2 stress have the ability to significantly alter glutathione metabolism. These findings suggest that EGCG, methyl gallate, and gallic acid may have potential therapeutic properties.

Protective potential of 17β-estradiol against co-exposure of 4-hydroxynonenal and 6-hydroxydopamine in PC12 cells

4-hydroxynonenal (4-HNE) and 6-hydroxydopamine (6-OHDA)-mediated damage in dopaminergic neurons is well documented. Protective potential of steroidal hormone (17β-estradiol) has also been suggested. However, therapeutic potential of such promising hormone is hampered due to complex brain anatomy and physiology. Thus, the present investigations were studied to suggest the applicability of dopamine expressing PC12 cells as in vitro tool to screen the pharmacological potential of 17β-estradiol against 4-HNE and 6-OHDA. MTT assay was conducted for cytotoxicity assessment of both 4-HNE (1 μM to 50 μM) and 6-OHDA (10-4 to 10-7 M). Non-cytotoxic concentrations, that is, 4-HNE (1 μM) and 6-OHDA (10-6 M) were selected to study the synergetic/additive responses. PC12 cells were found to be more vulnerable towards co-exposure of individual exposure of 4-HNE and 6-OHDA, even at non-cytotoxic concentrations. Then, cells were subjected to pre-treatment (24 hours) of 17β-estradiol (1 μM), followed by a permutation of combinations of both 4-HNE and 6-OHDA. Pretreatment of 17β-estradiol was found to be significantly effective against the cytotoxic responses of 4-HNE and 6-OHDA, when the damage was at lower level. However, 17β-estradiol was found to be ineffective against higher concentrations. Physiological-specific responses of PC12 cells against 4-HNE/6-OHDA and 17β-estradiol suggest its applicability as first tier of screening tool.

NGF induced differentiated PC12 cells as in vitro tool to study 4-hydroxynonenal induced cellular damage

Investigations were carried out to examine the suitability of PC12 cells as an in vitro tool to examine 4-hydroxynonenal (4-HNE)-induced toxicity in nervous tissue. On day 8 of differentiation, markers of neural effects and oxidative stress were measured following exposure of PC12 cells to 1-50 microM 4-HNE for 1-8h. Endpoints included dopamine DA-D(2) receptor and glutathione S-transferase (GSTP1-1) protein levels, 4-HNE-protein binding, glutathione (GSH) concentrations and intracellular calcium levels. GSH levels were maximally depleted after 4h. 4-HNE also induced depletion of GSTP1-1 and increased intracellular Ca(++), with the latter seen as early as 1h after exposure. Responses at 8h were not greater than responses at earlier times. The experiments suggest that PC12 cells could be an in vitro tool for understanding toxicant-cell interactions, especially those that result in oxidative stress.

Ozone as u-shaped dose responses molecules (hormetins)

Redox environment involves a broad network of pro-oxidant and antioxidant components. Health benefit or damage can be induced as a consequence of an adaptive cellular stress response. A consequence of hormetic amplification is an increase in the homeodynamic space of a living system in terms of an increased defense capacity and a reduced load of damaged macromolecules. Ozone, when used at appropriate doses, promotes the formation of reactive oxygen species and lipid peroxides allows them to become late and long-lasting messengers. Healthy aging may be achieved by hormesis through mild and periodic, but not severe or chronic, physical and mental challenges, and by the use of nutritional hormesis incorporating mild stress-inducing molecules called hormetins. The paradoxical concept that ozone eventually induces an antioxidant response capable of reversing a chronic oxidative stress is common in the animal and vegetal kingdom; it is already supported by findings of an increased level of antioxidant enzymes during ozone therapy. Those facts can include ozone as a hormetin. The established scientific foundations of hormesis are ready to pave the way for new and effective approaches in redox-related disease research and intervention; ozone therapy can be a good candidate.

Protective effects of methyl gallate on H2O2-induced apoptosis in PC12 cells

Neurodegenerative disorders are a class of diseases that have been linked to apoptosis induced by elevated levels of reactive oxygen species (ROS). ROS activates the apoptotic cascade through mitochondrial dysfunction and damage to lipids, proteins and DNA. Recently, fruit and tea-derived polyphenols have been found to be beneficial in decreasing oxidative stress and increasing overall health. Further, polyphenols including epigallocatechin gallate (EGCG) have been reported to inhibit apoptotic signaling and increase neural cell survival. In an effort to better understand the beneficial properties associated with polyphenol consumption, the aim of this study was to explore the neuroprotective effects of EGCG, methyl gallate (MG), gallic acid (GA) and N-acetylcysteine (NAC) on H(2)O(2)-induced apoptosis in PC12 cells and elucidate potential protective mechanisms. Cell viability data demonstrates that MG and NAC pre-treatments significantly increase viability of H(2)O(2)-stressed cells, while pre-treatments with EGCG and GA exacerbates stress. Quantitation of apoptosis and mitochondrial membrane potential shows that MG pre-treatment prevents mitochondria depolarization, however does not inhibit apoptosis and is thus evidence that MG can inhibit mitochondria-mediated apoptosis. Subsequent analysis of DNA degradation and caspase activation reveals that MG inhibits activation of caspase 9 and has a partial inhibitory effect on DNA degradation. These findings confirm the involvement of both intrinsic and extrinsic apoptotic pathways in H(2)O(2)-induced apoptosis and suggest that MG may have potential therapeutic properties against mitochondria-mediated apoptosis.

Protective effects of resveratrol and quercetin against MPP+ -induced oxidative stress act by modulating markers of apoptotic death in dopaminergic neurons

Reactive oxygen species produced by oxidative stress may participate in the apoptotic death of dopamine neurons distinctive of Parkinson's disease. Resveratrol, a red wine extract, and quercetin, found mainly in green tea, are two natural polyphenols, presenting antioxidant properties in a variety of cellular paradigms. The aim of this study was to evaluate the effect of resveratrol and quercetin on the apoptotic cascade induced by the administration of 1-methyl-4-phenylpyridinium ion (MPP(+)), a Parkinsonian toxin, provoking the selective degeneration of dopaminergic neurons. Our results show that a pre-treatment for 3 h with resveratrol or quercetin before MPP(+) administration could greatly reduce apoptotic neuronal PC12 death induced by MPP(+). We also demonstrated that resveratrol or quercetin modulates mRNA levels and protein expression of Bax, a pro-apoptotic gene, and Bcl-2, an anti-apoptotic gene. We then evaluated the release of cytochrome c and the nuclear translocation of the apoptosis-inducing factor (AIF). Altogether, our results indicate that resveratrol and quercetin diminish apoptotic neuronal cell death by acting on the expression of pro- and anti-apoptotic genes. These findings support the role of these natural polyphenols in preventive and/or complementary therapies for several human neurodegenerative diseases caused by oxidative stress and apoptosis.

Ascorbic acid promotes detoxification and elimination of 4-hydroxy-2(E)-nonenal in human monocytic THP-1 cells

4-Hydroxy-2(E)-nonenal (HNE), a reactive aldehyde derived from oxidized lipids, has been implicated in the pathogenesis of cardiovascular and neurological diseases, in part by its ability to induce oxidative stress and by protein carbonylation in target cells. The effects of intracellular ascorbic acid (vitamin C) on HNE-induced cytotoxicity and protein carbonylation were investigated in human THP-1 monocytic leukemia cells. HNE treatment of these cells resulted in apoptosis, necrosis, and protein carbonylation. Ascorbic acid accumulated in the cells at concentrations of 6.4 or 8.9 mM after treatment with 0.1 or 1 mM ascorbate in the medium for 18 h. Pretreatment of cells with 1.0 mM ascorbate decreased HNE-induced formation of reactive oxygen species and formation of protein carbonyls. The protective effects of ascorbate were associated with an increase in the formation of GSH-HNE conjugate and its phase 1 metabolites, measured by LC-MS/MS, and with increased transport of GSH conjugates from the cells into the medium. Ascorbate pretreatment enhanced the efflux of the multidrug resistant protein (MRP) substrate, carboxy-2',7'-dichlorofluorescein (CDF), and it prevented the HNE-induced inhibition of CDF export from THP-1 cells, suggesting that the protective effect of ascorbate against HNE cytotoxicity is through modulation of MRP-mediated transport of GSH-HNE conjugate metabolites. The formation of ascorbate adducts of HNE was observed in the cell exposure experiments, but it represented a minor pathway contributing to the elimination of HNE and to the protective effects of ascorbate.

Evaluation of the cytotoxicity and genotoxicity of curcumin in PC12 cells

Neurotoxicity induced by reactive oxygen species can appear as an adverse effect of chemotherapy treatment with platinum compounds, such as cisplatin. The use of this drug in clinical practice is limited due to its adverse effects, including nephrotoxicity, ototoxicity, neurotoxicity and genotoxicity. Functional foods or nutraceuticals have demonstrated potential neuroprotective activity in several experiments and models. This study aimed to investigate the possible cytotoxicity and genotoxicity/antigenotoxic effects of curcumin in PC12 cells exposed to cisplatin. Cell viability and genotoxicity/antigenotoxicity were evaluated by the MTT assay and micronucleus test, respectively. PC12 cells were treated with different concentrations of cisplatin and curcumin (0.5 -- 128 microg/mL). Analysis of the results showed that high concentrations of curcumin were cytotoxic and increased micronuclei frequency compared to the control group. In the associated treatments, at all three concentrations evaluated, curcumin significantly reduced the total frequency of micronuclei induced by cisplatin. Determining the cytotoxic and genotoxic/antigenotoxic effects of this frequently used antioxidant in a neuronal model is important to assess possible hazards when combined with other chemical agents, including chemotherapy drugs used in cancer therapy.

Dopamine (DA) induced irreversible proteasome inhibition via DA derived quinones

This study demonstrated that DA and its oxidative metabolites: H2O2 and aminochrome (AM), cyclized DA quinones, could all directly inhibit proteasome activity. DA and AM, especially AM, could induce intensive and irreversible proteasome inhibition, whereas proteasome inhibition induced by H2O2 was weaker and GSH reversible. It was concluded that DA induced irreversible proteasome inhibition via DA-derived quinones, rather than through small molecular weight ROS. The AM was also more toxic than H2O2 to dopaminergic MN9D cells. Furthermore the cytotoxicity and proteasome inhibition induced by DA, AM and H2O2 could be abrogated by GSH, ascorbic acid (AA), Vitamin E, SOD (superoxidase dismutase) or CAT (catalase) with different profiles. Only GSH was potent to abrogate DA, AM or H2O2-induced cell toxicity and proteasome inhibition, as well as to reverse H2O2-induced proteosome inhibition. Therefore, therapeutic strategies to increase GSH level or to use GSH substitutes should function to control PD onset and development.

Environmental toxicity, oxidative stress and apoptosis: ménage à trois

Apoptosis is an evolutionary conserved homeostatic process involved in distinct physiological processes including organ and tissue morphogenesis, development and senescence. Its deregulation is also known to participate in the etiology of several human diseases including cancer, neurodegenerative and autoimmune disorders. Environmental stressors (cytotoxic agents, pollutants or toxicants) are well known to induce apoptotic cell death and to contribute to a variety of pathological conditions. Oxidative stress seems to be the central element in the regulation of the apoptotic pathways triggered by environmental stressors. In this work, we review the established mechanisms by which oxidative stress and environmental stressors regulate the apoptotic machinery with the aim to underscore the relevance of apoptosis as a component in environmental toxicity and human disease progression.

Dopamine auto-oxidation aggravates non-apoptotic cell death induced by over-expression of human A53T mutant alpha-synuclein in dopaminergic PC12 cells

In this study, we demonstrated that transient transfection and over-expression of human mutant A53T alpha-synuclein (alpha-syn) could induce expression level- and time-dependent, non-apoptotic cell death in PC12 cells, while wild-type and mutant A30P alpha-syn could not. The non-apoptotic cell death induced by over-expression of A53T alpha-syn in PC12 cells was found to be dopamine (DA) related. It could be alleviated by nerve growth factor but not by chemicals that abrogate endoplasmic reticulum stress. Furthermore, PC12 cell death could be alleviated by N-acetyl-cysteine (NAC) as well as by L-cysteine; but not by cell permeable tyrosinase inhibitors. NAC could prevent DA auto-oxidation and tyrosinase-catalyzed DA oxidation, whereas L-cysteine could potently abrogate DA auto-oxidation but could not prevent tyrosinase-catalyzed DA oxidation. Both NAC and L-cysteine could increase the reduced and total GSH levels, and concurrently decrease the oxidized GSH level in PC12 cells. On the other hand, over-expression of human mutant A53T alpha-syn could decrease the reduced and total GSH levels, and increase the oxidized GSH level in the cells. Taken together, we concluded that auto-oxidation of endogenous DA aggravates non-apoptotic cell death induced by over-expression of human mutant A53T alpha-syn in PC12 cells.

Apoptosis in arsenic trioxide-treated Calu-6 lung cells is correlated with the depletion of GSH levels rather than the changes of ROS levels

Arsenic trioxide (ATO) can regulate many biological functions such as apoptosis and differentiation in various cells. We investigated an involvement of ROS such as H(2)O(2) and O(2)(*-), and GSH in ATO-treated Calu-6 cell death. The levels of intracellular H(2)O(2) were decreased in ATO-treated Calu-6 cells at 72 h. However, the levels of O(2)(*-) were significantly increased. ATO reduced the intracellular GSH content. Many of the cells having depleted GSH contents were dead, as evidenced by the propidium iodine staining. The activity of CuZn-SOD was strongly down-regulated by ATO at 72 h while the activity of Mn-SOD was weakly up-regulated. The activity of catalase was decreased by ATO. ROS scavengers, Tiron and Trimetazidine did not reduce levels of apoptosis and intracellular O(2)(*-) in ATO-treated Calu-6 cells. Tempol showing a decrease in intracellular O(2)(*-) levels reduced the loss of mitochondrial transmembrane potential (DeltaPsi(m)). Treatment with NAC showing the recovery of GSH depletion and the decreased effect on O(2)(*-) levels in ATO-treated cells significantly inhibited apoptosis. In addition, BSO significantly increased the depletion of GSH content and apoptosis in ATO-treated cells. Treatment with SOD and catalase significantly reduced the levels of O(2)(*-) levels in ATO-treated cells, but did not inhibit apoptosis along with non-effect on the recovery of GSH depletion. Taken together, our results suggest that ATO induces apoptosis in Calu-6 cells via the depletion of the intracellular GSH contents rather than the changes of ROS levels.

alpha-Synuclein enhances secretion and toxicity of amyloid beta peptides in PC12 cells

alpha-Synuclein is the fundamental component of Lewy bodies which occur in the brain of 60% of sporadic and familial Alzheimer's disease patients. Moreover, a proteolytic fragment of alpha-synuclein, the so-called non-amyloid component of Alzheimer's disease amyloid, was found to be an integral part of Alzheimer's dementia related plaques. However, the role of alpha-synuclein in pathomechanism of Alzheimer's disease remains elusive. In particular, the relationship between alpha-synuclein and amyloid beta is unknown. In the present study we showed the involvement of alpha-synuclein in amyloid beta secretion and in the mechanism of amyloid beta evoked mitochondria dysfunction and cell death. Rat pheochromocytoma PC12 cells transfected with amyloid beta precursor protein bearing Swedish double mutation (APPsw) and control PC12 cells transfected with empty vector were used in this study. alpha-Synuclein (10microM) was found to increase by twofold amyloid beta secretion from control and APPsw PC12 cells. Moreover, alpha-synuclein decreased the viability of PC12 cells by about 50% and potentiated amyloid beta toxicity leading to mitochondrial dysfunction and caspase-dependent programmed cell death. Inhibitor of caspase-3 (Z-DEVD-FMK, 100microM), and a mitochondrial permeability transition pore blocker, cyclosporine A (2microM) protected PC12 cells against alpha-synuclein or amyloid beta evoked cell death. In contrast Z-DEVD-FMK and cyclosporine A were ineffective in APPsw cells containing elevated amount of amyloid beta treated with alpha-synuclein. It was found that the inhibition of neuronal and inducible nitric oxide synthase reversed the toxic effect of alpha-synuclein in control but not in APPsw cells. Our results indicate that alpha-synuclein enhances the release and toxicity of amyloid beta leading to nitric oxide mediated irreversible mitochondria dysfunction and caspase-dependent programmed cell death.

The central role of glutathione in the pathophysiology of human diseases

Reduced glutathione (L-gamma-glutamyl-L-cysteinyl-glycine, GSH) is the prevalent low-molecular-weight thiol in mammalian cells. It is formed in a two-step enzymatic process including, first, the formation of gamma-glutamylcysteine from glutamate and cysteine, by the activity of the gamma-glutamylcysteine synthetase; and second, the formation of GSH by the activity of GSH synthetase which uses gamma-glutamylcysteine and glycine as substrates. While its synthesis and metabolism occur intracellularly, its catabolism occurs extracellularly by a series of enzymatic and plasma membrane transport steps. Glutathione metabolism and transport participates in many cellular reactions including: antioxidant defense of the cell, drug detoxification and cell signaling (involved in the regulation of gene expression, apoptosis and cell proliferation). Alterations in its concentration have also been demonstrated to be a common feature of many pathological conditions including diabetes, cancer, AIDS, neurodegenerative and liver diseases. Additionally, GSH catabolism has been recently reported to modulate redox-sensitive components of signal transduction cascades. In this manuscript, we review the current state of knowledge on the role of GSH in the pathogenesis of human diseases with the aim to underscore its relevance in translational research for future therapeutic treatment design.

Dietary sources and antioxidant effects of ergothioneine

Ergothioneine is a native membrane-impermeable thiol compound that is specifically accumulated in cells via the organic cation transporter OCTN1. In humans, OCTN1 and ergothioneine have been implicated in the etiopathogenesis of autoimmune disorders. However, available evidence about dietary sources and the functional role of ergothioneine in human physiology is scarce. Here, we analyzed the ergothioneine content in common foods using liquid chromatography tandem-mass spectrometry. Additionally, we assessed the protective potency of ergothioneine against various oxidative stressors in OCTN1-expressing cells in comparison with the main intracellular thiol antioxidant glutathione by evaluating cell viability with the MTT reduction assay. Only some food contained ergothioneine with highest concentrations detected in specialty mushrooms, kidney, liver, black and red beans, and oat bran. Ergothioneine exhibited cell protection only against copper(II)-induced toxicity but was far less potent than glutathione, indicting that ergothioneine is not involved in the intracellular antioxidant thiol defense system.

Vitamin E, antioxidant and nothing more

All of the naturally occurring vitamin E forms, as well as those of synthetic all-rac-alpha-tocopherol, have relatively similar antioxidant properties, so why does the body prefer alpha-tocopherol as its unique form of vitamin E? We propose the hypothesis that all of the observations concerning the in vivo mechanism of action of alpha-tocopherol result from its role as a potent lipid-soluble antioxidant. The purpose of this review then is to describe the evidence for alpha-tocopherol's in vivo function and to make the claim that alpha-tocopherol's major vitamin function, if not only function, is that of a peroxyl radical scavenger. The importance of this function is to maintain the integrity of long-chain polyunsaturated fatty acids in the membranes of cells and thus maintain their bioactivity. That is to say that these bioactive lipids are important signaling molecules and that changes in their amounts, or in their loss due to oxidation, are the key cellular events that are responded to by cells. The various signaling pathways that have been described by others to be under alpha-tocopherol regulation appear rather to be dependent on the oxidative stress of the cell or tissue under question. Moreover, it seems unlikely that these pathways are specifically under the control of alpha-tocopherol given that various antioxidants other than alpha-tocopherol and various oxidative stressors can manipulate their responses. Thus, virtually all of the variation and scope of vitamin E's biological activity can be seen and understood in the light of protection of polyunsaturated fatty acids and the membrane qualities (fluidity, phase separation, and lipid domains) that polyunsaturated fatty acids bring about.

Redox regulation of 7-ketocholesterol-induced apoptosis by beta-carotene in human macrophages

The aim of this study was to verify the hypothesis that beta-carotene may prevent 7-ketocholesterol (7-KC)-induced apoptosis in human macrophages. Therefore, THP-1 macrophages were exposed to 7-KC (5-50 microM) alone and in combination with beta-carotene (0.25-1 microM). 7-KC inhibited the growth of macrophages in a dose- and a time-dependent manner by inducing an arrest of cell cycle progression in the G0/G1 phase and apoptosis. Concomitantly, p53, p21, and Bax expressions were increased by 7-KC, whereas the levels of AKT, Bcl-2, and Bcl-xL were decreased. beta-Carotene prevented the growth-inhibitory effects of 7-KC in a dose- and time-dependent manner as well as the effects of 7-KC on the expression of cell cycle- and apoptosis-related proteins. 7-KC also enhanced reactive oxygen species (ROS) production through an increased expression of NAD(P)H oxidase (NOX-4). The effects of 7-KC were counteracted by the addition of the NAD(P)H oxidase inhibitor DPI or by cotransfection of siNOX-4 mRNA. beta-Carotene prevented 7-KC-induced increase in ROS production and in NOX-4 expression, as well as the phosphorylation of p38, JNK, and ERK1/2 induced by 7-KC. These data suggest a possible antiatherogenic role of beta-carotene through the prevention of 7-KC toxicity in human macrophages.

Molecular mechanisms of euplotin C-induced apoptosis: involvement of mitochondrial dysfunction, oxidative stress and proteases

The metabolite euplotin C (EC), isolated from the marine ciliate Euplotes crassus, is a powerful cytotoxic and pro-apoptotic agent in tumour cell lines. For instance, EC induces the rapid depletion of ryanodine Ca(2+) stores, the release of cytochrome c from the mitochondria, and the activation of caspase-3, leading to apoptosis. The purpose of this study was to gain further insight into the mechanisms of EC-induced apoptosis in rat pheochromocytoma PC12 cells. We found that EC increases Bax/Bcl-2 ratio and that Bax is responsible of the EC-induced dissipation of the mitochondrial membrane potential (Deltapsi(m)). In addition, EC induces the generation of reactive oxygene species (ROS) without involvement of p53. The inhibition of ROS generation prevents, at least in part, the pro-apoptotic effects of EC as well as the effects of EC on Bax, Deltapsi(m) and intracellular free Ca(2+), indicating a cross-talk between different pathways. However, definition of the effector cascade turns out to be more complex than expected and caspase-independent mechanisms, acting in parallel with caspases, should also be considered. Among them, EC increases the expression/activity of calpains downstream of ROS generation, although calpains seem to exert protective effects.

Effects of the plant flavonoids silymarin and quercetin on arsenite-induced oxidative stress in CHO-K1 cells

Chronic toxic effects of arsenic resulting from drinking water are a human health problem, especially in South-America and Asia. Arsenic is capable of influencing various cellular processes, causing adverse effects, including cancer. Although the exact mechanism of the action is not known, a correlation between oxidative stress, tumour promotion and arsenic exposure has been observed. We examined the effects of silymarin and quercetin, in counteracting oxidative stress produced by acute or sub-chronic sodium arsenite exposure. The stress responses to arsenite included an increase in the heat shock protein 70 kDa expression, lipid peroxidation assayed by conjugated dienes measure, and gamma-glutamyl-transpeptidase activity. We found that all these stress responses were eliminated by silymarin and quercetin in acute experiments. Both flavonoids diminished the conjugated dienes formation during sub-chronic cultures. Our results suggest that these antioxidant flavonoids, which may be easily incorporated into the diet, may afford a protective effect against arsenite-induced cytotoxicity.